Patent Publication Number: US-9423761-B2

Title: Image forming device that facilitates maintenance of waste toner storage member

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2012-241111 filed Oct. 31, 2012 and Japanese Patent Application No. 2013-117477 filed Jun. 4, 2013. The entire content of each of these priority applications is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an electrophotographic image forming device. 
     BACKGROUND 
     A tandem-type color printer having photosensitive drums for the ink colors black, yellow, magenta, and cyan is known in the art as an electrophotographic image forming device. 
     One such color printer that has been proposed includes a plurality of developing devices, each of which has a photosensitive drum; an intermediate transfer belt opposing the tops of the developing devices; and a cleaning unit disposed above the intermediate transfer belt for collecting residual toner deposited on the belt. 
     Consequently, maintenance of the cleaning unit must be performed separately from maintenance on the developing devices, making maintenance of the cleaning unit more difficult. 
     SUMMARY 
     In view of the foregoing, it is an object of the present invention to provide an image forming device that facilitates maintenance of a waste toner storage member in the cleaning unit. 
     In order to attain the above and other objects, the present invention provides an image forming device includes a main body; a cartridge; a supporting member; a belt unit; a waste toner storage member; and a conveying member. The cartridge is configured to retain a photosensitive body extending in a longitudinal direction and having a longitudinal dimension. The supporting member is configured to support the cartridge. The belt unit includes a belt; and a cleaning member. The cleaning member is configured to remove residual toner remaining on the belt. The waste toner storage member is supported by the supporting member and configured to store the residual toner removed by the cleaning member. The conveying member is configured to convey the residual toner removed by the cleaning member to the waste toner storage member. The belt unit is configured to be movable between a contact position in which the belt contacts the photosensitive body and a separated position in which the belt is separated from the photosensitive body. The conveying member is provided in the belt unit, coupled to the waste toner storage member when the belt unit is disposed in the contact position, and separated from the waste toner storage member when the belt unit is disposed in the separated position. The convening member is formed with a first opening, and a first shutter member is configured to open the first opening when the belt unit is disposed in the contact position and close the first opening when the belt unit is disposed in the separated position. The waste toner storage member is formed with a second opening, and a second shutter member is configured to open the second opening when the belt unit is disposed in the contact position and close the second opening when the belt unit is disposed in the separated position. 
     According to another aspect, the present invention provides an image forming device includes a main body; a cartridge; a supporting member; a belt unit; a waste toner storage member; and a conveying member. The cartridge is configured to retain a photosensitive body extending in a longitudinal direction and having a longitudinal dimension. The supporting member is configured to support the cartridge. The belt unit includes a belt; and a cleaning member. The cleaning member is configured to remove residual toner remaining on the belt. The waste toner storage member is supported by the supporting member and configured to store the residual toner removed by the cleaning member. The conveying member is configured to convey the residual toner removed by the cleaning member to the waste toner storage member. The belt unit is configured to be movable between a contact position in which the belt contacts the photosensitive body and a separated position in which the belt is separated from the photosensitive body. The conveying member is configured to allow the residual toner to be conveyed from the cleaning member to the waste toner storage member when the belt unit is in the contact position, and interrupt the residual toner from being conveyed from the cleaning member to the waste toner storage member when the belt unit is in the separated position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a vertical cross-sectional view of a printer according to a first embodiment of an image-forming device of the present invention; 
         FIG. 2  is a cross-sectional view taken along a II-II line of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a conveying unit shown in  FIG. 1 ; 
         FIG. 4  is an explanatory diagram showing a mounting and removing operation of a process cartridge shown in  FIG. 1 ; 
         FIG. 5  is a vertical cross-sectional view of a printer according to a second embodiment; 
         FIG. 6  is a cross-sectional view taken along a VI-VI line of  FIG. 5 ; and 
         FIG. 7  is a an explanatory diagram showing a mounting and removing operation of a process cartridge shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     A printer according to embodiments of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     1. Overall Structure of a Printer 
     A printer  1  shown in  FIG. 1  is a horizontal tandem-type intermediate transfer color printer. 
     In the following description, upward and downward directions related to the printer  1  will be given based on the state of the printer  1  when the printer  1  is resting on a level surface. Hence, the side of the printer  1  at the top of  FIG. 1  will be considered the upper side, and the side at the bottom will be considered the lower side. Further, the left side of the printer  1  in  FIG. 1  will be considered the front side, and the right side will be considered the rear side. Left and right sides of the printer  1  will be based on the perspective of a user facing the front of the printer  1 . Hence, the near side of the printer  1  in  FIG. 1  will be considered the right side, and the far side will be considered the left side. 
     The printer  1  is provided with a main casing  2  and, within the main casing  2 , a process unit  4 , a scanning unit  3 , a transfer unit  5 , and a fixing unit  6 . The printer  1  also includes an image-reading unit  10  disposed above the main casing  2 . 
     The main casing  2  has a box-like shape and is generally rectangular in a side view. An access opening  7  is formed in the front side of the main casing  2 . A front cover  8  is pivotally provided on the front of the main casing  2  over the access opening  7 . The front cover  8  can be pivoted about its lower edge between a closed position (see  FIG. 1 ) for covering the access opening  7 , and an open position (see  FIG. 4 ) for exposing the access opening  7 . An upper cover  80  is provided on the top of the main casing  2  and is capable of pivoting about its rear edge. The upper cover  80  pivots along with pivoting of a belt unit  20  described later. 
     The process unit  4  is disposed in the vertical center of the main casing  2 . The process unit  4  includes a process frame  31 , and process cartridges  9 . 
     The process frame  31  has a frame-like structure with a closed bottom. The plurality of process cartridges  9  is retained inside the process frame  31 . The process frame  31  is capable of moving in the front-rear direction between a mounted position (see  FIG. 1 ) mounted inside the main casing  2 , and a withdrawn position (see  FIG. 4 ) withdrawn to the outside of the main casing  2 . 
     The process cartridges  9  are arranged parallel to each other and are spaced at intervals in the front-rear direction. Specifically, the process cartridges  9  are juxtaposed in the front-rear direction and include, in order from the front side toward the rear side, a black process cartridge  9 K, a yellow process cartridge  9 Y, a magenta process cartridge  9 M, and a cyan process cartridge  9 C. Each of the process cartridges  9  integrally retains a photosensitive drum  11 , a charging roller  12 , and a developing device  13 . 
     Each photosensitive drum  11  is rotatably supported in the top end of the corresponding process cartridge  9  with its top surface exposed in the top end of the process cartridge  9 . The photosensitive drums  11  have a general cylindrical shape and are oriented with their axes in the left-right direction. Hence, the longitudinal direction of the photosensitive drums  11  is aligned in the left-right direction. 
     Each charging roller  12  is disposed on the lower rear side of the corresponding photosensitive drum  11  and contacts the photosensitive drum  11  on the lower rear side. 
     Each developing device  13  is disposed on the lower front side of the correspond photosensitive drum  11 . The developing device  13  includes a developer frame  14 , and a developing roller  15 . 
     The developer frame  14  is formed in a cylindrical shape and is elongated in the left-right direction. In cross section, the developer frame  14  has a general U-shape, with the opening of the “U” on the top. 
     The developing roller  15  is rotatably supported in the top end of the developer frame  14 , with its upper peripheral surface exposed through the top of the developer frame  14 . The developing roller  15  contacts the photosensitive drum  11  from the lower front side. 
     The developing device  13  is further provided with a supply roller  16  for supplying toner to the developing roller  15 , and a thickness-regulating blade  17  for regulating the thickness of toner carried on the developing roller  15 . A toner-accommodating chamber  19  that accommodates toner is disposed in space provided on the rear side of the supply roller  16 . The toner-accommodating chamber  19  is divided vertically into two spaces. An auger screw  18  is disposed in each of the spaces. 
     The auger screws  18  are aligned in the left-right direction. The auger screws  18  function to circulate toner in the toner-accommodating chamber  19 . 
     The scanning unit  3  is disposed beneath the process unit  4  for confronting the lower side of the process unit  4  when the process unit  4  is in the mounted position. The scanning unit  3  irradiates laser beams toward the photosensitive drums  11  based on image data, as indicated by solid lines in the drawing. 
     The transfer unit  5  is disposed above the process unit  4  when the process unit  4  is in the mounted position. The transfer unit  5  includes a belt unit  20 , and a secondary transfer roller  21 . 
     The belt unit  20  is elongated in the front-rear direction so as to confront the top sides of all photosensitive drums  11 . The belt unit  20  includes a drive roller  22 , a follow roller  23 , an intermediate transfer belt  24 , and four primary transfer rollers  25 . 
     The drive roller  22  is rotatably supported in the rear end of the belt unit  20 . 
     The follow roller  23  is rotatably supported in the front end of the belt unit  20 . 
     The intermediate transfer belt  24  is looped around the drive roller  22  and follow roller  23  so that the lower portion of the loop contacts the top peripheral surfaces of all photosensitive drums  11 . When the drive roller  22  is driven to rotate, the intermediate transfer belt  24  circulates so that its lower portion moves rearward, and the follow roller  23  rotates along with the circulating movement of the intermediate transfer belt  24 . 
     The primary transfer rollers  25  are arranged parallel to each other and are spaced at intervals in the front-rear direction. More specifically, the primary transfer rollers  25  are disposed between the drive roller  22  and follow roller  23  within the loop of the intermediate transfer belt  24  at positions above the corresponding photosensitive drums  11 . The primary transfer rollers  25  contact the lower portion of the intermediate transfer belt  24  from above. 
     The belt unit  20  is also capable of pivoting about a rotational shaft  22 A of the drive roller  22 . The belt unit  20  can pivot between a contact position (see  FIG. 1 ) in which the intermediate transfer belt  24  contacts all photosensitive drums  11 , and a separated position (see  FIG. 4 ) in which the intermediate transfer belt  24  is separated from all photosensitive drums  11 . 
     The secondary transfer roller  21  is disposed on the rear side of the drive roller  22 , with the intermediate transfer belt  24  interposed therebetween. 
     The fixing unit  6  is disposed above the secondary transfer roller  21 . The fixing unit  6  includes a heating roller  26 , and a pressure roller  27  confronting the heating roller  26 . 
     The image-reading unit  10  is disposed above the main casing  2 , with a gap formed between the bottom of the image-reading unit  10  and the top of the upper cover  80 . The image-reading unit  10  functions to read image data from an original. 
     When a print job is inputted into the printer  1 , toner in the developing device  13  is tribocharged between the supply roller  16  and developing roller  15 , and the developing roller  15  carries a thin layer of toner on its surface, regulated at a uniform thickness by the thickness-regulating blade  17 . 
     In the meantime, the charging roller  12  applies a uniform charge to the surface of the photosensitive drum  11 . Subsequently, the scanning unit  3  exposes the surface of the photosensitive drum  11  based on prescribed image data, forming an electrostatic latent image on the surface of the photosensitive drum  11  based on the image data. Next, the toner carried on the surface of the developing roller  15  is supplied to the latent image formed on the surface of the photosensitive drum  11 , developing the latent image into a toner image. 
     Toner images carried on the surfaces of all photosensitive drums  11  are sequentially transferred onto the lower portion of the intermediate transfer belt  24 . This operation forms a color image on the surface of the intermediate transfer belt  24 . 
     A paper tray  28  is provided in the bottom section of the main casing  2  for accommodating sheets of paper P. Various rollers provided in the main casing  2  convey the paper P between the intermediate transfer belt  24  and secondary transfer roller  21  one sheet at a time and at a prescribed timing. The color image formed on the intermediate transfer belt  24  is transferred onto the sheet as the sheet passes in an upward direction between the intermediate transfer belt  25  and secondary transfer roller  21 . 
     Next, the sheets of paper P pass between the heating roller  26  and pressure roller  27  in the fixing unit  6 . The heating roller  26  and pressure roller  27  apply heat and pressure to the paper P, fixing the color image to the paper P. 
     Subsequently, the various rollers convey the sheets of paper P forward and discharge the sheets onto a discharge tray  29  provided on the supper cover  80  of the main casing  2 . 
     2. Detailed Description of the Process Unit 
     (1) Process Frame 
     As shown in  FIGS. 1 and 2 , the process frame  31  includes a frame body  32 , a pair of left and right process-side positioning plates  33 , and a process-side positioning shaft  34 . 
     The frame body  32  is formed of a hard resin material. The frame body  32  has a frame-like structure with a closed bottom and open top. The frame body  32  includes a pair of left and right side walls  35 , a front wall  36 , a rear wall  37 , and a bottom wall  38 . 
     The side walls  35  are disposed so as to confront each other across a gap in the left-right direction. The side walls  35  have a generally flat plate shape that extends both vertically and in the front-rear direction. Each side wall  25  includes a guide roller  39 , and a guide rail  40 . 
     The guide roller  39  is rotatably disposed in the upper rear corner of the respective side wall  35 . 
     The guide rail  40  is formed on the top edge of the side wall  35  and extends in the front-rear direction. The guide rail  40  protrudes outward in the left-right direction to form a ridge-like shape. 
     The front wall  36  bridges the front ends of the side walls  35 . The front wall  36  has a generally flat plate shape and is elongated both vertically and in the left-right direction. 
     The rear wall  37  bridges the rear ends of the side walls  35 . The rear wall  37  has a generally flat plate shape and is elongated both vertically and in the left-right direction. 
     The bottom wall  38  bridges the bottom edges of the side walls  35 . The bottom wall  38  has a generally flat plate shape and is elongated in the front-rear and left-right directions. A plurality of through-holes  41  is formed in the bottom wall  38 . 
     The through-holes  41  penetrate the bottom wall  38  at positions below the photosensitive drums  11 . 
     The process-side positioning plates  33  are disposed at positions confronting the inner left and right sides of the respective side walls  35 . The process-side positioning plates  33  are formed of metal, such as stainless steel or steel. The process-side positioning plates  33  have a general L-shape in a side view. Specifically, each process-side positioning plate  33  is configured of a body part  52 , and an extended part  53 . 
     Each body part  52  is positioned on the inside of the upper edge on the corresponding side wall  35  with respect to the left-right direction. The body part  52  has a flat plate shape that is generally rectangular in a side view and extends in the front-rear direction, spanning nearly the entire front-rear dimension of the side wall  35 . The body part  52  includes a fitting groove  43 . 
     The fitting groove  43  is cut out from the rear edge of the body part  52  to form a general U-shape in a side view that is open on the rear side. 
     Each extended part  53  is positioned inside the front end of the corresponding side wall  35  with respect to the left-right direction. The extended part  53  has a flat plate shape that is generally rectangular in a side view. The extended part  53  extends continuously downward from the lower edge on the front end of the body part  52 , spanning nearly the entire vertical dimension of the side wall  35 . 
     The process-side positioning shaft  34  is provided in the lower front corner of the process frame  31  and penetrates the bottom ends of the extended parts  53  and the lower front corners of the side walls  35 . The process-side positioning shaft  34  is formed of metal, such as stainless steel. The process-side positioning shaft  34  has a general rod shape and extends in the left-right direction. The left and right ends of the process-side positioning shaft  34  protruded outward in the corresponding left and right directions from the outer left and right surfaces of the side walls  35 . 
     (2) Drum Cleaners 
     Each process cartridge  9  is also provided with a drum cleaner  44 . 
     The drum cleaner  44  is disposed on the rear side of the corresponding photosensitive drum  11 . The drum cleaner  44  includes a waste toner storage unit  45 , and a scraping blade  46 . 
     The waste toner storage unit  45  has a box-like shape and extends in the vertical and left-right directions. A collection opening  47  is formed in the waste toner storage unit  45 . 
     The collection opening  47  penetrates the front wall of the waste toner storage unit  45  at the top portion thereof. 
     The scraping blade  46  has a generally flat plate shape and is elongated in the left-right direction. The bottom edge, i.e., base edge, of the scraping blade  46  is supported on the bottom peripheral edge defining the collection opening  47  formed in the waste toner storage unit  45 . The top edge, i.e., the free edge of the scraping blade  46  contacts the peripheral surface of the photosensitive drum  11 . 
     The drum cleaner  44  provided for the black process cartridge  9 K also includes a receiving part  48 . 
     The receiving part  48  is provided in the upper left portion of the drum cleaner  44  corresponding to the black process cartridge  9 K. The receiving part  48  has a general cylindrical shape, with a closed bottom, and is elongated vertically. The receiving part  48  includes a drum-cleaner-side through-hole  49 , and a drum-cleaner-side shutter  50 . 
     The drum-cleaner-side through-hole  49  has a generally rectangular shape in a side view and penetrates the right wall of the receiving part  48  in the upper portion thereof. 
     The drum-cleaner-side shutter  50  is provided inside the receiving part  48 . The drum-cleaner-side shutter  50  has a general cylindrical shape, with a closed top, and is elongated vertically. The vertical dimension of the drum-cleaner-side shutter  50  is approximately half that of the receiving part  48 . The drum-cleaner-side shutter  50  is capable of sliding between an open position (see  FIG. 2 ) in which the drum-cleaner-side shutter  50  is disposed ins the lower end of the receiving part  48  for opening the drum-cleaner-side through-hole  49 , and a closed position (see  FIG. 4 ) in which the drum-cleaner-side shutter  50  is disposed in the upper end of the receiving part  48  for closing the drum-cleaner-side through-hole  49 . A compression spring  51  is interposed between the bottom wall of the receiving part  48  and the top wall of the drum-cleaner-side shutter  50  for constantly urging the drum-cleaner-side shutter  50  upward toward the closed position. 
     3. Detailed Description of the Belt Unit 
     (1) Belt Cleaner 
     The belt unit  20  is also provided with a belt cleaner  61 . 
     The belt cleaner  61  includes a cleaning unit  62 , and a conveying unit  63 . 
     The cleaning unit  62  is disposed above the intermediate transfer belt  24  at a position aligned with the yellow process cartridge  9 Y. The cleaning unit  62  includes a cleaner frame  64 , a scraping blade  65 , a scraping brush  66 , and an auger screw  67 . 
     The cleaner frame  64  is box-shaped and generally rectangular in a side view. The cleaner frame  64  is further provided with a collection hold  68  formed therein, and a connecting part  74  provided thereon. 
     The collection hole  68  penetrates the bottom wall of the cleaner frame  64  at the rear end thereof. 
     The connecting part  74  has a general cylindrical shape with a closed left end. The connecting part  74  protrudes leftward from the left wall of the cleaner frame  64  at the front end thereof. The right end of the connecting part  74  is in communication with the cleaner frame  64 . 
     The scraping blade  65  has a generally flat plate shape that is elongated in the left-right direction. The front edge, i.e., the base edge of the scraping blade  65  is supported on the front peripheral edge defining the collection hole  68  formed in the cleaner frame  64 . The rear edge, i.e., the free end of the scraping blade  65  contacts the top surface on the upper portion of the intermediate transfer belt  24 . 
     The scraping brush  66  is disposed in the rear side of the cleaner frame  64  and confronts the collection hole  68  from above. The lower side of the scraping brush  66  contacts the top surface of the scraping blade  65  from above. 
     The auger screw  67  is disposed in the rear end of the cleaner frame  64  on the front side of the scraping brush  66 . The auger screw  67  is elongated in the left-right direction. The right end of the auger screw  67  is rotatably supported in the right wall of the cleaner frame  64 , and the left end of the auger screw  67  is rotatably supported in the left wall of the connecting part  74 . 
     The conveying unit  63  is disposed on the left side of the intermediate transfer belt  24  and is aligned vertically with the drum cleaner  44  of the black process cartridge  9 K. As shown in  FIGS. 2 and 3 , the conveying unit  63  includes a conveying cylinder  69 , an auger screw  75 , and a belt-cleaner-side shutter  70 . 
     The conveying cylinder  69  has a general cylinder shape that is elongated vertically and closed on both ends. The rear side of the conveying cylinder  69  at its upper end is connected to the front side of the connecting part  74  constituting the cleaning unit  62 . The top end of the conveying cylinder  69  is in communication with the connecting part  74 . The conveying cylinder  69  also has a belt-cleaner-side communication hole  71 , and a flange part  72 . 
     The belt-cleaner-side communication hole  71  is generally rectangular in a side view and penetrates the right wall of the conveying cylinder  69  at the lower end thereof. 
     The flange part  72  is formed around the entire circumference of the conveying cylinder  69  at substantially the vertical center thereof and protrudes radially outward from the outer peripheral surface of the conveying cylinder  69  to form a ridge. 
     The auger screw  75  is provided in the conveying cylinder  69  in a vertical orientation. The top end of the auger screw  75  is rotatably supported in the top wall of the conveying cylinder  69 , and the bottom end is rotatably supported in the bottom wall of the conveying cylinder  69 . The auger screw  75  further includes a blade  76 . 
     The blade  76  is provided on the bottom end of the auger screw  75  at a position corresponding to the belt-cleaner-side communication hole  71  in the left-right direction. The blade  76  has a generally flat plate shape that extends radially outward from the rotational shaft of the auger screw  75 . 
     The belt-cleaner-side shutter  70  is fitted around the lower end of the conveying cylinder  69 . The belt-cleaner-side shutter  70  has a generally cylindrical shape and extends vertically. The belt-cleaner-side shutter  70  is capable of sliding vertically between an open position (see  FIG. 2 ) for exposing the belt-cleaner-side communication hole  71  formed in the conveying cylinder  60 , and a closed position (see  FIG. 3 ) for closing the belt-cleaner-side communication hole  71 . The belt-cleaner-side shutter  70  also has a spring-accommodating section  77 . 
     The spring-accommodating section  77  is formed in the vertical center of the belt-cleaner-side shutter  70  to provide this center region with an expanded diameter. The flange part  72  of the conveying cylinder  69  is fitted inside the spring-accommodating section  77 . 
     A compression spring  73  is interposed between the bottom surface of the flange part  72  and the bottom side on the inner peripheral surface of the spring-accommodating section  77 . The compression spring  73  constantly urges the belt-cleaner-side shutter  70  downward toward the closed position. 
     (2) Coupled State of the Belt Cleaner and Drum Cleaners 
     When the process unit  4  is in its mounted position and the belt cleaner  61  is disposed in the contact position, the bottom end of the conveying cylinder  69  is fitted into the receiving part  48  of the drum cleaner  44 , as shown in  FIG. 2 . In this way, the conveying unit  63  is coupled to the waste toner storage unit  45  of the black process cartridge  9 K. 
     At this time, the bottom end of the belt-cleaner-side shutter  70  is in contact with the top end of the receiving part  48  and, thus, the belt-cleaner-side shutter  70  is disposed in its open position against the urging force of the compression spring  73 . 
     Further, the bottom end of the conveying cylinder  69  is in contact with the top end of the drum-cleaner-side shutter  50 , placing the drum-cleaner-side shutter  50  in its open position against the urging force of the compression spring  51 . 
     In this state, the belt-cleaner-side communication hole  71  opposes the drum-cleaner-side through-hole  49 . 
     4. Main Casing 
     As shown in  FIGS. 2 and 4 , guide grooves  83  are formed on the inside of the main casing  2 . 
     The guide grooves  83  are recessed grooves formed one in each of the inner left and right surfaces on the corresponding left and right side walls of the main casing  2 . The guide grooves  83  are substantially linear, extending in the front-rear direction beneath the belt unit  20 . The guide rollers  39  and guide rails  40  of the process unit  4  are fitted into the corresponding guide grooves  83 . 
     As shown in  FIG. 1 , the main casing  2  is also provided with a pair of left and right body-side positioning plates  81 , and a body-side positioning shaft  82 . 
     The body-side positioning plates  81  are respectively positioned within the main casing  2  on the left-right outer sides of the scanning unit  3  so as to oppose the left-right outer sides. The body-side positioning plates  81  are formed of metal, such as stainless steel or steel. The body-side positioning plates  81  have a general L-shape in a side view. Each body-side positioning plate  81  includes a body part  84 , and an extended part  85 . 
     The body parts  84  are disposed in positions opposing the outer left and right sides of the scanning unit  3 . The body parts  84  have a flat plate shape that is generally rectangular in a side view and has approximately the same front-rear dimension as the process unit  4 . Each body part  84  includes a fitting groove  86 . 
     The fitting groove  86  is formed in the front edge of the corresponding body part  84  so as to recess rearward from the front edge. The fitting groove  86  has a general U-shape in a side view and is open on the front side. 
     The extended parts  85  have a flat plate shape and are generally rectangular in a side view. The extended parts  85  extend continuously upward from the top edges of the body parts  84  at the rear ends of the same. The top ends of the extended parts  85  are positioned lower than the rear ends of the guide grooves  83  formed in the main casing  2 . 
     The body-side positioning shat  82  bridges the upper ends of the extended parts  85 . The body-side positioning shaft  82  is formed of a metal, such as stainless steel or steel. The body-side positioning shaft  82  has a general rod shape and is oriented in the left-right direction. 
     5. Cleaning Operation 
     During an image-forming operation on the printer  1  described above, the drum cleaners  44  clean the surfaces of the respective photosensitive drums  11 , and the belt cleaner  61  cleans the surface of the intermediate transfer belt  24 . 
     In some cases, not all toner in the toner images carried on the surfaces of the photosensitive drums  11  is transferred onto the lower portion of the intermediate transfer belt  24  during the image-forming operation described above. In the following description, toner that is not transferred from the surfaces of the photosensitive drums  11  will be called “residual toner.” 
     As each photosensitive drum  11  continues to rotate clockwise in a right side view after transfer operation, the scraping blade  46  of the corresponding drum cleaner  44  scrapes off any residual toner remaining on the surface of the photosensitive drum  11 . 
     Residual toner scraped off the photosensitive drum  11  by the scraping blade  46  falls through the collection opening  47  and is stored in the waste toner storage unit  45 . 
     Residual toner may also be left on the surface of the intermediate transfer belt  24  when a color image carried on the surface of the intermediate transfer belt  24  is transferred onto the paper P in the image-forming operation described above. 
     As the intermediate transfer belt  24  continues to circulate after the transfer operation, the scraping blade  65  of the belt cleaner  61  scrapes off any residual toner remaining on the surface of the intermediate transfer belt  24 . 
     Residual toner scraped off the intermediate transfer belt  24  by the scraping blade  65  is conveyed through the collection hole  68  by the rotating scraping brush  66 , and is collected in the front end of the cleaner frame  64 . 
     Residual toner collected in the cleaner frame  64  is conveyed leftward by the rotating auger screw  67  and supplied through the connecting part  74  into the top end of the conveying cylinder  69 . 
     Toner supplied into the conveying cylinder  69  is conveyed downward by its own weight and by the rotating auger screw  75 . The toner is then conveyed through the belt-cleaner-side communication hole  71  and drum-cleaner-side through-hole  49  by the blade  76  and stored in the waste toner storage unit  45 . Hence, while the belt unit  20  is disposed in the contact position, the conveying unit  63  allows residual toner to be conveyed from the cleaning unit  62  to the waste toner storage unit  45  of the black process cartridge  9 K. 
     6. Mounting and Removing the Process Cartridges 
     To remove a process cartridge  9  from the main casing  2 , first the operator opens the front cover  8  and lifts the front end of the belt unit  20  upward. 
     Consequently, the belt unit  20  pivots clockwise in a right side view about the rotational shaft  22 A of the drive roller  22 , as shown in  FIG. 4 , moving to its separated position. The upper cover  80  follows the pivoting belt unit  20  by pivoting clockwise in a right side view about its rear edge. 
     Through this operation, the intermediate transfer belt  24  separates from the top surfaces of the photosensitive drums  11 . The conveying cylinder  69  also moves upward, separating from the waste toner storage unit  45  of the black process cartridge  9 K. Hence, the conveying cylinder  69  is extracted from the receiving part  48 . 
     Thus, when the belt unit  20  is shifted into its separated position, the conveying unit  63  moves upward together with the belt unit  20  and is retracted from the path of the process unit  4 . 
     As a result, the urging force of the compression spring  73  moves the belt-cleaner-side shutter  70  into its closed position, and the urging force of the compression spring  51  moves the drum-cleaner-side shutter  50  into its closed position. 
     This action blocks the conveyance of residual toner from the cleaning unit  62  to the waste toner storage unit  45  of the black process cartridge  9 K. 
     Next, to remove the process cartridge  9  from the main casing  2 , the operator pulls the process unit  4  forward out of the main casing  2 . 
     Through this operation, the process-side positioning shaft  34  is extracted from the fitting grooves  86  formed in the body-side positioning plates  81  and the body-side positioning shaft  82  is extracted from the fitting grooves  43  formed in the process-side positioning plates  33 , as the process unit  4  is shifted into the withdrawn position. 
     Next, the operator pulls the process cartridge  9  upward out of the process frame  31 , thereby completing the operation to remove a process cartridge  9  from the main casing  2 . 
     In order to mount a process cartridge  9  in the main casing  2 , the operation for removing a process cartridge  9  described above is performed in reverse. 
     Specifically, the operator places the process cartridge  9  above the process frame  31  and mounts the process cartridge  9  downward into the process frame  31 . 
     Next, the operator pushes the process unit  4  rearward into the main casing  2 . 
     Through this operation, the process-side positioning shaft  34  is fitted into the fitting grooves  86  formed in the body-side positioning plates  81  and the body-side positioning shaft  82  is fitted into the fitting grooves  43  formed in the process-side positioning plates  33 , as the process unit  4  is shifted into its mounted position. 
     Next, the operator pushes the front end of the belt unit  20  downward. 
     As a result, the belt unit  20  pivots counterclockwise in a right side view about the rotational shaft  22 A of the drive roller  22  until arriving in the contact position illustrated in  FIGS. 1 and 2 . The upper cover  80  also follows the pivoting movement of the belt unit  20 , pivoting counterclockwise in a right side view about its rear edge. 
     Through this operation, the intermediate transfer belt  24  is placed in contact with the top surfaces of the photosensitive drums  11 , and the conveying cylinder  69  is fitted into the receiving part  48 , as described above. 
     As a consequence, the bottom end of the belt-cleaner-side shutter  70  contacts the top end of the receiving part  48  and the belt-cleaner-sidle shutter  70  moves into the open position against the urging force of the compression spring  73 . Further, the bottom end of the conveying cylinder  69  contacts the top end of the drum-cleaner-side shutter  50 , moving drum-cleaner-side shutter  50  into the open position against the urging force of the compression spring  51 . At this time, the drum-cleaner-side communication hole  71  is aligned with the drum-cleaner-side through-hole  49  in the left-right direction. 
     This completes the operation to mount a process cartridge  9  in the main casing  2 . 
     7. Operational Advantages 
     (1) According to the printer  1 , the waste toner storage unit  45 , which stores residual toner from the belt cleaner  61 , is provided in the black process cartridge  9 K retained in the process frame  31 , as shown in  FIGS. 1 and 4 . 
     Hence, maintenance can be performed on the waste toner storage unit  45  efficiently at the same time maintenance is performed on the black process cartridge  9 K. 
     Additionally, the operation for separating the belt unit  20  from the photosensitive drums  11  can be used to interrupt the conveyance of residual toner from the belt cleaner  61  to the waste toner storage unit  45 . 
     Hence, maintenance can be performed on the waste toner storage unit  45  after performing a simple operation. 
     In this way, the configuration of the embodiment facilitates maintenance of the waste toner storage unit  45 , which stores residual toner from the belt cleaner  61 . 
     (2) According to the printer  1 , as shown in  FIGS. 1 and 4 , the process frame  31  can move between a mounted position inside the main casing  2  ( FIG. 1 ) and a withdrawn position outside of the main casing  2  ( FIG. 4 ). 
     Hence, maintenance can be performed on the process framed  31  after the process frame  31  is pulled out of the main casing  2 . 
     Thus, this construction facilitates maintenance the process frame  31 . 
     (3) According to the printer  1 , as shown in  FIG. 2 , the conveying unit  63  is disposed adjacent to the left side of the belt unit  20 . 
     Accordingly, space on the left side of the charging roller  12  can be used efficiently for disposing the conveying unit  63 . 
     (4) According to the printer  1 , as shown in  FIG. 4 , the belt unit  20  can pivot about its rear end, i.e., the end that opposes the secondary transfer roller  21 . 
     This configuration reduces the range over which the rear end of the belt unit  20  moves as the belt unit  20  pivots. 
     As a result, less space is required around the opposing parts of the intermediate transfer belt  24  and secondary transfer roller  21 . In particular, the fixing unit  6  can be disposed directly above the secondary transfer roller  21  without interfering with the pivoting belt unit  20 . 
     (5) According to the printer  1 , as shown in  FIG. 1 , residual toner is conveyed from the belt cleaner  61  to the waste toner storage unit  45  of the forwardmost black process cartridge  9 K. 
     In other words, the waste toner storage unit  45 , which accommodates residual toner collected from the belt cleaner  61 , is disposed adjacent to the photosensitive drum  11  for black, i.e., the photosensitive drum  11  furthest away from the pivot point of the belt unit  20  (the rear end of the belt unit  20 ). 
     Thus, the belt cleaner  61  can be retracted far from the waste toner storage unit  45  of the black process cartridge  9 K when the belt unit  20  is pivoted. 
     With this configuration, the conveyance of residual toner from the belt cleaner  61  to the waste toner storage unit  45  of the black process cartridge  9 K can be reliably interrupted. 
     (6) According to the printer  1 , when the belt unit  20  is disposed in the separated position shown in  FIG. 4 , the belt-cleaner-side shutter  70  can close the belt-cleaner-side communication hole  71  formed in the conveying unit  63  and the drum-cleaner-side shutter  50  can close the drum-cleaner-side through-hole  49  formed in the waste toner storage unit  45  of the black process cartridge  9 K. 
     Accordingly, the conveyance of residual toner from the belt cleaner  61  to the waste toner storage unit  45  of the black process cartridge  9 K can be reliably interrupted when the belt unit is disposed in its separated position. This configuration also reliably prevents toner from leaking out through the belt-cleaner-side communication hole  71 . 
     (7) According to the printer  1 , when the belt unit  20  is disposed in the separated position shown in  FIG. 4 , the conveying unit  63  is retracted together with the belt unit  20  from the path of the process unit  4 . 
     Hence, the conveying unit  63  can be reliably retracted from the path of the process unit  4  by pivoting the belt unit  20 . 
     Thus, after placing the belt unit  20  in its separated position, the process unit  4  can be smoothly moved in an out of the main casing  2 . 
     (8) According to the printer  1 , as shown in  FIG. 4 , maintenance can be performed on the waste toner storage unit  45 , which accommodates residual toner collected room the belt cleaner  61 , at the same time maintenance is performed on the black process cartridge  9 K. 
     Accordingly, the construction of the embodiment better facilitates maintenance of the waste toner storage unit  45 . 
     8. Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 5-7 , wherein like parts and components are designated with the same reference numerals to avoid duplicating description. 
     (1) Overall Description of the Printer 
     In the first embodiment described above, the drum cleaner  44  having the waste toner storage unit  45  is provided for each of the process cartridges  9 , and residual toner cleaned off the intermediate transfer belt  24  is conveyed from the belt cleaner  61  to the waste toner storage unit  45  of the black process cartridge  9 K. 
     In the second embodiment, a waste toner storage unit  91  is provided solely for a black developer cartridge  90  among the plurality of developer cartridges  90 , and residual toner cleaned off the intermediate transfer belt  24  is conveyed to the waste toner storage unit  91 . 
     (2) Detailed Description of the Printer in the Second Embodiment 
     (2-2) Overall Structure 
     In the second embodiment, scorotron charges  92  are provided in place of the charging rollers  12  in the first embodiment, and drum-cleaning rollers  93  are provided in place of the drum cleaners  44 . 
     Each scorotron charge  92  is disposed in a position opposing but separated from the lower rear side of the corresponding photosensitive drum  11 . 
     Each drum-cleaning roller  93  is disposed on the rear side of the corresponding photosensitive drum  11  so as to contact the photosensitive drum  11  from the rear. 
     The photosensitive drums  11 , scorotron chargers  92 , and drum-cleaning rollers  93  are permanently (i.e., non-detachably) retained in the process frame  31 . 
     Also in the second embodiment, the developer cartridges  90  are provided in place of the developing devices  13  described in the first embodiment. 
     Other than being detachably mountable in the process frame  31 , the developer cartridges  90  have the same configuration as the developing devices  13 . That is, the developer cartridges  90  function to supply toner to the corresponding photosensitive drums  11  during an image-forming operation. 
     In the second embodiment, an opening  107  is formed in the right side wall  35  of the process frame  31  for mounting and removing the developer cartridges  90 . 
     (2-2) Detailed Description of the Process Unit 
     The waste toner storage unit  91  is integrally provided on the front side of the black developer cartridge  90 . The waste toner storage unit  91  has a box-like shape and is elongated in the left-right direction. The waste toner storage unit  91  is also provided with a coupling part  95 . 
     The coupling part  95  is provided on the right sided of the waste toner storage unit  91 . The coupling part  95  is box-like shaped and expands above the left side of the waste toner storage unit  91 . 
     The process frame  31  includes a relay member  94 . 
     The relay member  94  is disposed in the approximate left-right center of the process frame  31  on the front end thereof. The relay member  94  includes a receiving part  96 , a conveyance tube  98 , a coupling part  97 , and an auger screw  102 . 
     The receiving part  96  is integrally provided on the rear side of the front wall  36  in the left-right center thereof. The receiving part  96  has a general cylindrical shape that is closed on the bottom and is elongated vertically. The receiving part  96  has a relay-member-side communication hole  99 , and a relay-member-side shutter  100 . 
     The relay-member-side communication hole  99  has a general rectangular shape in a side view and penetrates the rear wall of the receiving part  96  on the upper end thereof. 
     The relay-member-side shutter  100  is disposed inside the receiving part  96 . The relay-member-side shutter  100  has a general cylindrical shape with a closed top and is elongated vertically. The vertical length of the relay-member-side shutter  100  is approximately half that of the receiving part  96 . The relay-member-side shutter  100  is capable of sliding between an open position (see  FIG. 5 ) in which the relay-member-side shutter  100  is disposed in the lower end of the receiving part  96  for opening the relay-member-side communication hole  99 , and a closed position (see  FIG. 7 ) in which the relay-member-side shutter  100  is disposed in the upper end of the receiving part  96  for closing the relay-member-side communication hole  99 . A compression spring  101  is interposed between the bottom wall of the receiving part  96  and the top wall of the relay-member-side shutter  100  for constantly urging the relay-member-side shutter  100  upward toward the closed position. 
     The conveyance tube  98  has a general cylindrical shape and extends first rearward from the rear peripheral side of the relay-member-side communication hole  99 , bends and extends downward, and again bends and extends rightward. 
     The coupling part  97  has a general cylindrical shape that is oriented in the left-right direction. The coupling part  97  is formed continuously with the right end of the conveyance tube  98 . The right end of the coupling part  97  is detachably coupled with the coupling part  95  of the waste toner storage unit  91 . 
     The auger screw  102  is disposed inside the lower end of the conveyance tube  98  and the coupling part  97  and is oriented in the left-right direction. 
     (2-3) Detailed Description of the Belt Unit 
     In the belt cleaner  61  according to the second embodiment, the cleaning unit  62  is disposed above the intermediate transfer belt  24  and is vertically aligned with the black photosensitive drum  11 . In place of the scraping blade  65  and scraping brush  66  described in the first embodiment, the cleaning unit  62  further includes a belt-cleaning roller  103 , a relay roller  104 , and a scraping blade  105 . 
     The belt-cleaning roller  103  is disposed inside the rear end of the cleaner frame  64  at a position opposing the collection hole  68  from above. The belt-cleaning roller  103  contacts the top of the upper portion constituting the intermediate transfer belt  24 . 
     The relay roller  104  is disposed on the rear side of the auger screw  67  and the front side of the belt-cleaning roller  103  and contacts the front side of the belt-cleaning roller  103 . 
     The scraping blade  105  has a generally flat plate shape that is elongated in the left-right direction. The scraping blade  105  is disposed on the rear side of the auger screw  67  and the front side of the relay roller  104 . The top end (i.e., base end) of the scraping blade  105  is supported on the top wall of the cleaner frame  64 . The bottom end (i.e., free end) of the scraping blade  105  contacts the front side of the relay roller  104 . 
     In the belt cleaner  61  according to the second embodiment, the cleaner frame  64  includes a connecting part  106  disposed in its left-right center. 
     The connecting part  106  has a generally square cylindrical shape and protrudes forward from the front end of the cleaner frame  64  in approximately the left-right center thereof. The rear end of the connecting part  106  is in communication with the cleaner frame  64 . 
     In the belt cleaner  61  according to the second embodiment, the auger screw  67  extends in the left-right direction. The right half of the auger screw  67  is formed with a right-handed screw shape, while the left half is formed with a left-handed screw shape for conveying residual toner toward the left-right center of the auger screw  67 . The right end of the auger screw  67  is rotatably supported in the right wall of the cleaner frame  64 , and the left end of the auger screw  67  is rotatably supported in the left wall of the cleaner frame  64 . 
     In the belt cleaner  61  according to the second embodiment, the conveying unit  63  is formed continuously with the front end of the connecting part  106  constituting the cleaning unit  62 . The conveying unit  63  is disposed on the front side of the intermediate transfer belt  24  in the approximate left-right center thereof. The conveying unit  63  and the relay member are configured of a conveying member (not shown). 
     When the process unit  4  is disposed in the mounted position and the belt cleaner  61  is disposed in the contact position, the bottom end of the conveying cylinder  69  is fitted into the receiving part  96  of the relay member  94 , as shown in  FIG. 5 , whereby the conveying unit  63  is coupled to the relay member  94 . 
     At this time, the bottom en of the belt-cleaner-side shutter  70  contacts the top end of the receiving part  96  and is disposed in the open position against the urging force of the compression spring  73 . 
     Further, the top end of the relay-member-side shutter  100  contacts the bottom end of the conveying cylinder  69  and is disposed in the open position against the urging force of the compression spring  101 . 
     Accordingly, the belt-cleaner-side communication hole  71  is aligned with the relay-member-side communication hole  99  in the front-rear direction. 
     (2-4) Cleaning Operation 
     During an image-forming operation on the printer  1  according to the second embodiment, the drum-cleaning rollers  93  clean the surfaces of the corresponding photosensitive drums  11 , and the belt cleaner  61  cleans the surface of the intermediate transfer belt  24 . A cleaning bias is also applied to both the drum-cleaning rollers  93  and the belt-cleaning roller  103 . 
     In the image-forming operation described above, toner remaining on the surface of each photosensitive drum  11  after the toner image carried on the photosensitive drum  11  is transferred to the lower portion of the intermediate transfer belt  24  is electrostatically attracted to the surface of the corresponding drum-cleaning roller  93  as the photosensitive drum  11  rotates clockwise in a right side view. 
     Also in the image-forming operation, toner remaining on the surface of the intermediate transfer belt  24  after the color image carried on the intermediate transfer belt  24  is transferred onto the paper P is electrostatically attracted to the surface of the belt-cleaning roller  103  as the intermediate transfer belt  24  continues to circulate. 
     The residual toner retained on the belt-cleaning roller  103  is subsequently attracted electrically to the relay roller  104 . Thereafter, the scraping blade  105  scrapes the residual toner off the relay roller  104 , and the toner is conveyed to the front end of the cleaner frame  64 . 
     The auger screw  67  rotates to convey toner from the front end of the cleaner frame  64  toward the left-right center thereof in order to supply the toner into the top end of the conveying cylinder  69  through the connecting part  106 . 
     Toner supplied into the conveying cylinder  69  if conveyed downward by its own weight and the rotating auger screw  75 . The blade  76  at the bottom of the auger screw  75  supplies the toner into the conveyance tube  98  of the relay member  94  through the belt-cleaner-side communication hole  71  and relay-member-side communication hole  99 . 
     Residual toner supplied into the conveyance tube  98  drops downward through the conveyance tube  98  and is conveyed through the coupling part  97  by the rotating auger screw  102  and stored in the waste toner storage unit  91 . 
     In other words, when the belt unit  20  is in the contact position, the conveying unit  63  allows residual toner to be conveyed from the cleaning unit  62  to the waste toner storage unit  91 . 
     Further, while the image-forming operation described above is not being executed, residual toner retained electrostatically on the surface of the drum-cleaning rollers  93  is collected in the waste toner storage unit  91 . 
     More specifically, residual toner retained on the drum-cleaning rollers  93  is expelled onto the surfaces of the corresponding photosensitive drums  11  by a controlled cleaning bias applied to the drum-cleaning rollers  93 . 
     As each photosensitive drum  11  continues to rotate, the residual toner expelled onto the peripheral surface of the photosensitive drum  11  comes into confrontation with the intermediate transfer belt  24 . 
     At this time, the residual toner is transferred from the surface of the photosensitive drum  11  onto the surface of the intermediate transfer belt  24 . 
     As described above, residual toner transferred onto the surface of the intermediate transfer belt  24  is electrically attracted to the surface of the belt-cleaning roller  103  as the intermediate transfer belt  24  circulates, and is subsequently scraped off the relay roller  104  by the scraping blade  105  and collected in the cleaner frame  64 . 
     Thereafter, residual toner collected in the cleaner frame  64  is conveyed toward the left-right center of the same by the rotating auger screw  67 , conveyed little by little through the conveying cylinder  69  and relay member  95 , and stored in the waste toner storage unit  91 . 
     (2-5) Mounting and Removing the Developer Cartridges 
     In order to remove a developer cartridge  90  from the main casing  2 , first the operator opens the front cover  8  and lifts the front end of the belt unit  20  upward. 
     Consequently, the belt unit  20  pivots clockwise in a right side view about the rotational shaft  22 A of the drive roller  22 , as shown in  FIG. 7 , moving to its separated position. The upper cover  80  follows the pivoting belt unit  20  by pivoting clockwise in a right side view about its rear edge. 
     Through this operation, the intermediate transfer belt  24  separates from the top surfaces of the photosensitive drums  11 . The conveying cylinder  69  also moves upward, separating from the relay member  94 . Hence, the conveying cylinder  69  is extracted from the receiving part  96 . 
     Thus, when the belt unit  20  is shifted into its separated position, the conveying unit  63  moves upward together with the belt unit  20  and is retracted from the path of the process unit  4 . 
     As a result, the urging force of the compression spring  73  moves the belt-cleaner-side shutter  70  into its closed position, and the urging force of the compression spring  101  moves the relay-member-side shutter  100  into its closed position. 
     This action blocks the conveyance of residual toner from the cleaning unit  62  to the waste toner storage unit  91 . 
     Next, to remove the developer cartridge  90  from the main casing  2 , the operator pulls the process unit  4  forward out of the main casing  2 . 
     Through this operation, the process-side positioning shaft  34  is extracted from the fitting grooves  86  formed in the body-side positioning plates  81  and the body-side positioning shaft  82  is extracted from the fitting grooves  43  formed in the process-side positioning plates  33 , as the process unit  4  is shifted into the withdrawn position. 
     Next, the operator pulls the developer cartridge  90  rightward out of the process frame  31  through the opening  107 , thereby completing the operation to remove a developer cartridge  90  from the main casing  2 . 
     In order to mount a developer cartridge  90  in the main casing  2 , the operation for removing a developer cartridge  90  described above is performed in reverse. 
     Specifically, the operator places the developer cartridge  90  in position on the right side of the process frame  31  and mounts the developer cartridge  90  into the process frame  31  via the opening  107 . 
     Next, the operator pushes the process unit  4  reserved into the main casing  2 . 
     Through this operation, the process-side positioning shaft  34  is fitted into the fitting grooves  86  formed in the body-side positioning plates  81  and the body-side positioning shaft  82  is fitted into the fitting grooves  43  formed in the process-side positioning plates  33 , as the process unit  4  is shifted into its mounted position. 
     Next, the operator pushes the front end of the belt unit  20  downward. 
     As a result, the belt unit  20  pivots counterclockwise in a right side view about the rotational shaft  22 A of the drive roller  22  until arriving in the contact position illustrated in  FIGS. 5 and 6 . The upper cover  80  also follows the pivoting movement of the belt unit  20 , pivoting counterclockwise in a right side view about its rear edge. 
     Through this operation, the intermediate transfer belt  24  is placed in contact with the top surfaces of the photosensitive drums  11 , and the conveying cylinder  69  is fitted into the receiving part  96 , as described above. 
     As a consequence, the bottom end of the belt-cleaner side shutter  70  contacts the top end of the receiving part  96  and the belt-cleaner-side shutter  70  moves into the open position against the urging force of the compression spring  73 . Further, the bottom end of the conveying cylinder  69  contacts the top end of the relay-member-side shutter  100 , moving the relay-member-side shutter  100  into the open position against the urging force of the compression spring  101 . At this time, the belt-cleaner-side communication hole  71  is aligned with the relay-member-side communication hole  99  in the front-rear direction. 
     This completes the operation to mount a developer cartridge  90  in the main casing  2 . 
     (3) Operational Advantages of the Second Embodiment 
     (3-1) According to the second embodiment, as shown in  FIG. 5 , the conveying unit  63  is disposed adjacent to the front side of the belt unit  20  in the left-right center of the photosensitive drums  11 , i.e., within the left-right dimension of the photosensitive drums  11 . 
     Accordingly, space on the front side of the belt unit  20  can be used efficiently for disposing the conveying unit  63 . 
     (3-2) According to the second embodiment, when the belt unit  20  is disposed in the separated position shown in  FIG. 7 , the belt-cleaner-side shutter  70  can close the belt-cleaner-side communication hole  71  formed in the conveying unit  63  and the relay-member-side shutter  100  can close the relay-member-side communication hole  99  formed in the relay member  94 . 
     Accordingly, the conveyance of residual toner from the belt cleaner  61  to the waste toner storage unit  91  can be reliably interrupted by placing the belt unit  20  in its separated position. This configuration also reliably prevents toner from leaking out through the belt-cleaner-side communication hole  71  and relay-member-side communication hole  99 . 
     (3-3) According to the second embodiment, the waste toner storage unit  91  coupled to the relay member  94  can be detached therefrom, as illustrated by the dashed lines in  FIG. 6 . 
     Accordingly, the waste toner storage unit  91  can be separated from the process unit  4  together with the developer cartridge  90  so that maintenance can be performed on the waste toner storage unit  91  separate from the relay member  94 . 
     (3-4) According to the second embodiment, maintenance can be performed on the waste toner storage unit  91  at the same time maintenance is performed on the black developer cartridge  90 . 
     Accordingly, the construction of the second embodiment better facilitates maintenance of the waste toner storage unit  91 . 
     (3-5) The printer  1  according to the second embodiment obtains the same operational advantages described in the first embodiment. 
     While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.