Sheet conveying device and image forming apparatus

Abstract

To reduce variation in conveyance timing while accommodating various sheet sizes.SOLUTION: A sheet conveying device includes: a first roller pair; a second roller pair; an abutting portion; skew feeding means; moving means for moving the first roller pair in a sheet width direction; separating means for switching the second roller pair between a contacting state and a separating state; and control means. When conveying a first sheet of a first length, the control means moves the first roller pair in the sheet width direction by the moving means on the basis of a detection result of detection means with the second roller pair in the separating state and then hands over the first sheet from the first roller pair to the skew feeding means. When conveying a second sheet of a second length that is shorter than the first length, the control means moves the first roller pair in the sheet width direction by the moving means on the basis of the detection result of the detection means with the second roller pair in the contacting state by the separating means and hands over the second sheet from the first roller pair to the skew feeding means via the second roller pair.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet, and an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] Conventionally, there is known a sheet conveying device of a so-called side registration type, which conveys a sheet obliquely by a skew roller and strikes its side edge against a reference member to correct the skew of the sheet. Patent Document 1 describes that the sheet position in the sheet width direction is corrected based on the detection result of a sheet position detection sensor by sliding movement of a conveying roller pair (slide roller) provided upstream of the skew roller in the sheet conveying direction. According to this document, by correcting the sheet position before the start of skew feeding, the distance conveyed while the sheet strikes the reference member becomes closer to a constant, thereby reducing the variation in conveying timing downstream of the skew roller, and improving productivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-013356 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration of the above document, when the sheet position is corrected by the slide roller, the slide roller is moved while the sheet is not restrained by the pair of conveying rollers or the conveying guide upstream of the slide roller in order to avoid damage to the sheet or poor correction. Here, in the case of a sheet that is relatively long in the sheet conveying direction, the timing at which the sheet is released from the pair of conveying rollers upstream is delayed compared to a short sheet, so it is desirable to secure the movement time of the slide roller. However, if the distance from the slide roller to the oblique feed roller is widened to secure the movement time of the slide roller, it becomes difficult to convey a short sheet.

[0005] Therefore, an object of the present invention is to provide a configuration capable of reducing variations in conveying timing while accommodating sheets of various sizes. [Means for solving the problem]

[0006] One aspect of the present invention includes a first roller pair that transports a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet transport direction and transports the sheet, an abutting portion against which an end of the sheet in a sheet width direction perpendicular to the sheet transport direction is abutted, a skew conveying means that is disposed downstream of the second roller pair in the sheet transport direction and moves the sheet toward the abutting portion in the sheet width direction toward downstream in the sheet transport direction and transports the sheet while the end of the sheet abuts against the abutting portion, a detection means that detects a position of the sheet in the sheet width direction, a moving means that moves the first roller pair in the sheet width direction, a separation means that switches the second roller pair between a contact state in which the rollers abut against each other and a separation state in which the rollers are separated from each other, and a detection means that detects a position of the sheet in the sheet width direction, ... and a control means for controlling a moving means for moving the first roller pair in the sheet width direction based on a detection result of the detection means, wherein, when a first sheet having a length in the sheet transport direction of a first length is transported, the control means sets the second roller pair to the separated state using the separating means, moves the first roller pair in the sheet width direction based on a detection result of the detection means, and then transfers the first sheet from the first roller pair to the oblique feeding means, and when a second sheet having a length in the sheet transport direction of a second length shorter than the first length is transported, the control means sets the second roller pair to the abutting state using the separating means, moves the first roller pair in the sheet width direction based on a detection result of the detection means, and transfers the second sheet from the first roller pair to the oblique feeding means via the second roller pair. Effect of the Invention

[0007] According to the present invention, it is possible to reduce variation in transport timing while handling sheets of various sizes. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a printer according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of a registration unit according to an embodiment. [Diagram 3]FIG. 2 is a side view of a registration unit according to an embodiment. [Figure 4] FIG. 2 is a top view of a registration unit according to an embodiment. [Diagram 5] 5A to 5D are top views showing the operation of a registration unit according to an embodiment. [Figure 6] 5A to 5D are side views showing the operation of a registration unit according to an embodiment. [Figure 7] 5A to 5D are top views showing the operation of a registration unit according to an embodiment. [Figure 8] 5A to 5D are side views showing the operation of a registration unit according to an embodiment. [Figure 9] FIG. 4 is a block diagram showing a control configuration of a registration unit according to an embodiment. [Figure 10] 11 is a flowchart showing a control method of a registration unit according to an embodiment. [Figure 11] 5A and 5B are side views illustrating a drive configuration and a separation configuration of a pair of conveying rollers according to an embodiment. [Figure 12] FIG. 4 is a perspective view for explaining a drive configuration of a pair of pre-registration rollers according to an embodiment. [Figure 13] FIG. 4 is a perspective view for explaining a sliding configuration of a pair of pre-registration rollers according to an embodiment. [Figure 14] 1A and 1B are a perspective view and a cross-sectional view illustrating a separation configuration of a pair of pre-registration rollers according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] (Image forming device) A printer 1 as an image forming apparatus according to one embodiment will be described. Fig. 1 is a schematic diagram of the printer 1. The printer 1 is an electrophotographic full-color laser beam printer. As shown in Fig. 1, the printer 1 is divided into a first housing 1a having a unit for feeding sheets and forming images, and a second housing 1b having a unit for fixing and cooling.

[0011] The first housing 1a has feeding units 10a and 10b, pulling units 20a and 20b, a registration unit 30, an image forming unit 90, a pre-fixing transport unit 57, and a first double-sided transport unit 60. The image forming unit 90 is an example of an image forming means that forms an image on a sheet.

[0012] The second housing 1b includes a fixing unit 100, a cooling unit 110, a branching conveying unit 120, a reversing conveying unit 130, a second double-sided conveying unit 150, and a decurling unit 170.

[0013] The image forming section 90 includes four process cartridges 99Y, 99M, 99C, and 99K for forming yellow, magenta, cyan, and black toner images (hereinafter simply referred to as images), respectively, and four exposure devices 93.

[0014] The process cartridge 99Y has a photosensitive drum 91 as an image carrier, a charger, a developing unit 92, and a cleaner 95. The photosensitive drum 91 is configured by coating an organic photoconductive layer on the outer periphery of an aluminum cylinder, and is rotated by a drive motor (not shown). The process cartridges 99M, 99C, and 99K have substantially the same configuration as the process cartridge 99Y, except that the colors of the images they form are different.

[0015] The image forming unit 90 also has an intermediate transfer belt 50 that is rotated in the direction of the arrow T by a driving roller 52. The intermediate transfer belt 50 is an intermediate transfer body in this embodiment. The intermediate transfer belt 50 is an endless belt member that is wound around a tension roller 51, a driving roller 52, and a secondary transfer inner roller 53. Four primary transfer rollers 55 corresponding to the respective photosensitive drums 91 are disposed inside the intermediate transfer belt 50. A secondary transfer outer roller 54 is provided on the outside of the intermediate transfer belt 50, facing the secondary transfer inner roller 53. A secondary transfer portion T2 is formed as a nip portion between the secondary transfer outer roller 54 and the secondary transfer inner roller 53, as a transfer portion where an image is transferred to a sheet. A belt cleaner 56 is disposed in contact with the outer surface of the intermediate transfer belt 50.

[0016] The pre-fixing transport unit 57 is a transport unit that transports the sheet S from the secondary transfer portion T2 toward a sheet discharge port provided on a side surface (the side surface on the second housing side) of the first housing 1a. The first double-sided transport unit 60 is a transport unit that transports the sheet S received from the second housing 1b toward the registration unit 30. A part of the first double-sided transport unit 60 is used as a transport path for the sheet S fed from the feeding unit 10b.

[0017] The feeding unit 10a has a lift plate 11a which moves up and down while stacking sheets S, a pickup roller 12a which feeds the sheets S stacked on the lift plate 11a, and a separation roller pair 13a which separates the fed sheets one by one. Similarly, the feeding unit 10b has a lift plate 11b which moves up and down while stacking sheets S, a pickup roller 12b which feeds the sheets S stacked on the lift plate 11b, and a separation roller pair 13b which separates the fed sheets one by one.

[0018] The feeding units 10a and 10b are examples of feeding means for feeding the sheet S to the image forming section 90. For example, a manual feeding device that feeds a sheet from a manual feed tray (multipurpose tray) provided in an openable and closable manner on the side of the first housing 1a may be used as the feeding means. Also, a large-capacity feeding device (optional feeder) connected to the first housing 1a may be used as the feeding means. Note that the sheet S as the recording material can be a variety of sheet materials with different sizes and materials, such as paper such as plain paper and cardboard, sheet materials with surface treatments such as plastic film, cloth, and coated paper, and sheet materials with special shapes such as envelopes and index paper.

[0019] The registration unit 30 is a sheet conveying device that conveys the sheet S fed from the feeding units 10a and 10b toward the secondary transfer portion T2. ​​The registration unit 30 has a plurality of conveying roller pairs (31, 32), a conveying sensor 33 that detects the position of the sheet S in the conveying direction, and a CIS 34 that detects the position of the sheet S in the width direction. The registration unit 30 will be described in detail later.

[0020] The fixing unit 100 is a fixing device of a thermal fixing type, and includes a pair of fixing rollers 101 consisting of a heat roller and a pressure roller, and a heating means such as a halogen lamp or an induction heating mechanism for heating the heat roller.

[0021] The cooling unit 110 has an upper cooling belt 111a rotated in the direction of arrow T by a driving roller 112a, and a lower cooling belt 111b rotated together with the upper cooling belt 111a by a driving roller 112b. A heat sink 113 is disposed so as to be in contact with the inner surface of the upper cooling belt 111a. The heat sink 113 cools the sheet S by dissipating heat received from the sheet S via the upper cooling belt 111a.

[0022] The branching conveying unit 120 has a conveying path that branches the conveying path of the sheet S, and a switching guide that switches the conveying path. The reversing conveying unit 130 switches back and conveys the sheet S received from the branching conveying unit 120, and sends it back to the branching conveying unit 120 or sends it to the second double-sided conveying unit 150. The second double-sided conveying unit 150 is connected to the first double-sided conveying unit 60 of the first housing 1a. The decurling unit 170 has a pair of decurling rollers consisting of a small-diameter hard roller and a large-diameter soft roller as a correction means for correcting the curvature (curl) of the sheet after image formation.

[0023] (Image formation operation) Next, the image forming operation of the printer 1 will be described. When the control unit of the printer 1 receives image information from an external device (not shown), the control unit starts the following image forming operation. In the image forming unit 90, the rotational driving of each photosensitive drum 91 and the intermediate transfer belt 50 is started. When an image signal (video signal) based on the image information is sent from the control unit to the exposure device 93, the exposure device 93 irradiates the photosensitive drum 91 with a laser beam corresponding to the image signal. As a result, the surface of the photosensitive drum 91, which has been charged to a predetermined polarity and potential by the charger, is exposed to light, and an electrostatic latent image is formed on the surface of the photosensitive drum 91. The developing unit 92 develops the electrostatic latent image using a developer containing toner, and forms an image on the surface of the photosensitive drum 91.

[0024] The images formed on the photosensitive drums 91 of the process cartridges 99Y, 99M, 99C, and 99K are primarily transferred onto the intermediate transfer belt 50 by the primary transfer rollers 55. At this time, multiple transfer is performed so that the images of each color are superimposed on each other, forming a full-color image on the intermediate transfer belt 50. The image carried on the intermediate transfer belt 50 is transported to the secondary transfer portion T2 by the rotation of the intermediate transfer belt 50. Toner remaining on the photosensitive drums 91 without being transferred to the intermediate transfer belt 50 is collected by a cleaner 95.

[0025] In parallel with the formation of an image in the image forming section 90, the sheets S are fed one by one from either the feeding units 10a or 10b, and conveyed to the registration unit 30 via the drawing roller pairs 21a and 21b.

[0026] The registration unit 30 corrects the positional deviation and skew of the sheet S, and transports the sheet S to the secondary transfer portion T2 at a predetermined transport timing. In the secondary transfer portion T2, a transfer voltage is applied to a secondary transfer outer roller 54, so that an image is transferred from the intermediate transfer belt 50 to the sheet S. Toner that is not transferred to the sheet S and remains on the intermediate transfer belt 50 is collected by a belt cleaner 56.

[0027] The sheet S that has passed through the secondary transfer portion T2 is transported to the fixing unit 100 by the pre-fixing transport unit 57. The fixing unit 10 performs a fixing process in which the image on the sheet S is heated and pressurized while the sheet S is nipped and transported by a pair of fixing rollers 101. This causes the toner to melt and then solidify, thereby fixing the image on the sheet S. The sheet S that has passed through the fixing unit 100 is cooled by the cooling unit 110 while being transported by the upper cooling belt 111a and the lower cooling belt 111b.

[0028] Next, the branching conveying unit 120 selects a path to convey the sheet S to either the decurl unit 170 (discharge path) or the inversion conveying unit 130 (inversion path). When an image is formed on only one side (first side) of the sheet S, the sheet S with the image formed on the first side is conveyed from the branching conveying unit 120 to the decurl unit 170, where the curl is corrected and the sheet S is discharged outside the apparatus as a product. When an optional device such as a finisher or a large-capacity stacker is connected to the second housing 1b, the sheet S as a product is delivered to the optional device.

[0029] When forming images on both sides of the sheet S, the sheet S with the image formed on the first side is transported by the branching transport unit 120 to the inverting transport unit 130, and is switchback-transported in the inverting transport unit 130. Next, the sheet S is transported from the inverting transport unit 130 to the registration unit 30 via the second double-sided transport unit 150 and the first double-sided transport unit 60. Furthermore, while the sheet S passes through the secondary transfer portion T2 and the fixing unit 100, an image is formed on the second side of the sheet S in the same manner as the image formation on the first side. Then, the sheet S with the images formed on the first and second sides is transported from the branching transport unit 120 to the decurling unit 170, where the curl is corrected and the sheet S is either discharged outside the apparatus as a product or handed over to an optional device.

[0030] In addition, by switching back and transporting the sheet as the finished product in the inversion transport unit 130 and then delivering it to the decurling unit 170, it is possible to discharge the sheet so that the side on which the image was just formed faces downward (so-called face-down discharge).

[0031] (Registration Unit) A specific configuration of the registration unit 30, which is a sheet conveying device in this embodiment, will be described. Fig. 2 is a perspective view of the registration unit 30. Fig. 3 is a side view of the registration unit 30 as viewed from one side in the sheet width direction D2. Fig. 4 is a top view of the registration unit 30. In Figs. 2 to 4, illustrations of conveying guides forming a sheet conveying path, bearing members supporting each roller, etc. are omitted.

[0032] In the following description, the direction in which a sheet is conveyed along the sheet conveying path in the registration unit 30 is referred to as the sheet conveying direction D1. The direction perpendicular to the sheet conveying direction D1 is referred to as the sheet width direction D2. The sheet width direction D2 is the main scanning direction during image formation, and the sheet conveying direction D1 is the sub-scanning direction during image formation.

[0033] 2 to 4, the registration unit 30 has pairs of conveying rollers 311, 312, and 313, a pair of pre-registration rollers (hereinafter referred to as a pair of pre-registration rollers) 314, and a pair of relay rollers 315. The registration unit 30 also has pairs of oblique conveying rollers 301, 302, and 303, and a pair of registration rollers (hereinafter referred to as a pair of registration rollers) 32. The registration unit 30 also has slide mechanisms 37, 38, and 39, a side reference plate 304, a conveying sensor 33, a CIS 34, and a registration sensor 35. The pairs of oblique conveying rollers 301 to 303 configure an oblique conveying unit 300 that obliquely conveys the sheet and abuts it against the side reference plate 304.

[0034] The pre-registration roller pair 314 is an example of a first roller pair. The relay roller pair 315 is an example of a second roller pair arranged downstream of the first roller pair in the sheet conveying direction D1. The slide mechanism 37 of the pre-registration roller pair 314 is an example of a moving means. The separation mechanism of the relay roller pair 315 is an example of a separating means. The oblique feed unit 300 is an example of a oblique feed means. The abutting surface 304a of the side reference plate 304 is an example of an abutting portion. The CIS 34 is an example of a detection means (position detection means) that detects the position of the sheet in the sheet width direction D2. The first conveying roller pair 311 is an example of an upstream roller pair arranged upstream of the first roller pair in the sheet conveying direction D1.

[0035] In the sheet conveying direction D1, a second conveying roller pair 312, a third conveying roller pair 313, a pre-registration roller pair 314 (fourth conveying roller pair), and a relay roller pair 315 (fifth conveying roller pair) are arranged in this order from the first conveying roller pair 311 toward the downstream. In addition, in the sheet conveying direction D1, a first oblique feed roller pair 301, a second oblique feed roller pair 302, a third oblique feed roller pair 303, and a registration roller pair 32 are arranged in this order from the relay roller pair 315 toward the downstream. The registration unit 30 conveys the sheet from the upstream side toward the downstream side in the sheet conveying direction D1 while transferring the sheet between these multiple roller pairs.

[0036] The distance in the sheet conveying direction D1 from the relay roller pair 315 to the most upstream oblique roller pair 301 of the oblique conveying unit 300 is set to be shorter than the distance in the sheet conveying direction D1 from the pre-registration roller pair 314 to the relay roller pair 315. In other words, the distance in the sheet conveying direction from the second roller pair to the first oblique roller pair is shorter than the distance in the sheet conveying direction from the first roller pair to the second roller pair. As a result, in a conveying mode in which the relay roller pair 315 is in contact as described below, even if the sheet length is short, the sheet can be reliably handed over from the relay roller pair 315 (second roller pair) to the oblique conveying unit 300.

[0037] The second and third conveying roller pairs 312, 313, the pre-registration roller pair 314, the relay roller pair 315, and each of the skew roller pairs 301-303 are configured to be capable of contacting and separating by the separating motors 511-517. That is, each of the roller pairs is configured to be capable of switching between a contact state (nip state, pressurized state) in which the rollers contact each other so as to be able to nip and convey the sheet, and a separation state (open state, pressure release state) in which the rollers are separated from each other. Each of the roller pairs is capable of switching between a contact state and a separation state independently of each other. Note that the separation state is not necessarily a state in which a gap is formed between the rollers. The separation state may be a state in which the contact pressure between the rollers is weaker than that in the contact state, so that the force applied from the roller pair to the sheet does not substantially affect the conveyance of the sheet.

[0038] In this embodiment, the most upstream conveying roller pair 311 and the registration roller pair 32 are not provided with a separation mechanism and are always in contact with each other.

[0039] By disposing at least one roller pair (312, 313) that can be separated between the conveying roller pair 311 and the pre-registration roller pair 314, which are fixed in contact with each other, it becomes easy to handle long sheets. That is, when sliding the pre-registration roller pair 314, which will be described later, it becomes possible to keep the roller pair between the conveying roller pair 311 and the pre-registration roller pair 314 separated. Note that, when handling longer sheets is required, the conveying roller pair 311 may also be configured to be separated. Furthermore, when the upper limit of the length of the sheets to be handled is shorter than that of this embodiment, the separation mechanism of the conveying roller pairs 312, 313 may be omitted.

[0040] The pre-registration roller pair 314 is configured to be movable (slidable) in the sheet width direction D2 by a slide mechanism 37 (arrow B in FIGS. 2 and 4). The slide mechanism 37 will be described in detail later.

[0041] The side reference plate 304 has an abutment surface 304a as an abutting portion against which one end (hereinafter, referred to as a side end) of the sheet in the sheet width direction D2 abuts. The abutment surface 304a is a surface extending in the sheet conveying direction D1, and serves as a reference surface for correcting the skew of the sheet by the skew unit 300 abutting the side end of the sheet. When viewed from the upstream side of the sheet conveying direction D1, the side reference plate 304 is a member having a U-shaped cross section with surfaces extending from the upper and lower ends of the abutment surface 304a to the other side (upper side in FIG. 4) in the sheet width direction D2. The side reference plate 304 can be molded, for example, by die-casting aluminum, and the abutment surface 304a is machined to improve the accuracy, and the abutment surface 304a is further coated with a fluororesin.

[0042] In this embodiment, the side reference plate 304 is configured to be movable in the sheet width direction D2 by a slide mechanism 38 (FIG. 4) (arrow C in FIG. 2 and FIG. 4). This allows the position of the side reference plate 304 to be adjusted according to the size of the sheet in the sheet width direction D2 (hereinafter referred to as the sheet width). Specifically, the side reference plate 304 is positioned at a position separated from the conveyance center X0 (FIG. 4) in the sheet width direction D2 by a distance equal to half the sheet width plus a margin for skew feeding. This allows the movement distance in the sheet width direction D2 when the sheet is struck against the side reference plate 304 by skew feeding to be approximately constant regardless of the sheet width, thereby improving the accuracy of skew correction and productivity. Here, the conveyance center X0 is the center position in the sheet width direction D2 in the sheet conveyance path upstream of the pre-registration roller pair 314. The rollers (outer periphery parts that contact the sheet) of the conveyance roller pairs 311 to 313 are arranged symmetrically with respect to the conveyance center X0.

[0043] Each of the skew roller pairs 301, 302, and 303 includes skew rollers 301a, 302a, and 303a disposed obliquely with respect to the sheet conveying direction D1, and driven rollers 301b, 302b, and 303b opposed to the skew rollers 301a, 302a, and 303a. The rotation axes of the skew rollers 301a, 302a, and 303a are obliquely inclined with respect to the sheet width direction D2. In other words, the skew rollers 301a, 302a, and 303b apply a conveying force to the sheet in a direction obliquely inclined with respect to the sheet conveying direction D1 so as to move the sheet toward one side of the sheet width direction D2 (the side of the side reference plate 304, the lower side in FIG. 4) toward the downstream of the sheet conveying direction D1.

[0044] The skew roller pairs 301, 302, and 303 thus apply a conveying force oblique to the sheet conveying direction D1 to convey the sheet while shifting the sheet widthwise to the side reference plate 304. Even after the side edge of the sheet comes into contact with the abutment surface 304a of the side reference plate 304, the skew roller pairs 301, 302, and 303 convey the sheet downstream in the sheet conveying direction D1 while abutting the side edge against the abutment surface 304a. As a result, the skew of the side edge of the sheet is corrected with reference to the abutment surface 304a of the side reference plate 304.

[0045] In this embodiment, the direction of the rotation axis of the driven rollers 301b, 302b, and 303b is substantially parallel to the sheet width direction D2, but the driven rollers 301b, 302b, and 303b may also be inclined in the same manner as the oblique feed rollers 301a, 302a, and 303a. The number and arrangement of the oblique feed roller pairs can be changed as appropriate. For example, a pair of oblique feed rollers may be added at the same position as the pair of oblique feed rollers 301 in the sheet conveying direction D1 and on the opposite side of the side reference plate 304 with respect to the conveying center X0.

[0046] The skew rollers 301a, 302a, and 303b are driven to rotate by receiving a driving force from a driving motor, for example, via a universal joint. The driven rollers 301b, 302b, and 303b are connected to a separation mechanism and are provided movably so as to come into contact with and separate from the skew rollers 301a, 302a, and 303b. The separation mechanism is composed of, for example, a swingable arm that rotatably supports the driven rollers 301b, 302b, and 303b, and a cam mechanism that swings the arm by the driving force of a separation motor. The arm swings in accordance with the rotation angle of the separation motor, and the driven rollers 301b, 302b, and 303b move, so that the skew roller pairs 301, 302, and 303 switch between a contact state and a separation state.

[0047] The pair of registration rollers 32 is configured to be movable (slidable) in the sheet width direction D2 by a slide mechanism 39 (arrow A in Figs. 2 and 4). The pair of registration rollers 32 transports the sheet S, whose skew has been corrected, in the sheet transport direction D1 toward the secondary transfer section T2 (Fig. 1). At that time, the pair of registration rollers 32 is controlled to move the sheet, which has been abutted against the side reference plate 304 for skew correction, in the sheet width direction D2 to match the reference position of the image formed by the image forming section 90. The pair of registration rollers 32 is also controlled to adjust the timing at which the sheet is sent to the secondary transfer section T2 in accordance with the timing at which the image formed by the image forming section 90 arrives at the secondary transfer section T2.

[0048] The CIS (Contact Image Sensor) 34 is an example of a detection means for detecting the position of the sheet in the sheet width direction D2. The CIS is an image sensor having a substrate having light receiving elements arranged along the sheet width direction D2, an irradiation unit (LED and light guide) for irradiating the sheet with light, and a lens for forming an image of the reflected light from the sheet on the light receiving element. A controller 550 (FIG. 9) described later can detect the side edge position of the sheet before starting the skew feeding of the sheet based on the detection result of the CIS 34. For example, the controller 550 can detect the side edge of the sheet by edge detection processing from one-dimensional imaging data acquired by the CIS 34.

[0049] The CIS 34 is disposed at a position offset to one side (the side of the side reference plate 304) with respect to the conveying center X0 in the sheet width direction D2 (FIG. 4). This is because only one side edge position of the sheet is sufficient to perform sheet position correction, which will be described later, using the detection result of the CIS 34. The detection range of the CIS 34 is set so that it can detect the respective side edge positions of the sheet S with the smallest sheet width and the sheet S with the largest sheet width among the sheet sizes permitted for use in the image forming apparatus.

[0050] The conveyance sensor 33 and the registration sensor 35 are examples of sheet detection means for detecting the leading and trailing ends of a sheet. The conveyance sensor 33 is disposed, for example, between the pair of pre-registration rollers 314 and the pair of relay rollers 315. The registration sensor 35 is disposed near the pair of registration rollers 32. A controller 550 (FIG. 9) described later can determine the timing to start skew feeding of the sheet based on the timing when the conveyance sensor 33 detects the leading edge of the sheet. The controller 550 can also adjust the speed of the pair of registration rollers 32 based on the timing when the registration sensor 35 detects the leading edge of the sheet. The controller 550 can also monitor the detection signals of the conveyance sensor 33 and the registration sensor 35 to detect abnormalities in sheet conveyance (such as retention jams).

[0051] The transport sensor 33 may be, for example, a reflective photoelectric sensor having a light-emitting portion and a light-receiving portion. In this case, light emitted by the light-emitting portion is reflected by the sheet, and the light-receiving portion detects the reflected light, thereby detecting the timing of the sheet passing. In addition to the reflective photoelectric sensor, a known sensor may be used, such as a sensor that combines a flag that swings when pressed by the sheet and a photoelectric sensor that is blocked by the flag. As with the transport sensor 33, the registration sensor 35 may also be a known sensor, such as a reflective photoelectric sensor.

[0052] (Registration unit control configuration) The control configuration of the registration unit 30 will be described with reference to Fig. 9. The operation of the registration unit 30 is controlled by a controller 550 mounted on the printer 1. The controller 550, which is an example of a control means, includes a CPU 551 as a program execution means, a RAM 552 and a ROM 553 as a storage means, and an interface (I / O) 604 for an external device or a network.

[0053] The CPU 551 loads and executes a program stored in the ROM 553 or the like. This allows the CPU 551 to execute each step of a control method described in the flowchart of Fig. 10. The ROM 553 is an example of a computer-readable non-transitory storage medium that stores a program for controlling the sheet conveying device or the image forming apparatus.

[0054] The CPU 551 performs control based on information input by a user via an operation unit 400 serving as a user interface and detection signals from the above-mentioned transport sensor 33, CIS 34, and registration sensor 35. The detection signals from the transport sensor 33 and registration sensor 35 are input to the CPU 551 via an AD conversion unit 555. Also, the detection signal from the CIS 34 is input to the CPU 551 via the AD conversion unit 555. The CPU 551 drives and controls a group of motors (501-509, 511-517, 521-523) which are actuators of the registration unit 30 via a driver 556.

[0055] Each roller pair of the registration unit 30 is rotated by drive motors 501 to 509. Drive motors 501, 502, and 503 drive the transport roller pairs 311, 312, and 313, respectively. Drive motor 504 drives the pre-registration roller pair 314. Drive motor 505 drives the relay roller pair 315. Drive motors 506, 507, and 508 drive the oblique feed roller pairs 301, 302, and 303, respectively. Drive motor 509 drives the registration roller pair 32.

[0056] The separation motor 511 brings the second conveying roller pair 312 into contact with and separates the rollers. The separation motor 512 brings the third conveying roller pair 313 into contact with and separates the rollers. The separation motor 513 brings the pre-registration roller pair 314 into contact with and separates the rollers. The separation motor 514 brings the relay roller pair 315 into contact with and separates the rollers. The separation motors 515-517 bring the first to third oblique feed roller pairs 301-303 into contact with and separate the rollers.

[0057] The slide motor 521 drives the slide mechanism 37 (FIG. 4) to move (slide) the pre-registration roller pair 314 in the sheet width direction D2. The slide motor 522 drives the slide mechanism 38 (FIG. 4) to move (slide) the side reference plate 304 in the sheet width direction D2. The slide motor 523 drives the slide mechanism 39 (FIG. 4) to move (slide) the registration roller pair 32 in the sheet width direction D2.

[0058] Each of the above motors (501 to 509, 511 to 51, 521 to 523) may be, for example, a stepping motor whose rotation angle can be controlled with high precision.

[0059] (Details of the conveyor roller pair) 11, the pairs of conveying rollers 312, 313 and the pair of relay rollers 315 will be described in detail. Each of the pairs of conveying rollers 312, 313 and the pair of relay rollers 315 is composed of driving rollers 312a, 313a, 315a and driven rollers 312b, 313b, 315b.

[0060] The drive rollers 312a, 313a, 315a are connected to drive motors 502, 503, 504, which are drive sources, respectively, via a belt transmission mechanism 330. Thus, the conveying roller pairs 312, 313, 315 are configured to rotate by receiving drive force from the drive motors 502, 503, 504. Similarly, the most upstream conveying roller pair 311 is configured to rotate by receiving drive force from the drive motor 501 via a belt transmission mechanism. Each of the driven rollers 312b, 313b, 315b is connected to a spacing mechanism 650.

[0061] The configuration and operation of the spacing mechanism 650 will be described below using the relay roller pair 315 as an example. The spacing mechanism 650 has a spacing motor 514, gears 655 and 656, an eccentric cam 653, and an arm 651. The arm 651 swings around a swing shaft 652 and rotatably supports the rotation shaft of the driven roller 315b. When the rotation of the spacing motor 514 is transmitted to the eccentric cam 653 via the gears 655 and 656, the arm 651 swings in response to the rotation of the eccentric cam 653. Due to the swing of the arm 651, the driven roller 315b moves in the up and down direction in the figure so as to come into contact with and separate from the drive roller 315a.

[0062] Therefore, by controlling the rotation angle of the separation motor 514, the relay roller pair 315 can be switched between a contact state and a separation state. A similar separation mechanism 650 is also provided for the conveying roller pair 312, 313, and is configured so that the conveying roller pair 312, 313 can be switched between a contact state and a separation state by controlling the rotation angle of the separation motors 511, 512.

[0063] (Details of the pre-registration roller pair) The pre-registration roller pair 314 will be described in detail with reference to Figs. 12 to 14. Fig. 12 is a perspective view of a drive mechanism 800 that drives and rotates the pre-registration roller pair 314. Fig. 13 is a schematic perspective view of a slide mechanism 37 that slides the pre-registration roller pair 314. Fig. 14(a) is an enlarged perspective view of a separation mechanism 700 that switches the pre-registration roller pair 314 between a contact state and a separated state. Fig. 14(b) is a cross-sectional view of the separation mechanism 700.

[0064] The pre-registration roller pair 314 is rotationally driven by a drive mechanism 800, configured to be movable in the sheet width direction D2 by a slide mechanism 37, and configured to be switchable between a contact state and a separated state by a separation mechanism 700.

[0065] 12 and 13, the pre-registration roller pair 314 is composed of an upper roller 401 and a lower roller 402. The lower roller 402 is rotatably supported by the frame 201 of the printer 1, and the upper roller 401 is rotatably supported by an arm 405 that is a part of the separation mechanism 700.

[0066] As shown in Fig. 12, the drive mechanism 800 includes a drive motor 504, drive gears 802 and 803, and a roller gear 412. The drive motor 504 is fixed to the frame 201. The roller gear 412 is provided on the rotation axis of the lower roller 402 and rotates integrally with the lower roller 402. The drive gears 802 and 803 are rotatably supported by shafts fixed to the frame 201, and connect the output shaft of the drive motor 504 and the roller gear 412. The rotation of the drive motor 504 is transmitted to the roller gear 412 via the drive gears 802 and 803, thereby rotating the lower roller 402, which is a drive roller. As a result, the pre-registration roller pair 314 is rotationally driven.

[0067] In order to maintain meshing with the roller gear 412 even when the pre-registration roller pair 314 slides, the tooth width d of the drive gear 803 in the sheet width direction D2 is set to be longer than the slide stroke of the pre-registration roller pair 314. Instead of driving the pre-registration roller pair 314 via a gear train, the drive motor 504 and the lower roller 402 may be connected by a timing belt. In that case, the drive motor 504 may be configured to slide together with a part of the frame 201 as the pre-registration roller pair 314 slides.

[0068] As shown in FIG. 13, the slide mechanism 37 includes a slide motor 521, pulleys 609, 610, 611, and 612, timing belts 613 and 614, a holder 415, a home position sensor 615, and a separation sensor 706 (FIG. 14(b)).

[0069] The holder 415 rotatably supports the end of the lower roller 402 on the roller gear 412 side, and is configured to move integrally with the lower roller 402 in the axial direction (sheet width direction D2). The holder 415 is fixed to a timing belt 614 by 616. The timing belt 614 is stretched in the sheet width direction D2 by pulleys 610 and 611.

[0070] As shown in Fig. 12, pulley 610 is an integral member with pulley 609. Pulley 609 is connected to pulley 612 provided on the output shaft of slide motor 521 (Fig. 13) via timing belt 613. Note that illustration of slide motor 521 is omitted in Fig. 12. With this configuration, timing belts 613 and 614 rotate in response to forward and reverse rotation of slide motor 521, and lower roller 402 reciprocates together with holder 415 in sheet width direction D2.

[0071] On the other hand, the upper roller 401 of the pre-registration roller pair 314 is configured to move together with the lower roller 402 in the sheet width direction D2 by being engaged with the lower roller 402 by an engagement member (not shown).

[0072] The home position sensor 615 is a sensor (e.g., a photointerrupter) that detects the sensor flag 416 provided in the holder 415 when the pre-registration roller pair 314 is in a predetermined home position. The controller 550 can detect the home position of the pre-registration roller pair 314 based on the detection signal of the home position sensor 615.

[0073] As shown in Fig. 14(a and b), the spacing mechanism 700 includes a spacing motor 513, an arm 405, a pressure spring 407, cams 702 and 703, and a spacing shaft 701. The arm 405, which rotatably supports the upper roller 401, is swingable around a shaft 201a formed on the frame 201 (Fig. 13). The pressure spring 407 biases the arm 405 in a direction in which the upper roller 401 contacts the lower roller 402. The arm 405 and the pressure spring 407 are also provided on the opposite side to one side in the sheet width direction D2 shown in Fig. 14(a).

[0074] The cams 702 and 703 are provided at both ends of a spacing shaft 701 extending in the sheet width direction D2, and each abuts against the arm 405. In addition, as shown in FIG. 14A, a gear 702b is formed on the cam 702. The rotation of the spacing motor 513 is input to the gear 702b to rotate the cam 702, and at the same time, the other cam 703 also rotates via the spacing shaft 701. Due to the rotation of the cams 702 and 703, the upper roller 401 moves so as to abut against and separate from the lower roller 402. As a result, the pre-registration roller pair 314 switches between a contact state and a separated state according to the rotation angle of the spacing motor 513.

[0075] 14(b), a sensor flag 703b is formed on the cam 703 to be detected by a separation sensor 706. The separation sensor 706 is a sensor (e.g., a photointerrupter) that detects the sensor flag 703b when the separation shaft 701 is at a predetermined rotation angle. The controller 550 can grasp the rotation angles of the cams 702 and 703 based on the detection signal of the separation sensor 706.

[0076] The configuration of the spacing mechanism (spacing means) for each roller pair (312 to 315) described above is one example, and for example, cams 702, 703 driven by spacing motor 513 may directly press the bearing portion of upper roller 401 of pre-registration roller pair 314. Also, instead of a spacing mechanism using a motor, a configuration may be used in which the roller shaft is moved by, for example, a plunger solenoid to switch between the contact state and the separated state of the roller pair.

[0077] Further, the slide mechanism 37 of the pre-registration roller pair 314 is an example of a moving means, and the pre-registration roller pair 314 may be slid in the sheet width direction D2 by a mechanism using a worm gear or a linear cam instead of a timing belt, for example.

[0078] (Reduction of variation in transport timing caused by sliding of the pre-registration roller pair) In this embodiment, before the sheet is obliquely fed by the oblique feeding unit 300 and abuts against the side reference plate 304, an operation is performed to correct the sheet position in the sheet width direction D2 upstream of the oblique feeding unit 300. This reduces variation in the conveyance timing of the sheet downstream of the side reference plate 304. A specific description will be given below.

[0079] If there is variation in the sheet position in the sheet width direction D2 at the start of oblique feeding by the oblique feeding unit 300, the timing at which the side edge of the sheet abuts against the side reference plate 304 after the start of oblique feeding varies. If the side edge of the sheet is far away from the side reference plate 304 at the start of oblique feeding, the timing at which the side edge of the sheet abuts against the side reference plate 304 will be delayed. Conversely, if the side edge of the sheet is close to the side reference plate 304 at the start of oblique feeding, the timing at which the side edge of the sheet abuts against the side reference plate 304 will be earlier. If the timing at which the side edge of the sheet abuts against the side reference plate 304 varies, the distance conveyed by the oblique feeding unit 300 while the sheet is abutting against the side reference plate 304 (sliding state) will change.

[0080] When the sheet is conveyed in a rubbing state, the sheet receives additional conveying resistance (friction resistance) from the side reference plate 304, and the sheet conveying speed in the sheet conveying direction D1 decreases. As a result, due to the variation in the sheet position in the sheet width direction D2 at the start of the skew conveying, the timing at which the sheet passes a predetermined position downstream of the side reference plate 304 varies. For example, the timing at which the registration sensor 35 detects the leading edge of the sheet after the skew conveying abuts varies based on the time point at which the conveying sensor 33 detects the leading edge of the sheet before the start of the skew conveying.

[0081] If such a variation in the transport timing exists, the productivity (throughput) of the sheet transport device may decrease. This is because, when attempting to transport sheets at a constant target interval, the target interval is set longer in advance so that the variation in the transport timing can be absorbed. In the configuration of this embodiment, this corresponds to setting the paper interval longer in order to transfer images at a constant interval (paper interval) at the secondary transfer portion T2.

[0082] In contrast, in this embodiment, before the oblique feeding unit 300 starts oblique feeding, the pair of pre-registration rollers 314 are moved in the sheet width direction D2 based on the detection result of the sheet position by the CIS 34. This makes it possible to align the distance from the side edge of the sheet to the side reference plate 304 at the start of oblique feeding. As a result, the distance the sheet is conveyed in the rubbing state becomes approximately constant, and the variation in the timing at which the registration sensor 35 detects the leading edge of the sheet after the oblique feeding abuts is reduced. Furthermore, by reducing the variation in the conveying timing, it becomes possible to set the paper interval at the secondary transfer portion T2 to be shorter, for example, which contributes to improving the productivity of the printer 1.

[0083] The movement of the pair of pre-registration rollers 314 based on the result of detection of the sheet position by the CIS 34 will be described in detail below.

[0084] (Conveying operation when the sheet length is greater than or equal to a predetermined length) Hereinafter, the conveying operation according to the size of the sheet in the sheet conveying direction (hereinafter referred to as the sheet length) performed by the registration unit 30 of this embodiment will be described with reference to the flowchart of Fig. 10. Each step of the flowchart of Fig. 10 is realized by the CPU 551 of the controller 550 (Fig. 9) reading and executing a program from the ROM 552. Also, each step of Fig. 10 is performed as a part of a job when the controller 550 executes a job of an image forming operation (a print job).

[0085] First, the conveying operation when the sheet length is equal to or longer than the predetermined length will be described with reference to the flowchart in Fig. 10 and Figs. 5(a-d) and 6(a-d). Figs. 5(a-d) are top views of the registration unit 30 showing the conveying operation of the sheet S1 whose sheet length Ls1 is equal to or longer than the predetermined length. Figs. 6(a-d) are side views of the registration unit 30 showing the conveying operation of the sheet S1 whose sheet length Ls1 is equal to or longer than the predetermined length. In Figs. 5(a-d), the rollers in the contact state are shown in black, and the rollers in the separated state are shown only by frame lines.

[0086] Before an image formation job is input, the controller 550 acquires information on the sheet size in advance. The sheet size can be acquired, for example, by referring to the sheet size input by the user via the operation unit 400 (FIG. 9) or by automatically detecting the sheet size using a sheet size sensor provided in the feeding units 10a and 10b (FIG. 1). When an image formation job is input, the controller 550 determines whether the sheet length of the sheet used in the current job is equal to or longer than a predetermined length (S1).

[0087] When the sheet length is equal to or longer than a predetermined length, the relay roller pair 315 downstream of the pre-registration roller pair 314 is separated (S2a, FIG. 5(a), FIG. 6(a)). Thereafter, the sheet S1 is transported in a transport mode (S2a to S9a) in which the relay roller pair 315 (second roller pair) is separated.

[0088] 5(a) and 6(a), the sheet S1 conveyed from a conveying unit (the feeding units 10a and 10b or the first double-sided conveying unit in FIG. 1) upstream of the registration unit 30 is conveyed by conveying roller pairs 311 to 313. When the leading edge of the sheet S1 reaches the CIS 34, the side edge position Xd of the sheet S1 is detected by using the CIS 34 (S3a).

[0089] A deviation ΔX between the detected side edge position Xd (FIG. 5A) of sheet S1 and a target position Xn of the side edge of sheet S1 is calculated. In this embodiment, the target position Xn is the side edge position of sheet S1 when the center of sheet S1 in the sheet width direction D2 coincides with the conveying center X0 (a position away from the conveying center X0 by half the sheet width Ws1, called the side edge position).

[0090] Next, a slide operation (shift operation, position correction operation) of the pre-registration roller pair 314 is performed to correct the deviation amount ΔX (S4a, arrow B in FIG. 5(b)). Specifically, after the leading edge of the sheet S1 enters the pre-registration roller pair 314, the conveying roller pair 312, 313 upstream of the pre-registration roller pair 314 are separated (FIG. 6(b)). Then, after the trailing edge of the sheet S1 leaves the most upstream conveying roller pair 311, the pre-registration roller pair 314 is slid so that the deviation amount ΔX is compensated for and the side edge of the sheet S1 approaches the target position Xn. This shifts the sheet position so that the center of the sheet S1 is aligned with the conveying center X0. The conveying of the sheet S1 continues even while the pre-registration roller pair 314 is sliding.

[0091] Here, the pre-registration roller pair 314 is slid after the rear end of the sheet S1 passes through the most upstream conveying roller pair 311 because the conveying roller pair 311 is always in contact with the sheet S1. Since the sheet length Ls1 of the sheet S1 is longer than the path length L0 from the conveying roller pair 311 to the pre-registration roller pair 314, the rear end of the sheet S1 is sandwiched between the conveying roller pair 311 when the leading end of the sheet S1 reaches the pre-registration roller pair 314. When the leading end of the sheet S1 is conveyed a distance (Ls1-L0) from the pre-registration roller pair 314, the rear end of the sheet S1 passes through the conveying roller pair 311. As a result, the rear end side of the sheet S1 is not restrained by the conveying roller pair 311, and the pre-registration roller pair 314 can move the sheet S1 in the sheet width direction D2 without generating stress (shear force) in the sheet S1 in the sheet width direction D2.

[0092] Moreover, the sliding of the pre-registration roller pair 314 is completed before the sheet is sandwiched between the roller pair downstream of the pre-registration roller pair 314. In this embodiment, when the sheet length is equal to or longer than a predetermined length, the relay roller pair 315 is separated, so that the sliding of the pre-registration roller pair 314 may be completed before the leading edge of the sheet S1 reaches the most upstream oblique feed roller pair 301 of the oblique feed unit 300. This makes it possible to extend the period during which the pre-registration roller pair 314 can slide, and therefore to widen the range in which the position of the sheet S1 in the sheet width direction D2 can be corrected, compared to when the relay roller pair 315 is in a contact state.

[0093] Thus, in this embodiment, when conveying a first sheet (S1) whose length is equal to or longer than a predetermined length, the movement of the first roller pair by the moving means (slide mechanism 36) is started after the leading edge of the first sheet reaches the first roller pair (pre-registration roller pair 314) and the trailing edge of the first sheet passes through the upstream roller pair (conveyance roller pair 311). Also, in this embodiment, the movement of the first roller pair by the moving means is terminated before the leading edge of the first sheet reaches the oblique conveying means (oblique conveying unit 300). This makes it possible to complete the position correction of the first sheet while the sheet is not restrained by roller pairs other than the first roller pair, and to avoid damage to the sheet.

[0094] In addition, if the deviation amount ΔX calculated using the CIS 34 is large and the sliding of the pre-registration roller pair 314 cannot be completed before the oblique feed roller pairs 301 to 303 switch to the abutting state, an error may be notified and the conveying operation may be stopped.

[0095] After the leading edge of the sheet S1 reaches the pair of oblique feed rollers 301, the pair of oblique feed rollers 301-303 are switched to the contact state (S6a). At this stage, the force with which the pair of oblique feed rollers 301-303 pinch the sheet S1 is weaker than the pinch force of the pair of pre-registration rollers 314, so the conveying force applied to the sheet S1 by the pair of pre-registration rollers 314 is dominant, and the sheet S1 continues to move in the sheet conveying direction D1. The timing at which the sheet S1 is switched to the contact state is determined based on the timing at which the conveying sensor 33 detects the leading edge of the sheet S1.

[0096] Thereafter, the pair of pre-registration rollers 314 are switched to the separated state (S7a, FIG. 6(c)). As a result, the oblique conveying force applied to the sheet S1 by the pair of oblique feed rollers 301, 302, and 303 becomes dominant, and the sheet S1 is conveyed while being shifted toward the side reference plate 304 (arrow E in FIG. 5(c)).

[0097] In this embodiment, the pre-registration roller pair 314 separates after the leading edge of the sheet S1 reaches the second oblique feed roller pair 302. That is, the pre-registration roller pair 314 separates while the sheet S1 is sandwiched between the most upstream oblique feed roller pair 301 (first oblique feed roller pair) and the second oblique feed roller pair 302 (second oblique feed roller pair). This makes it possible to more reliably deliver the sheet S1 from the pre-registration roller pair 314 to the oblique feed unit 300. Note that the timing for bringing the oblique feed roller pairs 301 to 303 into contact with each other is set after the leading edge of the sheet S1 reaches the second oblique feed roller pair 302, thereby shortening the time during which the sheet S1 slips against the oblique feed rollers 301a and 301b.

[0098] When the side edge of the sheet S1 abuts against the abutment surface 304a of the side reference plate 304 (S8a), the skew roller pairs 301-303 slip, and the sheet S1 rotates following the abutment surface 304a, thereby correcting the skew of the sheet S1. Even after the skew of the sheet S1 is corrected, the skew roller pairs 301-303 continue to convey the sheet S1 in the sheet conveying direction D1 while keeping the side edge of the sheet S1 in contact with the abutment surface 304a.

[0099] When the leading edge of the sheet S1 reaches the pair of registration rollers 32 (S9a), the pair of skew rollers 301-303 are switched to a separated state (FIGS. 5(d) and 6(d)). After that, the pair of registration rollers 32 slides (arrow A in FIG. 5(d)) so as to align the sheet S1 with the reference position of the image formed by the image forming unit 90.

[0100] By repeatedly executing the above process, the registration unit 30 conveys the sheet S1 conveyed one by one while correcting the position and skew.

[0101] (Conveying operation when the sheet length is less than the specified length) Next, the conveying operation when the sheet length is less than the predetermined length will be described with reference to the flowchart in Fig. 10 and Figs. 7(a-d) and 8(a-d). Figs. 7(a-d) are top views of the registration unit 30 showing the conveying operation of the sheet S2 whose sheet length Ls2 is less than the predetermined length. Figs. 8(a-d) are side views of the registration unit 30 showing the conveying operation of the sheet S2 whose sheet length Ls2 is less than the predetermined length. In Figs. 7(a-d), the rollers in the contact state are shown in black, and the rollers in the separated state are shown only by frame lines.

[0102] If the sheet length is less than the predetermined length, the relay roller pair 315 downstream of the pre-registration roller pair 314 is brought into contact with the sheet S2 (S2b, FIG. 5(a), FIG. 6(a)). After that, the sheet S2 is conveyed in the conveying mode (S2b to S9b) in which the relay roller pair 315 (second roller pair) is brought into contact with the sheet S2.

[0103] 7(a) and 8(a), the sheet S2 conveyed from the conveying unit upstream of the registration unit 30 is conveyed by conveying roller pairs 311 to 313. When the leading edge of the sheet S2 reaches the CIS 34, the side edge position Xd of the sheet S2 is detected by using the CIS 34 (S3b).

[0104] A deviation ΔX between the detected side edge position Xd (FIG. 7A) of sheet S2 and a target position Xn of the side edge of sheet S2 is calculated. In this embodiment, the target position Xn is the side edge position of sheet S2 when the center of sheet S2 in the sheet width direction D2 coincides with the conveying center X0 (a position away from the conveying center X0 by half the sheet width Ws2, called the side edge position).

[0105] Next, a sliding operation (shifting operation, position correction operation) of the pre-registration roller pair 314 is performed to correct the misalignment amount ΔX (S4b, arrow B in FIG. 7(b)). Specifically, after the leading edge of the sheet S2 enters the pre-registration roller pair 314, the conveying roller pair 312, 313 upstream of the pre-registration roller pair 314 are separated (FIG. 8(b)). Then, the pre-registration roller pair 314 is slid so that the side edge of the sheet S2 approaches the target position Xn by compensating for the misalignment amount ΔX. This shifts the sheet position so that the center of the sheet S2 is aligned with the conveying center X0. Conveyance of the sheet S2 continues even while the pre-registration roller pair 314 is sliding.

[0106] Here, the sheet length Ls2 of the sheet S2 is shorter than the path length L0 from the pair of conveying rollers 311, which are always in contact with each other, to the pair of pre-registration rollers 314. Therefore, when the leading edge of the sheet S2 enters the pair of pre-registration rollers 314, the sheet S2 is not sandwiched between the pair of conveying rollers 311. Therefore, in the case of the sheet S2 having the short sheet length Ls2, the pair of pre-registration rollers 314 can start sliding immediately after the leading edge of the sheet S2 enters the pair of pre-registration rollers 314.

[0107] In the case of sheet S2 having a short sheet length Ls2, relay roller pair 315 is in contact with sheet S2, and therefore sliding of pre-registration roller pair 314 is completed before the sheet is sandwiched between relay roller pair 315. In this case, by starting sliding of pre-registration roller pair 314 immediately after the leading edge of sheet S2 enters pre-registration roller pair 314, a period during which sliding of pre-registration roller pair 314 can be performed can be secured.

[0108] Thus, in this embodiment, when conveying a second sheet (S2) whose length is less than a predetermined length, the movement of the first roller pair by the moving means (slide mechanism 36) is started after the leading edge of the second sheet reaches the first roller pair (pre-registration roller pair 314), and the movement of the first roller pair by the moving means is terminated before the leading edge of the second sheet reaches the second roller pair (relay roller pair 315). This makes it possible to complete the position correction of the first sheet while the sheet is not restrained by roller pairs other than the first roller pair, and to avoid damage to the sheet.

[0109] In addition, if the deviation amount ΔX calculated using the CIS 34 is large and the sliding of the pre-registration roller pair 314 cannot be completed before the leading edge of the sheet S2 switches to the relay roller pair 315, an error may be notified and the conveying operation may be stopped.

[0110] After the sliding of the pre-registration roller pair 314 is completed, the sheet S2 enters the relay roller pair 315 and is delivered to the oblique feed unit 300 via the relay roller pair 315 (S5b). If the gap between the transport roller pair is wide with respect to the sheet length, there is a possibility that the reliability of the sheet delivery may decrease. In this embodiment, however, in the case of the sheet S2 having a short sheet length Ls2, the relay roller pair 315 is brought into contact with the sheet S2. This makes it possible to more reliably transport the sheet S2 from the pre-registration roller pair 314 to the oblique feed unit 300 via the relay roller pair 315 even for the sheet S2 having a short sheet length Ls2.

[0111] After the leading edge of sheet S2 reaches the pair of oblique feed rollers 301, the pair of oblique feed rollers 301-303 are switched to the contact state (S6b). At this stage, the force with which the pair of oblique feed rollers 301-303 pinch sheet S2 is weaker than the pinch force of the pair of pre-registration rollers 314, so the conveying force applied to sheet S1 by the pair of pre-registration rollers 314 is dominant, and sheet S2 continues to move in the sheet conveying direction D1. The timing at which sheet S1 is switched to the contact state is determined based on the timing at which the conveying sensor 33 detects the leading edge of sheet S1.

[0112] Thereafter, the pre-registration roller pair 314 is switched to the separated state (S7b, FIG. 8(c)). As a result, the oblique conveying force applied to the sheet S2 by the oblique feed roller pair 301, 302, 303 becomes dominant, and the sheet S2 is conveyed while being shifted toward the side reference plate 304 (arrow E in FIG. 7(c)).

[0113] In this embodiment, the pre-registration roller pair 314 separates at a timing after the leading edge of the sheet S2 reaches the second oblique feed roller pair 302. That is, the pre-registration roller pair 314 separates in a state in which the sheet S2 is sandwiched between the most upstream oblique feed roller pair 301 (first oblique feed roller pair) and the second oblique feed roller pair 302 (second oblique feed roller pair). This makes it possible to more reliably deliver the sheet S2 from the pre-registration roller pair 314 to the oblique feed unit 300.

[0114] In particular, in this embodiment, the distance from the relay roller pair 315 to the most upstream oblique feed roller pair 301 is shorter than the distance from the pre-registration roller pair 314 to the relay roller pair 315, so that it is possible to handle shorter sheets. Note that the timing at which the oblique feed roller pairs 301 to 303 are brought into contact with each other is set after the leading edge of the sheet S2 reaches the second oblique feed roller pair 302, so that the time during which the sheet S2 slips against the oblique feed rollers 301a and 301b can be shortened.

[0115] When the side edge of the sheet S2 abuts against the abutment surface 304a of the side reference plate 304 (S8b), the skew roller pairs 301-303 slip, and the sheet S2 rotates following the abutment surface 304a, thereby correcting the skew of the sheet S2. Even after the skew of the sheet S2 is corrected, the skew roller pairs 301-303 continue to convey the sheet S2 in the sheet conveying direction D1 while keeping the side edge of the sheet S2 in contact with the abutment surface 304a.

[0116] When the leading edge of the sheet S2 reaches the pair of registration rollers 32 (S9b), the pair of skew rollers 301-303 are switched to a separated state (FIGS. 7(d) and 8(d)). After that, the pair of registration rollers 32 slides (arrow A in FIG. 7(d)) ​​so as to align the sheet S1 with the reference position of the image formed by the image forming unit 90.

[0117] By repeatedly executing the above process, the registration unit 30 conveys the sheet S2 conveyed one by one while correcting the position and skew.

[0118] (Advantages of this embodiment) As described above, in this embodiment, the controller 550 changes the mode of the conveying operation depending on whether the sheet length is equal to or greater than a predetermined length.

[0119] In the case of sheet S1 having a relatively long sheet length Ls1, the controller 550 sets the relay roller pair 315 in a separated state, slides the pre-registration roller pair 314 by the slide mechanism 37 based on the detection result of the CIS 34, and then transfers the sheet S1 from the pre-registration roller pair 314 to the oblique feeding unit 300. In other words, in the case of conveying a first sheet having a first length in the sheet conveying direction, the control means of this embodiment sets the second roller pair in a separated state by the separating means, moves the first roller pair in the sheet width direction by the moving means based on the detection result of the detecting means, and then transfers the first sheet from the first roller pair to the oblique feeding means.

[0120] As a result, for a comparatively long sheet S1, by separating the relay roller pair 315, it is possible to secure time for sliding the pre-registration roller pair 314. In addition, since the sheet S1 is comparatively long, the sheet S1 can be smoothly delivered to the oblique feeding unit 300 even in a state where the relay roller pair 315 is separated.

[0121] Furthermore, in the case of sheet S2 having a relatively short sheet length Ls2, the controller 550 places the relay roller pair 315 in contact, slides the pre-registration roller pair 314 by the slide mechanism 37 based on the detection result of the CIS 34, and transfers the sheet S2 from the pre-registration roller pair 314 to the oblique feeding unit 300 via the relay roller pair 315. In other words, in the case of transporting a second sheet having a second length in the sheet transport direction shorter than the first length, the control means of this embodiment places the second roller pair in contact with the separation means, moves the first roller pair in the sheet width direction by the moving means based on the detection result of the detection means, and then transfers the second sheet from the first roller pair to the oblique feeding means via the second roller pair.

[0122] This allows the relatively short sheet S2 to be more reliably delivered to the oblique feeding unit 300 via the relay roller pair 315. Also, if the sheet S2 is short, there is a relatively large amount of time before the leading edge of the sheet S2 reaches the relay roller pair 315 in contact with the sheet S2, so that it is possible to ensure time for the pre-registration roller pair 314 to slide even in the state where the relay roller pair 315 is in contact with the sheet S2.

[0123] In this manner, according to this embodiment, it is possible to accommodate sheets of various sizes, and by sliding the pair of pre-registration rollers 314 before the oblique feeding unit 300 starts oblique feeding, it is possible to reduce variation in the transport timing.

[0124] (Setting conditions for the specified length) As described above, in this embodiment, depending on whether the sheet length is equal to or greater than a predetermined length, a conveying mode in which the relay roller pair 315 (second roller pair) is in contact with the sheet is switched to a conveying mode in which the relay roller pair 315 is in a separated state. A preferable setting value of the predetermined length, which is a threshold for switching the conveying mode, will be described below. Note that which conveying mode is applied when the sheet length is equal to the predetermined length may be changed.

[0125] The predetermined length is preferably equal to or less than the distance in the sheet conveying direction D1 from the conveying roller pair 311, which is always in contact, to the pre-registration roller pair 314 (equal to or less than the distance in the sheet conveying direction from the upstream roller pair to the first roller pair, equal to or less than L0 in FIG. 6B). In this case, for a long sheet whose leading edge has already passed the pre-registration roller pair 314 when its trailing edge leaves the conveying roller pair 311, a conveying mode in which the relay roller pair 315 is in a separated state is always applied. This makes it possible to secure time for the pre-registration roller pair 314 to slide for the long sheet.

[0126] The predetermined length is set to be longer than the distance in the sheet conveying direction D1 from the pre-registration roller pair 314 to the most upstream oblique feed roller pair 301 of the oblique feed unit 300 (the distance in the sheet conveying direction from the first roller pair to the oblique feed means). This allows the sheet to be delivered from the pre-registration roller pair 314 to the oblique feed unit 300 even in a state in which the relay roller pair 315 is separated.

[0127] Furthermore, the predetermined length is preferably set longer than the distance in the sheet conveying direction D1 from the pre-registration roller pair 314 to the second oblique conveying roller pair 302 of the oblique conveying unit 300 (the distance in the sheet conveying direction from the first roller pair to the second oblique conveying roller pair). Since the oblique conveying roller pairs 301 to 303 are configured to convey the sheet while slipping against the sheet, the clamping force of the oblique conveying roller pairs 301 to 303 is usually weaker than the clamping force of the other conveying roller pairs. Therefore, by setting the predetermined length longer than the above distance, the sheet can be delivered from the pre-registration roller pair 314 to the oblique conveying unit 300 more reliably. That is, in a conveying mode in which the relay roller pair 315 is in a separated state, the sheet can be clamped by at least two oblique conveying roller pairs 301 and 302 before the rear end of the sheet passes through the pre-registration roller pair 314, so that the possibility of conveying failure is reduced.

[0128] In a configuration example in which this embodiment is applied, the predetermined length is set to 295.7 mm. This means that when the sheet length is A4 size in long-side feed or A3 size in short-side feed, or when the sheet length is longer than that, a conveying mode in which the relay roller pair 315 is in a separated state is applied. The value of the predetermined length can be appropriately selected depending on the specific configuration of the image forming apparatus.

[0129] (Other embodiments) In the above-described embodiment, the configuration in which the CIS 34 is used as the detection means for detecting the sheet position in the sheet width direction D2 has been exemplified. Instead of the CIS 34, for example, a CCD type image sensor may be used. Also, a photoelectric sensor for detecting the sheet at a predetermined position (target position) in the sheet width direction D2 may be used as the detection means. In that case, after the movement of the pre-registration roller pair 314 is started, the movement of the pre-registration roller pair 314 may be terminated based on the detection of the side edge of the sheet by the photoelectric sensor. Also, the arrangement of the detection means is not limited to the upstream of the pre-registration roller pair 314, but may be downstream of the pre-registration roller pair 314.

[0130] In the above embodiment, the target position Xn when correcting the sheet position in the sheet width direction D2 by the pair of pre-registration rollers 314 is set to the side edge position of the sheet when the sheet is located on the conveying center. The target position is not limited to the target position based on the conveying center, but if the target position is set to a position a preset distance away from the side reference plate 304, it is possible to reduce variation in conveying timing.

[0131] In the above-described embodiment, the printer 1 is exemplified as an intermediate transfer type electrophotographic device as an image forming apparatus, but the technology disclosed herein can be applied to other image forming apparatuses. The "image forming apparatus" includes commercial printing presses (production printers), office or home single-function printers, copiers, and multifunction machines. The image forming means is not limited to an intermediate transfer type electrophotographic unit, and may be, for example, a direct transfer type electrophotographic unit, an inkjet type image forming unit, or an offset printing mechanism.

[0132] Furthermore, the "sheet transport device" is not limited to a device that transports a sheet toward an image forming means in an image forming apparatus, but may be, for example, a device that transports a sheet in a sheet processing device. The sheet processing device is a device (also called a finisher) that is used in connection with the main body of the image forming apparatus in order to perform processes such as bookbinding and sorting on sheets after image formation. The sheet transport device may also be a device that is used independently of the image forming apparatus (for example, a sorting device that sorts sheet-like items such as mail, or an inspection device that inspects sheet-like products while transporting them).

[0133] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0134] Summary of the Disclosure The present disclosure includes at least the following configurations.

[0135] (Configuration 1) a first roller pair for conveying a sheet; a second roller pair disposed downstream of the first roller pair in a sheet conveying direction and configured to convey a sheet; an abutting portion against which an end of the sheet in a sheet width direction perpendicular to the sheet conveying direction is abutted; a skew conveying means arranged downstream of the second roller pair in the sheet conveying direction, moving the sheet toward the abutting portion in the sheet width direction downstream in the sheet conveying direction and conveying the sheet while abutting an end of the sheet against the abutting portion; a detection means for detecting a position of the sheet in the sheet width direction; a moving means for moving the first roller pair in the sheet width direction; a separation means for switching the second roller pair between a contact state in which the rollers are in contact with each other and a separation state in which the rollers are separated from each other; a control means for controlling the moving means and the separating means, The control means When a first sheet having a first length in the sheet conveying direction is conveyed, the separating means places the second roller pair in the separated state, and the moving means moves the first roller pair in the sheet width direction based on a detection result of the detection means, and then the first sheet is delivered from the first roller pair to the oblique conveying means, When a second sheet having a second length in the sheet conveying direction that is shorter than the first length is conveyed, the second roller pair is brought into the contact state by the separating means, and the first roller pair is moved in the sheet width direction by the moving means based on the detection result of the detection means, and the second sheet is delivered from the first roller pair to the oblique conveying means via the second roller pair. A sheet conveying device comprising:

[0136] (Configuration 2) The sheet conveying device further includes an upstream roller pair disposed upstream of the first roller pair in the sheet conveying direction and configured to be in constant contact with each other, The control means when conveying the first sheet, after a leading edge of the first sheet reaches the first roller pair and a trailing edge of the first sheet leaves the upstream roller pair, the moving unit starts moving the first roller pair; when conveying the second sheet, after a leading edge of the second sheet reaches the first roller pair, the moving unit starts moving the first roller pair; 2. The sheet conveying device according to configuration 1,

[0137] (Configuration 3) The control means When the first sheet is conveyed, the movement of the first roller pair by the moving means is terminated before a leading edge of the first sheet reaches the oblique conveying means; when conveying the second sheet, the movement of the first roller pair by the moving means is terminated before a leading edge of the second sheet reaches the second roller pair; 3. The sheet conveying device according to configuration 2.

[0138] (Configuration 4) the control means is configured to, when a length of the sheet in the sheet conveying direction is equal to or longer than a predetermined length, cause the second roller pair to be in the separated state by the spacing means and to convey the sheet, and when the length of the sheet in the sheet conveying direction is less than the predetermined length, cause the second roller pair to be in the contact state by the spacing means and to convey the sheet, the predetermined length is longer than a distance in the sheet conveying direction from the first roller pair to the oblique conveying means and is equal to or shorter than a distance in the sheet conveying direction from the upstream roller pair to the first roller pair; 4. The sheet conveying device according to configuration 2 or 3.

[0139] (Configuration 5) At least one roller pair is disposed between the upstream roller pair and the first roller pair in the sheet conveying direction, and is configured to be capable of contacting and separating the rollers from each other, the control means separates the at least one roller pair before causing the moving means to start moving the first roller pair. 5. The sheet conveying device according to any one of configurations 2 to 4.

[0140] (Configuration 6) The oblique feed means includes a first oblique feed roller pair and a second oblique feed roller pair disposed downstream of the first oblique feed roller in the sheet conveying direction, a distance in the sheet conveying direction from the second roller pair to the first oblique feed roller pair is shorter than a distance in the sheet conveying direction from the first roller pair to the second roller pair; 6. The sheet conveying device according to any one of configurations 1 to 5.

[0141] (Configuration 7) The control means When the first sheet is conveyed, the rollers of the first roller pair are separated from each other after a leading edge of the first sheet reaches the second oblique feed roller, thereby starting the oblique feed of the first sheet by the first oblique feed roller pair and the second roller pair; When the second sheet is conveyed, the rollers of the first roller pair and the second roller pair are separated from each other after the leading edge of the second sheet reaches the second oblique feed roller, thereby starting the oblique feed of the first sheet by the first oblique feed roller pair and the second roller pair. 7. The sheet conveying device according to configuration 6,

[0142] (Configuration 8) The sheet conveying device further includes an upstream roller pair disposed upstream of the first roller pair in the sheet conveying direction and configured to be in constant contact with each other, the control means is configured to, when a length of the sheet in the sheet conveying direction is equal to or longer than a predetermined length, cause the second roller pair to be in the separated state by the spacing means and to convey the sheet, and when the length of the sheet in the sheet conveying direction is less than the predetermined length, cause the second roller pair to be in the contact state by the spacing means and to convey the sheet, the predetermined length is longer than a distance in the sheet conveying direction from the first roller pair to the second oblique feed roller pair and is equal to or shorter than a distance in the sheet conveying direction from the upstream roller pair to the first roller pair; 8. The sheet conveying device according to configuration 6 or 7,

[0143] (Configuration 9) the control means causes the moving means to move the first roller pair in the sheet width direction so that the side edge of the sheet approaches a target position that is a preset distance away from the abutting portion in the sheet width direction, based on a detection result of the detection means. 9. The sheet conveying device according to any one of configurations 1 to 8.

[0144] (Configuration 10) the target position is a side end position of the sheet when a center of the sheet in the sheet width direction coincides with a conveyance center of a conveyance path along which the sheet is conveyed to the first roller pair; 10. The sheet conveying device according to configuration 9,

[0145] (Configuration 11) The detection unit is disposed upstream of the first roller pair in the sheet conveying direction. 11. The sheet conveying device according to any one of configurations 1 to 10.

[0146] (Configuration 12) The detection means is an image sensor having a plurality of light receiving elements arranged along the sheet width direction. 12. The sheet conveying device according to any one of configurations 1 to 11.

[0147] (Configuration 13) A sheet conveying device according to any one of configurations 1 to 12, an image forming unit for forming an image on the sheet conveyed by the sheet conveying device; An image forming apparatus comprising: [Explanation of symbols]

[0148] 34...detection means (CIS) / 37...movement means (slide mechanism) / 304a...butting portion (butting surface) / 311...upstream roller pair (transport roller pair) / 314...first roller pair (pre-registration roller pair) / 315...second roller pair (relay roller pair) / 300...skew unit (skew means) / 550...control means (controller) / 650...separation means (separation mechanism)

Claims

1. A first roller pair for conveying a sheet, A second roller pair that is disposed downstream of the first roller pair in the sheet conveyance direction and conveys the sheet, A butting portion against which an end portion of the sheet in the sheet width direction orthogonal to the sheet conveyance direction abuts, A skew feeding means that is disposed downstream of the second roller pair in the sheet conveyance direction and moves the sheet in the sheet width direction toward the side of the butting portion downstream in the sheet conveyance direction, and conveys the sheet while butting an end portion of the sheet against the butting portion, Detection means for detecting the position of the sheet in the sheet width direction, Moving means for moving the first roller pair in the sheet width direction, Separation means for switching the second roller pair between a contacting state in which the rollers contact each other and a separated state in which the rollers are separated from each other, Control means for controlling the moving means and the separation means, and comprising, The control means, When conveying a first sheet whose length in the sheet conveyance direction is a first length, after moving the first roller pair in the sheet width direction by the moving means based on the detection result of the detection means, passing the first sheet from the first roller pair through the second roller pair in the separated state and conveying the first sheet to the skew feeding means, When conveying a second sheet whose length in the sheet conveyance direction is a second length shorter than the first length, after moving the first roller pair in the sheet width direction by the moving means based on the detection result of the detection means, conveying the second sheet from the first roller pair through the second roller pair in the contacting state to the skew feeding means, A sheet conveyance device characterized by the above.

2. Further comprising an upstream roller pair that is disposed upstream of the first roller pair in the sheet conveyance direction and is configured such that the rollers are always in contact with each other, The control means, When conveying the first sheet, starting the movement of the first roller pair by the moving means based on the fact that the leading end of the first sheet has reached the first roller pair and the trailing end of the first sheet has passed through the upstream roller pair, When conveying the second sheet, starting the movement of the first roller pair by the moving means based on the fact that the leading end of the second sheet has reached the first roller pair, The sheet conveyance device according to claim 1, characterized by the above.

3. The control means, When conveying the first sheet, before the leading edge of the first sheet reaches the skew feeding means, the movement of the first roller pair by the moving means is terminated. When conveying the second sheet, before the leading edge of the second sheet reaches the second roller pair, the movement of the first roller pair by the moving means is terminated. The sheet conveying device according to claim 2, characterized in that.

4. When the length of the sheet in the sheet conveying direction is equal to or greater than a predetermined length, the control means executes sheet conveyance with the second roller pair in the separated state by the separating means, and when the length in the sheet conveying direction is less than the predetermined length, the control means is configured to execute sheet conveyance with the second roller pair in the contacting state by the separating means. The predetermined length is longer than the distance in the sheet conveying direction from the first roller pair to the skew feeding means and equal to or less than the distance in the sheet conveying direction from the upstream roller pair to the first roller pair. The sheet conveying device according to claim 2, characterized in that.

5. Further comprising at least one roller pair disposed between the upstream roller pair and the first roller pair in the sheet conveying direction, and configured such that the rollers can contact and separate from each other. Before starting the movement of the first roller pair by the moving means, the control means separates the at least one roller pair. The sheet conveying device according to claim 2, characterized in that.

6. The skew feeding means includes a first skew feeding roller pair and a second skew feeding roller pair disposed downstream of the first skew feeding roller pair in the sheet conveying direction. The distance in the sheet conveying direction from the second roller pair to the first skew feeding roller pair is shorter than the distance in the sheet conveying direction from the first roller pair to the second roller pair. The sheet conveying device according to claim 1, characterized in that.

7. The control means When conveying the first sheet, after the leading edge of the first sheet reaches the second skew feeding roller pair, the rollers of the first roller pair are separated from each other, thereby starting the skew feeding of the first sheet by the first skew feeding roller pair and the second skew feeding roller pair. When transporting the second sheet, after the leading edge of the second sheet reaches the second pair of skew rollers, the rollers of the first pair of rollers and the second pair of rollers are separated from each other, thereby starting the skew feeding of the second sheet by the first pair of skew rollers and the second pair of skew rollers. The sheet conveying device according to claim 6, characterized in that.

8. Further comprising an upstream pair of rollers arranged upstream of the first pair of rollers in the sheet conveying direction and configured such that the rollers are always in contact with each other. When the length of the sheet in the sheet conveying direction is equal to or greater than a predetermined length, the control means executes the conveyance of the sheet with the second pair of rollers in the separated state by the separation means, and when the length in the sheet conveying direction is less than the predetermined length, the control means is configured to execute the conveyance of the sheet with the second pair of rollers in the contact state by the separation means. The predetermined length is longer than the distance in the sheet conveying direction from the first pair of rollers to the second pair of skew rollers and equal to or less than the distance in the sheet conveying direction from the upstream pair of rollers to the first pair of rollers. The sheet conveying device according to claim 6, characterized in that.

9. Based on the detection result of the detection means, the control means moves the first pair of rollers in the sheet width direction by the moving means so that the side edge of the sheet approaches a target position that is separated from the abutting portion by a preset distance in the sheet width direction. The sheet conveying device according to claim 1, characterized in that.

10. The target position is the side edge position of the sheet when the center of the sheet in the sheet width direction coincides with the conveyance center of the conveyance path along which the sheet is conveyed to the first pair of rollers. The sheet conveying device according to claim 9, characterized in that.

11. The detection means is arranged upstream of the first pair of rollers in the sheet conveying direction. The sheet conveying device according to claim 1, characterized in that.

12. The detection means is a line sensor having a plurality of light receiving elements arranged along the sheet width direction. The sheet conveying device according to claim 1, characterized in that.

13. A sheet conveying device according to any one of claims 1 to 12, Image forming means for forming an image on a sheet conveyed by the sheet conveying device, An image forming apparatus, characterized by comprising.

Images