Abstract:
An image forming device includes a photosensitive unit, a developer cartridge, and a developing device. The photosensitive unit includes a photosensitive body. The developer cartridge accommodates developer therein and has a supported portion supported by the photosensitive unit. The developing device is disposed between the photosensitive unit and the developer cartridge and is supported by the photosensitive unit and is pivotally movable about the supported portion. The developing device includes a developer carrying member carrying the developer thereon. The developer carrying member is movable, in accordance with the pivotal movement of the developing device, between a contact position at which the developer carrying member is in contact with the photosensitive body and a separate position at which the developer carrying member is separated from the photosensitive body.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2010-165769 filed Jul. 23, 2010 and Japanese Patent Application No. 2010-165770 filed Jul. 23, 2010. The entire content of each of these priority applications is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming device. 
       BACKGROUND 
       [0003]    One type of electrophotographic color printer known in the art is a tandem-type color laser printer provided with a process cartridge for each of the toner colors yellow, magenta, cyan, and black. Each process cartridge includes a photosensitive member, and a developing roller for supplying toner to the photosensitive member. 
         [0004]    A process cartridge detachably mountable in the body of such a tandem-type color laser printer is proposed. The process cartridge includes a drum unit provided with a photosensitive drum, and a developing unit provided with a developing roller and serving to accommodate toner. 
         [0005]    The developing unit in this process cartridge is integrally provided with a developing device frame and a covering member. The developing unit is rotatably supported relative to the drum unit by a projected portion projecting from the developing device frame, and a cylindrical portion projecting from the covering member. The developing unit rotates relative to the drum unit about the projected portion and the cylindrical portion serving as the center of rotation. By rotating the developing unit relative to the drum unit, the developing roller separates from the photosensitive drum. 
       SUMMARY 
       [0006]    The conventional process cartridge described above is integrally provided with the developing unit and the drum unit and is detachably mounted in the body of the printer. Further, the developing unit can rotate about the projected portion and cylindrical portion for separating the developing roller from the photosensitive drum. 
         [0007]    However, there has been demand for a developing unit having a developer cartridge accommodating toner (developer) that is separable from a developing device provided with a developing roller so that only the developer cartridge need be replaced for each drum unit (photosensitive member unit). 
         [0008]    To achieve this, consideration has been given for a structure that rotates the developing device about a rotational center passing through the developing device in order to separate the developing roller from the photosensitive drum. 
         [0009]    However, when the center of rotation is established within the developing device, the developing device rotates when the developer cartridge is mounted on or removed from the photosensitive member unit, making it difficult to fix the position of the developer cartridge relative to the developing device. Consequently, the operation for mounting and removing the developer cartridge relative to the photosensitive member unit is complex. 
         [0010]    Further, another conventional color printer has a drawer unit for integrally retaining a plurality of photosensitive drums, and developer cartridges that are detachably mounted in the drawer unit. The developer cartridges are provided so as to be movable between a contact position in which developing rollers contact the respective photosensitive drums and are capable of forming images on the same, and a separated position in which the developing rollers are separated from the photosensitive drums. 
         [0011]    However, in the above conventional color laser printer, the drawer unit can be inserted into the main casing of the printer while the developing rollers remain in the separated position. If an image-forming operation is executed while the printer is in this state, the printer cannot form images normally. 
         [0012]    It is an object of the present invention to provide an image-forming device capable of facilitating operations to mount a developer cartridge on a photosensitive member unit and to remove the developer cartridge from the same. 
         [0013]    Further, it is another object of the present invention to provide an image-forming device capable of preventing such malfunctions. 
         [0014]    In order to attain the above and other objects, the invention provides an image forming device including a photosensitive unit, a developer cartridge, and a developing device. The photosensitive unit includes a photosensitive body. The developer cartridge accommodates developer therein and has a supported portion supported by the photosensitive unit. The developing device is disposed between the photosensitive unit and the developer cartridge and is supported by the photosensitive unit and is pivotally movable about the supported portion. The developing device includes a developer carrying member carrying the developer thereon. The developer carrying member is movable, in accordance with the pivotal movement of the developing device, between a contact position at which the developer carrying member is in contact with the photosensitive body and a separate position at which the developer carrying member is separated from the photosensitive body. 
         [0015]    According to another aspect, the present invention provides an image forming device including a main frame, an image forming unit, a plurality of developer cartridges, an emitting unit, and a plurality of blocking members. The main frame provides therein an accommodation space. The image forming unit is movable between an accommodated position in which the image forming unit is positioned in the accommodation space and a pulled out position in which the image forming unit is displaced from the accommodated space. The image forming device includes a plurality of photosensitive members juxtaposedly arrayed. The plurality of developer cartridges each accommodates therein developer, and each is detachably mounted on the image forming unit in one to one correspondence with each photosensitive member. The emitting unit is provided in the main frame and is configured to emit a laser beam toward each photosensitive member. Each of the plurality of blocking members is provided at each developer cartridge and is movable between a blocking position at which the laser beam directing toward each photosensitive member is shut-off and a transmitting position allowing the laser beam to reach each photosensitive member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    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: 
           [0017]      FIG. 1  is a cross-section side view of an image-forming device according to an embodiment of the invention; 
           [0018]      FIG. 2  is a perspective view of a drawer unit provided in the image-forming device shown in  FIG. 1 ; 
           [0019]      FIG. 3  is a cross-section side view of the drawer unit shown in  FIG. 2 ; 
           [0020]      FIG. 4  is a top view of the drawer unit shown in  FIG. 2 ; 
           [0021]      FIG. 5(   a ) is a perspective view of a developer cartridge provided in the image-forming device shown in  FIG. 1  when the developer cartridge is in an open position; 
           [0022]      FIG. 5(   b ) is a left side of the developer cartridge shown in  FIG. 5(   a ); 
           [0023]      FIG. 6  is a perspective view of the developer cartridge provided in the image-forming device shown in  FIG. 1  when the developer cartridge is in a closed position; 
           [0024]      FIG. 7(   a ) is a perspective view of the developer cartridge provided in the image-forming device shown in  FIG. 5(   a ) when a handle part of the developer cartridge is in a stand state; 
           [0025]      FIG. 7(   b ) is a left side of the developer cartridge shown in  FIG. 5(   a ) when the handle part of the developer cartridge is in a collapsed state; 
           [0026]      FIG. 8  is an explanatory diagram showing how to mount the developer cartridge on the drawer unit; 
           [0027]      FIG. 9  ( a ) is a perspective view of a process unit provided in the image forming device when the process unit is mounted in a main body of the image forming device; 
           [0028]      FIG. 9(   b ) is a front view of the process unit when the process unit is mounted in the main body; 
           [0029]      FIG. 10(   a ) is a side view of the process unit when each developing device is pressed by a corresponding separating cam; 
           [0030]      FIG. 10(   b ) is a cross-section side view of the process unit when each developing device is pressed by the corresponding separating cam; 
           [0031]      FIG. 11  is a cross-section side view of the image forming device during a test pattern reading operation performed by the image forming device; 
           [0032]      FIG. 12  is a perspective view of the process unit in a color mode performed by the image forming device; 
           [0033]      FIG. 13(   a ) is a side view of the process unit when each developing device is not pressed by a corresponding separating cam in the color mode; 
           [0034]      FIG. 13(   b ) is a cross-section side view of the process unit when each developing device is not pressed by the corresponding separating cam in the color mode; 
           [0035]      FIG. 14  is a perspective view of the process unit in a monochrome mode performed by the image forming device; 
           [0036]      FIG. 15(   a ) is a side view of the process unit when each developing device is pressed by a corresponding separating cam in the monochrome mode; and 
           [0037]      FIG. 15(   b ) is a cross-section side view of the process unit when each developing device is not pressed by the corresponding separating cam in the monochrome mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    An image forming device according to embodiment of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
         [0039]    The terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used throughout the description assuming that the image forming device is disposed in an orientation in which it is intended to be used. In use, the image forming device is disposed as shown in  FIG. 1 . 
         [0040]    1. Overall Structure of a Color Laser Printer 
         [0041]    A printer  1  is a direct tandem color laser printer of a horizontal type, whereby photosensitive drums for forming individual colors are juxtaposed horizontally in a tandem arrangement. The printer  1  includes a main casing  2  and, provided in the main casing  2 , a sheet-feeding unit  3  for feeding sheets of a paper P to be printed, and an image-forming unit  4  for forming images on the paper P supplied by the sheet-feeding unit  3 . 
         [0042]    (1) Main Casing 
         [0043]    The main casing  2  has a substantially rectangular box shape in a side view for accommodating the sheet-feeding unit  3  and sheet-feeding unit  3 . A front cover  5  is provided on one side wall of the main casing  2 . The front cover  5  is capable of pivoting relative to the main casing  2  about its lower end and, thus, can be opened to allow mounting and removal of a process unit  10  described later. 
         [0044]    In the following description, the side of main casing  2  on which the front cover  5  is provided (the right side in  FIG. 1 ) will be called the “front side,” and the opposite side (the left side in  FIG. 1 ) will be called the “rear side.” Further, the left and right sides of the main casing  2  will be based on the perspective of a user looking at the printer  1  from the front side. In other words, the near side in  FIG. 1  will be the “left side,” while the far side will be the “right side.” 
         [0045]    (2) Sheet-Feeding Unit 
         [0046]    The sheet-feeding unit  3  includes a paper tray  6  for accommodating sheets of paper P. The paper tray  6  is removably mounted in the bottom section of the main casing  2 . A pair of feeding rollers  7  is disposed above the front end of the paper tray  6 , and a pair of registration rollers  8  is disposed above the feeding rollers  7 . 
         [0047]    The feeding rollers  7  rotate to supply sheets of paper P accommodated in the paper tray  6  to the registration rollers  8  one sheet at a time, and the registration rollers  8  convey the sheets toward the image-forming unit  4  (between photosensitive drums  15  (described later) and a conveying belt  24  (described later)) at a prescribed timing. 
         [0048]    (3) Image-Forming Unit 
         [0049]    The image-forming unit  4  includes a scanning unit  9 , a process unit  10 , a transfer unit  11 , and a fixing unit  12 . 
         [0050]    (3-1) Scanning Unit 
         [0051]    The scanning unit  9  is disposed in the top section of the main casing  2 . Four exit holes  17  are formed in the bottom portion of the scanning unit  9  at positions spaced at intervals in the front-to-rear direction and corresponding to positions of four photosensitive drums  15  (described later). As indicated by solid lines in  FIG. 1 , the scanning unit  9  irradiates laser beams toward the corresponding photosensitive drums  15  (described later) based on image data. The laser beams exit from the corresponding exit holes  17 , pass the rear sides of corresponding toner cartridges  14  (described later), and selectively expose the photosensitive drums  15  (described later). 
         [0052]    (3-2) Process Unit 
         [0053]    (3-2-1) Structure of the Process Unit 
         [0054]    The process unit  10  is disposed in the main casing  2  below the scanning unit  9  and above the transfer unit  11 . The process unit  10  includes a single drawer unit  13 , and four toner cartridges  14  provided for each of the four printing colors. The process unit  10  can be slidably moved between an accommodated position inside the main casing  2 , and a withdrawn position outside the main casing  2 . 
         [0055]    The drawer unit  13  is mounted in the main casing  2  and can slide relative to the main casing  2  in the front-to-rear direction. The drawer unit  13  includes four photosensitive drums  15 , four Scorotron chargers  16 , and four developing devices  18 . 
         [0056]    The photosensitive drums  15  are cylindrical in shape and oriented with their axes extending in the left-to-right direction (longitudinal direction). The four photosensitive drums  15  are arranged parallel to each other and spaced at intervals in the front-to-rear direction. The photosensitive drums  15  specifically include, in order from front to rear, a black photosensitive drum  15 K, a yellow photosensitive drum  15 Y, a magenta photosensitive drum  15 M, and a cyan photosensitive drum  15 C. 
         [0057]    Each of the Scorotron chargers  16  is positioned diagonally above and rearward of the respective photosensitive drum  15 . The Scorotron chargers  16  face the respective photosensitive drums  15  but are separated therefrom. 
         [0058]    The developing devices  18  are supported in the drawer unit  13  at positions above the corresponding photosensitive drums  15  so as to confront the photosensitive drums  15 . The developing devices  18  specifically include, in order from front to rear, a black developing device  18 K, a yellow developing device  18 Y, a magenta developing device  18 M, and a cyan developing device  18 C. Each of the developing devices  18  is also provided with a developing roller  19 . 
         [0059]    As will be described later, the developing roller  19  is rotatably supported in the lower end of the developing device  18  so that the peripheral surface of the developing roller  19  is exposed on the rear side. The developing roller  19  opposes and contacts the upper front edge of the respective photosensitive drum  15 . 
         [0060]    Each developing device  18  includes a supply roller  20  for supplying toner to the developing roller  19 , and a thickness-regulating blade  21  for regulating the layer thickness of toner supplied to the developing roller  19 . 
         [0061]    The toner cartridges  14  are supported in the drawer unit  13  at positions above corresponding developing devices  18  so as to confront the same. The toner cartridges  14  specifically include, in order from front to rear, a black toner cartridge  14 K, a yellow toner cartridge  14 Y, a magenta toner cartridge  14 M, and a cyan toner cartridge  14 C. The toner cartridges  14  are detachably supported in the drawer unit  13  and function to accommodate toner of the corresponding color. 
         [0062]    (3-2-2) Developing Operations of the Process Unit 
         [0063]    Toner accommodated in the toner cartridge  14  is supplied onto the supply roller  20  in the developing device  18 , and the supply roller  20  in turn supplies the toner to the developing roller  19 . 
         [0064]    As the developing roller  19  rotates, the thickness-regulating blade  21  regulates the thickness of the layer of toner supplied to the developing roller  19  so that the developing roller  19  carries a uniform thin layer of toner on the surface thereof. Further, the toner supplied to the developing roller  19  is positively tribocharged between the developing roller  19  and thickness-regulating blade  21 . 
         [0065]    In the meantime, the Scorotron charger  16  applies a uniform positive charge to the surface of the photosensitive drum  15  as the photosensitive drum  15  rotates. Subsequently, the scanning unit  9  irradiates laser beams (indicated by solid lines in  FIG. 1 ), exposing the surfaces of the photosensitive drums  15  in a high-speed scan to form electrostatic latent images on the surfaces of the photosensitive drums  15  corresponding to an image to be formed on the paper P. 
         [0066]    As the photosensitive drum  15  continues to rotate, the positively charged toner carried on the surface of the developing roller  19  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  15 . The toner develops the latent image into a visible toner image by reversal. 
         [0067]    (3-3) Transfer Unit 
         [0068]    The transfer unit  11  is disposed inside the main casing  2  above the sheet-feeding unit  3  and below the process unit  10 . The transfer unit  11  is elongated in the front-to-rear direction and includes a drive roller  22 , a follow roller  23 , a conveying belt  24 , and four transfer rollers  25 . 
         [0069]    The drive roller  22  and follow roller  23  are disposed in parallel to each other and are separated in the front-to-rear direction. 
         [0070]    The conveying belt  24  is looped around the drive roller  22  and follow roller  23  and is positioned so that its upper portion confronts and contacts each of the photosensitive drums  15  from below. When the drive roller  22  is driven to rotate, the conveying belt  24  circulates so that its upper portion in contact with the photosensitive drums  15  moves rearward. 
         [0071]    Each of the transfer rollers  25  is disposed within the inner space defined by the conveying belt  24  at positions opposing respective photosensitive drums  15  through the upper portion of the conveying belt  24 . 
         [0072]    When a sheet of paper P is supplied from the sheet-feeding unit  3  onto the conveying belt  24 , the conveying belt  24  conveys the sheet rearward so that the sheet passes sequentially through transfer positions at which the transfer rollers  25  confront the photosensitive drums  15 . As the conveying belt  24  conveys the sheet of paper P, each photosensitive drum  15  sequentially transfers a toner image of the corresponding color onto the paper P to form a color image thereon. 
         [0073]    (3-4) Fixing Unit 
         [0074]    The fixing unit  12  is positioned on the rear side of the transfer unit  11 . The fixing unit  12  includes a heating roller  26 , and a pressure roller  27  disposed in confrontation with the heating roller  26 . After a color image is transferred onto the paper P, the image is fixed to the paper P by heat and pressure as the paper P passes between the heating roller  26  and pressure roller  27  in the transfer unit  11 . 
         [0075]    (4) Sheet Discharge 
         [0076]    A U-shaped path is formed in the main casing  2  on the downstream side of the transfer unit  11  and leads from the transfer unit  11  to the top of the main casing  2 . A sheet-discharge tray  29  is formed on the top of the main casing  2  above the scanning unit  9 . Pairs of discharge rollers  28  are provided along the U-shaped path. 
         [0077]    After the toner image has been fixed to the sheet of paper P in the transfer unit  11 , the discharge rollers  28  convey the sheet along the U-shaped path and discharge the sheet onto the sheet-discharge tray  29 . 
         [0078]    2. Detailed Description of the Process Unit 
         [0079]    (1) Drawer Unit 
         [0080]    As shown in  FIG. 2 , the drawer unit  13  includes a drawer frame  31  having a substantially rectangular frame-like shape in a plan view, and the developing devices  18  supported in the drawer frame  31 . 
         [0081]    (1-1) Drawer Frame 
         [0082]    The drawer frame  31  includes a pair of left and right side plates  32 , a front beam  33  bridging the front ends of the side plates  32 , and a rear beam  34  bridging the rear ends of the side plates  32 . 
         [0083]    The side plates  32  are substantially rectangular in shape in a side view and elongated in the front-to-rear direction. The side plates  32  are arranged parallel to each other and spaced away from each other in the left-to-right direction (the longitudinal direction of the photosensitive drums  15 ). Each of the photosensitive drums  15 , Scorotron chargers  16 , and developing devices  18  is held between the left and right side plates  32  on the left and right sides thereof. 
         [0084]    Formed in each of the side plates  32  are cartridge guide grooves  35 , separating cam receiving units  36 , and pairs of developing device support grooves  39  (see  FIG. 3 ). 
         [0085]    The cartridge guide grooves  35  are cut out in the inside surfaces of the side plates  32 , extending downward from the top edges of the side plates  32  to a position just above the respective developing devices  18 . The upper ends of the cartridge guide grooves  35  widen toward the top, giving the cartridge guide grooves  35  a general Y-shape in a side view. The cartridge guide grooves  35  have a width capable of receiving cartridge support parts  95  (described later) on the toner cartridges  14 . 
         [0086]    Outer case fitting grooves  37  are formed in the inside surfaces of the side plates  32 , one on the front side of each cartridge guide groove  35 . The outer case fitting grooves  37  are in communication with the corresponding cartridge guide grooves  35 . Specifically, each outer case fitting groove  37  is cut out substantially in an arc shape when viewed from the side, continuing from the front edge of the corresponding cartridge guide groove  35  and curving downward toward the front. The outer case fitting grooves  37  are formed with a width capable of receiving engaging pieces  98  (described later) of outer cases  82  (described later) with some play. 
         [0087]    The separating cam receiving units  36  are formed in the inner surfaces of the left and right side plates  32  below each of the cartridge guide grooves  35  and on the outside of both left and right sides of the developing devices  18 . The separating cam receiving units  36  are substantially rectangular in a side view and form recesses in the inside surfaces of the left and right side plates  32  that recede partway into the side plates  32 . 
         [0088]    A separating cam exposure hole  40  and a developing roller shaft insertion hole  43  are formed in each of the separating cam receiving units  36  (see  FIGS. 2 and 9 ). A separating cam  38  is accommodated in each separating cam receiving unit  36 . 
         [0089]    The separating cam exposure holes  40  are vertically elongated holes formed in the upper portions of the side plates  32 , penetrating the side plates  32  in the left-to-right direction. The inner end of each separating cam exposure hole  40  is in communication with the upper end of a separating cam receiving unit  36 . 
         [0090]    The developing roller shaft insertion holes  43  are elongated holes extending in the front-to-rear direction and are formed in the side plates  32  at positions diagonally below and rearward of corresponding separating cam exposure holes  40 . The developing roller shaft insertion holes  43  are in substantially the vertical center of the side plates  32  and penetrate the side plates  32  in the left-to-right direction. The inner ends of the developing roller shaft insertion holes  43  are in communication with the lower ends of corresponding separating cam receiving units  36 . 
         [0091]    As shown in  FIG. 10(   a ), the separating cam  38  is integrally provided with a supporting part  46  that is substantially cylindrical in shape, a pressing lever part  47  extending continuously downward from the supporting part  46 , and an operating lever part  48  extending continuously forward from the supporting part  46 . In a side view, the separating cam  38  has a general L-shape. 
         [0092]    The supporting part  46  is rotatably supported inside the separating cam receiving unit  36  at a position above the developing roller  19 , when projected in a left-to-right direction. 
         [0093]    The pressing lever part  47  extends downward from the supporting part  46  to a position on the rear side of a corresponding developing roller shaft  69  (described later). The lower end of the pressing lever part  47  confronts the developing roller shaft  69  from the rear side. A contact part  50  that is substantially rectangular in a side view is formed on the lower end of the pressing lever part  47 . The contact part  50  protrudes forward from the pressing lever part  47  and contacts the developing roller shaft  69 . 
         [0094]    The operating lever part  48  extends forward from the supporting part  46 . A substantially cylindrical operating part  49  is provided on the front end of the operating lever part  48  and extends outward therefrom in both left and right directions. The left and right outer ends of each operating part  49  are inserted into respective separating cam exposure holes  40  formed in the separating cam receiving units  36  from the inner sides thereof and are exposed on the left and right outer sides of the side plates  32 . A compressed spring  51  disposed at the front end of each operating lever part  48  constantly urges the front end upward. 
         [0095]    As shown in  FIG. 3 , the developing device support grooves  39  are formed in the inner side surfaces of the left and right side plates  32  at intervals in the front-to-rear direction. The upper ends of the separating cam receiving units  36  are respectively interposed between ends of the developing device support grooves  39  in the front-to-rear direction. In a side view, both developing device support grooves  39  in each pair are formed as elongated holes following the circumference of a circle centered on the bottom end of the corresponding cartridge guide groove  35 . The width of the developing device support grooves  39  is sufficient for receiving developing device support bosses  70  (described later) of the developing devices  18 . 
         [0096]    (1-2) Developing Devices 
         [0097]    As shown in  FIGS. 3 and 4 , each developing device  18  includes a developing device frame  61 , and a developing device shutter  62 . 
         [0098]    Each developing device frame  61  is formed in a triangular box shape that is elongated in the left-to-right direction. In a side view, the developing device frame  61  is shaped substantially like an isosceles triangle with its vertex angle pointing downward to the rear. The lower portion of the developing device frame  61  is open on the rear side. The developing roller  19  is rotatably supported in the lower portion of the developing device frame  61 . 
         [0099]    The top wall constituting the developing device frame  61  is substantially arc-shaped in a side view, opening upward, so as to follow the outer peripheral surface of the corresponding toner cartridge  14 . Formed in the top wall of each developing device frame  61  are three developer openings  64 , and a pair of left and right cartridge fixing holes  65 . 
         [0100]    The developer openings  64  are arranged in a series at intervals in the left-to-right direction. Each developer opening  64  is substantially rectangular in a plan view and is elongated in the left-to-right direction. The developer openings  64  penetrate the upper wall of the developing device frame  61  vertically to allow passage of toner. 
         [0101]    The cartridge fixing holes  65  ( FIG. 4 ) are formed in the top wall of the developing device frame  61 , one near each of the left and right ends thereof. The cartridge fixing holes  65  are substantially rectangular in a plan view and are shaped to fit cartridge fixing protrusions  91  (described later) on the toner cartridge  14 . 
         [0102]    The developing device shutter  62  is supported on the top wall of the corresponding developing device frame  61  so as to be capable of sliding in front and rear directions. Each of the developing device shutters  62  has a plate shape. In a side view, the developing device shutters  62  are substantially arc-shaped, opening upward, so as to conform to the outer peripheral surface of the corresponding toner cartridges  14 . 
         [0103]    Formed in each developing device shutter  62  are three developing device shutter openings  66 , a pair of left and right cartridge fixing protrusion insertion holes  68 , and a pair of left and right shutter fixing holes  67 . 
         [0104]    The developing device shutter openings  66  are arranged in a series at intervals in the left-to-right direction at positions corresponding to the developer openings  64 . The developing device shutter openings  66  are substantially rectangular in a plan view. 
         [0105]    The cartridge fixing protrusion insertion holes  68  are disposed one on each left and right end of the developing device shutter  62  at positions corresponding to the cartridge fixing holes  65  of the developing device  18 . Each cartridge fixing protrusion insertion hole  68  is substantially rectangular in a plan view and elongated in the front-to-rear direction at a length substantially equivalent to the sliding range of the developing device shutter  62 . Thus, the cartridge fixing holes  65  are constantly exposed in the cartridge fixing protrusion insertion holes  68  when the developing device shutter  62  slides. 
         [0106]    The shutter fixing holes  67  are formed in the developing device shutter  62  at positions inside the rear ends of the cartridge fixing protrusion insertion holes  68  with respect to the left-to-right direction. Each shutter fixing hole  67  is substantially rectangular in a plan view and penetrates the developing device shutter  62 . The shutter fixing hole  67  is shaped to receive shutter fixing protrusions  85  (described later) on an outer case  82  (described later). 
         [0107]    The developing device shutter  62  is moved between a closed position for covering the developer openings  64  (see  FIG. 3 ) and an open position for revealing the developer openings  64  (see  FIG. 10(   b )). The developing device shutter  62  moves in a rearward direction from the closed position to the open position. 
         [0108]    When the developing device shutter  62  is in the closed position, the developing device shutter openings  66  are positioned forward of the developer openings  64 . Hence, the developing device shutters  62  cover the developer openings  64  to restrict the passage of toner. 
         [0109]    When the developing device shutter  62  is in the open position, the developing device shutter openings  66  are positioned in opposition to the developer openings  64 , thereby exposing the developer openings  64  to allow the passage of toner. 
         [0110]    An auger  71  is provided inside each developing device frame  61 . The auger  71  extends in the left-to-right direction and is rotatably disposed below the corresponding developer opening  64 . By rotating, the auger  71  conveys toner supplied into the developing device frame  61  from the toner cartridge  14  in left and right directions. 
         [0111]    As described above, each of the developing device frames  61  accommodates the supply roller  20 , developing roller  19 , and thickness-regulating blade  21 . The supply roller  20  confronts the corresponding auger  71  vertically, but is separated a slight distance therefrom. The developing roller  19  contacts the supply roller  20  from a direction diagonally below and rearward thereof. The thickness-regulating blade  21  contacts the top of the developing roller  19 . 
         [0112]    The developing roller  19  also includes a developing roller shaft  69  as a rotational shaft. The left and right ends of the developing roller shaft  69  are rotatably supported in the developing device  18 . More specifically, the left and right ends of the developing roller shaft  69  penetrate the left and right side walls of the developing device  18 , protruding toward the left and right side plates  32  of the drawer frame  31 , and are positioned in the bottom ends of the corresponding separating cam receiving units  36 . 
         [0113]    Each developing device frame  61  also includes a pair of front and rear developing device support bosses  70  formed on both left and right side walls near the upper edge of the developing device frame  61 . 
         [0114]    The developing device support bosses  70  are substantially cylindrical in shape and protrude outward in left and right directions from the left and right edges, respectively. 
         [0115]    By slidably fitting the developing device support bosses  70  into the corresponding developing device support grooves  39 , the developing device  18  is retained while being capable of pivoting in front and rear directions relative to the drawer frame  31  about the lower ends of the cartridge guide grooves  35 . The developing device  18  contacts the photosensitive drum  15  when pivoting forward and separates from the photosensitive drum  15  when pivoting rearward. 
         [0116]    (2) Toner Cartridges 
         [0117]    As shown in  FIG. 5(   a ), the toner cartridge  14  has a general cylindrical shape and is elongated in the left-to-right direction. The toner cartridge  14  includes an inner case  81 , an outer case  82 , and a handle part  87 . 
         [0118]    (2-1) Inner Case 
         [0119]    As shown in  FIGS. 5(   a ) and  6 , the inner case  81  has a hollow, substantially cylindrical shape and is elongated in the left-to-right direction. The inner case  81  functions to accommodate toner. 
         [0120]    Cartridge support parts  95 , cartridge fixing protrusions  91 , and pressure-receiving parts  94  are provided on the inner case  81 , while three cartridge openings  83  are formed in the inner case  81 . 
         [0121]    The cartridge support parts  95  are provided one on each left and right end of the inner case  81  and are aligned with the central axis of the inner case  81 . The cartridge support parts  95  are substantially cylindrical in shape and extend outward from the left and right ends of the inner case  81  in the left and right directions, respectively. 
         [0122]    The cartridge openings  83  are formed in the bottom region of the inner case  81 . The cartridge openings  83  are substantially rectangular in a plan view and are arranged in a series at intervals in the left-to-right direction corresponding to positions opposing the developer openings  64 . 
         [0123]    The cartridge fixing protrusions  91  are provided one near each left and right end of the inner case  81 . The cartridge fixing protrusions  91  are substantially square pillar-shaped and protrude downward from the bottom of the inner case  81 . 
         [0124]    The pressure-receiving parts  94  are formed on the top edge of the inner case  81 , with one on each left and right end thereof. In a side view, each pressure-receiving part  94  is substantially triangular-shaped with one vertex pointing toward the front so that the pressure-receiving part  94  protrudes forward. The top edge of each pressure-receiving part  94  is aligned in the front-to-rear direction. 
         [0125]    As shown in  FIG. 8 , toner seals  100  are affixed to the surface of the inner case  81  so as to surround the periphery of the cartridge openings  83 . The toner seals  100  form seals between the inner case  81  and outer case  82  to prevent toner leakage. 
         [0126]    (2-2) Outer Case 
         [0127]    The outer case  82  is hollow with a substantially cylindrical shape for covering the outer peripheral surface of the inner case  81 . The inner case  81  is accommodated in the outer case  82 , but is capable of rotating relative to the outer case  82 . 
         [0128]    More specifically, in cross section, the outer case  82  has a general arc shape that conforms to the outer peripheral surface of the inner case  81 . 
         [0129]    Three outer case openings  84 , a pair of left and right cartridge fixing protrusion insertion holes  96 , and cartridge support part insertion holes  99  are formed in each outer case  82 . Additionally, pressure-receiving part insertion holes (not shown) are formed in the upper edge of the outer case  82 . These insertion holes are open on the front side for receiving the pressure-receiving parts  94  of the inner case  81 . 
         [0130]    The outer case  82  is also provided with a pair of left and right shutter fixing protrusion  85 , and a pair of left and right engaging pieces  98 . 
         [0131]    The outer case openings  84  are substantially rectangular in a plan view and are arranged in a series at intervals in the left-to-right direction so as to correspond to positions opposing the developer openings  64 . 
         [0132]    The cartridge fixing protrusion insertion holes  96  are formed near the left and right ends of the outer case  82  at positions corresponding to the cartridge fixing protrusions  91  provided on the inner case  81 . The cartridge fixing protrusion insertion holes  96  are substantially rectangular in a plan view and have a front-to-rear length substantially equivalent to that of the cartridge fixing protrusion insertion holes  68  formed in the developing device shutter  62 . The cartridge fixing protrusions  91  are inserted through the cartridge fixing protrusion insertion holes  96 . 
         [0133]    The cartridge support part insertion holes  99  are formed one in each of the left and right endfaces of the outer case  82  and are aligned with the center axis of the same. The cartridge support part insertion holes  99  are substantially circular in a side view and can receive the cartridge support parts  95  of the inner case  81 . The cartridge support parts  95  are inserted through the cartridge support part insertion holes  99  from the inner sides thereof and are capable of rotating relative to the cartridge support part insertion holes  99 . 
         [0134]    The shutter fixing protrusions  85  are disposed just inside the rear ends of the cartridge fixing protrusion insertion holes  96  with respect to the left and right directions. The shutter fixing protrusions  85  have a substantially square pillar shape and protrude downward from the outer case  82 . 
         [0135]    The engaging pieces  98  are formed one on each left and right endface of the outer case  82  at a position above the cartridge support part insertion hole  99 . The engaging pieces  98  are ridges elongated in the front-to-rear direction and protruding outward from the endfaces in the left and right directions. In a side view, the engaging pieces  98  are curved in a substantially arc shape that share its arc center with the central axis of the outer case  82 . 
         [0136]    The outer case  82  can move between a closed position (see  FIG. 5(   a )) for covering the outer case openings  84 , and an open position (see  FIG. 6)  for uncovering the outer case openings  84 . The outer case  82  is rotated clockwise in a left side view when moving from the closed position to the open position. 
         [0137]    When the outer case  82  is in the closed position, the outer case openings  84  are positioned forward of the cartridge openings  83 , and the inner wall surface of the outer case  82  covers the cartridge openings  83  (see  FIG. 5(   a )). 
         [0138]    Accordingly, the outer case  82  restricts the passage of toner through the cartridge openings  83  in this state. 
         [0139]    When the outer case  82  is in the open position, the outer case openings  84  confront and expose the cartridge openings  83  (see  FIG. 6 ). Accordingly, the outer case  82  allows passage of toner through the cartridge openings  83  in this state. 
         [0140]    (2-3) Handle Part 
         [0141]    As shown in  FIG. 7(   a ), the handle part  87  includes a first handle part  88  and a second handle part  89  for a user&#39;s gripping. 
         [0142]    The first handle part  88  is formed on the lower rear end of the handle part  87  in substantially the left-to-right center of the rear portion of the outer case  82 . The first handle part  88  is a ridge-like protrusion elongated in the left-to-right direction and protrudes rearward when the outer case  82  is in the closed position. 
         [0143]    The first handle part  88  is disposed in a first position extending rearward when the outer case  82  is in the closed position and is in a second position extending diagonally upward and rearward when the outer case  82  is in the open position. 
         [0144]    The protruding length of the first handle part  88  is set such that the first handle part  88  projects into the irradiating path of the laser beam when disposed in the first position inside the main casing  2  (see the black toner cartridge  14 K in  FIG. 11 ), but is retracted from the irradiating path when in the second position (see the non-black toner cartridges  14  in  FIG. 11 ). 
         [0145]    The second handle part  89  includes a grip member  101 , and a pair of left and right restricting members  102 . 
         [0146]    The grip member  101  is formed in a flat plate shape. In a plan view, the grip member  101  appears substantially U-shaped, with the opening of the “U” on the rear side. The rear ends of the grip member  101  are rotatably coupled with the rear end of the first handle part  88 . A slide groove  103  is formed one in each of the outer left and right surfaces of the grip member  101  and is elongated in the front-to-rear direction. The slide grooves  103  receive the rear ends of the corresponding restricting members  102 . 
         [0147]    The restricting members  102  are rods formed in a narrow plate shape that curves gently while extending in the front-to-rear direction. The front end of each restricting member  102  is rotatably coupled in the top of the outer case  82 , while the rear end is slidably fitted in the corresponding slide groove  103  of the grip member  101 . 
         [0148]    The second handle part  89  is operated between a collapsed state in which the grip member  101  contacts the outer periphery of the outer case  82 , and a raised state in which the grip member  101  is separated from the outer periphery of the outer case  82 . 
         [0149]    More specifically, when the second handle part  89  is in the collapsed state shown in  FIG. 5(   b ), the restricting members  102  are fitted in the rear ends of the corresponding slide grooves  103  formed in the grip member  101 . In this state, the grip member  101  and restricting members  102  are collapsed onto the outer case  82  such that they almost entirely overlap one another in a left-to-right projection. 
         [0150]    When the second handle part  89  is in the raised state shown in  FIG. 7(   b ), the restricting members  102  are fitted into the front ends of the corresponding slide grooves  103  formed in the grip member  101 . In this state, the grip member  101  and restricting members  102  are erected to form a general L-shape in a left-to-right projection. 
         [0151]    3. Internal Structure of the Main Casing 
         [0152]    As shown in  FIG. 1 , the main casing  2  is provided with pressing members  111 , a patch sensor  112 , a CPU  113 , and pressing cams  114  (see  FIG. 9(   a )). 
         [0153]    (1) Pressing Members 
         [0154]    Four of the pressing members  111  are provided on the upper left and right edges of the main casing  2  at positions corresponding to the pressure-receiving parts  94  of the toner cartridges  14 . The pressing members  111  apply pressure to the tops of the pressure-receiving parts  94 . 
         [0155]    (2) Patch Sensor and CPU 
         [0156]    The patch sensor  112  is disposed diagonally below and rearward of the drive roller  22  provided in the transfer unit  11 . The CPU  113  is connected to the patch sensor  112 . 
         [0157]    (3) Pressing Cams 
         [0158]    As shown in  FIG. 9 , one of the pressing cams  114  is provided on each of the left and right sides of the main casing  2  adjacent to the process unit  10 . Each pressing cam  114  includes a black pressing cam  115 , and a color pressing cam  116 . 
         [0159]    The black pressing cam  115  is disposed adjacent to the separating cam  38  corresponding to the black developing device  18 K. The black pressing cam  115  applies pressure to the top of the operating part  49  constituting the separating cam  38  that corresponds to the black developing device  18 K. This black pressing cam  115  includes a drive shaft  117 , and a levering member  118 . 
         [0160]    The drive shaft  117  is rotatably supported in the main casing  2  and extends in the front-to-rear direction. The drive shaft  117  is rotated by a drive force inputted from the main casing  2 . 
         [0161]    The levering member  118  is integrally provided with a cylindrical part  119  elongated in the front-to-rear direction, and a lever part  120  extending tangentially from the peripheral surface of the cylindrical part  119 . 
         [0162]    The drive shaft  117  of the black pressing cam  115  is inserted into the cylindrical part  119  of the levering member  118  in a relatively non-rotatable manner. 
         [0163]    The color pressing cam  116  is disposed adjacent to the separating cams  38  corresponding to developing devices  18  for toner colors yellow, magenta, and cyan and applies pressure to the tops of the operating parts  49  constituting the separating cams  38  corresponding to these color developing devices  18 . The color pressing cam  116  includes one long drive shaft  117 , and three levering members  118  corresponding to the three colors yellow, magenta, and cyan. 
         [0164]    The drive shaft  117  of the color pressing cam  116  is inserted into the cylindrical part  119  of each levering member  118  so as to be relatively non-rotatable with the same. Hence, the three levering members  118  are integrally held on a single drive shaft  117 . 
         [0165]    4. Mounting and Removal of the Toner Cartridges Relative to the Main Casing 
         [0166]    Next, the operations for mounting a toner cartridge in and removing a toner cartridge from the main casing will be described with reference to  FIG. 8 . For this description, it will be assumed that the developing device shutters  62  of the developing devices  18  and the outer cases  82  of the toner cartridges  14  are in their respective closed positions. 
         [0167]    To install a toner cartridge  14  in the main casing  2 , first the operator pulls the drawer unit  13  out from the main casing  2  to the withdrawn position and mounts the toner cartridge  14  in the drawer unit  13 . 
         [0168]    When mounting a toner cartridge  14  in the drawer unit  13 , the operator grips the second handle part  89  (in the raised state) of the toner cartridge  14 , and positions the toner cartridge  14  over the drawer unit  13  so that the pressure-receiving parts  94  are facing forward and the cartridge fixing protrusions  91  and shutter fixing protrusions  85  are facing downward. The operator aligns the cartridge support parts  95  with the corresponding cartridge guide grooves  35  formed in the side plates  32  and inserts the toner cartridge  14  downward into the drawer unit  13 . 
         [0169]    At this time, the cartridge support parts  95  are fitted into the bottoms of the cartridge guide grooves  35  and the toner cartridge  14  is mounted in the drawer unit  13 , as illustrated by the state of the black toner cartridge  14 K in  FIG. 8 . 
         [0170]    Through this process, the cartridge fixing protrusions  91  of the inner case  81  are inserted through cartridge fixing protrusion insertion holes  68  formed in the developing device shutter  62  and fitted in the cartridge fixing holes  65  formed in the developing device  18 , thereby fixing the inner case  81  to the developing device  18 . In addition, the shutter fixing protrusions  85  formed on the outer case  82  are fitted into the shutter fixing holes  67  formed in the developing device shutter  62 , fixing the outer case  82  to the developing device shutter  62 . Further, the engaging pieces  98  formed on the outer case  82  oppose outer case fitting grooves  37  formed in the drawer frame  31  in the front-to-rear direction. 
         [0171]    Next, the operator presses the second handle part  89  of the toner cartridge  14  into the collapsed state. More specifically, the operator collapses the grip member  101  by sliding the rear ends of the restricting members  102  rearward in the corresponding slide grooves  103  formed in the grip member  101 . 
         [0172]    Next, the operator grips the handle part  87  of the toner cartridge  14  and rotates the outer case  82  forward. Through this operation, the outer case  82  rotates about the cartridge support parts  95  of the inner case  81  into the open position illustrated by the non-black toner cartridges  14  in  FIG. 8 . The developing device shutter  62  is also moved to the open position together with the outer case  82 . 
         [0173]    By performing this operation, the cartridge openings  83  formed in the inner case  81 , the outer case openings  84  formed in the outer case  82 , the developing device shutter openings  66  formed in the developing device shutter  62 , and the developer openings  64  formed in the developing device  18  are all in communication with one another, allowing toner to pass from the inner case  81  to the developing device  18 . 
         [0174]    Further, when rotating the outer case  82 , the engaging pieces  98  are fitted into the corresponding outer case fitting grooves  37  formed in the drawer frame  31 . 
         [0175]    After mounting the toner cartridges  14  in the drawer unit  13 , the drawer unit  13  is slid to the accommodated position inside the main casing  2 , completing the operation to mount the toner cartridges  14  in the main casing  2 . 
         [0176]    In order to remove a toner cartridge  14  from the main casing  2 , the above operations for mounting the toner cartridge  14  in the main casing  2  are performed in reverse. 
         [0177]    That is, the operator first pulls the drawer unit  13  out to the withdrawn position, then grips the first handle part  88  and rotates the toner cartridge  14  rearward. Next, the operator lifts the grip member  101  of the second handle part  89  until the second handle part  89  is in the raised state. By continuing to lift upward, the operator pulls the toner cartridge  14  upward and out of the drawer unit  13 . 
         [0178]    Once the toner cartridges  14  have been mounted in the main casing  2 , the lever parts  120  of the pressing cams  114  are respectively positioned above operating parts  49  constituting the separating cams  38  for all colors, as shown in  FIGS. 9(   a ) and  9 ( b ). 
         [0179]    Further, the pressing members  111  in the main casing  2  apply pressure to the tops of the pressure-receiving parts  94  for each toner cartridge  14 , as shown in  FIG. 10(   a ). 
         [0180]    At this time, the toner cartridge  14  is integrally mounted with the developing device  18 . Accordingly, when the pressure-receiving parts  94  of the toner cartridge  14  are pressed, the developing device  18  is pressed toward the photosensitive drum  15  together with the toner cartridge  14 . 
         [0181]    Here, the urging force of the compressed springs  51  applied to the operating lever parts  48  of the separating cams  38  is greater than the force with which the pressing members  111  push against the pressure-receiving parts  94 . Therefore, the urging force of the compressed springs  51  constantly urge the separating cams  38  to rotate counterclockwise in a left side view and to press the developing roller shaft  69  of the developing device  18  forward with the contact parts  50 . 
         [0182]    With this construction, the developing device  18  is constantly separated from the photosensitive drum  15 , as shown in  FIG. 10(   b ). That is, when the developing device  18  is separated from the photosensitive drum  15 , the pressure applied by the separating cams  38  to the developing device  18  is greater than the pressure applied by the pressing members  111  to the developing device  18 . 
         [0183]    5. Detecting the Open/Closed State of the Outer Cases 
         [0184]    When the toner cartridges  14  are mounted in the main casing  2 , the printer  1  initially performs the developing operation and transferring operation described earlier to form test patterns (patches) of toner by directly transferring toner onto the surface of the conveying belt  24 . 
         [0185]    As the conveying belt  24  circulates and the test patterns are brought opposite the patch sensor  112 , the patch sensor  112  reads the test patterns to measure positional offset among test patterns in each color and image density. 
         [0186]    By measuring positional offset among colors and image density for each color, the patch sensor  112  can simultaneously detect whether the outer case  82  of each toner cartridge  14  is open or closed. More specifically, when the outer case  82  of a toner cartridge  14  is in the open position, as in the examples of the non-black toner cartridges  14  shown in  FIG. 11 , the first handle part  88  is disposed in the second position. In the second position, the first handle part  88  extends diagonally upward and rearward and is retracted forward from the irradiating path of the laser beam. Consequently, the first handle part  88  does not block the laser beam being irradiated from the scanning unit  9  onto the corresponding photosensitive drum  15 . Therefore, the laser beam can be irradiated on the photosensitive drum  15  to form a test pattern on the same. 
         [0187]    In contrast, when the outer case  82  of a toner cartridge  14  is in the closed position, as in the example of the black toner cartridge  14 K in  FIG. 11 , the first handle part  88  is disposed in the first position. In the first position, the first handle part  88  extends rearward and advances into the irradiating path of the laser beam. In other words, the outer case  82  is opened and closed in association with movement of the first handle part  88 . Thus, when in the first position, the first handle part  88  blocks the laser beams being irradiated from the scanning unit  9  toward the corresponding photosensitive drum  15 . Accordingly, the laser beam does not expose the photosensitive drum  15  and does not form a test pattern thereon. 
         [0188]    In other words, the first handle part  88  functions as a shielding member and prevents the formation of test patterns in colors corresponding to the toner cartridges  14  whose outer cases  82  are in the closed position. If any colors are absent from the test patterns read from the patch sensor  112 , the patch sensor  112  transmits information on the missing colors to the CPU  113 . In this way, the CPU  113  can determine based on information of absent colors received from the patch sensor  112  that the first handle parts  88  of toner cartridges  14  corresponding to absent colors are not in the second position, i.e., that the outer cases  82  of toner cartridges  14  for the corresponding colors are not disposed in the open position. This information is displayed as an error on a display panel or the like (not shown). 
         [0189]    When the CPU  113  does not receive any information for missing colors, the CPU  113  determines that the outer cases  82  for all colors are disposed in the open position. 
         [0190]    6. Contact/Separation States of the Developing Devices 
         [0191]    The operating mode of the color laser printer  1  can be switched between a color mode for forming color images, and a monochrome mode for forming black-only images. 
         [0192]    (1) Color Mode 
         [0193]    In the color mode, the developing rollers  19  of all developing devices  18  contact the corresponding photosensitive drums  15 , as shown in  FIG. 13(   b ). 
         [0194]    In order to place the developing rollers  19  of all developing devices  18  in contact with all photosensitive drums  15 , both the black pressing cam  115  and the color pressing cam  116  are rotated as shown in  FIG. 12 . Through this rotation, the lever parts  120  of both pressing cams  114  contact the operating parts  49  of the corresponding separating cams  38  from above and move the operating parts  49  downward against the urging force of the compressed springs  51 . 
         [0195]    As a result, the separating cams  38  rotate clockwise in a left side view, retracting the contact parts  50  from the corresponding developing roller shafts  69 , as shown in  FIG. 13(   a ) (release position). Hence, the pressure applied by the contact parts  50  to the corresponding developing roller shafts  69  is removed. 
         [0196]    When the pressure of the contact parts  50  is removed from the developing roller shaft  69 , the pressure of the pressing members  111  causes the developing device  18  to pivot clockwise in a left side view together with the toner cartridge  14  about the cartridge support parts  95  of the toner cartridges  14 . 
         [0197]    When the developing devices  18  pivot in this way, the developing rollers  19  of all developing devices  18  are placed in contact with the corresponding photosensitive drums  15 . That is, by removing the pressure on the corresponding developing roller shafts  69 , the separating cams  38  allow the developing rollers  19  of the developing devices  18  to contact the photosensitive drums  15 . 
         [0198]    (2) Monochrome Mode 
         [0199]    In the monochrome mode, the developing roller  19  of the black developing device  18 K is in contact with the black photosensitive drum  15 K, while the developing rollers  19  of the non-black developing devices  18  are separated from the non-black photosensitive drums  15 , as illustrated in  FIG. 15(   b ). 
         [0200]    To achieve this mode, the black pressing cam  115  is rotated, but the color pressing cam  116  is not rotated, as illustrated in  FIG. 14 . Consequently, only the separating cam  38  corresponding to the black developing device  18 K is rotated clockwise in a left side view, as illustrated in  FIG. 15(   a ). This rotation removes the pressure applied by the contact parts  50  corresponding to the black developing device  18 K against the developing roller shaft  69 . When the pressure of the contact parts  50  against the developing roller shaft  69  is removed, the pressure of the corresponding pressing members  111  causes the black developing device  18 K to pivot clockwise in a left side view together with the black toner cartridge  14 K about the cartridge support parts  95  of the black toner cartridge  14 K. 
         [0201]    At this time, the developing rollers  19  of the non-black developing devices  18  remain separated from the corresponding photosensitive drums  15  due to the pressure applied by the corresponding separating cams  38  (pressing position). Accordingly, the developing roller  19  of the black developing device  18 K is placed in contact with the black photosensitive drum  15 K, while the developing rollers  19  of the non-black developing devices  18  are separated from the non-black photosensitive drums  15 . 
         [0202]    7. Operations and Effects 
         [0203]    (1) In the color laser printer  1  according to the above-described embodiment, each toner cartridge  14  is provided with the cartridge support parts  95 , which are supported in the drawer unit  13 , as shown in  FIGS. 15(   a ) and  15 ( b ). By pivoting the developing device  18  about these cartridge support parts  95 , the developing roller  19  can be placed in contact with or separated from the corresponding photosensitive drum  15 . 
         [0204]    Accordingly, the toner cartridge  14  can easily be positioned relative to the drawer unit  13  through the cartridge support parts  95 . Further, the developing device  18  can be pivoted about the cartridge support parts  95  of a toner cartridge  14  after the toner cartridge  14  is positioned, i.e., while the toner cartridge  14  is fixed in position relative to the drawer unit  13 . 
         [0205]    As a result, the toner cartridge  14  can easily be mounted in and removed from the drawer unit  13 , even with a construction that allows the developing roller  19  of the corresponding developing device  18  to be separated from the photosensitive drum  15 . 
         [0206]    (2) In the printer  1  according to the above-described embodiment, the developing device  18  pivots together with the toner cartridge  14 , as shown in  FIGS. 15(   a ) and  15 ( b ). This construction can prevent toner from leaking between the developing device  18  and the toner cartridge  14  when the developing device  18  is pivoted. 
         [0207]    (3) The printer  1  according to the above-described embodiment is provided with pressing members  111  for pressing the developing devices  18  toward the photosensitive drums  15 , as shown in  FIG. 1 . Therefore, the developing rollers  19  of the developing devices  18  can be reliably placed in contact with the corresponding photosensitive drums  15 . 
         [0208]    (4) As shown in  FIGS. 15(   a ) and  15 ( b ), the printer  1  according to the above-described embodiment is provided with the separating cams  38  for separating the developing rollers  19  of the developing devices  18  from the photosensitive drums  15 . 
         [0209]    The separating cams  38  can separate the developing rollers  19  of the developing devices  18  from the corresponding photosensitive drums  15  by applying pressure to the developing devices  18  with the contact parts  50 , thereby allowing the developing rollers  19  of the developing devices  18  to contact the photosensitive drums  15  by removing this pressure applied to the developing devices  18 . 
         [0210]    Hence, by applying pressure to or removing pressure from the developing devices  18 , the separating cams  38  can reliably place the developing rollers  19  of the developing devices  18  in contact with the photosensitive drums  15  or separate the developing rollers  19  from the photosensitive drums  15 . 
         [0211]    (5) When separating the developing rollers  19  of the developing devices  18  from the corresponding photosensitive drums  15 , the separating cams  38  apply pressure to the developing devices  18  of a force greater than the force of pressure that the pressing members  111  apply to the developing devices  18 . Accordingly, when applying pressure to the developing devices  18 , the separating cams  38  can reliably separate the developing rollers  19  from the photosensitive drums  15 , even while the pressing members  111  are pressing the developing devices  18  toward the corresponding photosensitive drums  15 . 
         [0212]    (6) As shown in  FIGS. 5(   a ) and  5 ( b ), the cartridge support parts  95  of the printer  1  are aligned with the central axis of each toner cartridge  14 . Since the developing device  18  pivots about the cartridge support parts  95  of the corresponding toner cartridge  14 , the developing devices  18  can be pivoted along a path following the outer periphery of the cylindrical toner cartridge  14 . This construction enables the developing device  18  to be pivoted while the toner cartridge  14  is fixed in position relative to the drawer unit  13 . 
         [0213]    (7) As shown in  FIGS. 5(   a ) through  6 , each toner cartridge  14  is provided with the outer case  82 , which can move between the open position for exposing the cartridge openings  83  formed in the inner case  81  to allow the passage of toner, and the closed position for covering the cartridge openings  83  to prevent the passage of toner. 
         [0214]    The outer case  82  is also provided with the handle part  87 . By operating the handle part  87 , the operator can reliably open and close the corresponding outer case  82 . Specifically, when removing the toner cartridge  14  from the drawer unit  13 , the operation of the handle part  87  places the outer case  82  in the closed position to restrict the passage of toner. When mounting the toner cartridge  14  in the drawer unit  13 , the operation of the handle part  87  places the outer case  82  in the open position to allow the passage of toner. Thus, this construction reliably prevents toner leakage when the toner cartridge  14  is mounted in and removed from the drawer unit  13 . 
         [0215]    (8) As shown in  FIGS. 5(   a ) through  6 , each toner cartridge  14  is provided with the cartridge fixing protrusions  91  for fixing the inner case  81  to the developing device frame  61  when the toner cartridge  14  is mounted in the drawer unit  13 . Hence, the toner cartridge  14  and developing device frame  61  can be fixed in relation to one another when the toner cartridge  14  is mounted in the drawer unit  13 . This construction reliably enables the developing device  18  and toner cartridge  14  to pivot together. 
         [0216]    (9) As shown in  FIGS. 5(   a ) through  6 , each developing device  18  is provided with the developing device shutter  62 , which is capable of moving between the open position for exposing the developer openings  64  formed in the developing device frame  61  to allow the passage of toner, and the closed position for covering the developer openings  64  to restrict the passage of toner. The toner cartridge  14  is also provided with the shutter fixing protrusions  85  for fixing the outer case  82  to the developing device shutter  62  when the toner cartridge  14  is mounted in the drawer unit  13 . 
         [0217]    Accordingly, the developing device shutter  62  can be opened and closed together with the outer case  82 . Thus, when the toner cartridge  14  is removed from the drawer unit  13 , the developing device shutter  62  is moved to the closed position together with the outer case  82  in order to restrict the passage of toner. When mounting the toner cartridge  14  in the drawer unit  13 , the developing device shutter  62  is moved to the open position together with the outer case  82  in order to allow the passage of toner. 
         [0218]    This construction can reliably prevent toner leakage when mounting the toner cartridge  14  in and removing the toner cartridge  14  from the drawer unit  13 . 
         [0219]    (10) As shown in  FIGS. 5(   a ) through  6 , the inner case  81  is hollow and substantially cylindrical in shape. The outer case  82  has substantially arcuate shape in a cross section and conforms to the outer periphery of the inner case  81 . The outer case  82  can be moved between open and closed positions by rotating relative to the inner case  81 . 
         [0220]    Therefore, the outer case  82  can be switched between open and closed positions by rotating along the outer periphery of the inner case  81 . Thus, the space required for opening and closing the outer case  82  is efficiently provided along the outer periphery of the inner case  81 , thereby conserving space. 
         [0221]    (11) As shown in  FIGS. 5(   a ) through  6 , the outer case  82  rotates about the cartridge support parts  95 . Hence, the outer case  82  can be opened and closed while the toner cartridge  14  is fixed in position relative to the drawer unit  13 . 
         [0222]    (12) With the color laser printer  1  according to the above-described embodiment, the cartridge guide grooves  35  are formed in the side plates  32  of the drawer unit  13 , and the cartridge support parts  95  of the toner cartridge  14  are supported in these cartridge guide grooves  35 . Accordingly, the cartridge guide grooves  35  guide the toner cartridge  14  in the mounting and removal operations. With the cartridge support parts  95  supported in the cartridge guide grooves  35 , the toner cartridge  14  is reliably mounted in and removed from the drawer unit  13  and can be positioned relative to the drawer unit  13 . 
         [0223]    (13) As shown in  FIG. 3 , pairs of the developing device support grooves  39  are formed in both side plates  32  constituting the drawer unit  13  for pivotably holding the developing devices  18 . Hence, each developing device  18  can be reliably pivoted along the developing device support grooves  39 . 
         [0224]    (14) As shown in  FIG. 11 , when the outer case  82  of the corresponding toner cartridge  14  is in the closed position, the respective first handle part  88  is disposed in the first position for blocking the laser beam emitted from the scanning unit  9  toward the photosensitive drum  15 . When the outer case  82  is in the open position, the first handle part  88  is disposed in the second position for not blocking the laser beam. Hence, when the outer case  82  of the toner cartridge  14  is in the closed position, the first handle part  88  can block the laser beam irradiated from the scanning unit  9  toward the photosensitive drum  15 , preventing image formation. 
         [0225]    This construction prevents malfunctions of the main casing  2  when the toner cartridge  14  is mounted in the main casing  2  while the corresponding outer case  82  remains in the closed position. 
         [0226]    (15) As shown in  FIG. 11 , the first handle part  88  functions as a shielding member. Accordingly, the first handle part  88  can be used as a shielding member in addition to its function as a handle part, eliminating the need to provide a separate shielding member. Thus, this construction reduces the number of required parts for the toner cartridge  14 . 
         [0227]    (16) As shown in  FIG. 1 , the printer  1  is also provided with the patch sensor  112  for reading test patterns, and the CPU  113  for determining whether the first handle parts  88  are disposed in their second positions based on the test patterns read by the patch sensor  112 . Accordingly, the test pattern reading operations performed by the patch sensor  112  can also be used to determine whether the first handle parts  88  are disposed in their second positions. 
         [0228]    (17) As shown in  FIG. 11 , the outer case  82  is opened and closed in association with movement of the first handle part  88 . Therefore, when the outer case  82  is in the open position, the first handle part  88  is reliably retracted from the irradiating path of the laser beam. Hence, the printer  1  can perform reliable image-forming operations when the outer cases  82  are in their open positions.