Image forming apparatus

Abstract

To provide an image forming device which reduces a conveyance load of a pair of second rollers, and which suppresses a jam.SOLUTION: An image forming device includes: a first conveyance passage; a second conveyance passage; a curved conveyance passage connected to the second conveyance passage and constituted so as to curve, and joining the first conveyance passage; a first pair of rollers; a second pair of rollers arranged along the curved conveyance passage; an inner guide; and an outer guide opposing to the inner guide, and for constituting at least part of the curved conveyance passage between the first pair of rollers and the second pair of rollers together with the inner guide. The outer guide can move to a first position and a second position which is a position further separated from the inner guide than the first position.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet.

Background Art

[0002] Conventionally, an image forming apparatus has been proposed that can switch between a pressure contact state and a separated state between a loop roller and a plurality of intermediate transfer rollers (see Patent Document 1). A guide plate that can be retracted from a normal position to a retracted position is provided in a conveyance path where the plurality of intermediate transfer rollers are provided. By moving the guide plate to the retracted position, the frictional resistance applied to the sheet passing through the bent conveyance path can be reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the sheet passes through the bent conveyance path, the conveyance resistance increases due to the stiffness of the sheet. Further, when a pair of conveyance rollers is provided along the bent conveyance path, the conveyance load on the pair of conveyance rollers increases due to the conveyance resistance of the sheet, and there is a risk of jamming.

[0005] An object of the present invention is to provide an image forming apparatus that reduces the conveyance load on a second pair of rollers and suppresses jamming.

Means for Solving the Problems

[0006] The present invention relates to an image forming apparatus comprising: an image forming unit for forming an image on a sheet; a first transport path through which a sheet being transported toward the image forming unit passes; a second transport path for transporting the sheet, on which an image has been formed on a first surface by the image forming unit, toward the first transport path again; and a curved structure that is continuous with the second transport path. ,before First transport route Joining A curved transport path and arranged along the second transport path Among the multiple pairs of conveying rollers, the one located furthest downstream in the sheet conveying direction , a first pair of rollers having a nip portion for conveying a sheet, a second pair of rollers arranged along the curved conveying path and adjacent to the first pair of rollers in the sheet conveying direction for conveying a sheet, an inner guide, an outer guide facing the inner guide and forming at least a portion of the curved conveying path between the first pair of rollers and the second pair of rollers together with the inner guide, provided on the outside in the curvature direction of the curved conveying path, and movable to a first position and a second position which is further from the inner guide than the first position, and the outer guide From the adjacent second position Towards the first position In the direction The device comprises a biasing section for biasing, wherein the nip lines of the first roller pair and the nip lines of the second roller pair intersect each other, and the outer guide moves from a first position to a second position when the rear end of the sheet being conveyed by the second roller pair is pressed by the rear end of the first roller pair as the rear end passes over the nip section of the first roller pair. [Effects of the Invention]

[0007] According to the present invention, the conveying load on the second roller pair can be reduced, and jamming can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram showing the printer according to the first embodiment. [Figure 2] A diagram showing the surrounding configuration of a U-turn transport path. [Figure 3] (a) is a diagram showing the outer guide in the closed position, and (b) is a diagram showing what happens when the rear end of the sheet passes through the conveyor roller pair. [Figure 4] (a) is a diagram showing the outer guide in the open position, and (b) is a diagram showing the state when the rear end of the sheet has passed through the outer guide. [Figure 5] A diagram showing the peripheral configuration of a U-turn transport path according to the second embodiment. [Figure 6] A diagram showing the drive configuration according to the third embodiment. [Figure 7] A block diagram showing a control block according to the third embodiment. [Figure 8] A flowchart illustrating the control of the drive mechanism. [Figure 9] (a) is a diagram showing a sheet being transported along a U-turn transport path, and (b) is a diagram showing the state when the rear end of the sheet passes over the transport roller pair. [Figure 10] (a) is a diagram showing the outer guide in the open position, and (b) is a diagram showing the state when the rear end of the sheet has passed through the outer guide. [Modes for carrying out the invention]

[0009] <First Embodiment> First, a first embodiment of the present invention will be described. The printer 100, which serves as an image forming apparatus according to the first embodiment, is an electrophotographic laser beam printer. As shown in Figure 1, the printer 100 includes a cassette feeding unit 1B, a manual feed unit 64, and an image forming unit 1C.

[0010] When an image formation command is output to the printer 100, the image formation process by the image formation unit 1C is started based on image information input from an external computer or the like connected to the printer 100. The image formation unit 1C comprises four exposure units 13Y, 13M, 13C, and 13K, and four process cartridges 10Y, 10M, 10C, and 10K that form images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). The image formation unit 1C also includes an intermediate transfer belt 31 that is taut by a drive roller 33, a tension roller 34, and a secondary transfer inner roller 32, and is rotatable in the direction of arrow B.

[0011] Note that the four process cartridges 10Y, 10M, 10C, and 10K have the same configuration except that the colors of the images they form are different. Only the image forming process of the process cartridge 10Y will be described, and the descriptions of the process cartridges 10M, 10C, and 10K will be omitted.

[0012] The exposure device 13Y irradiates laser light toward the photosensitive drum 11Y of the process cartridge 10Y based on the input image information. At this time, the photosensitive drum 11Y is pre-charged by the charger 12Y, and an electrostatic latent image is formed on the photosensitive drum 11Y when irradiated with the laser light. Then, the electrostatic latent image is developed by the developing device 14Y, and a yellow (Y) toner image is formed on the photosensitive drum 11Y. After the toner image is transferred to the intermediate transfer belt 31, the toner remaining on the photosensitive drum 11Y is recovered by the cleaner 15Y.

[0013] Similarly, magenta (M), cyan (C), and black (K) toner images are also formed on the photosensitive drums of the process cartridges 10M, 10C, and 10K. The toner images of each color formed on the photosensitive drums are transferred to the intermediate transfer belt 31 by the primary transfer rollers 35Y, 35M, 35C, and 35K, and are conveyed to the secondary transfer inner roller 32 by the rotating intermediate transfer belt 31. Note that the image forming process of each color is performed at the timing of overlapping with the upstream toner image primarily transferred onto the intermediate transfer belt 31.

[0014] In parallel with the above-described image forming process, the sheet P is fed from the cassette feeding unit 1B or the manual feeding unit 64. The cassette feeding unit 1B has a plurality of cassettes 61, 62, 63 (three in this embodiment), and the sheet P is fed from these cassettes 61, 62, 63 by the pickup rollers 61a, 62a, and 63a, respectively. The manual feeding unit 64 has a manually rotatable tray 104, and the sheet P loaded on the manual tray 104 is fed by the pickup roller 64a.

[0015] The sheet P fed from these pickup rollers 61a, 6 , 63a, 64a is conveyed to the registration roller pair 110 by the conveyance roller pairs 70 to 75 and the pre-registration roller pair 78. The pre-registration roller pair 78 conveys the sheet P toward the nip portion of the stopped registration roller pair 110. Thereby, the leading end of the sheet P can be made to follow along the nip portion, and the skew of the sheet P is corrected.

[0016] [[ID=A]] Then, the sheet P is conveyed by the registration roller pair 110 at a predetermined timing, and a predetermined pressure and an electrostatic bias are applied to the first surface of the sheet P at the transfer nip 1E formed by the secondary transfer inner roller 32 and the secondary transfer outer roller 41. Thereby, the full-color toner image on the intermediate transfer belt 31 is transferred to the first surface of the sheet P. The remaining toner remaining on the intermediate transfer belt 31 is recovered by the cleaner 36.

[0017] The sheet P onto which the toner image has been transferred is conveyed to the fixing device 5 by the air suction belt 42, and a predetermined pressure and heat are applied to melt and fix the toner image. The sheet P that has passed through the fixing device 5 is conveyed to the discharge conveyance path 82 when it is discharged onto the discharge tray 66 as it is by the fixing conveyance roller pair 52, or to the reverse induction path 83 when images are to be formed on both surfaces of the sheet P or the like.

[0018] A guide member 81 is provided rotatably at the branch portion between the discharge conveyance path 82 and the reverse induction path 83. The guide member 81 is for switching the path according to a discharge job for discharging the sheet P onto the discharge tray 66, a reverse discharge job for reversing and discharging the sheet P, or a duplex conveyance job for conveying the sheet P again to the image forming unit 1C. And by switching the path by this guide member 81, the sheet is guided to the discharge conveyance path 82 or the reverse induction path 83 according to the set job. <000,0103> For example, in the case of a discharge job, the guide member 81 rotates downward and moves to the discharge position where the sheet is discharged. As a result, the sheet P conveyed by the fixing conveyor roller pair 52 is conveyed along the upper surface of the guide member 81 to the discharge conveyor path 82 and discharged into the discharge tray 66 by the discharge roller pair 77.

[0020] In the case of a double-sided transport job, the guide member 81 rotates upward and moves to a retraction position that guides the sheet to the reversal guidance path 83. As a result, the sheet P transported by the fixing transport roller pair 52 is guided along the lower surface of the guide member 81 to the reversal guidance path 83 and is pulled into the switchback path 84 by the first reversal roller pair 79. Then, a switchback operation that reverses the rotation direction of the second reversal roller pair 86 reverses the front and rear ends and the front and back sides of the sheet P, and the sheet P is transported to the double-sided transport path 88. After this, the sheet P transported to the double-sided transport path 88 is sent to the transfer nip 1E, which serves as the image forming unit, via the U-turn transport path 94 and the straight transport path 76.

[0021] Furthermore, multiple pairs of transport rollers 90-93 are provided along the double-sided transport path 88 to transport the sheet P. The subsequent image formation process for the back surface (second surface) is the same as the image formation process for the front surface (first surface) described above, so the explanation is omitted.

[0022] In the case of a reverse discharge job, the guide member 81 also rotates upward and moves to the retraction position. As a result, the sheet P is transported to the reverse guidance path 83 by the fixing transport roller pair 52 and pulled into the switchback path 84 by the first reverse roller pair 79. Then, the front and rear ends of the sheet P are swapped by a switchback operation that reverses the rotation direction of the first reverse roller pair 79, and the sheet P is transported to the reverse transport path 89. After this, the sheet P is transported to the discharge roller pair 77 and discharged into the discharge tray 66 by the discharge roller pair 77.

[0023] [Peripheral configuration of the U-turn transport path] Next, the peripheral configuration of the U-turn transport path 94 will be described using Figures 1 and 2. As shown in Figures 1 and 2, the straight transport path 76, which serves as the first transport path, is the transport path through which the sheet P, which is being transported toward the transfer nip 1E, passes. The double-sided transport path 88, which serves as the second transport path, is a transport path for transporting the sheet P, which has an image formed on its first surface by the transfer nip 1E, toward the straight transport path 76 again. The U-turn transport path 94, which serves as the curved transport path, is configured to be continuous with the double-sided transport path 88 and curve, and merges with the straight transport path 76.

[0024] The straight transport path 76 and the double-sided transport path 88 each extend linearly in a substantially horizontal direction and are arranged to be substantially parallel to each other. The U-turn transport path 94 is formed in a substantially U shape and switches the direction in which the sheet P moves in the opposite direction, i.e., from right to left in Figure 1. In addition, the sheet P fed from cassettes 61, 62, and 63 passes through the cassette transport path 73, which merges with the U-turn transport path 94. Furthermore, the sheet P fed from the manual feed tray 104 passes through the manual feed path 25, which merges with the U-turn transport path 94 and the straight transport path 76 at their junction.

[0025] As shown in Figure 2, the printer 100 is equipped with a double-sided merging sensor 40, a vertical path roller pair 74, and a pre-registration roller pair 78 along the U-turn transport path 94. The double-sided merging sensor 40 detects the position of the sheet P being transported along the U-turn transport path 94. Among the multiple transport roller pairs 90 to 93 arranged along the double-sided transport path 88, an inner guide 120 and an outer guide 95 are provided between the transport roller pair 93, which is the first roller pair located furthest downstream in the sheet transport direction CD, and the vertical path roller pair 74. The vertical path roller pair 74, which is the second roller pair, is positioned adjacent to the transport roller pair 93 in the sheet transport direction CD. In other words, there are no other roller pairs between the transport roller pair 93 and the vertical path roller pair 74 in the sheet transport direction CD. Furthermore, the nip line L1 of the transport roller pair 93 and the nip line L2 of the vertical path roller pair 74 intersect each other.

[0026] The outer guide 95 faces the inner guide 120 and together with the inner guide 120 constitutes at least a portion of the U-turn transport path 94 between the transport roller pair 93 and the longitudinal path roller pair 74. The outer guide 95 is also provided on the outside in the curvature direction of the U-turn transport path 94 and is configured to rotate between a closed position (shown in Figures 3(a) and 3(b)) and an open position (shown in Figures 4(a) and 4(b)) around a pivot axis 97. In the closed position, which is the first position, the outer guide 95 has a substantially uniform gap with the inner guide 120. The open position, which is the second position, is a position further from the inner guide 120 than in the closed position.

[0027] The outer guide 95 is biased toward the closed position by a compression spring 96 acting as a biasing element, and is positioned in the closed position by, for example, abutting against a stopper (not shown). Note that other types of springs such as leaf springs, elastic materials such as rubber or sponge, or magnets that generate a biasing force (attractive / repulsive force) may be used instead of the compression spring 96. The pivot shaft 97 is located downstream of the outer guide 95 in the sheet transport direction CD, and the upstream end 95a of the outer guide 95 in the sheet transport direction CD moves as the outer guide 95 rotates between the closed and open positions.

[0028] More specifically, if we define the position of the upstream end 95a when the outer guide 95 is in the closed position as the third position, and the position of the upstream end 95a when the outer guide 95 is in the open position as the fourth position, then the fourth position is further from the inner guide 120 than the third position.

[0029] [Operation of the external guide] Next, the operation of the outer guide 95 when the sheet P passes through the U-turn transport path 94 will be explained using Figures 3(a) to 4(b). As shown in Figure 3(a), the sheet P passing through the double-sided transport path 88 is transported toward the U-turn transport path 94 by the transport roller pair 93. When the leading edge P1 of the sheet P reaches the longitudinal pass roller pair 74, the sheet P is transported mainly by the longitudinal pass roller pair 74. When the sheet P passes through the U-turn transport path 94, the sheet P also curves along the curved U-turn transport path 94, and the stiffness of the sheet P increases the transport resistance. As a result, the transport load on the longitudinal pass roller pair 74 that transports the sheet increases.

[0030] As shown in Figure 3(b), once the rear end P2 of the sheet P leaves the transport roller pair 93, the sheet P is transported solely by the longitudinal pass roller pair 74. If the transport load on the longitudinal pass roller pair 74 exceeds a predetermined value, the longitudinal pass transport motor M12, which is the drive source for the longitudinal pass roller pair 74, may lose synchronism.

[0031] Therefore, in this embodiment, the outer guide 95, which constitutes part of the U-turn transport path 94, is configured to be rotatable. When the rear end P2 of the sheet P passes the transport roller pair 93, the sheet P, which has curved along the U-turn transport path 94, tries to return to its original position, that is, a straight position, due to the stiffness of the sheet P. For this reason, as shown in Figure 4(a), the outer guide 95 is pressed by the sheet P held between the longitudinal path roller pair 74, and the outer guide 95 rotates from the closed position to the open position around the pivot axis 97 against the biasing force of the compression spring 96.

[0032] This reduces the curvature of the sheet P and makes the sheet P less rigid. As a result, the transport load on the vertical path roller pair 74 is reduced, and jams caused by step loss or other issues in the vertical path transport motor M12 can be suppressed. Furthermore, since the transport load on the vertical path roller pair 74 can be reduced without reducing the curvature of the U-turn transport path 94, the printer 100 can be made smaller. As shown in Figure 4(b), when the rear end P2 of the sheet P passes the outer guide 95, the outer guide 95 returns to the closed position shown in Figure 3(a) due to the biasing force of the compression spring 96.

[0033] In the U-turn transport path 94, types of sheets that increase the transport load on the vertical pass roller pair 74 include thick paper such as New Pigeon (350gsm), Ibest W (360gsm), and New DV (400gsm). Also, in the sheet transport direction CD, smaller sheets (for example, B5 (182mm), A5 (148mm)) have increased stiffness due to their curved shape, which increases the transport load on the vertical pass roller pair 74.

[0034] <Second Embodiment> Next, a second embodiment of the present invention will be described. In the second embodiment, the vertical path roller pair 74 and the pre-registration roller pair 78 are configured to be driven by a single vertical path transport motor M2. For this reason, the same configuration as in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0035] As shown in Figure 5, the printer of this embodiment has a pre-registration roller pair 78 positioned along the U-turn transport path 94 and downstream of the longitudinal path roller pair 74 in the sheet transport direction CD. The pre-registration roller pair 78, as a third roller pair, transports the sheet P passing through the U-turn transport path 94 together with the longitudinal path roller pair 74.

[0036] The vertical path roller pair 74 and the pre-registration roller pair 78 are driven by a single drive source, the vertical path conveyor motor M2. This configuration, where one vertical path conveyor motor M2 drives two roller pairs, places a greater load on the system than a configuration where one vertical path conveyor motor M2 drives only one roller pair (for example, the vertical path roller pair 74 in the first embodiment). Therefore, the vertical path conveyor motor M2 is more likely to lose synchronization.

[0037] However, in this embodiment as well, similar to the first embodiment, the outer guide 95 is rotatable between a closed position and an open position around the pivot axis 97. Therefore, when the rear end P2 of the sheet P passes the conveyor roller pair 93, the sheet P, which has curved along the U-turn conveyor path 94, tries to return to its original position, i.e., a straight position, due to the stiffness of the sheet P. Then, as shown in Figure 4(a), the outer guide 95 is pressed by the sheet P held between the longitudinal path roller pair 74, and the outer guide 95 rotates from the closed position to the open position around the pivot axis 97 against the biasing force of the compression spring 96.

[0038] This reduces the curvature of sheet P and decreases its rigidity. Consequently, the transport load on the vertical pass roller pair 74 and the pre-registration roller pair 78 is reduced, and jams caused by step loss or other issues in the vertical pass transport motor M2 can be suppressed.

[0039] <Third Embodiment> Next, a third embodiment of the present invention will be described. The third embodiment is the first embodiment to which a drive mechanism 300 for driving the outer guide 95 is added. For this reason, components similar to those in the first embodiment will not be shown in the figures, or will be described using the same reference numerals in the figures.

[0040] As shown in Figure 6, the printer of this embodiment has a drive mechanism 300 for driving the outer guide 95. The drive mechanism 300 includes an eccentric cam 98 that can rotate around a rotation axis 98a, a tension spring 99 that biases the outer guide 95 toward the outer circumferential surface 98b of the eccentric cam 98, and a cam drive motor M3 that drives the eccentric cam 98.

[0041] The outer guide 95 is configured to always contact the outer circumferential surface 98b of the eccentric cam 98 by a tension spring 99. Therefore, the outer guide 95 rotates between a closed position and an open position around the pivot axis 97 depending on the contact position with the eccentric cam 98.

[0042] [Control Block] Figure 7 is a block diagram showing the control block of the printer in this embodiment. As shown in Figure 7, the printer has a controller 401. The controller 401 has a CPU (Central Processing Unit) 402, RAM (Random Access Memory) 403, and ROM (Read Only Memory) 404. The CPU 402 executes various programs stored in the ROM 404. The RAM 403 is used as a workspace for the CPU 402, etc.

[0043] The CPU 402 is connected to the control unit 405, through which the user can instruct the printer to change various settings and execute print jobs. The CPU 402 is also connected to the duplex transport motor M1, the vertical path transport motor M2, and the cam drive motor M3 via drivers 406, 407, and 408, respectively. The duplex transport motor M1 drives the transport roller pair 90-93. The vertical path transport motor M2 drives the vertical path roller pair 74. The cam drive motor M3 drives the eccentric cam 98.

[0044] Furthermore, the signal from the double-sided merging sensor 40, which acts as a detection unit, is input to the CPU 402 via the AD conversion unit 409. The double-sided merging sensor 40 can detect the presence or absence of sheet P at predetermined detection positions within the U-turn transport path 94, thereby enabling the detection of the position of sheet P.

[0045] [Operation of the external guide] Next, the operation of the external guide 95 will be explained with reference to the flowchart in Figure 8 and Figures 9(a) to 10(b). As shown in Figure 8, the CPU 402 first determines whether the input job is a double-sided transport job or not (step S10). If the input job is not a double-sided transport job (step S10: No), the process is terminated.

[0046] If the input job is a double-sided transport job (step S10: Yes), the CPU 402 controls the guide member 81, the first reversing roller pair 79 and the second reversing roller pair 86 (see Figure 1) to transport the sheet P to the double-sided transport path 88 (step S11). The sheet P is then transported by the transport roller pairs 90-93, and the position of the leading edge P1 is detected by the double-sided merging sensor 40, as shown in Figures 9(a) and 9(b) (step S12).

[0047] Next, the CPU 402 determines whether the leading edge P1 of the sheet P has reached the longitudinal pass roller pair 74 based on the detection result of the double-sided merging sensor 40 (step S13). If it is determined that the leading edge P1 has reached the longitudinal pass roller pair 74 (step S13: Yes), the CPU 402 rotates the outer guide 95 from the closed position to the open position by driving the eccentric cam 98, as shown in Figure 10(a) (step S14).

[0048] The timing of the rotation of the outer guide 95 from the closed position to the open position is after the leading edge P1 of the sheet P reaches the longitudinal pass roller pair 74 and before the rear end P2 of the sheet P passes the outer guide 95. Preferably, the timing of the rotation of the outer guide 95 from the closed position to the open position is after the leading edge P1 of the sheet P reaches the longitudinal pass roller pair 74 and just before the rear end P2 of the sheet P passes the nip of the conveyor roller pair 93.

[0049] Next, the CPU 402 determines whether the rear end P2 of the sheet P has passed the outer guide 95 based on the detection result of the double-sided merging sensor 40 (step S15). If it is determined that the rear end P2 has passed the outer guide 95 (step S15: Yes), the CPU 402 drives the eccentric cam 98 to return the outer guide 95 from the open position to the closed position, as shown in Figure 10(b). The timing of returning the outer guide 95 from the open position to the closed position does not need to be before the leading edge of the subsequent sheet reaches the outer guide 95. This prevents, for example, the subsequent sheet from getting caught on the outer guide 95, and allows the sheet P to be transported stably on the U-turn transport path 94.

[0050] As described above, by using the drive mechanism 300 to rotate the outer guide 95 from the closed position to the open position, the curvature of the sheet P passing through the U-turn transport path 94 is reduced, and the stiffness of the sheet P is decreased. Therefore, the transport load on the vertical path roller pair 74 is reduced, and jams caused by step loss of the vertical path transport motor M2 can be suppressed. In addition, by rotating the outer guide 95 with the drive mechanism 300, the outer guide 95 can be driven at any timing regardless of the stiffness of various types of sheets or the biasing force of the springs that bias the outer guide 95, thereby improving mechanical reliability.

[0051] In this embodiment, the outer guide 95 was configured to rotate from the closed position to the open position after the leading edge P1 of the sheet P reached the pair of vertical pass rollers 74, but this is not limited to this configuration. For example, the outer guide 95 may be configured to rotate from the closed position to the open position before the leading edge P1 of the sheet P passes the outer guide 95 and reaches the pair of vertical pass rollers 74.

[0052] <Other Embodiments> In all of the embodiments described above, the outer guide 95 was configured to be rotatable about the pivot axis 97, but it is not limited to this. For example, the outer guide 95 may be configured to slide from a closed position to an open position. In other words, the outer guide 95 may move in any way that reduces the curvature of the sheet P being transported along the U-turn transport path 94.

[0053] Furthermore, although the invention has been described using an electrophotographic printer 100 in all of the embodiments described above, the present invention is not limited thereto. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from a nozzle.

[0054] Furthermore, the embodiments described above may be combined as appropriate.

[0055] The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of Symbols]

[0056] 1E: Image forming unit (transfer nip) / 40: Detection unit (double-sided merging sensor) / 74: Second roller pair (vertical path roller pair) / 76: First transport path (straight transport path) / 78: Third roller pair (pre-registration roller pair) / 88: Second transport path (double-sided transport path) / 90~93: Multiple transport roller pairs / 93: First roller pair (transport roller pair) / 94: Curved transport path (U-turn transport path) / 95: Outer guide / 95a: Upstream end / 96: Biasing unit (compression spring) / 97: Rotating axis / 100: Image forming apparatus (printer) / 120: Inner guide / 300: Drive mechanism / CD: Sheet transport direction / L1, L2: Nip line / M2: Drive source (vertical path transport motor) / P: Sheet / P1: Front end / P2: Rear end

Claims

1. An image forming unit that forms an image on a sheet, A first transport path through which the sheet being transported toward the image forming unit passes, A second transport path for transporting the sheet on which an image has been formed on the first surface by the image forming unit back towards the first transport path, A curved transport path is configured to be continuous with the second transport path and to merge with the first transport path, Among the multiple pairs of conveying rollers arranged along the second conveying path, a first pair of rollers is located furthest downstream in the sheet conveying direction and has a nip portion for conveying the sheet, A second pair of rollers is arranged along the curved conveying path and adjacent to the first pair of rollers in the sheet conveying direction, and conveys the sheet. Internal guide and, An outer guide is provided opposite the inner guide, and together with the inner guide, constitutes at least a portion of the curved conveying path between the first roller pair and the second roller pair, and is located on the outside in the curvature direction of the curved conveying path, and is movable to a first position and a second position which is further away from the inner guide than the first position. The external guide is biased in a direction from the second position toward the first position, The nip wires of the first roller pair and the nip wires of the second roller pair intersect each other. The outer guide moves from the first position to the second position when the rear end of the sheet being conveyed by the second pair of rollers passes over the nip portion of the first pair of rollers and is pressed by the rear end. An image forming apparatus characterized by the following features.

2. The aforementioned external guide is rotatable between the first position and the second position about the pivot axis. The upstream end of the outer guide in the sheet transport direction is located at a third position when the outer guide is in the first position, and at a fourth position which is further from the inner guide than the third position when the outer guide is in the second position. The image forming apparatus according to feature 1.

3. The aforementioned outer guide is positioned adjacent to the first roller pair in the sheet transport direction. The image forming apparatus according to claim 1 or 2.

4. The outer guide is held in the first position until the rear end of the sheet being conveyed by the second pair of rollers passes the nip portion of the first pair of rollers. The image forming apparatus according to any one of claims 1 to 3.

5. The second pair of rollers transports the sheet when the outer guide is moving from the first position to the second position. The image forming apparatus according to any one of claims 1 to 4.

6. After moving to the second position, the outer guide remains in the second position until the rear end of the sheet being conveyed by the second roller pair passes the outer guide. The image forming apparatus according to any one of claims 1 to 5.

7. When the rear end of the sheet being conveyed by the second roller pair passes through the outer guide, the outer guide moves from the second position to the first position due to the biasing force of the biasing part. The image forming apparatus according to any one of claims 1 to 6.

8. A third pair of rollers is positioned along the curved conveying path and downstream of the second pair of rollers in the sheet conveying direction, and conveys the sheet. The system comprises a drive source that drives the second pair of rollers and the third pair of rollers, The image forming apparatus according to any one of claims 1 to 7.

9. A third pair of rollers is provided, which is positioned downstream of and adjacent to the second pair of rollers in the sheet conveying direction, and which conveys the sheet. The curved conveying path is curved from the second pair of rollers to the third pair of rollers. The image forming apparatus according to any one of claims 1 to 7.

10. The first transport path and the second transport path are provided so as to be substantially parallel to each other. The aforementioned curved transport path is arranged in a U-shape. The image forming apparatus according to any one of claims 1 to 9.

11. The outer guide is positioned below the inner guide, with the curved transport path in between. The image forming apparatus according to any one of claims 1 to 10.

Images