Abstract:
An image-forming device includes: a main body; a plurality of developing units; a holding unit; a guiding unit; and a lifting mechanism. Each developing unit is configured to accommodate developer, and has a developing roller. The holding unit is configured to hold the plurality of developing units. The guiding unit is configured to enable the holding unit to move between an inside position that is inside the main body and an outside position that is outside the main body. The lifting mechanism includes a door provided on the main body. The lifting mechanism is configured to allow the guiding unit to move up and down in association with opening and closing of the door.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/467,180, filed on Aug. 25, 2014, which is a continuation of U.S. patent application Ser. No. 14/098,811, filed on Dec. 6, 2013, now U.S. Pat. No. 8,818,233, which is a divisional of U.S. patent application Ser. No. 13/902,165, filed on May 24, 2013, now U.S. Pat. No. 8,606,142, which is a divisional of U.S. patent application Ser. No. 13/585,159, filed on Aug. 14, 2012, now U.S. Pat. No. 8,457,520, which is a divisional of U.S. patent application Ser. No. 13/268,290, filed on Oct. 7, 2011, now U.S. Pat. No. 8,265,522, which is a divisional of U.S. patent application Ser. No. 12/768,347, filed on Apr. 27, 2010, now U.S. Pat. No. 8,064,793, which is a divisional of U.S. patent application Ser. No. 12/238,854, filed on Sep. 26, 2008, now U.S. Pat. No. 7,720,413, which is a divisional of U.S. patent application Ser. No. 11/316,946, filed on Dec. 27, 2005, now U.S. Pat. No. 7,447,467, which claims priority from Japanese Patent Application No. 2004-378081, filed on Dec. 27, 2004. The contents of the above noted applications are incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates to an image-forming device for forming images on a recording medium. 
       BACKGROUND 
       [0003]    One type of image-forming device well known in the art has developing cartridges that can be detachably mounted in the image-forming device. This type of image-forming device, such as that disclosed in Japanese unexamined patent application publication No. 2001-272899, includes image-forming units, which have rollers such as photosensitive drums and which are removed from the body of the image-forming device in a direction parallel to the axes of these rollers. 
         [0004]    In an image-forming device disclosed in United States patent application publication No. 2004/165910A1, a cover is positioned on the body of the image-forming device above the developing cartridges. The cover rotates about hinges in order to cover or expose the developing cartridges. When exposed, the developing cartridges can be removed from the image-forming device. 
       SUMMARY 
       [0005]    However, since the plural rollers are pulled outward along the axial direction in the image-forming device disclosed in Japanese unexamined patent application publication No. 2001-272899, a large hole through which the rollers are withdrawn must be formed in the frame of the device. This hole makes it difficult to maintain the stiffness of the image-forming device. 
         [0006]    Also, since developer is supplied downward from the developer-accommodating section in this image-forming device, there is a danger that developer will leak into the inside of the image-forming device. 
         [0007]    Further, it is necessary to have the bearings or other members, used to hold and position each roller, recede from the shafts of the rollers. Accordingly, problems such as maintaining an accurate position of each roller arise. 
         [0008]    Additionally, since the large hole is formed in one side wall of the frame that is located on the side of one longitudinal end of the shaft of each roller. Accordingly, the shaft of each roller is supported only at its other longitudinal end by the other side wall of the frame. It is therefore difficult to maintain the accurate position of each roller. 
         [0009]    In the image-forming device described in United States patent application publication No. 2004/165910A1, it is possible to prevent leakage of developer to a degree since the developer is supplied upward from the developer-accommodating section. However, since the cover that is opened and closed when mounting and removing the developing cartridges is very large, it is difficult to securely fasten the cover on the device body (the portion of the body excluding the cover). In other words, the cover can easily shift in relation to the main body, which can weaken the stiffness of the image-forming device. 
         [0010]    In view of the foregoing, it is an object of the invention to provide an image-forming device for forming images with developer that has a body with enhanced stiffness and that prevents developer from contaminating the interior of the device. 
         [0011]    In order to attain the above and other objects, one or more aspects of the invention provides an image-forming device. The image-forming device may include: a main body; a plurality of developing units; a holding unit; a guiding unit; and a lifting mechanism. Each developing unit may be configured to accommodate developer, and may have a developing roller. The holding unit may be configured to hold the plurality of developing units. The guiding unit may be configured to enable the holding unit to move between an inside position that is inside the main body and an outside position that is outside the main body. The lifting mechanism may include a door provided on the main body. The lifting mechanism may be configured to allow the guiding unit to move up and down in association with opening and closing of the door. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Illustrative aspects in accordance with the invention will be described in detail with reference to the following figures wherein: 
           [0013]      FIG. 1  is a side cross-sectional view of a printer according to an illustrative aspect of the invention; 
           [0014]      FIG. 2  is a side cross-sectional view of the printer when a door is open; 
           [0015]      FIG. 3  is a side cross-sectional view of the printer showing the developing unit being pulled out; 
           [0016]      FIG. 4  is a side cross-sectional view of the printer showing a photosensitive drum unit being pulled out after the developing unit has been removed; 
           [0017]      FIG. 5(   a ) is a side cross-sectional view of the printer showing the photosensitive drum unit being removed while the developing unit is still mounted; 
           [0018]      FIG. 5(   b ) is a cross-sectional view illustrating the photosensitive drum unit mounted in a photosensitive-drum-unit guide mechanism in the main body of the printer; 
           [0019]      FIG. 5(   c ) is a side view of a right-side guide wall in the photosensitive-drum-unit guide mechanism seen from the left side thereof and illustrating male coupling members provided on the right-side guide wall; 
           [0020]      FIG. 5(   d ) is a side view of a right-side wall of a frame in the photosensitive drum unit seen from the inner (left) side thereof and illustrating female coupling members and intermediate gears provided on the inner (left) side of the right-side wall; 
           [0021]      FIG. 6  is a side cross-sectional view showing a variation of the printer (multifunction device) according to the above-described aspect; 
           [0022]      FIG. 7  is a side cross-sectional view of a printer according to another illustrative aspect of the invention; 
           [0023]      FIG. 8(   a ) is an explanatory diagram illustrating a developing unit and a transfer unit mounted in the printer when a cleaning unit is attached to the transfer unit and the developing unit is at a location where photosensitive drums in the developing unit are in contact with an intermediate transfer belt in the transfer unit; 
           [0024]      FIG. 8(   b ) is another explanatory diagram illustrating the developing unit and the transfer unit mounted in the printer when the cleaning unit is detached from the transfer unit and the developing unit is at a location where the photosensitive drums in the developing unit are out of contact with the intermediate transfer belt in the transfer unit; 
           [0025]      FIG. 9  is a side view of the printer showing guide mechanisms provided in the main body of the printer and used for mounting the developing unit and the transfer unit into the printer; 
           [0026]      FIG. 10  is a side cross-sectional view of the printer when the developing unit is being removed; and 
           [0027]      FIG. 11  is a side cross-sectional view of the printer in which the transfer unit is being removed. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    An image-forming device according to some aspects 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. 
         [0029]      FIG. 1  is a side cross-sectional view of a printer  10  according to some aspects of the invention. As shown in  FIG. 1 , the printer  10  is a tandem color laser printer that includes a developing unit  11 , a photosensitive drum unit  81 , a lifting mechanism  20  for raising the developing unit  11 , a transfer unit  50   a,  a fixing unit  60 , a feeding unit  70 , a discharge tray  80 , and an exposing device  35 . 
         [0030]    In the following description, the expressions “front”, “rear”, “upper”, “lower”, “right”, and “left” are used to define the various parts when the printer  10  is disposed in an orientation in which it is intended to be used. In this example, the side of the printer  10  on which a door  21  (to be described later) is provided will be referred to as the “front side” hereinafter. The right-to-left direction will be referred to also as the “widthwise direction” hereinafter. 
         [0031]    Next, each of these components will be described in greater detail. First the developing unit  11  will be described. 
         [0032]    The developing unit  11  includes a tray  12  functioning as a holder; and developer cartridges  31 M,  31 C,  31 Y, and  31 Bk for forming visible images with toner in each of the colors magenta (M), cyan (C), yellow (Y), and black (Bk), respectively. Hereinafter, components having reference numerals with letters appended to signify the color (e.g., M, C, Y, and Bk) will be collectively or generically referred to by the reference numeral alone (e.g., developer cartridges  31  or developer cartridge  31 ) unless referring to a specific color. 
         [0033]    Each developer cartridge  31  includes a developer case  39  ( 39 M,  39 C,  39 Y, and  39 Bk) functioning as an outer casing of the developer cartridge  31  and accommodating toner therein. 
         [0034]    Developing rollers  36  ( 36 M,  36 C,  36 Y, and  36 Bk) are provided in the respective developer cartridges  31  mounted in the developing unit  11 . Each developing roller  36  is formed in a cylindrical shape with an electrically conductive silicone rubber as the base material, the surface of which is coated with a resin or a rubber material containing fluorine. However, the developing roller  36  need not be configured of a conductive silicone rubber as the base material, but may instead be configured of a conductive urethane rubber, for example. The average roughness (Rz) at ten points on the surface of the developing rollers  36  is set to 3-5 μm that is smaller than the average particle size of toner, which is 9 inn. 
         [0035]    The developer cartridges  31  are also provided with supply rollers  37  ( 37 M,  37 C,  37 Y, and  37 Bk). Each supply roller  37  is formed of a conductive sponge roller and is configured to contact the respective developing roller  36  with pressure applied by the elastic force of the sponge. The supply roller  37  can be configured of an appropriate foam member formed of a conductive silicone rubber, EPDM, urethane rubber, or the like. 
         [0036]    Each developer cartridge  31  also includes a thickness-regulating blade  38  ( 38 M,  38 C,  38 Y, and  38 Bk). The thickness-regulating blade  38  includes a base part that is plate-shaped and formed of stainless steel or the like and is fixed to a wall of the respective developer case  39 , and a free end formed of an insulating silicone rubber or an insulating rubber or synthetic resin containing fluorine. The free end of each thickness-regulating blade  38  contacts the respective developing roller  36  from the lower side with pressure. 
         [0037]    The developing rollers  36  described above are each provided above the respective developer case  39 . Each developer case  39  has an opening  39   a  ( FIG. 3 ) near the top through which toner is supplied externally to the developing roller  36 . 
         [0038]    The tray  12  is configured of a bottom wall  12   c  that is rectangular in shape, side walls  12   d  erected from peripheral edges of the bottom wall  12   c,  and a plurality of partitioning plates  12   a  dividing the internal space formed by the bottom wall  12   c  and side walls  12   d.    
         [0039]    Slits  12   b  are formed in the bottom wall  12   c  for each of the developer cartridges  31  so as not to block the paths of laser beams emitted from the exposing device  35  toward the photosensitive drum unit  81 . The slits  12   b  are formed for each of the developer cartridges  31  at positions separated from the partitioning plates  12   a . Components constituting the photosensitive drum unit  81  (specifically, photosensitive drums  32 , chargers  34 , and the like described later) are positioned above the respective slits  12   b.  This construction decreases the likelihood of toner falling through the slits  12   b,  thereby preventing toner from contaminating the interior of the printer  10  below the tray  12 . 
         [0040]    A U-shaped cutout part  12   e  (see  FIG. 3 ) is formed in the side walls  12   d  for each of the developer cartridges  31 . The developing rollers  36  are rotatably supported in the respective cutout parts  12   e  via support shafts  36   a  (see  FIG. 2 ). 
         [0041]    The developer cartridges  31  are mounted in the tray  12  by engaging the support shafts  36   a  of the developing rollers  36  in the respective cutout parts  12   e  and by bringing the periphery of the developer cartridges  31  into contact with the side walls  12   d  and the partitioning plates  12   a.  Thus, the developer cartridges  31  can be properly positioned in the tray  12 , with the support shafts  36   a  extending horizontally in the widthwise (right-to-left) direction. 
         [0042]    Next, the photosensitive drum unit  81  will be described in greater detail. The photosensitive drum unit  81  includes a frame  82  having a square or rectangular tube shape. Within the frame  82 , the photosensitive drum unit  81  includes photosensitive drums  32  ( 32 M,  32 C,  32 Y, and  32 Bk), cleaning rollers  33  ( 33 M,  33 C,  33 Y, and  33 Bk), and chargers  34  ( 34 M,  34 C,  34 Y, and  34 Bk). Inverted U-shaped cutout parts  82   c  (see  FIG. 2 ) are formed in the frame  82  corresponding to each of the developer cartridges  31 . The cutout parts  82   c  can engage with the support shafts  36   a  of the developing rollers  36 . 
         [0043]    Each photosensitive drum  32  (organic photoconductors) mounted in the photosensitive drum unit  81  is formed, for example, of an aluminum hollow tube covered by a photosensitive layer with a positive charging nature. The photosensitive layer is formed at a thickness of 20 μm or greater. Further, the aluminum hollow tube is used as a grounding layer. 
         [0044]    The cleaning rollers  33  are resilient rollers formed of an electrically conductive sponge or the like and are disposed in sliding contact with the lower sections of the photosensitive drums  32 . Since the printer  10  employs a cleanerless developing method, residual toner that the cleaning rollers  33  remove from the photosensitive drums  32  is once again returned to the photosensitive drums  32  within a prescribed cycle after the developing process has been completed. The toner is then recovered by the developing rollers  36  and returned to the developer cartridges  31 . 
         [0045]    The chargers  34  are Scorotron-type charging devices. The chargers  34  confront, but do not contact, the surfaces of the respective photosensitive drums  32  from the bottom side thereof at a position downstream of the respective cleaning rollers  33  in the rotational direction of the photosensitive drums  32 . 
         [0046]    The exposing device  35  is configured of a laser scanning unit well known in the art. The exposing device  35  is disposed below and separated a prescribed distance from the developing unit  11 , vertically overlapping the photosensitive drums  32  and chargers  34 . The exposing device  35  irradiates laser beams on the surfaces of the photosensitive drums  32  at a position downstream of the chargers  34  in the rotational direction of the photosensitive drums  32 . The exposing device  35  irradiates laser beams onto the surfaces of the photosensitive drums  32  based on image data in order to form electrostatic latent images for each color on the surfaces of the photosensitive drums  32 . 
         [0047]    When disposed below the developing unit  11  in this way, the exposing device  35  is less likely to be influenced by vibrations than when disposed in the top of the device. 
         [0048]    With this construction, the supply rollers  37  supply positively charged toner to the respective developing rollers  36 , and the respective thickness-regulating blades  38  maintain the toner carried on the developing rollers  36  at a uniform thin layer. Subsequently, positively charged electrostatic latent images formed on the photosensitive drums  32  can be developed with the positively charged toner according to the reverse developing method at the point of contact between the developing rollers  36  and the respective photosensitive drums  32 , thereby forming an image of very high quality. 
         [0049]    Next, the transfer unit  50   a  will be described in greater detail. The transfer unit  50   a  includes an intermediate transfer belt  58 , drive rollers  51  and  52  about which the intermediate transfer belt  58  is looped and supported, and intermediate transfer rollers  53  ( 53 M,  53 C,  53 Y, and  53 Bk). 
         [0050]    The intermediate transfer belt  58  is a conductive sheet manufactured of polycarbonate, polyimide, or the like and formed in a belt shape. The intermediate transfer belt  58  travels circularly in contact with each of the photosensitive drums  32 . The intermediate transfer rollers  53  are disposed within the loop of the intermediate transfer belt  58  at positions opposing the respective photosensitive drums  32 . 
         [0051]    The intermediate transfer belt  58  is disposed such that the surface opposing the photosensitive drums  32  moves in a horizontal direction from the magenta developer cartridge  31 M toward the black developer cartridge  31 Bk. 
         [0052]    A prescribed voltage is applied to the intermediate transfer rollers  53  in order to temporarily transfer a toner image formed on each of the photosensitive drums  32  onto the intermediate transfer belt  58 . A secondary transfer roller  54  is disposed at a position in which the toner image is transferred onto a paper P, that is, opposite the drive roller  52 , downstream of the photosensitive drums  32  with respect to the moving direction of the intermediate transfer belt  58  and on the surface of the intermediate transfer belt  58  that opposes the photosensitive drums  32 . A prescribed potential is applied to the secondary transfer roller  54 . As a result, a four-color toner image carried on the intermediate transfer belt  58  is transferred onto the paper P. 
         [0053]    A cleaning unit  55  is disposed on the opposite side of the intermediate transfer belt  58  from the photosensitive drums  32 . The cleaning unit  55  includes a scraping member  56 , and a case  57 . Toner remaining on the intermediate transfer belt  58  after the transfer operation is scraped off by the scraping member  56  and collected in the case  57 . 
         [0054]    Next, the fixing unit  60  will be described in greater detail. The fixing unit  60  includes a heating roller  61  and a pressure roller  62  that rotate in contact with each other. A heater  63  such as a halogen lamp is provided inside the heating roller  61  for emitting heat when electrified to raise the temperature of the heating roller  61 . After a toner image has been transferred onto the paper P, the toner image is fixed to the paper P by heat and pressure as the paper P is pinched between and conveyed by the heating roller  61 , heated to a fixing temperature of about 180° C. during the printing operation, and the pressure roller  62  that applies pressure to the heating roller  61 . 
         [0055]    The fixing unit  60  is not disposed on either the tray  12  or the photosensitive drum unit  81 , but in the top section of the printer  10 . Accordingly, the fixing unit  60  is not affected by movement of the tray  12  or photosensitive drum unit  81 . 
         [0056]    Next, the feeding unit  70  will be described in greater detail. The feeding unit  70  is disposed in the bottommost section of the printer  10  and includes a loading tray  71  for accommodating the paper P, and a pickup roller  72  for feeding the paper P. The feeding unit  70  is configured to feed the paper P at a prescribed timing in relation to an image-forming process performed by the exposing device  35 , developer cartridges  31 , photosensitive drums  32 , and intermediate transfer belt  58 . A pair of conveying rollers  73  disposed downstream of the pickup roller  72  in the feeding direction receive the paper P fed by the feeding unit  70  and convey the paper P to the point of contact (nip point) between the intermediate transfer belt  58  and the secondary transfer roller  54 . 
         [0057]    The discharge tray  80  is disposed on the discharge side of the fixing unit  60  for accommodating discharged sheets of paper P. Pairs of conveying rollers  91  and  93  disposed downstream of the fixing unit  60  receive the paper P and discharge the paper P onto the discharge tray  80 . 
         [0058]    Next, the lifting mechanism  20  will be described in greater detail. The lifting mechanism  20  includes a rotational shaft  21   a,  a door  21  that swings open and closed about the rotational shaft  21   a,  a support base  22  for supporting the developing unit  11 , a plurality of lifting members  25  fixed directly beneath the support base  22 , a plurality of lifting support members  24  that slidably support the lifting members  25 , a horizontal moving member  26 , a horizontal movement support member  27  for slidably supporting the horizontal moving member  26  in the horizontal direction, and linking members  23  connecting the door  21  to the horizontal moving member  26  and the horizontal moving member  26  to the lifting members  25 . 
         [0059]    An end wall  22   a  is provided on an end of the support base  22  (hereinafter referred to as the “rear end”) opposite the end on which the door  21  is provided (hereinafter referred to as the “front end”). When the developing unit  11  is resting on the support base  22  in contact with the end wall  22   a  and the door  21  is rotated open or closed, the support base  22  is lifted or lowered, thereby allowing the developing unit  11  (the developing rollers  36 ) to be mounted on or detached from the photosensitive drums  32 . The operations of the lifting mechanism  20  will be described in greater detail later. 
         [0060]    Next, the operations of the printer  10  will be described in detail. 
         [0061]    First, the chargers  34  apply a uniform charge to the photosensitive layers on the surfaces of the respective photosensitive drums  32  as the photosensitive drums  32  are driven to rotate. Next, these photosensitive layers are exposed to the exposing device  35  based on image data for each of the colors magenta, cyan, yellow, and black. The developer cartridges  31  develop the latent images formed on the photosensitive surfaces of the respective photosensitive drums  32  in the colors magenta, cyan, yellow, and black, respectively, by depositing magenta toner, cyan toner, yellow toner, and black toner on the respective latent images. The toner images in magenta, cyan, yellow, and black formed on the photosensitive drums  32  in this way are temporarily transferred onto the surface of the intermediate transfer belt  58 . The toner image for each color is formed at slightly different times with consideration for the velocity of the intermediate transfer belt  58  and the positions of the photosensitive drums  32  in order to transfer the toner images so that the toner images in each color are superimposed on the intermediate transfer belt  58 . Any toner remaining on the photosensitive drums  32  after the transfer is temporarily retained by the respective cleaning rollers  33 . 
         [0062]    The four-color toner image formed on the intermediate transfer belt  58  as described above is transferred to the paper P fed from the feeding unit  70  at the nip point between the secondary transfer roller  54  and intermediate transfer belt  58 . After the toner image is fixed to the paper P in the fixing unit  60 , the paper P is discharged onto the discharge tray  80 , thereby completing the formation of a four-color image. 
         [0063]    Next, the operations of the lifting mechanism  20  will be described with reference to  FIGS. 1 and 2 . 
         [0064]    When the door  21  is closed, as shown in  FIG. 1 , the support base  22  is raised upward. In other words, the horizontal moving member  26  is moved to the rear side, and the lifting members  25  are moved vertically upward by the linking members  23  connecting the lifting members  25  to the horizontal moving member  26 . Accordingly, the support base  22  is also moved vertically upward. 
         [0065]    In this state, that is, when the support base  22  is pushed upward, the support shafts  36   a  of the developing rollers  36  are engaged in the cutout parts  82   c  (see  FIG. 2 ) formed in the frame  82 . Hence, the developing unit  11  and the photosensitive drum unit  81  are positioned relative to each other. The position of the developing unit  11  at this time shown in  FIG. 1  will be referred to as the “first accommodating position” hereinafter. 
         [0066]    From this state, when the door  21  is opened as shown in  FIG. 2 , the support base  22  is pulled downward near the exposing device  35 . 
         [0067]    More specifically, the linking members  23  that move when the door  21  opens pull the horizontal moving member  26 , moving the horizontal moving member  26  from the rear side toward the front side. By moving the horizontal moving member  26  to the front side, the lifting members  25  are moved vertically downward by the linking members  23 . 
         [0068]    As the developing unit  11  moves vertically downward along with the support base  22 , the support shafts  36   a  of the developing rollers  36  disengage from the cutout parts  82   c  formed in the frame  82 , enabling the developing unit  11  to be moved freely over the top surface of the support base  22 . The position of the developing unit  11  at this time shown in  FIG. 2  will be referred to as the “standby position” hereinafter. As a result, the developing unit  11  can be pulled in a substantially horizontal direction (forward direction) that is orthogonal to support shafts  32   a  to be described later, at which the photosensitive drums  32  are supported on the frame  82 . 
         [0069]    Next, the operation for removing the developing unit  11  and the photosensitive drum unit  81  will be described with reference to  FIGS. 3 through 5(   c ). 
         [0070]    As shown in  FIG. 3 , the developing unit  11  can be pulled part way from the body of the printer  10  so that only the magenta developer cartridge  31 M or another developer cartridge  31  can be removed from the developing unit  11 . 
         [0071]    By continuing to pull the developing unit  11 , the developing unit  11  can be entirely removed from the body of the printer  10 , as shown in  FIG. 4 . The position of the developing unit  11  shown in  FIG. 3  just before the developing unit  11  is pulled out completely from the printer  10  will be referred to as the “first removal position”. 
         [0072]    Even when the developing unit  11  is pulled out completely from the printer  10 , the developer cartridges  31  still remain mounted in the developing unit  11  on the bottom wall  12   c  of the tray  12 . Accordingly, the developing unit  11  can be placed nearly anywhere, including on a sloped or irregular surface. 
         [0073]    As shown in  FIG. 4  and  FIG. 5(   a ), the photosensitive drum unit  81  can be pulled and removed from the body of the printer  10  in the same direction (removal direction or forward direction) in which the developing unit  11  is removed from the printer  10 , after the developing unit  11  has been removed. The position of the photosensitive drum unit  81  shown in  FIG. 1  when the photosensitive drum unit  81  is mounted in the printer  10  will be referred to as the “second accommodating position”. The position of the photosensitive drum unit  81  shown in  FIG. 4  just before the photosensitive drum unit  81  is pulled out completely from the printer  10  will be referred to as the “second removal position”. 
         [0074]    As shown in  FIG. 5(   a ), the photosensitive drum unit  81  can be removed without first removing the developing unit  11 . To accomplish this, a photosensitive-drum-unit guide mechanism  85  is provided in the body of the printer  10  for detachably fixing the photosensitive drum unit  81 . Protruding parts are provided on the photosensitive drum unit  81  for engaging with the photosensitive-drum-unit guide mechanism  85 . 
         [0075]    More specifically, a plurality of protruding parts  82   a  is formed on the frame  82  of the photosensitive drum unit  81 . The protruding parts  82   a  are elongated along the horizontal. Insertion through-holes  82   b  are also formed in the frame  82  corresponding to each of the photosensitive drums  32 . The photosensitive drums  32  each have a support shaft  32   a  that inserts into the respective insertion through-holes  82   b . When inserted into the insertion through-holes  82   b,  the support shafts  32   a  protrude slightly from the outer surfaces of the frame  82 . 
         [0076]    The photosensitive-drum-unit guide mechanism  85  includes first engaging grooves  85   a  for engaging with the plurality of protruding parts  82   a  formed on the frame  82 , and second engaging grooves  85   b  for engaging with the support shafts  32   a  of the photosensitive drums  32 . 
         [0077]    The second engaging grooves  85   b  are provided with: engaging parts (indentations)  85   c  ( 85   c M,  85   c C,  85   c Y, and  85   c Bk) for engaging with the support shafts  32   a  of the photosensitive drums  32  ( 32 M,  32 C,  32 Y, and  32 Bk), respectively; and urging members (plate spring, for example)  85   d  ( 85   d M,  85   d C,  85   d Y, and  85   d Bk) for urging the support shafts  32   a  of the photosensitive drums  32  ( 32 M,  32 C,  32 Y, and  32 Bk) into the respective engaging parts  85   c  ( 85   c M,  85   c C,  85   c Y, and  85   c Bk) and for restricting the support shafts  32   a  from moving out therefrom. 
         [0078]    The bottom of the second engaging grooves  85   b  are formed at a slant at slanted areas  85   e  ( 85   e M,  85   e C,  85   e Y, and  85   e Bk) near the engaging parts  85   c  ( 85   c M,  85   c C,  85   c Y, and  85   c Bk). 
         [0079]    When mounting the photosensitive drum unit  81  into the body of the printer  10 , the photosensitive drum unit  81  is inserted into the photosensitive-drum-unit guide mechanism  85  along the first engaging grooves  85   a  and second engaging grooves  85   b  and is fixed in position with the support shafts  32   a  of the photosensitive drums  32  contacting the engaging parts  85   c.  As a result, the photosensitive drums  32  are brought into contact with the intermediate transfer belt  58  as shown in  FIG. 2 . Thus, the support shafts  32   a  of the photosensitive drums  32  are properly positioned in the main body of the printer  10 . The support shafts  32   a  extend horizontally in the widthwise (right-to-left) direction that is orthogonal to the forward direction, that is, the removal directions of the developing unit  11  and the photosensitive drum unit  81 . 
         [0080]    When removing the photosensitive drum unit  81  from the body of the printer  10 , the pulling action applies a force opposing the urging force of the urging members  85   d,  so that the support shafts  32   a  separate from the engaging parts  85   c  and are pulled out along the second engaging grooves  85   b.  As a result, the frame  82  moves slightly downwardly and forwardly along the slanted areas  85   e  of the bottom surface of the second engaging grooves  85   b,  and the photosensitive drums  32  are brought out of contact with the intermediate transfer belt  58  as shown in  FIG. 4 . 
         [0081]    More specifically, as shown in  FIG. 5(   b ), the frame  82  has a right-side wall  82 R, a left-side wall  82 L, a front-side wall  82 F, and a rear-side wall  82 B. The insertion through-holes  82   b  are formed through each of the right-side wall  82 R and the left-side wall  82 L. 
         [0082]    A pair of caps  32   b  are fitted to a pair of opposite axial ends (right-side and left-side axial ends) of each tube-shaped photosensitive drum  32 . A drum gear  43  ( 43 M,  43 C,  43 Y, or  43 Bk) is attached to one axial end (right-side axial end) of each photosensitive drum  32  ( 32 M,  32 C,  32 Y, or  32 Bk). Each drum gear  43  is fixedly secured to the corresponding photosensitive drum  32 , and is incapable of rotating relative to the photosensitive drum  32 . In other words, each photosensitive drum  32  rotates together with the corresponding drum gear  43 . 
         [0083]    The rotational shaft  32   a  is provided to extend along the central axis of each photosensitive drum  32 . The rotational shaft  32   a  extends rightwardly to pass through the cap  32   b  and the drum gear  43  at the right-side end of the photosensitive drum  32 , and extends leftwardly to pass through the other cap  32   b  at the left-side end of the photosensitive drum  32 . Thus, the rotational shaft  32   a  protrudes axially outwardly of the photosensitive drum  32  in the widthwise (right-to-left) direction. The photosensitive drum  32  is capable of rotating relative to the rotational shaft  32   a.    
         [0084]    Each photosensitive drum  32  is supported on the frame  82 , with its rotational shaft  32   a  being inserted through the corresponding insertion through-hole  82   b . As shown in  FIG. 5(   b ), the support shafts  32   a  are inserted through the insertion through-holes  82   b  and protrude outwardly from the frame  82  in the widthwise direction, that is, protrude rightwardly from the right-side wall  82 R and leftwardly from the left-side wall  82 L. The protruding amounts of the support shafts  32   a  are different from one another. That is, the protruding amount of the support shaft  32   a  in the photosensitive drum  32 Bk is the smallest, the protruding amount of the support shaft  32   a  in the photosensitive drum  32 Y is the second smallest, the protruding amount of the support shaft  32   a  in the photosensitive drum  32 C is the third smallest, and the protruding amount of the support shaft  32   a  in the photosensitive drum  32 M is the largest. 
         [0085]    The photosensitive-drum-unit guide mechanism  85  has a pair of guide walls (right-side guide wall  85 R and a left-side guide wall  85 L) that are distant from each other in the widthwise (right-to-left) direction. Each guide wall  85 R,  85 L includes the first engaging groove  85   a  ( FIG. 5(   a )) and the second engaging groove  85   b . As shown in  FIG. 5(   b ), the photosensitive drum unit  81  is mounted in the space between the pair of guide walls  85 L and  85 R, with the right-side wall  82 R confronting the right-side guide wall  85 R and the left-side wall  82 L confronting the left-side guide wall  85 L. 
         [0086]    Each second engaging groove  85   b  has: a black-groove part  85   b Bk for receiving the protruding support shaft  32   a  of the black photosensitive drum  32 Bk; a yellow-groove part  85   b Y for receiving the protruding support shaft  32   a  of the yellow photosensitive drum  32 Y; a cyan-groove part  85   b C for receiving the protruding support shaft  32   a  of the cyan photosensitive drum  32 C; and a magenta-groove part  85   b M for receiving the protruding support shaft  32   a  of the magenta photosensitive drum  32 M. 
         [0087]    The black-groove part  85   b Bk, yellow-groove part  85   b Y, cyan-groove part  85   b C, and magenta-groove part  85   b M are located as being shifted from one another in the widthwise (right-to-left) direction. That is, the black-groove part  85   b Bk is on the innermost side, the yellow-groove part  85   b Y is on the second innermost side, the cyan-groove part  85   b C is on the third innermost side, and the magenta-groove part  85   b M is on the outermost side. 
         [0088]    In each guide wall  85 R,  85 L, the black-groove part  85   b Bk, yellow-groove part  85   b Y, cyan-groove part  85   b C, and magenta-groove part  85   b M extend rearwardly from the front end (not shown) of the guide wall  85 R,  85 L by the lengths that are different from one another. That is, the black-groove part  85   b Bk extends the farthest, the yellow-groove part  85   b Y extends the second farthest, the cyan-groove part  85   b C extends the third farthest, and the magenta-groove part  85   b M extends the shortest. 
         [0089]    As shown in  FIGS. 5(   b ) and  5 ( c ), each guide wall  85 R,  85 L has: a black end wall  85   f Bk at the farthest end of the black-groove part  85   b Bk; an yellow end wall  85   f Y at the farthest end of the yellow-groove part  85   b Y; a cyan end wall  85   f C at the farthest end of the cyan-groove part  85   b C; and a magenta end wall  85   f M at the farthest end of the magenta-groove part  85   b M. 
         [0090]    As shown in  FIG. 5(   a ) and  FIG. 5(   c ), each guide wall  85 R,  85 L has: the black engaging part  85   c Bk on the top of the black-groove part  85   b Bk near the black end wall  85   f Bk; the yellow engaging part  85   c Y on the top of the yellow-groove part  85   b Y near the yellow end wall  85   f Y; the cyan engaging part  85   c C on the top of the cyan-groove part  85   b C near the cyan end wall  85   f C; and the magenta engaging part  85   c M on the top of the magenta-groove part  85   b M near the magenta end wall  85   f M. The support shaft  32   a  of each photosensitive drum  32  ( 32 Bk,  32 Y,  32 C, or  32 M) is engaged in the corresponding engaging part  85   c  ( 85   c Bk,  85   c Y,  85   c C, or  85   c M). 
         [0091]    As shown in  FIG. 5(   b ) and  FIG. 5(   c ), each guide wall  85 R,  85 L has: the black slanted area  85   e Bk on the bottom of the black-groove part  85   b Bk near the black end wall  85   f Bk; the yellow slanted area  85   e Y on the bottom of the yellow-groove part  85   b Y near the yellow end wall  85   f Y; the cyan slanted area  85   e C on the bottom of the cyan-groove part  85   b C near the cyan end wall  85   f C; and the magenta slanted area  85   e M on the bottom of the magenta-groove part  85   b M near the magenta end wall  85   f M. In other words, the bottom surface of each groove part  85   b Bk,  85   b Y,  85   b C, or  85   b M gradually rises at the corresponding slanted area  85   e Bk,  85   e Y,  85   e C, or  85   e M to reach the corresponding end wall  85   f Bk,  85   f Y,  85   f C, or  85   f M. 
         [0092]    As shown in  FIG. 5(   b ) and  FIG. 5(   c ), each guide wall  85 R,  85 L has: the black urging member  85   d Bk on the bottom of the black-groove part  85   b Bk at the black slanted area  85   e Bk; the yellow urging member  85   d Y on the bottom of the yellow-groove part  85   b Y at the yellow slanted area  85   e Y; the cyan urging member  85   d C on the bottom of the cyan-groove part  85   b C at the cyan slanted area  85   e C; and the magenta urging member  85   d M on the bottom of the magenta-groove part  85   b M at the magenta slanted area  85   e M. Each urging member  85   d  is a plate spring, in this example, for urging the support shaft  32   a  of the corresponding photosensitive drum  32  into the corresponding engaging part  85   c  and for restricting the support shaft  32   a  from moving out therefrom. Accordingly, both of the right-side and left-side ends (longitudinal ends) of the rotational shafts  32  that protrude out of the frame  82  are held in the engaging parts  85   c  by the urging members  85   d  on both of the right-side and left-side guide walls  85 R and  85 L in the main body (photosensitive-drum-unit-guide mechanism  85 ) of the printer  10 . 
         [0093]    As shown in  FIG. 5(   d ), two female coupling members  41  are provided on the right-side wall  82 R. Each female coupling member  41  is provided on the inner side of the frame  82 , that is, on the left side of the right-side wall  82 R. Each female coupling member  41  is rotatable about its rotational axis that extends in the widthwise (right-to-left) direction. Each female coupling member  41  has a receiving bore  41   a  that extends along the rotational axis of the female coupling member  41  and that is opened on the right-side axial end of the female coupling member  41 . The open end of the receiving bore  41   a  is exposed outside of the frame  82  (right side of the right-side wall  82 R) via a through-hole (not shown) that is formed through the right-side wall  82 R. An outer gear  41   b  is formed on the outer periphery of a part of the female coupling member  41  that is on the inner side of the frame  82  (left side of the right-side wall  82 R). 
         [0094]    As shown in  FIG. 5(   c ), two male coupling members  40  are provided on the right-side guide wall  85 R. Each male coupling member  40  is rotatable about its rotational axis that extends in the widthwise (right-to-left) direction. Although not shown, a motor is provided in the body of the printer  10  on the outer side of the photosensitive-drum-unit guide mechanism  85 , that is, on the right side of the right-side guide wall  85 R. The male coupling members  40  are connected to the motor. The male coupling members  40  can therefore be driven by the motor to rotate about its rotational axis. 
         [0095]    When the photosensitive drum unit  81  is mounted in the photosensitive-drum-unit guide mechanism  85 , the male coupling members  40  move to protrude inwardly in the widthwise direction from the photosensitive-drum-unit guide mechanism  85 . That is, the male coupling members  40  move to protrude leftwardly from the right-side guide wall  85 R. The male coupling members  40  are inserted into the receiving bores  41   a  of the female coupling members  41 . As a result, the male coupling members  40  are engaged with the female coupling members  41 . It is noted that the male coupling members  40  are retracted from the female coupling members  41 , while the photosensitive drum unit  81  is moving relative to the photosensitive-drum-unit guide mechanism  85  so as to be mounted in or removed from the photosensitive-drum-unit guide mechanism  85 . 
         [0096]    As shown in  FIG. 5(   b ) and  FIG. 5(   d ), the drum gears  43  ( 43 Bk,  43 Y,  43 C, and  43 M), which are provided on the right-side axial ends of the photosensitive drums  32  ( 32 Bk,  32 Y,  32 C, and  32 M), are located on the inside of the frame  82 , that is, on the left side of the right-side wall  82 R. As shown in  FIG. 5(   d ), four intermediate gears  42  are provided on the inner side of the frame  82 , that is, on the left side of the right-side wall  82 R. Each intermediate gear  42  is in engagement with the outer gear  41   b  of one female coupling member  41  and one drum gear  43  that sandwich the subject intermediate gear  42  therebetween. Accordingly, when the photosensitive drum unit  81  is mounted in the photosensitive-drum-unit guide mechanism  85 , the power is transmitted from the motor in the body of the printer  10  through the male coupling members  40 , the female coupling members  41 , the intermediate gears  42 , and the drum gears  43  to the photosensitive drums  32 . Accordingly, the photosensitive drums  32  can be driven to rotate. 
         [0097]    The printer  10  having the construction described above is provided in the body thereof with: the exposing device  35  that forms electrostatic latent images on the surfaces of the photosensitive drums  32 ; the plurality of developer cartridges  31  that have the developer cases  39  accommodating toner and having openings formed on the top side and that have developing rollers  36  disposed near the openings in the developer cases  39  and developing latent images formed by the exposing device  35  into visible images by supplying toner from the developer cases  39  onto the photosensitive drums  32 ; and the secondary transfer roller  54  and intermediate transfer rollers  53  for transferring the visible images formed on the photosensitive drums  32  onto a recording medium. The printer  10  also includes the tray  12  that is accommodated at the first accommodating position in the body of the printer  10  independent of the photosensitive drums  32 . The tray  12  retains the plurality of the developer cartridges  31  arranged in a row in the removal direction that is orthogonal to the support shafts  32   a  of the photosensitive drums  32  and is substantially horizontal. The tray  12  can be pulled from the first accommodating position to the first removal position in the substantially horizontal removal direction orthogonal to the support shafts  32   a.    
         [0098]    This construction maintains the rigidity of the printer  10  and prevents the interior of the printer  10  from being contaminated with toner. The construction also facilitates movement of the tray  12 . 
         [0099]    The construction also ensures accuracy in positioning the components of the printer  10 , and particularly the support shafts  32   a  for the photosensitive drums  32 . 
         [0100]    For example, if the printer  10  were configured so that the rollers, such as the photosensitive drums  32  and the developing rollers  36 , are withdrawn along the axial direction thereof, it would be difficult to reliably fix the support shafts of the rollers when mounted in the printer  10 . The support shafts of the rollers would tend to wobble and to become out of the right positions. However, since the printer  10  is configured so that the developing rollers  36  are removed as a single unit in a substantially horizontal direction orthogonal to the axial direction of the developing rollers  36  and the photosensitive drums  32  are removed as a single unit in a substantially horizontal direction orthogonal to the axial direction of the photosensitive drums  32 , it is possible to prevent wobble in the support shafts of the rollers. It is possible to bring the support shafts in the right positions. 
         [0101]    Because the photosensitive drums  32  are removed as a single unit in the forward direction that is orthogonal to the axial direction of the photosensitive drums  32  (right-to-left direction), it is unnecessary to form openings in either side (right-side or left-side) of the main body that are located on the longitudinal ends of the support shafts  32   a.  Accordingly, the main body of the printer  10  can support the support shafts  32   a  on both longitudinal ends thereof. That is, the photosensitive-drum-unit guide mechanism  85  can support the support shafts  32   a  at their right and left ends by both of the right-side and left-side guide walls  85 R and  85 L, respectively. This construction ensures that the support shafts  32   a  are located in the right positions. While being supported by the right and left side walls  82 R and  82 L of the frame  82 , the photosensitive drums  32  can be easily removed from the printer  10  in the direction that is orthogonal to the axial direction of the support shafts  32   a.    
         [0102]    The bottom of the second engaging grooves  85   b  are formed at a slant at the slanted areas  85   e  ( 85   e M,  85   e C,  85   e Y, and  85   e Bk) near the engaging parts  85   c  ( 85   c M,  85   c C,  85   c Y, and  85   c Bk) so that the photosensitive drums  32  are not damaged by sliding against the intermediate transfer belt  58  when removing the photosensitive drum unit  81 . In other words, the second engaging grooves  85   b  are configured so that the photosensitive drums  32  will not contact the transfer unit  50   a  (intermediate transfer belt  58 ) until the support shafts  32   a  arrive in the engaging parts  85   c.    
         [0103]    The printer  10  is configured so that the developer cartridges  31  can be pulled out while the photosensitive drums  32  and the exposing device  35  remain in the main body of the printer  10 . Accordingly, the weight of the portion being removed can be lessened, preventing the printer  10  from falling over. Further, by reducing the number of components that are removed, the size of the opening in the body of the printer  10  through which the components are removed (the size of the opening formed in the frame of the printer  10  by opening the cover  21 ) can be reduced, making the printer  10  rigid. 
         [0104]    Further, the tray  12  can be moved by the moving mechanism constructed from the linking members  23 , lifting support members  24 , lifting members  25 , and horizontal moving member  26  between the first accommodating position ( FIG. 1 ) and the standby position ( FIG. 2 ) that is located between the first accommodating position and the first removal position ( FIG. 3 ). This construction facilitates movement of the tray  12 . 
         [0105]    It is noted that an operation for accommodating the tray  12  in the first accommodating position or removing the tray  12  from the first accommodating position requires a relatively large amount of force, in order to fixedly secure the developing unit  11  relative to the main body of the printer  10  and in order to accurately position the developing unit  11  relative to the main body of the printer  10 . When moving the tray  12 , this operation for accommodating the tray  12  in the first accommodating position or removing the tray  12  from the first accommodating position is performed using the moving mechanism constructed from the linking members  23 , lifting support members  24 , lifting members  25 , and horizontal moving member  26 . Accordingly, the printer  10  facilitates movement of the tray  12 . 
         [0106]    Further, the first accommodating position ( FIG. 1 ) and the standby position ( FIG. 2 ) are separate from each other vertically and are both positioned between the photosensitive drums  32  and the exposing device  35 . Hence, when moving the tray  12  from the first accommodating position to the standby position, the tray  12  can easily be moved vertically by using the support base  22 , linking members  23 , lifting support members  24 , lifting members  25 , and horizontal moving member  26 . 
         [0107]    Further, the tray  12  is capable of sliding over the top surface of the support base  22  so that the tray  12  can be moved between the first accommodating position and the first removal position over the top surface of the support base  22 . Hence, the tray  12  can be moved along the support base  22 , allowing for smooth movement of the tray  12 . 
         [0108]    The printer  10  includes the door  21  positioned on the path of the tray  12  that moves over the support base  22 , and is capable of moving the tray  12  from the first accommodating position ( FIG. 1 ) to the first removal position ( FIG. 3 ) when the door  21  is opened. The printer  10  includes the lifting mechanism  20  that moves the tray  12  from the first accommodating position to the standby position by driving the support base  22  when the door  21  is changed from a closed state to an open state, and moves the tray  12  from the standby position back to the first accommodating position by raising the support base  22  when the door  21  is changed from the open state to the closed state. With this construction, the support base  22  is driven in association with movement of the door  21 , thereby efficiently moving the tray  12 . Further, the support base  22  is configured so that the tray  12  can be separated from the body of the printer  10  after being moved to the first removal position. 
         [0109]    The printer  10  also includes: the frame  82  that retains the photosensitive drums  32  and that is accommodated at the second accommodating position ( FIG. 1 ) in the main body; and the photosensitive-drum-unit guide mechanism  85  for moving the frame  82  between the second accommodating position and the second removal position ( FIG. 4 ) that is separate from the second accommodating position in the removal direction, which is substantially horizontal. 
         [0110]    With this construction, both the developer cartridges  31  and the photosensitive drums  32  can be easily removed from the body of the printer  10 . 
         [0111]    The direction for removing the developing unit  11  and the direction for removing the photosensitive drum unit  81  are the same direction. Since both the tray  12  and the frame  82  can be removed from the printer  10  in the same direction, space need only be allocated on one side of the printer  10  when considering installation locations, facilitating installation of the printer  10 . 
         [0112]    The tray  12  includes the plurality of partitioning plates  12   a  and side walls  12   d  for detachably holding the developer cartridges  31 . Each of the developer cartridges  31  has peripheral parts that engage with the partitioning plates  12   a  and side walls  12   d.  Hence, the developer cartridges  31  can be mounted in or removed from the tray  12 , enabling the developer cartridges  31  to be individually replaced. As a result, the running cost of the printer  10  can be decreased. 
         [0113]    Further, the support base  22  is configured so that the tray  12  can be separated from the body of the printer  10  after being moved to the first removal position. Hence, by removing the tray  12  from the printer  10 , cleaning or other maintenance can easily be performed on the tray  12  and the interior of the printer  10 . 
         [0114]    Further, the developer cases  39  have openings formed on the top side for supplying toner externally, and the developing rollers  36  are disposed near the openings of the respective developer cases  39 . The tray  12  has a box shape constructed of the bottom wall  12   c  and the side walls  12   d  erected on the periphery of the bottom wall  12   c.  Thus providing the bottom wall  12   c  on the tray  12  strengthens the tray  12 . 
         [0115]    Further, any toner that may spill from the developer cartridges  31  is collected on the bottom wall  12   c,  thereby preventing toner from contaminating the interior of the printer  10 . 
         [0116]    The developing rollers  36  have support shafts  36   a  for positioning, and the side walls  12   d  of the tray  12  include cutout parts  12   e  that engage with these support shafts  36   a.  Hence, by disposing the developing rollers  36  near the top edge of the tray  12 , the cutout part  12   e  retaining the support shafts  36   a  can be made shallower, thereby preventing a decline in the strength of the tray  12 . 
         [0117]    By improving the stiffness of the printer  10 , as described above, it is possible to restrain vibrations during image formation. Accordingly, the construction described above prevents toner from falling into the interior of the printer  10  due to such vibrations. 
         [0118]    The developer is transferred upward from the developing unit  11  onto the intermediate transfer belt  58 , and then is transferred from the intermediate transfer belt  58  to the recording medium. The recording medium is prevented from falling. The developer transferred onto the intermediate transfer belt  58  is prevented from falling into the printer  10 . 
         [0119]    In the printer  10 , each of the developing unit  11  and the photosensitive drum unit  81  can be removed from the printer  10  after being withdrawn to the prescribed position (first and second removal position). However, the units may be configured more like a desk drawer. In other words, an engaging part can be provided for temporarily stopping the unit when the unit is withdrawn to the prescribed position (first removal position). From this position, the front of the unit is lifted upward, allowing the unit to pass over the engaging part so that the unit can be removed from the body of the printer  10 . 
         [0120]    Further, in the printer  10 , a visible image is temporarily transferred from the photosensitive drums  32  onto the intermediate transfer belt  58  and subsequently transferred from the intermediate transfer belt  58  to a recording medium. However, the visible image may instead be transferred directly from the photosensitive drums  32  onto the recording medium. 
         [0121]    Further, the support base  22  is configured so that the tray  12  can be separated from the body of the printer  10  after being moved to the first removal position. However, the support base  22  may instead be configured to support the tray  12  without allowing the tray  12  to be separated from the body of the printer  10 . 
         [0122]    Further, the printer  10  is provided only with an image-forming function, but may be configured as a multifunction device  5 , such as that shown in  FIG. 6 . In addition to the printer  10 , this multifunction device  5  is provided with a scanner  110  disposed above the printer  10 . 
         [0123]    The multifunction device  5  reads images from a document with the scanner  110 , the exposing device  35  forms electrostatic latent images on the photosensitive drums  32  based on the image data generated by the scanner  110 , the developing unit  11  develops the electrostatic latent images into visible images, and the transfer unit  50   a  transfers the visible images onto a recording medium. 
         [0124]    As shown in  FIG. 6 , the discharge tray  80  of the multifunction device  5  is disposed between the scanner  110  and the printer  10 . Since the multifunction device  5  has a low center of gravity with the developer cartridges  31  arranged horizontally, the printer  10  remains stable even when providing the scanner  110  above the printer  10 . Since the multifunction device  5  must have high rigidity when providing the scanner  110  on the top in this way, the structure described above for improving the rigidity of the printer  10  can maintain the overall rigidity of the multifunction device  5  when the scanner  110  is disposed on the top in this way. Further, by positioning the scanner  110  on the top, neither the tray  12  nor the photosensitive drum unit  81  conflicts with the scanner  110  when removed from the printer  10 . In other words, since the scanner  110  does not interfere with the removal of the tray  12  or the photosensitive drum unit  81 , there is no need to move the scanner  110  in order to remove the tray  12  or the photosensitive drum unit  81 . 
         [0125]    Further, since the discharge tray  80  is disposed between the body of the printer  10  and the scanner  110 , the overall height of the multifunction device  5  can be lower than when the discharge tray  80  is provided above the scanner  110 . Further, since the discharge tray  80  does not protrude from the device, the amount of space occupied by the device can be reduced. 
         [0126]    Further, a control panel  112  can be disposed near the scanner  110  and may be provided with operating parts  114  that can be operated by the user. The multifunction device  5  configured in this way is more user-friendly than a conceivable device that provides the control panel  112  on the outer wall of the printer  10 . 
         [0127]    Next, a printer  15  according to another aspect of the invention will be described, wherein like parts and components are designated with the same reference numerals to avoid duplicating description. Only areas of the printer  15  that differ from the printer  10  described above will be described below. 
         [0128]    The printer  15  will be described with reference to  FIG. 7  through  FIG. 11 . 
         [0129]    The printer  15  includes: a first door  21   b  that corresponds to the door  21  in the above-described printer  10  and that is used for removing the tray  12 ; and a second door  21   c  that is positioned above the first door  21   b  and that is for removing a transfer unit  50   b.    
         [0130]    Further, though the above-described printer  10  includes the photosensitive drum unit  81 , the printer  15  does not include the photosensitive drum unit  81 . Though the photosensitive drums  32 , cleaning rollers  33 , and chargers  34  are provided in the photosensitive drum unit  81  in the printer  10 , the photosensitive drums  32 , cleaning rollers  33 , and chargers  34  are provided in the developer cartridge  31  together with the developing rollers  36  and the supply rollers  37  as shown in  FIG. 10 . Thus, the photosensitive drums  32  are disposed near the developing rollers  36 . Inverted U-shaped cutout parts  12   h  are formed in the tray  12  for engaging with the support shafts  32   a  of the photosensitive drums  32 , as shown in  FIG. 8(   a ). 
         [0131]    As illustrated in  FIG. 7 ,  FIG. 8(   a ), and  FIG. 10 , the developer cartridges  31  are fixed in a prescribed position by engaging the support shafts  32   a  of the photosensitive drums  32  in the cutout parts  12   h  and placing the outer periphery of the developer cartridges  31  in contact with the side walls  12   d  and partitioning plates  12   a . Hence, by using the support shafts  32   a  of the photosensitive drums  32  nearest the top ends of the tray  12  to position the developer cartridges  31  with relation to the tray  12 , the cutout parts  12   h  formed in the tray  12  can be made shallow. 
         [0132]    More specifically, the photosensitive drums  32  have support shafts  32   a  for positioning, and the side walls  12   d  of the tray  12  include cutout parts  12   h  that engage with these support shafts  32   a.  Hence, by disposing the photosensitive drums  32  and developing rollers  36  near the top edge of the tray  12 , the cutout part  12   h  retaining the support shafts  32   a  can be made shallower, thereby preventing a decline in the strength of the tray  12 . 
         [0133]    As shown in  FIG. 8(   a ), the tray  12  also has protruding parts  12   i  that can engage with first engaging grooves  87   a  ( FIG. 9)  described later. 
         [0134]    The printer  15  also has the transfer unit  50   b  in place of the above-described transfer unit  50   a  of the printer  10 . As shown in  FIG. 8(   a ), the transfer unit  50   b  has the same components with the transfer unit  50   a.  In other words, the transfer unit  50   b  has the drive roller  51  and drive roller  52 , the intermediate transfer belt  58 , and the intermediate transfer rollers  53 . The transfer unit  50   b  further includes a transfer member holder  59  for supporting the components of the transfer unit  50   b.    
         [0135]    The transfer member holder  59  includes protruding parts  59   c  capable of engaging in engaging grooves  89   a  and  89   b  ( FIG. 9 ) described later, and cutout parts  59   a  and  59   b  for engaging with protruding parts  55   a  described later. 
         [0136]    The printer  15  also includes a cleaning unit  55   b  in place of the above-described cleaning unit  55  of the printer  10 . The cleaning unit  55   b  has the same components with the cleaning unit  55 . In other words, the cleaning unit  55   b  has the scraping member  56  and the case  57 . As shown in  FIG. 8(   b ), the cleaning unit  55   b  further has protruding parts  55   a  that can be slid along and engaged with in the cutout parts  59   a  and  59   b  formed in the transfer member holder  59 . With this construction, the cleaning unit  55   b  can be mounted and removed independently of the transfer member holder  59 . 
         [0137]    As shown in  FIG. 9 , the body of the printer  15  includes a developer guide mechanism  87  for allowing the developing unit  11  to be freely mounted and removed, and a transfer unit guide mechanism  89  for allowing the transfer unit  50   b  to be freely mounted and removed. 
         [0138]    The developer guide mechanism  87  includes the first engaging grooves  87   a  for engaging with the plurality of protruding parts  12   i  formed on the tray  12 , and second engaging grooves  87   b  for engaging with the support shafts  32   a  of the photosensitive drums  32 . 
         [0139]    For each of the support shafts  32   a,  the second engaging grooves  87   b  of the developer guide mechanism  87  are provided with engaging parts  87   c  for engaging the support shafts  32   a,  and urging members (plate springs, for example)  87   d  for urging the support shafts  32   a  into the engaging parts  87   c  so as not to move therefrom. 
         [0140]    For each of the protruding parts  12   i,  the first engaging grooves  87   a  are provided with engaging parts  87   e  for engaging with the protruding parts  12   i,  and urging members (plate springs, for example)  87   f  for urging the protruding parts  12   i  into the engaging parts  87   e  so the protruding parts  12   i  do not move therefrom. 
         [0141]    Although not shown, the developer guide mechanism  87  has left-side and right-side guide walls similar to the left-side and right-side guide walls  85 R and  85 L described with reference to  FIG. 5(   b ). 
         [0142]    The second engaging groove  87   b  provided with the engaging parts  87   c  and the urging members  87   d  is formed in each of the left-side and right-side guide walls in the developer guide mechanism  87 , and has the same configuration with the above-described second engaging groove  85   b  that is provided with the engaging parts  85   c  and the urging members  85   d  ( FIG. 5(   a ),  FIG. 5(   b ), and  FIG. 5(   c )). 
         [0143]    Although not shown, slanted areas and end walls are formed in each second engaging groove  87   b  in the same manner as the above-described slanted areas  85   e  and the end walls  85   f  ( FIG. 5(   a ),  FIG. 5(   b ), and  FIG. 5(   c )). Although not shown, the male coupling members  40  are provided on the developer guide mechanism  87  in the same manner as described above with reference to  FIG. 5(   c ). 
         [0144]    Although not shown, the photosensitive drums  32  are held by the tray  12 , with their support shafts  32   a  protruding in the same manner as described above with reference to  FIG. 5(   b ). Both of the longitudinal ends (right-side and left-side ends) of the support shafts  32  that protrude out of the tray  12  are held in the engaging parts  87   c  of the second engaging grooves  87   b  by the urging members  87   d  on both of the right-side and left-side guide walls in the developer guide mechanism  87 . 
         [0145]    Although not shown, the photosensitive drums  32  have the drum gears  43  in the same manner as described above with reference to  FIG. 5(   d ). The female coupling gears  41  and the intermediate gears  42  are provided in the tray  12  in the same manner as described above with reference to  FIG. 5(   d ). 
         [0146]    The protruding parts  12   i  on the front and rear sides of the tray  12  protrude outwardly from the tray  12  in the widthwise (right-to-left) direction with different protruding amounts in the same manner as the support shafts  32   a  described above with reference to  FIG. 5(   b ). 
         [0147]    The first engaging groove  87   a  provided with the engaging parts  87   e  and the urging members  87   f  is provided in each of the left-side and right-side guide walls of the developer guide mechanism  87 , and has the same configuration with the above-described second engaging groove  87   b  that is provided with the engaging parts  85   c  and the urging members  85   d.  Although not shown, slanted areas and end walls are formed in each first engaging groove  87   a  in the same manner as the above-described slanted areas  85   d  and end walls  85   f.    
         [0148]    With this construction, the tray  12  can be inserted into the developer guide mechanism  87  along the first engaging grooves  87   a  and second engaging grooves  87   b  when mounting the tray  12  into the body of the printer  15  and can be fixed in a right position when the support shafts  32   a  are engaged with the engaging parts  87   c  and the protruding parts  12   i  are engaged with the engaging parts  87   e.  As a result, the photosensitive drums  32  are brought into contact with the intermediate transfer belt  58  as shown in  FIG. 7  and  FIG. 8(   a ). When removing the tray  12  from the body of the printer  15 , the pulling force on the tray  12  opposes the urging force of the urging members  87   d  and urging members  87   f  until the support shafts  32   a  and protruding parts  12   i  separate from the engaging parts  87   c  and engaging parts  87   e,  respectively. As a result, the tray  12  moves slightly downwardly and forwardly along the slanted areas of the bottom surfaces of the first and second engaging grooves  87   a  and  87   b,  and the photosensitive drums  32  are brought out of contact with the intermediate transfer belt  58  as shown in  FIG. 8(   b ) and  FIG. 10 . Subsequently, the tray  12  can be removed as the support shafts  32   a  and protruding parts  12   i  are guided along the second engaging grooves  87   b  and first engaging grooves  87   a,  respectively. 
         [0149]    The first engaging grooves  87   a  and second engaging grooves  87   b  are formed at a slant near the engaging parts  87   c  and engaging parts  87   e  so that the photosensitive drums  32  are not damaged by sliding against the intermediate transfer belt  58  when removing the tray  12 . In other words, the first engaging grooves  87   a  and second engaging grooves  87   b  are configured so that the photosensitive drums  32  will not contact the transfer unit  50   b  (intermediate transfer belt  58 ) until the support shafts  32   a  arrive in the engaging parts  87   c.    
         [0150]    The transfer unit guide mechanism  89  is disposed above the developer guide mechanism  87  and includes the engaging grooves  89   a  and  89   b  for engaging with the protruding parts  59   c  formed on the transfer member holder  59 . 
         [0151]    The engaging grooves  89   a  are formed at a slope that is higher on the front side of the printer  15  (the side toward the removal direction). The engaging grooves  89   a  include: engaging parts  89   c  on the rear side (the side away from the removal direction) for engaging the protruding parts  59   c  formed on the transfer member holder  59  at its rear side; and urging members  89   d  for urging the protruding parts  59   c  to prevent the protruding parts  59   c  from moving out of the engaging parts  89   c.  The engaging grooves  89   b  are formed in a substantially vertical direction and are for receiving the protruding parts  59   c  formed on the transfer member holder  59  at its front side. 
         [0152]    When mounting the transfer member holder  59  in the transfer unit guide mechanism  89  having this construction, the protruding parts  59   c  are inserted into the engaging grooves  89   a  and  89   b  until the protruding parts  59   c  on the rear side contact the engaging parts  89   c,  at which time the transfer member holder  59  is fixed in position. 
         [0153]    To remove the transfer member holder  59 , the front side of the transfer member holder  59  (the protruding parts  59   c  at the front side that engage with the engaging grooves  89   b ) is lifted until the protruding parts  59   c  are extracted from the engaging grooves  89   b.  From this position (with the front side of the transfer member holder  59  lifted), the front side of the transfer member holder  59  is pulled to remove the transfer member holder  59 . 
         [0154]    With the printer  15  having the construction described above, the developer cartridges  31  can be removed individually, such as the magenta developer cartridge  31 M shown in  FIG. 10 , by first opening the first door  21   b  and then pulling out the developing unit  11 . 
         [0155]    As shown in  FIG. 11 , the transfer unit  50   b  can be removed by opening the second door  21   c.  At this time, the cleaning unit  55   b  is removed together with the transfer unit  50   b.    
         [0156]    Further, when the second door  21   c  is opened, the cleaning unit  55   b  alone can be removed without removing the transfer unit  50   b.  Hence, this construction facilitates maintenance of the cleaning unit  55   b.    
         [0157]    Since the transfer unit  50   b  is inserted and removed through the side of the printer  15  rather than the top, the mechanism for inserting and removing the transfer unit  50   b  can be employed in a multifunction device such as that shown in  FIG. 6  with the scanner  110  provided on the top. 
         [0158]    The printer  15  can obtain the same effects as those obtained by the printer  10 . 
         [0159]    While the invention has been described in detail with reference to the above-described aspects 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. 
         [0160]    In each of the above-described printers  10  and  15  and multifunction device  5 , the plurality of photosensitive drums  32  are provided in one to one correspondence with the plurality of developer cartridges  31 , that is, in one to one correspondence with the plurality of different colors. However, only a single photosensitive drum  32  may be provided for all the plurality of developer cartridges  31 , that is, for all the plurality of different colors. In this case, the exposing device  35  forms a plurality of electrostatic latent images for the plurality of colors on the single photosensitive drum  32  at different locations or at different timings. Each developer cartridge  31  develops a corresponding electrostatic latent image formed on the photosensitive member into a visible image of a corresponding color. The transfer unit  50   a  or  50   b  transfers the visible images formed on the single photosensitive member to a recording medium. Or, two or more photosensitive drums  32 , whose number is smaller than the number of the developer cartridges  31 , may be provided. Each photosensitive drum  32  may be used for forming one or two electrostatic latent images to be developed by corresponding one or two developing cartridges  31 . 
         [0161]    A photosensitive member other than the photosensitive drum, such as a photosensitive belt, for example, may be used instead of the photosensitive drum.