Image forming apparatus

Abstract

To provide an image forming apparatus that can reduce a conveyance failure.SOLUTION: An image forming apparatus comprises: an image forming unit; a first conveyance path and a second conveyance path through which a sheet on which an image is formed by the image forming unit is conveyed; a guide member that is movable to a first position to guide the sheet to the first conveyance path and a second position to guide the sheet to the second conveyance path; a moving mechanism that can execute a moving operation to move the guide member from the first position toward the second position to guide a first sheet to the second conveyance path; and a positioning unit that, upon abutment of the guide member, determines a position of the guide member to the second position. When a second sheet preceding the first sheet is on the first conveyance path, the moving mechanism starts the moving operation at a first timing, and when the second sheet is not on the first conveyance path, starts the moving operation at a second timing earlier than the first timing.SELECTED DRAWING: Figure 7

Description

Technical Field

[0005]

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

Background Art

[0002] Conventionally, an image forming apparatus has been proposed that switches the conveyance path of a sheet to a sheet discharge conveyance path or a sheet inversion conveyance path by rotating a switching member between a first switching position and a second switching position (see Patent Document 1). This image forming apparatus rotates the switching member so as to contact the preceding sheet being conveyed, aiming to shorten the distance between the preceding sheet and the succeeding sheet (hereinafter referred to as the intersheet distance).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The switching member described in Patent Document 1 is biased in one direction by a spring, and the first switching position and the second switching position are switched by energizing a solenoid. When guiding the first sheet of a print job to the sheet inversion conveyance path, the switching member moves from the first switching position to the second switching position. At this time, there is no preceding sheet in the sheet discharge conveyance path. Then, the switching member is positioned at the second switching position by hitting against a stopper or the like without contacting the preceding sheet.

[0005] When the switching member hits against the stopper without contacting the preceding sheet, it bounces due to the impact, and there is a risk of conveyance failures such as jams.

[0006] Therefore, an object of the present invention is to provide an image forming apparatus capable of reducing conveyance failures. [Means for solving the problem]

[0007] The present invention relates to an image forming apparatus comprising: an image forming unit for forming an image on a sheet; a first transport path and a second transport path for transporting the sheet on which the image formed by the image forming unit is transported; a guide member movable to a first position for guiding the transported sheet to the first transport path and to a second position for guiding the sheet to the second transport path; a moving mechanism capable of performing a moving operation to move the guide member from the first position to the second position in order to guide the first sheet to the second transport path; and a positioning unit that positions the guide member to the second position when the guide member, which is moved by the moving operation of the moving mechanism, abuts against it, wherein the moving mechanism starts the moving operation at a first timing when the second sheet preceding the first sheet is in the first transport path, and when the second sheet is not in the first transport path , the The movement operation is started at two timings. death , The time interval between the timing at which the leading edge of the first sheet passes a predetermined position and the second timing is shorter than the time interval between the timing at which the leading edge of the first sheet passes a predetermined position and the first timing. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, transport defects can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing a printer according to the first embodiment. [Figure 2] (a) is a schematic diagram showing the guide member located at the first position, and (b) is a schematic diagram showing the guide member located at the second position. [Figure 3] (a) is a cross-sectional view showing the movement mechanism with the guide member in the first position, and (b) is a cross-sectional view showing the movement mechanism with the guide member in the second position. [Figure 4] (a) is an exploded perspective view showing the missing tooth gear unit, and (b) is a perspective view showing the second missing tooth gear. [Figure 5](a) is a cross-sectional view showing the cam section with the guide member in the first position, and (b) is a cross-sectional view showing the cam section with the guide member in the second position. [Figure 6] (a) is a cross-sectional view showing the arrangement relationship between the guide member and the sheet at the first position, (b) is a cross-sectional view showing the arrangement relationship between the guide member and the sheet as it moves toward the second position, and (c) is a cross-sectional view showing the arrangement relationship between the guide member and the sheet at the second position. [Figure 7] A flowchart illustrating the transport path switching control according to the first embodiment. [Figure 8] A flowchart illustrating the transport path switching control according to the second embodiment. [Modes for carrying out the invention]

[0010] <First Embodiment> [Overall structure] First, a first embodiment of the present invention will be described. The printer 100, which serves as an image forming apparatus according to the first embodiment, is an electrophotographic laser beam printer. As shown in Figure 1, the printer 100 includes an image forming unit 102 for forming an image on a sheet S, a sheet feeding device 113, a fixing device 96, a sheet ejection device 130, and a control unit 99. The control unit 99 includes a CPU 99a, a ROM 99b for storing various programs, and a RAM 99c used as a working area for the CPU 99a.

[0011] The image forming unit 102 comprises four process cartridges 7a, 7b, 7c, and 7d, each forming toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K), and a scanner unit 3. These four process cartridges 7a, 7b, 7c, and 7d are arranged in a substantially horizontal direction.

[0012] Note that the four process cartridges 7a, 7b, 7c, and 7d have the same configuration except that the colors of the images they form are different. Therefore, only the configuration of the process cartridge 7a and the image forming process will be described, and the descriptions of the process cartridges 7b, 7c, and 7d will be omitted.

[0013] The process cartridge 7a has a photosensitive drum 1a, a charging roller 2a, and a developing unit 4a. The photosensitive drum 1a is formed by applying an organic photoconductive layer to the outer circumference of an aluminum cylinder and rotates by a drive motor (not shown). The developing unit 4a has a developing roller 40a and a developer coating roller 41a. An intermediate transfer belt 112 is disposed above the process cartridges 7a, 7b, 7c, and 7d. The intermediate transfer belt 112 is stretched between a drive roller 112g and a tension roller 112f.

[0014] Inside the intermediate transfer belt 112, primary transfer rollers 112a, 112b, 112c, and 112d are provided. A secondary transfer roller 116 is provided on the opposite side of the drive roller 112g across the intermediate transfer belt 112, and the intermediate transfer belt 112 and the secondary transfer roller 116 form a secondary transfer nip 115 as a transfer portion.

[0015] The fixing device 96 has a fixing roller 96a heated by a heater and a pressure roller 96b pressed against the fixing roller 96a. The fixing roller 96a and the pressure roller 96b form a fixing nip 96c as a fixing portion for fixing the toner image onto the sheet. The sheet feeding device 113 is provided at the lower part of the printer 100 and accommodates the sheet S.

[0016] The sheet discharging device 130 has a guide member 181 that switches the conveyance path of the sheet S to a discharge conveyance path 201 or a reverse conveyance path 202, a discharge roller pair 120 as a discharge portion provided in the discharge conveyance path 201, and a reverse roller pair 180 provided in the reverse conveyance path 202.

[0017] Next, the image forming operation of the printer 100 configured as described above will be explained. When an image signal is input from a personal computer or the like (not shown) to the scanner unit 3, laser light corresponding to the image signal is irradiated from the scanner unit 3 onto the photosensitive drum 1a of the process cartridge 7a.

[0018] At this time, the surface of the photosensitive drum 1a is uniformly charged in advance to a predetermined polarity and potential by the charging roller 2a, and an electrostatic latent image is formed on the surface when the photosensitive drum 1a is irradiated with laser light from the scanner unit 3. The electrostatic latent image formed on the photosensitive drum 1a is developed by the developing unit 4a, and a yellow (Y) toner image is formed on the photosensitive drum 1a.

[0019] Similarly, the photosensitive drums of the process cartridges 7b, 7c, and 7d are also irradiated with laser light from the scanner unit 3, and magenta (M), cyan (C), and black (K) toner images are formed on the respective photosensitive drums. The toner images of each color formed on each photosensitive drum are transferred to the intermediate transfer belt 112 by the primary transfer rollers 112a, 112b, 112c, and 112d, and are conveyed to the secondary transfer roller 116 by the intermediate transfer belt 112 rotated by the drive roller 112g. In addition, each color image forming process is performed at a timing to overlap with the upstream toner image primarily transferred onto the intermediate transfer belt 112. Further, after the toner image is transferred, the toner remaining on the surface of the photosensitive drum 1a is removed by a drum cleaning blade (not shown).

[0020] In parallel with this image forming process, the sheets S contained in the cassette 111 of the sheet feeding device 113 are fed out by the pickup roller 9 and separated one by one by a pair of separation rollers 10 located downstream of the pickup roller 9 in the conveying direction. One of the rollers of the pair of separation rollers 10 is connected to a torque limiter (not shown), and when only one sheet is fed by the pickup roller 9, the torque limiter rotates freely and is carried along by the pickup roller 9. In addition, when two or more sheets are fed by the pickup roller 9, the other roller of the pair of separation rollers 10 stops rotating to prevent the conveying of the second and subsequent sheets. Note that the other roller of the pair of separation rollers 10 may be driven in the opposite direction to the sheet conveying direction, and a separation pad may be provided instead of one of the rollers of the pair of separation rollers 10.

[0021] Then, the sheet S, which has been transported by the pickup roller 9 and the separation roller pair 10, has its skew corrected by the registration roller pair 117. Furthermore, the registration roller pair 117 transports the sheet S toward the secondary transfer nip 115 in accordance with the image transported by the intermediate transfer belt 112. The sheet S has the full-color toner image from the intermediate transfer belt 112 transferred to it at the secondary transfer nip 115 by the secondary transfer bias applied to the secondary transfer roller 116. In other words, the secondary transfer nip 115, which is part of the image forming unit 102, transfers the toner image to the first surface of the sheet. The sheet S, on which the toner image has been transferred, is subjected to predetermined heat and pressure by the fixing nip 96c of the fixing device 96, and the toner is melted and fixed (fixed).

[0022] The sheet S that has passed through the fixing device 96 is transported to the sheet transport path 203 by the outlet roller pair 97 located at the outlet of the fixing device 96. The sheet S transported along the sheet transport path 203 by the outlet roller pair 97 is guided by the guide member 181 to the discharge transport path 201, which serves as the first transport path, and is discharged to the discharge tray 121 by the discharge roller pair 120.

[0023] When images are formed on both sides of the sheet S, the sheet S with the image formed on the first side is guided by the guide member 181 to the reversal transport path 202, which serves as the second transport path. Then, after the rear end of the sheet S passes the front end of the guide member 181, it is switched back by the reversal roller pair 180. In other words, the front and rear ends of the sheet S are swapped by the switchback. The sheet S that has been switched back by the reversal roller pair 180 is guided by the guide member 181 to the double-sided transport path 206 and then transported again toward the secondary transfer nip 115 by the double-sided transport roller pair 182. At the secondary transfer nip 115, an image is formed on the second side of the sheet S, and it is discharged to the discharge tray 121 by the discharge roller pair 120.

[0024] [Sheet ejection device] Next, the sheet discharge device 130 will be described in detail using Figures 2(a) to 5(b). As shown in Figures 2(a) to 3(b), the sheet discharge device 130 includes a guide member 181, a moving mechanism 205 (see Figures 3(a) and 3(b)), a pair of discharge rollers 120, a pair of reversing rollers 180, and guide sections 118, 119a, 119b, and 119c.

[0025] Guide sections 119a, 119b, and 119c are composed of the frame of the printer 100, and the guide sections 118, 119a, 119b, and 119c form the sheet transport path 203, the discharge transport path 201, the reversal transport path 202, and the double-sided transport path 206. More specifically, the sheet transport path 203 is formed by the guide sections 118 and 119a, and the discharge transport path 201 is formed by the guide sections 119a and 119b. In addition, the reversal transport path 202 is formed by the guide sections 118, 119b, and 119c, and the double-sided transport path 206 is formed by the guide sections 118 and 119c.

[0026] As shown in Figures 3(a) and 3(b), a transport sensor 140 is positioned in the sheet transport path 203 to detect the presence or absence of a sheet. More specifically, the transport sensor 140 is positioned downstream of the fixing nip 96c and upstream of the guide member 181 in the sheet transport direction D.

[0027] The sheet transport path 203 branches into a discharge transport path 201 and a reversal transport path 202 at the branching section 200. The guide member 181 is positioned at the branching section 200 and is supported by the guide portion 119b so as to be rotatable around the pivot axis 181a. The guide member 181 is configured to be movable between a first position shown in Figure 2(a) and a second position shown in Figure 2(b), and moves (rotates) between the first position and the second position by the action of the moving mechanism 205, which will be described later.

[0028] As shown in Figure 2(a), the guide member 181 guides the sheet being transported by the outlet roller pair 97 to the discharge transport path 201, which serves as the first transport path, at the first position. Then, for example, the sheet for a single-sided printing job or the sheet with images formed on both sides in a double-sided printing job is discharged outside the machine by the discharge roller pair 120.

[0029] Furthermore, as shown in Figure 2(b), the guide member 181 guides the sheet being transported by the outlet roller pair 97 to the reversing transport path 202, which serves as the second transport path, at the second position. The sheet on the reversing transport path is first transported in the first transport direction D1 by the reversing roller pair 180. Then, after the rear end of the sheet passes through the branching section 200, the sheet is transported in the second transport direction D2, opposite to the first transport direction D1, by the reversing roller pair 180. As a result, the sheet is transported to the double-sided transport path 206. In other words, the reversing roller pair 180, which acts as the reversing part, can transport the sheet in the first transport direction D1 and the second transport direction D2 by rotating in both forward and reverse directions.

[0030] As shown in Figures 3(a) and 3(b), the moving mechanism 205 includes a drive motor M, a drive input gear 210, a solenoid unit 212, a toothless gear unit 211, a link member 213, a link spring 214, a biasing spring 217, and a positioning spring 218. The drive input gear 210 rotates in only one direction by the drive motor M. The solenoid unit 212 includes a solenoid 212b and an arm member 212a that is moved by the solenoid 212b, and a locking portion 212c is provided at the tip of the arm member 212a.

[0031] The toothless gear unit 211 is positioned in two phases by being locked by the solenoid unit 212, as shown in Figures 3(a) and 3(b). Here, the position of the toothless gear unit 211 shown in Figures 3(a) and 5(a) is defined as the first standby position, and the position of the toothless gear unit 211 shown in Figures 3(b) and 5(b) is defined as the second standby position. The toothless gear unit 211 reaches the second standby position by rotating 180° in the direction of arrow R1 from the first standby position, and returns to the first standby position by rotating 180° in the direction of arrow R1 from the second standby position. When the toothless gear unit 211 is in the first or second standby position, the compression spring 215, which will be described later, is charged.

[0032] As shown in Figure 4(a), the gear comprises a first missing tooth gear 211a, a second missing tooth gear 211b, and a compression spring 215. The first missing tooth gear 211a has a first gear 211u and a rib portion 211q that protrudes from the side surface of the first gear 211u in the axial direction of the first missing tooth gear 211a. In addition, an axial hole 211t is formed in the center of the first missing tooth gear 211a.

[0033] The first gear 211u has teeth 211k formed on one radial side and the other radial side of the shaft hole 211t. The two teeth 211k are not continuous in the circumferential direction, and two missing teeth 211j are formed between these two teeth 211k. That is, the two teeth 211k are formed with a phase difference of 180° from each other, and the two missing teeth 211j are also formed with a phase difference of 180° from each other.

[0034] The rib portion 211q is integrally provided with the first gear 211u and is formed in a substantially annular shape. The rib portion 211q has locking portions 211g formed on one radial side and the other side of the axial hole 211t. The locking portion 212c of the arm member 212a of the solenoid unit 212 can be locked to the locking portions 211g. The two locking portions 211g are positioned to correspond to the two missing tooth portions 211j, and two sliding contact surfaces 211h are provided between the two locking portions 211g. The two sliding contact surfaces 211h are positioned to correspond to the two tooth portions 211k, allowing the locking portion 212c to slide against them. The first gear 211u and the rib portion 211q are in the same phase each time they rotate 180° around the rotation axis 211c.

[0035] Furthermore, as shown in Figures 4(a) and 4(b), the second toothless gear 211b includes a second gear 211w, a boss portion 211o protruding from one side in the axial direction of the second gear 211w, a flange portion 211y provided on the other side of the second gear 211w, and a cam portion 211e. Similar to the first gear 211u, the second gear 211w has teeth 211m formed on one side and the other side in the radial direction, sandwiching the cylindrical boss portion 211o. The two teeth 211m are not continuous in the circumferential direction, and two toothless portions 211i are formed between these two teeth 211m. That is, the two teeth 211m are formed with a phase difference of 180° from each other, and the two toothless portions 211i are also formed with a phase difference of 180° from each other.

[0036] A support portion 211p is formed on the surface between the boss portion 211o and the tooth portion 211m, facing the first missing tooth gear 211a. The support portion 211p supports one end 215a of the compression spring 215. Additionally, a support portion (not shown) is provided on the surface of the first missing tooth gear 211a facing the second missing tooth gear 211b, supporting the other end 215b of the compression spring 215. The compression spring 215 is compressed between the first missing tooth gear 211a and the second missing tooth gear 211b, and the boss portion 211o of the second missing tooth gear 211b is inserted into the axial hole 211t of the first missing tooth gear 211a, thereby unitizing the first missing tooth gear 211a and the second missing tooth gear 211b. At this time, the first missing tooth gear 211a is biased in the R1 direction around the rotation axis 211c by the compression spring 215 relative to the second missing tooth gear 211b.

[0037] Furthermore, the second toothless gear 211b has a restricting projection 211s that faces the first toothless gear 211a. The first toothless gear 211a is restricted from rotating relative to the second toothless gear 211b by an engaging portion (not shown) that engages with the restricting projection 211s, so as not to rotate relative to the second toothless gear 211b by more than a predetermined angle in the R1 direction.

[0038] The flange portion 211y of the second toothless gear 211b is formed integrally with the second gear 211w. Two recesses 211f are formed on the outer circumferential surface of the flange portion 211y, with a phase difference of 180° between them. A positioning spring 218 (see Figures 3(a) and 3(b)) can engage with the recesses 211f, and when the positioning spring 218 is engaged with the recesses 211f, the second toothless gear 211b is positioned in either the first or second standby position.

[0039] A cam portion 211e is provided on the side of the flange portion 211y opposite to the second gear 211w. The cam portion 211e has a curved portion 211n extending radially around the rotation axis 211c and a sliding contact portion 211r formed at the tip of the curved portion 211n. Thus, the cam portion 211e has a predetermined cam profile including the sliding contact portion 211r and the curved portion 211n that curves toward the sliding contact portion 211r.

[0040] As shown in Figures 3(a)(b) and 5(a)(b), the link member 213 is configured to be rotatable about a pivot axis 213a and is biased in the direction of arrow F by a link spring 214. One end 213c is formed on one side of the pivot axis 213a, and the other end 213b is formed on the other side. The one end 213c is configured to be in contact with the cam portion 211e, and the link member 213 rotates in the direction of arrow H against the biasing force of the link spring 214 when the one end 213c is pressed by the cam portion 211e.

[0041] The other end 213b of the link member 213 can press against the pressed portion 181c provided on the guide member 181. The link member 213 is biased by the biasing spring 217 to rotate in the direction of arrow I (see Figure 5(b)), but the rotation of the link member 213 in the direction of arrow I is restricted by the engagement of the other end 213b with the pressed portion 181c. The biasing force of the link spring 214 is set to be greater than the biasing force of the biasing spring 217.

[0042] Furthermore, as shown in Figure 5(b), a positioning portion 220 is formed on the guide portion 119a, and a stopper portion 221 that can abut against the positioning portion 220 is formed on the guide member 181. The guide member 181 is positioned at the second position when the stopper portion 221 abuts against the positioning portion 220.

[0043] In single-sided printing jobs, where printing is performed on only one side of a sheet, and double-sided printing jobs, where printing is performed on both sides of a sheet, the guide member 181 is in the first position when guiding the sheet to the discharge transport path 201. At this time, as shown in Figures 3(a) and 5(a), the toothless gear unit 211 is in the first standby position when the locked portion 211g is locked by the locking portion 212c. When the toothless gear unit 211 is in the first standby position, the toothless portion 211j of the first toothless gear 211a and the toothless portion 211i of the second toothless gear 211b face the drive input gear 210. Therefore, the driving force of the drive input gear 210, which rotates in one direction (arrow E direction) by the drive motor M, is not transmitted to the toothless gear unit 211.

[0044] Furthermore, when the missing-tooth gear unit 211 is in the first standby position, as shown in Figure 5(a), the cam portion 211e is separated from one end 213c of the link member 213. Therefore, no force acts on the link member 213 from the cam portion 211e, the link member 213 is biased in the direction of arrow F by the link spring 214, and the guide member 181 is biased in the direction of arrow I (see Figure 5(b)) by the biasing spring 217. As described above, the biasing force of the link spring 214 is set to be greater than the biasing force of the biasing spring 217, so the guide member 181 is lifted in the direction of arrow G and held in the first position. That is, the link spring 214, as the biasing part, biases the guide member 181 to the first position. Note that when the guide member 181 is held in the first position, the link member 213 or the guide member 181 may abut against a stopper or the like (not shown).

[0045] When performing a double-sided printing job, once the leading edge of the sheet with the image formed on the first side is transported to a predetermined position, the control unit 99 (see Figure 1) supplies current to the solenoid 212b of the solenoid unit 212, causing the solenoid 212b to operate. This causes the locking portion 212c of the arm member 212a to separate from the locked portion 211g. The control unit 99 is configured to control the drive motor M and the solenoid 212b. Therefore, the control unit 99 can control the moving mechanism 205, which includes these drive motor M and solenoid 212b.

[0046] As a result, the biasing force of the compression spring 215 causes the first missing tooth gear 211a to rotate relative to the second missing tooth gear 211b in the R1 direction. Then, the teeth 211k of the first missing tooth gear 211a mesh with the drive input gear 210, causing the second missing tooth gear 211b to rotate in the R1 direction along with the first missing tooth gear 211a. Consequently, the teeth 211m of the second missing tooth gear 211b also mesh with the drive input gear 210.

[0047] When the toothless gear unit 211 rotates 180° in the R1 direction, the locking portion 212c of the arm member 212a locks the locked portion 211g of the first toothless gear 211a, stopping the first toothless gear 211a. Then, the second toothless gear 211b stops with the compression spring 215 charged as the positioning spring 218 engages with the recess 211f of the flange portion 211y. As a result, the toothless gear unit 211 is positioned in the second standby position shown in Figures 3(b) and 5(b).

[0048] When the toothless gear unit 211 is in the second standby position, the toothless portion 211j of the first toothless gear 211a and the toothless portion 211i of the second toothless gear 211b face the drive input gear 210. Therefore, the driving force of the drive input gear 210, which is rotated in one direction (arrow E direction) by the drive motor M, is not transmitted to the toothless gear unit 211.

[0049] As the toothless gear unit 211 rotates from the first standby position to the second standby position, the sliding contact portion 211r of the cam portion 211e slides against and presses against one end 213c of the link member 213. As a result, the link member 213 rotates in the direction of arrow H, against the biasing force of the link spring 214, around the pivot axis 213a. As the link member 213 rotates in the direction of arrow H, the pressing force applied by the other end 213b of the link member 213 against the pressed portion 181c of the guide member 181 is weakened. Therefore, the guide member 181 rotates in the direction of arrow I around the pivot axis 181a due to the biasing force of the biasing spring 217. The guide member 181 is then positioned in the second position when the abutment portion 221 abuts against the positioning portion 220.

[0050] Thus, in this embodiment, the control unit 99 can move the guide member 181 to the first or second position by exciting the solenoid 212b. In other words, the moving mechanism 205 can perform a movement operation to move the guide member 181 from the first position to the second position. After the rear end of the sheet guided to the reversing transport path 202 by the guide member 181 located at the second position passes the front end of the guide member 181, the guide member 181 is moved from the second position to the first position. As a result, the sheet that has been switched back by the reversing roller pair 180 is guided to the double-sided transport path 206.

[0051] [Relationship between guide elements and sheets] Next, the relationship between the guide member 181 and the sheet will be explained using Figures 6(a) to 6(c). Figures 6(a) to 6(c) are cross-sectional views showing the positional relationship between the guide member 181 and the sheet when the preceding sheet S1, which is the second sheet, is being transported to the discharge transport path 201, and the succeeding sheet S2, which is the first sheet, is being guided to the reversal transport path 202. In this embodiment, the sheet used as recording material includes sheet-shaped paper, cloth, envelopes, etc.

[0052] In this embodiment, while the lead sheet S1 is being transported along the discharge transport path 201, the moving mechanism 205 starts a movement operation to move the guide member 181 from the first position to the second position. That is, as shown in Figures 6(a) and 6(b), while the lead sheet S1 is being transported along the discharge transport path 201, the guide member 181 rotates in the direction of arrow I from the first position to the second position and comes into contact with the lead sheet S1. At this time, the guide member 181 is in a position between the first position and the second position.

[0053] The guide member 181 maintains the position shown in Figure 6(b) until contact with the preceding sheet S1 is released, and then moves to the second position as shown in Figure 6(c) once the rear end of the preceding sheet S1 has passed the guide member 181. In this way, by initiating the above movement operation while the preceding sheet S1 is being transported along the discharge transport path 201, it becomes possible to immediately guide the following sheet S2 to the reversal transport path 202. As a result, the distance between the preceding sheet S1 and the following sheet S2, known as the paper gap, can be shortened, and throughput can be improved.

[0054] Furthermore, by bringing the guide member 181 into contact with the preceding sheet S1 while it is rotating from the first position to the second position, the impact when the guide member 181 reaches the second position can be reduced. In other words, by the guide member 181 contacting the preceding sheet S1, the impact when the positioning portion 220 of the guide member 181 abuts against the abutment portion 221 can be reduced, and the bounce of the guide member 181 against the positioning portion 220 can be reduced. As a result, the subsequent sheet S2 will not be transported to the wrong transport path (e.g., the discharge transport path 201), and transport defects such as jams can be reduced.

[0055] At this time, if the contact time (or distance) between the lead sheet S1 and the guide member 181 is long, the image printed on the lead sheet S1 may rub against the guide member 181, potentially resulting in a defective image. For this reason, it is desirable for the contact time between the guide member 181 and the lead sheet S1 to be short.

[0056] On the other hand, for example, when transporting the first sheet of a double-sided printing job, the preceding sheet S1 is not in the discharge transport path 201. In this case, the guide member 181 rotates from the first position to the second position without contacting the preceding sheet S1 in order to guide the sheet to the reversal transport path 202. As a result, the impact when the positioning portion 220 of the guide member 181 abuts against the abutment portion 221 is greater than when the guide member 181 contacts the preceding sheet S1, as described above.

[0057] As a result, the bounce of the guide member 181 against the positioning section 220 becomes relatively large, increasing the risk that the subsequent sheet S2 will be transported to the wrong transport path (for example, the discharge transport path 201), leading to transport failures such as jamming.

[0058] Therefore, in this embodiment, if the lead sheet S1 is not in the discharge transport path 201, the movement operation to move the guide member 181 from the first position to the second position is started at an earlier timing than when the lead sheet S1 is in the discharge transport path 201.

[0059] [Transport path switching control] Next, following the flowchart shown in Figure 7, we will explain the transport path switching control, which moves the guide member 181 between the first and second positions to switch the transport path along which the sheet travels.

[0060] As shown in Figure 7, when a print job is started, a TOP signal is output to the scanner unit 3, which serves as the reference for drawing the image (step S11). The TOP signal is a reference timing signal for the output of the video signal, and the image forming unit 102 starts forming the image in accordance with the TOP signal.

[0061] The following describes transport path switching control using a double-sided printing job as an example. Next, the control unit 99 (see Figure 1) determines whether there is a preceding sheet S1 in the discharge transport path 201 based on the detection result of the transport sensor 140 (see Figures 3(a) and 3(b)) (step S12). In this embodiment, in order to shorten the distance between sheets of paper, the transport control is performed so that the preceding sheet S1 transported in the discharge transport path 201 and the following sheet S2 transported in the reversal transport path 202 pass each other in a double-sided printing job. Therefore, when the guide member 181 is rotated from the first position to the second position to guide the following sheet S2 to the reversal transport path 202, if the transport sensor 140 is ON, it can be estimated that there is a preceding sheet S1 in the discharge transport path 201.

[0062] If the transport sensor 140 is ON (step S12: Yes), the control unit 99 switches the transport path at the first timing (step S13). That is, at the first timing, the control unit 99 starts a movement operation to move the guide member 181 from the first position to the second position so that the guide member 181 contacts the preceding sheet S1 being transported along the discharge transport path 201. Since the guide member 181 contacts the preceding sheet S1 on its way from the first position to the second position, the bounce of the guide member 181 against the positioning unit 220 can be reduced, thereby reducing transport defects such as jams. In addition, as described above, the distance between sheets can be shortened, so throughput can be improved. Furthermore, since the guide member 181 contacts the second surface Sb opposite to the first surface Sa (see Figure 6(b)) of the sheet to which the toner image is transferred, friction between the image on the sheet and the guide member 181 is suppressed, thereby reducing image defects.

[0063] Furthermore, if the transport sensor 140 is OFF in step S12 (step S12: No), the control unit 99 switches the transport path at a second timing that is faster than the first timing (step S14). By starting the movement operation to move the guide member 141 from position 1 to position 2 at the second timing, even if the preceding sheet S1 is not in the discharge transport path 201, the bounce of the guide member 181 is attenuated when the following sheet S2 reaches the guide member 181. This reduces transport failures.

[0064] Here, as mentioned above, TOPThe first and second timings have been described based on the timing at which the signal is output, but are not limited to this. For example, if we use the timing at which the leading edge of the subsequent sheet S2 passes the secondary transfer nip 150 as a reference, the first and second timings can be defined as follows: The first timing is the timing one hour after the leading edge of the subsequent sheet S2 has passed the secondary transfer nip 150, and the second timing is the timing two hours after the leading edge of the subsequent sheet S2 has passed the secondary transfer nip 150, which is shorter than the first hour. These first and second timings are the timings at which the control unit 99 activates the solenoid 212b.

[0065] As mentioned above, an example of switching the transport path at the first timing is when guiding the second and subsequent sheets of a double-sided printing job to the inverted transport path 202. Similarly, an example of switching the transport path at the second timing is when guiding the first sheet of a double-sided printing job to the inverted transport path 202.

[0066] In this embodiment, the presence or absence of the lead sheet S1 in the discharge transport path 201 is determined based on the detection result of the transport sensor 140, and the start timing of the movement of the guide member 181 is controlled. This allows for precise control of the contact time (or contact distance) between the lead sheet S1 and the guide member 181. In other words, the contact time between the image formed on the lead sheet S1 and the guide member 181 can be minimized, reducing friction between the guide member 181 and the image on the lead sheet S1 and reducing image defects.

[0067] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment is configured by modifying the transport path switching control of the first embodiment. For this reason, components similar to those in the first embodiment will not be shown in the figures, or will be described using the same reference numerals.

[0068] [Transport path switching control] Next, the transport path switching control according to the second embodiment will be described following the flowchart shown in Figure 8.

[0069] As shown in Figure 8, when a print job is started, a TOP signal is output to the scanner unit 3, which serves as a reference for drawing the image (step S11). The TOP signal is a reference timing signal for the output of the video signal, and the image forming unit 102 starts forming the image in accordance with the TOP signal.

[0070] The following describes transport path switching control using a double-sided printing job as an example. Next, the control unit 99 (see Figure 1) determines whether there is a preceding sheet S1 in the discharge transport path 201 based on the information of the printing job (step S22). That is, for example, when guiding the second and subsequent sheets S2 of a double-sided printing job to the inversion transport path 202, it can be estimated that there is a preceding sheet S1 in the discharge transport path 201. When guiding the first sheet of a double-sided printing job or the first sheet after a special sequence to the inversion transport path 202, it can be estimated that there is no preceding sheet S1 in the discharge transport path 201.

[0071] If it is determined that there is a preceding sheet S1 in the discharge transport path 201 (step S22: Yes), the control unit 99 switches the transport path at the first timing (step S13). That is, at the first timing, the control unit 99 starts a movement operation to move the guide member 181 from the first position to the second position so that the guide member 181 contacts the preceding sheet S1 being transported in the discharge transport path 201. As the guide member 181 contacts the preceding sheet S1 while rotating from the first position to the second position, the bounce of the guide member 181 against the positioning part 220 can be reduced, thereby reducing transport defects such as jams. In addition, as described above, the distance between sheets can be shortened, so throughput can be improved.

[0072] Furthermore, if it is determined in step S22 that there is no preceding sheet S1 in the discharge transport path 201 (step S22: No), the control unit 99 switches the transport path at a second timing that is faster than the first timing (step S14). By starting the movement operation to move the guide member 141 from position 1 to position 2 at the second timing, even if there is no preceding sheet S1 in the discharge transport path 201, the bounce of the guide member 181 is attenuated when the following sheet S2 reaches the guide member 181. This reduces transport failures.

[0073] In this embodiment, it is possible to determine whether or not there is a preceding sheet S1 in the discharge transport path 201 without providing a sensor to detect the presence or absence of a sheet, thereby reducing costs.

[0074] <Other Embodiments> In all of the embodiments described above, the guide member 181 was moved between the first and second positions by the moving mechanism 205, but this is not limited to this. The configuration of the moving mechanism 205 can be anything; for example, the guide member 181 may be moved between the first and second positions by a motor that rotates in forward and reverse directions.

[0075] Furthermore, although the above-described configurations have been explained using the timing at which the guide member 181 begins to move from the first position to the second position as an example, the configurations are not limited to this. For example, the timing at which the guide member 181 begins to move from the second position to the first position may be different for the first and second timings, as described above.

[0076] Furthermore, although the positioning portion 220 was formed on the guide portion 119a in all of the embodiments described above, it is not limited to this. For example, the positioning portion 220 may be formed on other guide portions other than the guide portion 119a, or on the side plate frame, etc.

[0077] Furthermore, in all of the embodiments described above, the first toothless gear 211a and the second toothless gear 211b each had two missing teeth, but this is not limited to this. The number of missing teeth is not limited to two; an even number is sufficient, and by changing the shape of the cam portion 211e, the guide member 181 can be switched between the first and second positions even if the first toothless gear 211a and the second toothless gear 211b each have four or more missing teeth.

[0078] Furthermore, although the invention has been described using an electrophotographic printer 100 in all of the embodiments described above, the present invention is not limited thereto. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from a nozzle.

[0079] The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0080] Furthermore, the disclosure of this embodiment includes the following configuration examples and method examples. (Composition 1) An image forming unit that forms an image on a sheet, A first transport path and a second transport path through which sheets on which images have been formed by the image forming unit are transported. A guide member that is movable to a first position that guides the sheet to be transported to the first transport path and to a second position that guides it to the second transport path, A moving mechanism capable of performing a moving operation to move the guide member from a first position to a second position in order to guide the first sheet to the second transport path, The system includes a positioning unit that positions the guide member at the second position when the guide member, which moves as a result of the movement of the moving mechanism, abuts against it. The moving mechanism starts the moving operation at a first timing if the second sheet preceding the first sheet is on the first transport path, and starts the moving operation at a second timing earlier than the first timing if the second sheet is not on the first transport path. An image forming apparatus characterized by the following: (Configuration 2) When the second sheet is in the first transport path, the guide member contacts the second sheet as it moves from the first position to the second position by the movement operation initiated at the first timing. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) The image forming unit has a transfer unit that transfers the toner image to the first surface of the sheet. The guide member, while moving from the first position to the second position by the movement operation initiated at the first timing, contacts the second surface of the second sheet opposite to the first surface. The image forming apparatus according to configuration 2, characterized in that... (Composition 4) The first timing is the time when one hour has elapsed since the leading edge of the first sheet passed through the transfer section. The second timing is the time when a second time has elapsed, which is shorter than the first time, since the leading edge of the first sheet passed through the transfer section. The image forming apparatus according to configuration 3, characterized in that it is a picture forming apparatus. (Composition 5) A discharge unit for discharging the sheet being transported along the first transport path to the outside of the machine, The system includes a reversing unit capable of transporting the sheet on the second transport path in a first transport direction and a second transport direction opposite to the first transport direction, An image forming apparatus according to any one of configurations 1 to 4, characterized by the above. (Composition 6) The guide member is positioned at the branching point between the first transport path and the second transport path. An image forming apparatus according to any one of configurations 1 to 5, characterized by the above. (Composition 7) The guide member is supported so as to be rotatable between the first position and the second position. An image forming apparatus according to any one of configurations 1 to 6 characterized by the above. (Composition 8) The moving mechanism has a biasing part that biases the guide member to the first position, An image forming apparatus according to any one of configurations 1 to 7, characterized by the above. (Composition 9) A sensor for detecting that the second sheet is in the first transport path, The system includes a control unit that controls the moving mechanism based on the detection results of the aforementioned sensor, An image forming apparatus according to any one of configurations 1 to 8, characterized by the above. (Composition 10) It is equipped with a fuser unit that fixes the toner image onto the sheet, The sensor is positioned downstream of the fixing section and upstream of the guide member in the sheet transport direction. The image forming apparatus according to configuration 9, characterized by the features described therein. (Composition 11) The system includes a control unit that controls the moving mechanism based on information about the print job, An image forming apparatus according to any one of configurations 1 to 8, characterized by the above. (Composition 12) In a double-sided printing job in which images are formed on a first surface of a sheet and a second surface opposite to the first surface, when the first sheet is the first sheet, the control unit controls the moving mechanism to start the moving operation at the second timing. The image forming apparatus according to configuration 11, characterized by the features described above. (Composition 13) The aforementioned moving mechanism has a solenoid, The control unit operates the solenoid at the first timing or the second timing. An image forming apparatus according to any one of configurations 9 to 12, characterized by the features described herein. [Explanation of Symbols]

[0081] 96c: Fixing unit (fixing nip) / 99: Control unit / 100: Image forming apparatus (printer) / 102: Image forming unit / 115: Transfer unit (secondary transfer nip) / 120: Discharge unit (discharge roller pair) / 140: Sensor (conveyor sensor) / 180: Reversal unit (reversal roller pair) / 181: Guide member / 200: Branching section / 201: First conveying path (discharge conveying path) / 202: Second conveying path (reversal conveying path) / 205: Moving mechanism / 212b: Solenoid / 214: Biasing unit (link spring) / 220: Positioning unit / D: Conveying direction / D1: First conveying direction / D2: Second conveying direction / S1: Second sheet (preceding sheet) / S2: First sheet (following sheet) / Sa: First surface / Sb: Second surface

Claims

1. An image forming unit that forms an image on a sheet, A first transport path and a second transport path through which the sheet on which the image formed by the image forming unit is transported, A guide member that is movable to a first position that guides the sheet to be transported to the first transport path and to a second position that guides it to the second transport path, A moving mechanism capable of performing a moving operation to move the guide member from a first position to a second position in order to guide the first sheet to the second transport path, The system includes a positioning unit that positions the guide member at the second position when the guide member, which moves as a result of the movement of the moving mechanism, abuts against it. The moving mechanism starts the moving operation at a first timing if the second sheet preceding the first sheet is on the first transport path, and starts the moving operation at a second timing if the second sheet is not on the first transport path. The time interval between the timing at which the leading edge of the first sheet passes a predetermined position and the second timing is shorter than the time interval between the timing at which the leading edge of the first sheet passes a predetermined position and the first timing. An image forming apparatus characterized by the following:

2. When the second sheet is in the first transport path, the guide member contacts the second sheet as it moves from the first position to the second position by the movement operation initiated at the first timing. The image forming apparatus according to feature 1.

3. The image forming unit has a transfer unit that transfers the toner image to the first surface of the sheet. The guide member, while moving from the first position to the second position by the movement operation initiated at the first timing, contacts the second surface of the second sheet opposite to the first surface. The image forming apparatus according to feature 2.

4. The timing at which the leading edge of the first sheet passes the predetermined position is the timing at which the leading edge of the first sheet passes the transfer section. The image forming apparatus according to feature 3.

5. A discharge unit for discharging the sheet being transported along the first transport path to the outside of the machine, The system includes a reversing unit capable of transporting the sheet on the second transport path in a first transport direction and a second transport direction opposite to the first transport direction, The image forming apparatus according to feature 1.

6. The guide member is positioned at the branching point between the first transport path and the second transport path. The image forming apparatus according to feature 1.

7. The guide member is supported so as to be rotatable between the first position and the second position. The image forming apparatus according to feature 1.

8. The moving mechanism has a biasing part that biases the guide member to the first position. The image forming apparatus according to feature 1.

9. A sensor for detecting that the second sheet is in the first transport path, The system includes a control unit that controls the moving mechanism based on the detection results of the aforementioned sensor, The image forming apparatus according to feature 1.

10. It is equipped with a fuser unit that fixes the toner image onto the sheet, The sensor is positioned downstream of the fixing section and upstream of the guide member in the sheet transport direction. The image forming apparatus according to feature 9.

11. In a double-sided printing job in which images are formed on a first surface of a sheet and a second surface opposite to the first surface, the system further includes a control unit that controls the moving mechanism to start the moving operation at a second timing when the first sheet is the first sheet. The image forming apparatus according to feature 1.

12. The aforementioned moving mechanism has a solenoid, The control unit operates the solenoid at the first timing or the second timing. The image forming apparatus according to any one of claims 9 to 11.

Images