JP4941159B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a color laser printer.

As an image forming apparatus such as a color laser printer, a so-called tandem type is known in which photosensitive drums corresponding to yellow, magenta, cyan, and black are arranged in parallel.
In this tandem image forming apparatus, a developing roller is provided in association with each photosensitive drum. With the developing roller in contact with the photosensitive drum, the photosensitive drum and the developing roller are rotated in opposite directions, whereby toner is supplied to the electrostatic latent image formed on the photosensitive drum, and the toner image is formed on the photosensitive drum. Supported. A toner image of a corresponding color is formed on each photosensitive drum, and the toner image of each color is transferred onto the paper so as to form a color image on the paper. In addition, a black toner image is formed only on the black photosensitive drum, and the black toner image is transferred onto the paper, thereby forming a monochrome image on the paper.

When a monochrome image is formed, toner images are not formed on yellow, magenta, and cyan photosensitive drums other than black, so that it is not necessary to rotationally drive the developing rollers associated with these photosensitive drums.
Therefore, as a tandem type image forming apparatus, when the motor rotates in the first direction, the black developing roller rotates by the rotational driving force of the motor, and the motor rotates in the second direction (opposite to the first direction). A configuration has been proposed in which all the developing rollers are rotated by the driving force of the motor when rotated in the direction (for example, see Patent Document 1).

  Also, a contact / separation member that can move linearly in the arrangement direction of the photosensitive drums is provided, and the linear movement of the contact / separation member causes the all-color separation state in which the development rollers are separated from all the photosensitive drums, In which the developing roller is separated from the yellow, magenta and cyan photosensitive drums, and the all-color contact state in which the developing roller is in contact with all the photosensitive drums are proposed (for example, , See Patent Document 2).

Specifically, the contact / separation member is connected to a crank gear to which the rotational driving force of the motor is input via a conversion member for converting the rotation of the crank gear into a linear movement of the contact / separation member. The crank gear is rotated in one direction by the rotational driving force of the motor. When the rotation position of the crank gear is a predetermined origin position, the contact / separation member is at one end position, and all the colors are in contact with each other. When the crank gear is rotated 90 degrees from the all-color contact state, the contact / separation member moves to the intermediate position, and the developing roller is separated from the yellow, magenta, and cyan photosensitive drums, resulting in a black contact state. When the crank gear is rotated 90 degrees from the black contact state, the contact / separation member moves to the other end position, the developing roller is separated from the black photosensitive drum, and all the colors are separated. When the crank gear is rotated 90 degrees from the all color separation state, the contact / separation member returns to the intermediate position, the developing roller comes into contact with the black photosensitive drum, and the black contact state is established again. When the crank gear is rotated 90 degrees from the black contact state, the contact / separation member returns to the one end position, and the full color contact state is established again.
JP 2007-72021 A JP 2007-101636 A

Combining the configurations according to each of the above proposals, it is possible to switch to the black contact state during monochrome image formation, rotate only the black developing roller, and stop the rotation of the yellow, magenta, and cyan developing rollers. It is done. Thereby, it is possible to suppress the deterioration of the yellow, magenta and cyan developing rollers.
When switching from a color image forming mode (color mode) to a monochrome image forming mode (monochrome mode), when the driving of yellow, magenta, and cyan developing rollers is stopped in the contact state of all colors, these developing rollers And the rotating photosensitive drum rub against each other, and the developing roller and / or the photosensitive drum are worn. Therefore, when switching from the color mode to the monochrome mode, the contact / separation member is moved from one end position to the other end position to switch from the all-color contact state to the all-color separation state, and the rotation of the developing roller is driven in the all-color separation state. The motor that generates the force (referred to as “development motor” in this section) is rotated in the reverse direction, and only the black development roller is rotated. Then, the contact / separation member is moved from the other end position to the intermediate position to separate all colors. The state must be switched to the black contact state. Therefore, the crank gear is rotated 270 degrees, and the contact / separation member is reciprocated 0.75 times, and it takes time to switch from the color mode to the monochrome mode.

  In addition, when switching from the monochrome mode to the color mode, if the developing motor is reversely rotated in the black contact state, the black developing roller temporarily stops when the developing motor is reversed. Therefore, the black developing roller and the rotating photosensitive drum Rub against each other. Therefore, when switching from the monochrome mode to the color mode, the crank gear is rotated 270 degrees and the contact / separation member is moved from the intermediate position to the other end position via the one end position and the intermediate position. Switch to the color separation state, reverse the development motor in the all color separation state, rotate the crank gear 180 degrees, move the contact / separation member from the other end position to the one end position, and contact all colors from the all color separation state Must switch to state. Therefore, the crank gear is rotated by a total of 450 degrees, and the contact / separation member is reciprocated 1.25 times. Switching from the monochrome mode to the color mode takes longer than switching from the color mode to the monochrome mode. End up. In addition, the yellow, magenta, and cyan developing rollers that have stopped rotating come into contact with the rotating photosensitive drums because they pass through the all-color contacting state while switching from the black contacting state to the all-color separated state. There is also a problem that the photosensitive drum is worn.

  Accordingly, an object of the present invention is to form an image in a state where all the developing means are in contact with the image carrier in a short time and to form an image in a state where one developing means is in contact with the image carrier. It is an object of the present invention to provide an image forming apparatus capable of switching between modes to be performed.

In order to achieve the above object, according to a first aspect of the present invention, in the image forming apparatus, a plurality of image carriers, a developing unit provided corresponding to each of the image carriers, and the developing unit are transmitted. Development driving means for generating rotational driving force in both forward and reverse directions for driving, driving means for generating rotational driving force in both forward and reverse directions, and the rotational driving force in the forward direction generated by the driving means. It is provided so as to be capable of reciprocating linear movement between the two positions via the third position. In the first position, all the developing means are brought into contact with the image carrier, and one of the developing means is in the second position. A developing unit is brought into contact with the image carrier, the remaining developing units other than the developing unit are separated from the image carrier, and all the developing units are separated from the image carrier at the third position. e Bei a linear motion member, said linear motion member is the When in the second position, the rotational driving force in the positive direction generated by the developing driving means is transmitted to one developing means, and when the linear motion member is in the first position, the developing driving means is generated. The rotational driving force in the reverse direction is transmitted to all the developing means .

  According to a second aspect of the present invention, in the first aspect of the present invention, the rotating body rotated in one direction by a positive rotational driving force generated by the driving means, and the rotation of the rotating body is the linear motion. A crank mechanism for converting the member into a reciprocating linear movement, and the linear motion member is when the rotational position of the rotating body is the origin position and when the rotational position is rotated by about 180 ° from the origin position. And when the rotational position of the rotating body is rotated by about 90 ° from the origin position, the rotational position of the rotating body is shifted from the origin position. When the position is rotated by about 270 °, the first position is arranged.

According to a third aspect of the present invention, in the second aspect of the present invention, based on the origin detection means for detecting that the rotational position of the rotating body is the origin position, and the output of the origin detection means. And control means for controlling the driving means.
According to a fourth aspect of the present invention, in the second aspect of the present invention, the drive means is controlled based on a position detection means for detecting the position of the linear motion member and an output of the position detection means. And a control means.

  According to the first aspect of the present invention, the linear motion member reciprocates linearly between the first position and the second position via the third position by the positive rotational driving force generated by the driving means. . When the linear motion member is in the first position, all the developing means come into contact with the image carrier. When the linear motion member is in the second position, one developing means comes into contact with the image carrier. When the linear motion member is in the third position between the first position and the second position, all the developing means are separated from the image carrier.

  Thus, from a mode in which an image is formed in a state where all the developing means are in contact with the image carrier (referred to as “all contact mode” in this section), one developing means is in contact with the image carrier. When switching to an image forming mode (referred to as “single contact mode” in this section), the linear motion member is moved from the first position to the second position, and the linear motion member is at the third position in the middle of the movement. Sometimes, only the developing means to be brought into contact with the image carrier is brought into the driving state, and then the linear motion member is moved from the third position to the second position so that one developing means in the driving state is brought into contact with the image carrier. Can be made. Therefore, the single contact mode can be switched to the full contact mode by reciprocating the linear motion member by 0.5.

  Further, when switching from the single contact mode to the full contact mode, the linear motion member is moved from the second position toward the first position, and when the linear motion member is at the third position on the way, all the developing means are moved. After the driving state, all the developing means can be brought into contact with the image carrier by moving the linear motion member from the third position to the first position. Therefore, the full contact mode can be switched to the single contact mode by reciprocating the linear motion member by 0.5.

Therefore, the single contact mode and the all contact mode can be switched in a short time.
In addition, since the developing unit whose driving is stopped does not contact the image carrier in the middle of switching from the single contact mode to the full contact mode, wear of the developing unit and / or the image carrier due to such contact does not occur.
Further, since the driving means can generate the rotational driving force in both forward and reverse directions, the reverse rotational driving force generated by the driving means is used as the driving force of the member that is driven when the linear motion member is not moved. Can be used. As a result, the configuration of the image forming apparatus can be simplified.

  According to the second aspect of the present invention, the rotating body is rotated in one direction by the positive rotational driving force generated by the driving means. Then, the rotation of the rotating body is converted into the reciprocating linear movement of the linear motion member by the crank mechanism. When the rotational position of the rotating body is a position rotated about 90 degrees in one direction from the origin position, the linear motion member is in the second position, and the rotational position of the rotating body is rotated about 270 degrees in the one direction from the origin position. When in position, the linear motion member is in the first position. Therefore, the single contact mode and the all contact mode can be switched by rotating the rotating body in one direction by about 180 degrees.

According to the third aspect of the present invention, it is detected that the rotational position of the rotating body is the origin position, and the drive means is controlled based on this. Therefore, the rotation position (rotation angle) of the rotating body can be accurately controlled, and the linear motion member can be accurately moved to each of the first position, the second position, and the third position.
According to the fourth aspect of the present invention, the position of the linear motion member is detected, and the driving means is controlled based on the detected position. Therefore, the linear motion member can be accurately moved to each of the first position, the second position, and the third position.

1. Overall Configuration FIG. 1 is a side sectional view schematically showing a configuration of a color laser printer as an example of an image forming apparatus of the present invention.
The color laser printer 1 is a tandem type color laser printer. In the box-shaped main body casing 2, a paper feeding unit 3 for feeding paper P, an image forming unit 4 for forming an image on the fed paper P, and a paper P on which an image is formed And a paper discharge unit 5 for discharging the paper.
(1) Paper Feed Unit The paper feed unit 3 includes a paper feed tray 6 for storing the paper P in a stacked state, and a paper feed roller 7 for feeding the paper P in the paper feed tray 6 one by one. It has. The paper P sent out from the paper feed tray 6 passes through the paper transport path 8 and is transported toward the image forming unit 4.
(2) Image Forming Unit The image forming unit 4 includes a black process unit 9K, a yellow process unit 9Y, a magenta process unit 9M, and a cyan process unit 9C. The black process unit 9K, the yellow process unit 9Y, the magenta process unit 9M, and the cyan process unit 9C are arranged in this order in the transport direction of the paper P.

Hereinafter, the black process unit 9K, the yellow process unit 9Y, the magenta process unit 9M, and the cyan process unit 9C are referred to as “process unit 9” unless it is particularly necessary to distinguish them.
Each process unit 9 includes a photosensitive drum 10, a charger 11, a developing device 12, and a collection member 13 as an example of an image carrier.

The photosensitive drum 10 has a cylindrical shape. The outermost layer of the photosensitive drum 10 is formed of a positively chargeable photosensitive layer.
The charger 11 is, for example, a positively charged scorotron charger. The charger 11 includes a wire and a grid, and generates a corona discharge by applying a charging bias.
The developing device 12 is disposed downstream of the charger 11 in the rotation direction of the photosensitive drum 10. The developing device 12 is provided with a developing roller 14 as an example of developing means for storing toner of each color and supplying the toner to the surface of the photosensitive drum 10.

The developing roller 14 has a configuration in which a metal shaft is covered with a conductive rubber material. The developing roller 14 is disposed to face the photosensitive drum 10 and extend in a direction parallel to the central axis of the photosensitive drum 10.
The recovery member 13 is configured by covering a metal shaft with a conductive rubber material, and has a roller shape. The collection member 13 is disposed so as to extend in a direction parallel to the central axis of the photosensitive drum 10, and the circumferential surface thereof is in contact with the surface of the photosensitive drum 10.

  During image formation (development), the photosensitive drum 10 is rotationally driven in a predetermined direction (clockwise in the figure). With this rotation, the surface of the photosensitive drum 10 is uniformly positively charged by corona discharge from the charger 11. Then, the positively charged portion is exposed by high-speed scanning of the laser beam from the exposure device 15, whereby electrostatic latent images of respective colors corresponding to the image to be formed on the paper P are formed on the surface of the photosensitive drum 10. It is formed. With the circumferential surface of the developing roller 14 in contact with the surface of the photosensitive drum 10, the developing roller 14 is driven to rotate in the direction opposite to the photosensitive drum 10 (counterclockwise in the drawing), thereby forming on the surface of the photosensitive drum 10. Toner is supplied to the electrostatic latent image. As a result, the electrostatic latent image is developed and a toner image is carried on the surface of the photosensitive drum 10.

The exposure device 15 may be configured by an LED array and provided in each process unit 9 or may be disposed above the image forming unit 4 as a scanner unit including a light source and a polygon mirror. .
Below the four process units 9, a transfer unit 16 for transferring the toner image carried on the surface of each photosensitive drum 10 onto the paper P is disposed.

  The transfer unit 16 is endlessly stretched between the driving roller 17, the driven roller 18 disposed opposite to the driving roller 17 on the upstream side in the conveyance direction of the paper P, and the driving roller 17 and the driven roller 18. And a belt-like transport belt 19. The driving roller 17, the driven roller 18, and the conveyance belt 19 are arranged so that the surface of the upper portion of the conveyance belt 19 is in contact with each photosensitive drum 10. The driving roller 17 is rotated in a direction opposite to the photosensitive drum 10 (counterclockwise in the figure) by a driving force from a motor (not shown). When the driving roller 17 is rotated, the conveying belt 19 runs around in the same direction as the driving roller 17 and the driven roller 18 is driven and rotated.

In addition, the transfer unit 16 includes a transfer roller 20 that is disposed so as to face each photosensitive drum 10 with the conveyance belt 19 interposed therebetween.
The paper P transported from the paper feed unit 3 to the image forming unit 4 is supplied onto the transport belt 19, and sequentially passes between the photosensitive drums 10 and the transport belt 19 as the transport belt 19 rotates. To be transported. During this conveyance, the toner image carried on the photosensitive drum 10 is transferred onto the paper P by the transfer bias applied to the transfer roller 20. The toner remaining on the photosensitive drum 10 after the transfer is transferred from the photosensitive drum 10 to the collecting member 13 by electrostatic force when facing the collecting member 13. The toner transferred to the collecting member 13 is accumulated on the peripheral surface of the collecting member 13 by electrostatic adsorption.

Further, the image forming unit 4 includes a fixing unit 21 for fixing the toner image transferred to the paper P.
The fixing unit 21 includes a heating roller 22 and a pressure roller 23. The pressure roller 23 is pressed against the heating roller 22 from below. The paper P transported by the transport belt 19 is sent between the heating roller 22 and the pressure roller 23. Then, while the paper P passes between the heating roller 22 and the pressure roller 23, the toner image transferred to the paper P is fixed to the paper P by heating and pressing.
(3) Paper Discharge Unit The paper discharge unit 5 includes a paper conveyance path 24 having a substantially C-shaped cross section that opens toward the image forming unit 4 side. The paper P conveyed from the fixing unit 21 passes through the paper conveyance path 24 and is discharged by a paper discharge roller 25 onto a paper discharge tray 26 formed on the upper surface of the main body casing 2.
(4) Image Forming Mode The color laser printer 1 includes, as an image forming mode, a color mode in which a color image is formed on the paper P by superimposing black, yellow, magenta and cyan toner images, and a black toner image. A monochrome mode for forming a monochrome image on the paper P. In the color laser printer 1, each developing device 12 is provided to be movable with respect to the photosensitive drum 10. Then, by moving the developing device 12, in the color mode, all the developing rollers 14 are brought into contact with all the photosensitive drums 10, and in the monochrome mode, the developing roller 14 of the black process unit 9K is in the photosensitive drum 10. , The developing roller 14 of the yellow process unit 9Y, the magenta process unit 9M, and the cyan process unit 9C is brought into a black contact state in which the developing roller 14 is separated from the photosensitive drum 10.

Hereinafter, the photosensitive drum 10 of the black process unit 9K is referred to as “black photosensitive drum 10K”, and the developing device 12 of the black process unit 9K is referred to as “black developing device 12K”. The photosensitive drum 10 of the yellow process unit 9Y is referred to as “yellow photosensitive drum 10Y”, and the developing device 12 of the yellow process unit 9Y is referred to as “yellow developing device 12Y”. The photosensitive drum 10 of the magenta process unit 9M is referred to as “magenta photosensitive drum 10M”, and the developing device 12 of the magenta process unit 9M is referred to as “magenta developing device 12M”. The photosensitive drum 10 of the cyan process unit 9C is referred to as “cyan photosensitive drum 10C”, and the developing device 12 of the cyan process unit 9C is referred to as “cyan developing device 12C”.
2. Image Forming Mode Switching (1) Electrical Configuration FIG. 2 is a block diagram showing an electrical configuration for switching the image forming mode.

The color laser printer 1 includes a control unit 31 as an example of a control unit including a microcomputer including a CPU, a RAM, a ROM, and the like. A development motor 32 (development drive means) and a contact / separation motor 33 as an example of a drive means are connected to the control unit 31 as control targets.
Both the developing motor 32 and the contact / separation motor 33 are DC brushless motors that generate rotational driving force in both forward and reverse directions.

  The rotational driving force generated by the developing motor 32 is input to a gear mechanism (not shown). The gear mechanism transmits the rotational drive force in the forward direction generated by the developing motor 32 (rotational drive force during forward rotation) to the developing roller 14 of the black developing device 12K, and the rotational drive force in the reverse direction generated by the developing motor 32. (Rotational driving force at the time of reverse rotation) is transmitted to all the developing rollers 14. The configuration of this gear mechanism is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-72021.

A forward rotation driving force generated by the contact / separation motor 33 (rotational driving force during forward rotation), as will be described later, is a switching mechanism 41 for switching the contact state of the four developing rollers 14 to the photosensitive drum 10 (see FIG. 3).
Further, the contact / separation motor 33 is provided with an encoder 34 as an example of an origin detection means. The pulse signal output from the encoder 34 is input to the control unit 31. Based on the pulse signal input from the encoder 34, the control unit 31 detects that the rotation position of the contact / separation motor 33 is the origin position, and the rotation angle of the contact / separation motor 33 (final) based on the origin position. Specifically, the rotation angle of a crank gear 45 described later is controlled.
(2) Switching Mechanism FIG. 3 is a side view schematically showing the switching mechanism together with the photosensitive drum and the developing device.

The switching mechanism 41 includes a long and substantially plate-like linearly moving member 42. The linear motion member 42 extends in the direction in which the photosensitive drums 10 are arranged (hereinafter, this direction is referred to as “front-rear direction”), and is provided so as to be movable in the front-rear direction and not movable in the vertical direction. A rack gear 43 is formed on the upper surface of the linear motion member 42. The rack gear 43 has a large number of gear teeth arranged in the front-rear direction (longitudinal direction of the linear motion member 42). Further, a support shaft 44 is provided at the end of the linear motion member 42 on the black developing device 12K side so as to protrude from the side surface in a direction orthogonal to the front-rear direction (hereinafter, this direction is referred to as “width direction”). Yes.
Further, the switching mechanism 41 is provided in association with a crank gear 45 as an example of a rotating body, an erection member 46 erected between the linear motion member 42 and the crank gear 45, and each developing device 12. Each cam 47, four cam gears 48 provided coaxially with each cam 47, and four pinion gears 49 disposed between the rack gear 43 and each cam gear 48 and meshed with the rack gear 43 and the cam gear 48. .

  The crank gear 45 is disposed at a position facing the end of the linear motion member 42 on the black developing device 12K side in the front-rear direction, and is provided to be rotatable around a rotation axis extending in the width direction. A large number of gear teeth are formed on the peripheral surface of the crank gear 45. A transmission gear (not shown) is engaged with the gear teeth. The crank gear 45 receives the rotational driving force in the positive direction of the contact / separation motor 33 (see FIG. 2) via the transmission gear. The crank gear 45 rotates in one direction (clockwise in FIG. 3) by the input of the rotational driving force in the positive direction. A support shaft 50 extending in the width direction is provided at the peripheral edge of the crank gear 45. The support shaft 50 is disposed at the uppermost position shown in FIG. 3C when the rotation position of the crank gear 45 is the origin position (described later).

The origin position of the crank gear 45 is set to a rotation position when the rotation position of the contact / separation motor 33 is the origin position. Thus, detecting that the rotation position of the contact / separation motor 33 is the origin position is equivalent to detecting that the rotation position of the crank gear 45 is the origin position.
One end of the erection member 46 is rotatably connected to the support shaft 44, and the other end is rotatably connected to the support shaft 50. Since the linear motion member 42 is provided so as not to move in the vertical direction, when the crank gear 45 is rotated in one direction, one end of the erection member 46 rotates with the support shaft 44, and accordingly, the support shaft 50. The other end of the erection member 46 connected to is moved in the front-rear direction. As a result, the linear motion member 42 moves in the front-rear direction. That is, the erection member 46 and the support shafts 44 and 50 constitute a crank mechanism for converting the rotation of the crank gear 45 into the linear movement of the linear motion member 42.

  The four cams 47 are rotatably supported by a cam shaft 51 extending in the width direction. A cam 47 provided in association with the black developing device 12K (hereinafter referred to as “black cam 47” when referring to the cam 47 individually) is symmetrical about the cam shaft 51 at the periphery of the disk. An arcuate cutout 52 is formed at one position. The cam 47 provided in association with each of the yellow developing device 12Y, the magenta developing device 12M, and the cyan developing device 12C has a shape in which one circular arc-shaped notch 52 is formed on the periphery of the disk. For example, each developing device 12 is provided with a protruding portion 53 that protrudes in the width direction from the side surface, and each cam 47 has a circumferential surface that abuts against the protruding portion 53 of the corresponding developing device 12. Is provided.

The cam gear 48 is rotatably supported on the cam shaft 51 and is provided so as not to rotate relative to the cam 47.
The pinion gear 49 rotates as the linear motion member 42 moves. The rotation of the pinion gear 49 is transmitted to the cam gear 48, so that the cam 47 rotates integrally with the cam gear 48. The diameter and the number of teeth of the pinion gear 49 are determined such that the cam 47 rotates 90 ° when the crank gear 45 rotates 90 ° in one direction.

  As shown in FIG. 3A, the support shaft 50 provided on the crank gear 45 is positioned farthest from the black cam 47 in a state in which the crank gear 45 is rotated about 270 ° in one direction from the origin position. It arrange | positions and opposes the support shaft 44 provided in the linearly-moving member 42 in the front-back direction. Thereby, the erection member 46 extends in the front-rear direction, and the linear motion member 42 is disposed at the first position closest to the crank gear 45. Further, the four cams 47 are arranged such that when the linear motion member 42 is arranged at the first position, one notch portion 52 of the black cam 47 and the notch portions 52 of the remaining three cams 47 face upward. Is provided. Therefore, when the linear motion member 42 is disposed at the first position, the protruding portions 53 of the developing devices 12 enter the notches 52, all the developing devices 12 are disposed at the lowermost position, and all the developing rollers 14 are disposed. All the colors come into contact with the photosensitive drum 10.

  As shown in FIG. 3B, the support shaft 50 provided on the crank gear 45 is disposed at a position closest to the black cam 47 in a state where the crank gear 45 is rotated about 90 ° in one direction from the origin position. Then, it faces the support shaft 44 provided on the linear motion member 42 in the front-rear direction. Thereby, the erection member 46 extends in the front-rear direction, and the linear motion member 42 is disposed at the second position farthest from the crank gear 45. Further, one notch portion 52 of the black cam 47 and the notch portions 52 of the remaining three cams 47 face downward, and the protruding portion 53 of the black developing device 12K enters the other notch portion 52 of the black cam 47. The other protrusions 53 of the developing devices 12 are in contact with the peripheral surface outside the notch 52 of the cam 47. Therefore, when the linear motion member 42 is disposed at the second position, the yellow developing device 12Y, the magenta developing device 12M, and the cyan developing device 12C are lifted upward from the black developing device 12K, and only the developing roller 14 of the black developing device 12K. Is in a black contact state in contact with the photosensitive drum 10.

As shown in FIG. 3C, the support shaft 50 provided on the crank gear 45 is disposed at the uppermost position above the rotation axis of the crank gear 45 in a state where the rotational position of the crank gear 45 is the origin position. The Thereby, the erection member 46 is inclined so that the end portion on the support shaft 50 side is located above the end portion on the support shaft 44 side, and the linear motion member 42 is between the first position and the second position. In the third position. Further, the support shaft 50 provided on the crank gear 45 is disposed at the lowest position below the rotation axis of the crank gear 45 in a state in which the crank gear 45 is rotated about 180 ° in one direction from the origin position. Thereby, the erection member 46 is inclined so that the end portion on the support shaft 50 side is positioned below the end portion on the support shaft 44 side, and the linear motion member 42 is between the first position and the second position. In the third position. When the linear motion member 42 is disposed at the third position, both the cutout portions 52 of the black cam 47 face in the front-rear direction, and the cutout portions 52 of the remaining three cams 47 face away from the black cam 47 side. . As a result, the protruding portions 53 of all the developing devices 12 come into contact with the peripheral surface of the cam 47 outside the notch 52. Therefore, as compared with the state shown in FIG. 3A, all the developing devices 12 are lifted upward, and all the developing rollers 14 are separated from the photosensitive drum 10.
(3) Switching Process FIG. 4 is a flowchart for explaining the color / monochrome switching process.

At the time of switching from the color mode to the monochrome mode, the color / monochrome switching process shown in FIG. 4 is executed by the control unit 31 in order to shift from the all-color contact state to the black contact state.
First, the contact / separation motor 33 is driven to rotate forward (forward rotation on) (S 1), and the contact / separation motor 33 outputs a rotational drive force in the forward direction. The crank gear 45 is rotated in one direction (clockwise in FIG. 3) from a position at a rotation angle of 270 ° (a position rotated about 270 ° in one direction from the origin position) by this positive rotational driving force. By the rotation of the crank gear 45, the linear movement member 42 moves from the first position toward the second position.

  When the rotation angle of the crank gear 45 becomes 0 °, that is, when the rotation position of the crank gear 45 reaches the origin position (S2: YES), the contact / separation motor 33 is temporarily stopped (off) (S3). As a result, the linear motion member 42 stops at the third position (see FIG. 3C), and at this time, all of the developing rollers 14 are separated from the photosensitive drum 10 in a state of separation of all colors. In this all color separation state, the developing motor 32 that is being driven for reverse rotation is stopped (S4). Then, the developing motor 32 is driven to rotate forward (turned on normally) (S5). Only the developing roller 14 of the black developing device 12K is rotationally driven by the forward rotation of the developing motor 32.

Thereafter, the contact / separation motor 33 is driven to rotate forward again (S6). The crank gear 45 rotates in one direction from the position where the rotation angle is 0 ° by the positive rotational driving force from the contact / separation motor 33. As the crank gear 45 rotates, the linear motion member 42 moves from the third position toward the second position.
When the rotation angle of the crank gear 45 reaches 90 °, that is, when the rotation position of the crank gear 45 reaches about 90 ° in one direction from the origin position (S7: YES), the contact / separation motor 33 is stopped (S8). ). As a result, the linear motion member 42 stops at the second position (see FIG. 3B), and a black contact state in which only the developing roller 14 of the black developing device 12K contacts the photosensitive drum 10 is established.

FIG. 5 is a flowchart for explaining the monochrome / color switching process.
When switching from the monochrome mode to the color mode, the monochrome / color switching process shown in FIG. 5 is executed by the control unit 31 in order to shift from the black contact state to the all-color contact state.
First, the contact / separation motor 33 is driven to rotate forward (S11), and a rotation drive force in the forward direction is output from the contact / separation motor 33. With this positive rotational driving force, the crank gear 45 rotates in one direction (clockwise in FIG. 3) from the position at the rotation angle of 90 °. By the rotation of the crank gear 45, the linear motion member 42 moves from the second position toward the first position.

  When the rotation angle of the crank gear 45 reaches 180 °, when the rotation position of the crank gear 45 reaches a position rotated about 180 ° in one direction from the origin position (S12: YES), the contact / separation motor 33 is temporarily stopped (S13). ). As a result, the linear motion member 42 stops at the third position (see FIG. 3C), and at this time, all of the developing rollers 14 are separated from the photosensitive drum 10 in a state of separation of all colors. In this all-color separation state, the developing motor 32 that is normally driven is stopped (S14). Then, the developing motor 32 is driven in reverse rotation (reverse rotation on) (S15). All the developing rollers 14 are rotationally driven by the reverse driving of the developing motor 32.

Thereafter, the contact / separation motor 33 is driven to rotate forward again (S16). The crank gear 45 rotates in one direction from the position at a rotation angle of 180 ° by the positive rotational driving force from the contact / separation motor 33. As the crank gear 45 rotates, the linear motion member 42 moves from the third position toward the first position.
When the rotation angle of the crank gear 45 reaches 270 ° (S17: YES), the contact / separation motor 33 is stopped (S18). As a result, the linear motion member 42 stops at the first position (see FIG. 3A), and all the developing rollers 14 come into contact with the photosensitive drum 10 to be in an all-color contact state.
3. Effect Due to the positive rotational driving force generated by the contact / separation motor 33, the linearly moving member 42 reciprocates linearly between the first position and the second position via the third position. When the linear motion member 42 is in the first position, all the developing rollers 14 come into contact with the photosensitive drum 10. When the linear motion member 42 is in the second position, one developing roller 14 contacts the photosensitive drum 10. When the linear motion member 42 is in the third position between the first position and the second position, all the developing rollers 14 are separated from the photosensitive drum 10.

  Thus, from a color mode in which an image is formed with all the developing rollers 14 in contact with the photosensitive drum 10, a monochrome mode in which an image is formed with the developing roller 14 of the black developing device 12K in contact with the photosensitive drum 10. When the linear movement member 42 is moved from the first position to the second position and the linear movement member 42 is in the third position in the middle of the movement, only the developing roller 14 of the black developing device 12K is driven. After that, the developing roller 14 of the black developing device 12K can be brought into contact with the photosensitive drum 10 by moving the linear motion member 42 from the third position to the second position. Therefore, the color mode can be switched to the monochrome mode by reciprocating the linear motion member 42 by 0.5.

  When switching from the monochrome mode to the color mode, the linear motion member 42 is moved from the second position toward the first position, and when the linear motion member 42 is in the third position on the way, all the developing rollers 14 are moved. After the drive state is set, all the developing rollers 14 can be brought into contact with the photosensitive drum 10 by moving the linear movement member 42 from the third position to the first position. Therefore, the monochrome mode can be switched to the color mode by reciprocating the linear movement member 42 by 0.5.

Therefore, the color mode and the monochrome mode can be switched in a short time.
Moreover, since the developing roller 14 whose driving is stopped does not contact the photosensitive drum 10 during the switching from the color mode to the monochrome mode, the developing roller 14 and / or the photosensitive drum 10 is not worn by such contact.
Further, since the contact / separation motor 33 can generate rotational drive force in both forward and reverse directions, the reverse rotation drive force generated by the contact / separation motor 33 is driven when the linear motion member 42 is not moved. It can be used as a driving force for a member (for example, a paper feed roller 7). As a result, the configuration of the color laser printer 1 can be simplified.

  Furthermore, in the color laser printer 1, the crank gear 45 is rotated in one direction by the forward rotational driving force generated by the contact / separation motor 33. The rotation of the crank gear 45 is converted into the reciprocating linear movement of the linear motion member 42 by the crank mechanism. When the rotational position of the crank gear 45 is a position rotated about 90 degrees in one direction from the origin position, the linear motion member 42 is in the second position, and the rotational position of the crank gear 45 is about 270 in one direction from the origin position. The linear motion member 42 is in the first position when the position is rotated by a predetermined degree. Therefore, the color mode and the monochrome mode can be quickly switched by rotating the crank gear 45 about 180 degrees in one direction.

In the color laser printer 1, it is detected that the rotational position of the crank gear 45 is the origin position, and the contact / separation motor 33 is controlled based on this. Therefore, the rotation angle (rotation position) of the crank gear 45 can be accurately controlled, and the linear motion member 42 can be accurately moved to each of the first position, the second position, and the third position.
4). Other Embodiments FIG. 6 is a block diagram showing another embodiment of the electrical configuration for switching the image forming mode.

  In the configuration shown in FIG. 6, a position detection switch 61 as an example of a position detection unit for detecting the position of the linear motion member 42 is provided instead of the encoder 34 shown in FIG. 2. For example, as shown by a broken line in FIG. 3B, the position detection switch 61 is a position at which the linear motion member 42 comes into contact and is turned on when the linear motion member 42 is disposed at the second position. Is arranged.

  The on / off signal output from the position detection switch 61 is input to the control unit 31. The control unit 31 detects that the linear motion member 42 is disposed at the second position based on the on / off signal input from the position detection switch 61. Then, the rotation angle of the contact / separation motor 33 (finally, the rotation angle of a crank gear 45 described later) is controlled with reference to the time when the linear motion member 42 is disposed at the second position.

Also with this configuration, the linear motion member 42 can be accurately moved to the first position, the second position, and the third position.
5. Other Embodiments Although a tandem color laser printer 1 has been taken up, the present invention transfers toner images for each color from each image carrier to an intermediate transfer belt, and then collectively transfers the image from the intermediate transfer belt to a sheet. It can also be applied to an intermediate transfer type color laser printer.

1 is a side sectional view schematically showing a configuration of a color laser printer as an example of an image forming apparatus of the present invention. FIG. 3 is a block diagram illustrating an electrical configuration for switching an image forming mode. FIG. 3 is a side view schematically showing a switching mechanism together with a photosensitive drum and a developing device. It is a flowchart for demonstrating a color / monochrome switching process. It is a flowchart for demonstrating a monochrome / color switching process. FIG. 10 is a block diagram showing another form of the electrical configuration for switching the image forming mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color laser printer 10 Photosensitive drum 14 Developing roller 31 Control part 33 Contact / separation motor 34 Encoder 44 Support shaft 45 Crank gear 46 Construction member 50 Support shaft 61 Position detection switch

Claims (4)

A plurality of image carriers;
Developing means provided corresponding to each of the image carriers;
Development driving means for generating rotational driving force in both forward and reverse directions for transmission to the developing means; driving means for generating rotational driving force in both forward and reverse directions;
A positive rotational drive force generated by the driving means is provided so as to be reciprocally linearly movable between the first position and the second position via the third position, and at the first position, all the development is performed. Means is brought into contact with the image carrier, one developing means is brought into contact with the image carrier in the second position, and the remaining developing means other than the developing means are separated from the image carrier, Bei example a linear motion member for separating all of said developing means from said image bearing member at the third position,
When the linear movement member is in the second position, the rotational driving force in the positive direction generated by the development driving means is transmitted to one of the development means, and when the linear movement member is in the first position, wherein said rotational driving force in the reverse direction in which the developing drive means is generated you characterized in that it is communicated to all of the developing means, the image forming apparatus. A rotating body that is rotated in one direction by a positive rotational driving force generated by the driving means;
A crank mechanism for converting the rotation of the rotating body into a reciprocating linear movement of the linear motion member,
The linear motion member is disposed at the third position when the rotational position of the rotating body is the origin position and when the rotational position is rotated by about 180 ° from the origin position, and the rotational position of the rotating body is When the rotation position is about 90 ° from the origin position, the second position is arranged. When the rotation position of the rotating body is about 270 ° rotation from the origin position, the first position is The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed. Origin detecting means for detecting that the rotational position of the rotating body is the origin position;
The image forming apparatus according to claim 2, further comprising a control unit that controls the driving unit based on an output of the origin detection unit. Position detecting means for detecting the position of the linear motion member;
The image forming apparatus according to claim 2, further comprising: a control unit that controls the driving unit based on an output of the position detection unit.

Images