阅读说明：本技术 图像形成设备 (Image forming apparatus with a toner supply unit ) 是由 春田晃太郎 佐伯正仁 西村祥一郎 渡边知范 于 2019-12-24 设计创作，主要内容包括：提供一种图像形成设备,具有：感光鼓；显影辊,能够在接触位置和分离位置之间移动,在接触位置,显影辊接触感光鼓,在分离位置,显影辊与感光鼓分离；移动机构,在接触位置和分离位置之间移动显影辊；定影器,包括加热构件和按压构件,按压构件在加热构件和按压构件之间的位置夹持片状物；夹持力调节器,在第一夹持力和第二夹持力之间切换定影器中的夹持力,第二夹持力大于第一夹持力；马达；和驱动力传送器,将来自马达的驱动力传送至显影辊。驱动力传送器进一步将驱动力传送至移动机构和夹持力调节器。(Provided is an image forming apparatus having: a photosensitive drum; a developing roller movable between a contact position where the developing roller contacts the photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum; a moving mechanism that moves the developing roller between the contact position and the separation position; a fixer including a heating member and a pressing member that sandwiches the sheet at a position between the heating member and the pressing member; a clamping force adjuster that switches a clamping force in the fuser between a first clamping force and a second clamping force, the second clamping force being greater than the first clamping force; a motor; and a driving force transmitter transmitting a driving force from the motor to the developing roller. The driving force transmitter further transmits the driving force to the moving mechanism and the grip adjuster.)

1. An image forming apparatus, characterized by comprising:

a photosensitive drum;

a developing roller configured to be movable between a contact position where the developing roller contacts the photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum;

a moving mechanism configured to move the developing roller between the contact position and the separation position;

a fixer including a heating member and a pressing member configured to nip a sheet at a position between the heating member and the pressing member;

a nip force adjuster configured to switch a nip force between the heating member and the pressing member in the fuser between a first nip force and a second nip force, the second nip force being greater than the first nip force;

a motor; and

a driving force transmitter configured to transmit a driving force from the motor to the developing roller, the driving force transmitter further configured to transmit the driving force from the motor to the moving mechanism and the grip adjuster.

2. The image forming apparatus according to claim 1,

wherein the motor is capable of bi-directional rotation in a forward direction and a reverse direction;

wherein the driving force transmitter is configured to transmit the driving force from the motor to the developing roller when the motor rotates in the forward direction;

wherein the moving mechanism is configured to move the developing roller between the contact position and the separation position when the motor rotates in the forward direction; and is

Wherein the nip force adjuster is configured to switch the nip force in the fuser from the first nip force to the second nip force when the motor rotates in the forward direction, and to switch the nip force from the second nip force to the first nip force when the motor rotates in the reverse direction.

3. The image forming apparatus according to claim 2,

wherein the moving mechanism includes a first cam configured to control a position of the developing roller, the first cam being configured to rotate by receiving the driving force from the motor; and is

Wherein the drive force transmitter includes a first clutch configured to switch a state of the first cam between rotation and standstill by switching between a state in which the drive force transmitter can transmit the drive force from the motor to the first cam and a state in which the drive force from the motor is interrupted without being transmitted to the first cam.

4. The image forming apparatus according to claim 3, further comprising

A developing cartridge including the developing roller,

wherein the first cam is configured to rotate about an axis parallel to a rotational axis direction, which is a direction of a rotational axis of the developing roller, the first cam including a first cam portion protruding in the rotational axis direction; and is

Wherein the moving mechanism includes a cam follower configured to contact the first cam portion in the first cam and press the developing cartridge by slidably moving in the rotational axis direction.

5. The image forming apparatus according to claim 4, further comprising

A supporting member configured to support the developing cartridge,

wherein the developing cartridge includes a slider member configured to slidably move in the rotational axis direction by being pressed by the cam follower; and is

Wherein the slider member includes an inclined surface that is inclined with respect to the rotational axis direction, the inclined surface being configured to contact the support member and push the developing cartridge in a direction orthogonal to the rotational axis direction.

6. The image forming apparatus according to claim 4,

the driving force transmitter is mechanically connected to the moving mechanism, and the driving force transmitter is configured to interrupt the driving force from the motor without transmitting to the developing roller when the developing roller is located at the separation position.

7. The image forming apparatus according to claim 6,

wherein the driving force transmitter includes:

a second cam portion configured to rotate integrally with the first cam;

a clutch including a planetary gear assembly, the clutch being switchable between a transmittable state in which the clutch is capable of transmitting the driving force from the motor to the developing roller and an interrupted state in which the driving force from the motor is interrupted; and

a lever swingable to contact and separate from the second cam portion, the lever being configured to place the clutch in the transmittable state when the lever separated from the second cam portion is engaged with one of the elements in the planetary gear assembly that rotates with rotation of the motor in the forward direction; the lever is configured to place the clutch in the off state at least one of when the lever contacting the second cam portion is disengaged from one of the elements in the planetary gear assembly and when one of the elements in the planetary gear assembly rotates with rotation of the motor in the reverse direction.

8. The image forming apparatus according to any one of claims 3 to 7,

wherein the clamping force adjuster includes a second cam configured to move one of the heating member and the pressing member to switch the clamping force, the second cam being configured to rotate by receiving the driving force from the motor;

wherein the driving force transmitter includes a second clutch configured to switch a state of the second cam between rotation and standstill by switching between a state in which the driving force transmitter can transmit the driving force from the motor to the second cam and a state in which the driving force from the motor is interrupted without being transmitted to the second cam.

9. The image forming apparatus according to claim 1,

wherein the heating member and the pressing member are separated from each other when the nip force in the fixer is at the first nip force.

10. The image forming apparatus according to claim 9,

wherein the second clamping force comprises a third clamping force greater than the first clamping force and a fourth clamping force greater than the third clamping force; and is

Wherein the clamping force adjuster is configured to switch the clamping force between the first clamping force and the third clamping force and between the first clamping force and the fourth clamping force.

11. An image forming apparatus, characterized by comprising:

a photosensitive drum;

a developing roller configured to be movable between a contact position where the developing roller contacts the photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum;

a moving mechanism configured to move the developing roller between the contact position and the separation position;

a fuser including a heating member and a pressing member;

a nip force adjuster configured to switch a nip force between the heating member and the pressing member in the fuser between a first nip force and a second nip force, the second nip force being greater than the first nip force; and

a developing motor for driving the developing roller to rotate,

wherein the developing motor is configured to drive the developing roller, the moving mechanism, and the grip adjuster.

12. The image forming apparatus according to claim 11, further comprising:

a belt unit configured to transfer a toner image formed on the photosensitive drum to a sheet; and

a process motor configured to drive the photosensitive drum and the belt unit.

13. The image forming apparatus according to any one of claims 11 and 12, further comprising a fuser motor configured to drive the heating member.

14. The image forming apparatus according to any one of claims 11 and 12,

wherein the developing motor is bidirectionally rotatable in a forward direction and a reverse direction;

wherein the developing roller is configured to be driven by a driving force from the developing motor when the developing motor rotates in the forward direction;

wherein the moving mechanism is configured to move the developing roller between the contact position and the separation position by a driving force from the developing motor when the developing motor rotates in the forward direction; and

wherein the nip adjuster is configured to switch the nip force in the fuser from the first nip force to the second nip force when the developing motor rotates in the forward direction, and to switch the nip force from the second nip force to the first nip force when the developing motor rotates in the reverse direction.

Technical Field

The present disclosure relates to an image forming apparatus having a photosensitive drum, a developing roller, and a fixer, capable of forming an image electrophotographically.

Background

Image forming apparatuses for forming images electrophotographically are known. For example, an electrophotographic image forming apparatus having a cam that adjusts a nip force in a fixer and a dedicated motor that moves the cam is disclosed in japanese patent provisional publication No. h 05-297763. As another example, an electrophotographic image forming apparatus having a moving device that moves a developing roller between a contact position where the developing roller is in contact with a photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum is disclosed in japanese patent provisional publication No. 2015-69031. According to this publication, the image forming apparatus is equipped with a single motor that can drive both the rotation of the developing roller and the movement of the moving device.

Disclosure of Invention

In this regard, in general, it may be preferable to reduce the number of motors that drive the movable member in the image forming apparatus.

An advantage of the present disclosure is to provide an image forming apparatus in which rotation of a developing roller, contact/separation movement of the developing roller, and adjustment of a nip force in a fuser can be driven by a single motor.

According to the present disclosure, there is provided an image forming apparatus having a photosensitive drum, a developing roller, a moving mechanism, a fixer, a nip adjuster, a motor, and a driving force transmitter. The developing roller is configured to be movable between a contact position where the developing roller contacts the photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum. The moving mechanism is configured to move the developing roller between the contact position and the separation position. The fuser includes a heating member and a pressing member. The pressing member is configured to sandwich the sheet at a position between the heating member and the pressing member. The nip adjuster is configured to switch a nip force between the heating member and the pressing member in the fuser between a first nip force and a second nip force. The second clamping force is greater than the first clamping force. The driving force transmitter is configured to transmit a driving force from the motor to the developing roller. The driving force transmitter is further configured to transmit the driving force from the motor to the moving mechanism and the grip adjuster.

Alternatively, the motor may be capable of bi-directional rotation in a forward direction and a reverse direction. The driving force transmitter may be configured to transmit the driving force from the motor to the developing roller when the motor rotates in the forward direction. The moving mechanism may be configured to move the developing roller between the contact position and the separation position when the motor rotates in the forward direction. The nip adjuster may be configured to switch the nip force in the fuser from the first nip force to the second nip force when the motor rotates in the forward direction, and to switch the nip force from the second nip force to the first nip force when the motor rotates in the reverse direction.

Alternatively, the moving mechanism may include a first cam configured to control the position of the developing roller. The first cam may be configured to rotate by receiving a driving force from the motor. The drive force transmitter may include a first clutch configured to switch a state of the first cam between rotation and rest by switching between a state in which the drive force transmitter can transmit the drive force from the motor to the first cam and a state in which the drive force from the motor is interrupted without being transmitted to the first cam.

Alternatively, the image forming apparatus may further have a developing cartridge including the developing roller. The first cam may be configured to rotate about an axis parallel to the direction of the axis of rotation. The rotational axis direction may be a direction of a rotational axis of the developing roller. The first cam may include a first cam portion protruding in the rotational axis direction. The moving mechanism may include a cam follower configured to contact a first cam portion of the first cam and press the developing cartridge by slidably moving in the rotational axis direction.

Alternatively, the image forming apparatus may further have a supporting member configured to support the developing cartridge. The developing cartridge may include a slider member configured to be slidably moved in the rotational axis direction by being pressed by the cam follower. The slider member may include an inclined surface inclined with respect to the rotational axis direction. The inclined surface may be configured to contact the support member and urge the developing cartridge in a direction orthogonal to the rotational axis direction.

Alternatively, the driving force transmitter may be mechanically connected to the moving mechanism. The driving force transmitter may be configured to interrupt the driving force from the motor without transmitting to the developing roller when the developing roller is located at the separation position.

Alternatively, the driving force transmitter may include a second cam portion, a clutch, and a lever. The second cam portion may be configured to rotate integrally with the first cam. The clutch may comprise a planetary gear assembly. The clutch may be switchable between a conveyable state in which the clutch is capable of transmitting the driving force from the motor to the developing roller and an interrupted state in which the driving force from the motor is interrupted. The lever is swingable to contact and separate from the second cam portion. The lever may be configured to place the clutch in a transmittable state when the lever, which is separate from the second cam portion, engages one of the elements of the planetary gear assembly that rotates with rotation of the motor in the forward direction. The lever may be configured to place the clutch in the disengaged state at least one of when the lever contacting the second cam portion is disengaged from one of the elements in the planetary gear assembly and when one of the elements in the planetary gear assembly rotates with rotation of the motor in the reverse direction.

Alternatively, the clamping force adjuster may include a second cam configured to move one of the heating member and the pressing member to switch the clamping force. The second cam may be configured to rotate by receiving a driving force from the motor. The drive force transmitter may include a second clutch configured to switch the state of the second cam between rotation and rest by switching between a state in which the drive force transmitter can transmit the drive force from the motor to the second cam and a state in which the drive force from the motor is interrupted without being transmitted to the second cam.

Alternatively, the heating member and the pressing member may be separated from each other when the clamping force in the fixer is at the first clamping force.

Alternatively, the second clamping force may include a third clamping force greater than the first clamping force, and a fourth clamping force greater than the third clamping force. The clamp force adjuster may be configured to switch the clamp force between the first clamp force and the third clamp force and between the first clamp force and the fourth clamp force.

According to the present disclosure, there is further provided an image forming apparatus having a photosensitive drum, a developing roller, a moving mechanism, a fuser, a nip adjuster, and a developing motor. The developing roller is configured to be movable between a contact position where the developing roller contacts the photosensitive drum and a separation position where the developing roller is separated from the photosensitive drum. The moving mechanism is configured to move the developing roller between the contact position and the separation position. The fuser includes a heating member and a pressing member. The nip adjuster is configured to switch a nip force between the heating member and the pressing member in the fuser between a first nip force and a second nip force. The second clamping force is greater than the first clamping force. The developing motor is configured to drive the developing roller, the moving mechanism, and the grip adjuster.

Alternatively, the image forming apparatus may further have a belt unit configured to transfer the toner image formed on the photosensitive drum to the sheet, and a process motor configured to drive the photosensitive drum and the belt unit.

Alternatively, the image forming apparatus may further have a fuser motor configured to drive the heating member.

Alternatively, the developing motor may be capable of bidirectional rotation in the forward direction and the reverse direction. The developing roller may be configured to be driven by a driving force from the developing motor when the developing motor rotates in the forward direction. The moving mechanism may be configured to move the developing roller between the contact position and the separation position by a driving force from the developing motor when the developing motor is rotated in the forward direction. The nip adjuster may be configured to switch the nip force in the fuser from the first nip force to the second nip force when the developing motor rotates in the forward direction, and to switch the nip force from the second nip force to the first nip force when the developing motor rotates in the reverse direction.

Drawings

Fig. 1 is an overall cross-sectional view of an image forming apparatus according to an embodiment of the present disclosure.

Fig. 2 is a perspective view of a support member, a cam, and a cam follower in an image forming apparatus according to an embodiment of the present disclosure.

Fig. 3A is a perspective view of a developing cartridge for an image forming apparatus according to an embodiment of the present disclosure. Fig. 3B is a side view of a developing cartridge for an image forming apparatus according to an embodiment of the present disclosure.

Fig. 4A is a schematic view of the developing cartridge and its periphery when the cam follower is in the standby position. Fig. 4B is a schematic view of the developing cartridge and its periphery when the cam follower is in the operable position.

Fig. 5 is an inside view of a side frame in a support member in an image forming apparatus according to an embodiment of the present disclosure.

Fig. 6 is a block diagram illustrating a driving system in an image forming apparatus according to an embodiment of the present disclosure.

Fig. 7 is a perspective view of the driving force transmitter in the image forming apparatus according to the embodiment of the present disclosure, viewed from an upper left perspective.

Fig. 8 is a side view of the driving force transmitter in the image forming apparatus according to the embodiment of the present disclosure, viewed from left to right in the axial direction.

Fig. 9 is a perspective view of the driving force transmitter in the image forming apparatus according to the embodiment of the present disclosure, viewed from an upper right perspective.

Fig. 10 is a side view of the driving force transmitter in the image forming apparatus according to the embodiment of the present disclosure, viewed from right to left in the axial direction.

Fig. 11A and 11B are exploded views of the clutch in the image forming apparatus according to the embodiment of the present disclosure, as viewed from the side of the sun gear and the side of the carrier, respectively.

Fig. 12A and 12B are a side view of the moving mechanism with the clutch in the conveyable state beside the lever and the coupling gear as viewed in the axial direction, and a perspective view of the moving mechanism, respectively, in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 13A and 13B are a side view of a moving mechanism having a cam that rotates from the position shown in fig. 12A to 12B beside a lever, a clutch, and a coupling gear when a developing roller of yellow is in a contact position to form an image, as viewed in the axial direction, and a perspective view of the moving mechanism, respectively, in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 14A and 14B are a side view of a moving mechanism having a cam that rotates from the position shown in fig. 13A to 13B beside a lever, a clutch, and a coupling gear when the developing roller is at the separation position and the clutch is in the conveyable state, and a perspective view of the moving mechanism, respectively, as viewed in the axial direction in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 15A and 15B are a side view of the moving mechanism having the cam rotated from the position shown in fig. 14A to 14B beside the lever, the clutch, and the coupling gear when the developing roller is at the separation position and the clutch is in the interruption state, and a perspective view of the moving mechanism, respectively, as viewed in the axial direction in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 16A and 16B are a side view of a moving mechanism having a cam that rotates from the position shown in fig. 15A to 15B beside a lever, a clutch, and a coupling gear when a developing roller of yellow is paused before moving to a contact position, as viewed in the axial direction, and a perspective view of the moving mechanism, respectively, in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 17A to 17C illustrate a fixer and a second cam in an image forming apparatus according to an embodiment of the present disclosure, in which a nip force between a heating roller and a pressure roller is large, small, and none (zero), respectively.

Fig. 18A to 18B are flowcharts illustrating a flow of steps to be performed when a print job is received in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 19A to 19C are flowcharts illustrating a flow of steps to be performed when a color image is printed in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 20 is a timing chart illustrating control of the YMC clutch and the K clutch based on signals output from the sensors when a color image is printed in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 21 is a timing chart illustrating movements of the cam, the separation sensor, and the developing roller when printing a color image in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 22A to 22B are flowcharts showing a flow of steps to be performed when a monochrome image is printed in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 23 is a timing chart illustrating control of the K clutch based on a signal output from the sensor and movement of the developing roller for black when a monochrome image is printed in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 24A to 24D illustrate separation and contact movement of the developing roller when printing a color image in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 25A to 25D illustrate the separation and contact movement of the developing roller continuing from the position in fig. 24D when a color image is printed in the image forming apparatus according to the embodiment of the present disclosure.

Fig. 26A to 26C illustrate separation and contact movement of the developing roller when printing a monochrome image in the image forming apparatus according to the embodiment of the present disclosure.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

As shown in fig. 1, an image forming apparatus 1 according to the embodiment is a color printer, and has a main casing 10, the main casing 10 accommodating a sheet feeder 20, an image forming device 30, and a controller 2.

The sheet feeder 20 is disposed at a lower position in the main casing 10, and includes a sheet tray 21 storing the sheets S, and a feeder device 22 feeding the sheets S from the sheet tray 21 to the image forming device 30. The sheet tray 21 is movable to be pulled forward, for example, leftward in fig. 1, to be detached from the main casing 10. The feeder device 22 is arranged at a forward position in the main housing 10 and comprises a feeder roller 23, a separator roller 24, a separator pad 25 and a positioning roller 27. In the following description, reference will be made to directions relating to the image forming apparatus 1 and each part or item included in the image forming apparatus 1 based on the arrow indications in fig. 1. For example, in fig. 1, the left-hand side, right-hand side, upper side, and lower side of the observer will be referred to as front side, rear side, upper side, and lower side, respectively. Further, the farther side and the closer side of the observer in fig. 1 will be referred to as the left-hand side and the right-hand side in the image forming apparatus 1, respectively. The front-to-back direction or the back-to-front direction may be referred to as a front-to-back direction, the left-to-right direction or the right-to-left direction may be referred to as a lateral direction, and the up-to-down direction or the down-to-up direction may be referred to as a vertical direction. The sheet S in the present embodiment is a printing medium on which the image forming apparatus 1 can form an image, and includes, but is not limited to, plain paper, an envelope, a postcard, a tracing paper, a cardboard, a resin sheet, and a sticker sheet.

In the sheet feeder 20, one sheet S in the sheet tray 21 may be picked up by a feeder roller 23 and separated from the other sheets S by a separator roller 24 and a separator pad 25. When the separated sheet S is further conveyed, the position of the leading edge of the sheet S may be adjusted by the registration roller 27, which may be a pause. Thereafter, as the registration roller 27 starts rotating, the sheet S may be fed to the image forming apparatus 30. At a position downstream of the separator roller 24 in the conveying direction in which the sheet S is conveyed, a feeder sensor 28A is disposed, and the feeder sensor 28A can detect the sheet S passing therethrough. At a position upstream of the registration roller 27 in the conveying direction, a pre-registration sensor 28B is arranged, and the pre-registration sensor 28B can detect the sheet S passing therethrough. At a position downstream of the registration roller 27 in the conveying direction, a rear registration sensor 28C is arranged.

The image forming apparatus 30 includes an exposure device 40, a plurality of photosensitive drums 50, a plurality of developing cartridges 60, a belt unit 70, and a fixer 80.

The exposure device 40 includes a laser diode, a deflector, a lens, and a mirror, which are not shown. The exposure device 40 may emit a laser beam at the photosensitive drum 50 to expose the photosensitive drum 50 and scan the surface of the photosensitive drum 50.

The photosensitive drums 50 include a first photosensitive drum 50Y, a second photosensitive drum 50M, a third photosensitive drum 50C, and a fourth photosensitive drum 50K, which are provided corresponding to the first color, the second color, the third color, and the fourth color, respectively. The first, second, third and fourth colors may be, for example, yellow, magenta, cyan and black. In the following paragraphs and figures, the corresponding color of an item may be identified by a suffix Y, M, C or K appended to the item's reference symbol that represents yellow, magenta, cyan, or black, respectively. On the other hand, when items are generally described without reference to their respective colors, these items may be representatively described in the singular form with a single reference numeral without the suffix Y, M, C or K; and ordinal words (e.g., first, second, etc.) may be omitted.

The developing cartridge 60 is disposed corresponding to the photosensitive drum 50. In particular, the developing cartridge 60 includes a first developing cartridge 60Y, a second developing cartridge 60M, a third developing cartridge 60C, and a fourth developing cartridge 60K. The first developing cartridge 60Y includes a first developing roller 61Y, and the first developing roller 61Y can supply yellow toner to the first photosensitive drum 50Y. The second developing cartridge 60M includes a second developing roller 61M, and the second developing roller 61M can supply the magenta toner to the second photosensitive drum 50M. The third developing cartridge 60C includes a third developing roller 61C, and the third developing roller 61C can supply cyan toner to the third photosensitive drum 50C. The fourth developing cartridge 60K includes a fourth developing roller 61K, and the fourth developing roller 61K can supply the black toner to the fourth photosensitive drum 50K.

The first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are arranged in a row in the stated order from upstream to downstream along the sheet moving direction. In other words, in the sheet moving direction of the sheet S, the first developing roller 61Y is at the most upstream position, and the fourth developing roller 61K is at the most downstream position. The sheet moving direction is a direction in which the sheet S is conveyed in the belt unit 70 (for example, at the rear in fig. 1 and to the right of the viewer).

The developing cartridge 60 is movable between a position where the developing roller 61 at the contact position contacts the corresponding photosensitive drum 50 as indicated by a solid line in fig. 1 and a position where the developing roller 61 at the separation position is separated from the corresponding photosensitive drum 50 as indicated by a chain line in fig. 1. When the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are at the respective separated positions, the second developing cartridge 60M, the third developing cartridge 60C, and the fourth developing cartridge 60K coincide with the optical paths of the laser beams emitted by the exposure device 40 for scanning the first photosensitive drum 50Y, the second photosensitive drum 50M, and the third photosensitive drum 50C, and the first photosensitive drum 50Y, the second photosensitive drum 50M, and the third photosensitive drum 50C correspond to the first developing cartridge 60Y, the second developing cartridge 60M, and the third developing cartridge 60C, respectively, with which the second developing cartridge 60M, the third developing cartridge 60C, and the fourth developing cartridge 60K abut upstream in the sheet moving direction. In other words, when the second developing roller 61M is at the separation position, the second developing cartridge 60M is at a position to interrupt the optical path of the laser beam emitted at the first photosensitive drum 50Y; when the third developing roller 61C is at the separation position, the third developing cartridge 60C is at a position to interrupt the optical path of the laser beam emitted at the second photosensitive drum 50M; and when the fourth developing roller 61K is located at the separation position, the fourth developing cartridge 60K is located at a position to interrupt the optical path of the laser beam emitted at the third photosensitive drum 50C.

As shown in fig. 2, the photosensitive drum 50 is rotatably supported by a supporting member 90. The supporting member 90 removably supports the developing cartridge 60. The support member 90 is detachably attached to the main housing 10 through an opening (not shown) that can be exposed when the front cover 11 (see fig. 1) of the main housing 10 is opened. The support member includes a side frame 91 and connecting frames 92, 93. The side frame 91 includes a pair of right-hand side frame 91R and left-hand side frame 91L spaced apart from each other in the axial direction of the photosensitive drum 50. The connecting frame 92 connects the side frame 91R and the side frame 91L to each other at a forward position, and the connecting frame 93 connects the side frame 91R and the side frame 91L to each other at a rearward position. On the supporting member 90, a charger 52 (see fig. 1) is disposed, and the charger 52 can charge the photosensitive drum 50.

The image forming apparatus 1 includes a moving mechanism 5, and the moving mechanism 5 can move the developing roller 61 between a contact position where the developing roller 61 is in contact with the corresponding photosensitive drum 51 and a separation position where the developing roller 61 is separated from the corresponding photosensitive drum 51. The moving mechanism 5 can move the developing roller 61 between the contact position and the separation position by a driving force from a developing motor 3D (see fig. 8), the developing motor 3D being capable of bidirectional rotation in the forward direction and the reverse direction. In particular, when the developing motor 3D rotates in the forward direction, the moving mechanism 5 may move the developing roller 61.

The moving mechanism 5 includes a first cam 150 and a cam follower 170. The first cam 150 is rotatable about an axis parallel to the rotation axis 61X (see fig. 1) of the developing roller 61, and includes a first cam 150Y for yellow, a first cam 150M for magenta, a first cam 150C for cyan, and a first cam 150K for black. The first cam 150 may control the position of the developing roller 61, and may be rotated in a predetermined rotational direction by a driving force from the developing motor 3D. The first cam 150 includes a first cam portion 152A protruding in a rotational axis direction, which is a direction of the rotational axis 61X of the developing roller 61.

The cam follower 170 is movable between an operable position where the cam follower 170 contacts a cam surface 152F, which is an end surface of the first cam portion 152A that places the developing roller 61 at the separation position shown in fig. 4B, and a standby position where the cam follower 170 causes the developing roller 61 to be placed at the contact position shown in fig. 4A. The cam follower 170 may contact the first cam portion 152A of the first cam 150 and slidably move to an operable position to push the developing cartridge 60. When in the standby position, the cam follower 170 is separated from the developing cartridge 60.

Referring back to fig. 2, the first cam 150 and the cam follower 170 are arranged to correspond to each of the first, second, third, and fourth developing cartridges 60Y, 60M, 60C, and 60K. The first cam 150 and the cam follower 170 are arranged at laterally outer positions with respect to the side frame 91L. In other words, the first cam 150 and the cam follower 170 are arranged at the leftward position with respect to the side frame 91L. The first cam 150 and cam follower 170 are further described below.

At upper positions with respect to the side frames 91R, 91L in the support member 90, contact portions 94 are arranged. Each contact portion 94 may contact the slider member 64 as will be described further below. The contact portion 94 includes a roller, and while the axial direction of the photosensitive drum 50 extends in the first direction, and the first photosensitive drum 50Y, the second photosensitive drum 50M, the third photosensitive drum 50C, and the fourth photosensitive drum 50K are aligned in the second direction, the roller in the contact portion 94 may rotate about an axis extending in a third direction, for example, the vertical direction, the third direction extending orthogonal to the first direction and the second direction.

The supporting member 90 includes pressing members 95 for the first, second, third, and fourth developing cartridges 60Y, 60M, 60C, and 60K. In particular, two (2) pressing members 95 may be provided for each of the first, second, third, and fourth developing cartridges 60Y, 60M, 60C, and 60K. The pressing members 95 are arranged at one end and the other end of the corresponding developing cartridge 60 in the axial direction of the photosensitive drum 50. The pressing member 95 is urged rearward by a spring 95A (see fig. 4A to 4B). When the developing cartridge 60 is attached to the supporting member 90, the pressing member 95 may press the protrusion 63D in the developing cartridge 60 to push the developing roller 61 toward the photosensitive drum 50.

The developing cartridge 60 shown in fig. 3A to 3B, which is any one of the first developing cartridge 60Y, the second developing cartridge 60M, the third developing cartridge 60C, and the fourth developing cartridge 60K, includes a housing 63 accommodating toner, a slider member 64, and a coupling 65.

The housing 63 has a first projecting portion 63A and a second projecting portion 63B projecting in the rotational axis direction on one lateral face thereof, for example, the leftward face. The first projecting portion 63A is arranged coaxially with the rotation axis 61X of the developing roller 61, and projects in the rotation axis direction. The second protruding portion 63B is arranged at a position spaced apart from the first protruding portion 63A by a predetermined distance. The second protruding portion 63B is arranged at an upper position with respect to the first protruding portion 63A. The first protruding portion 63A and the second protruding portion 63B are rollers rotatable about axes extending parallel to the rotational axis direction. Although not shown in the drawings, on the other lateral face of the housing 63 in the lateral direction, for example, the right-hand face, there are arranged a first protruding portion and a second protruding portion which are in the same form as the first protruding portion 63A and the second protruding portion 63B, respectively, at laterally symmetrical positions.

The housing 63 includes a projection 63D, and the projection 63D is pressed by a pressing member 95 at a forward position on each lateral face thereof. Therefore, the protrusion 63D is arranged at the end surface of the housing 63 in the rotational axis direction.

The coupling 65 may be engaged with a coupling shaft 119, which will be described further below, so that a rotational driving force may be input from the coupling shaft 119 to the coupling 65.

The slider member 64 is slidable to move in the rotational axis direction with respect to the housing 63. The slider member 64 may be pressed by the cam follower 170 to be slidably moved in the rotational axis direction.

As shown in fig. 4A to 4B, the slider member 64 includes a shaft 181, a first contact member 182, and a second contact member 183. The first contact member 182 is fixed to one end, e.g., a left end, of the shaft 181, and the second contact member 183 is fixed to the other end, e.g., a right end, of the shaft 181.

The shaft 181 is arranged to extend through the housing 63 via a hole formed in the housing 63 in the rotational axis direction to be slidably supported by the housing 63.

The first contact member 182 includes a pressing surface 182A and an inclined surface 182B, the pressing surface 182A being an end surface of the first contact member 182 in the rotation axis direction, and the inclined surface 182B being inclined with respect to the rotation axis direction. The pressing surface 182A is a surface to be pressed by the cam follower 170. When the slider member 64 is pressed by the cam follower 170 in the rotational axis direction, the inclined surface 182B may contact the left contact portion 94 in the support member 90 and push the developing cartridge 60 in a direction orthogonal to the rotational axis direction, for example, a direction parallel to the sheet moving direction, to move the developing cartridge 60 (see fig. 4B). The inclined surface 182B is inclined as the inclined surface 182B extends from one end toward the other end, for example, from left to right, so as to be closer to the developing roller 61 side with respect to the corresponding photosensitive drum 50 in the second direction. In other words, the leftward portion of the inclined surface 182B is closer to the rear, and the rightward portion of the inclined surface 182B is closer to the front.

The second contact member 183 includes an inclined surface 183B, and the inclined surface 183B is inclined similarly to the inclined surface 182B of the first contact member 182. When the slider member 64 is pressed by the cam follower 170 in the rotational axis direction, the inclined surface 183B may contact the right contact portion 94 in the supporting member 90 and push the developing cartridge 60 in a direction parallel to the sheet moving direction to move the developing cartridge 60 in the same manner as the inclined surface 182B (see fig. 4B).

At a position between the first contact member 182 and the housing 63, a spring 184 is arranged, the spring 184 urging the slider member 64 toward one side in the rotational axis direction, for example, leftward. The spring 184 may be a compression coil spring arranged to coil around the outer circumference of the shaft 181.

As shown in fig. 5, the support member 90 has a first support surface 96A and a second support surface 96B on the inner side of the left side frame 91L. When the developing roller 61 moves from the contact position to the separation position, the first supporting surface 96A and the second supporting surface 96B may support the first protruding portion 63A and the second protruding portion 63B of the casing 63 from below, respectively. The first support surface 96A and the second support surface 96B extend in the sheet moving direction. The first support surface 96A is arranged to support the first protruding portion 63A. When the developing cartridge 60 is being attached to the supporting member 90, the first supporting surface 96A can guide the developing roller 61 and position the developing roller 61 at a predetermined position. The second support surface 96B is arranged to support the second protruding portion 63B at an upper position with respect to the first support surface 96A. Although not shown in the drawings, the support member 90 has first and second support surfaces in a symmetrical form with the first and second support surfaces 96A and 96B, respectively, at positions on the inner side on the side of the side frame 91R on the right.

When the developing roller 61 is located at the contact position where the developing roller 61 contacts the corresponding photosensitive drum 50, as seen in the first developing cartridge 60Y, the second developing cartridge 60M, and the third developing cartridge 60C shown in fig. 5, the first projecting portion 63A is located at the rearward position on the first supporting surface 96A. On the other hand, when the developing roller 61 is located at the separation position where the developing roller 61 is separated from the corresponding photosensitive drum 50, as seen in the fourth developing cartridge 60K, the first projecting portion 63A is located at the forward position on the first supporting surface 96A. Thus, when the developing roller 61 is moved from the contact position to the separation position, the moving mechanism 5 can move the developing roller 61 in a direction from a position on the downstream side to a position on the upstream side along the sheet moving direction.

As shown in fig. 12A to 12B, the first cam 150 includes a disc portion 151, a gear portion 150G, an edge cam 152, and a clutch control cam 153. The first cam 150 can move the corresponding developing roller 61 between the contact position and the separation position by rotating.

The disk portion 151 has an approximately disk shape, and is rotatably supported by the support plate 102 (see fig. 9). The gear portion 150G is formed on the outer circumference of the disk portion 151. The edge cam 152 includes a first cam portion 152A, and the first cam portion 152A forms a part of the moving mechanism 5 for the developing roller 61 and protrudes from the disk portion 151. The edge cam 152 includes a cam surface 152F at one end in the rotational axis direction thereof. The cam surface 152F includes a first retaining surface F1, a second retaining surface F2, a first guide surface F3, and a second guide surface F4. The first holding surface F1 may hold the cam follower 170 in the standby position. The second retaining surface F2 may retain the cam follower 170 in the operable position. The first guide surface F3 connects the first holding surface F1 with the second holding surface F2 and is inclined with respect to the first holding surface F1. When the first cam 150 rotates, the first guide surface F3 may guide the cam follower 170 from the first holding surface F1 to the second holding surface F2. The second guide surface F4 connects the second holding surface F2 with the first holding surface F1 and is inclined with respect to the first holding surface F1. When the first cam 150 rotates, the second guide surface F4 may guide the cam follower 170 from the second holding surface F2 to the first holding surface F1.

The clutch control cam 153 cooperates with the lever 160 to switch transmission or disconnection with the clutch 150. The clutch control cam 153 includes a base circular portion 153A and a second cam portion 153B, the base circular portion 153A forming a partial cylindrical form, the second cam portion 153B protruding from the base circular portion 153A in a diameter direction of the first cam 150. The clutch control cam 153 is integrally formed with the disk portion 151. Therefore, the second cam portion 153B rotates in synchronization with the first cam 150.

The cam follower 170 includes a slidable shaft 171 and a contact portion 172. The slidable shaft 171 is slidably supported by a shaft fixed to the main housing 10 but not shown so as to slide in the rotational axis direction. The slidable shaft 171 is urged by the spring 173 in a direction in which the contact portion 172 tends to contact the cam face 152F of the first cam 150. Accordingly, the cam follower 170 is pushed to the standby position. The spring 173 is a tension coil spring, one end of which is hooked to the slidable shaft 171, and the other end of which is hooked to a spring hook that is disposed in the main casing 10 but not shown. The contact portion 172 extends from the slidable shaft 171. An end surface of the contact portion 172 at one end in the rotational axis direction faces the cam surface 152 and contacts the cam surface 152F.

As shown in fig. 9, the first cams 150Y, 150M, 150C, 150K have substantially the same configuration except that the circumference of the first cam portion 152A in the rotational direction in the first cam 150Y alone is larger than the circumference of the other first cam portions 152A in the first cams 150M, 150C, 150K. The first cams 150C, 150K each have a detectable portion 154, and the detectable portion 154 protrudes from the disk portion 151 in the rotational axis direction. Meanwhile, in the main casing 10, separation sensors 4C, 4K for cyan and black are arranged. The separation sensors 4C, 4K are phase sensors that detect the phases of the first cams 150C, 150K, respectively. The separation sensors 4C, 4K may output separation signals when the first cams 150C, 150K are in a predetermined phase range in which the third developing roller 61C and the fourth developing roller 61K are in the separation position. When the first cams 150C, 50K are not in the predetermined phase range, the separation sensors 4C, 4K do not output separation signals. In the present embodiment, for convenience, the separation sensors 4C, 4K outputting the separation signals may be represented as "the separation sensors 4C, 4K are ON". Further, the split signal may be referred to as an ON signal. Meanwhile, it may be expressed that the separation sensors 4C, 4K do not output the separation signal as "the separation sensors 4C, 4K output the OFF signal". The voltage required to output the separation signal in the phase sensors 4C, 4K may be greater than or less than the voltage at which the phase sensors 4C, 4K do not output the separation signal.

The separation sensors 4C, 4K each include an emitter 4P that emits light and a receiver 4R that can receive the light emitted from the emitter 4P. When the detectable portion 154 is in a position between the transmitter 4P and the receiver 4R to interrupt the light from the transmitter 4P, the receiver 4R may not receive the light from the transmitter 4P, and the separation sensors 4C, 4K may output an ON signal to the controller 2. On the other hand, when the detectable portion 154 is displaced from the position between the transmitter 4P and the receiver 4R, the receiver 4R may receive the light from the transmitter 4P, and the separation sensors 4C, 4K may output an OFF signal to the controller 2. It may be noted that the first cams 150Y, 150M also have the same formation as the detectable portion 154; however, neither the first cam 150Y nor the second cam 150M is provided with a separation sensor. Therefore, a similar formation to the detectable portion 154 in the first cam 150Y or the second cam 150M may not be used as the detectable portion.

Referring back to fig. 1, a belt unit 70 is disposed between the sheet tray 21 and the photosensitive drum 50. The belt unit 70 includes a driving roller 71, a driven roller 72, a conveyor belt 73 as an endless belt, and four (4) transfer rollers 74. The conveyor belt 73 is stretched around the driving roller 71 and the driven roller 72, and its upper outer surface faces the photosensitive drum 50. The transfer roller 74 is disposed inside the conveyor belt 73 to nip the conveyor belt 73 in cooperation with the first photosensitive drum 50Y, the second photosensitive drum 50M, the third photosensitive drum 50C, and the fourth photosensitive drum 50K. The belt unit 70 can convey the sheet S placed on the upper outer surface thereof by moving the conveyor belt 73, so that the toner images formed on the first photosensitive drum 50Y, the second photosensitive drum 50M, the third photosensitive drum 50C, and the fourth photosensitive drum 50K can be transferred onto the sheet S.

The fixer 80 is disposed at a backward position with respect to the photosensitive drum 50 and the belt unit 70. The fixer 80 includes a heating roller 81 and a pressing roller 82, and the pressing roller 82 is disposed to face the heating roller 81 to nip the sheet S at a position between the heating roller 81 and the pressing roller 82. At a position downstream of the fixer 80 in the sheet conveying direction, an ejection sensor 28D is arranged to detect the sheet S passing therethrough. At an upper position with respect to the fixer 80, a conveyer roller 15 is arranged, and at an upper position with respect to the conveyer roller 15, a discharge roller 16 is arranged.

In the image forming apparatus 30 configured as above, the surface of the photosensitive drum 50 can be uniformly charged by the charger and selectively exposed to the light emitted from the exposure device 40. Thereby, an electrostatic latent image based on image data can be formed on the surface of the photosensitive drum 50.

Meanwhile, the toner in the housing 63 may be supplied to the surface of the developing roller 61, and when the developing roller 61 contacts the corresponding photosensitive drum 50, the toner may be supplied to the electrostatic latent image formed on the surface of the photosensitive drum 50. Thus, a toner image can be formed on the photosensitive drum 50.

When the sheet S on the conveyor belt 73 passes through a position between the photosensitive drum 50 and the transfer roller 74, the toner image formed on the photosensitive drum 50 can be transferred onto the sheet S. Further, when the sheet S is conveyed to pass through a position between the heating roller 81 and the pressing roller 82, the toner image transferred to the sheet S may be fixed to the sheet S.

The sheet S discharged from the fixer 80 may be conveyed by the conveyor roller 15 and the discharge roller 16 to rest on the discharge tray 13 formed on the upper face of the main casing 10.

As shown in fig. 6, the image forming apparatus 1 includes a developing motor 3D, a process motor 3P, a fuser motor 3F, a driving force transmitter 100, and a grip adjuster 200. The driving force transmitter 100 may transmit the driving force from the developing motor 3D to the developing roller 61. The nipping force adjuster 200 can switch the strength of the nipping force between the heating roller 81 and the pressing roller 82. The developing motor 3D is capable of bidirectional rotation in the forward direction and the reverse direction, and can drive the developing roller 61, the moving mechanism 5, and the grip adjuster 200. The process motor 3P can drive the photosensitive drum 50 and the driving roller 71 in the belt unit 70. The fixing motor 3F can drive the heating roller 81.

Next, a configuration of driving or stopping the rotation of the developing roller 61 and a configuration of moving the developing roller 61 to contact or separate from the photosensitive drum 50 will be described in the following paragraphs.

As shown in fig. 7 to 8, the driving force transmitter 100 is mechanically connected to a first cam 150 as a part of the moving mechanism 5. The driving force transmitter 100 is arranged to transmit the driving force from the developing motor 3D to the developing roller 61 when the developing roller 61 is in the contact position and the developing motor 3D rotates in the forward direction. On the other hand, the driving force transmitter 100 is arranged not to transmit the driving force from the developing motor 3D to the developing roller 61 when the developing roller 61 is at the separation position. Therefore, when the developing roller 61 is in the contact position and the developing motor 3D is rotated in the forward direction, the developing roller 61 can be rotated by the driving force from the developing motor 3D. Further, the driving force transmitter 100 can transmit not only the driving force from the developing motor 3D to the developing roller 61 but also to the moving mechanism 5 and the grip regulator 200. In other words, the driving force from the developing motor 3D can be distributed to the developing roller 61, the moving mechanism 5, and the grip adjuster 200 by the driving force transmitter 100.

As shown in fig. 8, the driving force transmitter 100 includes a driving force transmitter gear train 100D, the driving force transmitter gear train 100D may transmit the driving force from the developing motor 3D to the developing roller 61, and is mechanically connected with a driving force control gear train 100C, and the driving force control gear train 100C may control transmission of the driving force from the driving force transmitter gear train 100D. The driving force transmitter gear train 100D is mechanically connected to the clamping force control gear train 100E, and the clamping force control gear train 100E can control transmission of the driving force from the developing motor 3D to the clamping force adjuster 200 (see fig. 10). In fig. 8 and 10, the intermeshing conveying flow through the gears in the driving force transmitter gear train 100D is indicated by thick solid lines, and the intermeshing conveying flow through the gears in the driving force control gear train 100C and the clamping force control gear train 100E is indicated by thick broken lines.

The driving force transmitter gear train 100D includes a first idler gear 110, a second idler gear 113, a third idler gear 115, a clutch 120, and a coupling gear 117. The first idler gear 100 includes two (2) first idler gears 110A, 110B; the second idler gears 113 include three (3) second idler gears 113A, 113B, 113C; the third idler gear 115 includes four (4) third idler gears 115Y, 115M, 115C, 115K; the clutches 120 include four (4) clutches 120Y, 120M, 120C, 120K; and the coupling gears 117 include four (4) coupling gears 117Y, 117M, 117C, 117K. The gears forming the driving force transmitter gear train 110D are supported by the support plate 102 or a frame, not shown, and are rotatable about a rotational axis parallel to the rotational axis of the photosensitive drum 50.

The developing motor 3D includes an output shaft 3A, and the output shaft 3A can be rotated when the developing motor 3D is started. Attached to the output shaft 3A is a gear not shown.

As shown in fig. 7, each of the first idler gears 110 is a two-wheel gear having a large-diameter gear 110L and a small-diameter gear 110S. The number of teeth in the small diameter gear 110S is smaller than that in the large diameter gear 110L. The large diameter gear 110L and the small diameter gear 110S rotate integrally. The first idler gear 110A is arranged at a forward position with respect to the output shaft 3A, and the first idler gear 110B is arranged at a rearward position with respect to the output shaft 3A. The small diameter gear 110S of the first idler gears 110A, 110B meshes with the output shaft 3A.

As shown in fig. 8, on the forward side with respect to the output shaft 3A, the small diameter gear 110S in the first idler gear 110A meshes with the second idler gear 113A. On the backward direction side of the output shaft 3A, the small diameter gear 110S in the first idler gear 110B meshes with the second idler gear 113B.

The third idler gears 115Y, 115M, 115C, 115K are provided in colors corresponding to yellow, magenta, cyan, and black, respectively, and are arranged in the stated order from front to back. In other words, the third idler gear 115Y for yellow is at the forwardmost position among the third idler gears 115Y, 115M, 115C, 115K, and the third idler gear 115K for black is at the rearwardmost position among the third idler gears 115Y, 115M, 115C, 115K. The third idler gears 115Y, 115M mesh with the second idler gear 113A. The third idler gear 115C meshes with the second idler gear 113B. The third idler gears 115C, 115K mesh with the second idler gear 113C. Therefore, the third idler gear 115K can receive the driving force from the third idler gear 115C through the second idler gear 113C.

The clutches 120Y, 120M, 120C, 120K are in the same configuration. The clutches 120Y, 120M, 120C, 120K are engaged with the third idler gears 115Y, 115M, 115C, 115K, respectively, to receive driving force from the third idler gears 115Y, 115M, 115C, 115K. The clutch 120 will be further described below.

The coupling gears 117 are each engaged with one of the clutches 120Y, 120M, 120C, 120K. Each of the coupling gears 117 includes a coupling shaft 119 (see fig. 7), and the coupling shaft 119 is rotatable integrally with the coupling gear 117. The coupling shaft 119 is movable in the direction of its axis in conjunction with the opening/closing movement of the front cover 11. When the front cover 11 is closed, the coupling shaft 119 can engage with the coupling 65 (see fig. 3A) in the developing cartridge 60.

With the driving force transmitter gear train 110D, the coupling gear 117Y for yellow may receive the driving force from the developing motor 3D through the first idler gear 110A, the second idler gear 113A, the third idler gear 115Y, and the clutch 120Y. The coupling gear 117M for magenta may receive a driving force from the developing motor 3D through the first idler gear 110A, the second idler gear 113A, the third idler gear 115M, and the clutch 120M. The coupling gear 117C for cyan may receive a driving force from the developing motor 3D through the first idler gear 110B, the second idler gear 113B, the third idler gear 115C, and the clutch 120C. The coupling gear 117K for black may receive a driving force from the developing motor 3D through the first idler gear 110B, the second idler gear 113B, the third idler gear 115C, the second idler gear 113C, the third idler gear 115K, and the clutch 120K.

As shown in fig. 9 and 10, the driving force control gear train 110C includes a fourth idler gear 131, a fifth idler gear 132, a YMC clutch 140A, a K clutch 140K, a sixth idler gear 133, a seventh idler gear 134, an eighth idler gear 135, a ninth idler gear 136, a tenth idler gear 137, and a first cam 150 including the aforementioned first cams 150Y, 150M, 150C, 150K. The fourth idler gear 131 includes two (2) fourth idler gears 131A, 131B; the fifth idler gear 132 includes two (2) fifth idler gears 132A, 132B; the sixth idler gear 133 includes two (2) idler gears 133A, 133B. The gears forming the driving force control gear train 110C are supported by the support plate 102 or a frame, not shown, and are rotatable about a rotation axis parallel to the rotation axis of the photosensitive drum 50.

Each of the fourth idler gears 131 is a two-wheel gear having a large-diameter gear 131L and a small-diameter gear 131S (see fig. 9). The number of teeth in the small diameter gear 131S is smaller than that in the large diameter gear 131L. The large diameter gear 131L and the small diameter gear 131S rotate integrally. The fourth idler gear 131A is disposed at a forward position with respect to the first idler gear 110A, and the fourth idler gear 131B is disposed at a rearward position with respect to the first idler gear 110B. The large-diameter gear 131L of the fourth idler gears 131A, 131B meshes with the small-diameter gear 110S of the first idler gears 110A, 110B, respectively.

The fifth idler gear 132A is disposed at a forward position with respect to the fourth idler gear 131A, and the fifth idler gear 132B is disposed at a rearward position with respect to the fourth idler gear 131B. The fifth idler gears 132A, 132B are respectively meshed with the small-diameter gear 131S in the fourth idler gears 131A, 131B.

YMC clutch 140A may switch transmission and disconnection of driving force control gear train 110C, and driving force control gear train 110C forms a transmission flow to transmit the driving force from developing motor 3D to first cams 150Y, 150M, 150C. In other words, YMC clutch 140A may switch the state of first cams 150Y, 150M, 150C between rotating and stationary. In particular, YMC clutch 140A is switchable between a transmittable state in which YMC clutch 140A can transmit the driving force from developing motor 3D to first cams 150Y, 150M, 150C, and an interruption state in which YMC clutch 140A can disconnect the driving force from developing motor 3D so as not to be transmitted to first cams 150Y, 150M, 150C, so that the state of first cams 150Y, 150M, 150C can be switched between rotation and rest.

YMC clutch 140A includes large diameter gear 140L and small diameter gear 140S. The number of teeth in the small diameter gear 140S is smaller than that in the large diameter gear 140L. YMC clutch 140A is disposed at a forward position with respect to fifth idler gear 132A, with large-diameter gear 140L meshing with fifth idler gear 132A. YMC clutch 140A may be, for example, an electromagnetic clutch in which large-diameter gear 140L and small-diameter gear 140S may rotate integrally when YMC clutch 140A is energized or activated; and when YMC clutch 140A is de-energized or deactivated, large diameter gear 140L may freewheel so that small diameter gear 140S may remain stationary.

K-clutch 140K is in a similar configuration as YMC clutch 140A. Therefore, the K clutch 140K can switch transmission and disconnection of the driving force control gear train 110C, and the driving force control gear train 110C forms a transmission flow to transmit the driving force from the developing motor 3D to the first cam 150K. In particular, the K clutch 140K is switchable between a transmittable state in which the K clutch 140K can transmit the driving force from the developing motor 3D to the first cam 150K, and an interruption state in which the K clutch 140K can disconnect the driving force from the developing motor 3D so as not to be transmitted to the first cam 150K, so that the state of the first cam 150K can be switched between rotation and rest. The K-clutch 140K includes a large-diameter gear 140L and a small-diameter gear 140S. The number of teeth in the small diameter gear 140S is smaller than that in the large diameter gear 140L. The K-clutch 140A is arranged at a backward position with respect to the fifth idler gear 132B, with the large-diameter gear 140L meshing with the fifth idler gear 132B.

Each sixth idler gear 133 is a two-wheel gear having a large-diameter gear 133L and a small-diameter gear 133S (see fig. 7). The number of teeth in the small diameter gear 133S is smaller than that in the large diameter gear 133L. The large diameter gear 133L and the small diameter gear 133S rotate integrally. Fourth idler gear 133A is disposed in a forward position relative to YMC clutch 140A, and fourth idler gear 133B is disposed in a rearward position relative to K clutch 140K. The large-diameter gear 133L of the sixth idler gears 133A, 133B meshes with the small-diameter gear 140S of the YMC clutch 140A and the K clutch 140K, respectively.

The seventh idler gear 134 is disposed between the sixth idler gear 133A and the first cam 150Y. The seventh idler gear 134 meshes with the small-diameter gear 133S (see fig. 7) in the sixth idler gear 133A and the gear portion 150G in the first cam 150Y.

The eighth idler gear 135 is disposed between the first cam 150Y and the first cam 150M. The eighth idler gear 135 meshes with a gear portion 150G in the first cam 150Y and a gear portion 150G in the first cam 150M.

The ninth idler gear 136 is disposed between the first cam 150M and the first cam 150C. The ninth idler gear 136 meshes with a gear portion 150G in the first cam 150M and a gear portion 150G in the first cam 150C.

The tenth idler gear 137 is disposed between the sixth idler gear 133B and the first cam 150K. The tenth idler gear 137 meshes with the small-diameter gear 133S in the sixth idler gear 133B (see fig. 7) and the gear portion 150G in the first cam 150K.

With the driving force control gear train 110C, the first cam 150Y for yellow may receive the driving force from the developing motor 3D through the first idler gear 110A, the fourth idler gear 131A, the fifth idler gear 132A, YMC, the clutch 140A, the sixth idler gear 133A, and the seventh idler gear 134. The first cam 150M for magenta may receive a driving force from the first cam 150Y for yellow through the eighth idler gear 135. The first cam 150C for cyan may receive a driving force from the first cam 150M for magenta through the ninth idler gear 136. First cams 150Y, 150M, 150C may rotate in synchronization when YMC clutch 140A is activated, and first cams 150Y, 150M, 150C may stop rotating when YMC clutch 140A is deactivated.

On the other hand, the first cam 150K for black may receive the driving force from the developing motor 3D through the first idler gear 110B, the fourth idler gear 131B, the fifth idler gear 132B, K clutch 140K, the sixth idler gear 133B, and the tenth idler gear 137. When the K-clutch 150K is activated, the first cam 150K may rotate, and when the K-clutch 140K is deactivated, the first cam 150K may stop rotating.

In the following paragraphs, the detailed construction and movement of the clutch 120 will be described. As shown in fig. 11A-11B, each clutch 120 includes a planetary gear assembly. The clutch 120 is capable of switching between a transmittable state in which the clutch 120 can transmit the driving force from the developing motor 3D to the developing roller 61 and an interrupted state in which the clutch 120 can disconnect the driving force from the developing motor 3D so as not to be transmitted to the developing roller 61. The clutch 120 includes a sun gear 121 rotatable about an axis, a ring gear 122, a carrier 123, and planet gears 124 supported by the carrier 123.

The sun gear 121 includes a disk portion 121B that is rotatable integrally with the gear portion 121A, and a pawl portion 121C that is disposed on the outer periphery of the disk portion 121. The claw portions 121C each have a tip end that is inclined to one side in the rotational direction of the sun gear 121. The ring gear 122 includes an internal gear 122A disposed on an inner peripheral surface and an input gear 122B disposed on an outer peripheral surface.

The carrier 123 includes four (4) shaft portions 123A that rotatably support the planetary gears 124. The carrier 123 includes an output gear 123B disposed on an outer circumferential surface thereof.

The planetary gears 124 include four (4) planetary gears 124, each of which is supported by one shaft portion 123A in the carrier 123. The planetary gears 124 mesh with the gear portion 121A of the sun gear 121, and mesh with the internal gear 122A in the ring gear 122.

In the clutch 120, the input gear 122B meshes with the third idler gear 115, and the output gear 123B meshes with the coupling gear 117 (see fig. 7). In this arrangement, when the sun gear 121 is restricted from rotating, the clutch 120 is in a transmittable state in which the driving force input to the input gear 122B can be transmitted to the output gear 123B. On the other hand, when the sun gear 121 is allowed to rotate, the clutch 120 is in an interrupted state in which the driving force input to the input gear 122B cannot be transmitted to the output gear 123B. When the clutch 120 is in the interrupted state and the output gear 123B is under load, and when the driving force is input to the input gear 122B, the output gear 123B does not rotate, so that the sun gear 121 idles.

As shown in fig. 10, the driving force transmitter 100 includes a second cam portion 153B and a lever 160, the second cam portion 153B being formed in the first cam 150. The lever 160 is swingably supported by a support shaft 102A fixed to the support plate 102. The lever 160 may be engaged with the sun gear 121, which is one of elements in the planetary gear assembly, in cooperation with the first cam 150 to restrict the sun gear 121 from rotating so that the clutch 120 may be placed in a transmittable state, and the lever 160 may release the sun gear 121 so that the clutch 120 may be placed in an interrupted state.

Specifically, as shown in fig. 12A, the lever 160 includes a rotation support portion 161, a first arm 162 extending from the rotation support portion 161, and a second arm 163 extending from the rotation support portion 161 in a direction different from that of the first arm 162.

The rotation supporting portion 161 has a hollow cylindrical shape into which the supporting shaft 102A of the supporting plate 102 is inserted to support the rod 160.

One end of the second arm 163 extends toward the outer peripheral surface of the disk portion 121B of the clutch 120. The lever 160 is urged by a torsion spring, not shown, so that one end of the second arm 163 is urged against the outer peripheral surface of the sun gear 121 or the disk portion 121B. One end of the second arm 163 forms a hook 163A. The hook 163A may be engaged with one claw portion 121C formed on the outer circumferential surface of the sun gear 121 to restrict the sun gear 121 from rotating, the sun gear 121 being rotatable by the rotation of the developing motor 3D in the forward direction.

The lever 160 may contact the second cam portion 153B at an end portion 162A of the first arm 162. The lever 160 is movable between an engaged position in which the end portion 162A of the first arm 162 faces the base circular portion 153A while the hook portion 163A is engaged with one of the claw portions 121C in the sun gear 121 that is one of the elements in the planetary gear assembly, and a disengaged position in which the end portion 162A of the first arm 162 is pushed by the second cam portion 153B so that the hook portion 163A is disengaged from the claw portion 121C in the sun gear 121 that is one of the elements in the planetary gear assembly. When the lever 160 is separated from the second cam portion 153B and located at the engaged position, the lever 160 may place the clutch 120 in the transmittable state, and when the lever 160 contacts the second cam portion 153B and located at the separated position, the lever 160 may place the clutch 120 in the interrupted state.

The movement of the lever 160 will be described below with reference to fig. 12A-12B to 16A-16B. It is to be noted that, although fig. 12A-12B to 16A-16B show the items for yellow among the four colors of yellow, magenta, cyan, and black, the corresponding items for the other colors, that is, the corresponding items for magenta, cyan, and black, may function in the same manner as the items for yellow, except that the phases in the first cams 150Y, 150M, 150C, 150K are different.

As shown in fig. 12A to 12B, when the clutch control cam 153 rotates, the end portion 162A of the first cam 162 following the second cam portion 153B may be separated from the second cam portion 153B and face the base circular portion 153A. Meanwhile, the hook 163A in the second arm 163 may be engaged with one of the claw portions 121C in the sun gear 121 in the clutch 120 to place the lever 160 in the engaged position. When the lever 160 restricts the rotation of the sun gear 121, the clutch 120 may be placed in a transmittable state in which the output gear 123B is rotatable when the input gear 122B is rotated. Thereby, the driving force from the developing motor 3D rotating in the forward direction can be transmitted to the developing roller 61 through the driving force transmitter gear train 100D, and the developing roller 61 can be rotated when the developing motor 3D rotates in the forward direction. Meanwhile, the cam follower 170 is located at a position where the end surface of the contact portion 172 is on the first holding surface F1 of the cam surface 152F. Therefore, the slidable shaft 171 is separated from the slider member 64 in the developing cartridge 60 (see fig. 4A), and the developing roller 61 is located at the contact position.

When the first cam 150 is rotated from the position shown in fig. 12A to 12B to the position shown in fig. 13A to 13B, the contact portion 172 of the cam follower 170 slides on the first holding surface F1 to be closer to the first guide surface F3. In order to stop the first cam 150Y of the four (4) first cams 150 at the position where the first developing roller 61Y is at the contact position, the first cam 150Y may be stopped at a position where the contact portion 172 is on the first guide surface F3 as shown in fig. 13A to 13B.

To separate the developing roller 61 from the photosensitive drum 50, the first cam 150Y may be further rotated so that the contact portion 172 may slide on the first guide surface F3 and be pushed by the first guide surface F3 to contact the second holding surface F2, as shown in fig. 14A to 14B. Meanwhile, the slidable shaft 171 may push the slider member 64 in the developing cartridge 60 in the rotational axis direction. Thereby, the developing cartridge 60 can be moved forward by the reaction force from the supporting member 90 (see fig. 4B). When the contact portion 172 is at a position on the first guide surface F3 closer to the second holding surface F2 than the first holding surface F1, the developing roller 61 may start to separate from the photosensitive drum 50. When the contact portion 172 is on the second holding face F2, the developing roller 61 is maintained at the separation position.

When the developing roller 61 is at the separation position, the first cam 150 may be further rotated to a position where the end portion 162A of the arm 162 in the lever 160 may contact the second cam portion 153B, as shown in fig. 15A-15B. When the first arm 162 is pushed by the second cam portion 153B, the lever 160 may swing, and the hook 163A, which is out of hook with the claw portion 121C in the sun gear 121, may move to the separated position. Therefore, the sun gear 121 in the clutch 120 can be released from the lever 160 for rotation and placed in an interrupted state in which the output gear 123B cannot transmit the driving force even when the input gear 122B rotates. Thereby, the driving force from the developing motor 3D cannot be transmitted to the developing roller 61. In other words, even when the developing motor 3D rotates, only the sun gear 121 idles, and the developing roller 61 does not rotate.

In order to place and maintain the developing roller 61 at the separation position, the first cam 150 may be stopped at a position in which the lever 160 is at the separation position as shown in fig. 15A to 15B. However, in order to specifically maintain the first developing roller 61Y at the separation position, the first cam 150Y for yellow among the first cams 150Y, 150M, 150C, 150K may be further rotated from the position shown in fig. 15A to 15B and stopped at a position where the contact portion 172 is at one end of the second holding surface F2 closer to the second guide surface F4 than the first guide surface F3, for example, a position on the second holding surface F2 closest to or adjacent to the boundary between the second holding surface F2 and the second guide surface F4, as shown in fig. 16A to 16B.

To move the developing roller 61 from the separation position to the contact position, the first cam 150 may be rotated from the position shown in fig. 15A to 15B or fig. 16A to 16B, so that the contact portion 172 may slide on the second guide surface F4 to the position shown in fig. 12A to 12B where the contact portion 172 faces the first holding surface F1. Thereby, the slidable shaft 171 can be moved in the rotational axis direction by the urging force of the spring 173 to be separated from the slider member 64. The slider member 64 may return to the position shown in fig. 4A, and the developing cartridge 60 may return to the position indicated by the solid line in fig. 1. Therefore, the developing roller 61 can contact the photosensitive drum 50. In other words, the developing roller 61 may contact the photosensitive drum 50 when the contact portion 172 passes through a position on the second guide surface F4 adjacent to the second holding surface F2 (see fig. 16B).

Therefore, the clutch 120 can be placed in the conveyable state with the lever 160 in the engaged position where the lever 160 faces the base circular portion 153A and engages with the sun gear 121.

In the image forming apparatus 1 of the present embodiment, in order to transfer the toner image to the sheet S, the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are sequentially moved to the respective contact positions when the sheet S is conveyed, and the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are sequentially moved to the separation position after the toner image is transferred to the sheet S. In this regard, the first cams 150Y, 150M, 150C are assembled in an arrangement in which the phases of the first cam portions 152A are different from each other by a predetermined angle (see fig. 9). In particular, the first cams 150M, 150C have the same form, while the first cam 150Y has a first cam portion 152A whose circumference in the direction of rotation is greater than the circumference in the direction of rotation of the first cam portion 152A of the first cams 150M, 150C. Further, downstream ends of the first cam portions 152A of the first cams 150Y, 150M, 150C in the rotational direction are arranged at different rotational positions different from each other by a predetermined angle; and the upstream ends of the first cam portions 152A of the first cams 150Y, 150M, 150C in the rotational direction are arranged to coincide with each other. Meanwhile, the first cam 150K has the same form as the first cams 150M, 150C, but the controller 2 controls the first cam 150K to delay the phase shift by a predetermined angle as compared with the first cams 150M, 150C.

When the developing motor 3D rotates in the reverse direction, the sun gear 121, which is one of the elements in the planetary gear assembly, can rotate in the direction indicated by the arrow shown in the chain line in fig. 12A, that is, the direction opposite to the rotational direction when the developing motor 3D rotates in the forward direction, and the hook 163A does not engage with the claw portion 121C. Therefore, when the sun gear 121 rotates in the reverse direction together with the reverse rotation of the developing motor 3D, the lever 160 does not restrict the rotation of the sun gear 121. While the sun gear 121 is freely rotated, the clutch 120 is in an interrupted state in which the driving force input in the input gear 122B is not transmitted to the output gear 123B. In this regard, when the developing motor 3D rotates in the reverse direction, the lever 160 may place the clutch 120 in the interrupt state. In other words, when the developing motor 3D rotates in the reverse direction, the driving force from the developing motor 3D is not transmitted to the developing roller 61.

As shown in fig. 7 to 8, the clamping force control gear train 100E includes an eleventh idler gear 191, a twelfth idler gear 192, an N-clutch 145, a thirteenth idler gear 193, and a fourteenth idler gear 194. The gear forming the clamping force control gear train 100E is supported by a frame, not shown, and is rotatable about a rotation axis parallel to the rotation axis of the photosensitive drum 50.

The eleventh idler gearwheel 191 meshes with the third idler gearwheel 115K, which third idler gearwheel 115K is in a forward position with respect to the eleventh idler gearwheel 191. The clamping force control gear train 110E may receive the driving force through the third gear 115K.

The twelfth idler gear 192 is located at an upper position relative to the eleventh idler gear 191. The twelfth idler gear 192 is a two-wheel gear having a large-diameter gear 192L and a small-diameter gear 192S. The number of teeth in the small diameter gear 192S is smaller than that in the large diameter gear 192L. The large diameter gear 192L and the small diameter gear 192S rotate integrally. The large-diameter gear 192L of the twelfth idler gear 192 meshes with the eleventh idler gear 191.

The N clutch 145 can switch the transmission and disconnection of the clamping force control gear train 100E, and the clamping force control gear train 100E forms a transmission flow that transmits the driving force from the developing motor 3D to the second cam 210 (see fig. 17) in the clamping force adjuster 200. In particular, the N clutch 145 can be switched between a transmittable state in which the N clutch 145 can transmit the driving force from the developing motor 3D to the second cam 210, and an interruption state in which the N clutch 145 can disconnect the driving force from the developing motor 3D so as not to be transmitted to the second cam 210, so that the state of the second cam 210 can be switched between rotation and rest.

The N-clutch 145 includes a large-diameter gear 145L and a small-diameter gear 145S. The number of teeth in the small diameter gear 145S is smaller than that in the large diameter gear 145L. The N-clutch 145 is arranged in an upper position with respect to the twelfth idler gear 192, with the large-diameter gear 145L meshing with the small-diameter gear 192S in the twelfth idler gear 192. The N clutch 145 may be, for example, an electromagnetic clutch in which the large diameter gear 145L and the small diameter gear 145S may rotate integrally when the N clutch 145 is energized or activated; and when N clutch 145 is de-energized or deactivated, large diameter gear 145L may freewheel so that small diameter gear 145S may remain stationary.

As shown in fig. 9 to 10, the thirteenth idler gear 193 is located at a backward position with respect to the twelfth idler gear 192 and at a lower position with respect to the N clutch 145. The thirteenth idler gear 193 is a two-wheel gear having a large-diameter gear 193L and a small-diameter gear 193S. The number of teeth in the small diameter gear 193S is smaller than that in the large diameter gear 193L. The large diameter gear 193L and the small diameter gear 193S rotate integrally. The large-diameter gear 193L in the thirteenth idler gear 193 meshes with the small-diameter gear 145S in the N clutch 145.

The fourteenth idler gear 194 is located at a position rearward with respect to the eleventh idler gear 191 and at a position lower than the thirteenth idler gear 193. The fourteenth idler gear 194 is a two-wheel gear having a large-diameter gear 194L and a small-diameter gear 194S. The number of teeth in the small diameter gear 194S is smaller than that in the large diameter gear 194L. The large diameter gear 194L and the small diameter gear 194S rotate integrally. The large-diameter gear 194L in the fourteenth idle gear 194 meshes with the small-diameter gear 193S in the thirteenth idle gear 193, and the small-diameter gear 194S in the fourteenth idle gear 194 meshes with the gear portion 230 in the second cam 210.

The nip adjuster 200 can switch the nip force between the heating roller 81 and the pressure roller 82 in the fixing device 80 between the first nip force as shown in fig. 17C and the second nip force as shown in fig. 17A to 17B. The grip adjuster 200 may switch the grip force in the fuser 80 to the second grip force when the developing motor 3D rotates in the forward direction, and the grip adjuster 200 may switch the grip force in the fuser 80 to the first grip force when the developing motor 3D rotates in the reverse direction.

As shown in fig. 17C, when the nip force in the fixer 80 is at the first nip force, the heating roller 81 and the pressing roller 82 are separated from each other. In other words, the first clamping force generates no (zero) pressure. The second clamping force is higher than the first clamping force. The second clamping force according to the present embodiment includes a third clamping force (see fig. 17B) higher than the first clamping force and a fourth clamping force (see fig. 17A) higher than the third clamping force. The clamp force adjuster 200 can switch the clamp force between a first clamp force and a third clamp force and between a first clamp force and a fourth clamp force. In the following paragraphs, the first clamping force, the third clamping force and the fourth clamping force may be referred to as a zero clamping force, a smaller clamping force and a larger clamping force, respectively. The nip range N1 between the heating roller 81 and the pressure roller 82 at a larger nip force is larger than the nip range N2 between the heating roller 81 and the pressure roller 82 at a smaller nip force.

In the following paragraphs, the configuration of the fixer 80 will be described in detail. As shown in fig. 17A, the fixer 80 includes a frame 84 that rotatably supports the heating roller 81, a lever 85 that rotatably supports the pressing roller 82, and a spring 86 that can press the pressing roller 82 to the heating roller 81. Although only one of each is shown in fig. 17A to 17C, the lever 85, the spring, and the portion of the frame 84 that engages with the lever 85 and the spring 86 are arranged on each side of the fixer 80 in the rotational axis direction.

The frame 84 includes a shaft portion 84A and a first spring engageable portion 84B. The lever 85 includes a shaft engageable portion 85A, a second spring engageable portion 85B and a cam contact surface 85C. The lever 85 is engaged with the shaft portion 84A of the frame 84 at the shaft-engageable portion 85A to be swingably supported by the frame 84 so as to swing about the shaft portion 84A. Thereby, the pressing roller 82 supported by the lever 85 can move to contact and separate from the heating roller 81 supported by the frame 84. The spring 86 may be a tension coil spring. One end of the spring 86 is engaged with a first spring engageable portion 84B in the frame 84, and the other end of the spring 86 is engaged with a second spring engageable portion 85B in the lever 85.

The grip adjuster 200 includes a pair of second cams 210 (only one of the pair is shown), a shaft portion 220, and a gear portion 230 (see fig. 10), each of the second cams 210 being provided corresponding to the cam contact surface 85C of each of the levers 85, the shaft portion 220 extending in the rotational axis direction to connect the pair of second cams 210 to each other, the gear portion 230 being disposed on one end of the shaft portion 220 in the rotational axis direction. The pair of second cams 210, the shaft portion 220, and the gear portion 230 are formed to rotate integrally. As shown in fig. 10, the gear portion 230 meshes with the small diameter gear 194S in the fourteenth idler gear 194 forming the clamping force control gear train 100E.

As shown in fig. 17B, the second cam 210 may control the nip force between the heating roller 81 and the pressing roller 82. The second cam 210 can rotate in the first rotation direction R1 or the second rotation direction R2 opposite to the first rotation direction R1 by receiving the driving force from the developing motor 3D. In particular, when the developing motor 3D rotates in the forward direction, the second cam 210 may rotate in the first rotation direction R1 by receiving the driving force from the developing motor 3D, and when the developing motor 3D rotates in the reverse direction, the second cam 210 may rotate in the second rotation direction R2 by receiving the driving force from the developing motor 3D. The second cam 210 may move one of the heating roller 81 and the pressure roller 82 to be closer to or separate from the other of the heating roller 81 and the pressure roller 82, thereby switching the nip force. For example, the second cam 210 may move the pressing roller 82 so as to move closer to the heating roller 81 or separate from the heating roller 81.

The second cam 210 can move the heating roller 82 by rotating to switch the nip force between the heating roller 81 and the pressing roller 82 in the fixing device 80 between zero nip force and a small nip force, or between zero nip force and a large nip force. The second cam 210 is rotatably supported by a frame, not shown, together with the shaft portion 220 to rotate about an axis parallel to the rotational axes of the heating roller 81 and the pressing roller 82. The second cam 210 has a cam surface 213 on its outer periphery. The cam surface 213 includes a first cam surface 213A and a second cam surface 213B, the first cam surface 213A may contact the cam contact surface 85C of the lever 85 to result in zero clamping force, and the second cam surface 213B may contact the cam contact surface 85C of the lever 85 to result in a smaller clamping force. The second cam 210 is formed such that the distance between the first cam surface 213A and the rotational axis of the second cam 210 is greater than the distance between the second cam surface 213B and the rotational axis of the second cam 210. As shown in fig. 17A, the outer peripheral surface of the second cam 210 is separated from the cam contact surface 85C of the lever 85 to cause a large clamping force.

The controller 2 may control the overall movement in the image forming apparatus 1. The controller 2 includes a CPU, ROM, RAM, and input/output devices, which are not shown. The controller 2 may execute a predetermined program to process the operation.

For example, based on signals from the feeder sensor 28A, the pre-registration sensor 28B, the rear registration sensor 28C, and the separation sensors 4K, 4C, the controller 2 may control the YMC clutch 140A and the clutch 140K to control the contact and separation movement of the developing roller 61 with respect to the photosensitive drum 50, and may control the N clutch 145 to control the nip force between the pressure roller 82 and the heat roller 81 in the fixer 80.

When the second, third, and fourth developing rollers 61M, 61C, and 61K are at the respective separation positions, the second, third, and fourth developing rollers 61M, 61C, and 61K may interrupt the optical paths of the laser beams emitted at the first, second, and third photosensitive drums 50Y, 50M, and 50C, respectively, which are located at upstream adjacent positions of the second, third, and fourth photosensitive drums 50M, 50C, and 50K, respectively, corresponding to the second, third, and fourth developing rollers 61M, 61C, and 61K, respectively, in the sheet moving direction. Therefore, the image forming apparatus 1 is arranged such that the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are moved to or located at the respective contact positions before the upstream adjoining photosensitive drum 50 is exposed to the laser beam, that is, before the first photosensitive drum 50Y, the second photosensitive drum 50M, and the third photosensitive drum 50C are exposed to the laser beam.

In this regard, due to the difference in the circumferential length of the first cam portions 152A in the rotational direction in the first cams 150Y, 150M, 150C and the mechanical setting of the phases of the first cams 150Y, 150M, 150C different from each other, the second developing roller 61M and the third developing roller 61C can be brought into respective contact positions before the first photosensitive drum 50Y and the second photosensitive drum 50M at the upstream abutting positions are exposed to the laser beam from the exposure device 40. In particular, in order to position the second developing roller 61M at the contact position before the first photosensitive drum 50Y is exposed to the laser beam, the first cams 150Y, 150M are in an arrangement such that the second developing roller 61M moves to contact the second photosensitive drum 50M when or before the first developing roller 61Y contacts the first photosensitive drum 50Y. In other words, t1 indicating the time when the first developing roller 61Y contacts the first photosensitive drum 50Y and t2 indicating the time when the second developing roller 61M contacts the second photosensitive drum 50M are set to the relationship: t2 is not less than t 1. In the present embodiment, more specifically, t1 and t2 are set equal (t2 ═ t1) or simultaneous.

Meanwhile, the fourth developing roller 61K may be controlled differently depending on whether the image to be formed is a color image or a monochrome image. When printing a color image, the controller 2 may control the first cam 150K to move by a predetermined angle in a retarded phase with respect to the first cam 150C in consideration of the movement of the third developing roller 61C. In other words, when printing a color image using the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K, the controller 2 may move the third developing roller 61C to the contact position and the fourth developing roller 61K to the contact position before the third photosensitive drum 50C is exposed to the laser beam. The controller 2 may move the third developing roller 61C to the separation position after the toner image is completely developed on the third photosensitive drum 50C by the third developing roller 61C and before the toner image is completely developed on the fourth photosensitive drum 50K by the fourth developing roller 61K. After that, when the toner image is completely developed on the fourth photosensitive drum 50K, the controller 2 may move the fourth developing roller 61K to the separation position.

On the other hand, when printing a monochrome image on the sheet S using only the fourth developing roller 61K, the controller 2 may maintain the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C at respective separation positions, and move the fourth developing roller 61K to the contact position before the fourth photosensitive drum 50K is exposed to the laser beam. After the toner image is completely developed on the fourth photosensitive drum 50K by the fourth developing roller 61K, the controller 2 may move the fourth developing roller 61K to the separation position.

The controller 2 further controls the timing at which the first developing roller 61Y for yellow, which is the most upstream position in the sheet conveying direction among the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K, contacts the first photosensitive drum 50Y to synchronize with the conveyance of the sheet S. In other words, after the conveyance of the sheet S is started and before the sheet S reaches the first photosensitive drum 50Y, the controller 2 controls the first cams 150Y, 150M, 150C to rotate through the YMC clutch 140A. Thereafter, controller 2 controls YMC clutch 140A to stop rotation of first cams 150Y, 150M, 150C at a pause timing, which is the instant when first period T1 has elapsed since the ON signal from separation sensor 4C was interrupted, in other words, since controller 2 started receiving the OFF signal while first developing roller 61Y was separated from first photosensitive drum 50Y. Thereafter, controller 2 controls YMC clutch 140A to move first cams 150Y, 150M, 150C to rotate, and an image may be printed on sheet S after first developing roller 61Y contacts first photosensitive drum 50Y at the recovery timing, which is the instant when second period T2 has elapsed since pre-registration sensor 28B as a sheet sensor detects the leading edge of sheet S thus passing.

Meanwhile, to switch the nip force in the fixer 80 from zero nip force as shown in fig. 17C to a smaller nip force as shown in fig. 17B or a larger nip force as shown in fig. 17A, the controller 2 may keep the YMC clutch 140A and the K clutch 140K deactivated, control the developing motor 3D to rotate in the forward direction, and activate the N clutch 145. Thereby, the second cam 210 can be rotated in the first rotational direction R1 from the posture shown in fig. 17C.

To switch the clamping force to the smaller clamping force, the controller 2 may rotate the second cam 210 for a predetermined period of time T8 from a position in which the first cam surface 213A contacts the cam contact surface 85C of the lever 85 to a position in which the second cam surface 213B contacts the cam contact surface 85C, and deactivate the N clutch 145. On the other hand, to switch the clamping force to the larger clamping force, the controller 2 may rotate the second cam 210 for a predetermined period of time T8 from a position in which the first cam surface 213A contacts the cam contact surface 85C of the lever 85 to a position in which the outer circumferential surface is separated from the cam contact surface 85C, and deactivate the N clutch 145. Thereby, the lever 85 can be pulled upward by the spring 86, and the pressing roller 82 supported by the lever 85 can contact the heating roller 81 with a predetermined clamping force. The controller 2 may stop the forward rotation of the developing motor 3D after deactivating the N clutch 145. It may be noted that the predetermined period T8 for switching the clamping force from zero clamping force to a smaller clamping force and the predetermined period T8 for switching the clamping force from zero clamping force to a larger clamping force are different periods.

Further, in order to switch the nip force in the fixer 80 from a small nip force as shown in fig. 17B or a large nip force as shown in fig. 17A to a zero nip force as shown in fig. 17C, the controller 2 may maintain the YMC clutch 140A and the K clutch 140K deactivated, control the developing motor 3D to rotate in the reverse direction, and activate the N clutch 145. Thereby, the second cam 210 can be rotated in the second rotational direction R2 from the posture shown in fig. 17A or the posture shown in fig. 17B.

To switch the clamping force from the smaller clamping force, the controller 2 may rotate the second cam 210 for a predetermined period of time T9 from a position in which the second cam surface 213B contacts the cam contact surface 85C of the lever 85 to a position in which the first cam surface 213A contacts the cam contact surface 85C, and deactivate the N clutch 145. On the other hand, to switch the clamping force from the large clamping force, the controller 2 may rotate the second cam 210 for a predetermined period of time T9 from a position where the outer peripheral surface is separated from the cam contact surface 85C of the lever 85 to a position where the first cam surface 213A contacts the cam contact surface 85C, and deactivate the N clutch 145. Thereby, the lever 85 can be pushed down by the second cam 210, and the pressing roller 82 can be separated from the heating roller 81. The controller 2 may stop the reverse rotation of the developing motor 3D after deactivating the N clutch 145. It may be noted that the predetermined period T9 for switching the clamping force from the smaller clamping force to the zero clamping force and the predetermined period T9 for switching the clamping force from the larger clamping force to the zero clamping force are different periods.

In the following paragraphs, exemplary processing to be executed by the controller 2 will be described with reference to fig. 18A-18B to 23. When the image forming apparatus 1 is on standby for a print job, the developing rollers 61 including the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are all located at the respective separation positions, and the fixer 80 is in a state of zero nip force.

As shown in fig. 18A, when the controller receives the print job, in S11, the controller 2 controls the development motor 3D to rotate in the forward direction. In S12, the controller 2 activates the N clutch 145 to rotate the second cam 210. In S13, the controller 2 determines whether a predetermined period T8 has elapsed since the activation of the N clutch 145. If the controller 2 determines that the predetermined period T8 has elapsed (S13: yes), the controller 2 deactivates the N clutch 145 to stop the rotation of the second cam 210 in S14.

In S21, the controller 2 determines whether the image to be printed on the first page in the received print job is a color image. If the controller 2 determines that the image to be printed on the first page is a color image (S21: YES), in S22, the controller 2 performs color image printing. On the other hand, if the controller 2 determines that the image to be printed on the first page is not a color image but a monochrome image (S21: No), in S23, the controller 2 performs monochrome image printing. After printing the image of the first page in S22 or S23, the controller 2 determines whether the image of the next page remains in the print job in S24. If the image of the next page remains (S24: YES), the flow returns to S21 and the previous steps are repeated.

If no image of the next page remains in the print job (S24: no), in S31, as shown in fig. 18B, the controller 2 stops the forward rotation of the developing motor 3D, and in S32, starts rotating the developing motor 3D in the reverse direction. In S33, the controller 2 activates the N clutch 145 to rotate the second cam 210. In S34, the controller 2 determines whether a predetermined period T9 has elapsed since the activation of the N clutch 145. If the predetermined period of time T9 has elapsed (S34: yes), the controller 2 deactivates the N clutch 145 to stop the rotation of the second cam 210 in S35. In S36, the controller stops the reverse rotation of the developing motor 3D and ends the flow.

In the following paragraphs, the flow of processing for color image printing will be described with reference to the flowcharts in fig. 19A to 19C and the timing chart in fig. 20. Fig. 19A to 19C and fig. 20 show the flow of the process of printing a color image for a page. Further, in fig. 20, although the top row indicates the movement of the developing roller 61Y for yellow on the time axis, the movements of the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K for magenta, cyan, and black are overlaid on the same time line.

For color image printing in S22 (see also fig. 18A), the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are all located at respective separation positions before the image forming operation. Therefore, as shown in fig. 19A, in S201(t0), the controller 2 activates YMC clutch 140A and K clutch 140K to rotate first cams 150Y, 150M, 150C, 150K. Shortly after the first cams 150Y, 150M, 150C, 150K start rotating (t31), the separation sensors 4C, 4K output OFF signals. After that, the controller 2 drives the feeder roller 23(t51) for a predetermined period of time so that the sheet S can be picked up and conveyed in S202.

After the conveyance of the sheet S is started and before the sheet S reaches the first photosensitive drum 50Y, in S210 the controller 2 determines whether a first period T1 has elapsed since the separation sensor 4C for cyan started outputting the OFF signal. If controller 2 determines that the first period T1 has elapsed (S210: yes), in S211 (T32), controller 2 deactivates YMC clutch 140A so that first cams 150Y, 150M, 150C stop rotating at the time of the pause. The first period T1 is set to have a length in which the contact portion 172 of the cam follower 170 for yellow reaches the position on the second holding surface F2 of the first cam 150Y that is closest to the second guide surface F4. Therefore, when the rotation of the first cams 150Y, 150M, 150C is resumed, the second guide face F4 of the first cam 150Y reaches the cam follower 170 soon. In other words, the cam follower 170 for yellow may quickly move to the second guide face F4 of the first cam 150Y, and the first developing roller 61Y may start to move to the contact position.

In S212, when the preregistration sensor 28B starts outputting the ON signal, that is, when the leading edge of the sheet S passes the preregistration sensor 28B, the controller 2 determines whether the second period T2 has elapsed since T53. If the controller 2 determines that the second period T2 has elapsed (S212: yes), in S213 (T33), the controller 2 activates the YMC clutch 140A to resume rotation of the first cams 150Y, 150M, 150C at the resumption time. The second period T2 is set to have a length in which the development of the toner image on the first photosensitive drum 50Y by the first developing roller 61Y can be presented in time without delaying the transfer of the developed toner image onto the sheet S.

In S220, after the conveyance of the sheet S is started and before the sheet S reaches the fourth photosensitive drum 50K, the controller 2 determines whether a first period T21 has elapsed since the separation sensor 4K for black started outputting the OFF signal. If the controller 2 determines that the first period T21 has elapsed (S220: yes), in S221 (T42), the controller 2 deactivates the K clutch 140K to stop the rotation of the first cam 150K at the time of the pause. The first period T21 is set to have a length in which the contact portion 172 of the cam follower 170 for black may be located on the second holding surface F2 of the first cam 150K at the closest to the second guide surface F4 at the time of pause. Therefore, when the rotation of the first cam 150K is resumed, the cam follower 170 for the black color may quickly move to the second guide surface F4, and the fourth developing roller 61K may start to move to the contact position. It may be noted that the first period T21 and the first period T1 are different from each other.

In S222, as shown in fig. 19B, the controller 2 determines whether a third period T3 has elapsed since the YMC clutch 140 was activated at the recovery time (T33). If the third period of time T3 has elapsed (S222: yes), in S223 (T36), the controller 2 deactivates the YMC clutch 140A to stop the rotation of the first cams 150Y, 150M, 150C. The third period T3 is set to have a length in which the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C are moved and located at the respective contact positions.

In S224, the controller 2 determines whether a second period T22 has elapsed since T54 when the rear registration sensor 28C starts outputting the ON signal, that is, since the leading edge of the sheet S passes the rear registration sensor 28C. If the controller 2 determines that the second period T22 has elapsed (S224: yes), in S225 (T43), the controller 2 activates the K clutch 140K to rotate the first cam 150K. The second period T22 is set to have a length in which the development of the black toner image on the fourth photosensitive drum 50K by the fourth developing roller 61K can be presented in time for transfer onto the sheet S. Therefore, the fourth developing roller 61K is located at the contact position shortly before the third photosensitive drum 50 is exposed to the laser beam.

In S226, the controller 2 determines whether a predetermined period T23 has elapsed since T43 when the K clutch 140K was activated. If the controller 2 determines that the predetermined period T23 has elapsed (S226: yes), in S227 (T44), the controller 2 deactivates the K clutch 140K to stop the rotation of the first cam 150K. The predetermined period T23 is set to have a length in which the fourth developing roller 61K is moved and located at the contact position.

In S230, the controller 2 determines whether a fourth period T4 has elapsed since T57 when the rear registration sensor 28C starts outputting the OFF signal, that is, since the rear edge of the sheet S passes the rear registration sensor 28C. If controller 2 determines that the fourth period T4 has elapsed (S230: YES), in S231 (T37), controller 2 activates YMC clutch 140A to rotate first cams 150Y, 150M, 150C to sequentially separate first, second, and third developing rollers 61Y, 61M, 61C from first, second, and third photosensitive drums 50Y, 50M, 50C, respectively, as shown in FIG. 19C. The fourth period T4 is set to have a length in which the first developing roller 61Y is ready to move to the separation position after the toner image of yellow is completely developed on the first photosensitive drum 50Y by the first developing roller 61Y and shortly after the transfer of the toner image from the first photosensitive drum 50Y to the sheet S is completed.

In S232, the controller 2 determines whether a predetermined period T13 has elapsed since T57 when the rear position sensor 28C starts outputting the OFF signal. If the controller 2 determines that the predetermined period T13 has elapsed (S232: yes), the controller 2 activates the K clutch 140K to rotate the first cam 150K in S233 (T45). The predetermined period T13 is set to have a length in which the fourth developing roller 61K is ready to move to the separation position after the toner image of black is completely developed on the fourth photosensitive drum 50K by the fourth developing roller 61K and shortly after the transfer of the toner image from the fourth photosensitive drum 50K to the sheet S is completed.

In S240, the controller 2 determines whether the separation sensor 4C for cyan is outputting an ON signal (i.e., a separation signal). If the controller 2 determines that the separation sensor 4C is outputting the OFF signal (S240: no), the controller 2 repeats S240. If controller 2 determines that separation sensor 4C is outputting an ON signal (S240: yes), in S241 (t40), controller 2 deactivates YMC clutch 140A to stop rotation of first cams 150Y, 150M, 150C.

In S242, the controller 2 determines whether the separation sensor 4K for black is outputting an ON signal. If the controller 2 determines that the separation sensor 4K is outputting the OFF signal (S240: no), the controller 2 repeats S242. If the controller 2 determines that the separation sensor 4K is outputting the ON signal (S242: yes), in S243 (t46), the controller 2 deactivates the K clutch 140K to stop the rotation of the cam 150K.

According to the above-described flow, the first developing roller 61Y, the second developing roller 60M, the third developing roller 61C, and the fourth developing roller 61K may be sequentially moved from the respective separating positions to the respective contacting positions for printing a color image on a page, and after printing the color image on the page, sequentially moved from the respective contacting positions to the respective separating positions. Specifically, as shown in fig. 21, the first developing roller 61Y is moved to contact the first photosensitive drum 50Y at t1, the second developing roller 61M is moved to contact the second photosensitive drum 50M at t2, the third developing roller 61C is moved to contact the third photosensitive drum 50C at t3, and the fourth developing roller 61K is moved to contact the fourth photosensitive drum 50K at t 4. Meanwhile, in the present embodiment, t1 coincides with t2 (t1 — t 2). Meanwhile, t1 is earlier than t3(t1< t3), t2 is earlier than t3(t2< t3), and t3 is earlier than t4(t3< t 4). Therefore, when the length between t1 and t2 is represented as | t1-t2|, and when the length between t2 and t3 is represented as | t2-t3|, the length | t1-t2| is shorter than the length | t2-t3| (| t1-t2| < | t2-t3 |). In this regard, in the present embodiment, an earlier time may be represented by a smaller value, and a later time may be represented by a larger value. Thus, subtracting the value representing the earlier time from the value representing the later time results in a positive value, and subtracting the value representing the later time from the value representing the earlier time results in a negative value. Further, an absolute value between the value representing the earlier time and the value representing the later time represents a length of a period between the earlier time and the later time. Optionally, but not necessarily, t2 may be set earlier than t1(t2< t1), which results in a negative value. If t2 is set earlier than t1, the second developing roller 61M should be moved to the contact position earlier than the first developing roller 61Y.

Further, the first developing roller 61Y is moved to be separated from the first photosensitive drum 50Y at t11, the second developing roller 61M is moved to be separated from the second photosensitive drum 50M at t12, the third developing roller 61C is moved to be separated from the third photosensitive drum 50C at t13, and the fourth developing roller 61K is moved to be separated from the fourth photosensitive drum 50K at t 14. In the present embodiment, t11 is earlier than t12, t12 is earlier than t13, and t13 is earlier than t14(t11 < t12 < t13 < t 14). Therefore, when the length between t1 and t2 is represented as | t1-t2|, and when the length between t11 and t12 is represented as | t11-t12|, the absolute value between t1 and t2 is set to be smaller than the absolute value between t11 and t12 (| t1-t2| < | t11-t12 |).

In the following paragraphs, the flow of processing of monochrome image printing will be described with reference to the flowcharts in fig. 22A to 22B and the timing chart in fig. 23. Fig. 22A-22B and fig. 23 show the flow of processing for printing a monochrome image for a page.

For monochrome image printing in S23 (see also fig. 18A), the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are all located at respective separated positions before the image forming operation. Further, during an image forming operation for monochrome image printing, controller 2 controls YMC clutch 140A to remain inoperative, so that first developing roller 61Y, second developing roller 61M, and third developing roller 61C are maintained at the respective separated positions. Meanwhile, to move the fourth developing roller 61K to the contact position, as shown in fig. 22A, in S301(t0), the controller 2 activates the K clutch 140K to rotate the first cam 150K. Shortly after the first cam 150K starts rotating (t61), the separation sensor for black 4K outputs an OFF signal. Thereafter, the controller 2 drives the feeder roller 23(t61) for a predetermined time, so that the sheet S can be picked up and conveyed in S302.

After the conveyance of the sheet S is started and before the sheet S reaches the fourth photosensitive drum 50K, in S310 the controller 2 determines whether a first period T21 has elapsed since the separation sensor 4K for black started outputting the OFF signal. If the controller 2 determines that the first period T21 has elapsed (S310: yes), in S311 (T62), the controller 2 deactivates the K clutch 140K to stop the rotation of the first cam 150K at the time of the pause. The first period T21 is set to have a length in which the contact portion 172 of the cam follower 170 for black may be located on the second holding surface F2 of the first cam 150K at a position closest to the second guide surface F4. Therefore, when the rotation of the first cam 150K is resumed, the cam follower 170 for the black color may quickly move to the second guide surface F4, and the fourth developing roller 61K may start to move to the contact position. It is to be noted that the first period T21 for monochrome image printing and the first period T1 for color image printing are different from each other.

In S312, the controller 2 determines whether a second period T22 has elapsed since T54 when the preregistration sensor 28B started outputting the ON signal, that is, since the leading edge of the sheet S passed the post-registration sensor 28C. If the controller 2 determines that the second period T22 has elapsed (S312: yes), in S313 (T63), the controller 2 activates the K clutch 140K to resume rotation of the first cam 150K at the resumption time. The second period T22 is set to have a length in which the development of the toner image of black on the fourth photosensitive drum 50K by the fourth developing roller 61K can be presented in time for transfer onto the sheet S. The second period T2 for monochrome image printing and the second period T2 for color image printing are different from each other.

In S324, as shown in fig. 22B, the controller 2 determines whether a predetermined period T23 has elapsed since T63 when the K clutch 140K is activated. If the controller 2 determines that the predetermined period T23 has elapsed (S324: yes), in S325 (T66), the controller 2 deactivates the K clutch 140K to stop the rotation of the first cam 150K. The predetermined period T23 is set to have a length in which the fourth developing roller 61K is moved and located at the contact position.

In S332, the controller 2 determines whether a predetermined period T13 has elapsed since T57 when the rear position sensor 28C starts outputting the OFF signal. If the controller 2 determines that the predetermined period T13 has elapsed (S332: yes), in S333 (T67), the controller 2 activates the K clutch 140K to rotate the first cam 150K.

In S342, the controller 2 determines whether the separation sensor 4K for black is outputting an ON signal. If the controller 2 determines that the separation sensor 4K is outputting the OFF signal (S342: no), the controller 2 repeats S342. If the controller 2 determines that the separation sensor 4K is outputting the ON signal (S342: yes), in S343 (t70), the controller 2 deactivates the K clutch 140K to stop the rotation of the cam 150K.

Meanwhile, the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C are maintained at the respective separated positions. In other words, the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C can be prevented from rotating so as not to develop any toner image.

In the following paragraphs, detailed behaviors of the sheet S and the developing roller 61 will be described with reference to fig. 24A to 24D to fig. 26A to 26C.

For color image printing using the first, second, third, and fourth developing rollers 61Y, 61M, 61C, and 61K in the image forming apparatus 1, in order to transfer toner images onto the sheet S, the first, second, third, and fourth developing rollers 61Y, 61M, 61C, and 61K may be moved to respective contact positions in synchronization with conveyance of the sheet S, and after the toner images are developed on the first, second, third, and fourth photosensitive drums 50Y, 50M, 50C, and 50K, the first, second, third, and fourth developing rollers 61Y, 61M, 61C, and 61K may be moved to respective separation positions.

For example, as shown in fig. 24A, before the sheet S reaches the first photosensitive drum 50Y at the most upstream position in the conveying direction among the four (4) photosensitive drums 50, the first developing roller 61Y, the second developing roller 61M, the third developing roller 61C, and the fourth developing roller 61K are all located at respective separating positions. At the separation position, the second developing cartridge 60M coincides with the optical path of the laser beam for scanning the first photosensitive drum 50Y, the third developing cartridge 60C coincides with the optical path of the laser beam for scanning the second photosensitive drum 50M, and the fourth developing cartridge 60K coincides with the optical path of the laser beam for scanning the third photosensitive drum 50C.

When the sheet S approaches the first photosensitive drum 50Y, as shown in fig. 24B, the first developing cartridge 60Y and the second developing cartridge 60M may be simultaneously moved to position the first developing roller 61Y and the second developing roller 61M at respective contact positions before the first photosensitive drum 50Y is exposed to the laser beam. Therefore, the optical path of the laser beam emitted at the first photosensitive drum 50Y is not obstructed and is not interrupted by the second developing cartridge 60M, so that the first photosensitive drum 50Y can be clearly exposed to the laser beam. The first developing roller 61Y may develop a toner image on the first photosensitive drum 50Y, and the developed toner image may be transferred from the first photosensitive drum 50Y to the sheet S.

When the sheet S approaches the second photosensitive drum 50M, as shown in fig. 24C, the third developing cartridge 60C may be moved so that the third developing roller 61C is located at the contact position before the second photosensitive drum 50M is exposed to the laser beam. Therefore, the optical path of the laser beam emitted at the second photosensitive drum 50M is not obstructed, and is not interrupted by the third developing cartridge 60C, so that the second photosensitive drum 50M can be clearly exposed to the laser beam. The second developing roller 61M may develop the toner image on the second photosensitive drum 50M, and the developed toner image may be transferred from the second photosensitive drum 50M to the sheet S.

When the sheet S approaches the third photosensitive drum 50C, as shown in fig. 24D, the fourth developing cartridge 60K may be moved so that the fourth developing roller 61K is located at the contact position before the third photosensitive drum 50C is exposed to the laser beam. Therefore, the optical path of the laser beam emitted at the third photosensitive drum 50C is not obstructed and is not interrupted by the fourth developing cartridge 60K, so that the third photosensitive drum 50C can be clearly exposed to the laser beam. The third developing roller 61C may develop the toner image on the third photosensitive drum 50C, and the developed toner image may be transferred from the third photosensitive drum 50C to the sheet S. Further, the fourth developing roller 61K moved to the contact position can develop the toner image on the fourth photosensitive drum 50K.

After the toner image is completely developed on the first photosensitive drum 50Y by the first developing roller 61Y and before the toner image is completely developed on the second photosensitive drum 50M by the second developing roller 61M, as shown in fig. 25A, the first developing cartridge 60Y is moved so that the first developing roller 61Y is located at the separation position.

After the toner image is completely developed on the second photosensitive drum 50M by the second developing roller 61M and before the toner image is completely developed on the third photosensitive drum 50C by the third developing roller 61C, as shown in fig. 25B, the second developing cartridge 60M is moved so that the second developing roller 61M is located at the separation position.

After the toner image is completely developed on the third photosensitive drum 50C by the third developing roller 61C and before the toner image is completely developed on the fourth photosensitive drum 50K by the fourth developing roller 61K, as shown in fig. 25C, the third developing cartridge 60C is moved so that the third developing roller 61C is located at the separation position.

After the toner image is completely developed on the fourth photosensitive drum 50K by the fourth developing roller 61K, as shown in fig. 25D, the fourth developing cartridge 60K is moved so that the fourth developing roller 61K is located at the separation position.

For monochrome image printing using only the fourth developing roller 61K in the image forming apparatus 1, in order to transfer a toner image onto the sheet S, as shown in fig. 26A to 26C, the first developing roller 61Y, the second developing roller 61M, and the third developing roller 61C for the unused colors, i.e., yellow, magenta, and cyan, are maintained at the respective separation positions. Meanwhile, the fourth developing roller 61K for black may be moved to the contact position for developing the toner image, and moved to the separation position in synchronization with the conveyance of the sheet S after the complete development of the toner image on the fourth photosensitive drum 50K.

For example, as shown in fig. 26B, the fourth developing cartridge 60K may be moved before the fourth photosensitive drum 50K is exposed to the laser beam so that the fourth developing roller 61K is located at the contact position. After the toner image is completely developed on the fourth photosensitive drum 50K, as shown in fig. 26C, the fourth developing roller 61K may be moved to the separation position.

The benefits obtainable by the above-described image forming apparatus 1 will be described below. In the image forming apparatus 1 according to the embodiment, the driving force transmitter 100 can transmit not only the driving force from the developing motor 3D to the developing roller 61 but also to the moving mechanism 5 and the grip adjuster 200. Therefore, the developing motor 3D that can drive the developing roller 61 can cause the moving mechanism 5 to move the developing roller 61 to contact or separate from the photosensitive drum 50 and cause the nip adjuster 200 to switch the nip force in the fuser 80. In other words, the actions of driving the developing roller 61, moving the developing roller 61 to contact or separate from the photosensitive drum 50, and switching the nip force in the fuser 80 can be driven by only a single motor, i.e., by the developing motor 3D, without providing a dedicated motor for each action.

Further, the driving force transmitter 100 is arranged not to transmit the driving force from the developing motor 3D to the developing roller 61 when the developing roller 61 is located at the separation position. In other words, when the developing roller 61 is located at the separation position where the developing roller 61 does not develop the toner image, the developing roller 61 can be suppressed from rotating. Therefore, the rotational movement of the developing roller 61 can be reduced, and toner exhaustion or damage can be suppressed.

In the image forming apparatus 1 according to the embodiment, by using the cam surface 213 of the second cam 210, when the developing motor 3D rotates in the forward direction, the nip force in the fuser 80 can be switched from zero nip force to smaller nip force or larger nip force, and when the developing motor 3D rotates in the reverse direction, the nip force in the fuser 80 can be switched from smaller nip force or larger nip force to zero nip force. Thus, the second cam may not necessarily be provided with two distinct cam surfaces: a cam surface that switches the clamping force from zero clamping force to a lesser clamping force or a greater clamping force, and another cam surface that switches the clamping force from a lesser clamping force or a greater clamping force to zero clamping force. In this regard, the second cam 210 may be provided in a smaller size.

Further, when the nip force in the fixer 80 is at zero nip force, the heating roller 81 and the pressing roller 82 are separated from each other. Therefore, when the sheet S is jammed at a position between the heating roller 81 and the pressure roller 82, the sheet S can be easily removed by placing the fixer 80 at zero nip force, and the jam can be easily cleared.

Further, the developing motor 3D rotating in the forward direction can move the developing roller 61 between the contact position and the separation position, and switch the nip force in the fixer 80 from zero nip force to a smaller nip force or a larger nip force. Therefore, once the image forming apparatus 1 receives the print job and starts the rotation of the developing motor 3D in the forward direction to perform image printing, it is possible to smoothly print the image for the print job without switching the rotation direction of the developing motor 3D. For example, if the clamping force can be switched from zero clamping force to smaller clamping force or larger clamping force by reverse rotation of the developing motor, once the image forming apparatus receives a print job, the developing motor may be rotated in the reverse direction so that the clamping force can be switched from zero clamping force to smaller clamping force or larger clamping force; after the gripping force is switched, the developing motor rotating in the reverse direction may be suspended, and the developing motor may be rotated again in the forward direction to move and rotate the developing roller 61 to the contact position. In this regard, according to the image forming apparatus 1, the forward rotation of the developing motor 3D can be maintained by the action of switching the nip force and printing the image. Therefore, the operation time from inputting a print job to outputting an image on the sheet S can be shortened.

Further, according to the image forming apparatus 1, when the image forming apparatus 1 stands by for image printing, the developing roller 61 is located at the separation position. In this regard, the developing roller 61 can be suppressed from idly contacting the photosensitive drum 50. Therefore, the developing roller 61 can be suppressed from being exhausted or damaged, and the adhesion of toner between the developing roller 61 and the photosensitive drum 50 can be suppressed. Further, when the image forming apparatus 1 is on standby for image printing, the nip force in the fixer 80 is zero, in other words, the heating roller 81 and the pressing roller 82 are separated. Therefore, the pressing roller 82 can be suppressed from being pushed against the heating roller 81 without fixing any image, and the pressing roller 82 can be suppressed from being exhausted or damaged.

Further, the image forming apparatus 1 can switch the clamping force between zero clamping force and a smaller clamping force and between zero clamping force and a larger clamping force. In this regard, the nip force in the fixer 80 may be set at a smaller nip force or a larger nip force. Therefore, a more preferable nip force for the property or texture of the sheet S, such as thickness, material, and the like, may be selected to fix the toner image on the sheet S.

Although examples of carrying out the present invention have been described, those skilled in the art will appreciate that many variations and permutations of the image forming apparatus are within the spirit and scope of the invention as set forth in the appended claims. It is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

For example, the second cam 210 in the nip adjuster 200 may not necessarily move the pressure roller 82 to switch the nip force, but may move the heating roller 81 to switch the nip force between the pressure roller 82 and the heating roller 81. Further, the nip adjuster 200 may move both the heating roller 81 and the pressure roller 82 to switch the nip force between the pressure roller 82 and the heating roller 81.

For another example, the clamping force between the pressing roller 82 and the heating roller 81 may not necessarily be switchable between three (3) levels of zero clamping force, small clamping force, and large clamping force, but may be switchable between two (2) levels or among four (4) or more levels. For another example, the heating roller 81 and the pressing roller 82 at zero nip force may not necessarily be separated from each other, but may contact each other.

For another example, the heating roller 81 may be replaced with a heater unit having a heating endless belt, for example. Further, the pressing roller 82 may be replaced with, for example, a pressing unit having a pressing endless belt.

For another example, the belt unit 70 having the conveying belt 73 may be replaced with a belt unit having an intermediate transfer belt.

For another example, the image forming apparatus 1 may not necessarily be limited to an image forming apparatus that forms a color image with four color toners, but may be an image forming apparatus that forms a color image with three color, five color, or a different number of color toners. For another example, the image forming apparatus may be a monochrome printer having a single set of a photosensitive drum, a developing roller, a cam, and the like, which forms a monochrome image with a single color toner.

For another example, the image forming apparatus may be a multifunction peripheral or a copying machine.