Sheet folding device and image forming system

Abstract

The present invention comprises: a first conveying means for conveying a sheet at a first position; a second conveying means for conveying, at a second position, the sheet transferred from the first conveying means; a detection means for detecting the sheet at a third position downstream of the second position in the sheet conveyance direction from the first position toward the second position; a folding means for performing a folding process on the sheet by holding and conveying the slack in the sheet formed between the first position and the second position, on the basis of the output of the detection means; and a control means for controlling the operation of the first conveying means and the second conveying means so as to substantially eliminate, during the sheet conveying process from the second position to the third position, the slack that occurred in the sheet being conveyed from the first position to the second position.

Description

Sheet Folding Apparatus and Image Forming System Field of the Invention

[0001] The present invention relates to a sheet folding apparatus that performs folding processing on a sheet, and an image forming system provided with the same. Description of Related Art

[0002] Conventionally, sheet folding apparatuses that perform folding processing on sheets are known, such as half-folding that forms one fold line on a sheet to fold it in half, tri-folding that forms two fold lines to fold the sheet into a Z-shape or C-shape, and bellows folding that forms three or more fold lines to fold the sheet into a bellows shape.

[0003] For example, the sheet folding apparatus described in Japanese Patent Laid-Open No. 2022-119433 adopts a method of folding the sheet by pushing the non-nipped region of the sheet with a folding guide when the sheet spans two pairs of conveying rollers.

[0004] An object of the present invention is to further develop the conventional sheet folding apparatus, and to provide a sheet folding apparatus improved over the prior art and an image forming system equipped with the same.

[0005] A typical configuration according to the present invention for solving the above problem is characterized by comprising: a first conveying unit that conveys a sheet at a first position; a second conveying unit that conveys the sheet delivered from the first conveying unit at a second position; a detecting unit that detects the sheet at a third position downstream of the second position in the sheet conveying direction from the first position toward the second position; a folding unit that performs folding processing on the sheet by nipping and conveying the slack of the sheet formed between the first position and the second position based on the output of the detecting unit; and a control unit that controls the operations of the first conveying unit and the second conveying unit so that the slack generated in the sheet conveyed from the first position to the second position is substantially eliminated in the sheet conveying process from the second position to the third position.

[0006] Further features of the present invention will become apparent from the following description of exemplary embodiments, explained in conjunction with the accompanying drawings.

[0007] Cross-sectional diagram of an image forming system

[0008] Cross-sectional diagram of a sheet folding device

[0009] Cross-sectional diagram of a sheet folding unit

[0010] Perspective diagram illustrating the drive transmission mechanism to the reversing roller pair.

[0011] Control block diagram of the sheet folding unit

[0012] Flowchart for controlling sheet transport speed during sheet folding process

[0013] (a) to (d) are explanatory diagrams showing the sheet transport operation during the sheet folding process.

[0014] Diagram illustrating the disruption of seat posture.

[0015] (a) to (f) are diagrams illustrating the sheet folding operation.

[0016] (a) and (b) are explanatory diagrams showing the sagging of the sheet before the folding process. Description of the Embodiment

[0017] An image forming system equipped with a sheet folding device (sheet folding processing device) according to an embodiment of the present invention will be described with reference to the drawings.

[0018] <Overall Configuration of the Image Forming System> As shown in Figure 1, the image forming system A according to this embodiment comprises an image forming apparatus 100 that forms an image on a sheet (recording paper), a sheet folding apparatus 200 that performs a predetermined folding process on the sheet, and a sheet processing apparatus 300 that discharges and loads the folded sheet.

[0019] The image forming apparatus 100 includes a sheet feeding unit 102 that supplies sheets stored in sheet cassettes 101a, 101b, and 101c, and an image forming unit 103 that forms an image on the supplied sheet.

[0020] The sheets stored in the sheet cassettes 101a, 101b, and 101c are supplied to the image forming unit 103 at a predetermined timing by the sheet feeding unit 102.

[0021] In this embodiment, the image forming unit 103 forms an image using an electrophotographic method with toner. Yellow, magenta, cyan, and black toner images formed on four photoreceptors 103Y, 103M, 103C, and 103K are first transferred to an intermediate transfer belt 103a, and these toner images are secondarily transferred to a conveyed sheet to form a color image. The sheet is then pressed and heated in the fixing unit 103b to fix the toner image, and then discharged to the sheet folding processing device 200 by the discharge roller 104.

[0022] The sheet folding processing device 200 folds the sheet, which has been image-formed and conveyed by the image forming device 100 as described later, at a predetermined folding position.

[0023] The sheet processing device 300 either discharges the sheets that have been transported through the sheet folding processing device 200 as they are, or discharges and loads them after performing post-processing such as stapling multiple sheets together.

[0024] When image formation is performed on a sheet using the image forming system A, the process is based on information regarding the sheet's characteristics, such as its shape, size, basis weight, and surface finish, as well as processing information such as binding, folding, and perforation. This information is either input via the operation unit 400 by the user, or from an external device (host PC) connected to the image forming system A via a network. Based on this information, the image forming apparatus 100, the sheet folding apparatus 200, and the sheet processing apparatus 300 are controlled, and their respective processes are performed.

[0025] Furthermore, the image formation method is not limited to the electrophotographic method described above; an inkjet method using ink is also acceptable. Whether it is a thermal inkjet method or a piezo inkjet method is not a requirement.

[0026] <Sheet Folding Processing Device> Next, the sheet folding processing device 200 will be described. In this embodiment, the sheet folding processing device 200 determines the presence or absence of a folding processing signal based on the operation of the operation unit 400 by the user or information from an external device connected to the network, and performs a predetermined folding operation based on the given information.

[0027] As shown in Figure 2, the sheet folding processing device 200 has an entrance sensor S1 that detects when a sheet discharged from the image forming apparatus 100 has been transported into the sheet folding processing device 200, and an entrance roller pair 201 for guiding the transported sheet into the interior.

[0028] When the sheet folding processing device 200 receives instructions from the user (inputted job) via the operating unit 400 operated by the user or via an external device, and the instructions include folding, it switches the switching flapper F1 to the position shown in the figure and transports the sheet toward the sheet folding unit B described later.

[0029] The edges of the sheet, conveyed by the entrance roller pair 201, pass through the lateral registration detection sensor S2. If the position of the sheet edge in the width direction perpendicular to the sheet conveying direction is outside the predetermined position, it is detected by the lateral registration detection sensor S2. When the lateral registration detection sensor S2 detects a deviation in the width direction, the first shift roller pair 202a and the second shift roller pair 202b, which are in a nip position on the sheet, move by a predetermined amount in the front-back direction of Figure 2, thereby performing a sheet shift operation. As a result, the lateral registration of the sheet is corrected.

[0030] Subsequently, the sheet sent to the transport roller pair 203 is sent to the stopper guide 204. If the user's instruction, input via the operation unit 400 or information from an external device, is to fold each sheet individually, the stopper guide 204 is switched to a retracted position (not shown) and the sheet is transported to the transport roller pair 205.

[0031] When folding multiple sheets at once, the stopper guide 204 is raised and lowered by a lifting motor (not shown) to a predetermined position corresponding to the size of the sheets, the stopper guide 204 is switched to the position shown, and the sheets are accumulated on the stopper guide 204. At this time, the switching to and return of the stopper guide 204 to the retracted position is performed by controlling a motor (not shown).

[0032] The upstream end of the sheet bundle accumulated in the stopper guide 204 is moved away from the sheet transport path by the passing flappers F2 (F2a, F2b). The passing flappers F2 are used depending on the size of the sheet bundle to be folded in the transport direction; passing flapper F2a is used when it exceeds a predetermined value, and passing flapper F2b is used when it falls below the predetermined value. When one is in use, the other stops, but their operation is the same, so passing flapper F2a will be described here.

[0033] When folding multiple sheets together, the second shift roller pair 202b and the transport roller pair 203 are separated by a stacking separation motor (not shown). However, if the sheet size is below a predetermined value, the second shift roller pair 202b is not separated.

[0034] The sheet, held in place by the abutment guide 204, is pushed in by the rotation of the abutment paddle 206, ensuring it is firmly pressed against the abutment guide 204. The abutment paddle 206 retracts from the transport path once it has pushed the sheet in.

[0035] The subsequent sheet is transported to the right of the preceding sheet, which has been moved aside by the passing flapper F2a, by the inlet roller pair 201 and the first shift roller pair 202a. When the upstream end of the subsequent sheet passes the first shift roller pair 202a, the abutment paddle 206 rotates again, abutting the subsequent sheet against the abutment guide 204. Once the abutment against the abutment guide 204 is complete, the rear end of the sheet is moved aside from the transport path by the passing flapper F2a.

[0036] By repeating the same operation, multiple sheets are secured together on the stopper guide 204.

[0037] When a predetermined number of sheets are placed on the stopper guide 204, the second shift roller pair 202b and the transport roller pair 203 are nipped by the drive of the overlapping separation motor. When the sheets are nipped, the stopper guide 204 is retracted by a motor (not shown) and the sheet bundle is transported to the transport roller pair 205.

[0038] When a sequentially conveyed sheet bundle is detected by the pre-registration detection sensor S3, the sheet bundle is conveyed a predetermined distance (for a predetermined time) and abutted against the stopped registration roller pair 207. At this time, a loop is formed in the sheet bundle between the conveyance roller pair 208 and the registration roller pair 207, and a registration process is performed in which the leading end of the sheet bundle follows the registration roller pair 207.

[0039] When the registration process is completed, the registration roller pair 207 starts conveying, supplies the sheets to the sheet folding unit B, and the sheet folding unit B executes a predetermined folding process on the sheet bundle. The configuration of this sheet folding unit B and the sheet folding process control will be specifically described later.

[0040] The sheets that have undergone the predetermined folding process in the sheet folding unit B are discharged to the folding tray 209. Note that depending on the type of folding process performed on the sheets, the sheets may be discharged to the sheet processing apparatus 300. For example, in the case of Z-folding processing for A3 size sheets, the sheets may be conveyed to the sheet processing apparatus 300 and subjected to binding processing or the like together with other sheets.

[0041] When discharging the sheets to the folding tray 209, the switching flappers F3 and F4 are switched, and the sheets are conveyed to the folding tray 209 by a plurality of sets of conveyance roller pairs 210. The sheets conveyed to the folding tray 209 are leaned against the stopper 211. This stopper 211 predicts the stacked amount of sheets based on information from a counter, and moves as the number of folded sheets increases to secure an appropriate sheet stacking space.

[0042] When discharging the sheets to the sheet processing apparatus 300, the switching flapper F3 is switched, and the sheets conveyed by the conveyance roller pair 210 are conveyed to the sheet processing apparatus 300 by the discharge roller pair 212.

[0043] Note that when the folding process by the sheet folding processing device 200 is not executed (when the instruction from the user does not include the folding process), the sheet conveyed into the sheet folding processing device 200 by the inlet roller pair 201 is delivered to the relay conveyance roller pair 213, and guided to the discharge roller pair 212 by switching the switching flappers F1 and F4. Then, the sheet conveyed to the discharge roller pair 212 is conveyed to the sheet processing device 300.

[0044] <Sheet Folding Unit> Next, the configuration of the sheet folding unit B that performs folding processing on a sheet and sheet folding control will be described.

[0045] (Folding Section) As shown in Figure 3, the sheet folding unit B according to the present embodiment includes five folding rollers, and the plurality of folding rollers constitute four folding sections. That is, in the first folding section including the first folding roller 1a and the second folding roller 1b as folding means, a nip portion a is formed by the first folding roller 1a and the second folding roller 1b being in pressure contact with each other. Then, by pinching the deflected (curved) sheet with the nip portion a, a folding process of folding the sheet (forming a fold line on the sheet) is enabled. Details of the folding process will be described later.

[0046] Similarly, in the second folding section including the second folding roller 1b and the third folding roller 1c, a nip portion b is formed by the second folding roller 1b and the third folding roller 1c being in pressure contact with each other, and processing can be performed by the nip portion b. Further, in the third folding section including the third folding roller 1c and the fourth folding roller 1d, a nip portion c is formed by the third folding roller 1c and the fourth folding roller 1d being in pressure contact with each other, and folding processing can be performed by the nip portion c. Further, in the fourth folding section including the fourth folding roller 1d and the fifth folding roller 1e, a nip portion d is formed by the fourth folding roller 1d and the fifth folding roller 1e being in pressure contact with each other, and folding processing can be performed by the nip portion d.

[0047] Each folding roller 1a to 1e also functions as a conveying roller for transporting the sheet, and when not performing folding, it grips and transports the sheet. The roller pair 1a and 1f, consisting of the first folding roller 1a and the folding sub-roller 1f pressed against it, functions as the upstream conveying section (first conveying means) for feeding the sheet to the nip section a of the first folding section, and the first roller pair 2a, located downstream in the conveying direction, functions as the second conveying section (second conveying means). When the sheet transported by the upstream roller pair 1a and 1f reaches the first roller pair 2a downstream, and the sheet is transported by the two sets of roller pairs, the sheet is loosened between the roller pairs 1a and 1f and the first roller pair 2a, and the loosened sheet is fed to the nip section a of the first folding roller 1a and second folding roller 1b, located between the two sets of roller pairs in the conveying direction, thereby performing the folding process on the sheet in the first folding section. The control of each roller pair when performing the folding process will be described later.

[0048] Similarly, when the sheet is folded by the second folding section, the folding roller pair 1a and 1b functions as the upstream transport roller pair, and the second roller pair 2b located downstream of them functions as the downstream transport roller pair. When the sheet transported by the upstream roller pair 1a and 1b reaches the downstream second reversing roller pair 2b, and the sheet is transported by the two sets of roller pairs, the sheet is slackened between the folding roller pair 1a and 1b and the second roller pair 2b, and the sheet is fed into the nip section b, thereby performing the folding process on the sheet.

[0049] The same applies when the sheet is folded by the third folding section; the folding roller pair 1b and 1c function as the upstream transport roller pair, and the third roller pair 2c located downstream of them functions as the downstream transport roller pair. When the sheet transported by the upstream roller pair 1b and 1c reaches the downstream third roller pair 2c, and the sheet is transported by the two sets of roller pairs, the sheet is slackened between the folding roller pair 1b and 1c and the third roller pair 2c and fed into the nip section c, thereby performing the folding process on the sheet.

[0050] Similarly, when folding the sheet using the fourth folding section, the folding roller pair 1c and 1d functions as the upstream transport roller pair, and the fourth reversing roller pair 2d, located downstream of them, functions as the downstream transport roller pair. When the sheet transported by the upstream roller pair 1c and 1d reaches the downstream fourth roller pair 2d and is transported by the two roller pairs, the sheet is slackened between the folding rollers 1c and 1d and the fourth roller pair 2d, and fed into the nip section d, thereby performing the folding process on the sheet.

[0051] (Drive Transmission Mechanism) Furthermore, the drive transmission section of the first to fourth roller pairs 2a to 2d is equipped with a torque limiter and a one-way clutch. Therefore, the roller pairs 2a to 2d are configured to slip if a rotational torque exceeding a set torque is generated in the rotational direction, and only rotation in one direction is transmitted to the rotating shaft.

[0052] The configuration of the torque limiter and one-way clutch will be explained using the first roller pair 2a as an example. The second roller pair 2b to the fourth roller pair 2d have the same configuration as the first roller pair 2a, so their explanation will be omitted.

[0053] Figure 4 is a perspective view illustrating the drive transmission mechanism 20 that transmits rotational driving force to the first roller pair 2a. One of the rollers 2a1 constituting the first roller pair 2a is provided on the rotating shaft 22a, which is connected to a drive motor M2a that functions as a drive source via a torque limiter 21.

[0054] The driving force of the drive motor M2a is transmitted to the gear train via the motor gear G1, and then transmitted from gear G2 to the rotating shaft 22a via the torque limiter 21, thereby transmitting the force to the roller 2a1. Gears G3 and G4 are provided on the rotating shaft 22a. Gears G5 and G6 that mesh with these are provided on the rotating shaft 22b. Therefore, gears G3 and G4 rotate in conjunction with the rotation of the rotating shaft 22a, and the rotational driving force of the motor M2a is transmitted to the other roller 2a2 via the gears G5 and G6 that mesh with them. The torque limiter 21 is configured to slip if a rotational torque exceeding a set torque is generated on the roller 2a1.

[0055] The gear G2 incorporates a one-way clutch 23. The one-way clutch 23 transmits only the rotational driving force in one direction (forward direction) input from the drive motor M2a to the rotating shaft 22a, and is connected to slip when it is subjected to an external force that attempts to rotate in the opposite direction. In this embodiment, the one-way clutch 23 slips when the drive motor M2a rotates in the direction that rotates the roller 2a1, and transmits drive to the rotating shaft 22a when the roller 2a1 attempts to rotate against the driving force of the drive motor M2a. Therefore, as will be described later, when the roller 2a1 is rotated at a reduced speed based on the detection result of the sensor Sa, it is possible to suppress the roller 2a1 from rotating at a speed faster than the rotational speed of the drive motor M2a due to the pressing force of the sheet of the upstream roller pair. This makes it possible to suppress the shifting of the fold position due to the sheet being pressed when the roller 2a1 is rotated at a reduced speed.

[0056] As described later, while the first roller pair 2a is decelerated and rotated by the drive motor M2a based on the detection result of the sensor Sa, the slack portion of the sheet is gripped by the folding roller pair 1a and 1b and the sheet is pulled out. At this time, the rotation direction of the first roller pair 2a by the drive motor M2a is opposite to the rotation direction of the folding roller pair 1a and 1b. When the force pulling the sheet by the folding roller pair 1a and 1b exceeds the conveying force of the sheet by the first roller pair 2a, the torque limiter 21 slips, and the connection between the rotating shaft 22a and the gear G2 is disconnected, causing the first roller pair 2a to rotate in the opposite direction. In other words, the torque limiter 21 allows the first roller pair 2a to rotate in the opposite direction to the direction driven by the drive motor M2a when the sheet is nipped by the folding roller pair 1a and 1b. Therefore, the first roller pair 2a does not obstruct the movement of the sheet being pulled out by the folding roller pair 1a and 1b.

[0057] When the sheet is pulled out from the nip portion between roller 2a1 and roller 2a2 pressed against it by the folding roller pair 1a and 1b, the slip caused by the torque limiter 21 is eliminated, and the driving force from motor M2a is transmitted to roller 2a1, resuming forward rotation.

[0058] The drive transmission mechanism, which includes the torque limiter 21 and the one-way clutch 23 described above, is similarly provided for the other roller pairs 2b to 2d.

[0059] (Folding Sensor) As shown in Figure 3, a first folding sensor Sa is provided as a detection means for detecting the sheet at a position downstream of the first roller pair 2a in the sheet transport direction from the roller pair consisting of the first folding roller 1a and the folding sub-roller 1f toward the first roller pair 2a. The control unit 5, which will be described later, detects the sheet being transported by the roller pair consisting of the first folding roller 1a and the folding sub-roller 1f and the first roller pair 2a using the first folding sensor Sa, and after a predetermined time has elapsed, it reduces the sheet transport speed by the first roller pair 2a to a lower speed than the sheet transport speed by the roller pair consisting of rollers 1a and 1f, thereby creating slack in the sheet. In this embodiment, the state in which the sheet is not taut between the upstream roller pair and the downstream roller pair that grip and transport the sheet will be referred to as slack (or looseness, bending) occurring in the sheet. Details of the control during sheet transport will be described later.

[0060] Similarly, a second folding sensor Sb is provided downstream of the second roller pair 2b in the transport direction of the second roller pair 2b, a third folding sensor Sc is provided downstream of the third roller pair 2c in the transport direction of the third roller pair 2c, and a fourth folding sensor Sd is provided downstream of the fourth roller pair 2d in the transport direction of the fourth roller pair 2d. The control unit 5, similar to the first folding sensor Sa, decelerates the second roller pair 2b to the fourth roller pair 2d when forming slack in the sheet based on the detection results of the second to fourth folding sensors Sb to Sd, thereby forming slack while transporting the sheet with each roller pair.

[0061] (Flying Guide) A first flying guide 4a is provided opposite the nip section a. This flying guide 4a is pivotable between a first position and a second position by a guide motor. When in the first position, it does not obstruct the transport of the sheet by the roller pair 1a and 1f to the first roller pair 2a. On the other hand, when the flying guide 4a pivots to the second position, the sheet transported by the roller pair 1a and 1f is guided by the flying guide 4a and is sent directly to the folding rollers 1a and 1b without being transported to the first roller pair 2a. As a result, the transported sheet is transported without being folded at the nip section a. In other words, the first flying guide 4a enables sheet transport without folding at the nip section a.

[0062] As guide members having the same function as the first skip guide 4a, a second skip guide 4b is provided at a position opposite to the nip portion b, a third skip guide 4c is provided at a position opposite to the nip portion c, and a fourth skip guide 4d is provided at a position opposite to the nip portion d.

[0063] <Sheet Folding Control> Next, the sheet folding control by the sheet folding unit B will be explained. Figure 5 is a control block diagram for controlling the driving of each component of the folding unit B.

[0064] As shown in Figure 5, the control unit 5, which functions as a control means, performs folding on the sheet by controlling various devices (control targets) based on information input from the operation unit 400 and external devices. At this time, the control unit 5 receives detection signals from each folding sensor Sa, Sb, Sc, and Sd, and controls the driving of the folding motors M1a, M1b, M1c, M1d, and M1f that drive the first folding roller 1a, second folding roller 1b, third folding roller 1c, fourth folding roller 1d, fifth folding roller 1e, and folding sub-roller 1f, respectively, based on this information.

[0065] Similarly, the control unit 5 controls the driving of the drive motors M2a, M2b, M2c, and M2d that drive the first roller pair 2a, the second roller pair 2b, the third roller pair 2c, and the fourth roller pair 2d, respectively.

[0066] Furthermore, the control unit 5 controls the drive of the registration motor M207 that drives the registration roller pair 207, and controls the drive of the transport motor M210 that drives the transport roller pair 210.

[0067] Furthermore, the control unit 5 controls the driving of the guide motors M4a, M4b, M4c, and M4d for operating the first launch guide 4a, the second launch guide 4b, the third launch guide 4c, and the fourth launch guide 4d, respectively. In this example, all control targets are controlled by a single control unit, but this configuration is not the only one. For example, a control unit may be provided for each control target, or one control unit may be provided for every two control targets.

[0068] The sheet folding process is performed by driving and controlling each motor via the control unit 5. In this embodiment, as shown in the flowchart of Figure 6, sheet transport is controlled to substantially eliminate any slack in the sheet before folding, thereby enabling the folding process to be executed.

[0069] (Sheet Transport Speed ​​Control) Next, the sheet transport speed control by the control unit 5 during the sheet folding process will be explained using Figures 6 to 9(f). The sheet folding unit B has four folding sections, but the procedure for folding and removing slack from the sheet before folding is the same for all folding sections, so the first folding section will be used as an example here. The control unit 5 controls each control target, thereby executing a series of sequences described later.

[0070] The sheet, transported from the registration roller pair 207 to the folding unit B, is further transported upward in the direction of gravity by the roller pair of the first folding roller 1a and the folding sub-roller 1f (Figure 7(a)). The sheet P, transported by the first folding roller 1a and the folding sub-roller 1f, is then guided by the guide member 3a and reaches the nip portion of the first roller pair 2a (Figure 7(b)). Subsequently, the sheet P is transported a predetermined distance by the roller pair of the first folding roller 1a and the folding sub-roller 1f and the first roller pair 2a (Figure 7(c)).

[0071] Subsequently, based on the detection by sensor Sa of the sheet (leading edge) being transported by the upstream roller pair 1a, 1f and the downstream roller pair 2a (Figure 7(d)), the upstream roller pair 1a, 1f and the downstream roller pair 2a begin a slack-forming operation for folding.

[0072] Here, it is preferable to provide a space between the upstream roller pair 1a, 1f and the downstream roller pair 2a to create slack in the sheet during the folding process. Therefore, it is not possible to provide a guide member that guides the sheet linearly in the shortest possible distance from the roller pair 1a, 1f to the roller pair 2a. The guide member 3a is positioned at an angle that does not hinder the formation of slack in the sheet by the roller pair 1a, 1f and the roller pair 2a, and is capable of guiding the sheet from the upstream roller pair 1a, 1f toward the nip of the downstream roller pair 2a. As shown in Figure 3, guide members 3b that guide the sheet conveyed by the folding roller pair 1a, 1b to the second roller pair 2b, guide member 3c that guides the sheet conveyed by the folding roller pair 1b, 1c to the third roller pair 2c, and guide member 3d that guides the sheet conveyed by the folding roller pair 1c, 1d to the fourth roller pair 2d are also positioned in a similar manner.

[0073] At this time, the transport path until the sheet is handed over to the downstream roller pair 2a varies depending on the characteristics of the sheet, which could cause sagging in the sheet before folding and lead to a misalignment of the folding position. This is a problem that also occurs with roller pairs 2b, 2c, and 2d. The problems of this embodiment will be explained below using Figure 8. A series of sequences are executed by controlling various devices with the control unit 5.

[0074] For example, as shown in Figure 8, sheet PA (solid line), which has a small basis weight and low rigidity, is less stiff and easily bent, while sheet PB (dashed line), which has a large basis weight and high rigidity, is stiffer and less likely to bend (PA and PB are sheets of the same size). Therefore, when the sheets are transported from the upstream roller pair 1a, 1f to the downstream first roller pair 2a, the leading edge of the less rigid sheet PA takes a path closer to the folding roller pair 1a, 1b, while the leading edge of the more rigid sheet PB takes a path further away from the folding roller pair 1a, 1b (almost the shortest distance). Consequently, depending on the characteristics of the sheets, the length of the sheet transport path from the upstream roller pair 1a, 1f to the downstream roller pair 2a is not constant. In other words, before slack is formed for the folding process, sheet PA will be more slack than sheet PB, and sheet PB will be less slack than sheet PA (in this example, there is almost no slack). Such a phenomenon can also occur depending on whether or not the sheet is curled.

[0075] In this state, when the sheet is transported with the transport speed V1 of the upstream roller pair 1a, 1f and the transport speed V2 of the downstream roller pair 2a being V1 ≥ V2, sheet PA will be transported in a more slack state than sheet PB. Therefore, when attempting to create slack in the sheet in order to fold it, according to the detection result of sensor Sa, the timing at which the slack in the sheet is gripped and pulled in by the nip portion a of the first folding roller 1a and the second folding roller 1b will be earlier for sheet PA, which has more slack than sheet PB. As a result, the position at which a fold is formed on sheet PA, which has more slack than sheet PB, will be different from the position at which a fold is formed on sheet PB.

[0076] Thus, if slack was present in the sheet before the slack-forming process for folding began, specifically before the sheet reached the downstream roller pair 2a from the upstream roller pair 1a, 1f, there was a risk that the folding position would be misaligned.

[0077] In other words, the amount of slack that occurs before the leading edge of the sheet reaches the sensor Sa varies from sheet to sheet, causing variations in the position where the fold is formed. Therefore, if the folding position is designed based on a sheet passing through a transport path like sheet PB, the folding position will be shifted for a sheet passing through a transport path like sheet PA. Thus, there was a risk that the folding position would shift depending on the type of sheet.

[0078] Therefore, in this embodiment, the slack described above is substantially eliminated during the period from when the sheet (received from the upstream roller pair 1a, 1f) reaches the transport position (nip portion) by the downstream roller pair 2a until it reaches the detection position by the sensor Sa. After that, slack for the folding process is formed in the sheet. As a result, it is possible to suppress deviations in the folding position due to the characteristics of the sheet, etc. In other words, in this embodiment, slack elimination control is performed to substantially eliminate slack before the sheet transported by the downstream roller pair reaches the sensor Sa. In this embodiment, when the folding process is performed, the upstream transport section roller pair 1a, 1f and the downstream transport section roller pair 2a start rotating before the sheet is transported to the sheet folding unit B by the registration roller pair 207. At this time, the sheet transport speed V2 by the downstream roller pair 2a is controlled to be faster than the sheet transport speed V1 by the upstream roller pair 1a, 1f (Figure 6: St1, St2). In this embodiment, the sheet transport speed V1 by the upstream roller pair 1a, 1f is 780 [mm / s], while the sheet transport speed V2 by the downstream roller pair 2a is set to 858 [mm / s], which is faster than V1. In other words, in this embodiment, the sheet transport speed V2 by the downstream roller pair 2a is set to be approximately 10% faster than the sheet transport speed V1 by the upstream roller pair 1a, 1f.

[0079] As a result, the sheet being transported by the upstream roller pair 1a, 1f and the downstream roller pair 2a is pulled by the downstream roller pair 2a (Figure 7(c)). Therefore, even if there is slack in the sheet when the leading edge reaches the downstream roller pair 2a, the slack is eliminated (the slack disappears) as the sheet is transported by the upstream roller pair 1a, 1f and the downstream roller pair 2a before it reaches the detection position by the sensor Sa. In other words, disturbances in the posture between roller pairs due to the type of sheet are eliminated.

[0080] The inventors have found that under conditions of 25°C and 50% humidity, the basis weight is 52 g / m². ２ Sheet PA with a basis weight of 128 g / m² ２ Verification was performed using sheet PB. As a result, the sheet length from the nip of the upstream roller pair 1a, 1f to the nip of the downstream roller pair 2a was 47.3 mm for sheet PA and 47.1 mm for sheet PB. As described above, the sheet transport speed V1 by the upstream roller pair 1a, 1f was set to 780 [mm / s], the sheet transport speed V2 by the downstream roller pair 2a was set to 858 [mm / s], and the sensor Sa was placed 27.8 mm away in the transport direction from the nip of the downstream roller pair 2a. With this configuration, it was possible to substantially eliminate the slack (looseness) that occurred in sheet PA before the leading edge of the sheet reached sensor Sa. In this example, sheet PB hardly slackened due to its rigidity.

[0081] Then, based on the detection of the sheet by sensor Sa, a folding process (creation of slack to form a fold) is performed on the sheet. Specifically, based on the detection of the sheet by sensor Sa, the speed control is switched so that the sheet transport speed of roller pair 2a is slower than the sheet transport speed of roller pairs 1a and 1f. As a result, since the slack according to the characteristics of the sheet is substantially eliminated in advance at the stage before the slack for folding is formed, it is possible to suppress misalignment of the fold position. Furthermore, it is possible to suppress misalignment of the fold position not only depending on the type of sheet, but also depending on whether or not the sheet is curled, even if it is the same type of sheet. Note that the numerical values ​​used in the above verification are merely examples. Any configuration that can eliminate the slack in the sheet that occurred before folding and then create slack in the sheet for folding after the slack has been eliminated is acceptable, and is not limited to the numerical values ​​in this verification result.

[0082] In the example of this embodiment described above, the sheet transport speed V2 of roller pair 2a was set to be 10% faster than the sheet transport speed V1 of the upstream roller pairs 1a and 1f, but this is not the only option. For example, any speed difference that does not cause damage to the sheets transported by roller pair 2a and roller pairs 1a and 1f is acceptable.

[0083] In the embodiments described above, an example was explained in which the shift in the folding position of the sheet is suppressed by substantially eliminating the slack that occurred before the folding process was performed on the sheet. However, the scope of application of the present invention is not limited to this. It is not necessary to completely remove the slack of the sheet as described above, as long as a similar effect can be obtained. For example, even if some slack remains in the sheet at the start of slack formation for the folding process, the slack of the sheet can be converged to a certain value, thereby suppressing the shift in the folding position of the sheet from the desired position.

[0084] Furthermore, there may be some cases where the sheet does not sag (the sag that leads to misalignment of the folding position as described above) depending on the basis weight of the sheet and whether or not it curls, and the same can be applied to such sheet folding processing devices.

[0085] Furthermore, various speed settings are possible as long as they can achieve similar effects, not limited to the examples described above. For example, when the sheet is initially introduced to the upstream roller pair 1a, 1f, the sheet transport speeds of the upstream roller pair 1a, 1f and the downstream roller pair 2a are set to be the same. Then, during the transport process from when the sheet fed from the nip of the upstream roller pair 1a, 1f reaches the downstream roller pair 2a until the sheet is detected by the sensor Sa, the following speed settings may be used. In other words, a period may be set during the above transport process in which the sheet transport speed of the roller pair 2a is faster than the sheet transport speed of the upstream roller pair 1a, 1f, thereby substantially eliminating the slack in the sheet or converging the slack to a constant value. At this time, the control unit 5 determines the timing when the sheet reaches the downstream roller pair 2a based on the detection signal from the sensor (not shown), and performs the above speed control from this point until a predetermined time has elapsed. This predetermined time corresponds to the time from the above timing until the sheet is detected by the sensor Sa.

[0086] After the slack in the sheet that occurred before the folding process is eliminated by the difference in transport speed between roller pair 1a, 1f and the downstream roller pair 2a, the downstream roller pair 2a rotates freely due to the action of the torque limiter 21, so that it does not pull the sheet with the upstream roller pair 1a, 1f, and transports the sheet together with the upstream roller pair 1a, 1f at approximately the same transport speed as the upstream roller pair 1a, 1f.

[0087] Furthermore, by allowing the downstream roller pair 2a to rotate freely using the torque limiter 21, the sheet transport speed V2 of the roller pair 2a driven by the drive motor M2a can be set significantly higher than the sheet transport speed V1 of the roller pairs 1a and 1f. Therefore, even if the sheet transport speed V2 of the roller pair 2a is increased, the sheet will not be pulled too hard between the roller pairs 1a and 1f, and any slack that occurs before the folding process can be eliminated. As a result, the rate of increase in the sheet transport speed of the roller pair 2a can be kept constant regardless of the thickness or number of sheets, that is, regardless of the degree of bending of the sheet, as shown in Figure 8.

[0088] As described above, when the downstream end P1 of the sheet is detected by the folding sensor Sa (Figure 7(d)), the conveying speed of the roller pair 2a is reduced to V3 after a predetermined time has elapsed and it is rotated (Figure 6: St3-St5). At this time, the conveying speed V3 is slower than the sheet conveying speed V1 by the upstream roller pair 1a, 1f. As a result, the conveyed sheet gradually forms slack between the upstream roller pair 1a, 1f and the downstream roller pair 2a (Figure 9(a)). When the slack becomes large enough, it is pulled into the nip portion a of the folding roller pair 1a, 1b (Figure 9(b)). The predetermined time during which the sheet is conveyed after passing the folding sensor Sa is set according to the size and folding position of the sheet.

[0089] After the slack portion of the sheet is pulled into the nip portion a of the folding roller pair 1a, 1b, the sheet is conveyed by the folding roller pair 1a, 1b, thereby forming a fold Pa in the sheet. In this embodiment, the folding process is defined as forming slack in the sheet and gripping the slack portion of the sheet with the folding roller pair 1a, 1b. At this time, the rotational direction transmitted to the roller pair 2a that is nipping the sheet and the rotational direction transmitted to the folding roller pair 1a, 1b are inversely related, but the gripping force (nip pressure) by the folding roller pair 1a, 1b is set to be greater than the set torque of the torque limiter 21 than that of the roller pair 2a. Therefore, the sheet gripped by the folding roller pair 1a, 1b is conveyed in such a way that it is pulled out from the roller pair 2a.

[0090] When performing a continuous folding process on a sheet in which the first fold has been formed in the first folding section, the folded edge Pa of the sheet is used as the leading edge and the sheet is transported to the second roller pair 2b, as shown in Figure 9(c). At this time, as shown in Figure 9(d), the folding roller pair 1a and 1b become the upstream transport section, and the second roller pair 2b becomes the downstream transport section. Then, by controlling the sheet transport speed of the upstream folding roller pair 1a and 1b and the downstream second roller pair 2b in the same manner as the folding process described above, the slack in the sheet is eliminated, and then slack for folding (crease formation) is created in the sheet and it is sent to the nip section b between the second folding roller 1b and the third folding roller 1c (Figure 9(e)). Then, by continuing to transport the sheet with the second folding roller 1b and the third folding roller 1c, the crease Pb is formed and the second folding process is performed. Subsequently, by activating the lifting guides 4c and 4d, the sheets are transported without folding by the third folding roller 1c and the fourth folding roller 1d, and the fourth folding roller 1d and the fifth folding roller 1e. The transport roller pair 210 then transports the sheets from the sheet folding unit B to the downstream roller pair, and the folded sheets are discharged into the folding tray 209.

[0091] The folding process described above explains the operation when performing an inward tri-fold (C-fold). However, when performing accordion folds, which create three or more folds in the sheet, or outward tri-folds (Z-folds), the folding process is carried out by appropriately controlling each roller of the sheet folding unit B. In this case, as described above, by eliminating the slack in the sheet and then creating slack for the folding process, it is possible to suppress the misalignment of the fold positions depending on the type of sheet. Furthermore, if folding is not performed at any of the four folding sections of the sheet folding unit B, it is possible to transport the sheet without folding by operating the corresponding skip guide.

[0092] As described above, the sheet folding apparatus of this embodiment can improve the accuracy of the sheet's folding position by eliminating the slack in the sheet that has occurred between the upstream roller pairs 1a and 1f and the roller pair 2a, and then performing the folding process on the sheet.

[0093] Next, the elimination of sheet slack in the above-described embodiment will be explained using Figures 10(a) and 10(b). Figures 10(a) and 10(b) illustrate the sheet slack between pairs of rollers that occurs before the folding process.

[0094] Figure 10(a) shows an example of a configuration for substantially eliminating slack between roller pairs. The sheet, gripped and conveyed by the nip n1 of the folding roller 1a and the folding sub-roller 1f, reaches the nip n2 of the first conveyor roller pair 2a as its leading edge is guided by the guide member 3a. In Figure 10(a), X1 is defined as the intersection of a perpendicular line extending through the nip n1 to a virtual line (shown as a dashed line) connecting the rotation center of the folding roller 1a and the rotation center of the folding sub-roller 1f, and the guide surface of the guide member 3a. In this example, when the distance from the nip n1 to the intersection X1 is L1 and the distance from the intersection X1 to the nip n2 is L2, slack of length L1 + L2 may occur in the sheet between the roller pair of the folding roller 1a and the folding sub-roller 1f and the first conveyor roller pair 2a. In this case, the sensor Sa is positioned so that the slack L1 + L2 of the sheet that occurred before the folding process can be eliminated by performing the slack elimination process described above. Specifically, after the slack (L1 + L2) in the sheet is eliminated by the transport control described above, the sensor Sa is positioned at the location where the leading edge of the sheet reaches. By positioning the sensor Sa in this way, it is possible to eliminate the slack in the sheet that occurred before the folding process and then create slack in the sheet for the folding process. The slack elimination process in this embodiment can eliminate at least the slack L1 + L2 described above, and with this configuration, it is possible to suppress misalignment of the folding position when folding the sheet.

[0095] Next, another example will be explained using Figure 10(b). The position shown in Figure 10(b) is an example in which the sheet reaches the nip n2 of the first transport roller pair 2a by following a path even longer than the sheet path shown in Figure 10(a). In Figure 10(b), the nearest contact point X2 is defined as the position on the guide surface of the guide member 3a that is closest to the folding roller 1b (an example of a folding means) among the guide surfaces that the sheet can contact. Note that the nearest contact point X2 does not include the position where a sheet that has failed to transport will contact, and is the point closest to the folding roller 1b that a sheet that can be folded normally can contact when guided along the guide surface of the guide member 3a.

[0096] In the example shown in Figure 10(b), when the distance from the nip n1 between the folding roller 1a and the folding sub-roller 1f to the nearest contact point X2 is L3, and the distance from the nearest contact point X2 to the nip n2 of the first transport roller pair 2a is L4, a slack of length L3 + L4 may occur in the sheet between the roller pair formed by the folding roller 1a and the folding sub-roller 1f and the first transport roller pair 2a. In this case, the sensor Sa is positioned so that the slack L3 + L4 of the sheet that occurred before the folding process can be eliminated by performing the slack elimination process described above. Specifically, the sensor Sa is positioned at the location where the leading edge of the sheet reaches after the slack (L3 + L4) in the sheet has been eliminated by the transport control described above. By positioning the sensor Sa in this location, it is possible to eliminate the slack in the sheet that occurred before the folding process and then create slack in the sheet for the folding process. The sagging elimination process in this embodiment can eliminate at least the sagging L3 + L4 described above, and with this configuration, misalignment of the folding position when folding the sheet can be suppressed.

[0097] In the above-described embodiment, the speed of the downstream roller pair (first roller pair 2a) was increased before the sheet was transported to the sheet folding unit B. However, the speed may be increased after the sheet reaches the downstream roller pair (first roller pair 2a). Alternatively, a sensor may be provided to detect slack between the downstream roller pair (first roller pair 2a) and the upstream roller pair (first folding roller 1a, folding sub-roller 1f), and the speed of the downstream roller pair (first roller pair 2a) may be increased only if slack is detected before the folding process.

[0098] Furthermore, in the above-described embodiment, the slack in the sheet was eliminated by making the transport speed V2 of the downstream roller pair (first roller pair 2a) faster than the transport speed V1 of the upstream roller pair (first folding roller 1a, folding sub-roller 1f). However, other configurations are also acceptable as long as they can eliminate the slack that occurs before the slack is formed for the folding process. For example, the slack in the sheet may be eliminated by making the transport speed V1 of the upstream roller pair (first folding roller 1a, folding sub-roller 1f) slower than the transport speed V2 of the downstream roller pair (first roller pair 2a). In any case, it is sufficient to eliminate the slack in the sheet by controlling the transport speed V2 of the downstream roller pair (first roller pair 2a) to be relatively faster than the transport speed V1 of the upstream roller pair (first folding roller 1a, folding sub-roller 1f).

[0099] Furthermore, the configuration does not have to be limited to a pair of rollers, as long as it can eliminate the slack in the sheet. For example, a separation mechanism can be provided to separate a pair of rollers located vertically downward (the first folding roller 1a and folding sub-roller 1f in this embodiment), and when the sheet is nipped by a pair of rollers vertically upward (the first pair of rollers 2a in this embodiment), the pair of rollers vertically downward is separated, and then the sheet is nipped again, thus eliminating the slack in the sheet by utilizing gravity. Alternatively, after separating the upstream pair of rollers, the sheet may be pulled in the opposite direction to the conveying direction by another member to eliminate the slack in the sheet.

[0100] In the embodiment described above, the transport speed V3 of the first roller pair 2a was set slower than the transport speed V1 of the first folding roller 1a and folding sub-roller 1f to create slack in the sheet for folding (forming a crease). However, other configurations are acceptable as long as they can create slack in the sheet. For example, the rotation direction of the first roller pair 2a may be reversed from the rotation direction of the first folding roller 1a and folding sub-roller 1f, that is, the sheet transport direction may be reversed to create slack in the sheet for folding between the first roller pair 2a and the roller pair formed by the first folding roller 1a and folding sub-roller 1f. Even in this case, as described above, the shift in the folding position of the sheet can be suppressed by controlling the slack that has formed before the folding process.

[0101] In the embodiments described above, folding roller 1a and folding roller 1b are examples of folding means, folding roller 1a and folding sub-roller 1f are examples of first conveying means, and roller pair 2a is an example of second conveying means. This configuration is merely an example, and other configurations are acceptable as long as they achieve similar effects. For example, in this embodiment, the folding means and some of the rollers of the first conveying means are used interchangeably, but separate roller pairs may be used to configure the folding means and the first conveying means.

[0102] Although the present invention has been described with reference to exemplary embodiments, the present invention is not limited to the exemplary embodiments disclosed. The scope of the following claims is given in the broadest sense to encompass all variations, equivalent structures and functions.

[0103] This application claims priority based on Japanese Patent Application No. 2025-069052, filed on 18 April 2025, and Japanese Patent Application No. 2026-066763, filed on 15 April 2026, and all of the contents of those applications are incorporated herein by reference.

Claims

1. A sheet folding device comprising: a first conveying means for conveying a sheet to a first position; a second conveying means for conveying the sheet received from the first conveying means to a second position; a detection means for detecting a sheet at a third position downstream of the second position in the sheet conveying direction from the first position to the second position; a folding means for performing a folding process on the sheet by gripping and conveying the slack in the sheet formed between the first position and the second position based on the output of the detection means; and a control means for controlling the operation of the first conveying means and the second conveying means in the sheet conveying process from the second position to the third position so that the slack that occurred in the sheet being conveyed from the first position to the second position is substantially eliminated.

2. The sheet folding apparatus according to claim 1, characterized in that the control means controls the sheet conveying speed by the second conveying means to be faster than the sheet conveying speed by the first conveying means during the conveying process.

3. An image forming system comprising an image forming apparatus for forming an image on a sheet, and a sheet folding apparatus according to claim 1 or 2 for performing a folding process on the sheet on which the image has been formed by the image forming apparatus.

4. A sheet folding device comprising: a first conveying means for conveying a sheet to a first position; a second conveying means for conveying a sheet received from the first conveying means to a second position; a detection means for detecting a sheet at a third position downstream of the second position in the sheet conveying direction from the first position to the second position; a folding means for performing a folding process on a sheet by gripping and conveying the slack in the sheet formed between the first position and the second position based on the detection result of the detection means; and a control means for controlling the operation of the first conveying means and the second conveying means so that the sheet conveying speed of the second conveying means is faster than the sheet conveying speed of the first conveying means for a period of time during the sheet conveying process from the second position to the third position.

5. The sheet folding device according to claim 4, comprising: a drive source; and a drive transmission means for transmitting rotational driving force from the drive source to the second conveying means, wherein the drive transmission means interrupts the transmission of drive from the drive source to the second conveying means when a load exceeding a predetermined amount is applied to the second conveying means, and the control means makes the sheet conveying speed of the first conveying means faster than the sheet conveying speed of the second conveying means based on the detection result of the detection means, and maintains the direction of the rotational driving force applied from the drive source.

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