JP5264101B2 - Transfer unit and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a transfer unit capable of achieving the miniaturization and stably obtaining a high-quality image without changing transfer conditions between in a monochromatic mode and in a color mode. <P>SOLUTION: The transfer unit includes: a transfer belt 4; a plurality of photoreceptor drums 2a to 2d (image carrier); and a plurality of transfer rollers 3a to 3d; wherein the color mode to transfer respective color toner images to the transfer belt 4 and the monochromatic mode to transfer a monochromatic toner image to the transfer belt 4 are selectable, and when selecting the monochromatic mode, the transfer belt 4 and the transfer rollers 3a to 3c are separated from the plurality of color photoreceptor drums 2a to 2c except the monochromatic photoreceptor drum. A pair of back up rollers 7 and 8 is arranged before and behind the monochromatic transfer roller 3d. The back up rollers 7 and 8 are integrally rotated by taking the rotational center O of the black photoreceptor drum 2d as a fulcrum so as not to change a transfer nip formed between the black photoreceptor drum 2d and the transfer belt 4 between in the color mode and in the monochromatic mode. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a transfer unit for transferring toner images of respective colors formed on a plurality of image carriers onto a transfer belt, and an image forming apparatus including the transfer unit.

  In recent years, there has been a strong demand for colorization of image forming apparatuses such as copiers and printers that form images by electrophotography, and color image forming apparatuses have been developed in response to this demand and are already in practical use. Since this type of color image forming apparatus requires an output speed comparable to that of a monochrome image, a tandem type color image forming apparatus has attracted attention.

  In a tandem type color image forming apparatus, at least an endless intermediate transfer belt stretched between a driving roller, a tension roller, and a driven roller, a monochrome black image carrier, and three types of yellow, magenta, and cyan A system is provided in which a color image carrier is provided and toner images of each color formed on each image carrier are transferred to the intermediate transfer belt.

  By the way, in the color image forming apparatus, a color mode for outputting a color image and a monochrome mode for outputting a monochrome image of a single black color can be selected. When operating yellow, magenta, and cyan color image carriers that are not used for formation, these color image carriers come into contact with the intermediate transfer belt, and the color image carrier and the intermediate transfer belt are worn to reduce their lifespan. Problem occurs.

Therefore, in Patent Document 1, the color transfer roller contact / separation mechanism is constituted by a color frame that holds the color transfer roller, and the axis of the backup roller for stabilizing the nip of the transfer roller is used as a rotation axis. Proposals have been made to rotate the.
Japanese Patent Laying-Open No. 2005-062642

  However, the configuration proposed in Patent Document 1 requires a large member such as a color frame, and thus there is a problem that the transfer unit and the image forming apparatus including the transfer unit are increased in size.

  The present invention has been made in view of the above problems, and the object of the present invention is to stably obtain a high-quality image without changing the transfer conditions in the monochrome mode and the color mode while reducing the size. Another object of the present invention is to provide a transfer unit that can be used and an image forming apparatus including the transfer unit.

In order to achieve the above object, the invention described in claim 1 is characterized in that at least an endless transfer belt stretched between a driving roller, a tension roller and a driven roller, a plurality of image carriers including monochrome, and A plurality of transfer rollers that come into contact with the respective image carriers through a transfer belt, and a color mode for transferring the toner images of the respective colors formed on the plurality of image carriers to the transfer belt, and a monochrome image carrier A monochrome mode for transferring the formed monochrome toner image to the transfer belt can be selected. In the monochrome mode, the transfer belt and the transfer roller are separated from a plurality of color image carriers other than those for monochrome. in the transfer unit, before and after the monochrome transfer roller, it is arranged a pair of backup rollers serving as a backup ID sensor, the backs The ID sensor and up roller integrally rotates the rotation center of the monochrome image bearing member as a fulcrum, so that the transfer nip of the transfer belt and the monochrome image bearing member does not change the color mode and the monochrome mode It is characterized by that.

According to a second aspect of the present invention, there is provided an endless transfer belt stretched between at least a driving roller, a tension roller, and a driven roller, a plurality of image carriers including those for monochrome, and the above-described each through the transfer belt. A plurality of transfer rollers in contact with the image carrier, a color mode for transferring each color toner image formed on the plurality of image carriers to the transfer belt, and a monochrome toner image formed on the monochrome image carrier. a selectable monochrome mode to be transferred to the transfer belt, the transfer unit and the monochrome mode from a plurality of color for image bearing members other than for monochrome as to separate the transfer roller and the transfer belt, the transfer color thereby rotatably supported by the roller and the release roller vertically movable ring arm, back in the vicinity of the monochrome transfer roller Place Ppurora, and characterized by moving a transfer roller for the with the backup roller monochrome, the transfer nip of the transfer belt and the monochrome image bearing member was prevented from being changed in color mode and the monochrome mode To do.

According to a third aspect of the present invention, the image forming apparatus includes the transfer unit according to the first or second aspect.

  According to the present invention, the pair of backup rollers are integrally rotated with the rotation center of the monochrome image carrier as a fulcrum, or the backup roller and the monochrome transfer roller arranged in the vicinity of the monochrome transfer roller are moved. This prevents the transfer nip between the monochrome image carrier and the transfer belt from changing between the color mode and the monochrome mode, so the transfer conditions in the monochrome mode and the color mode are the same, resulting in a high-quality monochrome image. It can be obtained stably.

  Further, according to the present invention, since a large-scale member is not used, the transfer unit and the image forming apparatus including the transfer unit can be reduced in size.

[First invention]
Embodiments of the first invention will be described below with reference to the accompanying drawings.

  1 and 2 are cross-sectional views of a main part of the image forming apparatus including the transfer unit according to the first invention. FIG. 1 shows a state in the color mode, and FIG. 2 shows a state in the monochrome mode.

  The image forming apparatus according to the present embodiment can output a color image and a monochrome image, and a yellow image forming unit 1Y, a magenta image forming unit 1M, a cyan image forming unit 1C, and a black image forming unit are provided inside the main body. Units 1Bk are arranged in tandem at regular intervals.

  Each of the image forming units 1Y, 1M, 1C, and 1Bk includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers, and transfer rollers 3a, 3b, 3c, and 3d as primary charging means, and is not shown. A primary charger, a developing device, and a drum cleaning device are provided.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (clockwise) by a driving device (not shown). The developing device (not shown) accommodates yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (Bk) toner, and is formed on each of the photosensitive drums 2a to 2d. Each electrostatic latent image is made to adhere to each color toner, and each electrostatic latent image is developed to make each color toner image visible.

  The transfer rollers 3a to 3d as the primary charging means are disposed so as to be able to contact the photosensitive drums 2a to 2d via the endless intermediate transfer belt 4 at each primary transfer portion. Here, the transfer rollers 3a to 3d and the intermediate transfer belt 4 constitute a transfer unit according to the present invention. The intermediate transfer belt 4 includes a drive roller 5, a belt contact / separation fulcrum roller 6, and a pair of backup rollers 7, 8. The transfer rollers 3a to 3d are arranged between the tension roller 9 and the secondary transfer counter roller 10 so as to be able to run on the lower surfaces of the photosensitive drums 2a to 2d. It is arranged in the circumference and pressed against each of the photosensitive drums 2a to 2d via the intermediate transfer belt 4 with a predetermined pressure. The secondary transfer counter roller 10 is in contact with the secondary transfer roller 11 through the intermediate transfer belt 4 in the secondary transfer portion. As a material for the intermediate transfer belt 4, a derivative resin such as polycarbonate, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), or the like is selected.

  Thus, in the present embodiment, the black photosensitive drum 2d is arranged on the downstream side in the transport direction of the intermediate transfer belt 4 from the positions of the other three color photosensitive trams 2a to 2c.

  Further, the backup rollers 7 and 8 are disposed within the circumference of the intermediate transfer belt 4 and before and after the black transfer roller 3d (in the traveling direction (counterclockwise direction) of the intermediate transfer belt 4). One backup roller 8 also serves as a backup for the ID sensor 12, and the backup rollers 7 and 8 and the ID sensor 12 are supported so as to be integrally rotatable with the rotation center O of the black photosensitive drum 2d as a fulcrum. Yes.

  The transfer rollers 3 a to 3 d are urged toward the photosensitive drums 2 a to 2 d by the spring 13, and in the color mode shown in FIG. 1, all the transfer rollers 3 a to 3 d are exposed to the photosensitive drums via the intermediate transfer belt 4. The drums 2a to 2d are pressed with a predetermined pressure. The tension roller 9 is pressed against the intermediate transfer belt 4 by a spring 14 to apply a predetermined tension to the intermediate transfer belt 4. Further, although not shown, a belt cleaning device is provided on the downstream side of the secondary transfer portion of the transfer unit.

  On the other hand, a registration roller 15 is disposed in the middle of the conveyance path L below the transfer unit in the main body of the image forming apparatus and upstream of the secondary transfer unit (left side in FIG. 1). A conveying belt 16 is disposed on the downstream side (right side in FIG. 1), and a fixing device 17 is further provided on the downstream side thereof. Here, the fixing device 17 includes a fixing roller 18 and a pressure roller 19 that rotate while being pressed against each other. Although not shown, a paper feed cassette containing a plurality of sheets stacked therein is detachably installed at the bottom of the image forming apparatus main body.

  Next, an image forming operation by the image forming apparatus having the above configuration will be described.

  The image forming apparatus according to the present embodiment can select a color mode for outputting a color image and a monochrome mode for outputting a monochrome image. When the color mode is selected, as shown in FIG. All the transfer rollers 3 a to 3 d are pressed against the photosensitive drums 2 a to 2 d via the intermediate transfer belt 4.

When an image start signal is issued in the above state,
In each of the image forming units 1Y, 1M, 1C, and 1Bk, the photosensitive drums 2a to 2d are rotationally driven at a predetermined process speed in the arrow direction (clockwise) in FIG. 1, and these photosensitive drums 2a to 2d are not shown. It is uniformly charged by the primary charger. When the laser light modulated by the color image signal for each color is irradiated to each of the photosensitive drums 2a to 2d from, for example, a laser scanner unit (not shown), the color image signals corresponding to the respective color image signals on the photosensitive drums 2a to 2d An electrostatic latent image is formed.

  Then, first, the electrostatic latent image formed on the photosensitive drum 2a of the yellow image forming unit 1Y is developed by a developing device (not shown) and visualized as a yellow toner image. The yellow toner image is rotated in the direction indicated by the arrow (counterclockwise) in FIG. 1 by the action of the transfer roller 3a at the primary transfer portion between the photosensitive drum 2a and the transfer roller 3a. Primary transferred onto.

  The intermediate transfer belt 4 on which the yellow toner image is primarily transferred as described above moves to the next magenta image forming unit 1M. In the magenta image forming unit 1M, similarly to the above, the magenta toner image formed on the photosensitive drum 2b is transferred onto the intermediate transfer belt 4 so as to be superimposed on the yellow toner image in the primary transfer portion.

  Similarly, cyan and black toners respectively formed on the photosensitive drums 2c and 2d of the cyan and black image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 4, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 4. The transfer residual toner that is not transferred onto the intermediate transfer belt 4 but remains on the photosensitive drums 2a to 2d is removed by drum cleaning devices (not shown), and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  The full color toner image on the intermediate transfer belt 4 is transferred from a paper feed cassette (not shown) to the transport path L in accordance with the timing at which the leading end of the full color toner image reaches the secondary transfer portion between the secondary transfer counter roller 10 and the secondary transfer roller 11. Is fed to the secondary transfer section by the registration roller 15. Then, in the secondary transfer portion, the full color toner image on the intermediate transfer belt 4 is secondarily transferred collectively onto the paper by the action of the secondary transfer roller 11. Incidentally, the untransferred toner remaining on the intermediate transfer belt 4 without being transferred onto the sheet is removed by a belt cleaning device (not shown), and the intermediate transfer belt 4 is prepared for the next image formation.

  The sheet on which the full color toner image has been transferred as described above is conveyed to the fixing device 17, and the full color toner image is heated in the process of being conveyed while being sandwiched between the fixing roller 18 and the pressure roller 19 in the fixing device 17. Then, it is pressurized and thermally fixed on the surface of the paper. The sheet on which the toner image is fixed is discharged to a discharge tray (not shown) outside the apparatus main body.

  On the other hand, when the monochrome mode is selected, as shown in FIG. 2, the backup rollers 7 and 8 and the ID sensor 12 rotate integrally by a predetermined angle clockwise with the rotation center O of the black photosensitive drum 2d as a fulcrum. Move. Then, the color transfer rollers 3a to 3c and the intermediate transfer belt 4 are separated from the color photosensitive drums 2a to 2c. At this time, the rotation amounts of the backup rollers 7 and 8 and the ID sensor 12 are set so that the transfer nip between the intermediate transfer belt 4 and the monochrome photosensitive drum 2d is the same as that in the color mode. Accordingly, in this monochrome mode, the transfer roller 5d and the intermediate transfer belt 4 are in contact with the black photosensitive drum 2d only in the black image forming unit 1Bk.

  Thus, in the monochrome mode, only the black image forming unit 1Bk operates and the other yellow, magenta, and cyan image forming units 1Y, 1M, and 1C are paused. The black toner image formed on 2d is primarily transferred onto the intermediate transfer belt 4 at the primary transfer portion, and the black toner image transferred onto the intermediate transfer belt 4 is supplied to the secondary transfer portion at an appropriate timing. Secondary transferred onto paper. Then, the sheet on which the black toner image has been transferred is conveyed to the fixing device 17, where the black toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the black toner image is fixed. The paper is discharged to a paper discharge tray (not shown) outside the apparatus main body.

  As described above, in the present embodiment, the pair of backup rollers 7 and 8 are integrally rotated with the rotation center O of the black photosensitive drum 2d as a fulcrum, so that the black photosensitive drum 2d and the intermediate transfer belt 4 are rotated. Since the transfer nip is not changed between the color mode and the monochrome mode, the transfer conditions in the monochrome mode and the color mode are the same, and a high-quality monochrome image can be stably obtained.

  In this embodiment, since a large-scale member is not used, the transfer unit and the image forming apparatus including the transfer unit can be reduced in size.

[Second invention]
Next, an embodiment of the second invention will be described with reference to FIGS.

  3 and 4 are cross-sectional views of the main part of the image forming apparatus including the transfer unit according to the second invention. FIG. 3 shows a state in the color mode, and FIG. 4 shows a state in the monochrome mode. 5 is an enlarged detail view of part A in FIG. 3, FIG. 6 is an enlarged detail view of part B in FIG. 4, and in FIGS. 3 to 6, the same elements as those shown in FIGS. Reference numerals are attached, and repetitive description thereof will be omitted below.

  In the present embodiment, the color transfer rollers 3a to 3c and the release roller 21 are rotatably supported by a link arm 20 that can move up and down, and in the vicinity of the black transfer roller 3d (the black transfer roller 3d and the tension roller 9). A backup roller (idle roller) 22 is arranged between the other components, and the other configuration is the same as that of the image forming apparatus according to the first invention shown in FIGS.

  Thus, when the color mode is selected in the image forming apparatus according to the present embodiment, all the transfer rollers 3a to 3d are connected to the respective photosensitive drums 2a via the intermediate transfer belt 4 as shown in FIG. The release roller 21 abuts against the intermediate transfer belt 4 and pushes up the intermediate transfer belt 4.

  In the above state, as in the first invention, yellow, magenta, cyan, and black toner images are superimposed and transferred onto the intermediate transfer belt 4 to form a full-color toner image. Is transferred onto the supplied paper in synchronization with the timing of reaching the secondary transfer portion. The sheet on which the full color toner image has been transferred in this manner is conveyed to the fixing device 17, and after the full color toner image is fixed in the fixing device 17, the paper is discharged to a discharge tray (not shown) outside the apparatus main body. Is done.

  On the other hand, when the monochrome mode is selected, as shown in FIG. 4, the link arm 20 moves downward, and the color transfer rollers 3a to 3c, the release roller 21 and the intermediate transfer belt 4 are moved to the color photosensitive drums 2a to 2b. While moving away from 2c, the black transfer roller 3d and the backup roller 22 move in the direction of the arrow in FIG. At this time, the intermediate transfer belt 4 is inclined by an angle α shown in FIG. 4 with respect to the state in the color mode shown in FIG. 3, but the transfer nip between the black photosensitive drum 2d and the intermediate transfer belt 4 is different from that in the color mode. Similarly, the black transfer roller 3d and the backup roller 22 are moved in the direction of the arrow by an angle α as shown in FIG.

  Thus, in the monochrome mode, only the black image forming unit 1Bk operates and the other yellow, magenta, and cyan image forming units 1Y, 1M, and 1C are paused. The black toner image formed on 2d is primarily transferred onto the intermediate transfer belt 4 at the primary transfer portion, and the black toner image transferred onto the intermediate transfer belt 4 is supplied to the secondary transfer portion at an appropriate timing. Secondary transferred onto paper. Then, the sheet on which the black toner image has been transferred is conveyed to the fixing device 17, where the black toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the black toner image is fixed. The paper is discharged to a paper discharge tray (not shown) outside the apparatus main body.

  As described above, in this embodiment, the transfer nip between the black photosensitive drum 2d and the intermediate transfer belt 4 is moved by moving the backup roller 22 and the black transfer roller 3d disposed in the vicinity of the black transfer roller 3d. Therefore, the transfer conditions in the monochrome mode and in the color mode are the same, and a high-quality monochrome image can be stably obtained.

  Further, according to the present invention, since a large-scale member is not used, the transfer unit and the image forming apparatus including the transfer unit can be reduced in size.

It is sectional drawing (color mode) of the principal part of an image forming apparatus provided with the transfer unit which concerns on 1st invention. It is sectional drawing (monochrome mode) of the principal part of an image forming apparatus provided with the transfer unit which concerns on 1st invention. It is sectional drawing (color mode) of the principal part of an image forming apparatus provided with the transfer unit which concerns on 2nd invention. It is sectional drawing (monochrome mode) of the principal part of an image forming apparatus provided with the transfer unit which concerns on 2nd invention. It is the A section enlarged detail drawing of FIG. It is the B section enlarged detail drawing of FIG.

Explanation of symbols

1Y Yellow image forming unit 1M Magenta image forming unit 1C Cyan image forming unit 1Bk Black image forming unit 2a to 2d Photosensitive drum (image carrier)
3a to 3d Transfer roller 4 Intermediate transfer belt (transfer belt)
5 Driving roller 6 Belt contact / separation fulcrum roller 7, 8 Backup roller 9 Tension roller 10 Secondary transfer counter roller 11 Secondary transfer roller 12 ID sensor 13, 14 Spring 15 Registration roller 16 Conveying belt 17 Fixing device 18 Fixing roller 19 Pressure Roller 20 Link arm 21 Release roller 22 Backup roller (idle roller)
L Conveyance path O Rotation center of black photosensitive drum

Claims (3)

An endless transfer belt stretched between at least a driving roller, a tension roller, and a driven roller, a plurality of image carriers including those for monochrome, and a plurality of abutting the image carriers via the transfer belt A color mode that includes a transfer roller and transfers toner images of each color formed on a plurality of image carriers to the transfer belt; and a monochrome mode that transfers a monochrome toner image formed on a monochrome image carrier to the transfer belt In the transfer unit in which the transfer belt and the transfer roller are separated from a plurality of color image carriers other than those for monochrome in the monochrome mode,
A pair of backup rollers that also serve as backups for the ID sensor are arranged before and after the monochrome transfer roller, and the backup roller and the ID sensor are integrally rotated with the rotation center of the monochrome image carrier as a fulcrum. A transfer unit characterized in that the transfer nip between the image carrier and the transfer belt does not change between the color mode and the monochrome mode. An endless transfer belt stretched between at least a driving roller, a tension roller, and a driven roller, a plurality of image carriers including those for monochrome, and a plurality of abutting the image carriers via the transfer belt A color mode that includes a transfer roller and transfers toner images of each color formed on a plurality of image carriers to the transfer belt; and a monochrome mode that transfers a monochrome toner image formed on a monochrome image carrier to the transfer belt In the transfer unit in which the transfer belt and the transfer roller are separated from a plurality of color image carriers other than those for monochrome in the monochrome mode,
The color for the transfer roller and the release roller while rotatably supported by a vertically movable ring arm, a backup roller disposed in the vicinity of the monochrome transfer roller moves between the monochrome transfer roller and said backup roller, said A transfer unit, wherein a transfer nip between a monochrome image carrier and the transfer belt is not changed between a color mode and a monochrome mode. An image forming apparatus comprising the transfer unit according to claim 1 or 2, wherein.

Images