Sheet transport 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 for conveying a sheet and an image forming device for forming an image on the sheet.

Background Art

[0002] Conventionally, there is known a so-called side registration type sheet conveying device that corrects skewing of a sheet by obliquely conveying the sheet by an oblique conveying roller and abutting its side edge against a reference member. 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 the sliding movement of a pair of conveying rollers (slide rollers) provided upstream of the oblique conveying roller in the sheet conveying direction. According to this document, by correcting the sheet position before the start of oblique conveyance, the distance that the sheet is conveyed while abutting against the reference member approaches a constant value, so that the variation in conveyance timing downstream of the oblique conveying roller is reduced, and improvement in productivity and the like becomes possible.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration described in the above document, when correcting the sheet position with a slide roller, the slide roller is moved while the sheet is not constrained by the upstream transport roller pair or transport guide, etc., to avoid damage to the sheet or improper correction. Here, in the case of a sheet with a relatively long length in the sheet transport direction, the timing of its release from the upstream transport roller pair etc. is delayed compared to a short sheet, so it is desirable to ensure sufficient movement time for the slide roller. However, if the distance from the slide roller to the inclined transport roller is widened to ensure sufficient movement time for the slide roller, it becomes difficult to transport short sheets.

[0005] Therefore, the present invention aims to provide a configuration that can accommodate sheets of various sizes while reducing variations in transport timing. [Means for solving the problem]

[0006] One aspect of the present invention includes a first pair of rollers for conveying a sheet, a second pair of rollers positioned downstream of the first pair of rollers in the sheet conveying direction and for conveying a sheet, a stopper portion against which the end of the sheet in the sheet width direction perpendicular to the sheet conveying direction abuts, an oblique conveying means positioned downstream of the second pair of rollers in the sheet conveying direction and for moving the sheet toward the stopper portion in the sheet width direction toward the downstream of the sheet conveying direction, conveying the sheet while abutting the end of the sheet toward the stopper portion, a detection means for detecting the position of the sheet in the sheet width direction, a moving means for moving the first pair of rollers in the sheet width direction, and the second pair of rollers 、 The contact state in which rollers come into contact with each other The aforementioned The system includes a separation means for switching between a separated state where rollers are separated from each other and a separated state, and a control means for controlling the moving means and the separation means, wherein the control means controls when transporting a first sheet whose length in the sheet transport direction is a first length. ,before 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 through the second pair of rollers which are in the separated state The first sheet is fed into the aforementioned oblique feeding means. TransportWhen transporting a second sheet whose length in the sheet transport direction is shorter than the first length: ,before Based on the detection result of the detection means, the moving means moves the first roller pair in the sheet width direction. after From the previous 1st roller pair In the aforementioned contact state The second sheet is fed to the oblique feeding means via the second roller pair. Transport This is a sheet conveying device characterized by the following: [Effects of the Invention]

[0007] According to the present invention, it is possible to accommodate sheets of various sizes while reducing variations in transport timing. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of a printer according to one embodiment. [Figure 2] A perspective view of a registration unit according to one embodiment. [Figure 3] A side view of a registration unit according to one embodiment. [Figure 4] A top view of a registration unit according to one embodiment. [Figure 5] Top views (a-d) illustrating the operation of a registration unit according to one embodiment. [Figure 6] Side views (a-d) illustrating the operation of a registration unit according to one embodiment. [Figure 7] Top views (a-d) illustrating the operation of a registration unit according to one embodiment. [Figure 8] Side views (a-d) illustrating the operation of a registration unit according to one embodiment. [Figure 9] A block diagram showing the control configuration of a registration unit according to one embodiment. [Figure 10] A flowchart illustrating a control method for a registration unit according to one embodiment. [Figure 11]Side views (a, b) for explaining the drive configuration and separation configuration of a pair of conveyance rollers according to an embodiment. [Figure 12] Perspective view for explaining the drive configuration of a pair of pre-registration rollers according to an embodiment. [Figure 13] Perspective view for explaining the slide configuration of a pair of pre-registration rollers according to an embodiment. [Figure 14] Perspective view (a) and cross-sectional view (b) for explaining the separation configuration of a pair of pre-registration rollers according to an embodiment.

Mode for Carrying Out the Invention

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

[0010] (Image Forming Apparatus) The printer 1 as an image forming apparatus according to an 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 units for feeding a sheet and forming an image, and a second housing 1b having units for fixing and cooling.

[0011] The first housing 1a includes feed units 10a, 10b, extraction units 20a, 20b, a registration unit 30, an image forming unit 90, a pre-fixing conveyance unit 57, and a first duplex conveyance unit 60. The image forming unit 90 is an example of an image forming means for forming an image on a sheet.

[0012] The second housing 1b includes a fixing unit 100, a cooling unit 110, a branch conveyance unit 120, a reverse conveyance unit 130, a second duplex conveyance unit 150, and a decal unit 170.

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

[0014] The process cartridge 99Y includes a photosensitive drum 91 as an image carrier, a charger, a developer 92, and a cleaner 95. The photosensitive drum 91 is constructed by coating an organic photoconductive layer on the outer circumference of an aluminum cylinder and is rotationally driven 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 they produce different color images.

[0015] The image forming unit 90 also has an intermediate transfer belt 50 that rotates in the direction of arrow T by the drive roller 52. The intermediate transfer belt 50 is the intermediate transfer body in this embodiment. The intermediate transfer belt 50 is an endless belt member that is wrapped around the tension roller 51, the drive roller 52, and the secondary transfer inner roller 53. Inside the intermediate transfer belt 50 are four primary transfer rollers 55 corresponding to each photosensitive drum 91. Outside the intermediate transfer belt 50, a secondary transfer outer roller 54 is provided opposite the secondary transfer inner roller 53. A secondary transfer section T2 is formed as a nip between the secondary transfer outer roller 54 and the secondary transfer inner roller 53, which is the transfer section on which the image is transferred to the sheet. A belt cleaner 56 is also positioned 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 section T2 toward the sheet discharge port provided on the side of the first housing 1a (the side facing the second housing). 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. In addition, a portion of the first double-sided transport unit 60 is used as a transport path for the sheet S supplied from the feeding unit 10b.

[0017] The feeding unit 10a includes a lift plate 11a that moves up and down while loading sheets S, a pickup roller 12a that feeds the sheets S loaded on the lift plate 11a, and a pair of separation rollers 13a that separates the fed sheets one by one. Similarly, the feeding unit 10b includes a lift plate 11b that moves up and down while loading sheets S, a pickup roller 12b that feeds the sheets S loaded on the lift plate 11b, and a pair of separation rollers 13b that separates the fed sheets one by one.

[0018] The feeding units 10a and 10b are examples of feeding means for feeding sheets S to the image forming unit 90. As a feeding means, for example, a manual feeding device that feeds sheets from a manual feed tray (multipurpose tray) that is openable and closable on the side of the first housing 1a may be used. Alternatively, a large-capacity feeding device (optional feeder) connected to the first housing 1a may be used as a feeding means. The sheets S used as recording material can be a variety of sheet materials of different sizes and materials, such as plain paper and cardboard, plastic film, cloth, sheet materials with surface treatments such as 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 sheets S supplied from the feeding units 10a and 10b toward the secondary transfer section T2. ​​The registration unit 30 includes 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. Details of the registration unit 30 will be described later.

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

[0021] The cooling unit 110 has drive roller 112 b The upper cooling belt 111 rotates in the direction of arrow T. band drive roller 112 a The upper cooling belt 111 b The lower cooling belt 111 rotates as if accompanying it. a It has the upper cooling belt 111 b The heatsink 113 is positioned so as to be in contact with the inner surface. The heatsink 113 and the cooling belt 111 are located above the sheet S. b The sheet S is cooled by dissipating the heat received through it.

[0022] The branching transport unit 120 has a transport path that branches the transport path of the sheet S, and a switching guide that switches the transport path. The reversing transport unit 130 transports the sheet S received from the branching transport unit 120 in a switchback manner and sends it back to the branching transport unit 120, or sends it to the second double-sided transport unit 150. The second double-sided transport unit 150 is connected to the first double-sided transport unit 60 of the first housing 1a. The decal unit 170 has a pair of decal 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 process) Next, the image forming operation of printer 1 will be described. When the control unit of 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 drive of each photosensitive drum 91 and the intermediate transfer belt 50 is started. Also, when an image signal (video signal) based on the image information is transmitted from the control unit to the exposure device 93, the exposure device 93 irradiates the photosensitive drum 91 with laser light corresponding to the image signal. As a result, the surface of the photosensitive drum 91, which has been pre-charged to a predetermined polarity and potential by the charger, is exposed, and an electrostatic latent image is formed on the surface of the photosensitive drum 91. The developer 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 each process cartridge 99Y, 99M, 99C, and 99K are first transferred to the intermediate transfer belt 50 by the primary transfer roller 55. At this time, multiple transfers are performed so that the images of each color overlap, forming a full-color image on the intermediate transfer belt 50. The image supported on the intermediate transfer belt 50 is transported to the secondary transfer section T2 by the rotation of the intermediate transfer belt 50. Toner remaining on the photosensitive drum 91 that is not transferred to the intermediate transfer belt 50 is collected by the cleaner 95.

[0025] In parallel with the image formation process in the image forming unit 90, one sheet S is fed at a time from either the feeding unit 10a or 10b, and the sheet S is transported to the registration unit 30 via the pair of pull-out rollers 21a and 21b.

[0026] The registration unit 30 corrects for misalignment and skew of the sheet S and transports the sheet S to the secondary transfer unit T2 at a predetermined transport timing. In the secondary transfer unit T2, a transfer voltage is applied to the secondary transfer outer roller 54, thereby transferring the image from the intermediate transfer belt 50 to the sheet S. Toner that remains on the intermediate transfer belt 50 without being transferred to the sheet S is collected by the belt cleaner 56.

[0027] The sheet S, having passed through the secondary transfer section T2, is transported to the fixing unit 100 by the pre-fixing transport unit 57. Fixing unit 10 0 The fixing unit 100 performs a fixing process by heating and pressurizing the image on the sheet S while the sheet S is being transported by the fixing roller pair 101. As a result, the toner melts and then solidifies, fixing the image to the sheet S. After passing through the fixing unit 100, the sheet S is cooled by the cooling unit 110 and the upper cooling belt 111 b and lower cooling belt 111 a It is cooled while being transported.

[0028] Next, the branching transport unit 120 selects a path for transporting the sheet S to either the decal unit 170 (discharge path) or the inversion transport unit 130 (inversion path). If an image is to be formed on only one side (first side) of the sheet S, the sheet S with the image formed on the first side is transported from the branching transport unit 120 to the decal unit 170, where the curl is corrected and then the sheet S is discharged outside the device as a finished product. If optional equipment such as a finisher or a large-capacity stacker is connected to the second housing 1b, the sheet S as a finished product is handed over to the optional equipment.

[0029] When forming images on both sides of a sheet S, the sheet S with an image formed on the first side is transported to the inversion transport unit 130 by the branching transport unit 120, where it is transported in a switchback manner. Subsequently, the sheet S is transported from the inversion 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 section 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 images formed on both the first and second sides is transported from the branching transport unit 120 to the decal unit 170, where the curl is corrected and the finished product is discharged outside the device or handed over to an optional device.

[0030] Furthermore, by having the resulting sheet be transported in a switchback manner by the reversal transport unit 130 before being handed over to the decal unit 170, it is also possible to eject the sheet so that the side with the image formed immediately beforehand faces downwards (so-called face-down ejection).

[0031] (Registration Unit) The specific configuration of the registration unit 30, which is a sheet conveying device in this embodiment, will now be described. Figure 2 is a perspective view of the registration unit 30. Figure 3 is a side view of the registration unit 30 as seen from one side in the sheet width direction D2. Figure 4 is a top view of the registration unit 30. In Figures 2 to 4, the illustration of conveying guides that form the sheet conveying path and bearing members that support each roller is omitted.

[0032] In the following description, the direction in which the sheet is transported along the sheet transport path in the registration unit 30 is referred to as the sheet transport direction D1. The direction perpendicular to the sheet transport 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 transport direction D1 is the secondary scanning direction during image formation.

[0033] As shown in Figures 2 to 4, the registration unit 30 has transport roller pairs 311, 312, 313, a pre-registration roller pair (hereinafter referred to as the pre-registration roller pair) 314, and an intermediate roller pair 315. The registration unit 30 also has oblique feed roller pairs 301, 302, 303, and a registration roller pair (hereinafter referred to as the registration roller pair) 32. The registration unit 30 also has slide mechanisms 37, 38, 39, a side reference plate 304, a transport sensor 33, a CIS 34, and a registration sensor 35. The oblique feed roller pairs 301 to 303 constitute an oblique feed unit 300 that obliquely feeds the sheet and abuts it against the side reference plate 304.

[0034] The pre-regulating roller pair 314 is an example of a first roller pair. The intermediate roller pair 315 is an example of a second roller pair positioned downstream of the first roller pair in the sheet transport direction D1. The sliding mechanism 37 of the pre-regulating roller pair 314 is an example of a moving means. The separation mechanism of the intermediate roller pair 315 is an example of a separation means. The oblique transport unit 300 is an example of an oblique transport means. The abutment surface 304a of the side reference plate 304 is an example of an abutment portion. The CIS 34 is an example of a detection means (position detection means) for detecting the position of the sheet in the sheet width direction D2. The first transport roller pair 311 is an example of an upstream roller pair positioned upstream of the first roller pair in the sheet transport direction D1.

[0035] In the sheet transport direction D1, the second transport roller pair 312, the third transport roller pair 313, the pre-registration roller pair 314 (the fourth transport roller pair), and the intermediate roller pair 315 (the fifth transport roller pair) are arranged in order downstream from the first transport roller pair 311. Also, in the sheet transport direction D1, the first oblique transport roller pair 301, the second oblique transport roller pair 302, the third oblique transport roller pair 303, and the registration roller pair 32 are arranged in order downstream from the intermediate roller pair 315. The registration unit 30 transports the sheet from the upstream side to the downstream side in the sheet transport direction D1, while passing the sheet between these multiple roller pairs.

[0036] Furthermore, the distance D1 in the sheet transport direction from the intermediate roller pair 315 to the uppermost diagonal transport roller pair 301 of the diagonal transport unit 300 is set to be shorter than the distance D1 in the sheet transport direction from the pre-resist roller pair 314 to the intermediate roller pair 315. In other words, the distance in the sheet transport direction from the second roller pair to the first diagonal transport roller pair is shorter than the distance in the sheet transport direction from the first roller pair to the second roller pair. As a result, in the transport mode in which the intermediate roller pair 315 is in contact with the sheet, as will be described later, the sheet can be reliably transferred from the intermediate roller pair 315 (second roller pair) to the diagonal transport unit 300 even when the sheet length is short.

[0037] The second and third transport roller pairs 312, 313, the pre-resist roller pair 314, the intermediate roller pair 315, and each of the oblique transport roller pairs 301 to 303 are configured to be able to come into contact with and separate from each other by separation motors 511 to 517. That is, each roller pair is configured to be able to switch between a contact state (nip state, pressurized state) in which the rollers come into contact with each other so that the sheet can be gripped and transported, and a separated state (open state, pressure released state) in which the rollers are separated from each other. Each roller pair can be switched between the contact state and the separated state independently of each other. Note that the separated state is not necessarily a state in which there is a gap between the rollers. The separated state may be a state in which the contact pressure between the rollers is weakened compared to the contact state so that the force applied to the sheet from the roller pair does not substantially affect the transport of the sheet.

[0038] In this embodiment, the uppermost transport roller pair 311 and the register roller pair 32 do not have a separation mechanism and are always in contact with each other.

[0039] By arranging at least one pair of rollers (312, 313) that can be separated between the transport roller pair 311 and the pre-regulating roller pair 314, which are fixed in contact, it becomes easier to handle long sheets. In other words, when the pre-regulating roller pair 314 is slid as described later, it is possible to separate the roller pair between the transport roller pair 311 and the pre-regulating roller pair 314. If handling longer sheets is required, the transport roller pair 311 may also be configured to be separable. Furthermore, if the upper limit of the sheet length to be handled is shorter than in this embodiment, the separation mechanism for the transport roller pair 312, 313 may be omitted.

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

[0041] The side reference plate 304 has a butt surface 304a which serves as a butt portion against which one end of the sheet in the sheet width direction D2 (hereinafter referred to as the side end) abuts. The butt surface 304a is a surface that extends in the sheet transport direction D1 and serves as a reference surface for correcting the skewness of the sheet when the side end of the sheet abuts against it by the skew transport unit 300. When viewed from the upstream side in the sheet transport direction D1, the side reference plate 304 is a U-shaped member in cross-section, with surfaces extending from the upper and lower ends of the butt surface 304a to the other side in the sheet width direction D2 (upper side in Figure 4). The side reference plate 304 can be made, for example, from die-cast aluminum, with the butt surface 304a precisely machined and 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 sliding mechanism 38 (Figure 4) (arrow C in Figures 2 and 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 distance from the transport center X0 (Figure 4) in the sheet width direction D2 that is half the sheet width plus a margin for oblique transport. As a result, regardless of the sheet width, the distance traveled in the sheet width direction D2 when the sheet abuts the side reference plate 304 by oblique transport becomes approximately constant, thus improving the accuracy of oblique correction and increasing productivity. Here, the transport center X0 is the central position in the sheet width direction D2 in the sheet transport path upstream of the pre-regulator pair 314. The rollers (outer circumference that contacts the sheet) of the transport roller pairs 311 to 313 are arranged symmetrically with respect to the transport center X0.

[0043] Each of the inclined roller pairs 301, 302, and 303 has inclined rollers 301a, 302a, and 303a positioned diagonally with respect to the sheet conveying direction D1, and driven rollers 301b, 302b, and 303b facing the inclined rollers 301a, 302a, and 303a. The rotation axes of the inclined rollers 301a, 302a, and 303a are inclined diagonally with respect to the sheet width direction D2. That is, the inclined rollers 301a, 302a, and 303a This applies a conveying force to the sheet in a direction that is oblique to the sheet conveying direction D1, so as to move downstream in the sheet conveying direction D1 toward one side of the sheet width direction D2 (towards the side of the side reference plate 304, the lower side in Figure 4).

[0044] The diagonal conveying roller pairs 301, 302, and 303 apply a diagonal conveying force to the sheet relative to the sheet conveying direction D1, thereby conveying the sheet while bringing it closer to the side reference plate 304. Furthermore, even after the side edge of the sheet contacts the abutment surface 304a of the side reference plate 304, the diagonal conveying roller pairs 301, 302, and 303 continue to convey the sheet downstream in the sheet conveying direction D1 while keeping the side edge abutting against the abutment surface 304a. As a result, the diagonal alignment of the side edge of the sheet is corrected relative to the abutment surface 304a of the side reference plate 304.

[0045] In this embodiment, the rotation axis direction of the driven rollers 301b, 302b, and 303b is substantially parallel to the sheet width direction D2. However, the driven rollers 301b, 302b, and 303b may also have the same inclination as the inclined rollers 301a, 302a, and 303a. Furthermore, the number and arrangement of the inclined roller pairs can be changed as appropriate. For example, an additional pair of inclined rollers may be added in the same position as the inclined roller pair 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] Inclined feed rollers 301a, 302a, 303 a The driven rollers 301b, 302b, and 303b are connected to a separation mechanism, and the oblique feed rollers 301a, 302a, and 303 a The rollers are provided to be movable so as to contact and separate from each other. The separation mechanism consists 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 the separation motor. Depending on the rotation angle of the separation motor, the arm swings and the driven rollers 301b, 302b, and 303b move, so that the inclined feed roller pair 301, 302, and 303 switches between a contact state and a separated state.

[0047] The register roller pair 32 is configured to be movable (slidable) in the sheet width direction D2 by a sliding mechanism 39 (arrow A in Figures 2 and 4). The register roller pair 32 transports the skew-corrected sheet S toward the secondary transfer section T2 (Figure 1) in the sheet transport direction D1. At that time, the register roller pair 32 is controlled to move the sheet in the sheet width direction D2 to match the reference position of the image formed by the image forming section 90, after the sheet has been brought against the side reference plate 304 for skew correction. The register roller pair 32 is also controlled to adjust the timing of feeding the sheet to the secondary transfer section T2 in accordance with the timing of the image formed by the image forming section 90 reaching the secondary transfer section T2.

[0048] The Contact Image Sensor (CIS) 34 is an example of a detection means for detecting the position of a sheet in the sheet width direction D2. The CIS is an image sensor having a substrate with a light-receiving element arranged along the sheet width direction D2, an illumination unit (LED and light guide) for irradiating the sheet with light, and a lens for imaging the reflected light from the sheet onto the light-receiving element. The controller 550 (Figure 9), described later, can detect the position of the side edge of the sheet before oblique feeding of the sheet begins, 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 the one-dimensional imaging data acquired by the CIS 34.

[0049] Furthermore, the CIS34 is positioned in the sheet width direction D2, offset to one side (the side of the side reference plate 304) relative to the transport center X0 (Figure 4). This is because, in order to perform sheet position correction, which will be described later, using the detection results of the CIS34, it is sufficient to detect only the side edge position of one side of the sheet. In addition, the detection range of the CIS34 is set so that it can detect the side edge positions of the smallest sheet S and the largest sheet S within the sheet sizes permitted for use in the image forming apparatus.

[0050] The transport sensor 33 and the registration sensor 35 are examples of sheet detection means for detecting the leading and trailing ends of a sheet. The transport sensor 33 is positioned, for example, between the pre-registration roller pair 314 and the intermediate roller pair 315. The registration sensor 35 is positioned near the registration roller pair 32. The controller 550 (Figure 9), described later, can determine the timing to start diagonal feeding of the sheet based on the timing when the transport sensor 33 detects the leading end of the sheet. The controller 550 can also adjust the speed of the registration roller pair 32 based on the timing when the registration sensor 35 detects the leading end of the sheet. Furthermore, the controller 550 can monitor the detection signals from the transport sensor 33 and the registration sensor 35 to detect abnormalities in sheet transport (such as jams).

[0051] For example, a reflective photoelectric sensor having a light-emitting part and a light-receiving part can be used as the transport sensor 33. In this case, the light emitted by the light-emitting part is reflected by the sheet, and the timing of the sheet's passage is detected by the light-receiving part detecting the reflected light. In addition to reflective photoelectric sensors, other known sensors can be used, such as a sensor that combines a flag that swings when pressed by the sheet with a photoelectric sensor that is shielded by this flag. The registration sensor 35 can also be a known sensor such as a reflective photoelectric sensor, similar to the transport sensor 33.

[0052] (Control configuration of the registration unit) The control configuration of the registration unit 30 will be described with reference to Figure 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, RAM 552 and ROM 553 as storage means, and an interface (I / O) to external devices or networks. 55 It is equipped with 4 and .

[0053] The CPU 551 loads and executes a program stored in the ROM 553 or the like. This configures the CPU 551 to be able to execute each step of the control method described in the flowchart in Figure 10, for example. The ROM 553 is an example of a computer-readable non-transient storage medium that stores a program for controlling a sheet transport device or an image forming device.

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

[0055] Each pair of rollers in the registration unit 30 is rotationally driven 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 intermediate 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 transport roller pair 312 into contact with and separates them. The separation motor 512 brings the third transport roller pair 313 into contact with and separates them. The separation motor 513 brings the pre-resist roller pair 314 into contact with and separates them. The separation motor 514 brings the intermediate roller pair 315 into contact with and separates them. The separation motors 515 to 517 bring the first to third oblique transport roller pairs 301 to 303 into contact with and separate them, respectively.

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

[0058] The above motors (501~509, 511~51 7 For example, in 521-523), a stepping motor that can control the rotation angle with high precision can be used.

[0059] (Details of the conveyor roller pair) Figure 11 will be used to illustrate the details of the conveyor roller pairs 312, 313 and the intermediate roller pair 315. Each of the conveyor roller pairs 312, 313 and the intermediate roller pair 315 consists of drive rollers 312a, 313a, 315a and driven rollers 312b, 313b, 315b.

[0060] The drive rollers 312a, 313a, and 315a are each driven by a belt drive Structure Drive motors 502, 503, 50 are the drive source via this. 5 This connects the transport roller pairs 312, 313, 315 to the drive motors 502, 503, 50 5 They are configured to rotate by receiving driving force from the drive motor 501. Similarly, the upstream transport roller pair 311 is also configured to rotate by receiving driving force from the drive motor 501 via a belt transmission mechanism. Each driven roller 312b, 313b, and 315b is connected to the separation mechanism 650.

[0061] The configuration and operation of the separation mechanism 650 will be explained below using the intermediate roller pair 315 as an example. The separation mechanism 650 includes a separation motor 514, gears 655 and 656, an eccentric cam 653, and an arm 651. The arm 651 swings around a pivot axis 652 and rotatably supports the rotation axis of the driven roller 315b. When the rotation of the separation motor 514 is transmitted to the eccentric cam 653 via the gears 655 and 656, the arm 651 swings in accordance with the rotation of the eccentric cam 653. Due to the swing of the arm 651, the driven roller 315b moves in the vertical 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 separated state. A similar separation mechanism 650 is also provided for the transport roller pair 312 and 313, and the transport roller pair 312 and 313 can be switched between a contact state and a separated state by controlling the rotation angles of the separation motors 511 and 512.

[0063] (Details of the pre-regulator) Figures 12 to 14 illustrate the details of the pre-resist roller pair 314. Figure 12 is a perspective view of the drive mechanism 800 that rotates the pre-resist roller pair 314. Figure 13 is a schematic perspective view of the slide mechanism 37 that slides the pre-resist roller pair 314. Figure 14(a) is an enlarged perspective view of the separation mechanism 700 that switches the pre-resist roller pair 314 between a contact state and a separated state. Figure 14(b) is a cross-sectional view of the separation mechanism 700.

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

[0065] As shown in Figures 12 and 13, the pre-resist roller pair 314 consists of an upper roller 401 and a lower roller 402. The lower roller 402 is rotatably supported on the frame 201 of the printer 1, and the upper roller 401 is rotatably supported on an arm 405 which is part of the separation mechanism 700.

[0066] As shown in Figure 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 mounted 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 to 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, causing the lower roller 402, which is the drive roller, to rotate. This rotates the pre-resist roller pair 314.

[0067] 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-resist roller pair 314 so that the meshing with the roller gear 412 is maintained even when the pre-resist roller pair 314 slides. Alternatively, instead of driving the pre-resist 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-resist roller pair 314 slides.

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

[0069] The holder 415 is configured to rotatably support the end of the lower roller 402 on the roller gear 412 side and to move integrally with the lower roller 402 in the axial direction (sheet width direction D2). The holder 415 is fixed to the 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 Figure 12, pulley 610 is an integral component with pulley 609. Pulley 609 is connected to pulley 612, which is provided on the output shaft of slide motor 521 (Figure 13), via timing belt 613. Note that the slide motor 521 is not shown in Figure 12. With this configuration, timing belts 613 and 614 rotate in accordance with the forward and reverse rotation of slide motor 521, and the lower roller 402 reciprocates in the sheet width direction D2 together with the holder 415.

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

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

[0073] The separation mechanism 700, as shown in Figures 14(a, b), includes a separation motor 513, an arm 405, a pressure spring 407, cams 702 and 703, and a separation shaft 701. The arm 405, which rotatably supports the upper roller 401, is pivotable around an axis 201a formed on the frame 201 (Figure 13). The pressure spring 407 biases the arm 405 in a direction that brings the upper roller 401 into contact with the lower roller 402. The arm 405 and the pressure spring 407 are also provided on the opposite side of the sheet width direction D2 shown in Figure 14(a).

[0074] Cams 702 and 703 are provided at both ends of a separation shaft 701 extending in the sheet width direction D2, and each contacts the arm 405. As shown in Figure 14(a), a gear 702b is formed on cam 702. When the rotation of the separation motor 513 is input to the gear 702b, cam 702 rotates, and simultaneously the other cam 703 also rotates via the separation shaft 701. Due to the rotation of cams 702 and 703, the upper roller 401 moves to contact and separate from the lower roller 402. As a result, the pre-resist roller pair 314 switches between a contact state and a separated state depending on the rotation angle of the separation motor 513.

[0075] As shown in Figure 14(b), a sensor flag 703b is formed on the cam 703, which is detected by the separation sensor 706. The separation sensor 706 is a sensor (e.g., a photointerrupter) that detects the sensor flag 703b when the separation axis 701 is at a predetermined rotation angle. The controller 550 can determine the rotation angles of the cams 702 and 703 based on the detection signal from the separation sensor 706.

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

[0077] Furthermore, the sliding mechanism 37 of the pre-resist roller pair 314 is just one example of a means of movement. For example, instead of a timing belt, a mechanism using a worm gear or a linear cam may be used to slide the pre-resist roller pair 314 in the sheet width direction D2.

[0078] (Reduces variations in transport timing by sliding the pre-resist 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 upstream of the oblique feeding unit 300 to correct the sheet position in the sheet width direction D2. This reduces variations in the sheet transport timing downstream of the side reference plate 304. A detailed explanation follows below.

[0079] If there is variation in the sheet position in the sheet width direction D2 at the start of diagonal transport by the diagonal transport unit 300, the timing at which the side edge of the sheet abuts against the side reference plate 304 after the start of diagonal transport will vary. If the side edge of the sheet is far from the side reference plate 304 at the start of diagonal transport, 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 diagonal transport, the timing at which the side edge of the sheet abuts against the side reference plate 304 will be earlier. When the timing at which the side edge of the sheet abuts against the side reference plate 304 varies, the distance over which the sheet is transported by the diagonal transport unit 300 while in contact with the side reference plate 304 (sliding state) will change.

[0080] When the sheet is being transported in a rubbing state, the sheet experiences extra transport resistance (frictional resistance) from the side reference plate 304, causing the sheet transport speed in the sheet transport direction D1 to decrease. As a result, variations in the sheet position in the sheet width direction D2 at the start of oblique transport cause variations in the timing at which the sheet passes a predetermined position downstream of the side reference plate 304. For example, the timing at which the registration sensor 35 detects the leading edge of the sheet after oblique transport, relative to the point at which the transport sensor 33 detects the leading edge of the sheet before oblique transport begins, will vary.

[0081] Such variations in transport timing can reduce the productivity (throughput) of the sheet transport device. This is because, in order to transport sheets at a constant target interval, the target interval is set to be longer in advance to absorb variations in transport timing. In the configuration of this embodiment, this is achieved by setting the distance between sheets to be longer in order to transfer images at a constant interval (between sheets) in the secondary transfer unit T2.

[0082] In contrast, in this embodiment, before the oblique feeding unit 300 starts oblique feeding, the pre-registration roller pair 314 is moved in the sheet width direction D2 based on the sheet position detection result by the CIS 34. This makes it possible to equalize 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 over which the sheet is transported in a sliding state becomes approximately constant, and variations in the timing of the registration sensor 35 detecting the leading edge of the sheet after oblique feeding contact are reduced. Furthermore, by reducing variations in transport timing, it becomes possible to set a shorter gap between sheets in the secondary transfer section T2, for example, which contributes to improving the productivity of the printer 1.

[0083] Details of the movement of the pre-regulator pair 314 based on the seat position detection results by CIS34 are described below.

[0084] (Transportation operation when the sheet length exceeds a specified length) The following describes the sheet transport operation performed by the registration unit 30 of this embodiment according to the sheet size in the sheet transport direction (hereinafter referred to as sheet length), with reference to the flowchart in Figure 10. Each step in the flowchart in Figure 10 is performed by the CPU 551 of the controller 550 (Figure 9) and the ROM 55 3 This is achieved by reading and executing a program. Furthermore, each step in Figure 10 is performed as part of a job when the controller 550 executes an image formation job (print job).

[0085] First, the transport operation when the sheet length is greater than or equal to a predetermined length will be explained using the flowchart in Figure 10 and Figures 5(a-d) and 6(a-d). Figure 5(a-d) is a top view of the registration unit 30 showing the transport operation of a sheet S1 with a sheet length Ls1 greater than or equal to a predetermined length. Figure 6(a-d) is a side view of the registration unit 30 showing the transport operation of a sheet S1 with a sheet length Ls1 greater than or equal to a predetermined length. In Figures 5(a-d), the rollers of the rollers in contact are shown in black, and the rollers in separated states are shown only by their outlines.

[0086] Before an image forming job is submitted, the controller 550 shall acquire sheet size information in advance. Methods for acquiring the sheet size include, for example, referring to the sheet size entered by the user via the operation unit 400 (Figure 9), or automatically detecting the sheet size using sheet size sensors provided in the feeding units 10a and 10b (Figure 1). When an image forming job is submitted, the controller 550 determines whether the sheet length of the sheet to be used for this job is greater than or equal to a predetermined length (S1).

[0087] If the sheet length is greater than or equal to a predetermined length, the intermediate roller pair 315 downstream of the pre-resist roller pair 314 is separated (S2a, Figure 5(a), Figure 6(a)). Subsequently, the sheet S1 is transported in a transport mode (S2a to S9a) in which the intermediate roller pair 315 (second roller pair) is separated.

[0088] As shown in Figures 5(a) and 6(a), the sheet S1, which has been transported from the transport unit upstream of the registration unit 30 (the feeding units 10a, 10b in Figure 1 or the first double-sided transport unit), is transported by the transport 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 using the CIS 34 (S3a).

[0089] The amount of deviation ΔX between the detected side edge position Xd of the sheet S1 (Figure 5(a)) and the target position Xn of the side edge of the sheet S1 is calculated. In this embodiment, the target position Xn is the side edge position of the sheet S1 when the center of the sheet width direction D2 of the sheet S1 coincides with the transport center X0 (a position that is half the sheet width Ws1 away from the transport center X0, the nominal side edge position).

[0090] Next, a sliding operation (shift operation, position correction operation) of the pre-regulating roller pair 314 is performed to correct the displacement amount ΔX (S4a, arrow B in Figure 5(b)). Specifically, after the leading edge of the sheet S1 enters the pre-regulating roller pair 314, the transport roller pairs 312 and 313 upstream of the pre-regulating roller pair 314 are separated (Figure 6(b)). Then, after the rear end of the sheet S1 has passed the uppermost transport roller pair 311, the pre-regulating roller pair 314 is slid to compensate for the displacement amount ΔX and bring the side edge of the sheet S1 closer to the target position Xn. As a result, the sheet position is shifted so that the center of the sheet S1 aligns with the transport center X0. The transport of the sheet S1 continues even while the pre-regulating roller pair 314 is sliding.

[0091] Here, the reason for waiting for the rear end of the sheet S1 to pass the upstream transport roller pair 311 before sliding the pre-resist roller pair 314 is that the transport roller pair 311 is always in contact with the sheet. Since the sheet length Ls1 of the sheet S1 is longer than the path length L0 from the transport roller pair 311 to the pre-resist roller pair 314, the rear end of the sheet S1 is held in place by the transport roller pair 311 when the front end of the sheet S1 reaches the pre-resist roller pair 314. When the front end of the sheet S1 is transported a distance of (Ls1-L0) from the pre-resist roller pair 314, the rear end of the sheet S1 passes the transport roller pair 311. As a result, the rear end of the sheet S1 is no longer constrained by the transport roller pair 311, making it possible to move the sheet S1 in the sheet width direction D2 by the pre-resist roller pair 314 without generating stress (shear force) in the sheet width direction D2 on the sheet S1.

[0092] Furthermore, the sliding of the pre-regulating roller pair 314 is completed before the sheet is gripped by the roller pair downstream of the pre-regulating roller pair 314. In this embodiment, if the sheet length is greater than a predetermined length, the intermediate roller pair 315 is separated, so the sliding of the pre-regulating roller pair 314 only needs to be completed before the leading edge of the sheet S1 reaches the uppermost diagonal feed roller pair 301 of the diagonal feed unit 300. As a result, the period during which the sliding of the pre-regulating roller pair 314 can be performed is extended compared to the case where the intermediate roller pair 315 is in contact, and the range in which the position of the sheet S1 in the sheet width direction D2 can be corrected is widened.

[0093] Thus, in this embodiment, when transporting a first sheet (S1) whose length is greater than or equal to 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-resist roller pair 314) and the rear end of the first sheet has passed the upstream roller pair (transport roller pair 311). Furthermore, in this embodiment, the movement of the first roller pair by the moving means is stopped before the leading edge of the first sheet reaches the diagonal transport means (diagonal transport unit 300). This makes it possible to complete the position correction of the first sheet during the period when the sheet is not restrained by roller pairs other than the first roller pair, thereby avoiding damage to the sheet.

[0094] Furthermore, if the displacement ΔX calculated using CIS34 is large and the sliding of the pre-regulating roller pair 314 cannot be completed before the diagonal conveying roller pair 301-303 switches to a contact state, an error may be reported and the conveying operation may be stopped.

[0095] After the leading edge of the sheet S1 reaches the pair of inclined rollers 301, the pair of inclined rollers 301-303 are switched to a contact state (S6a). At this stage, the gripping force of the pair of inclined rollers 301-303 on the sheet S1 is weaker than the gripping force of the pair of pre-resist rollers 314. Therefore, the conveying force applied to the sheet S1 by the pair of pre-resist rollers 314 is dominant, and the sheet S1 continues to move in the sheet conveying direction D1. , thisThe timing for switching to the contact state is determined based on the timing when the transport sensor 33 detects the leading edge of the sheet S1.

[0096] Subsequently, the pre-regulating roller pair 314 is switched to a separated state (S7a, Figure 6(c)). As a result, the diagonal conveying force applied to the sheet S1 by the diagonal conveying roller pair 301, 302, and 303 becomes dominant, and the sheet S1 is conveyed while being moved towards the side reference plate 304 (arrow E in Figure 5(c)).

[0097] In this embodiment, the pre-regulating roller pair 314 separates after the leading edge of the sheet S1 has reached the second pair of inclined rollers 302. That is, the pre-regulating roller pair 314 separates while the sheet S1 is being held between the upstream pair of inclined rollers 301 (first pair of inclined rollers) and the second pair of inclined rollers 302 (second pair of inclined rollers). This allows the sheet S1 to be transferred from the pre-regulating roller pair 314 to the inclined roller unit 300 more reliably. Furthermore, by setting the timing for the inclined roller pairs 301 to 303 to come into contact after the leading edge of the sheet S1 has reached the second pair of inclined rollers 302, the time during which the sheet S1 slips against the inclined rollers 301a and 301b can be shortened.

[0098] When the side edge of sheet S1 abuts against the abutment surface 304a of the side reference plate 304 (S8a), the pair of inclined rollers 301-303 slip, and the sheet S1 rotates to follow the abutment surface 304a, thereby correcting the inclination of sheet S1. Even after the inclination of sheet S1 is corrected, the pair of inclined rollers 301-303 continue to transport sheet S1 in the sheet transport direction D1 while keeping the side edge of sheet S1 in contact with the abutment surface 304a.

[0099] When the leading edge of the sheet S1 reaches the register roller pair 32 (S9a), the oblique feed roller pair 301-303 are switched to a separated state (Figures 5(d) and 6(d)). Subsequently, the register roller pair 32 is moved to slide position (arrow A in Figure 5(d)) so that the sheet S1 is aligned with the reference position of the image formed by the image forming unit 90.

[0100] By repeatedly performing the above process, the registration unit 30 transports each sheet S1 while correcting its position and skew.

[0101] (Transportation operation when the sheet length is less than the specified length) Next, the transport operation when the sheet length is less than a predetermined length will be explained using the flowchart in Figure 10 and Figures 7(a-d) and 8(a-d). Figure 7(a-d) is a top view of the registration unit 30 showing the transport operation of a sheet S2 with a sheet length Ls2 less than a predetermined length. Figure 8(a-d) is a side view of the registration unit 30 showing the transport operation of a sheet S2 with a sheet length Ls2 less than a predetermined length. In Figures 7(a-d), the rollers of the rollers in contact are shown in black, and the rollers in separated states are shown only by their outlines.

[0102] If the sheet length is less than a predetermined length, the intermediate roller pair 315 downstream of the pre-resist roller pair 314 is brought into contact with the sheet (S2b, Figures 5(a) and 6(a)). Subsequently, the sheet S2 is transported in a transport mode (S2b to S9b) in which the intermediate roller pair 315 (second roller pair) is brought into contact with the sheet.

[0103] As shown in Figures 7(a) and 8(a), the sheet S2, which has been transported from the transport unit upstream of the registration unit 30, is transported by the transport roller pairs 311 to 313. When the leading edge of the sheet S2 reaches the CIS 34, the position Xd of the side edge of the sheet S2 is detected using the CIS 34 (S3b).

[0104] The amount of deviation ΔX between the detected side edge position Xd of the sheet S2 (Figure 7(a)) and the target position Xn of the side edge of the sheet S2 is calculated. In this embodiment, the target position Xn is the side edge position of the sheet S2 when the center of the sheet width direction D2 of the sheet S2 coincides with the transport center X0 (a position that is half the sheet width Ws2 away from the transport center X0, the nominal side edge position).

[0105] Next, a sliding operation (shift operation, position correction operation) of the pre-regulating roller pair 314 is performed to compensate for the displacement amount ΔX (S4b, arrow B in Figure 7(b)). Specifically, after the leading edge of the sheet S2 enters the pre-regulating roller pair 314, the transport roller pair 312 and 313 upstream of the pre-regulating roller pair 314 are separated (Figure 8(b)). Then, the pre-regulating roller pair 314 is slid so that the displacement amount ΔX is compensated for and the side edge of the sheet S2 approaches the target position Xn. As a result, the sheet position is shifted so that the center of the sheet S2 aligns with the transport center X0. The transport of the sheet S2 continues even while the pre-regulating roller pair 314 is sliding.

[0106] Here, the sheet length Ls2 of sheet S2 is always shorter than the path length L0 from the contacting transport roller pair 311 to the pre-resist roller pair 314. Therefore, when the leading edge of sheet S2 enters the pre-resist roller pair 314, sheet S2 is not gripped by the transport roller pair 311. Consequently, in the case of sheet S2 with a short sheet length Ls2, the pre-resist roller pair 314 can begin sliding immediately after the leading edge of sheet S2 enters the pre-resist roller pair 314.

[0107] In the case of a short sheet S2 with a sheet length Ls2, the intermediate roller pair 315 is in contact with the sheet, so the sliding of the pre-resist roller pair 314 is completed before the sheet is gripped by the intermediate roller pair 315. In this case, by starting the sliding of the pre-resist roller pair 314 immediately after the leading edge of the sheet S2 enters the pre-resist roller pair 314, a period during which the sliding of the pre-resist roller pair 314 can be performed can be secured.

[0108] Thus, in this embodiment, when transporting a second sheet (S2) whose sheet 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-resist roller pair 314), and the movement of the first roller pair by the moving means is stopped before the leading edge of the second sheet reaches the second roller pair (intermediate roller pair 315). This ensures that the sheet is not restrained by any roller pair other than the first roller pair during the period when the second sheet is not restrained by any roller pair other than the first roller pair.2 This allows for the completion of seat position correction and avoids damage to the seat.

[0109] Furthermore, if the displacement ΔX calculated using CIS34 is large and the sliding of the pre-resist roller pair 314 cannot be completed before the leading edge of the sheet S2 switches to the intermediate roller pair 315, an error may be reported and the transport operation may be stopped.

[0110] After the pre-regulating roller pair 314 has finished sliding, the sheet S2 enters the intermediate roller pair 315 and is handed over to the diagonal conveying unit 300 via the intermediate roller pair 315 (S5b). If the distance between the conveying roller pairs is wide relative to the sheet length, the reliability of sheet transfer may decrease. In this embodiment, when the sheet length Ls2 of the sheet S2 is short, the intermediate roller pair 315 is brought into contact with the sheet. This makes it possible to more reliably convey the sheet S2 from the pre-regulating roller pair 314 to the diagonal conveying unit 300 via the intermediate roller pair 315, even for sheets with a short sheet length Ls2.

[0111] After the leading edge of the sheet S2 reaches the pair of inclined rollers 301, the pair of inclined rollers 301-303 are switched to a contact state (S6b). At this stage, the force with which the pair of inclined rollers 301-303 grips the sheet S2 is weaker than the gripping force of the pair of pre-resist rollers 314, so the pair of pre-resist rollers 314 grips the sheet S2 2 The conveying force applied to the sheet is dominant, and the sheet S2 continues to move in the sheet conveying direction D1. , this The timing for switching to the contact state is determined by the transport sensor 33 detecting the sheet S 2 It is determined based on the timing of detection of the tip.

[0112] Subsequently, the pre-regulating roller pair 314 is switched to a separated state (S7b, Figure 8(c)). As a result, the diagonal conveying force applied to the sheet S2 by the diagonal conveying roller pair 301, 302, and 303 becomes dominant, and the sheet S2 is conveyed while being moved towards the side reference plate 304 (arrow E in Figure 7(c)).

[0113] In this embodiment, the pre-regulating roller pair 314 separates at the timing after the leading edge of the sheet S2 has reached the second pair of inclined rollers 302. In other words, the pre-regulating roller pair 314 separates while the sheet S2 is being held between the upstream pair of inclined rollers 301 (first pair of inclined rollers) and the second pair of inclined rollers 302 (second pair of inclined rollers). This allows the sheet S2 to be transferred from the pre-regulating roller pair 314 to the inclined conveying unit 300 more reliably.

[0114] In particular, in this embodiment, the distance from the intermediate roller pair 315 to the upstream diagonal roller pair 301 is shorter than the distance from the pre-regulating roller pair 314 to the intermediate roller pair 315, making it possible to handle shorter sheets. Furthermore, by setting the timing for the diagonal roller pairs 301 to 303 to come into contact with each other after the leading edge of the sheet S2 reaches the second diagonal roller pair 302, the time during which the sheet S2 slips against the diagonal rollers 301a and 301b can be shortened.

[0115] When the side edge of sheet S2 abuts against the abutment surface 304a of the side reference plate 304 (S8b), the pair of inclined rollers 301-303 slip, and the sheet S2 rotates to follow the abutment surface 304a, thereby correcting the inclination of sheet S2. Even after the inclination of sheet S2 is corrected, the pair of inclined rollers 301-303 continue to transport sheet S2 in the sheet transport direction D1 while keeping the side edge of sheet S2 in contact with the abutment surface 304a.

[0116] When the leading edge of sheet S2 reaches the register roller pair 32 (S9b), the diagonal feed roller pair 301-303 is switched to a separated state (Figure 7(d), Figure 8(d)). After that, sheet S 2 The slide movement of the register roller pair 32 (arrow A in Figure 7(d)) ​​is performed so that it aligns with the reference position of the image formed by the image forming unit 90.

[0117] By repeatedly performing the above process, the registration unit 30 transports each sheet S2 while correcting its position and skew.

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

[0119] When the sheet S1 has a relatively long sheet length Ls1, the controller 550 separates the relay roller pair 315 and slides the pre-regulating roller pair 314 using the sliding mechanism 37 based on the detection result of the CIS 34, and then transfers the sheet S1 from the pre-regulating roller pair 314 to the diagonal conveying unit 300. In other words, when the control means of this embodiment is conveying a first sheet whose length in the sheet conveying direction is a first length, the separation means separates the second roller pair and moves the first roller pair in the sheet width direction using the moving means based on the detection result of the detection means, and then transfers the first sheet from the first roller pair to the diagonal conveying means.

[0120] This allows time for the pre-resist roller pair 314 to slide by keeping the intermediate roller pair 315 separated for relatively long sheets S1. Also, because the sheet S1 is relatively long, the transfer to the diagonal conveying unit 300 is performed smoothly even with the intermediate roller pair 315 separated.

[0121] Furthermore, in the case of a sheet S2 with a relatively short sheet length Ls2, the controller 550 sets the relay roller pair 315 into contact with the pre-regulating roller pair 314 using the sliding mechanism 37 based on the detection result of the CIS 34, and transfers the sheet S2 from the pre-regulating roller pair 314 to the diagonal conveying unit 300 via the relay roller pair 315. In other words, when conveying a second sheet whose length in the sheet conveying direction is shorter than the first length, the control means of this embodiment sets the second roller pair into contact with the first roller pair using the separation means, moves the first roller pair in the sheet width direction using 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 diagonal conveying means via the second roller pair.

[0122] This allows for more reliable transfer of relatively short sheets S2 to the diagonal feeding unit 300 via the relay roller pair 315. Furthermore, if the sheet S2 is short, there is ample time for the leading edge of the sheet S2 to reach the relay roller pair 315 in contact, thus ensuring sufficient time for the pre-resist roller pair 314 to slide even when the relay roller pair 315 is in contact.

[0123] Thus, according to this embodiment, while accommodating sheets of various sizes, variations in conveying timing can be reduced by sliding the pre-resist roller pair 314 before the start of inclined conveying by the inclined conveying unit 300.

[0124] (Conditions for setting the predetermined length) As described above, in this embodiment, the transport mode is switched between a transport mode in which the intermediate roller pair 315 (second roller pair) is in contact with the sheet and a transport mode in which the intermediate roller pair 315 is separated, depending on whether the sheet length is greater than or equal to a predetermined length. The following describes preferred settings for the predetermined length, which is the threshold for switching the transport mode. Note that the transport mode applied when the sheet length is equal to the predetermined length may be changed.

[0125] The predetermined length is preferably less than or equal to the distance D1 in the sheet transport direction from the always-contacting transport roller pair 311 to the pre-resist roller pair 314 (less than or equal to the distance in the sheet transport direction from the upstream roller pair to the first roller pair, or less than or equal to L0 in Figure 6(b)). In this case, for long sheets where the leading edge of the sheet has already passed the pre-resist roller pair 314 when the trailing edge of the sheet has passed the transport roller pair 311, a transport mode in which the intermediate roller pair 315 is separated is always applied. This ensures that there is enough time for the pre-resist roller pair 314 to slide for long sheets.

[0126] Furthermore, the predetermined length is set to be longer than the distance D1 in the sheet transport direction from the pre-regulating roller pair 314 to the uppermost diagonal transport roller pair 301 of the diagonal transport unit 300 (the distance in the sheet transport direction from the first roller pair to the diagonal transport means). This allows the sheet to be transferred from the pre-regulating roller pair 314 to the diagonal transport unit 300 even when the intermediate roller pair 315 is separated.

[0127] Furthermore, it is preferable to set the predetermined length to be longer than the distance D1 in the sheet transport direction from the pre-regulating roller pair 314 to the second diagonal transport roller pair 302 of the diagonal transport unit 300 (the distance in the sheet transport direction from the first roller pair to the second diagonal transport roller pair). Since the diagonal transport roller pairs 301 to 303 are configured to transport the sheet while slipping against it, the gripping force of the sheet by the diagonal transport roller pairs 301 to 303 is usually weaker than the gripping force of the other transport roller pairs. Therefore, by setting the predetermined length to be longer than the above distance, the transfer of the sheet from the pre-regulating roller pair 314 to the diagonal transport unit 300 can be made more reliable. That is, in a transport mode in which the intermediate roller pair 315 is separated, at least two diagonal transport roller pairs 301 and 302 can grip the sheet before the rear end of the sheet passes the pre-regulating roller pair 314, thus reducing the possibility of transport failure.

[0128] In the configuration example to which this embodiment is applied, the predetermined length is set to 295.7 mm. This means that when the sheet length is longer than A4 size with long-side feeding or A3 size with short-side feeding, a transport mode in which the intermediate roller pair 315 is separated is applied. The value of the predetermined length is appropriate depending on the specific configuration of the image forming apparatus. change It is possible.

[0129] (Other embodiments) In the embodiment described above, a configuration using a CIS34 as a detection means for detecting the sheet position in the sheet width direction D2 was illustrated. Instead of the CIS34, for example, a CCD type image sensor may be used. Alternatively, a photoelectric sensor that detects the sheet at a predetermined position (target position) in the sheet width direction D2 may be used as the detection means. In that case, the movement of the pre-resist roller pair 314 can be terminated after the movement of the pre-resist roller pair 314 has started, based on the photoelectric sensor detecting the side edge of the sheet. Furthermore, the detection means is not limited to being placed upstream of the pre-resist roller pair 314, but may also be placed downstream of the pre-resist roller pair 314.

[0130] Furthermore, in the embodiment described above, the target position Xn when correcting the sheet position in the sheet width direction D2 by the pre-regulator pair 314 was set to the side edge position of the sheet when the sheet is located on the conveying center. However, by setting the target position to a position a predetermined distance away from the side reference plate 304, rather than being limited to a target position relative to the conveying center, it is possible to reduce variations in conveying timing.

[0131] In the embodiments described above, a printer 1 as an intermediate transfer type electrophotographic device was exemplified as the image forming apparatus, but the technology of this disclosure is applicable to other image forming apparatuses as well. "Image forming apparatus" includes printing presses for commercial printing (production printers), single-function printers for office or home use, copiers, and multifunction devices. Furthermore, the image forming means is not limited to an intermediate transfer type electrophotographic unit, but 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 sheets toward the image forming means in an image forming apparatus, but may also be a device that transports sheets in a sheet processing device, for example. A sheet processing device is a device (also called a finisher) that is connected to the main body of an image forming apparatus and used to perform processes such as binding or sorting on sheets after image formation. In addition, the sheet transport device may be a device 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 manufactured goods while transporting them).

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

[0134] (Summary of this disclosure) This disclosure includes at least the following components:

[0135] (Composition 1) A first pair of rollers that transport the sheet, A second pair of rollers is positioned downstream of the first pair of rollers in the sheet conveying direction and conveys the sheet, A stopper portion against which the end of the sheet in the sheet width direction perpendicular to the sheet transport direction is abutted, An oblique conveying means is positioned downstream of the second roller pair in the sheet conveying direction, moves the sheet toward the abutment portion in the sheet width direction toward the downstream of the sheet conveying direction, and conveys the sheet while abutting the edge of the sheet toward the abutment portion, A detection means for detecting the position of the sheet in the sheet width direction, A moving means for moving the first roller pair in the sheet width direction, A means for switching the second roller pair between a contact state in which the rollers are in contact with each other and a separated state in which the rollers are separated from each other, The system comprises control means for controlling the moving means and the separating means, The control means is When transporting a first sheet whose length in the sheet transport direction is a first length, the separating means moves the second roller pair into the separated state, and based on the detection result of the detection means, the moving means moves the first roller pair in the sheet width direction, and then the first sheet is transferred from the first roller pair to the oblique transport means. When transporting a second sheet having a second length shorter than the first length in the sheet transport direction, the separation means brings the second roller pair into contact with the first roller pair, and based on the detection result of the detection means, the moving means moves the first roller pair in the sheet width direction, thereby transferring the second sheet from the first roller pair to the oblique transport means via the second roller pair. A sheet conveying device characterized by the following features.

[0136] (Configuration 2) Further comprising an upstream pair of rollers positioned upstream of the first pair of rollers in the sheet transport direction, configured such that the rollers are always in contact with each other, The control means is When transporting the first sheet, the movement of the first roller pair by the moving means is initiated after the leading edge of the first sheet reaches the first roller pair and the rear end of the first sheet has passed the upstream roller pair. When transporting the second sheet, the movement of the first roller pair by the moving means is initiated after the leading edge of the second sheet reaches the first roller pair. A sheet conveying device according to configuration 1, characterized by the features described above.

[0137] (Composition 3) The control means is When transporting the first sheet, the movement of the first roller pair by the moving means is terminated before the leading edge of the first sheet reaches the oblique transport means. When transporting the second sheet, 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. A sheet conveying device according to configuration 2, characterized in that it is a sheet conveying device.

[0138] (Composition 4) The control means is configured such that when the length of the sheet in the sheet transport direction is greater than or equal to a predetermined length, the separation means sets the second roller pair in the separated state and transports the sheet, and when the length in the sheet transport direction is less than the predetermined length, the separation means sets the second roller pair in the contact state and transports the sheet. The predetermined length is longer than the distance in the sheet transport direction from the first roller pair to the oblique feeding means, and less than or equal to the distance in the sheet transport direction from the upstream roller pair to the first roller pair. A sheet conveying device according to configuration 2 or 3, characterized by the above.

[0139] (Composition 5) The sheet further comprises at least one pair of rollers positioned between the upstream pair of rollers and the first pair of rollers in the sheet transport direction, and configured to be able to come into contact with and separate from each other. The control means separates at least one pair of rollers before the movement of the first pair of rollers by the moving means. A sheet conveying device according to any one of configurations 2 to 4, characterized by the above.

[0140] (Composition 6) The inclined feeding means includes a first pair of inclined rollers and a second pair of inclined rollers positioned downstream of the first inclined rollers in the sheet conveying direction. The distance from the second pair of rollers to the first pair of oblique rollers in the sheet transport direction is shorter than the distance from the first pair of rollers to the second pair of rollers in the sheet transport direction. A sheet conveying device according to any one of configurations 1 to 5, characterized by the above.

[0141] (Composition 7) The control means is When transporting the first sheet, after the leading edge of the first sheet reaches the second inclined conveying roller, the rollers of the first roller pair are separated, thereby initiating the inclined conveying of the first sheet by the first inclined conveying roller pair and the second roller pair. When transporting the second sheet, the first pair of rollers and the second pair of rollers are separated after the leading edge of the second sheet reaches the second inclined conveying roller, thereby initiating the inclined conveying of the first sheet by the first pair of inclined conveying rollers and the second pair of rollers. A sheet conveying device according to configuration 6, characterized by the features described above.

[0142] (Composition 8) Further comprising an upstream pair of rollers positioned upstream of the first pair of rollers in the sheet transport direction, configured such that the rollers are always in contact with each other, The control means is configured such that when the length of the sheet in the sheet transport direction is greater than or equal to a predetermined length, the separation means sets the second roller pair in the separated state and transports the sheet, and when the length in the sheet transport direction is less than the predetermined length, the separation means sets the second roller pair in the contact state and transports the sheet. The predetermined length is longer than the distance in the sheet transport direction from the first roller pair to the second oblique feed roller pair, and less than or equal to the distance in the sheet transport direction from the upstream roller pair to the first roller pair. A sheet conveying device according to configuration 6 or 7, characterized by the above.

[0143] (Composition 9) Based on the detection result of the detection means, the control means moves the first roller pair in the sheet width direction using the moving means so that the side edge of the sheet approaches a target position that is a predetermined distance away from the abutment portion in the sheet width direction. A sheet conveying device according to any one of configurations 1 to 8, characterized by the above.

[0144] (Composition 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 transport center of the transport path through which the sheet is transported to the first roller pair. A sheet conveying device according to configuration 9, characterized by the features described therein.

[0145] (Composition 11) The detection means is positioned upstream of the first roller pair in the sheet transport direction. A sheet conveying device according to any one of configurations 1 to 10, characterized by the above.

[0146] (Composition 12) The detection means is an image sensor having a plurality of light-receiving elements arranged along the width direction of the sheet. A sheet conveying device according to any one of configurations 1 to 11, characterized by the features described herein.

[0147] (Composition 13) A sheet transport device according to any one of configurations 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: [Explanation of Symbols]

[0148] 34...Detection means (CIS) / 37...Moving means (slide mechanism) / 304a...Butt section (butt surface) / 311...Upstream roller pair (conveyor roller pair) / 314...First roller pair (pre-resist roller pair) / 315...Second roller pair (intermediate roller pair) / 300...Diagonal feeding unit (diagonal feeding means) / 550...Control means (controller) / 650...Separation means (separation mechanism)

Claims

1. A first pair of rollers that transport the sheet, A second pair of rollers is positioned downstream of the first pair of rollers in the sheet conveying direction and conveys the sheet, A stopper portion against which the end of the sheet in the sheet width direction perpendicular to the sheet transport direction is abutted, An oblique conveying means is positioned downstream of the second roller pair in the sheet conveying direction, moves the sheet toward the abutment portion in the sheet width direction toward the downstream of the sheet conveying direction, and conveys the sheet while abutting the edge of the sheet toward the abutment portion, A detection means for detecting the 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 pair of rollers 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, The system comprises control means for controlling the moving means and the separating means, The control means is When transporting a first sheet whose length in the sheet transport direction is a first length, 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 then the first sheet is transported to the oblique transport means by passing the second roller pair, which is separated from the first roller pair, through it. When transporting a second sheet having a second length shorter than the first length in the sheet transport direction, 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 then the second sheet is transported from the first roller pair to the inclined transport means via the second roller pair in contact with the first roller pair. A sheet conveying device characterized by the following features.

2. Further comprising an upstream pair of rollers positioned upstream of the first pair of rollers in the sheet transport direction, configured such that the rollers are always in contact with each other, The control means is When transporting the first sheet, the movement of the first roller pair by the moving means is initiated based on the fact that the leading edge of the first sheet reaches the first roller pair and the rear end of the first sheet has passed the upstream roller pair. When transporting the second sheet, the movement of the first roller pair by the moving means is initiated based on the fact that the leading edge of the second sheet has reached the first roller pair. The sheet conveying device according to feature 1.

3. The control means is When transporting the first sheet, the movement of the first roller pair by the moving means is terminated before the leading edge of the first sheet reaches the oblique transport means. When transporting the second sheet, 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. The sheet conveying device according to feature 2.

4. The control means is configured such that when the length of the sheet in the sheet transport direction is greater than or equal to a predetermined length, the separation means sets the second roller pair in the separated state and transports the sheet, and when the length in the sheet transport direction is less than the predetermined length, the separation means sets the second roller pair in the contact state and transports the sheet. The predetermined length is longer than the distance in the sheet transport direction from the first roller pair to the oblique feeding means, and less than or equal to the distance in the sheet transport direction from the upstream roller pair to the first roller pair. The sheet conveying device according to feature 2.

5. The sheet further comprises at least one pair of rollers positioned between the upstream pair of rollers and the first pair of rollers in the sheet transport direction, and configured to be able to come into contact with and separate from each other. The control means separates at least one pair of rollers before the movement of the first pair of rollers by the moving means. The sheet conveying device according to feature 2.

6. The aforementioned inclined conveying means includes a first inclined conveying roller pair and a second inclined conveying roller pair arranged downstream of the first inclined conveying roller pair in the sheet conveying direction, The distance from the second pair of rollers to the first pair of oblique rollers in the sheet transport direction is shorter than the distance from the first pair of rollers to the second pair of rollers in the sheet transport direction. The sheet conveying device according to feature 1.

7. The control means is When transporting the first sheet, after the leading edge of the first sheet reaches the second pair of inclined rollers, the rollers of the first pair of rollers are separated, thereby initiating the inclined transport of the first sheet by the first pair of inclined rollers and the second pair of inclined rollers. When transporting the second sheet, the rollers of the first roller pair and the second roller pair are separated after the leading edge of the second sheet reaches the second pair of inclined rollers, thereby initiating the inclined transport of the second sheet by the first and second pairs of inclined rollers. The sheet conveying device according to feature 6.

8. Further comprising an upstream pair of rollers positioned upstream of the first pair of rollers in the sheet transport direction, configured such that the rollers are always in contact with each other, The control means is configured such that when the length of the sheet in the sheet transport direction is greater than or equal to a predetermined length, the separation means sets the second roller pair in the separated state and transports the sheet, and when the length in the sheet transport direction is less than the predetermined length, the separation means sets the second roller pair in the contact state and transports the sheet. The predetermined length is longer than the distance in the sheet transport direction from the first roller pair to the second oblique roller pair, and less than or equal to the distance in the sheet transport direction from the upstream roller pair to the first roller pair. The sheet conveying device according to feature 6.

9. Based on the detection result of the detection means, the control means moves the first roller pair in the sheet width direction using the moving means so that the side edge of the sheet approaches a target position that is a predetermined distance away from the abutment portion in the sheet width direction. The sheet conveying device according to feature 1.

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 transport center of the transport path through which the sheet is transported to the first roller pair. The sheet conveying device according to feature 9.

11. The detection means is positioned upstream of the first roller pair in the sheet transport direction. The sheet conveying device according to feature 1.

12. The detection means is a line sensor having a plurality of light-receiving elements arranged along the width direction of the sheet. The sheet conveying device according to feature 1.

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