JP2010217398A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus satisfactorily reducing an impact force occurring when transferring an image. <P>SOLUTION: An image forming apparatus 1 is provided with: an intermediate transfer belt 21 carrying a toner image; a transfer part 50; and a driving part for moving the transfer part 50. The transfer part 50 has: a transfer roller 51 facing the intermediate transfer belt 21; a roller member 52 provided approximately in parallel with the transfer roller 51; and a belt member 53 wound around the transfer roller 51 and the roller member 52. In the state where the transfer part 50 is located in a position PG2, the secondary transfer roller 51 is off a position facing the intermediate transfer belt 21 and a stretched portion of the belt member 53 faces the intermediate transfer belt 21. The rear end part of a paper PA leaves a part wherein the intermediate transfer belt 21 and the stretched portion of the belt member 53 face each other, in the state where the transfer part 50 has been moved to the position PG2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer.

  In an image forming apparatus, a final image is formed on a sheet by directly or indirectly transferring an image formed on a photoconductor to a sheet (transfer material).

  For example, as a tandem type electrophotographic printer, there is an apparatus that superimposes and transfers an image of each color component on a plurality of photoconductors to an intermediate transfer belt, and transfers the image (full color image) on the intermediate transfer belt to a sheet. Exists (see Patent Document 1).

  In such an image forming apparatus, when a sheet passes through a nip portion which is a facing portion between a transfer roller (secondary transfer roller) and a driving roller of an intermediate transfer belt, intermediate transfer is performed by applying a voltage to the secondary transfer roller. The image on the belt is transferred to the paper.

JP 2006-317627 A

  However, when the sheet passes through such a nip portion, a large impact force may be generated when the rear end portion of the sheet passes through the nip portion. In particular, when the paper is relatively thick, the rear end portion of the paper is released from the nip portion so as to be repelled by the nip portion, and a relatively large impact force is generated. Such an impact force causes image disturbance and is a factor that adversely affects image formation. Specifically, the impact force at the time of paper collision is transmitted to the fixing unit provided on the downstream side of the transfer unit via the paper, and paper misalignment at the fixing unit may occur, causing image distortion. is there. Alternatively, when the impact force is transmitted to the intermediate transfer belt in a period in which the next image after the transfer onto the paper PA is formed on the intermediate transfer belt (on the next transfer belt) It may adversely affect image formation. Note that with the technique of Patent Document 1, the impact force is not sufficiently reduced.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of satisfactorily reducing the impact force generated during image transfer.

  In order to solve the above problems, the invention of claim 1 is an image forming apparatus, wherein an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, A driving unit that relatively moves the transfer unit and the image carrier, the transfer unit including a transfer roller, a first roller provided substantially parallel to the transfer roller, and the transfer roller; And a belt member wound around a plurality of rollers including the first roller, and the transfer portion is movable between a first position and a second position by a driving operation of the driving means. In the state where the transfer portion is present at the first position, the transfer roller faces the image carrier, and in the state where the transfer portion is present at the second position, the transfer roller is The belt deviates from the position facing the image carrier and the belt A tension part of the material is opposed to the image carrier, and the driving unit moves the transfer unit to the second position, and from the opposing part of the tension part of the image carrier and the belt member, The rear end portion of the transfer material is separated.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the invention, the driving unit moves the transfer unit to the second position when the thickness of the transfer material is larger than a predetermined threshold value. The rear end portion of the transfer material is separated from the facing portion between the image carrier and the transfer roller.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect of the present invention, the image carrier is an intermediate transfer belt that temporarily carries the toner image from a photoconductor, and the intermediate The transfer belt is wound around a plurality of rollers including a second roller, and in a state where the transfer portion is present at the first position, the transfer roller faces the second roller, and the transfer belt In the state where the portion is present at the second position, the transfer roller is disengaged from the position opposed to the second roller, and the stretched portion of the belt member is opposed to the second roller. The transfer portion is moved to the second position, and a rear end portion of the transfer material is separated from a facing portion between the second roller and a stretched portion of the belt member.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the first roller is allowed to move relative to the first roller and the transfer roller side. It further comprises elastic support means for elastically supporting

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the belt member has an elastic layer made of a conductive elastic material.

  The invention according to claim 6 is an image forming apparatus, an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, the transfer unit, and the image carrier. Drive means for relatively moving the body, and the transfer section includes a transfer roller, a first roller provided upstream of the transfer roller in the conveying direction of the transfer material, and the transfer roller. A belt member wound around a plurality of rollers including the first roller, and the transfer unit is relative to the image carrier toward the downstream side in the transfer direction of the transfer material by the driving unit. After the transition from the first state in which the transfer roller faces the image carrier to the second state in which the stretched portion of the belt portion faces the image carrier, An image carrier and a stretch portion of the belt portion The rear end of the transfer material sandwiched therebetween by passing the characterized in that the leaving from the opposite part of the two.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect of the invention, the transfer portion is downstream of the transfer material in the conveyance direction in the substantially extending direction of the stretched portion of the belt member by the driving unit. It is moved toward.

  According to the first to seventh aspects of the invention, when the transfer material is detached from between the transfer portion and the image carrier, the impact force of the transfer material removal is alleviated by the bending of the belt member. That is, it is possible to satisfactorily reduce the impact force generated during image transfer.

  In particular, according to the invention described in claim 4, since the belt member bends not only according to the elasticity of the belt member but also according to the elasticity of the elastic force applying means, the impact force of the transfer material detachment is further appropriately reduced. The

  In particular, according to the invention described in claim 5, when the transfer material is detached from between the transfer portion and the image carrier, the transfer material is released due to the deformation of the belt member accompanied by the deformation of the elastic layer of the belt member. Impact force is reduced.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment. It is a side view which shows a transfer part. It is a perspective view which shows a transcription | transfer part. FIG. 6 is a diagram illustrating a state in which a leading end of a sheet collides with a belt member of a transfer unit. FIG. 6 is a diagram illustrating a state in which a leading end of a sheet enters a nip portion. It is a figure which shows a mode that a sheet | seat passes a nip part. FIG. 6 is a diagram illustrating a state where a rear end of a sheet is detached from a nip portion. FIG. 6 is a diagram illustrating a state in which a rear end of a sheet is detached from a nip portion and guided to a belt member. It is a figure which shows the transfer part which concerns on 2nd Embodiment. It is a partially expanded view which shows the cross section of the belt member which concerns on 2nd Embodiment. It is a figure which shows the transfer part which concerns on a modification.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1. First Embodiment>
<1-1. Equipment overview>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an apparatus that develops an electrostatic latent image on an image carrier to form an image. Here, as the image forming apparatus, an electrophotographic apparatus, more specifically, a tandem type full-color electrophotographic apparatus is illustrated.

  As shown in FIG. 1, the image forming apparatus 1 includes a plurality (specifically, four) of imaging units 10 (specifically, 10Y, 10M, 10C, and 10K). Specifically, the image forming apparatus 1 includes a yellow imaging unit 10Y, a magenta imaging unit 10M, a cyan imaging unit 10C, and a black imaging unit 10K. Each imaging unit 10 is an electrophotographic image of each color component (specifically, each component of Y (yellow), M (magenta), C (cyan), K (black)) in the final output image). It is formed by a method and transferred to an intermediate transfer belt (also referred to as an intermediate transfer member) 21. Then, the image of each color component superimposed on the intermediate transfer belt 21 is further transferred onto a sheet (transfer material) PA, whereby a full color image is formed on the sheet PA. The intermediate transfer belt 21 is also expressed as an image carrier that temporarily carries a toner image transferred from each photoconductor 11 (described later).

  The four imaging units 10 (10Y, 10M, 10C, and 10K) are arranged in the lower linear portion mainly at the lower portion of the lower linear portion of the intermediate transfer belt 21 that is wound around the driving roller 23 and the winding roller 24. Are arranged in series. Each imaging unit 10 includes a photoconductor 11, a charger 12, an exposure device 13, a developing device 14, a first transfer device (primary transfer device) 15, an eraser (static eliminating device) 16, and a cleaner 17. Yes. Specifically, in each imaging unit 10, a charger 12, an exposure device 13, a developing device 14, a first transfer device 15, an eraser 16, and a cleaner 17 are provided so as to surround the outer periphery of the substantially cylindrical photoconductor 11. Arranged clockwise in order. Among these, the first transfer device 15 (specifically, a transfer roller) is disposed at a position facing the photoconductor 11 with the intermediate transfer belt 21 therebetween.

  The intermediate transfer belt 21 moves in the direction of the arrow AR <b> 1 by driving the driving roller 23. A transfer unit 50 is provided at a position facing the drive roller 23 with the intermediate transfer belt 21 therebetween. The transfer unit 50 will be described in detail later.

  In addition, a paper feeding unit 30 is provided below each imaging unit 10 and the transfer unit 50 (upstream on the transport path). The paper feed unit 30 includes a paper feed tray 31, a feed roller 32, a paper feed roller 33, and a suction roller 34, and is configured to supply the paper PA toward the timing rollers 41 and 42 and the transfer unit 50. Has been. Further, a fixing device 45 is provided on the downstream side in the transport direction of the paper PA that has passed the position of the transfer roller (secondary transfer roller) 51 of the transfer section 50, and the paper discharge section 46 is further downstream in the transport direction. Is provided.

  The image forming apparatus 1 prints out an image based on image data transmitted from another information processing apparatus (such as a personal computer) connected via a network or the like by using the printing mechanism as described above. Functions as a color page printer.

  Further, the transfer unit 50 described above is upstream of the vicinity of the position where the intermediate transfer belt 21 and the secondary transfer roller 51 face each other (and from the position of the timing rollers 41 and 42) in the paper transport path (transfer material transport path). Is also provided from the position on the downstream side to the vicinity of the facing position. Next, the configuration and the like of the transfer unit 50 will be described in detail.

<1-2. Transfer part 50>
2 and 3 are diagrams illustrating the configuration of the transfer unit 50 (also referred to as 50A) according to the first embodiment. FIG. 2 is a side view showing the transfer unit 50, and FIG. 3 is a perspective view showing the transfer unit 50. 3 shows only the configuration of one end side (front side in FIG. 2) of the secondary transfer roller 51 and the driven roller 52, the same applies to the other end side (back side in FIG. 2). A configuration is provided.

  As shown in FIGS. 2 and 3, the transfer unit 50 is wound around a secondary transfer roller 51, a driven roller 52 disposed substantially parallel to the secondary transfer roller 51, and both rollers 51 and 52. And an endless belt member 53. The driven roller 52 is provided upstream of the secondary transfer roller 51 in the conveyance direction of the paper PA. In the belt member 53, a stretched portion PT <b> 1 (described below) between the secondary transfer roller 51 and the driven roller 52 is provided on the upstream side in the transport direction with respect to the secondary transfer roller 51.

  As shown in FIG. 2, the portion PT1 is a portion on the sheet conveyance path side of the portion stretched between the secondary transfer roller 51 and the driven roller 52 in the belt member 53, and is between the contact CP2 and the contact CP1. It is a substantially straight portion. Here, the contact CP <b> 1 is a contact between the secondary transfer roller 51 and the substantially linear portion of the belt member 53, and the contact CP <b> 2 is a contact between the driven roller 52 and the substantially linear portion of the belt member 53. Since the portion PT1 is a portion stretched between the two rollers 51 and 52, it is also expressed as a stretched portion. Further, the portion PT1 is not in contact with the outer peripheral portion of the secondary transfer roller 51 and is not in contact with the outer peripheral portion of the driven roller 52. In other words, the portion PT1 is not supported by either the secondary transfer roller 51 or the driven roller 52. Therefore, the part PT1 is also referred to as a non-supporting part. Alternatively, the portion PT1 is also expressed as a portion that can be bent in response to an external force, that is, a flexible portion.

  Each of the secondary transfer roller 51 and the driven roller 52 has a rotation shaft extending in the width direction of the conveyed paper (the depth direction in FIG. 2), and rotates around each rotation shaft. The secondary transfer roller 51 is mechanically connected to a rotation drive motor (drive device), and rotates according to the rotation drive operation of the motor. That is, the secondary transfer roller 51 is a transfer roller as well as a drive roller. When the secondary transfer roller 51 rotates, the belt member 53 wound around the secondary transfer roller 51 and the driven roller 52 rotates in a circular manner. The belt member 53 is made of a resin material such as polyimide (PI) or polyphenylene-sulfide (PPS), for example. The belt member 53 contains a substance that imparts conductivity (for example, carbon black). By imparting electrical conductivity to the belt member 53, the toner image on the intermediate transfer belt 21 is appropriately transferred to the paper PA in response to voltage application by the secondary transfer roller 51.

  Further, the secondary transfer roller 51 and the driven roller 52 can relatively move in a direction in which the distance between them is expanded or contracted. Then, by applying an elastic force by the spring 54 in a direction that increases the relative distance between the secondary transfer roller 51 and the driven roller 52, the belt member 53 wound around the secondary transfer roller 51 and the driven roller 52 is applied to the belt member 53. A tension F is applied. In other words, the spring 54 is driven by an elastic force in a direction to return the driven roller 52 to the position before the movement while allowing the driven roller 52 to move to the downstream side in the transport direction (secondary transfer roller 51 side). The driven roller 52 is elastically supported by being applied to the roller 52.

  Specifically, plate-like slide members 55 are provided on both ends of the secondary transfer roller 51 (and the driven roller 52). A spring 54 is provided between the secondary transfer roller 51 and the driven roller 52 via a slide member 55 and a standing member 56 fixed to the slide member 55. Appropriate elastic force (biasing force) is applied between them. Specifically, as shown in FIG. 3, the shaft member of the secondary transfer roller 51 is disposed through the circular hole 55 c of the slide member 55, and the shaft member of the driven roller 52 is the long hole 55 d of the slide member 55. It is arranged to pass through. The driven roller 52 can move in the extending direction of the long hole 55d, and the driven roller 52 and the secondary transfer roller 51 can relatively move in the direction in which the distance between them is expanded or contracted. A spring 54 is provided between the standing member 56 and the bearing portion 52 c of the driven roller 52. The spring 54 is provided in a state in which the spring 54 is contracted from the natural length, and a force in a direction that further increases the relative distance between the secondary transfer roller 51 and the driven roller 52 acts on the spring 54. An appropriate tension (tension) F acts on the belt member 53 wound around the secondary transfer roller 51 and the driven roller 52 by the elastic force of the spring 54 and the like.

  Further, the transfer unit 50 is provided so as to be able to move in parallel along the direction AR3. Specifically, the shaft member of the slide member 55 of the transfer unit 50 is supported by the slide bearing mechanism 58 so as to be slidable along the direction AR3, and the slide member 55 is movable along the direction AR3. Along with the parallel movement operation (slide movement operation) of the slide member 55, other components (specifically, the secondary transfer roller 51, the driven roller 52, the belt member 53, and the like) of the transfer unit 50 are also in the AR3. Translate along In this way, each element of the transfer unit 50 moves in parallel along the direction AR3. The direction AR3 is also expressed as a substantially extending direction of the stretched portion PT1 of the belt member 53.

  The slide member 55 is driven by the drive unit 70. The drive unit 70 includes a motor 71 and a gear (pinion) 72. The drive shaft of the motor 71 is connected to a gear 72, and the gear 72 meshes with a planar gear (rack) 55 f provided on the side of the slide member 55. The rotational drive of the motor 71 is transmitted to the rack 55f via the gear 72, and the rotational motion of the motor is converted into the linear motion of the slide member 55. That is, the slide member 55 is driven along the direction AR3 by the rack and pinion mechanism. As a result, the transfer unit 50 moves in parallel along the direction AR3. In other words, the transfer unit 50 is moved relative to the intermediate transfer belt 21 (and the drive roller 23) by the drive unit 70.

  The transfer unit 50 is movable between at least the next two positions PG1 (FIG. 4) and position PG2 (FIG. 6) along the direction AR3.

  The position PG <b> 1 of the transfer unit 50 is a position where the secondary transfer roller 51 of the transfer unit 50 faces the drive roller 23. In a state where the transfer unit 50 exists at the position PG1, as shown in FIG. 4, the secondary transfer roller 51 faces the intermediate transfer belt 21 (specifically, the drive roller 23).

  On the other hand, the position PG <b> 2 of the transfer unit 50 is a position where the secondary transfer roller 51 of the transfer unit 50 deviates from the facing position of the driving roller 23 (also referred to as a facing contact position or a facing proximity position) to the downstream side in the transport direction. In a state where the transfer unit 50 exists at the position PG2, as shown in FIG. 6, the secondary transfer roller 51 is separated from the facing position of the intermediate transfer belt 21 (and the facing position of the driving roller 23) and the belt member 53 is stretched. The portion PT1 faces the intermediate transfer belt 21.

<1-3. Operation>
Next, a transfer operation using the transfer unit 50 will be described in detail. The transfer operation and the like are controlled by a controller (control unit) built in the image forming apparatus 1.

  When the paper PA supplied by the paper supply unit 30 and transported from the upstream side of the transport path passes through the positions of the timing rollers 41 and 42, the paper thickness sensor 61 provided on the upstream side of the transfer unit 50 in the paper transport path. The thickness D of the paper is detected by (see FIG. 1).

  In this embodiment, the subsequent operation differs depending on the detected thickness D. Specifically, the subsequent operation differs depending on whether the thickness D is larger than a predetermined threshold DT (for example, 0.5 mm (millimeters)) or smaller than the threshold DT. When the thickness D is equal to the threshold value DT, any of the following two operations may be executed.

  First, a case where the thickness D of the paper PA is smaller than the threshold value DT will be described.

  After the sheet PA has passed the position of the timing rollers 41 and 42 (see FIG. 1), the secondary transfer roller 51 starts to rotate at an appropriate timing. As a result, the belt member 53 moves from the upstream side (lower side in FIG. 2) to the downstream side (upper side in FIG. 2) of the paper PA, as indicated by an arrow AR2 in FIG. And proceed. Here, it is assumed that the conveyance speed of the belt member 53 is substantially the same as the conveyance speed of the intermediate transfer belt 21.

  Further, the timing rollers 41 and 42 convey the paper PA, which is a transfer target of the toner image, toward the portion PT1 of the belt member 53. Then, as shown in FIG. 2, the sheet PA conveyed from the upstream side further advances along the conveyance path. When the paper PA further travels along the transport path, it collides with the portion PT1 of the belt member 53 with a collision angle θ. The impact force that acts on the portion PT1 of the belt member 53 from the front end portion of the thin paper PA is smaller than the impact force that acts on the portion PT1 of the belt member 53 from the front end portion of the thick paper PA. Further, such an impact force is absorbed by the portion PT1 being bent and the spring 54 being further contracted.

  Thereafter, the front end of the paper PA is conveyed downstream (upward in the drawing) at a speed substantially the same as the speed of the belt member 53 according to the rotation operation of the belt member 53 while being in contact with the belt member 53. The Then, the paper PA reaches and enters the nip portion N3 that is a portion where the secondary transfer roller 51 and the intermediate transfer belt 21 (and the drive roller 23) face each other. In other words, the sheet PA enters a portion where the winding portion of the intermediate transfer belt 21 with respect to the driving roller 23 and the winding portion of the belt member 53 with respect to the secondary transfer roller 51 are opposed to each other. Then, the paper PA passes through the nip portion N3. When the sheet PA passes through the nip portion N3, the full-color toner image formed on the intermediate transfer belt 21 is transferred onto the sheet PA by the transfer unit 50 (particularly, voltage application to the secondary transfer roller 51). Transcribed.

  When the paper PA further advances downstream in the transport direction, the rear end portion of the paper PA leaves the nip portion N3. Note that the impact force acting when the thin paper PA is detached is smaller than the impact force acting when the thick paper PA is detached.

  The toner image transferred onto the paper PA is heated by the fixing device 45 and fixed on the paper PA. Thereafter, the paper PA is discharged to the paper discharge unit 46.

  When the thickness D is smaller than the threshold value DT, the above operation is executed.

  Next, an operation when the thickness D of the paper PA is larger than the threshold value DT will be described.

  After the sheet PA has passed the position of the timing rollers 41 and 42 (see FIG. 1), the secondary transfer roller 51 starts to rotate at an appropriate timing. As a result, the belt member 53 advances from the upstream side to the downstream side of the conveyance path on the conveyance path side of the paper PA, as indicated by an arrow AR2 in FIG.

  Then, the paper PA conveyed by the timing rollers 41 and 42 is conveyed toward the portion PT1 of the belt member 53, and collides with the portion PT1 of the belt member 53 with a collision angle θ as shown in FIG. To do. In order to reduce the impact force at the time of collision, the collision angle θ is preferably a relatively small acute angle (specifically, 45 degrees or less). Further, the collision angle θ is more preferably 30 degrees or less.

  As shown in FIG. 4, when the paper PA collides with the portion PT <b> 1 of the belt member 53, the portion PT <b> 1 is bent by the elasticity of the spring 54 and the elasticity of the belt member 53. In particular, the collision force acting on the portion PT1 of the belt member 53 from the front end portion of the paper PA is absorbed by the portion PT1 being bent and the spring 54 being further contracted. In this way, the impact force due to the collision of the paper PA is absorbed, and the impact force transmitted to the secondary transfer roller 51 and the intermediate transfer belt 21 is reduced. Therefore, adverse effects on image formation can be suppressed.

  Thereafter, the leading end portion of the paper PA is conveyed downstream (upward in the drawing) at a speed substantially equal to the speed of the belt member 53 according to the rotation operation of the belt member 53 while being in contact with the belt member 53. . In addition, the bending of the belt member 53 caused when the paper PA collides is reduced during the transport operation.

  Then, as shown in FIG. 5, the sheet PA enters a nip portion N <b> 3 (see also FIG. 4) that is a portion where the driving roller 23 and the secondary transfer roller 51 face each other. In other words, the leading end portion of the paper PA enters a portion where the winding portion of the intermediate transfer belt 21 with respect to the driving roller 23 and the winding portion of the belt member 53 with respect to the secondary transfer roller 51 are opposed to each other.

  Thereafter, in a period in which the non-end portion (the portion between the front end portion and the rear end portion) of the paper PA passes near the drive roller 23, the transfer unit 50 changes the direction AR3 according to the drive operation of the drive unit 70. It slides from position PG1 to position PG2 toward the downstream side in the transport direction along (FIG. 3) (see FIG. 6). Note that during this drive period by the drive unit 70, the increase in the speed (speed relative to the intermediate transfer belt 21) of the belt member 53 in the vicinity of the nip portion N4 due to the slide movement of the transfer unit 50 to the downstream side in the transport direction is 2. It is preferable to cancel by reducing the rotation speed of the next transfer roller 51. In other words, the rotational speed of the secondary transfer roller 51 is set so that the moving speed of the belt member 53 at the nip portion N4 (described below) and the moving speed of the intermediate transfer belt 21 at the nip portion N4 are substantially the same. It is preferably adjusted (decelerated). Here, the nip portion N4 is a facing portion between the driving roller 23 and the portion PT1 of the belt member 53.

  When the transfer unit 50 exists at the position PG2, the paper PA passes through the nip N4. In other words, the sheet PA is sandwiched between both the intermediate transfer belt 21 (specifically, the portion of the intermediate transfer belt 21 wound around the drive roller 23) and the portion PT1 of the belt member 53, and is in contact with the both. Pass through.

  As described above, when the thickness D of the paper PA is larger than the threshold value DT, the transfer unit 50 is moved to the position PG2 by the driving unit 70 toward the downstream side in the transport direction of the paper PA. By this movement, the relationship between the intermediate transfer belt 21 and the transfer unit 50 changes from the state ST1 to the state ST2 as follows. That is, from the state ST1 (see FIG. 4) in which the secondary transfer roller 51 faces the intermediate transfer belt 21 (and the drive roller 23), the stretched portion PT1 of the belt member 53 becomes the intermediate transfer belt 21 (and the drive roller 23). Transition to the opposing state ST2 (FIG. 6). Then, as shown in FIG. 6, the paper PA passes through a facing portion (nip portion N <b> 4) between the intermediate transfer belt 21 and the stretched portion PT <b> 1 of the belt member 53.

  The full-color toner image formed on the intermediate transfer belt 21 is transferred to the transfer portion 50 (particularly, voltage is applied to the secondary transfer roller 51 and the belt member 53) when the paper PA passes through the nip portions N3 and N4. Is transferred onto the paper PA.

  Thereafter, as shown in FIGS. 7 and 8, the rear end portion of the sheet PA is detached from the nip portion N4.

  When the paper PA passes through the nip portion N4, the paper PA advances toward the downstream side in the transport direction while being in contact with and sandwiched between the intermediate transfer belt 21 and the stretched portion PT1 of the belt member 53. At this time, as shown in FIG. 7 (and FIG. 6 etc.), the secondary transfer roller 51 does not exist on the right side (opposite to the drive roller 23) with respect to the stretched portion PT1 of the belt member 53. That is, the stretched portion PT1 of the belt member 53 is not supported by the secondary transfer roller 51, and the portion PT1 is movable to the right side. Therefore, before the paper PA is detached from the nip portion N4, the belt member 53 has a state of being slightly bent rightward due to its elasticity.

  Then, as shown in FIG. 8, when the paper PA is detached from the nip portion N4, the stretched portion PT1 is gradually returned to the left side from the state where it is moved to the right side due to the elasticity of the belt member 53 or the like. To do.

  In this way, the rear end portion of the sheet PA is detached from the nip portion N4 (FIG. 8). Here, when the rear end portion of the sheet PA is separated from the nip portion N4, the operation of restoring the bending of the belt member 53 is mainly accompanied. The impact force in this restoring operation is the impact force when the paper PA is detached from the nip portion N3 (for example, the secondary transfer roller 51 rapidly returns toward the winding portion of the intermediate transfer belt 21 around the drive roller 23). Is very small compared to the impact force at the time of collision. The fact that the belt member 53 is lighter than the secondary transfer roller 51 also contributes to suppression of impact force. Thus, the impact force when the rear end portion of the paper PA is separated from the nip portion N4 is very small.

  Further, after the rear end portion of the paper PA is separated from the nip portion N4, the paper PA contacts the belt member 53 and is further guided to the downstream side in the transport direction (FIG. 8). Specifically, the rear end portion of the paper PA remains in contact with the belt member 53 and moves downstream (upward in the drawing) at substantially the same speed as that of the belt member 53 according to the rotation operation of the belt member 53. Be transported.

  Thereafter, the rear end portion of the paper PA moves away from the belt member 53 and further proceeds downstream in the transport direction.

  The toner image transferred onto the paper PA is heated by the fixing device 45 and fixed on the paper PA. Thereafter, the paper PA is discharged to the paper discharge unit 46. The transfer unit 50 is driven by the drive unit 70 and returns to the original position PG1.

  When the thickness D is larger than the threshold value DT, the above operation is executed.

  As described above, according to the image forming apparatus 1, when the thickness D of the paper PA is larger than the threshold value DT, the transfer unit 50 is moved to the position PG2, and the intermediate transfer belt 21 (and the drive roller 23). And the rear end portion of the sheet PA is separated from the portion of the belt member 53 facing the portion PT1 (FIGS. 7 and 8). As described above, in the state where the transfer portion 50 exists at the position PG2, since the portion PT1 of the belt member 53 faces the intermediate transfer belt 21 (and the drive roller 23), the elasticity of the belt member 53 is increased. Etc., the impact force when the paper is detached is alleviated. That is, it is possible to satisfactorily reduce the impact force generated during image transfer (specifically, when the rear end portion of the paper PA is detached from the transfer portion 50). Therefore, it is possible to prevent image distortion by reducing the impact force transmitted via the paper PA to the fixing unit provided on the downstream side of the transfer unit. Further, when the rear end of the paper PA is separated from the transfer unit 50, the impact at the time of paper separation is also obtained in a situation where the next image after the image that has been transferred to the paper PA is formed on the intermediate transfer belt. By reducing the force, it is possible to reduce the influence on the image forming operation (related to the next image) on the intermediate transfer belt.

  Further, the secondary transfer roller 51 and the driven roller 52 are provided so as to be relatively movable in a state where an elastic force is applied between them by a spring 54. Therefore, the portion PT1 bends not only according to the elasticity of the belt member 53 but also according to the elasticity of the spring 54. Thereby, the impact force at the time of separation of the rear end portion of the paper PA is further appropriately reduced.

<2. Second Embodiment>
<2-1. Overview>
The second embodiment is a modification of the first embodiment. Below, it demonstrates centering on difference with 1st Embodiment.

  FIG. 9 is a side view showing the transfer unit 50 (specifically, 50B) according to the second embodiment. FIG. 10 is an enlarged cross-sectional view in the vicinity of the portion PR1 in FIG. 9, and is a diagram illustrating a detailed configuration of the belt member 53 (specifically 53B) according to the second embodiment.

  As shown in FIG. 10, the belt member 53 </ b> B includes a base layer 531 and an elastic layer 532. Specifically, the elastic layer 532 is formed by being laminated on the outer side (outer peripheral side) of the base layer 531.

  The base layer 531 is made of, for example, a resin material such as polyimide (PI) or polyphenylene sulfide (PPS). The base layer 531 of the belt member 53 contains a substance that imparts conductivity (for example, carbon black).

  On the other hand, the elastic layer 532 is made of a conductive elastic material. Specifically, as the material of the elastic layer 532, for example, rubber such as NBR or EPDM is used. Further, the rubber that is a material of the elastic layer 532 of the belt member 53 contains a substance that imparts conductivity (for example, carbon black). Such a conductive rubber is preferably used for the elastic layer 532. The conductive rubber of the elastic layer 532 is preferably a material whose hardness is reduced by foaming (that is, a foamable conductive elastic member (such as foamable conductive rubber)).

  Since the base layer 531 and the elastic layer 532 have conductivity, the toner image on the intermediate transfer belt 21 is appropriately transferred to the paper PA in response to voltage application to the secondary transfer roller 51.

  In the second embodiment, the same operation as that of the first embodiment is performed using the transfer unit 50B having such a belt member 53B. According to this, it is possible to obtain the same effects as those of the first embodiment, and it is also possible to obtain the following effects. Specifically, since the belt member 53B has the elastic layer 532 on the outer peripheral side thereof, the impact force when the leading end portion of the paper PA collides with the portion PT1 due to the elasticity of the elastic layer 532 in the portion PT1. In addition to being reduced, the impact force when the rear end portion of the paper PA is separated from the nip portion N4 is also reduced. In addition, when foamable rubber is used for the elastic layer 532, a suitable impact reducing action can be obtained.

<3. Other>
Although the embodiments of the present invention have been described above, the present invention is not limited to the contents described above.

  For example, in each of the above embodiments, the case where tension is applied to the belt member 53 by the spring 54 is illustrated, but the present invention is not limited to this. Specifically, a transfer unit 50C as shown in FIG. 11 may be provided. In the transfer portion 50C, it is assumed that the spring 54 as the elastic force applying means is not provided, and the shaft member of the driven roller 52 is disposed through the circular hole 55e of the slide member 55. That is, the positions of the central axes of the rollers 51 and 52 are fixed so that the relative distance between the secondary transfer roller 51 and the driven roller 52 is always the same. Using such a transfer portion 50C also reduces the impact force generated when the leading end of the paper PA collides, and reduces the impact force generated when the trailing end of the paper PA is separated from the nip portion N4. Is possible. Specifically, the impact force is reduced by the belt member 53 being bent by the elasticity of the belt member 53 itself. However, in order to bend the belt member 53 more appropriately, the secondary transfer roller 51 and the driven roller 52 are relatively moved in a state where the elastic force (repulsive force) by the spring 54 is applied as in the above-described embodiments. It is preferable to provide it.

  In each of the above embodiments, the case where the transfer unit 50 moves along the direction AR3 that is the substantially extending direction of the stretched part PT1 of the belt member 53 is illustrated, but the present invention is not limited to this. For example, the transfer unit 50 may be slid to the downstream side in the transport direction along a direction having a predetermined inclination angle with respect to the direction AR3. Even in such a case, in the state ST2 (FIG. 6) in which the intermediate transfer belt 21 (and the drive roller 23) and the stretched portion PT1 of the belt member 53 face each other, the sheet PA is in contact with both. By arranging the two so as to pass through, the same effect as described above can be obtained.

  Further, in each of the above embodiments, the case where the thickness D of the paper PA is detected by the paper thickness sensor 61 is illustrated, but the present invention is not limited to this, and the thickness D is detected by other methods. Also good. For example, the thickness D of the paper PA may be acquired based on the print setting content included in the print instruction transmitted from the information processing apparatus (personal computer or the like) that is the print output request source. Specifically, in the information processing apparatus of the print output request source, print setting information (information indicating the paper thickness (including paper type information)) set by the operator of the information processing apparatus on the setting screen of the printer driver From this, the thickness D of the paper PA may be acquired.

  In each of the above embodiments, the case where different operations are performed according to the thickness D of the paper PA is illustrated, but the present invention is not limited to this, and the same operation is performed regardless of the thickness D of the paper PA. It may be.

  Further, in each of the above embodiments, the case where the transfer unit 50 moves after the front end portion of the paper PA has entered the facing portion (specifically, the nip portion N3) of the drive roller 23 and the transfer unit 50 is illustrated. It is not limited to this. For example, the transfer unit 50 may be moved in advance to the position PG2 before the leading end portion of the paper PA enters the facing portion between the drive roller 23 and the transfer unit 50. According to this, since the leading end portion of the sheet PA enters the nip portion N4 (a portion where the driving roller 23 and the stretched portion PT1 face each other), the leading end portion of the sheet PA is formed between the driving roller 23 and the transfer portion 50. It is also possible to reduce the impact force when rushing into the facing portion.

  In each of the above embodiments, a tandem color printer is exemplified as the image forming apparatus. However, the image forming apparatus is not limited to this, and the image forming apparatus is not limited to this. The idea described above may be applied. The image carrier is not limited to the intermediate transfer belt 21 and may be, for example, a photosensitive drum in a four-cycle color printer.

  Further, the image forming apparatus is not limited to an apparatus having only a printing function, and may be, for example, a multifunction machine having a scanning function and / or a copying function.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10, 10Y, 10M, 10C, 10K Imaging unit 21 Intermediate transfer belt 23 (Intermediate transfer belt) drive roller 50, 50A, 50B, 50C Transfer part 51 Secondary transfer roller 52 Driven roller 53 Belt member 54 Spring 55 Slide member 61 Paper thickness sensor 532 Elastic layer N3, N4 Nip part PA Paper PT1 Stretched part (flexible part)

Claims (7)

An image forming apparatus,
An image carrier for carrying a toner image;
A transfer unit that transfers the toner image on the image carrier to a transfer material;
Driving means for relatively moving the transfer section and the image carrier;
With
The transfer portion is
A transfer roller;
A first roller provided substantially parallel to the transfer roller;
A belt member wound around a plurality of rollers including the transfer roller and the first roller;
Have
The transfer section is movable between a first position and a second position by a driving operation of the driving means,
In the state where the transfer portion is present at the first position, the transfer roller faces the image carrier,
In a state where the transfer portion is present at the second position, the transfer roller is disengaged from the facing position of the image carrier, and the stretched portion of the belt member faces the image carrier,
The driving unit moves the transfer unit to the second position, and separates a rear end portion of the transfer material from a portion facing the image carrier and a stretched portion of the belt member. Image forming apparatus. The image forming apparatus according to claim 1,
The driving unit moves the transfer unit to the second position when the thickness of the transfer material is larger than a predetermined threshold, and starts the transfer material from a facing portion between the image carrier and the transfer roller. An image forming apparatus, wherein a rear end portion of the image forming apparatus is separated. The image forming apparatus according to claim 1, wherein:
The image carrier is an intermediate transfer belt that temporarily carries the toner image from a photoconductor,
The intermediate transfer belt is wound around a plurality of rollers including a second roller,
In the state where the transfer portion is present at the first position, the transfer roller faces the second roller,
In the state where the transfer portion is present at the second position, the transfer roller is disengaged from the position opposed to the second roller, and the stretched portion of the belt member faces the second roller,
The drive means moves the transfer portion to the second position, and detaches a rear end portion of the transfer material from a portion facing the second roller and a stretched portion of the belt member. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
Elastic support means for elastically supporting the first roller while allowing relative movement between the first roller and the transfer roller;
An image forming apparatus further comprising: 5. The image forming apparatus according to claim 1, wherein:
The image forming apparatus, wherein the belt member has an elastic layer made of a conductive elastic material. An image forming apparatus,
An image carrier for carrying a toner image;
A transfer unit that transfers the toner image on the image carrier to a transfer material;
Driving means for relatively moving the transfer section and the image carrier;
With
The transfer portion is
A transfer roller;
A first roller provided upstream of the transfer roller in the transport direction of the transfer material;
A belt member wound around a plurality of rollers including the transfer roller and the first roller;
Have
A first state in which the transfer roller is opposed to the image carrier by moving the transfer portion relative to the image carrier toward the downstream side in the transport direction of the transfer material by the driving unit. The transfer portion passing between the image carrier and the stretched portion of the belt portion after the stretched portion of the belt portion transitions to the second state facing the image carrier. An image forming apparatus, wherein a rear end portion of the material is detached from a facing portion of the both. The image forming apparatus according to claim 6.
The image forming apparatus according to claim 1, wherein the transfer unit is moved by the driving unit toward the downstream side in the conveyance direction of the transfer material in a substantially extending direction of the stretched portion of the belt member.

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