Abstract:
A color image forming device includes a housing, a photosensitive unit, an exposing unit, at least three developing units, a transfer unit, and a fixing unit. The housing has a recording medium discharge opening adapted to discharge recording media from the housing in a forward direction. The photosensitive unit includes a photosensitive belt with a photosensitive layer. The exposing unit exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive belt. The developing units are provided within the housing in a forward portion of the housing with respect to the photosensitive unit. Each of the developing units includes a developing-agent bearing member bearing thereon a different color developing agent and supplies the developing agent to the photosensitive belt to develop corresponding latent images into visible images. The transfer unit receives the visible images from the photosensitive belt and transfers the visible images onto a recording medium. The fixing unit is provided within the housing in a rear portion of the housing with respect to the photosensitive unit. The fixing unit fixes the visible images onto the recording medium and transports the recording medium toward a recording medium discharge opening.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to an image forming device such as color laser printer or color LED printer.  
           [0003]    2. Description of the Related Art  
           [0004]    A well-known color laser printer for forming a color image includes a plurality of developing devices, a photosensitive belt, an intermediate transfer body, and a fixing unit. Each developing device stores a different color of toner and includes a developing roller. The photosensitive belt bears a visible image developed by the color of toner supplied from the corresponding developing roller. The intermediate transfer body receives transfer of individual monochrome images from the photosensitive belt one at a time. The monochrome images are superimposed one on top of the other to produce a multi-color image borne on the intermediate transfer body. The intermediate transfer body transfers the multi-color image onto a sheet. The fixing unit fixes the multi-color image onto the sheet.  
         SUMMARY OF THE INVENTION  
         [0005]    A color image forming device according to the present invention includes a housing, a photosensitive unit, an exposing unit, a plurality of developing units, a transfer unit, and a fixing unit. The housing has a recording medium discharge opening adapted to discharge recording media from the housing in a forward direction. The photosensitive unit includes a photosensitive member with a photosensitive layer. The exposing unit exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member. The developing units are provided within the housing in a forward portion of the housing with respect to the photosensitive unit. Each of the developing units includes a developing-agent bearing member bearing thereon a different color developing agent and supplies the developing agent to the photosensitive member to develop corresponding latent images into visible images. The transfer unit receives the visible images from the photosensitive member and transfers the visible images onto a recording medium. The fixing unit is provided within the housing in a rear portion of the housing with respect to the photosensitive unit. The fixing unit fixes the visible images onto the recording medium and transports the recording medium toward a recording medium discharge opening.  
           [0006]    With this configuration, the sheets are easy for the user to retrieve because they are discharged in the forward direction toward the user Also, the developing units are easy to exchange because they are provided in the forward portion of the housing, which is the portion nearest to where the user normally faces the printer.  
           [0007]    According to a second aspect of the present invention, an image forming device includes a photosensitive unit including a photosensitive member with a photosensitive layer; an exposing unit that exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member; a plurality of developing units each including a developing-agent bearing member that is disposed in contact with the photosensitive member, the photosensitive member and the developing-agent bearing members all moving downward at contact positions where the developing-agent bearing members contact the photosensitive member, each developing-agent bearing member bearing thereon a different color developing agent and supplying the developing agent to the photosensitive member at the contact positions to develop corresponding latent images into visible images; a first transfer body that receives transfer of the visible images borne on the photosensitive member; a second transfer body that receives transfer of the visible images from the first transfer body and that transfers the visible image onto a recording medium; and a fixing unit that fixes the visible images onto the recording medium.  
           [0008]    According to a third aspect of the present invention, an image forming device includes a photosensitive unit including a photosensitive member with a photosensitive layer; an exposing unit that exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member; a plurality of developing units each including a developing-agent bearing member that is disposed in contact with the photosensitive member, the photosensitive member moving upward and the developing-agent bearing members all moving downward at contact positions where the developing-agent bearing members contact the photosensitive member, each developing-agent bearing member bearing thereon a different color developing agent and supplying the developing agent to the photosensitive member at the contact positions to develop corresponding latent images into different-colored monochrome visible images; an intermediate transfer belt that receives the different-colored monochrome visible images one at a time from the photosensitive member in an overlapping manner to bear a multi-color image, the intermediate transfer belt transferring the multicolor image onto a recording medium; and a fixing unit that fixes the multi-color image onto the recording medium, the fixing unit being disposed on the opposite side of the photosensitive member than the developing-agent bearing members.  
           [0009]    According to a fourth aspect of the present invention, an image forming device includes a photosensitive unit including a photosensitive member with a photosensitive layer; an exposing unit that exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member; a plurality of developing units each including a developing-agent bearing member that is disposed in contact with the photosensitive member, the photosensitive member and the developing-agent bearing members all moving upward at positions where the developing-agent bearing members contact the photosensitive member, each developing-agent bearing member bearing thereon a different color developing agent and supplying the developing agent to the photosensitive member to develop corresponding latent images into different-colored monochrome visible images; an intermediate transfer belt that receives the different-colored monochrome visible images one at a time from the photosensitive member in an overlapping manner to bear a multi-color image, the intermediate transfer belt transferring the multicolor image onto a recording medium; and a fixing unit that fixes the multi-color image onto the recording medium, the fixing unit being disposed on the opposite side of the photosensitive member than the developing-agent bearing members.  
           [0010]    According to a fourth aspect of the present invention, an image forming device includes a photosensitive unit including a photosensitive member with a photosensitive layer; an exposing unit that exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member; a plurality of developing units each including a developing-agent bearing member that is disposed in contact with the photosensitive member, the developing-agent bearing members including at least one developing-agent bearing member that is disposed on one side of the photosensitive member and at least one developing-agent bearing member that is disposed on the opposite side of the photosensitive member, the photosensitive member and the developing-agent bearing member that is disposed on the opposite side of the photosensitive member both moving upward at positions where the photosensitive member and the developing-agent bearing member that is disposed on the opposite side of the photosensitive member contact each other, each developing-agent bearing member bearing thereon a different color developing agent and supplying the developing agent to the photosensitive member to develop corresponding latent images into different-colored monochrome visible images; an intermediate transfer belt that receives different-colored monochrome visible images one at a time from the photosensitive member in an overlapping manner to bear a multi-color image, the intermediate transfer belt transferring the multicolor image onto a recording medium; and a fixing unit that fixes the multi-color image onto the recording medium, the fixing unit being disposed to one side of the photosensitive member, wherein the photosensitive member and the developing-agent bearing member that is disposed on the same side of the photosensitive member as the fixing unit both move downward where the photosensitive member and the developing-agent bearing member that is disposed on the same side as the fixing unit contact each other.  
           [0011]    According to a fifth aspect of the present invention, an image forming device includes a photosensitive unit including a photosensitive member with a photosensitive layer; an exposing unit that exposes the photosensitive layer based on a multi-color image to form a series of latent images on the photosensitive member; a plurality of developing units each including a developing-agent bearing member that is disposed in contact with the photosensitive member, the developing-agent bearing members including at least one developing-agent bearing member that is disposed on one side of the photosensitive member and at least one developing-agent bearing member that is disposed on the opposite side of the photosensitive member, the photosensitive member moving upward and the developing-agent bearing member that is disposed on the opposite side of the photosensitive member moving downward at positions where the photosensitive member and the developing-agent bearing member that is disposed on the opposite side of the photosensitive member contact each other, each developing-agent bearing member bearing thereon a different color developing agent and supplying the developing agent to the photosensitive member to develop corresponding latent images into different-colored monochrome visible images; an intermediate transfer belt that receives different-colored monochrome visible images one at a time from the photosensitive member in an overlapping manner to bear a multi-color image, the intermediate transfer belt transferring the multicolor image onto a recording medium; and a fixing unit that fixes the multi-color image onto the recording medium, the fixing unit being disposed to one side of the photosensitive member, wherein the photosensitive member and the developing-agent bearing member that is disposed on the same side of the photosensitive member as the fixing unit both move downward where the photosensitive member and the developing-agent bearing member that is disposed on the same side as the fixing unit contact each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    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:  
         [0013]    [0013]FIG. 1 is a cross-sectional view showing a color laser printer according to a first embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a cross-sectional view showing a color laser printer according to a second embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a cross-sectional view showing a color LED printer according to a third embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a cross-sectional view showing a color LED printer according to a fourth embodiment of the present invention; and  
         [0017]    [0017]FIG. 5 is a cross-sectional view showing a color LED printer according to a fifith embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Color laser printers according to different embodiments of the present invention will be described with reference to the attached drawings. Unless otherwise noted, directional expressions such as “front”, “rear”, “above” and “below” are used throughout the description to define the various parts when the printers are disposed in an orientation in which they are intended to be used.  
         [0019]    [0019]FIG. 1 is a sectional side view showing a color laser printer according to a first embodiment of the present invention. The laser printer  1  comprises a housing  2 , a sheet-supply unit  4  for supplying sheets  3 , and an image-forming unit  5  for forming a predetermined image on the supplied sheet.  
         [0020]    The sheet-supply unit  4  includes a sheet-supply tray  45  and a sheet-supply roller  46 . Sheets  3  are stacked in the sheet-supply tray  45  of the sheet-supply unit  4 . Sheets are fed out one at a time from the top of the stacked sheets by a sheet-supply roller  46  to the image-forming unit  5 .  
         [0021]    The image-forming unit  5  includes a scanner unit  6 , four developing cartridges  7 , a photosensitive belt mechanism  8 , a first transfer roller  9 , a second transfer belt mechanism  10 , a third transfer roller  11 , a charging roller  12 , and a fixing unit  13 .  
         [0022]    The scanner unit  6  is located in the rear side of the housing  2  at a position over the secondary transfer belt mechanism  10 . The scanner unit  6  includes a laser beam emitter (not shown), a polygon mirror  14  driven to rotate, a lens  49 , and a reflecting mirror  50   a  in a scanner housing  47 . The scanner housing  47  is mounted substantially parallel to an upper surface of a second transfer belt  27  of the second transfer belt mechanism  10 . The scanner housing  47  has an opening  48  in its upper-rear surface. The scanner unit  6  further includes a reflecting mirror  50   b  disposed above the opening  48 . When the scanner unit  6  operates, the laser beam emitter emits a laser beam based on image data. As indicated by the arrow in FIG. 1, the laser beam reflects off the polygon mirror  14 , passes through the lens  49 , reflects off the reflecting mirror  50   a  to exit the scanner housing  47  through the hole  48 . The laser beam further reflects off the reflecting mirror  50   b  to impinge on a surface of a photosensitive belt  22  in the photosensitive belt mechanism  8 .  
         [0023]    Because the opening  48  is located opposite to the surface facing the second transfer belt  27  of the second transfer belt mechanism  10 , toner can be effectively prevented from entering into the scanner housing  47 .  
         [0024]    The developing cartridges  7  consist of a yellow developing cartridge  7 Y containing yellow toner, a magenta developing cartridge  7 M containing magenta toner, a cyan developing cartridge  7 C containing cyan toner, and a black developing cartridge  7 K containing black toner. The developing cartridges  7  are positioned in the front portion within the housing  2 , aligned in parallel with each other, one on top of the other separated from each other by a certain spacing.  
         [0025]    All of the developing cartridges  7 Y,  7 M,  7 C, and  7 K have substantially the same configuration, so a single developing cartridge  7  will be described as representative example. The developing cartridge  7  includes a developing roller  15 , a layer-thickness regulating blade  16 , a feed roller  17 , and a toner container  18 . The developing roller  15  is horizontally movable into and out of contact with the surface of the photosensitive belt  22 .  
         [0026]    Each toner container  18  holds a positively-charging non-magnetic, single-component toner in a corresponding one of colors of yellow, magenta, cyan, and black. Each toner container  18  includes two agitators  19  separated by a predetermined distance in the front-to-rear direction. Rotation of the agitators  19  effectively circulates toner in the toner containers  18  and supplies the toner to the feed roller  17 .  
         [0027]    In each developing cartridge  7 , the feed roller  17 , and the developing roller  15  are rotatable in pressing contact with each other to a certain extent. The developing roller  15  rotates counterclockwise so that its surface moves downward where it contacts the photosensitive belt  22 , that is, at the nip portion between the developing roller  15  and the photosensitive belt  22 .  
         [0028]    A predetermined developing bias voltage is applied between the developing roller  15  and the photosensitive belt  22 . In addition, the layer-thickness regulating blade  16  presses against an upper part of the feed roller  17 , that is, a surface opposite to the surface facing the photosensitive belt  22 .  
         [0029]    Rotation of the agitators  19  move toner contained in the toner container  18  to the developing roller  15  by rotation of the feed roller  17 . At this time, the toner is positively charged by friction between the feed roller  17  and developing roller  15 , and then fed onto the developing roller  15 . As the developing roller  15  rotates, the toner is fed into an area between the layer-thickness regulation blade  16  and the developing roller  15 . The toner is charged sufficiently by friction between the blade  16  and the developing roller  15 . The charged toner is then carried on the developing roller  15  as a thin layer having a predetermined thickness.  
         [0030]    The photosensitive belt mechanism  8  is located to the rear of the four developing cartridges  7 . The photosensitive belt mechanism  8  includes a photosensitive belt supporting roller  20  next to the yellow developing cartridge  7 Y at the top of four cartridges, a photosensitive belt driving roller  21  directly under the photosensitive belt supporting roller  20  and facing the black developing cartridge  7 B at the bottom of four cartridges, and an endless photosensitive belt  22  wound around the photosensitive belt supporting roller  20  and the photosensitive belt driving roller  21 . The photosensitive belt  22  has a photosensitive layer of organic photosensitive material formed on a surface thereof. The photosensitive belt  22  is mounted so as to extend in a vertical direction to face and contact all of the developing rollers  15 .  
         [0031]    The photosensitive belt driving roller  21  is provided with a driving gear (not shown). Transmission of power from a motor (not shown) to the driving gear rotates the photosensitive belt driving roller  21  clockwise. This rotation and the interlocked clockwise rotation of the photosensitive belt supporting roller  20  conveys the photosensitive belt  22  clockwise around the photosensitive belt supporting roller  20  and the photosensitive belt driving roller  21 . As a result, any particular point on the photosensitive belt  22  moves downward from the top most developing roller  15 Y of the yellow developing cartridge  7 Y toward the lower-most developing roller  15 B of the black developing cartridge  7 B. In other words, the photosensitive belt  22  is moved downward at the contact portion (a nip portion) with each developing roller  15 . It should be noted that the photosensitive belt mechanism a is provided with a tension roller  43  disposed on the opposite side of the photosensitive belt  22  with respect to the developing cartridges  7 .  
         [0032]    The first transfer roller  9  is formed of resilient material, and positioned in the bottom of the housing  2  in confrontation with the black developing cartridge  7 K through the photosensitive belt  8 . The first transfer roller  9  has substantially the same diameter as that of the photosensitive belt driving roller  21 . The first transfer roller  9  is located adjacent to the photosensitive belt  22  at a position shifted away from the photosensitive belt driving roller  21  so that the first transfer roller  9  does not contact the photosensitive belt  22  where the photosensitive belt  22  contacts the photosensitive belt driving roller  21 , that is, so as to prevent contact at the nip portion between the photosensitive belt driving roller  21  and the photosensitive belt  22 . The first transfer roller  9  is provided with a driving gear (not shown) having the same number of gear teeth as a driving gear (not shown) of the photosensitive belt driving roller  21 . Transmission of power from a motor (not shown) to the driving gear rotates the first transfer roller  9  counterclockwise. As a result, a surface of the first transfer roller  9  moves in the same direction as that of the photosensitive belt  22  where it contacts the photosensitive belt  22 .  
         [0033]    The second transfer belt mechanism  10  is located below the scanner unit  6  and to the rear of the photosensitive belt mechanism  8 . In other words, the second transfer belt mechanism  10  is located at the opposite side of the developing cartridges  7  with respect to the photosensitive belt mechanism  8 . The second transfer belt mechanism  10  includes the second endless transfer belt  27  and four rollers, that is, a first belt roller  23 , a second belt roller  24 , a third belt roller  25 , and a forth belt roller  26 .  
         [0034]    The first belt roller  23  has substantially the same diameter as those of the photosensitive belt driving roller  21  and the first transfer roller  9 . The first belt roller  23  is located in contact with the second transfer belt  27  at a position shifted from the first transfer roller  9  so that the first belt roller  23  does not contact the second transfer belt  27  at the same place as where the second transfer belt  27  contacts the first transfer roller  9 , that is, at the nip portion between the first transfer roller  9  and the second transfer belt  27 . The first belt roller  23  is provided with a driving gear (not shown) having the same number of gear teeth as a driving gear (not shown) the photosensitive belt driving roller  21  and the first transfer roller  9 . Power from a motor (not shown) is transmitted to the driving gear to rotate the first belt roller  23  clockwise.  
         [0035]    The second belt roller  24  is located to the rear of and below the first belt roller  23 . The second belt roller  24  is located facing the third transfer roller  11  through the second transfer belt  27 . The second belt roller  24  follows driving rotation of the first belt roller  23 , as transmitted by the second transfer belt  27 , and rotates clockwise accordingly.  
         [0036]    The third belt roller  25  is located to the rear of and above the first belt roller  23 . The third belt roller  25  follows driving rotation of the second belt roller  24 , as transmitted by the second transfer belt  27 , and rotates clockwise accordingly.  
         [0037]    The forth belt roller  26  is located in front of the third belt roller  25  and to the rear the first belt roller  23 . The forth belt roller  26  follows driving rotation of the third belt roller  25 , as transmitted by the third transfer belt  27 , and rotates clockwise accordingly.  
         [0038]    The first, second, third, and forth belt rollers  23 ,  24 ,  25 , and  26  are located to form a substantially rhomboidal configuration. The second transfer belt  27  is wound around the first, second, third, and forth belt rollers  23 ,  24 ,  25 , and  26 . Rotation of the first belt roller  23  conveys the second transfer belt  27  around the rollers  23 ,  24 ,  25 , and  26 .  
         [0039]    The second transfer belt  27  is made from a resin, such as conductive polycarbonate, or polyimide, dispersed throughout with electrically conductive particles such as carbon. The second transfer belt  27  confronts the first belt roller  23  at a position downstream with respect to the moving direction of the second transfer belt  27 . Accordingly, the second transfer belt  27  moves in the same direction as the first transfer roller  23  at the nip portion where the second transfer belt  27  contacts the first transfer roller  23 . The second transfer belt  27  has an entire length equal to an integral multiple of the total of the circumferential lengths of the photosensitive belt driving roller  22 , the first transfer roller  9 , and the first belt roller  23 .  
         [0040]    The third transfer roller  11  is located to sandwich the second transfer belt  27  between itself and the second belt roller  23  of the second transfer belt mechanism  10 , in order to contact a surface of the second transfer belt  27 . The third transfer roller  11  is configured to rotate in the same direction as the second transfer belt  27 , that is, clockwise at the nip portion where the third transfer roller  11  contacts the second transfer belt  27 . A predetermined transfer bias voltage is applied between the third transfer roller  11  and the second transfer belt  27 .  
         [0041]    The above structure allows the third transfer roller  11  to be located at the opposite side of the scanner unit  6  and the second transfer belt mechanism  10 , so that toner will not enter into the scanner unit  6  in the event that toner scatters around when the color toner image is transferred.  
         [0042]    The charging roller  12  is located upstream from the photosensitive supporting roller  20  in the moving direction of the photosensitive belt  22  in contact with a surface of the photosensitive belt  22 . The charging roller  12  rotates in the same clockwise direction as the photosensitive belt  22  at a nip portion where the charging roller  12  contacts the photosensitive belt  22 . A predetermined voltage is applied to the charging roller  12  to charge the surface of the photosensitive belt  22  to a uniform positive charge.  
         [0043]    After the surface of the photosensitive belt  22  is positively charged uniformly by the charging roller  12 , the surface of the photosensitive belt  22  is exposed by high speed scanning of the laser beam from the scanner unit  6  to form an electrostatic latent image based on image data.  
         [0044]    Contact between the photosensitive belt  22  and the developing roller  15  of a certain one of the developing cartridges  7  develops the electrostatic latent image into a monochromatic visible image of the color contained in that developing cartridge  7 . The monochromatic visible image is then transferred on the first transfer roller  9  when the image is brought into confrontation with the first transfer roller  9 . The monochromatic visible image transferred on the first transfer roller  9  is then transferred to the second transfer belt  27  when the image is brought into confrontation with the second transfer belt  27 . Thus, each monochromatic visible image transferred on the first transfer roller  9  is superimposed onto previous different-colored images on the second transfer belt  27  to form a multicolored image.  
         [0045]    Described in more detail, first the yellow developing cartridge  7 Y is moved horizontally rearward to bring the yellow developing roller  15 Y into contact with the photosensitive belt  22  on which is formed an electrostatic latent image that corresponds to the yellow portion of a multi-color image. At the same time, the developing rollers  15 M,  15 C, and  15 K of the magenta developing cartridge  7 M, the cyan developing cartridge  7 C, and the black developing cartridge  7 K are moved horizontally forward to separate the developing rollers  15 M,  15 C, and  15 K from the photosensitive belt  22 . As a result, the electrostatic latent image that corresponds to the yellow portion of a multi-color image is developed into a yellow visible image on the photosensitive belt  22  with the toner contained in the yellow developing cartridge  7 Y. Then, when movement of the photosensitive belt  22  moves the yellow visible image into confrontation with the first transfer roller  9 , the yellow visible image is transferred to the second transfer belt  27 .  
         [0046]    Then, an electrostatic latent image that corresponds to the magenta portion of a multi-color image is formed on the photosensitive belt  22 . At this time, the magenta developing cartridge  7 M is moved horizontally to bring the developing roller  15 M into contact with the photosensitive belt  22 . Simultaneously, the other developing cartridges  7  are moved to separate the developing rollers  15 Y,  15 C, and  15 K from the photosensitive belt  22 . The electrostatic latent image that corresponds to the magenta portion of a multi-color image is developed into magenta visible image on the photosensitive belt  22  from the toner contained in the magenta developing cartridge  7 M. The magenta visible image is then transferred onto the first transfer roller  9 . After that, when the magenta visible image faces the second transfer belt  27 , the magenta visible image on the first transfer roller  9  is transferred onto the second transfer belt  27 , which supports the yellow toner image thereon, so that the magenta visible image overlaps the yellow toner image.  
         [0047]    The operation described above is similarly repeated for the cyan and black toners contained in the cyan and black developing cartridges  7 C and  7 K, respectively. Therefore, a multicolor image is formed on the second transfer belt  27 .  
         [0048]    The multicolor image formed on the second transfer belt  27  as described above is transferred on a sheet  3  in a single transfer action, as the sheet  3  passes between the second transfer belt  27  and the third transfer roller  11 .  
         [0049]    The laser printer  1  further includes a charge removing lamp  42  for removing charge from the surface of the photosensitive belt  22  after image transfer. The charge removing lamp  42  faces the photosensitive belt  22  at a position on the opposite side of the photosensitive belt  22  from the developing cartridges  7 . The charge removing lamp  42  is located downstream from the first transfer roller  9  in the moving direction of the photosensitive belt  22 . The charge removing lamp  42  is located upstream with respect to the charging roller  12 . Accordingly, the charge on the surface of the photosensitive belt  22  is removed by the charge removing lamp  42 , every time a visible image is transferred to the first transfer belt  9 .  
         [0050]    The fixing unit  13  is located to the rear of the second transfer belt  27  and at the opposite side of the photosensitive belt mechanism  8  from the developing cartridges  7 . The fixing unit  13  includes a heating roller  28 , and a pressing roller  29  for pressing the heating roller  28 . The heating roller  28  has a metallic halogen lamp for heating. The heating roller  28  thermally fixes the multicolor image onto the sheet while the sheet  3  is passing between the heating roller  28  and the pressing roller  29 . The sheet  3  on which the multicolor image is thermally fixed is discharged through a discharge opening in the housing  2  forward onto a sheet-ejecting tray  30  formed on an upper part of the housing  2 . Because the discharge opening in the housing  2  is adapted to discharge sheets  3  forward toward the front of the housing  2 , the user can quickly and easily view the images printed on the sheets  3 .  
         [0051]    The color laser printer  1  further includes a belt cleaner  31  for recovering toner remaining on the photosensitive belt  22 . The belt cleaner  31  is located over the first belt roller  23  of the second transfer belt  27  at the opposite side of the photosensitive belt  22  from the developing cartridges  7 . The belt cleaner  31  includes a belt cleaning roller  32 , a recovering roller  33 -, and a removing blade  34  in a cleaning box  35 . The belt cleaner  31  further includes a recovering box  37 , which is connected with the cleaning box  35  through a connecting tube  36 .  
         [0052]    The cleaning box  35  is located downstream from the first transfer roller  9  in the moving direction of the photosensitive belt  22 . The cleaning box  35  is located at the opposite side of the photosensitive belt mechanism  8  from the developing cartridges  7 . The cleaning box  35  has an opening on the surface thereof facing the photosensitive belt  22 . The belt cleaning roller  32  is supported rotatably in the opening. The belt cleaning roller  32  is located in contact with the photosensitive belt  22 . The belt cleaning roller  32  is applied with a predetermined cleaning bias voltage with respect to the photosensitive belt  22 . The recovering roller  33  rotates in contact with the belt cleaning roller  32  from the side opposite the photosensitive belt  22 . The belt cleaning roller  32  is applied with a predetermined bias voltage. The removing blade  34  is configured to contact the recovering roller  33  from below.  
         [0053]    The recovering box  37  is located inside the loop of the photosensitive belt  22  wound around the photosensitive belt supporting roller  20  and the photosensitive belt driving roller  21 . The recovering box  37  is connected with the cleaning box  35  through the connecting tube  36  positioned at the side of photosensitive belt  22 .  
         [0054]    The toner remaining on the photosensitive belt  22  after the image is transferred to the first transfer roller  9  is electrically captured by the belt cleaning roller  32 , when the movement of the photosensitive belt  22  moves the remaining toner into confrontation with the belt cleaning roller  32 . When the remaining toner contacts the recovering roller  33 , the remaining toner captured onto the belt cleaning roller  32  is then electrically recovered by the recovering roller  33 . The remaining toner recovered on the recovering roller  33  is removed by the removing blade  34 , and then recovered to the recovering box  37  through the connecting tube  36 .  
         [0055]    As described above, the recovering box  37  is located inside of the photosensitive belt  22  wound around the photosensitive belt supporting roller  20  and the photosensitive belt driving roller  21 . This leads to effective use of the inner space defined by the photosensitive belt  22  so that the printer can be made more compact.  
         [0056]    The color laser printer  1  further includes a transfer cleaner  38  for recovering toner on the third transfer roller  11 . The transfer cleaner  38  is located at the side of the third transfer roller  11 , and includes a transfer cleaning roller  39  and a removing blade  40  provided in a cleaning box  41  The cleaning box  41  is located to face the third transfer roller  11  downstream from the second transfer belt  27  in the moving direction of the third transfer roller  11 . The cleaning box  41  has an opening facing the third transfer roller  11 . The transfer cleaning roller  39  is supported rotatably at the opening of the cleaning box  41  in contact with the third transfer roller  11 . The transfer cleaning roller  39  is applied with a predetermined bias voltage with respect to the third transfer roller  11 . The removing blade  40  contacts the transfer cleaning roller  39  from the side opposite from the third transfer roller  11 .  
         [0057]    Any toner clinging to the third transfer roller  11  is electrically captured by the transfer cleaning roller  39  when rotation of the third transfer roller  11  moves the toner into confrontation with the transfer cleaning roller  39 . The remaining toner captured on the transfer cleaning roller  39  is removed by the removing blade  34  and collected in the cleaning box  41 .  
         [0058]    The developing rollers  15  rotate and the photosensitive belt  22  moves downward at the nip portion where the developing rollers  15  contact the photosensitive belt  22 . Then, each color image is transferred from the photosensitive belt  22  to the first transfer roller  9  and then from the first transfer roller  9  to the second transfer belt  27 . In other words, each image is transferred twice. After that, each image is transferred to a sheet  3  by the third transfer roller  11 . Accordingly, four developing cartridges  7  and the fixing unit  13  are located on opposite sides of the photosensitive belt mechanism  8 .  
         [0059]    The developing rollers  15  and the photosensitive belt  22  can be rotated and moved, respectively, in the same direction at their nip portions. In addition, the photosensitive belt  22  and the first transfer roller  9 , the first transfer roller  9  and the second transfer belt  27 , and the second transfer belt  27  and the third transfer roller  11  can be rotated and moved in the same direction at their respective nip portions. As a result, the four developing cartridges  7  and the fixing unit  13  need not be located at the same side of the photosensitive belt mechanism  8  stacked on top of each other. As a result, the printer can be made more compact using a simple configuration.  
         [0060]    Each single-color visible image carried on the photosensitive belt  22  is transferred to the first transfer roller  9  and then onto the second transfer belt  27 . Single-color images transferred subsequently from the first transfer roller  9  to the second transfer belt  27  are superimposed onto previously transferred single-colored images to form a multicolor image. That is, each single-color visible image is transferred from the first transfer roller  9  onto the second transfer belt  27  without being superimposed by another image on the first transfer roller  9 . Therefore, each single-color visible image on the photosensitive belt  22  is temporarily transferred to the first transfer roller  9  as a single color image. Accordingly, large difference in electric potential will not develop between unexposed portions of the photosensitive belt  22  and the second transfer belt  27  through toner so that undesirable increases in the charge-to-mass ratio of toner that forms the visible image can be effectively suppressed. Similarly, undesirable increases in the charge-to-mass ratio of toner that forms subsequently superimposing visible images can also be suppressed. Therefore, multicolor images with good quality can be formed.  
         [0061]    The first transfer is performed by the first transfer roller  9  provided between the photosensitive belt  22  and the second transfer belt  27 . Therefore, power for the first transfer can be transmitted using a gear. The first transfer roller  9  can be precisely rotated so that transfer accuracy is improved. An image having good quality can be formed.  
         [0062]    The photosensitive belt mechanism  8  is used instead of a photosensitive drum. The printer  1  can be made more compact because a photosensitive belt is smaller than a photosensitive drum.  
         [0063]    The second transfer is performed by the second transfer belt mechanism  10  provided between the first transfer roller  9  and the third transfer roller  11  Therefore, the printer  1  can be made more compact because a transfer belt is smaller than a roller.  
         [0064]    The photosensitive belt driving roller  21 , the first transfer roller  9 , and the first belt roller  23  all have substantially the same diameter. Therefore, by rotating these rollers  21 ,  9 ,  23  at a constant speed, any phase shift caused by eccentric rotation of the rollers  21 ,  9 ,  23  can be adjusted. Therefore, the single-color visible images can be transferred to and superimposed on the same position precisely.  
         [0065]    In addition, the driving gear of the photosensitive belt driving roller  21 , the driving gear of the first transfer roller  9 , and the driving gear of the first belt roller  23  have substantially the same number of gear teeth. Therefore, the photosensitive driving roller  21 , the first transfer roller  9 , and the first belt roller  23  can be rotated at a constant speed easily and precisely. Therefore, each single-color visible image can be transferred and superimposed at the same position precisely.  
         [0066]    It should be noted that the driving gear of the photosensitive belt driving roller  21 , the driving gear of the first transfer roller  9 , and the driving gear of the first belt roller  23  may be coupled to a single motor through a gear train, so that they are linked with each other.  
         [0067]    As described above, the first transfer roller  9  is located so as to not contact a part of the photosensitive belt  22  that contacts the photosensitive belt driving roller  21 , which is located in confrontation with first transfer roller  9 . The first transfer roller  9  is also located so as to not contact a part of the second transfer belt  27  that contacts the first belt roller  23 , which is located in confrontation with the first transfer roller  9 . Accordingly, the first transfer roller  9  and the photosensitive belt driving roller  21  are located at positions shifted from each other through the photosensitive belt  22 . The first transfer roller  9  and the first belt roller  23  are located at positions shifted from each other through the second transfer belt  27 . In other words, the photosensitive belt driving roller  21 ,,the first transfer roller  9 , and the first belt roller  23  are located at positions all shifted from each other. Therefore, pressure from other rollers is not applied at the nip portions between belts and rollers, so that good transfer is ensured.  
         [0068]    The second transfer belt  27  has a length equal to an integral multiple of the total peripheral of the photosensitive belt driving roller  21 , the first transfer roller  9 , and the first belt roller  23 . Any phase shift between the photosensitive belt driving roller  21 , the first transfer roller  9 , and the first belt roller  23  can be adjusted, so that each single-color visible image can be transferred and overlapped at the same position precisely. Accordingly, a multicolor image with better quality can be formed.  
         [0069]    A link member (not shown) is provided for selectively connecting the photosensitive belt mechanism  9  and the first transfer roller  9  to each other. When the photosensitive belt mechanism  8  and the first transfer roller  9  are coupled to each other by the link member, they can be mounted into and removed from the housing  2  as an integral unit. Therefore, maintenance can be effectively performed using simple operations.  
         [0070]    A link member (not shown) is provided for selectively connecting the first transfer roller  9  and the second transfer belt mechanism  10  to each other. When the first transfer roller  9  and the second transfer belt mechanism  10  are coupled to each other by the link member, they can be mounted into and removed from the housing  2  as an integral unit. Therefore, maintenance can be effectively performed using simple operations.  
         [0071]    The color laser printer  1  may further include a transfer roller  44  positioned under the photosensitive driving roller  21  as indicated by two-dot chain line in FIG. 1. The transfer roller  44  is located to face the photosensitive belt driving roller  21  through the transfer belt  22 . The transfer roller  44  is configured to transfer a single-color visible image carried on the photosensitive belt  22  to a sheet  3  directly. If such a transfer roller  44  is provided, a monochrome image can be formed readily at a high speed by forming a black visible image on the photosensitive belt  22  by means of the developing roller  15  of the black developing cartridge  7 K and transferring the formed black visible image onto a sheet  3  directly.  
         [0072]    Each of vertically-stacked developing cartridges is inclined with respect to a horizontal so that the front end of each cartridge is higher than the rear end. This forms a space between the front end of the black developing cartridge and the sheet-supply tray  45 . The sheet-supply roller  46  is located in the predetermined space. This configuration effectively uses the space around the front side of each of the inclined developing cartridges  7 . Therefore, the printer can be made compact.  
         [0073]    Next, a color laser printer  151  according to a second embodiment of the present invention will be described with reference to FIG. 2. In the description of the color laser printer  151 , components that have corresponding components in the printer  1  will be referred to using reference numbers of the corresponding components added with 100.  
         [0074]    As in the first embodiment, a fixing unit  113  and four developing cartridges  107  are disposed on opposite sides of a photosensitive belt mechanism  108 . However, according to the second embodiment, developing rollers  115  and a photosensitive belt  122  move in the opposite direction at the nip portion. That is, the developing rollers  115  rotate downward at the nip portion and the photosensitive belt  122  moves upward at the nip portion, rather than both the photosensitive belt and the developing rollers moving downward at the nip portion. Also, a single intermediate transfer belt  153  is provided, rather than the first transfer roller  9  and the second transfer belt mechanism  10 .  
         [0075]    A sheet feed portion  104  of the color laser printer  151  is disposed with the opposite orientation of the sheet feet portion  4  of the first embodiment. Also, registration rollers  152  are disposed above a sheet-feed roller  146 . The sheet-feed roller  146  feeds out uppermost sheets  3  in a sheet feet tray  145  one at a time toward the rear of a housing  102 . After the registration rollers  52  perform a predetermined registration operation, the sheets are transported to image forming portion  105 .  
         [0076]    The image forming portion  105  includes a scanner unit  106 , four developing cartridges  107 , a photosensitive belt mechanism  8 , a charge roller  12 , a fixing portion  13 , the intermediate transfer belt mechanism  153 , and the transfer roller  154 .  
         [0077]    The scanner unit  106  is located in the housing  102  at a position over the sheet-supply portion  104  and below the intermediate transfer belt mechanism  153 . In other words, relative vertical positions of the scanner unit  106  and the intermediate transfer belt mechanism  153  are inverted compared to the scanner unit  6  and the second transfer belt mechanism  10  of the first embodiment. The scanner unit  106  includes a laser beam emitter (not shown), a polygon mirror  114  driven to rotate, a lens  149 , and a reflecting mirror  150  a in a scanner housing  147 . The scanner unit  106  further includes a reflecting mirror  150   b  disposed below an opening  148 . When the scanner unit  106  operates, the laser beam emitter emits a laser beam based on image data. As indicated by the arrow in FIG. 2, the laser beam reflects off the polygon mirror  114 , passes through the lens  149 , reflects off the reflecting mirror  150   a  to exit the scanner housing  147  through the hole  148 . The laser beam further reflects off the reflecting mirror  150   b  to impinge on a surface of the photosensitive belt  122 .  
         [0078]    The four developing cartridges  107  and the photosensitive belt mechanism  108  have the same configuration as the developing cartridges  7  and the photosensitive belt mechanism  8  of the first embodiment. However, the four developing cartridges  107  are stacked in the opposite order from the developing cartridges  7 . That is, as shown in FIG. 2, the yellow developing cartridge  7 Y is positioned on the bottom of the stack, followed by the magenta developing cartridge  7 M and the cyan developing cartridge  7 C in this order, and the black developing cartridge  7 K positioned on the top of the stack. Also, the photosensitive belt  122  circulates between the photosensitive belt support roller  120  and a photosensitive belt drive roller  121  in the opposite direction from the photosensitive belt  22  of the first embodiment. That is, the photosensitive belt  122  circulates in the counterclockwise direction as viewed in FIG. 2. For this reason, the photosensitive belt  122  moves from the developing roller  115  of the yellow developing cartridge  107 Y, which is in the lowermost position, to the developing roller  115  of the black developing cartridge  107 K, which is in the uppermost position. The photosensitive belt  122  moves in the opposite direction of the developing rollers  115  at the nip portion, that is, the developing rollers  115  move downward and the photosensitive belt  122  moves upward at the nip portion.  
         [0079]    The intermediate transfer belt mechanism  153  is positioned above the scanner unit  106  and to the rear of the photosensitive belt mechanism  108 . That is, the intermediate transfer belt mechanism  153  is located on the opposite side of the photosensitive belt mechanism  108  than the four developing cartridges  107 . The intermediate transfer belt mechanism  153  includes an intermediate transfer belt  158 , an intermediate transfer belt drive roller  155 , a first intermediate transfer support roller  156 , and a second intermediate transfer support roller  157 . The intermediate belt  158  is an endless belt wrapped around the three rollers  155 ,  156 , and  157 .  
         [0080]    The intermediate transfer belt drive roller  155  is positioned in confrontation with the photosensitive belt drive roller  121 , with the photosensitive belt  122  and the intermediate transfer belt  158  sandwiched therebetween. The first intermediate transfer support roller  156  is positioned diagonally below and to the rear of the intermediate transfer belt drive roller  155 . The first intermediate transfer support roller  156  is disposed in confrontation with a transfer roller  154  to be described later, with the intermediate transfer belt  158  sandwiched therebetween. The second intermediate transfer support roller  157  is disposed to the front of the first intermediate transfer support roller  156  and below the intermediate transfer belt drive roller  155 .  
         [0081]    The rollers  155 ,  156 ,  157  are disposed to define an imaginary triangle. The intermediate transfer belt  158  is wrapped around the rollers  155 ,  156 ,  157 . Drive force of the intermediate transfer belt drive roller  155  conveys the intermediate transfer belt  158  in a circulating manner around the outer periphery of the rollers  155 ,  156 ,  157 , following the clockwise direction. By this, the intermediate transfer belt  158  moves in the same direction as the photosensitive belt  122  at the nip portion between the intermediate transfer belt  158  and the photosensitive belt  122 , near the intermediate transfer belt drive roller  155 .  
         [0082]    The transfer roller  154  is disposed so as to contact the surface of the intermediate transfer belt  158  at a position in confrontation with the first intermediate transfer belt roller  156 , with the intermediate transfer belt  158  sandwiched between the transfer roller  154  and the intermediate transfer belt  158 . The transfer roller  154  rotates counterclockwise so as to move in the same direction as the intermediate transfer belt  158  at the nip portion between the transfer roller  154  and the intermediate transfer belt  158 . A predetermined transfer bias is applied between the transfer roller  154  and the intermediate transfer belt  158 .  
         [0083]    A charge roller  112  is provided with the same configuration as the charge roller  12  of the first embodiment. The charge roller  112  is positioned near to and upstream from the photosensitive belt support roller  120  with respect to the movement direction of the photosensitive belt  122  so as to contact the surface of the photosensitive belt  122 . The charge roller  112  rotates clockwise and moves in the same direction as the photosensitive belt  122  at the nip portion between itself and the photosensitive belt  122 .  
         [0084]    After the surface of the photosensitive belt  122  is positively charged uniformly by the charging roller  112 , the surface of the photosensitive belt  122  is exposed by high speed scanning of the laser beam from the scanner unit  106  to form an electrostatic latent image based on image data.  
         [0085]    Contact between the photosensitive belt  122  and the developing roller  115  of one of the certain developing cartridge  107  develops the electrostatic latent image into a monochromatic visible image of the color contained in that developing cartridge  107 . The monochromatic visible image is then transferred on the intermediate transfer belt  158  when the monochromatic visible image is brought into confrontation with the intermediate transfer belt  158 . The monochromatic visible images in the different colors are transferred one on top of the other on the intermediate transfer belt  158  to form a multicolored image.  
         [0086]    First a yellow visible image is formed on the photosensitive belt  122  with the toner contained in the yellow developing cartridge  107 Y, which is in the lowermost position of the developing cartridge stack. Then, when movement of the photosensitive belt  122  moves the yellow visible image into confrontation with the first transfer roller  109 , the yellow visible image is transferred to the second transfer belt  127 . Then, an electrostatic latent image is again formed on the photosensitive belt  122  and developed into a magenta visible image on the photosensitive belt  122  from the toner contained in the magenta developing cartridge  107 M, which is the second from the lowest developing cartridge in the stack. When the magenta visible image is moved into confrontation with the intermediate transfer belt  158 , the magenta visible image is transferred onto the intermediate transfer belt  158  in an overlapping manner onto the yellow visible image.  
         [0087]    The operations described above are repeated for the cyan and black toners contained in the cyan and black developing cartridges  107 C and  107 K, respectively Therefore, a multicolor image is formed on the intermediate transfer belt  158 .  
         [0088]    The multicolor image formed on the intermediate transfer belt  158  is transferred on a sheet  3  in a single transfer action, as the sheet  3  passes between the intermediate transfer belt  158  and the transfer roller  154 .  
         [0089]    The laser printer  151  further includes a belt cleaner  131  and a charge removing lamp  142  with the same configuration as the belt cleaner  131  and the charge removing lamp  142  of the first embodiment. The belt cleaner  131  is located over the charging roller  112  at the opposite side of the photosensitive belt  122  from the developing cartridges  107 . The charge removing lamp  142  is disposed in confrontation with the photosensitive belt  122  at a position downstream from the intermediate transfer belt  158 , and upstream from the belt cleaner unit  131 , with respect to the movement direction of the photosensitive belt  122 .  
         [0090]    A transfer cleaner  138  is provided with the same configuration as the transfer cleaner  38  of the first embodiment. The transfer cleaner  138  is located below the transfer roller  154  so that a transfer cleaning roller  139  thereof contacts the transfer roller  154  from below.  
         [0091]    A fixing unit  113  is provided with the same configuration as the fixing unit  13  of the first embodiment. The fixing unit  113  is disposed above the transfer roller  154  on the opposite side of the photosensitive belt mechanism  108  than the developing cartridges  107 . Sheets  3  that have a multi-color image thermally fixed thereon by the fixing unit  113  are discharged onto a discharge tray  130  formed at the upper portion of the housing  103 .  
         [0092]    As described above, the developing rollers  115  and the photosensitive belt  122  move in the opposite directions at nip portions where the developing rollers  115  contact the photosensitive belt  122 . That is, the developing rollers  115  move downward and the photosensitive belt  122  moves upward at the nip portions. With this configuration, the developing cartridges  107  and the fixing unit  113  can be disposed on both sides of the photosensitive belt  122 , without stacking the plurality of developing rollers  115  above the fixing portion  113  and without performing two intermediate transfers in the manner of the color laser printer  1  of FIG. 1. The configuration of the printer  151  is simple and compact.  
         [0093]    The photosensitive belt mechanism  108  is configured as an integral unit that can be detachably removed from the opening in the top of the housing  102 . Also, the intermediate transfer belt mechanism  153  can be separated from the photosensitive belt mechanism  108  while the photosensitive belt mechanism  108  is being removed, by pivoting the intermediate transfer belt mechanism  153  rearward around the first transfer belt support roller  156  as indicated by arrow  159  of FIG. 2.  
         [0094]    With this configuration, the photosensitive belt mechanism  108  is exchanged in the following manner. First, intermediate transfer belt mechanism  153  is moved rearward away from the photosensitive belt mechanism  108 . Then the photosensitive belt mechanism  108  is pulled out from the housing  102  through the top of the housing  102 . Next, a new photosensitive belt mechanism  108  is mounted into the housing  102  through the top of the housing  102 . Then, the intermediate transfer belt mechanism  153  is moved forward back into contact with the photosensitive belt mechanism  108 . By these simple operations, the photosensitive belt mechanism  108  can be easily exchanged. Maintenance can be efficiently performed. It should be noted that in the color laser printer  1  of FIG. 1, the photosensitive belt mechanism  8  can also be configured as an integral unit and one or both of the first and second transfer rollers  9 ,  10  can be configured separable from the photosensitive belt mechanism  8 , so that the photosensitive belt mechanism  108  can be detachably removed from the opening in the top of the housing  2 .  
         [0095]    Next, a color LED printer  261  according to a third embodiment of the present invention will be described with reference to FIG. 3. In the description of the color LED printer  261 , components that have corresponding components in the printer  151  will be referred to using reference numbers of the corresponding components added with 100.  
         [0096]    As in the second embodiment, a fixing unit  213  and four developing cartridges  207  are disposed on opposite sides of a photosensitive belt mechanism  208 . However, according to the third embodiment, the developing rollers  215  and a photosensitive belt  222  move upward at the nip portions where the developing rollers  215  contact the photosensitive belt  222 , rather than moving in opposite directions like the developing rollers  115  and the photosensitive belt  122  of the second embodiment.  
         [0097]    The color LED printer  261  includes a sheet supply portion  204  with the same configuration as the sheet supply portion  104  of the second embodiment. The sheet supply portion  204  uses a sheet-supply roller  46  to feed each sheet at the top of the stacked sheets out to the image-forming unit  205 .  
         [0098]    An image-forming unit  205  of the third embodiment includes four developing cartridges  207 , a photosensitive belt mechanism  208 , an intermediate transfer belt mechanism  253 , a transfer roller  253 , a charging roller  212 , and a fixing unit  213 . However, the image-forming unit  205  includes an LED array  262  instead of the scanner unit  106 .  
         [0099]    The LED array  262  is located on the opposite side of the photosensitive belt  222  than the developing cartridges  207  at a location in confrontation with the photosensitive belt support roller  220 , in order to emit light based on image data, and accordingly expose the surface of the photosensitive belt  222  that contacts the photosensitive belt support roller  220 .  
         [0100]    The four developing cartridges  207  have the same configuration and positioning as the four developing cartridges  107  of the second embodiment. That is, the yellow developing cartridge  207 Y is in the lowermost position of the developing cartridge stack. Then comes the magenta developing cartridge  207 M and the cyan developing cartridge  207 C in this order. The black developing cartridge  207 K is disposed in the upper position of the developing cartridge stack. It should be noted that this vertical order can be reversed.  
         [0101]    The sheet-supply roller  217  and the developing rollers  215  of the developing cartridge  207  are provided rotatable while in a slightly compressed condition. The developing rollers  215  rotate in the clockwise direction to move upward at the nip portion where the developing rollers  215  contact the photosensitive belt  222 . Layer-thickness regulating blades  216  are positioned so as to press against the surface of each developing roller  215  from below.  
         [0102]    The photosensitive belt mechanism  208  has the same configuration as the photosensitive belt mechanism  108  of FIG. 2, and includes a photosensitive belt  222  that circulates in the counterclockwise direction between a photosensitive belt support roller  220  and a photosensitive belt drive roller  221 .  
         [0103]    The photosensitive belt  222  moves from the developing roller  215  of the yellow developing cartridge  207 Y, which is in the lowermost posit ion, to the developing roller  215  of the black developing cartridge  207 K, which is in the uppermost position. The photosensitive belt  222  moves in the same direction as the developing rollers  215  at the nip portion, that is, the developing rollers  215  and the photosensitive belt  222  move upward at the nip portion.  
         [0104]    The intermediate transfer belt mechanism  253  is disposed to the rear of the photosensitive belt mechanism  208 , that is, on the opposite side of the photosensitive belt mechanism  208  than the developing cartridges  207 . The intermediate transfer belt mechanism  253  has the same configuration as the intermediate transfer belt mechanism  153  of the second embodiment, and includes an intermediate transfer belt drive roller  255 , a first intermediate transfer belt support roller  256 , a second intermediate transfer belt support roller  257 , and an intermediate transfer belt  258 . The intermediate transfer belt  258  is wrapped around the three rollers  255 ,  256 ,  257 .  
         [0105]    The intermediate transfer belt drive roller  255  is positioned in confrontation with the photosensitive belt drive roller  221  with the photosensitive belt  222  and the intermediate transfer belt  258  sandwiched therebetween. The first intermediate transfer support roller  256  is positioned diagonally below and to the rear of the intermediate transfer belt drive roller  255 . The first intermediate transfer support roller  256  is disposed in confrontation with a transfer roller  254 , with the intermediate transfer belt  258  sandwiched therebetween. The second intermediate transfer support roller  257  is disposed to the rear of the first intermediate transfer support roller  256  and below the intermediate transfer belt drive roller  255 .  
         [0106]    The rollers  255 ,  256 ,  257  are disposed to define an imaginary triangle. The intermediate transfer belt  258  is wrapped around the rollers  255 ,  256 ,  257 . Drive force of the intermediate transfer belt drive roller  255  conveys the intermediate transfer belt  258  in a circulating manner around the outer periphery of the rollers  255 ,  256 ,  257 , following the clockwise direction. By this, the intermediate transfer belt  258  moves in the same direction as the photosensitive belt  222  at the nip portion between the intermediate transfer belt  258  and the photosensitive belt  222 , near the intermediate transfer belt drive roller  255 .  
         [0107]    The transfer roller  254  is disposed so as to contact the surface of the intermediate transfer belt  258  at a position below and in confrontation with the first intermediate transfer belt roller  256 , with the intermediate transfer belt  258  sandwiched between the transfer roller  254  and the intermediate transfer belt  258 . The transfer roller  254  rotates counterclockwise so as to move in the same direction as the intermediate transfer belt  258  at the nip portion between the transfer roller  254  and the intermediate transfer belt  258 . A predetermined transfer bias is applied between the transfer roller  254  and the intermediate transfer belt  258 .  
         [0108]    A charge roller  212  is provided with the same configuration as the charge roller  112  of the second embodiment. The charge roller  212  is positioned near to and upstream from the photosensitive belt support roller  220  with respect to the movement direction of the photosensitive belt  222  so as to contact the surface of the photosensitive belt  222 . The charge roller  212  rotates clockwise and moves in the same direction as the photosensitive belt  222  at the nip portion between itself and the photosensitive belt  222 .  
         [0109]    After the surface of the photosensitive belt  222  is positively charged uniformly by the charging roller  212 , the surface of the photosensitive belt  222  is exposed by the LED array  262  to form an electrostatic latent image based on image data. Contact between the photosensitive belt  222  and the developing roller  215  of one of the certain developing cartridge  207  develops the electrostatic latent image into a monochromatic visible image of the color contained in that developing cartridge  207 . The monochromatic visible image is then transferred on the intermediate transfer belt  258  when the monochromatic visible image is brought into confrontation with the intermediate transfer belt  258 . The monochromatic visible images in the different colors are transferred one on top of the other on the intermediate transfer belt  258  to form a multicolored image.  
         [0110]    In other words, first a yellow visible image is formed on the photosensitive belt  222  with the toner contained in the yellow developing cartridge  207 Y, which is in the lowermost position of the developing cartridge stack Then, when movement of the photosensitive belt  222  moves the yellow visible image into confrontation with the first transfer roller  209 , the yellow visible image is transferred to the second transfer belt  227 . Then, an electrostatic latent image is again formed on the photosensitive belt  222  and a magenta visible image is formed on the photosensitive belt  222  from the toner contained in the magenta developing cartridge  207 M, which is the second from the lowest developing cartridge in the stack. When the magenta visible image is moved into confrontation with the intermediate transfer roller  258 , the magenta visible image is transferred onto the intermediate transfer roller  258  in an overlapping manner onto the yellow visible image.  
         [0111]    The operations described above are repeated for the cyan and black toners contained in the cyan and black developing cartridges  207 C and  207 K, respectively. Therefore, a multicolor image is formed on the intermediate transfer belt  258 .  
         [0112]    The multicolor image formed on the intermediate transfer belt  258  is transferred on a sheet  3  in a single transfer action, as the sheet  3  passes between the intermediate transfer belt  258  and the transfer roller  254 .  
         [0113]    The laser printer  151  further includes a belt cleaner  231  and a charge removing lamp  242  with the same configuration as the belt cleaner  131  and the charge removing lamp  142  of the second embodiment. The belt cleaner  231  is located over the charging roller  212  at the opposite side of the photosensitive belt  222  from the developing cartridges  207 . The charge removing lamp  242  is disposed in confrontation with the photosensitive belt  222  at a position downstream from the intermediate transfer belt  258 , and upstream from the belt cleaner unit  231 , with respect to the movement direction of the photosensitive belt  222 .  
         [0114]    A fixing unit  213  is provided with the same configuration as the fixing unit  113  of the second embodiment. The fixing unit  213  is disposed to the rear of the transfer roller  254  on the opposite side of the photosensitive belt mechanism  208  than the developing cartridges  207 . Sheets  3  that have a multi-color image thermally fixed thereon by the fixing unit  213  are discharged onto a discharge tray  230  formed at the upper portion of the housing  203 .  
         [0115]    As described above, the developing cartridges  207  are arranged in the opposite vertical order than the developing cartridges  7  of the first embodiment, and the developing rollers  215  and the photosensitive belt  222  move in the same direction at nip portions where the developing rollers  215  contact the photosensitive belt  222 . With this configuration, the developing cartridges  207  and the fixing unit  213  can be disposed on both sides of the photosensitive belt  222 , without stacking the plurality of developing rollers  215  above the fixing portion  213  and without performing two intermediate transfers in the manner of the color laser printer  1  of FIG. 1. The configuration of the printer  261  is simple and compact.  
         [0116]    It should be noted that a motor  263  is provided as the drive source of the photosensitive belt drive motor  221 . The motor  263  is disposed within the loop shape of the photosensitive belt  222  of the photosensitive belt mechanism  208  at a position near the photosensitive belt drive roller  221 . The motor  263  drives rotation of the photosensitive belt drive roller  221  through a gear  264 , in order to move the photosensitive belt  222 . Because the motor  263  is located within the loop of the photosensitive belt  222 , the space within the loop of the photosensitive belt  222  can be effectively utilized, and the printer  261  can be made more compact.  
         [0117]    Because the LED array  262  is located between the photosensitive belt support roller  220  and the first intermediate transfer belt support roller  256 , the space between the photosensitive belt mechanism  208  and the intermediate transfer belt mechanism  253  can be effectively utilized and the printer  261  can be made more compact.  
         [0118]    Next, a color LED printer  371  according to a fourth embodiment of the present invention will be described with reference to FIG. 4. In the description of the color LED printer  371 , components that have corresponding components in the printer  261  will be referred to using reference numbers of the corresponding components added with 100.  
         [0119]    As shown in FIG. 4, the color LED printer  371  includes developing cartridges  307  disposed on both sides of the photosensitive belt mechanism  308 . That is, the black developing cartridge  307 K is disposed to the rear of the photosensitive belt mechanism  308  and the other developing cartridges  307 C,  307 M, and  307 Y are disposed to the front of the photosensitive belt mechanism  308 . Both the photosensitive belt  322  and the developing roller  315  of the black developing cartridge  307 K move downward at the nip portion between the photosensitive belt  322  and the developing roller  315  of the black developing cartridge  307 K. The photosensitive belt  322  and the developing rollers  315  of the other developing cartridges  307 C,  307 M, and  307 Y move upward at the nip portion between photosensitive belt  322  and the developing rollers  315  of the other developing cartridges  307 C,  307 M, and  307 Y. This configuration enables the printer  371  to be made more compact.  
         [0120]    The LED array  362  is located on the same side of the photosensitive belt  322  as the other developing cartridges  307 C,  307 M, and  307 Y at a location in confrontation with the photosensitive belt support roller  320 , in order to emit light based on image data, and accordingly expose the surface of the photosensitive belt  322  that contacts the photosensitive belt support roller  320 .  
         [0121]    Of the four developing cartridges  307 , the black developing cartridge  307 K has substantially the same configuration as the black developing cartridge  107 K of the color laser printer  151  of FIG. 2 and is disposed on the same side of the photosensitive belt mechanism  308  as the fixing unit  313 . The other developing cartridges  307 C,  307 M, and  307 Y have substantially the same configuration as the developing cartridges  207 C,  207 M, and  207 Y of the color LED printer  261  and are disposed on the opposite side of the photosensitive belt mechanism  308  than the fixing unit  313 .  
         [0122]    The black developing cartridge  307 K is disposed above the intermediate transfer belt mechanism  353  in substantially parallel alignment with the upper surface of the intermediate transfer belt  358  of the intermediate transfer belt mechanism  353 . The developing roller  315  of the black developing cartridge  307 K rotates clockwise downward at the nip portion between the developing roller  315  and the photosensitive belt  322 .  
         [0123]    It should be noted that the black developing cartridge  307 K has a larger toner container  318  than the toner containers  318  of the other developing cartridges  307 C,  307 M, and  307 Y, because black toner is consumed in greater quantities during image formation than the other colors of toner. Because the black developing cartridge  307 K is disposed on a different side of the photosensitive belt mechanism  308  than the other developing cartridges  307 C,  307 M, and  307 Y and also has a larger toner container  318 , the black developing cartridge  307 K will need to be exchanged less frequently and maintenance is facilitated.  
         [0124]    With respect to the other developing cartridges  307 C,  307 M, and  307 Y, the yellow developing cartridge  307 Y is in the lowermost position of the developing cartridge stack. Then comes the magenta developing cartridge  307 M and the cyan developing cartridge  307 C in this order, with the cyan developing cartridge  307 C disposed in the upper position of the developing cartridge stack. In the same manner as the color LED printer  261  shown in FIG. 3, the developing rollers  315  rotate in the clockwise direction to move upward at the nip portion where the developing rollers  315  contact the photosensitive belt  322 . Layer-thickness regulating blades  316  are positioned so as to press against the surface of each developing roller  315  from below  
         [0125]    The photosensitive belt mechanism  308  has the same configuration as the photosensitive belt mechanism  308  of FIG. 3, and includes a photosensitive belt  322  that circulates in the counterclockwise direction around a photosensitive belt support roller  320  and a photosensitive belt drive roller  321 .  
         [0126]    The photosensitive belt  322  moves on the same side as the fixing unit  312  downward in the same direction as the developing roller  315  of the black developing cartridge  317 K at the nip portion between the photosensitive belt  322  and the developing roller  315  of the black developing cartridge  317 . On the other hand, the photosensitive belt  322  moves on the opposite side from the fixing unit  312  upward in the same direction as the developing rollers  315  of the other developing cartridges  307 C,  307 M, and  307 Y at the nip portion between the photosensitive belt  322  and the developing rollers  315  of the other developing cartridges  307 C,  307 M, and  307 Y.  
         [0127]    The intermediate transfer belt mechanism  353  is disposed below the black developing cartridge  307 K and to the rear of the photosensitive belt mechanism  308 . The intermediate transfer belt mechanism  353  has the same configuration as the intermediate transfer belt mechanism  253  of FIG. 3 and includes an intermediate transfer belt drive roller  355 , a first intermediate transfer belt S support roller  356 , a second intermediate transfer belt support roller  357 , and an intermediate transfer belt  358 . The intermediate transfer belt  358  is wrapped around the three rollers  355 ,  356 ,  357 .  
         [0128]    The intermediate transfer belt drive roller  355  is positioned in confrontation with the photosensitive belt  322  at a position downstream from the photosensitive belt drive roller  321 , with the intermediate transfer belt  358  sandwiched therebetween. The first intermediate transfer support roller  356  is positioned diagonally below and to the rear of the intermediate transfer belt drive roller  355 . The first intermediate transfer support roller  356  is disposed in confrontation with a transfer roller  354 , with the intermediate transfer belt  358  sandwiched therebetween. The second intermediate transfer support roller  357  is disposed to the rear of and above the first intermediate transfer support roller  356 .  
         [0129]    The rollers  355 ,  356 ,  357  are disposed to define an imaginary triangle. The intermediate transfer belt  358  is wrapped around the rollers  355 ,  356 ,  357 . Drive force of the intermediate transfer belt drive roller  355  conveys the intermediate transfer belt  358  in a circulating manner around the cuter periphery of the rollers  355 ,  356 ,  357 , following the clockwise direction. By this, the intermediate transfer belt  358  moves in the same direction as the photosensitive belt  322  at the nip portion between the intermediate transfer belt  358  and the photosensitive belt  322 , near the intermediate transfer belt drive roller  355 .  
         [0130]    The transfer roller  354  has the same configuration as the transfer roller  254  of FIG. 3 and is disposed so as to contact the surface of the intermediate transfer belt  358  at a position below and in confrontation with the first intermediate transfer belt roller  356 , with the intermediate transfer belt  358  sandwiched between the transfer roller  356  and the intermediate transfer belt  358 . The transfer roller  354  rotates counterclockwise so as to move in the same direction as the intermediate transfer belt  358  at the nip portion between the transfer roller  354  and the intermediate transfer belt  358 . A predetermined transfer bias is applied between the transfer roller  354  and the intermediate transfer belt  358 .  
         [0131]    A charge roller  312  is provided with the same configuration as the charge roller  212  of the third embodiment. The charge roller  312  is positioned near to and upstream from the photosensitive belt support roller  320  with respect to the movement direction of the photosensitive belt  322 , so as to contact the surface of the photosensitive belt  322 . The charge roller  312  rotates clockwise and moves in the same direction as the photosensitive belt  322  at the nip portion between itself and the photosensitive belt  322 .  
         [0132]    After the surface of the photosensitive belt  322  is positively charged uniformly by the charging roller  312 , the surface of the photosensitive belt  322  is exposed by the LED array  362  to form an electrostatic latent image based on image data. Contact between the photosensitive belt  322  and the developing roller  315  of one of the certain developing cartridge  307  develops the electrostatic latent image into a monochromatic visible image of the color contained in that developing cartridge  307 . The monochromatic visible image is then transferred on the intermediate transfer belt  358  when the monochromatic visible image is brought into confrontation with the intermediate transfer belt  358 . The monochromatic visible images in the different colors are transferred one on top of the other onto the intermediate transfer belt  358  to form a multicolored image.  
         [0133]    In other words, first a yellow visible image is formed on the photosensitive belt  322  with the toner contained in the yellow developing cartridge  307 Y, which is in the lowermost position of the developing cartridge stack. Then, when movement of the photosensitive belt  322  moves the yellow visible image into confrontation with the first transfer roller  309 , the yellow visible image is transferred to the second transfer belt  327 . Then, an electrostatic latent image is again formed on the photosensitive belt  322  and a magenta visible image is formed on the photosensitive belt  322  from the toner contained in the magenta developing cartridge  307 M, which is the second from the lowest developing cartridge in the stack. When the magenta visible image is moved into confrontation with the intermediate transfer roller  358 , the magenta visible image is transferred onto the intermediate transfer roller  358  in an overlapping manner onto the yellow visible image.  
         [0134]    The operations described above are repeated for the cyan toner contained in the cyan developing cartridge  307 C. Then, the operations described above are repeated for the black toner contained in the black developing cartridge  307 K. Therefore, a multicolor image is formed on the intermediate transfer belt  358 .  
         [0135]    The multicolor image formed on the intermediate transfer belt  358  is transferred on a sheet  3  in a single transfer action, as the sheet  3  passes between the intermediate transfer belt  358  and the transfer roller  354 .  
         [0136]    The color LED printer  371  further includes a belt cleaner  331  and a charge removing lamp  342  with the same configuration as the belt cleaner  231  and the charge removing lamp  242  of the third embodiment. The belt cleaner  331  is located over the charging roller  312  at the same side of the photosensitive belt  322  as the black developing cartridge  307 K. The charge removing lamp  342  is disposed in confrontation with the photosensitive belt  322  at a position downstream from the intermediate transfer belt  358 , and upstream from the belt cleaner unit  331 , with respect to the movement direction of the photosensitive belt  322 .  
         [0137]    A fixing unit  313  is provided with the same configuration as the fixing unit  213  of the third embodiment. The fixing unit  313  is disposed to the rear of the transfer roller  354  on the opposite side of the photosensitive belt mechanism  308  than the other three developing cartridges  307 C,  307 M, and  307 Y. Sheets  3  that have a multi-color image thermally fixed thereon by the fixing unit  313  are discharged onto a discharge tray  330  formed at the upper portion of the housing  303 .  
         [0138]    A motor  374  is provided for driving the intermediate transfer belt drive motor  355 . The motor  374  is disposed within the loop of the intermediate transfer belt  358  of the intermediate transfer belt mechanism  353  at a position near the intermediate transfer belt drive roller  355 . The motor  374  drives rotation of the intermediate transfer belt drive roller  355  so that the intermediate transfer belt  358  moves. By locating the motor  374  within the loop of the intermediate transfer belt  358 , the space within the loop of the intermediate transfer belt  358  can be effectively utilized so that that the printer  371  can be made smaller. It should be noted that the printers of the other embodiments can also be modified to locate a motor for driving the transfer belt roller within the loop of the transfer belt to make the printers more compact. Also, the printer  1  of the first embodiment can be modified so that the first transfer roller  9  is replaced with a mechanism having the same configuration as the second transfer belt mechanism  10 , and the second transfer belt mechanism  10  is replaced with a mechanism having the same configuration as the first transfer roller  9 . In this case, the motor for driving the first belt roller can be disposed within the loop of the first transfer belt so that the printer  1  can be made more compact.  
         [0139]    The printer  371  can be made shorter by an amount equivalent to how the developing cartridges  307  are distributed on either side of the photosensitive belt mechanism  308 . That is, in the present embodiment, the printer  371  can be made shorter by an amount equivalent to the black developing cartridge  307 K because the four developing cartridges  307  are not stacked on top of each other, and instead the black developing cartridge  307 K is disposed on one side of the photosensitive belt mechanism  308  and the other developing cartridges  307 C,  307 M, and  307 Y are disposed on the other side of the photosensitive belt mechanism  308 . The printer  371  can also be made smaller because the developing roller  315  of the black developing cartridge  307 K and also the photosensitive belt  322  move downward at the nip portion and the other three developing cartridges  307 C,  307 M, and  307 Y and the fixing unit  313  are disposed on opposite sides of the photosensitive belt mechanism  308 . Further the printer  371  can be made that much smaller because all of the developing rollers  315  rotate in the same direction as the photosensitive belt  322  where they contact the photosensitive belt  322 . Therefore, even higher quality images visible can be formed from toner supplied by the developing rollers  315 .  
         [0140]    As shown in two-dot chain line in FIG. 4, the printer  371  can be provided with a cover  373  for selectively closing and opening up an opening in the top of the housing  302 . The cover  373  is pivotably supported on the front end of the housing  302 . The black developing cartridge  307 K and the cyan developing cartridge  307 C, which are the developing cartridges  307  that are located at the highest positions, are disposed adjacent to the cover  373 . By opening the cover  373 , the black developing cartridge  307 K and the cyan developing cartridge  307 C can be easily removed In this way, the cover  373  facilitates exchange operations for the black developing cartridge  307 K and the cyan developing cartridge  307 C, so that maintenance can be efficiently performed.  
         [0141]    Next, a color LED printer  472  according to a fifth embodiment of the present invention will be described with reference to FIG. 5. In the description of the color laser printer  472 , components that have corresponding components in the printer  261  will be referred to using reference numbers of the corresponding components added with 100. The color LED printer  472  of the fifth embodiment has substantially the same configuration as the color LED printer  371  of the fourth embodiment, except that developing rollers  415  of the other developing cartridges  407 C,  407 M, and  407 Y rotate in the opposite direction than the developing rollers  315  of the fourth embodiment.  
         [0142]    Explained in greater detail, the yellow developing cartridge  407 Y is in the lowermost position of the stack of the other developing cartridges  407 C,  407 M, and  407 Y. Then comes the magenta developing cartridge  407 M and the cyan developing cartridge  407 C in this order, with the cyan developing cartridge  407 C disposed in the upper position of the developing cartridge stack. The developing cartridges  407  have the same configuration as the developing cartridges  207  of FIG. 2, that is, the developing rollers  415  rotate in the counterclockwise direction to move downward at the nip portion where the developing rollers  415  contact the photosensitive belt  422 .  
         [0143]    In the same manner as the printer  371 , the printer  471  can be made shorter by an amount equivalent to how the developing cartridges  407  are distributed on either side of the photosensitive belt mechanism  408 . The printer  471  can also be made smaller because the other three developing cartridges  407 C,  407 M, and  407 Y and the fixing unit  413  are disposed on opposite sides of the photosensitive belt mechanism  408 . Moreover, the developing roller  415  of the black developing cartridge  407 K move in the same direction as the photosensitive belt  422  at the nip portion. However, the developing rollers  415  of the other three developing cartridges  407 C,  407 M, and  407 Y move in the opposite direction of the photosensitive belt  422  at the nip portion. This enables selectively positioning the developing cartridges  407  so that even better quality visible images can be formed from the toner supplied from the developing rollers  415 .  
         [0144]    A motor  474  is provided for driving the intermediate transfer belt drive motor  455 . The motor  474  is disposed within the loop of the intermediate transfer belt  458  and so produces the same effects as the motor  374  of the fourth embodiment.  
         [0145]    As shown in two-dot chain line in FIG. 5, the printer  472  can be provided with a cover  473  for selectively closing and opening up an opening in the top of the housing  402 , in the same manner as the printer  371 . The same effects as the cover  373  can be achieved.  
         [0146]    It should be noted that the scanner unit  6  of the first embodiment can be replaced with an LED array interposed between the photosensitive belt mechanism  8  and either the first transfer roller  9  or second transfer belt mechanism  10 .