Abstract:
An image forming device includes a plurality of developing devices, and a plurality of sloping members disposed in one-to-one correspondence with the plurality of developing devices. Each developing device includes a developer accommodating chamber and a developing roller disposed above the developer accommodating chamber. Each developing device is movable between a first position and a second position lower than the first position in a height direction generally parallel to a vertical direction. Each sloping member has a sloped surface movable in the height direction and a biasing member biasing the sloped surface upward in the height direction. Each sloping member is movable between a third position where the corresponding developing device is placed on the sloped surface and a fourth position where the corresponding developing device is released from being pressed by the sloped surface in a predetermined direction generally perpendicular to the vertical direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 13/906,692 filed May 31, 2013, which is a continuation application of U.S. patent application Ser. No. 13/347,983 filed Jan. 11, 2012, which is a continuation application of U.S. patent application Ser. No. 12/406,246 filed Mar. 18, 2009 and claims priority from Japanese Patent Application No. 2008-164972 filed Jun. 24, 2008. The entire contents of the above noted applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming device such as a laser printer. 
       BACKGROUND 
       [0003]    As a conventional electrophotographic image forming device such as a laser printer, Japanese laid-open patent publication No. 2006-1844553 discloses an image forming device including a photosensitive drum unit provided with a plurality of photosensitive drums, and a developing device unit (developing device tray) provided with a plurality of developing devices. The photosensitive drum unit and developing device unit are configured to be detachably mounted in the main body of the image forming device. 
         [0004]    In this image forming device, however, when the developing device unit is being removed from the main body, first the entire developing device unit is necessary to be detached from the photosensitive drum unit for separating the developing rollers of the developing devices from the photosensitive drum unit. The developing device unit is then to be pulled out from the main body. Hence, this image forming device necessitates a large-sized mechanism for supporting the weight of the whole developing device unit as well as for allowing the developing device unit to be movable. 
       SUMMARY 
       [0005]    In view of the foregoing, it is an object of the present invention to provide an image forming device having a simple-structured mechanism that enables a developing device unit to be detachably mounted in a main body of the image forming device. 
         [0006]    In order to achieve the above and other objects, the present invention provides an image forming device including: a plurality of developing devices; and a plurality of sloping members disposed in one-to-one correspondence with the plurality of developing devices. Each of the plurality of developing devices includes a developing roller defining an axis line and a developer accommodating chamber configured to accommodate developer therein, each of the plurality of developing rollers being disposed above the developer accommodating chamber such that the axis line extends in a direction generally perpendicular to a vertical direction, each of the plurality of developing devices being movable between a first position and a second position lower than the first position in a height direction generally parallel to the vertical direction. Each of the plurality of sloping members has a sloped surface that is movable in the height direction and including a biasing member configured to bias the sloped surface upward in the height direction, each of the plurality of sloping members being movable between a third position where the corresponding developing device is placed on the sloped surface and a fourth position where the corresponding developing device is released from being pressed by the sloped surface in a predetermined direction generally perpendicular to the vertical direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic cross-sectional view illustrating a configuration of a multifunctional peripheral as an image forming device according to an embodiment of the present invention; 
           [0009]      FIGS. 2A to 2C  are explanatory diagrams showing a color developing position of a developing device unit according to an embodiment of the present invention, wherein  FIG. 2A  shows an external configuration of the developing device unit and a photosensitive drum unit,  FIG. 2B  is a partially enlarged view of  FIG. 2A , and  FIG. 2C  shows an internal configuration of the developing device unit and the photosensitive drum unit; 
           [0010]      FIGS. 3A to 3C  are explanatory diagrams showing an intermediate position of the developing device unit, wherein  FIG. 3A  shows an external configuration of the developing device unit and the photosensitive drum unit,  FIG. 3B  is a partially enlarged view of  FIG. 3A , and  FIG. 3C  shows an internal configuration of the developing device unit and the photosensitive drum unit; 
           [0011]      FIGS. 4A to 4D  are explanatory diagrams showing a detachable position of the developing device unit, wherein  FIG. 4A  shows an external configuration of the developing device unit and the photosensitive drum unit,  FIG. 4B  is a partially enlarged view of  FIG. 4A ,  FIG. 4C  shows an internal configuration of the developing device unit and the photosensitive drum unit, and  FIG. 4D  is an enlarged view of a hook engaging section; 
           [0012]      FIGS. 5A to 5C  are explanatory diagrams showing a monochromatic developing position of the developing device unit, wherein  FIG. 5A  shows an external configuration of the developing device unit and the photosensitive drum unit,  FIG. 5B  is a partially enlarged view of  FIG. 5A , and  FIG. 5C  shows an internal configuration of the developing device unit and the photosensitive drum unit; 
           [0013]      FIG. 6  is a schematic view illustrating a state in which a discharge tray is opened; 
           [0014]      FIG. 7  is a schematic view illustrating a state in which the photosensitive drum unit is being pulled out; and 
           [0015]      FIG. 8  is a schematic view illustrating a state in which the developing device unit is being pulled out. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    A multifunctional peripheral (hereinafter simply referred to as “MFP”) as an image forming device according to one embodiment of the present invention will be described with reference to  FIGS. 1 through 8 . 
         [0017]    Note that, directions will be used throughout the description assuming that the MFP is disposed in an orientation in which a user intends to use the MFP. More specifically, a term “front side” designates the right side of the MFP in  FIG. 1 , while a term “rear side” designates the left side of the MFP in  FIG. 1 . Also, a far side in  FIG. 1  with respect to the paper width direction will be referred to as a “right side” while a near side in  FIG. 1  with respect to the paper width direction will be referred to as a “left side”. Further, an up-to-down direction in  FIG. 1  will be referred to as a “vertical direction”. 
         [0018]    As shown in  FIG. 1 , the MFP  1  includes a main casing  2 , and a flat head scanner  3  disposed in an uppermost portion of the main casing  2 . In more detail, the MFP  1  includes a sheet feed unit  4 , an image forming unit  5 , a pair of discharge rollers  6 , and an exposure unit  7 . The sheet feed unit  4  feeds sheets of paper (hereinafter simply referred to as ‘sheet P’) as an example of a recording sheet, the image forming unit  5  forms images on the sheet P supplied from the sheet feed unit  4 , and the discharge rollers  6  discharge the sheet P on which images are formed by the image forming unit  5 . The exposure unit  7  exposes a photosensitive drum  32  (described later) to light. 
         [0019]    A front cover  2 A is provided in the front side of the main casing  2 , and the front cover  2 A has a bottom end pivotably supported to the main casing  2 . The front door  2 A is, therefore, allowed to pivotally move in a front-to-rear direction about the bottom end thereof. 
         [0020]    A discharge tray  2 B is provided in an upper portion of the main casing  2 . The sheet P discharged out of the main casing  2  is piled in the discharge tray  2 B. A rear cover  2 C is provided in the rear side of the main casing  2 . 
         [0021]    The flat head scanner  3  is a conventional image scanning device. The flat head scanner  3  irradiates light onto a sheet and scans images on the sheet, and generates image data according to the scanned images. 
         [0022]    The sheet feed unit  4  is disposed in a bottom portion of the main casing  2 . The sheet feed unit  4  includes a sheet feed cassette  71 , a separation roller  72 , sheet feed rollers  73 ,  74  and  75 , a first conveying roller  76 , and a second conveying roller  77 . The sheet feed cassette  71  is configured to be detachably mounted in the main casing  2  and accommodates sheets P in a stacked state. The separation roller  72  and sheet feed rollers  73 ,  74  and  75  are disposed rearward and upward of the sheet feed cassette  4  in the main casing  2 . The first conveying roller  76  is disposed rearward of a photosensitive drum unit  30  (described later), and the second conveying roller  77  is disposed in opposition to the first conveying roller  76 . The separation roller  72  picks up one sheet at a time out of the sheets P stacked in the sheet feed cassette  71 . The sheet feed rollers  73 ,  74  and  75  then convey the sheet P upward. Subsequently, the first conveying roller  76  and the second conveying roller  77  nip the conveyed sheet P therebetween and convey the sheet P to the image forming unit  5 . 
         [0023]    The image forming unit  5  mainly includes a photosensitive drum unit  30 , a developing device unit  40 , a transfer unit  50  and a fixing unit  60 . 
         [0024]    As shown in  FIG. 2C , the photosensitive drum unit  30  includes a supporting frame  31 , four photosensitive drums  32 , and a Scorotron charger  33 . The supporting frame  31  constitutes an outer surface of the photosensitive drum unit  30 , thereby defining an outline thereof. Openings are formed in upper and bottom surfaces of the supporting frame  31 . 
         [0025]    The developing device unit  40  includes a supporting member  41  and four developing cartridges  42 , as shown in  FIG. 2C . 
         [0026]    The supporting member  41  includes a frame  41 A constituting an outer surface of the supporting member  41 , and four developing device holders  41 B for supporting the developing cartridges  42 . An opening is formed in an upper surface of the frame  41 A, while another opening is formed in a bottom surface thereof. Each of the developing cartridges  42  is detachably mounted in each developing device holder  41 B. The developing device holder  41 B has an axis  43  at the rear side thereof. The axis  43  is fixed to the frame  41 A, thereby allowing the developing device holder  41 B to be pivotably movably supported to the frame  41 A about the axis  43 . 
         [0027]    The developing cartridge  42  includes a developing roller  42 A, a supply roller  42 B, a thickness-regulating blade  42 C and a toner accommodating chamber  42 D. Note that all of the four developing cartridges  42  have a configuration the same as each other except in that each accommodates toner of a different color in respective toner accommodating chamber  42 D. When the developing device unit  40  is mounted in the main casing  2 , each developing roller  42 A supported by respective developing device holder  41 B comes into contact with respective ones of the photosensitive drums  32  upward and rearward of the developing roller  42 A, as shown in  FIG. 1 . When the photosensitive drum unit  30  is mounted in the main casing  2 , each photosensitive drum  32  comes in contact with each of the developing rollers  42 A at the diagonally bottom of the photosensitive drum  32 , while being in contact with respective ones of first transfer rollers  52  (described later) via an intermediate transfer belt  51  (described later) at the top of the photosensitive drum  32 . 
         [0028]    As shown in  FIG. 1 , the transfer unit  50  is disposed between the photosensitive drum unit  30  and the discharge tray  2 B in the main casing  2 . The transfer unit  50  includes an intermediate transfer belt  51 , four first transfer rollers  52 , a second transfer roller  53 , a drive roller  54 , a follow roller  55 , and a cleaning unit  56 . 
         [0029]    The drive roller  54  and the follow roller  55  are disposed with a distance therebetween in the front-to-rear direction. The intermediate transfer belt  51  is an endless belt, and is stretched around the drive roller  54  and the follow roller  55 . The intermediate transfer belt  51  opposes and contacts each of the photosensitive drums  32  at the bottom portion of the outer circumferential surface of the intermediate transfer belt  51 . The second transfer roller  53  is disposed in opposition to and in contact with the intermediate transfer belt  51  at a rear end portion of the intermediate transfer belt  51 . 
         [0030]    The first transfer rollers  52  are rotatably provided inside the loop of the intermediate transfer belt  51  so as to be in contact with the back side of the bottom portion of the inner circumferential surface of the intermediate transfer belt  51 . Each of the first transfer rollers  52  is disposed in opposition to each of the photosensitive drums  32  so that the intermediate transfer belt  51  can be nipped therebetween. 
         [0031]    The second transfer roller  53  is provided in the rear cover  2 C and is disposed in a position opposing to the drive roller  54  so that the intermediate transfer belt  51  can be nipped therebetween. A transfer bias is applied to the first transfer rollers  52  and the second transfer roller  53  under a constant current control during transfer operations. 
         [0032]    The cleaning unit  56  is disposed above the front portion of the intermediate transfer belt  51 . The cleaning unit  56  is provided with a cleaning roller  57  and a toner accumulation section  58  disposed rearward of the cleaning roller  57 . The cleaning roller  57  cleans up the toner remained on the outer circumferential surface of the intermediate transfer belt  51 , and the removed toner is then stored in the toner accumulation section  58 . 
         [0033]    The fixing unit  60  is disposed above the rear portion of the intermediate transfer belt  51 . The fixing nit  60  includes a heat roller  61  and a pressure roller  62  disposed in opposition to the heat roller  61 . The pressure roller  62  applies pressure to the heat roller  61 . 
         [0034]    Next, operations performed in the image forming unit  5  having the above-described configuration will be described. 
         [0035]    In the image forming unit  5 , each Scorotron charger  33  applies a uniform charge to the surface of each photosensitive drum  32 , and the exposure unit  7  then irradiates a laser to the surface of the photosensitive drum  32  to perform exposure. In this way, a lower potential is produced on areas exposed to the laser beam on the surface of the photosensitive drum  32 , thereby forming an electrostatic latent image on the surface of each photosensitive drum  32  according to the scanned image data. 
         [0036]    Meanwhile, as the supply roller  42 B rotates, the toner accommodated in the toner accommodating chamber  42 D is supplied to the developing roller  42 A. In accordance with the rotation of the developing roller  42 A, the toner supplied to the surface of the developing roller  42 A passes between the thickness-regulating blade  42 C and the developing roller  42 A, thereby maintaining a thin layer of uniform thickness on the surface of the developing roller  42 A. The toner is thus carried on the circumferential surface of the developing roller  42 A. 
         [0037]    When each developing roller  42 A comes into contact with respective ones of the photosensitive drums  32 , the toner borne on the surface of the developing roller  42 A is supplied to the surface of each photosensitive drum  32  on which the electrostatic latent image is formed, thus being selectively carried thereon. In this way, the latent image on each of the photosensitive drums  32  is developed into a visible toner image. The toner images in each color borne on the surface of each photosensitive drum  32  are then sequentially transferred onto the outer circumferential surface of the intermediate transfer belt  51  in conjunction with the transfer bias applied to the four first transfer rollers  52 . 
         [0038]    When the sheet P conveyed to the image forming unit  5  passes between the intermediate transfer belt  51  and the second transfer roller  53 , the toner images transferred on the intermediate transfer belt  51  are then transferred onto the surface of the sheet P in cooperation with the transfer bias applied to the second transfer roller  53 . The sheet P is then conveyed to the fixing unit  6 , whereby the toner images transferred on the surface of the sheet P is thermally-fixed thereto as the sheet P passes between the heat roller  61  and the pressure roller  62 . The sheet P is finally discharged out of the main casing  2  onto the discharge tray  2 B by the rotation of the discharge rollers  6 . 
         [0039]    Next, detailed configurations for enabling the photosensitive drum unit  30  and the developing device unit  40  to be detachably mountable in the main body  2  will be described while referring to  FIGS. 2A to 5 . Note that, although  FIGS. 2A to 5  only show configurations seen from the left side of the MFP  1  and the descriptions therefor only are given hereinafter, the same configurations are also provided on the right side of the MFP  1 . 
         [0040]    As shown in  FIGS. 2A and 2B , four through-holes  41 C are formed on left and right side walls of the frame  41 A, i.e., on walls disposed in a direction orthogonal to the rotational axis of the developing roller  42 A. An operation portion  41 D is provided in the developing device holder  41 B so that each operation portion  41 D can protrude outward from each through-hole  41   c.  The through-hole  41 C has a shape elongated in the vertical direction so that the operation portion  41 D can be vertically movable. In addition, a first operation lever  80 , a second operation lever  90 , a second operation lever driving member  100 , and a lock mechanism  110  are also provided in the MFP  1  as shown in  FIG. 2A . 
         [0041]    The first operation bar  80  is provided on the frame  41 A. The first operation bar  80  includes two bars  81 , sloping members  82 , and two disengagement members  83 . Each bar  81  is movably supported on the left and right side walls of the frame  41 A and extends in the front-to-rear direction. The two bars  81  are connected at the front side of the frame  41 A so as to be integrally movable relative to the frame  41 A in the front-to-rear direction. Each developing roller  42 A is juxtaposed in the front-to-rear direction, and the bars  81  are thus configured to be movable along a direction orthogonal to the axes of the four developing rollers  42 A. Each of the sloping members  82  is adapted to be engageable with each of the operation portions  41 D. The sloping member  82  has an upper surface sloped diagonally downward from the front to the rear thereof. The sloped upper surface has a front half portion serving as a pivotable member  82 A configured to be pivotably movable in the vertical direction about the rear end of the pivotable member  82 A. A spring  82 B is provided to bias the pivotable member  82 A upward from the bottom thereof. The disengagement member  83  is provided at the rear end of each operation bar  81  so as to protrude downward therefrom. 
         [0042]    The second operation bar  90  is provided in the main casing  2  and illustrated by double dotted chain lines in  FIGS. 2A and 2B . The second operation bar  90  includes four first recesses  91  and a second recess  92 . Each first recess  91  is adapted to be engageable with each of the operation portions  41 D. The first recesses  91  are arranged in line with an interval interposed therebetween, the interval being the same as that between each of the operation portions  41 D. The second recess  92  is configured to be engageable only with the operation portion  41 D located at a position closest to the front side of the MFP  1 . 
         [0043]    The second operation bar driving member  100  is provided on the second operation bar  90 , and is configured to meshingly engage the second operation bar  90  at the rear end thereof. A control unit (not shown) controls the second operation bar driving member  100  to rotate so that the second operation bar  90  can be slidingly movable in the front-to-rear direction. 
         [0044]    The lock mechanism  110  is provided on the frame  41 A at the rear end thereof. The lock mechanism  110  includes a rod-like member  111 , a hook portion  112 , a biasing member  113 , and a holding member  114 . The hook portion  112  is formed at the bottom end of the rod-like member  111 . The biasing member  113  biases the upper end portion of the rod-like member  111  away from the frame  41 A, i.e., to the rear. The holding member  114  holds the upper end portion of the rod-like member  111  and prevents the rod-like member  113  from falling off the frame  41 A. When the developing device unit  40  is completely mounted in the main body  2  and the first operation bar  80  is pushed rearward, the hook portion  112  is configured to protrude downward so that a hook engaging portion  2 D formed in the main casing  2  can engage the hook portion  112  (Refer to  FIG. 4D ). 
         [0045]    As shown in  FIGS. 2A ,  2 B,  3 A,  3 B,  4 A and  4 B, the photosensitive drum unit  30  is provided with four grooves  34  on left and right side walls of the supporting frame  31 . The grooves  34  engage the rotational axes of the developing rollers  42 A so as to guide the movement of developing rollers  42 A, as well as to position the developing rollers  42 A relative to the photosensitive drums  32 . 
         [0046]    As shown in  FIGS. 2A and 2B , each of the operation portions  41 D are placed on each pivotable member  82 A of the sloping members  82 , and the pivotable member  82 A is biased upward by the spring  82 B. Each of the operation portion  41 D is thus engaged with corresponding first recess  91  of the second operation bar  90 . At this time, four developing rollers  42 A are brought into such a position that each of the four developing rollers  42 A can be in contact with respective ones of the photosensitive drums  32 , as shown in  FIG. 2C . When four developing rollers  42 A are placed at this position, the MFP  1  can utilize the four photosensitive drums  32 , thereby performing a color developing operation. Therefore, this position is called a color developing position. In this state, upper portions of the developing rollers  42 A and lower portions of the photosensitive drums  32  overlap when seen from the front side of the MFP  1 . 
         [0047]    When the second operation bar driving member  100  moves the second operation bar  90  rearward from the color developing position shown in  FIGS. 2A and 2B , each of the operation portions  41 D is released from the engagement with the corresponding first recesses  91  of the second operation bar  90  as shown in  FIGS. 3A and 3B . At this time, four developing rollers  42 A are slightly spaced apart from the corresponding photosensitive drums  32  respectively as shown in  FIG. 3C . This position is called an intermediate position, where the cleaning unit  56  can perform a cleaning operation at the MFP  1 , for example. 
         [0048]    When a user pulls the first operation bar  80  forward from the color developing position shown in  FIGS. 2A and 2B , the engagement between each operation portion  41 D and each sloping member  82  of the first operation bar  80  is released as shown in  FIGS. 4A and 4B . At this time, four developing rollers  42 A are spaced apart from the corresponding photosensitive drums  32  and are completely accommodated in the frame  41 A. In other words, the developing rollers  42 A are displaced into a position where the upper portions of the developing rollers  42 A do not overlap with the lower portions of the photosensitive drums  32  when seen from the front side of the MFP  1 . Therefore, the photosensitive drums  32  and the developing rollers  42 A do not interfere with each other when either the photosensitive drum unit  30  or the developing roller unit  40  is pulled out from the main casing  2 . This position is thus called a detachable position. 
         [0049]    At the same time, when the user pulls the first operation bar  80  forward, the disengagement member  83  of the first operation bar  80  is coupled to the upper portion of the rod-like member  111 , thereby pivotally moving the same. Hence, the hook portion  112  is moved upward, thereby releasing the engagement with the main casing  2  (more precisely, engagement with the hook engaging portion  2 D). In this way, at least one of the developing device unit  40  and photosensitive drum unit  30  are made detachable from the main casing  2 . 
         [0050]    In the present embodiment, a pair of first guides  44  and  45  and a first wheel  46  are provided on outer surfaces of the left and right side walls of the frame  41 A of the developing device unit  40  for facilitating detachment of the developing device unit  40 . The first guides  44  and  45  extend in the front-to-rear direction, and the first wheel  46  is disposed at the rear end of both side walls of the frame  41 A. In the main casing  2 , a second guide  121 , a stopper  122 , and a second wheel  123  are provided for the same purpose. The second guide  121  is formed along the first guide  45 . The stopper  122  is disposed at the rear end of the second guide  121  for preventing the first wheel  46  from moving further to the rear, while the second wheel  123  is disposed at the front end of the second guide  121 . When a user pulls the first operation bar  80  forward, the second wheel  123  rotates and the first guide  44  moves on the second wheel  123  in conjunction with the rotation of the second wheel  123 , thereby enabling the developing device unit  40  to move forward. In the meantime, the first wheel  46  rotates along the second guide  121 . The developing device unit  40  is thus pulled out from the main casing  2 . 
         [0051]    When the second operation bar driving member  100  moves the second operation bar  90  forward from the color developing position shown in  FIGS. 2A and 2B , each operation portion  41 D is disengaged from each of the first recesses  91  of the second operation bar  90 , but only one of the operation portions  41 D, which is located closest to the front of the MFP  1 , is then brought into engagement with the second recess  92  as shown in  FIGS. 5A and 5B . In this state, as shown in  FIG. 5C , of the developing rollers  42 A, the one closest to the front of the MFP  1  is at a developing position where the developing roller  42 A is in contact with the corresponding photosensitive drum  32 , while other three developing rollers  42 A are slightly separated from respective photosensitive drums  32 . Hence, the MFP  1  can perform monochromatic printing at this position using one of the photosensitive drums  32  located at the forefront in the main casing  2 . This position is thus called a monochromatic developing position. 
         [0052]    Next, operations for removing the photosensitive drum unit  30  and the developing device unit  40  from the main casing  2  will be described with reference to  FIGS. 6 through 8 . As shown in  FIG. 7 , a grip  35  is provided on the front portion of the outer surface of the supporting frame  31 , while guide wheels  36  are provided on the rear portion of the outer surface of the supporting frame  31 . Wheel accommodation sections  124  and guide sections  125  are also provided on left and right sides in the main casing  2 , as shown in  FIGS. 6 to 8 . 
         [0053]    First, a user opens the discharge tray  2 B upward from a state shown in  FIG. 1 , as shown in  FIG. 6 . The user then opens the front cover  2 A and pulls the first operation bar  80 , thereby shifting the developing rollers  42 A to the detachable position while releasing the hook portion  112  from the main body  2 . The photosensitive drum unit  30  and the developing device unit  40  are thus ready to be pulled out. 
         [0054]    At this time, when the user holds the grip  35  and pulls the same forward, the guide wheels  36  move onto the guide sections  125  from the wheel accommodation sections  124 , and rotate along the guide sections  125 . The user can thus pull the photosensitive drum unit  30  out of the main casing  2 , and replace the photosensitive drums  32 . 
         [0055]    Alternatively, as shown in  FIG. 8 , when the user pulls the first operation bar  80  forward, the developing device unit  40  can be pulled out from the main casing  2 . At this time, the user can replace the developing cartridges  42  accommodated in the developing device holders  41 B. 
         [0056]    As described above, the plurality of developing cartridges  42  are designed to shift to the detachable position relative to the frame  41 . Therefore, the user can only pull out the developing device unit  40  when detaching the developing device unit  40  from the main casing  2 . In other words, the entire developing device unit  40  is not necessary to be supported when each of the developing cartridges  42  is spaced away from respective ones of the photosensitive drums  32 , thereby achieving a simple-structured mechanism for detaching the developing device unit  40  from the main casing  2 . Also, the user can simply pull out the developing device unit  40  when replacing the developing cartridges  42 , leading to prevention of a fall of the main casing  2 . 
         [0057]    Further, positions of the developing cartridges  42  can be changed by manipulating the operation portions  41 D protruding from the through-holes  41 C formed on the side walls of the frame  41 , thereby facilitating positional changes of the developing cartridges  42 . Additionally, the operation portion  41 D is formed on the developing device holder  41 B which is pivotally supported to the frame  41 A. Hence, the through-hole  41 C is not necessary to be formed up to the upper peripheral end section of the frame  41 A, thereby leading to high rigidity of the frame  41 A. 
         [0058]    The intermediate position realizes a slight separation between the developing cartridges  42  and the photosensitive drums  32  by shifting the developing cartridges  32  by a small amount, facilitating cleaning of the photosensitive drums  32  and the intermediate transfer belt  51 . 
         [0059]    Positions of the plurality of developing cartridges  42  are configured to be switchable between the color developing position and the monochromatic developing position. Hence, even if the MFP  1  runs out of color toner (cyan, yellow, and magenta), the MFP  1  can still perform monochromatic printing. 
         [0060]    Further, since the grooves  34  are provided in the photosensitive drum unit  30  for engagement with the developing cartridges  42 , the developing cartridges  42  can be easily positioned relative to the photosensitive drums  32 . 
         [0061]    Further, the positional change of the plurality of developing cartridges  42  between the color developing position and the detachable position can be easily realized by simply operating the first operation bar  80 . At the same time, since the first operation bar  80  is provided on the frame  41 A, the first operation bar  80  does not interfere with the operation portions  41 D when the developing device unit  40  is being removed from the main casing  2 . 
         [0062]    Likewise, simply operating the first operation bar  80  and the second operation bar  90  allows the plurality of developing cartridges  42  to change the position thereof easily from any one of the color developing position, the detachable position and the intermediate position to another. Also, since the first operation bar  80  and the second operation bar  90  are provided in the front-to-rear direction with respect to the developing device unit  40 , the developing device unit  40  can be removed from the main casing  2  without being interrupted. 
         [0063]    Further, the grooves  34  formed on the photosensitive drum unit  30  facilitate positioning of axial ends of each developing roller  42 A. Therefore, the rotational axes of the respective pair of the photosensitive drum  32  and the corresponding developing roller  42 A are reliably maintained in parallel to each other. 
         [0064]    Although the present invention has been described with respect to the specific embodiment thereof, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention. 
         [0065]    More specifically, the developing device holder  41 B is pivotally supported to the frame  41 A in the above-described embodiment. But, as a variation, the developing device unit  40  may be configured to allow the developing devices having developing rollers to be slidably movable relative to the supporting member. 
         [0066]    The photosensitive drum unit  30  and the developing device unit  40  are arranged to be pulled out from the front side of the main body  2  in the front-to-rear direction in the above-described embodiment. However, the photosensitive drum unit  30  and the developing device unit  40  may be configured to be taken out from either left or right side of the main body  2  of the MFP  1 . 
         [0067]    Further, the developing roller  42 A is arranged to be in contact with the photosensitive drum  32  in the developing positions (both color and monochromatic) in the above-described embodiment. However, as long as printing operations can be performed on the surfaces of the photosensitive drums  32 , the developing roller  42 A may be placed in a position close to, but spaced apart from the photosensitive drum  32  in the developing positions. That is, in this embodiment, the developing rollers  42 A may be disposed in proximity to the photosensitive drums  32 , regardless of whether or not the developing rollers  42 A are in direct contact with the photosensitive drums  32 . 
         [0068]    In the above embodiment, the first recesses  91  and the second recess  92  are formed on the second operation bar  90  and each is designed to be engageable with respective one of the operation portion  41 A. In accordance with movements of the second operation bar  90 , the developing rollers  42 A and the photosensitive drums  32  are brought in close to each other when the operation portions  41 D are engaged with either the first recesses  91  or the second recess  92 , while the developing rollers  42 A and the photosensitive drums  32  are in separation to each other when the operation portions  41 D are disengaged from either the first recesses  91  or the second recess  92 . However, protrusions may be formed on the lower surface of the second operation bar  90  instead of the first recesses  91  and the second recess  92 . In this case, in accordance with the movements of the second operation bar  90 , the developing rollers  42 A and the photosensitive drums  32  are configured to be distanced from each other when the protrusions push the operation portions  41 D downward, while the developing rollers  42 A and the photosensitive drums  32  are configured to be positioned close to each other when the operation portions  41 D are in a position off the protrusions. Note that, in this case, too, as long as the MFP  1  can perform printing, the developing rollers  42 A may not necessarily be in direct contact with the photosensitive drums  32 , but may be disposed in a position slightly distanced from the photosensitive drums  32 . 
         [0069]    Further, this invention can be applied to a color copier, and also to a color printer that is not provided with an image scanning unit (a flat head scanner). 
         [0070]    As a light source, the exposure unit  7  employs a laser in the above-described embodiment. However, LEDs, electroluminescence elements and florescent materials may also be an alternative light source.