JP2013133223A - Paper conveying device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper conveying device and image forming apparatus, in which the firm contact of conveyance roller pair provided in a curved path is prevented from being canceled by the tension of paper.SOLUTION: The paper conveying device comprises: a registration roller 25 configured to sandwich paper and adjust its position to a position orthogonal to a conveyance direction; a first roller pair 22, a second roller pair 23, and a third roller pair 24 arranged upstream of the registration roller 25 in the conveyance direction and arranged in that order from the upstream side along the paper conveyance direction; and a control part configured to control the drive of the registration roller 25, first roller pair 22, second roller pair 23, and third roller pair 24. The second roller pair 23 has a curved path at least on the upstream or downstream side in the conveyance direction. The control part controls the drive of the first roller pair 22 and the second roller pair 23 such that paper is looped between the first and second roller pairs 22 and 23.

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus that convey sheets in a bent path.

  In the image forming apparatus, a pair of transport rollers is used to transport a sheet. The pair of conveyance rollers is configured by a pair of rollers that are pressure-bonded to each other, and conveys the paper while pinching the sheet at the nip portion between the rollers. The conveyance roller pair is used for various applications in addition to conveyance depending on a place where the conveyance roller pair is arranged. For example, a pair of conveyance rollers provided upstream of a sheet conveyance path of a transfer unit that transfers an image to a sheet is called a registration roller, and is used for alignment of a toner image of a transfer unit and a sheet (for example, a patent) Reference 1).

  A pair of conveying rollers provided upstream of the registration rollers is called a loop forming roller pair, and is used to form a loop on the paper in order to eliminate paper skew. In Patent Document 1, the loop forming roller pair is driven to form a loop on the paper in a state where the leading edge of the paper is abutted against the gate means provided near the registration roller. When forming the loop, the registration rollers are separated, and when the formation of the loop is finished, the registration rollers are pressure-bonded to separate the loop forming roller pair. Thus, some conveyance roller pairs can be switched between pressure bonding and pressure bonding release.

  Depending on the design of the transport roller pair, a plurality of transport roller pairs may be disposed upstream of the loop forming roller pair, and the paper transport path formed by the three transport roller pairs may be bent.

  In such a bending path, the nip portion of the conveyance roller pair located at the center of the three pairs of conveyance rollers is located away from the line connecting the nip portions of the conveyance roller pairs located upstream and downstream. Here, due to a difference in the relative sheet conveyance speed of the conveyance roller pair, the sheet may be pulled between the conveyance roller pairs positioned upstream and downstream. The tension applied to the pulled paper acts in a direction in which the rollers on the inner side of the bending path among the pair of conveyance rollers positioned in the middle approach the line connecting the nip portions of the conveyance roller pairs positioned upstream and downstream. For this reason, when the tension of the pulled paper becomes greater than the pressure-bonding force, the driven roller having the pressure-release mechanism in the pair of conveyance rollers located in the middle is pushed up by the paper, and the paper is separated from the drive roller. As a result, the sheet conveyance force by the intermediate conveyance roller pair is lost, and a sheet conveyance defect occurs.

JP 2008-24507 A

  The present invention has been made based on the above-described problems, and provides a sheet conveying apparatus and an image forming apparatus that can prevent the pressure-bonding of the conveying roller pair provided in the bending path from being released due to the tension of the sheet. .

  The above object of the present invention is achieved by the following means.

  (1) A registration roller that holds the paper and adjusts the position in a direction orthogonal to the conveyance direction, and is arranged in order from the upstream side in the conveyance direction of the registration roller and upstream from the conveyance direction. A sheet conveying apparatus comprising: a first roller pair, a second roller pair, and a third roller pair that convey; and a control unit that controls driving of the registration roller, the first roller pair, the second roller pair, and the third roller pair. The second roller pair has a bending path at least on the upstream side in the transport direction or the downstream side in the transport direction, and the control unit is between the first roller pair and the second roller pair, A paper conveying apparatus that controls driving of the first roller pair and the second roller pair so as to form a loop on the paper.

  (2) The sheet conveyance according to (1), wherein the nip portion of the second roller pair is located away from a line connecting the nip portions of the first roller pair and the third roller pair. apparatus.

  (3) The third roller pair is a loop-forming roller pair that is disposed on the upstream side in the immediate conveyance direction of the registration roller and forms a loop between the registration roller and (1) Or the paper conveying apparatus as described in (2).

  (4) The second roller pair is composed of a driving roller and a driven roller, the roller located inside the bending path is the driven roller, the other roller is the driving roller, and the pressure bonding of the second roller pair is released. The paper conveyance device according to any one of (1) to (3), wherein the pressure-bonding release mechanism is provided in the driven roller.

  (5) The control unit maintains a loop of the paper formed between the first roller pair and the second roller pair until a rear end of the paper passes through the first roller pair. The sheet conveying device according to any one of (1) to (4), wherein the sheet conveying device is controlled as follows.

  (6) When the control unit swings the registration roller in a direction orthogonal to the paper conveyance direction, the controller releases the pressure bonding of the second roller pair when the paper reaches the loop forming roller. The sheet conveying apparatus according to any one of (3) to (5), characterized in that:

  (7) An image forming unit that forms a toner image on an image carrier, a transfer unit that transfers the toner image from the image carrier to the paper, and the paper that is transported to the transfer unit (1) to (1) 6) The image forming apparatus comprising: the paper conveying device according to any one of 6).

  According to the present invention, since a loop is formed in the paper on the upstream side of the pair of conveyance rollers not on the line connecting the nip portions of the upstream and downstream conveyance roller pairs, the rollers of the conveyance roller pair are pushed up, It is possible to reliably prevent the occurrence of paper conveyance failure.

1 is a cross-sectional view schematically showing a configuration of an image forming apparatus according to an embodiment. It is a top view which shows roughly the mechanism which rotates and rock | fluctuates a registration roller. It is a figure which shows roughly the mechanism which cancels | releases crimping | compression-bonding of the driven roller of a conveyance roller pair. FIG. 3 is a cross-sectional view illustrating a paper transport device. FIG. 4 is a block diagram illustrating a relationship between a sheet conveying device and a control unit according to the present embodiment. 6 is a flowchart illustrating a procedure of a process of conveying a sheet by the sheet conveying apparatus according to the embodiment. It is sectional drawing which illustrates a mode that a paper is conveyed in the paper conveying apparatus which concerns on this embodiment.

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

An image forming apparatus A shown in FIG. 1 is called a tandem color image forming apparatus, and four sets of image forming units form a color image on paper using an electrophotographic image forming process.
A document is placed on a document table provided with a slit SL at the top, and the placed document is scanned and exposed by a scanning optical system of the image reading device SC, and reflected light from the document is transmitted through a mirror to a line image sensor. Is read and photoelectrically converted. The photoelectrically converted image signal for each color is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like by an image processing unit (not shown), and then the light of the image forming unit 10 of the corresponding color. Each is input to the writing unit 3.

  The four image forming units include an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image forming unit that forms a cyan (C) color image. The unit 10C is an image forming unit 10K that forms a black (K) color image.

The image forming unit 10Y includes a photosensitive drum 1Y, and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a photosensitive drum cleaning device 5Y disposed around the photosensitive drum 1Y. Similarly, the image forming unit 10M includes a photosensitive drum 1M, and a charging unit 2M, an optical writing unit 3M, a developing device 4M, and a photosensitive drum cleaning device 5M disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charging unit 2C, an optical writing unit 3C, a developing device 4C, and a photosensitive drum cleaning device 5C arranged around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, and a charging unit 2K, an optical writing unit 3K, a developing device 4K, and a photosensitive drum cleaning device 5K disposed around the photosensitive drum 1K. The photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units 10Y, 10M, 10C, and 10K, the charging units 2Y, 2M, 2C, and 2K, the optical writing units 3Y, 3M, 3C, and 3K, and the photosensitive units. The body drum cleaning devices 5Y, 5M, 5C, and 5K have the same functions. Therefore, in the following description, symbols Y, M, C, or K are not used unless otherwise specified.
The surface of the photosensitive drum 1 is charged by a charging unit 2 formed of a corona discharge electrode such as a scorotron method, and is scanned and exposed based on an image signal by an optical writing unit 3 to form an electrostatic latent image corresponding to the image signal. The The developing device 4 develops the electrostatic latent image formed on the photosensitive drum 1 with toner using electrostatic force, and forms a toner image corresponding to each color.

  In the image forming process of the present embodiment, the photosensitive drum 1 and the intermediate transfer belt 6 are used as the image carrier.

  The intermediate transfer belt 6 is an endless belt, is constructed by a plurality of rollers, and is supported so as to be able to run. The toner images of the respective colors formed on the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the intermediate transfer belt 6 by the primary transfer units 7Y, 7M, 7C, and 7K, and each color (Y, M, C, The color toner image on which the toner layer K) is superimposed is primarily transferred onto the intermediate transfer belt 6. The color toner image formed on the intermediate transfer belt 6 is secondarily transferred onto the paper P conveyed by the paper conveying device 20 in the secondary transfer portion 7A. The paper P on which the color toner image has been transferred is subjected to heat and pressure at the nip portion N of the fixing device 30, whereby the color toner image is melted and fixed on the paper P. Then, the paper P is discharged out of the apparatus by the paper discharge roller 35.

  The paper transport unit 20 transports the paper P along the paper transport path 29 from the paper feed trays 291, 292, and 293 and the manual feed tray Tr that store paper to the secondary transfer unit 7 A. The paper P is fed by the paper feed roller 21 and conveyed to the intermediate conveyance roller pair 23 via the conveyance roller pair 26.

  Further, the paper P is fed by the manual paper feed roller pair 22 and transported to the intermediate transport roller pair 23, and is transported to the secondary transfer unit 7 </ b> A through the loop forming roller pair 24 and the registration roller 25. The registration roller 25 is configured to swing in a direction orthogonal to the transport direction (hereinafter also referred to as the width direction) in order to adjust the position of the color toner image that is secondarily transferred to the paper P. .

  Next, FIG. 2 is a top view schematically showing a mechanism for rotationally driving and swinging the registration roller according to the present embodiment.

  As shown in FIG. 2, the registration roller 25 includes drive motors M <b> 1 and M <b> 2, pulleys 251 and 253, a drive belt 252, a rotation shaft 254, a swing cam 255, and an urging spring 256.

  The drive motor M1 is composed of a stepping motor or the like, and the drive is transmitted through the pulley 251, the drive belt 252, and the pulley 253, and the drive roller of the registration roller 25 is rotated.

  The drive motor M2 is composed of a stepping motor or the like, and rotationally drives the swing cam 255. Here, the urging spring 256 urges the rotating shaft 254 to contact the inclined surface of the oscillating cam 255, and when the drive motor M2 rotates the oscillating cam 255, the rotating shaft 254 rotates the oscillating cam. The position of contact with the inclined surface of 255 changes, the contact position changes in the width direction (left-right direction in FIG. 2), and the registration roller 25 can swing in the width direction. The distance that the registration roller 25 swings in the width direction is indicated by ΔQ.

  Next, FIG. 3 is a diagram schematically illustrating a mechanism for releasing the pressure bonding of each transport roller pair.

  The crimp release mechanism 200 according to the present embodiment includes a pressing member 200K and a lever member 200L. The pressing member 200K is composed of a solenoid or the like, is disposed in the vicinity of the lever member 200L, and presses a part of the lever member 200L. The pressing member 200K presses the arm portion extending below the lever member 200L based on an instruction from the control unit 90, or releases the pressing. The lever member 200L is formed in an L shape having two arm portions, and is pivotally supported at a connection point of the arm portions, and is configured to be rotatable around this point. When the arm portion extending downward of the lever member 200L is pressed, the lever member 200L is rotated by the pressing force. The pressing force is transmitted to the other arm portion extending horizontally as a force for lifting the driven roller of the pair of conveying rollers that is pressure-bonded by a spring (not shown) or the like, and the pressure-bonding by the driven roller is released. Note that the pressing members 200 are provided at both ends in the width direction of the rotation shafts of the transport roller pair.

  When the registration roller 25 is swung, a press release mechanism 200 is provided so as to release the press of the upstream conveying roller pair. In the present embodiment, the rollers 25a, 24b, 23b, and 26b are drive rollers, and the rollers 25b, 24a, 23a, and 26a are driven rollers. The rollers 25b, 24a, 23a and 26a, which are driven rollers, are provided with a pressure release mechanism 200 so that they can be separated from the driving roller by pressure release. The manual feed roller pair 22 is a fixed roller pair. Regarding each roller pair of the present invention described in the claims, the first roller pair is the manual feed roller pair 22, the second roller pair is the intermediate transport roller pair 23, and the third roller pair is the loop forming roller pair 24. Applicable. The intermediate transport roller pair 23 (also referred to as a second roller pair) has a bent path on the upstream side, and the nip portion thereof is a nip portion of the manual feed roller pair 22 and the loop forming roller pair 24 as shown in FIG. The driven roller 23a on the inner side of the bending path is separated by releasing the pressure bonding.

  Each of the above units is connected to a control unit 90 having a CPU (Central Processing Unit) (not shown), and is appropriately controlled by the control unit 90. The relationship between the control unit 90 and the paper transport unit 20 is as shown in FIG. As shown in FIG. 5, the control unit 90 is connected to each component of the paper transport unit 20 via a bus, and controls each transport roller and the like constituting the paper transport unit 20. Further, the control unit 90 determines whether or not the registration roller 25 is swung in the width direction. Further, the control unit 90 appropriately controls the pressure bonding and release of the driven rollers such as the intermediate conveyance roller pair 23 and the rotation driving depending on whether or not the registration roller 25 is swung. Details of these control processes will be described later with reference to FIGS. A program corresponding to these processes is stored in a storage unit (not shown) included in the control unit 90. Each function of the above-described units of the image forming apparatus A is implemented by the CPU executing a corresponding program.

  Next, with reference to FIG. 6 to FIG. 7, a processing procedure for controlling each transport roller to transport the paper by the paper transport unit according to the present embodiment will be described in detail.

  FIG. 6 is a flowchart showing a procedure of processing for transporting paper by the paper transport unit according to this embodiment, and FIG. 7 is a cross-sectional view illustrating a state of transporting paper in the paper transport unit according to this embodiment. 6 is stored in a storage unit or the like of the control unit 90, and the CPU of the control unit 90 executes the program to execute the sheet conveyance process. To be implemented.

  As shown in FIG. 6, first, the control unit 90 obtains paper size information (step S11). In this step, the size of the paper P placed on the paper feed trays 291, 292, 293 or Tr is detected by the paper size detection sensor, and based on the detection result, the controller 90 detects the paper P in the paper transport direction. Obtain size information. This size information is used in step S20 described later.

  Subsequently, it is determined whether or not the sheet P has reached the intermediate transport roller pair 23 (step S12). The timing at which the paper P arrives at the intermediate transport roller pair 23 is detected by, for example, the sensor Sn1 shown in FIG. Alternatively, the timing at which the paper P arrives at the intermediate transport roller pair 23 is determined based on the transport speed after the leading edge of the paper P passes the manual feed roller pair 22 and the distance to the intermediate transport roller pair 23. May be. When it is determined that the sheet P has not reached the intermediate conveyance roller pair 23 (step S12: NO), the control unit 90 waits until it reaches.

  On the other hand, when it is determined that the sheet P has reached the intermediate transport roller pair 23 (step S12: YES), the intermediate transport roller pair 23 and the manual feed roller pair 22 on the upstream side of the intermediate transport roller pair 23 are between. Thus, a loop of the paper P is formed on the upstream side of the intermediate transport roller pair 23 (step S13). The loop can be formed, for example, by increasing the relative rotation speed of the manual feed roller pair 22 relative to the intermediate transport roller pair 23. A state in which a loop is formed on the paper P being transported between the manual paper feed roller pair 22 and the intermediate transport roller pair 23 is as shown in FIG. By forming a loop, when the paper P is pulled by the manual paper feed roller pair 22 and the loop forming roller pair 24 downstream of the intermediate transport roller pair 23, the driven roller 23a above the intermediate transport roller pair 23 is pushed up. It is prevented that it is done.

  Subsequently, the control unit 90 performs rotation control so that the manual paper feed roller pair 22 and the intermediate transport roller pair 23 have the same linear speed (step S14), and maintains the loop formed in step S13. The state of paper conveyance in this step is as shown in FIG.

  Subsequently, it is determined whether or not the paper P has reached the loop forming roller pair 24 (step S15). The timing at which the paper P arrives at the loop forming roller pair 24 can be calculated based on, for example, the conveyance speed of the paper P and the distance to the loop forming roller pair 24. When it is determined that the paper P has not reached the loop forming roller pair 24 (step S15: NO), the control unit 90 waits until it reaches.

  On the other hand, when it is determined that the paper P has reached the loop forming roller pair 24 (step S15: YES), the control unit 90 has transported the paper P from the intermediate transport roller pair 23 and the paper feed trays 291, 292, and 293. In that case, the pressure bonding of the upstream conveying roller pair 26 is released (step S16). Before the paper P reaches the registration roller 25, by releasing the pressure bonding of the upstream pair of pressure-removable rollers, a skew of the paper P is formed when a loop is formed on the upstream side of the registration roller 25 as will be described later. (Skew) can be easily solved.

  Subsequently, it is determined whether or not the sheet P has reached the registration roller 25 (step S17). Whether the paper P has reached the registration roller 25 can be detected by the sensor Sn2. When it is determined that the paper P has not reached the registration roller 25 (step S17: NO), the control unit 90 waits until it reaches.

  On the other hand, when it is determined that the paper P has reached the registration roller 25 (step S17: YES), a registration loop is formed on the upstream side of the registration roller 25 (step S19). In this step, the control unit 90 forms a registration loop on the paper P between the registration roller 25 and the loop forming roller pair 24 in order to eliminate the skew in the conveyance direction of the paper P conveyed to the registration roller 25. To do. Specifically, the paper P is abutted against the nip portion of the registration roller 25 that has been stopped in advance. Thereafter, the loop forming roller pair 24 is continuously rotated to feed the paper P, thereby forming a registration loop on the paper P. The paper P abutted against the registration roller 25 is positioned so that the leading end thereof is parallel to the rotation axis of the registration roller 25, thereby eliminating the skew.

  Subsequently, rotation of the registration roller 25 is started (step S19), and the paper P from which the skew has been eliminated in step S19 is conveyed to the transfer unit. A state in which the sheet P is conveyed to the transfer portion while maintaining the registration loop on the upstream side of the registration roller 25 is as shown in FIG. In addition, after the registration roller 25 starts to rotate, the driven roller 24a of the loop forming roller pair 24 is released from the pressure bonding.

  Subsequently, it is determined whether or not the registration roller 25 is swung in a direction orthogonal to the conveyance direction (step S20). In this step, the control unit 90 determines whether or not to swing the registration roller 25 in a direction orthogonal to the transport direction, based on the size information of the paper P acquired in step S11. Specifically, when the size of the paper P in the paper conveyance direction is larger than the vertical dimension (42 cm) of the A3 size, for example, the leading edge of the paper P being conveyed is nipped by the registration roller 25 and the paper P The rear end may be nipped by the manual paper feed roller pair 22 in some cases. Here, if the registration roller 25 is swung in the width direction while the rear end of the paper P is nipped by the manual paper feed roller pair 22, the paper P is twisted. Therefore, in this step S20, it is determined whether or not the conveyed paper P is of a size that can swing the registration roller 25, thereby preventing the paper P from being twisted during swinging.

  If it is determined that the paper P is of a size that can swing the registration roller 25 (step S20: YES), the sensor Sn3 detects the position of the paper P in the width direction, and the amount of deviation from the reference position is thereby detected. Detect and start swinging the registration roller 25 (step S21). In this step, with the paper P sufficiently nipped by the registration rollers 25, the control unit 90 swings the paper P by a distance corresponding to the shift amount in the width direction, and the paper P is positioned at the reference position. Oscillate as follows. By doing so, the paper P can be accurately positioned with respect to the secondary transfer portion 7A.

  Thereafter, the process of conveying the sheet by the sheet conveying unit 20 is ended.

  Returning to step S20, if it is determined that the registration roller 25 does not swing in the width direction, that is, the size of the paper P obtained in step S11 is larger than the predetermined size (step S20: NO), the registration roller 25 is moved. Step S21 that swings in the width direction is skipped, the sheet is conveyed to the transfer unit, and the process is terminated.

  As described above, according to this embodiment, the nip portion of the intermediate conveyance roller pair 23 is located away from the line connecting the nip portion of the upstream manual feed roller pair 22 and the downstream loop forming roller pair 24. In this case, a loop is formed on the paper P being transported between the manual feed roller pair 22 and the intermediate transport roller pair 23, so that the driven roller 23 a of the intermediate transport roller pair 23 is caused by the waist force of the paper P. It can be prevented from being pushed up. Accordingly, the conveyance failure of the paper P can be solved. At this time, the driven roller 23a of the intermediate conveyance roller pair 23 on the inner corner side of the bending path including the manual feed roller pair 22, the intermediate conveyance roller pair 23, and the loop forming roller pair 24 can follow the drive roller 23b. Since the sheet conveying force is not impaired, the effect of preventing a conveyance defect becomes more remarkable. Further, in the present embodiment, the rollers of the intermediate conveyance roller pair 23 are released from the pressure bonding before the registration loop is formed, so that the skew caused by the registration roller 25 can be easily eliminated. In this embodiment, since it is determined whether or not the registration roller 25 is swung according to the size in the transport direction of the paper P, the resist is swung while the rear end side of the paper P is nipped by the fixed roller. Can be prevented from being twisted.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.

  For example, in the above-described embodiment, the form in which the sheet conveyance control according to the present invention is executed for the sheet conveyed from the manual feed tray Tr is described, but the present invention is not limited to this. The present invention can also be applied to the paper P conveyed from the paper feed trays 291, 292, and 293.

  Moreover, in the said embodiment, the form which forms a loop between the manual conveyance roller pair 22 and the intermediate conveyance roller pair 23 was described. However, it is not limited to this. As long as any three pairs of rollers form a bending path on the sheet conveyance path, a loop may be formed between the two pairs of rollers on the upstream side.

  In the above embodiment, the driven roller 23a of the intermediate transport roller pair 23 is released from the pressure bonding in step S16. However, it is not limited to this. As long as the loop is not formed on the upstream side of the registration roller 25, the driven roller 23a of the intermediate transport roller pair 23 may be released from pressure bonding at any timing.

A: Image forming apparatus,
M1 / M2: Drive motor,
N: Nip part,
P: paper,
Sn: sensor,
Tr: Bypass tray,
6: Intermediate transfer belt,
7A: secondary transfer part,
10Y, 10M, 10C, 10K: image forming unit,
20: paper transport section,
21: First paper feed roller,
22: Manual feed roller pair (first roller pair),
23: Intermediate transport roller pair (second roller pair),
24: Loop forming roller pair (third roller pair),
25: Registration roller,
251,253: pulley,
252: Drive belt,
254: A rotation axis of the registration roller 25,
255: rocking cam,
256: biasing spring,
26: pair of transport rollers,
Rollers 25a, 24b, 23b, 26b: driving rollers,
Rollers 25b, 24a, 23a, 26a: driven rollers,
29: Paper transport path,
291 292 293: paper feed tray,
200: Pressure release mechanism,
200K: pressing member,
200L: lever member,
90: Control unit.

Claims (7)

A registration roller that holds the paper and adjusts the position in a direction perpendicular to the conveyance direction;
A first roller pair, a second roller pair, and a third roller pair that are arranged in order from the upstream side in the paper conveyance direction on the upstream side in the conveyance direction of the registration rollers, and convey the paper;
A control unit that controls driving of the registration roller, the first roller pair, the second roller pair, and the third roller pair;
A paper transport device comprising:
The second roller pair has a bending path at least on the upstream side in the transport direction or on the downstream side in the transport direction,
The control unit controls driving of the first roller pair and the second roller pair so as to form a loop on the paper between the first roller pair and the second roller pair. Paper transport device.   2. The sheet conveying device according to claim 1, wherein the nip portion of the second roller pair is located away from a line connecting the nip portions of the first roller pair and the third roller pair.   The said 3rd roller pair is arrange | positioned in the conveyance direction immediate upstream of the said registration roller, and is a loop formation roller pair which forms a loop between the said registration rollers, The Claim 1 or Claim 2 characterized by the above-mentioned. The paper transport device described in 1.   The second roller pair is composed of a driving roller and a driven roller, the roller located inside the bending path is the driven roller, the other roller is the driving roller, and the pressure cancellation is performed to cancel the pressure bonding of the second roller pair. The sheet conveying apparatus according to claim 1, wherein a mechanism is provided on the driven roller.   The control unit controls to maintain a loop of the paper formed between the first roller pair and the second roller pair until a rear end of the paper passes through the first roller pair. The sheet conveying apparatus according to claim 1, wherein   When the control unit swings the registration roller in a direction orthogonal to the paper conveyance direction, the controller releases the pressure bonding of the second roller pair when the paper reaches the loop forming roller. The paper conveying apparatus as described in any one of Claims 3-5. An image forming unit for forming a toner image on the image carrier;
A transfer portion for transferring the toner image from the image carrier to the paper;
The paper transport device according to any one of claims 1 to 6, wherein the paper is transported to the transfer unit.
An image forming apparatus comprising: