Abstract:
A transfer unit includes: a transfer belt mounted over a plurality of rollers to run to transfer toner images on a plurality of image carriers to a front side of the transfer belt; transfer rollers provided for the respective image carriers to give a transfer potential to the transfer belt to transfer the toner images thereto; a drive mechanism configured to move only the transfer rollers for formation of a multicolor image into and out of contact with the transfer belt; a cleaning member contactable with a back side of the transfer belt to clean the back side; and a shifting mechanism configured to, upon contact of the transfer rollers with the transfer belt, shift the cleaning member into contact with the back side of the transfer belt and, upon departure of the transfer rollers from the transfer belt, shift the cleaning member out of contact with the back side.

Description:
INCORPORATION BY REFERENCE 
       [0001]    This application claims priority to Japanese Patent Application No. 2013-159052 filed on Jul. 31, 2013, the entire contents of which are incorporated by reference herein. 
       BACKGROUND 
       [0002]    The present disclosure relates to transfer units and image forming apparatuses. 
         [0003]    An image forming apparatus is known in which toner images formed on respective peripheral surfaces of photosensitive drums (image carriers) of different colors for forming a multicolor image are once transferred to an endlessly running transfer belt to superpose the toner images of different colors on each other to form a multicolor toner image and the multicolor toner image is secondarily transferred to a recording medium to form a multicolor image. There is also known another image forming apparatus of a type in which toner images are transferred from photosensitive drums directly to a recording medium being conveyed by a transfer belt. 
         [0004]    In the above image forming apparatuses, during transfer of toner from the photosensitive drums, the toner may scatter to contaminate the apparatus interior and in some cases contaminate even the back side of the transfer belt. To prevent deterioration of image quality due to unstable run of an intermediate transfer belt caused by deposition of scattering toner and other foreign matters on the back side of the transfer belt, a mechanism for cleaning the back side of the transfer belt is known. 
       SUMMARY 
       [0005]    A technique improved over the aforementioned technique is proposed herein as one aspect of the present disclosure. 
         [0006]    A transfer unit according to an aspect of the present disclosure includes a transfer belt, a plurality of transfer rollers, a drive mechanism, a cleaning member, and a shifting mechanism. 
         [0007]    The transfer belt is mounted over a plurality of rollers to run thereover and configured so that respective toner images formed on a plurality of image carriers for different colors necessary to form multicolor and black-and-white images are transferred to a front side of the transfer belt or a recording medium placed on the front side of the transfer belt. 
         [0008]    The plurality of transfer rollers are provided for the respective image carriers and configured to give a transfer potential to the transfer belt to allow the toner images to be transferred to the transfer belt. 
         [0009]    The drive mechanism is configured to move, among the transfer rollers for formation of a multicolor image and the transfer roller for formation of a black-and-white image, the transfer rollers for formation of a multicolor image into and out of contact with the transfer belt. 
         [0010]    The cleaning member is capable of contact with a back side of the transfer belt and operable to clean the back side of the transfer belt. 
         [0011]    The shifting mechanism is configured to, when the drive mechanism moves the transfer rollers for formation of a multicolor image into contact with the transfer belt, shift the cleaning member to a position in contact with the back side of the transfer belt and, when the drive mechanism moves the transfer rollers for formation of a multicolor image out of contact with the transfer belt, shift the cleaning member to a position out of contact with the back side of the transfer belt. 
         [0012]    An image forming apparatus according to another aspect of the present disclosure includes the aforementioned transfer unit, the plurality of image carriers, a plurality of charging sections, a plurality of exposure sections, a plurality of developing sections, and a second transfer section. 
         [0013]    The plurality of charging sections are configured to charge respective peripheral surfaces of the image carriers. 
         [0014]    The plurality of exposure sections are configured to expose the respective peripheral surfaces of the image carriers charged by the charging sections to light. 
         [0015]    The plurality of developing sections are configured to supply toner to respective electrostatic latent images formed on the respective peripheral surfaces of the image carriers by the exposure of the exposure sections to develop the electrostatic latent images. 
         [0016]    The second transfer section is configured to transfer a toner image on the transfer belt to a recording medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a front cross-sectional view showing the structure of an image forming apparatus including a transfer unit according to one embodiment of the present disclosure. 
           [0018]      FIG. 2  is a perspective view showing a schematic structure of the interior of a casing of an intermediate transfer unit. 
           [0019]      FIG. 3  is a perspective view showing the appearance of the intermediate transfer unit when viewed from below in  FIG. 2 . 
           [0020]      FIG. 4  is a plan view showing the intermediate transfer unit when viewed from below in  FIG. 3  and shows a schematic structure of the intermediate transfer unit. 
           [0021]      FIG. 5  is a side view of the intermediate transfer unit, showing a region where a drive mechanism and a cleaning unit engage each other. 
           [0022]      FIG. 6  is a side view showing a state where the drive mechanism has moved a first support member to a position where primary transfer rollers for formation of a multicolor image are out of contact with an intermediate transfer belt. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Hereinafter, a description will be given of one embodiment of the present disclosure with reference to the drawings. First, a description will be given of the structure of an image forming apparatus according to the embodiment of the present disclosure.  FIG. 1  is a front cross-sectional view showing the structure of the image forming apparatus  1  according to the embodiment of the present disclosure. 
         [0024]    As shown in  FIG. 1 , the image forming apparatus  1  is a multifunction peripheral having multiple functions including, for example, a copy function, a print function, a scan function, and a facsimile function. The image forming apparatus  1  is made up so that an apparatus body  11  thereof includes an operating section  47 , an image forming section  12 , a fixing section  13 , a paper feed section  14 , a document feed section  6 , a document reading section  5 , and so on. 
         [0025]    In a document reading operation of the image forming apparatus  1 , the document reading section  5  optically reads an image of an original document being fed from the document feed section  6  or an image of an original document placed on an original glass plate  161  to generate image data. The image data generated by the document reading section  5  is stored on an internal HDD, a network-connected computer or the like. 
         [0026]    In an image forming operation of the image forming apparatus  1 , the image forming section  12  forms a toner image on a recording paper sheet P serving as a recording medium fed from the paper feed section  14 , based on image data generated by the document reading operation, image data stored on the internal HDD or like image data. Each of image forming units  12 M,  12 C,  12 Y, and  12 Bk of the image forming section  12  includes a photosensitive drum  121 , a charging device  123 , an exposure device  124 , a developing device  122 , and a primary transfer roller  126 . 
         [0027]    The developing device  122  of each of the image forming units  12 M,  12 C,  12 Y, and  12 Bk contains toner for developing an electrostatic latent image. The developing device  122  is configured to supply toner to the surface of the associated photosensitive drum  121  where charging of the charging device  123  and exposure of the exposure device  124  have been completed. 
         [0028]    In the case of multicolor printing, the image forming unit  12 M for magenta, the image forming unit  12 C for cyan, the image forming unit  12 Y for yellow, and the image forming unit  12 Bk for black of the image forming section  12  form respective toner images on their respective photosensitive drums  121  through charging, exposure, and developing processes based on respective images of respective different color components constituting the above image data and then allow their respective primary transfer rollers  126  to transfer the toner images to an intermediate transfer belt (transfer belt)  125  mounted over a drive roller  125 A and a driven roller  125 B. 
         [0029]    The intermediate transfer belt  125 , the primary transfer rollers  126 , the drive roller  125 A, and the driven roller  125 B are incorporated in an intermediate transfer unit  50 . 
         [0030]    The outer peripheral surface of the intermediate transfer belt  125  is set to an image carrying surface to which toner images are to be transferred. The intermediate transfer belt  125  is driven by the drive roller  125 A while engaging against the peripheral surfaces of the photosensitive drums  121 . The intermediate transfer belt  125  endlessly runs between the drive roller  125 A and the driven roller  125 B while synchronizing with the rotation of each photosensitive drum  121 . 
         [0031]    The toner images of different colors transferred to the intermediate transfer belt  125  are superposed each other on the intermediate transfer belt  125  by controlling their transfer timings, resulting in a multicolor toner image. A secondary transfer roller  210  transfers the multicolor toner image formed on the outer peripheral surface of the intermediate transfer belt  125 , at a nip N between the secondary transfer roller  210  and the drive roller  125 A with the intermediate transfer belt  125  in between, to a recording paper sheet P conveyed from the paper feed section  14  along a conveyance path  190 . Thereafter, the fixing section  13  fixes the toner image on the recording paper sheet P by the application of heat and pressure. The recording paper sheet P having a multicolor image fixed thereon by the completion of the fixing treatment is discharged to a paper output tray  151 . 
         [0032]    Next, a description will be given of the intermediate transfer unit  50 . 
         [0033]      FIG. 2  is a perspective view showing a schematic structure of the interior of a casing of the intermediate transfer unit  50 . 
         [0034]      FIG. 3  is a perspective view showing the appearance of the intermediate transfer unit  50  when viewed from below in  FIG. 2 . Note that  FIG. 3  shows a state where the intermediate transfer belt  125  is removed. 
         [0035]    As described previously, the intermediate transfer unit  50  incorporates the intermediate transfer belt  125 , the primary transfer rollers  126 , the drive roller  125 A, and the driven roller  125 B. 
         [0036]    A frame  51  supports various mechanisms incorporated in the intermediate transfer unit  50 . Mounted to the frame  51  are the primary transfer rollers  126 , the drive roller  125 A, the driven roller  125 B as well as two backup rollers  129 , a primary transfer roller  126  of an image forming unit  12 Bk for black, a cleaning unit  53 , and a drive mechanism  52 . 
         [0037]    The backup rollers  129  are configured to press the intermediate transfer belt  125  mounted over the drive roller  125 A and the driven roller  125 B outwardly from inside the intermediate transfer belt  125  to apply tension to the intermediate transfer belt  125 . 
         [0038]    The drive mechanism  52  supports, among the primary transfer rollers  126  for formation of a multicolor image and the primary transfer roller  126  for formation of a black-and-white image, the primary transfer rollers  126  for formation of a multicolor image, i.e., the respective primary transfer rollers  126  of the image forming unit  12 M for magenta, the image forming unit  12 C for cyan, and the image forming unit  12 Y for yellow. The drive mechanism  52  is a mechanism for moving these primary transfer rollers  126  for formation of a multicolor image into and out of contact with the intermediate transfer belt  125 . 
         [0039]    The drive mechanism  52  includes a pair of first pivot shafts  521 , a first support member  522 , and a rotational drive section  524  (see  FIG. 5 ). 
         [0040]    The first pivot shafts  521  extend in a direction along the rotational axes of the drive roller  125 A and the driven roller  125 B. The first pivot shafts  521  serve as fulcrums for turning the first support member  522  in directions toward and away from the frame  51  and the intermediate transfer belt  125 . 
         [0041]    The first support member  522  rotatably journals the primary transfer rollers  126  for formation of a multicolor image arranged in a row in a direction of run of the intermediate transfer belt  125 . The first support member  522  is configured to turn on the first pivot shafts  521  as fulcrums. By this turning movement, the first support member  522  moves the primary transfer rollers  126  for formation of a multicolor image in directions toward and away from contact with the back side of the intermediate transfer belt  125 . 
         [0042]    The rotational drive section  524  includes a drive source configured to supply a rotational drive force, a rotary shaft rotatable by a rotational drive force supplied from the drive source, a cam having different diameters at different circumferential positions of its peripheral surface and configured to corotate with the rotary shaft, an unshown pressing part configured to press the first support member  522  in a direction away from the back side of the intermediate transfer belt  125  and the frame  51  and formed of, for example, a pressing spring, and a control unit configured to control the drive of the drive source. The cam is rotatably mounted, with its peripheral surface in contact with the first support member  522 , to the intermediate transfer unit  50 . When the cam rolls on the first support member  522  to change the amount of pressing of the first support member  522  toward the back side of the intermediate transfer belt  125  and the frame  51  against the pressing of the pressing part, the first support member  522  turns, with the rotation of the cam, in directions toward and away from contact with the back side of the intermediate transfer belt  125 . Depending upon differences in diameter among circumferential positions of the peripheral surface of the cam, the first support member  522  changes from a position in contact with the back side of the intermediate transfer belt  125  to a position out of contact therewith or vice versa. 
         [0043]    In forming a multicolor image, the control unit controls the drive of the drive source to rotate the cam and stop the rotation of the cam at a position where the distance from the center of rotation of the cam to the peripheral surface thereof (to the first support member  522 ) reaches, for example, the maximum. In this state, the amount of pressing of the first support member  522  toward the back side of the intermediate transfer belt  125  reaches, for example, the maximum and the control unit is configured to move the first support member  522  to a position where all the primary transfer rollers  126  for different colors for formation of a multicolor image come into contact with the back side of the intermediate transfer belt  125 . 
         [0044]    On the other hand, in forming a black-and-white image, the control unit controls the drive of the drive source to rotate the cam and stop the rotation of the cam at a position where the distance from the center of rotation of the cam to the peripheral surface thereof reaches, for example, the minimum. In this state, the amount of pressing of the first support member  522  toward the back side of the intermediate transfer belt  125  reaches, for example, the minimum and the control unit is configured to turn the first support member  522  to a position where all the primary transfer rollers  126  for different colors for formation of a multicolor image are away from the back side of the intermediate transfer belt  125 . 
         [0045]    The cleaning unit  53  is a mechanism for cleaning the back side (inner surface) of the intermediate transfer belt  125 . The cleaning unit  53  includes a cleaning member  531  (see  FIG. 4 ) and a shifting mechanism  530  (see  FIG. 4 ). The details of the cleaning unit  53  will be described hereinafter. 
         [0046]    The drive roller  125 A is rotatably journaled at one end of the frame  51  and the driven roller  125 B is journaled at the other end thereof. The intermediate transfer belt  125  is mounted between both the drive roller  125 A and driven roller  125 B journaled in the above manner and is, in this state, capable of running with the rotation of the drive roller  125 A and in the direction of rotation thereof. All the primary transfer rollers  126  are disposed inside the intermediate transfer belt  125  mounted in the above manner. 
         [0047]    Next, a further description will be given of the structures of the drive mechanism  52  and the cleaning unit  53 . 
         [0048]      FIG. 4  is a plan view showing the intermediate transfer unit  50  when viewed from below in  FIG. 3  and shows a schematic structure of the intermediate transfer unit  50 . 
         [0049]      FIG. 5  is a side view of the intermediate transfer unit  50 , showing a region where the drive mechanism  52  and the cleaning unit  53  engage each other. 
         [0050]    First, a description will be given of the structure of the cleaning unit  53 . The cleaning unit  53  includes a cleaning member  531  and a shifting mechanism  530 . 
         [0051]    The cleaning member  531  extends in the direction along the rotational axes of the drive roller  125 A and the driven roller  125 B and has a length close to the width of the intermediate transfer belt  125  (the dimension thereof in a direction perpendicular to the direction of run thereof). The cleaning member  531  is capable of contact with the back side of the intermediate transfer belt  125  and is operable to clean (brush) the back side of the intermediate transfer belt  125  by scraping waste toner, dust, and so on deposited on the back side with friction against the back side when making contact therewith. The cleaning member  531  is made of an electrically conductive material. 
         [0052]    The shifting mechanism  530  is a turning mechanism configured to turn the cleaning member  531  in directions toward and away from contact with the back side of the intermediate transfer belt  125 . The shifting mechanism  530  includes a pair of second pivot shafts  532  and a second support member  533 . 
         [0053]    The second pivot shafts  532  extend in the direction along the rotational axes of the drive roller  125 A and the driven roller  125 B. The second pivot shafts  532  serve as fulcrums for turning the second support member  533  in directions toward and away from the frame  51  and the intermediate transfer belt  125 . 
         [0054]    The second support member  533  extends in the direction along the aforementioned rotational axes like the cleaning member  531  and supports the cleaning member  531 . The second support member  533  is attached to a surface of the cleaning member  531  opposite to another surface of the cleaning member  531  facing the back side of the intermediate transfer belt  125 . The second support member  533  is configured to turn on the second pivot shafts  532  as fulcrums in the directions of the arrows A while supporting the cleaning member  531 . Thus, the second support member  533  can turn the cleaning member  531  in the directions toward and away from contact with the back side of the intermediate transfer belt  125 . The cleaning unit  53  is disposed opposite the first support member  522  side of the first pivot shafts  521  in the direction of run of the intermediate transfer belt  125  where the primary transfer rollers  126  for formation of a multicolor image are disposed. 
         [0055]    Subsequently, a description will be given of the structure of mechanism in which the drive mechanism  52  and the cleaning unit  53  engage each other. 
         [0056]    The first support member  522  of the drive mechanism  52  is provided with a pair of engagement portions  525  engaging with the respective associated first pivot shafts  521 . Each of the engagement portions  525  includes a first engagement portion  525 A and a second engagement portion  525 B. The first engagement portion  525 A engages with one side portion of the associated first pivot shaft  521 . The second engagement portion  525 B engages with the other side portion of the associated first pivot shaft  521 . Each of the first pivot shafts  521  is embraced by these first and second engagement portions  525 A,  525 B of the engagement portion  525 . Thus, the engagement portions  525  are journaled by the first pivot shafts  521  to allow the first support member  522  to turn in the directions of the arrows B. 
         [0057]    On the other hand, the second support member  533  of the shifting mechanism  530  is provided, at end portions opposite the side thereof where the cleaning member  531  is supported with respect to the second pivot shafts  532 , with second hooking portions  533 A hooking over ends of the second engagement portions  525 B. 
         [0058]    Each second hooking portion  533 A includes a recess  5331 . The recess  5331  is formed in a size that allows the end of the second engagement portion  525 B to fit therein. The ends of the second engagement portions  525 B fit as first hooking portions  522 A into the respective associated recesses  5331 , whereby the first support member  522  engages with the second support member  533 . 
         [0059]    As described previously, the first support member  522  supporting the primary transfer rollers  126  for formation of a multicolor image is pressed by the pressing part to turn in the direction away from the back side of the intermediate transfer belt  125 . On the other hand, the second support member  533  supporting the cleaning member  531  is pressed by an unshown pressing member to turn the cleaning member  531  in the direction toward the back side of the intermediate transfer belt  125 . 
         [0060]    The frame  51  is provided with a bearing  51 B for the primary transfer roller  126  for black. The first support member  522  is provided with a plurality of bearings  517  for the respective primary transfer rollers  126  for different colors for formation of a multicolor image.  FIG. 5  and  FIG. 6  described hereinafter show only the bearing  517  for the primary transfer roller  126  for yellow. 
         [0061]      FIG. 6  is a side view showing a state where the drive mechanism  52  has moved the first support member  522  to a position where the primary transfer rollers  126  for formation of a multicolor image are out of contact with the intermediate transfer belt  125 . 
         [0062]    With reference to  FIGS. 5 and 6 , a description will be given of the operations of the drive mechanism  52  and the shifting mechanism  530 . 
         [0063]      FIG. 5  shows a state where the drive mechanism  52  has turned the first support member  522 , by the aforementioned control over the rotation of the cam, to a position where the primary transfer rollers  126  for formation of a multicolor image come into contact with the back side of the intermediate transfer belt  125 , wherein the cleaning member  531  is shown in contact with the back side of the intermediate transfer belt  125 . 
         [0064]    At this time, since the second support member  533  supporting the cleaning member  531  is pressed by the pressing member to turn the cleaning member  531  in the direction toward the back side of the intermediate transfer belt  125  (the direction −Y in  FIG. 5 ), the second hooking portions  533 A are urged to turn on the second pivot shafts  532  as fulcrums toward the +Y side in  FIG. 5 . 
         [0065]    In this state, the first hooking portions  522 A of the first support member  522  of the drive mechanism  52  enter the recesses  5331  of the second hooking portions  533 A. The first support member  522  is pressed toward the +Y side (in the direction away from the back side of the intermediate transfer belt  125 ) by the aforementioned pressing part, but the cam allows the first support member  522  to keep s stable stop against turning due to the pressing. Therefore, the force of the second hooking portions  533 A to turn toward the +Y side is restrained by the engagement of the second hooking portions  533 A against the first hooking portions  522 A. 
         [0066]    Thus, the second support member  533  stops with the second hooking portions  533 A engaging against the first hooking portions  522 A and is held in this state. In the embodiment of the present disclosure, the attitude of the second support member  533  is set so that when the second support member  533  stops in this state, the top surface of the cleaning unit  531  is in contact with the back side of the intermediate transfer belt  125 . 
         [0067]    On the other hand, when the drive mechanism  52  turns the first support member  522  toward the +Y side, by the control over the rotation of the cam, to a position where the primary transfer rollers  126  for formation of a multicolor image are out of contact with the back side of the intermediate transfer belt  125 , the first hooking portions  522 A of the first support member  522  turn on the first pivot shafts  521  as fulcrums to come closer to the −Y side than their position shown in  FIG. 5 . 
         [0068]    By the turning movement of the first hooking portions  522 A toward the −Y side, the first hooking portions  522 A press up the second hooking portions  533 A hooked thereover to turn them toward the −Y side. The force of the first hooking portions  522 A to press the second hooking portions  533 A is set greater than the pressing force applied to the second support members  533  by the pressing member (the pressing force that allows the second support members  533  to turn in the direction in which the cleaning member  531  moves toward the back side of the intermediate transfer belt  125  (the direction −Y in  FIG. 5 )). Therefore, by the pressing of the first hooking portions  522 A against the second hooking portions  533 A, the cleaning member  531  side of the second support member  533  turns on the second pivot shafts  532  as fulcrums toward the +Y side (in the direction away from the back side of the intermediate transfer belt  125 ). In this case, the respective amounts of turning movement of the first support member  522  and the second support member  533  are set so that when the first support member  522  is moved to the position where the primary transfer rollers  126  for formation of a multicolor image are out of contact with the back side of the intermediate transfer belt  125 , the cleaning member  531  is moved out of contact with the back side of the intermediate transfer belt  125  by the pressing of the first hooking portions  522 A against the second hooking portions  533 A. 
         [0069]    To sum up, in the embodiment of the present disclosure, the first hooking portions  522 A provided on the side of the first support member  522  closer to the shifting mechanism  530  than the first pivot shafts  521  and the second hooking portions  533 A provided on the side of the second support member  533  closer to the drive mechanism  52  than the second pivot shafts  532  hook together. When in this state the rotational drive section  524  turns the first support member  522  in the direction in which the primary transfer rollers  126  for formation of a multicolor image move out of contact with the back side of the intermediate transfer belt  125 , the first hooking portions  522 A press the second hooking portions  533 A to turn the second support member  533  on the second pivot shafts  532  as fulcrums in the direction in which the cleaning member  531  moves out of contact with the back side of the intermediate transfer belt  125 . 
         [0070]    Under this configuration, when the drive mechanism  52  moves the primary transfer rollers  126  for formation of a multicolor image to a position in contact with the intermediate transfer belt  125 , the shifting mechanism  530  moves the cleaning member  531  to a position in contact with the back side of the intermediate transfer belt  125 . On the other hand, when the drive mechanism  52  moves the primary transfer rollers  126  for formation of a multicolor image to a position out of contact with the intermediate transfer belt  125 , the shifting mechanism  530  moves the cleaning member  531  to a position out of contact with the back side of the intermediate transfer belt  125 . 
         [0071]    Thus, in the embodiment of the present disclosure, the cleaning member  531  cleans the back side of the intermediate transfer belt  125  only during the formation of multicolor images. The back side of the intermediate transfer belt  125  has a relatively small amount of toner deposited thereon as compared to the front side thereof (the surface thereof to which toner images are transferred from the photosensitive drums  121 ) and therefore need not always be cleaned by contact with the cleaning member  531 . Therefore, while a period of time for which the cleaning member  531  is made contact with the back side of the intermediate transfer belt  125  is ensured, the cleaning member  531  is kept out of contact with the back side of the intermediate transfer belt  125  for a certain period of time. Thus, the cleaning member  531  and the intermediate transfer belt  125  can be released from friction against each other for a certain period of time to extend their lives while the cleaning effect of the cleaning member  531  can be maintained. 
         [0072]    Unlike this, in a general cleaning mechanism, the cleaning member is always made contact with the back side of the transfer belt to clean the back side by the friction of the cleaning member against the back side of the transfer belt. Therefore, the cleaning member and the transfer belt are reduced in life by abrasion. 
         [0073]    The embodiment of the present disclosure can solve this problem. Specifically, the embodiment of the present disclosure can extend the lives of the cleaning member  531  and the intermediate transfer belt  125  while maintaining the cleaning effect of the cleaning member  531  on the back side of the intermediate transfer belt  125 . 
         [0074]    The image forming apparatus  1  of the present disclosure is not limited to the above embodiment and can be modified in various ways. For example, although in the embodiment of the present disclosure the cleaning member  531  is made contact with the back side of the intermediate transfer belt  125  by the turning of the second support members  533  during formation of a multicolor image, the attitudes and positions of the second support member  533  and the cleaning member  531  during formation of a multicolor image may be set so that when the cleaning member  531  makes contact with the back side of the intermediate transfer belt  125 , the cleaning member  531  presses the intermediate transfer belt  125 , which is mounted over the drive roller  125 A and the driven roller  125 B, outwardly from the inner side (back side) of the intermediate transfer belt  125  to allow the intermediate transfer belt  125  to bulge out. Thus, during formation of a multicolor image, the cleaning member  531 , like the backup rollers, presses the intermediate transfer belt  125  mounted over the drive roller  125 A and the driven roller  125 B outwardly from inside the intermediate transfer belt  125 . Therefore, tension can be applied to the intermediate transfer belt  125  not only by the backup rollers but also by the cleaning member  531 . 
         [0075]    Although in the embodiment of the present disclosure the description has been given of the intermediate transfer unit  50  configured so that toner images are transferred from the photosensitive drums  121  to the intermediate transfer belt  125 , the present disclosure is not limited to this embodiment. For example, the present disclosure also includes an embodiment where a transfer unit is configured so that the transfer belt conveys a recording paper sheet P and toner images are transferred from the photosensitive drums  121  directly to the recording paper sheet P. 
         [0076]    Although in the embodiment of the present disclosure the cleaning member  531  is made of an electrically conductive material, materials that are used for the cleaning member  531  are not limited to electrically conductive materials. 
         [0077]    Various modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein.