JP4819977B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile using an electrophotographic method, and more particularly to driving an image carrier and a driven member acting on the image carrier.

  2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic process, an image forming unit provided with an electrophotographic photosensitive member (hereinafter referred to as a “photosensitive member”) each serving as an image carrier and a process unit that acts on the photosensitive member. There is a color image forming apparatus that employs a so-called in-line method in which a plurality of images are juxtaposed.

  In an in-line image forming apparatus, an image on a photoconductor is sequentially transferred to an intermediate transfer member or a transfer material on a transfer material carrier that is arranged to face a plurality of image forming units. In general, four image forming units for forming images of yellow, magenta, cyan, and black are provided as a plurality of image forming units, and a drum type is used as the photosensitive member ( Quadruple drum system).

  In such an in-line image forming apparatus, the photosensitive member in each image forming unit and the process means such as the developing means are integrally formed into a cartridge, which is attached to and detached from the image forming apparatus main body. There is something that made it possible. According to such a process cartridge system, for example, when the developer runs out, an image can be formed again by replacing the process cartridge by the user without relying on the service person. In addition, since other consumables such as a photoconductor can be replaced at the same time, the maintainability is remarkably improved.

  For example, a description will be given in connection with the four-drum type image forming apparatus.

  Conventionally, as shown in FIG. 18, a “four motor system” in which four photoreceptors 1 a, 1 b, 1 c and 1 d are driven by one motor 101 a, 101 b, 101 c and 101 d is generally employed. (See Patent Document 1).

  In addition, as shown in FIG. 19, there may be employed a “one motor system” in which one motor 101 drives all four photosensitive members 1a, 1b, 1c, and 1d (see Patent Document 2).

  When the “1-motor system” is adopted, an electronic clutch or a mechanical clutch mechanism is used to switch between the full-color mode and the mono-color mode. The full color mode is, for example, a multicolor mode that drives all of the four photoconductors 1a, 1b, 1c, and 1d, and the monocolor mode is a single color mode that drives, for example, only the black photoconductor 1d. The “1-motor system” is advantageous in terms of cost compared to the “4-motor system”.

  On the other hand, Patent Document 3 describes that the first motor drives the photosensitive drums for yellow, magenta, and cyan, and the second motor drives the photosensitive drum for black.

JP 2003-208024 A JP 2004-205688 A JP 2003-43781 A

  However, the “4-motor system” tends to be expensive due to the large number of motors. In addition, the “4-motor system” may occupy a large space or increase the weight from the viewpoint of configuration, and may be an obstacle factor for providing a compact and low-cost image forming apparatus.

  Further, in the “1-motor system”, the photosensitive member rotates unevenly due to the engagement accuracy of the clutch mechanism, and as a result, color misregistration and banding (periodic image unevenness due to the rotational variation of the photosensitive member) may appear remarkably. There is.

  In the configuration described in Patent Document 3, the first motor also drives the developing roller corresponding to the photosensitive drum driven by the first motor, and the second motor is driven by the second motor. The developing roller corresponding to the photosensitive drum to be driven is also driven. In other words, although the first motor and the second motor are used, no consideration has been given to the driving load related to the photosensitive drum and the developing roller.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of preventing image displacement on an image carrier while reducing costs and leveling the driving loads of a plurality of driving sources.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a plurality of image carriers on which toner images are formed, a plurality of driven members that act on each of the plurality of image carriers, and a plurality of first ones among the plurality of image carriers. First driving means for driving an image carrier, and second driving means for driving a second image carrier different from the plurality of first image carriers among the plurality of image carriers. An image forming apparatus in which the number of the first image carriers driven by one driving means is larger than the number of the second image carriers driven by the second driving means, wherein the second driving means is the second driving means. An image forming apparatus that drives a driven body that acts on an image carrier and at least one driven body that acts on the plurality of first image carriers .

  According to the present invention, it is possible to prevent image shift on the image carrier while reducing costs, and to equalize the driving loads of the plurality of driving sources.

1 is a diagram illustrating an image forming apparatus that is an embodiment of the present invention. It is sectional drawing of a process cartridge. FIG. 6 is an explanatory diagram when a process cartridge is mounted on the apparatus main body. FIG. 6 is an explanatory diagram when positioning the process cartridge to the apparatus main body. It is a figure which shows the positioning part to the apparatus main body of a process cartridge. FIG. 2 is a diagram illustrating a state in which a developing roller is separated from a photosensitive drum in the image forming apparatus of FIG. 1. It is a figure which shows a separation cam drive device. It is a figure for demonstrating a motion of a separation cam. FIG. 6 is a diagram illustrating a contact state between a transfer belt and a photosensitive drum in a multicolor mode. FIG. 4 is a diagram illustrating a contact state and a separation state of a transfer belt and a photosensitive drum in a single color mode. It is a figure which shows the drive system of a photosensitive drum and a developing roller. It is a figure for demonstrating the reduction ratio of a drum drive train, and the surrounding speed fluctuation | variation of a front | former stage gear. It is a figure for demonstrating the relationship between the drum drive gear and exposure stage gear in an exposure point and a transfer point. It is a figure for demonstrating the phase alignment of the drum drive gear adjacent to the distance between the centers of a photosensitive drum. FIG. 6 is a diagram for explaining image color misregistration between adjacent image forming units. It is a figure which shows a phase alignment apparatus. It is a figure which shows the drive system of the photosensitive drum of another Example of this invention, and a developing roller. It is a conceptual diagram which shows the process cartridge drive structure of 4 motor systems. It is a conceptual diagram which shows the process cartridge drive structure of 1 motor system. It is a conceptual diagram which shows the process cartridge drive structure of a 2 motor system. It is a figure which shows the other image forming apparatus which can apply this invention.

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

Example 1
[overall structure]
First, the overall configuration of the image forming apparatus will be described with reference to FIG. FIG. 1 is a longitudinal sectional view showing the overall configuration of the image forming apparatus A of this embodiment. The image forming apparatus A of this embodiment is a full-color laser beam printer capable of forming a full-color image on a transfer material (for example, recording paper, OHP sheet, etc.) as a recording material by an electrophotographic method according to an image information signal. It is. The image information signal is transmitted from an external device such as a personal computer, an image reading device, or a digital camera that can communicate with the device main body B by wire or wirelessly. However, the present invention is not limited to this, and can be embodied in any form such as a copying machine or a facsimile.

  The image forming apparatus A includes four image forming units Pa, Pb, Pc, and Pd as image forming units. In this embodiment, the configurations and operations of the image forming units Pa, Pb, Pc, and Pd are substantially the same except that the color of the toner used is different.

  The image forming portions Pa, Pb, Pc, and Pd include four drum-shaped photosensitive members arranged in a substantially vertical direction as image bearing members, that is, photosensitive drums 1a, 1b, 1c, and 1d. As will be described in detail later, the photosensitive drum is rotated counterclockwise in FIG. 1 by the driving means shown in FIG.

  Around the photosensitive drums 1a, 1b, 1c, and 1d, there are charging members 2a, 2b, 2c, and 2d, which are charging means for uniformly charging the surface of the photosensitive drum along the rotation direction, and lasers based on image information. There is a scanner unit 3 which is an exposure unit that irradiates a beam and forms an electrostatic latent image on a photosensitive drum. Further, on the downstream side, developing means (developing units) 4 a, 4 b, 4 c, and 4 d, which transfer toner images on the photosensitive drums onto the transfer material S, are formed by attaching developer toner to the electrostatic latent image. There is an electrostatic transfer means 5 to be used. Further, downstream thereof, cleaning means (cleaning units) 6a, 6b, 6c, and 6d for removing residual toner remaining on the surface of the photosensitive drum after the transfer process are disposed.

  In this embodiment, the photosensitive drums 1a, 1b, 1c, 1d, charging members 2a, 2b, 2c, 2d, scanner unit 3, developing means 4a, 4b, 4c, 4d, cleaning means 6a, 6b, 6c, 6d, etc. Images of different colors (yellow, magenta, cyan, black) are formed by the four image forming portions Pa, Pb, Pc, Pd provided. In the following, it is assumed that yellow is Y, magenta is M, cyan is C, and black is Bk.

  Here, in this embodiment, the photosensitive drum, the charging unit, the developing unit, and the cleaning unit are integrally formed into a cartridge to form process cartridges 7a, 7b, 7c, and 7d. The process cartridges 7a, 7b, 7c, and 7d are detachably attached to the apparatus main body B through mounting means such as guide grooves 34A1, 34A2, 34A3, 34A4, 34B1, 34B2, 34B3, and 34B4 (see FIG. 3) described later. It is configured. The process cartridge is not limited to the embodiment, and the photosensitive drum and at least one of charging means, developing means, and cleaning means as process means acting on the photosensitive drum are integrally formed as a cartridge, and the process cartridge is And can be removed.

  Hereinafter, each element of the image forming apparatus A will be described in detail with reference to FIG. FIG. 2 shows a longitudinal section of the process cartridge.

  Here, in the following description, the front side of the image forming apparatus A refers to the side where the process cartridge is inserted into the apparatus main body B, that is, the right side in FIG. The left and right sides of the image forming apparatus A are viewed from the front side.

  The photosensitive drums 1a, 1b, 1c, and 1d are OPC photosensitive members in which an organic photoconductive layer is applied to the outer peripheral surface of an aluminum cylinder having a diameter of 25 mm, for example. Both ends of the photosensitive drums 1a, 1b, 1c, and 1d are rotatably supported by support members. The photosensitive drums 1a, 1b, 1c, and 1d, as will be described in detail later, are transmitted to one end by a driving force from a driving motor (see FIG. 11), so that the direction of the arrow X in FIG. It is rotated (counterclockwise).

  As the charging means 2a, 2b, 2c, and 2d, a contact charging type that includes a charging member that contacts the photosensitive drums 1a, 1b, 1c, and 1d can be used. In this embodiment, conductive rollers (charging rollers) 2a, 2b, 2c, and 2d formed in a roller shape are used as charging members. The charging rollers 2a, 2b, 2c, and 2d are brought into contact with the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, and a charging bias voltage is applied to the charging rollers 2a, 2b, 2c, and 2d, thereby the photosensitive drum 1a. The surfaces 1b, 1c and 1d are uniformly charged.

  The scanner unit 3 is arranged in a substantially horizontal direction of the photosensitive drums 1a, 1b, 1c, and 1d. In this embodiment, image light corresponding to an image signal is emitted from one laser diode (not shown) to one photosensitive drum. This image light is applied to the polygon mirror 9 that is rotated at high speed by a scanner motor (not shown). For example, one polygon mirror is provided for every two photosensitive drums. In the present embodiment, two polygon mirrors, a first polygon mirror 9a and a second polygon mirror 9b, are provided. The first polygon mirror 9a is for scanning the light applied to the image forming portions Pa and Pb that form images of Y and M colors. The second polygon mirror 9b scans the light applied to the image forming portions Pc and Pd that form images of C and Bk colors. The image light reflected by the polygon mirror 9 passes through the imaging lenses 10a, 10b, 10c, and 10d provided for the photosensitive drums 1a, 1b, 1c, and 1d, and the surface of the charged photosensitive drum. Are selectively exposed.

  Thus, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum. As shown in FIG. 3, the scanner unit 3 is formed shorter than the pitch between the side plates 32 (the left side plate 32A and the right side plate 32B) in the longitudinal direction of the photosensitive drum (in the rotational axis direction of the photosensitive drum). The scanner unit 3 is attached to an intermediate frame 35 that is positioned between the left and right side plates 32A and 32B.

  Each of the developing means 4a, 4b, 4c, and 4d is a developer container that stores a developer of each color of Y, M, C, and Bk (in this embodiment, a negatively charged nonmagnetic one-component developer (toner)). As a toner container 41. The toner container 41 includes developing rollers 40a, 40b, 40c, and 40d as developer carriers (developing members), a developer transport mechanism 42, a toner supply roller 43 as a developer supply member, and development as a developer regulating member. A blade 44 or the like is attached. The toner in the toner container 41 is sent to the toner supply roller 43 by the transport mechanism 42. The toner is applied to the outer periphery of the developing rollers 40a, 40b, 40c, and 40d by the developing blade 44 that is in pressure contact with the outer periphery of the toner supply roller 43 and the developing rollers 40a, 40b, 40c, and 40d, and is given an electric charge. The toner supply roller 43 rotates in the arrow Z direction (clockwise) in FIG. Further, the developing roller rotates in the arrow Y direction (clockwise) in FIG. Then, by applying a developing bias to the developing rollers 40a, 40b, 40c, and 40d facing the photosensitive drums 1a, 1b, 1c, and 1d on which the electrostatic latent images are formed, the photosensitive drums 1a and 1b are set according to the latent images. Toner is supplied onto 1c and 1d.

  In this embodiment, there is provided a transfer belt (electrostatic transfer belt) 11 as a recording material carrying member that circulates and moves so as to face and contact all the photosensitive drums 1a, 1b, 1c, and 1d. The transfer belt 11 constitutes transfer means for transferring the toner image on the photosensitive drum to a recording material. The transfer belt 11 electrostatically attracts and carries the transfer material S as a transfer target and conveys it. The transfer belt 11 is a film-like member having a volume resistivity of 1011 to 1014 Ω · cm and a thickness of about 110 μm. The transfer belt 11 is supported by a roller with three axes in the vertical direction. The transfer belt 11 electrostatically attracts the transfer material S to the left outer peripheral surface in FIG. 1, and circulates and moves so that the transfer material S comes into contact with the photosensitive drums 1a, 1b, 1c, and 1d. Thus, the transfer material S is conveyed by the transfer belt 11 to a transfer portion (transfer position) N facing the photosensitive drums 1a, 1b, 1c, and 1d.

  Also, transfer rollers 12a, 12b, 12c, and 12d as transfer members are juxtaposed so as to contact the inside of the transfer belt 11 at positions facing the four photosensitive drums 1a, 1b, 1c, and 1d. Yes. A positive charge is applied to the transfer material S from the transfer rollers 12 a, 12 b, 12 c, and 12 d via the transfer belt 11. Due to the electric field formed by this electric charge, the negative toner images on the photosensitive drums 1a, 1b, 1c and 1d are transferred to the transfer material S in contact with the photosensitive drums 1a, 1b, 1c and 1d.

  More specifically, in this embodiment, the transfer belt 11 is an endless belt having a circumferential length of about 560 mm and a thickness of 110 μm, and is stretched around three rollers: a driving roller 13, a driven roller 14, and a tension roller 15. . The transfer belt 11 rotates (rotates) in the direction of the arrow (clockwise) in FIG. 1 when the driving force is transmitted to the driving roller 13 by the driving source. Thus, the toner image is transferred to the transfer material S while the transfer belt 11 circulates and the transfer material S is conveyed from the driven roller 14 side to the drive roller 13 side.

  In addition, the transfer material S may not be fed due to an unexpected situation, and toner may remain on the transfer belt 11. At this time, in this embodiment, a predetermined peripheral speed difference is provided between the photosensitive drum and the transfer belt 11 to rotate the transfer belt 11 quickly. As a result, the toner on the transfer belt 11 can be efficiently transferred to the photosensitive drum and collected by the cleaning means in the process cartridge, and the transfer belt 11 can be cleaned.

  The feeding unit 16 supplies and conveys the transfer material S to the image forming unit, and a plurality of transfer materials S are stored in the feeding cassette 17. At the time of image formation, the feeding roller 18 (D-cut roller) and the registration roller pair 19 are rotationally driven according to the image forming operation. The transfer material S in the feed cassette 17 is separated and fed one by one by the feed roller 18, and the leading end of the transfer material S hits the registration roller pair 19 to form a loop. Thereafter, the transfer material S is fed to the transfer belt 11 by the registration roller pair 19 so as to be synchronized with a predetermined image writing position. Further, an electrostatic adsorption roller 22 for electrostatically adsorbing the transfer material S to the transfer belt 11 is in contact with the transfer belt 11 at a position facing the driven roller 14.

  The fixing unit 20 as a fixing unit fixes the unfixed toner image transferred to the transfer material S to the transfer material S. The fixing unit 20 includes a rotating fixing roller pair (a heating roller 21a and a pressure roller 21b that is in pressure contact with the rotating roller pair), and applies heat and pressure to the transfer material S at the pressure contact portion. That is, the transfer material S onto which the toner image is transferred from the photosensitive drum is conveyed by the fixing roller pair 21a and 21b when passing through the fixing unit 20. At this time, the transfer material S is given heat and pressure by the pair of fixing rollers 21a and 21b. Accordingly, for example, in a later-described multicolor mode, toner images of a plurality of colors are fixed on the surface of the transfer material S.

  Next, the image forming operation will be described by taking full color image formation as an example. The process cartridges 7a, 7b, 7c, and 7d are sequentially driven in accordance with the image formation timing (image forming operation to be recorded on the transfer material S), and the photosensitive drums 1a, 1b, 1c, and 1d are driven according to the drive. 1 is rotated in the direction of the arrow (counterclockwise) in FIG. The scanner unit 3 is driven corresponding to the operation of each process cartridge 7a, 7b, 7c, 7d. That is, first, the charging rollers 2a, 2b, 2c, and 2d apply a uniform charge to the peripheral surfaces of the photosensitive drums 1a, 1b, 1c, and 1d, and then the scanner unit 3 receives the photosensitive drums 1a, 1b, 1c, and 1d. The exposure according to the image signal is performed on the peripheral surface.

  Thereby, electrostatic latent images are formed on the peripheral surfaces of the photosensitive drums 1a, 1b, 1c, and 1d. The developing rollers 40a, 40b, 40c, and 40d in the developing units 4a, 4b, 4c, and 4d transfer the toner to the low potential portion of the electrostatic latent image. As a result, toner images are formed (developed) on the peripheral surfaces of the photosensitive drums 1a, 1b, 1c, and 1d. Next, the leading end of the toner image formed on the peripheral surface of the photosensitive drum 1 a on the most upstream side in the conveyance direction of the transfer material S is rotationally conveyed to a point substantially facing the transfer belt 11. At that timing, the registration roller pair 19 feeds the transfer material S to the transfer belt 11 so that the recording start position of the transfer material S coincides with the opposite point.

  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. In addition, when a voltage is applied 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. It is electrostatically attracted to the outer periphery of the transfer belt 11. As a result, the transfer material S is stably adsorbed to the transfer belt 11 and conveyed to the transfer portion N of the most downstream photosensitive drum 1d. In the process of transferring the transfer material S in this way, the photosensitive drums 1a, 1b, 1b, 1b, and 2d are generated by the electric field formed between the photosensitive drums 1a, 1b, 1c, 1d and the transfer rollers 12a, 12b, 12c, 12d. The toner images on 1c and 1d are sequentially transferred onto the transfer material S. The transfer material S onto which the four color toner images have been transferred is separated (curvature separation) from the transfer belt 11 by the curvature of the belt driving roller 13 and conveyed to the fixing unit 20. After the toner image is thermally fixed by the fixing unit 20, the transfer material S is discharged by the discharge roller pair 23 to the discharge unit 24 outside the apparatus main body with the image surface facing down.

[Process cartridge]
Next, the process cartridge will be described in more detail. FIG. 2 shows a main cross section of the process cartridge 7a for storing toner. The process cartridges 7a, 7b, 7c, and 7d of Y, M, C, and Bk have the same configuration. Here, the process cartridge 7a will be described, and the description of the other process cartridges 7b, 7c, and 7d will be omitted. .

  The process cartridge 7a is divided into a photosensitive unit 50 having a photosensitive drum 1a, a charging roller 2a and a cleaning unit 6a, and a developing unit 4a having a developing roller 40a for developing an electrostatic latent image on the photosensitive drum 1a. ing. In the photosensitive unit 50, the photosensitive drum 1a is rotatably attached to a cleaning frame 51 that forms a housing of the photosensitive unit 50 via bearings (left bearing 31A, right bearing 31B) (see FIG. 3). ing. On the periphery of the photosensitive drum 1a, a charging roller 2a for uniformly charging the surface of the photosensitive drum 1a, and a cleaning member for removing toner (residual toner) remaining on the photosensitive drum 1a after the transfer process. A blade 60 is provided. Further, the residual toner removed from the surface of the photosensitive drum 1 a by the cleaning blade 60 is sequentially sent to the waste toner chamber 53 by the waste toner transport mechanism 52. The waste toner chamber 53 is provided behind the cleaning frame 51. The photosensitive drum 1a is transmitted with a driving force from a driving source (see FIG. 11) in the apparatus main body B on one end side (back side of the paper surface in FIG. 2) in the longitudinal direction (rotational axis direction of the photosensitive drum 1a). . As a result, the photosensitive drum 1a is driven to rotate in the direction of the arrow X (counterclockwise) in FIG. 2 according to the image forming operation.

  The developing unit 4a includes a developing roller 40a that contacts the circumference of the photosensitive drum 1a during image formation and rotates in the arrow Y direction (clockwise) in FIG. 2, and a toner container 41 that contains toner. Further, the developing unit 4a has a toner supply roller 43 that contacts the circumference of the developing roller 40a and rotates in the direction of arrow Z (clockwise) in FIG. 2, and a developing blade 44 that contacts the circumference of the developing roller 40a. Further, the developing unit 4 a includes a transport mechanism 42 that stirs the toner stored in the toner container 41 and transports the toner to the toner supply roller 43, and a developing frame 45 that forms a housing of the developing unit 4 a. The developing roller 40a is rotatably supported by the developing frame body 45 via a bearing member. The developing frame 45 functions as a holding unit for the developing roller 40a. In this embodiment, the rotation axes of the photosensitive drum 1a, the developing roller 40a, and the toner supply roller 43 are substantially parallel.

  The developing unit 4a is configured so that the entire developing unit 4a is centered on support shafts 49 respectively provided on bearing members 47 attached to both ends in the longitudinal direction of the developing roller 40a (the rotation axis direction of the developing roller 40a). The photoconductor unit 50 is supported so as to be swingable. As described above, the developing unit 4 a is suspended from the photosensitive unit 50.

  When the process cartridge 7a is a single unit, the developing unit 4a is always urged by a pressure spring 54, which is an urging unit, so that the developing roller 40a contacts the photosensitive drum 1a by a rotational moment about the support shaft 49. Has been. The state where the process cartridge 7a is a single state is a state where the process cartridge 7a is not attached to the apparatus main body B. Further, the toner container 41 of the developing unit 4a is integrally provided with a rib 46a which is a contact portion for contacting a separating means (described later) of the apparatus main body B when the developing roller 40a is separated from the photosensitive drum 1a. It has been.

[Removal of process cartridge]
Next, with reference to FIGS. 3 to 5, the attaching / detaching operation of the process cartridge 7 d will be described. In FIG. 3, for easy understanding of the configuration, the process cartridge 7d, in which the photosensitive drum 1d, the charging roller 2d, the developing unit 4d, and the cleaning unit 6d are integrally formed, includes only the photosensitive drum 1d and the bearings 31A and 31B. It is simplified and shown.

  As described above, when the process cartridge 7d is a single unit, the developing roller is always in contact with the photosensitive drum as shown in FIG. As shown in FIG. 3, the process cartridge 7d is mounted along guide grooves (left guide groove 34A4, right guide groove 34B4) as mounting means provided in the apparatus main body B. The left guide grooves 34A1, 34A2, 34A3 and the right guide grooves 34B1, 34B2, 34B3 are guide grooves for the process cartridges 7a, 7b, 7c, respectively. In other words, the process cartridge 7d is mounted on the apparatus main body B by inserting the bearings (the left bearing 31A and the right bearing 31B) that support the photosensitive drum 1d along the guide grooves 34A4 and 34B4 from the arrow direction in the drawing. . At this time, for example, the transfer belt 11 is retracted together with the door C (see FIG. 1) on the front side of the apparatus main body B to open the insertion portion of the process cartridge. As shown in FIG. 5, the position of the process cartridge 7d is determined by pressing the bearing 31A against the abutting surfaces 37 and 38 as positioning means for the guide groove 34A4.

  The process cartridge pressing method in the apparatus main body B is as follows. As shown in FIGS. 4A and 4B, shafts 39 are caulked on the left and right side plates 32A and 32B, respectively. A pressing lever 70 as a pressing member is rotatably attached to the shaft 39. Further, one end of a tension spring (torsion coil spring) 30 as a pressing force generating means is fixed to the pressing lever 70. The other end of the tension spring 30 is fixed to the fixing portion 72. The fixing portion 72 is provided on the rod 71. The rod 71 can be interlocked with the opening and closing of the door C of the apparatus main body B, and is indicated by solid and broken arrows in the drawing along guide shapes (for example, bending up) 33 provided on the left and right side plates 32A and 32B, respectively. It can move in the direction shown.

  When the door C is opened, as shown in FIG. 4B, the rod 71 moves in the direction indicated by the broken line arrow in the drawing, and the pressing lever 70 is moved by the action portion 73 provided on the rod 71 in the drawing. Move in the direction indicated by the arrow (counterclockwise). As a result, the insertion portion of the process cartridge 7d is opened, and the process cartridge 7d can be inserted and removed. At this time, the tension spring 30 is close to the natural length of the spring, and the pressing force hardly acts.

  When the process cartridge 7d is inserted and the door C is further closed, as shown in FIG. 4A, the rod 71 moves in the direction indicated by the solid arrow in the figure, and the pressing lever 70 is changed to the solid arrow in the figure. Rotate in the direction shown (clockwise). As a result, when the tension spring 30 is pulled, the bearing 31A is pressed against the abutting portions 37 and 38 of the side plate 32A with a force of about 10 N in the direction of the solid arrow in the figure.

  As shown in FIGS. 1 and 6, on the back side in the insertion direction of the process cartridges 7a, 7b, 7c, 7d of the apparatus main body B, the pressure springs 54 of the developing units 4a, 4b, 4c, 4d (see FIG. 2) Separating means is provided for swinging the developing frame 45 against the urging force to separate the developing rollers 40a, 40b, 40c, and 40d from the photosensitive drums 1a, 1b, 1c, and 1d. The separation means are separation cams 80a, 80b, 80c, and 80d such as plate cams. The separation cams 80a, 80b, 80c, and 80d push up the ribs 46a, 46b, 46c, and 46d provided in the developing units 4a, 4b, 4c, and 4d for the respective colors Y, M, C, and Bk. The separation cams 80a, 80b, 80c, and 80d are provided corresponding to the process cartridges 7a, 7b, 7c, and 7d, respectively.

  The contact and separation of the developing rollers 40a, 40b, 40c, and 40d with respect to the photosensitive drums 1a, 1b, 1c, and 1d by the separation cams 80a, 80b, 80c, and 80d are performed as follows. As shown in FIG. 7, in this embodiment, the separation cam driving device 90 as the driving means of the separation means has a stepping motor 91 as the separation means driving source. Although not limited to this, in this embodiment, the driving force of one stepping motor 91 is branched by the drive transmission gear train 92 included in the separating cam driving device 90, and all the separating cams 80a and 80b are separated. , 80c, 80d. Thereby, in the present embodiment, the separation cams 80a, 80b, 80c, 80d can rotate in the same direction with the same phase.

  The separation cams 80a, 80b, 80c, and 80d are rotated by the stepping motor 91. With this rotation, the separation cams 80a, 80b, 80c, and 80d are connected to the process cartridges 7a, 7b, 7c, and the ribs 46a, 46b, 46c, and 46d, respectively. 7d developing units 4a, 4b, 4c, 4d are swung. As a result, the developing rollers 40a, 40b, 40c, and 40d are brought into contact with and separated from the photosensitive drums 1a, 1b, 1c, and 1d. That is, the positions of the developing rollers 40a, 40b, 40c, and 40d with respect to the photosensitive drums 1a, 1b, 1c, and 1d are in contact with the photosensitive drums 1a, 1b, 1c, and 1d, and the photosensitive drums 1a, 1b, 1c, and d. It switches between the separated positions separated from 1d.

In this example,
(I) The separation cams 80a, 80b, 80c, and 80d are in contact with the ribs 46a, 46b, 46c, and 46d at the maximum radius in the image forming portions Pa, Pb, Pc, and Pd of all colors Y, M, C, and Bk. A standby state (standby mode) in which all the developing rollers 40a, 40b, 40c, and 40d are separated from the photosensitive drums 1a, 1b, 1c, and 1d,
(Ii) The separation cams 80a, 80b, 80c, and 80d take the minimum radial position in the image forming portions Pa, Pb, Pc, and Pd of all colors Y, M, C, and Bk, and the ribs 46a, 46b, 46c, and 46d A full color state (multicolor mode being the first mode) in which all the developing rollers 40a, 40b, 40c, 40d are in contact with the photosensitive drums 1a, 1b, 1c, 1d, and
(Iii) The developing rollers 40a, 40b, and 40c are separated from the photosensitive drums 1a, 1b, and 1c in the Y, M, and C image forming portions Pa, Pb, and Pc, and the developing is performed only in the Bk image forming portion Pd. A monocolor state in which the roller 40d is in contact with the photosensitive drum 1d (a monochromatic mode which is the second mode),
The three modes can be selected.

  In the multi-color mode, the developing rollers 40a, 40b, 40c, and 40d are sequentially arranged in this order at predetermined time intervals in the Y, M, C, and Bk image forming portions Pa, Pb, Pc, and Pd. 1a, 1b, 1c, and 1d are contacted to form an image. Similarly, when the developing rollers 40a, 40b, 40c, and 40d are separated from the photosensitive drums 1a, 1b, 1c, and 1d, the developing rollers 40a, 40b, 40c, and 40d are sequentially arranged in the above order at predetermined time intervals. Are separated from the photosensitive drums 1a, 1b, 1c and 1d.

  The separation cam driving device 90 is controlled by a controller 200 of an engine control unit that performs overall control of the operation of the image forming apparatus A. The controller 200 includes a calculation unit, a control unit, and a storage unit, and performs sequence control of the separation cam drive device 90 according to the control program for the separation means stored in the storage unit. That is, the controller 200 has a function as control means for the separation cams 80a, 80b, 80c, and 80d.

[Process cartridge drive unit]
Next, an operation mechanism when the process cartridges 7a, 7b, 7c, and 7d are mounted on the apparatus main body B will be described.

  When the process cartridges 7a, 7b, 7c, and 7d are attached to the apparatus main body B, as shown in FIG. 6, all the separation cams 80a, 80b, and four-color image forming portions Pa, Pb, Pc, and Pd 80c and 80d are in contact with the ribs 46a, 46b, 46c and 46d at the maximum radius.

  Accordingly, as the process cartridges 7a, 7b, 7c, 7d are inserted, the ribs 46a, 46b, 46c, 46d provided on the developing units 4a, 4b, 4c, 4d are moved to the separation cams 80a, 80b, 80c, 80d. As a result, the developing rollers 40a, 40b, 40c, and 40d are separated from the photosensitive drums 1a, 1b, 1c, and 1d by a predetermined gap. At this time, the separation cams 80a, 80b, 80c, 80d of the image forming units Pa, Pb, Pc, Pd are at the home positions shown in FIGS. 7 and 8B, and all the image forming units Pa, Pb, Pd, The ribs 46a, 46b, 46c and 46d are pushed up by Pc and Pd.

  This separated state is always maintained when the power is turned off and when development is not performed. Therefore, even when the process cartridges 7a, 7b, 7c, and 7d are mounted and not used for a long time, the developing rollers 40a, 40b, 40c, and 40d are always separated from the photosensitive drums 1a, 1b, 1c, and 1d. It becomes a state. Therefore, it is possible to reliably prevent permanent deformation of the roller layer that occurs when the developing rollers 40a, 40b, 40c, and 40d are brought into contact with the photosensitive drums 1a, 1b, 1c, and 1d for a long period of time.

  Next, drive configurations of the photosensitive drums 1a, 1b, 1c, and 1d and the developing rollers 40a, 40b, 40c, and 40d, and their operations in the multicolor mode and the single color mode will be described.

  As described above, the “4-motor system” has problems that the cost tends to increase, the weight of the apparatus increases, and the space occupied by the driving apparatus tends to increase. Further, the “1-motor system” has a problem caused by uneven rotation of the photosensitive member due to the engagement of the clutch portion.

  Therefore, in this embodiment, as shown in the conceptual diagram of FIG. 20, the “two-motor system” is adopted. That is, the three photosensitive drums 1a, 1b, and 1c for Y, M, and C are driven by one motor 101A via gears, belts, or rollers, and the remaining photosensitive drum 1d for Bk is driven by another motor 101B. Drive with.

  When this “two-motor system” is adopted, the Bk photosensitive drum 1d is driven in the Bk single color mode, while the drive transmission to the other photosensitive drums 1a, 1b, and 1c is released, and the motor itself is rotated. This can be realized by stopping, and the clutch portion can be omitted. Therefore, it is possible to avoid problems such as color misregistration and deterioration of banding caused by uneven rotation of the photosensitive drum, which is caused by an increase in the accumulated eccentricity due to the engagement error of the clutch portion and the accuracy of the component parts.

  In the “two-motor system”, the load torque ratio is 3: 1 under a condition where the drive gear ratio is constant, and the load difference increases. However, the load torque imbalance can be eliminated by optimizing the torque distribution considering not only the photosensitive drum side but also the developing roller side where the driving force is transmitted from the same driving source. Therefore, it is possible to use two same motors. As a result, it is possible to prevent a mistake that another motor is erroneously attached at the time of assembly, and there is a cost advantage. This will be described in detail below.

  First, an outline of the entire drive system is shown in FIG.

  As shown in FIG. 11, in this embodiment, a process cartridge driving device (hereinafter simply referred to as “driving device”) 100 includes a first driving motor (hereinafter referred to as “first motor”) 101A serving as a first driving means. And a second drive motor (hereinafter referred to as “second motor”) 101B as second drive means. The driving device 100 includes four process cartridges 7a, 7b, 7c, and 7d, and more specifically, the photosensitive drums 1a, 1b, 1c, and 1d and the developing roller 40a included in each of the at least four process cartridges 7a, 7b, 7c, and 7d. , 40b, 40c, and 40d.

  The first motor 101A follows the first photosensitive drum drive train (hereinafter referred to as “drum drive train”) Td1, the first idler gear 102A, the first and second front gears 103A1 of the next stage of the first motor 101A. , 103A2, photosensitive drum driving gears (hereinafter referred to as “drum driving gears”) 104a, 104b, 104c. Then, the photosensitive drums 1a, 1b, and 1c included in the process cartridges 7a, 7b, and 7c for the respective color images of Y, M, and C are rotated.

  At the same time, the first motor 101A is connected to the clutch gear 107a corresponding to the image forming portion Pa for forming a yellow image via two idler gears along the first developing roller drive train Tr1. The two idler gears are a first-stage idler gear 105A and a second-stage idler gear 106A. Finally, it meshes with the input gear of the process cartridge 7a for Y image and drives the developing roller 40a.

  Similarly to the first motor 101A, the second motor 101B is arranged along the second drum drive train Td2 with the second idler gear 102B, the third front gear 103B, and the drum drive gear 104d at the next stage of the second motor 101B. Drive. Then, the photosensitive drum 1d provided in the Bk image process cartridge 7d is rotated.

  At the same time, the second motor 101B is connected to the clutch gears 107b, 107c, and 107d through the three idler gears along the second developing roller drive train Tr2 in the same manner as the first motor 101A. The three idler gears are a first-stage idler gear 105B, a second-stage idler gear 106B1, and a third-stage idler gear 106B2. The clutch gears 107b, 107c, and 107d correspond to the image forming portions Pb, Pc, and Pd that form M, C, and Bk color images. Finally, it engages with the input gears of the process cartridges 7b, 7c, and 7d for the respective color images of M, C, and Bk, and drives the developing rollers 40b, 40c, and 40d.

  That is, among the plurality of image carriers, the plurality of first image carriers 1a, 1b, and 1c form a toner image in the first mode, and do not form a toner image in the second mode. The second image carrier 1d, which is different from the plurality of first image carriers 1a, 1b, and 1c, forms a toner image in both the first mode and the second mode. The first driving means 101A drives a plurality of first image carriers 1a, 1b, 1c, and the second driving means 101B is a second image carrier 1d and a driven body that acts on the second image carrier 1d. 40d drives at least one driven body acting on the plurality of first image carriers 1a, 1b, 1c.

  In the present embodiment, the first driving unit 101A drives at least one driven body that acts on the plurality of first image carriers 1a, 1b, and 1c.

  In this embodiment, the first driving means 101A and the second driving means 101B have the same number of driving force supply targets.

  The driven body is a member driven by driving means (driving source).

  As described above, in this embodiment, the driving device 100 includes the first motor 101A and the second motor 101B in order to drive the photosensitive drums 1a, 1b, 1c, and 1d of the image forming units Pa, Pb, Pc, and Pd. It has two motors. In particular, in the present embodiment, these two motors 101A and 101B each bear a load of four rollers in order to optimize torque distribution.

  Next, the operation of the driving apparatus 100 during the image output operation will be described separately for the multicolor mode and the single color mode.

(Multicolor mode)
As described above, in the multicolor mode, a full color image can be formed by forming images of each color of Y, M, C, and Bk in the image forming units Pa, Pb, Pc, and Pd.

  In the multicolor mode, when an image output operation is started by a print signal, the two motors 101A and 101B that drive the process cartridges 7a, 7b, 7c, and 7d and the drive motor for the transfer belt 11 rotate. At this time, all the clutches of the first and second developing roller drive trains Tr1 and Tr2, that is, the clutch gears 107a, 107b, 107c, and 107d are disengaged, and all the developing rollers 40a, 40b, 40c, and 40d are rotated. do not do.

  Next, as shown in FIG. 8, when the stepping motor 91 of the separation cam driving device 90 rotates, the separation cams 80a, 80b, 80c, and 80d start to rotate counterclockwise from the home position shown in FIG. 8B. . At that time, the clutch gear 107a provided in the first developing roller drive train Tr1 is turned on, and the developing roller 40a rotates. Immediately thereafter, the stepping motor 91 rotates by a predetermined amount and all the separation cams 80a, 80b, 80c, 80d rotate by a predetermined amount (phase θ) counterclockwise, whereby the process cartridge 7a by the separation cam 80a. The rib 46a is released from being pushed up. As a result, the developing frame 45 of the process cartridge 7a is swung by the urging force of the pressure spring 54, whereby the developing roller 40a and the photosensitive drum 1a come into contact with each other, and image formation is started.

Similarly, having the clutch gear 107 b, 107c, together with 107d are sequentially ON, a predetermined time interval (only cam phase difference θ in FIG spaced cams 8 0a, 80b, 80c, interval 80d is rotated), developing roller 40b, 40 c, 40 d are sequentially abut.

  In this way, as shown in FIG. 8C, the push-up by the separation cams 80a, 80b, 80c, 80d of the ribs 46a, 46b, 46c, 46d of all the process cartridges 7a, 7b, 7c, 7d is released. As a result, the developing rollers 40a, 40b, 40c, and 40d in all the process cartridges 7a, 7b, 7c, and 7d come into contact with the photosensitive drums 1a, 1b, 1c, and 1d, and an image can be formed in the multi-color mode.

  At this time, as shown in FIG. 9, the photosensitive drums 1 a, 1 b, 1 c, and 1 d are transferred from the photosensitive drums 1 a, 1 b, 1 c, and 1 d to the image forming units Pa, Pb, Pc, and Pd via the transfer belt 11. Abut.

  After the image formation in the image forming portion Pa is completed, the stepping motor 91 further rotates, and accordingly, the separation cams 80a, 80b, 80c, and 80d further rotate counterclockwise from the state shown in FIG. First, in the image forming portion Pa, the separation cam 80a pushes up the rib 46a against the urging force of the pressure spring 54 of the process cartridge 7a, and the developing frame body 45 swings, so that the developing roller 40a is photosensitive. Separated from the drum 1a. Subsequently, the clutch gear 107a is turned off, and the rotation of the developing roller 40a is stopped. Thereafter, similarly to the contact, the developing rollers 40b, 40c, and 40d are sequentially separated from the photosensitive drums 1b, 1c, and 1d with a predetermined time interval (interval at which the separating cam 80 rotates by the cam phase difference θ). . Further, the clutch gears 107b, 107c, and 107d are sequentially turned off. Thus, the state shown in FIG. 8B is obtained, and the image output in the multicolor mode is completed.

  In this embodiment, the process cartridges 7a, 7b, and 7d after the developing rollers 40a, 40b, 40c, and 40d are separated from the photosensitive drums 1a, 1b, 1c, and 1d in all the image forming units Pa, Pb, Pc, and Pd. The first motor 101A and the second motor 101B that drive 7c and 7d and the drive motor for the transfer belt 11 stop rotating.

(Single color mode)
In the monochrome mode, first, when an image output operation is started by a print signal, the second motor 101B that drives the process cartridge 7d and the drive motor for the transfer belt rotate. At this time, all the clutches of the second developing roller drive train Tr2, that is, the clutch gears 107b, 107c, and 107d are disconnected, and the developing rollers 40b, 40c, and 40d do not rotate. At this time, in this embodiment, the first motor 101A is stopped, the gear clutch 107a of the first developing roller drive train Tr1 is disconnected, and the developing roller 40a naturally does not rotate.

  Next, as in the transition from FIG. 8B to FIG. 8C in the multicolor mode, the stepping motor 91 of the separation cam drive device 90 rotates. Here, in the monochromatic mode, as shown in FIG. 8A, only the separation cam 80d rotates counterclockwise by θ ′. In this embodiment, a clutch is provided in the drive trains corresponding to the separation cams 80a, 80b, and 80c corresponding to the image forming portions Pa, Pb, and Pc, among the drive trains related to the contact and separation of the developing roller with respect to the photosensitive drum. . In the monochrome mode, only the separation cam 80d can be rotated by turning off the clutch. As a result, only the developing roller 40d can be brought into contact with the photosensitive drum 1d, and an image can be output in the monochromatic mode without bringing the developing rollers 40a, 40b, and 40c into contact with the photosensitive drums 1a, 1b, and 1c. Become.

  Then, after the separation cam 80d starts to rotate, the clutch gear 107d provided in the second developing roller drive train Tr2 is turned on, and the developing roller 40d rotates. Immediately after that, the stepping motor 91 rotates by a predetermined amount and the separation cam 80d rotates by a predetermined amount (phase θ ′) counterclockwise, so that the push-up of the rib 46d of the process cartridge 7d by the separation cam 80d is released. The As a result, the developing frame 45 of the process cartridge 7d is swung by the biasing force of the pressure spring 54, whereby the developing roller 40d and the photosensitive drum 1d come into contact with each other, and image formation is started.

  At this time, as shown in FIG. 10, the image forming unit for the color used in the single color mode, that is, the photosensitive drums 1a, 1b other than the image forming unit Pd in this embodiment, by moving means such as a cam mechanism and a link mechanism. 1 c is separated from the transfer belt 11. That is, the transfer means retracts the transfer rollers 12a, 12b, and 12c from the photosensitive drums 1a, 1b, and 1c, and separates the transfer belt 11 from the photosensitive drums 1a, 1b, and 1c. In this manner, for the image forming portions Pa, Pb, and Pc that are not used in the single color mode, it is possible to prevent the life of the photosensitive drums 1a, 1b, and 1c and the transfer belt 11 from being wasted. As a result, high-quality image output can be maintained until the end of the product life.

  At the end of the monochromatic mode, the stepping motor 91 is further rotated, whereby the separation cam 80d is further rotated counterclockwise to a position away from the rib 46d of the process cartridge 7d. As a result, in all the four color image forming portions Pa, Pb, Pc, and Pd, the developing rollers 40a, 40b, 40c, and 40d are separated from the photosensitive drums 1a, 1b, 1c, and 1d. Subsequently, the clutch gear 107d is turned off, and the rotation of the developing roller 40d is stopped. Thus, the image output in the single color mode is completed.

  In the present embodiment, in the image forming unit Pd, after the developing roller 40d is separated from the photosensitive drum 1d, the second motor 101B that drives the process cartridge 7d and the drive motor for the transfer belt 11 stop rotating.

  As described above, by adopting the “two-motor system”, even when it is necessary to stop the photosensitive drums 1a, 1b, and 1c in the single color mode, it is possible to cope with the problem by simply stopping the first motor 101A. . Even when the first motor 101A is stopped, the second motor 101B is operated, so that the photosensitive drum 1d and the developing roller 40d can be driven, and an image can be formed in the single color mode.

  That is, according to the present embodiment, the image forming apparatus A is different from the first mode (multicolor mode) in which the number of image forming units that form an image among the plurality of image forming units Pa, Pb, Pc, and Pd is different. 2 modes (monochromatic mode). The plurality of image forming units Pa, Pb, Pc, and Pd form an image in the first mode with the second image forming unit Pd that forms an image in both the first mode and the second mode, and the second mode A plurality of first image forming portions Pa, Pb, and Pc that do not form an image in the mode. The second image forming unit is an image forming unit for Bk in this embodiment, and the plurality of first image forming units are image forming units for Y, M, and C in this embodiment. The image forming apparatus A includes a first driving unit (first motor) 101A and a second driving unit (second motor) 101B. The first driving unit supplies driving force to the photosensitive drums 1a, 1b, and 1c of the image forming portions Pa, Pb, and Pc for Y, M, and C. The second driving unit supplies driving force to the photosensitive drum 1d and the developing roller 40d of the Bk image forming unit Pd.

  Here, the second driving unit 101B further supplies driving force to at least one developing roller (developing rollers 40b and 40c in this embodiment) among the image forming portions Pa, Pb, and Pc for Y, M, and C. be able to. Further, the first driving unit 101A can further supply driving force to at least one developing roller (the developing roller 40a in this embodiment) of the image forming portions Pa, Pb, and Pc for Y, M, and C. . Preferably, the first driving unit 101A and the second driving unit 101B have the same number of driving force supply targets.

  By doing so, it is not necessary to rotate the first motor 101A that drives the process cartridges 7a, 7b, and 7c for each of the colors Y, M, and C in the single color mode. For this reason, the operation sound at the time of monochromatic mode printing can be reduced, and there is an advantage from the viewpoint of noise standards such as “Blue Angel”. Further, power saving can be achieved from the viewpoint of power consumption of the apparatus main body B.

  In addition, a clutch mechanism (clutch means) is provided in a drive train that transmits a driving force to at least one (all in the present embodiment) of the developing rollers of the plurality of image forming units provided in the image forming apparatus A. Therefore, the image forming unit can drive the developing roller at a timing different from the driving timing of the photosensitive drum. Thereby, the life of the developing roller can be extended by driving the developing roller in accordance with the timing of contact and separation of the developing roller with respect to the photosensitive drum.

  Here, even when the image is output in the single color mode, when the transfer material S having a large basis weight is used, the contact between the photosensitive drum and the transfer belt 11 in a single image forming unit is caused by the temperature and humidity environment. However, the transfer force of the transfer material S is not sufficient, and the image output accuracy may be inferior. The transfer material S having a large basis weight is, for example, a cardboard or a small size paper such as a postcard.

  On the other hand, even in the single color mode, a sufficient conveying force of the transfer material S can be obtained by contacting the photosensitive drum and the transfer belt 11 not only in one of the image forming portions Pd but also in a plurality of image forming portions. Securement becomes possible. In this case, in order to prevent the rubbing between the photosensitive drum and the transfer belt 11, the photosensitive drum at the position where it abuts on the transfer belt 11 is driven. In the present embodiment, since the developing roller has the clutch mechanism (clutch gears 107a, 107b, 107c) as described above, even if the first motor 101A is rotated, the developing roller 40a is not necessarily synchronized with it. Does not rotate. Therefore, even when a plurality of photosensitive drums are brought into contact with the transfer belt 11 in the single color mode, it is possible to prevent the life of the developing roller from being wasted.

  By the way, unlike the present embodiment, even in the “2-motor system”, the following cases can be considered from the viewpoint of load balance in driving the photosensitive drum. In other words, it can be considered that the first motor 101A drives the Y and M photosensitive drums 1a and 1b, and the second motor 101B drives the C and Bk photosensitive drums 1c and 1d. In this case, in the Bk single color mode, it is necessary to provide a clutch mechanism between the second motor 101B and the drum drive gear 104c in order to cut off the drive transmission to the photosensitive drum 1c.

  However, when the clutch mechanism is provided, the amount of eccentricity increases due to the configuration, and the rotational speed fluctuation of the clutch output unit increases. As a result, similar to the “one motor system” in which the four photosensitive drums 1 a, 1 b, 1 c, and 1 d are driven by a single motor, there is a concern that color misregistration and banding deteriorate. In order to avoid this problem, if the component accuracy is excessively increased, there are concerns about problems such as cost. For this reason, the “two-motor system” of this embodiment is superior to the case where the four photosensitive drums are branched at 2 to 2.

  In the “two-motor system” of this embodiment, the first motor 101A drives the photosensitive drums 1a, 1b, and 1c for three colors Y, M, and C, and the second motor 101B drives the photosensitive drum 1d for Bk. In addition, the second motor 101B also drives a developing roller of a color different from Bk. As a result, the load of the drive source can be made substantially uniform, so that the configuration can be simplified and the cost can be reduced by sharing the drive source, and the load balance of the drive source can be optimized.

  The driving device 100 is controlled by a controller 200 of an engine control unit that performs overall control of the operation of the image forming apparatus A. As described above, the controller 200 includes a calculation unit, a control unit, and a storage unit, and performs sequence control on the drive device 100 according to the control program of the drive device 100 stored in the storage unit. That is, the controller 200 has a function as a control unit of the driving device 100. The controller 200 can independently control the driving of the first motor 101A and the second motor 101B.

[Drum drive train gear configuration]
Next, the detailed configuration regarding the first and second drum drive trains Td1 and Td2 will be further described.

  In the present embodiment, in the first drum drive train Td1, a gear (motor gear) provided coaxially with the driving shaft of the first motor 101A meshes with the large-diameter side gear of the first idler gear 102A. The small-diameter side gear of the first idler gear 102A meshes with the large-diameter side gears of the first and second front gears 103A1 and 103A2. The small diameter side gear of the first front gear 103A1 meshes with the drum drive gears 104a and 104b, and the small diameter side gear of the second front gear 103A2 meshes with the drum drive gear 104c.

  On the other hand, in the second drum drive train Td2, a gear (motor gear) provided coaxially with the drive shaft of the second motor 101B meshes with the large-diameter side gear of the second idler gear 102B. The small-diameter side gear of the idler gear 102B meshes with the large-diameter side gear of the third front gear 103B. The small-diameter side gear of the third front gear 103B meshes with the drum drive gear 104d.

  In the present embodiment, the first and second drum drive trains Td1 and Td2 are each set to a value in which the gear ratio between the meshing gears is a certain value. Specifically, the gears that mesh with each other from the gear (motor gear) provided on the same axis as the driving shaft of the first and second motors 101A and 101B, which are driving means, to the front gears 103A1, 103A2, and 103B, respectively. Are connected at a gear ratio of 1 / N1. Note that N1 is a natural number, and N1 may be different for each meshing. The front gears 103A1, 103A2, and 103B are gears that directly mesh with the drum drive gears 104a, 104b, 104c, and 104d, respectively. The drum drive gears 104a, 104b, 104c, and 104d are provided coaxially with the photosensitive drums 1a, 1b, 1c, and 1d, respectively, and rotate in the same cycle as the photosensitive drums 1a, 1b, 1c, and 1d. .

  Here, in this embodiment, the first motor 101A and the second motor 101B, and the first idler gear 102A and the second idler gear 102B have the same configuration. Further, the first to third front gears 103A1, 103A2, 103B and the drum driving gears 104a, 104b, 104c, 104d have the same configuration. Therefore, hereinafter, the motors or gears having the same configuration will be described in a general manner by omitting the suffixes given to the reference numerals when it is not necessary to distinguish them.

In the present embodiment, the number of teeth of each gear in the drum drive train is set as follows.
(I) Gear on the drive shaft of the motor 101: Number of teeth 18
(Ii) Large diameter side of idler gear 102: 72 teeth
Small diameter side: Number of teeth 24
(Iii) Large diameter side of the front gear 103: Number of teeth 48

  Thus, in the present embodiment, the tooth number ratio between (i) and (ii) is 1/4, and the tooth number ratio between (ii) and (iii) is 1/2.

  Here, in order to facilitate understanding, for example, in the case of two-stage reduction such as a gear on the driving shaft of the motor 101 → an idler gear 102 → a front-stage gear 103, the reduction ratio between the meshing gears is ½, respectively. Consider the case. FIG. 12 shows a schematic diagram of the speed fluctuation during one rotation of the front gear 103 at this time. In general, the speed variation of the gear often takes the form of a sine wave. This is also followed in this example.

  As can be seen from the composite wave in FIG. 12, by connecting the drive trains with a reduction ratio of 1/2, the rotation speed of each drive must always be the same speed for each rotation of the front gear 103. The front gear 103 is rotated (zero in FIG. 12). The reduction ratio is not limited to N1 = 2, and in the case of 1 / N1, the front gear 103 rotates at the same speed every time the front gear 103 rotates in the same manner. In other words, whatever the speed fluctuation amount and phase of the gear upstream of the front gear 103 can be canceled up to the front gear 103.

Further, as shown in FIGS. 13A and 13B, the position where the optical image is irradiated by the scanner unit 3 in the circumferential direction of the photosensitive drum 1 is an exposure point Pe, and the transfer material S in the circumferential direction of the photosensitive drum 1. A position where the toner image is transferred from the photosensitive drum 1 is defined as a transfer point Pt. When the angle between the exposure point Pe and the transfer point Pt (the opening angle in the rotation direction of the photosensitive drum 1) is 360 / N2 [°] (N2 is a natural number) with respect to the rotation center of the photosensitive drum 1, The number of teeth of the drive gear 104 is Z2, the number of teeth of the front gear 103 that meshes directly with the drum drive gear 104 is Z1, and between the front gear 103 and the drum drive gear 104,
Z1 / Z2 = 1 / (N2 × N3)
(N3 is a natural number)
It is preferable that the relationship is established. Thereby, regarding the rotational speed of the photosensitive drum 1, the speeds at the time of exposure (FIG. 13A) and the time of transfer (FIG. 13B) can be made the same.

  More specifically, in this embodiment, N2 = 2, Z1 = 30, and Z2 = 120.

  Therefore, in this embodiment, Z1 / Z2 = 30/120 = 1/4 = 1 / (2 × N3) and N3 = 2.

  As a result, for each photosensitive drum 1, it is possible to cancel the rotational unevenness of the photosensitive drum 1, that is, the image pitch unevenness due to the gear speed fluctuation component in the drive train from the motor 101 as the driving means to the drum driving gear 104. it can.

  Next, a method for reducing color misregistration between images of a plurality of colors for the drum drive train Td will be described.

In order to reduce color misregistration between images of a plurality of colors, the following two points are important for the drum drive train Td.
(I) The speed fluctuation history (profile) of the drum driving gear per rotation is the same for all of the plurality of image forming units.
(II) In addition to (I), in all of the plurality of image forming units, transfer is performed at the same speed in the speed fluctuation during one rotation of the drum drive gear.

  Regarding (I), when the speed fluctuation histories of the drum drive gears 104a and 104b are different between a plurality of image forming units, for example, between the two image forming units Pa and Pb, two image forming units are formed as shown in FIG. A speed difference between the drum driving gears 104a and 104b occurs between the parts Pa and Pb. This speed difference leads to color misregistration.

  In order to prevent this, regarding the drum drive gear, it is preferable to use gears of the same shape formed by the same mold forming or simultaneous integral processing for all image forming portions.

Regarding (II), as shown in FIG. 14, it is preferable to set the phase relationship in the combination of two adjacent drum drive gears 104a and 104b as follows. That is, it is preferable that the two eccentric drum drive gears 104a and 104b have the same maximum eccentric direction at least during image formation. Further, the phase in the maximum eccentric direction advances by an angle θ with respect to the drum drive gear 104b corresponding to the photosensitive drum 1b with the later transfer order with reference to the meshing position of the drum drive gears 104a and 104b and the preceding gear 103A1. It is preferable to have a phase relationship. This angle θ is defined as follows: d is the diameter of the photosensitive drum and Lp is the distance between the rotation centers of adjacent photosensitive drums.
θ = (πd−Lp) / πd × 360 [°]
It is preferable to satisfy the relationship. Thereby, it is possible to realize transfer between adjacent image forming units at the same rotational speed of the drum drive gear, that is, the peripheral speed of the photosensitive drum. Based on this idea, in this embodiment, d = 25 mm and Lp = 75 mm, so that θ is set to 16.2 °.

  As described above, by combining the speed fluctuation histories of a plurality of gears and additionally shifting the phase by an angle θ, as shown in FIG. 15B, the color due to the difference in rotational speed between the plurality of drum drive gears 104a and 104b. The deviation can be canceled.

  More specifically, in the present embodiment, the method for providing the phase difference of the angle θ between the drum drive gears of the adjacent image forming units is as follows. On the side of the first motor 101A to which the drive train is directly connected, each drum drive gear is assembled with a phase difference of the angle θ as described above. The first motor 101A side to which the drive train is directly connected is between the drum drive gear 104a and the drum drive gear 104b, and between the drum drive gear 104b and the drum drive gear 104c.

  However, due to the drive configuration of the present embodiment as described above, the phase difference of the angle θ cannot be maintained by assembling the drum drive gear 104c and the drum drive gear 104d that are not directly connected with a phase difference. Therefore, in this embodiment, the drum drive gear 104c and the drum drive gear 104d are phase-matched by electrical control.

  FIG. 16 is a schematic diagram of a phase matching device 108 that performs phase matching between the drum driving gear 104c and the drum driving gear 104d, which is included in the image forming apparatus A of the present embodiment.

  The drum drive gears 104c and 104d are provided with slits 104cs and 104ds, which are detected parts for detecting the phase, respectively. Further, photointerrupters (photosensors) 109c and 109d as phase detection means are provided in the vicinity of the slits 104cs and 104ds, respectively. Outputs of the photo interrupters 109c and 109d are connected to a controller 200 of an engine control unit that performs overall control of the operation of the image forming apparatus A. Accordingly, the controller 200 can grasp the passage timing of the slits 104cs and 104ds via the photo interrupters 109c and 109d when the drum driving gears 104c and 104d are rotated. The controller 200 can check the phase difference between the drum drive gears 104c and 104d from the timing.

  The controller 200 electrically feedback-controls the first and second motors 101A and 101B through the motor control unit so that a desired phase difference is established between the drum driving gears 104c and 104d. In this embodiment, the controller 200 checks the phase difference before image formation, for example, at the time of initialization of the apparatus, and performs feedback control of the first and second motors 101A and 101B. As described above, in this embodiment, the controller 200 has a function as a phase matching control unit for the drum drive gears 104c and 104d.

  As a result, a phase difference of a predetermined angle θ can be provided between the plurality of drum drive gears even with respect to the drum drive train that is not directly connected to the drive train and cannot be phase-set.

  Further, it is preferable to optimize the conditions for fluctuations in the rotational speed of the photosensitive drum as described above, and to optimize the conditions for fluctuations in the rotational speed of the transfer belt 11.

Specifically, in order to reduce color misregistration between images of a plurality of colors on the transfer material S, the transfer speed of the transfer material S at the transfer position of each color image, that is, the speed of the transfer belt 11 is also made the same. There is a need. For this purpose, the diameter D of the driving roller 13 (shaft for driving the transfer belt 11) 13 of the transfer belt 11, the thickness t of the transfer belt 11, and the distance between the rotation centers of adjacent photosensitive drums are Lp.
Lp = π (D + t)
It is preferable that the relationship is established.

  More specifically, in this embodiment, the diameter D of the driving roller 13 is 23.8 mm, the thickness t of the transfer belt 11 is 110 μm, and the distance Lp between the rotation centers of adjacent photosensitive drums is 75 mm.

  As a result, the speed of the transfer belt 11 can be made the same during the transfer of each color image in the speed fluctuation of the transfer belt 11 due to the shake of the drive roller 13.

  In order to reduce color misregistration, the following conditions are preferable in addition to or instead of optimizing the speed fluctuation conditions of the transfer belt 11 as described above.

  That is, the distance between the transfer position of the toner image from the photosensitive drum to the transfer material S in each of the two adjacent image forming units in the transport direction of the transfer material S is determined by the driving roller of the transfer belt 11 (driving the transfer belt 11). It is preferable that it is substantially an integral multiple of the outer peripheral distance of the axis.

  More specifically, in this embodiment, the distance between the transfer positions is 75 mm, which is the same as the distance between the rotation centers of adjacent photosensitive drums. The drive roller 13 has a diameter of 23.8 mm. Therefore, the distance between the transfer positions is approximately one time the outer peripheral distance of the drive roller 13.

  As described above, according to the present embodiment, the “two-motor system” is adopted for the drive transmission configuration related to image formation. As a result, it is possible to avoid the problems that the cost tends to increase, the weight of the device increases, and the space occupied by the drive device tends to increase when the “4-motor system” is adopted. In addition, it avoids the problems of color misregistration and deterioration of banding caused by uneven rotation of the photosensitive drum due to the engagement of the clutch provided in the drum drive train, which is required when the “1 motor system” is adopted, and is low cost and high image quality. Can be achieved.

  According to this embodiment, the “two-motor system” is adopted, and at least the photosensitive drums 1a, 1b, and 1c for Y, M, and C are used for one motor 101A, and the other motor 101B is used for Bk. The photosensitive drum 1d and the developing roller 40d are driven. Accordingly, it is possible to flexibly cope with switching between the multi-color mode / single-color mode accompanied by contact and separation between the transfer belt and the photosensitive drum, and to control the image forming operation in each mode. Therefore, it is possible to provide a high-quality image until the end of the life of the image forming apparatus by reducing the operation noise when outputting a monochrome image and preventing the waste of the life of the transfer belt and the process cartridge.

  In addition, one motor 101A drives three photosensitive drums and one developing roller, and the other motor 101B drives one photosensitive drum and three developing rollers. It is possible to reduce the cost and improve the assemblability by using a common motor.

Example 2
Next, another embodiment according to the present invention will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, here, elements having the same or equivalent functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, detailed description thereof will be omitted, and different portions will be described.

  In Example 1, the developing roller 40a for yellow was driven by the first motor 101A, and the developing rollers 40b, 40c, and 40d for M, C, and Bk were driven by the second motor 101B. From the viewpoint of the life of the developing unit and the like, the M and C developing rollers 40b and 40c were separated from the photosensitive drums 1b and 1c and the drive transmission was cut off during image output in the multicolor mode. In this case, a load fluctuation of the second motor 101B may occur, and as a result, a local speed fluctuation of the photosensitive drum 1d or a shock to the entire image forming apparatus A may occur. For this reason, in an extreme case, it is conceivable that it may lead to an image defect.

  In order to prevent this, in the case where the drive transmission of the M and C developing rollers 40b and 40c is not interrupted until the transfer process of the photosensitive drum 1d is completed, in particular, the lifetime of the M and C process cartridges 7b and 7c. Will be wasted.

  Therefore, in this embodiment, as shown in FIG. 17, the Y and M developing rollers 40a and 40b are driven by the first motor 101A, and the C and Bk developing rollers 40c and 40d are driven by the second motor 101B. .

  In other words, in this embodiment, the first motor 101A moves along the first developing roller drive train Tr1 via the first-stage idler gear 105A and the second-stage idler gear 106A, and the Y and M clutch gears 107a and 107b. Connect to. Finally, it engages with the input gears of the process cartridges 7a and 7b for Y and M color images, and drives the developing rollers 40a and 40b. On the other hand, the second motor 101B is connected to the C and Bk clutch gears 107c and 107d through the first stage idler gear 105B and the second stage idler gear 106B along the second developing roller drive train Tr2. Finally, it engages with the input gears of the process cartridges 7c and 7d for C and Bk color images, and drives the developing rollers 40c and 40d.

  Here, in order to avoid a shock, each developing roller has its developing roller until the transfer process of the image from the photosensitive drum driven by the first or second motor 101A or 101B that transmits driving to the developing roller is completed. The condition is that driving is not stopped.

  In this case, according to this embodiment, it is only necessary to wait for the separation of the C developing roller for the C and Bk image forming portions Pc and Pd until the transfer process in the Bk image forming portion is completed. . For this reason, it is possible to suppress wasting the life of the process cartridge.

Example 3
Next, still another embodiment according to the present invention will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, here, elements having the same or equivalent functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, detailed description thereof will be omitted, and different portions will be described.

  The Y, M, and C developing rollers 40a, 40b, and 40c have driving configurations other than those in the first and second embodiments as long as the output of the motor and the life of the process cartridge including the developing roller are sufficient. It is also possible. For example, all of the Y, M, and C developing rollers 40a, 40b, and 40c can be driven by the second motor 101B. As described above, the present invention can be applied to the Y, M, and C developing rollers 40a, 40b, and 40c, regardless of which of the first motor 101A and the second motor 101B is driven. In this case as well, as in the first and second embodiments, there is no need to provide a clutch mechanism in the drum drive train when switching between the single color mode and the multicolor mode, and the problem of worsening of banding and color misregistration can be avoided. Is possible.

  In some cases, one clutch mechanism may be provided for each of the drive train for the Bk developing roller 40d and each of the Y, M, and C developing rollers 40a, 40b, and 40c. Thereby, the two clutch mechanisms in the three colors Y, M, and C can be reduced, and the cost can be reduced. Further, in order to improve the transportability of the transfer material S, it is possible to flexibly control the image output mode in which the transfer belt 11 and the photosensitive drum are brought into contact with each other in a single color mode and rotated.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned embodiment. For example, in the first to third embodiments, the image forming apparatus is a direct transfer type image forming apparatus that sequentially transfers toner images from a plurality of photosensitive drums onto a transfer material conveyed by a transfer belt to form a recorded image. As explained.

  However, the present invention is not limited to an image forming apparatus using a transfer belt. For example, there is an intermediate transfer type image forming apparatus as shown in FIG. That is, the intermediate transfer type image forming apparatus includes, for example, the photosensitive drums 1a, 1b, 1c, and 1d, and the charging units 2a, 2b, 2c, and 2d as process units that act on the photosensitive drum, the developing unit 40a, 40b, 40c, 40d, and a plurality of image forming units 7a, 7b, 7c, 7d provided with cleaning means 6a, 6b, 6c, 6d. The toner image on the photosensitive drum is transferred to primary transfer rollers 301a, 302b, and an intermediate transfer body (for example, an endless belt-shaped intermediate transfer belt) 300 serving as a transfer body that rotates around each image forming unit. The images are sequentially superimposed and transferred by 302c and 302d. The intermediate transfer member 300 constitutes transfer means for transferring the toner image on the photosensitive drum to a recording material. Thereafter, the toner image is secondarily transferred collectively by the secondary transfer roller 302 onto a transfer material S conveyed by a separately provided transfer material conveyance system. Thereafter, the transfer material S passes through the fixing unit 20, and an image is formed on the transfer material. It is apparent from the above description that the present invention can be equally applied to such an intermediate transfer type image forming apparatus, and the same effect as described above can be obtained.

  Further, the order of the toner images transferred to the transfer medium by the plurality of image forming units is not limited to those in the above embodiments. That is, in the image forming apparatus of each of the above embodiments, the image forming units that form images of Y, M, C, and Bk colors can be arranged in any order in the transfer direction of the transfer target.

  In the above embodiment, the four image forming units corresponding to Y, M, C, and Bk have been described. However, the present invention is applicable if there are at least three image forming units, and the first motor drives two photosensitive drums, and the second motor drives one photosensitive drum and at least two developing rollers. If it exists, the effect of this invention can be acquired.

  In the above embodiment, the developing roller is described as an example of the driven body. However, the driven body may be a charging roller or a cleaning member as long as it is driven by acting on the photosensitive drum.

1a, 1b, 1c, 1d Photosensitive drums 40a, 40b, 40c, 40d Developing roller 101A First drive motor 101B Second drive motor

Claims (4)

A plurality of image carriers on which toner images are formed, a plurality of driven members acting on each of the plurality of image carriers, and a first driving a plurality of first image carriers among the plurality of image carriers . Drive means; and second drive means for driving a second image carrier that is different from the plurality of first image carriers among the plurality of image carriers, and the first drive means drives the first drive means. An image forming apparatus in which the number of one image carrier is larger than the number of second image carriers driven by the second driving unit,
2. The image forming apparatus according to claim 1, wherein the second driving unit drives a driven body that acts on the second image carrier and at least one driven body that acts on the plurality of first image carriers . It said first drive means, the image forming apparatus according to claim 1, characterized in that to drive the at least another one of the driven member acting on the first image bearing member of the plurality.   The drive train that transmits driving force from the second drive means to at least one driven body that acts on the plurality of first image carriers has at least one driven body that acts on the plurality of first image carriers. 3. The image forming apparatus according to claim 1, further comprising a clutch unit that cuts off transmission of the driving force from the second driving unit so as not to drive the body.   A first mode for driving the plurality of first image carriers and the second image carrier to form toner images on the plurality of first image carriers and the second image carrier; and the plurality of first images. 4. The second mode in which the second image carrier is driven without driving the image carrier, and a second mode in which a toner image is formed on the second image carrier can be executed. The image forming apparatus according to claim 1.

Images