Cleaning device and image forming apparatus

An image forming apparatus, including: an image carrier that carries an image; a charge roll that charges the image carrier; and a cleaning member that contacts the charge roll and cleans the charge roll, wherein the cleaning member is configured to include a surface layer that is formed by an elastic body and contacts the charge roll, an inner layer that is configured by an elastic body softer than the surface layer and supports the surface layer, and a support member that supports the inner layer and causes the surface layer to contact the charge roll.

BACKGROUND

1. Technical Field

The present invention relates to an image forming apparatus that employs an electrophotographic system, such as a copier and a printer.

2. Related Art

Conventionally, devices that utilize a corona discharge phenomenon, such as scorotron chargers, have come to be widely used as charge devices in image forming apparatus that employ the electrophotographic system, such as copiers and printers. But in the case of charge devices utilizing the corona discharge phenomenon, the occurrence of ozone and nitrogen oxide, which are harmful to humans and Earth's environment, is becoming a problem. In contrast, contact charging, where a conductive charge roll is brought into direct contact with an image carrier to charge the image carrier, has become mainstream in recent years because there are considerably few occurrences of ozone and nitrogen oxide and it is power-efficient.

SUMMARY

According to an aspect of the invention, there is provided an image forming apparatus including: an image carrier that carries an image; a charge roll that charges the image carrier; and a cleaning member that contacts the charge roll and cleans the charge roll, wherein the cleaning member is configured to include a surface layer that is formed by an elastic body and contacts the charge roll, an inner layer that is configured by an elastic body softer than the surface layer and supports the surface layer, and a support member that supports the inner layer and causes the surface layer to contact the charge roll.

DETAILED DESCRIPTION

An image forming apparatus pertaining to an exemplary embodiment of the present invention will be described below with reference to the drawings.

An image forming apparatus10of the present exemplary embodiment shown inFIG. 1is a 4-cycle full-color laser printer. As is shown, a photoconductor drum12(image carrier) is rotatably disposed in the apparatus10in the somewhat upper right portion from the center. A conductive cylinder whose diameter of about 47 mm and whose surface is covered with a photoconductor layer formed with an organic photoconductive photoreceptor (OPC) or the like, for example, is used as the photoconductor drum12. The photoconductor drum12is driven to rotate by an unillustrated motor at a process speed of about 150 mm/sec along the direction indicated by the arrow.

The surface of the photoconductor drum12is charged to a predetermined electric potential by a charge roll14disposed substantially directly under the photoconductor drum12. Thereafter, the surface of the photoconductor drum12is exposed to a laser beam LB by an exposure device16disposed under the charge roll14, whereby an electrostatic latent image corresponding to image information is formed on the surface of the photoconductor drum12.

The electrostatic latent image formed on the photoconductor drum12is developed by a rotary developing unit18that includes developing units18Y,18M,18C, and18K of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) disposed along the circumferential direction of the rotary developing unit18, and the electrostatic latent image becomes a predetermined color toner image.

At this time, each of the steps of charging, exposing, and developing is repeated a predetermined number of times on the surface of the photoconductor drum12in correspondence to the colors of the image to be formed. In the developing step, the rotary developing unit18rotates such that the developing units18Y,18M,18C, and18K of the corresponding colors move to a development position facing the photoconductor drum12.

For example, when a full-color image is to be formed, each of the steps of charging, exposing, and developing is repeated four times on the surface of the photoconductor drum12in correspondence to the respective colors of yellow, magenta, cyan, and black, and toner images corresponding to the respective colors of yellow, magenta, cyan, and black are sequentially formed on the surface of the photoconductor drum12. When the toner images are formed, the number of times that the photoconductor drum12rotates differs in accordance with the size of the image. For example, if the recording medium on which the image is to be formed is A4-size, the photoconductor drum12rotates three times, whereby one image is formed. In order words, each time the photoconductor drum12rotates three times, a toner image corresponding to the respective colors of yellow, magenta, cyan, and black is formed on the surface of the photoconductor drum12.

The toner images of the respective colors of yellow, magenta, cyan, and black sequentially formed on the photoconductor drum12are transferred, at a first transfer position where an intermediate transfer belt20is wrapped around the outer periphery of the photoconductor drum12, by a first transfer roll22in a state where the toner images are mutually superposed on the intermediate transfer belt20.

The toner images of yellow, magenta, cyan, and black multiply transferred onto the intermediate transfer belt20are transferred all at once by a second transfer roll26onto recording paper24fed at a predetermined timing.

The recording paper24is sent by a pickup roll30from a paper supply cassette28disposed in the lower portion of the image forming apparatus10, separated one sheet at a time and supplied by a feed roll32and a retard roll34, and transported to a second transfer position of the intermediate transfer belt20in a state synchronized by a registration roll36with the toner images transferred onto the intermediate transfer belt20.

The intermediate transfer belt20is stretched at a predetermined tension by: a wrap-in roll38that defines a wrap position of the intermediate transfer belt20upstream in the rotational direction of the photoconductor drum12; the first transfer roll22that transfers the toner images formed on the photoconductor drum12onto the intermediate transfer belt20; a wrap-out roll40that defines a wrap position of the intermediate transfer belt20downstream of the wrap position; a backup roll42that contacts the second transfer roll26via the intermediate transfer belt20; a first cleaning backup roll46that faces a cleaning device44of the intermediate transfer belt20; and a second cleaning backup roll48. The intermediate transfer belt20follows the rotation of the photoconductor drum12, for example, such that it circulates and moves at the predetermined process speed (about 150 mm/sec).

Here, the intermediate transfer belt20is configured such that the cross-sectional shape formed by the stretched intermediate transfer belt20has a flat, slender, substantially trapezoidal shape in order to make the image forming apparatus10compact.

An image forming unit52is integrally configured by: the photoconductor drum12; the charge roll14; the intermediate transfer belt20; the plural rolls22,38,40,42,46, and48that stretch the intermediate transfer belt20; the cleaning device44for the intermediate transfer belt20; and a later-described cleaning device78for the photoconductor drum12. For this reason, the entire image forming unit52can be removed from the image forming apparatus10by opening an upper cover54of the image forming apparatus10and lifting up by hand a handle (not shown) disposed in the upper portion of the image forming unit52.

The cleaning device44of the intermediate transfer belt20includes a scraper58, which is disposed such that it contacts the surface of the intermediate transfer belt20stretched by the first cleaning backup roll46, and a cleaning brush60, which is disposed such that it presses against the surface of the intermediate transfer belt20stretched by the second cleaning backup roll48. Residual toner and paper dust removed by the scraper58and the cleaning brush60are collected inside the cleaning device44.

It will be noted that the cleaning device44is configured such that it is pivotable about a pivot shaft62in the counter-clockwise direction ofFIG. 1, is withdrawn to a position away from the surface of the intermediate transfer belt20until second transfer of the toner image of the final color ends, and contacts the surface of the intermediate transfer belt20when second transfer of the toner image of the final color ends.

Moreover, the recording paper24to which the toner images have been transferred from the intermediate transfer belt20is transported to a fixing device64, where the recording paper24is heated and pressured by the fixing device64such that the toner images are fixed to the recording paper24. Thereafter, in the case of one-sided printing, the recording paper24to which the toner images have been fixed is discharged by a discharge roll66into a discharge tray68disposed in the upper portion of the image forming apparatus10.

In the case of two-sided printing, the recording paper24to which the toner images have been fixed to a first side (front side) by the fixing device64is not discharged by the discharge roll66into the discharge tray68; rather, the trailing end portion of the recording paper24is nipped by the discharge roll66, the discharge roll66is reversely rotated, the transportation path of the recording paper24is switched to a two-sided paper transportation path70, the front and back sides of the recording paper24are inverted by a transportation roll72disposed in the two-sided paper transportation path70, the recording paper24is again transported to the second transfer position of the intermediate transfer belt20, and the toner images are transferred to the second side (back side) of the recording paper24. Then, the toner images on the second side (back side) of the recording paper24are fixed by the fixing device64and the recording paper24is discharged into the discharge tray68.

Moreover, a manual-feed tray74can be optionally loaded in the side of the image forming apparatus10such that the manual-feed tray74can be freely opened and closed. Recording paper24of optional sizes and types disposed in the manual-feed tray74is supplied by a paper supply roll76and transported to the second transfer position of the intermediate transfer belt20via a transportation roll73and the registration roll36, so that images can be formed on recording paper24of optional sizes and types.

It will be noted that each time the photoconductor drum12rotates one time, residual toner and paper dust are removed from the surface of the photoconductor drum12after the step transferring the toner images has ended by a cleaning blade80of the cleaning device78disposed diagonally below the photoconductor drum12, so that the photoconductor drum12is prepared for the next image forming step.

As shown inFIG. 2, the charge roll14is disposed under the photoconductor drum12such that it contacts the photoconductor drum12. The charge roll14(charge member) has a conductive shaft14A on whose periphery a charge layer14B is formed, and the shaft14A is rotatably supported. A roll-like cleaning roll100(elastic member) that contacts the surface of the charge roll14is disposed under the charge roll14opposite from the photoconductor drum12.

A shaft100A is disposed in the axial core of the cleaning roll100, and the shaft100A is rotatably supported. A sponge104is disposed on the outer peripheral surface of the shaft100A, and the sponge104has a two-layer structure with different hardnesses. The hardness of the surface of the sponge104is 127 to 166 N, for example, which is harder than the hardness (e.g., hardness of 29.4 to 68.6 N) of the axial core of the sponge104. Below, the surface of the sponge104will be referred to as a surface layer104A, and the inside of the sponge104will be referred to as an inner layer104B.

The “hardness” used in the present invention means pressure at the time of 25% compression of the original thickness (in the case of the present invention, when the thickness becomes 75 mm) when a measurement object (in the case of the present invention, a sponge) with a thickness of 100 mm is pressed by a columnar pressing member with a diameter of 200 mm.

Additionally, the cleaning roll100is pressed with a predetermined load against the charge roll14, and the sponge104is elastically deformed along the circumferential surface of the charge roll14to form a nip portion101. The photoconductor drum12is driven to rotate in the clockwise direction ofFIG. 2(the direction of arrow2) by the unillustrated motor, and the charge roll14is rotated in the direction of arrow4by the rotation of the photoconductor drum12. Further, the roll-like cleaning roll100is rotated in the direction of arrow6by the rotation of the charge roll14.

Further, a charge-use power supply is connected to the charge roll14, and bias in which alternating current is superposed on direct current, or just direct current bias, is applied. The application of bias to the cleaning roll100is not particularly prescribed, but in the present invention, the shaft14A of the charge roll14and the shaft100A of the cleaning roll100are rotatably supported by the same bearings (described later), and the cleaning roll100has the same electric potential as the charge roll14.

Additionally, because the cleaning roll100is rotated following the rotation of the charge roll14, contamination (foreign matter) such as toner and external additive adhering to the surface of the charge roll14is cleaned off by the cleaning roll100. Additionally, this foreign matter is collected inside cells in the foam of the cleaning roll100, and it is thought that when the foreign matter collected inside the cells clumps together and becomes an appropriate size, the foreign matter is returned to the photoconductor drum12from the cleaning roll100via the charge roll14and collected by the cleaning device78that cleans the photoconductor drum12, whereby cleaning performance is maintained and continued.

In regard to the cleaning roll100serving as an elastic member of the charge roll14, free-cutting steel or stainless steel is used as the material of the shaft100A. The material and surface treatment method are timely selected in accordance with the purpose, such as slidability. Material that is not conductive may be treated by a common treatment such as plating to make it conductive, or may of course be used as is.

Further, because the cleaning roll100contacts the charge roll14with an appropriate nip pressure via the sponge104, a material having strength where there is little bending at the time of nipping and a shaft diameter having sufficient rigidity with respect to the shaft length are selected.

The surface layer104A and the inner layer104B of the sponge104are made of a foam body having a porous three-dimensional structure. The material of the sponge104is selected from a material including foam resin or rubber such as polyurethane, polyethylene, polyamide, or polypropylene. Further, polyurethane, which has strong tearing strength and strong tensile strength, is particularly preferably used for the sponge104in order to ensure that the sponge104effectively cleans foreign matter such as the external additive adhering by following the rotation of and rubbing the charge roll14, that the surface of the charge roll14is not damaged by the rubbing of the sponge104, and that breakage and damage do not occur over a long period of time.

Further, the charge roll14has the conductive shaft14A on which a cylindrical conductive elastic layer and a surface layer are sequentially formed as the charge layer14B.

Free-cutting steel or stainless steel is used as the material of the shaft14A. The material and surface treatment method are timely selected in accordance with the purpose, such as slidability. Material that is not conductive may be treated by a common treatment such as plating to make it conductive.

The conductive elastic layer configuring the charge layer14B of the charge roll14contains an elastic material such as rubber and a conductive material such as carbon black or an ion conductive material that adjusts the resistance of the conductive elastic layer. Materials that can ordinarily be added to rubber—such as a softening agent, a plasticizing agent, a hardening agent, a vulcanizing agent, a vulcanization accelerating agent, an anti-aging agent, and a filling agent such as silica and calcium carbonate—may also be added as needed. The charge layer14B is formed by covering the peripheral surface of the conductive shaft14A with a mixture to which materials ordinarily added to rubber have been added. A conductive agent in which is dispersed a material that conducts electricity using electrons and/or ions as charge carriers—such as carbon black arranged in a matrix material or an ion conductive agent—can be used as a conductive agent for the purpose of adjusting the resistance. Further, the elastic material may be a foam body.

The surface layer configuring the charge layer14B is formed in order to prevent contamination by foreign matter such as toner. The material of the surface layer is not particularly limited; resin or rubber, for example, may be used. Examples include polyester, polyimide, copolymer nylon, silicone resin, acrylic resin, polyvinyl butyral, ethylene-tetrafluoroethylene copolymer, melamine resin, fluoro-rubber, epoxy resin, polycarbonate, polyvinyl alcohol, cellulose, polyvinylidene chloride, vinyl chloride, polyethylene, and ethylene vinyl-acetate copolymer.

Further, a conductive material can be added to the surface layer to adjust the resistance. It is preferable for the conductive material to be one whose particle diameter is 3 μm or less.

Further, a conductive agent in which is dispersed a material that conducts electricity using electrons and/or ions as charge carriers—such as carbon black arranged in a matrix material, conductive metal oxide particles, or an ion conductive agent—can be used as a conductive agent for the purpose of adjusting the resistance.

The conductive metal oxide particles that are conductive particles for adjusting the resistance are conductive particles such as tin oxide, tin oxide doped with antimony, zinc oxide, anatase titanium oxide, and indium tin oxide (ITO). Any agent can be used as long as it is a conductive agent where electrons serve as charge carriers, and the conductive metal oxide particles are not particularly limited. These can be used singly, or two or more different types can be used together. Further, although the conductive metal oxide particles may be of any particle diameter as they do not inhibit the present invention, tin oxide, tin oxide doped with antimony, and anatase titanium oxide are preferable in terms of resistance adjustment and strength, and tin oxide and tin oxide doped with antimony are particularly preferable.

By controlling the resistance with this conductive material, stable characteristics are obtained without the resistance of the surface layer changing due to environmental conditions.

Moreover, fluorine or silicone resin is used in the surface layer. In particular, it is preferable for the resin to be configured by a fluorine degeneration acrylate polymer. Microparticles may also be added to the surface layer. Thus, the microparticles act such that the surface layer becomes hydrophobic and the adherence of foreign matter to the charge roll14is prevented. It is also possible to add insulating particles such as alumina or silica to impart unevenness to the surface of the charge roll14, reduce the burden when the surface layer rubs the photoconductor drum12, and improve abrasion resistance between the charge roll14and the photoconductor drum12.

Next, the attachment structure of the charge roll14and the cleaning roll100will be described in detail.

As shown inFIG. 3, in the present exemplary embodiment, the charge roll14and the cleaning roll100are attached to a single frame120via a pair of bearing members110and are housed inside the frame120. The photoconductor drum12is also attached to the frame120, and these are unitized.

As shown inFIGS. 4A and 4B, one of the bearing members110is formed in a flat rectangular parallelepiped shape (block shape) and has a single configuration. This bearing member110is formed by a synthetic resin material such as polyacetal or polycarbonate that is rigid, slidable, and has excellent resistance to abrasion. Further, the synthetic resin material may also include glass fiber or carbon fiber in order to further raise its resistance to abrasion.

Two bearing holes112and114, between which a predetermined interval L1is disposed along the longitudinal direction (vertical direction inFIGS. 4A and 4B), are formed in the bearing member110. A support portion14adisposed on the end portion of the shaft14A of the charge roll14is rotatably inserted through the bearing hole112, and a support portion100adisposed on the end portion of the shaft100A of the cleaning roll100is rotatably inserted through the other bearing hole114. Further, as is shown, the inner diameter of the bearing hole114is configured to be larger than the shaft diameter of the shaft100A (support portion100a).

The support portions14aat both ends of the shaft14A of the charge roll14and the support portions100aat both ends of the shaft100A of the cleaning roll100are rotatably supported in the pair of bearing members110. Additionally, the cleaning roll100is pressed with a predetermined load against the charge roll14, whereby the sponge104is elastically deformed along the circumferential surface of the charge roll14to form the nip portion101, as described above (seeFIG. 2).

The relative positions of the charge roll14and the cleaning roll100are maintained at a substantial constant, and the cleaning roll100is pressed with a predetermined load against the charge roll14, whereby the support portion100aof the shaft100A of the cleaning roll100is brought into contact with and supported by an inner peripheral surface portion114A of the bearing hole114opposite from the charge roll14.

Additionally, as described above, the sponge104is elastically deformed along the peripheral surface of the charge roll14and forms the nip portion101(seeFIG. 2). Further, the bearing holes114that contact and support the support portions100aof the shaft100A of the cleaning roll100are configured to have shapes that impart a degree of freedom to the pressing direction toward the charge roll14(the direction of arrow8) with respect to the support portions100aof the shaft100A.

As shown inFIG. 3, a pair of attachment portions124, to which the pair of bearing members110are attached, is integrally disposed on both end portions (left and right side end portions inFIG. 3) of a body portion122of the frame120along the axial direction of the charge roll14and the cleaning roll100.

Guide grooves126along the extension direction of the attachment portions124are formed in the attachment portions124. The bearing members110are configured to be fitted into the guide grooves126and disposed in the leading end sides thereof, such that the bearing members110may be guided in the guide grooves126and slide along the extension direction of the attachment portions124(the direction toward and away from the photoconductor drum12).

The outer sides of the pair of attachment portions124are thick, the leading end sides extend, and a pair of bearing portions132that support the photoconductor drum12are disposed on the leading end sides. Bearing holes134are coaxially formed in the pair of bearing portions132. Support portions12adisposed on end portions of a shaft12A of the photoconductor drum12are rotatably inserted into the bearing holes134, whereby the photoconductor drum12is attached to the frame120together with the charge roll14and the cleaning roll100.

Further, compression coil springs128that bias the bearing members110toward the photoconductor drum12are disposed inside base ends of the guide grooves126. The bearing members110are biased toward the photoconductor drum12(the direction of arrow8) and the charge roll14is pushed against the photoconductor drum12by the spring force of the compression coil springs128. Thus, when the photoconductor drum12rotates, the charge roll14rotates following the rotation of the photoconductor drum12and charges the photoconductor drum12, and the cleaning roll100rotates following the rotation of the charge roll14and cleans the charge roll14.

Next, the action of the present exemplary embodiment will be described.

In the present invention, as shown inFIGS. 5B and 5C, the sponge104disposed on the outer peripheral surface of the shaft100A of the cleaning roll100has a two-layer structure, and the hardness of the surface (the surface layer104A) of the sponge104is harder than the hardness of the axial core (inner layer104B) of the sponge104.

As shown inFIG. 5A, because a sponge200is used in a state where it is pressed against the charge roll14, the reaction force of the sponge200is applied to the shaft100A, and the shaft100A becomes deformed by that reaction force.

When the state of contact (nip width) between the sponge200and the charge roll14becomes uneven in the axial direction of the charge roll14, the sponge200cannot uniformly remove contamination on the charge roll14, the contamination remains on the surface of the charge roll14, the charge roll14becomes unable to uniformly charge the photoconductor drum12, and unevenness in the image quality to be outputted occurs.

For this reason, as shown inFIGS. 5B and 5C, the inner layer104B that is formed by a soft sponge is disposed on the axial core of the cleaning roll100, whereby the bending amount of the shaft100A can be absorbed by the inner layer104B, affects on the surface layer104A of the sponge104can be eliminated, and the state of contact between the cleaning roll100and the charge roll14can be uniformly maintained. Thus, excellent capability of the cleaning roll100to clean the charge roll14can be obtained. Further, because the bending amount of the shaft100A is absorbed, the diameter of the shaft100A can be made small and the image forming apparatus10can be made compact.

Here, as shown inFIGS. 2 and 3, the cylindrical charge layer14B is disposed on the outer peripheral surface of the shaft14A of the charge roll14, but as shown inFIG. 6, when the charge layer14B has a crown shape where the outer diameter of the center portion in the axial direction is larger than the outer diameter of the end portions, a sponge106configured by a surface layer106A and an inner layer106B may be formed to match this crown shape, and the thickness of the inner layer106B may be changed to make the axial-direction center portion of the sponge106thinner than the end portions.

Further, here, as shown inFIG. 5B, the inner layer104B is disposed on the outer peripheral surface of the shaft100A of the cleaning roll100and the surface layer104A is disposed on the outer peripheral surface of the inner layer104B to give the sponge104a two-layer structure, but it is not necessary to limit the sponge104to two layers. As shown inFIG. 7, the hardness of a sponge108may be changed in the longitudinal direction of the sponge108.

Because the reaction force received from the charge roll14is larger at the axial-direction center portion of the sponge108, the hardness of an axial-direction center portion108A of the sponge108(e.g., hardness of 29.4 to 49 N) is made lower (by using a softer material for the center portion108A) than the hardness of end portions108B (e.g., hardness of 49 to 98 N), and at the center portion108A, the absorption rate of the reaction force received from the charge roll14is raised to lower the affects on a surface layer108C (e.g., hardness of 127 to 166 N) of the sponge108.

Further, as shown inFIGS. 8A to 8C, the cleaning roll100may be disposed such that an axial line P of the shaft100A of the cleaning roll100is caused to intersect an axial line Q of the shaft14A of the charge roll14.FIG. 8Ais a bottom view showing the disposition of the cleaning roll100and the charge roll14,FIG. 8Bis a front view showing the disposition of the cleaning roll100and the charge roll14, andFIGS. 8C to 8Eare cross-sectional views ofFIG. 8B.

By causing the axial line P of the shaft100A of the cleaning roll100to intersect the axial line Q of the shaft14A of the charge roll14in this manner, the nip width can be made uniform in the axial direction of the sponge104even if the center portion of the shaft100A becomes bent because the sponge104wraps around the surface of the charge roll14. Thus, the cleaning performance due to the sponge104can be further improved.

In the present exemplary embodiment, the roll-like sponge104is described as an example of the elastic member, but the elastic member is not limited to this. For example, as shown inFIG. 9, a layer-like sponge member140that has a plate-like shape may also be used. The sponge member140is disposed separately from the charge roll14and is supported by a holder142disposed facing the charge roll14.

Additionally, the hardness (e.g., 127 to 166 N) of an upper layer portion140A of the sponge member140contacting the charge roll14is configured to be higher than the hardness (e.g., 29.4 to 68.6 N) of a lower layer portion140B, so that in comparison to a single layer sponge material202as shown inFIG. 10A, bending of the holder142is absorbed by the lower layer portion140B as shown inFIG. 10Bto reduce affects on the upper layer portion140A resulting from the bending of the holder142. Thus, the state of contact between the sponge member140and the charge roll14can be uniformly maintained and the cleaning performance due to the sponge member140can be improved.

Further, as shown inFIG. 11, when the charge roll14has a crown shape, the sponge member140may be formed to match the crown shape in the same manner as inFIG. 6.

Moreover, as shown inFIG. 12, the hardness of a center portion146A may be configured to be less than the hardness of both end portions146B in the lower layer portion146of the sponge member144in a same manner as inFIG. 7.

Further, here, a sponge is used as an example of the elastic member, but it is not necessary for the elastic member to be porous because it suffices for the elastic member to be able to contact and clean the charge roll14.

The present invention has been described in detail by way of exemplary embodiments, but the present invention is not limited to these. Various other embodiments are implementable within the scope of the invention.

For example, a configuration is described where the charge roll14is brought into contact with the underside of the photoconductor drum12and the cleaning roll100is brought into contact with the underside of the charge roll14, but the positional relationship between the photoconductor drum12, the charge roll14, and the cleaning roll100is not limited to this. For example, the present invention can also be applied to a configuration where the charge roll14is brought into contact with the upper side of the photoconductor drum12and the cleaning roll100is brought into contact with the upper side of the charge roll14. Moreover, the present invention can be applied even when the charge roll14does not contact the photoconductor drum12.

Moreover, the image forming apparatus applying the present invention is not limited to a 4-cycle configuration where the rotary developing unit18is used to repeatedly conduct 4 times the formation of toner images on the photoconductor drum12. For example, even in a configuration where image forming units of yellow, magenta, cyan, and black are arranged in a row along the moving direction of the intermediate transfer belt20, the present invention can be applied to the photoconductor drum12, the charge roll14, and the cleaning roll100of each image forming unit.