Patent Publication Number: US-2023152728-A1

Title: Developing cartridge having electrode

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/405,225, filed Aug. 18, 2021, which is a continuation of U.S. patent application Ser. No. 17/193,426, filed Mar. 5, 2021, issued as U.S. Pat. No. 11,231,660 on Jan. 25, 2022, which is a continuation of U.S. patent application Ser. No. 17/038,310 filed Sep. 30, 2020, issued as U.S. Pat. No. 11,307,511 on Apr. 19, 2022, which is a continuation of U.S. patent application Ser. No. 16/867,129 filed May 5, 2020, issued as U.S. Pat. No. 10,824,090 on Nov. 3, 2020, which is a continuation of U.S. patent application Ser. No. 16/578,756 filed Sep. 23, 2019, issued as U.S. patent application Ser. No. 10,649,363 on May 12, 2020, which is a continuation of U.S. patent application Ser. No. 16/290,326 filed Mar. 1, 2019, issued as U.S. Pat. No. 10,459,366 on Oct. 29, 2019, which is a continuation of U.S. patent application Ser. No. 16/180,408 filed Nov. 5, 2018, issued as U.S. Pat. No. 10,429,763 on Oct. 1, 2019, which is a continuation of U.S. patent application Ser. No. 15/370,515 filed Dec. 6, 2016, issued as U.S. patent application Ser. No. 10,151,998 on Dec. 11, 2018, which is a continuation of U.S. patent application Ser. No. 15/075,434 filed Mar. 21, 2016, issued as U.S. Pat. No. 9,547,253 on Jan. 17, 2017, which is a continuation of U.S. patent application Ser. No. 14/593,123 filed Jan. 9, 2015, issued as U.S. Pat. No. 9,423,765 on Aug. 23, 2016, which is a Continuation-in-Part of International Application No. PCT/JP2012/080824 filed Nov. 29, 2012 in Japan Patent Office as a Receiving Office, which claims priority from Japanese Patent Application 2012-154132 filed Jul. 9, 2012. The contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present invention relates to a developing cartridge adapted to be mounted on an image forming device that employs an electrophotographic system. 
     Background 
     As described in Japanese unexamined patent application publication No. 2005-70402, an image-forming device known in the art that employs an electrophotographic system has a developing cartridge that is detachably mounted in a device body for supplying developer to a photosensitive drum. 
     One such developing cartridge that has been proposed is a developing unit comprising a developing roller that carries toner, a supply roller that supplies toner to the developing roller, a first contact member that electrically connects to a rotational shaft of the developing roller, and a second contact member that electrically connects to a rotational shaft of the supply roller. 
     Description 
     SUMMARY 
     In this developing unit, the first contact member and the second contact member are retained in a cover member that covers ends of rotational shafts in the developing roller and the supply roller, such that contact parts on the first and the second contact members protrude from an outer surface of the cover member. 
     However, to make the developing unit described in the Patent Document described above more compact, the first and the second contact members must be placed in close proximity to each other. 
     When the first and the second contact members are placed in close proximity to each other, it becomes more difficult to ensure that the first and the second contact members are insulated from each other. 
     In view of the foregoing, it is an object of the present invention to provide a developing cartridge that can be made compact while reliably insulating a developing electrode and a supply electrode from each other. 
     In order to attain the above and other objects, the present invention provides a developing cartridge. The developing cartridge may include a casing, a developer-carrying member, a supply member, a developing electrode, a supply electrode, and an insulating member. The casing may be configured to accommodate therein developer. The developer-carrying member may be configured to rotate about a rotational axis extending in an axial direction and carry the developer thereon. The supply member may be configured to supply the developer to the developer-carrying member. The developing electrode may be configured to be electrically connected to the developer-carrying member. The supply electrode may be configured to be electrically connected to the supply member. The insulating member may insulate the developing electrode and the supply electrode with each other. The developing electrode, the insulating member, and the supply electrode may be overlapped in this order in the axial direction. 
     According to another aspect of the present invention, the present invention provides a developing cartridge. The developing cartridge may include a casing, a developer-carrying member, a supply member, a developing electrode, a supply electrode, and an insulating member. The casing may be configured to accommodate therein developer. The developer-carrying member may be configured to rotate about a rotational axis extending in an axial direction and carry the developer thereon. The supply member may be configured to supply the developer to the developer-carrying member. The developing electrode may be configured to be electrically connected to the developer-carrying member. The supply electrode may be configured to be electrically connected to the supply member and arranged to confront the developing electrode in the axial direction with a gap therebetween. The insulating member may insulate the developing electrode and the supply electrode with each other and be arranged between the developing electrode and the supply electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG.  1    is a central cross-sectional view of a printer in which a developing cartridge is mounted according to an embodiment of the present invention; 
         FIG.  2    is a right side view of the developing cartridge shown in  FIG.  1   ; 
         FIG.  3    is an exploded perspective view of a power supply unit provided on the developing cartridge shown in  FIG.  2    as viewed from right and rear; 
         FIG.  4    is a right side view of a cartridge frame shown in  FIG.  3   ; 
         FIG.  5    is a right side view showing a state where the supply electrode is mounted on the cartridge frame shown in  FIG.  4   ; 
         FIG.  6    is a right side view showing a state where a bearing member is mounted on the cartridge frame shown in  FIG.  5   ; 
         FIG.  7    is a cross-sectional view of the developing cartridge shown in  FIG.  2    taken along a line VII-VII; 
         FIG.  8    is a bottom view of the developing cartridge shown in  FIG.  2   ; 
         FIG.  9    is a schematic explanation view illustrating a mounting operation of the developing cartridge relative to a drum cartridge, wherein a rear end portion of the developing cartridge is inserted into a cartridge accommodating portion of the drum cartridge; 
         FIG.  10    is a schematic explanation view illustrating a mounting operation of a process cartridge relative to a main casing, wherein the process cartridge is completely mounted in the main casing; and 
         FIG.  11    is a right side view showing a placement of a developing cartridge rested on a level surface according to a modification of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     1. Printer 
     As shown in  FIG.  1   , the printer  1  is provided with a main casing  2  having a box-like shape. 
     Within the main casing  2 , the printer  1  is also provided with a sheet-feeding unit  3  for feeding sheets S of paper, and an image-forming unit  4  for forming images on the sheets S supplied by the sheet-feeding unit  3 . 
     Directions related to the printer  1  will be specified based on the orientation of the printer  1  when resting on a level surface, and specifically will refer to the directions indicated by arrows in  FIG.  1   . 
     (1) Main Casing 
     The main casing  2  is formed with a cartridge access opening  5  for mounting and removing a process cartridge  15  (described later), and a paper-introducing opening  6  through which the sheets S are inserted into the main casing  2 . 
     The cartridge access opening  5  is formed in the top portion of the main casing  2  and penetrates the main casing  2  in the top-bottom direction. 
     The paper-introducing opening  6  is formed in the front side of the main casing  2  at the bottom portion thereof and penetrates the front side in the front-rear direction. 
     The main casing  2  also includes a top cover  7  disposed on the top portion thereof, and a sheet-feeding cover  8  disposed on the front thereof. The top cover  7  is provided with a discharge tray  41  into which sheets S are discharged. 
     The top cover  7  is disposed so as to be capable of pivoting (moving) about its rear edge between a closed position for covering the cartridge access opening  5 , and an open position for exposing the cartridge access opening  5 . 
     The sheet-feeding cover  8  is disposed so as to be capable of pivoting (moving) about its bottom edge between a first position for covering the paper-introducing opening  6 , and a second position for exposing the paper-introducing opening  6 . 
     (2) Sheet-Feeding Unit 
     The sheet-feeding unit  3  includes a sheet-supporting part  9  provided in the bottom portion of the main casing  2 . 
     The sheet-supporting part  9  is in communication with the exterior of the main casing  2  through the paper-introducing opening  6 . 
     When the sheet-feeding cover  8  is in the second position, sheets S of paper are inserted into the sheet-feeding unit  3  through the paper-introducing opening  6  such that the rear portions of the sheets S are stacked on the sheet-supporting part  9  and the front portions of the sheets S are stacked on the top surface of the sheet-feeding cover  8 . 
     The sheet-feeding unit  3  further includes a pickup roller  11  disposed above the rear edge of the sheet-supporting part  9 , a feeding roller  12  disposed on the rear side of the pickup roller  11 , a feeding pad  13  arranged so as to confront the lower rear side of the feeding roller  12 , and a feeding path  14  extending continuously upward from the rear edge of the feeding pad  13 . 
     (3) Image-Forming Unit 
     The image-forming unit  4  includes a process cartridge  15 , a scanning unit  16 , and a fixing unit  17 . 
     (3-1) Process Cartridge 
     The process cartridge  15  can be mounted in and removed from the main casing  2 . When mounted in the main casing  2 , the process cartridge  15  is arranged above the rear portion of the sheet-feeding unit  3 . 
     The process cartridge  15  includes a drum cartridge  18 , and a developing cartridge  19 . The drum cartridge  18  as an example of the external device is detachably mountable in the main casing  2 . The developing cartridge  19  is detachably mountable in the drum cartridge  18 . 
     The drum cartridge  18  includes a photosensitive drum  20 , a transfer roller  21 , and a scorotron charger  22 . 
     The photosensitive drum  20  is formed in a general cylindrical shape that is elongated in the left-right direction (axial direction). The photosensitive drum  20  is rotatably provided at the rear region of the drum cartridge  18 . 
     The transfer roller  21  is formed in a general columnar shape that is elongated in the left-right direction. The transfer roller  21  is in pressure contact with the rear side of the photosensitive drum  20 . 
     More specifically, the transfer roller  21  is disposed on the rear side of the photosensitive drum  20  with its central axis positioned slightly lower than the central axis of the photosensitive drum  20 . Note that the bottom surface of the transfer roller  21  is higher than the bottom surface of the photosensitive drum  20 . That is, a virtual line segment (not shown) connecting the central axis of the transfer roller  21  to the central axis of the photosensitive drum  20  forms an acute angle of approximately 3° with a virtual line (not shown) extending horizontally in the front-rear direction. Accordingly, the weight of the transfer roller  21  does not affect the pressure with which the transfer roller  21  contacts the photosensitive drum  20  (transfer pressure). 
     The scorotron charger  22  is arranged to confront the upper front side of the photosensitive drum  20  with a gap therebetween. 
     The scorotron charger  22  is disposed at a position separated from the transfer roller  21  in the circumferential direction of the photosensitive drum  20 . More specifically, the scorotron charger  22  is disposed such that a virtual line segment (not shown) connecting the central axis of the photosensitive drum  20  with the central axis of the transfer roller  21  forms an angle of approximately 120° with a virtual line segment (not shown) connecting the central axis of the photosensitive drum  20  with a charging wire  23  (described later). 
     The scorotron charger  22  further includes the charging wire  23 , and a grid  24 . 
     The charging wire  23  is stretched in a taut state to extend in the left-right direction and is disposed so as to confront but remain separated from the upper front side of the photosensitive drum  20 . 
     The grid  24  is formed to have a general angular U-shape in a side view and is formed with the opening of the “U” facing diagonally upward and forward so as to surround the charging wire  23  from the lower rear side. 
     The developing cartridge  19  is disposed on the lower front side of the photosensitive drum  20 . The developing cartridge  19  includes a developing-cartridge frame  25  as an example of the casing. 
     The developing-cartridge frame  25  defines therein a toner-accommodating chamber  26  and a development chamber  27 . The toner-accommodating chamber  26  and the development chamber  27  are provided side by side in the front-rear direction, with a communication opening  28  allowing communication therebetween. The toner-accommodating chamber  26  and the development chamber  27  have substantially the same capacity. 
     The toner-accommodating chamber  26  accommodates therein toner (developer). An agitator  29  is provided in the approximate front-rear and vertical center region of the toner-accommodating chamber  26 . In other words, the agitator  29  is positioned lower than the photosensitive drum  20 . 
     In the development chamber  27 , a bottom wall  46  (described later) has a top surface formed with a supply-roller groove  30 , a developing-roller opposing surface  31 , and a lower-film adhering surface  32 . 
     The supply-roller groove  30  is formed in a general semicircular shape conforming to the circumferential surface of a supply roller  33  (described later), with the convex shape of the supply-roller groove  30  depressed obliquely downward and rearward. 
     The developing-roller-opposing surface  31  is formed in a general arc shape that conforms to the circumferential surface of a developing roller  34  (described later). The developing-roller opposing surface  31  extends continuously from the rear edge of the supply-roller groove  30  toward the upper rear side. 
     The lower-film adhering surface  32  is formed continuously with the rear edge of the developing-roller opposing surface  31  and extends rearward therefrom. Thus, the lower-film adhering surface  32  is arranged higher than the developing-roller opposing surface  31 . 
     The lower-film adhering surface  32  is also arranged so as to confront the bottom portion of the photosensitive drum  20  in the top-bottom direction, with a gap therebetween. The lower-film adhering surface  32  is arranged to overlap the central axis of the photosensitive drum  20  when projected vertically. 
     The supply roller  33  as an example of the supply member, the developing roller  34  as an example of the developer-carrying member, a thickness-regulating blade  35 , and a lower film  36  are provided in the development chamber  27 . 
     The supply roller  33  is formed in a general columnar shape that is elongated in the left-right direction. The supply roller  33  is provided in the front region of the development chamber  27  with its bottom portion disposed in the supply-roller groove  30 . The supply roller  33  is capable of rotating about its central axis. With this configuration, the supply roller  33  is disposed on the rear side of the toner-accommodating chamber  26  and is arranged at the same approximate height as the toner-accommodating chamber  26 . 
     The developing roller  34  is formed in a general columnar shape that is elongated in the left-right direction. The developing roller  34  is provided in the rear region of the development chamber  27  such that the bottom circumferential surface of the developing roller  34  opposes the developing-roller opposing surface  31  with a gap therebetween. The developing roller  34  is capable of rotating about its central axis (rotational axis). 
     The developing roller  34  is also disposed so as to contact the upper rear side of the supply roller  33  and so that the upper rear side surfaces of the developing roller  34  are exposed outside the development chamber  27  and contact the lower front surface of the photosensitive drum  20 . In other words, the developing roller  34  is arranged on the upper rear side of the supply roller  33  and the lower front side of the photosensitive drum  20 . The central axes of the supply roller  33 , the developing roller  34 , and the photosensitive drum  20  are positioned along substantially the same line following a radial direction of the photosensitive drum  20 . 
     The developing roller  34  is also disposed in a position separated from the scorotron charger  22  in the circumferential direction of the photosensitive drum  20 . More specifically, the developing roller  34  is arranged such that a virtual line segment (not shown) connecting the central axis of the photosensitive drum  20  to the charging wire  23  forms an angle of approximately 120° with a virtual line segment (not shown) connecting the central axis of the photosensitive drum  20  to the central axis of the developing roller  34 . Hence, the developing roller  34 , the scorotron charger  22 , and the transfer roller  21  are arranged at substantially equal intervals along the circumferential direction of the photosensitive drum  20 . 
     The top edge of the thickness-regulating blade  35  is fixed to the rear edge of the top wall defining the development chamber  27 . The bottom edge of the thickness-regulating blade  35  contacts the developing roller  34  from the front side thereof. 
     The rear portion of the lower film  36  is fixed to the lower-film adhering surface  32 . The front edge of the lower film  36  contacts the circumferential surface of the developing roller  34  above the developing-roller opposing surface  31 . 
     (3-2) Scanning Unit 
     The scanning unit  16  is arranged on the front side of the process cartridge  15  in a position opposing but separated from the photosensitive drum  20  in the front-rear direction. 
     The scanning unit  16  irradiates a laser beam L toward the photosensitive drum  20  based on image data, thereby exposing the circumferential surface of the photosensitive drum  20 . 
     More specifically, the scanning unit  16  irradiates the laser beam L rearward to expose the circumferential surface of the photosensitive drum  20  on the front side thereof In other words, the exposure point at which the photosensitive drum  20  is exposed (the circumferential surface on the front side of the photosensitive drum  20 ) is configured to be on the opposite side of the nip part, where the photosensitive drum  20  and transfer roller  21  contact each other, with respect to the central axis of the photosensitive drum  20 . 
     At this time, the developing cartridge  19  is arranged beneath the path of the irradiated laser beam L, while the scorotron charger  22  is disposed above the path of the irradiated laser beam L. 
     The main casing  2  has inner surfaces provided with guide parts  37  positioned at the space between the scanning unit  16  and the photosensitive drum  20  for guiding mounting and removal of the process cartridge  15 . When removing the process cartridge  15  from the main casing  2 , the guide parts  37  guide the process cartridge  15  so that the developing cartridge  19  mounted in the drum cartridge  18  moves upward, passing from the bottom side of the irradiation path on the laser beam L to the top side thereof. 
     At this time, various rollers provided in the process cartridge  15  (the transfer roller  21 , the supply roller  33 , and the developing roller  34 ) also pass upward through the irradiation path of the laser beam L. 
     (3-3) Fixing Unit 
     The fixing unit  17  is disposed above the rear portion of the drum cartridge  18 . More specifically, the fixing unit  17  includes a heating roller  38  disposed above the scorotron charger  22 , and a pressure roller  39  that is in pressure contact with the upper rear side of the heating roller  38 . 
     Hence, the heating roller  38  is disposed near the upper edge (open side edge) of the grid  24  in the scorotron charger  22 . 
     (4) Image-Forming Operation 
     The agitator  29  rotates to supply toner from the toner-accommodating chamber  26  of the developing cartridge  19  to the supply roller  33  through the communication opening  28 . The supply roller  33  in turn supplies the toner onto the developing roller  34 , at which time the toner is positively tribocharged between the supply roller  33  and the developing roller  34 . 
     The thickness-regulating blade  35  regulates the thickness of toner supplied to the developing roller  34  as the developing roller  34  rotates so that a thin layer of toner having uniform thickness is carried on the surface of the developing roller  34 . 
     In the meantime, the scorotron charger  22  uniformly charges the surface of the photosensitive drum  20 . The scanning unit  16  subsequently exposes the surface of the photosensitive drum  20 , forming an electrostatic latent image on the circumferential surface of the photosensitive drum  20  based on image data. Next, the toner carried on the developing roller  34  is supplied to the electrostatic latent image on the circumferential surface of the photosensitive drum  20  so that a toner image (developer image) is carried on the circumferential surface of the photosensitive drum  20 . 
     The rotating pickup roller  11  supplies sheets S stacked on the sheet-supporting part  9  between the feeding roller  12  and the feeding pad  13 , and the rotating feeding roller  12  separates the sheets S, conveys each separated sheet S onto the feeding path  14 , and supplies the sheets S one at a time to the image-forming unit  4  (between the photosensitive drum  20  and the transfer roller  21 ) at a prescribed timing. 
     Each sheet S is conveyed upward between the photosensitive drum  20  and the transfer roller  21 , at which time the toner image is transferred from the photosensitive drum  20  onto the sheet S, forming an image on the sheet S. 
     Next, the sheet S passes between the heating roller  38  and the pressure roller  39 . At this time, the heating roller  38  and the pressure roller  39  apply heat and pressure to the sheet S to thermally fix the image to the sheet S. 
     The sheet S is subsequently conveyed toward discharge rollers  40 . The discharge rollers  40  discharge the sheet S onto the discharge tray  41  formed on the top surface of the main casing  2 . 
     In this way, the sheet S is supplied from the sheet-supporting part  9  and conveyed along a conveying path that has a general C-shape in a side view, passing first between the photosensitive drum  20  and the transfer roller  21  (the nip part) and next between the heating roller  38  and the pressure roller  39 , and subsequently being discharged onto the discharge tray  41 . 
     2. Developing Cartridge 
     As shown in  FIGS.  2  and  3   , the developing cartridge  19  includes the developing-cartridge frame  25  described above, and a power supply unit  43  provided on the right side of the developing-cartridge frame  25 . 
     A drive unit  42  is provided on the left side of the developing-cartridge frame  25 . The drive unit  42  has a gear train (not shown) that receives a drive force inputted from the main casing  2 . Further, the following description will include a detailed description of the structure related to power supply for the developing cartridge  19  (the structure on the right side of the developing cartridge  19 ), but will omit a description of the structure related to the drive force inputted into the developing cartridge  19  (the structure on the left side of the developing cartridge  19 ). 
     Further, in the following description of the developing cartridge  19 , descriptions related to the developing cartridge  19  will be given under the assumption that the side of the developing cartridge  19  in which the developing roller  34  is provided is the rear side, and the side in which the thickness-regulating blade  35  is provided is the top. That is, the top, bottom, front, and rear directions related to the developing cartridge  19  differ slightly from the top, bottom, front, and rear directions related to the printer  1 . When the developing cartridge  19  is mounted in the printer  1 , the rear side of the developing cartridge  19  faces the upper rear side of the printer  1 , and the front side of the developing cartridge  19  faces the lower front side of the printer  1 . 
     (1) Developing-Cartridge Frame 
     As shown in  FIGS.  3  and  4   , the developing-cartridge frame  25  is formed with a box-like shape that is elongated in the left-right direction and is open on the rear side. More specifically, the developing-cartridge frame  25  includes a right wall  44 , a left wall (not shown), a front wall  45  (see  FIG.  1   ), a bottom wall  46 , and a top wall  47 . 
     The right wall  44  and the left wall (not shown) are formed with a general rectangular shape in a side view that is elongated in the vertical and front-rear directions. The right wall  44  and the left wall are disposed on opposing sides of the developing-cartridge frame  25  in the left-right direction. Each of the right wall  44  and the left wall are formed with a developing-roller-shaft exposing hole  49  and a supply-roller-shaft exposing hole  48 . 
     The developing-roller-shaft exposing holes  49  are formed in the rear ends of the right wall  44  and the left wall (not shown) in the approximate vertical center region thereof. The developing-roller-shaft exposing holes  49  have a general circular shape in a side view and penetrate the right wall  44  and the left wall in the left-right direction. The diameter of the developing-roller-shaft exposing holes  49  is greater than the outer diameter of the rotational shaft in the developing roller  34  (hereinafter called the developing-roller shaft A 1 ). The developing-roller-shaft exposing holes  49  are also open on the upper rear side. 
     The supply-roller-shaft exposing holes  48  are formed near the bottom end portions of the corresponding right wall  44  and the left wall (not shown) and are positioned on the lower front sides of the respective developing-roller-shaft exposing holes  49 . The supply-roller-shaft exposing holes  48  are formed in a general rectangular shape in a side view and penetrate the right wall  44  and the left wall in the left-right direction. The dimensions of the supply-roller-shaft exposing holes  48  are greater than the outer diameter of the rotational shaft in the supply roller  33  (hereinafter called the supply-roller shaft A 2 ). Further, the upper rear sides of the supply-roller-shaft exposing holes  48  are in communication with the lower front sides of the corresponding developing-roller-shaft exposing holes  49 . Each of the supply-roller-shaft exposing holes  48  is provided with a shaft seal  55  fitted therein. 
     The shaft seal  55  is formed of a resinous sponge or the like. The shaft seal  55  has a general square columnar shape that is substantially rectangular in a side view and has a slightly larger outer dimension than the dimensions of the supply-roller-shaft exposing hole  48 . A through-hole  59  having a slightly smaller diameter than the outer diameter of the supply-roller shaft A 2  is formed at the approximate center of the shaft seal  55  when viewed from the side. The supply-roller shaft A 2  is inserted into the through-hole  59 . 
     The left and right ends of the developing-roller shaft A 1  are exposed on the outer left-right sides of the corresponding right wall  44  and the left wall (not shown) through the developing-roller-shaft exposing holes  49 . The left and right ends of the supply-roller shaft A 2  are exposed on the outer left-right sides of the right wall  44  and the left wall through the corresponding supply-roller-shaft exposing holes  48 . Note that the left ends of the developing-roller shaft A 1  and the supply-roller shaft A 2  are coupled to a gear train (not shown) of the drive unit  42  so that the drive unit  42  can transmit a drive force to the developing-roller shaft A 1  and the supply-roller shaft A 2 . 
     The right wall  44  is also provided with a plurality of (three) positioning protrusions  50 , a threaded part  51 , and a supply-electrode opposing part  52 . 
     The positioning protrusions  50  are arranged with one positioning protrusion  50  on the lower rear side of the developing-roller-shaft exposing hole  49 , one on the upper front side of the developing-roller-shaft exposing hole  49 , and one above the threaded part  51 . The positioning protrusions  50  are formed in a general columnar shape and protrude rightward from the right surface of the right wall  44 . 
     The threaded part  51  is disposed above the supply-roller-shaft exposing hole  48 . The threaded part  51  is integrally provided with a large-diameter part  56 , and a small-diameter part  57 . 
     The large-diameter part  56  is formed in a general cylindrical shape and protrudes rightward from the right surface of the right wall  44 . 
     The small-diameter part  57  is formed in a general cylindrical shape that is coaxial with the large-diameter part  56  and protrudes rightward from the right surface of the large-diameter part  56 . The inner diameter of the small-diameter part  57  is equivalent to the inner diameter of the large-diameter part  56 , while the outer diameter of the small-diameter part  57  is smaller than the outer diameter of the large-diameter part  56 . 
     The large-diameter part  56  and the small-diameter part  57  share an inner circumferential surface  58  on which a thread ridge is formed continuously across both the large-diameter part  56  and the small-diameter part  57 . 
     The supply-electrode opposing part  52  is formed in a plate shape that is generally rectangular in a side view and that extends upward from the top edge of the right wall  44  in the approximate front-rear center thereof. The supply-electrode opposing part  52  includes a plurality of (two) ridges  53 , and a protection wall  54 . 
     The ridges  53  are formed in a plate shape having a general triangular shape in a front view, with its apex oriented rightward so as to protrude rightward from the approximate front-rear center of the supply-electrode opposing part  52 . Further, the ridges  53  are arranged parallel to each other and are spaced apart in a direction diagonally between the lower front side and the upper rear side. 
     The protection wall  54  is formed in a plate shape that is generally rectangular in a rear side view and extends rightward from the front edge of the supply-electrode opposing part  52  at the front side of the ridges  53 . 
     The front wall  45  (see  FIG.  1   ) has a general plate shape that is elongated in the left-right direction. The front wall  45  integrally bridges the front edges of the right wall  44  and the left wall (not shown). 
     The bottom wall  46  is formed in a general plate shape that is elongated in the left-right direction. The bottom wall  46  extends continuously rearward from the bottom edge of the front wall  45  and integrally bridges the bottom edges of the right wall  44  on the left wall (not shown). Note that the rear edge of the bottom wall  46  curves upward and rearward to conform to the circumferential surface of the supply roller  33  and subsequently extends diagonally upward toward the rear so as to cover the bottom of the developing roller  34 . 
     The top wall  47  is formed in a general plate shape that is elongated in the left-right direction and is arranged in opposition to the top edges of the front wall  45 , the right wall  44 , and the left wall (not shown). The peripheral edges of the top wall  47  are fixed to the top edges of the front wall  45 , the right wall  44 , and the left wall through welding or another method. 
     (2) Power Supply Unit 
     As shown in  FIGS.  2  and  3   , the power supply unit  43  includes a supply electrode  61 , a bearing member  62  as an example of the insulating member, and a developing electrode  63 . 
     (2-1) Supply Electrode 
     As shown in  FIGS.  3  and  5   , the supply electrode  61  is formed of a conductive resin material and has a rod-like shape that is elongated in a direction diagonally between the upper front side and the lower rear side. The supply electrode  61  is integrally provided with a supply-side contact part  64  as an example of the supply-side contact part of the present invention, a coupling part  66 , and a supply-roller-shaft insertion part  65 . 
     The supply-side contact part  64  is disposed on the upper front end portion of the supply electrode  61 . The supply-side contact part  64  is formed in a square cylindrical shape that has a general rectangular shape in a side view. The supply-side contact part  64  is elongated in the left-right direction with the right end closed and the left end opened. The right surface of the supply-side contact part  64  is divided into a contact surface  67  as an example of the supply contact, and a guide surface  68 . 
     The contact surface  67  constitutes the upper half of the right surface on the supply-side contact part  64  and is elongated vertically. 
     The guide surface  68  constitutes the lower half of the right surface on the supply-side contact part  64  and slopes continuously downward toward the left from the bottom edge of the contact surface  67 . 
     The coupling part  66  is formed in a plate shape that is bent like a crank and is elongated in a diagonal direction between the upper front side and the lower rear side. More specifically, the coupling part  66  includes a first coupling part  69 , a fitting part  70 , and a second coupling part  71 . 
     The first coupling part  69  constitutes the upper front half of the coupling part  66 . The first coupling part  69  is formed in a rod-like shape and extends diagonally downward and rearward from the left edge on the rear side of the supply-side contact part  64 . Here, the upper front end portion of the first coupling part  69  is bent leftward to form a step part  72 . The step part  72  is elongated vertically. 
     The fitting part  70  has a general circular shape in a side view and is provided continuously on the lower rear edge of the first coupling part  69 . The fitting part  70  is formed with a supply-side insertion hole  73 . 
     The supply-side insertion hole  73  is formed in a general circular shape in a side view and penetrates the radial center region of the fitting part  70  in the left-right direction. The supply-side insertion hole  73  and the fitting part  70  share the same center. The diameter of the supply-side insertion hole  73  is greater than the outer diameter of the small-diameter part  57  constituting the threaded part  51  and smaller than the outer diameter of the large-diameter part  56 . Further, the difference between the diameter of the supply-side insertion hole  73  and the outer diameter of the small-diameter part  57  is greater than the difference between the inner diameter of the supply-roller-shaft insertion part  65  and the outer diameter of the supply-roller shaft A 2 . 
     The second coupling part  71  is formed in a bent rod-like shape. More specifically, the second coupling part  71  extends continuously downward from the bottom edge of the fitting part  70 , and subsequently bends and extends diagonally downward and rearward at its bottom edge. Here, the second coupling part  71  bends toward the left in a vertical midpoint thereof to form a step part  74 . The step part  74  is elongated in a diagonal direction between the upper rear side and the lower front side. 
     The supply-roller-shaft insertion part  65  is provided on the lower rear end portion of the supply electrode  61  and is formed continuously with the lower rear edge of the second coupling part  71 . The supply-roller-shaft insertion part  65  is formed in a general cylindrical shape and is elongated in the left-right direction. The inner diameter of the supply-roller-shaft insertion part  65  is slightly greater than (approximately equal to) the outer diameter of the supply-roller shaft A 2 . 
     (2-2) Bearing Member 
     As shown in  FIGS.  3  and  6   , the bearing member  62  is formed of an insulating resin material in a plate shape that is generally rectangular in a side view and elongated in a direction diagonally between the upper front side and the lower rear side. The bearing member  62  is formed of a harder material than the supply electrode  61  and the developing electrode  63 . The bearing member  62  is integrally provided with an insulating part  81  as an example of the contact receiving part, a fixing part  83 , and a bearing part  82 . 
     The insulating part  81  is disposed on the upper front end portion of the bearing member  62 . The insulating part  81  is formed in a square cylindrical shape that has a general L-shape in a side view. The insulating part  81  is elongated in the left-right direction and closed on the right end. The insulating part  81  includes a first insulating part  84 , and a second insulating part  85 . 
     The first insulating part  84  constitutes the front portion of the insulating part  81 . The first insulating part  84  is formed in a general rectangular shape in a side view and is elongated vertically with substantial thickness in the front-rear direction. 
     The second insulating part  85  constitutes the rear portion of the insulating part  81 . The second insulating part  85  is formed in a general rectangular shape in a side view and extends continuously rearward from the top end of the first insulating part  84 . The second insulating part  85  has substantial thickness in the vertical direction. The second insulating part  85  has a top surface  86  that extends in the front-rear direction and a rear surface  87  that extends continuously in a direction angled downward toward the rear from the rear edge of the top surface on the first insulating part  84 . A connecting part  88  disposed between the top surface  86  and the rear surface  87  is formed in a general arc shape that curves downward toward the rear. 
     The fixing part  83  is formed in a general plate shape that extends continuously downward and rearward from the left edge on the rear part of the first insulating part  84  and the left edge on the bottom part of the second insulating part  85 . The fixing part  83  is formed with a screw insertion hole  89  (indicated by a dashed line in  FIG.  3   ) and a fixing-part-side fitting hole  90 . The fixing part  83  is also provided with a screw insertion part  91  as an example of the insertion portion of the present invention. 
     The screw insertion hole  89  is formed in the approximate vertical center region of the bearing member  62 . The screw insertion hole  89  has a general circular shape in a side view and penetrates the bearing member  62  in the left-right direction. The screw insertion hole  89  has a larger diameter than the diameters of the large-diameter part  56  and the small-diameter part  57  constituting the threaded part  51 . 
     The fixing-part-side fitting hole  90  is formed in the upper side of the screw insertion hole  89  and penetrates in the left-right direction. The fixing-part-side fitting hole  90  is an elongate hole whose longitudinal dimension extends diagonally between the upper front side and the lower rear side. The dimension of the fixing-part-side fitting hole  90  in a diagonal direction between the lower front side and the upper rear side is slightly greater than (approximately equal to) the outer diameter of the positioning protrusion  50 . 
     The screw insertion part  91  is formed in a general cylindrical shape and protrudes rightward from the peripheral edge of the screw insertion hole  89 . The screw insertion part  91  shares a central axis with the screw insertion hole  89 . The screw insertion part  91  is in communication with the screw insertion hole  89  at its left end and has an inner diameter equivalent to that of the screw insertion hole  89 . The screw insertion part  91  has an inner circumferential surface  92  on which a thread ridge is not formed. 
     The bearing part  82  is connected to the lower rear end of the fixing part  83 . The bearing part  82  is formed in a plate shape having a general rectangular shape in a side view. The bearing part  82  is formed with a developing-roller-shaft insertion hole  93 , a plurality of (two) bearing-part-side fitting holes  95 , and a supply-roller-shaft insertion hole  96 . The fixing part  83  is also provided with a supply-roller-shaft cover part  94 . 
     The developing-roller-shaft insertion hole  93  is formed in the approximate vertical center region on the rear end portion of the bearing part  82 . The developing-roller-shaft insertion hole  93  has a general circular shape in a side view and penetrates the bearing part  82  in the left-right direction. The diameter of the developing-roller-shaft insertion hole  93  is slightly larger than (approximately equal to) the outer diameter of the developing-roller shaft A 1 . 
     The bearing-part-side fitting holes  95  are provided one each on the lower rear side of the developing-roller-shaft insertion hole  93  and the upper front side of the developing-roller-shaft insertion hole  93 . The bearing-part-side fitting holes  95  have a general square shape in a side view. The inner dimensions of the bearing-part-side fitting holes  95  are slightly larger than (approximately equal to) the outer diameter of the positioning protrusion  50 . 
     The supply-roller-shaft insertion hole  96  is formed on the lower front side of the developing-roller-shaft insertion hole  93 . The supply-roller-shaft insertion hole  96  has a general circular shape in a side view and penetrates in the left-right direction. The inner diameter of the supply-roller-shaft insertion hole  96  is slightly larger than (approximately equal to) the outer diameter of the supply-roller shaft A 2 . 
     The supply-roller-shaft cover part  94  is formed in a general cylindrical shape with the right end closed. The supply-roller-shaft cover part  94  protrudes rightward from the peripheral edge of the supply-roller-shaft insertion hole  96  and shares a central axis with the supply-roller-shaft insertion hole  96 . The supply-roller-shaft cover part  94  is in communication with the supply-roller-shaft insertion hole  96  on its left end and has an inner diameter equivalent to the inner diameter of the supply-roller-shaft insertion hole  96 . 
     (2-3) Developing Electrode 
     As shown in  FIGS.  2  and  3   , the developing electrode  63  is formed in a plate shape that has a general rectangular shape in a side view and a longitudinal dimension elongated in a direction diagonally between the upper front side and the lower rear side. The developing electrode  63  is formed of a conductive resin material. The developing electrode  63  is integrally provided with a developing-side contact part  101  as an example of the developing-side contact part of the present invention, a fixing part  102 , and a developing-roller-shaft fitting part  103 . 
     The developing-side contact part  101  is arranged at the upper front end of the developing electrode  63 . The developing-side contact part  101  has a square cylindrical shape that is elongated in the left-right direction and closed on the right end and has a general rectangular shape in a side view. The right surface of the developing-side contact part  101  constitutes a contact surface  104  as an example of the developing contact of the present invention. The contact surface  104  extends in the front-rear and vertical directions. 
     The fixing part  102  extends continuously downward and rearward from the bottom end of the developing-side contact part  101 . The fixing part  102  has a block-like shape with a left-right dimension equivalent to that of the developing-side contact part  101 . A screw accommodating part  106  and a guiding surface  105  are formed on the fixing part  102 . 
     The screw accommodating part  106  is a recess formed in the right surface of the fixing part  102  beneath the developing-side contact part  101 . The screw accommodating part  106  has a general rectangular shape in a side view and is open on the lower front side. The left-right dimension (depth) of the screw accommodating part  106  is greater than the left-right dimension of the head portion of a screw  110  (described later). The inner dimensions of the screw accommodating part  106  are greater than the diameter of the head portion of the screw  110 . A developing-side insertion hole  107  is also formed in the left wall of the screw accommodating part  106 . 
     The developing-side insertion hole  107  is formed in a general circular shape in a side view and penetrates the center region of the left wall constituting the screw accommodating part  106  in the left-right direction. The diameter of the developing-side insertion hole  107  is larger than the outer diameter of the screw insertion part  91  provided on the bearing member  62 . Further, the difference between the diameter of the developing-side insertion hole  107  and the outer diameter of the screw insertion part  91  is greater than the difference between the inner diameter of a developing-roller-shaft cover part  108  (described later) and the outer diameter of the developing-roller shaft A 1 . 
     The guiding surface  105  is the lower rear portion of the right surface on the fixing part  102  positioned on the lower rear side of the screw accommodating part  106 . The guiding surface  105  slopes leftward toward the lower rear side. 
     The developing-roller-shaft fitting part  103  is formed in a general plate shape and extends continuously rearward from the left end of the fixing part  102 . The developing-roller-shaft fitting part  103  is formed with an insertion hole  109  (indicated by a dashed line in  FIG.  3   ). The developing-roller-shaft fitting part  103  is also provided with the developing-roller-shaft cover part  108 . 
     The insertion hole  109  penetrates the developing-roller-shaft fitting part  103  at a position below and rearward of the developing-side insertion hole  107 . The insertion hole  109  has a general circular shape in a side view and penetrates the developing-roller-shaft fitting part  103  in the left-right direction. The diameter of the insertion hole  109  is slightly greater than (approximately equal to) the outer diameter of the developing-roller shaft A 1 . 
     The developing-roller-shaft cover part  108  is formed in a general cylindrical shape and protrudes rightward from the peripheral edge of the insertion hole  109 . The developing-roller-shaft cover part  108  shares a central axis with the insertion hole  109 . The developing-roller-shaft cover part  108  is in communication with the insertion hole  109  at its left end and has an inner diameter equal to the inner diameter of the insertion hole  109 . 
     (2-4) Assembled State of the Power Supply Unit Relative to the Developer-Cartridge Frame 
     As shown in  FIGS.  3  and  5   , the supply-side contact part  64  covers the ridges  53  of the supply-electrode opposing part  52 , and the supply-roller-shaft insertion part  65  is fitted around the radial outside of the supply-roller shaft A 2 . In this way, the supply electrode  61  is supported on the right wall  44  of the developing-cartridge frame  25 . 
     Thus, the supply electrode  61  is electrically connected to the supply-roller shaft A 2 . 
     In addition, the small-diameter part  57  of the threaded part  51  is loosely inserted into the supply-side insertion hole  73 . The amount of play between the supply-side insertion hole  73  and the small-diameter part  57  of the threaded part  51  is the difference between the diameter of the supply-side insertion hole  73  and the outer diameter of the small-diameter part  57 . Further, the supply-side contact part  64  is disposed in confrontation with the rear side of the protection wall  54  constituting the developing-cartridge frame  25 , with a gap therebetween. The step part  72  of the first coupling part  69  is disposed on the rear side of the supply-electrode opposing part  52  constituting the developing-cartridge frame  25 . Further, the step part  74  of the second coupling part  71  is disposed in the upper front side of the supply-roller-shaft exposing hole  48 . 
     As shown in  FIGS.  3  and  6   , the bearing member  62  is supported on the right wall  44  of the developing-cartridge frame  25  while overlapping the right sides of the supply-roller-shaft insertion part  65  and the coupling part  66  of the supply electrode  61  in the left-right direction. 
     The developing-roller shaft A 1  is also rotatably inserted through the developing-roller-shaft insertion hole  93 . The positioning protrusion  50  positioned on the lower rear side of the developing-roller-shaft exposing hole  49  is fitted into the bearing-part-side fitting hole  95  provided on the lower rear side of the developing-roller-shaft insertion hole  93 . The positioning protrusion  50  provided on the upper front side of the developing-roller-shaft exposing hole  49  is fitted into the bearing-part-side fitting hole  95  provided on the upper front side of the developing-roller-shaft insertion hole  93 . 
     In this way, the bearing member  62  is positioned relative to the developing-cartridge frame  25  and rotatably supports the developing roller  34 . 
     Further, the supply-roller shaft A 2  is rotatably fitted in the supply-roller-shaft cover part  94 . The positioning protrusion  50  disposed above the threaded part  51  is fitted into the fixing-part-side fitting hole  90 . 
     As shown in  FIGS.  6  and  8   , the insulating part  81  is arranged to confront the rear side of the supply-side contact part  64  constituting the supply electrode  61  in the front-rear direction, with a gap therebetween. The first insulating part  84  protrudes rightward such that its right surface is further right than the contact surface  67  of the supply-side contact part  64 . 
     As shown in  FIGS.  6  and  7   , the screw insertion part  91  is disposed in confrontation with the right end of the threaded part  51 , with the left surface of the screw insertion part  91  contacting the right surface of the threaded part  51  from the right side. Internal spaces in the screw insertion part  91  and the threaded part  51  are in communication with each other in the left-right direction. 
     As shown in  FIGS.  2  and  3   , the developing electrode  63  is supported on the bearing member  62  by fitting the developing-roller-shaft cover part  108  around the developing-roller shaft A 1  so that the developing electrode  63  overlaps the fixing part  83  and the upper half of the bearing part  82  from the right side. 
     Thus, the developing electrode  63  is electrically connected to the developing-roller shaft A 1  and insulated from the supply electrode  61 . 
     Specifically, the developing electrode  63  is provided on the right side of the supply electrode  61  with the bearing member  62  interposed therebetween in the left-right direction. In other words, the developing electrode  63  opposes the right side of the supply electrode  61  with a gap therebetween, and the bearing member  62  is disposed between the supply electrode  61  and the developing electrode  63 . 
     As shown in  FIGS.  2  and  8   , the developing-side contact part  101  of the developing electrode  63  is provided on the rear side of the first insulating part  84  and beneath the second insulating part  85 . More specifically, the developing-side contact part  101  is separated from the first insulating part  84  in the front-rear direction and confronts but is separated from the second insulating part  85  vertically. 
     Further, the first insulating part  84  of the bearing member  62  is disposed between the contact surface  104  of the developing electrode  63  and the contact surface  67  of the supply electrode  61 . The first insulating part  84  protrudes farther rightward than the contact surface  104  of the developing electrode  63  and the contact surface  67  of the supply electrode  61 . 
     As shown in  FIG.  7   , the screw insertion part  91  is inserted into the developing-side insertion hole  107  with play. The amount of play between the developing-side insertion hole  107  and the screw insertion part  91  is the difference between the diameter of the developing-side insertion hole  107  and the outer diameter of the screw insertion part  91 . Further, the right end (outer left-right end) of the screw insertion part  91  protrudes slightly to the right of (outward in the left-right direction from) the left wall (inner left-right wall) of the screw accommodating part  106 . 
     In this way, the bearing member  62  is interposed between the supply electrode  61  and the developing electrode  63  and insulates the supply electrode  61  and the developing electrode  63  from each other. 
     The supply electrode  61 , the bearing member  62 , and the developing electrode  63  are fixed to the developing-cartridge frame  25  by a common screw  110 . 
     More specifically, the screw  110  is inserted through the screw insertion part  91  and screwed into the threaded part  51  of the developing-cartridge frame  25  such that the right half of its shaft is accommodated in the screw insertion part  91 , and the left half of its shaft is screwed into the threaded part  51 . Further, the bearing surface of the screw  110  is in contact with the right end of the screw insertion part  91  from the right side thereof. 
     In other words, the screw  110  is only in contact with the screw insertion part  91  and the threaded part  51 , and does not contact the developing electrode  63  and the supply electrode  61 . 
     The right side of the head of the screw  110  is positioned near (slightly leftward of) the contact surface  104  of the developing-side contact part  101 . 
     3. Drum Cartridge 
     As shown in  FIG.  9   , the drum cartridge  18  is provided with a drum accommodating section  121  that accommodates the photosensitive drum  20 , and a cartridge mounting section  122  in which the developing cartridge  19  is mounted. 
     In the following description of the drum cartridge  18 , directions related to the drum cartridge  18  will be specified based on the orientation of the drum cartridge  18  when resting on a level surface, and specifically will refer to the directions indicated by arrows in  FIG.  9   . That is, the up, down, front, and rear directions related to the drum cartridge  18  differ slightly from the up, down, front, and rear directions related to the printer  1 . When the drum cartridge  18  is mounted in the printer  1 , the rear side of the drum cartridge  18  faces the upper rear side of the printer  1 , and the front side of the drum cartridge  18  faces the lower front side of the printer  1 . 
     The drum accommodating section  121  is provided in the rear region of the drum cartridge  18 . The drum accommodating section  121  has a general cylindrical shape that is elongated in the left-right direction. 
     Note that the photosensitive drum  20  is provided with a drum shaft A 3  that extends along the central axis of the photosensitive drum  20  in the left-right direction. The photosensitive drum  20  is rotatably supported in the left and right side walls of the drum accommodating section  121  by the corresponding left and right ends of the drum shaft A 3 . The left and right ends of the drum shaft A 3  penetrate the side walls of the drum accommodating section  121  and protrude outward therefrom in respective left and right directions. 
     The transfer roller  21  and the scorotron charger  22  described above are also supported in the drum accommodating section  121 . 
     The cartridge mounting section  122  extends continuously forward from the bottom end of the drum accommodating section  121 . The cartridge mounting section  122  is a frame-like structure with a closed bottom and an open top. 
     4. Main Casing 
     As indicated in phantom in  FIG.  10   , a device-side developing electrode  116  and a device-side supply electrode  117  are provided on the inner right wall of the main casing  2 . The device-side developing electrode  116  is an example of the external developing electrode, and the device-side supply electrode  117  is an example of the external supply electrode. 
     Directions related to the process cartridge  15  will be specified based on the orientation of the process cartridge  15  when the process cartridge  15  is mounted in the printer  1  and the printer  1  is resting on a level surface, and specifically will refer to the directions indicated by arrows in  FIG.  10   . 
     The device-side developing electrode  116  is provided in the rear section of the main casing  2  and is positioned to contact the contact surface  104  of the developing-side contact part  101  when the process cartridge  15  is completely mounted in the main casing  2 . The device-side developing electrode  116  can be displaced in the left and right directions and is constantly urged leftward. The device-side developing electrode  116  is electrically connected to a power supply (not shown) provided in the main casing  2 . 
     The device-side supply electrode  117  is provided on the front side of the device-side developing electrode  116  in the rear section of the main casing  2  and is positioned to contact the contact surface  67  of the supply-side contact part  64  when the process cartridge  15  is completely mounted in the main casing  2 . The device-side supply electrode  117  can be displaced in the left and right directions and is constantly urged leftward. The device-side supply electrode  117  is electrically connected to the power supply (not shown) in the main casing  2 . 
     5. Mounting the Developing Cartridge in the Main Casing 
     (1) Mounting the Developing Cartridge in the Drum Cartridge 
     To mount the developing cartridge  19  in the main casing  2 , first the developing cartridge  19  is mounted in the drum cartridge  18 . 
     To mount the developing cartridge  19  in the drum cartridge  18 , first the operator inserts the rear end of the developing cartridge  19  down into the rear end of the cartridge mounting section  122 , as illustrated in  FIG.  9   . 
     Next, the operator rotates the front end of the developing cartridge  19  downward and forward about the rear end of the developing cartridge  19 , as indicated by the arrow in  FIG.  9   , while pushing the rear end of the developing cartridge  19  toward the drum accommodating section  121  of the drum cartridge  18 . 
     Through this operation, the rear end of the second insulating part  85  (the connecting part  88  for connecting the top surface  86  and the rear surface  87 ) constituting the bearing member  62  on the rear end of the developing cartridge  19  contacts the right end of the drum accommodating section  121  from the front side thereof 
     Next, the operator rotates the developing cartridge  19  counterclockwise in a right side view about the rear end of the second insulating part  85  (the connecting part  88 ). Hence, the rear end of the second insulating part  85  (the connecting part  88 ) functions as a guide part for guiding mounting of the developing cartridge  19  in the drum cartridge  18 . 
     When the front end of the developing cartridge  19  is accommodated in the front region of the cartridge mounting section  122 , the process of mounting the developing cartridge  19  in the drum cartridge  18  is completed, and the process cartridge  15  is formed (see  FIG.  10   ). 
     To remove the developing cartridge  19  from the drum cartridge  18 , the mounting operation described above is performed in reverse on the developing cartridge  19  and the drum cartridge  18 . 
     That is, the operator rotates the front end of the developing cartridge  19  upward and rearward about the rear end of the developing cartridge  19 , and subsequently the operator lifts the developing cartridge  19  upward and removes the developing cartridge  19  from the drum cartridge  18 . 
     During this removal operation, the rear end of the second insulating part  85  (the connecting part  88 ) contacts the right end of the drum accommodating section  121  on the front side at a point in the rotation of the developing cartridge  19 . 
     After the rear end of the second insulating part  85  (the connecting part  88 ) has contacted the drum accommodating section  121 , the developing cartridge  19  rotates clockwise in a right side view about the rear end of the second insulating part  85  (the connecting part  88 ). Hence, the rear end of the second insulating part  85  (the connecting part  88 ) guides removal of the developing cartridge  19  from the drum cartridge  18 . 
     (2) Mounting the Process Cartridge in the Main Casing 
     To mount the developing cartridge  19  in the main casing  2 , next the process cartridge  15  is mounted in the main casing  2 . 
     To mount the process cartridge  15  in the main casing  2 , first the operator places the top cover  7  of the main casing  2  in the open position, as illustrated in  FIG.  1    and described above. 
     Next, the operator grips the front end of the process cartridge  15  and inserts the process cartridge  15  into the main casing  2  so that the left and right ends of the drum shaft A 3  in the photosensitive drum  20  are fitted into the guide parts  37  of the main casing  2 . 
     Next, the operator pushes the process cartridge  15  diagonally downward and rearward along the guide parts  37  and subsequently rotates the process cartridge  15  counterclockwise in a right side view about the drum shaft A 3  of the photosensitive drum  20 . 
     Just before the process cartridge  15  is completely mounted in the main casing  2  as the operator continues to rotate the process cartridge  15 , the device-side developing electrode  116  inside the main casing  2  contacts from the lower rear side of the guiding surface  105  on the fixing part  102 , and the device-side supply electrode  117  inside the main casing  2  contacts the guide surface  68  on the supply-side contact part  64  from below. 
     Note that the developing-side contact part  101  moves slightly forward at this time an amount equivalent to the play between the developing electrode  63  and the developing-roller shaft A 1  and then contacts the first insulating part  84  of the bearing member  62 . This contact restricts the developing-roller-shaft cover part  108  from moving any further forward. 
     The supply-side contact part  64  also moves slightly upward and forward an amount equivalent to the play between the supply electrode  61  and the supply-roller shaft A 2  and is disposed in confrontation to the protection wall  54  of the developing-cartridge frame  25 , with a slight gap formed between the two in the front-rear direction. 
     As indicated by a dashed line in  FIG.  10   , the device-side developing electrode  116  is subsequently displaced rightward against the force urging it leftward as the developing-side developing electrode  116  slides along the slope of the guiding surface  105  in a direction diagonally upward and forward relative to the guiding surface  105 . Thereafter, the device-side developing electrode  116  slides diagonally upward and forward relative to the screw  110  and comes into contact with the contact surface  104  above the right surface on the head of the screw  110 . Since the right surface on the head of the screw  110  is disposed in proximity to (slightly leftward of) the contact surface  104  of the developing-side contact part  101 , as described above (see  FIG.  7   ), the device-side developing electrode  116  slides smoothly over the right surface on the head of the screw  110  while contacting the contact surface  104  at this time, without becoming trapped in the screw accommodating part  106 . 
     Through this contact, the device-side developing electrode  116  and the developing electrode  63  are electrically connected. 
     Similarly, the device-side supply electrode  117  is displaced rightward against the force urging it leftward while sliding along the slope of the guide surface  68  in a direction upward relative to the guide surface  68  until coming into contact with the contact surface  67 . Through this contact, the device-side supply electrode  117  is electrically connected to the supply electrode  61 . 
     The process cartridge  15  is completely mounted in the main casing  2  when the drum shaft A 3  of the photosensitive drum  20  is disposed in the rear ends of the guide parts  37  and the front end of the process cartridge  15  is positioned beneath the irradiating path of the laser beam L, as illustrated in  FIG.  1   . 
     Subsequently, the operator places the top cover  7  of the main casing  2  in the closed position. 
     When the printer  1  is operated thereafter, power from a power supply (not shown) in the main casing  2  is supplied to the developing-roller shaft A 1  sequentially via the device-side developing electrode  116  and the developing electrode  63  and to the supply-roller shaft A 2  sequentially via the device-side supply electrode  117  and the supply electrode  61 . 
     To remove the process cartridge  15  from the main casing  2 , the operation for mounting the process cartridge  15  described above is performed in reverse on the process cartridge  15  and main casing  2 . 
     That is, after the top cover  7  is placed in the open position, the process cartridge  15  is pulled diagonally upward and forward. 
     6. Operational Advantages 
     (1) With the developing cartridge  19  described above, the bearing member  62  is disposed between the developing electrode  63  and the supply electrode  61  in the left-right direction, as illustrated in  FIGS.  2  and  3   . Accordingly, the developing electrode  63  and the supply electrode  61  can be insulated from each other without being separated in the front-rear direction. In other words, the developing electrode  63  and the supply electrode  61  can be arranged in proximity to each other in the front-rear direction. 
     As a result, the developing cartridge  19  can be made more compact at least in the front-rear direction while ensuring that the developing electrode  63  and the supply electrode  61  are reliably insulated from each other. 
     (2) As shown in  FIGS.  3  and  6   , the bearing member  62  that functions to support the developing roller  34  is also used for insulating the developing electrode  63  and the supply electrode  61 . 
     Since this construction does not require a separate member for being used to insulate the developing electrode  63  and the supply electrode  61 , the overall number of parts can be reduced. 
     (3) As shown in  FIG.  2   , movement of the developing electrode  63  can be restricted through contact between the developing-side contact part  101  of the developing electrode  63  and the insulating part  81  of the bearing member  62 . Similarly, movement of the supply electrode  61  can be restricted through contact between the supply-side contact part  64  of the supply electrode  61  and the insulating part  81  of the bearing member  62 . 
     Accordingly, the bearing member  62  can be used for restricting movement of both the supply electrode  61  and the developing electrode  63 , thereby reducing the number of required parts. Further, the bearing member  62  can reliably insulate the developing electrode  63  and the supply electrode  61  by restricting movement of the developing electrode  63  and the supply electrode  61 . 
     (4) As shown in  FIG.  8   , the bearing member  62  has the first insulating part  84  disposed between the contact surface  104  of the developing-side contact part  101  and the contact surface  67  of the supply-side contact part  64  and extending farther rightward than the contact surface  104  and the contact surface  67 . 
     Hence, the first insulating part  84  can be reliably positioned between the contact surface  104  of the developing-side contact part  101  and the contact surface  67  of the supply-side contact part  64 . This configuration ensures a more considerable insulating distance than an arrangement in which the first insulating part  84  extends rightward (outward in the left-right direction) by the same length as the developing-side contact part  101  and the supply-side contact part  64 . 
     Thus, this configuration can reliably insulate the contact surface  104  of the developing-side contact part  101  from the contact surface  67  of the supply-side contact part  64 . 
     (5) As shown in  FIG.  7   , the developing electrode  63 , the bearing member  62 , and the supply electrode  61  are all fixed to the right wall  44  of the developing-cartridge frame  25  by a common screw. 
     Hence, the developing electrode  63 , the bearing member  62 , and the supply electrode  61  can be fixed to the right wall  44  of the developing-cartridge frame  25  while using fewer parts. 
     (6) As shown in  FIG.  7   , the screw  110  can be screwed into the threaded part  51  of the developing-cartridge frame  25  while encased by the screw insertion part  91  of the bearing member  62 . 
     Accordingly, this construction can prevent the shaft of the screw  110  that is inserted through the screw insertion part  91  (right half) and the shaft of the screw  110  screwed into the threaded part  51  (left half) from contacting the developing electrode  63  and the supply electrode  61 . 
     Thus, this construction reliably prevents electricity from being conducted between the developing electrode  63  and the supply electrode  61  through the screw  110 . 
     (7) According to the developing cartridge  19  described above, the screw  110  contacts only the screw insertion part  91  and the threaded part  51  and does not contact the developing electrode  63  and the supply electrode  61 . 
     Hence, this construction can reliably prevent the screw  110  from contacting the developing electrode  63  and the supply electrode  61 . 
     Accordingly, this construction can prevent electricity from being conducted between the developing electrode  63  and the supply electrode  61  via the screw  110 . 
     (8) As shown in  FIGS.  3  and  7   , the screw  110  can be inserted through the screw insertion part  91  which is inserted through the developing-side insertion hole  107  formed in the developing electrode  63 . 
     Accordingly, the screw insertion part  91  is interposed between the screw  110  and the peripheral edge of the developing-side insertion hole  107 , thereby insulating the developing electrode  63  and the screw  110  from each other. 
     Moreover, since the screw insertion part  91  has a cylindrical shape that is elongated in the left-right direction, the screw insertion part  91  can ensure an insulated condition between the developing electrode  63  and the screw  110  in the left-right direction. 
     (9) As shown in  FIGS.  5  and  7   , the screw can be screwed into the threaded part  51  which is inserted into the supply-side insertion hole  73  formed in the supply electrode  61 . 
     Hence, the threaded part  51  is interposed between the screw  110  and the peripheral edge of the supply-side insertion hole  73 , thereby insulating the supply electrode  61  and the screw  110  from each other. 
     Moreover, since the threaded part  51  has a cylindrical shape that is elongated in the left-right direction, the threaded part  51  can ensure an insulating condition between the supply electrode  61  and the screw  110  along a direction orthogonal to the left-right direction. 
     (10) As shown in  FIGS.  3  and  6   , the bearing member  62  has the bearing part  82  provided separately from the screw insertion part  91  for rotatably supporting the developing-roller shaft A 1 . 
     Accordingly, this construction can position the bearing member  62  with reference to the developing-roller shaft A 1 . 
     By positioning the developing electrode  63  relative to the bearing member  62 , the bearing member  62  can ensure good precision in positioning the developing electrode  63  relative to the developing roller  34 . 
     Thus, this construction can ensure that electricity is conducted between the developing-roller shaft A 1  and the developing electrode  63 . 
     (11) As shown in  FIGS.  6  and  7   , the inner diameter of the screw insertion part  91  is larger than the inner diameter of the threaded part  51 . 
     Accordingly, when the screw insertion part  91  and the supply electrode  61  are aligned with each other, the threaded part  51  can easily be seen in a plane orthogonal to the left-right direction. 
     Thus, the screw  110  can be easily screwed into the threaded part  51  through the screw insertion part  91 . 
     (12) As shown in  FIG.  9   , the rear end of the second insulating part  85  (the connecting part  88  for connecting the top surface  86  to the rear surface  87 ) constituting the bearing member  62  can be used to facilitate mounting of the developing cartridge  19  in the drum cartridge  18 . In other words, the developing cartridge  19  can be smoothly mounted in the drum cartridge  18  using the bearing member  62 , which is formed of a harder material than the developing-side contact part  101  and the supply-side contact part  64 . 
     7. Variations of the Embodiment 
     (1) A variation of the developing cartridge  19  will be described next with reference to  FIG.  11   . Note that directions related to the developing cartridge  19  will be specified based on the orientation of the developing cartridge  19  when resting on a flat surface, and specifically based on the directions indicated by arrows in  FIG.  11   . 
     As shown in  FIG.  11   , the developing cartridge  19  described above can be placed on a horizontal surface H such that the front end of the developing cartridge  19  is separated from the horizontal surface H. 
     At this time, the rear end of the bottom wall  46  (the portion of the bottom wall  46  disposed rearward of the supply roller  33 ) is in contact with the horizontal surface H. 
     To lift the developing cartridge  19 , the operator grips the front end of the developing cartridge  19  and lifts the developing cartridge  19  upward. 
     (2) The printer  1  described above is an example of the image forming device of the present invention, but the present invention is not limited to the embodiments described above. 
     In addition to the monochrome printer described above, the image-forming device of the present invention may be configured as a color printer. 
     When configured as a color printer, the image-forming device may be configured as a direct tandem color printer provided with a plurality of photosensitive bodies and a recording medium conveying member; or may be configured as an intermediate transfer tandem color printer provided with a plurality of photosensitive bodies, an intermediate transfer body, and a transfer member. 
     In addition to the separable process cartridge  15  that allows the drum cartridge  18  and the developing cartridge  19  to be separated from each other, as described above, the process cartridge  15  may be an integrated unit in which the drum cartridge  18  and the developing cartridge  19  are integrally provided. 
     It is also possible to provide the photosensitive drum  20  in the main casing  2 , while enabling only the developing cartridge  19  to be mounted in and removed from the main casing  2 . 
     Further, in place of the photosensitive drum  20  described above, a photosensitive belt or other member may be used as the photosensitive body. 
     Similarly, instead of the developing roller  34  described above, a developing sleeve, a developing belt, a brush roller, or other device may be used as the developer-carrying body. 
     Further, instead of the supply roller  33  described above, a supply sleeve, a supply belt, a brush roller, or other member may be used as the supply member. 
     Further, instead of the agitator  29  described above, an auger screw, a conveying belt, or another member may be used as the conveying member. 
     Further, instead of the transfer roller  21  described above, a contact-type transfer member such as a transfer belt, a transfer brush, a transfer blade, and a film-like transfer device, or a non-contact-type transfer member such as a corotron-type transfer member may be used as the transfer member. 
     Further, instead of the scorotron charger  22  described above, a non-contact-type charger such as a corotron-type charger and a charger provided with a sawtooth discharge member, or a contact-type charger such as a charging roller may be used as the charger. 
     Further, instead of the scanning unit  16  described above, an LED unit or the like may be used as the exposure member. 
     The image-forming device of the present invention may also be configured as a multifunction peripheral that is equipped with an image-reading unit and the like. 
     While the developing electrode  63  described above is formed of a conductive resin material, the developing electrode  63  may instead be formed of metal. The supply electrode  61  may be similarly formed of metal. 
     While the bearing member  62  described above is formed of an insulating resin material, the bearing member  62  may instead be formed of an insulating rubber. Further, while the bearing member  62  described above rotatably supports both the developing-roller shaft A 1  and the supply-roller shaft A 2 , the bearing member  62  may be configured to rotatably support only one of these shafts. 
     Conductive grease may be added between the supply-roller-shaft insertion part  65  and the supply-roller shaft A 2 , and between the insertion hole  109  and the developing-roller shaft A 1 .