Patent Application
20230288846
The present invention relates to an image forming apparatus such as a laser printer, copy machine, and a facsimile with an electrophotographic method.
Conventionally, an image forming apparatus including a structure which uses an intermediary transfer member is well-known. This image forming apparatus transfers a toner image formed on a surface of a photosensitive drum onto a primary transfer member provided in a portion (a first transfer portion) facing the photosensitive drum by applying a voltage (hereinafter, referred to as a primary transfer) in a primary transfer process. Further, as repeating the primary transfer process with toners of several colors, multi-colored toner images are formed on a surface of the intermediary transfer member. In a secondary transfer process multi-colored toner images formed on the surface of the intermediary transfer member are collectively transferred onto a surface of a recording material such as a sheet of paper by applying a voltage on a secondary transfer member (hereinafter, referred to as a secondary transfer). The toner image transferred on the surface of the recording material such as a sheet of paper is fixed on the recording material by a fixing means and then the multi-colored image is formed. For example, a technique of forming a low resistance conductive layer inside of a peripheral surface of a base layer of an intermediary transfer belt and applying a primary transfer voltage as electric current flows from electric current supplying member of the primary transfer which is provided in an area where is not right underneath of the photosensitive drum to a circumferential direction of the intermediary transfer belt in order to improve transferring is disclosed in Japanese Laid-Open Patent Application No. 2018-036624. Also, for example, a technique of adjusting the primary transfer voltage according to a rate of deteriorated toner is disclosed in Japanese Laid-Open Patent Application No. 2012-150137.
In a structure using the intermediary transfer belt including a conventional inside conductive layer an electric potential inside of the intermediary transfer belt tends to be substantially constant. Thus, there is a case even an upstream portion of a rotational direction of the intermediary transfer belt with respect to a primary transfer nip portion where is a contact point of the photosensitive drum and the intermediary transfer belt has a potential that is close to the primary transfer voltage. Therefore, it is possible to occur discharging current at the upstream of the primary transfer nip portion with respect to the rotational direction of the intermediary transfer belt and it makes possible to occur a pre-transfer which the toner formed on the photosensitive drum before the primary transfer has transferred before reaching the primary transfer nip portion. The pre-transfer tends to occur especially when the charging amount of the toner is low.
Further, with the conventional technique that determines the primary transfer voltage depending on a detected result of degree of the toner deterioration, the primary transfer voltage must be determined with considering a balance of not only the pre-transfer but the malfunction of the primary transfer because of shortage of primary transfer current. To determine the primary transfer voltage with considering the balance of the pre-transfer and the malfunction of the primary transfer, it is necessary to configure a primary transfer contrast comprising of a potential on the photosensitive drum and the primary transfer voltage. Thus, it is required even for the image forming apparatus with the intermediary transfer belt including the low resistance inside layer to obtain an excellent performance of the primary transfer.
The present invention is developed in a situation described above. The object of this invention is to obtain an excellent performance of the primary transfer even when the image forming apparatus with the intermediary transfer belt including the low resistance inside layer is used.
To solve the problem as described above, the present invention provides as follows:
(1) an image forming apparatus for forming an image on a recording material, the image forming apparatus comprising: a photosensitive member; a charging member configured to charge the photosensitive member; an exposing unit configured to form an electrostatic latent image by exposing the photosensitive member depending on an image signal; a developing member configured to form a toner image by developing the electrostatic latent image with the toner; an intermediary transfer member provided with a first layer having conductivity and a second layer having conductivity and a lower resistance value than that of the second layer, and to which the toner image is transferred in a nip portion between itself and the photosensitive member; a voltage applying portion configured to apply a transfer voltage to the intermediary transfer member; and a control portion configured to control a primary transfer contrast which is a difference between the transfer voltage applied by the voltage applying portion in the nip portion and a potential of a part exposed by the exposing unit on the photosensitive member, wherein, by applying the transfer voltage to the intermediary transfer member from the voltage applying portion, the control portion transfers the toner image from the photosensitive member to the intermediary transfer member by flowing a current in a circumferential direction, wherein the control portion controls the primary transfer contrast by controlling the transfer voltage based on information on a usage state of the toner related to a number of printed sheets of the recording material, and wherein the control portion controls so that the transfer voltage becomes lower as the number of printed sheets is larger.
(2) an image forming apparatus for forming an image on a recording material, the image forming apparatus comprising: a photosensitive member; a charging member configured to charge the photosensitive member; an exposing unit configured to form an electrostatic latent image by exposing the photosensitive member depending on an image signal; a rotary provided with a plurality of developing devices each including a developing member configured to form a toner image by developing the electrostatic latent image with the toner by contacting the photosensitive member and an accommodating portion configured to accommodate the toner, and configured to be capable of switching the developing member to be contacted to the photosensitive member by rotating; an intermediary transfer member provided with a first layer having conductivity and a second layer having conductivity and a lower resistance value than that of the second layer, and to which the toner image is transferred in a nip portion between itself and the photosensitive member; a voltage applying portion configured to apply a transfer voltage to the intermediary transfer member; and a control portion configured to control a primary transfer contrast which is a difference between the transfer voltage applied by the voltage applying portion in the nip portion and a potential of a part exposed by the exposing unit on the photosensitive member, wherein, by applying the transfer voltage to the intermediary transfer member from the voltage applying portion, the control portion transfers the toner image from the photosensitive member to the intermediary transfer member by flowing a current in a circumferential direction, wherein the control portion controls the primary transfer contrast by controlling the transfer voltage based on information on a usage state of the toner related to a number of printed sheets of the recording material, and wherein the control portion controls so that the transfer voltage becomes lower as the number of printed sheets is larger.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Part (a) and part (b) of
Part (a) and part (b) of
Part (a) and part (b) of
A present invention will be exemplary described with referring to the drawings as below. Note that, sizes, materials, shapes and relative positions of component parts described in these embodiments are modifiable corresponding to a structure of an apparatus this invention is applied to or variable conditions, and a scope of this invention is not limited to these disclosed embodiments in the following.
The image forming portion (a) includes a photosensitive drum 1a which is a photosensitive member of a drum shape, a charging roller 2a as a charging means, a developing unit 4a as a developing means, and a drum cleaning device 5a. In the embodiment 1 the photosensitive drum 1a, the charging roller 2a, the developing roller 4a, and the drum cleaning device 5a are integrated as a replaceable toner cartridge. Note that, the replaceable toner cartridge may have a structure that includes at least the photosensitive drum 1a and the developing unit 4a or a structure that provides several cartridges for each color.
The photosensitive drum 1a is an image bearing member bearing a toner image and driven to rotate in a direction of an arrow R1 (counterclockwise) in the drawing at a predetermined process speed (for example 200 mm/sec in the embodiment 1). The developing unit 4a includes a developing container 41a as an accommodating portion which accommodates the yellow toner, and a developing roller 42a as a developing member which carries the yellow toner accommodated in the developing container 41a and develops a yellow image on the photosensitive drum 1a. The developing roller 42a rotates with contacting on the photosensitive drum 1a. A toner is a powder of which ground material is thermoplastic resin and includes a pigment to form colors, a parting agent, a charging control agent to control charging amount, and so on. Also, the photosensitive drum 1a is made of a conductive hollow bear pipe such as an SUS (stainless used steel) coated with a photosensitive layer. The drum cleaning device 5a is a means to collect the toner deposited on the photosensitive drum 1a. The drum cleaning device 5a includes a cleaning blade contacting on the photosensitive drum 1a and a waste toner box accommodates the toner and etc. removed from the photosensitive drum 1a by the cleaning blade.
When the image forming operation starts by a control portion 274 such as a DC controller receiving an image signal, the photosensitive drum 1a is driven to rotate. The photosensitive drum 1a is evenly charged at a predetermined potential (a dark portion potential Vd) in a predetermined polarity (negative polarity in the embodiment 1) by the charging roller 2a and receives an exposure by an exposing device 3a of an exposing means corresponding to an image signal as rotating. Thereby, an electrostatic latent image (a light portion potential VL) corresponding to an image of yellow component of an objective multi-colored image is formed. Next, the electrostatic latent image is developed by the developing roller 42a and visualized as a yellow toner image (hereinafter simply referred as a toner image) at a developing position. The developing roller 42a stably develops by rotating in 1.5 times faster speed, for example 300 mm/sec, than the photosensitive drum 1a in a same direction. A voltage is applied to the charging roller 2a as the dark portion potential Vd to be −600V and an exposure amount of the exposing device 3a is determined as the light portion potential VL to be −150V in the embodiment 1. Also, the developing roller 42a is applied with for example −350V as a developing voltage Vdc. An absolute value of a difference between the light portion potential VL and the developing voltage Vdc is called a developing contrast. Note that, an emission strength of a laser light quantity emitted from the exposing device 3a on to the photosensitive drum 1a is for example 0.5 (μJ/cm2) maximum in the embodiment 1.
Here, a normal charging polarity of the toner deposited on the surface developing roller 42a is negative polarity. The toner is supplied on the surface of the developing roller 42a from a toner supplying roller (not showing in the figures) rotating as being contact on the developing roller 42a and the supplied toner is deposited on the surface of the developing roller 42a. By going through a regulating blade (not showing in the figures) contacting on the surface of the developing roller 42a the toner deposited on the surface of the developing roller 42a is levelled at a predetermined thickness and is charged with negative polarity by friction in between the regulating blade.
Though the electrostatic latent image is reversal-developed by the toner charged with the same polarity as a polarity of the photosensitive drum 1a is charged by the charging roller 2a in the embodiment 1, it is not limited to this. For example, it is applied to an image forming apparatus that an electrostatic latent image is developed by a toner charged with an opposite polarity as a polarity of the photosensitive drum 1a charged. In the embodiment 1 more than 150V voltage is needed as a developing contrast in order for the 100% of toner on the developing roller 42a to be developed onto the photosensitive drum 1a when the surface of photosensitive drum 1a is the light portion potential VL.
An intermediary transfer belt 10 which is an endless and movable intermediary transfer member provided in a position where is contact on each image forming portion a, b, c, and d of each photosensitive drum 1a, 1b, 1c, and 1d as being stretched with three shafts of rollers as stretching members; a driving roller 11, a stretching roller 12, and a secondary transfer resisting roller 13. The intermediary transfer belt 10 is stretched in tension of 60 N for example by the stretching roller 12, and is moved in a direction of an arrow R2 in the drawing (clockwise) by the secondary transfer resisting roller 13 rotating by driving force.
The toner image formed on the photosensitive drum 1a is transferred onto the intermediary transfer belt 10 by a positive polarity voltage being applied to a primary transfer roller 6a from a primary transfer power source 23 in a process it goes through a primary transfer nip portion N1a in which the photosensitive drum 1a is contact on the intermediary transfer belt 10 (primary transfer). The primary transfer power source 23 functionates as a primary applying means applies a primary transfer voltage which is a transfer voltage to a primary transfer roller 6 which is a transfer means. Thereafter, a remained toner that left on the photosensitive frum 1a without primary transferring onto the intermediary transfer belt 10 is removed from the surface of the photosensitive drum 1a by a drum cleaning device 5a collecting. Similarly in the following, a toner image of magenta as a second color, a toner image of cyan as a third color, and a toner image of black as a fourth color are formed and is transferred onto the intermediary transfer belt one after another. Therefore, a toner image with four colors corresponding to an objective multi-colored image is formed on the intermediary transfer belt 10.
The primary transfer roller 6 contacting on the intermediary transfer belt 10 is applied voltage at the primary transfer in the embodiment 1. Therefore, electric current flows on an inner circumferential surface of the intermediary transfer belt 10 and a primary transfer potential is formed by this electric current at the primary transfer nip portions N1a, N1b, N1c, and N1d in each image forming portions a, b, c, and d. Thus, there is a feature that the primary transfer rollers 6a, 6b, 6c, and 6d are all applied same primary transfer voltage. After the primary transfer, the toner image with four colors carried by the intermediary transfer belt 10 goes through a secondary transfer nip portion N2 formed between a secondary transfer roller 20 and the intermediary transfer belt 10 by their contacting. In this process the toner image with four colors is transferred all together on a surface of a transfer material (recording material) P such as a printing sheet or an OHP sheet fed from a sheet feeding roller 50 (secondary transfer).
A secondary transfer roller 20 is made of for example an 8 mm outer diameter nickel plated steel rod covered with a foamed sponge body up to 18 mm outer diameter. Here, the foamed sponge body is made of NBR (nitril-butadiene rubber) adjusted to be 108 Ω·cm volume resistivity/5 mm thick and epichlorohydrin rubber. Note that, rubber hardness of the foamed sponge body is 30° hardness rate as weighted 500 g load when it is measured with Asker hardness measure type C. The secondary transfer roller 20 is contact on the outer circumferential surface of the intermediary transfer belt 10, is pressed onto the secondary transfer resisting roller 13 located in a position facing to the secondary transfer resisting roller 20 with 50 N pressure power through the intermediary transfer belt 10, and forms the secondary transfer nip portion N2.
The secondary transfer roller 20 is rotated as following the intermediary transfer belt 10 and electric current flows down to the secondary transfer resisting roller 13 from the secondary transfer roller 20 by being applied voltage from a secondary transfer power source 21. Therefore, the toner image carried by the intermediary transfer belt 10 is secondary-transferred onto the transfer material P at the secondary transfer nip portion N2. Note that, the toner image is secondary-transferred onto the transfer material P by the intermediary transfer belt 10 as following. A voltage applied to the secondary transfer roller 20 from the secondary transfer power source 21 is controlled for electric current flows down to the secondary transfer resisting roller 13 from the secondary transfer roller 20 through the intermediary transfer belt 10 to be constant. Further, a magnitude of electric current to execute secondary transfer is determined beforehand depending on an environment where the image forming apparatus is provided or a kind of transfer material P. the secondary transfer power source 21 is connected to the secondary transfer roller 20 and applies the secondary transfer voltage to the secondary transfer roller 20. Also, the secondary transfer power source 21 is able to output between 100V and 4000V.
After the toner image with four colors is transferred on the transfer material P in the secondary transfer, the transfer material P is heated and pressed in a fixing device which is a fixing means and four colors of toner are melted, mixed and then fixed on the transfer material P. On the other hand, the remained toner on the intermediary transfer belt 10 after the secondary transfer is cleaned and removed by a belt cleaning device 16 (collecting means) provided in the downstream from the secondary transfer nip portion N2 with respect to the moving (rotating) direction. The belt cleaning device 16 includes a cleaning blade 16a which is a contact member and a waste toner container 16b. The cleaning blade 16a which is the contact member is contact on an outer circumferential surface of the intermediary transfer belt 10 at the position facing the secondary transfer resisting roller 13. The waste toner container 16b accommodates the toner collected by the cleaning blade 16a. Note that, the cleaning blade 16a is referred as to a blade 16a in the following explanation. An optical sensor 60 which is a detecting means is used when adjusting control is executed to adjust position or density of an image formed in the image forming apparatus 100. With the operations described above, full-colored printing image is formed in the image forming apparatus 100 in the embodiment 1.
Next, controlling in the embodiment 1 will be described with the control block view.
The formatter 273 forwards the exposure data converted to an exposing control device 277 provided in a control portion 274. The exposing control device 277 controls the exposing device 3 by a command from a CPU 276. In the image forming apparatus 100 in
The control portion 274 is equipped with the CPU 276, a memory 275, etc. and programmed to operate beforehand. The CPU 276 executes to form an electrostatic latent image by controlling a charging power source 281, a developing power source 280, the primary power source 23, and the secondary power source 21 and executes image forming by controlling to transfer a developed toner image, etc. Also, the CPU 276 executes process of receiving a signal from the optical sensor 60 when correcting control is executed to correct a position and density of the image formed in the image forming apparatus 100. Note that, the CPU 276 which is a control means controls the primary transfer contrast corresponding to a usage condition of the toner described below. The primary transfer contrast is difference between the potential at the primary transfer nip portion N1 and the potential at the portion where is exposed by the exposing device 3 on the photosensitive drum 1 (on the photosensitive member) when the primary transfer voltage is applied to the transfer roller 6 by the primary transfer power source 23.
The intermediary transfer belt 10, the stretching members of the intermediary transfer belt 10 (the driving roller 11, the stretching roller 12, and the secondary transfer resisting roller 13), and the primary transfer roller 6 will be described in the following. The intermediary transfer belt 10 is provided in a position facing to each image forming portion a, b, c, and d. The intermediary transfer belt 10 is an endless belt added a conductive agent to give conductivity in its resin material and stretched by three shafts of the driving roller 11, the stretching roller 12, and the secondary transfer resisting roller 13, which are the stretching members, in 60 N tension in total pressure by the stretching roller 12.
As shown in
The primary transfer roller 6 which is made from 6 mm outer diameter SUS rod nickel-plated and straight shaped including a metal roller is driven to rotate as following a rotation of the intermediary transfer belt 10. In the embodiment 1 outer diameter of the photosensitive drum 1 is 24 mm, for example. The primary transfer roller 6 is contact on over a predetermined area in its longitudinal side crossing orthogonally a moving direction (the arrow R2) of the intermediary transfer belt 10. Here, a distance between a perpendicular L1 heading to the intermediary transfer belt 10 from the center of the photosensitive drum 1 and a perpendicular L2 heading to the intermediary transfer belt 10 from the center of the primary transfer roller 6 is referred as W. Here, a line connecting a dot where a predetermined photosensitive drum 1 is contact on the intermediary transfer belt 10 and a dot where adjacent photosensitive drum 1 contacting on the intermediary transfer belt 10 is referred as a virtual line S1 in a cross-sectional view of the part (a) of
Next, the intermediary transfer belt 10 will be described. The intermediary transfer belt 10 includes a base layer 10a which is a first layer contacting on the photosensitive drum 1, an inner layer 10b which is a second layer contacting on the primary transfer roller 6 and of which resistance value is lower than the base layer 10a. The part (b) of
In the embodiment 1 volume resistivity measured from a side of the base layer 10a and surface resistivity measured from a side of the inner layer 10b are used as a resistance value of the intermediary transfer belt 10. The volume resistivity is measured by Hiresta-UP (MCT-HT450) of Mitsubishi Chemical Corporation with type UR ring probe (MCP-HTP12 model). A metal surface of UFL registration table is used as an opposite probe electrode. The surface resistivity is measured by the same resistivity meter with type UR 100 ring probe (MCP-HTP16 model). A Teflon (R: registered trademark) surface of UFL registration table is used as an opposite probe electrode.
The volume resistivity is measured from the surface of the intermediary transfer belt 10 by pressing the probe with 1 kg pressure on condition of applying 250V voltage and measuring for 10 seconds. The volume resistivity of the intermediary transfer belt 10 in the embodiment 1 is 3.55×1010 (Ω·cm). The surface resistivity of the inner layer 10b is measured from the inner surface by pressing the probe with 1 kg pressure on condition of applying 10V and measuring for 10 seconds. The surface resistivity of the inner layer 10b of the intermediary transfer belt 10 in the embodiment 1 is 1.00×106 (Ω·cm). These resistivity values are measured in an environment that a room temperature is 23° C. and a room humidity is 50%.
Next, the primary transfer voltage control which is a feature of the embodiment 1 will be described. The CPU 276 controls a primary transfer contrast by controlling the primary transfer voltage. A consumption of the toner is shown by a number of printed sheets and the CPU 276 controls the primary transfer voltage to be lower as the number of printed sheets increasing.
Hereinafter, in the embodiment 1 each term on a line L3 (or referred as a virtual line L3) which crosses the intermediary transfer belt 10 perpendicularly upstream as described above and is a tangent of the photosensitive drum 1 is defined as follows. A contact point of the virtual line L3 and the photosensitive drum 1 is referred as Cd, a cross point of the virtual line L3 and the surface of the base layer 10a of the intermediary transfer belt 10 is referred as Ca, an area of the surface of the base layer 10a from Ca to the primary transfer nip portion N1 along the intermediary transfer belt is referred as a nip upstream area Un.
When a positive voltage is applied to the primary transfer roller 6, the nip upstream area also has a positive polarity because the potential of the inner surface layer 10b is almost similar with the voltage applying to the primary transfer roller 6. An area where a toner image is formed of the surface of the photosensitive drum 1 (hereinafter, referred as an image forming area) is charged with a light portion potential VI and the toner is charged with negative polarity as well. Therefore, a potential difference occurs between the base layer 10a and the surface of the photosensitive drum 1 in the nip upstream area Un. Further, as a distance between the surface of the photosensitive drum 1 and the base layer 10a becomes narrow from the contact point Cd to the primary transfer nip portion N1 in
A table 1 shows a result of malfunction of the primary transfer and evaluation of the pre-transfer image when the primary transfer voltage is changed in a yellow image forming portion a according to a rank and by a number of printed sheets. The result is similar with magenta, cyan, and black.
The table 1 shows the primary transfer voltage (V) in a first column, the light portion potential VL (−V) in a second column, and the primary transfer contrast (V) in a third column A fourth column in the table 1 shows the number of printed sheets (printing number) and transfer malfunction and the rank (A, B, C, and D) of pre-transfer as printing 0 sheet, 1000 sheets, 2000 sheets, 3000 sheets, 4000 sheets, and 5000 sheets. In the embodiment 1 usage condition of the toner is told by the number of printed sheets.
First, a definition of a rank transfer malfunction will be described. A rank A is a state that primary transfer malfunction can be slightly recognized even on the photosensitive drum 1. A rank B is a state that the toner which could not be primary-transferred remains on the photosensitive drum 1 after going through the primary transfer nip portion N1. A rank C is a state a deficit on the image by primary transfer malfunction can be slightly recognized. A rank D is a state that a deficit on the image by primary transfer malfunction can be obviously recognized.
Next, a definition of pre-transfer will be described. A rank A is a state that pre-transfer does mostly not occur. A rank B is a state that toner scattering can be spotted as the toner printed on a sheet is observed with a microscope. A rank C is a state that a slight difference of density can be recognized on the image. A rank D is a state that a difference of density can be obviously recognized on the image.
Next, an evaluation result of primary transfer malfunction will be described with the Table 1. Primary transfer malfunction is a defective image that occurs as the toner is not transferred onto the intermediary transfer belt from the photosensitive drum 1 and has characteristic that looks like toner missing in various spots on the image. Also, primary transfer malfunction has characteristic that the defective image suddenly stands out when the voltage becomes less than a predetermined threshold value. A solid image is formed as an image to be evaluated.
In the table 1, in the case of printing in the state that the number of printed sheets is almost 0, the result is rank A in printing with 350V or larger primary transfer voltage. The result is rank B in printing with 300V primary transfer voltage. The result is rank D in printing with 250V or less primary transfer voltage.
In the case of printing in the state that the number of printed sheets is almost 1000, the result is rank A in printing with 300V or larger primary transfer voltage. The result is rank B in printing with 150V, 200V, and 250V primary transfer voltage. The result is rank D in printing with 100V or less primary transfer voltage.
In the case of printing in the state that the number of printed sheets is almost 2000, the result is rank A in printing with 250V or larger primary transfer voltage. The result is rank B in printing with 150V and 200V primary transfer voltage. The result is rank D in printing with 100V or less primary transfer voltage.
In the case of printing in the state that the number of printed sheets is almost 3000, the result is rank A in printing with 200V or larger primary transfer voltage. The result is rank B in printing with 150V primary transfer voltage. The result is rank D in printing with 100V or less primary transfer voltage.
In the case of printing in the state that the number of printing sheet is almost 4000, the result is rank A in printing with 200V or larger primary transfer voltage. The result is rank B in printing with 100V and 150V primary transfer voltage.
In the case of printing in the state that the number of printing sheet is almost 5000, the result is rank A in printing with 150V or larger primary transfer voltage. The result is rank B in printing with 100V or less primary transfer voltage.
The results in the table 1 show that the primary transfer voltage with which the primary transfer malfunction occurs tends to be lower as the number of printed sheets increasing. In the case of printing in the state that the number of printing sheet is almost 5000, the primary transfer malfunction is not spotted on the image even with 100V primary transfer voltage in the results.
Next, a tendency of pre-transfer will be described. Pre-transfer is a defective image occurs by transferring the toner on the photosensitive drum 1 to the intermediary transfer belt 10 in the nip upstream area Un and is also a defective image that the difference of density occurs by scattering a dot in places on the image. A 50% half tone image is used as the image to be evaluated.
In the table 1, in the case of printing in the state that the number of printed sheets is almost 0, the result is rank A in printing with 350V or less primary transfer voltage. The result is rank B in printing with 400V primary transfer voltage. The result is rank C in printing with 450V or larger primary transfer voltage.
Next, in the case of printing in the state that the number of printed sheets is almost 1000, the result is rank A in printing with 300V or less primary transfer voltage. The result is rank B in printing with 350V primary transfer voltage. The result is rank C in printing with 400V and 450V primary transfer voltage. The result is rank D in printing with 500V or larger primary transfer voltage.
Next, in the case of printing in the state that the number of printed sheets is almost 2000, the result is rank A in printing with 250V or less primary transfer voltage. The result is rank B in printing with 300V primary transfer voltage. The result is rank C in printing with 350V, 400V and 450V primary transfer voltage. The result is rank D in printing with 500V or larger primary transfer voltage.
Next, in the case of printing in the state that the number of printed sheets is almost 3000, the result is rank A in printing with 200V or less primary transfer voltage. The result is rank B in printing with 250V and 300V primary transfer voltage. The result is rank C in printing with 350V, 400V, and 450V primary transfer voltage. The result is rank D in printing with 500V or larger primary transfer voltage.
Next, in the case of printing in the state that the number of printed sheets is almost 4000, the result is rank A in printing with 200V or less primary transfer voltage. The result is rank B in printing with 250V and 300V primary transfer voltage. The result is rank C in printing with 350V and 400V primary transfer voltage. The result is rank D in printing with 450V or larger primary transfer voltage.
Next, in the case of printing in the state that the number of printing sheet is almost 5000, the result is rank A in printing with 150V or less primary transfer voltage. The result is rank B in printing with 200V, 250V, and 300V primary transfer voltage. The result is rank C in printing with 350V and 400V primary transfer voltage. The result is rank D in printing with 450V or larger primary transfer voltage. The results above show that the primary transfer voltage with which the pre-transfer occurs tends to be lower as the number of printed sheets increasing.
Next, the reason that the primary transfer voltage with which the primary transfer malfunction and the pre-transfer occurs is lower as the number of printed sheets increasing will be described.
Next, the relation between the number of printed sheets and the primary transfer voltage will be described. As the table 1 showing, the primary transfer malfunction tends to increase while the primary transfer voltage decreases. Because an amount of the toner moving from the photosensitive drum 1 to the intermediary transfer belt 10 in the primary transfer nip portion N1 is decreasing when the primary transfer current is decreasing. In other words, the primary transfer voltage is needed be larger because the more toner charge amount, the more toner moving current amount needed. As described in
Next, a relation between the toner charge amount and the pre-transfer will be described. In the image forming apparatus of the embodiment 1, a discharge current occurs in the nip upstream area Un as well because the base layer 10a of the intermediary transfer belt is charged with positive polarity. The negative polarity of the toner charge amount is decreasing or reversing to the positive polarity by the discharge current going through the toner image on the photosensitive drum 1. Thus, as phenomenon that a portion of the toner image on the photosensitive drum 1 is transferred onto the nip upstream area Un on the intermediary transfer belt 10 is the pre-transfer. As the negative charge amount of the toner image on the photosensitive drum 1 increasing, the negative charge amount is kept at high rate if the discharge current goes through and hardly occurs the pre-transfer. This feature means, when the number of printed sheets is lower and the negative charge amount is larger, the primary transfer voltage that causes the pre-transfer is larger.
As described above, the primary transfer voltage that causes the primary transfer malfunction and the pre-transfer depends on the negative charge amount of the toner. In view of the tendency in the table 1, a controlling method is needed to consider a balance the primary transfer voltage not to make these image malfunction occur. Specifically, the primary transfer voltage is controlled to be lower corresponding to the number of the printed sheets.
In an example in
Note that, though the primary transfer voltage is selected corresponding to the number of printed sheets in
Furthermore, a value that is multiplied the rotational number of the developing member and the toner consumption amount is defined as a toner deteriorating index number and the primary transfer voltage corresponding to the toner deteriorating index number may be selected. Also, when an outer diameter of the photosensitive drum 1 is changed, a distance between the surface of the photosensitive drum 1 in the nip upstream area Un and the surface of the base layer 10a of the intermediary transfer belt 10. Therefore, a proper value of the primary transfer voltage is changed corresponding to a property of the image forming apparatus because a threshold value that the discharge current occurs is changed and the primary transfer voltage that the difference of the density occurs by the pre-transfer is changed as well.
Next, a way how the excellent primary transfer voltage to be selected as including all image forming portion a, b, c, and d will be described. In the embodiment 1 a same primary transfer voltage is applied to all the primary transfer roller 6a, 6b, 6c, and 6d, therefore, the primary transfer voltage is cannot be selected for each image forming portion a, b, c, and d. Therefore, as considered the primary transfer voltage the primary transfer malfunction and the pre-transfer those which are expected by the number of printed sheets of each image forming portion a, b, c, and d occurs, the primary transfer voltage needs to be selected based on a balance of these.
As described above, the image malfunction tends to stand out when the primary transfer voltage is less than a threshold value about the primary transfer malfunction. Therefore, in the embodiment 1 the primary transfer control is executed to the image forming portion with the least number of printed sheets not to occur the primary transfer malfunction. In order to execute this control, the primary transfer voltage control is executed corresponding to the number of printed sheets based on
In S3 the primary transfer voltage corresponding to the number of printed sheets is set. The primary transfer voltage is set to a targeted voltage for each determined number of printed sheets and a relation between the number of printed sheets and the primary transfer voltage to be in linear function by when the number reaches the predetermined number of printed sheets. In
Also, in spite of a state of an operation of the primary transfer voltage control in the left side of
When the main assembly printing sheet number is 0, the cartridges of all colors are new and the toner charge amount of all colors is the highest. Therefore, 350V primary transfer voltage is selected as the initial value. This corresponds to an operation in S1 in
Then, the lower primary transfer voltage is selected to apply corresponding to the main assembly printing sheet number in the point Ta as a starting point, 350V primary transfer voltage is selected again in the point Tb when the timing the black cartridge is replaced to prevent from occurring the primary transfer malfunction. Further, the lower primary transfer voltage is selected to apply corresponding to the main assembly printing sheet number in the point Tb as a starting point, the primary transfer voltage in the point Tc is 200V. Since the minimum primary transfer voltage selected is 200V in part (b) of
Hereinafter, the CPU 276 selects 350V for the primary transfer voltage in the timing when the cartridge of any color is replaced in any timing and selects the lower primary transfer voltage corresponding to the main assembly printing sheet number from the timing when the cartridge is replaced. By executing these controls, it is possible to select the primary transfer voltage that suppresses the primary transfer malfunction and the pre-transfer despite each color or each number of printed sheets. As described above, the CPU 276 restores the primary transfer voltage to the initial value in spite of the printing number as the cartridge is replaced and controls the primary transfer voltage corresponding to the number of printed sheets that printed after restoring the initial value.
In an example in
In the embodiment 1, in the image forming apparatus using the intermediary transfer belt including the inner surface conductive layer, the method to suppress that the primary transfer malfunction and the pre-transfer caused by the discharge current in the nip upstream area occur has been described above. In order to supply the excellent primary transferred image the controlling method which the lower primary transfer voltage is applied as the toner charge amount is less is described in the embodiment 1. Further, the control method that the primary transfer is selected corresponding to the replaced toner cartridge in the timing when the toner cartridge is replaced as considering the characteristic that all image forming portions have the same primary transfer voltage was described above.
As
The image forming apparatus in
A toner image formed on the photosensitive drum 1100 to which a primary transfer roller 260 applies a positive voltage in a primary transfer nip portion is transferred onto the intermediary transfer belt 110. The toner image is conveyed on the intermediary transfer belt 110 and reaches the primary transfer nip portion again in order to form a multi-colored image in the image forming apparatus in
Since the discharge current occurs in the nip upstream area and the pre-transfer occurs in the image forming apparatus in
Note that, the image forming apparatus with the rotary system is provided a developing unit of each color 40a, 40b, 40c, and 40d, a charging roller 200, a drum cleaning device 150, a driving roller 120, a pair of secondary transfer rollers 130, a primary transfer power source 230, and a secondary transfer power source 220. The rotary 400 includes the multiple developing units including the developing member 420 and an accommodating portion accommodates toner and in the image forming apparatus in
In
Next, in S25, the control portion 1274 controls the C developing unit 40c to move to the image forming position by rotating the rotary 400 when forming image M ends. In S26, the control portion 1274 sets the primary transfer voltage for C. Next, in S27, the control portion 1274 controls the K developing unit 40d to move to the image forming position by rotating the rotary 400 when forming image of C ends. In S28, the control portion 1274 sets the primary transfer voltage for K. When forming image of K ends, as going back to the process in S21, the control portion 1274 controls the Y developing unit 40a again to move to the image forming position by rotating the rotary 400 in order to form a next image.
Note that, processes in S31, S32, S33, and S34 in
Further, in the image forming apparatus in
As described above, according to the embodiment 1, an excellent primary transfer performance can be obtained even in the image forming apparatus with the intermediary transfer belt including the inner low resistance layer.
The primary transfer contrast which is a difference between the primary transfer voltage and the potential of the surface of the photosensitive drum 1 (hereinafter, referred as a surface potential) contributes to the primary transfer performance. In the embodiment 1 the method which the excellent primary transfer performance is obtained by controlling the primary transfer voltage was described. In an embodiment 2, about the primary transfer contrast, a method that adjusts the surface potential of a photosensitive drum 1 adding to a primary transfer voltage as a method that forms a proper primary transfer contrast considering a balance between a primary transfer malfunction and a pre-transfer will be described. An image forming apparatus in the embodiment 2 is the same as the image forming apparatus in
First, the primary transfer contrast will be described with an image forming portion a as an example.
In the nip upstream area Un described in the embodiment 1, the discharge current occurs by the difference between the light portion potential VL and the potential of the intermediary transfer belt 10. The potential of the intermediary transfer belt 10 is almost similar by the inner surface layer 10b upstream and downstream of the primary transfer nip portion N1 with respect to the rotational direction of the intermediary transfer belt 10. In the embodiment 2, an absolute value |VL-Vt1| of the difference between the light portion potential VL and a primary transfer voltage (Vt1) is defined as a primary transfer contrast. As the primary transfer contrast is larger, the discharge current occurs more often in the nip upstream area Un. The embodiment 2 is characterized that the primary transfer contrast is adjusted by adjusting the light portion potential VL with the exposing device 3a as adding to the primary transfer voltage.
On the other hand, in the image forming apparatus in
Since the number of printed sheets of Y, M, and C are 0, the primary transfer voltage is set to be 350V of the initial value as following
The table 2 shows the primary transfer voltage (V) in a first column, the light portion potential (−V) in a second column, and the primary transfer contrast (V) in a third column. In the table 2, the rank (A, B, C, or D) of the primary transfer malfunction or the pre-transfer is shown when the number of printed sheets of Y in a fourth column, M in a fifth column, and C in a sixth column are 0 sheets. In seventh column in the table 2, the rank (A, B, C, or D) of the primary transfer malfunction or the pre-transfer is shown when the number of printed sheets of K is 5000.
In an ‘a’ row in the table 2, evaluation results are shown in a case that the light portion potential VL is set to −150V as same as the embodiment 1. The primary transfer contrast is 500V. The rank of both primary transfer malfunction and pre-transfer of Y, M, and C are the rank A, because the number of printed sheets of Y, M, and C are 0 and the primary transfer voltage is proper setting value for 0 sheets. On the other hand, about K, the pre-transfer is the rank C though the primary transfer malfunction is the rank A. Because, the number of printed sheets of K is 5000 and the toner charge amount decreases by toner deterioration.
In a ‘b’ row in the table, evaluation results are shown in a case that the light portion potential VL is set to −100V with stronger exposure amount than ‘a’ row and the primary transfer contrast is 450V. In Y, M, and C, the primary transfer malfunction is the rank B and the pre-transfer is the rank C. On the other hand, about K, the primary transfer malfunction is the rank A as well as ‘a’ and the pre-transfer is the rank B as better than ‘a’. According to these results, the more proper primary transfer is obtained by adjusting exposure amount of the laser as the light portion potential VL of Y, M, and C is −150V and the light portion potential VL of K is −100V for 350V primary transfer voltage.
In the embodiment 2, usage condition of toner is shown by a number of printed sheets as well. A CPU 276 controls the primary transfer voltage to decrease and the exposure amount to increase as the number of printed sheets increases. The CPU 276 controls the primary transfer voltage corresponding to the number of printed sheets (for example 0) of a predetermined cartridge (for example Y, M, or C) that is with one of the least number of printed sheets out of multiple cartridges. The CPU 276 controls the exposure amount corresponding to the number of printed sheets (for example 5000 sheets) of the other cartridge that is different from the predetermined cartridge for the other cartridge (for example, K).
In the S5, the CPU 276 detects the number of printed sheets in a timing when the primary transfer voltage is determined. Note that, the CPU 276 is regarded as counting the printed sheets as described above. In S6, the CPU 276 determines the proper primary transfer contrast for the number of printed sheets detected in S5. For example, based on the relation in part (b) of
As described above, in the embodiment 2, each image forming portion a, b, c, or d obtains the proper primary transfer contrast in the image forming apparatus as same as the embodiment 1. In the embodiment 2, the method that adjusts the laser exposing amount and finely adjusts the light portion potential VL based on the predetermined primary transfer voltage.
It was described in the embodiment 2 that the primary transfer contrast for the number of printed sheets in all image forming portions a, b, c, and d have the same tendency. However, in a case that each image forming portion a, b, c, or d has the different proper primary transfer contrast, the laser exposing amount may be determined as the light portion potential VL corresponding to each image forming portion. Also, though the controlling process to determine the laser exposing amount after the primary transfer voltage is determined is described in the embodiment 2, it is not limited to this process but the primary transfer voltage may be determined after the laser exposing amount is determined. Further, the description in the embodiment 2 is effective to the image forming apparatus with the rotary system shown in
As described above, according to the embodiment 2, it is possible that the excellent primary transfer performance is obtained in the image forming apparatus with the intermediary transfer belt including the inner surface of low resistance layer as well.
In an embodiment 3, a method to form the primary transfer contrast by applying a voltage to the photosensitive drum will be described.
The toner usage condition is indicated by the number of printed sheets in the embodiment 3 as well. The CPU 276 controls the surface potential of the photosensitive drum 1a to decrease as the number of printed sheets increases. A table 3 shows results of the evaluation of the primary transfer malfunction and the pre-transfer of the primary transfer contrast changed by adjusting the drum voltage in each number of the printed sheets. In the table 3, the results of evaluation in a condition which the light portion potential VL obtained by the laser exposing is fixed with −150V and the net light portion potential VL′ is changed by adjusting the drum potential Vdr is shown. Since the primary transfer potential is 0V, an absolute value of the net light portion potential VL′ is the primary transfer contrast. The results of evaluation of the same primary transfer contrast in
The table 3 shows the primary transfer voltage (V) in a first column, the drum potential (−V) the net light portion potential VL′ (−V) in a third column, and the primary transfer contrast (V) in a fourth column. A fifth column in the table 1 shows the number of printed sheets (printing number) and transfer malfunction and the rank (A, B, C, and D) of pre-transfer as printing 0 sheet, 1000 sheets, 2000 sheets, 3000 sheets, 4000 sheets, and 5000 sheets.
Next, a result of primary transfer malfunction will be described with the Table 3.
In the table 3, in the case of printing in the state that the number of printing sheet is almost 0, the result is rank A in printing with 350V or larger absolute value of the drum potential. The result is rank B in printing with 300V drum potential. The result is rank D in printing with 250V or less drum potential.
In the case of printing in the state that the number of printing sheet is almost 1000, the result is rank A in printing with 300V or larger absolute value of the drum potential. The result is rank B in printing with 150V, 200V, and 250V drum potential. The result is rank D in printing with 100V drum potential.
In the case of printing in the state that the number of printing sheet is almost 2000, the result is rank A in printing with 250V or larger absolute value of drum potential. The result is rank B in printing with 150V and 200V drum potential. The result is rank D in printing with 100V drum potential.
In the case of printing in the state that the number of printing sheet is almost 3000, the result is rank A in printing with 200V or larger absolute value of the drum potential. The result is rank B in printing with 150V drum potential. The result is rank D in printing with 100V drum potential.
In the case of printing in the state that the number of printing sheet is almost 4000, the result is rank A in printing with 200V or larger primary transfer voltage. The result is rank B in printing with 100V and 150V primary transfer voltage.
In the case of printing in the state that the number of printing sheet is almost 5000, the result is rank A in printing with 150V or larger absolute value of drum potential. The result is rank B in printing with 100V drum potential.
The results in the table 3 show that the absolute value of the drum potential with which the primary transfer malfunction occurs tends to be lower as the number of printed sheets increasing. In the case of printing in the state that the number of printing sheet is almost 5000, the primary transfer malfunction is not spotted on the image even with 100V absolute value of the drum potential in the results.
Next, a tendency of pre-transfer will be described.
In the table 3, in the case of printing in the state that the number of printing sheet is almost 0, the result is rank A in printing with 350V or less absolute value of the drum potential. The result is rank B in printing with 400V drum potential. The result is rank C in printing with 450V or larger drum potential.
Next, in the case of printing in the state that the number of printing sheet is almost 1000, the result is rank A in printing with 300V or less absolute value of the drum potential. The result is rank B in printing with 350V drum potential. The result is rank C in printing with 400V and 450V drum potential. The result is rank D in printing with 500V or larger drum potential.
Next, in the case of printing in the state that the number of printing sheet is almost 2000, the result is rank A in printing with 250V or less absolute value of the drum potential. The result is rank B in printing with 300V drum potential. The result is rank C in printing with 350V, 400V and 450V drum potential. The result is rank D in printing with 500V or larger drum potential.
Next, in the case of printing in the state that the number of printing sheet is almost 3000, the result is rank A in printing with 200V or less absolute value of the drum potential. The result is rank B in printing with 250V and 300V drum potential. The result is rank C in printing with 350V, 400V, and 450V drum potential. The result is rank D in printing with 500V or larger drum potential.
Next, in the case of printing in the state that the number of printing sheet is almost 4000, the result is rank A in printing with 200V or less absolute value of the drum potential. The result is rank B in printing with 250V and 300V drum potential. The result is rank C in printing with 350V and 400V drum potential. The result is rank D in printing with 450V or larger drum potential.
Next, in the case of printing in the state that the number of printing sheet is almost 5000, the result is rank A in printing with 150V or less absolute value of the drum potential. The result is rank B in printing with 200V, 250V, and 300V drum potential. The result is rank C in printing with 350V and 400V drum potential. The result is rank D in printing with 450V or larger drum potential.
The results above show that the absolute value of the drum potential with which the pre-transfer occurs tends to be lower as the number of printed sheets increasing.
It is possible that
In the embodiment 3, though the method adjusting the drum voltage as an adjusting means for the primary transfer contrast in the image forming apparatus 300 with a tandem system shown in
As described above, according to the embodiment 3, it is possible that the excellent primary transfer performance is obtained in the image forming apparatus with the intermediary transfer belt including the inner surface of low resistance layer as well.
According to the present invention, it is possible that the excellent primary transfer performance is obtained in the image forming apparatus with the intermediary transfer belt including the inner surface of low resistance layer as well.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-037940 filed Mar. 11, 2022, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-037940 | Mar 2022 | JP | national |
