Image formation apparatus

Abstract

To provide an image formation apparatus capable of acquiring a high quality product.SOLUTION: An image formation apparatus includes: an image formation part for forming an image on a sheet; a first movement section which is provided upstream of the image formation part in the sheet conveyance direction and moves a sheet in a wide direction orthogonal to the sheet conveyance direction with the sheet sandwiched to move the sheet in the width direction; and a re-conveyance part which inverts the front and rear of a sheet with an image on a first face by the image formation part to convey the sheet to the image formation part again. The re-conveyance part includes a second movement part which moves the sheet in the width direction with the sheet sandwiched to move the sheet in the width direction.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus for forming an image on a sheet. [Background technology]

[0002] Generally, in an image forming apparatus such as a copy machine, a sheet may shift laterally in the width direction of the sheet while being conveyed. If an image is formed on the sheet in a state where the sheet is shifted laterally, the image is printed shifted from the center of the sheet, and the quality of the sheet is poor. For this reason, a shift mechanism is known that detects the position of the edge of the sheet in the width direction and corrects the lateral shift (positional misalignment) of the sheet before forming an image on the sheet.

[0003] Conventionally, an image forming device has been proposed that detects the position of the edge of the first page in the width direction of the sheet, and corrects the image forming position of the third page relative to the photoconductor based on the amount of deviation of the edge of the first page from a reference position (see Patent Document 1). This image forming device aims to improve image quality and productivity of the image forming device by reducing the amount of sheet shift in order to correct the image forming position in advance based on the amount of deviation of the sheet two pages before. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-143643 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the image forming apparatus described in Patent Document 1 shifts the sheet in the width direction only by the registration rollers arranged before the transfer roller where the image is transferred to the sheet. Therefore, if the amount of shift of the sheet by the registration rollers is large, the sheet may be skewed when shifting in the width direction, or the amount of shift may vary greatly. This causes the image formed on the sheet to be misaligned, resulting in a low-quality product.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of producing high-quality finished products. [Means for solving the problem]

[0007] The present invention is an image forming apparatus comprising: an image forming unit that forms an image on a sheet; a skew correction unit having a first registration roller pair that is provided upstream of the image forming unit in a sheet conveying direction and that corrects skew of the sheet by abutting a leading edge of the sheet against the first registration roller pair; and a first moving unit that moves the sheet in a width direction of the sheet perpendicular to the conveying direction while the sheet is sandwiched between the first registration roller pair; an inversion unit that inverts a leading edge and a trailing edge of the sheet on a first surface of which an image has been formed by the image forming unit; a re-conveying unit that re-conveys the sheet inverted by the inversion unit toward the skew correction unit; and a control unit, The image forming apparatus includes a pair of reversing rollers that rotate in a second direction opposite to the first direction to reverse the sheet, and a second moving unit that moves the sheet in the width direction while the sheet is clamped by the pair of reversing rollers, thereby moving the sheet in the width direction, wherein the re-conveying unit has a second registration roller pair that corrects skew of the sheet by abutting the leading edge of the sheet, and the control unit controls the sheet so that, when an image is formed on a second side of the sheet opposite the first side, the position of the sheet in the width direction is corrected by the second moving unit, and after the skew of the sheet has been corrected, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

[0008] The present invention also provides an image forming apparatus, comprising: an image forming unit that forms an image on a sheet; a skew correction unit that has a first registration roller pair that is provided upstream of the image forming unit in a sheet transport direction and corrects skew of the sheet by abutting a leading edge of the sheet; and a first moving unit that moves the sheet in a width direction of the sheet perpendicular to the transport direction while the sheet is sandwiched between the first registration roller pair; an inversion unit that inverts a leading edge and a trailing edge of the sheet on a first surface of which an image is formed by the image forming unit; a re-conveying unit that re-conveys the sheet inverted by the inversion unit toward the skew correction unit; and a control unit. The re-conveying unit has a second registration roller pair that corrects sheet skew by abutting the leading edge of the sheet, and a second moving unit that moves the sheet in the width direction by moving the sheet in the width direction while the sheet is clamped by the second registration roller pair, and the control unit controls the sheet so that when an image is formed on a second side of the sheet opposite the first side, the position of the sheet in the width direction is corrected by the second moving unit, and after the skew of the sheet is corrected, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit. Effect of the Invention

[0009] According to the present invention, it is possible to provide an image forming apparatus capable of obtaining high-quality products. [Brief description of the drawings]

[0010] [Figure 1] 1 is an overall schematic view showing a printer according to a first embodiment. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] 6 is a flowchart showing a skew correction operation and a shift operation by the registration unit. [Diagram 5](a) is a plan view showing a state in which the sheet is skewed, (b) is a plan view showing a state in which the end position of the sheet is detected, (c) is a plan view showing a state in which the sheet is transported by a pair of registration rollers, and (d) is a plan view showing a sheet that has been shifted. [Figure 6] FIG. [Figure 7] 11 is a flowchart showing a shift operation by the reversing and conveying unit. [Figure 8] FIG. 1A is a schematic diagram showing how a sheet is transported toward a reversing shift section, FIG. 1B is a schematic diagram showing a state in which the sheet is stopped by the reversing shift section, and FIG. 1C is a schematic diagram showing how the inverted sheet is transported. [Figure 9] FIG. 4 is a perspective view showing a second double-sided conveying unit. [Figure 10] 11 is a flowchart showing a skew correction operation performed by the second double-sided conveying unit. [Figure 11] FIG. 11 is a perspective view showing a second double-sided conveying unit according to a second embodiment. [Figure 12] FIG. [Figure 13] 13 is a flowchart showing a skew correction operation and a shift operation performed by the second double-sided conveying unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <First embodiment> [Overall structure] First, a first embodiment of the present invention will be described. The image forming apparatus 1 of this embodiment is an electrophotographic full-color laser beam printer. As shown in Fig. 1, the image forming apparatus 1 has a housing 1A as a first housing having a unit for feeding sheets and forming images, and a housing 1B as a second housing having a unit for fixing and cooling the sheets, and the housing 1B is connected to the housing 1A.

[0012] The housing 1A has feeding units 10a and 10b, pulling units 20a and 20b, a registration unit 30, an image forming unit 90, and a first double-sided conveying unit 70. The housing 1B has a fixing unit 100, a cooling unit 110, a branching conveying unit 120, a reversing conveying unit 130, a second double-sided conveying unit 150, and a decurl unit 170.

[0013] The image forming unit 90 includes four process cartridges 99Y, 99M, 99C, and 99Bk that form toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), respectively, and exposure devices 93, 96, 97, and 98. The four process cartridges 99Y, 99M, 99C, and 99Bk have the same configuration except for the colors of the images they form. Therefore, only the configuration and image forming process of the process cartridge 99Y will be described, and descriptions of the process cartridges 99M, 99C, and 99Bk will be omitted.

[0014] The process cartridge 99Y has a photosensitive drum 91, a charging roller (not shown), a developing device 92, and a cleaner 95. The photosensitive drum 91 is formed by coating an organic photoconductive layer on the outer periphery of an aluminum cylinder, and is rotated by a drive motor (not shown). The image forming unit 90 is provided with an intermediate transfer belt 50 that is rotated in the direction of arrow T1 by a drive roller 52, and the intermediate transfer belt 50 is wound around a tension roller 51, the drive roller 52, and a secondary transfer inner roller 53. Primary transfer rollers 55Y, 55M, 55C, and 55Bk are provided on the inner side of the intermediate transfer belt 50, and a secondary transfer outer roller 54 is provided on the outer side of the intermediate transfer belt 50 in opposition to the secondary transfer inner roller 53.

[0015] The feeding unit 10a has a lift plate 11a which moves up and down while stacking sheets S, a pickup roller 12a which feeds the sheets S stacked on the lift plate 11a, and a separation roller pair 13a which separates the fed sheets one by one. Similarly, the feeding unit 10b has a lift plate 11b which moves up and down while stacking sheets S, a pickup roller 12b which feeds the sheets S stacked on the lift plate 11b, and a separation roller pair 13b which separates the fed sheets one by one.

[0016] The registration unit 30 has a pair of pre-registration rollers 31 that transports the sheet, and a pair of registration rollers 32 as a second moving section and a second skew correction section that corrects skew of the sheet. The registration unit 30 also has a registration sensor 33 that detects the position of the sheet S in the transport direction, and a CIS 34 that detects the position of the sheet in the width direction. The fixing unit 100 has a pair of fixing rollers 101 that can heat the sheet.

[0017] The cooling unit 110 has an upper cooling belt 111a rotated in the direction of arrow T2 by an upper cooling drive roller 112a, and a lower cooling belt 111b rotated in the direction of arrow T2 by a lower cooling drive roller 112b, and a heat sink 113 that cools the sheet.

[0018] Next, a description will be given of an image forming operation of the thus configured image forming apparatus 1. When an image signal is input to the exposure device 93 from a personal computer (not shown) or the like, the exposure device 93 irradiates a laser beam corresponding to the image signal onto the photosensitive drum 91 of the process cartridge 99Y.

[0019] At this time, the surface of the photosensitive drum 91 is uniformly charged to a predetermined polarity and potential by a charging roller, and an electrostatic latent image is formed on the surface by irradiating the surface with laser light from an exposure device 93 via a mirror 94. The electrostatic latent image formed on the photosensitive drum 91 is developed by a developing device 92, and a yellow (Y) toner image is formed on the photosensitive drum 91.

[0020] Similarly, the photosensitive drums of the process cartridges 99M, 99C, and 99Bk are irradiated with laser light from exposure devices 96, 97, and 98, and magenta (M), cyan (C), and black (K) toner images are formed on the photosensitive drums. The toner images of each color formed on the photosensitive drums are transferred to the intermediate transfer belt 50 by the primary transfer rollers 55Y, 55M, 55C, and 55Bk. The full-color toner image is then conveyed to the secondary transfer nip N formed by the secondary transfer inner roller 53 and the secondary transfer outer roller 54 by the intermediate transfer belt 50 rotated by the drive roller 52. The toner remaining on the photosensitive drum 91 is collected by the cleaner 95. The image forming process of each color is performed at a timing to overlap the upstream toner image that has been primarily transferred onto the intermediate transfer belt 50.

[0021] In parallel with this image forming process, a sheet S is fed from one of the feeding units 10a, 10b, and conveyed to the registration unit 30 by one of the drawing units 20a, 20b. In the registration unit 30, a pre-registration roller pair 31 abuts the leading edge of the sheet S against a nip portion of a registration roller pair 32 that is stopped. This corrects the skew of the sheet S, and the sheet is conveyed to a secondary transfer nip N as an image forming unit at a predetermined conveying timing. A full-color toner image on an intermediate transfer belt 50 is transferred to a first sheet surface (front surface) of the sheet S by a secondary transfer bias applied to a secondary transfer outer roller 54. Residual toner remaining on the intermediate transfer belt 50 is collected by a belt cleaner 56.

[0022] The sheet S onto which the toner image has been transferred is transported to the fixing unit 100 by the pre-fixing transport section 60. The sheet S is then guided to the nip section of a pair of fixing rollers 101, where a predetermined amount of heat and pressure are applied to melt and fix the toner (fix it). After passing through the fixing unit 100, the sheet S is transported in the cooling unit 110 while being sandwiched between an upper cooling belt 111a and a lower cooling belt 111b, which are endless belts. The heat of the sheet S is then transferred to the heat sink 113 via the upper cooling belt 111a, and the sheet S is cooled.

[0023] Next, the branching conveying unit 120 selects a path for conveying the sheet S to either the decurl unit 170 or the inversion conveying unit 130. After the sheet S is conveyed to the inversion conveying unit 130, the sheet S can be inverted in the secondary transfer nip N so that the first sheet surface on which the image is formed faces downward, and the sheet S can be conveyed to the decurl unit 170.

[0024] When an image is formed on only one side of the sheet S, the sheet S is conveyed from the branching conveying unit 120 to the decurl unit 170, where the curl of the sheet is corrected by a small-diameter hard roller and a large-diameter soft roller. Then, the sheet S that has passed through the decurl unit 170 is discharged onto the discharge tray 171.

[0025] When images are formed on both sides of the sheet S, the sheet S is transported to the inversion transport unit 130 by the branching transport unit 120 and is switched back in the inversion transport unit 130. The switched back sheet S is transported from the inversion transport unit 130 to the second double-sided transport unit 150 and the first double-sided transport unit 70 and is guided to the registration unit 30. Thereafter, an image is formed on the second sheet surface (back surface) of the sheet S in the secondary transfer nip N, and the sheet S is discharged to the discharge tray 171 via the branching transport unit 120 and the decurling unit 170.

[0026] The branching conveying unit 120, the inverting conveying unit 130, the second double-sided conveying unit 150 and the first double-sided conveying unit 70 constitute a re-conveying section 500 that inverts the sheet having an image formed on its first side and conveys the sheet again to the secondary transfer nip N.

[0027] In addition, in the image forming apparatus 1 according to this embodiment, as an example, a center-based sheet transport method is adopted in which the center of the width direction perpendicular to the transport direction in the transport path 65 is aligned with the center of the width direction of the sheet to transport the sheet.

[0028] [Registration Unit] 1 and 2, the registration unit 30 is provided in a conveying path 65 that connects the pull-out unit 20a and the secondary transfer nip N. The registration unit 30 also has a registration roller pair 32, a pre-registration roller pair 31, a registration sensor 33, and a CIS (Contact Image Sensor) 34. The pre-registration roller pair 31 is disposed upstream of the registration roller pair 32 in the sheet conveying direction A, and the registration sensor 33 and the CIS 34 are provided between these roller pairs.

[0029] 2, the registration roller pair 32, which is a pair of rotating bodies, has an upper roller 32a as a first roller, and a lower roller 32b as a second roller fixed to a rotating shaft 32S. An input gear 38 is fixed to the rotating shaft 32S, and the input gear 38 is driven by a registration drive motor 36 via an idler gear 39. The pre-registration roller pair 31 is driven by a pre-registration drive motor 35. Each roller of the pre-registration roller pair 31 and the registration roller pair 32 rotates about an axis extending in the width direction W.

[0030] A rack 41 is supported on the rotating shaft 32S so as to be rotatable relative to the rotating shaft 32S but immovable in the axial direction. The rack 41 receives a driving force from a shift motor 37 via a pinion gear 40, and shifts the rotating shaft 32S in the axial direction. The upper roller 32a shifts in the axial direction in conjunction with the lower roller 32b as a flange portion 42 integral with the upper roller 32a is sandwiched by an input gear 38 of the lower roller 32b. The pair of registration rollers 32 sandwiching the sheet S moves in a width direction W perpendicular to the conveying direction A, so that the sheet moves in the width direction W, and the position of the sheet in the width direction W is corrected.

[0031] The idler gear 39 has a wider tooth width than the input gear 38. This is to maintain the gear meshing and enable the registration roller pair 32 to rotate even when the registration roller pair 32 and the input gear 38 move in the width direction.

[0032] The CIS 34 detects the position of the edge in the width direction W of the conveyed sheet S (hereinafter, referred to as the edge position). The control unit 200 (see FIG. 3) calculates the amount of deviation between the design reference position of the sheet and the edge position detected by the CIS 34, and shifts the registration unit 30 by the amount of deviation. This causes the position of the sheet S in the width direction W to coincide with the transfer position in the image forming unit 90, resulting in a high-quality product.

[0033] The CIS 34 is disposed at a position offset to one side with respect to the center of the conveying path 65 in the width direction W. This is because it is necessary to detect the edge position of only one side of the sheet S in the position correction of the sheet S. The CIS 34 is configured to be able to detect the edge positions of the smallest and largest sheets among the sheet sizes permitted for use in the image forming apparatus 1. The CIS 34 is disposed as close as possible to the pair of registration rollers 32 so as not to reduce the detection accuracy of the CIS 34.

[0034] In the registration unit 30, the leading edge of the conveyed sheet S is abutted against the nip portion of the stopped registration roller pair 32 to bend the sheet S and align the leading edge of the sheet S with the nip portion, thereby correcting the skew. After the registration sensor 33 detects the leading edge of the sheet S, the sheet S is fed a predetermined amount by the pre-registration roller pair 31, and then conveyed by the registration roller pair 32 to the secondary transfer nip N.

[0035] Furthermore, the gap between the CIS 34 and the lower guide 65a facing the CIS 34 is kept constant, and a predetermined space is formed in the conveying path 65 by the lower guide 65a and the upper guides 65b and 65c so that the sheet can bend. The conveying amount of the sheet S by the pre-registration roller pair 31 is set so that an appropriate amount of bending is formed in the sheet S.

[0036] [Control Block] 3 is a control block diagram showing a control unit 200 of the image forming apparatus 1. The control unit 200 has a CPU 201, a memory 202, an operation unit 203, an image formation control unit 205, a sheet conveyance control unit 206, a sensor control unit 207, and a shift control unit 208. The CPU 201 executes a predetermined control program or the like to realize various processes performed by the image forming apparatus 1. The memory 202 is composed of, for example, a RAM or a ROM, and stores various programs and various data in a predetermined storage area. The operation unit 203 accepts input of various information related to sheets (for example, sheet size, sheet basis weight, sheet surface properties, etc.), execution and cancellation of jobs, etc.

[0037] The image formation control unit 205 issues instructions to the image forming unit 90 including the exposure devices 93, 96, 97, 98, etc., and controls the image forming operation. The sheet transport control unit 206 issues instructions to the pre-registration drive motor 35, the registration drive motor 36, the inversion drive motor 136, the second pre-registration drive motor 153, the second registration drive motor 154, etc., thereby controlling the transport operation of the sheet S. The sensor control unit 207 issues instructions to start and stop detection to the registration sensor 33, the inversion sensor 138, the second registration sensor 157, etc., and receives the detection results of each of these sensors.

[0038] The shift control unit 208 receives the detection results of the CIS 34 and the inversion CIS 139, and issues instructions such as starting and stopping the driving of the shift motor 37 and the inversion shift motor 137, thereby controlling the movement of the sheet S in the width direction W, i.e., the shift operation. In addition, the CPU 201 can be connected to an external computer 204 connected via a network, for example, and can receive various pieces of information related to the sheet, print jobs, and the like from the computer 204.

[0039] [Skewing correction and shifting operations by the registration unit] Next, the skew correction operation (first skew correction operation) and shift operation by the registration unit 30 will be described with reference to the flowchart shown in Fig. 4. First, when a print instruction is input from the operation unit 203 or computer 204, the control unit 200 starts a print job (step S101). Note that the user can also instruct the number of copies to be printed and specify the type of sheets to be used for printing from the operation unit 203 or computer 204.

[0040] The control unit 200 starts feeding the sheet S (step S102) and determines whether printing is being performed on the first or second side of the sheet in the print job (step S103). If it is determined that printing is being performed on the first side of the sheet, the control unit 200 controls the image forming unit 90 to form a toner image on the intermediate transfer belt 50 at a predetermined image writing position g1 for the first side (step S104). The image writing position g1 here is a value based on the result of a writing position adjustment performed at the time of shipment from the factory, etc., and is stored in the memory 202 as a fixed value specific to the device body.

[0041] Specifically, the control unit 200 controls the exposure devices 93, 96, 97, and 98 to form electrostatic latent images at image writing positions g1 on the photosensitive drums of the process cartridges 99Y, 99M, 99C, and 99K. Then, as described above, the electrostatic latent images formed on the photosensitive drums are developed into toner images by the developing devices, and these toner images are transferred to the intermediate transfer belt 50 by the primary transfer rollers 55Y, 55M, 55C, and 55K.

[0042] Meanwhile, the sheet S is transported to the pre-registration roller pair 31. Here, as shown in Fig. 5(a), the transported sheet S rotates clockwise with respect to the transport direction A, is skewed, and is shifted to the left with respect to the transport direction A. The dotted squares shown in Figs. 5(a) to (d) show a schematic state in which the leading edge of the sheet S, which has been transported without skew or lateral shift, abuts on the nip portion of the registration roller pair 32. The end position of the sheet in the width direction W at this time is set as the zero point, and the left side is set as the plus direction.

[0043] Next, the control unit 200 feeds the sheet S by a set feed amount using the pre-registration roller pair 31 based on the detection result of the registration sensor 33 (step S105). As a result, the sheet S is abutted against the stopped registration roller pair 32 as shown in Fig. 5(b) and a predetermined amount of bending is formed (step S106). In this way, the skew correction of the sheet S is performed, and the sheet S is sandwiched and conveyed by the registration roller pair 32 that has started to be rotated as shown in Fig. 5(c) (step S107).

[0044] Then, the end position of the sheet S after the skew correction is detected by the CIS 34 (step S108), and the control unit 200 calculates the shift amount of the sheet based on the detection result (L1). In this case, the shift amount can be obtained by subtracting the image writing position (g1) from the detection result (L1) of the CIS 34 (L1-g1).

[0045] The control unit 200 moves the pair of registration rollers 32, which sandwich the sheet S, in the width direction W by the shift amount (L1-g1) via the shift control unit 208 and the shift motor 37. This allows the sheet S to be moved in the width direction W by the shift amount (L1-g1) (step S109). This corrects the position of the sheet S in the width direction W to correspond to the image writing position g1.

[0046] Then, the sheet shifted by the shift amount (L1-g1) by the registration roller pair 32 has the toner image on the intermediate transfer belt 50 transferred to it by the secondary transfer nip N (step S110). After that, the toner image is fused and fixed by the fixing unit 100 (step S111).

[0047] In the case of a single-sided job, the sheet S on which the toner image is fixed is discharged to the discharge tray 171 and the job is completed (step S112), but in the case of a double-sided job, the sheet S is inverted for image formation on the second side. Next, the control unit 200 determines whether or not there is a subsequent sheet (step S113). If the control unit 200 determines that there is no subsequent sheet (step S113: No), the print job is completed (step S114). If the control unit 200 determines that there is a subsequent sheet (step S113: Yes), the control unit 200 returns the registration roller pair 32 to the home position (center position) (step S115). Then, the process returns to step S103.

[0048] If the control unit 200 determines in step S103 that the second side of the print job is being printed, the control unit 200 controls the image forming unit 90 to form a toner image at image writing position g2 on the second side (step S116). Note that the image writing position g2 on the second side may be the same position as or different from the image writing position g1 on the first side in the width direction. The skew correction operation by the registration roller pair 32 for the sheet on which an image is formed on the second side is the same as that for the sheet on which an image is formed on the first side, and therefore a description thereof will be omitted (steps S117 to S119).

[0049] Then, after the skew correction is performed, the CIS 34 detects the edge position of the second side of the sheet S (step S120), and the control unit 200 calculates the shift amount of the sheet S based on this detection result (L2). In this case, the shift amount can be obtained by subtracting the image writing position (g2) from the detection result (L2) of the CIS 34 (L2-g2).

[0050] The control unit 200 moves the registration roller pair 32, which sandwiches the sheet S, in the width direction W by the shift amount (L2-g2) via the shift control unit 208 and the shift motor 37. This allows the sheet S to be moved in the width direction W by the shift amount (L2-g2) (step S121). For example, when the image writing position on the second side is g2=g1=0, the sheet S is shifted by the shift amount L2, and the sheet S is moved to the same position as the position before the image formation on the first side. This allows the positions of the images formed on the first side and the second side to match, and these images are formed in the center of the sheet S, resulting in a high-quality product.

[0051] Then, the toner image on the intermediate transfer belt 50 is transferred to the sheet shifted by the shift amount (L2-g2) by the registration roller pair 32 by the secondary transfer nip N (step S122). Thereafter, similar to the processing of the first side, this toner image is fused and fixed by the fixing unit 100, and the sheet is discharged to the discharge tray 171 (steps S111 and S112).

[0052] Here, since the printing of the second side involves conveying the sheet a long distance after the registration unit 30 corrects the skew and lateral deviation of the first side, the skew and lateral deviation are often greater than that of the printing of the first side due to the variation of the parts of each unit. Therefore, the shift amount of the registration roller pair 32 becomes large. When the registration roller pair 32 shifts, the sheet S experiences a large resistance to sliding against the conveying guide member, and especially when the size of the sheet S is large, the resistance is large because the sheet S is nipped by other rollers. As a result, when the shift amount is large, when the registration roller pair 32 shifts due to these resistances, the sheet S may be skewed, the shift amount of the sheet S may be smaller than expected, or the sheet S may become wrinkled.

[0053] Furthermore, when the shift amount is large, it takes a long time to shift the registration roller pair 32 and for the registration roller pair 32 to return to the home position (center position) after the sheet S passes through the registration roller pair 32. This may result in a loss of productivity. In order to reduce the above problems, in this embodiment, the reversing conveying unit 130 also performs a shift operation (lateral registration shift) of the sheet S.

[0054] [Reversing transport unit] Next, the configuration of the reverse conveying unit 130 will be described. As shown in Fig. 6, the reverse conveying unit 130 as a reverse section has a conveying roller pair 131, a reverse shift section 132 as a first moving section, a reverse sensor 138, a reverse CIS 139 as a first detecting section, and a switching member 143. The reverse shift section 132 has a first reverse shift roller pair 132a and a second reverse shift roller pair 132b, and the reverse sensor 138 and the reverse CIS 139 are provided between the conveying roller pair 131 and the first reverse shift roller pair 132a.

[0055] The conveying roller pair 131 is driven by a reverse drive motor 136 via a belt 136a. The rotation of the conveying roller pair 131 is transmitted to an idler gear 135 via a belt 136b. An input gear 134 is fixed to a rotating shaft 132S of the first reverse shift roller pair 132a, and the input gear 134 is driven by the idler gear 135. The first reverse shift roller pair 132a and the second reverse shift roller pair 132b are connected by a belt 136c and configured to move in conjunction with each other. Each roller of the first reverse shift roller pair 132a and the second reverse shift roller pair 132b rotates around an axis extending in the width direction W. For example, the first reverse shift roller pair 132a has a third roller and a fourth roller that rotate around an axis extending in the width direction W, and these third roller and fourth roller move in the width direction W while sandwiching a sheet.

[0056] A rack 141 is supported on the rotating shaft 132S so as to be rotatable relative to the rotating shaft 132S but immovable in the axial direction. The rack 141 receives a driving force from a reverse shift motor 137 via a pinion gear 140, and shifts the rotating shaft 132S in the axial direction. The first reverse shift roller pair 132a and the second reverse shift roller pair 132b, which are holding the sheet S, move in the width direction W, whereby the sheet moves in the width direction W and the position of the sheet in the width direction W is corrected. In this way, the shift operation by the reverse conveying unit 130 is realized.

[0057] The idler gear 135 has a wider tooth width than the input gear 134. This is to maintain the meshing of the gears and enable the rotation of the reverse shift part 132 even when the first reverse shift roller pair 132a and the input gear 134 move in the width direction.

[0058] The inversion CIS 139 is disposed at a position offset to one side with respect to the center of the inversion conveying path 165 in the width direction W, and detects the end position in the width direction W of the conveyed sheet S. This is because, in correcting the position of the sheet S, it is necessary to detect the end position of only one side of the sheet S. Also, in order not to decrease the detection accuracy of the inversion CIS 139, the inversion CIS 139 is disposed as close as possible to the first inversion shift roller pair 132a.

[0059] [Shift operation by the reversing transport unit] Next, the shift operation by the reversing conveying unit 130 will be described with reference to the flowchart shown in Fig. 7. When a print job is double-sided printing, the sheet S having an image formed on the first side is conveyed to the reversing conveying unit 130 by the branching conveying unit 120. As shown in Fig. 8(a), the switching member 143 of the reversing conveying unit 130 is biased in a positioned state by a biasing member (not shown).

[0060] The sheet S conveyed from the branch conveying unit 120 is conveyed to the conveying roller pair 131, and is conveyed while pressing the switching member 143 against the biasing force of the biasing member. Next, the position of the sheet S in the conveying direction A is detected by the inversion sensor 138 (step S201). After that, the end position of the sheet S is detected by the inversion CIS 139 (step S202). The control unit 200 calculates the shift amount of the sheet based on the detection result (L3) and the deviation amount (g3). The deviation amount (g3) is the amount of deviation of the sheet S in the width direction W when conveyed from the inversion conveying unit 130 to the registration unit 30, which is obtained in advance when the image forming apparatus 1 is installed, etc. Then, the shift amount of the sheet S can be obtained by subtracting the deviation amount (g3) from the detection result (L3) of the inversion CIS 139 (L3-g3).

[0061] Next, as shown in FIG. 8(b), based on the detection result of the inversion sensor 138, the control unit 200 stops driving the inversion drive motor 136 when the trailing end of the sheet S has advanced a predetermined distance from the switching member 143, thereby stopping the sheet S (step S203).

[0062] After the sheet S stops, the control unit 200 moves the reverse shift unit 132, which is clamping the sheet S, in the width direction W by the shift amount (L3-g3) via the shift control unit 208 and the reverse shift motor 137. This makes it possible to move the sheet S in the width direction W by the shift amount (L3-g3) (step S204).

[0063] In parallel with such a shift operation, the control unit 200 reverses the reverse drive motor 136 (step S205). As a result, a switchback is performed by the first reverse shift roller pair 132a and the second reverse shift roller pair 132b of the reverse shift unit 132. That is, the sheet S is conveyed in a first direction A1 (see FIG. 8(a)), and then conveyed in a second direction A2 (see FIG. 8(c)) opposite to the first direction A1.

[0064] During the switchback operation, the sheet S is guided while being in sliding contact with the reversing guide 142 serving as a guide member. At this time, the second surface of the sheet S opposite to the first surface on which the image is formed is in sliding contact with the reversing guide 142. Also, no guide member is provided on the opposing side of the reversing guide 142, and the first surface side of the sheet S guided by the reversing guide 142 is not guided by another guide member. Then, as shown in FIG. 8(c), the sheet S is guided by the switching member 143 to the second double-sided conveying unit 150, where the image is formed on the second surface.

[0065] Next, the control unit 200 determines whether there is a subsequent sheet (step S206). If the control unit 200 determines that there is no subsequent sheet (step S206: No), the shift operation by the reverse conveying unit 130 ends. If the control unit 200 determines that there is a subsequent sheet (step S206: Yes), the control unit 200 returns the reverse shift unit 132 to the home position (center position) (step S207). Then, the process returns to step S201.

[0066] In this embodiment, step S205 is performed after step S204, but the order may be reversed or these steps may be performed simultaneously.

[0067] [Second double-sided transport unit] Next, a configuration of the second double-sided conveying unit 150 will be described. As shown in Fig. 9, the second double-sided conveying unit 150 as a double-sided conveying section has a second registration roller pair 152 as a skew correction section, a second pre-registration roller pair 151, and a second registration sensor 157. The second pre-registration roller pair 151 is disposed upstream of the second registration roller pair 152 in the sheet conveying direction A, and the second registration sensor 157 is provided between these roller pairs.

[0068] The second registration roller pair 152, which is a rotating body pair, has an upper roller 152a and a lower roller 152b fixed to a rotating shaft 152S. An input gear 156 is fixed to the rotating shaft 152S, and the input gear 156 is driven by a second registration drive motor 154 via an idler gear 155. In addition, the second pre-registration roller pair 151 is driven by a second pre-registration drive motor 153.

[0069] The second double-sided conveying unit 150 is provided in the housing 1B, and performs skew correction on the sheet S before the sheet S is discharged from the housing 1B to the housing 1A. Note that the second double-sided conveying unit 150 performs a skew correction operation on the sheet S, but does not perform a shift operation.

[0070] [Skew correction operation by the second duplex transport unit] Next, the skew correction operation (second skew correction operation) by the second double-sided conveying unit 150 will be described with reference to the flowchart shown in Fig. 10. When a print job is double-sided printing, the sheet S with an image formed on the first side undergoes a shift operation in the reversing conveying unit 130 as described above. Then, the position of the sheet S sent from the reversing conveying unit 130 to the double-sided conveying unit 150 in the conveying direction A is detected by the second registration sensor 157 (step S301).

[0071] Next, the control unit 200 feeds the sheet S by a set feed amount using the second pre-registration roller pair 151 based on the detection result of the second registration sensor 157. As a result, the sheet S is abutted against the stopped second registration roller pair 152, and a predetermined amount of bending is formed (step S302). In this way, skew correction of the sheet S is performed, and the sheet S is sandwiched and conveyed by the second registration roller pair 152 that has started to be rotated (step S303).

[0072] Next, the control unit 200 determines whether or not there is a subsequent sheet (step S304). If the control unit 200 determines that there is no subsequent sheet (step S304: No), the skew correction operation by the second double-sided conveying unit 150 ends. If the control unit 200 determines that there is a subsequent sheet (step S304: Yes), the process returns to step S301.

[0073] As described above, in this embodiment, in a double-sided printing job, after image formation on the first side of the sheet S, the shift operation is performed at two locations, the reverse conveying unit 130 and the registration unit 30. Therefore, the shift amount of the sheet S can be distributed to the shift operations at these two locations. Furthermore, by performing the shift operation at the reverse conveying unit 130, the sheet S is not nipped by rollers other than the reverse shift section 132 performing the shift operation. In other words, regardless of the size of the sheet S, the sheet S is not nipped by rollers other than the reverse shift section 132 and does not become a resistance, and the shift operation can be performed stably.

[0074] Furthermore, the sheet S switched back by the reverse shift section 132 has its second surface, on which no image is formed, guided by the reverse guide 142. And, since no guide member is provided on the opposing side of the reverse guide 142, the first surface, which is the image surface of the sheet S, is not guided by the guide member. Since the image surface, on which an image is formed, has a large frictional resistance, only the second surface, which is not the image surface, is guided by the reverse guide 142, so that the resistance caused by the sliding between the sheet S and the reverse guide 142 can be reduced. Therefore, there is also little resistance in the shift operation of the reverse shift section 132.

[0075] In addition, the reverse shift unit 132 simultaneously shifts the first reverse shift roller pair 132a and the second reverse shift roller pair 132b in the width direction W. In this way, by performing the shift operation while the sheet S is nipped by the two pairs of rollers, it is possible to reduce the occurrence of slippage between the sheet S and the rollers during the shift operation, which causes the sheet S to skew, and to perform a stable shift operation. Therefore, it is possible to reduce the skew and lateral deviation of the sheet S and obtain a high-quality product. In particular, in this embodiment, it is possible to reduce the skew and lateral deviation of the sheet S when forming an image on the second surface of the first sheet of a job. Therefore, it is possible to obtain a high-quality product more quickly than a device that corrects the position of the subsequent sheet based on the position of the preceding sheet.

[0076] Furthermore, since the shift amounts of the reversing and conveying unit 130 and the registration unit 30 are reduced, the time required to return the roller pair to the home position after the shift operation is shortened, thereby improving productivity.

[0077] Moreover, the registration unit 30 is provided in the housing 1A, and the inverting and conveying unit 130 is provided in the housing 1B. In this way, by performing the shifting operation in the separate housings, the lateral deviation in each housing can be corrected. Then, after the lateral deviation is corrected in each housing, the sheet S is conveyed to another housing, so that the shift amount of the sheet S in each housing can be reduced. Therefore, the length in the width direction W of the guide members forming each conveying path can be reduced, and costs and space can be reduced.

[0078] Furthermore, in this embodiment, in a double-sided printing job, after image formation on the first side of the sheet S, skew correction operations are performed at two locations, the double-sided conveying unit 150 and the registration unit 30. Therefore, the amount of skew correction of the sheet S can be distributed to the skew correction operations at these two locations, and the amount of skew correction at each location can be reduced. Since the skew correction operation bends the sheet S, if the amount of skew correction is large, the sheet S may become distorted and wrinkles may occur. However, in this embodiment, the amount of skew correction can be reduced, and therefore wrinkles in the sheet S can be suppressed.

[0079] Moreover, the registration unit 30 is provided in the housing 1A, and the duplex conveying unit 150 is provided in the housing 1B. In this way, by performing the skew correction operation in separate housings, the skew can be corrected in each housing. Then, since the sheet S is conveyed to another housing after the skew correction in each housing, the amount of skew correction of the sheet S in each housing can be reduced. Therefore, the skew correction capacity required in each housing can be specified, and a skew correction mechanism with an optimal amount of skew correction within a range of excess or deficiency can be selected.

[0080] <Second embodiment> Next, a second embodiment of the present invention will be described, in which the reverse conveying unit 130 does not perform a shift operation, but the second double-sided conveying unit 180 performs a skew correction operation and a shift operation. For this reason, the same configurations as those in the first embodiment will be described with the same reference numerals or omitted from the illustrations.

[0081] [Second double-sided transport unit] First, the configuration of the second double-sided conveying unit 180 according to the second embodiment will be described. As shown in Fig. 11, the second double-sided conveying unit 180 has a second registration roller pair 182 as a first moving unit and a first skew correction unit, and a second pre-registration roller pair 181. The second double-sided conveying unit 180 also has a second registration sensor 187 and a second CIS 188. The second pre-registration roller pair 181 is disposed upstream of the second registration roller pair 182 in the sheet conveying direction A, and the second registration sensor 187 and the second CIS 188 are provided between these roller pairs.

[0082] The second registration roller pair 182, which is a rotating body pair, has an upper roller 182a as a third roller, and a lower roller 182b as a fourth roller fixed to a rotating shaft 182S. An input gear 186 is fixed to the rotating shaft 182S, and the input gear 186 is driven by a second registration drive motor 184 via an idler gear 185. The second pre-registration roller pair 181 is driven by a second pre-registration drive motor 183. Each roller of the second pre-registration roller pair 181 and the second registration roller pair 182 rotates about an axis extending in the width direction W.

[0083] A rack 191 is supported on the rotating shaft 182S so as to be rotatable relative to the rotating shaft 182S but immovable in the axial direction. The rack 191 receives a driving force from a second shift motor 189 via a pinion gear 190, and shifts the rotating shaft 182S in the axial direction. The upper roller 182a shifts in the axial direction in conjunction with the lower roller 182b as a flange portion 192 integral with the upper roller 182a is clamped by an input gear 186 of the lower roller 182b. The second registration roller pair 182, which is clamping the sheet S, moves in the width direction W, and the position of the sheet in the width direction W is corrected.

[0084] The idler gear 185 has a wider tooth width than the input gear 186. This is to maintain the meshing of the gears and enable the rotation of the second registration roller pair 182 even when the second registration roller pair 182 and the input gear 186 move in the width direction.

[0085] Similarly to CIS 34 (see FIG. 2), second CIS 188 as a first detection unit is disposed at a position offset to one side from the center of the conveying path in the width direction W. In addition, second CIS 188 is disposed as close as possible to second registration roller pair 182 so as not to reduce the detection accuracy of second CIS 188.

[0086] [Control Block] 12 is a control block diagram showing a control unit 200 of the image forming apparatus 1 according to the second embodiment. A sheet transport control unit 206 issues instructions to the pre-registration drive motor 35, the registration drive motor 36, the inversion drive motor 136, the second pre-registration drive motor 183, the second registration drive motor 184, etc., thereby controlling the transport operation of the sheet S. A sensor control unit 207 issues instructions to start and stop detection to the registration sensor 33, the second registration sensor 187, etc., and receives the detection results of these sensors.

[0087] The shift control unit 208 receives the detection results of the CIS 34 and the second CIS 188, and issues instructions such as starting and stopping the driving of the shift motor 37 and the second shift motor 189, thereby controlling the movement of the sheet S in the width direction W, that is, the shift operation.

[0088] [Skewing correction and shifting operations by the second duplex conveying unit] Next, the skew correction operation (second skew correction operation) and shift operation by the second double-sided conveying unit 180 will be described with reference to the flowchart shown in Fig. 13. When a print job is double-sided printing, the sheet S with an image formed on the first side is switched back in the reversing conveying unit 130. In this embodiment, the reversing conveying unit 130 does not perform a shift operation. Then, the position of the sheet S in the conveying direction A sent from the reversing conveying unit 130 to the double-sided conveying unit 180 is detected by the second registration sensor 187 (step S401).

[0089] Next, the control unit 200 feeds the sheet S by a set feed amount using the second pre-registration roller pair 181 based on the detection result of the second registration sensor 187. As a result, the sheet S is abutted against the stopped second registration roller pair 182, and a predetermined amount of bending is formed (step S402). In this way, skew correction of the sheet S is performed, and the sheet S is sandwiched and conveyed by the second registration roller pair 182 that has started to be rotated (step S403).

[0090] Thereafter, the second CIS 188 detects the edge position of the sheet S (step S404). The control unit 200 calculates the shift amount of the sheet based on the detection result (L4) and the misalignment amount (g4). The misalignment amount (g4) is the amount of misalignment of the sheet S in the width direction W when the sheet S is conveyed from the second double-sided conveying unit 180 to the registration unit 30, and is obtained in advance, such as when the image forming apparatus 1 is installed. The shift amount of the sheet S can be calculated by subtracting the misalignment amount (g4) from the detection result (L4) of the second CIS 188 (L4-g4).

[0091] Then, the control unit 200 moves the second registration roller pair 182, which sandwiches the sheet S, in the width direction W by the shift amount (L4-g4) via the shift control unit 208 and the second shift motor 189. This makes it possible to move the sheet S in the width direction W by the shift amount (L4-g4) (step S405).

[0092] Next, the control unit 200 determines whether or not there is a subsequent sheet (step S406). If the control unit 200 determines that there is no subsequent sheet (step S406: No), the skew correction operation and shift operation by the second double-sided conveying unit 180 are terminated. If the control unit 200 determines that there is a subsequent sheet (step S406: Yes), the control unit 200 returns the second registration roller pair 182 to the home position (center position) (step S407). Then, the process returns to step S401.

[0093] As described above, in this embodiment, in a double-sided printing job, after the image is formed on the first side of the sheet S, the skew correction operation and the shift operation are performed at two locations, the second double-sided conveying unit 180 and the registration unit 30. Therefore, the same effects as those of the first embodiment can be achieved.

[0094] Furthermore, since the second double-sided conveying unit 180 is positioned near the exit from the housing 1B to the housing 1A, the amount of skew and the position in the width direction W of the sheet S discharged from the housing 1B can be made clearer than in the first embodiment.

[0095] <Other embodiments> In the first embodiment, the shift operation is performed in the reversing conveying unit 130, and the skew correction operation is performed in the second double-sided conveying unit 150. In the second embodiment, the shift operation and the skew correction operation are performed in the second double-sided conveying unit 180, but this is not limited to this. That is, at least one of the shift operation and the skew correction operation may be performed in the re-conveying section 500. In addition, it is not limited to which unit performs these shift operation and skew correction operations. For example, the skew correction operation and the shift operation may be performed in the reversing conveying unit 130, or only the shift operation may be performed in the first double-sided conveying unit 70.

[0096] In the first embodiment, both the first reverse shift roller pair 132a and the second reverse shift roller pair 132b of the reverse shift unit 132 are configured to be movable in the width direction W, but this is not limited thereto. For example, only one of the first reverse shift roller pair 132a and the second reverse shift roller pair 132b may be configured to be movable in the width direction W. Also, the second reverse shift roller pair 132b may be omitted, and the sheet S may be moved in the width direction W by only the first reverse shift roller pair 132a while being sandwiched therebetween.

[0097] In addition, a CCD sensor or a CMOS sensor may be used instead of CIS 34, inversion CIS 139, and second CIS 188. If the position of the sheet in the width direction can be detected by these sensors, it is not necessary to detect the position of the edge of the sheet in the width direction.

[0098] In addition, instead of a method of correcting the skew of a sheet by abutting the sheet against the registration roller pair 32 or the second registration roller pair 182, a method of abutting the sheet against a shutter member provided upstream in the conveying direction of the roller pair may be applied.

[0099] In addition, in each of the above-described embodiments, the electrophotographic image forming apparatus 1 has been described, but the present invention is not limited to this. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from a nozzle.

[0100] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions. [Explanation of symbols]

[0101] 1: image forming apparatus / 1A: first housing / 1B: second housing / 32: second moving section, second skew correction section (pair of registration rollers) / 32a: first roller (upper roller) / 32b: second roller (lower roller) / 34: second detection section (CIS) / 65: conveying path / 130: reversing section (reversing conveying unit) / 132: first moving section (reversing shift section) / 132a: third roller, fourth roller (first reversing shift roller pair) / 139: first detection section (reversing CIS) / 142: guide member (reversal guide) / 150: duplex conveying section (second duplex conveying unit) / 152: skew correction section (second registration roller pair) / 182: first moving section, first skew correction section (second registration roller pair) / 182a: third roller (upper roller) / 182b: fourth roller (lower roller) / 188: first detection section (second CIS) / 500: re-conveying section / A: conveying direction / A1: first direction / A2: second direction / N: image forming section (secondary transfer nip) / W: width direction

Claims

1. an image forming unit that forms an image on a sheet; a skew correction unit including a first registration roller pair that is provided upstream of the image forming unit in a sheet conveying direction and corrects skew of the sheet by abutting a leading edge of the sheet against the first registration roller pair, and a first moving unit that moves the sheet in a width direction of the sheet perpendicular to the conveying direction while the sheet is sandwiched between the first registration roller pair; an inverting unit that inverts a leading end and a trailing end of a sheet on a first surface of which an image has been formed by the image forming unit; a re-conveying unit that re-conveys the sheet inverted by the reversing unit toward the skew correction unit; A control unit, the inversion unit has a pair of inversion rollers that rotate in a first direction while clamping a sheet, and then rotate in a second direction opposite to the first direction to invert the sheet, and a second moving unit that moves the sheet in the width direction while clamping the sheet between the pair of inversion rollers, thereby moving the sheet in the width direction; the re-conveying section includes a second registration roller pair that corrects skew of the sheet by abutting the leading edge of the sheet against the second registration roller pair; the control unit controls the sheet such that, when forming an image on a second surface of the sheet opposite to the first surface, the position of the sheet in the width direction is corrected by the second moving unit, and after skew of the sheet is corrected, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

1. An image forming apparatus comprising:

2. the control unit controls the sheet such that, when forming an image on the second surface of the sheet, the position of the sheet in the width direction is corrected by the second moving unit, and after skew of the sheet is corrected by the second registration roller pair, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

2. The image forming apparatus according to claim 1,

3. the control unit controls the sheet such that, when forming an image on the second surface of the sheet, the position of the sheet in the width direction is corrected by the second moving unit, and after skew of the sheet is corrected by the first registration roller pair, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

2. The image forming apparatus according to claim 1,

4. the control unit controls the sheet such that, when forming an image on the second surface of the sheet, the position of the sheet in the width direction is corrected by the second moving unit, and after skew of the sheet is corrected by the second registration roller pair and the first registration roller pair, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

2. The image forming apparatus according to claim 1,

5. the pair of reversing rollers includes a first pair of reversing rollers and a second pair of reversing rollers provided downstream of the first pair of reversing rollers in the transport direction, the control unit controls the sheet such that, when the sheet is moved in the width direction by the second moving unit, the sheet is moved in the width direction while being sandwiched between both the first reversing roller pair and the second reversing roller pair.

5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

6. The inversion portion is A pair of conveying rollers for conveying a sheet; a reversal position detection unit that detects a trailing end of a sheet being conveyed in order to reverse the sheet; a side edge detection unit that detects the position of a side edge of the sheet in the width direction; It has The conveying roller pair, the reversing position detection unit, the side edge detection unit, the first reversing roller pair, and the second reversing roller pair are arranged in this order from the upstream to the downstream in the conveying direction.

6. The image forming apparatus according to claim 5,

7. a first side edge detection unit that is disposed upstream of the first registration roller pair in the conveying direction and detects a position of a side edge of the sheet in the width direction of the sheet; a second side edge detection unit disposed upstream of the pair of reversing rollers in the conveying direction and configured to detect a position of a side edge of the sheet in the width direction of the sheet, the control unit moves the sheet sandwiched between the first registration roller pair in the width direction by the first moving unit based on a detection result of the first side end detection unit, and moves the sheet sandwiched between the reversing roller pair in the width direction by the second moving unit based on a detection result of the second side end detection unit.

6. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

8. a conveying path that guides the sheet conveyed in the conveying direction, the control unit causes the first moving unit and the second moving unit to move the sheet such that a center of the conveying path and a center of the sheet coincide with each other in the width direction.

8. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

9. a first housing having the image forming unit and the skew correction unit; a second housing having the inverted portion and connected to the first housing, 9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. The first registration roller pair includes a first roller and a second roller that rotate around an axis extending in the width direction, The pair of reversing rollers includes a third roller and a fourth roller each rotating about an axis extending in the width direction, the control unit causes a first moving unit to move the sheet in the width direction while the sheet is sandwiched between the first roller and the second roller, and causes a second moving unit to move the sheet in the width direction while the sheet is sandwiched between the third roller and the fourth roller.

10. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

11. the control unit causes the second moving unit to move the sheet in the width direction when the pair of reversing rollers rotates in the second direction.

11. The image forming apparatus according to claim 1,

12. an image forming unit that forms an image on a sheet; a skew correction unit including a first registration roller pair that is provided upstream of the image forming unit in a sheet conveying direction and corrects skew of the sheet by abutting a leading edge of the sheet against the first registration roller pair, and a first moving unit that moves the sheet in a width direction of the sheet perpendicular to the conveying direction while the sheet is sandwiched between the first registration roller pair; an inverting unit that inverts a leading end and a trailing end of a sheet on a first surface of which an image has been formed by the image forming unit; a re-conveying unit that re-conveys the sheet inverted by the reversing unit toward the skew correction unit; A control unit, the re-conveying unit includes a second registration roller pair that corrects sheet skew by abutting a leading edge of the sheet against the second registration roller pair, and a second moving unit that moves the sheet in the width direction while the sheet is sandwiched between the second registration roller pair, thereby moving the sheet in the width direction; the control unit controls the sheet such that, when forming an image on a second surface of the sheet opposite to the first surface, the position of the sheet in the width direction is corrected by the second moving unit, and after skew of the sheet is corrected, the position of the sheet in the width direction is corrected again by the first moving unit, and the sheet is transported to the image forming unit.

1. An image forming apparatus comprising:

Images