Abstract:
In a developing device, a developing roller has: a first rotational shaft extending in a first direction; and a first roller body covering the first rotational shaft and configured to carry developer. A supply roller has: a second rotational shaft extending in the first direction; and a second roller body covering the second rotational shaft and configured to supply the developer to the developing roller. A housing accommodates the developing roller, the supply roller, and the developer. The housing includes a first wall and a second wall opposed with each other in the first direction. The first wall is formed with a first cutout. The second wall being formed with a second cutout. The first rotational shaft and the second rotational shaft are positioned in both the first cutout and the second cutout when projected in the first direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-190027 filed Aug. 31, 2011. The entire content of this application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a developing device that is detachably mountable in an image-forming device. 
     BACKGROUND 
     An electrophotographic printer known in the art has developing devices detachably mounted therein. Each developing device includes a developing frame, a developing roller and a supply roller that are supported in the developing frame. 
     One such developing device that has been proposed is a developer cartridge that includes a cartridge frame, a developing roller rotatably supported in the cartridge frame, and a supply roller rotatably supported in the cartridge frame while confronting and contacting the developing roller. Receiving grooves extending in the general front-rear direction are formed in both left and right side walls of the cartridge frame for receiving ends of rotational shafts provided in the developing roller and supply roller, and a rib vertically intersecting the groove in the right side wall through the approximate front-rear center thereof so as to bridge the top and bottom of the groove. 
     SUMMARY 
     However, the rib bridges the receiving groove in the right side wall of this developer cartridge. Thus, when mounting the supply roller in the cartridge frame, it is necessary to hold the supply roller at an angle while inserting the right end of the supply roller into a portion of the groove in the right side wall that is positioned rearward of the rib and to subsequently insert the left end of the supply roller through the front side of the groove formed in the left side wall. Accordingly, this construction complicates the operation for mounting the supply roller in the cartridge frame. 
     Therefore, it is an object of the present invention to provide a developing device capable of streamlining the operation for mounting the supply roller in the developing-device casing. It is another object of the present invention to provide a method of manufacturing such a developing device. 
     In order to attain the above and other objects, the invention provides a developing device. The developing device includes a developing roller, a supply roller, and a housing. The developing roller has: a first rotational shaft extending in a first direction; and a first roller body covering the first rotational shaft and configured to carry developer. The supply roller has: a second rotational shaft extending in the first direction; and a second roller body covering the second rotational shaft and configured to supply the developer to the developing roller. The housing accommodates the developing roller, the supply roller, and the developer. The housing includes a first wall and a second wall opposed with each other in the first direction. The first wall is formed with a first cutout. The second wall is formed with a second cutout. The first rotational shaft and the second rotational shaft are positioned in both the first cutout and the second cutout when projected in the first direction. 
     According to another aspect, the present invention provides a method for assembling a developing device. The method includes: preparing a developing roller having: a first rotational shaft extending in a first direction; and a first roller body covering the first rotational shaft and configured to carry developer; preparing a supply roller having: a second rotational shaft extending in the first direction; and a second roller body covering the second rotational shaft and configured to supply the developer to the developing roller; and preparing a housing comprising: a first wall, and a second wall opposed with each other in the first direction, where the first wall is formed with a first cutout, the second wall is formed with a second cutout, the housing is formed with an opening, the first cutout and the of the second cutout configures a part of the opening; assembling, to the housing, the supply roller with one end of the second rotational shaft being moved in the first cutout and another end of the second rotational shaft being moved in the second cutout; and assembling, to the housing, the developing roller with one end of the first rotational shaft being moved in the first cutout and another end of the second rotational shaft being moved in the second cutout until the developing roller contacts the supply roller. 
    
    
     
       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 lateral cross-sectional view of a printer according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of a developer cartridge according to the first embodiment of the present invention when viewed from a left-top side; 
         FIG. 3  is a lateral cross-sectional view of the developer cartridge shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of a lower frame when vied from a left-top side; 
         FIG. 5  is a right side view of the lower frame shown in  FIG. 4 ; 
         FIG. 6  is an explanation diagram illustrating assembling a supply roller in the lower frame and first and second sealing members; 
         FIG. 7  is an explanatory diagram illustrating assembling a developing roller and bearing members in the lower frame; 
         FIG. 8  is an enlarged view of a left side of the lower frame when the developing roller is assembled in the lower frame; 
         FIG. 9(   a ) is a right side view of a lower frame according to a second embodiment of the present invention; 
         FIG. 9(   b ) is a plan view of a developing roller according to the second embodiment; 
         FIG. 9(   c ) is an enlarged view showing a right end of the lower frame when the developing roller shown in  FIG. 9(   b ) is mounted in the lower frame shown in  FIG. 9(   a ); 
         FIG. 10(   a ) is a plan view showing a supply roller according to a third embodiment; and 
         FIG. 10(   b ) is a plan view showing a developing roller cartridge according to fourth embodiment; and 
         FIG. 10(   c ) is a plan view showing a developing roller cartridge according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     1. Printer 
     As shown in  FIG. 1 , a printer  1  is a direct tandem-type color printer. 
     In the following description, directions with respect to the printer  1  and developer cartridges  23  (described later) will correspond to the directions of the arrows indicated in the drawings and will assume that the printer  1  and the developer cartridges  23  are in a level orientation. In addition, the left-right direction will be equivalent to the width direction. 
     Specifically, the vertical and front-rear directions of the printer  1  differ from the vertical and front-rear directions of the developer cartridges  23 . The developer cartridges  23  are mounted in the printer  1  and drum cartridges  22  so that their front side faces the upper front side of the printer  1  and their rear side faces the bottom rear side of the printer  1 . 
     The printer  1  includes a main casing  2 . Four photosensitive drums  3  are arranged inside the main casing  2  parallel to each other and juxtaposed in the front-rear direction. The four photosensitive drums  3  are differentiated according to the colors (black, yellow, magenta, and cyan) of toner images. 
     Disposed in opposition to each photosensitive drum  3  are a Scorotron charger  4 , an LED unit  5 , and a developing roller  6 . 
     The surfaces of the photosensitive drums  3  are uniformly charged by the corresponding Scorotron chargers  4  and are subsequently exposed to light emitted by the corresponding LED units  5  based on image data, forming electrostatic latent images on the surfaces of the respective photosensitive drums  3 . Toner carried on the developing rollers  6  is supplied to the corresponding latent images, producing visible toner images on the surfaces of the photosensitive drums  3 . 
     Sheets P of a paper are accommodated in a paper cassette  7  inside the main casing  2 . Various rollers are provided for supplying the sheets P from the paper cassette  7  to a conveying belt  8 . 
     The conveying belt  8  is disposed between the photosensitive drums  3 , and transfer rollers  9  disposed at positions confronting the respective photosensitive drums  3 . A transfer bias is applied to the transfer roller  9  for sequentially transferring the toner images carried on the photosensitive drums  3  onto the sheet P so that the images are superimposed. 
     After toner images in the four colors have been transferred onto the sheet P, the sheet P is conveyed to a fixing unit  10 . The fixing unit  10  fixes the toner images to the sheet P with heat. Various rollers are provided for subsequently discharging the sheet P into a discharge tray  11 . 
     2. Process Cartridges 
     The printer  1  is provided with four process cartridges  21  corresponding to the four printing colors. 
     The process cartridges  21  are detachably mounted in the main casing  2  and are arranged parallel to one another and juxtaposed in the front-rear direction. 
     A top cover  49  is provided in the top wall of the main casing  2  and can be opened and closed. The process cartridges  21  can be mounted in or removed from the main casing  2  by opening the top cover  49 . 
     Each process cartridge  21  includes a drum cartridge  22  detachably mounted in the main casing  2 , and a developer cartridge  23  detachably mounted in the drum cartridge  22 . 
     (1) Drum Cartridges 
     The drum cartridge  22  is configured of a drum frame  24 . The drum frame  24  further includes a drum support part  25 , and a developer-cartridge-accommodating part  26 . 
     The drum support part  25  constitutes the lower rear side of the drum frame  24  and functions to support the corresponding photosensitive drum  3 , the Scorotron charger  4 , and a drum cleaning roller  15 . 
     The photosensitive drums  3  are substantially cylindrical in shape and elongated in the left-right direction. The photosensitive drums  3  are rotatably supported in bottom ends of the respective drum support parts  25  and exposed through openings formed in the bottoms of the same. The Scorotron chargers  4  are disposed so as to confront the corresponding photosensitive drums  3  from a position diagonally above and rearward therefrom, but are separated from the same. The drum cleaning rollers  15  are disposed on the rear side of their corresponding photosensitive drums  3 , confronting and contacting the same. 
     The developer-cartridge-accommodating part  26  of each drum frame  24  is provided above and forward from the drum support part  25  and is formed with an opening on the top and rear sides to allow mounting and removal of the corresponding developer cartridge  23 . 
     (2) Developer Cartridges 
     As shown in  FIGS. 2 and 3 , each of the developer cartridges  23  is configured of a developer frame  30 . The developer frame  30  is a housing and generally box-shaped and elongated in the left-right direction. The developer frame  30  includes a lower frame  31 , and an upper frame  32  assembled on the lower frame  31 . 
     (2-1) Lower Frame 
     As shown in  FIG. 6 , the lower frame  31  is integrally configured of a pair of side walls  35  arranged parallel to each other and separated in the width direction; a bottom wall  36  connecting the bottom edges of the pair of side walls  35 ; and a front wall  37  connecting the front edges of the pair of side walls  35  and the bottom wall  36 . 
     Each side wall  35  has a generally flat plate shape. First contact parts  56  are formed on the front portion of each side wall  35 , and first openings  27  and flange parts  44  are formed in the rear portion of each side wall  35 . 
     Each of the first contact parts  56  has a generally flat plate shape. The first contact parts  56  are respectively provided on the top edges of the left and right side walls  35  and extend continuously outward from the top edges in corresponding left and right directions. 
     As shown in  FIGS. 4 and 8 , the flange part  44  includes upper flange parts  67  provided on the top edges of the left and right side walls  35  and a lower flange part  68  provided on the bottom edge and the rear edge of the right side wall  35 . 
     Each upper flange part  67  has a generally flat plate shape. The upper flange parts  67  extend continuously outward from the top edges of the side walls in corresponding left and right directions. 
     As shown in  FIG. 8 , the lower flange part  68  is L-shaped form in a side view continuously protruding outward from the bottom end and rear end of the right side wall  35 . 
     As shown in  FIG. 4 , the first openings  27  extend in a direction X (see  FIG. 5 ) from each of left and right ends of the developing cartridge  23 . Specifically, the first openings  27  are formed at mutually opposing positions in the left and right side walls  35 , respectively. As shown in  FIG. 5 , the first openings  27  are recesses formed in the upper rear edges of the corresponding left and right side walls  35  that penetrate toward the bottom front sides of the same along the direction X orthogonal to the left-right direction. The direction X corresponds to the direction in which a rubber roller  17  and sponge roller  19  (described later) oppose each other (see  FIG. 3 ). 
     Each opening  27  includes a developing-roller-shaft-exposing groove  28  occupying the upper portion thereof, and a supply-roller-shaft-exposing groove  29  occupying the lower portion thereof. 
     As shown in  FIG. 5 , each exposing groove  29  is generally rectangular in a side view. A closed edge  33  is formed at the lower end of each exposing groove  29 . The sides of the exposing grooves  29  are formed longer than the diameter of an exposed part  80  of a supply roller shaft  18  (described later). 
     Each exposing groove  28  is continuously formed from upper end of the exposing hole  29 . Open edges  34  are provided at the rear end of each exposing groove  28 . That is, the closed edge  33  and the open edges  34  are provided as ends of the opening  27  in the direction X. 
     More specifically, as shown in  FIG. 4 , the exposing groove  28  formed in the left side wall  35  (the left exposing groove  28 ) has a substantial circular shape whose lower end is cut to be in communication with the exposing groove  29  (that is, the exposing groove  28  is continuously formed from the exposing groove  29 ). The substantial circular shape of the exposing groove  28  fits the outer surface of a left developing-roller-shaft exposed part  82  (described later). Further, as shown in  FIG. 7 , the diameter of the left exposing groove  28  (the length of the left exposing groove  28  in a length direction orthogonal to the direction X and the left-right direction) is formed larger than the diameter of left developing-roller-shaft exposed part  82  (described later). 
     As shown in  FIG. 5 , the exposing groove  28  formed in the right side wall  35  (the right exposing groove  28 ) is formed of a lower rear edge that extends diagonally upward and rearward from the top end of a front edge defining the exposing groove  29 , and an upper front edge depressed diagonally upward and forward. Further, the width of the right exposing groove  28  (the length of the right exposing groove  28  in the length direction) is formed larger than the outer diameter of contact members  100  (described later). 
     Retaining parts  85  are also formed in the right exposing groove  28 . The retaining parts  85  have a generally flat plate shape and protrude inward in front and rear directions from left portions of the lower rear edge and upper front edge constituting the right exposing groove  28  (see  FIG. 4 ). Center portions of the retaining parts  85  relative to the second direction X are formed in a general arc shape that conforms to the outer peripheral surface of a right developing-roller-shaft exposed part  81  (described later). Specifically, the center portion of the front retaining part  85  relative to the second direction X is recessed in a direction obliquely upward and forward, while the center portion of the rear retaining part  85  relative to the second direction X is recessed in a direction obliquely downward and rearward. 
     As shown in  FIG. 8 , a toner fill hole  98  is formed in the right side wall  35 . The toner fill hole  98  is generally circular in a side view and is formed in a front-side portion of the right side wall  35 . 
     As shown in  FIG. 3 , the front portion of the bottom wall  36  is formed continuously of a curved wall  40 , and a bent wall  41 , while the rear portion of the bottom wall  36  is formed continuously of an arc-shaped wall  42 , and a rib part  43 . 
     The curved wall  40  has a general arc shape that follows the rotational path of an agitator  12  (described later). 
     The bent wall  41  has an upward bend formed at a midpoint in the front-rear direction. More specifically, beginning from its rear edge, the bent wall  41  slopes upward toward the front from the front edge of the curved wall  40  and subsequently bends so as to slope downward toward the front. 
     The arc-shaped wall  42  has a general arc shape that follows the rotational path of a supply roller  13  (described later). 
     The rib part  43  has a general T-shape in a side view, with the bottom of the “T” formed continuously with the rear edge of the arc-shaped wall  42  and the head of the “T” protruding rearward. 
     The front portion and the rear portion of the bottom wall  36  are formed continuously by coupling the rear edge of the curved wall  40  with the front edge of the arc-shaped wall  42 . 
     A partitioning wall  45  is formed between the front portion and the rear portion of the bottom wall  36 . The partitioning wall  45  is formed as a continuous extension from the curved wall  40  and the arc-shaped wall  42 , protruding upward. That is, the partitioning wall  45  protrudes toward the upper frame  32  while extending in the left-right direction. 
     The distal end of the partitioning wall  45  vertically confronts but is separated from the bottom surface of a rear-side top wall  53  (described later) of the upper frame  32 . 
     As shown in  FIGS. 4 and 6 , a plurality (two in the embodiment) of fixing parts  46  is formed in the bottom wall  36  adjacent to the front side of the partitioning wall  45 . 
     The fixing parts  46  are disposed at the front side of the partitioning wall  45 . The fixing parts  46  are adjacent and the partitioning wall  45 . The fixing parts  46  are arranged in the left-right direction and separated each other. Each fixing part  46  is generally cylindrical in shape and is erected upward from the curved wall  40  (see  FIG. 3 ). The distal ends of the first fixing parts  46  protrude upward from the rear-side top wall  53  (described later). 
     As shown in  FIG. 4 , the receiving parts  50  are disposed at positions spaced inward in right and left directions from the corresponding side walls  35  for receiving right and left supply-roller-shaft exposed parts  79  and  80  (described later). The receiving parts  50  have a generally flat plate shape and protrude diagonally upward and rearward from the arc-shaped wall  42 . When projected in the left-right direction, the receiving parts  50  overlap the closed edges  33  of the exposing holes  29  (see  FIG. 5 ). 
     A receiving groove  51  is formed in each receiving part  50  for receiving the supply roller shaft  18  (described later). The receiving grooves  51  are generally U-shaped in a side view and are recessed into the receiving parts  50  in the direction X so as to be open on the upper rear side (see  FIG. 4 ). As shown in  FIG. 5 , the receiving groove  51  formed in the right receiving part  50  has a lower portion defined as a narrow groove  54 , and an upper portion defined as a wide groove  55 . 
     The narrow groove  54  is generally U-shaped in a side view. The width (the length in the length direction) of the narrow groove  54  is narrower than the width (the length in the length direction) of the left receiving groove  51  and wider than the diameter of a small-diameter part  70  formed on the supply roller shaft  18  (described later). 
     The wide groove  55  is formed continuously with the two ends of the narrow groove  54  (the ends at the open side of the narrow groove  54 ). After initially curving outward in the width direction, the wide groove  55  extends along the direction X. The width (the length in the length direction) of the wide groove  55  is greater than that of the narrow groove  54  and approximately equivalent to that of the receiving groove  51 . The width (the length in the direction orthogonal to the direction X and the left-right direction) of the wide groove  55  is also substantially equivalent to the outer diameter of the supply roller shaft  18  (described later). 
     As shown in  FIG. 3 , the bottom portion of the front wall  37  is formed continuously from the front edge of the bent wall  41 , sloping upward toward the front, while the upper portion of the front wall  37  extends straight upward continuously from the top edge of the lower portion. 
     A second contact part  57  is formed on the top edge of the front wall  37 . As shown in  FIG. 6 , the second contact part  57  has a generally flat plate shape that extends continuously forward from the top edge of the front wall  37 . 
     (2-2) Upper Frame 
     As shown in  FIG. 3 , the upper frame  32  is integrally provided with a front-side top wall  52 , and a rear-side top wall  53 . The front-side top wall  52  is configured of an expanded part  58 , and a contact part  62 . The expanded part  58  constitutes the central portion of the front-side top wall  52  and expands upward. 
     The contact part  62  has a substantially flat plate shape and is provided along both left and right sides and the front side of the expanded part  58  so as to surround the same. When the upper frame  32  is assembled to the lower frame  31 , the contact part  62  conforms to the shape of the first and second contact parts  56  and  57 . 
     As shown in  FIG. 3 , the rear-side top wall  53  has a generally flat plate shape and extends continuously rearward from the rear edge of the front-side top wall  52 . 
     (2-3) Developer Frame 
     As shown in  FIG. 3 , when the lower frame  31  and the upper frame  32  are assembled together, as will be described later, a space formed in the developer frame  30  is divided by the partitioning wall  45  into the toner-accommodating chamber  38  constituting the space forward of the partitioning wall  45 , and a developing chamber  39  constituting the space rearward of the partitioning wall  45 . In other words, the partitioning wall  45  partitions the developer frame  30  into the toner-accommodating chamber  38  and the developing chamber  39 . 
     (2-4) Toner-Accommodating Chamber 
     As shown in  FIG. 3 , the toner-accommodating chamber  38  is filled with toner. An agitator  12  is also provided in the toner-accommodating chamber  38  and positioned in the vertical and front-to-rear center thereof. 
     The agitator  12  includes a rotational shaft  83  that is rotatably supported in the side walls  35 , and an agitating blade  84  provided on the rotational shaft  83 . The agitating blade  84  is fixed to the outer peripheral surface of the rotational shaft  83  and extends radially outward therefrom. By supporting the rotational shaft  83  in the side walls  35 , the agitator  12  is rotatably supported in the developer frame  30 . 
     (2-5) Developing Chamber 
     As shown in  FIG. 3 , an opening  69  is formed in the rear side of the developing chamber  39 . The opening  69  is specifically defined by the rear edges of the side walls  35 , the rear edge of the rib part  43 , and the rear edge of the rear-side top wall  53 . 
     The developing roller  6 , a supply roller  13 , and a thickness-regulating blade  14  are provided inside the developing chamber  39 . The developing roller  6  is disposed in the rear end of the developing chamber  39  between the side walls  35  so that the rear and top portions of the developing roller  6  are exposed through the opening  69 . 
     The developing roller  6  is configured of a developing roller shaft  16 , and a rubber roller  17  provided around the developing roller shaft  16 . The rubber roller  17  covers the developing roller shaft  16  while leaving the left and right ends exposed. The outer peripheral surface of the rubber roller  17  carries the developer. By rotatably supporting the developing roller shaft  16  in the side walls  35 , the developing roller  6  is rotatably disposed in the developer frame  30 . 
     The developing roller  6  is oriented such that the developing roller shaft  16  extends in the left-right direction. The left end of the developing roller shaft  16  protruding out from the rubber roller  17  is defined as a left developing-roller-shaft exposed part  82 , while the right end protruding from the rubber roller  17  is defined as a right developing-roller-shaft exposed part  81 . The right developing-roller-shaft exposed part  81  has a shorter left-right dimension than the left developing-roller-shaft exposed part  82 . 
     As shown in  FIG. 8 , engaging grooves  99  are formed in the right exposed part  81 . Specifically, a pair of the engaging grooves  99  is formed in the right exposed part  81  of the developing roller shaft  16  at positions on either side of a portion of the right exposed part  81  aligned with the retaining parts  85 . The engaging grooves  99  are recessed radially into the outer peripheral surface of the developing roller shaft  16 . 
     The contact member  100  is provided for each of the engaging grooves  99 . In other words, a pair of the contact members  100  is provided on the supply roller shaft  18  at a position corresponding to the engaging grooves  99  with respect to the left-right direction. The contact members  100  have a generally flat plate shape. In a side view, the contact members  100  are generally C-shaped, with the opening of the C shape facing upward. The free ends of the contact members  100  are configured as hook-like parts  101 . The hook-like parts  101  are bent inward along a radial direction of the developing roller shaft  16  to form hook-like shapes in a side view. By engaging the hook-like parts  101  in the engaging grooves  99 , the contact members  100  are positioned parallel to each other while separated in the left-right direction. 
     As will be described later in greater detail, by rotatably supporting the developing roller shaft  16  in the side walls  35 , the developing roller  6  is rotatably disposed in the developer frame  30 . 
     As shown in  FIG. 3 , the supply roller  13  is disposed inside the arc-shaped wall  42  on the lower front side of the developing roller  6 . As shown in  FIG. 6 , the supply roller  13  includes a supply roller shaft  18 , and a sponge roller  19 . 
     The outer peripheral surface of the sponge roller  19  supplies toner to the surface of rubber roller  17 . The sponge roller  19  covers the supply roller shaft  18  while leaving the left and right ends exposed. 
     The supply roller  13  is oriented so that the supply roller shaft  18  extends in the left-right direction. The left end of the supply roller shaft  18  protruding out of the sponge roller  19  is defined as a left supply-roller-shaft exposed part  80 , while the right end of the supply roller shaft  18  protruding out of the sponge roller  19  is defined as a right supply-roller-shaft exposed part  79 . The right supply-roller-shaft exposed part  79  is formed with a shorter left-right dimension than the left supply-roller-shaft exposed part  80 . 
     A small-diameter part  70  is formed in the right exposed part  79 . The small-diameter part  70  is formed in the right exposed part  79  at a position corresponding to the narrow groove  54  formed in the right receiving part  50  and is formed by recessing the outer peripheral surface of the supply roller shaft  18  radially inward so that the diameter of the small-diameter part  70  is smaller than the diameter of the left exposed part  80 . 
     The supply roller  13  is positioned so that the sponge roller  19  of the supply roller  13  confronts and contacts the rubber roller  17  of the developing roller  6 . As will be described later in greater detail, by rotatably supporting the left and right ends of the supply roller shaft  18  in the walls  35 , the supply roller  13  is rotatably provided in the developer frame  30 . 
     As shown in  FIG. 3 , the thickness-regulating blade  14  is fixed to the distal ends of the fixing parts  46  so that the rear end portion of the thickness-regulating blade  14  contacts the top of the rubber roller  17 . 
     As shown in  FIGS. 6 and 7 , two each of first side sealing members  59 , second side sealing members  60 , and bearing members  61  are provided in the developing chamber  39 . 
     The first side sealing members  59  are disposed in positions corresponding to the exposing holes  29 . The first side sealing members  59  are generally rectangular in a side view. A through-hole  63  penetrates the center portion of each first side sealing member  59  in the left-right direction to allow passage of the supply roller shaft  18 . As will be described later in greater detail, the left and right ends of the supply roller shaft  18  are inserted through the corresponding first side sealing members  59 , with one of the first side sealing members  59  positioned between the left receiving part  50  and the left side wall  35  and the other between the right receiving part  50  and the right side wall  35 . 
     The second side sealing members  60  are generally U-shaped in a side view, following the curved shape on the lower side of the exposing grooves  28 . As will be described later in greater detail, the second side sealing members  60  are disposed above the corresponding first side sealing members  59 , with one second side sealing member  60  interposed between each of the left and right ends of the supply roller shaft  18  and corresponding one of the left and right ends of the rubber roller  17 . 
     As shown in  FIG. 7 , the bearing members  61  are formed of a resin material having good tribological properties (such as an electrically conductive polyacetal resin) in a flat plate shape that is substantially rectangular in a side view. That is, the bearing members  61  are formed separately from the developer frame  30 . 
     The two bearing members  61  are further distinguished as a left bearing member  65  corresponding to the left side wall  35 , and a right bearing member  66  corresponding to the right side wall  35 . 
     The right bearing member  66  has a developing-roller-shaft-supporting hole  86 , a developing-roller-shaft collar  87 , and a supply-roller-shaft-supporting part  88 . 
     The supporting hole  86  is generally circular in a side view and penetrates the upper rear portion of the right bearing member  66 . The supporting hole  86  is formed with substantially the same (slightly larger) diameter as the outer diameter of the right exposed part  81 . 
     The collar  87  has a generally cylindrical shape and protrudes rightward from the peripheral edge of the supporting hole  76 . 
     The supporting part  88  is formed on the left surface of the right bearing member  66  at a position below and forward of the supporting hole  86 . The supporting part  88  is generally cylindrical in shape and protrudes leftward from the left surface of the right bearing member  66 . The supporting part  88  is formed with substantially the same (slightly larger) inner diameter as the outer diameter of the right exposed part  79 . 
     The left bearing member  65  has a developing-roller-shaft-supporting hole  72  and a supply-roller-shaft-supporting hole  73 . The supporting hole  72  is generally circular in a side view and penetrates the upper rear portion of the left bearing member  65 . The supporting hole  72  is formed with substantially the same (slightly larger) diameter as the outer diameter of the left exposed part  82 . 
     The supporting hole  73  is generally circular in a side view and penetrates a portion of the left bearing member at a front lower side of the supporting hole  73 . The supporting hole  73  is formed with substantially the same (slightly larger) diameter as the outer diameter of the left exposed part  80 . 
     As will be described later in greater detail, the left bearing member  65  is fitted into the left side wall  35  from the outer side thereof, while the right bearing member  66  is fitted into the right side wall  35  from the outer side thereof. 
     3. Assembling the Developer Cartridge 
     Next, the process for assembling the developer cartridge  23  will be described. 
     (1) Assembling the Supply Roller in the Lower Frame 
     To assemble the developer cartridge  23 , first the supply roller  13  and the lower frame  31  are prepared as described above, and the supply roller  13  is assembled in the lower frame  31 , as shown in  FIG. 6 . 
     To assemble the supply roller  13  in the lower frame  31 , the supply roller  13  is positioned on the upper rear side of the lower frame  31  so that the left exposed part  80  is positioned above and rearward of the left opening  27 , and the right exposed part  79  is positioned above and rearward of the right opening  27 . Next, the supply roller  13  is moved downward along the second direction X so that the left exposed part  80  and right exposed part  79  pass through the corresponding exposing grooves  28  (between the open edges  34 ) and enter the exposing holes  29 . Through this operation, the right and left exposed parts  79  and  80  move through the corresponding openings  27  as the supply roller  13  is inserted. 
     When the supply roller  13  reaches a prescribed position inside the arc-shaped wall  42  ( FIG. 3 ), the left exposed part  80  is positioned within the receiving groove  51  of the left receiving part  50  ( FIG. 4 ), and the small-diameter part  70  of the right exposed part  79  is positioned in the narrow groove  54  of the right receiving part  50  ( FIG. 5 ). In other words, the small-diameter part  70  is disposed to corresponding to the narrow groove  54  with respect to the left-right direction. Consequently, the small-diameter part  70  becomes engaged with the narrow groove  54 , thereby fixing the position of the supply roller  13  relative to the lower frame  31 . 
     This completes the process of mounting the supply roller  13  in the lower frame  31 . At this time, the left exposed part  80  of the supply roller shaft  18  is inserted through the left exposing hole  29  and protrudes leftward from the left side wall  35 . When projected in the left-right direction, the supply roller shaft  18  is positioned within the supply-roller-shaft-exposing holes  29 . 
     (2) Mounting the First and Second Side Sealing Members in the Lower Frame 
     Next, the first and second side sealing members  59  and  60  are mounted in the lower frame  31 . To mount the first and second side sealing members  59  and  60  in the lower frame  31 , first the first side sealing members  59  are inserted into the lower frame  31 , as shown in  FIG. 6 . 
     To mount the first side sealing members  59  in the lower frame  31 , the first side sealing members  59  are positioned on the left and right outer sides of the corresponding left and right exposed parts  80  and  79 , with their through-holes  63  aligned with the respective left and right exposed parts  80  and  79 . Next, the first side sealing members  59  are inserted inward into the developing chamber  39  in respective left and right directions until coming into contact with respective left and right outer surfaces of the corresponding receiving parts  50 . At this time, the left and right exposed parts  80  and  79  are inserted through the through-holes  63  formed in the first side sealing members  59 . 
     Next, the second side sealing members  60  are placed above the corresponding first side sealing members  59 . This completes the process for assembling the first and second side sealing members  59  and  60  in the lower frame  31 . 
     (4) Mounting the Developing Roller in the Lower Frame 
     Next, the developing roller  6  is assembled in the lower frame  31 . To mount the developing roller  6  in the lower frame  31 , the developing roller  6  is positioned above and rearward of the lower frame  31 , as shown in  FIG. 7 , so that the left exposed part  82  is positioned above and rearward of the left exposing groove  28  and the right exposed part  81  is positioned above and rearward of the right exposing groove  28 . Next, the developing roller  6  is moved downward in the second direction X while the left exposed part  82  and the right exposed part  81  pass through the corresponding open edges  34  until the rubber roller  17  contacts the sponge roller  19 . 
     More specifically, the right exposed part  81  is inserted into the right exposing groove  28  from a position above and rearward thereof so that the contact members  100  on the right exposed part  81  fit on both left and right sides of the retaining parts  85 . The left exposed part  82  is also inserted into the left exposing groove  28  from a position diagonally above and rearward thereof. Consequently, the retaining parts  85  are interposed between the pair of contact members  100 , as shown in  FIG. 8 , with the inner left and right surfaces of the contact members  100  contacting the outer left and right surfaces of the retaining parts  85 . This completes the operation for assembling the developing roller  6  to the lower frame  31 . 
     At this time, the developing roller shaft  16  is positioned closer to the open edges  34  than the supply roller shaft  18 . When projected in the left-right direction, the developing roller shaft  16  is positioned in the exposing grooves  28 . 
     Further, one of the second side sealing members  60  is interposed between the left exposed part  80  of the supply roller shaft  18  and the left end of the rubber roller  17 , and the other second side sealing member  60  is interposed between the right exposed part  79  and the right end of the rubber roller  17 . 
     (5) Assembling the Bearing Members on the Lower Frame 
     Next, the bearing members  61  are mounted on the lower frame  31 . That is, as shown in  FIG. 7 , the left bearing member  65  is mounted on the left side wall  35  from the left side, and the right bearing member  66  is mounted on the right side wall  35  from the right side. 
     When mounting the left bearing member  65  on the left side wall  35 , the left bearing member  65  is moved toward the left side wall  35  from the left side so that the left exposed part  80  is inserted through the supporting hole  73  and the left end of the developing roller shaft  16  is inserted through the supporting hole  72 . 
     When mounting the right bearing member  66  on the right side wall  35 , the right bearing member  66  is moved toward the side wall  35  from the right side so that the right exposed part  79  is inserted through the supporting part  88  and the right exposed part  81  is inserted through the supporting hole  86  and the collar  87 . By performing this operation, the right side portion of the right exposed part  81  is covered by the collar  87 , as shown in  FIGS. 2 and 7 . 
     At this time, the upper edge of the left bearing member  65  opposes the upper flange part  67  on the left side wall  35  vertically, as shown in  FIG. 7 . Similarly, the upper edge of the right bearing member  66  opposes the upper flange part  67  of the right side wall  35  vertically. 
     Additionally, the lower portion on the rear edge of the right bearing member  66  opposes the rear portion of the lower flange part  68  in the front-rear direction, while the lower edge of the right bearing member  66  opposes the lower portion of the lower flange part  68  vertically (see  FIG. 8 ). 
     The above operations complete the process of mounting the bearing member  61  on the lower frame  31 . After completing these operations, the left exposed part  80  is rotatably supported in the supporting hole  73 , and the right exposed part  79  is rotatably supported in the supporting part  88 . Further, the left exposed part  82  is rotatably supported in the supporting hole  72 , and the right exposed part  81  is rotatably supported in the supporting hole  86 . Note that the right exposed part  81  protruding rightward from the supporting hole  86  is covered by the collar  87 . 
     (6) Assembling the Upper Frame and Thickness-Regulating Blade on the Lower Frame 
     Next, the upper frame  32  is assembled to the lower frame  31 , as illustrated in  FIGS. 2 and 4 . To assemble the upper frame  32  on the lower frame  31 , the upper frame  32  is placed on top of the lower frame  31  such that the contact part  62  of the upper frame  32  is aligned with the first and second contact parts  56  and  57  of the lower frame  31  (see  FIG. 8 ). Subsequently, the contact part  62  is welded to the first and second contact parts  56  and  57 . 
     Assembling the lower frame  31  and the upper frame  32  in this way forms the developer frame  30 . At this time, the fixing parts  46  of the lower frame  31  protrude out from the rear-side top wall  53  (see  FIG. 4 ). Note that when assembling the developer cartridge  23 , the upper frame  32  is first assembled to the lower frame  31  to form the developer frame  30 , after which the supply roller  13 , the first side sealing members  59 , the second side sealing members  60 , the developing roller  6 , and the bearing members  61  can be sequentially assembled as described above. 
     Next, the thickness-regulating blade  14  is fixed to the fixing parts  46 . This completes assembly of the developer cartridge  23 . 
     Thereafter, the toner-accommodating chamber  38  is filled with toner via the toner fill hole  98 . Once the toner-accommodating chamber  38  is filled, a cap (not shown) is press-fitted into the toner fill hole  98  to seal the toner in the toner-accommodating chamber  38 . 
     4. Operational Advantages 
     (1) As shown in  FIG. 4 , the opening  27  is formed in each of the side walls  35  of the developer cartridge  23 . The openings  27  extend in the direction X, as shown in  FIG. 5 , with the top sides serving as the open edges  34  and the bottom sides serving as the closed edges  33 . 
     Therefore, when the supply roller  13  is assembled in the lower frame  31 , as shown in  FIG. 6 , the supply roller  13  can be inserted into the lower frame  31  so that the left exposed part  80  and the right exposed part  79  pass through the exposing grooves  28  of the corresponding openings  27  toward the closed edges  33 . 
     As a result, the operation for mounting the supply roller  13  in the lower frame  31  can be made more efficient. Hence, the invention offers a simple construction for increasing efficiency in the operation for mounting the supply roller  13  in the lower frame  31  and for improving production efficiency of the developer cartridge  23 . 
     (2) The lower frame  31  has the bottom wall  36 , as shown in  FIG. 4 . The receiving parts  50 , in which the respective receiving grooves  51  are formed, are provided on the bottom wall  36 . Accordingly, when mounting the supply roller  13  in the lower frame  31 , the receiving grooves  51  can receive the supply roller shaft  18 , as shown in  FIG. 6 . 
     As a result, the supply roller  13  can be placed smoothly into a prescribed position in the lower frame  31 . Hence, it is possible to further improve efficiency in the operation for mounting the supply roller  13  in the lower frame  31 . 
     Further, since the supply roller  13  can be positioned relative to the lower frame  31  with accuracy, it is possible to improve the accuracy in positioning the developing roller  6  and the supply roller  13  relative to each other through a simple construction. 
     (3) The left and right ends of the supply roller shaft  18  are defined as the left and right exposed parts  80  and  79 , respectively. The small-diameter part  70  is formed in the right exposed part  79 . Further, receiving parts  50  are disposed one inside each of the side walls  35 , with respect to the left-right direction, so that a gap is formed between the receiving parts  50  and corresponding side walls  35 . The narrow groove  54  is formed in the right receiving part  50 , as shown in  FIG. 5 . With this construction, the small-diameter part  70  engages with the narrow groove  54 , as shown in  FIG. 6 , when the supply roller  13  is mounted in the lower frame  31 . This configuration positions the supply roller shaft  18  in the left-right direction relative to the lower frame  31 , thereby smoothly placing the supply roller  13  in a prescribed position within the lower frame  31 . 
     Hence, this construction can improve the efficiency of the operation for mounting the supply roller  13  in the lower frame  31 . Further, by restricting left-right movement of the supply roller  13 , this construction can prevent the supply roller  13  from falling out of the developer frame  30 . 
     (4) As shown in  FIG. 8 , a pair of contact members  100  is provided on the right exposed part  81 . The contact members  100  are disposed so as to fit on both left and right sides of the retaining parts  85  when the developing roller  6  is mounted in the lower frame  31 . At this time, the left and right surfaces of the retaining parts  85  are in contact with the inside left and right surfaces of the contact members  100 . Therefore, the developing roller shaft  16  can be positioned in the left-right direction relative to the lower frame  31 . As a result, the developing roller  6  can be smoothly placed in a prescribed position within the lower frame  31 . 
     Therefore, this construction can improve the efficiency in the operation for mounting the developing roller  6  in the lower frame  31 , while improving the accuracy for positioning the rubber roller  17  and the sponge roller  19  relative to each other. Further, by restricting left-right movement of the developing roller shaft  16 , this construction can prevent the developing roller  6  from falling out of the developer frame  30 . 
     (5) The developer cartridge  23  is also provided with the left bearing member  65  and the right bearing member  66 , as shown in  FIG. 7 . Both the left and right bearing members  65  and  66  are formed of an electrically conductive polyacetal resin material having excellent tribological properties. This configuration allows for smooth rotation of the developing roller  6  and the supply roller  13  and maintains the relative positions of the rubber roller  17  and the sponge roller  19  constant. 
     (6) The right bearing member  66  also includes the collar  87 . As shown in  FIGS. 2 and 7 , the collar  87  covers the right end portion of the right exposed part  81  when the right bearing member  66  is assembled in the lower frame  31 . Therefore, the right bearing member  66  can reliably support the right exposed part  81 . This construction can improve the accuracy in positioning the rubber roller  17  and the sponge roller  19  relative to each other. 
     (7) The side walls  35  are also provided with the upper flange parts  67 , as shown in  FIG. 7 . The upper flange parts  67  vertically oppose the upper edges of the corresponding bearing members  61  when the bearing members  61  are attached to the corresponding side walls  35 . Therefore, attaching the bearing members  61  to the side walls  35  can enhance the strength of the side walls  35 , thereby improving the strength of the lower frame  31 . 
     Accordingly, through a simple construction, it is possible to improve efficiency in the operation for mounting the supply roller  13  in the lower frame  31 , while also enhancing the strength of the lower frame  31 . 
     5. Second Embodiment 
     Next, a second embodiment of the present invention will be described.  FIG. 9(   a ) is a right side view of the lower frame  31  in a developer cartridge according to the second embodiment of the present invention;  FIG. 9(   b ) is a plan view of the developing roller  6  in the developer cartridge according to the second embodiment; and  FIG. 9(   c ) is an enlarged view showing the right end of the lower frame  31  when the developing roller  6  shown in  FIG. 9(   b ) is mounted in the lower frame  31  shown in  FIG. 9(   a ). In  FIGS. 9(   a )- 9 ( c ), like parts and components to those described in  FIGS. 1 through 8  are designated with the same reference numerals to avoid duplicating description. 
     As described in the first embodiment with reference to  FIG. 8 , the right exposed part  81  is provided with the pair of contact members  100 . However, in the second embodiment shown in  FIG. 9(   b ), a small-diameter part  90  is formed in the right exposed part  81 . The small-diameter part  90  is formed by recessing the outer peripheral surface of the right exposed part  81  radially inward so that the diameter of the small-diameter part  90  is smaller than the diameter of the left exposed part  82 . 
     As shown in  FIG. 9(   c ), the developer frame includes the holding part  91  that is disposed adjacent the cutout of the side wall  35 . The small-diameter part  90  is gripped by holding parts  91 . As shown in  FIG. 9(   a ), the holding parts  91  are formed on the lower rear edge and upper front edge of the right exposing groove  28 , and specifically on the left side portions thereof. The holding parts  91  have a generally flat plate shape and protrude inward in front and rear directions, respectively. The inner edges of the holding parts  91  with respect to the front-rear direction extend linearly along the direction X. The gap formed between the holding parts  91  in a direction orthogonal to both the second direction X and the left-right direction is substantially equivalent to the diameter of the small-diameter part  90 . 
     With this construction, the holding parts  91  engage the small-diameter part  90  when the developing roller  6  is mounted in the lower frame  31 . Accordingly, the holding parts  91  hold the right exposed part  81 , as shown in  FIG. 9(   b ), thereby fixing the left-right position of the developing roller shaft  16  relative to the lower frame  31 . 
     Hence, the structure of the second embodiment described above enables the developing roller  6  to be smoothly placed in a prescribed position within the lower frame  31 , while reducing the number of required parts. The structure of the second embodiment also enables the developing roller  6  to be positioned relative to the lower frame  31  with accuracy. 
     Consequently, the above construction can improve efficiency in the operation for mounting the developing roller  6  in the lower frame  31 , while also improving accuracy in positioning the rubber roller  17  and the sponge roller  19  relative to each other. Further, by restricting left and right movement of the developing roller  6 , the above structure can prevent the developing roller  6  from falling out of the developer frame  30 . 
     6. Third, Fourth, and Fifth Embodiments 
     Next, third, fourth, and fifth embodiments of the invention will be described.  FIG. 10(   a ) is a plan view showing the supply roller  13  in a developer cartridge according to a third embodiment; and  FIGS. 10(   b ) and  10 ( c ) are plan views showing the developing roller  6  in a developer cartridge according to fourth and fifth embodiments, respectively. In  FIGS. 10(   a )- 10 ( c ), like parts and components to those described in  FIGS. 1 through 9  are designated with the same reference numerals to avoid duplicating description. 
     In the first embodiment described above, the small-diameter part  70  is formed in the right exposed part  79 , as shown in  FIG. 6 , and the narrow groove  54  for engaging with the small-diameter part  70  is formed in the right receiving groove  51 , as shown in  FIG. 5 . However, in the third embodiment shown in  FIG. 10(   a ), the small-diameter part  70  is not formed on the right exposed part  79 , nor is the narrow groove  54  formed in the right receiving groove  51 . Instead, the right end of the sponge roller  19  contacts the left surface of the receiving part  50  when the supply roller  13  is mounted in the lower frame  31 . In this way, the supply roller  13  can be positioned in the left-right direction relative to the lower frame  31 . 
     The structure of the third embodiment described above can obtain the same operational advantages described in the first embodiment. 
     In the fourth embodiment shown in  FIG. 10(   b ), the right end of the rubber roller  17  contacts the left surface of the holding part  91  when the developing roller  6  is mounted in the lower frame  31 . Hence, the developing roller  6  can be reliably positioned in the left-right direction relative to the lower frame  31 . As a result, the fourth embodiment can obtain the same operational advantages described in the first embodiment. 
     In the fifth embodiment shown in  FIG. 10(   c ), only a single contact member  100  is provided on the right exposed part  81 . When the developing roller  6  is mounted in the lower frame  31 , the retaining part  85  is interposed between the contact member  100  and the right end of the rubber roller  17 . In other words, the left surface of the contact member  100  contacts the right surface of the retaining part  85 , while the right endface of the rubber roller  17  contacts the left surface of the retaining part  85 . Hence, the developing roller  6  can be reliably positioned in the left-right direction relative to the lower frame  31 . As a result, the fifth embodiment can also obtain the same operational advantages described in the first embodiment.