Photoconductor unit

Abstract

To reduce the risk of damaging a drum gear and a separation holding member when inversely rotating a photoconductive drum in the state of releasing separation between the photoconductive drum and a charging roller in the structure of separating the photoconductive drum and the charging roller.SOLUTION: A photoreceptor unit includes: a photoconductive drum; a charging roller; a drum gear; and a separation holding member rotatably held on the rotation shaft of the charging roller, including an engagement part engaging with the drum gear to receive drive force from the drum gear and a collision part provided to face the drum gear and colliding with the drum gear and rotatable between a separation position and a release position. The separation holding member rotates from the separation position to the release position when the photoconductive drum rotates in a first direction in the state of being in the separation position; and when the photoconductive drum rotates in a second direction in the state of being in the release position, the collision part collides with the drum gear without engaging the engagement part with the drum gear.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a photoreceptor unit including a photosensitive drum and a charging roller.

Background Art

[0002] A contact charging method is known in which a charging roller having an elastic layer is brought into contact with a photosensitive drum by a biasing force by a spring or the like to charge the photosensitive drum. When the charging roller and the photosensitive drum are brought into contact with each other for a long period of time, the portion of the charging roller that has been in contact with the photosensitive drum may be deformed, and there is a risk of image defects when image formation is performed. [[ID=第十三]] [[ID=第十四]]

[0003] [[ID=第十五]] No. [[ID=第十六]]

[0004] [[ID=第十七]] [[ID=第十八]] [[ID=第十九]] [[ID=第二十]] [[ID=第二十一]] [[ID=第二十二]] [[ID=第二十三]]

[0005] [[ID=第二十四]] [[ID=第二十五]] [[ID=第二十六]]<000002?[[ID=第二十七]] [[ID=第二十八]]

[0005] [[ID=第二十九]] [[ID=第三十]] [[ID=第三十一]]

Patent Document 1

[0006] However, in the configuration of Patent Document 1, when the photosensitive drum is rotated in reverse while the separation between the photosensitive drum and the charging roller is released, the sliding friction between the rotation axis of the charging roller and the separation-holding member causes the separation-holding member to rotate in reverse until it hits the drum gear. When the separation-holding member engages with the drum gear, the photosensitive drum and the charging roller separate again. If the photosensitive drum rotates in reverse again while the photosensitive drum and the charging roller are separated, the separation-holding member will hit the drum container supporting the photosensitive drum. In this way, if the driving force to rotate the photosensitive drum in reverse is applied to the separation-holding member while the photosensitive drum is unable to rotate in reverse, there is a risk of damage to the drum gear and the separation-holding member.

[0007] The present invention has been made in view of the above-mentioned problems. The object of the present invention is to provide a configuration in which a photosensitive drum and a charging roller are separated, in which the photosensitive drum is rotated in reverse when the separation between the photosensitive drum and the charging roller is released, thereby reducing the risk of damage to the drum gear and the separation holding member. [Means for solving the problem]

[0008] To achieve the above objective, a photoreceptor unit according to one aspect of the present invention has the following configuration: a photoreceptor drum rotatable in a first direction and a second direction opposite to the first direction; a rotatable charging roller for contacting the photoreceptor drum and charging the photoreceptor drum; a drum gear provided coaxially with the rotation axis of the photoreceptor drum and rotating by a driving force; and a separation holding member rotatably held on the rotation axis of the charging roller, having an engaging portion that engages with the drum gear and receives a driving force from the drum gear. To prevent it from getting caught between adjacent teeth of the drum gearThe device includes a separation-holding member having a stopper portion provided opposite to the drum gear and abutting against the drum gear, and a separation-holding member that is rotatable between a separation position, which maintains a separated state in which the photosensitive drum and the charging roller are separated when the engaging portion is engaged with the drum gear, and a release position, which releases the separated state between the photosensitive drum and the charging roller and brings the photosensitive drum and the charging roller into contact, wherein the separation-holding member rotates from the separation position to the release position when the photosensitive drum rotates in the first direction while in the separation position, and when the photosensitive drum rotates in the second direction while in the release position, the stopper portion abuts against the drum gear without the engaging portion engaging with the drum gear. As a result, the abutting portion abuts against the drum gear, thereby restricting the rotation of the separation holding member from the release position to the separation position. It is characterized by the following: [Effects of the Invention]

[0009] According to the present invention, in a configuration in which a photosensitive drum and a charging roller are separated, when the photosensitive drum is rotated in reverse while the separation between the photosensitive drum and the charging roller is released, the risk of damage to the drum gear and the separation holding member can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing the configuration of an image forming apparatus according to the first embodiment. [Figure 2] This is a perspective view showing the configuration of a drum cartridge according to the first embodiment. [Figure 3] This is a cross-sectional view showing the configuration of a drum cartridge according to the first embodiment. [Figure 4] This is a perspective view showing the configuration near the separation-holding member when the separation between the photosensitive drum and the charging roller is maintained. [Figure 5] This is a perspective view showing the configuration near the separation-holding member when the separation between the photosensitive drum and the charging roller is released. [Figure 6] This is a perspective view showing the configuration of the separation-holding member in this embodiment. [Figure 7]This is a side view showing the configuration near the separation holding member in this embodiment (relationship between the separation holding member and the drum gear when the photosensitive drum rotates in reverse). [Figure 8] This is a side view showing the configuration near the separation-holding member in a conventional example (relationship between the separation-holding member and the drum gear when the photosensitive drum rotates in reverse). [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention as defined in the claims, and not all combinations of features described in the first embodiment are necessarily essential to the solution of the present invention. The present invention can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices.

[0012] [First Embodiment] (Configuration of an image forming apparatus) First, the overall configuration and operation of the image forming apparatus will be explained using Figure 1. Figure 1 is a cross-sectional view showing the configuration of the image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 is a tandem type image forming apparatus employing an intermediate transfer method that is capable of forming full-color images using an electrophotographic method.

[0013] The image forming apparatus 1 includes image forming units that form toner images of each of the following colors: Y (yellow), M (magenta), C (cyan), and K (black). The configuration and operation of these image forming units are substantially the same, except that the toner colors used are different. Therefore, in the following, unless otherwise specified, the Y, M, C, and K at the end of the symbols indicating that an element is for one of the colors will be omitted, and the elements will be described comprehensively.

[0014] The image forming unit has a photosensitive drum 12 (photosensitive member) as an image carrier which is a drum-shaped (cylindrical) electrophotographic photosensitive member. The photosensitive drum 12 is rotationally driven by transmission of a driving force from driving means provided in the image forming apparatus 1. In the image forming unit, the following means are arranged in order along the circumferential direction of the photosensitive drum 12.

[0015] First, a charging roller 13 which is a rotatable roller-shaped charging member as charging means is arranged. Next, a laser scanner 22 is arranged so that the surface of the photosensitive drum 12 receives exposure by the laser scanner like exposure means (electrostatic latent image forming means).

[0016] Next, a developing device 20 as developing means is arranged. Toner is supplied to the developing device 20 from a toner cartridge 21 as a toner storage container via a toner conveyance path. Next, a primary transfer roller 31 which is a roller-shaped primary transfer member as primary transfer means is arranged.

[0017] In the image forming unit, a cleaning blade 14 as cleaning means for the photosensitive drum 12 is arranged in contact with the photosensitive drum Also, in the image forming unit, a cleaning roller 15 which is a roller-shaped charging cleaning member as cleaning means for the charging member is arranged in contact with the charging roller

[0018] Further, the image forming apparatus 1 has an intermediate transfer belt 30 formed of an endless belt body as an intermediate transfer member so as to contact each photosensitive drum 12 of each image forming unit. The intermediate transfer belt 30 is wound around a plurality of support rollers (tension rollers) with a predetermined tension. [[ID=,18]]

[0019] A primary transfer roller 31 is positioned on the inner circumferential surface (back side) of the intermediate transfer belt 30, facing each photosensitive drum 12. The primary transfer roller 31 is pressed against the photosensitive drum 12 via the intermediate transfer belt 30, forming a primary transfer section (primary transfer nip section) where the intermediate transfer belt 30 and the photosensitive drum 12 come into contact. The primary transfer roller 31 rotates in conjunction with the rotation of the intermediate transfer belt 30.

[0020] Furthermore, a secondary transfer roller 32, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is positioned on the outer peripheral surface (surface side) of the intermediate transfer belt 30, facing the secondary transfer outer roller 33. The secondary transfer roller 32 is pressed against the secondary transfer outer roller 33 via the intermediate transfer belt 30, forming a secondary transfer portion (secondary transfer nip portion) where the intermediate transfer belt 30 and the secondary transfer roller 32 come into contact.

[0021] Furthermore, a belt cleaning device 40, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface of the intermediate transfer belt 30, opposite the tension roller 35. The intermediate transfer belt 30 is formed in an endless manner from a dielectric resin such as polyimide.

[0022] In addition, the image forming apparatus 1 is equipped with a feed and transport roller 51 for feeding and transporting recording material P such as recording paper, and a fuser 70 for fixing the toner image onto the recording material P.

[0023] During image formation, the surface of the rotating photosensitive drum 12 is uniformly charged to a predetermined potential of a predetermined polarity by the charging roller 13. In the first embodiment, a voltage is applied to the charging roller 13 from a high-voltage power supply (charging power supply), causing a discharge to occur on the surface of the photosensitive drum 12, thereby charging the surface of the photosensitive drum 12.

[0024] After the surface of the photosensitive drum 12 is uniformly charged, the surface of the photosensitive drum 12 is scanned and exposed by a laser scanner 22 (exposure device) based on the image information signal, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 12. The latent image formed on the photosensitive drum 12 is developed as a toner image using toner as a developer supplied from the toner cartridge 21 to the developing device 20. In the first embodiment, the normal charging polarity of the toner is negative polarity.

[0025] The developing device 20 has a developing sleeve, which serves as a developer carrier that holds toner and transports it to the opposite position (developing position) from the photosensitive drum 12. The developing sleeve is rotationally driven. During development, a predetermined developing voltage (developing bias) is applied to the developing sleeve from a high-voltage power supply, which serves as the developing power supply.

[0026] The toner image formed on the photosensitive drum 12 is transferred (primary transfer) to the surface of the intermediate transfer belt 30 in the primary transfer section by the action of the primary transfer roller 31. At this time, the primary transfer roller 31 is supplied with a primary transfer voltage (primary transfer bias) from the primary transfer power supply (high voltage power supply), which is a voltage with the opposite polarity (positive polarity in the first embodiment) to the charge polarity of the toner during development.

[0027] During the formation of a full-color image, the above-described operations are performed in each image forming unit, and the toner images of each color—Y (yellow), M (magenta), C (cyan), and K (black)—formed on each photosensitive drum 12 are sequentially transferred onto the intermediate transfer belt 30, overlapping each other. After the transfer, any small amount of residual toner remaining on the photosensitive drum 12 is removed by the cleaning blade 14, which acts as a cleaning element, and collected in the recovery unit.

[0028] Meanwhile, one sheet of recording material P is fed from the feed cassette 50 and transported to the register roller pair 60. The register roller pair 60 then transports the recording material P between the intermediate transfer belt 30 and the secondary transfer outer roller 33 in synchronization with the toner image on the intermediate transfer belt 30.

[0029] The color toner image on the intermediate transfer belt 30 is transferred (secondary transfer) to the surface of the recording material P in the secondary transfer section by the action of the secondary transfer roller 32. As the recording material P passes through the secondary transfer section, a secondary transfer voltage (secondary transfer bias), which is a voltage with the opposite polarity to the charge polarity of the toner during development, is applied to the secondary transfer roller 32 from the secondary transfer power supply (high voltage power supply). After transfer, any small amount of residual toner remaining on the intermediate transfer belt 30 is removed and collected by the belt cleaning device 40, and the belt is prepared again for the next image formation.

[0030] The toner image transferred onto the recording material P is fixed by heating and pressurizing it in the fuser unit 70, and then discharged onto the discharge tray 90 by the discharge roller pair 80.

[0031] (Drum cartridge configuration) A drum cartridge 10 (photoreceptor unit) according to the first embodiment will be described with reference to Figures 2, 3, and 4. Figure 2 is a perspective view showing the configuration of the drum cartridge 10 according to the first embodiment. Figure 3 is a cross-sectional view showing the configuration of the drum cartridge 10 according to the first embodiment. Figures 4(A) and 4(B) are perspective views showing the vicinity of the separation holding member when the separation between the photosensitive drum 12 and the charging roller 13 is maintained. Figure 4(B) corresponds to a perspective view of Figure 4(A) when viewed from a direction opposite to the photosensitive drum 12.

[0032] The drum cartridge 10 includes a photosensitive drum 12 as a photoreceptor and a charging roller 13 as a charging member that charges the surface of the photosensitive drum 12. The drum cartridge 10 also includes a cleaning roller 15 as a cleaning member that cleans the surface of the charging roller 13 and a cleaning blade 14 as a cleaning member that cleans the surface of the photosensitive drum 12.

[0033] In the drum cartridge 10, the photosensitive drum 12, the charging roller 13, the cleaning roller 15, and the cleaning blade 14 are integrally held by a drum container 11 which serves as a frame (support frame) for supporting the photosensitive drum 12.

[0034] The photosensitive drum 12 is held in the drum container 11 via bearings so as to be rotatable around its axis of rotation. The photosensitive drum 12 is also provided with a coupling 122 for receiving driving force and rotating, and a drum gear 121 which is mounted coaxially with the axis of rotation of the photosensitive drum 12 and rotates by the driving force. When the drum cartridge 10 is mounted in the image forming apparatus 1, the coupling 122 receives driving force from a motor, which is a driving source provided in the image forming apparatus 1.

[0035] Furthermore, a cleaning blade 14 is fixed to the drum container 11. The cleaning blade 14 is positioned to contact the surface of the photosensitive drum 12 in a counter-direction with respect to the rotation direction of the photoreceptor during image formation.

[0036] The charging roller 13 is rotatably supported relative to the drum container 11 by having its charging roller rotation shaft 13a held in a charging roller bearing 161.

[0037] Furthermore, the electrostatic roller bearing 161 is slidably supported relative to the drum container 11. Specifically, the electrostatic roller bearing 161 is configured to slide in the direction toward the rotation axis of the photosensitive drum 12. This allows the electrostatic roller 13, which is supported relative to the drum container 11, to move along the direction toward the rotation axis of the photosensitive drum 12 on a plane perpendicular to the rotation axis of the photosensitive drum 12.

[0038] Furthermore, a charging roller pressure spring 163 is provided between the drum container 11 and the charging roller bearing 161 as a first biasing means. In a cross-section perpendicular to the rotation axis of the photosensitive drum 12, the charging roller pressure spring 163 biases the charging roller 13 in the direction toward the rotation axis of the photosensitive drum 12 (biasing direction). As a result, the charging roller 13 is in contact with the photosensitive drum 12 under pressure.

[0039] The cleaning roller 15 is rotatably supported relative to the drum container 11 by having its cleaning roller rotation shaft 15a held in a cleaning roller bearing. The cleaning roller bearing is slidably supported relative to the electrostatic roller bearing 161.

[0040] Furthermore, a cleaning roller pressure spring 164 is provided between the charging roller bearing 161 and the cleaning roller bearing as a second biasing means. In a cross-section perpendicular to the rotation axis of the photosensitive drum 12, the cleaning roller pressure spring 164 biases the cleaning roller 15 in the direction toward the rotation axis of the charging roller 13 (biasing direction). As a result, the cleaning roller 15 is in contact with the charging roller 13 under pressure.

[0041] In the first embodiment, the biasing direction by the first biasing means, the charging roller pressure spring 163, and the biasing direction by the second biasing means, the cleaning roller pressure spring 164, are substantially the same, but they may be in different directions.

[0042] The photosensitive drum 12 rotates by receiving a driving force from a drive source provided in the image forming apparatus 1. As the photosensitive drum 12 rotates, the charging roller 13 rotates in response due to the frictional force with the photosensitive drum 12. Furthermore, as the charging roller 13 rotates, the cleaning roller 15 rotates in response due to the frictional force with the charging roller 13.

[0043] (Separation holding mechanism) Next, a separation-holding mechanism, including a separation-holding member for maintaining the separation state between the photosensitive drum 12 and the charging roller 13, will be explained using Figure 4.

[0044] The drum cartridge 10 is provided with a separation-holding member 17 for maintaining a separated state between the photosensitive drum 12 and the charging roller 13. The separation-holding member 17 ensures clearance by separating the charging roller 13 from the photosensitive drum 12, and from the charging roller 13 from the cleaning roller 15. This prevents the drum cartridge 10 from being affected by vibrations during transportation for distribution.

[0045] The spacing-holding members 17 are provided at both ends of the charging roller rotation shaft 13a in a gap-fitted state so as to be rotatable with respect to the charging roller rotation shaft 13a as the pivot axis. Therefore, the spacing-holding members 17 can move in conjunction with the movement of the charging roller 13. Since the configuration of both ends of the charging roller rotation shaft 13a is the same, the first embodiment will be explained using diagrams (Figures 4(A) and 4(B)) that show only one end of the charging roller rotation shaft 13a.

[0046] The separation-holding member 17 is provided with a first separation-holding portion 174 for separating the photosensitive drum 12 and the charging roller 13, and for ensuring clearance between the photosensitive drum 12 and the charging roller 13. The separation-holding member 17 is also provided with a second separation-holding portion 175 (separation portion) for separating the charging roller 13 and the cleaning roller 15, and for ensuring clearance between the charging roller 13 and the cleaning roller 15.

[0047] In Figures 4(A) and 4(B), the photosensitive drum 12 and the charging roller 13 are separated, and the charging roller 13 and the cleaning roller 15 are also separated (hereinafter referred to as the separated state). In the separated state, the first separation holding part 174 is pressed by the pressure (biasing force) of the charging roller pressure spring 163, which is the first biasing means, and is sandwiched between the charging roller rotation shaft 13a and the drum gear 121. At the same time, the second separation holding part 175 is pressed against the cleaning roller 15 by the pressure (biasing force) of the cleaning roller pressure spring 164, which is the second biasing means, and is sandwiched between the charging roller rotation shaft 13a and the rotation shaft 15a of the cleaning roller 15.

[0048] As shown in Figures 4(A) and 4(B), a first separation-holding part 174, sandwiched between the photosensitive drum 12 and the charging roller 13, separates the elastic layer 13b of the charging roller 13 from the photosensitive drum 12. Also, as shown in Figures 4(A) and 4(B), a second separation-holding part 175, sandwiched between the charging roller 13 and the cleaning roller 15, separates the elastic layer 13b of the charging roller 13 from the cleaning roller 15. This ensures, for example, that clearance is maintained between the elastic layer 13b of the charging roller 13 and the photosensitive drum 12, and also between the elastic layer 13b of the charging roller 13 and the cleaning roller 15 during the transport of the drum cartridge 10.

[0049] Furthermore, in the separated state where the photosensitive drum 12 and the charging roller 13 are separated, the first separation holding part 174 is provided with an engaging part 171 on the side facing the drum gear 121, which has gear teeth with the same pitch as the surface pitch of the gear teeth of the drum gear 121. When the photosensitive drum 12 and the charging roller 13 are separated, the separation holding member 17 is positioned in a separated position that maintains the separated state in which the photosensitive drum 12 and the charging roller 13 are separated, with the engaging part 171 engaged with the drum gear 121.

[0050] (Automatic release of separation state) Next, the automatic release of the separated state in the separated holding mechanism will be explained using Figures 4 and 5. Figures 5(A) and 5(B) are perspective views showing the vicinity of the separated holding member 17 when the separation between the photosensitive drum 12 and the charging roller 13 is released (i.e., the photosensitive drum 12 and the charging roller 13 are in contact). Figure 5(B) is a perspective view of Figure 5(A) as seen from the direction opposite to the photosensitive drum 12.

[0051] When a new drum cartridge 10 is installed in the image forming apparatus 1 and the image forming apparatus 1 is started, the image forming apparatus 1 performs an initial operation. During the initial operation performed by the image forming apparatus 1, a driving force (rotational force) is input in the rotational direction A from the motor provided in the image forming apparatus 1 to the coupling 122 of the photosensitive drum 12.

[0052] As shown in Figure 4(A), when the photosensitive drum 12 starts rotating from a state where there is a gap between the photosensitive drum 12 and the charging roller 13, and between the charging roller 13 and the cleaning roller 15, the photosensitive drum 12 rotates in direction A and the drum gear 121 rotates. Then, the engaging portion 171 of the separation holding member 17, which is engaged with the drum gear 121, rotates in response to the rotational force of the drum gear 121.

[0053] As the separation holding member 17 rotates in direction C, the first separation holding portion 174 is released from being sandwiched between the charging roller rotation shaft 13a and the drum gear 121. Also, as the separation holding member 17 rotates in direction C, the second separation holding portion 175 is released from being sandwiched between the charging roller rotation shaft 13a and the rotation shaft 15a of the cleaning roller 15.

[0054] As a result, as shown in Figure 5(A), the first separation holding portion 174 is released from being sandwiched between the photosensitive drum 12 and the charging roller 13. The charging roller bearing 161 is biased toward the photosensitive drum 12 (biasing direction) by the charging roller pressure spring 163. Therefore, the photosensitive drum 12 and the charging roller 13 are in contact under pressure, and the charging roller 13 rotates in direction C, driven by the photosensitive drum 12 which is rotating in direction A.

[0055] Similarly, the second separation-holding part 175 rotates in conjunction with the rotation of the separation-holding member 17, and is released from being sandwiched between the charging roller 13 and the cleaning roller 15. The cleaning roller bearing is biased toward the charging roller 13 (biasing direction) by the cleaning roller pressure spring 164. As a result, the charging roller 13 and the cleaning roller 15 come into contact under pressure and become capable of driven rotation.

[0056] (Conventional example) Here, the configuration of the separation-holding member in the conventional example will be explained using Figure 8. Figure 8 is a side view showing the configuration of the vicinity of the separation-holding member 170 in the conventional example, and shows the relationship between the separation-holding member 170 and the drum gear 121 when the photosensitive drum 12 rotates in the reverse direction in the conventional example.

[0057] As mentioned above, the cleaning blade 14 is in contact with the photosensitive drum 12 in order to clean the developer on the photosensitive drum 12. However, when the photosensitive drum 12 rotates in direction A, which is the rotation direction during image formation, and then stops rotating after image formation is complete, the developer gets stuck between the cleaning blade 14 and the photosensitive drum 12.

[0058] As a result, the developer may adhere to the photosensitive drum 12, potentially causing horizontal streaks in the toner image during the next image formation. To address this, the image forming apparatus 1 can perform a control (reverse rotation mode) that rotates the photosensitive drum 12 in the opposite direction to the rotation direction during image formation (direction B) after the image formation is complete, thereby releasing the developer trapped between the cleaning blade 14 and the photosensitive drum 12 in the reverse rotation direction.

[0059] While the reverse rotation mode is running, the charging roller 13, which is driven by the photosensitive drum 12, also rotates in the opposite direction (direction D) to the rotation direction (direction C) during image formation. As a result, the separation holding member 170, which is rotatably held in place by clearance fitting with the charging roller rotation shaft 13a, also rotates along with it due to sliding friction. Consequently, as shown in Figure 8, the engaging portion 171 of the separation holding member 170 comes into contact with the drum gear 121 of the photosensitive body.

[0060] Then, when the engaging portion 171 of the separation-holding member 170 comes into contact with the drum gear 121, as shown in Figure 8, the drum gear 121 and the engaging portion 171 of the separation-holding member 170 engage, causing the separation-holding member 170 to rotate in the opposite direction (direction D).

[0061] As mentioned above, the charging roller bearing 161 is held slidably, so as the separation holding member 170 rotates in the reverse direction, the charging roller bearing 161 is pushed down by the separation holding member 170 and moves in the opposite direction to the pressurizing direction of the charging roller 13. As a result, the engaging portion 171 of the separation holding member 170 moves to a separated position that maintains the state in which the photosensitive drum 12 and the charging roller 13 are separated.

[0062] Furthermore, if the coupling 122 receives a driving force and the separation holding member 170 rotates in the opposite direction (direction D), as shown in Figure 4(A), the separation holding member 170 will abut against the drum container 11, preventing it from rotating in the opposite direction (direction D). In this state, if the coupling 122 of the photosensitive drum 12 receives further driving force, a force will be applied to the drum gear 121 or the engaging portion 171 of the separation holding member 170.

[0063] Therefore, in the conventional separation-holding member 170, when the photosensitive drum 12 is rotated in reverse while the separation between the photosensitive drum 12 and the charging roller 13 is released, there is a risk that the drum gear 121 or the engaging portion 171 of the separation-holding member 170 may be damaged.

[0064] (This embodiment) Next, the configuration of the spacing-holding member 17 in this embodiment will be described with reference to Figures 6 and 7. Figure 6 is a perspective view showing the configuration of the spacing-holding member 17 in this embodiment. Figure 7 is a side view showing the vicinity of the spacing-holding member 17 in this embodiment, and shows the relationship between the spacing-holding member 17 and the drum gear 121 when the photosensitive drum 12 rotates in reverse in this embodiment.

[0065] As shown in Figure 6, the separation-holding member 17 in this embodiment has an engaging portion 171 and a stopper portion 172. In contrast, the separation-holding member 17 in the conventional example described in Figure 8 has an engaging portion 171 but does not have a stopper portion 172.

[0066] In this embodiment, when the photosensitive drum 12 rotates in the reverse direction (direction B), the spacing holding member 17 rotates together with the charging roller rotation shaft 13a, and as the spacing holding member 17 rotates, the abutment portion 172 of the spacing holding member 17 comes into contact with the drum gear 121 of the photosensitive drum 12.

[0067] As the drum gear 121 abuts against the abutment portion 172, the engaging portion 171 no longer engages with the drum gear 121, and the separation holding member 17 does not rotate further in the opposite direction (direction D). Therefore, the separation holding member 17 does not rotate further in the opposite direction (direction D) from the state shown in Figure 7 and abut against the drum container 11.

[0068] This reduces the risk of damage to the drum gear 121 or the engaging portion 171 of the separation holding member 17 when the photosensitive drum 12 is rotated in reverse while the separation between the photosensitive drum 12 and the charging roller 13 is released. When the photosensitive drum 12 is rotated in reverse while the separation between the photosensitive drum 12 and the charging roller 13 is released, the separation holding member 17 is in a release position that releases the separation between the photosensitive drum 12 and the charging roller 13, bringing the photosensitive drum 12 and the charging roller 13 into contact.

[0069] On the other hand, if the abutment portion 172 is inserted between the teeth of the drum gear 121, the end of the abutment portion 172 may rotate due to the driving force from the drum gear 121. For this reason, it is desirable to configure the drum gear 121 so that the abutment portion 172 does not get inserted between the teeth of the drum gear 121.

[0070] Therefore, in this embodiment, the abutment portion 172 is positioned in the direction of the rotation axis of the photosensitive drum 12 relative to the drum gear 121 (see Figure 4(A)), which is composed of serrated teeth, so that the abutment portion 172 does not get caught between the teeth of the drum gear 121.

[0071] On the other hand, if the drum gear 121 is made up of spur teeth, for example, in order to configure it so that the abutment portion 172 does not get caught between the teeth of the drum gear 121, the settings should be as follows. That is, if the teeth of the drum gear 121 are spur teeth, the width of the abutment portion 172 in a cross section perpendicular to the rotation axis of the photosensitive drum 12 should be set to be longer than the distance between adjacent teeth of the drum gear 121.

[0072] As shown in Figure 7, in a cross-section perpendicular to the rotation axis of the photosensitive drum 12, the angle formed by the line segment L and the opposing surface 172s of the abutment portion 172 that faces the drum gear 121 is defined as angle X. The line segment L is the line segment connecting the contact point Z where the abutment portion 172 and the drum gear 121 abut, and the rotation center O of the photosensitive drum 12. In this embodiment, as shown in Figure 7, by arranging the opposing surface 172s of the abutment portion 172 so that angle X is approximately a right angle, the risk of the end of the abutment portion 172 engaging with the teeth of the drum gear 121 is reduced, making it difficult for the separation holding member 17 to rotate together.

[0073] As described above, in this embodiment, in a configuration in which the photosensitive drum 12 and the charging roller 13 are separated via a separation holding member 17, in addition to providing an engaging portion 171 on the separation holding member 17, abutting portion 172 is also provided on the separation holding member 17. This reduces the risk of damage to the drum gear 121 or the engaging portion 171 of the separation holding member 17 when the photosensitive drum 12 is rotated in reverse while the separation between the photosensitive drum 12 and the charging roller 13 is released.

[0074] (Other embodiments) The present invention is not limited to the embodiments described above, and various modifications (including organic combinations of each embodiment) are possible based on the spirit of the invention, and these are not excluded from the scope of the invention.

[0075] In the above embodiment, an example was described in which, when the photosensitive drum 12 is rotated in the reverse direction while the separation between the photosensitive drum 12 and the charging roller 13 is released, the member that the separation holding member 17 rotates in the reverse direction and abuts is the drum container 11. However, the embodiment is not limited to this. Any member fixed inside the drum cartridge 10 is acceptable as long as the member that the separation holding member 17 rotates in the reverse direction and abuts is not the drum container 11. For example, in a configuration in which the drum container 11 has a plate-shaped projection that protrudes from the side wall, the member that the separation holding member 17 rotates in the reverse direction and abuts is the plate-shaped projection.

[0076] Furthermore, in the above embodiment, as shown in Figure 1, the image forming apparatus 1 first transfers the toner images supported on each of the photosensitive drums 12 to the intermediate transfer belt 30. Subsequently, the image forming apparatus 1 brings the recording material P into contact with the intermediate transfer belt 30 and secondarily transfers the toner images supported on the intermediate transfer belt 30 to the recording material P. In the above embodiment, an image forming apparatus 1 with the above configuration has been described as an example, but it is not limited to this. The present invention can also be applied to an image forming apparatus with a configuration in which the recording material P is brought into direct contact with the photosensitive drum 12 and the toner images supported on the photosensitive drum 1 are directly transferred to the recording material P. [Explanation of Symbols]

[0077] 10 Drum Cartridges 12 Photosensitive drums 13 Electrostatic roller 17 Separation-holding member 121 Drum Gear 171 Engaging part 172 Buttocks

Claims

1. A photosensitive drum that is rotatable in a first direction and in a second direction opposite to the first direction, A rotatable charging roller that contacts the photosensitive drum to charge the photosensitive drum, A drum gear is provided coaxially with the rotation axis of the photosensitive drum and rotates by a driving force, A separation-holding member rotatably held on the rotation axis of the charging roller, having an engaging portion that engages with the drum gear and receives driving force from the drum gear, and abutting portion that is provided opposite the drum gear so as not to get caught between adjacent teeth of the drum gear and abuts against the drum gear, and the separation-holding member is rotatable between a separation position that holds the photosensitive drum and the charging roller separated when the engaging portion is engaged with the drum gear, and a release position that releases the separation state between the photosensitive drum and the charging roller and brings the photosensitive drum and the charging roller into contact, Equipped with, The aforementioned separation holding member is When the photosensitive drum rotates in the first direction while in the separated position, it rotates from the separated position to the release position. When the photosensitive drum rotates in the second direction while in the release position, the abutting portion abuts against the drum gear without the engaging portion engaging with the drum gear. The abutting portion abuts against the drum gear, thereby restricting the rotation of the separation holding member from the release position to the separation position. A photosensitive unit characterized by the following features.

2. The system further comprises a rotatable cleaning roller for contacting and cleaning the charging roller, The separation holding member further has a separation portion that separates the charging roller and the cleaning roller, and separates the charging roller and the cleaning roller through the separation portion when in the separated position. The photoreceptor unit according to feature 1.

3. The teeth of the drum gear are helical teeth. The abutment portion is positioned in the direction of the rotation axis of the photosensitive drum. The photoreceptor unit according to feature 1.

4. The teeth of the drum gear are spur teeth, In a cross-section perpendicular to the rotation axis of the photosensitive drum, the width of the abutment portion is longer than the distance between adjacent teeth of the drum gear. The photoreceptor unit according to feature 1.

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