Sheet conveyance device and image formation apparatus

Abstract

To provide a sheet conveyance device which can execute a stable passage switching operation.SOLUTION: Disclosed is a sheet conveyance device which comprises: a first conveyance passage and a second conveyance passage through which a sheet is conveyed; a switching member for switching a passage through which a sheet is conveyed between the first conveyance passage and the second conveyance passage; a movement mechanism provided with a driving source, and moving the position of the switching member; and a control unit for controlling the driving source. Provided that the timing at which a leading edge of the sheet reaches an upstream position in a sheet conveyance direction by a first predetermined distance from the switching member is defined as a first timing, and the timing at which a rear end of a preceding sheet conveyed before the above-mentioned sheet passes through a downstream position in the sheet conveyance direction by a second prescribed distance from the switching member is defined as a second timing, the control unit controls the driving source at the first timing when the first timing is faster than the second timing, and controls the driving source at the second timing when the second timing is faster than the first timing.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet and an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] An image forming apparatus has been proposed in which a switching member is moved to a position to switch a sheet conveyance path (see Patent Document 1). In Patent Document 1, the path switching operation is controlled using a sensor arranged upstream of the switching member in the conveyance direction. That is, the switching member switches the path based on the leading edge of the sheet reaching a predetermined position upstream of the switching member in the sheet conveyance direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-52242 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there are cases where the operation of the switching member is delayed due to wear of the moving mechanism that moves the switching member, etc. In such cases, the switching member cannot switch the path in time for the conveyance of the sheet, which may result in damage to the sheet or a jam.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet conveying device and an image forming apparatus that perform stable switching operations. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet transporting device comprising: a first transport path and a second transport path along which a sheet is transported; a switching member that switches the path of the transported sheet between the first transport path and the second transport path; a moving mechanism having a drive source and moving the position of the switching member; and a control unit that controls the drive source, wherein the first timing is the timing when the leading edge of a sheet reaches a position upstream in the sheet transport direction by a first predetermined distance from the switching member; and the second timing is the timing when the trailing edge of a preceding sheet transported before the sheet passes a position downstream in the sheet transport direction by a second predetermined distance from the switching member; and the control unit controls the drive source so that, if the first timing is earlier than the second timing, the switching member switches the path along which the sheet is transported at the first timing; and, if the second timing is earlier than the first timing, the control unit controls the drive source so that the switching member switches the path along which the sheet is transported at the second timing.

[0007] Another aspect of the present invention is a sheet transporting device comprising a first transport path and a second transport path along which a sheet is transported, a switching member that switches the path of the transported sheet between the first transport path and the second transport path, a moving mechanism that has a drive source and moves the position of the switching member, and a control unit that controls the drive source, wherein the control unit controls the drive source so that the switching member switches the path along which the sheet is transported at a first timing when the paper-to-paper distance from the rear end of a preceding paper to the front end of a succeeding paper transported after the preceding paper is short, and controls the drive source so that the switching member switches the path along which the sheet is transported at a second timing that is earlier than the first timing when the paper-to-paper distance is long. [Effects of the Invention]

[0008] According to the present invention, the switching member can perform a stable path switching operation. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing the entire image forming apparatus according to an embodiment; [Figure 2] 1A is a diagram showing the switching member in a first position, and FIG. 1B is a diagram showing the switching member in a second position. [Figure 3] 1A is a flowchart of path control when a switching member is moved from a second position to a first position in the first embodiment, and FIG. 1B is a flowchart of path control when a switching member is moved from a first position to a second position in the first embodiment. [Figure 4] FIG. 1 is a block diagram showing a system configuration. [Figure 5] FIG. 3 is a cross-sectional view showing the positional relationship between a switching member and a seat in the first embodiment. [Figure 6] 1A is a cross-sectional view showing the positional relationship between the switching member and the seat at a first timing in the first embodiment, and FIG. 1B is a cross-sectional view showing the positional relationship between the switching member and the seat at a second timing in the first embodiment. [Figure 7] 10A is a flowchart of path control when a switching member is moved from a first position to a second position in the second embodiment, and FIG. 10B is a flowchart of path control when a switching member is moved from the second position to the first position in the second embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing the positional relationship between a switching member and a seat according to a second embodiment. [Figure 9] 10A is a cross-sectional view showing the positional relationship between the switching member and the seat at a first timing in the second embodiment, and FIG. 10B is a cross-sectional view showing the positional relationship between the switching member and the seat at a second timing in the second embodiment. [Figure 10] 1A is a cross-sectional view of the movement mechanism when the switching member is located at a first position in the first embodiment, and FIG. 1B is a cross-sectional view of the movement mechanism when the switching member is located at a second position in the first embodiment. [Figure 11] 10A is a cross-sectional view of the movement mechanism when the switching member is located at a first position in the second embodiment, and FIG. 10B is a cross-sectional view of the movement mechanism when the switching member is located at a second position in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) The following describes embodiments of the present invention with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, etc. of the components described below are not intended to limit the scope of the present invention unless otherwise specified.

[0011] FIG. 1 is a cross-sectional view of an intermediate transfer tandem image forming apparatus 100 in which four color image forming units are arranged side by side on an intermediate transfer belt. Sheets S are stored in a stacked state on a lift-up device 193 of a sheet feeding device 192, and are fed by a sheet feeding unit 110 in accordance with the image formation timing of the image forming apparatus 100. The sheets S fed by the sheet feeding unit 110 pass through a transport path and are transported to a skew correction unit 120. After the skew correction unit 120 corrects the skew and timing of the sheet S, the sheet S is sent to a secondary transfer unit 130. The secondary transfer unit 130 is a nip unit for transferring a toner image to the sheet S, formed by a substantially opposing secondary transfer inner roller 131 and secondary transfer outer roller 132, and transfers a toner image to the sheet S by applying a predetermined pressure force and an electrostatic load bias.

[0012] The process of conveying the sheet S to the secondary transfer unit 130, as described above, is now described. The process of forming a toner image sent to the secondary transfer unit 130 will be described. The image forming unit 140 is primarily composed of a photoconductor 141, an exposure device 142, a developing device 143, and a primary transfer device 144. The surface of the photoconductor 141 has been uniformly charged in advance by a charging device. The exposure device 142 emits light based on the image information signal sent to the photoconductor 141, and an electrostatic latent image is formed via appropriate means such as a diffraction device. The electrostatic latent image thus formed on the photoconductor 141 is subjected to toner development by the developing device 143, and a toner image is formed on the photoconductor 141. The primary transfer device 144 then applies a predetermined pressure and electrostatic load bias, and the toner image is transferred onto the intermediate transfer belt 145. The image forming unit 140 described above is provided in four sets: yellow (Y), magenta (M), cyan (C), and black (K).

[0013] Next, the intermediate transfer belt 145 will be described. The intermediate transfer belt 145 is driven to be transported in the direction of arrow A in FIG. 1. Therefore, the image formation processes by the aforementioned Y, M, C, and K image forming units are processed in parallel. The image formation process for each color is performed at a timing to overlap the upstream toner image that has been primarily transferred onto the intermediate transfer belt 145. As a result, a full-color toner image is finally formed on the intermediate transfer belt 145 and transported to the secondary transfer unit 130.

[0014] Through the sheet S transport process and image formation process described above, a full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 130. The sheet S is then transported to the fuser 150. The fuser 150 applies a predetermined pressure from substantially opposing rollers or belts, and generally applies a heating effect from a heat source such as a heater, to melt and fix the toner on the sheet S. The sheet S with the resulting fixed image is either discharged by the first discharge rollers 160 onto a lower discharge tray 170 that forms a lower discharge unit 190, or is transported toward the second discharge rollers 161. At this time, the transport path along which the sheet S is transported is branched by the first switching member 151. The sheet S transported to the second discharge rollers 161 is either discharged onto the upper discharge tray 171 that forms the upper discharge unit 191, or, in the case of double-sided printing, is transported to the double-sided transport path 180. In the case of double-sided printing, after the rear end of the sheet S passes the second switching member 152, the sheet is conveyed to the double-sided conveying path 180 by the reversing operation of the second discharge roller 161. After passing through the double-sided conveying path 180, the sheet S is again subjected to skew correction and timing correction by the skew correction device 120, and then sent to the secondary transfer unit 130, where the image on the second side is transferred and fixed by the fixing unit 150. The sheet is then discharged onto the lower discharge tray 170 or the upper discharge tray 171. That is, in the case of double-sided printing, the double-sided conveying path 180 is a conveying path for conveying the sheet S, with an image formed on one side thereof, back to the secondary transfer unit 130. The lower discharge tray 170 and the upper discharge tray 171, on which the discharged sheet S is stacked, have an upward slope from upstream to downstream in the discharge direction of the sheet S. Therefore, the discharged sheet S can be aligned upstream in the discharge direction due to the weight of the sheet S itself.

[0015] (Configuration of switching member) The details of the configuration around the switching member 151 in the first embodiment will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view of the switching member 151 and its vicinity. FIG. 2(a) shows the switching member 151 in a first position, and FIG. 2(b) shows the switching member 151 in a second position. The switching member 151 is integrally formed of a guide member 151a and a shaft 151b, and rotates around the shaft 151b. A driving source P (described later) moves the switching member 151 to a first position (FIG. 2(a)) for guiding the sheet S to a first transport path 201. In this embodiment, the first transport path 201 is a path leading to the upper discharge tray 171 or the duplex transport path 180. By stopping the driving of the driving source P, the switching member 151 moves to a second position (FIG. 2(b)) for guiding the sheet S to a second transport path 202 by the action of a spring 155 serving as a pressing member O or its own weight. In this embodiment, the second transport path 202 is a path leading to the lower paper discharge tray 170 .

[0016] (Configuration of the moving mechanism) Next, the movement mechanism of the first embodiment will be described with reference to Figure 10. The movement mechanism 158 is composed of a solenoid 153 as a drive source P, a link member 154, and a spring 155 as a pressing member. The link member 154 rotates around a fulcrum 154a and is rotatably connected to the solenoid 153. The link member 154 is also connected to a switching member 151. The spring 155 is disposed below the link member 154 and is connected to the link member 154. A control unit C (see Figure 4), which will be described later, is capable of supplying power to the drive source P, and the control unit C switches between supplying and stopping the power supply to the drive source P. In other words, the control unit C switches the solenoid 153, which is the drive source P, between an energized state (ON) and a de-energized state (OFF).

[0017] FIG. 10(a) shows the movement mechanism 158 when the switching member 151 is located at the first position, and FIG. 10(b) shows the movement mechanism 158 when the switching member 151 is located at the second position. The following describes the case where the switching member 151 switches from the second position to the first position. When power is supplied from the control unit C from the state shown in FIG. 10(b), the solenoid 153 is attracted, and the tip of the link member 154 is lifted. The switching member 151 then rotates clockwise around the shaft 151b, thereby moving the switching member 151 to the first position. At this time, the attractive force of the solenoid 153 is made greater than the biasing force of the spring 155, causing the switching member 151 to rotate clockwise. When the switching member 151 rotates clockwise, it comes into contact with the plate 157 and stops. This position is the first position of the switching member 151. The following describes the case where the switching member 151 switches from the first position to the second position. When the supply of power from the control unit C is stopped, the attraction of the solenoid 153 is stopped, and the tip of the link member 154 is lowered due to the biasing force of the spring 155 and the weight of the iron core of the solenoid 153. The switching member 151 then rotates counterclockwise around the shaft 151b and moves to the second position. As the switching member 151 rotates counterclockwise, the stopper portion 151c of the switching member 151 abuts against the abutment portion of a guide positioned opposite the switching member 151, thereby stopping the switching member 151. This position is the second position of the switching member 151. That is, when the solenoid 153, which is the driving source, is energized, the switching member 151 moves to the first position, and when the solenoid 153, which is the driving source, is deenergized, the switching member 151 moves to the second position. In other words, when the driving source P is driven, the switching member 151 moves to the first position, and when the driving of the driving source P is stopped, the switching member 151 moves to the second position.

[0018] (Details of route switching control) Here, the sheet conveyance path switching control in this embodiment will be described with reference to Figures 3, 4, 5, and 6. Figure 3(a) shows a flowchart of path control when the switching member 151 is moved from the second position to the first position, and Figure 3(b) shows a flowchart of path control when the switching member 151 is moved from the first position to the second position. Figure 4 is a block diagram showing the system configuration. Figure 5 is a diagram showing the positional relationship between the switching member 151 and the sheet when the switching member 151 is moved from the second position to the first position, and Figure 6 is a diagram showing the positional relationship between the switching member 151 and the sheet when the switching member 151 is moved from the first position to the second position.

[0019] First, the system configuration will be described using FIG. 4. As shown in FIG. 4, the image forming apparatus 100 has an operation unit U, a control unit C, and a paper position detection unit T. The operation unit U accepts user operations such as an instruction to start image formation. The paper position detection unit T is a timer for identifying the position of the sheet S being transported. The control unit C is connected to the paper position detection unit T and a drive source P and controls the drive source P based on the paper position value detection unit T. To transport the sheet S to the first transport path 201 or the second transport path 202, the control unit C drives the drive source P at a predetermined timing (described later) according to the settings of the operation unit U to move the switching member 151 to the first position or the second position. Specifically, the control unit C estimates the time when the sheet will reach a predetermined position based on information about the type of sheet (e.g., sheet length, thickness, material) set by the operation unit U and the timer serving as the paper position detection unit T, and determines the timing to drive the drive source P.

[0020] In this embodiment, the paper position detection means T uses a timer. When a print job starts, a TOP signal that draws a toner image on the image forming unit 140 is output for each sheet. The control unit C uses the TOP signal corresponding to each sheet as a trigger to estimate the time it takes for the sheet to reach a predetermined position (described later). The memory stores, for each sheet type, the time required from the output of the TOP signal until the leading edge of the sheet reaches a position d1 upstream from the switching point (described later). The memory also stores, for each sheet type, the time required from the output of the TOP signal until the trailing edge of the sheet reaches a position d2 downstream from the switching point (described later). Note that "upstream" refers to upstream in the sheet transport direction, and "downstream" refers to downstream in the sheet transport direction. Based on the timing of the output of the TOP signal and the required times stored in the memory, the control unit C estimates the timing when the leading edge of the sheet reaches a position d1 upstream from the switching point and the timing when the trailing edge of the sheet reaches a position d2 downstream from the switching point. The control unit C switches control of the drive source P at either the first timing when the leading edge of the sheet S1 reaches a position a distance d1 upstream from the switching point, or the second timing when the trailing edge of the preceding sheet S2, which follows the sheet S1, reaches a position a distance d2 downstream from the switching point, whichever occurs first. In this embodiment, the TOP signal that creates a toner image in the image forming unit is used as the timer trigger, but the time when the sheet reaches the secondary transfer unit 130 may also be used as the trigger. Also, while a timer is used for the paper position detection means T in this embodiment, a detection means using a sensor may also be used. Note that in this embodiment, a timer is used and no sensor is provided around the switching member 151, which reduces the number of components, thereby saving space and reducing costs.

[0021] Next, a flowchart of path control will be described using Figures 3, 5, and 6. Due to an increase in the sliding resistance of the movement mechanism in accordance with the number of times the switching member 151 is operated, a difference may occur between the timing at which the control unit C switches the power supply to the driving source P and the actual timing at which the switching member 151 completes its operation of moving to the first position or the second position. In particular, the mechanical responsiveness is lower when the control unit C stops the power supply to the driving source P and the solenoid returns to its pre-drive state than when the control unit C starts the power supply to the driving source P and the solenoid is attracted. Therefore, there is a risk of a difference occurring between the timing at which the control unit C stops the power supply to the driving source P and the timing at which the switching operation of the switching member 151 is completed.

[0022] Details of the movement of the switching member 151 from the second position to the first position by the driving source P will be described with reference to FIGS. 3A and 5. The above operation is a transition from FIG. 2B to FIG. 2A. FIG. 5 is a schematic cross-sectional view of the switching member 151 and its vicinity when the leading edge of the sheet S1 reaches a position upstream of the switching point sp by a distance d1. The switching point sp is the position where the leading edge of the switching member 151 is located in the sheet conveying direction. When the switching member 151 is moved from the second position to the first position, the control unit C drives the driving source P (FIG. 3A, S102) at the timing when the leading edge of the sheet S1 reaches a position upstream of the switching point sp by a distance d1 (FIG. 3A, S101), thereby moving the switching member 151. The timing when the leading edge of the sheet S1 reaches a position upstream of the switching point by a distance d1 is the first timing. In this case, the difference between the input signal to the drive source P and the timing at which the switching member 151 completes its operation is minute, and the path switching control can be sufficiently ensured by keeping the time at which the transport path switching is completed and the time at which the sheet S1 arrives at the switching point sp almost constant.

[0023] Details of moving the switching member 151 from the first position to the second position by stopping the driving of the driving source P will be described with reference to FIGS. 3(b) and 6. The movement of the switching member 151 from the first position to the second position is a transition movement from FIG. 2(a) to FIG. 2(b). As described above, the control unit C stops supplying power and de-energizes the solenoid 153, thereby moving the switching member 151 from the first position to the second position. The return operation caused by stopping the supply of power to the solenoid 153 has lower mechanical responsiveness and takes more time than the attraction operation caused by energizing the solenoid 153. In other words, the mechanical responsiveness of the moving mechanism 158 is lower when the driving source P is stopped and the switching member 151 moves from the first position to the second position than when the driving source P is driven and the switching member 151 moves from the second position to the first position. That is, it takes more time to move the switching member 151 from the first position to the second position than to move the switching member 151 from the second position to the first position. In this embodiment, to allow sufficient time for switching when moving the switching member 151 from the first position to the second position, the supply of power to the driving source P is stopped at either a first timing or a second timing, whichever is earlier, as will be described later.

[0024] A flowchart of path control when the switching member 151 is moved from the first position to the second position will be described using Fig. 3(b). Fig. 6(a) is a schematic cross-sectional view of the vicinity of the switching member 151 when the leading edge of the sheet S1 reaches a position a distance d1 upstream from the switching point sp. Fig. 6(b) is a schematic cross-sectional view of the vicinity of the switching member 151 when the trailing edge of the sheet S2, which has been transported downstream of the sheet S1, has passed the switching point sp and been transported a further distance d2.

[0025] If the leading edge of the sheet S1 reaches the switching point within the distance d1 (FIG. 3(b) S201: Yes, FIG. 6(a)), the control unit C stops driving the drive source P and starts moving the switching member 151 from the first position to the second position (FIG. 3(b) S203). The timing when the leading edge of the sheet S1 reaches a position upstream of the switching point by the distance d1 is the first timing. If the leading edge of the sheet S1 does not reach the switching point within the distance d1 (FIG. 3(b) S201: No), it is determined whether the trailing edge of the sheet S2 preceding the sheet S1 has been transported a distance d2 or more after passing the switching point (FIG. 3(b) S202). If the trailing edge of the sheet S2 has been transported a distance d2 or more after passing the switching point (FIG. 3(b) F2: Yes, FIG. 6(b)), the control unit C stops driving the drive source P and starts moving the switching member 151 from the first position to the second position (FIG. 3(b) S203). The second timing is the timing when the trailing edge of this sheet S2 has been transported a distance d2 after passing the switching point sp. In other words, the second timing is the timing when the trailing edge of the preceding sheet, which is transported before sheet S1, reaches a position downstream from the switching point sp by the distance d2. That is, the controller C stops driving the drive source P at either the first timing when the leading edge of the subsequent sheet S1 reaches a position upstream from the switching point by the distance d1, or the second timing when the trailing edge of the preceding sheet S2 reaches a position downstream from the switching point by the distance d2. In other words, the controller C starts moving the switching member 151 if the trailing edge of the preceding sheet S2 passes a position downstream from the switching point by the distance d2 earlier than the leading edge of the subsequent sheet S1 reaches a position upstream from the switching point by the distance d1. The preceding sheet S2 is the sheet transported immediately before the subsequent sheet S1.

[0026] In this embodiment, the switching point sp is a position where the leading edge of the switching member 151 is located in the sheet conveying direction. The distance d1 (first predetermined distance) is longer than the distance the sheet is conveyed in a predetermined time from the start to the completion of switching of the switching member 151. The distance d2 (second predetermined distance) is preferably the distance from the switching point sp to a position downstream of the switching member 151 in the sheet conveying direction. This prevents the trailing edge of the sheet S2 from contacting the switching member 151, reducing the risk of damage to the sheet S2. However, the distance d2 may be about half the length of the switching member 151, as long as it is within an acceptable range of damage to the sheet S2.

[0027] In this embodiment, when the switching member 151 moves from the first position to the second position, the driving of the driving source P is stopped at either the first timing or the second timing, whichever is earlier. However, the comparison of the two timings is not limited to when the switching member 151 moves from the first position to the second position. For example, when the switching member 151 moves from the second position to the first position, the driving source P may be driven at either the first timing or the second timing, whichever is earlier. However, the mechanical responsiveness of the movement mechanism 158 is lower when the driving of the driving source P is stopped than when the solenoid 153, which is the driving source P, is driven. Therefore, it is particularly effective to have a first timing and a second timing when the control unit C stops the driving of the driving source P and moves the switching member 151 from the first position to the second position. Furthermore, although the first timing and the second timing are compared in this embodiment, the comparison is not limited thereto, and multiple timings, such as a third timing and a fourth timing, may also be compared. Furthermore, the distance d1 when the switching member 151 moves from the first position to the second position may be different from the distance d1 when the switching member 151 moves from the second position to the first position.

[0028] In this embodiment, the path switching control of the switching member 151 in the image forming apparatus 100 has been described, but this is not limiting. Similar control may be performed by a switching member that switches the sheet transport path in a post-processing device, which is an optional unit. Also, in this embodiment, the movement mechanism 158 includes the solenoid 153, but this is not limiting and a motor may also be used.

[0029] Due to an increase in the sliding resistance of the movement mechanism in accordance with the number of times the switching member 151 is operated, there is a difference between the timing at which the drive source P stops driving and the actual timing at which the switching member 151 completes moving to the second position or the first position. However, in this embodiment, in addition to the path switching timing based on the leading edge position of sheet S1, a path switching timing based on the trailing edge position of sheet S2, which is transported before sheet S1, is added. This ensures a sufficient gap between the time when the transport path switching is completed and the arrival time of sheet S1, thereby enabling stable path switching. This configuration is particularly effective when the sheet transport interval is sufficiently wide.

[0030] In this embodiment, examples of when it is effective to switch the switching member 151 at the earlier of the first timing and the second timing include mixed-size jobs and mixed-paper-type jobs. In jobs that contain a mixture of sheets with different lengths in the transport direction, such as A4 and A3, the inter-sheet distance, which is the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet, varies throughout the job. When the inter-sheet distance is large, the switching member 151 is likely to be switched at the second timing, which is based on the trailing edge of the preceding sheet. Furthermore, in mixed-paper-type jobs, the sheet transport speed differs depending on the sheet type. For example, thick paper is transported at half the speed of plain paper. Therefore, since the paper spacing is not constant, having the first and second timings allows for ample time for path switching.

[0031] (Second embodiment) In the first embodiment, when the switching member 151 is switched from the first position to the second position, the operation of the driving source P is switched at the earlier of the first timing or the second timing. In the second embodiment, when the switching member 151 is switched from the second position to the first position, the operation of the driving source P is switched at the earlier of the first timing or the second timing.

[0032] The movement mechanism of the second embodiment will be described with reference to FIG. 11. The movement mechanism of the first embodiment and the movement mechanism of the second embodiment differ in the arrangement of the solenoid 153 and the spring 155 relative to the link member 154. Therefore, detailed explanations other than the arrangement are the same as those of the first embodiment and will be omitted. As shown in FIG. 10, in the first embodiment, the solenoid 153 is arranged above the link member 154. Therefore, when power is supplied to the drive source P by the control unit C, the solenoid 153 is attracted, and the switching member 151 rotates clockwise, switching from the second position to the first position. In contrast, as shown in FIG. 11, in the second embodiment, the solenoid 153 is arranged below the link member, and the link member 154 and the solenoid 153 are connected. The spring 155 is arranged above the link member 154 and connected to the link member 154. Therefore, in the second embodiment, when power is supplied to the driving source P by the control unit C, the solenoid 153 is attracted, the switching member 151 rotates counterclockwise around the axis 151b, and the switching member 151 switches from the first position to the second position. As in the first embodiment, the mechanical responsiveness is lower when the control unit C stops the supply of power to the driving source P and the solenoid returns to its pre-drive state than when the control unit C starts the supply of power to the driving source P and the solenoid is attracted. Therefore, in the second embodiment, when the control unit C stops the supply of power to the driving source P and moves the switching member 151 from the second position to the first position, it is effective to switch the path at either the first timing or the second timing, whichever is earlier.

[0033] The details of the configuration around the switching member 151 in the second embodiment will be described with reference to Figures 8 and 9. The second embodiment is similar to the first embodiment except for the position downstream of the switching point sp by a distance d2. In the second embodiment, the position downstream of the switching point sp by a distance d2 is on the second transport path 202.

[0034] The details of moving the switching member 151 from the first position to the second position by driving the driving source P are described with reference to FIGS. 7A and 8. The above operation is a transition from FIG. 2A to FIG. 2B. FIG. 8 is a schematic cross-sectional view of the vicinity of the switching member 151 when the leading edge of the sheet S1 reaches a position d1 upstream from the switching point sp. When moving the switching member 151 from the first position to the second position, the control unit C drives the driving source P (FIG. 7A, S302) at the timing when the leading edge of the sheet S1 reaches a position d1 upstream from the switching point sp (FIG. 7A, S301). This timing when the leading edge of the sheet S1 reaches a position d1 upstream from the switching point sp is the first timing. In this case, the difference between the input signal to the driving source P and the operation completion timing of the switching member 151 is small, and the path switching control can sufficiently maintain a constant time between the time when the transport path switching is completed and the time when the sheet S1 arrives at the switching point sp.

[0035] Details of moving the switching member 151 from the second position to the first position by stopping the driving of the driving source P will be described using FIGS. 7(b) and 9. The movement from the second position to the first position is a transition movement from FIG. 2(b) to FIG. 2(a). As described above, stopping the driving of the driving source P of the solenoid moves the switching member 151 from the second position to the first position. The mechanical responsiveness is lower when the controller C stops the supply of power to the driving source P and the solenoid returns to its pre-driving state than when the controller C starts the supply of power to the driving source P and the solenoid is attracted. In other words, it takes more time to complete the movement of the switching member 151 from the second position to the first position than when the controller C starts the supply of power to the driving source P and the solenoid is attracted. Therefore, to allow sufficient time for the switching member 151 to move from the second position to the first position, the driving of the driving source P is stopped at either the first timing or the second timing, which will be described later.

[0036] A flowchart of path control when the switching member 151 is moved from the second position to the first position will be described using Fig. 7(b). Fig. 9(a) is a schematic cross-sectional view of the vicinity of the switching member 151 when the leading edge of the sheet S1 reaches a position a distance d1 upstream from the switching point sp in the second embodiment. Fig. 9(b) is a schematic cross-sectional view of the vicinity of the switching member 151 when the trailing edge of the sheet S2, which is being transported downstream of the sheet S1, has been transported a distance d2 after passing the switching point sp in the second embodiment.

[0037] When the leading edge of the sheet S1 reaches a position that is a distance d1 upstream from the switching point (FIG. 7(b) S401: Yes, FIG. 9(a)), the driving of the drive source P is stopped, and the switching member 151 starts moving from the second position to the first position (FIG. 7(b) S403). The timing when the leading edge of the sheet S1 reaches a position that is a distance d1 upstream from the switching point is the first timing. When the leading edge of the sheet S1 is not within the distance d1 before reaching the switching point (FIG. 7(b) S401: No), it is determined whether the trailing edge of the sheet S2 preceding the sheet S1 has been transported a distance d2 or more after passing the switching point (FIG. 7(b) S402). When the trailing edge of the sheet S2 has been transported a distance d2 or more after passing the switching point (FIG. 7(b) S402: Yes, FIG. 9(b)), the control unit C stops the driving of the drive source P, and starts moving the switching member 151 from the second position to the first position (FIG. 7(b) S403). The timing when the trailing edge of this sheet S2 has been transported a distance d2 after passing the switching point sp is the second timing. That is, the driving of the drive source P is stopped at either the first timing when the leading edge of the subsequent sheet S1 reaches a position the distance d1 upstream from the switching point, or the second timing when the trailing edge of the preceding sheet S2 reaches a position the distance d2 downstream from the switching point, whichever occurs first. The preceding sheet S2 is the sheet that is transported immediately before the subsequent sheet S1. In other words, if the trailing edge of the sheet S2 preceding sheet S1 has passed the distance d2 from the switching member at a timing earlier than the timing when the leading edge of sheet S1 reaches a position the distance d1 upstream from the switching member, movement of the switching member 151 is started.

[0038] In the second embodiment, there are two timings for moving the switching member 151 when it is moved from the first position to the second position. As in the first embodiment, a sufficient time can be secured between the time when the transport path switching is completed and the time when the sheet S1 arrives, so stable path switching can be expected.

[0039] (Modification of the second embodiment) In the modified example of the second embodiment, the spring effect is sufficient in the arrangement of the movement mechanism of the first embodiment shown in FIG. 10 . In this case, the difference between the timing at which the drive source P stops driving and the timing at which the switching member 151 completes its operation is small, resulting in sufficient path switching control that maintains a nearly constant time between the completion time of the transport path switching and the arrival time of the sheet S1 at the switching point sp. However, because the spring effect is sufficient, the drive time of the drive source P is longer than in the first embodiment when switching the switching member 151 by driving the solenoid. Therefore, in the arrangement shown in FIG. 10 , when the spring effect is sufficiently high, it takes longer to drive the drive source P and switch the switching member 151 from the second position to the first position than to stop driving the drive source P and move the switching member 151 from the first position to the second position. Even in this case, it is effective to start switching the switching member 151 at either the first timing or the second timing, whichever is earlier, when switching the switching member 151 from the second position to the first position, as shown in FIG. 7( b) of the second embodiment. However, the modified example of the second embodiment differs from the second embodiment in that the drive source P is driven when the switching member is moved from the second position to the first position in the flowchart of FIG. 7(b) (S403 in FIG. 7(b)). The modified example of the second embodiment shows a case in which there are two timings for moving the transport switching member by driving the drive source P. In this case, as in the first embodiment, a sufficient time can be secured between the time when the transport path switching is completed and the time when the sheet S1 arrives, so stable path switching can be expected. However, if the drive input time of the drive source P is long, there is a risk that the life of electrical components will be shortened and power consumption will increase. Therefore, from the viewpoint of the life of electrical components and reduced power consumption, the first embodiment is preferable to the second embodiment.

[0040] (Third embodiment) Next, a third embodiment will be described. The operation of the switching member 151 is the same as in the first embodiment, so the explanation of the drawings will be omitted.

[0041] In the third embodiment, when the switching member 151 is moved from the first position to the second position, the paper transport interval is intentionally widened to induce switching of the switching member 151 based on the trailing edge of the sheet S2. This is particularly effective for transporting small, thin sheets of paper, whose transport efficiency decreases due to the effects of charging. In the first and second embodiments, depending on the transport interval, the path switching operation may occur while the trailing edge of the sheet S2 is passing through the switching member 151, which may cause contact between the sheet S2 and the switching member 151, promoting frictional charging or damaging the sheet S2. In contrast, in the third embodiment, the sheet S2 is transported while reliably ensuring that the trailing edge of the sheet S2 passes through the switching member 151.

[0042] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention.

[0043] Specifically, in the first, second, and third embodiments described above, the present invention is applied to an image forming apparatus equipped with a tandem type, intermediate transfer type electrophotographic mechanism, but is not limited to this. For example, the present invention may be applied to an image forming apparatus equipped with a direct transfer type electrophotographic mechanism in which a toner image formed on a photosensitive member is transferred to a sheet without passing through an intermediate transfer member. Furthermore, the present invention is not limited to an electrophotographic mechanism, and may be applied to an image forming apparatus equipped with an inkjet type printing unit or an offset printing mechanism. [Explanation of symbols]

[0044] 100 Image forming device 140 Image forming unit 151 first switching member 152 second switching member 170 Lower paper output tray 171 Upper output tray 180 Double-sided transport path 201 First transport route 202 Second transport route

Claims

1. a first conveying path and a second conveying path along which the sheet is conveyed; a switching member that switches a path of the conveyed sheet between the first conveying path and the second conveying path; a movement mechanism including a drive source and configured to move the position of the switching member; a control unit that controls the drive source; and a timing when the leading edge of the sheet reaches a position upstream of the switching member in the sheet conveying direction by a first predetermined distance is defined as a first timing, and a timing when the trailing edge of a preceding sheet conveyed before the sheet passes a position downstream of the switching member in the sheet conveying direction by a second predetermined distance is defined as a second timing; When the first timing is earlier than the second timing, the control unit controls the drive source so that the switching member switches the path along which the sheet is transported at the first timing, and when the second timing is earlier than the first timing, the control unit controls the drive source so that the switching member switches the path along which the sheet is transported at the second timing. A sheet conveying device characterized by:

2. the drive source is a solenoid, When the driving source is energized, the switching member is moved to a first position, and when the driving source is not energized, the switching member is moved to a second position; When the switching member is moved from the second position to the first position, the control unit starts driving the drive source at the first timing, and when the switching member is moved from the first position to the second position, the control unit stops driving the drive source at an earlier timing of either the first timing or the second timing.

2. The sheet transport device according to claim 1.

3. The first predetermined distance is longer than a distance that the sheet is conveyed in a predetermined time from when the driving source starts to when the switching member completes switching.

2. The sheet transport device according to claim 1.

4. a first conveying path and a second conveying path along which the sheet is conveyed; a switching member that switches a path of the conveyed sheet between the first conveying path and the second conveying path; a moving mechanism that includes a drive source and moves the position of the switching member; a control unit that controls the drive source; and the control unit controls the drive source so that the switching member switches the path along which the sheet is transported at a first timing when the inter-paper distance from the rear end of the preceding paper to the front end of the succeeding paper transported after the preceding paper is short, and controls the drive source so that the switching member switches the path along which the sheet is transported at a second timing that is earlier than the first timing when the inter-paper distance is long. A sheet conveying device characterized by:

5. The sheet conveying device according to any one of claims 1 to 4, an image forming unit that forms an image on the sheet conveyed by the sheet conveying device, An image forming apparatus characterized by:

6. The sheet conveying device according to claim 1 ; an image forming unit that forms an image on the sheet conveyed by the sheet conveying device; an output tray into which sheets are discharged; a double-sided conveying path for conveying a sheet having an image formed on one side thereof by the image forming unit back to the image forming unit, The first transport path is a path toward the paper discharge tray, and the second transport path is a path toward the double-sided transport path. An image forming apparatus characterized by:

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