JP2011197541A - Drum unit and image forming apparatus with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drum unit capable of suppressing the deflection of a photoreceptor drum by fixing an earth plate to a flange member, and an image forming apparatus equipped with the same.SOLUTION: The drum unit 20 includes: the photoreceptor drum 30; a drum shaft 70; a support member 40 which integrally rotatably supports the photoreceptor drum 30 and the drum shaft 70; and the earth plate 50. At a mounting part 46 of the support member 40, a positioning projection 42 for positioning the earth plate 50, and a rotation stop projection 49 for stopping the rotation of the earth plate 50 are formed. The earth plate 50 has: a positioning hole 65 into which the positioning projection 42 is inserted; a rotation stop hole 67 into which the detent projection 49 is inserted; and a fixing member 80 which inclines to extend from the edge of the rotation stop hole 67 toward the rotation stop projection 49, and fixes the rotation stop projection 49 to the rotation stop hole 67 by the contact of its end 82a with the rotation stop projection 49.

Description

  The present invention relates to a drum unit having a photosensitive drum on which a toner image is formed, and an image forming apparatus including the drum unit.

  Image forming apparatuses such as copiers, printers, facsimiles, and the like provide a photosensitive drum on which an electrostatic latent image is formed by light irradiation based on image data, and supplies toner to the electrostatic latent image on the photosensitive drum. And a transfer unit that transfers the toner image on the photosensitive drum onto a sheet. The photosensitive drum is unitized together with other components to form a drum unit.

  As a drum unit, the thing of patent document 1 is known. The drum unit of Patent Document 1 includes a photosensitive drum, a flange member that is fitted into an end opening of the photosensitive drum, a ground plate that is attached to a mounting surface of the flange member facing the inside of the photosensitive drum, and a photosensitive drum. And a drum shaft that passes coaxially through the flange member. The ground plate electrically connects the photosensitive drum and the drum shaft.

  An insertion hole through which the drum shaft is inserted is formed in the flange member. Also, a boss set coaxially with the insertion hole and a pair of protrusions facing each other with the boss interposed therebetween are formed on the mounting surface of the flange member. The ground plate has a boss hole corresponding to the boss and a protrusion hole corresponding to the pair of protrusions. The ground plate is positioned by inserting the boss through the boss hole and is prevented from rotating by inserting the protrusion through the projection hole. By attaching the ground plate in this way, the ground plate is brought into contact with the inner peripheral surface of the photosensitive drum, and the photosensitive drum is grounded.

JP-A-8-6438

  However, in the drum unit of Patent Document 1, due to the dimensional tolerance and geometrical tolerance of the pair of projections of the flange member and the projection hole of the ground plate, the projection and the projection hole in a state where the pair of projections are inserted into the corresponding projection holes. Some gaps may be formed between the two. If the photosensitive drum rotates in a state where such a gap is formed, the ground plate moves within the range of the gap with respect to the mounting surface of the flange member. For this reason, the rotation speed of the photosensitive drum is not constant, and the photosensitive drum is likely to swell. As a result, problems such as color misregistration of the toner image occur.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a drum unit capable of suppressing the deflection of a photosensitive drum by fixing a ground plate to a flange member, and an image forming apparatus including the drum unit. .

  In order to achieve the above object, a drum unit according to the present invention has a cylindrical photosensitive drum, a drum shaft inserted through the photosensitive drum, and a shape that can be fitted into an end of the photosensitive drum. The photosensitive drum and a supporting member that supports the drum shaft so that the photosensitive drum rotates integrally with the drum shaft, and a mounting portion of the supporting member facing the inside of the photosensitive drum, A ground plate that electrically connects the body drum and the drum shaft, and the mounting portion of the support member is positioned around the positioning projection, a positioning projection for positioning the ground plate, A rotation prevention projection for preventing the earth plate from rotating is formed, and the earth plate has a positioning hole through which the positioning projection is inserted, and a front An anti-rotation hole into which the anti-rotation protrusion is inserted, and an inclined portion extending from an edge of the anti-rotation hole toward the anti-rotation protrusion, and an end of the anti-rotation protrusion is in contact with the anti-rotation protrusion so that the anti-rotation protrusion And a fixing member for fixing to the rotation stop hole.

  According to the drum unit of the present invention, since the anti-rotation projection is fixed to the anti-rotation hole by the fixing member, a gap is formed between the anti-rotation projection and the anti-rotation hole due to dimensional tolerance and geometrical tolerance. Even when the photosensitive drum is rotated, the ground plate can be prevented from moving within the gap with respect to the mounting portion of the support member during rotation of the photosensitive drum. As a result, inconveniences such as a flicker of the photosensitive drum and a color shift of the toner image can be suppressed.

  In a preferred embodiment of the present invention, the ground plate is attached to the attachment portion, and has a flexible ground plate main body having the positioning hole and the rotation prevention hole, and the fixing member is the ground plate. A pair of locking pieces formed by making a cut in the main body, and each locking piece has a base end connected to the ground plate main body and a free end that can be lifted with respect to the base end. The free end portion of one locking piece and the free end portion of the other locking piece are opposed to each other, and the anti-rotation projection is in contact with the one free end portion in the lifted state. The one free end portion and the other free end portion are sandwiched between the other free end portions in the lifted state by a return force that attempts to return to substantially the same level as the base end portion. ing.

  According to this configuration, the anti-rotation protrusion is formed into the anti-rotation hole by simply sandwiching the anti-rotation protrusion between one free end and the other free end using the return force of the pair of locking pieces. Can be fixed.

  In another preferred embodiment of the present invention, the ground plate body has an outer peripheral portion set to a size that does not contact the inner peripheral surface of the photosensitive drum, and the outer peripheral portion includes the outer peripheral portion. A claw portion that protrudes outward from the portion and contacts the inner peripheral surface of the photosensitive drum is provided.

  In the drum unit according to the present invention, since the ground plate is restrained from moving with respect to the attachment portion of the support member, the state in which the claw portion of the ground plate properly contacts the inner peripheral surface of the photosensitive drum is maintained. Can do.

  An image forming apparatus according to the present invention includes a drum unit having a photosensitive drum on which a toner image is formed, and a developing device that supplies toner to the photosensitive drum and forms the toner image on the photosensitive drum. The drum unit according to any one of claims 1 to 3 is used as the drum unit.

  According to the drum unit and the image forming apparatus including the drum unit according to the present invention, the ground plate can be fixed to the flange member to suppress the deflection of the photosensitive drum. As a result, inconveniences such as color misregistration of the toner image can be suppressed.

It is explanatory drawing of the cross-sectional view of the image forming apparatus to which the drum unit which concerns on embodiment of this invention was applied. It is a partially cutaway exploded perspective view of a drum unit. It is a partially cut-out assembly perspective view of a drum unit. It is a perspective view which shows the state by which the earth board was attached to the flange member of the drum unit. It is sectional drawing cut | disconnected along the VV line | wire of FIG. 4, and has shown the state by which the rotation prevention protrusion was being fixed to the rotation prevention hole by a pair of locking piece. It is a top view which shows the state by which the rotation prevention protrusion was being fixed to the rotation prevention hole by a pair of locking piece.

  First, an image forming apparatus to which a drum unit according to an embodiment of the present invention is applied will be described. FIG. 1 is a cross-sectional explanatory view showing an embodiment of an image forming apparatus to which a drum unit is applied. As shown in FIG. 1, an image forming apparatus 10 is used as, for example, a copying machine, and has an apparatus main body 11 having a box shape called an in-body discharge type, and an upper part of the apparatus main body 11. And an image reading unit 16 for reading a document image.

  The image reading unit 16 includes an image reading device 17 mounted inside the outer cover body 170, and an automatic document feeder 18 disposed on the outer cover body 170.

  On the other hand, in the apparatus main body 11, an image forming unit 12 that forms an image based on image data of a document read by the image reading device 17, and a fixing process for an image formed by the image forming unit 12 and transferred to the paper P The fixing unit 13 that performs the above and the paper storage unit 14 that stores the transfer paper P are internally provided. At the top of the apparatus main body 11, a paper discharge unit 15 having an in-body paper discharge tray 151 that receives the discharged paper P after the fixing process is provided.

  The automatic document feeder 18 extends to the document feeder cover 181 covering the contact glass 180 fitted in the upper surface opening of the image reading device 17, the document feeder 182 disposed on the document feeder cover 181, and the document feeder 182. And a paper feed tray 183 provided.

  The document feeding unit 182 supplies documents one by one from the bundle of documents placed on the sheet feeding tray 183 onto the contact glass 180 for reading the document surface by the image reading device 17. The document for which the document image has been read is discharged onto the document pressing cover 181. The document image data read by the image reading unit 16 is converted into an electric signal, and the converted electric signal is output to the image forming unit 12.

  The image reading device 17 includes a box-shaped casing 171 and a reading unit which is built in the casing 171 so as to be reciprocable in the left-right direction in FIG. 1 and obtains reflected light by irradiating light on the document surface. 172 and a CCD unit 173 that collects reflected light from the reading unit 172 and captures it as image data. The read image data is converted into a digital signal and then output to an exposure apparatus 123 described later.

  The image forming unit 12 forms a toner image on the paper fed from the paper storage unit 14, and is sequentially arranged from the upstream side (right side in FIG. 1) to the downstream side (left side in FIG. 1). The magenta unit 12M, the cyan unit 12C, the yellow unit 12Y, and the black unit 12K are included.

  Each unit 12M, 12C, 12Y, 12K includes a drum unit 20 having a photosensitive drum 30 and a developing device 121. The photosensitive drum 30 of the drum unit 20 rotates in the counterclockwise direction in FIG. 1 and receives toner supplied from the corresponding developing device 121 to form a toner image on the peripheral surface thereof.

  A charger 122 is provided immediately below each photoconductor drum 30, and an exposure device 123 is provided below each charger 122. The circumferential surface of each photosensitive drum 30 is uniformly charged by the charger 122. The exposure device 123 irradiates the charged peripheral surface of the photosensitive drum 30 with laser light corresponding to each color M, C, Y, and K based on the image data input by the image reading unit 16. Thereby, an electrostatic latent image is formed on the peripheral surface of each photosensitive drum 30. When toner is supplied from the developing device 121 to the electrostatic latent image on the circumferential surface of each photosensitive drum 30, a toner image is formed on the circumferential surface of each photosensitive drum 30.

  A transfer belt 124 that is stretched between the driving roller 124 a and the driven roller 124 b is provided above the photosensitive drum 30 so as to be in contact with the photosensitive drum 30. The transfer belt 124 is pressed against the circumferential surface of the photoconductive drum 30 by a transfer roller 125 provided corresponding to each photoconductive drum 30, while being synchronized with the rotation of the photoconductive drum 30 and a driving roller 124 a. It circulates between the driven roller 124b.

  When the transfer belt 124 circulates, the magenta toner image is transferred onto the surface of the transfer belt 124 by the photosensitive drum 30 of the magenta unit 12M. Hereinafter, on the magenta toner image, the cyan toner image is sequentially formed by the photosensitive drum 30 of the cyan unit 12C, the yellow toner image is formed by the photosensitive drum 30 of the yellow unit 12Y, and finally the photosensitive member of the black unit 12K. A black toner image is overcoated by the drum 30. As a result, a color toner image is formed on the surface of the transfer belt 124, and this color toner image is transferred to the paper P conveyed from the paper storage unit 14.

  A paper conveyance path 111 extending in the vertical direction is formed at the left position of the image forming unit 12. In the paper conveyance path 111, a conveyance roller pair 112 is provided, and a second transfer roller 113 that is in contact with the surface of the transfer belt 124 is provided at a position facing the transfer roller 124a. The sheet P from the sheet storage unit 14 is conveyed toward the nip portion between the transfer belt 124 and the second transfer roller 113 by the rotation of the conveyance roller pair 112. The sheet P is pressed and nipped between the transfer belt 124 and the second transfer roller 113, whereby the toner image on the transfer belt 124 is transferred to the sheet P.

  The paper storage unit 14 has a paper tray 141 that is detachably mounted at a position below the exposure device 123. In the paper tray 141, a bundle of sheets made up of stacked sheets P is stored. The sheets P are fed one by one from the sheet bundle by the pickup roller 142 and introduced into the sheet conveyance path 111.

  The fixing unit 13 performs a fixing process on the toner image transferred to the paper P, and includes a fixing roller 131 having an energized heating element as a heating source, and a pressure roller 132 disposed to face the fixing roller 131. Including. The transferred paper P is heated by heat treatment by the fixing roller 131 while being pressed and clamped between the fixing roller 131 and the pressure roller 132. As a result, the toner image is fixed on the paper P, and a stable color image is formed on the paper P.

  The color-printed paper P that has been subjected to the fixing process is discharged toward the in-body paper discharge tray 151 through a paper discharge conveyance path 114 extending from the upper part of the fixing unit 13.

  The drum unit will be described below with reference to FIGS. FIG. 2 is an exploded perspective view of the drum unit with a part cut away, and FIG. 3 is an assembly perspective view with a part cutout of the drum unit. 2 and 3, the thickness dimension of the photosensitive drum 30 is exaggerated.

  As shown in FIGS. 2 and 3, the drum unit 20 includes a cylindrical photosensitive drum 30 on which an electrostatic latent image and a toner image are formed on the peripheral surface, and one end of the photosensitive drum 30 (in FIG. 2). A flange member 40 (support member) that is inserted into the opening of the left end portion, a shaft support disk 60 that is inserted into the opening of the other end portion (right end portion in FIG. 2) of the photosensitive drum 30, and the flange member 40 And a drum shaft 70 that is concentric with the pivotal support disk 60 and penetrates the pivotal support disk 60 so as to be integrally rotatable therewith.

  The photosensitive drum 30 is laminated on the entire surface of the metal base tube 31 made of aluminum or an aluminum alloy, the organic photosensitive layer 32 stacked on the entire outer peripheral surface of the metal base tube 31, and the entire inner peripheral surface of the metal base tube 31. And an insulating coating 33. The metal tube 31 has a thickness dimension of several millimeters, whereas the organic photosensitive layer 32 and the insulating coating 33 are formed extremely thin from several μm to several tens of μm.

  The organic photosensitive layer 32 is formed of an organic photoreceptor material such as a charge transport agent, a charge generator, and a binder resin (binder resin). Organic photoreceptors mainly include single-layer type photoreceptors and laminated photoreceptors. Particularly, it can be used for either positive or negative charge-type photoreceptors, has a simple structure, and is easy to manufacture. A single-layer type photoreceptor is preferable because it can effectively suppress film defects when forming layers, has few interfaces between layers, and easily improves optical characteristics.

The insulating film 33 is for preventing a toner image from becoming a black spot due to a current flowing through the metal tube 31 and causing a minute discharge breakdown (leak), and for preventing rust. . In the present embodiment, the insulating film 33 is formed of an aluminum oxide film (Al ₂ O ₃ ). The insulating coating 33 can be obtained by using an oxalic acid, sulfuric acid, or chromic acid aqueous solution as an electrolytic solution, and subjecting the inner peripheral surface side of the metal base tube 31 to an anodic oxidation treatment.

  The flange member 40 is integrally formed with a cylindrical main body portion 41 having a shape that can be fitted into the opening at the left end portion of the photosensitive drum 30, and a surface of the cylindrical main body portion 41 facing outward in the axial direction of the photosensitive drum 30. And a formed flange 43. The cylindrical main body 41 and the flange 43 are formed with an insertion hole 44 concentrically passing therethrough and set concentrically with the photosensitive drum 30. The flange member 40 will be described in detail later.

  The shaft support disk 60 is for closing the opening at the right end of the photosensitive drum 30. The shaft support disc 60 is concentric with a cylindrical disc body 61 having an outer diameter dimension slightly larger than the inner diameter dimension of the photosensitive drum 30 and one end portion (right end portion in FIG. 2) of the disc body 61. And a flange 62 formed of The outer diameter of the flange 62 is set to be equal to the outer diameter of the photosensitive drum 30.

  The outer diameter dimension of the disk main body 61 of the pivotal support disk 60 is set to be several μm to several tens μm larger than the inner diameter dimension of the photosensitive drum 30. Therefore, the shaft support disc 60 is fixed to the photoconductive drum 30 by press-fitting the disc main body 61 into the photoconductive drum 30. Further, a shaft hole 63 set concentrically with the photosensitive drum 30 is provided in the shaft support disc 60.

  The drum shaft 70 is attached to the photosensitive drum 30 so as to be rotatable integrally with the photosensitive drum 30. The drum shaft 70 is concentrically protruded from both ends of the large diameter shaft 71 and the large diameter shaft 71 in opposite directions. A pair of small-diameter shafts 72 is provided.

  The large-diameter shaft 71 extends into the photosensitive drum 30 concentrically with the photosensitive drum 30 in a state where the cylindrical main body 41 of the flange member 40 and the shaft support disc 60 are mounted on the photosensitive drum 30.

  On the other hand, one small-diameter shaft 72 (left side in FIG. 2) is inserted into the insertion hole 44 of the flange member 40 and protrudes from the flange 43 side to the outside. The other small-diameter shaft 72 (right side in FIG. 2) is inserted through the shaft hole 63 of the shaft support disc 60 and protrudes from the flange 62 side to the outside.

  As described above, the cylindrical main body 41 of the flange member 40 is fitted into the opening at the left end of the photosensitive drum 30, and the shaft support disk 60 is fitted into the opening at the right end of the photosensitive drum 30. In addition, the drum shaft 70 is supported by the flange member 40 and the pivotal support disk 60, so that the photosensitive drum 30 rotates integrally with the drum shaft 70. The driving force of a motor (not shown) arranged at a proper position in the apparatus main body 11 is transmitted to, for example, the small-diameter shaft 72 on the right side, whereby the drum shaft 70 and consequently the photosensitive drum 30 rotate. Further, the left small-diameter shaft 72 is rotatably supported by a bearing (not shown) disposed at an appropriate position in the apparatus main body 11.

  In the drum unit 20 configured as described above, the ground plate 50 is used to electrically connect the photosensitive drum 30 and the drum shaft 70. FIG. 4 is a perspective view showing a state where the ground plate 50 is attached. The ground plate 50 is attached to the flange member 40 as shown in FIG.

  The flange member 40 has the cylindrical main body 41 and the flange 43 as described above. The cylindrical main body portion 41 has a cylindrical insertion portion 45 and an attachment portion 46 to which the ground plate 50 is attached.

  The fitting portion 45 is a portion set to have a smaller diameter than the flange 43, and a step portion 47 is formed between the fitting portion 45 and the flange 43. The outer dimension of the fitting portion 45 is set to be several μm to several tens of μm larger than the inner diameter dimension of the photosensitive drum 30. Therefore, the flange member 40 is fixed to the photosensitive drum 30 by press-fitting the fitting portion 45 into the photosensitive drum 30. In a state where the fitting portion 45 is press-fitted, the step portion 47 is in contact with the end surface of the photosensitive drum 30.

  The mounting portion 46 is a cylindrical portion that is set to have a smaller diameter than the insertion portion 45 and is located inside the insertion portion 45, and is concentric with the photosensitive drum 30 in the axial direction of the flange member 40 (that is, the photosensitive drum). It has a cylindrical boss 42 (positioning protrusion) that projects in the axial direction of 30. The cylindrical boss 42 has a hole constituting a part of the insertion hole 44 through which the drum shaft 70 is inserted.

  The attachment portion 46 further includes a plurality of protrusions 48 and 49 disposed around the cylindrical boss 42. A pair of protrusions 48 are provided with the cylindrical boss 42 interposed therebetween, and are configured as positioning protrusions. On the other hand, a pair of protrusions 49 is provided with the cylindrical boss 42 interposed therebetween, and is configured as a detent protrusion. Similarly to the cylindrical boss 42, the protrusion 48 and the rotation stopper protrusion 49 also protrude in the axial direction of the flange member 40. Further, the protrusion 48 and the anti-rotation protrusion 49 are located at equal intervals around the cylindrical boss 42 in the circumferential direction of the mounting portion 46, that is, in the rotation direction of the photosensitive drum 30.

  The ground plate 50 is a plate-like member made of a metal material such as stainless steel or brass having flexibility, and includes a ground plate main body 51 and a plurality of claws protruding from the ground plate main body 51. And a pair of connection pieces 53 projecting from the ground plate main body 51.

  The ground plate main body 51 is a circular portion having an outer dimension set smaller than the fitting portion 45, and a first positioning hole 65 into which the cylindrical boss 42 of the mounting portion 46 can be inserted is provided at the center position. Is formed. In addition, the ground plate body 51 is formed with a pair of second positioning holes 66 with the first positioning holes 65 interposed therebetween, and a pair of detent holes 67 with the first positioning holes 65 interposed therebetween. The second positioning hole 66 and the rotation preventing hole 67 are located at equal intervals around the first positioning hole 65.

  The ground plate body 51 is positioned with respect to the mounting portion 46 by inserting the cylindrical boss 42 through the first positioning hole 65 and inserting the projection 48 into the second positioning hole 66. Further, the ground plate main body 51 is prevented from rotating with respect to the attachment portion 46 by inserting a rotation preventing projection 49 corresponding to the rotation preventing hole 67.

  The claw portion 52 is for obtaining an electrical connection state with the metal base tube 31 for grounding in a state where the ground plate main body 51 is located in the photosensitive drum 30. A plurality protrudes radially outward from the outer peripheral portion 51a. The claw parts 52 are located at equal intervals along the outer peripheral part 51a of the ground plate main body 51, for example. Each claw portion 52 is formed in a substantially isosceles triangle shape with the outer peripheral portion 51a of the ground plate main body 51 as a base, and the tip thereof is a sharp end. Further, each claw portion 52 extends in a direction opposite to the direction in which the flange member 40 is inserted into the photosensitive drum 30 in a state of being inclined with respect to the ground plate main body 51.

  The protruding amount of each claw portion 52 from the ground plate body 51 is such that when the flange member 40 is fitted into the photosensitive drum 30, the tip interferes with the insulating film 33 of the photosensitive drum 30 to scrape the insulating film 33 and remove the metal. It is set so that it can reach the raw tube 31. The tip of the claw portion 52 scrapes the insulating film 33 so that the claw portion 52, and hence the ground plate main body 51, are electrically connected to the photosensitive drum 30. The outer peripheral portion 51 a of the ground plate main body 51 is set to a size that does not contact the inner peripheral surface of the photosensitive drum 30.

  The pair of connection pieces 53 are elongated pieces that rise from the outer peripheral portion 51 a of the ground plate main body 51 and extend toward the drum shaft 70 inserted through the insertion hole 44. In FIG. 4, the drum shaft 70 is omitted for simplification of the drawing. Since the pair of connection pieces 53 extend from positions facing each other on the outer peripheral portion 51 a of the ground plate main body 51, their tip portions are in contact with the drum shaft 70 so as to sandwich the drum shaft 70. As a result, the photosensitive drum 30 is electrically connected to the drum shaft 70 via the ground plate 50.

  The electric charges generated in the organic photosensitive layer 32 due to the electrical connection between the photosensitive drum 30 and the drum shaft 70 are in the order of the claw portion 52 of the ground plate 50, the ground plate main body 51, the connection piece 53, and the drum shaft 70. Grounded through.

  In the present embodiment, the ground plate 50 having the above-described configuration is further provided with a fixing member 80 for fixing the anti-rotation protrusion 49 of the flange member 40 to the anti-rotation hole 67 in the rotation direction of the photosensitive drum 30. The fixing member 80 is composed of a pair of locking pieces formed by making a cut in the ground plate main body 51.

  As shown in FIG. 4, each locking piece 80 includes a base end portion 81 and a free end portion 82. The base end portion 81 is integrally connected to the ground plate main body 51 at the edge of the anti-rotation hole 67 and is formed on the anti-rotation protrusion 49 in the substantially circumferential direction of the ground plate main body 51, that is, in the substantially circumferential direction of the photosensitive drum 30. Opposite. In addition, the base end portion 81 of one locking piece 80 and the base end portion 81 of the other locking piece 80 are opposed to each other with the anti-rotation protrusion 49 interposed therebetween.

  The free end portion 82 is a strip that extends from the base end portion 81 in the substantially circumferential direction of the ground plate main body 51 and can be lifted with respect to the base end portion 81 from the same plane level as the base end portion 81. The free end portion 82 of one locking piece 80 and the free end portion 82 of the other locking piece 80 are opposed to each other with the anti-rotation protrusion 49 interposed therebetween. Since the locking piece 80 is formed of a flexible material, when the free end portion 82 is lifted, the free end portion 82 is lifted from the lifted state by its own restoring force, that is, the same level as the base end portion, that is, the original end portion 82. It has the property of returning to position.

  FIG. 5 is a cross-sectional view taken along the line VV in FIG. 4, and shows a state in which the anti-rotation protrusion 49 is fixed to the anti-rotation hole 67 by a pair of engagement pieces 80. FIG. 6 is a plan view showing a state in which the rotation prevention protrusion 49 is fixed to the rotation prevention hole 67 by a pair of locking pieces 80.

  As shown in FIGS. 4 and 5, one (right side) free end portion 82 lifted by the anti-rotation protrusion 49 extends from the right to the left in an inclined direction toward the anti-rotation protrusion 49. The tip 82 a abuts against the rotation prevention protrusion 49. Further, the other free end portion 82 (left side) lifted by the anti-rotation protrusion 49 extends from the left to the right toward the anti-rotation protrusion 49, and the tip 82 a thereof extends to the anti-rotation protrusion 49. It is in contact. The distal end 82 a of each free end portion 82 has a curved shape that matches the peripheral surface of the anti-rotation protrusion 49.

  In such a state, the free end portion 82 on the right side exerts a restoring force that attempts to return to a level substantially the same as that of the base end portion 81 on the anti-rotation protrusion 49 obliquely to the left. On the other hand, the free end portion 82 on the left side exerts a return force that attempts to return to a level substantially the same as that of the base end portion 81 to the anti-rotation protrusion 49 obliquely downward to the right. Therefore, the anti-rotation protrusion 49 is sandwiched between the pair of free end portions 82. Thereby, the rotation prevention protrusion 49 is fixed to the rotation prevention hole 67.

  FIG. 4 shows a configuration in which one locking piece 80 and the other locking piece 80 are opposed to each other in the substantially circumferential direction of the ground plate body 51, but the present invention is not limited to this. The piece 80 and the other locking piece 80 may be opposed to each other in the radial direction of the ground plate main body 51.

  According to the drum unit 20 according to the present embodiment described above, the anti-rotation projections 49 are fixed to the corresponding anti-rotation holes 67 by the pair of locking pieces 80 that are the fixing members 80. Therefore, even if a slight gap G (FIG. 6) is formed between the rotation prevention protrusion 49 and the rotation prevention hole 67, the ground plate 50 is connected to the flange member 40 during the rotation of the photosensitive drum 30. It can suppress moving within the range of the clearance gap G with respect to the attachment part 46 of this. As a result, inconveniences such as a flare of the photosensitive drum 30 and a color shift of the toner image can be suppressed. In FIG. 6, the gap G is exaggerated.

  Further, by using the return force of the pair of locking pieces 80, the rotation preventing projection 49 is simply inserted between the one free end portion 82 and the other free end portion 82 so that the rotation preventing projection 49 is prevented from being rotated. Since it is fixed to 67, the structure of the drum unit 20 is not complicated.

  Further, since the movement of the ground plate 50 with respect to the mounting portion 46 of the flange member 40 is suppressed, the state in which the claw portion 52 of the ground plate 50 properly contacts the metal tube 31 of the photosensitive drum 30 is maintained. can do. As a result, the photosensitive drum 30 is grounded smoothly.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Drum unit 30 Photosensitive drum 40 Flange member (support member)
42 Cylindrical boss (positioning protrusion)
48 Projection 49 Anti-rotation projection 50 Ground plate 51 Ground plate body 52 Claw portion 65 First positioning hole 66 Second positioning hole 67 Anti-rotation hole 70 Drum shaft 80 Locking piece (fixing member)
81 Base end portion 82 Free end portion 82a Tip

Claims (4)

A cylindrical photosensitive drum;
A drum shaft inserted through the photosensitive drum;
A support member that supports the photosensitive drum and the drum shaft so that the photosensitive drum rotates integrally with the drum shaft;
An earth plate that is attached to an attachment portion of the support member facing the inside of the photosensitive drum and electrically connects the photosensitive drum and the drum shaft;
With
The mounting portion of the support member is formed with a positioning projection for positioning the ground plate, and a rotation-preventing projection positioned around the positioning projection to prevent the ground plate from rotating,
The ground plate includes a positioning hole through which the positioning protrusion is inserted, a rotation prevention hole through which the rotation prevention protrusion is inserted, and an inclination extending from an edge of the rotation prevention hole toward the rotation prevention protrusion; A drum unit comprising: a fixing member that fixes the rotation-preventing protrusion to the rotation-preventing hole by an end portion coming into contact with the rotation-preventing protrusion. The drum unit according to claim 1, wherein the ground plate is attached to the attachment portion, and has a flexible ground plate main body having the positioning hole and the rotation preventing hole.
The fixing member is a pair of locking pieces formed by making a cut in the ground plate body,
Each locking piece has a base end connected to the ground plate body, and a free end that can be lifted with respect to the base end,
The free end portion of one locking piece and the free end portion of the other locking piece are opposed to each other,
The non-rotating projection is formed between the one free end in the lifted state and the other free end in the lifted state, and the one free end and the other free end are A drum unit that is sandwiched by a restoring force that attempts to return to the same level as the base end. The drum unit according to claim 2, wherein the ground plate main body has an outer peripheral portion set to a size that does not contact the inner peripheral surface of the photosensitive drum,
A drum unit in which the outer peripheral portion is provided with a claw portion protruding outward from the outer peripheral portion and contacting the inner peripheral surface of the photosensitive drum. A drum unit having a photosensitive drum on which a toner image is formed;
A developing device for supplying toner to the photosensitive drum to form the toner image on the photosensitive drum;
With
An image forming apparatus using the drum unit according to claim 1 as the drum unit.

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