CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2014-071835, filed on Mar. 31, 2014, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects described herein relate to a photosensitive body cartridge for an electrophotographic image forming apparatus. 
     BACKGROUND 
     A known image forming apparatus includes a printer that includes a photosensitive drum and a scraper roller for scraping and collecting foreign matter adhering to a surface of a photosensitive drum. 
     In such a printer, a drum gear is attached to an end portion of a shaft of the photosensitive drum, and a scraper-roller gear is attached to a rotating shaft of the scraper roller. A driving force is transmitted from the drum gear to the scraper-roller gear via a plurality of idle gears. A peripheral speed of the scraper roller relative to the photosensitive drum is increased to collect or remove foreign matter from the surface of the photosensitive drum effectively. 
     SUMMARY 
     In a first example aspect, a drum cartridge includes a photosensitive drum rotatable about an axis, a first cleaning roller including a first shaft extending in a direction extending along the axis, and a second cleaning roller including a second shaft extending in the direction, the second cleaning roller including a surface contacting a surface of the first cleaning roller, the second cleaning roller spaced apart from the photosensitive drum. The drum cartridge further includes a bearing through which the first shaft and the second shaft are inserted, a first cleaning gear rotatable with the first cleaning roller, and a second cleaning gear rotatable with the second cleaning roller and meshing with the first cleaning gear. The drum cartridge further includes a drum gear being rotatable with the photosensitive drum, a first idle gear meshing with the drum gear, and a second idle gear meshing with the first idle gear. The drum cartridge includes a coupling joining the second cleaning gear and the second idle gear, the coupling being rotatable in unison with the second cleaning gear and the second idle gear 
     In a further example aspect, a method is disclosed that includes receiving, at a drum gear, a first rotational force applying a first rotational speed to a photosensitive drum, and transmitting a second rotational force to a first cleaning gear to rotate a first cleaning roller at a second rotational speed. Transmitting the second rotational force to the first cleaning roller includes rotating a first idle gear in response to rotation of the drum gear, the first idle gear engaged by the drum gear, rotating a second idle gear in response to rotation of the first idle gear, the second idle gear engaged by the first idle gear, rotating a second cleaning gear rotationally coupled to the second idle gear, and applying the second rotational force to the first cleaning gear from the second cleaning gear. 
     A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1  is a central cross-sectional view depicting a drum cartridge in an illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 2  is a central cross-sectional view depicting an image forming apparatus in which the drum cartridge depicted in  FIG. 1  is installed in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 3  is a perspective view depicting the drum cartridge depicted in  FIG. 1  as viewed from the left rear in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 4A  is a right side view depicting a rear portion of the drum cartridge depicted in  FIG. 1  in the illustrative embodiment according to one or more aspects of the disclosure, wherein a pair of release levers is located at a first position. 
         FIG. 4B  is a side sectional view depicting of the rear portion of the drum cartridge depicted in  FIG. 1  in the illustrative embodiment according to one or more aspects of the disclosure, wherein the pair of release levers is located at the first position. 
         FIG. 5A  is a right side view depicting of the rear portion of the drum cartridge depicted in  FIG. 1  in the illustrative embodiment according to one or more aspects of the disclosure, wherein the pair of release levers is located at a second position. 
         FIG. 5B  is a side sectional view depicting of the rear portion of the drum cartridge depicted in  FIG. 1  in the illustrative embodiment according to one or more aspects of the disclosure, wherein the pair of release levers is located at the second position. 
         FIG. 6  is a cross-sectional view taken along line A-A in  FIG. 4A  in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 7A  is a partial perspective view depicting the drum cartridge depicted in  FIG. 1  as viewed from the right front in the illustrative embodiment according to one or more aspects of the disclosure, wherein a cover frame is removed from the drum cartridge. 
         FIG. 7B  is a cross sectional view of  FIG. 7A , passing through the centers of first and second rollers in their diametric directions in the illustrative embodiment according to one or more aspects of the disclosure, wherein a base frame is omitted for convenience in drawing. 
         FIG. 8A  is a perspective view depicting a first electrode and a second electrode depicted in  FIG. 7A  as viewed from the right rear in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 8B  is a perspective view depicting the first electrode and the second electrode depicted in  FIG. 7A  as viewed from the left front in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 9  is a disassembled perspective view depicting a drive unit depicted in  FIG. 3  as viewed from the upper right in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 10  is a disassembled perspective view depicting the drive unit depicted in  FIG. 3  as viewed from the right rear in the illustrative embodiment according to one or more aspects of the disclosure, wherein a drum frame is omitted for convenience in drawing. 
         FIG. 11A  is a right side sectional view depicting the drive unit depicted in  FIG. 3  in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 11B  is a top plan view depicting a power transmission mechanism depicted in  FIG. 11A  in the illustrative embodiment according to one or more aspects of the disclosure, wherein a drum frame and a gear holder are omitted for convenience in drawing. 
         FIG. 12  is a perspective view depicting the drum cartridge depicted in  FIG. 1  as viewed from the left rear in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 13A  illustrates an initial state of the drum cartridge depicted in  FIG. 1  with respect to a main body of the image forming apparatus in a procedure to install the drum cartridge in the main body in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 13B  illustrates an intermediate state of the drum cartridge with respect to the main body in the installation procedure, subsequent to the initial state depicted in  FIG. 13A , in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 14A  illustrates an intermediate state of the drum cartridge with respect to the main body in the installation procedure, subsequent to the initial state depicted in  FIG. 13B , in the illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 14B  illustrates a state of the drum cartridge with respect to the main body in the installation procedure at the time of completion of the installation of the drum cartridge in the main body in the illustrative embodiment according to one or more aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In general, the present disclosure relates to a photosensitive body cartridge useable in an electrophotographic image forming apparatus. 
     In a known printer, the scraper roller may be configured to come into contact with and move away from the photosensitive drum. The scraper roller may be urged toward the photosensitive drum by an urging spring. With this configuration, while the scraper roller is allowed to move slightly away from the photosensitive drum, the photosensitive drum and the scraper roller are in contact with each other at all times. Nevertheless, due to slight movement of the scraper roller away from the photosensitive drum, a state of engagement of teeth of any two gears disposed between the drum gear and the scraper roller gear in the gear train may be changed. This may cause variation in the peripheral speed of the scraper roller relative to the photosensitive drum, whereby foreign matter adhering to the surface of the photosensitive drum might not be removed therefrom evenly. However, some embodiments of the disclosure address such issues by providing a drum cartridge in which cleaning is performed on a surface of a photosensitive drum with stability and certainty. In the drum cartridge according to some aspects of the disclosure, cleaning may be performed on the surface of the photosensitive drum with stably and certainty. Such features can be accomplished, for example, via use of a coupling provided between gears provided in the drum cartridge that accommodates such movement of a roller. 
     1. Overview of Drum Cartridge 
     As depicted in  FIG. 1 , a drum cartridge  1  has a generally rectangular frame shape having a bottom in plan view. The drum cartridge  1  is an example of a photosensitive body cartridge. The drum cartridge  1  includes a photosensitive drum  2 , a scorotron charger  3 , a transfer roller  4 , and a cleaning unit  5 . 
     In the description below, the side on which the photosensitive drum  2  is disposed in the drum cartridge  1  is defined as the rear of the drum cartridge  1  and the opposite side of the drum cartridge  1  is defined as the front of the drum cartridge  1 . The right and left of the drum cartridge  1  are defined with reference to the front of the drum cartridge  1 . More specifically, the orientation of the drum cartridge  1  is defined with reference to directional arrows appended in each drawing. 
     As depicted in  FIG. 4B , a direction that a pair of roller shaft guides  201  extends, hereinafter, is referred to as “extending direction”. As depicted in  FIG. 13A , a direction that the drum cartridge  1  is attached to and detached from the main body  12 , hereinafter, is referred to as “attaching and detaching direction”. 
     The photosensitive drum  2  has a generally cylindrical shape extending in the right-left direction. The photosensitive drum  2  is supported at a rear end portion of the drum cartridge  1 . 
     The scorotron charger  3  is disposed above the photosensitive drum  2  and is spaced apart from the photosensitive drum  2 . 
     The transfer roller  4  is disposed below the photosensitive drum  2 . The transfer roller  4  is in contact with a lower surface of photosensitive drum  2 . 
     The cleaning unit  5  is disposed behind the photosensitive drum  2 . The cleaning unit  5  includes a first roller  6 , a second roller  7 , a sponge scraper  8 , and a storage  9 . The first roller  6  is an example of a first cleaning roller. The second roller  7  is an example of a second cleaning roller. 
     The first roller  6  is disposed above and behind the photosensitive drum  2 . The first roller  6  is in contact with an upper rear surface of the photosensitive drum  2 . 
     The second roller  7  is disposed above and behind the first roller  6 . The second roller  7  is in contact with an upper rear surface of the first roller  6 . 
     The sponge scraper  8  is disposed above the second roller  7 . The sponge scraper  8  is in contact with an upper surface of the second roller  7 . 
     The storage  9  has a generally box shape with its upper front portion opened. The storage  9  is disposed below the second roller  7 . 
     2. Usage of Drum Cartridge 
     As depicted in  FIG. 2 , the drum cartridge  1  is installed in an image forming apparatus  11  and used therein. 
     The image forming apparatus  11  may be an electrophotographic monochrome printer. The image forming apparatus  11  includes a main body  12 , a process cartridge  13 , a scanner unit  14 , and a fixing unit  15 . The main body  12  is an example of an apparatus body. 
     The main body  12  has a generally box shape. The main body  12  has an opening  16  defined therein and includes a front cover  17 , a sheet feed tray  18 , and a sheet discharge tray  19 . 
     The opening  16  is defined in a front end portion of the main body  12 . The opening  16  provides communication between the inside and the outside of the main body  12  in the front-rear direction to allow the process cartridge  13  to pass therethrough. 
     The front cover  17  is disposed at a front end of the main body  12 . The front cover  17  has a generally flat plate shape. The front cover  17  extends in the upper-lower direction and is supported by a front wall of the main body  12  so as to be pivotable on its lower end portion. The front cover  17  is configured to expose or close the opening  16 . 
     The sheet feed tray  18  is disposed at a bottom portion of the main body  12 . The sheet supply tray  27  is configured to accommodate therein one or more sheets P. 
     The sheet discharge tray  19  is defined at a front half portion of an upper wall of the main body  12 . The sheet discharge tray  19  is recessed relative to an upper surface of the main body  12  for supporting one or more sheets P thereon. 
     The process cartridge  13  is positioned at a substantially middle position of the main body  12  in the upper-lower direction. The process cartridge  13  is configured to be installed in and detached from the main body  12 . The process cartridge  13  includes the drum cartridge  1  and a developing cartridge  20 . 
     The developing cartridge  20  is attached to the drum cartridge  1  while being positioned in front of the photosensitive drum  2 . The developing cartridge  20  includes a developing roller  21 , a supply roller  22 , a layer thickness regulating blade  23 , and a toner container  24 . 
     The developing roller  21  is rotatably supported at a rear end portion of the developing cartridge  20 . The developing roller  21  has a generally cylindrical shape extending in the right-left direction. The developing roller  21  is in contact with a front surface of the photosensitive drum  2 . 
     The supply roller  22  is disposed in front of and below the developing roller  2 . The supply roller  22  has a generally cylindrical shape extending in the right-left direction and is rotatably supported by the developing cartridge  20 . The supply roller  22  is in contact with an lower-front surface of the developing roller  21 . 
     The layer thickness regulating blade  23  is disposed in front of and above the developing roller  21 . The layer thickness regulating blade  23  is in contact with an front surface of the developing roller  21 . 
     The toner container  24  is disposed in front of the supply roller  22  and the layer thickness regulating blade  23 . The toner container  24  is configured to store toner therein. 
     The scanner unit  14  is disposed above the process cartridge  13 . The scanner unit  14  is configured to emit a laser beam toward the photosensitive drum  2  based on image data. 
     The fixing unit  15  is disposed behind the process cartridge  13 . The fixing unit  15  includes a heating roller  26  and a pressing roller  27 . The pressing roller  27  is in pressure contact with a lower-rear surface of the heating roller  26 . 
     As the image forming apparatus  11  starts an image forming operation, the scorotron charger  3  charges a surface of the photosensitive drum  2  uniformly and the scanner unit  14  exposes the surface of the photosensitive drum  4  with a laser beam. Thus, an electrostatic latent image based on image data is formed on the surface of the photosensitive drum  2 . 
     The supply roller  22  supplies toner to the developing roller  21  from the toner container  24 . Meanwhile, toner is positively charged between the developing roller  21  and the supply roller  22  and is then carried by the developing roller  21 , and the layer-thickness regulating blade  23  regulates a layer thickness of toner carried by the developing roller  21 . 
     The developing roller  21  then supplies the toner carried thereon to the surface of the photosensitive drum  2 , i.e., the electrostatic latent image formed on the surface of the photosensitive drum  2 . Thus, the photosensitive drum  2  carries a toner image on the surface thereof. 
     Rollers rotate to convey sheets P, one by one, to between the photosensitive drum  2  and the transfer roller  4  at a predetermined timing from the sheet feed tray  18 . The transfer roller  4  transfers the toner image formed on the surface of the photosensitive drum  2  onto a sheet P while the sheet P passes between the photosensitive drum  2  and the transfer roller  4 . 
     Then, the heating roller  26  and the pressing roller  27  apply heat and pressure, respectively, to the sheet P to thermally fix the toner image transferred onto the sheet P while the sheet P passes therebetween. After the toner image is fixed on the sheet P, the sheet P is discharged onto the sheet discharge tray  19 . 
     The surfaces of the first and second rollers  6  and  7  are charged to positive potential that is higher than the potential of the surface of the photosensitive drum  2 . More specifically, the surfaces of the first and second rollers  6  and  7  are charged such that the surface of the second roller  7  has positive potential higher than the positive potential of the first roller  6 . 
     The first roller  6  removes paper dust from the surface of the photosensitive drum  2  when contacting the paper dust. That is, the first roller  6  cleans the surface of the photosensitive drum  2 . The second roller  7  then removes the paper dust from the first roller  6  when contacting the paper dust. 
     Thereafter, the sponge scraper  8  scrapes and removes the paper dust from the second roller  7  and the collected paper dust is stored in the storage  9 . 
     3. Details of Drum Cartridge 
     As depicted in  FIGS. 1 and 3 , the drum cartridge  1  includes a drum frame  31 , the photosensitive drum  2 , the scorotron charger  3 , the transfer roller  4 , the cleaning unit  5 , and a drive unit  32 . 
     (1) Drum Frame 
     As depicted in  FIG. 3 , the drum frame  31  includes a base frame  35  and a cover frame  36 . 
     The base frame  35  has a generally rectangular shape in plan view and has a bottom. The base frame  35  is made of resin material, for example, polystyrene (“PS”). The base frame  35  includes a right sidewall  38 , a left sidewall  39 , a bottom wall  40 , a rear wall  41 , and a front wall  42  that are integrated with each other. 
     The right sidewall  38  has a generally L-shaped plate shape in side view. The right sidewall  38  includes a rear portion  45  and a front portion  46 . 
     As depicted in  FIG. 4A , the rear portion  45  constitutes a rear portion of the right sidewall  38 . The rear portion  45  has a generally rectangular plate shape in side view. An upper surface of the rear portion  45  extends upward and rearward. As depicted in  FIG. 7A , the rear portion  45  includes a first guide recess  47 , a second guide recess  48 , and a recess  49 . 
     As depicted in  FIGS. 4A and 7A , the first guide recess  47  is recessed downward relative to the upper surface of the rear portion  45  of the right wall  38  and has a generally U-shape. 
     The second guide recess  48  is recessed downward relative to the upper surface of the rear portion  45  of the right wall  38  and has a generally U-shape. The second guide recess  48  is disposed in front of the first guide recess  47 . 
     The recess  49  is disposed at a front end portion of the rear portion  45 . The recess  49  extends to a substantially middle portion of the rear portion  45  in the up-down direction and has a generally rectangular shape in side view. An upper portion of the recess  49  protrudes upward from the rear portion  45  of the right wall  38  and has a semicircular shape in side view. The recess  49  has a drum-shaft pass-through hole  50 . 
     As depicted in  FIGS. 6 and 7A , the drum-shaft pass-through hole  50  penetrates through a substantially central portion of the recess  49  in the upper-lower direction and in the front-rear direction and has a circular shape in side view. The drum-shaft pass-through hole  50  has a diameter that is slightly larger than a diameter of a drum shaft  86  of the photosensitive drum  2 . 
     As depicted in  FIG. 1 , the front portion  46  constitutes a front portion of the right sidewall  38 . The front portion  46  extends frontward from a lower front end of the rear portion  45  and has a generally rectangular plate shape in side view. 
     As depicted in  FIG. 3 , the left sidewall  39  is disposed to the left of the right sidewall  38  and is spaced apart from the right sidewall  38 . The left sidewall  39  has a generally L-shaped plate shape in side view. The left sidewall  39  includes a rear portion  51  and a front portion  52 . 
     The rear portion  51  constitutes a rear portion of the left sidewall  39 . As depicted in  FIGS. 9 and 12 , the rear portion  51  has a crank-like shape in plan view. The rear portion  51  includes a first portion  53 , a second portion  54 , and a third portion  55 . 
     The first portion  53  constitutes a front portion of the rear portion  51  of the left sidewall  39 . As depicted in  FIG. 9 , the first portion  53  has a generally rectangular plate shape in side view. The first portion  53  has a larger-diameter through hole  56 . 
     The larger-diameter through hole  56  penetrates through a substantially middle portion of the first portion  53  in side view and has a circular shape in side view. The larger-diameter through hole  56  has a diameter that is larger than the diameter of the drum-shaft pass-through hole  50  of the right sidewall  38 . The center of the larger-diameter through hole  56  is coincide with the center of the drum-shaft pass-through hole  50  of the right sidewall  38  of the base frame  35  as viewed in the right-left direction. 
     As depicted in  FIGS. 9 and 12 , the second portion  54  constitutes a rear portion of the rear portion  51  of the left sidewall  39 . The second portion  54  is disposed to the right of the first portion  53 . The second portion  54  has a generally rectangular plate shape in side view. The second portion  54  includes a first retaining portion  57  and a semicircular portion  58 . 
     The first retaining portion  57  has a generally rectangular plate shape in front view. The first retaining portion  57  protrudes leftward from a rear end of the second portion  54 . The first retaining portion  57  has a through hole in its middle portion for catching a first hook  179  of a gear holder  151 . 
     The semicircular portion  58  is disposed at a substantially middle portion of the second portion  54  in the front-rear direction. The semicircular portion  58  is recessed downward relative to an upper surface of the second portion  54  and has a generally semicircular shape in side view. 
     The third portion  55  is disposed between a rear end portion of the first portion  53  and a front end portion of the second portion  54 . The third portion  55  has a generally rectangular plate shape in bottom view. 
     As depicted in  FIG. 3 , the front portion  52  constitutes a front portion of the left sidewall  39  of the base frame  35 . The front portion  52  extends frontward from a lower front end of the rear portion  51  of the left sidewall  39  and has a generally rectangular plate shape in side view. 
     The bottom wall  40  is disposed such that its front portion is disposed between a lower end portion of the right sidewall  38  and a lower end portion of the left sidewall  39  and its rear portion is disposed between a substantially middle portion of the right sidewall  38  in the up-down direction and a substantially middle portion of the left sidewall  39  in the up-down direction as depicted in  FIGS. 1 and 12 . The bottom wall  40  has a crank-like shape in side view, and has a generally plate shape extending in the right-left direction. As depicted in  FIGS. 1 and 4B , the bottom wall  40  includes a transfer-roller supporting portion  61  and a pair of guide ribs  62 . 
     The transfer-roller supporting portion  61  is disposed in a rearward position at a middle portion of the bottom wall  40 . The transfer-roller supporting portion  61  is recessed downward in the bottom wall  40  and has a generally U shape in side view. The transfer-roller supporting portion  61  supports the transfer roller  4  therein so as to be rotatable. 
     As depicted in  FIG. 4B , the guide ribs  62  are spaced apart from each other in the right-left direction at a rear end portion of the bottom wall  40 . The guide ribs  62  are disposed at right and left end portions, respectively, of the bottom wall  40 . The guide ribs  62  protrude upward from an upper surface of the bottom wall  40  and have a generally rectangular plate shape in side view. Upper surfaces of the guide ribs  62  extend along the extending direction. 
     As depicted in  FIGS. 1 and 3 , the rear wall  41  of the base frame  35  is disposed between a rear end portion of the right sidewall  38  and a rear end portion of the left sidewall  39 . A lower end of the rear wall  41  is contiguous to a rear end of the bottom wall  40 . The rear wall  41  has a generally rectangular plate shape in rear view. As depicted in  FIGS. 4B and 7A , the rear wall  41  includes a pair of release-lever supporting bosses  63 . 
     The release-lever supporting bosses  63  are disposed above and to the rear of the guide ribs  62 , respectively, of the bottom wall  40  and at right and left end portions, respectively, of an upper end portion of the rear wall  41 . The release-lever supporting bosses  63  protrude rightward and leftward from the right and left end portions, respectively, of the rear wall  41 . The release-lever supporting bosses  63  have a generally cylindrical shape. 
     As depicted in  FIGS. 1 and 3 , the front wall  42  of the base frame  35  is disposed between a front end portion of the right sidewall  38  and a front end portion of the left sidewall  39 . A lower end of the front wall  42  is contiguous to a front end of the bottom wall  40 . The front wall  42  has a generally rectangular plate shape in front view. 
     The cover frame  36  is disposed above a rear end portion of the base frame  35  while covering the photosensitive drum  2 . As depicted in  FIGS. 4A and 9 , the cover frame  36  includes a right sidewall  65 , a left sidewall  66 , and a top wall  67 , which are integrated with each other. 
     As depicted in  FIG. 4A , the right sidewall  65  has a rectangular plate in side view. A lower surface of the right sidewall  65  extends along the extending direction. The right sidewall  65  includes a first concave portion  69 , a second concave portion  70 , and a projecting portion  71 . 
     The first concave portion  69  is recessed upward relative to the lower surface at a rear end portion of the right sidewall  65 . The first concave portion  69  has a generally U shape. 
     The second concave portion  70  is defined in front of the first concave portion  69  and is recessed upward relative to the lower surface of the right sidewall  65 . The second concave portion  70  also has a generally U shape. 
     The projecting portion  71  is disposed in front of the second concave portion  70 . The projecting portion  71  extends downward from the right sidewall  65  and has a generally rectangular plate shape in side view. The projecting portion  71  has a drum-shaft pass-through hole  72 . 
     The drum-shaft pass-through hole  72  penetrates through a substantially central portion of the projecting portion  71  in the upper-lower direction and in the front-rear direction and has a circular shape in side view. The drum-shaft pass-through hole  72  has a diameter that is slightly larger than the diameter of the drum shaft  86  of the photosensitive drum  2 . 
     As depicted in  FIG. 9 , the left sidewall  66  of the cover frame  36  has a generally rectangular plate shape in side view. The left sidewall  66  includes a first positioning boss  73 , a second positioning boss  74 , and a semicircular portion  75 . 
     The first positioning boss  73  protrudes leftward from a rear end portion of a left surface of the left sidewall  66  and has a generally cylindrical shape. 
     The second positioning boss  74  protrudes leftward from a front end portion of the left surface of the left sidewall  66  and has a generally cylindrical shape. 
     The semicircular portion  75  is disposed in front of the first positioning boss  73  and is recessed upward relative to a lower surface of the left sidewall  66 . The semicircular portion  75  has a generally semicircular shape in side view. 
     As depicted in  FIGS. 1 and 3 , the top wall  67  of the cover frame  35  is disposed between an upper end portion of the right sidewall  65  and an upper end portion of the left sidewall  66 . As depicted in  FIG. 1 , the top wall  67  includes a charger supporting portion  77  and a rear portion  78 . 
     The charger supporting portion  77  constitutes a front portion of the top wall  67 . The charger supporting portion  77  extends in the right-left direction and has an inverted U-shape in side view. The charger supporting portion  77  includes the scorotron charger  3 . 
     The rear portion  78  constitutes a rear portion of the top wall  67 . The rear portion  78  has a generally rectangular plate shape in plan view extending in the right-left direction. As depicted in  FIGS. 4B and 9 , the rear portion  78  includes a second retaining portion  80 , and a pair of guide ribs  81 . 
     The second retaining portion  80  is disposed at a left rear end portion of the rear portion  78  of the top wall  67 . The second retaining portion  80  penetrates through the rear portion  78  of the top wall  67  in the up-down direction for catching a second hook  180  of the gear holder  151  therein. 
     As depicted in  FIG. 4B , the guide ribs  81  of the cover frame  36  are disposed at the rear portion  78  of the top wall  67  and are spaced apart from each other in the right-left direction. The guide ribs  81  are disposed at right and left end portions, respectively, of the rear portion  78  of the top wall  67 . The guide ribs  81  protrude downward from a lower surface of the rear portion  78  and have a generally triangular shape in side view. Lower surfaces of the guide ribs  81  extend the extending direction. 
     As depicted in  FIG. 3 , the drum frame  31  includes the base frame  35  and the cover frame  36 , in which the cover frame  36  is assembled to the base frame  35 . 
     More specifically, the cover frame  36  is assembled to the base frame  35  such that, in the up-down direction, the right sidewall  65  of the cover frame  36  overlaps the rear portion  45  of the right sidewall  38  of the base frame  35 , the left sidewall  66  of the cover frame  36  overlaps the rear portion  51  of the left sidewall  39  of the base frame  35 , and a rear end portion of the rear portion  78  of the cover frame  36  overlaps the rear wall  41  of the base frame  35 . 
     In this state, as depicted in  FIGS. 4A and 6 , in the right end portion of the drum frame  31 , a lower end of the right sidewall  65  of the cover frame  36  is in contact with an upper end of the rear portion  45  of the right sidewall  38  of the base frame  35  and the projecting portion  71  of the right sidewall  65  of the cover frame  36  overlaps the right sidewall  38  of the base frame  35  as viewed in the right-left direction. Further, the drum-shaft pass-through hole  50  of the base frame  35  is coincide with the drum-shaft pass-through hole  72  of the cover frame  36  in the right-left direction. 
     As depicted in  FIG. 4A , the first guide recess  47  of the right sidewall  38  of the base frame  35  faces the first concave portion  69  of the right sidewall  65  of the cover frame  36  in the up-down direction. Thus, the first guide recess  47  and the first concave portion  69  constitute a second-electrode receiving portion  202  for receiving a contact portion  145  of a second electrode  118 . That is, the second-electrode receiving portion  202  extends in the up-down direction across a boundary of the base frame  35  and the cover frame  36 . 
     The second guide recess  48  of the right sidewall  38  of the base frame  35  faces the second concave portion  70  of the right sidewall  65  of the cover frame  36  in the up-down direction. Thus, the second guide recess  48  and the second concave portion  70  constitute a first-electrode receiving portion  203  for receiving a contact portion  145  of a first electrode  117 . The first-electrode receiving portion  203  is an example of a guide. That is, the first-electrode receiving portion  203  extends in the up-down direction across the boundary of the base frame  35  and the cover frame  36 . 
     As depicted in  FIGS. 6 and 9 , in the left portion of the drum frame  31 , a lower end of the left sidewall  66  of the cover frame  36  is in contact with an upper end of the left sidewall  39  of the base frame  35 . 
     In this state, as depicted in  FIG. 9 , the semicircular portion  58  of the left sidewall  39  of the base frame  35  faces the semicircular portion  75  of the left sidewall  66  of the cover frame  35  in the up-down direction. Thus, the semicircular portion  58  of the left sidewall  39  of the base frame  35  and the semicircular portion  75  of the left sidewall  66  of the cover frame  35  define an opening  200  in which an Oldham coupling  155  is disposed. 
     As depicted in  FIG. 4B , the upper surfaces of the guide ribs  62  of the bottom wall  40  of the base frame  35  face the lower surfaces of the guide ribs  81 , respectively, of the top wall  67  of the cover frame  36  while being spaced apart therefrom at a certain interval in the attaching and detaching direction. Thus, the pair of guide ribs  62  and the pair of guide ribs  81  constitute a pair of roller shaft guides  201 . 
     In the drum frame  31  configured as described above, as depicted in  FIGS. 1 and 3 , a first accommodating portion  204  is defined by the rear portion  45  of the right sidewall  38  of the base frame  35 , the rear portion  51  of the left sidewall  39  of the base frame  35 , the rear portion of the bottom wall  40  of the base frame  35 , the rear wall  41  of the base frame  35 , and the cover frame  36 . The first accommodating portion  204  is configured to accommodate therein the photosensitive drum  2  and the cleaning unit  5 . 
     In the drum frame  31 , a second accommodating portion  205  is further defined by the front portion  46  of the right sidewall  38  of the base frame  35 , the front portion  52  of the left sidewall  39  of the base frame  35 , a front portion of the bottom wall  40  of the base frame  35 , and the front wall  42  of the base frame  35 . The second accommodating portion  205  is disposed in front of the first accommodating portion  204  and is configured to accommodate therein the developing cartridge  20 . 
     (2) Photosensitive Drum 
     As depicted in  FIG. 6 , the photosensitive drum  2  includes a drum body  83 , a pressing member  84 , a bearing member  85 , and a drum shaft  86 . The drum shaft  86  is an example of a first rotating shaft. 
     The drum body  83  has a generally cylindrical shape extending in the right-left direction. The drum body  83  is disposed between the right sidewall  38  and the left sidewall  39  of the base frame  35 . More specifically, the drum body  83  includes a metal base tube and a photosensitive resin layer. The base tube has a generally cylindrical shape extending in the right-left direction. The photosensitive layer covers a surface of the base tube. 
     The pressing member  84  is disposed at a right end portion of the drum body  83 . The pressing member  84  includes a right flange  88 , a frictional member  89 , and a compression spring  90 . 
     The right flange  88  has a generally cylindrical shape with its left end closed. The right flange  88  has an outside diameter that is substantially the same as an inside diameter of the drum body  83 . The right flange  88  has a through hole in its central portion of the closed end. The through hole allows the drum shaft  86  to pass therethrough. The right flange  88  is fixed to the right end portion of the drum body  83  so as not be relatively rotatable. 
     The frictional member  89  has a generally cylindrical shape with its right end closed. The frictional member  89  has an outside diameter that is slightly smaller than an inside diameter of the right flange  88 . The frictional member  89  has a through hole in its central portion of the closed end. The through hole allows the drum shaft  86  to pass therethrough. The frictional member  89  is fitted to a right end portion of the right flange  88  so as to be slidable therein in the right-left direction. 
     The compression spring  90  is a coil spring extending in the right-left direction. The compression spring  90  is disposed between the closed end of the right flange  88  and the closed end of the frictional member  89  in a compressed state. 
     Therefore, the compression spring  90  presses the drum body  83  leftward via the right flange  88  while pressing the frictional member  89  rightward. 
     The bearing member  85  is disposed at a left end portion of the drum body  83 . The bearing member  85  includes a first left flange  91  and a second left flange  92 . 
     The first left flange  91  includes a shaft pass-through portion  93  and a flange gear  94 , which are integrated with each other. 
     The shaft pass-through portion  93  has generally cylindrical shape with its left end closed. The shaft pass-through portion  93  has an outside diameter that is substantially the same as the inside diameter of the drum body  83 . The shaft pass-through portion  93  has a through hole in its central portion of the closed end. The through hole allows the drum shaft  86  to pass therethrough. 
     The flange gear  94  protrudes leftward from the left end of the shaft pass-through portion  93  contiguously and has a generally cylindrical shape. The flange gear  94  has an outside diameter that is larger than an outside diameter of the shaft pass-through portion  93 . 
     The second left flange  92  is made of resin material, for example, polyacetal resin (“POM”). The second left flange  92  includes a drum gear  96 , a disc portion  97 , an engagement portion  98 , and a smaller-diameter cylindrical portion  99 . The drum gear  96  is an example of a photosensitive body gear. 
     The drum gear  96  has a generally cylindrical shape extending in the right-left direction. The drum gear  96  has an outside diameter that is larger than an outside diameter of the flange gear  94 . 
     The disc portion  97  protrudes inwardly from a substantially central portion of the drum gear  96  in the diametric direction of the drum gear  96 . 
     The engagement portion  98  protrudes rightward from a right surface of the disc portion  97  and has a generally cylindrical shape. The engagement portion  98  has an outside diameter that is substantially the same as the inside diameter of the flange gear  94 . The engagement portion  98  has an inside diameter that is larger than the diameter of the drum shaft  86  and an outside diameter of the smaller-diameter cylindrical portion  99 . 
     The smaller-diameter cylindrical portion  99  is hollow and penetrates through the center of the disc portion  97  in the right-left direction. The smaller-diameter cylindrical portion  99  has an outside diameter that is slightly smaller than an inside diameter of the larger-diameter through hole  56  of the left sidewall  39  of the base frame  35 . The smaller-diameter cylindrical portion  99  has an inside diameter that is substantially the same as the outside diameter of the drum shaft  86 . A left end of the smaller-diameter cylindrical portion  99  is located further to the left than a left end of the drum gear  96 . 
     The drum shaft  86  extends in the right-left direction while passing through the center of the photosensitive drum  2  in the diametric direction. The drum shaft  86  has a generally cylindrical shape. The drum shaft  86  penetrates through the through hole of the pressing member  84  and the smaller-diameter cylindrical portion  99  of the bearing member  85 . 
     The photosensitive drum  2  is rotatably positioned at a front portion of the first accommodating portion  204  of the drum frame  31  while a right end portion of the drum shaft  86  penetrates through the drum-shaft pass-through hole  72  of the right sidewall  65  and the drum-shaft pass-through hole  50  of the right sidewall  38  of the base frame  35  and a left end portion of the drum shaft  86  penetrates through the larger-diameter through hole  56  of the left sidewall  39  of the base frame  35 . 
     In this state, the smaller-diameter cylindrical portion  99  of the bearing member  85  is positioned within the larger-diameter through hole  56  of the left sidewall  39  as viewed in the right-left direction. 
     (3) Scorotron Charger 
     As depicted in  FIGS. 1 and 4B , the scorotron charger  3  is supported by the charger supporting portion  77  of the cover frame  36 . Thus, the scorotron charger  3  is disposed above the photosensitive drum  2  and is spaced apart from the photosensitive drum  2 . The scorotron charger  3  includes a charging wire  101 , a grid  102 , a wire cleaner  103 , a charger electrode  104 , and a grid electrode  105 , as depicted in  FIG. 4A . 
     As depicted in  FIG. 1 , the charging wire  101  extends in the right-left direction while being supported by the right sidewall  65  and the left sidewall  66  of the cover frame  36 . The charging wire  101  is disposed above the photosensitive drum  2  and is spaced apart from the photosensitive drum  2 . 
     The grid  102  has a U shape in side view. The grid  102  is disposed so as to surround the charging wire  101  from below. 
     As depicted in  FIGS. 4B and 9 , the wire cleaner  103  is disposed at an upper end portion of the charger supporting portion  77  and is supported so as to be slidable in the right-left direction for cleaning the charging wire  101 . The wire cleaner  103  has a generally rectangular plate shape in plan view. The wire cleaner  103  includes a cleaner  106  and a protrusion  107 . 
     As depicted in  FIG. 4B , the cleaner  106  is disposed inside the grid  102 . The cleaner  106  includes a cleaning member, e.g., a sponge or a nonwoven fabric, which pinches the charging wire  101 . The cleaner  106  is movable along the charging wire  101 . 
     As depicted in  FIG. 9 , the protrusion  107  protrudes leftward from a substantially middle portion of a left end portion of the cleaner  106  in the front-rear direction. 
     As depicted in  FIG. 4A , the charger electrode  104  is electrically connected with the charging wire  101 . The charger electrode  104  is exposed via the front end portion of the left sidewall  66  of the cover frame  36 . 
     The grid electrode  105  is electrically connected with the grid  102 . The grid electrode  105  is exposed via a substantially middle portion of the left sidewall  66  of the cover frame  36  in the front-rear direction. 
     (4) Cleaning Unit 
     As depicted in  FIGS. 1 and 4B , the cleaning unit  5  includes the first roller  6 , the second roller  7 , the sponge scraper  8 , the storage  9 , a pair of bearings  114 , a pair of urging members  115 , a pair of release levers  116 , the first electrode  117 , and the second electrode  118 . 
     The first roller  6  is disposed at a front end portion of the cleaning unit  5 . The first roller  6  includes a first-roller shaft  121  and a first-roller body  122 . 
     The first-roller shaft  121  has a generally cylindrical shape in the right-left direction. The first-roller shaft  121  has a diameter that is smaller than the width of the roller shaft guides  201 . Each of right and left end portions of the first-roller shaft  121  is inserted into the roller shaft guides  201 , respectively, from inside in the right-left direction. 
     The first-roller body  122  covers a substantially middle portion of the first-roller shaft  121  in the right-left direction and has a generally cylindrical shape. A lower-front surface of the first-roller body  122  is in contact with an upper-rear surface of the photosensitive drum  2 . 
     The second roller  7  is disposed above and behind the first roller  6 . The second roller  7  includes a second-roller shaft  124  and a second-roller body  125 , which are integrated with each other. 
     The second-roller shaft  124  has a generally cylindrical shape extending in the right-left direction. The second-roller shaft  124  has a diameter that is smaller than a diameter of the first-roller shaft  121  and the width of the roller shaft guides  201 . Each of right and left end portions of the second-roller shaft  124  is inserted into the roller shaft guides  201 , respectively, from inside in the right-left direction. 
     The second-roller body  125  protrudes outward in a diametric direction of the second-roller shaft  124  from a substantially middle portion of the second-roller shaft  124  in the right-left direction. The second-roller body  125  has a diameter that is larger than a diameter of the second-roller shaft  124 . 
     The bearings  114  are disposed within the corresponding roller shaft guides  201 , respectively. As depicted in  FIGS. 7A and 7B , each of the bearings  114  includes a first-roller-shaft pass-through portion  127 , a second-roller-shaft pass-through portion  128 , and a connecting portion  129 . 
     The first-roller-shaft pass-through portion  127  has a generally cylindrical shape extending in the right-left direction. The first-roller-shaft pass-through portion  127  has an inside diameter that is substantially the same as an outside diameter of the first-roller shaft  121 . 
     The second-roller-shaft pass-through portion  128  is disposed above and behind the first-roller-shaft pass-through portion  127 . The second-roller-shaft pass-through portion  128  has a generally cylindrical shape extending in the right-left direction. The second-roller-shaft pass-through portion  128  includes a protrusion  130  (refer to  FIG. 7B ). 
     The protrusion  130  protrudes upwardly rearward from an upper rear surface of the second-roller-shaft pass-through portion  128 . The protrusion  130  has a generally cylindrical shape. 
     The connecting portion  129  connects a lower front end portion of the first-roller-shaft pass-through portion  127  and an upper rear end portion of the second-roller-shaft pass-through portion  128 . The connecting portion  129  extends in the extending direction and has a generally rectangular column shape. 
     The bearings  114  support the first-roller shaft  121  of the first roller  6  such that the first roller  6  is rotatable while both end portions of the first-roller shaft  121  pass through the first-roller-shaft pass-through portions  127  of the bearings  114 , respectively. The bearings  114  further support the second-roller shaft  124  of the second roller  7  such that the second roller  7  is rotatable while both end portions of the second-roller shaft  124  pass through the second-roller-shaft pass-through portions  128  of the bearings  114 , respectively. 
     As described above, the bearings  114  support the first roller  6  and the second roller  7  in the roller shaft guides  201 , respectively, such that the first roller  6  and the second roller  7  are rotatable. 
     That is, the pair of bearings  114  is configured to be movable along the extending direction along with the first roller  6  and the second roller  7 . 
     The urging members  115  are coil springs that extend in the extending direction. In each of the urging member  115 , a lower front end portion is fitted to the protrusion  130  of a corresponding one of the bearings  114  and an upper rear end portion is in contact with an upper end portion of an inner surface of the rear wall  41  of the base frame  35 . 
     With this configuration, the urging members  115  urge the respective bearings  114  downwardly frontward. That is, the urging members  115  are configured to urge the first roller  6  toward the photosensitive drum  2  such that the first roller  6  is kept in contact with the photosensitive drum  2 . 
     As depicted in  FIG. 3 , the release levers  116  are disposed at both end portions of the drum frame  31  in the right-left direction. As depicted in  FIGS. 4B and 7A , each of the release levers  116  includes a proximal portion  132 , a hook  133 , and a handle  134 . 
     The proximal portion  132  has a generally obtuse triangular plate shape in side view. The proximal portion  132  has an obtuse-angled portion at its upper rear end in side view. The proximal portion  132  has an engagement hole  135 . 
     The engagement hole  135  is defined in the obtuse-angled portion of the proximal portion  132  and has a circular shape in side view. The engagement hole  135  penetrates through the proximal portion  132 . The engagement hole  135  has a diameter that is substantially the same as a diameter of the release-lever supporting bosses  63  of the rear wall  41 . 
     The hook  133  is contiguous to a front end portion of the proximal portion  132  in side view. The hook  133  has a generally arc shape in side view. The hook  133  extends downward and curved in side view from a front end of the proximal portion  132 . The radius of curvature of an inner surface of the hook  133  is slightly larger than a diameter of the second-roller shaft  124 . 
     The handle  134  is contiguous to a rear end of the proximal portion  132  in side view. That is, the handle  134  is disposed opposite to the hook  133  with respect to the engagement hole  135 . The handle  134  has a generally rectangular plate shape in rear view and extends in a direction perpendicular to a direction that the proximal portion  132  extends. 
     The release levers  116  are supported by the release-lever supporting bosses  63  of the rear wall  41  via the engagement holes  135 , respectively. This configuration enables the release levers  116  to pivot on the respective release-lever supporting bosses  63 . 
     More specifically, the pair of release levers  116  is pivotable between a first position and a second position. When the pair of release levers  113  is located at the first position, as depicted in  FIG. 4B , the handles  134  extend along a rear surface of the rear wall  41  and the hooks  133  are located above the second-roller-shaft pass-through portions  128  of the bearings  114  with being spaced apart therefrom. When the pair of release levers  113  is located at the second position, as depicted in  FIG. 5B , the handles  134  are located distant from the rear wall  41  and the hooks  133  are caught on the second-roller-shaft pass-through portions  128  of the bearings  114 , respectively. 
     As depicted in  FIG. 4B , when the pair of release levers  116  is located at the first position, the pair of bearings  114  is urged downwardly frontward by the pair of urging members  115  and thus the first roller  6  comes into contact with the upper rear surface of the photosensitive drum  2 . As depicted in  FIG. 5B , in response to the pivoting of the pair of release levers  116  from the first position to the second position, the pair of bearings  114  move upwardly rearward against the urging force of the pair of urging members  115  and thus the first roller  6  is separated from the photosensitive drum  2 . The pair of release levers  116  is located at the first position at all times as depicted in  FIG. 4B . 
     As depicted in  FIG. 7A , the first electrode  117  is disposed at a right end portion of the cleaning unit  5 . The first electrode  117  is made of conductive resin. The first electrode  117  is configured to supply first cleaning bias to the first roller  6  by establishing an electrical connection with a third apparatus electrode  193  of the main body  12 . As depicted in  FIGS. 8A and 8B , the first electrode  117  includes a roller-shaft supporting portion  137 , a contact portion  138 , and a connecting plate  139 . 
     The roller-shaft supporting portion  137  has a generally cylindrical shape with its right end closed. The roller-shaft supporting portion  137  has an inside diameter that is substantially the same as the diameter of the first-roller shaft  121 . 
     The contact portion  138  may be a drop-shaped hollow cylinder with its right end closed in side view. The contact portion  138  includes a curved portion  140 , a first straight portion  141 , and a second straight portion  142 . A portion that constitutes a lower peripheral surface of the contact portion  138  and has a semicircular shape in side view is defined as the curved portion  140 . A portion that constitutes a peripheral surface of the contact portion  138  and extends obliquely upward toward the rear from a front end of the curved portion  140  is defined as the first straight portion  141 . A portion that constitutes a peripheral surface of the contact portion  138  and extends obliquely upward toward the front from a rear end of the curved portion  140  is defined as the second straight portion  142 . The first straight portion  141  and the second straight portion  142  extend such that a distance therebetween becomes narrower toward their tips and their tips are in contact with each other. Therefore, the upper end of the first straight portion  141  is contiguous to the upper end of the second straight portion  142 . 
     The connecting plate  139  connects a lower right end portion of the roller-shaft supporting portion  137  and an upper left end portion of the contact portion  138 . The connecting plate  139  has a generally rectangular plate shape in side view. 
     As depicted in  FIGS. 7A and 7B , the first electrode  117  is disposed such that the roller-shaft supporting portion  137  receives a left end portion of the first-roller shaft  121  so as to be rotatable and the contact portion  138  is positioned in the first-electrode receiving portion  203  as depicted in  FIG. 4A . 
     The contact portion  138  of the first electrode  117  is disposed such that the contact portion  138  is positioned at a relatively lower position in the first-electrode receiving portion  203  when the pair of release levers  116  is located at the first position, i.e., when the first roller  6  is in contact with the upper rear surface of the photosensitive drum  2 . 
     In this state, the curved portion  140  of the first electrode  117  is in contact with a lower portion of an inner surface of the first-electrode receiving portion  203 , and the first straight portion  141  and the second straight portion  142  of the first electrode  117  are not in contact with any portion of the inner surface of the first-electrode receiving portion  203  and are spaced apart from the inner surface of the first-electrode receiving portion  203 . 
     During movement of the pair of release levers  116  from the first position to the second position, the contact portion  138  of the first electrode  117  moves upward in the first-electrode receiving portion  203  while slightly turning substantially clockwise in right side view. 
     When the pair of release levers  116  is located at the second position, i.e., when the first roller  6  is separated from the photosensitive drum  2 , the curved portion  140  of the first electrode  117  is in contact with a front portion of the inner surface of the first-electrode receiving portion  203 , and the first straight portion  141  and the second straight portion  142  of the first electrode  117  are not in contact with any portion of the inner surface of the first-electrode receiving portion  203  and are spaced apart from the inner surface of the first-electrode receiving portion  203 . 
     As described above, the first electrode  117  moves along the up-down direction in the first-electrode receiving portion  203  while slightly turning in side view in response to the movement of the pair of release levers  116  between the first position and the second position. That is, the first electrode  117  moves along a direction intersecting the direction that the first roller  6  moves, i.e., along a direction intersecting the extending direction while slightly turning. 
     As depicted in  FIG. 7A , the second electrode  118  is disposed at a right end portion of the cleaning unit  5  and in front of and below the first electrode  117 . The second electrode  118  is made of conductive resin. The second electrode  118  is configured to supply second cleaning bias to the second roller  7  by establishing an electrical connection with a fourth apparatus electrode  194  of the main body  12 . As depicted in  FIGS. 8A and 8B , the second electrode  118  includes a roller-shaft supporting portion  144 , a contact portion  145 , and a connecting plate  146 . 
     The roller-shaft supporting portion  144  has a generally cylindrical shape with its right end closed. The roller-shaft supporting portion  144  has an inside diameter that is substantially the same as the diameter of the second-roller shaft  124 . 
     The contact portion  145  may be a drop-shaped hollow cylinder with its right end closed in side view. The contact portion  145  includes a curved portion  147 , a first straight portion  148 , and a second straight portion  149 . A portion that constitutes a lower peripheral surface of the contact portion  145  and has a semicircular shape in side view is defined as the curved portion  147 . A portion that constitutes a peripheral surface of the contact portion  145  and extends obliquely upward toward the rear from a front end of the curved portion  147  is defined as the first straight portion  148 . A portion that constitutes a peripheral surface of the contact portion  145  and extends obliquely upward toward the front from a rear end of the curved portion  147  is defined as the second straight portion  149 . The first straight portion  148  and the second straight portion  149  extend such that a distance therebetween becomes narrower toward their tips and their tips are in contact with each other. Therefore, the upper end of the first straight portion  148  is contiguous to the upper end of the second straight portion  149 . 
     The connecting plate  146  connects a lower right end portion of the roller-shaft supporting portion  144  and an upper left end portion of the contact portion  145 . The connecting plate  146  has a generally rectangular plate shape in side view. The connecting plate  146  has a dimension in the up-down direction that is shorter than a dimension of the connecting plate  139  of the first electrode  117  in the up-down direction. 
     As depicted in  FIGS. 7A and 7B , the second electrode  118  is disposed such that the roller-shaft supporting portion  144  receives a left end portion of the second-roller shaft  124  so as to be rotatable and the contact portion  145  is positioned in the second-electrode receiving portion  202  as depicted in  FIG. 4A . 
     The contact portion  145  of the second electrode  118  is disposed such that the contact portion  145  is positioned at a relatively lower position in the second-electrode receiving portion  202  when the pair of release levers  116  is located at the first position, i.e., when the first roller  6  is in contact with the upper rear surface of the photosensitive drum  2 . 
     In this state, the curved portion  147  of the second electrode  118  is in contact with a lower portion of an inner surface of the second-electrode receiving groove  202 , and the first straight portion  148  and the second straight portion  149  of the second electrode  118  are not in contact with any portion of the inner surface of the second-electrode receiving portion  202  and are spaced apart from the inner surface of the second-electrode receiving groove  202 . 
     During movement of the pair of release levers  116  from the first position to the second position, i.e., during movement of the first roller  6  away from the photosensitive drum  2  and upwardly rearward movement of the second roller  7  along with the first roller  6 , the contact portion  145  of the second electrode  118  moves upward in the second-electrode receiving portion  202  while slightly turning substantially clockwise in right side view. 
     When the pair of release levers  116  is located at the second position, i.e., when the first roller  6  is separated from the photosensitive drum  2 , the curved portion  147  of the second electrode  118  is in contact with a front portion of the inner surface of the second-electrode receiving groove  202 , and the first straight portion  148  and the second straight portion  149  of the second electrode  118  are not in contact with any portion of the inner surface of the second-electrode receiving portion  202  and are spaced apart from the inner surface of the second-electrode receiving groove  202 . 
     As described above, the second electrode  118  moves along the up-down direction in the second-electrode receiving portion  202  while slightly turning in side view in response to the movement of the pair of release levers  116  between the first position and the second position. That is, the second electrode  118  moves along a direction intersecting the direction that the second roller  7  moves, i.e., along a direction intersecting the extending direction while slightly turning. 
     In other words, the second electrode  118  behaves substantially the same in the second-electrode receiving portion  202  as the first electrode  117  behaves in the first-electrode receiving portion  203 . 
     (5) Drive Unit 
     As depicted in  FIGS. 9 and 10 , the drive unit  32  is disposed at the left end of the drum cartridge  1 . The drive unit  32  includes a power transmission mechanism  150  and a gear holder  151 . 
     (5-1) Power Transmission Mechanism 
     The power transmission mechanism  150  is configured to transmit driving force to the photosensitive drum  2  and the first roller  6 . The driving force is inputted from a drive source (not depicted) of the main body  12  of the image forming apparatus  1 . The drive source is an example of an external drive source. The power transmission mechanism  150  includes the flange gear  94 , the drum gear  96 , a first idle gear  154 , the Oldham coupling  155 , a first roller gear  156 , and a transfer roller gear  157  (refer to  FIG. 6 ). The first roller gear  156  is an example of a first cleaning gear. 
     The flange gear  94  is supported by the left end portion of the drum body  83  so as not to be rotatable relative to the drum body  83 . As depicted in  FIG. 12 , the flange gear  94  is disposed to the right of the second portion  54  of the rear portion  51  of the left sidewall  39  of the base frame  35 . 
     As depicted in  FIGS. 6 and 12 , the drum gear  96  is fitted to the flange gear  94  so as not to be rotatable relatively. The drum gear  96  is interposed between the first portion  53  and the second portion  54  of the rear portion  51  of the left sidewall  39  of the base frame  35  in the right-left direction. A lower rear portion of the drum gear  96  is exposed from the drum frame  31  and meshes with a drive gear (not depicted) of the main body  12 . This configuration enables transmission of driving force from the drive source (not depicted) to the drum gear  96  via the drive gear (not depicted) of the main body  12 . That is, the drum gear  96  is configured to input driving force transmitted from the drive source (not depicted) of the main body  12  to the photosensitive drum  2 . The drum gear  96  rotates counterclockwise in right side view as depicted in  FIG. 11A . 
     As depicted in  FIGS. 9 and 10 , the first idle gear  154  has a generally cylindrical shape extending in the right-left direction. A lower front portion of the first idle gear  154  meshes with an upper rear portion of the drum gear  96  as depicted in  FIGS. 11A and 11B . The first idle gear  154  rotates clockwise in right side view as depicted in  FIG. 11A . 
     As depicted in  FIGS. 9 and 10 , the Oldham coupling  155  includes a larger-diameter hub  160 , a smaller-diameter hub  161 , and a slider  162 . 
     The larger-diameter hub  160  constitutes a left portion of the Oldham coupling  155 . The larger-diameter hub  160  includes a second idle gear  164 , a closed portion  165 , and a projection  166 , which are integrated with each other. The larger-diameter hub  160  further has a through hole  167 . The second idle gear  164  is an example of a third intermediate gear. 
     The second idle gear  164  has a generally cylindrical shape extending in the right-left direction. The second idle gear  164  has a diameter that is smaller than an outside diameter of the drum gear  96  and is larger than an outside diameter of the first idle gear  154 . A front portion of the second idle gear  164  meshes with a rear portion of the first idle gear  154  as depicted in  FIGS. 11A and 11B . The second idle gear  164  rotates counterclockwise in right side view as depicted in  FIG. 11A . 
     As depicted in  FIGS. 9 and 10 , the closed portion  165  has a generally disc shape in side view and closes a left end of the second idle gear  164 . 
     As depicted in  FIG. 10 , the projection  166  protrudes rightward from a right surface of the closed portion  165  and extends along a diametric direction of the closed portion  165 . 
     As depicted in  FIGS. 9 and 10 , the through hole  167  penetrates through substantially centers of the closed portion  165  and the projection  166  in side view. The through hole  167  has a generally circular shape in side view. 
     The smaller-diameter hub  161  constitutes a right portion of the Oldham coupling  155 . The smaller-diameter hub  161  includes a second roller gear  168 , a disc portion  169 , and a projection  170 , which are integrated with each other. The second roller gear  168  is an example of a second cleaning gear. 
     The second roller gear  168  constitutes a right portion of the smaller-diameter hub  161 , and has a generally cylindrical shape extending in the right-left direction. The second roller gear  168  has a diameter that is smaller than a diameter of the second idle gear  164 . The second roller gear  168  is attached to the left end portion of the second-roller shaft  124  so as not to be rotatable relatively. That is, the second roller gear  168  is configured to input driving force to the second roller  7 . The driving force is transmitted from the drive source (not depicted) of the main body  12 . 
     The disc portion  169  constitutes a substantially middle portion of the second roller gear  168  in the right-left direction. The disc portion  169  is disposed to the left of the second roller gear  168  adjacently. The disc portion  169  is coaxial with the second roller gear  168 . The disc portion  169  has a diameter that is larger than a diameter of the second roller gear  168  and is smaller than the diameter of the second idle gear  164 . 
     The projection  170  constitutes a right portion of the second roller gear  168 . The projection  170  protrudes leftward from a left surface of the disc portion  169  and extends in a diametric direction of the disc portion  169 . 
     The slider  162  is interposed between the larger-diameter hub  160  and the smaller-diameter hub  161 . The slider  162  has a generally cylindrical shape extending in the right-left direction. The slider  162  has a first groove  172  and a second groove  173 . 
     The first groove  172  is recessed rightward relative to a left surface of the slider  162  and extends along a diametric direction of the slider  162 . The first groove  172  has a width that is slightly wider than a width of the projection  166  of the larger-diameter hub  160 . 
     The second groove  173  is recessed leftward relative to a right surface of the slider  162  and extends along the diametric direction of the slider  162 . The second groove  173  has a width that is slightly wider than a width of the projection  170  of the smaller-diameter hub  161 . The second groove  173  extends in a direction perpendicular to a direction that the first groove  172  extends as viewed in the right-left direction. 
     The first groove  172  of the slider  162  receives therein the projection  166  of the larger-diameter hub  160  and the second groove  173  of the slider  162  receives therein the projection  170  of the smaller-diameter hub  161 , thereby constituting the Oldham coupling  155 . That is, the Oldham coupling  155  includes the second idle gear  164  and the second roller gear  168 . 
     With this configuration, the slider  162  slides relative to the projection  166  of the larger-diameter hub  160  and the projection  170  of the smaller-diameter hub  161 , whereby the second idle gear  164  and the second roller gear  168  rotate interlocked with each other even when their rotating axes are deviated. Thus, driving force inputted into the second idle gear  164  is surely transmitted to the second roller gear  168 . As depicted in  FIG. 11A , the second roller gear  168  rotates counterclockwise in right side view in a similar manner to the second idle gear  164 . 
     The Oldham coupling  155  is disposed such that the Oldham coupling  155  extends across the inside and the outside of the first accommodating portion  204  of the drum frame  31  via the opening  200 . 
     As depicted in  FIGS. 10 and 11B , the first roller gear  156  has a generally cylindrical shape extending in the right-left direction. The first roller gear  156  has a diameter that is larger than the diameter of the second roller gear  168 . The first roller gear  156  is attached to the left end portion of the first-roller shaft  121  so as not to be rotatable relatively. As depicted in  FIGS. 11A and 11B , the first roller gear  156  is disposed between the drum gear  96  and the Oldham coupling  155  in the extending direction. An upper front portion of the first roller gear  156  overlaps a lower rear portion of the first idle gear  154  as viewed in the right-left direction. An upper rear portion of the first roller gear  156  meshes with a lower front portion of the second roller gear  168 . That is, the first roller gear  156  is configured to input driving force, which is transmitted from the drive source of the main body  12 , to the first roller  6 . As depicted in  FIG. 11A , the first roller gear  156  rotates clockwise in right side view. 
     As depicted in  FIG. 6 , the transfer roller gear  157  is disposed at a left end portion of the transfer roller  4 . The transfer roller gear  157  has a generally cylindrical shape extending in the right-left direction. An upper portion of the transfer roller gear  157  meshes with a lower portion of the flange gear  94 . 
     (5-2) Gear Holder 
     As depicted in  FIGS. 9 and 10 , the gear holder  151  is a separate part from the drum frame  31 . The gear holder  151  is disposed to the left of the power transmission mechanism  150  in the drive unit  32 . The gear holder  151  has a generally rectangular plate shape in side view. The gear holder  151  is made of, for example, resin material, e.g., acrylonitrile butadiene styrene (“ABS”), or metal. The material, e.g., polyacetal resin (“POM”), used for the gear holder  151  has higher heat resistance and higher abrasion resistance to the material used for the second left flange  92  than the material, e.g., polystyrene (“PS”), used for the base frame  35 . The gear holder  151  includes a drum-shaft supporting portion  176 , a first-idle-gear supporting portion  177 , a larger-diameter-hub supporting portion  178 , a first hook  179 , and a second hook  180 . The gear holder  151  further has a first boss hole  181  and a second boss hole  182 . 
     The drum-shaft supporting portion  176  protrudes rightward from the right surface of the gear holder  151  at a lower front portion of the gear holder  151 . The drum-shaft supporting portion  176  has a generally cylindrical shape. The drum-shaft supporting portion  176  has an outside diameter that is substantially the same diameter of the larger-diameter through hole  56  in the left sidewall  39  of the base frame  35 . The drum-shaft supporting portion  176  has an inside diameter that is substantially the same as the diameter of the drum shaft  86 . 
     The first-idle-gear supporting portion  177  is disposed at a substantially middle portion of the gear holder  151  in the front-rear direction and above and behind the drum-shaft supporting portion  176 . The first-idle-gear supporting portion  177  protrudes rightward from the right surface of the gear holder  151  and has a generally cylindrical shape. The drum-shaft supporting portion  176  has a diameter that is substantially the same as an inside diameter of the first idle gear  154 . 
     The larger-diameter-hub supporting portion  178  is disposed at the rear portion of the gear holder  151  and at a substantially middle portion of the gear holder  151  in the front-rear direction. The larger-diameter-hub supporting portion  178  is further disposed behind and below the first-idle-gear supporting portion  177 . The larger-diameter-hub supporting portion  178  protrudes rightward from the right surface of the gear holder  151  and has a generally cylindrical shape. The larger-diameter-hub supporting portion  178  has a diameter that is substantially the same as a diameter of the through hole  167  of the larger-diameter hub  160 . 
     The first hook  179  is disposed at a lower rear end portion of the gear holder  151  and behind and below the larger-diameter-hub supporting portion  178 . The first hook  179  protrudes rightward from the right surface of the gear holder  151 . The first hook  179  is bent at a particular portion and further extends rearward. 
     The second hook  180  is disposed at a substantially middle portion of the gear holder  151  in the front-rear direction. The second hook  180  is further disposed behind and above the first-idle-gear supporting portion  177  and in front of and above the larger-diameter-hub supporting portion  178 . The second hook  180  protrudes rightward from the right surface of the gear holder  151 . The second hook  180  is bent at a particular portion and further extends upward. 
     The first boss hole  181  is defined in an upper rear end portion of the gear holder  151 . The first boss hole  181  penetrates through the gear holder  151  and has an oval shape in side view. 
     The second boss hole  182  is defined in an upper front end portion of the gear holder  151 . The second boss hole  182  penetrates through the gear holder  151  and has a circular shape in side view. 
     The wire-cleaner retaining portion  183  is disposed at an upper end portion of the gear holder  151  and between the second boss hole  182  and the first-idle-gear supporting portion  177 . The wire-cleaner retaining portion  183  has a generally rectangular shape in side view and includes an opening that penetrates through the gear holder  151 . 
     The gear holder  151  is attached to the drum frame  31  from the left and covers the power transmission mechanism  150 . 
     More specifically, the gear holder  151  supports the first idle gear  154  and the larger-diameter hub  160  including the second idle gear  164  while the first-idle-gear supporting portion  177  penetrates through the first idle gear  154  and the larger-diameter-hub supporting portion  178  penetrates through the through hole  167  of the larger-diameter hub  160  of the Oldham coupling  155 . 
     The drum-shaft supporting portion  176  receives the drum shaft  86  of the photosensitive drum  2  while passing through the larger-diameter through hole  56  of the left sidewall  39  of the base frame  35 . 
     A left end surface of the drum-shaft supporting portion  176  is flush with the right surface of the first portion  53  of the rear portion  51 . Thus, the left end surface of the drum-shaft supporting portion  176  contacts a left end surface of the smaller-diameter cylindrical portion  99  of the second left flange  92  of the bearing member  85 . 
     The first boss hole  181  receives the first positioning boss  73  of the left sidewall  66  of the cover frame  36  and the second boss hole  182  receives the second positioning boss  74  of the left sidewall  66  of the cover frame  36 , thereby positioning the gear holder  151  with respect to the drum frame  31 . 
     The first hook  179  is caught on the first retaining portion  57  of the second portion  54  of the rear portion  51  of the left sidewall  39  and the second hook  180  is caught on the second retaining portion  80  of the rear portion  78  of the top wall  67  of the cover frame  36 . That is, the gear holder  151  connects the base frame  35  and the cover frame  36  with each other. 
     As described above, the gear holder  151  is assembled to the drum frame  31  while protecting the power transmission mechanism  150 . 
     As depicted in  FIG. 6 , a lower portion of the gear holder  151  overlaps an upper portion of the left sidewall  39  as viewed in the right-left direction. 
     When the wire cleaner  103  of the scorotron charger  3  is located at a left end portion of the charger supporting portion  77 , the protrusion  107  of the wire cleaner  103  is in engagement with the wire-cleaner retaining portion  183 . 
     With this configuration, the position of the wire cleaner  103  is fixed while the wire cleaner  103  is not used. 
     (5-3) Transmission of Driving Force from Drive Source 
     As depicted in  FIGS. 11A and 11B , as driving force is transmitted to the drum gear  96  from the drive gear (not depicted) of the main body  12 , the drum gear  96  rotates counterclockwise in right side view. The drum gear  96  thus transmits the driving force to the first idle gear  154 . 
     As the driving force is transmitted to the first idle gear  154  from the drum gear  96 , the first idle gear  154  rotates clockwise in right side view. The first idle gear  154  thus transmits the driving force to the second idle gear  164  of the larger-diameter hub  160  of the Oldham coupling  155 . 
     In the Oldham coupling  155 , as the driving force is transmitted to the second idle gear  164  of the larger-diameter hub  160  from the first idle gear  154 , the larger-diameter hub  160  rotates counterclockwise in right side view. The larger-diameter hub  160  thus transmits the driving force to the smaller-diameter hub  161  via the slider  162 . 
     As the driving force is transmitted to the smaller-diameter hub  161  from the larger-diameter hub  160 , the second roller gear  168  of the smaller-diameter hub  161  rotates counterclockwise in right side view in a similar manner to the second idle gear  164 . The second roller gear  168  of the smaller-diameter hub  161  thus transmits the driving force to the first roller gear  156 . 
     As the driving force is transmitted to the first roller gear  156  from the first roller gear  156 , the first roller gear  156  rotates clockwise in right side view. 
     Thus, the photosensitive drum  2 , which is configured to rotate in response to input of driving force to the drum gear  96 , rotates counterclockwise in right side view and the first roller  6 , which is configured to rotate clockwise in right side view in response to input of driving force to the first roller gear  156 , rotates clockwise in right side view. That is, the photosensitive drum  2  and the first roller  6  rotate in the same direction at their contacting point. 
     As described above, the number of rotations of the first roller gear  156  with respect to the number of rotations of the drum gear  96  is reduced via the first idle gear  154 , the second idle gear  164 , and the second roller gear  168  of the power transmission mechanism  150 . Thus, a ratio of a peripheral speed of the first roller  6  relative to the photosensitive drum  2  becomes approximately 0.3. In other words, the first idle gear  154 , the second idle gear  164 , and the second roller gear  168  constitute a reduction mechanism. 
     The photosensitive drum  2  rotates while being pressed toward the left. Therefore, the left end surface of the smaller-diameter cylindrical portion  99  of the photosensitive drum  2  is rubbed against the right end surface of the drum-shaft supporting portion  176  of the power transmission mechanism  150 . 
     As described above, the smaller-diameter cylindrical portion  99  of the second left flange  92  is made of polyacetal resin (“POM”) and the drum-shaft supporting portion  176  of the gear holder  151  is made of acrylonitrile butadiene styrene (“ABS”). The smaller-diameter cylindrical portion  99  of the second left flange  92  is made of polyacetal resin (“POM”) and the left sidewall  39  of the base frame  35  of the drum frame  31  is made of polystyrene (“PS”). A threshold value that the rubbing surfaces of the smaller-diameter cylindrical portion  99  and the drum-shaft supporting portion  176  deform or melt due to heat generated by friction is higher than a threshold value that the rubbing surfaces of the smaller-diameter cylindrical portion  99  of the second left flange  92  and the left sidewall  39  of the base frame  35  of the drum frame  31  deform or melt due to heat generated by friction. 
     4. Details of Main Body of Image Forming Apparatus 
     As depicted in  FIG. 14B , the main body  12  includes a first apparatus electrode  191 , a second apparatus electrode  192 , the third apparatus electrode  193 , and the fourth apparatus electrode  194 . 
     The first apparatus electrode  191  is disposed such that the first apparatus electrode  191  is in contact with the charger electrode  104  in the right-left direction in a state where the drum cartridge  1  is installed and positioned at a particular position in the main body  12 . 
     The second apparatus electrode  192  is disposed such that the second apparatus electrode  192  is in contact with the grid electrode  105  in the right-left direction in the state where the drum cartridge  1  is installed in the main body  12 . 
     The third apparatus electrode  193  is disposed such that the third apparatus electrode  193  is in contact with the contact portion  138  of the first electrode  117  in the right-left direction in the state where the drum cartridge  1  is installed and positioned at the particular position in the main body  12 . 
     The fourth apparatus electrode  194  is disposed such that the fourth apparatus electrode  194  is in contact with the contact portion  145  of the second electrode  118  in the right-left direction in the state where the drum cartridge  1  is installed and positioned at the particular position in the main body  12 . 
     The first apparatus electrode  191 , the second apparatus electrode  192 , the third apparatus electrode  193 , and the fourth apparatus electrode  194  are configured to be movable in the right-left direction and are urged leftward at all times. The first apparatus electrode  191 , the second apparatus electrode  192 , the third apparatus electrode  193 , and the fourth apparatus electrode  194  are electrically connected with a power supply (not depicted) of the main body  12 . 
     5. Installation and Removal of Drum Cartridge with Respect to Main Body of Image Forming Apparatus 
     A procedure to install the drum cartridge  1  to the main body  12  of the image forming apparatus  1  will be described. 
     In order to install the drum cartridge  1  to the main body  12 , as a first step, as depicted in  FIG. 2 , an operator positions the developing cartridge  20  in the second accommodating portion  205  of the drum cartridge  1  to assemble the process cartridge  13 . 
     Then, the operator opens the front cover  17  and inserts the process cartridge  13  into the main body  12  via the opening  16  from an upper front position with respect to the main body  12 . 
     In response to this, as depicted in  FIG. 13A , the first apparatus electrode  191  moves upwardly frontward relative to the drum cartridge  1  so as to be situated below the grid electrode  105  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . 
     Further, the second apparatus electrode  192  moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the curved portion  147  of the contact portion  145  of the second electrode  118  while sliding over the right surface of the right sidewall  38  of the base frame  35  and the right surface of the right sidewall  65  of the cover frame  36 . 
     Meanwhile, the third apparatus electrode  193  and the fourth apparatus electrode  194  are not in contact with the right sidewall  38  and are situated behind the drum cartridge  1 . 
     Then, the operator further inserts the process cartridge  13  into the main body  12 . In response to this, as depicted in  FIG. 13B , the first apparatus electrode  191  moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the grid electrode  105  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . 
     Further, the second apparatus electrode  192  overrides the contact portion  145  of the second electrode  118  from the curved portion  147  and further moves upwardly frontward relative to the drum cartridge  1  so as to be situated on the right surface of the contact portion  145  of the second electrode  118  while sliding over the contact portion  145  of the second electrode  118 . 
     The third apparatus electrode  193  moves upwardly frontward relative to the drum cartridge  1  so as to be situated at a lower rear end portion of the right sidewall  38  of the base frame  35  while sliding over the right surface of the right sidewall  38  of the base frame  35 . 
     Meanwhile, the fourth apparatus electrode  194  is not in contact with the right sidewall  38  and is situated behind the drum cartridge  1 . 
     The operator further inserts the process cartridge  13  into the main body  12 . In response to this, as depicted in  FIG. 14A , the first apparatus electrode  191  moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the charger electrode  104  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . 
     The second apparatus electrode  192  crosses the contact portion  145  of the second electrode  118  and further moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the grid electrode  105  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . 
     The third apparatus electrode  193  moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the curved portion  140  of the contact portion  138  of the first electrode  117  while sliding over the right surface of the right sidewall  38  of the base frame  35 . 
     The fourth apparatus electrode  194  moves upwardly frontward relative to the drum cartridge  1  so as to be situated behind the curved portion  147  of the contact portion  145  of the second electrode  118  while sliding over the right surface of the right sidewall  38  of the base frame  35  and the right surface of the right sidewall  65  of the cover frame  36 . 
     The operator further inserts the process cartridge  13  into the main body  12 . In response to this, as depicted in  FIG. 14B , the first apparatus electrode  191  moves upwardly frontward relative to the drum cartridge  1  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . When the process cartridge  13  reaches the particular position, the first apparatus electrode  191  comes into contact with the charger electrode  104  from the right. 
     The second apparatus electrode  192  moves upwardly frontward relative to the drum cartridge  1  while sliding over the right surface of the right sidewall  65  of the cover frame  36 . When the process cartridge  13  reaches the particular position, the second apparatus electrode  192  comes into contact with the grid electrode  105  from the right. 
     The third apparatus electrode  193  overrides the contact portion  138  of first electrode  117  from the curved portion  140  and further moves upwardly frontward relative to the drum cartridge  1  while sliding over the contact portion  138  of first electrode  117 . When the process cartridge  13  reaches the particular position, the third apparatus electrode  193  comes into contact with the contact portion  138  of the first electrode  117  from the right. 
     The fourth apparatus electrode  194  overrides the contact portion  145  of the second electrode  118  from the curved portion  147  and further moves upwardly frontward relative to the drum cartridge  1  while sliding over the contact portion  145  of the second electrode  118 . When the process cartridge  13  reaches the particular position, the fourth apparatus electrode  194  comes into contact with the contact portion  145  of the second electrode  118  from the right. 
     Through the above-described procedure, the installation of the process cartridge  13  in the main body  12  is completed. 
     In order to remove the drum cartridge  1  from the main body  12 , the installation procedure is performed in reverse. 
     More specifically, as depicted in  FIG. 2 , the operator opens the front cover  17  and pulls the process cartridge  13  to the upper front position with respect to the main body  12  via the opening  16 . The operator then detaches the developing cartridge  20  from the process cartridge  13 . Thus, the removal of the drum cartridge  1  from the main body  12  is completed. 
     6. Effects 
     (1) According to the drum cartridge  1 , as depicted in  FIGS. 11A and 11B , driving force transmitted to the drum gear  96  from the drive source of the main body  12  is further transmitted to the first roller gear  156  via the first idle gear  154  and the Oldham coupling  155 . With this configuration, a ratio of the peripheral speed of the first roller  6  relative to the photosensitive drum  2  may be widely changed. 
     According to the above-described embodiment, the Oldham coupling  155  is provided for transmitting driving force from the first idle gear  154  to the first roller gear  156 . Therefore, even when the first roller  6  moves slightly relative to the photosensitive drum  2  due to their rotations, the Oldham coupling  155  may absorb the deviation of the rotating axes of the gears, whereby driving force transmitted from the outside of the drum cartridge  1  may be transmitted to the first roller  6  stably. 
     Accordingly, a ratio of the peripheral speed of the first roller  6  relative to the photosensitive drum  2  may be widely changed. Further, driving force may be transmitted from the photosensitive drum  2  to the first roller  6  stably without an occurrence of the deviation of the rotating axes among the gears. Thus, instability in rotation of the photosensitive drum  2  caused due to the deviation of the rotating axes among the gears may be restricted, whereby an image may be formed on a sheet P with stable quality. 
     Accordingly, cleaning may be performed on the surface of the photosensitive drum  2  using the first roller  6  with stably and certainty. 
     (2) According to the drum cartridge  1 , as depicted in  FIGS. 11A and 11B , the rotating speed of the first roller  6  relative to the photosensitive drum  2  may be reduced using the first idle gear  154 , the second idle gear  164 , and the second roller gear  168 . 
     Thus, cleaning of the surface of the photosensitive drum  2  may be performed evenly using the first roller  6  as compared with a case where the rotating speed of the first roller  6  is increased relative to the rotating speed of the photosensitive drum  2 . 
     (3) According to the drum cartridge  1 , as depicted in  FIG. 11A , the first roller gear  156  is disposed between the drum gear  96  and the Oldham coupling  155 , whereby space may be used effectively. 
     Thus, the first roller gear  156 , the drum gear  96 , and the Oldham coupling  155  may be assembled effectively. 
     (4) According to the drum cartridge  1 , as depicted in  FIGS. 1 and 10 , the provision of the second roller  7  may enhance the ability to remove and collect paper dust. 
     Further, the Oldham coupling  155  includes the second roller gear  168  for inputting driving force to the second roller  7 , thereby restricting an increase of a parts count. 
     (5) According to the drum cartridge  1 , as depicted in  FIGS. 11A and 11B , the second idle gear  164  is further disposed in the driving force transmitting route from the drum gear  96  to the first roller gear  156 , whereby a ratio of the peripheral speed of the first roller  6  relative to the photosensitive drum  2  may be surely widely changed. 
     (6) According to the drum cartridge  1 , as depicted in  FIG. 11A , as viewed in the right-left direction, the first idle gear  154  and the first roller gear  156  partially overlap each other, thereby restricting an increase in size of the drum cartridge  1 . 
     (7) According to the drum cartridge  1 , as depicted in  FIGS. 10 and 11A , the gear holder  151  may improve the stability of the engagement between the first idle gear  154  and the second idle gear  164 . 
     With this configuration, driving force may be surely transmitted from the first idle gear  154  to the second idle gear  164 . Thus, the driving force may be further surely transmitted from the drum gear  96  to the first roller gear  156 . 
     Further, the deviation of rotating axes among the gears may be restricted. Therefore, instability in rotation of the photosensitive drum  2  may be restricted and thus image formation may be implemented with stability. 
     (8) According to the drum cartridge  1 , as depicted in  FIG. 11A , the second idle gear  164  and the first idle gear  154 , which have the respective diameters that are smaller than the diameter of the drum gear  96 , may reduce the rotating speed of the first roller  6  relative to the photosensitive drum  2 . 
     Thus, while a reduction in size of the drum cartridge  1  is achieved, the rotating speed of the first roller  6  relative to the photosensitive drum  2  may be reduced and cleaning may be performed on the surface of the photosensitive drum  2  with certainty. 
     (9) According to the drum cartridge  1 , as depicted in  FIGS. 1 and 11B , while the photosensitive drum  2  and the first roller  6  rotate in the same direction at their contacting point, a ratio of the peripheral speed of the first roller  6  relative to the photosensitive drum  2  may be widely changed and cleaning may be performed on the surface of the photosensitive drum  2  using the first roller  6  with certainty.
A drum cartridge and a method are disclosed. An example of the drum cartridge includes a photosensitive drum, a first cleaning roller, and a second cleaning roller. The drum cartridge includes a first cleaning gear rotatable with the first cleaning roller, a second cleaning gear rotatable with the second cleaning roller and engaging with the first cleaning gear, a drum gear being rotatable with the photosensitive drum, a first idle gear engaging with the drum gear, a second idle gear engaging with the first idle gear, and a coupling joining the second cleaning gear and the second idle gear, the coupling being rotatable in unison with the second cleaning gear and the second idle gear.