Sheet transport device and image forming system

Abstract

To solve the problem in which occurrence of jam in sheet conveyance needs to be reduced further.SOLUTION: A sheet conveyance device includes holding means for holding a first conveyance guide so as to move. The first conveyance guide can move between a first position in which a distance between itself and a second conveyance guide is a first distance, and a second position which is a second distance farther away from the first distance. A sheet inverted by inversion means is conveyed toward a conveyance roller pair by the first conveyance guide positioned in the first position.SELECTED DRAWING: Figure 18

Description

Technical Field

[0001] The present invention relates to a sheet conveying apparatus for conveying sheets and an image forming system for forming an image on a sheet.

Background Art

[0002] As an option of an image forming apparatus exemplified by an electrophotographic multifunction printer, a sheet processing apparatus that performs processing such as binding processing and sorting processing on a sheet on which an image has been formed by an image forming apparatus main body is used. Patent Document 1 describes a mechanism provided with a backflow prevention flapper for the purpose of preventing sheet backflow when a sheet is reversed in a buffer processing section. This backflow prevention flapper is rotatable and biased in one direction by a spring, and is configured to move against the spring force when the sheet abuts against the flapper.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In the configuration of Patent Document 1, there is a demand for a configuration that can further reduce the occurrence of jams. Therefore, an object of the present invention is to provide a sheet conveying apparatus and an image forming system that can reduce the occurrence of jams.

Means for Solving the Problem

[0005] One aspect of the present invention comprises: a first transport path for receiving a sheet; a reversing means for reversing a sheet that has passed through the first transport path; a second transport path for transporting a sheet that has passed through the first transport path between the reversing means and the first transport path; a pair of transport rollers for gripping and transporting a sheet that has been reversed and transported in the second transport path by the reversing means; a first transport guide disposed between the reversing means and the pair of transport rollers to constitute the second transport path; a second transport guide disposed between the reversing means and the pair of transport rollers and facing the first transport guide to constitute the second transport path; a holding means for movably holding the first transport guide; and a transporter that is transported along the first transport path. The device comprises a first conveying means for conveying the sheet being conveyed along the first conveying path in a first direction which is the conveying direction of the sheet, wherein the first conveying guide is movable to a first position where the distance from the second conveying guide is a first distance, to a second position where the distance is a second distance greater than the first distance, and to a third position where the distance is a third distance greater than the second distance, wherein the sheet conveyed by the first conveying means is guided toward the reversing means by the first conveying guide located at the second position, and the sheet reversed by the reversing means is guided toward the pair of conveying rollers by the first conveying guide located at the first position. [Effects of the Invention]

[0006] According to the present invention, the generation of jam can be reduced. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of the image forming system according to Example 1. [Figure 2] A schematic diagram of the buffer section according to Example 1. [Figure 3] Figures (a-d) illustrating the buffer operation in Example 1. [Figure 4] Figures (a-d) illustrating the buffer operation in Example 1. [Figure 5]Block diagram of the image forming system according to Example 1. [Figure 6] A flowchart showing the operation sequence of the inlet roller according to Example 1. [Figure 7] A flowchart showing the operation sequence of the buffer-pre-roller according to Example 1. [Figure 8] A flowchart showing the operation sequence of the reversing roller according to Example 1. [Figure 9] A flowchart showing the operation sequence of the internal discharge roller according to Example 1. [Figure 10] Perspective views (a-b) illustrating the movable guide member according to Example 1. [Figure 11] A perspective view from one end in Figure 10(a). [Figure 12] A cross-sectional view illustrating a movable guide member according to Example 1. [Figure 13] A cross-sectional view illustrating a movable guide member according to Example 1. [Figure 14] A cross-sectional view illustrating a movable guide member according to Example 1. [Figure 15] Cross-sectional views (a-b) illustrating the movable guide member according to Example 1. [Figure 16] Cross-sectional views (a-b) illustrating the movable guide member according to Example 1. [Figure 17] Cross-sectional views (a-b) illustrating the movable guide member according to Example 1. [Figure 18] Cross-sectional views (a-b) illustrating the movable guide member according to Example 1. [Figure 19] A cross-sectional view illustrating the driven rotating body according to Example 1. [Figure 20] A perspective view illustrating the recessed portion in Example 1. [Modes for carrying out the invention]

[0008] Hereinafter, exemplary embodiments for carrying out the present invention will be described with reference to the drawings. [Examples]

[0009] FIG. 1 is a schematic diagram of an image forming system 1S according to Embodiment 1. The image forming system 1S of the present embodiment is constituted by an image forming apparatus 1, an image reading apparatus 2, a document feeder 3, and a post-processing apparatus 4 which is a sheet conveying apparatus. The image forming system 1S forms an image on a sheet serving as a recording material, performs processing on the sheet by the post-processing apparatus 4 as necessary, and outputs the sheet. Hereinafter, after briefly describing the simple operation of each apparatus, the post-processing apparatus 4 will be described in detail.

[0010] The document feeder 3 conveys documents placed on a document tray 18 to image reading units 16 and 19. The image reading units 16 and 19 are each image sensors that read image information from a document surface, and reading of both sides of a document is performed in a single document conveyance. The document from which image information has been read is discharged to a document discharge unit 20. In addition, the image reading apparatus 2 reciprocates the image reading unit 16 by a driving device 17, thereby reading image information from a stationary document set on a platen glass (including documents that cannot be used with the document feeder 3, such as booklet documents).

[0011] The image forming apparatus 1 is an electrophotographic apparatus including a direct transfer type image forming unit 1B. The image forming unit 1B includes a cartridge 8 provided with a photosensitive drum 9, and a laser scanner unit 15 disposed above the cartridge 8. When performing an image forming operation, the surface of the rotating photosensitive drum 9 is charged, and the laser scanner unit 15 exposes the photosensitive drum 9 based on image information, thereby writing an electrostatic latent image on the drum surface. The electrostatic latent image carried on the photosensitive drum 9 is developed into a toner image by charged toner particles, and the toner image is conveyed to a transfer portion where the photosensitive drum 9 and the transfer roller 10 face each other. A controller of the image forming apparatus 1 (a printer control unit 100 described later) causes the image forming unit 1B to perform an image forming operation based on image information read by the image reading units 16 and 19 or image information received from an external computer via a network.

[0012] The image forming apparatus 1 is equipped with multiple feeding devices 6 that feed sheets as recording material one by one at predetermined intervals. The sheets fed from the feeding devices 6 are corrected for skew by registration rollers 7 and then transported to the transfer section, where the toner image supported on the photosensitive drum 9 is transferred. A fixing unit 11 is located downstream of the transfer section in the sheet transport direction. The fixing unit 11 has a pair of rotating bodies that grip and transport the sheets, and a heating element such as a halogen lamp for heating the toner image, and performs image fixing by heating and pressurizing the toner image on the sheet.

[0013] When an image-formed sheet is discharged from the image forming apparatus 1, the sheet that has passed through the fixing unit 11 is transported to the post-processing device 4 via the horizontal transport unit 14. In the case of a sheet where the image formation of the first side has been completed in double-sided printing, the sheet that has passed through the fixing unit 11 is handed over to the reversing roller 12, which then transports it in a switchback manner, and it is transported again to the registration roller 7 via the re-transport unit 13. After passing through the transfer unit and fixing unit 11 again to form an image on the second side, it is transported to the post-processing device 4 via the horizontal transport unit 14.

[0014] The image forming unit 1B described above is an example of an image forming means for forming an image on a sheet. An electrophotographic unit using an intermediate transfer method may be used, which transfers a toner image formed on a photoreceptor to the sheet via an intermediate transfer body. Alternatively, an inkjet or offset printing unit may be used as the image forming means.

[0015] (Post-processing device) The post-processing device 4 has a binding processing unit 4A that performs a binding process on the sheets, and binds the sheets received from the image forming apparatus 1 and discharges them as a sheet bundle. Alternatively, the post-processing device 4 can simply discharge the sheets received from the image forming apparatus 1 without performing a binding process.

[0016] The post-processing device 4 is provided with a receiving path 81, an internal discharge path 82, a first discharge path 83, and a second discharge path 84 as transport paths for transporting sheets. The post-processing device 4 is also provided with an upper discharge tray 25, which is a first loading means, and a lower discharge tray 37, which is a second loading means, as destinations for discharging sheets. The receiving path 81 is the first transport path in this embodiment for receiving and transporting sheets from the image forming apparatus 1, and the internal discharge path 82 is the third transport path in this embodiment for transporting sheets toward the binding processing device 4A. The first discharge path 83, which is the second transport path, is a transport path for discharging sheets to the upper discharge tray 25, and is also a transport path for transporting sheets that have been inverted by the inversion roller 24 to the internal discharge path 82.

[0017] The second discharge path 84 is a transport path (fourth transport path) that discharges the sheet to the lower discharge tray 37.

[0018] The receiving path 81 is equipped with an inlet roller 21, a buffer-pre-roller 22, and an inlet sensor 27. The first discharge path 83 is equipped with a reversing roller 24 as a reversing means. The internal discharge path 82 is equipped with an internal discharge roller 26, an intermediate transport roller 28, a kick-out roller 29, and an intermediate pre-loading sensor 38. The second discharge path 84 is equipped with a bundle discharge roller 36. The inlet sensor 27 and the intermediate pre-loading sensor 38 are both examples of sheet detection means that detect the passage of a sheet at a predetermined detection position in the transport path within the sheet processing device. As described later, optical sensors can be used as the inlet sensor 27 and the intermediate pre-loading sensor 38 to detect the presence or absence of a sheet at the detection position using light.

[0019] The sheet transport path in the post-processing device 4 will be described below. However, the buffer operation by the buffer unit 4B, including the reversing roller 24, and the detailed configuration and operation of the binding processing unit 4A will be described later.

[0020] The sheet discharged from the horizontal transport section 14 of the image forming apparatus 1 is received by the inlet roller 21 and transported through the receiving path 81 toward the buffer-pre-roller 22. The inlet sensor 27 detects the sheet at a detection position between the inlet roller 21 and the buffer-pre-roller 22. The buffer-pre-roller 22 transports the sheet received from the inlet roller 21 toward the first discharge path 83. The first discharge path 83 extends upward to allow the sheet discharged from the receiving path 81 to reach the inversion roller 24, and also extends downward from the receiving path 81 to allow the sheet inverted by the inversion roller 24 to reach the inner discharge roller 26.

[0021] Furthermore, at a predetermined timing after the entrance sensor 27 detects the passage of the rear end of the sheet, the buffer-front roller 22 accelerates the sheet's transport speed to a speed faster than the transport speed in the horizontal transport section 14. Alternatively, the sheet's transport speed by the entrance roller 21 may be set higher than that of the horizontal transport section 14, and the transport speed may be accelerated by the entrance roller 21 upstream of the buffer-front roller 22. In this case, it is preferable to install a one-way clutch between the transport roller of the horizontal transport section 14 and the motor that drives it, so that the transport roller can rotate freely even if the sheet is pulled by the entrance roller 21.

[0022] When the sheet is to be discharged to the upper discharge tray 25, the reversing roller 24 discharges the sheet received from the buffer roller 22 to the upper discharge tray 25. In this case, the reversing roller 24 decelerates to a predetermined discharge speed at a predetermined timing after the rear end of the sheet has passed the buffer roller 22.

[0023] When the sheet is to be discharged to the lower discharge tray 37, the reversing roller 24 performs a switchback transport of the sheet received from the buffer-front roller 22 to transport the sheet to the internal discharge path 82. A backflow prevention valve 23 is located at the branching point where the receiving path 81 and the internal discharge path 82 branch off from the first discharge path 83 upstream of the reversing roller 24 in the sheet discharge direction by the reversing roller 24. The backflow prevention valve 23 has the function of preventing the sheet that has been switched back by the reversing roller 24 from flowing back into the receiving path 81.

[0024] The internal discharge roller 26, intermediate transport roller 28, and kick-off roller 29, located in the internal discharge path 82, transport the sheets received from the reversing roller 24 toward the binding processing unit 4A, passing them along in sequence. The intermediate loading sensor 38 detects the sheets between the intermediate transport roller 28 and the kick-off roller 29.

[0025] The binding processing unit 4A has a stapler, which is the binding means in this embodiment. After aligning multiple sheets received from the internal discharge path 82, it staples the sheet bundle at predetermined positions using the stapler. The sheet bundle stapled by the binding processing unit 4A is passed to the bundle discharge roller 36 via the second discharge path 84, which is the fourth transport path, and discharged to the lower discharge tray 37 by the bundle discharge roller 36, which is the discharge means. The post-processing device 4 is equipped with a discharge section D, which is an opening for discharging sheets that are transported in the discharge direction by the bundle discharge roller 36 from inside the device to outside the device.

[0026] Both the upper discharge tray 25 and the lower discharge tray 37 are movable vertically relative to the housing of the post-processing device 4. The post-processing device 4 is equipped with sheet surface detection sensors that detect the upper surface position (sheet stacking height) of the sheets in the upper discharge tray 25 and the lower discharge tray 37. When either sensor detects a sheet, the corresponding tray is lowered in the A2 and B2 directions. Furthermore, when the sheet surface detection sensor detects that a sheet has been removed from either the upper discharge tray 25 or the lower discharge tray 37, that tray is lowered in the A1 and B1 directions. Thus, the upper discharge tray 25 and the lower discharge tray 37 are controlled to move up and down in order to maintain a constant upper surface height of the stacked sheets.

[0027] (Buffer operation) Next, we will provide a detailed explanation of the buffer operation using Figures 2 to 4. Figure 2 is a schematic diagram of the buffer unit 4B, and Figures 3 and 4 show the buffer operation.

[0028] As shown in Figure 2, the buffer section 4B includes a reversing roller 24 (a pair of reversing rollers), a backflow prevention valve 23, and an internal discharge roller 26 (a pair of intermediate rollers). In addition, the inlet roller 21, the pre-buffer roller 22, and the inlet sensor 27, which are located in the receiving path 81, also participate in the buffer operation.

[0029] Hereinafter, the transport guides that form the sheet transport path (part of the receiving path 81) between the inlet roller 21 and the buffer-pre-roller 22 will be referred to as the "inlet upper guide 40" and the "inlet lower guide 41". Furthermore, the transport guides that form the sheet transport path (part of the internal discharge path 82) between the internal discharge roller 26 and the intermediate transport roller 28 will be referred to as the "internal discharge upper guide 46" and the "internal discharge lower guide 47". In addition, the transport guide that guides the sheet from the same side as the inlet upper guide 40 between the buffer-pre-roller 22 and the reversing roller 24 will be referred to as the "reversing upper guide 42". Furthermore, the transport guide that guides the sheet from the same side as the internal discharge lower guide 47 between the reversing roller 24 and the internal discharge roller 26 will be referred to as the "reversing lower guide 43".

[0030] The sheet being transported by the entrance roller 21 is guided to the buffer-front roller 22 by the entrance upper guide 40 and the entrance lower guide 41. An entrance sensor 27 is positioned on the entrance upper guide 40. As the entrance sensor 27, a reflective photosensor can be used to determine the presence or absence of a sheet at the detection position by irradiating infrared light toward the receiving path 81 and detecting the reflected light from the sheet. In this case, a hole larger than the diameter of the spot beam of the entrance sensor 27 is provided in the part of the entrance lower guide 41 facing the entrance sensor 27 so that infrared light is not reflected when no sheet is passing through.

[0031] A backflow prevention valve 23 is positioned downstream of the buffer pre-roller 22, at the point where the receiving path 81 and the internal discharge path 82 branch off from the first discharge path 83. The backflow prevention valve 23 is rotatably supported by the internal discharge upper guide 46 via a rotating shaft 23a. The backflow prevention valve 23 is constantly biased by a spring (not shown) in the C2 direction (clockwise in the figure) toward a position (position in Figure 2) where the tip of the backflow prevention valve 23 overlaps with the reversing upper guide 42 when viewed from the axial direction of the rotating shaft 23a (width direction of the sheet). The spring constant of the spring is set to such a magnitude that when the sheet being fed from the buffer pre-roller 22 comes into contact with the backflow prevention valve 23, the backflow prevention valve 23 rotates in the C1 direction (counterclockwise in the figure) against the biasing force of the spring. Therefore, the backflow prevention valve 23 allows the sheet being conveyed from the buffer pre-roller 22 toward the reversing roller 24 to pass through. On the other hand, when the rear end of the sheet in the receiving path 81 passes the backflow prevention valve 23, the backflow prevention valve 23 rotates in the C2 direction to restrict the backflow of the sheet from the reversing roller 24 to the buffer pre-roller 22.

[0032] The reversing roller 24 is composed of a reversing upper roller 24a and a reversing lower roller 24b. In this embodiment, driving force is input to both the reversing upper roller 24a and the reversing lower roller 24b, and the rotations of the reversing upper roller 24a and the reversing lower roller 24b are always synchronized.

[0033] The reversing roller 24 is configured to be able to contact and separate from the plunger solenoid 45. Specifically, one end of a separation lever 44 is connected to the roller shaft of the reversing upper roller 24a, and the separation lever 44 is rotatably supported on the lever pivot axis 44a relative to the reversing upper guide 42. The solenoid connecting shaft 44b provided at the other end of the separation lever 44 is connected to the plunger of the plunger solenoid 45.

[0034] When the plunger solenoid 45 is energized, the plunger is attracted in the D1 direction by magnetic force, causing the separation lever 44 to rotate in the E1 direction, and the reversing roller 24 enters a separated state (the nip portion of the roller pair is open). When the energization to the plunger solenoid 45 is stopped, the biasing force of the pressure spring 48 connected to the roller shaft of the reversing upper roller 24a causes the reversing upper roller 24a to come into contact with the reversing lower roller 24b, and the reversing roller 24 enters a contact state (the nip portion is closed). At this time, as the reversing upper roller 24a moves, the separation lever 44 rotates in the E2 direction, and the plunger of the plunger solenoid 45 moves in the D2 direction.

[0035] The internal discharge rollers 26 are a pair of rollers adjacent to the reversing rollers 24 in the sheet transport direction in the internal discharge path 82, and are a pair of rollers capable of forward and reverse rotation. In other words, the internal discharge rollers 26 can transport sheets in both the sheet transport direction from the reversing rollers 24 toward the binding processing unit 4A (forward feeding direction of the internal discharge path 82) and the reverse feeding direction from the binding processing unit 4A toward the reversing rollers 24.

[0036] Next, the buffer operation of the buffer unit 4B will be explained in detail using Figures 3 and 4. The buffer operation is an operation in which a predetermined number of sheets constituting the next sheet bundle are kept waiting in the buffer unit 4B until the binding process for the previous sheet bundle is completed in the binding processing unit 4A. By performing the buffer operation, the image forming system can execute image forming jobs, including binding, without reducing the productivity of the image forming apparatus 1 (number of images output per unit time).

[0037] Hereafter, to distinguish between the sheets, they will be referred to as "Sheet S1," "Sheet S2," and "Sheet S3" in the order they are handed over from the image forming apparatus 1 to the post-processing device 4. Furthermore, of the two ends of the sheet in the sheet transport direction, the one that passes the entrance roller 21 first will be referred to as the "first end," and the one that passes the entrance roller 21 later will be referred to as the "second end." Also, the sheet transport speed in the horizontal transport section 14 of the image forming apparatus 1 will be V1, and the transport speed after acceleration inside the post-processing device 4 will be referred to as V2. The sheet transport direction by the entrance roller 21 will be referred to as the first direction.

[0038] Figure 3(a) shows the state when the rear end (second end S1b) of sheet S1 in the receiving path 81 passes the detection position of the inlet sensor 27. When the inlet sensor 27 detects the passage of the second end S1b of sheet S1, the buffer front roller 22 and the reversing roller 24 accelerate sheet S1 from speed V1 to speed V2. By accelerating sheet S1 in this way, the gap between it and the following sheet S2 widens, ensuring the sheet gap necessary for the reversing operation (switchback) by the reversing roller 24. At the point shown in Figure 3(a), the reversing roller 24 is rotating in the rotation direction R1 before reversing, and is transporting sheet S1 toward the upper discharge tray 25.

[0039] Figure 3(b) shows the state when the rear end (second end S1b) of the sheet S1 in the receiving path 81 has passed the backflow prevention valve 23. The reversing roller 24 temporarily stops rotating at a predetermined timing after the rear end (second end S1b) of the sheet S1 has passed the backflow prevention valve 23. The predetermined timing is determined based on the elapsed time from the time when the inlet sensor 27 detects the passage of the rear end (second end S1b) of the sheet S1.

[0040] Figure 3(c) shows the state after the reversing roller 24 has started rotating in the rotation direction R2, which is the rotation direction after reversal, and has transferred the sheet S1 to the internal discharge roller 26. Here, the sheet conveying direction by the reversing roller 24 is the second direction, which is the opposite direction to the first direction.

[0041] The internal discharge roller 26 receives the sheet S1 while rotating in the rotational direction R3 and transports the sheet S1 in the forward direction in the internal discharge path 82. Furthermore, after the leading edge (second end S1b) of the sheet S1 in the internal discharge path 82 passes the position of the backflow prevention valve 23, the leading edge (first end S2a) of the sheet S2 in the receiving path 81 reaches the backflow prevention valve 23. Therefore, the sheets S1 and S2 are transported so as to pass each other at the branching point of the transport path.

[0042] Figure 3(d) shows the state at the point when the leading edge (second end S1b) of sheet S1 in the internal discharge path 82 has been transported a predetermined amount by the internal discharge roller 26 and the internal discharge roller 26 has temporarily stopped. After the point shown in Figure 3(c), the plunger solenoid 45 is energized before the leading edge (first end S2a) of sheet S2 in the receiving path 81 reaches the reversing roller 24. As a result, the reversing upper roller 24a moves in the E1 direction and the reversing roller 24 separates. Sheet S1 is held by the stopped internal discharge roller 26, and a portion of sheet S1 is located between the separated reversing rollers 24. Therefore, sheet S2, which is sent from the receiving path 81 to the first discharge path 83 by the buffer pre-roller 22, is transported by sliding over sheet S1. Sheet S2 is also accelerated from speed V1 to speed V2 by the buffer pre-roller 22 after the inlet sensor 27 detects the passage of the rear end (second end S2b) of sheet S2.

[0043] Figure 4(a) shows the state after the internal discharge roller 26 has started transporting the sheet S1 in the reverse direction. The internal discharge roller 26 starts rotating in the rotation direction R4 when the sheet S2 has been transported to a predetermined position, transporting the sheet S1 in the reverse direction toward the reversing roller 24. The target speed of the internal discharge roller 26 is set to speed V2, the same as the buffer front roller 22. When the speeds of the sheets S1 and S2 become approximately equal (relative speed is approximately zero), the power supply to the plunger solenoid 45 is stopped. As a result, the reversing upper roller 24a moves in the direction E2, and the reversing roller 24 comes into contact again, and the sheets S1 and S2 are held between the reversing roller 24 in an overlapping state. The reversing roller 24 also starts rotating in the rotation direction R1 in synchronization with the internal discharge roller 26, and is controlled to have the same peripheral speed (speed V2) as the buffer front roller 22 and the internal discharge roller 26 before switching from the separated state to the contact state.

[0044] Figure 4(b) shows the state after the rear end (second end S2b) of sheet S2 in the receiving path 81 has passed through the backflow prevention valve 23. The reversing roller 24 temporarily stops rotating at a predetermined timing after the rear end (second end S2b) of sheet S2 has passed through the backflow prevention valve 23. At this time, both sheets S1 and S2, which are stacked, stop moving, but the second end S1b of sheet S1 protrudes by a predetermined amount k in the forward direction of the internal discharge path 82 compared to the second end S2b of sheet S2. This amount k is controlled by the internal discharge roller 26 starting to transport sheet S1 in the reverse direction at a predetermined timing, as explained using Figure 4(a).

[0045] Figure 4(c) shows the state after the reversing roller 24 has started rotating in the rotational direction R2 and has handed over the stacked sheets S1 and S2 to the internal discharge roller 26. The internal discharge roller 26 receives the sheets S1 and S2 while rotating in the rotational direction R3 and transports the sheets S1 and S2 in the forward direction in the internal discharge path 82. The sheets S1 and S2 are transported in their stacked state through the internal discharge path 82 toward the binding processing unit 4A.

[0046] Furthermore, after the leading edge (second end S2b) of sheet S2 in the internal discharge path 82 passes the position of the backflow prevention valve 23, the leading edge (first end S3a) of the third sheet S3 in the receiving path 81 reaches the backflow prevention valve 23. Therefore, sheets S2 and S3 are transported so as to pass each other at the branching point of the transport path. Also, after sheet S2 is gripped by the internal discharge roller 26, the reversing upper roller 24a moves in the E1 direction, and the reversing roller 24 separates again in preparation for receiving the subsequent sheet S3.

[0047] Figure 4(d) shows the state after the reversing roller 24 switches from a separated state to a contact state. The reversing roller 24 switches from a separated state to a contact state after the first end S2a of the sheet S2 detaches from the reversing roller 24, and grips the sheet S3. After this, the reversing roller 24 performs the reversing operation of the sheet S3, and sheet S3, following sheets S1 and S2, is transported to the binding processing unit 4A via the internal discharge path 82.

[0048] (When buffering three or more sheets) Figures 3(a) to 4(d) above illustrate the operation of buffering two sheets S1 and S2, but the buffer unit 4B of this embodiment can also buffer three or more sheets. In this case, as shown in Figure 4(c), the internal discharge roller 26 stops while holding sheets S1 and S2, and at a predetermined timing after the second end of the third sheet S3 (third sheet) is detected by the inlet sensor 27, sheets S1 and S2 are transported in the reverse direction. Then, after the transport speed of the internal discharge roller 26 synchronizes with the transport speed of the pre-buffer roller 22, the reversing roller 24 comes into contact with it, and the reversing roller 24 grips the three stacked sheets S1, S2, and S3. At this time, as the internal discharge roller 26 starts the reverse transport of sheets S1 and S2 at a predetermined timing, the second end of the second sheet S2 protrudes from the second end of the third sheet by a predetermined amount k in the forward direction.

[0049] Furthermore, by repeatedly opening and closing the reversing roller 24 and reversing the internal discharge roller 26 in an appropriate sequence, the buffer unit 4B can buffer, for example, up to five sheets. By having a buffer function that can stack three or more sheets in this way, the post-processing device 4 can process sheets without reducing the productivity of the image forming apparatus 1, thereby contributing to an improvement in the productivity of the entire image forming system.

[0050] (Roller drive control) Next, the control configuration that realizes the operation described using Figures 3 and 4 will be explained. Figure 5 is a block diagram showing the configuration of the image forming system 1S according to this embodiment. The image forming apparatus 1 is equipped with a printer control unit 100, and the post-processing device 4 is equipped with a finisher control unit 400. The printer control unit 100 and the finisher control unit 400 are connected to each other via a communication interface and cooperate to control the operation of the image forming system 1S.

[0051] The printer control unit 100 includes a central processing unit (CPU) 101 and a memory 102. The CPU 101 reads and executes programs stored in the memory 102 and provides overall control of the image forming apparatus 1. For example, the CPU 101 executes processes such as causing the image forming unit 1B to perform image forming operations and causing the image reading device 2 to perform reading operations to acquire image information. The memory 102 includes non-volatile storage media such as read-only memory (ROM) and volatile storage media such as random access memory (RAM), and serves as a storage location for programs and data, as well as a workspace for the CPU 101 when executing programs. The memory 102 is an example of a non-transient storage medium that stores programs for controlling the image forming apparatus.

[0052] The printer control unit 100 is connected to an external device such as a personal computer or portable information device via an external interface (I / F) 104 and receives execution commands for image forming jobs to the image forming system 1S. The printer control unit 100 is also connected to the operation display unit 103, which is the user interface of the image forming system 1S. The operation display unit 103 includes a display device such as a liquid crystal panel that presents information to the user, and input devices such as physical buttons and a touch panel function of the liquid crystal panel that accept input operations from the user. The printer control unit 100 controls the display content of the display device and receives information input via the input devices by communicating with the operation display unit 103.

[0053] The finisher control unit 400 includes a central processing unit (CPU) 401, a memory 402, and a timer 403. The CPU 401 reads and executes programs stored in the memory 402 and provides overall control of the post-processing unit 4. The memory 402 includes non-volatile storage media such as read-only memory (ROM) and volatile storage media such as random access memory (RAM), and serves as a storage location for programs and data, as well as a workspace for the CPU 401 when executing programs. The memory 402 is an example of a non-transient storage medium that stores programs for controlling the post-processing unit.

[0054] Timer 403 is a circuit element with a timing function and is implemented as an integrated circuit with an RTC function or as a module of a program executed by CPU 401. Not limited to Timer 403, each function of the printer control unit 100 and finisher control unit 400 may be implemented on the control unit's circuit as independent hardware such as an ASIC, or they may be implemented in software as functional units of a program. Furthermore, the printer control unit 100 may handle some or all of the functions of the finisher control unit 400, as described below.

[0055] The post-processing unit 4 is equipped with multiple motors (M1 to M11) in addition to the inlet sensor 27, intermediate loading sensor 38, plunger solenoid 45, and stapler 51 mentioned above, which serve as a drive source for conveying the sheets or as a drive source for the stapling processing unit 4A. Of these, the inlet motor M1 rotates the inlet roller 21. The buffer pre-motor M2 rotates the buffer pre-roller 22. The reversing motor M3 rotates the reversing roller 24. The internal discharge motor M4 rotates the internal discharge roller 26. The kick-out motor M5 rotates the kick-out roller 29. Although each of the above rollers has been described as being driven by an independent motor (M1 to M5), it is also possible to control multiple rollers with a common motor, provided that the drive state of each roller can be appropriately controlled according to the following description.

[0056] The operation sequence for each roller will be explained below in accordance with the flowcharts in Figures 6 to 9. Each step in the flowchart is processed by the CPU 401 of the finisher control unit 400 executing a program read from memory 402. Each operation sequence is started when the finisher control unit 400 receives a notification from the printer control unit 100 indicating that it has started executing an image forming job with the lower discharge tray 37 as the sheet discharge destination.

[0057] In the following explanation, the starting and stopping of roller rotation, as well as the change in rotation speed, refer to the process by which CPU 401 sends signals to the drive circuits of each motor (M1 to M5) to command the rotation speed and direction of rotation. Furthermore, "start timer" and "stop timer," etc., refer to the function of timer 403 that counts down the execution timing of the target process based on the occurrence time of a predetermined event, based on a preset waiting time.

[0058] (Operation sequence of the entrance roller) First, the operation sequence of the inlet roller 21 will be explained using Figure 6.

[0059] In S101, the entrance roller 21 is started to rotate at the target speed V1. In S102, the system waits while determining whether the entrance sensor 27 has detected the passage of the rear end of the sheet in the receiving path 81. If the entrance sensor 27 detects the passage of the rear end of the sheet, in S103 the system determines whether the sheet being transported is the final sheet. If it is not the final sheet, the system returns to S102 and continues processing. If the sheet being transported in S103 is the final sheet, the rotation of the entrance roller 21 is stopped in S104 and the operation sequence is terminated.

[0060] (Operation sequence of the roller before the buffer) Next, the operation sequence of the buffer pre-roller 22 will be explained using Figure 7.

[0061] In S201, the buffer front roller 22 is started to rotate at the target speed V1. In S202, the system waits while determining whether the inlet sensor 27 has detected the passage of the rear end of the sheet in the receiving path 81. When the inlet sensor 27 detects the passage of the rear end of the sheet, in S203, the system starts accelerating the buffer front roller 22 to the target speed V2 and sets a deceleration timer. The end time of the deceleration timer is set to be the time when the rear end of the sheet passes the buffer front roller 22 or later.

[0062] In S204, the system waits while the deceleration timer counts down. Once the countdown is complete, S205 starts the process of decelerating the buffer front roller 22 to the target speed V1. In S206, it is determined whether the sheet being transported is the final sheet or not. If it is not the final sheet, the system returns to S202 and continues processing. If the sheet being transported in S206 is the final sheet, the rotation of the buffer front roller 22 is stopped in S207 and the operation sequence ends.

[0063] (Movement sequence of the reversing roller) Next, the operation sequence of the reversing roller 24 will be explained using Figure 8.

[0064] In S301, it is determined whether the sheet being transported is subject to buffering. If it is subject to buffering, the process proceeds to S302; otherwise, it proceeds to S321. Sheets subject to buffering are those of the next part that are handed over from the image forming apparatus 1 to the post-processing device 4 before the binding process for the previous part of the sheet bundle is completed, when the image forming job that forms a multi-part sheet bundle is executed in the binding processing unit 4A. The number of sheets subject to buffering is predetermined according to the contents of the image forming job notified by the printer control unit 100 (in particular, the interval at which sheets are discharged from the image forming apparatus 1, the length of the sheets in the transport direction, and the process speed).

[0065] Lines S302 to S320 describe the operations performed on the buffered sheet. In S302, it is determined whether the sheet being transported is the first sheet. If it is the first sheet, the process proceeds to S303; otherwise, it proceeds to S307.

[0066] In S303, the reversing roller 24 is started to rotate at the target speed V1 and in the rotation direction R1 before reversal, and the reversing roller 24 is brought into contact with the nip portion. In S304, the system waits while determining whether the inlet sensor 27 has detected the passage of the rear end of the sheet in the receiving path 81. When the inlet sensor 27 detects the passage of the rear end of the sheet, in S305 the process of accelerating the reversing roller 24 to the target speed V2 is started, and in S306 various timers are set. The end time of the reversal timer is set so that it occurs after the second end of the sheet has passed the backflow prevention valve 23 but before it has passed the reversal roller. The end time of the separation timer is set to coincide with the timing after the leading edge (second end of the sheet) of the sheet, which has been inverted by the inverting roller 24, reaches the internal discharge roller 26. The end time of the stop timer is set to synchronize with the stopping of the internal discharge roller 26 (S408 in Figure 9).

[0067] After S306, the process merges with the handling of cases where the sheet being transported is not the first sheet, and proceeds to S313.

[0068] In S307, the system waits while determining whether the entrance sensor 27 has detected the passage of the rear end of the sheet in the receiving path 81. Once the entrance sensor 27 detects the passage of the rear end of the sheet, various timers are set in S308. The end time of the start timer is set to synchronize with the start of reverse movement of the sheet by the internal discharge roller 26 (S411 in Figure 9). The end time of the nip timer is set to coincide with the timing after the peripheral speed of the reversing roller 24, which started rotating in S310 below, reaches speed V2. The end time of the reversal timer is set so that the timing is after the rear end of the sheet in the receiving path 81 has passed the backflow prevention valve 23 but before it has passed the reversal roller. The end time of the separation timer is set to coincide with the timing after the leading edge (second end of the sheet) of the sheet, which has been inverted by the inverting roller 24, reaches the internal discharge roller 26. The end time of the stop timer is set to synchronize with the stopping of the internal discharge roller 26 (S419 in Figure 9).

[0069] In S309, the system waits while the start timer counts down. While the reversing roller 24 is waiting in a separated state, the sheet being transported reaches the reversing roller 24 and overlaps with the sheet being held by the internal discharge roller 26 (Figure 3(d)). When the countdown ends, in S310, the reversing roller 24 is started to rotate at the target speed V1 and in the rotation direction R1 before reversal. In S311, the system waits while the nip timer counts down. When the countdown ends, in S312, the power to the plunger solenoid is stopped and the reversing roller 24 is brought into contact (Figure 4(a)). At this time, the reversing roller 24 switches from a separated state to a contact state while rotating at the same peripheral speed as the internal discharge roller 26. After S312, the process merges with the process for when the sheet being transported is the first sheet, and the system proceeds to S313.

[0070] In S313, the system waits while the reversal timer counts down. When the countdown is complete, in S314 the reversal roller 24 is temporarily stopped (Figure 4(b)), the rotation direction is switched from the rotation direction R1 before reversal to the rotation direction R2 after reversal, and the system restarts at the target speed V2. In S315, it is determined whether to continue the buffer operation (whether the next sheet to be transported is also subject to the buffer operation), and if so, the system proceeds to S316. In S316, the system waits while the separation timer counts down. When the countdown is complete, in S317 the power supply to the plunger solenoid is stopped and the reversal roller 24 separates (Figure 4(c)). In S318, the system waits while the stop timer counts down. When the countdown is complete, the reversal roller is stopped in S319. In S320, it is determined whether the sheet being transported is the final sheet, and if it is not the final sheet, the system returns to S301 and continues processing. If the sheet being transported in S320 is the final sheet, the operation sequence is terminated. On the other hand, if it is determined in S315 that the buffer operation should not be continued, the system waits in S331 until the stop timer finishes, and then resets the stop timer in S332. The end time of the reset stop timer is set to the timing after the rear end of the sheet in the internal discharge path 82 has passed the reversing roller 24. After S332, the process merges with S318 and the above-described process is performed.

[0071] S321 to S329 describe operations on sheets that are not buffered. In this case, the sheet is reversed and conveyed by the reversing roller 24 while the reversing roller 24 remains in contact with the sheet. Specifically, in S321, the reversing roller 24 is started to rotate at the target speed V1 and in the rotation direction R1 before reversal, and the reversing roller 24 is set to a contact state that forms a nip portion. In S322, the system waits while determining whether the inlet sensor 27 has detected the passage of the rear end of the sheet in the receiving path 81. When the inlet sensor 27 detects the passage of the rear end of the sheet, S323 starts the process of accelerating the reversing roller 24 to the target speed V2, and S324 sets various timers. The end time of the reversal timer is set so that it occurs after the second end of the sheet has passed the backflow prevention valve 23 but before it has passed the reversal roller. The end time of the stop timer is set to coincide with the timing after the rear end of the sheet in the internal discharge path 82 has passed the reversing roller 24.

[0072] In S325, the system waits while counting down the reversal timer. When the countdown is complete, in S326, the reversal roller 24 is temporarily stopped, its rotation direction is switched from the rotation direction R1 before reversal to the rotation direction R2 after reversal, and it is restarted at the target speed V2. In S327, the system waits while counting down the stop timer. When the countdown is complete, the reversal roller is stopped in S328. In S329, it is determined whether the sheet being transported is the final sheet or not. If it is not the final sheet, the system returns to S301 and continues processing. If the sheet being transported in S329 is the final sheet, the operation sequence is terminated.

[0073] (Operation sequence of the internal discharge roller) Next, the operation sequence of the internal discharge roller 26 will be explained using Figure 9.

[0074] In S401, the system waits while determining whether the entrance sensor 27 has detected the passage of the trailing edge of the sheet in the receiving path 81. When the entrance sensor 27 detects the passage of the trailing edge of the sheet, in S402, it is determined whether the sheet being transported is subject to buffering. If it is subject to buffering, the system proceeds to S403; otherwise, it proceeds to S421. In S403, it is determined whether the sheet being transported is the first sheet in a sheet bundle to be processed by the binding processing unit 4A. If it is the first sheet, the system proceeds to S404; otherwise, it proceeds to S409.

[0075] In S404, various timers are set based on the timing at which the entrance sensor 27 detected the passage of the rear end of the sheet in S401. The start timer's end time is set to a timing that allows the internal discharge roller 26 to accelerate to the target speed V2 before the sheet, which has been inverted by the inverting roller 24, reaches the internal discharge roller 26. The end time of the stop timer is set to coincide with the timing when the leading edge of the sheet in the internal discharge path 82 has passed the reversing roller 24 and been transported a predetermined distance.

[0076] In S405, the system waits while the start timer counts down. When the countdown is complete, in S406, the internal discharge roller 26 is started to rotate at the target speed V2 and in the rotation direction R3 along the forward direction in the internal discharge path 82. In S407, the system waits while the stop timer counts down. When the countdown is complete, in S408, the internal discharge roller 26 is stopped and the system returns to S401. The timing of stopping the internal discharge roller 26 in S408 is synchronized with the timing of stopping the reversing roller 24 in S319 in Figure 8. Also, by stopping the internal discharge roller 26 in S408, the first sheet, which is the buffer target, is held by the internal discharge roller 26 when the system stops (Figure 3(d)).

[0077] S409 to S418 describe the operation when transporting the sheets to be buffered (excluding the first sheet). However, note that during the execution of S409 to S413, the internal discharge roller 26 contacts not the sheet being transported, but the sheet being held by the internal discharge roller 26 (the sheet in buffer). For example, in Figures 3(d) to 4(c), when the internal discharge roller 26 operates with the second sheet S2 as the "sheet being transported," the internal discharge roller 26 actually moves the first sheet S1, which is the sheet in buffer, until the second end S2a of sheet S2 reaches the internal discharge roller 26 between Figures 4(b) and 4(c).

[0078] In S409, various timers are set based on the timing at which the entrance sensor 27 detected the passage of the rear end of the sheet in S401. The end time of the start timer is set so that the amount of displacement between the sheet in the buffer, which is started to be transported in the reverse direction in S411 below, and the sheet being transported becomes a predetermined displacement amount k. The end time of the reversal timer is set to synchronize with the timing when the reversal roller 24 starts rotating in the reversed rotation direction R2 (S314 in Figure 8). The end time of the stop timer is set to coincide with the timing when the second end of the sheet being transported (or the second end of the uppermost sheet when multiple sheets are held by the internal discharge roller 26 as buffers) has passed the internal discharge roller 26 and been transported a predetermined distance.

[0079] In S410, the system waits while the start timer counts down. When the countdown is complete, in S411, the internal discharge roller 26 is started to rotate at a target speed V2 and in a rotational direction R4 along the reverse direction in the internal discharge path 82. As a result, the sheets in the buffer are transported in the reverse direction and overlap with the sheets being transported from the buffer front roller 22 by a predetermined amount of displacement k (Figure 4(a, b)). The transport speed (V2) at which the internal discharge roller 26 transports the sheets in the reverse direction is equal to the transport speed at which the buffer front roller 22 feeds the sheets to the reversing roller 24.

[0080] In S412, the system waits while counting down the reversal timer. When the countdown is complete, in S413 the internal discharge roller 26 is temporarily stopped, its rotation direction is reversed (R4→R3), the transport direction is switched from reverse to forward, and the system is restarted at the target speed V2. This reversal operation of the internal discharge roller 26 is performed in sync with the reversal operation of the reversal roller 24 (S314 in Figure 8). As a result, the sheet being transported and the sheet in the buffer are transferred from the reversal roller 24 to the internal discharge roller 26 in an overlapping state (Figure 4(c)).

[0081] In S414, the system waits while counting down the stop timer. When the countdown is complete, S415 determines whether to continue the buffer operation (whether the next sheet to reach the internal discharge roller 26 is also subject to buffering). If the buffer operation is to be continued, S416 stops the internal discharge roller 26 based on the end of the stop timer, and the system returns to S401 to continue processing. In this case, the processing in S409 to S414 is repeated for the next sheet, resulting in a state where three or more sheets are stacked in the buffer section. If the buffer operation is not to be continued, S417 resets the stop timer and continues the rotation of the internal discharge roller 26. The end time of the reset stop timer is set to coincide with the timing after the trailing end of the sheet in the internal discharge path 82 (the first end of the sheet being transported) has passed the internal discharge roller 26. In this case, S418 waits while counting down the stop timer, and when the countdown is complete, the internal discharge roller 26 is stopped. In S420, it is determined whether the sheet being transported is the final sheet. If it is not the final sheet, the process returns to S401 and continues; if it is the final sheet, the operation sequence ends.

[0082] S421 to S423 describe operations on sheets that are not buffered. In this case, the internal discharge roller 26 does not transport the sheet received from the reversing roller 24 in the reverse direction, but simply transports it in the forward direction toward the binding processing unit 4A. That is, in S421, various timers are set based on the timing in S401 when the entrance sensor 27 detects the passage of the rear end of the sheet. The start timer's end time is set to a timing that allows the internal discharge roller 26 to accelerate to the target speed V2 before the sheet, which has been inverted by the inverting roller 24, reaches the internal discharge roller 26. The end time of the stop timer is set to coincide with the timing after the rear end of the sheet in the internal discharge path 82 has passed the internal discharge roller 26.

[0083] In S422, the system waits while the start timer counts down. Once the countdown is complete, in S423, the internal discharge roller 26 is started to rotate at the target speed V2 and in the rotational direction R3 along the forward direction in the internal discharge path 82. Then, in S418, the system waits while the stop timer counts down. Once the countdown is complete, in S419, the internal discharge roller 26 is stopped. In S420, it is determined whether the sheet being transported is the final sheet. If it is not the final sheet, the system returns to S401 and continues processing. If it is the final sheet, the operation sequence ends.

[0084] Next, the movable inversion upper guide 420 will be described using Figures 10 to 20. In the explanations of Figures 2 to 9, the check valve 23 was rotatably supported on the internal discharge upper guide 46 via a rotating shaft 23a. In the configurations of Figures 10 to 20, a movable inversion upper guide 420 is used instead of the check valve 23. In the explanations of Figures 10 and onward, the explanation of configurations similar to those in Figures 1 to 9 will be omitted.

[0085] Figures 10 and 12(a) illustrate a configuration in Figure 2 in which a movable inversion upper guide 420 is employed. An inlet upper guide 4000 is provided as a fixed guide corresponding to the inlet upper guide 40 in Figure 2. Downstream of the inlet roller 21 and the inlet sensor 27, a receiving path 810 as a first transport path is formed by the inlet upper guide 4000 and the inlet lower guide 410, which is a third transport guide. The inlet upper guide 4000 rotatably supports the buffer front roller 220, which corresponds to the buffer front roller 22. The inlet upper guide 4000 also includes a buffer front sensor 170 upstream of the buffer front roller 220. The inlet upper guide 400 is equipped with rail grooves (4000c, 4000d) which are guide sections and is a holding means for movably holding the movable inversion upper guide 420 (first transport guide).

[0086] The inversion upper guide 420 supports the inversion upper roller 240a, which is the first inversion roller, on the downstream end side in the conveying direction of the buffer front roller 220, which is the first conveying means.

[0087] As shown in Figure 10(a), the inlet upper guide 4000 is provided with rail grooves (4000c, 4000d) at both ends with respect to the axial direction of the reversing upper roller 240a. The reversing upper guide 420 is provided with a guided portion 420c having a boss guided by the rail groove 4000c, and a guided portion 420d having a boss guided by the rail groove 4000b. The reversing upper guide 420 is provided with a holding portion 420a at one end for holding the reversing upper roller shaft 240d, and a holding portion 420b at the other end for holding the reversing upper roller shaft 240d.

[0088] In the axial direction of the reversing upper roller 240a, one end is provided with a separation lever 150 that rotatably supports the reversing upper roller shaft 420d, which is the rotation axis of the reversing upper roller 240a. Similarly, the other end is provided with a separation lever 151. The moving mechanism is composed of the separation levers 150 and 151. The separation lever 150 is movable in directions A1 and A2 of Figure 10 around a support shaft 150a provided on a main frame (not shown). Similarly, the separation lever 151 is movable in directions A1 and A2 of Figure 10 around a support shaft 151a provided on a main frame (not shown). Furthermore, the separation lever 151 is equipped with gear teeth 151b, which are driven receiving gears, and the separation lever 150 is equipped with gear teeth 150b, which are driven receiving gears.

[0089] The gear teeth 150b of the separation lever 150 are driven and connected to the stepping motor 155 via the drive transmission gear 154. The drive transmission gear 154 also transmits the drive of the stepping motor 155 to the drive transmission gear 157 via the drive shaft 156. As a result, the separation lever 151 operates in sync with the separation lever 150 as the stepping motor 155 rotates. With the above configuration, the inversion upper roller 240a and the second inversion roller, the inversion lower roller 240b, can come into contact and separate, and the inversion upper guide 420 also moves in conjunction with the separation and contact movements of the inversion upper roller 240a. The inversion lower roller 240b is supported by the lower roller shaft 240c.

[0090] In Figure 10(a), the inversion upper roller 240a and the inversion lower roller 240b are in contact, and the inversion upper guide 420 is in a lowered position (first position). When the stepping motor 155 is driven, the drive transmission gear 154 rotates in the direction B shown in the figure, and the separation lever 150 moves in the direction A1 shown in the figure. As a result, the inversion roller 240 separates as shown in Figure 10(b), and the inversion upper guide 420 moves to a raised position (second position). The separation lever 150 is provided with a light-shielding flag 150c, which detects the position of the separation lever 150 by shielding / transmitting the infrared light of the photosensor 158.

[0091] Next, the drive transmission to the reversing roller pair 240, which is the reversing means, will be explained. Figure 11 is a perspective view from one end of Figure 10(a). A reversing roller drive motor 159 is provided, and rotating belts 160, 161, and 162 that rotate by receiving the driving force from the reversing roller drive motor 159, and gear pulleys 163, 164, and 165 which are integrated gears and pulleys.

[0092] The inverting upper roller shaft 240d is equipped with a pulley 167, which is a pulley that engages with and rotates integrally with the inverting upper roller shaft 240d. The inverting lower roller shaft 240c is equipped with a pulley 166, which is a pulley that engages with and rotates integrally with the inverting lower roller shaft 240c. The drive from the inverting roller drive motor 159 is transmitted to pulleys 166 and 167 via rotating belts 160-162 and gear pulleys 163-165.

[0093] Furthermore, since the gear pulley 164 has a rotation center coaxial with the support shaft 151a, the distance between the axes of the rotating belt 161 does not change even when the reversing upper roller 240a is separated. As described above, driving force is input to both the reversing upper roller 240a and the reversing lower roller 240b, and the rotations of the reversing upper roller 240a and the reversing lower roller 240b are always synchronized.

[0094] The following describes the operation during paper feeding.

[0095] (Buffer operation) Next, the buffer operation will be explained in detail using Figures 12 to 18. In Figure 12, the sheet transport path (part of the receiving path 810) between the inlet roller 210 and the pre-buffer roller 220 is formed by the "inlet upper guide 4000" and the "inlet lower guide 410". The transport guides that form the sheet transport path (part of the internal discharge path 820) downstream from the internal discharge roller 260, which is a pair of transport rollers, are the "internal discharge upper guide 460" and the "internal discharge lower guide 470". The "reversing upper guide 420" is a transport guide that guides the sheet from the same side as the inlet upper guide 4000 between the pre-buffer roller 220 and the reversing roller 240. The second transport guide, the "reversing lower guide 430", guides the sheet from the same side as the internal discharge lower guide 470 between the reversing roller 240 and the internal discharge roller 260.

[0096] The sheet being transported by the entrance roller 210 is guided to the buffer-pre-roller 220 by the entrance upper guide 4000 and the entrance lower guide 410. An entrance sensor 270 is positioned near the downstream side of the entrance roller 210. A reflective photosensor can be used to determine the presence or absence of a sheet at the detection position by irradiating infrared light toward the entrance sensor 270 and detecting the reflected light from the sheet. In this case, a hole larger than the diameter of the spot light of the entrance sensor 270 is provided in the part of the entrance lower guide 410 facing the entrance sensor 270 so that infrared light is not reflected when no sheet is passing through. The buffer-pre-sensor 170 is a detection means for determining the presence or absence of a sheet, similar to the entrance sensor 270, and detects sheets that are stuck in the path due to jams or the like.

[0097] Figure 12 shows the inverting roller 240a in contact with the inverting upper guide 420 in the first position. The internal discharge path 820 (third transport path) is aligned with the first discharge path 830 (second transport path) via the merging section 171, and the receiving path 810 (first transport path) is configured to merge with the merging section 171 from an oblique angle toward the first discharge path.

[0098] Figure 13 shows the state where the reversing roller 240a is separated and the reversing upper guide 420 is in the second position. As the reversing upper roller 240a separates, the reversing upper guide 420 is lifted, and the other end moves along the rail grooves 4000c and 4000d of the inlet upper guide 400, causing the reversing upper guide 420 to move from the first position to the second position, and the path width of the first discharge path 830 widens. Here, widening the path width of the first discharge path 830 means that the distance between the reversing lower guide 430 and the reversing upper guide 420 widens. In other words, the reversing upper guide 420 can move between a first position where the distance from the reversing lower guide 430 is a first distance, and a second position where the distance is a second distance greater than the first distance.

[0099] When the sheet is transported from the receiving path 810 to the first discharge path 830, the direction of transport of the sheet changes angle (F2 in Figure 13), and when the sheet is transported from the first discharge path 830 to the internal discharge path 820, the sheet is transported in a straight line (F1 in Figure 12).

[0100] Figure 14 shows the inversion upper guide 420 in a state where it has risen further upward from the second position. The inversion upper roller 240a moves further apart from the state in Figure 13, lifting the inversion roller 240 side of the inversion upper guide 420, and the 420c portion of the inversion upper guide 420 moves the inlet upper guide 400c portion.

[0101] As a result, the inversion upper guide 420 moves approximately parallel to the inversion lower guide 430, resulting in the state shown in Figure 14. If a jam occurs near the confluence section 171, the jam is removed by accessing it from the inversion roller 240 side in this state.

[0102] As shown in Figures 12 to 14, the branching point between the receiving path 810 and the internal discharge path 820 is equipped with a reverse branching roller 122 as a driven rotating body. When the sheet is transported from the receiving path 810 to the first discharge path 830, the rear end of the sheet passes over the reverse branching roller 122, and the sheet returns from its bent state to a straight shape. After that, it is reversed by the reverse roller 240 and can be transported along the reverse lower guide 430 toward the internal discharge roller 260.

[0103] The internal discharge roller 260 is a pair of rollers adjacent to the reversing roller 240 in the sheet transport direction in the internal discharge path 820, and is a pair of rollers capable of forward and reverse rotation. In other words, the internal discharge roller 260 can transport sheets in both the sheet transport direction from the reversing roller 240 toward the binding processing unit 4A (forward feeding direction of the internal discharge path 820) and the reverse feeding direction from the binding processing unit 4A toward the reversing roller 240.

[0104] Next, the buffer operation of the buffer unit 4B will be explained in detail using Figures 15 to 18. The buffer operation is an operation in which a predetermined number of sheets constituting the next sheet bundle are kept waiting in the buffer unit 4B until the binding process for the previous sheet bundle is completed in the binding processing unit 4A. By performing the buffer operation, the image forming system 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).

[0105] Hereafter, to distinguish between the sheets, they will be referred to as "Sheet S1," "Sheet S2," and "Sheet S3" in the order they are handed over from the image forming apparatus 1 to the post-processing device 4. Furthermore, of the two ends of the sheet in the sheet transport direction, the one that passes the entrance roller 210 first will be referred to as the "first end," and the one that passes the entrance roller 210 later will be referred to as the "second end." In addition, the sheet transport speed in the horizontal transport section 14 of the image forming apparatus 1 will be V1, and the transport speed after the transport speed is accelerated inside the post-processing device 4 will be referred to as V2.

[0106] Figure 15 shows the state when the rear end (second end S1b) of sheet S1 in the receiving path 810 passes the detection position of the inlet sensor 270. When the inlet sensor 270 detects the passage of the second end S1b of sheet S1, the buffer front roller 220 and the reversing roller 240 accelerate sheet S1 from speed V1 to speed V2. By accelerating sheet S1 in this way, the gap between it and the following sheet S2 widens, ensuring the sheet gap necessary for the reversing operation (switchback) by the reversing roller 240.

[0107] At the point shown in Figure 15(a), the inversion upper guide 420 is in the second position. Before the first end S1b of the sheet S1 passes the inversion roller 240 and the second end S1b passes the buffer front roller 220, the inversion upper guide 420 moves to the first position. The timing of the operation is determined based on the elapsed time since the inlet sensor 270 detected the passage of the rear end (second end S1b) of the sheet S1.

[0108] Figure 15(b) shows the state of the sheet S1 at the point when the rear end (second end S1b) of the sheet S1 in the receiving path 810 has passed the reversing branch roller 172. The reversing roller 240 temporarily stops rotating at a predetermined timing after the rear end (second end S1b) of the sheet S1 has passed the reversing branch roller 172. The predetermined timing is determined based on the elapsed time from the time when the entrance sensor 270 detects the passage of the rear end (second end S1b) of the sheet S1.

[0109] From the state shown in Figure 15(b), the reversing roller 240 begins to rotate in the rotation direction R2, which is the rotation direction after reversal, and passes under the rear end (second end S1b) of S1, the reversing branch roller 172, toward the internal discharge roller 260. At this time, because the reversing upper guide 420 is in the first position, the first discharge path 830 is narrow, which restricts the orientation of the sheet, and the sheet can be transferred to the internal discharge roller 260 without flowing backward toward the receiving path 810. If the reversing upper guide 420 were in the second position where the path is wider, the orientation of the sheet would not be restricted, and there would be a possibility of backflow toward the receiving path 810 (first conveying path).

[0110] Figure 16(a) shows the state after sheet S1 has been handed over to the internal discharge roller 260. The internal discharge roller 260 receives sheet S1 while rotating in the rotational direction R3 and transports sheet S1 in the forward direction in the internal discharge path 820. Also, after the leading edge (second end S1b) of sheet S1 in the internal discharge path 820 passes the position of the reversal branch roller 172, the leading edge (first end S2a) of sheet S2 in the receiving path 810 reaches the reversal branch roller 172. Therefore, sheet S1 and sheet S2 are transported so that they pass each other at the branching point of the transport path.

[0111] Figure 16(b) shows the state at the point when the leading edge (second end S1b) of sheet S1 in the internal discharge path 820 has been transported a predetermined amount from the internal discharge roller 260 and the internal discharge roller 260 has temporarily stopped. After the point shown in Figure 20(c), the stepping motor 159 is driven before the leading edge (first end S2a) of sheet S2 in the receiving path 810 reaches the inversion upper guide 420. As a result, the inversion upper roller 240a moves in the E1 direction and the inversion upper guide 420 moves to the second position. Sheet S1 is held by the stopped internal discharge roller 260, and a portion of sheet S1 is located between the separated inversion rollers 240. Therefore, sheet S2, which is sent from the receiving path 810 to the first discharge path 830 by the buffer pre-roller 220, is transported by sliding over sheet S1. In this case, if the path width of the first discharge path 830 is narrow, the sliding resistance when conveying the sheet will increase, and the tip of S2 may not be able to pass through the first discharge path 830, causing a jam. To prevent this, the inversion upper guide 420 is moved to a second position with a wider path width, so that the sheet can be conveyed without getting stuck in the first discharge path 830.

[0112] Figure 17(a) shows the state after the internal discharge roller 260 has started transporting the sheet S1 in the reverse direction. The internal discharge roller 260 starts rotating in the rotation direction R4 when the sheet S2 has been transported to a predetermined position, transporting the sheet S1 in the reverse direction toward the reversing roller 240. The target speed of the internal discharge roller 260 is set to speed V2, the same as the buffer front roller 220. The stepping motor 109 is driven when the speeds of the sheets S1 and S2 become approximately equal (relative speed is approximately zero). As a result, the reversing upper roller 240a moves in the direction E2, the reversing roller 240 comes into contact with the sheet S1 again, and the sheet S1 and S2 are sandwiched between the reversing roller 240 in an overlapping state. Furthermore, the reversing roller 240 starts rotating in rotational direction R1 in synchronization with the inner discharge roller 260, and is controlled to have the same peripheral speed (velocity V2) as the buffer front roller 220 and the inner discharge roller 260 before switching from a separated state to a contact state.

[0113] Figure 17(b) shows the state after the rear end (second end S2b) of sheet S2 in the receiving path 810 has passed the reversing branch roller 172. The reversing roller 240 temporarily stops rotating at a predetermined timing after the rear end (second end S2b) of sheet S2 has passed the reversing branch roller 172. At this time, both sheets S1 and S2, which are stacked, stop moving, but the second end S1b of sheet S1 protrudes by a predetermined amount k in the forward direction of the internal discharge path 820 compared to the second end S2b of sheet S2. This amount k is controlled by the internal discharge roller 260 starting to transport sheet S1 in the reverse direction at a predetermined timing, as explained using Figure 17(a).

[0114] Figure 18(a) shows the state after the reversing roller 240 has started rotating in the rotational direction R2 and has handed over the stacked sheets S1 and S2 to the internal discharge roller 260. The internal discharge roller 260 receives the sheets S1 and S2 while rotating in the rotational direction R3 and transports the sheets S1 and S2 in the forward direction in the internal discharge path 820. The sheets S1 and S2 are transported in their stacked state through the internal discharge path 820 toward the binding processing unit 4A.

[0115] Furthermore, after the leading edge (second end S2b) of sheet S2 in the internal discharge path 820, the leading edge (first end S3a) of the third sheet S3 in the receiving path 810 reaches the reversal branching roller 172. Therefore, sheets S2 and S3 are transported so as to pass each other at the branching point of the transport path. Also, after sheet S2 is gripped by the internal discharge roller 260, the reversal upper roller 240a moves in the E1 direction, and the reversal roller 240 is separated again before the leading edge of the subsequent sheet S3 reaches the reversal upper guide 420. As a result, when the leading edge of sheet S3 passes through the first discharge path, the width of the first discharge path is widened, allowing the sheets to be transported without jamming.

[0116] Figure 18(b) shows the state after the reversing roller 240 switches from a separated state to a contact state. The reversing roller 240 switches from a separated state to a contact state after the first end S2a of the sheet S2 separates from the reversing roller 240, and grips the sheet S3. After this, the reversing roller 240 performs the reversing operation of the sheet S3, and sheet S3, following sheets S1 and S2, is transported to the binding processing unit 4A via the internal discharge path 820.

[0117] When a sheet moves from the receiving path 810 (first transport path) to the first discharge path (second transport path), the sheet may be pressed against the reversal branching section (the section where the reversal branching roller 122 is provided), potentially causing image damage. The reversal branching roller 122 is rotatable and is provided to prevent image damage. A perspective view of the reversal branching roller 122 is shown in Figure 19. The rollers are provided at two locations in the axial direction, and the spacing of the reversal branching roller 122 is set so that even the smallest width sheet passes over the reversal branching roller 122.

[0118] Furthermore, the recess 430a in the inversion lower guide 430 in Figure 20 is provided to reduce the noise of the sheet contacting the guide. The rear end S1b of the conveyed sheet, after passing through the inversion branch roller 172 from the state shown in Figure 15(a), comes into forceful contact with the inversion lower guide 830. By providing a recess at the point where the rear end of the sheet makes contact, the noise of contact can be reduced.

[0119] In this embodiment, by changing the position of the inversion upper guide 420 when the sheet is conveyed from the buffer front roller 210 and when the sheet is inverted and conveyed by the inversion roller 240, it is possible to suppress the occurrence of jams during sheet conveyance.

[0120] (Other embodiments) In the above embodiment 1, a configuration was described in which the inversion guide 420 of the buffer section 4B is moved. The present invention can also be applied to a configuration in which the buffer section 4B does not buffer the sheet. In that case, the buffer section 4B is an inversion section that inverts a single sheet.

[0121] In the above embodiment 1, a post-processing device 4 directly connected to the image forming apparatus 1 was described as an example of a sheet conveying device. However, this technology can also be applied to sheet conveying devices that receive and convey sheets from the image forming apparatus 1 via an intermediate unit (for example, a relay conveying unit installed in the discharge space in an in-body discharge type image forming apparatus).

[0122] Furthermore, an image forming system equipped with a sheet transport device and an image forming device includes a system in which modules having the functions of an image forming device 1 and a post-processing device 4 are mounted within a single housing.

[0123] Furthermore, the stapler 51 is just one example of a processing means for processing sheets. For example, the stapler may be used to discharge unstapled bundles of sheets in the intermediate loading section to the lower discharge tray 37. Also, the post-processing device 4 in the above embodiment is an example of a sheet transporting device that transports sheets. This technology can be applied to sheet transporting devices other than sheet processing devices that process sheets (recording materials) on which images have been formed in an image forming apparatus. [Explanation of symbols]

[0124] 1. Image forming apparatus 1S Image Forming System 4. Sheet processing device, sheet transport device (post-processing device) 4B Buffer section 240 Reversible Roller Pair (Reversible Roller) 260 Intermediate Roller Pair (Internal Discharge Roller) 290 Conveyor Roller (Kick-off Roller) 810 First transport path (receiving path) 82 Third transport path (internal discharge path) 84. Second transport path (second discharge path) 4000 Entrance Guide 420 Reversal Up Guide 430 Reversal Down Guide 460 Internal discharge upper guide 470 Internal discharge guide

Claims

1. A first transport path for receiving the sheet, A reversing means for reversing the sheet that has passed through the first transport path, A second transport path for transporting the sheet that has passed through the first transport path between the reversing means and the first transport path, A pair of conveying rollers that grip and convey the sheet that is inverted and conveyed in the second conveying path by the inversion means, A first transport guide is positioned between the reversing means and the transport roller pair to constitute the second transport path, A second conveyor guide is positioned between the reversing means and the pair of conveyor rollers and opposite the first conveyor guide, and is used to form the second conveyor path. A holding means for movably holding the first transport guide, With respect to a first direction which is the direction in which the sheet being transported along the first transport path is transported, the system comprises a first transport means for transporting the sheet being transported along the first transport path, The first transport guide is movable to a first position where the distance from the second transport guide is a first distance, to a second position where the distance is a second distance greater than the first distance, and to a third position where the distance is a third distance greater than the second distance. The sheet transported by the first transport means is guided toward the reversing means by the first transport guide located at the second position. A sheet conveying device characterized in that the sheet inverted by the inversion means is guided toward the pair of conveying rollers by the first conveying guide located at the first position.

2. The sheet conveying device according to claim 1, characterized in that the second conveying path is configured to extend below the first conveying path.

3. The system includes a moving mechanism that moves the first transport guide at a predetermined timing, The first conveying means conveys the sheet toward the reversing means, The sheet conveying device according to claim 1, characterized in that when the leading edge of the sheet is conveyed by the first conveying means, the position of the first conveying guide by the moving mechanism is the second position.

4. The sheet reaches the reversing means before the rear end of the sheet is conveyed by the first conveying means. The sheet conveying device according to claim 3, characterized in that the moving mechanism moves the first conveying guide from the second position to the first position before the rear end of the sheet is conveyed by the first conveying means.

5. The sheet conveying device according to claim 4, characterized in that the reversing means conveys the sheet in a second direction which is opposite to the first direction after the rear end of the sheet has been conveyed by the first conveying means, so that the sheet can reach the conveying roller pair.

6. The reversing means comprises a first reversing roller and a second reversing roller that clamps the sheet together with the first reversing roller. The first transport guide includes the first reversing roller, The sheet conveying device according to any one of claims 1 to 5, characterized in that the first reversing roller grips the sheet with the second reversing roller when the first conveying guide is in the first position, and moves away from the second reversing roller when the first conveying guide is in the second position.

7. The sheet conveying device according to claim 6, characterized in that, when the first conveying guide is located at the second position and the first reversing roller is spaced apart from the second reversing roller, the sheet conveyed by the first conveying means is conveyed in the first direction by the second reversing roller.

8. The sheet conveying device according to claim 6, characterized in that when the first conveying guide moves from the second position to the third position, the first reversing roller moves in a direction away from the second reversing roller.

9. The sheet conveying device according to claim 5, characterized in that the second conveying guide has a recess on the upstream side of the conveying roller pair with respect to the second direction.

10. The sheet conveying device according to claim 1, further comprising a third conveying guide located downstream of the first conveying means and upstream of the first conveying guide, the third conveying guide having a driven rotating body that rotates in contact with the sheet and together with the holding means to form the first conveying path.

11. The sheet conveying device according to claim 1, further comprising a first loading means for loading sheets discharged from the inversion means on the downstream side of the inversion means in the first direction, wherein the inversion means is capable of discharging sheets into the first loading means.

12. A second loading means is positioned downstream of the transport roller pair in the second direction and loads the sheets transported by the transport roller pair, The sheet conveying device according to claim 5, further comprising a processing means for performing a binding process on sheets loaded on the second loading means.

13. An image forming apparatus that forms an image on a sheet, The sheet transport device according to claim 12, which receives and processes a sheet from the image forming apparatus, comprises An image forming system characterized by the following features.

Images