Sheet conveying device and image forming apparatus

Abstract

To provide a sheet conveyance device capable of detecting whether or not jamming has occurred in a sheet serving as a recording material.SOLUTION: The sheet conveyance device comprises: a conveyance unit configured to convey a sheet through a conveyance passage; a first moving member; a second moving member movable with respect to the first moving member; and a detection unit that detects movement of the second moving member. The first moving member has a first projected part. The first projected part can move between a first projection position for projection toward the conveyance passage and a first retreating position. The second moving member has a second projected part. The second projected part can move between a second projection position for projection toward the conveyance passage and a second retreating position. When the second projected part is pushed by the sheet, the second moving member can move from the second projection position toward the second retreating position in a state where the first moving member is at the first retreating position.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a sheet transport device that transports a sheet and an image forming apparatus including the same. [Background technology]

[0002] 2. Description of the Related Art Image forming apparatuses such as printers, copiers, and multifunction peripherals are equipped with sheet transport devices that transport sheets as recording materials. In the sheet transport devices, a phenomenon in which a sheet gets stuck in a transport path, that is, a so-called jam, may occur.

[0003] Patent Document 1 discloses an image forming apparatus having a paper discharge sensor for detecting a jam of a recording material. The image forming apparatus of Patent Document 1 determines that a jam of the recording material has occurred if the trailing edge of the recording material is not detected even after the timing when the trailing edge of the recording material passes the paper discharge sensor after the trailing edge of the recording material is detected by the paper discharge sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-176986 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the image forming apparatus of Patent Document 1 has a problem in that after the paper discharge sensor detects the recording material, a jam of the recording material cannot be detected until the timing when the trailing edge of the recording material passes the paper discharge sensor has passed.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a sheet conveying device capable of detecting early on whether or not a jam of a sheet serving as a recording material has occurred. [Means for solving the problem]

[0007] In order to solve the above problems, one of the inventions related to the present application is as follows.

[0008] a transport section configured to transport the sheet through a transport path; a first moving member having a first protruding portion, the first protruding portion being movable between a first protruding position where the first protruding portion protrudes toward the transport path and a first retracted position retracted from the first protruding position, the first moving member being configured to be moved from the first protruding position toward the first retracted position by the first protruding portion coming into contact with the sheet; a second moving member having a second protruding portion and movable relative to the first moving member, the second moving member being movable between a second protruding position where the second protruding portion protrudes toward the transport path and a second retracted position retracted from the second protruding position, the second moving member being configured to be moved from the second retracted position to the second protruding position by the first moving member moving from the first protruding position to the first retracted position; A detection unit configured to detect movement of the second moving member; having When the second protruding portion is pushed by the sheet, the second moving member is movable from the second protruding position toward the second retracted position in a state in which the first moving member is in the first retracted position. A sheet conveying device comprising: Effect of the Invention

[0009] According to the present invention, it is possible to provide a sheet transport device capable of detecting early on whether or not a jam of a sheet serving as a recording material has occurred. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] 1 is a cross-sectional view of a fixing device according to a first embodiment. [Diagram 3] FIG. 2 is an exploded perspective view showing a first flag, a second flag, and a paper discharge sensor according to the first embodiment. [Figure 4] FIG. 2 is a perspective view showing a state in which a first flag, a second flag, and a paper discharge sensor according to the first embodiment are assembled. [Diagram 5] 1 is a cross-sectional view of a fixing device according to a first embodiment. [Figure 6] 1 is a cross-sectional view of a fixing device according to a first embodiment. [Figure 7] 5A to 5C are diagrams illustrating detection timing of a paper discharge sensor according to the first embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a fixing unit according to a second embodiment. [Figure 9] FIG. 11 is an exploded perspective view showing a first flag, a second flag, and a paper discharge sensor according to a second embodiment. [Figure 10] FIG. 11 is a perspective view showing a state in which a first flag, a second flag, and a paper discharge sensor according to a second embodiment are assembled. [Figure 11] FIG. 11 is a cross-sectional view of a fixing device according to a second embodiment. [Figure 12] FIG. 11 is a cross-sectional view of a fixing device according to a second embodiment. [Figure 13] FIG. 11 is a cross-sectional view of a fixing device according to a second embodiment. [Figure 14] 13A to 13C are diagrams illustrating detection timing of a paper discharge sensor according to a second embodiment. [Figure 15] FIG. 4 is a schematic diagram showing a control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The best mode for carrying out the present invention will be described in detail below with reference to the drawings and examples. However, the functions, materials, shapes, relative positions, etc. of the components described in the examples are not intended to limit the scope of the present invention unless otherwise specified. EXAMPLES

[0012] A first embodiment of the present invention will now be described with reference to the drawings.

[0013] In this embodiment, an image forming apparatus in which four process cartridges can be detachably attached is exemplified as the image forming apparatus. However, the number of process cartridges to be attached to the image forming apparatus is not limited to this. It is set appropriately as needed.

[0014] In the embodiment described below, a laser beam printer is exemplified as one aspect of an image forming apparatus.

[0015] (Overall configuration of image forming apparatus) The overall configuration of an image forming apparatus 100 will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view of the image forming apparatus 100.

[0016] The image forming apparatus 100 includes a feed tray 1 on which sheets 2 serving as recording materials are stacked, a feed roller 3, a pair of transport rollers 4, a secondary transfer roller 6, a pressure roller 14, a heating unit 13, a discharge roller 15, and a driven roller 16. The driven roller 16 is rotated by the discharge roller 15. The sheet 2 is, for example, paper.

[0017] The image forming apparatus 100 has photosensitive drums (7Y, 7M, 7C, 7K) as image carriers that carry electrostatic latent images, and developing devices (9Y, 9M, 9C, 9K). Each of the developing devices (9Y, 9M, 9C, 9K) has a developing roller that comes into contact with the corresponding photosensitive drum (7Y, 7M, 7C, 7K) and develops the electrostatic latent image.

[0018] A yellow image is formed on the intermediate transfer belt 11 (described later) by a process cartridge that contains yellow toner and has a photosensitive drum 7Y and a developing device 9Y. A magenta image is formed on the intermediate transfer belt 11 by a process cartridge that contains magenta toner and has a photosensitive drum 7M and a developing device 9M. A cyan image is formed on the intermediate transfer belt 11 by a process cartridge that contains cyan toner and has a photosensitive drum 7C and a developing device 9C. A black image is formed on the intermediate transfer belt 11 by a process cartridge that contains black toner and has a photosensitive drum 7K and a developing device 9K. Each process cartridge is removably attached to the image forming apparatus 100.

[0019] The image forming apparatus 100 has an exposure device (laser scanner) 8 arranged above the photosensitive drums (7Y, 7M, 7C, 7K) and an intermediate transfer belt 11 arranged below the photosensitive drums (7Y, 7M, 7C, 7K). Inside the intermediate transfer belt 11, primary transfer units (10Y, 10M, 10C, 10K), a drive roller 5, and a tension roller 12 are arranged. Each of the primary transfer units (10Y, 10M, 10C, 10K) is pressed toward each of the photosensitive drums (7Y, 7M, 7C, 7K). The intermediate transfer belt 11 is stretched around the drive roller 5, the tension roller 12, and the primary transfer units (10Y, 10M, 10C, 10K).

[0020] The sheets 2 stacked and stored in the feed tray 1 are fed by a feed roller 3 rotating clockwise in the figure, and sent to a conveying roller pair 4. The sheets 2 conveyed by the conveying roller pair 4 are sent to a transfer nip formed between a drive roller 5 and a secondary transfer roller 6.

[0021] Each of the photosensitive drums (7Y, 7M, 7C, 7K) rotates counterclockwise in the figure. Laser light from a laser scanner 8 is irradiated onto each of the charged photosensitive drums (7Y, 7M, 7C, 7K), and an electrostatic latent image is formed on each of the photosensitive drums (7Y, 7M, 7C, 7K). The electrostatic latent images are developed by developing devices (9Y, 9M, 9C, 9K), and a toner image is formed on each of the photosensitive drums (7Y, 7M, 7C, 7K).

[0022] By applying a voltage to the primary transfer units (10Y, 10M, 10C, 10K), the toner images formed on the photosensitive drums (7Y, 7M, 7C, 7K) are transferred to the intermediate transfer belt 11. By driving the drive roller 5 to rotate clockwise in the figure, the intermediate transfer belt 11 moves at approximately the same speed as the movement speed of the surfaces of the photosensitive drums (7Y, 7M, 7C, 7K).

[0023] When forming a color image, toner images of yellow, magenta, cyan, and black are developed on the photosensitive drums (7Y, 7M, 7C, and 7K). The toner images formed on the photosensitive drums (7Y, 7M, 7C, and 7K) are sequentially transferred onto the intermediate transfer belt 11 by primary transfer units 10Y, 10M, 10C, and 10K.

[0024] The toner image transferred to the intermediate transfer belt 11 is transferred to the sheet 2 in a transfer nip formed between the drive roller 5 and the secondary transfer roller 6. Each process cartridge and the intermediate transfer belt 11 function as an image forming unit that forms an image on the sheet 2. The transfer nip is a transfer unit where the toner image is transferred from the image forming unit to the sheet 2.

[0025] The sheet 2 onto which the toner image has been transferred is sent to a fixing nip formed between a heating unit 13 and a pressure roller 14. In the fixing nip, the sheet 2 and the toner image are heated and pressurized, so that the toner image is fixed onto the sheet 2. The sheet 2 onto which the toner image has been fixed is discharged by a discharge roller 15 and a driven roller 16.

[0026] In the image forming apparatus 100, a portion related to the conveyance of the sheet 2 can be called a sheet conveying device. The feed roller 3, the pair of conveying rollers 4, the secondary transfer roller 6, the intermediate transfer belt 11, the pressure roller 14, the heating unit 13, the discharge roller 15, and the driven roller 16 function as a conveying section that conveys the sheet 2.

[0027] (Configuration of Fixing Device) Next, a description will be given of the fixing device 200 according to this embodiment. Fig. 2 is a cross-sectional view of the fixing device 200 according to this embodiment.

[0028] The image forming apparatus 100 has a fixing device 200. The fixing device 200 can be said to be a part of a sheet conveying device that conveys the sheet 2. The fixing device 200 has a heating unit (heating section) 13, a pressure roller 14, a discharge roller 15, and a driven roller 16. The fixing device 200 further has a first flag 21, a second flag 22, a paper discharge sensor 23, and a conveying guide 26. The discharge roller 15 and the driven roller 16 function as a discharge section that conveys the sheet 2 toward the outside of the image forming apparatus 100.

[0029] The heating unit 13 for heating the sheet 2 includes a cylindrical fixing film 17, a heater 18 that is inscribed in the fixing film 17 and heats the fixing film, a heat-resistant holder 19, and a stay 20. The fixing film 17 is, for example, a thin-walled cylindrical plastic film that is highly heat-resistant and highly thermally conductive. The heater 18 is a heating element formed by applying a conductor to an insulating-coated metal base material. The heater 18 generates heat when power is supplied from a power source (not shown). The heater 18 is supported by the holder 19 in a state where it is fitted and fixed in a groove of the holder 19. The fixing film 17 is attached in a manner that covers the outer periphery of the heater 18, the holder 19, and the stay 20, and is capable of rotational movement.

[0030] The heating unit 13 is configured to contact the pressure roller 14 with a predetermined pressure by receiving the force of a pressure spring, thereby forming a fixing nip. The pressure roller 14 has a core 14a and a heat-resistant elastic layer 14b formed in a roller shape on the outer periphery of the core 14a. Since the heat-resistant elastic layer 14b of the pressure roller 14 has elasticity, a fixing nip having a predetermined width in the conveying direction of the sheet S is formed between the heating unit 13 and the pressure roller 14. The pressure roller 14 is driven to rotate at a predetermined speed by a drive train (not shown). The rotation of the pressure roller 14 generates a frictional force between the fixing film 17 and the pressure roller 14, and the fixing film 17 is rotated by the pressure roller 14.

[0031] With the pressure roller 14 and the fixing film 17 rotating and the heater 18 generating heat, the sheet 2 carrying the unfixed toner image is transported to the fixing nip between the fixing film 17 and the pressure roller 14. The sheet 2 that has reached the fixing nip is transported while being sandwiched between the pressure roller 14 and the fixing film 17. During this process, heat from the heater 18 is applied to the sheet 2 via the fixing film 17, and the unfixed toner image is heated and pressurized to be fixed to the sheet 2.

[0032] The curvatures of the pressure roller 14 and the fixing film 17 are set so that the sheet 2 that has passed through the fixing nip is separated from the pressure roller 14 and the fixing film 17. The sheet 2 is transported by the pressure roller 14 and the fixing film 17 downstream of the fixing nip.

[0033] A conveying path 42 is disposed downstream of the fixing nip (downstream of the heating unit 13) in the conveying direction of the sheet 2. The conveying path 42 guides the sheet 2 toward a discharge section downstream of the heating unit 13 (downstream of the fixing nip). The sheet 2 is conveyed through the conveying path 42 by the pressure roller 14. The sheet 2 passing through the conveying path 42 comes into contact with and rotates a first flag 21 protruding into the conveying path 42. The operation of the first flag 21 will be described in detail later.

[0034] After rotating the first flag 21, the sheet 2 reaches a discharge nip formed by the discharge roller 15 and the driven roller 16. In this embodiment, a plurality of driven rollers 16 are in contact with the discharge roller 15. The discharge rollers 15 and the driven rollers 16 discharge the sheet 2 into a discharge tray formed on the upper part of the image forming apparatus 100.

[0035] On the other hand, the fixing device 200 is provided with a re-conveying path 43 for guiding the sheet 2 that has passed through the conveying path 42 toward the upstream side of the conveying path 42. The sheet 2 that has passed through the re-conveying path 43 is conveyed again to the image forming unit, passes through the fixing nip, and is conveyed to the conveying path 42.

[0036] When forming images on both sides of the sheet 2, first, one side (front side) of the sheet 2 faces the intermediate transfer belt 11, and an image is formed on the front side of the sheet 2. The sheet 2 with the image formed on its front side passes through the conveying path 42 and is conveyed toward the re-conveying path 43. In this embodiment, the sheet 2 passes through the conveying path 42, and a part of the sheet 2 protrudes from the image forming apparatus 100 toward the discharge tray. In this state, the discharge rollers 15 rotate in the reverse direction, and the sheet 2 is conveyed to the re-conveying path 43 with the rear end of the sheet 2 on the downstream side.

[0037] The sheet 2 that has passed through the re-conveyance path 43 reaches the image forming section again so that the back surface of the sheet 2 faces the intermediate transfer belt 11, and an image is formed on the back surface of the sheet 2.

[0038] (Details of sheet detection configuration) A sheet detection configuration for detecting the sheet 2 will be described with reference to FIGS. 2, 3, 4, 5, 6, 7, and 15. FIG.

[0039] Fig. 3 is an exploded perspective view showing the first flag (first moving member) 21, the second flag (second moving member) 22, and the paper discharge sensor (detection unit) 23. Fig. 4 is a perspective view showing the first flag 21, the second flag 22, and the paper discharge sensor 23 in an assembled state.

[0040] The fixing device 200 of the image forming apparatus 100 includes a first flag 21, a second flag 22, and a paper discharge sensor 23. The paper discharge sensor 23 is a detection unit configured to detect the movement of the second flag 22.

[0041] The second flag 22 is configured to be movable relative to the first flag 21. In this embodiment, the second flag 22 is attached to the first flag 21. The first flag 21 is movable between a first protruding position (FIG. 2) described later and a first retracted position (FIG. 5) retracted from the first protruding position. The second flag 22 is movable between a second protruding position (FIG. 5) described later and a second retracted position (FIG. 2) retracted from the second protruding position.

[0042] 3 and 4, the first flag 21 has a first protrusion 21a, a rotation stopper (support portion, regulating portion) 21b, and a shaft portion 21c. The second flag 22 has a second protrusion 22a, a regulated portion (supported portion) 22b, a detected portion 22c, and a hole 22d. The second flag 22 is attached to the first flag 21 by inserting the shaft portion 21c into the hole 22d. With respect to the conveying direction of the sheet 2 in the conveying path 42, the second protrusion 22a is disposed upstream of the first protrusion 21a.

[0043] In other words, one of the first flag 21 and the second flag 22 has an engaging portion (shaft portion), and the other of the first flag 21 and the second flag 22 has an engaged portion (hole portion) that engages with the engaging portion. The first flag 21 may have a hole portion, and the second flag 22 may have a shaft portion. Also, both the first flag 21 and the second flag 22 may have a hole portion (engaged portion) that engages with a shaft portion (engaging portion) supported by the transport guide 26.

[0044] The first flag 21 and the second flag 22 are attached to a transport guide (frame) 26 of the fixing device 200. Specifically, the shaft portion 21c is rotatably supported by the transport guide 26, and the second flag 22 is rotatably supported by the shaft portion 21c. As a result, the first flag 21 and the second flag 22 are supported rotatably (rockably) around a rotation axis (rocking axis, center of rotation) RF. In other words, the first flag 21 is rotatable around the rotation axis RF, and the second flag 22 is also rotatable around the rotation axis RF.

[0045] In this embodiment, the paper discharge sensor 23 is attached to the transport guide 26. The first flag 21, the second flag 22, and the paper discharge sensor 23 are positioned by the transport guide 26 as a single frame, improving the positional accuracy relative to each other.

[0046] 15 is a schematic diagram showing a control unit of the sheet transport device. The image forming apparatus 100 includes a control unit connected to the paper discharge sensor 23, and a motor M as a drive source for driving the transport unit. The control unit is configured to control the motor M. The motor M and the control unit can be said to be a part of the sheet transport device.

[0047] In this embodiment, the paper discharge sensor 23 is an optical sensor. When the detected portion 22c of the second flag 22 enters the slit of the paper discharge sensor 23, the paper discharge sensor 23 enters a light-shielding state. When the detected portion 22c retreats from the slit of the paper discharge sensor 23, the paper discharge sensor 23 enters a light-transmitting state. When the light-transmitting state and the light-shielding state are switched, a signal output from the paper discharge sensor 23 changes. Based on this signal change, the control unit detects the movement of the second flag 22. Based on the signal output from the paper discharge sensor 23, the control unit controls the motor M to drive or stop the conveying unit.

[0048] A flag biasing spring (biasing member, first biasing member) 24 is disposed between the first flag 21 and the second flag 22. The flag biasing spring 24 is a torsion coil spring. The shaft portion 21c is inserted into the flag biasing spring 24. One end of the flag biasing spring 24 presses the first flag 21, and the other end presses the second flag 22. That is, the flag biasing spring 24 biases the first flag 21 and the second flag 22. As a result, the restricted portion 22b of the second flag 22 is pressed against the rotation stop portion 21b of the first flag 21, and the rotation stop portion 21b of the first flag 21 and the restricted portion 22b of the second flag 22 come into contact with each other. Then, with the rotation prevention portion 21b and the regulated portion 22b in contact with each other, the first flag 21 moves from the first protruding position to the first retracted position, and the second flag 22 moves integrally with the first flag from the second retracted position to the second protruding position.

[0049] A flag holding spring (second biasing member, holding biasing member) 25 is attached to the first flag 21. The flag holding spring 25 is a torsion coil spring. A shaft portion 21c is inserted into the flag holding spring 25. One end of the flag holding spring 25 presses the transport guide 26, and the other end presses the first flag 21. The flag holding spring 25 generates a biasing force between the first flag 21 and the transport guide 26, thereby maintaining the position of the first flag 21.

[0050] Further, the first protruding portion 21a of the first flag 21 comes into direct contact with the sheet 2. A tip roller 29 is rotatably attached to the tip of the first protruding portion 21a. The tip roller 29 reduces the frictional force acting on the sheet 2.

[0051] Next, the movement of the first flag 21 by the sheet 2 will be described with reference to Figures 2 and 5. Figure 5 is a cross-sectional view of the fixing device 200 in a state in which the first flag 21 has been moved by the sheet 2.

[0052] 2, when not being pressed by the sheet 2, the first flag 21 is positioned by the flag holding spring 25 at a first protruding position where the first protruding portion 21a protrudes toward the conveying path 42. Meanwhile, the regulated portion 22b of the second flag 22 is pressed against the rotation stopper portion 21b of the first flag 21, and the second flag 22 is positioned at a second retracted position. When the second flag 22 is in the second retracted position, the second protruding portion 22a retracts from the conveying path 42. Also, the detected portion 22c of the second flag 22 enters a slit portion of the paper discharge sensor 23, and the paper discharge sensor 23 is in a light-shielding state.

[0053] 5, when the sheet 2 adds the fixing nip and comes into contact with the first protruding portion 21a of the first flag 21, the first flag 21 moves from the first protruding position to the first retracted position. Specifically, the first protruding portion 21a is pressed by the sheet 2 conveyed by the pressure roller 14, and the first flag 21 rotates counterclockwise (first direction) in FIGS. 2 and 5 about the rotation axis RF. Then, the first flag 21 moves from the first protruding position to the first retracted position.

[0054] 5, the first flag 21 rotates and moves from the first protruding position to the first retracted position, whereby the second flag 22 moves from the second retracted position to the second protruding position where the second protruding portion 22a protrudes toward the transport path 42. Specifically, the first flag 21 rotates and moves from the first protruding position to the first retracted position, whereby the second flag 22 rotates counterclockwise together with the first flag 21 in FIGS. 2 and 5. As a result, as shown in FIG. 5, the second flag 22 is located at the second protruding position.

[0055] 5, when the first flag 21 moves from the first protruding position to the first retracted position, the second flag 22 moves from the second retracted position to the second protruding position, and the detected portion 22c retracts from the slit portion of the paper discharge sensor 23. As a result, the paper discharge sensor 23 switches from a light-blocking state to a light-transmitting state, and the output of the paper discharge sensor 23 (a signal output from the paper discharge sensor 23) changes. This change in output enables the control unit to detect the leading edge position of the sheet 2, and if the leading edge position of the sheet 2 is not within a predetermined range, the control unit can stop the conveying unit.

[0056] When a jam (paper jam, sheet jam) occurs in the sheet 2, it may become difficult to clear the jam if the conveyance of the sheet 2 is continued. By stopping the conveyance unit early, it is possible to prevent the user from having difficulty clearing the jam.

[0057] When the first flag 21 is pressed by the sheet 2, the second protrusion 22a of the second flag 22 protrudes toward the conveying path 42. At this time, it is desirable that the protrusion amount of the second protrusion 22a is an amount that does not make contact with the sheet 2 that is being normally conveyed. In other words, when the second flag 22 is in the second protruding position, the second protrusion 22a is located at a position away from the sheet 2 that is being normally conveyed on the conveying path 42, and a gap is formed between the sheet 2 and the second protrusion 22a.

[0058] This can prevent the sheet 2 from rubbing against the second protruding portion 22a when the sheet 2 is being normally conveyed. Also, when an image is printed on both sides of the sheet 2, it can prevent the second protruding portion 22a from coming into contact with the sheet 2 and tearing off the image.

[0059] When the sheet 2 is normally conveyed and the trailing end of the sheet 2 passes the first protruding portion 21a, the first flag 21 biased by the flag holding spring 25 rotates clockwise around the rotation axis RF, and the first flag 21 moves from the first retracted position to the first protruding position. When the first flag 21 moves from the first retracted position to the first protruding position, the second flag 22 also moves from the second protruding position to the second retracted position. As a result, the detected portion 22c blocks the paper discharge sensor 23, and the paper discharge sensor 23 switches from the light-transmitting state to the light-blocking state, and the output of the paper discharge sensor 23 (the signal output from the paper discharge sensor 23) changes. Due to this change in output, the control unit detects the trailing end position of the sheet 2, and can stop the conveying unit if the trailing end position of the detected sheet 2 is not within a predetermined range.

[0060] 6, a description will be given of behavior when a jam occurs after the leading edge of the sheet 2 passes the first flag 21. FIG. 6 is a cross-sectional view of the fixing device 200, showing a state in which a jam occurs in the sheet 2 in the conveying path 42.

[0061] Even if a jam occurs downstream of the first flag 21, the control unit of the image forming apparatus 100 cannot immediately detect the abnormality. Therefore, the conveying unit (in this case, the pressure roller 14 and the fixing film 17) continues to convey the sheet 2. As a result, the sheet 2 is folded into an accordion shape as shown in FIG. 6.

[0062] In this embodiment, the second flag 22 can move from the second protruding position to the second retracted position while the first flag 21 is in the first retracted position by the second protruding portion 22a coming into contact with the sheet 2. Here, when viewed along the rotation axis RF, the rotation direction of the first flag 21 when moving from the first protruding position to the first retracted position is opposite to the rotation direction of the second flag 22 when moving from the second protruding position to the second retracted position.

[0063] When a jam occurs in the conveying path 42, the sheet 2 bent like an accordion comes into contact with the second protruding portion 22a of the second flag 22 in the second protruding position, and moves the second flag 22 against the biasing force of the flag biasing spring 24. When the sheet 2 comes into contact with the second protruding portion 22a while the first flag 21 is in the first retracted position and the second flag 22 is in the second protruding position, the second flag 22 moves relative to the first flag 21 from the second protruding position to the second retracted position. At this time, the second flag 22 rotates in the opposite direction to when the sheet 2 is being conveyed normally, and the regulated portion 22b moves away from the rotation stopper portion 21b.

[0064] The first flag 21 is in contact with the seat 2 and is therefore restricted from moving from the first retracted position to the first protruding position. However, the second flag 22 is configured to be movable from the second protruding position to the second retracted position relative to the first flag 21. Therefore, when the first flag 21 is in the first retracted position, the second flag 22 can move from the second protruding position to the second retracted position.

[0065] Specifically, when the first flag 21 is in the first retracted position and the second flag 22 is in the second projecting position, the movement of the second flag 22 in the direction from the second retracted position to the second projecting position (counterclockwise in FIG. 5) is restricted by the rotation stopper 21b of the first flag 21. On the other hand, when the first flag 21 is in the first retracted position and the second flag 22 is in the second projecting position, the movement of the second flag 22 in the direction from the second projecting position to the second retracted position (clockwise in FIG. 5) is permitted. Therefore, even when the first flag 21 is in the first retracted position by the sheet 2, the second protruding portion 22a is pushed by the sheet 2, so that the second flag 22 can move from the second projecting position to the second retracted position. As a result, as shown in FIG. 6, the second flag 22 can be positioned at a position where the paper discharge sensor 23 can detect the movement of the second flag 22.

[0066] The biasing force of the flag biasing spring 24 is large enough that when the first flag 21 moves from the first protruding position to the first retracted position, the second flag 22 can move from the second retracted position to the second protruding position together with the first flag 21. Furthermore, it is desirable that the biasing force of the flag biasing spring 24 is large enough that the second flag 22 can move relative to the first flag 21 against the biasing force of the flag biasing spring 24 even for the sheet 2 with the weakest rigidity among the sheets 2 usable in the image forming apparatus 100.

[0067] As described above, when a jam occurs in the conveying path 42, the second flag 22 rotates about the rotation axis RF while the first flag 21 is in the first protruding position, and the second flag 22 can rotate from the second protruding position toward the second retracted position. As a result, the detected portion 22c blocks the paper discharge sensor 23, the paper discharge sensor 23 switches from a light-transmitting state to a light-blocking state, and the output of the paper discharge sensor 23 (a signal output from the paper discharge sensor 23) changes. In other words, when the sheet 2 is being conveyed normally, the paper discharge sensor 23 switches from a light-transmitting state to a light-blocking state earlier than the rear end of the sheet 2 passes the first protruding portion 21a.

[0068] The control unit can detect that an abnormality has occurred in the conveyance of the sheet 2 based on the fact that the sheet discharge sensor 23 reacts at a timing different from the predetermined timing and the output has changed. When it is detected that an abnormality has occurred in the conveyance of the sheet 2, the control unit stops the motor M and stops the conveyance unit.

[0069] Detection of abnormal transport of the sheet 2 will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining the detection timing of the paper discharge sensor 23. The vertical axis of Fig. 7 indicates the output of the paper discharge sensor 23, which is OFF when the paper discharge sensor 23 is in a light-shielded state and ON when the paper discharge sensor 23 is in a light-transmitting state. The horizontal axis of Fig. 7 indicates time.

[0070] First, when there is no sheet 2 on the conveying path 42, the signal of the sheet discharge sensor 23 is turned OFF. When the sheet 2 normally abuts against the first flag 21, the signal of the sheet discharge sensor 23 is turned ON.

[0071] When the conveyance of the sheet 2 is normal, the signal of the discharge sensor 23 remains ON while the sheet 2 having a predetermined sheet length passes. After that, when the trailing end of the sheet 2 passes the first flag 21, the signal of the discharge sensor 23 returns to OFF. The control unit judges whether the timing at which the output (signal) of the discharge sensor 23 switches from ON to OFF is within a predetermined trailing end detection area. If the timing at which the signal switches from ON to OFF is within the trailing end detection area, the control unit judges that the conveyance of the sheet 2 is normal. Then, the conveyance of the sheet 2 continues. On the other hand, if the timing at which the signal switches from ON to OFF is outside the trailing end detection area, the control unit judges that the conveyance of the sheet 2 is abnormal, and stops the motor M and the conveying unit to stop the conveyance of the sheet 2.

[0072] The trailing end detection area is determined based on the timing when the trailing end of the sheet 2 leaves the first protruding portion 21a of the first flag 21, the first flag 21 moves to the first protruding position, and the second flag 21 moves to the second retracted position when the sheet 2 is normally conveyed. The trailing end detection area is determined in consideration of the sheet length of the sheet 2 and the variation in conveyance of the sheet 2. The control unit acquires the sheet length of the sheet 2 based on information input by the user or the output of a sensor that detects the size of the sheet 2, and sets the trailing end detection area based on the sheet length of the sheet 2. The control unit can calculate the trailing end detection area based on the sheet length of the sheet 2. The control unit may also set the trailing end detection area by referring to information on the trailing end detection area stored in a storage device of the image forming apparatus 100. The control unit also stops conveyance of the sheet 2 when the timing when the signal switches from ON to OFF is later than the trailing end detection area.

[0073] Next, a case where the sheet 2 is not normally conveyed will be described. Specifically, a case where the sheet 2 abuts against the first flag 21, the signal of the paper discharge sensor 23 turns ON, and then the sheet 2 gets jammed downstream of the first flag 21 will be described.

[0074] As described above, when the sheet 2 becomes jammed downstream of the first flag 21, the sheet 2 is bent like an accordion. The bent sheet 2 presses the second protruding portion 22a of the second flag 22, and the second flag 22 moves from the second protruding position toward the second retracted position while the first flag 21 is in the first retracted position (see FIG. 6).

[0075] As a result, the second detectable portion 22c blocks the discharge sensor 23, and the signal of the discharge sensor 23 changes from ON to OFF. When the second flag 22 moves to the second retracted position due to the jammed sheet 2 in this manner, the signal of the discharge sensor 23 switches to OFF at an earlier timing than the rear end detection area. When the signal of the discharge sensor 23 switches to OFF at an earlier timing than the rear end detection area, the control unit determines that a jam has occurred in the sheet 2, stops the motor M, and stops the conveying unit.

[0076] To summarize the above operations, the control unit stops conveying the sheet 2 when the sheet 2 abuts against the first flag 21 and the sheet discharge sensor 23 detects the movement of the second flag 22 before a predetermined time has elapsed after the sheet 2 abuts against the first flag 21 and the sheet discharge sensor 23 detects the movement of the second flag 22. The predetermined time is the time required from when the leading edge of the sheet 2 presses the first flag 21 until the trailing edge of the sheet 2 leaves the first flag 21 when the sheet 2 is normally conveyed in the conveying path 42. In this embodiment, the end of the predetermined time coincides with the earlier one of the two ends of the above-mentioned trailing edge detection area.

[0077] As described above, by configuring the first flag 21 and the second flag 22 as separate bodies, when the sheet 2 is bent in an accordion-like shape, an abnormality in the conveyance of the sheet 2 can be detected earlier than the time required for the rear end of the sheet 2 to pass the position of the first flag 21. As a result, the image forming apparatus 100 can be stopped earlier. This prevents the jam from progressing, and prevents the user from having difficulty clearing the jam. EXAMPLES

[0078] A second embodiment of the present invention will be described. The same parts as those in the first embodiment are given the same reference numerals as those in the first embodiment, and the description thereof will be omitted. The sheet conveying device according to the second embodiment has a second flag 32 that is different in shape from the second flag 22 in the first embodiment.

[0079] (Details of the paper discharge sensor detection configuration) A sheet detection configuration for detecting the sheet 2 will be described with reference to FIGS. 8, 9, 10, 11, 12, 13, and 14. FIG.

[0080] Fig. 8 is a cross-sectional view of the fixing device 300 according to this embodiment. Fig. 9 is an exploded perspective view showing the first flag 21, the second flag (second moving member) 32, and the paper discharge sensor 23. Fig. 10 is a perspective view showing the first flag 21, the second flag 32, and the paper discharge sensor 23 in an assembled state.

[0081] The second flag 32 according to this embodiment has a shape in which a third protrusion 32e is added to the second flag 22 in the first embodiment. Specifically, the second flag 32 has a second protrusion 32a, a regulated portion 32b, a detected portion 32c, a hole 32d, and a third protrusion 32e. The second protrusion 32a, the regulated portion 32b, the detected portion 32c, and the hole 32d of the second flag 32 have the same functions and configurations as the second protrusion 22a, the regulated portion 22b, the detected portion 22c, and the hole 22d of the second flag 22 in the first embodiment, respectively.

[0082] The second flag 32 is attached to the first flag 21 in the same manner as the second flag 22 in the first embodiment.

[0083] The second flag 32 has a third protrusion 32e that protrudes toward the re-conveyance path 42 and comes into contact with the sheet 2 passing through the re-conveyance path 43. As shown in Fig. 8, when the first flag 21 and the second flag 32 are not in contact with the sheet 2, the first flag 21 is in the first protruding position and the second flag 32 is in the second retracted position. In this state, the third protrusion 32e is in the third protruding position protruding toward the re-conveyance path 43.

[0084] The movement of the first flag 21 and the second flag 32 by the sheet 2 will be described with reference to Fig. 11. Fig. 11 is a cross-sectional view of the fixing device 300 in a state in which the first flag 21 has been moved by the sheet 2.

[0085] As in the first embodiment, when the sheet 2 abuts against the first protruding portion 21a of the first flag 21, the first flag 21 moves from the first protruding position to the first retracted position, and the second flag 32 moves from the second retracted position to the second protruding position. As a result, the detected portion 32c that had been blocking the paper discharge sensor 23 moves, the paper discharge sensor 23 switches to a light-transmitting state, and the output of the paper discharge sensor 23 turns ON. Meanwhile, the third protruding portion 32e retracts from the third protruding position.

[0086] 12, the behavior of the first flag 21 and the second flag 32 during double-sided printing in which images are printed on both sides of the sheet 2 will be described. Fig. 12 is a cross-sectional view of the fixing device 300 in a state in which the second flag 32 has been moved by the sheet 2 passing through the re-conveyance path 43.

[0087] As in the first embodiment, when the sheet 2 is normally transported through the transport path 42, the rear end of the sheet 2 moves downstream of the first flag 21 and separates from the first flag 21. As a result, as shown in FIG. 8, the first flag 21 moves to the first protruding position by the biasing force of the flag holding spring 25. As the first flag 21 moves to the first protruding position, the second flag 32 moves from the second protruding position to the second retracted position. Also, the third protruding portion 32e moves to the third protruding position. As the second flag 32 moves to the second retracted position, the detected portion 32c blocks the paper discharge sensor 23, the paper discharge sensor 23 switches to a light-blocking state, and the output of the paper discharge sensor 23 turns OFF.

[0088] The re-conveyance path 43 is disposed above the conveyance path 42. When the trailing end of the sheet 2 separates from the first flag 21, the trailing end of the sheet 2 is lifted from the conveyance path 42 toward the re-conveyance path 43 due to the rigidity of the sheet 2.

[0089] Starting from the output of the paper discharge sensor 23 being turned OFF, the control unit reverses the discharge rollers 15. The reversed discharge rollers 15 transport the sheet 2 to the re-conveyance path 43 and contact the third protrusion 32e. When the sheet 2 presses the third protrusion 32e, the second flag 32 moves from the second retracted position toward the second protruding position. At this time, the regulated portion 32b of the second flag 32 presses the rotation stopper portion 21b, so that the first flag 21 moves integrally with the second flag 32. As the second flag 32 moves, the detected portion 32c retreats from the paper discharge sensor 23, the paper discharge sensor 23 switches to a light-transmitting state, and the output of the paper discharge sensor 23 turns ON.

[0090] The control unit determines whether the conveyance of the sheet 2 to the re-conveyance path 43 is normal or not based on the timing when the output of the sheet discharge sensor 23 is turned ON.

[0091] 13, a description will be given of behavior when a jam occurs after the leading edge of the sheet 2 passes through the first flag 21. FIG. 13 is a cross-sectional view of the fixing device 200, showing a state in which a jam occurs in the sheet 2 in the conveying path 42.

[0092] As in the first embodiment, in this embodiment, the bent sheet 2 presses the second protruding portion 32a of the second flag 32. Because the first flag 21 is in contact with the sheet 2, the movement of the first flag 21 from the first retracted position to the first protruding position is restricted. However, because the second flag 32 is configured to be movable relative to the first flag 21, the second flag 32 can move from the second protruding position to the second retracted position while the first flag 21 is in the first retracted position. As a result, the detected portion 32c of the second flag 32 blocks the paper discharge sensor 23, the paper discharge sensor 23 switches to a light-shielding state, and the output of the paper discharge sensor 23 is turned OFF.

[0093] Detection of abnormal transport of the sheet 2 will be described with reference to Fig. 14. Fig. 14 is a diagram for explaining the detection timing of the sheet discharge sensor 23. The vertical axis of Fig. 14 indicates the output of the sheet discharge sensor 23, which is OFF when the sheet discharge sensor 23 is in a light-shielded state and ON when the sheet discharge sensor 23 is in a light-transmitted state. The horizontal axis of Fig. 14 indicates time.

[0094] As in the first embodiment, when there is no sheet 2 in the conveying path 42, the signal of the sheet discharge sensor 23 is OFF. When the sheet 2 normally abuts against the first flag 21, the signal of the sheet discharge sensor 23 is ON.

[0095] When the conveyance of the sheet 2 is normal, the signal of the sheet discharge sensor 23 remains ON while the sheet 2 having a predetermined sheet length passes. After that, when the trailing edge of the sheet 2 passes the first flag 21, the signal of the sheet discharge sensor 23 returns to OFF. As in the first embodiment, the control unit determines whether or not to stop conveyance of the sheet 2 (driving of the conveyance unit by the motor M) based on whether or not the timing at which the signal of the sheet discharge sensor 23 switches from ON to OFF is the predetermined timing.

[0096] The output of the paper discharge sensor 23 when single-sided printing is performed, in which an image is printed on one side of the sheet 2, is the same as that described in the first embodiment, and therefore a description thereof will be omitted.

[0097] When double-sided printing is performed in which images are printed on both sides of the sheet 2, the output of the discharge sensor 23 turns OFF when the rear end of the sheet 2 leaves the first flag 21. The sheet 2 is then transported to the re-transport path 43 by the inverted discharge rollers 15. As a result, the sheet 2 comes into contact with the third protruding portion 32e of the second flag 32, and the second flag 32 is moved from the second retracted position toward the second protruding position. The output of the discharge sensor 23 then turns ON again.

[0098] If the timing when the output of the discharge sensor 23 turns ON again is within a predetermined leading edge detection region (reversal), the control unit determines that the conveyance of the sheet 2 is normal and continues conveying the sheet 2. On the other hand, if the timing when the output of the discharge sensor 23 turns ON again is not within the predetermined leading edge detection region (reversal), the control unit stops the motor M and stops the conveying unit.

[0099] When the sheet 2 is transported through the re-transport path 43, the sheet 2 leaves the third protruding portion 32e. Then, the first flag 21 moves to the first protruding position, and the second flag 32 moves to the second retracted position. As a result, the detected portion 32c blocks the paper discharge sensor 23, the paper discharge sensor 23 switches to a light-blocking state, and the output of the paper discharge sensor 23 turns OFF.

[0100] If the timing when the output of the discharge sensor 23 is turned OFF is within a predetermined trailing end detection region (reversal), the control unit determines that the conveyance of the sheet 2 is normal and continues conveying the sheet 2. On the other hand, if the timing when the output of the discharge sensor 23 is turned OFF is not within the predetermined trailing end detection region (reversal), the control unit stops the motor M and stops the conveying unit. The trailing end detection region (reversal) is set based on the sheet length of the sheet 2.

[0101] As in the first embodiment, if the conveyance of the sheet 2 is not performed normally, the signal of the paper discharge sensor 23 is switched OFF at a timing earlier than the rear end detection area due to the jammed sheet 2. If the signal of the paper discharge sensor 23 is switched OFF at a timing earlier than the rear end detection area, the control unit determines that a jam of the sheet 2 has occurred, stops the motor M, and stops the conveyance unit.

[0102] In the sheet conveying device of this embodiment, the first flag 21 and the second flag 32 are configured as separate bodies, and therefore, when the sheet 2 is bent in an accordion-like shape, an abnormality in the conveyance of the sheet 2 can be detected earlier than the time required for the rear end of the sheet 2 to pass the position of the first flag 21. In addition, the sheet conveying device of this embodiment can detect an abnormality in the conveyance of the sheet 2 in the re-conveyance path 43. As a result, the image forming apparatus 100 can be stopped earlier. Therefore, the progress of the jam is suppressed, and it is suppressed that it becomes difficult for the user to handle the jam. In addition, since the occurrence of a jam of the sheet 2 in the conveyance path 42 and the re-conveyance path 43 can be detected by the single second flag 32, it is possible to reduce the arrangement space and cost of parts compared to the case where a flag and a sensor are separately provided.

[0103] In addition, the paper discharge sensor 23 and the second flags 22, 32 may be positioned so that the paper discharge sensor 23 is in a light-transmitting state when the second flags 22, 32 are in the second retracted position, and the paper discharge sensor 23 is in a light-blocking state when the second flags 22, 32 are in the second protruding position.

[0104] Furthermore, in this embodiment, an image is formed on the sheet 2 via the intermediate transfer belt 11, but the present invention can also be applied to a configuration in which the sheet 2 comes into contact with a photosensitive drum to form an image on the sheet 2.

[0105] In this embodiment, an image forming apparatus in which four process cartridges can be detachably attached has been exemplified as an image forming apparatus, but the present invention can also be used in an image forming apparatus in which one process cartridge can be detachably attached. Also, the present invention can be applied to a configuration in which a portion corresponding to the process cartridge according to this embodiment is fixed to the image forming apparatus. Even in this case, the present invention can be applied to a configuration in which the sheet 2 comes into contact with the photosensitive drum and an image is formed on the sheet 2. [Explanation of symbols]

[0106] 21 First flag (first moving member) 21a 1st protrusion 21b Rotation stopper (regulating portion, support portion) 23 Paper discharge sensor (detection unit) 22, 32 Second flag (second moving member) 22a, 32a 2nd protrusion 22b, 32b Regulated part (supported part) 32e Third protrusion 42 Transport Path 43 Re-transportation route

Claims

1. a conveying section configured to convey the sheet through a conveying path; a first moving member having a first protruding portion, the first protruding portion being movable between a first protruding position where the first protruding portion protrudes toward the transport path and a first retracted position retracted from the first protruding position, the first moving member being configured to be moved from the first protruding position toward the first retracted position by the first protruding portion coming into contact with the sheet; a second moving member having a second protruding portion and movable relative to the first moving member, the second protruding portion being movable between a second protruding position where the second protruding portion protrudes toward the transport path and a second retracted position retracted from the second protruding position, the second moving member being configured to be moved from the second retracted position to the second protruding position by the first moving member moving from the first protruding position to the first retracted position; A detection unit configured to detect movement of the second moving member; having When the second protruding portion is pushed by the sheet, the second moving member is movable from the second protruding position toward the second retracted position in a state in which the first moving member is in the first retracted position. A sheet conveying device comprising:

2. The first moving member is rotatable about a rotation axis, and the second moving member is rotatable about the rotation axis, 2. The sheet conveying device according to claim 1, wherein, when viewed along the rotation axis, the rotation direction of the first movable member when moving from the first protruding position to the first retracted position is opposite to the rotation direction of the second movable member when moving from the second protruding position to the second retracted position.

3. 3 . The sheet transport device according to claim 1 , wherein the second protrusion is disposed upstream of the first protrusion in a transport direction of the sheet in the transport path.

4. a biasing member that biases the first moving member and the second moving member, 4. The sheet conveying device according to claim 1, wherein the first moving member has a supporting portion, the second moving member has a supported portion, and the biasing member biases the first moving member and the second moving member so that the supported portion is pressed against the supporting portion.

5. 5. The sheet conveying device according to claim 4, wherein the biasing member biases the first moving member and the second moving member so that the first moving member moves from the first protruding position to the first retracted position while the support portion and the supported portion are in contact with each other.

6. The sheet conveying device according to claim 4 or 5, characterized in that when the first moving member is in the first retracted position and the second moving member moves from the second protruding position toward the second retracted position, the supported portion moves away from the supporting portion.

7. A sheet conveying device as described in any one of claims 1 to 6, characterized in that when the first moving member moves between the first protruding position and the first retracted position, the output of the detection unit changes, and when the second moving member moves from the second protruding position toward the second retracted position while the first moving member is in the first retracted position, the output of the detection unit changes.

8. a re-conveying path for guiding the sheet that has passed through the conveying path toward an upstream side of the conveying path; 8. The sheet transport device according to claim 1, wherein the second moving member has a third protrusion that protrudes toward the re-transport path, and the third protrusion is configured to contact the sheet passing through the re-transport path.

9. 9. A sheet transport device according to claim 1, wherein when the second movable member is in the second protruding position, the second protruding portion is configured to abut against the sheet when a jam of the sheet occurs in the transport path.

10. 10. A sheet transport device according to claim 1, wherein when the second movable member is in the second protruding position, the second protruding portion is positioned at a position away from the sheet that is normally transported in the transport path.

11. The sheet conveying device according to any one of claims 1 to 10, further comprising a control unit that stops conveying the sheet when the detection unit detects movement of the second moving member before a predetermined time has elapsed after the sheet abuts against the first moving member and the detection unit detects the movement of the second moving member.

12. 12. The sheet transport device according to claim 1, wherein the transport path is disposed downstream of a heating unit that heats the sheet in a transport direction of the sheet.

13. 13. The sheet transport device according to claim 1, wherein the second moving member is attached to the first moving member.

14. A sheet conveying device according to any one of claims 1 to 13, an image forming section for forming an image on the sheet; An image forming apparatus comprising:

Images