Patent Publication Number: US-9429898-B2

Title: Developing cartridge including electrode and protrusion

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2015-017786 filed Jan. 30, 2015. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a developing cartridge to be assembled in an electro-photographic type image forming apparatus. 
     BACKGROUND 
     A developing cartridge attachable to an electro-photographic type image forming apparatus is known in the prior art. The prior art discloses a developing cartridge including a developing roller, and a developing electrode made from electro-conductive resin. 
     Upon attachment of the developing cartridge to an image forming apparatus, the developing electrode is in contact with an electrode at the image forming apparatus side. Thus, electric power can be supplied from the image forming apparatus to the developing roller through the developing electrode. 
     SUMMARY 
     According to the disclosed developing cartridge, the developing electrode protrudes outside in an axial direction of the developing roller because the developing electrode can be in contact with the electrode of apparatus side. Thus, high mechanical strength of the developing electrode is required on the ground that the developing cartridge may drop. 
     In view of the foregoing, it is therefore an object of the disclosure to provide a developing cartridge capable of providing an increased mechanical strength of the electrode. 
     In order to attain the above and other objects, the disclosure provides a developing cartridge may include a casing, a developing roller, a first protrusion, and an electrode. The casing may be configured to accommodate developer therein. The developing roller may include a developing roller shaft extending in a first direction. The first protrusion may be positioned at an outer surface of the casing. The first protrusion may protrude outward from the outer surface in the first direction. The electrode may be positioned at the outer surface. The electrode may be configured to be electrically connected to the developing roller shaft. The electrode may include a second protrusion protruding outward in the first direction. The second protrusion may have an inner space extending in the first direction. The inner space may be positioned in the second protrusion. The first protrusion may be positioned in the inner space. 
     The developing cartridge of the present disclosure can suppress breakage of an electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the disclosure as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is an example of a perspective view of a developing cartridge according to one embodiment; 
         FIG. 2  is an example of a schematic cross-sectional view of a center portion of an image forming apparatus in which the developing cartridge illustrated in  FIG. 1  is assembled; 
         FIG. 3  is an example of a perspective view of the developing cartridge illustrated in  FIG. 1  and showing a state where an electrode member is removed; 
         FIG. 4  is an example of an exploded perspective view of the developing cartridge illustrated in  FIG. 3  and showing the state where the electrode member is removed; 
         FIG. 5A  is an example of a right side view of the electrode member illustrated in  FIG. 3 ; 
         FIG. 5B  is an example of a left side view of the electrode member illustrated in  FIG. 3 ; 
         FIG. 6  is an example of a plan view of the developing cartridge illustrated in  FIG. 1 ; 
         FIG. 7  is an example of a cross-sectional view of the developing cartridge taken along a line VII-VII in  FIG. 6 ; 
         FIG. 8  is an example of a cross-sectional view of the developing cartridge taken along a line VIII-VIII in  FIG. 7 ; 
         FIG. 9  is an example of a cross-sectional view of the developing cartridge taken along a line IX-IX in  FIG. 7 ; 
         FIG. 10A  is an example of a view for description of the developing cartridge partially assembled to a housing of the image forming apparatus, and showing a state where an electrode of the image forming apparatus is brought into contact with a rear end portion of the developing electrode; and 
         FIG. 10B  is an example of a view for description of the developing cartridge fully assembled to the housing of the image forming apparatus, and showing a state where the electrode of the image forming apparatus is in contact with a right surface of the developing electrode. 
     
    
    
     DETAILED DESCRIPTION 
     A developing cartridge according to one embodiment will be described with reference to  FIGS. 1 to 10B . 
     1. Outline of Developing Cartridge 
     As illustrated in  FIGS. 1 and 2 , a developing cartridge  1  includes a casing  31 , a developing roller  2 , a supply roller  3 , and a layer thickness regulation blade  4 . Regarding directions in the following description, an extending direction of the developing roller  2  will be referred to as the “leftward/rightward direction”, and the “upward/downward direction” referred herein is a direction when the developing cartridge  1  is oriented in a horizontal posture. Further, the “frontward/rearward direction” referred herein is a direction determined on the leftward/rightward direction and the upward/downward direction. These directions are exemplified in  FIG. 1 . 
     The casing  31  has an internal space defined as a toner accommodating portion  5  configured to accommodate therein toner. 
     The developing roller  2  is positioned at a rear end portion of the developing cartridge  1  and is rotatably supported by the casing  31 . The developing roller  2  includes a developing roller shaft  2 A and a roller portion  2 B. 
     The developing roller shaft  2 A is cylindrical and extends in the leftward/rightward direction. The roller shaft  2 A is made of metal. 
     The roller portion  2 B is hollow cylindrical and extends in the leftward/rightward direction. The roller portion  2 B is made of an electrically conductive rubber. The roller portion  2 B covers a center of the roller shaft  2 A, while left and right end portions of the roller shaft  2 A are not covered with the roller portion  2 B. Incidentally, the roller portion  2 B is positioned between a left wall  33 L (described later) and a right wall  33 R (described later) of the cartridge frame  31 . A portion of the roller portion  2 B is exposed to an outside through the cartridge frame  31 . The roller shaft  2 A penetrates through the roller portion  2 B in the leftward/rightward direction. Alternatively, the roller shaft  2 A may extend from both ends of the roller portion  2 B in the leftward/rightward direction, respectively. 
     The supply roller  3  is adapted to supply toner in the toner accommodating portion  5  to the developing roller  2 . The supply roller  3  is rotatably supported by the casing  31 , and is positioned between the developing roller  2  and the toner accommodating portion  5 . The supply roller  3  includes a supply roller shaft  3 A and a roller portion  3 B. 
     The supply roller shaft  3 A is cylindrical and extends in the leftward/rightward direction. The roller shaft  3 A is made of metal. 
     The roller portion  3 B is hollow cylindrical and extends in the leftward/rightward direction. The roller portion  3 B is made of an electrically conductive sponge. The roller portion  3 B covers a center of the roller shaft  3 A, while left and right end portions of the roller shaft  3 A are not covered with the roller portion  3 B. Incidentally, the roller portion  3 B is positioned between the left wall  33 L (described later) and the right wall  33 R (described later) of the cartridge frame  31 . A portion of the roller portion  2 B is exposed to an outside through the cartridge frame  31 . The roller portion  3 B is in contact with a surface of the roller portion  2 B of the developing roller  2 . The roller shaft  3 A penetrates through the roller portion  3 B in the leftward/rightward direction. Alternatively, the roller shaft  3 A may extend from both ends of the roller portion  3 B in the leftward/rightward direction, respectively. 
     The layer thickness regulation blade  4  is adapted to regulate a thickness of a toner layer formed on a surface of the roller portion  2 B. The layer thickness regulation blade  4  is in contact with the surface of the roller portion  2 B. 
     The toner accommodating portion  5  accommodates therein the agitator  6 . The agitator  6  extends in the leftward/rightward direction and is rotatably supported in the toner accommodating portion  5 . 
     2. Using Manner of Developing Cartridge 
     As illustrated in  FIG. 2 , the developing cartridge  1  is installed in an image forming apparatus  11 . A combination of the developing cartridge  1  and a drum cartridge  21  constitute a process cartridge  10 . 
     The image forming apparatus  11  is an electro-photographic type monochromatic printer, and includes a housing  12 , a scanner unit  13 , and a fixing unit  14 . 
     The housing  12  is box shaped whose front end is formed with an opening  15 . The housing  12  includes a front cover  16 , a sheet tray  17 , and a discharge tray  18 . The process cartridge  10  can be attached to and detached from the housing  12  through the opening  15 . 
     The front cover  16  is provided at the front end portion of the housing  12  and is plate-shaped. The front cover  16  is configured to open and close the opening  15 . The sheet tray  17  is configured to accommodate sheets P. 
     The drum cartridge  21  includes a photosensitive drum  22 , a scorotron charger  23 , and a transfer roller  24 . 
     The photosensitive drum  22  is rotatably supported by a frame of the drum cartridge  21 . The photosensitive drum  22  has a cylindrical shape extending in the leftward/rightward direction. 
     The scorotron charger  23  is disposed above the photosensitive drum  22  and is spaced away therefrom. 
     The transfer roller  24  is positioned below the photosensitive drum  22  and is in contact with the surface of the photosensitive drum  22 . 
     The developing cartridge  1  is attached to the photosensitive drum  22  so that the roller portion  2 B of the developing roller  2  is in contact with the surface of the photosensitive drum  22 . 
     The scanner unit  13  is positioned above the process cartridge  10 , and is adapted to emit laser beam based on image data to the photosensitive drum  22 . 
     The fixing unit  14  is positioned rearward of the process cartridge  10 , and includes a heat roller  19  and a pressure roller  20 . 
     Upon start of the image forming operation in the image forming apparatus  11 , the peripheral surface of the photosensitive drum  22  is uniformly charged by the scorotron charger  23  and is exposed to light by the scanner unit  13 . Thus, an electrostatic latent image based on the image data is formed on the peripheral surface of the photosensitive drum  22 . 
     The agitator  6  agitates toner in the toner accommodating portion  5  and supplies toner to the supply roller  3 . The supply roller  3  supplies toner that has been supplied by the agitator  6  to the developing roller  2 . In this case, triboelectric charging is performed between the developing roller  2  and the supply roller  3  so that the toner is charged with positive polarity. The toner is then carried on the developing roller  2 . The layer thickness regulation blade  4  regulates thickness of a layer of the toner carried on the developing roller  2  into a uniform thickness. 
     The toner carried on the developing roller  2  is supplied to the electrostatic latent image on the peripheral surface of the photosensitive drum  22 . Thus a toner image is carried on the peripheral surface of the photosensitive drum  22 . 
     Each sheet P is supplied from the sheet tray  17  to a position between the photosensitive drum  22  and the transfer roller  24  at a prescribed timing by the rotation of rollers. Toner image carried on the peripheral surface of the photosensitive drum  22  is transferred onto the sheet P when the sheet P passes through a position between the photosensitive drum  22  and the transfer roller  24 . 
     Thereafter, the sheet P is heated and pressed when the sheet P passes through a position between the heat roller  19  and the pressure roller  20 . Thus, the toner image on the sheet P is thermally fixed to the sheet P. Then, the sheet P is discharged onto the discharge tray  18 . 
     3. Details of Developing Cartridge 
     As illustrated in  FIG. 3 , the developing cartridge  1  includes the casing  31 , a developing electrode  32 , and a drive unit  30 . In the embodiment, the position of the toner accommodating portion  5  relative to the casing  31  is defined as an inner position. Further, the position opposite to the inner position (the position of the toner accommodating portion  5  relative to the casing  31 ) is defined as an outer position. Further, an exposed surface of the casing  31  will be referred to as an outer surface of the casing  31 . 
     (1) Casing 
     As illustrated in  FIGS. 3 and 4 , the casing  31  has a box shape. The casing  31  includes the toner accommodating portion  5  ( FIG. 2 ). The casing  31  supports the developing roller  2  ( FIG. 2 ), the supply roller  3 , and the layer thickness regulation blade  4 . The casing  31  includes the right wall  33 R, the left wall  33 L, a lower wall  34 , a front wall  35 , and an upper wall  36 . A space surrounded by the left wall  33 L, the right wall  33 R, the lower wall  34 , the front wall  35 , and the upper wall  36  is defined as the toner accommodating portion  5 . 
     The right wall  33 R is positioned at the right end portion of the casing  31 . Specifically, the right wall  33 R is disposed at a position corresponding to one end portion (right end portion) of the developing roller  2  in the leftward/rightward direction. Further, the left wall  33 L is positioned at a position corresponding to the other end portion (left end portion) of the developing roller  2  in the leftward/rightward direction. The other end portion is separated from the one end portion of the developing roller  2  and is positioned at the opposite side of the developing roller  2  from the one end portion in the leftward/rightward direction. The right wall  33 R has a rectangular plate shape which extends in the frontward/rearward direction and the upward/downward direction. The right wall  33 R includes a first right wall  37  and a second right wall  38 . 
     The first right wall  37  constitutes the main part of the right wall  33 R in the frontward/rearward direction. The first right wall  37  has a rectangular plate shape which extends in the frontward/rearward direction and the upward/downward direction. The first right wall  37  includes a protrusion  39 . The protrusion  39  has a columnar shape and extends outward from the outer surface of the first right wall  37 . The protrusion  39  has a screw hole  39 A. The screw hole  39 A is a circular hole recessed leftward from the right surface of the protrusion  39 . 
     The second right wall  38  is disposed at a position corresponding to the right end portion of the developing roller  2  in the leftward/rightward direction. The second right wall  38  includes a wall  38 A and a wall  38 B. 
     The wall  38 A has a plate shape which extends from the first right wall  37  in the leftward/rightward direction. 
     The wall  38 B has a plate shape which extends from the right end of the wall  38 A in the frontward/rearward direction. The wall  38 B includes an insertion hole  40 , an insertion hole  41  and a reinforcement protrusion  42 . 
     The insertion hole  40  is positioned at the rear end portion of the wall  38 B and penetrates the wall  38 B in the leftward/rightward direction. The insertion hole  40  is a hole having a substantial circular shape. The right end portion of the developing roller shaft  2 A is inserted into the insertion hole  40  with a play. 
     The insertion hole  41  is positioned at the front lower side of the insertion hole  40 . The insertion hole  41  is a rectangular hole and penetrates the wall  38 B in the leftward/rightward direction. The right end portion of the supply roller shaft  3 A is inserted into the insertion hole  41  with a play. 
     As illustrated in  FIGS. 3 and 7 , the reinforcement protrusion  42  is positioned between the protrusion  39  and the insertion hole  40  in the frontward/rearward direction. The reinforcement protrusion  42  protrudes outward from the outer surface of the wall  38 B. The length of the reinforcement protrusion  42  from the outer surface of the wall  38 B in the leftward/rightward direction is preferably 15.4 mm. The length of the reinforcement protrusion  42  from the outer surface of the wall  38 B in the leftward/rightward direction may be no shorter than 14.4 mm and no longer than 16.4 mm. Further, the length of the reinforcement protrusion  42  in the upward/downward direction is preferably 5.9 min. The length of the reinforcement protrusion  42  in the upward/downward direction may be no shorter than 5.4 mm and no longer than 6.4 mm. The reinforcement protrusion  42  has a U-shape when viewed in the leftward/rightward direction. 
     The protrusion  39  is positioned at the opposite side of the developing roller shaft  2 A with respect to the reinforcement protrusion  42 . Specifically, the reinforcement protrusion  42  includes an upper reinforcement portion  42 A, a rear reinforcement portion  42 B, and a lower reinforcement portion  42 C. 
     The upper reinforcement portion  42 A is positioned at the upper end portion of the reinforcement protrusion  42 . The upper reinforcement portion  42 A has a plate shape which extends in the frontward/rearward direction. The length of the upper reinforcement portion  42 A in the frontward/rearward direction is 5 mm, preferably. The length of the upper reinforcement portion  42 A in the frontward/rearward direction may be no shorter than 4.5 mm and no longer than 5.5 mm. 
     The rear reinforcement portion  42 B is positioned at the rear end portion of the reinforcement protrusion  42 . The rear reinforcement portion  42 B has a plate shape which extends in the upward/downward direction. Preferably, the length of the rear reinforcement portion  42 B in the frontward/rearward direction is 2 mm. Further, the length of the rear reinforcement portion  42 B in the frontward/rearward direction may be no shorter than 1.5 mm and no longer than 2.5 mm. 
     The lower reinforcement portion  42 C is positioned at the lower end portion of the reinforcement protrusion  42 . The lower reinforcement portion  42 C has a plate shape which extends in the frontward/rearward direction. The length of the lower reinforcement portion  42 C in the frontward/rearward direction is 6.0 mm, preferably. Further, the length of the lower reinforcement portion  42 C in the frontward/rearward direction may be no shorter than 5.5 mm and no longer than 6.5 mm. 
     As illustrated in  FIG. 3 , the left wall  33 L is located at the left end portion of the casing  31 . The left wall  33 L has a rectangular plate shape which extends in the frontward/rearward direction and the upward/downward direction. Similarly to the right wall  33 R, the left wall  33 L has an insertion hole (not illustrated) through which the left end portion of the developing roller shaft  2 A is inserted, and an insertion hole (not illustrated) through which the left end portion of the supply roller shaft  3 A is inserted. 
     As illustrated in  FIG. 4 , the lower wall  34  has a plate shape which extends in the frontward/rearward direction. The lower wall  34  is connected to the right wall  33 R and the left wall  33 L. 
     The front wall  35  has a plate shape which extends upward from the front end portion of the lower wall  34  and is connected to the front end portion of the lower wall  34 . The front wall  35  is further connected to the right wall  33 R and the left wall  33 L. 
     The upper wall  36  has a rectangular plate shape. The upper wall  36  is fixed to the front wall  35 , the left wall  33 L, and the right wall  33 R. 
     (2) Developing Electrode 
     (2-1) Configuration of Developing Electrode 
     As illustrated in  FIGS. 1, 3, and 4 , the developing electrode  32  is attached to the outer surface of the casing  31 . Specifically, the developing electrode  32  is attached to the rear end portion of the outer surface of the right wall  33 R. The developing electrode  32  is positioned between the developing roller  2  and the agitator  6  ( FIG. 2 ) in the frontward/rearward direction. The developing electrode  32  is made of a conductive resin. The developing electrode  32  includes a developing roller bearing  53 , a supply roller bearing  54 , a protrusion  52 , and a reinforcement portion  57 . As illustrated in  FIG. 1 , the protrusion  52  of the developing electrode  32  protrudes outward from the right wall  33 R when the developing electrode  32  is attached to the outer surface of the right wall  33 R. 
     As illustrated in  FIGS. 4, 5A, and 5B , the developing roller bearing  53  has a cylindrical shape which extends from the developing electrode  32  in the leftward/rightward direction. The cylindrical shape extending in the leftward/rightward direction is preferably 12.1 mm. Further, the length of the cylindrical shape extending in the leftward/rightward direction may be no shorter than 11.9 mm and no longer than 12.3 mm. 
     The developing roller bearing  53  has an insertion hole  53 A into which the right end portion of the developing roller shaft  2 A is rotatably fitted. When the peripheral surface of the right end portion of the developing roller shaft  2 A contacts the developing roller bearing  53 , the developing electrode  32  is electrically connected to the developing roller shaft  2 A. Further, the insertion hole  53 A of the developing roller bearing  53  may be different from a through hole, as long as the insertion hole  53 A is a hole into which the right end portion of the developing roller shaft  2 A is rotatably fitted. The diameter of the insertion hole  53 A is 7.55 mm, preferably. Further, the diameter of the insertion hole  53 A may be no shorter than 7.52 mm and no longer than 7.58 mm. 
     As illustrated in  FIGS. 4, 5A, and 5B , the supply roller bearing  54  has a cylindrical shape which extends from the developing electrode  32  in the leftward/rightward direction. Preferably, the length of the cylindrical shape extending in the leftward/rightward direction of the supply roller bearing  54  is 6.3 mm. Further, the length of the cylindrical shape extending in the leftward/rightward direction of the supply roller bearing  54  may be no shorter than 6.1 mm and no longer than 6.5 mm. The right end of the supply roller bearing  54  is closed. The supply roller bearing  54  includes an insertion hole  54 A into which the right end portion of the supply roller shaft  3 A is rotatably fitted. When the peripheral surface of the right end portion of the supply roller shaft  3 A contacts the supply roller bearing  54 , the developing electrode  32  is electrically connected to the supply roller shaft  3 A. 
     Further, the insertion hole  54 A of the supply roller bearing  54  may be a through hole, as long as the insertion hole  54 A is a hole into which the right end portion of the supply roller shaft  3 A is rotatably fitted. The diameter of the insertion hole  54 A is 5.05 mm, preferably. Further, the diameter of the insertion hole  54 A may have a size equal to or larger than 5.02 mm and equal to or smaller than 5.08 mm. 
     In this way, the developing electrode  32  serves as bearings for supporting the developing roller shaft  2 A and the supply roller shaft  3 A. 
     As illustrated in  FIGS. 4 and 5A , the protrusion  52  protrudes outward in the leftward/rightward direction. The protrusion  52  has a prismatic shape which extends in the leftward/rightward direction. Preferably, the projection amount of the protrusion  52  is 17.6 mm. Further, the protrusion amount of the protrusion  52  may be no shorter than 15.6 mm and no longer than 19.6 mm. The protrusion  52  includes an upper end surface  52 A ( FIGS. 1 and 3 ), a right end surface  52 B, a reinforcement rib  52 C, and a fixed portion  56 . 
     The upper end surface  52 A is the upper portion of the protrusion  52 . The upper end surface  52 A extends in the leftward/rightward direction. 
     The right end surface  52 B is the right end portion of the protrusion  52 . The right end surface  52 B is a surface which extends in the frontward/rearward direction. The right end surface  52 B includes a first surface S 1  and a second surface S 2 . 
     The second surface S 2  is a surface which extends in the leftward/rightward direction. In the embodiment, the second surface S 2  extends in parallel to the right wall  33 R as shown in  FIG. 6 . The second surface S 2  is farther from the right wall  33 R than the developing roller bearing  53  in the leftward/rightward direction. 
     As illustrated in  FIGS. 5A and 5B , the first surface S 1  is positioned between the developing roller bearing  53  and the second surface S 2  in the frontward/rearward direction. In other words, as illustrated in  FIG. 1 , the first surface S 1  is positioned between the developing roller  2  and the second surface S 2  in the frontward/rearward direction. Further, the first surface S 1  is connected to the second surface S 2 . The first surface S 1  is an inclined surface such that the larger the distance from the right wall  33 R is, the closer to the second surface S 2  a part of the first surface S 1  is. 
     The plurality of reinforcement ribs  52 C includes ribs each reinforcing the protrusion  52 . As shown in  FIG. 4 , each reinforcement rib  52 C is positioned at the lower surface of the protrusion  52  and extends in the leftward/rightward direction. The plurality of the reinforcement ribs  52 C is disposed with a gap therebetween in the frontward/rearward direction. Specifically, three reinforcement ribs  52 C are disposed with a gap therebetween in the frontward/rearward direction. Each reinforcement rib  52 C protrudes downward from the lower surface of the protrusion  52 . The length of each reinforcement rib  52 C in the upward/downward direction is shortened as the distance from the right wall  33 R increases. 
     As illustrated in  FIG. 5B , the protrusion  52  has a space  60  therein. The space  60  extends in the leftward/rightward direction. The space  60  is defined by an inner surface of the protrusion  52 . The reinforcement protrusion  42  is positioned in the space  60 . Specifically, the reinforcement protrusion  42  is inserted into the space  60  and is positioned inside the protrusion  52 . The space  60  has a size so that the reinforcement protrusion  42  is insertable. Preferably, the length of the space  60  in the leftward/rightward direction is 16.5 mm. Further, the length of the space  60  in the leftward/rightward direction may be no shorter than 15.5 mm and no longer than 17.5 mm. 
     As illustrated in  FIGS. 4 and 5B , the fixed portion  56  has a cylindrical shape which extends in the leftward/rightward direction. Preferably, the length of the cylindrical shape extending in the leftward/rightward direction of the fixed portion  56  is 6.6 mm. Further, the length of the cylindrical shape extending in the leftward/rightward direction of the fixed portion  56  may be no shorter than 6.4 mm and no longer than 6.8 mm. The protrusion  52  includes one end portion and other end portion further from the developing roller shaft  2 A than the one end portion of the protrusion, and the fixed portion  56  is provided on the other portion of the protrusion  52 . The other end portion of the protrusion  52  is farther from the developing roller shaft  2 A than the one end portion of the protrusion  52  in the front/read direction. The one end portion of the protrusion  52  is positioned closer to the developing roller shaft  2 A in the frontward/rearward direction than the other end portion of the protrusion  52 . The fixed portion  56  has a screw insertion hole  56 A into which the right end portion of the protrusion  39  is insertable. The screw insertion hole  56 A has a size so that the right end portion of the protrusion  39  is insertable. 
     The screw insertion hole  56 A penetrates the fixed portion  56  in the leftward/rightward direction. The screw insertion hole  56 A is a circular hole. The diameter of the screw insertion hole  56 A is preferably 4.98 mm. Further, the diameter of the screw insertion hole  56 A may be no shorter than 4.97 mm and no longer than 4.99 mm. 
     As illustrated in  FIGS. 4 and 5A , the reinforcement portion  57  is positioned below the developing roller bearing  53 . The reinforcement portion  57  includes a surrounding portion  57 A and a plurality of connection portions  57 B. 
     The surrounding portion  57 A extends in the leftward/rightward direction so as to surround the developing roller bearing  53 . The surrounding portion  57 A is curved along the peripheral surface of the developing roller bearing  53 . 
     The connection portions  57 B are positioned between the surrounding portion  57 A and the developing roller bearing  53 . Specifically, four connection portions  57 B are disposed in the circumferential direction of the developing roller bearing  53  with a gap between two adjacent connection portions  57 B. Each connection portion  57 B connects the surrounding portion  57 A and the developing roller bearing  53 . 
     (2-2) Attachment of Developing Electrode 
     As illustrated in  FIGS. 1 and 6 , the developing electrode  32  is attached to the outer surface of the right wall  33 R of the casing  31  by a screw  61 . 
     Specifically, when the developing electrode  32  is attached to the outer surface of the right wall  33 R, the right end portion of the developing roller shaft  2 A is rotatably fitted into the insertion hole  53 A of the developing roller bearing  53  as illustrated in  FIG. 7 . When the surface of the right end portion of the developing roller shaft  2 A contacts the developing roller bearing  53 , the developing electrode  32  is electrically connected to the developing roller shaft  2 A. 
     The right end portion of the supply roller shaft  3 A is rotatably fitted into the insertion hole  54 A of the supply roller bearing  54 . When the surface of the right end portion of the supply roller shaft  3 A contacts the supply roller bearing  54 , the developing electrode  32  is electrically connected to the supply roller shaft  3 A. 
     As illustrated in  FIGS. 7 and 8 , the reinforcement protrusion  42  is positioned inside the space  60 . Specifically, as illustrated in  FIG. 7 , the reinforcement protrusion  42  is positioned in a part of the space  60  corresponding to the one end portion of the protrusion  52 , and the one end portion of the protrusion  52  is closer to the developing roller shaft  2 A than the other end portion of the protrusion  52 . In other words, the reinforcement protrusion  42  is not positioned in the other part of the space  60  corresponding to the other end portion of the protrusion  52 , and the other end portion of the protrusion  52  is farther from the developing roller shaft  2 A than the one end portion of the protrusion  52 . Specifically, the upper reinforcement portion  42 A of the reinforcement protrusion  42  extends along the inner surface of the upper portion of the protrusion  52 . The rear reinforcement portion  42 B of the reinforcement protrusion  42  extends along the inner surface of the rear end portion of the protrusion  52 . The lower reinforcement portion  42 C of the reinforcement protrusion  42  extends along the inner surface of the lower end portion of the right end surface  52 B of the protrusion  52 . 
     As illustrated in  FIGS. 8 and 9 , the right end of the reinforcement protrusion  42  is farther from the right wall  33 R than the right end of the developing roller shaft  2 A. In other words, the right end of the reinforcement protrusion  42  is disposed outside the right end of the developing roller  2 A in the left/right direction. 
     As illustrated in  FIGS. 7 to 9 , the right end portion of the protrusion  39  is positioned inside the screw hole  56 A of the fixed portion  56 . That is, the right end portion of the protrusion  39  is inserted into the screw hole  56 A of the fixed portion  56  in the leftward/rightward direction. Then, the fixed portion  56  is fixed to the protrusion  39  when the screw  61  is inserted into the screw insertion hole  56 A. 
     Further, as illustrated in  FIGS. 1 and 7 , the protrusion  52  of the developing electrode  32  is positioned between the axis A 1  of the developing roller shaft  2 A and the axis A 2  of the screw  61  in the frontward/rearward direction. 
     (3) Drive Portion 
     As illustrated in  FIG. 1 , the drive unit  30  is positioned at the outer surface of the left wall  33 L. The drive unit  30  includes, for example, a gear train including a plurality of gears. The gear train (not shown) includes a gear which rotates the developing roller shaft  2 A. Further, the gear train (not shown) further includes a gear which rotates the supply roller shaft  3 A. 
     4. Attachment of Developing Cartridge to Housing 
     When the developing cartridge  1  is attached to the housing  12 , the developing cartridge  1  is attached to the drum cartridge  21  and the developer cartridge  1  is inserted into the housing  12  in a state where the developer cartridge  1  is attached to the drum cartridge  21 . 
     When the developing cartridge  1  is inserted into the housing  12 , an electrode  71  provided inside the housing  12  contacts the first surface S 1  of the protrusion  52  as illustrated in  FIG. 10A . Then, the electrode  71  slides on the first surface S 1  and is guided along the first surface S 1  toward the second surface S 2 . 
     When the developing cartridge  1  is further inserted into the housing  12 , the electrode  71  contacts the second surface S 2  of the protrusion  52  as illustrated in  FIG. 10B . Then, the attachment of the developing cartridge  1  to the housing  12  is completed. Accordingly, the developing electrode  32  can receive the electric power via the electrode  71 . 
     5. Correspondence Relationships 
     The toner is an example of developer. The outer surface of the right wall  33 R is an example of an outer surface of the casing. The leftward/rightward direction is an example of a first direction. The reinforcement protrusion  42  is an example of a first protrusion. The developing electrode  32  is an example of an electrode. The protrusion  52  is an example of a second protrusion. The space  60  is an example of a space. The one end portion of the protrusion  52  is an example of a first end portion. The fixed portion  56  is an example of a second end portion. The frontward/rearward direction is an example of a second direction crossing the first direction. The protrusion  39  is an example of a third protrusion. The screw  61  is an example of a fixing member. The screw hole  56 A is an example of a through hole. The right end surface  52 B is an example of a portion of the second protrusion between an axis of the developing roller shaft and an axis of the screw. The first right wall  37  is an example of a first surface. The second right wall  38  is an example of a second surface. The right end of the reinforcement protrusion  42  is an example of an outer end of the first protrusion. The right end of the protrusion  52  is an example of an outer end of the second protrusion. The roller portion  2 B is an example of a roller member. The right wall  33 R is an example of a first wall. The left wall  33 L is an example of a second wall. The right surface of the right wall  33 R is an example of an outer surface of the first wall. The image forming apparatus  11  is an example of an image forming apparatus. The electrode  71  is an example of an electrical contact. The developing roller bearing  53  is an example of a bearing. The supply roller bearing  54  is an example of a bearing. 
     6. Effects 
     (1) According to the developing cartridge  1 , as illustrated in  FIGS. 7 and 9 , the reinforcement protrusion  42  positioned at the outer surface of the right wall  33 R of the casing  31  is positioned inside the space  60  defined by the right end surface  52 B of the developing electrode  32 . With this construction, the protrusion  52  of the developing electrode  32  can be reinforced by the reinforcement protrusion  42 . 
     (2) According to the developing cartridge  1 , the reinforcement protrusion  42  extends from the outer surface of the right wall  33 R of the casing  31  as illustrated in  FIG. 3 . Since the reinforcement protrusion  42  extends from the outer surface of the right wall  33 R, the rigidity of the reinforcement protrusion  42  can be improved. As a result, the protrusion  52  of the developing electrode  32  can be further reinforced. 
     (3) According to the developing cartridge  1 , the developing electrode  32  is configured to be electrically connected to the supply roller shaft  3 A at the supply roller bearing  54  as illustrated in  FIG. 7 . With this construction, electric power can be supplied to both the developing roller  2  and the supply roller  3  via the developing electrode  32 , and the protrusion  52  of the developing electrode  32  can be reinforced by the reinforcement protrusion  42 . 
     (4) According to the developing cartridge  1 , the reinforcement protrusion  42  is positioned at one end portion of the protrusion  52  near the developing roller shaft  2 A, as illustrated in  FIG. 9 . With this construction, the one end portion of the protrusion  52  closer to the developing roller shaft  2 A can be reliably reinforced. 
     (5) According to the developing cartridge  1 , the fixed portion  56  of the protrusion  52  is fixed to the protrusion  39  by the screw  61  as illustrated in  FIGS. 9 and 10A . Accordingly, the other end portion of the protrusion  52  farther from the developing roller shaft  2 A than the one end portion of the protrusion  52  in the frontward/rearward direction can be reinforced by the fixed portion  56 , the screw  61 , and the protrusion  39 . 
     (6) According to the developing cartridge  1 , the protrusion  52  has a portion positioned between the axis A 1  of the developing roller shaft  2 A and the axis A 2  of the screw  61  in the frontward/rearward direction, as illustrated in  FIGS. 7 and 10A . With this configuration, the developing roller shaft  2 A and the screw  61  can protect the front portion and the rear portion of the protrusion  52 . 
     (7) According to the developing cartridge  1 , as illustrated in  FIG. 7 , the developing electrode  32  includes the developing roller bearing  53  supporting the developing roller shaft  2 A, and the supply roller bearing  54  supporting the supply roller shaft  3 A. With this construction, the developing electrode  32  can supply the electrical power to the developing roller shaft  2 A and the supply roller shaft  3 A while bearing the developing roller shaft  2 A and the supply roller shaft  3 A. 
     Accordingly, the configuration of the developing cartridge  1  can be simplified without separately providing other bearings for supporting the developing roller shaft  2 A and the supply roller shaft  3 A. 
     (8) According to the developing cartridge  1 , as illustrated in  FIGS. 3 and 4 , the reinforcement protrusion  42  protrudes from the right surface of the wall  38 B and the protrusion  39  protrudes from the outer surface of the first right wall  37 . With this configuration, the reinforcement protrusion  42  and the protrusion  39  can be provided in different walls. 
     (9) According to the developing cartridge  1 , as illustrated in  FIG. 9 , the right end portion of the reinforcement protrusion  42  is farther from the outer surface of the right wall  33 R than the right end portion of the developing roller shaft  2 A is. Accordingly, the protrusion  52  of the developing electrode  32  can be reliably reinforced by the reinforcement protrusion  42 . 
     (10) According to the developing cartridge  1 , the developing electrode  32  is made of a conductive resin. Therefore, the developing electrode  32  can be easily molded by a conductive resin. 
     (11) According to the developing cartridge  1 , as illustrated in  FIG. 10A , the developing electrode  32  is attached to the outer surface of the right wall  33 R of the casing  31  by the screw  61 . With this construction, the developing electrode  32  can be attached to the outer surface of the casing  31  with a simple configuration. 
     (12) According to the developing cartridge  1 , as illustrated in  FIG. 10B , the protrusion  52  of the developing electrode  32  contacts the electrode  71  of the image forming apparatus  11  when the developing cartridge  1  is attached to the image forming apparatus  11 . With this construction, the electric power can be supplied from the image forming apparatus  11  to the developing roller  2  and the supply roller  3  via the developing electrode  32 . 
     7. Modifications and Variations 
     In the above described embodiment, the reinforcement protrusion  42  extends from the outer surface of the right wall  33 R, but the embodiment is not limited thereto. For example, a reinforcement protrusion may be positioned in the space  60  and extend along the space  60 . Further, a reinforcement protrusion extending along the space  60  may be attached to the outer surface of the right wall  33 R. 
     Further, in the embodiment, the developing roller shaft  2 A is directly connected to the developing roller bearing  53 , but the embodiment is not limited thereto, as long as the developing roller shaft  2 A and the developing roller bearing  53  can be electrically connected to each other. The developing roller shaft  2 A may be indirectly connected to the developing roller bearing  53 . For example, the developing roller shaft  2 A may be electrically connected to the developing roller bearing  53  via a conductive metal member. Further, the developing roller shaft  2 A may be electrically connected to the developing electrode  32  via a conductive metal member. 
     Further, in the embodiment, the supply roller shaft  3 A is directly connected to the supply roller bearing  54 , but the embodiment is not limited thereto, as long as the supply roller shaft  4 A and the supply roller bearing  54  can be electrically connected to each other. The supply roller shaft  3 A and the supply roller bearing  54  may be indirectly connected to each other. For example, the supply roller shaft  3 A and the supply roller bearing  54  may be electrically connected to each other via a conductive metal member. Further, the supply roller shaft  3 A may be electrically connected to the developing electrode  32  via a conductive metal member. 
     Further, in the embodiment, as illustrated in  FIGS. 7 and 8 , the reinforcement protrusion  42  is positioned inside the space  60  of the protrusion  52 . Specifically, as shown in  FIG. 7 , the reinforcement protrusion  42  is positioned in one end portion of the protrusion  52  near the developing roller shaft  2 A, but is not positioned in the other end portion of the protrusion  52  separated from the developing roller shaft  2 A. At least a part of the reinforcement protrusion  42  may be positioned at the other end portion of the protrusion  52  separated from the developing roller shaft  2 A. 
     In the above-described embodiment, the developing electrode  32  is attached to the casing  31  by the screw  61 , but the method of attaching the developing electrode  32  to the casing  31  is not particularly limited. For example, the developing electrode  32  can be attached to the casing  31  by a method such as welding. In that case, the welded portion is an example of the fixed portion. 
     While the disclosure has been described in detail with reference to the specific example embodiment thereof, this is merely an example, and various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure.