JP5806125B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that transfers a toner image from a plurality of image carriers onto a sheet via an intermediate transfer belt.

  Some electrophotographic image forming apparatuses use an intermediate transfer method in which toner images are sequentially superimposed and transferred from a plurality of image carriers to an intermediate transfer belt, and the toner images are secondarily transferred from the intermediate transfer belt to a sheet. There are some (for example, refer to Patent Document 1). The color image forming apparatus displaces the intermediate transfer belt according to each operation state during monochrome image formation, color image formation, and non-image formation. The intermediate transfer belt contacts only the black image carrier during monochrome image formation, contacts all image carriers during color image formation, and is separated from all image carriers during non-image formation.

  In the conventional image forming apparatus as described above, if the intermediate transfer belt meanders, the image quality is adversely affected during image formation, and the end portion in the width direction of the intermediate transfer belt is the intermediate transfer belt even during non-image formation. May be bent by being strongly pressed against the flange portion of the stretching roller that stretches. Even during non-image formation, if the end portion in the width direction of the intermediate transfer belt is bent, the image quality during image formation is adversely affected. For this reason, it is important to suppress meandering of the intermediate transfer belt.

JP 2008-233196 A

  Therefore, the meandering correction mechanism of the intermediate transfer belt may be configured as follows, in which the meandering of the intermediate transfer belt is suppressed by adjusting the tension of the intermediate transfer belt by a mechanical mechanism without using a sensor. In other words, the meandering correction mechanism urges the tension roller in the direction in which the tension of the intermediate transfer belt increases. The meandering correction mechanism includes a deviation transmission member that moves along the axial direction due to a deviation force of the intermediate transfer belt along the axial direction of the tension roller, and is along the axial direction of the deviation transmission member. The urging force applied to both ends of the tension roller is increased or decreased according to the amount of movement.

  However, in the above-described meandering correction mechanism, even if the meandering of the intermediate transfer belt occurs, if the deviation force is small, the deviation transmission member may not move along the axial direction, or the movement starts. There is a risk of timing being delayed. The reason is that in the conventional image forming apparatus, the intermediate transfer belt and the tension roller do not vibrate during the non-image forming period because the intermediate transfer belt is not displaced from the reference position for a long time compared to during the image forming period. This is probably because a static frictional force acts between the offset transmission member and the shaft member.

  If the offset transmission member does not move or the movement start timing is delayed despite the occurrence of the meandering of the intermediate transfer belt, the accuracy of the meandering correction of the intermediate transfer belt is lowered.

  An object of the present invention is to provide an image forming apparatus capable of improving the accuracy of meandering correction of an intermediate transfer belt during a non-image forming period.

  The image forming apparatus according to the present invention includes a plurality of image carriers, an endless intermediate transfer belt, a separation / contact mechanism unit, a plurality of stretching rollers, a meandering correction mechanism unit, and a control unit. The image carrier carries a toner image. The intermediate transfer belt has a toner image transferred from at least one of the plurality of image carriers at the time of image formation. The separation / contact mechanism portion displaces the intermediate transfer belt in the separation / contact direction with respect to each of the plurality of image carriers. The tension roller stretches the intermediate transfer belt. The tension roller includes a driving roller for rotating the intermediate transfer belt, and a tension roller whose both ends in the axial direction are independently movable in a direction in which the tension of the intermediate transfer belt is changed. The meandering correction mechanism urges the tension roller in a direction in which the tension of the intermediate transfer belt increases. The meandering correction mechanism includes a displacement transmission member that moves along the axial direction by a displacement force of the intermediate transfer belt along the axial direction of the tension roller, and the amount of movement of the displacement transmission member along the axial direction Accordingly, the urging force applied to both ends of the tension roller is increased or decreased. The control unit displaces the intermediate transfer belt from a predetermined reference position separated from all of the plurality of image carriers at a predetermined timing during the rotation of the intermediate transfer belt during the non-image forming period, and then returns to the reference position. A belt displacement process is performed to control the separation / contact mechanism so as to return it. When executing the belt displacement process, the control unit displaces the intermediate transfer belt from the reference position to a predetermined separation position that is separated from all of the plurality of image carriers and at least partially different from the reference position. Let

  In this configuration, the belt displacement process is executed at a predetermined timing during the non-image forming period and during the rotation of the intermediate transfer belt, so that the tension of the intermediate transfer belt changes and vibration is transmitted to the meandering correction mechanism. The For this reason, even when the offset force of the intermediate transfer belt is small, the offset transmission member easily moves due to the offset force of the intermediate transfer belt. As a result, the biasing force applied to both ends of the tension roller is increased or decreased with high accuracy according to the amount of movement of the offset transmission member along the axial direction.

  In addition, since the intermediate transfer belt is displaced from the reference position to a predetermined separation position until it comes into contact with the image carrier, the intermediate transfer belt of the intermediate transfer belt is compared with the case where the intermediate transfer belt is displaced to a position where it comes into contact with the image carrier. Since the displacement distance is short, the belt displacement process can be completed in a short time.

  Further, since the intermediate transfer belt does not contact the image carrier, the residual toner on the image carrier does not adhere to the intermediate transfer belt. For this reason, it is possible to suppress deterioration in image quality.

  In the configuration described above, the control unit, when executing the belt displacement process, moves the intermediate transfer belt from the reference position to the first separation position close to only the monochrome image carrier among the plurality of image carriers and the plurality of image carriers. It can comprise so that it may displace to at least any one among the 2nd separated positions which approached all the bodies.

  In this configuration, the first separation position can be displaced by displacing from the reference position halfway to the monochrome image forming position, and the second separation can be performed by displacing from the reference position to the middle of the color image formation position. It can be displaced to a position. Therefore, it is sufficient that the intermediate transfer belt can be displaced between the monochrome image forming position, the color image forming position, and the reference position, and no special structure is required as the separation / contact mechanism portion. The accuracy of the meandering correction can be improved.

  In addition, a shaft member that supports the tension roller so as to be rotatable and movable in the axial direction is provided, and the offset transmission member has a diameter-expanded portion that is larger than the tension roller, and the tension roller in the axial direction is The meandering correction mechanism is an urging member that urges the shaft member in the direction in which the tension of the intermediate transfer belt is increased. An urging member having an end portion pivotally supported by the offset transmission member and a base end portion pivotally supported at a predetermined position of the apparatus frame may be further included.

  In this configuration, when the intermediate transfer belt meanders and deviates toward one side of the tension roller in the axial direction, the deviation transmission member on the downstream side in the deviation direction moves along the axial direction. This changes the inclination angle of the biasing member at least downstream in the offset direction with respect to the axial direction, changes the biasing force of the biasing member, and changes the tension of the intermediate transfer belt at least downstream in the offset direction. To do. In this way, the meandering of the intermediate transfer belt is corrected. At this time, during the non-image forming period and during the rotation of the intermediate transfer belt, the belt displacement process is executed and vibrations are transmitted to the meandering correction mechanism, so even if the offset force of the intermediate transfer belt is small, The displacement transmission member can be moved by the displacement force of the intermediate transfer belt, and the inclination angle of the urging member can be easily changed. As a result, the biasing force applied to both ends of the tension roller is increased or decreased with high accuracy according to the amount of movement of the offset transmission member along the axial direction.

  Further, the offset transmission member further includes a sliding member whose rotation about the shaft member is restricted on each side opposite to the tension roller with respect to the enlarged diameter portion in the axial direction. It is preferable that each of the moving members is pivotally supported.

  In this configuration, the working end is pivotally supported by the sliding member whose rotation is restricted, so that the arrangement and contraction degree of the biasing member when the amount of deviation of the intermediate transfer belt is a certain value is stabilized. Further, the accuracy of the meandering correction of the intermediate transfer belt is further improved.

  In addition, the control unit can be configured to execute belt displacement processing during maintenance with toner replenishment. Maintenance with toner replenishment is performed during the non-image formation period, and during maintenance with toner replenishment, the intermediate transfer belt is rotated for a long time, but the belt displacement process is executed, which adversely affects image formation efficiency and image quality. Without giving, the accuracy of meandering correction of the intermediate transfer belt can be improved.

  Further, the control unit can be configured to execute a belt displacement process when adjusting the toner density. The toner density is adjusted during the non-image formation period, and the intermediate transfer belt is rotated for a long time when the toner density is adjusted. However, the belt displacement process is executed, so that the image formation efficiency and image quality are not adversely affected. In addition, the accuracy of meandering correction of the intermediate transfer belt can be improved.

  According to the present invention, the accuracy of meandering correction of the intermediate transfer belt during the non-image forming period can be improved.

1 is a schematic front sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a front view illustrating a schematic configuration of an intermediate transfer unit, where (A) illustrates a state during non-image formation, (B) illustrates a state during monochrome image formation, and (C) illustrates a state during color image formation. Show. FIG. 2 is a schematic plan view of an intermediate transfer unit. 4A and 4B are partially enlarged views of an intermediate transfer unit, in which FIG. 5A shows a state where a primary transfer roller is at a separation position, and FIG. 5B shows a state where a primary transfer roller is at a pressing position. It is a block diagram of a primary transfer roller. 4A and 4B are diagrams illustrating a structure and an arrangement state of a cam, in which FIG. 5A illustrates a state during non-image formation, FIG. 5B illustrates a state during monochrome image formation, and FIG. 5C illustrates a state during color image formation. . FIG. 3 is a side sectional view of an intermediate transfer unit. FIG. 4 is a diagram illustrating a state where an intermediate transfer belt is offset toward the back side. FIG. 4 is a diagram illustrating a state where an intermediate transfer belt is offset toward the front side. It is a flowchart which shows the process sequence of a control part.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 100 forms a multi-color or single-color image on a predetermined sheet based on image data read from a document. Examples of the paper include sheet-like recording media such as plain paper, thick paper, photographic paper, and OHP film. The image forming apparatus 100 includes an image reading unit 120, an image forming unit 110, a paper feed unit 80, and a paper discharge unit 90.

  The image reading unit 120 generates image data by irradiating the image surface of the document with light and detecting the amount of reflected light.

  The image forming unit 110 includes four image forming stations 30A, 30B, 30C, and 30D, an intermediate transfer unit 40, a secondary transfer unit 50, an exposure unit 60, and a fixing unit 70.

  The intermediate transfer unit 40 includes an intermediate transfer belt 41 that is an endless belt, a first stretching roller 42, a second stretching roller 43, and a tension roller 44. As the intermediate transfer belt 41, a resin film having no elasticity such as polyimide is used. The first stretching roller 42, the second stretching roller 43, and the tension roller 44 are arranged in parallel to each other. The first tension roller 42, the second tension roller 43, and the tension roller 44 stretch the intermediate transfer belt 41. As an example, the first stretching roller 42 is a driving roller, and the second stretching roller 43 is a driven roller.

  The tension roller 44 is urged by a spring (not shown) in a direction in which it is pressed against the inner peripheral surface of the intermediate transfer belt 41. The tension roller 44 adjusts the tension of the intermediate transfer belt 41.

  The image forming stations 30 </ b> A to 30 </ b> D perform electrophotographic image forming processing using toners of black, cyan, magenta, and yellow hues, respectively. The image forming stations 30 </ b> A to 30 </ b> D are arranged side by side so as to face a predetermined area of the intermediate transfer belt 41. The image forming stations 30B to 30D are configured in the same manner as the image forming station 30A.

  The image forming station 30A includes a monochrome photosensitive drum 31A carrying black toner. The image forming stations 30B, 30C, and 30D include color photosensitive drums 31B, 31C, and 31D that carry color toners, respectively. Each of the photoreceptor drums 31A to 31D constitutes an image carrier.

  The image forming station 30A includes a charging device 32A, a developing device 33A, a primary transfer roller 34A, and a cleaner device 35A around the photosensitive drum 31A. Similarly, the image forming stations 30B, 30C, and 30D have primary transfer rollers 34B, 34C, and 34D, respectively.

  The photosensitive drum 31A rotates in a predetermined direction by receiving a driving force from a driving source (not shown). The charger 32A charges the peripheral surface of the photosensitive drum 31A to a predetermined potential.

  The exposure unit 60 drives the semiconductor laser based on the image data of each hue of black, cyan, magenta, and yellow, and distributes the laser beam of each hue to the respective photosensitive drums 31A to 31D of the image forming stations 30A to 30D. Shine. Electrostatic latent images based on image data of each hue of black, cyan, magenta, and yellow are formed on the peripheral surfaces of the photosensitive drums 31A to 31D.

  The developing device 33A supplies black toner, which is the hue of the image forming station 30A, to the peripheral surface of the photosensitive drum 31A, and visualizes the electrostatic latent image into a toner image.

  The outer peripheral surface of the intermediate transfer belt 41 faces the photosensitive drums 31A to 31D in order. A primary transfer roller 34A is disposed at a position facing the photosensitive drum 31A across the intermediate transfer belt 41. A primary transfer roller 34B is disposed at a position facing the photosensitive drum 31B with the intermediate transfer belt 41 interposed therebetween. A primary transfer roller 34C is disposed at a position facing the photosensitive drum 31C with the intermediate transfer belt 41 interposed therebetween. A primary transfer roller 34D is disposed at a position facing the photosensitive drum 31D with the intermediate transfer belt 41 interposed therebetween.

  The primary transfer roller 34A receives a toner image carried on the photosensitive drum 31A on the intermediate transfer belt 41 by applying a primary transfer bias having a polarity opposite to that of toner (for example, minus) and opposite polarity (eg, plus). Primary transfer to the outer peripheral surface.

  The toner remaining on the outer peripheral surface of the photosensitive drum 31A is removed by the cleaner device 35A.

  When forming a monochrome image, the above-described image forming process is performed only by the monochrome image forming station 30A. In addition, when forming a full-color image, the image forming station 30B to 30D in addition to the image forming station 30A performs the same image forming process as the image forming station 30A for each hue of cyan, magenta, and yellow. A toner image of each hue of black, cyan, magenta, and yellow is applied to the outer peripheral surface of the intermediate transfer belt 41 by applying a primary transfer bias to the primary transfer rollers 34A to 34D of the image forming stations 30A to 30D. The images are sequentially transferred so as to be superimposed on each other.

  The paper feed unit 80 includes a paper feed cassette 81, a manual feed tray 82, a paper main transport path 83, and a paper sub transport path 84. The paper feed cassette 81 stores a plurality of sheets of a size and type that are relatively frequently used. On the manual feed tray 82, paper of a size or type that is relatively infrequently used is placed.

  The main paper transport path 83 is formed so as to extend from the paper feed cassette 81 and the manual feed tray 82 to the paper discharge unit 90 between the intermediate transfer belt 41 and the secondary transfer unit 50 and via the fixing unit 70. Yes. The paper sub-transport path 84 is a paper transport path for forming a double-sided image, and the sheet on which the image is formed on one side is reversed between the intermediate transfer belt 41 and the secondary transfer unit 50 with the front and back sides reversed. It is formed so that it can be conveyed between.

  The secondary transfer unit 50 includes a secondary transfer roller 50A. The secondary transfer roller 50A is applied with a secondary transfer bias having a polarity opposite to that of the toner (for example, minus) and opposite to that of the toner (for example, plus), so that the toner image carried on the outer peripheral surface of the intermediate transfer belt 41 is formed. Transferred to paper.

  The fixing unit 70 includes a fixing roller 71 and a pressure roller 72, and heats and pressurizes the paper on which the toner image is transferred, thereby fixing the toner image on the paper.

  The paper discharge unit 90 includes a paper discharge tray 91 and a paper discharge roller 92. The sheet on which the toner image has been fixed is discharged to a discharge tray 91 by a discharge roller 92. The paper is stored in the paper discharge tray 91 with the surface on which the toner image is fixed facing down.

  As shown in FIGS. 2A to 2C, the intermediate transfer belt 41 is stretched between a first stretching roller 42 and a second stretching roller 43 to move in a predetermined loop shape. Configure the route. The photosensitive drum 31D, the photosensitive drum 31C, and the photosensitive drum 31B are sequentially arranged from the upstream side in the moving direction 93 of the intermediate transfer belt 41 in the region facing the photosensitive drums 31A to 31D along the outer peripheral surface of the intermediate transfer belt 41. And a photosensitive drum 31A. In the moving direction 93, the first stretching roller 42 is disposed on the downstream side, and the second stretching roller 43 is disposed on the upstream side. As described above, the primary transfer rollers 34A to 34D are arranged at positions facing the photosensitive drums 31A to 31D with the intermediate transfer belt 41 interposed therebetween. In this embodiment, the intermediate transfer belt 41 is disposed above the photosensitive drums 31A to 31D.

  The primary transfer rollers 34 </ b> A to 34 </ b> D are configured to be displaceable in the direction of separating from and contacting the photosensitive drums 31 </ b> A to 31 </ b> D that face each other. Accordingly, the primary transfer roller 34A is displaceable at least between a pressing position where the intermediate transfer belt 41 is pressed against the opposing photosensitive drum 31A and a separation position where the intermediate transfer belt 41 is separated from the opposing photosensitive drum 31A. It is. The primary transfer rollers 34B to 34D are the same as the primary transfer roller 34A.

  As shown in FIG. 2A, at the time of non-image formation, all of the primary transfer rollers 34A to 34D are arranged at the respective separated positions, so that the intermediate transfer belt 41 is separated from all the photosensitive drums 31A to 31D. It is arranged at a predetermined reference position that is spaced apart.

  As shown in FIG. 2B, at the time of monochrome image formation, the monochrome primary transfer roller 34A is arranged at the pressing position, and the color primary transfer rollers 34B to 34D are arranged at the separated positions. The intermediate transfer belt 41 is disposed at a monochrome image forming position separated from the color photosensitive drums 31B to 31D while being in pressure contact with only the monochrome photosensitive drum 31A.

  As shown in FIG. 2C, at the time of color image formation, the primary transfer rollers 34A to 34D are arranged at the pressing positions, so that the intermediate transfer belt 41 is placed on all the photosensitive drums 31A to 31D. It is arranged at the color image forming position that is in pressure contact.

  The primary transfer rollers 34 </ b> A to 34 </ b> D are displaced in the separation / contact direction by the separation / contact mechanism 20.

  The separation / contact mechanism portion 20 includes a first link member 21, a second link member 22, a cam 23, and first to fourth swing members 24A, 24B, 24C, and 24D.

  A cam 23 is disposed between the first link member 21 and the second link member 22 along the moving direction 93 of the intermediate transfer belt 41. The first link member 21 and the second link member 22 are arranged so that the longitudinal direction thereof is parallel to the moving direction 93, and are movable within a predetermined range along the moving direction 93 of the intermediate transfer belt 41. The first link member 21 and the second link member 22 are urged toward the cam 23 and are in pressure contact with the cam 23.

  As shown in FIG. 3, the first link member 21, the second link member 22, and the cam 23 are between the first stretching roller 42 and the second stretching roller 43, and are on the front surface of the image forming apparatus 100. It is arranged on each of the side and the back side. The primary transfer roller 34A is pivotally supported by the first link member 21 disposed on the front side and the first link member 21 disposed on the back side. The primary transfer rollers 34 </ b> B to 34 </ b> D are respectively pivotally supported by the second link member 22 disposed on the front side and the second link member 22 disposed on the back side.

  The front-side cam 23 and the rear-side cam 23 are fixed to a single cam shaft 231 and rotate with the same phase around the cam shaft 231. The cam shaft 231 rotates when power is transmitted from the drive source 232. For example, a stepping motor is used as the drive source 232. The drive source 232 is controlled by the control unit 400.

  As shown in FIGS. 4A and 4B, the first to fourth swinging members 24A to 24D each have a shape bent in an L shape. The second to fourth swing members 24B to 24D are configured in the same manner as the first swing member 24A except for the mounting direction with respect to the second link member 22 in the moving direction 93. The second to fourth swing members 24B to 24D are attached to the first swing member 24A symmetrically in FIG.

  The first end 241A of the first swing member 24A is rotatably supported by a frame (not shown) of the intermediate transfer unit 40 on the photosensitive drum 31A side with respect to the first link member 21. The second end 242A of the first swing member 24A supports the primary transfer roller 34A in a rotatable manner. Similarly, the first end portions of the second to fourth swing members 24B to 24D are rotatable to a frame (not shown) of the intermediate transfer unit 40 on the photosensitive drums 31B to 31D side with respect to the second link member 22. It is supported by. The second ends of the second to fourth swinging members 24B to 24D respectively support the primary transfer rollers 34B to 34D so as to be rotatable.

  As shown in FIG. 5, the first swing member 24A is urged in a direction away from the photosensitive drum 31A by a spring 244A. Similarly, the second to fourth swinging members 24B to 24D are urged by springs in directions away from the photosensitive drums 31B to 31D. In FIGS. 4A and 4B, the description of the spring 244A is omitted.

  The first link member 21 has a slit 25 that is long in a direction orthogonal to the moving direction 93 at a position corresponding to the primary transfer roller 24A. The second link member 22 has a long slit in a direction orthogonal to the moving direction 93 at a position corresponding to each of the primary transfer rollers 24B to 24D.

  The first swing member 24A has a protrusion 243A that protrudes in the direction of the rotation axis of the primary transfer roller 34A at the bent portion. The protrusion 243 </ b> A is displaced along the longitudinal direction of the slit 25 in the slit 25 of the first link member 21. The protrusions of the second to fourth swing members 24B to 24D are displaced in the respective slits of the second link member 22 along the longitudinal direction of the respective slits.

  Therefore, as shown in FIG. 4B, when the first link member 21 moves downstream in the direction away from the cam shaft 231, that is, in the moving direction 93 of the intermediate transfer belt 41, it resists the elastic force of the spring 244 A. The protrusion 243A descends in the slit 25, and the primary transfer roller 34A descends and is displaced to the pressing position. As a result, the intermediate transfer belt 41 is pressed against the photosensitive drum 31A. On the other hand, as shown in FIG. 4A, when the first link member 21 moves upstream in the direction approaching the cam shaft 231, that is, in the moving direction 93, the protrusion 243 </ b> A moves in the slit 25 by the elastic force of the spring 244 </ b> A. Ascending, the primary transfer roller 34A rises and is displaced to the separation position. As a result, the intermediate transfer belt 41 is separated from the photosensitive drum 31A.

  Similarly, when the second link member 22 moves to the upstream side in the direction away from the cam shaft 231, that is, the moving direction 93, the primary transfer rollers 34 </ b> B to 34 </ b> D move down to the respective pressing positions, and the second link member When 22 moves to the downstream side in the direction approaching the camshaft 231, that is, the moving direction 93, it moves upward and moves to each separated position.

  As shown in FIGS. 6A to 6C, the cam 23 includes a first cam portion 233 and a second cam portion 234. The first cam portion 233 and the second cam portion 234 are fixed to the cam shaft 231 at a position shifted along the cam shaft 231 and rotate around the cam shaft 231. The first link member 21 is in pressure contact with the working peripheral surface of the first cam portion 233. The second link member 22 is in pressure contact with the working peripheral surface of the second cam portion 234. The 1st cam part 233 and the 2nd cam part 234 are each comprised by the eccentric cam.

  As shown in FIG. 6A, the cam 23 is disposed at a predetermined first angle during non-image formation. As a result, both the first link member 21 and the second link member 22 approach the cam shaft 231. For this reason, all the primary transfer rollers 34A to 34D are arranged at the separated positions. Accordingly, the intermediate transfer belt 41 is disposed at a predetermined reference position that is separated from all the photosensitive drums 31A to 31D.

  As shown in FIG. 6B, at the time of monochrome image formation, the cam 23 is rotated by 90 degrees counterclockwise in FIG. 6B with reference to the non-image formation state, that is, the first angle. Arranged at two angles. As a result, the first link member 21 is separated from the cam shaft 231, and the second link member 22 approaches the cam shaft 231. For this reason, the primary transfer roller 34A for monochrome is displaced to the pressing position, and the primary transfer rollers 34B to 34D for color are arranged at the separated positions. Accordingly, the intermediate transfer belt 41 is disposed at a monochrome image forming position separated from the color photosensitive drums 31B to 31D while being in pressure contact with only the monochrome photosensitive drum 31A.

  As shown in FIG. 6C, at the time of full-color image formation, the cam 23 is rotated at a predetermined first angle rotated 180 degrees counterclockwise in FIG. 6C with reference to the non-image formation state, that is, the first angle. Arranged at three angles. As a result, both the first link member 21 and the second link member 22 are separated from the cam shaft 231. For this reason, all the primary transfer rollers 34A to 34D are arranged at the pressing positions. Therefore, the intermediate transfer belt 41 is disposed at a color image forming position in pressure contact with all the photosensitive drums 31A to 31D.

  As shown in FIG. 7, the image forming apparatus 100 further includes a meandering correction mechanism unit 300 for correcting the meandering of the intermediate transfer belt 41.

  The meandering correction mechanism 300 includes offset transmission members 310A and 310B and biasing members 320A and 320B. The offset transmission members 310 </ b> A and 310 </ b> B are configured to move along the axial direction 94 by the offset force of the intermediate transfer belt 41 along the axial direction 94 of the tension roller 44. The meandering correction mechanism unit 300 urges the tension roller 44 in the direction in which the tension of the intermediate transfer belt 41 increases, and both ends of the tension roller 44 according to the amount of movement along the axial direction 94 of the offset transmission members 310A and 310B. The urging force applied to the part is configured to increase or decrease, respectively. A specific configuration example will be described below.

  The tension roller 44 is supported by the shaft member 45 so as to be rotatable about the shaft member 45 and movable along the shaft member 45.

  The shaft member 45 is supported by the apparatus frames 101A and 101B so that both ends can be independently moved in the direction in which the tension of the intermediate transfer belt 41 is changed, that is, in the vertical direction in FIG. The shaft member 45 is restricted from rotating. As an example, in FIG. 7, the left side is the front surface F side of the image forming apparatus 100, and the right side is the back surface R side of the image forming apparatus 100.

  In the axial direction 94 of the tension roller 44, diameter-expanding members 311A and 311B are arranged so as to be adjacent to both ends of the tension roller 44, respectively. Each of the diameter-expanding members 311 </ b> A and 311 </ b> B has a diameter-expanded portion that is larger in diameter than the tension roller 44 at the end far from the tension roller 44 in the axial direction 94. The portions other than the enlarged diameter portion in the axial direction 94 of each of the enlarged diameter members 311 </ b> A and 311 </ b> B are formed to have the same diameter as the tension roller 44. The diameter-expanding members 311A and 311B are inserted into the shaft member 45, are movable in the axial direction 94, and are rotatably supported by the shaft member 45.

  A sliding member 312A is arranged on the opposite side of the tension roller 44 with respect to the diameter-expanding member 311A in the axial direction 94. A sliding member 312B is disposed on the opposite side of the tension roller 44 with respect to the diameter-expanding member 311B in the axial direction 94. The sliding members 312A and 312B are inserted into the shaft member 45 so as to be adjacent to the diameter-expanding members 311A and 311B in the axial direction 94, and are movable in the axial direction 94. The sliding members 312 </ b> A and 312 </ b> B are restricted from rotating around the shaft member 45. The enlarged diameter member 311A and the sliding member 312A constitute one offset transmission member 310A, and the enlarged diameter member 311B and the sliding member 312B constitute another offset transmission member 310B.

  The biasing member 320A includes a first bracket 321A, a second bracket 322A, a mandrel 323A, and an elastic member 324A. The first bracket 321A is pivotally supported by the sliding member 312A. The second bracket 322A is pivotally supported by the apparatus frame 101A at a predetermined position opposite to the tension roller 44 with respect to the pivot point of the first bracket 321A. That is, the base end portion of the urging member 320A is pivotally supported by the apparatus frame 101A at a predetermined position opposite to the tension roller 44 with respect to the working end portion.

  One end of the mandrel 263A is fixed to one of the first bracket 321A and the second bracket 322A, and is inserted into the other bracket so as to be displaceable. As an example, the mandrel 263A has one end fixed to the second bracket 322A and is inserted through the first bracket 321A so as to be displaceable. The elastic member 264A is disposed between the first bracket 321A and the second bracket 322A and is extrapolated to the mandrel 263A. Since the elastic member 264A expands and contracts along the mandrel 263A, the direction of the elastic force does not distort even if the degree of contraction increases.

  The biasing member 320B includes a first bracket 321B, a second bracket 322B, a mandrel 323B, and an elastic member 324B, and is configured in the same manner as the biasing member 320A. The first bracket 321B is pivotally supported by the sliding member 312B. The second bracket 322B is pivotally supported by the apparatus frame 101B at a predetermined position opposite to the tension roller 44 with respect to the pivot point of the first bracket 321B.

  In other words, the shaft fulcrum of the second brackets 322A and 322B is disposed closer to the end of the shaft member 45 than the shaft fulcrum of the first brackets 321A and 321B in the axial direction 94.

  In this manner, the biasing member 320A is disposed so as to be inclined toward the sliding member 312A in the axial direction 94 of the tension roller 44 from the end side to the center side of the shaft member 45. The biasing member 320B is inclined and arranged in a direction approaching the sliding member 312B as it goes from the end side of the shaft member 45 to the center side in the axial direction 94.

  Further, the shaft fulcrums of the second brackets 322 </ b> A and 322 </ b> B are disposed on the opposite side of the intermediate transfer belt 41 with respect to the shaft member 45. For this reason, the urging members 320 </ b> A and 320 </ b> B urge the shaft member 45 in a direction in which the tension of the intermediate transfer belt 41 is increased.

  FIG. 8 shows a state in which the intermediate transfer belt 41 has been displaced from the ideal position in the width direction to be traveled, that is, has caused meandering. When the intermediate transfer belt 41 meanders and shifts to one side in the axial direction 94, for example, the rear surface R side, the end in the width direction of the intermediate transfer belt 41 pushes the enlarged diameter portion of the enlarged diameter member 311B. The offset transmission member 310B on the downstream side in the offset direction moves along the shaft member 45 to the back surface R side.

  As a result, the inclination angle of the biasing member 320B on the downstream side in the offset direction with respect to the axial direction 94 approaches perpendicular to the axial direction 94, and the degree of contraction of the biasing member 320B increases. For this reason, the pressing force of the urging member 320B against the shaft member 45 is increased on the downstream side of the intermediate transfer belt 41 in the axial direction 94 of the tension roller 44, that is, the back surface R side, and the tension of the intermediate transfer belt 41 is strong. Become.

  Further, the displacement transmission member 310A disposed on the upstream side in the displacement direction moves downstream in the displacement direction by the elastic force of the biasing member 320A along with the displacement of the intermediate transfer belt 41. Thus, the inclination angle of the biasing member 320A on the upstream side in the offset direction with respect to the axial direction 94 approaches the axial direction 94, and the degree of contraction of the biasing member 320A is reduced. For this reason, on the upstream side in the offset direction of the intermediate transfer belt 41 in the axial direction 94, the pressing force of the biasing member 320A against the offset transmission member 310A becomes small, and the tension of the intermediate transfer belt 41 becomes weak.

  Since the endless belt that does not have elasticity has a property of moving from a stronger tension to a weaker tension, the intermediate transfer belt 41 moves to the front surface F side. As a result, the meandering of the intermediate transfer belt 41 toward the back surface R is corrected.

  FIG. 9 shows a state where the intermediate transfer belt 41 meanders to the front surface F side. Also in this case, as in the case shown in FIG. 8, when the intermediate transfer belt 41 meanders and shifts to the front surface F side, the end portion in the width direction of the intermediate transfer belt 41 pushes the enlarged diameter portion of the enlarged diameter member 311A. Accordingly, the offset transmission member 310A on the downstream side in the offset direction, that is, on the front surface F side, moves along the shaft member 45 to the front surface F side. Accordingly, the degree of contraction of the biasing member 320A on the downstream side in the offset direction is increased, and the tension of the intermediate transfer belt 41 on the front surface F side is increased. Further, the tension of the intermediate transfer belt 41 is weak on the upstream side in the offset direction, that is, on the back surface R side. Therefore, the intermediate transfer belt 41 moves to the back surface R side. As a result, meandering of the intermediate transfer belt 41 toward the front surface F is corrected.

  In this way, the intermediate transfer belt 41 meanders and pushes the enlarged diameter portions of the enlarged diameter members 311A and 311B, so that the tension of the intermediate transfer belt 41 on the downstream side in the offset direction is increased and the upstream tension is weak. Therefore, the position in the width direction of the intermediate transfer belt 41 is maintained at a position where the balance between the force to move to the front F side of the intermediate transfer belt 41 and the force to move to the rear R side is balanced.

  Further, a meandering amount of the intermediate transfer belt 41 is corrected by a simple mechanism without requiring a sensor or an electric circuit for detecting the amount of deviation of the intermediate transfer belt 41.

  Further, the rotation direction of the urging member 320A around the shaft fulcrum of the second bracket 322A and the rotation direction of the urging member 320B around the shaft fulcrum of the second bracket 322B, and the intermediate portion between the portions in pressure contact with the tension roller 44 Since the running direction of the transfer belt 41 is different, the biasing members 320A and 320B are not rotated by the running force of the intermediate transfer belt 41 even if the amount of deviation of the intermediate transfer belt 41 is increased. Therefore, the tension applied to the intermediate transfer belt 41 by the tension roller 44 does not become excessively weak. For this reason, the meandering of the intermediate transfer belt 41 can be stably corrected.

  It is preferable that the surface including the locus of rotation centered on the base end portion of each of the urging members 320 </ b> A and 320 </ b> B is orthogonal to the traveling direction of the intermediate transfer belt 41 at the portion in pressure contact with the tension roller 44. As a result, even when the amount of deviation of the intermediate transfer belt 41 increases, the biasing members 320A and 320B are more reliably prevented from rotating by the running force of the intermediate transfer belt 41. For this reason, the meandering of the intermediate transfer belt 41 can be corrected more stably.

  Further, since the diameter expanding members 311A and 311B are rotatable, friction between the intermediate transfer belt 41 and the diameter expanding members 311A and 311B is reduced, and wear at both ends of the intermediate transfer belt 41 is reduced.

  Further, the biasing member 320A, 320B is pivotally supported by the sliding members 312A, 312B whose rotation is restricted, so that the bias when the offset amount of the intermediate transfer belt 41 is a certain value. The arrangement and the degree of contraction of the members 320A and 320B are stabilized, and the accuracy of meandering correction of the intermediate transfer belt 41 is further improved.

  The offset transmission member disposed at least downstream in the offset direction along the axial direction 94 of the intermediate transfer belt 41 among the offset transmission members 310A and 310B moves along the axial direction 94 together with the intermediate transfer belt 41. Then, the meandering correction effect of the intermediate transfer belt 41 is exhibited. The offset transmission member arranged on the upstream side in the offset direction also moves along the axial direction 94 together with the intermediate transfer belt 41, so that the meandering correction effect of the intermediate transfer belt 41 is further increased.

  Further, the diameter-expanding members 311A and 311B can be configured integrally with the tension roller 44.

  Next, in the image forming apparatus 100 including the meandering correction mechanism unit 300 configured as described above, the meandering amount per unit time of the intermediate transfer belt 41, that is, the movement along the axial direction 94 during the non-image forming period. Even when the amount is small and the displacement force of the intermediate transfer belt 41 is small, the structure for preventing the displacement transmission members 310A and 310B from moving and the delay of the movement start timing of the displacement transmission members 310A and 310B will be described. To do.

  As shown in FIG. 10, the control unit 400 is in a non-image forming period (S1), and during the rotation of the intermediate transfer belt 41 (S2), a timing when a predetermined time has elapsed from the start of the rotation of the intermediate transfer belt 41. The belt displacement process is executed (S4) at a timing when a predetermined time has elapsed since the previous execution of the belt displacement process (S3).

  As the belt displacement process, the control unit 400 displaces the intermediate transfer belt 41 from the predetermined reference position shown in FIG. 2A that is separated from all of the plurality of photosensitive drums 31A to 31D, and then returns the intermediate transfer belt 41 to the reference position. The separation / contact mechanism 20 is controlled. The time required for one belt displacement process is, for example, several hundred milliseconds.

  During the non-image forming period and during the rotation of the intermediate transfer belt 41, the belt displacement process is executed at predetermined time intervals, whereby the tension of the intermediate transfer belt 41 changes and vibration is transmitted to the meandering correction mechanism unit 300. Is done. Therefore, even when the offset force of the intermediate transfer belt 41 is small, the offset transmission members 310A and 310B are easily moved by the offset force of the intermediate transfer belt 41. As a result, the urging forces applied to both ends of the tension roller 44 are increased or decreased with high accuracy according to the amount of movement of the offset transmission members 310A and 310B along the axial direction 94. Therefore, the accuracy of meandering correction of the intermediate transfer belt 41 during the non-image forming period can be improved.

  Since the belt displacement process is executed during the non-image forming period, the accuracy of meandering correction of the intermediate transfer belt 41 can be improved without adversely affecting the image forming efficiency and image quality.

  In the first embodiment, when the belt displacement process is executed, the control unit 400 places the intermediate transfer belt 41 away from the reference position from all of the plurality of photosensitive drums 31A to 31D in FIG. A reference position shown in A) is configured to be displaced to a predetermined separation position that is at least partially different.

  Since the intermediate transfer belt 41 is displaced from the reference position to a predetermined separation position until the intermediate transfer belt 41 comes into contact with the photosensitive drums 31A to 31D, it is compared with a case where the intermediate transfer belt 41 is displaced to a position in contact with the photosensitive drums 31A to 31D. Since the displacement distance of the intermediate transfer belt 41 is short, the belt displacement process can be completed in a short time.

  Further, since the intermediate transfer belt 41 does not contact the photosensitive drums 31 </ b> A to 31 </ b> D, residual toner on the photosensitive drums 31 </ b> A to 31 </ b> D does not adhere to the intermediate transfer belt 41. For this reason, it is possible to suppress deterioration in image quality.

  More specifically, when executing the belt displacement process, the controller 400 moves the intermediate transfer belt 41 from the reference position closer to only the monochrome photosensitive drum 31A among the plurality of photosensitive drums 31A to 31D. It is configured to be displaced to at least one of the one separation position and the second separation position approaching all of the plurality of photosensitive drums 31A to 31D.

  It can be displaced to the first separation position by displacing from the reference position to the middle of the monochrome image formation position, and can be displaced to the second separation position by displacing from the reference position to the middle of the color image formation position. be able to. For this reason, it is sufficient if the intermediate transfer belt 41 can be displaced between the monochrome image forming position, the color image forming position, and the reference position, and no special structure is required as the separation / contact mechanism portion 20, so that the intermediate transfer belt 41 can be reduced at low cost. The accuracy of the meandering correction of the transfer belt 41 can be improved.

  The following four examples are given as specific examples of the belt displacement process in the first embodiment. That is, in the first embodiment, the reference position, the first separation position, the second separation position, and the reference position are displaced in this order. In the second embodiment, the reference position, the second separation position, the first separation position, and the reference position are displaced in this order. In the third embodiment, the reference position, the second separation position, and the reference position are displaced in this order. In the fourth embodiment, the reference position, the first separation position, and the reference position are displaced in this order.

  Among the above four examples in the first embodiment, it is most preferable to displace the reference position, the first separation position, and the reference position in this order as in the fourth example. This is because only the monochrome primary transfer roller 34A needs to be displaced and the color primary transfer rollers 34B to 34D do not need to be displaced when the displacement process is executed, so that the burden on the separation / contact mechanism unit 20 is small. .

  In the second embodiment, the control unit 400 causes the intermediate transfer belt 41 to contact only the monochrome photosensitive drum 31A among the plurality of photosensitive drums 31A to 31D from the reference position when the belt displacement process is executed. It is configured to be displaced to at least one of the image forming position and the color image forming position in contact with all of the plurality of photosensitive drums 31A to 31D.

  The intermediate transfer belt 41 only needs to be able to be displaced between the monochrome image forming position, the color image forming position, and the reference position, and no special structure is required as the separation / contact mechanism unit 20. The accuracy of the meandering correction can be improved.

  The following four examples are given as specific examples of the belt displacement process in the second embodiment. That is, in the first embodiment, the reference position, the monochrome image formation position, the color image formation position, and the reference position are displaced in this order. In the second embodiment, the reference position, the color image formation position, the monochrome image formation position, and the reference position are displaced in this order. In the third embodiment, the reference position, the color image forming position, and the reference position are displaced in this order. In the fourth embodiment, the reference position, the monochrome image forming position, and the reference position are displaced in this order.

  Among the above four examples in the second embodiment, it is most preferable to displace the reference position, the monochrome image forming position, and the reference position in this order as in the fourth example. This is because only the monochrome primary transfer roller 34A needs to be displaced and the color primary transfer rollers 34B to 34D do not need to be displaced when the displacement process is executed, so that the burden on the separation / contact mechanism unit 20 is small. .

  In one belt displacement process, the operation of returning from the reference position after the displacement from the reference position may be repeated a plurality of times.

  The belt displacement process can be configured to be executed at least one of a maintenance with toner replenishment and a toner density adjustment.

  Maintenance with toner replenishment is performed during the non-image formation period, and during the maintenance with toner replenishment, the intermediate transfer belt 41 is rotated for a long time. However, the belt displacement process is executed, which adversely affects image formation efficiency and image quality. The accuracy of the meandering correction of the intermediate transfer belt 41 can be improved.

  The toner density is adjusted during the non-image forming period, and when the toner density is adjusted, the intermediate transfer belt 41 is rotated for a long time. However, the belt displacement process is executed, which adversely affects the image forming efficiency and the image quality. The accuracy of the meandering correction of the intermediate transfer belt 41 can be improved.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

20 Separation / contact mechanism 31A to 31D Photosensitive drum (image carrier)
34A to 34D Primary transfer roller 40 Intermediate transfer unit 41 Intermediate transfer belt 42 First tension roller 43 Second tension roller 44 Tension roller 45 Shaft member 93 Moving direction 94 Axial direction 100 Image forming apparatus 300 Meander correction mechanism section 310A, 310B Deviation transmission member 311A, 311B Expanding member 312A, 312B Sliding member 320A, 320B Biasing member 400 Control unit

Claims (6)

A plurality of image carriers that carry toner images;
An endless intermediate transfer belt to which a toner image is transferred from at least one of the plurality of image carriers during image formation;
A separation / contact mechanism for displacing the intermediate transfer belt in a separation / contact direction with respect to each of the plurality of image carriers;
A tension roller that stretches the intermediate transfer belt, a driving roller that rotates the intermediate transfer belt, and a tension roller that can move independently at both ends in the axial direction to change the tension of the intermediate transfer belt. Including a plurality of stretch rollers,
A meandering correction mechanism that biases the tension roller in a direction in which the tension of the intermediate transfer belt increases, and is a shift that moves along the axial direction due to a shift force of the intermediate transfer belt along the axial direction. A meandering correction mechanism that includes a transmission member and increases / decreases the urging force applied to both ends according to the amount of movement of the offset transmission member along the axial direction;
The intermediate transfer belt is displaced from a predetermined reference position separated from all of the plurality of image carriers at a predetermined timing during the rotation of the intermediate transfer belt during a non-image forming period and then moved to the reference position. A controller that executes a belt displacement process for controlling the separation / contact mechanism so as to return,
When the belt displacement process is performed, the control unit is a separation position in which the intermediate transfer belt is separated from all of the plurality of image carriers from the reference position, and at least partly differs from the reference position. An image forming apparatus that is displaced to a predetermined separation position.   The controller, when executing the belt displacement process, moves the intermediate transfer belt from the reference position to a first separation variation position in which only the monochrome image carrier among the plurality of image carriers is approached and the plurality of the plurality of image carriers. The image forming apparatus according to claim 1, wherein the image forming apparatus is displaced to at least one of the second separation variation positions approaching all of the image carrier. A shaft member that supports the tension roller so as to be rotatable and movable along the axial direction;
The offset transmission member has a diameter-expanded portion that is larger than the tension roller, and is adjacent to both end portions of the tension roller in the axial direction and is movable along the axial direction. Inserted into
The meandering correction mechanism is an urging member that urges the shaft member in a direction in which the tension of the intermediate transfer belt increases, and the working end is pivotally supported by the offset transmission member to provide a base end. The image forming apparatus according to claim 1, further comprising an urging member pivotally supported at a predetermined position of the frame. The offset transmission member further includes a sliding member whose rotation around the shaft member is restricted on each side opposite to the tension roller with respect to the enlarged diameter portion in the axial direction,
The image forming apparatus according to claim 3, wherein the action end is pivotally supported by the sliding member.   5. The image forming apparatus according to claim 1, wherein the control unit executes the belt displacement process during maintenance with toner replenishment.   The image forming apparatus according to claim 1, wherein the control unit executes the belt displacement process when adjusting a toner density.

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