Patent Publication Number: US-7907875-B2

Title: Developer cartridge and developing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2007-051422 filed on Mar. 1, 2007, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Aspects of the present invention relate to a developing device attached to an image forming apparatus and a developer cartridge. 
     BACKGROUND 
     There has been proposed an image forming apparatus such as a laser printer, in which a developer cartridge detachably attached to a developing cabinet of a developing device. 
     For example, JP-A-7-225514 discloses a configuration in which a developer cartridge is detachably attached to a casing of a developing device. 
     A first opening is formed in the developer cartridge, and a second opening is formed in the casing of the developing device. When the developer cartridge is attached to the casing of the developing device to bring the first and second openings into mutual communication, toner accommodated in the developer cartridge can be supplied to the developing device by way of the first and second openings. 
     SUMMARY 
     Aspects of the present invention provide a developer cartridge and a developing device which enable reliable prevention of leakage of developer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary side sectional view of an image forming apparatus according to an aspect of the present invention; 
         FIG. 2A  is an exemplary side sectional view of a developing unit and a developer cartridge, wherein the developing unit is in a state in which the developer cartridge is attached to a process frame the developer cartridge, and  FIG. 2B  is a partial enlarged view of  FIG. 2A ; 
         FIG. 3  is a schematic perspective view of the developing unit of  FIG. 2  as viewed from a front right side of the developing unit; 
         FIG. 4  is an exemplary perspective view, as viewed from the front right side of the developing unit of  FIG. 3 , showing the developing unit in a state in which the developer cartridge is detached from the process frame; 
         FIG. 5  is a schematic perspective view of the developing unit as viewed from the front right side; 
         FIG. 6  is an exemplary perspective view of the developer cartridge of  FIG. 4 , as viewed from a back left side, in a state in which an inside cabinet is in an opened position; 
         FIG. 7  is an exemplary perspective view of the developer cartridge of  FIG. 4 , as viewed from the back left side, in a state in which the inside cabinet is in a closed position; 
         FIG. 8  is an exemplary perspective view, as viewed from a back left side, of the inside cabinet of the developer cartridge of  FIG. 6 ; 
         FIGS. 9A and 9B  show a modified example of a developing unit and a developer cartridge shown in  FIGS. 2A and 2B ; 
         FIG. 10  is an exemplary perspective view of the developer cartridge of  FIG. 9 , as viewed from a back left side, in a state in which an outside cabinet is in an opened position; 
         FIG. 11  is an exemplary perspective view of the developer cartridge of  FIG. 9 , as viewed from the back left sides in a state in which the outside cabinet is in a closed position; 
         FIG. 12  is an exemplary perspective view, as viewed from a back left side, of the inside cabinet of the developer cartridge of  FIG. 10 ; and 
         FIG. 13  is an exemplary perspective view, as viewed from a back left side, of the outside cabinet of the developer cartridge of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     &lt;General Overview&gt; 
     According to an aspect of the present invention, there is provided a developer cartridge including: a cartridge cabinet configured to accommodate developer, the cartridge cabinet including: a cartridge-side opening that allows communication between an inside of the cartridge cabinet and an outside of the cartridge cabinet; and a slope provided at a lower edge of the cartridge-side opening, the slope inclining in a direction crossing a horizontal direction when the cartridge-side opening is oriented in a horizontal direction. 
     According to another aspect of the present invention, there is provided a developing device including: a developer cartridge including: a cartridge cabinet configured to accommodate developer, the cartridge cabinet including: a cartridge-side opening that allows communication between an inside of the cartridge cabinet and an outside of the cartridge cabinet; and a slope provided at a lower edge of the cartridge-side opening, the slope inclining in a direction crossing a horizontal direction when the cartridge-side opening is oriented in a horizontal direction; a developing cabinet, the developer cartridge being detachably attached to the developing cabinet, the developing cabinet including a developing-side opening located in a position opposed to the cartridge-side opening and configured to receive the developer; an open/close member that is operable to: close the developing-side opening by ascending operation; and open the developing-side openings by descending operation; and a developer carrier that is supported by the developing cabinet and carries the developer to a photosensitive member, wherein the developing cabinet further includes a slope at a lower edge of the developing-side opening, the slope inclining downwardly from an outside of the developing cabinet to an inside of the developing cabinet with respect to a horizontal direction when the developing-side opening is oriented in the horizontal direction. 
     According to still another aspect of the present invention, there is provided a developing device including: a developer cartridge including: a cartridge cabinet configured to accommodate developer, the cartridge cabinet including: a cartridge-side opening that allows communication between an inside of the cartridge cabinet and an outside of the cartridge cabinet; and a slope provided at a lower edge of the cartridge-side opening, the slope inclining in a direction crossing a horizontal direction when the cartridge-side opening is oriented in a horizontal direction; a developing cabinet including a developing-side opening that is locatable in a position opposed to the cartridge-side opening and is configured to receive the developer from the cartridge-side opening; and a developer carrier that is supported by the developing cabinet and carries the developer to a photosensitive member. 
     According to still another aspect of the present invention, there is provided a developing device including: a cartridge housing part to which a developer cartridge is detachably attached; a developing cabinet including a developing-side opening configured to receive developer supplied from the developer cartridge; an open/close member that is operable to: close the developing-side opening by ascending operation; and open the developing-side opening by descending operation; a developer carrier that is supported by the developing cabinet and is configured to supply the developer to a photosensitive member; and a slope provided at a lower edge of the developing-side opening, the slope inclining downwardly with respect to a horizontal direction from an outside of the developing cabinet to an inside of the developing cabinet when the developing-side opening is oriented in the horizontal direction. 
     &lt;Illustrative Aspects&gt; 
     Illustrative aspects of the invention will be described with reference to the drawings. 
     In the developer cartridge and the developing device disclosed in JP-A-7-225514, when the toner accommodated in the developer cartridge is supplied to the developing device, toner passes through the first and second openings. For this reason, when supply of toner is stopped, toner in the middle of passing through the first and second openings may stay at a lower edge of the first opening in the developer cartridge and a lower edge of an opening of the second opening in the developing device. When the developer cartridge is detached from the casing of the developing device in this state, the toner staying at the respective lower edges of the first and second openings may leak outside. 
     Aspects of the present invention provide a developer cartridge and a developing device which enable reliable prevention of leakage of developers 
     (Image Forming Apparatus) 
       FIG. 1  is an exemplary side sectional view showing an image forming apparatus according to an aspect of the present invention. In  FIG. 1 , the image forming apparatus is embodied in the form of a laser printer by way of an example. However, one of ordinary skill in the art will appreciate that the present inventive concept will apply equally to any apparatus which uses developer for producing images on a recording medium.  FIG. 2A  is an exemplary side sectional view of a developing unit and a developer cartridge, wherein the developing unit is in a state in which the developer cartridge is attached to a process frame the developer cartridge, and  FIG. 2B  is a partial enlarged view of  FIG. 2A . 
     As shown in  FIG. 1 , the image forming apparatus  1  includes a feeder unit  4  for feeding a sheet  3  into a body casing  2 , an image forming unit  5  for creating an image on the fed sheet  3 , and a sheet discharge part  6  for discharging the sheet  3  with a formed image. 
     (1) Body Casing 
     The body casing  2  has a substantially box shape, and a clear aperture is formed in one sidewall of the casing, and a front cover  7  for opening or closing the clear aperture is provided. A developing unit  17  (described later) can be detachably attached to the body casing  2  by opening the front cover  7 . 
     Incidentally, in the following description, a side (right side in  FIG. 1 ) where the front cover  7  is provided is referred to as a front side (front face side) and an opposite side (left side in  FIG. 1 ) is referred to as a back side (rear side). A proximal side of  FIG. 1  in a thicknesswise direction of a sheet is referred to as a left side, and a distal side of  FIG. 1  in the thicknesswise direction of the sheet is referred to as a right side. A horizontal direction is synonymous with a widthwise direction. Moreover, descriptions of the developing unit  17  and a developer cartridge  31  (described later) are provided with respect to a state where frame-side passage openings  34  and cartridge-side passage openings  47  (described later) are horizontally oriented. 
     (2) Feeder Unit 
     The feeder unit  4  includes a sheet feeding tray  9 , a sheet feeding roller  10 , a sheet feeding pad  11 , paper dust removal rollers  12  and  13 , a register roller  14 , and a sheet pressing plate  15 . The sheet  3  located at the topmost position on the sheet pressing plate  15  is fed one at a time by the sheet feeding roller  10  and the sheet feeding pad  11 . After passing through the respective rollers  12  through  14 , the sheet is conveyed to a transfer position (described later) of the image forming unit  5 . 
     (3) Image Forming Unit 
     The image forming unit  5  includes a scanner unit  6 , a developing unit  17  as one example of developing device, and a fixing part  18 . In  FIG. 1 , the developing unit  17  is embodied in the form of a process cartridge by way of an example. However, one of ordinary skill in the art will appreciate that the present inventive concept will apply equally to any unit which may be used for developing. 
     (3-1) Scanner Unit 
     The scanner unit  16  is provided in an upper internal portion of the body casing  2 . The scanner unit  16  includes a laser emission section (not shown), a polygon mirror  19  to be rotationally driven, and a plurality of lenses  20  and a plurality of reflection mirrors  21 . As indicated by a chain line, a laser beam that is emitted from the laser emission section and that is based on image data is reflected by the polygon mirror  19 , passes through or undergoes reflection on the plurality of lenses  20  and the plurality of reflection mirrors  21  in order to scan over the surface of a photosensitive drum  25  (described later) of the developing unit  17 . 
     (3-2) Developing Unit 
     The developing unit  17  is disposed beneath the scanner unit  16  within the body casing  2 , and is detachably attached to the body casing  2 . 
     As shown in  FIG. 2 , the developing unit  17  has a process frame  22  and a developer cartridge  31 . The process frame  22  as one example of developing cabinet includes a transfer path  29  for allowing passage of the sheet  3 . The developer cartridge  31  is detachably attached to a cartridge housing part  33  (described later) of the process frame  22 . 
     A vertically-extending partition wall  57  is provided at a substantially center position of the process frame  22  in a longitudinal direction thereof. A rear portion of the partition wall  57  is taken as a developing part  32 , and a front portion of the partition wall  57  is taken as the foregoing cartridge housing part  33 . The frame-side passage openings  34  are formed in the partition wall  57  as one example of developing-side openings. 
     The developing part  32  includes the photosensitive drum  25  as one example of photosensitive member, a scorotron-type charger  26 , a transfer roller  28 , an auger  35 , a supply roller  36 , a developing roller  37  as one example of developer carrier, and a layer thickness regulation blade  38  are provided in the developing part  32 . 
     The photosensitive drum  25  is rotatably supported by the process frame  22 . While being spaced apart from the photosensitive drum  25 , the scorotron-type charger  26  is supported by the process frame  22  above the photosensitive drum  25 . The transfer roller  28  is disposed opposite the photosensitive drum  25  from below and rotatably supported by the process frame  22 . The developing roller  37  is longitudinal in the widthwise direction, as well as being disposed opposite and at the front of the photosensitive drum  25 . The supply roller  36  is disposed opposite and at the front of the developing roller  37 . The developing roller  37  and the supply roller  36  are rotatably supported by the process frame  22 . The layer thickness regulation blade  38  has a leaf spring member  45  having a thin plate shape, and a pressure-contact rubber  46  provided at the lower end of the leaf spring member  45 . The upper end of the leaf spring member  45  is fixed to the process frame  22 , and the pressure-contact rubber  46  presses the surface of the developing roller  37  by elastic force of the leaf spring  45 . The auger  35  is disposed opposite the frame-side passage openings  34  at the rear of the frame-side passage openings  34 . The auger  35  has an auger shaft  39  and a screw  40  provided around the auger shaft  39 . The auger shaft  39  is disposed in such a way that the axial center of the auger shaft extends along the widthwise direction, as well as being rotatably supported by the process frame  22  at a position above the supply roller  36   
     The developer cartridge  31  is detachably attached to the process frame  22  at the cartridge housing part  33 . The developer cartridge  31  has a substantially cylindrical shape. The developer cartridge  31  includes the cartridge-side passage openings  47  (described later) as one example of cartridge-side openings for enabling communication between an inside of the developer cartridge  31  and an outside of the developer cartridge  31 . 
     An agitator  93  (described later) is provided in the developer cartridge  31 . Further, the developer is accommodated in the developer cartridge  31 . In the image forming apparatus  1  of the aspect, the developer comprises a suspension polymerization toner which is a nonmagnetic one-component toner with positive electrification. 
     The developer in the developer cartridge  31  is agitated by rotation of the agitator  93  and subsequently received by the frame-side passage openings  34 , to thus become discharged to the inside of the developing part  32 . The discharged developer is supplied to the supply roller  36  while being conveyed, by rotation of the auger  35 , from the center to respective ends in the widthwise direction. Some of the developer is returned to the inside of the developer cartridge  31  by way of the frame-side passage openings  34  and the cartridge-side passage openings  47 . As a result, circulation of the developer between the developer cartridge  31  and the developing part  32  of the process frame is ensured. 
     The developer supplied to the supply roller  36  is supplied to the developing roller  37  by rotation of the supply roller  36 . At this time, the developer is frictionally electrified with positive polarity between the supply roller  36  and the developing roller  37 . Subsequently, the developer supplied to the developing roller  37  enters between the pressure-contact rubber  46  and the developing roller  37  in conjunction with rotation of the developing roller  37 , and is carried as a thin layer on the surface of the developing roller  37  while being regulated between the rubber and the roller in terms of a layer thickness. 
     After being uniformly electrified with positive polarity by the scorotron-type charger  26  along with rotation of the photosensitive drum  25 , the surface of the photosensitive drum  25  is exposed to a laser beam emitted from the scanner unit  16 , whereupon an electrostatic latent image based on image data is formed. Subsequently, when the developer carried on the surface of the developing roller  37  comes into contact with the photosensitive drum  25  by rotation of the developing roller  37 , the electrostatic latent image formed on the surface of the photosensitive drum  25  is supplied. As a result, the electrostatic latent image is developed (visualized), and the developer image is carried on the surface of the photosensitive drum  25 . The developer image is transferred onto the sheet  3  conveyed (to a position) between the photosensitive drum  25  and the transfer roller  28 . 
     (3-3) Fixing Part 
     As shown in  FIG. 1 , the fixing part  18  is provided at the rear of the developing unit  17 . The fixing part  18  has a heating roller  48 , a pressurizing roller  49  brought into intimate contact with the heating roller  48  from below, and a pair of conveyor rollers  50  disposed at the rear of these rollers. 
     The fixing part  18  thermally fixes the developer transferred on the sheet  3  at the transfer position during the course of the sheet  3  passing between the heating roller  48  and the pressurizing roller  49 . Subsequently, the sheet  3  is conveyed to the sheet discharge part  6  by the pair of conveyor rollers  50 . 
     (4) Sheet Discharge Part 
     The sheet discharge part  6  has a sheet discharging path  51 , a sheet discharging roller  52 , and a sheet discharging tray  53 . The sheet  3  conveyed from the fixing part  18  to the sheet discharging path  51  is conveyed from the sheet discharging path  51  to the sheet discharging roller  52 , and the sheet is discharged onto the sheet discharging tray  53  by the sheet discharging roller  52 . 
     (Developing Unit) 
       FIG. 3  is a schematic perspective view of the developing unit of  FIG. 2  as viewed from a front right side of the developing unit.  FIG. 4  is an exemplary perspective view, as viewed from the front right side of the developing unit of  FIG. 3 , showing the developing unit in a state in which the developer cartridge is detached from the process frame.  FIG. 5  is a schematic perspective view of the developing unit as viewed from the front right side.  FIG. 6  is an exemplary perspective view of the developer cartridge of  FIG. 4 , as viewed from a back left side, in a state in which an inside cabinet is in an opened position.  FIG. 7  is an exemplary perspective view of the developer cartridge of  FIG. 4 , as viewed from the back left side, in a state in which the inside cabinet is in a closed positions  FIG. 8  is an exemplary perspective view, as viewed from a back left side, of the inside cabinet of the developer cartridge of  FIG. 6 . 
     (1) Process Frame 
     As shown in  FIG. 2A , the process frame  22  integrally has the developing part  32  and the cartridge housing part  33 . 
     (1-1) Developing Part 
     As shown in  FIGS. 2A and 3 , the developing part  32  integrally has an upper wall  54 , a bottom wall  55 , sidewalls  56 , and a front wall  57 . Both sidewalls  56  are disposed opposite each other while being spaced apart from each other in the widthwise direction. Each of the sidewalls  56  is arranged along a longitudinal direction. 
     The developing roller  37  is rotatably supported by front sections of both sidewalls  56 , to thus be supported by the process frame  22 . 
     The supply roller  36  is rotatably supported by the front sections of both sidewalls  56  at the front of the developing roller  37 , to thus be supported by the process frame  22 . 
     As a result of an auger shaft  39  being rotatably supported by the front sections of both sidewalls  56 , the auger  35  is supported by the process frame  22  above the supply roller  36 . 
     As shown in  FIG. 2A , a curved portion extending along an outer peripheral surface of the developer cartridge  31  is formed in an intermediate area of the front wall  57  with respect to the vertical direction thereof. 
     As shown in  FIG. 5 , the frame-side passage opening  34  as one example of the developer passage opening is formed in a curved portion of the front wall  57 . 
     Specifically, the frame-side passage opening  34  is formed in number of three while being spaced, at an interval, apart from each other in the widthwise direction. Each of the frame-side passage openings  34  has a substantially rectangular shape which is elongated in the widthwise direction. Of the frame-side passage openings  34 , the frame-side passage opening  34  formed in the center of the front wall  57  in the widthwise direction thereof is taken as a frame-side feed opening  60 , and the frame-side passage openings  34  on both sides of the frame-side feed opening  60  in the widthwise direction are taken as frame-side return openings  61 . 
     As shown in  FIG. 11 , widthwise outer side edges of the frame-side return openings  61  are located inside (positions closer to the center in the widthwise direction) in the widthwise direction when compared with outer side edges of a roller portion of the supply roller  36 . 
     Slopes (called frame-side slopes  78 ) are formed so as to extend over the entirety of each of the lower edges of the respective frame-side passage openings  34  (the frame-side supply openings  60  and the frame-side return openings  61 ) are formed in the partition wall  57 . As shown in  FIG. 2B , the frame-side slopes  78  are inclined downwardly along a direction crossing the horizontal direction, that is, a direction from the outside of the process frame  22  to the inside thereof. Provided that a tilt angle of the frame-side slopes  78  with respect to a horizontal plane is defined as X, the tilt angle X is set so as to become larger than an angle of repose of the developer (e.g., about 30° in the nonmagnetic one-component toner used in the image forming apparatus  1 ). 
     As shown in  FIG. 5 , a frame-side seal  62  for preventing leakage of the developer from the frame-side passage openings  34  is provided on the curved portion of the front wall  57  around the edges of the frame-side passage openings  34 . 
     The frame-side seal  62  is formed, from an elastic material such as felt, in the form of a strip extending in the widthwise direction. Cutouts corresponding to the respective frame-side passage openings  34  are formed in the frame-side seal  62 . The frame-side seal  62  is affixed to a position, which is located intermediate with respect to the vertical direction of the front wall  57 , along the widthwise direction in such a way that the respective cutouts oppose the respective frame-side passage openings  34 . 
     As a result, the frame-side seal  62  is provided on the surface (a front) of the curved portion of the front wall  57  so as to cover the edges of the respective frame-side passage openings  34  and become continuous among the respective frame-side passage openings  34 . For the sake of convenience, the frame-side seal  62  is not shown in any drawings except  FIG. 5   
     (1-2) Cartridge Housing Part 
     The cartridge housing part  33  has side plates  63  and a bottom plate  64 . The side plates  63  and the bottom plate  64  of the cartridge housing part  33  are formed integrally so as to become continual from the bottom wall  55  and both side walls  56  of the developing part  32 . 
     Shutter support sections  65  are provided on widthwise inner side walls of both side plates  63 . Each of the shutter support sections  65  has a substantially rectangular shape bulging from the widthwise inner side walls of the side plates  63  to the inside, and vertically extends from the rear ends of the side plates  63 . 
     A shutter guide section  144  is provided on the widthwise inner side surface of each of the shutter support sections  65 . Each of the shutter guide sections  144  forms a convex line which bulges from the widthwise inner side surface of the shutter support section  65  to the inside, and is disposed opposite the curved portion of the front wall  57  with a nominal space therebetween in the longitudinal direction. Each of the shutter guide sections  144  has a substantially curved shape having substantially the same curvature as that of the curved portion of the front wall  57   
     The upper end surface of each of the shutter support sections  65  is positioned somewhat lower than the upper edge of each of the side plates  63 . The upper end surfaces of the respective shutter support sections  65  are taken as upper fixed sections  66 . 
     A lower fixing part  67  that slightly projects to the front with a rectangular shape as viewed from the top is formed in the widthwise center of the front edge of the bottom plate  64 . 
     A shutter  68  for closing and opening the frame-side passage openings  34  is provided in the cartridge housing part  33 . 
     As shown in  FIG. 4 , the shutter  68  has a substantially rectangular plate shape extending in the widthwise direction and is formed so as to have a substantially curved shape having substantially the same curvature of the curved portion of the front wall  57 . The shutter  68  is formed so as to extend between the shutter guide sections  144  in the widthwise direction and to extend slightly shorter than the respective shutter guide sections  144  with respect to the vertical direction. Three shutter opening sections  69  capable of opposing the respective frame-side passage openings  34  in a one-to-one relationship are formed in the shutter  68 . 
     The shutter  68  is disposed opposite the curved portion of the partition wall  57 , and both widthwise ends of the shutter  68  are slidably sandwiched between the front wall  57  and the respective shutter guide sections  144 . 
     As a result, the shutter  68  is supported along the respective shutter guide sections  144 , in a vertically swayable manner, between an open position (see  FIG. 2A ) where the frame-side passage openings  34  are opened and a close position (see  FIG. 4 ) where the frame-side passage openings  34  are closed. When the shutter  68  is in the open position, the respective frame-side passage openings  34  oppose the corresponding shutter opening sections  69 , to thus become opened outside (to the front) When the shutter  68  is in the close position, the respective frame-side passage openings  34  are closed from the front by a portion of the shutter  68  that is lower than the shutter opening sections  69 . In short, the shutter  68  closes the frame-side passage openings  34  by ascending action and opens the frame-side passage openings  34  by descending action. 
     The cartridge housing part  33  is provided with a swing arm  70 . The swing arm  70  has a substantially U-shaped form as viewed from the top. The swing arm  70  integrally has a grip rod  71  extending in the widthwise direction and arm side plates  72  extending backwardly from both widthwise ends of the grip rod  71 . 
     A boss  73  protruding outwardly in the widthwise direction is provided on a rear end portion of each of the arm side plates  72 . Each of the bosses  73  is rotatably supported by a round hole  74  formed in each of the side plates  63 . 
     An acceptance recess  75  cut so as to recede downwardly is formed in an upper side edge of a rear end portion of each of the arm side plates  72 . 
     An upwardly-depressed grip section  76  is formed in the widthwise center of the grip rod  71 . A pressing-and-projecting section  77  is provided at an either widthwise end of the grip rod  71 . 
     While taking the bosses  73  of the respective arm side plates  72  as fulcrums, the swing arm  70  sways between a press release position (see  FIGS. 4 and 5 ) where the lower edges of the respective arm side plates  72  come into contact with a front edge of the bottom plate  64  and a press position (see  FIGS. 2 and 3 ) where the swing arm  70  presses the developer cartridge  31  from the front when the developer cartridge  31  is housed in the cartridge housing part  33 . 
     (2) Developer Cartridge 
     As shown in  FIGS. 6 through 8 , the developer cartridge  31  has an inside cabinet  81  for storing the developer and an outside cabinet  82  for housing the inside cabinet  81 . The inside cabinet  81  and the outside cabinet  82  function as one example of cartridge cabinet. 
     (2-1) Inside Cabinet 
     As shown in  FIG. 8 , the inside cabinet  81  integrally has a cylindrical inner peripheral wall  83  extending in the widthwise direction and disc-shaped inner sidewalls  84  which close both widthwise ends of the inner peripheral wall  83 . 
     A boss section  85  that bulges in a widthwise direction and which has a thick plate disc shape is provided in the center of each of inner side walls  84 . 
     A slide projection  86  is provided at an upper portion of each of the inner sidewall  84  and at a position which is radially outside of the boss section  85 . The slide projection  86  has a substantially circular-arc shape (the shape of a circular arc having a center angle of about 60°) along an outer peripheral surface of the inner sidewall  84  as viewed sideway, as well as being provided so as to protrude from the inner sidewall  84  outwardly in the widthwise direction. 
     A pair of nipping projections  87  radially protrude from a peripheral end face of a rear portion of each inner sidewall  84 . The pair of nipping projections  87  are disposed on a peripheral end face of each of the inner sidewalls  84  while being spaced apart from each other at an interval (corresponding to the peripheral length of the shutter  68 ) in the circumferential direction. 
     In the inner peripheral wall  83  that is enclosed by the pairs of nipping projections  87  disposed both axial ends of the inner peripheral wall  83  (i.e., the four nipping projections  87 ), inner passage openings  89  as one example of the cartridge-side passage openings  47  are formed in the inner peripheral wall  83 . 
     The inner passage openings  89  are formed in an upper portion of the enclosed area  88 . The inner passage openings  89  are specifically formed in number of three while being spaced apart from each other in the widthwise direction. Each of the inner passage openings  89  has a substantially rectangular shape that is elongated in the widthwise direction. Of the inner passage openings  89 , the inner passage opening  89  formed in the widthwise center position is taken as an inner supply opening  90 , and the inner passage openings  89  formed on both sides of the inner supply opening  90  in the widthwise direction are taken as inner return openings  91 . 
     Slopes (called the inner slopes  79 ) are formed in the inner peripheral wall  83  along all of the lower edges of the respective inner passage openings  89  (the inner supply opening  90  and the inner return openings  91 ). As shown in  FIG. 2B , the inner slopes  79  are inclined downwardly in a direction crossing the horizontal direction, more specifically, a direction from the outside of the inside cabinet  81  to the outside thereof. When a tilt angle of the inner slopes  79  with reference to a horizontal plane is specified as Y, the tilt angle Y is set so as to become greater than the foregoing repose angle of the developer. 
     As shown in  FIG. 2A , the agitator  93  is provided within the inside cabinet  81 . The agitator  93  has an agitator shaft  94  extending in the widthwise direction and agitating vanes  95  radially extending from the agitator shaft  94  to the outside. The agitator shaft  94  is rotatably supported by both inner sidewalls  84  and rotated by driving force from a motor (not shown) during operation of image forming. As mentioned above, the agitating vanes  95  also rotate, to thus agitate the developer in the developer cartridge  31   
     (2-2) Outside Cabinet 
     In order to house the inside cabinet  81  in a rotatable manner, the outside cabinet  82  is formed so as to become slightly larger than the inside cabinet  81  in both the widthwise direction and the radial direction. As shown in  FIG. 6 , the outside cabinet  82  integrally has a substantially cylindrical outer peripheral wall  101  extending in the widthwise direction and outer sidewalls  102  having a substantially disc shape and closing both widthwise ends of the outer peripheral wall  101 . 
     A circular boss hole  103  for accepting the boss section  85  is formed in each of the outer sidewalls  102 . Further, a slide hole  104  into which the slide projection  86  is to be inserted is formed in an upper portion of each of the outer sidewalls  102 . The slide holes  104  are arranged so as to oppose the slide projections  86  in the widthwise direction. Each of the slide holes  104  has a substantially circular-arc shape, which is longer than the slide projection  86 , as viewed from sideways. 
     A rearwardly-protruding upper fixing part  105  is formed at an upper rearward position along the peripheral end face of each of the outer sidewalls  102 . A positioning boss  106  protruding to the outside in the widthwise direction is provided at a rear end portion of each upper fixing part  105 . 
     As shown in  FIG. 4 , a forwardly-protruding section  107  to be pressed (hereinafter called a “press section”) is provided at a lower front portion of the peripheral end face of each outer sidewall  102 . The press section  107  has a substantially rectangular shape as viewed from the front and is formed, into a substantially circular-arc shape as viewed from sideway, so as to extend from the front center of each outer sidewall  102  to a lower portion thereof. 
     As shown in  FIG. 7 , four elongated holes  108  into which the pairs of nipping projections  87  (i.e., the four nipping projections  87 ) are to be inserted are formed at both widthwise ends of the outer peripheral wall  101 . The respective elongated holes  108  are arranged so as to oppose the respective nipping projections  87  in the radial direction. Each of the elongated holes  108  has a substantially rectangular shape extending in the vertical direction as viewed from the rear and has a length equivalent to a swing range between the open position and the close position of the shutter  68 . 
     Outer passage openings  109  as one example of outer opening constituting the cartridge-side passage openings  47  are formed between the four elongated holes  108  (i.e., a space between the two upper elongated holes  108  and the two lower elongated holes  108 ) on the outer peripheral wall  101 . 
     The outer passage openings  109  are formed in number of three while being spaced apart from each other in the widthwise direction. Each of the outer passage openings  109  has a substantially rectangular shape elongated in the widthwise direction. Of the outer passage openings  109 , the outer passage opening  109  formed in the widthwise center position is taken as an outer supply opening  110 , and the outer passage openings  109  formed on both sides of the outer supply opening  110  in the widthwise direction are taken as outer return openings  111 . 
     Slopes (called outer slopes  80 ) are formed in the inner peripheral wall  83  along all lower edges of the respective outer passage openings  109  (the outer supply opening  110  and the outer return openings  111 ). As shown in  FIG. 2B , the outer slopes  80  are inclined downwardly in a direction crossing the horizontal direction, more specifically, a direction from the outside of the outside cabinet  82  to the outside thereof. When a tilt angle of the outer slopes  80  with reference to a horizontal plane is specified as Z, the tilt angle Z is set so as to become greater than the foregoing repose angle of the developer. 
     When the developer cartridge  31  is attached to the process frame  22 , the outer supply opening  110  opposes the frame-side supply opening  60 , and the two outer return openings  111  oppose the two frame-side return openings  61  (see  FIG. 2A ). 
     As shown in  FIG. 2A , a grip section  113  is provided in the center of the front side of the outer peripheral wall  101  in the widthwise direction. 
     The grip section  113  has an upper grip plate  114  and a latch arm  115 . The upper grip plate  114  projects from an upper side to a front side of the outer peripheral wall  101  and has a substantially rectangular shape. The latch arm  111  extends from the upper grip plate  114  downwardly and has a substantially J-shape as viewed from sideways. An upper end of the latch arm  115  is supported, in a swayable manner, by a support shaft  116  provided on the upper grip plate  114 . A latch claw  117  to be latched to the lower fixing part  67  is provided on a lower end of the latch arm  115 . A lower grip plate  118  projecting to the front and having a substantially rectangular shape is provided in the vicinity of the upper end of the latch arm  115 . The lower grip plate  118  is arranged so as to extend in parallel to the upper grip plate  114  while being spaced apart from the upper grip plate  114 . 
     A compression spring (not shown) for biasing the upper grip plate  114  and the lower grip plate  118  in a direction where they depart from each other is interposed between the grip plates. 
     (2-3) Relative Arrangement of Inside Cabinet and Outside Cabinet 
     The inside cabinet  81  is housed in the outside cabinet  82  in a rotatable manner. Put another way, the outside cabinet  82  and the inside cabinet  81  are relatively rotatable. 
     Specifically, an outer circumferential surface of the inner peripheral wall  83  is fitted to an inner circumferential surface of the outer peripheral wall  101  so as to be slidable in a circumferential direction. Although unillustrated, outer circumferential surfaces of both inner side walls  84  are fitted to inner circumferential surfaces of both outer sidewalls  102  so as to be slidable in the circumferential direction. As shown in  FIGS. 6 and 71  the boss sections  85  are supported by the boss holes  103  in a rotatable manner. The slide projections  86  are inserted into the corresponding slide holes  104 . The respective nipping projections  87  are inserted into the respective elongated holes  108  and project to the radial outside from the respective elongated holes  108 . 
     While taking the boss sections  85  as fulcrums, the inside cabinet  81  is allowed to perform relative rotation with respect to the outside cabinet  82  between a close position (see  FIG. 7 ) where the inner passage openings  89  do not oppose the outer passage openings  109  and an open position (see  FIG. 6 ) where the inner passage openings  89  oppose the outer passage openings  109 . 
     As shown in  FIG. 7 , when the inside cabinet  81  is located at the close position, the respective slide projections  86  are arranged at the front ends of the respective slide holes  104 , and the respective nipping projections  87  are arranged at upper ends of the respective elongated holes  108 . The inner passage openings  89  are arranged at positions higher than the outer passage openings  109 , and the outer passage openings  109  are closed by a lower portion of the enclosed area  88 . 
     While taking the boss sections  85  as fulcrums, the inside cabinet  81  is rotated relatively to the outside cabinet  82  in a direction (a downward direction) where the inner passage openings  89  move toward the outer passage openings  109 . Thereupon, the respective slide protections  86  perform sliding movements within the respective slide holes  104  from the front ends to the rear ends thereof, and the respective nipping projections  87  perform sliding movements within the respective elongated holes  108  from the upper ends to the lower ends thereof. 
     Subsequently, when the respective slide projections  86  come into contact with the rear edges of the respective slide holes  104  and when the respective nipping projections  87  come into contact with the lower edges of the respective elongated holes  108 , the inside cabinet  81  comes to the open position as shown in  FIG. 6 . 
     When the inside cabinet  81  is situated at the open position, the respective slide projections  86  are positioned at the rear ends of the respective slide holes  104 , and the respective nipping projections  87  are placed at the lower ends of the respective elongated holes  108 . Thus, the inner passage openings  89  oppose the outer passage openings  109 , to thus open mutual communication. 
     When, while taking the boss sections  85  as fulcrums, the inside cabinet  81  is rotated relatively to the outside cabinet  82  in a direction where the inner passage openings  89  ascend from the outer passage openings  109  (see a solid arrow in  FIG. 2B ), the respective slide projections  86  come into contact with the front edges of the respective slide holes  104 , and the respective nipping projections  87  come into contact with the upper edges of the respective elongated holes  108 . As shown in  FIG. 7 , the inside cabinet  81  is put to the close position. As the inside cabinet  81  moves from the open position to the close position, the tilt angle Y of the foregoing inner slope  79  becomes greater, that is, the tilt angle of the inner slope  79  to the inner downward of the inside cabinet  81  becomes greater (see  FIG. 2B ). 
     (3) Attachment and Detachment of Developer Cartridge to and from Process Frame 
     (3-1) Attachment of Developer Cartridge to Process Frame 
     As shown in  FIG. 4 , in order to attach the developer cartridge  31  to the process frame  22 , the upper grip plate  114  and the lower grip plate  118  of the grip section  113  are grasped in a direction where the upper and lower grip plates approach each other. Subsequently, the developer cartridge  31  (the inside cabinet  81  is put in the close position) is attached to the cartridge housing part  33  (the shutter  68  is placed at the close position, and the swing arm  70  is put in the press release position). 
     Specifically, the respective positioning bosses  106  are put on the respective upper fixing parts  66 , and the pair of both widthwise nipping projections  87  (see  FIGS. 6 and 7 ) nip upper and lower edges of both widthwise ends of the shutter  68 . The respective slide projections  86  are fitted into the respective acceptance recess sections  75 . 
     Subsequently, grasping of the grip section  113  is released, whereupon the latch claw  117  is latched to the lower fixing part  67  (see  FIG. 2A ), and the developer cartridge  31  is housed in the cartridge housing part  33 . 
     Since the positioning bosses  106  are put on the upper fixing parts  66  and the latch claw  117  is engaged with the lower fixing part  67 , the outside cabinet  82  is fixed to the cartridge housing part  33 . As a result, attachment of the developer cartridge  31  to the process frame  22  is completed. 
     The swing arm  70  is swayed from the press release position to the press position. As shown in  FIGS. 2A and 3 , the respective pressing and projecting sections  77  press the respective press sections  107  in the rearward direction. As a result, the developer cartridge  31  is pressed toward the developing part  32 . 
     As a result of the swing arm  70  being swayed from the press release position to the press position, the respective slide projections  86  fitted to the respective acceptance recess sections  75  perform rearward sliding movements within the respective slide holes  104  along with swaying action of the respective side plate arms  72 , to thus come to the rear ends of the respective slide holes  104 . Further, the pair of nipping projections  87  provided at both ends in the widthwise direction perform downward sliding movements within the respective elongated holes  108  while holding the shutter  68 , to thus come to the lower ends of the respective elongated holes  108  (see  FIG. 6 ). 
     As shown in  FIG. 2A , the inside cabinet  81  is put in the open position, so that the inner passage openings  89  oppose the outer passage openings  109 , to thus establish mutual communication. Moreover, the shutter  68  is put at the open position, and the frame-side passage openings  34  oppose the cartridge-side passage openings  47  (the inner passage openings  89  and the outer passage openings  109 ) in the horizontal direction, to thus establish mutual communication. 
     During operation of image forming, the developer in the inside cabinet  81  is supplied from the inner supply opening  90  and the outer supply opening  110  toward the developing part  32  by agitating action of the agitator  93 , and the developer is accepted in the developing part  32  by way of the frame-side supply opening  60  (see  FIGS. 5 and 6 ). 
     In the meantime, the developer supplied to the inside of the developing part  32  by way of the frame-side supply opening  60  is conveyed from the center position to both sides in the widthwise direction by the auger  35 , to thus be supplied to the supply roller  36  in midstream. The developer supplied to the supply roller  36  is supplied to the developing roller  37  as mentioned above. In contrast, the developer that is not supplied to the supply roller  36  is conveyed to the frame-side return openings  61  and returned from the developing part  32  to the inside of the inside cabinet  81  by passing the outer return openings  111  and the inner return openings  91 . Thereby, the developer is circulated between the developing part  32  and the inside cabinet  81  (see  FIGS. 5 and 6 ). 
     (3-2) Detachment of Developer Cartridge from Process Frame 
     In order to detach the developer cartridge  31  from the process frame  22 , the swing arm  70  is first swayed from the press position to the press release position. Thereupon, the respective pressing-and-projecting sections  77  depart from the respective press sections  107 , thereby releasing the developing part  32  of the developer cartridge  31  from a pressed state. 
     Moreover, when the swing arm  70  is swayed from the press position to the press release position, the respective slide projections  86  fitted into the respective acceptance recess sections  75  perform forward sliding movements within the respective slide holes  104  along with swaying action of the respective side plate arms  72 , to thus come to the front ends of the respective slide holes  104  (see  FIG. 7 ). Further, the pair of nipping projections  87  provided at both widthwise ends perform upward sliding movements within the respective elongated holes  108  while nipping the shutter  68 , to thus be arranged at the upper ends of the respective elongated holes  108  (see  FIG. 7 ). 
     As a result, the inside cabinet  81  is put at the close position, and the lower portion of the enclosed area  88  opposes the outer passage openings  109 , thereby closing the outer passage openings  109 . The shutter  68  is placed at the close position, and the frame-side passage openings  34  oppose the shutter  68 , to thus become closed (see  FIG. 4 ). 
     When the upper grip plate  114  and the lower grip plate  118  of the grip section  113  are grasped in the direction where they approach each other, the latch claw  117  is disengaged from the upper fixing part  66 . Accordingly, so long as the developer cartridge  31  is pulled forwardly from the cartridge housing part  33  in the disengaged state, the developer cartridge  31  is detached from the process frame  22  (see  FIG. 4 ). 
     As shown in  FIG. 2 , the developer cartridge  31  can be realized as a double structure including the outside cabinet  82  in which the outer passage openings  109  is formed and the inside cabinet  81  in which the inner passage openings  89  capable of opposing the outer passage openings  109  are formed and which stores the developer. Moreover, the developer can be caused to move to the inside and outside of the outside cabinet  82  and the inside cabinet  81  by way of the outer passage openings  109  and the inner passage openings  89  by the outer passage openings  109  to oppose the inner passage openings  89 . 
     The outer slopes  80 , which are inclined in the direction crossing the horizontal direction when the outer passage openings  109  are oriented in the horizontal direction, are formed at the respective lower edges of the outer passage openings  109 . Moreover, the inner slopes  79 , which are inclined in the direction crossing the horizontal direction when the inner passage openings  89  are oriented in the horizontal direction, are formed at the respective lower edges of the inner passage openings  89 . 
     As a result, the developer moves along the corresponding outer slopes  80  and inner slopes  79  at the respective lower edges of the outer passage openings  109  and the inner passage openings  89 , so that the developer does not stay at the respective lower edges of the outer passage openings  109  and the inner passage openings  89 . Thus, leakage of the developer can be prevented reliably. 
     The inside cabinet  81  is rotatable with respect to the outside cabinet  82 , and the inner slopes  79  of the inside cabinet  81  are inclined downwardly from the outside to the inside. As a result, when the inside cabinet  81  is rotated with respect to the outside cabinet  82 , the developer moves at the lower edges of the inner passage openings  89  to the inside of the inside cabinet  81  along the inner slopes  79 . Therefore, the developer does not stay at the lower edges of the inner passage openings  89  or a space between the inside cabinet  81  and the outside cabinet  82 , thereby preventing leakage of the developer reliably. 
     The outer slopes  80  of the outside cabinet  82  are inclined downwardly from the inside to the outside. In a state where the outer passage openings  109  and the inner passage openings  89  oppose each other along the horizontal direction, front edges (upper edges) of the outer slopes  80  and rear edges (upper edges) of the inner slopes  79  become continuous. The outer slopes  80  and the inner slopes  79  constitute upwardly-tapered triangular shapes when viewed from sideways (see  FIG. 2A ). Therefore, the developer reliably moves to the outside of the outside cabinet  82  along the outer slopes  80  and also moves to the inside of the inside cabinet  81  without fail. 
     As shown in  FIG. 2B , as the inside cabinet  81  is rotated in the direction in which the inner passage openings  89  ascend from the outer passage openings  109 , to thus close the outer passage openings  109 , the inclination of the inner slopes  79  to the inner downward direction with reference to the horizontal direction becomes greater (the tilt angle Y becomes greater). Accordingly, the developer can be caused to move from the lower edges of the inner passage openings  89  to the inside of the inside cabinet  81 . Therefore, leakage of the developer can be prevented more thoroughly. 
     The tilt angle Y of the inner slopes  79  with respect to the horizontal plane and the tilt angle Z of the outer slopes  80  with respect to the horizontal plane are greater than the angle of repose of the developer. Therefore, the developer reliably moves along the corresponding inner slopes  79  and outer slopes  80  at the respective lower edges of the inner passage openings  89  and outer passage openings  109 . Accordingly, the developer does not stay at the respective lower edges of the inner passage openings  89  and the outer passage openings  109 , and leakage of the developer can be prevented more thoroughly. 
     The frame-side slopes  78 , which are inclined downwardly with respect to the horizontal direction from the outside to the inside when the frame-side passage openings  34  are oriented in the horizontal direction, are formed at the respective lower edges of the frame-side passage openings  34 . The developer therefore moves to the inside of the process frame  22  along the frame-side slopes  78  at the frame-side passage openings  34 , so that the developer does not stay at the respective lower edges of the frame-side passage openings  34  or a space between the process frame  22  and the developer cartridge  31 . Thus, leakage of the developer can be prevented reliably. 
     As mentioned above, the shutter  68  closes the frame-side passage openings  34  by ascending action. Accordingly, at the time of operation for closing the frame-side passage openings  34 , movement of the developer to the outside is hindered at the lower edges of the frame-side passage openings  34 , so that leakage of the developer can be prevented reliably. 
     The tilt angle X of the frame-side slopes  78  with respect to the horizontal plane is greater than the angle of repose of the developer. Therefore, the developer reliably moves to the inside of the process frame  22  along the frame-side slopes  78  at the lower edges of the frame-side passage openings  34 . Hence, the developer does not stay at the lower edges of the frame-side passage openings  34  and the space between the process frame  22  and the developer cartridge  31 , and leakage of the developer can be prevented more thoroughly. 
     As shown in  FIG. 2A , in a state where the developer cartridge  31  is attached to the process frame  22 , the cartridge-side passage openings  47  (the outer passage openings  109  and the inner passage openings  89 ) and the frame-side passage openings  34  oppose each other along the horizontal direction. As a result, the inner slopes  79 , the outer slopes  80 , and the frame-side slopes  78  are inclined without fail in a direction crossing the horizontal direction. Accordingly, the developer moves along the corresponding inner slopes  79 , the outer slopes  80 , and the frame-side slopes  78  at the respective lower edges of the cartridges-side passage openings  47  and the frame-side passage openings  34 . Therefore, the developer does not stay at the lower edges of the cartridge-side passage openings  47  and the frame-side passage openings  34 , and leakage of the developer can be prevented more thoroughly. 
     In a state where the cartridge-side passage openings  47  and the frame-side passage openings  34  oppose each other along the horizontal direction, rear edges (lower edges) of the outer slopes  80  and front edges (upper edges) of the frame-side slopes  78  are continuous with the shutter opening sections  69  of the shutter  68  sandwiched therebetween. Therefore, the developer moved to the outside of the outside cabinet  82  along the outer slopes  80  smoothly reaches the frame-side slopes  78  and reliably moves to the inside (in the developing part  32 ) of the process frame  22 . Incidentally, when slopes continuous to the outer slopes  80  and the frame-side slopes  78  are formed at the lower edges of the shutter opening sections  69  of the shutter  68 , the developer moving from the outer slopes  80  can be caused to reach the frame-side slopes  78  more smoothly. 
     MODIFIED EXAMPLES 
     (1) Modified Examples of Inside Cabinet and Outside Cabinet 
     In the above-described aspects, the inside cabinet  81  is rotatable relatively to the outside cabinet  82 . In contrast, the outside cabinet  82  may also be rotatable relatively to the inside cabinet  81 . 
     The inside cabinet  81  and the outside cabinet  82  of that case will be described hereunder. 
       FIGS. 9A and 9B  show a modified example of a developing unit and a developer cartridge shown in  FIGS. 2A and 2B .  FIG. 10  is an exemplary perspective view of the developer cartridge of  FIG. 9 , as viewed from a back left side, in a state in which an outside cabinet is in an opened position.  FIG. 11  is an exemplary perspective view of the developer cartridge of  FIG. 9 , as viewed from the back left side, in a state in which the outside cabinet is in a closed position.  FIG. 12  is an exemplary perspective view, as viewed from a back left side, of the inside cabinet of the developer cartridge of  FIG. 10 .  FIG. 13  is an exemplary perspective view, as viewed from a back left side, of the outside cabinet of the developer cartridge of  FIG. 10 . 
     (1-1) Inside Cabinet 
     By reference to  FIG. 12 , the inside cabinet  81  integrally has the above-described inner peripheral wall  82  and the inner sidewalls  84 . The boss section  85  provided in the center of each of the inner sidewalls  84  has a substantially cylindrical shape differing from the foregoing thick disc-shaped geometry. 
     The slide projection  86  is not provided on each of the inner sidewalls  84 , and the nipping projection  87  is provided along a peripheral end face of each of the inner sidewall  84 . 
     In the meantime, a developer inner plate  96  is integrally provided on a widthwise outer side surface of each of the inner sidewalls  84 . The developer inner plate  96  substantially assumes the shape of the letter U when viewed from sideways, and an inner portion of the letter U (i.e., an inner portion  97 ) is formed so as to become deep downwardly in an oblique rear direction. The deepest portion of each of the inner portion  97  has a substantially circular shape, and the boss section  85  is placed at the center of the circular shape. When viewed from sideways, the inner portions  97  are formed so as to spread into the shape of a fan from the deepest portion to an obliquely upward and forward direction. 
     The upper fixing part  105  and the positioning boss  106  are provided at a rear upper portion of each of the developer inner plates  96 , and a front end portion of each of the inner inner plates  96  forms the above-described press section  107 . 
     The above-described grip section  113  is provided at a position on a side (the front side) opposite to the inner passage opening  89  corresponding to the center of the inner peripheral wall  83 . 
     As in the case of the above-described example, the inner slopes  79  that are downwardly inclined from the outside to the inside of the inside cabinet  81  are formed at the respective lower edges of the inner passage openings  89  of the inner peripheral wall  83 . 
     (1-2) Outside Cabinet 
     In response to the inside cabinet  81  of the modification, the outside cabinet  82  is also different from that described in connection with the above-described aspect. 
     Referring to  FIG. 13 , the outside cabinet  82  of the modification is not provided with the outer sidewalls  102 , and both widthwise ends of the outer peripheral wall  101  are opened to the outside in the widthwise direction. The above-described pair of nipping projections  87  (the four nipping projections  87 ) is provided at either widthwise end of the outer peripheral wall  101 , and the outer passage openings  109  are formed within the area on the outer peripheral wall  101  surrounded by the nipping projections  87 . The elongated holes  108  are not provided in the outer peripheral wall  101  in response to the nipping projections  87 . In the meantime, an exposure hole  99  for uncovering the above-described grip section  113  is formed in a position on a side (front side) opposite to the outer passage opening  109  corresponding to the center of the outer peripheral wall  101 . 
     In the meantime, developer outer plates  98  are integrally provided at the positions that deviate clockwise from the outer passage openings  109  through about 90° when viewed from the left. The respective developer outer plates  98  extend from both widthwise ends of the outer peripheral wall  101  to the radially inside of the outer peripheral wall  101 . When viewed from the side, the developer outer plates  98  have a substantially triangular shape which becomes narrower toward the radial inside thereof. A circular hole (a fitting hole  147 ) is formed in the position of each developer outer plate  98  corresponding to the center of the circle of the outer peripheral wall  101 . The above-described slide projection  86  is provided at a position on each developer outer plate close to the outer peripheral wall  101 . 
     Even in the modification, the outer slopes  80  are formed at the lower edges of the respective outer passage openings  109  in the outer peripheral wall  101 . The outer slopes  80  of the modification are downwardly inclined from the outside to the inside of the outside cabinet  82  (see  FIG. 9 ). As in the case of the above-described aspect, the tilt angle Z of the outer slope  80  is set so as to become greater than the angle of repose of the developer (see  FIG. 95 ). 
     (1-3) Relative Arrangement Between Inside Cabinet and Outside Cabinet 
     As in the above-described aspect, the inside cabinet  81  is housed in the outside cabinet  82 . 
     Specifically, as shown in  FIGS. 10 and 11 , the grip section  113  is exposed through the exposure hole  99  of the outer peripheral wall  101 , and the boss sections  85  are fitted into the fitting holes  147  of the respective developer outer plates  98 . The respective developer outer plates  98  are situated within the inner portions  97  of the corresponding developer inner plates  96 . 
     As a result of the boss sections  85  being fitted into the fitting holes  147 , the outside cabinet  82  is allowed to perform relative rotatable movement around the boss sections  85  with respect to the inside cabinet  81  between the close position (see  FIG. 11 ) and the open position (see  FIG. 10 ). 
     As shown in  FIG. 11 , when the outside cabinet  82  is situated at the close position, the outer passage openings  109  are situated at positions higher than the inner passage openings  89 , and the inner passage openings  89  are closed by a portion of the outer peripheral wall  101  that is lower than the outer passage openings  109 . 
     While taking the boss sections  85  as fulcrums, the outside cabinet  82  is rotated relatively to the inside cabinet  81  in a direction (downward direction) in which the outer passage openings  109  face the inner passage openings  89 . 
     Subsequently, when the respective developer outer plates  98  come into contact with rear edges of the corresponding inner portions  97 , the outside cabinet  82  is placed at the open position, as shown in  FIG. 10 . 
     When the outside cabinet  82  is situated at the open position, the inner passage openings  89  oppose the outer passage openings  109 , such that they come into mutual communication and are opened. 
     When the outside cabinet  82  is rotated relatively to the inside cabinet  81 , while taking the boss sections  85  as fulcrums, in a direction where the outer passage openings  109  ascend from the inner passage openings  89  (see a thick arrow in  FIG. 9B ), the respective developer outer plates  98  come into contact with the front edges of the corresponding inner portions  97 , whereupon the outside cabinet  82  is put in the close position. 
     The tilt angle Z of the outer slopes  80 , that is, the downward inclination of the outer slopes  80  to the inside of the outside cabinet  82 , becomes greater as the outside cabinet  82  moves from the open position to the close position (see  FIG. 9B ). 
     When the developer cartridge  31  of the modification is attached to the process frame  22 , the positioning bosses  106  are placed on the respective upper fixing parts  66 , and the latch claws  117  are latched to the lower fixing parts  67 , whereby the inside cabinet  81  is fixed to the cartridge housing part  33  (see  FIG. 9A ). 
     When the swing arm  70  is swayed from the press release position to the press position, the respective slide projections  86  fitted into the respective acceptance recess sections  75  slide rearwardly in conjunction with rotatable movement of the respective arm side plates  72 , and the pair of nipping projections  87  provided at both widthwise ends slide downwardly while nipping the shutter  68 . 
     As a result, the outside cabinet  82  is placed at the open position (see  FIG. 10 ) and the outer passage openings  109  oppose the inner passage openings  89  as shown in  FIG. 9A , whereby they are brought into mutual communication. Moreover, the shutter  68  is placed at the open position, and the frame-side passage openings  34  oppose the cartridge-side passage openings  47  (the inner passage openings  89  and the outer passage openings  109 ) in the horizontal direction, whereby they are brought into mutual communication. 
     In the meantime, the swing arm  70  is swayed from the press position to the press release position, thereby releasing the inside cabinet  81  from the cartridge housing part  33 . Further, the developer cartridge  31  is pulled forwardly from the cartridge housing part  33 , whereupon the developer cartridge  31  is detached from the process frame  22 . 
     As shown in  FIG. 9 , in the modification, the outside cabinet  82  can rotate with respect to the inside cabinet  81 , and the outer slopes  80  of the outside cabinet  82  are downwardly inclined from the outside to the inside. 
     As a result, when the outside cabinet  82  rotates with respect to the inside cabinet  81 , the developer moves to the inside of the outside cabinet  82  along the outer slopes  80  at the lower edges of the outer passage openings  109 . That is, the developer moves to the inner passage openings  89 . As mentioned above, the inner slopes  79  of the inside cabinet  81  are also inclined downwardly from the outside to the inside, and hence the developer moves to the inside of the inside cabinet  81  along the inner slopes  79  at the lower edges of the inner passage openings  89 . 
     Consequently, the developer moves to the inside of the inside cabinet  81  along the corresponding outer slopes  80  and the inner slopes  79  at the respective lower edges of the outer passage openings  109  and those of the inner passage openings  89 . Since the developer located at the lower edges of the outer passage openings  109  and the lower edges of the inner passage openings  89  is brought into the inside, leakage of the developer can be prevented reliably. 
     As shown in  FIG. 9A , in a state where the outer passage openings  109  and the inner passage openings  89  oppose each other in the horizontal direction, the front edges (lower edges) of the outer slopes  80  and the rear edges (upper edges) of the inner slopes  79  are continuous. Therefore, the developer located on the outer slopes  80  smoothly reach the inner slopes  79 , to thus move to the inside of the inside cabinet  81  reliably. 
     As shown in  FIG. 9B , the downward inclination of the outer slopes  80  of the outside cabinet  82  to the inside with reference to the horizontal direction becomes greater (the tilt angle Z becomes greater) as the outside cabinet  82  rotates in the direction where the outer passage openings  109  ascend from the inner passage openings  89 , to thus close the inner passage openings  89 . As a result, the developer can be caused to move from the lower edges of the outer passage openings  109  to the inside of the internal housing  81  reliably. Therefore, leakage of the developer can be prevented more thoroughly. 
     In the above-described aspects, the developing unit  17  integrally has the photosensitive drum  25  and the developing roller  37 , and the developing unit  17  is detachably attached to the body casing  2 . In addition, for example, the developing unit  17  may also be embodied as a developing cartridge not having the photosensitive drum  25 , and another unit (a drum cartridge) having the photosensitive drum  25  may be provided, and the developing cartridge may be detachably attached to the drum cartridges. Moreover, there may also be adopted a configuration in which only the developer cartridge  31  is detachably attached while the developing unit  17  remains attached to the body casing  2 . 
     (2) Additional Modified Examples 
     In addition to the above-described modified example of the outer slopes  80 , which are inclined downwardly from the outside to the inside of the outside cabinet  82 , the inside cabinet  81  may also rotate in the direction where the inner passage openings  89  descend from the outer passage openings  109  in order to close the outer passage openings  109 . That is, in contrast with the above-described modified example, the inside cabinet  81  rotates with respect to the outside cabinet  82 . 
     In this case, when the inside cabinet  81  closes the outer passage openings  109 , the inner passage openings  89  descend from the outer passage openings  109 . Hence, the developer can be moved from the lower edges of the outer passage openings  109  to the inner passage openings  89  without fail. Moreover, when the inside cabinet  81  rotates with respect to the outside cabinet  82 , the developer moves to the inside of the inside cabinet  81  along the inner slopes  79  at the lower edges of the inner passage openings  89 . Therefore, leakage of the developer can be prevented more thoroughly. 
     Further, the body casing  2  may include the photosensitive drum  25 , the scorotron-type charger  26 , and the transfer roller  28 , and the developing cartridge can also be detachably attached to the body casing  2 . 
     Still further, although aspects of the present inventive concept have been described in relation to a laser printer, the present inventive concept is not limited to a monochrome laser printer. Rather, the present inventive concept can also be applied to a color laser printer, including a tandem type and an intermediate transfer type printer.