Belt device and unit device including belt device and image forming apparatus using the belt device and unit device

CROSS-REFERENCE TO RELATED APPLICATIONS

This document claims priority and contains subject matter related to Japanese Patent Applications Nos. JPAP11-166288 filed on Jun. 14, 1999, JPAP11-365318 filed on Dec. 22, 1999 and JPAP2000-114451 filed on Apr. 14, 2000, and the entire contents thereof are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus such as, a copying machine, a facsimile, a printer, etc., and more particularly to an image forming unit device including a belt-formed member and a belt device in which the belt-formed member drives accurately even when the belt-formed member temporarily separates from some of opposing members.

2. Discussion of the Background

As an image forming apparatus, a tandem multicolor image forming apparatus, that includes an intermediate transfer element supported by a plurality of supporting rollers and a plurality of photoconductive elements as opposing members (image bearing members) arranged side by side in a line opposite to the intermediate transfer element and contacting the intermediate transfer element is known (e.g. in Japanese Utility Model Laid-Open No. 59-192159 and Japanese Patent Laid-Open publication No. 8-160839). In the apparatus, visible images corresponding to respective colors formed on surfaces of respective photoconductive elements are transferred onto the intermediate transfer element one after another while being superimposed with each other (a primary transfer). The visible image thus formed on the intermediate transfer element is then transferred onto a transfer member a t one time (a secondary transfer) to form a multicolor image on the transfer member. In those multicolor image forming apparatuses, there are apparatuses configured such that a black and white image forming mode using a single photoconductive element and a multicolor image forming mode superimposing toner images of a plurality of colors with each other using a plurality of photoconductive elements are selectable.

FIG. 27

illustrates a fullcolor electrophotographic copying machine using liquid developer as an example of the above-described tandem multicolor image forming apparatus. In the apparatus, four drum-shaped photoconductive elements

501

Y,

501

M,

501

C and

501

B corresponding to respective colors of yellow Y, magenta M, cyan C and black BK are provided side by side in a line such that the axes of rotation of photoconductive elements are located in parallel and in the same plane. Around respective photoconductive elements

501

Y,

501

M,

501

C and

501

B rotating in a clockwise direction, charging devices, writing systems to form an electrostatic image by irradiation of beam light corresponding to respective colors, developing units with liquid developer for respective colors etc. (not shown) are provided respectively in an order of a liquid electrophotographic printing process. Further, an intermediate transfer belt

505

as an intermediate transfer member is supported by a tension roller

502

, guide rollers

503

and

504

etc. so as to rotate in a counterclockwise direction. The intermediate transfer belt

505

is disposed so as to contact each primary transfer area of photoconductive elements

501

Y,

501

M,

501

C and

501

B. The intermediate transfer belt

505

is pressed by spanning rollers

506

Y,

506

M,

506

C and

506

B so that it windingly contacts respective photoconductive elements. An image on the intermediate transfer belt

505

, which has been formed as a result of transferring images of respective colors (Y, M, C and BK) at the primary transfer areas of respective photoconductive elements

501

Y,

501

M,

501

C and

501

B superimposing one after another, is conveyed to a secondary transfer area where a portion of the intermediate transfer belt

505

spanned between guide rollers

503

and

504

contacts a secondary transfer roller

507

. Then, the image is transferred onto a transfer sheet

508

at the secondary transfer area to form a multicolor image on the transfer sheet

508

. Further, a cleaning device

509

is provided at a place where the intermediate transfer belt

505

is supported by the tension roller

502

.

In the fullcolor electrophotographic copying machine with liquid developer, a color mode can be freely selected from among, for example, a single color mode and a multicolor mode with four colors (a full color mode), two colors or three colors. For example, when a single color mode (black color mode) is selected, a black color image is formed on the transfer sheet

508

using the photoconductive element

501

B, electrophotographic copying process members and the intermediate transfer belt

505

.

When a single color image forming operation is performed in the above-described electrophotographic copying machine having selectable single color and multicolor modes, inconveniences may be caused because the photoconductive elements which are not involved in the image forming operation are located in contact with or in close proximity to the intermediate transfer element.

For example, life times of the photoconductive elements may be decreased because the photoconductive elements are kept in contact with the intermediate transfer element even when the photoconductive elements are not involved in the image forming operation. In the apparatus illustrated in

FIG. 27

, even in the black color mode, photoconductive elements

501

Y,

501

M and

501

C, which are not involved in the image forming operation, are kept in contact with the intermediate transfer belt

505

and are rubbed by it. Therefore the life times of these photoconductive elements may be decreased.

Further, when photoconductive elements which are not involved in the image forming operation are kept in contact with or in close proximity to the intermediate transfer element, developer remaining on the photoconductive elements may be flown by the intermediate transfer element and scattered inside the apparatus. Developer remaining on the photoconductive elements may also adhere to a surface of the intermediate transfer element, which results in unnecessary consumption of developer.

The above-described inconveniences such as the life times of opposing members, such as photoconductive elements being decreased due to unnecessary contact of a belt-formed member, such as the intermediate transfer element, with the opposing members are caused not only in the above-described exemplary construction where a plurality of photoconductive elements are located side by side in a line so as to oppose and contact the belt-formed intermediate transfer element, but also in a construction where a plurality of opposing members are disposed side by side in a line so as to oppose and contact a belt-formed member supported by a plurality of supporting rollers driven while being temporarily separated from part of the plurality of opposing members. The above-described inconveniences are also caused, for example, in a construction where a belt-formed photoconductive element drives while the belt-formed photoconductive element is temporarily separated from part of a plurality of developer bearing members as the plurality of opposing members, or in a construction where a belt-formed transfer sheet conveying member drives while the belt-formed transfer sheet conveying member is temporarily separated from part of a plurality of photoconductive elements as the plurality of opposing members. Further, the above-described scattering of developer and unnecessary consumption of the developer occur not only when the plurality of opposing members are located side by side in a line opposing and contacting the belt-formed member but also when the plurality of opposing members are located side by side in a line opposing the belt-formed member in close proximity.

For example, in Japanese Patent Laid-Open Publication No. 9-146383, an example of an image forming apparatus, configured such that a transfer sheet conveying belt partly moves to separate from three photoconductive elements out of four, is described.

The inventors discovered the following shortcoming as a result of a further study on a construction that enables the intermediate transfer element as the belt-formed member to separate from part of the plurality of photoconductive elements as the plurality of opposing members. When the intermediate transfer element is separated from part of the photoconductive elements that are not involved in the image forming operation, a tension of the intermediate transfer element may vary. For example, when the intermediate transfer element is configured to contact each of the photoconductive elements with a certain contacting angle in order to form a primary transfer nip of a required width between the intermediate transfer element and each photoconductive element, the tension of the intermediate transfer element may be decreased when the intermediate transfer element is separated from some of the photoconductive elements which are not in use. Further, when part of a plurality of supporting rollers pivot in order to separate the intermediate transfer element from part of the photoconductive elements which are not involved in the image forming operation, the tension of the intermediate transfer element may be decreased or increased depending on a position of a pivot.

When the intermediate transfer element is driven while the tension has varied, the intermediate transfer element may not be driven accurately. For example, when the intermediate transfer element is frictionally driven by rubber rollers, if the tension of the intermediate transfer element is decreased, the intermediate transfer element may not be accurately driven by the rubber rollers due to slides of the intermediate transfer element over the rubber rollers. Contrarily, if its tension is increased, a driving load imposed on the intermediate transfer element may become too excessive to drive the intermediate transfer element accurately. What is meant herein by saying that the intermediate transfer belt is driven accurately is to minimize a change in the speed of the intermediate transfer element.

The above-described inconvenience of inaccurate drive of a belt-formed intermediate transfer element due to a variation in the tension of the intermediate transfer element may be caused not only when a plurality of photoconductive elements are disposed side by side in a line opposing and contacting the belt-formed intermediate transfer element as described above, but also when a plurality of opposing members are arranged side by side in a line opposing and contacting or in close proximity to a belt-formed member supported by a plurality of supporting rollers frictionally driven while being temporarily separated from part of the plurality of opposing members. For example, the inconvenience may also be caused when a belt-formed photoconductive element is driven while being separated from part of a plurality of developer bearing members as a plurality of opposing members or when a belt-formed transfer sheet conveying member is driven while being temporarily separated from part of a plurality of photoconductive elements as a plurality of opposing members. Further, the inconvenience may also be caused not only when the plurality of opposing members are arranged side by side in a line so as to contact the belt-formed member but also when they are arranged side by side in a line so as to oppose the belt-formed member in close proximity.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.

The present invention advantageously provides a novel image forming apparatus, an image forming unit device having a belt-formed member and a belt device for use in the image forming apparatus, for preventing inconveniences caused by unnecessary contact of the belt-formed member with opposing members, or proximity of the two members by making it possible to separate the belt-formed member from part of the opposing members.

The present invention also advantageously provides a novel image forming apparatus, an image forming unit device having a belt-formed member and a belt device for use in the image forming apparatus, for driving the belt-formed member accurately even when the belt-formed member is separated from part of a plurality of opposing members located in close proximity to the belt-formed member or contacting the belt-formed member.

According to an embodiment of the present invention, an image forming apparatus includes a belt-formed member supported by a plurality of supporting rollers, the belt-formed member being a belt-formed intermediate transfer element, a plurality of opposing members located side by side in a line and opposing said belt-formed member, each of the plurality of opposing members being a latent image bearing member to form a latent image to be transferred onto the intermediate transfer element and a separation device to separate the intermediate transfer element located in close proximity to the plurality of latent image bearing members or in contact with the plurality of latent image bearing members from part of the plurality of latent image bearing members.

Other objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.

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

is a schematic drawing illustrating an exemplary construction of a printer as an example of an image forming apparatus according to an embodiment of the present invention.

FIG. 2

is an enlarged view of a construction of the printer.

FIG. 3

is a block diagram illustrating a data processing system of the printer.

FIG. 4

is an enlarged view of a construction of a printer with another construction.

FIG. 5

is a schematic drawing illustrating an exemplary construction of a copying machine as an example of an image forming apparatus according to another embodiment of the present invention.

FIG. 6

explains a location of an intermediate transfer belt in a multicolor mode of the copying machine.

FIG. 7

explains a location of the intermediate transfer belt in a black color mode of the copying machine.

FIG. 8

explains a mechanism of a pivot subunit.

FIG. 9

explains a driving, section of the pivot mechanism.

FIG. 10

is an enlarged sectional view illustrating a construction of a tension roller driving mechanism.

FIG. 11

is an enlarged partial perspective view illustrating a construction of the tension roller driving, mechanism.

FIG. 12

is a front view illustrating a fixed guide member employed in the tension roller driving mechanism.

FIG. 13

is a partial sectional view illustrating another exemplary construction of the tension roller driving mechanism.

FIG. 14

is an enlarged view illustrating a cleaning device provided to the tension roller.

FIG. 15

is a block diagram illustrating a date processing system of the copying machine according to another embodiment of the present invention.

FIGS. 16A and 16B

explain a relation between a contacting angle (θ) of the intermediate transfer belt and an amount of change in a circumferential length (Δ

1

) of the intermediate transfer belt when a supporting roller is moved.

FIG. 17

explains a contacting length (L

1

) and a non-contacting length (L

2

) of the intermediate transfer belt.

FIG. 18

is an enlarged view of a construction of the image forming apparatus according to another embodiment of the present invention.

FIGS. 19A and 19B

are enlarged sectional views illustrating the tension roller driving mechanism.

FIG. 20

is a block diagram illustrating a data processing system of the image forming apparatus.

FIG. 21

explains a construction of the image forming apparatus in the multicolor mode according to another embodiment of the present invention.

FIG. 22

explains a construction of the image forming apparatus in black color mode according to another embodiment of the present invention.

FIG. 23

is a side view of the tension roller according to another embodiment of the present invention.

FIG. 24

is an enlarged view of a construction of the image forming apparatus according to another embodiment of the present invention.

FIG. 25

is an enlarged view of a construction of the image forming apparatus according to another embodiment of the present invention.

FIG. 26

is an enlarged view of a construction of the image forming apparatus according to another embodiment of the present invention.

FIG. 27

is an enlarged view illustrating a construction of an image forming apparatus in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,

FIG. 1

is a schematic drawing illustrating an internal construction of an electrographic multicolor printer with liquid developer (hereinafter referred to as printer) as an example of an image forming apparatus according to an embodiment of the present invention. The printer receives image data from a personal computer (PC) etc., and performs a printing process.

As illustrated in

FIG. 1

, four drum-shaped photoconductive elements

10

Y,

10

M,

10

C and

10

B, as opposing members (latent image bearing members), corresponding to respective colors of yellow Y, magenta M, cyan C and black B, are disposed side by side in a line. Each axis of rotation of the photoconductive elements

10

Y,

10

M

10

C and

10

B is located in the same plane and in parallel with each other axis. The photoconductive element

10

B for a black color mode (single color mode) is located close to a common secondary transfer area.

Above the photoconductive elements

10

Y,

10

M,

10

C and

10

B, an intermediate transfer unit

70

is removably provided to a main body of the apparatus. The intermediate transfer unit

70

includes an intermediate transfer belt

100

in an endless form as a belt-formed member (an intermediate transfer element) supported by a plurality of rotatable supporting rollers

70

-

76

and

80

. The intermediate transfer belt

100

is spanned around spanning roller

71

-

76

and

80

, as supporting rollers so as to windingly contact part of respective photoconductive elements

10

Y,

10

M,

10

C and

10

B.

Primary transfer rollers (not shown) are located at positions opposite to respective photoconductive elements interposing the intermediate transfer belt

100

between those primary transfer rollers and a respective photoconductive element. A transfer bias may be applied to the primary transfer roller as necessary. In the secondary transfer area, where a toner image is transferred from the intermediate transfer belt

100

onto a transfer sheet

200

, located along a sheet conveying path for the transfer sheet, a secondary transfer roller

81

is provided press-contacting the intermediate transfer belt

100

and spanned around a driving roller

72

and a guide roller

73

as supporting rollers. A transfer bias may also be applied to the secondary transfer roller

81

as necessary.

For the intermediate transfer belt

100

, a belt configured to be a double layer structure may be used. A first layer including an elastic member formed on a surface side where toner image is formed and a second layer including a resin sheet on back side thereof and having a volume resistivity of 10

7

to 10

12

Ωcm may be used. For the first layer, a polyurethan rubber layer of 200 to 700 μm in thickness may be used, and as for the resin sheet layer, a polyurethan resin sheet of 100 to 500 μm in thickness and which is not stretched in a circumferential direction may be used. Further, the intermediate transfer belt

100

may include a combination of a first layer of rubber on the surface (e.g. a nitrile rubber, a urethan rubber, the Butyl-rubber and a natural rubber) and a second layer of a fiber buried rubber, or a combination of the first coated layer including a fluorine resin and the second layer of an elastic conductive element having a volume resistivity of 10

5

to 10

9

Ωcm, where a non-elastic core (e.g. a nylon cord and a steel cord) is extendedly buried in the circumferential direction.

For supporting rollers

71

-

76

and

80

, a grounded conductive roller (e.g. a metal roller) may be used. As for the primary transfer roller and the secondary transfer roller

81

, a columned or cylindrical-shaped conductive roller having a conductive rubber layer on its surface (e.g. a metal roller or a metal pipe) may be used. When the intermediate transfer belt

100

having a conductive layer on its underside is used, a floating state conductive roller (e.g. a metal roller) or a nonconductive roller is used for supporting rollers

72

-

76

and

80

other than the tension roller

71

and the primary transfer roller.

The tension roller

71

is made of a conductive roller so that the conductive layer of the intermediate transfer belt

100

has a predetermined potential by a bias voltage applied to the tension roller

71

. When the transfer bias is applied to the secondary transfer roller

81

, a transfer electric field is formed by the potential difference between the conductive layer of the intermediate transfer belt

100

and the secondary transfer roller

81

. Around the respective photoconductive elements

10

Y,

10

M,

10

C and

10

B, electrophotographic image forming processing members, such as charging devices

20

Y,

20

M,

20

C and

20

B and developing units with liquid developer

40

Y,

40

M,

40

C and

40

B are provided in order of the image forming process. Further, light irradiating paths where laser beam light LBy, LBm, LBc, and LBb is irradiated through are also disposed around respective photoconductive elements

10

Y,

10

M,

10

C and

10

B. Because developing units with liquid developer

40

Y,

40

M,

40

C and

40

B have the same structure as to each other except containing toners of different colors, those developing units can be replaced with respect to each other.

A sheet transfer path

202

is formed to convey the transfer sheet

200

from a sheet feeding tray

201

located below photoconductive elements

10

Y,

10

M,

10

C and

10

B to the secondary transfer area. A registration roller

203

to adjust a time to feed the transfer sheet

200

is located right before, in a sheet conveying direction, a guide roller

73

which is one of the supporting rollers. A first conveying belt unit

204

, a primary fixing unit

91

, a secondary conveying belt unit

205

, a secondary fixing unit

92

, an exit tray

206

, etc., are properly located along a sheet discharging path

207

at a downstream side of the secondary transfer area with respect to the transfer sheet conveying direction.

In the printer according to the embodiment of the present invention, the tension roller

71

and spanning rollers

75

,

76

and

80

are pivoted about a shaft of the driving roller

72

so as to be vertically swingable. By the pivotal movement of the tension roller

71

and spanning rollers

75

,

76

and

80

, part of the intermediate transfer belt

100

, which is an intermediate transfer element (a belt-formed member), pivots around the shaft of the driving roller

72

to vertically move. As a result, the intermediate transfer belt

100

can be positioned either at a place where the intermediate transfer belt

100

contacts all of the photoconductive elements

10

Y,

10

M,

10

C and

10

B or a separated position where the intermediate transfer belt

100

contacts only the photoconductive element

10

B, separated from other photoconductive elements

10

Y,

10

M and

10

C. The separation of the intermediate transfer belt

100

from part of photoconductive elements

10

Y,

10

M and

10

C is achieved by a belt position change mechanism

110

that changes the positions of the tension roller

71

and spanning rollers

75

,

76

and

80

through a belt uplift mechanism

111

U and a belt lift down mechanism

111

D illustrated in FIG.

3

.

According to the embodiment of the present invention, a cleaning device

79

to clean the intermediate transfer belt

100

is located at the side of the pivot of the intermediate transfer belt

100

instead of a position where the cleaning device

509

is placed in FIG.

27

. In other words, the cleaning device

79

is provided at a position opposed to the driving roller

72

which is the center of the pivot. Though a blade-formed cleaning device is illustrated in

FIG. 1

as an example of the cleaning device

79

, the cleaning device

79

may be formed like a roller, web or the like.

FIG. 3

is a block diagram explaining a data process control system of the printer according to the embodiment of the present invention. A decoder

120

receives image data transmitted from a personal computer (PC), converts it to image data corresponding to respective colors and then bit-maps each image data so as to be stored in page memories

121

Y,

121

M,

121

C and

121

B. A mode determination circuit

122

determines between a single color mode (black color mode) and a multicolor mode such as a full color mode based on the received image data. An engine control CPU (central processing unit)

123

, which functions as a drive control device and a control device to control operations of each unit of the printer, is connected to the mode determination circuit

122

.

When the mode determination circuit

122

recognizes the multicolor mode for a full color based on the image data transmitted from the personal computer PC, the engine control CPU

123

activates the belt lift down mechanism

111

D. Then the belt position change mechanism

110

lifts down the tension roller

71

etc. to a position indicated by a solid line in

FIG. 2

so as to contact the primary transfer areas of the photoconductive elements

10

Y,

10

M,

10

C and

10

B, which is an initial position of the intermediate transfer belt

100

(hereinafter a returning of the intermediate transfer belt to the initial position is referred to as replacement of the intermediate transfer belt). A multicolor image formation by superimposing respective color toner images on each other becomes possible by the replacement of the intermediate transfer belt

100

. The replacement of the intermediate transfer belt

100

is performed while image data for the multicolor image formation is being bit-mapped and stored in respective page memories

121

Y,

121

M,

121

C and

121

B (four times longer than a time for a single color). Therefore, the apparatus can be set ready for a multicolor image forming operation without requiring an additional time for the process. Similarly, the intermediate transfer belt

100

can be cleaned several times by the cleaning device

79

by rotating the intermediate transfer belt

100

while image data for the multicolor image formation is being bit-mapped and stored in respective page memories

121

Y,

121

M,

121

C and

121

B, and thereby a cleanliness of the intermediate transfer belt

100

is increased without taking an additional time for the cleaning.

Contrarily, when the mode determination circuit

122

recognizes the single color mode based on the image data transmitted from the personal computer PC, the engine control CPU

123

activates the belt uplift mechanism

111

U so that the belt position change mechanism

110

swingingly moves the tension roller

71

and spanning rollers

75

,

76

and

80

etc. to a separated position indicated by a dotted line in

FIG. 2

, where the intermediate transfer belt

100

contacts only the photoconductive element

10

B and is separated from other photoconductive elements

10

Y,

10

M and

10

C. As a result, an operation for an image forming and printing of the black color mode with the photoconductive element

10

B, surrounding developing unit

40

B with liquid developer, the intermediate transfer belt

100

and so forth becomes possible. Consequently, although the intermediate transfer belt

100

rotates as in a case of the multicolor mode, the intermediate transfer belt

100

does not contact photoconductive elements

10

Y,

10

M and

10

C which are not involved in the image formation and printing process, and thereby the life of photoconductive elements

10

Y,

10

M and

10

C may not be decreased. Especially, because the black color mode, which is most frequently used, is set as the single color mode, the life of photoconductive elements

10

Y,

10

M and

10

C may be advantageously extended. Because the developing units with liquid developer

40

Y,

40

M,

40

C and

40

B have the same structure as to each other and are replaceable with each other, a desired color can be easily set for the single color mode by placing a developing unit with liquid developer of the desired color at the photoconductive element located at a foremost right end (at the side of a common image transfer area).

When the cleaning device

79

is positioned at a place shown in

FIG. 2

, i.e., at a tip end side of the pivot of the intermediate transfer belt

100

, the cleaning device

509

has to move along with the intermediate transfer belt

100

as indicated by a two-dotted and dashed line in FIG.

2

. Therefore, a load imposed on the belt position change mechanism

110

is increased and a distance the cleaning device

509

has to move is also increased, which may result in inconvenience of, for example, a leakage of developer etc. According to the embodiment of the present invention, because the cleaning device

79

is located at the base end side of the pivot of the intermediate transfer

100

, the increase of the load imposed on the belt position change mechanism

110

as well as the distance the cleaning device

79

moves are minimized, which may suppress inconvenience of the leakage of developer from the cleaning tank etc.

In the printer according to the embodiment of the present invention, either the black color mode (single color mode) or the multicolor mode is selectable. However in actuality, various modes with a combination of colors, such as 2 colors printing with black BK and cyan C colors, 3 colors printing with black BK, cyan C and magenta M colors and so forth, may be required. In order to cope with the requirement for various modes, a stepped belt position change mechanism

112

to change the position of spanning rollers

75

,

76

and

80

in steps as shown in

FIG. 4

may be employed to control a position of the intermediate transfer belt

100

. The stepped belt position change mechanism

112

functions to change the number of the photoconductive elements separating from the intermediate transfer belt

100

in steps and uplifts or lifts down spanning rollers

75

,

76

and

80

individually and independently. In the multicolor mode, for example, when a two colors mode with black color BK and cyan color C is set, the intermediate transfer belt

100

is brought into contact only with photoconductive elements

10

C and

10

B separating from photoconductive elements

10

Y and

10

M by uplifting the tension roller

71

and spanning rollers

76

and

80

while keeping the spanning roller

75

at a lifted down position as indicated by a chained line in FIG.

4

. Further, in the multicolor mode, for example, when three colors mode with black BK, cyan C and magenta M colors is set, the intermediate transfer belt

100

is brought into contact only with photoconductive elements

10

M,

10

C and

10

B separating from the photoconductive element

10

Y by uplifting the tension roller

71

and spanning roller

80

while keeping the spanning rollers

75

and

76

at the lifted down position as indicated by a two-dotted and dashed line in FIG.

4

. As a result, the position of the intermediate transfer belt

100

can be controlled precisely so as not to contact photoconductive elements which are not involved in the image forming and printing operation which advantageously extends the life of photoconductive elements

10

Y,

10

M and

10

C.

Furthermore, the printer according to the embodiment of the present invention may be preferably configured such that mechanical devices (driving devices for the photoconductive elements and developing units) for the photoconductive elements which are separated from the intermediate transfer belt

100

(for example, photoconductive elements

10

Y,

10

M and

10

C in a case of the black color mode) are controlled to be stopped. By this control, the life of the photoconductive elements, developing units with liquid developer and its driving devices can be extended, and a consumption of electricity and a vibration can be reduced. Further, unnecessary consumption of developer through the unnecessary operation of the developing unit is avoided.

Further, in the printer according to the embodiment of the present invention, the intermediate transfer belt

100

is configured to partly pivot so as to separate from part of the photoconductive elements, however, it may be configured such that photoconductive elements are driven to uplift or lift down so as to separate from the intermediate transfer belt

100

. In this case, because the photoconductive elements, which are movable independently, change positions, the separation mechanism can be made simpler compared with the one in which the intermediate transfer belt

100

partly pivots by moving the above-described supporting rollers. Further, because the space for moving part of photoconductive elements is less than the one in which the intermediate transfer belt

100

partly pivots, it is also advantageous to reduce a size of the apparatus.

In the embodiment of the present invention, when a change in a tension of the intermediate transfer belt

100

occurs in the separation of the intermediate transfer belt

100

from part of the photoconductive elements, it is desirable to change a distance of at least one of the supporting rollers relative to the other supporting rollers. For example, the tension roller

71

may be configured to move toward the outside of the apparatus so as to suppress a change in the tension of the intermediate transfer belt

100

as explained in the following embodiment of the present invention. The intermediate transfer belt

100

can be driven accurately by the driving roller

72

by suppressing the change in the tension of the intermediate transfer belt

100

.

Now, an electrophotographic copying machine with liquid toner as an example of an image forming apparatus according to the another embodiment of the present invention is explained.

FIG. 5

is a schematic drawing illustrating an internal construction of the copying machine. The copying machine has four sets of image forming sections

1

Y,

1

M,

1

C and

1

B, an intermediate transfer unit

70

which is detachable/attachable to a main body of the copying machine, a fixing device

90

, and an image reading unit (scanning unit), a sheet feeding unit and a controlling unit which are not shown.

The above four sets of image forming sections

1

Y,

1

M,

1

C and

1

B each includes photoconductive drums

10

Y,

10

M,

10

C and

10

B, developing units

40

Y,

40

M,

40

C and

40

B etc. Developing units

40

Y,

40

M,

40

C and

40

B use yellow toner, magenta toner, cyan toner and black toner respectively.

Electrostatic latent images of corresponding colors are formed on surfaces of corresponding photoconductive drums

10

Y,

10

M,

10

C and

10

B and are developed in respective developing units

40

Y,

40

M,

40

C and

40

B into toner images (visible images) with respective colors. The color toner images on the photoconductive drums are transferred to an intermediate transfer belt

100

being superimposed one after another, creating a multicolor toner image. Then, the multicolor toner image on the intermediate transfer belt

100

is transferred at one time to a transfer sheet

200

.

Because the four sets of image forming sections have the same construction, the image forming section

1

B will be described as an example of an image forming section.

The image forming section

1

B includes a photoconductive drum

10

B as an image bearing member, a charging device

20

B to uniformly charge a surface of the photoconductive drum

10

B, a laser writing unit

30

irradiating a laser beam light (LB), a liquid-type developing unit

40

B, a discharging device

50

B and a cleaning device

60

B having a cleaning blade. A visible image is formed on the photoconductive drum

10

B with the charging device

20

B, the laser writing unit

30

and the developing unit

40

B etc.

The liquid-type developing unit

40

B includes a developing roller

41

B as a developer carrier, a developer reservoir

42

B to store a developer, a developer scoop up roller

43

B provided so as to be immersed in liquid developer in the developer reservoir

42

B and a developer coating roller

44

B which laminates and coats the developer scooped up by the developer scoop up roller

43

B on the developing roller

41

B.

The liquid developer used in the liquid-type developing unit includes toner particles to make a latent image visible, which are dispersed at a high ratio in a carrier liquid and insulating material, having a viscosity as high as 100 to 10,000 mPa s.

The intermediate transfer unit

70

includes supporting rollers

71

,

72

,

73

,

74

,

75

,

76

,

78

and

80

, the intermediate transfer belt

100

(opposing member) which is spanned around those rollers, primary transfer bias rollers

77

B,

77

Y,

77

M and

77

C as primary transfer bias applying members and an intermediate transfer belt cleaning device

79

having a cleaning blade

79

a.

The supporting roller

72

is connected to a driving means (not shown) and is configured to function as a drive roller also to rotatively drive the intermediate transfer belt

100

.

It is preferable that the intermediate transfer belt

100

is elastic at its surface contacting a transfer sheet without being elastic in a circumferential direction. Because the elastic surface of the intermediate transfer belt

100

is brought into intimate contact with the transfer sheet by adhering to a concave surface of the transfer sheet, a satisfactory transfer of the toner image onto the transfer sheet can be obtained.

As in the first embodiment the intermediate transfer belt

100

, may be configured to be a double layer construction, having a first layer including an elastic member formed on a surface side where a toner image formed and a second layer including a resin sheet is formed on a back side thereof, and having a volume resistivity of 10

7

to 10

12

Ωcm. For the first layer, a polyurethan rubber layer of 200 to 700 μm in thickness may be used. And as for the resin sheet layer, a polyurethan resin sheet of 100 to 500 μm in thickness, which is not stretched in a circumferential direction, may be used. Further, the intermediate transfer belt

100

may include a combination of a first layer of rubber formed on the surface (e.g. a nitrile rubber, a urethan rubber, the Butyl-rubber and a natural rubber) and a second layer of a fiber buried rubber, or a combination of a first coated layer including a fluorine resin and a second layer of an elastic conductive element having the volume resistivity of 10

5

to 10

9

Ωcm. The elastic conductive element may include a polyurethan rubber with carbon dispersed.

When the intermediate transfer belt

100

is configured to have the thickness of 200 to 2000 μm, a volume resistivity of 10

5

to 10

9

Ωcm and a hardness of 15° to 80° in JIS A (Japanese Industrial Standards A), a specified effect will be obtained. The non-elastic core prevents the elastic conductive element from being stretched in the circumferential direction and it may include, for example, a nylon cord or a steel cord of 50 to 400 μm in diameter. The surface coated layer is provided to increase a transferability of a secondary transfer by improving a release of toner particles and to achieve a smoother separation of the transfer sheet

200

after the secondary transfer operation. The surface coated layer may include, for example, a layer including a fluorine resin coated in 5 to 60 μm thickness.

As for supporting rollers

71

-

76

and

80

, a grounded conductive roller (e.g. a metal roller) may be used. As for the primary transfer roller

77

and the secondary transfer roller

81

, a columned or cylindrical-shaped conductive roller (e.g. a metal roller or a metal pipe) having a conductive rubber layer (e.g. a hydrin rubber) on its surface may be used.

When the intermediate transfer belt

100

having a conductive layer on its underside is used, a floating state conductive roller (e.g. a metal roller) or a nonconductive roller is used for supporting rollers

72

-

76

and

80

other than the tension roller

71

and for the primary transfer roller

77

. The tension roller

71

is made of a conductive roller so that the conductive layer of the intermediate transfer belt

100

has a predetermined potential by a bias voltage applied to the tension roller

71

. When the transfer bias is applied to the secondary transfer roller

81

, a transfer electric field is formed by the potential difference between the conductive layer of the intermediate transfer belt

100

and the secondary transfer roller

81

.

A secondary transfer section to transfer a toner image formed on the intermediate transfer belt

100

to the transfer sheet

200

includes a secondary transfer roller

81

around which the intermediate transfer belt

100

windingly contacts and forms a secondary transfer nip therebetween and a secondary transfer power supply (not shown) as a transfer bias applying device, connected to the secondary transfer roller

81

.

The intermediate transfer belt

100

is windingly brought into contact with the photoconductive drums

10

B,

10

C,

10

M and

10

Y with specified contacting angles by the supporting rollers

74

,

75

,

76

,

78

and

80

(hereinafter referred to as spanning roller as necessary) which are located adjacent to respective photoconductive drums. The intermediate transfer belt

100

is spanned around a supporting roller

71

located at the left end in

FIG. 5

with the greatest contacting angle (hereinafter referred to as a tension roller as necessary) so as to maintain a specified belt tension. Further, the intermediate transfer belt

100

is rotatively driven in a counterclockwise direction indicated by an arrow by a supporting roller

72

(hereinafter referred to as a driving roller as necessary) opposite to a secondary transfer roller

81

located at the right end in FIG.

5

. The primary transfer bias roller

77

B is provided opposite to the photoconductive drum

10

B and the intermediate transfer belt

100

is interposed between the primary transfer roller

77

B and the photoconductive drum

10

B. The primary transfer roller

77

B also functions as an electrode applying a primary transfer bias while being applied with a specified primary transfer bias by a primary transfer power supply (not shown).

FIGS. 6 and 7

illustrate locations of the intermediate transfer belt

100

in multicolor and black and white image forming processes respectively. In the multicolor image forming process shown in

FIG. 6

, the intermediate transfer belt

100

is supported by respective supporting rollers so as to contact the photoconductive drums

10

B,

10

Y,

10

M and

10

C with a specified contacting angle of θ.

In the black and white image forming process illustrated in

FIG. 7

, the intermediate transfer belt

100

moves to a position where the intermediate transfer belt

100

is separated from the photoconductive drums

10

Y,

10

M and

10

C while it remains in contact with only the photoconductive drum

10

B for black color, the drum closest to a secondary transfer area, located at the right end in

FIG. 7. A

separation device, for moving the intermediate transfer belt

100

to the separated position, pivotably moves a pivot subunit (not shown), to which shafts of the supporting rollers

71

,

75

,

76

and

80

and the primary transfer roller

77

Y,

77

M and

77

C are attached, about the spanning roller

74

located between the photoconductive drums

10

B and

10

C, by a pivot mechanism (not shown), in a clockwise direction as indicated by arrow A in FIG.

7

.

FIG. 8

explains a pivot mechanism of the pivot subunit

701

which is part of the intermediate transfer unit

70

. The intermediate transfer unit

70

includes the pivotable pivot subunit

701

and a fixed subunit

702

. Spanning rollers

75

,

76

and

80

, and primary transfer rollers

77

Y,

77

M and

77

C are rotatably provided to a sideboard

701

a

of the pivot subunit

701

. The primary transfer roller

77

B for black color, the driving roller

72

, the guide roller

73

and spanning rollers

74

and

78

are rotatably provided to a sideboard

702

a

of the fixed subunit

702

. The pivot subunit

701

pivots about the shaft of the fixed spanning roller

74

. Above the spanning roller

74

, an oblong hole

701

b

for the pivot is provided on the sideboard

701

a

so that a guide pin

702

b

provided to the fixed subunit

702

passes through the oblong hole

701

b.

When the pivot subunit

701

pivots, the guide pin

702

b

guides the pivoting of the pivot subunit

701

.

FIG. 9

illustrates a driving section of the pivot mechanism to pivot the pivot subunit

701

. The driving section includes a timing belt

706

in an endless form spanned around pulleys

704

and

705

. A shaft

704

a

of the pulley

704

is rotatably supported by a main body of the apparatus. The pulley

705

is connected to a rotation shaft of a motor

707

that is supported by the main body of the apparatus. The motor

707

can reverse the direction of rotation and is controlled by an engine control CPU (central processing unit) described later. A fixing member

703

is provided at a spanned portion of the timing belt

706

between pulleys

704

and

705

so as to sandwich support the timing belt

706

. The fixing member

703

is fixed to the sideboard

701

a

of the pivot subunit

701

.

In the above-described driving section, when the motor

701

rotates in a normal or reverse direction, the fixing member

703

moves in a vertical direction (in a direction indicated by a double-headed arrow H in

FIG. 9

) along with the movement of the timing belt

706

. By the movement of the fixing member

703

, the pivot subunit

701

, to which the fixing member

703

is fixed, pivots as indicated by an arrow I in FIG.

9

.

When the intermediate transfer belt

100

is moved to the separated position, the intermediate transfer belt

100

is slackened and a tension of the intermediate transfer belt

100

tends to be reduced. Therefore, a relative distance change device is provided to move the tension roller

71

in a direction (the direction indicated by an arrow B in

FIG. 7

) that increases a relative distance of the tension roller

71

and the other supporting rollers when the above mentioned supporting rollers etc. are rotatively moved. The movement of the tension roller

71

prevents the tension of the intermediate transfer belt

100

from lowering. Positions of parts designated with a dash (′) in

FIG. 7

(and in

FIG. 10

) show virtual intermediate positions of the corresponding parts when they are moved.

FIGS. 10 and 11

are expanded sectional and perspective views respectively illustrating an example of a tension roller driving mechanism as the relative distance changing device according an embodiment of the present invention. The tension roller driving mechanism includes a biasing member that moves together with the tension roller

71

and applies a resilient bias to a bearing

71

a

for the tension roller

71

so that the tension roller

71

press contacts the intermediate transfer belt

100

. The tension roller driving mechanism also includes a fixed guide member

103

which thrusts an other end of a junction member

102

to move the biasing member toward the tension roller

71

. The biasing member includes a spring

101

, an end of which touches the bearing

71

a

of the tension roller

71

and the junction member

102

performs a reciprocating motion being thrusted by an other end of the spring

101

. The junction member

102

includes two oblong holes

102

a

and pins

104

attached to the side of the pivot unit through the oblong holes

102

a.

The junction member

102

performs reciprocating motion while being supported by the pins

104

and pivots together with the tension roller

71

.

The fixed guide member

103

is fixed to a body of the image forming apparatus and includes recesses

103

a

and

103

b

where an end of the junction member

102

is engagedly held temporarily in the multicolor and the black and white image forming processes respectively as illustrated in FIG.

12

. Because the end of the junction member

102

is engagedly held with the recesses

103

a

or

103

b

of the fixed guide member

103

, the end of the junction member can be held firmly in respective positions that stabilizes the tension of the intermediate transfer belt

100

maintained by the junction member

102

via the spring

101

.

For the fixed guide member

103

, a resin that possesses a low coefficient of friction such as polyacetal, polycarbonate and polyamide is preferable. Because a friction produced when the end of the junction member

102

moves in contact with a surface of the fixed guide member

103

is lowered, a load imposed on the pivot of the pivot subunit

701

, which includes part of the above mentioned supporting rollers, is decreased.

For the biasing member to apply a resilient bias to the bearing

71

a

of the tension roller

71

, a set of cylindroid members

105

and

106

with different diameters, which are configured such that one cylindroid member moves back and forth through the other cylindroid member having a spring

107

in it as illustrated in FIG.

13

. An end of the cylindroid member

105

is attached to the bearing

71

a

of the tension roller

71

. The other cylindroid member

106

is fixed to the pivot subunit

701

so as to perform a reciprocating movement and to contact the fixed guide member

103

at its end.

As illustrated in

FIG. 14

, the cleaning unit

79

including a cleaning blade

79

a

and a cleaning roller

79

b

is configured to move integrally with a bearing

71

a

of the tension roller

71

. Accordingly, even when the tension roller

71

is moved in a direction indicated by an arrow B in

FIG. 14

, the cleaning blade

79

a

and the cleaning roller

79

b

of the cleaning device

79

securely contact the intermediate transfer belt

100

, and thereby a satisfactory cleaning performance for the intermediate transfer belt

100

is maintained.

FIG. 15

is a block diagram explaining a data process control system of the copying machine according to embodiment of the present invention. Image data transmitted from a scanning device is converted to image data corresponding to respective colors at an image data processing section

124

and is stored in page memories

121

Y,

121

M,

121

C and

121

B corresponding to respective colors of yellow, magenta, cyan and black. The mode determination circuit

122

determines a single color mode (black color mode) or a multicolor mode based on the image data output from each page memory. The engine control CPU

123

controls a driving device

113

for the pivot subunit

701

etc. according to a result of an image forming mode discrimination at the mode discrimination circuit

122

. By this control, unnecessary contact of the intermediate transfer belt

100

with the photoconductive elements

10

Y,

10

M and

10

C which are not used and the change in the tension of the intermediate transfer belt

100

can be avoided according to the determined image forming mode. Especially, when the image forming operation is switched from the black color mode to the multicolor mode, it is preferable that the apparatus is controlled such that the pivot subunit

701

pivots and rotatively drives the intermediate transfer belt

100

and cleans the intermediate transfer belt

100

two or more times by the cleaning device

79

utilizing a time when image data for the multicolor image forming is processed. By this control, a time for the copying machine to start the image forming operation after a copy start button is pressed is shortened and the cleaning performance for the intermediate transfer belt

100

is enhanced without taking an additional time for the cleaning.

Next, an image forming operation of the copying machine will be described. As illustrated in

FIG. 5

, a surface of the photoconductive drum

10

B is uniformly charged with a charging device

20

B while the photoconductive drum

10

B is rotating in a direction indicated by an arrow. Then, an electrostatic latent image is formed on the surface of the photoconductive drum

10

B being exposed to a laser light beam LB irradiated from the laser writing unit

30

. The developing roller

41

B is uniformly coated, for example, in the thickness of about 0.5 to 20 μm, via the developer applying roller

44

B with liquid developer adhered to the developer scoop up roller

43

B which is immersed in high-viscosity liquid developer in the developer reservoir

42

B. The developing roller

41

B is brought into contact with the photoconductive drum

10

B so that toner in liquid developer is applied to the latent image formed on the surface of the photoconductive drum

10

B by virtue of an electric field, and thereby a visible toner image is formed.

The toner image formed on the photoconductive drum

10

B is moved to a primary transfer area along with the rotation of the photoconductive drum

10

B where the photoconductive drum

10

B abuts against the intermediate transfer belt

100

. In the primary transfer area, a back of the intermediate transfer belt

100

is applied with a negative bias voltage of, for example, −300 to −500, through the primary transfer bias roller

77

B. Then the toner of the toner image formed on the photoconductive drum

10

B is attracted to the intermediate transfer belt

100

by a force of an electric field generated by the applied voltage to transfer the toner image to the intermediate transfer belt

100

(a primary transfer). The toner image is formed on the intermediate transfer belt

100

in order of yellow, magenta, cyan and black, and the toner images of respective colors are transferred to the intermediate transfer belt

100

superimposed one after another to form a full color image (visible image).

The intermediate transfer belt

100

having the multicolor toner image travels to a secondary transfer area where the intermediate transfer belt

100

abuts against a transfer sheet

200

conveyed from a sheet feeding unit (not shown) in a direction indicated by an arrow in FIG.

5

. In the secondary transfer area, a back of the transfer sheet

200

is applied with a negative bias voltage of, e.g., −800 to −2000 through the secondary transfer roller

81

, which presses the transfer sheet

200

with a force of about 50 N/cm

2

. The toner on the intermediate transfer belt

10

is attracted and transferred onto the transfer sheet

200

at one time by virtue of an electric field generated by the application of the voltage and the pressure exerted to the transfer sheet

200

(a secondary transfer).

The transfer sheet

200

carrying the transferred toner image is separated from the intermediate transfer belt

100

by a transfer sheet separation member

61

and is discharged to an exit tray after the toner imager is fixed onto the transfer sheet

200

by a toner image fixing device

90

. After the secondary transfer operation, the surface of the photoconductive drum

10

B is uniformly discharged by a discharging device

50

B and is cleaned by a cleaning device

60

B and remaining residual toner is removed to be ready for a next image forming operation.

When a black and white image is formed in the above configured copying machine, as illustrated in

FIG. 7

, the pivot subunit (not shown) disposed at the side of a color image forming section pivots while an image forming operation is not performed such that the intermediate transfer belt

100

moves to the separated position where the intermediate transfer belt

100

remains in contact only with the photoconductive drum

10

B for black color which is the closest drum to the secondary transfer area, (disposed at the right side end in

FIG. 7

) while being separated from the other photoconductive drums

10

Y,

10

M and

10

C. A toner image is formed only on the surface of the photoconductive drum

10

B and is then transferred to the intermediate transfer belt

100

. The toner image on the intermediate transfer belt

100

is then transferred onto the transfer sheet

200

at the secondary transfer area to form a black and white image on the transfer sheet

200

.

According to the embodiment of the present invention, even when the intermediate transfer belt

100

is tentatively separated from the three photoconductive drums

10

Y,

10

M and

10

C for the multicolor image forming process in a black and white image forming operation, a change in the intermediate transfer belt

100

is suppressed and thereby the intermediate transfer belt

100

is frictionally driven accurately. Thus a quality degradation of a produced image caused by a deviation of the image position or image size etc. is suppressed.

According to the embodiment of the present invention, the tension roller

71

, with which the intermediate transfer belt

100

is in contact with the largest contacting angle among the supporting rollers, moves when the intermediate transfer belt

100

moves to the separated position.

Generally, the larger the contacting angle of the intermediate transfer belt

100

with a supporting roller is, the larger the amount of a change in a circumferential length of the intermediate transfer belt

100

relative to a unit of travel of the supporting roller is. For example, when a contacting angle (θ) of the intermediate transfer belt

100

with a supporting roller

700

is 180°, the amount of a change (Δ

1

) in the circumferential length of the intermediate transfer belt

100

is 2D when the supporting roller

700

is moved by a distance of D toward the outside of the apparatus as indicated by an arrow B in FIG.

16

A. Contrarily, as shown in

FIG. 16B

, when the contacting angle (θ) of the intermediate transfer belt

100

with the supporting roller

70

is less than 180°, the amount of a change (Δ

1

) in a circumferential length of the intermediate transfer belt

100

is less than 2D even when the supporting roller

700

is moved toward the outside of the apparatus by the same distance of D described in FIG.

16

A.

In this embodiment, because the tension roller

71

, with which the intermediate transfer belt

100

is in contact and which has the largest contacting angle among the supporting rollers, is moved, the amount of movement of the tension roller

71

to prevent the tension of the intermediate transfer belt

100

from being decreased is minimized.

Further, the amount of a movement of the tension roller

71

is set such that the intermediate transfer belt

100

is spanned around a plurality of supporting rollers while being tensioned when the intermediate transfer belt

100

is pivoted such that, referring to

FIG. 17

, a sum of (1) a length of a path out of an intermediate transfer belt path

601

over which the intermediate transfer belt

100

windingly in contact with a plurality of contacting members such as the supporting rollers etc. and (2) a length of a path out of the intermediate transfer belt path

601

over which the intermediate transfer belt

100

is not in contact with any contacting member, does not change. As illustrated in

FIG. 17

, L

1

and L

3

are the length of paths over which the intermediate transfer belt

100

windingly in contact with contacting members

602

and

603

, respectively. L

2

is the length of the path over which the intermediate transfer belt

100

is spanned straightly between contacting members

602

and

603

where the intermediate transfer belt

100

does not contact any contacting member. In this embodiment, contacting members

602

and

603

correspond to supporting rollers and photoconductive elements.

The change in the tension of the intermediate transfer belt

100

is securely suppressed by setting the amount of the movement of the tension roller

71

as described above.

In the above-described embodiment of the present invention, the intermediate transfer belt

100

is configured to partly pivot so as to separate from part of photoconductive elements

10

Y,

10

M,

10

C and

10

B, however, as illustrated in

FIG. 18

, part of photoconductive elements

10

Y,

10

M and

10

C may be configured to be brought down so as to be separated from the intermediate transfer belt

100

. The change in the tension of the intermediate transfer belt

100

can be suppressed by moving the tension roller

71

, along with the separating movement, by a specified distance D in a direction of a tension applied to the intermediate transfer belt

100

.

A mechanism to move the photoconductive elements can be simpler compared with the one that partly pivots the intermediate transfer belt

100

as described above. It is also advantageous in reducing the size of the apparatus because the mechanism to move the photoconductive elements requires less space than the one to move the intermediate transfer belt

100

.

An eccentric cam

109

may be employed in a mechanism to move the tension roller

71

as illustrated in

FIGS. 19A and 19B

. The eccentric cam

109

is rotated about 90° i.e., from a state illustrated in

FIG. 19A

to a state in

FIG. 19B

so as to move the tension roller

71

by thrusting the bearing

71

a

through a spring

101

. Especially, when the eccentric cam

109

is employed, because the tension roller

71

can be moved in multiple steps by adjusting the angle of the rotation of the eccentric cam

109

, an adjustment of the tension of the intermediate transfer belt

100

can be easily made.

FIG. 20

is a block diagram explaining a data process control system of the image forming apparatus (a printer) configured to move the tension roller

71

by the eccentric cam

109

. In the image forming apparatus, the driving device

114

for the eccentric cam

109

and the driving device

113

for the pivot subunit

701

are controlled according to a result of an image forming mode discrimination. By this control, unnecessary contact of the intermediate transfer belt

100

with photoconductive elements and a change in the tension of the intermediate transfer belt

100

are securely avoided in response to the determination of the image forming mode.

As illustrated in

FIGS. 21 and 22

, the photoconductive element

10

B for black color may be located in a different level in a direction orthogonal to the axes of photoconductive elements

10

Y,

10

M and

10

C. To be specific, as illustrated in

FIG. 21

, photoconductive elements

10

Y,

10

M and

10

C are disposed such that a center line of photoconductive elements

10

Y,

10

M and

10

C (indicated by a chained line C

1

) is located further from the intermediate transfer belt

100

than a center line of the photoconductive element

10

B (indicated by a chained line C

2

), which is in parallel with C

1

, by a level difference of E. As illustrated in

FIG. 23

, which is a view from a direction indicated by an arrow F in

FIG. 21

, in this configuration the tension roller

71

acts to correct shifting of the intermediate transfer belt

10

to one side. One end

71

b

of a shaft of the tension roller

71

is fixed to a housing

70

a

of the intermediate transfer unit

70

and the eccentric cam

710

abuts against the other end

71

c

of the shaft via a bearing. The end

71

c

of the shaft moves in a direction (vertical direction indicated by a double-headed arrow G) orthogonal to a direction to which a tension is applied to the intermediate transfer belt

100

so as to correct the shifting of the intermediate transfer belt

100

to a width direction.

A chained line and a two-dotted and dashed line in the proximity of the intermediate transfer belt

100

(a solid line) in

FIGS. 21 and 22

illustrates edges of the intermediate transfer belt

100

when the intermediate transfer belt

100

is moved by the tension roller

71

to correct a shifting of the intermediate transfer belt

100

in the width direction.

The cleaning device

79

to clean a surface of the intermediate transfer belt

100

is configured to move integrally with the tension roller

71

(see FIG.

14

). Therefore, even when the tension roller

71

changes its position to correct a shifting of balance of the intermediate transfer belt

100

, the cleaning blade

79

a

and the cleaning roller

79

b

securely contact the intermediate transfer belt

100

, and thereby the intermediate transfer belt

100

is kept well-cleaned.

In this configuration, when the intermediate transfer belt

100

is separated from the photoconductive elements

10

Y,

10

M and

10

C in the black color mode, positions of the spanning rollers

78

and

78

′ and the primary transfer roller

77

B relating to the photoconductive element

10

B remain unchanged as illustrated in FIG.

22

. Alternatively, spanning rollers

74

,

75

,

76

and

80

, and primary transfer rollers

77

Y,

77

M and

77

C relating to photoconductive elements

10

Y,

10

M and

10

C are moved in an upward direction, separating from these photoconductive elements, by a driving mechanism (not shown). Thus, the intermediate transfer belt

100

can be separated from photoconductive elements

10

Y,

10

M and

10

C by moving only part of the spanning rollers and primary transfer rollers.

In the above-described separation of the intermediate transfer belt from the photoconductive elements, supporting rollers

82

and

83

for applying a supplementary pressure to the intermediate transfer belt

100

(hereinafter referred to as supplementary roller) are moved in an upward direction to press an underside of the portion of the intermediate transfer belt

100

spanned between the driving roller

72

and the tension roller

71

so as to prevent the tension of the intermediate transfer belt

100

from changing (a decrease in the tension). Further, in this configuration, the tension roller

71

is not required to be moved greatly in order to suppress the change in the tension of the intermediate transfer belt

100

caused by the above-described separation of the intermediate transfer belt

100

from photoconductive elements. Therefore, the conditions of the tension of the intermediate transfer belt

100

given by the tension roller

71

, and the function of the tension roller

71

to correct a shifting of the intermediate transfer belt

100

are hardly influenced by the separation of the intermediate transfer belt

100

from photoconductive elements, thus making it possible to maintain the quality of images.

As illustrated in

FIG. 21

, in the multicolor mode where the intermediate transfer belt

100

contacts photoconductive elements

10

Y,

10

M and

10

C, supplementary rollers

82

and

83

are located so as to securely separate from the underside of the intermediate transfer belt

100

even when maximum shifting correction is made to the intermediate transfer belt by the tension roller

71

. Consequently, in the multicolor mode, the function of the tension roller

71

to correct a shifting of the intermediate transfer belt

100

may not be affected by a contact of supplementary rollers

82

and

83

with the intermediate transfer belt

100

.

In the above described embodiment of the present invention, a belt-formed member and an opposing member which contacts the belt-formed member are described as the intermediate transfer belt

100

and the photoconductive drums respectively. However, the present invention can also be applied when the belt-formed member is a photoconductive belt

300

and a plurality of opposing members, contacting the photoconductive belt

300

, are developer rollers

41

B,

41

Y,

41

M and

41

C, as illustrated in FIG.

24

.

In the image forming apparatus illustrated in

FIG. 24

, charging devices

305

B,

305

Y,

305

M and

305

C are disposed to oppose supporting rollers

304

B,

304

Y,

304

M and

304

C at an upstream side of respective developing rollers in the moving direction of the photoconductive belt

300

. Opposing rollers

307

B,

307

Y,

307

M and

307

C are provided at positions opposed to developing rollers

41

B,

41

Y,

41

M and

41

C respectively while the photoconductive belt

300

is interposed between the opposing rollers and the developing rollers. The photoconductive belt

300

is uniformly charged by the charging devices

305

B,

305

Y,

305

M and

305

C and is exposed to laser beam lights corresponding to colors of an original image from a laser writing unit and then electrostatic latent images corresponding to respective colors are formed on the photoconductive belt

300

. When a black and white image is formed in the image forming apparatus, supporting rollers

301

,

304

Y,

304

M and

304

C and opposing rollers

307

Y,

307

M,

307

C as well as the photoconductive belt

300

are pivoted about the supporting rollers

304

B located between developing rollers

41

B and

41

C in a direction indicated by an arrow A in FIG.

24

. Then, the photoconductive belt

300

is separated from developing rollers

41

Y,

41

M and

41

C. During the pivotal movement, the supporting roller

301

, which also works as a tension roller, moves toward the outside of the apparatus as indicated by an arrow B in

FIG. 24

so as to prevent a tension of the photoconductive belt

300

from decreasing, thus enabling the photoconductive belt

300

to be driven accurately even in the black and white image forming operation.

Especially, in the configuration illustrated in

FIG. 24

, the photoconductive belt

300

and the belt-formed member may be disposed contacting or in the vicinity of developing rollers

41

B,

41

Y,

41

M and

41

C as a plurality of opposing members (developer bearing member). The arrangement of the photoconductive belt

300

and developing rollers

41

B,

41

Y,

41

M and

41

C can be determined according to a development system such as contacting and non-contacting development systems. The present invention can be applied to both developing systems.

Further, as illustrated in

FIG. 25

, the present invention can also be applied to an image forming apparatus configured such that a belt-formed member is a transfer sheet conveying belt

400

to convey a transfer sheet

200

to a transfer area while a plurality of opposing members opposed to the transfer sheet conveying belt

400

are photoconductive drums

10

B,

10

Y,

10

M and

10

C of respective colors. In the image forming apparatus illustrated in

FIG. 25

, the transfer sheet conveying belt

400

is supported by a plurality of supporting rollers

401

,

402

,

403

and

404

and charging devices

405

B,

405

Y,

405

M and

405

C are arranged opposing to respective photoconductive drums

10

B,

10

Y,

10

M and

10

C while interposing the transfer sheet conveying belt

400

between the charging devices and the photoconductive drums. Supporting rollers

401

and

403

serve as a belt driving roller and a tension roller respectively.

When a black and white image is formed in the image forming apparatus, the supporting roller (the tension roller)

403

as well as charging devices

405

Y,

405

M and

405

C are pivoted about the supporting roller

404

located between photoconductive drums

10

B and

10

C in a direction indicated by an arrow A in FIG.

25

. Thereby the transfer sheet conveying belt

400

is separated from the photoconductive drums

10

Y,

10

M and

10

C. In the pivotal movement, the supporting roller

403

, which also functions as a tension roller, is moved toward the outside of the apparatus as indicated by an arrow B to prevent a tension of the transfer sheet conveying belt

400

from decreasing, thus enabling the transfer sheet conveying belt

400

to be frictionally driven accurately even in the black and white image forming operation.

The present invention may be also applied to an image forming apparatus configured such that a tension of a belt-formed member is increased when the belt-formed member separates from some of the opposing members as illustrated in FIG.

26

. The image forming apparatus shown in

FIG. 26

is configured in a manner similar to the apparatus illustrated

FIG. 4

, however, a pivot of a pivot subunit including part of supporting rollers

71

,

75

,

76

and

80

is positioned differently. In the image forming apparatus shown in

FIG. 26

, a pivot

601

is positioned such that a tension of the intermediate transfer belt

100

is increased in the above described pivotal movement.

When a black and white image is formed in the image forming apparatus, part of supporting rollers

77

Y,

77

M and

77

C are pivoted about the pivot

601

in a direction indicated by an arrow A in FIG.

26

. Thereby, the intermediate transfer belt

10

is separated from the photoconductive drums

10

Y,

10

M and

10

C. During the pivotal movement, the supporting roller

71

, which also functions as a tension roller, moves toward the inside of the apparatus as indicated by an arrow B in

FIG. 26

to prevent the tension of the intermediate transfer belt

100

from being increased which consequently suppresses a driving load from increasing and enables the intermediate transfer belt

100

to be frictionally driven accurately even in the black and white image forming operation.

The positions of the supporting rollers designated with a dash (′) in

FIG. 26

indicate virtual intermediate positions of corresponding rollers when they are moved.

In the above described embodiments of the present invention, the description has been made for the image forming apparatus using high viscosity liquid developer, however, the present invention can also be applied to image forming apparatuses using dry developer or liquid developer other than the high viscosity developer.

Further, in the above-described embodiments of the present invention, a belt-formed member such as an intermediate transfer belt is described in an endless form, however, the present invention may be applied to belts other than such an endless belt and produces the same effect. For example, it can be applied to a configuration in which a belt supplied from a supplying roller is driven so as to be wound up by a winding roller. In this configuration, for example, the belt is supported by a plurality of supporting rollers with a constant tension such that a portion of the belt spanned around the reel roller and the supplying roller opposes a plurality of opposing members. A route that the belt is spanned is changed so as to separate from part of the opposing members when necessary. In the separating operation, relative distances between the supporting rollers are adjusted so as to suppress the change in the tension of the belt.

Moreover, in the above-described embodiments, the description has been made with respect to image forming apparatuses, however the present invention can be applied to a belt device including a belt-formed member supported by a plurality of supporting rollers and a plurality of opposing members which are located opposite to the belt-formed member and side by side in a line, contacting the belt-formed member or in the vicinity of the belt-formed member. According to the present invention, unnecessary contact of the opposing members with the belt-formed member is suppressed and thereby decrease of the life of the opposing member is avoided.

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.

Number	Date	Country
11-166288	Jun 1999	JP
11-365318	Dec 1999	JP
12-114451	Apr 2000	JP

Number	Name	Date
5156308	Aoyama	Oct 1992
5248847	Aoyama	Sep 1993
5652080	Yoshino et al.	Jul 1997
5652948	Sakaguchi et al.	Jul 1997
5666616	Yoshino et al.	Sep 1997
5678149	Takekoshi et al.	Oct 1997
5708938	Takeuchi et al.	Jan 1998
5765082	Numazu et al.	Jun 1998
5923930	Tsukamoto et al.	Jul 1999
5953559	Obu	Sep 1999
5987281	Kurotori et al.	Nov 1999
5987282	Tsukamoto et al.	Nov 1999
5987291	Masuda	Nov 1999
6021287	Tanaka	Feb 2000
6029023	Munemori et al.	Feb 2000
6038421	Yoshino et al.	Mar 2000
6061542	Minami et al.	May 2000
6134402	Nakayama et al.	Oct 2000
6192007	Yamamoto et al.	Feb 2001

Number	Date	Country
59-192159 U	Dec 1984	JP
08160839 A	Sep 1996	JP
09146383 A	Jun 1997	JP

Belt device and unit device including belt device and image forming apparatus using the belt device and unit device

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (3)

US Referenced Citations (19)

Foreign Referenced Citations (3)