JP4735336B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having an intermediate transfer belt and a developing device related to image formation, such as an electrophotographic copying machine, a printer, and a FAX.

  Conventionally, in an electrophotographic image forming apparatus equipped with four photosensitive drums and an intermediate transfer belt (hereinafter also simply referred to as a belt), the first copy out time (FCOT) of a monochrome image print is shortened. In order to further increase the monochrome toner storage space, the three-color (Y, M, C) photosensitive drum is urged by a driving roller and a tension spring in one direction (horizontal direction) as shown in FIG. It arrange | positions so that it may contact | abut to the tension surface of the belt stretched by the movable follower roller. On the other hand, a monochrome (black) image-forming photosensitive drum is located downstream of the three-color photosensitive drums and between the driven roller and the secondary transfer unit (for example, an oblique transfer surface of the intermediate transfer belt in FIG. 3). Has been placed.

  FIG. 3 is a view showing an example of a conventional driven roller.

In such an arrangement, at the time of monochrome (K) image formation, an inner stretching roller capable of detaching and attaching the belt is provided on the surface of the three color photosensitive drums, or an outer stretching roller is provided to provide a belt. In some cases, the belt is separated from the surface of the drum by pushing down from the photosensitive drum. (For example, refer to Patent Document 1).
JP 2003-330284 A

  However, a method in which the driven roller can be moved in one direction with a spring, or a method in which the rotation center of the inner stretching roller that can be separated and moved is moved and an outer stretching roller is provided to push the belt down from the surface of the photosensitive drum. However, there is a problem in that color misregistration between three colors (superimposed image) and black occurs due to a change in the path due to belt elongation and tension fluctuation.

  An object of the present invention is to provide an image forming apparatus capable of obtaining a stable superimposed image without the occurrence of color misregistration as described above.

  The above object is achieved by the following configuration.

  The latent image is formed on the four photosensitive drums by the writing unit, the latent image is converted into a toner image by the developing unit, and each toner image is transferred onto the intermediate transfer belt to form a superimposed toner image. In the image forming apparatus for collectively transferring the superimposed toner image onto the transfer material, the intermediate transfer belt is stretched by at least three tension rollers provided on the inner side, and the first and second belts are arranged in the order of the belt running direction. Three of the four photosensitive drums are arranged so as to abut on the tensioning surface formed by connecting the outer peripheral surfaces of the second two stretching rollers at equal intervals. The pieces are arranged so as to abut on the tensioning surface downstream from the third tensioning roller, and the second and third tensioning rollers are composed of two stations, and can be moved at equal distances in opposite directions. An image forming apparatus.

  Since the belt path can be kept as constant as possible, image shift can be prevented.

  The image forming apparatus according to the present invention will be described below.

  FIG. 1 is a schematic diagram illustrating an example of the overall configuration of the image forming apparatus.

  In FIG. 1, 10 is a charger (photosensitive drum (drum)) 11 is a scorotron band electrode, 12 is a writing device which is an image writing means composed of a head in which light emitting diodes are arranged, and 13 is a developing means. 14 is a cleaning device for cleaning the surface of the photoreceptor 10, 15 is a cleaning blade, 16 is a developing sleeve, and 20 is an intermediate transfer belt. The image forming unit 1 includes a photoconductor 10, a charger 11, a developing device 13, a cleaning device 14, and the like. Waste toner remaining on the photoconductor 10 is scraped off by a cleaning blade 15. Is conveyed to the back side (from the front side to the back side). The toner is supplied from the toner bottle 18 to the developing device via the toner hopper 19.

  Here, since the mechanical configuration of the image forming means 1 for each color is the same, in FIG. 1, only the configuration of the Y (yellow) series is given a reference symbol, and M (magenta), C (cyan), and Reference numerals are omitted for the components of K (black).

  The arrangement of the image forming means 1 for each color is in the order of Y, M, C, K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 contacts the stretched surface of the intermediate transfer belt 20. The contact point rotates in the same direction as the traveling direction of the intermediate transfer belt 20 and at the same linear speed.

  The intermediate transfer belt 20 includes a driving roller 21 that is a first stretching roller, a driven roller 22 that is a second stretching roller, a driven roller 23 that is a third stretching roller, and a fourth roller. It is stretched by a conveying roller 24 and a ground roller 25 which are stretching rollers, and is adjusted by a tension roller 26 from the outside. These rollers, the intermediate transfer belt 20, the primary transfer roller 27, the cleaning device 28, and the like constitute the belt unit 2.

  The three-color photosensitive drums are arranged at equal intervals on the belt tensioning surface between the driving roller 21 and the driven roller 22, and the arrangement of the K photosensitive drums is separated from the arrangement of the other three colors. It is disposed between the roller 23 and the secondary transfer roller 25. By arranging in this way, a large space in the vicinity of the K image forming means can be secured, and in particular, there is an advantage that the capacity of the K toner bottle having a high printing frequency can be increased. Details of the driven rollers 22 and 23 according to the present invention will be described later.

  The intermediate transfer belt 20 is driven by rotation of the driving roller 21 by a driving motor (not shown).

  The photosensitive member 10 is formed by forming a photosensitive layer such as a conductive layer, an a-Si layer, or an organic photosensitive member (OPC) on the outer periphery of a cylindrical metal base formed of, for example, an aluminum material, and the conductive layer is grounded. In the state, it rotates counterclockwise as indicated by the arrow in FIG.

  An electric signal corresponding to the image data from the reading device 80 is converted into an optical signal by a light emitting diode, and is projected onto the photoconductor 10 by each writing device 12.

  Note that a digital exposure method using laser light may be used instead of a writing method using a light emitting diode.

  The developing device 13 is a developing sleeve formed of a cylindrical non-magnetic stainless steel or aluminum material that maintains a predetermined interval with respect to the peripheral surface of the photoconductor 10 and rotates in the reverse direction at the closest position to the rotation direction of the photoconductor 10. 16.

The intermediate transfer belt 20 is an endless belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm. For example, the intermediate transfer belt 20 may be an engineering plastic such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy. A semiconductive seamless belt having a thickness of 0.04 to 0.10 mm, in which a conductive material is dispersed.

  The primary transfer roller 25 is applied with a DC voltage having the opposite polarity (positive polarity in the present embodiment) to the toner (negative polarity in the present embodiment), and the toner image formed on the photoconductor 10 is intermediately transferred. It has a function of transferring onto the belt 20.

  Reference numeral 27 denotes a secondary transfer roller that can be brought into contact with and released from the earth roller 25, and a voltage having a polarity opposite to that of the toner is applied to retransfer the toner image formed on the intermediate transfer belt 20 onto the transfer material P. .

  A cleaning device 28 is provided to face the driving roller 21 with the intermediate transfer belt 20 interposed therebetween. After the toner image is transferred to the transfer material P, the residual toner is scraped off by the cleaning blade 29 and is conveyed by the conveying screw 281 to the back side of the apparatus (from the front side to the back side of the sheet).

  70 is a paper feed roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a transport roller. A paper discharge roller 81 discharges the fixed transfer material to a paper discharge tray 82.

  A fixing device 4 includes a heating roller 41 heated by a halogen lamp 46 and a pressure roller 42 pressed by a pressure mechanism (not shown). A transfer material carrying a toner image is sandwiched and added by a nip T. Press to fix.

  A control unit B1 is a control unit that controls each drive unit, image forming process, fixing temperature, and the like.

  The image forming process will be described below with reference to FIG.

  Simultaneously with the start of image recording, the photosensitive member 10 of the color signal Y is rotated counterclockwise as indicated by an arrow by starting a photosensitive member driving motor (not shown), and at the same time, a potential is applied to the photosensitive member 10 by the charging action of the charger 11. Be started.

  After the photoconductor 10 is applied with a potential, writing of an image corresponding to the Y image data is started by the writing device 12, and an electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the photoconductor 10. It is formed.

  The electrostatic latent image is reversely developed in a non-contact state by a Y developing unit 13, and a Y toner image is formed on the photoconductor 10 as the photoconductor 10 rotates.

  The Y toner image formed on the photoconductor 10 is primarily transferred onto the intermediate transfer belt 20 by the action of the Y transfer roller 25.

  After that, the photoreceptor 10 is cleaned of residual toner by a cleaning blade 15 and enters the next image forming cycle (hereinafter, the same applies to the M, C, and K cleaning processes, and the description is omitted).

  Next, the writing device 12 performs image writing corresponding to an M (magenta) color signal, that is, M image data, and an electrostatic latent image corresponding to the M image of the original image is formed on the surface of the photosensitive member 10. The The electrostatic latent image is converted into an M toner image on the photosensitive member 10 by the M developing unit 13, and is synchronized with the Y toner image on the intermediate transfer belt 20 by the M transfer roller 25. The toner image is superimposed on the toner image and primarily transferred.

  By a similar process, the Y and M superimposed toner images are synchronized, and the C (cyan) toner image is superimposed on the Y and M superimposed toner images by the C transfer roller 25 1. Next transferred. Next, the toner image (K) formed by the K image forming unit disposed in a position separated from the C image forming unit is synchronized with the Y, M, and C superimposed toner images already formed. ) Are superimposed on the Y, M, and C superimposed toner images by the K transfer roller 25, and Y, M, C, and K superimposed toner images are formed.

  From the above, the intermediate transfer belt 20 on which the superimposed toner images of at least two colors are carried is sent in the clockwise direction as shown by the arrow, and the transfer material P is sent out from the paper cassette 72 by the paper feed roller 70 and conveyed. The toner is conveyed to the timing roller 71 via the roller 73 and temporarily stopped, and then the timing roller 71 is driven to synchronize with the superimposed toner image on the intermediate transfer belt 20 so that a DC voltage having a polarity opposite to that of the toner is generated. The toner image is fed to the transfer area S of the applied transfer roller 27 (in contact with the intermediate transfer belt 20), and the superimposed toner image on the intermediate transfer belt 20 is secondarily transferred to the transfer material P.

  Thereafter, the intermediate transfer belt 20 travels, the residual toner on the belt is cleaned by the cleaning device 28, and the next image forming cycle starts.

  The toner that has been scraped off is stored in the cleaning device 28, transported in the axial direction (from the front surface to the back surface of the paper in the drawing) by the rotation of the transport screw 281, and stored in a storage box via a waste pipe (not shown). .

  The transfer material P onto which the superimposed toner image has been transferred is further sent to the fixing device 40, and is sandwiched between the heating roller 41 and the pressure roller 42 heated by the halogen lamp 46, and is fixed by being pressed. The transfer material P on which the toner image is fixed is conveyed to a paper discharge tray 82 by a paper discharge roller 81.

  The present invention will be described below with reference to FIGS.

  As described above, the photosensitive drums of three colors (Y, M, and C) are brought into contact with the same tension surface of the belt, and the photosensitive drums of the other one color (K) are brought into contact with another tension surface. In this case, if a movable follower roller is provided between the tension contact surfaces, there arises a problem that a color shift between the three colors (superimposed image) and black occurs due to a change in the path due to a belt tension variation, elongation, or the like. . That is, in FIG. 3, the belt length between the transfer positions (P1 to P2) between the C drum and the K drum changes as indicated by the dotted line when the driven roller moves by d. As a result, the color misalignment between the three-color (Y, M, C) superimposed image and the K image occurs.

  The present invention is proposed in order to avoid such inconvenience.

  FIG. 2 is a diagram illustrating a driven roller mechanism for preventing color misregistration.

  In FIG. 2, the driven roller mechanism 3 includes driven rollers 22 and 23 and shaft support members 30 that support the driven rollers 22 and 23 in parallel with each other at both ends of the rotation shafts 22A and 23A. The rotating shaft 31 is integrated with the member at the center of the shaft support member 30, and the spring 32 applies tension to the belt 20. One hook of the spring 32 is engaged with the rotating shaft 31, and the other hook is engaged with a spring stopper 34 provided on the belt unit frame (front and rear) 33A, 33B. Further, both end portions of the rotation shaft 31 are inserted into slide grooves g provided in the frame bodies 33A and 33B of the belt unit 2. That is, the driven rollers 22 and 23 are supported by the frame bodies 33A and 33B via the slide groove g of the shaft support member 30, and are drawn in the direction of the arrow W by the spring 32, and the belt 20 is stretched.

  FIG. 4 is an enlarged view of the vicinity of the driven roller according to the present invention.

  The color shift between the three-color superimposed image and the K (black) image occurs when the belt length from the C transfer position P1 to the K transfer position P2 changes from a predetermined length. Therefore, it is possible to avoid color misregistration by suppressing a change in the belt length between the transfer positions (P1 to P2).

  That is, in FIG. 4, the shaft support member 30 is continuously pulled in the direction of the arrow W by the spring 32, and the belt 20 is stretched with a predetermined tension, for example, by forming a path indicated by a solid line. When the tensile strength from the driving side increases, even if the shaft support member 30 rotates about the rotation shaft 31 along the slide groove g as a fulcrum, it moves in the same distance in the opposite directions and becomes A = A ′. The state indicated by the dotted line can be maintained, and the change in the path (belt length between P1 and P2) due to the tension fluctuation can be suppressed.

  Therefore, by applying this driven roller mechanism, it is possible to suppress the above color shift as much as possible.

1 is a schematic diagram illustrating an example of an overall configuration of an image forming apparatus. It is a figure which shows the driven roller mechanism for preventing a color shift. It is the figure which showed an example of the conventional driven roller. It is the figure which expanded the vicinity of the driven roller concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoconductor 11 Charger 13 Developing device 18, 18A Toner bottle 19, 19A Toner hopper 20 Intermediate transfer belt 21 Drive roller 22, 23 Drive roller 3 Drive roller mechanism 30 Shaft support member 31 Rotating shaft 32 Spring 33A, 33B Belt unit frame Body g Slide groove

Claims (4)

The latent image is formed on the four photosensitive drums by the writing unit, the latent image is converted into a toner image by the developing unit, and each toner image is transferred onto the intermediate transfer belt to form a superimposed toner image. In the image forming apparatus for collectively transferring the superimposed toner image onto the transfer material, the intermediate transfer belt is stretched by at least three tension rollers provided on the inner side, and the first and second belts are arranged in the order of the belt running direction. Three of the four photosensitive drums are arranged so as to abut on the tensioning surface formed by connecting the outer peripheral surfaces of the second two stretching rollers at equal intervals. The pieces are arranged so as to abut on the tensioning surface downstream from the third tensioning roller, and the second and third tensioning rollers are composed of two stations, and can be moved at equal distances in opposite directions. An image forming apparatus. The image forming apparatus according to claim 1, wherein the other one of the photosensitive drums forms a black image. The image forming apparatus according to claim 1, wherein the writing unit is a digital exposure method using a head in which light emitting diodes are arranged. The image forming apparatus according to claim 1, wherein the writing unit is a digital exposure method using a laser beam.

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