Patent Publication Number: US-9417557-B2

Title: Developing cartridge including housing having opening for filling housing with developer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2014-170209 filed on Aug. 25, 2014, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Aspects of the present invention relates to a developing cartridge which is attached to an image forming apparatus employing an electrophotographic system. 
     BACKGROUND 
     In related art, a process cartridge which is attached to an image forming apparatus employing an electrophotographic system has been known. The process cartridge is attached to the image forming apparatus in a state where an inside thereof is filled with toner. 
     As such a process cartridge, a process cartridge including a cartridge frame in which a toner developing frame and a cleaning frame are coupled is known. This process cartridge includes developing means, such as a photosensitive drum and a developing roller, in the cartridge frame. In the cartridge frame, the toner developing frame includes a toner containing section and a toner filling port. In the process cartridge, the toner containing section is filled with toner through the toner filling port. The process cartridge in this state is attached to the image forming apparatus. When an image forming operation is started, the toner in the toner containing section is supplied to the developing roller through a toner supply opening and the toner moves from the developing roller to the photosensitive drum. 
     In the above-described process cartridge, the toner containing section is filled with toner in a state where the toner supply opening is sealed with a toner sealing member. Accordingly, in an unused process cartridge, there is a possibility that only the toner containing section is filled with toner and toner is not uniformly provided to the vicinity of the developing roller. 
     When such an unused process cartridge is attached to an image forming apparatus, a certain time is required until the developing roller carries the toner after the image forming operation is started. As a result, image formation failure may occur just after the image forming operation is started. 
     SUMMARY 
     Therefore, an object of an aspect of the invention is to provide a developing cartridge which can smoothly form an image even just after an unused developing cartridge is attached to an image forming apparatus. 
     According to an aspect of the invention, there is provided a developing cartridge including: a housing; a developing roller rotatable around a rotation axis extending in a first direction; a developing gear supported by an end portion of the developing roller; and a driving force receiving member rotatable around a rotation axis extending in the first direction by receiving a driving force from an image forming apparatus body and including a gear portion engaging with the developing gear, wherein the housing has an opening for filling the housing with developer, and wherein at least a part of the driving force receiving member overlaps the opening when viewed in the first direction. 
     According to another aspect of the invention, there is provided a developing cartridge including: a housing configured to contain developer therein and including a first side wall and a second side wall which are located with a gap therebetween; a developing roller located between the first side wall and the second side wall and configured to rotate around a rotation axis extending in a first direction; a supply roller located between the first side wall and the second side wall and configured to supply developer to the developing roller by rotating around a rotation axis extending in the first direction; and a driving force receiving member located on an opposite side of the second side wall with respect to the first side wall, configured to rotate around a rotation axis extending in the first direction, and configured to rotate the developing roller and the supply roller by receiving a driving force from an image forming apparatus body, wherein the first side wall has an opening for filling the housing with developer, and wherein, when viewed in the first direction, at least a part of the opening is located at the developing roller side than a tangent line passing through one edge point among two edge points of the driving force receiving member, the two edge points being edge points at which straight lines, which are parallel to a straight line orthogonal to both the rotation axis of the supply roller and the rotation axis of the driving force receiving member, respectively serve as tangent lines of the driving force receiving member, and the one edge point being located farthest from the developing roller among the two edge points. 
     According to another aspect of the invention, there is provided a developing cartridge including: a housing including, a first side wall and a second side wall which are located with a gap therebetween, a developer containing chamber configured to contain developer therein, and a development chamber communicating with the developer containing chamber and accommodating therein a developing roller which is configured to rotate around a rotation axis extending in a first direction in which the first side wall and the second side wall face each other; and a driving force receiving member located on an opposite side of the second side wall with respect to the first side wall, configured to rotate around a rotation axis extending in the first direction, and configured to rotate the developing roller by receiving a driving force from an image forming apparatus body, wherein the first side wall has an opening for filling the housing with developer, and wherein at least a part of the opening is located at the developing roller side than a straight line extending along a third direction and passing through one edge point among two edge points of the driving force receiving member, the developer containing chamber and the development chamber being arranged in a second direction, the two edge points being edge points of the driving force receiving member in the second direction when the driving force receiving member is projected in the third direction perpendicular to both the first direction and the second direction, and the one edge point being located farthest from the developing roller among the two edge points. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an embodiment of a developing cartridge according to the invention; 
         FIG. 2  is a cross-sectional view illustrating a central part of a printer including the developing cartridge illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating the developing cartridge illustrated in  FIG. 1  when viewed from the upper-left side; 
         FIG. 4  is an exploded perspective view illustrating a left end portion of the developing cartridge illustrated in  FIG. 1  when viewed from the upper-left side; 
         FIG. 5A  is a perspective view illustrating the left end portion of the developing cartridge illustrated in  FIG. 1  when viewed from the lower-left side and illustrating a state where a gear cover is detached therefrom; 
         FIG. 5B  is a cross-sectional view of the developing cartridge taken along line A-A in  FIG. 5A ; 
         FIG. 6A  is a side view illustrating the developing cartridge illustrated in  FIG. 1  and illustrating a tangent line passing through an edge point of a developing coupling; 
         FIG. 6B  is a side view illustrating the developing cartridge illustrated in  FIG. 1  and illustrating a tangent line passing through a second edge point of the developing coupling; 
         FIG. 6C  is a side view illustrating the developing cartridge illustrated in  FIG. 1  and illustrating a straight line passing through a third edge point of the developing coupling; 
         FIG. 7A  is a cross-sectional view illustrating the left end portion of the developing cartridge illustrated in  FIG. 1  and illustrating a state where the developing coupling and the gear cover are detached therefrom; 
         FIG. 7B  is a cross-sectional view illustrating a state where a cap is attached to the left end portion of the developing cartridge illustrated in  FIG. 7A ; 
         FIG. 8A  is a perspective view illustrating a developing cartridge according to a second embodiment of the invention and illustrating a left end portion of the developing cartridge when viewed from the upper-left side; 
         FIG. 8B  is an exploded perspective view illustrating the left end portion of the developing cartridge illustrated in  FIG. 8A  when viewed from the upper-left side; 
         FIG. 9  is a perspective view illustrating a developing cartridge according to a third embodiment of the invention and is an exploded perspective view illustrating a left end portion of the developing cartridge when viewed from the upper-left side; 
         FIG. 10A  is a side view illustrating the developing cartridge illustrated in  FIG. 9 ; and 
         FIG. 10B  is a side view illustrating the developing cartridge illustrated in  FIG. 9  and illustrating a state where a support shaft unit, a gear cover, and a developing coupling are detached therefrom. 
     
    
    
     DETAILED DESCRIPTION 
     1. Summary of Developing Cartridge 
     As illustrated in  FIG. 1 , a developing cartridge  1  includes a developing roller  2 , a supply roller  3 , a thickness regulating blade  4 , and an agitator  6 . As will be described later, the inside of the developing cartridge  1  is partitioned into a toner containing chamber  5  serving as an example of the developer containing chamber and a development chamber  7 . 
     In the following description, directions of the developing cartridge  1  are mentioned based on a state where the developing cartridge  1  is horizontally placed. Specifically, the directions are based on arrows in  FIG. 1 . That is, the upper side in  FIG. 1  is defined as an upper side and the lower side in  FIG. 1  is defined as a lower side. The right side in  FIG. 1  is defined as a front side and the left side in  FIG. 1  is defined as a rear side. The right-left direction is based on a state where the developing cartridge  1  is viewed from the front side. That is, the front side of  FIG. 1  is defined as a left side and the rear side in  FIG. 1  is defined as a right side. The right-left direction is an example of the first direction, the front-rear direction is an example of the second direction, and the upper-lower direction is an example of the third direction. 
     The developing roller  2  is rotatably supported by a rear end portion of the developing cartridge  1 . The developing roller  2  has a substantially cylindrical shape extending in the right-left direction. Specifically, the developing roller  2  can rotate around a rotation axis L 1  extending in the right-left direction. 
     The supply roller  3  is rotatably supported by the developing cartridge  1  on the lower-front side of the developing roller  2 . The supply roller  3  has a substantially cylindrical shape extending in the right-left direction. Specifically, the supply roller  3  can rotate around a rotation axis L 2  extending in the right-left direction. The supply roller  3  is in contact with the lower-front end portion of the developing roller  2 . 
     The thickness regulating blade  4  is located on the upper-front side of the developing roller  2 . The thickness regulating blade  4  is in contact with the front end portion of the developing roller  2 . 
     The agitator  6  is located on the front side of the developing roller  2  and the supply roller  3  with a gap therebetween. The agitator  6  is rotatably supported by the central portion of the developing cartridge  1  and extends in the right-left direction. Specifically, the agitator  6  can rotate around a rotation axis L 3  extending in the right-left direction. 
     The toner containing chamber  5  is located on the front side of the supply roller  3  and the thickness regulating blade  4 . The toner containing chamber  5  is configured to contain therein toner serving as an example of the developer. The agitator  6  is located in the toner containing chamber  5 . The development chamber  7  is located on the rear side of the toner containing chamber  5 . 
     2. Use Mode of Developing Cartridge 
     As illustrated in  FIG. 2 , a printer  11  is a direct tandem type color printer which is placed horizontally. 
     In the following description, the upper-lower direction of the printer  11  is mentioned based on a state where the printer  11  is horizontally placed. Specifically, the upper-lower direction is based on the arrows illustrated in  FIG. 2 . That is, the upper side in  FIG. 2  is defined as an upper side and the lower side in  FIG. 2  is defined as a lower side. The right side in  FIG. 2  is defined as a front side and the left side in  FIG. 2  is defined as a rear side. The right-left direction of the printer  11  is based on a state where the printer  11  is viewed from the front side. That is, the front side in  FIG. 2  is defined as a left side and the rear side in  FIG. 2  is defined as a right side. 
     The printer  11  includes a body casing  12 , a plurality of process cartridges  13 , a plurality of LED units  14 , a transfer unit  15 , and a fixing unit  16 . 
     The body casing  12  has a substantially box shape. The body casing  12  includes an opening  17 , a top cover  18 , and a sheet feeding tray  19 . 
     The opening  17  is located at the top end portion of the body casing  12 . The opening  17  allows the inside and the outside of the body casing  12  to communicate with each other in the vertical direction so as to allow the process cartridges  13  to pass therethrough. 
     The top cover  18  is located at the top end portion of the body casing  12 . The top cover  18  has a substantially plate shape extending in the front-rear direction. The rear end portion of the top cover  18  is swingably supported by a back wall of the body casing  12 . The top cover  18  opens and closes the opening  17  by vertically swinging with the rear end portion thereof as a fulcrum as indicated by a virtual line. The top cover  18  includes a sheet discharging tray  20 . 
     The sheet discharging tray  20  is located substantially at the center in the front-rear direction of the top cover  18 . The sheet discharging tray  20  is depressed downward from the top surface of the top cover  18  so as to place a sheet P thereon. 
     The sheet feeding tray  19  is located at the bottom of the body casing  12 . The sheet feeding tray  19  is configured to place a sheet P thereon. 
     The plurality of process cartridges  13  correspond to yellow, magenta, cyan, and black, respectively, and are arranged in parallel to each other with a gap therebetween in the front-rear direction in the body casing  12 . The respective process cartridges  13  can be attached to or detached from the body casing  12  through the opening  17 . Each of the process cartridges  13  includes a drum cartridge  21  and the above-mentioned developing cartridge  1 . 
     The drum cartridge  21  includes a photosensitive drum  22  and a scorotron charger  23 . 
     The photosensitive drum  22  has a substantially cylindrical shape extending in the right-left direction. The photosensitive drum  22  is rotatably supported by the lower-rear end portion of the drum cartridge  21 . 
     The scorotron charger  23  is located to face the upper-rear side of the photosensitive drum  22  with a gap therebetween. 
     The developing cartridge  1  is attached to the drum cartridge  21  such that the rear end portion thereof faces the lower-rear side on the upper-front side of the photosensitive drum  22 . The developing roller  2  of the developing cartridge  1  is in contact with the upper-front end portion of the photosensitive drum  22 . The developing cartridge  1  is attached to or detached from the drum cartridge  21 . 
     The respective LED units  14  are supported by the top cover  18  so as to be located above the photosensitive drums  22  of the corresponding processes cartridges  13 . 
     The transfer unit  15  is located below the process cartridges  13 . The transfer unit  15  includes a driving roller  24 , a driven roller  25 , a transport belt  26 , and a plurality of transfer rollers  27 . 
     The driving roller  24  is rotatably supported by the rear end portion of the transfer unit  15 . 
     The driven roller  25  is rotatably supported by the front end portion of the transfer unit  15 . 
     The transport belt  26  is suspended on the driving roller  24  and the driven roller  25 . The upper part of the transport belt  26  is in contact with the lower end portions of the photosensitive drums  22 . The transport belt  26  circumferentially moves such that the upper part thereof moves from the front side to the rear side by driving of the driving roller  24  and the driven roller  25  being driven. 
     The transfer rollers  27  are located below the photosensitive drums  22 , respectively. The transfer rollers  27  are in contact with the bottom surface of the upper part of the transport belt  26 . 
     The fixing unit  16  is located on the rear side of the transfer unit  15 . The fixing unit  16  includes a heating roller  28  and a pressure roller  29  in contact with the lower-rear end portion of the heating roller  28 . 
     When the printer  11  starts an image forming operation, the scorotron chargers  23  uniformly charge the surfaces of the photosensitive drums  22 . Thereafter, the LED units  14  expose the surfaces of the photosensitive drums  22 . Accordingly, an electrostatic latent image based on image data is formed on the surfaces of the photosensitive drums  22 . 
     The agitator  6  agitates toner in the toner containing chamber  5  and carries the toner to the development chamber  7 . The supply roller  3  supplies the toner in the development chamber  7  to the developing roller  2 . At this time, the toner is frictionally charged to a positive polarity between the developing roller  2  and the supply roller  3  and is carried on the developing roller  2 . 
     The developing roller  2  supplies the carried toner to the electrostatic latent image on the surface of the corresponding photosensitive drum  22 . Accordingly, a toner image is carried on the surface of the photosensitive drum  22 . 
     A sheet P is transported to the upper-front side from the sheet feeding tray  19  is U-turned to the upper-rear side, and is fed between the foremost photosensitive drum  22  and the transport belt  26  at a predetermined timing one by one, by rotations of various rollers. Thereafter, the sheet P is transported from front to rear by the transport belt  26 . The toner images on the photosensitive drums  22  are transferred onto the sheet P when the sheet P passes between the photosensitive drums  22  and the transfer rollers  27 . 
     Thereafter, the sheet P is heated and pressurized when the sheet P passes between the heating roller  28  and the pressure roller  29 . At this time, the toner image on the sheet P is thermally fixed to the sheet P. Thereafter, the sheet P is discharged to the sheet discharging tray  20 . 
     3. Details of Developing Cartridge 
     As illustrated in  FIGS. 1 and 3 , the developing cartridge  1  includes a developing frame  31  serving as an example of the housing and a drive unit  41 . 
     (1) Developing Frame 
     The developing frame  31  has a substantially rectangular tubular shape which extends in the right-left direction and of which the rear end portion is opened. The developing frame  31  includes a pair of side walls  32 , a bottom wall  33 , a front wall  34 , and a top wall  35 . 
     The side walls  32  are respectively located at both end portions in the right-left direction of the developing frame  31 . Each of the side walls  32  has a substantially rectangular plate shape when viewed from the side surface extending in the front-rear direction. The side walls  32  respectively rotatably support both end portions in the right-left direction of the developing roller  2 , both end portions in the right-left direction of the supply roller  3 , and both end portions in the right-left direction of the agitator  6  at the rear end portions thereof. Among the side walls  32 , the side wall located on the left side is a left side wall  32 A serving as an example of the first side wall and the side wall located on the right side is a right side wall  32 B serving as an example of the second side wall. 
     The bottom wall  33  is located at the lower end portion of the developing frame  31 . Both end portions in the right-left direction of the bottom wall  33  are connected to the lower end portions of the side walls  32 . The bottom wall  33  includes a first bottom wall portion  33 A, a second bottom wall portion  33 B, and a third bottom wall portion  33 C. 
     The first bottom wall portion  33 A is located in a front half portion of the bottom wall  33 . The first bottom wall portion  33 A has a substantially V shape in a cross-sectional view of which substantially the center in the front-rear direction is concave downward. 
     The second bottom wall portion  33 B is located on the rear side of the first bottom wall portion  33 A. The second bottom wall portion  33 B has a substantially arc shape in a cross-sectional view. The second bottom wall portion  33 B is connected to the rear end portion of the first bottom wall portion  33 A and extends rearward so as to be curved along the outer circumferential surface of the supply roller  3 . 
     The junction of the first bottom wall portion  33 A and the second bottom wall portion  33 B is a protruding portion  33 D. The protruding portion  33 D has a substantially triangular shape in a cross-sectional view having a vertex on the upper side. The vertex of the protruding portion  33 D is located at the center in the upper-lower direction and at the center in the front-rear direction in the developing cartridge  1 . 
     The third bottom wall portion  33 C is located on the rear side of the second bottom wall portion  33 B. The third bottom wall portion  33 C has a substantially L shape in a cross-sectional view. The third bottom wall portion  33 C is connected to the rear end portion of the second bottom wall portion  33 B, extends rearward on the lower side of the developing roller  2 , and then extends downward. 
     The front wall  34  is located at the front end portion of the developing frame  31 . The front wall  34  has a substantially plate shape connected to the front end portion of the bottom wall  33  and extending upwardly. Both end portions in the right-left direction of the front wall  34  are respectively connected to the front end portions of the pair of side walls  32 . The front wall  34  includes a grip  42 . 
     The grip  42  has a substantially plate shape protruding forward from the center in the right-left direction of the top end portion of the front wall  34  and extending in the right-left direction. 
     The top wall  35  is located at the upper end portion of the developing frame  31 . The top wall  35  has a substantially plate shape extending in the right-left direction. The front end portion of the top wall  35  is connected to the upper end portion of the front wall  34 . Both end portions in the right-left direction of the top wall  35  are respectively connected to the upper end portions of the pair of side walls  32 . The top wall  35  includes a first top wall portion  35 A and a second top wall portion  35 B. 
     The first top wall portion  35 A is located in the central portion of the top wall  35  and in a front half portion thereof. The first top wall portion  35 A extends rearward from the front side, is curved such that the upper-rear portion thereof swells, and extends rearward. 
     The second top wall portion  35 B is connected to the rear end portion of the first top wall portion  35 A and extends rearward. The second top wall portion  35 B supports the thickness regulating blade  4 . 
     The junction of the first top wall portion  35 A and the second top wall portion  35 B is a junction  35 C. The junction  35 C is located on the upper part and in the central portion in the front-rear direction in the developing cartridge  1 . 
     The space between the protruding portion  33 D and the junction  35 C is a communication port  36 . In the developing cartridge  1 , the front part of the communication port  36  is defined as the toner containing chamber  5  and the rear part of the communication port  36  is defined as the development chamber  7 . That is, the toner containing chamber  5  and the development chamber  7  communicate with each other via the communication port  36  and are arranged in the front-rear direction. In the developing cartridge  1 , the developing roller  2  and the agitator  6  are arranged in the front-rear direction and, specifically, a straight line L 11  connecting the rotation axis L 1  of the developing roller  2  and the rotation axis L 3  of the agitator  6  extends along the front-rear direction. 
     (2) Configuration of Driving Unit 
     (2-1) Left Side Wall 
     As illustrated in  FIG. 4 , the left end portion of the developing roller  2 , the left end portion of the supply roller  3 , and the left end portion of the agitator  6  protrude leftward from the left side wall  32 A of the developing cartridge  1 . The left side wall  32 A includes a filling tube  45 . 
     The filling tube  45  is located at the rear end portion of the left side wall  32 A and is located on the front side of the left end portion of the developing roller  2  and the left end portion of the supply roller  3  exposed from the left side wall  32 A. The filling tube  45  has a substantially cylindrical shape extending in the right-left direction and protrudes outward in the right-left direction from both surfaces of the left side wall  32 A. The opening portion in the filling tube  45  is a filling port  46  serving as an example of the opening. 
     The filling port  46  has a substantially cylindrical shape in a side view and penetrates the filling tube  45  in the right-left direction. That is, the filling port  46  penetrates the left side wall  32 A in the right-left direction and communicates with the development chamber  7  of the developing cartridge  1 . As illustrated in  FIG. 5B , the left end portion of the filling port  46  is closed by a cap  47  serving as an example of the closing member. 
     (2-2) Driving Unit 
     As illustrated in  FIGS. 3 and 4 , the driving unit  41  is located on the left side of the left side wall  32 A and includes a support shaft unit  51 , a gear train  52 , and a gear cover  53 . 
     (2-2-1) Support Shaft Unit 
     As illustrated in  FIGS. 4 and 5B , the support shaft unit  51  is attached to the rear portion of the left surface of the left side wall  32 A. The support shaft unit  51  includes a base  54 , a coupling support shaft  55  serving as an example of the support shaft, and an idle gear support shaft  56 . 
     The base  54  has a substantially rectangular plate shape in a side view and covers the rear portion of the left surface of the left side wall  32 A. The base  54  includes a first insertion hole  57  and a second insertion hole  58 . 
     The first insertion hole  57  has a substantially circular shape in a side view and penetrates the upper-rear portion of the base  54  in the right-left direction. The diameter of the first insertion hole  57  is larger than the diameter of the left end portion of the developing roller  2 . 
     The second insertion hole  58  has a substantially circular shape in a side view and penetrates the lower portion at the center in the front-rear direction of the base  54  in the right-left direction. The diameter of the second insertion hole  58  is larger than the diameter of the left end portion of the supply roller  3 . 
     The coupling support shaft  55  has a substantially cylindrical shape extending from the upper portion to the left side at the center in the right-left direction of the base  54 . The coupling support shaft  55  includes a first shaft portion  61 , a second shaft portion  62 , and a third shaft portion  63 . The coupling support shaft  55  is located on the left side of the left side wall  32 A, that is, on the opposite side of the right side wall  32 B with respect to the left side wall  32 A (see  FIG. 3 ). 
     The first shaft portion  61  has a substantially cylindrical shape extending in the right-left direction and the right end portion thereof is connected to the left surface of the upper portion of the base  54  at the center in the right-left direction. 
     The second shaft portion  62  has a substantially cylindrical shape extending from the left end portion of the first shaft portion  61  to the left side. The outer diameter of the second shaft portion  62  is smaller than the outer diameter of the first shaft portion  61  and the inner diameter of the second shaft portion  62  is smaller than the inner diameter of the first shaft portion  61 . 
     The third shaft portion  63  has a substantially cylindrical shape extending from the left end portion of the second shaft portion  62  to the left side. The outer diameter of the third shaft portion  63  is smaller than the outer diameter of the second shaft portion  62  and the inner diameter of the third shaft portion  63  is smaller than the inner diameter of the second shaft portion  62  and slightly larger than the outer diameter of the filling tube  45 . 
     An opening in the coupling support shaft  55  is a penetration hole  64 . That is, the penetration hole  64  penetrates the inside of the first shaft portion  61 , the inside of the second shaft portion  62 , and the inside of the third shaft portion  63 . 
     The idle gear support shaft  56  has a substantially cylindrical shape extending from the lower-front portion of the base  54  to the left side. 
     The support shaft unit  51  is attached to the rear portion of the left surface of the left side wall  32 A by inserting the filling tube  45  into the penetration hole  64  of the coupling support shaft  55 , inserting the left end portion of the developing roller  2  into the first insertion hole  57 , and inserting the supply roller  3  into the second insertion hole  58 . As illustrated in  FIG. 5B , the left end portion of the filling tube  45  comes in contact with the inner circumferential surface on the right side of the third shaft portion  63  of the support shaft unit  51 . 
     (2-2-2) Gear Train 
     As illustrated in  FIGS. 4 and 5A , the gear train  52  includes a developing coupling  71  serving as an example of the driving force receiving member, a developing gear  72 , a supply gear  73 , an idle gear  74 , and an agitator gear  75 . 
     As illustrated in  FIGS. 4 and 5B , the developing coupling  71  has a substantially cylindrical shape extending in the right-left direction and is rotatably supported by the coupling support shaft  55 . The developing coupling  71  includes a first coupling gear portion  76  serving as an example of the gear portion, a second coupling gear portion  77 , and a coupling portion  78  in an integrated manner. 
     The first coupling gear portion  76  is located at the right end portion of the developing coupling  71 . The first coupling gear portion  76  has a substantially cylindrical shape extending in the right-left direction. The inner diameter of the first coupling gear portion  76  is slightly larger than the outer diameter of the first shaft portion  61  of the coupling support shaft  55 . The first coupling gear portion  76  has gear teeth on the entire circumferential surface thereof. 
     The second coupling gear portion  77  has a substantially cylindrical shape extending toward the left side from the left end portion of the first coupling gear portion  76 . The outer diameter of the second coupling gear portion  77  is smaller than the outer diameter of the first coupling gear portion  76 . The inner diameter of the second coupling gear portion  77  is smaller than the inner diameter of the first coupling gear portion  76  and slightly larger than the outer diameter of the second shaft portion  62  of the coupling support shaft  55 . The second coupling gear portion  77  has gear teeth on the entire circumferential surface thereof. 
     The coupling portion  78  has a substantially cylindrical columnar shape extending to the left side from the left end portion of the second coupling gear portion  77 . The outer diameter of the coupling portion  78  is smaller than the outer diameter of the second coupling gear portion  77 . The coupling portion  78  includes an inner concave portion  81 , an outer concave portion  82 , and a pair of protrusions  83 . 
     The inner concave portion  81  is concave to the left side from the right end face of the coupling portion  78  and has a substantially circular shape in a side view. The diameter of the inner concave portion  81  is smaller than the inner diameter of the second coupling gear portion  77  and slightly larger than the outer diameter of the third shaft portion  63  of the coupling support shaft  55 . 
     The outer concave portion  82  is concave to the right side from the left end face of the coupling portion  78  and has a substantially circular shape in a side view. 
     The protrusions  83  are located in the outer concave portion  82 . The protrusions  83  are located to face each other in the radial direction of the outer concave portion  82 . The protrusions  83  protrude inward in the radial direction to the center of the outer concave portion  82  from the inner circumferential surface of the outer concave portion  82 . 
     The developing coupling  71  is rotatably supported by the support shaft unit  51  by receiving the first coupling gear portion  76  in the first shaft portion  61  of the coupling support shaft  55  so as to be relatively rotatable, receiving the second coupling gear portion  77  in the second shaft portion  62  of the coupling support shaft  55  so as to be relatively rotatable, and receiving the inner concave portion  81  of the coupling portion  78  in the third shaft portion  63  of the coupling support shaft  55  so as to be relatively rotatable. Accordingly, as illustrated in  FIG. 5A , the developing coupling  71  can rotate around a rotation axis L 4  extending in the right-left direction. 
     As illustrated in  FIGS. 4 and 5A , the developing gear  72  has a substantially cylindrical shape extending in the right-left direction. The developing gear  72  is attached to the left end portion of the developing roller  2  so as not to be relatively rotatable. The developing gear  72  engages with the rear end portion of the first coupling gear portion  76  of the developing coupling  71 . 
     The supply gear  73  has a substantially cylindrical shape extending in the right-left direction. The supply gear  73  is attached to the left end portion of the supply roller  3  so as not to be relatively rotatable. The supply gear  73  engages with the lower-rear end portion of the second coupling gear portion  77  of the developing coupling  71 . 
     The idle gear  74  is located on the lower-front side of the developing coupling  71 . The idle gear  74  has a substantially cylindrical shape extending in the right-left direction. As illustrated in  FIG. 4 , the idle gear  74  includes a large-diameter gear  85  and a small-diameter gear  86  in an integrated manner. 
     The large-diameter gear  85  is located in the left half of the idle gear  74 . The large-diameter gear  85  has a substantially cylindrical shape extending in the right-left direction. The large-diameter gear  85  engages with the lower-front end portion of the second coupling gear portion  77  of the developing coupling  71 . 
     The small-diameter gear  86  has a substantially cylindrical shape extending from the right end face of the large-diameter gear  85  to the right side. The outer diameter of the small-diameter gear  86  is smaller than the outer diameter of the large-diameter gear  85 . The inner diameter of the small-diameter gear  86  is smaller than the inner diameter of the large-diameter gear  85  and is slightly larger than the diameter of the idle gear support shaft  56 . 
     The idle gear  74  is rotatably supported by the support shaft unit  51  attached to the left side wall  32 A by receiving the idle gear support shaft  56  in the small-diameter gear  86  so as to be relatively rotatable. Accordingly, the idle gear  74  can rotate around a rotation axis L 5  extending in the right-left direction as illustrated in  FIG. 5A . 
     As illustrated in  FIGS. 4 and 5A , the agitator gear  75  is located on the upper-front side of the idle gear  74 . The agitator gear  75  has a substantially cylindrical shape extending in the right-left direction. The agitator gear  75  includes a gear portion  88  and an engaging portion  89  in an integrated manner. 
     The gear portion  88  is located in the left half of the agitator gear  75 . The gear portion  88  has a substantially cylindrical shape extending in the right-left direction. The gear portion  88  engages with the upper-front end portion of the small-diameter gear  86  of the idle gear  74 . 
     The engaging portion  89  has a substantially cylindrical shape extending from the right end face of the gear portion  88  to the right side. The outer diameter of the engaging portion  89  is smaller than the outer diameter of the gear portion  88 . The engaging portion  89  is attached to the left end face of the agitator  6  so as not to be relatively rotatable. 
     (2-2-3) Gear Cover 
     As illustrated in  FIGS. 3 and 4 , the gear cover  53  covers the gear train  52  from the left side. The gear cover  53  has a substantially box shape which is opened to the right side. The gear cover  53  includes a coupling exposing opening  91 . 
     The coupling exposing opening  91  is located in the rear portion of the left wall of the gear cover  53 . The coupling exposing opening  91  has a substantially circular shape in a side view and penetrates the left wall of the gear cover  53  in the right-left direction. The gear cover  53  is screwed to the left side wall  32 A so as to expose the outer concave portion  82  of the developing coupling  71  from the coupling exposing opening  91  and to collectively cover the gear train  52 . 
     4. Relative Arrangement of Filling Port 
     In a projection image of the right-left direction of the developing cartridge  1 , the filling port  46  of the filling tube  45  overlaps the development chamber  7 . Specifically, as illustrated in  FIG. 1 , the filling port  46  of the filling tube  45  overlaps an area above the supply roller  3  in the development chamber  7  when projected in the right-left direction. That is, the filling port  46  is located above the supply roller  3 . 
     As illustrated in  FIG. 6A , the filling port  46  overlaps the developing coupling  71  when projected in the right-left direction. 
     The filling port  46  is located at the developing roller  2  side than a tangent line L 7  passing through an edge point  71 A of the developing coupling  71 . Specifically, the edge point  71 A of the developing coupling  71  is an edge point of an addendum circle of the developing coupling  71  which is located in a straight line L 6  orthogonal to both the rotation axis L 1  of the developing roller  2  and the rotation axis L 4  of the developing coupling  71  and is located on the opposite side of the developing roller  2  with respect to the rotation axis L 4  of the developing coupling  71 . In other words, the edge point  71 A of the developing coupling  71  is an edge point located farthest from the developing roller  2  among the edge points of the addendum circle of the developing coupling  71  located on the straight line L 6 . The tangent line L 7  is a tangent line to the edge point  71 A of the developing coupling  71 . The straight line L 6  extends along a direction connecting the lower-rear side and the upper-front side. The tangent line L 7  extends along a direction connecting the upper-rear side and the lower-front side. The filling port  46  is located on the rear side of the tangent line L 7 . 
     A distance B from the rotation axis L 1  of the developing roller  2  to the filling port  46  is smaller than a distance C from the rotation axis L 1  of the developing roller  2  to the edge point  71 A of the developing coupling  71 . 
     As illustrated in  FIG. 6B , the filling port  46  is located at the developing roller  2  side than a tangent line L 9  passing through an edge point  71 B of the developing coupling  71 . Specifically, the edge point  71 B of the developing coupling  71  is an edge point located farthest from the developing roller  2  among two edge points of the addendum circle of the developing coupling  71 . Here, the two edge points are points at which straight lines, which are parallel to a straight line L 8  orthogonal to both the rotation axis L 2  of the supply roller  3  and the rotation axis L 4  of the developing coupling  71 , respectively serve as tangent lines of the developing coupling  71 . The tangent line L 9  is a tangent line to the edge point  71 B of the developing coupling  71 . The straight line L 8  extends along the direction connecting the lower-rear side and the upper-front side. The tangent line L 9  extends in parallel to the straight line L 8  and specifically extends along the direction connecting the lower-rear side and the upper-front side. The filling port  46  is located on the rear side of the tangent line L 9 . 
     As illustrated in  FIG. 6C , the filling port  46  is located at the developing roller  2  side than a tangent line L 10  passing through an edge point  71 C of the developing coupling  71 . Specifically, the edge point  71 C of the developing coupling  71  is an edge point which is located farthest from the developing coupling  71  among two edge points of the addendum circle of the developing coupling  71 , when projected in the upper-lower direction. In other words, the edge point  71 C is an edge point which is located farthest from the developing coupling  71  among two edge points of the addendum circle of the developing coupling  71 , when projected in a vertical direction perpendicular to the horizontal plane H, and is a front edge point of the developing coupling  71 . The tangent line L 10  extends along the upper-lower direction, that is, the vertical direction. The filling port  46  is located on the rear side of the tangent line L 10 . 
     5. Filling of Toner 
     When filling toner into the developing cartridge  1 , as illustrated in  FIGS. 7A and 7B , an operator locates the left side wall  32 A of the developing cartridge  1  illustrated in  FIG. 3  on the upside. In the following description, the directions are based on a state where the left side wall  32 A of the developing cartridge  1  is located on the upside. 
     Specifically, as illustrated in  FIG. 7A , the operator holds the developing cartridge  1  so as to locate the left side wall  32 A on the upside in a state where the gear cover  53  and the developing coupling  71  of the developing cartridge  1  are detached therefrom. 
     At this time, the cap  47  is not attached to the filling port  46  of the filling tube  45 , and the penetration hole  64  and the filling port  46  of the filling tube  45  communicate with each other. 
     In this state, the operator inputs toner to the lower side from the penetration hole  64 . 
     Then, the toner moves downward in the third shaft portion  63  of the coupling support shaft  55  and then moves downward in the filling tube  45 . The toner moving in the filling tube  45  filled in the development chamber  7  of the developing cartridge  1  as illustrated in  FIG. 1 . The toner filled in the development chamber  7  also fills the toner containing chamber  5  through the communication port  36 . 
     When the operation of filling toner is completed, as illustrated in  FIG. 7B , the operator attaches the cap  47  to the filling port  46  of the filling tube  45  to close the filling port  46  with the cap  47 . Further, as illustrated in  FIG. 5B , while fitting the developing coupling  71  to the coupling support shaft  55 , as illustrated in  FIGS. 3 and 4 , the gear cover  53  is attached to the left side wall  32 A so as to cover the gear train  52  with the gear cover  53 . 
     At this time, as illustrated in  FIG. 5B , the cap  47  is located between the filling port  46  of the filling tube  45  and the developing coupling  71 . 
     6. Operation of Gear Train 
     In attaching the developing cartridge  1  to the body casing  12 , the operator first attaches the developing cartridge  1  to the drum cartridge  21  to configure a process cartridge  13  as illustrated in  FIG. 2 . Then, the operator opens the top cover  18  and inserts the process cartridge  13  into the body casing  12  from the upside via the opening  17 . Subsequently, the operator closes the top cover  18 . 
     Then, as illustrated in  FIG. 3 , a body coupling  110  of the body casing  12  moves into the outer concave portion  82  of the coupling portion  78  so as not to be relatively rotatable and engages with the protrusions  83  by a known interlocking mechanism which is not illustrated. When the image forming operation is started, the body coupling  110  inputs a driving force to the coupling portion  78  of the developing coupling  71  as illustrated in  FIG. 5A . Then, the developing coupling  71  rotates in the clockwise direction when viewed from the left side. At this time, the developing coupling  71  transmits the driving force to the developing gear  72 , the supply gear  73 , and the idle gear  74 . 
     When the driving force is transmitted to the developing gear  72  and the supply gear  73 , the developing roller  2  and the supply roller  3  rotate in the counterclockwise direction when viewed from the left side. 
     When the driving force is transmitted to the idle gear  74 , the idle gear  74  rotates in the counterclockwise direction when viewed from the left side and transmits the driving force to the agitator gear  75  engaging with the small-diameter gear  86 . Then, the agitator  6  rotates in the clockwise direction when viewed from the left side. 
     At this time, as described above, the development chamber  7  of the developing cartridge  1  is filled with toner. Accordingly, even when the image forming operation is performed just after the process cartridge  13  is attached to the body casing  12 , the developing roller  2  sufficiently carries the toner. 
     7. Operational Advantages 
     (1) According to the developing cartridge  1 , as illustrated in  FIG. 6A , the filling port  46  overlaps the developing coupling  71  when projected in the right-left direction. Further, the filling port  46  is located at the developing roller  2  side than the tangent line L 7  passing through the edge point  71 A of the developing coupling  71 . That is, the filling port  46  is located on the rear side of the tangent line L 7 . Further, the distance B from the rotation axis L 1  of the developing roller  2  to the filling port  46  is smaller than the distance C from the rotation axis L 1  of the developing roller  2  to the edge point  71 A of the developing coupling  71 . 
     Accordingly, the filling port  46  can be located close to the developing roller  2 . 
     As a result, when toner is filled into the developing frame  31  through the filling port  46 , it is possible to fill the vicinity of the developing roller  2  with the toner. 
     Therefore, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to cause the developing roller  2  to smoothly carry toner. Accordingly, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to smoothly form an image. 
     Further, in the toner filling operation, when filling toner into the developing frame  31  through the filling port  46 , the toner may be attached to the vicinity of the filling port  46 . 
     However, according to the above-mentioned configuration, even when the vicinity of the filling port  46  becomes dirty with the toner, it is possible to cover the dirt with the developing coupling  71 . Accordingly, it is possible to make the dirt around the filling port  46  inconspicuous. 
     (2) According to the developing cartridge  1 , as illustrated in  FIG. 1 , the filling port  46  is located above the supply roller  3 . 
     Accordingly, when filling toner into the developing frame  31  through the filling port  46 , it is possible to fill the vicinity of the supply roller  3  with the toner. 
     As a result, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to smoothly supply toner from the supply roller  3  to the developing roller  2 . Therefore, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to smoothly form an image. 
     (3) According to the developing cartridge  1 , as illustrated in  FIG. 4 , the coupling support shaft  55  has the penetration hole  64  communicating with the filling port  46 . 
     Accordingly, it is possible to fill toner into the filling port  46  using the penetration hole  64  of the coupling support shaft  55 . 
     As a result, it is possible to easily fill the developing frame  31  with toner. 
     (4) According to the developing cartridge  1 , as illustrated in  FIG. 5B , the cap  47  is located between the filling port  46  and the developing coupling  71 . 
     Accordingly, it is possible to cover the cap  47  with the developing coupling  71 . 
     As a result, it is possible to reliably close the filling port  46  with the cap  47 . 
     (5) According to the developing cartridge  1 , as illustrated in  FIG. 6A , the filling port  46  is located on the rear side of the tangent line L 7 . The distance B from the rotation axis L 1  of the developing roller  2  to the filling port  46  is smaller than the distance C from the rotation axis L 1  of the developing roller  2  to the edge point  71 A of the developing coupling  71 . The developing gear  72  and the supply gear  73  engage with the developing coupling  71 . 
     Accordingly, it is possible to dispose the filling port  46 , the developing gear  72 , and the supply gear  73  in a limited space in the developing cartridge  1 . 
     As a result, it is possible to achieve a decrease in size of the developing cartridge  1 . 
     (6) According to the developing cartridge  1 , as illustrated in  FIG. 6B , the filling port  46  is located to be at the developing roller  2  side than the tangent line L 9  passing through the edge point  71 B of the developing coupling  71 . That is, the filling port  46  is located on the rear side of the tangent line L 9 . 
     Accordingly, it is possible to locate the filling port  46  to be closer to the developing roller  2  than the tangent line L 9 . 
     As a result, when toner is filled into the developing frame  31  through the filling port  46 , it is possible to fill the vicinity of the developing roller  2  with the toner. 
     Accordingly, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to cause the developing roller  2  to smoothly carry toner. Therefore, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to smoothly form an image. 
     (7) According to the developing cartridge  1 , as illustrated in  FIG. 6C , the filling port  46  is located to be at the developing roller  2  side than the tangent line L 10  passing through the edge point  71 C of the developing coupling  71 . That is, the filling port  46  is located on the rear side of the tangent line L 10 . 
     Accordingly, it is possible to locate the filling port  46  to be closer to the developing roller  2  than the tangent line L 10 . 
     As a result, when toner is filled into the developing frame  31  through the filling port  46 , it is possible to fill the vicinity of the developing roller  2  with the toner. 
     Accordingly, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to cause the developing roller  2  to smoothly carry toner. Therefore, even just after an unused developing cartridge  1  is attached to the printer  11 , it is possible to smoothly form an image. 
     8. Modification Example 
     Modification Examples of the developing cartridge  1  will be described below with reference to  FIGS. 8A to 10B . In the following modification examples, the same elements as in the first embodiment will be referenced by the same reference signs and description thereof will not be repeated. 
     (1) Second Embodiment 
     (1-1) Details of Developing Cartridge According to Second Embodiment 
     In the first embodiment, the developing cartridge  1  includes the toner containing chamber  5  and the development chamber  7  in the developing frame  31 . 
     On the other hand, in a developing cartridge  1  according to a second embodiment, as illustrated in  FIGS. 8A and 8B , the development chamber  7  also functions as the toner containing chamber  5  in the developing frame  31 . 
     That is, in the second embodiment, the developing cartridge  1  does not include the agitator  6 . Further, the front wall  34  is located on the front side of the developing coupling  71  in the front-rear direction. 
     In the developing cartridge  1 , the development chamber  7  is defined by the front wall  34 , a pair of side walls  32 , the bottom wall  33 , and the top wall  35 . 
     In the toner filling operation, when toner is filled through the filling port  46 , the development chamber  7  is filled with the toner. 
     (1-2) Operational Advantages of Second Embodiment 
     According to the developing cartridge  1  of the second embodiment, as illustrated in  FIGS. 8A and 8B , the development chamber  7  also functions as the toner containing chamber  5 . 
     Accordingly, in comparison with a case where the toner containing chamber  5  is separately provided, it is possible to achieve a decrease in size of the developing cartridge  1 . 
     According to the developing cartridge  1  of the second embodiment, it is possible to obtain the same operational advantages as in the first embodiment. 
     (2) Third Embodiment 
     (2-1) Details of Developing Cartridge According to Third Embodiment 
     In the first embodiment, the filling port  46  overlaps the developing coupling  71  when projected in the right-left direction. 
     On the other hand, in a third embodiment, as illustrated in  FIG. 10B , a part of a filling port  100  is located outside a projection area of the developing coupling  71  when projected in the right-left direction. 
     That is, in the third embodiment, similarly to the second embodiment, the development chamber  7  also functions as the toner containing chamber  5  in the developing frame  31 . Further, as illustrated in  FIG. 9 , the developing cartridge  1  includes the filling port  100  instead of the filling port  46 . 
     The filling port  100  is located in the front portion of the left side wall  32 A. The filling port  100  has a substantially polygonal shape in a side view and penetrates the left side wall  32 A in the right-left direction. 
     The left side wall  32 A includes a stepped portion  101 . The stepped portion  101  is located in the left side wall  32 A so as to surround the filling port  100  and has a frame shape in a side view. The stepped portion  101  is depressed to the right side from the left surface of the left side wall  32 A. A cap  102  is attached to the stepped portion  101 . 
     The cap  102  has a substantially polygonal shape in a side view and the outline thereof has substantially the same shape as the outline of the stepped portion  101 . Further, the cap  102  is attached to the stepped portion  101  so as to be flush with the left surface of the left side wall  32 A. 
     In filling toner into the developing frame  31 , an operator locates the left side wall  32 A on the upside and holds the developing cartridge  1  in a state where the support shaft unit  51 , the gear train  52 , the gear cover  53 , and the cap  102  are detached from the developing frame  31 . 
     The operator fills toner into the developing frame  31  through the filling port  100 . When the toner filling operation is completed, the operator attaches the cap  102  to the stepped portion  101  and additionally attaches the support shaft unit  51 , the gear train  52 , and the gear cover  53  to the left side wall  32 A. 
     As illustrated in  FIGS. 10A and 10B , an outer circumferential edge  71 D of the developing coupling  71  is located in the upper-front portion of the developing cartridge  1  when projected the right-left direction. The outer circumferential edge  71 D of the developing coupling  71  is an example of the projection area. 
     As illustrated in  FIG. 10B , the lower-front portion of the filling port  100  is located outside the outer circumferential edge  71 D of the developing coupling  71  when projected in the right-left direction. 
     (2-2) Operational Advantages of Third Embodiment 
     According to a developing cartridge  1  of a third embodiment, as illustrated in  FIG. 10B , it is possible to form the filling port  100  to be large such that the lower-front portion thereof is located outside the outer circumferential edge  71 D of the developing coupling  71 . 
     As a result, it is possible to easily fill the developing frame  31  with toner through the filling port  100 . 
     According to the developing cartridge  1  of the third embodiment, it is possible to obtain the same operational advantages as in the first embodiment. 
     (3) Other Modification Example 
     In the above-mentioned embodiments, toner is filled into the filling port  46  through the penetration hole  64  of the coupling support shaft  55  in the toner filling operation. However, toner may be filled from the filling port  46  in a state where the support shaft unit  51  is detached from the developing cartridge  1 . In this case, after the toner is completely filled, the cap  47  is attached to the filling port  46  and then the support shaft unit  51  is attached to the left side wall  32 A of the developing cartridge  1 . 
     In the above-mentioned embodiment, toner is carried by the developing roller  2 . However, for example, a magnetic roller or a brush roller may be used instead of the developing roller  2 . 
     In the above-mentioned embodiment, the supply roller  3  supplies toner to the developing roller  2 . However, a brush-shaped roller may be used instead of the supply roller  3 . 
     In the above-mentioned embodiment, the developing coupling  71  is described as an example of the driving force receiving member. However, a gear may be used as the driving force receiving member instead of the developing coupling  71 . A driving force may be applied to the developing cartridge  1  from the body of the printer  11  using the gear. 
     In the above-mentioned embodiment, a tandem color printer is described as the printer  11 . However, a four-cycle electrophotographic printer or a monochrome printer may be used instead of the printer  11 . 
     The invention provides illustrative, non-limiting aspects as follows: 
     According to an aspect of the invention, there is provided a developing cartridge including: a housing; a developing roller rotatable around a rotation axis extending in a first direction; a developing gear supported by an end portion of the developing roller; and a driving force receiving member rotatable around a rotation axis extending in the first direction by receiving a driving force from an image forming apparatus body and including a gear portion engaging with the developing gear, wherein the housing has an opening for filling the housing with developer, and wherein at least a part of the driving force receiving member overlaps the opening when viewed in the first direction. 
     According to this configuration, at least a part of the driving force receiving member overlaps the opening when viewed in the first direction. Further, the gear portion of the driving force receiving member engages with the developing gear fixed to an end portion of the developing roller. 
     Accordingly, the opening can be located close to the developing roller. 
     Further, when developer is filled into the housing through the opening, it is possible to fill the vicinity of the developing roller with the developer. 
     As a result, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to cause the developing roller to smoothly carry developer. 
     Accordingly, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to smoothly form an image. 
     Further, even when the vicinity of the opening becomes dirty by toner, it is possible to cover the dirt with the driving force receiving member. 
     Accordingly, it is possible to make the dirt around the opening inconspicuous. 
     The above developing cartridge may further include a supply roller located inside the housing on one side in a third direction, which is perpendicular to both the first direction and a second direction perpendicular to the first direction, and configured to supply developer to the developing roller. The opening may be located on another side in the third direction with respect to the supply roller. 
     According to this configuration, when filling developer into the housing through the opening, it is possible to fill the vicinity of the supply roller with the developer. 
     Accordingly, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to smoothly supply developer from the supply roller to the developing roller. 
     As a result, even just after the unused developing cartridge is attached to the image forming apparatus, it is possible to smoothly form an image. 
     In the above developing cartridge, the housing may include a first side wall and a second side wall which are located with a gap therebetween. The first side wall may have the opening. 
     In the above developing cartridge, the developing roller may be located between the first side wall and the second side wall. 
     The above developing cartridge may further include a support shaft located on an opposite side of the second side wall with respect to the first side wall and configured to rotatably support the driving force receiving member. The support shaft may have a penetration hole communicating with the opening. 
     According to this configuration, it is possible to fill developer into the opening using the penetration hole of the support shaft. 
     Accordingly, it is possible to easily fill the housing with developer. 
     The above developing cartridge may further include a support shaft rotatably supporting the driving force receiving member and having a cylindrical shape. The opening may be located in the support shaft. 
     In the above developing cartridge, the support shaft may be extending in the first direction. 
     The above developing cartridge may further include a closing member closing the opening. The closing member may be located between the opening and the driving force receiving member. 
     According to this configuration, it is possible to cover the closing member with the driving force receiving member. 
     Accordingly, it is possible to reliably close the opening with the closing member. 
     In the above developing cartridge, when projected in the first direction, at least a part of the opening may be located outside a projection area of the driving force receiving member. 
     According to this configuration, it is possible to form the opening to be large so as to be located outside the projection area of the driving force receiving member. 
     Accordingly, it is possible to easily fill the housing with developer through the opening. 
     The above developing cartridge may further include a supply roller configured to supply developer to the developing roller, and a supply gear configured to engage with the gear portion and transmit a driving force from the driving force receiving member to the supply roller. 
     According to this configuration, the supply gear engages with the gear portion of the driving force receiving member. Further, the developing gear also engages with the gear portion of the driving force receiving member. Further, at least a part of the driving force receiving member overlaps the opening when viewed in the first direction. 
     Accordingly, it is possible to dispose the opening, the supply gear, and the developing gear in a limited space in the developing cartridge. 
     As a result, it is possible to achieve a decrease in size of the developing cartridge. 
     According to another aspect of the invention, there is provided a developing cartridge including: a housing configured to contain developer therein and including a first side wall and a second side wall which are located with a gap therebetween; a developing roller located between the first side wall and the second side wall and configured to rotate around a rotation axis extending in a first direction; a supply roller located between the first side wall and the second side wall and configured to supply developer to the developing roller by rotating around a rotation axis extending in the first direction; and a driving force receiving member located on an opposite side of the second side wall with respect to the first side wall, configured to rotate around a rotation axis extending in the first direction, and configured to rotate the developing roller and the supply roller by receiving a driving force from an image forming apparatus body, wherein the first side wall has an opening for filling the housing with developer, and wherein, when viewed in the first direction, at least a part of the opening is located at the developing roller side than a tangent line passing through one edge point among two edge points of the driving force receiving member, the two edge points being edge points at which straight lines, which are parallel to a straight line orthogonal to both the rotation axis of the supply roller and the rotation axis of the driving force receiving member, respectively serve as tangent lines of the driving force receiving member, and the one edge point being located farthest from the developing roller among the two edge points. 
     According to this configuration, the opening can be located closer to the developing roller than a tangent line passing through the one edge point among the two edge points of the driving force receiving member, the two edge points being edge points at which straight lines, which are parallel to a straight line orthogonal to both the rotation axis of the supply roller and the rotation axis of the driving force receiving member, respectively serve as tangent lines of the driving force receiving member, and the one edge point being located farthest from the developing roller among the two edge points. 
     Accordingly, when developer is filled into the housing through the opening, it is possible to fill the vicinity of the developing roller with the developer. 
     As a result, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to cause the developing roller to smoothly carry the developer. 
     Accordingly, even just after the unused developing cartridge is attached to the image forming apparatus, it is possible to smoothly form an image. 
     In the above developing cartridge, the supply roller may be located inside the housing on one side in a third direction, which is perpendicular to both the first direction and a second direction perpendicular to the first direction. The opening may be located on another side in the third direction with respect to the supply roller. 
     The above developing cartridge may further include a support shaft located on an opposite side of the second side wall with respect to the first side wall and configured to rotatably support the driving force receiving member. The support shaft may have a penetration hole communicating with the opening. 
     The above developing cartridge may further include a closing member closing the opening. The closing member may be located between the opening and the driving force receiving member. 
     In the above developing cartridge, when projected in the first direction, at least a part of the opening is located outside a projection area of the driving force receiving member. 
     The above developing cartridge may further include a developing gear supported by an end portion of the developing roller; a gear portion engaging with the developing gear; and a supply gear configured to engage with the gear portion and transmit a driving force from the driving force receiving member to the supply roller. The driving force receiving member may include the gear portion. 
     According to another aspect of the invention, there is provided a developing cartridge including: a housing including, a first side wall and a second side wall which are located with a gap therebetween, a developer containing chamber configured to contain developer therein, and a development chamber communicating with the developer containing chamber and accommodating therein a developing roller which is configured to rotate around a rotation axis extending in a first direction in which the first side wall and the second side wall face each other; and a driving force receiving member located on an opposite side of the second side wall with respect to the first side wall, configured to rotate around a rotation axis extending in the first direction, and configured to rotate the developing roller by receiving a driving force from an image forming apparatus body, wherein the first side wall has an opening for filling the housing with developer, and wherein at least a part of the opening is located at the developing roller side than a straight line extending along a third direction and passing through one edge point among two edge points of the driving force receiving member, the developer containing chamber and the development chamber being arranged in a second direction, the two edge points being edge points of the driving force receiving member in the second direction when the driving force receiving member is projected in the third direction perpendicular to both the first direction and the second direction, and the one edge point being located farthest from the developing roller among the two edge points. 
     According to this configuration, the opening can be located closer to the developing roller than a straight line extending along the third direction and passing through the one edge point among the two edge points of the driving force receiving member, the two edge points being edge points of the driving force receiving member in the second direction when the driving force member is projected in the third direction, and the one edge point being located farthest from the developing roller among the two edge points. 
     Accordingly, when developer is filled into the housing through the opening, it is possible to fill the vicinity of the developing roller with the developer. 
     As a result, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to cause the developing roller to smoothly carry developer. 
     Accordingly, even just after the unused developing cartridge is attached to the image forming apparatus, it is possible to smoothly form an image. 
     According to the developing cartridge of an aspect of the invention, even just after an unused developing cartridge is attached to an image forming apparatus, it is possible to smoothly form an image.