Patent Publication Number: US-8971758-B2

Title: Photosensitive member cartridge, process cartridge and image forming apparatus using the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-190040 filed Aug. 31, 2011. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an electro-photographic type image forming apparatus, a photosensitive member cartridge and a process cartridge for use in the image forming apparatus. 
     BACKGROUND 
     Known is an electro-photographic type tandem color laser printer that detachably accommodates a plurality of photosensitive member cartridges. Such photosensitive member cartridge includes a cartridge frame formed with bearing portions, and a photosensitive drum whose lateral end portions are supported to the bearing portions of the cartridge frame. 
     Among such photosensitive member cartridges, there is proposed a photosensitive member cartridge whose cartridge frame is separable into an upper frame and a lower frame. Specifically, the cartridge frame can be divided into the upper and lower frames along a plane passing through a vertical center of each bearing portion. 
     This photosensitive member cartridge is assembled such that its photosensitive drum is first assembled to the lower frame and subsequently the upper frame is engaged with the lower frame. Assembly of the photosensitive drum to the cartridge frame is thus facilitated, compared to a case where a cartridge frame is integrally formed. 
     SUMMARY 
     In the above-described photosensitive member cartridge, rigidity of the cartridge frame could be insufficient since the cartridge frame is configured of the upper frame and the lower frame. Therefore, conceivably, the photosensitive drum supported to the cartridge frame may not be accurately positioned relative to the cartridge frame. As a result, when the photosensitive member is mounted in a main body of a printer, positioning accuracy of the photosensitive drum relative to the main body may not be obtained sufficiently, possibly leading to image formation failure. 
     In view of the foregoing, it is an object of the present invention to provide a photosensitive member cartridge capable of facilitating assembly of a photosensitive member to an upper frame and a lower frame, while capable of realizing accurate positioning of the photosensitive member relative to the upper and lower frames. The present invention also aims to provide a process cartridge and an image forming apparatus using the photosensitive member cartridge. 
     According to an aspect of the present invention, there is provided a photosensitive member cartridge including a photosensitive member, a frame and a pair of holding members. The photosensitive member defines a first axis extending in an axial direction and configured to rotate about the first axis, the photosensitive member having axial end portions opposite to each other in the axial direction. The frame includes a pair of photosensitive member receiving portions configured to receive the axial end portions of the photosensitive member, the frame including a first frame and a second frame separable from each other in a prescribed direction perpendicular to the axial direction and mating with each other such that the first frame provides a part of each photosensitive member receiving portion, and the second frame provides a remaining part of each photosensitive member receiving portion. The pair of holding members is configured to hold the axial end portions of the photosensitive member, each holding member being engaged with both of the first frame and the second frame. 
     According to another aspect of the present invention, there is provided a process cartridge including a photosensitive member cartridge and a developing cartridge detachably mountable on the photosensitive member cartridge. The photosensitive member cartridge includes a photosensitive member, a frame and a pair of holding members. The photosensitive member defines a first axis extending in an axial direction and configured to rotate about the first axis, the photosensitive member having axial end portions opposite to each other in the axial direction. The frame includes a pair of photosensitive member receiving portions configured to receive the axial end portions of the photosensitive member, the frame including a first frame and a second frame separable from each other in a prescribed direction perpendicular to the axial direction and mating with each other such that the first frame provides a part of each photosensitive member receiving portion, and the second frame provides a remaining part of each photosensitive member receiving portion. The pair of holding members is configured to hold the axial end portions of the photosensitive member, each holding member being engaged with both of the first frame and the second frame. The developing cartridge includes a developing frame and a developer carrying member. The developing frame has end portions opposite to each other in the axial direction. The developer carrying member defines a second axis extending in the axial direction and configured to rotate about the second axis, the developer carrying member being rotatably supported to the end portions of the developing frame, the developer carrying member being in confrontation with and in contact with the photosensitive member when the developing cartridge is mounted on the photosensitive member cartridge. 
     According to still another aspect of the present invention, there is provided an image forming apparatus including: a process cartridge which includes a photosensitive member cartridge and a developing cartridge detachably mountable on the photosensitive member cartridge; and a main casing in which the process cartridge is detachably mountable. The photosensitive member cartridge includes a photosensitive member, a frame and a pair of holding members. The photosensitive member defines a first axis extending in an axial direction and configured to rotate about the first axis, the photosensitive member having axial end portions opposite to each other in the axial direction. The frame includes a pair of photosensitive member receiving portions configured to receive the axial end portions of the photosensitive member, the frame including a first frame and a second frame separable from each other in a prescribed direction perpendicular to the axial direction and mating with each other such that the first frame provides a part of each photosensitive member receiving portion, and the second frame provides a remaining part of each photosensitive member receiving portion. The pair of holding members is configured to hold the axial end portions of the photosensitive member, each holding member being engaged with both of the first frame and the second frame. The developing cartridge includes a developing frame and a developer carrying member. The developing frame has end portions opposite to each other in the axial direction. The developer carrying member defines a second axis extending in the axial direction and configured to rotate about the second axis, the developer carrying member being rotatably supported to the end portions of the developing frame, the developer carrying member being in confrontation with and in contact with the photosensitive member when the developing cartridge is mounted on the photosensitive member cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a color printer as an image forming apparatus according to one embodiment of the present invention, the color printer including a main casing in which a plurality of process cartridges are mounted; 
         FIG. 2  is a perspective view of the process cartridge according to the present embodiment when viewed from leftward and upward thereof, the process cartridge including a drum cartridge and a developing cartridge; 
         FIG. 3  is a perspective view of an upper frame and a lower frame constituting a drum cartridge frame of the drum cartridge; 
         FIG. 4A  is a perspective view of a holding member provided at the drum cartridge when viewed from upward and leftward thereof; 
         FIG. 4B  is a perspective view of the holding member when viewed from downward and rightward thereof; 
         FIG. 5  is an explanatory view showing a photosensitive drum and a pair of bearing members assembled thereto; 
         FIG. 6  is an explanatory view showing how the photosensitive drum of  FIG. 5  is assembled to the lower frame and how the upper frame is subsequently assembled to the lower frame supporting the photosensitive drum; 
         FIG. 7  is an explanatory view showing how the holding member is subsequently assembled to the upper and lower frame assembled to each other: 
         FIG. 8  is a perspective view of the drum cartridge according to the present embodiment when viewed from upward and leftward thereof; 
         FIGS. 9A-9   c  are left side views explaining how the holding member is assembled to the upper frame and the lower frame, wherein:  FIG. 9A  shows a left side view of the upper frame and the lower frame in a state where the holding member is not yet assembled thereto;  FIG. 9B  shows a left side view of the upper frame and the lower frame in a state where the holding member is being assembled to the upper frame and the lower frame; and  FIG. 9C  shows a left side view of the upper frame and the lower frame in a state where the holding member has been assembled thereto; 
         FIG. 10  is a left side view of the process cartridge of  FIG. 2  in a state where the process cartridge has been mounted in the printer of  FIG. 1 , wherein the photosensitive drum is in contact with a developing roller of the developing cartridge; 
         FIG. 11  is a left side view of the process cartridge of  FIG. 2  in a state where the process cartridge has been mounted in the printer of  FIG. 1 , wherein the developing roller of the developing cartridge is separated from the photosensitive drum; and 
         FIGS. 12A-12B  are views explaining how the process cartridge of  FIG. 2  is mounted in the printer of  FIG. 1 , wherein:  FIG. 12A  is a back side view of the process cartridge when the process cartridge is being mounted into the main casing of the printer; and  FIG. 12B  is a back side view of the process cartridge of  FIG. 2  when the process cartridge has been mounted in the main casing of the printer. 
     
    
    
     DETAILED DESCRIPTION 
     A printer  1  as an image forming apparatus according to one embodiment of the present invention will be described while referring to  FIGS. 1 to 12B  wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     1. Overall Structure of Color Printer 
     As shown in  FIG. 1 , the printer  1  is a horizontal direct tandem type color printer. 
     With regard to the printer  1  and a drum cartridge  22  detached from the printer  1  (shown in  FIGS. 2 to 9C ), directions will be referred to assuming that the printer  1  and the drum cartridge  22  are respectively placed on a horizontal plane. Specifically, directions will be referred to based on those shown in each drawing. Incidentally, a left-to-right direction (a lateral direction) of drum cartridge  22  in  FIGS. 2 to 9C  will be identical to those of the printer  1  (when the drum cartridge  22  is mounted in the printer  1 ). 
     In other words, directions (top-to-bottom and front-to-rear directions) with respect to the printer  1  are different from directions (top-to-bottom and front-to-rear directions) with respect to the drum cartridge  22  detached from the printer  1 . The drum cartridge  22  is mounted in the printer  1  such that a front portion of the drum cartridge  22  is oriented toward an upper-front portion of the printer  1 , and a rear portion of the drum cartridge  22  is oriented toward a lower-rear portion of the printer  1 . 
     Referring to  FIG. 1 , the printer  1  includes a main casing  2  having a generally box shape as an example of a claimed main casing. The main casing  2  has an upper end portion provided with a top cover  50  which can be opened or closed. In the main casing  2 , four photosensitive drums  3  corresponding to four colors of toner (black, yellow, magenta and cyan) are juxtaposedly arrayed in a front-to-rear direction. 
     A scorotron charger  4 , an LED unit  5  and a developing roller  6  (as an example of a claimed developer carrying member) are provided in confrontation with each photosensitive drum  3 . 
     After an outer peripheral surface of the photosensitive drum  3  is uniformly charged by the scorotron charger  4 , the surface is exposed to light by the LED unit  5  based on a predetermined image data to form an electrostatic latent image on the surface. Then a visible toner image corresponding to the electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum  3  by supplying toner carried on the developing roller  6  to the corresponding photosensitive drum  3 . 
     A sheet cassette  7  is provided at a bottom portion of the main casing  2  for accommodating sheets P therein in a stacked state. The sheets P accommodated in the sheet cassette  7  are conveyed to a conveyer belt  8  by a variety of rollers. 
     The conveyer belt  8  extends in the front-to-rear direction and is disposed at a position immediately below the photosensitive drums  3 . Transfer rollers  9  are provided opposite to the photosensitive drums  3  with respect to the conveyer belt  8 . The toner image formed on the outer peripheral surface of each photosensitive drum  3  is sequentially transferred and superimposed onto the sheet P due to a transfer bias applied to each transfer roller  9 , thereby providing a color image on the sheet P. 
     The sheet P on which the color image has been formed is then conveyed to a fixing unit  10  provided downstream of the conveyer belt  8 . The sheet P on which the color image is formed is thermally fixed to the sheet P at the fixing unit  10 . The sheet P carrying the color image is then discharged onto a discharge tray  11  provided at the top cover  50 . 
     2. Structure of Process Cartridge 
     The printer  1  detachably accommodates therein four process cartridges  21  corresponding to four colors of toner. When mounted, the process cartridges  21  are juxtaposedly arrayed in the front-to-rear direction within the main casing  2 . When the top cover  50  is opened, each process cartridge  21  is mountable in and removable from the main casing  2 . Each process cartridge  21  includes the drum cartridge  22  and a developing cartridge  23  detachable from and attachable to the drum cartridge  22 . 
     (1) Developing Cartridge 
     Referring to  FIG. 1 , each developing cartridge  23  includes a developing cartridge frame  30  having a generally box shape whose lower-rear side is open downward. The developing roller  6  is provided at a lower end portion of the developing cartridge frame  30 . 
     The developing roller  6  extends in a left-to-right direction (lateral direction), and includes a developing roller shaft  16  defining an axis X 2  extending in the lateral direction, and a rubber roller  17  provided around the developing roller shaft  16  to cover the same. The rubber roller  17  has a lower-rear portion exposed to an outside from the developing cartridge frame  30 . The developing roller shaft  16  has lateral end portions rotatably supported to left and right side walls  31  (see  FIG. 2 ) of the developing cartridge frame  30  respectively such that the developing roller  6  is rotatable about the axis X 2  (see  FIG. 10 ). The axis of the developing roller  6  serves as a rotational axis of the developing roller  6  and therefore will be referred to as a “second rotational axis X 2 ” hereinafter. 
     The developing cartridge  23  also includes a supply roller  13  for supplying toner to the developing roller  6 , a regulation blade  14  for regulating a thickness of a toner layer formed on the developing roller  9 , and agitator  12 . A toner container (shown without a reference numeral) is positioned above the supply roller  13  and the regulation blade  14  for containing toner as a developing agent. The agitator  12  is disposed within the toner container for agitating the toner stored therein. 
     A gear cover  160  is provided for each lateral end portion of the developing cartridge frame  30 , as shown in  FIG. 10 . Each gear cover  160  has a substantially box shape whose opening is oriented inward in the lateral direction. The gear cover  160  has such a size (lengths in the front-to-rear direction and in a top-to-bottom direction) that the gear cover  160  can entirely cover various gears disposed on each side wall  31  of the developing cartridge frame  30 . 
     Each gear cover  160  has a laterally outer surface on which an abutment portion  159  is formed. More specifically, the abutment portion  159  is provided at a rear portion of the laterally outer surface of the gear cover  160 . The abutment portion  159  has a substantially rectangular shape in a side view. As will be described later, each abutment portion  159  has a rear surface that is brought into contact with an abutment surface  149  of each separating member  146  when the developing cartridge  23  is mounted on the drum cartridge  22 . 
     (2) Drum Cartridge 
     The drum cartridge  22  includes a drum cartridge frame  24  (corresponding to a claimed frame) that is made from a polystyrene. The drum cartridge frame  24  is configured of a lower frame  33  (an example of a claimed first frame) and an upper frame  34  (an example of a claimed second frame). 
     The lower frame  33  includes a pair of lower frame side walls  35 , a front wall  5 , a rear wall  61  and a bottom wall  67 , as shown in  FIG. 3 . 
     The lower frame side walls  35  are disposed in opposition to each other in the lateral direction. Each lower frame side wall  35  has a frontward portion serving as a front side wall  36  and a rearward portion serving as a rear side wall  37 , the front side wall  36  and the rear side wall  37  integrally constituting each lower frame side wall  35 . 
     Referring to  FIGS. 9A-9C , the front side wall  36  has a rear portion extending in the front-to-rear direction and a front portion extending diagonally upward and frontward from a front end portion of the rear portion. 
     An engaged portion  47  is formed at a rear end portion of the front side wall  36 . The engaged portion  47  has a generally flat plate-like shape, protruding laterally outward from an upper peripheral end portion of an outer surface of each front side wall  36 . As shown in  FIG. 3 , an engaging hole  51  is formed on the engaged portion  47 . The engaging hole  51  has a generally rectangular shape in a plan view and penetrates through the engaged portion  47  in the top-to-bottom direction. 
     The rear side wall  37  has a frontward portion extending rearward from the rear end portion of the front side wall  36 , and a rearward portion extending diagonally upward and rearward from a rear end portion of the frontward portion, as shown in  FIGS. 9A-9C . 
     Each rear side wall  37  integrally includes a first frame engaging portion  38 , a separation shaft  39  and a lower receiver  40 , as shown in  FIG. 3 . 
     The first frame engaging portion  38  has a substantially flat plate-like shape, extending upward from an upper peripheral end portion of the frontward portion of the rear side wall  37 . The first frame engaging portion  38  has an upper end portion on which a hooked portion  48  is formed. The hooked portion  48  has a generally hook-like shaped cross-section in the top-to-bottom direction, protruding laterally outward from an outer surface of the first frame engaging portion  38 . 
     The separation shaft  39  is disposed on the outer surface of the first frame engaging portion  38 . The separation shaft  39  has a generally cylindrical shape protruding laterally outward from the outer surface of the first frame engaging portion  38 . 
     The lower receiver  40  is disposed rearward of the separation shaft  39 . The lower receiver  40  includes a lower receiving groove  43  and a lower collar  42 . The lower receiving groove  43  is formed on an upper peripheral end of the rear side wall  37  at a position generally center thereof in the front-to-rear direction. The lower receiving groove  43  is depressed downward from the upper peripheral end of the rear side wall  37  to provide a semi-circular shape in a side view. The lower receiving groove  43  has a peripheral end portion from which the lower collar  42  protrudes laterally outward. The lower receiving groove  43  thus has a semi-circular shaped side view, following an outer contour of the lower receiving groove  43 . 
     Also, as shown in  FIG. 9A , a lower groove  44  is formed below the lower collar  42 . The lower groove  44  is formed in an arcuate shape in conformance with an outer contour of the lower collar  42 . The lower groove  44  has a front portion defining a narrow-width groove  46 , and a rear portion defining a wide-width groove  45 . The wide-width groove  45  has a width about twice as wide as that of the narrow-width groove  46 . 
     The front wall  55  connects between front end portions of the lower frame side walls  35 . The front wall  55  is formed so as to extend diagonally upward and frontward, following an outer profile of a lower end portion of the front portion of each front side wall  36 . As shown in  FIG. 9A , the front wall  55  has an upper end portion on which a pair of pressing mechanisms  56  is provided. Specifically, the pressing mechanisms  56  are disposed on a back surface (rear surface) of the upper end portion of the front wall  55  to oppose each other in the lateral direction. Each pressing mechanism  56  is positionally coincident with each lateral end portion of a front wall of the developing cartridge frame  30  when the developing cartridge  23  is attached to the drum cartridge  22  (also see  FIG. 10 ). 
     Each pressing mechanism  56  includes a cylindrical portion  57  and a spring member  58 . The cylindrical portion  57  has a generally U-shaped cross-section in a side view whose opening is oriented frontward. The spring member  58  has a hollow coil-like shape extending in the front-to-rear direction. The spring member  58  is accommodated within an internal space defined by the cylindrical portion  57 . Specifically, in each pressing mechanism  56 , the spring member  58  is interposed in a compressed state between a front-side surface of the end wall of the cylindrical portion  57  and the back surface of the upper end portion of the front wall  55 . Therefore, the cylindrical portion  57  is movable in the front-to-rear direction relative to the front wall  55  and normally biased rearward due to a biasing force of the spring member  58 . 
     The rear wall  61  connects between rear end portions of the rearward portion of each rear side wall  37 . As shown in  FIG. 9A , the rear wall  61  extends diagonally upward and rearward in a left side view. The rear wall  61  has an upper end portion on which a pair of cutouts  63  is formed, as shown in  FIG. 3 . Each cutout  63  has generally U-shape in a front view which is open upward. The cutouts  63  are disposed to oppose each other in the lateral direction with a prescribed distance kept therebetween. 
     On the rear wall  61 , a pair of second frame engaging portions  62  and a pair of lower fixing portions  65  are formed (see  FIG. 3 ). 
     The second frame engaging portions  62  are disposed in coincidence with the cutouts  63  in the lateral direction. Each second frame engaging portion  62  is formed in a generally flat plate-like shape, having a width in the lateral direction substantially identical to that of each cutout  63  but a height larger than that of the cutout  63  in the top-to-bottom direction. Each second frame engaging portion  62  and its corresponding cutout  63  are integrally formed with each other (integral with the rear wall  61 ). 
     Each second frame engaging portion  62  has a rear surface on which a hook portion  64  is formed. The hook portion  64  has a hook-like shaped vertical cross-section, protruding rearward from an upper end portion of the rear surface of the second frame engaging portion  62 . 
     Each lower fixing portion  65  is provided at each lateral end portion of the rear wall  61 . The lower fixing portion  65  has a generally cylindrical shape and protrudes upward from an inner peripheral surface of each lateral end portion of the rear wall  61 . The lower fixing portion  65  has an upper surface on which a screw hole  66  is formed at a position diametrically center thereof. 
     The bottom wall  67  connects between bottom end portions of the front side walls  36 . The bottom wall  67  has a front end portion connected to a rear end portion of the front wall  55 . A rear end portion of the bottom wall  67  defines a first open portion  69  along with a lower peripheral end portion of each rear side wall  37  and a lower peripheral end portion of the rear wall  61 . The first open portion  69  thus has a generally rectangular shape in a plan view, as shown in  FIG. 3 . 
     Referring to  FIG. 3 , the upper frame  34  includes a pair of upper frame side walls  71  disposed in opposition to each other in the lateral direction and an upper wall  88  connecting between upper end portions of the upper frame side walls  71 . 
     As shown in  FIGS. 9A-9C , each upper frame side wall  71  has a frontward portion having a generally rectangular-shaped side view, and a rearward portion extending rearward from an upper-rear end portion of the frontward portion. The rearward portion also has a generally rectangular shape in a left side view. 
     Each upper frame side wall  71  includes a frame engaged portion  72  and an upper receiver  78 , as shown in  FIG. 3 . Each frame engaged portion  72  is adapted to be engaged with each first frame engaging portion  38 , and each upper receiver  78  is adapted to be coupled to each lower receiver  40  when the lower frame  33  and the upper frame  34  are combined (assembled to each other). 
     The frame engaged portion  72  extends frontward from a lower-front end portion of the upper frame side wall  71 . The frame engaged portion  72  has a generally rectangular frame-like shape with upper and lower portions in communication with each other in the top-to-bottom direction. The frame engaged portion  72  has a laterally outer wall on which a pair of slits  73  is formed, and a laterally inner wall on which a protruding rib  75  is formed, the outer wall and the inner wall being in confrontation with each other in the lateral direction. 
     More specifically, each slit  73  has a generally U-shape, depressing downward from an upper peripheral end of the outer wall. The slits  73  are aligned in the front-to-rear direction to provide an engaged portion  74  therebetween on the outer wall. In other words, the engaged portion  74  is defined by the pair of slits  73  aligned in the front-to-rear direction. The protruding rib  75  is formed on an outer surface of the inner wall at a position opposing the engaged portion  74  in the lateral direction, i.e., at a position center of the outer surface of the inner wall in the front-to-rear direction. The protruding rib  75  has a generally rectangular shape in a plan view, protruding laterally outward and extending in the top-to-bottom direction. 
     The upper receiver  78  is provided at the frontward portion of each upper frame side wall  71 . The upper receiver  78  includes an upper groove  80  and an upper collar  79 . The upper groove  80  is depressed upward from a lower peripheral end of each upper frame side wall  71  to form a semi-circular shape in a left side view. The upper collar  79  is semi-cylindrical shaped, protruding laterally outward from a peripheral end portion of the upper groove  80  to provide a semi-circular shaped side view, following an outer contour of the upper groove  80 . 
     Further, an upper groove  81  is formed above the upper collar  79  such that the upper groove  81  has an arcuate shape in conformance with an outer contour of the upper collar  79 . Referring to  FIG. 9A , the upper groove  81  has a front portion defining a wide-width groove  82  and a rear portion defining a narrow-width groove  83 . The wide-width groove  82  has a width about twice as wide as that of the narrow-width groove  83 . 
     Each upper frame side wall  71  further includes a depressed portion  77 , as shown in FIGS.  3  and  9 A- 9 C. The depressed portion  77  has a generally U-shaped side view, being depressed downward from an upper peripheral end of the frontward portion of each upper frame side wall  71 . 
     The upper wall  88  has a generally rectangular shape in a plan view, extending in the lateral direction, as shown in  FIG. 3 . On the upper wall  88 , a pair of penetrating holes  76 , a pair of upper fixing portions  89 , a pair of engaged holes  91  (see  FIG. 12 ), and a wire-exposing groove  93  are formed. 
     Each penetrating hole  76  is formed on each lateral end portion of the upper wall  88  such that each penetrating hole  76  is continuous with each depressed portion  77  formed on each upper frame side wall  71 . The penetrating hole  76  has a generally rectangular shape in a plan view and penetrates through the upper wall  88  in the top-to-bottom direction. 
     The upper fixing portions  89  are formed at a rear end portion of the upper wall  88  each at a position coincident with each lower fixing portion  65  of the lower frame  33  in the lateral direction (at each lateral end portion of the rear end portion of the upper wall  88 ). Each upper fixing portion  89  is depressed downward from an upper surface of the upper wall  88  and has a generally U-shape when viewed from its rear side. The upper fixing portion  89  has an upper surface on which a screw penetrating hole  90  is formed such that the screw penetrating hole  90  penetrates through the upper wall  88  in the top-to-bottom direction. 
     The engaged holes  91  are formed at the rear end portion of the upper wall  88  such that each engaged hole  91  is positioned to be coincident with each second frame engaging portion  62  in the lateral direction. Each engaged hole  91  has a generally rectangular shape in a plan view, penetrating through the upper wall  88  in the top-to-bottom direction. 
     The wire-exposing groove  93  is formed at a substantially center of the upper wall  88  in the front-to-rear direction, as shown in  FIG. 3 . The wire-exposing groove  93  has a generally rectangular shape in a plan view elongated in the lateral direction. The wire-exposing groove  93  also penetrates through the upper wall  88  in the top-to-bottom direction. 
     On the upper wall  88 , the scorotron charger  4  and a cleaning unit  95  are provided. 
     Referring to  FIG. 1 , the scorotron charger  4  includes a charging wire  86  and a grid  87 . The charging wire  86  is made of a tungsten wire, for example. The charging wire  86  extends in the lateral direction and has both axial end portions supported by the lateral end portions (right and left end portions) of the upper wall  88 . The charging wire  86  spans across the upper wall  88  in the lateral direction such that the charging wire  86  is exposed outside through the wire-exposing groove  93 . 
     The grid  87  has a generally U-shaped cross-section in a side view, whose open end is oriented upward. The grid  87  extends in the lateral direction and fixed to the upper wall  88  such that the charging wire  86  is surrounded by the grid  87 . The grid  87  has a bottom wall (a wall opposite to the open end) that is exposed downward from a lower surface of the upper wall  88 . The bottom wall of the grid  87  is positioned to face the photosensitive drum  3  (i.e., the bottom wall of the grid  87  is positioned between the charging wire  86  and the photosensitive drum  3 ) when the drum cartridge  22  is assembled, as shown in  FIG. 1 . 
     The cleaning unit  95  includes a pair of rail portions  92 , an operation portion  84 , a wire-nipping portion  96  (as an example of a claimed cleaning member) and a restricting portion  94 . 
     Each rail portion  92  has a generally flat plate-like shape extending in the lateral direction. Each rail portion  92  is provided along each of front and rear peripheral edge portions of the wire-exposing groove  93 . 
     The operation portion  84  is generally flat plate-like shaped, having a generally rectangular shape in a plan view. The operation portion  84  is placed on the pair of rail portions  92  such that the operation portion  84  is movable in the lateral direction along the rail portions  92 . The operation portion  84  includes a protrusion  85  as an example of a claimed engagement portion. The protrusion  85  has a generally rectangular shape in a plan view and protrudes leftward from a left end portion of the operation portion  84 . 
     The wire-nipping portion  96  is formed of a rectangular-shaped sponge material. As shown in  FIG. 3 , the wire-nipping portion  96  is supported to a lower surface of the operation portion  84  in a state where the wire-nipping portion  96  is deformed to nip the charging wire  86 . 
     The restricting portion  94  is generally flat plate-like shaped, having a generally rectangular shape in a plan view. The restricting portion  94  is positioned to oppose right end portions of the rail portions  92  in the lateral direction from rightward thereof. 
     In this cleaning unit  95 , the operation portion  84  is normally positioned on left end portions of the rail portions  92 . This position of the operation portion  84  is referred to as a “home position” hereinafter. As the operation portion  84  is moved rightward from its home position along the pair of rail portions  92 , the wire-nipping portion  96  wipes foreign matters away from the charging wire  86 . The charging wire  86  is thus cleaned up. 
     When the operation portion  84  is moved to the right end portions of the pair of rail portions  92 , a right end portion of the operation portion  84  is in abutment with a left end portion of the restricting portion  94 , thereby restricting the operation portion  84  from moving further rightward. When the cleaning is finished, the operation portion  84  is again placed on the left end portions of the rail portions  92  (back to its home position). 
     (3) Drum Frame 
     Referring to  FIG. 2 , when the lower frame  33  and the upper frame  34  are mated with (assembled to) each other as will be described later, the drum cartridge frame  24  has a front portion defining a developing cartridge accommodating portion  26  and a rear portion defining a drum cartridge accommodating portion  25 . 
     The drum cartridge accommodating portion  25  and the developing cartridge accommodating portion  26  are in communication with each other via a second opening portion  98 , which is defined by a front end portion of the upper wall  88 , a rear end portion of the bottom wall  67 , inner surfaces of the upper frame side walls  71  and inner surfaces of the lower frame side walls  35 . 
     (4) Developing Cartridge Accommodating Portion 
     As shown in  FIG. 8 , the developing cartridge accommodating portion  26  is defined specifically by the front side walls  36 , the front wall  55  and the bottom wall  67 . The developing cartridge accommodating portion  26  is open upward such that the developing cartridge  23  can be mounted on and removed from the developing cartridge accommodating portion  26 . 
     (5) Drum Cartridge Accommodating Portion 
     Specifically, the drum cartridge accommodating portion  25  is defined by the lower frame  33  and the upper frame  34 . In the drum cartridge accommodating portion  25 , the photosensitive drum  3  and a drum cleaning roller  15  are accommodated, as shown in  FIG. 6 . 
     The photosensitive drum  3  extends in an axial direction which is coincident with the lateral direction. The photosensitive drum  3  defines an axis X 1  extending in the lateral direction (see  FIG. 10 ). The photosensitive drum  3  includes a base cylinder  18  and a pair of flange portions  19 , as shown in  FIG. 5 . 
     The base cylinder  18  is made of a metal, and has a generally cylindrical shape extending in the lateral direction. The base cylinder  18  has an outer circumferential surface which is coated with a photosensitive layer. 
     Each flange portion  19  is disposed on each axial end portion of the base cylinder  18 . The flange portion  19  is made from a resin. Each flange portion  19  integrally includes a base-cylinder coupled portion  29  and a bearing coupled portion  20 . 
     Each base-cylinder coupled portion  29  is coupled to (inserted into an internal space of) each axial end portion of the base cylinder  18  such that the base-cylinder coupled portion  29  is incapable of rotating relative to the base cylinder  18 . 
     Each bearing coupled portion  20  is formed in a generally columnar shape protruding laterally outward from a central portion of each base-cylinder coupled portion  29 . The bearing coupled portion  20  and the base-cylinder coupled portion  29  are coaxially positioned relative to each other. 
     On the bearing coupled portion  20  coupled to the left end portion of the base cylinder  18  (to be referred to as “left bearing coupled portion  20 ”), a photosensitive drum gear  166  is provided such that the photosensitive drum gear  166  is incapable of rotating relative to the left bearing coupled portion  20 . The photosensitive drum gear  166  is ring-shaped, protruding radially outward from an outer peripheral surface of a right end portion of the left bearing coupled portion  20 . The photosensitive drum gear  166  is formed with engageable teeth  168  on an outer circumferential surface thereof. 
     The left bearing coupled portion  20  also has a left end surface on which a drum driving-force inputting portion  155  is formed. The drum driving-force inputting portion  155  receives a driving force transmitted from a driving source (not shown) disposed within the main casing  2  when the process cartridge  21  is mounted in the main casing  2 . 
     The drum driving-force inputting portion  155  is formed with four coupling holes  174  thereon. Each coupling hole  174  has a generally U-shape in a left side view which is open radially outward. 
     The coupling holes  174  are spaced away from one another at equi-intervals along a circumference of the drum driving-force inputting portion  155  such that the coupling holes  174  are positionally displaced by about 90 degrees relative to one another. 
     The drum cleaning roller  15  extends in the lateral direction. The drum cleaning roller  15  includes a cleaning roller shaft  27  extending in the lateral direction (axial direction) and a sponge roller  28  provided around the cleaning roller shaft  27 . 
     At a left end portion of the cleaning roller shaft  27 , a cleaning gear  167  is provided such that the cleaning roller gear  167  is incapable of rotating relative to the cleaning roller shaft  27 . Specifically, the cleaning gear  167  is provided on an outer circumferential surface of the left end portion of the cleaning roller shaft  27 . The cleaning gear  167  has an outer circumferential surface on which engaging teeth  169  are formed. 
     As shown in  FIG. 5 , the photosensitive drum  3  and the drum cleaning roller  15  are supported to a connecting member  114  and a pair of bearing members  120  such that the photosensitive drum  3  and the drum cleaning roller  15  are restricted from moving relative to each other. 
     The connecting member  114  is a flat plate-like member having a droplet-like shape in a side view. Specifically, the connecting member  114  has a rear portion whose width becomes narrower as extending rearward. The connecting member  114  is formed with a cleaning shaft insertion portion  115  and a flange penetrating hole  116 . 
     The cleaning shaft insertion portion  115  is formed at a rear end portion of the connecting member  114 . The cleaning shaft insertion portion  115  has a generally cylindrical shape protruding leftward from a left surface of the rear end portion of the connecting member  114 . The cleaning shaft insertion portion  115  penetrates through the connecting member  114  in the lateral direction. The cleaning shaft insertion portion  115  has an inner diameter substantially identical to a diameter of the cleaning roller shaft  27 . 
     The flange penetrating hole  116  is formed at a frontward portion of the connecting member  114 . The flange penetrating hole  116  has a generally circular shape in a side view, and penetrates through the connecting member  114  in the lateral direction. The flange penetrating hole  116  has a diameter greater than an outer diameter of the bearing coupled portion  20 . 
     The pair of bearing members  120  is formed of a polyacetal material, for example. The pair of bearing members  120  is configured of a right bearing member  121  and a left bearing member  131 . 
     The right bearing member  121  integrally includes a cylindrical portion  122 , a flange portion  124 , a bearing guide portion  125  and a cleaning shaft supporting portion  127 . 
     The cylindrical portion  122  has a generally cylindrical shape whose right end is closed (covered) by a right end wall (not shown). The cylindrical portion  122  has an inner diameter substantially identical to (slightly greater than) the outer diameter of the bearing coupled portion  20 . 
     More specifically, the cylindrical portion  122  includes a shaft supporting portion  123  and a pressing portion  129 . 
     The shaft supporting portion  123  is formed in a generally cylindrical shape to coaxially penetrate through the right end wall of the cylindrical portion  122  in the lateral direction. A shaft  130  extending in the lateral direction is held to the shaft supporting portion  123  at a position diametrically center thereof (the shaft  130  is positioned within an internal space of the shaft supporting portion  123 ). 
     The pressing portion  129  is a portion of the cylindrical portion  122 , the portion being interposed between a pair of slits extending rightward from a left end portion of the cylindrical portion  122 . A spring member  128  is disposed at an outer circumferential surface of the pressing portion  129  such that the pressing portion  129  is biased radially inward. 
     The flange portion  124  is generally flat plate-like shaped and has a generally circular ring-like shape in a side view. The flange portion  124  extends radially outward from an outer circumferential surface of the cylindrical portion  122  at a position mid-way thereof in the lateral direction. 
     The bearing guide portion  125  is generally flat plate-like shaped, extending frontward from a front portion of the flange portion  124 . The bearing guide portion  125  has a front end portion on which a guide groove  126  is formed. The guide groove  126  has a generally U-shape in a side view that is depressed rearward from the front end portion of the bearing guide portion  125 . 
     The cleaning shaft supporting portion  127  includes an extending portion  143  and a cylindrical portion  144 . 
     The extending portion  143  has a generally flat plate-like shape extending diagonally upward and rearward from an upper-rear end portion of the flange portion  124 . The cylindrical portion  144  has a generally cylindrical shape, penetrating through the extending portion  143  in the lateral direction. 
     The left bearing member  131  integrally includes a cylindrical portion  132 , a flange portion  134 , a bearing guide portion  135 , a cleaning shaft receiving portion  137  and an engaging portion  140 . 
     The cylindrical portion  132  has a generally cylindrical shape. 
     Specifically, the cylindrical portion  132  has an inner diameter substantially identical to (slightly larger than) the outer diameter of the bearing coupled portion  20 , and an outer diameter substantially identical to an outer diameter of the cylindrical portion  122  of the right bearing member  121 . 
     The cylindrical portion  132  is formed with a pressing portion  133 . The pressing portion  133  is a portion of the cylindrical portion  132 , the portion being interposed between a pair of slits extending rightward from a left end portion of the cylindrical portion  132 . 
     The flange portion  134  is generally flat plate-like shaped and has a generally circular ring-like shaped side view. The flange portion  124  extends radially outward from an outer circumferential surface of the cylindrical portion  132  at a position mid-way thereof in the lateral direction. 
     The bearing guide portion  135  is generally flat plate-like shaped, extending frontward from a front end portion of the flange portion  134 . The bearing guide portion  135  has a front end portion on which a guide groove  136  is formed. The guide groove  136  has a generally U-shape in a side view that is depressed rearward from the front end portion of the bearing guide portion  135 . 
     The cleaning shaft receiving portion  137  is generally flat plate-like shaped, extending diagonally upward and rearward from an upper-rear end portion of the flange portion  134 . The cleaning shaft receiving portion  137  is formed with a cleaning shaft receiving hole  138 . The cleaning shaft receiving hole  138  has a generally circular shape in a side view, penetrating through a central portion of the cleaning shaft receiving portion  137  in the lateral direction. The cleaning shaft receiving hole  138  has an inner diameter substantially identical to an outer diameter of the cleaning shaft insertion portion  115  of the connecting member  114 . 
     The engaging portion  140  is also flat plate-like shaped, extending upward from an upper end portion of the flange portion  134 . The engaging portion  140  has an upper end portion on which an engaging hole  141  is formed. 
     Referring to  FIG. 7 , a pair of holding members  101  and a pair of separating members  146  are also provided on the drum cartridge accommodating portion  25 . Specifically, each holding member  101  and each separating member  146  are disposed on each side wall of the drum cartridge frame  24  (i.e., on each lower frame side wall  35  and each upper frame side wall  71 ). 
     Hereinafter, a detailed description will be given only on the holding member  101  and the separating member  146  disposed on the left side of the drum cartridge frame  24 . 
     Each holding member  101  is made from a material having excellent slidability or a low friction coefficient (polyacetal, for example) relative to a main body guide section  153  (described later). Referring to  FIGS. 4A and 4B , the holding member  101  includes a cylindrical portion  102 , a cover portion  104  and an engaging portion  106 . 
     The cylindrical portion  102  has a generally hollow cylindrical shape, having a right side portion serving as a larger-diameter portion  110  and a left side portion serving as a smaller-diameter portion  109 . 
     The larger-diameter portion  110  has an inner diameter larger than that of the smaller-diameter portion  109 . The inner diameter of the larger-diameter portion  110  is substantially identical to an outer diameter of a cylindrical-shaped collar portion  100  (described later) that is formed by the lower collar  42  and the upper collar  79 . 
     The smaller-diameter portion  109  has an inner diameter substantially identical to the outer diameter of the cylindrical portion  132  of the left bearing member  131  (or the outer diameter of the cylindrical portion  122  of the right bearing member  121  in case of the holding member  101  disposed on the right side of the drum cartridge frame  24 ). 
     On an inner peripheral surface of the smaller-diameter portion  109 , a protruding portion  108  is formed as an example of a claimed pressing portion, as shown in  FIG. 4B . The protruding portion  108  protrudes radially inward from a front portion of the inner peripheral surface of the smaller-diameter portion  109 . The protruding portion  108  has a triangular-shaped side view and extends in the lateral direction. 
     A pair of coupling protrusions  103  is also formed on the cylindrical portion  102  as an example of a claimed coupling portion. Specifically, the coupling protrusions  103  are formed on the larger-diameter portion  110  so as to diametrically oppose each other. Each coupling protrusion  103  is formed in a generally L-shape in a front side view, protruding rightward from a right end portion of the larger-diameter portion  110  and then bending radially outward of the cylindrical portion  102 . 
     The cylindrical portion  102  has an outer circumferential surface whose lower portion is defined as a guided surface  112 , which is a surface guided by the main body guide section  153  (described later) while the completed process cartridge  21  is being mounted in the main casing  2 . Also, the outer circumferential surface of the cylindrical portion  102  has an upper-rear portion and a lower-rear portion each being defined as a positioned surface  111  (as an example of a claimed positioned portion), which is a surface brought into contact with a positioning section  154  (described later) disposed within the main casing  2  when the completed process cartridge  21  is mounted in the main casing  2  (see  FIG. 10 ). 
     The cylindrical portion  102  has a rear portion  173  and a front portion  172 . The rear portion  173  has a length (thickness) shorter than that of the front portion  172  in the lateral direction. The front portion  172  and the rear portion  173  are connected via two sloped surfaces  176 , as shown in  FIG. 4A . More specifically, the two sloped surfaces  176  are formed to diametrically oppose each other in the top-to-bottom direction, thereby connecting between a left surface of the front portion  172  and a left surface of the rear portion  173 . Each sloped surface  176  slopes such that the sloped surface  176  approaches toward the larger-diameter portion  110  (rightward) as extends rearward. 
     The smaller-diameter portion  109  has a left end portion from whose front end portion the cover portion  104  extends frontward. The cover portion  104  is flat plate-shaped, having a generally triangular shaped side view. A separation shaft hole  105  is formed on the cover portion  104  at a position generally center thereof. The separation shaft hole  105  is generally circular shaped in a side view and penetrates through the cover portion  104  in the lateral direction. 
     On a front end portion of the cover portion  104 , the engaging portion  106  is formed as an example of a claimed engaging portion. The engaging portion  106  is generally flat plate-like shaped and has a generally rectangular shape extending frontward and rightward in a top view. The engaging portion  106  has an upper surface on which a protrusion  107  is formed. The protrusion  107  has a generally rectangular-shaped side view, and protrudes upward from a right end portion of the upper surface of the engaging portion  106 . 
     Referring to  FIG. 9A , each separating member  146  integrally includes a shaft penetrating portion  147 , a lower blade portion  148  and an upper blade portion  151 . 
     The shaft penetrating portion  147  has a generally cylindrical shape extending in the lateral direction. The shaft penetrating portion  147  has an inner diameter substantially identical to a diameter of the separation shaft  39  formed on each rear side wall  37 . 
     The lower blade portion  148  extends downward from a lower portion of the shaft penetrating portion  147 . The lower blade portion  148  is generally flat plate-like shaped, and has a lower portion bending frontward. The lower portion of the lower blade portion  148  has a front surface serving as a pressed surface  150 , which is configured to be pressed by a main body lever  162  (described later) when the developing roller  6  of the mounted developing cartridge  23  is separated from the corresponding photosensitive drum  3 . 
     The upper blade portion  151  extends upward from an upper portion of the shaft penetrating portion  147 . The upper blade portion  151  is generally flat plate-like shaped, and has an upper portion bending frontward. The upper portion of the upper blade portion  151  has a front surface serving as the abutment surface  149 , which is configured to be in abutment with the abutment portion  159  formed on the developing cartridge  23  when the developing cartridge  23  is in the separation state. Details on how the separating members  146  function to separate the developing roller  6  from the photosensitive drum  3  will be described later. 
     (6) Assembly of Drum Cartridge 
     Next, how the drum cartridge  22  is assembled will be described. For assembling the drum cartridge  22 , the connecting member  114  and the pair of bearing members  120  are first assembled to the photosensitive drum  3  and the drum cleaning roller  15 , as shown in  FIG. 5 . 
     The left bearing coupled portion  20  of the photosensitive drum  3  is inserted into the flange penetrating hole  116  of the connecting member  114  from rightward thereof. At the same time, the left end portion of the cleaning roller shaft  27  is also inserted into the cleaning shaft insertion portion  115  of the connecting member  114  from rightward thereof. The connecting member  114  is thus assembled to the photosensitive drum  3  and the drum cleaning roller  15 . 
     Then, the pair of bearing members  120  is assembled to the photosensitive drum  3  and the drum cleaning roller  15 . 
     Specifically, the right bearing member  121  is assembled to the photosensitive drum  3  and the drum cleaning roller  15  from rightward thereof such that the bearing coupled portion  20  on the right side of the photosensitive drum  3  (to be referred to as “right bearing coupled portion  20 ”) is inserted into the cylindrical portion  122  and the right end portion of the cleaning roller shaft  27  is inserted into the cleaning shaft supporting portion  127 . 
     The left bearing member  131  is then assembled to the photosensitive drum  3  and the drum cleaning roller  15  from leftward thereof such that the left bearing coupled portion  20  is inserted into the cylindrical portion  132  and the cleaning shaft insertion portion  115  is inserted into the cleaning shaft receiving hole  138 . 
     In this way, the bearing members  120  (the right bearing member  121  and the left bearing member  131 ) are assembled to the photosensitive drum  3  and the drum cleaning roller  15 , thereby connecting the photosensitive drum  3  and the drum cleaning roller  15 . 
     At this time, the engageable teeth  168  of the photosensitive drum gear  166  and the engaging teeth  169  of the cleaning gear  167  meshingly engage each other such that the driving force inputted to the photosensitive drum  3  is transmitted to the drum cleaning roller  15 . Further, the photosensitive drum  3  is rotatably supported to the bearing members  120 , since the cylindrical portion  122  of the right bearing member  121  and the cylindrical portion  132  of the left bearing member  131  both have diameters slightly larger than the outer diameter of each bearing coupled portion  20 . 
     Next, the photosensitive drum  3  and the drum cleaning roller  15  are assembled to the lower frame  33 , as shown in  FIG. 6 . 
     For assembling the photosensitive drum  3  and the drum cleaning roller  15  to the lower frame  33 , the photosensitive drum  3  and the drum cleaning roller  15  are placed upward of the lower frame  33  and then assembled thereto such that a lower portion of each bearing coupled portion  20  of the photosensitive drum  3  positionally corresponds to each lower receiver  40  of the lower frame  33 . 
     As a result, the flange portion  124  and the flange portion  134  are positioned to oppose respective inner surfaces of the rear side walls  37  in the lateral direction. Lower portions of the cylindrical portion  122  and the cylindrical portion  132  are thus respectively received by the lower receivers  40 . 
     The photosensitive drum  3  and the drum cleaning roller  15  are thus assembled to (combined with) the lower frame  33 . At this time, a lower portion of the base cylinder  18  of the photosensitive drum  3  is exposed downward through the first open portion  69 . 
     Then, the upper frame  34  is assembled to the lower frame  33 . 
     For assembling the upper frame  34  to the lower frame  33 , the upper frame  34  is assembled to a rear portion of the lower frame  33  from above such that the first frame engaging portion  38  is positionally coincident with the frame engaged portion  72  in the front-to-rear direction, and the second frame engaging portions  62  are positionally coincident with the engaged holes  91  (see  FIG. 12 ) in the lateral direction. 
     At this time, as shown in  FIGS. 9A to 9C , the first frame engaging portion  38  is inserted into the frame engaged portion  72  from below. The first frame engaging portion  38  is then pressed laterally outward by the protruding rib  75  formed on the inner wall of the frame engaged portion  72 . The hooked portion  48  is thus engaged with an upper peripheral end of the engaged portion  74 . 
     Also, each second frame engaging portion  62  is inserted into the corresponding engaged hole  91  from below, thereby permitting the hook portion  64  to be engaged with an upper peripheral end of the corresponding engaged hole  91 . 
     The upper frame  34  has thus been assembled to the lower frame  33 , thereby defining the drum cartridge accommodating portion  25 . 
     Upon completion of assembly of the upper frame  34  to the lower frame  33 , each lower receiver  40  and each upper receiver  78  constitute a drum receiving portion  171  as an example of a claimed photosensitive member receiving portion, as shown in  FIG. 7 . 
     The drum receiving portion  171  includes a drum receiving hole (not shown) and the collar portion  100 . Specifically, each lower receiving groove  43  and each upper groove  80  form the drum receiving hole (not shown) having a circular shaped side view, and each lower collar  42  and each upper collar  79  form the collar portion  100  of a generally cylindrical shape. In other words, the drum cartridge frame  24  is separable into the lower frame  33  and the upper frame  34  in the top-to-bottom direction along a boundary defined by the lower receiver  40  and the upper receiver  78 . That is, the lower frame  33  provides a portion of the drum receiving portion  171  (the lower receiver  40 ) and the upper frame  34  provides a remaining portion of the drum receiving portion  171  (the upper receiver  78 ). 
     Also, upper portions of the cylindrical portion  122  and the cylindrical portion  132  are received by the respective upper receivers  78 . In other words, an upper portion of each bearing coupled portion  20  is received by each upper receiver  78 . 
     The upper frame  34  is then fixed to the lower frame  33  to complete the drum cartridge frame  24  as shown in  FIG. 2 . 
     Specifically, upon completion of the assembly of the upper frame  34  and the lower frame  33 , the screw hole  66  of each lower fixing portion  65  is exposed through the screw penetrating hole  90  of the corresponding upper fixing portion  89 . A screw member  157  is screwed into each screw hole  66  via the screw penetrating hole  90 . The upper frame  34  is thus fixed to the lower frame  33  by these screw members  157 , thereby completing the drum cartridge frame  24 . 
     In the completed drum cartridge frame  24 , both axial end portions of the photosensitive drum  3  are coupled to respective pairs of the lower receiver  40  and the upper receiver  78  such that the photosensitive drum  3  is rotatable about the axis X 1  (see  FIG. 10 ). The axis X 1  of the photosensitive drum  3  serves as a rotational axis of the photosensitive drum  3  and therefore will be referred to as a “first rotational axis X 1 ” hereinafter. 
     Further, as shown in  FIGS. 9A to 9C , the upper portion of the engaging portion  140  of the left bearing member  131  penetrates through the penetrating hole  76  ( FIGS. 3 and 6 ) from below to protrude upward of the depressed portion  77 . The engaging hole  141  of the engaging portion  140  is therefore positioned to oppose the protrusion  85  of the operation portion  84  in the lateral direction (i.e., the engaging hole  141  is positioned leftward of the protrusion  85 ). With this structure, the protrusion  85  can be engaged with the engaging hole  141  when the operation portion  84  is positioned at the left end portion of the pair of rail portions  92  (at the home position). 
     Further, the wide-width groove  45  of the lower groove  44  and the wide-width groove  82  of the upper groove  81  diametrically oppose each other with respect to the photosensitive drum  3 . Likewise, the narrow-width groove  46  of the lower groove  44  and the narrow-width groove  83  of the upper groove  81  also diametrically oppose each other with respect to the photosensitive drum  3  (see  FIG. 9A ). 
     Each bearing coupled portion  20  received by each collar portion  100  (that is, each bearing coupled portion  20  internally coupled to the cylindrical portion  122  or the cylindrical portion  132 ) protrudes laterally outward from the corresponding collar portion  100  (specifically, from an outer end portion of each collar portion  100  in the lateral direction). 
     Next, the pair of separating member  146  is assembled to the lower frame  33 . 
     As shown in  FIGS. 9A to 9B , for assembling the separating member  146  to the lower frame  33 , the separating member  146  is attached to the lower frame  33  from laterally outward thereof such that the separation shaft  39  of the lower frame  33  penetrates through the shaft penetrating portion  147  of the separating member  146 . At this time, the lower blade portion  148  of the separating member  146  is positioned below the separation shaft  39  in a state that the lower portion of the lower blade portion  148  is bent (oriented) frontward. 
     The pair of holding members  101  is subsequently assembled to the drum cartridge frame  24 . 
     For assembling the holding members  101  to the drum cartridge frame  24 , as shown in  FIGS. 4 and 9A , each holding member  101  is attached to the drum cartridge frame  24  from laterally outward thereof such that the engaging portion  106  of the holding member  101  is positioned frontward and the pair of coupling protrusions  103  is inserted into the corresponding wide-width grooves  45 ,  82  from laterally outward thereof. 
     As a result, the cylindrical portions  122 ,  132  of the bearing members  120  (right bearing member  121  and the left bearing member  131 ) are internally coupled to the corresponding smaller-diameter portions  109  of the holding members  101  respectively, and each collar portion  100  of the drum cartridge frame  24  is internally coupled to the larger-diameter portion  110  of each holding member  101 . In other words, each bearing coupled portion  20  of the photosensitive drum  3  is internally coupled to the cylindrical portion  102  and held by the holding member  101  via the cylindrical portion  122  or the cylindrical portion  132 . 
     At this time, the cylindrical portion  102  of each holding member  101  is coaxially positioned relative to the photosensitive drum  3 . In other words, the cylindrical portion  102  of each holding member  101  defines an axis coincident with the first rotational axis X 1  of the photosensitive drum  3 . 
     Then, the holding members  101  are engaged with the lower frame  33  and the upper frame  34 . 
     Specifically, as shown in  FIG. 9B , the holding member  101  is rotated in a direction Y (counterclockwise in a left side view) until the engaging portion  106  abuts on the engaged portion  47  of the lower frame  33  from below. Since the axis of the cylindrical portion  102  of the holding member  101  is coincident with the first rotational axis X 1  of the photosensitive drum  3 , each holding member  101  is also rotated about the first rotational axis X 1 . 
     In conjunction with rotation of the holding member  101 , as shown in  FIGS. 4 and 9C , each coupling protrusion  103  is also moved from the wide-width grooves  45 ,  82  to the narrow-width grooves  46 ,  83  along the lower groove  44  and the upper groove  81 . Bent portions of the L-shaped coupling protrusions  103  are thus engaged with peripheral end portions of the narrow-width grooves  46 ,  83 . In other words, the lower groove  44  and the upper groove  81  are respectively coupled to one of the coupling protrusions  103  as the holding member  101  is rotated. 
     The holding members  101  are thus engaged with the lower frame  33  and the upper frame  34  such that each holding member  101  covers the lower receiver  40  and the upper receiver  78 . 
     Also, when the engaging portion  106  of the holding member  101  abuts on a lower surface of the engaged portion  47 , the protrusion  107  is inserted into the engaging hole  51  (see  FIG. 3 ) of the engaged portion  47  from below. The engaging portion  106  of each holding member  101  is thus engaged with the lower frame  33 . 
     Assembly of the holding members  101  to the drum cartridge frame  24  (the lower frame  33  and the upper frame  34 ) is thus completed. 
     At this time, the protruding portion  108  formed on the cylindrical portion  102  of each holding member  101  presses the corresponding bearing coupled portion  20  toward the lower receiver  40  (precisely, toward an upper end portion of the lower receiver  40 ) via the cylindrical portion  122  or the cylindrical portion  132 , as shown in  FIG. 9C . A direction in which the protruding portion  108  presses the corresponding bearing coupled portion  20  is indicated by an arrow in  FIG. 9C . 
     Further, in accordance with rotation of the holding member  101 , the separation shaft  39  of the lower frame  33 , which penetrates through the shaft penetrating portion  147  of the separating member  146 , is inserted into the separation shaft hole  105  formed on the cover portion  104 . The separating member  146  is thus supported to the lower frame  33  such that the separating member  146  is covered by the cover portion  104  of each holding member  101  from laterally outward. 
     The drum driving-force inputting portion  155  of the left bearing coupled portion  20  is accommodated within the cylindrical portion  102  in the lateral direction and thus protected by the same, as shown in  FIG. 2 . 
     Assembly of the drum cartridge  22  is thus completed. At this time, as shown in  FIG. 8 , a front portion of the base cylinder  18  of the photosensitive drum  3  is exposed frontward from the second opening portion  98 . 
     (7) Attachment of Developing Cartridge to Drum Cartridge 
     For attaching the developing cartridge  23  to the drum cartridge  22 , the developing cartridge  23  is simply inserted into the developing cartridge accommodating portion  26  of the drum cartridge  22  from above. The developing cartridge  23  is thus mounted on the drum cartridge  22 , thereby the process cartridge  21  being completed. 
     When the process cartridge  21  is completed, as shown in  FIG. 10 , the lateral end portions of the front wall of the developing cartridge frame  30  are pushed (biased) toward the photosensitive drum  3  by the cylindrical portions  57  of the pressing mechanisms  56  due to the biasing forces of the spring members  58 . Therefore, the rubber roller  17  of the developing roller  6  and the base cylinder  18  of the photosensitive drum  3  are in direct contact with each other. 
     Also, as shown in  FIG. 10 , in the completed process cartridge  21 , the separating member  146  is positioned between a rotational center of the photosensitive drum  3  (the first rotational axis X 1 ) and a rotational center of the developing roller  6  (the second rotational axis X 2 ), when projected in the lateral direction. 
     3. Mounting of Process Cartridge in Main Casing 
     In order to mount the process cartridge  21  in the main casing  2 , first the top cover  50  is opened. Each process cartridge  21  is inserted into its designated position within the main casing  2  (a prescribed position corresponding to each color) from above. 
     Referring to  FIG. 10 , while the process cartridge  21  is being inserted into the main casing  2 , the guided surface  112  formed on the cylindrical portion  102  of each holding member  101  is guided downward and rearward along the main body guide sections  153  (as an example of a claimed guide section) provided in the main casing  2 . The main body guide section  153  is generally flat plate-like shaped, extending diagonally downward and rearward (shown as a chain line in  FIG. 10 ). The main body guide section  153  is made from an ABS (acrylonitrile butadiene styrene) material, for example. 
     Insertion of the process cartridge  21  into the main casing  2  is ended when each positioned surface  111  formed on the cylindrical portion  102  of each holding member  101  abuts on the positioning section  154  provided in the main casing  2 . The positioning section  154  is formed to have a generally L-shaped side view, and shown as a solid line in  FIG. 10 . 
     As described earlier, the drum driving-force inputting portion  155  is accommodated within the cylindrical portion  102  of the left bearing coupled portion  20 , as shown in  FIG. 12A . Therefore, during mounting of the process cartridge  21  into the main casing  2 , the drum driving-force inputting portion  155  is suppressed from being damaged due to collision or interference with some other members provided in the main casing  2 . 
     Further, as shown in  FIG. 12A  and described above with reference to  FIG. 4A , in the holding member  101  attached on the left side of the process cartridge  21 , the front portion  172  has a thickness thicker than that of the rear portion  173  in the lateral direction. In other words, the left surface of the rear portion  173  of the cylindrical portion  102  is positioned rightward relative to the left surface of the front portion  172  of the cylindrical portion  102  in the lateral direction. With this structure, while the process cartridge  21  is mounted in the main casing  2 , the rear portion  173  of the holding member  101  is prevented from causing interference with other members in the main casing  2  (for example, a drum driving force transmission section  175  (described next)), thereby realizing a smooth mounting of the process cartridge  21  into the main casing  2 . 
     The drum driving force transmission section  175  is provided in the main casing  2  for transmitting the driving force from the driving source (not shown) disposed in the main casing  2  to the photosensitive drum  3 . Specifically, the drum driving force transmission section  175  is disposed in the main casing  2  so as to oppose the drum driving-force inputting portion  155  of the photosensitive drum  3  from leftward thereof in the lateral direction when the process cartridge  21  has been completely mounted, as shown in  FIG. 12B . 
     The drum driving force transmission section  175  is rotatable relative to the main casing  2 . The drum driving force transmission section  175  has an engaging gear  177  on its left end, and a movable portion  178  on its right end. 
     The engaging gear  177  is generally disk-shaped. The engaging gear  177  has an outer circumferential surface on which gear teeth are formed so that the driving force transmitted from the driving source (not shown), such as a motor, can be inputted to the engaging gear  177 . 
     The movable portion  178  is provided rightward of the engaging gear  177 . The movable portion  178  is configured to advance and retract in the lateral direction in conjunction with movement (opening and closing movements) of the top cover  50 . The movable portion  178  has a right end surface on which four engaging protrusions  179  are formed such that each engaging protrusion  179  is engageable with each coupling hole  174  formed on the drum driving-force inputting portion  155  (see  FIG. 5 ). 
     When the top cover  50  is closed, mounting of the process cartridge  21  in the main casing  2  is completed. The process cartridge  21  is positioned relative to the main casing  2  when each positioned surface  111  abuts on the positioning section  154  of the main casing  2 . 
     At this time, the protruding portion  108  of each holding member  101  is oriented (protrudes) toward the rear surface of the positioning section  154 , as shown in  FIG. 11 . The protruding portions  108  thus serve to press the respective bearing coupled portions  20  toward the rear surface of the positioning section  154 . Also, the pressing portions  129 ,  133  formed on the right bearing member  121  and the left bearing member  131  (see  FIG. 5 ) respectively press the right and left bearing coupled portions  20  toward the bottom surface of the positioning section  154 . In other words, each bearing coupled portion  20  is pressed toward the positioning section  154 . 
     Further, in association with closing movement of the top cover  50 , the movable portion  178  of the drum driving force transmission section  175  advances rightward such that the each engaging protrusion  179  is engaged with one of the coupling holes  174  formed on the drum driving-force inputting portion  155 . As a result, the driving force from the driving source (not shown) disposed in the main casing  2  is transmitted to the photosensitive drum  3  via the drum driving force transmission section  175 . 
     4. Separation of Developing Cartridge from Drum Cartridge 
     As described above, the rubber roller  17  of the developing roller  6  and the base cylinder  18  of the photosensitive drum  3  are normally in contact with each other. However, the rubber roller  17  and the base cylinder  18  sometimes need to be separated from each other, for example, when image formation is not performed in the printer  1 . 
     For separating the developing roller  6  from the photosensitive drum  3 , the main body lever  162  (shown as a dotted line in  FIG. 11 ) is provided in the main casing  2 . 
     Specifically, the main body lever  162  functions to push the pressed surface  150  of each separating member  146 , which causes each separating member  146  to pivotally move clockwise in a left side view. The abutment surface  149  of each separating member  146  is therefore brought into abutment with the rear surface of the abutment portion  159  formed on the gear cover  160  of the developing cartridge  23 . 
     As the main body lever  162  further presses the pressed surface  150 , the abutment surface  149  pushes the corresponding abutment portion  159  frontward and upward such that the developing cartridge  23  is moved frontward and upward against the biasing force of the pressing mechanisms  56 . The rubber roller  17  of the developing roller  6  and the base cylinder  18  of the photosensitive drum  3  are thus separated from each other. 
     5. Advantageous Effects 
     (1) As described above, the drum cartridge frame  24  of the drum cartridge  22  includes the lower frame  33  and the upper frame  34  separable from each other in the top-to-bottom direction. The lower frame  33  has the pair of lower receivers  40  and the upper frame  34  has the pair of upper receivers  78  such that, upon mating the lower frame  33  with the upper frame  34 , each lower receiver  40  and each upper receiver  78  forms each drum receiving portion  171  for receiving each axial end portions of the photosensitive drum  3 . Specifically, for assembling the drum cartridge frame  24 , each bearing coupled portion  20  of the photosensitive drum  3  is received by the lower receiver  40  such that the photosensitive drum  3  is assembled to the lower frame  33  (see  FIG. 6 ). Subsequently, the upper frame  34  is assembled to the lower frame  33  such that the upper portion of each bearing coupled portion  20  is received by the upper receiver  78  (see  FIG. 7 ). 
     The assembly of the photosensitive drum  3  relative to the drum cartridge frame  24  (the lower frame  33  and the upper frame  34 ) can be thus facilitated. 
     Further, the pair of holding members  101  is assembled to the drum cartridge frame  24  with which the photosensitive drum  3  has been combined. Upon completion of assembly of the holding members  101  to the drum cartridge frame  24  having the photosensitive drum  3 , the cylindrical portion  102  of each holding member  101  supports each bearing coupled portion  20  of the photosensitive drum  3 , while the coupling protrusions  103  of each holding member  101  are engaged with the narrow-width groove  46  formed on the lower frame  33  and the narrow-width groove  83  formed on the upper frame  34  respectively. 
     With this structure, rigidity of the drum cartridge frame  24  can be enhanced, in other words, the lower frame  33  and the upper frame  34  can be assembled to each other tightly and stably. Therefore, the photosensitive drum  3  can be positioned relative to the drum cartridge frame  24  with high accuracy. 
     In the drum cartridge  22  of the present embodiment, therefore, the assembly of the photosensitive drum  3  to the drum cartridge frame  24  can be smoothly performed, while the positioning accuracy of the photosensitive drum  3  relative to the drum cartridge frame  24  can be improved. 
     (2) The pair of bearing members  120  (the right bearing member  121  and the left bearing member  131 ) is made from a material having excellent slidability (having a low friction coefficient), such as a polyacetar material. The bearing coupled portions  20  of the photosensitive drum  3  are internally coupled to the cylindrical portion  122  of the right bearing member  121  and the cylindrical portion  132  of the left bearing member  131  respectively such that the photosensitive drum  3  is rotatably supported to the pair of the right bearing member  121  and the left bearing member  131 . 
     Such simple-structured bearing members  120  can ensure smooth rotation of the photosensitive drum  3 . 
     Incidentally, the bearing members  120  are likely to be susceptible to attrition since the bearing members  120  rotatably support the photosensitive drum  3 . However, even in case that the bearing member  120  is abraded, the worn-out bearing member  120  only can be replaced. Maintenance of the drum cartridge  22  can be thus efficiently performed. And, since only the bearing member  120  is made from a polyacetal material which has excellent sliding performance, production costs of the drum cartridge  22  can be reduced. 
     (3) The holding member  101  includes the engaging portion  106  on which the protrusion  107  is formed. As shown in  FIG. 9B , when the holding member  101  is rotated in the direction Y (counterclockwise in a left side view), the engaging portion  106  is engaged with the engaged portion  47  of the lower frame  33  such that the engaging portion  106  contacts the lower surface of the engaged portion  47  and the protrusion  107  is inserted into the engaging hole  51  formed on the engaged portion  47  from below. 
     With this structure, the holding member  101  can be stably positioned relative to the lower frame  33 . The pair of holding members  101  can be thus reliably engaged with and held to the drum cartridge frame  24 . Simply rotating the holding member  101  can be realize engagement of the holding member  101  with the lower frame  33 , thereby facilitating assembly of the holding member  101  to the drum cartridge frame  24 . 
     (4) The lower groove  44  of the lower frame  33  and the upper groove  81  of the upper frame  34  are formed such that the lower groove  44  and upper groove  81  can receive the coupling protrusions  103  of each holding member  101  in a state that each coupling protrusion  103  is slidingly movable relative to the lower groove  44  and the upper groove  81 . Even in this state where the coupling protrusions  103  of the holding member  101  are slidingly movably coupled to the lower groove  44  and the upper groove  81 , the holding member  101  is rotatable relative to the lower frame  33  and the upper frame  34 . 
     Therefore, engagement of the engaging portion  106  of each holding member  101  with the corresponding engaged portion  47  of the lower frame  33  can be easily realized. 
     (5) The cylindrical portion  102  of each holding member  101  is formed with the protruding portion  108  thereon. The protruding portion  108  is integral with the cylindrical portion  102  and protrudes radially inward from the inner peripheral surface of the cylindrical portion  102 . The protruding portion  108  serves to press the corresponding bearing coupled portion  20  toward the upper end portion of the lower receiver  40  via the cylindrical portion  122  or the cylindrical portion  132 , as shown in  FIG. 9C . 
     This construction allows each bearing coupled portion  20  of the photosensitive drum  3  to be positioned relative to the lower receiver  40 . Therefore, positioning accuracy of the photosensitive drum  3  relative to the drum cartridge frame  24  can be improved. 
     (6) The scorotron charger  4  for charging the photosensitive drum  3  and the cleaning unit  95  for cleaning the charging wire  86  of the scorotron charger  4  are provided on the upper wall  88  of the upper frame  34 . 
     The cleaning unit  95  also includes the movable operation portion  84  on whose left end portion the protrusion  85  is formed. When the operation portion  84  is at its home position (on the left end portions of the rail portions  92 ), the protrusion  85  is inserted into the engaging hole  141  formed on the engaging portion  140  of the left bearing member  131  for engagement with the same. With this structure, the operation portion  84  is prevented from coming off from the rail portions  92 . 
     (7) The process cartridge  21  includes the drum cartridge  22  having the photosensitive drum  3 , and the developing cartridge  23  having the developing roller  6  and detachably mountable on the drum cartridge  22 . 
     When the developing cartridge  23  is mounted on the drum cartridge  22 , the rubber roller  17  of the developing roller  6  is in direct contact with the base cylinder  18  of the photosensitive drum  3 . Therefore, the photosensitive drum  3  is accurately positioned relative to the drum cartridge frame  24 , thereby realizing accurate positioning of the developing roller  6  relative to the photosensitive drum  3 . 
     (8) The pair of separating members  146  is disposed on the process cartridge  21 . Each separating member  146  is pivotally movably supported to the separation shaft  39  of the lower frame  33 . In a state where the developing cartridge  23  is mounted on the drum cartridge  22 , the separating member  146  is positioned between the rotational axis of the photosensitive drum  3  (the first rotational axis X 1 ) and the rotational axis of the developing roller  6  (the second rotational axis X 2 ) when projected in the lateral direction. 
     The separating member  146  is configured to press the abutment portion  159  formed on each gear cover  160  of the developing cartridge  23 , thereby separating the rubber roller  17  of the developing roller  6  from the base cylinder  18  of the photosensitive drum  3 . 
     In this way, such simple-structured separating member  146  can reliably perform separation and contact between the rubber roller  17  of the developing roller  6  and the base cylinder  18  of the photosensitive drum  3 . Since the separating member  146  is disposed at a position adjacent to the developing roller  6 , displacement of the developing roller  6  (separation and contact) relative to the photosensitive drum  3  can be further reliably performed. 
     (9) Each holding member  101  includes the cover portion  104 . The cover portion  104  serves to cover each separating member  146  from outward in the lateral direction for permitting the separating member  146  to be held to the lower frame  33 . Undesired contact of the separating member  146  with its surroundings in the lateral direction can also be prevented. 
     (10) The process cartridge  21  is detachably mountable in the main casing  2 . As described above, in the process cartridge  21 , positioning accuracy between the photosensitive drum  3  and the drum cartridge frame  24  can be enhanced. Hence, the photosensitive drum  3  can also be accurately positioned relative to the main casing  2 . 
     (11) The positioning section  154  is arranged in the main casing  2 . Each holding member  101  is formed with the positioned surfaces  111  serving to position the process cartridge  21  relative to the main casing  2 . 
     When the process cartridge  21  is mounted in the main casing  2 , the positioned surfaces  111  are in abutment with the positioning section  154  of the main casing  2 , thereby achieving positioning of the process cartridge  21  relative to the main casing  2 . In this way, positioning of the process cartridge  21  relative to the main casing  2  can be further improved. In other words, accurate positioning of the photosensitive drum  3  relative to the main casing  2  can be realized. 
     (12) The main body guide sections  153  are also provided in the main casing  2 . The cylindrical portion  102  of each holding member  101  is formed with the guided surface  112 . 
     During mounting of the process cartridge  21  into the main casing  2 , the guided surface  112  of each holding member  101  is guided along the corresponding main body guide section  153 . Mounting of the process cartridge  21  into the main casing  2  is thus facilitated. 
     (13) The holding member  101  is made from a polyacetal material, whereas the drum cartridge frame  24  (the lower frame  33  and the upper frame  34 ) is made from a polystyrene material. In other words, the holding member  101 , which has the guided surface  112  that is guided during mounting of the process cartridge  21  into the main casing  2 , is made from a material whose slidability is higher (better) than that of the drum cartridge frame  24  (the lower frame  33  and the upper frame  34 ). The sliding performance of the holding member  101  is also better than that of the main body guide section  15  made from an ABS (acrylonitrile butadiene styrene) material. Hence, mounting of the process cartridge  21  into the main casing  2  is further facilitated. 
     (14) The protruding portion  108  formed on each holding member  101  is formed to protrude toward the rear surface of the positioning section  154 , when the process cartridge  21  is mounted in the main casing  2 . Each bearing coupled portion  20  of the photosensitive drum  3  is therefore pressed toward the rear surface of the positioning section  154  by the corresponding protruding portion  108 . 
     As a result, the photosensitive drum  3  can be positioned relative to the positioning section  154  of the main casing  2  via the lower frame  33  and the upper frame  34 . Accurate positioning of the photosensitive drum  3  relative to the main casing  2  can be thus further enhanced. 
     While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.