JP7294037B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus having a photosensitive drum, a developing roller, and a fixing device.

2. Description of the Related Art Conventionally, an image forming apparatus is known in which a single motor drives a plurality of mechanisms. For example, Japanese Patent Application Laid-Open No. 2002-100003 discloses a configuration in which an image forming section including a photosensitive drum and a developing roller and a fixing section including a heating roller and a pressure roller are driven by the same motor. An image forming apparatus is disclosed that includes a clutch arranged in a force transmission path and a control section that controls the clutch so as to stop driving the image forming section at the timing when a sheet passes through the image forming section. . With this technology, it is possible to stop the rotation of the photosensitive drum before the sheet having the toner image transferred thereon by the photosensitive drum passes through the fixing section and is discharged.

JP-A-2000-267544

By the way, in order to drive a plurality of mechanisms stably at high speed, it is necessary to use a large motor. On the other hand, if a small motor is used, it becomes difficult to increase the speed when driving multiple mechanisms at the same time. A problem arises.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and is an image forming apparatus capable of reducing the waiting time until the image forming apparatus becomes ready for printing while suppressing the enlargement of the image forming apparatus. intended to provide

An image forming apparatus for achieving the above object comprises a photosensitive drum, a developing roller movable between a contact position in contact with the photosensitive drum and a spaced position away from the photosensitive drum, a heating section, and a heating section. a fixing device having a pressurizing portion that sandwiches a sheet therebetween; a motor; a separating mechanism that is driven by receiving a driving force from the motor to move the developing roller between a contact position and a separated position; a nip pressure adjusting mechanism that is driven by receiving force to switch the nip pressure between the heating unit and the pressurizing unit between a first nip pressure and a second nip pressure that is lower than the first nip pressure; And prepare.
The control unit drives the motor at the first rotation speed to drive the separating mechanism and the nip pressure adjusting mechanism at the same time to move the developing roller from the contact position toward the separating position, while increasing the nip pressure to the first nip pressure. to the second nip pressure, and after the nip pressure is switched to the second nip pressure, the motor is driven at a second rotation speed higher than the first rotation speed to drive the separating mechanism, and move the developing roller to the separation position. It is possible to perform a preparatory operation to move to

According to such a configuration, when the spacing mechanism and the nip pressure adjusting mechanism are driven simultaneously, the rotation speed of the motor is low, so that the spacing mechanism and the nip pressure adjusting mechanism can be stably driven. As a result, there is no need to use a large motor capable of driving the separating mechanism and the nip pressure adjusting mechanism at a high rotational speed, so the size of the motor can be suppressed and the size of the image forming apparatus can be reduced. can be suppressed. On the other hand, after the nip pressure is switched to the second nip pressure, the rotation speed of the motor is increased, so that the time until the developing roller is positioned at the separated position can be shortened. As a result, the time until the preparatory operation is completed can be shortened, so the waiting time until the image forming apparatus becomes ready for printing can be shortened.

The image forming apparatus includes a first transmission mechanism capable of transmitting the driving force from the motor to the spacing mechanism, and a second transmission branching from the first transmission mechanism and capable of transmitting the driving force from the motor to the nip pressure adjusting mechanism. a mechanism, wherein the second transmission mechanism is a first electromagnetic for switching between a transmission state in which the driving force from the motor is transmitted to the nip pressure adjusting mechanism and a disconnected state in which the driving force from the motor is not transmitted to the nip pressure adjusting mechanism; A clutch may be provided, and the control unit may have a configuration in which the first electromagnetic clutch is placed in a transmission state to drive the nip pressure adjustment mechanism, and the first electromagnetic clutch is placed in a disengagement state to stop the nip pressure adjustment mechanism.

According to this, compared to the case where the mechanism for transmitting the driving force from the motor to the spacing mechanism and the mechanism for transmitting the driving force from the motor to the nip pressure adjusting mechanism are provided independently, the size of the image forming apparatus is reduced. It is possible to suppress By switching the state of the first electromagnetic clutch, the nip pressure adjusting mechanism can be switched between driving and stopping, so that the nip pressure adjusting mechanism can be stopped while driving the separating mechanism.

The image forming apparatus described above includes a third transmission mechanism capable of transmitting a driving force from the motor to the developing roller, the first transmission mechanism branches off from the third transmission mechanism, and the first transmission mechanism receives a a second electromagnetic clutch that switches between a transmission state in which driving force is transmitted to the spacing mechanism and a disengaged state in which driving force from the motor is not transmitted to the spacing mechanism; is driven to disengage the second electromagnetic clutch to stop the separating mechanism.

According to this, it is possible to reduce the number of motors, so it is possible to suppress an increase in size of the image forming apparatus. By switching the state of the electromagnetic clutch, the separating mechanism and the nip pressure adjusting mechanism can be switched between driving and stopping. can be

In the image forming apparatus described above, the control section may be configured to perform a preparatory operation when the power of the image forming apparatus is turned on.

The image forming apparatus described above may include a housing and a cover capable of opening and closing an opening provided in the housing, and the control unit may be configured to execute a preparatory operation when the cover is closed. .

In the image forming apparatus described above, in the standby state for waiting for input of a print job, the control unit positions the developing roller at the separated position, sets the nip pressure to the second nip pressure, and sets the nip pressure to the second nip pressure. When the printing operation is started, after switching the nip pressure from the second nip pressure to the first nip pressure, the developing roller can be moved from the separated position to the contact position.

In the image forming apparatus described above, when the printing operation is finished, the control unit moves the developing roller from the contact position to the separated position, and then switches the nip pressure from the first nip pressure to the second nip pressure. can be done.

In the image forming apparatus described above, when the nip pressure is switched between the first nip pressure and the second nip pressure in the printing operation, the control unit drives the motor at the first rotation speed and brings the developing roller into contact. When moving between the position and the separated position, the motor can be configured to be driven at the second rotational speed.

According to this, when switching the nip pressure, the rotation speed of the motor is reduced, so that the load on the nip pressure adjustment mechanism can be reduced. On the other hand, when the developing roller is moved, the rotation speed of the motor is increased, so the developing roller can be moved quickly, and the waiting time during printing can be shortened.

According to the present invention, it is possible to shorten the waiting time until the image forming apparatus becomes ready for printing while suppressing the enlargement of the image forming apparatus.

1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment; FIG. FIG. 4 is a diagram showing an example of a configuration for bringing the developing roller into contact with and separating from the photosensitive drum; 10A and 10B are diagrams for explaining the separation sensor for cyan and the first detected parts provided on the separation cam for C; FIG. 10A and 10B are diagrams (a) and (b) for explaining the separation sensor for black and the second detected portion provided on the separation cam for K; FIG. 2A and 2B are diagrams illustrating an example of a configuration for switching the nip pressure of a fixing device; FIG. 6 is a flowchart showing an example of processing of a control unit; 4 is a flow chart showing an example of processing for color printing. FIG. 8 is a flowchart continued from FIG. 7 showing an example of processing for color printing; FIG. 4 is a timing chart illustrating operations of a developing motor, a developing roller, a developing clutch, a fixing device, and a fixing clutch when color printing is performed; FIG. 10 is a timing chart continued from FIG. 9 illustrating operations of a developing motor, a developing roller, a developing clutch, a fixing device, and a fixing clutch when color printing is performed; FIG. 7 is a flow chart showing an example of processing for initialization. 4 is a timing chart for explaining operations of a developing motor, a developing roller, a developing clutch, a fixing device, and a fixing clutch in the case of initialization;

As shown in FIG. 1, an image forming apparatus 1 according to the embodiment is a color printer, and includes a housing 10, a cover 11, a sheet feeding section 20, an image forming section 30, and a control section 2. there is In this embodiment, the left side of FIG. 1 is the front, the right side is the rear, and the top and bottom are the top and bottom.

The housing 10 is provided with an opening 10A in its front portion. The cover 11 can open and close the opening 10A. Specifically, the cover 11 is rotatable between a closed position, indicated by solid lines, at which the opening 10A is closed, and an open position, indicated by phantom lines, at which the opening 10A is opened. The housing 10 is provided with a cover sensor (not shown) for detecting the open/closed state of the cover 11, and the control unit 2 can determine the open/closed state of the cover 11 based on the signal from the cover sensor. It has become.

The sheet supply unit 20 includes a sheet tray 21 that stores sheets S and a supply mechanism 22 . The sheet tray 21 is arranged below the image forming section 30 and can be removed by pulling it forward from the housing 10 . The supply mechanism 22 includes a paper feed roller 23 , a separation roller 24 , a separation pad 25 , a transport roller 26 and registration rollers 27 . The sheet S is a medium on which an image can be formed by the image forming apparatus 1, and includes plain paper, envelopes, postcards, thin paper, thick paper, glossy paper, resin sheets, stickers, and the like.

The sheets S set on the sheet tray 21 are sent out by the paper feed roller 23, separated one by one between the separation roller 24 and the separation pad 25, and conveyed toward the registration roller 27 by the conveying roller 26. be transported. After that, the position of the front end of the sheet S is regulated by the registration rollers 27 whose rotation has stopped, and then the registration rollers 27 are rotated to supply the sheet S to the image forming section 30 .

The image forming apparatus 1 includes a paper feed sensor 28A, a pre-registration sensor 28B, and a post-registration sensor 28C that can detect the passage of the sheet S. The paper feed sensor 28A is arranged downstream of the paper feed roller 23 and the separation roller 24 in the sheet S conveying direction. The pre-registration sensor 28B is arranged downstream of the paper feed sensor 28A and the conveying roller 26 and upstream of the registration roller 27 in the sheet S conveying direction. The post-registration sensor 28</b>C is arranged downstream of the registration roller 27 and upstream of the photosensitive drum 50 in the sheet S conveying direction.

The image forming section 30 includes an exposure device 40 , a plurality of photosensitive drums 50 , a plurality of developing cartridges 60 , a conveying device 70 and a fixing device 80 .
The exposure device 40 includes a laser diode, a deflector, lenses and mirrors (not shown). The exposure device 40 is configured to expose the surface of each photosensitive drum 50 by emitting a plurality of light beams indicated by dashed lines for exposing the plurality of photosensitive drums 50 .

The photosensitive drums 50 include a Y photosensitive drum 50Y for yellow, an M photosensitive drum 50M for magenta, a C photosensitive drum 50C for cyan, and a K photosensitive drum 50K for black. The photosensitive drums 50Y, 50M, 50C, and 50K are arranged side by side in this order from the upstream side to the downstream side in the sheet S conveying direction. In the present specification and drawings, when the members provided corresponding to each color are indicated by distinguishing the colors, the symbols are denoted by Y, M, C, and K, and the explanation is given without distinguishing the colors. In this case, Y, M, C, and K are not attached to the code.

A developing cartridge 60 is provided corresponding to each photosensitive drum 50 . The developing cartridge 60 includes a Y developing cartridge 60Y having a Y developing roller 61Y that supplies toner to the Y photosensitive drum 50Y, an M developing cartridge 60M having an M developing roller 61M that supplies toner to the M photosensitive drum 50M, and a C photosensitive drum. It includes a C developing cartridge 60C having a C developing roller 61C that supplies toner to 50C, and a K developing cartridge 60K having a K developing roller 61K that supplies toner to the K photosensitive drum 50K. The developing rollers 61Y, 61M, 61C, and 61K are arranged in this order from the upstream side to the downstream side in the sheet S conveying direction.

In each developing cartridge 60, the position where the developing roller 61 is in contact with the corresponding photosensitive drum 50 among the plurality of photosensitive drums 50 indicated by the solid line corresponds to the developing roller 61 indicated by the phantom line. It is movable between a position at a spaced position away from the photosensitive drum 50 .

A plurality of photosensitive drums 50 are rotatably supported by a support member 90 . The support member 90 is provided with chargers 52 arranged corresponding to the respective photosensitive drums 50 . The support member 90 can be attached to and detached from the housing 10 through an opening 10A opened by opening the cover 11 . Further, the support member 90 detachably supports the plurality of developer cartridges 60 .

The conveying device 70 is provided between the sheet tray 21 and the plurality of photosensitive drums 50 . The conveying device 70 includes a driving roller 71 , a driven roller 72 , a conveying belt 73 made up of an endless belt, and four transfer rollers 74 . The conveying belt 73 is stretched between the driving roller 71 and the driven roller 72 and arranged so that the outer surface faces each photosensitive drum 50 . Each transfer roller 74 is arranged inside the conveying belt 73 so as to sandwich the conveying belt 73 with each photosensitive drum 50 .

The fixing device 80 is provided behind the plurality of photosensitive drums 50 and the conveying device 70 . The fixing device 80 includes a heating roller 81 as an example of a heating section, and a pressure roller 82 as an example of a pressure section that is arranged to face the heating roller 81 and sandwiches the sheet S between itself and the heating roller 81 . have. On the downstream side of the fixing device 80 in the conveying direction of the sheet S, a paper discharge sensor 28D capable of detecting passage of the sheet S, a conveying roller 15, and a discharge roller 16 are provided.

In the image forming section 30 , the surface of the photosensitive drum 50 is uniformly charged by the charger 52 and then exposed to light beams emitted from the exposure device 40 . As a result, an electrostatic latent image is formed on the photosensitive drum 50 based on the image data. Further, the toner accommodated in the developing cartridge 60 is carried on the surface of the developing roller 61 and supplied from the developing roller 61 positioned at the contact position to the electrostatic latent image formed on the photosensitive drum 50 . Thereby, a toner image is formed on the photosensitive drum 50 . Next, the sheet S supplied onto the conveying belt 73 is conveyed on the conveying belt 73 and passes between the photosensitive drum 50 and the transfer roller 74, whereby the toner image on the photosensitive drum 50 is transferred onto the sheet S. be done. Then, the toner image is thermally fixed on the sheet S by passing the sheet S between the heating roller 81 and the pressure roller 82 . After that, the sheet S is discharged onto the discharge tray 13 by the transport rollers 15 and the discharge rollers 16 .

As shown in FIG. 2, the image forming apparatus 1 includes a developing motor 3D, a process motor 3P, a fixing motor 3F, a separating mechanism 5, a nip pressure adjusting mechanism 6, a first transmission mechanism 100, a second transmission A mechanism 200 , a third transmission mechanism 300 , a fourth transmission mechanism 400 and a fifth transmission mechanism 500 are further provided.

The developing motor 3D is a motor that transmits driving force to the developing roller 61, the separating mechanism 5, and the nip pressure adjusting mechanism 6. FIG. In this embodiment, the developing motor 3D corresponds to the "motor". The developing motor 3D is configured to be able to switch the rotation speed of an output shaft (not shown). Specifically, the development motor 3D can switch its rotational speed between a first rotational speed and a second rotational speed higher than the first rotational speed. In this embodiment, the first rotation speed is approximately half the second rotation speed. In the following description, the first rotation speed may be referred to as half speed, and the second rotation speed may be referred to as full speed.

Further, the developing motor 3D is configured such that the rotation direction of the output shaft can be switched. Although the details will be described later, in the present embodiment, the nip pressure adjustment mechanism 6 switches the nip pressure between the heating roller 81 and the pressure roller 82 of the fixing device 80 from a low standby nip pressure to a high fixing nip pressure. The direction of rotation is assumed to be forward rotation, and the direction of rotation when switching from fixing nip pressure to standby nip pressure is assumed to be reverse rotation.

The separating mechanism 5 is a mechanism that is driven by receiving a driving force from the developing motor 3</b>D to move the developing roller 61 between the contact position and the separated position, and includes a separating cam 150 . The separation cam 150 is a cam that moves the corresponding developing roller 61 between the contact position and the separation position. The separating cams 150 include a Y separating cam 150Y that contacts and separates the Y developing roller 61Y, an M separating cam 150M that contacts and separates the M developing roller 61M, a C separating cam 150C that contacts and separates the C developing roller 61C, It also includes a K separation cam 150K for contacting/separating the K developing roller 61K.

Here, an example of a configuration for bringing the developing roller 61 into contact with and separating from the corresponding photosensitive drum 50, including the separation cam 150, will be described.
The supporting member 90 (see FIG. 1) supports each developing cartridge 60 so as to be movable in the direction in which the plurality of photosensitive drums 50 are arranged, that is, in the conveying direction of the sheet S on the conveying belt 73 . The support member 90 has a spring 97 that biases the developing cartridge 60 from the upstream side toward the downstream side in the sheet S conveying direction. A spring 97 is provided corresponding to each developer cartridge 60 .

Further, each developing cartridge 60 has a pressed portion 66 protruding in the direction of the rotation axis of the developing roller 61 on its side surface. In the developing cartridge 60 , the pressing portion 66 is pressed from the downstream side to the upstream side in the conveying direction of the sheet S by the separating cam 150 , so that the developing roller 61 is supported against the biasing force of the spring 97 . It moves to a position that is a separation position away from the photosensitive drum 50 . When the pressure of the separating cam 150 is released, the developing cartridge 60 moves to the contact position where the developing roller 61 contacts the corresponding photosensitive drum 50 by the biasing force of the spring 97 (see FIG. 1). .

The separating cam 150 is rotatable around an axis parallel to the rotational axis of the developing roller 61 . Y spacing cam 150Y, M spacing cam 150M, and C spacing cam 150C have cam ridges 152Y, 152M, and 152C on their outer peripheral surfaces, and K spacing cam 150K has two substantially symmetrical cam ridges 152K on its outer peripheral surface. have. The cam ridges 152Y, 152M, 152C, and 152K can press the pressed portion 66 of the developer cartridge 60 . The developing roller 61 is positioned at the separated position with the cam ridges 152Y, 152M, 152C, and 152K pressing the pressed portion 66 . On the other hand, the developing roller 61 is positioned at the contact position in a state in which the pressing of the pressed portion 66 by the cam ridges 152Y, 152M, 152C, and 152K is released.

In this embodiment, the same parts are used for the M spacing cam 150M and the C spacing cam 150C, and for the Y spacing cam 150Y, the length of the cam ridge 152Y in the rotational direction is the same as that of the spacing cams 150M and 150C. Components longer than the peaks 152M and 152C are used. On the other hand, for the K spacing cam 150K, a component is used in which each cam ridge 152K is shorter in the rotational direction than the cam ridges 152Y, 152M, and 152C.

As shown in FIGS. 3 and 4, the image forming apparatus 1 includes separation sensors 4C and 4K as phase sensors capable of detecting the phase of the separation cam 150. FIG. The separation sensor 4C is a sensor that detects the phase of the C separation cam 150C, and outputs a first signal when the C separation cam 150C is positioned within a predetermined phase range in which the C developing roller 61C is at the separation position. The first signal is not output when the cam 150C is not positioned within the predetermined phase range. The separation sensor 4K is a sensor for detecting the phase of the K separation cam 150K, and outputs a first signal when the K separation cam 150K is positioned within a predetermined phase range where the K developing roller 61K is in the separation position, The first signal is not output when the K separating cam 150K is not positioned within the predetermined phase range.

Specifically, the separation sensors 4C and 4K have a light emitting section 4P that emits detection light, and a light receiving section 4R that is arranged to face the light emitting section 4P and can receive the detection light from the light emitting section 4P. The C spacing cam 150C has a first detected portion 154A projecting in the rotational axis direction of the C spacing cam 150C. It has a detected portion 154K. The first detected portion 154A is arranged at a position where it is detected by the separation sensor 4C at the timing when the C developing roller 61C moves from the contact position to the separated position when the developing motor 3D is rotating forward. The second detected portion 154K is arranged at each of two positions detected by the separation sensor 4K at the timing when the K developing roller 61K moves from the contact position to the separated position when the developing motor 3D is rotating forward. ing.

The separation sensors 4C and 4K output the first signal when the detected portions 154A and 154K are interposed between the light emitting portion 4P and the light receiving portion 4R to block the detection light from the light emitting portion 4P and the light receiving portion 4R does not receive the detection light. The first signal is not output when the detected portions 154A and 154K are removed from between the light emitting portion 4P and the light receiving portion 4R and the light receiving portion 4R receives the detection light from the light emitting portion 4P. The separation sensor 4C directly detects the phase of the C separation cam 150C, but can indirectly detect the phases of the separation cams 150Y and 150M rotationally driven at the same time as the C separation cam 150C. In the following, the case where the first signal is output is called ON, and the case where the first signal is not output is sometimes called OFF. It does not matter which voltage is higher when the first signal is output or when it is not output.

Returning to FIG. 2, the third transmission mechanism 300 is composed of one or more gears, belts, and the like, and is a mechanism capable of transmitting driving force from the developing motor 3D to the developing roller 61. FIG. The third transmission mechanism 300 rotates the developing roller 61 by transmitting the driving force from the developing motor 3D before the developing roller 61 contacts the corresponding photosensitive drum 50 while it is moving from the separated position to the contact position. Further, the transmission of the driving force from the developing motor 3D is interrupted to stop the developing roller 61 after the developing roller 61 is separated from the corresponding photosensitive drum 50 while the developing roller 61 is moving from the contact position to the separated position. It is As a result, the developing roller 61 rotates when positioned at the contact position, and does not rotate when positioned at the separated position.

Also, the third transmission mechanism 300 has a one-way clutch 340 . The one-way clutch 340 transmits the driving force to the developing roller 61 when the developing motor 3D is rotating in the forward direction, and does not transmit the driving force to the developing roller 61 when the developing motor 3D is rotating in the reverse direction. As a result, the third transmission mechanism 300 transmits the driving force to the developing roller 61 when the developing motor 3D is rotating in the forward direction, and does not transmit the driving force to the developing roller 61 when the developing motor 3D is rotating in the reverse direction. It is

The first transmission mechanism 100 is composed of one or more gears, belts, or the like, and is a mechanism capable of transmitting the driving force from the developing motor 3D to the spacing cam 150 (spacing mechanism 5). ing. The first transmission mechanism 100 includes a YMC transmission mechanism 100A capable of transmitting the driving force from the developing motor 3D to the separating cams 150Y, 150M, and 150C, and a K transmission mechanism capable of transmitting the driving force from the developing motor 3D to the K separating cam 150K. mechanism 100K. The Y spacing cam 150Y, the M spacing cam 150M, and the C spacing cam 150C are mechanically connected via gears or the like, and are rotationally driven simultaneously by transmission of driving force from the developing motor 3D.

The first transmission mechanism 100 has a development clutch 140 as a second electromagnetic clutch. Developing clutch 140 includes a YMC clutch 140A provided in YMC transmission mechanism 100A and a K clutch 140K provided in K transmission mechanism 100K. The YMC clutch 140A switches between a transmission state in which the driving force from the developing motor 3D is transmitted to the separating cams 150Y, 150M, and 150C and a disconnected state in which the driving force from the developing motor 3D is not transmitted to the separating cams 150Y, 150M, and 150C. . The K clutch 140K switches between a transmission state in which the driving force from the developing motor 3D is transmitted to the K spacing cam 150K and a disconnected state in which the driving force from the developing motor 3D is not transmitted to the K spacing cam 150K. Hereinafter, when the developing clutch 140 (140A, 140K) is in the transmission state, it is called ON, and when it is in the disengaged state, it is sometimes called OFF.

The control unit 2 turns on the developing clutch 140 to drive the separating cam 150 , and turns off the developing clutch 140 to stop the separating cam 150 . Specifically, the control unit 2 turns ON the YMC clutch 140A to drive the separation cams 150Y, 150M and 150C, and turns OFF the YMC clutch 140A to stop the separation cams 150Y, 150M and 150C. The control unit 2 also turns on the K clutch 140K to drive the K separation cam 150K, and turns off the K clutch 140K to stop the K separation cam 150K.

The nip pressure adjusting mechanism 6 is a mechanism that switches the nip pressure between the heating roller 81 and the pressure roller 82 by being driven by receiving a driving force from the developing motor 3</b>D, and includes a switching cam 250 . The switching cam 250 is a cam that switches the nip pressure between the heating roller 81 and the pressure roller 82 between the fixing nip pressure and a standby nip pressure lower than the fixing nip pressure. In this embodiment, the fixing nip pressure corresponds to the "first nip pressure", and the standby nip pressure corresponds to the "second nip pressure".

Here, an example of a configuration for switching the nip pressure between the fixing nip pressure and the standby nip pressure, including the switching cam 250, will be described.
As shown in FIG. 5, the fixing device 80 includes a frame 84 supporting a heating roller 81, a lever 85 supporting a pressure roller 82, and a spring 86 capable of pressing the pressure roller 82 toward the heating roller 81. have. A portion of the frame 84 with which the lever 85 and the spring 86 are engaged, and the lever 85 and the spring 86 are provided on both left and right sides of the fixing device 80, respectively.

The frame 84 has a shaft portion 84A and a first spring engaging portion 84B, and the lever 85 has a shaft engaging portion 85A, a second spring engaging portion 85B, and a cam contact surface 85C. there is The shaft engaging portion 85A of the lever 85 is engaged with the shaft portion 84A, and the lever 85 is supported by the frame 84 so as to be swingable about the shaft portion 84A. This allows the pressure roller 82 to move with respect to the heating roller 81 . The spring 86 is a tension coil spring, one end of which is engaged with the first spring engaging portion 84B and the other end of which is engaged with the second spring engaging portion 85B.

The switching cam 250 is rotatable around an axis parallel to the rotation axes of the heating roller 81 and the pressure roller 82 . The switching cam 250 rotates in the first rotation direction R1 by receiving the driving force from the developing motor 3D rotating in the forward direction, and rotates in the second rotating direction R2 by receiving the driving force from the developing motor 3D rotating in the reverse direction. The switching cam 250 has a cam surface 253 on its outer peripheral surface. The cam surface 253 is a surface that can come into contact with the cam contact surface 85C, and when the nip pressure is the standby nip pressure shown in FIG. is separated from the cam contact surface 85C when the fixing nip pressure shown in FIG.

The switching cam 250 rotates in the second rotation direction R2 from the phase shown in FIG. The pressure roller 82 is pushed down together with the lever 85 against the urging force, and the nip pressure is switched from the fixing nip pressure to the waiting nip pressure lower than the fixing nip pressure. When the switching cam 250 rotates in the first rotation direction R1 from the phase shown in FIG. 5B, the cam surface 253 is separated from the cam contact surface 85C as shown in FIG. The pressure roller 82 is pulled up together with the lever 85 by the biasing force of 86, thereby switching the nip pressure from the standby nip pressure to the fixing nip pressure.

The image forming apparatus 1 includes a nip pressure detection sensor 7 for detecting whether the nip pressure of the fixing device 80 is the fixing nip pressure or the standby nip pressure. As an example, the nip pressure detection sensor 7 is a sensor that detects the phase of the switching cam 250, and outputs a second signal when the switching cam 250 is positioned within a predetermined phase range where the nip pressure is the standby nip pressure. The second signal is not output when the switching cam 250 is not positioned within the predetermined phase range. In the following, the case where the second signal is output is called ON, and the case where the second signal is not output is sometimes called OFF. It does not matter which voltage is higher when the second signal is output or when it is not output.

Returning to FIG. 2, the second transmission mechanism 200 is composed of one or more gears, belts, etc., and is a mechanism capable of transmitting the driving force from the developing motor 3D to the switching cam 250 (nip pressure adjusting mechanism 6). 1 is branched from the transmission mechanism 100 . The second transmission mechanism 200 has a fixing clutch 240 as a first electromagnetic clutch. The fixing clutch 240 switches between a transmission state in which the driving force from the developing motor 3D is transmitted to the switching cam 250 and a disconnected state in which the driving force from the developing motor 3D is not transmitted to the switching cam 250. FIG. In the following, the case where the fixing clutch 240 is in the transmitting state is called ON, and the case where the fixing clutch 240 is in the disengaged state is sometimes called OFF.

The control unit 2 turns on the fixing clutch 240 to drive the switching cam 250 , and turns off the fixing clutch 240 to stop the switching cam 250 .

The process motor 3P is a motor that transmits driving force to the supply mechanism 22, the photosensitive drum 50, the drive roller 71 of the conveying device 70, and the like.
The fourth transmission mechanism 400 includes one or more gears, belts, and the like, and is a mechanism capable of transmitting driving force from the process motor 3P to the photosensitive drum 50 and the like.

The fixing motor 3</b>F is a motor that transmits driving force to the heating roller 81 of the fixing device 80 .
The fifth transmission mechanism 500 is composed of one or more gears, belts, and the like, and is a mechanism capable of transmitting driving force from the fixing motor 3F to the heating roller 81 .

The control unit 2 is a device that controls the operation of the image forming apparatus 1 . The control unit 2 has a CPU, a ROM, a RAM, an input/output unit, etc., and executes each process by executing a pre-stored program. The control unit 2 controls the developing clutch 140 and the fixing clutch 240 based on signals from the separation sensors 4C and 4K, the nip pressure detection sensor 7, the pre-registration sensor 28B, the post-registration sensor 28C, and the like. It controls contact/separation with respect to the photosensitive drum 50 and switching of the nip pressure of the fixing device 80 .

The control unit 2 can perform an initialization operation, a warm-up operation, and a printing operation. In this embodiment, the initialization operation corresponds to the "preparation operation". After executing the initialization operation and the warm-up operation, the control unit 2 places the image forming apparatus 1 in a standby state to wait for input of a print job. In the standby state, the control unit 2 positions all the developing rollers 61 at the separated positions, and sets the nip pressure of the fixing device 80 to a standby nip lower than the fixing nip pressure which is the nip pressure when executing the printing operation. pressure.

When a print job is input in the standby state, the control section 2 starts the printing operation. When the image data included in the print job is a color image, the control unit 2 executes a color printing operation for forming an image on the sheet S using the plurality of developing rollers 61Y, 61M, 61C, and 61K, and the image data is In the case of a monochrome image, a monochrome printing operation is performed in which an image is formed on the sheet S using only the K developing roller 61K.

When a print job is input and a color printing operation is started, the controller 2 switches the nip pressure of the fixing device 80 from the standby nip pressure to the fixing nip pressure, and then moves the developing rollers 61Y, 61M, 61C, and 61K to the separated positions. to the contact position. Specifically, after starting to drive the nip pressure adjusting mechanism 6 to switch the nip pressure from the standby nip pressure to the fixing nip pressure, the control unit 2 stops driving the nip pressure adjusting mechanism 6 . is started to move the developing rollers 61Y, 61M, 61C and 61K from the separated positions to the contact positions.

Further, when ending the color printing operation, the controller 2 moves the developing rollers 61Y, 61M, 61C, and 61K from the contact positions to the separated positions, and then changes the nip pressure of the fixing device 80 from the fixing nip pressure to the standby nip pressure. switch to Specifically, the control unit 2 starts driving the spacing mechanism 5 to move the developing rollers 61Y, 61M, 61C, and 61K from the contact positions to the spacing positions, and then stops driving the spacing mechanism 5. The driving of the pressure adjusting mechanism 6 is started to switch the nip pressure from the fixing nip pressure to the standby nip pressure.

When a print job is input and a monochrome printing operation is started, the controller 2 switches the nip pressure of the fixing device 80 from the standby nip pressure to the fixing nip pressure, and then moves only the K developing roller 61K from the separated position to the contact position. move. Specifically, after starting to drive the nip pressure adjusting mechanism 6 to switch the nip pressure from the standby nip pressure to the fixing nip pressure, the control unit 2 stops driving the nip pressure adjusting mechanism 6 . is started to move the K developing roller 61K from the separated position to the contact position.

Further, when ending the monochrome printing operation, the controller 2 moves the K developing roller 61K from the contact position to the separated position, and then switches the nip pressure of the fixing device 80 from the fixing nip pressure to the standby nip pressure. Specifically, after starting to drive the separating mechanism 5 to move the K developing roller 61K from the contact position to the separating position, the control unit 2 stops driving the separating mechanism 5, and then the nip pressure adjusting mechanism 6 is moved. Driving is started to switch the nip pressure from the fixing nip pressure to the standby nip pressure.

In the printing operation, when switching the nip pressure of the fixing device 80 between the fixing nip pressure and the standby nip pressure, the control section 2 drives the developing motor 3D at half speed (first rotation speed). Specifically, when the printing operation is started and the nip pressure is switched from the standby nip pressure to the fixing nip pressure, the control unit 2 rotates the development motor 3D forward at half speed. Further, when ending the printing operation, when switching the nip pressure from the fixing nip pressure to the standby nip pressure, the control unit 2 reversely rotates the developing motor 3D at half speed.

In the printing operation, when the developing roller 61 is moved between the contact position and the separated position, the control section 2 drives the developing motor 3D at full speed (second rotational speed). Specifically, in the printing operation, the control unit 2 causes the developing motor 3D to rotate forward at full speed both when the developing roller 61 is moved from the separated position to the contact position and when it is moved from the contact position to the separated position. .

The initializing operation is an operation for positioning all the developing rollers 61 at the separated positions and setting the nip pressure of the fixing device 80 to the standby nip pressure. When executing the initialization operation, the control unit 2 reversely rotates the developing motor 3D. In the initializing operation, the control unit 2 first drives the developing motor 3D at half speed to simultaneously drive the separating mechanism 5 and the nip pressure adjusting mechanism 6, thereby moving the developing roller 61 from the contact position toward the separated position. At the same time, the nip pressure of the fixing device 80 is switched from the fixing nip pressure to the standby nip pressure.

After the nip pressure of the fixing device 80 is switched to the standby nip pressure, the controller 2 drives the developing motor 3D at full speed to drive the separating mechanism 5 and move the developing roller 61 to the separating position. Specifically, after the nip pressure of the fixing device 80 is switched to the standby nip pressure, the control section 2 stops driving the nip pressure adjusting mechanism 6 and temporarily stops driving the spacing mechanism 5 . Thereafter, after driving the developing motor 3D at full speed, the controller 2 resumes driving the spacing mechanism 5, drives only the spacing mechanism 5, and moves the developing roller 61 to the spacing position. After the developing roller 61 is positioned at the separated position, the controller 2 stops driving the separating mechanism 5 and stops driving the developing motor 3D.

The control unit 2 executes an initialization operation when the power of the image forming apparatus 1 is turned on. Also, the control unit 2 executes the initialization operation when the cover 11 is closed. In this embodiment, the control unit 2 executes the initialization operation when both the condition that the power of the image forming apparatus 1 is turned on and the condition that the cover 11 is closed are satisfied.

A warm-up operation is an operation performed after an initialization operation. In the warm-up operation, the control unit 2 performs, for example, cleaning to collect toner adhering to the photosensitive drum 50 and the conveying belt 73 by a belt cleaner (not shown), and raises the temperature of the heating roller 81 to a predetermined temperature in advance. perform an action.

Next, an example of processing of the control unit 2 will be described in detail with reference to FIGS. 6 to 12. FIG. 9, 10, and 12 are superimposed on the timing chart of the operation of the Y developing roller 61Y (Y), and the line type is changed to indicate the M developing roller 61M (M) and C developing roller 61C. It shows the operation of (C).

As shown in FIG. 6, the control unit 2 determines whether or not the power has been turned on (S1). If the power is not turned on (S1, No), the control unit 2 waits until it is turned on, and if the power is turned on (S1, Yes), it determines whether the cover 11 is closed. (S2). If the cover 11 is not closed (S2, No), the control unit 2 waits until the cover 11 is closed, and if the cover 11 is closed (including the case where the cover 11 is closed when the power is turned on) ( S2, Yes), the initialization operation is executed (S3). Details of the initialization operation will be described later.

After executing the initialization operation, the control unit 2 executes a warming-up operation (S4), and places the image forming apparatus 1 in a waiting state for waiting for input of a print job (S5). When the print job is input (S6), the control section 2 determines whether or not the image data included in the print job is a color image (S7). If the image is a color image (S7, Yes), the control unit 2 executes a color printing operation using the developing rollers 61Y, 61M, 61C, and 61K (S8). A monochrome printing operation using only the roller 61K is executed (S9). When the printing operation ends, the control section 2 puts the image forming apparatus 1 into the standby state again (S5). In the standby state, all the developing rollers 61 are at the separated position, and the nip pressure of the fixing device 80 is the standby nip pressure.

Next, details of the printing operation will be described.
As shown in FIGS. 7 and 9, when the color printing operation is started, the controller 2 rotates the developing motor 3D forward at half speed (S110, t30). After that, the control section 2 turns on the fixing clutch 240 (S111, t31), and rotates the switching cam 250 in the first rotation direction R1 (see FIG. 5B). As a result, the nip pressure of the fixing device 80 is switched from the standby nip pressure to the fixing nip pressure.

When the switching cam 250 rotates in the first rotation direction R1 and the phase of the switching cam 250 deviates from the predetermined phase range in which the nip pressure becomes the standby nip pressure, the nip pressure detection sensor 7 is switched from ON to OFF (S112, Yes). When the predetermined switching time T10 has elapsed since the nip pressure detection sensor 7 was switched OFF (S113, Yes), the control section 2 turns OFF the fixing clutch 240 (S114, t32), and stops the switching cam 250. . As a result, the nip pressure of the fixing device 80 is switched from the standby nip pressure to the fixing nip pressure. The switching time T10 is the time it takes for the nip pressure to switch from the standby nip pressure to the fixing nip pressure. It is set to the time until it switches to the fixing nip pressure.

Next, the controller 2 rotates the developing motor 3D forward at full speed (S120, t33). After that, the control unit 2 turns ON the YMC clutch 140A and the K clutch 140K (S131, t34), and rotates the separation cams 150Y, 150M, 150C, 150K. Then, when the separation sensors 4C and 4K are switched from ON to OFF (S132, Yes), the control section 2 turns off the YMC clutch 140A and the K clutch 140K (S133, t35), and the separation cams 150Y, 150M, 150C, Stop 150K.

Then, the controller 2 sets the sheet S in the sheet tray 21 to be picked up by the sheet feeding roller 23 (t36), and the control unit 2 controls the first time interval from the time (t37) when the leading edge of the conveyed sheet S passes the pre-registration sensor 28B. When T11 has passed (S141, Yes), the YMC clutch 140A is turned ON (S142, t38) to rotate the separating cams 150Y, 150M, 150C. As a result, the developing rollers 61Y, 61M, and 61C move from the separated positions to the contact positions. Of the developing rollers 61Y, 61M, 61C, first, the Y developing roller 61Y and the M developing roller 61M are positioned at the contact position substantially simultaneously, and then the C developing roller 61C is positioned at the contact position. The first time T11 is set to such a time that the development of the Y photosensitive drum 50Y by the Y developing roller 61Y can be completed in time for the transfer of the toner image onto the sheet S that has been conveyed.

Further, when the first time T21 has passed since the leading edge of the conveyed sheet S passed the post-registration sensor 28C (t39) (S143, Yes), the controller 2 turns on the K clutch 140K (S144). , t40), the K separation cam 150K is rotated. As a result, the K developing roller 61K moves from the separated position to the contact position. The K developing roller 61K is positioned at the contact position after the C developing roller 61C is positioned at the contact position. The first time T21 is set so that the development of the K photosensitive drum 50K by the K developing roller 61K can be completed in time for the toner image to be transferred onto the sheet S that has been conveyed.

Then, when the second time T12 has passed since the time when the YMC clutch 140A was turned on (t38) (S145, Yes), the control unit 2 turns off the YMC clutch 140A (S146, t41), and , 150C are stopped. The second time T12 is set such that all of the developing rollers 61Y, 61M, and 61C are positioned at the contact position.

Further, when the second time T22 has passed since the time (t40) when the K clutch 140K was turned on (S147, Yes), the control unit 2 turns off the K clutch 140K (S148, t42), and operates the K separation cam 150K. stop. The second time T22 is set such that the K developing roller 61K is positioned at the contact position.

After that, the control unit 2 determines whether or not the printing has ended (S151). If the printing is not finished (S151, No), the control unit 2 waits until the printing is finished, and if the printing is finished (S151, Yes), the process proceeds to the next step.

As shown in FIGS. 8 and 10, in the next step, the control unit 2 controls when the third time T13 has passed since the trailing edge of the sheet S passed the post-registration sensor 28C (t43) (S161, Yes ), the YMC clutch 140A is turned ON (S162, t44), and the separation cams 150Y, 150M, 150C are rotated. As a result, the developing rollers 61Y, 61M, and 61C move from the contact position to the separated position. The developing rollers 61Y, 61M, and 61C are positioned at the separated positions in order of the Y developing roller 61Y, the M developing roller 61M, and the C developing roller 61C. The third time T13 is set to a time during which the Y developing roller 61Y can move to the separated position after the Y developing roller 61Y completes the development of the Y photosensitive drum 50Y.

Further, when the third time T23 has passed since the trailing edge of the sheet S passed the post-registration sensor 28C (t43) (S163, Yes), the control section 2 turns ON the K clutch 140K (S164, t45). , K to rotate the separating cam 150K. As a result, the K developing roller 61K moves from the contact position to the separated position. The K developing roller 61K is positioned at the separated position after the C developing roller 61C is positioned at the separated position. The third time T23 is set to a time during which the K developing roller 61K can move to the separated position after the K developing roller 61K completes development on the K photosensitive drum 50K.

After that, when the separation sensor 4C is switched from OFF to ON (S165, Yes), the control section 2 turns off the YMC clutch 140A (S166, t46), and stops the separation cams 150Y, 150M, 150C. Further, when the separation sensor 4K is switched from OFF to ON (S167, Yes), the control section 2 turns OFF the K clutch 140K (S168, t47) and stops the K separation cam 150K.

After that, the controller 2 temporarily stops the developing motor 3D (S170, t48), and then reversely rotates the developing motor 3D at half speed (S180, t49). After that, the control section 2 turns on the fixing clutch 240 (S181, t50), and rotates the switching cam 250 in the second rotation direction R2 (see FIG. 5A). As a result, the nip pressure of the fixing device 80 is switched from the fixing nip pressure to the standby nip pressure.

When the switching cam 250 rotates in the second rotation direction R2 and the phase of the switching cam 250 enters a predetermined phase range in which the nip pressure becomes the standby nip pressure, the nip pressure detection sensor 7 is switched from OFF to ON. When the nip pressure detection sensor 7 is switched to ON (S182, Yes), the control section 2 turns the fixing clutch 240 OFF (S183, t51), and stops the switching cam 250. As a result, the nip pressure of the fixing device 80 is switched from the fixing nip pressure to the standby nip pressure. After that, the control section 2 stops the developing motor 3D (S190, t52) and ends the color printing operation.

Regarding the processing of the control unit 2 when executing the monochrome printing operation, the YMC clutch 140A remains OFF and does not move at all, and the developing rollers 61Y, 61M, and 61C remain positioned at the separated positions. This is substantially the same as when executing a print operation.

Next, details of the initialization operation will be described. The photosensitive drum 50 and the developing roller 61 are configured to remain stopped while the initialization operation is being performed.

As shown in FIGS. 11 and 12, when the initialization operation is started, the controller 2 reversely rotates the developing motor 3D at half speed (S210, t60). After that, the controller 2 turns on the developing clutch 140 (S211) and turns on the fixing clutch 240 (S212, t61). As a result, the separating mechanism 5 and the nip pressure adjusting mechanism 6 are driven simultaneously.

At this time, the spacing cam 150 of the spacing mechanism 5 rotates in a direction opposite to that in the printing operation. Further, the separating cam 150 rotates at a rotational speed slower than when the developing motor 3D is rotated at full speed, and the developing roller 61 moves at a slower speed than when the developing motor 3D is rotated at full speed. . Also, the switching cam 250 of the nip pressure adjusting mechanism 6 rotates in the second rotation direction R2 (see FIG. 5A), and the nip pressure of the fixing device 80 switches from the fixing nip pressure to the standby nip pressure.

When the nip pressure of the fixing device 80 is switched from the fixing nip pressure to the standby nip pressure and the nip pressure detection sensor 7 is switched from OFF to ON (S213, Yes), the control section 2 turns the fixing clutch 240 OFF (S214, t63), the switching cam 250 is stopped. After that, the controller 2 turns off the developing clutch 140 (S215, t64) and stops the separating cam 150 in order to switch the rotational speed of the developing motor 3D.

Then, the controller 2 reversely rotates the developing motor 3D at full speed (S220, t65). After that, the control section 2 turns on the development clutch 140 again (S221, t66), and rotates the separation cam 150. As shown in FIG. As a result, the spacing mechanism 5 is driven. At this time, the separating cam 150 rotates in a direction opposite to that in the printing operation. Also, the separating cam 150 rotates at the same rotational speed as in the printing operation, and the developing roller 61 moves at the same speed as in the printing operation.

After that, the control section 2 executes the processes of steps S222 to S226 for determining whether or not the developing roller 61 is positioned at the separated position for each of the YMC clutch 140A and K clutch 140K.

That is, after turning ON the K clutch 140K and rotating the K separation cam 150K in step S221, the control unit 2 determines whether or not the separation sensor 4K has been switched from OFF to ON (S222). Then, when the separation sensor 4K is switched to ON (S222, Yes, t67), the controller 2 determines whether or not the separation sensor 4K is switched from ON to OFF (S223). Then, when the separation sensor 4K is switched to OFF (S223, Yes, t68), the controller 2 determines again whether the separation sensor 4K is switched from OFF to ON (S224).

Then, when the separation sensor 4K is switched to ON (S224, Yes, t71), the controller 2 determines whether or not the predetermined time T8 has passed (S225). When the predetermined time T8 has passed (S225, Yes), the control unit 2 turns off the K clutch 140K (S226, t72) and stops the K separation cam 150K. The predetermined time T8 for the separation sensor 4K is the timing when the K developing roller 61K moves from the contact position to the separation position when the developing motor 3D is rotated forward in the printing operation, and the second detected portion of the K separation cam 150K is detected. The time is set so that 154K (see FIG. 4) can be positioned at the position detected by the separation sensor 4K.

Similarly, after turning ON the YMC clutch 140A in step S221 to rotate the separation cams 150Y, 150M, and 150C, the control unit 2 turns the separation sensor 4K from OFF to ON (t69), OFF (t70), and ON (t73). ), the control unit 2 determines whether or not the predetermined time T8 has elapsed (S225). Then, when the predetermined time T8 has passed (S225, Yes), the control section 2 turns off the YMC clutch 140A (S226, t74), and stops the separation cams 150Y, 150M, 150C. The predetermined time T8 for the separation sensor 4C is the timing when the C developing roller 61C moves from the contact position to the separation position when the development motor 3D is rotated forward in the printing operation, and the first detected portion of the C separation cam 150C is detected. 154A (see FIG. 3) is set to a position where it can be detected by the distance sensor 4C.

After turning off the development clutch 140, the control section 2 stops the development motor 3D (S230, t75) and ends the initialization operation. In the initializing operation, after the developing motor 3D is rotated at full speed (after t65), only the separating mechanism 5 is driven, and the nip pressure adjusting mechanism 6 is not driven.

According to the present embodiment described above, when the spacing mechanism 5 and the nip pressure adjusting mechanism 6 are simultaneously driven in the initializing operation, the rotating speed of the developing motor 3D is as low as half speed. The mechanism 6 can be stably driven. As a result, there is no need to adopt a large motor capable of driving the separating mechanism 5 and the nip pressure adjusting mechanism 6 at a high rotational speed, so that the development motor 3D can be prevented from becoming large, and the image forming apparatus can be improved. 1 can be suppressed.

On the other hand, after the nip pressure of the fixing device 80 is switched from the fixing nip pressure to the standby nip pressure and the nip pressure adjusting mechanism 6 is stopped, the rotation speed of the developing motor 3D is increased to full speed, and thereafter the developing roller 61 is separated. It is possible to shorten the time to locate the position. As a result, the time until the initialization operation is completed can be shortened, so the waiting time until the image forming apparatus 1 enters a printable standby state can be shortened.

A second transmission mechanism 200 for transmitting the driving force from the developing motor 3D to the nip pressure adjusting mechanism 6 is branched from the first transmission mechanism 100 for transmitting the driving force from the developing motor 3D to the spacing mechanism 5. Therefore, compared to the case where a mechanism for transmitting the driving force from the developing motor 3D to the spacing mechanism 5 and a mechanism for transmitting the driving force from the developing motor 3D to the nip pressure adjusting mechanism 6 are provided independently, image formation is much easier. An increase in size of the device 1 can be suppressed.

In such a configuration, the second transmission mechanism 200 is provided with the fixing clutch 240 that drives the nip pressure adjusting mechanism 6 when turned on and stops the nip pressure adjusting mechanism 6 when turned off. By switching the state of the fixing clutch 240, the nip pressure adjustment mechanism 6 can be switched between driving and stopping. As a result, the nip pressure adjusting mechanism 6 can be stopped while the spacing mechanism 5 is being driven.

Further, since the first transmission mechanism 100 is branched from the third transmission mechanism 300 for transmitting the driving force from the developing motor 3D to the developing roller 61, the motor for driving the developing roller 61 and the spacing mechanism 5 and the like are driven. There is no need to provide a separate motor for As a result, the total number of motors can be reduced, so that an increase in size of the image forming apparatus 1 can be suppressed.

In such a configuration, the first transmission mechanism 100 is provided with a developing clutch 140 that drives the separating mechanism 5 when turned ON and stops the separating mechanism 5 when turned OFF. Since the fixing clutch 240 is provided, the separating mechanism 5 and the nip pressure adjusting mechanism 6 can be switched between driving and stopping by switching the states of the developing clutch 140 and the fixing clutch 240 . As a result, while driving the developing roller 61, the spacing mechanism 5 and the nip pressure adjusting mechanism 6 can be driven or stopped.

Further, when switching the nip pressure of the fixing device 80 in the printing operation, the rotation speed of the developing motor 3D is reduced to half speed, so the load on the nip pressure adjustment mechanism 6 can be reduced. On the other hand, when the developing roller 61 is moved in the printing operation, the rotational speed of the developing motor 3D is increased to full speed, so that the developing roller 61 can be moved quickly and the waiting time during printing is shortened. be able to.

Although one embodiment of the invention has been described above, the invention is not limited to the above-described embodiment, and can be implemented with appropriate modifications as exemplified below.

For example, the configurations of the separation mechanism, the nip pressure adjustment mechanism, and the like described in the above embodiment are examples. That is, in the above-described embodiment, the spacing cam 150 has cam ridges on the outer peripheral surface, but the spacing cam may be an end face cam or the like. Further, in the above-described embodiment, the separating cam 150 is configured to directly press the developing cartridge 60. However, for example, a member other than the developing cartridge, such as a cam follower, may be pressed, and the separate member may press the developing cartridge. It may be configured to press. Further, in the above embodiment, the developing cartridge 60 is supported so as to move back and forth, but it may be supported so as to move up and down, for example.

In the above-described embodiment, the switching cam 250 is configured to switch the nip pressure of the fixing device 80 by switching the rotation direction. The nip pressure of the device 80 may be switchable between a fusing nip pressure and a standby nip pressure. Further, in the above-described embodiment, there is one type of fixing nip pressure for fixing, but the fixing nip pressure may be set in multiple stages according to the thickness of the sheet S, for example. In the above-described embodiment, as shown in FIG. 5B, the heating roller 81 and the pressure roller 82 are in contact with each other under the standby nip pressure. The pressure roller 82 may be spaced apart.

Further, in the above-described embodiment, the heating roller 81 is used as an example of the heating section, but the heating section may be a heating unit having an endless heating belt, for example. Further, in the above-described embodiment, the pressure roller 82 is used as the pressure unit, but the pressure unit may be a pressure unit having an endless pressure belt, for example.

Further, in the above-described embodiment, the nip pressure is switched by moving the pressure roller 82 (pressing portion) with respect to the heating roller 81 (heating portion). You can switch the nip pressure with .

Further, in the above embodiment, when the nip pressure of the fixing device 80 is switched in the printing operation, the developing motor 3D is driven at half speed, but it may be driven at full speed.

Further, in the above-described embodiment, the second transmission mechanism 200 for transmitting the driving force from the developing motor 3D to the nip pressure adjusting mechanism 6 replaces the first transmission mechanism 200 for transmitting the driving force from the developing motor 3D to the separating mechanism 5. Although it is branched from the transmission mechanism 100, it is not limited to this. For example, a transmission mechanism for transmitting the driving force from the motor to the nip pressure adjusting mechanism and a transmission mechanism for transmitting the driving force from the motor to the spacing mechanism may be provided independently.

Further, in the above embodiment, the "motor" according to the invention is the developing motor 3D, and the first transmission mechanism 100 and the second transmission mechanism 200 are the third motor for transmitting the driving force from the developing motor 3D to the developing roller 61. Although it is branched from the transmission mechanism 300, it is not limited to this. For example, the first transmission mechanism and the second transmission mechanism may be provided independently of the transmission mechanism that transmits the driving force to the developing roller, and the "motor" may be a motor separate from the motor that transmits the driving force to the developing roller. .

Further, in the above-described embodiment, the image forming apparatus 1 that prints a color image using toner of four colors was exemplified. good. Further, the image forming apparatus may be an apparatus that includes one photosensitive drum and one developing roller and prints a monochrome image using toner of one color. Also, the image forming apparatus is not limited to a printer, and may be a multifunction machine, a copier, or the like.

Each element described in the above embodiment and modifications may be implemented in any combination.

REFERENCE SIGNS LIST 1 image forming apparatus 2 control unit 3D developing motor 5 separating mechanism 6 nip pressure adjusting mechanism 10 housing 10A opening 11 cover 50 photosensitive drum 61 developing roller 80 fixing device 81 heating roller 82 pressure roller 100 first transmission mechanism 140 developing clutch 200 Second transmission mechanism 240 Fixing clutch 300 Third transmission mechanism S Seat

Claims (8)

a photosensitive drum;
a developing roller movable between a contact position that contacts the photosensitive drum and a separation position that separates from the photosensitive drum;
a fixing device having a heating section and a pressure section sandwiching a sheet between the heating section;
a motor;
a separation mechanism driven by receiving a driving force from the motor to move the developing roller between the contact position and the separation position;
A nip driven by receiving a driving force from the motor to switch the nip pressure between the heating portion and the pressure portion between a first nip pressure and a second nip pressure lower than the first nip pressure. a pressure adjustment mechanism;
a control unit;
The control unit
The motor is driven at a first rotation speed to simultaneously drive the separating mechanism and the nip pressure adjusting mechanism, thereby moving the developing roller from the contact position toward the separating position, while adjusting the nip pressure to the above-mentioned position. Switching from the first nip pressure to the second nip pressure,
After the nip pressure is switched to the second nip pressure, the motor is driven at a second rotation speed that is higher than the first rotation speed to drive the spacing mechanism and move the developing roller to the spacing position. , an image forming apparatus capable of executing a preparatory operation. a first transmission mechanism capable of transmitting the driving force from the motor to the spacing mechanism;
a second transmission mechanism branched from the first transmission mechanism and capable of transmitting driving force from the motor to the nip pressure adjustment mechanism;
The second transmission mechanism is a first electromagnetic clutch that switches between a transmission state in which driving force from the motor is transmitted to the nip pressure adjusting mechanism and a disconnected state in which driving force from the motor is not transmitted to the nip pressure adjusting mechanism. has
2. The control unit according to claim 1, wherein the first electromagnetic clutch is set in a transmitting state to drive the nip pressure adjusting mechanism, and the first electromagnetic clutch is set in a disengaged state to stop the nip pressure adjusting mechanism. image forming device. A third transmission mechanism capable of transmitting driving force from the motor to the developing roller,
The first transmission mechanism is
branched from the third transmission mechanism,
a second electromagnetic clutch that switches between a transmission state in which the driving force from the motor is transmitted to the spacing mechanism and a disconnected state in which the driving force from the motor is not transmitted to the spacing mechanism;
3. The image forming apparatus according to claim 2, wherein the control unit drives the separation mechanism by setting the second electromagnetic clutch to a transmission state, and stops the separation mechanism by setting the second electromagnetic clutch to a disengagement state. . 4. The image forming apparatus according to any one of claims 1 to 3, wherein the control section executes the preparatory operation when power of the image forming apparatus is turned on. a housing;
a cover that can open and close an opening provided in the housing,
5. The image forming apparatus according to any one of claims 1 to 4, wherein the controller executes the preparatory operation when the cover is closed. The control unit
When in a standby state waiting for input of a print job, the developing roller is positioned at the separated position and the nip pressure is set to the second nip pressure,
When a print job is input in the standby state and the printing operation is started, after switching the nip pressure from the second nip pressure to the first nip pressure, the developing roller is moved from the separated position to the contact position. 6. The image forming apparatus according to any one of claims 1 to 5, characterized in that: The control unit is characterized in that, when ending the printing operation, the nip pressure is switched from the first nip pressure to the second nip pressure after moving the developing roller from the contact position to the separated position. 7. The image forming apparatus according to claim 6. The control unit, in the printing operation,
when switching the nip pressure between the first nip pressure and the second nip pressure, driving the motor at the first rotational speed;
8. The image forming apparatus according to claim 6, wherein the motor is driven at the second rotational speed when moving the developing roller between the contact position and the separated position. .

Images