Sheet processing device and image forming system

Abstract

To allow a deviation amount of sheets in the conveyance direction to be controlled when forming a sheet bundle by stacking a plurality of sheets conveyed to a loading part, so as to improve the productivity of a sheet processing device while maintaining the accuracy of sheet alignment processing.SOLUTION: In a post-processing device (sheet processing device), at a buffer part provided in a conveyance passage for conveying a sheet to a loading part, a sheet bundle is formed in which sheets conveyed in the conveyance passage are stacked by deviating the positions to the upstream side in the sheet conveyance direction sequentially, and the sheet bundle is conveyed to the loading part from the buffer part. The post-processing device performs alignment processing for aligning the positions of the sheets in the sheet conveyance direction with respect to the sheet bundle loaded at the loading part, and sheet processing is performed with respect to the sheet bundle on which the alignment processing has been performed. The post processing device controls the deviation amount of the position of the sheets when stacking the sheets sequentially at the buffer part, according to the size of the sheet conveyed in the conveyance passage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sheet processing apparatus, an image forming apparatus, and an image forming system including the image forming apparatus and the sheet processing apparatus.

Background Art

[0002] A post-processing apparatus (sheet processing apparatus) that performs predetermined post-processing (sheet processing) such as binding or sorting on a sheet on which an image has been formed by an image forming apparatus may be connected to the image forming apparatus as an option. The post-processing apparatus may be configured to perform alignment processing for aligning the positions of the plurality of conveyed sheets before performing post-processing on the plurality of conveyed sheets.

[0003] Patent Document 1 describes a technique for adjusting the shift amount of sheets based on the type or basis weight of the sheets in a post-processing apparatus that feeds a plurality of sheets in a stacked state after shifting them in the conveyance direction and performs alignment processing on the plurality of sheets in the stack unit. This enables reliable alignment processing in the stack unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, by shifting and stacking multiple sheets in the transport direction and sending them to the stacking section (loading section), it becomes possible to more reliably perform alignment processing in the transport direction for each sheet in the loading section, depending on the amount of sheet shifting. However, while increasing the amount of sheet shifting improves the accuracy of alignment processing in the loading section, it also increases the overall length of the sheet bundle in the transport direction, thus increasing the time required for alignment processing. This leads to a decrease in the productivity of the post-processing equipment. On the other hand, uniformly reducing the amount of sheet shifting shortens the time required for alignment processing, leading to an increase in the productivity of the post-processing equipment, but it may result in a decrease in the accuracy of alignment processing.

[0006] Therefore, one aspect of the present invention provides a technology that can control the amount of sheet displacement in the transport direction when stacking multiple sheets that are transported to the loading section to generate a sheet bundle, in order to improve the productivity of the sheet processing device while maintaining the accuracy of the sheet alignment process. [Means for solving the problem]

[0007] A sheet processing apparatus according to one aspect of the present invention comprises: a loading section on which sheets to be processed are loaded; a buffer section provided in a transport path for transporting sheets to the loading section, which generates a sheet bundle by sequentially shifting the positions of the sheets being transported along the transport path upstream in the transport direction and transporting the sheet bundle from the buffer section to the loading section; an alignment means for performing alignment processing to align the positions of the sheets in the transport direction with respect to the sheet bundle loaded in the loading section; and a processing means for performing sheet processing on the sheet bundle after the alignment processing has been performed, wherein the control means controls the amount of positional shift of the sheets when sequentially stacking the sheets in the buffer section according to the size of the sheets being transported along the transport path. Furthermore, the control means reduces the amount of displacement when the size of the sheet being transported along the transport path is less than or equal to a threshold size, compared to when the size is not less than or equal to the threshold size. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, it becomes possible to control the amount of sheet displacement in the transport direction when stacking multiple sheets that are transported to the loading section to generate a sheet bundle, in order to improve the productivity of the sheet processing device while maintaining the accuracy of the sheet alignment process. [Brief explanation of the drawing]

[0009] [Figure 1] Cross-sectional view showing an example of the configuration of an image forming system. [Figure 2] Perspective view showing an example of the binding section configuration. [Figure 3] Cross-sectional view showing an example of the generation of sheet bundles in a tile-stacked state in the buffer section. [Figure 4] This diagram shows an example of vertical alignment of sheet bundles in the binding processing unit. [Figure 5] Block diagram showing an example of the hardware configuration of an image forming system. [Figure 6] Block diagram showing an example of the functional configuration of an image forming system. [Figure 7] A flowchart showing the processing procedure for sheet transport control. [Figure 8] Flowchart showing the procedure for processing the first sheet (S103) [Figure 9] Flowchart showing the procedure for processing the second sheet (S104) (First Embodiment) [Figure 10] Flowchart showing the procedure for processing the second sheet (S104) (Second Embodiment) [Figure 11] Flowchart showing the procedure for shifting the sheet stack (S404) (Second Embodiment) [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] [First Embodiment] <Image Forming System> Figure 1 is a cross-sectional view showing an example configuration of an electrophotographic image forming system according to an embodiment of the present disclosure. The image forming system 1S of this embodiment comprises an image forming apparatus 1 that forms an image on a sheet, and a post-processing device 4 connected to the downstream side of the image forming apparatus 1 in the sheet transport direction. The image forming system 1S further comprises an image reading device 2 and a document feeding device 3 connected to the image forming apparatus 1. The image forming system 1S forms an image on a sheet, which is a recording material, and performs post-processing (sheet processing) on ​​the sheet by the post-processing device 4 as needed. The post-processing device 4 is an example of a sheet processing device that performs predetermined sheet processing on the sheet. The configuration and operation of each device will be described below.

[0012] The document feeder 3 transports the document placed on the document tray 18 to the image reading units 16 and 19 of the image reading device 2. The image reading units 16 and 19 are image sensors that read images from the document. The image reading unit 16 is configured to read the image from the first side of the document, and the image reading unit 19 is configured to read the image from the second side, the reverse side of the first side of the document. Using the image reading units 16 and 19, both sides of the document can be read in a single document transport. After the images have been read by the image reading units 16 and 19, the document is discharged to the document discharge unit 20. The image reading device 2 can also read images from stationary documents (including booklet documents and other documents that cannot be used with the document feeder 3) set on the document glass by moving the image reading unit 16 back and forth using the drive unit 17.

[0013] The image forming apparatus 1 includes an image forming unit 1B of a direct transfer type and forms an image by an electrophotographic method. The controller (printer control unit 100 in FIG. 5) of the image forming apparatus 1 controls the image forming operation of the image forming unit 1B based on the image data obtained by reading by the image reading units 16 and 19 or the image data received from an external device via a network.

[0014] The image forming unit 1B includes a cartridge 8 having a photosensitive drum 9 and a laser scanner unit 15 disposed above the cartridge 8. When performing an image forming operation, the image forming unit 1B charges the surface of the photosensitive drum 9 while rotating the photosensitive drum 9. The laser scanner unit 15 exposes the photosensitive drum 9 based on the image data, thereby forming an electrostatic latent image on the drum surface of the photosensitive drum 9. The image forming unit 1B develops the electrostatic latent image carried on the photosensitive drum 9 into a toner image with charged toner particles. The toner image formed on the photosensitive drum 9 is conveyed to a transfer portion where the photosensitive drum 9 and the transfer roller 10 face each other as the photosensitive drum 9 rotates.

[0015] The image forming apparatus 1 includes a plurality of paper feeding units 6, and each paper feeding unit feeds sheets one by one to a conveyance path. The sheets fed from the paper feeding unit 6 are conveyed through the conveyance path, and after skew correction is performed by the registration roller 7, they reach the transfer portion. In the transfer portion, the toner image carried on the photosensitive drum 9 is transferred to the sheet by the transfer roller 10. A fixing unit 11 is disposed downstream of the transfer portion in the sheet conveyance direction. The fixing unit 11 has a pair of rotating bodies that sandwich and convey [the sheet], and a heating element such as a halogen lamp for heating the toner image on the sheet, and performs a fixing process of the image by heating and pressing the toner image on the sheet. Sheet 挟持して搬送する回転体対と、シート上のトナー像を加熱するためのハロゲンランプ等の発熱体とを有し、シート上のトナー像を加熱及び加圧することで画像の定着処理を行う。 It has a pair of rotating bodies that sandwich and convey [the sheet], and a heating element such as a halogen lamp for heating the toner image on the sheet, and performs a fixing process of the image by heating and pressing the toner image on the sheet.

[0016] When the sheet on which the image is formed in this way is discharged outside the image forming apparatus 1, the sheet that has passed through the fixing unit 11 is conveyed to the post-processing apparatus 4 through the conveyance path 14. When double-sided printing is performed on the sheet, the sheet on which the image formation on the first side has ended is passed to the reversing roller 12 after passing through the fixing unit 11, and the sheet is conveyed by the reversing roller 12 for back-and-forth conveyance. As a result, the sheet is conveyed again to the registration roller 7 through the conveyance path 13. Then, when the sheet is conveyed to the transfer unit, the image formed by the image forming unit 1B is transferred onto the second side of the sheet. The sheet on which the image formation on the second side has ended is conveyed to the post-processing apparatus 4 through the conveyance path 14 after passing through the fixing unit 11.

[0017] The image forming unit 1B may be configured to form an image by an intermediate transfer method in which the toner image formed on the photoreceptor is transferred onto the sheet via an intermediate transfer member. Further, the image forming unit 1B may be configured to form an image by an inkjet method or an offset printing method.

[0018] <Post-processing apparatus> The post-processing apparatus 4 has a binding processing unit 4A that performs binding processing as post-processing (sheet processing) on the sheet. The post-processing apparatus 4 performs binding processing on the sheet conveyed from the image forming apparatus 1 by the binding processing unit 4A, and discharges a plurality of bound sheets as a sheet bundle. Further, the post-processing apparatus 4 can also discharge the sheet conveyed from the image forming apparatus 1 without performing binding processing.

[0019] The post-processing device 4 has a receiving path 81, an internal discharge path 82, a first discharge path 83, and a second discharge path 84 as transport paths for transporting sheets. The post-processing device 4 has an upper discharge tray 25 and a lower discharge tray 37 as destinations for discharging sheets. The receiving path 81 is a transport path for transporting sheets received from the image forming apparatus 1. The internal discharge path 82 is a transport path for transporting sheets toward the binding processing device 4A. The first discharge path 83 is a transport path for discharging sheets toward the upper discharge tray 25. The second discharge path 84 is a transport path for discharging sheets toward the lower discharge tray 37.

[0020] The receiving path 81 has an inlet roller 21, an inlet sensor 27, and a buffer-pre-roller 22 arranged in order in the sheet transport direction. The first discharge path 83 has a reversing roller 24. The internal discharge path 82 has an internal discharge roller 26, an intermediate transport roller 28, a kick-out roller 29, and an intermediate pre-loading sensor 38. The second discharge path 84 has a bundle discharge roller 36. Both the inlet sensor 27 and the intermediate pre-loading sensor 38 detect sheets being transported at predetermined detection positions in the transport path within the post-processing device 4. These sensors may be optical sensors that use light to detect the presence or absence of sheets at the detection position.

[0021] The following describes the path through which the sheet is transported in the post-processing device 4. The sheet discharged from the image forming apparatus 1 via the transport path 14 is taken into the post-processing device 4 by the inlet roller 21 and enters the receiving path 81 to It is then transported towards the buffer-front roller 22. Receiving path 81 to The sheet being transported is detected by the entrance sensor 27 at a detection position between the entrance roller 21 and the buffer-pre-roller 22. The buffer-pre-roller 22 transports the sheet that has been transported by the entrance roller 21 toward the first discharge path 83.

[0022] When the upper discharge tray 25 is specified as the destination for the sheets, the reversing roller 24 discharges the sheets, which have been guided to the first discharge path 83 by the buffer-pre-roller 22, to the upper discharge tray 25. When the lower discharge tray 37 is specified as the destination for the sheets, the sheet, which has been guided to the first discharge path 83 by the buffer-pre-roller 22, is guided to the inner discharge path 82 by switchback transport. A backflow prevention valve 23 is located upstream of the reversing roller 24 in the direction of sheet discharge to the upper discharge tray 25 by the reversing roller 24, at the branching point (switchback branching point) where the receiving path 81 and the inner discharge path 82 branch off from the first discharge path 83. The backflow prevention valve 23 has the function of preventing sheets that have been transported via switchback by the reversing roller 24 from flowing back into the receiving path 81.

[0023] The internal discharge roller 26, intermediate transport roller 28, and kick-off roller 29, located in the internal discharge path 82, transport the sheets guided into the internal discharge path 82 by the reversing roller 24 toward the binding processing unit 4A, passing them in sequence. Sheets being transported in the internal discharge path 82 are detected by the intermediate loading pre-sensor 38 at a detection position between the intermediate transport roller 28 and the kick-off roller 29.

[0024] The binding processing unit 4A has a stapler 51. The binding processing unit 4A performs alignment processing on multiple sheets (sheet bundles) that have been transported through the internal discharge path 82 and loaded into the intermediate loading section, and then staples the predetermined positions of the multiple sheets with the stapler 51. The detailed configuration and operation of the binding processing unit 4A will be described later. The sheet bundles stapled by the binding processing unit 4A are transferred to the bundle discharge roller 36 through the second discharge path 84 by the sliding movement of the bundle discharge guide 34, which is the first transport mechanism of the binding processing unit 4A. After that, the sheet bundles are discharged to the lower discharge tray 37 by the bundle discharge roller 36, which is the second transport mechanism of the binding processing unit 4A.

[0025] Both the upper discharge tray 25 and the lower discharge tray 37 are movable vertically relative to the housing of the post-processing device 4. The post-processing device 4 is equipped with sheet sensors that detect the position (height from the tray surface) of the top surface of multiple sheets loaded on the upper discharge tray 25 and the lower discharge tray 37. Based on the detection result of the sheet sensor provided on the upper discharge tray 25, the upper discharge tray 25 is raised and lowered vertically (in the A1 or A2 direction) to maintain a constant position of the top surface of the sheets loaded on the upper discharge tray 25. Similarly, based on the detection result of the sheet sensor provided on the lower discharge tray 37, the upper discharge tray 4 is raised and lowered vertically (in the B1 or B2 direction) to maintain a constant position of the top surface of the sheets loaded on the lower discharge tray 37. under The discharge tray 37 is controlled to move up and down. In this embodiment, the upper discharge tray 25 and the lower discharge tray 37 are controlled by motors, but they may also be controlled by a biasing mechanism such as a spring.

[0026] <Binding processing section> Next, the configuration and operation of the binding processing unit 4A will be described with reference to Figure 2. Figure 2(A) is a perspective view showing the binding processing unit 4A, and Figure 2(B) is a perspective view showing the binding processing unit 4A with some components (intermediate upper guide 31) opened.

[0027] As shown in Figures 2(A), 2(B), and 1, the stapling section 4A includes a stapler 51, an intermediate upper guide 31 and an intermediate lower guide 32, a vertical alignment reference plate 39, a vertical alignment roller 33, and a bundle discharge guide 34. The stapling section 4A uses the stapler 51 to staple the sheets discharged from the internal discharge path 82 and loaded onto the intermediate loading section, forming a bundle of stapled sheets.

[0028] The intermediate upper guide 31 and the intermediate lower guide 32 constitute an intermediate loading section where the sheets to be processed are loaded. The intermediate lower guide 32 is a loading section where sheets discharged from the internal discharge path 82 by the kick-off roller 29, which is located at the downstream position in the internal discharge path 82, are loaded. Thus, the intermediate loading section is an example of a loading section where sheets to be processed (bound) are loaded.

[0029] A bundle-holding flag 30 is rotatably provided downstream of the kick-out roller 29 in the sheet transport direction. The lower surface of the bundle-holding flag 30 holds down the rear end of the sheet that has been discharged first from the internal discharge path 82 to the intermediate loading section (the preceding sheet). As a result, the leading edge of the sheet discharged later by the kick-out roller 29 (the subsequent sheet) passes above the rear end of the preceding sheet. In this way, the bundle-holding flag 30 has the function of preventing collisions between sheets in the intermediate loading section by moving the rear end of the sheet discharged from the internal discharge path 82 by the kick-out roller 29 downwards. The lower surface of the bundle-holding flag 30 is provided within the sheet width range so that it can hold down both ends of the sheet in the sheet width direction, according to the size of the sheet that can be processed in the binding processing section 4A.

[0030] The longitudinal alignment roller 33 is positioned above the intermediate lower guide 32. The longitudinal alignment roller 33 is molded from an elastic material such as synthetic rubber or elastomer resin and has a roller portion 33a whose outer surface is adjusted to have a predetermined coefficient of friction. The roller portion 33a is supported by a shaft portion 33b which is rotatably supported by the intermediate upper guide 31. The roller portion 33a is driven by a drive transmission device including a gear portion 33c to rotate intermittently one revolution at a time. The roller portion 33a, which is the outer circumference of the longitudinal alignment roller 33, is non-circular when viewed from the axial direction of the shaft portion 33b. In the standby state before the sheets are discharged to the intermediate loading section, the longitudinal alignment roller 33 is held at a rotation angle such that the roller portion 33a is not exposed from the intermediate upper guide 31. Also, during one rotation of the longitudinal alignment roller 33, the roller portion 33a is temporarily exposed from an opening 31a provided in the intermediate upper guide 31 and contacts the upper surface of the sheets loaded on the intermediate lower guide 32 to apply conveying force. The contact pressure of the longitudinal alignment roller 33 against the sheet is adjusted so that the longitudinal alignment roller 33 slips after the sheet abuts against the longitudinal alignment reference plate 39.

[0031] A flexible sheet member, a retaining guide 56, is positioned in the intermediate loading section. The retaining guide 56 is positioned to contact the intermediate lower guide 32 and presses the upper surface of the sheet loaded in the intermediate loading section with a predetermined pressure.

[0032] The longitudinal alignment reference plate 39 is located downstream of the longitudinal alignment roller 33 in the sheet discharge direction when the sheet is discharged from the internal discharge path 82 by the kick-out roller 29. The longitudinal alignment reference plate 39 has a reference wall 39a that protrudes upward from the upper surface of the intermediate lower guide 32, acting as a regulating member that contacts the edge of the sheet. In addition, two longitudinal alignment reference plates 39 are provided on both sides in the direction perpendicular to the sheet discharge direction (the width direction of the sheet).

[0033] Hereinafter, in the binding processing unit 4A, the direction in which the sheet discharged from the internal discharge path 82 by the kick-out roller 29 moves toward the longitudinal alignment reference plate 39 will be referred to as the "longitudinal alignment direction X1". The longitudinal alignment direction X1 is the direction along the sheet transport direction in the internal discharge path 82, and is also the direction in which the longitudinal alignment roller 33 moves the sheet toward the longitudinal alignment reference plate 39. The direction opposite to the longitudinal alignment direction X1 (i.e., the direction in which the sheet bundle is discharged from the binding processing unit 4A) will be referred to as the "bundle discharge direction X2".

[0034] The stapler 51 is loaded in the intermediate loading section and performs a stapling operation to fasten predetermined positions of multiple sheets that are aligned in the longitudinal alignment direction X1 and the sheet width direction. The stapler 51 is provided on the same side as the transverse alignment reference plate 52 in the sheet width direction and is provided to be movable in the longitudinal alignment direction X1 and the bundle discharge direction X2. In addition, the intermediate lower guide 32 has a width that allows it to load legal-sized sheets that are transported in the long-side feeding direction (the transport direction in which the longitudinal alignment direction X1 is the long side direction and the sheet width direction is the short side direction). Therefore, the stapler 51 can not only fasten the corners of the sheet bundle loaded in the intermediate loading section, but also perform a long-side fastening operation that fastens multiple positions along the long side of the sheet bundle while moving relative to the sheet bundle.

[0035] In the binding processing unit 4A of this embodiment, the vertical alignment roller 33 and the vertical alignment reference plate 39 constitute an alignment processing unit (alignment means) that performs alignment processing to align the position of the sheets in the sheet transport direction with respect to the sheet bundles loaded in the loading unit. The vertical alignment roller 33 is an example of an alignment roller that is rotationally driven to move the sheets in the transport direction, and the vertical alignment reference plate 39 is an example of a first reference plate provided along the width direction perpendicular to the transport direction. The stapler 51 is an example of a processing means that performs sheet processing (binding processing) on ​​the sheet bundles that have undergone alignment processing.

[0036] <Process for generating sheet bundles in a tiled state> In this embodiment, the post-processing device 4 prevents subsequent sheets from being transported to the binding processing unit 4A while the binding processing unit 4A is performing its binding process. To this end, it places subsequent sheets transported from the image forming apparatus 1 into the internal discharge path 82 and the first discharge path 83 (buffer section). At this time, the post-processing device 4 places the subsequent multiple sheets in a stacked state. The post-processing device 4 then transports the stacked sheet bundle from the buffer section to the binding processing unit 4A (intermediate stacking section). This makes it possible to continue image forming by the image forming apparatus 1 while the binding processing by the binding processing unit 4A (post-processing by the post-processing device 4) is performing its binding process, thereby preventing a decrease in the productivity of the image forming system.

[0037] When stacking multiple sheets, the post-processing device 4 generates a stacked sheet bundle by stacking the sheets in a buffer section while sequentially shifting their positions in the sheet transport direction. This allows the binding processing unit 4A to perform vertical alignment on the stacked sheets. The process for generating such a stacked sheet bundle will be described below with reference to Figure 3.

[0038] The post-processing device 4 guides the sheet P1, which has been led to the first discharge path 83, to the inner discharge path 82 by switchback transport using the reversing rollers 24, and stops the reversing rollers 24 and the inner discharge rollers 26 after it reaches the inner discharge rollers 26. This stops the sheet P1 at the position shown in Figure 3(A). At this time, the post-processing device 4 separates the roller pair of the reversing rollers 24.

[0039] Subsequently, the rear end of sheet P2, which was transported after sheet P1, is detected by the inlet sensor 27. The post-processing device 4, based on the timing at which the rear end of sheet P2 is detected by the inlet sensor 27, brings the roller pair of the reversing roller 24 into contact with the sheet after a predetermined time has elapsed from that timing (Figure 3(B)). Furthermore, the post-processing device 4 starts rotating the reversing roller 24 and the inner discharge roller 26 so that sheets P1 and P2 are transported in the direction of the upper discharge tray 25.

[0040] Here, the predetermined time mentioned above is the time required to determine the amount of positional shift in the sheet transport direction when overlapping sheet P2 with sheet P1. Increasing this time increases the amount of sheet shift, while decreasing this time decreases the amount of sheet shift. As will be described later, the post-processing device 4 of this embodiment controls (sets) the amount of sheet shift according to the size of the sheet to be processed in order to improve the productivity of the post-processing device 4 while maintaining the accuracy of the sheet alignment process (securing the amount of shift necessary for vertical alignment).

[0041] As shown in Figure 3(C), the post-processing device 4 rotates the reversing roller 24 and the internal discharge roller 26 so that their rotational directions are reversed when the rear end of the sheet P2 reaches the switchback branching point. As a result, sheets P1 and P2 are guided to the internal discharge path 82 and transported towards the binding processing unit 4A.

[0042] The post-processing device 4 stops the reversing roller 24 and the internal discharge roller 26 after the sheet P2, which has been guided to the internal discharge path 82, reaches the internal discharge roller 26. This stops the sheets P1 and P2 at the position shown in Figure 3(D). The post-processing device 4 further separates the roller pair of the reversing roller 24. The post-processing device 4 further separates the roller pair of the reversing roller 24 at that time.

[0043] In this way, as shown in Figure 3(D), a stack of sheets consisting of two sheets in a tile-like arrangement is generated in the internal discharge path 82 and the first discharge path 83. Furthermore, by repeating the above process, it is possible to generate a stack of sheets consisting of three or more sheets in a tile-like arrangement. In this way, the post-processing device 4 generates a stack of sheets (a stack of sheets in a tile-like arrangement) in the buffer section by sequentially shifting the positions of the sheets being transported along the transport path to the upstream side in the sheet transport direction.

[0044] While the binding process is being performed by the binding processing unit 4A, the post-processing device 4 retains the subsequent multiple sheets transported from the image forming apparatus 1 as a stack of sheets in the form of a tile-like pile, in the internal discharge path 82 and the first discharge path 83. The post-processing device 4 uses the internal discharge path 82 and the first discharge path 83 as buffer sections for retaining the subsequent multiple sheets transported from the image forming apparatus 1.

[0045] <Vertical alignment of sheet bundles> Figure 4 is a schematic diagram showing an example of longitudinal alignment for a sheet bundle consisting of three sheets in the intermediate loading section. Here, longitudinal alignment is the process of aligning the positions of multiple sheets in the sheet transport direction (alignment process). When the post-processing device 4 sends the sheet bundle in a stacked state to the binding processing unit 4A through the internal discharge path 82, it starts rotating the longitudinal alignment roller 33, thereby initiating longitudinal alignment for the sheet bundle loaded in the intermediate loading section within the binding processing unit 4A.

[0046] Figure 4(A) shows the internal discharge path 82 mosquitoThe sheet bundles, which have been discharged in a stacked state, are shown being loaded onto the intermediate loading section. The intermediate loading section is composed of an intermediate upper guide 31 and an intermediate lower guide 32. The intermediate loading section is equipped with a longitudinal alignment roller 33 and a longitudinal alignment reference plate 39 as components used for longitudinal alignment. Multiple sheets constituting the sheet bundle are successively brought against the longitudinal alignment reference plate 39 by the longitudinal alignment roller 33, thereby performing longitudinal alignment (alignment processing in the sheet transport direction) of the sheet bundle.

[0047] First, as shown in Figure 4(B), the bottom sheet of the sheet bundle stacked in the intermediate loading section is abutted against the vertical alignment reference plate 39 by the vertical alignment roller 33. Next, as shown in Figure 4(C), the second sheet from the bottom of the sheet bundle is abutted against the vertical alignment reference plate 39 by the vertical alignment roller 33. Furthermore, as shown in Figure 4(D), the top sheet of the sheet bundle is abutted against the vertical alignment reference plate 39 by the vertical alignment roller 33. This completes the vertical alignment of the sheet bundle stacked in the intermediate loading section.

[0048] In this embodiment, the post-processing device 4 generates a sheet bundle in the buffer section by sequentially shifting the positions of the sheets being transported along the transport path to the upstream side in the sheet transport direction and stacking them, and then sends the generated sheet bundle to the binding processing unit 4A (intermediate loading unit). As a result, in the intermediate loading unit, each sheet of the sheet bundle is brought against the vertical alignment reference plate 39 by the vertical alignment roller 33, thereby performing vertical alignment on all sheets of the sheet bundle. In this way, the alignment processing unit, which consists of the vertical alignment roller 33 and the vertical alignment reference plate 39, moves the sheets of the sheet bundle loaded in the intermediate loading unit one by one from the bottom down in the sheet transport direction by the vertical alignment roller 33, bringing the end of each sheet against the vertical alignment reference plate 39. As a result, the alignment processing unit performs alignment processing (vertical alignment) on the sheet bundle in the sheet transport direction.

[0049] In the buffer section, the amount of sheet displacement when generating stacked sheet bundles is determined based on the distance L between the position where the longitudinal alignment roller 33 contacts the sheet and the position of the longitudinal alignment reference plate 39, and the distance required for longitudinal alignment and the distance considering friction between sheets. When the size of the sheets to be processed is small (small surface area), the frictional force between the overlapping sheets is small, and the required longitudinal alignment capability is low. In other words, even if the amount of displacement between the overlapping sheets is small, the accuracy of the alignment process can be maintained. For this reason, the amount of sheet displacement can be reduced.

[0050] Therefore, by setting a smaller sheet displacement amount for smaller sheets being transported along the transport path, it is possible to improve the productivity of the sheet processing device by shortening the time required for sheet alignment processing while maintaining the accuracy of the sheet alignment processing. For example, the sheet displacement amount is set so that when the size of the sheet to be processed being transported along the transport path is below the threshold size, it is smaller than when the size is not below the threshold size. For example, if L=20[mm], ● If the sheet size is small (length in the sheet transport direction 210 mm or less, and width in the sheet width direction 148 mm or less), the shift amount is set to 25 mm. ●If the sheet size is not small, set the shift amount to 30mm.

[0051] The above example determines whether the sheet size is below a threshold size based on the length and width of the sheet to be processed, but this determination may also be made based on at least one of the sheet length or width. Furthermore, although an example was shown with two settings for the amount of sheet position shift, three or more settings corresponding to different sheet size ranges may also be provided.

[0052] <Configuration of the image forming system> Figure 5 is a block diagram showing an example of the hardware configuration of the image forming system 1S according to this embodiment. The image forming apparatus 1 includes a printer control unit 100, and the post-processing device 4 includes a finisher control unit 400. The printer control unit 100 and the finisher control unit 400 are connected to each other via a communication interface and cooperate to control the operation of the image forming system 1S.

[0053] The printer control unit 100 includes a central processing unit (CPU) 101 and a memory 102. The CPU 101 reads and executes programs stored in the memory 102 and provides overall control of the image forming apparatus 1. For example, the CPU 101 executes processes to cause the image forming unit 1B to perform image forming operations and processes to cause the image reading device 2 to perform reading operations to acquire image data. The memory 102 includes non-volatile storage media such as read-only memory (ROM) and volatile storage media such as random access memory (RAM), and is used as a storage location for programs and data, and as a workspace when the CPU 101 executes programs. The memory 102 is an example of a non-transient storage medium in which programs for controlling the image forming apparatus 1 are stored.

[0054] The printer control unit 100 is connected to external devices such as personal computers (PCs) and portable information devices via an external interface (I / F) 104. The printer control unit 100 receives various jobs, such as image forming jobs (print jobs), from external devices via the external I / F 104. The printer control unit 100 is also connected to the operation display unit 103, which is the user interface of the image forming system 1S. The operation display unit 103 includes a display device such as a liquid crystal panel that presents information to the user, and input devices such as physical buttons and a touch panel function of the liquid crystal panel for receiving input operations from the user. The printer control unit 100 controls the display content of the display device and receives information entered via the input devices by communicating with the operation display unit 103.

[0055] The finisher control unit 400 includes a CPU 401, a memory 402, and an input / output (I / O) port 403. The CPU 401 reads and executes programs stored in the memory 402 and provides overall control of the post-processing unit 4. The memory 402 includes non-volatile storage media such as ROM and volatile storage media such as RAM, and is used as a storage location for programs and data, and as a workspace for the CPU 401 when executing programs. The memory 402 is an example of a non-transient storage medium in which programs for controlling the post-processing unit 4 are stored.

[0056] Furthermore, the functions provided by the printer control unit 100 and the finisher control unit 400 may be implemented on the control unit's circuit as independent hardware such as an ASIC. P The functional units of the program may be implemented by software. Furthermore, some or all of the functions of the finisher control unit 400, as described below, can be implemented as functions of the printer control unit 100.

[0057] The CPU 401 and memory 402 are connected to the I / O port 403 via the bus 404. The I / O port 403 performs input and output of control signals between the CPU 401 and memory 402 and each device constituting the post-processing unit 4. In addition to the inlet sensor 27 and the intermediate loading pre-sensor 38, the I / O port 403 is connected to a plurality of motors (M1 to M14) that serve as a drive source for transporting the sheets or as a drive source for the binding processing unit 4A.

[0058] The inlet motor M1 rotates the inlet roller 21. The buffer front motor M2 rotates the buffer front roller 22. The first reversing motor M3 rotates the reversing roller 24. The second reversing motor M4 rotates in the first direction (for example, clockwise (CW direction)) to bring the roller pair of the reversing roller 24 into contact, and in the opposite direction to the first direction ( antiThe roller pair of the reversing roller 24 is separated by rotational drive in a clockwise direction (CCW direction). The third reversing motor M5 moves the roller pair of the reversing roller 24 in the first of two directions perpendicular to the conveying direction (towards the front) by rotational drive in the CW direction, and then moves it in the opposite direction to the first direction (towards the back) by rotational drive in the CCW direction.

[0059] The internal discharge motor M6 rotates the internal discharge roller 26. The kick-out motor M7 rotates the kick-out roller 29. The longitudinal alignment motor M8 supplies the driving force to operate the longitudinal alignment roller 33 intermittently, one rotation at a time. The jogger drive motor M9 moves the lateral alignment jogger 58 in the sheet width direction. The stapler move motor M10 moves the stapler 51 in the longitudinal alignment direction X1 and the bundle discharge direction X2. The stapler motor M11 causes the stapler 51 to perform the action of stapling the sheet bundles.

[0060] The guide drive motor M12 drives the guide drive unit 35 to slide the bundle discharge guide 34. The guide drive motor M12 moves the bundle discharge guide 34 in the longitudinal alignment direction X1 by rotational drive in the CW direction and in the bundle discharge direction X2 by rotational drive in the CCW direction. The first bundle discharge motor M13 rotates the bundle discharge roller 36. The second bundle discharge motor M14 brings the roller pair of the bundle discharge roller 36 into contact by rotational drive in the CW direction and separates the roller pair of the bundle discharge roller 36 by rotational drive in the CCW direction.

[0061] <Configuration of the control unit> Figure 6 is a block diagram showing an example of the functional configuration of the image forming system 1S according to this embodiment. Note that Figure 6 mainly shows the functional blocks related to sheet transport control in the post-processing device 4 of this embodiment, and functional blocks related to other functions are omitted.

[0062] The finisher control unit 400 includes a transport control unit 410 and an information acquisition unit 412, and the transport control unit 410 includes a sheet bundle control unit 411. 。The functions of each control unit 410 to 412 are realized by the CPU 401 of the finisher control unit 400 (Figure 5) executing a program read from memory 402.

[0063] The transport control unit 410 controls the transport of sheets in the transport path within the post-processing device 4 by driving the motors M1 to M14 to be controlled based on information output from various sensors such as the inlet sensor 27 and the intermediate loading sensor 38. The sheet bundle control unit 411 controls the generation of sheet bundles in a stacked state in the buffer section by driving the first reversing motor M3, the second reversing motor M4, and the internal discharge motor M6 based on information output from the inlet sensor 27 and the information acquisition unit 412. The information acquisition unit 412 acquires information (e.g., sheet size) set via the operation display unit 103 via the printer control unit 100.

[0064] <Processing Procedure> Referring to Figures 7, 8, and 9, the sheet transport control performed by the transport control unit 410 (CPU 401) in the post-processing device 4 of this embodiment will be described. Figure 7 is a flowchart of the processing procedure for sheet transport control. Figure 8 is a flowchart showing the procedure for the first sheet processing in S103 of Figure 7, and Figure 9 is a flowchart showing the procedure for the second sheet processing in S104 of Figure 7.

[0065] In the image forming system 1S, when the execution of an image forming job including post-processing (sheet processing) by the post-processing device 4 is started, the transport control unit 410 of the finisher control unit 400 performs the processing according to the procedure in Figure 7, in accordance with instructions from the printer control unit 100. The following processing is performed each time an image-formed sheet is transported from the image forming apparatus 1.

[0066] First, the transport control unit 410 (CPU 401) waits for the rear end of the sheet discharged from the image forming apparatus 1 via the transport path 14 and to be processed by the post-processing device 4 (hereinafter referred to as the "target sheet") to be detected by the entrance sensor 27. In S101, when the rear end of the target sheet transported from the image forming apparatus 1 is detected by the entrance sensor 27, the transport control unit 410 proceeds to processing in S102.

[0067] In S102, the transport control unit 410 determines whether the target sheet whose rear end is detected by the inlet sensor 27 is the first sheet of a sheet bundle (a sheet bundle to be bound in the binding process) which will be the processing unit in post-processing. If the target sheet is the first sheet of the sheet bundle, the transport control unit 410 proceeds to S103 and executes the first sheet processing according to the procedure in Figure 8. On the other hand, if the target sheet is not the first sheet of the sheet bundle (i.e., it is the second or later sheet), the transport control unit 410 proceeds to S104 and executes the second sheet processing according to the procedure in Figure 9. Once processing in S103 or S104 is completed, the transport control unit 410 terminates the processing according to the procedure in Figure 7.

[0068] The execution of the processes in S103 and S104 generates stacked sheet bundles in the buffer section (internal discharge path 82 and first discharge path 83). Subsequently, the transport control unit 410 transports the stacked sheet bundles generated in the buffer section to the intermediate loading section via the internal discharge path 82, where the binding processing unit 4A performs alignment processing and post-processing (binding processing) on ​​the transported sheet bundles. The bound sheet bundles are then discharged to the lower discharge tray 37 via the second discharge path 84.

[0069] <Processing the first sheet (S103)> The first sheet processing in S103 (processing of the first sheet) is performed according to the procedure shown in Figure 8. First, in S201, the transport control unit 410 (CPU 401) waits for the rear end of the target sheet, detected by the inlet sensor 27 in S101, to reach the switchback branching point. As described above, the switchback branching point is the position where the receiving path 81 and the internal discharge path 82 branch off from the first discharge path 83. When the rear end of the target sheet reaches the switchback branching point, the transport control unit 410 proceeds to processing in S202.

[0070] In S202, the transport control unit 410 switches (reverses) the rotation direction of the reversing roller 24, sending the target sheet whose rear end has reached the switchback branching point to the internal discharge path 82, and proceeds to S203. In S203, the transport control unit 410 waits for the target sheet (its leading edge) sent to the internal discharge path 82 to reach the internal discharge roller 26, and when it reaches the internal discharge roller 26, proceeds to S204. In S204, the transport control unit 410 drives the second reversing motor M4 to separate the reversing roller 24.

[0071] Subsequently, in S205, the transport control unit 410 drives the internal discharge motor M6 to transport the target sheet by the internal discharge roller 26 for a predetermined distance (10 mm in this embodiment). Once the target sheet has been transported for the predetermined distance, in S206, the transport control unit 410 stops driving the first reversing motor M3 and the internal discharge motor M6, thereby stopping the reversing roller 24 and the internal discharge roller 26, and ending the process according to the procedure in Figures 8 and 7. As a result, the first sheet of the sheet bundle (a sheet bundle to be bound in the binding process), which is the processing unit in post-processing, stops in the internal discharge path 82 at a position where the leading edge of the sheet has advanced a predetermined distance (10 mm) from the position of the internal discharge roller 26 (Figure 3(A)).

[0072] Furthermore, the determination of the position of the target sheet in S201 and S203, and the determination of the transport distance of the target sheet in S205, may be performed based on the elapsed time relative to the timing of detection of the rear end of the target sheet by the entrance sensor 27. Alternatively, these determinations may be performed based on the count value of the drive pulse of each motor.

[0073] <Processing of the second sheet (S104)> The second sheet processing in S104 (processing of the second and subsequent sheets) is performed according to the procedure shown in Figure 9. First, in S301, the transport control unit 410 (CPU 401) determines whether the target sheet is a sheet of a size less than or equal to a predetermined threshold size (small size). The transport control unit 410 obtains the sheet size set via the operation display unit 103 through the information acquisition unit 412 as the size of the target sheet, and makes a determination based on the acquired size. Alternatively, the information acquisition unit 412 may obtain the size of the target sheet from the image formation job settings.

[0074] In this way, the transport control unit 410 determines whether the size of the target sheet is less than or equal to a threshold size based on the sheet size set by the user. The threshold size is predetermined, for example, to be a size where the length in the transport direction of the sheet is 210 mm and the length (width) in the width direction of the sheet is 148 mm. If the transport control unit 410 determines that the target sheet is a small-sized sheet, it proceeds to process S302; if it determines that it is not a small-sized sheet, it proceeds to process S303.

[0075] The information acquisition unit 412 may also acquire the size of the target sheet by measuring at least one of the length and width of the sheet being transported along the transport path. In this case, a sensor capable of detecting the size of the sheet being transported is placed upstream of the buffer section in the sheet transport direction. The information acquisition unit 412 uses the sensor placed along the transport path to measure at least one of the length and width of the target sheet being transported along the transport path and acquires the measurement result. The transport control unit 410 determines whether the size of the target sheet is less than or equal to a threshold size based on the measurement result from the sensor.

[0076] In S302 and S303, the transport control unit 410 sets the transport start timing for the preceding sheet that is waiting at the position (buffer section) shown in Figure 3(A) on the internal discharge path 82 and the first discharge path 83. Here, the transport start timing for the preceding sheet is the timing at which the transport of the preceding sheet waiting in the buffer section toward the upper discharge tray 25 begins, based on the timing at which the rear end of the target sheet is detected by the inlet sensor 27. The preceding sheet is waiting at the position (buffer section) shown in Figure 3(A) on the internal discharge path 82 and the first discharge path 83.

[0077] In S302, the transport control unit 410 sets the transport start timing for the preceding sheet so that the amount of positional displacement in the transport direction when overlapping the preceding sheet with the target sheet is a first displacement (e.g., 25 mm). On the other hand, in S303, the transport control unit 410 sets the transport start timing for the preceding sheet so that the amount of positional displacement in the transport direction when overlapping the preceding sheet with the target sheet is a second displacement (e.g., 30 mm) which is greater than the first displacement.

[0078] Once the settings in S302 or S303 are complete, in S304 the transport control unit 410 waits until the transport start timing for the preceding sheet is reached, and then proceeds to S305. In S305, the transport control unit 410 starts rotating the reversing roller 24 and the inner discharge roller 26 so that the preceding sheet and the target sheet that is being transported overlapping the preceding sheet are transported in the direction of the upper discharge tray 25. Furthermore, in S306, the transport control unit 410 brings the roller pair of the reversing roller 24 into contact and proceeds to S307.

[0079] In S307, similar to S201, the transport control unit 410 waits for the rear end of the target sheet, detected by the inlet sensor 27 in S101, to reach the switchback branching point. When the rear end of the target sheet reaches the switchback branching point (as shown in Figure 3(C)), the transport control unit 410 proceeds to S307. In S308, similar to S202, the transport control unit 410 switches (reverses) the rotation direction of the reversing roller 24 to send the target sheet whose rear end has reached the switchback branching point to the internal discharge path 82, and proceeds to S309.

[0080] In S309, the transport control unit 410 determines whether there are any subsequent sheets to be added to the stacked sheet bundle generated in the buffer unit (whether there are any remaining sheets). If there are no subsequent sheets, the transport control unit 410 terminates the process according to the procedure in Figures 9 and 7. In this case, the stacked sheet bundle generated in the buffer unit is sent to the binding processing unit 4A (intermediate stacking unit) via the internal discharge path 82. In the binding processing unit 4A, vertical alignment is performed on the sheet bundle transported from the buffer unit, and then the binding process is carried out.

[0081] Meanwhile, if there is a subsequent sheet, the transport control unit 410 proceeds from S309 to S310. In S310, the transport control unit 410 waits for the target sheet (or its leading edge) sent to the internal discharge path 82 to reach the internal discharge roller 26, similar to S203, and proceeds to S311 once it reaches the internal discharge roller 26. In S311, the transport control unit 410 separates the reversing roller 24, similar to S204.

[0082] Subsequently, in S312, the transport control unit 410 transports the target sheet by the internal discharge roller 26 for a predetermined distance (10 mm in this embodiment), similar to S205. After the target sheet has been transported for the predetermined distance, in S313, the transport control unit 410 stops the reversing roller 24 and the internal discharge roller 26, similar to S206, and terminates the process according to the procedures in Figures 9 and 7. As a result, the target sheet stops in the internal discharge path 82 in a stacked state with respect to the preceding sheet, with its leading edge moving a predetermined distance (10 mm) from the position of the internal discharge roller 26 (Figure 3(A)). In this way, a sheet bundle in which one or more sheets, including the target sheet, are stacked in a stacked state with respect to the first sheet stops at the position shown in Figure 3(D). In this case, subsequent sheets are further added to the stacked sheet bundle generated in the buffer section by the process according to the procedures in Figures 7 and 9.

[0083] Furthermore, the determination of the position of the target sheet in S304, S307, and S310, and the determination of the transport distance of the target sheet in S312, may be performed based on the elapsed time relative to the timing of detection of the rear end of the target sheet by the entrance sensor 27. Alternatively, these determinations may be performed based on the count value of the drive pulse of each motor.

[0084] As described above, the post-processing device 4 of this embodiment includes a loading section (intermediate loading section) on which sheets to be processed are loaded, and a transport control unit 410. The transport control unit 410 generates a sheet bundle in a buffer section provided in the transport path for transporting sheets to the loading section, by sequentially shifting the positions of the sheets being transported along the transport path to the upstream side in the sheet transport direction. The transport control unit 410 controls the transport of sheets along the transport path so that the sheet bundle is transported from the buffer section to the loading section. The alignment processing unit performs alignment processing on the sheet bundle loaded in the loading section to align the positions of the sheets in the sheet transport direction. The binding processing unit 4A performs sheet processing (binding processing) on ​​the sheet bundle after alignment processing. The transport control unit 410 controls the amount of positional shift of the sheets when sequentially stacking the sheets in the buffer section according to the size of the sheets being transported along the transport path.

[0085] As described above, the post-processing device 4 of this embodiment controls the amount of positional shift of the sheets when stacking the sheets sequentially in the buffer section to generate a stacked sheet bundle, according to the size of the sheets to be processed. This makes it possible to shorten the overall length of the stacked sheet bundle in the sheet transport direction to match the size of the sheets. As a result, it becomes possible to shorten the time required to transport a sheet bundle consisting of small-sized sheets to the binding processing unit 4A (post-processing unit), and also shorten the time required for vertical alignment of the sheet bundle. Therefore, according to this embodiment, it is possible to improve the productivity of the post-processing device 4 (sheet processing device) while maintaining the accuracy of the sheet alignment process (ensuring vertical alignment capability).

[0086] [Second Embodiment] In the second embodiment, the intermediate loading section of the post-processing device 4 performs not only vertical alignment but also horizontal alignment (alignment processing to match the position of the sheets in the sheet width direction perpendicular to the sheet transport direction) on the stacked sheet bundles that have been transported and loaded from the buffer section. Furthermore, in order to prevent a decrease in the accuracy of horizontal alignment when the size of the sheets to be processed is small, a shift process is performed in the buffer section to shift the position of the sheet bundle in the sheet width direction as needed. In addition, the amount of sheet displacement when generating the sheet bundle is controlled based on whether or not the shift process is performed. Below, mainly the parts that differ from the first embodiment will be described, and the parts that are common with the first embodiment will be omitted from the description.

[0087] <Shifting sheet stacks> Referring to Figures 2 and 3, a shifting process will be described in which a stack of sheets in a tile-like state is shifted in the sheet width direction perpendicular to the sheet transport direction using the reversing roller 24. In this embodiment, after the sheet stack is fed to the binding processing unit 4A, the post-processing device 4 performs not only vertical alignment but also lateral alignment of the sheet stack by moving the lateral alignment jogger 58 shown in Figure 2(B) in the sheet width direction. Lateral alignment is a process (alignment process) that aligns the positions of multiple sheets in the sheet width direction.

[0088] In the binding processing unit 4A of this embodiment, the lateral alignment jogger 58 and the lateral alignment reference plate 52 constitute an alignment processing unit (alignment means) that performs alignment processing to align the position of sheets in the sheet width direction perpendicular to the sheet transport direction with respect to the sheet bundles loaded in the loading unit. The lateral alignment jogger 58 is an example of an alignment member provided along the sheet transport direction, and the lateral alignment reference plate 52 is an example of a second reference plate provided along the sheet transport direction. The alignment processing unit, composed of the lateral alignment jogger 58 and the lateral alignment reference plate 52, performs alignment processing in the sheet width direction (lateral alignment) with respect to the sheet bundles loaded in the intermediate loading unit. Specifically, the alignment processing unit performs lateral alignment by moving the sheet bundle in the sheet width direction using the lateral alignment jogger 58 (alignment member) so that the end of the sheet bundle loaded in the intermediate loading unit along the sheet transport direction contacts the lateral reference plate 52 and aligns with it.

[0089] In the lateral alignment process in the binding unit 4A, the narrower the width of the sheets included in the sheet bundle, the longer the distance between the edge of the sheet and the lateral alignment reference plate 52 in the sheet width direction, and the greater the amount of movement of the lateral alignment jogger 58 when lateral alignment is performed. In addition, the amount of movement of the sheet itself in the sheet width direction when lateral alignment is performed also increases. When the amount of movement of the sheet in the sheet width direction increases, a force is generated that causes the sheet bundle to be laterally aligned to pivot due to friction between the sheet bundle to be aligned and the intermediate lower guide 32 or the sheet that has been previously loaded onto the intermediate lower guide 32. This leads to a decrease in the lateral alignment capability of the binding unit 4A (a decrease in the accuracy of the alignment process).

[0090] Therefore, when performing post-processing (binding) on ​​narrow sheets, the post-processing device 4 of this embodiment performs a shifting operation in the buffer section to shift the sheet bundle, which is located at the position shown in Figure 3(C), in a direction perpendicular to the transport direction, after generating a stack of sheets in a tile-like state. More specifically, the transport control unit 410 performs the shifting operation on the sheet bundle when the size of the sheet to be processed is less than or equal to a threshold size (for example, the width of the sheet is 148 mm or less). This shifting operation is performed by driving the third reversing motor M5 to move the roller pair of the reversing roller 24. Thus, the reversing roller 24 of this embodiment is provided in the buffer section and is an example of a shifting means that shifts the position of the sheet bundle generated in the buffer section in the sheet width direction.

[0091] When the sheet bundle is transported to the binding processing unit 4A, the post-processing device 4 (transport control unit 410) adjusts the direction in which the distance between the end of the sheet and the transverse alignment reference plate 52 in the sheet width direction becomes shorter. - The sheet bundles are shifted. Specifically, the post-processing device 4 (transport control unit 410) performs a shifting process using the reversing roller 24 to shift the position of the sheet bundles in the sheet width direction so that the amount of sheet movement during lateral alignment (alignment processing in the sheet width direction by the alignment processing unit) is reduced. The sheet bundles that have undergone the shifting process are transported from the buffer unit through the internal discharge path 82 to the binding processing unit 4A.

[0092] In this way, the shifting process using the reversing roller 24 shifts the position of the sheet bundle in the sheet width direction, thereby shortening the distance between the edge of the sheet and the transverse alignment reference plate 52. As a result, even when performing transverse alignment on a sheet bundle that includes narrow sheets, the amount of sheet movement by the transverse alignment jogger 58 can be reduced, and the reduction in the transverse alignment capability of the binding processing unit 4A can be suppressed.

[0093] On the other hand, as described above, if a shifting process is performed using the reversing roller 24 before feeding the sheet bundle to the binding processing unit 4A, it is necessary to avoid collisions between the sheet bundle undergoing the shifting process and subsequent sheets transported from the image forming apparatus 1. For this reason, it is necessary to increase the distance (paper spacing) between sheets transported from the image forming apparatus 1, which may reduce the productivity of the image forming system 1S.

[0094] In this embodiment, the post-processing device 4 controls the amount of sheet shifting when generating stacked sheet bundles in the buffer section to prevent a decrease in productivity of the post-processing device 4, even when the spacing between sheets is widened due to the execution of the shifting process. Specifically, the transport control unit 410 makes the amount of shifting when performing shifting on a sheet bundle smaller than when not performing shifting on a sheet bundle. For example, the amount of shifting when not performing shifting on a sheet bundle is set to 30 mm, and the amount of shifting when performing shifting on a sheet bundle is set to 25 mm, which is 5 mm shorter than that. With this setting, the total length of the stacked sheet bundles transported from the buffer section to the intermediate loading section can be shortened, thus reducing the decrease in productivity of the post-processing device 4 even when the spacing between sheets is widened due to the execution of shifting.

[0095] Furthermore, in the post-processing device 4 of this embodiment, sheet shifting is performed when the size of the sheet to be processed is less than or equal to a threshold size. Therefore, when the size of the sheet to be processed is less than or equal to a threshold size, control is performed to reduce the amount of sheet displacement when generating the sheet bundle, as described above, along with the shifting process. Thus, when performing shifting, it is possible to reduce the decrease in productivity of the post-processing device 4 while maintaining the accuracy of the sheet transport direction alignment process (ensuring longitudinal alignment capability), similar to the first embodiment.

[0096] <Processing Procedure> Referring to Figures 7, 8, 10, and 11, the sheet transport control performed by the transport control unit 410 (CPU 401) in the post-processing device 4 of this embodiment will be described. In this embodiment, the processing in Figures 7 and 8 is the same as in the first embodiment. In S104 of Figure 7, the transport control unit 410 performs the processing according to the procedure in Figure 10.

[0097] <Processing of the second sheet (S104)> The second sheet processing in S104 (processing of the second and subsequent sheets) is performed according to the procedure shown in Figure 10. First, in S401, the transport control unit 410 (CPU 401) determines whether or not to perform the sheet stack shift processing in the buffer unit. In this embodiment, the transport control unit 410 determines to perform shift processing on the sheet stack if the size of the target sheet is less than or equal to the threshold size, and proceeds to S302. On the other hand, if the transport control unit 410 determines not to perform shift processing on the sheet stack, it proceeds to S303.

[0098] In S302 and S303, the transport control unit 410 sets the amount of positional shift in the transport direction when overlapping the target sheet with the preceding sheet, similar to the first embodiment. In S302, a first shift amount (e.g., 25 mm) is used, and in S303, a second shift amount (e.g., 30 mm) that is larger than the first shift amount is used.

[0099] The processing from S304 to S307 is the same as in the first embodiment. In S307, when the rear end of the target sheet detected by the entrance sensor 27 in S101 reaches the switchback branching point, the transport control unit 410 proceeds to S402.

[0100] In S402, the transport control unit 410 、 The transport control unit 410 determines whether there are any subsequent sheets to be added to the stacked sheet bundle generated in the buffer section (i.e., whether any remain). If there are subsequent sheets, the transport control unit 410 proceeds to S308; otherwise, it proceeds to S403. In S403, the transport control unit 410 determines whether to perform the sheet bundle shifting process in the buffer section, similar to S401. If shifting is not performed, it proceeds to S308; if shifting is performed, it proceeds to S404. In S404, the transport control unit 410 performs the sheet bundle shifting process in the buffer section according to the procedure shown in Figure 11.

[0101] On the other hand, if the process proceeds to S308, the transport control unit 410 performs the processing from S308 to S313, as in the first embodiment.

[0102] <Shift processing (S410)> Figure 11 is a flowchart showing the procedure for shifting the sheet bundle using the reversing roller 24 in S410. When the conveying control unit 410 starts the shifting process, in S501 it waits for the first sheet (the bottom sheet) of the stacked sheet bundle generated in the buffer section to pass the position of the internal discharge roller 26 (between the roller pair). The sheet bundle is currently being conveyed towards the upper discharge tray 25 as a result of the processes in S305 and S306. When the rear end of the first sheet of the conveying sheet bundle passes the position of the internal discharge roller 26, the conveying control unit 410 proceeds to S502.

[0103] In S502, the transport control unit 410 stops the reversing roller 24. At this time, since the entire sheet bundle has already passed the internal discharge roller 26, the sheet bundle stops while being held only by the roller pair of the reversing roller 24.

[0104] Next, in S503, the transport control unit 410 drives the third reversing motor M5 for a predetermined time to shift the position of the reversing roller 24 in the sheet width direction, - The position of the sheet bundle is shifted. At this time, the transport control unit 410 shifts the position of the sheet bundle in the direction in which the distance between the edge of the sheet and the transverse alignment reference plate 52 becomes shorter (for example, the direction towards the front in Figure 1). - A sheet stack shifting process is performed. In this way, the position of the reversing roller 24 is shifted, causing the position of the sheet stack held by the reversing roller 24 to shift in the sheet width direction. Depending on the amount of shift of the reversing roller 24 (sheet stack) (e.g., 20 mm), the distance the sheet stack moves in the sheet width direction when lateral alignment is performed in the binding processing unit 4A is shortened.

[0105] When the shift of the reversing roller 24 is complete, the transport control unit 410 proceeds to S504. In S504, the transport control unit 410 starts rotating the reversing roller 24 and the internal discharge roller 26 so that the sheet bundle is transported in the direction of the binding processing unit 4A, and proceeds to S505. In S505, the transport control unit 410 waits for the last sheet (topmost sheet) of the sheet bundle being transported to reach the internal discharge roller 26, and when it reaches the internal discharge roller 26, proceeds to S506.

[0106] In S506, the conveyance control unit 410 separates the reversing rollers 24. At this time, the last sheet in the sheet bundle is being conveyed while being held between the roller pair of the internal discharge rollers 26. Therefore, even if the reversing rollers 24 are separated, the conveyance of the sheet bundle continues.

[0107] Next, in S507, the transport control unit 410 drives the third reversing motor M5 for a predetermined time to shift the position of the reversing roller 24, which was shifted in S503, back to its original position, thereby shifting the position of the reversing roller 24 in the sheet width direction. Once the shift of the reversing roller 24 is complete, the transport control unit 410 proceeds to S508. In S508, the transport control unit 410 brings the reversing roller 24 into contact with the image forming apparatus 1 in preparation for transporting the subsequent sheet.

[0108] The determination of the seat position in S501 and S505 may be based on the elapsed time relative to the detection timing of the rear end of the target seat by the entrance sensor 27. Alternatively, the determination may be based on the count value of the drive pulse of each motor.

[0109] As described above, when sheet stack shifting is performed in the buffer section according to the procedure in Figure 11, it is necessary to avoid collisions between the sheet stack being shifted and subsequent sheets transported from the image forming apparatus 1. For this reason, it is necessary to increase the distance (paper spacing) between sheets transported from the image forming apparatus 1, which may reduce the productivity of the image forming system 1S.

[0110] In this embodiment, by performing the process according to the procedure in Figure 10, - When performing sheet stack shifting, the overall length of the stacked sheet bundles generated in the buffer section in the transport direction is shortened. This reduces the decrease in productivity of the post-processing device 4, even when the spacing between sheets is widened during the shifting process. Furthermore, sheet shifting is performed when the size of the sheet to be processed is below a threshold size, and accordingly, control is performed to reduce the amount of sheet displacement when generating the sheet bundle. Therefore, when performing shifting, it is possible to reduce the decrease in productivity of the post-processing device 4 while maintaining the accuracy of the sheet transport direction alignment process (ensuring vertical alignment capability).

[0111] [Other embodiments] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0112] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of symbols]

[0113] 1S: Image forming system, 1: Image forming apparatus, 4: Post-processing device, 4A: Binding processing unit, 400: Finisher control unit, 401: CPU, 410: Conveying control unit, 412: Information acquisition unit, 24: Reversing roller, 26: Internal discharge roller, 81: Receiving path, 82: Internal discharge path, 83: First discharge path, 33: Vertical alignment roller, 39: Vertical alignment reference plate, 52: Horizontal alignment reference plate, 58: Horizontal alignment jogger (alignment member)

Claims

1. A sheet processing device, A loading section where sheets to be processed are loaded, A buffer section provided in a transport path for transporting sheets to the loading section generates a sheet bundle by sequentially shifting the positions of the sheets being transported along the transport path upstream in the transport direction, and a control means controls the transport of sheets along the transport path so as to transport the sheet bundle from the buffer section to the loading section. Alignment means for performing alignment processing to align the position of the sheets in the transport direction with respect to the sheet bundle loaded in the loading section, The system includes processing means for performing sheet processing on the sheet bundle that has undergone the aforementioned matching process, The control means controls the amount of positional shift of the sheets when stacking the sheets sequentially in the buffer section, according to the size of the sheets being transported along the transport path. The control means reduces the amount of displacement when the size of the sheet being transported along the transport path is less than or equal to a threshold size, compared to when the size is not less than or equal to the threshold size. A sheet processing apparatus characterized by the following:

2. The control means reduces the amount of displacement as the size of the sheet being transported along the transport path decreases. The sheet processing apparatus according to feature 1.

3. The control means determines whether the size of the sheet being transported along the transport path is less than or equal to the threshold size, based on at least one of the length of the sheet in the transport direction and the width of the sheet in the width direction perpendicular to the transport direction. The sheet processing apparatus according to feature 1.

4. The control means determines, based on the sheet size set by the user, whether the size of the sheet being transported along the transport path is less than or equal to the threshold size. The sheet processing apparatus according to feature 1 or 3.

5. The system further includes measuring means provided upstream of the buffer in the transport direction for measuring at least one of the length of the sheet being transported along the transport path in the transport direction and the width of the sheet in the width direction perpendicular to the transport direction, The control means determines, based on the measurement results from the measurement means, whether the size of the sheet being transported along the transport path is less than or equal to the threshold size. The sheet processing apparatus according to feature 1 or 3.

6. The alignment means includes an alignment roller that is rotationally driven to move the sheet in the transport direction, and a first reference plate provided along the width direction perpendicular to the transport direction. The sheet bundle loaded in the loading section is moved one sheet at a time from the bottom downstream in the transport direction by the alignment roller, and the end of each sheet is brought against the first reference plate to perform alignment processing in the transport direction for the sheet bundle. A sheet processing apparatus according to any one of claims 1 to 5.

7. When the alignment process is initiated, the alignment roller contacts the bottom sheet of the sheet bundle loaded in the loading section. The sheet processing apparatus according to claim 6.

8. The alignment means further performs an alignment process to align the position of the sheets in the width direction perpendicular to the transport direction with respect to the sheet bundle loaded in the loading section. The sheet processing apparatus further comprises a shifting means provided in the buffer section for shifting the position of the sheet bundle generated in the buffer section in the width direction, The control means performs a shift operation by the shift means to shift the position of the sheet bundle in the width direction so that the amount of sheet movement in the width direction alignment process by the alignment means is reduced. A sheet processing apparatus according to any one of claims 1 to 7.

9. The alignment means includes an alignment member and a second reference plate provided along the transport direction, and performs the widthwise alignment process on the sheet bundle by moving the sheet bundle in the width direction with the alignment member so that the ends of the sheet bundle stacked in the loading section along the transport direction come into contact with the second reference plate and are aligned. The sheet processing apparatus according to feature 8.

10. The control means performs the shift process on the sheet bundle when the size of the sheets being transported along the transport path is less than or equal to a threshold size. The sheet processing apparatus according to claim 8 or 9.

11. The control means makes the amount of shift when performing the shift process on the sheet bundle smaller than when not performing the shift process on the sheet bundle. The sheet processing apparatus according to feature 10.

12. The processing means performs a binding process as the sheet processing, binding the bundle of sheets stacked in the stacking section. A sheet processing apparatus according to any one of claims 1 to 11.

13. An image forming apparatus that forms an image on a sheet, A sheet processing apparatus according to any one of claims 1 to 12, which is connected to the downstream side of the image forming apparatus in the sheet transport direction and performs sheet processing on sheets transported from the image forming apparatus through a transport path, An image forming system characterized by comprising the following features.

Images