Sheet transport apparatus and image forming apparatus

Abstract

To stabilize a sheet transport speed even if a component is replaced.SOLUTION: A control unit of a sheet transport apparatus (50) detects a position of an end of a sheet as seen in a width direction with a width position detection part (60) at a first timing at which the sheet is transported to a first transport rotating body pair (34-4) and moves the first transport rotating body pair (34-4) sandwiching the sheet with a first movement drive part (600) so that the end is located at a setting position (Lt) spaced apart from a butted part to the other side in the width direction to move the sheet in the width direction. The control unit detects a position of the one end with the width position detection part (60) at a second timing at which the end of the sheet as seen in the width direction is butted with the butted part (31) by diagonal feed rotating body pairs (32-1 to 32-3) and corrects the setting position (LT) based on the detected position of the end.SELECTED DRAWING: Figure 20

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 the case of 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). This side registration method has the advantage that, compared to a method in which a sheet is bent by abutting it against a pair of stopped rollers or a shutter, there is less decrease in the sheet conveying speed, which is expected to improve productivity, and it can also be used with sheets that are difficult to bend, such as cardboard.

[0003] In the above-mentioned side registration method, the conveying speed of the sheet may change depending on the time when the sheet is abutted against the abutting member and the time when the sheet is skewed while slipping by the pair of skew rollers. For this reason, a method has been proposed in which the end of the conveyed sheet is detected by a position sensor such as a CIS sensor, and the pair of conveying rollers upstream in the conveying direction is moved in the width direction before the sheet is conveyed to the pair of skew rollers to correct the width direction position of the sheet (see Patent Document 2). This stabilizes the distance between the end of the sheet conveyed to the pair of skew rollers and the abutting member, stabilizing the width direction distance at which the sheet is skewed by the pair of skew rollers, and stabilizing the time when the sheet is skewed and the time when the sheet is abutted against the abutting member. Therefore, it is possible to stabilize the conveying speed of the sheet, reducing the occurrence of paper jams and preventing a decrease in productivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-189355 [Patent Document 2] JP 2020-115861 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the image forming apparatus as described above, parts may be replaced, such as by replacing the position sensor or the abutting member, due to the life span or failure of the parts. When such parts are replaced, the position of the edge of the sheet detected by the position sensor may shift, or the position of the abutting member in the width direction may shift, due to the dimensional tolerance (individual difference) of the parts. This may cause an error in the distance between the edge of the sheet moved in the width direction by the conveying roller pair and the abutting member, resulting in variation in the sheet conveying speed. This may cause paper jams, etc., and may result in a decrease in productivity.

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a sheet transport device and an image forming apparatus that are capable of stabilizing the sheet transport speed even when parts are replaced. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a sheet conveying device including a first conveying rotor pair that sandwiches and conveys a sheet, a first movement drive unit that moves the first conveying rotor pair in a width direction perpendicular to a sheet conveying direction, a width position detection unit that detects a position of an end of the sheet in the width direction sandwiched by the first conveying rotor pair, abutment units that are disposed downstream of the first conveying rotor pair in the sheet conveying direction and on one side of the width direction with respect to the sheet being conveyed, a skew conveying rotor pair that skews the sheet toward the abutment units and abuts the end of the sheet in the width direction against the abutment units, and a first timing when the sheet is conveyed to the first conveying rotor pair. and a control unit that detects the position of an end portion of the sheet in the width direction using the width position detection unit, and moves the sheet in the width direction by moving the first pair of conveying rotors that clamp the sheet using the first movement drive unit so that the position of the end portion is a set position away from the abutment portion in the other side of the width direction, wherein the control unit detects the position of the end portion using the width position detection unit at a second timing when one end portion of the sheet in the width direction is abutted against the abutment portion by the pair of oblique conveying rotors, and corrects the set position based on the detected position of the end portion. Effect of the Invention

[0008] According to the present invention, even if parts are replaced, the sheet transport speed can be stabilized, and a decrease in productivity can be prevented. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating a printer according to a first embodiment. [Diagram 2] FIG. 2 is a top view showing the registration unit according to the first embodiment. [Diagram 3] 1A is a cross-sectional view showing the conveying section in a clamping and conveying state in the registration unit, and FIG. 1B is a cross-sectional view showing the conveying section in a non-clamping state in the registration unit. [Figure 4]FIG. 4 is a perspective view showing a part of a transport section in the registration unit. [Diagram 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 when viewed from a sheet conveying 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 the pair of oblique feed rollers and a part of the pressure mechanism therefor. [Figure 7] 1A is a side view showing the pair of skew rollers in a nip-and-convey state, and FIG. 1B is a side view showing the pair of skew rollers in a non-nip-and-convey 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] 4 is a perspective view showing a drive mechanism for a pair of conveying rollers in a conveying section of the registration unit; FIG. [Figure 10] 4 is a perspective view showing a slide mechanism for a pair of conveying rollers in a conveying section of the registration unit; FIG. [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 where a sheet is 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 where the sheet is conveyed from the states shown in (a) and (b) to a position where the sheet 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 has been performed by a pair of registration rollers of the registration unit according to the first embodiment, and FIG. [Figure 16] 6 is a flowchart showing control of a transport section of the registration unit during execution of a normal print job according to the first embodiment. [Figure 17] 6 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] (a) is a top view showing an ideal sheet position before skew correction in the registration unit, (b) is an enlarged view of (a), (c) is a top view showing a sheet position before skew correction that is deviated due to part tolerance in the registration unit, and (d) is an enlarged view of (c). [Figure 19] 13 is a top view showing a shift operation of a sheet before skew correction in the registration unit. FIG. [Figure 20] FIG. 13 is a top view showing the position of the sheet during skew correction in the registration unit. [Figure 21] 5 is a flowchart showing correction control of a 0 point position of a seat position detection sensor according to the first embodiment. [Figure 22] 6 is a time chart showing the relationship between each phase in which a sheet is transported in a registration unit and the position of a sheet end portion detected by a sheet position detection sensor. [Diagram 23] 13 is a top view showing a state in which the sheet has reached a pair of registration rollers. FIG. [Figure 24] 10 is a flowchart showing correction control of a 0 point position of a seat position detection sensor according to a second embodiment. [Diagram 25] FIG. 11 is a top view showing a state in which the skew correction of the sheet is completed. [Figure 26] 5 is a time chart showing the position of a sheet end portion detected by a sheet position detection sensor. [Figure 27] 13 is a flowchart showing correction control of a 0 point position of a seat position detection sensor according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <First embodiment> A first embodiment for carrying out the present invention 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 a recording medium, such as paper, envelopes, glossy paper, plastic film such as overhead projector sheets, and cloth.

[0011] [Configuration of image forming device] As shown in FIG. 1, the printer 1 has a control unit 9 (see FIG. 13) 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 device body 1A of the printer 1 contains a feed cassette 51 that stores sheets S, and an image forming engine 513 as an image forming unit that forms an image on the sheet 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 as an image carrier. The image forming engine 513 forms an image on the sheet S by a tandem type intermediate transfer method. The image forming process units PY to PK are electrophotographic units having photosensitive drums 1Y, 1M, 1C, and 1K that are photosensitive bodies, respectively.

[0012] The image forming process units PY to PK have a common configuration except that the color of the toner used for development is different. Here, the configuration of the image forming engine 513 and the image forming process of the toner image will be described using the yellow image forming process unit PY as an example. In addition to the photosensitive drum 1Y, the image forming process unit PY has an exposure device 511, a development device 510, and a drum cleaner 509. The photosensitive drum 1Y is a drum-shaped photosensitive body having a photosensitive layer on its outer periphery, and rotates in a direction (arrow A in the figure) along the rotation direction (arrow B in FIG. 1) of the intermediate transfer belt 506. The surface of the photosensitive drum 1Y is charged by receiving a charge from a charging means such as a charging roller. The exposure device 511 irradiates a laser beam modulated according to image information, scans the photosensitive drum 1Y by an optical system including a reflecting device 512, and draws an electrostatic latent image on the surface of the photosensitive drum 1Y. The developing device 510 contains a developer containing toner, and supplies the toner to the photosensitive drum 1Y to visualize the electrostatic latent image into a toner image. The toner image formed on the photosensitive drum 1Y is primarily transferred to the intermediate transfer belt 506 at a primary transfer portion, which is a nip portion between a primary transfer roller 507 and the intermediate transfer belt 506. Residual toner remaining on the photosensitive drum 1Y after transfer is removed by a drum cleaner 509.

[0013] The intermediate transfer belt 506 is wound around a driving roller 504, a driven roller 505, a secondary transfer inner roller 503, and a primary transfer roller 507, and is driven to rotate in a clockwise direction (arrow B) in FIG. 1 by the driving roller 504. The above-mentioned image forming process is carried out in parallel in each image forming process section PY to PK, and four color toner images are transferred in a superimposed manner to form a full-color toner image on the intermediate transfer belt 506. This toner image is transported to the secondary transfer section 1C while being supported by the intermediate transfer belt 506. The secondary transfer section 1C is configured as a nip section between the secondary transfer roller 56 as a transfer roller and the secondary transfer inner roller 503. A bias voltage of a polarity opposite to the charge polarity of the toner is applied to the secondary transfer roller 56, and the toner image is secondarily transferred to the sheet S. Residual toner remaining on the intermediate transfer belt 506 after the transfer is removed by a belt cleaner 508.

[0014] The sheet S onto which the toner image has been transferred is delivered to a fixing unit 58 by a pre-fixing transport section 57. The fixing unit 58 has a pair of fixing rollers that sandwich and transport 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 causes the toner particles to melt and adhere, and the toner image is fixed to the sheet S.

[0015] Next, a sheet transport process for transporting a sheet will be described. A sheet transport system 1D of the printer 1 transports a sheet S fed from a 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 double-sided transport section 502.

[0016] A feeding cassette 51 provided in the sheet feeding unit 1B is attached to the apparatus main body 1A so as to be removable, and stores sheets S in a stacked and supported state on a liftable tray 52 which 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 a roller or a pad. 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 is delivered to the registration unit 50.

[0017] The sheet S delivered to the registration unit 50 is conveyed toward the secondary transfer section 1C after skew correction and timing correction. At this time, the 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 formation process sections PY to PK based on the detection of the sheet by the sheet detection sensor 8. The sheet S, on which the toner image is transferred in the secondary transfer section 1C and the image is fixed by the fixing unit 58, is conveyed to a branch conveying section 59 that branches off the conveying path of the sheet S. When the image formation on the sheet S is completed, the sheet S is discharged by the pair of discharge rollers to a discharge tray 500 arranged outside the apparatus main body 1A.

[0018] 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 S 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, the sheet S is discharged to the discharge tray 500 after an image is formed on the back side of the sheet S.

[0019] [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 the present embodiment is a unit that corrects skew of a sheet by a side registration method.

[0020] In detail, as shown in FIG. 2, the registration unit 50 includes a conveying section 50A, a skew correction section 50B, and a registration roller pair 7, in that order from upstream to downstream in the sheet conveying direction. The registration unit 50 also includes a sheet position detection sensor 60 as a width position detection section that detects the position of the end 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, and FIG. 2 shows a configuration including conveying roller pairs 34-1, 34-2, 34-3, and 34-4. In the following description, when it is not necessary to distinguish between the conveying roller pairs 34-1, 34-2, 34-3, and 34-4, they will be referred to as "conveying roller pairs 34."

[0021] In the registration unit 50 in this embodiment, the pair of conveying rollers 34-4 serving as the first conveying rotator pair is provided with a slide mechanism 600 serving as a first movement drive unit. Also, Fig. 2 illustrates a configuration in which the sheet position detection sensor 60 is disposed at a position between the pair of conveying rollers 34-2 and the pair of conveying rollers 34-3. The sheet position detection sensor 60 can be disposed at a position where the end in the width direction of the sheet being conveyed through the conveying unit 50A can be detected, for example, at a position between the pair of conveying rollers 34-4 and the pair of conveying rollers 34-3, other than the position shown in Fig. 2.

[0022] The skew correction unit 50B includes a pair of skew rollers 32-1, 32-2, and 32-3 as a pair of skew rotating bodies, and a reference member 31 as an abutting unit. In the following description, when it is not necessary to distinguish between the pairs of skew rollers 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 end of the sheet in the width direction.

[0023] 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, thereby detecting 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 portion and a light-receiving portion. In this case, the light emitted by the light-emitting portion is reflected by the sheet that has reached the detection position, and the reflected light is detected by the light-receiving portion to detect the passing timing of the sheet. 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.

[0024] The skew roller pairs 32-1, 32-2, and 32-3 each rotate about 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 α with respect to the sheet conveying direction. Therefore, the skew roller pairs 32-1, 32-2, and 32-3 rotate in contact with the sheet, thereby moving the sheet so that the sheet 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 sheet is moved by the skew roller pair 32 so that the sheet approaches the reference surface 31a as it moves downstream in the sheet conveying direction V.

[0025] Here, the skew correction of the sheet by the skew correction unit 50B will be described. The skew correction unit 50B corrects the skew of the sheet by a so-called side registration method. Specifically, the skew correction unit 50B causes the side end of the sheet, that is, the sheet end in the width direction, to abut against a reference member 31 having a reference surface 31a extending along the sheet conveying direction. After the sheet abuts against the reference surface 31a, the skew of the sheet is corrected by moving the side end of the sheet along the reference surface 31a. Note that the sheet conveying direction is the proceeding direction of the sheet before the sheet approaches the reference member 31 in the skew correction unit 50B, and in this embodiment, it refers to the sheet conveying direction by the conveying roller pair 34 of the conveying unit 50A.

[0026] In addition to the pre-registration sensor P, the skew correction unit 50B is also provided with a pre-registration sensor (hereinafter, referred to as the "pre-registration sensor") Q as an arrival detection unit that detects the arrival of the leading edge of the sheet by detecting the presence or absence of the sheet. The pre-registration sensor Q is disposed downstream of the pair of skew rollers 32 and upstream of the pair of registration rollers 7 in the sheet conveying direction. As with the pre-registration sensor P, the pre-registration sensor Q may be a known sensor such as a reflective photoelectric sensor. The pre-registration sensor Q is a sensor for detecting the arrival of the sheet at the pair of registration rollers 7. Specifically, the pre-registration sensor Q detects that the sheet has reached the pair of registration rollers 7 when a predetermined delay time has elapsed since the pre-registration sensor Q detected the sheet. However, the function of the pre-registration sensor Q can be said to be to detect that the sheet has reached the pair of registration rollers 7. The pre-registration sensor Q may be disposed downstream of the pair of registration rollers 7, in which case it detects that the sheet has already reached the pair of registration rollers 7.

[0027] The registration roller pair 7 as the second conveying rotator pair can be moved by sliding the sheet in the width direction perpendicular to the sheet conveying direction by the slide mechanism 70 as the second movement drive unit while sandwiching the sheet. The slide mechanism 70 can be a mechanism similar to the slide mechanism 600 that moves the conveying roller pair 34-4 in the width direction. The registration roller pair 7 moves the sheet whose side end is abutted against the reference surface 31a of the reference member 31 in the width direction to match the position of the image to be transferred in the secondary transfer unit 1C. As a result, the center in the width direction of the sheet whose skew has been corrected in the registration unit 50 moves to the center in the width direction of the image to be transferred in the secondary transfer unit 1C (the center in the width direction of the image forming area). The method of adjusting the position of the sheet and the image formed on the sheet is not limited to this. For example, the registration roller pair 7 may move the center of the sheet to the conveying center of the printer 1, and adjust the center of the position in the main scanning direction of the toner image formed by the image forming process units PY to PK to the center in the width direction.

[0028] [Details of the transport section] The detailed configuration of the conveying section 50A will be described in detail with reference to Figs. 3(a), 3(b), and 4. Fig. 3(a) is a cross-sectional view showing the conveying section in a clamped conveying state in the registration unit. Fig. 3(b) is a cross-sectional view showing the conveying section in a non-clamped state in the registration unit. Fig. 4 is a perspective view showing a part of the conveying section in the registration unit. Figs. 3(a) and 3(b) show three parts of the four conveying roller pairs 34. In the present embodiment, the printer 1 has four conveying roller pairs 34 (see Fig. 2) as an example, but the number of conveying roller pairs is not limited to this.

[0029] 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 are each composed of 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 pair 34 is switchable between a clamping conveying state (Figure 3(a)) in which a sheet is clamped in a nip portion and conveyed, and a non-clamping state (Figure 3(b)) in which the nip portion is separated and the sheet is not clamped. Whether all the conveying roller pairs 34 are switchable between the clamping conveying state and the non-clamping state can be determined according to the maximum size of a sheet that the printer 1 can convey.

[0030] The conveying section 50A is provided with a cam mechanism 100 having an eccentric roller 103 as a switching section capable of switching between a clamping conveying state and a non-clamping state of the conveying roller pairs 34-1, 34-2, and 34-3. The eccentric roller 103 is driven to rotate via gears 105 and 106 by a conveying roller driving motor Md as a driving source, and swings an arm member 101 that abuts against a cam surface on the outer periphery. The arm member 101 is supported to be swingable with respect to the stay member 18 around a swing shaft 102, abuts against the eccentric roller 103 on one side of the swing shaft 102, and supports a driven shaft 20 that is a rotation shaft of the driven roller 14 on the other side. By swinging the arm member 101, the driven rollers 14 appear and disappear from the sheet conveying path formed by a guide member (not shown). Therefore, by controlling the rotation angle of the eccentric roller 103 via the conveying roller drive 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-clamped state in which the driven rollers 14 are separated from the drive roller 13 and a clamped conveying state in which the driven rollers 14 are in pressure contact with the drive roller 13.

[0031] 4, the drive roller 13 is a rubber roller attached to a drive roller shaft 301A, and is connected to a conveyor roller drive motor Mp, which is a drive source, via a belt transmission mechanism 302. The conveyor roller 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).

[0032] [Details of the skew correction unit] Next, the configuration of the skew correction unit 50B will be described in detail with reference to Figs. 5(a), 5(b), 6(a), 6(b), 7(a), and 7(b). Fig. 5(a) is a top view showing a part of the skew correction unit in the registration unit. Fig. 5(b) is a cross-sectional view showing a part of the skew correction unit in the registration unit as viewed from the sheet conveying direction. Fig. 6(a) is a perspective view showing the pair of skew rollers and their pressure mechanism. Fig. 6(b) is a side view showing the pair of skew rollers and a part of their pressure mechanism. Fig. 7(a) is a side view showing the pair of skew rollers in a nip-and-convey state. Fig. 7(b) is a side view showing the pair of skew rollers in a non-nip-and-convey state.

[0033] As shown in Fig. 5(a), the 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, and 330-3. The drive rollers 320-1, 320-2, and 330-3 have their rotation axes fixed in a state inclined according to the angle α by universal joints 321, 321, and 321. When it is not necessary to distinguish between the drive rollers 320-1, 320-2, and 330-3, they are referred to as drive rollers 320-n.

[0034] Each driving roller 320-n is connected to a correction roller driving motor Ms, which is a driving source, via a transmission mechanism including a universal joint 321, a belt 323, and a pulley. The correction roller driving motor Ms is a stepping motor, and is capable of controlling the driving speed and the timing of starting and stopping the driving of the driving roller 320-n.

[0035] 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 its accuracy, and further by applying a fluororesin such as PTFE (polytetrafluoroethylene) to the reference surface 31a by electroless nickel processing. This provides a reference surface 31a that is highly flat and has high slipperiness (low frictional resistance against the sheet), thereby improving the accuracy of skew correction of the sheet S.

[0036] As shown in Fig. 6(a), Fig. 6(b), Fig. 7(a), and Fig. 7(b), the pair of skew rollers 32-n arranged in the skew correction section 50B has a drive roller 320-n and a driven roller 331-n facing the drive roller 320-n. In addition, the skew correction section 50B is provided with a pressure mechanism 33 that moves the driven roller 331-n. The pressure mechanism 33 is capable of switching between a clamping conveying state in which the driven roller 331-n is pressed against the drive roller 320-n to form a nip and the sheet can be clamped and conveyed, and a non-clamping state in which the driven roller 331-n is separated from the drive roller 320-n.

[0037] The clamping conveying state of the pressure mechanism 33 means that at least one skew roller pair 32 is in the clamping conveying state, and the non-clamping state of the pressure mechanism 33 means that all skew roller pairs 32 are in the non-clamping state. Here, n is a number obtained by numbering the skew roller pairs 32 and the driven rollers 331 in order from the upstream of 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 are arranged in a state in which the skew roller pair 32-n shown in FIG. 6 and FIG. 7 is replaced with any of the skew roller pairs 32-1, 32-2, and 32-3.

[0038] The pressure mechanism 33 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. The driven roller 331-n is supported by the arm member 332 so as to be rotatable about a driven shaft, and can move in a direction approaching or separating from the oblique feed roller pair 32-n by the swinging of the arm member 332. The driven roller 331-n in this embodiment rotates along the sheet conveying direction about 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 is a driving source.

[0039] As shown in Fig. 7(a), in the clamping and 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 driving 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 driving roller 320-n.

[0040] 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 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.

[0041] [Seat position detection sensor configuration] Next, the configuration of the sheet position detection sensor 60 as the width position detection section 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 section of the registration unit. The sheet position detection sensor 60 includes an optical element such as a CIS (Contact Image Sensor), and is disposed 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 width direction in the sheet conveying direction V. This is to detect the position of the edge of the sheet on the side that hits the reference member 31.

[0042] [Drive and slide configuration of the transport roller pair] Next, the drive configuration of the conveying roller pair 34-4 in this embodiment and the configuration of a slide mechanism 600 that slides the conveying roller pair 34-4 will be described with reference to 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.

[0043] The conveying roller pair 34-4 is rotationally driven by a roller drive mechanism 800, and configured to be movable in a width direction perpendicular to the sheet conveying direction with the sheet sandwiched therebetween by a slide mechanism 600. The conveying roller pair 34-4 is also configured to be switchable between a sandwiching 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-sandwiching state in which the roller pair is separated.

[0044] 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. In addition, a roller gear 412 that transmits the drive 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).

[0045] As shown in FIG. 9, the roller drive mechanism 800 for rotating the conveying roller pair 34-4 includes a slide roller drive motor 801, 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 to 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 fixed to a fixed shaft 201b of the frame 201, and the drive gear 803 is fixed to a fixed shaft 201c so as to be freely rotatable. In this embodiment, a stepping motor is used as the slide roller drive motor 801. With this configuration, the driving 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.

[0046] As shown in FIG. 10, a slide mechanism 600 that moves the conveying roller pair 34-4 in the width direction perpendicular to the sheet conveying direction has a slide motor 601 that is 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 fixed to the pulley base 605, and a pulley shaft 608 is fixed to the pulley base 606 so as to be freely rotatable. Pulleys 609 and 610 are fixed to the pulley shaft 607, and a pulley 611 is fixed to the pulley shaft 608. 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 pulleys 609 and 612, and a timing belt 614 is stretched between the pulleys 610 and 611 (see FIG. 10).

[0047] As shown in FIG. 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 the home position, the sensor flag 416 is detected by a sensor 615 provided on the pulley support plate 604. The holder 415 is fixed to the 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 lower roller 402 of the conveying roller pair 34-4 reciprocates in the width direction perpendicular to the sheet conveying direction in accordance with the rotation of the timing belt 614. Further, 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 reciprocates together with the lower roller 402 in the width direction perpendicular to the sheet conveying direction. In this embodiment, as will be described later in detail, 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.

[0048] The pressure release mechanism 700, which brings the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4 into contact with and separates them, has a pressure release shaft 701 positioned in the frame 201, as shown in FIG. 11(a). The pressure release mechanism 700 also includes cams 702, 703 (see FIG. 11(b)) fixed to the pressure release shaft 701. As shown in FIG. 11(b), deep groove ball bearings 702a, 703a are press-fitted into the cams 702, 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 of a pressure release motor 704 is transmitted via the cam 702.

[0049] The deep groove ball bearing 702a is disposed at a position where it can come into contact with the pressure arm 405, and 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 way, the upper roller 401 and the lower roller 402 can be brought into contact with and separated from each other once. In addition, a pressure arm (not shown) is also provided on the side where the deep groove ball bearing 703a is provided in the axial direction of the pressure release shaft 701. In addition, a sensor flag 703b is formed on the cam 703 (see FIG. 11(b)). The phase of the pressure release shaft 701 is determined by detecting the sensor flag 703b by a sensor 706 fixed to a sensor support plate 705 fixed to the frame 201, and the rotation of the pressure release motor 704 is controlled according to the phase of the pressure release shaft 701. Further, the phases of the cams 702 and 703 are determined so that the sensor flag 703b shields the sensor 706 when the upper roller 401 and the lower roller 402 of the conveying roller pair 34-4 are in contact with each other.

[0050] [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.

[0051] 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 an external device or a network.

[0052] 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 the pre-registration sensor Q. The detection signals from the pre-registration sensor P and the 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 a program stored in the ROM 9c or the like. The CPU 9a drives and controls the motor group (Ms, Mp, Md, Mk-n, 601) that is the actuator of the registration unit 50 via drivers 903, 904, 905, 606-n, 907.

[0053] [Overview of the operation of the registration unit] (Transportation 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 performed in the registration unit 50 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 is conveyed from the state shown in Figs. 13(a) and 13(b) to a position where the sheet 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).

[0054] 13(a) and 13(b), when the sheet S being conveyed in the sheet conveying direction V reaches the sheet position detection sensor 60 in the registration unit 50, the position of the end of the sheet S (side end position) is detected by the sheet position detection sensor 60. The CPU 9a (see FIG. 12) calculates the amount of deviation from the detected side end 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 amount of shift in the shift operation before skew correction).

[0055] Next, as shown in Fig. 13(c) and Fig. 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 (putting them in a non-nip state). The CPU 9a shifts (moves) the conveying roller pair 34-4 in the direction of the arrow W2a by the shift amount calculated above, that is, shifts the sheet S so that the side edge of the sheet S is aligned with the 0 point position as the reference position of the sheet position detection sensor 60. 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 end of the sheet S is stabilized. That is, the sheet conveying speed is stabilized.

[0056] (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 Fig. 14(a) and Fig. 14(b). Fig. 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. Fig. 14(b) is a cross-sectional view of the state shown in Fig. 14(a).

[0057] 14(a) and 14(b), in the registration unit 50, the sheet S is conveyed in a direction inclined with respect to the sheet conveying direction V indicated by the arrow K in the drawing by the skew roller pairs 32-1 to 32-3 in a nip-and-convey state (pressurized state). As a result, the side edge of the sheet S is abutted against and contacts 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, the skew correction is performed by the skew roller pairs 32-1 to 32-3 after the conveying roller pairs 34-1 to 34-4 are separated, so that the skew correction can be performed without interference from the conveying roller pairs 34-1 to 34-4.

[0058] (Operation of the registration roller pair) 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 transferred by the secondary transfer unit 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 unit 1C.

[0059] In the registration unit 50, after the oblique roller pairs 32-1 to 32-3 are put into a non-clamping state (separated), the position of the sheet S in the width direction is shifted by the registration roller pair 7. Therefore, the position of the sheet S in the width direction can be shifted without interference from the oblique roller pairs 32-1 to 32-3.

[0060] <Registration unit control during print job> Next, for example, when a command to print one or more sheets is sent from an external computer or operation unit 400 to the control unit 9 and the print job is executed, the control in the registration unit 50 will be described in detail with reference to Figs. 16 and 17. Fig. 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. Fig. 17 is a flowchart showing the control of the skew correction unit and the registration roller pair of the registration unit when a normal print job is executed according to the first embodiment.

[0061] The control unit 9 first acquires sheet-related information (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 plain paper for office use, coated paper, thick paper, etc. The control unit 9 also acquires the number of sheets 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 an initial value of a stored value that is a value stored in a paper passing counter.

[0062] Next, the control unit 9 determines the nip pressure of the oblique roller pairs 32-1 to 32-3 (S2). In this process, the control unit 9 obtains table data that associates the nip pressure with each preset sheet type from the ROM 9c based on the sheet information obtained in the process of step S1, and determines the nip pressure of the oblique roller pairs 32-1 to 32-3. Then, the control unit 9 drives the driven roller pressure motor Mk-n (see FIG. 12) so as to achieve the determined nip pressure, thereby pressing the oblique roller pairs 32-1 to 32-3 to bring them into a nip conveying state (S3).

[0063] 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 process 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 from when 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 process of step S4, and starts counting.

[0064] 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 a signal output from the sheet position detection sensor 60.

[0065] 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, based on the detection result 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 amount of deviation.

[0066] After executing the process of step S8, the control unit 9 judges whether the pre-registration sensor P is turned ON or not (S9). In this process, the control unit 9 judges from the signal of the pre-registration sensor P whether the sheet whose side end position is detected by the sheet position detection sensor 60 has reached the pre-registration sensor P or not.

[0067] In the process of step S9, if it is determined that the pre-registration sensor P is not ON (No), 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.

[0068] On the other hand, when it is determined that the pre-registration sensor P is 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 the skew correction by the conveying roller pair 34-4 is possible. Therefore, in the process of step S12, the control unit 9 sets a release delay value, 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.

[0069] 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.

[0070] Then, the control unit 9 shifts the pair of conveying rollers 34-4 in the width direction by a shift amount according 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 shift 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 0 point position which is the reference position.

[0071] In the present 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 shift, the sheet may be shifted by the conveying roller pair 34-4 after stopping the sheet conveyance, and then the sheet conveyance may be resumed.

[0072] After executing the process of step S12, as shown in FIG. 17, the control unit 9 starts counting the pressurization delay of the skew roller pairs 32-1 to 32-3 (S13). At the time when the process of step S13 is executed, the shift before the skew correction of the sheet is completed in the registration unit 50. Also, 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 unit 9 sets a value of the pressurization 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.

[0073] Next, when the count 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 go from a clamping conveying state to a non-clamping state (S15). Then, when the count 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 is conveyed by the skew roller pairs 32-1 to 32-3 to perform skew correction (S16).

[0074] That is, by performing the processes of steps S13 to S16, the sheet is not sandwiched by 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, the sheet is sandwiched and conveyed by the skew roller pairs 32-1 to 32-3, so that skew correction of the sheet being conveyed while bringing the side edge of the sheet into contact with the reference surface 31a of the reference member 31 is performed.

[0075] Next, the control unit 9 determines whether the pre-registration sensor Q is turned ON (S17). In this process, the control unit 9 determines 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 based on the signal of the pre-registration sensor Q.

[0076] 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.

[0077] On the other hand, when it is determined that the pre-registration sensor Q has been 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 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 clamping conveying state to a non-clamping state, and starts counting.

[0078] 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 by the registration roller pair 7 and is not sandwiched by the skew roller pairs 32-1 to 32-3.

[0079] Next, the control unit 9 shifts the widthwise position of the sheet after the skew correction by 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 by 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.

[0080] 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 the value "1" 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., the shift before skew correction, the skew correction, and the shift after skew correction, have been completed.

[0081] Then, the control unit 9 judges whether the stored value of the paper passing counter is 0 or not (S22). In this process, if the control unit 9 judges 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 for the sheet to be transported next in the current print job. On the other hand, if the control unit 9 judges that the stored value of the paper passing counter is 0 (Yes in S22), the control unit 9 judges that the current print job is completed and ends this control.

[0082] [Errors caused by part replacement] As described above, when performing the skew correction operation of the sheet in the registration unit 50, the sheet position detection sensor 60 detects the position of the side edge of the sheet, and the conveying roller pair 31-4 shifts the sheet based on the detection result. However, when a part is replaced due to, for example, the expiration of the part's life or a failure of the sheet position detection sensor 60, an error may occur due to the dimensional variation (tolerance) of the part.

[0083] Fig. 18(a) is a top view showing an ideal sheet position before skew correction in the registration unit, Fig. 18(b) is an enlarged view of Fig. 18(a), Fig. 18(c) is a top view showing a sheet position before skew correction that is deviated due to component tolerance in the registration unit, and Fig. 18(d) is an enlarged view of Fig. 18(c).

[0084] 18(a) and 18(b), for example, when the sheet is shifted by the conveying roller pair 34-4 before the skew correction, the distance L between the side edge of the sheet and the reference surface 31a of the reference member 31 is configured to be the ideal distance Lt before the replacement of parts. Note that the imaginary line VL shown by the dotted line in the figure is an imaginary line obtained by extending the reference surface 31a in the sheet conveying direction.

[0085] In response to this, for example, suppose that the sheet position detection sensor 60 is replaced due to a malfunction of the CIS or the reference member 31 is replaced. In this case, as shown in Fig. 18(c) and Fig. 18(d), the installation position in the width direction of the sheet position detection sensor 30 and the installation position in the width direction of the reference member 31 may shift by the component tolerance ΔL. For this reason, an error (Lt-ΔL) occurs in the distance L between the side edge of the sheet shifted by the conveying roller pair 34-4 and the reference surface 31a of the reference member 31.

[0086] In this way, when an error ΔL occurs in the distance L between the side edge of the shifted sheet and the reference surface 31a of the reference member 31, the widthwise distance by which the sheet is skewed to the reference member 31 by the skew roller pairs 32-1 to 32-3 differs from the ideal distance. In addition, the distance by which the end surface of the sheet slides after the sheet is brought into contact with the reference surface 31a of the reference member 31 also differs from the ideal distance. Then, the sheet conveying speed when performing skew correction cannot be stabilized, and stable sheet conveyance may not be performed, which may cause a paper jam or the like. Therefore, in this embodiment, a configuration is provided for correcting the distance between the side edge of the sheet and the reference surface 31a of the reference member 31 after the shift so that it becomes the ideal distance, thereby realizing stable sheet conveyance. A specific embodiment of this will be described below.

[0087] [Correction of the distance L between the side edge of the sheet and the reference surface of the reference member] Next, a description will be given of a configuration for correcting an error ΔL from an ideal distance Lt between the side edge of the sheet and the reference surface 31a of the reference member 31, which is a feature of the first embodiment. Fig. 19 is a top view showing a shift operation of the sheet before skew correction in the registration unit. Fig. 20 is a top view showing the position of the sheet during skew correction in the registration unit.

[0088] As described above in the control of the print job, the shift amount for shifting the pair of conveying rollers 34-4 is determined based on the result of detection of the side edge position of the sheet by the sheet position detection sensor 60. To describe the control at this time in detail, the following control is performed.

[0089] 19, the sheet position detection sensor 60 is preset with a reference position (zero point position) as a set position where the side edge of the sheet and the reference surface 31a of the reference member 31 are at an ideal distance Lt. When a sheet is conveyed to the sheet position detection sensor 60, the deviation amount Lerr from the zero point position is detected, and the conveying roller pair 34-4 is shifted by the slide mechanism 600 (see FIG. 2) so that the deviation amount is cancelled. That is, by setting the deviation amount Lerr as the shift amount, the conveying roller pair 34-4 is shifted by the shift amount, so that the side edge of the sheet and the reference surface 31a of the reference member 31 are at the ideal distance Lt.

[0090] Therefore, when the distance L between the side edge of the sheet and the reference surface 31a of the reference member 31 deviates from the ideal distance Lt by an error ΔL due to part replacement or the like, the zero point position set in the sheet position detection sensor 60 can be corrected. In other words, as shown in Fig. 20, the zero point position after this correction can be corrected to a position offset by the distance Lt from the reference surface 31a (virtual line VL) of the reference member 31.

[0091] Therefore, in this embodiment, for example, after the replacement of parts is completed, one sheet is passed through the registration unit 50 to execute a zero point position correction control (correction mode) for correcting the error (tolerance). In this zero point position correction control, the sheet is passed through in the same manner as normal paper passing, and the sheet position detection sensor 60 measures the position of the side edge of the sheet again at the second timing when the sheet is abutted against the reference surface 31a of the reference member 31 (see FIG. 20). The position value measured at this second timing is the same as the result of measuring the virtual line VL extended from the reference surface 31a of the reference member 31 upstream in the sheet conveying direction by the sheet position detection sensor 60. Therefore, the position offset by the distance Lt from this detected value in the direction away from the reference surface 31a of the reference member 31 in the width direction may be set as the zero point position of the sheet position detection sensor 60.

[0092] For example, when a serviceman or the like replaces a part, it is possible to physically measure the error after the replacement, adjust the positions of the reference member 31 and the seat position detection sensor 60, and manually correct the zero point position. However, such work is undesirable because it places a large burden on the person.

[0093] In addition, in this embodiment, the 0 point position (setting position) is corrected, but the present invention is not limited to this, and the same effect can be obtained by correcting the shift amount (distance Lt). Therefore, correcting the setting position is synonymous with correcting the shift amount.

[0094] [Details of the correction control of the zero point position according to the first embodiment] Next, the details of the correction control (correction mode) of the zero point position according to the first embodiment will be described with reference to FIG. 21. FIG. 21 is a flowchart showing the correction control of the zero point position of the sheet position detection sensor according to the first embodiment. Note that the flowchart in FIG. 21 only shows the control of the skew correction unit and the pair of registration rollers of the registration unit 50. That is, in the correction control of the zero point position, the control of the conveying unit of the registration unit is the same as the control of the conveying unit of the registration unit when the above-mentioned print job is executed (see FIG. 16), so the figure is omitted. In other words, the correction control of the zero point position is the control shown in FIG. 16 and FIG. 21, but other than the detection and correction by the sheet position detection sensor 60 when the sheet hits the reference member 31, it is the same as when the print job is executed, so the description thereof will be omitted.

[0095] That is, as shown in Fig. 21, after the sheet is shifted by the conveying roller pair 34-4 (see S12 in Fig. 16), the skew roller pairs 32-1 to 32-3 are pressed against each other (S13, S14), and the conveying roller pair 34-4 is separated (S15, S16). Then, the skew roller pairs 32-1 to 32-3 correct the skew of the sheet (S16).

[0096] Here, the control unit 9 waits until the position of the side edge of the sheet detected by the sheet position detection sensor 60 becomes stable, and when it becomes stable, the sheet position detection sensor 60 detects the position of the side edge of the sheet (S30). Then, the control unit 9 performs a correction to set the detected position of the side edge of the sheet, that is, a position offset by a distance Lt in the width direction from the position of the reference surface 31a of the reference member 31, as the zero point position of the sheet position detection sensor 60 (S31). As a result, even if an error occurs due to part replacement or the like, the zero point position is corrected, and the side edge of the sheet can be shifted to the ideal distance Lt from the reference surface 31a of the reference member 31.

[0097] Thereafter, as in the case of the print job, when it is detected that the pre-registration sensor has turned ON (Yes in S17), the skew roller pairs 32-1 to 32-3 are separated (S18, S19), a shift is performed by the registration roller pair 7 (S20), and this control ends. Note that in this 0 point position correction control, since only one sheet is conveyed, the paper passing counter is not counted (see S21, S22 in FIG. 17). Also, if the pre-registration sensor does not turn ON (No in S17), a paper jam is displayed on the operation unit (S23), and this control ends.

[0098] [Timing of sheet side edge detection by sheet position detection sensor] Next, the timing at which the sheet position detection sensor 60 detects the side edge of the sheet in step S30 will be described with reference to Fig. 22. Fig. 22 is a time chart showing the relationship between each phase in which the sheet is transported in the registration unit and the position of the sheet edge detected by the sheet position detection sensor.

[0099] In the first embodiment, whether or not the side edge of the sheet is abutted against the reference surface 31a of the reference member 31 and the abutment is completed is determined using a detection value detected by the sheet position detection sensor 60. Changes in the detection value of the sheet position detection sensor 60 will be explained by dividing them into time phases a to e with respect to the position of the sheet in the conveying direction.

[0100] Phase a is a phase from when the leading edge of the sheet reaches the sheet position detection sensor 60 until the sheet is shifted in the width direction by the conveying roller pair 34-4, and the amount of deviation of the side edge position of the sheet from the 0 point position is measured as the first timing. This determines the amount of shift by the conveying roller pair 34-4. Phase b is a phase from when the conveying roller pair 34-4 starts shifting until when the skew roller pairs 32-1 to 32-3 start skew feeding, and the sheet is shifted by the conveying roller pair 34-4 and conveyed to the skew roller pairs 32-1 to 32-3.

[0101] Note that the position of the side edge of the sheet detected by phase a is the position before the deviation due to the component tolerance is corrected, and therefore the detected value deviates from the ideal distance Lt between the side edge of the sheet and the reference surface 31a of the reference member 31. However, unlike when a print job is executed, the correction control (correction mode) of the 0 point position is not a mode that requires high productivity, and therefore does not require a stable conveying speed to achieve high productivity. Therefore, it is acceptable even if the distance between the side edge of the sheet and the reference surface 31a of the reference member 31 deviates from the ideal distance Lt.

[0102] Phase c is a phase in which the sheet is skewed toward the reference member 31 by the skew roller pairs 32-1 to 32-3, that is, skew correction is started. In this phase c, the behavior of the sheet is unstable until the sheet is completely abutted against the reference member 31. The subsequent phase d is a phase in which the side edge of the sheet is stably abutted against the reference surface 31a of the reference member 31 and the detection value of the sheet position detection sensor 60 becomes stable. Then, phase e is a phase in which the sheet is shifted by the registration roller pair 7, and the position of the sheet is matched with the image transferred at the secondary transfer unit 1C.

[0103] In the first embodiment, the detection value of the sheet position detection sensor 60 is used to determine whether or not the phase has shifted from phase c to phase d, which is the second timing at which it is determined that the side edge of the sheet has been abutted against the reference surface 31a of the reference member 31. That is, if the abutment has been completed, the detection value of the sheet position detection sensor 60 maintains a stable value. Therefore, it is possible to determine whether the abutment has been completed based on whether the detection value of the sheet position detection sensor 60 has become a stable value. In the first embodiment, it is determined that the fluctuation (amplitude) of the detection value of the sheet position detection sensor 60 has converged to a range equal to or less than a predetermined threshold value δ, and it is determined that the second timing at which the abutment has been completed has been reached. Then, the detection value of the sheet position detection sensor 60 in phase d is used to correct and update the zero point position.

[0104] In this way, a position offset by the distance Lt from the detection result when the sheet abuts against the reference surface 31a of the reference member 31 is updated as a new zero point position of the sheet position detection sensor 60. As a result, even if an error (ΔL) (see FIG. 18) occurs in the distance Lt, which is the shift amount, due to dimensional variations (tolerances) caused by part replacement, it is possible to correct the error to the correct distance Lt. This makes it possible to stabilize the conveying speed when performing skew correction by the skew roller pairs 32-1 to 32-3, reduce the occurrence of problems such as paper jams, and prevent a decrease in productivity.

[0105] <Second embodiment> Next, a second embodiment which is a partial modification of the first embodiment will be described. Fig. 23 is a top view showing a state in which the sheet has reached the pair of registration rollers.

[0106] In the above-described first embodiment, the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 is determined by monitoring the detection value of the sheet position detection sensor 60 and determining that the detection value has converged. In the present second embodiment, the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 is determined more simply.

[0107] As shown in Fig. 23, in the skew correction section 50B of the registration unit 50, the sheet is abutted against the reference surface 31a of the reference member 31 to perform skew correction. Then, when the sheet reaches the pair of registration rollers 7, the abutment of the sheet should be completed. Therefore, in the second embodiment, the completion of the abutment is determined as the second timing when the leading edge of the sheet reaches the pair of registration rollers 7, rather than determining the timing when the detection value of the sheet position detection sensor 60 converges. That is, the zero point position of the sheet position detection sensor 60 is corrected using the detection value of the sheet position detection sensor 60 at the second timing when the leading edge of the sheet reaches the pair of registration rollers 7.

[0108] Here, to determine whether or not the sheet has reached the registration roller pair 7, a detection result of the sheet by a pre-registration sensor Q provided upstream in the conveying direction of the registration roller pair 7 is used. Specifically, it is determined that the sheet has reached the registration roller pair 7 by counting a predetermined delay time from the timing when the pre-registration sensor Q detects the sheet.

[0109] [Details of the correction control of the zero point position according to the second embodiment] Next, the details of the correction control (correction mode) of the 0 point position according to the second embodiment will be described with reference to FIG. 24. FIG. 24 is a flowchart showing the correction control of the 0 point position of the sheet position detection sensor according to the second embodiment. Note that, like the first embodiment, the flowchart of FIG. 24 also shows only the control of the skew correction unit and the pair of registration rollers of the registration unit 50. That is, in the correction control of the 0 point position, the control of the conveying unit of the registration unit is the same as the control of the conveying unit of the registration unit during execution of the above-mentioned print job (see FIG. 16), so the figure is omitted. In other words, the correction control of the 0 point position is the control shown in FIG. 16 and FIG. 24, but other than the detection and correction by the sheet position detection sensor 60 when the sheet hits the reference member 31, it is the same as during execution of the print job, so the description thereof will be omitted.

[0110] That is, as shown in Fig. 24, after the sheet is shifted by the conveying roller pair 34-4 (see S12 in Fig. 16), the skew roller pairs 32-1 to 32-3 are pressed against each other (S13, S14), and the conveying roller pair 34-4 is separated (S15, S16). Then, the skew roller pairs 32-1 to 32-3 correct the skew of the sheet (S16).

[0111] Here, when the control unit 9 detects that the pre-registration sensor Q has turned ON (Yes in S17), it counts a predetermined delay after detecting the pre-registration sensor Q turning ON, and when the count ends, it determines that the sheet has reached the pair of registration rollers 7. Then, when it determines that the sheet has reached the pair of registration rollers 7, the sheet position detection sensor 60 detects the position of the side edge of the sheet at that point (S40). Then, a correction is performed to set the detected position of the side edge of the sheet, that is, a position offset by a distance Lt in the direction away from the position of the reference surface 31a of the reference member 31, as the zero point position of the sheet position detection sensor 60 (S41). As a result, even if an error occurs due to part replacement or the like, the zero point position is corrected, and the side edge of the sheet can be shifted to the ideal distance Lt from the reference surface 31a of the reference member 31.

[0112] Thereafter, as in the case of the above print job, the skew roller pairs 32-1 to 32-3 are separated (S18, S19), a shift is performed by the registration roller pair 7 (S20), and this control ends. Note that in this 0 point position correction control, since only one sheet is conveyed, the paper passing counter does not count (see S21, S22 in FIG. 17). Also, if the pre-registration sensor does not turn ON (No in S17), a paper jam is displayed on the operation unit (S23), and this control ends.

[0113] As described above, in the second embodiment, since it is not necessary to monitor the detection value detected by the sheet position detection sensor 60, it is possible to easily determine when the sheet has completed striking the reference surface 31a of the reference member 31.

[0114] In the second embodiment described above, the other configurations, operations, and effects are similar to those of the first embodiment, and therefore description thereof will be omitted.

[0115] <Third embodiment> Next, a third embodiment, which is a partial modification of the first and second embodiments, will be described. Fig. 25 is a top view showing a state in which the skew correction of the sheet is completed. Fig. 26 is a time chart showing the position of the sheet end portion detected by the sheet position detection sensor.

[0116] In the first embodiment, the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 is determined by monitoring the detection value of the sheet position detection sensor 60 and determining that the detection value converges. In the second embodiment, the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 is determined by the pre-registration sensor Q detecting the sheet. In the third embodiment, the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 is determined before the sheet reaches the registration roller pair 7.

[0117] That is, if the timing for determining the completion of the abutment is the timing when the sheet reaches the registration roller pair 7 as in the second embodiment, the abutment of the sheet is certainly completed. However, there is a possibility that a lot of time has passed since the abutment of the sheet was actually completed. In this case, if the length of the sheet in the conveying direction is not long, the trailing end of the sheet may pass through the sheet position detection sensor 60, and therefore a restriction arises that the length of the sheet must be long. In the third embodiment, the determination can be made more simply than in the first embodiment, and as shown in FIG. 25, the completion of the abutment of the sheet is determined earlier than in the second embodiment, thereby reducing the restriction on the length of the sheet.

[0118] Specifically, in the third embodiment, as shown in Fig. 26, the time when the set time TC has elapsed since the start of skew correction by the skew correction unit 50B is set as the second timing at which it is determined that the abutment of the sheet has been completed. That is, the zero point position of the sheet position detection sensor 60 is corrected using the detection value of the sheet position detection sensor 60 at the second timing at which the set time TC has elapsed since the start of skew correction of the sheet. This makes it possible to simply determine the completion of the abutment, and also alleviates the constraints on the length of the sheet.

[0119] [Details of the correction control of the zero point position according to the third embodiment] Next, the details of the correction control (correction mode) of the zero point position according to the third embodiment will be described with reference to FIG. 27. FIG. 27 is a flowchart showing the correction control of the zero point position of the sheet position detection sensor according to the third embodiment. Note that, like the first and second embodiments, the flowchart of FIG. 27 also shows only the control of the skew correction unit and the pair of registration rollers of the registration unit 50. That is, in the correction control of the zero point position, the control of the conveying unit of the registration unit is the same as the control of the conveying unit of the registration unit during execution of the above-mentioned print job (see FIG. 16), so the figure is omitted. In other words, the correction control of the zero point position is the control shown in FIG. 16 and FIG. 27, but other than the detection and correction by the sheet position detection sensor 60 when the sheet hits the reference member 31, it is the same as during execution of the print job, so the description thereof will be omitted.

[0120] That is, as shown in Fig. 27, after the sheet is shifted by the conveying roller pair 34-4 (see S12 in Fig. 16), the skew roller pairs 32-1 to 32-3 are pressed against each other (S13, S14), and the conveying roller pair 34-4 is separated (S15, S16). Then, the skew roller pairs 32-1 to 32-3 correct the skew of the sheet (S16).

[0121] Here, the control unit 9 counts a set time TC from the start of the skew correction of the sheet, and when the count ends, it determines that the sheet has been abutted against the reference surface 31a of the reference member 31. Then, when it determines that the set time TC has elapsed from the start of the skew correction, the sheet position detection sensor 60 detects the position of the side edge of the sheet at that point (S50). Then, a correction is performed to set the detected position of the side edge of the sheet, that is, a position offset by a distance Lt in the width direction from the position of the reference surface 31a of the reference member 31, as the zero point position of the sheet position detection sensor 60 (S51). As a result, even if an error occurs due to part replacement or the like, the zero point position is corrected, and the side edge of the sheet can be shifted to the ideal distance Lt from the reference surface 31a of the reference member 31.

[0122] The set time TC may be set according to the type of sheet (particularly the basis weight according to the type) based on the sheet information input in step S1 (see FIG. 16). In particular, when the basis weight of the sheet is large, it is expected that the time required for skew correction will be long, so it is considered to set the set time longer as the basis weight increases. The set time TC may be set according to the size of the sheet based on the sheet information input in step S1 (see FIG. 16). In particular, when the sheet size is large, it is expected that the time required for skew correction will be long, so it is considered to set the set time longer as the size increases.

[0123] Thereafter, similarly to the case of the print job, when it is detected that the pre-registration sensor Q has turned ON (Yes in S17), the skew roller pairs 32-1 to 32-3 are separated (S18, S19), a shift is executed by the registration roller pair 7 (S20), and this control ends. Note that in this 0 point position correction control, since only one sheet is conveyed, the paper passing counter is not counted (see S21, S22 in FIG. 17). Also, if the pre-registration sensor does not turn ON (No in S17), a paper jam is displayed on the operation unit (S23), and this control ends.

[0124] As described above, in the third embodiment, since it is not necessary to monitor the detection value detected by the sheet position detection sensor 60, it is possible to easily determine the completion of the abutment of the sheet against the reference surface 31a of the reference member 31. Furthermore, it is possible to determine the completion of the abutment of the sheet against the reference surface 31a of the reference member 31 before the sheet reaches the registration roller pair 7, which makes it unnecessary to increase the length of the sheet.

[0125] In the above-described third embodiment, the other configurations, operations, and effects are similar to those of the first and second embodiments, and therefore description thereof will be omitted.

[0126] <Possibilities for other embodiments> In the above-described first to third embodiments, it has been described by using the method of each embodiment that the sheet has been abutted against the reference member 31. That is, it is determined that the sheet has been abutted against the reference member 31 when the detection value of the sheet position detection sensor 60 has stabilized, the sheet has reached the pair of registration rollers 7, and a set time has elapsed since the start of skew correction. However, it is not limited to this, and it may be determined that the sheet has been abutted against the reference member 31 by any method, such as detecting the position of the abutted sheet with another sensor or detecting the conveying resistance of a roller.

[0127] In the first to third embodiments, the registration unit 50 has been 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 cutting, binding, punching, folding, etc., of the sheet, or an image reading portion.

[0128] In the first to third embodiments, the control for executing the print job and the control for correcting the 0 point position are executed separately. However, the present invention is not limited to this, and both controls may be executed simultaneously, for example, when correcting the skew of the first sheet of a print job, the control for correcting the 0 point position may be executed.

[0129] In the present embodiment, the printer 1 is described as being an electrophotographic full-color laser beam printer, but the present invention is not limited to this. For example, the image forming unit that forms an image on a sheet may be any configuration or method, such as an inkjet printer.

[0130] The present disclosure can also be realized by a process in which a program for implementing one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0131] <Summary of this embodiment> [Configuration 1] a first conveying rotating body pair that sandwiches and conveys a sheet; a first movement drive unit that moves the first conveying rotating body pair in a width direction perpendicular to a sheet conveying direction; a width position detection unit that detects a position of an end portion in the width direction of the sheet held by the first conveying rotating body pair; an abutting portion disposed downstream of the first pair of conveying rotors in the sheet conveying direction and on one side of the sheet in the width direction; a pair of obliquely conveying rotors that obliquely convey a sheet toward the abutting portion and abut an end portion of the sheet in the width direction against the abutting portion; a control unit that detects a position of an end portion of the sheet in the width direction by the width position detection unit at a first timing when the sheet is conveyed to the first conveying rotating body pair, and moves the sheet in the width direction by moving the first conveying rotating body pair that sandwiches the sheet by the first movement drive unit so that the position of the end portion is a set position away from the abutment portion in the other side of the width direction, the control unit detects a position of the end by the width position detection unit at a second timing when one end of the sheet in the width direction is abutted against the abutment unit by the pair of obliquely conveying rotors, and corrects the set position based on the detected position of the end. A sheet conveying device comprising: [Configuration 2] The control unit determines that the second timing is a time when a change in the position of the end portion detected by the detection unit due to the sheet being obliquely fed by the pair of oblique feeding rotors converges to a threshold value or less. 2. The sheet conveying device according to configuration 1, [Configuration 3] a second conveying rotor pair that sandwiches and conveys the sheet that has been abutted against the abutment portion by the oblique conveying rotor pair; a second movement drive unit that moves the second conveying rotating body pair in a width direction perpendicular to a sheet conveying direction; an arrival detection unit that detects arrival of the sheet at the second conveying rotating body pair, The control unit is After the arrival detection unit detects that the sheet has reached the second conveying rotating body pair, the second movement drive unit moves the second conveying rotating body pair so as to align a position of the sheet with a position in the width direction of an image formed on the sheet by an image forming unit; The second timing is determined to be a time when the arrival detection unit detects that the sheet has reached the second conveying rotating body pair. 2. The sheet conveying device according to configuration 1, [Configuration 4] The control unit determines that the second timing is a time when a set time has elapsed since the pair of obliquely feeding rotors started to obliquely feed the sheet. 2. The sheet conveying device according to configuration 1, [Configuration 5] The control unit sets the set time in accordance with the type of sheet. 5. The sheet conveying device according to configuration 4. [Configuration 6] The control unit sets the set time in accordance with a size of a sheet. 6. The sheet conveying device according to configuration 4 or 5, [Configuration 7] a second conveying rotor pair that sandwiches and conveys the sheet that has been abutted against the abutment portion by the oblique conveying rotor pair; a second movement drive unit that moves the second conveying rotating body pair in a width direction perpendicular to a sheet conveying direction; an arrival detection unit that detects arrival of the sheet at the second conveying rotating body pair, the control unit, after detecting by the arrival detection unit that the sheet has reached the second conveying rotating body pair, moves the second movement drive unit to move the sheet in the width direction so as to align a position of the sheet with a position of an image formed on the sheet by an image forming unit in the width direction. 7. The sheet conveying device according to any one of configurations 1 to 6, [Configuration 8] The pair of oblique conveying rotors is switched between a clamping conveying state in which the pair of oblique conveying rotors clamps and conveys the sheet and a non-clamping state in which the pair of oblique conveying rotors releases the clamping of the sheet, the control unit switches the pair of oblique conveying rotors to the non-clamping state when the second conveying rotors move the sheet in the width direction. 8. The sheet conveying device according to configuration 7, [Configuration 9] the first conveying rotating body pair is switched between a clamping conveying state in which the first conveying rotating body pair clamps and conveys a sheet and a non-clamping state in which the first conveying rotating body pair releases the clamping of the sheet; The control unit switches the first conveying rotor pair to the non-clamping state when the sheet is obliquely conveyed by the oblique conveying rotor pair. 9. The sheet conveying device according to any one of configurations 1 to 8, [Configuration 10] A sheet conveying device according to any one of configurations 1 to 9, 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, 1. An image forming apparatus comprising: [Configuration 11] The image forming unit includes an image carrier that carries a toner image, and a transfer roller that transfers the toner image carried on the image carrier onto a sheet. 11. The image forming apparatus according to claim 10, [Explanation of symbols]

[0132] 1... printer (image forming device) / 7... pair of registration rollers (pair of second conveying rotors) / 9... control unit / 31... reference member (abutment unit) / 32-1 to 32-3... pair of skewed rotors / 34-4... pair of conveying rollers (pair of first conveying rotors) / 50... registration unit (sheet conveying device) / 56... secondary transfer roller (transfer roller) / 60... sheet position detection sensor (width position detection unit) / 70... slide mechanism (second movement drive unit) / 506... intermediate transfer belt (image carrier) / 513... image forming engine (image forming unit) / 600... slide mechanism (first movement drive unit) / S... sheet / Lt... distance (set position) / Q... pre-registration sensor (arrival detection unit) / TC... set time / δ... threshold

Claims

1. a pair of rotating bodies that sandwich a sheet and transport it in a sheet transport direction; a moving unit that can move the pair of rotating bodies in a width direction perpendicular to the sheet conveying direction; a detection unit that detects the position of a downstream end of the sheet in a first direction from one side to the other side in the width direction; an abutting member disposed downstream of the pair of rotating bodies in the sheet conveying direction, the abutting member having an abutting surface extending along the sheet conveying direction; a skew conveying unit disposed downstream of the pair of rotating bodies in the sheet conveying direction, the skew conveying unit skewing the sheet in an oblique direction that is oblique with respect to the sheet conveying direction so that the sheet approaches the abutment surface in the first direction; a control unit that, when the pair of rotating bodies sandwich a sheet and before the sheet reaches the oblique feeding section, causes the moving unit to move the pair of rotating bodies in the width direction based on a detection result from the detection unit so that a position of the downstream end of the sheet in the width direction becomes a set position on the detection unit that is a predetermined distance away from the abutting surface in a second direction opposite to the first direction, the control unit is capable of executing a mode in which, after the sheet reaches the oblique feeding unit, the set position is determined based on the position of the downstream end in a state in which the downstream end abuts on the abutting surface, which position is detected by the detection unit. A sheet conveying device characterized by:

2. The detection unit is arranged upstream of the pair of rotating bodies in the sheet conveying direction.

2. The sheet transport device according to claim 1.

3. The control unit moves the pair of rotating bodies in the width direction using the moving unit based on the position of the downstream end of the sheet clamped by the pair of rotating bodies so that the position of the downstream end in the width direction becomes the set position.

2. The sheet transport device according to claim 1.

4. the control unit determines the set position based on the position of the downstream end when the downstream end of the sheet obliquely fed by the oblique feeding unit abuts against the abutting surface and fluctuation in the position of the downstream end converges to a threshold value or less in the mode.

2. The sheet transport device according to claim 1.

5. The pair of rotating bodies and the detection unit are a first pair of rotating bodies and a first detection unit, respectively; a second pair of rotating bodies that sandwich and transport the sheet that has been abutted against the abutting portion by the oblique feeding portion; a second detection unit that detects that the sheet has reached the second pair of rotating bodies, In the mode, the control unit (1) detecting the position of the downstream end by the first detection unit based on the detection of the sheet by the second detection unit; (2) determining the set position based on the detection result of the first detection unit; 2. The sheet transport device according to claim 1.

6. The moving part is a first moving part, a second moving unit that can move the second rotating body pair in the width direction, the control unit moves the second rotating body pair holding the sheet by the second moving unit so as to align the position of the sheet with the position of an image formed on the sheet by the image forming unit in the width direction.

6. The sheet transport device according to claim 5.

7. the control unit determines the set position based on a detection result of the detection unit when a set time has elapsed since the oblique feeding unit started conveying the sheet in the mode.

2. The sheet transport device according to claim 1.

8. the control unit sets the set time in accordance with the type of sheet.

8. The sheet transport device according to claim 7.

9. the control unit sets the set time in accordance with the size of the sheet.

8. The sheet transport device according to claim 7.

10. The pair of rotating bodies, the detection unit, and the moving unit are a first pair of rotating bodies, a first detection unit, and a first moving unit, respectively; a second pair of rotating bodies that sandwich and transport the sheet that has been abutted against the abutting portion by the oblique feeding portion; a second moving unit that can move the second pair of rotating bodies in the width direction; a second detection unit that detects that the sheet has reached the second pair of rotating bodies, After the second detection unit detects that the sheet has reached the second pair of rotating bodies, the control unit moves the second pair of rotating bodies holding the sheet by the second moving unit 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.

11. the oblique feeding section is switched between a nipping and conveying state in which the sheet is nipped and conveyed, and a non-nipping state in which the nipping of the sheet is released, the control unit switches the oblique feeding unit to the non-clamping state when the second rotating body pair moves the sheet in the width direction.

11. The sheet transport device according to claim 10.

12. The pair of rotating bodies are switched between a nip conveying state in which the pair of rotating bodies nip and convey the sheet and a non-nip conveying state in which the pair of rotating bodies releases the nip of the sheet, the control unit switches the pair of rotating bodies to the non-clamping state when the oblique feeding unit obliquely feeds the sheet.

11. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

13. A sheet conveying device; an image forming unit that forms an image on the sheet conveyed by the sheet conveying device, the sheet conveying device, a pair of rotating bodies that sandwich a sheet and transport it in a sheet transport direction; a moving unit that can move the pair of rotating bodies in a width direction perpendicular to the sheet conveying direction; a detection unit that detects the position of a downstream end of the sheet in a first direction from one side to the other side in the width direction; an abutting member disposed downstream of the pair of rotating bodies in the sheet conveying direction, the abutting member having an abutting surface extending along the sheet conveying direction; a skew conveying unit disposed downstream of the pair of rotating bodies in the sheet conveying direction, the skew conveying unit skewing the sheet in an oblique direction that is oblique with respect to the sheet conveying direction so that the sheet approaches the abutment surface in the first direction; a control unit that, when the pair of rotating bodies sandwich a sheet and before the sheet reaches the oblique feeding section, causes the moving unit to move the pair of rotating bodies in the width direction based on a detection result from the detection unit so that a position of the downstream end of the sheet in the width direction becomes a set position on the detection unit that is a predetermined distance away from the abutting surface in a second direction opposite to the first direction, the control unit is capable of executing a mode in which, after the sheet reaches the oblique feeding unit, the set position is determined based on the position of the downstream end in a state in which the downstream end abuts on the abutting surface, which position is detected by the detection unit. An image forming apparatus characterized by:

14. The image forming unit includes an image carrier that carries a toner image, and a transfer roller that transfers the toner image carried on the image carrier onto a sheet.

14. The image forming apparatus according to claim 13.

15. A pair of conveying rollers that sandwich a sheet and convey it in a sheet conveying direction; a moving unit that can move the pair of conveying rollers in a width direction perpendicular to the sheet conveying direction; a detection unit that detects the position of a side edge of the sheet; an abutting member disposed downstream of the pair of conveying rollers in the sheet conveying direction, the abutting member having an abutting surface extending along the sheet conveying direction; a skew conveying unit disposed downstream of the pair of conveying rollers in the sheet conveying direction and configured to skew the sheet in a direction skewed with respect to the sheet conveying direction so that the sheet approaches the abutment surface in the width direction; a control unit that causes the moving unit to move the pair of conveying rollers in the width direction so that the sheet moves to a predetermined position based on a detection result from the detection unit before the sheet is obliquely fed by the oblique feeding unit, a first position, which is the position of the side edge of the sheet that has moved to the predetermined position, and a second position, which is the position of the side edge of the sheet that is detected by the detection unit in a state where the side edge of the sheet abuts against the abutment surface, are positions on the detection unit; The control unit determines the first position based on the second position. A sheet conveying device characterized by:

Images