Post-processing device, image forming device, and image forming system

Abstract

To provide a post-processing apparatus that improves accuracy of skew correction of stacked sheets, when performing post-processing including processing of superposing a plurality of sheets.SOLUTION: There is provided a post-processing apparatus comprising a control unit for controlling operations of first conveyance means, second conveyance means and third conveyance means, the apparatus provided with a circulation conveyance passage for circulating a sheet to a first conveyance passage, a second conveyance passage and a third conveyance passage. The control unit stops a preceding sheet at an arbitrary position of the circulation conveyance passage when superposing a plurality of sheets in the circulation conveyance passage; subsequently conveys a succeeding preceding sheet to the first conveyance passage so as to overlap with a following subsequent sheet by displacing in a conveyance direction with a predetermined displacement amount; and abuts the preceding sheet and the subsequent sheet that overlap in the first conveyance passage on the first conveyance means.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a post-processing device, an image forming device including the post-processing device, and an image forming system. [Background technology]

[0002] Post-processing devices are known that perform predetermined post-processing on sheet-like recording media on which images have been formed. Image forming apparatuses that include post-processing devices as part of them are also known, and image forming systems that connect post-processing devices and image forming apparatuses are also known.

[0003] When an image forming process on a sheet and subsequent processing (post-processing) are performed as a series of operations, the processing time for the post-processing may require waiting for the next image forming process, which may result in reduced productivity. To address this issue, post-processing devices are known that are equipped with a pre-stacking mechanism that temporarily stores sheets conveyed after image forming processes within the post-processing device, thereby reducing the waiting time on the image forming device due to the processing time for post-processing.

[0004] Patent Document 1 discloses an apparatus equipped with a circulating conveyance path to realize a pre-stacking mechanism without increasing the size of the apparatus. Patent Document 1 also discloses a technique for overlapping sheets by abutting a preceding sheet and a succeeding sheet against conveyance rollers arranged in the circulating conveyance path. Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology of Patent Document 1, when a sheet that has circulated along a circulating conveying path hits a conveying roller, it bends, hindering the conveyance of the subsequent sheet, and the skew of the subsequent sheet cannot be corrected.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a post-processing device that improves the accuracy of correcting skew of overlapped sheets when performing post-processing including overlapping processing on a plurality of sheets. [Means for solving the problem]

[0007] In order to solve the above technical problem, one aspect of the present invention is a post-processing device including a circulating conveyance path, which circulates the sheet along the first conveyance path, the second conveyance path, and the third conveyance path in this order by a first conveyance means that conveys the sheet downstream while the sheet is conveyed along a first conveyance path, a second conveyance means that conveys the sheet along a second conveyance path, and a third conveyance means that conveys the sheet along a third conveyance path, and further including a control unit that controls operations of the first conveyance means, the second conveyance means, and the third conveyance means, and the control unit stops a leading sheet at an arbitrary position on the circulating conveyance path when a plurality of the sheets are superimposed on each other on the circulating conveyance path, and then shifts the leading sheet by a predetermined amount in the conveyance direction relative to a subsequent sheet. Delay and overlap and conveying the preceding sheet and the succeeding sheet, which are overlapped on the first conveying path, to the first conveying path in such a manner that the preceding sheet and the succeeding sheet are conveyed ... The tip abutting against the first conveying means When this occurs, the operation of the first conveying means is stopped. It is characterized by: [Effects of the Invention]

[0008] According to the present invention, when post-processing including overlapping processing of a plurality of sheets is performed, the accuracy of correcting the skew of the overlapped sheets can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view showing an embodiment of an image forming apparatus including a post-processing device according to the present invention; [Figure 2] FIG. 2 is a block diagram showing an example of a control configuration according to the embodiment. [Figure 3] 1 is a diagram showing the internal configuration of a sheet folding device as an embodiment of a post-processing device according to the present invention; [Figure 4] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 5] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 6] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 7] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 8] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 9] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 10] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 11] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 12] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 13] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 14] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 15] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 16] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 17] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 18] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 19] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 20] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 21] FIG. 2 is an enlarged view of an internal configuration of the sheet folding device according to the embodiment. [Figure 22] 10 is a flowchart showing a first example of processing executed by the sheet folding device. [Figure 23] 10 is a flowchart showing a first example of processing executed by the sheet folding device. [Figure 24] 10 is a flowchart showing a first example of processing executed by the sheet folding device. [Figure 25] 10 is a flowchart showing a first example of processing executed by the sheet folding device. [Figure 26] 10 is a flowchart showing a first example of processing executed by the sheet folding device. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment of Image Forming Apparatus] First, an embodiment of an image forming apparatus according to the present invention will be described. Fig. 1 is an external view of a printer 1 as an image forming apparatus. The printer 1 has a printer main body 100 as an image forming unit, and a sheet folding device 200 as a post-processing device connectable to the printer main body 100. As shown in Fig. 1, the printer 1 is an internal discharge type, and the sheet folding device 200 is incorporated into a part of the printer main body 100. That is, in the printer 1, the post-processing device to which a recording medium on which an image has been formed is discharged corresponds to the sheet folding device 200. The internal configuration of the sheet folding device 200 will be described later.

[0011] [Control block functional configuration] Next, an embodiment of a control block that controls the operation of the printer main body 100 and the sheet folding device 200 according to this embodiment will be described with reference to Fig. 2. As shown in Fig. 2, the printer main body 100 includes a printer control unit 10 as a control block. The printer control unit 10 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, and a serial I / F 14.

[0012] The printer control unit 10 is connected to an image creation unit 20, an image reading unit 30, and an operation display unit 40. The image creation unit 20, the image reading unit 30, and the operation display unit 40 each include components for performing their respective functions. Each component included in the image creation unit 20, the image reading unit 30, and the operation display unit 40 operates based on a control signal from the printer control unit 10.

[0013] The image creation unit 20 is configured to perform image formation processing based on image data on a sheet P, which is a sheet-like recording medium. The image reading unit 30 is configured to acquire image data by reading an image formed on the sheet P. The operation display unit 40 has a function of serving both as an input unit for inputting operating conditions for the image creation unit 20 and the image reading unit 30, and as a display unit for displaying operation results, etc.

[0014] Control programs for controlling the image creation unit 20, image reading unit 30, and operation display unit 40 are stored in ROM 12. CPU 11 reads out the control programs stored in ROM 12 and loads them into RAM 13. CPU 11 then stores data necessary for control in RAM 13 and executes the control defined by the control programs while using RAM 13 as a work area.

[0015] 2, the sheet folding device 200 includes a post-processing control unit 50 as a control block. The post-processing control unit 50 includes a CPU 51, a ROM 52, a RAM 53, and a serial I / F .

[0016] The post-processing control unit 50 is connected to various loads 60 and various sensors 70. The various loads 60 include rollers and roller pairs, which will be described later. The rollers and roller pairs corresponding to the various loads 60 constitute conveying roller pairs and folding roller pairs, respectively. The various loads 60 are operated by drive motors that rotate each roller and each roller pair. The drive motors that constitute the various loads 60 are operated by instructions from a driver 61 connected to the post-processing control unit 50. The various loads 60 are configured to perform operations including conveying control of sheets P as recording media and folding processing of the sheets P.

[0017] The various sensors 70 are a plurality of sheet detection means that detect the position of the sheet P in the transport path, and a plurality of sensors 70 are arranged in the transport path described below. The transport amount and position of the sheet P to be subjected to post-processing are determined by the post-processing control unit 50 performing processing in accordance with a predetermined control program based on detection signals output from the various sensors 70 to the post-processing control unit 50. Note that the position of the sheet P can be calculated by the post-processing control unit 50 based on the operation amount of the various loads 60, which is the transport amount (transport distance) of the sheet P after the leading edge of the sheet P is detected by the sheet detection means.

[0018] A control program for the post-processing control unit 50 to execute predetermined processing functions is stored in ROM 52. The CPU 51 reads out the control program stored in ROM 52 and loads it in RAM 53. The CPU 51 then stores data necessary for control in RAM 53 and executes control of the folding operation defined by the control program while using the RAM 53 as a work area. As described above, the post-processing control unit 50 executes the control program stored in ROM 52, thereby enabling detection of the sheet P and control of the conveyance of the sheet P, which will be described later.

[0019] The printer control unit 10 provided in the printer main body 100 and the post-processing control unit 50 provided in the sheet folding device 200 are communicatively connected via the serial I / F 14 and serial I / F 54. This communication path is used to exchange control commands and information necessary for recording medium transport control, etc. The sheet folding device 200 switches between recording medium transport control, folding process, and the type of folding process based on the control commands and information about the sheet P sent from the printer main body 100, and information about the position of the recording medium obtained from various sensors 70.

[0020] The information about the sheet P sent from the printer main body 100 (printer control unit 10) to the sheet folding device 200 (post-processing control unit 50) includes sheet type information such as the type and thickness of the sheet P passed from the printer main body 100 to the sheet folding device 200. The information also includes information indicating the number of overlaps for the sheet P, the type of folding process for the sheet P, and whether or not an image of the folding position of the sheet P is present. The control command notified from the printer control unit 10 to the post-processing control unit 50 also includes information such as whether or not the passed sheet P corresponds to the last page (final sheet) of a unit to be processed collectively.

[0021] [First embodiment of post-processing device] Next, the internal configuration of the sheet folding device 200 according to the first embodiment of the post-processing device will be described. Fig. 3 is a schematic diagram showing the internal configuration of the sheet folding device 200. The sheet folding device 200 is equipped with a plurality of conveying paths, a plurality of roller pairs, and a plurality of sheet detection sensors. The plurality of roller pairs each constitute a conveying means or a folding means.

[0022] The sheet folding device 200 has roughly seven conveying paths: a first conveying path W1, a second conveying path W2, a third conveying path W3, a fourth conveying path W4, a fifth conveying path W5, a sixth conveying path W6, and a seventh conveying path W7, as shown in FIG.

[0023] Furthermore, the sheet folding device 200 has a plurality of roller pairs arranged along each of the first conveying path W1, the second conveying path W2, the third conveying path W3, the fourth conveying path W4, the fifth conveying path W5, and the sixth conveying path W6. That is, the roller pairs constituting the zeroth conveying means R0, the first conveying means R1, the second conveying means R2, the third conveying means R3, the fourth conveying means R4, the fifth conveying means R5, and the sixth conveying means R6 are arranged at respective positions on the conveying paths for conveying the sheet P. These conveying means start and stop conveying the sheet P by operating according to a control program executed by the post-processing control unit 50.

[0024] The sheet folding device 200 also includes a plurality of conveyance branching means. The plurality of conveyance branching means, for example, convey the sheet P from the first conveyance path W1 to the second conveyance path W2, and then switch to a circulating conveyance path that circulates the sheet P between the first conveyance path W1 and the third conveyance path W3. The conveyance branching means also switches the conveyance path so that the sheet P is conveyed downstream of the second conveyance path W2 from the first conveyance path W1 to a fourth conveyance path downstream without turning to the circulating conveyance path. The conveyance branching means also switches the conveyance path so that the sheet P is conveyed from the first conveyance path W1 to a fifth conveyance path downstream of the second conveyance path W2 via the second conveyance path W2. The sheet folding device 200 is provided with a plurality of conveyance branching means so as to switch the conveyance paths in this manner.

[0025] 4 to 10, the plurality of conveying / branching means include a first conveying / branching means J1, a second conveying / branching means J2, and a third conveying / branching means J3. These plurality of conveying / branching means are included in various loads 60 whose operation is controlled by the post-processing control unit 50. Therefore, the post-processing control unit 50 controls the operation of the plurality of conveying / branching means to control the conveying path of the sheet P. Note that a first folding means F1 and a second folding means F2 for folding the sheet P are also arranged along the circulating conveying path.

[0026] In the sheet folding device 200, a zeroth conveying means R0 serving as an inlet conveying roller pair is disposed near the entrance 21 that receives the sheet from the printer main body 100. In the zeroth conveying means R0, a drive motor that rotates and drives the zeroth conveying means R0 starts to rotate under the control of the post-processing control unit 50 that has received information notifying that the sheet P has been discharged from the printer main body 100. Thereafter, when the leading edge of the sheet P reaches the nip of the roller pair of the zeroth conveying means R0, the zeroth conveying means R0 conveys the sheet P downstream.

[0027] As will be described later, the sheet folding device 200 receives the next sheet P before discharging the sheet P conveyed from the printer main body 100 from the downstream exit 22, and performs conveying and folding processes with the previous sheet P and the subsequent sheet P overlapping each other. Therefore, in the following description, for the sake of convenience, the previous sheet P will be referred to as the "previous sheet P1." Furthermore, the sheet P following the previous sheet P1 and received by the sheet folding device 200 after the previous sheet P1 will be referred to as the "subsequent sheet P2." The sheet P received by the sheet folding device 200 after the subsequent sheet P2 and to be subjected to the overlapping process will be referred to as the "next sheet P3." Furthermore, a stack of multiple sheets P will be referred to as a "sheet stack Q."

[0028] The number of sheets P to be overlapped or folded in the sheet folding device 200 is not limited to three, and more sheets can be processed.

[0029] The first conveying means R1 is composed of a pair of rollers facing each other across the first conveying path W1, forming a nip between the rollers. The first folding means F1 is disposed between the first conveying path W1 and the second conveying path W2, facing each other, forming a nip between them. The path guided by this nip leads the preceding sheet P1 from the first conveying path W1 to the second conveying path W2.

[0030] Furthermore, the second transport means R2 guides the preceding sheet P1 guided to the second transport path W2 to the third transport path W3, and the third transport means R3 temporarily stops the transport of the preceding sheet P1 on the third transport path W3. The preceding sheet P1 temporarily stopped on the third transport path W3 resumes transport when the subsequent sheet P2 is received from the printer main body 100. As a result, the preceding sheet P1 returns to the upstream side of the first transport means R1 on the first transport path W1 and merges with the subsequent sheet P2. The circulating transport path is configured as described above.

[0031] In the above-described circulatory conveyance path, the preceding sheet P1 and the succeeding sheet P2 are stacked to form the sheet bundle Q. Next, a flow of the folding process for the sheet bundle Q will be described.

[0032] The sheet bundle Q is folded by the first folding means F1, which operates under the control of the post-processing control unit 50. The sheet bundle Q, which has been folded by the first folding means F1, is then transferred from the second conveying path W2 to the fifth conveying path W5. The fourth conveying means R4, the fifth conveying means R5, and the first folding means F1 are driven by the same drive motor. The drive motor can rotate in both forward and reverse directions, and by changing the rotation direction, the sheet bundle Q, in which the preceding sheet P1 and the succeeding sheet P2 are overlapped, is conveyed and folded again.

[0033] In addition, a branch claw 23 is disposed immediately behind the sixth conveying means R6. The branch claw 23 switches its guide position between when guiding the sheets P (sheet stack Q) to the sixth conveying path W6 side and when guiding the sheets P (sheet stack Q) to the seventh conveying path W7 side. The branch claw 23 can switch its position using, for example, a solenoid. Note that a drive mechanism including a motor, gears, cams, etc. may be used instead of a solenoid.

[0034] The sheet P that has passed through the fourth conveying path W4 or the fifth conveying path W5 is discharged and stacked on the discharge tray 24 of the sheet folding device 200. The seventh conveying path W7 is a path for delivering the sheet P to a post-processing device when the image forming system includes a post-processing device downstream of the sheet folding device 200. The post-processing device performs post-processing such as alignment and binding on the folded sheet P or the unfolded sheet P.

[0035] A first sheet detection sensor SN1 is disposed immediately after the zero conveying means R0 on the first conveying path W1. A second sheet detection sensor SN2 is disposed immediately before the first conveying means R1. A third sheet detection sensor SN3 is disposed immediately after the second conveying means R2 on the third conveying path W3. A fourth sheet detection sensor SN4 is disposed immediately after the third conveying means R3 on the third conveying path W3. A fifth sheet detection sensor SN5 is disposed immediately after the fourth conveying means R4 on the fourth conveying path W4. A sixth sheet detection sensor SN6 is disposed immediately after the fifth conveying means R5 on the fifth conveying path W5. A seventh sheet detection sensor SN7 is disposed immediately after the sixth conveying means R6 on the sixth conveying path W6.

[0036] The sheet folding device 200 shown in Fig. 3 can fold the overlapping sheets P inward and outward in three. Figs. 4 to 10 explain the operating means for overlapping two sheets P via a circulating conveyance path to generate a sheet bundle Q.

[0037] 4 shows the initial state before sheet P is transported from the printer main body 100. When the leading edge of preceding sheet P1 transported from the printer main body 100 reaches the paper discharge outlet of the printer main body 100, the post-processing control unit 50 starts rotating the zeroth transport means R0. This causes preceding sheet P1 to be received by first transport path W1 and transported as shown in FIG. 6. Furthermore, in order to transport preceding sheet P1 to second transport path W2 instead of fourth transport path W4, the post-processing control unit 50 moves first transport branch means J1 to the position shown in FIG. 4.

[0038] When the first sheet detection sensor SN1 detects the leading edge of the preceding sheet P1 conveyed by the zeroth conveying means R0, a detection signal is sent to the post-processing control unit 50. At that time, the first conveying means R1 is stopped. As shown in Fig. 5, the post-processing control unit 50 maintains the stopped state of the first conveying means R1 from when the detection signal is sent until the conveyance amount (first protrusion amount Δ1) of the preceding sheet P1 required to form a flexure in the preceding sheet P1 to correct the skew at the leading edge of the preceding sheet P1 reaches a predetermined value.

[0039] Thereafter, the post-processing control unit 50 starts the rotation of the first conveying means R1 at the timing when the first protrusion amount Δ1 reaches a predetermined value, that is, at the time when the skew correction of the leading edge of the preceding sheet P1 is completed.

[0040] When the leading edge of the preceding sheet P1 enters the nip of the first conveying means R1, the post-processing control section 50 rotates the first folding means F1, the second conveying means R2, and the third conveying means R3.

[0041] 7, the preceding sheet P1 is conveyed to the second conveying path W2 by the operation of the first conveying means R1 and the first folding means F1, and is conveyed along the downward slope of the second conveying path W2. The second conveying means R2 conveys the preceding sheet P1 to the third conveying path W3. The third conveying means R3 then conveys the preceding sheet P1 to the fourth sheet detection sensor SN4. When the leading edge of the preceding sheet P1 is detected by the fourth sheet detection sensor SN4, a detection signal is sent from the fourth sheet detection sensor SN4 to the post-processing control unit 50. After receiving the detection signal, the post-processing control unit 50 calculates the timing at which the preceding sheet P1 is conveyed and its leading edge reaches a position corresponding to the second protrusion amount Δ2 from the position of the fourth sheet detection sensor SN4.

[0042] As shown in Figure 8, when it is determined that the leading edge of the preceding sheet P1 has reached a position corresponding to the second protrusion amount Δ2, the rotation of the first conveying means R1, the first folding means F1, the second conveying means R2, and the third conveying means R3 is stopped, and the conveyance of the preceding sheet P1 is stopped.

[0043] Even when the conveyance of the preceding sheet P1 is stopped, the zeroth conveying means R0 continues to rotate in order to receive the succeeding sheet P2 conveyed next from the printer main body 100.

[0044] Next, after receiving a detection signal indicating that the leading edge of the subsequent sheet P2 has been detected by the first sheet detection sensor SN1, the post-processing control unit 50 calculates the timing for stopping the subsequent sheet P2. This timing corresponds to the timing for the leading edge of the subsequent sheet P2 to reach a position corresponding to the third protrusion amount Δ3 from the first sheet detection sensor SN1. Then, when the leading edge of the subsequent sheet P2 reaches a position corresponding to the third protrusion amount Δ3, the post-processing control unit 50 resumes rotation of the second conveying means R2 and the third conveying means R3. As a result, as shown in FIG. 9, the conveyance of the preceding sheet P1, which had been stopped, is resumed. In this way, the leading edge of the subsequent sheet P2 contacts the stopped first conveying means R1 slightly before the leading edge of the preceding sheet P1 contacts the first conveying means R1, thereby correcting the skew of the subsequent sheet P2.

[0045] The third protrusion amount Δ3 is calculated based on the motor speeds of the zeroth conveying means R0 and the third conveying means R3, and the positions of the zeroth conveying means R0, the third conveying means R3, the first sheet detection sensor SN1, the second sheet detection sensor SN2, and the fourth sheet detection sensor SN4, i.e., the distances between these members. The third protrusion amount Δ3 is also used to determine the amount of offset when the leading edges of the preceding sheet P1 and the following sheet P2 meet just before the first conveying means R1.

[0046] Thereafter, as shown in Figure 10, by restarting the rotation of the first conveying means R1, the leading edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2 merge just before the second sheet detection sensor SN2, and a sheet bundle Q is generated, which passes through the nip of the first conveying means R1 and is conveyed downstream.

[0047] Thereafter, the post-processing control unit 50 determines whether the overlapping and folding number setting notified from the printer main body 100 matches the number of sheets received, and if they match, performs the folding process described below. If they do not match, the process from Figures 7 to 9 is repeated, and the next sheet P3 (the sheet P following the subsequent sheet P2) conveyed from the printer main body 100 side is merged with the sheet stack Q and overlapped. Whether the sheet P has been conveyed to just before the nip of the second conveying means R2 can be determined, for example, from the number of drive steps of the motor that drives the first conveying means R1. Therefore, it is desirable that the drive motor that rotates and drives each conveying means be a stepping motor.

[0048] [Embodiment of folding process] Next, a description will be given of the flow of folding processing in the sheet folding device 200 according to this embodiment. Figures 11 to 14 are explanatory diagrams of the operation of folding the sheet bundle Q received from upstream into three on the outside.

[0049] 10, the joined sheet bundle Q is conveyed by the zeroth conveying means R0 and the first conveying means R1 as it is. Then, when the leading edge of the sheet bundle Q enters the nip of the first conveying means R1, the sheet bundle Q is conveyed to the fourth conveying means R4 side.

[0050] When the sheets have been conveyed to just before the nip of the fourth conveying means R4, the post-processing control unit 50 drives the motor to rotate the fourth conveying means R4 in the direction of the arcuate arrow in FIG. 11 in addition to the first conveying means R1, which is rotating in the direction of the arcuate arrow in FIG. 11. The leading edge of the sheet stack Q is conveyed from the point where it is detected by the fifth sheet detection sensor SN5 until the leading edge of the sheet stack Q reaches the fourth protrusion amount Δ4. When the leading edge of the sheet stack Q reaches the fourth protrusion amount Δ4, the post-processing control unit 50 temporarily stops the fourth conveying means R4.

[0051] Next, while rotating the first conveying means R1 in the conveying direction, the post-processing control unit 50 reversely rotates the fourth conveying means R4 (first folding means F1) so as to convey the sheet bundle Q in the opposite direction to the conveying direction shown in Fig. 11 (see Fig. 12). Due to this reverse rotation of the fourth conveying means R4, the sheet bundle Q is conveyed in the reverse direction.

[0052] 13, the first conveying means R1 rotates in the conveying direction to convey the sheet bundle Q, and the fourth conveying means R4 conveys the sheet bundle Q in the opposite direction to the conveying direction. As a result, a flexure is formed in the sheet bundle Q just before the nip of the first folding means F1. This flexure enters the nip, where the first fold is performed, forming the first fold.

[0053] The sheet bundle Q that has been subjected to the first fold is transported to the second transport path W2 and transported along the downward inclination of the second transport path W2 from the point where the leading edge of the sheet bundle Q is detected by the third sheet detection sensor SN3 until the leading edge of the sheet bundle Q reaches the fifth protrusion amount Δ5. When the leading edge of the sheet bundle Q reaches the fifth protrusion amount Δ5, the post-processing control unit 50 temporarily stops the second transport means R2.

[0054] Next, the post-processing control unit 50 rotates the second conveying unit R2 in the reverse direction relative to FIG. 13 while rotating the fourth conveying unit R4 (first folding unit F1) in the conveying direction. This reverse rotation of the second conveying unit R2 conveys the sheet bundle Q in the reverse direction. Meanwhile, the post-processing control unit 50 rotates the fourth conveying unit R4, which also functions as the first folding unit F1, in the direction continued from FIG. 13 to convey the sheet bundle Q. As a result, as shown in FIG. 14, a flexure is formed just before the nip of the second folding unit F2, which also functions as the fifth conveying unit R5. Then, this flexure enters the nip, where a second fold is performed, forming a second fold.

[0055] The sheet bundle Q that has been subjected to the second fold passes through the fifth transport path W5 and is transported to the discharge tray 24. The fourth protrusion amount Δ4 and the fifth protrusion amount Δ5 are determined based on the overall length of the sheet P and the folding method set for the sheet P (sheet bundle Q). Then, the post-processing control unit 50 determines whether the leading edge of the sheet P or the sheet bundle Q has moved to a position corresponding to the fourth protrusion amount Δ4 based on the amount of rotation of the fourth transport means R4 (i.e., the number of driving steps of the drive motor), and determines whether the leading edge of the sheet P or the sheet bundle Q has moved to a position corresponding to the fifth protrusion amount Δ5 based on the amount of rotation of the second transport means R2 (i.e., the number of driving steps of the drive motor).

[0056] In the case of an outward three-fold, the outward fold (first fold) is made at a position corresponding to 2 / 3 of the total length of the sheet P from the leading edge in the conveyance direction of the sheet P. Then, the inward fold (second fold) is made at a position corresponding to 2 / 3 of the total length of the sheet P. In the case of an inward three-fold, the outward fold (first fold) is made at a position corresponding to 1 / 3 of the total length of the sheet P from the leading edge in the conveyance direction of the sheet P, and the inward fold (second fold) is made at a position corresponding to 2 / 3 of the total length.

[0057] [First operation example] Next, an example of the operation of the sheet folding device 200 according to this embodiment will be described with reference to the drawings. Figures 15 and 16 are explanatory diagrams of the operation in which the leading edge of the preceding sheet P1 staying on the third conveying path W3 is shifted to precede the leading edge of the succeeding sheet P2 in the conveying direction, and the sheets are conveyed in an overlapping state.

[0058] As shown in FIG. 15, if the leading edge of the preceding sheet P1 precedes the following sheet P2, the leading edge of the preceding sheet P1 will strike the rollers of first conveying means R1 before the following sheet P2 contacts first conveying means R1. The preceding sheet P1, whose leading edge strikes the rollers of first conveying means R1, will bend as shown in FIG. 16. Since the following sheet P2 received from the printer main body 100 is positioned above the preceding sheet P1 on the first conveying path W1, the following sheet P2 will also bend due to the influence of the bending of the preceding sheet P1. As a result, as shown in FIG. 16, the following sheet P2 will be pushed aside by the preceding sheet P1, and the leading edge of the following sheet P2 will not reach the rollers of first conveying means R1 and will not be able to strike them.

[0059] As a result, the skew correction of the succeeding sheet P2 is insufficient, and when the succeeding sheet P2 and the preceding sheet P1 are overlapped, the leading edges of the sheets P included in the sheet stack Q are misaligned. Note that the above problem occurs even when the leading edges of the preceding sheet P1 and the succeeding sheet P2 staying on the third transport path W3 are overlapped so that they do not lead each other. However, the causes of this include variations in the first sheet detection sensor SN1 and the fourth sheet detection sensor SN4, curling of the sheet P, and mechanical variations in the mounting positions of each sensor. These factors cause the preceding sheet P1 to be transported first when overlapped, resulting in the above problem.

[0060] 17 and 18 are explanatory diagrams of the operation when the succeeding sheet P2 is conveyed overlapping the preceding sheet P1 with the leading edge of the succeeding sheet P2 shifted in the conveying direction to precede the leading edge of the preceding sheet P1 by an amount corresponding to the gap G. If conveyance is performed in the state shown in Fig. 17, the leading edge of the succeeding sheet P2 will abut against the rollers of the first conveying means R1 before the leading edge of the preceding sheet P1 contacts the first conveying means R1.

[0061] At this time, the succeeding sheet P2 is bent, but because the preceding sheet P1 is below the succeeding sheet P2 on the first transport path W1, the preceding sheet P1 is not affected by the bend of the succeeding sheet P2. Therefore, both the leading edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2 can reach the first transport means R1. This makes it possible to prevent insufficient skew correction due to the bend of the sheet P and misalignment between the leading edges of overlapping sheets, as shown in FIG. 16.

[0062] There are several methods for determining the timing to resume conveyance of the preceding sheet P1 staying on the third conveyance path W3. In the following example, a method will be described when the conveyance speed of the preceding sheet P1 and the conveyance speed of the subsequent sheet P2 are the same. In the following description, the point where the leading edge of the preceding sheet P1 joins the subsequent sheet P2 is designated as H, as shown in FIG.

[0063] Then, the distance from the meeting point H to the leading edge of the preceding sheet P1, which protrudes by the second protrusion amount Δ2, is set to be equal to or greater than the sum of the distance from the meeting point H to the leading edge of the succeeding sheet P2, which protrudes by the third protrusion amount Δ3, and the gap G. According to this setting, by restarting rotation of the third conveying means R3 at the timing when the leading edge of the succeeding sheet P2 reaches the third protrusion amount Δ3, the leading edge of the succeeding sheet P2 can be conveyed overlapping with the leading edge of the preceding sheet P1, shifted by the gap G.

[0064] Furthermore, if, due to reasons such as the device layout, it is difficult to set the distance from the meeting point H to the leading edge of the preceding sheet P1 that protrudes by the second protrusion amount Δ2 to a distance equal to or greater than the sum of the distance from the meeting point H to the leading edge of the succeeding sheet P2 that protrudes by the third protrusion amount Δ3 and the gap G, rotation of the third conveying means R3 is resumed at the timing when the leading edge of the succeeding sheet P2 has been conveyed further by the gap G from the third protrusion amount Δ3. By controlling in this manner, the leading edge of the succeeding sheet P2 can be conveyed overlapping with the leading edge of the preceding sheet P1 in a state shifted by the gap G.

[0065] [Second operation example] Next, a second operation example of the sheet folding device 200 according to this embodiment will be described with reference to the drawings. Figures 19 to 21 show an example of the shift amount (gap G) of the leading edges of the preceding sheet P1 and the succeeding sheet P2 when they are overlapped.

[0066] 19 shows an example in which the length of the gap G, which is the amount of shift between the leading edges of the preceding sheet P1 and the succeeding sheet P2 when they are superimposed, is defined as "shift amount A." The length of the gap G is measured in millimeters. Hereinafter, the units of length for the gap G and other protrusion amounts are all assumed to be millimeters, and descriptions thereof will be omitted.

[0067] 19, the leading edge of the overlapping sheets P is shifted by "shift amount A," and in this state, the overlapping sheets P (sheet stack Q) is abutted against the stopped first conveying means R1. In this case, the conveyance of the sheet stack Q is controlled so that the first protrusion amount Δ1 to the first conveying means R1 becomes "a."

[0068] Thereafter, the first conveying means R1 is driven to rotate, thereby conveying the preceding sheet P1 and the succeeding sheet P2 to the first folding means F1, the second conveying means R2, and the third conveying means R3. The post-processing control unit 50 then conveys the sheet stack Q (the preceding sheet P1 and the succeeding sheet P2) from when the fourth sheet detection sensor SN4 detects the leading edge of the preceding sheet P1 or the succeeding sheet P2 until the leading edge reaches a position corresponding to the second protrusion amount Δ2, which is a predetermined discharge amount. The post-processing control unit 50 then stops conveying when the leading edge of the preceding sheet P1 or the succeeding sheet P2 reaches a position corresponding to the second protrusion amount Δ2.

[0069] 20 illustrates a case where the preceding sheet P1 and the succeeding sheet P2 are held and stopped by the third conveying means R3, and then the next sheet P3 following the succeeding sheet P2 is conveyed from the printer main body 100. In this case, the post-processing control unit 50 monitors the elapsed time after the first sheet detection sensor SN1 detects the leading edge of the next sheet P3.

[0070] Then, after a certain period of time has elapsed, the post-processing control unit 50 drives the second conveying means R2 and the third conveying means R3 to overlap the next sheet P3, the subsequent sheet P2, and the preceding sheet P1, as shown in the example of Figure 20. When the next sheet P3 is overlapped on the sheet stack Q consisting of the preceding sheet P1 and the subsequent sheet P2, the length of the gap G at the beginning of these is defined as "shift amount B." Here, B is shorter than A, so that the relationship A>B holds.

[0071] The reason for the above-described control in the post-processing control unit 50 will be explained with reference to FIG. 21. As shown in FIG. 21(a), assume that the preceding sheet P1 and the succeeding sheet P2 are abutted against the first conveying means R1, the skew is corrected, and then the sheets are conveyed along the circulatory conveying path to a position where they are detected by the fourth sheet detection sensor SN4. At this time, the preceding sheet P1 passes on the inside of the circulatory conveying path, and the succeeding sheet P2 passes on the outside. In other words, the moving distance of the preceding sheet P1 is shorter than that of the succeeding sheet P2, like an inner wheel difference.

[0072] 21(b), even if the leading edges of the preceding sheet P1 and the following sheet P2 are aligned at the nip of the first conveying means R1, when the leading edges are detected by the fourth sheet detection sensor SN4, the preceding sheet P1 will be ahead of the following sheet P2. The leading amount C at this time is not limited to that caused by the "inner wheel difference," but is also due to variations in the entry of the preceding sheet P1 and the following sheet P2 into the nip of each conveying means depending on the curl state of the preceding sheet P1 and the following sheet P2.

[0073] Therefore, in order to align the leading edges of the preceding sheet P1 and the succeeding sheet P2 when the fourth sheet detection sensor SN4 detects the leading edges, the leading edge of the succeeding sheet P2 is made to advance relative to the leading edge of the preceding sheet P1 by an amount equivalent to the leading amount C. This leading amount C corresponds to the amount of shift at the timing when the sheets are conveyed downstream from the first conveying means R1.

[0074] Based on the above, the shift amount A of the subsequent sheet P2 when merging with the preceding sheet P1 can be set to a value obtained by adding the preceding amount C to the first protrusion amount Δ1 of the subsequent sheet P2, "a," and further adding "+α" as a margin. Also, the shift amount B of the next sheet P3 when merging with the sheet stack Q (preceding sheet P1 and subsequent sheet P2) can be set to a value obtained by adding "+α" as a margin to the first protrusion amount Δ1 of the next sheet P3, "a."

[0075] The above has been an explanation of an example in which three sheets P are stacked together, but when four or more sheets P are stacked together, the shift amount of the last sheet P to be stacked (final sheet PL) will be different from that of the previous sheets P, as described above.

[0076] [First example of control flow of sheet folding device 200] Next, a description will be given of an example of a control flow of the sheet folding device 200. Note that the control flows described below are all realized by the post-processing control unit 50 executing a control program.

[0077] 22 is a flowchart showing a first example of a control flow of the sheet folding device 200. First, the post-processing control unit 50 acquires information about the sheet P from the printer control unit 10 (S2101). Next, the post-processing control unit 50 stops the conveyance of the preceding sheet P1 when the preceding sheet P1 is conveyed on the circulatory conveyance path and reaches a position corresponding to the second protrusion amount Δ2 after the leading edge is detected by the fourth sheet detection sensor SN4 (S2102).

[0078] Thereafter, the sheet folding device 200 receives the succeeding sheet P2 (S2103). Next, the post-processing control unit 50 determines the type of the preceding sheet P1 (S2104).

[0079] If the preceding sheet P1 is "plain paper," after the leading edge of the succeeding sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to the shift amount A. Then, after the third protrusion amount Δ3 for the succeeding sheet P2 becomes the shift amount A, the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the succeeding sheet P2 to merge on the first conveying path W1 (S2105).

[0080] If the preceding sheet P1 is "cardboard," after the leading edge of the succeeding sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to a shift amount A' that is larger than the shift amount A. Then, after the third protrusion amount Δ3 for the succeeding sheet P2 becomes the shift amount A', the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the succeeding sheet P2 to merge on the first conveying path W1 (S2106).

[0081] In the case of thick paper, after the preceding sheet P1 and the following sheet P2 are overlapped, the following sheet P2 must travel a longer transport distance until it reaches the position of the fourth sheet detection sensor SN4, compared to plain paper, due to the thickness of the preceding sheet P1. Therefore, the amount of shift between the preceding sheet P1 and the following sheet P2 is increased in advance, and the third protrusion amount Δ3 is set to the shift amount A'. This makes it possible to reduce the shift of the leading edges of the preceding sheet P1 and the following sheet P2 when they reach the position where they are detected by the fourth sheet detection sensor SN4.

[0082] The preceding sheet P1 and the succeeding sheet P2 that have joined together on the first transport path W1 are abutted against the stopped first transport means R1, and the skew is corrected (S2107).

[0083] Thereafter, when the folding process is performed, the process is performed in the same manner as described above, and the sheet bundle Q is discharged (S2108).

[0084] [Second Example of Control Flow of Sheet Folding Device 200] 23 is a flowchart showing a second example of the control flow of the sheet folding device 200. First, the post-processing control unit 50 acquires information about the sheet P from the printer control unit 10 (S2201). Next, the post-processing control unit 50 stops the conveyance of the preceding sheet P1 when the preceding sheet P1 is conveyed on the circulatory conveyance path and reaches a position corresponding to the second protrusion amount Δ2 after the leading edge is detected by the fourth sheet detection sensor SN4 (S2202).

[0085] Thereafter, the sheet folding device 200 receives the succeeding sheet P2 (S2203). Next, the post-processing control unit 50 determines the type of the preceding sheet P1 (S2204).

[0086] If the preceding sheet P1 is "plain paper," after the leading edge of the succeeding sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to the shift amount A. Then, after the third protrusion amount Δ3 for the succeeding sheet P2 becomes the shift amount A, the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the succeeding sheet P2 to merge on the first conveying path W1 (S2205).

[0087] Thereafter, the preceding sheet P1 and the succeeding sheet P2 that have joined together on the first conveying path W1 are abutted against the stopped first conveying means R1 and skewed (S2207). The first protrusion amount Δ1 to the first conveying means R1 in S2207 is set to “a”.

[0088] If the preceding sheet P1 is "cardboard," after the leading edge of the succeeding sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to a shift amount A' that is longer than the shift amount A. Then, after the third protrusion amount Δ3 for the succeeding sheet P2 becomes the shift amount A', the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the succeeding sheet P2 to merge on the first conveying path W1 (S2206).

[0089] Thereafter, the preceding sheet P1 and the succeeding sheet P2 that have joined together on the first conveying path W1 are abutted against the stopped first conveying means R1 and skewed (S2208). The first protrusion amount Δ1 to the first conveying means R1 in S2208 is set to “a′” which is larger than “a”.

[0090] After S2207 or S2208, when folding processing is performed, the processing is performed in the flow already described, and the sheet bundle Q is discharged (S2108).

[0091] The first protrusion amount Δ1 when the next sheet P3 is joined with the sheet stack Q (the preceding sheet P1 and the succeeding sheet P2) and abuts against the stopped first conveying means R1 is set to a value even larger than "a'".

[0092] That is, if the shift amount of the preceding sheet P1 and the succeeding sheet P2 is changed to "A'" based on the sheet type information, the first protrusion amount Δ1 of the next sheet P3 is increased when the next sheet P3 is further overlapped. This makes it possible to correct the skew of the preceding sheet P1 and the succeeding sheet P2 while correcting the skew of the next sheet P3, thereby further improving the accuracy of their leading edges.

[0093] [Third Example of Control Flow of Sheet Folding Device 200] 24 is a flowchart showing a third example of the control flow of the sheet folding device 200. First, the post-processing control unit 50 acquires "printing surface information," which is information about the sheet P, from the printer control unit 10 (S2301). Next, the post-processing control unit 50 stops the conveyance of the preceding sheet P1 when the preceding sheet P1 is conveyed on the circulatory conveyance path and reaches a position corresponding to the second protrusion amount Δ2 after the leading edge is detected by the fourth sheet detection sensor SN4 (S2302).

[0094] Thereafter, the sheet folding device 200 receives the succeeding sheet P2 (S2303). Next, the post-processing control unit 50 determines whether the print surface of the preceding sheet P1 is the upper surface or the lower surface (S2304).

[0095] If the printing side of the preceding sheet P1 is "upper side," after the leading edge of the succeeding sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to the shift amount C. Then, after the third protrusion amount Δ3 for the succeeding sheet P2 becomes the shift amount C, the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the succeeding sheet P2 to merge on the first conveying path W1 (S2305).

[0096] If the printing surface of the preceding sheet P1 is "bottom side," after the leading edge of the subsequent sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to a shift amount C' larger than the shift amount C. Then, after the third protrusion amount Δ3 for the subsequent sheet P2 becomes the shift amount C', the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the subsequent sheet P2 to merge on the first conveying path W1 (S2306).

[0097] The preceding sheet P1 and the following sheet P2 that have merged on the first conveying path W1 are abutted against the stopped first conveying means R1 to correct the skew, and then, when folding processing is performed, the processing is carried out in the flow already described, and the sheet stack Q is discharged (S2307).

[0098] In this example, the shift amount of the preceding sheet P1 and the succeeding sheet P2 is changed depending on the state of the image forming surface of the overlapping sheet P. Here, the information that the post-processing control unit 50 receives from the printer control unit 10 is information about the image forming surface (printing surface) of the sheet P.

[0099] When the printed side is the upper side, the post-processing control unit 50 controls the shift amount between the preceding sheet P1 and the succeeding sheet P2 to be "C". When the printed side is the lower side, the post-processing control unit 50 controls the shift amount between the preceding sheet P1 and the succeeding sheet P2 to be "C'". In both "C" and "C'", the preceding sheet P1 is shifted ahead, and the relationship is C'>C.

[0100] If the print surface is on the upper side and image formation is performed using an electrophotographic method, the friction between the sheets P will be reduced due to the effect of toner adhering to the image formation surface. As a result, when folding the sheet stack Q, the succeeding sheet P2 will slip, causing the stack of sheets Q to shift out of alignment. By shifting the sheet P in advance in anticipation of this, it is possible to reduce the shift after folding.

[0101] [Fourth Example of Control Flow of Sheet Folding Device 200] 25 is a flowchart showing a fourth example of the control flow of the sheet folding device 200. First, the post-processing control unit 50 acquires "printing position information," which is information related to the sheet P, from the printer control unit 10 (S2401). Next, the post-processing control unit 50 stops the conveyance of the preceding sheet P1 when the preceding sheet P1 is conveyed on the circulatory conveyance path and reaches a position corresponding to the second protrusion amount Δ2 after the leading edge is detected by the fourth sheet detection sensor SN4 (S2402).

[0102] Thereafter, the sheet folding device 200 receives the succeeding sheet P2 (S2403). Next, the post-processing control unit 50 determines whether or not there is an image at the folding position (S2404).

[0103] When there is an image at the folding position (S2404: YES), after the leading edge of the subsequent sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to the shift amount D. Then, after the third protrusion amount Δ3 for the subsequent sheet P2 becomes the shift amount D, the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the subsequent sheet P2 to merge on the first conveying path W1 (S2405).

[0104] When there is no image at the folding position (S2404: NO), after the leading edge of the subsequent sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to "shift amount D'" which is larger than the shift amount D. Then, after the third protrusion amount Δ3 for the subsequent sheet P2 becomes "shift amount D'", the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the subsequent sheet P2 to merge on the first conveying path W1 (S2406).

[0105] The preceding sheet P1 and the following sheet P2 that have merged on the first conveying path W1 are abutted against the stopped first conveying means R1 to correct the skew, and then, when the folding process is performed, the process is carried out in the flow already described, and the sheet stack Q is discharged (S2407).

[0106] In this example, the printer receives position information for the image to be printed from the printer main body 100. If there is an image at the folding position of the sheet P, the shift amount for the preceding sheet P1 and the succeeding sheet P2 is changed to "D." Also, if there is an image at the folding position of the sheet P, the shift amount for the preceding sheet P1 and the succeeding sheet P2 is changed to "D'." Regardless of the shift amount, the preceding sheet P1 is shifted first.

[0107] If the image contacts the folding position and image formation is performed using an electrophotographic method, the friction between the sheets P will be reduced due to the effect of toner adhering to the image formation surface. As a result, when the sheet stack Q is folded, the succeeding sheet P2 will slip, causing the stack of sheets Q to shift out of alignment. By shifting the sheet P in advance in anticipation of this, it is possible to reduce the shift after folding.

[0108] [Fifth Example of Control Flow of Sheet Folding Device 200] 26 is a flowchart showing a fifth example of the control flow of the sheet folding device 200. First, the post-processing control unit 50 acquires "folding type information," which is information related to the sheet P, from the printer control unit 10 (S2501). Next, the post-processing control unit 50 stops the conveyance of the preceding sheet P1 when the preceding sheet P1 is conveyed on the circulatory conveyance path and reaches a position corresponding to the second protrusion amount Δ2 after the leading edge is detected by the fourth sheet detection sensor SN4 (S2502).

[0109] Thereafter, the sheet folding device 200 receives the succeeding sheet P2 (S2503). Next, the post-processing control unit 50 determines the type of overlapping folding (S2504).

[0110] When the type of overlapping fold is "outside tri-fold," after the leading edge of the subsequent sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to the shift amount E. Then, after the third protrusion amount Δ3 for the subsequent sheet P2 becomes the shift amount E, the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the subsequent sheet P2 to merge on the first conveying path W1 (S2505).

[0111] Thereafter, the preceding sheet P1 and the succeeding sheet P2, which have merged on the first conveying path W1, are pushed against the stopped first conveying means R1 to correct the skew, and then the specified "outer tri-fold" is performed, and the sheet stack Q is discharged (S2507).

[0112] When the type of overlapping fold is not "outside tri-fold," after the leading edge of the subsequent sheet P2 is detected by the first sheet detection sensor SN1, the third protrusion amount Δ3, which is the amount of protrusion from the position of the first sheet detection sensor SN1, is set to a shift amount E' that is larger than the shift amount E. Then, after the third protrusion amount Δ3 for the subsequent sheet P2 becomes the shift amount E', the post-processing control unit 50 resumes rotation of the third conveying means R3, and causes the preceding sheet P1 and the subsequent sheet P2 to merge on the first conveying path W1 (S2506).

[0113] Thereafter, the preceding sheet P1 and the succeeding sheet P2, which have merged on the first conveying path W1, are pushed against the stopped first conveying means R1 to correct the skew, and then the specified "inner tri-fold" is performed, and the sheet stack Q is discharged (S2508).

[0114] In this example, information on the type of fold to be performed by overlapping folding is received from the printer main body 100. If the type of fold is an outward tri-fold, the offset amount (offset amount) between the preceding sheet P1 and the subsequent sheet P2 is changed to "E." If the type of fold is an inward tri-fold, the offset amount (offset amount) between the preceding sheet P1 and the subsequent sheet P2 is changed to "E'." Regardless of the offset amount, the preceding sheet P1 is shifted first.

[0115] In the case of folding in three within the overlapping, by previously setting the shift amount of the leading edge to be larger than that in the case of folding in three, it is possible to improve the alignment accuracy on the leading edge side after the folding process is completed.

[0116] As described above, the sheet folding device 200 according to this embodiment can improve the accuracy of aligning the leading edges of the overlapped sheets and the accuracy of skew correction when performing post-processing including overlapping processing on a plurality of sheets.

[0117] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the technical gist thereof. The present invention covers all technical matters included in the technical ideas described in the claims. The above-described embodiments are preferred examples, but a person skilled in the art can realize various modifications from the disclosed contents. Such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0118] 1: Printer 10: Printer control unit 11: CPU 12:ROM 13: RAM 14: Serial I / F 20: Image creation section 21:Entrance 22:Exit 23: Branch claw 24: Output tray 30: Image reading unit 40: Operation display section 50: Post-processing control unit 51: CPU 52:ROM 53: RAM 54: Serial I / F 60: Load 61: Driver 70: Sensor 100: Printer body 200: Sheet folding device F1: First folding method F2: Second folding method J1: First conveying branch means J2: Second conveying branching means J3: Third conveying branch means P: Seat P1: Leading sheet P2: Subsequent sheet P3: Next sheet PL: Final seat Q: Sheet stack R0: Zeroth transport means R1: First transport means R2: Second transport means R3: Third transport means R4: Fourth conveyance means R5: Fifth transport means R6: Sixth conveyance means SN1: First sheet detection sensor SN2: Second sheet detection sensor SN3: Third sheet detection sensor SN4: Fourth sheet detection sensor SN5: Fifth sheet detection sensor SN6: Sixth sheet detection sensor SN7: Seventh sheet detection sensor W1: First transport route W2: Second transport route W3: Third transport route W4: Fourth transport route W5: Fifth transport route W6: Sixth transport route W7: Seventh transport route [Prior art documents] [Patent documents]

[0119] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-125312

Claims

1. A post-processing device including a circulating conveyance path, which circulates the sheet along the first conveyance path, the second conveyance path, and the third conveyance path in this order, by a first conveyance means which conveys a sheet conveyed along a first conveyance path downstream, a second conveyance means which conveys the sheet along a second conveyance path, and a third conveyance means which conveys the sheet along a third conveyance path, a control unit for controlling operations of the first conveying means, the second conveying means, and the third conveying means, When the plurality of sheets are superimposed on each other in the circulating conveyance path, the control unit The preceding sheet is stopped at an arbitrary position on the circulating conveying path, Thereafter, the preceding sheet is conveyed to the first conveying path so as to be delayed by a predetermined shift amount in the conveying direction relative to the succeeding sheet and overlapped therewith; When the leading edges of the preceding sheet and the succeeding sheet overlapping on the first conveying path abut against the first conveying means, the operation of the first conveying means is stopped. A post-processing device characterized by:

2. the control unit makes the shift amount of the final sheet in the overlapping of the plurality of sheets smaller than the previous shift amounts. The post-treatment device according to claim 1 .

3. The control unit changes the shift amount depending on the type of the sheet. The post-treatment device according to claim 1 or 2.

4. the control unit changes an abutment amount when the plurality of sheets stacked on the first transport path abuts against the first transport means in accordance with the shift amount. The post-processing device according to any one of claims 1 to 3.

5. the control unit changes the amount of shift of the final sheet in the overlapping of the plurality of sheets in accordance with the image forming surface of the overlapping sheets. The post-treatment device according to any one of claims 1 to 4.

6. the control unit changes the shift amount of the final sheet in the overlapping of the plurality of sheets in accordance with the relationship between the folding position in the folding process of the overlapping sheets and the position of the image to be formed on the sheet. The post-treatment device according to any one of claims 1 to 5.

7. the control unit changes the shift amount of the final sheet in the overlapping of the plurality of sheets according to the folding type in the folding process of the overlapping sheets. The post-treatment device according to any one of claims 1 to 5.

8. An image forming apparatus including an image forming unit that forms an image on a sheet, and a post-processing unit that performs post-processing on the sheet, 8. An image forming apparatus, wherein the post-processing section is a post-processing device according to claim 1.

9. An image forming system comprising: an image forming apparatus having an image forming unit that forms an image on a sheet; and a post-processing device as described in any one of claims 1 to 7 as a post-processing unit that performs post-processing on the sheet.

Images