JP6366245B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

The present invention is related to a sheet conveying apparatus and an image forming apparatus having the same.

  In a conventional electrophotographic image forming apparatus, a toner image formed on a photosensitive drum is transferred to a transfer belt, the toner image on the transfer belt is transferred to a sheet at a transfer portion, and then fixed on the sheet by a fixing portion. There is something to let you do. In such an image forming apparatus, a change in image density, a color shift, or the like may occur due to a change in the in-machine temperature during the image forming operation.

  In order to reduce the influence of such a change in the in-machine temperature, a patch pattern is formed on the transfer belt according to a predetermined standard when images are continuously formed on a sheet. Then, by reading this patch pattern, correction control for calibrating (correcting) the deviation of each color is executed. When such control is performed, the sheet is temporarily stopped on the sheet conveyance path, and after the control is completed, the sheet is conveyed toward the transfer unit in synchronization with image formation. At the time of this temporary stop, the sheet stands by in a state where skewing is corrected by a registration unit provided immediately upstream of the transfer unit in the sheet conveyance direction.

  In recent years, a sheet conveyance path (conveyance path) for conveying a sheet has been curved in order to reduce the size of the image forming apparatus main body. However, in order to further reduce the size of the image forming apparatus main body, the curvature of the curved portion of the sheet conveyance path has been increased. There is a need to make it even larger. As a configuration for increasing the curvature of the curved portion of the sheet conveying path, the direction of the nip line of the conveying roller pair is greatly inclined with respect to the sheet conveying direction of the sheet conveying path that guides the sheet upstream or downstream of the conveying roller pair. Some have achieved a sheet conveyance path with a large curvature.

  For example, by tilting the nip line direction of the conveyance roller pair greatly with respect to the conveyance direction of the sheet conveyed by the sheet conveyance path formed by the conveyance guide provided upstream of the conveyance roller pair, The conveyance direction is greatly changed by the conveyance roller pair. In this configuration, the sheet conveyance direction is greatly changed as the inclination angle of the nip line direction of the conveyance roller pair is larger with respect to the sheet conveyance direction of the sheet conveyance path. The nip line is a tangent to the peripheral surface of the roller at the nip portion of the conveying roller pair.

  In addition, when the upstream conveying roller pair is a separating roller pair that separates and conveys a sheet, a torque limiter may be provided, and the load of the torque limiter pulls the sheet with the downstream conveying roller pair. It becomes resistance of sheet conveyance when pulling out. Therefore, when the sheet is pulled out by the downstream conveying roller pair, a tension is applied to the sheet between the upstream separating roller pair and the downstream conveying roller pair. When these conveyance roller pairs constitute a conveyance path having a large curvature, the sheet is strongly pressed against one roller of the conveyance roller pair by the tension between the conveyance roller pairs.

  Further, when correction control for calibrating misregistration of each color is performed, the conveyance of the sheet is temporarily stopped in a state where the sheet is strongly pressed against the conveyance roller, so that the portion pressed against the conveyance roller of the sheet has a dent. Arise. Due to this dent, there is a possibility that a transfer failure of the toner image to the sheet may occur. In addition, when the sheet conveying speed of the downstream conveying roller pair is set to be higher than the sheet conveying speed of the upstream conveying roller pair, the degree of tension applied to the sheet is further increased, and the sheet is recessed. Becomes larger.

  Therefore, conventionally, the downstream conveying roller that is stopped in a state where the sheet is held by holding the shaft of one roller of the pair of downstream conveying rollers by the arm member and rotating the arm member by the cam member. There is a device that releases a pair of sheets (Patent Document 1). By releasing the nipping of the sheet, the tension between the downstream conveying roller pair and the upstream conveying roller can be eliminated, and the sheet can be prevented from being strongly pressed against the upstream conveying roller. .

JP-A-8-72340

  However, in the configuration in which the pair of conveyance rollers is separated in order to prevent the dents from being generated in this way, a mechanism for separating the pair of conveyance rollers that is unnecessary for conveyance of the sheet is necessary. It becomes difficult to reduce the size of the forming apparatus main body.

Therefore, the present invention has been made in view of such a current situation, and includes a sheet conveying apparatus and a sheet conveying apparatus that can prevent the occurrence of a sheet dent without adding an unnecessary configuration for conveying the sheet. An object of the present invention is to provide an image forming apparatus.

The present invention provides a sheet conveying apparatus, the first conveying unit that conveys the sheet in the first conveying direction while sandwiching the sheet, and the downstream of the first conveying unit in the first conveying direction, and sandwiches the sheet The second conveying unit that conveys a sheet in a second conveying direction that intersects the first conveying direction as viewed from the sheet width direction orthogonal to the first conveying direction, the first conveying unit, and the second conveying unit Driving means that can be driven independently, and driving of the first conveying section and the second conveying section are controlled by the driving means, and the sheet conveying speed by the second conveying section is controlled by the first conveying section. Control means that can be controlled to be faster than the speed , wherein the control means holds the sheet in a state of being sandwiched between the first conveying section and the second conveying section. Stop driving the transport unit The first conveying unit is driven by a predetermined amount in a state where the sheet is sandwiched between the first conveying unit and the second conveying unit and the driving of the second conveying unit is stopped, Thereafter, the second conveyance unit is driven to convey the stopped sheet.
Further, the present invention provides a sheet conveying apparatus, the first conveying unit that conveys the sheet in the first conveying direction while sandwiching the sheet, and the downstream of the first conveying unit in the first conveying direction. A second transport unit that transports a sheet in a second transport direction that intersects the first transport direction as viewed from a sheet width direction that is orthogonal to the first transport direction while being sandwiched, and the first transport in the first transport direction A guide unit that is provided between the first conveyance unit and the second conveyance unit and guides the sheet conveyed by the first conveyance unit to the second conveyance unit; and the first conveyance unit and the second conveyance unit are independent of each other. And driving means that can be driven, and driving of the first and second conveying sections is controlled by the driving means, and the sheet conveying speed by the second conveying section is determined from the sheet conveying speed by the first conveying section. To make it faster Includes a control capable of controlling means, wherein the control means stops the driving of the first said first conveyor sheets in a state of being nipped by the transport unit and the second conveying unit and the second conveying unit In such a state that the sheet is held between the first conveying unit and the second conveying unit so that the sheet does not contact the guide unit after that, and the driving of the second conveying unit is stopped. The first transport unit is driven by a predetermined amount.

As in the present invention, a sheet that is waiting in a state of being sandwiched between the first conveying unit and the second conveying unit is moved by driving the first conveying unit by a predetermined amount, thereby eliminating the configuration unnecessary for conveying the sheet. Without adding, it is possible to prevent the sheet from being dented.

1 is a diagram showing a schematic configuration of a full-color laser beam printer which is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a sheet feeding device provided in the full color laser beam printer. FIG. 4 is a diagram illustrating sheet feeding operation of the full color laser beam printer. FIG. 4 is a diagram illustrating a sheet conveyance path of the full color laser beam printer. FIG. 3 is a control block diagram of the full color laser beam printer. The figure explaining the deformation | transformation of the sheet | seat at the time of sheet | seat feeding standby. 6 is a flowchart for explaining sheet feeding operation control of the full-color laser beam printer.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a full-color laser beam printer which is an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 201 denotes a full-color laser beam printer (hereinafter referred to as a printer), 201A denotes a printer main body that is an image forming apparatus main body, 201B denotes an image forming unit that forms an image on a sheet, and 220 denotes a fixing unit. An image reading apparatus 202 is an upper apparatus installed substantially horizontally above the printer main body 201A. A discharge space S for discharging sheets is formed between the image reading apparatus 202 and the printer main body 201A. . A sheet feeding device 230 is provided in the lower part of the printer main body and constitutes a sheet feeding unit, 215 is a toner cartridge, 300 is an image forming operation of the image forming unit 201B, a sheet feeding operation of the sheet feeding device 230, and the like. It is a controller which is a control means which controls.

  The image forming unit 201B is of a four-drum full color type, and forms four toner images of the laser scanner 210 and four colors of yellow (Y), magenta (M), cyan (C), and black (K). The process cartridge 211 is provided. Here, each process cartridge 211 includes a photosensitive drum 212, a charger 213 as a charging unit, a developing unit 214 as a developing unit, and a cleaner as a cleaning unit (not shown). In addition, the image forming unit 201B includes an intermediate transfer unit 201C disposed above the process cartridge 211.

  The intermediate transfer unit 201C includes an intermediate transfer belt 216 wound around a driving roller 216a and a tension roller 216b. The intermediate transfer unit 201 </ b> C includes a primary transfer roller 219 that is provided inside the intermediate transfer belt 216 and that contacts the intermediate transfer belt 216 at a position facing the photosensitive drum 212. Here, the intermediate transfer belt 216 is formed of a film-like member and is disposed so as to be in contact with each photosensitive drum 212, and is rotated in the direction of an arrow by a driving roller 216a driven by a driving unit (not shown).

  Then, by applying a positive transfer bias to the intermediate transfer belt 216 by the primary transfer roller 219, each color toner image having a negative polarity on the photosensitive drum 212 is sequentially transferred to the intermediate transfer belt 216 in a multiple transfer manner. As a result, a color image is formed on the intermediate transfer belt 216. A secondary transfer roller 217 constituting a secondary transfer unit that transfers a color image formed on the intermediate transfer belt 216 to a sheet is provided at a position facing the driving roller 216a of the intermediate transfer unit 201C. .

  The sheet feeding device 230 includes a pickup roller 1 that is a sheet feeding unit disposed above the sheet feeding cassette 28 and the like, and is provided in the sheet feeding cassette 28 in parallel with the image forming operation on the intermediate transfer belt. The accommodated sheet P is fed. Thereafter, the sheet P fed by the sheet feeding device 230 is conveyed to the registration roller pair 240, and the skew feeding is corrected by the registration roller pair 240. After the skew is corrected, the sheet P is conveyed to the secondary transfer unit by the registration roller pair 240 at a timing when the color image formed on the intermediate transfer belt 216 coincides with the leading edge of the sheet.

  In the secondary transfer portion, the toner images formed by the image forming portion 201B are transferred onto the sheet P at once. Next, the sheet P onto which the toner image has been transferred in this manner is conveyed to the fixing unit 220, and is fixed to the sheet P as a color image by receiving heat and pressure. Thereafter, the sheet P on which the image has been fixed is discharged into the discharge space S by the discharge roller pairs 225a and 225b, and is stacked on the stacking portion 250 protruding from the bottom surface of the discharge space S. When images are formed on both sides of the sheet S, after the image is fixed, the sheet P is conveyed to the reconveying path R by a reversible roller pair 222 provided in the double-side reversing unit 201D and capable of forward and reverse rotation. Thereafter, it is conveyed again to the image forming unit 201B.

  Here, in addition to the pickup roller 1, the sheet feeding device 230 is disposed downstream of the pickup roller 1 in the sheet feeding direction, as shown in FIGS. 1 and 2, and conveys the sheet sent out by the pickup roller 1. A feed roller 2 as a conveying roller is provided. Furthermore, a retard roller 3 is provided which is supported so as to be press-contactable to the feed roller 2 and press-contacts the feed roller 2 and can be rotated (driven rotation) with respect to the feed roller 2.

  The feed roller 2 and the retard roller 3 constituting the first conveyance roller pair (separation roller pair) 3a that conveys the sheet together with the feed roller 2 constitutes a separation unit 2a that separates the sheet fed by the pickup roller 1. The Note that the sheets fed by the pickup roller 1 and separated one by one when passing through the separation unit 2a are transferred to the registration roller pair 240 by the drawing roller 4 and the roller 22 constituting the second transport roller pair 4a. Be transported.

  As shown in FIG. 4, an upstream sheet conveyance path R1 constituted by an upstream first guide 23 and an upstream second guide 24 is disposed between the first conveyance roller pair 3a and the second conveyance roller pair 4a. Yes. The direction of the nip line of the nip portion N of the feed roller 2 and the retard roller 3 constituting the first conveying roller pair 3a (tangent line of the roller peripheral surface at the nip portion) and the direction of guiding the sheet by the sheet conveying path R1 are as follows. It is greatly inclined.

  Similarly, the direction of the nip line of the nip portion of the drawing roller 4 and the roller 22 constituting the second conveying roller pair 4a and the direction of guiding the sheet by the sheet conveying path R1 are greatly inclined. As a result, a sheet conveyance path having a large curvature is formed between the first conveyance roller pair 3a and the sheet conveyance path R1. Similarly, a sheet conveyance path having a large curvature is configured between the sheet conveyance path R1 and the second conveyance roller pair 4a. Thus, by tilting the sheet conveyance direction of the sheet conveyance paths R1 and R2 and the nip line between the drawing roller 4 and the roller 22, the conveyance path R3 having a large curvature can be configured, and thus the printer main body 201A can be downsized. Can do.

  In FIG. 2, 5 is a feed roller motor as a first driving means, 6 is a drawing roller motor as a second driving means, 8 is a feed roller shaft, and 21 is a drawing roller shaft. Reference numeral 14 denotes a retard roller first shaft, and 16 denotes a retard roller second shaft connected to the retard roller first shaft 14 via a coupling 15. In the present embodiment, separate motors 5 and 6 are used to drive the feed roller 2 and the drawing roller 4. However, it has one motor and a drive system that transmits driving to each of the rollers 2 and 4, and the driving of one motor is transmitted to each of the rollers 2 and 4 by switching control of a clutch disposed in the driving system. May be controlled.

  The drive of the feed roller motor 5 is transmitted to the feed roller shaft 8 via a feed roller drive belt 29 and a feed roller pulley 7 fixed to one end of the feed roller shaft 8, and the feed roller shaft 8 rotates. The other end of the feed roller shaft 8 is provided with a pickup roller input gear 9 into which a one-way clutch that engages when the feed roller shaft 8 rotates in the sheet conveying direction is press-fitted. The pickup roller input gear 9 rotates a pickup roller gear 1 a integrated with the pickup roller 1 via an idler gear 10.

  When the pickup roller input gear 9 is rotated by the action of the one-way clutch due to the rotation of the feed roller shaft 8, the pickup roller gear 1a is rotated via the idler gear 10, and the pickup roller 1 is rotated in the sheet feeding direction. Here, the pickup roller 1 is pressed against the sheet of the sheet feeding cassette 28 from above by a pressing means (not shown). When the pickup roller 1 rotates in the sheet feeding direction, the sheet is sent out to the separation unit 2a. .

  The other end of the feed roller shaft 8 is provided with a feed roller holder 11 into which a one-way clutch that is engaged when the feed roller shaft 8 rotates in the sheet conveying direction is press-fitted. The feed roller 2 rotates in the sheet conveyance direction via the feed roller holder 11 due to the rotation of the feed roller shaft 8 in the sheet conveyance direction.

  Further, the feed roller shaft 8 is provided with a feed roller gear 12 that meshes with a retard roller gear 13 provided on the retard roller first shaft 14. Thus, when the feed roller shaft 8 rotates, the retard roller first shaft 14 rotates in the direction opposite to the sheet conveying direction (hereinafter referred to as the reverse feeding direction) via the feed roller gear 12 and the retard roller gear 13. The rotation of the retard roller first shaft 14 is transmitted to the retard roller second shaft 16 via the coupling 15.

  A retard roller 3 is provided on the retard roller second shaft 16 via a torque limiter 19. The retard roller second shaft 16 is held by a retard roller holder 17 pivotally supported at both ends so as to be pivotable in the vertical direction around a support portion 18 on the paper feed frame. Is constantly pressurized in the direction of the feed roller 2. Thereby, the retard roller 3 is pressed against the feed roller 2 with a predetermined pressure.

  Here, the retard roller second shaft 16 rotates the torque limiter 19, and the torque limiter 19 tries to rotate the coaxial retard roller 3 in the reverse feed direction. When two or more sheets enter the separating portion 2a, the rotation of the retard roller second shaft 16 is transmitted to the retard roller 3 through the torque limiter 19, and the retard roller 103 rotates in the reverse feeding direction. Thereby, it is possible to prevent double feeding of sheets.

  When one sheet enters the separation unit 2a or when no sheet enters, the torque due to the frictional force between the feed roller 2 and the retard roller 3 causes the feed roller 2 of the torque limiter 19 to move backward. It will exceed the torque to rotate. In this case, the torque limiter 19 idles, whereby the retard roller 3 rotates with the feed roller 2 in the sheet conveying direction.

  The driving of the drawing roller motor 6 is transmitted to the drawing roller shaft 21 via the drawing roller driving belt 30 and the drawing roller pulley 20 provided on the drawing roller shaft 21, whereby the drawing roller shaft 21 rotates and the drawing roller 4 rotates. . On the opposite side of the drawing roller 4, as shown in FIG. 4 described later, a roller 22 that constitutes the second conveying roller pair 4a together with the drawing roller 4 is rotatably attached to a vertical path door (not shown). The roller 22 is in pressure contact with the drawing roller 4 by pressure means (not shown).

  Next, the sheet feeding operation of the printer 201 configured as described above will be described with reference to FIG. When the feed roller motor 5 starts to rotate in the direction indicated by the arrow a with the pickup roller 1 in contact with the uppermost surface of the sheet, the feed roller 2 and the pickup roller 1 move in the sheet feeding direction and the sheet conveying direction indicated by the arrow b. Rotate. The retard roller shaft 16 rotates in the reverse feed direction indicated by the arrow c.

  Here, since the retard roller 3 is in contact with the feed roller 2, the frictional force between the rollers exceeds the torque of the torque limiter 19, and the retard roller 3 is rotated in the sheet conveying direction indicated by the arrow d. At the same time, the drawing roller motor 6 starts to rotate in the direction of the arrow e, and the drawing roller 4 rotates in the sheet conveying direction indicated by the arrow f.

  When the sheet P is fed from the sheet feeding cassette 28 by the pickup roller 1 rotating in the arrow b direction, the sheet P is conveyed to the separation nip portion N of the feed roller 2 and the retard roller 3. Then, the sheet P that has passed through the separation nip N is conveyed by the feed roller 2 that rotates in the arrow b direction while rotating the retard roller 3 in the arrow d direction.

  Next, the sheet P that has passed through the separation nip portion N is guided by an upstream sheet conveyance path R1 configured by a pair of opposed upstream first guide 23 and upstream second guide 24 shown in FIG. It is conveyed to the drawing roller 4. Thereafter, the sheet P passes through the downstream sheet conveyance path R <b> 2 constituted by the downstream first guide 25 and the downstream second guide 26 at a position facing the downstream first guide 25 by the drawing roller 4 and the roller 22. It is conveyed to the registration roller pair 240. A sheet detection sensor 27 that detects the presence / absence of a sheet of the registration roller pair 240 is disposed on the upstream side of the registration roller pair 240.

  In the present embodiment, as described above, the upstream sheet conveyance path R1 and the downstream sheet conveyance path R2 form a curved sheet conveyance path R3. As shown in FIG. The curved sheet conveying path R3 is disposed in the curved portion R4. In FIG. 4B, L1 is a line connecting the feed roller 2 and the drawing roller 4 with a tangent, and L2 is a case where the sheet forms a maximum loop between the upstream first guide 23 and the upstream second guide 24. Line. And let the length of each line L1, L2 be S1, S2.

  In the present embodiment, the curvature of the curved sheet conveyance path R3 is increased in order to reduce the size of the printer main body 201A. For this reason, the upstream first guide 23, the upstream second guide 24, the downstream first guide 25, and the downstream first guide member, which are guide members, are arranged so that the upstream conveyance direction D1 and the downstream conveyance direction D2 of the drawing roller 4 are not parallel to each other. Two guides 26 are arranged.

  FIG. 5 is a control block diagram of the printer 201 according to this embodiment. As shown in FIG. 5, a controller 300 having a CPU (not shown) includes a sheet detection sensor 27, a sheet presence / absence sensor 40 for detecting the presence / absence of a sheet in the sheet feeding cassette 28, an operation unit 301, and a feed roller motor. 5 and the drawing roller motor 6 are connected. The controller 300 controls the feed roller motor 5 and the drawing roller motor 6 in accordance with detection signals from the sheet detection sensor 27 and the sheet presence / absence sensor 40. The operation unit 301 inputs the sheet conveyance direction length information of the sheet to the controller 300, and the controller 300 is based on the sheet conveyance direction length information from the operation unit 301 as an input unit as described later. The rotation of the feed roller motor 5 is controlled.

  In this embodiment, in order to reduce the load on the feed roller motor 5, the feed roller motor 5 and the drawing roller motor are arranged so that the sheet conveying speed of the drawing roller 4 is faster than the sheet conveying speed of the feed roller 2. A rotational speed of 6 is set. For this reason, when the sheet P is conveyed to the drawing roller 4, the feed roller 2 is rotated around the sheet while the one-way clutch press-fitted into the feed roller holder 11 is idled due to the difference in sheet conveyance speed.

  Note that while the trailing edge of the sheet is held by the separation nip portion N, the torque limiter 19 continues to apply a force in the reverse feeding direction to the sheet. As a result, the sheet is tensioned by being pulled between the drawing roller 4 and the feed roller 2, so that the sheet assumes the L1 posture shown in FIG. Is strongly pressed against the drawing roller 4.

  In this embodiment, in order to reduce deterioration in image accuracy due to a change in the internal temperature or the like, correction control is executed to calibrate the color misregistration by forming a patch pattern on the transfer belt at a predetermined timing. In this correction control, a patch pattern (patch image) is formed on the surface of the intermediate transfer belt 216 by the process cartridge 211 of each color, the patch pattern is read by an optical sensor, and the controller 300 determines whether the image position is appropriate. If the patch pattern is not formed at an appropriate position, the color misregistration can be corrected by adjusting the writing timing by the laser scanner 210 to the photosensitive drum 212 of each process cartridge 211.

  At the time of this correction control, the sheet is put on standby in a state in which the skew is corrected by the registration roller pair 240. For this reason, when the standby time is long, that is, when the state in which the sheet is strongly pressed against the drawing roller 4 shown in FIG. 6A continues for a long time, the sheet P has a depression Pa as shown in FIG. There is a risk that transfer defects may occur due to the recesses Pa.

  Therefore, in this embodiment, in order to eliminate the tension between the separation nip portion N and the drawing roller 4, when the length of the sheet P is a length in which the sheet trailing edge is in the separation nip portion N during standby, The roller motor 5 is rotated by a predetermined amount, and the feed roller 2 is driven by a predetermined amount. Thereby, the tension between the separation nip portion N and the drawing roller 4 is eliminated, and the occurrence of the dent Pa of the sheet P at the position of the drawing roller 4 can be prevented.

  Next, the sheet conveyance operation control according to the present embodiment will be described with reference to the flowchart shown in FIG. As described above, when the sheet feeding operation is started, the feed roller 2 and the pickup roller 1 are rotated, and the retard roller 3 is rotated by the feed roller 2. At the same time, the drawing roller motor 6 starts to rotate, and the drawing roller 4 rotates in the sheet conveying direction.

  After the sheet is conveyed to the separation nip portion N, the sheet is conveyed to the drawing roller 4 by the feed roller 2 and the retard roller 3 that rotates with the feed roller 2, and then the sheet is conveyed to the registration roller pair 240 by the drawing roller 4. The Here, as described above, the rotation of the feed roller motor 5 and the drawing roller motor 6 is performed so that the sheet conveying speed of the drawing roller 4 is faster than the sheet conveying speed of the feed roller 2 in order to reduce the load on the feed roller motor 5. Speed is set.

  For this reason, when the sheet reaches the drawing roller 4, the one-way clutch press-fitted into the feed roller holder 11 idles, and the feed roller 2 comes to follow the sheet. Note that while the trailing edge of the sheet is held by the separation nip portion N, the torque limiter 19 continues to apply a force in the reverse feeding direction to the sheet.

  Thereafter, the sheet reaches the registration roller pair 240. When this is detected and the sheet detection sensor 27 is turned on (STEP 1), the controller 300 executes the control for reducing the influence due to the change in the in-machine temperature, etc., so that the feed roller motor 5 and the drawing roller motor 6 are controlled. Is turned OFF (STEP 2). As a result, the conveyance of the sheet is stopped, and the sheet stands by in a state where the skew feeding is corrected by the registration roller pair 240.

  Next, the controller 300 determines whether the sheet is longer than the length from the registration roller pair 240 to the separation nip N based on the sheet conveyance direction length information from the operation unit 301. That is, when the sheet is in a standby state, the leading end (downstream end) of the sheet is clamped by the registration roller pair 240, and the trailing end (upstream end) of the sheet is separated by the separation nip portion N. It is judged whether it is the length clamped by (STEP 3). Here, when the sheet is in a standby state and the sheet trailing edge is a length at the separation nip portion N (Y in STEP 3), the sheet trailing edge is separated from the separation nip when the sheet stops. It does not pass through part N.

  In this case, the sheet is pulled between the drawing roller 4 and the feed roller 2 due to the difference in conveying speed, assumes the L1 posture shown in FIG. 4B, and is strongly pressed against the peripheral surface of the drawing roller 4. It becomes like this. Therefore, when it is determined that the length of the sheet is long (Y in STEP 3), the controller 300 turns on the feed roller motor 5 in order to release the tension on the sheet between the separation nip portion N and the drawing roller 4. To rotate a predetermined amount (STEP 4). As a result, the feed roller 2 rotates (drives) by a predetermined amount and the sheet is conveyed by a predetermined amount, so that the tension between the separation nip portion N and the drawing roller 4 is released.

  At this time, although the sheet differs depending on the type of the sheet, if the sheet is conveyed beyond the length of the line L1 shown in FIG. The seat is buckled between the second guide 24 and the upstream second guide 24. For this reason, the predetermined amount for driving the feed roller 2 is that the upstream first guide 23 and the upstream that constitute the upstream sheet conveyance path R1 in which the sheet is a portion between the drawing roller 4 and the feed roller 2 of the sheet conveyance path R3. It is necessary that the amount does not contact the second guide 24.

  Therefore, in the present embodiment, the rotation amount of the feed roller 2 is set in advance so that the conveyance amount of the sheet is equal to or less than S2-S1, and the controller 300 rotates the feed roller motor 5 by the set amount. Let As a result, the stopped sheet moves and the tension between the separation nip portion N and the drawing roller 4 is eliminated, and the occurrence of a dent at the position of the drawing roller 4 of the sheet can be prevented.

  Next, when a predetermined time for rotating the feed roller motor 5 by the set amount has elapsed (Y in STEP 5), the feed roller motor 5 is turned off (STEP 6). Thereafter, the drawing roller motor 6 is turned on at the timing when the color image formed on the intermediate transfer belt 216 coincides with the leading edge of the sheet (STEP 7), and the conveyance of the sheet is resumed. As a result, the sheet is conveyed to the secondary transfer unit, and the toner images are transferred onto the sheet all at once. At this time, since no dent is generated in the sheet, no transfer failure occurs.

  Next, the presence / absence of a sheet in the sheet feeding cassette is detected by the sheet presence / absence sensor 40 (STEP 8). If a sheet remains in the sheet feeding cassette 28, that is, if the sheet is not the final sheet (N of STEP8), STEP1 to STEP7 are repeated. When there are no more sheets in the sheet feeding cassette 28, that is, when the sheet is the last sheet (Y in STEP 8), the sheet feeding operation is terminated (STEP 9).

  As described above, in the present embodiment, the first transport roller pair 3a is configured with a sheet waiting (stopped) while being sandwiched between the first transport roller pair 3a and the second transport roller pair 4a. The feed roller 2 to be driven is moved by a predetermined amount. Thereby, without adding a configuration unnecessary for the conveyance of the sheet, it is possible to prevent the occurrence of the dent of the sheet, and it is possible to prevent the transfer of the toner image onto the sheet from being poorly transferred.

  In the above description, the feed roller motor 5 is rotated every time when the leading edge of the sheet is waiting at the registration roller pair 240. However, if the feed roller motor 5 is rotated every time, the productivity is lowered. For this reason, the feed roller motor 5 may be rotated only when the standby time is equal to or longer than a predetermined time.

  In the above description, the feed roller motor 5 is rotated in a state where the leading end of the sheet reaches the registration roller pair 240, but the timing for rotating the feed roller motor 5 is not limited to this. For example, even when the sheet stands by between the drawing roller 4 and the registration roller pair 240, the feed roller motor 5 may be rotated.

  Further, in the description so far, the first conveying roller pair is constituted by the feed roller 2 and the retard roller 3, and the second conveying roller pair is constituted by the drawing roller 4 and the roller 22. However, the present invention is not limited to this. For example, the second conveying roller pair may be configured by the rollers of the double-side reversing unit 201D and the fixing unit 220. Further, the separation unit may be constituted by a feed roller 2, a separation roller or a separation pad.

  In the present embodiment, the example in which the sheet is stopped when the color misalignment correction is performed in the image forming unit 201B has been described. However, this is not the only reason why the sheet stops. For example, when a sheet is jammed while continuously feeding sheets, all the sheets conveyed in the image forming apparatus are stopped. For this reason, even if a jam occurs at a location other than between the sheet feeding device and the image forming unit, the sheet fed from the sheet feeding device stops between the drawing roller 4 and the feed roller 2. May end up. Since the stopped sheet is a usable sheet, there is a case where the conveyance is continued when the image formation is resumed by leaving it at the time of jam recovery. Even in such a case, the image defect of the sheet can be prevented by performing the control of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Pick-up roller, 2 ... Feed roller, 2a ... Separation part, 3 ... Retard roller, 3a ... 1st conveyance roller pair, 4 ... Extraction roller, 4a ... 2nd conveyance roller pair, 5 ... Feed roller motor, 6 ... Extraction Roller motor, 22 ... roller, 201 ... full color laser beam printer, 201A ... printer main body, 201B ... image forming unit, 230 ... sheet feeding device, 240 ... registration roller pair, 300 ... controller, 301 ... operation unit, N ... Separation nip, P ... sheet, Pa ... dent, R1 ... upstream sheet conveyance path, R2 ... downstream sheet conveyance path, R3 ... sheet conveyance path, R4 ... curved section

Claims (10)

A first transport unit that transports the sheet in the first transport direction while sandwiching the sheet;
The sheet is disposed downstream of the first conveying unit in the first conveying direction, and sandwiches the sheet in a second conveying direction that intersects the first conveying direction when viewed from the sheet width direction orthogonal to the first conveying direction. A second conveying unit for conveying
Driving means capable of independently driving the first transport unit and the second transport unit;
Control capable of controlling the driving of the first conveying unit and the second conveying unit by the driving means so that the sheet conveying speed by the second conveying unit is faster than the sheet conveying speed by the first conveying unit. Means, and
The control means stops the sheet held between the first conveyance unit and the second conveyance unit by stopping driving of the first conveyance unit and the second conveyance unit, and the first conveyance unit The first conveying unit is driven by a predetermined amount in a state where the sheet is sandwiched by the second conveying unit and the driving of the second conveying unit is stopped, and then the second conveying unit is driven and stopped. To transport the sheet
A sheet conveying apparatus. The control means drives the first transport unit by the predetermined amount in a state where the driving of the second transport unit is stopped, and then moves the second transport unit in a state where the driving of the first transport unit is stopped. To transport the sheet that has been stopped by driving,
The sheet conveying apparatus according to claim 1. A guide unit provided between the first transport unit and the second transport unit in the first transport direction and guiding the sheet transported by the first transport unit to the second transport unit;
The predetermined amount for driving the first conveyance unit is an amount that prevents the sheet conveyed by the first conveyance unit from coming into contact with the guide unit.
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. The control unit is configured to stop the driving of the second transport unit when the sheet held between the first transport unit and the second transport unit is stopped for a predetermined time or longer. Driving the predetermined amount, and then driving the second conveying unit to convey the stopped sheet,
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. A skew correction unit capable of correcting the skew of the sheet by abutting the leading edge of the sheet conveyed by the second conveyance unit;
The first conveying unit conveys a sheet in the first conveying direction, and separates the sheet by nipping the sheet together with the conveying rotating body and separating the sheets one by one. And
The control unit stops driving the first conveyance unit and the second conveyance unit for the sheet in which the skew is corrected by the skew correction unit and is sandwiched between the first conveyance unit and the second conveyance unit. The first conveyance unit is driven by the predetermined amount in a state where the sheet is sandwiched between the first conveyance unit and the second conveyance unit and the driving of the second conveyance unit is stopped. Then, the second transport unit is driven to transport the stopped sheet,
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. The separation unit is a retard roller including a torque limiter.
The sheet conveying apparatus according to claim 5. The drive means includes a first drive unit that drives the first transport unit, and a second drive unit that drives the second transport unit.
Sheet conveying device according to any one of claims 1 to 6, characterized in that. A first transport unit that transports the sheet in the first transport direction while sandwiching the sheet;
The sheet is disposed downstream of the first conveying unit in the first conveying direction, and sandwiches the sheet in a second conveying direction that intersects the first conveying direction when viewed from the sheet width direction orthogonal to the first conveying direction. A second conveying unit for conveying
A guide unit that is provided between the first transport unit and the second transport unit in the first transport direction and guides the sheet transported by the first transport unit to the second transport unit;
Driving means capable of independently driving the first transport unit and the second transport unit;
Control capable of controlling the driving of the first conveying unit and the second conveying unit by the driving means so that the sheet conveying speed by the second conveying unit is faster than the sheet conveying speed by the first conveying unit. Means, and
The control means stops the sheet held between the first conveying unit and the second conveying unit by stopping driving of the first conveying unit and the second conveying unit, and then the sheet is guided to the guide. The first conveying unit is driven by a predetermined amount in a state where the sheet is held between the first conveying unit and the second conveying unit and the driving of the second conveying unit is stopped so as not to contact the portion. Let
A sheet conveying apparatus. A sheet conveying apparatus according to any one of claims 1 to 8 ,
An image forming unit that forms an image on a sheet conveyed by the sheet conveying device;
An image forming apparatus. When the image forming unit performs color misregistration correction control, the control unit moves the sheet held between the first conveying unit and the second conveying unit to the first conveying unit and the second conveying unit. The sheet is stopped by driving the first conveying unit by a predetermined amount in a state where the driving of the second conveying unit is stopped, and then driving the second conveying unit. Transport,
The image forming apparatus according to claim 9 .

Images