Photosensitive member unit and image forming apparatus

A photosensitive member unit includes a photosensitive member, a rotary member, a charging roller, a separating member, and a one-way clutch. The charging roller is moved to and positioned at a separated position in a case where the photosensitive member rotates in a second direction when the separating member is positioned at a first position. The charging roller is moved to and positioned at a contact position in a case where the photosensitive member rotates in a first direction when the separating member is positioned at a second position.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a photosensitive member unit and an image forming apparatus forming an image on a recording material by utilizing an electrophotographic system or an electrostatic recording system.

Description of the Related Art

Hitherto, a contact charging system has been widely used as a primary charging method of an image forming apparatus of an electrophotographic system. In the contact charging method, a charging roller in which a conductive elastic layer is provided on an outer circumference of a conductive supporting member serving as a core metal and in which a resistant layer is coated on an outer circumference of the conductive elastic layer is used. That is, the charging roller is brought into contact with a photosensitive member such as a photosensitive drum by an urging spring or the like urging the charging roller to the photosensitive member. Then, the charging roller is applied with voltage and charges a surface of the photosensitive member by causing a minute electric discharge in a vicinity of a contact nip portion where the charging roller is in contact with the photosensitive member. Still further, those members such as the photosensitive member and the charging roller being made into a cartridge as a photosensitive member unit is widespread.

If the charging roller is left in contact with the photosensitive member for a long period of time in such photosensitive member unit constructed as described above, there is a possibility of causing image defects in forming an image by the following reasons. That is, there is a case where a part of the charging roller in contact with the photosensitive member is deformed due to the long-term contact or a case where a contact trace or the like is left at the part where the photosensitive member is in contact with the charging roller. Image defects may occur in forming an image in such cases.

In order to restrain occurrence of such image defects, there is known a photosensitive member unit including a separating member capable of switching a contact state and a separate state of the photosensitive member and the charging roller as disclosed in Japanese Patent Application Laid-open No. 2002-311690. In the photosensitive member unit, the separating member is disposed in parallel with a pressurizing direction of the charging roller when the photosensitive member is stopped from rotating in forming no image or the like. Because the charging roller is pressed in a direction reverse to the pressurizing direction, the charging roller is separated from the photosensitive member.

Then, as the photosensitive member is rotationally driven in a normal direction in forming an image or the like, the separating member rotates by being dragged centering on a shaft of the charging roller by an engagement of a gear portion, i.e., an engagement portion, of the photosensitive member and a gear portion of the charging roller. Then, the separating member that has been supporting the charging roller separately from the photosensitive member recedes from a part between the separating member and the photosensitive member, and the charging roller is urged by an urging spring toward the photosensitive member such that the charging roller comes into contact with the photosensitive member. When the photosensitive member is stopped to rotate in finishing an operation of forming an image or the like, the image forming apparatus rotates the photosensitive member in a reverse direction. Thereby, the gear portion of the photosensitive member engages with the gear portion of the separating member and the separating member rotates in a direction reverse to a normal operation. Then, the charging roller separates from the photosensitive member.

In the photosensitive member unit described in Japanese Patent Application Laid-open No. 2002-311690, however, the gear portion of the separating member is always in contact with the gear portion of the photosensitive member even when the charging roller is in contact with the photosensitive member and idles when the photosensitive member rotates. Due to that, because own weight of the separating member acts on a rotary member, the separating member vibrates as the rotary member rotates. Thus, there is a possibility of giving vibration to the photosensitive member in forming an image and of causing image defects such as image pitch irregularity. Meanwhile, it has been demanded lately to improve accuracy of a width of the contact nip between the charging roller and the photosensitive member due to an increase of an image forming speed and to cost reduction or the like by DC-conversion of charging high-voltage power supply. That is, it has been demanded to eliminate unwanted disturbances such as the vibration in forming an image.

Accordingly, the present disclosure aims at providing a photosensitive member unit and an image forming apparatus capable of, even though capable of switching contact and separate states of a photosensitive member and a charging roller by a separating member, restraining vibration of a photosensitive member otherwise caused by the separating member coming into contact with an engagement portion of the photosensitive member in forming an image.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a photosensitive member unit includes a photosensitive member configured to rotate in a first direction while bearing an electrostatic image in forming an image and in a second direction opposite to the first direction, a rotary member configured to rotate integrally with the photosensitive member and comprising a first engagement portion on an outer circumferential portion of the rotary member, a charging roller configured to move to a separate position in which the charging roller is separated from a surface of the photosensitive member and a contact position in which the charging roller is brought into contact with the surface of the photosensitive member, the charging roller being configured to be driven by the photosensitive member at the contact position and charge the surface of the photosensitive member by being applied with voltage, a separating member comprising a second engagement portion engageable with the first engagement portion and configured to move to a first position and a second position along with rotation of the charging roller, the first position being a position where the second engagement portion separates from the first engagement portion and the separating member allows the charging roller to be positioned at the contact position, the second position being a position where the second engagement portion engages with the first engagement portion and the separating member positions the charging roller at the separate position, and a one-way clutch interposed between the charging roller and the separating member in a power transmission path, the one-way clutch being configured to transmit rotation of the charging roller to the separating member in a case where the photosensitive member rotates in the second direction, the one-way clutch being configured to transmit rotation of the charging roller to the separating member or idle the charging roller with respect to the separating member in a case where the photosensitive member rotates in the first direction. The charging roller is moved to and positioned at the separate position in a case where the photosensitive member rotates in the second direction when the separating member is positioned at the first position. The charging roller is moved to and positioned at the contact position in a case where the photosensitive member rotates in the first direction when the separating member is positioned at the second position.

According to a second aspect of the present invention, a photosensitive member unit includes a photosensitive member configured to rotate in a first direction while bearing an electrostatic image in forming an image and in a second direction opposite to the first direction, a rotary member configured to rotate integrally with the photosensitive member and comprising a first engagement portion on an outer circumferential portion of the rotary member, a charging roller configured to move to a separate position in which the charging roller is separated from a surface of the photosensitive member and a contact position in which the charging roller is brought into contact with the surface of the photosensitive member, the charging roller being configured to be driven by the photosensitive member at the contact position and charge the surface of the photosensitive member by being applied with voltage, a separating member comprising a second engagement portion engageable with the first engagement portion and configured to move to a first position and a second position along with rotation of the charging roller, the first position being a position where the second engagement portion separates from the first engagement portion and the separating member allows the charging roller to be positioned at the contact position, the second position being a position where the second engagement portion engages with the first engagement portion and the separating member positions the charging roller at the separate position, and a torque limiting portion interposed between the charging roller and the separating member in a power transmission path, the torque limiting portion being configured to transmit a torque from the charging roller to the separating member in a case where the photosensitive member rotates in the second direction, the torque limiting portion being configured to limit transmission of torque from the charging roller to the separating member in a case where the photosensitive member rotates in the first direction. The charging roller is moved to and positioned at the separate position in a case where the photosensitive member rotates in the second direction when the separating member is positioned at the first position. The charging roller is moved to and positioned at the contact position in a case where the photosensitive member rotates in the first direction when the separating member is positioned at the second position.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

A first embodiment of the present disclosure will be described in detail with reference toFIGS. 1 through 12. A tandem type full-color printer will be described as one example of an image forming apparatus in the present embodiment. However, the present disclosure is not limited to what is mounted in the tandem type image forming apparatus1and may be what is mounted in another type image forming apparatus. The present disclosure is not also limited to what is mounted in a full-color printer and may be mounted in a monochrome or a mono-color printer. Alternatively, the present disclosure can be carried out in various uses such as a printer, various printing machines, a copier, a fax machine and a multi-function printer. Note that a sheet S is a recording material on which a toner image is formed and specifically includes a plain sheet of paper, a synthetic resin-made sheet that is a substitute of the plain sheet of paper, a thick sheet, an overhead projector sheet and the like.

Image Forming Apparatus

As illustrated inFIG. 1, the image forming apparatus1includes an apparatus body1a, a sheet feed cassette20, an image forming unit10and a control portion70. The image forming apparatus1can form a four-color full-color image on the recording material corresponding to an image signal from a host device such as an image reading apparatus2and a personal computer or from an external device such as a digital camera and a smartphone.

The image forming apparatus1includes image forming units10of respective colors of Y (yellow), M (magenta), C (cyan) and K (black), which are arrayed in a rotation direction of an intermediate transfer belt61. A configuration and an operation of each of the image forming units10is substantially the same except that colors of toners to be used are different. Therefore, the following description will be made by typically exemplifying the yellow image forming unit10.

The image forming unit10includes a photosensitive drum11which is a cylindrical electrophotographic photosensitive member serving as a photosensitive member. The photosensitive drum11is rotationally driven with a process speed, i.e., a circumferential speed, of 100 to 300 mm/sec by a driving force transmitted from a driving motor18(seeFIG. 2) provided in the apparatus body1a. As illustrated inFIG. 5, both end portions in a rotation axial direction of the photosensitive drum11are supported by a rotation shaft37serving as a rotary member integrally rotating with the photosensitive drum11. That is, the photosensitive drum11is coaxially provided on the rotation shaft37. As illustrated inFIG. 3, the photosensitive drum11is configured to be able to rotate in an R1direction, i.e., in a first direction, in forming an image by bearing an electrostatic image and in an R2direction, i.e., in a second direction, opposite to the R1direction.

As illustrated inFIG. 1, disposed around the photosensitive drum11in the image forming unit10sequentially along the rotation direction thereof are a charging roller12, a developing unit14, a primary transfer roller17and a drum cleaning unit15. An exposing unit16is disposed under the respective image forming units10. The image forming apparatus1also includes the intermediate transfer belt61formed of an endless belt member serving as an intermediate transfer member so as to come into contact with the photosensitive drum11of each image forming unit10.

The charging roller12is a rotatable roller-like charging member and is disposed so as to come into contact with the photosensitive drum11to charge a surface of the photosensitive drum11. The exposing unit16is a laser scanner unit and exposes the surface of the charged photosensitive drum11to form an electrostatic image on the surface of the photosensitive drum11.

The developing unit14stores toner serving as developer therein and develops the electrostatic image formed on the photosensitive drum11as a toner image by using the toner. Such developing unit14includes a developing sleeve14aserving as a developer bearing member capable of conveying the toner to a developing area facing the photosensitive drum11by rotating and moving while bearing the toner. The developing sleeve14ais rotationally driven.

The primary transfer roller17is a roller-like primary transfer member and primarily transfers the toner image formed on the photosensitive drum11onto the intermediate transfer belt61. The drum cleaning unit15is configured to clean transfer residual toner and others left on the photosensitive drum11after the primary transfer.

The intermediate transfer belt61is endlessly formed of dielectric resin such as polyimide. The intermediate transfer belt61is wrapped around a plurality of supporting rollers, i.e., stretch rollers, with a predetermined tension. Disposed at positions facing the respective photosensitive drums11on a side of an inner circumferential surface of the intermediate transfer belt61are the primary transfer rollers17described above. The primary transfer roller17is pressed against the photosensitive drum11through the intermediate transfer belt61and forms a primary transfer portion N1where the intermediate transfer belt61is in contact with the photosensitive drum11. The primary transfer roller17is driven along with the rotation of the intermediate transfer belt61.

A secondary transfer roller64which is a roller-like secondary transfer member is also disposed at a position facing a secondary transfer roller counter roller62on a side of an outer circumferential surface, i.e., a surface side, of the intermediate transfer belt61. The secondary transfer roller64is pressed against a secondary transfer counter roller62through the intermediate transfer belt61and forms a secondary transfer portion N2where the intermediate transfer belt61is in contact with the secondary transfer roller64. The toner image, which has been transferred onto the intermediate transfer belt61, is secondarily transferred onto the sheet S at the secondary transfer portion N2.

A belt cleaning unit66is disposed at a position facing a tension roller65on a side of the outer circumferential surface of the intermediate transfer belt61. The belt cleaning unit66cleans transfer residual toner left on the intermediate transfer belt61after the secondary transfer.

As illustrated inFIG. 2, the control portion70is composed of a computer and includes a CPU71, a ROM72storing programs that control respective portions, a RAM73temporarily storing data and an input/output circuit, i.e., I/F,74. The CPU71is a microprocessor controlling the entire control of the image forming apparatus1and is a main body of a system controller. Set values necessary for various controls are recorded in the ROM72and are invoked by the CPU71as necessary. Various data such as a number of prints that varies depending on an image forming operation is temporarily recorded in the RAM73to be utilized in various controls.

The CPU71is connected with an operating portion5, the driving motor18, a timer21and others through the input/output circuit74. The control portion70enables a user to operate and to set by commands from a computer knot illustrated) and connected with the apparatus body1aor through operations made by the operating portion5. The control portion70can control the rotation of the photosensitive drum11by controlling the driving motor18. The timer21can measure a stop time of the photosensitive drum11.

Next, an image forming operation will be described. The surface of the rotationally driven photosensitive drum11is homogeneously charged by the charging roller12with a predetermined potential of a predetermined polarity. According to the present embodiment, only DC voltage of −700 to 2000 V, e.g., −1300 V, is applied to the charging roller12from a charging high voltage power supply knot illustrated) to generate a discharge on the surface of the photosensitive drum11and to charge the surface of the photosensitive drum11at about −700 V.

After homogeneously charging the surface of the photosensitive drum11, the surface of the photosensitive drum11is scanned and exposed by the exposing unit16based on signals of image information to form an electrostatic image on the photosensitive drum11. Note that the image forming apparatus1of the present embodiment includes an image reading apparatus2, and the abovementioned image information includes image information of a document read by the image reading apparatus2and image information sent from an external terminal such as a personal computer connected with the image forming apparatus1.

The electrostatic image formed on the photosensitive drum11is developed as a toner image by the toner serving as developer by the developing unit14. In the present embodiment, a normal charging polarity of the toner is negative. In developing the toner image, a developing bias, which is a predetermined voltage, is applied to the developing sleeve14afrom a high voltage power supply serving as a developing power supply knot illustrated). An oscillation voltage in which a DC voltage, i.e., a DC component, is superimposed with an AC voltage, i.e., an AC component, is used as a developing voltage. The toner is supplied to the developing unit14from a toner bottle19serving as a toner storage container through a toner conveyance path knot illustrated).

The toner image formed on the photosensitive drum11is primarily transferred onto the surface of the intermediate transfer belt61at the primary transfer portion N1by an action of the primary transfer roller17. At this time, the primary transfer bias of the DC voltage which is inverse to the charging polarity of the toner in development, i.e., positive in the present embodiment, is applied to the primary transfer roller17from a primary transfer power supply (not illustrated). The abovementioned operation is carried out in the respective image forming units10in forming a full-color toner image, and toner images of the respective colors of yellow, magenta, cyan and black formed on the respective photosensitive drums11are transferred onto the intermediate transfer belt61so as to be sequentially superimposed. After the transfer, transfer residual toner slightly left on the photosensitive drum11is removed by the drum cleaning unit15and is collected in a collecting portion.

Meantime, the sheet S is fed one by one from the sheet feed cassette20and is conveyed to a registration roller pair23. After that, the registration roller pair23conveys the sheet S to a part between the intermediate transfer belt61and the secondary transfer roller64by synchronizing with the toner image on the intermediate transfer belt61.

The color toner image on the intermediate transfer belt61is secondarily transferred onto a surface of the sheet S at the secondary transfer portion N2by an action of the secondary transfer roller64. When the sheet S passes through the secondary transfer portion N2, secondary transfer bias of DC voltage inverse to the charging polarity of the toner during the development is applied to the secondary transfer roller64from a secondary transfer power supply, i.e., a high voltage power supply (not illustrated). After the transfer, residual toner slightly left on the intermediate transfer belt61is removed and collected by the belt cleaning unit66to be ready for a next image forming process.

The toner image transferred onto the sheet S is fixed by being heated and pressurized at a nip portion between a heating roller41and a pressurizing roller42of a fixing unit40, and then the sheet S is discharged onto a discharge tray51by a discharge roller pair50.

Drum Cartridge

Next, a schematic configuration of the drum cartridge3serving as the photosensitive member unit will be described with reference toFIGS. 3 through 5. In a case of the present embodiment, the drum cartridge3including the photosensitive drum11is configured to be removably attached to the apparatus body1a(seeFIG. 1) to be able to replace for maintenance or the like. For instance, the drum cartridge3is removably attached to the apparatus body1aby moving along a longitudinal direction, i.e., a rotation axial direction of the photosensitive drum11.

As illustrated inFIGS. 3 through 5, the drum cartridge3includes the photosensitive drum11serving as the photosensitive member, the charging roller12, a cleaning roller13serving as a cleaning member, a drum cleaning unit15, a contacting/separating mechanism4and others. These component parts are integrally held in a drum container30serving as a frame.

The photosensitive drum11is held in the drum container30rotatably centering on a rotational axis through bearings knot illustrated). The drum container30includes side walls30adisposed on both sides in the rotation axial direction of the photosensitive drum11, the charging roller12and the cleaning roller13and a connecting portion30bconnecting the side walls30aon both sides. Both side portions in the rotation axial direction of the photosensitive drum11are rotatably supported by the side walls30aon both sides in the rotation axial direction through bearings.

Provided at a first end portion of the rotation shaft37of the photosensitive drum11is a coupling39that rotates by receiving a driving force from the driving motor18(seeFIG. 2) provided in the apparatus body1ain a state of being attached to the apparatus body1a(seeFIG. 1). The coupling39couples with a coupling provided on a side of the apparatus body1awhen the drum cartridge3is attached to the apparatus body1ato transmit the driving force from the driving motor18provided in the apparatus body1a.

The drum container30is also provided with the drum cleaning unit15as illustrated inFIG. 3. The drum cleaning unit15includes a cleaning blade15a, a collecting portion15band a toner conveyance screw38. The cleaning blade15ais fixed to the drum container30and abuts with the surface of the photosensitive drum11in a counter direction with respect to the R1direction, which is the normal direction, of the photosensitive drum11in forming an image to clean the surface of the photosensitive drum11.

The collecting portion15bis provided in a vicinity of the cleaning blade15ato collect the transfer residual toner removed from the surface of the photosensitive drum11by the cleaning blade15a. The toner conveyance screw38conveys the toner collected in the collecting portion15bto outside of the drum cartridge3. The toner conveyed by the toner conveyance screw38to the outside of the drum cartridge3is collected in a waste toner container (not illustrated) and provided in the apparatus body1a.

As illustrated inFIGS. 4 and 5, a gear portion36serving as a first engagement portion or a first mesh portion is formed on an outer circumferential portion of the rotation shaft37of the photosensitive drum11. The gear portion36is configured to rotate integrally with the photosensitive drum11on the rotation shaft37of the photosensitive drum11. According to the present embodiment, the gear portion36is formed of a helical gear. The gear portion36rotates integrally with the photosensitive drum11as the driving force is inputted to the photosensitive drum11through the coupling39. A turning force of the gear portion36is transmitted to the toner conveyance screw38(seeFIG. 3). This arrangement makes it possible to rotate the toner conveyance screw38and to convey the transfer residual toner collected in the collecting portion15b(seeFIG. 3) to outside of the drum cartridge3.

The charging roller12serving as a charging member is disposed under the photosensitive drum11and is a roller-like member including a rotation shaft12aserving as a conductive supporting member, i.e., a core metal or a core, and an elastic layer12bof one layer or more formed around the rotation shaft12a. The charging roller12is brought into contact with the surface of the photosensitive drum11by a pressurizing spring32serving as an urging portion with a predetermined pressing force and is driven following the rotation of the photosensitive drum11.

The charging roller12is rotatably supported by the rotation shaft12athereof that is held by a charging roller bearing31. The charging roller bearing31is also supported slidably to the drum container30. Specifically, the charging roller bearing31is configured to be slidably guided by a slide guide portion30cprovided in the drum container30in a direction heading toward the rotational axis of the photosensitive drum11. In the illustrated example, a groove31cis formed on the charging roller bearing31along the slide direction, and the charging roller bearing31is guided in the direction heading toward the rotational axis of the photosensitive drum11as the slide guide portion30cengages with the groove31c.

Then, the charging roller12supported by the charging roller bearing31is movable along the direction heading toward the rotational axis of the photosensitive drum11in a plane vertical to the rotational axis of the photosensitive drum11. Thereby, the charging roller12is movable to a separate position Pb (seeFIG. 9) where the charging roller12is separated from the surface of the photosensitive drum11and to a contact position Pa (seeFIG. 6) where the charging roller12is in contact with the surface of the photosensitive drum11. Then, in a case where the charging roller12is positioned at the contact position Pa, the charging roller12is driven by the photosensitive drum11and charges the surface of the photosensitive drum11by the voltage applied to the charging roller12.

Still further, the pressurizing spring32is provided between the drum container30and the charging roller bearing31. The pressurizing spring32is constituted of a compression coil spring, for example, and urges the charging roller12in the direction heading toward the rotational axis of the photosensitive drum11, i.e., in an urging direction, in the plane vertical to the rotational axis of the photosensitive drum11. That is, the pressurizing spring32urges the charging roller bearing31in the same direction as the slide direction of the charging roller bearing31, i.e., in a direction heading toward the contact position Pa (seeFIG. 6) from the separate position Pb (seeFIG. 9) to urge the charging roller12to the photosensitive drum11. To that end, the pressurizing spring32pushes up the charging roller bearing31to press an end portion of the rotation shaft12aof the charging roller12upward and to form a nip portion N3where the charging roller12is pressed against and in contact with the photosensitive drum11.

As illustrated inFIG. 4, the contacting/separating mechanism4includes a separating member80and a one-way clutch90described later. The contacting/separating mechanism4enables the charging roller12to come into contact with the photosensitive drum11or to separate from the photosensitive drum11by positioning the charging roller12switchably to the contact position Pa (seeFIG. 6) and to the separate position Pb (seeFIG. 9). The contacting/separating mechanism4will be detailed later.

The cleaning roller13serving as the cleaning member is in contact with the charging roller12to clean the surface of the charging roller12. The cleaning roller13includes a rotation shaft13awhich is a rod-like supporting portion, i.e., a core metal or a core, and an elastic layer13bformed around the rotation shaft13aand is a roller-like member in which an outer circumferential surface thereof is in contact with the charging roller12. The cleaning roller13is brought in contact with the surface of the charging roller12by a pressurizing spring34with a predetermined pressing force and is driven following the rotation of the charging roller12.

The cleaning roller13is supported rotatably by the rotation shaft13athereof that is supported by a cleaning roller bearing33. The cleaning roller bearing33is also supported slidably to the charging roller bearing31. The cleaning roller bearing33is configured to be slidable in a direction heading toward the rotational axis of the charging roller12such that the cleaning roller13is movable along a direction heading toward the rotational axis of the charging roller12in a plane vertical to the rotational axis of the charging roller12. It is noted that the rotational axis of the charging roller12is common with a rotational axis of the separating member80described later in the present embodiment.

This arrangement makes it possible to provide the cleaning roller13to be movable to a roller contact position where the cleaning roller13comes into contact with the surface of the charging roller12and to a roller separate position where the cleaning roller13is separated from the surface of the charging roller12. Then, the cleaning roller13cleans the charging roller12at the roller contact position.

The pressurizing spring34is provided between the charging roller bearing31and the cleaning roller bearing33. The pressurizing spring34is constituted of a compression coil spring, for example, and urges the cleaning roller13in a direction, i.e., an urging direction, heading toward a rotation axial direction of the charging roller12in a plane vertical to a rotational axis of the charging roller12. Due to that, the cleaning roller13is pressurized and comes into contact with the charging roller12. That is, the pressurizing spring34urges the cleaning roller13in a direction heading to the roller contact position from the roller separate position. In other words, the cleaning roller13is supported by the cleaning roller bearing33so as to be movable along the urging direction urged by the pressurizing spring34. Still further, the urging direction of the pressurizing spring32is approximately the same as the urging direction of the pressurizing spring34in the present embodiment.

The cleaning roller13is also supported by the charging roller bearing31through the cleaning roller bearing33and the pressurizing spring34. Therefore, in a case where the charging roller12is moved in a direction of separating from the photosensitive drum11by the separating member80as described later, the cleaning roller13moves, in linkage with such movement, in the movement direction of the charging roller12.

Due to the configuration as described above, when the photosensitive drum11rotates by receiving the driving force from a driving source such as the driving motor18(seeFIG. 2) provided in the apparatus body1a, the charging roller12is driven by friction with the photosensitive drum11. When the charging roller12rotates, the cleaning roller13is also driven by friction with the charging roller12. The toner conveyance screw38(seeFIG. 3) also rotates by receiving a driving force, i.e., a turning force, from the gear portion36.

Next, the contacting/separating mechanism4capable of contacting/separating the charging roller12with/from the photosensitive drum11will be described in detail with reference toFIGS. 4 through 6. Note that althoughFIG. 4illustrates only a side of the first longitudinal end portion of the drum cartridge3, a side of a second end of the drum cartridge3is symmetrically constructed. The contacting/separating mechanism4includes the separating member80provided around an outer circumferential portion of the rotation shaft12aof the charging roller12and the one-way clutch90interposed between the rotation shaft12aand the separating member80in a power transmission path.

As illustrated inFIG. 4, the rotation shaft12aof the charging roller12is provided so as to project out of the elastic layer12bin an axial direction. Formed at an end portion side of the part projecting out of the elastic layer12bof the rotation shaft12ain the axial direction is a small-diameter portion12cin which an outer diameter thereof is reduced more than the other parts of the rotation shaft12a. The small-diameter portion12cis provided with the separating member80and the one-way clutch90coaxially with an axial center of the rotation shaft12a. The rotation shaft12aof the charging roller12is formed so as to project out in the axial direction further from the separating member80and edge portion thereof is rotatably supported by the charging roller bearing31.

As illustrated inFIGS. 4 and 5, the separating member80includes a fan-shaped gear portion81, serving as a second engagement portion or a second mesh portion, constituted of a helical gear engageable with, i.e., meshable with, the gear portion36formed around the rotation shaft37of the photosensitive drum11. The separating member80is rotatably provided coaxially with the charging roller12. That is, the gear portion81of the separating member80is provided to be engageable with the gear portion36of the photosensitive drum11from a lower side in terms of the direction of gravity. Still further, in a case where a radius of the photosensitive drum11is denoted as r1, a radius of the charging roller12as r2, a radius of a pitch circle of the gear portion36as r3 and a radius of a pitch circle of the gear portion81of the separating member80as r4 as illustrated inFIG. 9, they are set so as to satisfy a relationship of r1+r2<r3+r4. Accordingly, the photosensitive drum11and the charging roller12are inevitably separated when the gear portion81meshes with the gear portion36.

The separating member80is provided to be rotatable or movable to a first position P1(seeFIG. 6) and to a second position P2along the rotation of the charging roller12. As illustrated inFIG. 6, the first position P1of the separating member80is a position where the gear portion81is separated from the gear portion36and where the charging roller12is allowed to be positioned at the contact position Pa by being urged by the pressurizing spring32. As illustrated inFIG. 9, the second position P2of the separating member80is a position where the gear portion81engages with the gear portion36and where the charging roller12is positioned at the separate position Pb.

As illustrated inFIG. 6, the one-way clutch90includes an inner diametric portion91and an outer diametric portion92respectively having an approximately ringed shape. The inner diametric portion91serving as one example of a first cylindrical portion is provided with an inner circumferential surface fixed to an outer circumferential surface of the small-diameter portion12cof the charging roller12and with a rack gear93formed on an outer circumferential surface thereof. The inner diametric portion91is rotatable integrally with the charging roller12. The outer diametric portion92serving as one example of a second cylindrical portion is provided by being fixed to the separating member80at an outer circumferential side of the inner diametric portion91and includes a latch claw94engageable with the rack gear93and an urging spring95constituted of a torsion spring and urging the latch claw94toward the rack gear93. The outer diametric portion92is provided concentrically with the inner diametric portion91and is rotatable integrally with the separating member80. Each of teeth of the rack gear93includes a slope inclined from upstream to downstream in terms of an R3direction so as to gradually approach to the center of rotation of the inner diametric portion91and a step forming a step by connecting an uppermost-stream end of a slope of one tooth with a downmost-stream end of a slope of another tooth adjacent to upstream of the one tooth. Note that because the outer diametric portion92of the one-way clutch90is fixed with the separating member80, they always rotate integrally regardless of rotation directions. The rack gear93, the latch claw94and the urging spring95constitute a latch mechanism. This latch mechanism transmits rotation of the inner diametric portion91to the outer diametric portion92in a case where the photosensitive drum11rotates in the R2direction and idles the rotation of the inner diametric portion91with respect to the outer diametric portion92in a case where the photosensitive drum11rotates in the R1direction.

In a case where the photosensitive drum11rotates in the R2direction and the charging roller12rotates in an R4direction, the step of the tooth of the rack gear93engages with a tip of the latch claw94in the one-way clutch90. Therefore, the inner diametric portion91and the outer diametric portion92of the one-way clutch90are turned into a locked state in the R4direction, and the charging roller12rotates integrally with the separating member80. Meanwhile, in a case where the photosensitive drum11rotates in the R1direction and the charging roller12rotates in the R3direction, the tip of the latch claw94is guided slidably along the slope of the tooth of the rack gear93in the one-way clutch90. Accordingly, the locked state of the inner diametric portion91and the outer diametric portion92of the one-way clutch90in the R4direction is released, and the charging roller12idles with respect to the separating member80. That is, in a case where the photosensitive drum11rotates in the R2direction, the one-way clutch90transmits the rotation of the charging roller12to the separating member80, and in a case where the photosensitive drum11rotates in the R1direction, the one-way clutch90is configured to transmit rotation of the charging roller12to the separating member80or idle the charging roller12with respect to the separating member80.

Note that in the present embodiment, in a case where a torque required for the separating member80to rotate is equal to or more than a predetermined idling torque when the photosensitive drum11rotates in the R1direction, the one-way clutch90idles without transmitting the rotation of the charging roller12to the separating member80. In contrary to that, in a case where a torque required for the separating member80to rotate is smaller than the predetermined idling torque, the one-way clutch90transmits the rotation of the charging roller12to the separating member80. Still further, a regulating portion35is formed at a part of the drum container30. In a case where the photosensitive drum11rotates in the R1direction, the separating member80comes into contact with the regulating portion35at the first position P1and is regulated from moving in the R3direction beyond the first position P1. Note that an operation of the contacting/separating mechanism4will be detailed later. It is also noted that the one-way clutch90functions also as a torque limiting portion. That is, the torque limiting portion transmits a torque from the charging roller12to the separating member80in a case where the photosensitive drum11rotates in the R2direction and limits the transmission of the torque from the charging roller12to the separating member80in a case where the photosensitive drum11rotates in the R1direction.

While the case where the one-way clutch90includes the rack gear93and the latch claw94is being described in the present embodiment, the one-way clutch90is not limited to such configuration. The mechanism of the one-way clutch90is not specifically limited as long as the one-way clutch90turns into a locked state with a core metal when the one-way clutch90rotates in one direction with respect to the charging roller12and the one-way clutch90turns into an unlocked state when the one-way clutch90rotates in another direction. A configuration using a plurality of roller-like rotary members in contact with an outer circumference of the small-diameter portion12cof the charging roller12is also applicable for example as the one-way clutch90.

Operation of Contacting/Separating Mechanism

Next, an operation of separating the charging roller12from the photosensitive drum11will be described with reference toFIGS. 6 through 9.FIGS. 6 through 9are section views in a direction vertical to the rotation axial direction of the photosensitive drum11of the drum cartridge3.

As illustrated inFIG. 6, the separating member80is positioned at the first position P1and the charging roller12is positioned at the contact position Pa normally in forming an image to execute an image forming operation as the photosensitive drum11rotates in the R1direction as the normal direction. When the photosensitive drum11rotates normally in the R1direction, the charging roller12being pressed against and in contact with the photosensitive drum11is driven in the R3direction. When the charging roller12rotates in the R3direction, the small-diameter portion12cof the charging roller12also rotates in the R3direction. When the small-diameter portion12cof the charging roller12rotates in the R3direction, the rack gear93of the inner diametric portion91of the one-way clutch90fixed to the small-diameter portion12cof the charging roller12rotates in the R3direction. At this time, the claw tip portion of the latch claw94is urged toward the rack gear93by an urging force of the urging spring95. However, because the tip of the latch claw94is slidably guided along the slope of the tooth of the rack gear93, the latch claw94does not mesh with the rack gear93and is unable to rotate the separating member80in the R3direction.

At this time, in a case where the torque required for the separating member80to rotate in the R3direction is smaller than a predetermined idling torque, the one-way clutch90transmits rotation of the charging roller12to the separating member80. However, because the separating member80is in contact with the regulating portion35in the R3direction, the separating member80is turned into a state of being regulated at the first position P1and the separating member80cannot be rotated in the R3direction more than that. Then, the torque required for the separating member80to rotate in the R3direction increases to equal to or more than the predetermined idling torque. Therefore, the one-way clutch90idles without transmitting the rotation of the charging roller12to the separating member80, and the charging roller12is turned into a rotation state while stopping the separating member80. The gear portion81of the separating member80also does not contact with the gear portion36of the photosensitive drum11and is left in a state of being separated.

Next, if the photosensitive drum11is rotated reversely in the R2direction as illustrated inFIG. 7, the charging roller12being pressed against and in contact with the surface of the photosensitive drum11is driven by the photosensitive drum11and rotates in the R4direction while positioning at the contact position Pa. When the small-diameter portion12cof the charging roller12rotates in the R4direction, the rack gear93rotates in the R4direction. The latch claw94is urged toward the rack gear93by the urging spring95and engages with the rack gear93as the tip engages with the step. A turning force of the rack gear93is transmitted to the separating member80via the latch claw94, so that the separating member80separates from the regulating portion35of the drum container30and starts to rotate in the R4direction from the first position P1(seeFIG. 6).

Then, as the separating member80rotates further in the R4direction as illustrated inFIG. 8, the gear portion81of the separating member80comes into contact with the gear portion36provided in the photosensitive drum11and the gears of both gear portions start to mesh with each other. As the gear portion81meshes with the gear portion36, the separating member80moves the charging roller12in a direction of separating from the photosensitive drum11and moves the charging roller12toward the separate position Pb (seeFIG. 9) from the contact position Pa. Thereby, the photosensitive drum11rotates in the R2direction and the photosensitive drum11and the charging roller12are turned into a state in which they do not contact with each other in operations at the time of and after the gear portion81of the separating member80meshes with the gear portion36of the photosensitive drum11. Accordingly, a turning force transmission path from the photosensitive drum11to the separating member80through the small-diameter portion12cof the charging roller12is cut off. Meanwhile, because the gear portion81of the separating member80directly meshes with the gear portion36and the turning force is directly transmitted from the photosensitive drum11to the separating member80, the separating member80continues to rotate in the R4direction.

After that, because the control portion70(seeFIG. 2) stops the rotation of the photosensitive drum11in the R2direction at a predetermined rotation angle, the photosensitive drum11stops in a state in which the gear portion36of the photosensitive drum11is meshed with the gear portion81of the separating member80as illustrated inFIG. 9. At this time, the separating member80coaxially provided around the small-diameter portion12cof the charging roller12is pressed down by resisting against the pressurizing spring32to position the separating member80at the second position P2and to position the charging roller12at the separate position Pb. Thereby, the charging roller12and the photosensitive drum11are held in a separated state. That is, in a case where the photosensitive drum11rotates in the R2direction when the separating member80is positioned at the first position P1(seeFIG. 6), the one-way clutch90transmits the rotation of the driven charging roller12to the separating member80. Then, along with the movement of the separating member80to the second position P2, the gear portion81engages with the gear portion36and positions the charging roller12to the separate position Pb.

Next, in a case where the charging roller12is to be moved from the separate position Pb to the contact position Pa (seeFIG. 6), the photosensitive drum11is rotated in the R1direction. Because the gear portion36of the photosensitive drum11is meshing with the gear portion81of the separating member80, the separating member80rotates in the R3direction from the second position P2by rotating the photosensitive drum11in the R1direction. Then, as the engagement of the gear portion36of the photosensitive drum11with the gear portion81of the separating member80is released as illustrated inFIG. 8, the separating member80recedes from the gap between the charging roller12and the photosensitive drum11, and the charging roller12comes into contact with the photosensitive drum11by an urging force of the pressurizing spring32. That is, the charging roller12moves from the separate position Pb (seeFIG. 9) to the contact position Pa.

Here, if the photosensitive drum11rotates further normally in the R1direction, the charging roller12pressed against and in contact with the photosensitive drum11is driven in the R3direction and the rack gear93of the inner diametric portion91of the one-way clutch90rotates in the R3direction. At this time, the latch claw94does not mesh with the rack gear93and is unable to rotate the separating member80in the R3direction. However, because the separating member80is not in contact with the regulating portion35, the separating member80can rotate in the R3direction with a torque smaller than the predetermined idling torque. Due to that, because a torque required by the separating member80to rotate in the R3direction is smaller than the predetermined idling torque, the one-way clutch90transmits the rotation of the charging roller12to the separating member80and rotates the separating member80in the R3direction. After that, as illustrated inFIG. 6, as the separating member80reaches and comes into contact with the regulating portion35in the R3direction, the separating member80is turned into a state of being regulated at the first position P1. Thereby, the separating member80cannot be rotated more than that in the R3direction, the torque required by the separating member80to rotate in the R3direction increases equal to or more than the predetermined idling torque and the one-way clutch90idles without transmitting the rotation of the charging roller12to the separating member80. That is, in a case where the photosensitive drum11rotates in the R1direction when the separating member80is positioned at the second position P2(seeFIG. 9), the rotation of the gear portion36is transmitted from the gear portion81to the separating member80. Then, along with the movement of the separating member80to the first position P1, the gear portion81is separated from the gear portion36and the charging roller12is positioned at the contact position Pa.

Next, a rotation amount when the photosensitive drum11rotates in the R2direction will be described with reference toFIG. 10. The developing sleeve14aprovided within the developing unit14is disposed so as to face a developing area Ar1of the photosensitive drum11while keeping a predetermined distance. At this time, an angle formed centering on the center of rotation of the photosensitive drum11between the nip portion N3between the charging roller12and the photosensitive drum11and the developing area Ar1is set as θ. Then, numbers of teeth of the gear portion81of the separating member80and the gear portion36, modules and the position of the regulating portion35are set respectively such that the rotation angle of the photosensitive drum11in the R2direction for separating the charging roller12is under θ. Here, a length of the surface of the photosensitive drum11from the developing area Ar1on the photosensitive drum11to the nip portion N3where the photosensitive drum11is in contact with the charging roller12is denoted as L1. Then, a length of a moving locus of a part located at the developing area Ar1of the photosensitive drum11when the separating member80moves from the first position P1(seeFIG. 6) to the second position P2(seeFIG. 9) is denoted as L2. Here, an arrangement of components is set so as to meet a relationship of L1>L2. This arrangement makes it possible to prevent the developer that has adhered at the developing area Ar1on the surface of the photosensitive drum11from arriving at the nip portion N3between the photosensitive drum11and the charging roller12when the photosensitive drum11rotates in the R2direction. Therefore, it is possible to restrain the charging roller12from being contaminated by the toner.

According to the present embodiment, the contacting/separating mechanisms4are provided at both end portions in the rotation axial direction of the charging roller12. Then, the positions of the regulating portion35are matched between the two contacting/separating mechanisms4to match rotation angles and phases of the photosensitive drum11when the separating member80is moved from the first position P1(seeFIG. 6) to the second position P2(seeFIG. 9). This arrangement makes it possible to equalize times taken from when the separating members80at both end portions in the rotation axial direction are separated from the regulating portions35until the gear portion81comes into contact with the gear portion36and to improve accuracy of the rotation amount in the R2direction of the photosensitive drum11.

Next, operational procedures in separating the charging roller12from the photosensitive drum11by rotating the photosensitive drum11in the R2direction in the image forming apparatus1of the present embodiment will be described with reference to flowcharts illustrated inFIGS. 11 and 12. Here, if the charging roller12is continuously in pressure contact with the photosensitive drum11at a same location for a long period of time, there is a possibility that the charging roller12is deformed, thus causing image defects in a case where an image forming operation is executed after that. Then, in the present embodiment, cases where an image forming job is finished and where main power supply is turned off will be exemplified respectively as cases where the charging roller12is possibly continuously in pressure contact with the photosensitive drum11at the same location for a long period of time. Note that both cases where the image forming job is finished and where the main power supply is turned off are executed in the present embodiment, but the present embodiment is not limited to that and either one may be executed.

At first, an operational procedure in a case where a predetermined time T0has elapsed after finishing the image forming job will be described with reference to the flowchart inFIG. 11. After finishing the image forming job, the control portion70judges whether the predetermined time T0has elapsed by utilizing a timer21in Step S1. Or, the control portion70judges whether the predetermined time T0has elapsed in the same manner even if the photosensitive drum11stops for some reason during the image forming job. The predetermined time T0here may be four hours, for example. However, the predetermined time T0is not limited to four hours and may be appropriately set as three hours or as five hours. In a case where the control portion70judges that the predetermined time T0has not elapsed yet, i.e., NO in Step S1, the control portion70finishes the process. In a case where the control portion70judges that the predetermined time T0has elapsed, i.e., YES in Step S1, the control portion70separates the primary transfer roller17from the photosensitive drum11in Step S2.

Then, the control portion70rotationally drives the driving motor18in the normal direction to rotate the photosensitive drum11in the R1direction, i.e., in the normal direction, for a first time T1in Step S3. Here, the first time T1is set to be enough time for the separating member80to arrive at the first position P1, even if the separating member80is positioned at any place and may be 120 ms, for example. Thereby, the separating member80is positioned at the first position P1and the charging roller12is positioned at the contact position Pa where the charging roller12is in contact with the photosensitive drum11(seeFIG. 6).

Next, the control portion70rotationally drives the driving motor18in the reverse direction to rotate the photosensitive drum11in the R2direction, i.e., in the reverse direction, for a second time T2in Step S4. The second time T2is a time taken for the separating member80to move from the first position P1until stopping at the second position P2and may be 100 ms for example. Note that while the second time T2is set to be 100 ms here, it is not limited to such time and may be a time set in advance by which the separating member80can be stopped at the second position P2. Still further, the second time T2is set such that the rotation angle of the separating member80is an angle not greater than the angle θ centering on the center of rotation of the photosensitive drum11between the nip portion N3and the developing area Ar1. Thereby, the separating member80is positioned at the second position P2and the charging roller12is positioned at the separate position Pb where the charging roller12is separated from the photosensitive drum11in Step S5(seeFIG. 9).

While the first time T1is set to be longer than the second time T2in the present embodiment, the present embodiment is not limited to that and the first time T1may be equal to the second time T2. In this case, because the second time T2is determined based on a time during which the separating member80moves from the first position P1to the second position P2, the first time T1is matched with the second time T2. Still further, while the photosensitive drum11is rotated in the R1direction before rotating in the R2direction in the present embodiment, the present embodiment is not limited to that. For instance, because the photosensitive drum11is rotated in the R1direction in forming an image, the photosensitive drum11may be rotated in the R2direction without rotating in the R1direction after an elapse of the predetermined time T0.

Next, operational procedures in a case where the main power supply of the image forming apparatus1is turned off will be described with reference to the flowchart inFIG. 12. The control portion70judges whether the main power supply of the image forming apparatus1has been turned off in Step S10. Here, because it is unable to judge the elapse of the predetermined time T0after the case where the main power supply has been turned off, the judgement is triggered by a fact that the main power supply is put into a turned-off state. In a case where the control portion70judges that the main power supply is not being turned off, i.e., NO in Step S10, the control portion70finishes the process. In a case where the control portion70judges that the main power supply has been turned off, i.e., YES in Step S10, the control portion70separates the primary transfer roller17from the photosensitive drum11in Step S2. Because the operational procedures after that are the same with those illustrated in the flowchart inFIG. 11, they are denoted by the same reference numerals and their detailed description will be omitted here.

That is, the control portion70can execute the following controls after the elapse of the predetermined time T0after stopping the rotation of the photosensitive drum11or after the main power supply has been turned off. That is, the control portion70rotates the photosensitive drum11in the R1direction for the first time T1to position the separating member80at the first position P1and rotates the photosensitive drum11in the R2direction for the second time T2to position the separating member80at the second position P2. Therefore, because the photosensitive drum11is rotated in the R1direction before the photosensitive drum11is rotated in the R2direction, positioning of the separating member80to the first position P1and phase matching of the rotation can be steadily made and the operation of positioning the separating member80to the second position P2after that can be executed in high precision.

As described above, according to the drum cartridge3of the present embodiment, the contacting/separating mechanism4is capable of idling the charging roller12without transmitting the rotation of the charging roller12to the separating member80by positioning the separating member80at the first position P1in a case where the photosensitive drum11rotates in the R1direction. Still further, in a case where the separating member80is positioned at the first position P1, the gear portion81is separated from the gear portion36. Therefore, while it is possible to switch the contact/separation of the photosensitive drum11and the charging roller12by the separating member80, it is possible to restrain the vibration of the photosensitive drum11otherwise caused by the separating member80being in contact with the gear portion36of the photosensitive drum11in forming an image.

Still further, according to the drum cartridge3of the present embodiment, in a case where the radius of the photosensitive drum11is denoted as r1, the radius of the charging roller12as r2, the radius of the pitch circle of the gear portion36as r3 and the radius of the pitch circle of the gear portion81of the separating member80as r4, the relationship of r1+r2<r3+r4 is met. Therefore, the charging roller12can be steadily separated from the photosensitive drum11by meshing the gear portion81with the gear portion36.

Still further, according to the drum cartridge3of the present embodiment, in a case where the torque required by the separating member80to rotate is smaller than a predetermined idling torque, the one-way clutch90transmits the rotation of the charging roller12to the separating member80. Thereby, because the torque required for the separating member80to rotate in the R3direction when the separating member80moves from the second position P2to the first position P1is smaller than the predetermined idling torque, the one-way clutch90transmits the rotation of the charging roller12to the separating member80and rotates the separating member80. Therefore, because the separating member80separates steadily from the photosensitive drum11, it is possible to restrain the vibration of the photosensitive drum11otherwise caused by the separating member80being in contact with the gear portion36of the photosensitive drum11in forming an image.

Still further, according to the drum cartridge3of the present embodiment, the regulating portion35regulates the separating member80from moving in the R3direction beyond the first position P1. Therefore, the first position P1of the separating member80is mechanically determined at a fixed position. This arrangement makes it possible to stabilize the rotation angle and the phase of the photosensitive drum11until the separating member80moves from the first position P1to the second position P2and to improve accuracy in positioning the separating member80at the second position P2.

Note that while the case in which the present embodiment is applied to the photosensitive drum11as one example of the photosensitive member has been described in the drum cartridge3of the present embodiment described above, the present embodiment is not limited to that. For instance, the present embodiment is applicable to a photosensitive belt as the photosensitive member, and in such a case, the gear portion36is provided in a rotary roller nipping the photosensitive belt between the charging roller12and the rotary roller. Then, it is possible to restrain the vibration of the photosensitive belt by arranging such that the gear portion81of the separating member80does not come into contact with the gear portion36in a case where the photosensitive belt rotates in the R1direction.

Still further, while the case where the separating member80is rotatably provided coaxially with the charging roller12has been described in the drum cartridge3of the present embodiment described above, the present embodiment is not limited to that. For instance, the separating member may be a member having a straight shape along a tangential line of the nip portion N3between the photosensitive drum11and the charging roller12and being capable of reciprocating along the tangential line of the nip portion N3. In this case, a gear portion capable of meshing with the gear portion36is provided at a side portion on a side facing the gear portion36of the separating member, and the one-way clutch90is interposed between the separating member and the charging roller12. Then, in a case where the photosensitive drum11rotates in the R1direction, the charging roller12is made to idle without transmitting the rotation of the charging roller12to the separating member. This arrangement makes it possible to restrain the vibration of the photosensitive drum11otherwise caused by the contact of the separating member with the gear portion36of the photosensitive drum11in forming an image.

Second Embodiment

Next, a second embodiment of the present disclosure will be described in detail with reference toFIG. 13. The present embodiment is different from the configuration of the first embodiment in that a charging roller12is disposed above a photosensitive drum11. However, the configuration of the present embodiment is otherwise the same with that of the first embodiment, the respective components will be denoted by the same reference numerals and their detailed description will be omitted.

As illustrated inFIG. 13, the charging roller12is disposed above the photosensitive drum11in the present embodiment. That is, a gear portion81of a separating member80is provided to be engageable with a gear portion36of a photosensitive drum11from an upper side in the gravity direction. In the present embodiment, a predetermined idling torque of a one-way clutch90is set to be greater than a rotational moment generated by own weight of the separating member80positioned at a first position P1and acting in the R4direction for moving the separating member80from the first position P1to a second position P2(seeFIG. 9). That is, while the rotational moment acting in the R4direction is generated by own weight of the separating member80in rotating the separating member80in the R3direction, the separating member80can be rotated in the R3direction because the predetermined idling torque of the one-way clutch90is greater than the rotational moment.

Next, an operation for separating the charging roller12from the photosensitive drum11will be described. Here, an operation in moving the photosensitive drum11from the separate position Pb to the contact position Pa (seeFIG. 6) after rotating the photosensitive drum11in the R2direction to position the charging roller12at the separate position Pb (seeFIG. 9) will be described. The photosensitive drum11is rotated in the R1direction in a case of moving the charging roller12from the separate position Pb to the contact position Pa. Because the gear portion36of the photosensitive drum11meshes with the gear portion81of the separating member80at the separate position Pb, the separating member80rotates in the R3direction from the second position P2by rotating the photosensitive drum11in the R1direction. Then, as the mesh of the gear portion36of the photosensitive drum11with the gear portion81of the separating member80is released, the separating member80recedes from the gap between the charging roller12and the photosensitive drum11, and the charging roller12comes into contact with the photosensitive drum11by an urging force of the pressurizing spring32. That is, the charging roller12moves from the separate position Pb to the contact position Pa.

Here, if the photosensitive drum11further rotates normally in the R1direction, the charging roller12pressed and in contact with the photosensitive drum11is driven in the R3direction and the rack gear93of the inner diametric portion91of the one-way clutch90rotates in the R3direction. At this time, the latch claw94does not mesh with the rack gear93and is unable to rotate the separating member80in the R3direction. Meanwhile, the separating member80tends to rotate downward because a rotational moment caused by own weight acts in the R4direction, and there is a possibility of causing vibration in the photosensitive drum11as the gear portion81operates while in contact with the gear portion36.

Then, the contacting/separating mechanism4is arranged to be able to apply sliding friction in idling the charging roller12and the separating member80exceeding the rotational moment caused by own weight of the separating member80in the present embodiment. Specifically, the separating member80is provided with a slide portion in contact with the small-diameter portion12cso as to generate and to adjust the sliding friction between the small-diameter portion12cand the separating member80. This arrangement makes it possible to keep a gap L0between the separating member80and the gear portion36provided integrally with the photosensitive drum11without bringing these members into contact with each other in forming an image. Therefore, it is possible to reduce image defects such as pitch irregularity of images otherwise caused by the unwanted vibration or the like.

As described above, according to the drum cartridge3of the present embodiment, the contacting/separating mechanism4can transmit the rotation of the charging roller12to the separating member80by overcoming the rotational moment caused by own weight of the separating member80in a case where the photosensitive drum11rotates in the R1direction. Due to that, even if the charging roller12is disposed above the photosensitive drum11, it is possible to suppress the vibration of the photosensitive drum11otherwise caused by the contact of the separating member80with the gear portion36of the photosensitive drum11in forming an image.

According to the present disclosure, it is possible to restrain the vibration of the photosensitive member otherwise caused by the contact of the separating member with the engagement portion of the photosensitive member even though it is possible to switch the contact and the separation of the photosensitive member and the charging roller by the separating member.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2019-084269, filed Apr. 25, 2019 which is hereby incorporated by reference herein in its entirety.