Method and apparatus for image forming performing improved cleaning and discharging operations on image forming associated members

Information

  • Patent Grant
  • 6654574
  • Patent Number
    6,654,574
  • Date Filed
    Friday, October 25, 2002
    22 years ago
  • Date Issued
    Tuesday, November 25, 2003
    21 years ago
Abstract
An image forming apparatus includes an image carrying member, an intermediate transfer member, a charger, a transfer mechanism, a discharger, a direct current (d.c.) voltage source, and a d.c. voltage controller. The intermediate transfer member faces and contacts the image carrying member carrying a toner image, and receives the toner image therefrom during a first transfer. The charger charges the intermediate transfer member to cause an electric field around where the image carrying member and the intermediate transfer member contact each other, the electric field initiating the first transfer. The transfer mechanism transfers the toner image from the intermediate transfer member to a transfer sheet. The discharger discharges charge remaining on the intermediate transfer member. The d.c. voltage source applies a d.c. voltage to the discharger to cause the discharging. The d.c. voltage controller controls the d.c. voltage in accordance with a volume resistivity of the intermediate transfer member.
Description




CROSS-REFERENCE TO FOREIGN APPLICATION




This application claims priority rights of and is based on Japanese patent applications respectively filed in the Japanese Patent Office as listed below, the entire contents of which are hereby incorporated by reference.




JPAP10-333074 filed on Nov. 24, 1998




JPAP10-346365 filed on Dec. 7, 1998




JPAP10-346334 filed on Dec. 7, 1998




JPAP10-346435 filed on Dec. 7, 1998




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention generally relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming in which cleaning and discharging operations are efficiently performed relative to an image carrying member, an intermediate transfer member, and associated members.




2. Discussion of the Background




In image forming apparatuses such as copying machines, facsimile machines, printers, etc., a large number of techniques have been introduced, relating to cleaning and discharging of members associated with an image forming operation involving usage of toner. In particular, cleaning and discharging are important in a full-color image forming apparatus which is provided with an intermediate transfer member in addition to a commonly-used image carrying member. In such a full-color image forming apparatus, primary and secondary transfer operations are in turn performed so as to transfer a plurality of mono-color-toner images separately formed on the image carrying member onto a transfer sheet at one time via the intermediate transfer member.




More specifically, the image carrying member and the intermediate transfer member are arranged to contact each other so as to perform a primary transfer operation for transferring each mono-color-toner image from the image carrying member to the intermediate transfer member. For this, the full-color image forming apparatus is provided with a charge applying member for applying a charge to the intermediate transfer member to generates an electric field which generates a force to help such primary transfer operation. After a number of times of the primary transfer operation, a plurality of mono-color-toner images are overlaid with precision as one full-color-toner image on the intermediate transfer member. Then, a secondary transfer operation is performed to transfer this full-color-toner image held on the intermediate transfer member onto a transfer sheet which is also in contact with the intermediate transfer member.




The above-described intermediate transfer member is often used in a belt shape or a drum shape. An intermediate transfer belt, for example, typically has a medium range of a volume resistivity from about 10


8


Ωcm to about 10


11


Ωcm, which normally does not require operations for discharging the surface of the intermediate transfer belt. This helps the cost reduction.




In using such an intermediate transfer member having a medium range of volume resistivity, the surface of the intermediate transfer member is applied with a bias to perform the primary transfer operation and thus has a charge thereon. However, this charge will leak through members in contact with the rear surface of the intermediate transfer member and no charge will therefore remain on the surface of the intermediate transfer member in a relatively short time period after the application of the charge.




As a result, the intermediate transfer member has the voltage which is 0 and greatly different from the voltage of the toner image transferred through the primary transfer operation. Due to this voltage difference, toner particles forming the toner image, particularly the topmost-laid mono-color-toner image, are attracted to the surface of the intermediate transfer member. This results in a toner dispersion in which the toner particles are dispersed on the surface of the intermediate transfer member. Such a toner dispersion may badly cause a dirty background of an image, a blur of an image such as letters, and so forth and therefore make an image deteriorated in quality.




To avoid this problem, the image forming apparatus has used the intermediate transfer member which has a high volume resistivity of about 10


13


Ωcm. In using the intermediate transfer member having the high volume resistivity, the surface of the intermediate transfer member charges during the primary transfer operation due to an occurrence of discharge from the image carrying member and thus increases the voltage on the surface. Because of the high volume resistivity, the charge on the surface of the intermediate transfer member will not leak through the members in contact with the rear surface of the intermediate transfer member. Thereby, the difference of voltages between the intermediate transfer member and the toner image held on the intermediate transfer member is made relatively smaller. This helps to prevent the above-described toner dispersion.




In this case using the intermediate transfer member having the high volume resistivity, or the volume resistivity of at least 10


11


Ωcm, the charge will remain on the surface of the intermediate transfer member till the time when the next primary transfer operation starts. This makes it difficult to generate the same electric field as made during the previous primary transfer operation. In this case, accordingly, the charge remaining on the surface of the intermediate transfer member need to be discharged before starting the next primary transfer operation.




In addition, when a transfer sheet is jammed during the image forming operation in the image forming apparatus, the toner image held on the intermediate transfer member may pass a region where the secondary transfer operation is conducted, without being actually transferred onto a transfer sheet. This toner image needs, of course, to be removed before the next toner image is formed on the intermediate transfer member. However, a common cleaning member such as a cleaning blade alone cannot sufficiently remove the toner because the full-color image forming apparatus uses a relatively large amount of toner during one time of the image forming process.




Conventionally, a corona charger is widely used as a non-contact-type discharging member for discharging the image carrying member and other members associated with the image forming process in an image forming apparatus. Such a non-contact type of discharging member typically generates ozone during discharging, which is undesired from the environmental aspect. In addition, the discharging member needs an application of discharging bias which is generated from an expensive high voltage AC (alternating current) power source. This increase a manufacturing cost.




In addition, the above-described intermediate transfer member having a relatively high volume resistivity changes its volume resistivity in accordance with various environmental factors such as temperature, humidity, and so forth. The intermediate transfer member also changes a charger level on the surface thereof in accordance with a number of layers of mono-color toner image. With these changes, if the discharging bias is not variable, the discharging operation may not sufficiently be performed, causing a reduction of efficiency of the primary transfer operation.




As for the cleaning in the full-color image forming apparatus, it is required a relatively high level of cleaning performance, as described above. Conventionally, this is achieved by pressing the cleaning member relative to the intermediate transfer member. However, since the intermediate transfer member is rotating, the adjustment of pressure by the cleaning member has a relatively narrow margin and therefore it cannot be adjusted in a satisfactory manner.




In addition, the above-described discharging operation is needed to be performed relative to a transfer sheet carrying member as well as the intermediate transfer member. The transfer sheet carrying member carries a transfer sheet having a toner image transferred from the intermediate transfer member through the secondary transfer operation. During the secondary transfer operation, the transfer sheet carrying member is commonly applied with a bias to help the performance of the secondary transfer operation. This bias may remain on the transfer sheet carrying member after the secondary transfer operation and interferes the generation of the electric field for the next secondary transfer operation, resulting in an inferior image quality. Such a charge problem on the transfer sheet carrying member is addressed by employing a non-contact-type discharging member which involves an ozone problem.




SUMMARY OF THE INVENTION




The present application relates to a novel image forming apparatus which includes an image carrying member, an intermediate transfer member, a charging member, a transfer mechanism, a discharging member, a direct current voltage source, and a direct current voltage controller. The image carrying member rotates and carries a toner image on a rotating surface thereof. The intermediate transfer member is deposited at a position facing and in contact with the image carrying member, rotates and receives the toner image from the image carrying member during a first transfer operation. The charging member applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other, where the electric field generates a force for initiating the first transfer operation. The transfer mechanism performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The discharging member performs a discharging operation for discharging the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The direct current voltage source applies a direct current voltage to the discharging member to cause the discharging member to perform the discharging operation. The direct current voltage controller controls the direct current voltage in accordance with a volume resistivity of the intermediate transfer member.




The above-mentioned volume resistivity of the intermediate transfer member may be in a range of about 10


11


Ωcm to about 10


14


Ωcm, or in a range of about 10


12


Ωcm to about 10


13


Ωcm.




The present application also relates to a novel method of image forming which includes the steps of providing, rotating, charge applying, performing, direct current voltage applying, and controlling. The providing step provides a toner image to an carrying member for rotating and carrying the toner image on a rotating surface thereof. The rotating step rotates an intermediate transfer member which is arranged at a position facing and in contact with the image carrying member. The charge applying step applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other so that the electric field generates a force for initiating a first transfer operation for transferring the toner image from the image carrying member to the intermediate transfer member. The performing step performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The direct current voltage applying step applies a direct current voltage to the discharging member to cause the discharging member which discharges the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The controlling step controls the direct current voltage in accordance with a volume resistivity of the intermediate transfer member.




Further, the present application relates to another novel image forming apparatus which includes an image carrying member, an intermediate transfer member, a charging member, a transfer mechanism, a discharging member, a direct current voltage source, a voltage detect sensor, and a direct current voltage controller. The image carrying member rotates and carries a toner image on a rotating surface thereof. The intermediate transfer member which is deposited at a position facing and in contact with the image carrying member, rotates and receives the toner image from the image carrying member during a first transfer operation. The charging member applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other, where the electric field generates a force for initiating the first transfer operation. The transfer mechanism performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The discharging member performs a discharging operation for discharging the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The direct current voltage source applies a direct current voltage V to the discharging member to cause the discharging member to perform the discharging operation. The voltage detect sensor detects a surface voltage Va of the intermediate transfer member. The direct current voltage controller controls the direct current voltage V in a way such that the direct current voltage V relative to the surface voltage Va satisfies a range of






[−1.3Va−650# V #−1.3va+550].






Further, the present application also relates to a method of image forming which includes the steps of providing, rotating, charge applying, performing, detecting, direct current voltage applying, and controlling. The providing step provides a toner image to an carrying member for rotating and carrying the toner image on a rotating surface thereof. The rotating step rotates an intermediate transfer member which is arranged at a position facing and in contact with the image carrying member. The applying step applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other so that the electric field generates a force for initiating a first transfer operation for transferring the toner image from the image carrying member to the intermediate transfer member. The performing step performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The detecting step detects a surface voltage Va of the intermediate transfer member. The applying step applies a direct current voltage V to the discharging member to cause the discharging member which discharges the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The controlling step controls the direct current voltage V in a way such that the direct current voltage V relative to the surface voltage Va satisfies a range of






[−1.3Va−650 # V #−1.3va+550].






Further, the present application also relates to a novel image forming apparatus which includes an image carrying member, an intermediate transfer member, a charging member, a transfer mechanism, a discharging member, a direct current voltage source, a judging mechanism, and a direct current voltage controller. The image carrying member rotates and carries a toner image on a rotating surface thereof. The intermediate transfer member which is deposited at a position facing and in contact with the image carrying member, rotates and receives the toner image from the image carrying member during a first transfer operation which is performed for one time in a mono color mode and is repeated for a plurality of times in a multiple color mode to overlay a plurality of mono color toner images in turn on the intermediate transfer member. The charging member applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other, where the electric field generates a force for initiating the first transfer operation. The transfer mechanism performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The discharging member performs a discharging operation for discharging the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The direct current voltage source applies a direct current voltage to the discharging member to cause the discharging member to perform the discharging operation. The judging mechanism judges as to whether the apparatus is in the mono color mode or in the multiple color mode. The direct current voltage controller controls the direct current voltage in accordance with a result of judgement by the judging mechanism.




Further, the present application also relates to a novel method of image forming which includes providing, rotating, charge applying, performing, judging, direct current voltage applying, and controlling. The providing step provides a toner image to an carrying member for rotating and carrying the toner image on a rotating surface thereof. The rotating step rotates an intermediate transfer member which is arranged at a position facing and in contact with the image carrying member. The charge applying step applies a charge to the intermediate transfer member to cause an electric field around a region where the image carrying member and the intermediate transfer member contact with each other so that the electric field generates a force for initiating a first transfer operation for transferring the toner image from the image carrying member to the intermediate transfer member. The above-mentioned first transfer operation is performed for one time in a mono color mode and is repeated for a plurality of times in a multiple color mode to overlay a plurality of mono color toner images in turn on the intermediate transfer member. The performing step performs a second transfer operation for transferring the toner image from the intermediate transfer member to a transfer sheet. The judging step judges as to whether the apparatus is in the mono color mode or in the multiple color mode. The direct current voltage applying step applies a direct current voltage to the discharging member to cause the discharging member to discharge the charge remaining on the intermediate transfer member with contacting the intermediate transfer member after a completion of the second transfer operation. The controlling step controls the direct current voltage in accordance with a result of judgement by the judging mechanism.




Further, the present application also relates to a novel lubricant applying apparatus for applying a lubricant to an intermediate transfer member in an image forming apparatus. The above-mentioned novel lubricant applying apparatus includes a lubricant applying member for applying a lubricant to the intermediate transfer member and discharging a charge remaining on the intermediate transfer member.











BRIEF DESCRIPTION OF THE DRAWINGS




A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:





FIG. 1

illustrates an exemplary configuration of an image forming apparatus according to a first embodiment of the present invention;





FIG. 2

illustrates an exemplary structure around a photosensitive drum of the image forming apparatus of

FIG. 1

;





FIG. 3

illustrates an exemplary structure around a photosensitive drum of an image forming apparatus according to a second embodiment of the present invention;





FIG. 4

illustrates a block diagram of a specific example of a controller included in the image forming apparatus of

FIG. 2

;





FIG. 5

is a graph for explaining a relationship between a volume resistivity of an intermediate transfer belt and a surface voltage of the intermediate transfer belt after a secondary transfer operation in the image forming apparatus of

FIG. 2

;





FIGS. 6-8

illustrate block diagrams of other specific examples of the controller included in the image forming apparatus of

FIG. 2

;





FIG. 9

illustrates a main portion of a printer of an image forming apparatus according to a third embodiment of the present invention;





FIG. 10

illustrates a block diagram of an exemplary controller of the image forming apparatus of

FIG. 9

;





FIGS. 11A-11C

are graphs for explaining experimental results with variations of environmental conditions on an implementation version based on the image forming apparatus of

FIG. 9

;





FIG. 12

is a time chart for explaining a timing of application of a discharging bias in the implementation version of the image forming apparatus of

FIG. 9

;





FIG. 13

illustrates a main portion of a printer of an image forming apparatus according to a fourth embodiment of the present invention;





FIG. 14

illustrates an exemplary transfer unit of an image forming apparatus according to a fifth embodiment of the present invention;





FIG. 15

illustrates an exemplary configuration of an image forming apparatus according to a six embodiment of the present invention;





FIG. 16

illustrates an exemplary structure around a photosensitive drum of the image forming apparatus of

FIG. 15

;





FIG. 17

illustrates an exemplary structure around a photosensitive drum of a modified version of the image forming apparatus of

FIG. 15

;





FIG. 18

illustrates an exemplary structure around a photosensitive drum of an image forming apparatus according to a seventh embodiment of the present invention;





FIG. 19

illustrates a main portion of a printer of an image forming apparatus according to an eighth embodiment of the present invention;





FIG. 20

illustrates an enlarged cleaning blade of a belt cleaning unit of

FIG. 19

;





FIG. 21

illustrates a main portion of a printer of an image forming apparatus according to a ninth embodiment of the present invention;





FIG. 22

is an enlarged view of a cleaning blade of a belt cleaning unit and a cleaning facing roller of an intermediate transfer belt included in the image forming apparatus of

FIG. 21

;





FIG. 23

illustrates an exemplary transfer unit of an image forming apparatus according to a tenth embodiment of the present invention;





FIG. 24

illustrates an exemplary configuration of an image forming apparatus according to an eleventh embodiment of the present invention;





FIG. 25

illustrates an exemplary structure around a photosensitive drum of the image forming apparatus of

FIG. 24

;





FIG. 26

illustrates an exemplary structure of a lubricant applying unit of the image forming apparatus of

FIG. 24

;





FIG. 27

illustrates an exemplary structure of a brush roller of the lubricant applying unit of the image forming apparatus of

FIG. 24

;





FIG. 28

illustrates an exemplary structure around a photosensitive drum with respect to a modification made on the image forming apparatus of

FIG. 24

;





FIG. 29

illustrates a main portion of a printer of an image forming apparatus according to a twelfth embodiment of the present invention;





FIG. 30

illustrates an exemplary structure of a moving mechanism for moving a lubricant applying brush roller and a cleaning blade in the image forming apparatus of

FIG. 29

;





FIGS. 31A and 31B

illustrate enlarged structures of the moving mechanism of

FIG. 30

;





FIG. 32

illustrates a main portion of a printer of an image forming apparatus according to a thirteenth embodiment of the present invention;





FIG. 33

illustrates an exemplary transfer unit of an image forming apparatus according to a fourteenth embodiment of the present invention;





FIG. 34

illustrates an exemplary configuration of an image forming apparatus according to a fifteen embodiment of the present invention;





FIG. 35

illustrates an exemplary structure around a photosensitive drum of the image forming apparatus of

FIG. 34

;





FIG. 36

illustrates an exemplary structure around a photosensitive drum with respect to a first modification made on the image forming apparatus of

FIG. 34

;





FIG. 37

illustrates an exemplary structure around a photosensitive drum with respect to a second modification made on the image forming apparatus of

FIG. 34

;





FIG. 38

is a graph for explaining a relationship between a discharging bias of a discharging brush and a surface voltage on the intermediate transfer belt when a conductive plate is provided and when a conductive plate is not provided;





FIG. 39

illustrates an exemplary structure around a photosensitive drum with respect to a third modification made on the image forming apparatus of

FIG. 34

;





FIG. 40

illustrates a discharging brush roller of the third modification made on the image forming apparatus of

FIG. 34

;





FIG. 41

is a graph for explaining a relationship between a filling density of the discharging brush roller and the surface voltage of the intermediate transfer belt in the third modification made on the image forming apparatus of

FIG. 34

;





FIG. 42

is a graph for explaining a relationship between a brush pile gap of the discharging brush roller and the surface voltage of the intermediate transfer belt in the third modification made on the image forming apparatus of

FIG. 34

;





FIG. 43

illustrates a main portion of a printer of an image forming apparatus according to a sixteenth embodiment of the present invention;





FIG. 44

illustrates a main portion of a printer of an image forming apparatus according to a seventeenth embodiment of the present invention; and





FIG. 45

illustrates a main portion of a printer of an image forming apparatus according to an eighteenth embodiment of the present invention.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present invention is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner.




Various embodiment of the present invention will hereinafter be described with reference to the accompanying drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.




[Embodiment 1]




To begin with, a first embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 1

is a cross-sectional view schematically illustrating the configuration of the copier according to the first embodiment, and

FIG. 2

is an enlarged view schematically illustrating the structure around a photosensitive drum serving as an image carrier in the copier of FIG.


1


. The illustrated copier is generally formed of a color image reader unit


1


(hereinafter referred to as the “scanner unit


1


”) and a color image recording unit


2


(hereinafter referred to as the “printer unit


2


”).




First, the scanner unit


1


in the copier will be described in terms of the structure and operation. In this scanner unit


1


, an image of an original


3


carried on a contact glass is focused on a color sensor


7


through an illumination lamp


4


, a group of mirrors (


5




a


,


5




b


,


5




c


), and a lens


6


. The sensor


7


reads color image information of the original


3


, for example, for each separated color light components Blue (hereinafter abbreviated as “B”), Green (“G”), and Red (“R”), and transduces the color image information to electrical image signals. The color sensor


7


, which is composed of B, G, R color separating means and a photo-electric transducing element such as a CCD (charge coupled device), has the ability of simultaneously reading three colors. Respective image signals B, G, R produced in the scanner unit


1


are subjected to color conversion processing in an image processing unit based on their respective intensity levels. The color conversion processing results in color image data composed of Black (hereinafter abbreviated as “Bk”), Cyan (“C”), Magenta (“M”), and Yellow (“Y”). More specifically, an illumination/mirror optical system of the scanner unit


1


is responsive to a start signal associated with the printer unit


2


to scan an original in a direction indicated by an arrow A in

FIG. 1

to acquire color image data. In the first embodiment, image data for one color is acquired each time the illumination/mirror optical system scans an original, so that the illumination/mirror optical system must scan a total of four times in order to acquire color image data for the four colors Bk, C, M, Y.




Next, the printer unit


2


of the copier according to the first embodiment will be described in terms of the structure and operation.




The printer unit


2


includes an optical writing unit


8


as an exposing means, and a photosensitive drum


10


as an image carrier. The optical writing unit


8


transduces color image data from the above-mentioned scanner unit


1


to an optical signal, and forms a negative latent image corresponding to an original image on the photosensitive drum


10


which is uniformly charged in the negative polarity. The optical writing unit


8


may be composed of a semiconductor laser


8




a


; a light emission driving controller, not shown, for controlling emission and driving of the semiconductor laser


8




a


; a polygon mirror


8




b


; a rotation driving motor


8




c


for rotating the polygon mirror


8




b


; an fθ lens


8




d


; and a reflection mirror


8




e


. The photosensitive drum


10


is driven to rotate in the counter-clockwise direction, i.e., in a direction indicated by an arrow B in FIG.


1


.




The printer unit


2


further includes, around the photosensitive drum


10


, a photosensitive drum cleaning unit


11


; a discharging lamp


12


; a charger


13


; a potential sensor


14


; a set of a Bk developing device


15


, a C developing device


16


, an M developing device


17


and Y developing device


18


; a developer concentration pattern detector


19


; and an intermediate transfer unit


20


.




As can be seen in

FIG. 2

, the photosensitive drum cleaning unit


11


has a pre-cleaning discharger


11




a


, and a fur brush


11




b


and a photosensitive drum cleaning blade


11




c


as cleaning members, and is provided for cleaning the surface of the photosensitive drum


10


after primary transfer (transfer from the photosensitive drum to an intermediate transfer belt).




Each of the developing devices


15


-


18


has a developing paddle (


15




b


,


16




b


,


17




b


,


18




b


) as an agitating means for scooping up and agitating an associated developer; a toner concentration sensor (


15




c


,


16




c


,


17




c


,


18




c


) for sensing the toner concentration of the developer; and a developing sleeve (


15




a


,


16




a


,


17




a


,


18




b


) as a developer carrier for bringing a sleeve or ear of the developer into contact with the surface of the photosensitive drum


10


. For developers contained in the four developing devices, two-component developers may be used. Toners mixed in the developers are negatively charged. When the copier proceeds to a standby state, the four developing devices remove ears on the respective developing sleeves, and proceeds to an inoperative state.




The intermediate transfer unit


20


includes an intermediate transfer belt


21


; a primary transfer bias roller


22


as a charge supply means; a primary transfer power supply


28


connected to the primary transfer bias roller


22


; a ground roller


23


as a pre-primary transfer discharging means; a driving roller


24


as a belt driving means; and a driven roller


25


. The intermediate transfer belt


21


is passed over the primary transfer bias roller


22


, the ground roller


23


, the driving roller


24


, and the driven roller


25


. The driving roller


24


, connected to a driving motor


24




a


, controls the driving of the intermediate transfer belt


21


.




The intermediate transfer belt


21


is formed in a multi-layer structure composed of a surface layer, an intermediate layer and a base layer, and is placed such that the surface layer is positioned on the outer peripheral side which contacts the photosensitive drum


10


, and the base layer is positioned on the inner peripheral side. In addition, an adhesive layer is interposed between the intermediate layer and the base layer for adhering the two layers. The intermediate transfer belt


21


is formed to have the volume resistivity ρv, as measured by the method described in JISK6911, in a range of 10


7


Ωcm to 10


14


Ωcm, preferably in a range of 10


12


Ωcm to 10


14


Ωcm, and more preferably equal to approximately 10


13


Ωcm. It should be noted that while a material having the volume resistivity of 10


14


Ωcm or more might be utilized, it is not suitable for the intermediate transfer belt for the intended purpose in the present invention from a viewpoint of durability and so on.




Around the intermediate transfer belt


21


, there are disposed a contact-type discharger


50


; a belt cleaning unit


29


; and a transfer unit


30


. The belt cleaning unit


29


has a brush roller


29




a


and a rubber blade


29




b


as cleaning members, and a belt contact/separation mechanism


29




c


. This belt contact/separation mechanism


29




c


enables the intermediate cleaning unit


29


to move into and out of contact with the intermediate transfer belt


21


. The transfer unit


30


also has a secondary transfer bias roller


31


opposite to the driving roller


24


of the intermediate transfer unit


20


; a transfer cleaning blade


32


; and a transfer contact/separation mechanism


33


. This transfer contact/separation mechanism enables the transfer unit


30


to move into and out of contact with the intermediate transfer belt


21


.




The primary transfer bias roller


22


for tensioning the intermediate transfer belt


21


is positioned downstream of a primary transfer region defined by a nip formed by a contact between the intermediate transfer belt and the photosensitive drum


10


in a direction in which the surface of the intermediate transfer belt runs, i.e., in a belt moving direction. The primary transfer bias roller


22


is applied with a predetermined primary transfer bias by the primary transfer power supply


28


. The ground roller


23


is disposed upstream of the nip in the belt moving direction. The intermediate transfer belt


21


is pressed against the photosensitive drum


10


by the primary transfer bias roller


22


and the ground roller


23


, whereby the nip is formed.




The printer unit


2


also has a paper feed roller


41


for feeding a transfer paper


100


as a transfer material to a secondary transfer region formed between the secondary transfer bias roller


31


of the transfer unit


30


and the driving roller


24


of the intermediate transfer unit


20


; a resist roller


42


; transfer paper cassettes


43




a


,


43




b


,


43




c


for accommodating transfer papers


100


of various sizes; a hand feed tray


40


for use in copying an image on an OHP (overhead projector) sheet, rather thick paper, or the like; a paper conveying unit


44


; a fixing unit


45


; and a copy tray


46


.




Next, the operation of the copier will be described in connection with an illustrative image forming mode in which the development is performed in the order of Bk, C, M, Y. It should be of course understood that image formation is not limited to this particular order.




Once a copy operation is initiated, a Bk step is first started, wherein color image information of an original is read in the scanner unit


1


, and a Bk latent image is formed on the photosensitive drum


10


by laser light generated from the optical writing unit


8


based on Bk image data derived from the image information in the printer unit


20


. The Bk latent image is applied with toner by the Bk developing device


15


, and developed by forming a Bk toner image. In this event, the developing sleeve


15




a


has been previously rotated before the leading edge of the Bk latent image arrives at a developing position of the Bk developing device


15


in order to ensure that the Bk latent image is completely developed. In this way, since the developer has already formed a sleeve or ear when the leading edge of the Bk latent image arrives at the developing position of the Bk developing device


15


, it is ensured that the entire Bk latent image can be developed. Also, in the Bk developing device


15


, at the time the trailing edge of the Bk latent image has passed the developing position, the sleeve or ear of the developer formed on the developing sleeve


15




a


is immediately discontinued. This causes the Bk developing device


15


to proceed to an inoperative state. At this time, the Bk developing device


15


should be completely inoperative before the leading edge of a C latent image, to be next developed, arrives at the developing position of the Bk developing device


15


. The developer ear may be discontinued by switching the developing sleep


15




a


to the direction reverse to the rotating direction during the developing operation.




The Bk toner image thus formed on the photosensitive drum


10


by the Bk developing device


15


is transferred to the surface of the intermediate transfer belt


21


which is driven at the same speed as the photosensitive drum


10


(primary transfer), followed by termination of the Bk step.




In parallel with the primary transfer of the Bk toner image, the next C step is started on the photosensitive drum


10


. Specifically, color image information of the original is again read at a predetermined timing, a C latent image is formed on the photosensitive drum


10


by laser light based on C image data derived from the image information, and a C toner image is formed by the C developing device


16


. The rotation of the developing sleeve


16




a


in the C developing device


16


is started after the trailing edge of the Bk latent image has passed a developing position of the C developing device


16


and before the leading edge of the C latent image arrives at the developing position. Then, at the time the trailing edge of the C latent image has passed the developing position, a developer ear formed on the developing sleeve


16




a


is discontinued as is the case of the aforementioned Bk developing device


15


, and the C developing device


16


is made inoperative. Again, in this event, the C developing device


16


should be completely inoperative before the leading edge of the next M latent image arrives. The C toner image thus developed and formed on the photosensitive drum


10


is transferred to an image surface area of the intermediate transfer belt


21


in precise register with the Bk toner image which has been transferred to the image surface area.




Subsequently, in an M step and a Y step, the formation of latent image, development, and primary transfer are performed respectively based on their respective image data in a manner similar to the aforementioned C step. By transferring the respective Bk, C, M and Y toner images sequentially formed on the photosensitive drum


10


to the same image surface area on the intermediate transfer belt


21


, a complete toner image formed of the four color images in accurate register with one another is formed on the intermediate transfer belt


21


.




Now, the operation of the intermediate transfer belt


21


will be described referring again to FIG.


2


.




While the aforementioned Bk, C, M and Y toner images are transferred to the photosensitive drum


10


, for example, from the termination of the primary transfer of the first color (Bk) toner image to the initiation of the primary transfer of the second color (C) toner image, the intermediate transfer belt


21


may be driven in accordance with a constant speed forward mode, a skip forward mode, reciprocation (quick return) mode, or the like. While any driving mode selected from these illustrative driving modes may be fixedly employed for the intermediate transfer belt


21


, a suitable driving mode may be selected from the three modes in accordance with a copy size for increasing the copy speed, or a plurality of driving modes may be efficiently used in combination.




In the following, the illustrative driving modes will be briefly described. The constant speed forward mode performs the primary transfer while driving the intermediate transfer belt in one direction at a low speed. The skip forward mode, which also drives the intermediate transfer belt in one direction similarly to the constant speed forward mode, moves the intermediate transfer belt away from the photosensitive drum after a toner image has been transferred thereto, skip forwards the intermediate transfer belt in the same direction at a higher speed, and then brings the intermediate transfer belt back to the start position of the primary transfer for performing the next primary transfer. This sequence of operations is repeated for the four color toner images. The reciprocation (quick return) mode, unlike the skip forward mode, returns the intermediate transfer belt to the start position of the primary transfer in the reverse direction at a higher speed in preparation for the next primary transfer, after the primary transfer is performed to the intermediate transfer belt and the intermediate transfer belt is moved away from the photosensitive drum. This sequence of operations are repeated for the four color toner images.




During a time period in which a complete toner image is formed on the intermediate transfer belt


21


, specifically, during a time period from the time the first color (Bk) toner image had been transferred to the intermediate transfer belt


21


to the time the fourth color (Y) toner image has been transferred to the same, the discharging brush


51


, the belt cleaning unit


29


, and the transfer unit


30


are separated away from the intermediate transfer belt


21


by the respective contact/separation mechanisms.




The toner image transferred to the intermediate transfer belt


21


in the manner described above is conveyed to the secondary transfer region for secondary transfer to a transfer paper


100


. In this event, the secondary transfer bias roller


31


of the transfer unit


30


is generally pressed against the intermediate transfer belt


21


by the transfer contact/separation mechanism


33


at the timing the toner image is transferred to the transfer paper


100


. Subsequently, the secondary transfer bias roller


31


is applied with a predetermined secondary transfer bias by a secondary transfer power supply, not shown, to form a secondary transfer electric field in the secondary transfer region. The secondary transfer electric field causes the toner image on the intermediate transfer belt


21


to be transferred to the transfer paper


100


. The transfer paper


100


is conveyed from a transfer paper cassettes


43




a


,


43




b


,


43




c


of a size specified by an operator on an operation panel, not shown, in a direction toward the resist roller


42


, and fed into the secondary transfer region. More specifically, the transfer paper


100


is fed into the secondary transfer region at the timing coincident with the arrival of the leading edge of the toner image on the intermediate transfer belt


21


to the secondary transfer region.




The transfer paper


100


, on which the complete toner image formed of four color toner images in accurate register with one another has been collectively transferred from the intermediate transfer belt


21


, is subsequently conveyed to a fixing unit


45


by the paper conveying unit


44


. The unfixed toner image on the transfer paper


100


is melted between a pair of fixing rollers consisting of a fixing roller


45




a


controlled at a predetermined temperature and a press roller


45




b


, and the unfixed toner image is fixed. Then, after the fixation, the transfer paper


100


is conveyed to and stacked on the copy tray


46


.




After the primary transfer, the surface of the photosensitive drum


10


is cleaned by the photosensitive drum cleaning unit


11


, and uniformly discharged by the discharging lamp


12


. Also, after the secondary transfer, the surface of the intermediate transfer belt


21


is cleaned by the belt cleaning unit


29


which is pressed against the intermediate transfer belt


21


by the belt cleaning contact/separation mechanism


29




c.






For repetitively copying the same original, in the scanner unit


1


, the first color (Bk) step is started for the second copy at a predetermined timing subsequent to the fourth color (Y) step on the first copy. In the printer unit


2


, in turn, a Bk latent image is formed on the photosensitive drum


10


. On the intermediate transfer belt


21


, on the other hand, the first color (Bk) toner image for the second copy is transferred to the region on the intermediate transfer belt


21


, which has been cleaned by the belt cleaning unit


29


, subsequent to the secondary transfer of the complete toner image


2


for the first copy.




While the operation of the copier has been described in connection with a copy mode for producing full-color or four-color copies, the same description is applicable to other copy modes, i.e, a three-color copy mode and a two-color copy mode, except that used colors and associated mechanisms are different. For a single-color copy mode, a developer in a developing device associated with a selected color is maintained to form a sleeve or ear, i.e., the developing device is maintained in operative state until a predetermined number of copies have been produced. Also, with the discharging brush


51


, the belt cleaning unit


29


and the transfer unit


30


maintained in contact with the intermediate transfer belt


21


and with the intermediate transfer belt


21


maintained in contact with the photosensitive drum


10


, the intermediate transfer belt


21


is driven in the forward direction at a constant speed for producing copies.




In the following, description will be made on the configuration and operation of the contact-type discharger


50


which constitutes a characterizing portion of the first embodiment.




The contact-type discharger


50


of the first embodiment has the discharging brush


51


and the discharge power supply


59


for applying the discharging brush


51


with a discharging bias. As can be seen in

FIG. 2

, the contact-type discharger


50


is positioned downstream of the belt cleaning unit


29


and upstream of the ground roller


23


in the direction of the movement of the intermediate transfer belt


21


. Instead of the illustrated discharging brush


51


, a discharging blade, a discharge roller, and a discharging brush roller may be used by way of example.




The discharging brush


51


is grounded through the discharge power supply


59


. The discharging brush


51


is applied by the discharge power supply with a direct current or an alternate current discharging bias, or with a combination of direct current and alternate current discharging biases. In this event, when a direct current power supply for applying a direct current voltage is employed as the discharge power supply


59


, a reduction in cost is expected. The first embodiment employs a regulated direct current power supply as the discharge power supply


59


. In addition, since the residual potential on the intermediate transfer belt


21


is negative, the discharge power supply


59


applies the discharging brush


51


with a positive discharging bias.




The discharging bias thus applied to the discharging brush


51


forces a residual charge, which exists on the intermediate transfer belt


21


to form the residual potential, to efficiently flow into the discharging brush


51


, so that effective discharging can be accomplished. Thus, even when the surface moving speed of the intermediate transfer belt


21


is increased, for example, in order to perform the image formation at a higher speed, the intermediate transfer belt


21


can be stably discharged.




[Embodiment 2]




Next, a second embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 3

schematically illustrates the configuration of a main portion in a printer unit of the copier according to the second embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the first embodiment. The second embodiment differs from the first embodiment in that a printer unit has a variable discharge power supply and a control unit for controlling the variable discharge power supply. Since the copier of the second embodiment performs image forming operations basically in the same manner as the first embodiment, description on those parts that are constructed and operated in a manner similar to the first embodiment is omitted.




A contact-type discharger


150


according to the second embodiment has a discharging brush


51


, and a variable discharge power supply


159


for applying the discharging brush


51


with a variable direct current voltage, similarly to that in the first embodiment. The variable discharge power supply


159


is connected to a control unit which controls a direct current voltage applied to the discharging brush


51


.




A specific example (hereinafter referred to as the “first example”) of the control unit for controlling the variable bias power supply


159


will be described below with reference to FIG.


4


.





FIG. 4

is a block diagram illustrating the configuration of a controller


61


in the control unit


60


for controlling the variable discharge power supply


159


in accordance with the volume resistivity ρv of the intermediate transfer belt


21


. The controller


61


has a CPU


62


, a ROM


63


, a RAM


64


, and an I/O interface


65


. The I/O interface


65


is connected to the variable discharge power supply


159


; a driving motor


24




a


coupled to a driving roller


24


for driving the intermediate transfer belt


21


; a mark sensor


24




b


for detecting a mark attached on the inner peripheral surface of the intermediate transfer belt


21


for detecting a rotating position; and a calculator


66


for counting a total number of copies produced by the copier. The variable discharge power supply


159


for applying the discharging brush


51


with a direct current voltage is turned ON/OFF at a timing that is set based on an output signal of the mark sensor


24




b.






Now, explanation will be given of the relationship between the volume resistivity ρv of the intermediate transfer belt


21


and a surface potential on the intermediate transfer belt


21


after secondary transfer.





FIG. 5

shows a graph representing the relationship between the volume resistivity ρv of the intermediate transfer belt


21


and the surface potential on the intermediate transfer belt


21


after secondary transfer. Also, Table 1 below shows the relationship between the surface potential on the intermediate transfer belt


21


after secondary transfer and the evaluation for an image which is subsequently formed when the surface of the intermediate transfer belt


21


is charged at each potential as indicated. The image evaluation on Table 1 is made in the following manner: when an image produced in the next sequence of image formation with a surface potential equal to a value indicated in Table 1 exhibits a similar image quality to the preceding image, it is evaluated as ◯; and when such an image has a lower image quality than the preceding image, it is evaluated as Δ or X according to the degree of deterioration.


















TABLE 1









Surface Potential (V)




0




−100




−200




−300




−400




−500











Image














Δ




X




X




X














The graph of

FIG. 5

shows that when the volume resistivity ρv is 10


11


Ωcm or more, the residual potential due to a residual charge on the surface of the intermediate transfer belt after the secondary transfer is at −100 volts or less. Then, Table 1 shows that an image formed in the next sequence of image formation fails to be evaluated as ◯ when the residual potential is at −100 volts or less. Consequently, it is found that with the volume resistivity ρv equal to or higher than 10


11


Ωcm, the residual potential on the surface of the intermediate transfer belt adversely affects the next primary transfer, with the result that an image formed in such an environment suffers from a degraded quality. It is thought that the degraded image quality of a subsequently formed image as compared with that of the previously formed image is caused by an insufficient primary transfer bias due to the residual potential. It is therefore effective to provide such the intermediate transfer belt


21


with a discharging means. In addition, the volume resistivity ρv of the intermediate transfer belt


21


set in a range of 10


13


Ωcm to 10


14


Ωcm or more is preferable because dusts can be prevented from remaining on the intermediate transfer belt


21


after the primary transfer.





FIG. 5

also shows that as the volume resistivity ρv is higher, the residual potential on the intermediate transfer belt


21


is also higher. For preferably performing the primary transfer in the next image formation process, the discharging bias must be selected such that the intermediate transfer belt


21


is not discharged insufficiently or excessively, that is, such that the surface potential on the intermediate transfer belt is at −100 volts or lower. For this purpose, the variable discharge power supply


159


is controlled to generate a direct current which provides an optimal discharging bias in accordance with the volume resistivity ρv of the employed intermediate transfer belt


21


.




Further, while the volume resistivity ρv of the intermediate transfer belt


21


is determined in a design stage of a copier, the intermediate transfer belt


21


is deteriorated as it is repetitively used over time. This deterioration appears as a lower volume resistivity ρv, so that if a direct current voltage applied by the variable discharge power supply


159


is kept unchanged from the initial setting, an actually applied discharging bias will deviate from an optimal value. To solve this problem, the control unit


60


in the second embodiment controls the direct current generated by the variable discharge power supply


159


in accordance with this decreasing volume resistivity ρv over time.




Specifically, when the total number of copies counted by the calculator


66


reaches a predetermined value, the controller


61


in the control unit


60


controls the variable discharge power supply


159


to generate a higher direct current voltage. As a result, it is possible to correct a deviation of the discharging bias from the optimal value due to the decreasing volume resistivity ρv associated with the deteriorated intermediate transfer belt


21


, and hence accomplish stable and exact discharging over a long term.




Another specific example (hereinafter referred to as the “second example”) of the control unit for controlling the variable bias power supply


159


will be described below with reference to FIG.


6


.





FIG. 6

is a block diagram illustrating the configuration of a controller


61




a


in a control unit


60




a


for controlling the variable discharge power supply


159


in accordance with a surface potential of the intermediate transfer belt


21


. The control unit


60




a


of the second example has the same configuration as the control unit


60


in the foregoing first example except that an I/O interface


65




a


in the controller


61




a


is connected to a potential sensor


67


for sensing the potential on the surface of the intermediate transfer belt


21


instead of the calculator


66


in the first example. The potential sensor


67


is disposed upstream of the position at which the discharging brush


51


is disposed in the direction of the movement of the intermediate transfer belt


21


.




An optimal value for a direct current applied by the variable discharge power supply


159


varies depending on the potential on the surface of the intermediate transfer belt


21


, more specifically, the surface of the intermediate transfer belt


21


after secondary transfer. It is therefore desirable to control the variable discharge power supply


159


in accordance with the surface potential in order to achieve effective discharging.




In the second example, the potential sensor


67


senses the surface potential on the intermediate transfer belt


21


before it is discharged, and supplies the sensed surface potential data to a CPU


62




a


in the controller


61




a


to control the variable discharge power supply


159


in response to the surface potential data.




While an exact bias potential can be applied by virtue of the discharging bias control in response to the surface potential on the intermediate transfer belt


21


using the potential sensor


67


, the implementation of such control may result in a complicated configuration and an increased cost. Thus, when the discharging bias control is applied to a copier which has a single-color mode in which a single-color toner image formed on the photosensitive drum


10


is transferred to the intermediate transfer belt


21


and then transferred again from the intermediate transfer belt


21


to the transfer paper


100


, and a multi-color mode in which a plurality of toner images sequentially formed on the photosensitive drum are transferred to the intermediate transfer belt


21


one after the other in accurate register with one another, and the complete multi-color image is transferred to the transfer paper, the variable discharge power supply may be controlled to apply different discharging biases in accordance with the single-color mode or the multi-color mode. Specifically, when a copier has a single-color mode for producing copies using only a single developer for one color (hereinafter referred to as the “


1


C mode”) and a multi-color mode for producing copies using developers for four colors (hereinafter referred to as the “


4


C mode”), the controller


61




a


may control the variable discharge power supply


159


such that different discharging biases are applied corresponding to these copy modes.




Further, when the discharging bias control is applied to a copier which has a plurality of multi-color modes in accordance with the number of times toner images are transferred or superimposed, in which a plurality of toner images sequentially formed on the photosensitive drum


10


are transferred to the intermediate transfer belt


21


one after the other in accurate register with one another, and the complete multi-color image is transferred to the transfer paper, the control unit


61


may control the variable discharge power supply


159


to generate different direct current voltages in accordance with the number of toner images, in other words, the number of times toner images are transferred or superimposed one after the other to the intermediate transfer belt


21


. In this case, if a copier has an additional two-color mode (hereinafter referred to as the “


2


C mode”) for producing copies using developers for two colors in addition to the aforementioned


1


C mode and


4


C mode, the controller


61




a


may control the variable discharge power supply


159


to apply different discharging biases corresponding to the respective copy modes.




Next, a further specific example (hereinafter referred to as the “third example”) of the control unit for controlling the variable bias power supply


159


will be described below with reference to FIG.


7


.





FIG. 7

is a block diagram illustrating the configuration of a controller


61




b


in a control unit


60




b


for controlling the variable discharge power supply


159


in accordance with an environmental condition around the intermediate transfer belt


21


. The control unit


60




b


of the third example has the same configuration as the control unit


60


in the foregoing first example except that an I/O interface


65




b


in the controller


61




b


is connected to a temperature and humidity sensor


68


for sensing an environmental condition around the intermediate transfer belt


21


instead of the calculator


66


in the first example. While the third example employs the combined temperature and humidity sensor


68


as an environmental condition sensing means, separate sensors may be provided for individually sensing a temperature and a humidity. Alternatively, the control unit


60




b


may be provided with another environmental condition sensing means such as that for sensing the volume resistivity ρv of the intermediate transfer belt


21


, or any other environmental condition, other than temperature and humidity, which may affect a contact resistance between the intermediate transfer belt


21


and the discharging brush


51


.




As mentioned above, an optimal value for a direct current voltage applied by the variable discharge power supply


159


varies depending on the volume resistivity ρv of the intermediate transfer belt


21


. The volume resistivity ρv in turn varies depending on environmental conditions, particularly, on temperature and humidity. Also, since the third example employs a discharging brush


51


which is a contact-type discharge member, a contact resistance between the discharging brush


51


and the intermediate transfer belt


21


is also included in factors which vary the optimal value for the direct current voltage. The contact resistance likewise varies depending on environmental conditions, particularly on temperature and humidity. It is therefore desirable to control the variable discharge power supply


159


in accordance with such environmental conditions as mentioned above which cause variations in the optimal value for the direct current voltage, in order to achieve effective discharging.




To meet the foregoing requirements, in the third example, the temperature and humidity sensor


68


senses the temperature and humidity around the intermediate transfer belt


21


and supplies sensed temperature data and humidity data to a CPU


62




b


in the controller


61




b


which controls the variable discharge power supply


159


in response to the supplied data.




Next, a further specific example (hereinafter referred to as the “fourth example”) of the control unit for controlling the variable bias power supply


159


will be described below with reference to FIG.


8


.





FIG. 8

is a block diagram illustrating the configuration of a controller


61




c


in a control unit


60




c


for controlling the variable discharge power supply


159


in accordance with a surface moving speed the intermediate transfer belt


21


. The control unit


60




c


of the fourth example has the same configuration as the control unit


60


in the foregoing first example except that a CPU


62




c


in the controller


61




c


is supplied with a rotating speed of the driving motor


24




a


which drives the driving roller


24


for driving the intermediate transfer belt


21


.




An optimal value for a direct current voltage applied to the variable discharge power supply


159


varies depending on the surface moving speed of the intermediate transfer belt


21


. This is because a change in the surface moving speed causes variations in time period for which the discharging brush


51


remains in contact with the intermediate transfer belt


21


. More specifically, when the direct current voltage is fixed, an increase in the surface moving speed of the intermediate transfer belt


21


may result in insufficient discharging, while a decrease in the surface moving speed may result in excessive discharging. It is therefore beneficial to control the variable discharge power supply


159


in accordance with the surface moving speed of the intermediate transfer belt


21


which causes variations in the optimal value for the direct current voltage, in order to achieve effective discharging.




To meet the above requirements, in the fourth example, data on the rotating speed of the driving motor


24




a


is supplied to the CPU


62




c


in the controller


61




c


which calculates the current surface moving speed of the intermediate transfer belt


21


corresponding to the rotating speed of the driving motor


24




a


, and controls the variable discharge power supply


159


so as to apply the discharging brush


51


with an optimal discharging bias for the calculated surface moving speed.




It should be noted that the control unit according to the second embodiment may advantageously utilize a combination of the foregoing examples as appropriate to more exactly discharge the intermediate transfer belt


21


.




[Embodiment 3]




Next, a third embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 9

schematically illustrates the configuration of a main portion in a printer unit of the copier according to the third embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the first embodiment, and performs basically the same image forming operations as the copier of FIG.


1


. The third embodiment differs from the first embodiment mainly in the structure and operation of the printer unit.




As illustrated in

FIG. 9

, the printer unit of the third embodiment includes a photosensitive drum


10


as an image carrier, and, around the photosensitive drum


10


, an optical writing unit, not shown, as an exposing unit; a photosensitive drum cleaning unit


111


; a charger


13


; a revolver developing unit


110


; and an intermediate transfer unit


120


. The printer unit also includes a transfer unit


130


; an fixing unit


145


; and a paper feed unit, a controller and so on, not shown, similar to those in the first embodiment.




The photosensitive drum cleaning unit


111


has a fur brush


111




b


and a photosensitive drum cleaning blade


111




c


, and is provided for cleaning the surface of the photosensitive drum


10


after primary transfer. The fixing unit


145


has a pair of fixing rollers


145




a


, and a pair of delivery rollers, not shown.




The revolver developing unit


110


has a Bk developing device


115


; a C developing device


116


; an M developing device


117


; and a Y developing device


118


. A developing position in the developing device of each color opposite to the photosensitive drum


10


can be determined by the revolution of the revolver developing unit


110


.




The intermediate transfer unit


120


includes an intermediate transfer belt


121


; a primary transfer bias roller


122


as a charge supply means; a primary transfer power supply


128


connected to the primary transfer bias roller


122


; a ground roller


123


as a pre-primary transfer discharging means; a driving roller


124


; a driven roller


125


; a secondary transfer opposed roller


126


; and a cleaning opposed roller


127


. The intermediate transfer belt


121


is passed over the primary transfer bias roller


122


, the ground roller


123


, the driving roller


124


, the driven roller


125


, the secondary transfer opposed roller


126


; and the cleaning opposed roller


127


. The driving roller


124


is connected to a driving motor


124




a


. All the rollers, over which the intermediate transfer roller


121


is passed, are made of an electrically conductive material, and all the rollers except for the primary transfer bias roller


122


are respectively grounded. The primary transfer bias roller


122


is applied by the primary transfer power supply


128


with a predetermined primary transfer bias which is controlled to be a constant voltage or a constant current.




Around the intermediate transfer belt


121


, there are disposed a discharging brush roller


151


; a belt cleaning blade


129


; and a transfer unit


130


. These components are moved into and out of contact with the intermediate transfer belt


121


by respective contact/separation mechanisms, not shown, associated therewith.




Like the aforementioned first embodiment, the intermediate transfer belt


121


is formed in a multi-layer structure composed of a surface layer, an intermediate layer and a base layer. In addition, an adhesive layer is interposed between the intermediate layer and the base layer for adhering the two layers. The intermediate transfer belt


121


is formed to have a volume resistivity ρv in a range of 10


12


Ωcm to 10


14


Ωcm, and preferably equal to approximately 10


13


Ωcm. Advantageously, with the intermediate transfer belt


21


having the volume resistivity ρv equal to or larger than 10


12


Ωcm, dusts can be prevented from remaining on the intermediate transfer belt


121


after primary transfer. It should be noted that while in the third embodiment, the intermediate transfer belt


121


has high resistance surface layer and intermediate layer, and a middle resistance base layer with the volume resistivity ρv in a range of 10


8


Ωcm to 10


11


Ωcm, the intermediate transfer belt


121


is not limited to this particular structure. Also, the intermediate transfer belt


121


is made such that the surface resistivity on the surface layer side thereof is in a range of 10


7


Ωcm to 10


14


Ωcm.




The discharging brush


151


is connected to a variable discharge power supply


159


for applying the discharging brush


151


with a direct current voltage. The variable discharge power supply


159


in turn is connected to a control unit


160


which controls the direct current voltage applied to the discharging brush


151


.




The transfer unit


130


has a paper transfer belt


134


; a transfer cleaning blade


132


for cleaning the surface of the paper transfer belt


134


; a secondary transfer bias roller


131


opposing a secondary transfer opposed roller


126


of the intermediate transfer unit


120


; a secondary transfer power supply


139


connected to the secondary transfer bias roller


131


; a first supporting roller


135




a


positioned at one end of the paper feed unit; a third supporting roller


135




c


opposing the transfer cleaning blade


132


; a transfer paper discharger


136


; and a transfer belt discharger


137


. The paper transfer belt


134


is made of PVDF (polyvinylidene fluoride) to have a high volume resistance of 10


13


Ωcm or higher. It should be understood that the transfer unit


130


is not limited to the foregoing structure, and that in an alternative, the transfer unit


130


may employ, for example, a member of a different shape such as a drum instead of the paper transfer belt


134


.




Next, the operation of the copier according to the third embodiment will be described in connection with an illustrative image forming mode in which the development is performed in the order of Bk, C, M, Y. Before starting an image forming cycle, the photosensitive drum


10


is driven to rotate in a direction indicated by an arrow C in

FIG. 9

, i.e., in the counter-clockwise direction, causing the charger


113


to initiate corona discharge. In this event, in the third embodiment, the photosensitive drum


10


is uniformly charged at a predetermined potential with a negative charge. Also, the intermediate transfer belt


121


of the intermediate transfer unit


120


is driven at the same speed as the photosensitive drum


10


to rotate in a direction indicated by an arrow D, i.e., in the clockwise direction.




Like the aforementioned first embodiment, in the scanner unit, color image information of an original is read at a predetermined timing, and Bk image data derived from the image information is optically written onto the photosensitive drum


10


using laser light produced by the optical writing unit (for example, raster exposure). As a result, a Bk latent image is formed on the photosensitive drum


10


corresponding to the Bk image data. Subsequently, the Bk latent image formed on the photosensitive drum


10


is reversely developed with a negatively charged toner by the Bk developing device


115


in the revolver developing unit


110


. In this way, a Bk toner image is formed on the photosensitive drum


10


.




The Bk toner image thus formed on the photosensitive drum


10


is transferred to the surface of the intermediate transfer belt


121


by the action of a transfer electric field existing in a primary transfer region. The transfer electric field is formed by a charge given to the intermediate transfer belt


121


by the primary transfer bias roller


122


. In this event, the primary transfer bias roller


122


is applied by the primary transfer power supply


128


with a primary transfer bias of a suitable magnitude. For example, the primary transfer bias may be at 1.5 kV for the first color (Bk) toner image; in a range of 1.6 to 1.8 kV for a second color (C) toner image; in a range of 1.8 to 2.0 kV for a third color (M) toner image; and in a range of 2.0 to 2.2 kV for a fourth color (Y) toner image. The toner used in the primary transfer and remaining on the photosensitive drum


10


after the development is removed by the photosensitive drum cleaning unit


111


.




The image forming surface on the intermediate transfer belt


121


, on which the Bk toner image has been transferred, is again returned to the primary transfer region. In this event, the discharging brush roller


151


and the belt cleaning blade


129


are moved away from the intermediate transfer belt


121


by respective contact/separation mechanisms associated therewith so as not to disturb the toner image. Further, the first supporting roller


135




a


and the secondary transfer bias roller


131


in the transfer unit


130


are moved by associated transfer contact/separation mechanisms, not shown, such that the secondary transfer bias roller


131


is moved away from the intermediate transfer belt


121


. In this event, the secondary transfer power supply


139


connected to the secondary transfer bias roller


131


is inhibited from applying a voltage.




The above-mentioned state is held until the toner image transferred to the intermediate transfer belt


121


is transferred to a transfer paper


100


.




After the Bk step is terminated, a C step is started on the photosensitive drum


10


. Specifically, color image information of the original is again read at a predetermined timing, a C latent image is formed on the photosensitive drum


10


by laser light based on C image data derived from the image information, and a C toner image is formed by the C developing device


116


.




In the third embodiment, after the trailing edge of the Bk latent image has passed, the revolver developing unit


110


is immediately rotated. The rotation of the revolver developing unit


110


is completed before the leading edge of the C latent image formed on the photosensitive drum


10


arrives at a developing position of the C developing device


116


. In this way, the C developing device


116


is aligned to the developing position, so that it develops the C latent image coming up to the developing position with a C toner.




Subsequently, in either of an M step and a Y step, the formation of a latent image, development, and primary transfer are performed respectively based on their respective image data in a manner similar to the aforementioned C step. By transferring the respective Bk, C, M and Y toner images sequentially formed on the photosensitive drum


10


to the same image surface area on the intermediate transfer belt


21


, a complete toner image formed of the four color images in accurate register with one another is formed on the intermediate transfer belt


21


.




The complete toner image thus transferred to the intermediate transfer belt


121


is conveyed to the secondary transfer region for secondary transfer of the toner image to a transfer paper


100


. In this event, the secondary transfer bias roller


131


of the transfer unit


130


is pressed against the intermediate transfer belt


121


by a transfer contact/separation mechanism, not shown. Subsequently, the secondary transfer bias roller


131


is applied with a predetermined secondary transfer bias to form a secondary transfer electric field in the secondary transfer region. The secondary transfer electric field causes the toner image on the intermediate transfer belt


121


to be transferred to the transfer paper


100


. The transfer paper


100


is fed into the secondary transfer region at the timing coincident with the arrival of the leading edge of the toner image on the intermediate transfer belt


121


to the secondary transfer region.




The transfer paper


100


, on which the complete toner image formed of four color toner images in accurate register with one another has been collectively transferred from the intermediate transfer belt


121


, is subsequently conveyed to an area opposite to the transfer paper discharger


136


in the transfer unit


130


. When the transfer paper


100


passes this opposing area, the transfer paper


100


is discharged by the transfer paper discharger charger


136


now in operative state, and separated from the paper transfer belt


134


. Then, the separated transfer paper


100


is conveyed to pass between the pair of fixing rollers


145




a


of the fixing unit


145


. The unfixed toner image on the transfer paper


100


is melted in a fixing region formed of a nip between the fixing rollers


145




a


, and the unfixed toner image is fixed. Then, after the fixation, the transfer paper


100


is conveyed to and stacked on the copy tray


46


.




After the secondary transfer, the belt cleaning blade


129


is pressed against the intermediate transfer belt


121


by a contact/separation mechanism, not shown, to remove the toner used in the secondary transfer and remaining on the surface of the intermediate transfer belt


121


. In addition, the charge remaining on the surface of the paper transfer belt


134


, after the transfer paper


100


has been separated, is discharged by the transfer belt discharger


137


. Furthermore, the surface of the paper transfer belt


134


is cleaned by the transfer cleaning blade


132


.




In the following, description will be made on the operation of the control unit


160


which constitutes a characterizing portion of the third embodiment.

FIG. 10

is a block diagram illustrating the configuration of a controller


161


in the control unit


160


. The controller


161


has the same configuration as the second embodiment previously described with reference to FIG.


4


. The controller


161


has an I/O interface


165


which is connected to the variable discharge power supply


159


; a driving motor


124




a


coupled to a driving roller


124


for driving the intermediate transfer belt


121


; and a mark sensor


124




b


for detecting a mark attached on the inner peripheral surface of the intermediate transfer belt


21


for detecting a rotating position. The variable discharge power supply


159


for applying the discharging brush


151


with a direct current voltage is turned ON/OFF at a timing that is set based on an output signal of the mark sensor


124




b


. In the third embodiment, the control unit


160


variably controls the direct current voltage generated by the variable discharge power supply


159


in accordance with a potential on the surface of the intermediate transfer bent


121


, a surface moving speed of the same, and the temperature and humidity around the intermediate transfer belt


121


.




For controlling the direct current voltage of the variable discharge power supply


159


in accordance with the surface potential on the intermediate transfer belt


121


, data on a copy mode of the copier is supplied to a CPU


162


in the controller


161


of the control unit


160


. For controlling the direct current voltage of the variable discharge power supply


159


in accordance with the surface moving speed of the intermediate transfer belt


121


, data on the rotating speed of the driving motor


124




a


for driving the driving roller


124


is supplied to the CPU


162


. For controlling the direct current voltage of the variable discharge power supply


159


in accordance with temperature and humidity conditions around the intermediate transfer belt


121


, the CPU


162


is supplied with temperature data and humidity data through the I/O interface


165


from a temperature and humidity sensor


68


which is disposed near the position at which the discharging brush


151


contacts the intermediate transfer belt


121


, and connected to the I/O interface


165


.




Then, the CPU


162


in the controller


161


calculates an optimal discharging bias based on the various data supplied thereto, and forces the variable discharge power supply


159


to apply the discharging brush


151


with an optimal direct current voltage.




It should be understood that the copier according to the third embodiment can be used not only in the foregoing full-color copy mode but also in any other copy mode, as is the case of the aforementioned first embodiment.




Now, description will be made on one implementation of the present invention which uses the copier according to the third embodiment and a combination of the second, third and fourth examples in the second embodiment for controlling a discharging bias.




Explained first is an experiment conducted to reveal the relationship between a residual potential on the intermediate transfer belt and a discharging bias or a direct current voltage applied to the contact-type discharge member for removing the residual potential. In this experiment, the control unit


160


of the copier was not used.




The experiment involved measurements of affected images produced when an image forming process was executed with a residual potential maintained on the intermediate transfer belt


121


. It is desired that the intermediate transfer belt is discharged such that the surface potential is at zero volt on the intermediate transfer belt after the discharging. Actually, however, it is extremely difficult to bring the surface potential exactly to zero volt by the discharging.




Also, when the intermediate transfer belt is discharged insufficiently, the next primary transfer step is performed with a potential of the same polarity as that of a toner held on the intermediate transfer belt, resulting in an insufficient transfer bias and accordingly an incomplete transfer which will lead to an affected image. On the other hand, excessive discharging causes the intermediate transfer belt


121


to have a surface potential of the opposite polarity to the toner. The next primary transfer performed on the intermediate transfer belt


121


with the surface potential of the opposite polarity would result in a so-called pre-transfer where the primary transfer is performed before the primary transfer region, which leads to deteriorated dot reproductivity and consequently an affected image. To solve this problem, the inventors of the present invention and others measured the relationship between a surface potential Vb on the intermediate transfer belt


121


after discharging (hereinafter referred to as the “post-discharge potential Vb”) and affected images, and concluded in Table 2 below.














TABLE 2













Post-Discharge Potential Vb (volts)















Vb <−300




−300 Vb 300




Vb >300




















Affected Image Due to














X







Pre-Transfer







Affected Image Due to




X

















Insufficient Transfer















Thus, the measurements revealed that when the absolute value of the post-discharge potential Vb on the intermediate transfer belt


121


is at least 300 volts or less, images can be produced without affecting much by pre-transfer or insufficient transfer.




Keeping the foregoing measurement results in mind, the inventors of the present invention and others next conducted an experiment for revealing the relationship between a surface potential Va on the intermediate transfer belt


121


after a secondary transfer step has been completed and before the intermediate transfer belt


121


is discharged (hereinafter referred to as the “pre-discharge potential Va) and the post-discharge potential Vb, with a varying direct current voltage applied to the discharging brush roller.

FIG. 11A

is a graph showing the result of the experiment conducted at temperature of 23° C. and humidity of 65% (in a laboratory environment);

FIG. 11B

is a graph showing the result of the experiment conducted at temperature of 10° C. and humidity of 15% (in an low temperature and low humidity (L.L.) environment); and

FIG. 11C

is a graph showing the result of the experiment conducted at temperature of 27° C. and humidity of 80% (in a high temperature and high humidity (H.H.) environment).




In each of

FIGS. 11A

,


11


B,


11


C, it can be said that each plot is substantially linear when the pre-discharge potential Va on the intermediate transfer belt


121


is at −100 volts or less. From the results of the experiment represented by the graphs, the relationship between the pre-discharge potential Va, the post-discharge potential Vb, and a direct current voltage V applied to the discharging brush


151


can be expressed substantially by the following Equation 1:








Vb


=0.65


Va


+(25


+V


/2)  (Equation 1)






The post-discharge potential Vb which meets the condition of producing images with less pre-transfer and with sufficient transfer must fall within a range expressed by:






−300Va300  (Equation 2)






Therefore, the direct current voltage V applied to the discharging brush


151


for ensuring images with less pre-transfer and with sufficient transfer can be expressed by:






−1.3Va−650 V−1.3Va+550  (Equation 3)






In this implementation, the intermediate transfer belt


121


is formed to have a thickness of 0.15 mm, a width of 368 mm, and an inner peripheral length of 565 mm, and a surface moving speed of the intermediate transfer belt


121


is set at 200 mm/s. Also, the surface layer of the intermediate transfer belt


121


is formed of an insulating layer having a thickness of approximately 1 μm. The intermediate layer of the intermediate transfer belt


121


is formed of polyvinylidene fluoride in a thickness of approximately 75 μm. The volume resistivity ρv of the intermediate layer is 9×10


12


Ωcm when measured using a resistance measuring instrument “High Rester IP” manufactured by Yuka Denshi at temperature of 25° C. and humidity of 45% with a voltage of 100 volts applied thereto for 10 seconds, and 6×10


12


Ωcm when measured in the same environment using the same instrument with a voltage of 500 volts applied thereto for 10 seconds. The base layer is formed of PVDF and titanium oxide in a thickness of approximately 75 μm. The volume resistivity ρv of the base layer is 7×10


7


Ωcm when measured in the same environment using the same instrument with a voltage of 100 volts applied thereto for 10 seconds.




The surface resistance on the surface of the surface layer of the intermediate transfer belt


121


is 10


13


Ωcm when measured with resistance measuring instrument “High Rester IP” manufactured by Yuka Denshi. Other than this resistance measuring instrument, the surface resistivity may be measured in accordance with the surface resistance measuring method described in JISK6911.




In this implementation, the primary transfer bias roller


122


may be a nickel plated metal roller, and the ground roller


123


may be a metal roller. Other rollers may be metal rollers or rollers made of any conductive resin.




The primary transfer bias roller


122


is applied with a direct current primary transfer bias at 1.5 kV for the first color (Bk) toner image; 1.7 kV for the second color (C) toner image; 1.9 kV for the third color (M) toner image; and 2.1 kV for the fourth color (Y) toner image. The width of the nip in the primary transfer region is set to be 10 mm




The transfer unit


130


uses the secondary transfer bias controller


131


implemented by a roller having a surface layer made of a conductive sponge or a conductive rubber, and a core layer made of a metal or a conductive resin. The secondary transfer bias roller


131


is applied with a transfer bias that is a current regulated in a range of 10 to 50 μA. Appropriate values within this range are used depending on copy modes available to the copier and types of used transfer papers. Specific values for the regulated current for different types of papers and different modes are shown in Table 3 below.














TABLE 3











Secondary Transfer Current (μA)



























Normal Paper (1C Mode)




25







Normal Paper (4C Mode)




35







Thick Paper (1C Mode)




14







Thick Paper (4C Mode)




18







Very Thick Paper (1C Mode)




16







Very Thick Paper (4C Mode)




20















The paper transfer belt


134


is formed of a PVDF-based material having a volume resistivity ρv of 10


13


Ωcm in a thickness of 100 μm. The transfer paper discharger


136


and the transfer belt discharger


137


are implemented by dischargers which are applied with an alternate current voltage or with a combination of alternate current and direct current voltages. The transfer cleaning blade


132


is in contact with the surface of the paper transfer belt


134


on the opposite side of the third supporting roller


135




c.






The temperature and humidity sensor


68


described in the third example of the second embodiment is connected to the I/O interface


165


of the controller


161


. Data on temperature and humidity around the intermediate transfer belt


121


sensed by the temperature and humidity sensor


68


is supplied to the CPU


162


in the controller


161


. The CPU


162


is also supplied with information on a copy mode, in which the copier is to operate to produce the next copy, for controlling the discharging bias in accordance with the surface potential on the intermediate transfer belt


121


, more specifically, in accordance with the number of times toner images are transferred or superimposed onto the intermediate transfer belt


121


. Assume in this implementation that three types of copy modes, 1C mode, 2C mode and 4C mode, are available to the copier. The CPU


162


is further supplied with information on a transfer paper on which the copier produces a copy next time, more specifically, information for discriminating whether a normal paper, a thick paper, a very thick paper or an OHP sheet is used. Assume in this implementation that when the copier produces copies on normal papers at a normal speed, the speed of producing copies on thick papers, very thick papers and OHP sheets is one half of the normal speed.




As described above, this implementation employs a variable discharge power supply such as


159


, and the discharging bias applied to the discharging brush roller


151


is set as shown in the following Table 4, Table 5 and Table 6 in accordance with the aforementioned results of the experiments.














TABLE 4











Discharging Bias V (volts)



























1C Mode (Normal Speed)




0







2C Mode (Normal Speed)




0







4C Mode (Normal Speed)




50







1C Mode (Half Speed)




0







2C Mode (Half Speed)




0







4C Mode (Half Speed)




50













Note:











at temperature of 23° C. and humidity of 65%























TABLE 5











Discharging Bias V (volts)



























1C Mode (Normal Speed)




0







2C Mode (Normal Speed)




50







4C Mode (Normal Speed)




350







1C Mode (Half Speed)




0







2C Mode (Half Speed)




50







4C Mode (Half Speed)




350













Note:











at temperature of 10° C. and humidity of 15%























TABLE 6











Discharging Bias V (volts)



























1C Mode (Normal Speed)




0







2C Mode (Normal Speed)




0







4C Mode (Normal Speed)




50







1C Mode (Half Speed)




0







2C Mode (Half Speed)




0







4C Mode (Half Speed)




50













Note:











at temperature of 27° C. and humidity of 80%













Also in this implementation, four copies are produced from a single original sheet using normal papers of A4 size. It should be noted that in this implementation, the intermediate transfer belt


121


is formed with an image surface area for accommodating two images to speed the image formation. During the image formation, the discharging brush roller


151


is applied with a discharging bias at a timing which is controlled in accordance with a timing chart as illustrated in FIG.


12


. The discharging brush roller


151


is moved into and out of contact with the intermediate transfer belt


121


in association with timings at which the belt cleaning blade


129


which is moved into and out of contact with the intermediate transfer belt


121


. As illustrated in

FIG. 12

, the discharging bias is controlled in the following manner. The discharging bias is applied when the surface of the intermediate transfer belt has moved by 24 mm after the discharging brush roller


151


had been brought into contact with the intermediate transfer belt


121


. Then, the applied discharging bias is removed slightly before the discharging brush


151


is moved out of contact with the intermediate transfer belt


121


.




[Embodiment 4]




Next, a fourth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 13

schematically illustrates the configuration of a main portion in a printer unit of the copier according to the fourth embodiment. In general, the illustrated copier, which is intended for a reduction in cost, differs from the copier according to the second embodiment only in the following aspects. Therefore, similar constituent members in the fourth embodiment are designated the same reference numerals as those in the second embodiment, and description thereon is omitted.




In the fourth embodiment, an intermediate transfer belt


221


forming part of an intermediate transfer unit


220


has a middle resistance intermediate layer with a volume resistivity ρv in a range of 10


8


Ωcm to 10


11


Ωcm. Also, the intermediate transfer belt


221


, as a whole, has a volume resistivity ρv in a range of 10


10


Ωcm to 10


12


Ωcm. Further, the intermediate transfer belt


221


is made to have a surface resistivity on the surface side in a range of 10


7


Ωcm to 10


14


Ωcm. More specifically, the intermediate layer is formed of PVDF and titanium oxide with the volume resistivity ρv of 5×10


12


Ωcm when measured using the aforementioned resistance measuring instrument “High Rester IP” manufactured by Yuka Denshi at temperature of 25° C. and humidity of 45% with a voltage of 100 volts applied thereto for 10 seconds, and 2×10


11


Ωcm when measured in the same environment using the same instrument with a voltage of 500 volts applied thereto for 10 seconds. The surface layer of the intermediate transfer belt


221


is formed of an insulating layer having a thickness of approximately 1 μm. The base layer is formed of PVDF and titanium oxide in a thickness of approximately 75 μm. The volume resistivity ρv of the base layer is 7×10


7


Ωcm when measured in the same environment using the same instrument with a voltage of 100 volts applied thereto for 10 seconds. In addition, a surface moving speed of the intermediate transfer belt


221


is set at 156 mm/s. The use of the intermediate transfer belt


221


having such a middle resistance can prevent uneven charging from occurring on the surface of the intermediate transfer belt


221


after primary transfer. Additionally, in the fourth embodiment, a driving roller


224


in the intermediate transfer unit


220


is disposed downstream of a secondary transfer region and upstream of a primary transfer region in a direction of movement of the intermediate transfer belt


221


. Then, a belt cleaning blade


129


is disposed opposite to the driving roller


224


, so that the driving roller


224


may also serve as the cleaning opposed roller


127


that is used in the third embodiment.




A primary transfer bias roller


122


is applied with a direct current primary transfer bias at 1.7 kV for the first color (Bk) toner image; 1.8 kV for the second color (C) toner image; 1.9 kV for the third color (M) toner image; and 2.0 kV for the fourth (Y) toner image.




The fourth embodiment employs, as a transfer means, a secondary bias roller


231


disposed opposite to a secondary transfer opposed roller


126


in the intermediate transfer unit


220


, instead of the transfer unit used in the third embodiment. Thus, a fed transfer paper


100


is sandwiched between a secondary transfer bias roller


234


and the intermediate transfer belt


221


, and conveyed to pass between a pair of fixing rollers


145




a


of a fixing unit


145


. The configuration as described results in a reduction in the number of constituent members required for the secondary transfer step and accordingly a reduced cost as compared with the third embodiment.




The secondary transfer bias roller


231


is implemented by a roller made of conductive rubber, and is applied with a transfer bias that is a regulated current having values as shown in Table 7 below.














TABLE 7











Secondary Transfer Current (μA)



























Normal Paper (1C Mode)




10







Normal Paper (4C Mode)




18







Thick Paper (1C Mode)




 8







Thick Paper (4C Mode)




10







Very Thick Paper (1C Mode)




non







Very Thick Paper (4C Mode)




non















[Embodiment 5]




Next, a fifth embodiment of the present invention will be described in connection with an image forming apparatus which employs a transfer material carrier such as a belt for carrying and conveying a transfer material such as a paper, an OHP sheet or the like, and to which the present invention is applied.





FIG. 14

schematically illustrates the configuration of a transfer unit equipped in the copier according to the fifth embodiment. In the fifth embodiment, the present invention is utilized in a transfer material carrier for carrying and conveying a transfer material rather than in an intermediate transfer unit as in the foregoing embodiments.




The transfer unit


330


has a paper transfer belt


332


for carrying and conveying a transfer material such as a paper, an OHP sheet or the like; a cleaning blade


331


for cleaning the surface of the paper transfer belt


332


; a ground roller


335




a


positioned at one end of a paper feed unit, not shown, and serving as a pre-transfer discharging means; a transfer bias roller


334


as a charge supply means; a transfer power supply


338


connected to the transfer bias roller


334


; a tension roller


335




b


positioned at one end of a fixing unit, not shown; a cleaning opposed roller


335




c


disposed opposite to the cleaning blade


331


for aiding the cleaning blade


331


in cleaning the surface of the paper transfer belt


332


; a transfer paper discharger


336


; and a discharge roller


251


which is a contact-type discharge member. The paper transfer belt


332


used in the fifth embodiment may be formed of a middle resistance material having a volume resistivity ρv in a range of 10


8


Ωcm to 10


11


Ωcm. It should be understood that the transfer unit


330


is not limited to this configuration, and that in an alternative, the transfer unit


330


may employ, for example, a member of a different shape such as a drum instead of the paper transfer belt


332


.




The copier according to the fifth embodiment forms a toner image on a photosensitive drum


10


serving as an image carrier in a well known electronic photographic process, and transfers the toner image to a transfer material, or a transfer paper


100


in this embodiment, fed into a transfer region defined by a transfer nip formed between the photosensitive drum


10


and the paper transfer belt


332


. In this event, an intermediate transfer belt may also be used as the image carrier instead of the photosensitive drum


10


.




The ground roller


335




a


is disposed downstream of the transfer region in a direction of movement of the paper transfer belt


332


(hereinafter referred to as the “paper transfer belt moving direction). On the other hand, the transfer bias roller


334


is disposed upstream of the transfer region in the paper transfer belt moving direction. The transfer bias roller


334


is applied with a predetermined transfer bias from the transfer power supply


338


, whereby a transfer electric field is formed in the transfer region. Then, a toner image on the photosensitive drum


10


is transferred to the transfer paper


100


which is carried on and conveyed by the paper transfer belt


332


. Then, the transfer paper


100


, which has received the toner image transferred thereto, passes through a separation region in which the transfer paper


100


is discharged by the transfer paper discharger


336


to separate the transfer paper


100


from the paper transfer belt


332


. Then, the transfer paper


100


separated from the paper transfer belt


332


is conveyed to a fixing unit, not shown.




An area of the paper transfer belt


332


, from which the transfer paper


100


has been separated, is cleaned by the cleaning blade


331


. The discharge roller


251


is disposed downstream of the cleaning blade


331


in the paper transfer belt moving direction, such that the paper transfer belt


332


is discharged by the discharge roller


251


. The discharge roller


251


is grounded through the discharge power supply


259


. The discharger roller


251


is applied by the discharge power supply


259


with a direct current or an alternate current discharging bias, or a combination of direct current and alternate current discharging biases. In this event, when a direct current power supply for applying a direct current voltage is employed as the discharge power supply, a reduction in cost is expected. The fifth embodiment employs a regulated direct current power supply as the discharge power supply


259


.




It is also possible to employ a variable discharge power supply to vary a direct current voltage applied to the discharge roller


251


in accordance with a variety of factors which may cause variations in an optimal value for the discharging bias, in a manner similar to the discharging of the intermediate transfer belt in the aforementioned embodiments.




While the fifth embodiment has been described as employing a photosensitive drum as an image carrier for an illustrative purpose, the present invention can be applied to other image carriers having different structures, for example, to an endless photosensitive belt which is passed over two rollers for endless movement. In addition, while the fifth embodiment employs a bias roller as a charge supply means for use in the primary transfer or the secondary transfer for an illustrative purpose, other members of different shapes such as a blade, a brush and so on may also be employed instead. Similarly, while the fifth embodiment employs a ground roller as a pre-transfer discharging means for an illustrative purpose, other members of different shapes such as a blade, a brush and so on may also be employed instead.




Also, while the aforementioned first to fourth embodiments have each employed an intermediate transfer belt as an intermediate transfer body for an illustrative purpose, the present invention can be applied to other intermediate transfer bodies having configurations different from the foregoing, for example, an intermediate transfer drum, an intermediate transfer roller, and so on. Further, the electric characteristic such as the surface resistivity or the like, structure, thickness and so on of the intermediate transfer belt may be selected as appropriate depending on specific applications which may require different image forming conditions.




Furthermore, the foregoing embodiments have illustrated a developing unit which employs a reverse developing mode in which the photosensitive drum is negatively charged, and a two-component based developer is used. The present invention, however, is not limited to any specific developer or the polarity of a charging potential on the photosensitive drum, and can be applied to any image forming apparatus which may employ a one-component based developer, a normal developing mode, or the like.




[Embodiment 6]




Referring next to

FIGS. 15

to


17


, a sixth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 15

is a cross-sectional view schematically illustrating the configuration of the copier according to the sixth embodiment, and

FIG. 16

is an enlarged view schematically illustrating the structure around a photosensitive drum


10


in the copier of FIG.


15


. The following description will be mainly focused on only those portions which are different from the first embodiment illustrated in

FIGS. 1 and 2

.




A photosensitive drum cleaning unit


450


has, within a casing


452


, a fur brush


451


as a cleaning member; a residual toner recovering container


455


for containing the toner remaining after first transfer and swept away by the fur brush


451


; and a flicker


456


for removing residual toner attached on the fur brush. The photosensitive drum cleaning unit


450


is provided for cleaning the surface of the photosensitive drum


10


after primary transfer.




Around an intermediate transfer belt


21


, there are disposed a belt cleaning unit


460


, and a transfer unit


30


. The belt cleaning unit


460


is provided with a cleaning blade


461


disposed within a casing


462


, and a cleaning contact/separation mechanism


463


for moving the cleaning blade


461


into and out of contact with the intermediate transfer belt


21


as required.




In addition, the transfer unit


30


has a secondary transfer bias controller


34


opposing a driving roller


24


of the intermediate transfer unit


20


; a cleaning blade


31


disposed within a casing


32


; and a transfer contact/separation mechanism


33


. The transfer contact/separation mechanism


33


enables the secondary transfer bias controller


34


to come into contact with and separate away from the intermediate transfer belt


21


.




During a time period in which a complete toner image is formed on the intermediate transfer belt


21


, specifically, during a time period from the time the first color (Bk) toner image had been transferred to the intermediate transfer belt


21


to the time the fourth color (Y) toner image has been transferred to the same, the cleaning blade


461


of the belt cleaning unit


460


and the secondary bias roller


34


of the transfer unit


30


are separated away from the intermediate transfer belt


21


by the respective contact/separation mechanisms (


463


,


33


) associated therewith.




While the operation of the copier has been described in connection with a copy mode for producing full-color copies, the same description is applicable to other copy modes, i.e, a three-color copy mode and a two-color copy mode, except that used colors and associated mechanisms are different. For a single-color copy mode, a developer in a developing device associated with a selected color is maintained to form a sleeve or ear, i.e., the developing device is maintained in operative state until a predetermined number of copies have been produced. Also, with the belt cleaning unit


460


and the transfer unit


30


maintained in contact with the intermediate transfer belt


21


and with the intermediate transfer belt


21


maintained in contact with the photosensitive drum


10


, the intermediate transfer belt


21


is driven in the forward direction at a constant speed for producing copies.




In the following, description will be made on the configurations and operations of characterizing portions of the sixth embodiment, i.e., the photosensitive drum cleaning unit


450


for cleaning the photosensitive drum


10


; the cleaning unit


460


for cleaning the intermediate transfer belt


21


; and the cleaning blade


31


for cleaning the secondary transfer bias roller


34


of the transfer unit


30


.




First, the photosensitive drum cleaning unit


450


will be described in terms of its configuration with reference to FIG.


16


. Essentially, the photosensitive cleaning unit


450


of the sixth embodiment simultaneously cleans and discharges the photosensitive drum


10


. The sixth embodiment employs the fur brush


451


which is formed of a conductive roller and a conductive brush sheet wrapped around the roller.




The conductive roller, serving as a core bar of the fur brush


451


, is connected to a ground


454


. To improve a discharging efficiency, the fur brush


451


is fabricated such that the resistance between a portion contacting the photosensitive drum


10


, i.e., the brush tip and the ground


454


is equal to or lower than 10


8


Ω, and preferably, equal to or lower than 10


7


Ω. While the sixth embodiment employs a fur brush as a cleaning member, other cleaning members well known in the art may also be used, for example, a cleaning blade, a combination of a cleaning blade and a fur brush, and so on. In addition, the fur brush


451


with a narrowest possible gaps between edges of the wrapped conductive brush sheet would have an improved cleaning performance and eliminate uneven discharging because of a more uniform bristle density in the axial direction of the fur brush


451


.




Description will next be made on the operation of the photosensitive drum cleaning unit


450


. After a toner image formed on the photosensitive drum


10


has been transferred to the intermediate transfer belt


21


, the toner remaining on the photosensitive drum


10


after the primary transfer is brought into a cleaning region defined between the photosensitive drum


10


and the fur brush


451


. Then, the residual toner is swept away from the photosensitive drum


10


by the rotating fur brush


451


. It should be noted the fur brush


451


is driven to rotate at a speed relative to the intermediate transfer belt


21


in order to prevent the discharging performance from degrading and bristles of the fur brush


451


from lying down. In the sixth embodiment, the fur brush


451


is rotated in the direction reverse to the intermediate transfer belt


21


.




As mentioned above, the residual toner swept away by the fur brush


451


is received by the residual toner recovering container


455


within the casing


452


. Also, residual toner attached on the fur brush


451


is removed therefrom by the flicker


456


in contact with the fur brush


451


. The removed residual toner is received by the residual toner recovering container


455


. A recovering roller


453


is disposed inside the residual toner recovering container


455


. The recovering roller


453


is applied by a power supply, not shown, with a bias for attracting the residual toner. In this way, since the residual toner received by the residual toner recovering container


455


is collected by the recovering roller


453


, contamination inside the copier is obviated.




It should be noted that the fur brush


451


also discharges the photosensitive drum


10


simultaneously with the cleaning when it comes in contact therewith. Specifically, since the fur brush


451


is made of conductive materials and is grounded, the fur brush


451


, when in contact with the photosensitive drum


10


, causes a residual charge on the surface of the photosensitive drum


10


to flow into the fur brush


451


. In this way, the residual charge on the photosensitive drum


10


can be removed so that the photosensitive drum


10


is discharged.




Next, the belt cleaning unit


460


will be described in terms of the structure with reference again to FIG.


16


. The belt cleaning unit


460


of the sixth embodiment has the ability of simultaneously cleaning and discharging the intermediate transfer belt


21


. Unlike the photosensitive drum cleaning unit


450


, the belt cleaning unit


460


employs a conductive cleaning blade


461


as a cleaning member. The cleaning blade


461


is formed of a plate-shaped member which contacts the intermediate transfer belt


21


over its entire width.




The cleaning blade


461


is connected to a ground


464


, and is fabricated such that the resistance between a portion contacting the intermediate transfer belt


21


, i.e., the blade tip and the ground


464


is equal to or lower than 10


8


Ω, and preferably, equal to or lower than 10


7


Ω. While the sixth embodiment employs a cleaning blade as a cleaning member, other cleaning members well known in the art may also be used, as is the case of the photosensitive drum cleaning unit


450


.




Description will next be made on the operation of the belt cleaning unit


460


. Generally, after a toner image on the intermediate transfer belt


21


transferred from the photosensitive drum


10


(primary transfer) has been transferred to a transfer paper


100


(secondary transfer), the residual toner remaining on the intermediate transfer belt


21


is introduced into a cleaning region defined between the intermediate transfer belt


21


and the cleaning blade


461


. Then, the residual toner is removed from the intermediate transfer belt


21


by the cleaning blade


461


pressed against the intermediate transfer belt


21


, falls into the casing


461


and remains therein.




The cleaning blade


461


simultaneously discharges the intermediate transfer belt


21


when they are in contact. Specifically, as the cleaning blade


461


comes into contact with the intermediate transfer belt


21


, a residual charge on the intermediate transfer belt


21


after secondary transfer, negatively charged due to the discharging which occurs when a transfer paper is separated therefrom, flows into the cleaning blade


461


connected to the ground


464


. In this way, the residual charge on the intermediate transfer belt


21


can be removed to discharge the intermediate transfer belt.




Next, a modification to the sixth embodiment will be described with reference to FIG.


17


.

FIG. 17

is an enlarged view illustrating the configuration of the photosensitive drum and associated components therearound in the copier of the sixth embodiment including the modification. The illustrated copier is substantially similar to the sixth embodiment except that discharge power supplies (


458


,


468


) are connected to the fur brush


451


of the photosensitive drum cleaning unit


450


and to the cleaning blade


461


of the belt cleaning unit


460


, respectively, for applying respective discharging biases.




A bias applied to the fur brush


451


of the photosensitive drum cleaning unit


450


may be selected from a direct current or an alternate current bias, or a combination of direct current and alternate current biases as the case may be. Such a discharging bias promotes a residual charge existing on the photosensitive drum


10


to flow into the fur brush


451


, thus allowing for efficient discharging. In this way, the photosensitive drum


10


can be stably discharged even when the surface moving speed of the photosensitive drum


10


is increased, for example, in order to perform the image formation at a higher speed.




The cleaning blade


461


of the belt cleaning unit


460


is also applied with a discharging bias as described above, and similar effects can be produced thereby. It is further possible to apply a discharging bias to the cleaning blade


31


in the transfer unit


30


to discharge the secondary transfer bias roller


34


, in a manner similar to the cleaning blade


461


of the belt cleaning unit


460


.




[Embodiment 7]




Referring next to

FIG. 18

, a seventh embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”) in which the present invention is applied.

FIG. 18

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the seventh embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the sixth embodiment. The seventh embodiment differs from the sixth embodiment in a belt cleaning unit for cleaning an intermediate transfer belt in the printer unit. Since the copier of the seventh embodiment performs image forming operations basically in the same manner as the sixth embodiment, description on those parts that are constructed and operated in a manner similar to the sixth embodiment is omitted.




In

FIG. 18

, a belt cleaning unit


560


of the seventh embodiment has a fur brush


561


and cleaning blade


567


disposed within a casing


562


as cleaning members; and cleaning contact/separation mechanism


563


for moving the fur brush


561


and the cleaning blade


567


into and out of contact with an intermediate transfer belt


21


as required. The fur brush


561


has the ability of simultaneously cleaning and discharging the intermediate transfer belt


21


, and is the same as the fur brush


451


of the photosensitive cleaning unit


450


in the aforementioned sixth embodiment. The cleaning blade


567


, in turn, is disposed downstream of the fur brush


561


in a belt moving direction, and, unlike the fur brush


561


, only cleans the intermediate transfer belt


21


without discharging it.




The cleaning blade


567


is connected to a cleaning power supply for applying the same with a cleaning bias. This cleaning bias has a polarity which repels that of the residual toner remaining on the intermediate transfer belt


21


. Specifically, since the residual toner has the negative polarity, the cleaning blade


567


is applied with a cleaning bias of negative polarity. The applied cleaning bias produces a repellent force to disperse a portion of the residual toner remaining on the intermediate transfer belt


21


after secondary transfer from a cleaning region, before the cleaning blade


567


comes in contact with the intermediate transfer belt


21


, so that the residual toner is partially removed before cleaning. The remaining residual toner, not affected by the repellent force, is introduced into the cleaning region as it is, and removed by the cleaning blade


567


.




In the manner described above, the intermediate transfer belt


21


is cleaned by the cleaning blade


567


after the amount of residual toner remaining thereon has been previously reduced. In this way, even if a large amount of residual toner, for example, due to a jammed transfer paper


100


, must be removed from the intermediate transfer belt


21


by the cleaning blade


567


, it is possible to completely remove the residual toner from the intermediate transfer belt


21


. The residual toner dispersed by the repelling force of the cleaning bias is received on the inner wall of the casing


562


, and accumulated within the casing


562


. The residual toner removed by the cleaning blade


567


, in turn, falls into the casing


562


by the gravity and accumulated therein.




As appreciated, the seventh embodiment employs a combination of the fur brush


561


having the discharging ability and the cleaning blade


567


as cleaning members. Alternatively, the intermediate transfer belt


121


may be cleaned by a conventional cleaning blade without discharging ability and separately providing a discharging means, or by utilizing an intermediate transfer belt having such a volume resistivity ρv that does not require discharging, or the like. Further, the copier according to the seventh embodiment can be utilized not only in the foregoing full-color copy mode but also in any other copy mode, as is the case of the sixth embodiment.




[Embodiment 8]




Referring next to

FIG. 19

, an eighth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”) in which the present invention is applied.

FIG. 19

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the eighth embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the sixth embodiment, and performs image forming operations basically in the same manner as the copier of FIG.


15


. The eighth embodiment differs from the sixth embodiment mainly in the structure and operation of the printer unit.

FIG. 19

corresponds to

FIG. 9

, so that the following description will be mainly focused on only those portions which are different from FIG.


9


.




A photosensitive drum cleaning unit


550


has a fur brush


551


and a cleaning blade


557


, and is provided for cleaning the surface of a photosensitive drum


10


after primary transfer. It should be noted that the fur brush


551


and the cleaning blade


557


in the photosensitive drum cleaning unit


550


are identical in structure to the fur brush


561


and the cleaning blade


567


in the belt cleaning unit


560


.




Around an intermediate transfer belt


121


, there are disposed a belt cleaning unit


660


, and a transfer unit


130


which can be moved into and out of contact with the intermediate transfer belt


121


by respective contact/separation mechanisms, not shown, associated therewith.




An image surface area on the intermediate transfer belt


121


, on which a Bk toner image formed in the aforementioned process has been transferred, is again returned to a primary transfer region, as is the case of the sixth embodiment. In this event, the cleaning blade


661


of the belt cleaning unit


660


is moved away from the intermediate transfer belt


121


by a mechanism, not shown, associated therewith so as not to disturb the toner image. Further, a first supporting roller


135




a


and a secondary transfer bias roller


131


in the transfer unit


130


are also moved by associated transfer contact/separation mechanisms, not shown, such that the secondary transfer bias roller


131


is moved away from the intermediate transfer belt


121


. In this event, a secondary transfer power supply


139


connected to the secondary transfer bias roller


131


is inhibited from applying a voltage.




The above-mentioned state is held until the toner image transferred to the intermediate transfer belt


121


is transferred to a transfer paper


100


.




In the following, description will be made on the a cleaning opposed roller


127


, opposing the cleaning blade


661


through the intermediate transfer belt


121


, which constitutes a characterizing portion of the eighth embodiment. It should be noted that the cleaning blade


661


has the ability of simultaneously cleaning and discharging the intermediate transfer belt


121


, and has the same structure as the cleaning blade


461


of the belt cleaning unit


460


in the aforementioned sixth embodiment.




The cleaning opposed roller


127


of the eighth embodiment is connected to a cleaning power supply


140


for applying a cleaning bias. This cleaning bias has a polarity which generates an electric field that causes a residual toner remaining on the intermediate transfer belt


121


to separate therefrom. Specifically, since the residual toner has the negative polarity, the cleaning opposed roller


127


is applied with a cleaning bias of negative polarity. Such a cleaning bias applied to the cleaning opposed roller


127


results in the formation of the above-mentioned electric field in a region in front of the cleaning blade


661


, i.e., in a region upstream of the cleaning blade


661


in a belt moving direction. Consequently, a portion of residual toner remaining on the intermediate transfer belt


121


after secondary transfer is removed by the electric filed, before it is introduced into a cleaning region. The remaining residual toner, not affected by the electric field, is introduced into the cleaning region as it is, and removed by the cleaning blade


661


.




In one implementation, the fur brush


551


of the photosensitive cleaning unit


550


is formed of a metal roller and a conductive brush sheet wrapped around the metal roller. The conductive brush sheet is made of acrylic fiber dispersed with carbon and having a size of 6.5 deniers, and wrapped around the metal roller such that a gap between edges of the wrapped sheet is 1 mm or less. The fur brush


551


has a filling density of 100,000 per square inch. The resistance from the brush tip to the ground of the fur brush


551


is set at 10


6


Ω. For the cleaning blade


557


of the photosensitive drum cleaning unit


550


, a known one is used.




A cleaning blade


661


having a discharging ability is used for the belt cleaning unit


660


. The cleaning blade


661


is formed of a conductive material. The casing


662


of the belt cleaning unit


660


includes a blade mount


662


extending from the inner wall surface of the casing


662


, to which an electrode member


662




b


is secured, as can be seen in FIG.


20


. The electrode member


662




b


is connected to a discharge power supply


668


and also to a ground


664


. Further, the cleaning blade


661


is securely adhered on the electrode member


662




b


with a conductive adhesive


662




c.






In the manner described above, the intermediate transfer belt


121


is cleaned by the cleaning blade


661


after the amount of residual toner remaining thereon has been previously reduced by the electric field. In this way, even if a large amount of residual toner, for example, due to a jammed transfer paper


100


, must be removed from the intermediate transfer belt


121


by the cleaning blade


567


, it is possible to completely remove the residual toner from the intermediate transfer belt


121


. The residual toner removed by the electric field is received on the inner wall of the casing


662


, and accumulated within the casing


662


. The residual toner removed by the cleaning blade


661


, in turn, falls into the casing


662


by the gravity and accumulated therein.




As appreciated, the eighth embodiment employs a cleaning blade having a discharging ability as a cleaning member. Alternatively, the intermediate transfer belt


121


may be cleaned only by the cleaning blade


661


, for example, by separately providing a discharging means, by utilizing an intermediate transfer belt having such a volume resistivity ρv that does not require discharging, or the like. Further, the copier according to the eighth embodiment can be utilized not only in the foregoing full-color copy mode but also in any other copy mode, as is the case of the sixth embodiment.




[Embodiment 9]




Referring next to

FIG. 21

, a ninth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 21

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the ninth embodiment. In general, the illustrated copier is intended for a reduction in cost, and differs from the copier according to the eighth embodiment only in the following aspects. Therefore, similar constituent members in the ninth embodiment are designated the same reference numerals as those in the eighth embodiment, and description thereon is omitted.

FIG. 21

corresponds to

FIG. 11

so that the following description will be mainly focused on only those portions which are different from FIG.


11


.




A cleaning opposed roller


227


in the ninth embodiment also functions as a belt driving means. A cleaning blade


761


is disposed opposite to the cleaning opposed roller


227


through an intermediate transfer belt


221


.




In the following, a belt cleaning unit


760


, which constitutes a characterizing portion of the ninth embodiment, will be described with reference to FIG.


22


.





FIG. 22

is an enlarged view illustrating that a cleaning blade


761


of the belt cleaning unit


760


opposes the cleaning opposed roller


227


of the intermediate transfer unit


220


. The cleaning opposed roller


227


is grounded.




The cleaning blade


761


has the ability of simultaneously cleaning and discharging the intermediate transfer belt


221


. The cleaning blade


761


has a cleaner


761


positioned on the upstream side in a belt moving direction E of the intermediate transfer belt


221


; a discharger


761




b


positioned on the downstream side of the belt moving direction E; and an insulating layer


761




c


interposed between the cleaner


761




a


and the discharger


761




b


for insulating them.




The cleaner


761




a


is connected to a cleaning power supply


769


for applying the cleaner


761




a


with a bias of a polarity which repels that of residual toner


200


remaining on the intermediate transfer belt


221


. The discharger


761




b


in turn is connected to a discharge power supply


768


. Specifically, since the residual toner


200


is negatively charged, the cleaning power supply


769


applies the cleaner


761




a


with a bias of the same polarity as that of the residual toner


200


. On the other hand, the discharge power supply


768


applies the discharger


761




b


with a bias of the opposite polarity to that of the residual toner


200


.




By thus applying the cleaner


761




a


and the discharger


761




b


with respective biases, it is possible to maintain the cleaning performance by previously removing a portion of the residual toner before cleaning and simultaneously discharge the intermediate transfer belt


221


. Stated another way, even when a large amount of residual toner is deposited on the intermediate transfer belt


221


, the residual toner can be completely removed and the intermediate transfer belt


221


can be discharged by a single member. In addition, by completely removing the residual toner by the action of the cleaner


761




a


, the discharging performance of the discharger


761




b


can be improved, thereby making it possible to accomplish stable and effective discharging.




As a modification to the ninth embodiment, the cleaning opposed roller


227


may be modified to have a similar structure to the cleaning opposed roller


127


in the eighth embodiment, with the result that the cleaning performance can be further improved. Consequently, this leads to a further improvement in the discharging performance of the discharger


761




b


and more stable and effective discharging.




[Embodiment 10]




Next, a tenth embodiment of the present invention will be described in connection with an image forming apparatus which employs a transfer material carrier such as a belt for carrying and conveying a transfer material such as a paper, an OHP sheet or the like, and to which the present invention is applied.





FIG. 23

schematically illustrates a transfer unit of a copier according to the tenth embodiment. In the tenth embodiment, the present invention is utilized in a transfer material carrier for carrying and conveying a transfer material rather than in an intermediate transfer unit as in the foregoing embodiments.

FIG. 23

corresponds to

FIG. 12

so that the following description will be mainly focused on only those portions which are different from FIG.


12


.




An area of the paper transfer belt


332


, from which a transfer paper


100


has been separated, is moved to a cleaning region defined between the cleaning blade


331


and the cleaning opposed roller


335




c


. After completion of a normal transfer step, there is a bit of contaminants such as paper dusts, rather than toner, attached on the paper transfer belt


332


. Such contaminants may be sufficiently removed by any conventional cleaning member. However, for example, if a jammed transfer paper


100


results in a toner image on the photosensitive drum


10


transferred to the paper transfer belt


332


, instead of a transfer paper, an excessively large amount of toner must be removed by a cleaning member. This problem is particularly grave in a full color image forming apparatus. In this case, an amount of toner exceeding the cleaning capability of the cleaning blade


331


will be introduced into the cleaning region, so that a conventional cleaning member is not capable of completely removing such a large amount of toner. As a result, a portion of the toner, too much for the cleaning member to remove, may cause troubles such as an insufficient transfer bias or the like in the next transfer step.




In the tenth embodiment, however, a portion of toner is previously removed making use of an electric action, before cleaning, to reduce the amount of toner introduced into the cleaning region, such that the cleaning blade


331


removes only the remaining toner, in a manner similar to the ninth embodiment. In this way, since the amount of toner remaining on the paper transfer belt


332


is previously reduced before cleaning, even a large amount of toner can be completely removed from the paper transfer belt


332


.




The foregoing tenth embodiment utilizes an electric field as a means for removing a portion of residual toner before the paper transfer belt


332


comes in contact with the cleaning blade


331


. However, when a magnetic toner is employed in some copiers, a magnetic field generating means may be used to form a magnetic field which can remove a residual magnetic toner.




[Embodiment 11]




Referring next to

FIGS. 24

to


27


, an eleventh embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 24

is a cross-sectional view schematically illustrating the configuration of the copier according to the eleventh embodiment, and

FIG. 25

is an enlarged view schematically illustrating the structure around a photosensitive drum in the copier of FIG.


24


. The following description will be mainly focused on only those portions which are different from the first embodiment illustrated in

FIGS. 1

,


2


.




Around an intermediate transfer belt


21


, there are disposed a lubricant coating unit


850


, a cleaning belt (belt cleaning unit)


460


, and a transfer unit


30


. The lubricant coating unit


850


has a lubricant coating brush roller


851


, a lubricant container


852


, and a contact/separation mechanism


853


for moving the lubricant coating brush roller


851


into and out of contact with the intermediate transfer belt


21


. The lubricant coating brush roller


851


is associated with the contact/separation mechanism


853


, so that it is driven by the contact/separation mechanism


853


to come into and out of contact with the intermediate transfer belt


21


.




The cleaning unit


460


has a brush roller


465


and a cleaning blade


461


as cleaning members, and a cleaning unit contact/separation mechanism


463


. The cleaning unit contact/separation mechanism


463


enables the cleaning unit


460


to come into and out of contact with the intermediate transfer belt


21


.




While the seventh embodiment employs a combination of the cleaning blade


461


and the brush roller


465


as cleaning members, they may be used in separation, or other known cleaning members may also be used.




During a time period in which a complete toner image is formed on the intermediate transfer belt


21


, specifically, during a time period from the time the first color (Bk) toner image had been transferred to the intermediate transfer belt


21


to the time the fourth color (Y) toner image has been transferred to the same, the lubricant coating unit


850


, the cleaning unit


460


, and the transfer unit


30


are separated away from the intermediate transfer belt


21


by the respective contact/separation mechanisms (


853


,


463


,


33


) associated therewith.




While the operation of the copier has been described in connection with a copy mode for producing full-color copies, the same description is applicable to other copy modes, i.e, a three-color copy mode and a two-color copy mode, except that used colors and associated mechanisms are different. For a single-color copy mode, a developer in a developing device associated with a selected color is maintained to form a sleeve or ear, i.e., the developing device is maintained in operative state until a predetermined number of copies have been produced. Also, with the lubricant coating unit


850


, the cleaning unit


460


, and the transfer unit


30


maintained in contact with the intermediate transfer belt


21


and with the intermediate transfer belt


21


maintained in contact with the photosensitive drum


10


, the intermediate transfer belt


21


is driven in the forward direction at a constant speed for producing copies.




In the following, description will be made on the structure and operation of the lubricant coating unit


850


which constitutes a characterizing portion of the eleventh embodiment.

FIG. 26

is a cross-sectional view schematically illustrating the structure of the lubricant coating unit


850


according to the eleventh embodiment, and

FIG. 27

is a front view of a lubricant coating brush roller


851


in the lubricant coating unit


850


. The lubricant coating unit


850


is disposed downstream of a secondary transfer region and upstream of a primary transfer region in a belt moving direction, and downstream of the cleaning blade


461


and upstream of the primary transfer region in the belt moving direction.




The lubricant coating unit


850


is mounted to an arm


853




a


extending from the contact/separation mechanism


853


. A solid lubricant


855


and a spring


856


are contained in the lubricant container


852


of the lubricant coating unit


850


. The solid lubricant


855


may be, for example, a plate formed of fine particles of zinc stearate. The solid lubricant


855


is urged by the spring


856


toward the lubricant coating brush roller


851


to be in contact therewith. The lubricant coating brush roller


851


can be driven by a driving means, not shown, for rotation. When the lubricant


855


is actually coated on the intermediate transfer belt


21


after secondary transfer, the lubricant coating brush roller


851


is rotated to scrape off the solid lubricant


855


. The lubricant thus scraped off is transformed into powder which is then coated on the intermediate transfer belt


21


.




In the eleventh embodiment, the lubricant coating brush roller


851


also functions as a discharging member. Specifically, the lubricant coating brush roller


851


is brought into contact with the intermediate transfer belt


21


to coat the lubricant thereon and simultaneously discharge the intermediate transfer belt


21


. In this event, the lubricant coating brush roller


851


is driven to rotate in the same direction as the intermediate transfer belt


21


in order to prevent the discharging performance from degrading and its brush bristles from lying down. In addition, the lubricant coating brush roller


851


is controlled such that it rotates at a line velocity higher than that of the intermediate transfer belt


21


in a discharge region in which the lubricant coating brush roller


851


contacts the intermediate transfer belt


21


.




As illustrated in

FIG. 27

, the lubricant coating brush roller


851


is formed of a conductive roller and a conductive fabric sheet


851




b


having brush bristles


851




a


wrapped around the conductive roller. In this event, the brush roller


851


with a narrowest possible gaps between edges of the wrapped conductive brush sheet would eliminate uneven discharging because of a more uniform bristle density in the axial direction of the lubricant coating brush roller


851


. The conductive fabric sheet


851




b


is made, for example, of acrylic fiber dispersed with carbon, or the like. The conductive roller, serving as a core bar of the lubricant coating brush roller


851


, is connected to a ground


854


. To improve a discharging efficiency, the lubricant coating brush roller


851


is fabricated such that the resistance between a portion contacting the intermediate transfer belt


21


, i.e., the tip of the brush bristles


851




a


and the ground


854


is equal to or lower than 10


8


Ω, and preferably, equal to or lower than 10


7


Ω. Essentially, this resistance means the resistance of the conductive fabric sheet since the roller serving as a core bar of the lubricant coating brush roller


851


is conductive.




Next, a modification to the eleventh embodiment will be described with reference to FIG.


28


.

FIG. 28

is an enlarged view schematically illustrating a modified structure around a photosensitive drum


10


in the copier of the eleventh embodiment. The modification basically has substantially the same configuration as the eleventh embodiment, and differs from the eleventh embodiment only in that in the modification, the lubricant coating brush roller is connected to a discharge power supply


859


for applying a discharging bias, whereas in the eleventh embodiment, the lubricant coating brush roller


851


is simply grounded. Since the discharging bias permits a residual charge existing on the intermediate transfer belt


21


to flow into the lubricant coating brush roller


851


, thus allowing for efficient discharging. In this way, the photosensitive drum


10


can be stably discharged even when the surface moving speed of the photosensitive drum


10


is increased, for example, in order to perform the image formation at a higher speed.




[Embodiment 12]




Referring next to

FIGS. 29

to


31


A and


31


B, a twelfth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.

FIG. 29

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the twelfth embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the eleventh embodiment, and performs image forming operations basically in the same manner as the copier of FIG.


24


. The twelfth embodiment differs from the sixth embodiment mainly in the structure and operation of the printer unit.

FIG. 29

corresponds to

FIG. 9

, so that the following description will be mainly focused on only those portions which are different from FIG.


9


.




Around an intermediate transfer belt


121


, there are disposed a lubricant coating unit


850


identical to that used in the eleventh embodiment, and a transfer unit


130


. These components can be moved into and out of contact with the intermediate transfer belt


121


by respective contact/separation mechanisms, not shown, associated therewith.




The image forming surface on the intermediate transfer belt


121


, on which the Bk toner image has been transferred, is again returned to the primary transfer region, similarly to the eleventh embodiment. In this event, the lubricant coating brush roller


851


and the cleaning blade


170


are moved away from the intermediate transfer belt


121


by respective contact/separation mechanisms associated therewith so as not to disturb the toner image.




In the following, description will be made on the contact/separation mechanism for moving the lubricant coating brush roller


851


into and out of contact with the intermediate transfer belt


121


, and the contact/separation mechanism for moving the cleaning blade


170


into and out of contact with the intermediate transfer belt


121


, which constitute characterizing portions of the twelfth embodiment. Like the eleventh embodiment, the lubricant coating brush roller


851


also functions as a discharging member, and for this purpose, is connected to a discharge power supply


859


for applying the same with a discharging bias. Thus, the lubricant coating brush roller


851


, when in contact with the intermediate transfer belt


121


, can coat a lubricant on the intermediate transfer belt


121


and simultaneously discharge the intermediate transfer belt


121


.




First, the structures of the contact/separation mechanisms will be described with reference to FIG.


30


.

FIG. 30

schematically illustrates the structure of the contact/separation mechanism


173


which functions to move not only the lubricant coating brush roller


851


but also the cleaning blade


170


into and out of contact with the intermediate transfer belt


121


. The contact/separation mechanism


173


includes the lubricant coating unit


850


; the cleaning blade


170


; a first contact/separation cam


850




c


for moving the lubricant coating brush roller


851


into and out of contact with the intermediate transfer belt


121


; a second contact cam


170




c


for moving the cleaning blade


170


into and out of contact with the intermediate transfer belt


121


; and driving units, not shown, connected to these cams.




The lubricant coating unit


850


is supported at one end of a first bracket


850




a


. The first bracket


850




a


is supported for pivotal movements about a first bracket pivot shaft


850




b


. The other end of the first bracket


850




a


, opposite to the one end at which the lubricant coating unit


850


is supported, abuts to a cam surface of the first contact/separation cam


850




c


. In this event, the other end of the first bracket


850




a


is urged by a spring, not shown, toward the cam surface. The cleaning blade


170


, in turn, is secured to a second bracket


170




a


at one end thereof. The second bracket


170




a


is supported for pivotal movements about a second bracket pivot shaft


170




b


. The other end of the second bracket


170




a


, opposite to the one end at which the cleaning blade


170


is secured, abuts to a cam surface of the second contact/separation cam


170




c


. In this event, the other end of the second bracket


170




a


is urged by a spring, not shown, toward the cam surface.




The first contact/separation cam


850




c


is secured to a first cam shaft


850




d


connected to the driving unit. To the first cam shaft


850




d


, a first gear


850




e


is also secured at the end on the front side on the drawing. The second contact/separation cam


170




c


is secured to a second cam shaft


170




d


. To the second cam shaft


170




d


, a second gear


170




e


is also secured at the end on the front side on the drawing. The first gear


850




e


and the second gear


170




e


have the same number of teeth, and are meshed with each other on the same plane.




Next, the operation of the contact/separation mechanism


173


will be described with reference to

FIGS. 31A and 31B

. FIG.


31


A and

FIG. 31B

are enlarged views schematically illustrating a main portion of the contact/separation mechanism


173


when the lubricant coating brush roller


851


and the cleaning blade


170


are out of contact with the intermediate transfer belt


121


, and when the lubricant coating brush roller


851


and the cleaning blade


170


are into contact with the intermediate transfer belt


121


, respectively.




In

FIG. 31A

, the lubricant coating brush roller


851


and the cleaning blade


170


are separated from the intermediate transfer belt


121


. From the illustrated state, the first cam shaft


850




d


is rotated over 180° by a motor, not shown, disposed in the driving unit. This causes the first contact/separation cam


850




c


to also rotate over 180°, and the cam surface thereof to lift the other end of the first bracket


850




a


, thus bringing the lubricant coating brush roller


851


into contact with the intermediate transfer belt


121


. In addition, the rotation of the first cam shaft


850




d


also causes the second cam shaft


170




d


to rotate over 180° by way of the first gear


850




e


and the second gear


170




e


. The rotation of the second cam shaft


170




d


causes the second contact/separation cam


170




c


to lift the other end of the second bracket


170




a


to bring the cleaning blade


170


into contact with the intermediate transfer belt


121


. In this way, the state illustrated in

FIG. 31A

proceeds to the state illustrated in FIG.


31


B.




Further, when the motor is driven to rotate the first cam shaft


850




d


over another 180°, the lubricant coating brush roller


851


and the cleaning blade


170


are moved out of contact with the intermediate transfer belt


121


because the first bracket


850




a


and the second bracket


170




a


have their other ends urged toward the cam surface of the first contact/separation cam


850




c


and the cam surface of the second contact/separation cam


170




c


, respectively. In this way, the state illustrated in

FIG. 31B

proceeds to the state illustrated in FIG.


31


A.




As an additional feature, by adjusting the angle at which the first contact/separation cam


850




c


is secured to the first cam shaft


850




d


and the angle at which the second contact/separation cam


170




c


is secured to the second cam shaft


170




d


, it is possible to arbitrarily set an interval between a timing at which the cleaning blade


170


is moved into contact with the intermediate transfer unit


121


and a timing at which the lubricant coating brush roller


851


is subsequently moved into contact with the intermediate transfer unit


121


.




In the twelfth embodiment, the foregoing angles are set such that after the cleaning blade


170


has been brought into contact with the intermediate transfer belt


121


, the lubricant coating brush roller


851


is brought into contact with the intermediate transfer belt


121


at a timing the contacted surface of the intermediate transfer belt


121


passes a position at which the lubricant coating brush roller


851


is designed to contact the intermediate transfer belt


121


. In this way, since the surface discharged by the lubricant coating brush roller


851


in contact therewith has been cleaned, a less amount of contaminants or the like will attach to the lubricant coating brush roller


851


.




In one implementation, the lubricant coating brush roller


851


is formed of a metal roller and a conductive fabric sheet wrapped around the metal roller. The conductive fabric sheet is made of acrylic fiber dispersed with carbon and having a size of 6.5 deniers, and wrapped around the metal roller such that gap G between edges of the wrapped sheet is 1 mm or less. The lubricant coating brush roller


851


has a filling density of 100,000 per square inch. The resistance from the brush tip to the ground


854


of the lubricant coating brush roller


851


is set at 10


6


Ω.




It should be noted that the lubricant coating brush roller


851


need not be brought into contact with a completely cleaned surface, and an amount of contaminants not affecting a formed image may be regarded to fall within a tolerable range. Thus, depending on specific applications of the copier of the twelfth embodiment, it may be sufficient that a timing at which the lubricant coating brush roller


851


is brought into contact with the intermediate transfer belt


121


is controlled such that an uncleaned area of the intermediate transfer belt


121


contacted by the lubricant coating brush roller


851


is at least smaller than the case where the lubricant coating brush roller


851


and the cleaning blade


170


are simultaneously brought into contact with the intermediate transfer belt


121


.




While in the twelfth embodiment, the lubricant coating brush roller


851


and the cleaning blade


170


are controlled by a single contact/separation mechanism, an individual contact/separation mechanism may be provided for each of them. Further, the copier according to the twelfth embodiment can be utilized not only in the foregoing full-color copy mode but also in any other copy mode, as is the case of the eleventh embodiment.




[Embodiment 13]




Referring next to

FIG. 32

, a thirteenth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 32

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the thirteenth embodiment. In general, the illustrated copier is intended for a reduction in cost, and differs from the copier according to the twelfth embodiment only in the following aspects. Therefore, similar constituent members in the thirteenth embodiment are designated the same reference numerals as those in the twelfth embodiment, and description thereon is omitted.

FIG. 32

corresponds to

FIG. 11

so that the following description will be mainly focused on only those portions which are different from FIG.


11


.




For feeding a transfer paper


100


in the thirteenth embodiment, the fed transfer paper


100


is directly sandwiched between a secondary transfer bias roller


231


and an intermediate transfer belt


221


, and conveyed to pass between a pair of fixing rollers


145




a


of a fixing unit


145


.




In the following, description will be made on the structures and operations of a lubricant coating unit


850


and a cleaning blade


170


which constitute characterizing portions of the thirteenth embodiment. The lubricant coating unit


850


and the cleaning blade


170


in the thirteenth embodiment are substantially similar to the correspondents in the twelfth embodiment in basic structure, and differs in their positions.




In the thirteenth embodiment, a lubricant coating brush roller


851


of the lubricant coating unit


850


is also disposed opposite to a driving roller


224


which also serves as a cleaning opposed roller associated with the cleaning blade


170


. Since the driving roller


224


has a ground


222


connected to a casing, the driving roller


224


also serves as a grounding member disposed opposite to the lubricant coating brush roller


851


. As a result, an electric field is concentrically formed between the lubricant coating brush roller


851


and the driving roller


224


. The electric field thus formed allows for stable discharging of not only a charge on the surface of the intermediate transfer belt


121


but also a charge internal to the intermediate transfer belt


121


, so that the entire intermediate transfer belt


121


can be uniformly discharged. The lubricant coating brush roller


851


and the cleaning blade


170


may be disposed opposite to another supporting roller instead of the driving roller


224


.




The driving roller


224


opposing the lubricant coating brush roller


851


is formed of a metal roller coated with conductive rubber thereon. The resistance from the surface of the driving roller


224


to the ground


222


is set at 10


7


Ω.




[Embodiment 14]




Next, a fourteenth embodiment of the present invention will be described in connection with an image forming apparatus which employs a transfer material carrier such as a belt for carrying and conveying a transfer material such as a paper, an OHP sheet or the like, and to which the present invention is applied.





FIG. 33

schematically illustrates a transfer unit of a copier according to the fourteenth embodiment. In the fourteenth embodiment, the present invention is utilized in a transfer material carrier for carrying and conveying a transfer material rather than in an intermediate transfer unit as in the foregoing embodiments.

FIG. 33

corresponds to

FIG. 12

so that the following description will be mainly focused on only those portions which are different from FIG.


12


.




A transfer unit


330


has a paper transfer belt


332


for carrying a transfer paper


100


; a transfer cleaning blade


331


for cleaning the surface of the paper transfer belt


332


; a ground roller


335




a


positioned at one end of a sheet feed unit, not shown; a transfer bias roller


334


as a charge supply means; a transfer power supply


338


connected to the transfer bias roller


334


; a tension roller


335




b


positioned at one end of a fixing unit, not shown; a cleaning opposed roller


335




c


opposing the transfer cleaning blade


331


; a transfer paper discharger


336


; and a lubricant coating unit


350


for coating a lubricant on the surface of the paper transfer belt


332


.




A transfer paper


100


, on which a toner image has been transferred as described above, is discharged by the transfer paper discharger


336


, and passes a separation region where the transfer paper


100


is separated from the paper transfer belt


332


, and conveyed to the fixing unit, not shown. After the transfer paper


100


has been separated from the paper transfer belt


332


, the transfer cleaning blade


331


removes contaminants such as paper dusts from the surface of the paper transfer belt


332


. In this event, a lubricant coating brush roller


351


disposed in the lubricant coating unit


350


coats a lubricant on the cleaned surface of the paper transfer belt


332


in order to reduce a friction between the cleaning blade


331


and the paper transfer belt


332


. The lubricant coating brush roller


351


is disposed upstream of a transfer region and downstream of the separation region in a direction in which the paper transfer belt advances, and preferably, upstream of the transfer region and downstream of the transfer cleaning blade


331


in the paper transfer belt advancing direction.




[Embodiment 15]




Referring next to

FIGS. 34

to


42


, a fifteenth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.

FIG. 34

is a cross-sectional view schematically illustrating the configuration of the copier according to the fifteenth embodiment, and

FIG. 35

is an enlarged view schematically illustrating the structure around a photosensitive drum in the copier of FIG.


34


. The following description will be mainly focused on only those portions which are different from the first embodiment illustrated in

FIGS. 1

,


2


.




Referring first to

FIG. 35

, description will be made on the structure and operation of a corona charger


960


which constitutes a characterizing portion of the fifteenth embodiment. The corona charger


960


is disposed downstream of a secondary transfer region and upstream of a primary transfer region in a direction of movement of an intermediate transfer belt


21


. The corona charger


960


is connected to a discharge power supply


969


for applying the same with a direct current voltage for discharging the intermediate transfer belt


21


.




Since the corona charger


960


can discharge the intermediate transfer belt


21


in a non-contact manner, the mechanism associated with discharging the intermediate transfer belt


21


can be simplified as compared with a contact-type discharger. This is because a contact-type discharger requires a contact/separation mechanism for forming a color image using two or more colors. Specifically, while a toner image of each color is transferred to the intermediate transfer belt


21


, the contact/separation mechanism is required to move a discharging member of the contact-type discharger out of contact with the intermediate transfer belt


21


, and after secondary transfer is completed, the contact/separation mechanism is again required to move the discharging member into contact with the intermediate transfer belt


21


. However, since the corona charger


960


introduces the generation of ozone, it is not preferably in view of environmental protection. From this point of view, when a contact-type discharger is used, a discharging brush, a discharging blade, or the like may be used as a discharging member of the contact-type discharger.




Next, a modification to the fifteenth embodiment will be described with reference to FIG.


36


.

FIG. 36

is an enlarged view schematically illustrating a modified structure around a photosensitive drum in the copier of the fifteenth embodiment. This modification employs a contact-type discharger instead of the corona charger


960


, and a discharging brush


961


as a discharging member of the contact-type discharger. An intermediate transfer belt


21




a


used in this modification has a volume resistivity ρv of 10


12


Ωcm or less. A ground roller


23


for tensioning the intermediate transfer belt


21




a


is positioned such that the resistance from a portion of the intermediate transfer belt


21




a


contacting the discharging brush


961


to a ground


962


of the ground roller


23


is 10


8


Ω or less, and preferably 10


7


Ω or less. In this modification, the discharging brush


961


is not connected to a discharge power supply for applying the same with a discharging bias.




The volume resistivity ρv of the intermediate transfer belt


21




a


is set to be 10


12


Ωcm or less such that a charge can move within the intermediate transfer belt


21




a


. In this way, a residual charge remaining within the intermediate transfer belt


21




a


after secondary transfer, which cannot be discharged by the discharging brush


961


, can move to the ground


962


of the ground roller


23


, thus preventing a residual potential from affecting an image to be formed next time. In this case, even without applying a discharging bias, the surface potential on the intermediate transfer belt


21




a


can be driven to −100 volts or less.




Next, another modification to the fifteenth embodiment will be described with reference to FIG.


37


.

FIG. 37

is an enlarged view schematically illustrating a modified structure around a photosensitive drum in the copier of the fifteenth embodiment. While this modification is substantially similar to the foregoing modification, there are several differences between them. First, the discharging brush


961


is connected to a discharge power supply


969


for applying the same with a discharging bias. Also, an intermediate transfer belt


21




b


used in the second modification has a volume resistivity ρv in a range of 10


11


Ωcm to 10


14


Ωcm. Further, a conductive plate


963


is disposed, as a grounding member, opposite to the discharging brush


61


through the intermediate transfer belt


21




b


. As the grounding member, a conductive roller or the like, for example, may be used instead of the conductive plate


963


. The conductive plate


963


is in contact with the rear surface of the intermediate transfer belt


21




b


with which the discharging brush


961


comes into contact. The structure as described enables an electric field to be concentrically formed between the discharging brush


961


and the conductive plate


963


. The electric field thus formed allows for stable discharging of not only a charge on the surface of the intermediate transfer belt


21




b


but also a charge internal to the intermediate transfer belt


21




b


, so that the entire intermediate transfer belt


21




b


can be uniformly discharged.





FIG. 38

shows relationships between a discharging bias applied to the discharging brush


961


and the surface potential on the intermediate transfer belt


21




b


after discharging (hereinafter referred to as the “post-discharge potential”) when the conductive plate


963


is disposed opposite to the discharging brush


961


, and when the conductive plate


963


is not disposed. In

FIG. 38

, solid lines connecting two circles each indicate a range of variations in the surface potential on the intermediate transfer belt


21




b


when associated discharging biases are applied. As is apparent from this graph, for discharging the intermediate transfer belt


21




b


to be at such a surface potential that will not affect an image to be formed next time, i.e., in a range of −100 to +100 volts, a far less discharging bias is required for the discharging when the conductive plate


963


is disposed opposite to the discharging brush


961


. In addition, it can be seen that variations in potential on the intermediate transfer belt


21




b


after discharging are smaller when the conductive plate


963


is disposed.




Further, also in this modification, the resistance between a contacting portion of the conductive plate


963


with the intermediate transfer belt


21




b


and the ground


964


of the conductive plate


963


is preferably 10


8


Ω or less, and preferably 10


7


Ω or less to improve the discharging efficiency.




Next, a further modification to the fifteenth embodiment will be described with reference to

FIGS. 39 and 40

.

FIG. 39

is an enlarged view schematically illustrating a modified structure around a photosensitive drum in the copier of the fifteenth embodiment, and

FIG. 40

is a front view of a discharging brush roller for use in the copier. This modification employs a discharging brush roller


965


instead of the discharging brush


961


in the foregoing modifications. The discharging brush roller


965


is formed of a conductive roller and a conductive fabric sheet


965




b


having brush bristles


965




a


wrapped around the conductive roller. The conductive fabric sheet


965




b


is made, for example, of acrylic fiber dispersed with carbon, or the like. In a contact-type discharger having the discharging brush roller


965


of this modification, the discharging brush roller


965


may be fabricated such that the resistance between a portion contacting the intermediate transfer belt


21


, i.e., the tip of the brush bristles


986




a


and a ground


966


connected to the discharging brush roller


965


is 10


8


Ω or less, and preferably, 10


7


Ω or less to improve a discharging efficiency. Essentially, this resistance means the resistance of the conductive fabric sheet since the roller serving as a core bar of the discharging brush roller


965


is conductive.





FIG. 41

is a graph showing the relationship between a filling density of the discharging brush roller


965


and an evaluation of potential unevenness on the intermediate transfer belt


21


after discharging. The evaluation of potential unevenness is made on a five-level basis, where the least potential unevenness is evaluated as level


5


. Generally, the potential unevenness on the surface of the intermediate transfer belt


21


evaluated as level


3


or higher will not affect an image to be formed next time. It can therefore be understood from the graph that the filling density of the discharging brush roller


965


is preferably 20,000 per square inch or more. With the discharging brush roller


965


thus formed, an increased number of bristles can be in contact with the surface of the intermediate transfer belt


21


per unit area, so that the potential unevenness can be effectively suppressed on the intermediate transfer belt


21


after discharging.




When the discharging brush roller


965


is fabricated, the conductive fabric sheet


965




b


is wrapped around the conductive roller as mentioned above, in which case the potential unevenness also varies largely depending on a gap G between edges of the wrapped conductive fabric sheet


965




b


.

FIG. 42

shows the relationship between the gap G between edges of the wrapped conductive fabric sheet


965




b


and the evaluation of potential unevenness on the surface of the intermediate transfer belt


21


after discharging. The same five-level evaluation is also applied in FIG.


42


. To achieve level


3


or higher for the evaluation of potential unevenness, the discharging brush roller


965


should be fabricated such that the gap G is at least 2 mm or less. In other words, the gap G of 2 mm or less is effective in suppressing the potential unevenness on the surface of the intermediate transfer belt


21


after discharging.




In this modification, the discharge coating brush roller


965


is driven to rotate in the same direction as the intermediate transfer belt


21


in order to prevent the discharging performance from degrading and its brush bristles from lying down. In addition, the discharging brush roller


965


is controlled such that it rotates at a line velocity higher than that of the intermediate transfer belt


21


in a discharge region in which the discharging brush roller


965


contacts the intermediate transfer belt


21


.




[Embodiment 16]




Referring next to

FIG. 43

, a sixteenth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.

FIG. 43

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the sixteenth embodiment. The illustrated copier includes a scanner unit, not shown, which has the same configuration as that of the fifteenth embodiment, and performs image forming operations basically in the same manner as the copier of FIG.


34


. The sixteenth embodiment differs from the fifteenth embodiment mainly in the structure and operation of the printer unit.

FIG. 34

corresponds to

FIG. 9

, so that the following description will be mainly focused on only those portions which are different from FIG.


9


.




Around an intermediate transfer belt


121


, there are disposed a lubricant coating and discharging brush roller


1065


for coating a lubricant on and discharging the surface of the intermediate transfer belt


121


; a belt cleaning blade


170


; and a transfer unit


130


. These components can be moved into and out of contact with the intermediate transfer belt


121


by respective contact/separation mechanisms, not shown, associated therewith.




As mentioned above, the image forming surface on the intermediate transfer belt


121


, on which a Bk toner image has been transferred, is again returned to the primary transfer region. In this event, the lubricant coating and discharging brush roller


1065


and the belt cleaning blade


170


are moved away from the intermediate transfer belt


121


by respective contact/separation mechanisms associated therewith so as not to disturb the toner image.




After secondary transfer, residual toner remaining on the surface of the intermediate transfer belt


121


is removed by pressing the belt cleaning blade


170


against the intermediate transfer belt


121


by the associated contact/separation mechanism, not shown. Then, a lubricant contained in a lubricant container


1066


is coated on the surface of the intermediate transfer belt


121


by the lubricant coating and discharging brush roller


1065


pressed against the intermediate transfer belt


121


by the associated contact/separation mechanism, not shown, in order to improve the cleaning performance and the secondary transfer operability. The lubricant for use in this application may be, for example, a plate formed of fine particles of zinc stearate.




In the following, description will be made on the structures and operations of the lubricant coating and discharging brush roller


1065


and the belt cleaning blade


170


which constitute characterizing portions of the sixteenth embodiment. In the sixteenth embodiment, the lubricant coating and discharging brush roller


1065


functions to coat a lubricant on and discharge the surface of the intermediate transfer belt


121


. It should be noted that while the lubricant coating and discharging brush roller


1065


may be substantially similar to the discharging brush roller


965


previously described in the third modification of the fifteenth embodiment, the conductive fabric sheet forming the brush bristles has the resistance of approximately 10


6


Ω. The lubricant coating and discharging brush roller


1065


is connected to a variable discharge power supply


1069


for applying the same with a discharging bias. Also, the lubricant coating and discharging brush roller


1065


is disposed upstream of a primary transfer region and downstream of the belt cleaning blade


170


in a direction of movement of the intermediate transfer belt


121


.




The lubricant coating and discharging brush roller


1065


is formed of a metal roller and a conductive fabric sheet wrapped around the metal roller. The conductive fabric sheet is made of acrylic fiber dispersed with carbon and having a size of 6.5 deniers, and wrapped around the metal roller such that a gap G between edges of the wrapped sheet is 1 mm or less. The lubricant coating and discharging brush roller


1065


has a filling density of 100,000 per square inch. The resistance from the brush tip to the ground of the lubricant coating and discharging brush roller


1065


is set at 10


6


Ω.




A direct current voltage applied to the lubricant coating and discharging brush roller


1065


is calculated in accordance with the temperature and humidity around the intermediate transfer belt


121


, a surface potential on the intermediate transfer belt


121


based on the copy mode information, and a surface moving speed of the intermediate transfer belt


121


based on transfer paper information, and the variable discharge power supply


1069


is controlled to generate the calculated direct current voltage. Specifically, the discharging bias is set as shown in Tables 4, 5, and 6.




Since the structure and operation of the contact/separation mechanisms associated with the lubricant coating and discharging brush roller


1065


and the belt cleaning blade


170


are identical to those previously described with reference to

FIGS. 30

,


31


A,


31


B, description thereon is omitted here.




[Embodiment 17]




Referring next to

FIG. 44

, a seventeenth embodiment of the present invention will be described in connection with a full color electronic photocopier (hereinafter simply referred to as the “copier”), that is, an image forming apparatus in which the present invention is applied.





FIG. 44

schematically illustrates the configuration of a main portion of a printer unit in the copier according to the seventeenth embodiment. In general, the illustrated copier is intended for a reduction in cost, and differs from the copier according to the sixteenth embodiment only in the following aspects. Therefore, similar constituent members in the seventeenth embodiment are designated the same reference numerals as those in the sixteenth embodiment, and description thereon is omitted.

FIG. 44

corresponds to FIG.


11


so that the following description will be mainly focused on only those portions which are different from FIG.


11


.




Description will be made on the structures and operations of a lubricant coating and discharging brush roller


1065


and a belt cleaning roller


170


which constitute characterizing portions of the seventeenth embodiment. Like the foregoing sixteenth embodiment, the lubricant coating and discharging brush roller


1065


is used also as a discharging member. The seventeenth embodiment differs from the sixteenth embodiment in the positioning of the lubricant coating and discharging brush roller


1065


and the belt cleaning roller


170


.




Specifically, the lubricant coating and discharging brush roller


1065


is disposed opposite to a driving roller


224


which also serves as a cleaning opposed roller associated with the cleaning blade


170


, as can be seen in FIG.


44


.




The lubricant coating and discharging brush roller


1065


is formed of a metal roller and a conductive fabric sheet wrapped around the metal roller. The conductive fabric sheet is made of acrylic fiber dispersed with carbon and having a size of 6.5 deniers, and wrapped around the metal roller such that a gap G between edges of the wrapped sheet is 1 mm or less. The lubricant coating and discharging brush roller


1065


has a filling density of 100,000 per square inch.




The driving roller


224


opposing the lubricant coating and discharging brush roller


1065


is formed of a metal roller coated with conductive rubber thereon. The resistance from the surface of the driving roller


224


to the ground


222


is set at 10


7


Ω.




[Embodiment 18]




Next, an eighteenth embodiment of the present invention will be described in connection with an image forming apparatus which employs a transfer material carrier such as a belt for carrying and conveying a transfer material such as a paper, an OHP sheet or the like, and to which the present invention is applied.





FIG. 45

schematically illustrates a transfer unit of a copier according to the eighteenth embodiment. In the eighteenth embodiment, the present invention is utilized in a transfer material carrier for carrying and conveying a transfer material rather than in an intermediate transfer unit as in the foregoing embodiments.

FIG. 45

corresponds to

FIG. 12

so that the following description will be mainly focused on only those portions which are different from FIG.


12


.




A paper transfer belt


332


of the eighteenth embodiment is passed over a ground roller


335




a


positioned at one end of a sheet feed unit, not shown, and serving as a pre-transfer discharging means, and a tension roller


335




b


positioned at one end of a fixing unit, not shown.




A transfer paper


100


, on which a toner image has been transferred as described above, is separated from the paper transfer belt


332


, and conveyed to the fixing unit, not shown. The paper transfer belt


332


, after the transfer paper


100


has been separated therefrom, passes a region in which a discharging brush


361


disposed opposite to the tension roller


335




b


is brought into contact therewith, and is discharged by the discharging brush


361


.




Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.



Claims
  • 1. An image forming apparatus, comprising:an image carrying member configured to rotate and carry a toner image on a rotating surface thereof; an intermediate transfer member, facing and in contact with said image carrying member, configured to rotate and receive said toner image from said image carrying member during a first transfer operation which is performed one time in a mono color mode and which is repeated a plurality of times in a multiple color mode to overlay a plurality of mono color toner images in turn on said intermediate transfer member; a charging member configured to apply a charge to said intermediate transfer member to generate an electric field at a region where said image carrying member and said intermediate transfer member contact each other, said electric field generating a force for initiating said first transfer operation; a transfer mechanism, facing and in contact with said intermediate transfer member, configured to perform a second transfer operation for transferring said toner image from said intermediate transfer member to a transfer sheet; a cleaning member, in contact with said intermediate transfer member, configured to clean toner remaining on said intermediate transfer member after a completion of said second transfer operation; a discharging member configured to discharge a charge remaining on said intermediate transfer member by contacting a region of said intermediate transfer member which said cleaning member has cleaned off; a cleaning-member moving mechanism configured to move said cleaning member to contact and separate from said intermediate transfer member; and a discharging-member moving mechanism configured to move said discharging member to contact and separate from said intermediate transfer member, wherein said discharging-member moving mechanism and said cleaning-member moving mechanism are controlled to reduce an amount of non-cleaned surface area of said intermediate transfer member which said cleaning member has not cleaned off, in comparison with a case in which said discharging member and said cleaning member contact said intermediate transfer member at a same time.
  • 2. An image forming apparatus as defined in claim 1, wherein said discharging-member moving mechanism moves said discharging member and said cleaning member respectively to contact and separate from said intermediate transfer member.
  • 3. An image forming apparatus as defined in claim 1, wherein said discharging member is applied with at least one of a direct current bias, an alternating current bias, and direct and alternating current bias, to discharge said charge remaining on said intermediate transfer member.
  • 4. An image forming apparatus comprising:an image carrying member configured to carry a toner image thereon; and a cleaning member configured to clean toner remaining on said image carrying member after carrying said toner image, wherein said cleaning member cleans off a surface of said image carrying member such that said toner remaining in an antecedent region of said image carrying member is electrically or magnetically removed, wherein said cleaning member is applied with a bias having a repulsive polarity relative to a polarity of said toner remaining on said image carrying member.
  • 5. An image forming apparatus comprising:an image carrying member configured to carry a toner image thereon; a cleaning member configured to clean toner remaining on said image carrying member after carrying said toner image, wherein said cleaning member cleans off a surface of said image carrying member such that said toner remaining in an antecedent region of said image carrying member is electrically or magnetically removed; and a repulsive polarity member which contacts a rear surface of said image carrying member facing said cleaning member relative to said image carrying member, and which is applied with a bias to generate an electrical field in which said toner remaining on said image carrying member is forced to be removed therefrom.
  • 6. A cleaning apparatus for cleaning an image carrying member of an image forming apparatus including an intermediate transfer member, comprising:a cleaning member, in contact with said intermediate transfer member, configured to clean said image carrying member to remove toner remaining thereon after said image carrying member completes carrying a toner image, wherein said cleaning member is applied with a repulsive polarity relative to a polarity of said toner remaining on said image carrying member.
  • 7. An image forming apparatus, comprising:a cleaning member including a cleaning blade and configured to clean an image carrying member for carrying a toner image by contacting a surface of said image carrying member to remove toner remaining thereon after said image carrying member completes carrying a toner image; and a repulsive polarity member configured to be applied with a bias having a repulsive polarity relative to said toner remaining on said image carrying member, wherein said repulsive polarity member is positioned upstream from said cleaning blade relative to a moving direction of said image carrying member.
  • 8. A cleaning apparatus for cleaning an image carrying member of an image forming apparatus, comprising:a cleaning member including a cleaning blade and configured to clean said image carrying member for carrying a toner image by contacting a surface of said image carrying member to remove toner remaining thereon after said image carrying member completes carrying a toner image; and a repulsive polarity member configured to be applied with a bias having a repulsive polarity relative to said toner remaining on said image carrying member, wherein said repulsive polarity member is positioned upstream from said cleaning blade relative to a moving direction of said image carrying member.
  • 9. A method for cleaning an image carrying member of an image forming apparatus, comprising:providing a toner image to an image carrying member; transferring said toner image formed on said image carrying member onto a transfer member; positioning a cleaning member to contact said image carrying member after said image carrying member completes carrying said toner image to clean residual toner from said image carrying member; and creating an electric or magnetic field of a same polarity as a polarity of said residual toner at a region upstream from a point at which said image carrying member contacts said cleaning member to remove the residual toner remaining on said image carrying member by repelling said residual toner from said image carrying member before said cleaning member contacts said image carrying member.
Priority Claims (4)
Number Date Country Kind
10-333074 Nov 1998 JP
10-346334 Dec 1998 JP
10-346365 Dec 1998 JP
10-346435 Dec 1998 JP
Parent Case Info

This application is a Division of application Ser. No. 09/828,851 filed on Apr. 10, 2001 now U.S. Pat. No. 6,505,024 which is a Divisional of application Ser. No. 09/448,760, filed Nov. 24, 1999 now U.S. Pat. No. 6,269,228.

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