Sheet conveying device and image forming apparatus

Abstract

To provide a sheet conveyance device capable of improving productivity.SOLUTION: A sheet conveyance device includes: a conveyance part having a roller rotatable in a first rotation direction and a second rotation direction, and for conveying a sheet; a guide member movable in a first position and a second position; a driving source; a driving switching unit including an input part where a driving force is inputted from the driving source, an output part for outputting the driving force to the roller, and a switching part; and a driving cutoff unit capable of shifting to a transmit state in which the driving force transmitted from the switching part can be transmitted to the guide member or a non-transmit state in which it is not transmitted to the guide member. The roller is constituted so as to rotate by the driving force output from the output part of the driving switching unit, while the guide member is moving between the first position and the second position.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a sheet conveyance device for conveying a sheet and an image forming apparatus including the same.

Background Art

[0002] Generally, in an image forming apparatus that forms images on both sides of a sheet, when the image formation on the first side is completed, the sheet is switched back and conveyed to a duplex conveyance path for re-conveying to the image forming unit. At that time, a moving member capable of switching the conveyance path of the sheet is used to reliably convey the sheet to the duplex conveyance path. Recently, it has been desired to increase the printing speed during duplex printing of an image forming apparatus to improve productivity.

[0003] Conventionally, a printer has been proposed that includes an input gear, a planetary gear mechanism to which a driving force is input from the input gear, and a moving member and a discharge reversing roller that are respectively driven by the driving force output from the planetary gear mechanism (see Patent Document 1). The rotation direction of the input gear is switched by a driving motor and a solenoid. The moving member can switch the conveyance path of the sheet by moving between a first guide position and a second guide position, and the discharge reversing roller switches back the sheet by rotating forward and backward.

Prior Art Documents

Patent Documents

[0004] [[ID=२६]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the printer described in Patent Document 1, the moving member moves between the first guide position and the second guide position by switching the rotation direction of the input gear, but no driving force is input to the discharge reversal roller while the moving member is moving. In other words, the rotation direction of the discharge reversal roller is switched only after the movement of the moving member is complete, and the switching of the rotation direction takes time. As a result, productivity is reduced.

[0006] Therefore, the present invention aims to provide a sheet conveying device that can improve productivity. [Means for solving the problem]

[0007] The present invention relates to a sheet conveying device, comprising: a conveying unit for conveying a sheet, having a roller rotatable in a first rotational direction and a second rotational direction opposite to the first rotational direction; a guide member movable to a first position and a second position different from the first position for guiding the sheet; a drive source; an input unit to which driving force is input from the drive source; an output unit for outputting driving force to the roller; a switching unit that outputs the driving force transmitted from the input unit to the output unit in a first state so that the roller rotates in the second rotational direction, and outputs the driving force transmitted from the input unit to the output unit in a second state different from the first state so that the roller rotates in the first rotational direction; and a drive cutoff unit that can transition between a transmission state in which the driving force transmitted from the switching unit can be transmitted to the guide member and a non-transmission state in which the driving force is not transmitted to the guide member, wherein the roller is configured to be rotatable by the driving force output from the output unit of the drive switching unit while the guide member is moving between the first position and the second position. [Effects of the Invention]

[0008] According to the present invention, productivity can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing the printer according to the first embodiment. [Figure 2] (a) is a schematic diagram showing the transport of a sheet in single-sided printing mode, (b) is a schematic diagram showing the transport of a sheet in the first direction in double-sided printing mode, (c) is a schematic diagram showing the switchback of a sheet from the first direction to the second direction in double-sided printing mode, and (d) is a schematic diagram showing the transport of a sheet in the second direction in double-sided printing mode. [Figure 3] (a) is a perspective view showing the drive mechanism, and (b) is another perspective view showing the drive mechanism. [Figure 4] (a) is an exploded perspective view showing the inversion unit, and (b) is another exploded perspective view showing the inversion unit. [Figure 5] (a) is a rear view showing the inversion unit, (b) is an oblique view showing the inversion unit, (c) is a front view showing the inversion unit, and (d) is another oblique view showing the inversion unit. [Figure 6] (a) is a front view showing the reversing unit in forward rotation, (b) is a front view showing the reversing unit with the reversing gear omitted, and (c) is a perspective view showing the reversing unit in forward rotation. (d) is a front view showing the reversing unit in reverse, (e) is a front view showing the reversing unit with the reversing gear omitted, and (f) is a perspective view showing the reversing unit in reverse. [Figure 7] (a) is a timing chart showing the operating timing of the reversing roller, guide member, and clutch signal, and (b) is a perspective view showing the drive mechanism during period (b) in Figure 7(a). (c) is a perspective view showing the drive mechanism during period (c) in Figure 7(a), and (d) is a perspective view showing the drive mechanism during period (d) in Figure 7(a). [Figure 8] (a) is a timing chart showing the operating timing of the reversing roller, guide member and clutch signal; (b) is a perspective view showing the drive mechanism during period (b) in Figure 8(a); and (c) is a perspective view showing the drive mechanism during period (c) in Figure 8(a). [Figure 9] A schematic diagram showing a printer according to the second embodiment. [Figure 10](a) is a schematic diagram showing the transport of a sheet in single-sided printing mode, (b) is a schematic diagram showing the transport of a sheet in the first direction in double-sided printing mode, (c) is a schematic diagram showing the switchback of a sheet from the first direction to the second direction in double-sided printing mode, and (d) is a schematic diagram showing the transport of a sheet in the second direction in double-sided printing mode. [Figure 11] (a) is a perspective view showing the drive mechanism, (b) is a front view showing the uncoupling unit in a non-transmission state, and (c) is a front view showing the uncoupling unit in a transmission state. [Figure 12] (a) is a perspective view showing the drive mechanism of the push solenoid in a de-energized state, (b) is a perspective view showing the drive mechanism when the push solenoid switches from a de-energized state to an energized state, and (c) is a perspective view showing the drive mechanism of the push solenoid in an energized state. [Figure 13] (a) is a timing chart showing the operating timing of the reversing roller, guide member, and solenoid signal; (b) is a schematic diagram showing the sheet transport during period (b) in Figure 13(a); (c) is a schematic diagram showing the sheet transport at time (c) in Figure 13(a); (d) is a schematic diagram showing the sheet transport during period (d) in Figure 13(a); and (e) is a schematic diagram showing the sheet transport during period (e) in Figure 13(a). [Figure 14] A schematic diagram showing a printer according to the third embodiment. [Figure 15] (a) is a schematic diagram showing the transport of a sheet in single-sided printing mode, (b) is a schematic diagram showing the transport of a sheet in the first direction in double-sided printing mode, (c) is a schematic diagram showing the switchback of a sheet from the first direction to the second direction in double-sided printing mode, and (d) is a schematic diagram showing the transport of a sheet in the second direction in double-sided printing mode. [Figure 16] (a) is a perspective view showing the drive mechanism when the clutch unit is in a power-off state, (b) is a perspective view showing the drive mechanism when the clutch unit switches from a power-off state to a powered state, and (c) is a perspective view showing the drive mechanism when the clutch unit is powered. [Figure 17] (a) is a perspective view showing the drive mechanism according to the fourth embodiment, and (b) is another perspective view showing the drive mechanism according to the fourth embodiment. [Figure 18] (a) is an exploded perspective view showing the inversion unit, and (b) is another exploded perspective view showing the inversion unit. [Figure 19] (a) is a perspective view showing the drive mechanism in the power-off state of the clutch unit, (b) is a perspective view showing the drive mechanism when the clutch unit switches from the power-off state to the power-on state, and (c) is a perspective view showing the drive mechanism in the power-on state of the clutch unit. [Figure 20] (a) is a perspective view showing the drive mechanism according to the fifth embodiment, and (b) is another perspective view showing the drive mechanism according to the fifth embodiment. [Figure 21] (a) is an exploded perspective view showing the inversion unit, and (b) is another exploded perspective view showing the inversion unit. [Figure 22] (a) is a front view showing the operation of the inversion unit when the inversion switching gear is in the rotating state, and (b) is a rear view showing the operation of the inversion unit when the inversion switching gear is in the rotating state. (c) is a front view showing the operation of the inversion unit when the inversion switching gear is in the stopped state, and (d) is a rear view showing the operation of the inversion unit when the inversion switching gear is in the stopped state. [Figure 23] (a) is a perspective view showing the drive mechanism in the power-off state of the clutch unit, (b) is a perspective view showing the drive mechanism when the clutch unit switches from the power-off state to the power-on state, and (c) is a perspective view showing the drive mechanism in the power-on state of the clutch unit. [Figure 24] (a) is a perspective view showing the drive mechanism according to the sixth embodiment, and (b) is another perspective view showing the drive mechanism according to the sixth embodiment. [Figure 25] (a) is an exploded perspective view showing the inversion unit, and (b) is another exploded perspective view showing the inversion unit. [Figure 26] (a) is an exploded perspective view showing the planetary gear unit, and (b) is another exploded perspective view showing the planetary gear unit. [Figure 27](a) is a front view of the planetary gear unit when the planetary sun gear is rotating, (b) is a rear view of the planetary gear unit when the planetary sun gear is rotating. (c) is a front view of the planetary gear unit with the planetary input gear and planetary sun gear omitted, (d) is a rear view of the planetary gear unit. (e) is a front view of the planetary gear unit when the planetary sun gear is stationary, (f) is a rear view of the planetary gear unit when the planetary sun gear is stationary. (g) is a front view of the planetary gear unit with the planetary input gear and planetary sun gear omitted, (h) is a rear view of the planetary gear unit. [Figure 28] (a) is a front view showing the drive mechanism of the solenoid in a de-energized state, (b) is a rear view showing the drive mechanism of the solenoid in a de-energized state. (c) is a front view showing the drive mechanism when the solenoid switches from a de-energized state to an energized state, and (d) is a rear view showing the drive mechanism when the solenoid switches from a de-energized state to an energized state. [Figure 29] (a) is a front view showing the drive mechanism when the solenoid is energized, and (b) is a rear view showing the drive mechanism when the solenoid is energized. (c) is a front view showing the drive mechanism when the solenoid switches from energized to de-energized, and (d) is a rear view showing the drive mechanism when the solenoid switches from energized to de-energized. [Figure 30] (a) is a perspective view showing a drive mechanism according to a first modified example of the sixth embodiment, and (b) is another perspective view showing a drive mechanism according to a first modified example of the sixth embodiment. [Figure 31] (a) is a perspective view showing a reversal unit according to a second modification of the sixth embodiment, and (b) is another perspective view showing a reversal unit according to a second modification of the sixth 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 1, as an image forming apparatus, is an electrophotographic laser beam printer that forms a monochrome toner image. In the following description, the sheet S is the material on which the image is formed by the printer 1, and includes, for example, paper, an OHT sheet, etc.

[0011] As shown in Figure 1, the printer 1 includes a feeding unit 10 for feeding the loaded sheets S, an image forming unit 3 for forming an image on the sheets S, and a fixing device 40 for fixing the image transferred to the sheets S. The printer 1 also includes a pair of discharge rollers 50 that can discharge the sheets S to a discharge tray 54, and a pair of reversing rollers 51 that switch back the sheets S and transport them to a double-sided transport path R3. The discharge roller pair 50 and the reversing roller pair 51 constitute a transport unit 510. The transport unit 510, the guide member 53, and the drive mechanism 90 (described later) constitute a sheet transport device 1000. The reversing roller pair 51 includes a drive roller 51d and a driven roller 51e that rotates in accordance with the drive roller 51d.

[0012] When an image forming job is output to printer 1, the image forming process by image forming unit 3 is started based on image information input from an external computer or the like connected to printer 1. Image forming unit 3 comprises a laser scanner 70, a process cartridge 60 having a photosensitive drum 61, and a transfer roller 31. The process cartridge 60 is configured to be detachable from the main unit 2. A charging roller 62 and a developing roller 63 are provided around the photosensitive drum 61. The photosensitive drum 61 and the transfer roller 31 form a transfer nip T1.

[0013] The laser scanner 70 irradiates the photosensitive drum 61 with laser light based on the input image information. At this time, the photosensitive drum 61 is pre-charged by the charging roller 62, and when the laser light is irradiated, an electrostatic latent image is formed on the photosensitive drum 61. Subsequently, this electrostatic latent image is developed by the developing roller 63, and a monochrome toner image is formed on the photosensitive drum 61.

[0014] In parallel with the image forming process described above, the sheet S is fed from the feeding unit 10. The feeding unit 10 includes a cassette 10a that can be pulled out and attached to the main body 2 of the printer 1, a middle plate 13 that is supported by the cassette 10a so as to be able to move up and down, a coil spring 12 that biases the middle plate 13 upward, a feeding roller 11, and a separation pad 14.

[0015] When a feeding command is issued from the cassette 10a, the feeding roller 11 begins to rotate. In conjunction with this, the middle plate 13 rotates upward due to the biasing force of the coil spring 12, and the sheets S loaded on the middle plate 13 come into contact with the feeding roller 11. As a result, the sheets S are fed and separated one by one by the separation pad 14.

[0016] Furthermore, the cassette 10a does not necessarily need to have the middle plate 13 and the coil spring 12, and may be provided with a mechanism to raise and lower the feed roller 11. In addition, a separation roller or retard roller may be provided instead of the separation pad 14.

[0017] The sheet S, fed from the feeding unit 10, is corrected for skew by the registration roller pair 21 and transported in accordance with the transfer timing at the transfer nip T1. The toner image on the photosensitive drum 61 is transferred to the sheet S at the transfer nip T1 by an electrostatic load bias applied to the transfer roller 31. The remaining toner on the photosensitive drum 61 is collected by a cleaning blade (not shown). The sheet S, on which the toner image has been transferred, is subjected to predetermined heat and pressure by the fixing film 41 and pressure roller 42 of the fixing device 40, causing the toner to melt and solidify (fix) to it. A heating element such as a ceramic heater is arranged inside the fixing film 41.

[0018] In single-sided printing mode, where an image is formed on only one side of the sheet S, the sheet S, on which the toner image has been fixed by the fuser 40, is guided to the discharge transport path R1 by the guide member 53, as shown in Figure 2(a), and discharged to the discharge tray 54 by the discharge roller pair 50.

[0019] In the double-eye printing mode, where images are formed on both sides of a sheet S, the sheet S with the image formed on the first side is guided to the reversal transport path R2 by the guide member 53, as shown in Figure 2(b). The sheet S is then first transported in the first direction D1 by the reversal roller pair 51. When the rear end of the sheet S passes the guide member 53, the reversal roller pair 52 reverses direction, as shown in Figure 2(c), and the guide member 53 moves from the position indicated by the dashed line to the position indicated by the solid line. As a result, the sheet S is switched back and transported in the second direction D2, opposite to the first direction D1, as shown in Figure 2(d), and is guided to the double-sided transport path R3 by the guide member 53. The first direction D1 is the direction that moves the sheet S out of the machine, and the second direction D2 is the direction that moves the sheet S inward.

[0020] The sheet S is transported on a double-sided transport path R3 by a transport roller pair 81 and then transported again to the transfer nip T1 by a registration roller pair 21. At the transfer nip T1, an image is formed on the second surface of the sheet S and it is discharged to the discharge tray 54 by a discharge roller pair 50.

[0021] [Drive mechanism] Next, the drive mechanism 90 for driving the discharge roller pair 50, the reversing roller pair 51, and the guide member 53 will be described. As shown in Figures 3(a) and 3(b), the drive mechanism 90 includes a drive motor M that rotates in only one direction, a discharge reversing input gear 100, a reversing unit 200, a discharge drive train 300, a reversing drive train 400, a clutch drive train 500, and a clutch unit 600.

[0022] The discharge reversal input gear 100 is driven by a drive source, a first drive source, and a drive motor M (which acts as a motor) via a gear train (not shown). The reversal unit 200 is driven by the discharge reversal input gear 100 and outputs driving force to the discharge drive train 300, the reversal drive train 400, and the clutch drive train 500, respectively. The driving force transmitted to the discharge drive train 300 drives the discharge roller pair 50. The driving force transmitted to the reversal drive train 400 drives the reversal roller pair 51. The driving force transmitted from the reversal unit 200 to the clutch drive train 500 is transmitted to the clutch unit 600. The driving force transmitted to the clutch unit 600 drives the guide member 53.

[0023] Next, the reversing unit 200, discharge drive train 300, reversing drive train 400, clutch drive train 500, and clutch unit 600 will be described in more detail. The reversing unit 200 includes a reversing input gear 201, a reversing switching gear 202, and a reversing output gear 203. As will be described later, the reversing unit 200 can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202.

[0024] The discharge drive train 300 includes a discharge step gear 301 that meshes with the reversing input gear 201, and a discharge roller gear 302 that meshes with the discharge step gear 301. The discharge roller gear 302 is fixed to the drive shaft 50a of the discharge roller pair 50, and the rotation of the discharge roller gear 302 causes the discharge roller pair 50 to rotate via the drive shaft 50a.

[0025] The reversing drive train 400 includes a reversing step gear 401 that meshes with the reversing output gear 203, a reversing idler gear 402 that meshes with the reversing step gear 401, and a reversing roller gear 403 that meshes with the reversing idler gear 402. The reversing roller gear 403 is fixed to the drive shaft 51a of the drive roller 51d of the reversing roller pair 51, and the rotation of the reversing roller gear 403 causes the reversing roller pair 51 to rotate via the drive shaft 51a. The reversing idler gear 402 is arranged coaxially with the discharge step gear 301.

[0026] The clutch drive train 500 includes a clutch idler gear 501 that meshes with the reversing gear 202, and a clutch step gear 502 that meshes with the clutch idler gear 501.

[0027] The clutch unit 600 includes a clutch input gear 601 that meshes with the clutch stage gear 502, a clutch fixing part 602, a clutch output part 604, and a guide switching lever 605. The clutch fixing part 602 is held in place by the fixing of the rotation stopper 603. The clutch output part 604 is connected to the guide switching lever 605.

[0028] The clutch unit 600, acting as a drive interruption unit, switches the connection state between the clutch input gear 601 and the clutch output unit 604 depending on the energization state to the clutch unit 600. That is, when the clutch unit 600 is in a non-transmission state (dead power state), the clutch input gear 601 and the clutch output unit 604 are not drive-connected. On the other hand, when the clutch unit 600 is energized (transmission state), the clutch input gear 601 and the clutch output unit 604 are drive-connected.

[0029] The guide switching lever 605, which rotates integrally with the clutch output unit 604, has a contact portion 605a that can contact the contact portion 53b of the guide member 53. The guide member 53 is biased in the direction of arrow SD1 by a return spring 52, which acts as a biasing part. The return spring 52 is a torsion coil spring, with one end in contact with a member not shown and the other end in contact with the guide member 53, thereby biasing the guide member 53 in the direction of arrow SD1. The guide member 53, biased by the return spring 52, also has a stop portion 53a that abuts against a member not shown. The stop portion 53a abuts against the member not shown, holding the guide member 53 in the first position (the position shown by the dashed line in Figure 1).

[0030] As the guide switching lever 605 rotates, the contact portion 605a of the guide switching lever 605 presses against the abutment portion 53a of the guide member 53, causing the guide member 53 to move in the opposite direction to the direction of arrow SD1, against the biasing force of the return spring 52. As a result, the guide member 53 moves from the first position to the second position (the position shown by the solid line in Figure 1).

[0031] In other words, the clutch unit 600 can transmit the driving force transmitted from the reversing gear 202 to the guide member 53 when energized, but does not transmit the driving force transmitted from the reversing gear 202 to the guide member 53 when the power is off.

[0032] [Internal configuration of the inversion unit] Next, the internal configuration of the reversing unit 200 will be explained using Figures 4(a) and 4(b). As shown in Figures 4(a) and 4(b), the reversing unit 200, as a drive switching unit, comprises a reversing input gear 201, a reversing switching gear 202, a reversing output gear 203, an internal idler gear 204, an internal step gear 205, and a carrier unit 206. The reversing input gear 201, as an input unit, is an input member that rotates upon receiving the driving force transmitted from the aforementioned discharge reversing input gear 100. The reversing output gear 203, as an output unit, is an output member that outputs driving force to the reversing drive train 400 that rotates the reversing roller pair 51. The internal idler gear 204 and the internal step gear 205 are composed of two sets of gear trains arranged symmetrically and are drive transmission members for transmitting drive from the reversing input gear 201 to the reversing output gear 203.

[0033] The carrier unit 206 has an internal holder 207 and a stopper holder 208, and the internal holder 207 and the stopper holder 208 are connected so as to rotate together. The internal holder 207 rotatably supports the reversing input gear 201 and has the rotation axes of the reversing switching gear 202, the reversing output gear 203, the internal idler gear 204, and the internal step gear 205, respectively.

[0034] The stopper holder 208 holds the locking lever 209 and the compression spring 210. The locking lever 209 is supported by the stopper holder 208 so as to be rotatable about a pivot axis 209c. The locking lever 209 also has a projection 209a that can engage with a hole 202a formed in the reversing gear 202, and a locking portion 209b that can engage with a locked portion 201c of the reversing input gear 201. The locking lever 209 is movable between an engaged position in which the locking portion 209b engages with the locked portion 201c of the reversing input gear 201, and an unengaged position in which the locking portion 209b does not engage with the locked portion 201c. The reversing gear 202, carrier unit 206, locking lever 209, and compression spring 210 constitute a switching unit 310 that outputs the driving force transmitted from the reversing input gear 201 to the reversing output gear 203 in forward and reverse directions according to the state of the reversing gear 202.

[0035] The compression spring 210 biases the locking lever 209 toward the engagement position. When the reversing input gear 201 is locked by the locking lever 209 in the engagement position, the reversing input gear 201 and the carrier unit 206 become one unit.

[0036] In other words, in the first state, the switching unit 310 rotates integrally with the reversing input gear 201 because the locking lever 209, acting as an engaging member, engages with the reversing input gear 201. In the second state, the switching unit 310 separates the locking lever 209 from the reversing input gear 201. The reversing switching gear 202 is configured to control the operation of the locking lever 209 by its own rotational state.

[0037] Next, the meshing relationships of each gear in the reversing unit 200 will be explained using Figures 5(a) to 5(d). Figure 5(a) is a rear view of the reversing unit 200 with the reversing output gear 203 omitted, and Figure 5(b) is a perspective view of the reversing unit 200 with the reversing output gear 203 omitted. Figure 5(c) is a front view of the reversing unit 200 with the reversing input gear 201, reversing switching gear 202, and carrier unit 206 omitted. Figure 5(d) is a perspective view of the reversing unit 200 with the reversing input gear 201, reversing switching gear 202, and carrier unit 206 omitted.

[0038] As shown in Figures 5(a) and 5(b), the reversing input gear 201 has external teeth 201a that mesh with the aforementioned discharge reversing input gear 100 to input driving force, and internal teeth 201b that mesh with the internal idler gear 204, and is rotatably supported on the shaft portion of the internal holder 207. The internal idler gear 204 and the internal step gear 205 are composed of two sets of gear trains arranged symmetrically, and are rotatably supported on the rotating shafts 207a and 207b provided on the internal holder 207, respectively.

[0039] The internal stage gear 205 consists of a first tooth 205a and a second tooth 205b that rotate together, with the first tooth 205a meshing with the internal idler gear 204. As shown in Figures 5(c) and 5(d), the reversing output gear 203 has an external tooth 203a that outputs driving force to the reversing drive train 400, an internal tooth 203b that meshes with the second tooth 205b of the internal stage gear 205, and a hole through which the shaft of the internal holder 207 is inserted. The reversing output gear 203 is rotatably supported by the shaft of the internal holder 207. The internal idler gear 204 meshes with the internal tooth 201b of the reversing input gear 201, and the first tooth 205a of the internal stage gear 205 meshes with the internal idler gear 204. Furthermore, the second tooth 205b of the internal stage gear 205 meshes with the internal tooth 203b of the reversing output gear 203, thereby transmitting the driving force sequentially from the reversing input gear 201 to the reversing output gear 203.

[0040] In the reversing unit 200 configured as described above, driving force is transmitted from the discharge reversing input gear 100 to the external teeth 201a of the reversing input gear 201, obtaining unidirectional rotational drive in the direction of arrow RD1. In addition, the reversing roller gear 403 that rotates the reversing roller pair 51 receives drive from the external teeth 203a of the reversing output gear 203 via the reversing drive train 400, and when the rotation direction of the reversing output gear 203 is switched, the rotation direction of the reversing roller pair 51 also follows suit and is switched.

[0041] [Drive switching operation of the reversing unit] Next, the operation of the rotation direction switching of the reversing output gear 203 of the reversing unit 200 will be explained using Figures 6(a) to (f). Figure 6(a) is a front view of the reversing unit 200 in forward rotation. Figure 6(b) is a front view of the reversing unit 200 in forward rotation with the reversing switching gear 202 omitted. Figure 6(c) is a perspective view of the reversing unit 200 in forward rotation with the reversing input gear 201, reversing switching gear 202, and carrier unit 206 omitted. Figure 6(d) is a front view of the reversing unit 200 in reverse rotation. Figure 6(e) is a front view of the reversing unit 200 in reverse rotation with the reversing switching gear 202 omitted. Figure 6(f) is a perspective view of the reversing unit 200 in reverse rotation with the reversing input gear 201, reversing switching gear 202, and carrier unit 206 omitted.

[0042] In the following, the state of the reversing unit 200 when the reversing output gear 203 is rotating in the same direction as the reversing input gear 201, which is the direction of rotation of arrow RD1 (arrow RD2), will be referred to as forward rotation or the forward rotation state. Conversely, the state when the reversing output gear 203 is rotating in the direction of arrow RD3, which is opposite to the direction of rotation of the reversing input gear 201 (arrow RD1), will be referred to as reverse rotation or the reverse rotation state.

[0043] First, consider the state in which the reversing gear 202 can rotate freely without external restriction, as shown in Figures 6(a) and 6(b). At this time, the locking lever 209 is positioned by the compression spring 210 so that the locking portion 209b engages with the locked portion 201c of the reversing input gear 201. Therefore, the locking lever 209 rotates together with the reversing input gear 201 in the direction of arrow RD1. Also, since the projection 209a of the locking lever 209 engages with the hole 202a of the reversing gear 202, the reversing gear 202, which is in a state where it can rotate freely, also rotates together with the reversing input gear 201 in the direction of arrow RD1.

[0044] Furthermore, since the locking lever 209 is held by the stopper holder 208, the internal holder 207, which is integrated with the stopper holder 208, also rotates in the direction of arrow RD1. The internal idler gear 204, which is rotatably supported by the internal holder 207, is maintained in a stopped (fixed) state relative to the internal holder 207 because no relative displacement occurs between the internal holder 207 and the reversing input gear 201. Similarly, the internal step gear 205, which is rotatably supported by the internal holder 207, is also maintained in a stopped (fixed) state relative to the internal holder 207 because no relative displacement occurs between the internal idler gear 204 and the internal holder 207.

[0045] Therefore, the internal stage gear 205, together with the reversing input gear 201, the reversing switching gear 202, and the carrier unit 206, revolves around the rotation axis 201d of the reversing input gear 201 in the same direction as arrow RD1. The rotation in the direction of arrow RD1 input to the reversing input gear 201 is transmitted to the reversing output gear 203 via the internal idler gear 204 and the internal stage gear 205, which revolve in the same direction, as the reversing input gear 201 and the carrier unit 206 rotate together. In other words, as shown in Figure 6(c), the reversing output gear 203 receives driving force from the internal stage gear 205, which revolves while fixed to the internal holder 207, to its internal teeth 203b, causing it to rotate in the direction of arrow RD2, which is in the same direction as arrow RD1, and output rotational driving force.

[0046] In other words, when the reversing switching gear 202 rotates in the same direction and at the same rotational speed as the reversing input gear 201, the switching unit 310 (see Figure 4(a)) is in the first state. At this time, the switching unit 310 outputs the driving force transmitted from the reversing input gear 201 to the reversing output gear 203 so that the drive roller 51d of the reversing roller pair 51 rotates in the second rotational direction RR2 (see Figure 7(b)).

[0047] Next, as shown in Figures 6(d) and 6(e), consider the state in which the reversing gear 202 is restricted from an external source and its rotation is stopped. In the initial state, as described above, the locking lever 209 is positioned by the compression spring 210 so that the locking portion 209b engages with the locked portion 201c of the reversing input gear 201. In this state, when the locking lever 209 rotates together with the reversing input gear 201, the projection 209a of the locking lever 209 moves in the direction of arrow M1 along the edge of the hole 202a of the stopped reversing gear 202.

[0048] As a result, as shown in Figure 6(e), the locking lever 209 rotates from the engaged position to the disengaged position around the pivot axis 209c, against the biasing force of the compression spring 210. The rotation of the reversing input gear 201 in the direction of arrow RD1 is not transmitted to the stopper holder 208 and the internal holder 207 that hold the locking lever 209, and the stopper holder 208 and the internal holder 207 remain stationary.

[0049] On the other hand, the rotation in the direction of arrow RD1 input to the reversal input gear 201 is transmitted to the reversal output gear 203 via the internal idler gear 204 and internal step gear 205, which are rotatably supported by the stationary internal holder 207. As shown in Figure 6(f), the internal idler gear 204 meshes with the internal teeth 201b of the reversal input gear 201 and therefore rotates in the same direction as the reversal input gear 201. The internal step gear 205 also meshes with the internal teeth 203b of the reversal output gear 203 and therefore rotates in the same direction as the reversal output gear 203.

[0050] Since the internal idler gear 204 and the internal stage gear 205 rotate in opposite directions, the reversing output gear 203 rotates in the direction of arrow RD3, which is opposite to the direction of arrow RD1, and outputs rotational driving force.

[0051] In other words, when the reversing gear 202 is stopped by an external force, the switching unit 310 (see Figure 4(a)) is in the second state and is stopped. At this time, the switching unit 310 outputs the driving force transmitted from the reversing input gear 201 to the reversing output gear 203 so that the drive roller 51d of the reversing roller pair 51 rotates in the first rotation direction RR1 (see Figure 7(d)).

[0052] Thus, the reversing output gear 203 is configured to rotate in the direction of arrow RD2 and the opposite direction of arrow RD3, depending on whether or not the reversing switching gear 202 is stopped by an external force.

[0053] [Operation of the reversing roller pair and guide member] Next, the operation of the reversing roller pair 51 and the guide member 53 when the seat S is switched back will be described. Figure 7(a) is a timing chart showing the operation timing of the reversing roller pair 51, the guide member 53 and the clutch unit 600 when the clutch unit 600 is switched from a power-off state to a power-on state. Figure 7(b) is a perspective view showing the drive mechanism 90 during period (b) of Figure 7(a). Figure 7(c) is a perspective view showing the drive mechanism 90 during period (c) of Figure 7(a). Figure 7(d) is a perspective view showing the drive mechanism 90 during period (d) of Figure 7(a).

[0054] Figure 8(a) is a timing chart of the signals of the reversing roller pair 51, the guide member 53, and the clutch unit 600 when switching the clutch unit 600 from an energized state to an unenergized state. Figure 8(b) is a perspective view showing the drive mechanism 90 during period (b) of Figure 8(a). Figure 8(c) is a perspective view showing the drive mechanism 90 during period (c) of Figure 8(a). Note that in Figures 7(b) to (d) and Figures 8(b) and (c), the discharge drive train 300 and the discharge roller pair 50 are omitted from the illustration, and the rotation direction of each component is indicated by an arrow.

[0055] In the following explanation, for example, a print operation is performed and the drive motor M is driven, and the output reversal input gear 100 and the reversal input gear 201 are rotated by the driving force of the drive motor M.

[0056] As shown in Figures 7(a) and 7(b), when the clutch unit 600 is unpowered, the reversing roller pair 51 rotates in a direction that transports the sheet S in the second direction D2 (see Figure 2(c)). That is, the drive roller 51d of the reversing roller pair 51 rotates in the second rotation direction RR2. This rotation direction of the reversing roller pair 51 is defined as the reverse direction. Also, when transporting the sheet S in the first direction D1 (see Figure 2(b)), the rotation direction of the reversing roller pair 51 is defined as the forward direction. At this time, the drive roller 51d of the reversing roller pair 51 rotates in the first rotation direction RR1, which is opposite to the second rotation direction RR2. Similarly, when discharging the sheet S from the machine, the rotation direction of the discharge roller pair 50 is defined as the forward direction, and the rotation direction in the opposite direction is defined as the reverse direction.

[0057] When the clutch unit 600 is in a power-off state, the drive connection between the clutch input gear 601 and the guide switching lever 605 is released, so the rotation of the clutch input gear 601 is not transmitted to the guide switching lever 605. As a result, the guide member 53 is positioned in the first position (indicated as pos1 in the drawing) by the biasing force of the return spring 52, and is able to guide the sheet S conveyed by the fixing device 40 toward the discharge roller pair 50. The discharge roller pair 50 rotates in the forward direction. In other words, when the single-sided printing mode is executed and when the sheet S is discharged in the double-sided printing mode, the clutch unit 600 is in a power-off state.

[0058] In double-sided printing mode, when transporting the sheet S to the reversal transport path R2, the signal of the clutch unit 600 is switched from OFF to ON. As shown in Figures 7(a) and 7(c), when the signal of the clutch unit 600 is switched from OFF to ON, the clutch unit 600 transitions from a powered-off state to a powered-on state. As a result, the clutch input gear 601 and the guide switching lever 605 are driven together. The guide switching lever 605 rotates due to the driving force transmitted from the clutch input gear 601 via the reversal switching gear 202 and the clutch drive train 500, moving the guide member 53 from the first position to the second position (indicated as Pos2 in the drawing). Furthermore, while the guide member 53 is rotating from the first position to the second position, the rotation of the reversal switching gear 202 is not restricted and rotates together with the reversal input gear 201. That is, the switching section 310 of the reversal unit 200 (see Figure 4(a)) remains in the first state. Therefore, the discharge roller pair 50 continues to rotate in the forward direction, while the reversing roller pair 51 continues to rotate in the reverse direction.

[0059] After moving to the second position, the guide member 53 abuts against a member (not shown) and its rotation stops. Since the guide switching lever 605 continues to receive driving force from the reversing unit 200, the guide member 53 remains held in the second position. As shown in Figure 7(d), when the rotation of the guide member 53 stops, the guide switching lever 605, which is linked to the guide member 53, the clutch drive train 500, and the reversing gear 202 all stop simultaneously.

[0060] When the reversing gear 202 stops, the aforementioned reversing unit 200 switches from a forward rotation state to a reverse rotation state, and the rotation direction of the reversing output gear 203 switches from the direction of arrow RD2 to the direction of arrow RD3 (see Figures 6(c) and 6(f)). As a result, the rotation direction of the reversing drive train 400 that meshes with the reversing output gear 203 and the reversing roller pair 51 also switches in conjunction. Consequently, the reversing roller pair 51 rotates the sheet S in the first direction D1 (see Figure 2(b)), that is, in the forward rotation direction that transports the sheet S toward the outside of the printer 1.

[0061] In other words, based on the fact that the clutch unit 600 is energized and the guide member 53, which moves from the first position to the second position, stops at the second position, the switching section 310 of the reversing unit 200 (see Figure 4(a)) transitions from the first state to the second state. When the clutch unit 600 is energized and the guide member 53 is stopped at the second position, the switching section 310 of the reversing unit 200 (see Figure 4(a)) is in the second state. As a result, the sheet S is guided to the reversing transport path R2 by the guide member 53 located at the second position and transported in the first direction D1 by the reversing roller pair 51.

[0062] As shown in Figures 8(a) and 8(b), when the clutch unit 600 is energized, as described above, the guide member 53 is held in the second position and the reversing roller pair 51 rotates in the forward direction. When the rear end of the seat S passes the guide member 53, the signal of the clutch unit 600 is switched from ON to OFF, and the clutch unit 600 goes from energized to de-energized. As a result, the drive connection between the clutch input gear 601 and the guide switching lever 605 is released.

[0063] As a result, no driving force is input to the guide switching lever 605, and as shown in Figure 8(c), the guide member 53 rotates from the second position to the first position due to the biasing force of the return spring 52. When the guide member 53 begins to rotate from the second position to the first position, the rotation restriction on the reversal switching gear 202 is released, and it becomes able to rotate freely. As a result, the reversal unit 200 switches from the reverse rotation state to the forward rotation state, and the rotation direction of the reversal output gear 203 switches from the direction of arrow RD3 to the direction of arrow RD2 (see Figures 6(c) and 6(f)).

[0064] Therefore, the rotation direction of the reversing drive train 400, which meshes with the reversing output gear 203, and the reversing roller pair 51 are also switched in conjunction. As a result, the reversing roller pair 51 rotates in the reverse direction, which transports the sheet S in the second direction D2 (see Figure 2(c)), that is, toward the inside of the printer 1. In other words, while the guide member 53 is rotating between the first and second positions, the reversing roller pair 51 is configured to be rotatable by the driving force output from the reversing output gear 203. As a result, the sheet S is switched back, and the sheet S is guided to the double-sided transport path R3 by the guide member 53, which is located in the first position. Even when the guide member 53 is in the first position, the clutch unit 600 is in a power-off state, so the rotation of the reversing switching gear 202 is not restricted. Therefore, the discharge roller pair 50 continues to rotate in the forward direction.

[0065] [Effects of the First Embodiment] As described above, the drive mechanism 90 according to this embodiment is a mechanism that drives the reversing roller pair 51 and the guide member 53 using the driving force of the drive motor M. As described above, by using the drive mechanism 90 of this embodiment, the time during which the reversing roller pair 51 is stopped between the switching of the signal of the clutch unit 600 and the switching of the rotation direction of the reversing roller pair 51 is minimized. The time required for the rotation direction of the reversing roller pair 51 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0066] More specifically, as shown in Figure 8(a), when the signal of the clutch unit 600 switches from ON to OFF, the guide member 53 rotates from the second position to the first position due to the action of the reversing unit 200 and the clutch unit 600. Also, the rotation direction of the reversing roller pair 51 switches from the forward rotation direction to the reverse rotation direction.

[0067] At this time, the rotation direction switching operation of the reversing roller pair 51 is performed in parallel with the rotation of the guide member 53 from the second position to the first position. Therefore, the rotation direction switching operation of the reversing roller pair 51 is performed without waiting for the guide member 53 to complete its rotation to the first position, and there is virtually no stopping time for the reversing roller pair 51 during the rotation direction switching operation. Thus, the time required for the rotation direction of the reversing roller pair 51 to be switched is shortened, and productivity can be improved.

[0068] Furthermore, when the signal of the clutch unit 600 is switched from OFF to ON, the guide member 53 rotates from the first position to the second position due to the action of the reversing unit 200 and the clutch unit 600. While the guide member 53 is rotating from the first position to the second position, the reversing changeover gear 202 is not restricted in its rotation and rotates together with the reversing input gear 201. That is, the discharge roller pair 50 continues to rotate in the forward direction. Therefore, as shown in Figures 2(a) and 2(b), the guide member 53 can start moving from the first position to the second position before the sheet S is released from the discharge roller pair 50 and discharged outside the machine. This makes it possible to advance the timing of switching the signal of the clutch unit 600 and improve productivity.

[0069] [Modified version of the first embodiment] In this embodiment, the discharge stage gear 301 and the reversing stage gear 401 are arranged coaxially, but they may be arranged on different axes. Also, in this embodiment, the discharge drive train 300 is driven by a drive force transmitted from the reversing input gear 201 and is included in the drive mechanism 90, but the discharge roller pair 50 may be driven from a drive motor (not shown) via a separate drive train.

[0070] Furthermore, in this embodiment, a torsion coil spring was used as the return spring 52 that biases the guide member 53, but other spring types such as compression springs, tension springs, or leaf springs may also be used. Also, in this embodiment, the guide member 53 is moved via the guide switching lever 605, but as an alternative method, a method in which the guide member 53 and the output section of the clutch unit 600 are transmitted by a belt, link, or the like may also be used.

[0071] Furthermore, in this embodiment, the internal idler gear 204 and internal stage gear 205 arranged inside the reversing unit 200 are configured with two pairs of gears, but this is not limited to this configuration. For example, a method in which only one pair of gear trains of the internal idler gear 204 and internal stage gear 205 are arranged, or a method in which three or more pairs are arranged, may also be used.

[0072] <Second Embodiment> Next, a printer 1A according to a second embodiment of the present invention will be described. Printer 1A differs from the first embodiment in that it is provided with a triple discharge / reversal roller 55 in place of the discharge roller pair 50 and the reversal roller pair 51. Printer 1A also differs from the first embodiment in that it omits the discharge drive train 300, provides a reversal drive train 400A in place of the reversal drive train 400, and provides a guide member 56 in place of the guide member 53 and the guide switching lever 605. For this reason, components similar to those in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0073] [Overall structure] As shown in Figure 9, the printer 1A, as an image forming apparatus, includes a feeding unit 10 for feeding the loaded sheets S, an image forming unit 3 for forming an image on the sheets S, and a fixing device 40 for fixing the image transferred to the sheets S. The printer 1A also includes a discharge reversing triple roller 55 that can discharge the sheets S to a discharge tray 54 and switch back to transport them to a double-sided transport path R3, and a guide member 56.

[0074] The discharge reversing triple roller 55 has a drive roller 55b that can rotate in both forward and reverse directions, a discharge driven roller 55c that rotates with the drive roller 55b as a first driven roller, and a reversing driven roller 55d that rotates with the drive roller 55b as a second driven roller. The discharge driven roller 55c is pressed against the drive roller 55b to form a discharge nip N1 as a first nip. The reversing driven roller 55d is pressed against the drive roller 55b to form a reversing nip N2 as a second nip. The guide member 56 is movable between a first position shown by the dashed line in Figure 9 and a second position shown by the solid line in Figure 9. The discharge reversing triple roller 55, the guide member 56, and the drive mechanism 90A, which will be described later, constitute the sheet conveying device 2000.

[0075] In single-sided printing mode, where an image is formed on only one side of the sheet S, the sheet S, on which the toner image has been fixed by the fuser 40, is guided to the discharge transport path R1 by the guide member 56 located at the first position, as shown in Figure 10(a). The sheet S is then discharged to the discharge tray 54 by the discharge nip N1.

[0076] In the double-sided printing mode, where an image is formed on both sides of a sheet S, the sheet S with the image formed on the first side is guided to the reversal transport path R2 by a guide member 56 located at the second position, as shown in Figure 10(b). The sheet S is then first transported in the first direction D1 by a reversal nip N2, and when the rear end of the sheet S passes the guide member 56, the drive roller 55b reverses direction, as shown in Figure 10(c), and the guide member 56 moves from the second position shown by the dashed line to the first position shown by the solid line. As a result, the sheet S is switched back and transported in the second direction D2, opposite to the first direction D1, as shown in Figure 10(d), and is guided to the double-sided transport path R3 by the guide member 56 located at the first position.

[0077] The sheet S is transported on a double-sided transport path R3 by a transport roller pair 81 and then transported again to the transfer nip T1 by a registration roller pair 21. At the transfer nip T1, an image is formed on the second surface of the sheet S, and it is then discharged to the discharge tray 54 by the discharge nip N1.

[0078] [Drive mechanism] Next, the drive mechanism 90A for driving the discharge reversal triple roller 55 and guide member 56, which constitute the conveying section, will be described. As shown in Figure 11(a), the drive mechanism 90A includes a drive motor M, a discharge reversal input gear 100, a reversal unit 200, a reversal drive train 400A, a coupling switching gear train 500A, and a coupling release unit 700.

[0079] The discharge reversal input gear 100 is driven by the drive motor M via a gear train (not shown). The reversal unit 200 is driven by the discharge reversal input gear 100 and outputs driving force to the reversal drive train 400A and the coupling changeover gear train 500A, respectively. The driving force transmitted to the reversal drive train 400A drives the discharge reversal triple roller 55. The driving force transmitted to the reversal drive train 400 drives the reversal roller pair 51. The driving force transmitted from the reversal unit 200 to the coupling changeover gear train 500A is transmitted to the coupling release unit 700. The driving force transmitted to the coupling release unit 700 drives the guide member 56.

[0080] Next, the reversing unit 200, the reversing drive train 400A, the coupling switching gear train 500A, and the coupling release unit 700 will be described in more detail. The reversing unit 200 includes a reversing input gear 201, a reversing switching gear 202, and a reversing output gear 203. As described in the first embodiment, the reversing unit 200 can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202.

[0081] The reversing drive train 400A includes a reversing step gear 401 that meshes with the reversing output gear 203, and a reversing roller gear 403 that meshes with the reversing step gear 401. The reversing roller gear 403 is fixed to the drive shaft 55a of the drive roller 55b of the discharge reversing triple roller 55, and the rotation of the reversing roller gear 403 causes the drive roller 55b to rotate via the drive shaft 55a.

[0082] The coupling change gear train 500A includes a coupling change idler gear 503 and a coupling change gear pair 504. The coupling change idler gear 503 meshes with the reversing change gear 202 and the coupling change gear pair 504, and the rotation of the reversing change gear 202 is transmitted to the coupling release unit 700 via the coupling change idler gear 503 and the coupling change gear pair 504.

[0083] The coupling release unit 700, which acts as a drive disconnection unit, includes a push solenoid 701, a first ratchet gear 702, a second ratchet gear 703, a spring seat 704, and a coupling release spring 705. As shown in Figures 11(b) and 11(c), the first ratchet gear 702 has a first ratchet portion 702a. The second ratchet gear 703 has a second ratchet portion 703a that faces the first ratchet portion 702a and is supported so as to be rotatable relative to the rotation axis 702b of the first ratchet gear 702.

[0084] A release spring 705 is provided between the rotating shaft 702b of the first ratchet gear 702 and the spring seat 704, and the release spring 705 presses the rotating shaft 702b in a direction that moves the first ratchet part 702a away from the second ratchet part 703a. The spring seat 704 is fixed to a fixing member such as the frame of the device body 2. The push solenoid 701 is a push-type solenoid equipped with a solenoid shaft 701a that can be pushed out when energized, and the solenoid shaft 701a is positioned to contact the first ratchet gear 702. The push solenoid 701 and the solenoid shaft 701a constitute a connecting / separating mechanism 750 that engages or separates the first ratchet part 702a from the second ratchet part 703a.

[0085] When the push solenoid 701 is in a non-transmission state (power off), as shown in Figure 11(b), the first ratchet portion 702a and the second ratchet portion 703a are separated from each other by the action of the release spring 705. Therefore, the first ratchet gear 702 and the second ratchet gear 703 are not driven together. On the other hand, when the push solenoid 701 is energized (transmission state), as shown in Figure 11(c), the first ratchet gear 702 is pressed toward the second ratchet gear 703 by the solenoid shaft 701a against the biasing force of the release spring 705. As a result, the first ratchet portion 702a and the second ratchet portion 703a engage with each other, and the first ratchet gear 702 and the second ratchet gear 703 are driven together.

[0086] The guide member 56 is biased in the direction of arrow SD1 by a return spring 52. The return spring 52 is a torsion coil spring, with one end in contact with a member not shown and the other end in contact with the guide member 56, thereby biasing the guide member 56 in the direction of arrow SD1. Furthermore, the guide member 56, biased by the return spring 52, is held in the first position (the position shown by the dashed line in Figure 9) by abutting against the member not shown.

[0087] The guide member 56 has a guide switching gear 56a that meshes with the second ratchet gear 703, and when the push solenoid 701 is energized, the driving force is transmitted from the second ratchet gear 703, causing it to rotate from the first position to the second position (the position shown by the solid line in Figure 9).

[0088] [Operation of the discharge reversal triple roller and guide member] Next, the operation of the discharge reversal triple roller 55 and guide member 56 when the sheet S is switched back will be explained using Figures 12(a) to 13(e). Figure 12(a) is a perspective view showing the drive mechanism 90A when the push solenoid 701 is de-energized. Figure 12(b) is a perspective view showing the drive mechanism 90A when the push solenoid 701 switches from de-energized to energized. Figure 12(c) is a perspective view showing the drive mechanism 90A when the guide member 56 reaches the second position and abuts against an unshown member. Note that in Figures 12(a) to (c), the rotation direction of each member is indicated by an arrow.

[0089] In the following explanation, for example, a print operation is performed and the drive motor M is driven, and the output reversal input gear 100 and the reversal input gear 201 are rotated by the driving force of the drive motor M.

[0090] As shown in Figure 12(a), when the push solenoid 701 is deactivated, the discharge reversing triple roller 55 rotates in the direction shown in the figure. That is, the drive roller 55b of the discharge reversing triple roller 55 rotates in the second rotation direction RR2, and the discharge nip N1 of the discharge reversing triple roller 55 enables the sheet S to be discharged toward the discharge tray 54. The rotation direction of the discharge reversing triple roller 55 at this time is defined as the reverse direction. Furthermore, the rotation direction of the discharge reversing triple roller 55 when the sheet S is transported in the first direction D1 (see Figure 10(b)) by the reversing nip N2 of the discharge reversing triple roller 55 is defined as the forward direction. At this time, the drive roller 55b of the discharge reversing triple roller 55 rotates in the first rotation direction RR1 (see Figure 12(c)), which is opposite to the second rotation direction RR2.

[0091] When the push solenoid 701 is deactivated, the drive connection between the first ratchet gear 702 and the second ratchet gear 703 is released, and therefore the rotation of the first ratchet gear 702 is not transmitted to the guide switching gear 56a. As a result, the guide member 56 is positioned in the first position (indicated as pos1 in the drawing) by the biasing force of the return spring 52, and as shown in Figure 13(b), the sheet S can be guided toward the discharge transport path R1 by the discharge nip N1. In other words, when the single-sided printing mode is executed and when the sheet S is discharged in the double-sided printing mode, the push solenoid 701 is deactivated.

[0092] In double-sided printing mode, when transporting the sheet S to the reversal transport path R2, the signal of the push solenoid 701 is switched from OFF to ON, as shown in Figures 12(b) and 13(a)(c). When the signal of the push solenoid 701 is switched from OFF to ON, the push solenoid 701 transitions from a de-energized state to an energized state. As a result, the first ratchet gear 702 and the second ratchet gear 703 are driven together. The guide switching gear 56a rotates due to the driving force transmitted from the second ratchet gear 703, moving the guide member 56 from the first position to the second position (indicated as Pos2 in the drawings). Also, while the guide member 56 is rotating from the first position to the second position, the reversal switching gear 202 is not restricted in its rotation and rotates together with the reversal input gear 201. In other words, the discharge reversal triple roller 55 remains rotating in the reverse direction, which is the direction in which the sheet S is transported out of the machine by the discharge nip N1.

[0093] After moving to the second position, the guide member 56 abuts against a member not shown, and its rotation stops as shown in Figure 13(d). Since the guide switching gear 56a continues to receive driving force from the reversing unit 200, the guide member 56 remains held in the second position. As shown in Figure 12(c), when the rotation of the guide member 56 stops, the coupling release unit 700, the coupling switching gear train 500A, and the reversing switching gear 202, which are linked to the guide member 56, stop simultaneously.

[0094] When the reversing gear 202 stops, the aforementioned reversing unit 200 switches from the forward rotation state to the reverse rotation state, and the rotation direction of the reversing output gear 203 switches from the direction of arrow RD2 to the direction of arrow RD3. As a result, the rotation direction of the reversing drive train 400A that meshes with the reversing output gear 203 and the discharge reversing triple roller 55 also switches in conjunction. Consequently, the discharge reversing triple roller 55 rotates in the forward rotation direction, as shown in Figure 13(e). As a result, the sheet S is guided to the reversing transport path R2 by the guide member 56 located at the second position, and transported in the first direction D1 by the reversing nip N2 of the discharge reversing triple roller 55, as shown in Figure 10(b).

[0095] As shown in Figure 13(e), when the push solenoid 701 of the coupling release unit 700 is energized, the guide member 56 is held in the second position, as described above, and the discharge reversal triple roller 55 rotates in the forward direction. When the rear end of the sheet S passes the guide member 56, the signal of the push solenoid 701 is switched from ON to OFF, and the push solenoid 701 goes from energized to de-energized. As a result, the drive coupling between the first ratchet gear 702 and the second ratchet gear 703 is released.

[0096] As a result, no driving force is input to the guide switching gear 56a, and the guide member 56 rotates from the second position to the first position due to the biasing force of the return spring 52. When the guide member 56 begins to rotate from the second position to the first position, the rotation restriction on the reversing switching gear 202 is released, and it becomes able to rotate freely. As a result, the reversing unit 200 switches from the reverse rotation state to the forward rotation state, and as shown in Figure 12(a), the rotation direction of the reversing output gear 203 switches from the direction of arrow RD3 to the direction of arrow RD2.

[0097] Therefore, the rotation direction of the reversing drive train 400A, which meshes with the reversing output gear 203, and the discharge reversing triple roller 55 are switched in conjunction. As a result, the discharge reversing triple roller 55 rotates in the reverse direction, which transports the sheet S in the second direction D2 (see Figure 10(c)), i.e., toward the inside of the printer 1, by the reversing nip N2. In other words, while the guide member 56 is rotating between the first and second positions, the discharge reversing triple roller 55 is configured to be rotatable by the driving force output from the reversing output gear 203. As a result, the sheet S is switched back, and the sheet S is guided to the double-sided transport path R3 by the guide member 56 located in the first position. Even when the guide member 56 is in the first position, the coupling release unit 700 is in a released state, so the rotation of the reversing switching gear 202 is not restricted. Therefore, the discharge reversing triple roller 55 continues to rotate in the reverse direction.

[0098] [Effects of the second embodiment] As described above, the drive mechanism 90A according to this embodiment is a mechanism that drives the discharge reversing triple roller 55 and the guide member 56 using the driving force of the drive motor M. As described above, by using the drive mechanism 90A of this embodiment, the time during which the discharge reversing triple roller 55 is stopped between the switching of the signal of the push solenoid 701 and the switching of the rotation direction of the discharge reversing triple roller 55 is minimized. The time required for the rotation direction of the discharge reversing triple roller 55 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0099] More specifically, when the signal of the push solenoid 701 switches from OFF to ON, the guide member 56 rotates from the first position to the second position due to the action of the reversal unit 200 and the coupling release unit 700. While the guide member 56 is rotating from the first position to the second position, the reversal switching gear 202 is not restricted in its rotation and rotates together with the reversal input gear 201. That is, the discharge reversal triple roller 55 continues to rotate in the reverse direction. Therefore, as shown in Figures 13(c) and (d), the guide member 56 can start moving from the first position to the second position before the sheet S is discharged from the discharge nip N1 of the discharge reversal triple roller 55 and discharged outside the machine. This makes it possible to advance the timing of switching the signal of the push solenoid 701 and improve productivity.

[0100] Furthermore, when the signal from the push solenoid 701 switches from ON to OFF, the guide member 56 rotates from the second position to the first position due to the action of the reversing unit 200 and the coupling release unit 700. Also, the rotation direction of the discharge reversing triple roller 55 switches from the forward rotation direction to the reverse rotation direction.

[0101] At this time, the rotation direction switching operation of the discharge reversing triple roller 55 is performed in parallel with the rotation operation of the guide member 56 from the second position to the first position. Therefore, the rotation direction switching operation of the discharge reversing triple roller 55 is performed without waiting for the guide member 56 to complete its rotation to the first position, and there is virtually no stopping time for the discharge reversing triple roller 55 during the rotation direction switching operation.

[0102] In this way, the time required for the rotation direction of the discharge reversal triple roller 55 to switch is shortened, and the timing for switching the signal of the push solenoid 701 can be advanced, thereby improving productivity.

[0103] <Third Embodiment> Next, a printer 1B according to a third embodiment of the present invention will be described. Printer 1B differs from the first embodiment in that it is provided with a discharge reversing roller pair 57 instead of the discharge roller pair 50 and the reversing roller pair 51. Printer 1B also differs from the first embodiment in that it is provided with a guide member 58 instead of the guide member 53 and the guide switching lever 605, and that the clutch unit 600 is provided coaxially with the rotation center of the guide member 58. For this reason, components similar to those in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0104] [Overall structure] As shown in Figure 14, the printer 1B, as an image forming apparatus, includes a feeding unit 10 for feeding the loaded sheets S, an image forming unit 3 for forming an image on the sheets S, and a fixing device 40 for fixing the image transferred to the sheets S. The printer 1B also includes a pair of discharge reversing rollers 57 that can discharge the sheets S to a discharge tray 54 and switch back to transport them to a double-sided transport path R3, and a guide member 58.

[0105] The discharge reversal roller pair 57, which serves as the conveying section, includes a drive roller 57b that can rotate in both forward and reverse directions, and a driven roller 57c that presses against the drive roller 57b to form a discharge reversal nip N3 as a third nip. The driven roller 57c, as the third driven roller, rotates in conjunction with the drive roller 57b, which serves as the roller. The guide member 58 is movable between a first position shown by the solid line in Figure 15 and a second position shown by the dashed line in Figure 15. The discharge reversal roller pair 57, the guide member 58, and the drive mechanism 90B, which will be described later, constitute the sheet conveying device 3000.

[0106] In single-sided printing mode, where an image is formed on only one side of the sheet S, the sheet S is guided to the discharge inversion transport path R5 by a guide member 58 located at a first position, as shown in Figure 15(a), and discharged to the discharge tray 54 by a discharge inversion nip N3.

[0107] In the double-sided printing mode, where an image is formed on both sides of a sheet S, the sheet S with the image formed on the first side is guided to the discharge reversal transport path R5 by a guide member 58 located at the first position, as shown in Figures 15(a) and (b). The sheet S is then transported in the first direction D1 by the discharge reversal nip N3. At this time, the drive roller 57b of the discharge reversal roller pair 57 is rotating in the first rotation direction RR1. When the rear end of the sheet S passes the guide member 58, the drive roller 57b reverses direction, as shown in Figure 15(c), and the guide member 58 moves from the first position shown by the dashed line to the second position shown by the solid line. As a result, the sheet S is switched back and transported in the second direction D2, opposite to the first direction D1, as shown in Figure 15(d), and is guided to the double-sided transport path R3 by the guide member 58 located at the first position. At this time, the drive roller 57b of the discharge reversal roller pair 57 is rotating in the second rotation direction RR2.

[0108] As shown in Figure 14, the sheet S is transported on a double-sided transport path R3 by a transport roller pair 81 and then transported again to the transfer nip T1 by a registration roller pair 21. At the transfer nip T1, an image is formed on the second surface of the sheet S, and it is then discharged to the discharge tray 54 by the discharge inversion nip N3.

[0109] [Drive mechanism] Next, the drive mechanism 90B for driving the discharge reversal roller pair 57 and the guide member 58 will be described. As shown in Figure 16(a), the drive mechanism 90B includes a drive motor M, a discharge reversal input gear 100, a reversal unit 200, a discharge reversal drive train 400B, a coupling switching gear train 500B, and a clutch unit 600A.

[0110] The discharge reversal input gear 100 is driven by the drive motor M via a gear train (not shown). The reversal unit 200 is driven by the discharge reversal input gear 100 and outputs driving force to the discharge reversal drive train 400B and the coupling changeover gear train 500B, respectively. The driving force transmitted to the discharge reversal drive train 400B drives the discharge reversal roller pair 57. The driving force transmitted from the reversal unit 200 to the coupling changeover gear train 500B is transmitted to the clutch unit 600A. The driving force transmitted to the clutch unit 600A drives the guide member 58.

[0111] Next, the reversing unit 200, the discharge reversing drive train 400B, the coupling switching gear train 500B, and the clutch unit 600A will be described in more detail. The reversing unit 200 includes a reversing input gear 201, a reversing switching gear 202, and a reversing output gear 203. As described in the first embodiment, the reversing unit 200 can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202.

[0112] The discharge reversal drive train 400B includes a discharge reversal step gear 401A that meshes with the reversal output gear 203, and a reversal roller gear 403A that meshes with the discharge reversal step gear 401A. The reversal roller gear 403A is fixed to the drive shaft 57a of the drive roller 57b of the discharge reversal roller pair 57, and the rotation of the reversal roller gear 403A causes the drive roller 57b to rotate via the drive shaft 57a.

[0113] The coupling change gear train 500B includes a coupling change idler gear 503 and a coupling change gear pair 504. The coupling change idler gear 503 meshes with the reversing change gear 202 and the coupling change gear pair 504, and the rotation of the reversing change gear 202 is transmitted to the clutch unit 600A via the coupling change idler gear 503 and the coupling change gear pair 504.

[0114] The clutch unit 600A, acting as a drive interruption unit, includes a clutch input gear 601 that meshes with a coupling switching gear pair 504, a clutch fixing part 602, and a clutch output part 604. The clutch fixing part 602 is held in place by the fixing of a rotation stopper 603. The clutch output part 604 engages with the D-shaped rotating shaft 58a of the guide member 58 and rotates integrally with the guide member 58.

[0115] The clutch unit 600A switches the connection state between the clutch input gear 601 and the clutch output unit 604 depending on the power supply status to the clutch unit 600A. That is, when the clutch unit 600A is powered off, the clutch input gear 601 and the clutch output unit 604 are not driven together. On the other hand, when the clutch unit 600A is powered, the clutch input gear 601 and the clutch output unit 604 are driven together.

[0116] The guide member 58 is biased to a first position by a return spring 52. The return spring 52 is a torsion coil spring, with one end in contact with a member not shown and the other end in contact with the guide member 58. Due to the driving force transmitted from the clutch input gear 601, the guide member 58 moves against the biasing force of the return spring 52. As a result, the guide member 58 moves from the first position to the second position (the position shown by the dashed line in Figure 14).

[0117] [Operation of the discharge reversing roller pair and guide member] Next, the operation of the discharge reversal roller pair 57 and the guide member 58 when the sheet S is switched back will be described. In Figures 16(a) to (c), the rotation direction of each member is indicated by an arrow. In the following description, for example, a print operation is performed and the drive motor M is driven, and the discharge reversal input gear 100 and the reversal input gear 201 are rotating due to the driving force of the drive motor M.

[0118] As shown in Figure 16(a), when the clutch unit 600A is deactivated, the discharge reversing roller pair 57 rotates in a direction that transports the sheet S in the first direction D1 (see Figure 15(a)). That is, the drive roller 51d of the reversing roller pair 51 rotates in the first rotational direction RR1. The rotational direction of the discharge reversing roller pair 57 at this time is defined as the forward rotation direction. Furthermore, when transporting the sheet S in the second direction D2 (see Figure 15(c)), the rotational direction of the discharge reversing roller pair 57 is defined as the reverse rotation direction. At this time, the drive roller 51d of the reversing roller pair 51 rotates in the second rotational direction RR2.

[0119] When the clutch unit 600A is in a power-off state, the drive connection between the clutch input gear 601 and the clutch output unit 604 is released, so the rotation of the clutch input gear 601 is not transmitted to the guide member 58. As a result, the guide member 58 is positioned in the first position (indicated as pos1 in the drawing) by the biasing force of the return spring 52, and is able to guide the sheet S toward the discharge reversal conveying path R5. The discharge reversal roller pair 57 is rotating in the forward direction. In other words, when the single-sided printing mode is executed and when the sheet S is discharged in the double-sided printing mode, the clutch unit 600A is in a power-off state.

[0120] In double-sided printing mode, when the sheet S is transported to the discharge reversal transport path R5, the clutch unit 600A is initially in a de-energized state, similar to single-sided printing mode. The sheet S is then transported in the first direction D1, i.e., outwards from the machine, by the discharge reversal nip N3 of the discharge reversal roller pair 57. When the rear end of the sheet S passes the guide member 58, as shown in Figure 16(b), the signal of the clutch unit 600A is switched from OFF to ON, and the clutch unit 600 changes from a de-energized state to an energized state. This connects the drive of the clutch input gear 601 and the clutch output unit 604.

[0121] The guide member 58 moves from the first position to the second position against the biasing force of the return spring 52 due to the driving force transmitted from the clutch input gear 601. Furthermore, while the guide member 58 is rotating from the first position to the second position, the reversing changeover gear 202 is not restricted in its rotation and rotates together with the reversing input gear 201. In other words, the discharge reversing roller pair 57 continues to rotate in the forward direction.

[0122] After moving to the second position, the guide member 58 abuts against a member (not shown) and its rotation stops. Since the clutch output unit 604 continues to receive driving force from the reversing unit 200, the guide member 58 remains held in the second position. As shown in Figure 16(c), when the rotation of the guide member 58 stops, the clutch unit 600A, the coupling change gear train 500B, and the reversing change gear 202, which are linked to the guide member 58, stop simultaneously.

[0123] When the reversing gear 202 stops, the reversing unit 200 switches from a forward rotation state to a reverse rotation state, and the rotation direction of the reversing output gear 203 switches from the direction of arrow RD2 to the direction of arrow RD3. As a result, the rotation direction of the discharge reversing drive train 400B that meshes with the reversing output gear 203 and the discharge reversing roller pair 57 also switches in conjunction. Consequently, the discharge reversing roller pair 57 rotates the sheet S in the second direction D2 (see Figure 15(d)), that is, in the reverse direction that transports the sheet S toward the inside of the printer 1. As a result, the sheet S is guided into the double-sided transport path R3 by the guide member 58 located in the second position.

[0124] When the rear end of the seat S passes the guide member 58, the clutch unit 600A switches from an energized state to an unenergized state, and the drive mechanism 90B returns to the state shown in Figure 16(a).

[0125] [Effects of the third embodiment] As described above, the drive mechanism 90B according to this embodiment is a mechanism that drives the discharge reversing roller pair 57 and the guide member 58 using the driving force of the drive motor M. As described above, by using the drive mechanism 90B of this embodiment, the time during which the discharge reversing roller pair 57 is stopped between the switching of the signal of the clutch unit 600A and the switching of the rotation direction of the discharge reversing roller pair 57 is minimized. The time required for the rotation direction of the discharge reversing roller pair 57 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0126] <Fourth Embodiment> Next, a printer 1C (see Figure 1) according to a fourth embodiment of the present invention will be described. Printer 1C differs from the first embodiment in that a guide member 59 and a guide switching lever 605A are provided in place of the guide member 53 and the guide switching lever 605. Furthermore, printer 1C as an image forming apparatus differs from the first embodiment in that a reversing unit 200C is provided in place of the reversing unit 200, and a clutch drive train 500C is provided in place of the clutch drive train 500. For this reason, components similar to those in the first embodiment will not be shown or will be described using the same reference numerals in the figures.

[0127] [Drive mechanism] First, the drive mechanism 90C for driving the discharge roller pair 50, the reversing roller pair 51, and the guide member 59 will be described. As shown in Figures 17(a) and (b), the drive mechanism 90C includes a drive motor M, a discharge reversing input gear 100, a reversing unit 200A, a discharge drive train 300, and a reversing drive train 400. The drive mechanism 90C also includes a clutch drive train 500C, a clutch unit 600B, and a drive switching motor M2.

[0128] The discharge reversal input gear 100 is driven by the drive motor M via a gear train (not shown). The reversal unit 200A is driven by the discharge reversal input gear 100 and outputs driving force to the discharge drive train 300, the reversal drive train 400, and the clutch drive train 500C, respectively. The driving force transmitted to the discharge drive train 300 drives the discharge roller pair 50. The driving force transmitted to the reversal drive train 400 drives the reversal roller pair 51. The driving force transmitted from the reversal unit 200A to the clutch drive train 500C is transmitted to the clutch unit 600B. The driving force transmitted to the clutch unit 600B drives the guide member 59.

[0129] Next, the reversing unit 200A, the clutch drive train 500C, and the clutch unit 600B will be described in more detail. The reversing unit 200A, as a drive switching unit, has a reversing input gear 201A, a reversing switching gear 202A, and a reversing output gear 203. As will be described later, the reversing unit 200A can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202. The reversing switching gear 202A is configured to rotate in the same direction and at the same rotational speed as the reversing input gear 201A by the driving force of the drive switching motor M2, which is a second drive source. The discharge drive train 300 and the reversing drive train 400 transmit driving force to the discharge roller pair 50 and the reversing roller pair 51, respectively, in the same configuration as in the first embodiment.

[0130] The clutch drive train 500C includes a clutch idler gear 501 that meshes with the reversing gear 202A, and a clutch step gear 502 that meshes with the clutch idler gear 501 and the clutch input gear 601. The clutch drive train 500C also includes a clutch first input gear 505, a clutch second input gear 506, and a torque limiter 507. The clutch second input gear 506 meshes with the clutch step gear 502 and is driven to the clutch first input gear 505 via the torque limiter 507. The clutch first input gear 505 is driven by a drive changeover motor M2 via a drive gear train (not shown).

[0131] The clutch unit 600B, acting as a drive interruption unit, includes a clutch input gear 601 that meshes with a clutch stage gear 502, a clutch fixing part 602, a clutch output part 604, and a guide switching lever 605A. The clutch fixing part 602 is held in place by the fixing of a rotation stopper 603. The clutch output part 604 is connected to the guide switching lever 605A.

[0132] The clutch unit 600B switches the connection state between the clutch input gear 601 and the clutch output unit 604 depending on the power supply status to the clutch unit 600B. That is, when the clutch unit 600B is powered off, the clutch input gear 601 and the clutch output unit 604 are not driven and connected. On the other hand, when the clutch unit 600B is powered, the clutch input gear 601 and the clutch output unit 604 are driven and connected.

[0133] The guide switching lever 605A, which rotates integrally with the clutch output unit 604, has a groove-shaped engaging portion 605Aa that can engage with the projection 59a of the guide member 59. The return spring 52A is a torsion coil spring, with one end in contact with a member not shown and the other end in contact with the guide switching lever 605A, thereby biasing the guide member 59 in the direction of arrow SD1. Furthermore, the guide member 59, biased by the return spring 52A, is held in the first position (the position shown by the dashed line in Figure 1) by abutting against a member not shown.

[0134] As the guide switching lever 605A rotates, the engaging portion 605Aa of the guide switching lever 605A presses against the projection 59a of the guide member 59, causing the guide member 59 to move in the opposite direction to the direction of arrow SD1, against the biasing force of the return spring 52A. As a result, the guide member 59 moves from the first position to the second position (the position shown by the solid line in Figure 1).

[0135] [Internal configuration of the inversion unit] Next, the internal configuration of the reversing unit 200A will be described using Figures 18(a) and 18(b). As shown in Figures 18(a) and 18(b), the reversing unit 200A comprises a reversing input gear 201A, a reversing switching gear 202A, a reversing output gear 203, an internal idler gear 204, an internal step gear 205, and an internal holder 207A. The reversing input gear 201A, as an input unit, is an input member that rotates upon receiving the driving force transmitted from the aforementioned discharge reversing input gear 100. The reversing output gear 203 is an output member that outputs driving force to the reversing drive train 400 that rotates the reversing roller pair 51. The internal idler gear 204 and the internal step gear 205 are composed of two sets of gear trains arranged symmetrically and are drive transmission members for transmitting drive from the reversing input gear 201A to the reversing output gear 203.

[0136] The internal holder 207A rotatably supports the reversing input gear 201A and has the rotation axes of the reversing switching gear 202A, the reversing output gear 203, the internal idler gear 204, and the internal step gear 205. The internal holder 207A and the reversing switching gear 202A are connected to each other by the engagement of a projection 207Aa on the internal holder 207A and an engaging portion 202Aa on the reversing switching gear 202A. The reversing switching gear 202A, the internal holder 207A, the internal idler gear 204, and the internal step gear 205 constitute a switching unit 340 that outputs the driving force transmitted from the reversing input gear 201A to the reversing output gear 203 in forward or reverse direction according to the state of the reversing switching gear 202A.

[0137] The meshing relationship between the reversing input gear 201A, the reversing output gear 203, the internal idler gear 204, and the internal step gear 205 in the reversing unit 200A is the same as that shown in Figures 5(a) to (d) of the first embodiment, so no explanation is provided. Furthermore, the relationship between the rotational state of the reversing input gear 201A and the reversing output gear 203, depending on the operating state of the reversing switching gear 202A, is the same as that of the first embodiment.

[0138] The reversing gear 202A becomes operational (rotating) when the driving force from the drive switching motor M2 is transmitted via the clutch drive train 500C. Furthermore, when the clutch unit 600B is energized, the guide member 59 stops, causing the clutch stage gear 502 to stop. As a result, the clutch second input gear 506, which meshes with the clutch stage gear 502, also stops, and due to the action of the torque limiter 507, power is no longer transmitted from the clutch first input gear 505 to the clutch second input gear 506. Therefore, the reversing gear 202A does not receive driving force from the drive switching motor M2 and remains in a stopped state. Note that when the clutch unit 600B is unpowered, the reversing gear 202A remains operational regardless of the position of the guide member 59.

[0139] In other words, when the reversing switching gear 202A is in a stopped state, the rotation of the reversing input gear 201A is transmitted to the reversing output gear 203 via the internal idler gear 204 and the internal step gear 205. At this time, the reversing output gear 203 rotates in the direction of arrow RD3, which is the opposite direction of rotation to the reversing input gear 201A. At this time, the switching unit 340 is in the second state and outputs a driving force to the reversing output gear 203 so that the drive roller 51d of the reversing roller pair 51 rotates in the first rotation direction RR1 (see Figure 19(c)).

[0140] On the other hand, when the reversing gear 202A is operating (rotating) due to the driving force of the drive switching motor M2, the reversing gear 202A rotates in the same direction and at the same rotational speed as the reversing input gear 201A. Therefore, it is equivalent to the reversing input gear 201A and the reversing gear 202A rotating as a single unit. As a result, the reversing output gear 203 receives rotational driving force from the internal stage gear 205, which revolves while fixed to the internal holder 207A, and rotates in the same direction as the reversing input gear 201A, i.e., in the direction of arrow RD2. At this time, the switching unit 340 is in the first state and outputs driving force to the reversing output gear 203 so that the drive roller 51d of the reversing roller pair 51 rotates in the second rotation direction RR2 (see Figure 19(a)).

[0141] [Operation of the reversing roller pair and guide member] Next, the operation of the reversing roller pair 51 and the guide member 59 when the sheet S is switched back will be explained using Figures 19(a) to (c). In the following, the state of the reversing unit 200A when the reversing output gear 203 is rotating in the same direction as arrow RD1, which is the rotation direction of the reversing input gear 201A, is referred to as forward rotation or the forward rotation state. The state when the reversing output gear 203 is rotating in the direction of arrow RD3, which is opposite to the rotation direction of arrow RD1, which is the rotation direction of the reversing input gear 201A, is referred to as reverse rotation or the reverse rotation state. Furthermore, in the following explanation, for example, a print operation is performed and the drive motor M is driven, and the discharge reversing input gear 100 and the reversing input gear 201A are rotating due to the driving force of the drive motor M.

[0142] As shown in Figure 19(a), when the clutch unit 600B is deactivated, the reversing gear 202A rotates in the same direction and at the same rotational speed as the reversing input gear 201A, due to the driving force of the drive switching motor M2 being transmitted via the clutch drive train 500C. As a result, the reversing output gear 203 of the reversing unit 200A rotates in the forward direction, and the reversing roller pair 51 rotates in the direction that transports the sheet S in the second direction D2 (see Figure 2(c)), i.e., in the reverse direction.

[0143] When the clutch unit 600B is in a power-off state, the drive connection between the clutch input gear 601 and the guide switching lever 605A is released, so the rotation of the clutch input gear 601 is not transmitted to the guide switching lever 605A. As a result, the guide member 59 is positioned in the first position (indicated as pos1 in the drawing) by the biasing force of the return spring 52A, and is able to guide the sheet S conveyed by the fixing device 40 toward the discharge roller pair 50. The discharge roller pair 50 rotates in the forward direction. In other words, when the single-sided printing mode is executed and when the sheet S is discharged in the double-sided printing mode, the clutch unit 600B is in a power-off state.

[0144] In double-sided printing mode, when transporting a sheet to the reversing transport path R2, the signal of the clutch unit 600B is switched from OFF to ON. As shown in Figure 19(b), when the signal of the clutch unit 600B is switched from OFF to ON, the clutch unit 600B changes from a de-energized state to an energized state. This drives the clutch input gear 601 and the guide switching lever 605A together. The guide switching lever 605A rotates due to the driving force transmitted from the clutch input gear 601 via the reversing switching gear 202A and the clutch drive train 500C, moving the guide member 59 to the second position (indicated as Pos2 in the drawing). Furthermore, while the guide member 59 is rotating from the first position to the second position, the rotation of the reversing switching gear 202A is not restricted and it rotates together with the reversing input gear 201A. That is, the discharge roller pair 50 continues to rotate in the forward direction.

[0145] After moving to the second position, the guide member 59 abuts against a member not shown, and its rotation stops. Since the guide switching lever 605A continues to receive driving force from the reversing unit 200, the guide member 59 remains held in the second position. Because the operation of the guide switching lever 605A is restricted, the torque limiter 507 does not transmit torque above a predetermined level, and the clutch first input gear 505 rotates, but the drive train downstream of the clutch second input gear 506 stops. That is, as shown in Figure 19(c), when the rotation of the guide member 59 stops, the guide switching lever 605A, which is linked to the guide member 59, the clutch drive train 500C, and the reversing switching gear 202A all stop simultaneously.

[0146] When the reversing gear 202A stops, the aforementioned reversing unit 200A switches from a forward rotation state to a reverse rotation state, and the rotation direction of the reversing output gear 203 switches from the direction of arrow RD2 to the direction of arrow RD3 (see Figure 18(a)). As a result, the rotation direction of the reversing drive train 400 that meshes with the reversing output gear 203 and the reversing roller pair 51 also switches in conjunction. Consequently, the reversing roller pair 51 rotates the sheet S in the first direction D1 (see Figure 2(b)), that is, in the forward rotation direction that transports the sheet S toward the outside of the printer 1. As a result, the sheet S is guided to the reversing transport path R2 by the guide member 53 located at the second position and transported in the first direction D1 by the reversing roller pair 51.

[0147] When the clutch unit 600B is energized, as described above, the guide member 59 is held in the second position and the reversing roller pair 51 rotates in the forward direction. When the rear end of the seat S passes the guide member 53, the signal of the clutch unit 600B is switched from ON to OFF, and the clutch unit 600B goes from energized to de-energized. As a result, the drive connection between the clutch input gear 601 and the guide switching lever 605A is released.

[0148] As a result, no driving force is input to the guide switching lever 605A, and as shown in Figure 19(a), the guide member 59 rotates from the second position to the first position due to the biasing force of the return spring 52A. When the guide member 59 begins to rotate from the second position to the first position, the rotation restriction on the reversing switching gear 202A is released, and it becomes able to rotate freely. As a result, the reversing unit 200A switches from the reverse rotation state to the forward rotation state, and the rotation direction of the reversing output gear 203 switches from the direction of arrow RD3 to the direction of arrow RD2 (see Figure 18(a)).

[0149] Therefore, the rotation direction of the reversing drive train 400, which meshes with the reversing output gear 203, and the reversing roller pair 51 are also switched in conjunction. As a result, the reversing roller pair 51 rotates in the reverse direction, which transports the sheet S in the second direction D2 (see Figure 2(c)), that is, toward the inside of the printer 1. As a result, the sheet S is switched back and guided to the double-sided transport path R3 by the guide member 59 located in the first position. Even when the guide member 59 is in the first position, the clutch unit 600B is in a power-off state, so the rotation of the reversing switching gear 202 is not restricted. Therefore, the discharge roller pair 50 continues to rotate in the forward direction.

[0150] [Effects of the fourth embodiment] As described above, the drive mechanism 90C according to this embodiment is a mechanism that drives the reversing roller pair 51 and the guide member 59 using the driving force of the drive motor M. As described above, by using the drive mechanism 90C of this embodiment, the time during which the reversing roller pair 51 is stopped between the switching of the signal of the clutch unit 600B and the switching of the rotation direction of the reversing roller pair 51 is minimized. The time required for the rotation direction of the reversing roller pair 51 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0151] Furthermore, the reversing unit 200A has a configuration that omits the locking lever 209 and stopper holder 208 compared to the reversing unit 200 of the first embodiment. This is because the reversing switching gear 202A is configured to rotate in the same rotational direction and at the same rotational speed as the reversing input gear 201 by the driving force of the drive switching motor M2. As a result, the reversing unit 200A can be made smaller in the width direction (axial direction), and the drive mechanism 90C can be made smaller.

[0152] [Modified version of the fourth embodiment] In this embodiment, the rotation state of the reversing gear 202A is switched to either rotating or stopped. However, instead of stopping, the rotation direction of the reversing output gear 203 may be switched by changing the rotation speed or rotation direction.

[0153] Furthermore, in this embodiment, the same drive source was used to drive the reversing roller pair 51 and the drive source to drive the guide member 59, but a configuration in which two different drive sources are used to drive each component may also be used.

[0154] <Fifth Embodiment> Next, a printer 1D (see Figure 1) according to a fifth embodiment of the present invention will be described. The printer 1D as an image forming apparatus differs from the fourth embodiment in that a reversing unit 200B is provided instead of a reversing unit 200A, and a clutch drive train 500D is provided instead of a clutch drive train 500C. For this reason, components similar to those in the fourth embodiment will not be shown in the figures, or will be described using the same reference numerals in the figures.

[0155] [Drive mechanism] First, the drive mechanism 90D for driving the discharge roller pair 50, the reversing roller pair 51, and the guide member 59 will be described. As shown in Figures 20(a) and (b), the drive mechanism 90D includes a drive motor M, a discharge reversing input gear 100, a reversing unit 200B, a discharge drive train 300, and a reversing drive train 400. The drive mechanism 90D also includes a clutch drive train 500D, a clutch unit 600B, and a drive switching motor M2.

[0156] The discharge reversal input gear 100 is driven by the drive motor M via a gear train (not shown). The reversal unit 200B is driven by the discharge reversal input gear 100 and outputs driving force to the discharge drive train 300, the reversal drive train 400, and the clutch drive train 500D, respectively. The driving force transmitted to the discharge drive train 300 drives the discharge roller pair 50. The driving force transmitted to the reversal drive train 400 drives the reversal roller pair 51. The driving force transmitted from the reversal unit 200B to the clutch drive train 500D is transmitted to the clutch unit 600B, which acts as a drive disconnection unit. The driving force transmitted to the clutch unit 600B drives the guide member 59.

[0157] Next, the reversing unit 200B and the clutch drive train 500D will be described in more detail. The reversing unit 200B, as a drive switching unit, has a reversing input gear 201B, a reversing switching gear 202B, and a reversing output gear 203B. As will be described later, the reversing unit 200B can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202B. The reversing switching gear 202B is configured to rotate in the same direction and at the same rotational speed as the reversing input gear 201A by the driving force of the drive switching motor M2.

[0158] The clutch drive train 500D includes a clutch idler gear 501 that meshes with the reversing changeover gear 202B, and a clutch step gear 502 that meshes with the clutch idler gear 501 and the clutch input gear 601. The clutch drive train 500C includes a clutch first input gear 505, a clutch second input gear 506, and a torque limiter 507. The clutch second input gear 506 meshes with the clutch idler gear 501 and is driven to the clutch first input gear 505 via the torque limiter 507. The clutch first input gear 505 is driven by a drive changeover motor M2 via a drive gear train (not shown).

[0159] [Internal configuration of the inversion unit] Next, the internal configuration of the reversing unit 200B will be described using Figures 21(a) to 22(d). As shown in Figures 21(a) and 21(b), the reversing unit 200B includes a reversing input gear 201B as an input section, a reversing switching gear 202B, a reversing output gear 203B as an output section, and an internal idler gear 204B. The reversing input gear 201A is an input member that rotates upon receiving the driving force transmitted from the aforementioned discharge reversing input gear 100. The reversing output gear 203B is an output member that outputs driving force to the reversing drive train 400 that rotates the reversing roller pair 51. The internal idler gear 204B consists of a pair of symmetrically arranged gears and is a drive transmission member for transmitting drive from the reversing input gear 201B to the reversing output gear 203B. The reversing gear 202B has rotation axes for the reversing input gear 201B, the reversing output gear 203B, and the internal idler gear 204B, and is configured to hold each of the gears.

[0160] The internal idler gear 204B is rotatably positioned on a pair of rotating shafts 202Ba provided on the reversing switching gear 202B and meshes with the sun gear 201Ba provided at the center of the reversing input gear 201B. The internal idler gear 204B also meshes with the internal gear 203Ba provided on the reversing output gear 203B. In other words, the driving force of the reversing input gear 201B is transmitted to the reversing output gear 203B via the sun gear 201Ba, the pair of internal idler gears 204B, and the internal gear 203Ba. The reversing switching gear 202B and the internal idler gear 204B constitute a switching unit 350 that outputs the driving force transmitted from the reversing input gear 201B to the reversing output gear 203B in forward or reverse direction according to the state of the reversing switching gear 202B.

[0161] [Drive switching operation of the reversing unit] The operation of the rotation direction switching of the reversal output gear 203B of the reversal unit 200B will be explained using Figures 22(a) to (d). Figures 22(a) and (b) are front and rear views showing the operation of the reversal unit 200B when the reversal switching gear 202B is in a rotating state. Figures 22(c) and (d) are front and rear views showing the operation of the reversal unit 200B when the reversal switching gear 202B is in a stopped state. Here, Figures 22(a) and (c) omit the reversal output gear 203B, and Figures 22(b) and (d) omit the reversal input gear 201B and the reversal switching gear 202B.

[0162] As shown in Figures 22(a) and 22(b), when the reversing gear 202B is rotating, the driving force from the clutch first input gear 505 is transmitted to the reversing gear 202B, and it rotates in the same direction and at the same rotational speed as the reversing input gear 201B. At this time, the reversing gear 202B and the reversing input gear 201B are equivalent to rotating as a single unit. The internal idler gear 204B, which is rotatably supported by the reversing gear 202B, is maintained in a stationary (fixed) state relative to the reversing gear 202B because no relative displacement occurs between the reversing gear 202B and the reversing input gear 201B.

[0163] Therefore, the internal idler gear 204B revolves together with the reversing input gear 201B and the reversing selector gear 202B, in the same direction as arrow RD6 around the rotation axis of the reversing input gear 201B. The rotation in the direction of arrow RD6 input to the reversing input gear 201B is transmitted to the reversing output gear 203B via the internal idler gear 204B, which revolves in the same direction, as the reversing input gear 201B and the reversing selector gear 202B rotate together. In other words, as shown in Figure 22(b), the reversing output gear 203B receives rotational driving force from the internal idler gear 204B, which revolves while fixed to the reversing selector gear 202B, to its internal teeth 203ba. As a result, the reversing output gear 203B rotates in the direction of arrow RD7, which is the same direction as arrow RD6, and outputs rotational driving force. At this time, the switching unit 350 is in the first state and outputs a driving force to the reversing output gear 203B so that the drive roller 51d of the reversing roller pair 51 rotates in the second rotation direction RR2 (see Figure 23(a)).

[0164] As shown in Figure 22(c), when the reversing gear 202B is stationary, the rotation of the reversing input gear 201B in the direction of arrow RD6 is transmitted to the internal idler gear 204B, which meshes with the sun gear 201Ba. The internal idler gear 204B rotates around the rotation axis 202Ba in the direction of arrow RD9, which is opposite to the direction of rotation of the reversing input gear 201B, which is the direction of rotation of arrow RD6. Then, as shown in Figure 22(d), the reversing output gear 203B meshes with the internal idler gear 204B with its internal teeth 203ba, so it rotates in the same direction as the direction of rotation of the internal idler gear 204B, which is the direction of rotation of arrow RD9, which is the direction of arrow RD8. In other words, the reversing output gear 203B rotates in the direction of arrow RD8, which is opposite to the direction of rotation of the reversing input gear 201B, which is the direction of rotation of arrow RD6. The rotational direction of the rotational drive force input from the reversing input gear 201B is reversed between the sun gear 201Ba and the internal idler gear 204B. At this time, the switching unit 350 is in the second state and outputs a drive force to the reversing output gear 203B so that the drive roller 51d of the reversing roller pair 51 rotates in the first rotational direction RR1 (see Figure 23(c)).

[0165] [Operation of the reversing roller pair and guide member] Next, the operation of the reversing roller pair 51 and the guide member 59 when the sheet S is switched back will be explained using Figures 23(a) to (c). In the following, the state of the reversing unit 200B when the reversing output gear 203B is rotating in the same direction as arrow RD6, which is the rotation direction of the reversing input gear 201B (arrow RD8), will be referred to as forward rotation or the forward rotation state. The state when the reversing output gear 203B is rotating in the direction of arrow RD8, which is opposite to the rotation direction of arrow RD6, which is the rotation direction of the reversing input gear 201B, will be referred to as reverse rotation or the reverse rotation state. Furthermore, in the following explanation, for example, a print operation is performed and the drive motor M is driven, and the discharge reversing input gear 100 and the reversing input gear 201B are rotating due to the driving force of the drive motor M.

[0166] As shown in Figure 23(a), when the clutch unit 600B is deactivated, the reversing gear 202B rotates in the same direction and at the same rotational speed as the reversing input gear 201B, due to the driving force of the drive switching motor M2 being transmitted via the clutch drive train 500D. As a result, the reversing output gear 203B of the reversing unit 200B rotates in the forward direction, and the reversing roller pair 51 rotates in the direction that transports the sheet S in the second direction D2 (see Figure 2(c)), i.e., in the reverse direction.

[0167] When the clutch unit 600B is in a power-off state, the drive connection between the clutch input gear 601 and the guide switching lever 605A is released, so the rotation of the clutch input gear 601 is not transmitted to the guide switching lever 605A. As a result, the guide member 59 is positioned in the first position (indicated as pos1 in the drawing) by the biasing force of the return spring 52A, and is able to guide the sheet S conveyed by the fixing device 40 toward the discharge roller pair 50. The discharge roller pair 50 rotates in the forward direction. In other words, when the single-sided printing mode is executed and when the sheet S is discharged in the double-sided printing mode, the clutch unit 600B is in a power-off state.

[0168] In double-sided printing mode, when transporting the sheet S to the reversing transport path R2, the signal of the clutch unit 600B is switched from OFF to ON. As shown in Figure 23(b), when the signal of the clutch unit 600B is switched from OFF to ON, the clutch unit 600B changes from a de-energized state to an energized state. As a result, the clutch input gear 601 and the guide switching lever 605A are driven together. The guide switching lever 605A rotates due to the driving force transmitted from the clutch input gear 601 via the reversing switching gear 202A and the clutch drive train 500D, moving the guide member 59 to the second position (indicated as Pos2 in the drawing). Furthermore, while the guide member 59 is rotating from the first position to the second position, the rotation of the reversing switching gear 202B is not restricted and it rotates together with the reversing input gear 201B. That is, the discharge roller pair 50 continues to rotate in the forward direction.

[0169] After moving to the second position, the guide member 59 abuts against a member not shown, and its rotation stops. Since the guide switching lever 605A continues to receive driving force from the reversing unit 200, the guide member 59 remains held in the second position. Because the operation of the guide switching lever 605A is restricted, the torque limiter 507 does not transmit torque above a predetermined level, and the clutch first input gear 505 rotates, but the drive train downstream of the clutch second input gear 506 stops. As shown in Figure 23(c), when the rotation of the guide member 59 stops, the guide switching lever 605A, which is linked to the guide member 59, the clutch drive train 500D, and the reversing switching gear 202B all stop simultaneously.

[0170] When the reversing gear 202B stops, the aforementioned reversing unit 200B switches from a forward rotation state to a reverse rotation state, and the rotation direction of the reversing output gear 203B switches from the direction of arrow RD7 to the direction of arrow RD8 (see Figures 22(b) and 22(c)). As a result, the rotation direction of the reversing drive train 400 that meshes with the reversing output gear 203B and the reversing roller pair 51 also switches in conjunction. Consequently, the reversing roller pair 51 rotates the sheet S in the first direction D1 (see Figure 2(b)), that is, in the forward rotation direction that transports the sheet S toward the outside of the printer 1. As a result, the sheet S is guided to the reversing transport path R2 by the guide member 59 located in the second position and transported in the first direction D1 by the reversing roller pair 51.

[0171] When the clutch unit 600B is energized, as described above, the guide member 59 is held in the second position and the reversing roller pair 51 rotates in the forward direction. When the rear end of the seat S passes the guide member 53, the signal of the clutch unit 600B is switched from ON to OFF, and the clutch unit 600B goes from energized to de-energized. As a result, the drive connection between the clutch input gear 601 and the guide switching lever 605A is released.

[0172] As a result, no driving force is input to the guide switching lever 605A, and as shown in Figure 23(a), the guide member 59 rotates from the second position to the first position due to the biasing force of the return spring 52A. When the guide member 59 begins to rotate from the second position to the first position, the rotation restriction on the reversing switching gear 202A is released, and it becomes able to rotate freely. As a result, the reversing unit 200B switches from the reverse rotation state to the forward rotation state, and the rotation direction of the reversing output gear 203B switches from the direction of arrow RD8 to the direction of arrow RD7 (see Figures 22(b) and (d)).

[0173] Therefore, the rotation direction of the reversing drive train 400, which meshes with the reversing output gear 203B, and the reversing roller pair 51 are also switched in conjunction. As a result, the reversing roller pair 51 rotates in the reverse direction, which transports the sheet S in the second direction D2 (see Figure 2(c)), that is, toward the inside of the printer 1. As a result, the sheet S is switched back and guided to the double-sided transport path R3 by the guide member 59 located in the first position. Even when the guide member 59 is in the first position, the clutch unit 600B is in a power-off state, so the rotation of the reversing switching gear 202B is not restricted. Therefore, the discharge roller pair 50 continues to rotate in the forward direction.

[0174] [Effects of the Fifth Embodiment] As described above, the drive mechanism 90D according to this embodiment is a mechanism that drives the reversing roller pair 51 and the guide member 59 using the driving force of the drive motor M. As described above, by using the drive mechanism 90D of this embodiment, the time during which the reversing roller pair 51 is stopped between the switching of the signal of the clutch unit 600B and the switching of the rotation direction of the reversing roller pair 51 is minimized. The time required for the rotation direction of the reversing roller pair 51 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0175] Furthermore, the reversing unit 200B has a configuration that omits the internal holder 207A and the internal step gear 205 compared to the reversing unit 200A of the fourth embodiment. As a result, the reversing unit 200B can be easily constructed, and the cost of the drive mechanism 90D can be reduced.

[0176] <Sixth Embodiment> Next, a printer 1E (see Figure 9) according to the sixth embodiment of the present invention will be described. The printer 1E as an image forming apparatus has the same general configuration as the printer 1A according to the second embodiment, but the drive mechanism for driving the discharge reversal triple roller 55 and the guide member 71 is different from the drive mechanism 90A of the second embodiment.

[0177] [Drive mechanism] The drive mechanism 90E for driving the discharge reversal triple roller 55 and guide member 71 will now be described. As shown in Figures 24(a) and 24(b), the drive mechanism 90E includes a drive motor M, a discharge reversal input gear train 100A, a reversal unit 200C, an intermediate lever 607, a solenoid unit 800, and a planetary gear unit 900.

[0178] The discharge reversal input gear train 100A is driven by a drive motor M via a gear train (not shown). The reversal unit 200C is driven by the discharge reversal input gear train 100A and outputs driving force to the triple roller gear 404 and the planetary gear unit 900, respectively. The intermediate lever 607 is supported so as to be rotatable around the pivot axis 607a. One end of the intermediate lever 607 is provided with an engagement portion 607b that can engage with the boss portion 71a of the guide member 71, and the other end of the intermediate lever 607 is provided with a contact portion 607c that can contact the planetary output gear lever 903, which will be described later. The intermediate lever 607 is biased by a lever return spring 608 so that the contact portion 607c presses against the planetary output gear lever 903. The driving force transmitted to the planetary gear unit 900 is transmitted to the intermediate lever 607 via the planetary output gear lever 903, thereby driving the guide member 71.

[0179] Next, the discharge reversal input gear train 100A, the reversal unit 200C, the solenoid unit 800, and the planetary gear unit 900 will be described in more detail. The discharge reversal input gear train 100A includes a first discharge reversal input gear 101, a second discharge reversal input gear 102, and a third discharge reversal input gear 103. The first discharge reversal input gear 101 is driven by the drive motor M and meshes with the second discharge reversal input gear 102. The third discharge reversal input gear 103 has a recess 103a that engages with a protrusion 102a of the second discharge reversal input gear 102, and through the engagement of these protrusions 102a and recess 103a, it rotates integrally with the second discharge reversal input gear 102.

[0180] The reversing unit 200C, which functions as a drive switching unit, includes a reversing input gear 201, a reversing switching gear 202, and a reversing output gear 203. As described in the first embodiment, the reversing unit 200C can output forward rotation or reverse rotation (clockwise or counterclockwise) by switching the rotation state of the reversing switching gear 202. A triple roller gear 404 meshes with the reversing output gear 203, and the triple roller gear 404 is fixed to the drive shaft 55a of the drive roller 55b of the discharge reversing triple roller 55. Therefore, the discharge reversing triple roller 55 rotates as the triple roller gear 404 rotates.

[0181] The solenoid unit 800 includes a solenoid 801, a solenoid arm 801a, a solenoid lever 802, and an arm spring 803. The solenoid arm 801a is rotated when the solenoid 801 transitions between a de-energized state and an energized state. The solenoid lever 802 is rotatably supported around a pivot axis 802c, and one end 802b is engaged with the solenoid arm 801a. The other end of the solenoid lever 802 is provided with a locking claw 802a capable of locking the locking claw 902a of the planetary sun gear 902, which will be described later.

[0182] When solenoid 801 is de-energized, solenoid arm 801a is positioned biased by arm spring 803, and solenoid lever 802 is in a position where the locking claw 80a is separated from the locked claw 902a of planetary sun gear 902. When solenoid 801 is energized, solenoid arm 801a is driven by solenoid 801, and solenoid lever 802, which is engaged with solenoid arm 801a, rotates around pivot axis 802c. As a result, solenoid lever 802 is positioned so that the locking claw 802a engages with the locked claw 902a of planetary sun gear 902.

[0183] Furthermore, the solenoid unit 800 and the planetary gear unit 900 constitute a drive interruption unit 950 that can transition between a transmission state in which the driving force transmitted from the switching unit 360 can be transmitted to the guide member 71, and a non-transmission state in which the driving force is not transmitted to the guide member 71. As will be described later, the drive interruption unit 950 is in a non-transmission state when the solenoid 801 of the solenoid unit 800 is in a power outage state, and is in a transmission state when the solenoid 801 is energized.

[0184] [Internal configuration of the inversion unit] Next, the internal configuration of the reversal unit 200 will be described using Figures 25(a) and 25(b). As shown in Figures 25(a) and 25(b), the reversal unit 200 includes a reversal input gear 201, a reversal switching gear 202, a reversal output gear 203, a stopper holder 208, and an internal holder unit 212 including an internal idler gear 204. The reversal input gear 201 is an input member that rotates upon receiving the driving force transmitted from the aforementioned discharge reversal input gear train 100A. The reversal output gear 203 is an output member that outputs driving force to a triple roller gear 404 that rotates the drive roller 55b of the discharge reversal triple roller 55. The internal idler gear 204 consists of two sets of gear trains arranged symmetrically and is a drive transmission member for transmitting drive from the reversal input gear 201 to the reversal output gear 203. The internal holder unit 212 and the stopper holder 208 are connected so as to rotate as a single unit.

[0185] The internal holder unit 212 includes a first internal holder 212a, a second internal holder 212b, and an internal idler gear 204. The internal idler gear 204 is sandwiched between the first internal holder 212a and the second internal holder 212b and is rotatably held. The internal holder unit 212 rotatably holds the reversal input gear 201 and has support shafts that rotatably support the reversal switching gear 202 and the internal idler gear 204, respectively.

[0186] The stopper holder 208 holds the locking lever 209 and the compression spring 210. The locking lever 209 is supported by the stopper holder 208 so as to be rotatable about a pivot axis 209c. The locking lever 209 also has a projection 209a that can engage with a hole 202a formed in the reversing gear 202, and a locking portion 209b that can engage with a locked portion 201c of the reversing input gear 201. The locking lever 209 is movable between an engaged position in which the locking portion 209b engages with the locked portion 201c of the reversing input gear 201, and an unengaged position in which the locking portion 209b does not engage with the locked portion 201c. The reversing gear 202, stopper holder 208, internal holder unit 212, locking lever 209, and compression spring 210 constitute a switching unit 360 that outputs the driving force transmitted from the reversing input gear 201 to the reversing output gear 203.

[0187] The compression spring 210 biases the locking lever 209 toward the engagement position. When the reversal input gear 201 is locked by the locking lever 209 in the engagement position, the reversal input gear 201, the stopper holder 208, and the internal holder unit 212 become one unit. At this time, the switching unit 360 is in the first state and outputs a driving force to the reversal output gear 203 so that the drive roller 55b of the discharge reversal triple roller 55 rotates in the second rotation direction RR2 (see Figure 28(b)).

[0188] The reversing gear 202 is configured to control the operation of the locking lever 209 depending on its rotational state. When the locking lever 209 is in the disengaged position and the reversing gear 202 is stopped by an external force, the switching unit 360 enters a second state. In the second state, the switching unit 360 outputs a driving force to the reversing output gear 203 so that the drive roller 55b of the discharge reversing triple roller 55 rotates in the first rotational direction RR1 (see Figure 29(b)).

[0189] Furthermore, the reversing unit 200C is rotatably supported by the engagement of a discharge frame shaft 250, which is provided on a discharge frame (not shown), with a hole 212c in the internal holder unit 212 and a hole 203c in the reversing output gear 203.

[0190] The meshing relationship between the reversal input gear 201, the reversal output gear 203, and the internal idler gear 204 in the reversal unit 200C is the same as in the first to third embodiments, so a description is omitted.

[0191] [Internal structure of the planetary gear unit] Next, the internal configuration of the planetary gear unit 900 will be described using Figures 26(a) and 26(b). As shown in Figures 26(a) and 26(b), the planetary gear unit 900 includes a planetary input gear 901, a planetary sun gear 902, a planetary output gear lever 903, and a planetary gear 904.

[0192] The planetary input gear 901, as the first rotating element, is an input member that rotates upon receiving the driving force transmitted from the aforementioned reversal switching gear 202. The planetary output gear lever 903, as the third rotating element, is an output member that outputs driving force by bringing its lever portion 903a into contact with the contact portion 607c of the intermediate lever 607 (see Figure 24(a)). The planetary gear 904 consists of a pair of symmetrically arranged gears and is a drive transmission member for transmitting drive from the planetary input gear 901 to the planetary output gear lever 903. The planetary input gear 901 has support shafts that rotatably support the planetary sun gear 902, the planetary output gear lever 903, and the planetary gear 904, and is configured to hold each gear rotatably.

[0193] The planetary gear 904 is rotatably mounted on a pair of support shafts provided on the planetary input gear 901, inserted into the central shaft 901a of the planetary input gear 901, and meshes with the planetary sun gear 902, which acts as a second rotational element. The planetary gear 904 also meshes with the internal gear 903b provided on the planetary output gear lever 903. In other words, the driving force of the planetary input gear 901 is transmitted to the planetary output gear lever 903 via the planetary sun gear 902, the pair of planetary gears 904, and the internal gear 903b. The rotation of the planetary sun gear 902 can be restricted by a solenoid unit 800, which acts as a regulating unit.

[0194] [Drive switching operation of the planetary gear unit] Next, the drive switching operation of the planetary gear unit 900 will be explained using Figures 27(a) to (h). Figures 27(a) to (d) show the state when the planetary sun gear 902 is not engaged with the solenoid lever 802 and is in a rotating state, while Figures 27(e) to (h) show the state when the planetary sun gear 902 is engaged with the solenoid lever 802 and is in a stopped state. Figures 27(a) and (e) are front views of the planetary gear unit 900, and Figures 27(b) and (f) are rear views of the planetary gear unit 900 with the planetary output gear lever 903 omitted. Figures 27(c) and (g) are front views of the planetary gear unit 900 with the planetary input gear 901 and planetary sun gear 902 omitted, and Figures 27(d) and (h) are rear views of the planetary gear unit 900.

[0195] As shown in Figures 27(a) to (d), when the planetary sun gear 902 is not engaged by the solenoid lever 802, the planetary output gear lever 903 is pressed by the intermediate lever 607, which is biased by the lever return spring 608, and stops at the first lever position. The driving force transmitted to the planetary input gear 901 is transmitted to the planetary sun gear 902 via the planetary gear 904 because the planetary output gear lever 903 is stopped. The driving force is transmitted to the planetary sun gear 902 and it rotates, which makes it possible to maintain the planetary output gear lever 903 in the stopped state at the first lever position. At this time, the guide member 71 is in the first position (the position shown by the dashed line in Figure 9).

[0196] In other words, when the rotation of the planetary sun gear 902 is not restricted by the solenoid unit 800, the rotation of the planetary input gear 901 is transmitted to the planetary sun gear 902 via the planetary gear 904, causing the drive cutoff unit 950 to be in a non-transmission state.

[0197] As shown in Figures 27(e) to (h), the planetary sun gear 902 is stopped when the locking claw 902a of the planetary sun gear 902 is locked by the locking claw 802a of the solenoid lever 802. The driving force transmitted to the planetary input gear 901 is transmitted to the planetary output gear lever 903 via the planetary gear 904. The planetary output gear lever 903 rotates upon receiving the driving force, causing the intermediate lever 607 to rotate. As the intermediate lever 607 rotates, the guide member 71 moves from the first position to the second position (the position shown by the solid line in Figure 9).

[0198] In other words, when the rotation of the planetary sun gear 902 is restricted by the solenoid unit 800, the rotation of the planetary input gear 901 is transmitted to the planetary output gear lever 903 via the planetary gear 904, causing the drive cutoff unit 950 to enter a transmission state.

[0199] [Operation of the discharge reversal triple roller and guide member] Next, the operation of the discharge reversal triple roller 55 and guide member 71 when the sheet S is switched back will be explained using Figures 28(a) to 29(d). Figures 28(a) and 28(b) are front and rear views, respectively, of the drive mechanism 90E when the solenoid 801 is in a de-energized state. Figures 28(c) and 28(d) are front and rear views, respectively, of the drive mechanism 90E when the solenoid 801 switches from a de-energized state to an energized state. Figures 29(a) and 29(b) are front and rear views, respectively, of the drive mechanism 90E when the solenoid 801 is energized. Figures 29(c) and 29(d) are front and rear views, respectively, of the drive mechanism 90E when the solenoid 801 switches from an energized state to a de-energized state.

[0200] In the following explanation, for example, a print operation is performed and the drive motor M is driven, and the discharge reversal input gear train 100A and the reversal input gear 201 are rotated by the driving force of the drive motor M.

[0201] As shown in Figures 28(a) and 28(b), when the solenoid 801 is deactivated, the discharge reversing triple roller 55 rotates in the direction shown in the figure. The discharge nip N1 of the discharge reversing triple roller 55 allows the sheet S to be discharged toward the discharge tray 54, and the rotation direction of the discharge reversing triple roller 55 at this time is set to the reverse direction. Furthermore, when the reversing nip N2 of the discharge reversing triple roller 55 transports the sheet S toward the first direction D1 (see Figure 10(b)), the rotation direction of the discharge reversing triple roller 55 is set to the forward direction.

[0202] When the solenoid 801 is deactivated, the locking claw 802a of the solenoid lever 802 is separated from the locked claw 902a of the planetary sun gear 902, allowing the planetary sun gear 902 to rotate freely. On the other hand, the planetary output gear lever 903 is pressed by the intermediate lever 607, which is biased by the lever return spring 608, and stops at the first lever position. As a result, the driving force transmitted from the reversing gear 202 to the planetary input gear 901 is transmitted to the planetary sun gear 902, causing the planetary sun gear 902 to rotate freely.

[0203] Furthermore, since the planetary output gear lever 903 remains held in the first lever position, the intermediate lever 607 and the guide member 71 are also stopped. That is, the guide member 71 is in the first position (indicated as Pos1 in the drawing) that guides the sheet S to the discharge nip N1 of the discharge reversal triple roller 55. When single-sided printing mode is performed and when the sheet S is discharged in double-sided printing mode, the push solenoid 701 is deactivated.

[0204] In double-sided printing mode, when transporting the sheet S to the inverting transport path R2, the signal of the solenoid 801 is switched from OFF to ON, as shown in Figures 28(c) and (d). When the signal of the solenoid 801 is switched from OFF to ON, the solenoid 801 changes from a de-energized state to an energized state. As a result, the solenoid arm 801a is driven against the biasing force of the arm spring 803. Then, the locking claw 802a of the solenoid lever 802, which is linked to the solenoid arm 801a, locks the locked claw 902a of the planetary sun gear 902, and the planetary sun gear 902 comes to a stop. As a result, the driving force input to the planetary input gear 901 is transmitted to the planetary output gear lever 903.

[0205] The planetary output gear lever 903, upon receiving the driving force, rotates from the first lever position to the second lever position, and the lever portion 903a presses against the contact portion 607c of the intermediate lever 607, causing the intermediate lever 607 to rotate. The guide member 71, which engages with the intermediate lever 607, rotates from the first position to the second position (indicated as Pos2 in the drawing), which guides the sheet S to the reversing nip N2 of the discharge reversing triple roller 55, as the intermediate lever 607 rotates. After rotating to the second position, the guide member 71 abuts against a frame (not shown) and is held in the second position. While the guide member 71 is rotating from the first position to the second position, the reversing changeover gear 202 is not restricted from rotating and rotates together with the reversing input gear 201. That is, the discharge reversing triple roller 55 continues to rotate in the reverse direction, which is the direction in which the sheet S is transported out of the machine by the discharge nip N1.

[0206] As shown in Figures 29(a) and 29(b), when the solenoid 801 is energized, the guide member 71 stops at the second position, causing the intermediate lever 607 to be in a state where the planetary gear unit 900 and the reversing gear 202 are stopped. In this state, when the locking lever 209 rotates together with the reversing input gear 201, the projection 209a of the locking lever 209 moves in the direction of arrow M1 along the edge of the hole 202a of the stopped reversing gear 202.

[0207] As a result, the locking lever 209 rotates from the engaged position to the disengaged position on the pivot axis 209c, against the biasing force of the compression spring 210 (see Figure 25(b)). Then, as described in the first embodiment, the reversing unit 200 switches from the forward rotation state to the reverse rotation state, and the rotation direction of the reversing output gear 203 is switched. Consequently, the rotation direction of the triple roller gear 404 that meshes with the reversing output gear 203 and the discharge reversing triple roller 55 also switches in conjunction. As a result, the discharge reversing triple roller 55 rotates in the forward rotation direction. As a result, the sheet S is guided to the reversing transport path R2 by the guide member 71 located in the second position, and transported in the first direction D1 by the reversing nip N2 of the discharge reversing triple roller 55, as shown in Figure 10(b).

[0208] When the rear end of the seat S passes the guide member 71, the signal of the solenoid 801 is switched from ON to OFF, as shown in Figures 29(c) and (d). When the signal of the solenoid 801 is switched from ON to OFF, the solenoid 801 goes from being energized to being de-energized. As a result, the solenoid arm 801a returns to its initial position due to the biasing force of the arm spring 803. Then, the locking claw 802a of the solenoid lever 802, which is linked to the solenoid arm 801a, separates from the locked claw 902a of the planetary sun gear 902, and the planetary sun gear 902 becomes able to rotate freely. As a result, the driving force input to the planetary input gear 901 is transmitted to the planetary sun gear 902, and the transmission of driving force to the planetary output gear lever 903 is suppressed.

[0209] Therefore, the biasing force of the lever return spring 608 causes the intermediate lever 607 to rotate, and the guide member 71, which is linked to the intermediate lever 607, rotates from the second position to the first position. Also, as the guide member 71 begins to rotate, the reversing gear 202 moves from a stationary state to a rotating state, and the locking lever 209 rotates from the engaged position to the engaged position (see Figure 25(b)).

[0210] Then, as described in the first embodiment, the reversing unit 200 switches from the reverse rotation state to the forward rotation state, and the rotation direction of the reversing output gear 203 is switched. As a result, the rotation direction of the triple roller gear 404 that meshes with the reversing output gear 203 and the discharge reversing triple roller 55 are also switched in conjunction. Consequently, the discharge reversing triple roller 55 rotates in the reverse direction, and the reversing nip N2 transports the sheet S in the second direction D2 (see Figures 10(c) and 10(d)). As a result, the sheet S is switched back and guided to the double-sided transport path R3 by the guide member 71 located in the first position.

[0211] [Effects of the sixth embodiment] As described above, the drive mechanism 90E according to this embodiment is a mechanism that drives the discharge reversal triple roller 55 and the guide member 71 using the driving force of the drive motor M. The effects of this embodiment are the same as those of the third embodiment. That is, the time between the switching of the signal of the solenoid 801 and the switching of the rotation direction of the discharge reversal triple roller 55 is minimized, and the stopped state of the discharge reversal triple roller 55 is minimized. The time required for the rotation direction of the discharge reversal triple roller 55 to be switched is shortened, which allows for closer spacing between sheets of paper during double-sided printing, thereby increasing productivity.

[0212] [Modified version of the sixth embodiment] In this embodiment, a configuration in which two planetary gears 904 of the planetary gear unit 900 are arranged is used, but a configuration in which one or three or more planetary gears 904 are arranged may also be used.

[0213] Furthermore, in this embodiment, a configuration is used in which the planetary sun gear 902 is locked by the locking claw 802a of the solenoid lever 802, but a configuration in which the planetary sun gear 902 is directly locked by the claw portion of the solenoid arm 801a of the solenoid 801 may also be used.

[0214] Furthermore, in this embodiment, a configuration was used in which the driving force of the planetary output gear lever 903 is transmitted to the guide member 71 via the intermediate lever 607. However, a configuration in which the driving force of the planetary output gear lever 903 is directly transmitted to the guide member 71 may also be used. Furthermore, although this embodiment uses a configuration in which the sheet S is conveyed by a triple discharge and reversing roller 55, a configuration in which a pair of discharge rollers and a pair of reversing rollers are arranged may also be used.

[0215] Furthermore, in this embodiment, a configuration was used in which the driving force transmitted to the guide member 71 is switched by the planetary gear unit 900 and the solenoid unit 800, but the embodiment is not limited to this. For example, as shown in Figures 30(a) and 30(b), a configuration may be used in which the driving force transmitted to the guide member 71 is switched using a clutch unit 600. The clutch unit 600 has been described in the first embodiment, so its description will be omitted here.

[0216] Furthermore, in this embodiment, a configuration was used in which the rotation direction of the discharge reversal triple roller 55 is switched by the reversal unit 200C, but a configuration in which a reversal unit 200D is arranged as shown in Figures 31(a) and (b) may also be used. The reversal unit 200D differs from the reversal unit 200C in how it supports the unit. The internal holder unit 212 rotatably holds the reversal input gear 201 and has support shafts for the reversal switching gear 202, the internal idler gear 204, and the reversal output gear 203. The reversal unit 200C is supported by the discharge frame shaft 250 and the support shaft of the internal holder unit 212. On the other hand, the reversal unit 200D is provided with two shafts 212e and 212f extending from both ends of the internal holder unit 212, and the unit is supported by these two shafts 212e and 212f.

[0217] <Other embodiments> Although embodiments of the present invention have been described above, the present invention is not limited to the first to sixth embodiments described above. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferred effects arising from the present invention, and the effects of the present invention are not limited to those described in the embodiments.

[0218] Furthermore, although the electrophotographic image formation process has been used as an example of the image formation unit for forming an image on the sheet S in all of the above-described embodiments, the present invention is not limited thereto. For example, an inkjet image formation process that forms an image by ejecting ink liquid from a nozzle may be used as the image formation unit for forming an image on the sheet S.

[0219] Furthermore, in all of the embodiments described above, the printer's ejection reversal unit was used as an example of a sheet transport device that switches the transport direction of the sheet S, but the present invention is not limited to this. For example, the sheet transport device may be used in other switchback mechanisms of an image forming apparatus, or in switchback mechanisms such as an automatic document feeder (ADF) capable of automatically feeding originals or a post-processing device that performs post-processing on sheets.

[0220] Furthermore, although the above-described configurations have described a reversing unit that drives a guide member for guiding the sheet S and a discharge reversing unit for discharging and reversing the sheet S, the present invention is not limited thereto. For example, the present invention may be applied to configurations in which the reversing unit operates a feeding mechanism (such as raising and lowering a loading plate, raising and lowering a feeding roller, or rotating a feeding roller) or an image forming process mechanism (such as rotating a photosensitive drum and developing roller).

[0221] Furthermore, the configurations described in each of the embodiments described above may be combined as appropriate. [Explanation of Symbols]

[0222] 1,1B,1C,1D,1E: Image forming apparatus (printer) / 3: Image forming section / 51: Reversing roller pair / 51d, 55b, 57b: Roller (drive roller) / 52: Biasing section (return spring) / 53, 56, 58, 59, 71: Guide member / 55: Conveying section (discharge reversing triple roller 55) / 55c: First driven roller (discharge driven roller) / 55d: Second driven roller (reversing driven roller) / 57: Conveying section (discharge reversing roller pair) / 57c: Third driven roller (driven roller) / 200, 200A, 200B, 200C: Drive switching unit (reversing unit) / 201, 201A, 201B: Input section (reversing input gear) / 203, 203B: Output section (reversing output gear) / 209: Engaging member (locking lever) / 310, 340, 350, 360: Switching section / 510: Conveying section / 600, 600A, 600B, 700: Drive interruption unit (clutch unit, coupling release unit) / 702a: First ratchet section / 703a: Second ratchet section / 750: Contact / disconnection mechanism / 800: Regulating unit (solenoid unit) / 901: First rotating element (planetary input gear) / 902: Second rotating element (planetary sun gear) / 903: Third rotating element (planetary output gear lever) -) / 904: Planetary gear / 1000,2000,3000: Sheet conveying device / D1: First direction / D2: Second direction / M: Drive source, first drive source, motor (drive motor) / M2: Second drive source (drive switching motor) / N1: First nip (discharge nip) / N2: Second nip (reverse nip) / N3: Third nip (discharge reverse nip) / RR1: First rotation direction / RR2: Second rotation direction

Claims

1. a conveying unit that has a roller that can rotate in a first rotation direction and a second rotation direction opposite to the first rotation direction and conveys a sheet; a guide member that is movable between a first position and a second position different from the first position and that guides the sheet; A driving source; a drive switching unit including: an input section to which a driving force is input from the driving source; an output section to output the driving force to the roller; and a switching section that outputs the driving force transmitted from the input section to the output section in a first state so that the roller rotates in the second rotation direction, and that outputs the driving force transmitted from the input section to the output section in a second state different from the first state so that the roller rotates in the first rotation direction; a drive cutoff unit that can transition between a transmission state in which the drive force transmitted from the switching unit can be transmitted to the guide member and a non-transmission state in which the drive force is not transmitted to the guide member, The roller is configured to be rotatable by a driving force output from the output portion of the drive switching unit while the guide member is moving between the first position and the second position. A sheet conveying device characterized by:

2. When the drive-shutoff unit transitions from the non-transmission state to the transmission state, the guide member moves from the first position to the second position by the driving force transmitted from the switching portion via the drive-shutoff unit.

2. The sheet transport device according to claim 1.

3. the switching unit transitions from the first state to the second state based on the fact that the drive-shutoff unit is in the transmission state and the guide member, which moves from the first position to the second position, stops at the second position.

3. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

4. the switching unit is maintained in the first state while the drive-shutoff unit is in the transmission state and the guide member is moving from the first position to the second position; 4. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

5. the switching unit is in the second state when the drive / shutoff unit is in the transmission state and the guide member is stopped at the second position.

5. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

6. the switching unit transitions from the second state to the first state based on the transition of the drive-disconnecting unit from the transmitted state to the non-transmitted state and the movement of the guide member from the second position to the first position.

6. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

7. The drive-disconnecting unit further includes a biasing portion that biases the guide member to the first position when the drive-disconnecting unit is in the non-transmitting state.

7. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

8. The drive source is a motor that rotates in only one direction.

8. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

9. the input portion is rotated by the drive source, the switching unit rotates in the same direction and at the same rotation speed as the input unit in the first state; 9. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

10. The switching unit is stopped in the second state.

10. The sheet transport device according to claim 9.

11. the switching portion has an engaging member that can engage with the input portion, In the first state, the switching unit rotates integrally with the input unit as a result of the engagement member engaging with the input unit, and in the second state, the engagement member is separated from the input unit.

11. The sheet conveying device according to claim 9 or 10.

12. the drive source is a first drive source, a second drive source that drives the switching unit; In the first state, the switching unit rotates in the same direction and at the same rotation speed as the input unit by the driving force of the second driving source.

11. The sheet conveying device according to claim 9 or 10.

13. The drive cutoff unit is a clutch unit that is in the transmission state when energized and in the non-transmission state when not energized.

13. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

14. The drive-breaking unit has a first ratchet portion, a second ratchet portion engageable with the first ratchet portion, and a contact / disconnection mechanism that causes the first ratchet portion to engage with or separate from the second ratchet portion, and the first ratchet portion and the second ratchet portion are engaged with each other by the contact / disconnection mechanism to achieve the transmitted state, and the first ratchet portion and the second ratchet portion are separated from each other by the contact / disconnection mechanism to achieve the non-transmitted state.

13. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

15. the drive-shutoff unit includes a first rotating element that rotates in mesh with the switching portion and rotatably supports a planetary gear, a second rotating element that meshes with the planetary gear, a third rotating element that meshes with the planetary gear and is capable of transmitting a driving force to the guide member, and a restricting unit that restricts rotation of the second rotating element, When the rotation of the second rotating element is not restricted by the restricting unit, the rotation of the first rotating element is output to the second rotating element via the planetary gear, thereby achieving the non-transmitted state, When the rotation of the second rotating element is restricted by the restricting unit, the rotation of the first rotating element is transmitted to the third rotating element via the planetary gear, thereby achieving the transmitted state.

13. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

16. the conveying section includes a pair of discharge rollers and a pair of reversing rollers including the roller; When the rollers rotate in the second rotation direction, the pair of discharge rollers rotate in a direction to transport the sheet into the apparatus, and the pair of reversing rollers can transport the sheet in a first direction toward the apparatus, When the rollers rotate in the first rotation direction, the pair of discharge rollers rotate in a direction to discharge the sheet outside the apparatus, and the pair of reversing rollers can convey the sheet in a second direction opposite to the first direction.

16. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

17. the conveying section includes the roller, a first driven roller that forms a first nip together with the roller, and a second driven roller that forms a second nip together with the roller; When the roller rotates in the second rotation direction, the conveying unit can convey the sheet into the machine at the first nip and can convey the sheet in a first direction toward the outside of the machine at the second nip, When the roller rotates in the first rotation direction, the conveying unit can discharge the sheet at the first nip to the outside of the apparatus, and can convey the sheet at the second nip in a second direction opposite to the first direction.

16. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

18. the conveying section includes the roller and a third driven roller that forms a third nip together with the roller; the third nip is capable of conveying the sheet in a first direction toward the outside of the machine when the roller rotates in the second rotation direction, and is capable of conveying the sheet in a second direction opposite to the first direction when the roller rotates in the first rotation direction; 16. The sheet conveying device according to claim 1, wherein the sheet conveying device is a sheet conveying device.

19. an image forming unit that forms an image on a sheet; the sheet conveying device according to any one of claims 1 to 18, which conveys a sheet on which an image has been formed by the image forming unit. An image forming apparatus characterized by:

Images