JP4667106B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic method, and in particular, develops a plurality of image carriers and a latent image formed on the image carrier in contact with the image carrier. And an image forming apparatus capable of forming a color image.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic process, each of the image bearing members (photosensitive members) is, for example, a photosensitive drum and process means such as a charging unit, a developing unit, and a cleaning unit that act on the photosensitive unit. A plurality of image forming units provided with a plurality of image forming units are juxtaposed, and images are sequentially transferred onto a transfer belt (intermediate transfer belt) or a transfer material on a transfer belt (transfer material transport belt) disposed opposite to the plurality of image forming units. There is a color image forming apparatus adopting an inline method.

  In such an in-line type color image forming apparatus, the process means such as the photosensitive member and the developing means in each image forming unit are integrated into a cartridge to form a process cartridge, and the process cartridge is detachably attached to the apparatus main body. There are things arranged in According to this, for example, when the developer runs out, the user can replace the process cartridge and replace the process cartridge without relying on the service person, and other consumables such as the photosensitive member can be used. Since it can be replaced at the same time, the maintainability is greatly improved.

As a developing means of a process cartridge used in such an in-line type color image forming apparatus, a contact developing method in which development is generally performed with a developing roller in contact with a photosensitive member, a developing roller and a photosensitive member, and There are two known non-contact development methods in which development is performed with a predetermined gap between them, but the contact development method has the following problems.
(1) When the photosensitive member rotates at a timing other than during the developing operation, such as pre-rotation and post-rotation, the surface layer of the photosensitive member is scraped by rubbing with the developing roller, which becomes a factor of reducing the service life.
(2) When other color cartridges not involved in development are operated, such as during mono-color development, the life of the photoreceptor is greatly reduced.
(3) When no bias is applied during non-operation, pre-rotation, and post-rotation, the developer on the developing roller adheres to the photoconductor, wastes the developer, or the developer stains paper or the like Cause.
(4) The roller layer of the developing roller is permanently deformed when it is not used for a long time while attached to the main body of the image forming apparatus, causing unevenness on the image during development.

  In order to solve the above problems, proposals have been made in Patent Documents 1 and 2 and the like. This is a structure in which development is performed with toner by bringing the developing roller into contact with the photosensitive drum only during the period of developing the electrostatic latent image on the photosensitive drum, and a guide for contacting and separating the developing roller in the horizontal direction. By sliding, the developing roller is brought into contact with and separated from the photosensitive drum in the order of the first ST, the second ST, the third ST, and the fourth ST.

JP 2001-318506 A JP 2001-337511 A

  However, in the invention described in the above-mentioned Patent Document 1, since the developing rollers are contacted and separated in the order of 1ST → 2ST → 3ST → 4ST, it is originally necessary for 4ST black monocolor printing. The first to third ST developing rollers must be brought into contact with or separated from each other.

  In addition, since the guide that contacts and separates the developing roller is slid in the horizontal direction, when mono-color and full-color printing are mixed, the guide is once homed when switching from mono-color printing to full-color printing. It becomes necessary to slide to the position, and the throughput is reduced by the switching time.

  Therefore, the object of the present invention is to reduce the surface layer of the photoconductor and the like, the deformation of the developing means, the waste of the developer without reducing the throughput, and the in-line type that can avoid paper stains. An image forming apparatus is provided.

  Another object of the present invention is to provide an inline-type image forming apparatus that can achieve the above object with a simple configuration and at low cost.

In order to achieve the above object, an invention according to claim 1 includes an image carrier that carries an electrostatic latent image, and a developing roller, and is separated from a contact position where the image carrier and the developing roller are in contact. A plurality of developing means for developing the electrostatic latent image by the developing roller at the contact position, each of which includes a developer of different colors including black A first state in which the developing unit of the plurality of image forming units is in the separated position; a second state in which the developing unit of the plurality of image forming units is in the contact position; Of the plurality of image forming units, only the black image forming unit can be switched to the third state in which the developing unit is in the contact position, and full-color image formation is performed in the second state. In black An image forming apparatus for forming the image forming apparatus, wherein the image forming apparatus is provided corresponding to each developing unit of the plurality of image forming units, the motor being rotatable in the first and second directions. A plurality of cams that are moved between the contact position and the separation position, wherein the first switching from the first state to the second state is performed in conjunction with the rotation of the one motor in the first direction. A plurality of cams that perform the second switching from the first state to the third state in conjunction with the rotation of the one motor in the second direction, and in each of the plurality of cams, The image forming apparatus in which the rotation angle required for the second switching is smaller than the rotation angle required for moving the developing unit of the black image forming unit from the separation position to the contact position in the first switching. It is.

  According to the present invention, in an inline type image forming apparatus, it is possible to realize a function of rotating a developing roller when necessary and bringing it into contact with an image carrier without deteriorating image forming accuracy or transfer material conveyance accuracy. This makes it possible to reduce deterioration of the surface layer of the photoconductor, deformation of the developing means, waste of developer, avoid paper stains, and when mono-color and full-color prints coexist. Switching between mono-color printing → full-color printing and full-color printing → mono-color printing can be performed efficiently without reducing the throughput. Further, according to the present invention, the above-described effects can be obtained with a simple configuration and at a low cost.

  Hereinafter, an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

<Embodiment 1>
[overall structure]
First, the overall configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  In the present embodiment, the image forming apparatus uses a transfer material such as a recording sheet or an OHP sheet by an electrophotographic method in response to an image information signal from an external host device such as a personal computer that is communicably connected to the apparatus body. It is a full color laser beam printer that can form a full color image. However, the present invention is not limited to this, and can be embodied in any form such as a copying machine or a facsimile machine. FIG. 1 is a longitudinal sectional view showing the overall configuration of an image forming apparatus 100 according to the present embodiment.

  An image forming apparatus 100 shown in FIG. 1 includes four drum-shaped image carriers arranged in a substantially vertical direction, that is, photosensitive drums 1 (1a, 1b, 1c, 1d) as image carriers. ing. The photosensitive drum 1 is driven to rotate counterclockwise in FIG. 1 by a driving means (described later) shown in FIG.

  A charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 in order according to the rotation direction, and a laser beam are irradiated around the photosensitive drum 1 based on image information. A scanner unit 3 (3a, 3b, 3c, 3d) that forms an electrostatic latent image on the photosensitive drum 1, and a developing device 4 (4a) that attaches toner included in the developer to the electrostatic latent image and develops it as a toner image. 4b, 4c, 4d), an electrostatic transfer device 5 that transfers the toner image on the photosensitive drum 1 to the transfer material S, and a cleaning device 6 that removes transfer residual toner remaining on the surface of the photosensitive drum 1 after transfer. (6a, 6b, 6c, 6d) etc. are arranged.

  In the present embodiment, four image forming units Pa, Pb, Pc, and Pd, which are image forming units each including a photosensitive drum 1, a charging device 2, a scanner unit 3, a developing device 4, a cleaning device 5, and the like, respectively. Images of different colors (yellow, magenta, cyan, black) are formed.

  The photosensitive drum 1 and the charging device 2, the developing device 4 and the cleaning device 6 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge, and a process cartridge 7 ( 7a, 7b, 7c, 7d). FIG. 2 shows a longitudinal section of the process cartridge 7.

  In the following description, the front side of the image forming apparatus 100 refers to the side where the process cartridge 7 is inserted into the apparatus main body 100, that is, the right side in FIG. The left and right sides of the image forming apparatus 100 are those viewed from the front side of the apparatus. Hereinafter, each element will be described in more detail starting with the photosensitive drum 1.

  The photoconductor drum 1 is configured by applying an organic photoconductive layer (OPC photoconductor) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. Both ends of the photosensitive drum 1 are rotatably supported by a support member, and a driving force from a driving motor (described later) is transmitted to one end, thereby rotating counterclockwise in FIG. Driven.

  As the charging device 2, a contact charging type charging member can be used. The charging member is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1 and a charging bias voltage is applied to the roller so that the surface of the photosensitive drum 1 is made. Charge uniformly.

  The scanner unit 3 is arranged in a substantially horizontal direction of the photosensitive drum 1, and image light corresponding to an image signal is rotated at high speed by a scanner motor (not shown) by a laser diode (not shown). , 9c, 9d). The image light reflected by the polygon mirror 9 selectively exposes the surface of the charged photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d) to form an electrostatic latent image.

  4 and 5, the scanner unit 3 is formed longer than the pitch between the left and right side plates 32 in the longitudinal direction, and the opening holes 35 (35a, 35b, 35c, 35d, 35e, 35f, 35g, 35h) so that the projection 33 protrudes outward. At this time, the scanner unit 3 is pressed by the compression spring 36 with a force of about 1 kgf (≈9.8 N) downward by about 45 ° with respect to the horizontal as indicated by an arrow G in FIG. As a result, the scanner unit 3 is reliably pressed against the abutments 35A and 35B for positioning.

  The developing device 4 includes a toner container 41 (41a, 41b, 41c, 41d) that stores toners of yellow, magenta, cyan, and black, respectively, as a developer. Referring to FIG. The toner inside is fed into the toner supply roller 42 by the toner transport mechanism 42.

  The toner is applied to the outer periphery of the developing roller 40 rotating in the clockwise direction in FIG. 2 by the toner supply roller 43 rotating in the clockwise direction in FIG. 2 and the developing blade 44 pressed against the outer periphery of the developing roller 40. Apply charge. Then, a toner is supplied onto the photosensitive drum 1 in accordance with the latent image by applying a developing bias in which an AC voltage and a DC voltage are superimposed on the developing roller 40 facing the photosensitive drum 1 on which the latent image is formed. To do.

  An electrostatic transfer belt (transfer belt) 11 that circulates as a transfer material transport unit is disposed so as to face and contact all the photosensitive drums 1. The transfer belt 11 is composed of a film-like member having a volume resistivity of 1011 to 1014 Ω · cm and a thickness of about 150 μm. The transfer belt 11 is supported by rollers in four directions in the vertical direction, and circulates and moves so that the transfer material S is electrostatically attracted to the outer peripheral surface on the left side in FIG. . As a result, the transfer material S is conveyed to the transfer position by the transfer belt 11, and the toner image on the photosensitive drum 1 is transferred.

  Transfer rollers 12 (12a, 12b, 12c, 12d) are arranged in parallel at positions (transfer positions) that are in contact with the inside of the transfer belt 11 and face the four photosensitive drums 1 respectively. A positive charge is applied from the transfer roller 12 to the transfer material S via the transfer belt 11, and the electric field due to the charge causes the transfer material S in contact with the photosensitive drum 1 to be negatively charged on the photosensitive drum 1. The toner image is transferred. The transfer belt 11 constitutes an image carrier that carries and conveys a transfer material S onto which a toner image formed on each photosensitive drum 1 is transferred.

  In the present embodiment, the transfer belt 11 is a belt having a circumferential length of 675 mm and a thickness of 120 μm, and is stretched around four rollers including a driving roller 13, driven rollers 14 a and 14 b, and a tension roller 15. It is rotated in the direction of the arrow in FIG. 1 by being driven to rotate by a drive motor (not shown) which is a carrier driving means. While the transfer belt 11 circulates and moves the transfer material S from the driven roller 14a side to the drive roller 13 side, the toner image is transferred to the transfer material S.

  The paper feed unit 16 feeds and conveys the transfer material S to the image forming unit, and a plurality of transfer materials S are stored in the paper feed cassette 17. At the time of image formation, the paper feed roller 18 (half-moon roller) and the registration roller pair 19 are rotationally driven according to the image forming operation to separate and feed the transfer material S in the paper feed cassette 17 one by one. The leading edge of the roller contacts the registration roller pair 19 and temporarily stops. After forming a loop, the rotation of the transfer belt 11 and the image writing position are synchronized, and the sheet is fed to the transfer belt 11 by the registration roller pair 19. .

  The fixing unit 20 fixes a plurality of color toner images transferred to the transfer material S, and includes a heating roller 21a that rotates, and a pressure roller 21b that presses and applies heat and pressure to the transfer material S. Consists of. That is, the transfer material S to which the toner image on the photosensitive drum 1 is transferred is conveyed by the fixing roller pair 21a and 21b when passing through the fixing unit 20, and is given heat and pressure by the fixing roller pair 21a and 21b. It is done. As a result, toner images of a plurality of colors are fixed on the surface of the transfer material S.

  Next, the operation of the image forming apparatus 100 configured as described above will be described.

  Each process cartridge 7 is sequentially driven in accordance with the image formation timing, and each photosensitive drum 1 is driven to rotate counterclockwise in FIG. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging roller 2 imparts a uniform charge to the circumferential surface of the photosensitive drum 1, and the scanner unit 3 exposes the circumferential surface of the photosensitive drum 1 according to the image signal to perform photosensitive drum 1. An electrostatic latent image is formed on the peripheral surface.

  The developing roller 40 in the developing device 4 forms (develops) a toner image on the peripheral surface of the photosensitive drum 1 by transferring toner to a low potential portion of the electrostatic latent image. At the timing when the leading edge of the toner image formed on the peripheral surface of the most upstream photosensitive drum 1 is rotationally conveyed to a point (transfer position) facing the transfer belt 11, the image of the transfer material S is transferred to that point. The registration roller pair 19 starts rotating and feeds the transfer material S to the transfer belt 11 so that the formation start positions coincide.

  The transfer material S is pressed against the outer periphery of the transfer belt 11 so as to be sandwiched between the electrostatic adsorption roller 22 and the transfer belt 11. Further, by applying a voltage between the transfer belt 11 and the electrostatic attraction roller 22, charges are induced in the transfer material S that is a dielectric and the dielectric layer of the transfer belt 11, and the transfer material S is transferred. The belt 11 is electrostatically attracted to the outer periphery of the belt 11. As a result, the transfer material S is stably adsorbed to the transfer belt 11 and conveyed to the most downstream transfer position. In this way, while being transferred on the transfer belt 11, the toner images on the photosensitive drums 1 are sequentially transferred onto the transfer material S by the electric field formed between the photosensitive drums 1 and the transfer rollers 12.

  The transfer material S to which the four color toner images are transferred is separated from the transfer belt 11 by the curvature of the driving roller 13 and is carried into the fixing unit 20. After the toner image is thermally fixed by the fixing unit 20, the transfer material S is discharged out of the apparatus main body 100 by the paper discharge roller pair 23 with the image surface facing down.

[Process cartridge]
Next, the process cartridge will be described in more detail with reference to FIGS. 2 and 3 are a main sectional view and a perspective view of the process cartridge 7, respectively. The yellow, magenta, cyan, and black process cartridges 7 (7a, 7b, 7c, and 7d) have the same configuration.

  The process cartridge 7 includes a drum-shaped image carrier that is an image carrier, that is, a photosensitive drum unit 50 including a photosensitive drum 1, a primary charging unit (charging device) 2, and a cleaning unit (cleaning device) 6, and a photosensitive drum. 1 is divided into a developing unit 4 composed of developing means (developing device) for developing the electrostatic latent image on 1.

  In the photosensitive drum unit 50, the photosensitive drum 1 is rotatably attached to the cleaning frame 51 via bearings 31 (31a, 31b) (bearings). A charging device 2 for uniformly charging the surface of the photosensitive drum 1 and a cleaning blade 60 of a cleaning device 6 for removing toner remaining on the photosensitive drum are disposed on the periphery of the photosensitive drum 1. ing.

  Further, residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 60 is sequentially sent to a waste toner chamber 53 provided behind the cleaning frame 51 by the toner feeding mechanism 52. Then, by transmitting a driving force of a driving motor (described later) disposed in the apparatus main body 100 on the one end side of the process cartridge 7 on the front side in FIG. According to the image forming operation, it is rotationally driven in the arrow X direction (counterclockwise) in FIG.

  The developing unit 4 includes a developing roller 40 that contacts the photosensitive drum 1 and rotates in the arrow Y direction (clockwise) in FIG. 2, a toner container 41 that contains toner, and a developing frame 45. The developing roller 40 is rotatably supported by the developing frame body 45 through bearing members 47 and 48. Further, on the circumference of the developing roller 40, a toner supply roller 43 that rotates in the direction of arrow Z (clockwise) in FIG. 2 in contact with the developing roller 40, and developing as developer layer thickness regulating means on the developing roller 40 Each of the blades 44 is disposed. Further, in the toner container 41, a toner transport mechanism (developer stirring transport blade) 42 for stirring the stored toner and transporting it to the toner supply roller 43 is provided.

The developing unit 4 is swung with respect to the photosensitive drum unit 50 by a pin 49a around a support shaft 49 provided on bearing members 47 and 48 attached to both ends of the developing unit 4, respectively. The suspension structure is supported freely. When the process cartridge 7 is a single unit (not attached to the apparatus main body 100), the developing unit 4 is always kept in contact with the pressure spring 53 so that the developing roller 40 is brought into contact with the photosensitive drum 1 by a rotational moment about the support shaft 49. It is energized. Further, when the developing roller 40 is separated from the photosensitive drum 1, the separation / contact switching means 8 (described later) of the apparatus main body 100 abuts and functionally connects to the toner container 41 of the developing unit 4. A rib 46 as a receiving portion is integrally provided.

[Drive configuration]
Next, the operation mechanism when the process cartridge 7 is mounted on the apparatus main body 100 will be described in detail with reference to FIGS. In FIG. 4, only the photosensitive drum 1 and the bearing 31 are shown for the process cartridge 7 in order to explain the configuration of the present invention in an easy-to-understand manner, but actually, the process cartridge 7 is as described above. Further, the charging device 2, the developing device 4, the cleaning device 6 and the like are integrally formed (FIG. 2).

  As described above, when the process cartridge 7 is a single unit, the developing roller 40 is always in contact with the photosensitive drum 1 as shown in FIG. As shown in FIG. 4, the process cartridge 7 has guide grooves 34 (34a, 34b, 34c, 34d, 34e, 34f, 34g, 34h) as mounting means provided on the left and right side plates 32 from the direction of the arrow (front side of the apparatus). ) Is inserted into the apparatus main body 100 by inserting a bearing 31 that supports the photosensitive drum 1. At this time, the transfer belt 11 opens the insertion portion of the process cartridge 7 in contrast to the front door of the apparatus main body 100, for example. As shown in FIG. 6, the position of the process cartridge 7 is determined by pressing the bearing 31 against the abutting surfaces 37 and 38 of the guide groove 34.

  The method for pressing the process cartridge 7 in the apparatus main body 100 is as follows.

  That is, as shown in FIG. 5, a shaft 39 is crimped to the left and right side plates 32, and a torsion coil spring 30 is supported on the shaft 39, and its end 30a is fitted into a hole 32a of the left and right side plates and fixed. ing. In a state where the process cartridge 7 is not present, the torsion coil spring 30 is restricted in the rotational direction by a bending raising 32 b from the left and right side plates 32.

  Then, when the process cartridge 7 is inserted, the torsion coil spring 30 rotates counterclockwise in FIG. 5 against the force, and is positioned as shown in FIG. The bearing 31 is pressed against the abutting surfaces 37 and 38 of the guide groove 34 with a force of about 1 kgf (≈9.8 N) in the direction. At this time, the back side of the apparatus main body 100 in the insertion direction of the process cartridge 7 is against the urging force of the developing unit 4 by the pressure spring 53 (FIG. 2) as shown in FIGS. A separating cam 80 for separating the developing roller 40 from the photosensitive drum 1 is disposed.

  Up / down operation of the bosses 46 (46a, 46b, 46c, 46d) provided in the developing units 4 (4a, 4b, 4c, 4d) of yellow, magenta, cyan, and black as developing roller separation / contact switching means Separation cams 80 (80a, 80b, 80c, 80d) are provided for carrying out the operation. In the present embodiment, the separation cam 80 is rotated by the driving means shown in FIG. 9, ie, a stepping motor 90 (described later), and the boss 46 of the developing unit 4 is moved up and down along with this rotation. A position in contact with the drum 1 and a position in which the developing roller 40 is separated from the photosensitive drum 1 are created.

  In this embodiment, the maximum radius of the separation cams 80 (80a, 80b, 80c, 80d) of all colors of yellow, magenta, cyan, and black is in contact with the boss 46, and all the developing rollers 40 and the photosensitive drums 1 are in contact with each other. In the standby state of separation (FIG. 1, FIG. 11 (1)), all the separation cams 80 (80a, 80b, 80c, 80d) of all colors of yellow, magenta, cyan, and black are in contact with the boss 46 and all The full-color state in which the developing roller 40 and the photosensitive drum 1 are in contact ((5) in FIGS. 7 and 11) and the separation cams 80 (80a, 80b, 80c) of three colors of yellow, magenta, and cyan have the maximum radius. When the black separation cam 80d is in contact with the boss 46 with the minimum radius in contact with the boss 46, only the black developing roller 40 is in contact with the photosensitive drum 1 (FIG. 8, FIG. 8). 11 of the three states (8)) can be selected.

Further, in the full color mode, the developing roller 40 contacts the photosensitive drum 1 in the order of yellow (1st) → magenta (2st) → cyan (3st) → black (4st) to perform the developing operation (FIG. 11). ( States ( 1) to (5)). After the completion of the developing operation, the developing roller 40 moves away from the photosensitive drum 1 in the order of yellow (1st) → magenta (2st) → cyan (3st) → black (4st) to complete printing (FIG. 11 ( 5) to (1)).

  That is, in the present embodiment, as shown in the cam diagram of FIG. 11, each color separation cam 80 (80a, 80b, 80c, 80d) has a profile, and each color separation cam 80 (80a). , 80b, 80c, and 80d), the above-described mode switching can be performed.

  In the present embodiment, the unit that drives the process cartridge 7 includes a series motor 71d that drives the photosensitive drum 1 and a developing roller 40 from a driving motor 70d that is a driving unit provided for each color as shown in FIG. Branches to the driving series 72d. Further, development clutches 74d and 75d as drive switching means are provided on the drive side of the development roller 40 so that the rotation and stop of the development roller 40 can be switched when the photosensitive drum 1 is rotating.

  As described above, in the present embodiment, the photosensitive member driving means for driving the photosensitive drums 1 and the developing driving means for driving the developing rollers 40 are a common motor for each process cartridge. . The driving force from the apparatus main body 100 side is generated by the photosensitive member drive transmission means and the development drive transmission means that are functionally connected to the drive unit on the apparatus main body 100 side when the process cartridge 7 is mounted on the apparatus main body 100, respectively. It is transmitted to the photosensitive drum 1 and the developing roller 40.

  FIG. 10 shows only black (4st). The other colors (yellow, magenta, cyan) have the same configuration and the operation is the same.

  With such a driving configuration, the driving of the photosensitive drums 1 of the respective colors can be controlled independently. Therefore, it is possible to take control to always reduce the color misregistration that is a problem in the in-line type full-color image forming apparatus. The driving of the developing roller 40 can be stopped while the drum 1 is driven. Naturally, it is much cheaper to provide the clutch as described above than to provide another motor for driving the developing roller 40.

  In the present embodiment, the developing clutches 74d and 75d are connected and disconnected by the rotation of the clutch gear 97d. The clutch gear 97d has a cam shape in the thrust direction, and the clutch cam 73d moves in the thrust direction as the clutch gear 97d rotates. As a result, the clutch 75d moves in the thrust direction, so that the clutch 74d is connected and disconnected.

  The clutch gear 97d is connected to the gear 96d, and the gear 96d rotates with the rotation of the gear 95d via the shaft. The gear 95d and the gear 96d have the same number of teeth. The gear 95d is connected to a separation gear 94d attached to the separation shaft 81d. The separation gear 94d and the clutch gear 97d have the same number of teeth, and the phase relationship between the rotation of the separation cam 80d attached to the separation shaft 81d and the clutch gear 97d is always the same. Thereby, the rotation of the separation cam 80 and the ON / OFF operation of the clutches 74 and 75 are synchronized.

  As shown in FIG. 11, as the separation cam 80 rotates from the development contact position to the development separation position, the development clutches 74 and 75 shift from the ON state to the OFF state. In the present embodiment, the developing roller 40 stops rotating after the developing roller 40 is separated from the photosensitive drum 1, and the developing roller 40 contacts the photosensitive drum 1 after the developing roller 40 rotates. ing. Further, in the state (1) (home position) of FIG. 11, the developing rollers 40 of all the colors stop rotating, and in the state (5) (full color mode), the developing rollers 40 of all the colors rotate, and the state (8). In the (mono color mode), only black is rotated, and the developing rollers 40 of other colors are set in a stopped state.

[Operation]
When the process cartridge 7 is mounted on the apparatus main body 100, as shown in FIG. 1, the separation cams 80 for all the colors of yellow, magenta, cyan, and black are in contact with the boss 46 with the maximum radius. Accordingly, the boss 46 provided in the developing unit 4 rides on the separation cam 80 in accordance with the insertion operation of the process cartridge 7, and the developing roller 40 is separated from the photosensitive drum 1 by a predetermined gap. This separated state is always maintained when the power is turned off and when development is not performed. Accordingly, even when the process cartridge 7 is mounted and not used for a long time, the developing roller 40 is always separated from the photosensitive drum 1, so that the developing roller 40 is kept in the photosensitive drum 1 for a long time. Permanent deformation of the roller layer generated by the contact can be reliably prevented.

  The image forming operation is as follows.

  In the case of full-color printing (FIG. 11, (1) → (2) → (3) → (4) → (5) → (6) → (7) → (8) → (1)) When the operation is started, all the drive motors 70 that drive all the process cartridges 7 and the drive motor (not shown) of the transfer belt 11 rotate. At this time, since all the developing clutches 74 and 75 are disconnected, the developing roller 40 does not rotate.

  Next, the stepping motor 90 rotates, and the separation cam 80 (80a, 80b, 80c, 80d) rotates accordingly. First, the first development clutch is turned on, and the first development roller 40a rotates. Immediately thereafter, the first developing roller 40a comes into contact with the photosensitive drum 1a. In this state, image formation at the first st is possible ((2) in FIG. 11).

  Next, when the stepping motor 90 further rotates, the second st developing clutch is turned on and the developing roller 40b rotates. Immediately thereafter, the second developing roller 40b contacts the photosensitive drum 1b. In this state, image formation at the second st is possible ((3) in FIG. 11).

  Furthermore, when the stepping motor 90 rotates, image formation can be similarly performed in the order of the third st → the fourth st ((4), (5) in FIG. 11).

  After the first image formation is completed, the stepping motor 90 further rotates, and the separation cam 80 (80a, 80b, 80c, 80d) rotates accordingly. First, the first developing roller 40a is separated from the photosensitive drum 1b, and then the first developing roller 40a stops rotating ((6) in FIG. 11).

  Similarly, after the second st image formation is completed, the second st developing roller 40b is separated from the photosensitive drum 1b with the rotation of the stepping motor 90, and then the second st developing roller 40b stops rotating (FIG. 11). (7)). Further, when the stepping motor 90 rotates, the developing roller 40 is separated from the photosensitive drum 1 in the order of 3rd → 4st, and the rotation of the developing roller 40 is stopped ((8), (1 in FIG. 11). )). Thereafter, the drive motor 70 of the process cartridge 7 and the drive roller of the transfer belt 11 are stopped, and the printing operation is finished.

Next, the case of mono-color printing (FIG. 11, (1) → ( 8 ) → (1)) will be described.

  When the image forming operation is started by the print signal, all the drive motors 70 that drive the process cartridge 7 and the drive motors of the transfer belt 11 are rotated. At this time, since all the developing clutches 74 and 75 are disengaged, the developing roller 40 does not rotate ((1) in FIG. 11).

  Next, the stepping motor 90 rotates in the opposite direction to that in full color printing, and accordingly, the separation cam 80 (80a, 80b, 80c, 80d) rotates 62 degrees in the opposite direction to that in the full color mode.

With the rotation of the separation cam 80, first, the fourth st (black) developing clutch is turned on, and the fourth st developing roller 40d rotates. Immediately thereafter, the fourth developing roller 40d comes into contact with the photosensitive drum 1d. At this time, the first to third st separating cams 80a, 80b, 80c are in contact with the boss 46 at the maximum radius, and the developing clutches 74, 75 of the first to third st developing roller 40 are not connected, and the developing is performed. The roller 40 is separated from the photosensitive drum 1 (( 8 ) in FIG. 11). Thereby, only the 4th st can form an image.

  After the image formation is completed, the stepping motor 90 is rotated in the same direction as in full color printing, the fourth developing roller 40d is separated from the photosensitive drum 1d, and then the rotation of the developing roller 40d is stopped. Thereafter, the drive motor 70 of the process cartridge 7 and the drive roller of the transfer belt 11 are stopped.

  As a result, at the time of monocolor printing, only the black developing roller is in contact with the photosensitive drum and can only rotate, so in the process of shifting to the monocolor state as in the conventional example (Japanese Patent Laid-Open No. 2001-318506). There is no contact / separation operation of the color developing roller, and the surface layer of the color photosensitive drum 1 and the deterioration of the color developing roller due to rubbing against the color developing roller 40 during monocolor printing are reduced. Can do.

  Next, switching from full color printing to mono color printing will be described (FIG. 11, (5) → (6) → (7) → (8)).

  Switching from full color to mono color is the same as when the first to third st developing rollers are separated from the photosensitive drum and stopped rotating during full color printing ((5) → (6) → ( 7) → (8)). In the present embodiment, the developing roller separation operation starts at the same time as the first st image formation is completed, and the development roller separates immediately after the end of the image formation for the second and third st. It will be in the state of (8) of FIG. That is, it is possible to switch from full color to mono color print without reducing the throughput. Accordingly, it is possible to reduce the surface layer of the color photosensitive drum 1 and the deterioration of the color developing roller due to the rubbing with the color developing roller 40 during monocolor printing.

Next, switching from mono-color printing to full-color printing will be described (FIG. 11, ( 8 ) → (1) → (2) → (3) → (4) → (5)).

Switching from mono-color to full-color is the same sequence as normal full-color printing through mono-color printing (( 8 ) in FIG. 11) through the home position ((1) in FIG. 11). In the present embodiment, in the movement from ( 8 ) → (1) → (2) in FIG. 11, the throughput is prevented by turning the stepping motor 90 quickly, and from a single color to a full color between normal papers. Can be switched.

  In the image forming process, before the electrostatic latent image is formed by the scanner unit 3, the pre-rotation and electrostatic latent image for applying a uniform charge to the peripheral surface of the photosensitive drum 1 are converted into a toner image. After the development, steps such as post-rotation for neutralizing the potential of the peripheral surface of the photosensitive drum 1 are performed, and the photosensitive drum 1 rotates during these steps.

  As described above, in the present invention, since the separation is released in accordance with the developing operation timing, the developing roller 40 is separated during the pre-rotation and the post-rotation. Therefore, even during the image forming operation, the surface layer of the photosensitive drum 1 due to sliding with the developing roller 40 during the pre-rotation and post-rotation can be reduced.

That is, according to this embodiment, the conventional problems in the contact development method described above:
(1) When the photosensitive drum 1 rotates at a timing other than during the developing operation such as pre-rotation and post-rotation, the surface layer of the photosensitive drum 1 is scraped by sliding with the developing roller 40, thereby reducing the life. turn into.
(2) If the process cartridges 7 of other colors not involved in the development are also operated, such as during mono-color development, the life of the photosensitive drum 1 is greatly reduced.
(3) When a bias is not applied during non-operation, pre-rotation, and post-rotation, the developer on the developing roller 40 adheres to the photosensitive drum 1, and the developer is wasted or the developer is paper It may cause dirt.
(4) The roller layer of the developing roller 40 is permanently deformed when it is not used for a long time while attached to the apparatus main body 100, and this may cause unevenness on the image during development.
Such as
In monocolor printing, only the black developing roller is in contact with the photosensitive drum and rotates, so the color in the process of shifting to the monocolor state as in the conventional example (Japanese Patent Laid-Open No. 2001-318506). There is no abutment / separation operation of the developing roller, and the surface layer of the color photosensitive drum 1 and the deterioration of the color developing roller due to the rubbing against the color developing roller 40 during monocolor printing can be reduced. .

  In addition, since the developing roller is brought into contact with and separated from the photosensitive drum by the rotational movement of the cam, when mono-color and full-color printing are mixed, mono-color printing → full-color printing and full-color printing → mono-color printing. Switching can be performed efficiently and throughput is not reduced.

  Therefore, without deteriorating the throughput which is the object of the present invention, the deterioration of the surface layer of the photoreceptor, the deformation of the developing means, the waste of the developer can be reduced, and the paper stain can be avoided. An image forming apparatus can be provided.

  In addition, since the structure is simple and the position of the photosensitive drum 1 and the travel path of the transfer belt 11 that are important for the image formation accuracy are not moved, the image formation accuracy and the transfer belt 11 or transfer material S conveyance accuracy are not affected. Will not be damaged.

<Embodiment 2>
In each of the first exemplary embodiments, the image forming apparatus 100 is an image forming apparatus that forms a recorded image by sequentially transferring toner images from the plurality of photosensitive drums 1 to the transfer material S conveyed by the transfer belt 11. Although described, the present invention is not limited to this.

For example, a plurality of image forming units each including a plurality of photosensitive drums and a charging unit, a developing unit, a cleaning unit, and the like as process units that act on the photosensitive drums are rotated around each image forming unit. The toner images are sequentially superimposed and transferred onto an intermediate transfer belt as an intermediate transfer body that moves, and then the toner images are secondarily transferred and recorded collectively on a transfer material conveyed by a separately provided transfer material conveyance system. The present invention can be equally applied to a so-called intermediate transfer type image forming apparatus known to those skilled in the art, such as an image forming apparatus for obtaining an image, and the same effects as described above can be obtained.
The intermediate transfer member constitutes an image carrier that conveys the toner image transferred from each photosensitive drum.

  In such an image forming apparatus, the drive control of the photosensitive drum, the developing roller, and the intermediate transfer belt and the separation / contact control of the developing roller with respect to the photosensitive drum are performed in the first embodiment except that the transfer belt is an intermediate transfer belt. You can do the same. Here, the entire description of the first embodiment is incorporated by replacing the description of the transfer belt with the intermediate transfer belt.

FIG. 2 is a cross-sectional view of an embodiment of the image forming apparatus according to the present invention, and shows a state where the developing roller is separated from the photosensitive drum in all the process cartridges mounted on the apparatus main body. FIG. 2 is a cross-sectional view of a process cartridge mounted on the image forming apparatus in FIG. 1. FIG. 3 is an assembled perspective view of the process cartridge of FIG. 2. FIG. 5 is a perspective view showing the vicinity of the inner plate of the apparatus main body for explaining an embodiment of a method for mounting the process cartridge to the image forming apparatus according to the present invention. It is a fragmentary sectional view which shows the positioning part to the image forming apparatus of the process cartridge according to this invention. It is a fragmentary sectional view which shows the positioning part to the image forming apparatus of the process cartridge according to this invention. FIG. 2 is a view similar to FIG. 1 and showing a state in which the separation between the developing roller and the photosensitive drum is released in all process cartridges. FIG. 2 is a view similar to FIG. 1, illustrating a state in which the separation between the developing roller and the photosensitive drum is released in the black process cartridge and the developing roller is separated from the photosensitive drum in the other color process cartridge. It is a perspective view which shows the operation | movement switching mechanism according to this invention. It is a perspective view of the drive part of the process cartridge according to the present invention. It is a cam diagram (relationship between a separation cam and a developing clutch) according to the present invention.

Explanation of symbols

1 (1a, 1b, 1c, 1d) Photosensitive drum 2 (2a, 2b, 2c, 2d) Charging device 3 (3a, 3b, 3c, 3d) Scanner unit 4 (4a, 4b, 4c, 4d) Developing device, Development unit 5 Electrostatic transfer means 6 (6a, 6b, 6c, 6d) Cleaning device 7 (7a, 7b, 7c, 7d) Process cartridge 8 Separation / detachment switching means 8y Rack separation / contact switching means 8z Color separation / contact switching means 11 Electrostatic transfer belt (transfer belt, image carrier)
20 Fixing portion 40 (40a, 40b, 40c, 40d) Developing roller 46 (46a, 46b, 46c, 46d) Rib (receiving portion)
50 Photosensitive drum unit 53 Pressure spring 70 (70a, 70b, 70c, 70d) Process cartridge drive motor 71 (71a, 71b, 71c, 71d) Photosensitive drum drive series 72 (72a, 72b, 72c, 72d) Development roller drive series 80 (80a, 80b, 80c, 80d) Separating plate 90 Stepping motor 91 Switching member 92 (92a, 92b, 92c, 92d) Clutch (drive switching means)
93 cams

Claims (2)

An image carrier that carries an electrostatic latent image and a developing roller, and are movable between a contact position where the image carrier and the development roller are in contact with each other and a separation position where the image carrier is in contact with the development roller. Each having a developing unit that develops an electrostatic latent image with the developing roller , and includes a plurality of image forming units that use developers of different colors including black,
A first state in which the developing units of the plurality of image forming units are in the separated position; a second state in which the developing unit of the plurality of image forming units is in the contact position; and a plurality of image forming units. Of these, only the black image forming portion can be switched to the third state in which the developing means is in the contact position,
An image forming apparatus that performs full color image formation in the second state and performs black image formation in the third state,
One motor that can rotate in the first and second directions;
A plurality of cams provided corresponding to the developing means of each of the plurality of image forming units and moving each of the developing means to the contact position and the separation position; First switching to two states is performed in conjunction with rotation of the one motor in the first direction, and second switching from the first state to the third state is performed in the second direction of the one motor. With multiple cams linked to the rotation to
Have
In each of the plurality of cams, the rotation angle required for the second switching is required to move the developing unit of the black image forming unit from the separation position to the contact position in the first switching. An image forming apparatus smaller than the rotation angle . 2. The developing unit of a black image forming unit among the plurality of image forming units first moves to the contact position when the one motor is rotated in the second direction from the first state. Image forming apparatus.