Sheet conveying device and image forming apparatus

Abstract

To prevent reduction in accuracy of skew correction.SOLUTION: In a sheet skew feeding state from start of skew feeding of the sheet conveyed by the first conveyance rotator pair to abutment of the end portion of the sheet in the width direction against the abutment portion, It is possible to execute a first mode in which the first pair of skew-feed rotating members (32-1) and the second pair of skew-feed rotating members (32-3) are controlled to be in the nip-conveyance state, and a second mode in which the first pair of skew-feed rotating members (32-1) is controlled to be in the nip-conveyance state and the second pair of skew-feed rotating members (32-3) is controlled to be in the non-nip-conveyance state in the sheet skew-feed state.SELECTED DRAWING: Figure 19

Description

[Technical Field]

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

[0002] For example, in an image forming apparatus such as a printer, a so-called side registration method has been proposed in which a sheet is skewed by a pair of skew rollers and the edge of the sheet is abutted against an abutment member to correct the skew (see Patent Document 1). In the apparatus disclosed in Patent Document 1, a sheet conveyed by a pair of conveying rollers is abutted against a reference surface of a reference member by multiple skew rollers, and then conveyed to a registration roller. Patent Document 1 also proposes that, after the sheet abuts against the reference member, pressure on one or two of the multiple front skew rollers may be released to balance the moment generated by the rear skew roller and the multiple front skew rollers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-10326 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, sufficient conveying force is required to reliably strike a sheet such as plain paper or thick paper against a reference member, and the sheet is sandwiched between multiple skew rollers and skewed while being struck against the reference member. However, if the skewed sheet is a sheet with a small basis weight and low rigidity, such as thin paper, the striking force against the reference member becomes strong, and the sheet may buckle, which may reduce the accuracy of skew correction.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet conveying device and an image forming apparatus that are capable of preventing a decrease in the accuracy of skew correction. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet conveying device including a first pair of conveying rotors that sandwich and convey a sheet, an abutment portion that is arranged on one side of the width direction of the conveyed sheet that is perpendicular to the sheet conveying direction, a first pair of oblique conveying rotors that is arranged downstream of the first pair of conveying rotors in the sheet conveying direction and obliquely conveys the sheet toward the abutment portion, a second pair of oblique conveying rotors that is arranged downstream of the first pair of conveying rotors in the sheet conveying direction and obliquely conveys the sheet toward the abutment portion, a first switching mechanism that switches the first pair of oblique conveying rotors between a sandwiching conveying state in which the sheet is sandwiched and conveyed and a non-sandwiching state in which the sandwiching of the sheet is released, and a second switching mechanism that switches the second .... a second switching mechanism that switches the first switching mechanism to a non-clamping state in which the clamping of the sheet is released, and a control unit that controls the switching of the first switching mechanism and the switching of the second switching mechanism, wherein the control unit is capable of executing a first mode in which the first pair of oblique conveying rotors and the second pair of oblique conveying rotors are controlled to the clamping conveying state in the oblique sheet conveying state from the start of oblique conveying of the sheet conveyed by the first pair of conveying rotors until the end of the sheet in the width direction hits the abutment portion, and a second mode in which the first pair of oblique conveying rotors are controlled to the clamping conveying state and the second pair of oblique conveying rotors are controlled to the non-clamping state in the oblique sheet conveying state. [Effects of the Invention]

[0007] According to the present invention, it is possible to prevent the accuracy of skew correction from decreasing. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a printer according to a first embodiment. [Figure 2]FIG. 2 is a top view showing the registration unit according to the first embodiment. [Figure 3] 1A is a cross-sectional view showing the conveying section in the registration unit in a clamping and conveying state, and FIG. 1B is a cross-sectional view showing the conveying section in the registration unit in a non-clamping state. [Figure 4] FIG. 2 is a perspective view showing a part of a transport section in the registration unit. [Figure 5] 1A is a top view showing a part of a skew correction section in a registration unit, and FIG. 1B is a cross-sectional view showing a part of the skew correction section in a registration unit as viewed from the sheet conveyance direction. [Figure 6] 1A is a perspective view showing a pair of oblique feed rollers and a pressure mechanism therefor, and FIG. 1B is a side view showing a part of the pair of oblique feed rollers and a pressure mechanism therefor. [Figure 7] 1A is a side view showing the pair of skew rollers in a nipping and conveying state, and FIG. 1B is a side view showing the pair of skew rollers in a non-nipping and conveying state. [Figure 8] FIG. 4 is a perspective view showing a sheet position detection sensor in a conveying section of the registration unit. [Figure 9] FIG. 2 is a perspective view showing a drive mechanism for a pair of conveying rollers in a conveying section of the registration unit. [Figure 10] FIG. 4 is a perspective view showing a slide mechanism for a pair of conveying rollers in a conveying section of the registration unit. [Figure 11] 1A is a perspective view showing a pressure release mechanism for a pair of conveying rollers in a conveying section of a registration unit, and FIG. 1B is a cross-sectional view showing the pressure release mechanism for a pair of conveying rollers in a conveying section of a registration unit. [Figure 12] FIG. 2 is a block diagram showing a control system of the printer according to the first embodiment. [Figure 13](a) is a top view showing a state in which a sheet has been conveyed to a conveying section of a registration unit according to the first embodiment. (b) is a cross-sectional view of the state shown in (a). (c) is a top view showing a state in which the sheet has been conveyed from the states shown in (a) and (b) to a position where it can be conveyed by a conveying roller pair 34-4. (d) is a cross-sectional view of the state shown in (c). [Figure 14] 1A is a top view showing a state in which skew correction has been performed in the skew correction section of the registration unit according to the first embodiment, and FIG. [Figure 15] 1A is a top view showing a state in which a shift is performed by a pair of registration rollers of the registration unit according to the first embodiment, and FIG. 1B is a cross-sectional view of the state shown in FIG. [Figure 16] 10 is a flowchart showing control of a transport unit of a registration unit during execution of a normal print job according to the first embodiment. [Figure 17] 10 is a flowchart showing control of a skew correction unit and a pair of registration rollers of a registration unit during execution of a normal print job according to the first embodiment. [Figure 18] 6 is a flowchart showing a mode determination control for a pair of oblique feed rollers according to the first embodiment. [Figure 19] 10 is a cross-sectional view schematically illustrating a state of the skew correction unit in a second mode according to the first embodiment. FIG. [Figure 20] 10 is a flowchart showing a mode determination control for a pair of oblique feed rollers according to the second embodiment. [Figure 21] FIG. 11 is a schematic cross-sectional view showing a state of the skew correction unit in a second mode according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment The first embodiment will be described below with reference to Figs. 1 to 19. First, a schematic configuration of a printer 1 as an image forming apparatus equipped with a registration unit 50 as a sheet conveying device according to the first embodiment will be described. Fig. 1 is a schematic diagram showing an image forming apparatus according to the first embodiment. Note that in the printer 1, various sheets can be used as recording media, including paper such as paper and envelopes, glossy paper, plastic film such as sheets for overhead projectors, and cloth.

[0010] [Configuration of image forming device] As shown in FIG. 1, the printer 1 has a control unit 9 (see FIG. 12) that controls the overall operation of the printer 1 based on image information input from an external PC or image information read from a document. The printer 1 has a main body 1A that houses a feed cassette 51 that stores sheets S and an image forming engine 513 that serves as an image forming unit that forms images on the sheets S fed from the feed cassette 51. The image forming engine 513, which is an example of an image forming unit, includes four image forming process units PY, PM, PC, and PK that form yellow, magenta, cyan, and black toner images, respectively, and an intermediate transfer belt 506 that serves as an image carrier. The image forming engine 513 forms images on the sheets S using a tandem intermediate transfer method. Each of the image forming process units PY to PK is an electrophotographic unit that includes a photosensitive drum 508 that is a photosensitive member.

[0011] The image forming process units PY to PK share a common configuration except for the different colors of toner used for development. Here, the configuration of the image forming engine 513 and the toner image formation process will be described using the yellow image forming process unit PY as an example. In addition to the photosensitive drum 508, the image forming process unit PY also includes an exposure device 511, a development device 510, and a drum cleaner 509. The photosensitive drum 508 is a drum-shaped photosensitive body having a photosensitive layer on its outer periphery, and rotates in a direction (arrow A in FIG. 1 ) that is parallel to the rotation direction of the intermediate transfer belt 506 (arrow B in FIG. 1 ). The surface of the photosensitive drum 508 is charged by receiving electrical charge from a charging unit such as a charging roller (not shown). The exposure device 511 irradiates the photosensitive drum 508 with laser light modulated according to image information, and scans the photosensitive drum 508 using an optical system including a reflecting device 512, thereby drawing an electrostatic latent image on the surface of the photosensitive drum 508. Developing device 510 contains a developer containing toner, and supplies toner to photosensitive drum 508 to visualize the electrostatic latent image as a toner image. The toner image formed on photosensitive drum 508 is primarily transferred to intermediate transfer belt 506 at a primary transfer portion, which is a nip portion between primary transfer roller 507 and intermediate transfer belt 506. Residual toner remaining on photosensitive drum 508 after transfer is removed by drum cleaner 509.

[0012] Intermediate transfer belt 506 is wound around drive roller 504, driven roller 505, inner secondary transfer roller 503, and primary transfer roller 507, and is driven to rotate in the clockwise direction (arrow B) in FIG. 1 by drive roller 504. The image formation process described above is carried out in parallel in each image formation process unit PY to PK, and four color toner images are transferred in a superimposed manner to form a full-color toner image on intermediate transfer belt 506. This toner image is transported to secondary transfer unit 1C while still supported by intermediate transfer belt 506. Secondary transfer unit 1C is configured as a nip between secondary transfer roller 56, which serves as a transfer roller, and inner secondary transfer roller 503. A bias voltage of a polarity opposite to the charge polarity of the toner is applied to secondary transfer roller 56, thereby secondarily transferring the toner image to sheet S. Residual toner remaining on intermediate transfer belt 506 after transfer is removed by belt cleaner 514.

[0013] The sheet S onto which the toner image has been transferred is delivered to a fixing unit 58 by a pre-fixing conveyance section 57. The fixing unit 58 has a pair of fixing rollers that sandwich and convey the sheet S, and a heat source such as a halogen heater, and applies pressure and heat to the toner image carried on the sheet S. This melts and fixes the toner particles to the sheet S.

[0014] Next, the sheet transport process for transporting a sheet will be described. The sheet transport system 1D of the printer 1 transports the sheet S fed from the sheet feeding unit 1B as a sheet feeding device, and discharges the sheet S on which an image has been formed to the outside of the apparatus main body 1A. The sheet transport system 1D includes a sheet transport section 54, a registration unit 50, a pre-fixing transport section 57, a branch transport section 59, a reversing transport section 501, and a duplex transport section 502.

[0015] A feeding cassette 51 provided in the sheet feeding unit 1B is removably attached to the apparatus main body 1A, and stores sheets S stacked and supported on a liftable tray 52 that can be raised and lowered, and the sheets are fed one by one by a sheet feeding section 53. Examples of the sheet feeding section 53 include a belt type in which a suction fan attracts and conveys the sheet S to a belt member, and a friction separation type using rollers or pads. The sheet S sent out from the sheet feeding section 53 is conveyed along a feeding path 54a by a pair of conveying rollers of a sheet conveying section 54 and delivered to the registration unit 50.

[0016] The sheet S handed over to the registration unit 50 is subjected to skew correction and timing correction before being conveyed toward the secondary transfer section 1C. At this time, a pair of registration rollers 7 of the registration unit 50 sends the sheet S to the secondary transfer section 1C in accordance with the progress of the image formation process by the image forming process sections PY to PK, based on the detection of the sheet by a sheet detection sensor 8. The sheet S, on which the toner image has been transferred in the secondary transfer section 1C and the image has been fixed by a fixing unit 58, is conveyed to a branch conveyance section 59 that branches off from the conveyance path of the sheet S. When the image formation on the sheet S has been completed, the sheet S is discharged by a pair of discharge rollers to a discharge tray 500 arranged outside the apparatus main body 1A.

[0017] On the other hand, when an image is formed on the back side of the sheet S, the sheet S is delivered to the duplex conveying section 502 via the reversing conveying section 501. The reversing conveying section 501 has a pair of reversing rollers that can rotate forward and backward, and reverses the sheet by a switchback method that reverses the front and back sides of the sheet S. That is, the reversing conveying section 501 retracts the leading edge of the sheet, reverses the conveying direction to reverse the front and back sides of the sheet, and delivers the sheet to the duplex conveying section 502. The duplex conveying section 502 conveys the sheet S again toward the registration unit 50 via the feeding path 54b of the sheet conveying section 54. Then, after an image is formed on the back side of the sheet S, the sheet S is discharged to the discharge tray 500.

[0018] [Registration Unit Configuration] Next, the configuration of a registration unit 50 constituting the sheet conveying device will be described with reference to Fig. 2. Fig. 2 is a top view showing the registration unit. Note that the registration unit 50 according to this embodiment is a unit that corrects skew of a sheet using a side registration method.

[0019] Specifically, as shown in FIG. 2, the registration unit 50 includes, from upstream to downstream in the sheet conveying direction, a conveying section 50A, a skew correction section 50B, and a registration roller pair 7. The registration unit 50 also includes a sheet position detection sensor 60 as a width position detection section that detects the position of the edge of the sheet in the width direction perpendicular to the sheet conveying direction. The registration unit 50 also includes a slide mechanism 600 that moves one of the conveying roller pairs of the conveying section 50A in the width direction perpendicular to the sheet conveying direction. The conveying section 50A includes at least one conveying roller pair that conveys the sheet in the sheet conveying direction. FIG. 2 illustrates a configuration including conveying roller pairs 34-1, 34-2, 34-3, and 34-4. In the following description, when there is no need to distinguish between the conveying roller pairs 34-1, 34-2, 34-3, and 34-4, they will be referred to as "conveying roller pair 34."

[0020] In the registration unit 50 of this embodiment, a slide mechanism 600 serving as a first movement drive unit is provided on the conveying roller pair 34-4 serving as the first conveying rotor pair. Also, Fig. 2 illustrates a configuration in which the sheet position detection sensor 60 is disposed between the conveying roller pair 34-2 and the conveying roller pair 34-3. The sheet position detection sensor 60 can be disposed at a position other than that shown in Fig. 2 where it can detect the widthwise edge of the sheet being conveyed through the conveying unit 50A, for example, at a position between the conveying roller pair 34-4 and the conveying roller pair 34-3.

[0021] The skew correction unit 50B includes skew roller pairs 32-1, 32-2, and 32-3 as skew rotor pairs, and a reference member 31 as an abutment unit. These skew roller pairs 2-1, 32-2, and 32-3 are arranged on a straight line generally facing the sheet conveying direction V. In other words, these skew roller pairs 2-1, 32-2, and 32-3 are arranged so as to at least partially overlap each other when viewed from the sheet conveying direction V. In the first embodiment, the skew roller pair 32-1 constitutes a first skew rotor pair, the skew roller pair 32-3 constitutes a second skew rotor pair, and the skew roller pair 32-2 constitutes a third skew rotor pair. In the following description, when it is not necessary to distinguish between the skew roller pairs 32-1, 32-2, and 32-3, they will be referred to as "skew roller pair 32." The reference member 31 has a reference surface 31a extending in the sheet conveying direction and is disposed on one side in the width direction perpendicular to the sheet conveying direction. The reference surface 31a extends along the sheet conveying direction and serves as an abutting surface that can abut against one edge of the sheet in the width direction.

[0022] A pre-registration sensor (hereinafter referred to as "pre-registration sensor") P is disposed near the conveying roller pair 34-4 to detect the presence or absence of a sheet and thereby detect the arrival of the leading edge of the sheet. The pre-registration sensor P may be, for example, a reflective photoelectric sensor having a light-emitting element and a light-receiving element. In this case, the light emitted by the light-emitting element is reflected by the sheet that has reached the detection position, and the reflected light is detected by the light-receiving element, thereby detecting the timing of the sheet passing. As shown in FIG. 2, in this embodiment, the pre-registration sensor P is disposed between the conveying roller pair 34-4 and the skew roller pair 32-1 in the sheet conveying direction.

[0023] The skew roller pairs 32-1, 32-2, and 32-3 each rotate around an axis inclined with respect to the width direction. That is, the skew roller pairs 32-1, 32-2, and 32-3 are arranged parallel to each other so that the tangent direction at the contact portion with the sheet is inclined at an angle θ with respect to the sheet conveying direction V. Therefore, the skew roller pairs 32-1, 32-2, and 32-3 rotate in contact with the sheet, thereby moving the sheet so that it approaches the reference surface 31a of the reference member 31 in the width direction as it moves downstream in the sheet conveying direction V. Also, the skew roller pairs 32 move the sheet so that it approaches the reference surface 31a as it moves downstream in the sheet conveying direction V.

[0024] Here, skew correction of a sheet by the skew correction unit 50B will be described. The skew correction unit 50B corrects skew of a sheet by a so-called side registration method. Specifically, the skew correction unit 50B abuts the side edge of the sheet, i.e., the sheet end in the width direction, against a reference member 31 having a reference surface 31a extending along the sheet conveying direction V. After the sheet abuts against the reference surface 31a, the skew of the sheet is corrected by moving the side edge of the sheet along the reference surface 31a. The sheet conveying direction V is the direction in which the sheet travels by the conveying roller pair 34 of the conveying unit 50A, or the direction in which the sheet travels as it is conveyed toward the secondary transfer unit 1C by the registration roller pair 7.

[0025] In addition to the pre-registration sensor P, the skew correction unit 50B also has a pre-registration sensor (hereinafter referred to as the "pre-registration sensor") Q, which serves as an arrival detection unit that detects the presence or absence of a sheet and thereby detects the arrival of the leading edge of the sheet. The pre-registration sensor Q is disposed downstream of the skew roller pair 32 and upstream of the registration roller pair 7 in the sheet conveyance direction. Like the pre-registration sensor P, the pre-registration sensor Q can be a known sensor such as a reflective photoelectric sensor. The pre-registration sensor Q is a sensor that detects the arrival of a sheet at the registration roller pair 7. Specifically, the pre-registration sensor Q detects that the sheet has reached the registration roller pair 7 after a predetermined delay time has elapsed since the pre-registration sensor Q detected the sheet. In other words, the function of the pre-registration sensor Q is to detect that the sheet has reached the registration roller pair 7. The pre-registration sensor Q may be disposed downstream of the registration roller pair 7, in which case it will detect that the sheet has already reached the registration roller pair 7.

[0026] The registration roller pair 7, which serves as the second conveying rotator pair, can be moved by a slide mechanism 70, which serves as the second movement drive unit, by sliding the pair of registration rollers 7 in the width direction perpendicular to the sheet conveyance direction while sandwiching the sheet. The slide mechanism 70 may be a mechanism similar to the slide mechanism 600 that moves the pair of conveying rollers 34-4 in the width direction. The registration roller pair 7 moves the sheet, whose side edge abuts against the reference surface 31a of the reference member 31, in the width direction to match the position of the image to be transferred at the secondary transfer unit 1C. This moves the sheet so that the center of the width direction of the sheet whose skew has been corrected by the registration unit 50 coincides with the center of the width direction of the image to be transferred at the secondary transfer unit 1C (the center of the width direction of the image formation area). The method for adjusting the position of the sheet and the image to be formed on the sheet is not limited to this. For example, the registration roller pair 7 may move the sheet so that the center of the sheet coincides with the conveyance center of the printer 1, and adjust the center of the main scanning direction of the toner image formed by the image forming process units PY to PK to coincide with the center in the width direction.

[0027] [Detailed configuration of the transport section] The detailed configuration of the conveying unit 50A will be described in detail using Figures 3(a), 3(b), and 4. Figure 3(a) is a cross-sectional view showing the conveying unit in a clamping conveying state in the registration unit. Figure 3(b) is a cross-sectional view showing the conveying unit in a non-clamping state in the registration unit. Figure 4 is a perspective view showing a part of the conveying unit in the registration unit. Note that Figures 3(a) and 3(b) show three of the four conveying roller pairs 34. Also, in this embodiment, the printer 1 is shown as having four conveying roller pairs 34 (see Figure 2) as an example, but the number of conveying roller pairs is not limited to this.

[0028] As shown in Figures 3(a) and 3(b), in the conveying section 50A, the conveying roller pairs 34-1, 34-2, and 34-3 each include a drive roller 13 to which a driving force is input and a driven roller 14 that rotates following the drive roller 13. The conveying roller pairs 34 are switchable between a nip conveying state (Figure 3(a)) in which a sheet is sandwiched between the nip portions and conveyed, and a non-nip conveying state (Figure 3(b)) in which the nip portions are separated and the sheet is not sandwiched between the nip portions. Whether all of the conveying roller pairs 34 are switchable between the nip conveying state and the non-nip conveying state can be determined depending on the size of sheets that the printer 1 can convey.

[0029] The conveying section 50A is provided with a cam mechanism 100 having an eccentric roller 103 as a switching section that can switch between a sandwiching conveying state and a non-sandwiching state of the conveying roller pairs 34-1, 34-2, and 34-3. The eccentric roller 103 is driven to rotate by a pre-register pressure release motor Md (see FIG. 12) via gears 105 and 106, causing an arm member 101 that abuts against a cam surface on its outer periphery to swing. The arm member 101 is supported by a stay member 18 so as to be swingable about a swing shaft 102. One side of the swing shaft 102 abuts against the eccentric roller 103, and the other side supports a driven shaft 20, which is the rotation shaft of the driven roller 14. As the arm member 101 swings, the driven rollers 14 appear and disappear from a sheet conveying path formed by a guide member (not shown). Therefore, by controlling the rotation angle of the eccentric roller 103 via the pre-registration pressure release motor Md, which is a stepping motor, it is possible to switch the positional relationship between the driven roller 14 and the drive roller 13. In other words, by controlling the rotation angle of the eccentric roller 103, it is possible to switch between a non-clamping state in which the driven rollers 14 are separated from the drive rollers 13 and a clamping conveying state in which the driven rollers 14 are in pressure contact with the drive roller 13.

[0030] 4, the drive roller 13 is a rubber roller attached to a drive roller shaft 301A, and is connected to a pre-register drive motor Mp (see FIG. 12) serving as a drive source via a belt transmission mechanism 302. The pre-register drive motor Mp is a stepping motor, and is configured to be able to change the timing of starting and stopping the drive and the drive speed of the drive roller 13 (the peripheral speed of the drive roller 13).

[0031] [Detailed configuration of the skew correction unit] Next, the configuration of the skew correction unit 50B will be described in detail with reference to Figures 5(a), 5(b), 6(a), 6(b), 7(a), and 7(b). Figure 5(a) is a top view showing a part of the skew correction unit in the registration unit. Figure 5(b) is a cross-sectional view showing a part of the skew correction unit in the registration unit as viewed from the sheet conveyance direction. Figure 6(a) is a perspective view showing a pair of skew rollers and their pressure mechanism. Figure 6(b) is a side view showing a pair of skew rollers and part of their pressure mechanism. Figure 7(a) is a side view showing the pair of skew rollers in a nipping conveyance state. Figure 7(b) is a side view showing the pair of skew rollers in a non-nipping state.

[0032] 5(a), skew correction unit 50B is provided with skew roller pairs 32-1, 32-2, and 32-3, each of which has a drive roller 320-1, 320-2, or 330-3. These drive rollers 320-1, 320-2, and 330-3 have their rotation axes fixed by universal joints 321, 321, and 321 in a state inclined according to angle θ. When it is not necessary to distinguish between these drive rollers 320-1, 320-2, and 330-3, they are referred to as drive rollers 320-n.

[0033] Each drive roller 320-n is connected to a skew roller drive motor Ms (see FIG. 12) which is a drive source via a transmission mechanism including a universal joint 321, a belt 323, and a pulley. The skew roller drive motor Ms is a stepping motor, and is capable of controlling the drive speed and start / stop timing of the drive roller 320-n.

[0034] As shown in FIG. 5(b), the reference member 31 has a concave cross section consisting of a reference surface 31a against which the side edge of the sheet S abuts, an upper facing surface 31b facing the upper surface of the sheet S, and a lower facing surface 31c facing the lower surface of the sheet S. The reference member 31 is made of die-cast aluminum, and the reference surface 31a is preferably made by machining to improve precision, and then coated with a fluororesin such as PTFE (polytetrafluoroethylene) by electroless nickel processing. This provides a reference surface 31a with high flatness and high slipperiness (low frictional resistance to the sheet), thereby improving the accuracy of skew correction of the sheet S.

[0035] As shown in FIGS. 6(a), 6(b), 7(a), and 7(b), the skew roller pair 32-n arranged in the skew correction unit 50B includes a drive roller 320-n and a driven roller 331-n facing the drive roller 320-n. The skew correction unit 50B also includes a pressure mechanism 33-n that moves the driven roller 331-n. The pressure mechanism 33-n includes a pressure mechanism 33-1 that moves the driven roller 331-1 of the skew roller pair 32-1. The pressure mechanisms 33-n also include a pressure mechanism 33-2 that moves the driven roller 331-2 of the skew roller pair 32-2, and a pressure mechanism 33-3 that moves the driven roller 331-3 of the skew roller pair 32-3. In this embodiment, the pressure mechanism 33-1 constitutes a first switching mechanism, the pressure mechanism 33-2 constitutes a third switching mechanism, and the pressure mechanism 33-3 constitutes a second switching mechanism. When there is no need to distinguish between these pressure mechanisms 33-1, 33-2, and 33-3, they are referred to as pressure mechanisms 33-n. The pressure mechanism 33-n is capable of switching between a nip conveying state in which the driven roller 331-n is pressed against the drive roller 320-n to form a nip and can convey a sheet by nipping it, and a non-nip conveying state in which the driven roller 331-n is separated from the drive roller 320-n.

[0036] Here, n is a number obtained by numbering the skew roller pair 32, the driven roller 331, and the pressure mechanism 33 in order from the upstream in the sheet conveying direction V, and for example, the skew roller pair 32-1 means the skew roller pair 32 arranged at the most upstream (n=1). That is, in the skew correction unit 50B of this embodiment, a plurality of sets of driven rollers 331-n and pressure mechanisms 33-n are arranged in a state where the skew roller pair 32-n shown in FIGS. 6 and 7 is replaced with any of the skew roller pairs 32-1, 32-2, and 32-3.

[0037] The pressure mechanism 33-n includes an arm member 332, a link member 333, a pressure gear 334, a pressure spring 335, and a driven roller pressure motor Mk-n (see FIG. 12). The driven roller 331-n is rotatably supported by the arm member 332 around a driven shaft, and can move toward or away from the oblique feed roller pair 32-n by swinging the arm member 332. In this embodiment, the driven roller 331-n rotates along the sheet conveying direction around an axis extending in the width direction, but may be configured to be disposed on an axis parallel to the corresponding oblique feed roller pair 32-n. The arm member 332 is connected to the pressure gear 334 via the pressure spring 335 and the link member 333. The pressure gear 334 is connected to the output shaft of the driven roller pressure motor Mk-n, which serves as a drive source.

[0038] As shown in Fig. 7(a), in the clamping / conveying state, the pressure gear 334 rotates counterclockwise in the figure, and the arm member 332, pulled by the pressure spring 335, swings counterclockwise around the swing shaft 332-1. As a result, the driven roller 331-n is in pressure contact with the drive roller 320-n. On the other hand, as shown in Fig. 7(b), in the non-clamping state, the pressure gear 334 rotates clockwise in the figure and presses the link member 333, and the link member 333 swings the arm member 332 clockwise. As a result, the driven roller 331-n moves away from the drive roller 320-n.

[0039] The driven roller pressure motor Mk-n is a stepping motor, and can change the amount of extension of the pressure spring 335 in the pressure-applied state by controlling the rotation angle of the pressure gear 334. That is, the pressure mechanism 33-n according to this embodiment can switch between the clamping conveying state and the non-clamping state, and can change the pressure in the clamping conveying state.

[0040] [Seat position detection sensor configuration] Next, the configuration of the sheet position detection sensor 60 as the width position detection unit of this embodiment will be described with reference to Fig. 8. Fig. 8 is a perspective view showing the sheet position detection sensor in the conveying unit of the registration unit. The sheet position detection sensor 60 includes an optical element such as a CIS (Contact Image Sensor), and is arranged in the same direction as the reference member 31 and at a position offset in the width direction with respect to the center of the sheet in the sheet conveying direction V. This is to detect the position of the edge of the sheet on the side that abuts against the reference member 31.

[0041] [Drive and slide configuration of the conveying roller pair] Next, the drive configuration of the conveying roller pair 34-4 in this embodiment and the configuration of the slide mechanism 600 that slides the conveying roller pair 34-4 will be described using Figures 9, 10, 11(a) and 11(b). Figure 9 is a perspective view showing the drive mechanism of the conveying roller pair in the conveying section of the registration unit. Figure 10 is a perspective view showing the slide mechanism of the conveying roller pair in the conveying section of the registration unit. Figure 11(a) is a perspective view showing the pressure release mechanism of the conveying roller pair in the conveying section of the registration unit. Figure 11(b) is a cross-sectional view showing the pressure release mechanism of the conveying roller pair in the conveying section of the registration unit.

[0042] The conveying roller pair 34-4 is generally rotationally driven by a roller drive mechanism 800, and configured to be movable in the width direction perpendicular to the sheet conveying direction while sandwiching the sheet by a slide mechanism 600. The conveying roller pair 34-4 is also configured to be switchable by a pressure release mechanism 700 between a sandwich conveying state in which the sheet is sandwiched between the nip of the roller pair constituting the conveying roller pair 34-4, and a non-sandwich state in which the roller pair is spaced apart.

[0043] More specifically, as shown in FIG. 10, the conveying roller pair 34-4 is composed of an upper roller 401 and a lower roller 402 (see FIG. 11(a)). The lower roller 402 is rotatably supported by the frame 201 (see FIG. 11(a)), and the upper roller 401 is rotatably supported by a pressure arm 405 (see FIG. 10). The pressure arm 405 is rotatably fixed by a shaft 201a formed on the frame 201 (see FIG. 10). The upper roller 401 is pressed against the lower roller 402 by a tension spring 407. A roller gear 412 that transmits driving force from the roller drive mechanism 800 to the lower roller 402 is fixed to one end of the lower roller 402 (see FIG. 9).

[0044] As shown in FIG. 9, the roller drive mechanism 800 that rotates the conveying roller pair 34-4 includes a slide roller drive motor 801 (see FIG. 12), drive gears 802 and 803, and a roller gear 412. The slide roller drive motor 801 is fixed to the frame 201, and the drive of the slide roller drive motor 801 is transmitted to the roller gear 412 via the drive gears 802 and 803. The tooth surface of the drive gear 803 is formed with a length d that is longer than the reciprocating width of the roller gear 412 so that meshing with the roller gear 412 is maintained. The drive gear 802 is rotatably fixed to a fixed shaft 201b of the frame 201, and the drive gear 803 is rotatably fixed to a fixed shaft 201c. In this embodiment, a stepping motor is used as the slide roller drive motor 801. With this configuration, the drive force of the slide roller drive motor 801 is transmitted to the roller gear 412, causing the pair of conveying rollers 34-4 to rotate.

[0045] As shown in FIG. 10, the slide mechanism 600, which moves the conveying roller pair 34-4 in the width direction perpendicular to the sheet conveying direction, has a slide motor 601 (see FIG. 12) fixed to a motor base 602 and screwed to a motor support plate 603. A pulley support plate 604 is screwed above the motor support plate 603 via the slide motor 601. Pulley bases 605 and 606 are fixed to the pulley support plate 604. As shown in FIG. 9, a pulley shaft 607 is rotatably fixed to the pulley base 605, and a pulley shaft 608 is rotatably fixed to the pulley base 606. Pulleys 609 and 610 are fixed to the pulley shaft 607, and a pulley 611 is fixed to the pulley shaft 608. In addition, a pulley 612 is fixed to the tip of the output shaft of the slide motor 601. A timing belt 613 is stretched between the pulley 609 and the pulley 612, and a timing belt 614 is stretched between the pulley 610 and the pulley 611 (see FIG. 10).

[0046] 10 , a holder 415 is rotatably supported by a bearing at the end of the lower roller 402 on the roller gear 412 side. A sensor flag 416 is attached to the holder 415 to detect the home position in the width direction of the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4. When the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4 are at their home positions, the sensor flag 416 is detected by a sensor 615 provided on the pulley support plate 604. The holder 415 is fixed to a timing belt 614 by a stopper 616 and a screw (not shown). With this configuration, the timing belt 614 is rotated by the drive of the slide motor 601, and the rotation of the timing belt 614 causes the lower roller 402 of the conveying roller pair 34-4 to reciprocate in the width direction perpendicular to the sheet conveying direction. Additionally, the upper roller 401 of the conveying roller pair 34-4 is engaged with the lower roller 402 by an engagement member (not shown), and moves back and forth together with the lower roller 402 in the width direction perpendicular to the sheet conveying direction. In this embodiment, the slide motor 601 is driven based on the detection result of the position of the edge of the sheet in the width direction detected by the CIS 60, and the conveying roller pair 34-4 moves in the width direction.

[0047] As shown in FIG. 11(a), the pressure release mechanism 700, which brings the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4 into and out of contact with each other, has a pressure release shaft 701 that is positioned in the frame 201. The pressure release mechanism 700 also includes cams 702 and 703 (see FIG. 11(b)) fixed to the pressure release shaft 701. As shown in FIG. 11(b), deep groove ball bearings 702a and 703a are press-fitted into the cams 702 and 703 at positions eccentric to their respective rotation centers. As shown in FIG. 11(a), a gear 702b is formed on the cam 702, and the pressure release shaft 701 rotates when the drive force of a pressure release motor 704 (see FIG. 12) is transmitted via the cam 702.

[0048] The deep groove ball bearing 702a is positioned so that it can contact the pressure arm 405. When the pressure release shaft 701 rotates once, the deep groove ball bearing 702a swings the pressure arm 405 against the biasing force of the spring 407. By swinging the pressure arm 405 in this manner, the upper roller 401 and the lower roller 402 can be brought into contact with and separated from each other once. A pressure arm (not shown) is also provided on the axial side of the pressure release shaft 701 on the side where the deep groove ball bearing 703a is provided. The cam 703 is also formed with a sensor flag 703b (see FIG. 11(b)). The phase of the pressure release shaft 701 is determined by detecting the sensor flag 703b using a sensor 706 fixed to a sensor support plate 705 fixed to the frame 201. The rotation of the pressure release motor 704 is controlled in accordance with the phase of the pressure release shaft 701. The phases of the cams 702 and 703 of the sensor flag 703b are determined so that the sensor 706 is shielded when the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4 are in contact with each other.

[0049] [Printer control system configuration] Next, the configuration of the control system of the printer 1 will be described with reference to Fig. 12. Fig. 12 is a block diagram showing the control system of the printer according to the first embodiment.

[0050] 12, the registration unit 50 in the printer 1 is controlled by a control unit 9. The control unit 9 includes a CPU 9a as a calculation unit, a RAM 9b and a ROM 9c as storage units, and an interface (I / O) 9d for external devices or networks.

[0051] The CPU 9a performs control based on information input via the operation unit 400 as a user interface and detection signals from the pre-registration sensor P and pre-registration sensor Q. The detection signals from the pre-registration sensor P and pre-registration sensor Q are input to the CPU 9a via AD conversion units 901 and 902, respectively. In addition, the detection signal from the sheet position detection sensor 60 is input to the CPU 9a via an AD conversion unit 910. The CPU 9a loads and executes programs stored in the ROM 9c or the like. The CPU 9a drives and controls the motors (Ms, Mp, Md, Mk-n, 601, 701, 801) that are actuators of the registration unit 50 via drivers 903, 904, 905, 606-n, 907, 908, 909.

[0052] [Overview of the operation of the registration unit] (Transport unit operation) Next, an outline of the operation of the registration unit 50 will be described. First, the pre-skew correction shift operation of the conveying section 50A in the registration unit 50, which is performed before skew correction, will be described with reference to FIGS. 13(a) and 13(b). FIG. 13(a) is a top view showing a state in which a sheet is conveyed to the conveying section of the registration unit according to the first embodiment. FIG. 13(b) is a cross-sectional view of the state shown in FIG. 13(a). FIG. 13(c) is a top view showing a state in which the sheet has been conveyed from the state shown in FIGS. 13(a) and 13(b) to a position where it can be conveyed by the conveying roller pair 34-4. FIG. 13(d) is a cross-sectional view of the state shown in FIG. 13(c).

[0053] 13(a) and 13(b), when the sheet S being conveyed in the sheet conveying direction V reaches the sheet position detection sensor 60 at the registration unit 50, the sheet position detection sensor 60 detects the position of the edge (side edge position) of the sheet S. The CPU 9a (see FIG. 12) calculates the amount of deviation from the detected side edge position of the sheet S relative to the 0 point position as the reference position of the sheet position detection sensor 60, and calculates the amount of shift in the width direction by the conveying roller pair 34-4 (the shift amount of the shift operation before skew correction).

[0054] Next, as shown in FIGS. 13(c) and 13(d), when the sheet S reaches the conveying roller pair 34-4 in the nip-conveying state, the CPU 9a separates the conveying roller pairs 34-1, 34-2, and 34-3 (brings them into a non-nip state). The CPU 9a shifts (moves) the conveying roller pair 34-4 in the direction of the arrow W2a by the calculated shift amount, that is, shifts the sheet S so that the side edge of the sheet S is aligned with the zero point position, which is the reference position of the sheet position detection sensor 60. This zero point position is a set position where the edge of the sheet in the width direction is separated from the reference member 31 to the other side in the width direction. This completes the shift operation before skew correction, and when the sheet S is skew-corrected by the skew correction unit 50B, the distance in the width direction between the reference member 31 and the edge of the sheet S is stabilized. In other words, the sliding distance between the reference member 31 and the sheet S during skew correction is stabilized, and the conveying speed of the sheet S is stabilized.

[0055] (Operation of the skew correction unit) Next, the skew correction operation of the skew correction section 50B in the registration unit 50 will be described with reference to Figures 14(a) and 14(b). Figure 14(a) is a top view showing a state in which skew correction has been performed in the skew correction section of the registration unit according to the first embodiment. Figure 14(b) is a cross-sectional view of the state shown in Figure 14(a). In the description of the operation of the skew correction section, a case will be described in which, for example, the sheet S is a sheet with a large basis weight such as plain paper or thick paper, and skew correction of the sheet S is performed with all of the skew roller pairs 32-1 to 32-3 in a nipping and conveying state, as will be described in detail later.

[0056] 14(a) and 14(b), in the registration unit 50, the skew roller pairs 32-1 to 32-3 in a nip-and-convey state (pressure state) convey the sheet S in a direction inclined with respect to the sheet conveying direction V indicated by the arrow K in the drawing. As a result, the side edge of the sheet S abuts against and comes into contact with the reference surface 31a of the reference member 31. In the registration unit 50, when skew correction is performed, the skew roller pairs 32-1 to 32-3 are in a nip-and-convey state, and the conveying roller pairs 34-1 to 34-4 are in a non-nip-and-convey state. Therefore, in the registration unit 50, by performing skew correction by the skew roller pairs 32-1 to 32-3 after the conveying roller pairs 34-1 to 34-4 are separated, skew correction can be performed without interference from the conveying roller pairs 34-1 to 34-4.

[0057] (Operation of the registration roller pair) Next, the sheet alignment operation in the width direction of the registration roller pair 7 in the registration unit 50 will be described with reference to Figures 15(a) and 15(b). Figure 15(a) is a top view showing a state in which a shift has been performed by the registration roller pair of the registration unit according to the first embodiment. Figure 15(b) is a cross-sectional view of the state shown in (a).

[0058] 15(a) and 15(b), the registration roller pair 7 shifts the sheet S in the direction of the arrow W1a in the figure so that the widthwise position of the sheet S matches the widthwise position of the image to be transferred by the secondary transfer portion 1C (see FIG. 1). That is, the registration roller pair 7 performs a shift operation after skew correction in the direction of the arrow W1a while conveying the sheet S in the sheet conveying direction V so that the widthwise position matches the widthwise position of the image formed by the image forming engine 513 (see FIG. 1). As a result, the registration unit 50 can form an image on the sheet S in a state in which the widthwise position of the skew-corrected sheet S is adjusted to match the widthwise position of the image formed by the image forming engine 513 and transferred by the secondary transfer portion 1C.

[0059] In this embodiment, the position of the sheet S in the width direction is shifted by the registration roller pair 7 after the skew roller pairs 32-1 to 32-3 are put into a non-clamping state (separated). Therefore, the position of the sheet S in the width direction can be shifted without interference from the skew roller pairs 32-1 to 32-3.

[0060] <Registration unit control for print jobs> Next, the control of the registration unit 50 when, for example, an instruction to print one or more sheets is sent to the control unit 9 from an external computer, operation unit 400, etc., and the print job is executed will be described in detail using Figures 16, 17, and 18. Figure 16 is a flowchart showing the control of the transport unit of the registration unit when a normal print job is executed according to the first embodiment. Figure 17 is a flowchart showing the control of the skew correction unit and registration roller pair of the registration unit when a normal print job is executed according to the first embodiment. Figure 18 is a flowchart showing the control of determining the operating mode of the skew roller pair according to the first embodiment.

[0061] (Operation of the transport part of the registration unit) The control unit 9 first acquires information about sheets (hereinafter referred to as "sheet information") from information included in a print job input from an external computer or the operation unit 400 (or information previously set for the feed cassette 51) (S1). In this process, the control unit 9 acquires sheet information such as the basis weight, size, number of sheets, and type of sheet. Among the sheet information, the type information includes information indicating the type of paper, such as office plain paper, coated paper, thick paper, thin paper, etc. The control unit 9 also acquires the number of sheets to be passed through the registration unit 50 in the started print job from the number of sheets information included in the sheet information, and sets this as the initial value of a memory value to be stored in a paper passing counter.

[0062] Next, the control unit 9 determines the operation mode of the skew roller pairs 32-1 to 32-3 (S2). The operation mode of the skew roller pairs 32-1 to 32-3 is determined by executing the skew roller pair operation mode determination control shown in FIG. 18. As shown in FIG. 18, the control unit 9 determines whether the basis weight of the sheet S is 60 gsm or less from the sheet information acquired as described above (S31). If the basis weight of the sheet S is 60 gsm or less (Yes in S31), it determines to separate the skew roller pair 32-3 and to press the skew roller pairs 32-1 and 32-2 together (S32). That is, the second mode is selected and determined as the operation mode. On the other hand, if the basis weight of the sheet S is not 60 gsm or less (No in S31), it determines to press all of the skew roller pairs 32-1, 32-2, and 32-3 together (S33). That is, the first mode is selected and determined as the operation mode.

[0063] Once the operation mode of the skew roller pairs is determined in this manner, the control unit 9 determines the nip pressures of the skew roller pairs 32-1 to 32-3 (S3). In this process, the control unit 9 obtains table data from the ROM 9c that associates nip pressures with each preset sheet type based on the sheet information obtained in the process of step S1 and the determined operation mode, and determines the nip pressures of the skew roller pairs 32-1 to 32-3. Then, for example, if the determined operation mode is the first mode, the control unit 9 determines the magnitude of the nip pressure for the skew roller pairs 32-1 to 32-3. If the determined operation mode is the second mode, the control unit 9 determines the magnitude of the nip pressure for the skew roller pairs 32-1 to 32-3. The magnitude of the nip pressure for each skew roller pair 32-1 to 32-3 is determined depending on the type and basis weight of the sheet. That is, for example, the greater the basis weight and the more slippery the surface, the greater the nip pressure set for the skew roller pairs 32-1 to 32-3.

[0064] Next, the control unit 9 starts forming an image by the image forming engine 513 (S4). The control unit 9 starts counting the paper feed start delay based on the timing when the processing of step S4 started (S5). The paper feed start delay is the difference in time between the time that elapses from when an image is formed on the intermediate transfer belt 506 to when it is transported to the secondary transfer unit 1C and the time that elapses until the sheet is transported from the feed cassette 51 to the secondary transfer unit 1C. The control unit 9 sets a value to be counted as the paper feed start delay according to the image that started to be formed in the processing of step S4, and starts counting.

[0065] When the count of the paper feed start delay reaches a set value, the control unit 9 starts feeding a sheet from the feeding cassette 51 (S6). The control unit 9 causes the sheet position detection sensor 60 to detect the side edge position of the sheet at the first timing when the sheet is conveyed and reaches the sheet position detection sensor 60 (S7). The arrival of the sheet at the sheet position detection sensor 60 can be detected by the signal output of the sheet position detection sensor 60.

[0066] Next, the control unit 9 calculates the shift amount of the sheet (S8). In this process, the control unit 9 calculates the amount of deviation from the detection result of the sheet position detection sensor 60 to the zero point position set as the reference position of the sheet position detection sensor 60. Then, the control unit 9 determines the amount of shift for shifting the conveying roller pair 34-4 in the width direction perpendicular to the sheet conveying direction according to the calculated deviation amount.

[0067] After executing the process of step S8, the control unit 9 determines whether the pre-registration sensor P is turned ON (S9). In this process, the control unit 9 determines from the signal of the pre-registration sensor P whether the sheet whose side edge position is detected by the sheet position detection sensor 60 has reached the pre-registration sensor P.

[0068] In the process of step S9, if it is determined that the pre-registration sensor P is not ON (No in S9), the control unit 9 determines that a paper jam has occurred because the sheet has not been transported to the pre-registration sensor P at the timing when it should have been transported. The control unit 9 displays on the operation unit 400 that a paper jam has occurred (S23 in FIG. 17), and ends this control.

[0069] On the other hand, when it is determined that the pre-registration sensor P has turned ON (Yes in S9), the control unit 9 starts counting the release delay of the conveying roller pairs 34-1 to 34-3 (S10). At the time when the process of step S10 is executed, in the registration unit 50, the sheet has reached the pre-registration sensor P located downstream in the conveying direction from the conveying roller pair 34-4, and the shift operation before skew correction by the conveying roller pair 34-4 is possible. Therefore, in the process of step S12, the control unit 9 sets a value of the release delay, which is the time that elapses until the conveying roller pairs 34-1 to 34-3 change from a clamping conveying state to a non-clamping state, and starts counting.

[0070] When the count of the release delay in step S10 reaches the set value, the control unit 9 separates the drive roller 13 and the driven roller 14 of the conveying roller pairs 34-1 to 34-3 to put them in a non-clamped state (S11). As a result, in the registration unit 50, the sheet is clamped by the conveying roller pair 34-4 and is not clamped by the conveying roller pairs 34-1 to 34-3.

[0071] Then, the control unit 9 shifts the pair of conveying rollers 34-4 in the width direction by an amount corresponding to the detection result of the sheet position detection sensor 60 (S12). In this process, the control unit 9 shifts the pair of conveying rollers 34-4 by the amount calculated in the process of step S8, and shifts the sheet to a position where the distance from the reference surface 31a of the reference member 31 to the side edge of the sheet is a predetermined distance, that is, the zero point position which is the reference position.

[0072] In this embodiment, the sheet is shifted in the width direction by the conveying roller pair 34-4 in step S12 while being conveyed. However, in order to stabilize the sheet shifting, the sheet conveyance may be stopped, the sheet may be shifted by the conveying roller pair 34-4, and then the sheet conveyance may be resumed.

[0073] (Operation of the skew correction unit and the registration roller pair in the first mode) Next, the process proceeds to step S13 shown in Fig. 17 and onwards, where control of the skew correction unit and the registration roller pair is started. Note that here, the case where the first mode is selected and set as the operation mode of the skew roller pair in step S2 above will be explained, and the case where the second mode is selected and set will be collectively described later.

[0074] After executing the process of step S12, the control unit 9 starts counting the pressure delay of the skew roller pairs 32-1 to 32-3 (S13), as shown in Fig. 17. At the time when the process of step S13 is executed, the registration unit 50 has completed shifting of the sheet before skew correction. Also, in the registration unit 50, the skew roller pairs 32-1 to 32-3 are in a non-clamping state to prevent interference of the skew roller pairs 32-1 to 32-3 with the shift by the conveying roller pair 34-4. Therefore, in the process of step S13, the control unit 9 sets a value of the pressure delay, which is the time that elapses until the skew roller pairs 32-1 to 32-3 change from a non-clamping state to a clamping conveying state, and starts counting.

[0075] Next, at the timing when the counting of the pressure delay is completed, the control unit 9 presses the drive rollers 320-1 to 320-3 and the driven rollers 331-1 to 331-3 of the skew roller pairs 32-1 to 32-3 together (S14). Furthermore, the control unit 9 starts counting the release delay, which is the time it takes for the conveying roller pair 34-4 to change from a clamping conveying state to a non-clamping state (S15). Then, at the timing when the counting of the release delay is completed, the lower roller 402 and the upper roller 401 of the conveying roller pair 34-4 are separated, and skew conveyance is performed by the skew roller pairs 32-1 to 32-3 to perform skew correction (S16).

[0076] That is, by performing the processes of steps S13 to S16, the sheet is not sandwiched between the conveying roller pair 34-4 in the registration unit 50, and the sheet can be sandwiched and conveyed by the skew roller pairs 32-1 to 32-3 in the registration unit 50. In the registration unit 50, by sandwiching and conveying the sheet between the skew roller pairs 32-1 to 32-3, skew of the sheet being conveyed is corrected while the side edge of the sheet is brought into contact with the reference surface 31a of the reference member 31.

[0077] Next, the control unit 9 determines whether the pre-registration sensor Q is turned ON (S17). In this process, the control unit 9 determines from the signal of the pre-registration sensor Q whether the sheet whose skew has been corrected by the skew roller pairs 32-1 to 32-3 has reached the pre-registration sensor Q.

[0078] In the process of step S21, if it is determined that the pre-registration sensor Q is not ON (No in S17), the control unit 9 determines that a paper jam has occurred because the sheet has not been transported to the pre-registration sensor Q at the timing when it should have been transported. In this case, the control unit 9 displays on the operation unit 400 that a paper jam has occurred (S23), and ends the control process related to the registration correction and skew correction.

[0079] On the other hand, when it is determined that the pre-registration sensor Q has turned ON (Yes in S17), the control unit 9 starts counting the release delay of the skew roller pairs 32-1 to 32-3 (S18). At the time when the process of step S18 is executed, in the registration unit 50, the leading edge of the sheet has reached the pre-registration sensor Q, which is located downstream in the conveying direction from the skew roller pairs 32-1 to 32-3. Therefore, the sheet can be conveyed and shifted by the registration roller pair 7. Therefore, in the process of step S18, the control unit 9 sets a release delay value, which is the time that elapses until the skew roller pairs 32-1 to 32-3 change from a nipping conveying state to a non-nipping state, and starts counting.

[0080] Next, at the timing when the count of the release delay is completed, the control unit 9 separates the drive rollers 320-1 to 320-3 and the driven rollers 331-1 to 331-3 of the skew roller pairs 32-1 to 32-3 (S19). As a result, in the registration unit 50, the sheet is sandwiched between the registration roller pair 7 and is not sandwiched between the skew roller pairs 32-1 to 32-3.

[0081] Next, the control unit 9 shifts the widthwise position of the sheet after skew correction using the registration roller pair 7 so that the widthwise position of the sheet matches the widthwise position of the image transferred by the secondary transfer unit 1C (S20). In this process, the control unit 9 shifts the widthwise position of the sheet held between the registration roller pair 7 to a position corresponding to the center position in the widthwise direction of the image formed by the image forming engine 513.

[0082] Next, the control unit 9 subtracts 1 from the number of passed sheets counted by the paper passing counter (S21). In this process, the control unit 9 subtracts 1, which is the value corresponding to one sheet, from the stored value of the paper passing counter because a series of skew correction operations for one sheet, i.e., shift before skew correction, skew correction, and shift after skew correction, has been completed.

[0083] Then, the control unit 9 determines whether the stored value of the paper passing counter is 0 (S22). In this process, if it is determined that the stored value of the paper passing counter is not 0 (No in S22), the control unit 9 returns the process to step S3 to execute a series of skew correction operations on the next sheet to be conveyed in the current print job. On the other hand, if it is determined that the stored value of the paper passing counter is 0 (Yes in S22), the control unit 9 determines that the current print job is completed and ends this control.

[0084] [Problems with low basis weight sheets] As described above, the first mode is selected when the sheet S conveyed from the conveying roller pair 34-4 to the skew roller pairs 32-1 to 32-3 of the skew correction unit 50B is a sheet with a basis weight of 60 gsm or more, such as plain paper or cardboard. The skew roller pairs 32-1 to 32-3 then convey the sheet S in a state in which all three of them are in pressure contact (sandwich conveying state) until at least the widthwise edge of the sheet S abuts against the reference member 31. As shown in FIG. 14(a), the leading edge of the sheet S in the sheet conveying direction abuts against the reference member 31, and the widthwise edge of the sheet S turns in the direction of arrow M so as to follow the reference member 31, thereby correcting the skew of the sheet S.

[0085] At this time, as described above, the pressure with which the oblique feed roller pairs 32-1 to 32-3 nip the sheet S can be changed by the respective pressure mechanisms 33-n. For this reason, the oblique feed force (conveying force in the oblique feed direction) that the oblique feed roller pairs 32-1 to 32-3 apply to the sheet S, that is, the force with which the sheet S abuts against the reference member 31 (hereinafter referred to as the "abutting force"), is set variably according to the basis weight of the sheet S. In short, this abutting force is controlled to be a preset force for the basis weight of the sheet S.

[0086] Here, the force with which the sheet S buckles after hitting the reference member 31 (hereinafter referred to as the buckling load) tends to decrease as the basis weight of the sheet S decreases. Therefore, the nipping pressure is set so that the hitting force decreases as the basis weight decreases. However, there is a limit to the range in which the hitting force can be reduced by changing the nipping pressure in the skew roller pairs 32-1 to 32-3. For this reason, when conveying a sheet S such as thin paper with a basis weight of 60 gsm or less, even if the nipping pressure is reduced as much as possible to reduce the hitting force, the hitting force applied to the sheet S by the skew roller pairs 32-1 to 32-3 exceeds the buckling load of the sheet S. For this reason, there is a risk that the sheet S will buckle when it is skewed and hits the reference member 31, which could reduce the accuracy of skew correction.

[0087] Therefore, in this embodiment, the skew roller pairs 32-1 to 32-3 are configured to be able to operate in a second mode as well, thereby reducing the impact force of the skew roller pairs 32-1 to 32-3. The operation of the skew correction unit in this second mode will be described below.

[0088] (Operation of the skew correction unit in the second mode) As described above, when control of the registration unit 50 for a print job is started (see FIG. 16), the control unit 9 acquires sheet information (S1) and determines the operation mode of the skew roller pairs 32-1 to 32-3 based on the sheet information (S2). Here, as shown in FIG. 18, if it is determined that the sheet S is a sheet with a small basis weight, such as thin paper, and that the basis weight of the sheet S is 60 gsm or less (Yes in S31), the second mode is selected and determined as the operation mode (S32). In this step S32, it is determined whether the skew roller pair 32-3 should be separated and whether the skew roller pair 32-1 and 32-2 should be pressed together.

[0089] Thereafter, when the operation (S3 to S12) of the conveying section 50A of the registration unit 50 is completed, the skew correction section 50B starts operating in the second mode as shown in FIG. 17. That is, the control section 9 starts counting the pressure delay of the skew roller pairs 32-1 to 32-3 (S13). Here, in the registration unit 50, the skew roller pairs 32-1 to 32-3 are in a non-clamping state to prevent the skew roller pairs 32-1 to 32-3 from interfering with the shift by the conveying roller pair 34-4. Therefore, in the process of step S13, the control section 9 sets a value of the pressure delay, which is the time that elapses until the skew roller pairs 32-1 to 32-3 change from the non-clamping state to the clamping conveying state, and starts counting.

[0090] Next, at the timing when the count of the pressure delay is completed, the control unit 9 presses the pair of skew rollers 32-1 and 32-2 together while keeping the pair of skew rollers 32-3 apart (S14) because the second mode has been determined as the operation mode as described above. That is, the pressure mechanisms 33-1 and 33-2 of the pairs of skew rollers 32-1 and 32-2 are driven to press the drive rollers 320-1 and 320-2 and the driven rollers 331-1 and 331-2 together.

[0091] Furthermore, the control unit 9 starts counting the release delay, which is the time it takes for the conveying roller pair 34-4 to change from the clamping conveying state to the non-clamping state (S15). Then, when the counting of the release delay ends, the lower roller 402 and the upper roller 401 of the conveying roller pair 34-4 are separated, and skew feeding is performed by the skew roller pairs 32-1 and 32-2 to perform skew correction (S16).

[0092] That is, by performing the processes of steps S13 to S16, the sheet is not sandwiched between the conveying roller pair 34-4 in the registration unit 50, and the sheet can be sandwiched and conveyed by the skew roller pair 32-1, 32-2. In the second mode, the skew roller pair 32-3 is separated and does not apply a butting force to the sheet S, so the butting force against the reference member 31 applied to the sheet S only by the skew roller pair 32-1, 32-2 is smaller than in the first mode. In short, because there are only two skew roller pairs 32-1, 32-2 that apply a butting force to the sheet S, the butting force is also reduced to two-thirds. In other words, if the impact force exerted by one of the oblique feed roller pairs 32-1 to 32-3 on the sheet S is x [N] and the buckling load of the sheet S is y [N], then this second mode can accommodate sheet types with buckling loads in the range 2x≦y.

[0093] In this embodiment, the sheet skew state (hereinafter referred to as the "sheet skew state") is defined as the state from when the skew roller pairs 32-1 and 32-2 start to skew the sheet until the widthwise edge of the sheet S abuts against (follows) the reference member 31. In other words, the sheet skew state is the state into which the sheet S transitions after the widthwise movement of the sheet S by the conveying roller pair 34-4 until the edge of the sheet S abuts against the reference member 31. In this embodiment, the period from when the widthwise edge of the sheet S abuts against the reference member 31 until the edge abuts against the registration roller pair 7 is defined as a post-skew correction state, which is a post-abutment conveying state. In this embodiment, when the first mode or the second mode is selected, the nipping conveying state or the non-nipping state of the skew roller pairs 32-1 to 32-3 continues as is in both the sheet skew state and the post-skew correction state.

[0094] That is, in the first mode, in the sheet skew state, the skew roller pairs 32-1 to 32-3 are set to a nip-and-convey state, and even after the skew correction, the skew roller pairs 32-1 to 32-3 are still set to a nip-and-convey state. In the second mode, in the sheet skew state, only the skew roller pair 32-1 and 32-2 are set to a nip-and-convey state, and the skew roller pair 32-3 is set to a non-nip-and-convey state, and even after the skew correction, only the skew roller pair 32-1 and 32-2 are still set to a nip-and-convey state. This reduces the occurrence of buckling when the sheet S hits the reference member 31 in the sheet skew state, and also reduces the occurrence of buckling when the sheet S is further pressed against the reference member 31 after the skew correction.

[0095] In the present embodiment, the state of the skew roller pairs 32-1 to 32-3 is maintained unchanged in the first or second mode in the skewed sheet state and after skew correction. However, this is not limiting. That is, after performing the first or second mode in the skewed sheet state, in the skew-corrected state, the conveying force of the skew roller pairs 32-1 to 32-3 in the direction of pressing the sheet S against the reference member 31 may be further reduced. That is, the skew roller pair 32-2 may be switched from a nipping conveying state to a non-nipping state, or the nipping pressure of the skew roller pair 32-1, 32-2 may be reduced. Conversely, in the skew-corrected state, buckling does not occur due to the impact of the sheet S hitting the reference member 31. Therefore, the conveying force of the skew roller pairs 32-1 to 32-3 in the direction of pressing the sheet S against the reference member 31 may be increased. That is, the pair of oblique feed rollers 32-3 may be switched from a non-clamping state to a clamping conveying state, or the clamping pressure of the pair of oblique feed rollers 32-1 and 32-2 may be increased.

[0096] When the operation of the skew correction unit 50B is thus completed, that is, when the sheet skew state and the skew correction are completed, the process proceeds to the control of step S17 and subsequent steps described above. That is, the process shifts to the control of shifting the widthwise position of the sheet held by the registration roller pair 7. This control is the same in both the first mode and the second mode, so a description thereof will be omitted.

[0097] [Summary of the first embodiment] As described above, according to the first embodiment, the sheet is in a skewed state from when the sheet conveyed by the conveying roller pair 34-4 starts to be skewed until the end of the sheet in the width direction strikes the reference member 31. In this skewed sheet state, the control unit 9 can execute a first mode that controls the skew roller pair 32-1, 32-3 to a nip-and-convey state. In addition, the control unit 9 can execute a second mode that controls the skew roller pair 32-1 to a nip-and-convey state and the skew roller pair 32-3 to a non-nip-and-convey state in the skewed sheet state. Thus, in the skewed sheet state in which a sheet S with a small basis weight, such as thin paper, strikes the reference member 31, the second mode can be selected to reduce the striking force of the sheet S. This reduces the occurrence of buckling of the sheet S and prevents a decrease in the accuracy of skew correction.

[0098] Furthermore, according to the first embodiment, in the first mode, in a sheet oblique conveying state, the control unit 9 controls the oblique conveying roller pairs 32-1 to 32-3 to a nip conveying state. In the second mode, the control unit 9 controls the oblique conveying roller pair 32-1, 32-2 to a nip conveying state and the oblique conveying roller pair 32-3 to a non-nip conveying state. Thus, by selecting the second mode in the sheet oblique conveying state, the abutting force when the sheet S abuts against the reference member 31 can be reduced to two-thirds, and the occurrence of buckling of the sheet S can be reduced.

[0099] Furthermore, according to the first embodiment, in the second mode of the sheet skew state, the skew roller pair 32-3, which is disposed downstream of the skew roller pair 32-1 in the sheet conveying direction, is controlled to a non-nipping conveying state. This ensures that the sheet S can be conveyed from the conveying roller pair 34-4 to the skew correction unit 50B. Furthermore, if the skew roller pair 32-3 is controlled to a nipping conveying state, the abutting force when the sheet S abuts against the reference member 31 may eventually become large, which may increase the likelihood of buckling of the sheet. However, by setting the third skew roller pair 32-3 of the skew roller pairs 32-1 to 32-3 to a non-nipping state, it is possible to prevent the abutting force from becoming large immediately before the sheet S abuts against the reference member 31, thereby reducing the occurrence of buckling of the sheet.

[0100] Second Embodiment Next, a second embodiment, which is a partial modification of the first embodiment, will be described with reference to Figs. 20 and 21. Fig. 20 is a flowchart showing mode determination control for a pair of oblique feed rollers according to the second embodiment. Fig. 21 is a cross-sectional schematic diagram showing the state of the oblique feed correction unit in the second mode according to the second embodiment. In the description of this second embodiment, the same reference numerals are used for parts similar to those in the first embodiment, and their description will be omitted.

[0101] In the first embodiment, one of the skew roller pairs 32-1 to 32-3 is separated (in a non-clamping state) and the other two are pressed together (in a clamping conveying state) in the second mode. In contrast, in the second embodiment, two of the skew roller pairs 32-1 to 32-3 are separated (in a non-clamping state) and the other is pressed together (in a clamping conveying state) in the second mode.

[0102] In detail, when the control of the registration unit 50 for a print job is started (see FIG. 16), the control unit 9 acquires sheet information (S1) and determines the operation mode of the skew roller pairs 32-1 to 32-3 according to the sheet information (S2). Here, as shown in FIG. 20, if it is determined that the sheet S is a sheet with a small basis weight, such as thin paper, and that the basis weight of the sheet S is 60 gsm or less (Yes in S31), the second mode is selected and determined as the operation mode (S32-1). In this step S32-1, it is determined that the skew roller pair 32-3 and 32-2 are separated and that the skew roller pair 32-1 is pressed against the sheet. Note that the first mode (step S33-1) is the same as in the first embodiment, and therefore a detailed description thereof will be omitted.

[0103] Thereafter, when the operation (S3 to S12) of the conveying section 50A of the registration unit 50 is completed, the skew correction section 50B starts operating in the second mode as shown in FIG. 17. That is, the control section 9 starts counting the pressure delay of the skew roller pairs 32-1 to 32-3 (S13). Here, in the registration unit 50, the skew roller pairs 32-1 to 32-3 are in a non-clamping state to prevent the skew roller pairs 32-1 to 32-3 from interfering with the shift by the conveying roller pair 34-4. Therefore, in the process of step S13, the control section 9 sets a value of the pressure delay, which is the time that elapses until the skew roller pairs 32-1 to 32-3 change from the non-clamping state to the clamping conveying state, and starts counting.

[0104] Next, at the timing when the counting of the pressure delay is completed, the control unit 9 presses the pair of skew rollers 32-1 together while keeping the pair of skew rollers 32-3 and 32-2 apart (S14) because the second mode has been determined as the operation mode as described above. That is, the pressure mechanism 33-1 of the pair of skew rollers 32-1 is driven to press the drive roller 320-1 and the driven roller 331-1 together.

[0105] Furthermore, the control unit 9 starts counting the release delay, which is the time it takes for the conveying roller pair 34-4 to change from the clamping conveying state to the non-clamping state (S15). Then, when the counting of the release delay ends, the lower roller 402 and the upper roller 401 of the conveying roller pair 34-4 are separated, and the skew roller pair 32-1 performs skew feeding to correct the skew (S16).

[0106] That is, by performing the processes of steps S13 to S16, the sheet is not sandwiched between the conveying roller pair 34-4 in the registration unit 50, and the sheet can be sandwiched and conveyed by the skew roller pair 32-1. In the second mode, the skew roller pairs 32-3 and 32-2 are separated and do not apply abutting force to the sheet S. Therefore, the abutting force applied to the sheet S by the skew roller pair 32-1 alone against the reference member 31 is smaller than in the first mode. In other words, because there is only one skew roller pair 32-1 that applies abutting force to the sheet S, the abutting force is also reduced to one-third. In other words, if the abutting force applied to the sheet S by one of the skew roller pairs 32-1 to 32-3 is x [N] and the buckling load of the sheet S is y [N], the second mode can accommodate sheet types whose buckling load is in the range of x≦y.

[0107] In the second embodiment, in the first mode, the skew roller pairs 32-1 to 32-3 are in a nip-and-convey state in the sheet skew state, and the skew roller pairs 32-1 to 32-3 are also in a nip-and-convey state in the skew-corrected state. In the second mode, in the sheet skew state, only the skew roller pair 32-1 is in a nip-and-convey state, and the skew roller pairs 32-3 and 32-2 are in a non-nip-and-convey state, and only the skew roller pair 32-1 is in a nip-and-convey state in the skew-corrected state. This reduces the occurrence of buckling when the sheet S abuts against the reference member 31 in the sheet skew state, and also reduces the occurrence of buckling when the sheet S is further pressed against the reference member 31 in the skew-corrected state.

[0108] In the second embodiment, the state of the skew roller pairs 32-1 to 32-3 is maintained as is in the first or second mode in the sheet skew state and after skew correction. However, this is not limiting. That is, after performing the first or second mode in the sheet skew state, in the skew-corrected state, the conveying force of the skew roller pairs 32-1 to 32-3 in the direction of pressing the sheet S against the reference member 31 may be further reduced. That is, the clamping pressure of the skew roller pair 32-1 may be reduced. Conversely, in the skew-corrected state, buckling does not occur due to the impact when the sheet S hits the reference member 31, so the conveying force of the skew roller pairs 32-1 to 32-3 in the direction of pressing the sheet S against the reference member 31 may be increased. That is, the oblique feed roller pair 32-3 and / or the oblique feed roller pair 32-2 may be switched from a non-nipping state to a nipping conveying state, or the nipping pressure of the oblique feed roller pair 32-1 may be increased.

[0109] [Summary of the second embodiment] As described above, according to the second embodiment, the control unit 9 can execute a first mode in which, in a sheet skew state, the skew roller pairs 32-1 to 32-3 are controlled to a nip conveying state. Furthermore, in a sheet skew state, the control unit 9 can execute a second mode in which, in the sheet skew state, the skew roller pair 32-1 is controlled to a nip conveying state and the skew roller pairs 32-2 and 32-3 are controlled to a non-nip conveying state. As a result, in a sheet skew state in which a sheet S with a small basis weight, such as thin paper, is abutted against the reference member 31, the abutting force of the sheet S can be reduced by selecting the second mode. This can reduce the occurrence of buckling of the sheet S, thereby preventing a decrease in the accuracy of skew correction.

[0110] The other configurations, actions, and effects of the second embodiment are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0111] [Possibilities for other embodiments] In the first and second embodiments described above, the registration unit 50 is described as having three pairs of skew rollers 32-1 to 32-3. However, this is not a limitation, and any number of pairs of skew rollers may be provided as long as the number is two or more. If the registration unit 50 has two or more pairs of skew rollers, the second mode can be executed by separating one of the pairs of skew rollers (putting the rollers in a non-clamping state) in the sheet skew state.

[0112] In the first and second embodiments, the skew roller pair 32-3 located most downstream in the sheet conveying direction is separated (put into a non-clipping state) in the second mode. However, this is not limiting, and any of the two skew roller pairs may be separated (put into a non-clipping state) in the second mode. For example, in a case where the skew roller pairs 32-1 to 32-3 are provided, the skew roller pair 32-1 may be separated (put into a non-clipping state) in the second mode. Also, for example, if the sheet information includes the sheet size, it may be possible to determine which of the skew roller pairs 32-1 to 32-3 to separate depending on the sheet size. Also, for example, if the sheet information includes the roughness of the sheet surface, it may be possible to determine which of the skew roller pairs 32-1 to 32-3 to separate depending on the roughness of the sheet surface.

[0113] In the first and second embodiments, the operation mode to be executed in the sheet skew state is selectively determined from the first mode and the second mode depending on the basis weight of the sheet. However, this is not limiting, and the first mode and the second mode may be selectively determined based on any information in the sheet information. For example, the first mode and the second mode may be selectively determined based on the sheet size. Furthermore, the first mode and the second mode may be selectively determined based on the roughness of the sheet surface. Furthermore, the first mode and the second mode may be selectively determined based on a composite combination of any of these items of sheet information.

[0114] Furthermore, in the first and second embodiments, the position of the reference member 31 in the width direction is fixed. However, this is not limiting, and the reference member 31 may be configured to move in the width direction. For example, instead of adjusting the position of the sheet in the width direction by the conveying roller pair 34-4, the reference member 31 may be moved in the width direction in accordance with the detection result of the sheet position detection sensor 60. In other words, by moving the reference member 31 in the width direction, it is conceivable to keep constant the relative distance between the sheet and the reference member 31, and to keep constant the distance by which the sheet is skewed by the skew roller pair.

[0115] In the first and second embodiments, the registration unit 50 is described as performing skew correction upstream of the secondary transfer portion 1C. However, this is not limiting, and skew correction may be performed upstream of a processing portion for sheet cutting, binding, punching, folding, etc., or an image reading portion.

[0116] In addition, in this embodiment, the printer 1 is described as being an electrophotographic full-color laser beam printer, but this is not limited to this. For example, the image forming unit that forms an image on a sheet may be an inkjet printer or the like, and any configuration or method may be used.

[0117] The present disclosure can also be realized by providing a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0118] 1... printer (image forming apparatus) / 7... registration roller pair (second conveying rotor pair) / 9... control unit / 31... reference member (abutment unit) / 60... sheet position detection sensor (width position detection unit) / 70... slide mechanism (second movement drive unit) / 32-1... skew roller pair (first skew roller pair) / 32-2... skew roller pair (third skew roller pair) / 32-3... skew roller pair (second skew roller pair) / 33-1... pressure mechanism (third 1 switching mechanism) / 33-2... pressure mechanism (third switching mechanism) / 33-3... pressure mechanism (second switching mechanism) / 34-4... conveying roller pair (first conveying rotating body pair) / 50... registration unit (sheet conveying device) / 513... image forming engine (image forming unit) / 600... slide mechanism (first movement drive unit) / 700... pressure release mechanism (fourth switching mechanism) / Q... pre-registration sensor (arrival detection unit) / S... sheet

Claims

1. a first conveying rotating body pair that sandwiches and conveys a sheet; a striking portion disposed on one side of the sheet in a width direction perpendicular to the sheet conveying direction; a first oblique feeding rotor pair disposed downstream of the first conveying rotor pair in the sheet conveying direction and configured to obliquely feed the sheet toward the abutting portion; a second pair of obliquely feeding rotors disposed downstream of the first pair of conveying rotors in the sheet conveying direction, and obliquely feeding the sheet toward the abutting portion; a first switching mechanism that switches the first pair of obliquely feeding rotors between a nip conveying state in which the first pair of obliquely feeding rotors nip and convey a sheet and a non-nip conveying state in which the nip of the sheet is released; a second switching mechanism that switches the second pair of obliquely feeding rotors between a nipping and conveying state in which the second pair of obliquely feeding rotors nip and convey a sheet, and a non-nipping state in which the nipping of the sheet is released; a control unit that controls switching of the first switching mechanism and switching of the second switching mechanism, The control unit a first mode in which the first oblique conveying rotor pair and the second oblique conveying rotor pair are controlled to be in the sandwich conveying state in a sheet oblique conveying state from when the sheet conveyed by the first conveying rotor pair starts to be obliquely conveyed until an end portion in the width direction of the sheet abuts against the abutting portion; a second mode in which, in the sheet oblique feeding state, the first oblique feeding rotor pair is controlled to the nip conveying state and the second oblique feeding rotor pair is controlled to the non-nip conveying state; A sheet conveying device characterized by:

2. the second obliquely feeding rotating body pair is disposed downstream of the first obliquely feeding rotating body in the sheet conveying direction; 2. The sheet transport device according to claim 1.

3. The second obliquely feeding rotor pair is disposed at a position where at least a portion of the second obliquely feeding rotor pair overlaps with the first obliquely feeding rotor when viewed from the conveying direction.

3. The sheet transport device according to claim 2.

4. a third obliquely feeding rotor pair disposed downstream of the first pair of conveying rotors in the sheet conveying direction, and configured to obliquely feed the sheet toward the abutting portion; a third switching mechanism that switches the third obliquely feeding rotating body pair between a nipping conveying state in which the third obliquely feeding rotating body pair nip and conveys the sheet and a non-nipping state in which the nipping of the sheet is released, The control unit In the first mode, the first obliquely feeding rotor pair, the second obliquely feeding rotor pair, and the third obliquely feeding rotor pair are controlled to be in the sandwiching and conveying state, In the second mode, the first obliquely feeding rotor pair and the third obliquely feeding rotor pair are controlled to be in the sandwiching conveying state, and the second obliquely feeding rotor pair is controlled to be in the non-sandwiching state.

2. The sheet transport device according to claim 1.

5. the second pair of obliquely feeding rotors are disposed downstream of the first obliquely feeding rotor in the sheet conveying direction, the third obliquely feeding rotor pair is disposed downstream of the first obliquely feeding rotor pair and upstream of the second obliquely feeding rotor pair in the sheet conveying direction; 5. The sheet transport device according to claim 4.

6. the second obliquely feeding rotor pair is disposed at a position where at least a portion of the second obliquely feeding rotor pair overlaps with the first obliquely feeding rotor pair when viewed from the conveying direction, The third obliquely feeding rotor pair is disposed at a position where at least a portion of the third obliquely feeding rotor pair overlaps with the second obliquely feeding rotor pair when viewed from the conveying direction.

6. The sheet transport device according to claim 5.

7. a third obliquely feeding rotor pair disposed downstream of the first pair of conveying rotors in the sheet conveying direction, and configured to obliquely feed the sheet toward the abutting portion; a third switching mechanism that switches the third obliquely feeding rotating body pair between a nipping conveying state in which the third obliquely feeding rotating body pair nip and conveys the sheet and a non-nipping state in which the nipping of the sheet is released, The control unit In the first mode, the first obliquely feeding rotor pair, the second obliquely feeding rotor pair, and the third obliquely feeding rotor pair are controlled to be in the sandwiching and conveying state, In the second mode, the first obliquely conveying rotor pair is controlled to be in the sandwiching conveying state, and the second obliquely conveying rotor pair and the third obliquely conveying rotor pair are controlled to be in the non-sandwiching state.

2. The sheet transport device according to claim 1.

8. the second pair of obliquely feeding rotors are disposed downstream of the first obliquely feeding rotor in the sheet conveying direction, the third obliquely feeding rotor pair is disposed downstream of the first obliquely feeding rotor pair and upstream of the second obliquely feeding rotor pair in the sheet conveying direction; 8. The sheet transport device according to claim 7.

9. the second obliquely feeding rotor pair is disposed at a position where at least a portion of the second obliquely feeding rotor pair overlaps with the first obliquely feeding rotor pair when viewed from the conveying direction, The third obliquely feeding rotor pair is disposed at a position where at least a portion of the third obliquely feeding rotor pair overlaps with the second obliquely feeding rotor pair when viewed from the conveying direction.

9. The sheet transport device according to claim 8.

10. the control unit selectively executes the first mode and the second mode based on information about the sheet to be skewed in the sheet skew state.

2. The sheet transport device according to claim 1.

11. the control unit, in the sheet oblique feeding state, selects and executes the first mode when the basis weight of the sheet is a first basis weight, and selects and executes the second mode when the basis weight of the sheet is a second basis weight smaller than the first basis weight.

2. The sheet transport device according to claim 1.

12. a first movement drive unit that moves the first pair of conveying rotary members in a width direction perpendicular to a sheet conveying direction; a width position detection unit that detects the position of an end of the sheet in the width direction held by the first conveying rotary body pair, The control unit The width position detecting unit detects the position of an end of the sheet in the width direction, the sheet is moved in the width direction by moving the first conveying rotating body pair that sandwiches the sheet using the first movement drive unit so that the position of the end is a set position away from the abutting portion in the other side of the width direction; After the first conveying rotating body pair moves the sheet in the width direction, the sheet is shifted to the sheet oblique conveying state.

2. The sheet transport device according to claim 1.

13. a fourth switching mechanism that switches the first pair of conveying rotators between a nip conveying state in which the first pair of conveying rotators nip and convey a sheet and a non-nip conveying state in which the nip of the sheet is released, the control unit switches the first pair of conveying rotors to the non-clamping state by the fourth switching mechanism in the sheet oblique feeding state.

13. The sheet transport device according to claim 12.

14. a second conveying rotating body pair that sandwiches and conveys the sheet that has been abutted against the abutting portion; a second movement drive unit that moves the second pair of conveying rotors in a width direction perpendicular to a sheet conveying direction; an arrival detection unit that detects that the sheet has arrived at the second pair of conveying rotary members, the control unit continues the first mode or the second mode in a post-imping conveyance state from when the sheet oblique conveyance state ends until when the sheet is conveyed to the second conveyance rotating body pair, In response to the arrival detection unit detecting that the sheet has reached the second pair of conveying rotators, the second movement drive unit moves the second pair of conveying rotators, thereby moving the sheet in the width direction so as to align the position of the sheet with a position in the width direction of an image formed on the sheet by an image forming unit.

2. The sheet transport device according to claim 1.

15. When the arrival detection unit detects that the sheet has reached the second conveying rotator pair, the control unit switches the first oblique conveying rotator pair and the second oblique conveying rotator pair to the non-clamping state, and moves the second conveying rotator pair by the second movement drive unit.

15. The sheet transport device according to claim 14.

16. A sheet conveying device according to any one of claims 1 to 15; an image forming unit disposed downstream of the sheet conveying device in a sheet conveying direction and configured to form an image on the sheet, An image forming apparatus characterized by:

Images