Abstract:
A cartridge includes: a frame; an agitator; a coupling; a first transmission gear; a closing member; and a cover member. The frame has a first wall having a developer filling port, and a second wall spaced apart from the first wall. The agitator is supported to the first and second walls. The coupling is provided at the first wall and receives a drive force from an external drive source. The first transmission gear is provided at the first wall and transmits the drive force received by the coupling to the agitator. The closing member is provided at the first wall and closes the developer filling port. The cover member is provided at the first wall. The cover member includes: a first cover to cover the first transmission gear; and a second cover provided separately from the first cover and to cover the closing member.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2013-137421 filed Jun. 28, 2013. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a cartridge used in an electrophotographic image forming apparatus. 
     BACKGROUND 
     There is conventionally known, as an image forming apparatus, a printer in which a cartridge having a developing roller is detachably mountable. 
     As such a printer, there is proposed a printer including a developing device provided with a gear train for a drive system, and a side cover for protecting the gear train. 
     Such a printer further includes a toner replenishing member for replenishing the developing device with toner. The developing device and the toner replenishing member are detachably attached to a main casing of the printer. 
     SUMMARY 
     In such a configuration, it is considered that the gear train and a toner filling port are both disposed at one side of the developing device and collectively covered by a side cover. 
     The above technique allows reduction in size of the developing unit, however, when the side cover is removed for toner filling, even a member unnecessary for the toner filling, such as a gear in the drive system covered by the side cover, is exposed to an outside and may be subject to damage. 
     In view of the foregoing, it is an object of the present invention to provide a cartridge capable of increasing reliability. 
     In order to attain the above and other objects, the present invention provides a cartridge that may include: a frame; an agitator; a coupling; a first transmission gear; a closing member; and a cover member. The frame may have a first wall and a second wall spaced apart from the first wall. The first wall may have a developer filling port. The agitator may be supported to the first wall and the second wall. The coupling may be provided at the first wall and configured to receive a drive force from an external drive source. The first transmission gear may be provided at the first wall and configured to transmit the drive force received by the coupling to the agitator. The closing member may be provided at the first wall and configured to close the developer filling port. The cover member may be provided at the first wall. The cover member may include: a first cover that may be configured to cover the first transmission gear; and a second cover that may be provided separately from the first cover and configured to cover the closing member. 
     According to another aspect, the present invention provides a cartridge that may include: a frame; an agitator; a coupling; a first transmission gear; a closing member; and a cover member. The frame may be configured to accommodate developing agent therein. The frame may have a developer filling port. The agitator may be configured to agitate the developing agent. The coupling may be configured to receive a drive force from an external drive source. The first transmission gear may be configured to transmit the drive force received by the coupling to the agitator. The closing member may be configured to close the developer filling port. The cover member may include: a first cover that may be configured to cover the first transmission gear; and a second cover that may be provided separately from the first cover and configured to cover the closing member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings; 
         FIG. 1  is a central cross-sectional view of a developing cartridge as a cartridge according to one embodiment of the present invention; 
         FIG. 2  is a central cross-sectional view of a printer for which the developing cartridge in  FIG. 1  is used; 
         FIG. 3  is a perspective view of the developing cartridge in  FIG. 1  as viewed from a lower-left side thereof; 
         FIG. 4  is an exploded partial perspective view of the developing cartridge in  FIG. 1  as viewed from a lower-left side thereof, from which a gear train and a gear cover has been removed; 
         FIG. 5  is an exploded partial perspective view of the developing cartridge in  FIG. 1  as viewed from a lower-left side thereof, to which the gear train has been assembled and from which the gear cover has been removed; 
         FIG. 6  is an exploded perspective view of the developing cartridge in  FIG. 1  as viewed from an upper-left side thereof, to which the gear train has been assembled and from which the gear cover has been removed; 
         FIG. 7  is an exploded partial perspective view of the developing cartridge in  FIG. 1  as viewed from a lower-left side thereof, to which a first cover of the gear cover has been assembled and from which a second cover of the gear cover has been removed; 
         FIG. 8  is an explanatory view for illustrating the position of the gear train in  FIG. 5 ; 
         FIG. 9  is a perspective view of the second cover in  FIG. 5  as viewed from an upper front side thereof; 
         FIG. 10A  is an explanatory view for illustrating an assembly of the gear cover to a left wall of a frame of the developing cartridge in  FIG. 1 , in which the first cover has been assembled to the left wall of the frame and the second cover is in the course of being assembled to the left wall of the frame; 
         FIG. 10B  is an explanatory view for illustrating the assembly of the gear cover to the left wall of the frame, following  FIG. 10A , in which the first cover and the second cover have been assembled to the left wall of the frame; 
         FIG. 11  is a left side view of the developing cartridge in  FIG. 1  that has been attached to a main casing of the printer; 
         FIG. 12A  is a left side view of the developing cartridge in  FIG. 1  to which the first cover and the second cover have been assembled; 
         FIG. 12B  is a cross-sectional view of the developing cartridge taken along a line A-A in  FIG. 12A ; 
         FIG. 13A  is a left side view of the developing cartridge in  FIG. 1  in which the first cover has been assembled to the left wall but the second cover has been removed from the left wall; 
         FIG. 13B  is a cross-sectional view of the developing cartridge taken along a line B-B in  FIG. 13A ; 
         FIG. 14A  is a left side view of a developing cartridge according to a modification to the embodiment; and 
         FIG. 14B  is a cross-sectional view of the developing cartridge taken along a line C-C in  FIG. 14A . 
     
    
    
     DETAILED DESCRIPTION 
     1. General Structure of Developing Cartridge 
     A developing cartridge as an example of a cartridge according to one embodiment of the present invention will be described with reference to  FIG. 1 . 
     As illustrated in  FIG. 1 , the developing cartridge  1  is configured to be attached to and detached from a drum cartridge  18  (described later). The developing cartridge  1  includes a developing roller  4 , a supply roller  5 , a layer thickness regulation blade  6 , a toner chamber  7 , and an agitator  8 . 
     In the following description, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used assuming that the developing cartridge  1  is disposed in such an orientation that the developing roller  4  is disposed on a rear side. More specifically, in  FIG. 1 , a left side and a right side are a rear side and a front side, respectively. Further, in  FIG. 1 , a top side and a bottom side are a top side and a bottom side, respectively. Further, left and right sides of the developing cartridge  1  will be based on the perspective of a user facing the front of the developing cartridge  1 . Therefore, the near side of the developing cartridge  1  in  FIG. 1  will be referred to as the “left side,” and the far side thereof will be referred to as the “right side.” 
     The developing roller  4  is disposed at a rear end portion of the developing cartridge  1 . The developing roller  4  includes a developing roller shaft  4 A, and a rubber roller  4 B. 
     The developing roller shaft  4 A has a substantially columnar shape extending in a left-right direction. 
     The rubber roller  4 B covers the entire developing roller shaft  4 A, excluding left and right end portions thereof. 
     The developing roller  4  is rotatably supported to a left wall  37  (described later) and a right wall  38  (described later) such that the left and right end portions of the developing roller shaft  4 A protrude outward in the left-right direction from the left and right walls  37  and  38 , respectively. The rubber roller  4 B of the developing roller  4  contacts a photosensitive drum  20  (described later) from a front side thereof. 
     The supply roller  5  is disposed diagonally below and frontward of the developing roller  4 . The supply roller  5  includes a supply roller shaft  5 A, and a sponge roller  5 B. 
     The supply roller shaft  5 A has a substantially columnar shape extending in the left-right direction. 
     The sponge roller  5 B covers the entire supply roller shaft  5 A, excluding left and right end portions thereof. 
     The supply roller  5  is rotatably supported to the left wall  37  (described later) and the right wall  38  (described later) such that the left and right end portions of the supply roller shaft  5 A protrude outward in the left-right direction from the left and right walls  37  and  38 , respectively. The sponge roller  5 B of the supply roller  5  contacts the developing roller  4  from a lower-front side thereof. 
     The layer thickness regulation blade  6  is disposed diagonally above and frontward of the developing roller  4 . The layer thickness regulation blade  6  contacts the developing roller  4  from a front side thereof. 
     The developing cartridge  1  defines an internal space serving as a toner chamber  7 . The toner chamber  7  is positioned frontward of the supply roller  5  and the layer thickness regulation blade  6 . The toner chamber  7  is adapted to accommodate toner therein. The agitator  8  is disposed in the toner chamber  7 . 
     The agitator  8  includes an agitator shaft  8 A, and an agitating blade  8 B. 
     The agitator shaft  8 A has a substantially columnar shape extending in the left-right direction. 
     The agitating blade  8 B is formed of a film having flexibility. The agitating blade  8 B extends outward in a radial direction of the agitator shaft  8 A from a left-right center portion of the agitator shaft  8 A, that is, a portion excluding left and right end portions of the agitator shaft  8 A. 
     The agitator  8  is rotatably supported to the left wall  37  (described later) and the right wall  38  (described later) such that the left and right end portions of the agitator shaft  8 A protrude outward in the left-right direction from the left and right walls  37  and  38 , respectively. 
     2. Overall Structure of Printer 
     As illustrated in  FIG. 2 , a printer  11  to which the developing cartridge  1  is detachably mountable is an electrophotographic monochromatic printer. The printer  11  includes a main casing  12 , a process cartridge  13 , a scanner unit  14 , and a fixing unit  15 . 
     The main casing  12  has a substantially box-like shape. The main casing  12  has a front wall formed with an opening portion  16 . The main casing  12  includes a front cover  17 , a sheet cassette  29 , and a discharge tray  30 . 
     The opening portion  16  penetrates the front wall of the main casing  12  in a front-rear direction so as to allow the process cartridge  13  to pass therethrough. 
     The front cover  17  has a substantially plate-like shape. The front cover  17  is supported to the front wall of the main casing  12  and pivotally movable about its lower end portion. The front cover  17  opens and closes the opening portion  16 . 
     The sheet cassette  29  is disposed at a bottom portion of the main casing  12 . The sheet cassette  29  is adapted to accommodate sheets of paper P. 
     The discharge tray  30  is disposed at a top surface of the main casing  12 . 
     The process cartridge  13  is configured to be attached to and detached from the main casing  12 . The process cartridge  13  includes the developing cartridge  1  and the drum cartridge  18 . 
     The drum cartridge  18  includes the photosensitive drum  20 , a scorotron charger  21 , and a transfer roller  22 . 
     The photosensitive drum  20  is rotatably supported at a rear end portion of the process cartridge  13 . The photosensitive drum  20  has a substantially cylindrical shape elongated in the left-right direction. 
     The scorotron charger  21  is disposed rearward of the photosensitive drum  20  and spaced apart from the photosensitive drum  20 . 
     The transfer roller  22  is disposed below the photosensitive drum  20 . The transfer roller  22  contacts the photosensitive drum  20  from a lower side thereof. 
     The scanner unit  14  is disposed above the process cartridge  13 . As denoted by a dashed line of  FIG. 2 , the scanner unit  14  is adapted to emit a laser beam based on image data toward the photosensitive drum  20 . 
     The fixing unit  15  is disposed rearward of the process cartridge  13 . The fixing unit  15  includes a heating roller  25 , and a pressure roller  26  in pressure contact with the heating roller  25  from a lower-rear side thereof. 
     When the printer  11  performs an image forming operation, the scorotron charger  21  applies a uniform charge to a surface of the photosensitive drum  20 . Thereafter, the scanner unit  14  exposes the surface of the photosensitive drum  20 . As a result, an electrostatic latent image based on image data is formed on the surface of the photosensitive drum  20 . 
     The agitator  8  agitates the toner accommodated in the toner chamber  7  and supplies the agitated toner to the supply roller  5 . The supply roller  5  supplies the toner supplied from the agitator  8  to the developing roller  4 . At this time, the toner is positively tribo-charged between the developing roller  4  and the supply roller  5  to be carried on the developing roller  4 . The layer thickness regulation blade  6  regulates the toner carried on the developing roller  4  so that the developing roller  4  carries on its surface a thin layer of toner having a uniform thickness. 
     The toner carried on the developing roller  4  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  20 . As a result, a toner image is carried on the surface of the photosensitive drum  20 . 
     In the meantime, various rollers convey the sheets of paper P from the sheet cassette  29  at a prescribed timing, and supply the sheets P one at a time to a position between the photosensitive drum  20  and the transfer roller  22 . The toner image on the photosensitive drum  20  is transferred onto the sheet P upon passage to the position between the photosensitive drum  20  and the transfer roller  22 . 
     The sheet P onto which the toner image has been transferred passes between the heating roller  25  and the pressure roller  26 , at which time the heating roller  25  applies heat to the sheet P while the pressure roller  26  applies pressure to the sheet P, thermally fixing the toner image to the sheet P. Thereafter, the sheet P is discharged onto the discharge tray  30 . 
     3. Detailed Description of Developing Cartridge 
     The structure of the developing cartridge  1  according to the embodiment of the present invention will be described in greater detail with reference to  FIGS. 3 through 13B , wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     As illustrated in  FIGS. 3 and 4 , the developing cartridge  1  includes a frame  33 , and a drive unit  34 . 
     (1) Frame 
     The frame  33  is formed of a resin such as polystyrene (PS). The frame  33  has a substantially box-like shape elongated in the left-right direction. More specifically, the frame  33  includes the left wall  37  as an example of a first wall, the right wall  38  as an example of a second wall, a front wall  39 , a bottom wall  40 , and a top wall  41  (see  FIG. 6 ). 
     As illustrated in  FIG. 4 , the left wall  37  is disposed at a left end portion of the frame  33 . The left wall  37  has a plate-like shape that is substantially rectangular in a side view and elongated in the front-rear direction. The left wall  37  includes a toner filling portion  43 , a cap  55  as an example of a closing member, a first screwed portion  47 , a co-fastening screwed portion  48 , a second screwed portion  49 , a protruding portion  50 , an idle gear support shaft  51 , and a hooking portion  52 . 
     The toner filling portion  43  is disposed at a front end portion of the left wall  37 . The toner filling portion  43  includes a toner filling port  44 , a toner filling cylindrical portion  45 , and a cap positioning portion  46 . 
     The toner filling port  44  has a substantially circular shape in a side view, and penetrates the left wall  37  in the left-right direction. 
     The toner filling cylindrical portion  45  has a substantially hollow cylindrical shape. The toner filling cylindrical portion  45  extends leftward from a left surface of the left wall  37  at a peripheral edge defining the toner filling port  44 . The toner filling cylindrical portion  45  has an inner diameter substantially the same as an inner diameter of the toner filling port  44 . 
     The cap positioning portion  46  is disposed diagonally below and rearward of the toner filling port  44 . The cap positioning portion  46  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . 
     The cap  55  includes a closing portion  56  and a reed-like piece  57 . 
     The closing portion  56  is configured to close the toner filling port  44 . The closing portion  56  has a plate-like shape that is substantially circular in a side view. The closing portion  56  includes a cap cylindrical portion  59 , a detection gear support shaft  60 , a guide portion  61 , and a pair of stoppers  62 . 
     The cap cylindrical portion  59  has a substantially cylindrical shape extending rightward from a right surface of the closing portion  56  at a peripheral portion thereof. The cap cylindrical portion  59  has an outer diameter slightly smaller than the inner diameter of the toner filling port  44 . 
     The detection gear support shaft  60  has a substantially columnar shape extending leftward from a left surface of the closing portion  56  at a center portion thereof. 
     The guide portion  61  protrudes leftward from a left surface of the closing portion  56  at a front half of a peripheral portion thereof. The guide portion  61  has a substantially semi-circular arc shape centering on the detection gear support shaft  60  in a left side view. The guide portion  61  has a left end surface that is gradually inclined leftward from its upstream end in a counterclockwise direction in a left side view toward its intermediate portion in the counterclockwise direction in a left side view, extends parallel to the closing portion  56  at the intermediate portion, and is then gradually inclined rightward toward its downstream end in the counterclockwise direction in a left side view. 
     In the left side surface of the guide portion  61 , the upstream end in the counterclockwise direction in a left side view will be referred to as an upstream inclined portion  61 A, the intermediate portion in the counterclockwise direction in a left side view will be referred to as an intermediate flat portion  61 B, and the downstream end in the counterclockwise direction in a left side view will be referred to as a downstream inclined portion  61 C. 
     The pair of stoppers  62  is disposed respectively at upstream and downstream ends of the guide portion  61  in the counterclockwise direction in a left side view so as to be spaced apart therefrom. That is, the pair of stoppers  62  is disposed rearward of the upstream inclined portion  61 A and the downstream inclined portion  61 C, respectively, so as to be spaced apart therefrom. 
     The reed-like piece  57  continues from a lower-rear end portion of an outer peripheral surface of the closing portion  56  and protrudes therefrom diagonally below and rearward. The reed-like piece  57  has a plate-like shape that is substantially circular in a side view. The reed-like piece  57  has a positioning hole  65 . 
     The positioning hole  65  has a substantially circular shape in a side view and penetrates, in the left-right direction, a substantial up-down and front-rear center of the reed-like piece  57 . The positioning hole  65  has an inner diameter slightly larger than an outer diameter of the cap positioning portion  46 . 
     The cap cylindrical portion  59  of the closing portion  56  is inserted along an inner peripheral surface of the toner filling cylindrical portion  45 , and the cap positioning portion  46  of the left wall  37  is inserted into the positioning hole  65  of the reed-like piece  57 , whereby the cap  55  is assembled to the left wall  37  to close the toner filling port  44 . 
     As illustrated in  FIG. 6 , the first screwed portion  47  is disposed at an upper-rear end portion of the left wall  37 . The first screwed portion  47  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . The first screwed portion  47  has a first screw hole  47 A and includes a first engagement portion  47 B. 
     The first screw hole  47 A has a substantially circular shape in a side view and is recessed rightward from a left end face of the first screwed portion  47 . 
     The first engagement portion  47 B is disposed at a left end portion of the first screwed portion  47 . The first engagement portion  47 B has a substantially cylindrical shape extending leftward from a peripheral edge defining the first screw hole  47 A. 
     As illustrated in  FIG. 4 , the co-fastening screwed portion  48  is disposed at a lower end portion of a substantial front-rear center of the left wall  37 . The co-fastening screwed portion  48  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . The co-fastening screwed portion  48  has a co-fastening screw hole  48 A and includes a co-fastening engagement portion  48 B. 
     The co-fastening screw hole  48 A has a substantially circular shape in a side view and is recessed rightward from a left end face of the co-fastening screwed portion  48 . 
     The co-fastening engagement portion  48 B is disposed at a left end portion of the co-fastening screwed portion  48 . The co-fastening engagement portion  48 B has a substantially cylindrical shape extending leftward from a peripheral portion defining the co-fastening screw hole  48 A. 
     The second screwed portion  49  is disposed at an upper-front end portion of the left wall  37 . The second screwed portion  49  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . The second screwed portion  49  has a second screw hole  49 A and includes a second engagement portion  49 B. 
     The second screw hole  49 A has a substantially circular shape in a side view and is recessed rightward from a left end face of the second screwed portion  49 . 
     The second engagement portion  49 B is disposed at a left end portion of the second screwed portion  49 . The second engagement portion  49 B has a substantially cylindrical shape extending leftward from a peripheral portion defining the second screw hole  49 A. 
     As illustrated in  FIGS. 4 and 6 , the protruding portion  50  is disposed at a lower-rear end portion of the left wall  37 . The protruding portion  50  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . 
     As illustrated in  FIG. 4 , the idle gear support shaft  51  is disposed at an upper end portion of the substantial front-rear center of the left wall  37 . The idle gear support shaft  51  has a substantially columnar shape protruding leftward from the left surface of the left wall  37 . 
     The hooking portion  52  is disposed on the left wall  37  at a position between the cap positioning portion  46  and the co-fastening screwed portion  48  in the front-rear direction. The hooking portion  52  has a plate-like shape that is substantially U-like shaped in a bottom view. 
     As illustrated in  FIG. 3 , the right wall  38  is disposed at a right end portion of the frame  33 . Like the left wall  37 , the right wall  38  has a plate-like shape that is substantially rectangular in a side view and elongated in the front-rear direction. 
     The front wall  39  is bridged between a front end portion of the left wall  37  and a front end portion of the right wall  38 . The front wall  39  has a substantially plate-like shape extending in an up-down direction. 
     The bottom wall  40  is bridged between a lower end portion of the left wall  37  and a lower end portion of the right wall  38 . The bottom wall  40  extends rearward from a lower end portion of the front wall  39  while being curved. The bottom wall  40  has a substantially plate-like shape. 
     As illustrated in  FIG. 6 , the top wall  41  is disposed on an upper end portion of the left wall  37 , an upper end portion of the right wall  38 , and an upper end portion of the front wall  39 . The top wall  41  has a substantially plate-like shape extending in the left-right direction. The top wall  41  has a peripheral portion fixed to the upper end portion of the left wall  37 , the upper end portion of the right wall  38 , and the upper end portion of the front wall  39  by welding or the like. 
     (2) Drive Unit 
     As illustrated in  FIGS. 4 and 5 , the drive unit  34  includes a gear train  70  and a gear cover  71  as an example of a cover member. 
     (2-1) Gear Train 
     The gear train  70  is provided at the left wall  37 . The gear train  70  includes a developing coupling  74 , a developing gear  75  as an example of a developing roller drive gear, a supply gear  76  as an example of a supply roller drive gear, an idle gear  77  as an example of a second transmission gear, an agitator gear  78  as an example of an agitator drive gear, and a detection gear  79  as an example of a gear and as an example of a rotation body. 
     (2-1-1) Developing Coupling 
     The developing coupling  74  is rotatably supported at an upper-rear end portion of the left wall  37 . The developing coupling  74  has a substantially columnar shape extending in the left-right direction. The developing coupling  74  integrally includes a coupling gear portion  83  as an example of a first transmission gear and a coupling portion  84  as an example of a coupling. 
     The coupling gear portion  83  is disposed at a right end portion of the developing coupling  74 . The coupling gear portion  83  has a substantially disk-like shape having a thickness in the left-right direction. The coupling gear portion  83  has gear teeth formed on an entire outer peripheral surface thereof. 
     The coupling portion  84  has a substantially columnar shape protruding leftward from a left surface of the coupling gear portion  83 . The coupling portion  84  has an outer diameter smaller than an outer diameter of the coupling gear portion  83 . Further, the coupling portion  84  has a center axis aligned with a center axis of the coupling gear portion  83 . The coupling portion  84  includes a recessed portion  85  and a pair of projecting portions  86 . 
     The recessed portion  85  has a substantially circular shape in a side view. The recessed portion  85  is recessed rightward from a left end face of the coupling portion  84 . 
     The pair of projecting portions  86  each protrudes inward in a radial direction of the recessed portion  85  from an inner peripheral surface thereof in the radial direction. The pair of projecting portions  86  is disposed so as to face each other in the radial direction of the recessed portion  85 . The pair of projecting portions  86  each has a substantially rectangular columnar shape extending in the left-right direction. 
     (2-1-2) Developing Gear 
     The developing gear  75  is disposed diagonally below and rearward of the developing coupling  74 . The developing gear  75  has a substantially cylindrical shape extending in the left-right direction. The developing gear  75  has gear teeth formed on an entire outer peripheral surface thereof. The developing gear  75  is supported at a left end portion of the developing roller shaft  4 A so as not to be rotatable relative to the developing roller shaft  4 A. That is, the developing gear  75  is fixed to the developing roller shaft  4 A. The developing gear  75  is meshingly engaged with a lower-rear end portion of the coupling gear portion  83  of the developing coupling  74 . 
     (2-1-3) Supply Gear 
     The supply gear  76  is disposed below the developing coupling  74 . The supply gear  76  has a substantially columnar shape extending in the left-right direction. The supply gear  76  has gear teeth formed on an entire outer peripheral surface thereof. The supply gear  76  is supported at a left end portion of the supply roller shaft  5 A so as not to be rotatable relative to the supply roller shaft  5 A. That is, the supply gear  76  is fixed to the supply roller shaft  5 A. The supply gear  76  is meshingly engaged with a lower end portion of the coupling gear portion  83  of the developing coupling  74 . 
     (2-1-4) Idle Gear 
     As illustrated in  FIGS. 4 and 12B , the idle gear  77  integrally includes a large-diameter idle gear  77 A, an intermediate-diameter idle gear  77 B, and a small-diameter idle gear  77 C. 
     The large-diameter idle gear  77 A has a substantially annular shape having a thickness in the left-right direction. The large-diameter idle gear  77 A has gear teeth formed on an entire outer peripheral surface thereof. 
     The intermediate-diameter idle gear  77 B protrudes rightward from a right surface of the large-diameter idle gear  77 A. The intermediate-diameter idle gear  77 B has a substantially hollow cylindrical shape with a closed right end. The intermediate-diameter idle gear  77 B has an outer diameter smaller than an outer diameter of the large-diameter idle gear  77 A. The intermediate-diameter idle gear  77 B has an inner diameter substantially the same as an inner diameter of the large-diameter idle gear  77 A. 
     The small-diameter idle gear  77 C has a substantially hollow cylindrical shape extending rightward from a right surface of the intermediate-diameter idle gear  77 B. The small-diameter idle gear  77 C has an outer diameter smaller than the outer diameter of the intermediate-diameter idle gear  77 B. The small-diameter idle gear  77 C has an inner diameter slightly larger than an outer diameter of the idle gear support shaft  51  protruding from the left wall  37 . The small-diameter idle gear  77 C has gear teeth formed on an entire outer peripheral surface thereof. 
     In the idle gear  77 , a center axis of the large-diameter idle gear  77 A, a center axis of the intermediate-diameter idle gear  77 B, and a center axis of the small-diameter idle gear  77 C are aligned with each other. The center axis of the idle gear  77  will be referred to a rotation axis CL. 
     The idle gear  77  is rotatably supported at the left wall  37  with the small-diameter idle gear  77 C inserted into the idle gear support shaft  51 . As a result, the idle gear  7  is disposed frontward of the developing coupling  74 . The large-diameter idle gear  77 A of the idle gear  77  is meshingly engaged with a front end portion of the coupling gear portion  83  of the developing coupling  74 . 
     (2-1-5) Agitator Gear 
     As illustrated in  FIGS. 4 and 5 , the agitator gear  78  integrally includes a large-diameter agitator gear  78 A and a small-diameter agitator gear  78 B. 
     The large-diameter agitator gear  78 A has a substantially annular shape having a thickness in the left-right direction. The large-diameter agitator gear  78 A has gear teeth formed on an entire outer peripheral surface thereof. 
     The small-diameter agitator gear  78 B has a substantially hollow cylindrical shape protruding leftward from a left surface of the large-diameter agitator gear  78 A. The small-diameter agitator gear  78 B has an outer diameter smaller than an outer diameter of the large-diameter agitator gear  78 A. The small-diameter agitator gear  78 B has an inner diameter substantially the same as an inner diameter of the large-diameter agitator gear  78 A. The small-diameter agitator gear  78 B has gear teeth formed on an entire outer peripheral surface thereof. 
     The agitator gear  78  is supported at a left end portion of the agitator shaft  8 A so as not to be rotatable relative to the agitator shaft  8 A. That is, the agitator gear  78  is fixed to the agitator shaft  8 A. As a result, the agitator gear  78  is disposed diagonally below and frontward of the idle gear  77 . As illustrated in  FIG. 8 , the large-diameter agitator gear  78 A of the agitator gear  78  is meshingly engaged with a lower-front end portion of the small-diameter idle gear  77 C of the idle gear  77 . 
     (2-1-6) Detection Gear 
     As illustrated in  FIGS. 4 and 5 , the detection gear  79  includes a detection gear base plate  88 , a detection gear insertion portion  92 , a detection gear portion  89 , an abutting portion  90 , and a slide portion  91 . 
     The detection gear base plate  88  has a plate-like shape that is substantially circular in a side view. 
     The detection gear portion  89  has a substantially hollow cylindrical shape protruding rightward from a right surface of the detection gear base plate  88 . The detection gear portion  89  has gear teeth formed on a half portion of an outer peripheral surface thereof. That is, the detection gear portion  89  is a chipped gear (i.e. gear teeth are partially lacking). 
     The detection gear insertion portion  92  has a substantially hollow cylindrical shape extending in the left-right direction and having a center axis aligned with a center axis of the detection gear portion  89 . The detection gear insertion portion  92  penetrates the detection gear base plate  88  in the left-right direction. The detection gear insertion portion  92  has an inner diameter slightly larger than an outer diameter of the detection gear support shaft  60 . 
     The abutting portion  90  is disposed outward of the detection gear insertion portion  92  in a radial direction of the detection gear portion  89 . The abutting portion  90  protrudes leftward from a left surface of the detection gear base plate  88  and extends in a peripheral direction of the detection gear portion  89 . The abutting portion  90  has a substantially curved plate-like shape. 
     The slide portion  91  protrudes rightward from a right surface of the detection gear base plate  88  and extends in a radial direction of the detection gear base plate  88 . The slide portion  91  has a substantially plate-like shape. 
     The detection gear  79  is rotatably supported to the cap  55  with the detection gear support shaft  60  of the cap  55  inserted into the detection gear insertion portion  92 . That is, the detection gear  79  is supported at the left wall  37  through the cap  55 . As a result, the detection gear  79  is disposed frontward of the agitator gear  78 . The detection gear portion  89  of the detection gear  79  is adapted to meshingly engage the small-diameter agitator gear  78 B of the agitator gear  78 . 
     (2-2) Gear Cover 
     The gear cover  71  is assembled to the left wall  37  so as to cover the gear train  70  in its entirety. The gear cover  71  includes a first cover  95  and a second cover  96 . 
     (2-2-1) First Cover 
     As illustrated in  FIGS. 5 and 6 , the first cover  95  integrally includes a first portion  98  and a second portion  99 . 
     The first portion  98  constitutes an upper portion of the first cover  95 . The first portion  98  integrally includes a first base plate  101 , and a first peripheral wall  102  protruding rightward from a peripheral edge of the first base plate  101 . That is, the first portion  98  has a substantially box-like shape whose right end is opened and whose left end is closed. 
     The first portion  98  includes a coupling cover portion  105 , a developing roller cover portion  106 , and a first fixed portion  107 . 
     The coupling cover portion  105  is provided at a substantial up-down and front-rear center of the first base plate  101 . The coupling cover portion  105  has a drive input opening  109  and includes a cylindrical portion  110  as an example of a receiving portion. 
     The drive input opening  109  has a substantially circular shape in a side view. The drive input opening  109  penetrates the first base plate  101  in the left-right direction. 
     The cylindrical portion  110  has a substantially hollow cylindrical shape and extends leftward from a left surface of the first base plate  101  at a peripheral edge defining the drive input opening  109 . The cylindrical portion  110  has an inner diameter substantially the same as a diameter of the drive input opening  109 . Further, as illustrated in  FIG. 12B , the cylindrical portion  110  has a left-right length substantially the same as a left-right length of the coupling portion  84  of the developing coupling  74 . 
     As illustrated in  FIGS. 5 and 6 , a front end portion of the cylindrical portion  110  has a concave portion  112  extending in the left-right direction. Further, a peripheral surface of the cylindrical portion  110  has a first guide surface  111  at its front end. 
     The developing roller cover portion  106  is provided at a rear end portion of a substantial up-down center of the first base plate  101 . The developing roller cover portion  106  is disposed rearward of the coupling cover portion  105 . The developing roller cover portion  106  includes a collar portion  113 . 
     The collar portion  113  has a substantially hollow cylindrical shape with a closed left end and extends in the left-right direction. The collar portion  113  has an inner diameter slightly larger than an outer diameter of the developing roller shaft  4 A. 
     The first fixed portion  107  is provided at an upper-rear end portion of the first base plate  101 . The first fixed portion  107  is disposed above the developing roller cover portion  106 . The first fixed portion  107  is slightly recessed rightward from the developing roller cover portion  106 . The first fixed portion  107  has a first insertion hole  114 . 
     The first insertion hole  114  has a substantially circular shape in a side view. The first insertion hole  114  penetrates the first base plate  101  in the left-right direction. The first insertion hole  114  has an inner diameter slightly larger than an outer diameter of the first engagement portion  47 B. 
     The second portion  99  constitutes a lower portion of the first cover  95 . The second portion  99  is disposed below the first portion  98  with a stepped portion interposed therebetween. The second portion  99  integrally includes a second base plate  117  and a second peripheral wall  118  protruding rightward from a peripheral edge of the second base plate  117 . That is, the second portion  99  has a substantially box-like shape whose right end is opened and whose left end is closed. 
     The second portion  99  includes a supply roller cover portion  122 , an engaging portion  125 , a cutout portion  121 , and a first co-fastening portion  119 . 
     The supply roller cover portion  122  is provided at a substantial front-rear center of the second base plate  117 . The supply roller cover portion  122  is disposed below the coupling cover portion  105 . 
     The engaging portion  125  is provided at a rear end portion of the second base plate  117 . The engaging portion  125  is disposed below the developing roller cover portion  106  and rearward of the supply roller cover portion  122 . The engaging portion  125  has a substantially bottomed frame-like shape with a closed right end. As illustrated in  FIG. 11 , the engaging portion  125  has an engaging insertion hole  126 . 
     The engaging insertion hole  126  has a substantially circular in a side cross-sectional view. The engaging insertion hole  126  penetrates a right end portion of the engaging portion  125  in the left-right direction. 
     Further, as illustrated in  FIG. 5 , the engaging portion  125  includes a protruding wall  127 . 
     The protruding wall  127  protrudes rightward from a lower-right end portion and a rear-right end portion of the engaging portion  125 . The protruding wall  127  has a plate shape that is substantially L-like shaped in a side view. 
     As illustrated in  FIGS. 5 and 6 , the cutout portion  121  is formed by cutting a substantial front-rear center portion of a lower portion of the second peripheral wall  118  at a position rightward of the supply roller cover portion  122 . In other words, the cutout portion  121  is defined as a space rightward of the supply roller cover portion  122  and frontward of the engaging portion  125 . 
     The first co-fastening portion  119  is disposed frontward of the supply roller cover portion  122  and protrudes frontward from a front-right end portion of the second peripheral wall  118 . The first co-fastening portion  119  is recessed rightward from the coupling cover portion  105 . The first co-fastening portion  119  has a substantially box-like shape whose right end is opened and whose left end is closed. The first co-fastening portion  119  has a first co-fastening insertion hole  128 . 
     The first co-fastening insertion hole  128  has a substantially circular shape in a side view. The first co-fastening insertion hole  128  penetrates, in the left-right direction, an up-down and front-rear center of the left end of the first co-fastening portion  119 . The first co-fastening insertion hole  128  has an inner diameter larger than an outer diameter of the co-fastening engagement portion  48 B of the co-fastening screwed portion  48 . 
     (2-2-2) Second Cover 
     The second cover  96  is provided as a separate member from the first cover  95 , and thus separable from the first cover  95 . The second cover  96  integrally includes a third portion  131 , a fourth portion  132 , and a fifth portion  133 . 
     The third portion  131  constitutes an upper-rear portion of the second cover  96 . The third portion  131  integrally includes a third base plate  136 , and a third peripheral wall  137  protruding rightward from a peripheral edge of the third base plate  136 . That is, the third portion  131  has a substantially box-like shape whose right end is opened and whose left end is closed. 
     As illustrated in  FIGS. 9 and 12B , the third portion  131  includes an idle gear regulation portion  140  as an example of a support portion. 
     The idle gear regulation portion  140  has a substantially cylindrical shape protruding rightward from a right surface of the third base plate  136  at its substantial center. The idle gear regulation portion  140  has an outer diameter slightly smaller than the inner diameters of the large-diameter idle gear  77 A and the intermediate-diameter idle gear  77 B of the idle gear  77 , respectively. 
     A rear edge of the third base plate  136  of the third portion  131  is recessed frontward in a curved manner and is defined as a second guide surface  139 . 
     As illustrated in  FIGS. 5 and 6 , the fourth portion  132  constitutes a lower-rear portion of the second cover  96 . The fourth portion  132  continues from a lower-right edge of the third peripheral wall  137  of the third portion  131  and protrudes downward therefrom. The fourth portion  132  includes a fourth base plate  142 , and a fourth peripheral wall  143  protruding rightward from a lower edge of the fourth base plate  142 . That is, the fourth portion  132  has a plate-like shape that is substantially L-like shaped in a front cross-sectional view. 
     The fourth portion  132  includes a second co-fastening portion  145  and an engaging claw  146 . 
     The second co-fastening portion  145  is provided at a rear portion of the fourth base plate  142 . The second co-fastening portion  145  has a second co-fastening insertion hole  147 . 
     The second co-fastening insertion hole  147  has a substantially circular shape in a side view. The second co-fastening insertion hole  147  penetrates the fourth base plate  142  in the left-right direction. 
     As illustrated in  FIG. 9 , the engaging claw  146  protrudes rightward from a right end portion of the fourth peripheral wall  143  at its substantial front-rear center and is bent upward at a right end portion thereof. That is, the engaging claw  146  has a substantially hook-like shape. 
     As illustrated in  FIGS. 5 and 6 , the fifth portion  133  constitutes a front portion of the second cover  96 . The fifth portion  133  continues from front edges of the respective third and fourth portions  131  and  132 , and protrudes leftward therefrom. The fifth portion  133  includes a detection gear cover portion  150  and a second fixed portion  151 . 
     The detection gear cover portion  150  continues from the front edges of the respective third and fourth portions  131  and  132 , and protrudes leftward therefrom. The detection gear cover portion  150  has a substantially cylindrical shape with a closed left end. That is, the left end of the detection gear cover portion  150  is positioned leftward of the third and fourth portions  131  and  132 . The detection gear cover portion  150  has an abutting portion opening  154  and includes a detection gear regulation portion  155  (see  FIG. 9 ). 
     As illustrated in  FIG. 3 , the abutting portion opening  154  has a substantially C-like shape in a side view with a closed lower end so as to allow the abutting portion  90  of the detection gear  79  to protrude therethrough. The abutting portion opening  154  penetrates a left wall of the detection gear cover portion  150  in the left-right direction. 
     As illustrated in  FIGS. 9 and 12B , the detection gear regulation portion  155  has a substantially columnar shape protruding rightward from a right surface of the left wall of the detection gear cover portion  150  at a center thereof. The detection gear regulation portion  155  has an outer diameter slightly smaller than an inner diameter of the detection gear insertion portion  92 . 
     As illustrated in  FIGS. 5 and 6 , the second fixed portion  151  protrudes frontward from an upper-front end portion of the detection gear cover portion  150  at its right end. The second fixed portion  151  has a substantially box-like shape whose right end is opened and whose left end is closed. A left wall of the second fixed portion  151  is positioned rightward of the third base plate  136  and substantially flush with the fourth base plate  142 . The second fixed portion  151  has a second insertion hole  157 . 
     The second insertion hole  157  has a substantially circular shape in a side view. The second insertion hole  157  penetrates the left wall of the second fixed portion  151  in the left-right direction. The second insertion hole  157  has an inner surface slightly larger than an outer diameter of the second engagement portion  49 B. 
     4. Assembly and Removal of Gear Cover Relative to Frame 
     The gear cover  71  having the above-described configuration is assembled to the frame  33  by a user. 
     In order to assemble the gear cover  71  to the frame  33 , first, the first cover  95  of the gear cover  71  is assembled, from the left, to the left wall  37  to which the gear train  70  has been assembled, as illustrated in  FIG. 5 . More specifically, the first cover  95  is assembled, from the left, to the left wall  37  with the collar portion  113  receiving the developing roller shaft  4 A and with the cylindrical portion  110  receiving the coupling portion  84 . 
     Then, the first insertion hole  114  of the first cover  95  receives the first engagement portion  47 B of the left wall  37 , the first co-fastening insertion hole  128  of the first cover  95  receives the co-fastening engagement portion  48 B of the left wall  37  and, as illustrated in  FIG. 11 , the engaging insertion hole  126  of the engaging portion  125  of the first cover  95  receives the protruding portion  50  of the left wall  37 . 
     As a result, as illustrated in  FIG. 7 , a left end face of the supply gear  76  and a right surface of the supply roller cover portion  122  face each other in the left-right direction with a space therebetween. 
     Next, a first screw  67  as an example of a screw member is screwed into the first screw hole  47 A through the first insertion hole  114 . 
     Thus, the first cover  95  is assembled to the left wall  37  so as to cover the developing coupling  74 , the developing gear  75 , and the supply gear  76 . 
     Incidentally, a lower end portion of the supply gear  76  is exposed to outside through the cutout portion  121  of the supply roller cover portion  122 . Further, as described above, the coupling cover portion  105  covers a part of the idle gear  77 . 
     Subsequently, the second cover  96  is assembled, from the left, to the left wall  37 . 
     As illustrated in  FIGS. 10A and 10B , in this assembly of the second cover  96  to the left wall  37 , the second guide surface  139  of the second cover  96  is guided by the first guide surface  111  of the first cover  95  while slidingly contacting the first guide surface  111 . Then, the second insertion hole  157  of the second cover  96  receives the second engagement portion  49 B of the left wall  37 , and the second co-fastening insertion hole  147  of the second cover  96  receives the co-fastening engagement portion  48 B of the left wall  37 . Further, the engaging claw  146  is engaged with the hooking portion  52 . In this state, as illustrated in  FIG. 12B , the idle gear regulation portion  140  of the second cover  96  is inserted into the large-diameter idle gear  77 A of the idle gear  77 , and the detection gear regulation portion  155  of the second cover  96  is inserted into the detection gear insertion portion  92  of the detection gear  79 . 
     As a result, the third base plate  136  covers the idle gear  77  and the agitator gear  78 , and the detection gear cover portion  150  covers the detection gear  79 . Further, the idle gear  77  and the detection gear  79  are each rotatably supported to the left wall  37  without displacement of the rotation axis (center axis) thereof. 
     Then, as illustrated in  FIGS. 5 and 6 , a second screw  68  as an example of a screw member is screwed into the second screw hole  49 A through the second insertion hole  157 . 
     Further, as illustrated in  FIG. 7 , a co-fastening screw  69  as an example of a screw member is screwed into the co-fastening screw hole  48 A through the first co-fastening insertion hole  128  and the second co-fastening insertion hole  147 . That is, the first cover  95  and the second cover  96  are co-fastened by the common screw member. The second co-fastening portion  145  of the second cover  96  is disposed leftward of the first co-fastening portion  119  of the first cover  95 . 
     Thus, the second cover  96  is assembled to the left wall  37  so as to cover the idle gear  77 , the agitator gear  78 , the detection gear  79 , and the cap  55 . 
     In this manner, assembly of the developing cartridge  1  is completed. 
     To remove the gear cover  71  from the left wall  37 , the operation to assemble the gear cover  71  to the left wall  37  described above is performed in reverse. 
     More specifically, the second screw  68  is unscrewed from the second screw hole  49 A, and the co-fastening screw  69  is unscrewed from the co-fastening screw hole  48 A. This allows the second cover  96  to be separated from the first cover  95 , and only the second cover  96  is removed from the left wall  37 . 
     Then, the detection gear  79  is removed from the gear train  70 , and this allows the cap  55  to be removed from the toner filling port  44 . When the cap  55  is removed from the toner filing port  44 , the toner filling port  44  is exposed to an outside. Thus, toner can be supplied to the toner chamber  7  through the toner filing port  44 . 
     Further, as illustrated in  FIG. 13A , the front end portion of the cylindrical portion  110  is overlapped with a rear end portion of the idle gear  77  in a left side view. In other words, the first cover  95  covers a part of the idle gear  77 . This prevents the idle gear  77  from coming off from the left wall  37 . 
     To remove the idle gear  77  from the left wall  37 , the idle gear  77  is inclined frontward relative to the idle gear support shaft  51 , as illustrated in  FIG. 13B . Then, the overlap between the idle gear  77  and the first cover  95  is released as viewed in the left-right direction. That is, as viewed in the left-right direction, the idle gear  77  and the first cover  95  are no longer overlapped with each other, thus releasing the covering of the idle gear  77  by the first cover  95  is released. 
     This allows only the idle gear  77  to be removed from the left wall  37 . 
     Further, the removal of the idle gear  77  from the left wall  37  allows removal of the agitator gear  78  disposed inward in the left-right direction (i.e. rightward) of the idle gear  77 . 
     As a result, the idle gear  77  and the agitator gear  78  can be removed from the left wall  37  with the first cover  95  still assembled to the left wall  37  and can then be subjected to maintenance. 
     Subsequently, the first screw  67  is unscrewed from the first screw hole  47 A, and the first cover  95  is removed from the left wall  37 . Thus, the gear cover  71  is removed from the left wall  37 . 
     5. Attachment of Developing Cartridge to Main Casing and New Cartridge Detection Operation 
     In order to attach the developing cartridge  1  to the main casing  12 , the developing cartridge  1  is first attached to the drum cartridge  18  to constitute the process cartridge  13 . 
     As illustrated in  FIG. 11 , the drum cartridge  18  has left and right side walls at which collar receiving grooves  160  are formed respectively. The collar receiving groove  160  at the left side wall of the drum cartridge  18  receives the collar portion  113  of the gear cover  71  and fixes the collar portion  113  in position when the developing cartridge  1  is attached to the drum cartridge  18 . 
     The collar portion  113  rotatably receives the left end portion of the developing roller shaft  4 A. Thus, by attaching the developing cartridge  1  to the drum cartridge  18  with the collar portion  113  as a reference, the developing roller  4  is precisely fixed in position relative to the photosensitive drum  20 . 
     Subsequently, the drum cartridge  18  to which the developing cartridge  1  has been attached, that is, the process cartridge  13  is attached to the main casing  12 . 
     To attach the process cartridge  13  to the main casing  12 , as illustrated in  FIG. 2 , the front cover  17  is opened, and the process cartridge  13  is inserted, from the front, into the main casing  12  through the opening portion  16  and attached to the main casing  12 . 
     In this manner, the attachment of the process cartridge  13  to the main casing  12  is completed. 
     As illustrated in  FIG. 11 , when the developing cartridge  1  is a new cartridge, the abutting portion  90  of the detection gear  79  is positioned in the abutting portion opening  154  of the second cover  96  at a front end portion thereof. As illustrated in  FIG. 3 , a left edge of the abutting portion  90  is substantially flush with a left end face of the detection gear cover portion  150 . Further, as illustrated in  FIG. 8 , the detection gear portion  89  of the detection gear  79  is meshingly engaged with a front end portion of the small-diameter agitator gear  78 B of the agitator gear  78  at a downstream end portion thereof in the counterclockwise direction in a left side view. Further, the slide portion  91  of the detection gear  79  is positioned upstream of the guide portion  61  of the cap  55  in the counterclockwise direction in a left side view. That is, the guide portion  61  of the cap  55  is positioned upstream of the upstream inclined portion  61 A in the counterclockwise direction in a left side view. 
     When the printer  11  starts its warm-up operation, a drive input unit (not illustrated) of the main casing  12  inputs a drive force to the developing coupling  74 . 
     Upon receiving the drive force, the developing coupling  74  transmits the drive force to the idle gear  77  and the agitator gear  78  through the coupling gear portion  83 . Upon receiving the drive force, the idle gear  77  and the agitator gear  78  transmit the drive force to the detection gear portion  89  of the detection gear  79 . Then, the detection gear  79  rotates in the counterclockwise direction in a left side view, as illustrated in  FIG. 11 . 
     At this time, the slide portion  91  of the detection gear  79  is slidingly moved along the left end surface of the guide portion  61  in the counterclockwise direction in a left side view. Accordingly, the slide portion  91  is gradually moved leftward along the upstream inclined portion  61 A of the guide portion  61 , and the abutting portion  90  of the detection gear  79  protrudes leftward further than the left end face of the detection gear cover portion  150  through the abutting portion opening  154 . 
     Then, in a state where the abutting portion  90  protrudes leftward further than the abutting portion opening  154 , the detection gear  79  rotates in the counterclockwise direction in a left side view while the slide portion  91  is moved along the intermediate flat portion  61 B. Then, the abutting portion  90  abuts against an actuator  163  of the main casing  12 . As a result, the actuator  163  detects a condition of the developing cartridge  1 . 
     The slide portion  91  urges, with an urging force from an urging spring (not illustrated), the detection gear  79  rightward along a downstream end of the guide portion  61  in the counterclockwise direction in a left side view, that is, along the downstream inclined portion  61 C. 
     Then, the slide portion  91  abuts against one of the pair of stoppers  62  (i.e. upper stopper  62 ) from a front side thereof to stop the rotation of the detection gear  79 . Further, the meshing engagement of the detection gear portion  89  of the detection gear  79  with the small-diameter agitator gear  78 B of the agitator gear  78  is released. 
     As a result, the left edge of the abutting portion  90  becomes substantially flush with the left end face of the detection gear cover portion  150  once again. 
     When the developing cartridge  1  is a used cartridge, the abutting portion  90  of the detection gear  79  is positioned in the abutting portion opening  154  of the second cover  96  at a rear end portion thereof and the left edge of the abutting portion  90  is substantially flush with the left end face of the detection gear cover portion  150 . Further, the detection gear portion  89  of the detection gear  79  is not engaged with the small-diameter agitator gear  78 B of the agitator gear  78 . Further, the slide portion  91  of the detection gear  79  is positioned downstream of the guide portion  61  of the cap  55  in the counterclockwise direction in a left side view. Thus, when the printer  11  starts its warm-up operation, the detection gear  79  does not start rotating and maintains its posture. 
     As described above, the posture of the detection gear  79  can be changed depending on whether the developing cartridge  1  is a new cartridge or not. 
     6. Operations and Effects 
     (1) According to the developing cartridge  1  described above, as illustrated in  FIGS. 4 and 5 , the first cover  95  covers the coupling gear portion  83  of the developing coupling  74 , the second cover  96  covers the cap  55 , and the first and second covers  95  and  96  are configured to be separable from each other. 
     Thus, the second cover  96  can be separated from the first cover  95  and then removed from the left wall  37  in a state where the first cover  95  has been assembled to the left wall  37 . Accordingly, the toner filling port  44  can be exposed to an outside for toner supply with the coupling gear portion  83  of the developing coupling  74  being covered with the first cover  95 . 
     As a result, removal of only the second cover  96  from the left wall  37  allows supply of the toner. At the same time, the first cover  95  prevents damage to the coupling gear  83  of the developing coupling  74  to which the drive force is inputted. 
     This allows the toner to be supplied through the toner filling port  44  while protecting the coupling gear portion  83  of the developing coupling  74 , thereby increasing reliability of the developing cartridge  1 . 
     (2) Further, according to the developing cartridge  1 , as illustrated in  FIG. 6 , the first cover  95  covers the coupling gear portion  83 , and the coupling portion  84  integrally formed with the coupling gear portion  83 . The coupling portion  84  is positioned on the most upstream side among the gears of the gear train  70  for transmission of the drive force, and is the most important functional component for image formation among the gears of the gear train  70 . Thus, it is important to prevent the coupling portion  84  from being damaged. 
     Thus, the coupling portion  84  is covered and protected by the first cover  95 . This allows the drive force from the drive input unit (not illustrated) of the main casing  12  to be inputted reliably to the coupling portion  84 , thereby allowing the drive force inputted to the coupling portion  84  to be transmitted reliably to the agitator  8  by the coupling gear portion  83 . 
     (3) Further, according to the developing cartridge  1 , as illustrated in  FIG. 6 , the second cover  96  covers the agitator gear  78 . 
     Thus, the second cover  96  can be separated from the first cover  95  and then removed from the left wall  37  to allow a covered state of the agitator gear  78  to be released. 
     This facilitates maintenance of the agitator gear  78  with the coupling gear portion  83  of the developing coupling  74  being covered by the first cover  95 . 
     (4) Further, according to the developing cartridge  1 , as illustrated in  FIGS. 13A and 13B , even when the second cover  96  is removed from the left wall  37  for supply of the toner through the toner filling port  44 , the covered state of the idle gear  77  by the first cover  95  is not released unless the idle gear  77  is inclined in a direction intersecting a direction in which the rotation axis CL extends, that is, frontward. 
     Thus, the toner can be supplied while preventing the idle gear  77  from coming off from the left wall  37 . 
     (5) Further, according to the developing cartridge  1 , as illustrated in  FIGS. 12A and 12B , the frontward inclination of the idle gear  77  is regulated by the idle gear regulation portion  140 , thereby preventing the idle gear  77  from coming off from the left wall  37 . 
     This allows the drive force inputted from the drive force input unit (not illustrated) of the main casing  12  to the coupling gear portion  83  to be transmitted reliably to the agitator gear  78  through the idle gear  77 . 
     (6) Further, according to the developing cartridge  1 , as illustrated in  FIGS. 13A and 13B , the first cover  95  covers a part of the idle gear  77  by contacting the idle gear  77  from the left. 
     Thus, even in a state where the second cover  96  is removed from the left wall  37  and only the first cover  95  is assembled to the left wall  37 , the idle gear  77  can be prevented from coming off from the left wall  37 . 
     (7) Further, according to the developing cartridge  1 , as illustrated in  FIGS. 12A and 12B , the idle gear  77  is sandwiched between the agitator gear  78  and the first cover  95  so as to contact the agitator gear  78  and the first cover  95 . 
     Thus, even in a state where the second cover  96  is removed, the idle gear  77  is prevented from coming off from the left wall  37  by the first cover  95 , and the agitator gear  78  is prevented from coming off from the left wall  37  by the idle gear  77 . 
     (8) Further, according to the developing cartridge  1 , as illustrated in  FIG. 5 , the developing gear  75  is covered with the first cover  95 . 
     Thus, even in a state where the second cover  96  is separated from the first cover  95  and then removed from the left wall  37  for supply of the toner, the developing gear  75  can be covered by the first cover  95 . 
     (9) Further, according to the developing cartridge  1 , the first cover  95  is fixed in position relative to the left wall  37  with the developing roller shaft  4 A as a reference shaft. Further, as illustrated in  FIG. 11 , the collar receiving groove  160  formed in the drum cartridge  18  guides the collar portion  113  of the first cover  95  when attaching the developing cartridge  1  to the drum cartridge  18 . Hence, the developing cartridge  1  can be fixed in position relative to the drum cartridge  18  with the developing roller shaft  4 A as a reference shaft. 
     This can bring the developing roller  4  into contact with the photosensitive drum  20  precisely. 
     (10) Further, according to the developing cartridge  1 , as illustrated in  FIG. 4 , the detection gear  79  is positioned so as to overlap with the cap  55  as viewed in the left-right direction. Thus, the members constituting the developing cartridge  1  can be gathered into one place. 
     This allows reduction in size of the developing cartridge  1 . 
     (11) Further, according to the developing cartridge  1 , as illustrated in  FIG. 11 , the detection gear  79  configured to change its posture depending on whether the developing cartridge  1  is a new cartridge or a used cartridge is positioned so as to overlap with the cap  55  as viewed in the left-right direction. Thus, the members constituting the developing cartridge  1  can be gathered into one place. 
     This allows determination of whether the developing cartridge  1  is a new cartridge or a used cartridge while achieving reduction in size of the developing cartridge  1 . 
     (12) Further, according to the developing cartridge  1 , as illustrated in  FIG. 5 , the first cover  95  and the second cover  96  can be fixed together to the left wall  37  by screwing the common co-fastening screw  69  into the co-fastening screwed portion  48  of the left wall  37 , thereby improving assembly precision and reducing the number of components. 
     (13) Further, according to the developing cartridge  1 , as illustrated in  FIG. 5 , even when the first cover  95  and the second cover  96  are fixed together in an overlapped manner to the left wall  37  by means of the common co-fastening screw  69 , the second cover  96  can be removed from the left wall  37  by unscrewing the co-fastening screw  69  with the first cover  95  being assembled to the left wall  37 . 
     Thus, with the first cover  95  being assembled to the left wall  37 , the second cover  96  can be removed from the left wall  37  for supply of the toner through the toner filling port  44 . 
     As a result, the toner can be supplied while reliably covering the coupling gear portion  83  of the developing coupling  74  with the first cover  95 . 
     (14) Further, according to the developing cartridge  1 , as illustrated in  FIGS. 10A and 10B , the second cover  96  can be assembled to the left wall  37  with the second guide surface  139  of the second cover  96  fixed in position relative to the first guide surface  111  of the cylindrical portion  110  and guided by the first guide surface  111  of the cylindrical portion  110 . 
     Thus, the second cover  96  can be assembled to the left wall  37  while being fixed in position precisely relative to the first cover  95 . 
     (15) Further, according to the developing cartridge  1 , as illustrated in  FIG. 5 , the supply gear  76  is covered with the first cover  95 . 
     Thus, even when the second cover  96  is separated from the first cover  95  and then removed from the left wall  37  for supply of the toner, the supply gear  76  can be covered with the first cover  95 . 
     In addition, as illustrated in  FIG. 3 , the first cover  95  has the cutout portion  121  so that the lower end portion of the supply gear  76  is exposed to an outside. 
     This allows reduction in size of the first cover  95 , which in turn can achieve further reduction in size of the developing cartridge  1 . 
     7. Modifications 
     Various modifications are conceivable. In the following description, only parts differing from those of the embodiment will be described in detail. 
     For example, as illustrated in  FIG. 14 , the protruding portion  50  of the left wall  37  that has been inserted through the engaging insertion hole  126  formed in the engaging portion  125  of the first cover  95  may be force-fitted (such as caulking accompanied by plastic deformation) at its left end portion. 
     According to such a modification to the developing cartridge  1 , the force-fitting of the protruding portion  50  of the left wall  37  relative to the first cover  95  can prevent the first cover  95  from unintentionally coming off from the frame  33  at the time of removal of the second cover  96 . 
     As a result, the first cover  95  and the second cover  96  can be efficiently assembled to and removed from the left wall  37 . 
     In place of the force-fitting, the protruding portion  50  may be adhered to the engaging portion  125  by an adhesive agent, etc., to assemble the first cover  95  to the frame  33 . 
     Although the process cartridge  13  according to the above embodiment is a separate type in which the developing cartridge  1  and the drum cartridge  18  are separable from each other, the process cartridge  13  may be configured as an integrated type that integrally includes the developing cartridge  1  and the drum cartridge  18 . 
     Further, the cartridge according to the present invention may be configured as a toner cartridge in which the developing roller  4  is not provided but the agitator  8  is provided. 
     In place of the cap  55  as an example of a closing member, a sealing member or a shutter may be available. 
     In place of the detection gear  79 , a rotation body such as a drive transmission roller around which a belt is stretched and that is rotated by friction may be available. 
     While the present invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the present invention.