Abstract:
An image forming apparatus includes: a main body provided with a drive-force supplying part; a cartridge comprising a rotary body and a drive-force transmission part; and a moving member supporting the cartridge. The drive-force transmission part transmits a drive force transmitted from the drive-force supplying part to the rotary body. The moving member is accommodated in and withdrawn from the main body. The cartridge is attached to and detached from the moving member when moving member is withdrawn from the main body. The moving member includes a drive-force relay part having an input portion and an output portion, the input portion receiving the drive force from the drive-force supplying part, the output portion outputting the drive force from the input portion to the drive-force transmission part of the cartridge attached to the moving member.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2013-023032 filed Feb. 8, 2013. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming apparatus of an electro-photographic type. 
       BACKGROUND 
       [0003]    A known tandem-type color printer includes a main body and a plurality of cartridges detachably mountable in the main body. 
         [0004]    One of such conventional color printers includes a main body and a cartridge tray configured to be held in the main body to be slidable movable relative to the main body. In this color printer, the cartridge tray supports therein a plurality of cartridges juxtaposed to one another. That is, the plurality of cartridges is integrally and detachably mountable in the main body (see Japanese Patent Application Publication No. 2008-165025). 
       SUMMARY 
       [0005]    It is an object of the present invention to provide an improved image forming apparatus. 
         [0006]    In order to attain the above and other objects, there is provided an image forming apparatus including a main body, a cartridge and a moving member. The main body is provided with a drive-force supplying part configured to rotate to generate and transmit a drive force. The cartridge includes a rotary body and a drive-force transmission part, the rotary body defining a rotational axis extending in a first direction, the drive-force transmission part being configured to transmit the drive force from the drive-force supplying part to the rotary body. The moving member is configured to support the cartridge therein and to move in a second direction generally perpendicular to the first direction between an internal position accommodated in the main body and an external position withdrawn from the main body, the cartridge being configured to be attached to and detached from the moving member in the external position, the moving member comprising a drive-force relay part including an input portion and an output portion, the input portion being configured to receive the drive force from the drive-force supplying part of the main body, the output portion being configured to output the drive force from the input portion to the drive-force transmission part of the cartridge attached to the moving member. 
         [0007]    According to another aspect of the invention, there is provided an image forming apparatus including a main body, a tray configured to move into or be pulled out of the main body, and a cartridge configured to be attached to and detached from the tray. The main body is provided with a drive-force supplying member configured to transmit a drive force. The cartridge includes a rotary body and a drive-force transmission member, the drive-force transmission member being configured to transmit the drive force from the drive-force supplying member of the main body to the rotary body. The tray includes a drive-force relay member configured to transmit the drive force from the drive-force supplying member of the main body to the drive-force transmission member of the cartridge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    In the drawings: 
           [0009]      FIG. 1  is a schematic central cross-sectional view illustrating a general configuration of a printer according to a first embodiment of the present invention, wherein a process frame supporting a plurality of process cartridges is accommodated in a main casing of the printer; 
           [0010]      FIG. 2  is a schematic view showing a right side view of each of the plurality of process cartridges when mounted in the printer according to the first embodiment; 
           [0011]      FIG. 3  is a cross-sectional view of the printer according to the first embodiment taken along a plane A-A shown in  FIG. 2 ; 
           [0012]      FIG. 4  is a schematic central cross-sectional view of the printer according to the first embodiment, wherein the process frame supporting the plurality of process cartridges is pulled out from the main casing of the printer; 
           [0013]      FIG. 5A  is a view explaining how the process cartridge is attached to the process frame of the printer according to the first embodiment, wherein the process cartridge is placed above the process frame for attachment; 
           [0014]      FIG. 5B  is a view explaining how the process cartridge is attached to the process frame of the printer according to the first embodiment, wherein the process cartridge is being attached to the process frame; 
           [0015]      FIG. 5C  is a view explaining how the process cartridge is attached to the process frame of the printer according to the first embodiment, wherein the process cartridge has been attached to the process frame; 
           [0016]      FIG. 6A  is a view explaining a process frame and a cartridge according to a second embodiment of the present invention, wherein the process frame supporting the plurality of process cartridges has been mounted in the main casing and the front cover of the main casing is opened; and 
           [0017]      FIG. 6B  is a view explaining the process frame and the cartridge according to the second embodiment, wherein the process frame has been mounted in the main casing and the front cover is closed. 
       
    
    
     DETAILED DESCRIPTION 
     1. General Structure of the Printer 
       [0018]    A printer  1  is a horizontal direct tandem-type color laser printer, as shown in  FIG. 1 . The printer  1  is an example of an image forming apparatus according to a first embodiment of the present invention. 
         [0019]    First, a general structure of the printer  1  will be described with reference to  FIG. 1 . 
         [0020]    Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used assuming that the printer  1  is resting on a level surface. More specifically, in  FIG. 1 , a right side, a left side, a near side and a far side will be referred to as a rear side, a front side, a right side and a left side of the printer  1 , respectively. 
         [0021]    The printer  1  includes a substantially box-shaped main casing  2 , a process unit  5 , a scanner unit  6 , a transfer unit  7 , and a fixing unit  8 . 
         [0022]    The main casing  2  includes an aperture  3  and a front cover  4 . The front cover  4  is provided on the main casing  2  such that the front cover  4  is pivotably movably about a lower end portion thereof to open and close the aperture  3 . 
         [0023]    The process unit  5  includes a process frame  9  and four process cartridge  10  supported to the process frame  9 . 
         [0024]    The process frame  9  is formed in a substantially rectangular frame-like shape. The process frame  9  supporting the process cartridges  10  is configured to move, relative to the main casing  2 , in a front-rear direction between a mounted position (shown in  FIG. 1 ) and a pull-out position (shown in  FIG. 4 ). Specifically, the process frame  9  is accommodated in the main casing  2  in the mounted position, whereas the process frame  9  is pulled out frontward from the main casing  2  in the pull-out position. 
         [0025]    The four process cartridges  10  are arranged in parallel to and spaced apart from one another in the front-rear direction. Each of the process cartridges  10  includes a photosensitive drum  11 , a developing roller  13 , a supply roller (not shown), and a thickness regulating blade (not shown). 
         [0026]    The photosensitive drum  11  is formed in a substantially cylindrical shape elongated in a left-right direction. The photosensitive drum  11  is rotatably supported to a lower end portion of the process cartridge  10 . 
         [0027]    The developing roller  13  is disposed upward of and frontward of the photosensitive drum  11  so as to be in contact with the same. The developing roller  13  has a substantially columnar shape extending in the left-right direction. That is, the developing roller  13  defines a central axis extending in the left-right direction. The developing roller  13  is rotatable about the central axis. 
         [0028]    In each process cartridge  10 , toner is stored in a chamber (not shown) formed upward of the developing roller  13 . The supply roller (not shown) is configured to supply this toner to the corresponding developing roller  13 . The thickness regulating blade (not shown) is configured to regulate a thickness of the toner supplied to the developing roller  13 . 
         [0029]    The scanner unit  6  is placed in an upper portion of the main casing  2 . The scanner unit  6  is configured to emit a laser beam to each of the plurality of photosensitive drums  11  based on image data to expose each of the photosensitive drums  11  to light. 
         [0030]    The transfer unit  7  is disposed below the process unit  5 , i.e., below the four photosensitive drums  11 . The transfer unit  7  includes a drive roller  16 , a follow roller  17 , a conveyor belt  18 , and four transfer rollers  19 . 
         [0031]    The drive roller  16  is rotatably supported in a rear end portion of the transfer unit  7 . The follow roller  17  is rotatably supported in a front end portion of the transfer unit  7 . 
         [0032]    The conveyor belt  18  is stretched on and around the drive roller  16  and the follow roller  17  under tension. The conveyor belt  18  has an upper portion that is in contact with each of the photosensitive drums  11  from below. Rotation of the drive roller  16  causes the follow roller  17  to rotate in conjunction with the conveyor belt  18 . The conveyor belt  18  is thus configured to be circularly movable such that the upper portion of the conveyor belt  18  moves from the front to the rear 
         [0033]    The four transfer rollers  19  are disposed below the four photosensitive drums  11  respectively such that each pair of transfer roller  19  and the photosensitive drum  11  nips the upper portion of the conveyor belt  18  therebetween. 
         [0034]    The fixing unit  8  is disposed rearward of and upward of the transfer unit  7 . The fixing unit  8  includes a heating roller  20  and a pressure roller  21  disposed in opposition to each other. 
         [0035]    Upon input of a print job in the printer  1 , an image formation operation is initiated. The toner stored in each process cartridge  10  is tribocharged with a positive polarity between the supply roller (not shown) and the corresponding developing roller  13 , and is borne on a surface of the corresponding developing roller  13  as a thin layer of a uniform thickness by the thickness regulating blade (not shown). 
         [0036]    In the meantime, a charger (not shown) applies a uniform positive charge to a surface of each photosensitive drum  11 . The scanner unit  6  then exposes the surface of each photosensitive drum  11  to light based on prescribed image data, thereby forming an electrostatic latent image on the surface of each photosensitive drum  11  based on the image data. The toner borne on each developing roller  13  is then supplied to the electrostatic latent image on the surface of the corresponding photosensitive drum  11 . A toner image is thus carried on the surface of each photosensitive drum  11 . 
         [0037]    Sheets P are accommodated in a sheet feed tray  22  disposed in a bottom portion of the main casing  2 . Various rollers (not shown) are configured to convey the sheets P upward and rearward, along a U-shaped path, such that each sheet P is conveyed toward a position between the frontmost photosensitive drum  11  and the conveyor belt  18  one by one at a predetermined timing. The conveyor belt  18  then conveys each sheet P rearward such that each sheet P passes between each photosensitive drum  11  and its corresponding transfer roller  19 . As each sheet P is conveyed rearward with a transfer bias applied to each transfer roller  19 , the toner image carried on each of the photosensitive drums  11  is sequentially transferred onto the sheet P. 
         [0038]    The sheet P is then applied with heat and pressure when passing between the heating roller  20  and the pressure roller  21  in the fixing unit  8 . The toner image is thus thermally fixed on the sheet P. 
         [0039]    Thereafter, the sheet P is then conveyed upward and frontward along a U-shaped path, and is finally discharged onto a discharge tray  23  formed on in an upper wall of the main casing  2 . 
       2. Process Unit 
       [0040]    (2-1) Process Frame 
         [0041]    As shown in  FIGS. 2 and 3 , the process frame  9  includes a pair of left and right side plates  31 , a front beam  32 , and a rear beam  33 . 
         [0042]    The side plates  31  are disposed to oppose and be spaced apart from each other in the left-right direction. The side plates  31  have a substantially rectangular plate-like shape elongated in the front-rear direction in a side view. 
         [0043]    Each of the side plates  31  has a lower end portion on which a support rib  37  is formed to support the process cartridges  10 . Specifically, the support rib  37  protrudes inward from an inner surface of the lower end portion of each side plate  31  in the left-right direction. The support rib  37  is in a form of a rib (protrusion) extending in the front-rear direction. 
         [0044]    Hereinafter, for explanatory purpose, the left side plate  31  will be referred to as the left side plate  31  L, while the right side plate  31  will be referred to as the right side plate  31 R, whenever necessary. 
         [0045]    As shown in  FIG. 3 , the left side plate  31 L includes four relay electrodes  36  to correspond to the four process cartridges  10 . 
         [0046]    The relay electrodes  36  are disposed vertically midway on the left side plate  31 L in an up-down direction. The relay electrodes  36  are made of an electrically conductive material such as metal or electrically conductive resin. The relay electrodes  36  are generally columnar shaped and extend to penetrate the left side plate  31 L in the left-right direction. The four relay electrodes  36  are spaced apart from one another in the front-rear direction to correspond to the four process cartridges  10 . 
         [0047]    The right side plate  31 R includes four drum relay couplings  35  and four developing relay couplings  34 . 
         [0048]    The drum relay couplings  35  are provided on a lower end portion of the right side plate  31 R. The drum relay couplings  35  are arranged to be spaced away from one another in the front-rear direction so as to correspond to four drum couplings  42  (described later) of the photosensitive drums  11 . The drum relay couplings  35  are formed in a substantially columnar shape extending in the left-right direction. Each drum relay coupling  35  penetrates the right side wall  31 R in the left-right direction. Each drum relay coupling  35  includes an input portion  35 A and an output portion  35 B. 
         [0049]    The input portion  35 A is formed in a right end portion of each drum relay coupling  35  in a form of a recess. Specifically, the input portion  35 A is recessed leftward from a right surface of the drum relay coupling  35 . 
         [0050]    The output portion  35 B is formed in a left end portion of each drum relay coupling  35  in a form of a protrusion. Specifically, the output portion  35 B has a generally columnar shape and protrudes leftward from a left surface of each drum relay coupling  35 . 
         [0051]    The four developing relay couplings  34  are provided on an upper portion of the right side plate  31 R. The developing relay couplings  34  are arranged to be spaced away from one another in the front-rear direction such that each developing relay coupling  34  corresponds to a developing coupling  41  (described later) provided in each process cartridge  10 . Further, as shown in  FIG. 2 , each developing relay coupling  34  is positioned diagonally upward and frontward of the corresponding drum relay coupling  35 . The developing relay couplings  34  have a substantially columnar shape, extending in the left-right direction to penetrate the right side wall  31 R in the left-right direction. Each developing relay coupling  34  includes an input portion  34 A and an output portion  34 B. 
         [0052]    The input portion  34 A is formed in a right end portion of each developing relay coupling  34  in a form of a recess. Specifically, the input portion  34 A is recessed leftward from a right surface of each developing relay coupling  34 . 
         [0053]    The output portion  34 B is formed in a left end portion of each developing relay coupling  34  in a form of a protrusion. Specifically, the output portion  34 B protrudes leftward from a left surface of each developing relay coupling  34 . 
         [0054]    The front beam  32  is provided to bridge front end portions of the two side plates  31 . The front beam  32  has a generally plate-like shape extending in the left-right direction. 
         [0055]    The rear beam  33  bridges between rear end portions of the two side plates  31 . The rear beam  33  has a generally plate-like shape extending in the left-right direction. 
         [0056]    (2-2) Process Cartridge 
         [0057]    The process cartridges  10  are substantially box-shaped and elongated in the left-right direction, as shown in  FIG. 3 . Each process cartridge  10  includes a cartridge electrode  43 , the drum coupling  42 , and the developing coupling  41 . 
         [0058]    The cartridge electrode  43  is disposed vertically midway in a left wall constituting an outer casing of each process cartridge  10 . The cartridge electrode  43  has a generally plate-like shape and is made of an electrically conductive material such as metal or electrically conductive resin. Although not shown in the drawings, the cartridge electrode  43  is electrically connected to the corresponding developing roller  13  for supplying power thereto. 
         [0059]    The drum coupling  42  is disposed on a right end portion of each photosensitive drum  11 . The drum coupling  42  includes a supported portion  42 A and a pivoting portion  42 B. 
         [0060]    The supported portion  42 A is formed in a substantially columnar shape extending in the left-right direction. The supported portion  42 A is supported to the right end portion of the photosensitive drum  11  so as not to rotate relative to the same. 
         [0061]    The pivoting portion  42 B is formed in a substantially columnar shape extending in the left-right direction. The pivoting portion  42 B includes a pivot shaft  44  and a coupled portion  45 . 
         [0062]    The pivot shaft  44  has a generally rod-like shape and extends leftward from a left end portion of the pivoting portion  42 B. The pivot shaft  44  has a left end portion pivotally movably supported to a right end portion of the supported portion  42 A. The left end portion of the pivot shaft  44  cannot rotate relative to the right end portion of the supported portion  42 A. 
         [0063]    The coupled portion  45  is formed in a right end portion of the pivoting portion  42 B in a form of a recess. Specifically, the coupled portion  45  is recessed leftward from a right surface of the pivoting portion  42 B. 
         [0064]    With this structure, the pivoting portion  42 B can pivot relative to the supported portion  42 A. Specifically, the pivoting portion  42 B is pivotally movable about the left end portion of the pivot shaft  44  between a first inclined position (shown in  FIG. 5A ) and a first horizontal position (shown in  FIGS. 3 and 5C ) in a front view. In the first inclined position, the pivot shaft  44  of the pivoting portion  42 B is inclined lower right relative to the left-right direction, and in the first horizontal position, the pivot shaft  44  of the pivoting portion  42 B extends generally parallel to the left-right direction. 
         [0065]    The developing coupling  41  is provided in a right end portion of the process cartridge  10 . The developing coupling  41  is positioned upward and frontward of the corresponding drum coupling  42  to correspond to the developing roller  13 . The developing coupling  41  includes a supported portion  41 A and a pivoting portion  41 B. 
         [0066]    The supported portion  41 A is formed in a substantially columnar shape extending in the left-right direction. The supported portion  41 A is rotatably supported to the right end portion of the process cartridge  10 . Although not shown in the drawings, the supported portion  41 A has a left end portion whose entire circumferential surface is formed with gear teeth thereon. The gear teeth are in engagement with a gear train (not shown) to mechanically connect the supported portion  41 A to the developing roller  13 . 
         [0067]    The pivoting portion  41 B is formed in a substantially columnar shape extending in the left-right direction. The pivoting portion  41 B includes a pivot shaft  46  and a coupled portion  47 . 
         [0068]    The pivot shaft  46  is formed in a generally rod-like shape and extends leftward from a left end portion of the pivoting portion  41 B. The pivot shaft  46  has a left end portion pivotally movably supported to the supported portion  41 A. The pivot shaft  46  is incapable of rotating relative to the right end portion of the supported portion  41 A. 
         [0069]    The coupled portion  47  is formed in a right end portion of the pivoting portion  41 B in a form of a recess. Specifically, the coupled portion  47  is recessed leftward from a right surface of the pivoting portion  41 B. 
         [0070]    With this structure, the pivoting portion  41 B can pivot relative to the supported portion  41 A. More specifically, the pivoting portion  41 B is pivotally movable about the left end portion of the pivot shaft  46  between a second inclined position (see  FIG. 5A ) and a second horizontal position (see  FIGS. 3 and 5C ) in a front view. In the second inclined position, the pivot shaft  46  of the pivoting portion  41 B is inclined lower right relative to the left-right direction, whereas in the second horizontal position, the pivot shaft  46  of the pivoting portion  41 B extends generally parallel to the left-right direction. 
       3. Main Casing 
       [0071]    The main casing  2  includes four main-body electrodes  53 , four drum main-body couplings  52 , and four developing main-body couplings  51 , as shown in  FIG. 3 . 
         [0072]    The main-body electrodes  53  are disposed in a left wall (shown without a reference numeral in  FIG. 3 ) of the main casing  2 . The four main-body electrodes  53  are arranged to be spaced away from one another in the front-rear direction to correspond to the four relay electrodes  36  respectively. The main-body electrodes  53  have a generally pillar shape extending in the left-right direction and are made of an electrically conductive material such as metal or electrically conductive resin. The main-body electrodes  53  are configured to move in the left-right direction between a power supplying position (shown by a solid line in  FIG. 3 ) and a power-supply cancellation position (shown by an imaginary line in  FIG. 3 ). As shown in  FIG. 3 , the main-body electrode  53  in the power supplying position is advanced rightward from an inner surface of the left wall of the main casing  2  The main-body electrode  53  in the power-supply cancellation position is retracted leftward from the inner surface of the left wall of the main casing  2 . 
         [0073]    The drum main-body couplings  52  are rotatably provided in a right wall (shown without a reference numeral in  FIG. 3 ) of the main casing  2 . The drum main-body couplings  52  are spaced away from one another in the front-rear direction to correspond to the four drum relay couplings  35  respectively. The drum main-body couplings  52  are formed in a substantially columnar shape extending in the left-right direction. The drum main-body couplings  52  are configured to move in the left-right direction between a first driving-force transmission position (shown by a solid line in  FIG. 3 ) and a first driving-force-transmission cancellation position (shown by an imaginary line in  FIG. 3 ). The drum main-body coupling  52  in the first driving-force transmission position is advanced leftward from an inner surface of the right wall of the main casing  2 . The drum main-body coupling  52  in the first driving-force-transmission cancellation position is retracted rightward from the inner surface of the right wall of the main casing  2 . 
         [0074]    Each drum main-body coupling  52  includes an engaging protrusion  54 . The engaging protrusion  54  is formed on a left end portion of each drum main-body coupling  52 . The engaging protrusion  54  has a generally pillar-like shape and protrudes leftward from a left end face of the drum main-body coupling  52 . 
         [0075]    The developing main-body couplings  51  are rotatably disposed in the right wall of the main casing  2  each at a position diagonally frontward and upward of each drum main-body coupling  52 . The four developing main-body couplings  51  are arranged to be spaced part from one another in the front-rear direction so as to correspond to the four developing relay couplings  34  respectively. The developing main-body couplings  51  are formed in a substantially columnar shape extending in the left-right direction. The developing main-body couplings  51  are configured to move in the left-right direction between a second driving-force transmission position (shown by a solid line in  FIG. 3 ) and a second driving-force-transmission cancellation position (shown by an imaginary line in  FIG. 3 ). The developing main-body coupling  51  in the second driving-force transmission position is advanced leftward from the inner surface of the right wall of the main casing  2 , whereas the developing main-body coupling  51  in the second driving-force-transmission cancellation position is retracted rightward from the inner surface of the right wall of the main casing  2 . 
         [0076]    Each developing main-body coupling  51  includes an engaging protrusion  55 . The engaging protrusion  55  is formed on a left end portion of each developing main-body coupling  51 . The engaging protrusion  55  has a generally pillar-like shape and protrudes leftward from a left end face of the developing main-body coupling  51 . 
       4. Mounting Operation of the Process Cartridges 
       [0077]    (4-1) Mounting of the Process Cartridges on the Process Frame 
         [0078]    For mounting the process cartridges  10  in the main casing  2 , the process frame  9  is first withdrawn to the pull-out position, as shown in  FIG. 4 . Then, the process cartridges  10  are mounted on the withdrawn process frame  9 . 
         [0079]    For mounting the process cartridge  10  on the process frame  9 , first, the process cartridge  10  is held with the photosensitive drum  11  facing downward. Then, the process cartridge  10  is placed above the process frame  9 . 
         [0080]    At this time, the pivoting portion  42 B of the drum coupling  42  pivots downward about the left end portion of the pivot shaft  44 , due to self-weight of the pivoting portion  42 B, such that the pivoting portion  42 B has been displaced to the first inclined position. As a result, the coupled portion  45  of the drum coupling  42  is exposed (opened) rightward and downward. 
         [0081]    Likewise, the pivoting portion  41 B of the developing coupling  41  pivots downward about the left end portion of the pivot shaft  46 , due to self-weight of the pivoting portion  41 B, such that the pivoting portion  41 B has been displaced to the second inclined position. As a result, the coupled portion  47  of the developing coupling  41  is exposed (opened) rightward and downward. 
         [0082]    Then, the process cartridge  10  is inserted into the process frame  9  from above. Consequently, as shown in  FIG. 5B , an upper end portion of the coupled portion  45  of the drum coupling  42  comes in contact with the corresponding output portion  35 B such that the upper end portion of the coupled portion  45  covers the output portion  35 B of the drum relay coupling  35  from above. Likewise, an upper end portion of the coupled portion  47  of the developing coupling  41  comes in contact with the corresponding output portion  34 B such that the upper end portion of the coupled portion  47  covers the output portion  34 B of the developing relay coupling  34  from above. 
         [0083]    Then, the process cartridge  10  is further inserted into the process frame  9 . As the process cartridge  10  comes down, the pivoting portion  42 B of the drum coupling  42  pivots counterclockwise about the upper end portion of the coupled portion  45  in a front view, and is fitted onto the output portion  35 B of the corresponding drum relay coupling  35  from its left side. The pivoting portion  42 B is thus coupled to the corresponding output portion  35 B so as not to rotate relative to each other. 
         [0084]    Similarly, as the process cartridge  10  comes down, the pivoting portion  41 B of the developing coupling  41  pivots counterclockwise about the upper end portion of the coupled portion  47  in a front view, and is fitted onto the output portion  34 B of the corresponding developing relay coupling  34  from its left side. The pivoting portion  41 B is thus coupled to the corresponding output portion  34 B so as not to rotate relative to each other. 
         [0085]    As a result, as shown in  FIG. 5C , the pivoting portion  42 B of the drum coupling  42  now extends substantially horizontally (substantially parallel to the left-right direction), and is in the first horizontal position. The pivoting portion  41 B of the developing coupling  41  now extends substantially horizontally (substantially parallel to the left-right direction), and is in the second horizontal position. 
         [0086]    Incidentally, in the meantime, the cartridge electrode  43  of the process cartridge  10  is received in and fitted with the corresponding relay electrode  36  of the left side plate  31 L of the process frame  9 . 
         [0087]    The mounting of the process cartridge  10  on the process frame  9  is thus completed. 
         [0088]    For detaching the process cartridge  10  from the process frame  9 , the procedures to mount the process cartridge  10  on the process frame  9  described above can be performed in reverse. 
         [0089]    Specifically, the process cartridge  10  is first pulled out upward from the process frame  9 . 
         [0090]    As the process cartridge  10  is pulled upward, the pivoting portion  42 B of the drum coupling  42  pivots clockwise about the upper end portion of the coupled portion  45  in a front view and is displaced from the first horizontal position to the first inclined position. When the process cartridge  10  is completely detached from the process frame  9 , the pivoting portion  42 B is detached from the output portion  35 B of the corresponding drum relay coupling  35 . 
         [0091]    Similarly, as the process cartridge  10  is pulled upward, the pivoting portion  41 B of the developing coupling  41  pivots clockwise about the upper end portion of the coupled portion  47  in a front view and is displaced from the second horizontal position to the second inclined position. When the process cartridge  10  is completely detached from the process frame  9 , the pivoting portion  41 B is detached from the output portion  34 B of the corresponding developing relay coupling  34 . 
         [0092]    (4-2) Mounting of the Process Unit in the Main Casing 
         [0093]    For mounting the process cartridges  10  in the main casing  2 , the process unit  5  (the process frame  9  with the process cartridges  10  mounted therein) is pushed rearward into the main casing  2  to be accommodated therein. The process unit  5  thus moves from the pull-out position (shown in  FIG. 4 ) to the mounted position (shown in  FIG. 1 ). 
         [0094]    When the process unit  5  is in the mounted position, each drum relay coupling  35  is positioned to oppose the corresponding drum main-body coupling  52  in the left-right direction with a predetermined distance therebetween. At this time, the drum main-body coupling  52 , drum relay coupling  35 , and drum coupling  42  are coaxially aligned with one another in the left-right direction. That is, central axes of the drum main-body coupling  52 , drum relay coupling  35 , and drum coupling  42  are aligned with one another or substantially coincident with one another. 
         [0095]    Likewise, each developing relay coupling  34  is positioned to oppose and be separated from the corresponding developing main-body coupling  51  in the left-right direction. At this time, the developing main-body coupling  51 , developing relay coupling  34 , and developing coupling  41  are coaxially aligned with one another in the left-right direction. That is, central axes of the developing main-body coupling  51 , developing relay coupling  34 , and developing coupling  41  are aligned with one another, or substantially coincident with one another. 
         [0096]    Incidentally, each relay electrode  36  is positioned to oppose the corresponding main-body electrode  53  in the left-right direction with a distance kept therebetween. 
         [0097]    Then, the front cover  4  is closed. In association with closing of the front cover  4 , each of the drum main-body couplings  52  is displaced to the first driving-force transmission position as shown in  FIG. 3 . The engaging protrusion  54  of each drum main-body coupling  52  advances rightward and is fitted with the input portion  35 A of the corresponding drum relay coupling  35 . The engaging protrusion  54  is thus coupled to the input portion  35 A so as not to rotate relative to each other. 
         [0098]    Likewise, each of the developing main-body couplings  51  is displaced to the second driving-force transmission position. As a result, the engaging protrusion  55  of each developing main-body coupling  51  is inserted into and fitted with the input portion  34 A of the corresponding developing relay coupling  34  from its right side. The engaging protrusion  55  is thus coupled to the input portion  34 A so as not to rotate relative to each other. 
         [0099]    In the meantime, each of the main-body electrodes  53  is also displaced to its power supplying position as the front cover  4  closes. Each main-body electrode  53  comes in contact with the corresponding relay electrode  36  from its left side. 
         [0100]    For executing an image formation operation, the input portion  35 A of each drum relay coupling  35  is configured to receive a drive force from the corresponding drum main-body coupling  52 . Hence, each of the drum couplings  42  receives the drive force from the output portion  35 B of the corresponding drum relay coupling  35 . 
         [0101]    Likewise, the input portion  34 A of each developing relay coupling  34  is configured to receive a drive force from the corresponding developing main-body coupling  51 . Each of the developing couplings  41  thus receives the drive force from the output portion  34 B of the corresponding developing relay coupling  34 . 
         [0102]    Each of the cartridge electrodes  43  is supplied with power from the corresponding main-body electrode  53  through the corresponding relay electrode  36 . 
         [0103]    For withdrawing the process unit  5  from the main casing  2 , the front cover  4  is first opened. In association with opening of the front cover, each of the drum main-body couplings  52  is displaced to its first driving-force-transmission cancellation position, as indicated by the imaginary line in  FIG. 3 . As a result, the engaging projection portion  54  of each drum main-body coupling  52  is separated from the input portion  35 A of the corresponding drum relay coupling  35 . 
         [0104]    Likewise, each of the developing main-body couplings  51  is displaced to the second driving-force-transmission cancellation position. As a result, the engaging projection portion  55  of each developing main-body coupling  51  is detached from the input portion  34 A of the corresponding developing relay coupling  34 . 
         [0105]    In the meantime, each of the main-body electrodes  53  is displaced to the power-supply cancellation position. Each main-body electrode  53  is thus separated from the corresponding relay electrode  36 . 
         [0106]    Once the drum main-body couplings  52 , developing main-body couplings  51  and the main-body electrodes  53  have all been detached from the corresponding drum relay couplings  35 , developing relay couplings  34  and relay electrodes  36 , the process unit  5  is now ready to be pulled out from the main casing  2 . The process unit  5  is thus pulled out to move from the mounted position to the pull-out position. 
       5. Operations and Technical Advantages 
       [0107]    (1) As shown in  FIG. 3 , the printer  1  of the first embodiment can transmit the drive force from the developing main-body couplings  51  to the developing couplings  41  via the developing relay couplings  34 . 
         [0108]    Incidentally, suppose a drive force is to be transmitted directly from the developing main-body couplings  51  to the developing couplings  41 . In this case, the developing main-body couplings  51  need to be engaged with the developing couplings  41  via openings that should be formed in the process frame  9 . Such structure may possibly make it difficult to shorten a distance by which the developing main-body couplings  51  need to move (advance and retract) relative to the developing couplings  41 . 
         [0109]    If the distance by which the developing main-body couplings  51  move relative to the developing couplings  41  is long, the printer  1  may become larger in size with respect to the direction in which the developing main-body couplings  51  move (or in the left-right direction). 
         [0110]    In contrast thereto, according to the printer  1  of the present embodiment, the process frame  9  is provided with the developing relay couplings  34 . Therefore, the developing main-body couplings  51  are required to move only by such a distance short enough to reach the corresponding developing relay couplings  34  to be engaged therewith for transmitting the drive force to the developing couplings  41 . 
         [0111]    Consequently, the distance by which the developing main-body couplings  51  need to move can be shortened. As a result, the printer  1  can be made smaller in size. 
         [0112]    (2) According to the printer  1  of the present embodiment, the central axis (rotational axis) of each developing coupling  41  is substantially coincident with the central axis (rotational axis) of each developing main-body coupling  51 , as shown in  FIG. 3 . 
         [0113]    Therefore, the rotation of the developing main-body couplings  51  can be accurately synchronized with the rotation of the developing couplings  41 . 
         [0114]    (3) Even though the printer  1  includes the plurality of process cartridges  10 , the printer  1  of the present embodiment can be made compact. 
         [0115]    (4) According to the printer  1  of the present embodiment, engagement between the pivoting portions  41 B of the developing couplings  41  and the output portions  34 B of the corresponding developing relay couplings  34  can be realized in conjunction with mounting operations of the process cartridges  10  on the process frame  9 . In other words, mounting of the process cartridges  10  on the process frame  9  can establish mechanical connections between the developing couplings  41  and the developing relay couplings  34  through which the drive force can be transmitted. 
         [0116]    Further, engagement between the pivoting portions  41 B of the developing couplings  41  and the output portions  34 B of the developing relay couplings  34  can be released through detachment of the process cartridges  10  from the process frame  9 . 
         [0117]    Therefore, in the process frame  9  provided with the developing relay couplings  34 , the operations to attach/detach the process cartridges  10  relative to the process frame  9 , as well as the operations to engage/disengage the developing couplings  41  relative to the developing relay couplings  34  can be performed smoothly. 
       6. Second Embodiment 
       [0118]    Next, detailed constructions of a process cartridge  60  and a process frame  209  according to a second embodiment of the present invention will be described with reference to  FIGS. 6A and 6B . In the following description, like parts and components designated by the same reference numerals with those of the first embodiment to avoid duplicating description. 
         [0119]    (6-1) Overview of the Second Embodiment 
         [0120]    In the first embodiment, the developing coupling  41  of the process cartridge  10  includes the pivotably movable pivoting portion  41 B. The pivoting portion  41 B of the developing coupling  41  is configured to be engaged with the corresponding output portion  34 B of the developing relay coupling  34  provided in the process frame  9  in conjunction with the mounting of the process cartridge  10  on the process frame  9 . 
         [0121]    In contrast, the according to the second embodiment, the process frame  209  is provided with four developing relay couplings  61  configured to slide in the left-right direction. As shown in  FIG. 6A , a process unit  205  (the process frame  209  on which the process cartridges  60  are mounted) is first displaced to the mounted position. Subsequently, as shown in  FIG. 6B , the developing relay couplings  61  are pushed leftward as developing main-body couplings  51  advance and engage with input portions  69  of corresponding developing relay couplings  61 . As a result, output portions  70  of the developing relay couplings  61  are respectively inserted into and fitted with coupled portions  63  of developing couplings  62  provided in the respective process cartridges  60 . 
         [0122]    (6-2) Structures According to the Second Embodiment 
         [0123]    (6-2-1) Process Frame 
         [0124]    The process frame  209  of the second embodiment is provided with four drum relay couplings  64  and four developing relay couplings  61  to correspond to the four process cartridges  60 . 
         [0125]    The drum relay couplings  64  are formed as an Oldham coupling. Each drum relay coupling  64  includes a body portion  71  and a relay plate  72 . 
         [0126]    The body portion  71  is formed in a substantially columnar shape extending in the left-right direction. The body portion  71  includes an input portion  73 . 
         [0127]    The input portion  73  is formed in a right end portion of the body portion  71  in a form of a recess. Specifically, the input portion  73  is recessed leftward from a right surface of the body portion  71 . 
         [0128]    The relay plate  72  is formed in a generally circular disk-like shape and has a thickness in the left-right direction. The relay plate  72  is supported to a left end portion of the body portion  71  such that the relay plate  72  is slidable in a radial direction of the body portion  71  but in capable of rotating relative to the body portion  71 . The relay plate  72  includes an output portion  74  in a form of protrusion. 
         [0129]    The output portion  74  has a generally pillar shape and protrudes leftward from a left end surface of the relay plate  72 . 
         [0130]    The body portion  71  of the drum relay coupling  64  is supported to the right side plate  31 R such that the drum relay coupling  64  can slide in the left-right direction. The drum relay coupling  64  is thus movable between to a first engaged position (shown in  FIG. 6B ) and a first engagement cancellation position (shown in  FIG. 6A ). Specifically, the drum relay coupling  64  in the first engaged position is generally aligned with the right side plate  31 R in the left-right direction, and the drum relay coupling  64  in the first engagement cancellation position is retracted (offset) rightward relative to the first engaged position. The drum relay coupling  64  is constantly biased rightward toward the first engagement cancellation position by a biasing member (not shown). 
         [0131]    The developing relay coupling  61  is formed as an Oldham coupling. Each developing relay coupling  61  includes a body portion  67  and a relay plate  68 . 
         [0132]    The body portion  67  has a substantially columnar shape extending in the left-right direction. The body portion  67  includes the input portion  69 . 
         [0133]    The input portion  69  is formed in a right end portion of the body portion  67  in a form of recess. Specifically, the input portion  69  is recessed leftward from a right surface of the body portion  67 . 
         [0134]    The relay plate  68  has a generally circular disk-like shape and has a thickness in the left-right direction. The relay plate  68  is supported to a left end portion of the body portion  67  such that the relay plate  68  is slidable in a radial direction of the body portion  67  but is incapable of rotating relative to the body portion  67 . The relay plate  68  includes the output portion  70  in a form of protrusion. 
         [0135]    The output portion  70  has a generally pillar-like shape and protrudes leftward from a left end surface of the relay plate  68 . 
         [0136]    The body portion  67  of the developing relay coupling  61  is supported to the right side plate  31  R such that the developing relay coupling  61  can slide in the left-right direction. The developing relay coupling  61  is thus movable between a second engaged position (shown in  FIG. 6B ) and a second engagement cancellation position (shown in  FIG. 6A ). Specifically, the developing relay coupling  61  in the second engaged position is aligned with the right side plate  31 R in the left-right direction, whereas the developing relay coupling  61  in the second engagement cancellation position is retracted (offset) leftward relative to the second engaged position. The developing relay coupling  61  is constantly biased rightward toward the second engagement cancellation position by a biasing member (not shown). 
         [0137]    (6-2-2) Process Cartridges 
         [0138]    The process cartridge  60  of the second embodiment is provided with a drum coupling  65  and a developing coupling  62 . 
         [0139]    The drum coupling  65  is formed in a substantially columnar shape extending in the left-right direction. The drum coupling  65  is non-rotatably supported to the right end portion of a photosensitive drum  11 . The drum coupling  65  includes a coupled portion  66 . 
         [0140]    The coupled portion  66  is formed in a right end portion of the drum coupling  65 . The coupled portion  66  is formed as a recess depressed leftward from a right surface of the drum coupling  65 . 
         [0141]    The developing coupling  62  has a substantially columnar shape extending in the left-right direction. The developing coupling  62  is rotatably supported to a right end portion of the process cartridge  60  and is positioned upward and frontward of the drum coupling  65 . Although not shown in the drawings, the developing coupling  62  has a left end portion whose entire circumferential surface is formed with gear teeth thereon. The gear teeth are in engagement with a gear train (not shown) to mechanically connect the developing coupling  62  to the developing roller  13 . 
         [0142]    The developing coupling  62  includes the coupled portion  63 . 
         [0143]    The coupled portion  63  is formed in a right end portion of the developing coupling  62 . Specifically, the coupled portion  63  is formed as a recess depressed leftward from a right surface of the developing coupling  62 . 
         [0144]    (6-3) Mounting Operation of the Process Cartridges 
         [0145]    (6-3-1) Mounting of Process Cartridges on the Process Frame 
         [0146]    For mounting the process cartridges  60  in the main casing  2 , first, the process frame  209  is withdrawn to the pull-out position shown in  FIG. 4 , as in the first embodiment. Then, the process cartridges  60  are mounted on the process frame  209  withdrawn from the main casing  2 . 
         [0147]    For mounting the process cartridge  60  on the process frame  209 , first, the process cartridge  60  is held with the photosensitive drum  11  facing downward. The process cartridge  60  is then placed above the process frame  209  and inserted into the process frame  209  from above. 
         [0148]    Accordingly, lower end portions of both left and right end portions of the process cartridge  60  are respectively brought into contact with the support ribs  37  formed on the side plates  31  from above. Mounting of the process cartridge  60  on the process frame  209  is thus completed. 
         [0149]    Incidentally, when the process cartridge  60  is mounted on the process frame  209 , the cartridge electrode  43  of the process cartridge  60  is received by the corresponding relay electrode  36  of the process frame  209  (see  FIG. 6A ). 
         [0150]    For detaching the process cartridge  60  from the process frame  209 , the process cartridge  60  is pulled upward from the process frame  209 . 
         [0151]    (6-3-2) Mounting of the Process Unit in the Main Casing 
         [0152]    For mounting the process cartridges  10  in the main casing  2 , the process unit  205  (the process frame  209  with the process cartridges  60  mounted thereon) is pushed rearward into the main casing  2 . The process unit  205  is thus displaced from the pull-out position to the mounted position. 
         [0153]    When the process unit  205  is in the mounted position, each drum relay coupling  64  is positioned as to oppose the corresponding drum main-body coupling  52  while being separated therefrom in the left-right direction. At this time, the drum main-body coupling  52 , drum relay coupling  64 , and drum coupling  65  are coaxially aligned with one another in the left-right direction. That is, central axes of the drum main-body coupling  52 , drum relay coupling  64 , and drum coupling  65  are aligned with one another, or substantially coincident with one another. 
         [0154]    Likewise, each developing relay coupling  61  is positioned in opposition to and in separation from the corresponding developing main-body coupling  51  in the left-right direction. At this time, the developing main-body coupling  51 , developing relay coupling  61 , and developing coupling  62  are coaxially aligned with one another in the left-right direction. In other words, central axes of the developing main-body coupling  51 , developing relay coupling  61 , and developing coupling  62  are aligned with one another or substantially coincident with one another. 
         [0155]    Incidentally, each relay electrode  36  of the process frame  209  is positioned to oppose the corresponding main-body electrode  53  in the left-right direction with a predetermined distance kept therebetween. 
         [0156]    Then, the front cover  4  is closed. In association with closing of the front cover  4 , each of the drum main-body couplings  52  is displaced to the first driving-force transmission position. The engaging protrusion  54  of each drum main-body coupling  52  thus advances leftward to be fitted with the input portion  73  of the corresponding drum relay coupling  64 . As a result, the engaging protrusion  54  is coupled to the input portion  73  so as not to rotate relative to each other. 
         [0157]    Incidentally, the drum relay coupling  64  as a whole is pushed and slid leftward as the engaging protrusion  54  is coupled to the input portion  73 . 
         [0158]    As a result of the sliding of the drum relay coupling  64 , the output portion  74  of the drum relay coupling  64  is fitted into the coupled portion  66  of the corresponding drum coupling  65  from its right side. The output portion  74  of the drum relay coupling  64  is thus coupled to the coupled portion  66  of the drum coupling  65  so as not to rotate relative to each other. 
         [0159]    Likewise, each developing main-body coupling  51  is displaced to the second driving-force transmission position in association with closing of the front cover  4 . The engaging protrusion  55  of each developing main-body coupling  51  advances leftward and is fitted into the input portion  69  of the corresponding developing relay coupling  61  from its right side. The engaging protrusion  55  of the developing main-body coupling  51  is thus coupled to the input portion  69  of the developing relay coupling  61  so as not to rotate relative to each other. 
         [0160]    The developing relay coupling  61  as a whole is pushed and slid leftward as the developing main-body coupling  51  is coupled to the developing relay coupling  61 . 
         [0161]    As a result of the sliding of the developing relay coupling  61 , the output portion  70  of the developing relay coupling  61  is fitted into the coupled portion  63  of the corresponding developing coupling  62  from its right side. The output portion  70  of the developing relay coupling  61  is thus coupled to the coupled portion  63  of the developing coupling  62  so as not to rotate relative to each other. 
         [0162]    In the meantime, each of the main-body electrodes  53  is also displaced to its power supplying position as the front cover  4  closes. Each main-body electrode  53  comes in contact with the corresponding relay electrode  36  from its left side. 
         [0163]    For executing an image formation operation, each drum couplings  65  is configured to receive a drive force from the corresponding drum main-body coupling  52  via the corresponding drum relay coupling  64 . 
         [0164]    Likewise, each developing coupling  62  is configured to receive a drive force from the corresponding developing main-body coupling  51  via the corresponding developing relay coupling  61 . 
         [0165]    Further, each cartridge electrode  43  is supplied with power from the corresponding main-body electrode  53  through the corresponding relay electrode  36 . 
       7. Operations and Technical Advantages of the Second Embodiment 
       [0166]    (7-1) According to the above-described structure of the second embodiment, when the developing main-body coupling  51  is in the second driving-force-transmission cancellation position as shown in  FIG. 6A , the developing relay coupling  61  is retracted from the developing coupling  62  and is placed in the second engagement cancellation position due to the biasing force of the biasing member (not shown). 
         [0167]    Therefore, no interference occurs between the process cartridge  60  and the corresponding developing relay coupling  61  during attachment/detachment of the process cartridge  60  relative to the process frame  209 . 
         [0168]    As a result, smooth attachment and detachment of the process cartridge  60  relative to the process frame  209  can be ensured. 
         [0169]    (7-2) In the second embodiment, the developing relay coupling  61  is formed as an Oldham coupling 
         [0170]    Therefore, even if the central axis of the developing relay coupling  61  is slightly displaced (offset) from the central axis of the corresponding developing coupling  62 , the relay plate  68  of the developing relay coupling  61  can slide relative to the body portion  67 . Hence, the output portion  70  of the developing relay coupling  61  can be smoothly received in and fitted to the coupled portion  63  of the corresponding developing coupling  62 . 
       8. Variations and Modifications 
       [0171]    In the depicted embodiments, the developing roller  13  is an example of a claimed rotary body. However, the photosensitive drum  11  may be an alternative example of the claimed rotary body. 
         [0172]    In this case, taking the first embodiment as an example, the drum coupling  42 , drum relay coupling  35 , drum main-body coupling  52 , pivoting portion  42 B of the drum coupling  42  may correspond to claimed drive-force transmission part, drive-force relay part, drive-force supplying part and coupling, respectively. 
         [0173]    Taking the second embodiment as an example, the drum coupling  65 , drum relay coupling  64  and the drum main-body coupling  52  may correspond to the claimed drive-force transmission part, drive-force relay part and drive-force supplying part, respectively. 
         [0174]    While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.