Sheet transport device and image forming apparatus

Abstract

The present invention provides a sheet transport device and an image forming apparatus that can suppress damage to the sheet caused by the flapper. [Solution] A sheet conveying device comprising: a first conveying path through which sheets are conveyed; a reversing conveying path that reverses the conveying direction of sheets conveyed from the first conveying path; a second conveying path through which sheets conveyed from the reversing conveying path are conveyed; a reversal switching unit that switches between a first position for guiding sheets from the first conveying path to the reversing conveying path and a second position for guiding sheets from the reversing conveying path to the second conveying path; and a drive unit that switches the reversal switching unit between the first and second positions, wherein the second position is a position in which the reversal switching unit does not block the second conveying path but blocks the first conveying path, and the first position is a position in which the reversal switching unit does not block the first and second conveying paths and allows sheets to be conveyed from the reversing conveying path to the second conveying path.

Description

Technical Field

[0001] The present invention relates to a sheet conveying device for conveying a sheet and an image forming device for forming an image on the sheet.

Background Art

[0002] An image forming apparatus corresponding to a cut sheet generally has a reversing mechanism that performs a switchback operation to switch the conveying direction of the sheet using a reversing roller or a flapper which is a reversing switching member, and switches the front and back of the printed surface of the sheet. The flapper of the reversing mechanism in Patent Document 1 is biased in one direction by the self-weight of the flapper itself and a biasing spring, and the flapper is rotated by the propelling force of the sheet.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it is difficult for paper with low sheet rigidity to push aside a passive flapper as in Citation Document 1. Further, since the flapper is conveyed while being pushed aside by the sheet, there is a risk that the flapper may damage the sheet surface. Therefore, in a high-speed machine that requires high productivity and wide media compatibility, it is preferable to use a drive flapper that switches the posture of the flapper using an actuator instead of a passive flapper. However, depending on the interval between sheets, there is a risk that the flapper may contact the rear end of the sheet and damage the sheet.

[0005] Therefore, an object of the present invention is to provide a sheet conveying device and an image forming device capable of suppressing damage to the sheet by a flapper.

Means for Solving the Problems

[0006] One aspect of the present invention is a sheet conveying device comprising: a first conveying path on which a sheet is conveyed; a reversing conveying path that reverses the conveying direction of the sheet conveyed from the first conveying path; a second conveying path on which the sheet conveyed from the reversing conveying path is conveyed; a reversal switching unit that switches between a first position for guiding the sheet from the first conveying path to the reversing conveying path and a second position for guiding the sheet from the reversing conveying path to the second conveying path; and a drive unit that switches the reversal switching unit between the first and second positions, wherein the second position is a position in which the reversal switching unit does not block the second conveying path but blocks the first conveying path, and the first position is a position in which the reversal switching unit does not block the first and second conveying paths and a sheet can be conveyed from the reversing conveying path to the second conveying path. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress damage to the sheet caused by the flapper. [Brief explanation of the drawing]

[0008] [Figure 1] Cross-sectional view of an image forming system. [Figure 2] Cross-sectional view of the second reversal section. [Figure 3] Reversing flapper drive and reversing flapper according to the first embodiment. [Figure 4] Paper transport and reversing flapper operation in the first embodiment. [Figure 5] Paper transport and reversing flapper operation in the first embodiment. [Figure 6] Paper transport and reversing flapper operation in the first embodiment. [Figure 7] Paper transport and reversing flapper operation in the first embodiment. [Figure 8] Paper transport and reversing flapper operation in the first embodiment. [Figure 9] Paper transport and reversing flapper operation in the first embodiment. [Figure 10]Paper conveyance and reverse flapper operation in the first embodiment. [Figure 11] Reverse flapper drive and reverse flapper in the second embodiment. [Figure 12] Cross-sectional view of the second reversing section in the second embodiment. [Figure 13] Block diagram of the second reversing section. [Figure 14] Cross-sectional view of the reversing module. [Figure 15] Cross-sectional view of the fixing module. [Figure 16] Cross-sectional view of the periphery of the pre-reverse switching section. [Figure 17] Cross-sectional view of the periphery of the reverse flapper.

Mode for Carrying Out the Invention

[0009] Hereinafter, the present embodiment will be described with reference to the drawings. The following-described embodiment is a preferred embodiment of the present invention, and thus various technically preferable limitations are imposed. However, the scope of the present invention is not unduly limited by the following description. Also, not all of the configurations described in the present embodiment are essential constituent elements of the present invention.

[0010] <First Embodiment> In the present embodiment, the case where the image forming system is applied to the inkjet recording system 1 will be described. FIG. 1 is a schematic diagram showing an example of the schematic configuration of the inkjet recording system 1. This inkjet recording system 1 is a sheet-fed inkjet recording system 1 that manufactures a recording material in which an ink image is formed on a sheet using two liquids, a reaction liquid and ink.

[0011] The inkjet recording system 1 of the present embodiment is composed of a combination of an image forming apparatus and a plurality of sheet conveying devices. Here, a device that is self-supporting and independent in a housing by means of peripheral components such as casters or adjusters will be described by referring to it as a module.

[0012] The inkjet recording system 1 is composed of a paper feeding module 100, a printing module 200, a drying module 300, a fixing module 400, a cooling module 500, a reversing module 600, and a paper discharging and stacking module 700. The cut paper sheets supplied from the paper feeding module 100 are conveyed along the conveyance path, processed by each module, and discharged to the paper discharging and stacking module 700 as a sheet discharging device.

[0013] The paper feeding module 100, which is an example of a sheet feeding device, has storage bins 110a, 110b, and 110c for storing sheets. The storage bins 110a, 110b, and 110c are configured to be pull-outable to the front side of the device. The sheets are fed one by one in each of the storage bins 110a, 110b, and 110c by a separation belt and conveyance rollers (not shown) and conveyed to the printing module 200. Note that the number of the storage bins 110a, 110b, and 110c is not limited to three, and the configuration may have one, two, or four or more.

[0014] The printing module 200, which is an example of an image forming device for forming an image on a sheet, has an image forming pre-registration correction unit (not shown), a printing belt unit 220, and a recording unit 230. The sheet conveyed from the paper feeding module 100 is corrected for the inclination and position of the paper by the image forming pre-registration correction unit and conveyed to the printing belt unit 220. The recording unit 230 is disposed at a position facing the printing belt unit 220 across the conveyance path. The recording unit 230 is a sheet processing unit that performs a recording process (printing) on the conveyed sheet from above by a recording head to form an image. A plurality of recording heads are arranged along the conveyance direction. In the present embodiment, in addition to four colors of Y (yellow), M (magenta), C (cyan), and Bk (black), there are a total of five line-type recording heads corresponding to the reaction liquid. Note that the number of colors and the number of recording heads are not limited to five.

[0015] The inkjet method can employ methods using heating elements, piezoelectric elements, electrostatic elements, MEMS elements, etc. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The sheet printed by the recording unit 230 is transported by a print belt unit 220, ensuring clearance with the recording head. The sheet printed by the recording unit 230 is detected for image misalignment and color density by an inline scanner (not shown) located downstream of the recording unit 230 in the transport direction. The detection results are used to correct the printed image. In this embodiment, the recording unit 230 is an example of an image forming unit.

[0016] The drying module 300 includes a decoupling section 320, a drying belt unit 330, and a hot air blowing section 340. It reduces the liquid component in the ink applied to the sheet by the recording section 230 of the print module 200, thereby improving the adhesion between the sheet and the ink. The sheet printed by the recording section 230 of the print module 200 is transported to the decoupling section 320 located within the drying module 300. In the decoupling section 320, the sheet can be transported by air pressure from above and friction of the belt. By loosely holding the sheet on the belt during transport, it prevents the sheet from shifting on the print belt unit 220, which forms the ink image. The drying belt unit 330 is located below the sheet being transported, and the hot air blowing section 340 is located above the sheet being transported, with the belt in between them.

[0017] The sheets conveyed from the decoupling section 320 are transported by adsorption using the drying belt unit 330, and at the same time, the ink-applied surface is dried by hot air from the hot air blowing section 340. In addition to the method of applying hot air, the drying method may also be configured by combining a method of irradiating the sheet surface with electromagnetic waves (such as ultraviolet or infrared rays) or a conductive heat transfer method by contact with a heating element.

[0018] The fixing module 400 has a fixing belt unit 410. The fixing belt unit 410 has an upper belt unit and a lower belt unit, and the ink can be fixed to the sheet by passing the sheet conveyed from the drying module 300 between the heated upper belt unit and the lower belt unit.

[0019] The cooling module 500 has multiple cooling units 510 and cools the high-temperature sheet conveyed from the fixing module 400. The cooling units 510 are configured to cool the sheet by drawing in outside air into the cooling box with a fan, increasing the pressure inside the cooling box, and blowing air from nozzles formed in the conveying guide onto the sheet. The cooling units 510 are positioned both above and below the conveying path to cool the sheet from both sides.

[0020] Furthermore, the cooling module 500 has a transport path switching unit 520, which can switch the transport path of the sheet depending on whether the sheet is being transported to the inversion module 600 or to the double-sided transport path used during double-sided printing. During double-sided printing, the sheet is transported to the transport path below the cooling module 500. In this case, the sheet is further transported from the cooling module 500 along the double-sided transport path of the fuser module 400, drying module 300, print module 200, and paper feed module 100. The double-sided transport unit 430 of the fuser module 400 is provided with a first inversion unit 420 that inverts the front and back sides of the sheet. The sheet is then transported again to the pre-image registration correction unit, print belt unit 220, and recording unit 230 of the print module 200, where it is printed.

[0021] The reversal module 600 has a second reversal unit 641, which can reverse the front and back sides of the conveyed sheet, and the orientation of the ejected sheet can be freely changed.

[0022] The paper output and stacking module 700 has a top tray 720 and a stacking section 750, and aligns and stacks the sheets conveyed from the reversing module 600. Furthermore, the paper output and stacking module 700 has a top tray switching section 721. The top tray switching section 721 switches the destination of the sheets between the top tray 720 and the stacking section 750.

[0023] The control unit 10 includes a CPU, RAM, and ROM, and controls each part of the inkjet recording system 1. Based on detection signals input from various sensors and information stored in ROM, the CPU outputs output signals to each electrical component to operate it at the desired timing and with the required control amount. ROM and RAM store information data necessary for controlling each part, and the CPU reads data from the information stored in ROM and writes data to RAM. In this embodiment, the control unit 10 may also control an external computer connected to the inkjet recording system 1.

[0024] <Inversion Module> Next, the configuration of the inversion module 600 will be explained using Figures 2 and 14. Figure 14 is a cross-sectional view showing the sheet transport path of the inversion module 600. Figure 2 is a cross-sectional view showing the second inversion section 641 of the inversion module 600. The inversion module 600 includes an inlet transport path 607, a horizontal transport path 608, an outlet transport path 609, a downward transport path 605, a pre-inversion transport path 601, an inversion transport path 602, a post-inversion transport path 603, a return transport path 604, and an upward transport path 606. Furthermore, the inversion module 600 includes an inlet switching section 624, a pre-inversion switching section 623, an inversion flapper 610 which is an inversion switching section, an inversion roller 620, an inversion sensor 630, a plurality of transport rollers, and a plurality of sensors.

[0025] The reversing module 600 has an inlet transport path 607 that receives and transports sheets in a substantially horizontal direction from an upstream device (cooling module 500 in this embodiment), and an inlet switching section 624 that branches and switches the transport path from the inlet transport path 607. One of the paths branched from the inlet switching section 624 is a horizontal transport path 608 that transports sheets in a substantially horizontal direction to the merging section 625. Downstream from the merging section 625 in the sheet transport direction is an outlet transport path 609 for handing over sheets to a downstream device connected to the reversing module 600 (paper discharge and loading module 700 in this embodiment), and this is also a substantially horizontal transport path configuration. The horizontal transport path 608 connects the inlet switching section 624 and the merging section 625.

[0026] The other path branched from the inlet switching section 624 is a downward transport path 605 that bends approximately vertically downward from the inlet transport path 607 and transports the sheet approximately vertically downward. At the downstream end of the downward transport path 605 in the sheet transport direction, there is a pre-reversal switching section 623 that switches the path to one of two transport paths, the pre-reversal transport path 601 and the return transport path 604.

[0027] Figure 16 shows a cross-sectional view of the area around the pre-reversal switching section 623. Figure 16(a) shows the pre-reversal switching section 623 when guiding the sheet to the pre-reversal transport path 601. Figure 16(b) shows the pre-reversal switching section 623 when guiding the sheet to the return transport path 604. The pre-reversal switching section 623 swings around the pre-reversal switching axis 623a.

[0028] Viewed from the sheet width direction, the pre-reversal switching section 623 switches between a position overlapping with the transport guide 601b that constitutes the pre-reversal transport path 601 (Figure 16(b)) and a position overlapping with the transport guide 604b that constitutes the return transport path 604 (Figure 16(a)). The transport guide 601b is the transport guide 601a and 601b that constitute the transport path 601, located at a position farther from the pre-reversal switching axis 623a. The transport guide 604b is the transport guide 604a and 604b that constitute the transport path 604, located at a position farther from the pre-reversal switching axis 623a. In other words, the pre-reversal switching section 623 switches between a position that blocks the pre-reversal transport path 601 and a position that blocks the return transport path 604.

[0029] As shown in Figure 14, the pre-reversal transport path 601 is continuous with the reversal transport path 602, which switches back the leading and trailing ends of the sheet in the direction of travel. At the downstream end of the pre-reversal transport path 601, there is a reversal flapper 610 that guides the sheet from the pre-reversal transport path 601 to the reversal transport path 602, and then guides the sheet to the post-reversal transport path 603, which transports the sheet after it has been switched back in the reversal transport path 602.

[0030] The downstream end of the return transport path 604 and the downstream end of the transport path 603 after reversal merge and continue to the upward transport path 606 that returns towards the exit transport path 609. The return transport path 604 connects the pre-reversal switching section 623 and the merging section 626. When a sheet is discharged via the downward transport path 605, the return transport path 604, and the upward transport path 606, the printed side of the sheet is discharged facing upward (face up). On the other hand, when a sheet is discharged via the downward transport path 605, the pre-reversal transport path 601, the reversal transport path 602, the post-reversal transport path 603, and the upward transport path 606, the printed side of the sheet is discharged facing downward (face down).

[0031] As described above regarding the transport path configuration, the reversal module 600 is a sheet reversal transport device with three patterns of sheet transport paths. The three patterns of sheet transport paths are: a sheet transport path that reroutes the received sheet, a reversal transport path that reroutes the received sheet and also reverses it before transport, and a sheet transport path that transports the received sheet in a nearly straight line without bending it.

[0032] Specifically, the first sheet transport route is one in which the sheet is transported from the inlet transport path 607 to the exit transport path 609 via the downward transport path 605, the return transport path 604, and the upward transport path 606. The second sheet transport route is one in which the sheet is transported from the inlet transport path 607 to the exit transport path 609 via the downward transport path 605, the pre-reversal transport path 601, the reversal transport path 602, the post-reversal transport path 603, and the upward transport path 606. The third sheet transport route is one in which the sheet is transported from the inlet transport path 607 to the exit transport path 609 via the horizontal transport path 608.

[0033] Three sheet transport paths are available, allowing selection of a transport path suitable for the sheet type and job. When using relatively low-rigidity sheets, even if the sheets are transported via the detour path through the downward transport path 605 and the upward transport path 606, the risk of image damage caused by bending the sheets during transport is low, thus ensuring the quality of the final product. However, when using relatively high-rigidity sheets, transporting them via the detour path through the downward transport path 605 and the upward transport path 606 increases the risk of image damage caused by bending the sheets during transport, potentially reducing the quality of the final product. In other words, when a relatively high-rigidity sheet is bent, the rigidity, which is the force that tries to return it to its original planar shape, increases the contact force between the sheet and the sheet transport path. Because the sheet is transported under such high contact force, there is a risk of scratches occurring on the surface of the sheet in contact with the sheet transport path, or the image peeling off. For this reason, for high-rigidity sheets, it is preferable to use a transport path that minimizes sheet bending.

[0034] For example, if an inspection module 800, which is a reading device, is installed between the cooling module 500 and the inversion module 600, the sheet is transported via a downward transport path 605 and an upward transport path 606 in order to perform a purge inspection. If the image read by the inspection module 800 is a normal image, the sheet is discharged to the loading section 750; if the read image is an abnormal image, the sheet is discharged to the top tray 720. This allows the control unit 10 to obtain the result of the purge inspection before the leading edge of the sheet reaches the top tray switching section 721.

[0035] For example, when printing jobs that are transported downstream face up and jobs that are transported downstream face down are randomly mixed together, it is possible to select a mode that feeds the paper through the downward transport path 605 and the upward transport path 606. In the case of face-down jobs, the sheets must be transported through the downward transport path 605 and the upward transport path 606. In the case of face-up jobs, it is possible to feed the paper through the horizontal transport path 608, but if a face-up job follows a face-down job, the spacing between the sheets in the jobs needs to be relatively wide. Therefore, in this embodiment, if both face-up and face-down jobs are transported through the downward transport path 605 and the upward transport path 606, the decrease in overall productivity can be suppressed.

[0036] <Second Reversal Section> As shown in Figure 2, the second reversal unit 641 includes a pre-reversal transport path 601, a reversal transport path 602, a post-reversal transport path 603, a reversal roller 620, a reversal sensor 630, and a reversal flapper 610. Specifically, the second reversal unit 641 includes a pre-reversal transport path 601 through which the sheet passes before the switchback, a reversal transport path 602 that reverses the leading and trailing ends of the sheet in the direction of travel, and a post-reversal transport path 603 through which the sheet passes after the switchback. In Figure 2, the merging point 627 is the point where the pre-reversal transport path 601, the reversal transport path 602, and the post-reversal transport path 603 merge.

[0037] Furthermore, the second reversal unit 641 has reversal flappers 610 positioned at the end of the pre-reversal transport path 601 and the starting point of the post-reversal transport path 603 in the sheet transport direction, forming part of the pre-reversal transport path 601 and part of the post-reversal transport path 603. The reversal roller 620 is positioned on the reversal transport path 602, and for the switchback operation, the reversal roller 620 receives and transports the sheet before the switchback, stops the sheet at a predetermined position, and then transports the sheet in the reverse direction. The reversal sensor 630 is positioned on the reversal transport path 602 and detects the position of the sheet in order to control the timing of stopping the sheet during the switchback operation by the reversal roller 620. Note that the arrows in Figure 2 indicate the direction of sheet transport.

[0038] The pre-reversal transport path 601 is a curved transport path, while the post-reversal transport path 603 has a substantially horizontal transport path configuration. In this embodiment, near the confluence point 627, with the confluence point 627 as the center, the smaller of the angles formed by the reversal transport path 602 and the post-reversal transport path 603 is greater than the smaller of the angles formed by the reversal transport path 602 and the pre-reversal transport path 601. In Figure 2, the smaller of the angles formed by the reversal transport path 602 and the post-reversal transport path 603 is 180°. In this embodiment, the pre-reversal transport path 601 is an example of a first transport path, and the post-reversal transport path 603 is an example of a second transport path. However, the post-reversal transport path 603 may also be curved. It is preferable that the curvature of the post-reversal transport path 603 is smaller than the curvature of the pre-reversal transport path 601. In other words, it is preferable that the curvature of the post-reversal transport path 603 is smaller than the curvature of the pre-reversal transport path 601.

[0039] However, the pre-reversal transport path 601 may be integrated with the downward transport path 605. That is, in the pre-reversal transport path 601, the upstream side in the sheet transport direction may be substantially vertical, and the downstream side in the sheet transport direction where the reversal flapper 610 is located may be bent.

[0040] The mechanism for operating the inverting flapper 610 will now be described. Figure 3(a) shows the inverting flapper 610 and the inverting flapper drive unit 611. Figure 3(b) shows the inverting flapper 610 in the pre-inversion guiding position (first position) which guides the sheet from the pre-inversion transport path 601 to the inversion transport path 602. Figure 3(c) shows the inverting flapper 610 in the post-inversion guiding position (second position) which guides the sheet from the inversion transport path 602 to the post-inversion transport path 603.

[0041] The reversing flapper 610 is equipped with a reversing flapper shaft 612, and the reversing flapper 610 rotates around the reversing flapper shaft 612. The reversing flapper 610 is fixed to the reversing flapper shaft 612. The reversing flapper shaft 612 is rotatably supported on a side plate (not shown). Furthermore, in the sheet width direction, a reversing flapper arm 613, which is integrated with the reversing flapper shaft 612, is positioned at the end of the reversing flapper shaft 612 on the side where the reversing flapper drive unit 611 is located. In other words, the reversing flapper arm 613 is positioned on the outside of the reversing flapper shaft 612 in the sheet width direction.

[0042] The inverting flapper drive unit 611 is fixed to a side plate (not shown). The inverting flapper drive unit 611 includes a motor 614 which is the drive unit, a motor stand (not shown) which holds the motor, and a timing belt 616 which transmits the rotation of a motor pulley 615 mounted on the motor shaft. Furthermore, the inverting flapper drive unit 611 includes a camshaft 617 which is rotatably supported on the motor stand and rotated by the timing belt 616, a cam 618 which is fixed to the camshaft 617, and a flag 619 which is fixed to the camshaft 617. Furthermore, the inverting flapper drive unit 611 has an inverting flapper HP sensor 640 which is fixed to the motor stand and detects the phase of the camshaft 617.

[0043] In this embodiment, the inverting flapper HP sensor 640 uses a photointerrupter. During the rotation of the flag 619, the position rotated by a predetermined amount starting from the timing when the optical axis of the photointerrupter is blocked or when the flag 619 leaves the optical axis and light is transmitted is set as the arbitrary orientation of the inverting flapper 610. The inverting flapper arm 613 is biased by the inverting flapper spring 622 so that the cam contact portion 621 of the inverting flapper arm 613 and the cam 618 come into contact. With this configuration, the rotation of the motor 614 causes the cam 618 to rotate, which in turn causes the inverting flapper arm 613 to rotate around the inverting flapper shaft 612, and the orientation of the inverting flapper 610 is switched.

[0044] Figure 13 is a block diagram showing the configuration of the second reversal unit 641. Based on the sheet position information detected by sensors placed on the transport path, the drive of the motor 614 of the reversal flapper drive unit 611 is controlled. The reversal flapper drive unit 611 switches the orientation of the reversal flapper 610. In addition, the forward rotation, stopping, and reverse rotation of the reversal roller 620 are controlled based on the sheet position information. When the rotation direction of the reversal roller 620 is switched, the direction of travel of the sheet nipped by the reversal roller is switched.

[0045] <Operation of the inverting flapper> This section describes the operation of the reversing flapper when sheets are continuously fed through. To achieve high productivity, it is necessary to transport the sheets with extremely narrow spacing between them. In the reversing section, where the direction of sheet transport is reversed, the spacing between sheets refers to the distance between the sheet after the preceding switchback and the sheet before the following switchback. When the spacing between sheets is narrowed, there is a risk that the reversing flapper 610 may come into contact with the rear end of the sheet and damage it when its position is switched. In this embodiment, the reversing flapper 610 switches between a first position in which it does not block the pre-reversal transport path 601 and the post-reversal transport path 603, and a second position in which it blocks the pre-reversal transport path 601 but does not block the post-reversal transport path 603. This makes it possible to suppress damage to the sheet caused by the reversing flapper 610.

[0046] The sheet flow and the operation of the reversing flapper 610 in this embodiment will be explained using Figures 4 to 10. Figure 4 shows the reversing flapper 610 in a first position before the sheet is conveyed. Figures 5 and 6 show the reversing flapper 610 in a first position when the sheet is conveyed from the pre-reversal conveying path 601 to the reversing conveying path 602 before the switchback. Figures 7 and 8 show the reversing flapper 610 in a second position when the sheet is conveyed from the reversing conveying path 602 to the post-reversal conveying path 603. Figures 9 and 10 show the reversing flapper 610 in a first position when the sheet is conveyed from the reversing conveying path 602 to the post-reversal conveying path 603.

[0047] As shown in Figure 4, before the sheet is transported, the inverting flapper 610 receives the sheet before the switchback and is positioned in a first position which is a pre-inverting guide position (Figure 3(b)) that allows the sheet to be transported. When the inverting flapper 610 is in the first position, it is positioned so as not to block either the pre-inverting transport path 601 or the post-inverting transport path 603.

[0048] With the reversing flapper 610 in the first position, the leading edge of the sheet before the switchback passes through the reversing flapper 610 (Figure 5). The forward-rotating reversing roller 620 receives the sheet and continues to transport the sheet in direction A (Figure 6). Then, as shown in Figure 7, the reversing roller 620 stops rotating and stops the transport of the sheet when it has transported a predetermined distance after the reversing sensor 630 detects the passage of the leading edge of the sheet. The predetermined distance varies depending on the length of the sheet in the transport direction. At this time, immediately after the trailing edge of the sheet passes the tip 610 of the reversing flapper, the motor 614 switches the reversing flapper 610 to the second position, which is the post-reversal guide position (Figure 3(c)) that guides the sheet after the switchback to the post-reversal transport path 603. The second position of the reversing flapper 610 is the position that blocks the pre-reversal transport path 601.

[0049] As shown in Figure 8, with the reversing flapper 610 in the second position, the reversing roller 620 rotates in the reverse direction, transporting the sheet in direction B. Upstream of the post-reversal transport path 603, a post-reversal transport roller 650 is positioned, and the post-reversal transport roller 650 transports the sheet further downstream after the switchback. As shown in Figure 9, with the sheet being transported by the post-reversal transport roller 650, the motor 614 switches the reversing flapper 610 from the post-reversal guide position (second position) to the pre-reversal guide position (first position).

[0050] In this state, the rear end of the sheet passing through the inversion transport path 603 has not yet passed through the inversion flapper 610. However, since the inversion flapper 610 is positioned so as not to block the inversion transport path 603, it is possible to switch the orientation of the inversion flapper 610 even while a sheet is passing through. That is, after the leading edge of the sheet has passed the tip 610 of the inversion flapper, and before the rear end of the sheet reaches the tip 610 of the inversion flapper, the inversion flapper 610 can begin to switch from the inversion guide orientation to the pre-inversion guide orientation. By operating the inversion flapper 610 in this way, the inversion flapper 610 can be set to the pre-inversion guide orientation (first position) before the leading edge of the following sheet S2, which follows the preceding sheet S1, reaches the pre-inversion transport path side of the inversion flapper 610 (Figure 10). In this embodiment, the inversion flapper 610 is an example of an inversion switching unit.

[0051] In this embodiment, the reversing flapper 610 is switched from the second position to the first position after the leading edge of the sheet is nipped by the post-reversal transport roller 650, but this is not limited to this. When the sheet is transported from the reversing transport path 602 to the post-reversal transport path 603, if the leading edge of the sheet has exceeded the tip 610 of the flapper, the reversing flapper 610 may be switched from the second position to the first position.

[0052] In this embodiment, the post-inversion transport path 603 is formed on the straight line of the nip line of the inversion roller 620. Therefore, the sheet does not actively come into contact with the inversion flapper 610 as it passes through the post-inversion transport path 603. Even if the orientation of the inversion flapper 610 is changed while the sheet is passing through the post-inversion transport path 603, it is less affected by changes in the contact state of the sheet. Therefore, even if the orientation of the inversion flapper 610 is changed while the sheet is passing through the post-inversion transport path 603, paper transport by the inversion roller 620 and the post-inversion transport roller 650 can be performed stably.

[0053] Figure 17 shows a cross-sectional view of the area around the inversion flapper 610. Figure 17(a) shows the inversion flapper 610 in the first position, and Figure 17(b) shows the inversion flapper 610 in the second position. Conveyor guides 601a and 601b form the pre-inversion conveyor path 601. Furthermore, conveyor guides 603a and 603b form the post-inversion conveyor path 603.

[0054] In this embodiment, when the inverting flapper 610 is in the second position (Figure 17(b)), when viewed from the sheet width direction, the inverting flapper 610 and the transport guide 601b that forms the pre-inversion transport path 601 and is positioned opposite the inverting flapper 610 overlap. In other words, when the inverting flapper 610 is in the second position, the inverting flapper 610 intersects with the transport guide 601b that is positioned farther from the inverting flapper axis 612, among the transport guides 601a and 601b that constitute the pre-inversion transport path 601. However, when the inverting flapper 610 is in the second position, when viewed from the sheet width direction, the inverting flapper 610 does not need to completely block the pre-inversion transport path 601; it is sufficient for the inverting flapper 610 to block at least a portion of the pre-inversion transport path 601. In this embodiment, when a sheet is transported from the reversal transport path 602 to the post-reversal transport path 603, it is sufficient that the sheet is transported to the post-reversal transport path 603 without being transported to the pre-reversal transport path 601. As shown in Figure 17(a), when the reversal flapper 610 is in the first position, the reversal flapper 610 does not overlap with the transport guide 601b that forms the pre-reversal transport path 601, which is positioned opposite the reversal flapper 610. Furthermore, when the reversal flapper 610 is in the first position, the reversal flapper 610 does not overlap with the transport guide 603b that forms the post-reversal transport path 603, which is positioned opposite the reversal flapper 610.

[0055] Figure 15 is a cross-sectional view of the fixing module 400. The double-sided transport section of the fixing module 400 is equipped with a first reversal section 420 for reversing the front and back sides of the sheet. The first reversal section 420 of the double-sided transport section 430 includes a pre-reversal transport path 401, a reversal transport path 402, a post-reversal transport path 403, and a reversal flapper 404. The pre-reversal transport path 401 and the post-reversal transport path 403 of the first reversal section 420 are bent. The reversal flapper 404, which includes a part of the pre-reversal transport path 401 and a part of the post-reversal transport path 403, is positioned at the end of the pre-reversal transport path 401 and the starting point of the post-reversal transport path 403 in the sheet transport direction.

[0056] The first reversing unit 420, located in the double-sided transport unit 430, transports sheets that are printed on both sides. Compared to the second reversing unit 641, the number of sheets transported is smaller, resulting in relatively wider spacing between sheets. Therefore, because there is ample space between sheets, the reversing flapper 404 switches between a position overlapping with the transport guides constituting the pre-reversal transport path 401 and a position overlapping with the transport guides constituting the post-reversal transport path 403, when viewed from the sheet width direction. However, as with the second reversing unit 641, the reversing flapper 404 of the first reversing unit 420 may be switched between a first position where it does not block the pre-reversal transport path 401 and the post-reversal transport path 403, and a second position where the reversing flapper 404 blocks the pre-reversal transport path 401 but does not block the post-reversal transport path 403.

[0057] Thus, in this embodiment, the inverting flapper 610 switches between a second position in which it blocks the pre-inverting transport path 601 but not the post-inverting transport path 603, and a first position in which it does not block either the pre-inverting transport path 601 or the post-inverting transport path 603. The first position of the inverting flapper 610 is a position in which the inverting flapper 610 can transport a sheet from the pre-inverting transport path 601 to the inverting transport path 602, and can transport a sheet from the inverting transport path 602 to the post-inverting transport path 603. Therefore, the inverting flapper 610 can be switched from the second position to the first position without damaging the rear end of the sheet being transported from the inverting transport path 602 to the post-inverting transport path 603.

[0058] In this embodiment, the reversing flapper 610 is switched from the pre-reversal guide position (first position) to the post-reversal guide position (second position) at the timing when the reversing roller, which has sufficient time, switches from forward rotation to reverse rotation. Furthermore, while the sheet after the switchback is passing through the reversing flapper 610, the reversing flapper 610 switches from the post-reversal guide position (second position) to the pre-reversal guide position (first position). This allows the reversing flapper 610 to transition to a position that accepts the following paper with sufficient time. As a result, actuators and mechanisms with high output and high responsiveness are not required, and the increase in cost can be suppressed.

[0059] In the embodiments described above, the case in which the image forming system is applied to an inkjet-type inkjet recording system 1 has been explained, but it is not limited to this and may also be applied to an electrophotographic image forming system.

[0060] <Second Embodiment> Next, a second embodiment of the present invention will be described. In the first embodiment, a motor was used as the actuator to rotate the reversing flapper 610, but in the second embodiment, a solenoid 664 is used as the actuator. In addition, in the first embodiment, a reversing sensor 630 located in the reversing transport path 602 is used to control the stopping position of the seat for switchback. In the second embodiment, a pre-reversal sensor 668 located upstream of the reversing flapper 610 in the pre-reversal transport path 601 is used.

[0061] Thus, in the second embodiment, the type of actuator and the arrangement of sensors used to control the stopping position of the seat for switchback differ from those of the first embodiment. However, although the second embodiment describes two differences, the type of actuator and the arrangement of sensors, there may be only one difference in each. However, since the other configurations are the same as in the first embodiment, the same reference numerals are used and detailed explanations are omitted.

[0062] Figure 11 shows the reversing flapper drive and reversing flapper of the second embodiment. Figure 11(a) shows the reversing flapper 610 in the first position, and Figure 11(b) shows the reversing flapper 610 in the second position. The reversing flapper 660 is equipped with a reversing flapper shaft 667, and the reversing flapper 660 rotates around the reversing flapper shaft 667. The reversing flapper shaft 667 is rotatably supported on a side plate (not shown).

[0063] The reversing flapper drive unit 669 comprises a flapper arm 661, a solenoid 664, and a spring 663. The flapper arm 661 is fixed to the reversing flapper shaft 667 and includes a spring attachment portion 662 and a plunger engagement portion 666. The spring 663 is attached to the spring attachment portion 662 of the flapper arm 661. The solenoid 664 is fixed to a side plate (not shown). The plunger 665 of the solenoid 664 engages with the plunger engagement portion 666 of the flapper arm 661.

[0064] The flapper arm 661 is biased by the spring 663 so that the spring attachment portion 662 moves away from the solenoid 664. When voltage is applied to the solenoid 664, the plunger 665 is pulled into the solenoid body, causing the flapper arm 661 to rotate, and the reversing flapper 660 also rotates counterclockwise around the flapper shaft 667 (arrow in Figure 11(b)). In other words, when voltage is applied to the solenoid 664, the reversing flapper switches from the pre-reversal guide position (first position) to the post-reversal guide position (second position). When the voltage to the solenoid 664 is stopped, the plunger 665 switches from the post-reversal guide position (second position) to the pre-reversal guide position (first position) due to its own weight and the spring 663.

[0065] Figure 12 shows a cross-sectional view of the second reversal section of the second embodiment. The pre-reversal sensor 668 is positioned upstream of the reversal flapper 610 on the pre-reversal transport path 601. Starting from the moment the rear end of the sheet before the switchback passes the pre-reversal sensor 668, the reversal roller 620 stops rotating when the sheet has advanced a predetermined distance from that point. As a result, the sheet stops on the reversal transport path 602. At this time, immediately after the rear end of the sheet passes the tip 660 of the reversal flapper, the solenoid 664, which is the drive unit, switches the reversal flapper 660 from the pre-reversal guide position (first position) to the post-reversal guide position (second position).

[0066] With the reversing flapper 660 in the second position, the reversing roller 620 rotates in the reverse direction to transport the sheet. Subsequently, with the sheet being transported by the post-reversal transport roller 650, the solenoid 664 switches the reversing flapper 660 from the post-reversal guide position (second position) to the pre-reversal guide position (first position).

[0067] Sheet paper exhibits size variations due to cutting during the manufacturing process. Additionally, sheet paper undergoes size expansion and contraction during the image formation process due to increases and decreases in the moisture content of the sheet. In the second embodiment, since the pre-reversal sensor 668 detects the rear end of the sheet and stops the sheet after it has traveled a predetermined distance, variations in the sheet position when the front and rear ends of the sheet switch before and after the switchback can be reduced, thus stabilizing paper transport.

[0068] In other words, the rear end of the sheet when it is transported from the pre-reversal transport path 601 to the reverse transport path 602 becomes the front end of the sheet when it is transported from the reverse transport path 602 to the post-reversal transport path 603. Therefore, by switching the transport direction at a predetermined distance after the pre-reversal sensor 668 detects the rear end of the sheet, even if there is variation in the size of the sheets, the variation in the position of the front end of the sheet when it is transported from the reverse transport path 602 to the post-reversal transport path 603 is small.

[0069] In this embodiment as well, the inverting flapper 610 is switched between a first position in which it does not block the pre-inverting transport path 601 and the post-inverting transport path 603, and a second position in which the inverting flapper 610 blocks the pre-inverting transport path 601 but does not block the post-inverting transport path 603. This makes it possible to transport the sheet without damaging the rear end of the sheet. [Explanation of symbols]

[0070] 601 Pre-reversal transport path 602 Reversal transport path 603 Conveyor path after reversal 610 Reversing Flapper 611 Reversing Flapper Drive Unit 614 Motor 620 Reversing Roller 630 Inversion Sensor

Claims

1. The first transport path through which the sheets are transported, A reversing transport path that reverses the transport direction of the sheet transported from the first transport path, A second transport path through which the sheets transported from the aforementioned reversal transport path are transported, A reversal switching unit that switches between a first position for guiding the sheet from the first transport path to the reversal transport path, and a second position for guiding the sheet from the reversal transport path to the second transport path, A drive unit that switches the reversal switching unit between the first position and the second position, It has, The second position is such that the reversal switching unit does not block the second transport path, and does not block the first transport path. The first position is a position in which the reversal switching unit does not block the first transport path and the second transport path, and the sheet can be transported from the reversal transport path to the second transport path. A sheet conveying device characterized by the following features.

2. The curvature of the second transport path is smaller than the curvature of the first transport path. The sheet conveying device according to feature 1.

3. The second transport path is a horizontal transport path. The sheet conveying device according to feature 1.

4. The drive unit starts switching the reversal switching unit from the second position to the first position after the leading edge of the sheet has passed the leading edge of the reversal switching unit, and before the rear end of the sheet has passed the leading edge of the reversal switching unit. The sheet conveying device according to feature 1.

5. The system includes conveying rollers for conveying sheets arranged on the aforementioned reversing conveying path, The drive unit switches the reversal switching unit from the second position to the first position after the sheet has been nipped by the transport roller. The sheet conveying device according to feature 4.

6. After the rear end of the sheet being transported from the first transport path to the reverse transport path passes through the reverse switching section, the reverse switching section switches from the first position to the second position. The sheet conveying device according to feature 4.

7. A sheet conveying device according to any one of claims 1 to 6, An image forming unit that forms an image on a sheet, An image forming apparatus characterized by comprising:

Images