Sheet conveying device and image forming apparatus

Abstract

To provide a sheet conveyance device which improves accuracy of correction of conveyance deviation of a sheet in a conveyance direction, and can suppress vibration of the sheet after correction, and an image formation device which is provided with the sheet conveyance device.SOLUTION: An image formation device 10 includes a sheet conveyance unit 23 and a sheet correction mechanism 60. A roller unit 80 of the sheet correction mechanism 60 rotates to a sheet receiving position from an initial position before entry of the sheet, and is returned to the initial position from the sheet receiving position after entry of the sheet. A control part 90 decelerates rotation speed when the roller unit 80 is returned to second rotation speed V2 at a predetermined setting position from first rotation speed V1.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device capable of conveying a sheet, and an image forming apparatus including the sheet conveying device. [Background technology]

[0002] Image forming devices such as printers, copiers, facsimiles, and multifunction devices equipped with these functions are equipped with a sheet transport device that transports sheets such as print paper to an image transfer position. Conventional sheet transport devices are equipped with a pair of registration rollers that perform a registration operation (also called registration) on the sheet. Here, the registration operation refers to the operation of applying a transport force to the sheet in the transport direction while the leading edge of the sheet is abutted against the nip portion of the registration roller pair that is stationary. This registration operation corrects the skew of the sheet during transport.

[0003] A known device for correcting the inclination of a sheet is a skew correction mechanism that has a rotation mechanism that clamps and rotatably supports the sheet while it is being transported, and when the inclination of the sheet is detected, rotates the rotation mechanism in a direction that corrects the inclination (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-27859 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the rotation mechanism rotates at a predetermined speed during sheet skew correction using the skew correction mechanism, the rotation mechanism may vibrate when the rotation stops. In this case, if the sheet is transported to the image transfer position while the vibration has not subsided, the image will be transferred to the vibrating sheet, resulting in a problem of reduced image quality. On the other hand, slowing the sheet transport speed or temporarily suspending sheet transport to reduce vibration to a standard level increases the first print time, which is the time from receiving an image formation command to discharging the sheet. Furthermore, increasing the distance from the correction position to the image transfer position to reduce vibration to a standard level not only reduces the first print time, but also increases the size of the device in the transport direction. This problem can also occur when correcting sheet misalignment in the width direction.

[0006] The object of the present invention is to provide a sheet conveying device that can improve the accuracy of correcting sheet conveyance deviation in the conveying direction and suppress vibration of the sheet after correction, and an image forming apparatus equipped with the sheet conveying device. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a sheet transporting device including: a transport unit configured to transport a sheet in a transport direction toward an image transfer position where an image is transferred onto the sheet; a detection unit configured to detect a transport deviation of the sheet transported in the transport direction; a sheet correction unit disposed downstream of the transport unit in the transport direction and configured to displace from a predetermined sheet receiving position to a correction completion position when the detection unit detects the transport deviation and correct the transport deviation; and a speed control unit configured to control a displacement speed of the sheet correction unit during the displacement process from the sheet receiving position to the correction completion position by the sheet correction unit. The speed control unit displaces the sheet correction unit at a predetermined first speed to a set position defined between the sheet receiving position and the correction completion position, and displaces the sheet correction unit from the set position to the correction completion position at a second speed slower than the first speed.

[0008] According to another aspect of the present invention, a sheet conveying device includes a conveying unit that conveys a sheet in a conveying direction toward an image transfer position where an image is transferred onto the sheet, a detection unit that detects a conveyance deviation of the sheet conveyed in the conveying direction, a correction roller disposed downstream of the conveying unit in the conveying direction and that conveys the sheet conveyed in the conveying direction in the conveying direction, and a sheet correction unit that, when the conveyance deviation of the sheet is detected by the detection unit, corrects the conveyance deviation by displacing the correction roller from a predetermined sheet receiving position to a correction completion position by a displacement amount corresponding to the conveyance deviation after the sheet enters the correction roller, and a speed control unit that controls a displacement speed of the correction roller when the sheet correction unit displaces the correction roller from the sheet receiving position to the correction completion position. The speed control unit displaces the correction roller at a predetermined first speed to a set position between the sheet receiving position and the correction completion position, and displaces the correction roller from the set position to the correction completion position at a second speed slower than the first speed.

[0009] An image forming apparatus according to another aspect of the present invention includes a sheet conveying device, and performs a process of transferring an image onto a sheet conveyed to an image transfer position by the sheet conveying device. [Effects of the Invention]

[0010] According to the present invention, it is possible to improve the accuracy of correcting the conveyance deviation of the sheet in the conveyance direction, and to suppress vibration of the sheet after the correction. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the internal configuration of the image forming apparatus. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of the periphery of a sheet transport path of the image forming apparatus. [Figure 4]FIG. 4 is a block diagram showing the configuration of the image forming apparatus. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a sheet transport unit and a sheet correction mechanism provided in the image forming apparatus. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a sheet transport unit provided in the image forming apparatus. [Figure 7] FIG. 7 is a diagram showing the configuration of a sheet correction mechanism provided in the image forming apparatus. [Figure 8] FIG. 8 is a flowchart illustrating an example of a procedure for a sheet correction process executed by a control unit included in the image forming apparatus. [Figure 9] FIG. 9 is a flowchart showing an example of a speed control procedure in the inclination correction process and the lateral deviation correction process executed by the control unit of the image forming apparatus. [Figure 10] FIG. 10 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. [Figure 11] FIG. 11 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. [Figure 12] FIG. 12 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. [Figure 13] FIG. 13 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. [Figure 14] FIG. 14 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. [Figure 15] FIG. 15 is a diagram for explaining the operation of the sheet transport unit and the sheet correction mechanism provided in the image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The embodiment described below is merely an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0013] Fig. 1 is a perspective view showing the configuration of an image forming apparatus 10 according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing the internal configuration of the image forming apparatus 10. In Fig. 2, the image reading unit 12 is not shown. In the following description, a vertical direction D1 is defined based on the state in which the image forming apparatus 10 is installed and ready for use (the state in Fig. 1), a front-to-rear direction D2 is defined with the front side (front face) of the image forming apparatus 10 as the front, and a left-to-right direction D3 is defined when the image forming apparatus 10 is viewed from the front side (front face).

[0014] [Image forming apparatus 10] 1, image forming apparatus 10 is a multifunction device capable of printing images on sheets such as printing paper, and has various functions such as a print function, a copy function, a facsimile function, and a scan function. Image forming apparatus 10 is not limited to the multifunction device, and may be any device that has a print function for printing images on conveyed sheets, such as a printer, a copier, or a fax machine.

[0015] The image forming apparatus 10 includes an image reading unit 12 and an image forming unit 14. The image reading unit 12 performs a process of reading an image of a document, and is provided in the upper part of the image forming apparatus 10. The image forming unit 14 performs a process of forming a color image based on an electrophotographic method, and is provided in the lower part of the image forming apparatus 10. In addition, a sheet discharge unit 15 is provided to the right of the image forming unit 14.

[0016] A discharge space 21 is provided above the image forming unit 14. The sheet discharge unit 15 forms the discharge space 21 between the image forming unit 14 and the image reading unit 12, and connects the image forming unit 14 and the image reading unit 12 vertically.

[0017] The sheet discharge section 15 discharges the sheet after image formation into the discharge space 21. A sheet discharge outlet 15A (see FIG. 2) is formed on the left side surface of the sheet discharge section 15 on the discharge space 21 side. The sheet material is discharged from the sheet discharge outlet 15A.

[0018] Image forming unit 14 includes housing 11 as the device main body. Each component that constitutes image forming unit 14 is disposed inside housing 11. Housing 11 includes an exterior frame that covers the entire image forming unit 14, and an internal frame that supports each component that constitutes image forming unit 14.

[0019] 2 is a schematic diagram showing the internal configuration of the image forming apparatus 10. In FIG. 2, the image reading unit 12 is not shown.

[0020] Image forming section 14 forms a color image on a sheet such as printing paper based on a so-called tandem system. As shown in Fig. 2, image forming section 14 includes a plurality of image forming units 4, an intermediate transfer unit 5, an optical scanning device 13, a secondary transfer roller 20, a fixing device 16, a sheet tray 18, a sheet storage section 27, a feeding unit 28, an operation display section 17 (see Fig. 1), a sheet transport path 26 (hereinafter abbreviated as transport path 26), a sheet transport unit 23 (an example of a transport section of the present invention), a sheet correction mechanism 60 (an example of a sheet correction section of the present invention), a container mounting section 35, a toner container 3, and a control section 90 (see Fig. 4).

[0021] 2, the sheet storage section 27 is provided at the bottom of the image forming apparatus 10. The sheet storage section 27 stores sheets on which images are formed by the image forming unit 4, and is formed, for example, in the shape of a tray with an open top. The sheet storage section 27 is supported by the housing 11.

[0022] The feeding unit 28 picks up multiple sheets stacked in the sheet storage section 27 one by one and feeds the sheets toward the conveying path 26. The feeding unit 28 includes a pickup roller 29 and a pair of feeding rollers 30. The pickup roller 29 and the pair of feeding rollers 30 are provided on the upper side of the right side of the sheet storage section 27.

[0023] FIG. 3 is a schematic diagram showing the configuration of the vicinity of the conveyance path 26. The pair of feed rollers 30 receives a rotational driving force from a conveyance motor 56 (see FIG. 4) to convey the sheet downstream in the conveyance direction D11. As shown in FIG. 3, the pair of feed rollers 30 includes a drive roller 30A that rotates when the rotational driving force from the conveyance motor 56 is transmitted thereto, and a driven roller 30B that contacts the drive roller 30A and rotates accordingly. A drive transmission mechanism (not shown) that transmits the rotation of the drive roller 30A to the pickup roller 29 is provided between the pickup roller 29 and the drive roller 30A. The pickup roller 29 and the drive roller 30A are connected via the drive transmission mechanism. When the drive roller 30A is rotated by the conveyance motor 56, the drive transmission mechanism also rotates the pickup roller 29 in the same direction and at the same peripheral speed as the drive roller 30A.

[0024] When an instruction signal to start a sheet feeding operation is input to image forming apparatus 10, pickup roller 29 and feed roller pair 30 are rotated by the rotational driving force of conveyance motor 56, and a sheet is fed from sheet storage unit 27 to conveyance path 26. Specifically, pickup roller 29 picks up a sheet in sheet storage unit 27 and sends the sheet downstream in the feeding direction, and when the leading edge of the sheet reaches the nip portion of feed roller pair 30, feed roller pair 30 conveys the sheet to conveyance path 26.

[0025] The conveying path 26 is a guide path that guides the sheet fed by the feeding roller pair 30 to the sheet discharge opening 15A. As shown in Fig. 2, the conveying path 26 curves upward from the feeding roller pair 30 and then extends upward, passing through the secondary transfer roller 20 and reaching the sheet discharge opening 15A.

[0026] As shown in FIG. 3, the sheet transport unit 23 and the sheet correction mechanism 60 are provided on the transport path 26.

[0027] The sheet transport unit 23 transports the sheet sent out to the transport path 26 by the feeding unit 28 in a transport direction D11 toward an image transfer position P1 (see FIG. 3). The image transfer position P1 is a position where the drive roller 5B and the secondary transfer roller 20 face each other. The sheet transport unit 23 receives a rotational driving force from a transport motor 56 (see FIG. 4) to transport the sheet downstream in the transport direction D11. The configuration of the sheet transport unit 23 will be described later.

[0028] The sheet correction mechanism 60 is disposed on the conveying path 26 upstream of the image transfer position P1 in the conveying direction D11 and downstream of the sheet conveying unit 23 in the conveying direction D11. The sheet correction mechanism 60 corrects the orientation and position of a sheet conveyed on the conveying path 26 while being misaligned in a direction intersecting the conveying direction D11, and conveys the sheet downstream in the conveying direction D11. Examples of sheet conveyance misalignment include tilt with respect to the conveying direction D11 and lateral misalignment in the width direction perpendicular to the conveying direction D11. The configuration of the sheet correction mechanism 60 will be described later.

[0029] As shown in FIG. 2, each image forming unit 4 is provided below the intermediate transfer unit 5. Each image forming unit 4 performs an image formation process to form a toner image on the surface of the transfer belt 5A based on image data input from the outside. The multiple image forming units 4 are arranged side by side in the running direction of the transfer belt 5A (the direction indicated by arrow D10). From left to right on the transfer belt 5A, a yellow image forming unit 4Y, a cyan image forming unit 4C, a magenta image forming unit 4M, and a black image forming unit 4K are arranged in a row in that order.

[0030] Each image forming unit 4 includes a photosensitive drum 41, a charging device 42, a developing device 44, a primary transfer roller 45, etc. Image forming unit 4Y forms a toner image on the surface of photosensitive drum 41 using yellow toner. Image forming unit 4C forms a toner image on the surface of photosensitive drum 41 using cyan toner, image forming unit 4M forms a toner image on the surface of photosensitive drum 41 using magenta toner, and image forming unit 4K forms a toner image on the surface of photosensitive drum 41 using black toner. The toner images on photosensitive drum 41 are developed by developing device 44.

[0031] The intermediate transfer unit 5 includes a transfer belt 5A, a drive roller 5B, and a driven roller 5C. The transfer belt 5A is a belt member onto which the toner images of each color formed on the photosensitive drum 41 of each image forming unit 4 are transferred. The transfer belt 5A is provided above the photosensitive drum 41. The transfer belt 5A is an endless circular belt. The transfer belt 5A is rotatably supported by a drive roller 5B and a driven roller 5C that are provided at a distance in the left-right direction D3. The transfer belt 5A is supported so as to be stretched over the drive roller 5B and the driven roller 5C. As the surface of the transfer belt 5A passes between the photosensitive drum 41 and the primary transfer roller 45, the toner images from each photosensitive drum 41 are transferred onto the transfer belt 5A in order, superimposed on top of each other.

[0032] The optical scanning device 13 irradiates the photosensitive drum 41 of each image forming unit 4 with laser light based on input image data for each color. As a result, an electrostatic latent image is formed on each photosensitive drum 41.

[0033] The secondary transfer roller 20 is disposed opposite the drive roller 5B across the vertically extending transport path 26. The secondary transfer roller 20 performs a transfer process in which the toner image on the transfer belt 5A is transferred to a sheet by a transfer potential applied to the secondary transfer roller 20. The sheet onto which the toner image has been transferred is transported to the fixing device 16.

[0034] The fixing device 16 heats the toner image transferred to the sheet material to fix it to the sheet material, and includes a heating roller 16A and a pressure roller 16B. The sheet material conveyed to the fixing device 16 is conveyed while being sandwiched between the heating roller 16A and the pressure roller 16B. During this conveyance, heat is transferred from the heating roller 16A to the toner image transferred to the sheet material, heating the toner image. This fixes the toner image to the sheet material. The sheet material is then discharged to the sheet tray 18 by the sheet discharge section 15.

[0035] [Sheet transport unit 23] 3, the sheet transport unit 23 has a drive roller 23A that is rotationally driven by a driving force from a transport motor 56 (see FIG. 5), and a driven roller 23B that is disposed in contact with the outer circumferential surface of the drive roller 23A. The drive roller 23A and the driven roller 23B form a transport roller pair.

[0036] The sheet transport unit 23 is shown in FIG. 5. As shown in FIG. 5, the sheet transport unit 23 has two drive rollers 23A arranged at equal intervals along a front-rear direction D2 perpendicular to the transport direction D11. Hereinafter, the front-rear direction D2 may be referred to as the width direction D2. Each drive roller 23A is fixed to a rotation shaft 47 extending in the width direction D2, and this rotation shaft 47 is rotatably supported by the internal frame 11A of the housing 11. A driving force from a transport motor 56 (see FIG. 4) is transmitted to the rotation shaft 47. The driving force of the transport motor 56 is transmitted to the rotation shaft 47 via a transmission mechanism (not shown), such as a gear or a belt.

[0037] The sheet transport unit 23 also has two driven rollers 23B corresponding to each drive roller 23A. The drive roller 23A and the driven roller 23B form a transport roller pair. That is, the sheet transport unit 23 has two pairs of transport rollers arranged side by side in the width direction D2. Two rotation shafts 49 are provided on a guide member 26A (see FIG. 3) that forms a transport guide surface on the left side of the transport path 26. Each of the two driven rollers 23B is rotatably supported by the rotation shaft 49. The rotation shafts 49 are arranged to be spaced apart in the width direction D2, and one driven roller 23B is rotatably supported by each rotation shaft 49.

[0038] 3, driven roller 23B is biased toward drive roller 23A by spring 23C with a predetermined elastic force (spring force). This causes driven roller 23B to be pressed against drive roller 23A. When drive roller 23A is driven to rotate in this state, driven roller 23B is driven.

[0039] 6 is a schematic diagram showing the configuration of the sheet transport unit 23, and is a diagram of the sheet transport unit 23 as seen from the upstream side (see arrow VI) in the transport direction D11 in FIG. 5. As shown in FIG. 6, the rotation shaft 49 of the driven roller 23B is supported by a support portion 51 provided on the guide member 26A (see FIG. 3). The shaft end of each rotation shaft 49 is supported by the support portion 51.

[0040] The support portion 51 is supported by the guide member 26A (see FIG. 3) so as to be movable in the up-down direction D1. In this embodiment, the support portion 51 supports the driven roller 23B so as to be movable between a contact position (position shown in FIG. 6) described below and a release position described below. In other words, the driven roller 23B is supported so as to be movable between the contact position and the release position.

[0041] The support portion 51 is biased downward by the spring 23C. That is, the support portion 51 receives the spring force of the spring 23C and supports the shaft end of the rotation shaft 49 while biasing the shaft end downward.

[0042] 6, the driven roller 23B is elastically biased by the spring 23C toward the drive roller 23A with a predetermined spring force (elastic force). As a result, the drive roller 23A and the driven roller 23B are pressed together by the spring force. This spring force is an elastic force sufficient to sandwich and transport the sheet in the transport direction D11.

[0043] When the support portion 51 is lifted upward from the contact position and moved to the release position, the driven roller 23B is released from the pressure contact state with the drive roller 23A. In other words, the release position is a position where the driven roller 23B is separated from the drive roller 23A and is released from pressure contact with the drive roller 23A. Note that the release position is described as a position where the driven roller 23B is separated from the drive roller 23A, but it may also be a position where the surface of the driven roller 23B and the surface of the drive roller 23A are in contact as long as the sheet cannot be nipped and transported. In other words, the release position includes a position where the surface of the driven roller 23B and the surface of the drive roller 23A are in contact to the extent that the transport force of the driven roller 23B and the drive roller 23A is not transmitted to the sheet. This contact state is a state where the pressure contact state is released.

[0044] FIG. 4 is a block diagram showing the configuration of image forming apparatus 10. As shown in FIG. 4, a solenoid 64 is provided inside housing 11. Solenoid 64 is connected to control unit 90 and is activated when power is supplied by control unit 90. A plunger of solenoid 64 is connected to support portion 51 via a link member (not shown). When power is supplied to solenoid 64, the plunger is actuated to move support portion 51 from the contact position to the release position. When power is removed from solenoid 64, the plunger is returned to its original position by a tension spring provided in solenoid 64, and support portion 51 is returned to the contact position by the spring force of spring 23C.

[0045] 3, the conveying path 26 is provided with a misalignment detection sensor 61 (an example of a detection unit of the present invention). The misalignment detection sensor 61 detects conveyance misalignment of the sheet conveyed along the conveying path 26. When the sheet is conveyed at an angle with respect to the conveying direction D11, the misalignment detection sensor 61 acquires information (inclination information) indicating the inclination state, such as whether or not the sheet is inclined, the direction of the inclination, and the amount of inclination (inclination angle). In the conveying path 26, the misalignment detection sensor 61 is provided downstream of the sheet conveying unit 23 in the conveying direction D11 and upstream of the sheet correction mechanism 60 in the conveying direction D11.

[0046] As shown in FIG. 5, the misalignment detection sensor 61 is a line sensor extending in the width direction D2. The line sensor is composed of multiple image sensors arranged in a row along the width direction D2. The misalignment detection sensor 61 is connected to the control unit 90. The misalignment detection sensor 61 outputs a detection signal including image data (density data) of the leading edge of the sheet to the control unit 90. Upon receiving the detection signal from the misalignment detection sensor 61, the control unit 90 performs various determinations based on the detection signal. Specifically, the control unit 90 determines whether the sheet conveyed by the sheet conveying unit 23 is inclined with respect to the conveying direction D11 based on the detection signal, and if so, determines the direction of inclination. The control unit 90 also determines the amount of inclination (angle of inclination) of the sheet based on the inclination information. These determination methods are conventionally known, and therefore detailed description thereof will be omitted.

[0047] The misalignment detection sensor 61 may be a pair of reflective optical sensors provided at positions equally spaced apart from the center of the conveying path 26 in the width direction D2. The reflective optical sensor has a light-emitting element and a light-receiving element, receives reflected light emitted from the light-emitting element, and outputs a detection signal according to the amount of received light. Based on the difference in the changes in the detection signals sent from each of the pair of reflective optical sensors, the control unit 90 performs a process of determining whether the sheet conveyed by the sheet conveying unit 23 is inclined with respect to the conveying direction D11, a process of determining the direction of inclination if the sheet is inclined, and a process of determining the amount of inclination (angle of inclination) of the sheet based on the inclination information.

[0048] In the conveying path 26, a leading edge detection sensor 62 and an edge detection sensor 63 are provided downstream of the sheet correction mechanism 60 in the conveying direction D11.

[0049] The leading edge detection sensor 62 is provided near the center of the conveying path 26 in the width direction D2. The leading edge detection sensor 62 detects the leading edge of the sheet that has passed through the sheet correction mechanism 60. The leading edge detection sensor 62 is, for example, a reflective optical sensor. The leading edge detection sensor 62 is connected to the control unit 90, and a detection signal from the leading edge detection sensor 62 is sent to the control unit 90. The control unit 90 detects the leading edge of the sheet being conveyed on the conveying path 26 based on a change in the detection signal sent from the leading edge detection sensor 62. Note that such detection methods are conventionally known, and therefore a detailed description thereof will be omitted.

[0050] The edge detection sensor 63 (an example of a detection unit of the present invention) is disposed downstream in the conveying direction D11 from the leading edge detection sensor 62. It detects conveyance deviation of the sheet conveyed along the conveying path 26. When the sheet is conveyed with a lateral deviation in the width direction D2 perpendicular to the conveying direction D11, the edge detection sensor 63 acquires information (lateral deviation information) indicating the state of the lateral deviation, such as the presence or absence of lateral deviation, the direction of deviation, and the amount of lateral deviation.

[0051] The edge detection sensors 63 detect the positions of both ends in the width direction D2 of the sheet that has passed through the sheet correction mechanism 60. The edge detection sensors 63 are a pair of line sensors provided at positions spaced equally apart from the center of the conveying path 26 outward in the width direction D2. Each line sensor is composed of multiple image sensors arranged in a row along the width direction D2. In this embodiment, the edge detection sensors 63 are arranged so that the ends of the sheet in the width direction D2 pass through each line sensor.

[0052] The edge detection sensor 63 is connected to the control unit 90. The edge detection sensor 63 outputs a detection signal (density signal) including image data (density data) of both ends of the sheet to the control unit 90. When the control unit 90 acquires the detection signal from the edge detection sensor 63, it determines the position of the sheet in the width direction D2 based on the detection signal. Specifically, the control unit 90 determines whether the sheet is shifted laterally in the width direction D2, whether the sheet is shifted in either direction in the width direction D2, and if the sheet is shifted laterally in the width direction D2, the amount of shift (lateral shift amount). Note that such determination methods are conventionally known, and therefore detailed description thereof will be omitted.

[0053] [Sheet correction mechanism 60] 3, the sheet correction mechanism 60 is provided in the conveying path 26. The sheet correction mechanism 60 is provided on the conveying path 26 downstream of the sheet conveying unit 23 in the conveying direction D11. More specifically, the sheet correction mechanism 60 is provided on the conveying path 26 between the misalignment detection sensor 61 and the leading edge detection sensor 62.

[0054] 7 is a schematic diagram showing the configuration of the sheet correction mechanism 60, as seen from the upstream side (see arrow VII) in the conveyance direction D11 in FIG. 5. When a conveyance deviation of the sheet is detected by the deviation detection sensor 61 or the edge detection sensor 63, the sheet correction mechanism 60 displaces from a predetermined sheet receiving position to a correction completion position to correct the conveyance deviation of the sheet. As shown in FIG. 7, the sheet correction mechanism 60 has a rotating unit 65 (an example of a rotating unit of the present invention) and a slide unit 66 (an example of a slide unit of the present invention).

[0055] When the misalignment detection sensor 61 detects a sheet skew (an example of a conveyance misalignment), the rotation unit 65 corrects the sheet skew. In this embodiment, the rotation unit 65 corrects the sheet skew (an example of a conveyance misalignment) of a sheet conveyed by the sheet conveying unit 23 in a state inclined with respect to the conveyance direction D11, and conveys the corrected sheet in the conveyance direction D11. Specifically, before the sheet enters the sheet correction mechanism 60, the rotation unit 65 rotates the roller unit 80 from a predetermined initial position to a sheet receiving position where the roller unit 80 receives the sheet by an amount of rotation corresponding to the amount of skew (tilt angle) corresponding to the sheet skew. Then, after the sheet enters the rotation unit 65 at the sheet receiving position, the rotation unit 65 returns the roller unit 80 from the sheet receiving position to the initial position while clamping the sheet. As a result, the sheet is rotated from the position before correction to a predetermined specified position, and the skew of the sheet is corrected.

[0056] Here, the initial position is a position where the sheet can be conveyed straight downstream in the conveying direction D11 by a roller unit 80 (described later), and is a position where a rotation shaft 81 of the roller unit 80 is disposed straight along the width direction D2, as shown in Fig. 10. The sheet receiving position is a position where, when a first correction preparation operation (described later) is performed, the sheet is rotated in a direction corresponding to the inclination direction of the sheet (upstream in the conveying direction D11) by an amount of rotation where the sheet is straight with respect to the conveying direction D11 when the first correction preparation operation (described later) is performed, and is, for example, the position shown in Fig. 11. The sheet receiving position is a position where, when a second correction preparation operation (described later) is performed, the sheet is rotated in a direction corresponding to the inclination direction of the sheet (downstream in the conveying direction D11) by an amount of rotation where the sheet is straight with respect to the conveying direction D11 when the second correction preparation operation (described later) is performed.

[0057] The slide unit 66 corrects the lateral deviation of the sheet when the edge detection sensor 63 detects a lateral deviation of the sheet (an example of a conveyance deviation). In this embodiment, when a sheet conveyed by the sheet conveying unit 23 is deviated in the width direction D2, the slide unit 66 corrects the lateral deviation to return the sheet to a predetermined center position. Specifically, after the sheet enters the slide unit 66, the slide unit 66 clamps the sheet and moves from a slide reference position, which is the initial position of the slide unit 66, described below, in a lateral deviation correction direction (a direction opposite to the lateral deviation direction) by the amount of lateral deviation of the sheet in the width direction D2. As a result, the sheet slides from the position before correction to a predetermined specified position, and the lateral deviation of the sheet in the width direction D2 is corrected.

[0058] 5 and 7, the slide unit 66 has a base frame 67 that is long in the width direction D2. The base frame 67 is movably supported by the internal frame 11B of the housing 11 so as to be movable in the width direction D2. Specifically, the base frame 67 has a horizontal, flat base portion 67A and a support portion 67B (see FIG. 5) that is integrally formed with an upper end portion of the base portion 67A. The support portion 67B has shaft portions 68 that protrude outward from both ends of the base portion 67A in the width direction D2, and the shaft portions 68 are inserted into and supported by shaft holes formed in the internal frame 11B.

[0059] 5, a rack 71 is formed on the rear end surface of the support portion 67B. A pinion gear 72 is meshed with this rack 71. The slide unit 66 is equipped with a second correction motor 73. The pinion gear 72 is attached to the output shaft of the second correction motor 73. Therefore, the control unit 90 can drive and control the second correction motor 73 to slide the base frame 67 of the slide unit 66 in either direction (forward or backward) in the width direction D2.

[0060] 5, a protruding piece 69 that protrudes forward is formed on the front end of the base frame 67. An optical sensor 70 that can detect the protruding piece 69 is provided on the front inner frame 11B. The position of the protruding piece 69 is detected by the optical sensor 70. Using the position where the protruding piece 69 is detected by the optical sensor 70 (hereinafter referred to as the slide reference position) as a reference, the control unit 90 moves the base frame 67 in the width direction D2.

[0061] Further, a support portion 74 (see FIG. 7) for supporting a rotation shaft 76 (an example of a rotation fulcrum of the present invention) described later is provided near the front end portion of the base portion 67A.

[0062] 5 and 7, the rotating unit 65 has a rotating frame 75 supported by the base portion 67A of the base frame 67, a roller unit 80 rotatably supported by the rotating frame 75, and a first correction motor 85 that applies a driving force in the rotational direction to the rotating frame 75. The rotating frame 75 is a plate-like member formed in an elongated shape in the width direction D2, and has a rotating shaft 76 extending in the up-down direction D1 at its right end. The rotating shaft 76 is rotatably supported by a support portion 74 (see FIG. 7) provided on the base frame 67.

[0063] As shown in Figure 7, a pair of support walls 77, 78 are provided on the left surface 75A of the rotating frame 75 (the upper surface in Figure 7) at a predetermined distance in the width direction D2. The pair of support walls 77, 78 protrude vertically to the left from the left surface 75A. The predetermined distance is a length that allows a sheet to be conveyed between the pair of support walls 77, 78. A roller unit 80 is rotatably supported by the support walls 77, 78.

[0064] The roller unit 80 is rotationally driven by a third correction motor 79. The roller unit 80 transports the sheet that has entered the sheet correction mechanism 60 downstream in the transport direction D11. The roller unit 80 has a drive roller 80A that is rotated by the rotational driving force from the third correction motor 79, and a driven roller 80B that is arranged in contact with the outer circumferential surface of the drive roller 80A. The drive roller 80A and the driven roller 80B form a transport roller pair. This transport roller pair is an example of a correction roller of the present invention.

[0065] The roller unit 80 has four drive rollers 80A arranged at equal intervals along the width direction D2. Each drive roller 80A is fixed to a rotation shaft 81 extending in the width direction D2, and this rotation shaft 81 is rotatably supported by the support walls 77 and 78. A third correction motor 79 is fixed to the support wall 78. The rotational driving force of the third correction motor 79 is transmitted to the rotation shaft 81 via an output gear 79A fixed to the output shaft of the third correction motor 79 and an input gear 81A fixed to the end of the rotation shaft 81. The roller unit 80 also has four driven rollers 80B corresponding to each drive roller 80A. Each of the four driven rollers 80B is rotatably supported by a rotation shaft 82 provided on a guide member that forms the upper conveyance guide surface of the conveyance path 26. Two rotation shafts 82 are provided spaced apart in the width direction D2, and two driven rollers 80B are rotatably supported on each rotation shaft 82.

[0066] The driven roller 80B is biased toward the drive roller 80A by a spring 80C (see FIG. 3). This causes the driven roller 80B to be pressed against the drive roller 80A. When the drive roller 80A is driven to rotate in this state, the driven roller 80B is driven.

[0067] A first correction motor 85 is attached to the rear inner frame 11B. The first correction motor 85 is fixed to the outer surface of the inner frame 11B, and its output shaft 85A passes through the inner frame 11B and extends to the opposite side (front side). A pinion gear 86 is fixed to the tip of the output shaft 85A of the first correction motor 85. A rack 87 extending in the vertical direction D1 (a direction perpendicular to the plane of the paper in FIG. 7) is formed at the rear end of the left surface 75A of the rotating frame 75. The rack 87 meshes with the pinion gear 86. The rack 87 has parallel teeth aligned in the vertical direction D1. The control unit 90 controls and drives the first correction motor 85, thereby rotating the roller unit 80 together with the rotating frame 75 of the rotating unit 65 around the rotation shaft 76.

[0068] In this embodiment, when the inclination posture of a sheet conveyed in an inclined state with respect to the conveying direction D11 is a first inclined posture (first posture), the rotation unit 65 performs a first correction preparatory operation to rotate the roller unit 80 from the initial position toward the upstream side in the conveying direction D11. Here, the first inclined posture is a posture in which the front end of the sheet leads the rear end, and is a posture as shown by the dashed line in FIG. 10. Furthermore, when the inclined posture of a sheet conveyed in an inclined state is a second inclined posture (second posture) that is inclined opposite to the first inclined posture, the rotation unit 65 performs a second correction preparatory operation to rotate the roller unit 80 from the initial position toward the downstream side in the conveying direction D11. Here, the second inclined posture is a posture in which the rear end of the sheet leads the front end.

[0069] [Control unit 90] The control unit 90 performs overall control of the image forming apparatus 10, controls the operation of the sheet transport unit 23 and the operation of the sheet correction mechanism 60, and controls the transport speed of each transport roller pair. As shown in FIG. 4, the control unit 90 is composed of a CPU 91, a ROM 92, a RAM 93, a flash memory 94, a motor driver 95, and the like. The control unit 90 is an example of a speed control unit of the present invention. The control unit 90 is electrically connected to the motors 56, 73, 79, and 85, the sensors 61, 62, and 63, and the solenoid 64 via signal lines and the like. The motors 56, 73, 79, and 85 are connected to the motor driver 95 of the control unit 90 and are driven and controlled by individual control signals received from the motor driver 95.

[0070] During sheet correction by the sheet correction mechanism 60, if the roller unit 80 and slide unit 66 of the rotating unit 65 rotate at a predetermined set speed, the units 80 and 66 may vibrate in the displacement direction when the rotation stops. In this case, if the sheet is transported in the transport direction D11 and reaches the image transfer position P1 while the vibration has not yet subsided, the image will be transferred to the vibrating sheet, resulting in a problem of reduced image quality. On the other hand, slowing the sheet transport speed or temporarily suspending sheet transport to reduce the vibration to a standard level increases the first print time, which is the time from receiving an image formation command to discharging the sheet after the image has been fixed. Furthermore, increasing the distance from the correction position to the image transfer position P1 to reduce the vibration to a standard level not only reduces the first print time, but also increases the size of the device in the transport direction D11.

[0071] In this embodiment, as will be described later, during the rotation process in which the roller unit 80 rotates from the sheet receiving position to the initial position, the control unit 90 changes the rotation speed (displacement speed) from a preset first rotation speed V1 (an example of the first speed of the present invention) to a second rotation speed V2 (an example of the second speed of the present invention) that is slower than the first rotation speed V1. That is, the control unit 90 rotates the roller unit 80 at the first rotation speed V1 and then at the second rotation speed V2. The second rotation speed V2 is set to, for example, approximately 50% of the first rotation speed V1. Note that the deceleration rate of the second rotation speed V2 with respect to the first rotation speed V1 is not limited to 50%.

[0072] Furthermore, during the sliding process in which the slide unit 66 slides from the slide reference position in a direction in which lateral deviation can be corrected, the control unit 90 changes the sliding speed (displacement speed) from a preset first sliding speed V11 (an example of the first speed of the present invention) to a second sliding speed V12 (an example of the second speed of the present invention) that is slower than the first sliding speed V11. That is, the control unit 90 slides the slide unit 66 at the first sliding speed V11, and then slides it at the second sliding speed V12. The second sliding speed V12 is set to, for example, about 50% of the first sliding speed V11. Note that the deceleration rate of the second sliding speed V12 relative to the first sliding speed V11 is not limited to 50%.

[0073] In this way, the roller unit 80 or the slide unit 66 is decelerated during the sheet correction operation, which improves the accuracy of correcting the sheet transport deviation and suppresses vibration of the sheet after correction.

[0074] [Sheet correction processing] An example of the procedure for the sheet correction process executed by the control unit 90 will be described below using the flowcharts in Figures 8 and 9, while referring to the operation explanatory diagrams in Figures 10 to 15. Here, Figures 10 to 15 are diagrams for explaining the operation of the sheet transport unit 23 and the sheet correction mechanism 60, with the diagrams on the left side of the paper being a view from a direction perpendicular to the transport direction D11, and the diagrams on the right side being a view from the axial direction of each of the drive rollers 23A, 80A. The feed roller pair 30 is not shown in Figures 10 to 15.

[0075] It is assumed that in the image forming apparatus 10, before the sheet correction process is performed, the roller unit 80 of the rotating unit 65 is placed at the initial position and the slide unit 66 is placed at the slide reference position.

[0076] When an instruction signal indicating the start of an image formation operation is input to the image forming apparatus 10, the image forming process by the image forming apparatus 10 begins. Specifically, the motor driver 95 of the control unit 90 drives the transport motor 56, the third correction motor 79, and other motors (not shown), thereby rotating the drive roller 30A of the feed roller pair 30, the pickup roller 38, the drive roller 23A of the sheet transport unit 23, the drive roller 80A of the roller unit 80, the discharge roller pair, and the like. As a result, the sheet 100 is removed from the sheet storage unit 27 and fed to the transport path 26, and is transported downstream in the transport direction D11 by the feed roller pair 30 and the sheet transport unit 23. At this time, the control unit 90 controls each motor so that the transport speed of the sheet 100 becomes a reference speed V0. Here, the reference speed V0 is the speed at which the sheet 100 is transported during transfer by the secondary transfer roller 20.

[0077] In step S11, the control unit 90 determines whether or not the leading edge of the sheet 100 has been detected based on the detection signal output from the misalignment detection sensor 61. In other words, the control unit 90 determines whether or not the leading edge of the sheet 100 has passed the detection position detected by the misalignment detection sensor 61.

[0078] In step S11, when it is determined that the leading edge of the sheet 100 is detected at the detection position of the misalignment detection sensor 61 (see FIG. 10), the control unit 90 determines whether the sheet 100 being conveyed on the conveying path 26 is inclined with respect to the conveying direction D11 based on the detection signal of the misalignment detection sensor 61 (S12). This determination process is performed before the leading edge of the sheet 100 enters the sheet correction mechanism 60.

[0079] If it is determined in step S12 that the sheet 100 is inclined, then in the next step S13, the control unit 90 determines the inclined posture of the sheet 100 and calculates the amount of inclination based on the output signal of the deviation detection sensor 61. On the other hand, if it is determined in step S12 that the sheet 100 is not inclined, the control unit 90 proceeds to step S18.

[0080] Then, in step S14, the control unit 90 controls and drives the first correction motor 85 to rotate the roller unit 80 of the rotating unit 65 from the initial position to the sheet receiving position where skew correction starts in accordance with the amount of inclination before the sheet 100 enters the sheet correction mechanism 60 (see FIG. 11). Specifically, the roller unit 80 is rotated from the initial position to the sheet receiving position by the amount of inclination in the direction opposite to the direction in which the sheet 100 is inclined.

[0081] For example, as shown in FIG. 11, when the sheet 100 is transported in the first inclined posture, the rotating unit 65 performs the first correction preparation operation to rotate the roller unit 80 from the initial position to the upstream side in the transport direction D11 (toward the leading edge of the sheet 100).

[0082] Furthermore, for example, when the sheet 100 is transported in the second inclined posture (not shown), the rotating unit 65 performs the second correction preparation operation to rotate the roller unit 80 from the initial position downstream in the transport direction D11 (in the direction away from the leading edge of the sheet 100).

[0083] When the leading edge of the sheet 100 reaches the leading edge detection sensor 62 and is detected by the control unit 90 (S15), the control unit 90 controls the solenoid 64 in step S16 to move the driven roller 23B to the release position (see Figure 13).

[0084] Thereafter, in step S17, the control unit 90 performs a process (tilt correction process) of returning the roller unit 80 of the rotating unit 65 from the sheet receiving position to the initial position (see FIG. 13). That is, the control unit 90 rotates the roller unit 80 by the tilt amount in the direction opposite to the direction in which it was rotated in step S14. This corrects the tilt of the sheet 100.

[0085] For example, if the first correction preparation operation has been performed in step S14, the control unit 90 rotates the roller unit 80 downstream in the conveying direction D11 (in the direction away from the leading edge of the sheet 100) to return it from the sheet receiving position to the initial position. Also, if the second correction preparation operation has been performed in step S14, the control unit 90 rotates the roller unit 80 upstream in the conveying direction D11 (in the direction approaching the leading edge of the sheet 100) to return it from the sheet receiving position to the initial position.

[0086] 14, when the leading edge of the sheet 100 reaches the edge detection sensor 63, in the next step S18, the control unit 90 determines whether the sheet 100 is shifted to either side (front or rear) in the width direction D2 based on the detection signal of the edge detection sensor 63. If lateral shift in the width direction D2 has occurred, the process proceeds to step S19, where the direction of lateral shift is determined and the amount of lateral shift is calculated. On the other hand, if lateral shift has not occurred, the process proceeds to step S21.

[0087] In step S19, the control unit 90 determines the lateral deviation direction of the seat 100 and calculates the amount of lateral deviation. Then, in step S20, the control unit 90 performs a process (lateral deviation correction process) of sliding the slide unit 66 in the deviation correction direction (see the arrow in FIG. 14) according to the amount of lateral deviation. Specifically, the control unit 90 controls the drive of the second correction motor 73 to move the slide unit 66 from the slide reference position by the amount of lateral deviation in the direction opposite to the lateral deviation direction of the seat 100. This corrects the lateral deviation of the seat 100 (see FIG. 15). After the sliding movement in step S20 is performed, the process proceeds to step S21.

[0088] In step S21, the control unit 90 determines whether the trailing edge of the sheet 100 has passed through the sheet correction mechanism 60. If it is determined that the trailing edge of the sheet 100 has passed through the sheet correction mechanism 60, the control unit 90 moves the driven roller 23B from the release position to the contact position (S22) and returns the slide unit 66 to the slide reference position (S23). When the image forming process on the sheet is completed, the control unit 90 stops driving the motors 56, 73, 79, and 85, and ends the series of processes.

[0089] Next, the processing procedures for the speed control executed during the tilt correction processing in step S17 and the speed control executed during the lateral deviation correction processing in step S20 will be described with reference to Fig. 9. Here, Fig. 9 is a flowchart showing an example of the speed control procedures in the tilt correction processing and lateral deviation correction processing executed by the control unit 90.

[0090] As shown in Figure 9, when the inclination correction process is performed, first, the control unit 90 drives and controls the first correction motor 85 during the rotation process in which the roller unit 80 rotates from the sheet receiving position to the initial position, thereby rotating the roller unit 80 at the first rotation speed V1 (S101).

[0091] In the next step S102, the control unit 90 determines whether the roller unit 80 rotated at the first rotation speed V1 has reached a predetermined set position. The set position is a position determined by the rotating unit 65 between the sheet receiving position and the initial position as a correction completion position.

[0092] In this embodiment, the set position may be a position that is spaced closer to the initial position than the center position between the sheet receiving position and the initial position. More preferably, the set position is a position that is spaced from the sheet receiving position toward the initial position by a distance that is calculated by multiplying the distance from the sheet receiving position to the initial position by a set ratio that exceeds 50%. Note that the set ratio is not limited to 50% and may be any ratio that exceeds 50%, and is, for example, preferably a ratio that is set within a range of 70% to less than 100%, and more preferably a ratio that is set within a range of 80% to less than 90%.

[0093] When it is determined in step S102 that the set position has been reached, the control unit 90 controls the driving of the first correction motor 85 to rotate the roller unit 80 at the second rotation speed V2 (S103). That is, the control unit 90 reduces the rotation speed of the roller unit 80 from the first rotation speed V1 to the second rotation speed V2 at the set position.

[0094] In the next step S104, the control unit 90 determines whether the roller unit 80 has reached the initial position, and if the roller unit 80 has reached the initial position, determines that the correction is complete. Thereafter, the driving of the first correction motor 85 is stopped.

[0095] In this embodiment, as described above, during the rotation process in which the roller unit 80 rotates from the sheet receiving position to the initial position, the rotation speed of the roller unit 80 is decelerated from the first rotation speed V1 to the second rotation speed V2 at the installation position. At this time, a braking effect due to the deceleration acts on the roller unit 80, but because the roller unit 80 rotates at the second rotation speed V2, no vibration occurs in the roller unit 80. Furthermore, when the roller unit 80 is stopped, vibration in the rotation direction may occur due to inertia at the time of stopping, but because the roller unit 80 has been decelerated to the second rotation speed V2, the vibration is significantly smaller than when the roller unit 80 is stopped at the first rotation speed V1. As a result, vibration of the sheet after tilt correction can be effectively suppressed.

[0096] 9, when the lateral deviation correction process is performed, first, the control unit 90 controls and drives the second correction motor 73 to rotate the slide unit 66 at the first slide speed V11 during the slide process in which the slide unit 66 slides from the slide reference position to the correction completion position (S111). Here, the correction completion position is a position separated from the slide reference position in the lateral deviation direction by the lateral deviation amount calculated in step S19.

[0097] In the next step S112, the control unit 90 determines whether the slide unit 66, which is slid at the first slide speed V11, has reached a predetermined set position. The set position is a position determined by the slide unit 66 between the slide reference position and the correction completion position.

[0098] In this embodiment, the set position may be a position that is spaced closer to the correction completion position than a central position between the slide reference position and the correction completion position. More preferably, the set position is a position that is spaced from the slide reference position toward the correction completion position by a distance obtained by multiplying the distance from the slide reference position to the correction completion position by a set ratio exceeding 50%. Note that the set ratio is not limited to 50% and may be any ratio exceeding 50%, and is, for example, preferably a ratio set within a range of 70% to less than 100%, and more preferably a ratio set within a range of 80% to less than 90%.

[0099] When it is determined in step S112 that the set position has been reached, the control unit 90 controls the driving of the second correction motor 73 to rotate the slide unit 66 at the second slide speed V12 (S113). That is, the control unit 90 decelerates the slide speed of the slide unit 66 from the first slide speed V11 to the second slide speed V12 at the set position.

[0100] In the next step S114, the control unit 90 determines whether the slide unit 66 has reached the correction completion position, and determines that the correction has been completed if the slide unit 66 has reached the correction position. After that, the driving of the second correction motor 73 is stopped.

[0101] In this embodiment, as described above, during the sliding process in which the slide unit 66 slides from the slide reference position to the correction completion position where lateral deviation correction is completed, the slide speed of the slide unit 66 is decelerated from the first slide speed V11 to the second slide speed V12 at the installation position. At this time, a braking effect due to the deceleration acts on the slide unit 66, but because the slide unit 66 slides at the second slide speed V12, no vibration occurs in the slide unit 66. Furthermore, when the slide unit 66 is stopped, vibration in the sliding direction may occur due to inertia at the time of stopping, but because the slide unit 66 has been decelerated to the second slide speed V12, the vibration is significantly smaller than when the slide unit 66 is stopped at the first slide speed V11. As a result, vibration of the seat after lateral deviation correction can be effectively suppressed.

[0102] In the above embodiment, the sheet correction mechanism 60 is illustrated as having the rotation unit 65 and the slide unit 66, but the present invention is not limited to this configuration. For example, the sheet correction mechanism 60 may be configured to have only either the rotation unit 65 or the slide unit 66, and to perform only tilt correction or only lateral deviation correction.

[0103] Furthermore, in the above embodiment, the image forming apparatus 10 is exemplified as an example of the image forming apparatus of the present invention, but the present invention can also be understood as a sheet conveying device provided in the image forming apparatus. [Explanation of symbols]

[0104] 10: Image forming device 14: Image forming unit 20: Secondary transfer roller 23: Sheet transport unit 26: Sheet transport path 30: Feeding roller pair 60: Sheet correction mechanism 61: Skew detection sensor 65: Rotating unit 66: Slide unit 76: Rotating axis

Claims

1. a conveying section that conveys the sheet in a conveying direction toward an image transfer position where an image is transferred onto the sheet; a detection unit that detects a conveyance deviation of the sheet conveyed in the conveyance direction; a sheet correction unit that is provided downstream of the conveying unit in the conveying direction, and that, when the detection unit detects the conveyance deviation, is displaced from a predetermined sheet receiving position to a correction completion position to correct the conveyance deviation; a speed control unit that controls a displacement speed of the sheet correction unit during a displacement process from the sheet receiving position to the correction completion position by the sheet correction unit, The speed control unit displacing the sheet correction unit at a predetermined first speed to a set position determined between the sheet receiving position and the correction completion position; a sheet conveying device that displaces the sheet correction unit from the set position to the correction completion position at a second speed that is slower than the first speed;

2. 2. The sheet transport device according to claim 1, wherein the set position is a position spaced closer to the correction completion position than a central position between the sheet receiving position and the correction completion position.

3. 3. The sheet conveying device according to claim 2, wherein the set position is a position spaced from the sheet receiving position toward the correction completion position by a distance obtained by multiplying a set ratio exceeding 50% of the distance from the sheet receiving position to the correction completion position.

4. the sheet correction unit includes a correction roller that conveys the sheet conveyed in the conveyance direction, when the detection unit detects the conveyance deviation of the sheet, the sheet correction unit corrects the conveyance deviation by displacing the correction roller by a displacement amount corresponding to the conveyance deviation from the sheet receiving position to the correction completion position after the sheet enters the correction roller; 4. The sheet transport device according to claim 1, wherein the speed control unit controls, as the displacement speed, a roller displacement speed when the correction roller is displaced from the sheet receiving position to the correction completion position.

5. a conveying section that conveys the sheet in a conveying direction toward an image transfer position where an image is transferred onto the sheet; a detection unit that detects a conveyance deviation of the sheet conveyed in the conveyance direction; a sheet correction unit that is provided downstream of the conveying unit in the conveying direction, has a correction roller that conveys the sheet conveyed in the conveying direction in the conveying direction, and when the detection unit detects the conveying deviation of the sheet, corrects the conveying deviation by displacing the correction roller by a displacement amount corresponding to the conveying deviation from a predetermined sheet receiving position to a correction completion position after the sheet enters the correction roller; a speed control unit that controls a displacement speed of the correction roller when the sheet correction unit displaces the correction roller from the sheet receiving position to the correction completion position, The speed control unit displacing the correction roller at a predetermined first speed to a set position determined between the sheet receiving position and the correction completion position; a sheet conveying device that displaces the correction roller from the set position to the correction completion position at a second speed that is slower than the first speed;

6. The sheet correction unit 6. The sheet conveying device according to claim 4, further comprising a rotation unit that is capable of rotating the correction roller around a predetermined rotation fulcrum, rotates the correction roller from a predetermined initial position to the sheet receiving position by a rotation distance corresponding to the conveying deviation of the sheet before the sheet enters the correction roller, and returns the correction roller from the sheet receiving position to the initial position as the correction completion position after the sheet enters the correction roller.

7. The sheet correction unit The correction roller is slidable in the axial direction from a predetermined reference position, 6. The sheet conveying device according to claim 4, further comprising a slide unit that slides the correction roller in the axial direction from the reference position by a movement distance corresponding to the conveyance deviation of the sheet after the sheet enters the correction roller.

8. A sheet conveying device according to any one of claims 1 to 7, an image forming apparatus that transfers an image onto the sheet transported to an image transfer position by the sheet transport device;

Images