Image forming apparatus

Abstract

To suppress abnormal noise caused by a movable gear at the start of printing after a print command is received.SOLUTION: An image forming apparatus comprises a first gear and a movable gear. The movable gear is movable between a transmission position where it meshes with the first gear and a non-transmission position where it is separated from the first gear. A control unit can execute a first process (t3-t6), a second process (t38-t41), and a connection process (t45-t46). The first process is a process in which a motor (M1) is rotated forward and a switching mechanism (EC3) is brought into a transmission state to set a nip pressure to a first nip pressure. The second process is a process in which the motor is rotated in reverse and the switching mechanism is brought into the transmission state to set the nip pressure to a second nip pressure. The connection process is a process in which, while the switching mechanism is in a disconnected state, the motor is rotated forward to move the movable gear from the non-transmission position to the transmission position. The control unit performs the connection process after executing the second process, to wait for a print command in a state where the movable gear meshes with the first gear.SELECTED DRAWING: Figure 18

Description

[Technical Field]

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

[0002] Conventionally, an image forming apparatus is known that includes a sheet feeder that feeds sheets and a transmission mechanism that transmits a driving force to the sheet feeder (see Patent Document 1). The transmission mechanism includes a drive gear that can be rotated forward and backward by a motor, a movable gear that can move between a first position and a second position as the drive gear rotates, and a driven gear that meshes with the movable gear located at the first position and moves away from the movable gear located at the second position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-143702 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, for example, when starting printing and moving the movable gear from the second position to the first position to engage with the driven gear, it may take time for the movable gear to move from the second position to the first position and engage with the driven gear, or there may be a noticeable abnormal noise when the movable gear connects with the driven gear.

[0005] Therefore, an object of the present disclosure is to suppress abnormal noise caused by moving gears when starting printing after receiving a print command. [Means for solving the problem]

[0006] In order to solve the above-described problems, the image forming apparatus of the present disclosure includes a motor, an image forming unit, a fixing unit, a first cam, a first drive train, a second drive train, and a control unit. The motor can rotate in both forward and reverse directions. The image forming section forms an image on a sheet. The fixing unit fixes the image on the sheet by sandwiching the sheet between a heating rotor and a pressure rotor. The first cam is movable between a first position and a second position. The first position is a position where the nip pressure between the heating rotor and the pressure rotor is a first nip pressure, and the second position is a position where the nip pressure is a second nip pressure that is smaller than the first nip pressure. The first cam moves to the first position when the motor rotates forward, and moves to the second position when the motor rotates backward. The first drive train transmits the driving force of the motor to the heating rotor or the pressure rotor, and includes a first gear and a moving gear. The movable gear is movable between a transmitting position and a non-transmitting position. The transmission position is a position where the movable gear meshes with the first gear to transmit driving force to the first gear, and the non-transmission position is a position where the movable gear is separated from the first gear to not transmit driving force to the first gear. The movable gear moves toward the transmitting position when the motor rotates forward, and moves toward the non-transmitting position when the motor rotates backward. The second drive train transmits the driving force of the motor to the first cam and includes a switching mechanism. The switching mechanism is switchable between a transmission state in which the driving force is transmitted to the first cam and a disconnection state in which the driving force is not transmitted to the first cam. The control unit is capable of executing a first process, a second process, and a connection process. The first process is a process of rotating the motor in the forward direction and setting the switching mechanism in a transmission state, thereby setting the nip pressure to the first nip pressure. The second process is a process of setting the nip pressure to the second nip pressure by rotating the motor in the reverse direction and by putting the switching mechanism into a transmission state. The connection process is a process in which the motor is rotated forward when the switching mechanism is in the disconnected state, and the movable gear is moved from the non-transmission position to the transmission position. The control unit performs the connection process after performing the second process, thereby waiting for a print command in a state where the moving gear is meshed with the first gear.

[0007] The control unit performs the connection process after executing the second process, and is configured to wait for a print command with the movable gear meshed with the first gear, thereby preventing abnormal noise caused by the movable gear coming into contact with the first gear when printing begins after receiving the print command.

[0008] In addition, the control unit may rotate the motor forward at a first speed when performing a printing process to form an image on a sheet, and may rotate the motor forward at a second speed lower than the first speed when performing a connection process.

[0009] When the connection process is performed, the motor is rotated forward at a second speed that is slower than the first speed, thereby reducing abnormal noise caused by contact between the movable gear and the first gear.

[0010] Furthermore, the driving time of the motor in the connection process may be shorter than the driving time of the motor in the second process.

[0011] By making the motor drive time in the connection process shorter than the motor drive time in the second process, the connection process can be performed more quickly than, for example, when the motor drive time in the connection process is longer than the motor drive time in the second process.

[0012] Furthermore, the control unit may stop the motor after the connection process.

[0013] The switching mechanism may also be an electromagnetic clutch.

[0014] The image forming apparatus may also include a sensor that detects whether the first cam is in the first position or the second position.

[0015] The first drive train may transmit a driving force to the heating rotor, and the pressure rotor may rotate following the rotation of the heating rotor.

[0016] The image forming apparatus may further include a photosensitive drum, a cleaning member that cleans the surface of the photosensitive drum, and a process motor that drives the photosensitive drum. The control unit may be capable of executing a cleaning process for cleaning the photosensitive drum by driving the process motor, and may execute the cleaning process after the second process, and may execute the connection process after the cleaning process.

[0017] The image forming apparatus may further include a developing roller, a second cam, and a third drive train. The developing roller is movable between a contact position where it contacts the photosensitive drum and a spaced position where it is spaced from the photosensitive drum. The second cam moves the developing roller between the contact position and the separated position. The third drive train transmits the driving force of the motor to the second cam and includes a second electromagnetic clutch. The control unit may be capable of executing a pressure contact process and a separation process. The pressing process is a process in which the motor is rotated in the forward direction and the second electromagnetic clutch is connected, thereby moving the developing roller to the contact position. The separation process is a process in which the motor is rotated in the reverse direction and the second electromagnetic clutch is connected, thereby moving the developing roller to the separation position.

[0018] Furthermore, the control unit may execute the second process after the separation process.

[0019] The image forming apparatus may further include a supply roller and a fourth drive train. The supply roller supplies the sheet to the image forming unit. The fourth drive train transmits the driving force of the motor to the supply roller, and includes a second gear and a second moving gear. The second movable gear is movable between a second transmission position in which it meshes with the second gear to transmit driving force to the second gear, and a second non-transmission position in which it moves away from the second gear to not transmit driving force to the second gear. The second movable gear moves toward the second transmitting position when the motor rotates forward, and moves toward the second non-transmitting position when the motor rotates backward.

[0020] By configuring the second moving gear to move toward the second transmission position as the motor rotates forward, when the control unit performs the connection process, the second moving gear engages with the second gear, thereby preventing abnormal noise caused by the second moving gear coming into contact with the second gear when printing begins after receiving a print command.

[0021] The image forming apparatus of the present disclosure includes a motor, an image forming unit, a rotating body, a moving body, a first drive train, a second drive train, and a control unit. The motor can rotate in both forward and reverse directions. The image forming section forms an image on a sheet. The rotating body transports the sheet. The movable body is movable between a first position and a second position. The movable body moves to the first position when the motor rotates forward. The movable body moves to the second position when the motor rotates backward. The first drive train transmits the driving force of the motor to the rotor, and includes a first gear and a moving gear. The movable gear is movable between a transmission position where it meshes with the first gear to transmit driving force to the first gear, and a non-transmission position where it moves away from the first gear to not transmit driving force to the first gear. The movable gear moves toward the transmission position when the motor rotates forward. The movable gear moves toward the non-transmission position when the motor rotates reverse. The second drive train transmits the driving force of the motor to the moving body and includes a switching mechanism. The switching mechanism is switchable between a transmission state in which the driving force is transmitted to the movable body and a disconnection state in which the driving force is not transmitted to the movable body. The control unit is capable of executing a first process, a second process, and a connection process. The first process is a process for moving the moving body to a first position by rotating the motor in the forward direction and by putting the switching mechanism into a transmission state. The second process is a process of moving the moving body to the second position by rotating the motor in the reverse direction and putting the switching mechanism into a transmission state. The connection process is a process in which the motor is rotated forward when the switching mechanism is in the disconnected state, and the movable gear is moved from the non-transmission position to the transmission position. The control unit performs the connection process after performing the second process, thereby waiting for a print command in a state where the moving gear is meshed with the first gear.

[0022] The control unit performs the connection process after executing the second process, and is configured to wait for a print command with the movable gear meshed with the first gear, thereby preventing abnormal noise caused by the movable gear coming into contact with the first gear when printing begins after receiving the print command.

[0023] The image forming apparatus may further include a fixing unit. The fixing unit fixes the image on the sheet by sandwiching the sheet between a heating rotor and a pressure rotor. The rotor may be a heating rotor or a pressure rotor.

[0024] The moving body may be a first cam that sets the nip pressure between the heating rotor and the pressure rotor to a first nip pressure or a second nip pressure that is smaller than the first nip pressure. The first cam may set the nip pressure to a first nip pressure when located at the first position, in which case the first cam sets the nip pressure to a second nip pressure when located at the second position.

[0025] The rotating body may also be a supply roller that supplies a sheet to the image forming unit.

[0026] The image forming apparatus may further include a photosensitive drum and a developing roller. The developing roller is movable between a contact position where it contacts the photosensitive drum and a spaced position where it is spaced from the photosensitive drum. The moving body may be a second cam that moves the developing roller between the contact position and the separated position.

[0027] The switching mechanism may also be an electromagnetic clutch.

[0028] The image forming apparatus may also include a sensor that detects whether the first cam is in the first position or the second position.

[0029] The first drive train may transmit a driving force to the heating rotor, and the pressure rotor may rotate following the rotation of the heating rotor. [Effects of the Invention]

[0030] This can reduce noise caused by the moving gears when starting printing after receiving a print command. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an outline of a driving force transmission system of the image forming apparatus. [Figure 3] FIG. [Figure 4] FIG. 2 is a diagram showing a spacing cam, a cam follower, a shaft, and a stopper. [Figure 5] 1A and 1B are diagrams showing a configuration for moving a developer cartridge, in which the developer cartridge is positioned at a contact position (FIG. 1A) and at a separated position (FIG. 1B). [Figure 6] 1A is a perspective view showing a separation cam and a cam follower positioned in a non-pressing position, and FIG. 1B is a side view showing the separation cam and the cam follower positioned in a non-pressing position. [Figure 7] 1A is a perspective view showing a separation cam and a cam follower positioned at a pressing position, and FIG. 1B is a side view showing the separation cam and the cam follower positioned at a pressing position. [Figure 8] 1A and 1B are perspective views showing a gear cover. [Figure 9] 5A is a cross-sectional view showing a separation cam, a cam follower, a gear cover, and a spring, in which FIG. 5A shows the cam follower in a non-pressing position, and FIG. 5B shows the cam follower in a pressing position. [Figure 10] FIG. 4 is a diagram showing a development separation gear train. [Figure 11] 1A is a perspective view showing an idle gear of a first spaced gear train, and FIG. 1B is a perspective view showing the idle gear, a shaft portion of a gear cover, and a rotation resistance member. [Figure 12] FIG. 4 is a cross-sectional view showing an idle gear, a shaft portion of a gear cover, a rotation resistance member, and a metal plate. [Figure 13] FIG. 4 is a diagram showing an idle gear and a rotation resistance member. [Figure 14] FIG. 3 is a diagram showing a fixing drive gear train and a nip pressure adjusting gear train. [Figure 15] 3 is a diagram showing a fixing drive gear train, a first discharge roller gear, a discharge drive gear train, and a second discharge roller gear. FIG. [Figure 16] 1A and 1B are diagrams showing a nip pressure adjusting mechanism, in which FIG. 1A shows a small nip pressure and FIG. 1B shows a large nip pressure. [Figure 17] FIG. 4 is a diagram showing a sheet supply gear train. [Figure 18] 10 is a timing chart showing an example of the operation of the control unit. DETAILED DESCRIPTION OF THE INVENTION

[0032] Next, an embodiment of an image forming apparatus will be described. As shown in FIG. 1, the image forming apparatus 1 is a color printer and includes a housing 10, a front cover 11, a sheet supply unit 20, an image forming unit 30, a fixing unit 80, a second discharge roller 91 as a discharge roller, and a control unit 2. In this embodiment, the left side of FIG. 1 is referred to as the "front" and the right side of FIG. 1 is referred to as the "rear." The top of FIG. 1 is referred to as the "top" and the bottom of FIG. 1 is referred to as the "bottom." The front of the paper in FIG. 1 is referred to as the "right" and the back of the paper in FIG. 1 is referred to as the "left."

[0033] Housing 10 has an opening 10A at the front. Front cover 11 opens and closes opening 10A. Specifically, front cover 11 is rotatable relative to housing 10 between a closed position shown by solid lines and an open position shown by imaginary lines. The closed position is a position where opening 10A is closed, and the open position is a position where opening 10A is open.

[0034] The sheet supply unit 20 includes a sheet tray 21 and a sheet supply mechanism 22. Sheets S are set in the sheet tray 21. The sheet supply mechanism 22 is a mechanism that receives a driving force to supply sheets S toward photosensitive drums 50 (50Y, 50M, 50C, 50K) of the image forming unit 30, which will be described later. The sheet supply mechanism 22 includes a pickup roller 23, a separation roller 24, a separation pad 25, a conveyance roller 26, and a registration roller 27. The pickup roller 23, the separation roller 24, the conveyance roller 26, and the registration roller 27 are examples of supply rollers that supply sheets S to the image forming unit 30.

[0035] The sheet supply mechanism 22 feeds the sheet S from the sheet tray 21 using the pickup roller 23. Next, the sheet supply mechanism 22 separates the sheet S into a single sheet between the separation roller 24 and the separation pad 25. Thereafter, the sheet supply mechanism 22 supplies the sheet S toward the image forming unit 30 using the conveyance roller 26 and the registration roller 27.

[0036] The image forming section 30 includes an exposure unit 40, four photosensitive drums 50, four developing cartridges 60, and a transfer unit . The exposure unit 40 includes, for example, a light source, a deflector, a lens, and a mirror. The exposure unit 40 emits a light beam indicated by a dashed line to expose the surface of the photosensitive drum 50.

[0037] The photosensitive drums 50 include a photosensitive drum 50Y corresponding to yellow, a photosensitive drum 50M corresponding to magenta, a photosensitive drum 50C corresponding to cyan, and a photosensitive drum 50K corresponding to black. The four photosensitive drums 50 are arranged in the order of photosensitive drum 50Y, photosensitive drum 50M, photosensitive drum 50C, and photosensitive drum 50K from upstream to downstream in the conveyance direction of the sheet S.

[0038] Specifically, the photosensitive drum 50Y is disposed upstream of the photosensitive drum 50M in the transport direction of the sheet S. The photosensitive drum 50M is disposed upstream of the photosensitive drum 50C in the transport direction of the sheet S. The photosensitive drum 50C is disposed upstream of the photosensitive drum 50K in the transport direction of the sheet S.

[0039] In this specification and drawings, for components corresponding to each color, when the colors are to be distinguished, Y, M, C, K are added to the symbols, and when the colors are not to be distinguished, Y, M, C, K are not added to the symbols.

[0040] The image forming apparatus 1 further includes a drawer 55. The drawer 55 is movable between an inner position and an outer position in the direction in which the photosensitive drums 50 are arranged, through an opening 10A of the housing 10 that is exposed by opening the front cover 11. The inner position is a position where the drawer 55 is housed within the housing 10, and the outer position is a position where at least a portion of the drawer 55 is exposed to the outside of the housing 10. In this embodiment, the outer position is a position where the drawer 55 is pulled out from the inner position to the front. In this embodiment, the drawer 55 is detachable from the housing 10.

[0041] The drawer 55 has a frame 55F. The frame 55F rotatably supports four photosensitive drums 50 (50Y, 50M, 50C, and 50K). The frame 55F also supports four chargers 52. The chargers 52 charge the surfaces of the corresponding photosensitive drums 50.

[0042] The frame 55F also supports cleaning rollers 56, which are an example of cleaning members. The cleaning rollers 56 are rollers that clean the surfaces of the photosensitive drums 50. One cleaning roller 56 is provided for each of the four photosensitive drums 50.

[0043] The developer cartridges 60 include a developer cartridge 60Y containing yellow toner, a developer cartridge 60M containing magenta toner, a developer cartridge 60C containing cyan toner, and a developer cartridge 60K containing black toner. The developer cartridge 60Y has a developer roller 61Y that supplies yellow toner to the photosensitive drum 50Y. The developer cartridge 60M has a developer roller 61M that supplies magenta toner to the photosensitive drum 50M. The developer cartridge 60C has a developer roller 61C that supplies cyan toner to the photosensitive drum 50C. The developer cartridge 60K has a developer roller 61K that supplies black toner to the photosensitive drum 50K.

[0044] The developing roller 61Y is movable relative to the photosensitive drum 50Y between a contact position where it contacts the photosensitive drum 50Y and a separated position where it is separated from the photosensitive drum 50Y. The developing roller 61M is movable relative to the photosensitive drum 50M between a contact position where it contacts the photosensitive drum 50M and a separated position where it is separated from the photosensitive drum 50M. The developing roller 61C is movable relative to the photosensitive drum 50C between a contact position where it contacts the photosensitive drum 50C and a separated position where it is separated from the photosensitive drum 50C. The developing roller 61K is movable relative to the photosensitive drum 50K between a contact position where it contacts the photosensitive drum 50K and a separated position where it is separated from the photosensitive drum 50K.

[0045] The frame 55F of the drawer 55 detachably supports the developer cartridges 60 (60Y, 60M, 60C, 60K). Each developer cartridge 60 can be replaced when the drawer 55 is in the outer position or when the drawer 55 is removed from the housing 10.

[0046] The developing cartridge 60 is supported by the frame 55F so as to be movable back and forth between a developing position indicated by a solid line and a non-developing position indicated by a virtual line. The developing position is a position where the corresponding developing roller 61 is positioned in a contact position, and the non-developing position is a position where the corresponding developing roller 61 is positioned in a separated position.

[0047] Specifically, the developer cartridge 60Y is movable relative to the photosensitive drum 50Y between a development position where the developer roller 61Y is located at a contact position and a non-development position where the developer roller 61Y is located at a separated position. In other words, the developer cartridge 60Y is movable relative to the photosensitive drum 50Y between a development position where the developer roller 61Y is in contact with the photosensitive drum 50Y and a non-development position where the developer roller 61Y is separated from the photosensitive drum 50Y.

[0048] The developing cartridge 60M is movable relative to the photosensitive drum 50M between a developing position where the developing roller 61M is in contact with the photosensitive drum 50M and a non-developing position where the developing roller 61M is in a separated position. In other words, the developing cartridge 60M is movable relative to the photosensitive drum 50M between a developing position where the developing roller 61M is in contact with the photosensitive drum 50M and a non-developing position where the developing roller 61M is separated from the photosensitive drum 50M.

[0049] The developer cartridge 60C is movable relative to the photosensitive drum 50C between a developing position where the developer roller 61C is located at a contact position and a non-developing position where the developer roller 61C is located at a separated position. In other words, the developer cartridge 60C is movable relative to the photosensitive drum 50C between a developing position where the developer roller 61C is in contact with the photosensitive drum 50C and a non-developing position where the developer roller 61C is separated from the photosensitive drum 50C.

[0050] The developing cartridge 60K is movable relative to the photosensitive drum 50K between a developing position where the developing roller 61K is located at a contact position and a non-developing position where the developing roller 61K is located at a separated position. In other words, the developing cartridge 60K is movable relative to the photosensitive drum 50K between a developing position where the developing roller 61K is in contact with the photosensitive drum 50K and a non-developing position where the developing roller 61K is separated from the photosensitive drum 50K.

[0051] The transfer unit 70 includes a drive roller 71, a driven roller 72, an endless conveyor belt 73, and four transfer rollers 74. The conveyor belt 73 is stretched across the drive roller 71 and the driven roller 72, with its outer surface in contact with the four photosensitive drums 50. The transfer rollers 74 are disposed inside the conveyor belt 73, and sandwich the conveyor belt 73 between themselves and the corresponding photosensitive drums 50.

[0052] The fixing device 80 is a device that fixes the toner image (image) transferred onto the sheet S to the sheet S. The fixing device 80 has a heating section 81, a pressure section 82, and a first discharge roller 83 as a discharge roller. The heating section 81 includes a heating roller 81A as an example of a heating rotator, and a heater 81B. The heating roller 81A is a cylindrical roller made of metal. The heater 81B is a heater that heats the heating roller 81A, and is arranged to pass inside the heating roller 81A.

[0053] The pressure applying unit 82 sandwiches the sheet S between itself and the heating unit 81. Specifically, the pressure applying unit 82 is a pressure roller that sandwiches the sheet S between itself and the heating roller 81A. The pressure roller is a roller with a core metal covered with a rubber layer. The pressure roller is an example of a pressure rotating body. The fixing unit 80 receives a driving force to transport the sheet S between the heating roller 81A of the heating unit 81 and the pressure applying unit 82 (pressure roller). The fixing unit 80 also receives a driving force to transport the sheet S by the first discharge roller 83.

[0054] In the image forming unit 30, the surface of the photosensitive drum 50 is uniformly charged by the charger 52, and then exposed to a light beam emitted from the exposure unit 40. In this way, the image forming unit 30 forms an electrostatic latent image based on image data on the photosensitive drum 50. In addition, the image forming unit 30 supplies toner contained in the developer cartridge 60 to the photosensitive drum 50 from the developer roller 61 located at the contact position. In this way, the image forming unit 30 forms a toner image on the photosensitive drum 50.

[0055] The image forming unit 30 transfers the toner image formed on the photosensitive drum 50 onto the sheet S by transporting the sheet S supplied from the sheet supply unit 20 between the photosensitive drum 50 and the transfer roller 74. That is, the image forming unit 30 forms an image on the sheet S. Thereafter, the fixing unit 80 fixes the toner image onto the sheet S by transporting the sheet S onto which the toner image has been transferred between the heating roller 81A and the pressure unit 82.

[0056] The first discharge roller 83 and the second discharge roller 91 receive a driving force to discharge the sheet S from between the heating unit 81 and the pressure unit 82 to the outside of the housing 10. Specifically, the first discharge roller 83 and the second discharge roller 91 discharge the sheet S on which the toner image has been fixed to the discharge tray 13.

[0057] As shown in FIG. 2, the image forming apparatus 1 further includes a main motor M1 as an example of a motor, a process motor M2, a separating mechanism 5, and a nip pressure adjusting mechanism 200.

[0058] The main motor M1 is a motor that drives the separation cam 150 of the separation mechanism 5, the fixing unit 80, the nip pressure adjustment mechanism 200, and the sheet supply mechanism 22. In other words, the separation cam 150 of the separation mechanism 5, the fixing unit 80, the nip pressure adjustment mechanism 200, and the sheet supply mechanism 22 receive driving force from the main motor M1. The main motor M1 is rotatable forward and reverse. The main motor M1 rotates forward when the sheet S is transported from the sheet tray 21 toward the discharge tray 13 to form an image on the sheet S.

[0059] The process motor M2 is a motor that drives the photosensitive drum 50, the cleaning roller 56, the developing roller 61, and the transfer unit 70. In other words, the photosensitive drum 50, the cleaning roller 56, the developing roller 61, and the transfer unit 70 receive a driving force from the process motor M2.

[0060] As shown in Figures 2 and 3, the image forming apparatus 1 further includes a developer separation gear train GT1 as an example of a third drive train, a fixing drive gear train GT2 as an example of a first drive train, a nip pressure adjustment gear train GT3 as an example of a second drive train, a sheet supply gear train GT4 as an example of a fourth drive train, a drum drive gear train GT5, a first developer drive gear train GT6, and a second developer drive gear train GT7.

[0061] The developing separation gear train GT1 is a gear train that transmits the driving force of the main motor M1 to the separation cams 150 (150Y, 150M, 150C, 150K) of the separation mechanism 5. The fixing drive gear train GT2 is a gear train that receives the driving force of the main motor M1 from the development separation gear train GT1 and transmits it to the fixing device 80. Specifically, the fixing drive gear train GT2 receives the driving force of the main motor M1 from the development separation gear train GT1 and transmits it to the heating roller 81A.

[0062] The nip pressure adjusting gear train GT3 is a gear train that receives the driving force of the main motor M1 from the development separation gear train GT1 and transmits it to the nip pressure adjusting cam 230 of the nip pressure adjusting mechanism 200. The sheet supply gear train GT4 is a gear train that transmits the driving force of the main motor M1 to the sheet supply mechanism 22.

[0063] The drum drive gear train GT5 is a gear train that transmits the driving force of the process motor M2 to the photosensitive drums 50 (50Y, 50M, 50C, 50K). The first developing drive gear train GT6 is a gear train that transmits the driving force of the process motor M2 to the developing rollers 61Y, 61M, and 61C. The second developing drive gear train GT7 is a gear train that transmits the driving force of the process motor M2 to the developing roller 61K. Specifically, the second developing drive gear train GT7 receives the driving force of the process motor M2 from the first developing drive gear train GT6 and transmits it to the developing roller 61K. The cleaning roller 56 may rotate by receiving the driving force of the process motor M2 via the drum drive gear train GT5, the first development drive gear train GT6, or the second development drive gear train GT7, or may rotate by receiving the driving force via another gear train.

[0064] The separation mechanism 5 is a mechanism that receives a driving force from the main motor M1 to move the developing roller 61 between the contact position and the separation position. The separation mechanism 5 includes four separation cams 150 and four cam followers 170. The spacing cam 150 is an example of a second cam. The spacing cam 150 includes a spacing cam 150Y, a spacing cam 150M, a spacing cam 150C, and a spacing cam 150K.

[0065] The separation cam 150Y rotates by receiving a driving force from the main motor M1, and moves the developing roller 61Y between the contact position and the separation position. Specifically, the separation cam 150Y rotates to move the developing cartridge 60Y between the development position and the non-development position, thereby moving the developing roller 61Y between the contact position and the separation position. The separation cam 150M rotates by receiving a driving force from the main motor M1, and moves the developing roller 61M between the contact position and the separation position. Specifically, the separation cam 150M rotates to move the developing cartridge 60M between the development position and the non-development position, thereby moving the developing roller 61M between the contact position and the separation position.

[0066] The separation cam 150C rotates by receiving a driving force from the main motor M1, and moves the developing roller 61C between the contact position and the separation position. Specifically, the separation cam 150C rotates to move the developing cartridge 60C between the development position and the non-development position, thereby moving the developing roller 61C between the contact position and the separation position. The separation cam 150K rotates by receiving a driving force from the main motor M1, and moves the developing roller 61K between the contact position and the separation position. Specifically, the separation cam 150K rotates to move the developing cartridge 60K between the development position and the non-development position, thereby moving the developing roller 61K between the contact position and the separation position.

[0067] As shown in Fig. 4, the cam followers 170 include cam follower 170Y, cam follower 170M, cam follower 170C, and cam follower 170K. The cam followers 170 are slidable in the rotational axis direction of the separating cam 150. The rotational axis direction of the separating cam 150 corresponds to the direction in which the dashed dotted line shown in Fig. 4 extends. Hereinafter, the rotational axis direction of the separating cam 150 will also be simply referred to as the "rotational axis direction." The rotational axis direction is also the rotational axis direction of cam gears 115 (115Y, 115M, 115C, 115K) described below.

[0068] The cam follower 170Y is slidable in the direction of the rotation axis between a pressing position and a non-pressing position in response to rotation of the separating cam 150Y (cam gear 115Y). The pressing position of the cam follower 170Y is a position where the cam follower 170Y presses the developer cartridge 60Y to position the developer cartridge 60Y at the non-development position, and the non-pressing position is a position where the developer cartridge 60Y is positioned at the development position.

[0069] The cam follower 170M is slidable in the direction of the rotation axis between a pressing position and a non-pressing position in response to rotation of the separation cam 150M (cam gear 115M). The pressing position of the cam follower 170M is a position where it presses the developer cartridge 60M to position the developer cartridge 60M in the non-development position, and the non-pressing position is a position where it positions the developer cartridge 60M in the development position.

[0070] The cam follower 170C is slidable in the direction of the rotation axis between a pressing position and a non-pressing position in response to rotation of the separating cam 150C (cam gear 115C). The pressing position of the cam follower 170C is a position where it presses the developer cartridge 60C to position the developer cartridge 60C in the non-development position, and the non-pressing position is a position where it positions the developer cartridge 60C in the development position.

[0071] The cam follower 170K is slidable in the direction of the rotation axis between a pressing position and a non-pressing position in response to rotation of the separating cam 150K (cam gear 115K). The pressing position of the cam follower 170K is a position where it presses the developer cartridge 60K to position the developer cartridge 60K at the non-development position, and the non-pressing position is a position where it positions the developer cartridge 60K at the development position.

[0072] As shown in FIG. 5(a), the drawer 55 has a contact portion 55A, a pressing member 55B, and a spring 55C. The contact portion 55A is the portion that contacts the slide member 66 (described later) and is made of a roller that can rotate around a vertical axis. The pressing member 55B is biased rearward by the spring 55C. When the developer cartridge 60 is installed in the drawer 55, the pressing member 55B presses the developer cartridge 60 rearward by the biasing force of the spring 55C. This moves the developer cartridge 60 to a development position where the development roller 61 contacts the photosensitive drum 50.

[0073] The developer cartridge 60 has a case 65 that contains toner, and a slide member 66. The slide member 66 slides in the direction of the rotation axis when pressed by a cam follower 170. The slide member 66 has a shaft 66A, a first contact member 66B, and a second contact member 66C. The shaft 66A is supported by the case 65 so as to be able to slide in the direction of the rotation axis. The first contact member 66B is fixed to one end of the shaft 66A, and the second contact member 66C is fixed to the other end of the shaft 66A.

[0074] The first contact member 66B has a pressed surface 66D and an inclined surface 66E, and the second contact member 66C has an inclined surface 66F. The pressed surface 66D is a surface that is pressed by the cam follower 170. The inclined surfaces 66E, 66F are surfaces that are inclined in the left-right direction. As shown in FIG. 5(b), when the slide member 66 is pressed by the cam follower 170, the inclined surfaces 66E, 66F come into contact with the pressed portion 55A and move the developer cartridge 60 forward. This causes the developer cartridge 60 to move to a non-development position where the developing roller 61 is separated from the photosensitive drum 50. A spring 67 is disposed between the first contact member 66B and the case 65. The spring 67 biases the slide member 66 leftward.

[0075] 4, the separation cam 150 is an end face cam. The separation cam 150 has a disk portion 151, a boss 152, and a cam portion 153. The boss 152 extends in the direction of the rotation axis from the center of the disk portion 151. The boss 152 has a cylindrical shape.

[0076] The image forming apparatus 1 further includes four shafts 159 and a metal plate 15 (see FIG. 3). The metal plate 15 is a member that rotatably supports the gears of each gear train. The shafts 159 are fixed to the metal plate 15. The separating cam 150 (cam gear 115) is rotatably supported by the metal plate 15 as a result of a boss 152 engaging with the shaft 159.

[0077] The cam portion 153 protrudes in the rotational axis direction from the disk portion 151. Specifically, the cam portion 153 protrudes toward one side in the rotational axis direction from the disk portion 151. The cam portion 153 protrudes in the rotational axis direction from the surface of the disk portion 151 opposite to the metal plate 15 (see FIG. 3) in the rotational axis direction.

[0078] As shown in FIG. 6, the cam portion 153 has a holding surface 153A and a guide surface 153B. The holding surface 153A is a surface that holds the cam follower 170 in the pressing position. The holding surface 153A is approximately parallel to a plane that is perpendicular to the rotation axis of the separating cam 150 (cam gear 115).

[0079] The guide surface 153B is a surface that guides the cam follower 170 between the pressing position and the non-pressing position. The guide surface 153B is inclined with respect to a plane perpendicular to the rotation axis of the separating cam 150 (cam gear 115). Specifically, the guide surface 153B is inclined in the rotation direction of the separating cam 150 so as to move away from the disk portion 151 as it moves toward the holding surface 153A.

[0080] As shown in FIG. 7, the guide surface 153B moves the cam follower 170 from the pressing position to the non-pressing position when the separating cam 150 rotates in a first rotation direction R1. The first rotation direction R1 is the rotation direction of the separating cam 150 when the main motor M1 rotates forward. Also, as shown in FIG. 6, the guide surface 153B moves the cam follower 170 from the non-pressing position to the pressing position when the separating cam 150 rotates in a second rotation direction R2. The second rotation direction R2 is the rotation direction of the separating cam 150 when the main motor M1 rotates reversely. The second rotation direction R2 is the rotation direction opposite to the first rotation direction R1.

[0081] The cam follower 170 includes a slide shaft 171 , an arm 172 , a pin 173 , and a rib 174 .

[0082] The slide shaft 171 is slidable in the direction of the rotation axis. Specifically, the slide shaft 171 has a cylindrical shape. The slide shaft 171 is engaged with the boss 152 of the separating cam 150, and is thereby slidable in the direction of the rotation axis relative to the boss 152. This allows the cam follower 170 to slide in the direction of the rotation axis between the non-pressing position shown in FIG. 6 and the pressing position shown in FIG. 7.

[0083] The arm 172 extends from the slide shaft 171 in a direction perpendicular to the rotation axis direction. Specifically, the arm 172 extends from the slide shaft 171 toward the outside in the radial direction of the slide shaft 171. The arm 172 is plate-shaped.

[0084] The pin 173 extends from the arm 172 in the direction of the rotation axis. Specifically, the pin 173 extends from the end of the arm 172 farthest from the slide shaft 171 toward one side in the direction of the rotation axis. The pin 173 is cylindrical, and its tip has a convex curved surface. The tip of the pin 173 presses the developer cartridge 60 when the cam follower 170 moves from the non-pressing position to the pressing position. Specifically, the tip of the pin 173 presses the pressed surface 66D (see FIG. 5(b)) of the slide member 66 provided on the developer cartridge 60.

[0085] The rib 174 extends from the slide shaft 171 in a direction perpendicular to the rotation axis direction. Specifically, the rib 174 extends from the slide shaft 171 toward the outside in the radial direction of the slide shaft 171. The rib 174 extends in a direction different from the direction in which the arm 172 extends. In this embodiment, the rib 174 extends forward from the slide shaft 171, and the arm 172 extends diagonally downward and rearward from the slide shaft 171.

[0086] The image forming apparatus 1 further includes stoppers 530. Four sets of stoppers 530 are provided corresponding to the four cam followers 170 (see FIG. 4). The stoppers 530 restrict the rotation of the cam followers 170 around the rotation axis of the separation cam 150 (cam gear 115). Specifically, as shown in FIGS. 8(a) and 8(b), the image forming apparatus 1 includes a gear cover 500, and the gear cover 500 has stoppers 530.

[0087] The gear cover 500 is fixed to the metal plate 15 (see FIG. 3 ) to cover the separating cam 150 (cam gear 115) and the cam follower 170. The gear cover 500 has a cover wall 510. The cover wall 510 is a wall that covers the separating cam 150 and the cam follower 170, and faces the metal plate 15 in the direction of the rotation axis when the gear cover 500 is fixed to the metal plate 15.

[0088] The stoppers 530 extend in the rotation axis direction from the cover wall 510 toward the corresponding separating cams 150. The stoppers 530 are wall-shaped. The stoppers 530 sandwich the arms 172 of the cam followers 170 from both sides in the circumferential direction of the slide shaft 171 (see FIGS. 6 and 7). This restricts the rotation of the cam followers 170 around the bosses 152.

[0089] The cover wall 510 further has four insertion holes 520. As shown in Fig. 9, the insertion holes 520 are through holes through which the pins 173 of the cam followers 170 are inserted.

[0090] The image forming apparatus 1 further includes springs 430. Four springs 430 are provided corresponding to the four cam followers 170. The springs 430 bias the cam followers 170 from the pressed position shown in FIG. 9(b) toward the non-pressed position shown in FIG. 9(a). As an example, the springs 430 are compression coil springs. The springs 430 are located between the gear cover 500 and the slide shafts 171 of the cam followers 170. Specifically, the springs 430 are located between the cover wall 510 and the slide shafts 171.

[0091] The slide shaft 171 has a recess 171A. The recess 171A is an annular recess that opens toward the cover wall 510 in the direction of the rotation axis. At least one end of the spring 430 is disposed within the recess 171A. By providing the recess 171A, it is possible to prevent the spring 430 from shifting out of position.

[0092] As shown in Figure 7, when the developing cartridge 60 is located in the non-developing position, i.e., when the developing roller 61 is located in the separated position, the cam follower 170 is located in a pressing position in which the arm 172 is held by the holding surface 153A of the separating cam 150.

[0093] When main motor M1 rotates forward, separating cam 150 rotates in first rotation direction R1. Then, arm 172 of cam follower 170 is guided from holding surface 153A to guide surface 153B, slides on guide surface 153B, and disengages from cam portion 153. As a result, cam follower 170 slides from the pressing position to the non-pressing position shown in FIG. 6 due to the biasing force of spring 430 (see FIG. 9).

[0094] As a result, the developer cartridge 60 moves from the non-development position to the development position, and the developer roller 61 moves from the separation position to the contact position. In this way, when the main motor M1 rotates forward, the separation cam 150 moves the developer roller 61 from the separation position to the contact position.

[0095] On the other hand, when the main motor M1 rotates in the reverse direction, the separating cam 150 rotates in the second rotation direction R2. As a result, the arm 172 of the cam follower 170 contacts the guide surface 153B of the cam portion 153, slides along the guide surface 153B, and then contacts the holding surface 153A. As a result, the cam follower 170 slides from the non-pressing position to the pressing position shown in FIG. 7.

[0096] As a result, the developer cartridge 60 is pressed by the cam follower 170 to move from the developing position to the non-developing position, and the developer roller 61 moves from the contact position to the separated position. In this way, when the main motor M1 rotates in the reverse direction, the separating cam 150 moves the developer roller 61 from the contact position to the separated position.

[0097] As shown in FIG. 10, the development separation gear train GT1 includes a first separation gear train GT11 and a second separation gear train GT12. The first separation gear train GT11 is a gear train that transmits the driving force of the main motor M1 to the separation cams 150Y, 150M, and 150C.

[0098] The first spaced gear train GT11 includes gear 101, gear 102, gear 103, gear 104, gear 105, gear 106, gear 107, gear 108, gear 109, an electromagnetic clutch EC1 as a second electromagnetic clutch, gear 110, gear 111, gear 112, gear 113, gear 114, cam gear 115C, gear 116, cam gear 115M, idle gear 118, and cam gear 115Y.

[0099] The gear 101 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the motor gear MG1. The motor gear MG1 is a gear provided on the output shaft of the main motor M1. In other words, the image forming apparatus 1 includes the motor gear MG1. The motor gear MG1 meshes with the large diameter gear of the gear 101. The gear 101 is an example of one gear included in the development separation gear train GT1.

[0100] The gear 102 is in mesh with the small diameter gear of the gear 101. Gear 103 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with gear 102. The gear 104 is in mesh with the small diameter gear of the gear 103 .

[0101] Gear 105 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with gear 104. The gear 106 is in mesh with the small diameter gear of the gear 105 . The gear 107 is in mesh with the gear 106 . The gear 108 is in mesh with the gear 107 . The gear 109 is in mesh with the gear 108 .

[0102] The electromagnetic clutch EC1 can be switched between a transmission state and a disconnection state. As an example, the electromagnetic clutch EC1 is in the transmission state when energized and in the disconnection state when not energized. The transmission state is a state in which the driving force from the main motor M1 is transmitted to the separation cams 150Y, 150M, and 150C. The disconnection state is a state in which the driving force from the main motor M1 is not transmitted to the separation cams 150Y, 150M, and 150C. The electromagnetic clutch EC1 is controlled by the control unit 2 (see FIG. 1).

[0103] When the electromagnetic clutch EC1 is in a transmission state, the gear 110 rotates integrally with the gear 109. When the electromagnetic clutch EC1 is in a disengaged state, the gear 110 does not drive because no driving force is transmitted from the main motor M1. The gear 111 is in mesh with the gear 110 .

[0104] Gear 112 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with gear 111. Gear 113 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the small diameter gear of gear 112. Gear 114 meshes with the small diameter gear of gear 113.

[0105] The cam gear 115C is a gear having a separating cam 150C. In other words, the separating cam 150C has gear teeth on the outer periphery of the disk portion 151. The cam gear 115C is in mesh with the gear 114. The gear 116 meshes with the cam gear 115C.

[0106] The cam gear 115M is a gear having a separating cam 150M. In other words, the separating cam 150M has gear teeth on the outer periphery of the disc portion 151. The cam gear 115M meshes with the gear 116. The cam gear 115M receives the driving force of the main motor M1 from the cam gear 115C via the gear 116.

[0107] The idle gear 118 has a first gear portion 118B as a gear portion. The first gear portion 118B of the idle gear 118 is in mesh with the cam gear 115M.

[0108] The cam gear 115Y is a gear having a separating cam 150Y. In other words, the separating cam 150Y has gear teeth on the outer periphery of the disc portion 151. The cam gear 115Y meshes with the first gear portion 118B of the idle gear 118. The first gear portion 118B of the idle gear 118 meshes with both the cam gear 115Y and the cam gear 115M.

[0109] The separating cams 150Y, 150M, and 150C rotate in conjunction with each other. The length of the holding surface 153A of the separating cams 150Y, 150M, and 150C in the rotation direction of the separating cam 150 increases in the order of separating cam 150Y, separating cam 150M, and separating cam 150C. The phases of the downstream ends of the holding surfaces 153A of the separating cams 150Y, 150M, and 150C in the first rotation direction R1 are aligned, but the phases of the guide surfaces 153B are shifted. Specifically, the guide surface 153B of the separating cam 150Y is located downstream of the guide surface 153B of the separating cam 150M in the first rotation direction R1, and the guide surface 153B of the separating cam 150M is located downstream of the guide surface 153B of the separating cam 150C in the first rotation direction R1.

[0110] As a result, when the main motor M1 rotates forward from a state in which the cam followers 170Y, 170M, and 170C are in the pressing position and the separating cams 150Y, 150M, and 150C rotate in the first rotation direction R1, first, the cam follower 170Y moves from the pressing position to the non-pressing position, causing the developing roller 61Y to move from the separating position to the contact position. Next, the cam follower 170M moves from the pressing position to the non-pressing position, causing the developing roller 61M to move from the separating position to the contact position. Finally, the cam follower 170C moves from the pressing position to the non-pressing position, causing the developing roller 61C to move from the separating position to the contact position.

[0111] On the other hand, when the main motor M1 rotates in the reverse direction from a state in which the cam followers 170Y, 170M, and 170C are in the non-pressing position, causing the separation cams 150Y, 150M, and 150C to rotate in the second rotation direction R2, first, the cam follower 170C moves from the non-pressing position to the pressing position, causing the developing roller 61C to move from the contact position to the separation position. Next, the cam follower 170M moves from the non-pressing position to the pressing position, causing the developing roller 61M to move from the contact position to the separation position. Finally, the cam follower 170Y moves from the non-pressing position to the pressing position, causing the developing roller 61Y to move from the contact position to the separation position.

[0112] As shown in FIGS. 11(a) and 11(b), the idle gear 118 has a disk portion 118A, a first gear portion 118B, a second gear portion 118C, a first rib 118D, and a second rib 118E. The first gear portion 118B is formed on the outer periphery of a cylindrical portion that protrudes from the disk portion 118A toward one side in the direction of the rotation axis.

[0113] The second gear portion 118C is formed on the outer periphery of the second rib 118E. The diameter of the pitch circle of the second gear portion 118C is larger than the diameter of the pitch circle of the first gear portion 118B. The second gear portion 118C outputs a driving force toward a switching cam 190 (see FIG. 19) described later.

[0114] The first rib 118D is an annular rib that protrudes from the disk portion 118A toward one side in the direction of the rotation axis, and the second rib 118E is an annular rib that protrudes from the disk portion 118A toward the other side in the direction of the rotation axis.

[0115] 12, the first rib 118D protrudes toward the metal plate 15 in the direction of the rotation axis of the idle gear 118. The first rib 118D is located at the end of the idle gear 118 in a direction perpendicular to the rotation axis. Specifically, the first rib 118D is located at the outer end of the disk portion 118A in the radial direction. The first rib 118D comes into contact with the metal plate 15 due to the pressing force of the rotation resistance member 300, which will be described later.

[0116] The second rib 118E protrudes in a direction away from the metal plate 15 in the direction of the rotation axis of the idle gear 118. The tip of the second rib 118E protrudes in a direction away from the metal plate 15 further than the second gear portion 118C in the direction of the rotation axis of the idle gear 118. The inner diameter of the second rib 118E is smaller than the inner diameter of the first rib 118D. The inner diameter of the second rib 118E is larger than the diameter of the pitch circle of the first gear portion 118B.

[0117] The idle gear 118 is rotatable relative to the metal plate 15. Specifically, the gear cover 500 has a shaft portion 540. The shaft portion 540 protrudes from the cover wall 510 toward the other side in the rotational axis direction.

[0118] The idle gear 118 is engaged with the shaft portion 540, and is thereby rotatably supported by the gear cover 500. Then, the gear cover 500 is fixed to the metal plate 15, and the idle gear 118 is rotatable relative to the metal plate 15. In other words, the metal plate 15 rotatably supports the idle gear 118 via the gear cover 500.

[0119] The first gear portion 118B and the cam gears 115Y, 115M (see FIG. 3) that mesh with the first gear portion 118B are disposed on one side of the metal plate 15 in the direction of the rotation axis of the idle gear 118. The second gear portion 118C is disposed on the other side of the metal plate 15 in the direction of the rotation axis of the idle gear 118. The first rib 118D is disposed on the other side of the metal plate 15 in the direction of the rotation axis of the idle gear 118. Similarly, the second rib 118E is disposed on the other side of the metal plate 15 in the direction of the rotation axis of the idle gear 118.

[0120] 12, the first gear portion 118B and the cam gears 115Y and 115M are disposed on the right side of the metal plate 15. The second gear portion 118C, the first rib 118D, and the second rib 118E are disposed on the left side of the metal plate 15.

[0121] As shown in FIG. 11, the image forming apparatus 1 further includes a rotation resistance member 300. The rotation resistance member 300 is a member that applies rotation resistance to the idle gear 118. Specifically, the rotation resistance member 300 applies rotation resistance to the idle gear 118 by pressing the idle gear 118 in the direction of the rotation axis of the idle gear 118.

[0122] The rotation resistance member 300 is a spring. Specifically, the rotation resistance member 300 is a leaf spring made of a metal plate. The rotation resistance member 300 has a base portion 310 and four pressing portions 320.

[0123] The base portion 310 is a portion that is fixed to the shaft portion 540 of the gear cover 500 by the screw SC. The base portion 310 has a through hole 311 in the center. The through hole 311 is a hole through which the shank of the screw SC passes. The shaft portion 540 has a hole 541 into which the screw SC is screwed.

[0124] 13, the pressing portions 320 are portions that press the idle gear 118. The pressing portions 320 extend from the base portion 310. The four pressing portions 320 are arranged symmetrically with respect to the rotation axis of the idle gear 118. Specifically, the four pressing portions 320 are shifted in phase by 90 degrees in the rotation direction of the idle gear 118.

[0125] 12, the rotation resistance member 300 is disposed on the other side of the metal plate 15 in the direction of the rotation axis of the idle gear 118. When the rotation resistance member 300 is fixed to the shaft portion 540, the four pressing portions 320 come into contact with the idle gear 118 and press the idle gear 118 from the other side toward one side in the direction of the rotation axis of the idle gear 118.

[0126] Specifically, the four pressing portions 320 of the rotation resistance member 300 contact the second rib 118E of the idle gear 118 and press the second rib 118E from the other side to one side in the direction of the rotation axis of the idle gear 118. As a result, the first rib 118D of the idle gear 118 is pressed against the metal plate 15.

[0127] Since the inner diameter of the second rib 118E is larger than the diameter of the pitch circle of the first gear portion 118B, the pressing portion 320 presses the idle gear 118 at a position radially outward from the pitch circle of the first gear portion 118B.

[0128] 13, each pressing portion 320 has a contact portion 321. The contact portion 321 is a portion that convex toward one side in the direction of the rotation axis of the idle gear 118, and has a cross-sectional shape that is curved like an arc. The pressing portion 320 contacts the second rib 118E at a ridge portion (see the two-dot chain line) of the contact portion 321. The ridge portion of the contact portion 321 extends in the direction in which the pressing portion 320 extends from the base portion 310 so as to intersect with the second rib 118E.

[0129] By contacting the second rib 118E at such contact portion 321, the pressing portion 320 can come into uniform contact with the second rib 118E even if the position of the rotation resistance member 300 is slightly shifted in the direction perpendicular to the rotation axis of the idle gear 118. This allows a uniform load to be applied to the idle gear 118.

[0130] The rotation of the rotation resistance member 300 around the rotation axis of the idle gear 118 is restricted by a stopper provided on a cover that covers the rotation resistance member 300 .

[0131] 10, the second separating gear train GT12 is a gear train that receives the driving force of the main motor M1 from the first separating gear train GT11 and transmits it to the separating cam 150K. The second separating gear train GT12 includes a gear 121, an electromagnetic clutch EC2 as a second electromagnetic clutch, a gear 122, a gear 123, a gear 124, and a cam gear 115K. The gear 121 is in mesh with the gear 106 of the first spaced gear train GT11.

[0132] The electromagnetic clutch EC2 can be switched between a transmission state and a disconnection state. As an example, the electromagnetic clutch EC2 is in the transmission state when energized and in the disconnection state when not energized. The transmission state is a state in which the driving force from the main motor M1 is transmitted to the separation cam 150K. The disconnection state is a state in which the driving force from the main motor M1 is not transmitted to the separation cam 150K. The electromagnetic clutch EC2 is controlled by the control unit 2 (see FIG. 1).

[0133] When the electromagnetic clutch EC2 is in a transmission state, the gear 122 rotates integrally with the gear 121. When the electromagnetic clutch EC2 is in a disengaged state, the gear 122 does not drive because no driving force is transmitted from the main motor M1. The gear 123 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the gear 122.

[0134] Gear 124 meshes with the small diameter gear of gear 123. The cam gear 115K is a gear having a separating cam 150K. In other words, the separating cam 150K has gear teeth on the outer periphery of the disk portion 151. The cam gear 115K is in mesh with the gear 124.

[0135] As shown in FIG. 14, the fixing drive gear train GT2 includes a moving gear 131 and an output gear 132 as a first gear. The movable gear 131 is a gear that receives driving force from the main motor M1. The movable gear 131 is always in mesh with the large-diameter gear of the gear 103 of the first spaced gear train GT11. The movable gear 131 is movable relative to the output gear 132 between a transmission position indicated by a solid line and a non-transmission position indicated by a virtual line. Specifically, the movable gear 131 is oscillating around the gear 103 between the transmission position and the non-transmission position.

[0136] The transmission position is a position where the movable gear 131 meshes with the output gear 132 to transmit driving force to the output gear 132. The non-transmission position is a position where the movable gear 131 is separated from the output gear 132 to not transmit driving force to the output gear 132. The movable gear 131 moves to the transmission position when the main motor M1 rotates forward, and moves to the non-transmission position when the main motor M1 rotates reverse.

[0137] The output gear 132 is a gear that outputs a driving force toward the fixing device 80. Specifically, the output gear 132 outputs a driving force toward the heating roller 81A. The output gear 132 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the movable gear 131 that is positioned at the transmission position.

[0138] 15, the heating roller 81A has a heating roller gear 81G fixed to one end, and the small diameter gear of the output gear 132 is in mesh with the heating roller gear 81G. The pressure unit 82 (pressure roller) of the fixing device 80 is rotated by the rotation of the heating roller 81A.

[0139] The first discharge roller 83 and the second discharge roller 91 receive the driving force of the main motor M1 from the fixing drive gear train GT2. The first discharge roller 83 has a first discharge roller gear 83G fixed to one end of one of the rollers. The second discharge roller 91 has a second discharge roller gear 91G fixed to one end of one of the rollers.

[0140] The image forming apparatus 1 further includes a gear 133 and a discharge drive gear train GT21. The gear 133 meshes with the heating roller gear 81G, and the first discharge roller 83 meshes with the gear 133. As a result, the first discharge roller 83 rotates when it receives the driving force of the main motor M1 from the output gear 132 of the fixing drive gear train GT2 via the heating roller gear 81G and the gear 133.

[0141] The discharge drive gear train GT21 includes a gear 134A, a gear 134B, a gear 134C, a gear 134D, a gear 134E, a gear 134F, and a gear 134G. The gear 134A is in mesh with the small diameter gear of the output gear 132. Gear 134B meshes with gear 134A.

[0142] Gear 134C meshes with gear 134B. Gear 134D meshes with gear 134C. Gear 134E is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with gear 134D.

[0143] Gear 134F is a two-stage gear having a large diameter gear and a small diameter gear, and the small diameter gear meshes with the small diameter gear of gear 134E. Gear 134G meshes with the small diameter gear of gear 134F.

[0144] The second discharge roller gear 91G is in mesh with the gear 134G, so that the second discharge roller 91 rotates when it receives the driving force of the main motor M1 from the output gear 132 of the fixing drive gear train GT2 via the discharge drive gear train GT21.

[0145] 16, nip pressure adjustment mechanism 200 is a mechanism that switches the nip pressure between heating unit 81 and pressure unit 82 by receiving driving force from main motor M1. Specifically, nip pressure adjustment mechanism 200 switches the nip pressure between heating roller 81A and pressure unit 82 between a small nip pressure shown in FIG. 16(a) and a large nip pressure shown in FIG. 16(b). Here, the small nip pressure corresponds to the second nip pressure, and the large nip pressure corresponds to the first nip pressure.

[0146] The small nip pressure is a nip pressure that is smaller than the large nip pressure. In this embodiment, the small nip pressure is the nip pressure in a standby state before printing is performed, and the large nip pressure is the nip pressure when printing is performed. In this embodiment, the heating unit 81 and the pressure unit 82 are in contact even when the small nip pressure is applied.

[0147] The nip pressure adjusting mechanism 200 is provided in the fixing device 80. The fixing device 80 further includes a fixing frame 84 and the nip pressure adjusting mechanism 200. The fixing frame 84 supports the heating unit 81. Specifically, the fixing frame 84 rotatably supports the heating roller 81A. The fixing frame 84 has a shaft portion 84A and a spring engagement portion 84B on both sides in the direction of the rotation axis.

[0148] Nip pressure adjustment mechanism 200 includes arm 210, spring 220, and nip pressure adjustment cam 230, which is an example of a first cam. Arm 210, spring 220, and nip pressure adjustment cam 230 are provided on both sides of pressure unit 82 in the direction of the rotation axis.

[0149] The arm 210 rotatably supports the pressure applying unit 82 (pressure roller). The arm 210 has a first end 211, a second end 212, and a cam contact portion 213. The arm 210 is rotatably supported by the fixing frame 84 with the first end 211 engaged with the shaft portion 84A of the fixing frame 84. The cam contact portion 213 extends toward the nip pressure adjusting cam 230 at a position between the first end 211 and the second end 212.

[0150] The spring 220 biases the pressure applying unit 82 toward the heating unit 81. As an example, the spring 220 is a tension coil spring. One end of the spring 220 engages with the spring engaging unit 84B of the fixing frame 84, and the other end of the spring 220 engages with the second end 212 of the arm 210.

[0151] Nip pressure adjustment cam 230 receives driving force from main motor M1 to switch the nip pressure between heating unit 81 and pressure unit 82 between a small nip pressure and a large nip pressure. Nip pressure adjustment cam 230 receives driving force from main motor M1 to switch the nip pressure between heating roller 81A and pressure unit 82 (pressure roller) between the small nip pressure shown in FIG. 16(a) and the large nip pressure shown in FIG. 16(b).

[0152] The nip pressure adjusting cam 230 is rotatably supported by the fixing frame 84. Specifically, the nip pressure adjusting cam 230 is rotatable around an axis parallel to the rotation axis of the heating roller 81A. The nip pressure adjusting cam 230 is rotatable between a first position shown in FIG. 16(b) and a second position shown in FIG. 16(a). The nip pressure adjusting cam 230 is a plate cam. Specifically, the nip pressure adjusting cam 230 has a first portion 231 and a second portion 232 on its outer circumferential surface.

[0153] The first portion 231 is a portion that comes into contact with the cam contact portion 213 of the arm 210 when the nip pressure adjusting cam 230 is in the second position shown in Figure 16(a). When the nip pressure adjusting cam 230 is in the second position, the nip pressure between the heating unit 81 and the pressure applying unit 82 becomes a small nip pressure.

[0154] The second portion 232 is a portion that faces the cam contact portion 213 when the nip pressure adjustment cam 230 is in the first position shown in Figure 16(b). When the nip pressure adjustment cam 230 is in the first position, the second portion 232 is separated from the cam contact portion 213. When the nip pressure adjustment cam 230 is in the first position, the nip pressure between the heating portion 81 and the pressure applying portion 82 becomes a large nip pressure.

[0155] In nip pressure adjustment mechanism 200, nip pressure adjustment cam 230 rotates in third rotation direction R3 shown in Figure 16(a) and rotates approximately 270 degrees from the second position to the first position shown in Figure 16(b), thereby switching the nip pressure of heating unit 81 and pressure unit 82 from small nip pressure to large nip pressure. Third rotation direction R3 is the rotation direction of nip pressure adjustment cam 230 when main motor M1 rotates forward.

[0156] In addition, nip pressure adjustment mechanism 200 switches the nip pressure of heating unit 81 and pressure unit 82 from large nip pressure to small nip pressure by rotating nip pressure adjustment cam 230 in a fourth rotation direction R4 shown in Figure 16(b) from the first position to the second position shown in Figure 16(a). Fourth rotation direction R4 is the rotation direction of nip pressure adjustment cam 230 when main motor M1 rotates in the reverse direction. Fourth rotation direction R4 is the rotation direction opposite to third rotation direction R3.

[0157] The image forming apparatus 1 further includes a sensor SS. The sensor SS is a sensor that detects that the nip pressure adjusting cam 230 is in the second position. The sensor SS is, for example, a photointerrupter similar to sensors 4K and 4C described later, and has a light emitting portion and a light receiving portion.

[0158] The nip pressure adjusting cam 230 has a protrusion 235. When the nip pressure adjusting cam 230 is located at the second position, the protrusion 235 blocks light from the light emitting portion of the sensor SS. When the nip pressure adjusting cam 230 is located at the first position, the protrusion 235 is away from the light from the light emitting portion, and the light from the light emitting portion is received by the light receiving portion. Note that the sensor SS may detect that the nip pressure adjusting cam 230 is located at the first position.

[0159] As shown in FIG. 14, the nip pressure adjusting gear train GT3 includes an electromagnetic clutch EC3 as an example of a switching mechanism, a clutch connecting gear 135, a gear 136, and a gear 137.

[0160] The electromagnetic clutch EC3 can be switched between a transmission state and a disconnection state. As an example, the electromagnetic clutch EC3 is in the transmission state when energized and in the disconnection state when de-energized. The transmission state is a state in which the driving force of the main motor M1 is transmitted from the developer separation gear train GT1 to the nip pressure adjustment gear train GT3. In other words, the transmission state is a state in which the driving force from the main motor M1 is transmitted to the nip pressure adjustment cam 230. The disconnection state is a state in which the driving force of the main motor M1 is not transmitted from the developer separation gear train GT1 to the nip pressure adjustment gear train GT3. In other words, the disconnection state is a state in which the driving force from the main motor M1 is not transmitted to the nip pressure adjustment cam 230. The electromagnetic clutch EC3 is controlled by the control unit 2 (see FIG. 1).

[0161] When the electromagnetic clutch EC3 is in a transmission state, the clutch connection gear 135 rotates integrally with the gear 104 of the developer separation gear train GT1. The clutch connection gear 135 rotates coaxially with the gear 104. The gear 104 is an example of one of the gears in the developer separation gear train GT1. When the electromagnetic clutch EC3 is in a disengaged state, no driving force is transmitted from the main motor M1 to the clutch connection gear 135, and therefore the clutch connection gear 135 does not drive.

[0162] The gear 136 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear is in mesh with the clutch connecting gear 135. Gear 137 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the small diameter gear of gear 136. Nip pressure adjustment cam 230 (see FIG. 16) of nip pressure adjustment mechanism 200 receives the driving force of main motor M1 from the small diameter gear of gear 137 and rotates.

[0163] As shown in FIG. 17, the sheet supply gear train GT4 includes a gear 141, a gear 142, a gear 143, a gear 144, a gear 145, a gear 146, a second moving gear 147, and a second output gear 148 as a second gear. The gear 141 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the motor gear MG1. In other words, the motor gear MG1 meshes with the large diameter gear of the gear 141. The gear 141 is an example of one gear included in the sheet supply gear train GT4.

[0164] Gear 142 is a two-stage gear having a large diameter gear and a small diameter gear, and the large diameter gear meshes with the small diameter gear of gear 141. The gear 143 is in mesh with the small diameter gear of the gear 142 . The gear 144 meshes with the gear 143 .

[0165] The gear 145 meshes with the gear 144 . Gear 146 is a two-stage gear having a large diameter gear and a small diameter gear, and the small diameter gear meshes with gear 145.

[0166] The second movable gear 147 is movable between a second transmitting position indicated by a solid line and a second non-transmitting position indicated by a virtual line. The second transmitting position is a position where the second movable gear 147 meshes with the second output gear 148 to transmit driving force to the second output gear 148. The second non-transmitting position is a position where the second movable gear 147 does not transmit driving force to the second output gear 148 because the second movable gear 147 is separated from the second output gear 148. The second moving gear 147 is always in mesh with the large diameter gear of the gear 146 .

[0167] The second moving gear 147 moves to the second transmitting position when the main motor M1 rotates forward, and moves to the second non-transmitting position when the main motor M1 rotates backward.

[0168] The second output gear 148 outputs a driving force toward the sheet supply mechanism 22. The sheet supply mechanism 22 receives the driving force from the main motor M1 and supplies the sheet S toward the image forming unit 30.

[0169] The control unit 2 (see FIG. 1) includes a CPU, ROM, RAM, and input / output circuits, and performs control by executing pre-stored programs. The control unit 2 controls the driving and stopping of the main motor M1 and the rotation direction of the output shaft of the main motor M1. The control unit 2 also controls the driving and stopping of the process motor M2. The control unit 2 also controls the electromagnetic clutches EC1 to EC3.

[0170] As a result, the control unit 2 controls the contact and separation of the developing roller 61 with respect to the photosensitive drum 50. The control unit 2 also controls the driving and stopping of the photosensitive drum 50, the cleaning roller 56, the developing roller 61, and the heating roller 81A. The control unit 2 also controls the nip pressure of the heating unit 81 and the pressure unit 82 of the fixing unit 80.

[0171] The control unit 2 is capable of executing a color printing mode as a first printing mode and a monochrome printing mode as a second printing mode. The color printing mode is a printing mode in which an image is formed on the sheet S using the developing rollers 61Y, 61M, 61C, and 61K.

[0172] In the image forming apparatus 1, all of the developing rollers 61 are positioned at the separated positions in a standby state before printing is performed. The color printing mode is a printing mode in which all of the developing rollers 61 (61Y, 61M, 61C, 61K) are moved from the separated positions to the contact positions to form an image on the sheet S.

[0173] The monochrome printing mode is a printing mode in which only the developing roller 61K is used to form an image on the sheet S. Specifically, the monochrome printing mode is a printing mode in which only the developing roller 61K is moved from the separated position to the contact position to form an image on the sheet S.

[0174] 2, image forming apparatus 1 further includes sensors 4K and 4C. Sensor 4K is a sensor that detects the position of cam follower 170K. Sensor 4C is a sensor that detects the positions of cam followers 170Y, 170M, and 170C. Sensor 4C directly detects the position of cam follower 170C, and indirectly detects the positions of cam followers 170Y and 170M.

[0175] The sensors 4K and 4C have a light-emitting unit 4P and a light-receiving unit 4R. The light-emitting unit 4P emits detection light, and the light-receiving unit 4R can receive the detection light from the light-emitting unit 4P. The sensors 4K and 4C are positioned inside the gear cover 500, with the light-emitting unit 4P and the light-receiving unit 4R passing through a through-hole 550 (see FIG. 8) in the gear cover 500.

[0176] When cam follower 170K is in the pressed position, rib 174 fits between light-emitting portion 4P and light-receiving portion 4R, and when cam follower 170K is in the non-pressed position, rib 174 is positioned so as to be out of the gap between light-emitting portion 4P and light-receiving portion 4R. Similarly, when cam follower 170C is in the pressed position, rib 174 fits between light-emitting portion 4P and light-receiving portion 4R, and when cam follower 170C is in the non-pressed position, rib 174 is positioned so as to be out of the gap between light-emitting portion 4P and light-receiving portion 4R.

[0177] As a result, when cam follower 170 is in the pressed position, sensors 4K and 4C cannot receive the detection light from light-emitting unit 4P at light-receiving unit 4R because the detection light is blocked by rib 174. On the other hand, when cam follower 170 is in the non-pressed position, sensors 4K and 4C can receive the detection light from light-emitting unit 4P at light-receiving unit 4R. Sensors 4K and 4C detect whether cam follower 170 is in the pressed position or the non-pressed position based on a change in the state of receiving the detection light.

[0178] When the cam follower 170 is in the pressing position, the corresponding developing roller 61 is in the separating position, and when the cam follower 170 is in the non-pressing position, the corresponding developing roller 61 is in the contact position. Therefore, the sensors 4K and 4C can detect via the cam follower 170 whether the developing roller 61 is in the separating position or the contact position.

[0179] Rib 174 of cam follower 170K can be detected by sensor 4K, and rib 174 of cam follower 170C can be detected by sensor 4C. In this embodiment, the four cam followers 170 are common parts and all have ribs 174, but ribs 174 of cam followers 170Y and 170M do not function as parts detected by sensors 4K and 4C.

[0180] The control unit 2 is capable of executing a first process, a second process, and a connection process. The first process is a process in which the nip pressure is set to the first nip pressure by rotating the main motor M1 in the forward direction and by placing the electromagnetic clutch EC3 in a transmission state.

[0181] The second process is a process in which the nip pressure is set to the second nip pressure by rotating the main motor M1 in the reverse direction and by placing the electromagnetic clutch EC3 in a transmission state. The connection process is a process in which the main motor M1 is rotated forward while the electromagnetic clutch EC3 is in the disconnected state, and the movable gear 131 is moved from the non-transmission position to the transmission position. After the connection process, the control unit 2 stops the main motor M1.

[0182] By performing the connection process after executing the second process, the control unit 2 waits for a print command with the movable gear 131 meshed with the first gear 132. In other words, the control unit 2 keeps the movable gear 131 meshed with the output gear 132 in the state before receiving a print command. Note that even if the image forming apparatus 1 is powered off or goes into a sleep state after the connection process without the control unit 2 receiving a print command, the movable gear 131 remains in the transmission position and remains meshed with the output gear 132. As shown in FIG. 18, the drive time TD1 of the main motor M1 in the connection process is set to a time shorter than the drive time TD2 of the main motor M1 in the second process.

[0183] For example, the driving time TD1 of the main motor M1 in the connection process can be the time it takes for the moving gear 131 to move from the non-transmitting position to the transmitting position.

[0184] The control unit 2 is capable of driving the process motor M2 to execute a cleaning process for cleaning the photosensitive drum 50. In the cleaning process, the control unit 2 transfers the toner on the photosensitive drum 50 to the conveyor belt 73, and collects it in the waste toner box TB shown in FIG. 1. At this time, the toner on the photosensitive drum 50 may be collected by the cleaning roller 56, or the toner on the cleaning roller 56 may be transferred to the conveyor belt 73 via the photosensitive drum 50. After the second process (after time t41), the control unit 2 executes the cleaning process (time t43), and after the cleaning process, executes the connection process (time t45).

[0185] The control unit 2 is capable of executing a pressure contact process and a separation process. The pressure contact process is a process in which the main motor M1 is rotated forward and at least one of the electromagnetic clutches EC1 and EC2 is connected, thereby moving the developing roller 61 to the contact position.

[0186] The separation process is a process in which the main motor M1 is rotated in the reverse direction and at least one of the electromagnetic clutches EC1 and EC2 is connected, thereby moving the developing roller 61 to the separation position. After the separation process (time t36), the control unit 2 executes the second process (time t38).

[0187] When printing in monochrome printing mode, the control unit 2 controls only the electromagnetic clutch EC2 to perform the pressing process and separation process on only the developing roller 61K. When printing in color printing mode, the control unit 2 controls both the electromagnetic clutches EC1 and EC2 to perform the pressing process and separation process on the developing rollers 61 of each color.

[0188] Next, an example of the operation of the control unit 2 when printing is performed will be described. In the following, putting the electromagnetic clutches EC1 to EC3 into a transmission state will be referred to as "ON," and putting the electromagnetic clutches EC1 to EC3 into a disengaged state will be referred to as "OFF."

[0189] First, the operation of the control unit 2 when printing is performed in color printing mode will be described with reference to a timing chart. 18, in the image forming apparatus 1, all of the developing rollers 61 are positioned at the separated position in the standby state (time t0). Also, in the image forming apparatus 1, the nip pressure between the heating unit 81 and the pressure unit 82 is set to a small nip pressure in the standby state. Furthermore, in the image forming apparatus 1, a connection process, which will be described later, is executed immediately before printing is completed, so that in the standby state, the movable gear 131 and the second movable gear 147 are positioned at the transmission position.

[0190] When printing is performed in color printing mode, the control unit 2 drives the main motor M1 in the forward direction (time t1). At this time, the movable gear 131 and the second movable gear 147 are already in the transmission position, so the driving force of the main motor M1 is immediately transmitted to the heating roller 81A and the sheet supply mechanism 22 without generating abnormal noise due to a collision between the movable gear 131 and the output gear 132 or between the second movable gear 147 and the second output gear 148.

[0191] This rotates the heating roller 81A and the rollers of the sheet supply mechanism 22. Furthermore, a driving force is transmitted from the main motor M1 to the first discharge roller 83 and the second discharge roller 91, causing the first discharge roller 83 and the second discharge roller 91 to rotate.

[0192] Next, the control unit 2 drives the process motor M2 (time t2), whereby the driving force is transmitted from the process motor M2 to the photosensitive drum 50 and the cleaning roller 56, causing the photosensitive drum 50 to rotate.

[0193] Next, control unit 2 turns on electromagnetic clutch EC3 (time t3). As a result, driving force is transmitted from main motor M1 to nip pressure adjustment cam 230 of nip pressure adjustment mechanism 200, causing nip pressure adjustment cam 230 to rotate in third rotation direction R3 and move from the second position to the first position. As a result, the nip pressure of heating unit 81 and pressure unit 82 switches from the small nip pressure to the large nip pressure (times t4 to t5).

[0194] When the nip pressure of heating unit 81 and pressure unit 82 is switched to the large nip pressure, control unit 2 turns off electromagnetic clutch EC3 (time t6).

[0195] Thereafter, the control unit 2 turns on the electromagnetic clutch EC1 (time t7), whereby the driving force is transmitted from the main motor M1 to the separating cams 150Y, 150M, and 150C, causing the separating cams 150Y, 150M, and 150C to rotate in the first rotation direction R1.

[0196] After time t7, the driving force is transmitted from the process motor M2 to the developing rollers 61Y, 61M, and 61C, causing the developing rollers 61Y, 61M, and 61C to rotate (time t8). The driving force from the process motor M2 to the developing rollers 61Y, 61M, and 61C is transmitted or cut off by a driving force switching mechanism (not shown).

[0197] The driving force switching mechanism includes, for example, a third output gear, a third movable gear that moves between a transmission position and a non-transmission position, and a switching cam that switches the position of the third movable gear. The transmission position is a position where the third movable gear meshes with the third output gear. The non-transmission position is a position where the third movable gear is separated from the third output gear.

[0198] The switching cam can rotate between a first phase and a second phase. The first phase is a phase that positions the third movable gear in a non-transmitting position, and the second phase is a phase that positions the third movable gear in a transmitting position. The driving force of the main motor M1 is transmitted to the switching cam via the electromagnetic clutch EC1. The switching cam moves to the second phase when the main motor M1 rotates forward, and moves to the first phase when the main motor M1 rotates reversely. The driving force switching mechanism may be an electromagnetic clutch.

[0199] After time t8, the developing roller 61Y is moved from the separated position to the contact position by the separating cam 150Y rotating in the first rotation direction R1 (times t9 to t10). Next, the developing roller 61M is moved from the separated position to the contact position by the separating cam 150M rotating in the first rotation direction R1 (times t11 to t12). Next, the developing roller 61C is moved from the separated position to the contact position by the separating cam 150C rotating in the first rotation direction R1 (times t13 to t14).

[0200] When a predetermined time has elapsed since the sensor 4C detected that the developing rollers 61Y, 61M, 61C were positioned at the contact position, the control unit 2 turns off the electromagnetic clutch EC1 (time t15).

[0201] Furthermore, the control unit 2 turns on the electromagnetic clutch EC2 at the timing when the developing roller 61C moves from the separation position to the contact position and then the developing roller 61K moves from the separation position to the contact position (time t16). As a result, the driving force is transmitted from the main motor M1 to the separating cam 150K, and the separating cam 150K rotates in the first rotation direction R1.

[0202] After time t16, the driving force is transmitted from the process motor M2 to the developing roller 61K, causing the developing roller 61K to rotate (time t17). The driving force from the process motor M2 to the developing roller 61K is transmitted or cut off by a second driving force switching mechanism CM shown in FIG.

[0203] The second driving force switching mechanism CM has a planetary gear mechanism 180 and a switching lever 160. The driving force of the process motor M2 is transmitted via the planetary gear mechanism 180 to the developing roller 61K. The switching lever 160 can swing between a transmitting position and a non-transmitting position in response to the rotation of the separating cam 150 K. The separating cam 150 K has a protrusion 154 that engages with the switching lever 160 .

[0204] The planetary gear mechanism 180 has an input element, an output element, and a transmission element 181 . The input element receives the driving force of the process motor M2. The output element B outputs a driving force toward the developing roller 61K.

[0205] The transfer element 181 is capable of transferring a driving force from the input element to the output element when rotation is restricted, and does not transfer a driving force from the input element to the output element when rotation is not restricted.

[0206] When the switching lever 160 is in the transmission position, it engages with the transmission element 181 to restrict the rotation of the transmission element 181. As a result, the driving force of the process motor M2 input to the planetary gear mechanism 180 is transmitted to the developing roller 61K.

[0207] When the switching lever 160 is in the non-transmission position, it disengages from the transmission element 181 and does not restrict the rotation of the transmission element 181. As a result, the driving force of the process motor M2 input to the planetary gear mechanism 180 is not transmitted to the developing roller 61K. The second driving force switching mechanism may be an electromagnetic clutch.

[0208] Next, at a timing after time t14 when the developing roller 61C moves from the separation position to the contact position, the separating cam 150K rotating in the first rotation direction R1 moves the developing roller 61K from the separation position to the contact position (times t18 to t19).

[0209] When a predetermined time has elapsed since the sensor 4K detected that the developing roller 61K was positioned at the contact position, the control unit 2 turns off the electromagnetic clutch EC2 (time t20).

[0210] As described above, when the main motor M1 rotates forward, the control unit 2 controls the separation mechanism 5 to move the developing rollers 61Y, 61M, 61C, and 61K, which are located in the separation position, from the separation position to the contact position in the order of developing roller 61Y, developing roller 61M, developing roller 61C, and developing roller 61K (times t9 to t19).

[0211] Specifically, when the main motor M1 rotates forward, the separation mechanism 5 moves the developing roller 61Y from the separation position to the contact position, and then moves the developing roller 61M from the separation position to the contact position. After moving the developing roller 61M from the separation position to the contact position, the separation mechanism 5 moves the developing roller 61C from the separation position to the contact position. When the main motor M1 rotates forward, the control unit 2 controls the separation mechanism 5 by the electromagnetic clutch EC2 to move the developing roller 61C from the separation position to the contact position, and then moves the developing roller 61K from the separation position to the contact position.

[0212] After positioning the developing rollers 61Y, 61M, 61C, and 61K at the contact positions, the control unit 2 executes printing. When the sheet S is discharged onto the discharge tray 13 and printing is completed, the control unit 2 temporarily stops the main motor M1 (time t21). Thereafter, the control unit 2 drives the main motor M1 in reverse rotation (time t22).

[0213] As a result, the movable gear 131 moves from the transmission position to the non-transmission position, the driving force from the main motor M1 is no longer transmitted to the heating roller 81A, and the heating roller 81A and the pressure unit 82 (pressure roller) stop. Also, the second movable gear 147 moves from the transmission position to the non-transmission position, the driving force from the main motor M1 is no longer transmitted to the sheet supply mechanism 22, and the sheet supply mechanism 22 stops. Also, the driving force from the main motor M1 is no longer transmitted to the first discharge roller 83 and the second discharge roller 91, and the first discharge roller 83 and the second discharge roller 91 stop.

[0214] After driving the main motor M1 in reverse rotation, the control unit 2 turns on the electromagnetic clutch EC2 (time t23), which transmits the driving force from the main motor M1 to the separating cam 150K, causing the separating cam 150K to rotate in the second rotation direction R2.

[0215] Thereafter, first, the developing roller 61K is moved from the contact position to the separation position by the separation cam 150K rotating in the second rotation direction R2 (time t24 to t25). After time t25, the developing roller 61K stops (time t26).

[0216] When a predetermined time has elapsed since the sensor 4K detected that the developing roller 61K was positioned at the separated position, the control unit 2 turns off the electromagnetic clutch EC2 (time t27).

[0217] Furthermore, the control unit 2 turns on the electromagnetic clutch EC1 at the timing when the developing roller 61K moves from the contact position to the separation position and then the developing roller 61C moves from the contact position to the separation position (time t28). As a result, the driving force is transmitted from the main motor M1 to the separation cams 150Y, 150M, and 150C, and the separation cams 150Y, 150M, and 150C rotate in the second rotation direction R2.

[0218] Then, at a timing after time t25 when developing roller 61K moves from the contact position to the separated position, developing roller 61C is moved from the contact position to the separated position by separating cam 150C rotating in the second rotation direction R2 (times t29 to t30). Next, developing roller 61M is moved from the contact position to the separated position by separating cam 150M rotating in the second rotation direction R2 (times t31 to t32). Finally, developing roller 61Y is moved from the contact position to the separated position by separating cam 150Y rotating in the second rotation direction R2 (times t33 to t34). After time t34, the developing rollers 61Y, 61M, and 61C stop (time t35).

[0219] When a predetermined time has elapsed since the sensor 4C detected that the developing rollers 61Y, 61M, 61C have reached the separated position, the control unit 2 turns off the electromagnetic clutch EC1 (time t36).

[0220] As described above, when the main motor M1 rotates in the reverse direction, the control unit 2 controls the separation mechanism 5 to move the developing rollers 61Y, 61M, 61C, and 61K, which are located at the contact position, from the contact position to the separation position in the order of developing roller 61K, developing roller 61C, developing roller 61M, and developing roller 61Y (times t24 to t34).

[0221] Specifically, when the main motor M1 rotates in the reverse direction, the control unit 2 controls the separation mechanism 5 using the electromagnetic clutch EC1 to move the developing roller 61K from the contact position to the separation position, and then moves the developing roller 61C from the contact position to the separation position. Furthermore, the separation mechanism 5 moves the developing roller 61C from the contact position to the separation position, and then moves the developing roller 61M from the contact position to the separation position. Furthermore, the separation mechanism 5 moves the developing roller 61M from the contact position to the separation position, and then moves the developing roller 61Y from the contact position to the separation position.

[0222] After the developing rollers 61Y, 61M, 61C, and 61K are positioned at the separated positions, the control unit 2 stops the process motor M2 (time t37), which stops the driving force from the process motor M2 to the photosensitive drum 50, and the photosensitive drum 50 stops.

[0223] Thereafter, control unit 2 turns on electromagnetic clutch EC3 (time t38). As a result, driving force is transmitted from main motor M1 to nip pressure adjustment cam 230 of nip pressure adjustment mechanism 200, causing nip pressure adjustment cam 230 to rotate in fourth rotation direction R4 and move from the first position to the second position. As a result, the nip pressure of heating unit 81 and pressure unit 82 switches from the large nip pressure to the small nip pressure (time t39 to t40).

[0224] When the nip pressure of heating unit 81 and pressure unit 82 is switched to the small nip pressure, control unit 2 turns off electromagnetic clutch EC3 (time t41), and then stops main motor M1 (time t42).

[0225] Thereafter, the control unit 2 drives the process motor M2 to perform the cleaning process (time t43 to t44). After the cleaning process is completed, the control unit 2 rotates the main motor M1 in the forward direction to perform the connection process (t45 to t46).

[0226] When printing in monochrome printing mode, the control unit 2 keeps the electromagnetic clutch EC1 OFF and controls the main motor M1, process motor M2, electromagnetic clutch EC2, and electromagnetic clutch EC3 in the same manner as when printing in color printing mode.

[0227] As described above, according to this embodiment, the following effects can be obtained. By performing the connection process after the control unit 2 executes the second process, and by configuring the control unit 2 to wait for a print command with the movable gear 131 meshed with the output gear 132, it is possible to prevent abnormal noise from being generated when printing starts after receiving a print command due to the movable gear 131 and the output gear 132 coming into contact. Also, because there is no need to perform the connection process when printing starts after receiving a print command, the heating roller 81A can be driven immediately after receiving a print command.

[0228] By making the drive time TD1 of the main motor M1 in the connection process shorter than the drive time TD2 of the main motor M1 in the second process, the connection process can be performed more quickly than, for example, when the drive time of the main motor in the connection process is longer than the drive time of the main motor in the second process. Also, it is possible to prevent the output gear 132 meshed with the moving gear 131 from rotating unnecessarily.

[0229] By configuring the second moving gear 147 to move toward the second transmission position due to the forward rotation of the main motor M1, when the control unit 2 performs the connection process, the second moving gear 147 engages with the second output gear 148, thereby preventing abnormal noise caused by the second moving gear 147 and the second output gear 148 coming into contact when printing begins after receiving a print command.

[0230] Although one embodiment of the image forming apparatus has been described above, the image forming apparatus can be modified as appropriate as exemplified below.

[0231] The control unit 2 may rotate the main motor M1 in the forward direction at a first speed when performing a printing process to form an image on the sheet S, and may rotate the main motor M1 in the forward direction at a second speed that is slower than the first speed when performing a connection process. By rotating the main motor M1 in the forward direction at the second speed that is slower than the first speed when performing a connection process, it is possible to reduce abnormal noise caused by contact between the moving gear 131 and the output gear 132.

[0232] The rotating body that conveys the sheet is not limited to a heating rotating body, but may be, for example, a pressure rotating body.Furthermore, the rotating body may be a supply roller that supplies the sheet to the image forming unit.

[0233] The moving body is not limited to the first cam (nip pressure adjusting cam 230), but may be the second cam (separating cam 150) that moves the developing roller between the contact position and the separated position.

[0234] The first cam may be linearly movable. The second cam may be linearly movable.

[0235] The cleaning member may be a non-rotating blade or the like. The connection process may be performed between the start of the warm-up process and the standby state. The warm-up process is a process for raising the temperature of the heating roller to a preparatory temperature that is lower than the fixing temperature suitable for fixing.

[0236] The control unit executes a warm-up process when the image forming apparatus is powered on, for example. In the warm-up process, the control unit executes a first process and then executes a second process. For example, the control unit executes the second process immediately before the warm-up process ends, and then executes a connection process.

[0237] In the above embodiment, the fixing drive gear train GT2 is configured to transmit the driving force of the main motor M1 to the heating roller 81A (heating unit 81), but for example, the fixing drive gear train may be configured to transmit the driving force of the main motor to the pressure unit. Also, the fixing drive gear train may be configured to transmit the driving force of the main motor to both the heating unit and the pressure unit.

[0238] In the above embodiment, the heating unit 81 includes a heating roller 81A, but the heating unit may include an endless belt. Also, in the above embodiment, the pressure unit 82 is a pressure roller, but the pressure unit may include an endless belt and a pad that sandwiches the belt between the heating unit and the pad.

[0239] In the above embodiment, the nip pressure adjustment cam 230 is configured to switch the nip pressure between the heating unit 81 and the pressure applying unit 82 between two levels: small nip pressure and large nip pressure. However, for example, the nip pressure adjustment cam may be configured to switch the nip pressure between three or more levels. In other words, the first nip pressure may include multiple nip pressures. Furthermore, when the nip pressure is small, the nip pressure may be zero. Furthermore, when the nip pressure is second, the heating unit and the pressure applying unit may be spaced apart.

[0240] In the above embodiment, nip pressure adjustment cam 230 is configured to switch nip pressure by moving pressure unit 82, but for example, the nip pressure adjustment cam may be configured to switch nip pressure by moving the heating unit instead of the pressure unit. Also, the nip pressure adjustment cam may be configured to switch nip pressure by moving both the heating unit and the pressure unit.

[0241] In the above embodiment, the separating cams 150Y, 150M, and 150C are controlled integrally, but for example, the separating cams 150Y, 150M, and 150C may be individually controllable.

[0242] In the above embodiment, the stopper 530 is wall-shaped, but the stopper may be rod-shaped, for example. Also, in the above embodiment, the stopper 530 is formed integrally with the cover wall 510, but the stopper may be a member fixed to the cover wall, for example.

[0243] Furthermore, for example, the cross-sectional shape of the portion where the boss of the cam and the slide shaft of the cam follower engage may be triangular, rectangular, D-shaped, oval, or the like to restrict the rotation of the cam follower without providing a stopper.

[0244] In the above embodiment, the rotation resistance member 300 is a leaf spring. However, the rotation resistance member may be a spring other than a leaf spring, such as a coil spring. Furthermore, the rotation resistance member may be an elastic body other than a spring, such as a sponge. The direction in which the rotation resistance member presses the idle gear in the direction of the idle gear's rotation axis may be opposite to that in the above embodiment. Furthermore, the rotation resistance member may be configured to press the idle gear in a direction perpendicular to the direction of the idle gear's rotation axis.

[0245] In the above embodiment, the photosensitive drum 50 is rotatably supported in the drawer 55, but the photosensitive drum may be detachably attached to the drawer. Specifically, a drum cartridge having a photosensitive drum may be provided, and the drum cartridge may be detachably attached to the drawer. Alternatively, a cartridge having a photosensitive drum and a developing roller, in which the drum cartridge and the developing cartridge 60 of the above embodiment are integrated, may be provided, and the cartridge may be detachably attached to the drawer.

[0246] In the above embodiment, the image forming apparatus 1 is a color printer capable of forming color images, but the image forming apparatus may be, for example, a monochrome printer capable of forming only monochrome images. Also, for example, the image forming apparatus may be a copier or a multifunction peripheral.

[0247] The elements described in the above-described embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0248] 1. Image forming device 2. Control Unit 30 Image forming unit 80 Fixing unit 81A Heating roller 82 Pressure section 131 Moving Gear 132 Output gear 230 Nip pressure adjustment cam EC3 Electromagnetic Clutch GT2 Fixing drive gear train GT3 Nip pressure adjustment gear train M1 main motor S seat

Claims

1. a motor capable of rotating forward and backward; an image forming unit that forms an image on a sheet; a fixing unit that fixes an image on a sheet by sandwiching the sheet between a heating rotary member and a pressure rotary member; a first cam that is movable between a first position where a nip pressure between the heating rotator and the pressure rotator is set to a first nip pressure and a second position where the nip pressure is set to a second nip pressure that is smaller than the first nip pressure, the first cam moving to the first position by forward rotation of the motor and moving to the second position by reverse rotation of the motor; a first drive train that transmits the driving force of the motor to the heating rotor or the pressure rotor, First gear; a first drive train including a movable gear that is movable between a transmission position where it meshes with the first gear to transmit a driving force to the first gear and a non-transmission position where it separates from the first gear to not transmit a driving force to the first gear, the movable gear moving toward the transmission position by forward rotation of the motor and moving toward the non-transmission position by reverse rotation of the motor; a second drive train that transmits the driving force of the motor to the first cam, a second drive train including a switching mechanism that can switch between a transmission state in which a drive force is transmitted to the first cam and a disconnection state in which the drive force is not transmitted to the first cam; A control unit; Equipped with The control unit a first process of rotating the motor in a forward direction and setting the switching mechanism in the transmission state to set the nip pressure to the first nip pressure; a second process of rotating the motor in a reverse direction and setting the switching mechanism in the transmission state to set the nip pressure to the second nip pressure; a connection process for moving the movable gear from the non-transmission position to the transmission position by rotating the motor in the forward direction when the switching mechanism is in the disconnected state, The image forming apparatus performs the connection process after the second process, thereby waiting for a print command in a state in which the moving gear is engaged with the first gear.

2. The control unit When performing a printing process to form an image on a sheet, the motor is rotated forward at a first speed; 2. The image forming apparatus according to claim 1, wherein, when the connection process is performed, the motor is rotated forward at a second speed that is lower than the first speed.

3. 2. The image forming apparatus according to claim 1, wherein the driving time of the motor in the connection process is shorter than the driving time of the motor in the second process.

4. 2. The image forming apparatus according to claim 1, wherein the control unit stops the motor after the connection process.

5. 2. The image forming apparatus according to claim 1, wherein the switching mechanism is an electromagnetic clutch.

6. 2. The image forming apparatus according to claim 1, further comprising a sensor that detects whether the first cam is at the first position or the second position.

7. the first drive train transmits a driving force to the heating rotor, 2. The image forming apparatus according to claim 1, wherein the pressure rotating member rotates in accordance with the rotation of the heating rotating member.

8. A photosensitive drum; a cleaning member that cleans the surface of the photosensitive drum; a process motor that drives the photosensitive drum, The control unit a cleaning process for cleaning the photosensitive drum by driving the process motor; performing the cleaning process after the second process; 2. The image forming apparatus according to claim 1, wherein the connection process is executed after the cleaning process.

9. a developing roller movable between a contact position where it contacts the photosensitive drum and a spaced position where it is spaced from the photosensitive drum; a second cam that moves the developing roller between the contact position and the separated position; a third drive train that transmits the driving force of the motor to the second cam, the third drive train including a second electromagnetic clutch; The control unit a pressing process of moving the developing roller to the contact position by rotating the motor in the forward direction and engaging the second electromagnetic clutch; 9. The image forming apparatus according to claim 8, further comprising: a separation process for moving the developing roller to the separation position by rotating the motor in a reverse direction and connecting the second electromagnetic clutch.

10. The image forming apparatus according to claim 9 , wherein the control unit executes the second process after the separation process.

11. a supply roller for supplying a sheet to the image forming unit; a fourth drive train that transmits the driving force of the motor to the supply roller, A second gear; 2. The image forming apparatus according to claim 1, further comprising: a fourth drive train including a second movable gear that is movable between a second transmission position in which it meshes with the second gear to transmit driving force to the second gear and a second non-transmission position in which it does not transmit driving force to the second gear by separating from the second gear, the second movable gear moving toward the second transmission position by forward rotation of the motor and moving toward the second non-transmission position by reverse rotation of the motor.

12. a motor capable of rotating forward and backward; an image forming unit that forms an image on a sheet; a rotating body for conveying a sheet; a movable body that is movable between a first position and a second position, the movable body being moved to the first position by forward rotation of the motor and to the second position by reverse rotation of the motor; a first drive train that transmits the driving force of the motor to the rotating body, First gear; a first drive train including a movable gear that is movable between a transmission position where it meshes with the first gear to transmit a driving force to the first gear and a non-transmission position where it separates from the first gear to not transmit a driving force to the first gear, the movable gear moving toward the transmission position by forward rotation of the motor and moving toward the non-transmission position by reverse rotation of the motor; a second drive train that transmits the driving force of the motor to the moving body, a second drive train including a switching mechanism that can switch between a transmission state in which a drive force is transmitted to the movable body and a disconnection state in which the drive force is not transmitted to the movable body; A control unit; Equipped with The control unit a first process of moving the moving body to the first position by rotating the motor in a forward direction and setting the switching mechanism in the transmission state; a second process of moving the movable body to the second position by rotating the motor in a reverse direction and by setting the switching mechanism to the transmission state; a connection process for moving the movable gear from the non-transmission position to the transmission position by rotating the motor in the forward direction when the switching mechanism is in the disconnected state, The image forming apparatus performs the connection process after the second process, thereby waiting for a print command in a state in which the moving gear is engaged with the first gear.

13. The image forming apparatus further includes a fixing device that fixes an image on a sheet by sandwiching the sheet between the heating rotary member and the pressure rotary member, 13. The image forming apparatus according to claim 12, wherein the rotating body is the heating rotating body or the pressure rotating body.

14. The moving body is 14. The image forming apparatus according to claim 13, wherein the first cam sets the nip pressure between the heating rotor and the pressure rotor to a first nip pressure when located at the first position, and sets the nip pressure to a second nip pressure smaller than the first nip pressure when located at the second position.

15. 13. The image forming apparatus according to claim 12, wherein the rotating body is a supply roller that supplies a sheet to the image forming section.

16. A photosensitive drum; a developing roller that is movable between a contact position where it contacts the photosensitive drum and a spaced position where it is spaced from the photosensitive drum; 13. The image forming apparatus according to claim 12, wherein the moving body is a second cam that moves the developing roller between the contact position and the separated position.

17. 13. The image forming apparatus according to claim 12, wherein the switching mechanism is an electromagnetic clutch.

18. 15. The image forming apparatus according to claim 14, further comprising a sensor that detects whether the first cam is at the first position or the second position.

19. the first drive train transmits a driving force to the heating rotor, 14. The image forming apparatus according to claim 13, wherein the pressure rotating member rotates in accordance with the rotation of the heating rotating member.

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