Image forming apparatus

Abstract

This invention discloses an image forming apparatus. The image forming apparatus includes: an image forming unit; a pair of reversing rollers; a moving unit; and a receiving unit. The image forming unit is configured to hold a sheet and rotate it in a first direction, and then rotate and convey the sheet in a second direction. The moving unit moves the pair of reversing rollers; the receiving unit obtains the length of the sheet. When a first sheet is reversed and conveyed, the moving unit moves the pair of reversing rollers conveying the first sheet by a first movement amount in the width direction, and wherein, when a second sheet is reversed and conveyed, the moving unit moves the pair of reversing rollers conveying the second sheet by a second movement amount less than the first movement amount in the width direction, the length of the first sheet in the conveying direction being a first length, and the length of the second sheet in the conveying direction being a second length greater than the first length.

Description

Technical Field

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

[0002] Generally, in an image forming apparatus such as a photocopier, the sheet being transported can be laterally deviated in the width direction orthogonal to the sheet transport direction. If an image is formed on the laterally deviated sheet, the image can be printed away from the center position in the width direction of the sheet.

[0003] As discussed in Japanese Patent Application Publication No. 2009-143643, a shift mechanism for detecting the position of the end of a sheet in the width direction and correcting lateral deviation (positional deviation) of the sheet before forming an image on the sheet has therefore been known.

[0004] As discussed in Japanese Patent Application Publication No. 6-250464, some known image forming apparatuses include a reversing mechanism for folding back a sheet and conveying the sheet to form an image on a sheet surface opposite to the position where an image has been formed.

[0005] If a reverse shifting mechanism, which includes both a shifting mechanism and a reversing mechanism, shifts the skewed sheet laterally along the sheet conveying direction, the size of the device will increase because a large space in the width direction needs to be provided. Summary of the Invention

[0006] According to one aspect of the present invention, an image forming apparatus includes: an image forming unit configured to form an image on a sheet; a reversing roller pair configured to hold the sheet on which the image forming unit has formed the image and rotate it in a first direction, and then rotate it in a second direction to reverse and convey the sheet, the second direction being opposite to the first direction; a moving unit configured to move the reversing roller pair in a width direction of the sheet while the sheet is held by the reversing roller pair, the width direction being orthogonal to the conveying direction of the sheet; an obtaining unit configured to obtain information about the length of the sheet in the conveying direction; and a control unit. The control unit is configured to control the moving unit based on information about the length of the sheet obtained by the obtaining unit, wherein, when the first sheet is reversed and conveyed, the control unit controls the moving unit to move the reverse roller pair conveying the first sheet by a first movement amount in the width direction, and wherein, when the second sheet is reversed and conveyed, the control unit controls the moving unit to move the reverse roller pair conveying the second sheet by a second movement amount less than the first movement amount in the width direction, wherein the length of the first sheet in the conveying direction is a first length, and the length of the second sheet in the conveying direction is a second length greater than the first length.

[0007] Further features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0008] Figure 1 This is a general schematic diagram illustrating a printer (image forming apparatus) according to a first exemplary embodiment.

[0009] Figure 2 This is a perspective view of the aligned unit.

[0010] Figure 3 This is a control block diagram of the control unit shown in the figure.

[0011] Figure 4 This is a flowchart illustrating the skew correction and shifting operations to be performed by the alignment unit.

[0012] Figure 5A This is a plan view illustrating the state in which the sheet material is being conveyed skewed toward the alignment rollers. Figure 5B This is a plan view illustrating the state of the end position of the sheet material being detected close to the alignment roller pair. Figure 5C This is a plan view illustrating the state of the sheet being conveyed by the alignment rollers. Figure 5D This is a plan view illustrating the state of the sheet material being shifted by the alignment rollers.

[0013] Figure 6 This is a perspective view of the reverse transmission unit.

[0014] Figure 7 This is a flowchart illustrating the shift operation to be performed by the reverse transfer unit.

[0015] Figure 8A This is a schematic diagram showing the state in which the sheet material is being transferred toward the reverse transfer unit. Figure 8B This is a schematic diagram showing the state in which the sheet material is stopped by the reverse transfer unit. Figure 8C This is a schematic diagram illustrating the state of the inverted sheet being transferred by the reverse transfer unit.

[0016] Figure 9 This is a perspective view of the second double-sided transmission unit shown in the diagram.

[0017] Figure 10 This is a flowchart illustrating the skew correction operation of the second double-sided transmission unit.

[0018] Figure 11 This is a perspective view illustrating the second double-sided transmission unit according to a second exemplary embodiment.

[0019] Figure 12 This is a control block diagram of the control unit shown in the figure.

[0020] Figure 13 This is a flowchart illustrating the skew correction and shifting operations to be performed by the second double-sided transmission unit.

[0021] Figure 14A and 14B This diagram illustrates the state in which the sheet material is being conveyed at an angle. Detailed Implementation

[0022] [Image forming apparatus]

[0023] First, a first exemplary embodiment of the present invention will be described. The image forming apparatus 1 according to this exemplary embodiment is an electrophotographic full-color laser beam printer. For example... Figure 1 As shown, the image forming apparatus 1 includes a housing 1A serving as a first housing and a housing 1B serving as a second housing. The first housing includes units for sheet feeding and image forming, and the second housing includes units for sheet fixing and cooling. Housing 1B is connected to housing 1A.

[0024] Housing 1A includes feeding units 10a and 10b, pulling units 20a and 20b, alignment unit 30, image forming unit 90, and first double-sided transfer unit 70. Housing 1B includes fixing unit 100, cooling unit 110, branch transfer unit 120, reverse transfer unit 130, second double-sided transfer unit 150, and de-curling unit 170.

[0025] The image forming unit 90 includes four processing boxes 99Y, 99M, 99C, and 99Bk for forming 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 processing boxes 99Y, 99M, 99C, and 99Bk have the same configuration except for forming images of different colors. Therefore, only the configuration of processing box 99Y and its image forming process will be described, and the descriptions of processing boxes 99M, 99C, and 99Bk will be omitted.

[0026] The processing cartridge 99Y includes a photosensitive drum 91, a charging roller, a developing unit 92, and a cleaner 95. The photosensitive drum 91 is formed by applying an organic photoconductive layer to the outer periphery of an aluminum cylinder and is rotated by a drive motor. The image forming unit 90 includes an intermediate transfer belt 50, which is rotated in the direction of arrow T1 by a drive roller 52. The intermediate transfer belt 50 is wound around a tension roller 51, a drive roller 52, and a secondary transfer inner roller 53. Primary transfer rollers 55Y, 55M, 55C, and 55Bk are located inside the intermediate transfer belt 50. The secondary transfer outer roller 54 is located outside the intermediate transfer belt 50, opposite the secondary transfer inner roller 53.

[0027] Feeding unit 10a includes a lifting plate 11a that is raised and lowered while sheets S are stacked on it, a pick-up roller 12a that feeds the sheets S stacked on the lifting plate 11a, and a pair of separating rollers 13a that separates the fed sheets S one by one. Similarly, feeding unit 10b includes a lifting plate 11b that is raised and lowered while sheets S are stacked on it, a pick-up roller 12b that feeds the sheets S stacked on the lifting plate 11b, and a pair of separating rollers 13b that separates the fed sheets S one by one.

[0028] The alignment unit 30 includes a pre-alignment roller pair 31 for conveying the sheet S, and an alignment roller pair 32 serving as a first moving unit and a first skew correction unit for correcting sheet skew. The alignment unit 30 also includes an alignment sensor 33 for detecting the position of the sheet S in the conveying direction, and a contact image sensor (CIS) 34 serving as a first detection unit for detecting the position of the sheet S in a width direction intersecting the conveying direction. The fixing unit 100 includes a fixing roller pair 101 capable of heating the sheet S.

[0029] The cooling unit 110 includes an upper cooling belt 111a that rotates in the direction of arrow T2 via an upper cooling drive roller 112a. The cooling unit 110 also includes a lower cooling belt 111b that rotates in the direction of arrow T2 via a lower cooling drive roller 112b, and a heat sink 113 for cooling sheet S.

[0030] Next, the image forming operation to be performed by the image forming apparatus 1 configured as described will be described. An image signal is input from a personal computer outside the image forming apparatus 1 to an exposure device 93, and the exposure device 93 uses a laser corresponding to the image signal to irradiate the photosensitive drum 91 of the processing box 99Y.

[0031] Here, the surface of the photosensitive drum 91 is pre-charged uniformly to a predetermined polarity and potential by a charging roller. An electrostatic latent image is formed on the surface of the photosensitive drum 91 by laser irradiation from the exposure device 93 via a reflector 94. The electrostatic latent image formed on the photosensitive drum 91 is developed by the developing device 92, thereby forming a Y toner image on the photosensitive drum 91.

[0032] Similarly, lasers from exposure devices 96, 97, and 98 irradiate the photosensitive drums of each processing cartridge 99M, 99C, and 99Bk, forming M, C, and K toner images on the processing cartridges 99M, 99C, and 99Bk. The color toner images formed on each photosensitive drum 91 are transferred to the intermediate transfer belt 50 by primary transfer rollers 55Y, 55M, 55C, and 55Bk. The resulting full-color toner image is conveyed via the intermediate transfer belt 50, which is rotated by drive roller 52, to the secondary transfer clamping section N of the secondary transfer inner roller 53 and secondary transfer outer roller 54. Any remaining toner on the photosensitive drum 91 is collected by cleaner 95. The image formation process for each color is performed at a timed interval overlaid on the upstream toner image transferred from the primary transfer to the intermediate transfer belt 50.

[0033] In parallel with the image forming process, sheet S is fed from either of the feeding units 10a and 10b, and is conveyed to the alignment unit 30 via a corresponding of the pulling units 20a and 20b. In the alignment unit 30, the pre-alignment roller pair 31 brings the leading edge of sheet S against the clamping portion of the stationary alignment roller pair 32. This corrects the skewness of sheet S, and sheet S is conveyed to the secondary transfer clamping portion N, which serves as the image forming portion, at a predetermined transfer timing. The full-tone toner image on the intermediate transfer belt 50 is transferred to the first sheet surface (front side) of sheet S by a secondary transfer bias applied to the secondary transfer outer roller 54. Residual toner remaining on the intermediate transfer belt 50 is collected by the belt cleaner 56.

[0034] The toner image is transferred to the sheet S, which is then conveyed to the fixing unit 100 via the predetermined image transfer unit 60. The sheet S is then guided to the clamping portion of the fixing roller pair 101, and predetermined heat and pressure are applied to melt the toner and cause the toner to adhere (fix) thereon. After passing through the fixing unit 100, the sheet S is clamped between the upper cooling belt 111a and the lower cooling belt 111b, which are annular belts, and is conveyed in the cooling unit 110. The heat of the sheet S is transferred to the heat sink 113 via the upper cooling belt 111a, thereby cooling the sheet S.

[0035] The branch conveying unit 120 then selects whether to convey the sheet S to the de-curling unit 170 or the reverse conveying unit 130. The sheet S can be reversed once it is conveyed to the reverse conveying unit 130, so that the first sheet surface on which the image is formed at the secondary transfer clamping part N is facing down, and then it is conveyed to the de-curling unit 170.

[0036] When an image is formed only on one side of the sheet S, the sheet S is conveyed from the branch conveyor unit 120 to the de-curling unit 170, and the sheet S is de-curled using a small-diameter hard roller and a large-diameter soft roller. The sheet S after passing through the de-curling unit 170 is then discharged onto the discharge tray 171.

[0037] When images are formed on both sides of sheet S, sheet S is conveyed by branch conveyor unit 120 to reverse conveyor unit 130, and folded back in reverse conveyor unit 130. The folded sheet S is conveyed from reverse conveyor unit 130 to second double-sided conveyor unit 150 and first double-sided conveyor unit 70, and guided to alignment unit 30. The image is then formed on the second sheet surface (back side) of sheet S at secondary transfer clamping part N, and sheet S is discharged to discharge tray 171 via branch conveyor unit 120 and de-curling unit 170.

[0038] The branch transfer unit 120, the reverse transfer unit 130, the second double-sided transfer unit 150 and the first double-sided transfer unit 70 constitute a retransfer unit 500 that reverses the sheet S on the first side where the image has been formed and transfers the sheet S to the secondary transfer clamping part N again.

[0039] The following description of the image forming apparatus 1 according to this exemplary embodiment will assume, for example, that a center reference sheet transport method is used, in which sheet S is transported such that the center of sheet S in the width direction orthogonal to the transport direction coincides with the center of transport path 65 in the width direction.

[0040] [Alignment Unit]

[0041] like Figure 1 and 2 As shown, the alignment unit 30 is deployed in the transport path 65 connecting the pull-out unit 20a and the secondary transfer clamping part N. The alignment unit 30 includes an alignment roller pair 32, a pre-alignment roller pair 31, an alignment sensor 33, and a CIS 34. The pre-alignment roller pair 31 is located upstream of the alignment roller pair 32 in the transport direction A of the sheet S. The alignment sensor 33 and the CIS 34 are located between the roller pairs 31 and 32.

[0042] like Figure 2As shown, the alignment roller pair 32, which is a pair of rotating components, includes an upper roller 32a serving as a first roller and a lower roller 32b fixed to the rotation shaft 32S serving as a second roller. The input gear 38 is fixed to the rotation shaft 32S and is driven by the alignment drive motor 36 via the idler gear 39.

[0043] The pre-alignment roller pair 31 is driven by the pre-alignment drive motor 35. Each roller in the pre-alignment roller pair 31 and the alignment roller pair 32 rotates about an axis extending in the width direction W.

[0044] The rotating shaft 32S supports the rack 41, allowing the rack 41 to rotate relative to the rotating shaft 32S while preventing axial movement. The rack 41 receives driving force from the shift motor 37 via the pinion 40, causing the rotating shaft 32S to shift axially. The upper roller 32a, together with the lower roller 32b, is axially shifted. With the sheet S held in between, the alignment roller pair 32 moves in the width direction W, orthogonal to the conveying direction A, causing the sheet S to move in the width direction W, thereby correcting the position of the sheet S in the width direction W.

[0045] Compared to the input gear 38, the idler gear 39 has a larger tooth surface width. This is because even if the alignment roller pair 32 and the input gear 38 move in the width direction W, the gears 38 and 39 must be kept engaged with each other and the alignment roller 32 must be able to rotate.

[0046] CIS 34 detects the position of the end of the conveyed sheet S in the width direction W (hereinafter referred to as the end position). Control unit 200 (see...) Figure 3 The deviation between the reference position of the sheet S designed and the end position detected by the CIS 34 is calculated, and the alignment unit 30 is shifted according to the deviation. This makes the position of the sheet S in the width direction W the same as the transfer position in the image forming unit 90, resulting in a high-quality product.

[0047] CIS 34 is positioned offset to one side of the center of the conveyor path 65 in the width direction W. This is because the position of the sheet S can be corrected by detecting the end position of either side of the sheet S. CIS 34 is configured to detect the end positions of the sheet with the smallest width and the sheet with the largest width among the available sheet sizes of the image forming apparatus 1. To prevent a decrease in the detection accuracy of CIS 34, CIS 34 is positioned as close as possible to the alignment roller pair 32.

[0048] The alignment unit 30 corrects the skewness of the sheet S by pressing the leading edge of the conveyed sheet S against the clamping portion of the stationary alignment roller pair 32, causing the sheet S to warp so that the leading edge of the sheet S follows the clamping portion. After the alignment sensor 33 detects the leading edge of the sheet S, the pre-alignment roller pair 31 feeds the sheet S by a predetermined amount. The sheet S is then conveyed by the alignment roller pair 32 to the secondary transfer clamping portion N.

[0049] The gap between CIS 34 and the lower guide 65a opposite to CIS 34 is maintained at a constant distance. To allow the sheet S to warp, the lower guide 65a and the upper guides 65b and 65c form a predetermined space within the conveying path 65. The conveying amount of the pre-aligning roller pair 31 to the sheet S is set to an amount that allows the sheet S to warp appropriately.

[0050] [Control Block]

[0051] Figure 3 This is a control block diagram of the control unit 200 of the image forming apparatus 1. The control unit 200 includes a central processing unit (CPU) 201, a memory 202, an operation unit 203, an image forming control unit 205, a sheet transport control unit 206, a sensor control unit 207, and a shift control unit 208. The CPU 201 executes various types of processing performed by the image forming apparatus 1 by executing predetermined control programs. The memory 202 includes, for example, random access memory (RAM) and read-only memory (ROM), and stores various programs and various types of data in predetermined storage areas. The operation unit 203, serving as an acquisition unit, accepts inputs of various types of information about the sheet (e.g., sheet size, sheet weight, and sheet surface characteristics) and instructions for executing and canceling operations.

[0052] The image forming control unit 205 sends commands to the image forming unit 90, which includes exposure devices 93, 96, 97, and 98, and controls the image forming operation. The sheet transport control unit 206 sends commands to the pre-alignment drive motor 35, alignment drive motor 36, reverse drive motor 136, second pre-alignment drive motor 153, second alignment drive motor 154, etc. The sheet transport operation is thus controlled. The sensor control unit 207 sends detection start and detection end commands to the alignment sensor 33, reverse sensor 138, second alignment sensor 157, etc., and receives detection results from the sensors.

[0053] The shift control unit 208 receives detection results from the CIS 34 and the reverse CIS 139, and issues drive start and drive stop commands to the shift motor 37 and the reverse shift motor 137, thus controlling the movement of the sheet S in the width direction W, i.e., the shift operation. The CPU 201 can be connected to an external computer 204, for example, via a network connection, and can receive various types of information about the sheet and the print job from the computer 204.

[0054] [Alignment unit skew correction and shift operations]

[0055] Next, we will refer to Figure 4 The flowchart shown describes the skew correction operation (first skew correction operation) and shift operation to be performed by the alignment unit 30. In step S101, a print command is first input from the operation unit 203 or the computer 204, and the control unit 200 starts the print job. The user can issue commands from the operation unit 203 or the computer 204 regarding the number of copies to be printed and specify the type of sheet to be used for printing.

[0056] In step S102, the control unit 200 begins feeding the sheet S. In step S103, the control unit 200 determines which side of the sheet to print in the printing job, the first side or the second side. If it is determined that the first side of the sheet should be printed (yes in step S103), then the process proceeds to step S104. In step S104, the control unit 200 controls the image forming unit 90 to form a toner image at a predetermined first-side image writing position g1 on the intermediate transfer belt 50. As used herein, the image writing position g1 has a value based on the result of a writing position adjustment performed at the time of factory shipment and is stored in the memory 202 as a fixed value specific to the device body.

[0057] More specifically, the control unit 200 controls the exposure devices 93, 96, 97, and 98 to form electrostatic latent images on the photosensitive drums of the processing cartridges 99Y, 99M, 99C, and 99Bk at positions corresponding to the image writing position g1. As described above, the electrostatic latent image formed on the photosensitive drum is developed into a toner image by the developing device. The toner image is transferred to the intermediate transfer belt 50 via primary transfer rollers 55Y, 55M, 55C, and 55Bk.

[0058] Simultaneously, sheet S is conveyed until it reaches the pre-alignment roller pair 31. Assuming... Figure 5A As shown, the sheet S being conveyed here is rotated clockwise and tilted relative to the conveying direction A, and deviates to the left of the conveying direction A. Figures 5A to 5DThe dotted rectangle shown schematically indicates the state in which the leading edge of the sheet S, being conveyed without skew or lateral deviation, is close to the clamping portion of the alignment roller pair 32. Here, the end position of the sheet S in the width direction W is taken as the zero point, and the left side will be referred to as positive.

[0059] In step S105, alignment sensor 33 detects the leading edge of sheet S. In step S106, control unit 200, based on the detection result of alignment sensor 33, feeds sheet S by a set amount using pre-alignment roller pair 31. Sheet S is thus brought close to the stationary alignment roller pair 32, as... Figure 5B As shown, and warped by a predetermined amount. The skewness of sheet S is thus corrected. In step S107, sheet S is held and conveyed by alignment rollers 32 that are initially driven to rotate, as shown. Figure 5C As shown in the diagram, regardless of the length of the sheet S in the transport direction A, skew correction of the sheet S is performed using the alignment sensor 33.

[0060] In step S108, the CIS 34 detects the end position of the skew-corrected sheet S. The control unit 200 calculates the displacement of the sheet S based on the detection result (L1). Here, the displacement can be determined by subtracting the image writing position (g1) (L1-g1) from the detection result (L1) performed by the CIS 34.

[0061] In step S109, the control unit 200 moves the alignment roller pair 32 holding the sheet S by a displacement amount (L1-g1) in the width direction W via the shift control unit 208 and the shift motor 37. The sheet S can thus be moved by the displacement amount (L1-g1) in the width direction W. Therefore, the position of the sheet S in the width direction W is corrected to correspond to the image writing position g1. Regardless of the length of the sheet S in the transport direction A, the displacement of the sheet S in the width direction using the alignment sensor 33 is performed.

[0062] In step S110, at the secondary transfer clamping part N, the toner image on the intermediate transfer belt 50 is transferred to the sheet S, which is shifted by the alignment roller pair 32 by the same amount (L1-g1). In step S111, the toner image is melted and fixed by the fixing unit 100.

[0063] In step S112, if the print job is a single-sided print job, the sheet S with the toner image fixed is discharged into the discharge tray 171. If the print job is a double-sided print job, the sheet S undergoes a reversal process for image formation on the second side. In step S113, the control unit 200 determines whether there is a subsequent sheet. If the control unit 200 determines that there is no subsequent sheet ("No" in step S113), the process proceeds to step S114. In step S114, the control unit 200 ends the print job. If the control unit 200 determines that there is a subsequent sheet ("Yes" in step S113), the process proceeds to step S115. In step S115, the control unit 200 restores the alignment roller pair 32 to its original position (center position). The process then returns to step S103.

[0064] In step S103, if the control unit 200 determines that a second side needs to be printed in the printing job (No in step S103), the process proceeds to step S116. In step S116, the control unit 200 controls the image forming unit 90 to form a toner image at the second side image writing position g2. The second side image writing position g2 may be the same as or different from the first side image writing position g1 in the width direction W. The skew correction operation of the alignment roller pair 32 on the sheet on which the image is to be formed on the second side is similar to the skew correction operation to be performed on the sheet on which the image is to be formed on the first side. Therefore, its description will be omitted (steps S117 to S119).

[0065] In step S120, the CIS 34 detects the end position of the second surface of the skew-corrected sheet S. The control unit 200 calculates the displacement of the sheet S based on the detection result (L2). This displacement can be determined by subtracting the image writing position (g2) (L2-g2) from the detection result (L2) performed by the CIS 34.

[0066] In step S121, the control unit 200 moves the alignment roller pair 32 holding the sheet S by a displacement amount (L2-g2) in the width direction W via the shift control unit 208 and the shift motor 37, which constitutes another moving unit. The sheet S can thus be moved by the displacement amount (L2-g2) in the width direction W. For example, if the second side image writing position g2 = the first side image writing position g1 = 0, then the sheet S, shifted by the displacement amount L2, reaches the same position as before the image on the first side was formed. This makes the positions of the images formed on the first and second sides the same. Moreover, the image is formed at the center of the sheet S. Therefore, a high-quality product can be obtained.

[0067] In step S122, at the secondary transfer clamping section N, the toner image on the intermediate transfer belt 50 is transferred to the sheet S, which is shifted by the alignment roller pair 32 by the same amount (L2-g2). In step S111, similar to the processing of the first side, the toner image is melted and fixed by the fixing unit 100. In step S112, the sheet S with the toner image fixed is discharged into the discharge tray 171.

[0068] Printing the second side involves a long-distance transport after the skew and lateral deviation of the first side have been corrected by the alignment unit 30. Due to variations in the unit's components, the skew and lateral deviation of the second side are often greater than those in the first side printing. This increases the displacement of the alignment roller pair 32. When the alignment roller pair 32 is displaced, the sheet S slides on the transport guide with high resistance. The resistance is particularly high for large sheets S because the sheet S is held by other rollers. If the displacement is large, then due to the resistance, displacing the alignment roller pair 32 can cause the sheet S to skew, cause the displacement of the sheet S to be smaller than desired, and / or cause the sheet S to wrinkle.

[0069] Furthermore, if the displacement is large, it takes longer to shift the alignment roller pair 32 and to restore the alignment roller pair 32 to its original position (center position) after the sheet S exits the alignment roller pair 32. This hinders productivity. To reduce such problems, in this exemplary embodiment, the reverse conveying unit 130 also performs a shifting operation (lateral alignment shift) on the sheet S.

[0070] [Reverse Teleportation Unit]

[0071] Next, the configuration of the inverted transmission unit 130 will be described. For example... Figure 6 As shown, the reverse conveying unit 130, which serves as a reverse unit, includes a conveying roller pair 131, a reverse shifting unit 132 serving as a second moving unit, a reverse sensor 138, a reverse CIS 139 serving as a second detection unit, and a switching member 143. The reverse shifting unit 132 includes a first reverse shifting roller pair 132a and a second reverse shifting roller pair 132b serving as reverse rollers. The reverse sensor 138 and the reverse CIS 139 are located between the conveying roller pair 131 and the first reverse shifting roller pair 132a.

[0072] The conveyor roller pair 131 is driven by a reverse drive motor 136 via belt 136a. The rotation of the conveyor roller pair 131 is transmitted to the idler gear 135 via belt 136b. An input gear 134 is fixed to the rotation shaft 132S of the first reverse shifting roller pair 132a. The input gear 134 is driven by the idler gear 135. The first reverse shifting roller pair 132a and the second reverse shifting roller pair 132b are connected via belt 136c and configured to move together. Each roller in the first reverse shifting roller pair 132a and the second reverse shifting roller pair 132b rotates about an axis extending in the width direction W. For example, the first reverse shifting roller pair 132a includes a third roller and a fourth roller, each rotating about an axis extending in the width direction W. The third and fourth rollers move in the width direction W while the sheet S is held therebetween.

[0073] The rotating shaft 132S supports the rack 141, allowing the rack 141 to rotate relative to the rotating shaft 132S while maintaining axial immobility. The rack 141 receives driving force from the reverse transfer motor 137, which serves as the moving unit, via a pinion 140, causing the rotating shaft 132S to shift axially. With the sheet S held in between, the first reverse transfer roller pair 132a and the second reverse transfer roller pair 132b are moved in the width direction W, causing the sheet S to move in the width direction W and thus correcting its position. In this way, the shifting operation of the reverse transfer unit 130 is achieved.

[0074] Compared to the input gear 134, the idler gear 135 has a larger tooth surface width. This is because even if the first reverse shifting roller pair 132a and the input gear 134 move in the width direction W, the gears 134 and 135 must be kept meshed with each other so that the reverse shifting unit 132 can rotate.

[0075] The reverse CIS 139 is positioned to one side of the center of the reverse conveying path 165 in the width direction W, and detects the end position of the conveyed sheet S in the width direction W.

[0076] The reason is that the position of sheet S can be corrected by detecting the end position on either side of sheet S. In order to prevent a decrease in the detection accuracy of the reverse CIS 139, the reverse CIS 139 is positioned as close as possible to the first reverse transfer roller pair 132a.

[0077] [Reverse the shift operation of the transfer unit]

[0078] Next, we will refer to Figure 7 The flowchart shown illustrates the shifting operation of the reversing transfer unit 130. If the print job is a double-sided print job, the sheet with the image formed on the first side is transferred from the branch transfer unit 120 to the reversing transfer unit 130. Figure 8AAs shown, the switching member 143 of the inverted transmission unit 130 is offset in position by the biasing member.

[0079] The sheet S conveyed from the branch conveying unit 120 is conveyed to the conveying roller pair 131 and further conveyed while the biasing force of the biasing member presses against the switching member 143. In step S210, the control unit 200 determines the length of the sheet S in the conveying direction A based on information input to and obtained by the operation unit 203. More specifically, in step S210, the control unit 200 determines whether the length of the sheet S input to the operation unit 203 in the conveying direction A is greater than or equal to a predetermined length S. If it is determined that the length of the sheet S is not greater than or equal to the length S ("No" in step S210), then the process proceeds to step S201. In step S201, the reversing sensor 138 detects the position of the sheet S in the conveying direction A. In step S202, the reversing CIS 139 detects the end position of the sheet S. The control unit 200 calculates the displacement of the sheet S based on the detection result (L3) and the deviation amount g3. The deviation amount g3 refers to the amount by which the sheet S deviates in the width direction W when it is transferred from the inverted transfer unit 130 to the alignment unit 30. The deviation amount g3 is obtained in advance during the installation of the image forming apparatus 1 or at other timings. The amount of displacement of the sheet S can be determined by subtracting the deviation amount g3 (L3-g3) from the result (L3) of the detection performed by the inverted CIS 139.

[0080] In step S203, based on the detection result of the reversal sensor 138, the control unit 200 stops driving the reversal drive motor 136 to stop the sheet S when the trailing edge of the sheet S is a predetermined distance in front of the switching member 143. Figure 8B As shown in the image.

[0081] In step S204, after the sheet S stops, the control unit 200 moves the anti-transfer unit 132 holding the sheet S by a displacement amount (L3-g3) in the width direction W via the shift control unit 208 and the anti-transfer motor 137. This allows the sheet S to be shifted by a displacement amount (L3-g3) in the width direction W.

[0082] In step S205, the control unit 200 rotates the reverse drive motor 136 in the opposite direction in parallel with the aforementioned shifting operation. The sheet S is thus folded back through the first reverse shifting roller pair 132a and the second reverse shifting roller pair 132b of the reverse shifting unit 132. In other words, the sheet S is conveyed in the first direction A1 (see...). Figure 8A ), and then it is transmitted in the second direction A2, which is opposite to the first direction A1 (see Figure 8C ).

[0083] During the folding operation, the sheet S slides on and is guided by the reversing guide 142, which serves as a guiding member. Here, the second side of the sheet S, opposite to the first side forming the image, slides in contact with the reversing guide 142. There are no guiding members deployed opposite to the reversing guide 142, and the first side of the sheet S guided by the reversing guide 142 is not guided by any other guiding members. Figure 8C As shown, sheet S is guided to the second double-sided transfer unit 150 via switching member 143, and image formation is performed on the second side.

[0084] In step S206, the control unit 200 determines whether there is a subsequent sheet. If the control unit 200 determines that there is no subsequent sheet ("No" in step S206), the shifting operation of the reverse transfer unit 130 ends. If the control unit 200 determines that there is a subsequent sheet ("Yes" in step S206), the process proceeds to step S207. In step S207, the control unit 200 restores the reverse transfer unit 132 to its original position (center position). The process then returns to step S201.

[0085] In step S210, if the control unit 200 determines that the length of the sheet S in the conveying direction A is greater than or equal to a predetermined length S ("Yes" in step S210), then the process proceeds to step S211. In step S211, the reversing sensor 138 detects the sheet S. In step S212, the control unit 200 stops driving the reversing drive motor 136 based on the detection of the sheet S. In step S213, the control unit 200 rotates the reversing drive motor 136 in the reverse direction. The process proceeds to step S206. In other words, if the control unit 200 determines that the length of the sheet S is greater than or equal to the predetermined length S, then the shifting operation of the reversing conveying unit 130 is not performed.

[0086] In this exemplary embodiment, step S205 is performed after step S204. However, steps S204 and S205 may be performed in reverse order or simultaneously.

[0087] [Second Double-Sided Conveying Unit]

[0088] Next, the configuration of the second double-sided transmission unit 150 will be described. For example... Figure 9 As shown, the second double-sided conveying unit 150, which serves as a double-sided conveying unit, includes a second alignment roller pair 152, a second pre-alignment roller pair 151, and a second alignment sensor 157, which serve as a skew correction unit. The second pre-alignment roller pair 151 is located upstream of the second alignment roller pair 152 in the conveying direction A of the sheet S. The second alignment sensor 157 is located between the roller pairs 151 and 152.

[0089] The second alignment roller pair 152, which is a pair of rotating components, includes 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. The input gear 156 is driven by a second alignment drive motor 154 via an idler gear 155. The second pre-alignment roller pair 151 is driven by a second pre-alignment drive motor 153.

[0090] A second double-sided conveying unit 150 is deployed in housing 1B and corrects the skewness of sheet S before it is discharged from housing 1B to housing 1A. The second double-sided conveying unit 150 performs a skew correction operation on sheet S without performing a shifting operation.

[0091] [Tilting correction operation of the second double-sided conveyor unit]

[0092] Next, we will refer to Figure 10 The flowchart shown describes the skew correction operation (second skew correction operation) to be performed by the second duplex conveyor unit 150. If the printing job is a duplex printing job, the sheet S on which the image has been formed on the first side undergoes the displacement operation of the reversing conveyor unit 130 as described above. In step S301, the second alignment sensor 157 then detects the position of the sheet S conveyed from the reversing conveyor unit 130 to the duplex conveyor unit 150 in the conveying direction A.

[0093] In step S302, the control unit 200 feeds the sheet S by a set amount using the second pre-alignment roller pair 151 based on the detection result of the second alignment sensor 157. Therefore, the sheet S is pressed against the stationary second alignment roller pair 152 and warps by a predetermined amount. Thus, the skewness of the sheet S is corrected. In step S303, the sheet S is clamped and conveyed by the second alignment roller pair 152, which is now driven to rotate. Regardless of the length of the sheet S in the conveying direction A, skewness correction of the sheet S using the second alignment roller pair 152 is performed.

[0094] In step S304, the control unit 200 determines whether there is a subsequent sheet. If the control unit 200 determines that there is no subsequent sheet ("No" in step S304), then the skew correction operation of the second double-sided conveying unit 150 ends. If the control unit 200 determines that there is a subsequent sheet ("Yes" in step S304), then the process returns to step S301.

[0095] As described above, in this exemplary embodiment, the duplex printing operation involves a shifting operation at two locations—the inverted transfer unit 130 and the alignment unit 30—after an image is formed on the first side of the sheet S. The amount of shifting of the sheet S can therefore be distributed between the shifting operations at the two locations. During the shifting operation performed by the inverted transfer unit 130, the sheet S is not held by any rollers other than those of the inverted transfer unit 132 that performs the shifting operation. In other words, regardless of the size of the sheet S, the shifting operation can be performed stably without resistance from the sheet S being held by rollers other than those of the inverted transfer unit 132.

[0096] If the length of sheet S in the transport direction A is less than a predetermined length S (e.g., a first length), then sheet S is shifted by the reverse transport unit 130. On the other hand, if the length of sheet S in the transport direction A is greater than or equal to the predetermined length S (e.g., a second length greater than the first length), then the shifting operation of sheet S by the reverse transport unit 130 is not performed. This prevents the following problems caused by the shifting of long sheets from occurring. Figure 14A The illustration shows a first sheet of a first length being obliquely conveyed in the conveying direction H. Figure 14B The illustration shows a second length that is greater than the first length, and is skewed and Figure 14A The state in which a second sheet with the same angle as the first sheet is conveyed in the conveying direction H. The positional deviation in the width direction between the corner of one end of the second sheet in the conveying direction H and the corner of the other end of the second sheet in the conveying direction H is called the deviation Z2. The deviation Z2 is greater than the positional deviation in the width direction between the corner of one end of the first sheet in the conveying direction H and the corner of the other end of the first sheet in the conveying direction H. If the second sheet is shifted in the width direction while being held near one end (leading edge side) by the reversing conveying unit 130, the corner of the other end (rear edge side) of the second sheet may deviate significantly from its normal position in the width direction. This can cause the side edges of the second sheet, including the corner at the rear edge, to come into contact with other components of the image forming unit 90 (components that the sheet should not contact) and be damaged. In this exemplary embodiment, if the length of the sheet S is greater than or equal to a predetermined length S (e.g., a second length greater than the first length), then the shifting operation of the sheet S by the reversing conveying unit 130 is therefore not performed. This exemplary embodiment thus avoids the aforementioned problem. In this exemplary embodiment, the skewness of the sheet S, even with a length greater than the predetermined length S, is corrected by the second alignment roller pair 152 and by the alignment roller pair 32. The long sheet passing through the re-conveying unit 500 can therefore be shifted in the width direction W using the alignment roller pair 32.

[0097] Furthermore, the sheet S to be folded back by the anti-transfer unit 132 is guided by the reversing guide 142 on the second side where no image has yet been formed. Since there is no guide member provided opposite to the reversing guide 142, the first side of the sheet S, which is the image surface, is not guided by any guide member. The image surface where the image has been formed has high frictional resistance. By using the reversing guide 142 to guide only the second side, which is not the image surface, the sliding resistance between the sheet S and the reversing guide 142 can be reduced. This also reduces the resistance in the shifting operation performed by the anti-transfer unit 132.

[0098] Furthermore, the anti-shifting unit 132 simultaneously shifts the first anti-shifting roller pair 132a and the second anti-shifting roller pair 132b in the width direction W. Performing the shifting operation while the sheet S is held by these two roller pairs reduces skewing caused by slippage between the sheet S and the rollers during the shifting operation, and enables a stable shifting operation. Skewness and lateral deviation of the sheet S can therefore be reduced to obtain a high-quality product. In particular, in this exemplary embodiment, skewness and lateral deviation of the first sheet S during operation can be reduced when an image is formed on the second surface of the sheet S. Compared to an apparatus that corrects the position of the subsequent sheet based on the position of the preceding sheet, the image forming apparatus 1 according to this exemplary embodiment can therefore provide a high-quality product earlier.

[0099] The small displacement of the reverse conveyor unit 130 and the alignment unit 30 reduces the time required to restore the roller pairs to their original positions after the shifting operation, thus improving productivity.

[0100] Alignment unit 30 is deployed in housing 1A, and reverse transfer unit 130 is deployed in housing 1B. Since the shifting operation is performed in each individual housing, lateral deviation can be corrected within each housing. Because the sheet S is transferred to another housing after lateral deviation correction in each housing, the amount of sheet S shifted in each housing can be reduced. This reduces the length of the guide member forming the transfer path in the width direction W, enabling cost reduction and space savings.

[0101] Furthermore, in this exemplary embodiment, the duplex printing operation involves performing skew correction operations at two locations—the duplex transfer unit 150 and the alignment unit 30—after an image is formed on the first side of the sheet S. The amount of skew correction for the sheet S can therefore be distributed between the skew correction operations at the two locations, thereby reducing the amount of skew correction at each location. Since the skew correction operation causes the sheet S to warp, if the skew correction amount is large, the sheet S can deform and wrinkle. In this exemplary embodiment, since the skew correction amount can be reduced, wrinkling of the sheet S can be prevented.

[0102] Alignment unit 30 is deployed in housing 1A, and double-sided transfer unit 150 is deployed in housing 1B. Since the skew correction operation is performed in each individual housing, skew can be corrected within each housing. Because the sheet S is transferred to another housing after skew correction in each housing, the amount of skew correction for the sheet S in each housing can be reduced. The desired skew correction performance for each housing can therefore be defined, and a skew correction mechanism capable of performing skew correction in an appropriate amount without over- or under-correction can be selected.

[0103] Next, a second exemplary embodiment of the present invention will be described. In the second exemplary embodiment, the inverted transfer unit 130 does not perform a shifting operation, and the second double-sided transfer unit 180 performs a skew correction operation and a shifting operation. Components similar to those in the first exemplary embodiment will be omitted from the drawings or will be illustrated and described using the same reference numerals.

[0104] [Second Double-Sided Conveying Unit]

[0105] First, the configuration of the double-sided transmission unit 180 according to the second exemplary embodiment will be described.

[0106] like Figure 11 As shown, the second double-sided conveying unit 180 includes a second alignment roller pair 182 serving as a second moving unit and a second skew correction unit, and a second pre-alignment roller pair 181. The second double-sided conveying unit 180 also includes a second alignment sensor 187 and a second CIS unit 188. The second pre-alignment roller pair 181 is located upstream of the second alignment roller pair 182 in the conveying direction A of the sheet S. The second alignment sensor 187 and the second CIS unit 188 are located between the roller pairs 181 and 182.

[0107] The second alignment roller pair 182, as a pair of rotating components, includes an upper roller 182a serving as a third roller and a lower roller 182b fixed to a rotating shaft 182S serving as a fourth roller. An input gear 186 is fixed to the rotating shaft 182S. The input gear 186 is driven by a second alignment drive motor 184 via an idler gear 185. The second pre-alignment roller pair 181 is driven by a second pre-alignment drive motor 183. Each roller in the second pre-alignment roller pair 181 and the second alignment roller pair 182 rotates about an axis extending in the width direction W.

[0108] The rotating shaft 182S supports the rack 191, allowing the rack 191 to rotate relative to the rotating shaft 182S while maintaining axial immobility. The rack 191 receives driving force from the second shift motor 189 via a pinion 190, causing the rotating shaft 182S to shift axially. The upper roller 182a, along with the lower roller 182b, is axially shifted. With the sheet S held in between, the second alignment roller pair 182 moves in the width direction W, causing the sheet S to move in the width direction W, thus correcting the position of the sheet S in the width direction W.

[0109] Compared to the input gear 186, the idler gear 185 has a larger tooth surface width. This is because even if the second alignment roller pair 182 and the input gear 186 move in the width direction W, gears 185 and 186 must be kept meshed with each other to allow the second alignment roller pair 182 to rotate.

[0110] With CIS 34 (see Figure 2 Similarly, the second CIS 188, which serves as the second detection unit, is positioned biased towards the center of the conveying path in the width direction W. To prevent a decrease in the detection accuracy of the second CIS 188, the second CIS 188 is positioned as close as possible to the second alignment roller pair 182.

[0111] [Control Block]

[0112] Figure 12 This is a control block diagram illustrating the control unit 200 of the image forming apparatus 1 according to a second exemplary embodiment. The sheet transport control unit 206 issues commands to the pre-alignment drive motor 35, the alignment drive motor 36, the reverse drive motor 136, the second pre-alignment drive motor 183, and the second alignment drive motor 184. Therefore, the transport operation of the sheet S is controlled. The sensor control unit 207 issues detection start and detection end commands to the alignment sensor 33 and the second alignment sensor 187, and receives detection results from the sensors 33 and 187.

[0113] The shift control unit 208 receives the detection results from the CIS 34 and the second CIS 188, sends drive start and drive end commands to the shift motor 37 and the second shift motor 189, and controls the movement of the sheet S in the width direction W, i.e., the shift operation.

[0114] [Skewing correction and shifting operations of the second double-sided conveying unit]

[0115] Next, we will refer to Figure 13The flowchart shown describes the skew correction operation (second skew correction operation) and shifting operation of the second duplex conveying unit 180. If the printing job is a duplex printing job, the sheet S with the image formed on the first side is folded back in the reversing conveying unit 130. In this exemplary embodiment, the reversing conveying unit 130 does not perform a shifting operation. The sheet S is then conveyed from the reversing conveying unit 130 to the duplex conveying unit 180. In step S401, the second alignment sensor 187 detects the position of the sheet S in the conveying direction A.

[0116] In step S402, the control unit 200 feeds the sheet S by a set amount using the second pre-alignment roller pair 181 based on the detection result of the second alignment sensor 187. Therefore, the sheet S is pressed against the stationary second alignment roller pair 182 and warps by a predetermined amount. The skewness of the sheet S is thus corrected. In step S403, the sheet S is clamped and conveyed by the second alignment roller pair 182, which begins to rotate.

[0117] In step S410, the control unit 200 determines whether the length of the sheet S input to the operation unit 203 in the transport direction A is greater than or equal to a predetermined length S. If it is determined that the length of the sheet S is not greater than or equal to the length S ("No" in step S410), then the process proceeds to step S404. In step S404, the second CIS 188 detects the end position of the sheet S. The control unit 200 calculates the displacement of the sheet S based on the detection result (L4) and the deviation amount g4. The deviation amount g4 refers to the amount by which the sheet S deviates in the width direction W when it is transported from the second double-sided transport unit 180 to the alignment unit 30. The deviation amount g4 is obtained in advance during the installation of the image forming apparatus 1 or other timing. The displacement of the sheet S can be determined by subtracting the deviation amount g4 (L4-g4) from the detection result (L4) performed by the second CIS 188.

[0118] In step S405, the control unit 200 moves the second alignment roller pair 182 holding the sheet S by a displacement amount (L4-g4) in the width direction W via the displacement control unit 208 and the second displacement motor 189, which serves as a moving unit. The sheet S can thus be displaced by a displacement amount (L4-g4) in the width direction W.

[0119] In step S406, the control unit 200 determines whether there is a subsequent sheet. If the control unit 200 determines that there is no subsequent sheet ("No" in step S406), then the skew correction and shifting operations of the second double-sided conveying unit 180 end. If the control unit 200 determines that there is a subsequent sheet ("Yes" in step S406), then the process proceeds to step S407. In step S407, the control unit 200 restores the second alignment roller pair 182 to its original position (center position). The process then returns to step S401.

[0120] In step S410, if the control unit 200 determines that the length of the sheet S is greater than or equal to the predetermined length S ("Yes" in step S410), then the process proceeds to step S406. In other words, if the control unit 200 determines that the length of the sheet S is greater than or equal to the predetermined length S, then the second double-sided conveying unit 180 does not perform the shifting operation.

[0121] As described above, in this exemplary embodiment, the duplex printing operation involves performing skew correction and shifting operations at each of the two locations—the second duplex transfer unit 180 and the alignment unit 30—after the image is formed on the first side of the sheet S. Effects similar to those of the first exemplary embodiment can therefore be obtained.

[0122] The second double-sided conveying unit 180 is located near the outlet from housing 1B to housing 1A. Therefore, the amount of skewness of the sheet S discharged from housing 1B and the position of the sheet S in the width direction W can be defined more precisely than in the first exemplary embodiment.

[0123] <Other exemplary embodiments>

[0124] In the first exemplary embodiment, the reversing transfer unit 130 performs a shift operation, and the second double-sided transfer unit 150 performs a skew correction operation. In the second exemplary embodiment, the second double-sided transfer unit 180 performs both the shift operation and the skew correction operation. However, this is not limiting. More specifically, at least one of the shift operation and the skew correction operation can be performed in the retransfer unit 500. Which unit performs the shift operation and the skew correction operation is not limiting. For example, the reversing transfer unit 130 can perform both the skew correction operation and the shift operation. The first double-sided transfer unit 70 can perform only the shift operation.

[0125] In the aforementioned exemplary embodiments, as a mode for limiting the displacement of sheet S in the sheet width direction W by the reversing conveying unit 130 and the second double-sided conveying unit 150 of sheet S when the sheet length is greater than or equal to the length S, sheet S is described as not being shifted at all. However, if the sheet length is greater than or equal to the length S, the amount by which the reversing conveying unit 130 and the second double-sided conveying unit 150 shift sheet S can be limited to a predetermined setting amount. More specifically, if the sheet length is less than the length S, sheet S can be shifted beyond the predetermined setting amount based on the detection result performed by the CIS, without limiting the amount of sheet S shifted. On the other hand, if the sheet length is greater than or equal to the length S, the amount of sheet S shifted is limited to not exceeding the predetermined setting amount.

[0126] In the aforementioned exemplary embodiment, even if the length of the sheet S in the conveying direction A is greater than or equal to the predetermined length S, the sheet S is still shifted in the sheet width direction W using the alignment roller pair 32. However, if the length of the sheet S input to the operation unit 203 in the conveying direction A is greater than or equal to the predetermined length S, then the shift of the sheet S in the sheet width direction W using the alignment roller pair 32 can be limited.

[0127] Examples of other problems caused by the movement of a long sheet in the width direction W include skewing of the long sheet due to displacement in the width direction W. The contact area between the long sheet and the conveyor guide is larger than the contact area between the short sheet and the conveyor guide. Therefore, a long sheet moving in the width direction W may skew due to the high frictional resistance with the conveyor guide.

[0128] In a first exemplary embodiment, both the first anti-transfer roller pair 132a and the second anti-transfer roller pair 132b of the anti-transfer positioning unit 132 are movable in the width direction W. However, this is not limiting. For example, either the first anti-transfer roller pair 132a or the second anti-transfer roller pair 132b may be movable in the width direction W. The second anti-transfer roller pair 132b may be omitted, and the first anti-transfer roller pair 132a may individually clamp the sheet S and move in the width direction W.

[0129] A charge-coupled device (CCD) sensor or a complementary metal-oxide-semiconductor (CMOS) sensor can be used instead of CIS 34, inverted CIS 139, and the second CIS 188. If the position of the sheet S in the width direction W can be detected using such a sensor, then it is not necessary to detect the end position of the sheet S in the width direction W.

[0130] Instead of correcting the skewness of sheet S by bringing it close to alignment roller pair 32 or second alignment roller pair 182, a method for bringing sheet S close to a baffle member located upstream of the roller pair in the conveying direction A can be applied.

[0131] Although all the foregoing exemplary embodiments have been described using the electrophotographic image forming apparatus 1, the present invention is not limited thereto. For example, exemplary embodiments of the present invention can be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink droplets from a nozzle.

[0132] Exemplary embodiments of the present invention can also be implemented by processing for supplying a program for implementing one or more functions of the foregoing exemplary embodiments to a system or device via a network or storage medium, and for reading and executing the program by one or more processors in a computer of the system or device. Circuitry (such as application-specific integrated circuits (ASICs)) for implementing one or more functions can also be used for implementation.

[0133] While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims is to be given the broadest interpretation in order to cover all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: An image forming unit configured to form an image on a sheet; A reversing roller pair, configured to hold the sheet from which the image forming unit forms an image and rotate it in a first direction, and then rotate it in a second direction to reverse and convey the sheet, the second direction being opposite to the first direction; A moving unit is configured to move the reverse roller pair in the width direction of the sheet while the sheet is held by the reverse roller pair, the width direction being orthogonal to the conveying direction of the sheet; A receiving unit configured to obtain information about the length of the sheet in the conveying direction; as well as A control unit, configured to control the moving unit based on information about the length of the sheet obtained by the obtaining unit. Specifically, when the first sheet is reversed and conveyed, the control unit controls the moving unit to move the reverse roller pair conveying the first sheet by a first movement amount in the width direction, and In the case where the second sheet is reversed and conveyed, the control unit controls the moving unit to move the reverse roller pair conveying the second sheet by a second movement amount less than the first movement amount in the width direction, the length of the first sheet in the conveying direction is a first length, and the length of the second sheet in the conveying direction is a second length greater than the first length.

2. The image forming apparatus according to claim 1, wherein when the second sheet is reversed and conveyed, the control unit controls the moving unit such that the moving unit does not move the reverse roller pair conveying the second sheet in the width direction.

3. The image forming apparatus according to claim 1, further comprising a skew correction unit configured to correct skew of the sheet after the sheet has been conveyed by the reverse roller pair. After the skewness of the sheet is corrected by the skewness correction unit, the sheet is conveyed toward the image forming unit.

4. The image forming apparatus according to claim 1, further comprising: A skew correction unit is configured to correct the skew of a sheet whose conveying direction has been reversed by the reverse roller; as well as Another moving unit is configured to move the sheet whose skewness has been corrected by the skewness correction unit in the width direction. Wherein, when the first sheet is conveyed, after the image forming unit forms a first image on the first surface of the first sheet and before the image forming unit forms a second image on the second surface of the first sheet, the following operations are performed sequentially: the control unit controls the moving unit to move the reverse roller pair conveying the first sheet in the width direction; the skew correction unit corrects the skew of the first sheet; and controls the other moving unit to move the first sheet in the width direction. When the second sheet is being conveyed, after the image forming unit forms a first image on the first surface of the second sheet and before the image forming unit forms a second image on the second surface of the second sheet, the following operations are performed in sequence: the skew correction unit corrects the skew of the second sheet, and the other moving unit moves the second sheet in the width direction.

5. The image forming apparatus according to any one of claims 1 to 4, further comprising a detection unit configured to detect the position of the sheet conveyed by the reversing rollers in the width direction. The control unit is configured to control the moving unit to move the reverse roller pair in the width direction based on the position of the sheet detected by the detection unit in the width direction.

6. An image forming apparatus, comprising: An image forming unit configured to form an image on a sheet; A first moving unit is located upstream of the image forming unit in the sheet conveying direction and is configured to move the sheet in the width direction while clamping the sheet, the width direction being orthogonal to the conveying direction. A retransfer unit is configured to reverse the sheet on which the image forming unit has formed an image on the first surface and transfer the sheet to the image forming unit again, wherein the retransfer unit includes a second moving unit configured to move the sheet in the width direction by moving it while clamping the sheet. A receiving unit, configured to obtain information about the length of the sheet in the conveying direction; and The control unit is configured to control the second moving unit based on information about the length of the sheet obtained by the obtaining unit. Wherein, when the first sheet is conveyed, the control unit controls the second moving unit to move the first sheet in the width direction, and When the second sheet is being conveyed, the control unit controls the second moving unit not to move the second sheet in the width direction, the length of the first sheet is a first length, and the length of the second sheet is a second length greater than the first length.

7. The image forming apparatus according to claim 6, wherein the control unit is configured to control the first moving unit and the second moving unit such that, when the first sheet is conveyed, the first moving unit moves the first sheet in the width direction and the second moving unit moves the first sheet in the width direction, and when the second sheet is conveyed, the first moving unit moves the second sheet in the width direction and the second moving unit does not move the second sheet in the width direction.

8. The image forming apparatus according to claim 6, The retransfer unit includes a reversing unit and a double-sided transfer unit. The reversing unit is configured to transfer the sheet in a first direction and then in a second direction, opposite to the first direction. The double-sided transfer unit is configured to transfer the sheet transferred by the reversing unit toward the image forming unit. The second moving unit is included in the reversing unit.

9. The image forming apparatus according to claim 6, further comprising: A first detection unit is configured to detect the position of the sheet in the width direction; as well as A second detection unit is configured to detect the position of the sheet in the width direction. The first moving unit is configured to move the sheet in the width direction based on the detection result performed by the first detection unit, and The second moving unit is configured to move the sheet in the width direction based on the result of detection performed by the second detection unit.

10. The image forming apparatus according to any one of claims 6-9, The retransfer unit is configured to perform a skew correction operation to correct the skewness of the sheet by passing it close to the leading edge of the sheet, and When the sheet has the first length or the second length, the retransfer unit performs the skew correction operation.

11. An image forming apparatus, comprising: An image forming unit configured to form an image on a sheet; A reversing roller pair, configured to hold the sheet from which the image forming unit forms an image and rotate it in a first direction, and then rotate it in a second direction to reverse and convey the sheet, the second direction being opposite to the first direction; A moving unit is configured to move the reverse roller pair in the width direction of the sheet while the sheet is held by the reverse roller pair, the width direction being orthogonal to the conveying direction of the sheet; A receiving unit configured to obtain information about the length of the sheet in the conveying direction; as well as A control unit, configured to control the moving unit based on information about the length of the sheet obtained by the obtaining unit. Wherein, when the first sheet is reversed and conveyed, the control unit controls the moving unit to move the reverse roller pair conveying the first sheet in the width direction, and In the case where the second sheet is reversed and conveyed, the control unit controls the moving unit to restrict the movement of the reverse roller pair conveying the second sheet in the width direction, the length of the first sheet in the conveying direction is a first length, and the length of the second sheet in the conveying direction is a second length greater than the first length.

12. The image forming apparatus according to claim 11, wherein when the second sheet is reversed and conveyed, the control unit controls the moving unit so that the moving unit does not move the reverse roller pair conveying the second sheet in the width direction.

13. The image forming apparatus according to claim 11 or 12, in, When the second sheet is reversed and conveyed, the control unit controls the movement of the moving unit in the width direction relative to the reversing roller pair conveying the second sheet to a predetermined amount. The control unit is configured to control, when the first sheet is reversed and conveyed, that the moving unit moves the reverse roller pair conveying the first sheet in the width direction by more than the predetermined amount.

Images