JP2012159571A - Inter mediate transfer unit and color image forming device having the same - Google Patents

Abstract

An intermediate transfer unit and a color image forming apparatus including the intermediate transfer unit are provided that can switch the arrangement of a primary transfer roller and a backup roller with a simple configuration and reduce a load applied to a position control member.
Sliders 37a and 37b are supported on side frames 31 and 32 of an intermediate transfer unit 30 so as to be slidable in a horizontal direction. Both ends of the rotation shafts of the primary transfer rollers 6a to 6d and the backup roller 33 are rotatably supported by bearing holders 38a to 38e, and the bearing holders 38a to 38e are supported so as to be movable in the vertical direction with respect to the sliders 37a and 37b. Has been. The bearing holders 38a to 38d of the primary transfer rollers 6a to 6d are disposed between the holder body 55, the bearing portion 57 supported so as to be slidable up and down with respect to the holder body 55, and the holder body 55 and the bearing portion 57. The coil spring 60 is made up of.
[Selection] Figure 3

Description

  In the present invention, a plurality of image forming portions are arranged along an endless intermediate transfer belt, and toner images formed by sequentially laminating toner images of respective colors on the intermediate transfer belt are transferred onto a recording medium at a time. The present invention relates to an intermediate transfer unit used in an intermediate transfer type color image forming apparatus and a tandem type color image forming apparatus including the intermediate transfer unit.

  Conventionally, various image forming apparatuses have been proposed. Among them, there is a tandem type color image forming apparatus that forms a full color image by sequentially superimposing toner images of respective colors by a plurality of image forming units. Further, the tandem color image forming apparatus includes a direct transfer method for transferring the toner image formed by each image forming unit onto a recording medium conveyed by an endless conveying belt, and a plurality of image forming units. There is an intermediate transfer system in which toner images are sequentially superimposed (primary transfer) on an endless intermediate transfer belt and then transferred onto a recording medium (secondary transfer) at a time.

  In the intermediate transfer tandem color image forming apparatus, image formation using only black toner is performed in a monochrome mode for outputting a monochrome image. In this monochrome mode, if the image carrier of each of the yellow, magenta, and cyan image forming portions other than black is kept in contact with the intermediate transfer belt, the intermediate transfer belt is brought into contact with the yellow, magenta, and cyan image carrier. And the intermediate transfer belt may have an unnecessarily large driving torque.

  In view of this, a method has been proposed in which the image carrier of the yellow, magenta, and cyan image forming unit other than black is separated from the intermediate transfer belt in the monochrome mode. For example, in Patent Documents 1 and 2, there is a color mode in which a primary transfer roller is pressed against a yellow, magenta, cyan, and black image carrier with an intermediate transfer belt sandwiched using a single drive source, and only a black image carrier. An image forming apparatus is disclosed that can switch between a monochrome mode in which a primary transfer roller is pressed against an intermediate transfer belt and the other primary transfer rollers are separated, and a standby mode in which all primary transfer rollers are separated. .

  Patent Document 3 discloses an image forming apparatus that can be switched to four modes including a belt cleaning mode in addition to the above three modes.

Japanese Patent No. 3526798 Japanese Patent No. 3584706 Japanese Patent No. 4339575

  In both methods of Patent Documents 1 and 2, a spring member is attached to a rotating arm that supports the primary transfer roller, and the biasing force of the spring member always acts on a slider (moving member) that displaces the primary transfer roller. is doing. Also in Patent Document 3, the primary transfer roller is retracted by the cam surface of the transfer roller driving member pushing up the support member of the primary transfer roller against the spring biasing force. For this reason, the load applied to the slider at the time of mode switching increases, and a high torque drive source is required, and the slider and the rotating arm may be deformed or damaged.

  Further, when a backup roller is provided in the vicinity of the upstream side of the primary transfer roller on the most upstream side with respect to the traveling direction of the intermediate transfer belt, it is necessary to displace the backup roller at a timing different from that of the primary transfer roller at the time of mode switching. However, Patent Documents 1 to 3 do not describe switching of the arrangement of the backup roller.

  In view of the above problems, the present invention switches an arrangement of a primary transfer roller and a backup roller with a simple configuration and can also reduce a load applied to a position control member, and a color image forming apparatus including the intermediate transfer unit The purpose is to provide.

  In order to achieve the above object, the present invention provides an endless intermediate transfer belt that moves along a plurality of image forming units, a drive roller that rotates the intermediate transfer belt, and a rotation that follows the intermediate transfer belt. And a tension roller that applies a predetermined tension to the intermediate transfer belt, a unit main body that rotatably supports the drive roller and the tension roller, and the image forming unit disposed between the intermediate transfer belts. A plurality of primary transfer rollers that are arranged opposite to an image carrier and transfer a toner image formed on the image carrier onto the intermediate transfer belt, and are located on the most upstream side with respect to the traveling direction of the intermediate transfer belt. A backup roller disposed upstream of the primary transfer roller and pressing the intermediate transfer belt toward the image carrier; and the primary transfer roller -And a plurality of bearing holders that rotatably support both ends of the rotating shaft of the backup roller, and supported by the unit body so as to be reciprocally movable in parallel with the traveling direction of the intermediate transfer belt, In the intermediate transfer unit, comprising: a pair of sliders that support a plurality of bearing holders so as to be able to reciprocate vertically with respect to the traveling direction of the intermediate transfer belt; and a slider drive mechanism that reciprocates the sliders, the primary transfer roller The bearing holder is slidably supported by the slider, a bearing portion slidably supported by the holder body, and an attachment disposed between the bearing portion and the holder body. It is characterized by comprising a force member.

  According to the present invention, in the intermediate transfer unit configured as described above, the slider is moved back and forth so that all the primary transfer roller and the backup roller are in contact with the intermediate transfer belt, and the black image forming unit is arranged. Can be switched between a monochrome mode in which only the primary transfer roller disposed opposite to the image bearing member in contact with the intermediate transfer belt and a standby mode in which all the primary transfer rollers and backup rollers are separated from the intermediate transfer belt. It is characterized by that.

  According to the present invention, in the intermediate transfer unit configured as described above, a plurality of lower side portions, an upper step portion parallel to the lower step portion, and an inclined portion connecting the lower step portion and the upper step portion are provided on a side surface of the slider. Step holder ribs are formed, and the holder body is formed with a holding portion for slidably holding the step ribs, and the holding portions of the plurality of bearing holders are arranged in the lower step portion or the upper step portion. Thus, the arrangement of the primary transfer roller and the backup roller is switched to any one of a color mode, a monochrome mode, and a standby mode.

  According to the present invention, in the intermediate transfer unit having the above-described configuration, the slider can be switched to a belt cleaning mode in which only the backup roller is brought into contact with the intermediate transfer belt by reciprocating the slider.

  According to the present invention, in the intermediate transfer unit configured as described above, a plurality of lower side portions, an upper step portion parallel to the lower step portion, and an inclined portion connecting the lower step portion and the upper step portion are provided on a side surface of the slider. Step holder ribs are formed, and the holder body is formed with a holding portion for slidably holding the step ribs, and among the plurality of step ribs, an image carrier disposed in a black image forming portion Forming a retraction portion bent toward the upper step side on the lower step portion of the step rib held by the holding portion of the bearing holder that supports the primary transfer roller disposed opposite to the body, and forming a black image By disposing a holding part of the bearing holder that supports the primary transfer roller disposed opposite to the image carrier disposed in the part in the retracting part, the primary transfer roller and the It is characterized by switching the arrangement of the click-up roller in the belt cleaning mode.

  In the intermediate transfer unit configured as described above, the slider driving mechanism is driven by a single driving source.

  The present invention also provides an image forming apparatus on which the intermediate transfer unit having the above-described configuration is mounted.

  According to the first configuration of the present invention, the bearing holder of the primary transfer roller is configured such that the bearing portion is urged against the holder main body by the urging member, so that the primary transfer roller contacts the intermediate transfer belt. Sometimes the pressure of the primary transfer roller is generated. Therefore, when the primary transfer roller is separated from the intermediate transfer belt, the urging force of the urging member does not act on the slider or the bearing holder, so the load on the slider or the bearing holder is reduced when switching the arrangement of the primary transfer roller. An inexpensive low torque motor can be used as a drive source for the slider drive mechanism. Further, there is no possibility that the slider or the bearing holder is deformed or damaged.

  Also, according to the second configuration of the present invention, in the intermediate transfer unit of the first configuration, the slider can be reciprocated so that the color mode, the monochrome mode, and the standby mode can be switched. The primary transfer roller and backup roller are separated from the intermediate transfer belt to prevent the intermediate transfer belt from becoming dirty and the drive torque is increased, and in the standby mode, all primary transfer rollers and backup rollers are separated from the intermediate transfer belt to maintain tension. And the deformation and elongation of the intermediate transfer belt can be suppressed.

  According to the third configuration of the present invention, in the intermediate transfer unit having the second configuration, the arrangement of the primary transfer roller and the backup roller can be switched to three modes with a simple configuration. Further, since the step rib is sandwiched by the bearing holder sandwiching portion, the engagement between the slider and the bearing holder is difficult to disengage, and the arrangement of the primary transfer roller and the backup roller can be switched reliably.

  According to the fourth configuration of the present invention, in the intermediate transfer unit of the second configuration, the slider can be reciprocated to switch to a belt cleaning mode in which only the backup roller contacts the intermediate transfer belt. In the belt cleaning mode, only the backup roller is brought into contact with the intermediate transfer belt and pressed against the image carrier, and the surface of the image carrier can be cleaned simultaneously with the intermediate transfer belt while suppressing the driving torque of the intermediate transfer belt. it can.

  According to the fifth configuration of the present invention, in the intermediate transfer unit having the fourth configuration, the arrangement of the primary transfer roller and the backup roller can be switched to four modes with a simple configuration. Further, since the step rib is sandwiched by the bearing holder sandwiching portion, the engagement between the slider and the bearing holder is difficult to disengage, and the arrangement of the primary transfer roller and the backup roller can be switched reliably.

  According to the sixth configuration of the present invention, in the intermediate transfer unit having any one of the first to fifth configurations, the slider driving mechanism is driven by a single driving source, whereby the primary transfer roller and the backup are driven. Roller pressing or pressing release control can be simplified, and the cost of the intermediate transfer unit can be reduced.

  According to the seventh configuration of the present invention, by mounting the intermediate transfer unit having any one of the first to sixth configurations, the arrangement of the primary transfer roller and the backup roller is switched with a simple configuration, A low-cost image forming apparatus excellent in durability and capable of reducing the load applied to the position control member.

1 is a schematic side view showing the configuration of a tandem color image forming apparatus on which an intermediate transfer unit of the present invention is mounted. FIG. 2 is an external perspective view of the intermediate transfer unit according to the first embodiment of the present invention viewed from below. The perspective view which shows the roller evacuation mechanism in the intermediate transfer unit 30 of 1st Embodiment. The side view which looked at the slider 37a used for the intermediate transfer unit of 1st Embodiment from the inner side of the intermediate transfer unit 30 Partial enlarged view of the bearing holder 38a and the bearing holder 38e when the primary transfer roller 6a and the backup roller 33 are in contact with the intermediate transfer belt, as viewed from the inside of the intermediate transfer unit 30. Partial enlarged view of the bearing holder 38a and the bearing holder 38e when the primary transfer roller 6a and the backup roller 33 are separated from the intermediate transfer belt, as viewed from the inside of the intermediate transfer unit 30. Side view showing the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the intermediate transfer unit 30 of the first embodiment in the color mode. The perspective view which shows the operation state of the roller evacuation mechanism in the intermediate transfer unit 30 of the first embodiment in the monochrome mode. Side view showing arrangement of primary transfer rollers 6a to 6d and backup roller 33 in intermediate transfer unit 30 of the first embodiment in the monochrome mode. The perspective view which shows the operation state of the roller evacuation mechanism in the intermediate transfer unit 30 of the first embodiment in the standby mode. Side view showing the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the intermediate transfer unit 30 of the first embodiment in the standby mode. The side view which looked at the slider 37a used for the intermediate transfer unit of 2nd Embodiment of this invention from the inner side of the intermediate transfer unit 30 The perspective view which shows the operation state of the roller evacuation mechanism in the intermediate transfer unit 30 of 2nd Embodiment in belt cleaning mode. Side view showing arrangement of primary transfer rollers 6a to 6d and backup roller 33 in intermediate transfer unit 30 of the second embodiment in the belt cleaning mode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus on which the intermediate transfer unit of the present invention is mounted. Here, a tandem type color image forming apparatus is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (left side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). 1, an intermediate transfer belt 8 that rotates counterclockwise is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer sheet P as an example of a recording medium, and further fixed on the transfer sheet P in the fixing unit 13 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d clockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip portion with the roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  Then, by applying a predetermined transfer voltage to the primary transfer rollers 6 a to 6 d, cyan, magenta, yellow, and black toner images on the photosensitive drums 1 a to 1 d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream tension roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 is counterclockwise as the drive roller 11 is rotated by a drive motor (not shown). When rotation is started, the transfer paper P is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. Then, the full color image on the intermediate transfer belt 8 is transferred onto the transfer paper P. The transfer paper P onto which the toner image has been transferred passes through the paper transport path 18 and is transported to the fixing unit 13.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressurized by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper P, thereby forming a predetermined full color image. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when forming images on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 13 is once transported in the direction of the discharge roller 15, and the discharge roller after the rear end of the transfer paper P has passed through the branch portion 14. 15 is rotated in the reverse direction and the conveyance direction of the branching section 14 is switched, so that it is distributed from the rear end of the transfer paper P to the double-sided conveyance path 20 and re-conveyed to the secondary transfer nip part with the image surface reversed. . Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 13 to fix the toner image. , And discharged to the discharge tray 17.

  2 is an external perspective view of the intermediate transfer unit according to the first embodiment of the present invention mounted on the image forming apparatus shown in FIG. 1 as viewed from below, and FIG. 3 is an inside view of the intermediate transfer unit according to the first embodiment. It is a perspective view which shows the roller evacuation mechanism. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  The intermediate transfer unit 30 includes a unit main body 34 composed of two side frames 31 and 32 and an upper frame (not shown), primary transfer rollers 6a to 6d supported between the side frames 31 and 32, and tension. The roller 10, the driving roller 11, the backup roller 33, the guide roller 34, and an endless intermediate transfer belt 8 stretched around these rollers are included. In addition, a pair of handles (gripping portions) 35 a and 35 b are provided at the drawer side end portion (right end portion in FIG. 2) of the intermediate transfer unit 30.

  Sliders 37a and 37b are supported on the side frames 31 and 32 so as to be slidable in the horizontal direction. Both ends of the rotation shafts of the primary transfer rollers 6a to 6d and the backup roller 33 are rotatably supported by bearing holders 38a to 38e, and the bearing holders 38a to 38e are supported so as to be movable in the vertical direction with respect to the sliders 37a and 37b. Has been. Further, the tension roller 10, the drive roller 11, and the guide roller 34 are rotatably supported by the side frames 31, 32.

  A gear box 40 is installed inside the intermediate transfer unit 30, and a motor 41 is accommodated in the gear box 40. A first worm gear 42 is fixed to the drive output shaft of the motor 41, and the driving force of the motor 41 is transmitted from the first worm gear 42 to the worm wheel 43, the two-stage gear 44, and the second worm gear 45. A shaft 46 is fixed so as to pass through the second worm gear 45, and pinion gears 47 a and 47 b are fixed to both ends of the shaft 46.

  The pinion gears 47a and 47b are disposed at positions that mesh with the rack 48 formed on the lower surfaces of the sliders 37a and 37b, respectively, and the sliders 37a and 37b can be reciprocated in the horizontal direction by rotating the motor 41 forward and backward. It has become. The motor 41, the first worm gear 42, the worm wheel 43, the two-stage gear 44, the second worm gear 45, the shaft 46, and the pinion gears 47a and 47b constitute a slider driving mechanism for reciprocating the sliders 37a and 37b.

  4 is a side view of the slider 37a used in the intermediate transfer unit according to the first embodiment as viewed from the inside of the intermediate transfer unit 30. FIG. The slider 37b has the same configuration as the slider 37a except that it is bilaterally symmetric. On the inner surface of the slider 37a, four step ribs 50 to 53 including a first step rib 50, a second step rib 51, a third step rib 52, and a fourth step rib 53 are formed. Each step rib 50-53 includes one lower step portion 50a-53a, one upper step portion 50b-53b, and one inclined portion 50c-53c connecting the corresponding lower step portion 50a-53a and the upper step portion 50b-53b. It consists of and.

  5 and 6 are partially enlarged views of the bearing holder 38a of the primary transfer roller 6a and the bearing holder 38e of the backup roller 33 as viewed from the inside of the intermediate transfer unit 30. FIG. 5 shows a state where the primary transfer roller 6a and the backup roller 33 are in contact with the intermediate transfer belt 8, and FIG. 6 shows a state where the primary transfer roller 6a and the backup roller 33 are separated from the intermediate transfer belt 8. Yes. Further, the bearing holders 38b to 38d have the same configuration as that of the bearing holder 38a, and thus the description thereof is omitted.

  The bearing holder 38 a includes a holder main body 55, a bearing portion 57 that is slidably supported with respect to the holder main body 55, and a coil spring 60 that is disposed between the holder main body 55 and the bearing portion 57. The bearing portion 57 is biased in a direction (downward) away from the holder body 55 by the biasing force of the coil spring 60. The bearing holder 38e is configured such that the bearing portion 57 is fixed to the lower end position with respect to the holder main body 55, and the coil spring 60 is not provided.

  The holder main body 55 is formed with a holding portion 55a formed by arranging a pair of V-shaped ribs so that the apexes face each other. The bearing holders 38a and 38e are slidably supported by the sliders 37a and 37b by arranging the bearing holders 38a and 38e so that the clamping portion 55a sandwiches the first step ribs 50 of the sliders 37a and 37b from above and below. .

  Similarly, the bearing holder 38b of the primary transfer roller 6b is a second step rib 51, the bearing holder 38c of the primary transfer roller 6c is a third step rib 52, and the bearing holder 38d of the primary transfer roller 6d is a fourth step rib 53. Each is supported slidably.

  Next, operations of the primary transfer rollers 6a to 6d and the backup roller 33 in the intermediate transfer unit 30 of the first embodiment will be described. FIG. 7 is a side view showing the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the color mode for outputting a color image. Here, the tension roller 10, the drive roller 11, the guide roller 34, and the slider 37b on the front side of the apparatus are not shown, but the arrangement of the rollers and the slider 37b in the color mode is shown in FIG. Therefore, it demonstrates, referring FIG. 3 as needed.

  In the color mode, four primary transfer rollers 6a to 6d are brought into pressure contact with the photosensitive drums 1a to 1d via the intermediate transfer belt 8 in order to form images in the four image forming portions Pa to Pd. Further, the backup roller 33 needs to be disposed at a position where the intermediate transfer belt 8 is pressed in the direction of the photosensitive drums 1a to 1d.

  Therefore, by rotating the motor 41 (see FIG. 3) in a predetermined direction and sliding the sliders 37a and 37b in the right direction, the bearing holders 38a to 38e are moved to the lower step portions 50a of the step ribs 50 to 53 as shown in FIG. ~ 53a. At this time, the primary transfer rollers 6a to 6d and the backup roller 33 are in contact with the intermediate transfer belt 8, but the compression length of the coil spring 60 in the bearing holders 38a to 38d is reduced by the drag from the intermediate transfer belt 8 as shown in FIG. Therefore, a gap is formed between the holder main body 55 and the bearing portion 57, and the primary transfer rollers 6a to 6d are pressed against the photosensitive drums 1a to 1d via the intermediate transfer belt 8 with a predetermined pressure. Further, the backup roller 33 presses the intermediate transfer belt 8 downward at a predetermined position.

  FIG. 8 is a perspective view showing an operation state of the roller retracting mechanism in the intermediate transfer unit 30 in the monochrome mode for outputting a monochrome image, and FIG. 9 is an arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the monochrome mode. FIG.

  In the monochrome mode, since image formation is performed using only the black image forming portion Pd, the primary transfer roller 6d needs to be in pressure contact with the photosensitive drum 1d via the intermediate transfer belt 8.

  Therefore, by rotating the motor 41 in the reverse direction and sliding the sliders 37a and 37b to the left by a predetermined amount from the state of FIG. 7, the bearing holders 38a to 38c and 38e are moved to the first step rib 50 as shown in FIG. The third step rib 52 moves from the lower step portions 50a to 52a through the inclined portions 50c to 52c to the upper step portions 50b to 52b. On the other hand, the bearing holder 38 d remains on the lower step portion 53 a of the fourth step rib 53.

  Thereby, since the primary transfer rollers 6a to 6c and the backup roller 33 are separated from the intermediate transfer belt 8, it is possible to prevent the intermediate transfer belt 8 from being soiled by residual toner on the surface of the photosensitive drums 1a to 1c. Further, there is no possibility that the driving torque of the driving roller 11 that rotates the intermediate transfer belt 8 unnecessarily increases.

  FIG. 10 is a perspective view showing the operating state of the roller retracting mechanism in the intermediate transfer unit 30 in the standby mode in which no image is output. FIG. 11 shows the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the standby mode. FIG.

  In the standby mode, the motor 41 is further rotated in the reverse direction and the sliders 37a and 37b are slid leftward by a predetermined amount from the state shown in FIG. 9, whereby the bearing holder 38d is inclined from the lower step portion 53a of the fourth step rib 53. It passes through 53c and moves to the upper stage 53b. As a result, as shown in FIG. 11, all the bearing holders 38a to 38e are arranged in the upper stage portions 50b to 53b.

  As a result, the primary transfer rollers 6 a to 6 d and the backup roller 33 are separated from the intermediate transfer belt 8, so that the tension applied to the intermediate transfer belt 8 is loosened, and deformation and elongation of the intermediate transfer belt 8 are prevented. Can do.

  According to the present embodiment, since the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the three modes of the color mode, the monochrome mode, and the standby mode can be changed using the single motor 41, the primary transfer rollers 6a to 6a. 6d and the control for pressing or releasing the backup roller 33 can be simplified, and the cost of the image forming apparatus 100 can be reduced.

  Further, the bearing holders 38 a to 38 d of the primary transfer rollers 6 a to 6 d have a configuration in which the bearing portion 57 is urged against the holder main body 55 by the coil spring 60, so that the primary transfer rollers 6 a to 6 d are attached to the intermediate transfer belt 8. When contact is made, the compression length of the coil spring 60 changes, and the pressure contact force of the primary transfer rollers 6a to 6d is generated.

  That is, when the primary transfer rollers 6a to 6d are separated from the intermediate transfer belt 8, the urging force of the coil spring 60 does not act on the sliders 37a and 37b and the bearing holders 38a to 38d. Therefore, the load applied to the sliders 37a and 37b and the bearing holders 38a to 38d when switching between the modes is reduced, and an inexpensive low-torque motor 41 can be used. Further, there is no possibility that the sliders 37a and 37b and the bearing holders 38a to 38d are deformed or damaged.

  FIG. 12 is a side view of the slider 37a used in the intermediate transfer unit according to the second embodiment of the present invention when viewed from the inside of the intermediate transfer unit 30. FIG. In the present embodiment, a retracting portion 61 is formed in the lower step portion 53a of the fourth step rib 53 of the slider 37a. In addition, the structure of the other part of the slider 37a and the structure of the bearing holders 38a-38e are the same as that of 1st Embodiment shown in FIGS. The slider 37b has the same configuration as the slider 37a except that it is bilaterally symmetric.

  FIG. 13 is a perspective view showing an operation state of the roller retracting mechanism in the intermediate transfer unit 30 of the second embodiment in the belt cleaning mode in which the surface of the intermediate transfer belt 8 is cleaned during non-image formation. FIG. 6 is a side view showing the arrangement of primary transfer rollers 6a to 6d and a backup roller 33 in a cleaning mode. FIG. The arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the color mode, the monochrome mode, and the standby mode is the same as that in the first embodiment shown in FIGS.

  In the belt cleaning mode, the bearing holders 38a to 38c are moved to the first step by rotating the motor 41 backward from the color mode state (see FIG. 7) and sliding the sliders 37a and 37b to the left by a predetermined amount. The rib 50 to the third step rib 52 move from the lower step portions 50a to 52a to the upper step portions 50b to 52b through the inclined portions 50c to 52c. Further, the bearing holder 38 d moves to the retracting portion 61 formed in the lower step portion 53 a of the fourth step rib 53. On the other hand, the bearing holder 38e remains on the lower step portion 50a of the first step rib 50.

  Accordingly, the primary transfer rollers 6a to 6d are separated from the intermediate transfer belt 8 and the backup roller 33 presses the intermediate transfer belt 8 in the direction of the photosensitive drums 1a to 1d. Therefore, the backup roller 33 and the guide roller 34 (see FIG. 3). ), The intermediate transfer belt 8 is pressed against the photosensitive drums 1a to 1d.

  Accordingly, since the toner remaining on the surfaces of the photosensitive drums 1a to 1d moves to the intermediate transfer belt 8 side, the surfaces of the photosensitive drums 1a to 1d can be cleaned together with the intermediate transfer belt 8. Further, since the primary transfer rollers 6 a to 6 d are separated from the intermediate transfer belt 8, the driving torque of the driving roller 11 that rotates the intermediate transfer belt 8 can also be reduced.

  Then, by sliding the sliders 37a and 37b to the left by a predetermined amount from the state of FIG. 14, the bearing holder 38d moves from the retracting portion 61 to the lower step portion 53a again. Further, the bearing holder 38e moves from the lower step portion 50a to the upper step portion 50b. Thereby, the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 is switched to the monochrome mode shown in FIG. Further, by sliding the sliders 37a and 37b to the right by a predetermined amount from the state of FIG. 14, the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 is switched to the color mode shown in FIG.

  According to the present embodiment, the arrangement of the primary transfer rollers 6a to 6d and the backup roller 33 in the four modes of the color mode, the monochrome mode, the standby mode, and the belt cleaning mode can be changed using the single motor 41. The pressing or pressing release control of the transfer rollers 6a to 6d and the backup roller 33 can be simplified, and the cost of the image forming apparatus 100 can be reduced.

  Similarly to the first embodiment, the bearing holders 38a to 38d of the primary transfer rollers 6a to 6d are configured such that the bearing portion 57 is urged against the holder main body 55 by the coil spring 60, and thus the primary transfer roller 6a. When -6d is away from the intermediate transfer belt 8, the urging force of the coil spring 60 does not act on the sliders 37a, 37b and the bearing holders 38a-38d. Therefore, the load applied to the sliders 37a and 37b and the bearing holders 38a to 38d when switching between the modes is reduced, and an inexpensive low-torque motor 41 can be used. Further, there is no possibility that the sliders 37a and 37b and the bearing holders 38a to 38d are deformed or damaged.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the arrangement order of the image forming units Pa to Pd corresponding to each color of cyan, magenta, yellow, and black can be arbitrarily set. Although a color printer has been described as an example here, the present invention can be applied to various image forming apparatuses using an intermediate transfer belt such as a color copying machine and a facsimile.

  The present invention relates to a tandem provided with a plurality of image forming units including an image carrier and a developing device, and an endless intermediate transfer belt which is stretched around a plurality of rollers including a driving roller and moves along each image forming unit. It can be used for a color image forming apparatus of the type. By utilizing the present invention, an inexpensive low-torque motor can be used as a drive source for the slider drive mechanism, and an intermediate transfer unit that is low in cost and excellent in durability, with no risk of deformation or breakage of the slider or bearing holder, and An image forming apparatus can be provided.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
6a to 6d Primary transfer roller 8 Intermediate transfer belt 9 Secondary transfer roller 10 Tension roller 11 Drive roller 20 Tension roller 30 Intermediate transfer unit 33 Backup roller 34 Guide roller 37a, 37b Slider 38a-38e Bearing holder 41 Motor (drive source, slider) Drive mechanism)
42 1st worm gear (slider drive mechanism)
43 Worm wheel (slider drive mechanism)
44 Two-stage gear (slider drive mechanism)
45 Second worm gear (slider drive mechanism)
46 Shaft (Slider drive mechanism)
47a, 47b Pinion gear (slider drive mechanism)
50 First step rib 51 Second step rib 52 Third step rib 53 Fourth step rib 50a to 53a Lower step portion 50b to 53b Upper step portion 50c to 53c Inclination portion 55 Holder body 55a Holding portion 57 Bearing portion 60 Coil spring (biasing member) )
61 Retraction unit 100 Image forming apparatus

Claims (7)

An endless intermediate transfer belt that moves along a plurality of image forming units;
A driving roller for rotating the intermediate transfer belt;
A tension roller that rotates following the intermediate transfer belt and applies a predetermined tension to the intermediate transfer belt;
A unit main body rotatably supporting the drive roller and the tension roller;
A plurality of primary transfer rollers disposed opposite to the image carriers disposed in each of the image forming units with the intermediate transfer belt interposed therebetween, and transferring a toner image formed on the image carrier onto the intermediate transfer belt; A backup roller disposed on the upstream side of the primary transfer roller located on the most upstream side with respect to the traveling direction of the intermediate transfer belt, and pressing the intermediate transfer belt toward the image carrier;
A plurality of bearing holders for independently and rotatably supporting both ends of the rotation shafts of the primary transfer roller and the backup roller;
A pair of sliders supported by the unit body so as to be reciprocally movable in parallel with the traveling direction of the intermediate transfer belt, and supporting the plurality of bearing holders so as to be reciprocally movable perpendicular to the traveling direction of the intermediate transfer belt;
A slider drive mechanism for reciprocating the slider;
In the intermediate transfer unit with
The bearing holder of the primary transfer roller includes a holder body that is slidably supported by the slider, a bearing portion that is slidably supported by the holder body, and a gap between the bearing portion and the holder body. An intermediate transfer unit comprising an urging member disposed.   By reciprocating the slider, a color mode in which all the primary transfer rollers and backup rollers are brought into contact with the intermediate transfer belt, and the primary transfer disposed opposite to the image carrier disposed in the black image forming unit. 2. The monochrome mode in which only a roller is brought into contact with the intermediate transfer belt and a standby mode in which all the primary transfer roller and backup roller are separated from the intermediate transfer belt can be switched. Intermediate transfer unit. A plurality of step ribs having a lower step portion, an upper step portion parallel to the lower step portion, and an inclined portion connecting the lower step portion and the upper step portion are formed on the side surface of the slider, A clamping part for slidably clamping the step rib is formed,
The arrangement of the primary transfer roller and the backup roller is switched to one of a color mode, a monochrome mode, and a standby mode by disposing the holding portions of the plurality of bearing holders in the lower step portion or the upper step portion. The intermediate transfer unit according to claim 2.   The intermediate transfer unit according to claim 2, wherein the slider can be switched to a belt cleaning mode in which only the backup roller is brought into contact with the intermediate transfer belt by reciprocating the slider. A plurality of step ribs having a lower step portion, an upper step portion parallel to the lower step portion, and an inclined portion connecting the lower step portion and the upper step portion are formed on the side surface of the slider, A clamping part for slidably clamping the step rib is formed,
Among the plurality of step ribs, the lower step portion of the step rib sandwiched by the sandwiching portion of the bearing holder that supports the primary transfer roller disposed to face the image carrier disposed in the black image forming portion. Forming a retraction part bent on the upper stage side and a holding part of the bearing holder that supports the primary transfer roller disposed opposite to the image carrier disposed in the black image forming part as the retraction part 5. The intermediate transfer unit according to claim 4, wherein, by arranging, the arrangement of the primary transfer roller and the backup roller is switched to a belt cleaning mode.   6. The intermediate transfer unit according to claim 1, wherein the slider drive mechanism is driven by a single drive source.   An image forming apparatus comprising the intermediate transfer unit according to claim 1.