Sheet transport device and image forming apparatus

Abstract

To reduce the generation of sliding marks caused by a pair of rotating bodies in a non-clamping state. [Solution] The sheet conveying device comprises a stopper, a first pair of oblique conveying rotating bodies that obliquely convey the sheet toward the stopper, a first switching mechanism that switches the first pair of oblique conveying rotating bodies between a gripping conveying state and a non-gripping state, a first drive unit that rotationally drives the first pair of oblique conveying rotating bodies, a first pair of conveying rotating bodies that grips and conveys the sheet that is abutted against the stopper, a second drive unit that rotationally drives the first pair of conveying rotating bodies, and a control unit that controls the first switching mechanism, the first drive unit and the second drive unit. The control unit controls the rotational speed of the first pair of oblique conveying rotating bodies to a first speed when the sheet is obliquely conveyed toward the stopper by the first pair of oblique conveying rotating bodies (S13), and controls the rotational speed of the first pair of oblique conveying rotating bodies to a second speed that is slower than the first speed when the first pair of conveying rotating bodies is in a non-gripping state and the sheet is conveyed by the first pair of conveying rotating bodies (S18).

Description

Technical Field

[0001] The present invention relates to a sheet conveying device for conveying a sheet and an image forming apparatus.

Background Art

[0002] For example, in an image forming apparatus such as a printer, there has been proposed an apparatus that employs a so-called side registration method in which a sheet is obliquely fed by an obliquely feeding roller pair and the end of the sheet is abutted against an abutting member to correct skewing (see Patent Documents 1 and 2). In the apparatus of Patent Document 1, a sheet conveyed by a conveying roller pair is abutted against a reference surface of a reference member by a plurality of obliquely feeding rollers and conveyed to a registration roller. Thereafter, when the sheet is sandwiched by the registration roller, the sandwiching by the obliquely feeding rollers is released, and the registration roller is slid in the width direction by a certain amount, whereby the position of the sheet is aligned with the position of the image on the intermediate transfer belt and the sheet is conveyed.

[0003] Further, when the sheet conveyed by the conveying roller pair is farther from the reference member in the width direction, if the angle of the obliquely feeding roller is increased to cause the sheet to reach the reference member, the sheet may be strongly abutted against the reference member and buckle. Therefore, as in Patent Document 2, there has been proposed an apparatus in which the obliquely feeding roller on the back side farther from the reference member in the width direction has a larger angle than the obliquely feeding roller on the front side. In the apparatus of Patent Document 2, the pressurization of the obliquely feeding roller on the front side is released and the obliquely feeding roller on the back side is pressurized to bring the sheet closer to the reference member with the obliquely feeding roller on the back side, and thereafter, the obliquely feeding roller on the front side is pressurized and the pressurization of the obliquely feeding roller on the back side is released. Thereby, after bringing the sheet closer to the reference member with the obliquely feeding roller on the back side, the sheet is abutted against the reference member with the obliquely feeding roller on the front side, thereby preventing the sheet from being strongly abutted against the reference member.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Incidentally, in Patent Document 1, the rotation angle direction of the inclined feed roller and the rotation angle direction of the registration roller are different, and in Patent Document 2, the rotation angle direction of the inclined feed roller on the far side and the rotation angle direction of the inclined feed roller on the near side are different. In such configurations, when the pressure on one roller is released and the sheet is being transported by the other roller, a relative speed difference is created with respect to the sheet transport direction of the device. For this reason, for example, the roller with the pressure released may slide on the surface of the sheet with the above relative speed difference, leaving sliding marks on the surface of the sheet, and in particular in the case of double-sided printing, there is a risk of scraping off the image formed on the first surface of the sheet. In other words, in a system where the pressure on one roller is released and the sheet is being transported by the other roller, there is a problem that sliding marks may be left by the other roller.

[0006] Therefore, the present invention aims to provide a sheet conveying device and an image forming device that can reduce the generation of sliding marks caused by a pair of rotating bodies in a non-clamping state. [Means for solving the problem]

[0007] One aspect of the present invention includes: a stopper positioned on one side of the width direction perpendicular to the conveying direction of the sheet to be conveyed; a first pair of oblique conveying rotating bodies that obliquely convey the sheet toward the stopper; a first switching mechanism that switches the first pair of oblique conveying rotating bodies between a gripping conveying state in which the sheet is gripped and conveyed, and a non-gripping state in which the sheet is released from gripping; a first drive unit that rotationally drives the first pair of oblique conveying rotating bodies; a first pair of conveying rotating bodies that grips and conveys the sheet that is abutted against the stopper; and the first pair of conveying rotating bodies The sheet conveying device comprises a second drive unit that rotates the first drive unit and a control unit that controls the first switching mechanism, the first drive unit and the second drive unit, wherein the control unit controls the rotational speed of the first oblique driving rotating body pair to a first speed when the sheet is obliquely fed to the abutment part by the first oblique driving rotating body pair, and controls the rotational speed of the first oblique driving rotating body pair to a second speed slower than the first speed when the sheet is conveyed by the first conveying rotating body pair with the first oblique driving rotating body pair in the non-clamping state.

[0008] One aspect of the present invention comprises: a second pair of conveying rotating bodies that grip and convey a sheet; a stopper positioned on one side in the width direction perpendicular to the conveying direction of the sheet with respect to the sheet being conveyed; a first pair of oblique conveying rotating bodies positioned downstream of the second pair of conveying rotating bodies in the conveying direction of the sheet and obliquely conveying the sheet toward the stopper; a first switching mechanism that switches the first pair of oblique conveying rotating bodies between a gripping conveying state in which the sheet is gripped and conveyed, and an un-grip state in which the sheet is released from gripping; and a first drive unit that rotationally drives the first pair of oblique conveying rotating bodies. The sheet conveying device comprises a third drive unit that rotationally drives a second pair of conveying rotating bodies, and a control unit that controls the first switching mechanism, the first drive unit, and the third drive unit, wherein the control unit controls the rotational speed of the first pair of inclined rotating bodies to a first speed when the sheet is inclined to be conveyed to the abutment portion by the first pair of inclined rotating bodies, and controls the rotational speed of the first pair of inclined rotating bodies to a third speed that is slower than the first speed when the sheet is conveyed by the second pair of conveying rotating bodies with the first pair of inclined rotating bodies in a non-clamping state.

[0009] One aspect of the present invention includes: a stopper positioned on one side of the width direction perpendicular to the conveying direction of the sheet to be conveyed; a first pair of oblique conveying rotating bodies that obliquely conveys the sheet toward the stopper; a second pair of oblique conveying rotating bodies whose angle of oblique conveying direction with respect to the stopper is greater than that of the first pair of oblique conveying rotating bodies, and which obliquely conveys the sheet toward the first pair of oblique conveying rotating bodies; a first switching mechanism that switches the first pair of oblique conveying rotating bodies between a clamping conveying state in which the sheet is clamped and conveyed, and a non-clamping state in which the sheet is released from clamping; and a third switching mechanism that switches the second pair of oblique conveying rotating bodies between a clamping conveying state in which the sheet is clamped and conveyed, and a non-clamping state in which the sheet is released from clamping. The sheet conveying device comprises a first drive unit for rotationally driving a pair of conveying rotating bodies, a fourth drive unit for rotationally driving a second pair of oblique conveying rotating bodies, and a control unit for controlling the first switching mechanism, the third switching mechanism, the first drive unit, and the fourth drive unit, wherein the control unit controls the rotational speed of the first pair of oblique conveying rotating bodies to a first speed when the second pair of oblique conveying rotating bodies is in a non-clamping state and the first pair of oblique conveying rotating bodies is obliquely conveying the sheet to the abutment portion, and controls the rotational speed of the first pair of oblique conveying rotating bodies to a fourth speed that is faster than the first speed when the first pair of oblique conveying rotating bodies is in a non-clamping state and the second pair of oblique conveying rotating bodies is obliquely conveying the sheet to the first pair of oblique conveying rotating bodies.

[0010] One aspect of the present invention includes: a stopper positioned on one side of the width direction perpendicular to the conveying direction of the sheet to be conveyed; a first pair of oblique conveying rotating bodies that obliquely conveys the sheet toward the stopper; a second pair of oblique conveying rotating bodies whose angle of oblique conveying direction with respect to the stopper is greater than that of the first pair of oblique conveying rotating bodies, and which obliquely conveys the sheet toward the first pair of oblique conveying rotating bodies; a first switching mechanism that switches the first pair of oblique conveying rotating bodies between a clamping conveying state in which the sheet is clamped and conveyed, and a non-clamping state in which the sheet is released from clamping; and a second switching mechanism that switches the second pair of oblique conveying rotating bodies between a clamping conveying state in which the sheet is clamped and conveyed, and a non-clamping state in which the sheet is released from clamping; and The sheet conveying device comprises a first drive unit for rotationally driving a pair of conveying rotating bodies, a fourth drive unit for rotationally driving a second pair of oblique conveying rotating bodies, and a control unit for controlling the first switching mechanism, the second switching mechanism, the first drive unit, and the fourth drive unit, wherein the control unit controls the rotational speed of the second pair of oblique conveying rotating bodies to a fifth speed when the first pair of oblique conveying rotating bodies is in a non-clamping state and the sheet is obliquely conveyed to the first pair of oblique conveying rotating bodies by the second pair of oblique conveying rotating bodies, and controls the rotational speed of the second pair of oblique conveying rotating bodies to a sixth speed slower than the fifth speed when the second pair of oblique conveying rotating bodies is in a non-clamping state and the sheet is obliquely conveyed to the abutment part by the first pair of oblique conveying rotating bodies. [Effects of the Invention]

[0011] According to the present invention, the generation of sliding marks caused by a pair of rotating bodies in a non-clamping state can be reduced. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing a printer according to the first embodiment. [Figure 2] This is an overhead view showing a registration unit according to the first embodiment. [Figure 3] (a) is a cross-sectional view showing a part of the transport section in the registration unit in the clamped transport state. (b) is a cross-sectional view showing a part of the transport section in the registration unit in the non-clamped state. [Figure 4]This is a perspective view showing a part of the transport section in the registration unit. [Figure 5] (a) is an overhead view showing a part of the skew correction section in the registration unit. (b) is a cross-sectional view showing a part of the skew correction section in the registration unit as viewed from the sheet transport direction. [Figure 6] (a) is a perspective view showing a pair of oblique rollers and their pressurizing mechanism. (b) is a side view showing a part of the pair of oblique rollers and their pressurizing mechanism. [Figure 7] (a) is a side view showing a pair of oblique rollers in a clamping transport state. (b) is a side view showing a pair of oblique rollers in a non-clamping state. [Figure 8] This is a perspective view showing the sheet position detection sensor in the transport section of the registration unit. [Figure 9] This is a perspective view showing the drive mechanism of the transport roller pair in the transport section of the registration unit. [Figure 10] This is a perspective view showing the sliding mechanism of the transport roller pair in the transport section of the registration unit. [Figure 11] (a) is a perspective view showing the pressure release mechanism for the transport roller pair in the transport section of the registration unit. (b) is a cross-sectional view showing the pressure release mechanism for the transport roller pair in the transport section of the registration unit. [Figure 12] This is a block diagram showing the control system of the printer according to the first embodiment. [Figure 13] (a) is a top view showing the state in which a sheet is being transported to the transport section of the 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 the state in which the sheet has been shifted in the width direction by the transport roller pair 34-3 from the state shown in (a) and (b). (d) is a cross-sectional view of the state shown in (c). [Figure 14] (a) is a top view showing the state in which skew correction has been performed in the skew correction section of the registration unit according to the first embodiment. (b) is a cross-sectional view of the state shown in (a). [Figure 15](a) is a top view showing a state in which a shift is performed by a registration roller pair of a registration unit according to the first embodiment. (b) is a cross-sectional view of the state shown in (a). [Figure 16] It is a flowchart showing control of a conveyance unit of a registration unit at the time of executing a normal printing job according to the first embodiment. [Figure 17] It is a flowchart showing control of a skew correction unit and a registration roller pair of a registration unit at the time of executing a normal printing job according to the first embodiment. [Figure 18] It is a diagram showing the relationship between the conveyance direction speed and the abutting direction speed in the diagonal feed roller pair and the registration roller pair. [Figure 19] (a) is a diagram showing the relationship between the conveyance direction speed and the abutting direction speed among the diagonal feed roller pair, the registration roller pair, and the sheet in a state where the sheet is being diagonally fed by the diagonal feed roller pair. (b) is a diagram showing the relationship between the conveyance direction speed and the abutting direction speed among the diagonal feed roller pair, the registration roller pair, and the sheet in a state where the sheet is being conveyed by the registration roller pair. [Figure 20] It is a top view showing a registration unit according to the second embodiment. [Figure 21] It is a top view showing a state in which a sheet is being skewed by a diagonal feed roller pair 32-4 in a skew correction unit of a registration unit according to the second embodiment. [Figure 22] It is a flowchart showing control of a skew correction unit and a registration roller pair of a registration unit at the time of executing a normal printing job according to the second embodiment. [Figure 23](a) is a diagram showing the relationship between the conveying direction speed and the abutting direction speed between the inclined roller pair 32-4, the inclined roller pair 32-1, and the sheet when the sheet is being conveyed by the inclined roller pair 32-4 in the second embodiment. (b) is a diagram showing the relationship between the conveying direction speed and the abutting direction speed between the inclined roller pair 32-4, the inclined roller pair 32-1, and the sheet when the sheet is being conveyed by the inclined roller pair 32-1 in the second embodiment. [Modes for carrying out the invention]

[0013] <First Embodiment> The first embodiment will be described below with reference to Figures 1 to 19. First, the schematic configuration of the printer 1, which is an image forming apparatus equipped with a registration unit 50 as a sheet transport device according to the first embodiment, will be described. Figure 1 is a schematic diagram showing the printer according to the first embodiment. In the printer 1, various sheets can be used as recording media, such as paper such as paper and envelopes, glossy paper, plastic films such as overhead projector sheets, and cloth.

[0014] [Printer configuration] As shown in Figure 1, the printer 1 has a control unit 9 (see Figure 12) that controls the overall operation of the printer 1 based on image information input from an external PC or image information read from a document. The main body 1A of the printer 1 houses a feed cassette 51 for storing a sheet S and an image forming engine 513, which is an image forming unit that forms an image on the sheet S fed from the feed cassette 51. An example of an image forming unit, the image forming engine 513, comprises four image forming process units PY, PM, PC, and PK, which 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 intermediate transfer method. The image forming process units PY to PK are each electrophotographic units having a photosensitive drum 508, which is a photoreceptor.

[0015] The image forming process units PY to PK share a common configuration except for the color of the toner used for development. Here, the configuration of the image forming engine 513 and the image forming process of the toner image will be explained using the yellow image forming process unit PY as an example. In addition to the photosensitive drum 508, the image forming process unit PY includes an exposure device 511, a developing device 510, and a drum cleaner 509. The photosensitive drum 508 is a drum-shaped photoreceptor having a photosensitive layer on its outer circumference, and rotates in a direction (arrow A in the figure) along the rotation direction of the intermediate transfer belt 506 (arrow B in Figure 1). The surface of the photosensitive drum 508 is charged by receiving charge from a charging means such as a charging roller (not shown). The exposure device 511 irradiates the photosensitive drum 508 with a laser beam modulated according to the image information, and scans the photosensitive drum 508 with an optical system including a reflector 512 to draw an electrostatic latent image on the surface of the photosensitive drum 508. The developing device 510 contains a developer containing toner and supplies toner to the photosensitive drum 508 to make the electrostatic latent image visible as a toner image. The toner image formed on the photosensitive drum 508 is first transferred to the intermediate transfer belt 506 in the primary transfer section, which is the nip between the primary transfer roller 507 and the intermediate transfer belt 506. Any remaining toner on the photosensitive drum 508 after the transfer is removed by the drum cleaner 509.

[0016] The intermediate transfer belt 506 is wrapped around the drive roller 504, the driven roller 505, the secondary transfer inner roller 503, and the primary transfer roller 507, and is rotated by the drive roller 504 in the clockwise direction (arrow B) in Figure 1. The image forming process described above proceeds in parallel in each image forming process section PY to PK, and the four-color toner images are superimposed by multiple transfers to form a full-color toner image on the intermediate transfer belt 506. This toner image is carried to the secondary transfer section 1C while still supported on the intermediate transfer belt 506. The secondary transfer section 1C is configured as a nip section between the secondary transfer roller 56 and the secondary transfer inner roller 503, which act as transfer rollers. A bias voltage with the opposite polarity to the charge polarity of the toner is applied to the secondary transfer roller 56, thereby secondary transferring the toner image to the sheet S. After transfer, any remaining toner on the intermediate transfer belt 506 is removed by the belt cleaner 514.

[0017] The sheet S onto which the toner image has been transferred is passed to the fixing unit 58 by the pre-fixing transport unit 57. The fixing unit 58 has a pair of fixing rollers that grip 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. As a result, the toner particles melt and solidify, fixing the toner image to the sheet S.

[0018] Next, the sheet transport process for transporting the sheets will be described. The sheet transport system 1D of the printer 1 transports the sheets S supplied from the sheet supply unit 1B, which acts as a sheet feeding device, and discharges the sheets S on which the image has been formed to the outside of the main body 1A of the device. 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 reversal transport section 501, and a double-sided transport section 502 as a re-transport section.

[0019] The feeding cassette 51 provided in the sheet feeding unit 1B is removably attached to the main body 1A of the device, and stores sheets S in a state where they are loaded and supported on a liftable tray 52 that can be raised and lowered, and feeds them one by one by the sheet feeding unit 53. The sheet feeding unit 53 may be a belt system that uses a suction fan to attract and transport the sheets S to a belt member, or a friction separation system that uses rollers or pads. The sheets S sent out from the sheet feeding unit 53 are transported along the feeding path 54a by a pair of transport rollers of the sheet transport unit 54 and handed over to the registration unit 50.

[0020] The sheet S, which has been handed over to the registration unit 50, is transported to the secondary transfer unit 1C after skew correction and timing correction are performed. At this time, the registration roller pair 7 of the registration unit 50 feeds the sheet S to the secondary transfer unit 1C in accordance with the progress of the image formation process by the image formation process units PY~PK, based on the detection of the sheet by the sheet detection sensor 8. After the toner image is transferred in the secondary transfer unit 1C and the image is fixed by the fixing unit 58, the sheet S is transported to the branching transport unit 59, which branches the transport path of the sheet S. If image formation on the sheet S is complete, the sheet S is discharged by the discharge roller pair into the discharge tray 500 located outside the main body 1A of the device.

[0021] On the other hand, when forming an image on the back side of sheet S, sheet S is transferred to the double-sided transfer unit 502 via the reversal transfer unit 501. The reversal transfer unit 501 has a pair of reversal rollers that can rotate in both forward and reverse directions, and reverses the sheet by a switchback method that reverses the front and back sides of sheet S. That is, after retracting the leading edge of the sheet, the reversal transfer unit 501 reverses the front and back sides by reversing the transfer direction, and then transfers the sheet to the double-sided transfer unit 502. The double-sided transfer unit 502 then transfers sheet S again toward the registration unit 50 via the feed path 54b of sheet transfer unit 54. After the image is formed on the back side of sheet S, it is discharged to the discharge tray 500.

[0022] [Registration Unit Configuration] Next, with reference to Figure 2, the configuration of the registration unit 50 that constitutes the sheet transport device will be described. Figure 2 is an overhead view showing the registration unit. The registration unit 50 according to this embodiment is a unit that corrects the skew of the sheet using a side registration method.

[0023] More specifically, as shown in Figure 2, the registration unit 50 comprises, in order from upstream to downstream in the sheet transport direction, a transport section 50A, a skew correction section 50B, and a pair of registration rollers 7. The registration unit 50 also has a sheet position detection sensor 60 as a width position detection section that detects the position of the edge of the sheet in the width direction perpendicular to the sheet transport direction. Furthermore, the registration unit 50 has a slide mechanism 600 that moves one of the transport roller pairs of the transport section 50A in the width direction perpendicular to the sheet transport direction. The transport section 50A has at least one pair of transport rollers that transport the sheet in the sheet transport direction, and Figure 2 shows a configuration comprising transport roller pairs 34-1, 34-2, 34-3, and 34-4. In the following description, when it is not necessary to distinguish between transport roller pairs 34-1, 34-2, 34-3, and 34-4, they will be referred to as "transport roller pair 34".

[0024] In this embodiment, the registration unit 50 is provided with a slide mechanism 600 as a second moving drive unit on the transport roller pair 34-3, which is a second transport rotating body pair. Figure 2 illustrates a configuration in which the sheet position detection sensor 60 is positioned between the transport roller pair 34-2 and the transport roller pair 34-3. In addition to the configuration shown in Figure 2, the sheet position detection sensor 60 can also be positioned in a location where the transport unit 50A can detect the widthwise edge of the sheet being transported, for example, between the transport roller pair 34-1 and the transport roller pair 34-2.

[0025] The skew correction unit 50B comprises a pair of skew rollers 32-1, 32-2, and 32-3 as a first pair of skew rotating bodies, and a reference member 31 as a stopper. These pairs of skew rollers 2-1, 32-2, and 32-3 are arranged on a straight line generally facing the sheet conveying direction V. In other words, these pairs of skew rollers 2-1, 32-2, and 32-3 are arranged such that at least a portion of them overlap when viewed from the sheet conveying direction V. 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 "pair of skew rollers 32". The reference member 31 has a reference surface 31a extending in the sheet conveying direction and is positioned on one side in the width direction perpendicular to the sheet conveying direction. The reference surface 31a extends along the sheet conveying direction and becomes a stopper surface that can abut against one end of the sheet in the width direction.

[0026] A pre-registration sensor (hereinafter referred to as "pre-registration sensor") P is positioned near the transport roller pair 34-3 to detect the arrival of the leading edge of a sheet by detecting the presence or absence of the sheet. For example, a reflective photoelectric sensor having a light-emitting part and a light-receiving part can be used for the pre-registration sensor P. In this case, the light emitted by the light-emitting part is reflected by the sheet that has reached the detection position, and the timing of the sheet's passage is detected by the light-receiving part detecting the reflected light. As shown in Figure 2, in this embodiment, the pre-registration sensor P is positioned between the transport roller pair 34-3 and the transport roller pair 34-4 in the sheet transport direction.

[0027] The inclined roller pairs 32-1, 32-2, and 32-3 each rotate around an axis inclined with respect to the width direction. That is, the inclined roller pairs 32-1, 32-2, and 32-3 are arranged parallel to each other such that the tangential direction at the contact point with the sheet is inclined at an angle θ with respect to the sheet transport direction V. Therefore, as the inclined roller pairs 32-1, 32-2, and 32-3 rotate in contact with the sheet, they move the sheet so that it approaches the reference surface 31a of the reference member 31 in the width direction as it moves downstream in the sheet transport direction V. In addition, the sheet moves towards the reference surface 31a as it moves downstream in the sheet transport direction V due to the inclined roller pair 32.

[0028] Here, the sheet's skew correction by the skew correction unit 50B will be explained. The skew correction unit 50B corrects the sheet's skew using a so-called side registration method. Specifically, the skew correction unit 50B causes the side edge of the sheet, that is, the sheet's edge in the width direction, to abut against a reference member 31 having a reference surface 31a that extends along the sheet transport direction V. After the sheet abuts against the reference surface 31a, the sheet's skew is corrected by moving the side edge of the sheet along the reference surface 31a. The sheet transport direction V is the direction in which the sheet moves by the transport roller pair 34 of the transport unit 50A, or the direction in which the sheet moves toward the secondary transfer unit 1C by the registration roller pair 7.

[0029] Furthermore, in addition to the pre-registration sensor P, the diagonal correction unit 50B is also equipped with a pre-registration sensor (hereinafter referred to as "pre-registration sensor") Q, which acts as a 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 positioned downstream of the diagonal conveying roller pair 32 and upstream of the registration roller pair 7 with respect to the sheet conveying direction. Similar to the pre-registration sensor P, the pre-registration sensor Q can use a known sensor such as a reflective photoelectric sensor. The pre-registration sensor Q is a sensor for detecting when the sheet reaches the registration roller pair 7. Specifically, the pre-registration sensor Q detects the sheet and then detects that the sheet has reached the registration roller pair 7 after a predetermined delay time has elapsed. In other words, the pre-registration sensor Q's function is to detect when the sheet reaches the registration roller pair 7. Note that the pre-registration sensor Q may also be positioned downstream of the registration roller pair 7, in which case it will detect that the sheet had already reached the registration roller pair 7.

[0030] The registration roller pair 7, which serves as the first transport rotating body pair, can be moved by sliding it in the width direction perpendicular to the sheet transport direction while holding the sheet, using a slide mechanism 70, which serves as the first moving drive unit. The slide mechanism 70 can be the same mechanism as the slide mechanism 600 that moves the transport roller pair 34-3 in the width direction. The registration roller pair 7 also moves the sheet, whose side ends abut 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. This moves the sheet so that the center in the width direction of the sheet, which has been corrected for skew in the registration unit 50, becomes 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 formation area). Furthermore, 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 sheet so that its center becomes the transport center of the printer 1, and adjust it so that the center of the position in the main scanning direction of the toner image formed by the image formation process units PY~PK becomes the center in the width direction.

[0031] [Detailed configuration of the transport unit] The detailed configuration of the transport unit 50A will be explained in detail using Figures 3(a), 3(b), and 4. Figure 3(a) is a cross-sectional view showing a part of the transport unit in the clamped transport state in the registration unit. Figure 3(b) is a cross-sectional view showing a part of the transport unit in the non-clamped state in the registration unit. Figure 4 is a perspective view showing a part of the transport unit in the registration unit. Figures 3(a) and 3(b) show a portion of transport roller pair 34-1, which is one of the four transport roller pairs 34. Since transport roller pairs 34-2, 34-3, and 34-4 have the same configuration as transport roller pair 34-1, the following explanation will describe only the portion of transport roller pair 34-1, and the explanation of transport roller pairs 34-2, 34-3, and 34-4 will be omitted. In this embodiment, the printer 1 is shown as having four transport roller pairs 34 (see Figure 2) as an example, but the number of transport roller pairs is not limited to this.

[0032] As shown in Figures 3(a) and 3(b), in the transport section 50A, the transport roller pair 34-1 consists of a drive roller 13 to which driving force is input, and a driven roller 14 that rotates in accordance with the drive roller 13. The transport roller pair 34-1 can be switched between a gripping transport state (Figure 3(a)) in which the sheet is gripped and transported by the nip portion, and a non-gripping state (Figure 3(b)) in which the sheet is not gripped by the separated nip portions. Whether all transport roller pairs 34 can be switched between the gripping transport state and the non-gripping state can be determined according to the size of the sheet that the printer 1 can transport.

[0033] The conveying section 50A is provided with a cam mechanism 100 having an eccentric roller 103, which serves as a switching section capable of switching between a gripped conveying state and a non-grip state of the conveying roller pair 34-1. The eccentric roller 103 is rotationally driven by a register pre-pressure release motor Md (see Figure 12) via gears 105 and 106, causing an arm member 101 that contacts the cam surface on its outer circumference to swing. The arm member 101 is pivotably supported on a stay member 18 with respect to a pivot axis 102, contacting the eccentric roller 103 on one side of the pivot axis 102 and supporting the driven axis 20, which is the rotation axis of the driven roller 14, on the other side. Due to the swinging of the arm member 101, the driven rollers 14 each move in and out of the sheet conveying path formed by a guide member (not shown). Therefore, by controlling the rotation angle of the eccentric roller 103 via the register pre-pressure release motor Md, which is a stepping motor, the positional relationship between the driven roller 14 and the drive roller 13 can be switched. In other words, by controlling the rotation angle of the eccentric roller 103, it is possible to switch between a non-clamping state in which the driven rollers 14 are separated from the drive roller 13 and a clamping transport state in which the driven rollers 14 are pressed against the drive roller 13.

[0034] Furthermore, as shown in Figure 4, the drive roller 13 is a rubber roller attached to the drive roller shaft 301A and is connected to the drive source, the front-of-register drive motor Mp (see Figure 12), via the belt transmission mechanism 302. The front-of-register drive motor Mp is a stepping motor and is configured to allow changes in the timing of starting and stopping the drive and the drive speed of the drive roller 13 (peripheral speed of the drive roller 13).

[0035] [Detailed configuration of the skew correction unit] Next, the configuration of the skew correction unit 50B will be explained in detail using Figures 5(a), 5(b), 6(a), 6(b), 7(a), and 7(b). Figure 5(a) is an overhead view showing a part of the skew correction unit in the registration unit. Figure 5(b) is a cross-sectional view showing a part of the skew correction unit in the registration unit as viewed from the sheet transport direction. Figure 6(a) is a perspective view showing the skew roller pair and its pressurizing mechanism. Figure 6(b) is a side view showing a part of the skew roller pair and its pressurizing mechanism. Figure 7(a) is a side view showing the skew roller pair in the clamping transport state. Figure 7(b) is a side view showing the skew roller pair in the non-clamping state.

[0036] As shown in Figure 5(a), the oblique correction unit 50B is equipped with oblique feed roller pairs 32-1, 32-2, and 32-3, each of which has drive rollers 320-1, 320-2, and 330-3. These drive rollers 320-1, 320-2, and 330-3 have their rotation axes fixed in an inclined state according to the angle θ by universal joints 321, 321, and 321. When there is no need to distinguish between these drive rollers 320-1, 320-2, and 330-3, they are referred to as drive roller 320-n.

[0037] Each drive roller 320-n is connected to the drive source, the inclined roller drive motor Ms-n (see Figure 12), via a transmission mechanism including a universal joint 321, a belt 323, and a pulley. The inclined roller drive motor Ms-n is a stepping motor, and it can control the drive speed and the timing of starting and stopping the drive of the drive rollers 320-n. In other words, the drive rollers 320-1, 320-2, and 330-3 of the inclined roller pairs 32-1, 32-2, and 32-3 are rotationally driven by the inclined roller drive motors Ms-1, Ms-2, and Ms-3, respectively, which act as the first drive units.

[0038] As shown in Figure 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 opposing surface 31b facing the upper surface of the sheet S, and a lower opposing surface 31c facing the lower surface of the sheet S. The reference member 31 is made of die-cast aluminum, and it is preferable to use a reference surface 31a that has been precisely machined to achieve high precision, and further coated with a fluororesin such as PTFE (polytetrafluoroethylene) by electroless nickel plating. In this way, a reference surface 31a with high flatness and high slipperiness (low frictional resistance to the sheet) can be obtained, and the accuracy of correcting the skew of the sheet S can be improved.

[0039] As shown in Figures 6(a), 6(b), 7(a), and 7(b), the oblique feed roller pair 32-n arranged in the oblique correction unit 50B has a drive roller 320-n and a driven roller 331-n facing it. The oblique correction unit 50B also has a pressurizing mechanism 33-n that moves the driven roller 331-n. The pressurizing mechanism 33-n includes a pressurizing mechanism 33-1 that moves the driven roller 331-1 of the oblique feed roller pair 32-1. Furthermore, the pressurizing mechanism 33-n includes a pressurizing mechanism 33-2 that moves the driven roller 331-2 of the oblique feed roller pair 32-2, and a pressurizing mechanism 33-3 that moves the driven roller 331-3 of the oblique feed roller pair 32-3. In this embodiment, the pressurizing mechanism 33-1 constitutes the first switching mechanism, the pressurizing mechanism 33-2 constitutes the third switching mechanism, and the pressurizing mechanism 33-3 constitutes the second switching mechanism. When it is not necessary to distinguish between these pressurizing mechanisms 33-1, 33-2, and 33-3, they are referred to as pressurizing mechanism 33-n. Pressurizing mechanism 33-n can switch between a clamping transport state in which the driven roller 331-n is pressed against the drive roller 320-n to form a nip and the sheet is clamped and transported, and a non-clamping state in which the driven roller 331-n is separated from the drive roller 320-n.

[0040] Here, n is a number assigned to the inclined roller pair 32, driven roller 331, and pressurizing mechanism 33 in order from upstream in the sheet conveying direction V. For example, inclined roller pair 32-1 refers to the inclined roller pair 32 located at the uppermost position (n=1). In other words, in the inclination correction unit 50B of this embodiment, multiple sets of driven rollers 331-n and pressurizing mechanism 33-n are arranged in such a state that the inclined roller pair 32-n shown in Figures 6 and 7 is replaced by one of the inclined roller pairs 32-1, 32-2, or 32-3.

[0041] The pressurizing mechanism 33-n includes an arm member 332, a link member 333, a pressurizing gear 334, a pressurizing spring 335, and a driven roller pressurizing motor Mk-n (see Figure 12). The driven roller 331-n is rotatably supported by the arm member 332 around a driven axis and is movable toward or toward the oblique feed roller pair 32-n by the swing of the arm member 332. In this embodiment, the driven roller 331-n rotates along the sheet conveying direction about an axis extending in the width direction, but it may also be configured to be positioned on an axis parallel to the corresponding oblique feed roller pair 32-n. The arm member 332 is connected to the pressurizing gear 334 via the pressurizing spring 335 and the link member 333. The pressurizing gear 334 is connected to the output shaft of the driven roller pressurizing motor Mk-n, which is the drive source.

[0042] As shown in Figure 7(a), in the clamping transport 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 pivot axis 332-1. As a result, the driven roller 331-n is pressed against the drive roller 320-n. On the other hand, as shown in Figure 7(b), in the non-clamping state, the pressure gear 334 rotates clockwise in the figure, pressing against the link member 333, and the link member 333 swings the arm member 332 clockwise. As a result, the driven roller 331-n separates from the drive roller 320-n.

[0043] The driven roller pressurizing motor Mk-n is a stepping motor, and by controlling the rotation angle of the pressurizing gear 334, the amount of extension of the pressurizing spring 335 in the pressurized state can be changed. In other words, the pressurizing mechanism 33-n according to this embodiment can switch between a clamped transport state and a non-clamped state, and change the pressurizing force in the clamped transport state.

[0044] [Configuration of the seat position detection sensor] Next, with reference to Figure 8, the configuration of the sheet position detection sensor 60 as the width position detection unit in this embodiment will be described. Figure 8 is a perspective view showing the sheet position detection sensor in the transport unit of the registration unit. The sheet position detection sensor 60 is equipped with an optical element such as a CIS (Contact Image Sensor) and is positioned in the same direction as the reference member 31, and at an off-center position in the width direction, relative to the center of the sheet in the width direction with respect to the sheet transport direction V. This is to detect the position of the edge of the sheet that abuts against the reference member 31.

[0045] [Drive and sliding configuration of the transport roller pair] Next, the drive configuration of the transport roller pair 34-3 and the configuration of the sliding mechanism 600 for sliding the transport roller pair 34-3 in this embodiment will be described using Figures 9, 10, 11(a), and 11(b). Figure 9 is a perspective view showing the drive mechanism of the transport roller pair in the transport section of the registration unit. Figure 10 is a perspective view showing the sliding mechanism of the transport roller pair in the transport section of the registration unit. Figure 11(a) is a perspective view showing the pressure release mechanism of the transport roller pair in the transport section of the registration unit. Figure 11(b) is a cross-sectional view showing the pressure release mechanism of the transport roller pair in the transport section of the registration unit.

[0046] The conveying roller pair 34-3 is broadly configured to be rotationally driven by the roller drive mechanism 800 and to be movable in the width direction perpendicular to the sheet conveying direction by the sliding mechanism 600 while gripping the sheet. Furthermore, the conveying roller pair 34-3 is configured to be switchable between a gripping conveying state in which the sheet is gripped between the nip of the roller pair constituting the conveying roller pair 34-3 and a non-gripping state in which the roller pair is separated, by a pressure release mechanism 700 which serves as a second switching mechanism.

[0047] More specifically, as shown in Figure 10, the conveyor roller pair 34-3 consists of an upper roller 401 and a lower roller 402 (see Figure 11(a)). The lower roller 402 is rotatably supported by the frame 201 (see Figure 11(a)), and the upper roller 401 is rotatably supported by the pressure arm 405 (see Figure 10). The pressure arm 405 is rotatably fixed by a shaft 201a formed on the frame 201 (see Figure 10). The upper roller 401 is pressurized against the lower roller 402 by a tension spring 407. In addition, a roller gear 412 that transmits drive from the roller drive mechanism 800 to the lower roller 402 is fixed to one end of the lower roller 402 (see Figure 9).

[0048] The roller drive mechanism 800 that rotates the transport roller pair 34-3, as shown in Figure 9, is composed of a slide roller drive motor 801 (see Figure 12) as a third drive unit, 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. In addition, 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 as to maintain meshing with the roller gear 412. The drive gear 802 is rotatably fixed to the fixed shaft 201b of the frame 201, and the drive gear 803 is rotatably fixed to the fixed shaft 201c. In this embodiment, a stepping motor is used as the slide roller drive motor 801. With this configuration, the drive of the slide roller drive motor 801 is transmitted to the roller gear 412, causing the conveyor roller pair 34-3 to rotate.

[0049] The slide mechanism 600, which acts as a second moving drive unit for moving the transport roller pair 34-3 in the width direction, has a slide motor 601 (see Figure 12) that is fixed to a motor base 602 and screwed to a motor support plate 603, as shown in Figure 10. 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 Figure 9, a pulley shaft 607 is rotatably fixed to the pulley base 605, and a pulley shaft 608 is rotatably fixed to the pulley base 606. Pulleys 609 and 610 are fixed to the pulley shaft 607, and a pulley 611 is fixed to the pulley shaft 608. In addition, a pulley 612 is fixed to the tip of the output shaft of the slide motor 601. A timing belt 613 is stretched between pulley 609 and pulley 612, and a timing belt 614 is stretched between pulley 610 and pulley 611 (see Figure 10).

[0050] As shown in Figure 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 lower roller 402 of the conveyor roller pair 34-4. When the upper roller 401 and lower roller 402 of the conveyor roller pair 34-4 are in the home position, the sensor flag 416 is detected by a sensor 615 provided on the pulley support plate 604. The holder 415 is also fixed to the timing belt 614 by a stopper 616 and screws (not shown). With this configuration, the timing belt 614 rotates when driven by the slide motor 601, and the lower roller 402 of the conveyor roller pair 34-3 reciprocates in the width direction perpendicular to the sheet conveying direction as the timing belt 614 rotates. Furthermore, the upper roller 401 of the conveyor roller pair 34-3 is engaged with the lower roller 402 by an engaging member (not shown), and together with the lower roller 402, it reciprocates in the width direction perpendicular to the sheet conveying direction. In this embodiment, the slide motor 601 is driven to move the conveyor roller pair 34-3 in the width direction based on the detection result of the position of the sheet edge in the width direction detected by the CIS 60.

[0051] The pressure release mechanism 700, which causes the upper roller 401 and lower roller 402 of the conveyor roller pair 34-3 to come into contact with and separate from each other, has a pressure release shaft 701 positioned on the frame 201, as shown in Figure 11(a). The pressure release mechanism 700 also includes cams 702 and 703 (see Figure 11(b)) fixed to the pressure release shaft 701. Deep groove ball bearings 702a and 703a are press-fitted into the cams 702 and 703 at positions eccentric from their respective centers of rotation, as shown in Figure 11(b). Furthermore, as shown in Figure 11(a), a gear 702b is formed on the cam 702, and the drive of the pressure release motor 704 (see Figure 12) is transmitted via the cam 702, causing the pressure release shaft 701 to rotate.

[0052] Furthermore, the deep groove ball bearing 702a is positioned so as to be able to contact the pressure arm 405, and when the pressure release shaft 701 is rotated once, the deep groove ball bearing 702a causes the pressure arm 405 to oscillate against the biasing force of the spring 407. By oscillating 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 each. In addition, a pressure arm (not shown) is also provided on the side of the pressure release shaft 701 where the deep groove ball bearing 703a is provided in the axial direction. Furthermore, a sensor flag 703b is formed on the cam 703 (see Figure 11(b)). The sensor flag 703b is detected by a sensor 706 fixed to a sensor support plate 705 fixed to the frame 201, which determines the phase of the pressure release shaft 701, and the rotation of the pressure release motor 704 is controlled according to the phase of the pressure release shaft 701. Furthermore, the phases of the cams 702 and 703 are determined such that the sensor flag 703b is shielded from the sensor 706 when the upper roller 401 and lower roller 402 of the transport roller pair 34-3 are in contact.

[0053] [Drive and sliding configuration of the transport roller pair] Next, the drive configuration of the registration roller pair 7 and the configuration of the sliding mechanism for sliding the registration roller pair 7 in this embodiment will be described. The registration roller pair 7 in this embodiment has the same configuration as the transport roller pair 34-3 described above. That is, the roller drive mechanism of the registration roller pair 7 has the same configuration as the roller drive mechanism 800 of the transport roller pair 34-3, and the registration roller pair 7 is rotationally driven by the slide roller drive motor 1801 as the second drive unit. Furthermore, the sliding mechanism of the registration roller pair 7 has the same configuration as the sliding mechanism 600 of the transport roller pair 34-3, and the registration roller pair 7 is moved in the width direction by the slide motor 1601 as the first moving drive unit. Furthermore, the pressure release mechanism for bringing the registration roller pair 7 into contact with and separating from it has the same configuration as the pressure release mechanism 700 of the transport roller pair 34-3, and the registration roller pair 7 is brought into contact with and separated from it (switching between a clamped transport state and a non-clamped state) by the pressure release motor 1704. The structure of the other registration roller pair 7 is the same as that of the transport roller pair 34-3 described above, so its explanation will be omitted.

[0054] [Printer control system configuration] Next, the configuration of the control system of printer 1 will be described with reference to Figure 12. Figure 12 is a block diagram showing the control system of the printer according to the first embodiment.

[0055] As shown in Figure 12, the registration unit 50 in printer 1 is controlled by the control unit 9. The control unit 9 comprises a CPU 9a as an arithmetic unit, RAM 9b and ROM 9c as storage units, and an interface (I / O) 9d for external devices or networks.

[0056] The CPU 9a performs control based on information input via the user interface, the operation unit 400, 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 the AD conversion units 901 and 902, respectively. The detection signal from the seat position detection sensor 60 is also input to the CPU 9a via the AD conversion unit 920. The CPU 9a loads and executes a program stored in the ROM 9c, etc. The CPU 9a drives and controls the motor group (Ms, Mp, Md, Mk-n, 601, 701, 801, 1601, 1701, 1801), which are actuators of the registration unit 50, via drivers 903, 904, 905, 606-n, 907, 908, 909, 910, 911, and 912.

[0057] [Overview of the Registration Unit's Operation] (Operation of the transport unit) Next, an overview of the operation of the registration unit 50 will be described. First, the pre-skew correction shift operation of the transport section 50A, which is performed before skew correction in the registration unit 50, will be explained using Figures 13(a) and 13(b). Figure 13(a) is a top view showing the state in which a sheet has been transported to the transport section of the registration unit according to the first embodiment. Figure 13(b) is a cross-sectional view of the state shown in Figure 13(a). Figure 13(c) is a top view showing the state in which the sheet has been shifted by the transport roller pair 34-3 from the state shown in Figures 13(a) and 13(b). Figure 13(d) is a cross-sectional view of the state shown in Figure 13(c).

[0058] As shown in Figures 13(a) and 13(b), when a sheet S being transported in the sheet transport direction V reaches the sheet position detection sensor 60 in the registration unit 50, the sheet position detection sensor 60 detects the position of the edge of the sheet S (side edge position). The CPU 9a (see Figure 12) calculates the amount of deviation from the detected side edge position of the sheet S relative to the zero point position which is the reference position of the sheet position detection sensor 60, and calculates the amount of shift in the width direction by the transport roller pair 34-3 (shift amount of shift operation before diagonal correction).

[0059] Next, as shown in Figures 13(c) and 13(d), when the sheet S reaches the pair of transport rollers 34-3 in a gripping transport state, the CPU 9a separates the transport roller pair 34-1 and 34-2 (releasing them into a non-gripping state). The CPU 9a shifts the transport roller pair 34-3 in the direction of arrow W2a by the shift amount calculated above, that is, shifts the sheet S so that its side edge aligns with the zero point position, which is the reference position of the sheet position detection sensor 60. This zero point position is, in short, a set position where the widthwise edge of the sheet is separated from the reference member 31 in the other direction in the widthwise direction. As a result, the pre-skew correction shift operation is completed, and when the sheet S is corrected for skew by the skew correction unit 50B, the widthwise distance between the reference member 31 and the edge of the sheet S is stabilized. In other words, the sliding distance between the reference member 31 and the sheet S during skew correction is stabilized, and the transport speed of the sheet S is stabilized.

[0060] (Operation of the skew correction unit) Next, the skew correction operation of the skew correction unit 50B in the registration unit 50 will be explained using Figures 14(a) and 14(b). Figure 14(a) is a top view showing the state in which skew correction has been performed in the skew correction unit of the registration unit according to the first embodiment. Figure 14(b) is a cross-sectional view of the state shown in Figure 14(a).

[0061] After the pre-diagonal correction shift operation of the transport unit 50A is completed, that is, after the sheet S is moved in the width direction by the transport roller pair 34-3, the diagonal correction operation of the diagonal correction unit 50B begins. Then, as shown in Figures 14(a) and 14(b), in the registration unit 50, the sheet S is transported in a direction inclined with respect to the sheet transport direction V shown in the direction of arrow K in the figure by the diagonal transport roller pair 32-1 to 32-3, which are in a clamping transport state (pressurized state). As a result, the side edge of the sheet S abuts against the reference surface 31a of the reference member 31. In the registration unit 50, when diagonal correction is performed, the diagonal transport roller pair 32-1 to 32-3 is in a clamping transport state, and the transport roller pair 34-1 to 34-4 is in a non-clamping state. Therefore, in the registration unit 50, after the transport roller pair 34-1 to 34-4 separates, the oblique correction is performed by the oblique transport roller pair 32-1 to 32-3, thereby enabling oblique correction without interference from the transport roller pair 34-1 to 34-4.

[0062] (Operation of the registration roller pair) Next, the sheet alignment operation in the width direction of the registration roller pair 7 in the registration unit 50 will be explained using Figures 15(a) and 15(b). Figure 15(a) is a top view showing the state in which the shift has been performed by the registration roller pair of the registration unit according to the first embodiment. Figure 15(b) is a cross-sectional view of the state shown in (a).

[0063] As shown in Figures 15(a) and 15(b), the registration roller pair 7 shifts the sheet S in the direction of arrow W1a in the figures so that the widthwise position of the sheet S matches the widthwise position of the image transferred by the secondary transfer unit 1C (see Figure 1). In other words, the registration roller pair 7 performs a shift operation in the direction of arrow W1a while transporting the sheet S in the sheet transport direction V so that it matches the widthwise position of the image formed by the image forming engine 513 (see Figure 1). As a result, the registration unit 50 can form an image on the sheet S with the widthwise position of the skew-corrected sheet S adjusted to match the widthwise position of the image formed by the image forming engine 513 and transferred by the secondary transfer unit 1C.

[0064] In this embodiment, the widthwise position of the sheet S is shifted by the registration roller pair 7 after the diagonal feed roller pair 32-1 to 32-3 are set to a non-clamping state (separated). Therefore, the widthwise position can be shifted without interference from the diagonal feed roller pair 32-1 to 32-3.

[0065] <Control of the registration unit in print jobs> Next, the control of the registration unit 50 when a command to print one or more sheets is sent to the control unit 9 from an external computer or operation unit 400, etc., and the print job is executed will be explained in detail with reference to Figures 16 and 17. Figure 16 is a flowchart showing the control of the transport section of the registration unit when a normal print job is executed according to the first embodiment. Figure 17 is a flowchart showing the control of the skew correction section and the registration roller pair of the registration unit when a normal print job is executed according to the first embodiment.

[0066] (Operation of the transport section of the registration unit) The control unit 9 first obtains sheet information (hereinafter referred to as "sheet information") from information included in the print job input from an external computer or operation unit 400 (or information previously set for the paper feed cassette 51) (S1). In this process, the control unit 9 obtains 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 whether it is plain paper for office use, coated paper, cardboard, thin paper, etc. The control unit 9 also obtains the number of sheets to be fed into the registration unit 50 in the started print job from the number of sheets information included in the sheet information, and sets it as the initial value of the stored value, which is the value stored in the paper feed counter.

[0067] Next, the control unit 9 determines the clamping pressure of the diagonal feed roller pairs 32-1 to 32-3 (S2). In this process, the control unit 9 obtains table data from the ROM 9c that associates the clamping pressure with each pre-set sheet type, based on the sheet information obtained in step S1 and the determined operating mode, and determines the clamping pressure of the diagonal feed roller pairs 32-1 to 32-3. The magnitude of the clamping pressure for each diagonal feed roller pair 32-1 to 32-3 is determined according to the sheet type and basis weight. In other words, for example, the larger the basis weight and the more slippery the surface, the larger the clamping pressure for the diagonal feed roller pairs 32-1 to 32-3 is set.

[0068] Next, the control unit 9 starts the image formation process using the image forming engine 513 (S3). The control unit 9 also starts counting the paper feed start delay based on the timing at which the process in step S3 begins (S4). The paper feed start delay is the difference between the time elapsed from when the image is formed on the intermediate transfer belt 506 until it is transported to the secondary transfer unit 1C, and the time elapsed 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 has started to be formed in the process of step S3, and starts counting.

[0069] When the count for the paper feed start delay reaches the set value, the control unit 9 starts feeding sheets from the paper feed cassette 51 (S5). At the first timing when the sheet has been transported to and reached the sheet position detection sensor 60, the control unit 9 causes the sheet position detection sensor 60 to detect the side edge position of the sheet (S6). The arrival of the sheet at the sheet position detection sensor 60 can be detected by the signal output of the sheet position detection sensor 60.

[0070] Next, the control unit 9 calculates the amount of sheet shift (S7). In this process, the control unit 9 calculates the amount of displacement from the detection result of the sheet position detection sensor 60 to the 0 point position set as the reference position of the sheet position detection sensor 60. Then, the control unit 9 determines the amount of shift to shift the transport roller pair 34-3 in the width direction perpendicular to the sheet transport direction, according to the calculated amount of displacement.

[0071] After executing the process in step S8, the control unit 9 determines whether the pre-registration sensor P has been turned ON (S8). In this process, the control unit 9 determines from the signal of the pre-registration sensor P whether the sheet whose side edge position has been detected by the sheet position detection sensor 60 has reached the pre-registration sensor P.

[0072] In step S8, if it is determined that the pre-registration sensor P is not ON (No. in S8), 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 time it should have been transported. The control unit 9 displays on the operation unit 400 that a paper jam has occurred (S22 in Figure 17) and terminates this control.

[0073] On the other hand, if the control unit 9 determines that the pre-registration sensor P has turned ON (Yes in S8), the control unit 9 starts counting the release delay for the transport roller pair 34-1 and 34-2 (S9). By the time the process in step S9 is executed, the registration unit 50 has reached the pre-registration sensor P, which is located downstream of the transport roller pair 34-3 in the transport direction, and the shift operation before the diagonal correction by the transport roller pair 34-3 is possible. Therefore, in the process of step S9, the control unit 9 sets a release delay value, which is the time that elapses from the gripped transport state to the non-gripped state of the transport roller pair 34-1 and 34-2, and starts counting.

[0074] When the count for the release delay in step S9 reaches the set value, the control unit 9 separates the drive roller 13 and driven roller 14 of the transport roller pair 34-1 and 34-2 to a non-clamping state (S10). As a result, in the registration unit 50, the sheet is clamped by the transport roller pair 34-3, but not by the transport roller pair 34-1 and 34-2.

[0075] Then, the control unit 9 shifts the transport roller pair 34-3 in the width direction by a shift amount corresponding to the detection result of the sheet position detection sensor 60 (S11). In this process, the control unit 9 shifts the transport roller pair 34-3 by the shift amount calculated in step S7, 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.

[0076] In this embodiment, when the sheet is shifted in the width direction by the conveyor roller pair 34-3 in step S11, it is described as shifting the sheet while it is being conveyed. However, in order to stabilize the sheet shift, it is also possible to stop the sheet conveyance, perform the shift with the conveyor roller pair 34-3, and then resume the sheet conveyance.

[0077] (Operation of the skew correction unit and registration roller pair) Next, the process proceeds to step S12 and beyond, as shown in Figure 17, and moves on to the control of the skew correction unit and the registration roller pair. After executing the process in step S11, as shown in Figure 17, the control unit 9 starts counting the clamping delay and acceleration delay of the skew conveying roller pair 32-1 to 32-3 (S12). At the time when the process in step S12 is executed, the shift of the sheet before skew correction is completed in the registration unit 50. Also, in the registration unit 50, the skew conveying roller pair 32-1 to 32-3 is in a non-clamping state in order to avoid interference between the skew conveying roller pair 32-1 to 32-3 and the shift by the conveying roller pair 34-3. For this reason, in the process in step S12, the control unit 9 sets the values ​​of the clamping delay and acceleration delay, which are the time elapsed from the non-clamping state to the clamped conveying state of the skew conveying roller pair 32-1 to 32-3, and starts counting.

[0078] Next, at the time the clamping delay count 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 inclined roller pair 32-1 to 32-3 together (S13). Also, at the time the acceleration delay count is completed, the control unit 9 starts the rotation of the drive rollers 320-1 to 320-3 of the inclined roller pair 32-1 to 32-3, that is, accelerates the rotational speed of the inclined roller pair 32-1 to 32-3 (S13). In this embodiment, it is explained that in step S12 the clamping delay and the acceleration delay are set to approximately the same value. However, in order to prevent the transport speed from decreasing when the sheet S is clamped by the inclined roller pair 32-1 to 32-3, the rotation of the inclined roller pair 32-1 to 32-3 may be started in advance. Furthermore, the rotational speed of the inclined feed roller pair 32-1 to 32-3 should preferably be such that the speed in the sheet conveying direction V does not decrease, although this will be explained in more detail later.

[0079] Next, the control unit 9 starts counting the release delay, which is the time it takes for the transport roller pair 34-3 and 34-4 to move from a gripped transport state to a non-gripped state (S14). When the release delay count is completed, the lower roller 402 and upper roller 401 of the transport roller pair 34-3 and 34-4 are separated, and the diagonal transport is performed by the diagonal transport roller pair 32-1 to 32-3 to correct the diagonal movement (S15).

[0080] In other words, as a result of the execution of steps S12 to S15, the registration unit 50 is in a state where the sheet is not gripped by the transport roller pair 34-1 to 34-4, and the sheet can be gripped and transported by the oblique transport roller pair 32-1 to 32-3. The registration unit 50 corrects the oblique angle of the sheet as it is transported by gripping and transporting the sheet with the oblique transport roller pair 32-1 to 32-3, while keeping the side edge of the sheet in contact with the reference surface 31a of the reference member 31.

[0081] Next, the control unit 9 determines whether the pre-register sensor Q has been turned ON (S16). In this process, the control unit 9 determines from the signal of the pre-register sensor Q whether the sheet, which has been corrected for skew by the skew roller pairs 32-1 to 32-3, has reached the pre-register sensor Q.

[0082] In step S16, if it is determined that the pre-register sensor Q is not ON (S16 No.), the control unit 9 determines that a paper jam has occurred because the sheet has not been transported to the pre-register sensor Q at the time it should have been transported. In this case, the control unit 9 displays on the operation unit 400 that a paper jam has occurred (S22) and terminates the control processing related to registration correction and skew correction.

[0083] On the other hand, if the control unit 9 determines that the pre-register sensor Q is ON (Yes in S16), it starts counting the release delay and deceleration delay of the diagonal conveying roller pair 32-1 to 32-3 (S17). At the time the processing in step S17 is executed, the leading edge of the sheet has reached the pre-register sensor Q, which is located downstream in the conveying direction from the diagonal conveying roller pair 32-1 to 32-3, in the registration unit 50. Therefore, the sheet can be conveyed and shifted by the registration roller pair 7. For this reason, in the processing in step S17, the control unit 9 sets the release delay and deceleration delay values, which are the time elapsed from the gripped conveying state to the non-gripping state of the diagonal conveying roller pair 32-1 to 32-3, and starts counting.

[0084] Next, at the time the release delay count 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 inclined roller pair 32-1 to 32-3 (S18). As a result, in the registration unit 50, the sheet is held by the registration roller pair 7 and not held by the inclined roller pair 32-1 to 32-3. Also, at the time the deceleration delay count is completed, the control unit 9 decelerates the rotational speed of the drive rollers 320-1 to 320-3 of the inclined roller pair 32-1 to 32-3 (S18). In this embodiment, it is explained that in step S17, the gripping delay and the acceleration delay are set to approximately the same value. However, when the sheet S is gripped by the registration roller pair 7 and transport begins, it is acceptable to start separating the inclined roller pair 32-1 to 32-3 in advance so that the transport speed does not decrease when the sheet is gripped by the inclined roller pair 32-1 to 32-3. Furthermore, the reduction of the rotational speed of the inclined roller pair 32-1 to 32-3 will be discussed in more detail later.

[0085] Next, the control unit 9 shifts the widthwise position of the sheet after skew correction using the registration roller pair 7 so that the widthwise position of the sheet matches the widthwise position of the image transferred in the secondary transfer unit 1C (S19). 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.

[0086] Next, the control unit 9 subtracts 1 from the number of sheets counted by the paper feed counter (S20). In this process, the control unit 9 subtracts "1", the value corresponding to one sheet, from the stored value of the paper feed counter, because the series of skew correction operations for one sheet, namely the shift before skew correction, the skew correction, and the shift after skew correction, has been completed.

[0087] The control unit 9 then determines whether the stored value of the paper feed counter is 0 (S21). If it determines that the stored value of the paper feed counter is not 0 (No in S21), the control unit 9 returns to step S3 to perform a series of skew correction operations on the next sheet to be transported in the current print job. On the other hand, if it determines that the stored value of the paper feed counter is 0 (Yes in S21), the control unit 9 determines that the current print job is complete and terminates this control.

[0088] [Problems arising from the relative speed difference between the inclined roller pair and the registration roller pair] Next, problems arising from the relative speed difference between the inclined roller pairs 32-1 to 32-3 and the registration roller pair 7 will be explained using Figures 18 and 19. Figure 18 is a diagram showing the relationship between the conveying direction speed and the abutment direction speed between the inclined roller pairs and the registration roller pair. Figure 19(a) is a diagram showing the relationship between the conveying direction speed and the abutment direction speed between the inclined roller pairs, the registration roller pair and the sheet when the sheet is being conveyed by the inclined roller pairs. Figure 19(b) is a diagram showing the relationship between the conveying direction speed and the abutment direction speed between the inclined roller pairs, the registration roller pair and the sheet when the sheet is being conveyed by the registration roller pair.

[0089] As shown in Figure 18, the inclined roller pair 32-1 to 32-3 have an angle of inclination with respect to the sheet conveying direction V, and therefore have a conveying speed Vh1 and abutting speed Vs1 when rotating. The registration roller pair 7, on the other hand, is not inclined with respect to the sheet conveying direction V, and therefore has no abutting speed when rotating, and only a conveying speed Vh2. These speeds are the same as long as the rollers are rotating, whether they are in a clamped conveying state or a non-clamped state where the roller pairs are separated. It is preferable that the sheet S be conveyed at as close to the same speed as possible whether it is conveyed by the inclined roller pair 32-1 to 32-3 or by the registration roller pair 7 in the sheet conveying direction V. Therefore, the conveying speed Vh1 of the inclined roller pair 32-1 to 32-3 and the conveying speed Vh2 of the registration roller pair 7 are the same (Vh1 = Vh2).

[0090] As shown in Figures 19(a) and 19(b), the speed of the sheet S is defined as the conveying speed Vh3 and the abutting speed Vs3. First, in Figure 19(a), when the inclined roller pair 32-1 to 32-3 grips the sheet S and conveys it, the conveying speed Vh3 of the sheet S is equal to the conveying speed Vh1 of the inclined roller pair 32-1 to 32-3. In this case, the abutting speed Vs3 of the sheet S is equal to the abutting speed Vs1 of the inclined roller pair 32-1 to 32-3. In other words, in this state, there is no relative speed difference between the sheet S and the inclined roller pair 32-1 to 32-3.

[0091] Subsequently, as shown in Figure 19(b), a release delay is set based on the timing of detection of the leading edge of the sheet S by the pre-register sensor Q, and when the oblique feed roller pair 32-1 to 32-3 separate, the sheet S is transported by the registration roller pair 7. In this state, the transport direction velocity Vh3 of the sheet S becomes the transport direction velocity Vh2 of the registration roller pair 7. Also, as mentioned above, the transport direction velocity Vh1 of the oblique feed roller pair 32-1 to 32-3 and the transport direction velocity Vh2 of the registration roller pair 7 are the same, so the transport direction velocity Vh3 of the sheet S is also the same (Vh3=Vh2=Vh1).

[0092] However, in this state, the sheet S does not move in the direction of contact with the reference member 31, and the contact direction speed Vs3 is 0. As a result, a relative speed difference (Vs1-Vs3) is created between the contact direction speed Vs1 of the sheet S and the inclined feed roller pair 32-1~32-3. In other words, this relative speed difference causes slippage between the sheet S and the inclined feed roller pair 32-1~32-3, and sliding marks are created, especially in cardboard where the contact pressure (contact pressure) with the inclined feed roller pair 32-1~32-3 is large. Furthermore, in the case of synthetic paper with poor transferability, even if there are few sliding marks from the inclined feed roller pair 32-1~32-3, transfer failures or, in the case of double-sided printing, scraping of the image formed on the first surface of the sheet S may occur.

[0093] [Control of the rotational speed of the oblique roller pair in the first embodiment] To address the above-mentioned problems, in this first embodiment, the control unit 9 sets a release delay and a deceleration delay based on the timing of detection of the leading edge of the sheet S by the pre-register sensor Q (see S17). Then, when the count of the release delay and deceleration delay is completed, the control unit 9 separates (or immediately after) the diagonal feed roller pair 32-1 to 32-3 and decelerates the diagonal feed roller pair 32-1 to 32-3 (see S18). In short, the control unit 9 controls the rotational speed of the diagonal feed roller pair 32-1 to 32-3 to a first speed V11 when the sheet is diagonally fed to the reference member 31 by the diagonal feed roller pair 32-1 to 32-3. Then, when the sheet is transported by the registration roller pair 7 with the diagonal feed roller pair 32-1 to 32-3 in a non-clamping state, the rotational speed of the diagonal feed roller pair 32-1 to 32-3 is controlled to a second speed V12 which is slower than the first speed V11 (see S18). This makes it possible to reduce the relative speed difference (Vs1-Vs3) in the abutting direction between the sheet S and the oblique feed roller pair 32-1 to 32-3 while the sheet S is being conveyed by the registration roller pair 7. Consequently, it is possible to reduce the sliding marks on the sheet S caused by the oblique feed roller pair 32-1 to 32-3 when the sheet is not being held, and also reduce transfer defects and image scraping.

[0094] By the way, if the rotation of the inclined roller pair 32-1 to 32-3 is stopped, the conveying direction speed Vh1 of the inclined roller pair 32-1 to 32-3 becomes 0, which may cause a large relative speed difference (Vh3-Vh1) between it and the conveying direction speed Vh3 of the sheet S. Therefore, in this first embodiment, the control unit 9 sets the rotation speed of the inclined roller pair 32-1 to 32-3 to a range that satisfies 0 ≤ (Vh3-Vh1) ≤ Vs1. In particular, it is preferable to set it to a value that has a good balance between the relative speed difference in the conveying direction and the relative speed difference in the abutment direction. This makes it possible to reduce the relative speed difference (Vs1-Vs3) in the abutment direction between the sheet S and the inclined roller pair 32-1 to 32-3, while also reducing the relative speed difference (Vh3-Vh1) in the conveying direction. Furthermore, the rotational speeds of the inclined feed roller pairs 32-1 to 32-3 may be set separately depending on the type of sheet (e.g., cardboard or synthetic paper), as long as they are within the above range. In other words, it is preferable to set the rotational speeds of the inclined feed roller pairs 32-1 to 32-3 to a rotational speed that provides a high reduction effect against sliding marks and image scraping, depending on the type of sheet.

[0095] In the above explanation, we described the case where the sheet S is conveyed by the registration roller pair 7 and the inclined conveying roller pair 32-1 to 32-3 are rotating freely in a non-clamping state. However, the same applies when the sheet S is conveyed by the conveying roller pair 34-3 to 34-4. That is, even when the sheet S is conveyed by the conveying roller pair 34-3 to 34-4 to the inclined conveying roller pair 32-1 to 32-3 in a non-clamping state, if the rotation of the inclined conveying roller pair 32-1 to 32-3 is stopped, a relative speed difference in the conveying direction will occur (Vh3 - Vh1). Therefore, it is conceivable to rotate the inclined conveying roller pair 32-1 to 32-3 so that the conveying direction speed Vh1 of the inclined conveying roller pair 32-1 to 32-3 is the same as the conveying direction speed Vh3 of the sheet S. However, the sheet S does not move in the direction of abutment when it hits the reference member 31, and the abutment direction speed Vs3 is 0. Therefore, there is a risk that a relative speed difference (Vs1-Vs3) may occur between the sheet S and the abutting direction speed Vs1 of the diagonal feed roller pair 32-1~32-3.

[0096] Therefore, in this case as well, the control unit 9 can control the inclined roller pair 32-1 to 32-3 to a third speed, which is slower than the first speed, when transporting the sheet by the transport roller pair 34-3 with the inclined roller pair 32-1 to 32-3 in a non-clamping state. However, if the rotational speed of the inclined roller pair 32-1 to 32-3 is set so that the transport speed Vh1 is equal to the transport speed Vh3 of the sheet S, there is a risk that the relative speed difference (Vs1-Vs3) in the abutment direction will become large. Therefore, even in this case, the control unit 9 sets the rotational speed of the inclined roller pair 32-1 to 32-3 to a range that satisfies 0 ≤ (Vh3-Vh1) ≤ Vs1. In particular, it is preferable to set it to a value that provides a good balance between the relative speed difference in the transport direction and the relative speed difference in the abutment direction. This makes it possible to reduce the relative speed difference (Vs1-Vs3) in the direction of contact between the sheet S and the diagonal conveying roller pair 32-1 to 32-3, while also reducing the relative speed difference (Vh3-Vh1) in the conveying direction. Note that this third speed may be the same as the second speed described above.

[0097] In the above explanation, it was assumed that the rotational speed (conveying speed Vh2) of the registration roller pair 7 was constant. However, depending on when the sheet S reaches the registration roller pair 7, it is necessary to adjust the sheet speed to match the timing at which the toner image transferred to the intermediate transfer belt 506 reaches the secondary transfer section 1C. For this reason, the rotational speed of the registration roller pair 7 may be changed in accordance with the timing at which the toner image reaches the secondary transfer section 1C. In this case, the conveying speed Vh3 of the sheet S is also changed, so it is preferable that the rotational speeds of the oblique feed roller pair 32-1 to 32-3 are also changed according to the speed change ratio.

[0098] <Second Embodiment> Next, a second embodiment, which is a modified version of the first embodiment described above, will be explained using Figures 20 to 23. Figure 20 is an overhead view showing the registration unit according to the second embodiment. Figure 21 is an overhead view showing the state in which the sheet is being skewed by the skew feed roller pair 32-4 in the skew correction section of the registration unit according to the second embodiment. Figure 22 is a flowchart showing the control of the skew correction section and the registration roller pair of the registration unit during the execution of a normal print job according to the second embodiment. Figure 23(a) is a diagram showing the relationship between the transport direction speed and the abutment direction speed between the skew feed roller pair 32-4, the skew feed roller pair 32-1, and the sheet when the sheet is being skewed by the skew feed roller pair 32-4 in the second embodiment. Figure 23(b) is a diagram showing the relationship between the transport direction speed and the abutment direction speed between the skew feed roller pair 32-4, the skew feed roller pair 32-1, and the sheet when the sheet is being skewed by the skew feed roller pair 32-1 in the second embodiment. In this description of the second embodiment, the same reference numerals are used for parts similar to those in the first embodiment, and their descriptions are omitted.

[0099] [Configuration of the registration unit according to the second embodiment] The registration unit 50 constituting the sheet transport device according to this second embodiment is equipped with a pair of oblique feed rollers 32-4 compared to the first embodiment. The pair of oblique feed rollers 32-4 is positioned further away (separated) from the reference member 31 in the width direction than the pairs of oblique feed rollers 32-1 to 32-3. In other words, in the printer 1, the pairs of oblique feed rollers 32-1 to 32-3 are positioned towards the front, and the pair of oblique feed rollers 32-4 is positioned towards the back. Furthermore, the pair of oblique feed rollers 32-4 is positioned such that the tangential direction of the contact portion with the sheet is inclined at an angle θ2 with respect to the sheet transport direction V. This angle θ2 is larger than the angle θ1 of the tangential direction of the contact portion of the oblique feed rollers 32-1 to 32-3 with respect to the sheet transport direction V. In other words, the angle of the inclined roller pair 32-4 in the inclined direction relative to the reference member 31 is larger than that of the inclined roller pairs 32-1 to 32-3. That is, the inclined roller pair 32-4 is positioned to direct the sheet towards the reference member 31 more than the inclined roller pairs 32-1 to 32-3. For this reason, the inclined roller pair 32-4 is configured to have a greater abutment speed than the inclined roller pairs 32-1 to 32-3 at the same rotational speed. By installing the inclined roller pair 32-4 with such a large angle, it becomes possible to assist in correcting the skew of sheets with high transport resistance, which would be difficult to correct using only the inclined roller pairs 32-1 to 32-3. The other configurations of the inclined roller pair 32-4 are the same as those of the inclined roller pairs 32-1 to 32-3. In other words, the drive roller 320-4 (320-n), the driven roller 331-4 (331-n), the pressurizing mechanism 33-4 (33-n) as the third switching mechanism, and the inclined roller drive motor Ms-4 (Ms-n) as the fourth drive unit are the same as those of the inclined roller pairs 32-1 to 32-3. Therefore, a description of these structures will be omitted.

[0100] [Operation of Registration Unit 50] The operation of the registration unit 50 according to the second embodiment, which is equipped with the pair of oblique rollers 32-4, will now be described. As shown in Figure 21, before the sheet reaches the oblique correction unit 50B, the pair of oblique rollers 32-4 is put into a gripping and conveying state by a pressure mechanism (not shown). When the pair of oblique rollers 32-4 grips the sheet that has been conveyed from the conveying unit 50A, the sheet is conveyed in the direction of arrow L. In this way, first the sheet S is obliquely conveyed towards the reference member 31 using only the pair of oblique rollers 32-4 with a large angle. Then the sheet S is gripped by the pair of oblique rollers 32-1 to 32-3, and the pair of oblique rollers 32-4 is separated and put into a non-gripping state. After that, similar to the first embodiment, the sheet S is abutted against the reference member 31 by the pair of oblique rollers 32-1 to 32-3, the obliqueness is corrected, and it is conveyed to the registration roller pair 7.

[0101] (Control of the skew correction unit and registration roller pair) Next, the details of the control of the skew correction unit and the registration roller pair in the second embodiment will be explained with reference to Figure 22. Note that the control shown in Figure 22 is performed following the control of the operation of the transport unit 50A of the registration unit 50 (see Figure 16) as described in the first embodiment, but the operation of the transport unit 50A is the same, so its explanation will be omitted.

[0102] After executing the process in step S11 in Figure 16 above, as shown in Figure 22, the control unit 9 starts counting the acceleration delay of the diagonal conveying roller pair 32-1 to 32-3, and starts counting the clamping delay and acceleration delay of the diagonal conveying roller pair 32-4 (S12-1). At the time when the process in step S12-1 is executed, the shift of the sheet before diagonal correction is completed in the registration unit 50. Also, in the registration unit 50, the diagonal conveying roller pair 32-1 to 32-4 is in a non-clamping state in order to avoid interference between the diagonal conveying roller pair 32-1 to 32-4 and the shift by the transport roller pair 34-3. For this reason, in the process in step S12-1, the control unit 9 sets the values ​​for the clamping delay and acceleration delay, which are the time elapsed from the non-clamping state to the clamped transport state of the diagonal conveying roller pair 32-4, and starts counting. Furthermore, if the rotation of the inclined roller pairs 32-1 to 32-3 stops when the inclined roller pair 32-4 grips the sheet S and begins conveying it, there is a risk that the relative rotational difference between the inclined roller pair 32-4 and the inclined roller pairs 32-1 to 32-3 will become large. Therefore, in the processing of step S12-1, the control unit 9 sets the count value for the acceleration delay of the inclined roller pairs 32-1 to 32-3 and starts counting. Details regarding the rotational speed of the inclined roller pairs 32-1 to 32-3 at this time will be described later.

[0103] Next, at the timing when the acceleration delay count for the inclined roller pair 32-1 to 32-3 is completed, the rotation of the drive rollers 320-1 to 320-3 of the inclined roller pair 32-1 to 32-3 is started, accelerating the rotational speed of the inclined roller pair 32-1 to 32-3 (S13-1). Also, at the timing when the clamping delay count for the inclined roller pair 32-4 is completed, the drive roller 320-4 and the driven roller 331-4 of the inclined roller pair 32-4 are pressed together (S13-1). Also, at the timing when the acceleration delay count for the inclined roller pair 32-4 is completed, the rotation of the drive roller 320-4 of the inclined roller pair 32-4 is started, that is, the rotational speed of the inclined roller pair 32-4 is accelerated (S13-1). In this embodiment, it is explained that in step S12-1, the clamping delay and the acceleration delay of the inclined roller pair 32-4 are set to approximately the same value. However, to prevent a decrease in the conveying speed when the sheet S is gripped by the pair of inclined rollers 32-4, the rotation of the pair of inclined rollers 32-4 may be started in advance. Furthermore, although this will be explained in more detail later, it is preferable that the rotational speed of the pair of inclined rollers 32-4 does not decrease in the sheet conveying direction V.

[0104] Next, the control unit 9 starts counting the release delay, which is the time it takes for the transport roller pair 34-3 and 34-4 to move from a gripped transport state to a non-gripped state (S14). When the release delay count is completed, the lower roller 402 and upper roller 401 of the transport roller pair 34-3 and 34-4 are separated, and the diagonal transport is performed by the diagonal transport roller pair 32-1 to 32-4 to correct the diagonal movement (S15).

[0105] In other words, as a result of the execution of steps S12 to S15, the registration unit 50 is in a state where the sheet is not gripped by the transport roller pair 34-1 to 34-4, and the sheet can be gripped and transported by the oblique transport roller pair 32-1 to 32-4. In the registration unit 50, the sheet is gripped and transported by the oblique transport roller pair 32-4, and then the sheet is gripped and transported by the oblique transport roller pair 32-1 to 32-3. This corrects the oblique angle of the sheet as it is transported, with its side edges in contact with the reference surface 31a of the reference member 31.

[0106] Next, the control unit 9 starts counting the gripping delay and deceleration delay for the inclined roller pair 32-1 to 32-3, and starts counting the release delay and deceleration delay for the inclined roller pair 32-4 (S23). At the time the process in step S23 is executed, the registration unit 50 has started inclined feeding of the sheet by the inclined roller pair 32-4, and the inclined roller pair 32-1 to 32-3 is in a non-gripping state. For this reason, in the process in step S23, the control unit 9 sets the values ​​for the release delay and deceleration delay, which are the time elapsed from the gripped transport state to the non-gripping state of the inclined roller pair 32-4, and starts counting. Also, if the rotation of the inclined roller pair 32-4 stops when the inclined roller pair 32-1 to 32-3 grips the sheet S and starts transporting it, there is a risk that the relative rotation difference between the inclined roller pair 32-4 and the inclined roller pair 32-1 to 32-3 will become large. Therefore, in step S23, the control unit 9 sets the count value for the deceleration delay of the inclined roller pair 32-4 and starts counting. Furthermore, in step S13-1, since the rotational speed of the inclined roller pair 32-1 to 32-3 is accelerated before gripping the sheet S, the control unit 9 sets the count value for the deceleration delay of the inclined roller pair 32-1 to 32-3 and starts counting. Details regarding the rotational speeds of the inclined roller pair 32-1 to 32-3 and the inclined roller pair 32-4 will be described later.

[0107] Next, when the countdown for the clamping delay of the inclined roller pair 32-1 to 32-3 is completed, the drive rollers 320-1 to 320-3 and the driven rollers 331-1 to 331-3 of the inclined roller pair 32-1 to 32-3 are pressed together (S24). Also, when the countdown for the deceleration delay of the inclined roller pair 32-1 to 32-3 is completed, the rotational speed of the drive rollers 320-1 to 320-3 of the inclined roller pair 32-1 to 32-3 is reduced (S24). Furthermore, when the countdown for the release delay of the inclined roller pair 32-4 is completed, the lower roller 402 and upper roller 401 of the inclined roller pair 32-4 are separated (S24). Also, when the countdown for the deceleration delay of the inclined roller pair 32-4 is completed, the rotational speed of the drive roller 320-4 of the inclined roller pair 32-4 is reduced (S24). In this embodiment, it is explained that in step S23, the clamping delay and deceleration delay of the inclined roller pair 32-1 to 32-3, and the release delay and deceleration delay of the inclined roller pair 32-4 are set to approximately the same value. However, to prevent the transport speed from increasing when the sheet S is clamped by the inclined roller pair 32-1 to 32-3, the deceleration of the rotational speed of the inclined roller pair 32-1 to 32-3 may be started before clamping. Also, to prevent the transport speed from decreasing before the sheet S is clamped by the inclined roller pair 32-1 to 32-3, the separation of the inclined roller pair 32-4 may be started before deceleration.

[0108] The control of steps S16 to S22 thereafter, namely the correction of skewness by the skew movement of the skew roller pair 32-1 to 32-3 and the shift operation of the registration roller pair 7, is the same as in the first embodiment described above (see Figure 17), so its explanation will be omitted.

[0109] [Problems arising from the relative speed difference between the inclined roller pair 32-1~32-3 and the inclined roller pair 32-4] Next, we will explain the problems arising from the relative speed difference between the inclined roller pairs 32-1 to 32-3 and the inclined roller pair 32-4, using Figure 23.

[0110] As shown in Figures 23(a) and 23(b), the inclined roller pair 32-4 has an angle inclined with respect to the sheet conveying direction V, and therefore has a conveying speed Vh4 and abutting speed Vs4 when rotating. The notation for the rotational speeds of the inclined roller pairs 32-1 to 32-3 and the registration roller pair 7 is the same as in the first embodiment.

[0111] As shown in Figure 23(a), when the sheet S is transported to the diagonal correction unit 50B, the diagonal conveying roller pair 32-4 is in a gripping transport state, and the diagonal conveying roller pairs 32-1 to 32-3 are in a non-gripping state. In this case, the conveying speed Vh3 of the sheet S is controlled to be constant, that is, the conveying speed Vh4 of the diagonal conveying roller pair 32-4 is the same as the conveying speed Vh3. Also, since the sheet S is transported by the diagonal conveying roller pair 32-4, the abutting speed Vs3 of the sheet S is the same as the abutting speed Vs4 of the diagonal conveying roller pair 32-4.

[0112] Here, for example, if the rotation of the inclined roller pair 32-1 to 32-3 is stopped, a large relative speed difference will occur between the conveying direction speed Vh4 and the abutting direction speed Vs4 of the inclined roller pair 32-4. Therefore, it is conceivable to set the rotational speed of the inclined roller pair 32-1 to 32-3 so that the conveying direction speed Vh1 of the inclined roller pair 32-1 to 32-3 and the conveying direction speed Vh4 of the inclined roller pair 32-4 are the same (Vh3=Vh4=Vh1). However, the angle θ2 of the inclined roller pair 32-4 with respect to the sheet conveying direction V is a larger angle than the angle θ1 of the inclined roller pair 32-1 with respect to the sheet conveying direction V. Therefore, the abutment speed Vs4 of the diagonal feed roller pair 32-4 is greater than the abutment speed Vs1 of the diagonal feed roller pair 32-1 to 32-3 (Vs3 = Vs4 > Vs1), resulting in a relative speed difference (Vs4 - Vs1) in the abutment direction. Consequently, similar to the problems of the first embodiment described above, sliding marks may occur on cardboard, and transfer failures or image scraping may occur on synthetic paper with poor transferability.

[0113] Also, as shown in Fig. 23(b), the sheet S transitions from the state of being conveyed by the diagonal feed roller pair 32-4 to the state of being conveyed by the diagonal feed roller pairs 32-1 to 32-3. Then, the diagonal feed roller pair 32-4 is in a non-clamping state, and the diagonal feed roller pairs 32-1 to 32-3 are in a clamping conveyance state. In this case, the conveyance direction speed Vh3 of the sheet S is controlled to be constant, that is, the conveyance direction speed Vh1 of the diagonal feed roller pairs 32-1 to 32-3 is the same as the conveyance direction speed Vh3. Also, since the sheet S is conveyed by the diagonal feed roller pairs 32-1 to 32-3, the abutting direction speed Vs3 of the sheet S is also the same as the abutting direction speed Vs1 of the diagonal feed roller pairs 32-1 to 32-3.

[0114] Here, for example, if the rotation of the diagonal feed roller pair 32-4 stops, a large relative speed difference will occur between the conveyance direction speed Vh1 and the abutting direction speed Vs1 of the diagonal feed roller pairs 32-1 to 32-3. Therefore, it is conceivable to set the rotation speed of the diagonal feed roller pair 32-4 so that the conveyance direction speed Vh4 of the diagonal feed roller pair 32-4 is the same as the conveyance direction speed Vh1 of the diagonal feed roller pairs 32-1 to 32-3 (Vh3 = Vh1 = Vh4). However, the angle θ2 of the diagonal feed roller pair 32-4 with respect to the sheet conveyance direction V is larger than the angle θ1 of the diagonal feed roller pair 32-1 with respect to the sheet conveyance direction V. For this reason, the abutting direction speed Vs1 of the diagonal feed roller pairs 32-1 to 32-3 becomes smaller than the abutting direction speed Vs4 of the diagonal feed roller pair 32-4 (Vs3 = Vs1 < Vs4), and a relative speed difference (Vs1 - Vs4) occurs in the abutting direction. Therefore, similar to the problem of the first embodiment, there is a risk that sliding marks will occur in cardboard or transfer failure and image scraping will occur in synthetic paper with strict transferability.

[0115] [Control of Rotation Speed of Diagonal Feed Roller Pair in Second Embodiment] In response to the above-mentioned problems, the second embodiment provides the following control. First, the control unit 9 sets an acceleration delay for the diagonal roller pair 32-1 to 32-3 when transporting the sheet S with the diagonal roller pair 32-4, based on the timing of detection of the leading edge of the sheet S by the pre-resistance sensor P (see S12-1). Then, when the control unit 9 presses the diagonal roller pair 32-4 against the sheet (or immediately after) the acceleration delay count is completed, it accelerates the diagonal roller pair 32-1 to 32-3 to a rotational speed faster than the diagonal roller pair 32-4 (see S13-1). In short, the control unit 9 controls the rotational speed of the diagonal roller pair 32-1 to 32-3 to a first speed V11 when diagonally transporting the sheet to the reference member 31 with the diagonal roller pair 32-1 to 32-3. Then, when the sheet S is obliquely fed to the oblique roller pair 32-1 to 32-3 by the oblique roller pair 32-4 with the oblique roller pair 32-1 to 32-3 in a non-clamping state, the rotational speed of the oblique roller pair 32-1 to 32-3 is controlled to a fourth speed V14 which is faster than the first speed V11 (see S13-1). As a result, while the sheet S is being conveyed by the oblique roller pair 32-4, the relative speed difference (Vs4-Vs1) in the abutment direction between the oblique roller pair 32-1 to 32-3 and the sheet S can be reduced. Therefore, sliding marks on the sheet S caused by the non-clamping oblique roller pair 32-1 to 32-3 can be reduced, and transfer defects and image scraping can also be reduced.

[0116] Subsequently, the inclined roller pair 32-1 to 32-3 are clamped together while the inclined roller pair 32-4 is separated, and the system transitions to a state where the sheet S is conveyed by the inclined roller pair 32-1 to 32-3. In this case, since the inclined roller pair 32-1 to 32-3 was rotating at a faster speed (fourth speed V14) than the inclined roller pair 32-4, a deceleration delay is set for the inclined roller pair 32-1 to 32-3 (see S23). Then, when the inclined roller pair 32-1 to 32-3 are pressed together as the deceleration delay count is completed, the inclined roller pair 32-1 to 32-3 are decelerated to the first speed V11 so that the inclined roller pair 32-1 to 32-3 has a conveying speed Vh1 (see S24). This controls the conveying speed Vh3 of the sheet S to remain constant.

[0117] Furthermore, when the control unit 9 transports the sheet S using the inclined roller pair 32-1 to 32-3, it sets a deceleration delay for the inclined roller pair 32-4 (see S23). Then, when the control unit 9 presses the inclined roller pair 32-1 to 32-3 together (or immediately afterward) in response to the completion of the deceleration delay count, it decelerates the inclined roller pair 32-4 so that its rotational speed is slower than that of the inclined roller pair 32-1 to 32-3 (see S24). In short, the control unit 9 controls the rotational speed of the inclined roller pair 32-4 to the fifth speed V15 when the sheet is inclined to the inclined roller pair 32-1 to 32-3 by the inclined roller pair 32-4. Then, when the sheet is obliquely fed to the reference member 31 by the oblique feed roller pair 32-1 to 32-3 with the oblique feed roller pair 32-4 in a non-clamping state, the rotational speed of the oblique feed roller pair 32-4 is controlled to a sixth speed V16, which is slower than the fifth speed V15 (see S24). Note that this fifth speed may be the same as the first speed mentioned above. This makes it possible to reduce the relative speed difference (Vs1-Vs4) in the abutment direction between the oblique feed roller pair 32-4 and the sheet S while the sheet S is being conveyed by the oblique feed roller pair 32-1 to 32-3. Consequently, sliding marks on the sheet S caused by the non-clamping oblique feed roller pair 32-4 can be reduced, and transfer defects and image scraping can also be reduced.

[0118] Subsequently, the sheet S is transported by separating the oblique feed roller pair 32-1 to 3 while gripping the registration roller pair 7. However, since the control in this case is the same as that described in the first embodiment above, the explanation will be omitted.

[0119] Furthermore, the configuration, operation, and effects of the second embodiment are the same as those of the first embodiment described above, so their explanation will be omitted.

[0120] <Possibility of other embodiments> In the first embodiment described above, the registration unit 50 is equipped with three pairs of oblique rollers 32-1 to 32-3, and in the second embodiment, the registration unit 50 is equipped with four pairs of oblique rollers 32-1 to 32-4. However, the number of oblique roller pairs is not limited to these configurations and can be any number.

[0121] Furthermore, in the first and second embodiments, a registration unit 50 equipped with four transport roller pairs 34-1 to 34-4 was described. However, the number of transport roller pairs is not limited to this, and there may be any number of them. Also, in the first and second embodiments, a transport roller pair 34-3 that is slidable in the width direction was described, but the number of transport roller pairs is not limited to this, and other transport roller pairs may be slidable, and in particular, transport roller pair 34-4 may be slidable in the width direction.

[0122] Furthermore, while the first and second embodiments described a configuration in which the widthwise position of the reference member 31 is fixed, the system is not limited to this, and the reference member 31 may be configured to move in the widthwise direction. For example, instead of adjusting the widthwise position of the sheet with the transport roller pair 34-3, the reference member 31 may be moved in the widthwise direction according to the detection result of the sheet position detection sensor 60. In other words, by moving the reference member 31 in the widthwise direction, the relative distance between the sheet and the reference member 31 can be kept constant, thereby keeping the distance over which the sheet is transported by the diagonal transport roller pair constant.

[0123] Furthermore, in the first and second embodiments, the registration unit 50 was described as performing skew correction upstream of the secondary transfer unit 1C. However, the invention is not limited to this, and skew correction may be performed upstream of processing units such as sheet cutting, binding, hole punching, and folding, or the image reading unit.

[0124] Furthermore, although this embodiment describes printer 1 as an electrophotographic full-color laser beam printer, it is not limited to this. For example, the configuration and method of the image forming unit that forms the image on the sheet can be anything, such as an inkjet printer.

[0125] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of Symbols]

[0126] 1…Printer (image forming apparatus) / 7…Registration roller pair (first conveying rotating body pair) / 9…Control unit / 31…Reference member (buttock part) / 32-1~32-3…Oblique feed roller pair (first oblique feed rotating body pair) / 32-4…Oblique feed roller pair (second oblique feed rotating body pair) / 33-1~33-3…Pressurization mechanism (first switching mechanism) / 33-4…Pressurization mechanism (third switching mechanism) / 34-3…Conveyor roller pair (second conveying rotating body pair) / 50…Registration unit (sheet conveying device) / 60…Sheet position detection sensor (width position detection unit) / 502…Double-sided conveying unit (re-conveying unit) / 513…Image Image forming engine (image forming unit) / 600... Slide mechanism (second movement drive unit) / 700... Pressure release mechanism (second switching mechanism) / 801... Slide roller drive motor (third drive unit) / 1601... Slide motor (first movement drive unit) / 1801... Slide roller drive motor (second drive unit) / Ms-1~Ms-3... Inclined roller drive motor (first drive unit) / Ms-4... Inclined roller drive motor (fourth drive unit) / Q... Receiving roller front sensor (arrival detection unit) / S... Sheet / V11... First speed / V14... Fourth speed / V12... Second speed / V15... Fifth speed / V16... Sixth speed

Claims

1. A stopper portion is positioned on one side of the width direction perpendicular to the conveying direction of the sheet being conveyed, A pair of first oblique feeding rotating bodies that obliquely feed the sheet toward the abutment portion, A first switching mechanism switches the first pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A first drive unit that rotates the first pair of obliquely rotating bodies, A pair of first conveying rotating bodies that grip and convey the sheet that is abutted against the aforementioned abutment portion, A second drive unit that rotates the first pair of transporting rotating bodies, The system comprises the first switching mechanism, the first drive unit, and a control unit that controls the second drive unit, The control unit, When the sheet is obliquely fed to the abutment portion by the first oblique feeding rotating body pair, the rotational speed of the first oblique feeding rotating body pair is controlled to a first speed. When the first pair of obliquely rotating bodies is in the non-clamping state and the sheet is being transported by the first pair of conveying rotating bodies, the rotational speed of the first pair of obliquely rotating bodies is controlled to a second speed that is slower than the first speed. A sheet conveying device characterized by the following features.

2. A first moving drive unit moves the first pair of conveying rotating bodies in a width direction perpendicular to the sheet conveying direction, The system includes a reach detection unit that detects when a sheet reaches the first pair of conveying rotating bodies, The control unit, In response to the arrival detection unit detecting that the sheet has reached the first transport rotating body pair, the first movement drive unit moves the first transport rotating body pair so that the sheet is moved in the width direction so that its position aligns with the position in the width direction of the image formed on the sheet by the image forming unit. The sheet conveying device according to feature 1.

3. When the control unit detects that the sheet has reached the first conveying rotating body pair, it switches the first oblique conveying rotating body pair to the non-clamping state and moves the first conveying rotating body pair with the first moving drive unit. The sheet conveying device according to feature 2.

4. A second pair of conveying rotating bodies is positioned upstream of the first pair of oblique conveying rotating bodies in the sheet conveying direction, and the second pair of conveying rotating bodies grips and conveys the sheet, The system comprises a third drive unit that rotates the aforementioned second pair of transporting rotating bodies, The control unit controls the rotation speed of the first oblique rotating body pair to a third speed that is slower than the first speed when the first oblique rotating body pair is in a non-clamping state and the second conveying rotating body pair is conveying the sheet. The sheet conveying device according to feature 1.

5. The second pair of conveying rotating bodies is equipped with a second switching mechanism that switches between a clamping conveying state in which the sheet is clamped and conveyed, and a non-clamping state in which the sheet is released from clamping. When the control unit is obliquely feeding the sheet to the abutment portion with the first oblique rotating body pair, the control unit switches the second conveying rotating body pair to the non-clamping state using the second switching mechanism. The sheet conveying device according to feature 4.

6. A second moving drive unit moves the second pair of conveying rotating bodies in a width direction perpendicular to the sheet conveying direction, The system includes a width position detection unit for detecting the position of the end of the sheet held by the second pair of conveying rotating bodies in the width direction, The control unit, The width position detection unit detects the position of the end of the sheet in the width direction, The sheet is moved in the width direction by moving the second pair of conveying rotating bodies, which are holding the sheet, with the second moving drive unit so that the position of the end portion is set to be at a position away from the abutment portion in the other direction in the width direction. After the sheet has been moved in the width direction by the second pair of conveying rotating bodies, the first pair of oblique conveying rotating bodies is set to the clamping conveying state and the sheet is obliquely conveyed to the abutment portion by the first pair of oblique conveying rotating bodies. The sheet conveying device according to feature 4.

7. The angle of the oblique feeding direction with respect to the abutment portion is greater than that of the first oblique feeding rotating body pair, and the second oblique feeding rotating body pair feeds the sheet obliquely toward the first oblique feeding rotating body pair, A third switching mechanism switches the second pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. The system comprises a fourth drive unit that rotates the second pair of obliquely rotating bodies, The control unit controls the rotation speed of the first oblique rotating body pair to a fourth speed that is faster than the first speed when the second oblique rotating body pair obliquely feeds the sheet to the first oblique rotating body pair while the first oblique rotating body pair is in a non-clamping state. The sheet conveying device according to feature 1.

8. The angle of the oblique feeding direction with respect to the abutment portion is greater than that of the first oblique feeding rotating body pair, and the second oblique feeding rotating body pair feeds the sheet obliquely toward the first oblique feeding rotating body pair, A second switching mechanism switches the second pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. The system comprises a fourth drive unit that rotates the second pair of obliquely rotating bodies, The control unit, When the first pair of obliquely rotating bodies is in a non-clamping state and the sheet is obliquely fed to the first pair of obliquely rotating bodies by the second pair of obliquely rotating bodies, the rotation speed of the second pair of obliquely rotating bodies is controlled to a fifth speed. When the second pair of obliquely rotating bodies is in a non-clamping state and the sheet is obliquely fed to the abutment portion by the first pair of obliquely rotating bodies, the rotation speed of the second pair of obliquely rotating bodies is controlled to a sixth speed that is slower than the fifth speed. The sheet conveying device according to feature 1.

9. A second pair of rotating transport bodies that grips and transports the sheet, A stopper portion is positioned on one side of the width direction perpendicular to the conveying direction of the sheet being conveyed, A first oblique conveying rotating body pair is positioned downstream of the second conveying rotating body pair in the sheet conveying direction and obliquely conveys the sheet toward the abutment portion, A first switching mechanism switches the first pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A first drive unit that rotates the first pair of obliquely rotating bodies, A third drive unit that rotates the aforementioned second pair of transporting rotating bodies, The system comprises the first switching mechanism, the first drive unit, and a control unit that controls the third drive unit, The control unit, When the sheet is obliquely fed to the abutment portion by the first oblique feeding rotating body pair, the rotational speed of the first oblique feeding rotating body pair is controlled to a first speed. When the first pair of obliquely rotating bodies is in a non-clamping state and the sheet is being transported by the second pair of transporting rotating bodies, the rotational speed of the first pair of obliquely rotating bodies is controlled to a third speed that is slower than the first speed. A sheet conveying device characterized by the following features.

10. A stopper portion is positioned on one side of the width direction perpendicular to the conveying direction of the sheet being conveyed, A pair of first oblique feeding rotating bodies that obliquely feed the sheet toward the abutment portion, The angle of the oblique feeding direction with respect to the abutment portion is greater than that of the first oblique feeding rotating body pair, and the second oblique feeding rotating body pair feeds the sheet obliquely toward the first oblique feeding rotating body pair, A first switching mechanism switches the first pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A third switching mechanism switches the second pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A first drive unit that rotates the first pair of obliquely rotating bodies, A fourth drive unit that rotates the second pair of obliquely rotating bodies, The system comprises a control unit that controls the first switching mechanism, the third switching mechanism, the first drive unit, and the fourth drive unit, The control unit, When the second pair of obliquely rotating bodies is in a non-clamping state and the sheet is obliquely fed to the abutment portion by the first pair of obliquely rotating bodies, the rotation speed of the first pair of obliquely rotating bodies is controlled to a first speed. When the first pair of obliquely moving rotating bodies is in a non-clamping state and the sheet is obliquely moved to the first pair of obliquely moving rotating bodies by the second pair of obliquely moving rotating bodies, the rotation speed of the first pair of obliquely moving rotating bodies is controlled to a fourth speed that is faster than the first speed. A sheet conveying device characterized by the following features.

11. A stopper portion is positioned on one side of the width direction perpendicular to the conveying direction of the sheet being conveyed, A pair of first oblique feeding rotating bodies that obliquely feed the sheet toward the abutment portion, The angle of the oblique feeding direction with respect to the abutment portion is greater than that of the first oblique feeding rotating body pair, and the second oblique feeding rotating body pair feeds the sheet obliquely toward the first oblique feeding rotating body pair, A first switching mechanism switches the first pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A second switching mechanism switches the second pair of obliquely rotating bodies between a clamping transport state in which the sheet is clamped and transported, and a non-clamping state in which the sheet is released from clamping. A first drive unit that rotates the first pair of obliquely rotating bodies, A fourth drive unit that rotates the second pair of obliquely rotating bodies, The system comprises a control unit that controls the first switching mechanism, the second switching mechanism, the first drive unit, and the fourth drive unit, The control unit, When the first pair of obliquely rotating bodies is in a non-clamping state and the sheet is obliquely fed to the first pair of obliquely rotating bodies by the second pair of obliquely rotating bodies, the rotation speed of the second pair of obliquely rotating bodies is controlled to a fifth speed. When the second pair of obliquely rotating bodies is in a non-clamping state and the sheet is obliquely fed to the abutment portion by the first pair of obliquely rotating bodies, the rotation speed of the second pair of obliquely rotating bodies is controlled to a sixth speed that is slower than the fifth speed. A sheet conveying device characterized by the following features.

12. A sheet conveying device according to any one of claims 1 to 11, The system includes an image forming unit positioned downstream of the sheet conveying device in the sheet conveying direction, which forms an image on the sheet. An image forming apparatus characterized by the following:

13. The system includes a re-transport unit that re-transports the sheet, on which an image has been formed on the first surface by the image forming unit, to the sheet transport device. The image forming apparatus according to feature 12.

Images