Image forming apparatus

Abstract

To provide an image forming apparatus that can be made compact.SOLUTION: An image forming apparatus 1 includes a photosensitive drum 5, a belt unit 6, a pair of register rollers 24 that nip a sheet SH at a nip position N1 and transport the sheet SH toward a transport surface 69A1 of a belt 69, a first actuator 110 that oscillates when it comes into contact with the sheet SH transported from the nip position N1 toward the transport surface 69A1, a first sensor S1 that detects the position of the first actuator 110, and a first sensor board 210 on which the first sensor S1 is provided. The first sensor board 210 is located within a range A1 in the width direction from a first edge 69E1 located on one side of the width direction of the belt 69 to a second edge 69E2 located on the other side of the width direction. As viewed along the width direction, at least a portion of the first sensor board 210 is located between a first extension line LE1 of the transport surface 69A1 and a second extension line LE2 of a back surface 69A2.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] An example of a conventional image forming apparatus is disclosed in Patent Document 1. This image forming apparatus includes a photosensitive member, a transfer belt unit, a pair of conveying rollers, a third actuator, a third sensor, and a sensor board.

[0003] The photosensitive element rotates around a rotation axis extending in the width direction. The transfer belt unit has a circulating transfer belt. The outer peripheral surface of the transfer belt has a transport surface that faces the photosensitive element and transports the sheet in the transport direction.

[0004] The pair of conveying rollers includes a registration roller and a pinch roller, and nip the sheet at a nip position located upstream of the conveying surface in the conveying direction, and conveys the sheet toward the conveying surface.

[0005] The third actuator oscillates when it comes into contact with the sheet conveyed from the nip position toward the conveying surface. The third sensor detects the position of the third actuator. The third sensor is provided on the sensor substrate.

[0006] The sensor substrate is supported on one side surface in the width direction of the second frame shown in Fig. 4. The sensor substrate is located outside in the width direction with respect to the conveying area when the sheet is conveyed along the conveying path and the re-conveying path shown in Fig. 1. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-130809 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the conventional image forming device described above, the sensor board, which is equipped with a sensor that detects the position of the actuator that contacts the sheet being transported from the nip position toward the transport surface, is positioned outside the width direction of the sheet transport area, which makes the area around the sensor board bulky, resulting in the problem that it is difficult to achieve miniaturization.

[0009] SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and has an object to provide an image forming apparatus that can be made compact. [Means for solving the problem]

[0010] The image forming apparatus of the present invention comprises: a photoreceptor that rotates around a rotation axis extending in a width direction; a belt unit having a circulating belt, the outer peripheral surface of the belt having a conveying surface that faces the photosensitive member and conveys a sheet in a conveying direction, and a back surface that is located on the opposite side of the conveying surface from the photosensitive member and extends along the conveying surface; a pair of conveying rollers that nip the sheet at a nip position located upstream of the conveying surface in the conveying direction and convey the sheet toward the conveying surface; a first actuator that swings when it comes into contact with a sheet that is conveyed from the nip position toward the conveyance surface; a first sensor that detects a position of the first actuator; a first sensor substrate on which the first sensor is provided; Equipped with the first sensor substrate is located within a range in the width direction from a first edge of the belt located on one side in the width direction to a second edge of the belt located on the other side in the width direction, When viewed along the width direction, at least a portion of the first sensor substrate is located between a first extension line of the transport surface and a second extension line of the back surface.

[0011] In the image forming apparatus of the present invention, the first sensor board is located within the range from the first edge to the second edge of the belt in the width direction, so it does not become bulky outside the sheet conveying area in the width direction. This allows the image forming apparatus to effectively utilize the area around the belt and the conveying roller pair that does not interfere with the conveyed sheet, thereby achieving a compact size in the width direction.

[0012] In addition, when viewed along the width direction, at least a portion of the first sensor board is located between a first extension line of the conveying surface and a second extension line of the back surface. This also allows the image forming apparatus to effectively utilize the area around the belt and the pair of conveying rollers that does not interfere with the conveyed sheet, thereby achieving miniaturization in the direction perpendicular to the conveying surface.

[0013] Therefore, the image forming apparatus of the present invention can be made smaller. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention, showing a state in which a drawer is in an attached position. [Figure 2] FIG. 2 is a schematic cross-sectional view similar to FIG. 1, showing the drawer in the pulled-out position. [Figure 3] FIG. 3 is a partial cross-sectional view of the image forming apparatus according to the embodiment, showing the first to fourth actuators and the like. [Figure 4] FIG. 4 is a partial perspective view showing the side frame, the belt unit, the first roller, the first actuator, and the like. [Figure 5] FIG. 5 is a partial top view showing the side frame, the belt unit, the first roller, the first actuator, the first sensor board, the second sensor board, and the like. [Figure 6] FIG. 6 is a partial cross-sectional view showing the belt unit, the frame, the first roller, the first sensor board, and the like. [Figure 7]FIG. 7 is a schematic cross-sectional view similar to FIG. 1, showing a method for attaching and detaching the belt unit. [Figure 8] FIG. 8 is a perspective view showing the frame, the sensor cover, the first roller, the first actuator, the first sensor board, and the second sensor board. [Figure 9] FIG. 9 is a perspective view showing the frame, the first roller, the first actuator, the second actuator, and the second sensor board. [Figure 10] FIG. 10 is a perspective view showing a frame that supports the first actuator and a sensor cover that supports the second actuator and the first sensor board, in a separated state. [Figure 11] FIG. 11 is a perspective view showing a sensor cover that supports the second actuator and the first sensor substrate. [Figure 12] FIG. 12 is a partial side view showing the third actuator, the fourth actuator, the second sensor substrate, the third sensor, the fourth sensor, and the first sensor substrate. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0016] (Example) 1, an image forming apparatus 1 of the embodiment is one example of a specific aspect of the image forming apparatus of the present invention. The image forming apparatus 1 is a color printer that forms an image on a sheet by an electrophotographic method.

[0017] <General configuration of image forming apparatus> The image forming device 1 comprises an approximately box-shaped device main body 9, an image forming section 3 housed in the device main body 9, a sheet tray 9C, a feeding section 20, a discharge section 29, a re-conveying tray 30 and a control section C1.

[0018] The sheet tray 9C is located at the bottom of the apparatus main body 9. The sheet tray 9C accommodates stacked sheets SH before images are formed on them. The sheets SH are paper, overhead projector sheets, etc.

[0019] A discharge tray 9T is formed on the top surface of the apparatus main body 9. The discharge tray 9T supports the sheet SH on which the image formation has been completed.

[0020] The control unit C1 has a calculation unit mainly including a CPU, ROM, and RAM (not shown), and hardware for controlling the semiconductor laser, motors, etc. The ROM stores programs for the CPU to control various operations of the image forming apparatus 1, programs for executing the recognition process, etc. The RAM functions as a storage area for temporarily recording data and signals used when the CPU executes the programs, or as a work area for data processing.

[0021] The control unit C1 controls the entire image forming apparatus 1 including the feeding unit 20, the image forming unit 3, the discharge unit 29, and the re-feed tray 30.

[0022] The device body 9 has an opening 9H and a front cover 9F. The opening 9H is open at the upper part of the front surface of the device body 9. The front cover 9F has a swing center axis at its lower end, and closes the opening 9H when in an upright position.

[0023] As shown in FIG. 2, the front cover 9F swings so that the upper end moves forward and downward, projecting forward substantially horizontally, thereby opening the opening 9H.

[0024] The width direction of the image forming apparatus 1 is a direction perpendicular to the front-rear direction and the up-down direction. The side to the left when facing the opening 9H and front cover 9F of the apparatus main body 9, i.e., the back side of the paper in Figure 1, is defined as one of the width directions. The front-rear direction, up-down direction, and width direction shown in Figure 2 and subsequent figures are shown corresponding to Figure 1.

[0025] 1, the feeding unit 20, the image forming unit 3, and the discharge unit 29 are located above the sheet tray 9C in the device main body 9. The re-conveying tray 30 is located below the image forming unit 3 and above the sheet tray 9C in the device main body 9.

[0026] The image forming apparatus 1 includes a conveying path P1 and a re-conveying path P2.

[0027] The conveying path P1 is a path for conveying the sheets SH accommodated in the sheet tray 9C toward the image forming unit 3.

[0028] More specifically, the conveying path P1 is a path that starts from the front end of the sheet tray 9C, makes an upward U-turn, passes through the feeding unit 20, then proceeds rearward substantially horizontally, passes through the image forming unit 3, and then makes an upward U-turn, passes through the discharge unit 29, and reaches the discharge tray 9T. The conveying direction of the sheet SH conveyed along the conveying path P1 is defined as a conveying direction D1.

[0029] The re-conveying path P2 is a path for inverting a sheet SH, on one side of which an image has been formed by the image forming unit 3, and transporting it again toward the image forming unit 3, and is a path for guiding the sheet SH to a junction position J1, which is located upstream of the image forming unit 3 in the conveying direction D1 on the conveying path P1.

[0030] More specifically, the re-conveying path P2 proceeds downward from the discharge unit 29, changes direction at a position below the image forming unit 3 and above the sheet tray 9C, proceeds forward substantially horizontally, passes through the re-conveying tray 30, and then merges with the conveying path P1 at the merging position J1. The re-conveying direction of the sheet SH conveyed on the re-conveying path P2 is set as a re-conveying direction D2.

[0031] The re-conveyance path P2 has a first path P2 A and a second path P2 B. The first path P2 A is a path that advances forward along the re-conveyance tray 30 in a substantially horizontal direction.

[0032] The second path P2B is a path that slopes upward from the downstream end of the first path P2A in the re-conveying direction D2 toward the joining position J1.

[0033] The feeding section 20 includes a feeding roller 21, a separation roller 22, a separation pad 22A, a conveying roller pair 23, and a registration roller pair 24. The registration roller pair 24 is an example of the "conveying roller pair" in the present invention.

[0034] The feed roller 21 is located at the upstream end of the conveying path P1 in the conveying direction D1. The feed roller 21 sends out the sheets SH stored in the sheet tray 9C to the conveying path P1. When multiple sheets SH sent out by the feed roller 21 are stacked, the separation roller 22 and the separation pad 22A separate them one by one.

[0035] The conveying roller pair 23 is located downstream of the separation roller 22 in the conveying direction D1 on the conveying path P1 and upstream of the joining position J1 in the conveying direction D1. The conveying roller pair 23 conveys the sheet SH along the conveying path P1 toward the joining position J1.

[0036] 1 and 3, the registration roller pair 24 is located downstream in the conveying direction D1 of the junction position J1 on the conveying path P1 and upstream in the conveying direction D1 of the image forming unit 3. The registration roller pair 24 has a first roller 41 and a second roller 42. The second roller 42 faces the first roller 41 at a nip position N1.

[0037] The joining position J1 is located upstream of the nip position N1 on the conveying path P1 in the conveying direction D1. The first roller 41 and the second roller 42 cooperate to convey the sheet SH along the conveying path P1 in the conveying direction D1.

[0038] The first roller 41 and the second roller 42 come into contact with the leading edge of the sheet SH being conveyed toward the first roller 41 and the second roller 42 while stopped, and after a predetermined time has elapsed, start to rotate and convey the sheet SH toward the image forming unit 3. This prevents the sheet SH from being skewed.

[0039] In this way, the sheet SH fed by the feeding section 20 toward the image forming section 3 passes through the image forming section 3 in the portion of the transport path P1 that extends substantially horizontally.

[0040] 1, the image forming unit 3 is a direct transfer color electrophotographic unit, and includes a drawer 80, a belt unit 6, a scanner unit 8, and a fixing unit 7.

[0041] The drawer 80 is a well-known structure and will not be illustrated in a simplified manner, but is a frame-shaped body made up of a pair of side walls located at the front and back of the paper in Figure 1 and extending in the front-to-back direction, and multiple connecting members extending in the width direction and connecting the two side walls.

[0042] The device main body 9 accommodates a drawer 80. The position of the drawer 80 shown in Figures 1 and 3 is the mounting position accommodated in the device main body 9, and is the position where the image forming unit 3 performs the image forming operation.

[0043] 1, the drawer 80 has four photosensitive drums 5 corresponding to the four colors of toner: black, yellow, magenta, and cyan. The photosensitive drums 5 are an example of the "photosensitive member" of the present invention.

[0044] Each photosensitive drum 5 is centered on a rotation axis X5 extending in the width direction. The drawer 80 supports each photosensitive drum 5 so that it can rotate about the rotation axis X5. The photosensitive drums 5 are aligned in the front-rear direction along a portion of the transport path P1 that extends substantially horizontally.

[0045] The drawer 80 can accommodate four toner cartridges 3C. Each toner cartridge 3C corresponds to a photosensitive drum 5, and they are lined up in the front-to-rear direction along the substantially horizontal portion of the transport path P1. Each toner cartridge 3C contains toner of the corresponding color.

[0046] Each toner cartridge 3C has a developing roller, a charger, and a toner container (not shown), which are located around each photosensitive drum 5.

[0047] The device body 9 supports the drawer 80 by a guide rail (not shown) so that the drawer 80 can move forward from the attached position.

[0048] 2, with the front cover 9F opening 9H, the drawer 80 can be moved from the attached position to a pulled-out position where it is pulled out forward toward the outside of the device body 9. The second roller 42 is rotatably supported by the drawer 80. Therefore, when the drawer 80 moves to the pulled-out position, the second roller 42 also moves together with the drawer 80.

[0049] By moving the drawer 80 to the pulled-out position, it is possible to remove a sheet SH that has become jammed along the conveying path P1, or to replace consumables such as the toner cartridges 3C.

[0050] As shown in Figures 4 and 5, the belt unit 6 is a frame-shaped body that combines unit side walls 65L, 65R that are spaced apart from each other in the width direction and extend in the front-to-rear direction, and a plurality of connecting members (not shown) that extend in the width direction and connect the unit side walls 65L, 65R.

[0051] The belt unit 6 has a sheet guide 66. The sheet guide 66 extends in the width direction and is connected to the front ends of the unit side walls 65L, 65R. Although not shown in the figure, the rear ends of the unit side walls 65L, 65R are located behind the rear end of the drawer 80.

[0052] As shown in FIG. 1, the belt unit 6 includes a drive roller 6A, a driven roller 6B, and a belt 69.

[0053] The drive roller 6A is rotatably supported on the rear end portions of the unit side walls 65L, 65R at a position downstream in the transport direction D1 from each photosensitive drum 5. The driven roller 6B is rotatably supported on the front end portions of the unit side walls 65L, 65R at a position downstream in the transport direction D1 from the pair of registration rollers 24 and upstream in the transport direction D1 from each photosensitive drum 5.

[0054] The belt 69 is located between the unit side walls 65L and 65R in the width direction and is wound around the drive roller 6A and the driven roller 6B. The belt 69 is located below each photosensitive drum 5, sandwiching a substantially horizontal portion of the transport path P1 therebetween. The outer peripheral surface of the belt 69 has a transport surface 69A1 and a back surface 69A2.

[0055] As shown in FIGS. 1 and 4 to 6, the conveying surface 69A1 is an upwardly facing, generally flat surface that extends in the front-rear and width directions between the upper end of the drive roller 6A and the upper end of the driven roller 6B.

[0056] 1, the back surface 69A2 is a downward-facing, generally flat surface extending in the front-rear and width directions between the lower end of the drive roller 6A and the lower end of the driven roller 6B. The back surface 69A2 is located on the opposite side of the transport surface 69A1 from the photosensitive drums 5 and extends along the transport surface 69A1. The first path P2A is located on the opposite side of the back surface 69A2 from the photosensitive drums 5 and extends along the back surface 69A2.

[0057] 6, when viewed along the width direction, a portion of the first roller 41 is located between a first extension line LE1 of the conveying surface 69A1 and a second extension line LE2 of the back surface 69A2. In this embodiment, the first extension line LE1 and the second extension line LE2 extend horizontally in the front-rear direction.

[0058] When viewed in the width direction, the second roller 42 is located on the opposite side of the second extension line LE2 of the back surface 69A2 with respect to the first extension line LE1 of the conveying surface 69A1, and is spaced apart from the first extension line LE1. In other words, when viewed in the width direction, the second roller 42 is spaced upward from the first extension line LE1.

[0059] 1, the registration roller pair 24 nips the sheet SH at a nip position N1 located upstream of the conveying surface 69A1 in the conveying direction D1 and conveys the sheet SH toward the conveying surface 69A1. The belt 69 circulates while nipping the conveyed sheet SH between the conveying surface 69A1 and each photosensitive drum 5. The conveying surface 69A1 faces each photosensitive drum 5 and conveys the sheet SH in the conveying direction D1.

[0060] 4 to 6, the sheet guide 66 has a guide surface 66G. The guide surface 66G is an upwardly curved surface that is located between the first roller 41 and the conveying surface 69A1 in the conveying direction D1 and extends in the width direction.

[0061] As shown in FIG. 6, the guide surface 66G guides the surface of the sheet SH conveyed from the nip position N1 toward the conveying surface 69A1 that faces away from the photosensitive drums 5, that is, the surface of the sheet SH that faces downward.

[0062] 4 and 5, the device main body 9 has side frames 99L and 99R. The side frame 99L extends in the front-rear and up-down directions along one side surface in the width direction of the device main body 9. The side frame 99R extends in the front-rear and up-down directions along the other side surface in the width direction of the device main body 9.

[0063] Although not shown, the side frames 99L and 99R have guide rails (not shown) that support the drawer 80 so that the drawer 80 can move forward from the attached position.

[0064] 7, the device main body 9 detachably supports the belt unit 6. As shown in FIGS. 4 and 5, the side frames 99L, 99R support the unit side walls 65L, 65R when the belt unit 6 is attached to the device main body 9.

[0065] 5, an edge located on one side of the width direction of the belt 69 is referred to as a first edge 69E1. An edge located on the other side of the width direction of the belt 69 is referred to as a second edge 69E2. A central portion of the width direction of the belt 69 is referred to as a central portion 69C.

[0066] In the width direction, the range from the first end edge 69E1 to the second end edge 69E2 of the belt 69 is defined as a range A1.

[0067] In the width direction, the range from the first edge 69E1 of the belt 69 to the central portion 69C is defined as a first range AC1.

[0068] In the width direction, the range from the second edge 69E2 of the belt 69 to the central portion 69C is defined as a second range AC2.

[0069] The sheet guide 66 of the belt unit 6 has an anti-slip portion 66F and a recessed portion 66D. The anti-slip portion 66F and the recessed portion 66D are for the user to grip when attaching or detaching the belt unit 6. The anti-slip portion 66F and the recessed portion 66D are located within a second range AC2 in the width direction.

[0070] The anti-slip portion 66F is made up of a plurality of thin grooves formed on the guide surface 66G, and the grooves are aligned in the width direction and extend in the conveying direction D1.

[0071] The recess 66D has a first recess 66D1 and a second recess 66D2. The first recess 66D1 is recessed downward from a portion of the guide surface 66G that is located on the other side of the non-slip portion 66F in the width direction. The second recess 66D2 is connected to the bottom of the first recess 66D1 and is recessed toward one side in the width direction so as to slip under the non-slip portion 66F.

[0072] When removing the belt unit 6 from the device body 9, with the front cover 9F opening 9H, the user places the thumb of their right hand on the anti-slip portion 66F and inserts the index finger of their right hand into the first recess 66D1 and the second recess 66D2 to grasp the anti-slip portion 66F. Then, as shown in FIG. 7, the user lifts the front end of the belt unit 6 to tilt the belt unit 6, and then pulls it in the direction of tilting forward, upward, to move the belt unit 6 out of the device body 9. The user can also attach the belt unit 6 to the device body 9 by performing the reverse operation.

[0073] 1, the scanner unit 8 is located above each photosensitive drum 5 and each toner cartridge 3C. The scanner unit 8 includes a laser light source, a polygon mirror, an fθ lens, a reflecting mirror, etc. The scanner unit 8 irradiates each photosensitive drum 5 with a laser beam from above.

[0074] In the drawer 80, the surface of each photosensitive drum 5 is uniformly positively charged by a charger as it rotates, and then exposed to high-speed scanning of a laser beam emitted from the scanner unit 8. As a result, an electrostatic latent image corresponding to the image to be formed on the sheet SH is formed on the surface of each photosensitive drum 5.

[0075] Next, the developing roller supplies toner stored in the toner storage section to the surface of each photosensitive drum 5 in accordance with the electrostatic latent image, thereby forming a toner image. Then, the first roller 41 and the second roller 42 transport the sheet SH toward each photosensitive drum 5, and when the sheet SH passes between each photosensitive drum 5 and the belt 69, the upward surface of the sheet SH faces the corresponding photosensitive drum 5. The toner image carried on the surface of each photosensitive drum 5 is transferred to the upward surface of the sheet SH. The belt 69 is a transfer belt that transfers the toner image carried on the surface of the photosensitive drum 5 to the sheet SH.

[0076] The fixing unit 7 is located behind the drawer 80. The fixing unit 7 heats and presses the sheet SH while sandwiching and conveying it between a heating roller 7A and a pressure roller 7B, thereby thermally fixing the toner image onto the sheet SH.

[0077] The discharge section 29 has a discharge roller 29A, a pinch roller 29P, and a flapper 29F.

[0078] The discharge roller 29A is located at the most downstream side of the conveying path P1. The pinch roller 29P is pressed against the discharge roller 29A. The discharge roller 29A is controlled by the control unit C1 to rotate forward and backward.

[0079] The flapper 29F is located at a portion of the transport path P1 where the transport path P1 makes an upward U-turn behind the fixing unit 7. The flapper 29F can swing between a position shown by a solid line in FIG. 1 and a position shown by a two-dot chain line in FIG.

[0080] The flapper 29F is held by a spring (not shown) at the position indicated by the two-dot chain line in Fig. 1. The biasing force of this spring is weak enough that when a sheet SH conveyed along the conveying path P1 comes into contact with the flapper 29F, the flapper 29F swings to the position indicated by the solid line in Fig. 1.

[0081] When an image is formed on only one side of the sheet SH, the discharge roller 29A cooperates with the pinch roller 29P to rotate forward while pinching the sheet SH that has passed through the fixing unit 7, thereby discharging the sheet SH onto the discharge tray 9T. At this time, the flapper 29F is pushed by the sheet SH and swings to the position shown by the solid line in Fig. 1, and after the sheet SH has passed, it returns to the position shown by the two-dot chain line in Fig. 1.

[0082] When performing image formation on both sides of the sheet SH, the discharge roller 29A, the pinch roller 29P, and the flapper 29F function as a reversing mechanism for the sheet SH, and reverse the sheet SH with an image formed on one side.

[0083] That is, while the discharge roller 29A and the pinch roller 29P are nipping the sheet SH and discharging it to the discharge tray 9T, the control unit C1 switches the discharge roller 29A from forward rotation to reverse rotation at a predetermined timing after the sheet sensor (not shown) no longer detects the trailing edge of the sheet SH passing through the fixing unit 7. As a result, the discharge roller 29A and the pinch roller 29P reverse the sheet SH.

[0084] The predetermined timing is set so that it occurs after the trailing edge of the sheet SH passes the flapper 29F and the flapper 29F returns to the position shown by the two-dot chain line in Fig. 1. When the flapper 29F is in the position shown by the two-dot chain line in Fig. 1, the upper edge side of the flapper 29F crosses the conveying path P1 and follows the re-conveying path P2. As a result, the flapper 29F guides the inverted sheet SH to the re-conveying path P2.

[0085] The re-conveying tray 30 has a first re-conveying roller pair 25 and a second re-conveying roller pair 26. The second re-conveying roller pair 26 is located downstream of the first re-conveying roller pair 25 in the re-conveying direction D2.

[0086] The first re-conveying roller pair 25 conveys the sheet SH, which has been guided to the re-conveying path P2 by the discharge roller 29A, the pinch roller 29P, and the flapper 29F, toward the second re-conveying roller pair 26. The second re-conveying roller pair 26 takes over the sheet SH from the first re-conveying roller pair 25 and conveys it toward the joining position J1.

[0087] As a result, the re-conveyed sheet SH merges with the conveying path P1 at the merging position J1. Then, the image forming unit 3 forms an image on the other side of the re-conveyed sheet SH, and the discharge unit 29 discharges the sheet SH with the images formed on both sides onto the discharge tray 9T.

[0088] <First detection unit, second detection unit, third detection unit, and fourth detection unit> The image forming apparatus 1 includes a first detection unit 101, a second detection unit 102, a third detection unit 103, and a fourth detection unit 104.

[0089] The first detection unit 101 detects the presence or absence of the sheet SH at a position downstream of the nip position N1 on the conveying path P1 in the conveying direction D1 and upstream of each photosensitive drum 5 in the conveying direction D1, and transmits a detection signal to the control unit C1.

[0090] The control unit C1 determines that the leading edge of the sheet SH conveyed from the registration roller pair 24 has been detected based on the detection signal obtained from the first detection unit 101. Then, the control unit C1 determines the timing at which the leading edge of the sheet SH reaches each photosensitive drum 5, and controls the timing of the image forming operation by the image forming unit 3.

[0091] The first detection unit 101 has a first actuator 110 shown in Figures 1 to 5 and 8 to 10, and a first sensor S1 shown in Figures 6 and 11. The configurations of the first actuator 110 and the first sensor S1 will be described later.

[0092] 1, the second detection unit 102 is located downstream of the second re-conveying roller pair 26 on the re-conveying path P2 in the re-conveying direction D2 and upstream of the junction position J1 in the re-conveying direction D2. That is, the second detection unit 102 is located on the second path P2B. The second detection unit 102 detects the presence or absence of the sheet SH being conveyed on the second path P2B and transmits a detection signal to the control unit C1.

[0093] When an image forming operation is performed with a plurality of sheets SH present on the conveying path P1 and the re-conveying path P2, the control unit C1 stops the first re-conveying roller pair 25 and the second re-conveying roller pair 26 upon receiving a detection signal from the second detection unit 102 indicating the presence of a sheet SH. The control unit C1 determines that the rear end of the sheet SH conveyed on the conveying path P1 has been detected based on the signal received from the first detection unit 101. The control unit C1 then determines that the sheet SH conveyed on the conveying path P1 has passed the first detection unit 101, and controls the timing at which the first re-conveying roller pair 25 and the second re-conveying roller pair 26 start rotating. This makes it possible to prevent the sheet SH on the re-conveying path P2 from interfering with the sheet SH conveyed along the conveying path P1.

[0094] The second detection unit 102 has a second actuator 120 shown in Figures 3 and 9 to 11, and a second sensor S2 shown in Figures 6 and 11. The configurations of the second actuator 120 and the second sensor S2 will be described later.

[0095] As shown in Figure 1, the third detection unit 103 detects the presence or absence of a sheet SH at a position downstream in the conveying direction D1 from the conveying roller pair 23 on the conveying path P1 and upstream in the conveying direction D1 from the merging position J1, and transmits a detection signal to the control unit C1.

[0096] Based on the detection signal obtained from the third detection unit 103, the control unit C1 determines the timing at which the leading edge of the sheet SH fed from the sheet tray 9C reaches the pair of registration rollers 24, and controls the timing at which the pair of registration rollers 24 start rotating.

[0097] The third detection unit 103 has a third actuator 130 shown in Figures 3 and 12, and a third sensor S3 shown in Figures 8 and 12. The configurations of the third actuator 130 and the third sensor S3 will be described later.

[0098] 1, the fourth detection unit 104 is located downstream of the second detection unit 102 on the re-conveying path P2 in the re-conveying direction D2 and upstream of the merging position J1 in the re-conveying direction D2. The fourth detection unit 104 detects the presence or absence of the sheet SH at a position downstream of the second detection unit 102 on the second path P2B in the re-conveying direction D2, and transmits a detection signal to the control unit C1.

[0099] Based on the detection signal obtained from the fourth detection unit 104, the control unit C1 determines the timing at which the leading edge of the sheet SH being transported along the re-conveying path P2 reaches the pair of registration rollers 24, and controls the timing at which the pair of registration rollers 24 start rotating.

[0100] The fourth detection unit 104 has a fourth actuator 140 shown in Figures 3 and 12, and a fourth sensor S4 shown in Figures 8, 9, and 12. The configurations of the fourth actuator 140 and the fourth sensor S4 will be described later.

[0101] <Frame and feeding frame> The image forming apparatus 1 includes a frame 60 shown in Figures 3 to 6 and 8 to 10, and a feeding-side frame 50 shown in Figures 3 and 6. The frame 60 and the feeding-side frame 50 are each a resin molded product manufactured by injection molding of a thermoplastic resin or the like.

[0102] Although not shown in the figure, the frame 60 and the feeding side frame 50 are connected to the side frames 99L and 99R at one and the other widthwise positions relative to the conveying path P1 and the re-conveying path P2, with the frame 60 and the feeding side frame 50 being precisely positioned by fitting portions, engaging portions, etc.

[0103] As shown in FIG. 3, the frame 60 and the feeding-side frame 50 separate a part of the conveying path P1 from a part of the re-conveying path P2.

[0104] More specifically, the surface of the feeding-side frame 50 facing forward and downward defines a section of the conveying path P1 from the most upstream side in the conveying direction D1 to the joining position J1.

[0105] 9, the frame 60 has a guide wall 61. As shown in Fig. 3, the upward and rearward facing surface of the feeding-side frame 50 and the downward and forward facing surface of the guide wall 61 of the frame 60 define a second path P2B of the re-conveyance path P2.

[0106] The front-facing surface of the upper portion of the guide wall 61 of the frame 60 defines a portion of the conveying path P1 that extends from the joining position J1 toward the nip position N1.

[0107] The feeding-side frame 50 rotatably supports the separation roller 22 and one roller 23A of the pair of conveying rollers 23.

[0108] As shown in Fig. 8, the frame 60 rotatably supports the first roller 41. The axial direction of the first roller 41 is parallel to the width direction. As shown in Fig. 9, the frame 60 rotatably supports one roller 26P of the second re-conveying roller pair 26.

[0109] The frame 60 has a frame opening 60H. The frame opening 60H is a generally rectangular hole that passes through the center of the guide wall 61 in the width direction in the up-down direction.

[0110] <Sensor cover> 8, 10, and 11, the image forming apparatus 1 includes a sensor cover 70. The sensor cover 70 is a resin molded product manufactured by injection molding of a thermoplastic resin or the like. The sensor cover 70 includes a cover main body 71 and a cover opening 71H.

[0111] The cover body 71 has a first flat plate portion 71A, a second flat plate portion 71B, and a step portion 71C.

[0112] The first flat plate portion 71A is a front portion of the cover main body 71, and extends in the width direction and also extends a short distance in the front-rear direction.

[0113] The second flat plate portion 71B is a rear portion of the cover body 71, and extends in the width direction at a position spaced rearward and downward from the first flat plate portion 71A, and also extends a short distance in the up-down direction.

[0114] The step portion 71C is an intermediate portion of the cover body 71, and is bent in a stepped shape to connect the rear edge of the first flat plate portion 71A and the upper edge of the second flat plate portion 71B. The first flat plate portion 71A extends further in the other width direction than the second flat plate portion 71B and the step portion 71C.

[0115] The step portion 71C is an intermediate portion of the cover body 71, and is bent in a stepped shape to connect the rear edge of the first flat plate portion 71A and the upper edge of the second flat plate portion 71B. The first flat plate portion 71A extends further in the other width direction than the second flat plate portion 71B and the step portion 71C.

[0116] The cover opening 71H penetrates the center in the width direction of the cover main body 71 in the up-down direction. The front portion of the cover opening 71H is formed by cutting out a part of the first flat plate portion 71A. The rear portion of the cover opening 71H is formed by cutting out a part of the step portion 71C.

[0117] As shown in FIG. 8, the sensor cover 70 is attached to the frame 60 from above, and is fastened to the frame 60 by two screws 70F.

[0118] <First sensor substrate, first sensor, and second sensor> 5, 6, 8, 10, and 12, image forming apparatus 1 includes first sensor substrate 210. As shown in Fig. 11, substrate surface 210A of first sensor substrate 210 is a plane perpendicular to the width direction and faces the other side in the width direction.

[0119] The first sensor board 210 is attached to one end of the sensor cover 70 in the width direction on the rear surface side of the sensor cover 70, and is fastened to the sensor cover 70 by a screw 210F.

[0120] As shown in FIG. 6, when viewed in the width direction, a part of the upper end side of the first sensor board 210 is located between a first extension line LE1 of the transport surface 69A1 and a second extension line LE2 of the rear surface 69A2.

[0121] Lower edge 210E of first sensor substrate 210 is located on the second path P2B side and extends forward with an upward incline. That is, lower edge 210E of first sensor substrate 210 extends along second path P2B.

[0122] As shown in FIG. 5, the first sensor board 210 is located within a range A1 from the first edge 69E1 to the second edge 69E2 of the belt 69 in the width direction.

[0123] More specifically, the first sensor board 210 is located within a first range AC1 from the first edge 69E1 of the belt 69 to the central portion 69C in the width direction.

[0124] As shown in FIGS. 5 and 6, a part of the rear side of the first sensor board 210 overlaps a part of the sheet guide 66 when viewed in a direction perpendicular to the transport surface 69A1, ie, in the up-down direction.

[0125] 8, the first sensor board 210 supported by the sensor cover 70 is positioned so as to overlap with the first roller 41 in the width direction (axial direction of the first roller 41). The first sensor board 210 is positioned to one side in the width direction relative to the center of the first roller 41 in the width direction. The cover main body 71 covers the first sensor board 210 from above.

[0126] 6, a first sensor S1 and a second sensor S2 are provided on the substrate surface 210A of the first sensor substrate 210. The second sensor S2 is spaced rearward and downward from the first sensor S1.

[0127] The first sensor S1 and the second sensor S2 are each a photointerrupter that detects whether the optical path is interrupted. As will be described later, the first sensor S1 detects the position of the first actuator 110 in a non-contact manner. The second sensor S2 detects the position of the second actuator 120 in a non-contact manner.

[0128] <Second sensor board, third sensor, and fourth sensor> 5, 8, 9, and 12, image forming apparatus 1 includes second sensor substrate 220. Substrate surface 220A of second sensor substrate 220 is a plane perpendicular to the width direction and faces the other side in the width direction.

[0129] As shown in FIG. 8, the second sensor board 220 is attached to a wall located at the other end of the frame 60 in the width direction.

[0130] As shown in FIG. 5, the second sensor board 220 is located on the other side of the central portion 69C of the belt 69 in the width direction.

[0131] More specifically, the second sensor board 220 is located on the other side of the second end edge 69E2 of the belt 69 in the width direction.

[0132] As shown in FIG. 12, a portion of second sensor substrate 220 overlaps a portion of first sensor substrate 210 when viewed along the width direction.

[0133] 8, the second sensor board 220 supported by the frame 60 is located at a position that does not overlap with the first roller 41 in the width direction. In other words, the second sensor board 220 is located outside the conveying area of ​​the sheet SH in the width direction.

[0134] A third sensor S3 and a fourth sensor S4 are provided on the substrate surface 220A of the second sensor substrate 220. The third sensor S3 is spaced forward and downward from the fourth sensor S4.

[0135] The third sensor S3 and the fourth sensor S4 are each a photointerrupter that detects whether the optical path is interrupted. As will be described later, the third sensor S3 detects the position of the third actuator 130 in a non-contact manner. The fourth sensor S4 detects the position of the fourth actuator 140 in a non-contact manner.

[0136] <First actuator> As shown in FIG. 10, the first actuator 110 has a first shaft 111, a first contact portion 112, a first shielding portion 113, and a cam 114.

[0137] The first shaft 111 extends in the width direction. The frame 60 supports the first actuator 110 so that it can swing by rotatably supporting the first shaft 111 with a plurality of walls that protrude upward from the upper surface and front side of the guide wall 61.

[0138] An end 111A of the first shaft 111 located on one side in the width direction is located on one side in the width direction of the frame opening 60H. The end 111A of the first shaft 111 is located near the first sensor S1 shown in FIG.

[0139] 10, the other end 111B of the first shaft 111, which is located on the other side in the width direction, is located near the other end of the frame 60 in the width direction. As shown in Fig. 8, the other end 111B of the first shaft 111 is located on the other side in the width direction of the other end of the first roller 41 in the width direction. In other words, the other end 111B of the first shaft 111 is located outside the conveyance area of ​​the sheet SH in the width direction.

[0140] The cover body 71 covers the first shaft 111 from above, except for the other end 111B.

[0141] 10, the first contact portion 112 protrudes radially outward from a portion of the first shaft 111 that is located forward and above the frame opening 60H. As shown in FIG. 8, the cover opening 71H allows the first contact portion 112 to pass through.

[0142] 5, the first contact portion 112 is disposed at a position closer to the center portion 69C of the belt 69 in the width direction than the first sensor board 210. In this embodiment, the first contact portion 112 is disposed at approximately the same position as the center portion 69C of the belt 69 in the width direction.

[0143] 10, the first shielding portion 113 protrudes radially outward from one end 111A of the first shaft 111 at a position spaced apart from the first contact portion 112 on one side in the width direction. In other words, the first shielding portion 113 protrudes from the first shaft 111 in the vicinity of the first sensor S1 shown in Fig. 11. As shown in Fig. 8, the cover main body 71 covers the first shielding portion 113 from above.

[0144] 10, the cam 114 protrudes radially outward from the other end 111B of the first shaft 111 at a position spaced apart from the first contact portion 112 on the other side in the width direction. In other words, the cam 114 protrudes from the first shaft 111 on the outside in the width direction relative to the conveying area of ​​the sheet SH. As shown in FIG. 8, the cover main body 71 does not cover the cam 114.

[0145] 10, a tension coil spring 110F is located between the first shaft 111 and the guide wall 61. The tension coil spring 110F biases the first actuator 110 to swing in the counterclockwise direction on the paper surface of FIG.

[0146] 1 and 2, the drawer 80 has a cam pressing portion 84. The cam pressing portion 84 is located rearward of the second roller 42 and forward of each photosensitive drum 5. The cam pressing portion 84 is also located on the other side of the width direction from the other end of the second roller 42 in the width direction.

[0147] Although not shown, the cam pressing portion 84 presses the cam 114 when the drawer 80 moves to the mounted position shown in FIG. 1, and moves away from the cam 114 when the drawer 80 moves forward from the mounted position.

[0148] 8 to 10, when the cam pressing portion 84 is separated from the cam 114, the cam 114 protrudes upward due to the biasing force of the tension coil spring 110F. In this state, the first abutment portion 112 protrudes upward from the first shaft 111, and then bends and extends forward.

[0149] 2 and 8 to 10 is in the retracted position. As shown in Fig. 8, the first roller 41 has a smaller diameter at its central portion in the width direction than at other portions. In the retracted position, the first contact portion 112 enters the small diameter portion of the first roller 41.

[0150] 2, the first contact portion 112 in the retracted position is retracted downward from the space A1 through which the drawer 80 passes when moving from the attached position. This prevents the first contact portion 112 from interfering with the photosensitive drums 5, etc. of the drawer 80 when they pass above the first contact portion 112 in the retracted position.

[0151] That is, the cam 114 moves away from the cam pressing portion 84 of the drawer 80 that is moving from the attached position, thereby causing the first contact portion 112 to swing to a retracted position where it does not contact the drawer 80 .

[0152] When the cam pressing portion 84 presses the cam 114 as the drawer 80 moves to the attached position, the first actuator 110 swings clockwise on the paper in Fig. 3, and the first contact portion 112 moves to the first non-contact position shown by the solid line in Fig. 3. The position of the first contact portion 112 shown in Fig. 1 is also the first non-contact position.

[0153] 1 and 3, when the first contact portion 112 is in the first non-contact position, it is located downstream of the nip position N1 in the conveying direction D1 and upstream of each photosensitive drum 5 in the conveying direction D1. The first contact portion 112 protrudes into a space A1 through which the drawer 80 passes when moving from the attached position.

[0154] When the first contact portion 112 is in the first non-contact position, it can come into contact with the sheet SH being transported along the transport path P1 from the nip position N1 toward the transport surface 69A1. When the first contact portion 112 comes into contact with the sheet SH, the first actuator 110 swings clockwise on the paper surface of Figure 3, and the first contact portion 112 moves to the first contact position indicated by the two-dot chain line in Figure 3.

[0155] 10, the first shielding portion 113 has a shielding plate 113A at its tip. The shielding plate 113A extends in an arc shape in the circumferential direction of the first shaft 111. The first shielding portion 113 can block the optical path of the first sensor S1 shown in FIG. 11 by using the shielding plate 113A.

[0156] When the first contact portion 112 is in the retracted position, the shielding plate 113A in the position shown in FIG. 10 is located behind the first sensor S1 shown in FIG. 11, and opens the optical path of the first sensor S1.

[0157] Although not shown, when the first contact portion 112 is in the first non-contact position, the first shielding portion 113 shields the optical path of the first sensor S1 with the shielding plate 113A. When the first contact portion 112 comes into contact with the sheet SH and moves to the first contact position, the shielding plate 113A moves forward of the first sensor S1 shown in FIG. 11 and opens the optical path of the first sensor S1.

[0158] When the drawer 80 is in the attached position, the control unit C1 determines that the first detection unit 101 has detected the sheet SH when the optical path of the first sensor S1 switches from blocked to open, and controls the timing of the image formation operation by the image forming unit 3.

[0159] <Second actuator> As shown in FIG. 11, the second actuator 120 has a second shaft 121, a second contact portion 122, and a second shielding portion 123.

[0160] The second shaft 121 extends in the width direction. The sensor cover 70 supports the second actuator 120 so that it can swing by rotatably supporting the second shaft 121 with a plurality of walls located on the front side of the second flat plate portion 71B.

[0161] One end 121A of the second shaft 121 located on one side in the width direction is located on one side in the width direction of the cover opening 71H. One end 121A of the second shaft 121 is located near the second sensor S2.

[0162] The other end 121B of the second shaft 121, which is located on the other side in the width direction, is located on the other side in the width direction of the cover opening 71H.

[0163] The second contact portion 122 protrudes radially outward from a portion of the second shaft 121 that is located rearward and below the cover opening 71H. As shown in Fig. 9, the frame opening 60H allows the second contact portion 122 to pass through.

[0164] The second shielding portion 123 protrudes from one end 121A of the second shaft 121 in the radially outward direction of the second shaft 121 at a position spaced apart from the second contact portion 122 in one width direction. In other words, the second shielding portion 123 protrudes from the second shaft 121 in the vicinity of the second sensor S2.

[0165] As shown in FIG. 8, the cover body 71 covers the second shaft 121, the second contact portion 122, and the second shielding portion 123 from above.

[0166] 11, a tension coil spring 120F is located between the second shaft 121 and the cover main body 71. The tension coil spring 120F biases the second actuator 120 to swing in the counterclockwise direction on the page of FIG.

[0167] Due to the biasing force of the tension coil spring 120F, the second contact portion 122 is in the second non-contact position shown by the solid line in Fig. 3. The position of the second contact portion 122 shown in Figs. 9 and 11 is also the second non-contact position.

[0168] As shown in FIG. 3, the second contact portion 122 is located on the second path P2B of the re-conveyance path P2.

[0169] When the second contact portion 122 is in the second non-contact position, it can come into contact with the sheet SH being transported on the second path P2B of the re-conveyance path P2. When the second contact portion 122 comes into contact with the sheet SH, the second actuator 120 swings clockwise on the paper surface of Fig. 3, and the second contact portion 122 moves to the second contact position indicated by the two-dot chain line in Fig. 3.

[0170] 11, the second shielding portion 123 has a shielding plate 123A at its tip. The shielding plate 123A extends in an arc shape in the circumferential direction of the second shaft 121. The second shielding portion 123 can block the optical path of the second sensor S2 with the shielding plate 123A.

[0171] When the second contact portion 122 is in the second non-contact position, the second shielding portion 123 shields the optical path of the second sensor S2 with the shielding plate 123A. When the second contact portion 122 comes into contact with the sheet SH and moves to the second contact position, the shielding plate 123A moves below the first sensor S1, opening the optical path of the first sensor S1.

[0172] When an image forming operation is performed with a plurality of sheets SH present on the conveying path P1 and the re-conveying path P2, the control unit C1 determines that the second detection unit 102 has detected the leading edge of the sheet SH at the timing when the optical path of the second sensor S2 switches from blocked to open. Then, the control unit C1 stops the rotation of the first re-conveying roller pair 25 and the second re-conveying roller pair 26, and stops the sheet SH abutting against the second actuator 120 on the re-conveying path P2. When the sheet SH is stopped on the re-conveying path P2, the leading edge of the sheet SH is located upstream of the fourth contact unit 142 in the re-conveying direction D2.

[0173] <Third Actuator> 3, the third actuator 130 has a third shaft 131 and a third contact portion 132. The third actuator 130 also has a third shielding portion 133 shown in FIG.

[0174] 3, the third shaft 131 extends in the width direction and is rotatably supported by the feeding-side frame 50. The third shaft 131 is biased in the counterclockwise direction on the paper of FIGS. 3 and 12 by a tension coil spring (not shown).

[0175] 3, the third contact portion 132 protrudes from the third shaft 131 in the radially outward direction of the third shaft 131. Due to the biasing force of a tension coil spring (not shown), the third contact portion 132 is in a third non-contact position indicated by a solid line in FIG.

[0176] The third contact portion 132 is located downstream of the pair of transport rollers 23 in the transport path P1 in the transport direction D1 and upstream of the joining position J1 in the transport direction D1.

[0177] When the third contact portion 132 is in the third non-contact position, it can come into contact with the sheet SH being transported from the sheet tray 9C along the transport path P1 toward the nip position N1. When the third contact portion 132 comes into contact with the sheet SH, the third actuator 130 swings clockwise on the paper surface of Figure 3, and the third contact portion 132 moves to the third contact position indicated by the two-dot chain line in Figure 3.

[0178] 12, the third shielding portion 133 has a shielding plate 133A at its tip. The shielding plate 133A extends in an arc shape in the circumferential direction of the third shaft 131. The third shielding portion 133 can block the optical path of the third sensor S3 with the shielding plate 133A.

[0179] When the third contact portion 132 is in the third non-contact position, the shielding plate 133A is located forward and below the third sensor S3, and the third shielding portion 133 opens the optical path of the third sensor S3. When the third contact portion 132 comes into contact with the sheet SH and moves to the third contact position, the third shielding portion 133 blocks the optical path of the third sensor S3 with the shielding plate 133A.

[0180] The control unit C1 determines that the leading edge of the sheet SH fed from the sheet tray 9C has been detected based on the timing when the optical path of the third sensor S3 switches from open to closed. Then, the control unit C1 determines the timing when the leading edge of the sheet SH reaches the registration roller pair 24, and controls the timing when the first roller 41 and the second roller 42 start to rotate.

[0181] <Fourth Actuator> 3, the fourth actuator 140 has a fourth shaft 141 and a fourth contact portion 142. The fourth actuator 140 also has a fourth shielding portion 143 shown in FIG.

[0182] 3, the fourth shaft 141 extends in the width direction and is rotatably supported by the feeding-side frame 50. The fourth shaft 141 is biased in the clockwise direction on the paper of FIGS. 3 and 12 by a tension coil spring (not shown).

[0183] 3, the fourth contact portion 142 protrudes from the fourth shaft 141 in the radially outward direction of the fourth shaft 141. Due to the biasing force of a tension coil spring (not shown), the fourth contact portion 142 is in a fourth non-contact position shown by the solid line in FIG.

[0184] The fourth contact portion 142 is located on the re-transport path P2 between the second contact portion 122 of the second actuator 120 and the joining position J1.

[0185] When the fourth contact portion 142 is in the fourth non-contact position, it can come into contact with the sheet SH being transported on the second path P2B of the re-conveyance path P2. When the fourth contact portion 142 comes into contact with the sheet SH, the fourth actuator 140 swings counterclockwise on the paper surface of Fig. 3, and the fourth contact portion 142 moves to the fourth contact position indicated by the two-dot chain line in Fig. 3.

[0186] 12, the fourth shielding portion 143 has a shielding plate 143A at its tip. The shielding plate 143A extends in an arc shape in the circumferential direction of the fourth shaft 141. The fourth shielding portion 143 can block the optical path of the fourth sensor S4 with the shielding plate 143A.

[0187] When the fourth contact portion 142 is in the fourth non-contact position, the shielding plate 143A is located below the fourth sensor S4, and the fourth shielding portion 143 opens the optical path of the fourth sensor S4. When the fourth contact portion 142 comes into contact with the sheet SH and moves to the fourth contact position, the fourth shielding portion 143 blocks the optical path of the fourth sensor S4 with the shielding plate 143A.

[0188] The control unit C1 determines that the leading edge of the sheet SH being conveyed along the re-conveyance path P2 has been detected based on the timing when the optical path of the fourth sensor S4 switches from open to closed. Then, the control unit C1 determines the timing when the leading edge of the sheet SH reaches the registration roller pair 24, and controls the timing when the first roller 41 and the second roller 42 start to rotate.

[0189] <Action and effect> In the image forming apparatus 1 of the embodiment, as shown in FIG. 5, the first sensor substrate 210 is located within the range A1 from the first edge 69E1 to the second edge 69E2 of the belt 69 in the width direction, and therefore does not take up space outside the conveying area of ​​the sheet SH in the width direction.

[0190] As a result, the image forming device 1 can effectively utilize the area around the belt 69 and the pair of registration rollers 24 where the first sensor board 210 is positioned so as not to interfere with the sheet SH being transported, thereby achieving a smaller size in the width direction.

[0191] As shown in FIG. 6, when viewed in the width direction, a part of the upper end side of the first sensor board 210 is located between the first extension line LE1 of the transport surface 69A1 and the second extension line LE2 of the rear surface 69A2.

[0192] This also allows the image forming device 1 to effectively utilize the area around the belt 69 and the pair of registration rollers 24 where the first sensor board 210 is positioned so as not to interfere with the sheet SH being transported, thereby achieving miniaturization in the direction perpendicular to the transport surface 69A1, i.e., in the vertical direction.

[0193] Therefore, the image forming apparatus 1 of the embodiment can be made smaller.

[0194] 5 and 6, in this image forming apparatus 1, when viewed in the up-down direction, a part of the rear side of the first sensor board 210 overlaps a part of the sheet guide 66. This configuration makes it possible to achieve miniaturization in the direction in which the first extension line LE1 and the second extension line LE2 extend, i.e., in the front-to-rear direction.

[0195] 5, in the image forming apparatus 1, the first sensor board 210 is located within a first range AC1 from the first edge 69E1 to the central portion 69C of the belt 69 in the width direction. The first contact portion 112 of the first actuator 110 is disposed closer to the central portion 69C of the belt 69 in the width direction than the first sensor board 210. With this configuration, the first sensor board 210 does not interfere with the first contact portion 112 of the first actuator 110. The first contact portion 112 contacts the vicinity of the central portion in the width direction of the leading edge of the sheet SH conveyed from the nip position N1 toward the conveying surface 69A1, thereby preventing the sheet SH from skewing.

[0196] In the image forming apparatus 1, the sheet guide 66 has a recess 66D for gripping when attaching or detaching the belt unit 6. The recess 66D is located within a second range AC2 from the second edge 69E2 to the center 69C of the belt 69 in the width direction. With this configuration, a user attaching or detaching the belt unit 6 can easily attach or detach the belt unit 6 by inserting their right index finger into the first recess 66D1 and the second recess 66D2 of the recess 66D and gripping the anti-slip portion 66F of the sheet guide 66. In addition, the first recess 66D1 and the second recess 66D2 are located on the opposite side of the center 69C of the belt 69 from the first sensor board 210 in the width direction, and therefore do not interfere with the first sensor board 210.

[0197] 11, in this image forming apparatus 1, substrate surface 210A of first sensor substrate 210 is perpendicular to the width direction. This configuration makes it possible to further reduce the size in the width direction.

[0198] Furthermore, this image forming apparatus 1 can be further miniaturized in the width direction by providing the second sensor S2 together with the first sensor S1 on the first sensor substrate 210. This configuration also makes it possible to easily realize a layout on the substrate surface 210A of the first sensor substrate 210 in which the first sensor S1 is disposed at a position suitable for the first actuator 110, and the second sensor S2 is disposed at a position suitable for the second actuator 120.

[0199] 3, the second actuator 120 comes into contact with the sheet SH being conveyed on the second path P2B of the re-conveyance path P2. With this configuration, the second actuator 120 can detect the sheet SH heading toward the junction position J1 at a position close to the junction position J1.

[0200] 6, in this image forming apparatus 1, substrate surface 210A of first sensor substrate 210 is perpendicular to the width direction. Edge 210E of first sensor substrate 210 located on the second path P2B side extends along second path P2B. In this way, by aligning part of the shape of first sensor substrate 210 with second path P2B, it is possible to achieve miniaturization in both the width direction and the up-down direction.

[0201] 5, in this image forming apparatus 1, first sensor board 210 is located within a first range AC1 from first edge 69E1 to center 69C of belt 69 in the width direction. Second sensor board 220 is located on the other side of center 69C of belt 69 in the width direction. In this way, second sensor board 220 is located on the opposite side of first sensor board 210 from center 69C of belt 69 in the width direction, and therefore does not interfere with first sensor board 210.

[0202] Furthermore, in this image forming apparatus 1, second sensor board 220 is located on the other side in the width direction of second end edge 69E2 of belt 69. With this configuration, second sensor board 220 does not interfere with belt 69.

[0203] 12, in this image forming apparatus 1, when viewed along the width direction, a portion of the second sensor substrate 220 overlaps a portion of the first sensor substrate 210. With this configuration, it is possible to achieve a reduction in size in the front-to-rear direction in accordance with the length of overlap between the first sensor substrate 210 and the second sensor substrate 220 in the front-to-rear direction in which the first extension line LE1 and the second extension line LE2 extend, and it is also possible to achieve a reduction in size in the up-to-down direction in accordance with the length of overlap between the first sensor substrate 210 and the second sensor substrate 220 in the up-to-down direction.

[0204] Furthermore, this image forming apparatus 1 can be further miniaturized in the width direction by providing the fourth sensor S4 together with the third sensor S3 on the second sensor board 220.

[0205] 6, in this image forming apparatus 1, a part of the lower side of the first roller 41 is located between the first extension line LE1 and the second extension line LE2 when viewed along the width direction. This configuration makes it possible to achieve a compact size in the vertical direction.

[0206] In addition, in this image forming apparatus 1, the second roller 42 is located on the opposite side of the first extension line LE1 from the second extension line LE2 when viewed along the width direction, and is spaced apart from the first extension line LE1. This configuration makes it easy to align the sheet SH that has passed through the nip position N1 along the conveying surface 69A1.

[0207] Although the present invention has been described above with reference to the examples, it goes without saying that the present invention is not limited to the above examples and can be modified and applied as appropriate within the scope of the invention.

[0208] In the embodiment, the image forming apparatus of the present invention is embodied as the image forming apparatus 1, but the present invention is not limited to this configuration. For example, the configuration of the present invention may be applied to a multifunction peripheral equipped with an image reading device above the image forming apparatus.

[0209] In the embodiment, the first sensor S1 is a photointerrupter, but the present invention is not limited to this configuration. For example, the first sensor may be a contact sensor or a non-contact sensor that uses magnetism or electromagnetic induction. The same applies to the second to fourth sensors.

[0210] In the embodiment, the image forming apparatus 1 includes an image forming unit 3 having a drawer 80 for forming an image using a direct-transfer color electrophotographic system, a transfer belt 69, a scanner unit 8, a fuser 7, and the like. However, the present invention is not limited to this configuration. For example, the configuration of the present invention may be applied to an image forming apparatus including an image forming unit having an intermediate transfer belt, a secondary transfer roller, and the like for forming an image using an indirect-transfer color electrophotographic system. In this case, the rollers that feed a sheet to the nip point between the intermediate transfer belt and the secondary transfer roller may be the first roller and the second roller, respectively. The present invention may also be applied to an image forming apparatus that forms images using a monochrome electrophotographic system rather than a color electrophotographic system. Furthermore, the present invention may also be applied to a printer that has an inkjet head as the image forming unit, i.e., an image forming apparatus that forms images using an inkjet system. In this case, the rollers that transport a sheet to a position facing the inkjet head may be the first roller and the second roller, respectively. [Explanation of symbols]

[0211] 1...image forming apparatus, X5...rotation shaft, 5...photosensitive drum (photosensitive member) 69...Belt, 6...Belt unit, SH...Seat D1: conveying direction, 69A1: conveying surface, 69A2: back surface N1...nip position, 24...registration roller pair (conveyance roller pair) 110...first actuator, S1...first sensor 210...first sensor board, 69E1...first edge of belt 69E2...Second edge of belt A1: The area from the first edge to the second edge of the belt LE1: First extension line on the conveying surface, LE2: Second extension line on the back surface 66G...guide surface, 66...sheet guide 69C: Center of the belt width AC1...first region, 112...first contact portion, 9...device body 66D...recess, AC2...second area, 210A...substrate surface J1: Joint position, P2: Re-transport path 120...second actuator, S2...second sensor P2A...first pathway, P2B...second pathway 210E...Edge located on the second path side of the first sensor substrate 9C...sheet tray, 130...third actuator S3: Third sensor; 220: Second sensor board 140...fourth actuator, S4...fourth sensor 41...first roller, 42...second roller

Claims

1. a photosensitive member that rotates around a rotation axis extending in the width direction; a belt unit having a circulating belt, the outer peripheral surface of the belt having a conveying surface that faces the photosensitive member and conveys a sheet in a conveying direction, and a back surface that is located on the opposite side of the conveying surface from the photosensitive member and extends along the conveying surface; a pair of conveying rollers that nip the sheet at a nip position located upstream of the conveying surface in the conveying direction and convey the sheet toward the conveying surface; a first actuator that swings when it comes into contact with a sheet conveyed from the nip position toward the conveyance surface; a first sensor that detects a position of the first actuator; a first sensor substrate on which the first sensor is provided; Equipped with the first sensor substrate is located within a range in the width direction from a first edge of the belt located on one side in the width direction to a second edge of the belt located on the other side in the width direction, An image forming apparatus characterized in that, when viewed along the width direction, at least a portion of the first sensor substrate is located between a first extension line of the conveying surface and a second extension line of the back surface.

2. the belt unit includes a sheet guide having a guide surface that guides a surface of the sheet that is conveyed from the nip position toward the conveyance surface, the surface facing away from the photosensitive member; 2. The image forming apparatus according to claim 1, wherein at least a portion of the first sensor board overlaps a portion of the sheet guide when viewed in a direction perpendicular to the transport surface.

3. the first sensor substrate is located within a first range in the width direction from the first edge of the belt to a center portion of the belt in the width direction, the first actuator has a first contact portion that can contact the sheet transported from the nip position toward the transport surface, 3. The image forming apparatus according to claim 2, wherein the first contact portion is disposed at a position closer to the center of the belt than the first sensor board in the width direction.

4. an apparatus main body that detachably supports the belt unit; the sheet guide has a recess for gripping when the belt unit is attached or detached, 4. The image forming apparatus according to claim 3, wherein the recess is located within a second range from the second edge of the belt to the center of the belt in the width direction.

5. 5. The image forming apparatus according to claim 1, wherein a surface of the first sensor substrate is perpendicular to the width direction.

6. a re-conveyance path that guides the sheet that has passed through the photosensitive member to a joining position that is located upstream of the nip position in the conveyance direction; a second actuator that swings when it comes into contact with the sheet being conveyed in the re-conveyance path; a second sensor provided on the first sensor substrate and configured to detect a position of the second actuator; 5. The image forming apparatus according to claim 1, further comprising:

7. the re-conveyance path includes a first path located on the opposite side of the back surface from the photosensitive member and extending along the back surface, and a second path inclined from the first path toward the joining position, 7. The image forming apparatus according to claim 6, wherein the second actuator abuts against the sheet being transported in the second path.

8. the re-conveyance path includes a first path located on the opposite side of the back surface from the photosensitive member and extending along the back surface, and a second path inclined from the first path toward the joining position, a substrate surface of the first sensor substrate is perpendicular to the width direction; 7. The image forming apparatus according to claim 6, wherein an edge of the first sensor substrate located on the second path side extends along the second path.

9. a sheet tray for accommodating sheets; a third actuator that swings when it comes into contact with a sheet conveyed from the sheet tray toward the nip position; a third sensor that detects a position of the third actuator; a second sensor substrate on which the third sensor is provided; Equipped with the first sensor substrate is located within a first range in the width direction from the first edge of the belt to a center portion of the belt in the width direction, 5. The image forming apparatus according to claim 1, wherein the second sensor board is located on the other side of the belt in the width direction relative to the central portion of the belt.

10. 10. The image forming apparatus according to claim 9, wherein the second sensor board is located on the other side in the width direction of the belt relative to the second edge of the belt.

11. 10. The image forming apparatus according to claim 9, wherein at least a portion of the second sensor substrate overlaps at least a portion of the first sensor substrate when viewed along the width direction.

12. a re-conveyance path that guides the sheet that has passed through the photosensitive member to a joining position that is located upstream of the nip position in the conveyance direction; a fourth actuator that swings by contacting the sheet being conveyed in the re-conveyance path; a fourth sensor provided on the second sensor substrate and configured to detect a position of the fourth actuator; 10. The image forming apparatus according to claim 9, further comprising:

13. the conveying roller pair includes a first roller and a second roller facing the first roller at the nip position; 5. The image forming apparatus according to claim 1, wherein at least a portion of the first roller is located between the first extension line and the second extension line when viewed along the width direction.

14. 14. The image forming apparatus according to claim 13, wherein, when viewed along the width direction, the second roller is located on an opposite side of the first extension line from the second extension line and is spaced apart from the first extension line.

Images