[Title of Invention]

POST-PROCESSING DEVICE, IMAGE FORMING APPARATUS, AND IMAGE FORMING SYSTEM

[Technical Field]

[0001]

Embodiments of the present disclosure relate to a post-processing device, an image forming apparatus including the post-processing device, and an image forming system including the post-processing device.

[Background Art]

[0002]

Various types of post-processing devices are known to perform predetermined postprocessing operations on a sheet-shaped recording medium on which an image is formed. The post-processing devices are included in an image forming apparatus as a part of the image forming apparatus or coupled to the image forming apparatus to form an image forming system.

[0003]

When image formation processes to form an image on a sheet and the next processes (the post-processing) are performed as a series of operations, a long processing time of the postprocessing requires a waiting time for next image formation processes, which may decrease productivity. To reduce the waiting time in the image forming apparatus due to the long processing time of the post-processing, the post-processing device including a pre-stack mechanism temporarily stores sheets conveyed after the image formation processes in the post-processing device.

[Citation List]

[Patent Literature]

[0004]

[PTL 1]

Japanese Unexamined Patent Application Publication No.2014-125312 [Summary of Invention] [Technical Problem] [0005]

Japanese Unexamined Patent Application Publication No.2014-125312 discloses the post processing device including a sheet circulation path that enables producing the pre-stack mechanism without increasing the size of the post-processing device. In addition, Japanese Unexamined Patent Application Publication No.2014-125312 also discloses a technique of causing a preceding sheet and a following sheet to abut against a conveyance roller disposed in the sheet circulation path and overlaying the sheets.

[0006]

However the technique disclosed in Japanese Unexamined Patent Application Publication No.2014-125312 can not correct a skew of the following sheet because the preceding sheet conveyed in the sheet circulation path abuts against the conveyance roller and bends, and the bending of the preceding sheet interfere with the conveyance of the following sheet.

[0007]

An object of the present disclosure is to provide a post-processing device that improves accuracy of a skew correction of sheets overlaid when the post-processing device performs post processing including processes overlaying a plurality of sheets.

[Solution to Problem]

[0008]

A post-processing device includes a circulation conveyance path, a zeroth conveyer, and a controller. The circulation conveyance path includes a first conveyance path, a second conveyance path, a third conveyance path, a first conveyer, a second conveyer, and a third conveyer. The first conveyer conveys a preceding sheet from the first conveyance path. The second conveyer conveys the preceding sheet along the second conveyance path. The third conveyer conveys the preceding sheet from the third conveyance path to the first conveyance path. The circulation conveyance path is configured to circulate the preceding sheet through the first conveyance path, the second conveyance path, and the third conveyance path in turn by the first conveyer, the second conveyer, and the third conveyer. The zeroth conveyer conveys a following sheet toward the first conveyer in the first conveyance path. The controller controls operations of the zeroth conveyer, the first conveyer, the second conveyer, and the third conveyer. The controller controls the third conveyer to stop the preceding sheet, subsequently controls the zeroth conveyer and the third conveyer to overlay the preceding sheet with the following sheet to form a sheet bundle having a shift amount between a leading edge of the preceding sheet and a leading edge of the following sheet and strike the leading edge of the preceding sheet and the leading edge of the following sheet against the first conveyer.

[Advantageous Effects of Invention]

[0009]

According to the present disclosure, the post-processing device can improve accuracy of a skew correction of sheets overlaid when the post-processing device performs post processing including processes overlaying a plurality of sheets.

[Brief Description of Drawings] [0010]

The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

[FIG. 1]

FIG. 1 is a side view of an image forming apparatus including a post-processing device according to an embodiment of the present disclosure;

[FIG. 2]

FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus of FIG. 1;

[FIG. 3]

FIG. 3 is a diagram illustrating an inner configuration of a sheet folding device functioning as the post-processing device according to the present disclosure;

[FIG. 4]

FIG. 4 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure;

[FIG. 5]

FIG. 5 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a post-processing process;

[FIG. 6]

FIG. 6 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 5; [FIG. 7]

FIG. 7 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 6; [FIG. 8]

FIG. 8 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 7; [FIG. 9]

FIG. 9 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 8; [FIG. 10]

FIG. 10 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 9; [FIG. 11]

FIG. 11 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a folding operation next to the process in FIG. 10;

[FIG. 12]

FIG. 12 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a folding operation next to the folding operation in FIG. 11;

[FIG. 13]

FIG. 13 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a folding operation next to the folding operation in FIG. 12;

[FIG. 14]

FIG. 14 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a folding operation next to the folding operation in FIG. 13;

[FIG. 15]

FIG. 15 is an enlarged view of the inner configuration of the sheet folding device to illustrate a preceding sheet that precedes a following sheet;

[FIG. 16]

FIG. 16 is an enlarged view of the inner configuration of the sheet folding device to illustrate the preceding sheet pushing away the following sheet;

[FIG. 17]

FIG. 17 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure to illustrate the following sheet that precedes the preceding sheet;

[FIG. 18]

FIG. 18 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure, illustrating a process next to the process in FIG. 17; [FIG. 19]

FIG. 19 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure to illustrate a shift amount when the preceding sheet and the following sheet are overlaid each other;

[FIG. 20]

FIG. 20 is an enlarged view of the inner configuration of the sheet folding device according to the embodiment of the present disclosure to illustrate a shift amount when a next sheet is overlaid on the following sheet and the preceding sheet;

[FIGS. 21A and 21B]

FIGS. 21 A and 2 IB are enlarged views of the inner configuration of the sheet folding device in which the shift amount is not set.

[FIG. 22]

FIG. 22 is a flowchart of a control according to a first example performed by the sheet folding device;

[FIG. 23] FIG. 23 is a flowchart of a control according to a second example performed by the sheet folding device;

[FIG. 24]

FIG. 24 is a flowchart of a control according to a third example performed by the sheet folding device;

[FIG. 25]

FIG. 25 is a flowchart of a control according to a fourth example performed by the sheet folding device; and [FIG. 26]

FIG. 26 is a flowchart of a control according to a fifth example performed by the sheet folding device.

[Description of Embodiments]

[0011]

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

[0012]

[Outline of Image Forming Apparatus]

First, a description is given of an image forming apparatus according to an embodiment of the present disclosure. FIG. 1 is an external view of an image forming apparatus 1 that is appeared as a printer. The image forming apparatus 1 includes an image forming device 100 that is a printer body, and a sheet folding device 200 that functions as a post-processing device that is connectable to the image forming device 100. As illustrated in FIG. 1, the image forming apparatus 1 is an in-body ejection type apparatus, and the sheet folding device 200 is incorporated in a part of the image forming device 100. That is, the image forming apparatus 1 includes the sheet folding device 200 as a post-processing device that receives a recording medium on which an image is formed and performs post-processing on the recording medium. The configuration of the sheet folding device 200 is described below. [0013]

[Functional Configuration of Control Block]

Next, with reference to FIG. 2, a description is given of control blocks regarding control operations of the image forming device 100 and the sheet folding device 200, according to the present embodiment. As illustrated in FIG. 2, the image forming device 100 includes an image forming device controller 10 as a control block. The image forming device controller 10 includes a central processing unit (CPU) 11, a read only memory (ROM) 12, a randomaccess memory (RAM) 13, and a serial interface (serial VF) 14.

[0014]

The image forming device controller 10 is coupled to an image forming unit 20, an image reading unit 30, and an operation display unit 40 that is generally a control panel. Each of the image forming unit 20, the image reading unit 30, and the operation display unit 40 includes components to fully perform the functions. Each component of the image forming unit 20, the image reading unit 30, and the operation display unit 40 operates based on control signals issued by the image forming device controller 10.

[0015] The image forming unit 20 performs an image forming operation based on image data on a sheet P as a recording medium or a sheet- shaped recording medium. The image reading unit 30 reads an image formed on the sheet P and acquires the image data of the image on the sheet P. The operation display unit 40 functions as an input unit via which operating conditions in the image forming unit 20 and the image reading unit 30 are input and as a display unit that displays, for example, the operation results.

[0016]

The ROM 12 stores control programs for controlling the image forming unit 20, the image reading unit 30, and the operation display unit 40. The CPU 11 reads the control programs stored in the ROM 12 to the RAM 13. In addition, the CPU 11 stores data in the RAM 13 to use the data for the control and executes the control defined by the control programs while using the RAM 13 as a work area.

[0017]

As illustrated in FIG. 2, the sheet folding device 200 includes a post-processing controller 50 as a control block. The post-processing controller 50 includes a central processing unit (CPU) 51, a read only memory (ROM) 52, a random-access memory (RAM) 53, and a serial interface (serial I/F) 54.

[0018]

The post-processing controller 50 is coupled to various components 60 and various sensors 70. The various components 60 are, for example, sheet conveying rollers and pairs of sheet folding rollers, and include configurations to perform sheet folding operations on a recording medium or recording media. The various components 60 are, for example, sheet conveying rollers and pairs of sheet folding rollers, and include configurations to perform sheet folding operations on a recording medium or recording media. A drive motor drives the various components 60. For example, the drive motor drives and rotates various rollers and various roller pairs. The post-processing controller 50 controls a driver 61 coupled to the postprocessing controller 50 to drive the drive motor driving the various components 60. The various components 60 performs operations such as conveyance of the sheet P as the recording medium and folding processing to fold the sheet P.

[0019]

The various sensors 70 are a plurality of sheet detecting sensors to detect the sheet P at positions in a sheet conveyance path and disposed at the positions in the sheet conveyance path described below. The post-processing controller 50 performs control programs stored in advance and, based on detection signals output from the various sensors 70 to the postprocessing controller 50, determines conveyance amounts and positions of the sheet P that the post-processing is performed. Based on driving amounts of the various components 60, the post-processing controller 50 can calculate the conveyance amounts (conveyance distances) of the sheet P after the sheet detecting sensors detect a leading edge of the sheet P and determine the positions of the sheet P.

[0020]

The ROM 52 stores the control program for the post-processing controller 50 to perform predetermined processing. The CPU 51 reads the control programs stored in the ROM 52 to the RAM 53. In addition, the CPU 51 stores data in the RAM 53 to use the data for the control for sheet folding processing and executes the control for the sheet folding processing defined by the control programs while using the RAM 53 as a work area. As described above, the post-processing controller 50 performs the control program stored in the ROM 52, controls the sheet detecting sensors to detect the sheet P, and controls various components 60 to convey the sheet P.

[0021]

The image forming device controller 10 included in the image forming device 100 and the post-processing controller 50 included in the sheet folding device 200 are communicably coupled to each other via the serial I/F 14 and the serial I/F 54. This communication path is used to exchange control commands and data to be used for conveyance control of the recording medium, between the image forming device controller 10 and the post-processing controller 50. The sheet folding device 200 determines whether the conveyance control and the sheet folding operations are performed on a recording medium and switches the types of the sheet folding operation, based on the control commands and data related to the recording medium sent from the image forming device 100, and data related to the positions of the recording medium obtained from the various sensors 70.

[0022]

The image forming device 100 (that is, the image forming device controller 10) sends the sheet folding device 200 (that is, the post-processing controller 50) information related to the sheet P as data. The data include a type and a thickness of the sheet P sent from the image forming device 100 and received by the sheet folding device 200. Additionally, the data also includes the number of sheets P overlaid, the type of folding processes performed on the sheet P, and whether an image exists at the folding position in the sheet P. The control commands notified from the image forming device controller 10 to the post-processing controller 50 include a command notifying whether or not the delivered sheet P corresponds to the last page (that is, a final sheet) of the unit processed collectively.

[0023]

[Outline of Post-Processing Device]

The following describes an internal configuration of the sheet folding device 200 as the postprocessing device according to the embodiment of the present disclosure. FIG. 3 is a diagram illustrating a schematic configuration inside the sheet folding device 200. The sheet folding device 200 includes a plurality of sheet conveyance paths, a plurality of roller pairs, and a plurality of sheet detecting sensors. Each of the plurality of roller pairs functions as a conveyer or a folder.

[0024]

The sheet folding device 200 includes seven conveyance paths roughly distinguished from each other. As illustrated in FIG. 3, the sheet folding device 200 includes a first conveyance path Wl, a second conveyance path W2, a third conveyance path W3, a fourth conveyance path W4, a fifth conveyance path W5, a sixth conveyance path W6, and a seventh conveyance path W7.

[0025]

In addition, the sheet folding device 200 includes a plurality of roller pairs disposed along each of the first conveyance path Wl, the second conveyance path W2, the third conveyance path W3, the fourth conveyance path W4, the fifth conveyance path W5, and the sixth conveyance path W6. Each of the plurality of roller pairs is disposed in each of the conveyance paths to convey the sheet P and functions as a zeroth conveyer R0, a first conveyer Rl, a second conveyer R2, a third conveyer R3, a fourth conveyer R4, a fifth conveyer R5, and a sixth conveyer R6. The post-processing controller 50 performs the control programs to control these conveyers and start and stop the conveyance of the sheet P. [0026]

The sheet folding device 200 includes a plurality of switching guides. For example, the plurality of switching guides guides the sheet P from the first conveyance path Wl to the second conveyance path W2, and the sheet P guided and conveyed to the second conveyance path W2 is conveyed to the first conveyance path Wl through the third conveyance path W3. That is, the plurality of switching guides guides the sheet P to a circulation conveyance path in which the sheet P is circulated. Or, the plurality of switching guides guides the sheet P to the fourth conveyance path W4 downstream from the first conveyance path Wl, that is, does not guide the sheet P from the first conveyance path Wl to the circulation conveyance path downstream from the second conveyance path W2. Or, the plurality of switching guides guides the sheet P from the first conveyance path W1 to the second conveyance path W2 and further guides the sheet P to the fifth conveyance path W5 downstream from the second conveyance path W2. To perform the above-described switching of the conveyance paths, the sheet folding device 200 includes the plurality of switching guides.

[0027]

As illustrated in FIGS. 4 to 10, the plurality of switching guides include a first switching guide JI, a second switching guide J2, and a third switching guide J3. The plurality of switching guides are included in various components 60 controlled by the post-processing controller 50. The post-processing controller 50 controls operations of the plurality of switching guides to determine the conveyance paths of the sheet P. Additionally, the sheet folding device 200 includes a first folder Fl and a second folder F2 in the circulation conveyance path to fold the sheet P.

[0028]

The sheet folding device 200 includes the zeroth conveyer R0 serving as an entry roller pair in the vicinity of an entrance 21 that receives the sheet P from the image forming device 100. The post-processing controller 50 controls a drive motor that rotates the zeroth conveyer R0 to start rotation of the zeroth conveyer R0 after the post-processing controller 50 receives a signal informing that the sheet P will be ejected from the image forming device 100. Subsequently, the leading edge of the sheet P reaches the nip of the roller pair of the zeroth conveyer R0, and the zeroth conveyer R0 conveys the sheet P to the conveyance path downstream from the zeroth conveyer R0.

[0029]

As described below, before the sheet folding device 200 ejects the sheet P received from the image forming device 100 to an outlet 22 downstream from all conveyance paths, the sheet folding device 200 receives the next sheet P and performs a sheet overlay process in which the next sheet P is conveyed and overlaid on the previous sheet P and the folding process. In the following description, the sheet P received from the image forming device 100 in the above description, that is, a preceding sheet is referred to as “the preceding sheet Pl” for the sake of description. The next sheet P in the above description, that is, the sheet P following the preceding sheet Pl is referred to as “the following sheet P2”. The following sheet P2 is received by the sheet folding device 200 after the preceding sheet Pl is received by the sheet folding device 200. In addition, a sheet P that is received by the sheet folding device 200 next to the following sheet P2 and be subjected to the sheet overlay process is referred to as a “next sheet P3”. In addition, a plurality of sheets P stacked on each other is referred to as a “sheet bundle Q”.

[0030]

Note that the sheet folding device 200 may overlay and fold three or more sheets P. The number of sheets P to be stacked or folded in the sheet folding device 200 is not limited to three.

[0031]

The first conveyer R1 includes a pair of rollers facing each other across the first conveying path Wl, and a nip is formed between the rollers. The first folder Fl includes a pair of rollers facing each other and being disposed between the first sheet conveyance path W 1 and the second sheet conveyance path W2, and a nip is formed between the rollers. The path guided by the nip in the first conveyer R1 and the nip in the first folder Fl guides the preceding sheet Pl from the first conveyance path Wl to the second conveyance path W2. [0032]

The preceding sheet Pl guided to the second conveyance path W2 is conveyed to the third conveyance path W3 by the second conveyer R2. Subsequently, the third conveyer R3 temporarily stops the conveyance of the preceding sheet Pl in the third conveyance path W3. The third conveyer R3 starts the conveyance of the preceding sheet Pl that is temporarily stopped in the third conveyance path W3 when the sheet folding device 200 receives the following sheet P2 from the image forming device 100. As a result, the preceding sheet Pl returns to a portion upstream from the first conveyer R1 in the first conveyance path W 1 and meets the following sheet P2. As described above, the circulation conveyance path is configured.

[0033]

In the circulation conveyance path described above, the preceding sheet Pl and the following sheet P2 are overlaid to form a sheet bundle Q. The following describes the folding processes performed on the sheet bundle Q.

[0034]

The post-processing controller 50 controls the first folder Fl to perform the folding processes for the sheet bundle Q. The sheet bundle Q subjected to the folding processes by the first folder Fl is delivered from the second conveyance path W2 to the fifth conveyance path W5. The fourth conveyer R4, the fifth conveyer R5, and the first folder Fl are driven by the same drive motor. The drive motor is rotatable in both directions, which are the forward direction and the reverse direction. By changing the direction of rotation, the drive motor conveys the sheet bundle Q in which the preceding sheet Pl and the following sheet P2 are overlaid and performs a sheet folding processes.

[0035]

A bifurcating claw 23 is disposed downstream from the sixth conveyer R6 and adjacent to the sixth conveyer R6. The bifurcating claw 23 switches guide postures to guide the sheet P (or the sheet bundle Q) to the sixth conveyance path W6 or the seventh conveyance path W7. The bifurcating claw 23 may be driven by, for example, a solenoid to switch the guide postures. Instead of the solenoid, a drive mechanism including a motor, a gear, a cam, and the like may be used.

[0036]

The sheet P having passed through the fourth conveyance path W4 or the fifth conveyance path W5 is ejected and stacked on an output tray 24 of the sheet folding device 200. The seventh conveyance path W7 is a path for delivering the sheet P to a post-processing device when an image forming system is configured to include the post-processing device disposed downstream from the sheet folding device 200. The post-processing device performs postprocessing such as alignment processing or binding processing on the folded sheet P or the non-folded sheet P.

[0037]

A first sheet detecting sensor SN 1 is disposed downstream from the zeroth conveyer R0 and adjacent to the zeroth conveyer R0 on the first conveyance path W1. A second sheet detecting sensor SN2 is disposed upstream from the first conveyer R1 and adjacent to the first conveyer Rl. A third sheet detecting sensor SN3 is disposed downstream from the second conveyer R2 and adjacent to the second conveyer R2 on the third conveyance path W3. A fourth sheet detecting sensor SN4 is disposed downstream from the third conveyer R3 and adjacent to the third conveyer R3 on the third conveyance path W3. A fifth sheet detecting sensor SN5 is disposed downstream from the fourth conveyer R4 and adjacent to the fourth conveyer R4 on the fourth conveyance path W4. A sixth sheet detecting sensor SN6 is disposed downstream from the fifth conveyer R5 and adjacent to the fifth conveyer R5 on the fifth conveyance path W5. A seventh sheet detecting sensor SN7 is disposed downstream from the sixth conveyer R6 and adjacent to the sixth conveyer R6 on the sixth conveyance path W6.

[0038]

The sheet folding device 200 illustrated in FIG. 3 can perform a letter fold-in and a letter fold- out on the overlaid sheets P. With reference to FIGS. 4 to 10, the following describes operations in which the two sheets P are overlaid to form the sheet bundle Q in the sheet circulation path.

[0039]

FIG. 4 illustrates the sheet folding device 200 in an initial state before the sheet P is conveyed from the image forming device 100. The post-processing controller 50 in the sheet folding device 200 starts rotating the zeroth conveyer R0 when the leading edge of the preceding sheet Pl conveyed from the image forming device 100 reaches to the outlet of the image forming device 100. The zeroth conveyer R0 receives the preceding sheet Pl and conveys the preceding sheet Pl to the first conveyance path W1 as illustrated in FIG. 5. In addition, the post-processing controller 50 moves the first switching guide JI as illustrated in FIG. 4 to convey the preceding sheet Pl not to the fourth conveyance path W4 but to the second conveyance path W2.

[0040]

The first sheet detecting sensor SN1 detects the leading edge of the preceding sheet Pl conveyed by the zeroth conveyer R0 and notifies a detection signal to the post-processing controller 50. When the first sheet detecting sensor detects the leading edge of the preceding sheet Pl, the first conveyer is stopped. As illustrated in FIG. 5, the post-processing controller 50 maintains the first conveyer R1 stopped until a conveyance amount of the preceding sheet Pl required to form the bending of the preceding sheet Pl to correct the skew of the leading edge of the preceding sheet Pl (that is, a first protrusion amount) reaches a predetermined value after the detection signal is notified.

[0041]

As illustrated in FIG. 6, at a timing at which the first protrusion amount reaches the predetermined value, that is, the timing at which correcting the skew of the leading edge of the preceding sheet Pl is completed, the post-processing controller 50 starts rotation of the first conveyer Rl.

[0042]

When the leading edge of the preceding sheet Pl enters the nip of the first conveyer Rl, the post-processing controller 50 rotates the first folder Fl, the second conveyer R2, and the third conveyer R3.

[0043]

As illustrated in FIG. 7, rotations of the first conveyer Rl and the first folder Fl convey the preceding sheet Pl to the second conveyance path W2, and the preceding sheet Pl is conveyed along the downward slope of the second conveyance path W2. The second conveyer R2 convey the preceding sheet Pl conveyed along the downward slope of the second conveyance path W2 to the third conveyance path W3. Subsequently, the third conveyer R3 conveys the preceding sheet Pl to the fourth sheet detecting sensor SN4. The fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl and notifies a detection signal to the post-processing controller 50. After the post-processing controller 50 receives the detection signal from the fourth sheet detecting sensor SN4, the post-processing controller 50 calculates the timing at which the leading edge of the preceding sheet Pl reaches the position corresponding to the second protrusion amount A2 from the position of the fourth sheet detecting sensor SN4.

[0044]

When the post-processing controller 50 determines that the leading edge of the preceding sheet Pl reaches the position corresponding to the second protrusion amount A2, the postprocessing controller 50 stops the rotation of the first folder Fl, the second conveyer R2, and the third conveyer R3 to stop the conveyance of the preceding sheet Pl as illustrated in FIG. 8.

[0045] However, the post-processing controller 50 continues the rotation of the first conveyer R1 to receive the following sheet P2 conveyed next from the image forming device 100 even when the post-processing controller 50 stops the conveyance of the preceding sheet Pl.

[0046]

Subsequently, the post-processing controller 50 calculates a stop timing of the conveyance of the following sheet P2 conveyed as illustrated in FIG. 9 after the first sheet detecting sensor SN 1 detects the leading edge of the following sheet P2 and notifies a detection signal to the post-processing controller 50. At the stop timing, the leading edge of the following sheet P2 reaches a position away from the first sheet detecting sensor SN 1 by a third protrusion amount A3. When the leading edge of the following sheet P2 reaches the position corresponding to the third protrusion amount A3, the post-processing controller 50 resumes the rotation of the second conveyer R2 and the third conveyer R3. As a result, as illustrated in FIG. 9, the conveyance of the preceding sheet Pl, which has been stopped, is resumed. Thus, the leading edge of the following sheet P2 comes into contact with the first conveyer R1 slightly before the leading edge of the preceding sheet Pl comes into contact with the first conveyer Rl, and the skew of the following sheet P2 is corrected.

[0047]

The post-processing controller 50 calculates the third protrusion amount A3 based on a speed of the sheet moved by the zeroth conveyer R0, a speed of the sheet conveyed by the third conveyer R3, positions of the zeroth conveyer R0, the third conveyer R3, the first sheet detecting sensor SN1, the second sheet detecting sensor SN2, and the fourth sheet detecting sensor SN4, that is, distances between these members. The third protrusion amount A3 defines a shift amount between the leading edges of the preceding sheet Pl and the following sheet P2 when the leading edges of the preceding sheet Pl and the following sheet P2 meet each other before the preceding sheet Pl and the following sheet P2 come in contact with the first conveyer Rl.

[0048]

Thereafter, as illustrated in FIG. 10, the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 meet each other before the second sheet detecting sensor SN2 to form the sheet bundle Q, and the sheet bundle Q passes through the nip of the first conveyer Rl and is conveyed downstream from the nip of the first conveyer Rl. [0049]

Thereafter, the post-processing controller 50 determines whether a number of sheets to be folded notified by the image forming device 100 coincides a number of sheets received by the sheet folding device 200. When the number of sheets to be folded coincides the number of sheets received by the sheet folding device 200, the post-processing controller 50 performs folding processing described below. When the number of sheets to be folded does not coincide the number of sheets received by the sheet folding device 200, the post-processing controller 50 performs the processes as illustrated in FIGS. 7 to 9 again so that the next sheet P3 conveyed from the image forming device 100 (that is the sheet P conveyed after the following sheet P2 is conveyed) meets the sheet bundle Q to overlay the next sheet P3 on the sheet bundle Q. Note that the post-processing controller 50 can determine whether the sheet P is conveyed to a position immediately before the nip of the second conveyer R2 based on, for example, the number of drive steps of a drive motor that drives and rotates the first conveyer Rl. Accordingly, a stepping motor is preferably used as the drive motor to drive and rotate each conveyer.

[0050]

[Outline of Folding Processing]

The following describes folding operations in the sheet folding device 200 according to the present embodiment. FIGS. 11 to 14 are enlarged views of the inner configuration of the sheet folding device to illustrate letter fold-out operations performed on the sheet bundle Q formed in a portion upstream the first conveyer Rl.

[0051]

As described with reference to FIG. 10, the preceding sheet Pl meets the following sheet P2 to form the sheet bundle Q, and the zeroth conveyer R0 and the first conveyer Rl convey the sheet bundle Q. When the leading edge of the sheet bundle Q enters the nip of the first conveyer Rl, the sheet bundle Q is conveyed to the fourth conveyer R4.

[0052]

When the first conveyer Rl conveys the sheet bundle Q immediately before the nip of the fourth conveyer R4, the post-processing controller 50 drives a motor to rotate the fourth conveyer R4 in the direction indicated by the arc arrows in FIG. 11 in addition to the first conveyer Rl rotated in the direction of the arc arrows in FIG. 11. After the fifth sheet detecting sensor SN5 detects the leading edge of the sheet bundle Q and notifies the detection signal to the post-processing controller 50, the post-processing controller 50 drives the fourth conveyer R4 to convey the leading edge of the sheet bundle Q by a fourth protrusion amount A4. When the leading edge of the sheet bundle Q is conveyed by the fourth protrusion amount A4, the post-processing controller 50 temporarily stops the fourth conveyer R4. [0053]

Next, as illustrated in FIG. 12, the post-processing controller 50 reversely rotates the fourth conveyer R4 and the first folder Fl to convey the sheet bundle Q in a direction opposite to the conveyance direction illustrated in FIG. 11 while rotating the first conveyer Rl in the conveyance direction as illustrated in FIG. 11. The above-described reverse rotation of the fourth conveyer R4 conveys the sheet bundle Q in the direction opposite the conveyance direction.

[0054]

As illustrated in FIG. 13, the first conveyer Rl rotates to convey the sheet bundle Q in the conveyance direction, and the fourth conveyer R4 rotates in reverse to convey the sheet bundle Q in the direction opposite to the conveyance direction. As a result, the sheet bundle Q forms a bend before the nip of the first folder Fl. The bend enters the nip, and the first folder Fl performs the first folding, thereby forming the first fold line.

[0055]

The first folder Fl conveys the sheet bundle Q performed the first folding to the second conveyance path W2, and the sheet bundle Q is conveyed along the downward slope of the second conveyance path W2. The second conveyer R2 conveys the leading edge of the sheet bundle Q by a fifth protrusion amount A5 after the third sheet detecting sensor SN3 detects the leading edge of the sheet bundle Q. When the second conveyer R2 conveys the leading edge of the sheet bundle Q by the fifth protrusion amount A5, the post-processing controller 50 temporarily stops the second conveyer R2.

[0056]

Next, the post-processing controller 50 rotates the second conveyer R2 in the direction opposite to the direction illustrated in FIG. 13 while rotating the fourth conveyer R4 and the first folder Fl in the conveyance direction illustrated in FIG. 13. The above-described reverse rotation of the second conveyer R2 conveys the sheet bundle Q in the reverse direction from the second conveyer R2. In addition, the post-processing controller 50 rotates the fourth conveyer R4 and the first folder Fl in the direction illustrated in FIG. 13 to convey the sheet bundle Q. As a result, as illustrated in FIG. 14, a bend of the sheet bundle Q is formed before the nip of the second folder F2 that also functions the fifth conveyer R5. The bend enters the nip, and the second folder F2 performs the second folding, thereby forming the second fold line.

[0057] The sheet bundle Q on which the second folding is performed passes through the fifth conveyance path W5 and is conveyed to the output tray 24. The fourth protrusion amount A4 and the fifth protrusion amount A5 are determined based on the total length of the sheet P and a folding method set for the sheet P (or the sheet bundle Q). The post-processing controller 50 determines whether the sheet P or the sheet bundle Q moves by the fourth protrusion amount A4 based on the rotation amount of the fourth conveyer R4 (that is, the number of drive steps of the drive motor) and determines whether the sheet P or the sheet bundle Q moves by the fifth protrusion amount A5 based on the rotation amount of the second conveyer R2 (that is, the number of drive steps of the drive motor).

[0058]

When the sheet folding device 200 performs the letter fold-out operations on the sheet P, the sheet P is folded outside at a position corresponding to two thirds (2/3) of the entire length of the sheet P from the leading edge of the sheet P in the sheet conveyance direction as a first folding operation. Next, as a second folding operation, the sheet P is folded inside at a position corresponding to two thirds (2/3) of the entire length of the sheet P. When the sheet folding device 200 performs the letter fold-in operation on the sheet P, the sheet P is folded outside at a position corresponding to one third (1/3) of the entire length of the sheet P from the leading edge of the sheet P in the sheet conveyance direction as a first folding operation and folded inside at a position corresponding to two thirds (2/3) of the entire length of the sheet P as a second folding operation.

[0059]

[First Operation Example]

Next, a first operation example of the sheet folding device 200 according to the present embodiment is described with reference to FIGS. 15 to 18. With reference to FIGS. 15 and 16, movements of the preceding sheet Pl and the following sheet P2 are described when the leading edge of the preceding sheet Pl staying the third conveyance path W3 precedes the leading edge of the following sheet P2 and is shifted from the leading edge of the following sheet P2 in the sheet conveyance direction, and the preceding sheet Pl and the following sheet P2 are overlaid and conveyed.

[0060]

As illustrated in FIG. 15, the leading edge of the preceding sheet Pl preceding the leading edge of the following sheet P2 strikes against a roller of the first conveyer R1 before the following sheet P2 contacts the first conveyer Rl. The preceding sheet Pl bends as illustrated in FIG. 16 when the leading edge of the preceding sheet Pl strikes against the roller of the first conveyer Rl. Since the following sheet P2 received from the image forming device 100 is positioned above the preceding sheet Pl in the first conveyance path Wl, the above-described bending of the preceding sheet Pl causes a bending of the following sheet P2. As a result, as illustrated in FIG. 16, the preceding sheet Pl pushes away the following sheet P2, and the leading edge of the following sheet P2 does not reach the roller of the first conveyer Rl and does not strike the roller.

[0061]

As a result, the skew correction of the following sheet P2 is insufficient, and the leading edges of sheets of the sheet bundle Q are misaligned when the following sheet P2 and the preceding sheet Pl are overlaid. The above-described problem also occurs when the leading edge of the following sheet P2 coincides the leading edge of the preceding sheet Pl staying on the third conveyance path W3. However, the above-described problem is caused by a variation of the first sheet detecting sensor SN1, a variation of the fourth sheet detecting sensor SN4, a curl of the sheet P, a mechanical variation in attachment position of each sensor, or the like. The above-described factors causes the preceding sheet Pl to precede the following sheet P2 when the preceding sheet Pl and the following sheet P2 are overlaid, and the above-described problem occurs. [0062]

With reference to FIGS. 17 and 18, movements of the preceding sheet Pl and the following sheet P2 are described when the leading edge of the following sheet P2 precedes the leading edge of the preceding sheet Pl and is shifted from the leading edge of the preceding sheet Pl by a length G in the sheet conveyance direction, and the preceding sheet Pl and the following sheet P2 are overlaid and conveyed. When the preceding sheet Pl and the following sheet P2 are conveyed as illustrated in FIG. 17, the leading edge of the following sheet P2 strikes the roller of the first conveyer R1 before the leading edge of the preceding sheet Pl contacts the first conveyer Rl.

[0063]

When the leading edge of the following sheet P2 strikes against the roller of the first conveyer Rl, the following sheet P2 bends. However, since the preceding sheet Pl is below the following sheet P2 in the first conveyance path Wl, the bending of the following sheet P2 does not affect the conveyance of the preceding sheet Pl. Accordingly, the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 can reach the first conveyer Rl. As a result, the above-described configuration can prevent the insufficient skew correction caused by the bending of the preceding sheet Pl as illustrated in FIG. 16 and the misalignment between the leading edges of the sheets to be overlaid.

[0064]

Several methods are considered to determine a conveyance restart timing of the preceding sheet Pl staying on the third conveyance path W3. The following describes examples of the methods when the preceding sheet Pl and the following sheet P2 are conveyed at the same speed. In the following description, a point at which the leading edge of the preceding sheet Pl meets the following sheet P2 is referred to as a meeting point H as illustrated in FIG. 17. The distance from the meeting point H to the leading edge of the preceding sheet Pl protruding by the second protrusion amount A2 from the fourth sheet detecting sensor SN4 is set at a distance not less than the sum of the length G and the distance from the meeting point H to the leading edge of the following sheet P2 protruding by the third protrusion amount A3. The third conveyer R3 restarts rotation when the leading edge of the following sheet P2 reaches the position corresponding to the third protruding amount A3. As a result, the leading edge of the following sheet P2 precedes the leading edge of the preceding sheet Pl and is shifted from the leading edge of the preceding sheet Pl by the length G in the sheet conveyance direction, and the preceding sheet Pl and the following sheet P2 can be overlaid and conveyed. If a factor such as the layout of parts in the post-processing device prevents setting the distance from the meeting point H to the leading edge of the preceding sheet Pl that protrudes from the fourth sheet detecting sensor SN4 by the second protrusion amount A2 to be equal to or larger than the sum of the length G and the distance from the meeting point H to the leading edge of the following sheet P2 that protrudes from the first sheet detecting sensor SN1 by the third protrusion amount A3, the third conveyer R3 restarts rotation when the leading edge of the following sheet P2 is conveyed by the length G in addition to the third protrusion amount A3 from the first sheet detecting sensor SN1. As a result, the leading edge of the following sheet P2 precedes the leading edge of the preceding sheet Pl and is shifted from the leading edge of the preceding sheet Pl by the length G in the sheet conveyance direction, and the preceding sheet Pl and the following sheet P2 can be overlaid and conveyed.

[0065]

[Second Operation Example]

Next, a second operation example of the sheet folding device 200 according to the present embodiment is described with reference to FIGS. 19 to 21. With reference to FIGS. 19 to 21, the following describes a shift amount (that is, the length G) between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 when the preceding sheet Pl and the following sheet P2 are overlaid.

[0066]

In FIG. 19, the length G is set to be a shift amount A mm that is the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 when the preceding sheet Pl and the following sheet P2 are overlaid. The unit of the length G is millimeter. Hereinafter, the unit of the length G and the protrusion amounts is millimeter. [0067]

As illustrated in FIG. 19, the preceding sheet Pl is overlaid on the following sheet P2, and the leading edge of the following sheet P2 is shifted from the leading edge of the preceding sheet Pl by the shift amount A mm to form the sheet bundle Q. The sheet bundle Q strikes against the first conveyer R1 that is stopped. In this case, the post-processing controller 50 controls the conveyance of the sheet bundle Q so that the first protrusion amount Al of the sheet bundle Q that strikes against the first conveyer R1 becomes “a mm”.

[0068]

After the sheet bundle Q strikes against the first conveyer Rl, the post-processing controller 50 drives and rotates the first conveyer Rl to convey the sheet bundle Q including the preceding sheet Pl and the following sheet P2 to the first folder Fl. Subsequently, the postprocessing controller 50 drives and rotates the first conveyer Rl, the second conveyer R2, and the third conveyer R3 to convey the sheet bundle Q to the fourth sheet detecting sensor SN4. Then, the post-processing controller 50 conveys the sheet bundle Q (the preceding sheet Pl and the following sheet P2) until the leading edge of the preceding sheet Pl or the following sheet P2 reaches a position corresponding to the second protrusion amount A2 that is a predetermined protrusion amount after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl or the following sheet P2. The post-processing controller 50 stops the conveyance of the sheet bundle Q when the leading edge of the preceding sheet Pl or the following sheet P2 reaches the position corresponding to the second protrusion amount A2.

[0069]

While the third conveyer R3 holds and stops the preceding sheet Pl and the following sheet P2, the next sheet P3 is conveyed next to the following sheet P2 from the image forming device 100 as illustrated in FIG. 20. In this case, the post-processing controller 50 monitors an elapsed time since the first sheet detecting sensor SN 1 detects the leading edge of the next sheet P3.

[0070]

After the elapsed time becomes a predetermined time, as illustrated in FIG. 20, the postprocessing controller 50 drives the second conveyer R2 and the third conveyer R3 to overlay the preceding sheet Pl and the following sheet P2 onto the next sheet P3. When the sheet bundle Q including the preceding sheet Pl and the following sheet P2 is overlaid on the next sheet P3, the length G between the leading edge of the next sheet P3 and the leading edge of the sheet bundle Q is set to be a shift amount B mm. The shift amount B is shorter than the shift amount A, and the relationship of A> B is established.

[0071]

With reference to FIGS. 21A and 21B, the following describes the reason why the postprocessing controller 50 performs the above-described control. As illustrated in FIG. 21 A, it is assumed that the preceding sheet Pl and the following sheet P2 are brought into contact with the first conveyer Rl to correct each skew and neatly arrange the leading edges of the preceding sheet Pl and the following sheet P2, and then are conveyed along the circulation conveyance path to a position at which the fourth sheet detecting sensor SN4 detects the preceding sheet Pl or the following sheet P2. At this time, the preceding sheet Pl passes through an inner route in the circulation conveyance path, and the following sheet P2 passes through an outer route in the circulation conveyance path. That is, the movement of the preceding sheet Pl is shorter than the movement of the following sheet P2 like a difference in a car between track followed by front and back inner wheels when turning.

[0072]

As a result, as illustrated in FIG. 21B, the preceding sheet Pl precedes the following sheet P2 when the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl or the following sheet P2 even if the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 are aligned in the nip of the first conveyer Rl. A preceding amount C mm illustrated in FIG. 2 IB is not limited to an amount caused by the abovedescribed difference and is also caused by variations in positions at which the leading edges of the preceding sheet Pl and the following sheet P2 enter the nips of the first to third conveyers. The variations are increased by curls of the preceding sheet Pl and the following sheet P2.

[0073]

In order to align the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 when the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl or the leading edge of the following sheet P2, post-processing controller 50 controls the zeroth conveyer R0 and the third conveyer R3 so that the leading edge of the following sheet P2 precedes the leading edge of the preceding sheet Pl by the preceding amount C mm. The preceding amount C mm corresponds to a shift amount between the leading edges of the preceding sheet Pl and the following sheet P2 when the preceding sheet Pl and the following sheet P2 are conveyed downstream from the first conveyer Rl.

[0074]

Based on the above, the shift amount A mm between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 when the preceding sheet Pl meets the following sheet P2 is calculated as a sum of “a mm” as the first protrusion amount Al, the preceding amount C mm. and “+ a mm” as a margin. The shift amount B mm between the leading edge of the next sheet P3 and the leading edge of the sheet bundle Q (that includes the preceding sheet Pl and the following sheet P2) when the next sheet P3 meets the sheet bundle Q is calculated as a sum of “a mm” as the first protrusion amount Al of the next sheet P3 and “+ a mm” as the margin.

[0075]

In the above-described embodiment, the three sheets P are overlaid. When four or more sheets P are overlaid, the shift amount regarding the sheet P that is finally overlaid (that is, the final sheet PL) is different from the shift amount regarding the sheet that is not finally overlaid.

[0076]

[First Example of Control Flow of Sheet Folding Device 200]

Next, examples of control flows of the sheet folding device 200 is described. The postprocessing controller 50 performs control programs including control flows described below. [0077]

FIG. 22 is a flowchart illustrating a first example of a control flow of the sheet folding device 200. First, the post-processing controller 50 acquires information on the sheet P from the image forming device controller 10 in step S2101. Subsequently, the preceding sheet Pl is conveyed in the sheet circulation path, and the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl. The post-processing controller 50 stops conveying the preceding sheet Pl that reaches the position corresponding to the second protrusion amountA2 after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl in step S2102.

[0078] In step S2103, the sheet folding device 200 receives the following sheet P2. In step S2104, the post-processing controller 50 determines the type of the preceding sheet Pl.

[0079]

When the post-processing controller 50 determines that the preceding sheet Pl is a plain sheet, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount A mm. The third protrusion amountA3 is a protrusion amount of the leading edge of the following sheet P2 from the position of the first sheet detecting sensor SN 1 after the first sheet detecting sensor SN1 detects the leading edge of the following sheet P2. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount A mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2105.

[0080]

When the post-processing controller 50 determines that the preceding sheet Pl is the thick sheet, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount A' mm larger than the shift amount A mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount A' mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2106.

[0081]

When the preceding sheet is the thick sheet, the thickness of the preceding sheet Pl increases a conveyance distance of the following sheet P2 until the following sheet P2 is conveyed to the position of the fourth sheet detecting sensor SN4 after the following sheet is overlaid on the preceding sheet Pl, and the conveyance distance of the following sheet P2 overlaid on the thick sheet is longer than the conveyance distance of the following sheet P2 overlaid on the plain sheet. In the first example, the third protrusion amount A3 is set to be the shift amount A' mm to increase the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 in advance. The above-described control reduces the distance between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 when the preceding sheet Pl and the following sheet P2 reaches the position at which the fourth sheet detecting sensor SN4 detects the preceding sheet Pl or the following sheet P2.

[0082]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2107.

[0083]

In step S2108, the post-processing controller 50 performs the folding processing as described above when the folding processing is performed, and ejects the sheet bundle Q.

[0084]

[Second Example of Control Flow of Sheet Folding Device 200]

FIG. 23 is a flowchart illustrating a second example of a control flow of the sheet folding device 200. First, the post-processing controller 50 acquires information on the sheet P from the image forming device controller 10 in step S2201. Subsequently, the preceding sheet Pl is conveyed in the sheet circulation path, and the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl. The post-processing controller 50 stops conveying the preceding sheet Pl that reaches the position corresponding to the second protrusion amount A2 after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl in step S2202.

[0085] In step S2203, the sheet folding device 200 receives the following sheet P2. In step S2204, the post-processing controller 50 determines the type of the preceding sheet Pl.

[0086]

When the post-processing controller 50 determines that the preceding sheet Pl is a plain sheet, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount A mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount A mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2205.

[0087]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2207. In step S2207, the post-processing controller 50 controls the conveyance of the sheet bundle Q so that the first protrusion amount Al of the sheet bundle Q that strikes against the first conveyer R1 becomes “a mm”.

[0088]

When the post-processing controller 50 determines that the preceding sheet Pl is the thick sheet, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount A' mm larger than the shift amount A mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount A' mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path Wl in step S2206.

[0089]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2208. In step S2208, the post-processing controller 50 controls the conveyance of the sheet bundle Q so that the first protrusion amount Al of the sheet bundle Q that strikes against the first conveyer R1 becomes “a' mm” larger than “a mm”.

[0090]

After step S2207 or step S2208, the post-processing controller 50 performs the folding processing as described above when the folding processing is performed and ejects the sheet bundle Q in step S2209.

[0091]

When the next sheet P3 meets the sheet bundle Q including the preceding sheet Pl and the following sheet P2 to form the new sheet bundle that strikes against the first conveyer R1 stopped, the post-processing controller 50 sets the first protrusion amount Al to be a length longer than “a' mm”.

[0092]

That is, when the post-processing controller 50 changes the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 to “A'” based on the information about the type of the sheet, the post-processing controller 50 increases the first protrusion amount Al of the next sheet P3 that is overlaid on the following sheet P2 and the preceding sheet Pl. The above-described control enables correcting the skews of the preceding sheet Pl and the following sheet P2 during the correction of the skew of the next sheet P3. As a result, the above-described control can improve the accuracy of the alignment of the leading edges.

[0093]

[Third Example of Control Flow of Sheet Folding Device 200]

FIG. 24 is a flowchart illustrating a third example of a control flow of the sheet folding device 200. First, the post-processing controller 50 acquires information on a printed surface of the sheet as the information on the sheet P from the image forming device controller 10 in step S2301. Subsequently, the preceding sheet Pl is conveyed in the sheet circulation path, and the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl. The post-processing controller 50 stops conveying the preceding sheet Pl that reaches the position corresponding to the second protrusion amount A2 after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl in step S2302.

[0094]

In step S2303, the sheet folding device 200 receives the following sheet P2. In step S2304, the post-processing controller 50 determines whether the printed surface of the preceding sheet Pl is an upper surface or a lower surface.

[0095]

When the post-processing controller 50 determines that the printed surface of the preceding sheet Pl is the upper surface of the preceding sheet Pl, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount E mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount E mm, the postprocessing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2305.

[0096]

When the post-processing controller 50 determines that the printed surface of the preceding sheet Pl is the lower surface of the preceding sheet Pl, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount F mm larger than the shift amount E mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount F mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2306.

[0097]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2307. In addition, the post-processing controller 50 performs the folding processing as described above when the folding processing is performed, and ejects the sheet bundle Q in step S2307.

[0098]

In this example, the post-processing controller 50 changes the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 based on a state of the printed surface of the overlaid sheet. The post-processing controller 50 receives the information about the printed surface of the sheet P that is a surface of the sheet on which the image is formed from the image forming device controller 10.

[0099]

When the printed surface is the upper surface of the preceding sheet Pl, the post-processing controller 50 controls the zeroth conveyer R0 and the third conveyer R3 so that the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 becomes E mm. When the printed surface is the lower surface of the preceding sheet Pl, the post-processing controller 50 controls the zeroth conveyer R0 and the third conveyer R3 so that the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 becomes F mm. In the above-described both cases, the preceding sheet Pl precedes the following sheet P2 so as to make a relationship of F mm > E mm.

[0100]

When the printed surface is the upper surface of the preceding sheet Pl, if the image forming process is performed by the electrophotographic method, toner adhering to an image on the printed surface affects and reduces the friction between the sheets P. As a result, when the folding process is performed on the sheet bundle Q, the following sheet P2 slips, and the leading edges of the sheets overlaid in the sheet bundle Q are shifted. In anticipation of this, shifting the sheet P in advance can reduce the shift after the folding processing.

[0101]

[Fourth Example of Control Flow of Sheet Folding Device 200]

FIG. 25 is a flowchart illustrating a fourth example of a control flow of the sheet folding device 200. First, the post-processing controller 50 acquires information on printed image positions on the sheet P as the information on the sheet P from the image forming device controller 10 in step S2401. Subsequently, the preceding sheet Pl is conveyed in the sheet circulation path, and the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl. The post-processing controller 50 stops conveying the preceding sheet Pl that reaches the position corresponding to the second protrusion amount A2 after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl in step S2402. [0102]

In step S2403, the sheet folding device 200 receives the following sheet P2. In step S2404, the post-processing controller 50 determines whether the printed image is on a folding position.

[0103]

When the post-processing controller 50 determines that the printed image is on the folding position (Yes in step S2404), the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount G mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount G mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2405.

[0104]

When the post-processing controller 50 determines that the printed image is not on the folding position (No in step S2404), the post-processing controller 50 sets the third protrusion amount A3 to be a shift amount H mm larger than G mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount H mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2406.

[0105]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2407. In addition, the post-processing controller 50 performs the folding processing as described above when the folding processing is performed, and ejects the sheet bundle Q in step S2407.

[0106]

In this example, the post-processing controller 50 receives the information on the printed image positions from the image forming device 100. When the printed image is on the folding position of the sheet P, the post-processing controller 50 changes the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 to “G mm”. When the printed image is not on the folding position of the sheet P, the post-processing controller 50 changes the shift amount between the leading edge the preceding sheet Pl and the leading edge of the following sheet P2 to “H mm”. Regardless of the shift amount, the preceding sheet Pl is shifted in advance.

[0107]

When the printed image is on the folding position, if the image forming process is performed by the electrophotographic method, toner adhering to the image on the printed surface affects and reduces the friction between the sheets P. As a result, when the folding process is performed on the sheet bundle Q, the following sheet P2 slips, and the leading edges of the sheets overlaid in the sheet bundle Q are shifted. In anticipation of this, shifting the sheet P in advance can reduce the shift after the folding processing.

[0108]

[Fifth Example of Control Flow of Sheet Folding Device 200]

FIG. 26 is a flowchart illustrating a fifth example of a control flow of the sheet folding device 200. First, the post-processing controller 50 acquires information on a folding type as the information on the sheet P from the image forming device controller 10 in step S2501. Subsequently, the preceding sheet Pl is conveyed in the sheet circulation path, and the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl. The postprocessing controller 50 stops conveying the preceding sheet Pl that reaches the position corresponding to the second protrusion amount A2 after the fourth sheet detecting sensor SN4 detects the leading edge of the preceding sheet Pl in step S2502.

[0109]

In step S2503, the sheet folding device 200 receives the following sheet P2. In step S2504, the post-processing controller 50 determines what the folding type is.

[0110]

When the post-processing controller 50 determines that the folding type is letter fold-out, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount K mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount K mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path W1 in step S2505.

[0111]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2507.

[0112]

When the post-processing controller 50 determines that the folding type is not letter fold-out, the post-processing controller 50 sets the third protrusion amount A3 to be the shift amount E mm larger than K mm. Then, after the third protrusion amount A3 with respect to the following sheet P2 reaches the shift amount E mm, the post-processing controller 50 resumes the rotation of the third conveyer R3 and causes the preceding sheet Pl to meet the following sheet P2 in the first conveyance path Wl in step S2506.

[0113]

In the first conveyance path Wl, the preceding sheet Pl meets the following sheet P2, and the preceding sheet Pl and the following sheet P2 strike against the first conveyer R1 that is stopped to correct the skew in step S2508. Thereafter, the sheet folding device performs letter fold-in processing designated, and the sheet bundle Q is ejected in step S2508.

[0114]

In this example, the post-processing controller 50 receives the information on the folding type from the image forming device 100. When the folding type is letter fold-out, the postprocessing controller 50 changes the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 to “K mm”. When the folding type is letter fold-in, the post-processing controller 50 changes the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 to “L mm”. Regardless of the shift amount, the preceding sheet Pl is shifted in advance.

[0115]

Setting the shift amount between the leading edge of the preceding sheet Pl and the leading edge of the following sheet P2 in the letter fold-in processing larger than that in the letter fold- out can improve the accuracy of the alignment of the leading edges after the folding processing is completed.

[0116]

The sheet folding device 200 according to the present embodiment described above can improve accuracy of a skew correction of sheets overlaid and the accuracy of the alignment of the leading edges of the sheets overlaid when the post-processing device performs post processing including processes overlaying a plurality of sheets.

[0117]

The present disclosure is not limited to specific embodiments described above, and numerous additional modifications and variations are possible in light of the teachings within the technical scope of the present disclosure. It is therefore to be understood that the disclosure of the present specification may be practiced otherwise by those skilled in the art than as specifically described herein. Such embodiments and variations thereof are included in the scope and gist of the embodiments of the present disclosure and are included in the embodiments described in claims and the equivalent scope thereof.

[0118]

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions. [0119]

This patent application is based on and claims priority to Japanese Patent Application No. 2020-141859, filed on August 25, 2020, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

[Reference Signs List]

[0120]

I Image forming apparatus

10 Image forming device controller

I I Central processing unit (CPU)

12 Read only memory (ROM)

13 Random access memory (RAM)

14 Serial interface (PF)

20 Image forming unit

21 Entrance

22 Outlet

23 Bifurcating claw

24 Output tray

30 Image reading unit

40 Operation display unit

50 Post-processing controller

51 Central processing unit (CPU)

52 Read only memory (ROM)

53 Random access memory (RAM)

54 Serial interface (PF) 60 Components

61 Driver

70 Sensor

100 Image forming device 200 Sheet folding device Fl First folder

F2 Second folder

J 1 First switching guide

J2 Second switching guide

J3 Third switching guide

P Sheet

Pl Preceding sheet P2 Following sheet P3 Next sheet PL Final sheet Q Sheet bundle R0 Zeroth conveyer R1 First conveyer R2 Second conveyer R3 Third conveyer R4 Fourth conveyer R5 Fifth conveyer R6 sixth conveyer

SN 1 First sheet detecting sensor SN2 Second sheet detecting sensor SN3 Third sheet detecting sensor SN4 Fourth sheet detecting sensor SN5 Fifth sheet detecting sensor SN6 Sixth sheet detecting sensor SN7 Seventh sheet detecting sensor W 1 First conveyance path W2 Second conveyance path W3 Third conveyance path W4 Fourth conveyance path W5 Fifth conveyance path W6 Sixth conveyance path W7 Seventh conveyance path