JP2019163099A - Carrier device and image forming device - Google Patents

Abstract

To provide a carrier device which can correct the skew of a sheet high accurately.SOLUTION: A carrier device 30 comprises: skew correction rollers 31 for holding and carrying a sheet P; resist opposition rollers 32 and a resist roller 33 provided on the downstream side of the skew correction rollers 31; a detection part 39 capable of detecting a sheet position; and a control part. The skew correction rollers can correct the skew of the sheet P by being arranged side by side in the width direction of the sheet P, and relatively changing the sheet carrying speeds of the skew correction rollers. The control part makes the skew correction rollers correct the skew of the sheet P after calculating a skew amount of the sheet P on the basis of a detection result of the detection part in a position on the upstream side of the sheet carrying direction compared with nip portions of the resist opposition rollers and the resist roller, and makes the skew correction rollers correct the skew of the sheet P again after calculating a skew amount of the sheet P on the basis of a detection result of detecting the sheet position by the detection part in butting positions to the nip portions of the sheet P.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a conveyance device and an image forming apparatus.

  In a conveying apparatus that conveys a sheet, positional deviation such as skewing of the sheet and deviation in the width direction at the time of conveyance becomes a problem. For example, in an image forming apparatus that forms an image on a sheet, there is a problem in that an image position formed on the sheet is deviated from an ideal position due to skew during conveyance of the sheet.

  In view of this, an invention of a conveying device that corrects the skew while conveying a sheet has been conventionally made. For example, in the skew correction apparatus of Patent Document 1 (Japanese Patent Laid-Open No. 2000-95384), a skew detection sensor and two registration roller pairs are provided in the sheet width direction. Then, based on the skew amount of the sheet calculated from the detection result of the skew detection sensor, the sheet conveyance speed between the two registration roller pairs is relatively changed, so that one side and the other side in the sheet width direction are changed. The sheet feeding speed can be varied to correct the skew of the sheet.

  Further, in the sheet skew correction device of Patent Document 2 (Japanese Patent Application Laid-Open No. 2003-72982), a sheet is conveyed downstream by a registration timing roller to reach a contact point of a downstream registration roller pair. In this state, when the registration timing roller further rotates forward, the sheet is pressed against the nip portion of the registration roller pair on the downstream side to bend. Then, in the state where the sheet is abutted against the nip portion of the downstream registration roller pair, the downstream registration roller pair is reversed by an arbitrary rotation angle, whereby vibration can be applied to the leading edge of the sheet. The skew of the sheet is corrected by the front end of the sheet becoming a contact point by the above-described abutting operation and the vibration of the sheet by the subsequent reverse operation.

  As in the invention of Patent Document 1, in the configuration in which the skew of the sheet is corrected based on the difference in the sheet conveyance speed, the skew correction amount of the sheet with respect to the change in the speed greatly varies, and the skew of the sheet is corrected with high accuracy. Is difficult. In particular, depending on the type and thickness of the sheet, there is a variation in the amount of skew correction with respect to a given speed difference, which makes it more difficult to accurately correct the sheet skew.

  Further, in the invention of Patent Document 2, the sheet is pressed against the nip portion by uniformly abutting the leading end of the sheet on the nip portion line of the downstream registration roller pair, thereby correcting the skew of the sheet. However, when the sheet is greatly skewed and pressed against the nip portion, there is a problem that uniform pressing is not performed and the skew of the sheet is not sufficiently corrected. In particular, when a highly rigid sheet such as cardboard is conveyed, it has been difficult to press it uniformly.

  In view of such circumstances, an object of the present invention is to provide a conveying apparatus that can correct sheet skew with high accuracy.

  In order to solve the above-described problems, the present invention provides a pair of rollers that sandwich and convey a sheet, and a plurality of rollers are arranged in parallel in the width direction of the sheet, and the rotation speed of each of the sheets is relatively changed. A skew feeding correction roller for correcting skew feeding, a sandwiching roller provided on the downstream side of the skew feeding correction roller in the sheet feeding direction, and a detection roller for detecting the sheet position. And a control unit that controls the skew feeding correction roller, wherein the detection unit is more in the sheet transport direction than the abutting position where the leading edge of the sheet is abutted against the nip part of the nipping roller. When the sheet position is detected at the first upstream position, based on the detection result of the detection unit, the control unit calculates the skew amount of the sheet and applies the skew correction roller to the skew correction roller. When the skew of the sheet is corrected and the abutting position or the vicinity of the abutting position, which is a position downstream of the first position in the sheet conveying direction, is the second position, the detection unit When the sheet position is detected at the second position, based on the detection result of the detection unit, the control unit calculates the skew amount of the sheet and feeds the skew of the sheet to the skew correction roller. It is characterized by a transport device that corrects again.

  In the present invention, by correcting the skew of the sheet by the skew correction roller before reaching the sheet abutting position, the sheet is abutted against the nip portion of the sandwiching roller with a smaller skew amount. Can do. Further, by detecting the sheet at the abutting position or a position in the vicinity thereof and correcting the skew of the sheet again by the skew correction roller, the skew of the sheet can be corrected with high accuracy.

1 is a schematic configuration diagram of an image forming apparatus. It is a figure of the conveying apparatus which concerns on embodiment of this invention, (a) A figure is a top view, (b) A figure is a side view. It is a top view of the conveying apparatus concerning this embodiment. It is a top view of the conveying apparatus concerning this embodiment. It is a top view of the conveying apparatus concerning this embodiment. It is a top view of the conveying apparatus concerning this embodiment. It is a figure which shows the calculation method of the skew feeding amount of a paper. FIG. 6 is a side view showing a state where a sheet has hit a registration roller. It is a flowchart which shows the process of the paper conveyance operation | movement and skew feeding correction | amendment operation | movement of the conveying apparatus which concerns on this embodiment. It is a flowchart which shows the process of the paper conveyance operation | movement of the conveying apparatus which concerns on this embodiment, and the position shift correction | amendment operation | movement of the width direction. It is a figure which shows the structure of the control part which concerns on embodiment of this invention. It is sectional drawing which shows the structure of a skew feeding correction roller. It is sectional drawing which shows the moving mechanism of a registration roller. It is bb sectional drawing of FIG. It is a schematic block diagram which shows the image forming apparatus of different embodiment. It is a schematic block diagram which shows a post-processing apparatus.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

  In the color image forming apparatus 1 shown in FIG. 1, an image forming unit 3 in which four process units 9Y, 9M, 9C, and 9Bk are detachably provided is arranged. Each process unit 9Y, 9M, 9C, 9Bk contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (Bk) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each process unit 9 includes a photosensitive drum 10 that is a drum-like rotating body capable of carrying toner as a developer on the surface, and a charging roller 11 that uniformly charges the surface of the photosensitive drum 10. And a developing device 12 for supplying toner to the surface of the photosensitive drum 10, a cleaning device, and the like.

  An exposure unit is disposed above the process unit 9. The exposure unit is configured to emit laser light based on the image data.

  A transfer unit 4 is disposed immediately below the image forming unit 3. The transfer unit 4 includes a drive roller 13, a secondary transfer counter roller 15, a plurality of tension rollers, an endless intermediate transfer belt 16 stretched around these rollers so as to be able to run around, and a photosensitive drum of each process unit 9. 10 includes a primary transfer roller 17 disposed at a position facing the intermediate transfer belt 16 with respect to 10. Each primary transfer roller 17 presses the inner peripheral surface of the intermediate transfer belt 16 at each position, and a primary transfer nip is formed at a place where the pressed portion of the intermediate transfer belt 16 and each photosensitive drum 10 come into contact. Has been.

  A secondary transfer roller 18 is disposed at a position opposite to the drive roller 13 of the intermediate transfer belt 16 and the drive roller 13 across the intermediate transfer belt 16. The secondary transfer roller 18 presses the outer peripheral surface of the intermediate transfer belt 16, and a secondary transfer nip is formed at a location where the secondary transfer roller 18 and the intermediate transfer belt 16 are in contact with each other.

  The paper feeding unit 5 is located at the lower part of the image forming apparatus 1, and is a paper feeding cassette 19 as a sheet stacking unit that accommodates paper P as sheets, and a paper feeding roller that carries out the paper P from each paper feeding cassette. It consists of 20 mag.

  The transport path 6 is a transport path for transporting the paper P carried out from the paper supply unit 5. On the conveyance path 6, a plurality of conveyance roller pairs are appropriately arranged until reaching a paper discharge unit described later.

  On the conveyance path 6, the positional deviation of the paper P on the conveyance path 6 is corrected downstream of the paper feeding unit 5 and upstream of the secondary transfer nip position, and the paper P is moved downstream. A transport device 30 for transport is provided.

  The fixing device 7 includes a fixing roller 22 that is heated by a heating source, a pressure roller 23 that can press the fixing roller 22, and the like.

  The paper discharge unit 8 is provided on the most downstream side of the conveyance path 6 of the image forming apparatus 1. The paper discharge unit 8 is provided with a pair of paper discharge rollers 24 for discharging the paper P to the outside and a paper discharge tray 25 for stocking the discharged paper P.

  The conveyance path 6 is provided with a reverse conveyance path 6 a that separates the downstream of the fixing device 7, in addition to the path to the paper discharge unit 8. The reverse conveyance path 6 a joins the conveyance path 6 that continues from the sheet feeding unit 5 at its end.

  The basic operation of the image forming apparatus 1 will be described below with reference to FIG.

  In the image forming apparatus 1, when an image forming operation is started, an electrostatic latent image is formed on the surface of the photosensitive drum 10 of each process unit 9Y, 9C, 9M, 9Bk. The image information exposed to each photosensitive drum 10 by the exposure unit is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. An electrostatic latent image is formed on each photoconductive drum 10, and toner stored in each developing device is supplied to the photoconductive drum 10 by a drum-shaped developing roller, whereby the electrostatic latent image is visualized. A visible image is formed as a toner image (developer image).

  In the transfer unit 4, the intermediate transfer belt 16 is driven to travel in the direction of the arrow in the drawing by the rotational drive of the drive roller 13. Further, each primary transfer roller 17 is applied with a constant voltage or a constant current-controlled voltage having a polarity opposite to the charging polarity of the toner. As a result, a transfer electric field is formed in the primary transfer nip, and the toner images formed on the respective photosensitive drums 10 are sequentially superimposed and transferred onto the intermediate transfer belt 16 in the primary transfer nip. Thus, for example, the image forming unit 3, the exposure unit, the transfer unit 4, etc. function as an image forming unit that forms an image on the paper P.

  On the other hand, when the image forming operation is started, the sheet P stored in the sheet feeding cassette 19 is moved to the transport path 6 by rotating the sheet feeding roller 20 of the sheet feeding unit 5 below the image forming apparatus 1. Sent out.

  The paper P sent out to the transport path 6 is transported downstream by the transport device 30 and the roller pair on the transport path 6, and its positional deviation is corrected by the transport device 30, so that the secondary transfer roller 18 and the secondary transfer roller 18 are aligned. It is sent to a secondary transfer nip formed between the transfer opposing roller 15. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 16 is applied, and a transfer electric field is formed in the secondary transfer nip. The toner images on the intermediate transfer belt 16 are collectively transferred onto the paper P by the transfer electric field formed in the secondary transfer nip.

  The sheet P on which the toner image has been transferred is conveyed to the fixing device 7, and the sheet P is heated and pressed by the fixing roller 22 and the pressure roller 23, so that the toner image is fixed on the sheet P. Then, the paper P on which the toner image is fixed is separated from the fixing roller 22, transported by a pair of transport rollers, and discharged to the paper discharge tray 25 by the paper discharge roller 24 in the paper discharge unit 8.

  When double-sided printing is performed on the paper P, the paper P is conveyed to the paper discharge roller 24 and the paper discharge roller 24 rotates in reverse until the rear end of the paper P passes through the paper discharge roller 24. P is conveyed in the reverse direction and sent to the reverse conveyance path 6a. Thereafter, the paper P is transported on the reverse transport path 6a by the reverse transport roller, and is sent again to the upstream side of the transport device 30 in the transport path 6 in a state where the paper P is reversed. Then, after the positional deviation of the paper P is corrected by the transport device 30, the image is transferred and fixed on the back surface, and is discharged to the paper discharge tray 25 by the paper discharge roller 24.

  The above description is an image forming operation when a full color image is formed on the paper P. A single color image can be formed using any one of the four process units 9Y, 9C, 9M, and 9Bk. It is also possible to form two or three color images using two or three process units 9.

Next, the configuration of the transport device 30 will be described in more detail with reference to FIGS. 2 (a) and 2 (b). In the following description, the paper width direction (vertical direction in FIG. 2a) is also simply referred to as the width direction.
As shown in FIGS. 2A and 2B, the conveying device 30 includes skew correction rollers 31A and 31B, registration counter rollers 32A, 32B, and 32C, registration rollers 33, and skew detection CIS 34A. , 34B, a width direction detection CIS 35 as a second detection unit, an upper guide plate 36, and a lower guide plate 37.

  The skew correction rollers 31A and 31B are conveying members configured by a pair of rollers, and each sheet is rotated while the sheet P is nipped between the rollers, thereby conveying the sheet P downstream. can do. The skew correction roller 31A and the skew correction roller 31B are juxtaposed in the width direction of the paper, the skew correction roller 31A is disposed on one side in the width direction, and the skew correction roller 31B is disposed on the other side in the width direction. ing. The one side and the other side in the width direction are, for example, one side above the center position in the width direction of the registration roller 33 in FIG. 2A (the center position of the registration roller 33 arranged at the reference position), The lower side can be the other side.

  The registration facing rollers 32A, 32B, and 32C are arranged in parallel in the sheet width direction and face the common registration roller 33. The registration roller 33 forms a nip portion between each of the registration facing rollers 32A, 32B, and 32C, and sandwiches the paper P in the nip portion to be driven to rotate so that the paper P can be conveyed downstream. it can. In other words, the registration roller 33 and each registration counter roller 32 constitute a sandwiching roller that is a pair of rollers that sandwich and convey the paper P. Further, the registration roller 33 and the registration counter rollers 32A, 32B, and 32C are provided so as to be integrally movable in the width direction of the paper P. The registration roller 33 and the registration counter rollers 32A, 32B, and 32C integrally move in the width direction with the paper P being sandwiched, whereby the positional deviation in the width direction of the paper P can be corrected.

  The registration roller 33 may be a plurality of rollers divided in the width direction, like the registration counter roller 32. However, it is preferable that the registration roller 33 is a long axis roller because the squareness of the registration roller 33 can be further reduced.

  The skew detection CISs 34A and 34B and the width direction detection CIS 35 are contact image sensors in which a plurality of photosensors including light emitting elements such as LEDs and light receiving elements such as photodiodes are arranged in parallel. The skew detection CISs 34A and 34B have a plurality of photosensors arranged in parallel in the conveyance direction of the paper P, and the width direction detection CIS 35 has a plurality of photosensors arranged in parallel in the width direction of the paper P.

  The registration facing rollers 32A, 32B, and 32C are arranged at intervals in the width direction. The skew detection CIS 34A is interposed between the registration facing rollers 32A and 32B, and the registration opposing rollers 32B and 32C are inclined. Row detection lines 34B are arranged respectively. The skew detection CISs 34 </ b> A and 34 </ b> B extend in the sheet conveyance direction and are provided from a position immediately downstream of the skew correction roller 31 to a downstream side of the registration facing roller 32. However, a configuration in which four or more registration facing rollers 32 are provided may be used.

  The upper guide plate 36 and the lower guide plate 37 are provided above and below the conveyed paper P, respectively, so as to extend in the conveyance direction of the paper P. The paper P transported by the transport device 30 is guided by the upper guide plate 36 and the lower guide plate 37 and guided downstream in the transport direction.

  The upper guide plate 36 holds resist facing rollers 32A, 32B, 32C and skew detection CIS 34A, 34B. However, the lower guide plate 37 may be configured to hold these. Further, the lower guide plate 37 has a concave portion 37 a bent downward between the skew feeding correction roller 31 and the registration roller 33.

FIG. 12 is a diagram illustrating the configuration of the skew feeding correction rollers 31A and 31B in more detail.
As shown in FIG. 12, the skew feeding correction roller 31A is a roller pair composed of a driving roller 311A and a driven roller 312A. The driving roller 311A is driven to rotate by receiving a driving force from the motor 622 via a driving force transmitting means such as a gear. Further, the driven roller 312A rotates following the rotation operation of the driving roller 311A. By the rotation of the driving roller 311A and the driven roller 312A, the skew feeding correction roller 31A can convey the paper P sandwiched in the nip portion to the downstream side.

  The configuration of the skew feeding correction roller 31B is the same as that of the skew feeding correction roller 31A. Specifically, the skew feeding correction roller 31B is a roller pair composed of a driving roller 311B and a driven roller 312B. The driving roller 311B is rotated by the driving force of the motor 632, and the driven roller 312B is driven to rotate. . As described above, the skew correction rollers 31A and 31B are driven to rotate by using the independent motors 622 and 632 as drive sources, respectively, and are configured such that the respective rotation amounts, that is, the sheet conveyance speed can be changed independently. ing.

  Next, a process in which the transport device 30 corrects the positional deviation while transporting the paper P will be described with reference to FIGS. 2A, 3 to 8, and the flowcharts of FIGS.

  First, the paper P reaches the skew correction rollers 31A and 31B and is conveyed downstream by the skew correction rollers 31A and 31B (step S1 in FIG. 9). At this time, the conveying speeds of the skew feeding correction rollers 31A and 31B are set equal.

  2A, when the leading edge P1 of the paper P reaches the skew detection CIS 34A, 34B (step S2), the leading edge position of the paper P is detected by the skew detection CIS 34A, 34B. The skew amount of the paper P is calculated (step S3).

Specifically, as shown in FIG. 7, the skew detection CISs 34A and 34B are opposed to the sheet P among the photosensors arranged in the transport direction (left and right in the figure) by performing a detection operation. The sensor that performs the detection is in the detection state, and the sensor that does not face the paper P is in the non-detection state. That is, the photo sensor upstream of the leading edge P1 of the paper P is in the detection state, and the downstream side is in the non-detection state. Therefore, the positions of the points P1a and P1b that are the boundary between the detection state and the non-detection state can be calculated based on the detection results of the skew detection CISs 34A and 34B. And the separation distance M1 (mm) of both conveyance direction is computable from the positional information on the conveyance direction of the points P1a and P1b. By this distance M1 and the separation distance L1 (mm) in the width direction between the skew detection CISs 34A and 34B, the skew amount (tilt angle) θ1 of the paper P is
TANθ1 = M1 / L1 Formula (1)
It can be expressed as. Since the distance L is a value measured in advance, the skew feeding amount of the paper P can be calculated by the equation (1) using the calculated distance M1.

  Then, based on the calculated skew feed amount θ1, the paper feed speeds VA and VB of the skew feed correction rollers 31A and 31B are changed to correct the skew of the paper P while transporting the paper P (step S4). ). For example, in the case of FIG. 2 (a), the sheet P is preceded by the lower side of the figure and is located downstream of the upper side, so the sheet conveyance speed VA of the skew feeding correction roller 31A on the upper side of the figure is set to the lower side of the figure. The skew of the paper P can be corrected by making it relatively larger than the paper transport speed VB of the side skew correction roller 31B.

A specific method for obtaining the transport speeds VA and VB will be described with reference to FIG.
First, as shown in FIG. 7, the target position of skew correction completion is set as a vertical line N perpendicular to the transport direction, and a distance MA (mm) in the transport direction from the position P1a to the vertical line N is calculated. Then, the time until the leading edge position P1a of the paper P reaches the vertical line N is determined using the transport speed VA (mm / s) of the skew correction roller 31A.
MA / VA ... Formula (2)
It can be expressed as.

Further, a distance MB (mm) in the transport direction from the position P2a to the vertical line N is calculated. Then, the time until the leading edge position P2a of the paper P reaches the vertical line N is determined using the transport speed VB (mm / s) of the skew correction roller 31B.
MB / VB Formula (3)
It can be expressed as.

  By setting the conveyance speeds VA and VB so that the expressions (2) and (3) become equal, the position P1a and the position P2a can reach the position of the vertical line N at the same time. In other words, when the leading edge P1 of the paper P reaches the vertical line N, the skew of the paper P can be corrected. In the present embodiment, since the target is to correct the skew of the paper P before the paper P reaches (abuts) the registration counter roller 32, the position of the vertical line N is determined by the registration counter roller 32. Is also provided at a predetermined position on the upstream side.

  The position of the vertical line N is preferably closer to the position where the paper P is abutted against the registration facing roller 32. Accordingly, a conveyance distance (distance MA, MB) for skew correction can be increased, and a difference in conveyance speed VA, VB can be further reduced. Deformation can be suppressed. Further, when changing the conveying speeds VA and VB of the skew feeding correction roller 31A and the skew feeding correction roller 31B, it is preferable to change the average speed of both of them to be constant. Thereby, the time until the paper P reaches the registration facing roller 32 can be made substantially constant.

  The skew correction roller 31 transports the paper P downstream by the transport speeds VA and VB of the paper P calculated as described above. Therefore, as shown in FIG. 3, the skew is corrected as the sheet P is conveyed downstream.

  In the present embodiment, the skew detection CISs 34A and 35B provided in the transport direction of the paper P allow the paper P to be placed at an arbitrary position from when the paper P reaches these CISs until reaching the registration counter roller 32. Can be detected. Accordingly, the skew amount of the paper P can be calculated at this arbitrary position.

  Therefore, in the present embodiment, until the paper P reaches the registration facing roller 32, the detection operation of the leading edge P1 of the paper P, and the skew amount of the paper P and the target position based on the detection result. The distances MA and MB (see FIG. 7) to the vertical line N are repeatedly calculated. The skew amount and distance calculated in this way are fed back to the skew correction rollers 31A and 31B that correct the paper P while transporting it, and the paper transport speeds VA and VB are adjusted each time. (Step S5). As described above, the skew of the paper P can be corrected with high accuracy by finely adjusting the paper transport speeds VA and VB based on the repeated detection results.

  In this way, in order to calculate and correct the skew amount of the paper P, if the position for detecting the position of the leading edge of the paper P is the first position, the leading edge of the paper P is the second position in the next step S6. To determine whether or not Specifically, each time the positions of the leading ends P1a and P1b of the paper P are detected by the repeated detection operation described above, it is determined whether or not the leading ends P1a and P1b have reached the second position (step). S6). If the leading edge of the paper has not reached the second position, the detection operation and the paper transport operation are adjusted again. If the leading edge of the sheet has reached the second position, the sheet conveying operation by the skew feeding correction rollers 31A and 31B is stopped (step S7).

  The second position is a position downstream of the first position in the sheet conveyance direction. As shown in FIGS. 4 and 8A, the leading end P1 of the sheet P is aligned with the registration facing roller 32 and the registration roller 33. Is set at the abutting position where it abuts against the nip formed by or. The registration counter roller 32 and the registration roller 33 stop rotating, and the sheet P that has reached the registration counter roller 32 and the registration roller 33 receives a further conveying force from the skew feeding correction rollers 31A and 31B. The tip P1 is abutted against the nip portion. For this reason, the position where the leading edge P1 of the paper P reaches the nip portion is defined as the abutting position. Note that even when the second position is not strictly set as an abutting position but in the vicinity thereof, the abutting timing of the leading edge of the paper P can be detected and the skew amount at that time can be calculated.

  As shown in FIG. 4, at the moment when the skewed sheet P hits the nip portion between the registration facing roller 32 and the registration roller 33, the side of the position P1b that is the leading side of the leading end P1 hits the nip portion, This is a state where the position P1a has not reached the nip portion. In this state, as shown in FIG. 8A, when the skew feeding correction roller 31 further rotates, the paper P receives a force in the direction of the arrow in the figure and is pushed into the nip portion. As a result, as shown in FIG. 5, the side of the leading end P1 on the position P1a is also pushed into the nip portion, and the skew of the paper P is corrected. Further, as shown in FIG. 8B, the paper P is bent toward the concave portion 37 a formed in the lower guide plate 37.

  In this embodiment, when it is detected that the paper leading edge P1 has reached the second position as in step S6, the paper conveyance operation (rotation operation) of the skew feeding correction roller 31 is stopped in step S7. ing. Since there is a time difference between the detection operation in step S6 and the rotation of the skew correction roller 31 is stopped, the pushing operation of the paper P is performed by the rotation of the skew correction roller 31 during this time difference. Is called. However, after detecting that the leading edge P1 has reached the second position in step S6, the skew correction roller 31 is rotated by a predetermined amount, and then the rotation of the skew correction roller 31 is stopped. May be. Thereby, the pushing operation of the paper P can be reliably performed.

  As described above, in the configuration of the present embodiment, first, the skew of the paper P is corrected by changing the relative speed of the skew correction rollers 31A and 31B based on the detection result by the skew detection CIS 34A and 34B. To do. Thereafter, the skew of the paper P is corrected again by abutting the paper P against the nip portion. In the skew correction by changing the relative speed of the skew correction rollers 31A and 31B, the frictional force between the paper P and the skew correction rollers 31A and 31B varies depending on the paper type, paper thickness, temperature and humidity environment around the apparatus, and the like. Therefore, sufficient correction accuracy cannot be obtained. However, by performing skew correction by abutting the paper P against the nip after the skew correction by the skew correction rollers 31A and 31B, the skew of the paper P can be corrected with high accuracy. In addition, once the skew correction is performed before the paper P is abutted against the nip portion, the correction amount due to the abutment does not increase, so that the accuracy of the correction due to the abutment against the nip portion can be improved.

  However, even with the above correction, the skew of the paper P may not be corrected sufficiently. For example, when the surface layers of the registration facing roller 32 and the registration roller 33 are formed of rubber, if the paper P is a thick paper, the paper P stops in the middle when the front end of the paper comes into contact with the nip portion. The sheet P is not sufficiently pushed into the section, and the skew of the sheet P is not sufficiently corrected. Therefore, in the present embodiment, the skew of the paper P is corrected with high accuracy by performing the correction operation again after the abutment.

  Specifically, after the skew correction rollers 31A and 31B stop rotating, the paper P is detected again by the skew detection CIS 34A and 34B, and the skew amount of the paper P is calculated (step S8). Then, it is determined whether or not the calculated skew amount is equal to or less than a set target value (step S9).

  If the skew amount is less than or equal to the target value, it is assumed that the skew of the paper P has been sufficiently corrected, and the skew correction operation of the paper by the skew correction rollers 31A and 31B is terminated. The skew feeding correction rollers 31 </ b> A and 31 </ b> B transfer the paper P to the registration facing roller 32 and the registration roller 33 and are separated from the paper P.

  On the other hand, if the skew amount exceeds the target value, the skew correction roller 31A or the skew correction roller 31B is rotated by a minute amount in accordance with the calculated skew amount (step S10). For example, as shown in FIG. 4, when the lower side of the sheet P1 is preceded, the skew correction roller 31B on the lower side of the figure is reversely rotated by a minute amount, and the skew correction roller on the upper side of the figure is rotated. 31A is rotated forward. Thereby, as shown in FIG. 5, the skew of the paper P can be corrected again. In step S10, the rotation amount of the skew correction roller 31A disposed on one side in the width direction (upper side in the figure) and the skew correction roller 31B disposed on the other side in the width direction (lower side in the figure). Make the same rotation amount. Thus, the skew of the paper P can be corrected without greatly changing the position of the paper P in the transport direction (that is, without greatly changing the pushing state of the paper P into the nip portion).

  Then, after correcting the skew of the paper P, the paper P is detected again by the skew detection CIS 34A, 34B, and the skew amount of the paper P is calculated (step S8). Then, it is determined whether or not the calculated skew amount is equal to or less than a target value (step S9). The above operation is repeated until the skew amount becomes equal to or less than the target value. When the skew amount becomes equal to or less than the target value, the skew correction rollers 31A and 31B transfer the paper P to the registration facing roller 32 and the registration roller 33 and are separated from the paper P.

  As described above, in the configuration of the present embodiment, the sheet P is skewed based on the detection results of the skew detection CIS 34A and 34B in a state where the sheet P is abutted against the nip portion between the registration facing roller 32 and the registration roller 33. By performing a minute rotation operation of the correction roller 31, it is possible to correct the skew of the paper P that has not been corrected by the abutting operation. Further, in the minute rotation operation of the skew feeding correction roller 31, since the skew of the paper P is corrected in a state where the paper P hits the nip portion, a force in the twisting direction is applied to the paper P. The deformation is likely to occur. However, in the present embodiment, the above-mentioned minute correction is performed in a state where most of the skew of the paper P is corrected by the skew correction operation by changing the relative speed of the skew correction rollers 31A and 31B and the subsequent abutting operation. Since skew correction by a simple rotation operation can be performed, deformation of the paper P can be suppressed.

  In the minute rotation operation in step S10, it is preferable to set an upper limit value for the amount of rotation of the skew feeding correction roller 31 in the positive direction (the amount of rotation in the paper transport direction). That is, when the skew amount of the paper P detected in step S8 is large, it is necessary to increase the rotation amount in step S10 to correct the skew. On the other hand, if the amount of rotation in the positive direction becomes too large, the amount of pushing of the paper P into the nip portion becomes excessive, and the paper P may be deformed. Therefore, in the present embodiment, an upper limit is provided for the amount of rotation of the skew correction roller 31 in the positive direction. When the skew of the sheet P is large and correction is necessary beyond the upper limit value, the other skew correction roller 31 is rotated in the reverse direction by an amount exceeding the upper limit value. For example, the upper limit value of the rotation amount of the skew correction roller 31 in the positive direction is π [rad], and the skew correction roller 31A side is positive by a rotation amount of 1.5π [rad] for skew correction. When it is desired to rotate in the direction, the skew correction roller 31A is rotated forward by π [rad], and the skew correction roller 31A is rotated backward by −0.5π [rad].

  Next, with respect to the sheet conveyance operation and the width-direction misalignment correction operation by the registration roller and the registration counter roller after the above-described skew correction operation of the sheet P, the flowcharts of FIGS. Will be described.

  As shown in FIG. 5, when the skew correction operation of the paper P is completed, the skew correction roller 31 is separated from the paper P, and the registration roller 33 and the registration counter roller 32 rotate to convey the paper P to the downstream side. (Step S21 in FIG. 10). At this time, the sheet P (see FIG. 8B) that has been bent by being abutted against the nip portion of the registration roller 33 and the registration counter roller 32 is restored to its original flat shape by receiving a force to be conveyed downstream. .

  As shown in FIG. 5, the leading edge of the sheet P is detected by the skew detection CIS 34A, 34B, and the skew amount of the sheet P and the secondary transfer position (in the figure, the position of the secondary transfer counter roller 15). A distance M2 in the transport direction is calculated (step S22). The distance M2 can be an average distance from the positions P1a and P1b to the secondary transfer position, for example.

  Whether or not the skew of the paper P has been corrected is confirmed based on the skew amount calculated in this way. Further, the rotation amount of the registration roller 33, that is, the conveyance speed of the sheet P is adjusted by the calculated distance M2 (step S23), and the sheet P is timed and sent to the secondary transfer position.

  Then, as shown in FIG. 6, when the paper P reaches the width direction detecting CIS 35 (step S24), the position facing the width direction detecting CIS 35 in the side edge P2 of the paper P by the width direction detecting CIS 35. P2a is detected, and the positional deviation amount of the paper P in the width direction is calculated (step S25). For example, the positional deviation amount in the width direction is calculated as the distance L2 between the position Pa2 and the ideal position K in the width direction. Based on the calculated positional deviation amount in the width direction, the registration roller 33 and the registration facing roller 32 integrally move in the width direction, and the positional deviation amount in the width direction of the paper P is corrected (step S26). The positional deviation correction operation in the width direction is performed while the registration roller 33 and the registration counter roller 32 hold the paper P therebetween.

  Finally, when the paper P reaches the secondary transfer position, the transport operation of the paper P by the transport device 30 ends. The registration roller 33 and the registration counter roller 32 move away from the paper P and move integrally in the width direction, and return to the reference position. The reference position is a position at which the registration roller 33 is disposed at the center in the width direction of the sheet conveyance path, for example, the position shown in FIG.

  As described above, in this embodiment, the skew correction of the paper P and the positional deviation correction in the width direction can be performed independently. Therefore, as compared with the case where these corrections are performed at a time, the positional deviation of the paper P can be corrected more easily without requiring a complicated calculation of the movement amount.

A control unit that performs control for the above-described transport operation and sheet misalignment correction operation will be described with reference to FIG.
As shown in FIG. 11, the control unit 60 provided in the image forming apparatus includes a position recognition unit 61, a first motor control unit 62, a second motor control unit 63, a third motor control unit 64, A four-motor control unit 65 and a formed image control unit 66 are mainly provided.

  Based on the detection information of the skew detection CISs 34A and 34B, the position recognition unit 61 and the distance M1, M2 from the leading edge of the paper P to the vertical line N that is the target position (see FIG. 7). And the conveyance speeds VA and VB of the skew correction rollers 31A and 31B are calculated.

  The first motor control unit 62 is a part that controls the conveying operation of the skew correction roller 31A. In response to a signal from the first motor control unit 62, the first motor driver 621 drives the first motor 622 to rotate the skew correction roller 31A. The first motor encoder 623 detects the actual rotation amount of the skew feeding correction roller 31A, that is, the actual conveyance speed of the skew feeding correction roller 31A. The first motor control unit 62 controls the rotation amount of the skew correction roller 31A based on a command from the position recognition unit 61, and adjusts the conveyance speed of the skew correction roller 31A to the speed VA.

  The second motor control unit 63 is a part that controls the sheet transport operation of the skew feeding correction roller 31B. In response to a signal from the second motor control unit 63, the second motor driver 631 drives the second motor 632 to rotate the skew correction roller 31B. Then, the second motor encoder 633 detects the actual rotation amount of the skew feeding correction roller 31B, that is, the actual conveyance speed of the skew feeding correction roller 31B. The second motor control unit 63 controls the rotation amount of the skew correction roller 31B based on a command from the position recognition unit 61, and adjusts the conveyance speed of the skew correction roller 31B to the speed VB.

  The position recognition unit 61 calculates a distance M2 (see FIG. 5) between the leading edge of the paper P and the secondary transfer position based on the detection information of the skew detection CISs 34A and 34B. Then, the formed image control unit 66 transmits the timing at which the image is transferred to the position recognition unit 61 at the secondary transfer position. The position recognition unit 61 determines the conveyance speed of the registration roller 33 based on the calculated distance M2 and the timing of secondary transfer.

  The third motor control unit 64 is a part that controls the sheet conveying operation of the registration roller 33. In response to a signal from the third motor control unit 64, the third motor driver 641 drives the third motor 642 to rotate the registration roller 33. The third motor encoder 643 detects the actual rotation amount of the registration roller 33, that is, the actual conveyance speed of the registration roller 33. The third motor control unit 64 controls the rotation amount of the registration roller 33 based on a command from the position recognition unit 61 and adjusts the sheet conveyance speed of the registration roller 33 to the speed input from the position recognition unit 61.

  The fourth motor control unit 65 is a part that controls the movement operation of the registration roller 33 in the width direction. In response to a signal from the fourth motor control unit 65, the fourth motor driver 651 drives the fourth motor 652 to move the registration roller 33 in the width direction. Then, the actual movement amount of the registration roller 33 is detected by the fourth motor encoder 653.

  The position recognition unit 61 calculates the amount of positional deviation in the width direction of the paper P based on the detection result of the width direction detection CIS 35. Then, the position recognition unit 61 inputs the calculated position shift amount to the fourth motor control unit 65 as a movement amount in the width direction. The fourth motor control unit 65 drives the fourth motor 652 to move the registration roller 33 in the width direction by the input movement amount.

  Next, the configuration of the registration facing roller 32 and the registration roller 33 that perform the above-described operations will be described in more detail with reference to FIGS. Specific operations performed by the registration facing roller 32 and the registration roller 33 include a rotation operation for conveying a sheet and a movement operation in the width direction.

  The registration facing roller 32 and the registration roller 33 can be moved in the width direction by a roller moving mechanism. As shown in FIG. 13, the roller moving mechanism has a base frame 152 fixed on a main body frame 151. The base frame 152 has two upper and lower horizontal plates 153 and 154. On the upper horizontal plate 154, a roller holding member 110 that supports the resist-opposing roller 32 is movably disposed in the horizontal direction.

  The roller holding member 110 is configured by a plate-like frame that extends in a direction orthogonal to the conveyance direction of the paper P. Both ends of the plate-like frame are bent at a right angle upward, and 115 is fixed to the bent portion.

  Three resist rollers 33A, 33B, and 33C are provided as the resist facing roller 32. These registration facing rollers 32 are provided on the upper part of the registration rollers 33 and are held by an upper guide plate 36 (see FIG. 2A). As shown in FIG. 13, the rotation shaft of the registration roller 33 is supported by the bearing 115.

  A third motor encoder 643 is mounted on the rotation shaft of the registration roller 33 protruding outward from the bearing 115. Then, based on the number of rotations of the registration roller 33 detected by the third motor encoder 643, a third motor 642, which will be described later, is driven, and the registration counter roller 32 rotates following the rotation of the registration roller 33. Yes.

  A support shaft 110a serving as a guided portion that protrudes short downward is fixed to the lower surface on one side of the roller holding member 110. A guide roller 136 is rotatably attached to the lower end portion of the support shaft 110a, and a cam follower 135 is rotatably attached to an intermediate portion of the support shaft 110a.

  A fourth motor 652 and a fourth motor encoder 653 are arranged on the lower horizontal plate 153 side by side in the left-right direction. The fourth motor 652 is for correcting a positional deviation in the width direction, and a drive pulley 131 is fixed to the rotation shaft thereof.

  Instead of the fourth motor encoder 653, an arbitrary encoder (for example, a linear encoder) or an arbitrary sensor (for example, a laser displacement meter) for detecting the movement and position of a shift cam 134 and a roller holding member 110 described later may be provided. .

  A driven pulley 132 is rotatably supported between the upper and lower horizontal plates 153 and 154. The upper and lower ends of the rotation shaft 132a of the driven pulley 132 are rotatably supported by the upper and lower horizontal plates 153 and 154, respectively. A timing belt 133 is stretched between the driving pulley 131 and the driven pulley 132.

  A rotating plate 653a that is a rotating side component of the fourth motor encoder 653 is fixed to the rotating shaft 132a of the driven pulley 132 protruding downward from the lower horizontal plate 153. A plurality of slits are continuously formed in the peripheral portion of the rotating plate 653a, and a light projecting / receiving device which is a fixed side component of the fourth motor encoder 653 is disposed so as to sandwich the peripheral portion in the vertical direction.

  A shift cam 134 is fixed to the upper end portion of the rotation shaft 132a of the driven pulley 132 protruding upward from the upper horizontal plate 154. The cam curve of the shift cam 134 is formed to be a constant velocity cam curve. By using the constant velocity cam, the rotation angle of the shift cam 134 and the linear movement distance of the cam follower 135 described later are in a proportional relationship, and the shift position control of the support shaft 110a is facilitated.

  An elongated hole 154a is formed in the upper horizontal plate 154 at a position adjacent to the one side shift cam 134 as a guide portion extending in a direction orthogonal to the paper transport direction. A guide roller 136 at the lower end of the support shaft 110a is inserted into the elongated hole 154a. As shown in FIG. 14A, the cam follower 135 at the intermediate portion of the support shaft 110 a is in contact with the cam surface at the peripheral portion of the shift cam 134 by the force of the tension spring 113. The long hole 154a is for guiding the guide roller 136 to move in a straight line, and may be a long groove instead of the long hole. In addition, the arrow of Fig.14 (a) has shown the paper conveyance direction.

  As shown in FIG. 13, a fourth motor 652 for correcting displacement in the width direction, a drive pulley 131, a timing belt 133, a driven pulley 132, and a shift cam 134 are connected to a support shaft 110a as a guided portion via a cam follower 135. A shift driving unit that has a second pressing portion (cam outer peripheral surface) that abuts and moves the support shaft 110a in the direction orthogonal to the conveyance path of the paper P is configured.

  A bracket 155 is vertically disposed on the main body frame 151 on one end side in the axial direction of the resist facing roller 32. A third motor 642, which is a variable rotation speed roller driving motor for rotating the registration roller 33, is fixed to the outer surface of the bracket 155. The rotation shaft of the third motor 642 protrudes horizontally toward the inside of the bracket 155, and the pinion 141 is fixed to the rotation shaft protruding inward. The pinion 141 is meshed with a reduction gear 142 that is pivotally supported inside the bracket 155.

  The rotation shaft 142 a of the reduction gear 142 is connected to the rotation shaft 32 b 1 of the registration roller 33 of the registration facing roller 32 via a two-stage spline coupling 143. As a result, the rotational driving force of the third motor 642 is transmitted to the registration roller 33 via the pinion 141, the reduction gear 142, and the two-stage spline coupling 143, and the registration facing roller 32 is rotationally driven. Accordingly, the registration roller 33 is rotated by the third motor 642 while the registration counter roller 32 sandwiches the sheet P, so that the sheet P can be conveyed at an arbitrary conveyance speed.

  The two-stage spline coupling 143 is a kind of constant velocity universal joint. As shown in the partial enlarged view of FIG. 13, the first spline gear 143a, the second spline gear 143b, the intermediate spline gear 143c, the guide ring 143d, etc. It is configured.

  The first spline gear 143a is an external gear, and is installed on a rotation shaft 142a that rotates together with the reduction gear 142 of the first drive unit. The rotating shaft 142a is rotatably held by the bracket 155 via a bearing.

  The second spline gear 143b is also an external gear, and is connected to the rotation shaft 32b1 of the registration roller 33 of the registration facing roller 32. The intermediate spline gear 143c is an internal gear and extends in the width direction so as to always mesh with the two spline gears 143a and 143b even if the registration roller 33 (roller holding member 110) moves in the width direction.

  By using such a two-stage spline coupling 143, the resist facing roller 32 is driven to rotate favorably. That is, even if the registration facing roller 32 slides in the width direction, the driving force of the fixed third motor 642 is reliably and accurately transmitted to the registration roller 33.

  The guide ring 143d is a substantially annular stopper member installed at each of both ends in the width direction of the intermediate spline gear 143c. The two spline gears 143a and 143b move relatively in the width direction to thereby form a two-stage spline cup. It is prevented from falling off the ring 143.

  FIGS. 14A to 14B show the positional deviation correction operation in the width direction of the paper P. FIG. That is, when the fourth motor 652 is driven and the shift cam 134 is rotated, the roller holding member 110 slides to the right so as to resist the spring force of the tension spring 113 by the shift cam 134. At this time, since the cam follower 135 moves on the outer periphery of the shift cam 134 while rotating, the movement load of the roller holding member 110 acting on the fourth motor 652 for correcting the positional deviation in the width direction can be reduced. As described above, when the roller holding member 110 slides, the registration roller 33 and the registration counter roller 32 held by the roller holding member 110 slide.

  As described above, in this embodiment, the resist facing roller 32 is held by the roller holding member 110 that is movable in the width direction of the sheet conveyance path, and the rotational driving force of the fixed third motor 642 is the two-stage spline coupling 143. Is transmitted to the resist-opposing roller 32. Therefore, the third motor 642 and the fourth motor 652 for correcting the positional deviation in the width direction can be arranged on the fixed side, and the weight of the structure above the roller holding member 110 can be reduced.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

  In the embodiment described above, the present invention is applied to the conveyance device 30 installed in the electrophotographic image forming apparatus 1. However, the present invention is applied to the conveyance device installed in the inkjet image forming apparatus. The present invention can also be applied. The conveying device of the present invention can also be applied to a post-processing device for post-processing a sheet (paper) on which an image is formed. Hereinafter, an ink jet image forming apparatus will be described with reference to FIG. 15, and a post-processing apparatus will be described with reference to FIG.

  As shown in FIG. 15, the inkjet image forming apparatus 200 includes a paper feeding unit 210, a transport device 220, an image forming unit 230, a drying unit 240, and a paper discharge unit 250.

  The paper P sent out from the paper supply unit 210 is transported by the transport device 220 and, as in the above-described embodiment, the positional deviation and skew of the paper P are corrected, and the image forming unit 230 is corrected. Sent out.

  In the image forming unit 230, the paper P is positioned on the cylindrical drum 231 and is conveyed in the direction of the arrow in the drawing by the rotation of the cylindrical drum 231. Then, the paper P is conveyed at a predetermined timing to the lower part of each color discharge head 232 (image forming position on the paper P), and the ink of each color is discharged onto the paper P to form an image on the surface of the paper P. .

  The paper P on which the image is formed by the image forming unit 230 is transported to the drying unit 240 to evaporate moisture in the ink, and then discharged by the paper discharge unit 250 to a position where the operator can take it out.

  When double-sided printing is performed, after the drying process, the paper P is sent to the reverse conveyance path 260, and is sent again to the conveyance device 220 with the front and back sides of the paper P reversed. As a result, even when the image is formed on the back surface, the image forming unit 230 forms an image on the paper P in a state where the positional deviation of the paper P is corrected. Thereafter, the moisture in the ink is evaporated by the drying unit 240 and then discharged by the paper discharge unit 250 to a position where the operator can take it out.

  FIG. 16 shows an embodiment in which the present invention is applied to a post-processing apparatus. A post-processing device 300 illustrated in FIG. 16 includes a punching device 310 that performs punching processing on the paper P, a staple processing device 320 that performs binding processing on the paper P, a folding processing device 330 that performs half-folding processing on the paper P, and a plurality of processing devices. Trays (stacking units) 341, 342, and 343. The post-processing apparatus 300 transports the paper P transported from the image forming apparatus 1 to any one of the three transport paths Q1 to Q3, and performs different post-processing.

  The first transport path Q <b> 1 is a path for transporting the paper P that has been punched by the punching device 310 or the paper P that has not been punched to the first tray 341. The second transport path Q <b> 2 is a path for transporting the paper P to the staple processing device 320 and transporting the paper P subjected to the binding process to the second tray 342. The third transport path Q3 is a path for transporting the paper P to the folding processing device 330 and transporting the paper P subjected to the middle folding process to the third tray 343.

  Here, as shown in FIG. 20, the sheet P conveyed from the image forming apparatus 1 to the post-processing apparatus 300 is first described above by the resist facing roller 32 and the resist roller 33 provided on the upstream side of the punching apparatus 310. In the same manner as described above, skew correction of the paper P and positional deviation correction in the width direction are performed. As a result, it is possible to improve the accuracy of the subsequent punching process, binding process or half-folding process.

  Sheets include paper P (plain paper), cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, plastic film, prepreg, copper foil, etc. It is.

  In the above embodiment, the skew detection CIS 34A, 34B repeatedly detects the sheet P until the sheet P is abutted against the nip portion between the registration roller 33 and the registration counter roller 32, and the skew correction is performed each time. The conveyance speeds of the rollers 31A and 31B are adjusted (see Steps S5 and S6 in FIG. 9). However, once the conveyance speeds VA and VB are adjusted once in Step S4, the conveyance speeds are reached until the abutting position is reached. A configuration in which the speed is not adjusted may be used.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 30 Conveyance apparatus 31 Skew correction roller 32 Registration opposing roller 33 Registration roller 39 Detection part 34 CIS for skew detection
35 CIS for width direction detection (second detection part)
36 Upper guide plate 37 Lower guide plate 60 Control unit

JP 2000-95384 A JP 2003-72982 A

Claims (9)

A pair of rollers for nipping and conveying the sheet, and a plurality of the rollers in parallel in the width direction of the sheet, and a skew correction roller that corrects the skew of the sheet by relatively changing the rotation speed of each of the rollers,
A sandwiching roller, which is a pair of rollers for transporting a sheet, provided on the downstream side in the sheet transport direction of the skew feeding correction roller;
A detection unit for detecting the sheet position;
A conveying device comprising a control unit for controlling the skew feeding correction roller,
When the detection unit detects the sheet position at a first position upstream of the abutting position where the leading edge of the sheet is abutted against the nip portion of the clamping roller, the detection unit Based on the detection result, the control unit calculates the skew amount of the sheet and causes the skew correction roller to correct the skew of the sheet,
When the abutting position or the vicinity of the abutting position, which is a position downstream of the first position in the sheet conveying direction, is a second position,
When the detection unit detects the sheet position at the second position, based on the detection result of the detection unit, the control unit calculates a skew amount of the sheet and calculates the skew correction roller. And correcting the skew of the sheet again.   The conveying device according to claim 1, wherein the relative rotation speed of the plurality of skew feeding correction rollers is changed with an average speed of the plurality of skew feeding correction rollers being constant. The detection unit includes a plurality of contact image sensors in the width direction of the sheet, in which a plurality of photosensors are arranged in parallel in the conveyance direction of the sheet,
The conveying device according to claim 1, wherein the contact image sensor is provided from an upstream side to a downstream side in the sheet conveying direction of the clamping roller.   The detection unit detects the position of the sheet a plurality of times before the sheet reaches the abutting position, and the control unit controls the skew feeding correction roller by feedback control based on the detection result. The conveying apparatus according to claim 3, wherein skew feeding of the sheet is corrected. In the plurality of skew correction rollers, a skew correction roller disposed on one side in the width direction of the sheet and a skew correction roller disposed on the other side are paired. When the rotation in the sheet conveyance direction is a positive rotation, the rotation amount is a positive number, the rotation in the opposite direction to the sheet conveyance direction is a reverse rotation, and the rotation amount is a negative number,
5. The total amount of rotations of the pair of skew correction rollers when correcting skew of the sheet again is set to a predetermined upper limit value or less. 6. Conveying device.   The detection unit detects the sheet position after the second skew correction, and the control unit changes the conveyance speed of the clamping roller based on the detection result. The transfer device according to item. A second detection unit that is capable of detecting the position of the edge in the width direction of the sheet on the downstream side in the sheet conveyance direction from the sandwiching roller;
The sandwiching roller is provided movably in the width direction of the sheet,
The control unit calculates a positional deviation amount in the width direction of the sheet based on the detection result of the sheet by the second detection unit, and based on the positional deviation amount, The transport apparatus according to claim 1, wherein the amount of positional deviation in the width direction is corrected.   8. The re-correction operation of the skew of the sheet by the skew correction roller based on the detection result of the detection unit is repeatedly performed until the skew amount of the sheet becomes a target value or less. The transport apparatus according to item 1.   An image forming apparatus comprising the transport device according to claim 1.

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