JP5919187B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly to an image forming apparatus that cleans toner remaining on an image carrier using a cleaning blade. Is.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile, a toner image is formed on an image carrier such as a photosensitive drum, and the formed toner image is transferred to a transfer medium such as paper, and then the photosensitive drum The residual toner on the top is being cleaned. The cleaned residual toner is stored in the cleaning unit or in a residual toner storage container disposed outside the cleaning unit. In order to remove the residual toner on the photosensitive drum, a cleaning blade that is in pressure contact with the photosensitive drum is widely used.

  In such an image forming apparatus, when the cleaning blade is always pressed in the same position in the axial direction of the photosensitive drum, paper dust, toner external additives, etc. jammed in the gap between the cleaning blade tip and the photosensitive drum Are rubbed against the same portion of the photosensitive drum in the axial direction. As a result, there is a problem that as the number of printed sheets is increased, a line-shaped scratch (drum circumferential scratch) is generated in the circumferential direction of the photosensitive drum, and the influence appears on the image. In particular, in the DC charging roller system, the influence of drum peripheral scratches tends to appear in the image.

  As a countermeasure against this drum circumferential scratch, for example, as in Patent Documents 1 and 2, the cleaning blade does not damage the same place deeply with respect to the axial position by moving in the axial direction (thrust movement) while rotating the drum. A method to make it is proposed. However, in the method in which the photosensitive drum is always moved in the axial direction while the photosensitive drum is being driven to rotate, the pressure contact force of the cleaning blade to the photosensitive drum becomes weak, and the gap between the cleaning blade tip and the photosensitive drum becomes the toner. Becomes easier to slip through. In addition, a dash mark in which an external additive of toner adheres to the surface of the photosensitive drum is likely to occur. Further, in a color image forming apparatus provided with a plurality of photosensitive drums, color misregistration may occur if each photosensitive drum is moved in the axial direction during image formation.

  On the other hand, Patent Document 3 discloses an image forming apparatus in which a photosensitive drum can be relatively moved in the axial direction during non-image formation. In Patent Document 3, it may be possible to move in the axial direction at any timing regardless of the rotation state of the rotating shaft of the drum, or within a predetermined stroke range in the axial direction according to the rotation angle of the cam member. A movable configuration is also described.

JP-A-62-14171 JP-A-62-273586 JP 2006-276130 A

  In the method of Patent Document 3, since the photosensitive drum is moved in the axial direction during non-image formation, occurrence of color misregistration in the color image forming apparatus can be prevented. However, when the photosensitive drum is moved in the axial direction with a constant stroke, the same spot in the axial direction of the photosensitive drum may be rubbed against the deposit on the tip of the cleaning blade during image formation, and there is a risk of peripheral drum damage. there were.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus having a simple configuration capable of effectively cleaning residual toner on an image carrier without damaging a specific portion in the axial direction of the surface of the image carrier. With the goal.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image carrier, a charging device, an exposure device, a developing device, a cleaning blade, and a drive mechanism. The image carrier has a cylindrical shape in which a photosensitive layer is formed on the outer peripheral surface, and a rotation axis passing through the central axis of the cylinder is connected. The charging device charges the photosensitive layer of the image carrier. The exposure device irradiates the image carrier charged by the charging device with beam light to form an electrostatic latent image. The developing device supplies a developer to the electrostatic latent image formed on the image carrier by the exposure device to form a toner image. The cleaning blade is pressed against the outer peripheral surface of the image carrier and cleans residual toner on the image carrier. The drive mechanism moves the image carrier in multiple steps in each of the reciprocating forward path and the backward path, and the stop position of the image carrier in the forward path is different from the stop position in the backward path.

  According to the first configuration of the present invention, when the image carrier is reciprocated in the axial direction by the drive mechanism, the image carrier is moved stepwise in each of the reciprocating forward path and the return path. At the same time, since the stop position in the forward path of the image carrier is different from the stop position in the return path, the image carrier is not damaged by the foreign matter staying between the cleaning blade and the image carrier. Residual toner on the body is cleaned.

1 is a schematic configuration diagram of a color printer 100 according to an embodiment of the present invention. Enlarged view of the vicinity of the image forming portion Pa in FIG. Schematic view of the driving mechanism 40 of the photosensitive drums 1a to 1d in the color printer 100 as viewed from above. Schematic of the drive mechanism 40 as seen from the side (downward direction in FIG. 3) External perspective view of fixed cam 51 and rotating cam 53 Schematic diagram showing the amount of movement when moving the photosensitive drums 1a to 1d back and forth in the axial direction from one end to the other end of the moving range n times. 6 is a graph showing the relationship between the axial position of the photosensitive drums 1a to 1d and the phase of the rotating cam 43 when n = 5.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of a color printer 100 according to an embodiment of the present invention. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of respective colors. Here, organic photosensitive materials are disposed on the outer peripheral surface of the aluminum drum. An OPC photoreceptor in which a layer (OPC) is formed is used. Further, an intermediate transfer belt 8 that is rotated clockwise in FIG. 1 by a driving means (not shown) is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d in the counterclockwise direction in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the main body of the color printer 100, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. . A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9 with respect to the rotation direction of the intermediate transfer belt 8.

  Next, the image forming units Pa to Pd will be described. There are charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d, which are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a to 5d are provided.

  When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then the surfaces of the photosensitive drums 1a to 1d are irradiated with light by the exposure device 4. Then, electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d includes a developing roller disposed so as to face the photosensitive drums 1a to 1d, and each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer including yellow, cyan, magenta, and black toners. This toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing devices 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure device 4. A toner image is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and yellow, cyan, magenta, and the like on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a plurality of suspension rollers including a driven roller 10 and a drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). Is started, the transfer sheet P is conveyed from the registration roller pair 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the nip portion (secondary transfer nip) with the intermediate transfer belt 8 is transferred. Part), the full-color image is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13, and the toner image is fixed on the surface of the transfer paper P, so that a predetermined full color is obtained. An image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is redistributed to the registration roller pair 12b in a state where the image surface is reversed by rotating the discharge roller pair 15 in the reverse direction to be distributed to the paper conveyance path 18 by the branching section 14. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed, and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 5a, and a charge eliminating lamp 20 are disposed along the drum rotation direction (counterclockwise direction in FIG. 2). A primary transfer roller 6a is disposed between the rollers.

  The charging device 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a and applies a charging bias (DC voltage) to the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21. In the present invention, in order to reduce the amount of generated ozone and reduce the cost of a charging bias power source (not shown), a charging bias consisting only of a DC voltage is applied to the charging roller 21. Alternatively, a method of applying a bias in which an AC bias is superimposed on may be used.

  The developing device 3a is a two-component developing type having two stirring and conveying screws 25, a magnetic roller 27, and a developing roller 29, and a toner thin film is applied to the developing roller 29 using a magnetic brush that stands on the surface of the magnetic roller 27. A layer is formed, and a developing bias having the same polarity (positive) as the toner is applied to the developing roller 29 to cause the toner to fly on the drum surface.

  The cleaning device 5 a has a cleaning blade 31 and a toner discharge screw 33. A neutralizing lamp 20 is disposed between the cleaning device 5a and the charging device 2a. The neutralization lamp 20 removes residual charges on the surface of the drum by irradiating the surface of the photosensitive drum 1a with light.

  FIG. 3 is a schematic view of the driving mechanism 40 for the photosensitive drums 1a to 1d in the color printer 100 as viewed from above, and FIG. 4 is a schematic view of the driving mechanism 40 as viewed from the side (downward direction in FIG. 3). It is. A mechanism for reciprocally moving the photosensitive drums 1a to 1d in the axial direction will be described with reference to FIGS. The upper side of FIG. 3 corresponds to the front side (rear side) of FIG. 1, and the arrangement of the photosensitive drums 1a to 1d is reversed in FIGS.

  A drum rotating shaft 43 for inputting driving force to the photosensitive drums 1a to 1d is rotatably supported on the side frame 41 on the back side (front side in FIG. 1) of the color printer 100 main body. A driving force is input to one end of the drum rotating shaft 43 protruding outside the side frame 41 (upper side in FIG. 3) by a driving motor and a gear train (both not shown). A drum coupling 45 that can be connected to the photosensitive drums 1 a to 1 d is movable in the axial direction of the drum rotation shaft 43 at the other end of the drum rotation shaft 43 that protrudes inside the side frame 41 (lower side in FIG. 3). Extrapolated. A coil spring 47 is sandwiched between the tip 43a of the drum rotating shaft 43 and the drum coupling 45, and the drum coupling 45 is urged by the coil spring 47 toward the side frame 41 (upward in FIG. 3). ing. The photosensitive drums 1a to 1d are also slidably supported in the axial direction in the image forming portions Pa to Pd, and are urged toward the side frame 41 by urging means (not shown). In FIG. 3, only the drum rotation shaft 43 and the drum coupling 45 corresponding to the photosensitive drum 1a are shown.

  A fixed cam 51 and a rotating cam 53 are disposed between the side frame 41 and the drum coupling 45. The fixed cam 51 is fixed to the side frame 41, and the rotating cam 53 is rotatably attached to the drum rotating shaft 43. The rotating cam 53 is formed integrally with the cam drive gears 55a to 55d.

  A drive input gear 57 is engaged with the cam drive gears 55b and 55c. The drive input gear 57 is a two-stage gear that includes a first gear portion 57a having a large diameter and a second gear portion 57b having a small diameter. The first gear portion 57a is a spur gear that meshes with the cam drive gears 55b and 55c. The second gear portion 57b is a one-way gear capable of transmitting a driving force only in one direction (clockwise direction in FIG. 4), and is a claw gear having claw-shaped gear teeth formed on the outer peripheral surface. In addition, a one-way clutch is provided at the bearing portion of the drive input gear 57 so that it can rotate only in the clockwise direction with respect to the support shaft. A driving claw 61 that reciprocates by a solenoid 60 is engaged with the gear teeth of the second gear portion 57b. One end of the driving claw 61 is rotatably supported by the solenoid 60, and the other end is rotated downward by its own weight.

  An idle gear 59a is engaged with the cam drive gears 55a and 55b, and an idle gear 59b is engaged with the cam drive gears 55c and 55d. The idle gears 59 a and 59 b are spur gears, and the idle gears 59 a and 59 b are rotatably supported on a rotation shaft fixed to the side frame 41.

  FIG. 5 is an external perspective view of the fixed cam 51 and the rotating cam 53. As shown in FIG. 5, the fixed cam 51 has a cam body 51a and a cam follower 51b. The cam follower 51 b is an annular protrusion that protrudes from the side surface of the cam body 51 a and abuts on the cam surface 53 b of the rotating cam 53. The cam followers 51b are formed so that axial distances are different (displaced) in the circumferential direction, and a maximum portion (convex portion) and a minimum portion (concave portion) are formed one by one at a distance of 180 °.

  The rotating cam 53 has a cam body 53a and a cam surface 53b. The cam surface 53 b is formed in an annular shape on the side surface of the cam body 53 a and abuts on the cam follower 51 b of the fixed cam 51. The cam surface 53b has a maximum portion (convex portion) and a minimum portion (concave portion) of 180 so that the axial distance always changes (displaces) by a predetermined amount with respect to the unit rotation angle in the circumferential direction of the rotating cam 53. Formed one by one apart. Here, the fixed cam 51 having the cam follower 51b is fixed to the side frame 41, and the movement of the fixed cam 51 in the axial direction (vertical direction in FIG. 3) is restricted. Therefore, according to the contact position between the cam follower 51b and the cam surface 53b, the rotating cam 53 having the cam surface 53b moves relative to the fixed cam 51 having the cam follower 51b in the axial direction.

  When the iron core of the solenoid 60 is pulled, the drive claw 61 moves rightward in FIG. 3 and rotates the second gear portion 57b of the drive input gear 57 clockwise by a predetermined angle. As a result, the first gear portion 57a of the drive input gear 57 also rotates by a predetermined angle in the clockwise direction, and the cam drive gears 55b and 55c engaged with the first gear portion 57a also rotate by a predetermined angle in the counterclockwise direction.

  When the iron core of the solenoid 60 protrudes in preparation for the next rotation operation, the driving claw 61 moves in the left direction in FIG. 3, but the second gear portion 57b transmits the driving force only in the clockwise direction in FIG. Since it is a possible one-way gear, even if the second gear portion 57b is rotated counterclockwise by the driving claw 61, the driving force is not transmitted to the first gear portion 57a.

  When the cam drive gears 55b and 55c rotate by a predetermined angle in the counterclockwise direction, the idle gears 59a and 59b that mesh with the cam drive gears 55b and 55c rotate by a predetermined angle in the clockwise direction and engage with the idle gears 59a and 59b. The drive gears 55a and 55d also rotate by a predetermined angle in the counterclockwise direction. That is, all the cam drive gears 55a to 55d rotate by a predetermined angle in the counterclockwise direction.

  When the cam drive gears 55a to 55d rotate by a predetermined angle, the rotary cams 53 integrally formed with the cam drive gears 55a to 55d also rotate by a predetermined angle. As a result, the contact position between the cam follower 51b formed on each fixed cam 51 and the cam surface 53b formed on each rotary cam 53 changes, so that the biasing force of the coil spring 47 is resisted according to the contact position. Then, the drum coupling 45 moves in the axial direction, and the photosensitive drums 1a to 1d connected to the drum coupling 45 also move in the axial direction.

  The axial distance between the fixed cam 51 and the rotating cam 53 is minimized at a position where the minimum portion of the cam surface 53b contacts the maximum portion of the cam follower 51b and the maximum portion of the cam surface 53b contacts the minimum portion of the cam follower 51b. The photosensitive drums 1a to 1d are disposed at positions closest to the side frame 41 (uppermost in FIG. 3).

  When the rotating cam 53 further rotates, the photosensitive drums 1a to 1d gradually move downward in FIG. The maximum distance between the fixed cam 51 and the rotating cam 53 is maximized at a position where the maximum portion of the cam surface 53b contacts the maximum portion of the cam follower 51b and the minimum portion of the cam surface 53b faces the minimum portion of the cam follower 51b. The photosensitive drums 1a to 1d are arranged at the position farthest from the side frame 41 (lowermost in FIG. 3). When the rotating cam 53 further rotates, the photosensitive drums 1a to 1d move again upward in FIG. 3 and repeat reciprocating movement in the axial direction. At this time, the rotating shaft 43 of the photosensitive drums 1a to 1d rotates in the opposite direction (clockwise direction in FIG. 3) to the cam driving gears 55a to 55d, so that the rotation of the rotating shaft 43 is caused by frictional force. 55d. However, since the drive input gear 57 is provided with a one-way clutch, the rotation of the cam drive gears 55 b and 55 c is not transmitted to the drive input gear 57.

  As described above, since the photosensitive drums 1a to 1d reciprocate in the axial direction, the cleaning blade 31 (see FIG. 2) that contacts the photosensitive drums 1a to 1d is clogged with paper dust, toner external additives, and the like. Thus, there is no possibility that the same positions on the surfaces of the photosensitive drums 1a to 1d are repeatedly rubbed. Therefore, the residual toner on the photosensitive drums 1a to 1d is cleaned without damaging the surfaces of the photosensitive drums 1a to 1d.

  Moreover, the structure which fixes the cleaning blade 31 to cleaning apparatus 5a-5d, for example can be taken. As a result, since the configuration of the seal portion of the cleaning devices 5a to 5d is simpler than the configuration in which the cleaning blade 31 is reciprocated in the axial direction of the photosensitive drums 1a to 1d, the toner is removed from the cleaning devices 5a to 5d. There is no risk of splashing.

  The arrangement of the fixed cam 51 and the rotating cam 53 in the axial direction is reversed from that of the present embodiment, and the fixed cam 51 is fixed to the drum coupling 45 (for example, the photosensitive drums 1a to 1d are rotatably held). The rotation cam 53 may be disposed on the side frame 41 side and driven to rotate.

  Next, the movement amount (stroke) when the photosensitive drums 1a to 1d are reciprocated in the axial direction in the color printer 100 of the present invention will be described. FIG. 6 is a schematic diagram showing the amount of movement when the photosensitive drums 1a to 1d are reciprocally moved in the axial direction from the one end to the other end of the moving range n times.

  Now, let A (mm) be the total travel distance of one way (outward or return path) when the photosensitive drums 1a to 1d are reciprocated. The total number of movements for moving one way is n. In the forward path of the photosensitive drums 1a to 1d (from the left to the right in FIG. 6), for the first movement, for example, the drive claw 61 is reciprocated once by the solenoid 60 to set the movement distance to A / (2n−1). ) (Mm), and when moving from the second time to the n-th time thereafter, the drive claw 61 is reciprocated twice to set the movement distance to 2A / (2n-1) (mm). As a result, the photosensitive drums 1a to 1d move the total movement distance A in one direction by n movements.

  In the return path (right to left in FIG. 6) of the photosensitive drums 1a to 1d, the n + 1-th moving distance is A / (2n-1) (mm), and the subsequent n + 2 to 2n-th times. The moving distance is 2A / (2n-1) (mm). As a result, the photosensitive drums 1a to 1d are moved n times in the reverse direction over the total movement distance A, thereby completing the first reciprocation.

  Similarly to the above, the movement after the 2n + 1th time (after the second reciprocation of the photosensitive drums 1a to 1d) is moved by A / (2n-1) (mm) when the moving direction is changed, and thereafter 2A. / Repeat the movement to move by (2n-1) (mm).

  FIG. 7 is a graph showing the relationship between the axial positions of the photosensitive drums 1a to 1d and the phase of the rotating cam 43 when n = 5 in FIG. 6, and the axial positions of the photosensitive drums 1a to 1d are shown. The phase of the rotating cam 43 is indicated by a broken line with a bold line. As shown in FIG. 7, when the total number of one-way movements of the photosensitive drums 1a to 1d is five, the first movement distance is A / (2 × 5-1) = A / 9. The moving distance from the second time to the fifth time is set to 2A / (2 × 5-1) = 2A / 9. Further, the moving distance for the sixth time (first return) is A / 9, and the moving distance for the seventh to tenth times (second to fifth return) is 2A / 9. By doing so, the relative positions of the photosensitive drums 1a to 1d and the cleaning blade 31 are prevented from having the same positional relationship during reciprocation.

  Here, in the forward path of the photosensitive drums 1a to 1d, the first moving distance is A / (2n-1) (mm), and the subsequent moving distance from the second to the nth is 2A / (2n- 1) (mm). For example, the movement distance from the first to the (n-1) th time is A / (2n-1) (mm), and the nth movement distance is A / (2n-1) (mm). ), The same effect can be obtained. Also in the return path of the photosensitive drums 1a to 1d, the movement distance from the (n + 1) th time to the (2n-1) th time is A / (2n-1) (mm), and the second movement distance is A / (2n-1) (mm). ), The same effect can be obtained.

  Alternatively, the cam follower 51b and the cam surface 53b are not separated from each other by 180 °, and the photosensitive drums 1a to 1d are moved so that the total number of movements and the movement distance per time are different between the forward and backward paths of the photosensitive drums 1a to 1d. The stopping positions of the photosensitive drums 1a to 1d during the reciprocation may be varied. For example, if the total number of movements is n on the forward path and the movement distance per time is A / n, and the total number of movements is n + 1 on the return path and the movement distance per time is A / (n + 1), The positional relationship between the photosensitive drums 1a to 1d and the cleaning blade 31 can be shifted. Further, when the total number of movements of the photosensitive drums 1a to 1d is 2n (one reciprocation), the rotation direction of the cam follower 51b and the cam surface 53b are separated by 180 ° when the rotation cam 53 and the drive input gear 57 make one rotation. Is set to a position shifted by 1/4 rotation, the position of the photosensitive drums 1a to 1d during reciprocation can be set to a position shifted in the axial direction by A / 4n. Further, the axial distance of the cam follower 51b and the cam surface 53b with respect to the unit rotation angle in the circumferential direction does not change linearly, but it can also have a shape that is displaced by different curves at portions separated by 180 °.

  If the movement amount in the axial direction when the photosensitive drums 1a to 1d are reciprocated in the axial direction stepwise is set as shown in FIGS. 6 and 7, the photosensitive drums 1a to 1d are in the forward path and the backward path. Do not stop at the same position. Therefore, there is no possibility that foreign matter clogged in the gap between the cleaning blade 31 and the photosensitive drums 1a to 1d will scrape the same portion in the axial direction of the photosensitive drums 1a to 1d. Therefore, residual toner on the photosensitive drums 1a to 1d can be cleaned by using the cleaning blade 31 without damaging the photosensitive layers on the surfaces of the photosensitive drums 1a to 1d.

  In addition, the drive input gear 57 and the cam drive gears 55a to 55d are rotated by a predetermined angle by the reciprocating movement of the drive claw 61 by the solenoid 60, and the rotating cams 43 are also rotated by the predetermined angle, so that the shafts of the photosensitive drums 1a to 1d are rotated. Directional reciprocal movement can be performed simultaneously and in phase. Furthermore, since the photosensitive drums 1a to 1d are reciprocated in the axial direction using a single drive input means (solenoid 60 and drive claw 61), this contributes to simplification of the configuration and cost reduction.

  In place of the solenoid 60 and the drive claw 61, the drive input gear 57 can be rotated by a predetermined angle using a stepping motor whose rotation angle can be controlled by the number of drive pulses. However, when the solenoid 60 and the driving claw 61 are used, the photosensitive drums 1a to 1d can be moved in a short time. Therefore, it is difficult for the toner external additive or the like to slip through the gap between the photosensitive drums 1a to 1d and the cleaning blade 31, and the generation of dash marks can be suppressed. Moreover, since pulse control like a stepping motor is unnecessary, control can be simplified more.

  Here, for example, if the photosensitive drums 1a to 1d move in the axial direction during exposure by the exposure device 4 (during formation of electrostatic latent images on the surfaces of the photosensitive drums 1a to 1d), the photosensitive drums 1a to 1d are moved. The image position is shifted during writing to the image, and image distortion occurs in the axial direction (main scanning direction) of the photosensitive drums 1a to 1d. In addition, when the photosensitive drums 1a to 1d move in the axial direction during the primary transfer of the toner images by the primary transfer rollers 6a to 6d, the toner images are transferred during the primary transfer from the photosensitive drums 1a to 1d to the intermediate transfer belt 8. It will be rubbed.

  Further, as shown in FIG. 1, each of the photosensitive drums 1 a to 1 d is disposed at a predetermined distance along the moving direction of the intermediate transfer belt 8, so that each color toner image is transferred onto the intermediate transfer belt 8. There is a time lag in the primary transfer timing. Therefore, if each of the photosensitive drums 1a to 1d moves in the axial direction separately from the exposure by the exposure device 4 to the primary transfer, the color shift in the axial direction at the time of primary transfer of each color toner image by the primary transfer rollers 6a to 6d. May occur.

  Therefore, in the present embodiment, the photosensitive drums 1a to 1d are moved in a short time using the solenoid 60 and the driving claw 61 in addition to the exposure by the exposure device 4 or the primary transfer of the toner image by the primary transfer rollers 6a to 6d. At the same time, they are moved in the axial direction. As a result, it is possible to prevent the occurrence of image distortion, rubbing, and color shift as described above. Specifically, it is preferable that the photosensitive drums 1a to 1d are moved between sheets where no image forming operation is performed.

  The timing (frequency) at which the photosensitive drums 1a to 1d are moved stepwise must be such that the surface of the photosensitive drums 1a to 1d is not damaged. In general, it is known that scratches on the photosensitive drum occur when printing about 50,000 sheets. For example, the photosensitive drums 1a to 1d are moved stepwise for every 1,000 printed sheets. Damage to the body drums 1a to 1d can be sufficiently avoided.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, an example in which the present invention is applied to a tandem color printer 100 using an intermediate transfer belt has been described. However, the present invention is not limited thereto, and a direct transfer type that directly transfers a toner image onto a recording medium. The present invention may be applied to a color image forming apparatus, a monochrome image forming apparatus such as a monochrome copying machine or a monochrome printer.

  INDUSTRIAL APPLICABILITY The present invention can be used in image forming apparatuses such as copying machines, printers, facsimiles, and composite machines using electrophotography, and in particular, cleaning toner remaining on an image carrier using a cleaning blade. The image forming apparatus can be used.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
2a to 2d Charging device 3a to 3d Developing device 4 Exposure device 5a to 5d Cleaning device 6a to 6d Primary transfer roller (transfer means)
8 Intermediate transfer belt (intermediate transfer member)
31 Cleaning blade 40 Drive mechanism 41 Side frame 43 Drum rotation shaft 45 Drum coupling 47 Coil spring (biasing member)
51 Fixed cam 51a Cam body (fixed cam)
51b Cam follower 53 Rotating cam 53a Cam body (Rotating cam)
53b Cam surface 55a-55d Cam drive gear 57 Drive input gear 57a 1st gear part 57b 2nd gear part 59a, 59b Idle gear 60 Solenoid (drive input means)
61 Driven claw (drive input means)
100 color printer

Claims (6)

An image carrier having a cylindrical shape with a photosensitive layer formed on the outer peripheral surface, and having a rotation axis passing through the central axis of the cylinder, and
A charging device for charging the photosensitive layer of the image carrier;
An exposure device that forms an electrostatic latent image by irradiating the image carrier charged by the charging device with a beam of light;
A developing device for supplying a developer to the electrostatic latent image formed on the image carrier by the exposure device to form a toner image;
Transfer means for transferring a toner image formed on the image carrier by the developing device onto a recording medium or an intermediate transfer member;
A cleaning blade pressed against the outer peripheral surface of the image carrier and cleaning residual toner on the image carrier;
A drive mechanism for reciprocating the image carrier in the direction of the rotation axis;
In an image forming apparatus comprising:
The drive mechanism is, together with a plurality of times to move stepwise in each forward path and backward path of reciprocating the image bearing member, a stop position in the forward of said image bearing member, Ri stop position and the Do different in the return path ,
When the total travel distance of the forward path or the backward path when the image carrier is reciprocated in the direction of the rotation axis is A and the total number of movements for moving the forward path or the backward path is n times (n ≧ 2), the first time Alternatively, the n-th moving distance is A / (2n−1), and the other moving distance is 2A / (2n−1) . The drive mechanism moves the image carrier in the direction of the rotation axis when the image carrier is rotated except when an electrostatic latent image is formed by the exposure device and when a toner image is transferred by the transfer unit. The image forming apparatus according to claim 1, wherein: The drive mechanism is extrapolated to the rotating shaft, allows rotation of the rotating shaft, and is restricted in movement in the axial direction and circumferential direction with respect to the rotating shaft, and adjacent to the fixed cam, the driving mechanism A rotating cam supported to be rotatable on the rotating shaft and slidable in the axial direction, a driving means for rotating the rotating cam by a predetermined angle, and one of the opposing sides of the fixed cam and the rotating cam. An annular cam surface having a continuously changing axial distance in the circumferential direction, an annular cam follower provided on the other side surface and in contact with the cam surface, and a direction in which the cam surface and the cam follower contact each other. The image forming apparatus according to claim 1 , further comprising an urging member that urges the image carrier . A cam drive gear is integrally formed on the rotary cam, and the drive means includes a drive input gear meshing with the cam drive gear, and a drive input means for rotating the drive input gear by a predetermined angle in a predetermined direction. the image forming apparatus according to claim 3, characterized in that it has. The drive input gear is formed adjacent to the first gear portion that meshes with the cam drive gear, and the first gear portion in a drive input direction for inputting a drive force to the cam drive gear. And a second gear portion that rotates separately from the first gear portion in a direction opposite to the drive input direction, and the drive input means has an outer peripheral surface of the second gear portion. A drive claw that engages with a claw-shaped gear tooth formed on the drive claw to rotate the drive input gear in the drive input direction, and a solenoid that reciprocates the drive claw. Item 5. The image forming apparatus according to Item 4. The image forming apparatus according to any one of claims 1 to 5, characterized in that performing a plurality of the image bearing member, a reciprocating movement in the axial direction of the plurality of the image bearing member simultaneously and in phase.

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