JP2008249925A - Transfer unit and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer unit capable of simplifying a separation mechanism which separates a transfer belt from image carriers in a monochrome mode. <P>SOLUTION: The transfer unit includes: the endless intermediate transfer belt 7; a plurality of photoreceptor drums (image carriers) 2a to 2d; and a plurality of transfer rollers 5a to 5d disposed in contact with photoreceptor drums 2a to 2d via the intermediate transfer belt 7. The transfer unit can select a color mode in which toner images in respective colors formed on the photoreceptor drums 2a to 2d are transferred to the intermediate transfer belt 7 or the monochrome mode in which a monochrome toner image formed on the photoreceptor drum 2d is transferred to the intermediate transfer belt 7. In the monochrome mode, the transfer unit separates the intermediate transfer belt 7 and transfer rollers 5a to 5c from the color photoreceptor drums 2a to 2c for use other than the monochrome. In such the transfer unit, the separation of the intermediate transfer belt 7 and transfer rollers 5a to 5c from the photoreceptor drums 2a to 2c in the monochrome mode is performed from the operation of a drum unit. <P>COPYRIGHT: (C)2009,JPO&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 is a high 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, an endless intermediate transfer belt stretched between at least a driving roller, a tension roller, a driven roller, and a secondary transfer roller, a black image carrier for monochrome, yellow, and magenta A system in which three color image carriers of cyan are provided and toner images of each color formed on the image carriers are transferred to the intermediate transfer belt is employed.

  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 intermediate transfer belt are worn to shorten their lifespan. Problem arises.

  Therefore, when the monochrome mode is selected and a monochrome image is output, a color image forming apparatus in which the transfer roller and the intermediate transfer belt are separated from the yellow, magenta, and cyan color image carriers other than the black image carrier. Has been proposed. In such a color image forming apparatus, since the trajectory of the intermediate transfer belt with respect to the black image carrier is different between the color mode and the monochrome mode, the transfer nip between the black image carrier and the transfer roller contacting the black image carrier and the intermediate transfer belt The tension changes between the color mode and the monochrome mode, so that the transfer efficiency in the monochrome mode is deteriorated, and the intermediate transfer belt is likely to bend or vibrate.

In view of this, Japanese Patent Application Laid-Open No. H10-228561 proposes rotating the contact / separation mechanism of the color transfer roller about the axis of the backup roller for stabilizing the nip of the transfer roller.
Japanese Patent Laying-Open No. 2005-062642

  However, in the configuration proposed in Patent Document 1, a separation mechanism that separates the transfer roller and the intermediate transfer belt from the color image carrier in the monochrome mode has a backup roller, a link member that holds the backup roller, and swings the link member. Since the cam mechanism is configured to be complicated, the mechanism is complicated.

  Accordingly, an object of the present invention is to provide a transfer unit capable of simplifying a separation mechanism for separating the transfer belt and the image carrier in the monochrome mode, and an image forming apparatus including the transfer unit. .

  Further, the configuration disclosed in Patent Document 1 has a problem in that the shape change of the intermediate transfer belt is large when the transfer roller and the intermediate transfer belt are separated from the color image carrier in the monochrome mode, and the load on the tension roller is large. . Further, when the intermediate transfer belt is separated from the color image carrier, the number of members for holding the intermediate transfer belt is reduced. Therefore, it is difficult to stably convey the intermediate transfer belt in the monochrome mode. In order to prevent contact with the two, there is also a problem that it is necessary to ensure a large separation distance between the two.

  Accordingly, another object of the present invention is to reduce the load on the tension roller by suppressing the change in the shape of the transfer belt in the color mode and the monochrome mode, and to reduce the load on the transfer roller and the image carrier in the monochrome mode. It is an object of the present invention to provide a transfer unit capable of reliably separating the image forming apparatus 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 fixed 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 in which the formed monochrome toner image is transferred 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, in the monochrome mode, the drum unit that holds the image carrier so that the transfer belt and the transfer roller are separated from the color image carrier. Characterized in that to perform the operation al.

  According to a second aspect of the present invention, in the first aspect of the present invention, the transfer roller that contacts the color image carrier is pressed by a pressing member in the monochrome mode to be separated from the color image carrier, and the transfer belt. The movable roller around which is wound is moved.

  According to a third aspect of the present invention, in the second aspect of the present invention, the shape of the transfer belt in the monochrome mode is determined by a driving roller, a tension roller, two fixed rollers, and a movable roller.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the pressing member presses the transfer roller together with the transfer belt in the monochrome mode to separate them from the color image carrier. .

  The invention according to claim 5 is the invention according to any one of claims 2 to 4, wherein the pressing member presses the transfer roller or the transfer belt through a pulley or a low friction member in the monochrome mode. And

  According to a sixth aspect of the present invention, in the fourth or fifth aspect of the invention, the shape of the transfer belt in the monochrome mode is determined by a driving roller, a tension roller, three fixed rollers, and the pressing member.

  According to a seventh aspect of the invention, an image forming apparatus includes the transfer unit according to any one of the first to sixth aspects.

  According to the present invention, the separation mechanism is configured by the pressing member that operates in the monochrome mode and separates the transfer roller and the transfer belt from the color image carrier, and the separation mechanism is provided on the drum unit side. The unit is simplified.

  In addition, since the shape of the transfer belt is determined by a driving roller, a fixed roller, a movable roller, a tension roller, or a plurality of pressing members, a change in the shape of the transfer belt in the color mode and the monochrome mode can be suppressed to a small level. The load on the roller is reduced, and the transfer belt and the color image carrier in the monochrome mode are reliably separated.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
1 and 2 are cross-sectional views of a main part of an image forming apparatus including a transfer unit according to Embodiment 1 of the present invention, FIG. 3 is a partially enlarged detail view of FIG. 2, and FIG. 1 is a state in a color mode. FIG. 2 shows the 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, primary chargers 3a, 3b, 3c, and 3d arranged around the photosensitive drums 2a, 2b, 2c, and 2d. 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d as primary charging means, and drum cleaning devices 6a, 6b, 6c, 6d are provided.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in the direction of the arrow (counterclockwise) in the figure by a driving device (not shown). The primary chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  The developing devices 4a to 4d contain yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (Bk) toner, respectively, and are formed on the photosensitive drums 2a to 2d. Each color latent image is developed by attaching toner of each color to the electrostatic latent image and visualized as a toner image of each color.

  The transfer rollers 5a to 5d as primary charging means are disposed so as to be able to contact the photosensitive drums 2a to 2d via an endless intermediate transfer belt 7 at each primary transfer portion. Here, the transfer rollers 5a to 5d and the intermediate transfer belt 7 constitute a transfer unit according to the present invention. The intermediate transfer belt 7 includes a drive roller 8, a fixed roller 9, a movable roller 10, a tension roller 11, and a fixed roller. (Secondary transfer opposing roller) 12 is stretched between the photosensitive drums 2 a to 2 d so as to be able to run on the lower surface side, and the transfer rollers 5 a to 5 d are arranged inside the intermediate transfer belt 7. The photosensitive drums 2a to 2d are pressed with a predetermined pressure via the intermediate transfer belt 7. The fixed roller 12 is in contact with the secondary transfer roller 13 via the intermediate transfer belt 7 in the secondary transfer portion. As a material for the intermediate transfer belt 7, a derivative resin such as polycarbonate, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), or the like is selected.

  Incidentally, the transfer rollers 5a to 5d are rotatably supported by the bearing 14 and are urged by the spring 15 toward the photosensitive drums 2a to 2d. In the color mode shown in FIG. 1, all the transfer rollers 5 a to 5 d are pressed against the photosensitive drums 2 a to 2 d through the intermediate transfer belt 7 with a predetermined pressure. The tension roller 11 is pressed against the intermediate transfer belt 7 by a spring 16 to apply a predetermined tension to the intermediate transfer belt 7.

  A belt cleaning device 17 is provided on the downstream side of the secondary transfer portion of the transfer unit.

  Thus, in the present embodiment, a plurality of separation pressing members 18 are provided in the drum unit that holds the photosensitive drums 2a to 2d. These pressing members 18 are provided so as to be movable up and down in correspondence with the color photosensitive drums 2a to 2c except for the black photosensitive drum 2d, and move downward in the monochrome mode shown in FIG. The bearing rollers 14 to 5c are pressed to separate the transfer rollers 5a to 5c and the intermediate transfer belt 7 from the color photosensitive drums 2a to 2c.

  On the other hand, a conveyance belt 19 is disposed below the transfer unit in the main body of the image forming apparatus and downstream of the secondary transfer portion (left side in FIG. 1), and further, a fixing device 20 is provided downstream thereof. It has been.

  The fixing device 20 includes a heating roller 21, a fixing roller 22 disposed opposite to the heating roller 21, an endless fixing belt 23 stretched between the heating roller 21 and the fixing roller 22, and the fixing roller 20. A pressure roller 24 pressed against the fixing roller 22 with a belt 23 interposed therebetween is provided.

  On the other hand, a paper feed cassette (not shown) in which a plurality of sheets are stacked and accommodated is detachably installed at the bottom of the image forming apparatus main body. In the image forming apparatus main body, a transport path L1 extending from the paper feed cassette toward the secondary transfer unit is provided, and a plurality of paper feed rollers 25 are provided in the middle of the transport path L1. ing. A registration roller 26 is disposed near the secondary transfer portion of the transport path L1.

  Further, a conveyance path L2 extends from the fixing device 20 to a paper discharge tray (not shown) outside the apparatus main body, and a conveyance roller 27 and a paper discharge roller 28 are provided in the middle thereof.

  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 5 a to 5 d are pressed against the photosensitive drums 2 a to 2 d via the intermediate transfer belt 7.

  When an image start signal is issued in the above state, each of the photosensitive drums 2a to 2d is rotated and driven at a predetermined process speed in the arrow direction (counterclockwise direction) in FIG. 1 in each of the image forming units 1Y, 1M, 1C, and 1Bk. These photosensitive drums 2a to 2d are uniformly charged by primary chargers 3a to 3d. 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 the developing device 4a 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 5a at the primary transfer portion between the photosensitive drum 2a and the transfer roller 5a. Primary transferred onto.

  The intermediate transfer belt 7 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 7 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 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, in accordance with the timing at which the front end of the full-color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion between the secondary transfer counter roller 11 and the secondary transfer roller 12, the sheet feed cassette (not shown) moves to the transport path L1. Is fed to the secondary transfer section by the registration roller 26. Then, in the secondary transfer portion, the full color toner image on the intermediate transfer belt 7 is secondarily transferred collectively onto the paper by the action of the secondary transfer roller 12. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 17, and the intermediate transfer belt 7 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 20, and the full-color toner image is heated and pressed in the fixing device 20 and thermally fixed on the surface of the sheet. The sheet on which the toner image is fixed is conveyed along the conveyance path L2 by the conveyance roller 27, and is discharged to a discharge tray (not shown) outside the apparatus main body by the discharge roller 28.

  On the other hand, when the monochrome mode is selected, the pressing member 18 provided on the drum unit side moves downward to press the bearings 14 of the transfer rollers 5a to 5c downward as shown in FIG. The transfer rollers 5a to 5c are separated from the color photosensitive drums 2a to 2c. At the same time, the movable roller 10 moves downward. Therefore, the intermediate transfer belt 7 is reliably separated from the color photosensitive drums 2a to 2c. Accordingly, in this monochrome mode, the transfer roller 5d and the intermediate transfer belt 7 are in contact with the 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 7 at the primary transfer portion, and the black toner image transferred onto the intermediate transfer belt 7 is supplied to the secondary transfer portion at an appropriate timing. Secondary transferred onto paper. Then, the paper on which the black toner image is transferred is conveyed to the fixing device 20, where the black toner image is heated and pressurized and thermally fixed on the surface of the paper, and the black toner image is fixed. The paper is discharged by a paper discharge roller 28 to a paper discharge tray (not shown) outside the apparatus main body.

  As described above, in this embodiment, the separation mechanism is configured by the pressing member 18 that operates in the monochrome mode and separates the transfer rollers 5a to 5c and the intermediate transfer belt 7 from the color photosensitive drums 2a to 2c. Is provided on the drum unit side, the separation mechanism and the transfer unit are simplified.

  Further, the shape of the intermediate transfer belt 7 is determined by the driving roller 8, the fixed roller 9, the movable roller 10, the tension roller 11, and the fixed roller (secondary transfer counter roller) 12. Therefore, in the color mode and the monochrome mode, A change in the shape of the intermediate transfer belt 7 is suppressed to be small, the load on the tension roller 11 is reduced, and the intermediate transfer belt 7 and the color photosensitive drums 2a to 2c are reliably separated in the monochrome mode.

  By the way, in this embodiment, even if the transfer rollers 5a to 5c and the intermediate transfer belt 7 are separated from the photosensitive drums 2a to 2c in the monochrome mode, the intermediate transfer belt 7 rotates in contact with the transfer rollers 5a to 5c. Therefore, the transfer rollers 5a to 5c also rotate. Therefore, as shown in FIG. 4, a pulley 29 is rotatably supported at the tip of the pressing member 18, and this pulley 29 is pressed against the shaft portion of the transfer roller 5a (5b, 5c) to rotate the pulley 29. You may make it let it. Note that a low friction member may be used in place of the pulley 29.

  Further, as shown in FIG. 5, if the transfer roller 5a (5b, 5c) is pushed down by the pressing member 18 until it is separated from the intermediate transfer belt 7, the rotation of the transfer roller 5a (5b, 5c) is stopped. The member 18 can be brought into direct contact with the shaft portion of the transfer roller 5a (5b, 5c) to push down the transfer roller 5a (5b, 5c).

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 6 is a schematic view showing a state of the transfer unit according to the second embodiment of the present invention in the monochrome mode, and FIG. 7 is a partially enlarged detail view of FIG. 6. In these figures, FIGS. The same elements as those described above are denoted by the same reference numerals, and repetitive description thereof will be omitted below.

  In the present embodiment, the intermediate transfer belt 7 is stretched between the driving roller 8, the three fixed rollers 9, 30, 12 and the tension roller 11, and each tip portion of the pressing member 18 constituting the separation mechanism. A pulley 29 is rotatably supported on the pulley.

  Thus, in the monochrome mode, the pressing member 18 provided on the drum unit side moves downward, and the pulley 29 is pivotally supported at the tip of the pressing member 18 and rotates while contacting the outer periphery of the transfer rollers 5a to 5c. The transfer rollers 5a to 5c are pushed down together with the belt 7 to separate them from the color photosensitive drums 2a to 2c.

  Accordingly, in this monochrome mode, only in the black image forming unit 1Bk, the transfer roller 5d and the intermediate transfer belt 7 come into contact with the photosensitive drum 2d, and only the black image forming unit 1Bk operates to form other yellow, magenta and cyan images. Units 1Y, 1M, and 1C are suspended. Therefore, the black toner image formed on the photosensitive drum 2d in the black image forming unit 1Bk is primarily transferred onto the intermediate transfer belt 7 in the primary transfer portion, and thereafter a black image is formed in the same manner as described above.

  Thus, also in the present embodiment, the separation mechanism is configured by the pressing member 18 that operates in the monochrome mode and separates the transfer rollers 5a to 5c and the intermediate transfer belt 7 from the color photosensitive drums 2a to 2c. Is provided on the drum unit side, the separation mechanism and the transfer unit are simplified.

  The shape of the intermediate transfer belt 7 is determined by the driving roller 8, the three fixed rollers 9, 30, 12, the tension roller 11 and the three pressing members 18. The shape of the intermediate transfer belt 7 in the color mode and the monochrome mode is determined. Since the change in shape is suppressed to a small level, the load on the tension roller 11 is reduced and the intermediate transfer belt 7 and the color photosensitive drums 2a to 2c are reliably separated in the monochrome mode.

FIG. 3 is a cross-sectional view (color mode) of a main part of the image forming apparatus including the transfer unit according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view (monochrome mode) of a main part of the image forming apparatus including the transfer unit according to the first embodiment of the present invention. FIG. 3 is a partially enlarged detail view of FIG. 2. It is a fragmentary sectional view which shows the modification of the transfer unit which concerns on Embodiment 1 of this invention. It is a fragmentary sectional view which shows the modification of the transfer unit which concerns on Embodiment 1 of this invention. FIG. 10 is a schematic diagram of a transfer unit according to a second embodiment of the present invention in a monochrome mode. FIG. 7 is a partially enlarged detail view of FIG. 6.

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 Primary charger 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Drum cleaning device 7 Intermediate transfer belt 8 Drive roller 9 Fixed roller 10 Movable roller 11 Tension roller 12 Fixed roller (secondary transfer counter roller)
DESCRIPTION OF SYMBOLS 13 Secondary transfer roller 14 Bearing 15,16 Spring 17 Belt cleaning apparatus 18 Press member 19 Conveyance belt 20 Fixing apparatus 21 Heating roller 22 Fixing roller 23 Fixing belt 24 Pressure roller 25 Paper feed roller 26 Registration roller 27 Conveyance roller 28 Paper discharge Roller 29 Pulley 30 Fixed roller L1, L2 Transport path

Claims (7)

An endless transfer belt stretched between at least a driving roller, a tension roller, and a fixed roller; a plurality of monochrome image-bearing bodies; and a plurality of image carriers that are in contact with the image-bearing bodies 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 transfer unit characterized in that the transfer belt and the transfer roller in the monochrome mode are separated from the color image carrier by an operation from a drum unit that holds the image carrier.   The transfer roller in contact with the color image carrier is pressed by a pressing member in the monochrome mode to be separated from the color image carrier and the movable roller around which the transfer belt is wound is moved. Item 2. The transfer unit according to Item 1.   3. The transfer unit according to claim 2, wherein the shape of the transfer belt in the monochrome mode is determined by a driving roller, a tension roller, two fixed rollers, and a movable roller.   3. The transfer unit according to claim 2, wherein in the monochrome mode, the pressing member presses the transfer roller together with the transfer belt to separate them from the color image carrier.   The transfer unit according to claim 2, wherein the pressing member presses the transfer roller or the transfer belt via a pulley or a low friction member in the monochrome mode.   6. The transfer unit according to claim 4, wherein the shape of the transfer belt in the monochrome mode is determined by a driving roller, a tension roller, three fixed rollers, and the pressing member.   An image forming apparatus comprising the transfer unit according to claim 1.

Images