Image forming apparatus

Abstract

The present invention provides an image forming apparatus that can suppress jamming when the sheet is re-transported toward the image forming section. [Solution] The image forming apparatus 1 is capable of forward and reverse rotation by the driving force from the motor 4, and has a discharge roller 291a that discharges the sheet S conveyed from the fuser 6 from the discharge port 22 when rotating forward and guides the sheet S to the re-conveying path P2 when rotating reverse, a fixing drive gear 85 connected to the fixing gear 63, and an input gear 92 that transmits the driving force from the motor 4 to the fixing drive gear 85, and includes a first gear train 8B that transmits the driving force from the motor 4 to the fixing gear 63, a second gear train 8C that branches off from the input gear 92 and transmits the driving force from the motor 4 to the discharge roller 291a, and an electromagnetic clutch 95 that includes a clutch gear 952 and can switch whether or not to transmit the driving force from the motor 4 to the second gear train 8C by controlling the rotation of the clutch gear 952, the clutch gear 952 is arranged coaxially with the input gear 92.

Description

Technical Field

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

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, as an image forming apparatus capable of duplex printing, there is known one that drives a discharge roller that discharges a sheet toward a discharge tray, a conveyance unit that conveys a sheet in a conveyance path from a sheet cassette to the discharge roller via an image forming unit, and a re-conveyance roller that conveys a sheet to the image forming unit during duplex printing, with a common motor.

[0003] The discharge roller rotates forward when the motor rotates forward to discharge the sheet toward the discharge tray, and rotates backward when the motor rotates backward to convey the sheet again toward the image forming unit.

[0004] In the technology described in Patent Document 1, the motor is switched from forward rotation to reverse rotation at the timing when a predetermined time has elapsed since the rear end of the sheet conveyed along the conveyance path reaches the post-registration sensor and the post-registration sensor stops detecting the sheet. Also, when the front end of the sheet conveyed along the re-conveyance path by the re-conveyance roller reaches the pre-registration sensor and the pre-registration sensor detects the sheet, the motor is switched from reverse rotation to forward rotation.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technology described in Patent Document 1 above, when switching the motor from reverse rotation to forward rotation, if the rear end of the sheet being transported along the re-transport path has not yet come out of the discharge roller and the discharge roller is nipping at the rear end of the sheet, the discharge roller, which has been switched to forward rotation, may pull the sheet in the discharge direction, potentially causing a jam.

[0007] Therefore, the present invention provides an image forming apparatus that can suppress jamming when the sheet is re-transported toward the image forming section. [Means for solving the problem]

[0008] The image forming apparatus that solves the above problems has the following features.

[0009] That is, the image forming apparatus is an image forming apparatus that forms a toner image on a sheet, comprising: a transfer unit that transfers the toner image to a conveyed sheet; a motor capable of forward and reverse rotation; a fuser driven by the driving force from the motor and fixing the toner image transferred to the sheet, comprising: a heating rotating body; a pressurizing rotating body that forms a fixing nip between itself and the heating rotating body; a fixing gear that transmits the driving force from the motor to the heating rotating body or the pressurizing rotating body; a main body housing that houses the fuser, having a discharge port from which the sheet conveyed from the fuser is discharged; a re-convection path that conveys the sheet conveyed from the fuser back toward the transfer unit; and a discharge roller driven by the driving force from the motor and capable of forward and reverse rotation. The apparatus comprises: a discharge roller that discharges the sheet being transported from the fuser when it rotates in the forward direction from the discharge port and guides the sheet to the re-transport path when it rotates in the reverse direction; a first gear train that transmits the driving force from the motor to the fuser gear, the first gear train having a fuser drive gear supported by the main housing and connected to the fuser gear, and a branch gear that transmits the driving force from the motor to the fuser drive gear; a second gear train that branches off from the branch gear and transmits the driving force from the motor to the discharge roller; and an electromagnetic clutch including a rotatable clutch gear, the electromagnetic clutch which can switch whether or not to transmit the driving force from the motor to the second gear train by controlling the rotation of the clutch gear, wherein the clutch gear is arranged coaxially with the branch gear.

[0010] This configuration allows the discharge roller to be stopped at any desired timing. Therefore, the discharge roller can be stopped at the same time that the motor, which was rotating in reverse to transport the sheet towards the re-transport path by the discharge roller, is switched to forward rotation. As a result, even if the trailing end of the sheet is nipped by the discharge roller, the sheet will not be transported in the discharge direction by the discharge roller, and jams can be prevented when the sheet is re-transported towards the image forming unit. In addition, since the electromagnetic clutch can be switched on or off to transmit driving force to the second gear train, rotation of the gear located downstream of the electromagnetic clutch can be prevented when driving force is not transmitted to the paper discharge roller.

[0011] Furthermore, the fixing drive gear and the branching gear rotate coaxially.

[0012] This reduces the space required in the direction perpendicular to the axial direction when positioning the fixed drive gear and branch gear.

[0013] Furthermore, it is equipped with a one-way clutch located coaxially with the branching gear, which is capable of transmitting the driving force from the motor to the fixing drive gear when the motor is rotating in the forward direction.

[0014] This makes it possible to reduce the space required in the direction perpendicular to the axial direction when arranging a one-way clutch in addition to the branching gear and fixing drive gear in the first gear train.

[0015] Furthermore, the one-way clutch includes an input gear that is rotatable by receiving a driving force from the motor, and a transmission gear that is movable in the axial direction between a first position in which it is engaged with the input gear and separated from the fixed drive gear, and a second position in which it is connected to the fixed drive gear. When the input gear rotates in the first direction by receiving a driving force from the motor which is rotating in the forward direction, the transmission gear moves from the first position to the second position. When the input gear rotates in the second direction opposite to the first direction by receiving a driving force from the motor which is rotating in the reverse direction, the transmission gear moves from the second position to the first position.

[0016] As a result, corresponding to the switching between the forward rotation and the reverse rotation of the motor, the transmission and disconnection of the driving force to the fixing drive gear can be switched.

[0017] Also, the input gear is the branch gear.

[0018] As a result, the number of gears constituting the first gear train can be reduced, and the first gear train can be configured compactly.

[0019] Also, when the electromagnetic clutch transmits the driving force from the motor to the second gear train, the clutch gear and the branch gear rotate integrally.

[0020] As a result, the driving force can be efficiently transmitted toward both the discharge roller and the fixing device.

[0021] Also, the driving force from the motor is input to the branch gear, and the driving force is output from the clutch gear to a gear located downstream of the clutch gear in the second gear train.

[0022] As a result, even when the electromagnetic clutch is turned off and the driving of the discharge roller is stopped while the motor is rotating forward, the fixing device can be driven.

[0023] Also, the driving force from the motor is input to the clutch gear, and the driving force is output from the branch gear to the second gear train.

[0024] As a result, when the driving of the discharge roller is stopped, the driving of the fixing device can be stopped together.

[0025] Also, a frame that holds the electromagnetic clutch and a control board that controls the operation of the electromagnetic clutch are provided, and the electromagnetic clutch and the control board are arranged at different positions when viewed in the axial direction.

[0026] Thus, when the electromagnetic clutch and the control board are arranged on the frame, the electromagnetic clutch and the control board do not interfere with each other, and the influence of the noise and heat generation of the electromagnetic clutch on the control board can be reduced.

[0027] Further, it includes a control unit that controls the operation of the electromagnetic clutch, and a re-feed roller provided on the re-feed path and driven by the driving force from the motor. The control unit controls the electromagnetic clutch to block the transmission of the driving force from the motor to the second gear train after the leading end of the sheet conveyed along the re-feed path by the discharge roller has passed through the re-feed roller.

[0028] With such control, the discharge roller can be stopped at the timing of switching the motor, which was rotated reversely to convey the sheet to the re-feed path by the discharge roller, to forward rotation. Thus, even when the trailing end of the sheet is nipped by the discharge roller, the sheet is not conveyed in the discharge direction by the discharge roller, and the occurrence of jams can be suppressed.

[0029] Further, the control unit controls the electromagnetic clutch to transmit the driving force from the motor to the second gear train before the leading end of the sheet conveyed along the re-feed path reaches the image forming unit, thereby driving the discharge roller.

[0030] With such control, when the transmission of the driving force to the discharge roller is started, the leading end of the sheet can be in a state where it has not yet reached the image forming unit. Thus, it is possible to suppress the occurrence of disturbance in the image formed on the sheet due to the vibration at the start of the transmission of the driving force to the discharge roller.

[0031] Further, the control unit controls the electromagnetic clutch to transmit the driving force from the motor to the second gear train after the leading end of the sheet conveyed along the re-feed path has reached the image forming unit and before it reaches the fixing unit, thereby driving the discharge roller.

[0032] This allows for a shorter driving time for the discharge roller compared to the case where the driving force from the motor is transmitted to the second gear train before the leading edge of the sheet reaches the image forming section. In addition, in most cases, after the leading edge of the sheet reaches the image forming section, the trailing edge of the sheet has already left the discharge roller, so even if the sheet's transport position varies, the likelihood of jamming is low even if the discharge roller is driven to rotate in the forward direction.

[0033] Furthermore, the control unit drives the discharge roller by controlling the electromagnetic clutch to transmit the driving force from the motor to the second gear train between the time the leading edge of the sheet being transported along the re-transport path reaches the fuser and before it reaches the discharge roller.

[0034] This control method allows for a shorter driving time for the discharge roller compared to the case where the driving force from the motor is transmitted to the second gear train before the leading edge of the sheet reaches the image forming section. This makes it possible to drastically reduce the time during which the electromagnetic clutch is engaged and the driving force is transmitted to the second gear train, thereby saving power. [Effects of the Invention]

[0035] According to the present invention, jamming can be suppressed when the sheet is re-transported toward the image forming section. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic central cross-sectional view showing an image forming apparatus. [Figure 2] This is a perspective view showing an image forming apparatus with its front cover in the open position. [Figure 3] This is a perspective view showing the first and second main frame inside the enclosure. [Figure 4] This is a side cross-sectional view showing the fuser. [Figure 5] This is a perspective view showing the heating unit and pressure roller of the fuser. [Figure 6]This is a left side view showing the common gear train and the second gear train of the drive force transmission train supported by the first main frame. [Figure 7] This is a right side view showing the first gear train of the drive force transmission train supported by the first main frame. [Figure 8] This is a rear cross-sectional view showing the fixing drive gear, a one-way clutch separated from the fixing drive gear, and an electromagnetic clutch. [Figure 9] This is a rear cross-sectional view showing the fixing drive gear, the one-way clutch connected to the fixing drive gear, and the electromagnetic clutch. [Figure 10] This is an exploded perspective view showing the fixed drive gear and the one-way clutch. [Figure 11] This is a perspective view showing the input gear of a one-way clutch. [Figure 12] This is a perspective view showing the inclined engagement surface of the input gear. [Figure 13] This is a perspective view showing the transmission gear of a one-way clutch. [Figure 14] This is a perspective view showing the fixing drive gear. [Figure 15] This is a block diagram showing the control unit to which various sensors, motors, and electromagnetic clutches are connected. [Figure 16] This is a side view showing the positional relationship between the control board and the electromagnetic clutch, which are supported by the first main frame. [Figure 17] This is a rear cross-sectional view showing a modified example of the input and output of driving force to the input gear and electromagnetic clutch. [Modes for carrying out the invention]

[0037] Next, embodiments for carrying out the present invention will be described with reference to the attached drawings.

[0038] [Image forming apparatus] The image forming apparatus 1 shown in Figure 1 is an embodiment of an image forming apparatus equipped with a sheet transport device according to the present invention, and is a laser printer that forms an image on a sheet S by an electrophotographic method.

[0039] In the following explanation, the right side of Figure 1 is defined as the front side of the image forming apparatus 1, the left side of Figure 1 is defined as the rear side of the image forming apparatus 1, the front of the page in Figure 1 is defined as the left side of the image forming apparatus 1, and the back of the page in Figure 1 is defined as the right side of the image forming apparatus 1. Furthermore, the top and bottom sides of Figure 1 are defined as the top and bottom sides of the image forming apparatus 1, respectively.

[0040] The image forming apparatus 1 comprises a main body housing 2, a paper feeding unit 3, an image forming unit 5, a fuser 6, and a paper discharge unit 29.

[0041] The main housing 2 houses the paper feed unit 3, the image forming unit 5, the fuser unit 6, and the paper discharge unit 29. An opening 2A is located on the front of the main housing 2, and the main housing 2 has a front cover 21 that can open and close the opening 2A. The front cover 21 is configured to rotate around a pivot axis 21a at its lower end, and by rotating around the pivot axis 21a, it can move between a closed position that closes the opening 2A and an open position that opens the opening 2A.

[0042] The paper feeding unit 3 comprises a paper feeding tray 10 that supports the sheet S, a sheet transport unit 30, a transport roller pair 34, and a registration roller 35a. The paper feeding unit 3 is located at the bottom of the main body housing 2 and transports the sheet S supported by the paper feeding tray 10 to the image forming unit 5. The image forming apparatus 1 has a transport path P1 for the sheet S from the paper feeding unit 3 through the image forming unit 5 to the paper discharge unit 29.

[0043] The paper feed tray 10 has a pressure plate 12 and a pressing plate 13. The pressure plate 12 is a plate-shaped member that supports the sheet S from below. The pressure plate 12 is rotatable about a pivot point 12a at its rear end, and by rotating about the pivot point 12a, it can move up and down between a lowered position and an elevated position. The pressing plate 13 is located below the pressure plate 12 and can move the pressure plate 12 up and down between a lowered position and an elevated position.

[0044] The sheet transport unit 30 is a transport mechanism that separates and removes sheets S supported by the paper feed tray 10 one by one and transports them toward the image forming unit 5, and is equipped with a paper feed roller 31, a separation roller 32, and a separation pad 33.

[0045] The paper feed roller 31 is a roller for feeding the sheet S, supported by the paper feed tray 10, toward the separation roller 32. The separation roller 32 is located downstream of the paper feed roller 31 in the sheet transport direction, and the separation pad 33 is positioned opposite the separation roller 32 and is biased toward the separation roller 32.

[0046] The sheets S, fed towards the separation roller 32 by the paper feed roller 31, are separated one by one between the separation roller 32 and the separation pad 33. The separated sheets S are then fed into the transport path P1.

[0047] The sheet S, which has been sent onto the transport path P1, is transported toward the image forming unit 5 by the transport roller pair 34, the register roller 35a, and the pinch roller 35b positioned opposite the register roller 35a. The register roller 35a restricts the movement of the leading edge of the sheet S being transported from the paper feed tray 10 toward the image forming unit 5, stopping it temporarily, correcting the tilt of the sheet S, and then transporting the sheet S toward the image forming unit 5 at a predetermined timing. The register roller 35a is a roller for correcting the tilt of the sheet S being transported toward the transfer unit 5A of the image forming unit 5.

[0048] The image forming apparatus 1 has a pre-resist sensor 77 located upstream of the resist roller 35a in the sheet transport direction, and a post-resist sensor 78 located downstream of the resist roller 35a in the sheet transport direction.

[0049] The front register sensor 77 is a sensor for detecting the sheet S being transported along the transport path P1. For example, it is configured to turn on when the leading edge of the sheet S passes the front register sensor 77, and to turn off when the trailing edge of the sheet S passes the front register sensor 77, by detecting the trailing edge of the sheet S.

[0050] The post-checkout sensor 78 is a sensor for detecting the sheet S being transported along the transport path P1. For example, it is configured to turn on when the leading edge of the sheet S passes the post-checkout sensor 78, and to turn off when the trailing edge of the sheet S passes the post-checkout sensor 78, by detecting the trailing edge of the sheet S.

[0051] The image forming unit 5 is located downstream of the paper feeding unit 3 in the sheet transport direction and forms a toner image on the sheet S transported from the paper feeding unit 3. The image forming unit 5 includes a process cartridge 50 that transfers a toner image to the surface of the sheet S transported from the paper feeding unit 3, a transfer roller 55 positioned opposite the photosensitive drum 54 of the process cartridge 50, and an exposure unit 56 that exposes the surface of the photosensitive drum 54.

[0052] The process cartridge 50 is located above the paper feed section 3 in the main body housing 2 and includes a developer storage chamber 51, a supply roller 52, a developing roller 53, a photosensitive drum 54, and the like. The process cartridge 50 supports the pinch roller 35b.

[0053] The process cartridge 50 comprises a drum cartridge having a photosensitive drum 54 and a developing cartridge mounted on the drum cartridge and having a developing roller 53, and is detachably mounted on the main body housing 2. In this case, the process cartridge 50 is mounted on the main body housing 2 by inserting the drum cartridge and the developing cartridge mounted on the drum cartridge into the main body housing 2 as a single unit, and is detached from the main body housing 2 by removing the drum cartridge and the developing cartridge mounted on the drum cartridge from the main body housing 2 as a single unit.

[0054] The process cartridge 50 may consist of at least one of a photosensitive drum, a developing roller, and a toner container. The process cartridge 50 can be attached to and detached from the main body housing 2 when the front cover 21 is in the open position.

[0055] The photosensitive drum 54 is positioned with its axis aligned in the left-right direction when the process cartridge 50 is mounted in the main body housing 2. The photosensitive drum 54 has a metal drum shaft 54a that extends along the axial direction. The photosensitive drum 54 rotates about the drum shaft 54a.

[0056] In this embodiment, the process cartridge 50 comprises a drum cartridge having a photosensitive drum 54 and a developing cartridge mounted on the drum cartridge and having a developing roller 53. However, it can also be configured to include a cartridge having the photosensitive drum 54 and the developing roller 53, and a toner box mounted on the cartridge for containing toner.

[0057] Furthermore, in the image forming apparatus 1, a drum cartridge having a photosensitive drum 54 and a developing cartridge having a developing roller 53 can be configured to be mounted separately in the main body housing 2. That is, the process cartridge 50 can include at least one of a photosensitive drum, a developing roller, and a toner container, and can be configured to be detachably mounted in the main body of the apparatus.

[0058] The exposure unit 56 is equipped with a laser diode, a polygon mirror, a lens, and a reflector, and exposes the surface of the photosensitive drum 54 by irradiating the photosensitive drum 54 with laser light based on image data input to the image forming apparatus 1.

[0059] The developer chamber 51 contains toner, which is the developer. The toner contained in the developer chamber 51 is agitated by an agitator (not shown) and sent to the supply roller 52. The supply roller 52 then supplies the toner sent from the developer chamber 51 to the developing roller 53.

[0060] The developing roller 53 is positioned in close contact with the supply roller 52 and carries positively charged toner supplied from the supply roller 52 by a sliding contact member (not shown). A developing bias is also applied to the developing roller 53 by a bias application means (not shown).

[0061] The photosensitive drum 54 is positioned adjacent to the developing roller 53. The surface of the photosensitive drum 54 is uniformly charged by a charger (not shown) and then exposed by the exposure unit 56. The exposed portion of the photosensitive drum 54 has a lower potential than other portions, and an electrostatic latent image based on the image data is formed on the photosensitive drum 54. Then, positively charged toner is supplied from the developing roller 53 to the surface of the photosensitive drum 54 where the electrostatic latent image has been formed, causing the electrostatic latent image to become visible as a toner image.

[0062] The transfer roller 55 is positioned opposite the photosensitive drum 54, and a transfer bias is applied by a bias application means (not shown). With the transfer bias applied to the surface of the transfer roller 55, the sheet S is transported while being sandwiched between the photosensitive drum 54 on which the toner image has been formed and the transfer roller 55, thereby transferring the toner image formed on the surface of the photosensitive drum 54 to the surface of the sheet S.

[0063] The process cartridge 50, photosensitive drum 54, and transfer roller 55 constitute a transfer unit 5A that transfers a toner image onto a conveyed sheet S. The sheet S onto which the toner image has been transferred is conveyed from the transfer unit 5A to the fuser unit 6.

[0064] The fuser unit 6 comprises a heating unit 61 and a pressure roller 62, and fixes the toner image transferred to the sheet S by the transfer unit 5A. The heating unit 61 is heated by power supplied from a power source (not shown). The pressure roller 62 is positioned opposite the heating unit 61. One of the heating unit 61 and the pressure roller 62 is biased toward the other by a biasing mechanism (not shown), and the heating unit 61 and the pressure roller 62 are in close contact. The image forming apparatus 1 is equipped with a motor 4, and the pressure roller 62 of the fuser unit 6 is driven and rotated by the driving force from the motor 4. The motor 4 is configured to rotate in both forward and reverse directions.

[0065] When the sheet S on which the toner image has been transferred is transported to the fuser 6, the sheet S is heated while being held between the heating unit 61 and the pressure roller 62, thereby fixing the toner image to the sheet S. In this way, the fuser 6 fixes the toner image to the sheet S transported from the transfer unit 5A. The sheet S on which the toner image has been fixed by the fuser 6 is transported to the paper discharge unit 29 by a pair of post-fixing transport rollers 68 located downstream in the sheet transport direction of the fuser 6.

[0066] The image forming apparatus 1 has a sheet sensor 79 located between the fuser 6 and the post-fixing transport roller pair 68. The sheet sensor 79 is a sensor for detecting a sheet S being transported along the transport path P1. The sheet sensor 79 is configured to turn on when the leading edge of the sheet S passes the sheet sensor 79, for example, and to turn off when the trailing edge of the sheet S passes the sheet sensor 79, by detecting the trailing edge of the sheet S.

[0067] The paper discharge unit 29 is located downstream of the fixed-post transport roller pair 68 in the sheet transport direction, and discharges the sheet S, on which an image has been formed in the image forming unit 5, to the outside of the image forming apparatus 1, or transports the sheet S back towards the image forming unit 5.

[0068] The paper discharge unit 29 includes an discharge roller 291a, a driven roller 291b positioned opposite the discharge roller 291a, and a discharge tray 292. The discharge tray 292 is provided in the main body housing 2. Printed sheets S, on which toner images have been formed in the image forming unit 5, are discharged into the discharge tray 292. The main body housing 2 has an outlet 22 through which sheets S transported from the fuser unit 6 are discharged. The sheets S are discharged into the discharge tray 292 through the outlet 22.

[0069] Of the transport path P1, the transport path P1 downstream of the fuser 6 is formed as the discharge path P1a. The discharge roller 291a is configured to discharge the sheet S that has been transported from the fuser 6 along the discharge path P1a toward the outside of the main housing 2. The discharge path P1a is a path that guides the printed sheet S to the discharge tray 292. The discharge tray 292 is formed on the upper surface of the main housing 2 and supports the sheet S that has been discharged to the outside of the main housing 2 by the discharge roller 291a.

[0070] The discharge roller 291a is driven by the driving force from the motor 4 and is configured to rotate in both forward and reverse directions. The discharge roller 291a rotates in the forward direction when driven by the driving force from the forward-rotating motor 4, and rotates in the reverse direction when driven by the reverse-rotating motor 4.

[0071] The discharge roller 291a rotates in the forward direction when transporting the sheet S toward the discharge tray 292. In other words, when the discharge roller 291a rotates in the forward direction, it discharges the sheet S transported from the fuser 6 through the discharge port 22.

[0072] The image forming apparatus 1 has a re-transport path P2 that guides the single-sided printed sheet S, which has been transported along the transport path P1 and passed through the fuser 6, to the transport path P1 upstream of the register roller 33a in the sheet transport direction.

[0073] The re-transport path P2 branches off from the discharge path P1a at branching point Pb, which is located between the fixed transport roller pair 68 and the discharge roller 291a. It then extends forward between the image forming unit 5 and the paper feed tray 10, and merges with the transport path P1 at merging point Pa, which is located between the transport roller pair 34 and the registration roller 35a.

[0074] The sheet S, which has been transported from the fuser 6 to the paper discharge section 29, can be transported again to the image forming section 5 via the re-transport path P2 by reversing the rotation of the discharge roller 291a. In other words, when the discharge roller 291a rotates in reverse, it guides the sheet S to the re-transport path P2.

[0075] The sheet S, which has been transported to the re-transport path P2 by the discharge roller 291a, is transported toward the image forming unit 5 by a first re-transport roller pair 36 and a second re-transport roller pair 37 provided on the re-transport path P2. The first re-transport roller pair 36 and the second re-transport roller pair 37 are examples of re-transport rollers.

[0076] The sheet S, transported along the re-transport path P2, is transported to the transfer section 5A of the image forming section 5 after passing the confluence point Pa. In this case, after the leading edge of the sheet S transported along the re-transport path P2 enters the transport path P1 from the confluence point Pa, the motor 4, which is rotating in the reverse direction, is switched to forward rotation to drive the register roller 35a, and the register roller 35a transports the sheet S to the transfer section 5A.

[0077] Thus, the re-transport path P2 is a transport path that transports the sheet S transported from the fuser 6 back towards the transfer section 5A. The first re-transport roller pair 36 and the second re-transport roller pair 37 transport the sheet S back towards the transfer section 5A along the re-transport path P2 when the motor 4 is rotating in the forward direction. Also, the first re-transport roller pair 36 and the second re-transport roller pair 37 transport the sheet S back towards the transfer section 5A along the re-transport path P2 when the motor 4 is rotating in the reverse direction.

[0078] The image forming apparatus 1 is capable of double-sided printing by transporting a sheet S, on which a toner image has been formed on one side in the image forming unit 5, back to the image forming unit 5 via the re-transport path P2 to form a toner image on the other side of the sheet S.

[0079] As shown in Figures 2 and 3, the main body housing 2 comprises a first main body frame 26 and a second main body frame 27, which are spaced apart in the left-right direction. The first main body frame 26 is located at the left end of the main body housing 2, and the second main body frame 27 is located at the right end of the main body housing 2. The first main body frame 26 extends in the front-rear and up-down directions and is positioned so that its plate surface faces the left-right direction. The second main body frame 27 extends in the front-rear and up-down directions and is positioned so that its plate surface faces the left-right direction.

[0080] The transfer unit 5A, which includes the process cartridge 50, and the fuser 6 are positioned between the first main frame 26 and the second main frame 27. The first main frame 26 is positioned to the left of the transfer unit 5A and the fuser 6, and the second main frame 27 is positioned to the right of the transfer unit 5A and the fuser 6. The process cartridge 50, which constitutes the transfer unit 5A, is detachably supported by the first main frame 26 and the second main frame 27.

[0081] The first main frame 26 supports the motor 4. The first main frame 26 also supports the control board 751 on which electronic components such as the CPU 751a are mounted. The first main frame 26 is an example of a frame that holds the control board. The control board 751 constitutes a control unit 75 (see Figure 15) for controlling the operation of the motor 4 and other components in the image forming apparatus 1.

[0082] [Fuser] As shown in Figures 4 and 5, the heating unit 61 of the fuser 6 comprises a heater 611, a holder 612, a stay 613, and a belt 614. The heater 611 is a flat plate-shaped heater extending in the left-right direction. The heater 611 has a first surface 611A and a second surface 611B opposite to the first surface 611A, with the first surface 611A being supported by the holder 612.

[0083] The holder 612 is made of, for example, a resin material and has a guide surface 612a and a support wall 612b. The guide surface 612a contacts the inner circumferential surface 614a of the belt 614 and guides the belt 614. The support wall 612b has a support surface 612A that supports the heater 611. The support surface 612A of the support wall 612b is in contact with the first surface 611A of the heater 611. The stay 613 is a member that supports the holder 612 and is formed by bending a plate material with greater rigidity than the holder 612, such as a steel plate, into a roughly U-shape in cross-section.

[0084] The belt 614 is an endless belt having heat resistance and flexibility, and comprises a metal tube made of a metal such as stainless steel, and a fluororesin layer covering the metal tube. The heater 611, holder 612, and stay 613 are arranged inside the belt 614. The belt 614 is configured to rotate around the heater 611, holder 612, and stay 613. The inner circumferential surface 614a of the belt 614 is in contact with the heater 611. The belt 614 of the heating unit 61 is an example of a heating rotating body.

[0085] The pressure roller 62 is an example of a pressurizing rotating body and has a metal shaft 62A and an elastic layer 62B covering the shaft 62A. The pressure roller 62 is pressed against the heater 611 via a belt 614. The pressure roller 62 forms a fixing nip NP for heating and pressurizing the sheet S by sandwiching the belt 614 between itself and the heater 611. In other words, the pressure roller 62 forms a fixing nip NP between itself and the heater 611, and the sheet S is heated and pressurized together with the heater 611 at the fixing nip NP.

[0086] The pressure roller 62 is configured to rotate when a driving force is transmitted from the motor 4 of the image forming apparatus 1. The motor 4 drives all the rollers of the image forming apparatus 1. For example, the motor 4 drives the rollers of the paper feeding unit 3, the image forming unit 5, the fuser 6, and the paper discharge unit 29. The motor 4 also drives each drive unit related to image forming in the image forming apparatus 1. The fuser 6 has a fuser gear 63 for transmitting the driving force from the motor 4 to the pressure roller 62. The fuser gear 63 is fixed to the left end of the shaft 62A of the pressure roller 62 and can rotate integrally with the shaft 62A.

[0087] As the pressure roller 62 rotates, the frictional force between it and the belt 614 or the sheet S held between the fixing nip NP causes the belt 614 to rotate in a driven manner. As a result, the sheet S on which the toner image has been transferred is transported between the pressure roller 62 and the heated belt 614, and the toner image is heat-fixed.

[0088] In this embodiment, the fuser 6 comprises a heating unit 61 having a heater 611 and a belt 614, and a pressure roller 62. However, the fuser 6 can also be configured to include a heating roller with a built-in heater and a pressure roller pressed against the heating roller. Alternatively, the fuser 6 can be configured to include a heating roller with a built-in heater and a pressure belt pressed against the heating roller by an elastic member. In this case, the fuser 6 can be configured to include a fuser gear for transmitting the driving force from the motor 4 to the heating roller, thereby rotating the heating roller using the driving force from the motor 4.

[0089] [Drive force transmission train] As shown in Figures 6 to 9, the image forming apparatus 1 is equipped with a drive force transmission train 8. The drive force transmission train 8 is a drive force transmission train for transmitting the drive force from the motor 4 to the pressure roller 62 and discharge roller 291a of the fuser 6. The drive force transmission train 8 is supported by the first main frame 26 and has a common gear train 8A, a first gear train 8B, a second gear train 8C, and an electromagnetic clutch 95.

[0090] The common gear train 8A includes a motor gear 81, a first idler gear 82, a second idler gear 83, and a third idler gear 84. The first gear train 8B includes a one-way clutch 90, a fixed drive gear 85, and a fourth idler gear 86. The second gear train 8C includes a fifth idler gear 87, a sixth idler gear 88, and a discharge roller gear 89.

[0091] In the common gear train 8A, the motor gear 81 is fixed to the output shaft 4a of the motor 4, and the first idler gear 82 meshes with the motor gear 81. The second idler gear 83 meshes with the first idler gear 82, and the third idler gear 84 meshes with the second idler gear 83.

[0092] In the first gear train 8B, the input side of the one-way clutch 90 is connected to the third idler gear 84. The fixing drive gear 85 can be connected to the output side of the one-way clutch 90. The fourth idler gear 86 meshes with the fixing drive gear 85. The fourth idler gear 86 also meshes with the fixing gear 63 of the fixing unit 6. The fixing drive gear 85 is connected to the fixing gear 63 via the fourth idler gear 86. The fixing drive gear 85 is supported by the first main frame 26 of the main housing 2.

[0093] In the second gear train 8C, the fifth idler gear 87 can be connected to the input side of the one-way clutch 90 via the electromagnetic clutch 95. The sixth idler gear 88 meshes with the fifth idler gear 87, and the discharge roller gear 89 meshes with the sixth idler gear 88. The discharge roller gear 89 is fixed to the roller shaft of the discharge roller 291a and can rotate integrally with the discharge roller 291a. The second gear train 8C branches off from the one-way clutch 90 of the first gear train 8B.

[0094] The driving force from motor 4 is transmitted to the input side of the one-way clutch 90 by a common gear train 8A. Furthermore, the driving force from motor 4 can be transmitted to the fixing gear 63 by a first gear train 8B, which includes the one-way clutch 90. Additionally, the driving force from motor 4 can be transmitted to the discharge roller 291a by a second gear train 8C.

[0095] In this embodiment, the fixing gear 63 is configured to rotate integrally with the pressure roller 62 of the fuser 6, and the driving force from the motor 4 is transmitted to the pressure roller 62 of the fuser 6. However, the fixing gear 63 can also be configured to rotate integrally with the heating rotating body of the fuser 6, so that the driving force from the motor 4 is transmitted to the heating rotating body of the fuser 6.

[0096] [One-way clutch and fixed drive gear] The one-way clutch 90 is a clutch component that can transmit the driving force from the motor 4 to the fixed drive gear 85 when the motor 4 is rotating in the forward direction, but does not transmit the driving force from the motor 4 to the fixed drive gear 85 when the motor 4 is rotating in the reverse direction. As shown in Figures 8 to 10, the one-way clutch 90 comprises a fixed shaft 91, an input gear 92, and a transmission gear 93. The input gear 92 is the input-side gear in the one-way clutch 90. The transmission gear 93 is the output-side gear in the one-way clutch 90 and can be connected to the fixed drive gear 85.

[0097] In the one-way clutch 90, the input gear 92 and the transmission gear 93 are arranged in that order from left to right. The anchor drive gear 85 is located to the right of the transmission gear 93. In other words, in the left-right direction, the transmission gear 93 is located between the input gear 92 and the anchor drive gear 85.

[0098] The fixed shaft 91 is a long shaft member that extends in the left-right direction. The direction along which the fixed shaft 91 extends in the left-right direction is the axial direction X of the fixed shaft 91.

[0099] As shown in Figures 8 to 11, the input gear 92 is rotatably supported on a fixed shaft 91 and is rotatable by receiving a driving force from the motor 4. The input gear 92 is rotatable in a first direction W1 and a second direction W2 opposite to the first direction W1. The input gear 92 has a fitting portion 920, an input tooth portion 921, a transmission portion 922, an inclined cam surface 923, and an inclined engagement surface 924.

[0100] The mating portion 920 is formed from a cylindrical member and is rotatably fitted onto the fixed shaft 91. The input tooth portion 921 is formed from a cylindrical member with a larger diameter than the mating portion 920 and has a bottom wall 921a connecting the input tooth portion 921 and the mating portion 920. The bottom wall 921a is located at the left end of the input tooth portion 921 and faces in the left-right direction. Input teeth 921b are formed on the outer circumferential surface of the input tooth portion 921. The input teeth 921b mesh with the third idler gear 84. Driving force from the motor 4 is input to the input teeth 921b via the common gear train 8A.

[0101] The transmission portion 922 is a protruding piece that projects radially inward from the inner circumferential surface of the input tooth portion 921 and is configured to be engageable with the transmission gear 93. In this embodiment, two transmission portions 922 are formed, and the two transmission portions 922 are positioned such that the distance from one transmission portion 922 to the other transmission portion 922 in the circumferential direction is equal to the distance from the other transmission portion 922 to the first transmission portion 922.

[0102] The inclined cam surface 923 is formed on the bottom wall 921a of the input tooth portion 921 and is an inclined surface facing the anchoring drive gear 85 side in the axial direction X. Here, "the inclined cam surface 923 is an inclined surface facing the anchoring drive gear 85 side" means that the inclined cam surface 923 is an inclined surface that is visible when viewed from the anchoring drive gear 85 side, i.e., the right side, in the axial direction X.

[0103] The inclined cam surface 923 extends along the circumferential direction. The inclined cam surface 923 is inclined such that, with respect to the direction perpendicular to the axial direction X, the upstream side in the first direction W1 is closer to the anchor drive gear 85 in the axial direction X than the downstream side. The inclined cam surface 923 has a downstream end 923a in the first direction W1 and an upstream end 923b in the first direction W1. In the axial direction X, the upstream end 923b is located closer to the anchor drive gear 85 than the downstream end 923a.

[0104] The inclined engagement surface 924 is formed inside the input tooth portion 921 and is located upstream of the transmission portion 922 in the first direction W1. The inclined engagement surface 924 is an inclined surface that faces the side opposite to the anchoring drive gear 85 in the axial direction X. Here, as shown in Figure 12, "the inclined engagement surface 924 is an inclined surface that faces the side opposite to the anchoring drive gear 85" means that the inclined engagement surface 924 is an inclined surface that is visible when viewed from the side opposite to the anchoring drive gear 85 in the axial direction X, that is, from the left side.

[0105] The inclined engagement surface 924 extends along the circumferential direction. The inclined engagement surface 924 is inclined such that, with respect to the direction perpendicular to the axial direction X, the downstream side in the second direction W2 is closer to the fixed drive gear 85 in the axial direction X than the upstream side. In this embodiment, two inclined engagement surfaces 924 are formed, and the two inclined engagement surfaces 924 are positioned such that the distance from one inclined engagement surface 924 to the other inclined engagement surface 924 in the circumferential direction is equal to the distance from the other inclined engagement surface 924 to the first inclined engagement surface 924.

[0106] As shown in Figures 8 to 10 and Figure 13, the transmission gear 93 is supported on the input gear 92 so as to be movable in the axial direction X. The transmission gear 93 is fitted between the mating portion 920 and the input teeth portion 921 of the input gear 92. The transmission gear 93 is rotatable in a first direction W1 and a second direction W2. The transmission gear 93 has a cylindrical portion 930, a transmitted portion 931, a contact surface 932, a ratchet pawl 933, and an engaging pawl 934.

[0107] The cylindrical portion 930 is formed in a cylindrical shape and is fitted onto the outer circumference of the fitting portion 920 of the input gear 92. The cylindrical portion 930 is rotatable relative to the fitting portion 920 of the input gear 92. The transmitted portion 931 is a protruding piece that projects radially outward from the outer circumferential surface of the cylindrical portion 930.

[0108] In this embodiment, the transmitted portion 931 is formed in two locations, and the two transmitted portions 931 are positioned such that the distance from one transmitted portion 931 to the other transmitted portion 931 in the circumferential direction is equal to the distance from the other transmitted portion 931 to the first transmitted portion 931. The transmitted portion 931 is configured to engage with the transmission portion 922 of the input gear 92 when the input gear 92 rotates in the first direction W1.

[0109] The contact surface 932 is located at the input gear 92 side end of the transmitted portion 931 in the axial direction X, and is configured to contact the inclined cam surface 923 of the input gear 92 when the input gear 92 rotates in the first direction W1.

[0110] The ratchet pawl 933 protrudes toward the fixing drive gear 85 from the end of the cylindrical portion 930 on the fixing drive gear 85 side in the axial direction X. The ratchet pawl 933 has an engaging surface 933a and a sliding surface 933b that is formed continuously with the engaging surface 933a in the circumferential direction. Multiple ratchet pawls 933 are formed along the circumferential direction, and the engaging surface 933a and the sliding surface 933b are arranged alternately in the circumferential direction.

[0111] The engaging claws 934 protrude circumferentially from the transmitted portion 931 downstream in the first direction W1. In this embodiment, two engaging claws 934 are formed, and the two engaging claws 934 are positioned such that the distance from one engaging claw 934 to the other engaging claw 934 in the circumferential direction is equal to the distance from the other engaging claw 934 to the first engaging claw 934. The engaging claws 934 are configured to engage with the inclined engaging surface 924 of the input gear 92 when the input gear 92 rotates in the second direction.

[0112] The transmission gear 93, while engaged with the input gear 92, is movable in the axial direction X between a first position (shown in Figure 8) where the contact surface 932 is close to the bottom wall 921a of the input gear 92, and a second position (shown in Figure 9) where the contact surface 932 is further away from the bottom wall 921a of the input gear 92 compared to the first position.

[0113] As shown in Figures 8 to 10 and Figure 14, the fixing drive gear 85 is rotatably supported on the fixed shaft 91 to the right of the transmission gear 93. The fixing drive gear 85 and the input gear 92 are both supported on the fixed shaft 91 and rotate coaxially. The fixing drive gear 85 is connected to the fixing gear 63 of the fixing unit 6 and can transmit the driving force from the motor 4 to the fixing gear 63. The fixing drive gear 85 is rotatable in a first direction W1 and a second direction W2. The fixing drive gear 85 has a fitting portion 850, a ratchet recess 851, an output tooth portion 852, and a spacer 853.

[0114] The mating portion 850 is formed in a cylindrical shape and is rotatably fitted onto the fixed shaft 91. The cylindrical portion 930 of the transmission gear 93 is rotatably fitted onto the outer circumference of the input gear 92 side end of the mating portion 850. The transmission gear 93 is movable axially in the X direction relative to the mating portion 850.

[0115] The output tooth section 852 is formed from a cylindrical member with a larger diameter than the mating section 850, and gear teeth are formed on its outer circumferential surface. The output tooth section 852 meshes with the fourth idler gear 86. The output tooth section 852 is connected to the pressure roller 62 of the fuser 6 via the fourth idler gear 86 and the fuser gear 63. The output tooth section 852 is capable of transmitting the driving force from the motor 4 to the pressure roller 62 via the fourth idler gear 86 and the fuser gear 63.

[0116] The ratchet recess 851 is located at the input gear 92 side end of the output teeth 852 in the axial direction X. The ratchet recess 851 can engage with the ratchet pawl 933 of the transmission gear 93. Specifically, the ratchet recess 851 engages with the ratchet pawl 933 when the transmission gear 93 rotates in a first direction W1 relative to the anchor drive gear 85, and does not engage with the ratchet pawl 933 when the transmission gear 93 rotates in a second direction W2 relative to the anchor drive gear 85.

[0117] Each ratchet recess 851 has an engaging surface 851a and a sliding surface 851b that is formed continuously with the engaging surface 851a in the circumferential direction. Multiple ratchet recesses 851 are formed along the circumferential direction, and the engaging surface 851a and the sliding surface 851b are arranged alternately in the circumferential direction.

[0118] The ratchet recess 851 is separated from the ratchet pawl 933 of the transmission gear 93 in the axial direction X when the transmission gear 93 is in the first position, and can be connected to the ratchet pawl 933 of the transmission gear 93 in the axial direction X when the transmission gear 93 is in the second position. In other words, when the transmission gear 93 is in the first position, it is engaged with the input gear 92 and separated from the anchor drive gear 85, and when it is in the second position, it is engaged with the input gear 92 and connected to the anchor drive gear 85.

[0119] When the transmission gear 93 is in the second position, if the transmission gear 93 rotates in the first direction W1 relative to the anchor drive gear 85, the engaging surface 933a of the ratchet pawl 933 and the engaging surface 851a of the ratchet recess 851 engage, causing the transmission gear 93 and the anchor drive gear 85 to rotate together.

[0120] On the other hand, when the transmission gear 93 is in the second position, if the transmission gear 93 rotates in the second direction W2 relative to the anchor drive gear 85, the sliding surface 933b of the ratchet pawl 933 slides circumferentially against the sliding surface 851b of the ratchet recess 851, and the engagement between the engaging surface 933a and the engaging surface 851a is released. In this case, even if the transmission gear 93 rotates in the second direction W2, the anchor drive gear 85 does not rotate.

[0121] Furthermore, when the transmission gear 93 is in the first position, the ratchet recess 851 and the ratchet pawl 933 are separated, so the anchoring drive gear 85 does not rotate when the transmission gear 93 rotates in the first direction W1 and when it rotates in the second direction W2. Also, when the anchoring drive gear 85 rotates while the transmission gear 93 is in the first position, it does not connect with the anchoring drive gear 85.

[0122] The spacer 853 protrudes toward the input gear 92 from the input gear 92 side end of the fitting portion 850 in the axial direction X, and is configured to be able to contact the input gear 92. Multiple spacers 853 are formed intermittently along the circumferential direction on the outer peripheral edge of the fitting portion 850.

[0123] The spacer 853 contacts the input gear 92, thereby restricting the axial position X of the anchor drive gear 85 relative to the input gear 92. By restricting the position of the anchor drive gear 85 relative to the input gear 92 with the spacer 853, the transmission gear 93 is able to move in the axial direction X between the input gear 92 and the anchor drive gear 85.

[0124] [Operation of a one-way clutch] Next, we will explain the operation of the one-way clutch 90.

[0125] In the one-way clutch 90 shown in Figure 8, the transmission gear 93 is in a first position, and the contact surface 932 of the transmission gear 93 is in contact with the downstream end 923a of the inclined cam surface 923 of the input gear 92. The transmission gear 93, in the first position, is spaced apart from the fixed drive gear 85 in the axial direction X.

[0126] In this state, with the transmission gear 93 in the first position, even if the fixing drive gear 85 rotates in the first direction W1 and the second direction W2, the fixing drive gear 85 and the transmission gear 93 will not be connected. Therefore, with the transmission gear 93 in the first position, even if the pressure roller 62 connected to the fixing drive gear 85 rotates, the pressure roller 62 will not be connected to the motor 4 connected to the input gear 92.

[0127] As shown in Figure 8, when the input gear 92 rotates in the first direction W1 by receiving driving force from the motor 4 which is rotating in the forward direction, the inclined cam surface 923 that contacts the contact surface 932 of the transmission gear 93 moves in the circumferential direction, and a circumferential sliding resistance is acted on the transmission gear 93 between it and the inclined cam surface 923.

[0128] On the other hand, the transmission gear 93 has sliding resistance between its cylindrical portion 930, which fits into the fitting portion 850 of the anchoring drive gear 85, and the fitting portion 850 of the anchoring drive gear 85. The sliding resistance between the cylindrical portion 930 of the transmission gear 93 and the fitting portion 850 of the anchoring drive gear 85 is set to be greater than the circumferential sliding resistance generated between the transmission gear 93 and the inclined cam surface 923. Therefore, when the input gear 92 rotates in the first direction W1 while the contact surface 932 of the transmission gear 93 and the inclined cam surface 923 are in contact, the transmission gear 93 maintains a state in which its rotation relative to the anchoring drive gear 85 is suppressed and does not rotate together with the input gear 92 at the same speed.

[0129] As a result, the phase of the transmission gear 93 with respect to the inclined cam surface 923 in the first direction W1 is shifted, and the position of the inclined cam surface 923 that contacts the contact surface 932 of the transmission gear 93 moves from the downstream end 923a to the upstream side in the first direction W1. Since the inclined cam surface 923 is located closer to the anchor drive gear 85 on the upstream side of the first direction W1 than on the downstream side, when the position of the inclined cam surface 923 that contacts the contact surface 932 of the transmission gear 93 moves to the upstream side in the first direction W1, the transmission gear 93 is pressed and moved toward the anchor drive gear 85 in the axial direction X by the inclined cam surface 923.

[0130] As shown in Figure 9, when the inclined cam surface 923 that contacts the contact surface 932 of the transmission gear 93 reaches the upstream end 923b, the transmission gear 93 moves to the second position.

[0131] In this way, the transmission gear 93, located in the first position, prevents the input gear 92 from rotating at the same speed as the input gear 92 when the input gear 92 rotates in the first direction W1, thereby enabling movement from the first position to the second position.

[0132] After the transmission gear 93 moves to the second position, the transmission portion 922 of the input gear 92, which rotates in the first direction W1, comes into contact with the transmitted portion 931 of the transmission gear 93. As the transmission portion 922 comes into contact with the transmitted portion 931, a force in the first direction W1 acts from the input gear 92 to the transmission gear 93, causing the input gear 92 and the transmission gear 93 to rotate together in the first direction W1.

[0133] In this case, the sliding resistance between the cylindrical portion 930 of the transmission gear 93 and the fitting portion 850 of the fixed drive gear 85 is smaller than the force in the first direction W1 acting from the input gear 92 to the transmission gear 93, so that the transmission gear 93 can rotate smoothly against the sliding resistance.

[0134] Furthermore, when the transmission gear 93 rotates in the first direction W1 while it is in the second position, the engaging surface 933a of the ratchet pawl 933 on the transmission gear 93 and the engaging surface 941a of the ratchet recess 941 on the anchoring drive gear 85 engage, causing the transmission gear 93 and the anchoring drive gear 85 to rotate together in the first direction W1.

[0135] Thus, in the one-way clutch 90, the input gear 92 receives the driving force from the motor 4, which is rotating in the forward direction, and rotates in the first direction W1, causing the transmission gear 93 to move from the first position to the second position. As a result, the transmission gear 93 and the stationary drive gear 85 are connected, and the one-way clutch 90 transmits the driving force from the motor 4 in the first direction W1 to the stationary drive gear 85.

[0136] Conversely, in the one-way clutch 90, when the transmission gear 93 is in the second position, the input gear 92 receives the driving force from the motor 4, which is rotating in the reverse direction, and rotates in the second direction W2, causing the transmission gear 93 to move from the second position to the first position, as shown in Figure 8. As a result, the one-way clutch 90 releases the transmission of driving force to the fixed drive gear 85.

[0137] Specifically, when the transmission gear 93 is in the second position, and the input gear 92 rotates in the second direction W2 due to the driving force from the motor 4, the inclined engagement surface 924 of the input gear 92 and the engagement claw 934 of the transmission gear 93 engage. Since the downstream side of the inclined engagement surface 924 is closer to the fixed drive gear 85 than the upstream side in the second direction W2, when the engagement claw 934 engages with the inclined engagement surface 924 and is pressed in the second direction W2, the position of the inclined engagement surface 924 that abuts the engagement claw 934 moves to the upstream side in the second direction W2, and the transmission gear 93 is pulled toward the input gear 92 in the axial direction X by the inclined engagement surface 924.

[0138] In other words, when the transmission gear 93 is in the second position, if the input gear 92 rotates in the second direction W2, the transmission gear 93 is pulled toward the input gear 92 in the axial direction X by the inclined engagement surface 924 and moves to the first position. As a result, the transmission gear 93 and the anchoring drive gear 85 are separated, and the transmission of driving force from the input gear 92 to the anchoring drive gear 85 is released.

[0139] Thus, in the one-way clutch 90, by rotating the input gear 92 in the second direction, the inclined engagement surface 924 and the engagement claw 934 are engaged, and the transmission gear 93 is moved from the second position to the first position.

[0140] [Electromagnetic clutch] As shown in Figures 8 and 9, the electromagnetic clutch 95 includes a joint shaft 951, a clutch gear 952, a first disc 953, a second disc 954, and a drive unit 955.

[0141] The joint shaft 951 is formed in a cylindrical shape and has a connecting portion 951a and a support portion 951b. The connecting portion 951a is located at the right end of the joint shaft 951, and the support portion 951b is located to the left of the connecting portion 951a. The connecting portion 951a is connected to the fitting portion 920 of the input gear 92 via a D-cut connection, and the joint shaft 951 is rotatable integrally with the input gear 92. The support portion 951b is rotatably supported on the fixed shaft 91.

[0142] The clutch gear 952 is cylindrical in shape and is fitted onto the outer circumference of the right end of the joint shaft 951. The clutch gear 952 is supported by the fixed shaft 91 via the joint shaft 951 and is coaxial with the input gear 92. The clutch gear 952 is rotatable relative to the joint shaft 951. Gear teeth are formed on the outer surface of the clutch gear 952. The clutch gear 952 meshes with the fifth idler gear 87 of the second gear train 8C.

[0143] The first disc 953 is located at the left end of the clutch gear 952 and is rotatable integrally with the clutch gear 952. The second disc 954 is fixed to the left end of the joint shaft 951 and is rotatable integrally with the joint shaft 951.

[0144] The first disk 953 and the second disk 954 are opposite each other in the left-right direction. The first disk 953 is movable in the left-right direction. By moving in the left-right direction, the first disk 953 can move between a cutting position, which is separated from the second disk 954, and a transmission position, which is in contact with the second disk 954.

[0145] When the first disc 953 is in the cutting position, the first disc 953 and the second disc 954 are separated, allowing the joint shaft 951 and the clutch gear 952 to rotate relative to each other. When the first disc 953 is in the transmission position, the first disc 953 and the second disc 954 are in contact, allowing the joint shaft 951 and the clutch gear 952 to rotate as a single unit.

[0146] The first disk 953 is biased toward the cutting position by a biasing member (not shown). When the electromagnetic clutch 95, which is energized to the drive unit 955, is turned on, the drive unit 955 pulls the first disk 953 toward the second disk 954. On the other hand, when the electromagnetic clutch 95, which is not energized to the drive unit 955, is turned off, the drive unit 955 does not pull the first disk 953 toward the second disk 954.

[0147] When the electromagnetic clutch 95 is off, the first disc 953 is not pulled by the drive unit 955, and is moved to the disengagement position by the biasing force of the biasing member, allowing the joint shaft 951 and the clutch gear 952 to rotate relative to each other. Therefore, no driving force is transmitted between the joint shaft 951 and the clutch gear 952.

[0148] Furthermore, when the electromagnetic clutch 95 is engaged, the first disc 953 is attracted by the drive unit 955 and moves to the transmission position against the biasing force of the biasing member, allowing the joint shaft 951 and the clutch gear 952 to rotate together. Thus, it becomes possible to transmit driving force between the joint shaft 951 and the clutch gear 952.

[0149] When the electromagnetic clutch 95 is off, if a driving force from the forward-rotating motor 4 is input to the input gear 92 of the one-way clutch 90, the input gear 92 and the joint shaft 951 rotate together, but the driving force is not transmitted from the joint shaft 951 to the clutch gear 952, so the clutch gear 952 does not rotate. Consequently, the driving force input to the input gear 92 is not transmitted to the second gear train 8C connected to the clutch gear 952, and the discharge roller 291a does not rotate.

[0150] In this case, the input gear 92, which receives the driving force from the forward-rotating motor 4, rotates in the first direction W1. The driving force is then transmitted from the input gear 92 to the fixed drive gear 85 via the one-way clutch 90, causing the pressure roller 62 to rotate.

[0151] Furthermore, when the electromagnetic clutch 95 is turned on, if a driving force from the motor 4 that rotates in the forward direction is input to the input gear 92 of the one-way clutch 90, the input gear 92 and the joint shaft 951 rotate together, and furthermore, the joint shaft 951 and the clutch gear 952 rotate together. Consequently, the driving force input to the input gear 92 is transmitted to the second gear train 8C connected to the clutch gear 952, causing the discharge roller 291a to rotate in the forward direction.

[0152] In this case, the input gear 92, which receives the driving force from the forward-rotating motor 4, rotates in the first direction W1. The driving force is then transmitted from the input gear 92 to the fixed drive gear 85 via the one-way clutch 90, causing the pressure roller 62 to rotate.

[0153] In other words, when the electromagnetic clutch 95 is on, the driving force from the forward-rotating motor 4 input to the input gear 92 is transmitted to the first gear train 8B by the one-way clutch 90, and also branched off from the input gear 92 and transmitted to the second gear train 8C by the electromagnetic clutch 95. The input gear 92 is a branching gear that splits the input driving force into the first gear train 8B and the second gear train 8C.

[0154] Thus, the electromagnetic clutch 95 is an electromagnetic clutch that includes a rotatable clutch gear 952, and by controlling the rotation of the clutch gear 952, it is possible to switch whether or not to transmit driving force from the motor 4 to the second gear train 8C.

[0155] Furthermore, when the electromagnetic clutch 95 is turned on, if the driving force of the motor 4, which is rotating in the reverse direction, is input to the input gear 92, the driving force is transmitted to the second gear train 8C, causing the discharge roller 291a to rotate in the reverse direction. Also, since the input gear 92, to which the driving force of the motor 4, is input, rotates in the second direction W2, the driving force is not transmitted to the fixing drive gear 85 by the one-way clutch 90, and the pressure roller 62 does not rotate.

[0156] On the other hand, when the electromagnetic clutch 95 is off, if the driving force of the motor 4, which is rotating in the reverse direction, is input to the input gear 92, the driving force is not transmitted to the second gear train 8C, and therefore the discharge roller 291a does not rotate. Also, since the input gear 92, to which the driving force of the motor 4, is input, rotates in the second direction W2, the driving force is not transmitted to the fixing drive gear 85 by the one-way clutch 90, and the pressure roller 62 does not rotate.

[0157] Here, if the discharge roller 291a is rotated in the reverse direction to transport the sheet S to the re-transport path P2, and the leading edge of the sheet S being transported along the re-transport path P2 enters the transport path P1, and the motor 4 which is rotating in the reverse direction is switched to forward rotation, if the motor 4 and the discharge roller 291a remain connected, the discharge roller 291a will also be switched to forward rotation. In this case, if the rear end of the sheet S is nipped by the discharge roller 291a and the driven roller 291b, the sheet S may be transported in the discharge direction by the discharge roller 291a, potentially causing a jam.

[0158] However, in the image forming apparatus 1, the drive of the discharge roller 291a, to which the driving force is transmitted by the second gear train 8C, can be stopped at any timing by switching the electromagnetic clutch 95 on and off. Therefore, the drive of the discharge roller 291a can be stopped at the timing when the motor 4, which was rotating in reverse to transport the sheet S toward the re-transport path P2 by the discharge roller 291a, is switched to forward rotation. As a result, even if the rear end of the sheet S is nipped by the discharge roller 291a, the sheet S will not be transported in the discharge direction by the discharge roller 291a, and jamming can be suppressed.

[0159] Furthermore, since the electromagnetic clutch 95 can switch whether or not to transmit driving force to the second gear train 8C, when driving force is not transmitted to the paper discharge roller 291a, it is possible to suppress the rotation of extra gears such as the fifth idler gear 87 and the sixth idler gear 88 of the second gear train 8C, which are located downstream of the electromagnetic clutch 95.

[0160] Furthermore, in the drive force transmission train 8, the drive force from the motor 4 is input to the input gear 92 of the one-way clutch 90, and the input drive force is transmitted to the fixing drive gear 85 by the first gear train 8B. In addition, the input drive force is branched at the input gear 92 and output from the clutch gear 952 of the electromagnetic clutch 95 to the fifth idler gear 87 located downstream of the clutch gear 952 in the second gear train 8C. Therefore, even if the electromagnetic clutch 95 is turned off and the drive of the discharge roller 291a is stopped when the motor 4 is rotating in the forward direction, the fixing unit 6 can still be driven through the first gear train 8B.

[0161] In this case, since the input gear 92, which is a branching gear, and the fixing drive gear 85 are configured to rotate coaxially, it is possible to reduce the space required in the direction perpendicular to the axial direction X when arranging the fixing drive gear 85 and the input gear 92.

[0162] Furthermore, since the input gear 92 of the one-way clutch 90 is a branching gear, the number of gears constituting the first gear train 8B can be reduced, making it possible to configure the first gear train 8B in a compact manner.

[0163] Furthermore, since the branch gear formed by the input gear 92 and the one-way clutch 90 are located coaxially, the space required in the direction perpendicular to the axial direction X when arranging the branch gear, the fixed drive gear 85, and the one-way clutch 90 in the first gear train 8B can be reduced.

[0164] Furthermore, the one-way clutch 90 includes an input gear 92 that rotates in response to the driving force from the motor 4, and a transmission gear 93 that moves to a second position in response to the driving force from the motor 4 rotating in the forward direction, and moves to a first position in response to the driving force from the motor 4 rotating in the reverse direction. Therefore, it is possible to switch the transmission and disconnection of the driving force to the fixing drive gear 85 in response to the switching between forward and reverse rotation of the motor 4.

[0165] Furthermore, when the electromagnetic clutch 95 transmits the driving force from the motor 4 to the second gear train 8C, the clutch gear 952 and the input gear 92 rotate together, making it possible to efficiently transmit the driving force to both the discharge roller 291a and the fuser 6.

[0166] [Control of the electromagnetic clutch by the control unit] As shown in Figure 15, the control unit 75, which is configured on the control board 751, is connected to a pre-cash register sensor 77, a post-cash register sensor 78, and a seat sensor 79. The control unit 75 receives the detection results from the pre-cash register sensor 77, the post-cash register sensor 78, and the seat sensor 79. The control unit 75 is also connected to a motor 4 and an electromagnetic clutch 95. The control unit 75 can control the operation of the motor 4 and the electromagnetic clutch 95.

[0167] The control unit 75 is configured to turn off the electromagnetic clutch 95 after the leading edge of the sheet S, which is being transported along the re-transport path P2 by the reverse-rotating discharge roller 291a, has passed the first re-transport roller pair 36, thereby interrupting the transmission of the driving force from the motor 4 to the second gear train 8C.

[0168] In this case, the control unit 75 can determine, for example, that the leading edge of the sheet S being transported along the re-transport path P2 has passed the first re-transport roller pair 36 when a predetermined time has elapsed since the rear end of the sheet S being transported toward the discharge tray 292 by the forward-rotating discharge roller 291a passed the sheet sensor 79.

[0169] With this control of the electromagnetic clutch 95, after the leading edge of the sheet S has passed the first re-transport roller pair 36, the motor 4, which was rotating in reverse to transport the sheet S to the re-transport path P2 by the discharge roller 291a, can be switched to forward rotation at the same time.

[0170] As a result, even if the rear end of the sheet S is nipped by the discharge roller 291a, the sheet S will not be transported in the discharge direction by the discharge roller 291a, thereby suppressing jamming.

[0171] Furthermore, the control unit 75 can turn on the electromagnetic clutch 95 after turning it off to interrupt the transmission of the driving force from the motor 4 to the second gear train 8C, before the leading edge of the sheet S being transported along the re-transport path P2 reaches the image forming unit 5. This allows the driving force from the motor 4 to be transmitted to the second gear train 8C to drive the discharge roller 921a before the leading edge of the sheet S being transported along the re-transport path P2 reaches the image forming unit 5.

[0172] In this case, the control unit 75 can, for example, turn on the electromagnetic clutch 95 when the post-cash sensor 78 detects the leading edge of the sheet S, thereby starting to drive the discharge roller 921a.

[0173] In this way, by starting the drive of the discharge roller 921a before the leading edge of the sheet S reaches the image forming unit 5, the leading edge of the sheet S can be kept from having reached the image forming unit 5 when the transmission of driving force to the discharge roller 291a begins. This makes it possible to suppress distortion of the image formed on the sheet S due to vibrations at the start of the transmission of driving force to the discharge roller 291a.

[0174] [Second embodiment of control of electromagnetic clutch by control unit] The control unit 75 can also turn on the electromagnetic clutch 95 after it has turned off, interrupting the transmission of the driving force from the motor 4 to the second gear train 8C, before the leading edge of the sheet S being transported along the re-transport path P2 reaches the image forming unit 5 and then before it reaches the fuser 6. This allows the driving force from the motor 4 to be transmitted to the second gear train 8C and the discharge roller 291a to be driven before the leading edge of the sheet S being transported along the re-transport path P2 reaches the image forming unit 5 and then before it reaches the fuser 6.

[0175] In this case, the control unit 75 can, for example, turn on the electromagnetic clutch 95 at a predetermined time after the post-cash sensor 78 detects the leading edge of the sheet S, thereby starting to drive the discharge roller 921a.

[0176] In this way, by starting the drive of the discharge roller 921a before the leading edge of the sheet S reaches the fuser 6, the driving time of the discharge roller 291a can be shortened compared to the case where the driving force from the motor 4 is transmitted to the second gear train 8C before the leading edge of the sheet S reaches the image forming unit 5. Furthermore, in most cases, after the leading edge of the sheet S reaches the image forming unit 5, the rear end of the sheet S has already disengaged from the discharge roller 291a, so even if the transport position of the sheet S varies, the possibility of jamming is low even if the discharge roller 291a is driven to rotate in the forward direction.

[0177] [Third embodiment of control of electromagnetic clutch by control unit] The control unit 75 can also turn on the electromagnetic clutch 95 after it has turned off, interrupting the transmission of the driving force from the motor 4 to the second gear train 8C, before the leading edge of the sheet S being transported along the re-transport path P2 reaches the fuser 6 and then the discharge roller 291a. This allows the driving force from the motor 4 to be transmitted to the second gear train 8C and the discharge roller 291a to be driven before the leading edge of the sheet S being transported along the re-transport path P2 reaches the fuser 6 and then the discharge roller 291a.

[0178] In this case, the control unit 75 can, for example, turn on the electromagnetic clutch 95 at a predetermined time after the sheet sensor 79 detects the leading edge of the sheet S, thereby starting to drive the discharge roller 921a.

[0179] In this way, by starting the drive of the discharge roller 921a before the leading edge of the sheet S reaches the discharge roller 291a, the driving time of the discharge roller 291a can be shortened compared to the case where the driving force from the motor 4 is transmitted to the second gear train 8C before the leading edge of the sheet S reaches the image forming unit 5. As a result, the time during which the electromagnetic clutch 95 is turned on and the driving force is transmitted to the second gear train 8C can be made extremely short, thereby enabling power saving.

[0180] [Positional relationship between the control board and the electromagnetic clutch] As shown in Figure 16, the electromagnetic clutch 95 and the control board 751 are positioned at different locations when viewed from the left-right direction, which corresponds to the axial direction X. In other words, the electromagnetic clutch 95 and the control board 751 do not overlap when viewed from the left-right direction.

[0181] Therefore, when the electromagnetic clutch 95 and the control board 751 are arranged on the first main frame 26, the electromagnetic clutch 95 and the control board 751 do not interfere with each other, and the effects of noise and heat generation from the electromagnetic clutch 95 on the control board 751 can be reduced.

[0182] [Variations of input and output of driving force to input gear and electromagnetic clutch] In the drive force transmission train 8 shown in Figures 8 and 9, the third idler gear 84 of the common gear train 8A is connected to the input gear 92, and the clutch gear 952 of the electromagnetic clutch 95 is connected to the fifth idler gear 87 of the second gear train 8C. However, the drive force transmission train 8 can also be configured as shown in the drive force transmission train 801 in Figure 17.

[0183] In the drive force transmission train 801, the third idler gear 84 of the common gear train 8A is connected to the clutch gear 952 of the electromagnetic clutch 95, and the fifth idler gear 87 of the second gear train 8C is connected to the input gear 92. In the drive force transmission train 801, the drive force from the motor 4 is input to the clutch gear 952 via the common gear train 8A.

[0184] When the electromagnetic clutch 95 is ON, if the driving force from the forward-rotating motor 4 is input to the clutch gear 952, the driving force is transmitted to the input gear 92 via the joint shaft 951, and then output from the input gear 92 to the second gear train 8C. As a result, the discharge roller 291a rotates in the forward direction. Also, when the electromagnetic clutch 95 is ON, the driving force from the forward-rotating motor 4 input to the clutch gear 952 is transmitted to the input gear 92, and then further transmitted to the fixing drive gear 85 via the one-way clutch 90. As a result, the pressure roller 62 rotates.

[0185] On the other hand, when the electromagnetic clutch 95 is off, if a driving force from the forward-rotating motor 4 is input to the clutch gear 952, the driving force input to the clutch gear 952 is not transmitted to the input gear 92. Therefore, the driving force is not output to the second gear train 8C and is not transmitted to the fixing drive gear 85. As a result, neither the discharge roller 291a nor the pressure roller 62 rotates.

[0186] Furthermore, when the electromagnetic clutch 95 is ON, if the driving force from the motor 4 rotating in the reverse direction is input to the clutch gear 952, the driving force is transmitted to the input gear 92 via the joint shaft 951, and then output from the input gear 92 to the second gear train 8C. As a result, the discharge roller 291a rotates in the reverse direction. Also, when the electromagnetic clutch 95 is ON, if the driving force from the motor 4 rotating in the reverse direction is input to the clutch gear 952, the driving force is transmitted to the input gear 92, and the input gear 92 rotates in the second direction W2. Therefore, no driving force is transmitted from the input gear 92 to the fixing drive gear 85, and the pressure roller 62 does not rotate.

[0187] Furthermore, when the electromagnetic clutch 95 is off, if a driving force from the motor 4 rotating in the reverse direction is input to the clutch gear 952, the driving force input to the clutch gear 952 is not transmitted to the input gear 92. Consequently, the driving force is not output to the second gear train 8C and is not transmitted to the fixing drive gear 85. As a result, neither the discharge roller 291a nor the pressure roller 62 rotates.

[0188] Thus, in the drive force transmission train 801, when the electromagnetic clutch 95 is off, the drive force input to the clutch gear 952 is not transmitted to the second gear train 8C and the fixing drive gear 85. Therefore, when the drive of the discharge roller 291a is stopped, the drive of the fixing unit 6 can also be stopped at the same time. [Explanation of Symbols]

[0189] 1. Image forming apparatus 2 Main unit 4 motors 5 Image forming unit 5A Transfer section 6. Fuser 8. Power transmission train 8A Common gear train 8B First gear row 8C 2nd gear train 22 Outlet 26. First main frame 36. First re-transport roller pair 37. Second re-transport roller pair 61 Heating Unit 62 Pressure rollers 63 Fixing Gear 75 Control Unit 85 Fixing drive gear 87. 5th Idol Gear 90 1-way clutch 91 Fixed axis 92 Input Gear 93 Transmission Gear 95 Electromagnetic clutch 291a Discharge roller 751 Control board 952 Clutch Gear P1 transport route P2 Retransport Route S Seat

Claims

1. An image forming apparatus for forming a toner image on a sheet, A transfer unit that transfers the toner image onto the transported sheet, A motor capable of forward and reverse rotation, A fuser that is driven by the driving force from the motor and fixes the toner image transferred to the sheet, comprising a heating rotating body, a pressurizing rotating body that forms a fixing nip between itself and the heating rotating body, and a fixing gear that transmits the driving force from the motor to the heating rotating body or the pressurizing rotating body, A main body housing for the fuser, the main body housing having an outlet from which the sheet conveyed from the fuser is discharged, A re-transport path that transports the sheet transported from the fuser back towards the transfer section, A discharge roller driven by the driving force from the motor, which is capable of forward and reverse rotation, discharges the sheet being transported from the fuser through the discharge port when rotating forward, and guides the sheet to the re-transport path when rotating reverse, A first gear train for transmitting the driving force from the motor to the fixing gear, the first gear train having a fixing drive gear supported by the main housing and connected to the fixing gear, and a branch gear for transmitting the driving force from the motor to the fixing drive gear, A second gear train that branches off from the aforementioned branching gear and transmits the driving force from the motor to the discharge roller, An electromagnetic clutch including a rotatable clutch gear, wherein the rotation of the clutch gear can be controlled to switch whether or not to transmit driving force from the motor to the second gear train, Equipped with, The clutch gear is arranged coaxially with the branch gear in the image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the fixing drive gear and the branching gear rotate coaxially.

3. The image forming apparatus according to claim 2, further comprising a one-way clutch located coaxially with the branching gear and capable of transmitting the driving force from the motor to the fixing drive gear when the motor is rotating in the forward direction.

4. The aforementioned one-way clutch is An input gear that can rotate by receiving the driving force from the motor, The transmission gear has a first position in which it is separated from the fixing drive gear while engaged with the input gear, and a second position in which it is connected to the fixing drive gear, and is movable in the axial direction between these two positions. As the input gear receives the driving force from the motor, which is rotating in the forward direction, and rotates in the first direction, the transmission gear moves from the first position to the second position. The image forming apparatus according to claim 3, wherein the input gear receives a driving force from the motor which rotates in the reverse direction and rotates in a second direction opposite to the first direction, thereby moving the transmission gear from the second position to the first position.

5. The image forming apparatus according to claim 4, wherein the input gear is the branching gear.

6. The image forming apparatus according to claim 1, wherein the clutch gear and the branch gear rotate together when the electromagnetic clutch transmits the driving force from the motor to the second gear train.

7. The image forming apparatus according to claim 1, wherein driving force from the motor is input to the branching gear, and driving force is output from the clutch gear to a gear located downstream of the clutch gear in the second gear train.

8. The image forming apparatus according to claim 1, wherein a driving force from the motor is input to the clutch gear, and a driving force is output from the branch gear to the second gear train.

9. The frame comprises the electromagnetic clutch and a control board that controls the operation of the electromagnetic clutch, The image forming apparatus according to claim 1, wherein the electromagnetic clutch and the control board are arranged at different positions when viewed from the axial direction.

10. A control unit that controls the operation of the electromagnetic clutch, The re-transport path includes a re-transport roller that is provided in the re-transport path and is driven by the driving force from the motor, The control unit, The image forming apparatus according to claim 1, wherein, after the leading edge of the sheet being transported along the re-transport path by the discharge roller has passed the re-transport roller, the electromagnetic clutch is controlled to interrupt the transmission of the driving force from the motor to the second gear train.

11. The control unit, The image forming apparatus according to claim 10, wherein the discharge roller is driven by controlling the electromagnetic clutch to transmit the driving force from the motor to the second gear train before the leading edge of the sheet being transported along the re-transport path reaches the transfer section.

12. The image forming apparatus according to claim 10, wherein the control unit drives the discharge roller by controlling the electromagnetic clutch and transmitting the driving force from the motor to the second gear train when the leading edge of the sheet being transported along the re-transport path reaches the transfer section and before it reaches the fuser.

13. The image forming apparatus according to claim 10, wherein the control unit controls the electromagnetic clutch to transmit the driving force from the motor to the second gear train to drive the discharge roller after the leading edge of the sheet being transported along the re-transport path has reached the fuser and before it has reached the discharge roller.

Images