JP2019056815A - Image forming apparatus - Google Patents

Abstract

To reduce periodic unevenness of image density caused by a curve of a cylindrical image holding body compared with a case where the pressing load of a charging roller is constant.SOLUTION: An image forming apparatus 10 comprises: a cylindrical photoreceptor 102 where the amplitude during rotation is larger at a center part than that of both ends; a charging roller 60 that is pressed against the photoreceptor 102 by a compression coil spring 514; a fluctuation mechanism 511 that fluctuates the pressing load of the charging roller 60 pressing the photoreceptor 102 in a period different from the rotational period of the photoreceptor 102; an exposure device 22 that forms an electrostatic latent image on the surface of the charged photoreceptor 102; a developing device 28 that develops the electrostatic latent image with a developer containing toner to form a toner image; and a transfer roller 24 that transfers the toner image to a recording medium P.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an image forming apparatus.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses a technique relating to a photoreceptor and an image forming apparatus used in an electrophotographic apparatus such as a copying machine or a printer. In this prior art, the photoreceptor is composed of a drum body and two flange members. The drum body is composed of a cylinder having fitting holes formed at both ends, and a photosensitive layer formed on the outer circumferential surface of the cylinder, and the center of the outer circumferential surface of the drum body is deviated from the center of the fitting hole. I have a heart. Each of the two flange members includes an annular plate portion and a bearing portion, and the center of the annular plate portion is eccentric with respect to the center of the bearing portion. The annular plate portion is press-fitted into the fitting hole and fixed so that the eccentric direction of the drum body and the eccentric direction of the two flange members are substantially the same direction.

JP 2002-365974 A

  The purpose is to suppress periodic unevenness of the image density due to the curvature of the cylindrical image carrier as compared to the case where the pressing load of the charging roll is constant.

  According to the first aspect of the present invention, a curved cylindrical image holding body in which a shake at the time of rotation is larger at the center portion than at both end portions, and the image holding body is pressed by the pressing means to charge the image holding body. An electrostatic latent image is formed on the surface of the charged image carrier, a charging roll, a fluctuating means that fluctuates a pressing load applied to the image carrier by the charging roll at a cycle different from the rotation cycle of the image carrier. An electrostatic latent image forming means for developing, a developing means for developing the electrostatic latent image formed on the surface of the photosensitive member with a developer containing toner to form a toner image, and transferring the toner image to the transfer target And an image forming apparatus.

  According to the second aspect of the present invention, a curved cylindrical image holding body in which a shake at the time of rotation is larger at the center than at both ends, and the image holding body is pressed by the pressing means to charge the image holding body. Fluctuation means for varying the distance between the charging roll and the circumferential surface of the image carrier with the rotation axis of the charging roll at a different period from the rotation period of the image carrier, and a static on the surface of the charged image carrier. An electrostatic latent image forming means for forming an electrostatic latent image; a developing means for developing the electrostatic latent image formed on the surface of the photosensitive member with a developer containing toner; and a toner image And an image forming apparatus including a transfer unit that transfers the image onto a transfer target.

  According to a third aspect of the present invention, the fluctuating unit has a fluctuating mechanism that fluctuates the pressing force of the pressing unit that presses the charging roll at a cycle different from the rotation cycle of the image carrier. The image forming apparatus described in the above.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the pressing means is a compression coil spring, and the variation mechanism is a cam mechanism that periodically changes the amount of compression of the compression coil spring. It is.

  According to a fifth aspect of the present invention, the fluctuating means has a pressing member that is pressed against the charging roll and whose pressing force varies at a period different from the rotation period of the image holding member. The image forming apparatus according to claim 1, wherein the pressing force of the charging roll varies as the force varies.

  A sixth aspect of the present invention is the image forming apparatus according to the fifth aspect, wherein the pressing member is a cleaning member having a function of cleaning the charging roll.

  A seventh aspect of the present invention is the image forming apparatus according to the fifth or sixth aspect, wherein the pressing member has a cylindrical shape having an eccentric rotation shaft.

  The invention of claim 8 includes the pressing member, and a rotating shaft, and a winding member wound around the rotating shaft in a spiral shape so that a circumferential position is different between one end and the other end. An image forming apparatus according to claim 5 or 6.

  According to a ninth aspect of the present invention, in the image formation according to any one of the first to eighth aspects, the period different from the rotational period of the image carrier is a period smaller than the rotational period of the image carrier. Device.

  A tenth aspect of the present invention is the image forming apparatus according to the ninth aspect, wherein the period smaller than the rotation period of the image carrier is a period other than an integral fraction of the rotation period of the image carrier.

  The invention according to claim 11 is a curved cylindrical image holding body in which a shake at the time of rotation is larger at the center than at both ends, and the image holding body is pressed by the pressing means to charge the image holding body. An image forming apparatus comprising: a charging roll; and a changing unit that changes a pressing load pressed by the charging roll against the image holding body in the same period and opposite phase as a rotation period of the image holding body.

  According to the invention of claim 12, a curved cylindrical image holding body in which a shake at the time of rotation is larger at the center portion than at both end portions, and the image holding body is pressed by the pressing means to charge the image holding body. An image forming apparatus comprising: a charging roll; and a varying unit that varies a distance between the rotation axis of the charging roll and the peripheral surface of the image holding body in the same cycle and in opposite phase as the rotation cycle of the image holding body. is there.

  According to a thirteenth aspect of the present invention, the fluctuating means has a fluctuating mechanism that fluctuates the pressing force of the pressing means that presses the charging roll in the same period and opposite phase as the rotation period of the image carrier. An image forming apparatus according to claim 12.

  14. The image forming apparatus according to claim 13, wherein the pressing means is a compression coil spring, and the variation mechanism is a cam mechanism that periodically changes the amount of compression of the compression coil spring. It is.

  According to a fifteenth aspect of the present invention, the fluctuating means has a pressing member that presses against the charging roll, and the pressing force fluctuates in the same period and opposite phase as the rotation period of the image carrier. 13. The image forming apparatus according to claim 11, wherein the pressing force of the charging roll varies due to variation in the pressing force.

  The invention according to claim 16 is the image forming apparatus according to claim 15, wherein the pressing member is a cleaning member having a function of cleaning the charging roll.

  The invention according to claim 17 is the image forming apparatus according to claim 15 or 16, wherein the pressing member has a cylindrical shape having an eccentric rotation shaft.

  In the invention of claim 18, the pressing member includes a rotating shaft, and a winding member wound around the rotating shaft in a spiral shape so that the circumferential position is different between one end and the other end. An image forming apparatus according to claim 15 or 16.

  A nineteenth aspect of the present invention is the image forming apparatus according to any one of the first to eighteenth aspects, wherein the image carrier has a deflection width of 20 μm or more at the center portion larger than the both end portions.

  According to the first aspect of the present invention, it is possible to suppress periodic unevenness of the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing load of the charging roll is constant.

  According to the second aspect of the present invention, as compared with the case where the distance between the rotation axis of the charging roll and the peripheral surface of the image carrier is constant, the image density is periodically generated due to the curvature of the cylindrical image carrier. Unevenness can be suppressed.

  According to the third aspect of the present invention, it is possible to suppress periodic unevenness in the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing force of the pressing means is constant.

  According to invention of Claim 4, compared with the case of a tension coil spring, the structure which fluctuates pressing force is simple.

  According to the fifth aspect of the present invention, it is possible to suppress periodic unevenness in the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing force of the pressing member is constant. .

  According to the sixth aspect of the present invention, the structure is simple as compared with the case where dedicated parts are used.

  According to the seventh aspect of the present invention, the structure for changing the pressing force is simple as compared with the case where the pressing member is non-cylindrical.

  According to invention of Claim 8, compared with the case where a winding member is helically wound so that the circumferential direction position may become the same at a rotating shaft at one end and the other end, it is a cylindrical image holding body. The periodic unevenness of the image density due to the curvature of the image can be suppressed.

  According to the ninth aspect of the present invention, the image density caused by the curvature of the cylindrical image carrier is different from the case where the cycle different from the rotation cycle of the image carrier is larger than the rotation cycle of the image carrier. Periodic unevenness can be suppressed.

  According to the tenth aspect of the present invention, the period different from the rotation period of the image carrier is 1 / integer of the rotation period of the image carrier, resulting from the curvature of the cylindrical image carrier. It is possible to suppress periodic unevenness in image density.

  According to the invention of the eleventh aspect, it is possible to suppress periodic unevenness of the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing load of the charging roll is constant.

  According to the twelfth aspect of the present invention, as compared with the case where the distance between the rotation axis of the charging roll and the peripheral surface of the image holding member is constant, the periodicity of the image density due to the curvature of the cylindrical image holding member. Unevenness can be suppressed.

  According to the thirteenth aspect of the present invention, it is possible to suppress periodic unevenness in the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing force of the pressing means is constant.

  According to the fourteenth aspect of the present invention, the mechanism for changing the pressing force is easier than in the case of the tension coil spring.

  According to the fifteenth aspect of the present invention, it is possible to suppress periodic unevenness in the image density due to the curvature of the cylindrical image carrier, as compared with the case where the pressing force of the pressing member is constant. .

  According to the sixteenth aspect of the present invention, the structure is simple as compared with the case of using a dedicated part.

  According to the seventeenth aspect of the present invention, the structure for changing the pressing force is simple as compared with the case where the pressing member is non-cylindrical.

  According to the eighteenth aspect of the present invention, compared to the case where the winding member is spirally wound around the rotating shaft so that the circumferential position is the same at one end and the other end, the cylindrical image carrier The periodic unevenness of the image density due to the curvature of the image can be suppressed.

  According to the nineteenth aspect of the present invention, in an image carrier having a deflection width of 20 μm or more at the center portion larger than both end portions, the cylindrical image carrier is curved as compared with the case where the pressing load of the charging roll is constant. It is possible to suppress periodic unevenness in image density due to the above.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment. It is the schematic which shows the structure of a process cartridge. (A), (B), and (C) are process diagrams of a manufacturing process of a substrate of a photoreceptor. (A) (B) is process drawing of the manufacturing process of the base material of a photoreceptor. It is the perspective view which showed the punch type | mold and ironing type | mold used for the ironing process of the manufacturing process of the base material of a photoreceptor. (A), (B), and (C) are process diagrams of a manufacturing process of a substrate of a photoreceptor. (A), (B), and (C) are process diagrams of a manufacturing process of a substrate of a photoreceptor. (A), (B), and (C) are process diagrams of a manufacturing process of a substrate of a photoreceptor. (A) is the side view seen from the rotating shaft direction of the attachment part of the image forming apparatus of 1st embodiment, (B) is a perspective view. FIG. 2 is a configuration diagram schematically showing a cross-section along a rotation axis direction of a main part of the image forming apparatus of the first embodiment and a cam drive mechanism. It is the side view seen from the rotation axis direction of the attaching part of the image forming apparatus of a first embodiment, and a change mechanism. (A) is explanatory drawing explaining the concave phase state where the side where the charging roll contacts in the photoconductor is concave, and (B) is explanatory drawing explaining the convex phase state where the side where the charging roll contacts in the photoconductor is convex. It is. FIG. 6 is an explanatory diagram for explaining a periodic change in image density caused by the curvature of a photoreceptor in an image forming apparatus of a comparative example. It is a graph for demonstrating that the change of the image density in 1st embodiment is aperiodic. It is the side view seen from the direction of a rotation axis of the attachment part of the image forming device of a second embodiment. (A) is the front view which looked at the cleaning member of the image forming apparatus of 2nd embodiment from the direction orthogonal to a rotating shaft direction, (B) is the side view seen from the rotating shaft direction. 10 is a graph for explaining a periodic change in a pressing force with which a cleaning member of an image forming apparatus according to a second embodiment presses against a charging member. It is the side view which looked at the attachment part of the image forming apparatus of 3rd embodiment from the rotating shaft direction. (A) is a perspective view of the cleaning member of the image forming apparatus of the third embodiment, and (B) is a side view seen from the direction of the rotation axis. 10 is a graph for explaining a periodic change in pressing force with which a cleaning member of an image forming apparatus according to a third embodiment presses against a charging member. FIG. 10 is a side view of an attachment portion of an image forming apparatus according to a fifth embodiment viewed from the direction of the rotation axis and a configuration diagram illustrating a cleaning member drive mechanism. It is the side view which looked at the attachment part of the image forming apparatus of 6th Embodiment from the rotating shaft direction, and the block diagram which shows the cleaning member drive mechanism. It is the front view which looked at the principal part of the image forming device of other embodiments from the direction orthogonal to the direction of a rotation axis.

<First embodiment>
An image forming apparatus according to a first embodiment of the present invention will be described.

[Image forming apparatus]
First, the configuration of the image forming apparatus 10 according to the present embodiment will be described.

  As shown in FIG. 1, the image forming apparatus 10 includes a storage unit 32 that stores a recording medium P such as paper as an example of a transfer target, an image forming unit 14 that forms an image on the recording medium P, and an image. A fixing device 36 that fixes an image formed on the recording medium P by the forming unit 14 to the recording medium P, and a transport unit 16 that transports the recording medium P from the storage unit 32 to the image forming unit 14 are provided.

  The image forming unit 14 has a function of forming an image on the recording medium P using a developer containing toner. Specifically, the image forming unit 14 includes a drum-shaped photoconductor 102 as an example of an image holding body that holds an image (latent image). The photoreceptor 102 will be described later.

  The photoconductor 102 rotates in one direction (arrow A direction). Around the photoreceptor 102, in order from the upstream side in the rotation direction of the photoreceptor 102, a charging roll 60 as an example of a charging unit, an exposure device 22 as an example of an electrostatic latent image forming unit, and an example of a developing unit The developing device 28, a transfer roll 24 as an example of a transfer unit, and a removing unit 30 are provided.

  The charging roll 60 has a function of charging the photoconductor 102. The exposure device 22 has a function of exposing the photosensitive member 102 charged by the charging roll 60 to form an electrostatic latent image on the photosensitive member 102.

  A roll-shaped cleaning member 70 that contacts and cleans the surface of the charging roll 60 is provided at an upper portion of the charging roll 60 opposite to the photoconductor 102. The charging roll 60 and the cleaning member 70 will be described later.

  The developing device 28 has a function of developing the electrostatic latent image formed on the photoconductor 102 by the exposure device 22 with toner to form a toner image.

  The transfer roll 24 has a function of transferring the toner image formed on the photoreceptor 102 by the developing device 28 to the recording medium P.

  The removing unit 30 has a function of removing the toner remaining on the surface of the photoconductor 102 after the transfer. Specifically, the removing unit 30 is in contact with the surface of the photosensitive member 102 and has a blade 30A as a removing member that removes (scraps) the toner, and a storage unit 30B that stores the toner removed by the blade 30A. ,have.

  The transport unit 16 is provided along the transport path 35 and is transported along the transport path 35 for transporting the recording medium P transported by the transport roll 33, the transport roll 35 for transporting the recording medium P stored in the storage section 32. A plurality of conveyance roll pairs 34 that convey the recording medium P sent out by the roll 33 to between the photosensitive member 102 and the transfer roll 24 are provided.

  In the fixing device 36, the toner image transferred to the recording medium P by the transfer roll 24 is fixed to the recording medium P by heating and pressurizing the recording medium P.

Further, as shown in FIG. 2, the process cartridge 18 includes a transport device 50 that transports the toner removed by the removing unit 30, and a waste toner box as a storage unit that stores the toner transported by the transport device 50. 42 are provided.

  Inside the waste toner box 42, a transport body 46 that transports toner is provided. The conveyance body 46 includes a shaft portion 46A and a blade 46B formed in a spiral shape around the shaft portion 46A on the outer peripheral surface of the shaft portion 46A. In the transport body 46, the shaft portion 46A rotates, so that the blades 46B transport the toner in the axial direction and radial direction of the shaft portion 46A (see arrow E in FIG. 2). As shown in FIGS. 1 and 2, the image forming apparatus 10 includes a process cartridge 18 that is detachably provided on the image forming apparatus main body 11 (see FIG. 1). The process cartridge 18 of the present embodiment is provided with a photoreceptor 102, a charging roll 60, a developing device 28, and a removing unit 30.

  Further, the process cartridge 18 is provided with a toner cartridge 40 that stores toner supplied to the developing device 28.

  As shown in FIG. 2, the process cartridge 18 is provided with a transport device 50 that transports the toner removed by the removing unit 30 and a waste toner box 42 that stores the waste toner transported by the transport device 50. ing. The waste toner box 42 is disposed on the opposite side in the X direction from the removing unit 30 with the developing device 28 interposed therebetween.

  The transport device 50 includes a transport path 59 and a transport member 56. The conveyance path 59 is a path through which waste toner is conveyed from the storage unit 30 </ b> B of the removal unit 30 to the waste toner box 42. The conveyance member 56 is provided in the conveyance path 59 and has blades formed in a spiral shape around an axis of a shaft portion (not shown). Then, the conveyance member 56 is rotated by a driving unit (not shown), whereby the waste toner is conveyed from the storage unit 30B of the removal unit 30 to the waste toner box 42.

[Photoconductor]
Next, the photoconductor 102 will be described.

  1 and 2 includes a cylindrical base member 104 shown in FIG. 8C and a photosensitive layer (not shown) formed on the outer peripheral surface 104A of the base member 104. The photosensitive member 102 shown in FIG. Yes. The photosensitive layer includes a base layer (undercoat layer) formed on the outer peripheral surface 104A of the substrate 104, a protective layer (overcoat layer) formed on the surface, and the like.

(Manufacturing method of substrate)
Next, an example of the manufacturing process of the base material 104 will be described. As indicated by an arrow H in each figure, this direction is constant from the first step (FIG. 3A) to the last step (FIG. 9). In this embodiment, the H direction is the vertical direction. It is the upper side.

  The base material 104 is manufactured including impact processing for forming a cylindrical cylindrical material 206 (see FIG. 4) and ironing processing for correcting the cylindrical material 206 to form the base material 104 (see FIG. 8). The

-Impact processing-
As shown in FIGS. 3 and 4, in the impact processing, a cylindrical cylindrical material 206 having a bottom portion 205 on one side is formed from a slag 202 that is a lump of aluminum.

  As shown in FIG. 3A, for impact processing, a concave mold 204 in which a slag 202, which is an aluminum lump as an example of a metal lump, is stored, and a slag 202 accommodated in the concave mold 204 is pressed to form a slag. A columnar punch die 200 as an example of a first columnar shape for making 202 a cylindrical shape is used. The concave portion 204A of the concave mold 204 is circular, and the inner diameter of the concave portion 204A is 32.0 mm as an example. As an example, the outer diameter of the punch die 200 is 30.6 mm.

  As shown in FIG. 3A, in the impact process, first, the slag 202 is accommodated in the concave mold 204, and the punch mold 200 is further disposed above the concave mold 204.

  Next, as shown in FIGS. 3B and 3C, the punch die 200 moves downward and crushes and deforms the slag 202 accommodated in the concave die 204. As a result, the slag 202 is deformed along the peripheral surface of the punch die 200, and a cylindrical material 206 (see FIG. 3C) having a bottom portion 205 on the lower side is formed. As an example, the cylindrical material 206 has a thickness of 0.7 mm and an inner diameter of 30.6 mm.

  Next, as shown in FIG. 4A, the punch die 200 moves upward, and the cylindrical material 206 that is in close contact with the punch die 200 is separated from the concave die 204.

  Further, as shown in FIG. 4B, the cylindrical material 206 is pulled out (demolded) from the punch die 200.

-Ironing process-
In the ironing process, the thickness of the cylindrical material 206 is reduced to correct the shape of the cylindrical material 206.

  As shown in FIG. 5, for ironing, a punch die 220 as an example of a second columnar shape inserted into the cylindrical material 206 (see FIG. 4B) from the tip (lower end in the drawing), and the cylindrical material An annular mold 222 is used in which the inner peripheral surface 206A of 206 (see FIG. 4B) is copied to the outer peripheral surface 220A of the punch mold 220.

  The punch die 220 has a cylindrical shape extending in the vertical direction (one direction). As an example, the outer diameter of the punch die 220 is 29.2 mm. In addition, the annular shape 222 is an annular shape, and as an example, the inner diameter is 30.0 mm.

  As shown in FIG. 6A, in the ironing process, first, the punch die 220 is inserted into the cylindrical member 206 from the tip. 6A, 6B, 6C, 7A, and 7B, the outer peripheral surface 220A of the punch die 220 and the inner peripheral surface of the cylindrical material 206 are shown. Illustration of the gap with 206A is omitted.

  Next, as shown in FIG. 6B, FIG. 6C, FIG. 7A, FIG. 7B and FIG. From the position moved above the ring shape 222, it is moved downward to pass through the inside of the ring shape 222. As a result, the annular mold 222 presses the cylindrical material 206 against the punch mold 220, thereby reducing the thickness of the cylindrical material 206. Further, the inner peripheral surface 206 A of the cylindrical material 206 is brought into contact with the outer peripheral surface 220 A of the punch mold 220. follow.

  As shown in FIGS. 8A and 8B, the cylindrical material 206 is pulled out (demolded) from the punch mold 220.

-Resection process-
In the cutting step, the lower end portion 207 including the bottom portion 205 of the cylindrical material 206 is cut, and the cylindrical base material 104 having both ends opened is formed as shown in FIG. 8C.

  The lower end portion 207 including the bottom portion 205 of the cylindrical material 206 is cut out, and as shown in FIG. 8C, the cylindrical base material 104 having both ends opened is formed.

(Shape of substrate and photoreceptor)
Next, the shapes of the base material 104 and the photoreceptor 102 will be described.

  The base material 104 shown in FIG. 8C has a curved cylindrical shape in which the deflection at the time of rotation is larger in the central portion 112 than in the both end portions 110. The difference in the swing width is 20 μm (straightness: 10 μm) or more, and the swing width in the present embodiment is 30 μm. The reason why the substrate 104 has a curved shape in which the deflection during rotation of the substrate 104 is larger at the center than at both ends is mainly due to misalignment during impact machining and ironing.

  As shown in FIG. 12, the photosensitive member 102 in which the photosensitive layer is formed on the outer peripheral surface 104 </ b> A of the base material 104 has a curved cylindrical shape in which the center portion 112 has a larger runout during rotation than the both end portions 110. The center portion 112 swings more greatly than the both end portions 110 because it is fitted to the opening end portions of the both end portions 110 of the photosensitive member 102 (base material 104) and is centered by a flange (not shown) through which the rotating shaft 103 passes. . Note that the photosensitive member 102 in FIG. 12 is illustrated to be extremely curved compared to the actual case for easy understanding.

[Support structure for charging roll and cleaning member]
Next, a support structure for the charging roll 60 and the cleaning member 70 will be described.

  As shown in FIG. 9, the charging roll 60 has a conductive layer 64 formed around a conductive rotating shaft 62, and both ends of the rotating shaft 62 are rotatably supported by a pair of bearing members 300. (See also FIG. 10).

  A cylindrical cleaning member 70 that contacts and cleans the surface of the charging roll 60 is provided on the opposite side of the charging roll 60 to the photoreceptor 102 (see also FIGS. 1 and 2). The cleaning member 70 has a sponge layer 74 formed around the rotating shaft 72, and both end portions of the rotating shaft 72 are also rotatably supported by the bearing member 300 described above (see also FIG. 10). .

  As described above, the charging roll 60 and the cleaning member 70 are rotatably supported by the bearing member 300 at both ends of the rotation shafts 62 and 72 (see also FIG. 10).

  In each figure, the cleaning member 70 is illustrated as being in contact with the charging roll 60, but actually, the cleaning member 70 is applied with pressure against the charging roll 60.

  Further, as shown in FIG. 12, the charging roll 60 has a shape in which the central portion swells from both end portions in the axial direction. Note that, in the charging roll 60 of FIG. 12, the swelling of the central portion is illustrated larger than the actual size for easy understanding.

  As shown in FIG. 10, the photosensitive member 102, the charging roll 60, and the cleaning member 70 are assembled to a frame 500 that constitutes the process cartridge 18 (see FIG. 2). The photosensitive member 102 has a rotating shaft 103 passing therethrough, and a shaft end portion 103 </ b> A is rotatably inserted into the bearing hole 502.

  As shown in FIGS. 10 and 11, attachment portions 510 to which the bearing member 300 is attached are integrally provided at both end portions in the axial direction of the charging roll 60 and the cleaning member 70 in the frame 500. The guide grooves 512 are formed in both of the attachment portions 510, and the bearing member 300 is disposed in the guide grooves 512. The bearing member 300 is guided by the guide groove 512 and slides along the contact / separation direction indicated by the arrow R (hereinafter referred to as “contact / separation direction R”) with respect to the photoreceptor 102.

  A compression coil spring 514 that biases the bearing member 300 toward the photosensitive member 102 is provided in the guide groove 512. The bearing member 300 is biased toward the photosensitive member 102 by the spring force of the compression coil spring 514, and the charging roll 60 is pressed against the photosensitive member 102.

  As shown in FIGS. 9 and 11, the photosensitive member 102 is rotationally driven in a direction indicated by an arrow K1 in the drawing by a driving mechanism (not shown). The charging roller 60 is driven to rotate in the direction of the arrow K2 by the rotation of the photosensitive member 102, and the cleaning member 70 is driven to rotate in the direction of the arrow K3 by the rotation of the charging roller 60.

  As the cleaning member 70 is driven to rotate, foreign matters such as toner and external additives attached to the surface of the charging roll 60 are cleaned by the sponge layer 74 of the cleaning member 70.

[Variation mechanism]
Next, the fluctuation mechanism 511 that periodically reciprocates the bearing member 300 along the guide groove 512 will be described.

  10 and 11, the bearing member 300 periodically reciprocates in the guide groove 512 in a direction in which the bearing member 300 contacts and separates from the photosensitive member 102. As will be described later, the reciprocating movement of the shaft member 300 is a minute displacement.

  The fluctuation mechanism 511 includes a spring receiving member 516 and a cam mechanism 520. The spring receiving member 516 is provided on the opposite side to the bearing member 300 side with respect to the compression coil spring 514 in the guide groove 512.

  The cam mechanism 520 has a cam disc 522 and a cam rotation shaft 524. The cam rotation shaft 524 is provided at a position away from the circle center of the cam disk 522 and is eccentric. The cam rotation shaft 524 is rotated by a cam drive mechanism 526 (see FIG. 10) provided in the image forming apparatus main body 11 (see FIG. 1). When the process cartridge 18 (see FIG. 2) is attached to the image forming apparatus main body 11 (see FIG. 1), the cam drive mechanism 526 (see FIG. 10) is engaged with a gear (not shown) provided on the cam rotation shaft 524. It has become.

  When the cam rotation shaft 524 rotates, the cam disk 522 rotates, and the spring receiving member 516 periodically reciprocates in the guide groove 512 in the contact / separation direction R. As a result, the compression amount (length of the compressed state) of the compression coil spring 514 periodically changes, and the urging force (spring force) that urges the bearing member 300 toward the photosensitive member 102 side periodically changes. . Then, the urging force (spring force) that urges the bearing member 300 toward the photosensitive member 102 periodically changes, whereby the pressing load that the charging roll 60 presses against the photosensitive member 102 changes periodically.

  From another viewpoint, the urging force (spring force) that urges the bearing member 300 toward the photosensitive member 102 periodically changes, so that the bearing member 300, that is, the rotating shaft 62 of the charging roll 60 is brought into contact. Periodically reciprocates in the separation direction R. That is, the distance L (see FIG. 11) between the rotating shaft 62 (the axis center) of the charging roll 60 and the peripheral surface 102B of the photosensitive member 102 periodically changes. Note that the amount of reciprocation, that is, the amount of change in the distance L is a minute displacement because the eccentricity of the cam disk 522 is absorbed by the increase in the amount of compression of the compression coil spring 514.

  The charging roll 60 presses against the photoconductor 102 in conjunction with the rotation cycle of the cam disk 522 of the cam mechanism 520 of the changing mechanism 511 (the change cycle of the biasing force with which the bearing member 300 is biased toward the photoconductor 102). The period of change of the pressing load and the period of change of the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photosensitive member 102 are different from the rotational cycle of the photosensitive member 102.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Shorter period. Further, the cycle is a cycle other than an integral fraction of the rotation cycle of the photoconductor 102.

<Action>
Next, the operation of this embodiment will be described.

  First, an image of a comparative example that does not have a variation mechanism 511 in which the pressing load that the charging roll 60 presses against the photoconductor 102 is constant and the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 is constant. The forming apparatus will be described.

  As shown in FIG. 12, as described above, the photosensitive member 102 has a curved cylindrical shape in which the center portion 112 has a larger runout during rotation than the both end portions 110 for the reason of manufacturing the base material 104.

  In this case, as the photosensitive member 102 rotates, the side where the charging roll 60 comes into contact as shown in FIG. 12A and the side where the charging roll 60 comes into contact as shown in FIG. A convex convex phase state appears in the rotation period of the photoconductor 102.

  12A is in a concave phase state, the nip width of the charging roll 60 is such that both end portions 110 are wide and the central portion 112 is narrow, and the surface potential of the central portion 112 is lowered. When the photosensitive member 102 in FIG. 12B is in a convex phase state, the nip width of the charging roll 60 is such that the central portion 112 is wide and the both end portions 110 are narrow, and the surface potential of the both end portions 110 is lowered. In FIG. 12, there is a gap between the charging roller 60 at both end portions 110 or the central portion 112 of the photoconductor 102, but no gap is actually generated.

  Then, due to the uneven charging of the photosensitive member 102 in the axial direction caused by the uneven nip in the axial direction of the charging roll 60, the density of the image formed on the recording medium P as shown in FIG. Unevenness occurs. Specifically, when the photoconductor 102 is in the concave phase state (FIG. 12A), the density of the central portion 112 is high (hereinafter referred to as “central high density portion CN”), and the photoconductor 102 is in the convex phase. In the case of the state (FIG. 12B), the concentration at both ends 110 is high (hereinafter referred to as “end high concentration portion HN”).

  The central high density portion CN and the end high density portion HN are generated in the rotation cycle S of the photoconductor 102, respectively. Such periodic density changes are easily noticeable visually.

  The central high concentration portion CN and the end high concentration portion HN are not necessarily generated. In some cases, only one of the central high concentration portion CN and the end high concentration portion HN is generated. Further, the end high concentration portion HN may be generated at both ends, or only one of the ends may be generated.

  In addition, since the charging roll 60 of the present embodiment has a shape in which the central portion is swollen rather than both end portions in the axial direction, the end high concentration portion HN (FIG. 12B) is more likely to occur.

  On the other hand, in the image forming apparatus 10 of the present embodiment, the period of change in the pressing load that the charging roll 60 presses against the photoreceptor 102 and the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoreceptor 102 The period of the change is a period different from the rotation period of the photoconductor 102, is shorter than the rotation period of the photoconductor 102, and is a period other than an integer.

  Here, FIG. 14 shows a shake change caused by the curvature of the photosensitive member 102, a change in the pressing load of the charging roll 60, and a shake caused by the periodic displacement of the rotating shaft 62 (change in the distance L). 6 is a graph conceptually showing the relationship between the resulting change in image density. The center of the vertical axis of the graph is 0 point. Further, it does not specifically represent the density change of the central high density portion CN and the end high density portion HN described above, but as described above, the density caused by the cycle of the photosensitive member 102 and the cycle of the charging roll 60. It is the graph which represents the change of No. conceptually.

  As shown in FIG. 14, the change in image density due to the shake of both the photoconductor 102 and the charging roll 60 represented by the solid line, that is, the density unevenness of the image deviates from the rotation cycle of the photoconductor 102 and is non-periodically. The image density changes.

  As described above, when the density unevenness of the image is generated periodically, it is easily noticeable visually, but the non-periodic density unevenness is not easily noticeable visually. Therefore, as compared with the periodic density unevenness as in the comparative example, the density unevenness of the present embodiment is less noticeable visually, and the density unevenness is suppressed.

  As described above, the period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are as follows. Since the cycle is different from the rotation cycle, the density unevenness is less noticeable visually, and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Since the cycle is shorter than that in the case where the rotation period of the photosensitive member 102 is longer, the density unevenness is less noticeable visually and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Therefore, the density unevenness is less noticeable visually than in the case of a 1 / integer, and the density unevenness is suppressed.

<Second embodiment>
Next, an image forming apparatus according to a second embodiment of the present invention will be described. In addition, the same member as 1st embodiment attaches | subjects the same code | symbol, and the overlapping description is abbreviate | omitted or simplified. The present embodiment is different from the first embodiment in the support structure for the charging roll and the cleaning member, and the other structures are the same.

[Support structure for charging roll and cleaning member]
Next, a support structure for the charging roll 60 and the cleaning member 170 of the image forming apparatus 13 of this embodiment will be described.

  The main difference from the first embodiment is that the fluctuation mechanism 511 (see FIG. 11) is not provided and the rotation shaft 172 of the cleaning member 170 is eccentric as will be described later. .

  As shown in FIGS. 15 and 16, the cylindrical cleaning member 170 has a sponge layer 174 formed around the rotating shaft 172. The rotating shaft 172 is offset from the center of the circle of the circular sponge layer 174 of the cleaning member 170 and is eccentric. The columnar cleaning member 70 (see FIG. 9 and the like) of the first embodiment has the same structure except that the rotating shaft 172 is eccentric.

  As shown in FIG. 15, both end portions of the rotating shafts 62 and 172 of the charging roll 60 and the cleaning member 170 are rotatably supported by the bearing member 300.

  A guide groove 512 is formed in the attachment portion 513 of the frame 500 (see FIG. 10). The bearing member 300 is provided in the guide groove 512, is guided by the guide groove 512, and slides along the contact / separation direction R indicated by the arrow R with respect to the photoreceptor 102.

  A compression coil spring 514 that biases the bearing member 300 toward the photosensitive member 102 is provided in the guide groove 512. As described above, in this embodiment, since the fluctuation mechanism 511 (see FIG. 11) is not provided, the cam disk 522 and the spring receiving member 516 are not provided in the guide groove 512 (see FIG. 11). . Therefore, the compression coil spring 514 is configured to contact the end portion 515 of the attachment portion 513. The bearing member 300 is biased toward the photosensitive member 102 by the spring force of the compression coil spring 514, and the charging roll 60 is pressed against the photosensitive member 102.

  The photosensitive member 102 is rotationally driven in the direction of an arrow K1 in the drawing by a driving mechanism (not shown), and the charging roller 60 is driven to rotate in the direction of the arrow K2 by the rotation of the photosensitive member 102, and the cleaning member is rotated by the rotation of the charging roller 60. 170 rotates following the direction of arrow K3. As the cleaning member 70 is driven to rotate, foreign matters such as toner and external additives attached to the surface of the charging roll 60 are cleaned by the sponge layer 174 of the cleaning member 170.

  As the cleaning member 170 is driven to rotate, when the thick layer portion 174A (see also FIG. 16) of the sponge layer 174 is in contact with the charging roll 60, the pressing force against the charging roll 60 increases. When the thin thin layer portion 174B of 174 (see also FIG. 16) is in contact with the charging roll 60, the pressing force that presses against the charging roll 60 is reduced. That is, as shown in FIG. 17, the pressing force that presses against the charging roll 60 of the cleaning member 170 periodically changes.

  Here, the charging roll 60 is bent by the pressing force with which the cleaning member 170 is pressed against the charging roll 60. When the pressing force with which the cleaning member 170 presses against the charging roll 60 increases, the bending of the charging roll 60 increases. Then, as the deflection of the charging roll 60 increases, the pressing load that presses against the photosensitive member 102 increases. On the other hand, when the pressing force with which the cleaning member 170 is pressed against the charging roll 60 is reduced, the bending of the charging roll 60 is reduced, and the pressing load pressed against the photoconductor 102 is reduced.

  Further, the circumferential length of the cleaning member 170 is shorter than the circumferential length of the photosensitive member 102 and is other than an integer. Therefore, the period of change in the pressing force with which the cleaning member 170 presses against the charging roll 60, that is, the period of change in the pressing load with which the charging roll 60 presses against the photoconductor 102 is shorter than the rotation period of the photoconductor 102. Become. Further, the cycle is a cycle other than an integral number of the rotation cycle of the photoconductor 102.

<Action>
Next, the operation of this embodiment will be described.

  In the image forming apparatus 13 of the present embodiment, the period of change in the pressing force with which the cleaning member 170 presses against the charging roll 60, that is, the period of change in the pressing load with which the charging roll 60 presses against the photoconductor 102 is the photoconductor 102. , And a cycle shorter than the rotation cycle of the photoconductor 102, and a cycle other than an integer.

  Therefore, as in the first embodiment, as shown in FIG. 14, the change in the image density deviates from the rotation cycle of the photoconductor 102, changes aperiodically, and the density density also fluctuates. As described above, when the density unevenness of the image is generated periodically, it is easily noticeable visually, but the non-periodic density unevenness is not easily noticeable visually. Therefore, as compared with the periodic density unevenness as in the comparative example (see FIG. 13), the density unevenness of the present embodiment is less noticeable and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Since the cycle is shorter than that in the case where the rotation period of the photosensitive member 102 is longer, the density unevenness is less noticeable visually and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Therefore, the density unevenness is less noticeable visually than in the case of a 1 / integer, and the density unevenness is suppressed.

<Third embodiment>
Next, an image forming apparatus according to a third embodiment of the present invention will be described. In addition, the same member as 1st embodiment and 2nd embodiment attaches | subjects the same code | symbol, and the overlapping description is abbreviate | omitted or simplified. Moreover, this embodiment differs in structure of the cleaning member from 2nd embodiment, and others are the same.

[Support structure for charging roll and cleaning member]
Next, a support structure for the charging roll 60 and the cleaning member 270 of the image forming apparatus 15 will be described. As described above, the structure of the cleaning member 270 is the main difference from the second embodiment.

  As shown in FIGS. 18 and 19, the cleaning member 270 has a structure in which a winding member 274 made of a strip-like sponge is wound around the rotating shaft 272 in a spiral shape with an interval in the axial direction and adhered with an adhesive or the like. It is. Further, the winding member 274 is wound such that one end (start point) 274A and the other end (end point) 274B have different circumferential positions (phases).

  As shown in FIG. 18, both end portions of the rotating shafts 62 and 272 of the charging roll 60 and the cleaning member 270 are rotatably supported by the bearing member 300.

  The photosensitive member 102 is rotationally driven in the direction of an arrow K1 in the drawing by a driving mechanism (not shown), and the charging roller 60 is driven to rotate in the direction of the arrow K2 by the rotation of the photosensitive member 102, and the cleaning member is rotated by the rotation of the charging roller 60. 270 rotates following the direction of arrow K3. When the cleaning member 270 is driven to rotate, foreign matters such as toner and external additives attached to the surface of the charging roll 60 are cleaned by the winding member 274 of the cleaning member 270.

  Here, as described above, the cleaning member 270 is wound such that one end (start point) 274A and the other end (end point) 274B of the winding member 274 have different circumferential positions (phases) (see also FIG. 18). ). Therefore, when the cleaning member 270 is driven to rotate, the number of windings in which the winding member 274 is pressed against (contacts) the charging roll 60 changes.

  Specifically, as shown in FIG. 19 (A), the number of turns for three quarters is seven and the number of turns for six quarters is six. When the winding member 274 of the cleaning member 270 has seven winding portions in contact with the charging roll 60, the pressing force against the charging roll 60 is increased, and the winding number of the winding member 274 is increased. When the 6-roll portion of 6 turns comes into contact with the charging roll 60, the pressing force against the charging roll 60 is reduced. That is, as shown in FIG. 20, the pressing force that presses against the charging roll 60 of the cleaning member 270 periodically changes.

  When the pressing force of the cleaning member 270 that presses against the charging roll 60 increases, the charging roll 60 bends more and the pressing load that presses against the photoconductor 102 increases. On the other hand, when the pressing force of the cleaning member 270 that presses against the charging roll 60 is reduced, the bending of the charging roll 60 is reduced and the pressing load that is pressed against the photosensitive member 102 is reduced.

  Note that FIG. 20 described above is a graph schematically showing a change in the pressing force of the cleaning member 270, and the change in the pressing load that the charging roll 60 presses against the photoconductor 102 is the same.

  The period of change in the pressing force with which the cleaning member 270 presses against the charging roll 60, that is, the period of change in the pressing load with which the charging roll 60 presses against the photoconductor 102 is shorter than the rotation period of the photoconductor 102. It has become. Further, the cycle is a cycle other than an integral fraction of the rotation cycle of the photoconductor 102.

<Action>
Next, the operation of this embodiment will be described.

  In the image forming apparatus 15 of the present embodiment, the period of change in the pressing force with which the cleaning member 270 presses against the charging roll 60, that is, the period of change in the pressing load with which the charging roll 60 presses against the photoconductor 102 is the photoconductor 102. , And a cycle shorter than the rotation cycle of the photoconductor 102, and a cycle other than an integer.

  Therefore, as in the first embodiment, as shown in FIG. 14, the change in the image density deviates from the rotation cycle of the photoconductor 102, changes aperiodically, and the density density also fluctuates. As described above, when the density unevenness of the image is generated periodically, it is easily noticeable visually, but the non-periodic density unevenness is not easily noticeable visually. Therefore, compared with the periodic density unevenness as in the comparative example (FIG. 13), the density unevenness of the present embodiment is less noticeable, and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Since the cycle is shorter than that in the case where the rotation period of the photosensitive member 102 is longer, the density unevenness is less noticeable visually and the density unevenness is suppressed.

  The period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 and the period of change in the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102 are the rotation period of the photoconductor 102. Therefore, the density unevenness is less noticeable visually than in the case of a 1 / integer, and the density unevenness is suppressed.

<Fourth embodiment>
Next, an image forming apparatus according to a fourth embodiment of the present invention will be described. In addition, the same member as 1st embodiment-3rd embodiment attaches | subjects the same code | symbol, and the overlapping description is abbreviate | omitted or simplified. Further, this embodiment is different from the first embodiment in the rotation period of the cam disk 522 by the cam drive mechanism 526 (see FIG. 10) of the fluctuation mechanism 511 (FIGS. 10 and 11).

[Variation mechanism]
The rotation period of the cam disk 522 of the cam mechanism 520 of the fluctuation mechanism 511 of the present embodiment, that is, the period of change in the pressing load that the charging roll 60 presses against the photosensitive member 102 and the rotation of the photosensitive member 102 of the rotating shaft 62 of the charging roll 60. The cycle of the change in the distance L with respect to the peripheral surface 102B is the same cycle as the rotation cycle of the photoconductor 102 and has an opposite phase.

  When the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load is large, and the side where the charging roll 60 contacts as shown in FIG. 12B is convex. In the convex phase state, the pressing load is configured to be small.

<Action>
Next, the operation of this embodiment will be described.

  As described above, in the image forming apparatus of the present embodiment, the period of change in the pressing load that the charging roll 60 presses against the photoconductor 102 and the distance L between the rotating shaft 62 of the charging roll 60 and the peripheral surface 102B of the photoconductor 102. The period of the change is the same as the rotation period of the photoconductor 102 and has an opposite phase. When the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load is large, and the side where the charging roll 60 contacts as shown in FIG. In the convex phase state, the pressure load is configured to be small.

  Therefore, the periodic unevenness of the image density due to the curvature of the photoconductor 102, that is, the central high density portion CN and the end high density portion HN as shown in FIG. 13 are suppressed.

<Fifth embodiment>
Next, an image forming apparatus according to a fifth embodiment of the present invention will be described. In addition, the same member as 1st embodiment-4th embodiment attaches | subjects the same code | symbol, and the overlapping description is abbreviate | omitted or simplified. Further, in the present embodiment, the cleaning member 170 is not driven to rotate but is rotated by the cleaning member drive mechanism 600 in the second embodiment.

[Cleaning member drive mechanism]
As shown in FIG. 21, the image forming apparatus 17 of the present embodiment has a cleaning member drive mechanism 600. The cleaning member drive mechanism 600 is provided in the image forming apparatus main body 11 (see FIG. 1). Then, the rotation shaft 172 of the cleaning member 170 is rotated by the cleaning member drive mechanism 600. When the process cartridge 18 (see FIG. 2) is mounted on the image forming apparatus main body 11 (see FIG. 1), the cleaning member drive mechanism 600 is engaged with a gear (not shown) provided on the rotation shaft 172. Yes.

  The rotation cycle of the cleaning member 170 is the same cycle as the rotation cycle of the photoconductor 102 and has an opposite phase. Therefore, the period of the change in the pressing force with which the cleaning member 170 presses against the charging roll 60 (the change in the amount of bending of the charging roll 60), that is, the period of the change in the pressing load that the charging roll 60 presses against the photoconductor 102 is The rotation period of the photosensitive member 102 is the same as that of the photosensitive member 102 and has an opposite phase.

  When the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load is large, and the side where the charging roll 60 contacts as shown in FIG. 12B is convex. In the convex phase state, the pressing load is configured to be small.

<Action>
Next, the operation of this embodiment will be described.

  As described above, in the image forming apparatus 17 of the present embodiment, the period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 is the same as the rotation period of the photoconductor 102 and has an opposite phase. . When the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load is large, and the side where the charging roll 60 contacts as shown in FIG. In the convex phase state, the pressure load is configured to be small.

  Therefore, the periodic unevenness of the image density due to the curvature of the photoconductor 102, that is, the central high density portion CN and the end high density portion HN as shown in FIG. 13 are suppressed.

<Sixth embodiment>
Next, an image forming apparatus according to a sixth embodiment of the present invention will be described. In addition, the same member as 1st embodiment-5th embodiment attaches | subjects the same code | symbol, and the overlapping description is abbreviate | omitted or simplified. Further, the present embodiment is different from the third embodiment in that the cleaning member 270 is not driven and rotated but is rotated by the cleaning member drive mechanism 600, and the structure of the cleaning member is different from the fifth embodiment. Others are the same.

[Cleaning member drive mechanism]
As shown in FIG. 22, in the image forming apparatus 19 of the present embodiment, the rotation shaft 272 of the cleaning member 270 is rotated by the cleaning member drive mechanism 600. When the process cartridge 18 (see FIG. 2) is mounted on the image forming apparatus main body 11 (see FIG. 1), the cleaning member drive mechanism 600 is engaged with a gear (not shown) provided on the rotation shaft 272. Yes.

  The rotation cycle of the cleaning member 270 is the same cycle as the rotation cycle of the photoconductor 102 and has an opposite phase. Therefore, the period of change in the pressing force with which the cleaning member 270 presses against the charging roll 60 (the period of bending of the charging roll 60), that is, the period of change in the pressing load that the charging roll 60 presses against the photoconductor 102 is the photoconductor. The rotation period is the same as that of the rotation period 102 and has an opposite phase.

  In addition, when the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load increases, and the side where the charging roll 60 contacts as shown in FIG. In the convex phase state, the pressing load is reduced.

<Action>
Next, the operation of this embodiment will be described.

  As described above, in the image forming apparatus 19 of the present embodiment, the period of change in the pressing load applied by the charging roll 60 to the photoconductor 102 is the same as the rotation period of the photoconductor 102 and has an opposite phase. . When the side where the charging roll 60 contacts as shown in FIG. 12A is in a concave concave phase state, the pressing load is large, and the side where the charging roll 60 contacts as shown in FIG. In the convex phase state, the pressure load is configured to be small.

  Therefore, the periodic unevenness of the image density due to the curvature of the photoconductor 102, that is, the central high density portion CN and the end high density portion HN as shown in FIG. 13 are suppressed.

<Others>
In addition, this invention is not limited to the said embodiment.

  For example, in the above-described embodiment, the photosensitive member 102 (base material 104) has a curved cylindrical shape in which the center portion 112 has a larger deflection at the time of rotation than the both end portions 110. The deflection width is 20 μm ( The straightness is 10 μm or more, but is not limited thereto. The deflection width may be less than 20 μm (straightness: 10 μm).

  Further, for example, in the above embodiment, the charging roll 60 is pressed with the cleaning members 70, 170, and 270 rotating in a cylindrical shape (roll shape) having a function of cleaning the charging roll 60. It is not limited. A non-rotating cleaning member such as a plate shape other than the columnar shape may be used. Alternatively, a pressing member that does not have a cleaning function, for example, a pressing member for suppressing variation in the axial direction of the pressing load that the charging roll 60 presses against the photosensitive member 102 may be used. Furthermore, the pressing member may not be provided.

  Further, for example, in the second embodiment, the third embodiment, the fifth embodiment, and the sixth embodiment, the rotation shafts 172 and 272 of the cleaning members 170 and 270 can be rotated to the same bearing member 300 as the charging roll 60. Although it was supported, it is not limited to this.

  For example, as illustrated in FIG. 23, the rotation shaft 172 of the cleaning member 170 may be rotatably supported by a bearing member 800 different from the bearing member 300. In addition, although illustration is abbreviate | omitted, the rotating shaft 272 of the cleaning member 270 may be rotatably supported by the bearing member 800 independently.

  As described above, when the rotation shafts 172 and 272 of the cleaning members 170 and 270 are rotatably supported by the bearing member 800 different from the charging roll 60, the charging rolls are rotated along with the rotation of the cleaning members 170 and 270. The bearing member 300 (rotating shaft 62) that supports 60 moves in the R direction, and the pressing load that the charging roll 60 presses against the photoconductor 102 changes periodically.

  Further, the configuration of the image forming apparatus is not limited to the configuration of the above-described embodiment, and various configurations can be employed. Furthermore, the present invention can be implemented in various modes without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 13 Image forming apparatus 15 Image forming apparatus 17 Image forming apparatus 19 Image forming apparatus 22 Exposure apparatus (electrostatic latent image forming means)
24 Transfer roll (an example of transfer means)
28 Developing device (an example of developing means)
60 Charging roll 62 Rotating shaft 70 Cleaning member 102 Photosensitive member (an example of an image holding member)
170 Cleaning member (an example of a pressing member)
172 Rotating shaft 270 Cleaning member (an example of a pressing member)
272 Rotating shaft 274 Winding member 511 Fluctuation mechanism 514 Compression coil spring (an example of pressing means)
520 cam mechanism P recording medium (an example of a transfer medium)

Claims (19)

A curved cylindrical image carrier that has greater deflection at the center than at both ends during rotation;
A charging roll that is pressed against the image carrier by a pressing unit and charges the image carrier;
Fluctuating means for fluctuating the pressing load that the charging roll presses against the image holding body at a period different from the rotation period of the image holding body;
An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier;
Developing means for developing the electrostatic latent image formed on the surface of the image carrier with a developer containing toner to form a toner image;
Transfer means for transferring the toner image to a transfer object;
An image forming apparatus. A curved cylindrical image carrier that has greater deflection at the center than at both ends during rotation;
A charging roll that is pressed against the image carrier by a pressing unit and charges the image carrier;
Fluctuation means for varying the distance between the rotation axis of the charging roll and the peripheral surface of the image carrier at a cycle different from the rotation cycle of the image carrier;
An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier;
Developing means for developing the electrostatic latent image formed on the surface of the image carrier with a developer containing toner to form a toner image;
Transfer means for transferring the toner image to a transfer object;
An image forming apparatus. The varying means is
A variation mechanism that varies the pressing force of the pressing unit that presses the charging roll at a cycle different from the rotation cycle of the image carrier,
The image forming apparatus according to claim 1. The pressing means is a compression coil spring,
The fluctuation mechanism is a cam mechanism that periodically changes the compression amount of the compression coil spring.
The image forming apparatus according to claim 3. The changing means has a pressing member that contacts the charging roll and has a pressing force that changes at a period different from the rotation period of the image carrier,
When the pressing force of the pressing member varies, the pressing force of the charging roll varies.
The image forming apparatus according to claim 1. The pressing member is a cleaning member having a function of cleaning the charging roll.
The image forming apparatus according to claim 5. The pressing member has a cylindrical shape having an eccentric rotation axis.
The image forming apparatus according to claim 5. The pressing member is
A rotation axis;
A winding member that is spirally wound around the rotating shaft so that the circumferential position is different between one end and the other end;
With
The image forming apparatus according to claim 5. The cycle different from the rotation cycle of the image carrier is a cycle shorter than the rotation cycle of the image carrier.
The image forming apparatus according to claim 1. The cycle shorter than the rotation cycle of the image carrier is a cycle other than an integral fraction of the rotation cycle of the image carrier.
The image forming apparatus according to claim 9. A curved cylindrical image carrier that has greater deflection at the center than at both ends during rotation;
A charging roll that is pressed against the image carrier by a pressing unit and charges the image carrier;
Fluctuation means for varying the pressing load that the charging roll presses against the image carrier with the same period and opposite phase as the rotation period of the image carrier;
An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier;
Developing means for developing the electrostatic latent image formed on the surface of the image carrier with a developer containing toner to form a toner image;
Transfer means for transferring the toner image to a transfer object;
An image forming apparatus. A curved cylindrical image carrier that has greater deflection at the center than at both ends during rotation;
A charging roll that is pressed against the image carrier by a pressing unit and charges the image carrier;
Fluctuation means for varying the distance between the rotation axis of the charging roll and the peripheral surface of the image carrier in the same period and opposite phase as the rotation period of the image carrier;
An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged image carrier;
Developing means for developing the electrostatic latent image formed on the surface of the image carrier with a developer containing toner to form a toner image;
Transfer means for transferring the toner image to a transfer object;
An image forming apparatus. The varying means is
A fluctuation mechanism that fluctuates the pressing force of the pressing means that presses the charging roll in the same period and opposite phase as the rotation period of the image carrier;
The image forming apparatus according to claim 11 or 12. The pressing means is a compression coil spring,
The fluctuation mechanism is a cam mechanism that periodically changes the compression amount of the compression coil spring.
The image forming apparatus according to claim 13. The variation means includes a pressing member that contacts the charging roll and has a pressing force that varies in the same period and opposite phase as the rotation period of the image carrier,
When the pressing force of the pressing member varies, the pressing force of the charging roll varies.
The image forming apparatus according to claim 11 or 12. The pressing member is a cleaning member having a function of cleaning the charging roll.
The image forming apparatus according to claim 15. The pressing member has a cylindrical shape having an eccentric rotation axis.
The image forming apparatus according to claim 15 or 16. The pressing member is
A rotation axis;
A winding member that is spirally wound around the rotating shaft so that the circumferential position is different between one end and the other end;
With
The image forming apparatus according to claim 15 or 16. The image forming apparatus according to any one of claims 1 to 18, wherein the image carrier has a deflection width of 20 μm or more at the center portion larger than the both end portions.