JP2018065653A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a skew of a paper sheet with higher accuracy.SOLUTION: An image forming apparatus 1 includes: a correction part 510 which executes a correction operation of correcting a skew of a paper sheet to be conveyed; carrier roller pairs 609-612 which are arranged on the upstream side of the correction part 510 in a paper conveyance direction and convey a paper sheet toward the correction part 510; auxiliary parts 61-64 which are arranged on the upstream side of the correction part 510 in the paper conveyance direction and execute auxiliary operations for reducing contact resistance between a paper sheet moving along with a correction operation and any one of members in the apparatus; skew sensors 552, 553 which detect a skew of a paper sheet during conveyance; and a control unit 11 which makes the auxiliary parts 61-64 execute auxiliary operations when making the correction part 510 execute correction operations on the basis of a detection result of the skew sensors 552, 553.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses having a plurality of functions such as printers, copiers, and fax machines have been widely used. The image forming apparatus conveys a sheet from a sheet feeding unit to a transfer unit and a fixing unit by a plurality of conveyance rollers arranged on a sheet passing path, and forms an image on the sheet.

  In the image forming apparatus as described above, when the paper enters the transfer unit in a state where the paper is skewed or inclined with respect to the conveyance direction, the image forming position with respect to the paper is shifted. Corrective means may be provided. As the correction means, for example, the paper conveyance amount of the two conveyance roller pairs that are arranged side by side in the direction orthogonal to the paper conveyance direction and are controlled independently from each other is corrected, thereby correcting the skew of the paper. Things can be mentioned.

  Here, during the paper correction operation, if the rear end of the paper is sandwiched between the pair of transport rollers on the upstream side in the transport direction, the orientation of the paper cannot be changed smoothly, and the paper is sufficiently bent. May not be corrected or damage may occur such as wrinkles due to the load on the paper.

  On the other hand, for example, when the leading edge of the sheet reaches a predetermined position, the nip of the conveying roller pair upstream of the correction unit in the sheet conveying direction is released, and the trailing edge of the sheet is sandwiched between the conveying roller pair. There has been proposed a technique for reducing a tension applied to a sheet by performing a correction operation after the state is not set (see, for example, Patent Document 1).

JP 2008-230754 A

  However, in the above conventional technique, for example, when the upstream conveying roller pair is arranged in the bending path on the sheet passing path, or when the rigidity of the conveyed sheet is very high, Even when the nip of the conveying roller pair is released, the sheet may remain in contact with the roller surface. In general, on the surface of the rollers constituting the pair of transport rollers, a member having a high coefficient of friction such as rubber is provided to efficiently transport the paper, so that the paper is merely in contact with the roller surface. Also, the movement of the paper accompanying the correction operation is hindered. Even if the sheet does not contact the pair of conveyance rollers, the movement of the sheet is similarly inhibited when the sheet contacts another member in the machine. Therefore, it is difficult to correct the paper skew with higher accuracy only by releasing the nip of the upstream conveying roller pair.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that corrects the skew of a sheet with higher accuracy.

In order to solve the above problems, an invention according to claim 1 is an image forming apparatus,
A correction unit that performs a correction operation to correct the skew of the conveyed paper;
A pair of conveyance rollers that is provided upstream of the correction unit in the sheet conveyance direction and conveys the sheet toward the correction unit;
An auxiliary unit that is provided upstream of the correction unit in the paper conveyance direction and performs an auxiliary operation to reduce contact resistance between a sheet that moves with the correction operation and any member in the machine;
A detection unit for detecting the bending of the paper being conveyed;
And a control unit that causes the auxiliary unit to perform the auxiliary operation when the correction unit performs the correction operation based on a detection result of the detection unit.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The correction unit performs the correction operation by rotating the sheet with the thickness direction of the sheet as an axial direction.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The control unit superimposes the timing of the assisting operation by the assisting unit on the timing of the correcting operation by the correcting unit.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The auxiliary unit performs the auxiliary operation of moving the member in the paper width direction.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
The member is provided at a position where the contact resistance with the sheet moving with the correction operation is the largest.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects,
The member is provided in a U-shaped bending path through which the conveyed paper passes.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect,
The member is provided at a position having the smallest radius of curvature in the U-shaped bending path or a position upstream of the position in the paper conveyance direction.

The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7,
Provided on the downstream side of the correction unit with respect to the sheet conveyance direction, and includes a pair of registration rollers in which the leading end of the sheet in the sheet conveyance direction is abutted against the nip point.
The correction unit has a pair of loop rollers that abuts the leading end of the sheet in the sheet conveyance direction against the pair of registration rollers and forms a loop on the sheet.

The invention according to claim 9 is the image forming apparatus according to any one of claims 1 to 8,
The control unit does not cause the auxiliary unit to perform the auxiliary operation when the rigidity of the sheet is equal to or less than a predetermined value.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects,
The correction unit is provided in a plurality in the sheet width direction, and includes a correction roller pair that conveys the sheet toward the downstream side in the sheet conveyance direction, and a drive mechanism that independently rotates and drives the plurality of correction roller pairs. The correction operation is performed by generating a moment on the paper by changing the rotational drive speeds of the plurality of correction roller pairs.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect,
A plurality of the detection units are provided in the vicinity of the correction roller pair in the sheet conveyance direction, and are respectively disposed at the same position as the plurality of correction roller pairs in the sheet width direction.

The invention according to claim 12 is the image forming apparatus according to any one of claims 1 to 11,
A plurality of the transport roller pairs are provided along the paper transport direction.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects,
A plurality of the transport roller pairs are provided along the paper transport direction,
The control unit is characterized in that, among the pair of transport rollers, a sheet that is passing paper during the correction operation by the correction unit is separated.

The invention according to claim 14 is the image forming apparatus according to any one of claims 1 to 13,
The control unit causes the auxiliary unit to perform the auxiliary operation according to a length, a width, and a basis weight of a sheet in a conveyance direction.

The invention according to claim 15 is the image forming apparatus according to any one of claims 1 to 14,
The transport roller pair has a driving roller and a driven roller,
The auxiliary unit performs the auxiliary operation by moving the driving roller and the driven roller in a separated state in a paper width direction.

The invention according to claim 16 is the image forming apparatus according to claim 15,
A plurality of the transport roller pairs are provided along the paper transport direction,
A plurality of the auxiliary portions are provided along the paper conveyance direction according to the plurality of conveyance roller pairs,
The control unit increases the amount of movement of the transport roller pair as the auxiliary unit is provided on the upstream side in the paper transport direction.

The invention according to claim 17 is the image forming apparatus according to any one of claims 1 to 16,
The auxiliary unit has a half-moon roller in a state of being retracted out of the sheet passing path, and performs the assisting operation by rotating the half-moon roller to advance into the sheet passing path to contact the sheet. And

The invention according to claim 18 is the image forming apparatus according to any one of claims 1 to 17,
The auxiliary section performs the auxiliary operation by inclining an axis of the pair of conveying rollers arranged in the paper width direction with respect to the paper width direction.

The invention according to claim 19 is the image forming apparatus according to any one of claims 1 to 18,
The control unit does not cause the auxiliary unit to perform the auxiliary operation when a degree of bending based on a detection result of the detection unit is a predetermined value or less.

The invention according to claim 20 is the image forming apparatus according to any one of claims 1 to 19,
The detection unit is a line sensor extending in the sheet width direction, and is provided in the vicinity of the correction unit in the sheet conveyance direction.

The invention according to claim 21 is the image forming apparatus according to any one of claims 1 to 20,
The detection unit is a line sensor extending in the paper width direction, and is provided in the vicinity of the correction unit and at a position upstream of the correction unit in the paper conveyance direction in the paper conveyance direction. Features.

  According to the present invention, it is possible to provide an image forming apparatus that corrects the bending of a sheet with higher accuracy.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram illustrating a functional configuration of the image forming apparatus. FIG. It is the schematic which shows a registration roller pair, the correction | amendment part, and its periphery structure. It is the schematic which shows the registration roller pair, correction | amendment part, and its periphery structure seen from the arrow A direction of FIG. It is the schematic when a correction | amendment part, an auxiliary | assistant part, and its periphery structure are seen from upper direction. It is the schematic when a bending sensor and its periphery structure are seen from upper direction. It is the schematic which shows a registration roller pair, a loop roller pair, a conveyance roller pair, and its periphery structure. 6 is a flowchart illustrating an example of a sheet conveyance process. It is the schematic which shows the auxiliary | assistant part which concerns on the modification 1, and its periphery structure. It is the schematic which shows the auxiliary | assistant part which concerns on the modification 2, and its periphery structure. It is the schematic which shows the bending sensor which concerns on the modification 3, and its periphery structure. It is the schematic which shows the bending sensor which concerns on the modification 4, and its periphery structure.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated using drawing. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

<Image forming apparatus>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 1.

  The image forming apparatus 1 is an image forming apparatus such as a multifunction peripheral that forms an image on a sheet. As shown in FIG. 1, an operation display unit 13, a document reading unit 15, a paper feeding unit 17, an image forming unit 20, a fixing unit 30, a conveyance unit 50, a reverse conveyance unit 60, and the like are provided.

  The document reading unit 15 is a scanner or the like provided for copying. The document reading unit 15 reads a document set on a document table according to an instruction from the control unit 11 (see FIG. 2), and performs R (red) and G for each pixel. A bitmap-format original image having color values of (green) and B (blue) is generated. The original image having R, G, and B color values generated by the document reading unit 15 is color-converted to an original image having Y, M, C, and K color values by a color conversion unit (not shown), and then stored. Stored in the unit 12 (see FIG. 2).

  The operation display unit 13 is provided in the image forming apparatus 1 as a user interface. The operation display unit 13 generates an operation signal corresponding to a user operation and outputs the operation signal to the control unit 11. As the operation display unit 13, a keypad, a touch panel configured integrally with a display device, or the like can be used. As the display device, an operation screen or the like is displayed in accordance with an instruction from the control unit 11, and for example, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

  The paper supply unit 17 includes a plurality of paper supply trays, and supplies paper to the image forming unit 20 by the paper supply unit 171 in accordance with instructions from the control unit 11. Each paper feed tray stores cut paper of a predetermined paper type and size (for example, A3, A4, etc.) as paper.

  The conveyance unit 50 conveys the sheet fed from the sheet feeding unit 17 to the image forming unit 20 and the fixing unit 30 in accordance with an instruction from the control unit 11, and discharges the sheet on which the image has been formed and fixed from the sheet discharge port. Discharge to a tray (not shown). The conveyance unit 50 includes conveyance roller pairs 521 to 524 and the like which will be described later. The conveyance roller pairs 521 to 524 transfer paper from the paper supply unit 17 to the secondary transfer unit 23 of the image forming unit 20 in a paper passing path in the apparatus. Is provided on a transport route R1.

The reverse conveyance unit 60 reverses the sheet after passing through the fixing unit 30 and re-feeds the reversed sheet from the junction unit T to the conveyance path R1. The reverse conveyance unit 60 includes conveyance roller pairs 601 to 612 to be described later, and the conveyance roller pair 601 to 612 conveys the paper from the conveyance path switching unit 561 to the merging unit T among the paper passing paths in the apparatus. Is provided. The merging portion T is a merging point between the conveying path R1 and the reversing path R2, and is disposed on the downstream side of the sheet conveying direction in the conveying path R1 from the sheet feeding unit 17 and upstream in the sheet conveying direction from the secondary transfer unit 23. ing.
Here, in the present invention, the paper transport direction is a direction when the paper transported in the image forming apparatus 1 properly proceeds without being skewed or bent. The paper width direction is a direction orthogonal to the paper transport direction and is a direction along the surface direction of the paper transported in the paper transport direction.

  The image forming unit 20 displays an image composed of a plurality of colors Y, M, C, and K on a sheet based on the original image processed by the image processing unit 16 (see FIG. 3) according to an instruction from the control unit 11. To form. The image forming unit 20 includes four writing units 21Y, 21M, 21C, and 21K, an intermediate transfer belt 22, a secondary transfer unit 23, and the like.

The four writing units 21Y, 21M, 21C, and 21K are arranged in series (tandem) along the belt surface of the intermediate transfer belt 22 and form images of Y, M, C, and K colors, respectively. The writing unit 21Y includes a photoreceptor 211Y, a charging unit 212Y, an optical scanning device 213Y, a developing unit 214Y, a primary transfer roller 215Y, and a cleaning unit 216Y. At the time of image formation, in the writing unit 21Y, the charging unit 212Y applies a voltage to the photosensitive member 211Y for charging, and then the optical scanning device 213Y scans the photosensitive member 211Y with a light beam emitted based on the original image. An electrostatic latent image is formed. When a color material such as toner is supplied from the developing unit 214Y to develop the electrostatic latent image on the photoreceptor 211Y, a toner image is formed on the photoreceptor 211Y that is an image carrier.
Note that the writing units 21M, 21C, and 21K are configured in the same manner as the writing unit 21Y, and thus description thereof is omitted.

  When the toner images are formed on the photoconductors 211Y to 211K in the writing units 21Y to 21K, the toner images on the photoconductors 211Y to 211K are sequentially superimposed on the intermediate transfer belt 22 by the primary transfer rollers 215Y to 215K. Are transferred (primary transfer). As a result, a toner image having a plurality of colors is formed on the intermediate transfer belt 22. After the primary transfer, the color materials remaining on the photoreceptors 211Y to 211K are removed by the cleaning units 216Y to 216K.

  The intermediate transfer belt 22 is an endless belt-shaped image carrier that is wound and rotated by a plurality of rollers. The plurality of rollers include primary transfer rollers 215Y to 215K.

  The secondary transfer unit 23 is disposed on the conveyance path R1 of the sheet conveyed from the paper supply unit 17. The secondary transfer unit 23 transfers (secondary transfer) the toner image on the intermediate transfer belt 22 onto the sheet fed from the sheet feeding unit 17 and conveys it to the fixing unit 30.

  The fixing unit 30 thermally fixes the image on a sheet on which a toner image as a color material image is formed by the image forming unit 20 in accordance with an instruction from the control unit 11. That is, the fixing unit 30 heats and pressurizes the paper on which the toner image is formed by the image forming unit 20. When images are formed on both sides of a sheet, the sheet on which the image is fixed on one side by the fixing unit 30 is reversed to the sheet surface by the reverse conveyance unit 60 and then fed again to the position of the secondary transfer unit 23. Is done.

  As shown in FIG. 2, the image forming apparatus 1 includes a control unit 11, a storage unit 12, an operation display unit 13, a document reading unit 15, an image processing unit 16, a paper feeding unit 17, a communication unit 19, an image forming unit 20, A fixing unit 30, a transport unit 50, a reverse transport unit 60, and the like are provided. Each part of the image forming apparatus 1 is connected via a bus 40.

  The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like, and controls each unit of the image forming apparatus 1. The ROM is a storage unit that stores various programs and various data. In the control unit 11, the CPU reads various programs from the ROM and expands them appropriately in the RAM, and executes various processes in cooperation with the expanded programs and the CPU. For example, the control unit 11 causes the image processing unit 16 to perform image processing on a bitmap-format original image generated by the document reading unit 15 or received via the communication unit 19 and held in the storage unit 12. Based on the processed original image data, the image forming unit 20 forms an image on the paper.

  The storage unit 12 is an image memory that is configured by a DRAM (Dynamic Random Access Memory) or the like and temporarily stores various data such as image data related to various image processing. In addition, the storage unit 12 may include an HDD (Hard Disk Drive) and the like, and may store various data in a writable and readable manner.

  The image processing unit 16 is necessary for image data stored in the storage unit 12, image data obtained by reading an image from a document by the document reading unit 15, and image data input from an external device via the communication unit 19. Image processing is performed, and the image data after the image processing is output to the image forming unit 20. Image processing includes gradation processing, halftone processing, color conversion processing, and the like. The gradation processing is processing for converting the gradation value of each pixel of the image data into a gradation value corrected so that the density characteristic of the image formed on the paper matches the target density characteristic. The halftone processing includes error diffusion processing, screen processing using a systematic dither method, and the like. The color conversion process is a process for converting each gradation value of RGB into each gradation value of YMCK.

  The communication unit 19 includes a network card or the like, and is connected to a network such as a LAN (Local Area Network). The communication unit 19 communicates with an external device on the network, for example, a user terminal such as a PC (Personal Computer), a server, or the like. The communication unit 19 receives image data for forming an image from an external device via a network.

<Transport section>
Subsequently, the configuration of the transport unit 50 will be described in more detail with reference to FIGS. 1 and 3 to 6. FIG. 3 is a schematic diagram illustrating the registration roller pair 501, the correction unit 510, and the peripheral configuration thereof. FIG. 4 is a schematic diagram showing the registration roller pair 501, the correction unit 510, and the peripheral configuration thereof as seen from the direction of arrow A in FIG. 3. FIG. 5 is a schematic view of the correction unit 510, the conveyance roller pairs 609 to 612 and their peripheral configurations viewed from above, and the driven rollers 511b and 609b to 612b are omitted. FIG. 6 is a schematic view of the bending sensors 552 and 553 and the peripheral configuration viewed from above, and the driven roller 511b and the like are omitted.

  The conveyance unit 50 includes a registration roller pair 501, a driving motor 502, a correction unit 510, a conveyance roller pair 521 to 524, a discharge roller pair 526, a registration sensor 551, a bending sensor (detection unit) 552, 553, and a conveyance path switching unit. 561 etc. are comprised. Further, the correction unit 510 includes a loop roller pair (correction roller pair) 511 and 512, a drive motor (drive mechanism) 513 and 514, and the like. The registration roller pair 501, the loop roller pairs 511 and 512, and the transport roller pairs 521 to 524 are provided on the transport path R1.

  The registration roller pair 501 conveys paper to the secondary transfer unit 23 adjacent to the secondary transfer unit 23. More specifically, the registration roller pair 501 is a roller pair in which the front end in the paper transport direction of the paper transported from the loop roller pair 511, 512 is abutted against the nip point when the paper is transported from the loop roller pair 511, 512. After a loop is formed on the sheet by the loop roller pair 511 and 512 in the applied state, driving is started to feed the sheet to the secondary transfer unit 23. As shown in FIG. 3, the registration roller pair 501 includes a driving roller 501a and a driven roller 501b that is disposed to face the driving roller 501a and is driven by the driving roller 501a. The driven roller 501b is configured to be capable of being crimped and separated from the driving roller 501a in accordance with instructions from the control unit 11.

  As shown in FIGS. 3 and 4, the driving motor 502 is connected to the shaft of the driving roller 501 a of the registration roller pair 501 through a power transmission unit including gears and the like. The rotational driving speed of the registration roller pair 501 is adjusted by rotational driving.

  The loop roller pairs 511 and 512 are arranged side by side in the paper width direction as shown in FIGS. 4 and 5, and as shown in FIG. 3, the registration roller pair adjacent to the registration roller pair 501 in the paper conveyance direction. The sheet is conveyed to 501. As described above, the pair of loop rollers 511 and 512 conveys the sheet and abuts the leading end portion of the sheet in the sheet conveyance direction on the resist roller pair 501 in a stopped state to form a loop on the sheet.

  As shown in FIG. 3, the loop roller pair 511 includes a driving roller 511a and a driven roller 511b that is disposed to face the driving roller 511a and is driven by the driving roller 511a. The driven roller 511b is configured to be capable of being crimped and separated from the driving roller 511a in accordance with an instruction from the control unit 11. The loop roller pair 512 is configured in the same manner as the loop roller pair 511.

  As shown in FIG. 4, the driving motor 513 is connected to the shaft of the driving roller 511 a of the loop roller pair 511 via a power transmission unit including gears and the like, and rotates the driving roller 511 a according to an instruction from the control unit 11. Thus, the rotational driving speed of the loop roller pair 511 is adjusted. The drive motor 514 is configured in the same manner as the drive motor 513 and is connected to the shaft of the drive roller 512a of the loop roller pair 512.

  The correction unit 510 having the loop roller pairs 511 and 512 and the driving motors 513 and 514 configured as described above, according to instructions from the control unit 11, causes the pair of loop rollers 511 and 512 by the driving motors 513 and 514 during paper conveyance. The rotational drive speeds are different from each other. In this way, the correction unit 510 performs a correction operation of rotating the paper with the thickness direction of the paper as the axial direction. For example, as illustrated in FIG. 5, when the correction unit 510 reaches the loop roller pair 511 and 512 in the direction P1 in which the paper is bent with respect to the paper conveyance direction, the correction driving unit 510 sets the rotational driving speed of the loop roller pair 512 to the loop. By decelerating from the roller pair 511, the correction operation of rotating the paper in the arrow B direction can be performed. Thereby, the direction P1 bent with respect to the paper conveyance direction of the paper can be corrected to the direction P2.

  As shown in FIG. 1, the transport roller pairs 521 to 524 are respectively provided on the transport path R <b> 1 from the paper feed unit 17 to the loop roller pairs 511 and 512. Each of the transport roller pairs 521 to 524 transports the paper from the paper feeding unit 17 to the loop roller pairs 511 and 512 along the transport path R1.

  The paper discharge roller pair 526 discharges paper that has not passed through the reversing path R2 after passing through the fixing unit 30 to a paper discharge tray (not shown).

  The registration sensor 551 is provided in the vicinity of the registration roller pair 501, detects the presence or absence of paper in the registration roller pair 501, and outputs it to the control unit 11. Thereby, the control unit 11 can detect whether or not the sheet has passed through the registration roller pair 501. The registration sensor 551 includes a light-emitting element such as a light-emitting diode (LED) and a light-receiving element such as a photodiode (PD), and includes a reflection-type optical sensor that detects reflected light from the paper. The

  As shown in FIG. 6, the bending sensors 552 and 553 are provided in the vicinity of the loop roller pair 511 and 512, detect the presence or absence of paper in the vicinity of the loop roller pair 511 and 512, and output it to the control unit 11. Thereby, the control unit 11 can detect the degree of bending of the sheet from the difference in detection timing of the leading end of the sheet by the respective bending sensors 552 and 553. The degree of bending is information indicating the inclination of the leading end of the transported paper in the paper transport direction with respect to the paper width direction. Each of the bending sensors 552 and 553 includes a light-emitting element such as a light-emitting diode (LED) and a light-receiving element such as a photodiode (PD), and includes a reflection-type optical sensor that detects reflected light from the paper.

  For example, as shown in FIG. 6, when the paper reaches the vicinity of the bending sensors 552 and 553 in the direction P3, the bending sensor 553 first detects the presence or absence of the paper at a point P32 in the front end of the paper in the paper conveyance direction. Subsequently, the bending sensor 552 detects the presence / absence of the paper at a point P31 in the front end of the paper in the paper conveyance direction. Then, the control unit 11 calculates the degree of paper bending from the time difference between the timings when the points P31 and P32 are detected by the bending sensors 552 and 553, respectively.

  As shown in FIG. 1, the conveyance path switching unit 561 is provided downstream of the fixing unit 30 in the sheet conveyance direction and upstream of the sheet discharge roller pair 526 in the sheet conveyance direction. The path of the sheet that has passed through 30 is switched to the discharge roller pair 526 side or the reverse conveyance unit 60 side. The transport path switching unit 561 performs switching according to the selected printing mode (single-sided printing mode, double-sided printing mode, etc.). The paper on which single-sided printing has been completed in the single-sided printing mode or the paper on which double-sided printing has been completed in the double-sided printing mode is discharged by a paper discharge roller pair 526 onto a paper discharge tray (not shown).

《Reverse conveying unit》
Subsequently, the configuration of the reversing conveyance unit 60 will be described in more detail with reference to FIGS. 1, 5, and 7. FIG. 7 is a diagram illustrating a registration roller pair 501, a loop roller pair 511, 512, a transport roller pair 604 to 612, and a peripheral configuration thereof.

  The reverse conveyance unit 60 includes conveyance roller pairs 601 to 612, auxiliary units 61 to 64, paper sensors 651 to 659, and the like.

  As shown in FIGS. 1 and 7, the conveyance roller pairs 601 to 612 are respectively provided in the reversing path R2 from the conveying path switching unit 561 to the junction T, and convey the paper along the reversing path R2. The conveyance roller pairs 604 and 605 are provided on the switchback path R21 in the reversal path R2, and are reversely controlled to be reversed and merged by the conveyance roller pairs 606 to 612 with the rear end of the paper at the head. The paper is fed again from the section T to the transport path R1. The conveyance roller pairs 609 to 612 are provided at the position where the contact resistance with the sheet moving with the correction operation by the correction unit 510 is the largest. Here, the contact resistance refers to a force that acts so as to inhibit the movement of the paper accompanying the correction operation, and examples thereof include a frictional force with the drive rollers 609a to 612a that acts so as to inhibit the movement of the paper. . Further, the transport roller pair 612 is provided in a U-shaped bending path R22 bent in a U-shape, and further provided in a position having the smallest curvature radius in the U-shaped bending path R22.

  As shown in FIG. 7, each of the transport roller pairs 604 to 612 includes driving rollers 604 a to 612 a and driven rollers 604 b to 612 b that are arranged to face the driving rollers 604 a to 612 a and are driven by the driving rollers 604 a to 612 a. Have. The driven rollers 604b to 612b are configured to be capable of being crimped and separated from the driving rollers 604a to 612a in accordance with instructions from the control unit 11. Further, the peripheral surfaces of the drive rollers 604a to 612a are made of, for example, a member such as rubber in order to improve paper transportability, and the peripheral surfaces of the driven rollers 604b to 612b are made of, for example, a member such as a resin. The conveyance roller pairs 601 to 603 are configured in the same manner.

  The paper sensors 651 to 659 are provided in the vicinity of the transport roller pairs 604 to 612, respectively, detect the presence or absence of paper in the transport roller pairs 604 to 612, and output them to the control unit 11. Thereby, the control unit 11 can detect whether or not the paper is passing through the transport roller pairs 604 to 612, whether or not the paper has passed the transport roller pairs 604 to 612, and the like. Each of the paper sensors 651 to 659 includes a light emitting element such as a light emitting diode (LED) and a light receiving element such as a photodiode (PD), and is configured by a reflection type optical sensor that detects reflected light of the paper.

As illustrated in FIG. 5, the auxiliary units 61 to 64 are connected to the shafts of the drive rollers 609 a to 612 a of the transport roller pairs 609 to 612 via a power transmission unit including gears and the like. The auxiliary units 61 to 64 move the driving rollers 609 a to 612 a in the paper width direction, that is, the axial direction in accordance with instructions from the control unit 11. For example, as shown in FIG. 5, when the correction unit 510 performs a correction operation in which the thickness direction of the paper is an axis direction and rotates in the direction of the arrow B, the rear part in the paper conveyance direction of the paper is accompanied by the paper width along with the correction operation. In order to move in the direction of arrow C, the auxiliary portions 61 to 64 move the driving rollers 609a to 612a in the directions of arrows D1 to D4 in the axial direction, respectively. Thereby, the auxiliary | assistant parts 61-64 can perform the auxiliary | assistant operation | movement which reduces the contact resistance of a sheet | seat and any member in a machine, ie, drive roller pair 609a-612a. In the present invention, any member in the machine is a member disposed on or in the vicinity of the sheet passing path, such as a roller member (for example, a pair of conveying rollers 609 to 612), a guide plate, a protrusion, and an elastic member. Etc. Further, since the movement amount of the sheet accompanying the correction operation is larger toward the rear side in the sheet conveying direction of the sheet, that is, toward the upstream side in the sheet conveying direction, the auxiliary rollers 61 to 64 disposed on the upstream side in the sheet conveying direction are driven rollers 609a to 612a. Increase the amount of movement.
In addition, the auxiliary | assistant parts 61-64 are good also as what also moves the driven rollers 609b-612b of the conveyance roller pair 609-612.

<Operation of image forming apparatus>
A sheet conveyance process performed by the image forming apparatus 1 configured as described above will be described below with reference to FIG. FIG. 8 is a flowchart illustrating an example of the paper transport process.

The control unit 11 performs paper conveyance processing every time the input job is executed.
As shown in FIG. 8, first, the control unit 11 starts driving the sheet by sequentially driving the loop roller pairs 511 and 512, the conveyance roller pairs 521 to 524, 601 to 612, and the like from the upstream side in the sheet conveyance direction. Then, the sheet information of the sheet to be conveyed is acquired (step S101). In addition, when those roller pairs are already driven, the drive is continued.
The sheet information includes information such as the length, width, basis weight, and rigidity of the sheet in the conveyance direction. For example, the control unit 11 acquires paper information based on the content of a job input by the user via the operation display unit 13.

  Next, the control unit 11 determines whether the paper has reached the pair of loop rollers 511 and 512 based on the detection results of the bending sensors 552 and 553 (step S102). For example, the control unit 11 determines that the sheet has reached the pair of loop rollers 511 and 512 when both the bending sensors 552 and 553 detect the leading end of the sheet in the sheet conveyance direction.

  If it is determined that the sheet has not reached the loop roller pair 511, 512 (step S102; NO), the control unit 11 performs the process of step S102 again. On the other hand, when it is determined that the paper has reached the pair of loop rollers 511 and 512 (step S102; YES), the control unit 11 acquires the degree of bending based on the detection results of the bending sensors 552 and 553 (step S103). . For example, the control unit 11 calculates the degree of bending of the sheet based on the difference in timing when the bending sensors 552 and 553 detect the leading end of the sheet, and acquires this.

Next, the control unit 11 determines whether or not the acquired degree of bending is equal to or less than a predetermined value (step S104). When it is determined that the degree of bending is equal to or less than the predetermined value (step S104; YES), the control unit 11 determines that the leading end portion of the sheet in the sheet conveyance direction is not greatly inclined with respect to the sheet width direction and is conveyed. It is determined whether or not the rigidity of the sheet is equal to or less than a predetermined value (step S105). This determination is made based on the paper information acquired in step S101.
When it is determined that the acquired degree of bending is not less than or equal to the predetermined value (step S104; NO), the control unit 11 determines that the front end portion of the paper in the paper conveyance direction is greatly inclined with respect to the paper width direction. Step S108 described later is performed.

When it is determined that the sheet rigidity is equal to or less than the predetermined value (step S105; YES), the control unit 11 separates the pair of transport rollers 609 to 612 in which the sheet is passing (step S106). Specifically, the control unit 11 holds the paper by separating the driven rollers 609b to 612b from the driving rollers 609a to 612a for the conveyance roller pairs 609 to 612 in which the presence of the paper is detected by the paper sensors 656 to 659. Is released. At this time, the rotational driving of the driving rollers 609a to 612a is not stopped.
If it is determined that the sheet rigidity is not less than or equal to the predetermined value (step S105; NO), the control unit 11 performs a process of step S108 described later.

  Next, the control unit 11 performs a correction operation by the correction unit 510 (step S107). Specifically, the control unit 11 controls the drive motors 513 and 514 based on the degree of bending acquired in the process of step S103 to make the rotational drive speeds of the loop roller pairs 511 and 512 different from each other. As a result, a moment for rotating the sheet with the thickness direction of the sheet as an axial direction is generated, and the bending of the sheet is corrected. At this time, the conveyance roller pairs 609 to 612 that are passing the paper are in a separated state, and the bending degree and the rigidity of the paper are each equal to or less than predetermined values. The contact resistance is extremely small even if it contacts with ˜612. Therefore, in this case, it is possible to correct the skew of the paper with sufficiently high accuracy only by performing the correction operation by the correction unit 510.

  Further, when it is determined in step S104 that the degree of bending is not less than the predetermined value (step S104; NO), and in step S105, it is determined that the rigidity of the sheet is not less than the predetermined value (step S105; NO). ), The control unit 11 separates the conveyance roller pairs 609 to 612 that are passing the sheet (step S108). Specifically, the process of step S108 is performed in the same manner as the process of step S106. At this time, the rotational driving of the driving rollers 609a to 612a is not stopped.

After performing the process of step S108, the control part 11 performs the auxiliary | assistant operation | movement by the auxiliary parts 61-64 with the correction | amendment operation | movement by the correction | amendment part 510 (step S109). Specifically, the control unit 11 controls the drive motors 513 and 514 based on the degree of bending acquired in the process of step S103 to make the rotational drive speeds of the loop roller pairs 511 and 512 different from each other. As a result, a moment for rotating the sheet with the thickness direction of the sheet as an axial direction is generated, and the bending of the sheet is corrected. Then, the control unit 11 superimposes the timing of the assisting operation by the assisting units 61 to 64 on the timing of the correcting operation, and the transporting roller pairs 609 to 612 are performed by the assisting units 61 to 64 in accordance with the movement of the paper accompanying the correcting operation. The auxiliary operation of moving the driving rollers 609a to 612a toward one end in the axial direction is performed. At this time, since the amount of movement of the sheet accompanying the correction operation is larger toward the rear side of the sheet in the sheet conveyance direction, that is, toward the upstream side in the sheet conveyance direction, the auxiliary rollers 61 to 64 arranged on the upstream side in the sheet conveyance direction are driven rollers. The movement amount of 609a to 612a is increased. As a result, even when a part of the paper comes into contact with the separated drive rollers 609a to 612a in accordance with the correction operation, the drive rollers 609a to 612a are moved in accordance with the movement of the paper, so Contact resistance with 609 to 612 can be reduced. Further, since the movement amount and direction in the movement of the paper accompanying the correction operation differ depending on the length, width, and basis weight of the paper in the conveyance direction, the control unit 11 uses the auxiliary unit 61 based on the paper information acquired in step S101. ˜64 to perform the above auxiliary operation. As a result, the auxiliary operation can be performed with high accuracy in accordance with the size and characteristics of the paper.
In addition, the auxiliary | assistant operation | movement by the auxiliary | assistant parts 61-64 is not performed about what the driven rollers 609b-612b are not spaced apart by step S108 among conveyance roller pairs 609-612.

Here, when the degree of bending of the paper exceeds a predetermined value and the rigidity of the paper exceeds at least one of the predetermined values, when the paper comes into contact with the separated transport roller pairs 609 to 612 by the correction operation, Since the contact resistance is large, the movement of the sheet is hindered, and the bending of the sheet may not be corrected properly. In the paper transport process of the present embodiment, since the auxiliary operation is performed in accordance with the correction operation as described above, the transport roller pair 609 to 612 moves together with the moved paper, and the paper and the transport roller pair 609 to 612 contact each other. Resistance has been reduced. Accordingly, the movement of the paper is not hindered, and the correction operation of the paper by the correction unit 510 is appropriately performed, so that the correction of the bending of the paper can be performed with higher accuracy.
Note that, when an image is formed on the front surface of both sides of the sheet, the sheet does not pass through the conveyance roller pairs 609 to 612, so the control unit 11 does not cause the auxiliary units 61 to 64 to perform an auxiliary operation.

  After performing the processing of step S107 or step S109, the control unit 11 returns the conveyance roller pair 609 to 612 to which the sheet has passed to the initial position (step S110). Specifically, the control unit 11 detects that there is no paper by the paper sensors 656 to 659 among the transport roller pairs 609 to 612 in which the driven rollers 609b to 612b are separated from the driving rollers 609a to 612a. For the thing, the driven rollers 609b to 612b are returned to the state where they are pressure-bonded to the driving rollers 609a to 612a. Further, the control unit 11 moves the transport roller pairs 609 to 612 to the axial direction center side by the auxiliary units 61 to 64 and returns them to the position before the auxiliary operation is performed.

  Next, the control unit 11 determines whether or not the trailing end portion in the paper transport direction has passed the registration roller pair 501 based on the detection result by the registration sensor 551 (step S111). If it is determined that the sheet has not passed the registration roller pair 501 (step S111; NO), the control unit 11 performs the process of step S110 again.

  On the other hand, if it is determined that the sheet has passed the registration roller pair 501 (step S111; YES), the control unit 11 determines that the rear end of the sheet in the conveyance direction has been sent to the secondary transfer unit 23, and the next It is determined whether there is no sheet (step S112). For example, when image formation is performed on another sheet different from the sheet that has passed the registration roller pair 501, or when image formation is performed on the back surface of the sheet that has passed the registration roller pair 501, it is determined that there is the next sheet. Is done.

If it is determined that there is a next sheet (step S112; NO), the control unit 11 performs the process of step S101 again.
On the other hand, if it is determined that there is no next sheet (step S112; YES), the controller 11 drives the registration roller pair 501, the loop roller pairs 511 and 512, the transport roller pairs 521 to 524, 601 to 612, and the like. The paper conveyance process is terminated after stopping.

<< Technical Effects of this Embodiment >>
According to the present embodiment, the image forming apparatus 1 is provided on the upstream side of the correction unit 510 in the sheet conveyance direction with respect to the correction unit 510 that performs a correction operation for correcting the skew of the conveyed paper, and toward the correction unit 510. A pair of transport rollers 609 to 612 for transporting the paper and an auxiliary operation provided on the upstream side of the correction unit 510 in the paper transport direction to reduce the contact resistance between the paper moving with the correction operation and any member in the machine Auxiliary units 61 to 64, bending sensors 552 and 553 for detecting the bending of the paper being conveyed, and the correction unit 510 when performing correction operation based on the detection results of the bending sensors 552 and 553. The control unit 11 that causes the auxiliary operations to be performed in 61 to 64 can reduce the contact resistance when the sheet comes into contact with any member in the machine in accordance with the correction operation. Can. Thereby, since the movement of the paper accompanying the correction operation is not hindered, the paper bending correction operation can be performed with higher accuracy.

  Further, since the correction unit 510 performs the correction operation by rotating the paper with the thickness direction of the paper as an axial direction, it is possible to effectively correct the bending of the paper toward the registration roller pair 501.

  In addition, since the control unit 11 superimposes the timing of the auxiliary operation by the auxiliary units 61 to 64 with the timing of the correction operation by the correction unit 510, the auxiliary operation can be performed in accordance with the correction operation, and the correction is performed more reliably. It is possible to prevent the movement of the sheet accompanying the operation.

  In addition, since the auxiliary units 61 to 64 perform an auxiliary operation of moving the conveyance roller pairs 609 to 612 in the paper width direction, the paper is more reliably corrected when the paper rotates with the thickness direction as the axial direction along with the correction operation. It is possible to prevent the movement of the sheet accompanying the operation.

  Further, since the transport roller pair 609 to 612 is provided at a position where the contact resistance with the sheet moving with the correction operation is the largest, the sheet moving with the correction operation easily comes into contact with the transport roller pair 609 to 612. However, even with such an arrangement, it is possible to accurately correct the skew of the paper.

  Further, since the transport roller pair 612 is provided in the U-shaped bending path R22 through which the transported paper passes, the paper that moves along with the correction operation easily comes into contact with the transport roller pair 612. Even in such a case, it is possible to accurately perform the bending correction operation of the paper.

  Further, since the transport roller pair 612 is provided in the U-shaped bending path R22 at a position having the smallest curvature radius or at a position upstream of the position in the paper transport direction, the paper that moves in accordance with the correction operation is provided. Although it is easy to come into contact with the pair of conveyance rollers 612, even with such an arrangement, it is possible to accurately correct the skew of the sheet.

  Further, when the rigidity of the sheet is less than or equal to a predetermined value, the control unit 11 does not cause the auxiliary units 61 to 64 to perform an auxiliary operation. Therefore, when the rigidity exceeds a predetermined value, that is, the sheet accompanying the correction operation The auxiliary operation can be performed only when the movement is likely to be hindered.

  In addition, a plurality of correction units 510 are provided in the paper width direction, and each of the loop roller pairs 511 and 512 that convey the paper toward the downstream side of the paper conveyance direction and the plurality of loop roller pairs 511 and 512 are independently driven to rotate. Driving motors 513 and 514 that perform the correction operation by generating moments on the paper by changing the rotational driving speeds of the pair of loop rollers 511 and 512. Can correct the bend.

  Further, since the bending sensors 552 and 553 are provided in the vicinity of the loop roller pair 511 and 512 in the paper transport direction and are respectively disposed at the same position as the loop roller pair 511 and 512 in the paper width direction, the loop roller pair It is possible to accurately detect the bending of the paper when reaching 511 and 512.

  In addition, the transport roller pairs 609 to 612 are provided along the paper transport direction, and the control unit 11 separates the transport roller pairs 609 to 612 from which the paper is passing during the correction operation by the correction unit 510. Therefore, the movement of the sheet accompanying the correction operation can be prevented from being hindered.

  In addition, since the control unit 11 causes the auxiliary units 61 to 64 to perform an auxiliary operation according to the length, width, and basis weight of the paper in the conveyance direction, it is possible to perform an auxiliary operation suitable for the size and characteristics of the paper. it can.

  Further, the conveyance roller pairs 609 to 612 include driving rollers 609a to 612a and driven rollers 609b to 612b, and the auxiliary units 61 to 64 are separated from the driving rollers 609a to 612a and the driven rollers 609b to 609b. When the auxiliary operation is performed by moving 612b in the paper width direction, the conveyance roller pair 609 to 612 can be moved together with the movement of the paper accompanying the correction operation, and the paper and the conveyance roller pair 609 to 612 can be moved. Contact resistance can be more reliably reduced.

  Further, the conveyance roller pairs 609 to 612 are provided along the paper conveyance direction, the auxiliary units 61 to 64 are provided along the paper conveyance direction according to the conveyance roller pairs 609 to 612, and the control unit 11 is As the auxiliary portions 61 to 64 provided on the upstream side in the transport direction increase the moving amount of the transport roller pairs 609 to 612, the driving rollers 609 a to 612 a can be appropriately moved according to the movement mode of the paper, The contact resistance between the paper and the driving rollers 609a to 612a can be more reliably reduced.

  Further, when the degree of bending based on the detection results by the bending sensors 552 and 553 is equal to or less than the predetermined value, the control unit 11 does not cause the auxiliary units 61 to 64 to perform the auxiliary operation, so the degree of bending exceeds the predetermined value. In some cases, that is, only when the paper moves greatly with the correction operation, the auxiliary operation can be performed.

<< Modification 1 >>
Modification 1 of the image forming apparatus 1 of the above-described embodiment will be described with reference to FIG. FIG. 9 is a schematic diagram illustrating auxiliary units 61a to 64a and the peripheral configuration of the image forming apparatus according to the first modification, in which the driven rollers 511b and 609b to 612b are omitted. The points other than those described below are configured in the same manner as the image forming apparatus 1 of the above embodiment.

  The image forming apparatus of Modification 1 is different from the image forming apparatus 1 of the above-described embodiment in the following points. That is, the image forming apparatus according to the first modification includes auxiliary units 61 a to 64 a instead of the auxiliary units 61 to 64.

  The auxiliary portions 61a to 64a are provided corresponding to the transport roller pairs 609 to 612, respectively.

  The auxiliary portion 61a includes a half-moon roller 611a that is rotatably provided with the paper conveyance direction as an axial direction. The half-moon roller 611a is a roller member formed in a semicircular shape when viewed from the axial direction, and is provided on the drive roller 609a side with the reverse path R2 interposed therebetween. The half-moon roller 611a is configured to be able to advance or retreat into the paper passing path by rotating around the axis. The auxiliary unit 61a causes the half-moon roller 611a to rotate forward or backward in accordance with an instruction from the control unit 11 to advance either end of the portion corresponding to the string of the half-moon roller 611a into the paper path, and It is brought into contact with the rear part in the sheet conveying direction. As a result, the rear part in the paper transport direction is moved away from the drive roller 609a, and the contact resistance between the paper and the drive roller 609a is reduced. Further, after the paper passes through the transport roller pair 609, the auxiliary unit 61a causes the half-moon roller 611a to rotate forward or backward to retract the half-moon roller 611a out of the paper path and return it to the original position.

  The auxiliary parts 62a, 63a, 64a are similarly configured and have half-moon rollers 621a, 631a, 641a, respectively.

  As described above, according to the first modification, the auxiliary portions 61a to 64a have the half-moon rollers 611a, 621a, 631a, and 641a in a state where they are retracted outside the sheet passing path, and rotate the half-moon rollers 611a, 621a, 631a, and 641a. Since the auxiliary operation is performed by advancing into the sheet passing path and contacting the sheet, the contact resistance between the sheet moving with the correction operation and the conveying roller pairs 609 to 612 can be more reliably reduced and more accurately. It is possible to correct the skew of the paper.

<< Modification 2 >>
Modification 2 of the image forming apparatus 1 of the above-described embodiment will be described with reference to FIG. FIG. 10 is a schematic diagram illustrating auxiliary units 61b to 64b and the peripheral configuration of the image forming apparatus according to the second modification. The points other than those described below are configured in the same manner as the image forming apparatus 1 of the above embodiment.

  The image forming apparatus of Modification 2 is different from the image forming apparatus 1 of the above-described embodiment in the following points. That is, the image forming apparatus according to the first modification includes auxiliary units 61 b to 64 b instead of the auxiliary units 61 to 64.

  The auxiliary parts 61b to 64b are provided corresponding to the transport roller pairs 609 to 612, respectively.

The auxiliary portions 61b to 64b are connected to shafts of driving rollers 609a to 612a arranged along the paper width direction via a power transmission portion including gears and the like. The auxiliary units 61b to 64b incline the shafts of the drive rollers 609a to 612a with respect to the paper width direction in accordance with instructions from the control unit 11. Here, the correction unit 510 performs a correction operation in which the thickness direction of the paper is rotated around the axis, so that the rear portion of the paper in the paper conveyance direction temporarily moves with respect to the paper conveyance direction along with the correction operation. It is conveyed in an inclined direction. On the other hand, the auxiliary portions 61b to 64b incline the shafts of the drive rollers 609a to 612a with respect to the paper width direction, so that the direction in which the paper is fed by the drive rollers 609a to 612a is changed from the paper transport direction to the arrows E1 to E4. Each change can be made to match the movement of the paper, and the contact resistance between the paper and the transport roller pair 609 to 612 can be reduced.
In addition, the auxiliary | assistant parts 61-64 are good also as what also moves the driven rollers 609b-612b of the conveyance roller pair 609-612.

  Further, since the amount of movement of the sheet accompanying the correction operation is larger toward the rear side in the sheet conveyance direction, that is, toward the upstream side in the sheet conveyance direction, the auxiliary rollers 61b to 64b arranged on the upstream side in the sheet conveyance direction are driven rollers 609a to 612a. Increase the angle of tilting the axis.

  As described above, according to the second modification, the auxiliary units 61b to 64b perform the auxiliary operation by inclining the axes of the transport roller pairs 609 to 612 arranged in the paper width direction with respect to the paper width direction. Accordingly, the contact resistance between the moving sheet and the conveying roller pairs 609 to 612 can be more reliably reduced, and the sheet bending correction operation can be performed with higher accuracy.

<< Modification 3 >>
A third modification of the image forming apparatus 1 according to the above-described embodiment will be described with reference to FIG. FIG. 11 is a schematic diagram illustrating a bending sensor 552c and its peripheral configuration of an image forming apparatus according to Modification 3. The points other than those described below are configured in the same manner as the image forming apparatus 1 of the above embodiment.

  The image forming apparatus of Modification 3 differs from the image forming apparatus 1 of the above-described embodiment in the following points. That is, the image forming apparatus according to the third modification includes a bending sensor 552c instead of the bending sensors 552 and 553.

  The bend sensor 552c is a line sensor extending in the paper width direction, and is provided in the vicinity of the loop roller pair 511 in the paper transport direction. The bending sensor 552c detects the position of the edge of the sheet in the sheet width direction twice at different timings during sheet conveyance, and outputs the detected position to the control unit 11. Thereby, the control unit 11 can detect the degree of bending of the sheet from the difference in the position of the edge of the sheet in the sheet width direction. The bending sensor 552c includes, for example, a light emitting element such as a light emitting diode (LED) and a light receiving element such as a photodiode (PD), and a plurality of reflective optical sensors that detect reflected light from the paper are arranged in the paper width direction. Composed.

  For example, as shown in FIG. 11, when the sheet arrives in the vicinity of the bend sensor 552c in the direction P4, the bend sensor 552c detects the position P41 of the edge of the sheet in the sheet width direction, and after a predetermined time has elapsed, The position P42 of the edge in the paper width direction is detected. Then, the control unit 11 calculates the degree of bending of the sheet from the difference between the positions P41 and P42 in the sheet width direction of the edge of the sheet.

  As described above, according to the third modification, the bending sensor 552c is a line sensor extending in the paper width direction, and is provided in the vicinity of the correction unit 510 in the paper conveyance direction. Can be accurately detected.

<< Modification 4 >>
Modification 4 of the image forming apparatus 1 according to the above-described embodiment will be described with reference to FIG. FIG. 12 is a schematic diagram illustrating the bending sensors 552d and 553d and the peripheral configuration of the image forming apparatus according to the fourth modification. The points other than those described below are configured in the same manner as the image forming apparatus 1 of the above embodiment.

  The image forming apparatus of Modification 4 differs from the image forming apparatus 1 of the above-described embodiment in the following points. In other words, the image forming apparatus of Modification 4 includes bending sensors 552d and 553d instead of the bending sensors 552 and 553.

  The bending sensors 552d and 553d are line sensors extending in the paper width direction, and are respectively provided in the vicinity of the transport roller pair 612 and the vicinity of the loop roller pair 511 in the paper transport direction. The bending sensors 552d and 553d detect the position of the edge of the sheet in the sheet width direction and output the detected position to the control unit 11. Accordingly, the control unit 11 can detect the degree of bending of the sheet from the difference in the position of the edge of the sheet based on the detection results of the bending sensors 552d and 553d. Each of the bending sensors 552d and 553d includes a light emitting element such as a light emitting diode (LED) and a light receiving element such as a photodiode (PD), and a plurality of reflective optical sensors for detecting reflected light of the paper are arranged in the paper width direction. Configured.

  For example, as shown in FIG. 12, when the paper reaches the vicinity of the bending sensors 552d and 553d in the direction P5, the bending sensor 552d detects the position P51 of the edge of the paper in the paper width direction, and the bending sensor 553d A position P52 in the sheet width direction of the edge of the sheet is detected. After a predetermined time, the bending sensor 552d detects the position P53 of the edge of the sheet in the sheet width direction, and the bending sensor 553d detects the position P54 of the edge of the sheet in the sheet width direction. Then, the control unit 11 calculates the degree of bending of the sheet from the difference between the positions P51 and P53 and the difference between the positions P52 and P54 in the sheet width direction of the edge of the sheet.

  As described above, according to the fourth modification, the bending sensors 552d and 553d are line sensors extending in the paper width direction, and in the paper conveyance direction, the vicinity of the correction unit 510 and the position upstream of the correction unit 510. Therefore, it is possible to detect the bending of the sheet when reaching the loop roller pair 511 with higher accuracy than in the third modification.

<Others>
The descriptions in the above-described embodiments and modifications are examples of a suitable image forming apparatus according to the present invention, and the present invention is not limited to this.

  For example, in the embodiment and the modification described above, the registration roller pair 501 and the loop roller pairs 511 and 512 that transport the paper to the secondary transfer unit 23 are provided, but the present invention is not limited to this. For example, a pair of conveyance rollers may be provided instead of the pair of registration rollers 501 and the pair of loop rollers 511 and 512, respectively. In this case, the transport roller pair may not perform the leading edge alignment or loop formation of the paper.

  Further, in the above-described embodiment and modification, the correction unit 510 is configured to include the loop roller pair 511 and 512, but is not limited thereto. For example, the correction unit 510 may include three or more loop roller pairs in the paper width direction, and in this case, further includes a drive motor that independently drives the loop roller pairs. It is also good.

  In the above-described embodiment and modification, the auxiliary units 61 to 64 are provided corresponding to the transport roller pairs 609 to 612, but the present invention is not limited to this. For example, an auxiliary unit may be provided corresponding to one of the transport roller pairs 609 to 612, or an auxiliary unit corresponding to any of the transport roller pairs 521 to 524 and 601 to 608. It is good also as what is provided.

  In the above-described embodiment, the auxiliary units 61 to 64 move the conveyance roller pairs 609 to 612 in the paper width direction. However, the present invention is not limited to this. For example, the auxiliary units 61 to 64 move any member in the machine (for example, a guide member or a roller member provided in the sheet passing path) in any direction (for example, the sheet width direction or the direction away from the sheet). By doing so, an auxiliary operation for reducing the contact resistance between the paper and the member may be performed.

  In the above-described embodiment and modification, the conveyance roller pair 601 to 612 is configured to be capable of being crimped and separated, but is not limited thereto. For example, one of the conveyance roller pairs 601 to 612 may be configured to be capable of being crimped and separated, or the conveyance roller pairs 521 to 524 may be configured to be capable of being crimped and separated. Further, in this case, when the paper reaches the loop roller pair 511, 512, the control unit 11 puts the transport roller pair 521-524, 601-612 in the separated state for the paper passing through. It is good as a thing.

  In the above-described embodiment and modification, the correction operation is performed based on the degree of bending, but the auxiliary operation may be performed based on the degree of bending.

  In the above-described embodiment and modification, the auxiliary operation is not performed when the rigidity of the sheet is equal to or less than a predetermined value. However, the present invention is not limited to this. For example, the auxiliary operation may be performed regardless of the rigidity of the paper, or the auxiliary operation may be performed based on paper conditions other than the paper rigidity, such as length, width, basis weight, surface roughness, material, etc. in the transport direction. It is good also as what determines whether operation is performed. Further, they may be arbitrarily changed by the user.

  In the first modification described above, the auxiliary portions 61a to 64a perform the auxiliary operation by the rotation of the half-moon rollers 611a, 621a, 631a, and 641a. However, the present invention is not limited to this. For example, the auxiliary unit may have a conveyance roller that can rotate in any direction, and may perform the auxiliary operation by moving the conveyance roller to advance or retreat with respect to the sheet passing path.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 510 Correction | amendment part 511, 512 Loop roller pair (correction roller pair)
513, 514 Driving motor (drive mechanism)
552, 553 Bending sensor (detection unit)
609 to 612 Conveying roller pair 609a to 612a Driving roller 609b to 612b Driven roller

Claims (21)

A correction unit that performs a correction operation to correct the skew of the conveyed paper;
A pair of conveyance rollers that is provided upstream of the correction unit in the sheet conveyance direction and conveys the sheet toward the correction unit;
An auxiliary unit that is provided upstream of the correction unit in the paper conveyance direction and performs an auxiliary operation to reduce contact resistance between a sheet that moves with the correction operation and any member in the machine;
A detection unit for detecting the bending of the paper being conveyed;
An image forming apparatus comprising: a control unit that causes the auxiliary unit to perform the auxiliary operation when the correction unit performs the correction operation based on a detection result of the detection unit.   The image forming apparatus according to claim 1, wherein the correction unit performs the correction operation by rotating the paper with the thickness direction of the paper as an axial direction.   The image forming apparatus according to claim 1, wherein the control unit superimposes the timing of the auxiliary operation by the auxiliary unit on the timing of the correction operation by the correction unit.   The image forming apparatus according to claim 1, wherein the auxiliary unit performs the auxiliary operation of moving the member in a sheet width direction.   5. The image forming apparatus according to claim 1, wherein the member is provided at a position where contact resistance with a sheet that moves in accordance with the correction operation is the largest.   The image forming apparatus according to claim 1, wherein the member is provided in a U-shaped bending path through which a sheet to be conveyed passes.   The image forming apparatus according to claim 6, wherein the member is provided at a position having the smallest radius of curvature in the U-shaped bent path or a position upstream of the position in the sheet conveyance direction. . Provided on the downstream side of the correction unit with respect to the sheet conveyance direction, and includes a pair of registration rollers in which the leading end of the sheet in the sheet conveyance direction is abutted against the nip point.
The said correction | amendment part has a pair of loop rollers which abuts the front-end | tip part of the paper conveyance direction of a paper to the said registration roller pair, and forms a loop in the said paper. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit does not cause the auxiliary unit to perform the auxiliary operation when the sheet rigidity is equal to or less than a predetermined value. .   The correction unit is provided in a plurality in the sheet width direction, and includes a correction roller pair that conveys the sheet toward the downstream side in the sheet conveyance direction, and a drive mechanism that independently rotates and drives the plurality of correction roller pairs. 10. The image formation according to claim 1, wherein the correction operation is performed by generating a moment on the paper by changing a rotational driving speed of the plurality of correction roller pairs. 10. apparatus.   The said detection part is provided with two or more near the said correction roller pair in a paper conveyance direction, and is each arrange | positioned in the same position as the said several correction roller pair in a paper width direction. Image forming apparatus.   The image forming apparatus according to claim 1, wherein a plurality of the transport roller pairs are provided along a paper transport direction. A plurality of the transport roller pairs are provided along the paper transport direction,
13. The control unit according to claim 1, wherein a state in which a sheet is passing during the correction operation by the correction unit is separated from the pair of transport rollers. 13. The image forming apparatus described.   14. The image formation according to claim 1, wherein the control unit causes the auxiliary unit to perform the auxiliary operation according to a length, a width, and a basis weight of a sheet in a conveyance direction. apparatus. The transport roller pair has a driving roller and a driven roller,
The image according to claim 1, wherein the auxiliary unit performs the auxiliary operation by moving the driving roller and the driven roller in a separated state in a paper width direction. Forming equipment. A plurality of the transport roller pairs are provided along the paper transport direction,
A plurality of the auxiliary portions are provided along the paper conveyance direction according to the plurality of conveyance roller pairs,
The image forming apparatus according to claim 15, wherein the control unit increases the movement amount of the pair of transport rollers toward the auxiliary unit provided on the upstream side in the sheet transport direction.   The auxiliary unit has a half-moon roller in a state of being retracted out of the sheet passing path, and performs the assisting operation by rotating the half-moon roller to advance into the sheet passing path to contact the sheet. The image forming apparatus according to any one of claims 1 to 16.   The said auxiliary | assistant part performs the said auxiliary | assistant operation | movement by inclining the axis | shaft of the said conveyance roller pair arrange | positioned in the paper width direction with respect to the paper width direction. The image forming apparatus described.   19. The control unit according to claim 1, wherein the control unit does not cause the auxiliary unit to perform the auxiliary operation when a degree of bending based on a detection result by the detection unit is a predetermined value or less. The image forming apparatus described in the item.   20. The image according to claim 1, wherein the detection unit is a line sensor extending in a paper width direction, and is provided in the vicinity of the correction unit in the paper conveyance direction. Forming equipment.   The detection unit is a line sensor extending in the paper width direction, and is provided in the vicinity of the correction unit and at a position upstream of the correction unit in the paper conveyance direction in the paper conveyance direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images