Post-processing device and image forming system

Abstract

To achieve both maintenance of alignment accuracy of a sheet bundle and suppression of a jam.SOLUTION: A post-processing device comprises: buffer means for receiving a sheet transported from a first transportation path, and accumulating and holding temporarily a predetermined number of sheets; and loading means for loading the predetermined number of sheets transported from a second transportation path in a first direction. The post-processing device comprises: moving means for contacting an uppermost sheet among the predetermined number of sheets loaded on the loading means and moving the upper most sheet further in the first direction; and restricting means for restricting a position of a sheet bundle. The post-processing device controls the predetermined number of sheets which are accumulated on the buffer means temporarily and are transported to the loading means together. The post-processing device determines the predetermined number of sheets on the basis of a physical parameter affecting friction force generated on a surface of the sheet.SELECTED DRAWING: Figure 4

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a post-processing device and an image forming system.

Background Art

[0002] A post-processing device is an option for an image forming device, and performs post-processing such as binding and alignment on a sheet on which an image has been formed by the image forming device. Patent Document 1 describes a post-processing device that discharges a sheet to a processing tray by a discharge roller, moves the sheet using a paddle and a belt, and brings the sheet into contact with an edge regulating member. The paddle and the belt are rotating members that contact the upper surface of the sheet. The paddle and the belt move the sheet in a direction generally opposite to the discharge direction of the sheet by the discharge roller, and align the sheet bundle.

[0003] [[ID=1�]] Patent Document 2 describes a post-processing device provided with a buffer mechanism upstream of a post-processing mechanism, and temporarily stores a plurality of sheets while overlapping them in the buffer mechanism. The sheet bundle stored in the buffer mechanism is conveyed to a downstream alignment processing unit while maintaining the state of the sheet bundle, and alignment processing is applied.

Prior Art Documents

Patent Documents

[0006] The present invention, for example, The first transport path for transporting the sheets, A buffer means that receives sheets transported from the first transport path and temporarily holds a predetermined number of sheets stacked on top of each other, When the temporary holding in the buffer means ends, a second transport path is established to transport the predetermined number of sheets from the buffer means, A loading means for loading the predetermined number of sheets that have been transported from the second transport path toward the first direction, A moving means that contacts the uppermost sheet among the predetermined number of sheets loaded on the loading means and moves the uppermost sheet further toward the first direction, A regulating means provided downstream of the moving means in the first direction, which abuts against the end of the sheet bundle loaded on the loading means, and the downstream end in the first direction, to regulate the position of the sheet bundle, When a plurality of sheets are transported to the loading means and a forming operation is performed in which the sheet bundle is formed on the loading means, The predetermined number decision It has a control means that does the following, When the control means determines the predetermined number to be two or more, in the forming operation, the predetermined number of sheets are stacked in the buffer means, and the predetermined number of sheets are transported to the loading means via the second transport path. When the control means determines the predetermined number to be one sheet, in the forming operation, the sheet bundle is formed by transporting the sheets one by one to the loading means via the second transport path. The control means provides a post-processing device characterized by determining the predetermined number of sheets based on physical parameters that affect the frictional force generated on the surface of the sheet. [Effects of the Invention]

[0007] According to the present invention, it is possible to achieve both the maintenance of sheet bundle alignment accuracy and the suppression of jamming. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating an image forming system. [Figure 2] This is a diagram illustrating the process of overlapping sheets. [Figure 3] This is a diagram illustrating the synchronized operation. [Figure 4] This is a block diagram illustrating the control system. [Figure 5] This is a flowchart showing the control method. [Figure 6] This is a block diagram illustrating the control system. [Figure 7] This is a flowchart showing the control method. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] <Example 1> FIG. 1 is a schematic cross-section of an image forming system 100 having an image forming apparatus 1, an image reading apparatus 2, a document feeding apparatus 3, and a post-processing apparatus 4. The image forming apparatus 1 forms an image on a sheet P. The image forming method of the image forming apparatus 1 may be any of an electrophotographic method, an inkjet method, a thermal transfer method, etc., but here, as an example, the electrophotographic method is adopted. The image reading apparatus 2 reads a document fed from the document feeding apparatus 3 and creates image data. The post-processing apparatus 4 performs post-processing (e.g., punching, stapling, binding) on the sheet P.

[0011] The document feeding apparatus 3 conveys the document placed on the document tray 18 to the image reading units 16, 19. The image reading units 16, 19 can read both sides of the document at once by reading the document surfaces facing each other. The document feeding apparatus 3 discharges the document to the document discharge unit 20.

[0012] The image reading apparatus 2 can also read a document such as a booklet document that cannot be fed by the document feeding apparatus 3 by reciprocally scanning the image reading unit 16 with the driving apparatus 17. The image data generated by the image reading units 16, 19 is transmitted to the image forming apparatus 1.

[0013] The image forming apparatus 1 has a plurality of feeding devices 6 that accommodate a plurality of sheets P. The feeding device 6 feeds the sheets one by one at a predetermined feeding interval. The sheet P fed from the feeding device 6 is corrected for skew by the registration roller 7 and conveyed to the transfer nip portion by the registration roller 7. The transfer nip portion is constituted by a photosensitive drum 9 rotatably supported by an image forming cartridge 8 and a transfer roller 10 to which a predetermined transfer voltage is applied. The surface of the photosensitive drum 9 forms a toner image through the steps of exposure, charging, latent image formation, and development within the image forming cartridge 8. In particular, the laser scanner unit 15 forms an electrostatic latent image by exposing the surface of the uniformly charged photosensitive drum 9 with laser light. The transfer nip portion transfers the toner image from the photosensitive drum 9 to the sheet P. The sheet P is conveyed to the fixing device 11, and the fixing device 11 applies heat and pressure to the sheet P and the toner image to fix the toner image on the sheet P. The horizontal conveyance unit 14 conveys the sheet P that has passed through the fixing device 11 and discharges it to the post-processing device 4. When double-sided printing is executed, the sheet P is conveyed to the reversing roller 12, and the reversing roller 12 performs a switchback conveyance that exchanges the leading and trailing ends of the sheet P. As a result, the sheet P is sent to the refeeding unit 13. The refeeding unit 13 conveys the sheet P to the registration roller 7 again. Thereafter, an image is formed on the sheet P again.

[0014] The post-processing device 4 has a buffer unit 40 and a stage unit 41. The buffer unit 40 forms a sheet bundle by overlapping a plurality of sheets P while shifting them in the conveyance direction and temporarily holds the sheet bundle. The buffer unit 40 may temporarily hold only one sheet P. The stage unit 41 stores a predetermined number of sheets P and performs alignment processing and binding processing.

[0015] The post-processing device 4 discharges the sheet P conveyed from the horizontal conveyance unit 14 to any one of the front tray 30, the upper tray 25, or the lower tray 37. The sheet P received by the stage unit 41 is subjected to binding processing to form a sheet bundle. The sheet bundle is discharged to the lower tray 37. The sheet bundle may be discharged to the lower tray 37 without being subjected to binding processing.

[0016] The sheets P transported from the horizontal transport section 14 are transferred to the inlet roller 21 or discharge roller 31 of the post-processing device 4 by a transport path switching flapper (not shown). Sheets P transferred to the discharge roller 31 are then discharged directly to the front tray 30. Sheets P transferred to the inlet roller 21 are further transported along the first transport path R1 within the post-processing device 4.

[0017] An inlet sensor 27 is provided downstream of the inlet roller 21 in the direction of conveying the sheet P. The inlet sensor 27 is a sheet sensor that detects the passage of the leading edge and trailing edge of the sheet P received by the inlet roller 21, as well as the presence or absence of jams.

[0018] Downstream of the inlet sensor 27 are a line sensor 61, a lighting unit 63, and a rotary punch unit 62. The line sensor 61 and the lighting unit 63 detect the edge of the sheet P. The punch unit 62 is connected to a punching motor (not shown), an edge position adjustment motor, a punch position sensor, and a home position sensor. The punching motor drives the punch and die. The edge position adjustment motor drives the punch unit 62 in the width direction of the sheet P, adjusting the position of the edge of the sheet P relative to the punch unit 62. The width direction is perpendicular to the conveying direction of the sheet P. Thus, the line sensor 61, lighting unit 63, and punch unit 62 are used when punching the sheet. Instructions for punching and not punching are given via a touch panel (not shown) attached to the image forming apparatus 1, image reading device 2, document feeding device 3, etc., or via an external device.

[0019] Based on a predetermined timing determined by the time the rear end of the sheet P has passed, as detected by the inlet sensor 27, the buffer-front roller 22 accelerates the sheet P. The predetermined timing is when the final hole in the sheet P is completed during perforation, and when the rear end of the sheet P has passed the inlet sensor 27 during non-perforation. If the destination of the sheet P is the upper tray 25, when the rear end of the sheet P reaches between the buffer-front roller 22 and the reversing roller 24, the sheet P is decelerated to a predetermined discharge speed and discharged to the upper tray 25.

[0020] When the destination of sheet P is the lower tray 37, sheet P is sent from the first transport path R1 to the second transport path R2. A sheet sensor 46 provided in the first transport path R1 detects the timing when the rear end of sheet P passes the backflow prevention valve 23. At the timing when the rear end of sheet P passes the backflow prevention valve 23, sheet P stops temporarily. The backflow prevention valve 23 is biased clockwise by a spring (not shown). Subsequently, the reversing roller 24 switches back sheet P and transports it to the internal discharge roller 26.

[0021] The sheet sensor 47 detects when the leading edge of the sheet P reaches the internal discharge roller 26. At this stage, the reversing roller 24 releases its nip and prepares to receive the subsequent sheet P heading toward the reversing roller 24. The internal discharge roller 26 pauses temporarily with the sheet P held between them. When the sheet sensor 46 detects the arrival of the subsequent sheet P, the internal discharge roller 26 reverses, and the sheet P is conveyed again toward the reversing roller 24. In this way, the buffer unit 40 buffers multiple sheets P by overlapping the preceding and succeeding sheets. The buffer unit 40 can buffer multiple sheets P regardless of the length of the sheets P by repeatedly switching back the sheets P using the internal discharge roller 26. Details of the sheet P buffering (overlapping) operation will be described later.

[0022] The sheets P, transported from the internal discharge roller 26, are transported to the intermediate loading section 39 via intermediate transport rollers 28 and 29. A sheet sensor 38 is provided between the intermediate transport roller 28 and the intermediate transport roller 29. A longitudinal alignment reference plate 33 is positioned at the downstream end of the intermediate loading section 39. Alignment of the sheet bundle is performed when the ends of the sheets P abut against the longitudinal alignment reference plate 33. At this time, the longitudinal alignment roller 32 makes a small rotation so that the sheets P abut against the longitudinal alignment reference plate 33, assisting in the alignment of the sheets P. After the sheets P reach the longitudinal alignment reference plate 33, a lateral alignment jogger (not shown) performs an alignment operation with respect to a lateral alignment reference plate (not shown) to align the sheet bundle laterally.

[0023] Once the alignment of the sheet bundle, consisting of a predetermined number of sheets P, is complete, the stapler on the stage unit 41 performs a stapling operation on the sheet bundle. Subsequently, the bundle discharge guide 34 connected to the guide drive unit 35 moves, and the sheet bundle is pushed out from the intermediate loading unit 39 towards the bundle discharge roller 36.

[0024] When the leading edge of the sheet bundle reaches the bundle discharge roller 36, the guide drive unit 35 stops the bundle discharge guide 34 and returns it to its standby position. The bundle discharge roller 36 discharges the sheet bundle received from the bundle discharge guide 34 into the lower tray 37.

[0025] (Buffer operation) Figures 2(A) to 2(F) show details of the buffer operation of the buffer unit 40. The buffer operation is an operation in which a predetermined number of sheets P constituting the next sheet bundle are kept waiting in the buffer unit 40 until the binding process for the preceding sheet bundle is completed in the stage unit 41. By performing the buffer operation, the image forming system 100 can execute image forming jobs, including the binding process, without reducing the productivity of the image forming apparatus 1 (number of images output per unit time).

[0026] In Figures 2(A) through 2(F), to distinguish between multiple sheets P, "Sheet P1," "Sheet P2," and "Sheet P3" are defined according to the order in which they are handed over from the image forming apparatus 1 to the post-processing device 4. In other words, the smaller the number assigned to P, the earlier the sheet arrived at the post-processing device 4. The arrows indicate the direction of transport of the sheet P. Of the two ends of the sheet P with respect to the transport direction, the one that passes the entrance roller 21 first is defined as the "first end," and the one that passes the entrance roller 21 later is defined as the "second end."

[0027] Figure 2(A) shows the state when the leading edge (first end) of sheet P1 passes the position of sheet sensor 46. After this, sheet P1 is conveyed toward the reversing roller 24.

[0028] Figure 2(B) shows the state when the rear end (second end) of the sheet P1, which has been conveyed by the buffer front roller 22, reaches the reversal position SB1. After this, the rotation direction of the reversal roller 24 changes from forward to reverse, and the conveying direction of the sheet P1 is reversed (switchback). As a result, the sheet P1 is conveyed toward the internal discharge roller 26. When the sheet sensor 47 detects that the rear end (second end) of the sheet P1 has reached the reversal position SB2, the reversal roller 24 stops. The sheet P1 is prevented from going toward the buffer front roller 22 by the sheet backflow prevention valve 23.

[0029] Figure 2(C) shows the state when the rear end (second end) of sheet P1 is at the reversal position SB2 and the front end (first end) of sheet P2 has passed the sheet sensor 46. After this, sheet P2 is transported toward the reversal roller 24 by the buffer front roller 22, similar to sheet P1 as described in Figure 2(A). The internal discharge roller 26 starts to reverse in order to overlap sheet P1 and sheet P2. As a result, sheet P1 is transported toward the reversal roller 24. The reversal timing of the internal discharge roller 26 is adjusted so that sheet P1 and sheet P2 overlap with a predetermined shift amount relative to the transport direction. In other words, the second end of sheet P1 and the second end of sheet P2 are shifted, and the second end of sheet P2 becomes closer to the reversal roller 24 than the second end of sheet P1.

[0030] Figure 2(D) shows the state when the rear end (second end) of sheet P2 reaches the reversal position SB1. As shown in Figure 2(D), sheet P1 is positioned on the underside of sheet P2 (sheet bundle). After this, the reversal roller 24 starts to reverse so that the sheet bundle P1 & P2 are transported to the stage section 41 as a sheet bundle. As a result, the sheet bundles P1 and P2 are transported towards the internal discharge roller 26. When the reversing roller 24 starts to reverse direction, the internal discharge roller 26 starts to rotate forward.

[0031] Figure 2(E) shows the state where the rear end (second end) of sheet bundles P1 & P2 is at the reversal position SB2. Note that the rear end (second end) of sheet P1 is located downstream of the reversal position SB2, and the rear end (second end) of sheet P1 is located at the reversal position SB2. Figure 2(E) also shows the state when the leading edge (first end) of sheet P3 has passed the sheet sensor 46. Sheet P3 is conveyed toward the reversal roller 24 by the buffer front roller 22, similar to sheets P1 and P2 described in Figures 2(A) and 2(C). On the other hand, sheet bundles P1 & P2 are conveyed toward the stage section 41, unlike sheet P1 described in Figure 2(C).

[0032] Figure 2(F) shows how sheet bundles P1 and P2 are transported to the stage section 41, and how sheet P3 is transported toward the reversing roller 24. Sheet P3 then proceeds to the reversing position SB1, similar to sheet P1 in Figure 2(B).

[0033] As described above, in Example 1, multiple sheets P transported from the image forming apparatus 1 form a sheet bundle in the buffer section 40. Note that in Figures 2(A) to 2(F), the number of sheets P stacked M is two, but this is just one example. The buffer section 40 can also buffer three or more sheets P. In this case, in Figure 2(E), the sheet bundle P1 & P2 held by the internal discharge roller 26 is transported by the internal discharge roller 26 toward the reversing roller 24 as shown in Figure 2(C). This performs stacking on the subsequent sheet P3. By repeating this stacking, three or more sheets P can be buffered.

[0034] (matching operation) Figures 3(A) to 3(E) show the sheet bundle alignment operation in the transport direction performed by the stage unit 41. Here, an example is described in which, starting from a state where sheet bundles P1 and P2 have already been aligned in the stage unit 41, another sheet bundle P3 to P5 consisting of three sheets P is transported from the buffer unit 40 to the stage unit 41.

[0035] Figure 3(A) shows the rear end (second end) of the sheet bundle P3-P5, consisting of three sheets P3, P4, and P5, reaching the sheet sensor 38 and then entering the stage section 41. The longitudinal alignment roller 32 of the stage section 41 descends from its standby position toward the stage section 41 where sheets P1 and P2 are stacked in order to perform alignment processing on the sheet bundle P3-P5 (arrow in the figure). The longitudinal alignment roller 32 may come into contact with sheet P2. Subsequently, the longitudinal alignment roller 32 begins to rotate before the sheet bundle P3-P5 reaches the longitudinal alignment roller 32.

[0036] Figure 3(B) shows sheet P3 of the three sheet bundles P3-P5 reaching the longitudinal alignment roller 32. The longitudinal alignment roller 32 rotates counterclockwise, causing the edge of sheet P3 to abut against the longitudinal alignment reference plate 33. This aligns the edge of sheet P3 with the edges of sheet P1 and sheet P2 (alignment process).

[0037] Figure 3(C) shows the state after the alignment of sheets P3 and P4 of the three sheet bundles P3 to P5 is complete, and the top sheet P5 has reached the longitudinal alignment roller 32. As the longitudinal alignment roller 32 continues to rotate counterclockwise, the edge of sheet P5 abuts against the longitudinal alignment reference plate 33. This aligns the edge of sheet P5 with the respective edges of sheets P1 to P4.

[0038] Figure 3(D) shows the state after the alignment process of sheet bundles P3 to P5 has been completed. At this time, the vertical alignment roller 32 moves away from the stage section 41 so as not to obstruct the discharge of sheet bundles P1 to P5.

[0039] Figure 3(E) shows how the aligned sheet bundles P1 to P5 are pushed out to the discharge port by the bundle discharge guide 34. Once the pushing is complete, the bundle discharge guide 34 returns to its standby position to receive the subsequent sheets P being transported from the buffer section 40. The staple unit of the stage section 41 may perform stapling between the timings shown in Figure 3(D) and Figure 3(E).

[0040] (Relationship between coordinated transport force and frictional force) Next, the relationship between the alignment transport force and frictional force related to the alignment operation of sheets and sheet bundles will be explained with reference to Figures 3(B) and 3(C).

[0041] ●When aligning a single sheet P First, using Figure 3(C), the transport force of the longitudinal alignment roller 32 and the frictional force that hinders the alignment operation of the sheet P when a single sheet P is aligned will be explained. Here, it is assumed that only sheet P5 is transported from the buffer section 40 by itself, and that sheets P1 to P4 have already been transported from the buffer section 40 and aligned.

[0042] The sheet P5, which is in contact with the rotating longitudinal alignment roller 32, receives a transport force Ffeed that propagates from the longitudinal alignment roller 32 toward the longitudinal alignment reference plate 33. Meanwhile, the sheet P5 is transported while in contact with the sheet P4. Therefore, the sheet P5 receives a frictional force Ffric_bottom due to contact with the sheet P4, which acts as a force that hinders the alignment operation.

[0043] If the conveying force Ffeed exceeds the frictional force Ffric_bottom, the sheet P5 will advance until its edge abuts against the longitudinal alignment reference plate 33. When the edge of the sheet P5 abuts against the longitudinal alignment reference plate 33, a frictional force Fedge acts between the sheet P5 and the longitudinal alignment roller 32. Therefore, the frictional force acting on the sheet P5 increases. As a result, the relative magnitudes of the conveying force Ffeed and the frictional force Ffric_bottom+Fedge are reversed, and the advance of the sheet P stops.

[0044] If the conveying force Ffeed falls below the frictional force Ffric_bottom, sheet P5 cannot advance toward the longitudinal alignment reference plate 33. As a result, the end of sheet P5 cannot reach the longitudinal alignment reference plate 33, and misalignment occurs for sheet P5.

[0045] Misalignment can also occur if the conveying force Ffeed is too high. If the conveying force Ffeed exceeds the frictional force Ffric_bottom+Fedge, the sheet P5 will be pushed towards the longitudinal alignment reference plate 33 even after its end has struck the longitudinal alignment reference plate 33. This causes the sheet P5 to buckle between the longitudinal alignment roller 32 and the longitudinal alignment reference plate 33, resulting in a jam. Even if the sheet P5 does not buckle, it may still deflect between the longitudinal alignment roller 32 and the longitudinal alignment reference plate 33. As shown in Figure 3(D), when the longitudinal alignment roller 32 separates, the sheet P5 moves towards the tip (first end) to eliminate the deflection of the sheet P5. At this time, the end of the sheet P5 that was striking the longitudinal alignment reference plate 33 also moves towards the tip (first end), which can cause misalignment.

[0046] Therefore, the conveying force Ffeed of the longitudinal alignment roller 32 must be small enough that it does not cause buckling or deflection of the sheet P. The relationship between the conveying force and the frictional force is adjusted to satisfy equation (1). As a result, the accuracy of alignment by the longitudinal alignment roller 32 is improved.

[0047] Ffric_bottom < Ffeed < (Ffric_bottom + Fedge) ···(1) The frictional force Ffric_bottom acting between multiple sheets P largely depends on the state of the sheets P. For example, it increases when the contact area between two sheets P is large and when the smoothness of the sheets P is high. In particular, when the area of ​​the image is large relative to the surface area of ​​the sheets P and when the temperature of the sheets P is kept high, the degree of adhesion between multiple overlapping sheets P increases. Therefore, the frictional force also increases significantly. In the case where a single sheet P5 is transported to the stage section 41, the temperature of sheet P5 tends to decrease due to heat dissipation during transport. Also, sheet P4, which is affected by friction during alignment, and sheet P5, which is to be aligned, are not in a pressed state until alignment is complete. Therefore, the increase in frictional force is minor.

[0048] ●When aligning sheet bundles Next, using Figure 3(B), the conveying force of the longitudinal alignment roller 32 and the frictional force that hinders the alignment operation when aligning a sheet bundle will be explained. The sheet P3 in contact with the rotating longitudinal alignment roller 32 receives a conveying force Ffeed from the longitudinal alignment roller 32 toward the longitudinal alignment reference plate 33. On the other hand, the sheet P3 receives a frictional force Ffric_bottom from the sheet P2 as a force that hinders the alignment operation.

[0049] If the conveying force Ffeed exceeds the frictional force Ffric_bottom, the sheet P3 will advance until its edge abuts against the longitudinal alignment reference plate 33. When the edge of the sheet P3 abuts against the longitudinal alignment reference plate 33, the frictional force Fedge acting between the sheet P3 and the longitudinal alignment roller 32 increases. This reverses the relative magnitudes of the conveying force Ffeed and the frictional force Ffric_bottom, and the advance of the sheet P3 stops.

[0050] If the conveying force Ffeed is less than the frictional force Ffric_bottom, the sheet P3 cannot advance toward the longitudinal alignment reference plate 33. As a result, the end of the sheet P3 cannot reach the longitudinal alignment reference plate 33. Consequently, misalignment occurs for the sheet P3. Misalignment can also occur if the conveying force Ffeed is too high. If the conveying force Ffeed exceeds the frictional force Ffric_bottom, even after the end of the sheet P3 hits the longitudinal alignment reference plate 33, the sheet P3 is pushed further toward the longitudinal alignment reference plate 33. This causes the sheet P3 to buckle between the longitudinal alignment roller 32 and the longitudinal alignment reference plate 33, resulting in a jam. Even if the sheet P3 does not buckle, it may deflect between the longitudinal alignment roller 32 and the longitudinal alignment reference plate 33. When the longitudinal alignment roller 32 separates, the sheet P3 advances toward its leading edge (first end) to eliminate the deflection of the sheet P3. The rear end (second short) of sheet P3, which was abutting against the vertical alignment reference plate 33, also moves towards the front end (first end). As a result, misalignment occurs.

[0051] The frictional force Ffric_bottom acting between sheet P3 and sheet P2 largely depends on the state of sheets P3 and P2. For example, the frictional force Ffric_bottom increases when the contact area between sheets P3 and P2 is large, and when the smoothness of sheets P3 and P2 is high. When the area of ​​the image is large relative to the surface area of ​​sheet P, and when the temperature of sheet P is kept high, the degree of adhesion between sheets P increases. Therefore, the frictional force increases significantly. In the case where the sheets are transported to the stage section 41 in a bundle, the bundle is formed in the buffer section 40. Because multiple sheets are stacked on top of each other, heat dissipation from the bundle is difficult. Therefore, the temperature of the bundle does not easily decrease during transport. The bundle of sheets is transported toward the stage section 41 while being pressed together. Therefore, a high frictional force exists between sheet P3 and sheet P4, which need to be separated during alignment.

[0052] Thus, there are cases where equation (1) cannot be satisfied even with sheet bundles. In other words, there are situations where sheet bundles cannot be transported to the stage unit 41.

[0053] When the post-processing device 4 receives a print request that requires transport to the stage unit 41, it determines, based on the sheet information, whether or not to generate a sheet bundle in the buffer unit 40. In other words, if transporting a sheet bundle to the stage unit 41 would cause misalignment, the formation of the sheet bundle is suppressed. As a result, each sheet P is transported to the stage unit 41 one by one.

[0054] (Control system) Figure 4 shows the control system in the image forming system 100. The external device 400 is a computer that supplies print data to the controller 401. The controller 401 is a control board that comprehensively controls the entire image forming system 100. The engine control unit 402 controls image forming in the image forming apparatus 1. The post-processing control unit 403 comprehensively controls each part of the post-processing device 4. The post-processing control unit 403 includes a processor 450 (e.g., CPU) and memory 460 (e.g., ROM and RAM). The processor 450 realizes various functions by executing control programs stored in the memory 460.

[0055] The mode determination unit 410 determines the number of sheets M formed in the buffer unit 40 based on physical parameters that affect the frictional force generated on the surface of the sheets P. M is an integer of 1 or more. When M=1, multiple sheets P are not stacked. The transport mode when M=1 may be called the single transport mode. The transport mode when M is 2 or more may be called the bundle transport mode. Thus, determining the number of sheets M in the sheet bundle is essentially equivalent to determining the transport mode.

[0056] The mode determination unit 410 determines the transport mode (number of sheets M) based on the print reservation information input from the controller 401. The print reservation information includes the output port, type of post-processing, type of sheet P, size of sheet P, transport speed, and fixing temperature. The memory 460 may store a determination table indicating the transport mode or number of sheets M associated with the print reservation information. The memory 460 may also store equation (1).

[0057] The transport control unit 411 controls the transport of the sheet P by controlling motors M22, M24, M26, and M35. A drive circuit called a motor driver (not shown) exists between the transport control unit 411 and motors M22, M24, M26, and M35. Motor M22 is a motor that rotates the buffer front roller 22. Motor M24 is a motor that rotates the reversing roller 24. Motor M26 is a motor that rotates the inner discharge roller 26. Motor M35 is a motor that drives the guide drive unit 35. The alignment control unit 412 controls motor M32. Motor M32 is a motor that rotates the longitudinal alignment roller 32. The sensor control unit 413 supplies power to the inlet sensor 27 and sheet sensors 38, 46, and 47 to acquire detection results. The punch control unit 414 controls the punch unit 62. The staple control unit 415 controls the staple unit 490.

[0058] Solenoid SL24 is a solenoid that switches the nip state and the release state of the reversing roller 24. Solenoid SL32 is a solenoid that raises or lowers the longitudinal alignment roller 32.

[0059] (flowchart) Figure 5 shows the control method executed by the processor 450 according to the control program. In S501, the processor 450 (mode determination unit 410) obtains print reservation information from the controller 401.

[0060] In S502, the processor 450 (mode determination unit 410) determines from the print reservation information output port information whether sheet P is a sheet to be sent to the buffer unit 40. If sheet P is not a sheet to be sent to the buffer unit 40, the processor 450 skips S503 and S504. If sheet P is a sheet to be sent to the buffer unit 40, the processor 450 proceeds to S503.

[0061] In S503, the processor 450 (mode determination unit 410) determines whether sheet P is a sheet to be sent to the stage unit 41 based on the output information of the print reservation information. If sheet P is not a sheet to be transported to the stage unit 41, the mode determination unit 410 determines that the sheet overlapping operation can be performed and terminates the series of determination processes. The mode determination unit 410 also notifies the transport control unit 411 that sheet P is not a sheet to be transported to the stage unit 41. On the other hand, if sheet P is a sheet to be transported to the stage unit 41, the processor 450 proceeds to S504.

[0062] In S504, the processor 450 (mode determination unit 410) determines the transport mode (number of sheets to be stacked M) based on the print reservation information. For example, if the type information of sheet P included in the print reservation information indicates gloss paper, the mode determination unit 410 determines that stacking of sheet P will not be performed. In other words, the number of sheets to be stacked M is determined to be 1. When sheet P is gloss paper, the condition that sheet stack alignment cannot be performed correctly (Ffric_bottom >= Ffeed) is met. Therefore, the mode determination unit 410 determines that stacking of sheet P will not be performed. The mode determination unit 410 notifies the transport control unit 411 that stacking of sheet P will not be performed. On the other hand, if the type information of sheet P satisfies the condition that sheet stack alignment can be performed correctly (Ffric_bottom < Ffeed), the mode determination unit 410 determines that stacking of sheet P is possible. The mode determination unit 410 notifies the transport control unit 411 of the instruction to perform stacking of sheet P. When the number of sheets to be stacked M is determined, the mode determination unit 410 notifies the transport control unit 411 of the number of sheets M.

[0063] In this way, the number of sheets M to be stacked is determined based on parameters that affect the frictional force of sheet P. For example, it is determined whether or not to stack sheets P. As a result, stacking is skipped for sheets P with low matching accuracy. In other words, stacking is performed for sheets P with high matching accuracy. This makes it possible to maintain the matching accuracy of the sheet bundle while suppressing jams.

[0064] In Example 1, the buffer unit 40 determines whether overlay can be performed based on the sheet type information (whether or not it is gloss paper) included in the print reservation information. However, this is only one example. For example, conditions may be added to determine that overlay is not possible for types other than gloss paper. Also, if equation (1) is satisfied, it is possible to determine that overlay is possible even for gloss paper. Furthermore, the number of sheets to be overlaid M may be determined not only based on the type of sheet P, but also, for example, the size of sheet P, the image information formed on sheet P (image formation rate or area of ​​the image formation region), and one or more of the image formation surfaces of sheet P (single-sided / double-sided). For example, calculation formulas for obtaining Ffric_bottom, Ffeed, and Fedge from these parameters may be stored in the ROM of memory 460. The processor 450 obtains Ffric_bottom, Ffeed, and Fedge by substituting the parameters obtained from the print reservation information into the calculation formula. Furthermore, the processor 450 determines whether Ffric_bottom, Ffeed, and Fedge satisfy equation (1).

[0065] In Example 1, the criteria for determining overlap are predetermined, but the criteria may be changed dynamically. For example, the processor 450 may acquire the jam occurrence rate for each type of sheet based on the detection results of the inlet sensor 27 and the sheet sensors 38, 46, and 47, and store it in the memory 460. Furthermore, the processor 450 may also store in the memory 460 the occurrence of misalignment due to the transport of the sheet bundle. Therefore, the processor 450 may reduce the number of overlapping sheets M for sheet types P with a high jam occurrence rate or sheet types P with a high misalignment occurrence rate. For example, the number of overlapping sheets M may be reduced from 2 to 1, or from 3 to 2. Such additions of conditions may be performed autonomously by the post-processing device 4 or by user instruction.

[0066] As described above, depending on the parameters of the sheet P being transported to the post-processing device 4, it is determined whether to transport the sheet P to the stage unit 41 individually or as a sheet bundle. This maintains the alignment accuracy in the stage unit 41 and reduces the likelihood of jams occurring.

[0067] <Example 2> Example 2 differs from Example 1 in that it considers environmental information as a condition for determining whether the sheets are being superimposed. Environmental information includes, for example, the ambient temperature and humidity of the environment in which the sheet P or the image forming system 100 is placed. Since this environmental information is also a parameter that affects the frictional force of the sheet P, it is taken into consideration when determining the number of sheets to be superimposed M.

[0068] Figure 6 shows the control system of Embodiment 2. An environmental sensor 600 that detects environmental information (e.g., ambient temperature, ambient humidity) is connected to the engine control unit 402. The mode determination unit 410 requests environmental information from the controller 401. Upon receiving this request, the controller 401 requests environmental information from the engine control unit 402. Upon receiving this request, the engine control unit 402 obtains environmental information from the environmental sensor 600 and returns the environmental information to the controller 401. The controller 401 transmits the environmental information to the processor 450 of the post-processing control unit 403. This allows the mode determination unit 410 to obtain environmental information about the environment in which the sheet P or image forming system 100 is placed. The ROM area of ​​the memory 460 may store a table or calculation formula for determining the number of overlays M, taking the environmental information into consideration.

[0069] Figure 7 shows the control method executed by the processor 450 according to the control program. Note that in Example 2, the same reference numerals are used for elements common to Example 1, and their explanation is omitted.

[0070] In S700, the processor 450 (mode determination unit 410) acquires environmental information (temperature and humidity information) from the environmental sensor 600 mounted on the image forming apparatus 1. Subsequently, the processor 450 executes S501 to S503. If sheet P is a sheet to be sent to the stage unit 41, the processor 450 proceeds to S710.

[0071] In S710, the processor 450 (mode determination unit 410) determines the transport mode (number of sheets to be stacked) based on the print reservation information and environmental information. For example, if the type information of sheet P indicates gloss paper, the number of sheets to be stacked M is determined to be 1. If the type information of sheet P does not indicate cardboard, that is, if the type information of sheet P indicates plain paper or thin paper, the number of sheets to be stacked M is determined to be 2 or more. If the type information of sheet P indicates cardboard, the mode determination unit 410 further considers the environmental information. For example, if the environment in which the image forming apparatus 1 is installed is a high-temperature and high-humidity environment, the friction force Ffric_bottom becomes too high, so the number of sheets to be stacked M is determined to be 1. If the environment in which the image forming apparatus 1 is installed is not a high-temperature and high-humidity environment, the number of sheets to be stacked M is determined to be 2 or more. Alternatively, a calculation formula or table that outputs the number of sheets to be stacked M when ambient temperature and ambient humidity are input may be used. Similarly, a calculation formula or table that outputs the number of sheets to be stacked M when ambient temperature, ambient humidity and the above-mentioned parameters are input may be used.

[0072] In Example 2, environmental information is taken into consideration, making it possible to achieve both the maintenance of matching accuracy and the reduction of jams. In Example 2, environmental information is taken into consideration in addition to print reservation information, but this is just one example. For example, the number of overlapping sheets M may be set to 1 for paper types other than gloss paper. Even for gloss paper, the number of overlapping sheets may be set to 2 or more. As explained in Example 1, parameters may include the size of the sheet P, the image formation rate, the area of ​​the image formation region, and the printing surface (single-sided / double-sided).

[0073] In Example 2, the environmental sensor 600 is located inside the image forming apparatus 1, but this is just one example. The environmental sensor 600 may be connected inside the post-processing device 4.

[0074] <Technical concepts derived from examples> [Perspective 1] As illustrated in Figure 1, the first transport path R1 is an example of a first transport path for transporting sheets P. The buffer section 40 functions as a buffer means that receives sheets P transported from the first transport path R1 and stacks and temporarily holds a predetermined number M of sheets. The second transport path R2 is an example of a second transport path that transports a predetermined number M of sheets P from the buffer means once the temporary holding in the buffer means is complete. The stage section 41 is an example of a loading means that loads a predetermined number M of sheets P transported from the second transport path R2 toward the first direction. The longitudinal alignment roller 32 functions as a moving means that contacts the uppermost sheet P among the predetermined number M of sheets P loaded on the loading means and moves the uppermost sheet P further toward the first direction. The longitudinal alignment reference plate 33 is an example of a regulating means that is provided downstream of the moving means in the first direction and contacts the end of the sheet bundle loaded on the loading means, specifically the downstream end in the first direction, to regulate the position of the sheet bundle. The post-processing control unit 403 functions as a control means that controls a predetermined number M of sheets, which is the number of sheets temporarily stored in the buffer means and transported together to the loading means. The post-processing control unit 403 determines the predetermined number M based on physical parameters that affect the frictional force generated on the surface of the sheets P. This makes it possible to maintain the alignment accuracy of the sheet bundles and suppress jams at the same time.

[0075] [Perspective 2] The post-processing control unit 403 may determine a predetermined number of sheets M to be two or more, thereby stacking two or more sheets P in the buffer means to generate a sheet bundle, and transporting the sheet bundle to the loading means via the second transport path R2. This may be called the bundle transport mode. On the other hand, the post-processing control unit 403 may determine a predetermined number of sheets M to be one, thereby temporarily holding one sheet in the buffer means, and transporting that single sheet to the loading means via the second transport path R2. When sheet bundles are transported to the loading means in this way, the matching accuracy may decrease or jams may occur. In such cases, the predetermined number of sheets M is determined to be 1, and sheets P are transported to the loading means one by one.

[0076] [Perspectives 3-6] The means of movement may be a rotating body that rotates in contact with the uppermost sheet. The rotating body may be a belt or a roller. The rotating body may be a paddle. The means of movement may also be a friction member that moves linearly in contact with the uppermost sheet. For example, a friction member (e.g., a pad) that moves linearly by a solenoid when it comes into contact with sheet P may be used. In this way, any member that moves sheet P by utilizing friction with sheet P can be used. The conveying force Ffeed generated by the means of movement is influenced by the frictional force acting between the means of movement and the surface of sheet P.

[0077] [perspective 7] The staple unit 490 is an example of a post-processing means that performs post-processing on a sheet bundle consisting of N sheets loaded on a loading means. Here, N is a predetermined number or greater. Figures 3(A) to 3(E) show an example where N=5, but N can be M or greater.

[0078] [Perspective 8] The bundle discharge guide 34 is an example of a discharge means for discharging a bundle of N sheets loaded on a loading means in a second direction opposite to the first direction.

[0079] [Perspective 9] The predetermined number of sheets M may be two or more. As illustrated in Figure 2(E), the sheets may be stacked with an offset such that the end of the preceding sheet that arrives first at the buffer means is closer to the loading means than the end of the subsequent sheet that arrives later at the buffer means. As a result, as shown in Figure 3(A), the sheets P constituting the sheet bundle will contact the vertical alignment roller 32 in order from the lower sheet P to be aligned. In other words, the alignment accuracy will be further improved.

[0080] [Perspective 10] The buffer front roller 22, the reversing roller 24, and the internal discharge roller 26 function as switchback means, feeding the preceding sheet from the first transport path R1 to the buffer means and pulling the preceding sheet from the buffer means to the second transport path R2. After the switchback means has pulled the preceding sheet from the buffer means to the second transport path R2, it stops transporting the preceding sheet. Furthermore, when a subsequent sheet arrives from the first transport path R1, the switchback means feeds the subsequent sheet and the preceding sheet to the buffer means, thereby overlapping the preceding and succeeding sheets.

[0081] [Perspectives 11, 12] The physical parameters may include environmental information about the surrounding environment of the sheet or the surrounding environment of the post-processing device. The environmental information may include at least one of the temperature and humidity of the surrounding environment, because temperature and humidity are parameters that affect the frictional force of the sheet P.

[0082] [Perspective 13] The physical parameters may include information regarding the surface properties of sheet P or any processing treatments applied to the sheet's surface. Such processing treatments include, for example, gloss treatments and coating treatments.

[0083] [Perspectives 14, 15] The physical parameters may include information about the image printed on sheet P. This information may include, for example, the image formation rate, which is the ratio of the image to the surface area of ​​sheet P, or the area of ​​the image-forming region on sheet P.

[0084] [Perspective 16] Information regarding the image printed on sheet P may include information indicating whether the image is formed on only one side of sheet P, on both sides of sheet P, or not on both sides of sheet P. If the image is not formed on both sides of sheet P, sheet P may be inserted into the sheet bundle as a laminated sheet (insert sheet).

[0085] [Perspectives 17, 18] The physical parameters may include the sheet's fixing temperature. The physical parameters may also include the sheet's transport speed. These parameters also affect the frictional force of the sheet P.

[0086] [Perspective 19] The control means (e.g., processor 450) may determine a predetermined number M based on the type of sheet P. The type information indicating the type of sheet P may be basis weight, brand name (product name, product identification information), etc.

[0087] [perspective 20] The memory 460 may function as a storage means for storing the jam occurrence rate for each type of sheet P. The processor 450 may relatively reduce the predetermined number M for sheets of a type with a high jam occurrence rate, and increase the predetermined number M for sheets of a type with a low jam occurrence rate.

[0088] [Perspective 21] The memory 460 may function as a storage means for storing the rate of occurrence of regulation failures (inconsistency failures) by the regulation means for each type of sheet. The processor 450 may relatively reduce the predetermined number M for types of sheets with a high rate of regulation failures, and increase the predetermined number M for types of sheets with a low rate of regulation failures.

[0089] [Perspective 22] The image forming system 100 includes an image forming apparatus 1 that forms an image on a sheet P, and a post-processing apparatus 4 that applies post-processing to the sheet P output from the image forming apparatus 1. The post-processing apparatus 4 is the post-processing apparatus 4 described in any one of views 1 to 18.

[0090] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of symbols]

[0091] 4...Post-processing unit, 40...Buffer unit, 41...Stage unit, R1...First transport path, R2...Second transport path, 32...Vertical alignment roller, 33...Vertical alignment reference plate, 403...Post-processing control unit

Claims

1. The first transport path for transporting the sheets, A buffer means that receives sheets transported from the first transport path and temporarily holds a predetermined number of sheets stacked on top of each other, When the temporary holding in the buffer means ends, a second transport path is established to transport the predetermined number of sheets from the buffer means, A loading means for loading the predetermined number of sheets that have been transported from the second transport path toward the first direction, A moving means that contacts the uppermost sheet among the predetermined number of sheets loaded on the loading means and moves the uppermost sheet further toward the first direction, A regulating means provided downstream of the moving means in the first direction, which abuts against the end of the sheet bundle loaded on the loading means, and the downstream end in the first direction, to regulate the position of the sheet bundle, The system includes a control means for determining a predetermined number of sheets when a stacking operation is performed in which a plurality of sheets are transported to the stacking means and a sheet bundle is formed on the stacking means, When the control means determines the predetermined number to be two or more, in the forming operation, the predetermined number of sheets are stacked in the buffer means, and the predetermined number of sheets are transported to the loading means via the second transport path. When the control means determines the predetermined number to be one sheet, in the forming operation, the sheet bundle is formed by transporting the sheets one by one to the loading means via the second transport path. The post-processing device is characterized in that the control means determines the predetermined number of sheets based on physical parameters that affect the frictional force generated on the surface of the sheet.

2. The post-processing apparatus according to claim 1, characterized in that the moving means is a rotating body that rotates in contact with the uppermost seat.

3. The post-processing apparatus according to claim 2, characterized in that the rotating body is a roller.

4. The post-processing apparatus according to claim 2, characterized in that the rotating body is a paddle.

5. The post-processing apparatus according to claim 1, characterized in that the moving means is a friction member that contacts the uppermost sheet and moves in a straight line.

6. The post-processing apparatus according to any one of claims 1 to 5, further comprising a post-processing means for performing post-processing on the sheet bundle consisting of N sheets loaded on the loading means, wherein the N sheets are equal to or greater than the predetermined number.

7. The post-processing apparatus according to any one of claims 1 to 6, further comprising a discharge means for discharging the sheet bundle, which consists of N sheets loaded on the loading means, in a second direction opposite to the first direction.

8. The post-processing device according to any one of claims 1 to 7, characterized in that, when the predetermined number of sheets is two or more, the edges of the preceding sheets that arrive first at the buffer means are offset and stacked so that they are closer to the stacking means than the edges of the subsequent sheets that arrive later to the buffer means.

9. The system further includes a switchback means for feeding the lead sheet from the first transport path to the buffer means and pulling the lead sheet from the buffer means to the second transport path. The post-processing device according to claim 8, characterized in that the switchback means stops transporting the preceding sheet after it has pulled the preceding sheet from the buffer means to the second transport path, and when the succeeding sheet arrives from the first transport path, it sends the succeeding sheet and the preceding sheet to the buffer means so that the preceding sheet and the succeeding sheet are superimposed.

10. The post-processing apparatus according to any one of claims 1 to 9, characterized in that the physical parameters include environmental information of the surrounding environment of the sheet or the surrounding environment of the post-processing apparatus.

11. The post-processing apparatus according to claim 10, characterized in that the environmental information includes at least one of the temperature and humidity of the surrounding environment.

12. The post-processing apparatus according to claim 10 or 11, characterized in that the physical parameters include information regarding the surface properties of the sheet or processing treatments applied to the surface of the sheet.

13. The post-processing apparatus according to any one of claims 10 to 12, characterized in that the physical parameters include information relating to an image printed on the sheet.

14. The post-processing apparatus according to claim 13, characterized in that the information relating to the image printed on the sheet includes the image formation rate, which is the ratio of the image to the surface area of ​​the sheet, or the area of ​​the image formation region on the sheet.

15. The post-processing apparatus according to claim 14, characterized in that the information relating to the image printed on the sheet includes information indicating that the image was formed on only one side of the sheet, that the image was formed on both sides of the sheet, or that the image was not formed on both sides of the sheet.

16. The post-processing apparatus according to any one of claims 10 to 15, characterized in that the physical parameters include the fixing temperature of the sheet.

17. The post-processing apparatus according to any one of claims 10 to 16, characterized in that the physical parameters include the conveying speed of the sheet.

18. The first transport path for transporting the sheets, A buffer means that receives sheets transported from the first transport path and temporarily holds a predetermined number of sheets stacked on top of each other, When the temporary holding in the buffer means ends, a second transport path is established to transport the predetermined number of sheets from the buffer means, A loading means for loading the predetermined number of sheets that have been transported from the second transport path toward the first direction, A moving means that contacts the uppermost sheet among the predetermined number of sheets loaded on the loading means and moves the uppermost sheet further toward the first direction, A regulating means provided downstream of the moving means in the first direction, which abuts against the end of the sheet bundle loaded on the loading means, and the downstream end in the first direction, to regulate the position of the sheet bundle, The system includes a control means for determining a predetermined number of sheets when a stacking operation is performed in which a plurality of sheets are transported to the stacking means and a sheet bundle is formed on the stacking means, When the control means determines the predetermined number to be two or more, in the forming operation, the predetermined number of sheets are stacked in the buffer means, and the predetermined number of sheets are transported to the loading means via the second transport path. When the control means determines the predetermined number to be one sheet, in the forming operation, the sheet bundle is formed by transporting the sheets one by one to the loading means via the second transport path. The control means is characterized by determining the predetermined number of sheets based on the type of sheet.

19. The system further includes a storage means for storing the jam formation rate for each type of sheet, The post-processing apparatus according to claim 18, characterized in that the control means relatively reduces the predetermined number of sheets for types of sheets with a high jam formation rate and increases the predetermined number of sheets for types of sheets with a low jam formation rate.

20. The system further includes a storage means for storing the rate of failure to regulate by the regulating means for each type of sheet, The post-processing apparatus according to claim 18, characterized in that the control means relatively reduces the predetermined number of sheets for types of sheets with a high rate of failure and increases the predetermined number of sheets for types of sheets with a low rate of failure.

21. An image forming system comprising an image forming apparatus for forming an image on a sheet, and a post-processing apparatus for applying post-processing to the sheet output from the image forming apparatus, The image forming system is characterized in that the post-processing device is the post-processing device described in any one of claims 1 to 20.

Images