Abstract:
An image forming device including an accommodating member, a moving section, a driving section, a transmitting section, and first and second switching sections. The accommodating member is movable between an accommodating position and a pulled-out position. A charger includes a charging wire and a wire cleaner movable therealong. The moving section is configured to move the wire cleaner. The driving section is configured to generate a drive force to move the moving section. The transmitting section is movable to one of a first path on which the transmitting section is drivingly connected to the driving section and a second path on which the transmitting section is disconnected from the driving section. The transmitting section is configured to transmit the drive force from the driving section to the moving section when the transmitting section is moved to the first path. The first switching section is configured to switch a position of the transmitting section from the second path to the first path. The second switching section is configured to switch a position of the transmitting section from the first path to the second path.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2010-148558 filed Jun. 30, 2010. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an image forming device such as a laser printer. 
     BACKGROUND 
     A conventional image forming device such as a laser printer includes a main casing, and within the main casing, a drum unit is detachably mounted. The drum unit includes a photosensitive drum, a developing cartridge retaining a developing roller, and a charger for uniformly charging a surface of the photosensitive drum. A scorotron charger having a charging wire and a grid electrode has been widely used as the charger. 
     While using the image forming device, dust such as paper dust are deposited on the charging wire. If dust is deposited on the charging wire, charging performance of the wire to charge the surface of the photosensitive drum is degraded. In order to prevent dust from being deposited on the charging wire, the charger includes a wire cleaner for cleaning the charging wire. The wire cleaner is moved along the charging wire, so that the charging wire can be cleaned. 
     SUMMARY 
     In order to maintain satisfactory charging performance of a charging wire, regular cleaning to the charging wire is required. However, for a user, it is rather cumbersome to regularly clean the charging wire. Then, a mechanism for moving a wire cleaner in interlocking relation to the detaching and attaching movement of a drum unit with respect to a main casing is demanding. 
     However, when cleaning the charging wire, the wire cleaner is required to be moved throughout an overall length of the charging wire. Unless the wire cleaner is moved throughout the overall length of the charging wire, dust collected by the wire cleaner may remain on the charging wire. That is, if the wire cleaner is not moved from one end of the charging wire to another end thereof, a portion of the charging wire is cleaned but remaining portion thereof remains uncleaned. This may cause non-uniform charge on the surface of the photosensitive drum. Further, a portion of the charging wire on which dust has been deposited may cause abnormal electrical discharge. 
     In view of the foregoing, it is an object of the present invention to provide an image forming device capable of saving time and effort of a user on cleaning a charging wire, and capable of uniformly charging a surface of a photosensitive drum. 
     In order to attain the above and other objects, the present invention provides an image forming device including: a main casing; a photosensitive member; a charger; an accommodating member; a moving section; a driving section; a transmitting section; a first switching section; and a second switching section. The photosensitive member has an axis defining an axial direction and a surface including an image forming region on which an electrostatic latent image is formed. The image forming region has a width in the axial direction. The charger includes: a charging wire extending in the axial direction and configured to charge the surface of the photosensitive member; and a wire cleaner movable along the charging wire while being in sliding contact with the charging wire. The accommodating member is configured to accommodate therein the photosensitive member and the charger, and movable in a moving direction between an accommodating position where the accommodating member is accommodated in the main casing and a pulled-out position where the accommodating member is pulled outward of the main casing. The moving section is accommodated in the accommodating member and configured to move the wire cleaner. The driving section extends in the main casing and is configured to generate a drive force to move the moving section. The transmitting section is accommodated in the accommodating member and movable selectively to one of a first path on which the transmitting section is connected to the driving section and a second path on which the transmitting section is disconnected from the driving section. The transmitting section is configured to transmit the drive force from the driving section to the moving section when the transmitting section is moved to the first path. The first switching section is disposed at the main casing and located at a pulled-out position side relative to the driving section. The first switching section is configured to switch a position of the transmitting section from the second path to the first path. The second switching section is disposed at the main casing and located at an accommodating position side relative to the driving section. The second switching section is configured to switch a position of the transmitting section from the first path to the second path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings; 
         FIG. 1  is a schematic cross-sectional view of a color printer according to one embodiment of the present invention; 
         FIG. 2  is a perspective view of a drum unit of the printer according to the embodiment, in which a pinion gear is disposed at a first position; 
         FIG. 3  is a perspective view of the drum unit, in which the pinion gear is disposed at a second position; 
         FIG. 4A  is a perspective view of the drum unit in which each outer frame of each charger is omitted to particularly show a plurality of wire cleaner movement mechanisms and support plates suspending the same; 
         FIG. 4B  is a plan view of the drum unit in which each outer frame of each charger and each support plate are omitted to particularly show the plurality of wire cleaner movement mechanisms and charging wires; 
         FIG. 4C  is a perspective view of the plurality of wire cleaner movement mechanisms, a plurality of wire cleaners, a coupling belt, and a drive force transmission mechanism in the printer according to the embodiment; 
         FIG. 5  is an enlarged perspective view of the wire cleaner shown in  FIG. 4C ; 
         FIG. 6  is an exploded perspective view of the wire cleaner shown in  FIG. 5 ; 
         FIG. 7A  is an enlarged perspective view of the pinion gear shown in  FIG. 2 ; 
         FIG. 7B  is an enlarged perspective view of the pinion gear shown in  FIG. 3 ; 
         FIG. 8  is a perspective view showing a state in which the drum unit shown in  FIG. 1  is disposed at a pulled-out position; 
         FIG. 9  is an enlarged perspective view of a regulation member shown in  FIG. 8 ; 
         FIG. 10A  is a view for description of a movement of the pinion gear for cleaning operation in the printer according to the embodiment; 
         FIG. 10B  is a view showing a state of the pinion gear subsequent to the state shown in  FIG. 10A ; 
         FIG. 10C  is a view showing a state of the pinion gear subsequent to the state shown in  FIG. 10B ; 
         FIG. 10D  is a view showing a state of the pinion gear subsequent to the state shown in  FIG. 10C ; 
         FIG. 10E  is a view showing a state of the pinion gear subsequent to the state shown in  FIG. 10D ; and 
         FIG. 10F  is a view showing a state of the pinion gear subsequent to the state shown in  FIG. 10E . 
     
    
    
     DETAILED DESCRIPTION 
     1. General Structure of Color Printer 
     A tandem type color printer as an image forming device according to one embodiment of the present invention will be described while referring to  FIG. 1 . The color printer  1  includes a main casing  2  constituting a main body. Within the main casing  2 , a drum unit  3 , an exposure unit  10 , a sheet supply cassette  11 , and a fixing unit  14  are provided. 
     Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used throughout the description assuming that the color printer  1  is disposed in an orientation in which it is intended to be used. In use, the color printer  1  is disposed as shown in  FIG. 1 . More specifically, in  FIG. 1 , a left side and a right side are a front side and a rear side, respectively. 
     The main casing  2  has a front cover  4  positioned at a front side thereof and a discharge tray  15  positioned at a top surface thereof. The front cover  4  is pivotally movable between an open position and a closed position. When the front cover  4  is in the open position, the drum unit  3  is horizontally movable in a frontward/rearward direction. More specifically, the drum unit  3  is movable between an accommodating position at which the drum unit  3  is accommodated in the main casing  2  and a pulled-out position at which the drum unit  3  is pulled out of the main casing  2 . 
     The drum unit  3  includes a plurality of (four) photosensitive drums  5 , a plurality of (four) chargers  6 , and a plurality of (four) developing cartridges  7 . Each of the photosensitive drums  5  has an axis extending in a leftward/rightward direction, and is rotatably supported to the drum unit  3 . The four photosensitive drums  5  are provided for four colors of black, yellow, magenta, and cyan, respectively. The photosensitive drums  5  are juxtaposed with each other in the frontward/rearward direction in order of black, yellow, magenta, and cyan from the front side of the color printer  1 , and spaced apart from each other at a predetermined distance. 
     The four chargers  6  are provided in one-on-one correspondence with respect to the four photosensitive drums  5 . Each of the chargers  6  is disposed diagonally above and rearward of the corresponding photosensitive drum  5 . The charger  6  is a scorotron charger provided with a charging wire  37  ( FIG. 5 ) for charging a surface of the corresponding photosensitive drum  5 . 
     The four developing cartridges  7  are provided in one-on-one correspondence with respect to the four photosensitive drums  5 . Each of the developing cartridges  7  is detachably mounted in the drum unit  3 , and includes a cartridge frame  8  and a developing roller  9  accommodated in the cartridge frame  8 . 
     The exposure unit  10  is disposed above the drum unit  3 . The exposure unit  10  is adapted to project a plurality of (four) laser beams corresponding to the four colors used by the color printer  1 . 
     After surfaces of the photosensitive drums  5  are uniformly charged by the chargers  6  in association with rotations of the photosensitive drums  5 , the surfaces are selectively exposed to the laser beams emitted from the exposure unit  10 . With this exposure, electrical charge is selectively removed from the surfaces of the photosensitive drums  5 . Thus, electrostatic latent images are formed on the surfaces of the photosensitive drums  5 . When the electrostatic latent images confront the developing rollers  9 , toner is supplied to the electrostatic latent images by the developing rollers  9 . Hence, toner images are formed on the surfaces of the photosensitive drums  5 . 
     Incidentally, instead of the exposure unit  10 , four LED arrays can be provided in one-on-one correspondence with respect to the four photosensitive drums  5 . 
     The sheet supply cassette  11  accommodating a sheet P therein is disposed at a lower portion of the main casing  2 . The sheet P accommodated in the sheet supply cassette  11  is fed by various rollers toward a conveying belt  12 . The conveying belt  12  is disposed such that a top portion of the conveying belt  12  confronts the four photosensitive drums  5  from below. A plurality of (four) transfer rollers  13  are provided at positions confronting the corresponding photosensitive drums  5 , with the top portion of the conveying belt  12  interposed therebetween. The sheet P conveyed onto the conveying belt  12  passes sequentially through positions between the photosensitive drums  5  and the conveying belt  12  as the conveying belt  12  circulates. The toner images formed on the surfaces of the photosensitive drums  5  are transferred onto the sheet P when the toner images confront the sheet P. 
     The fixing unit  14  is positioned downstream of the conveying belt  12  in a sheet feeding direction of the sheet P. The sheet P onto which the toner images are transferred is conveyed to the fixing unit  14 . In the fixing unit  14 , the toner images are fixed to the sheet P by heat and pressure. The sheet P to which the toner images are fixed is discharged to the discharge tray  15  by various rollers. 
     2. Drum Unit 
     As shown in  FIGS. 2 and 3 , the drum unit  3  further includes a pair of side plates  21 ,  22  (a right side plate  21  and a left side plate  22 ), a front beam  23 , and a rear beam  24 . The right side plate  21  is arranged in confrontation with and spaced away from the left side plate  22  in the rightward/leftward direction. The front beam  23  bridges between the right side plate  21  and the left side plate  22  at a front portion thereof. The rear beam  24  bridges between the right side plate  21  and the left side plate  22  at a rear portion thereof. 
     The four photosensitive drums  5 , the four chargers  6 , and the four developing cartridges  7  (shown in  FIG. 1 ) are collectively supported to the right side plate  21  and the left side plate  22 . Further, in an outer frame (not shown) of each charger  6 , a wire cleaner movement mechanism  25  is disposed between the right side plate  21  and the left side plate  22  and at upper and rearward positions in a space of the outer frame. 
     (1) Wire Cleaner Movement Mechanism 
     As shown in  FIG. 4A , in the outer frame (not shown) of each charge  6 , a support plate  6 A extends in leftward/rightward direction and is fixed to the outer frame. Alternatively, each support plate  6 A can be positioned within the outer frame and is fixed to the side plates  21 ,  22 . As shown in  FIGS. 4A through 4C , each of the wire cleaner movement mechanisms  25  includes a drive pulley  30 , a driven pulley  31 , and an endless drive belt  32 . In the present embodiment, four drive pulleys  30 , four driven pulleys  31 , and four endless drive belts  32  are provided. 
     The drive pulley  30  is disposed rightward of an image forming region of the corresponding photosensitive drum  5  in which the electrostatic latent image is formed. The drive pulley  30  includes a disk-shaped drive portion  30   a , a disk-shaped coupling portion  30   b , and a shaft portion  30   c.    
     The coupling portion  30   b  is disposed above the drive portion  30   a . The coupling portion  30   b  is arranged coaxially with the drive portion  30   a  and has a diameter smaller than that of the drive portion  30   a . The shaft portion  30   c  extends vertically, and is arranged coaxially with the drive portion  30   a  and the coupling portion  30   b . The shaft portion  30   c  has an upper end portion rotatably supported to the support plate  6 A. The drive portion  30   a , the coupling portion  30   b , and the shaft portion  30   c  are integrally rotatable relative to the support plate  6 A. 
     The driven pulley  31  is disposed leftward of the image forming region of the corresponding photosensitive drums  5 . The driven pulley  31  includes a disk-shaped driven portion  31   a  and a shaft portion  31   b . The driven portion  31   a  has an outer diameter substantially the same as that of the drive portion  30   a  of the drive pulley  30 . The shaft portion  31   b  extends vertically, and is arranged coaxially with the driven portion  31   a  and is rotatable integrally therewith. The shaft portion  31   b  has an upper portion rotatably supported to the support plate  6 A. In this way the wire cleaner movement mechanism  25  is rotatably supported to and suspended from the support plate  6 A. 
     The drive belt  32  is an endless belt. The drive belt  32  is stretched around the drive portion  30   a  of the drive pulley  30  and the driven portion  31   a  of the driven pulley  31 . When the drive pulley  30  rotates, the drive belt  32  circulates, thereby rotating the driven pulley  31 . Incidentally, as shown in  FIG. 4B , the charging wire  37  is not aligned with an imaginary line connecting between a rotation axis of the shaft portion  30   c  and a rotation axis of the shaft portion  31   b , but is positioned slightly frontward of the imaginary line. 
     Each of the drive belts  32  has a wire cleaner  35 . In the present embodiment, four wire cleaners  35  are provided in the four chargers  6 , respectively. 
     (2) Wire Cleaner 
     As shown in  FIGS. 5 and 6 , each of the wire cleaners  35  includes a fixing member  36 , a sponge  38 , and a supporting member  39 . 
     (2-1) Fixing Member 
     The fixing member  36  is fixed to and suspended from the drive belt  32 . The fixing member  36  is integrally formed with a tubular portion  40  and an arm  41 . The tubular portion  40  is a generally cylindrical shape having an upper closed end and a lower open end. The tubular portion  40  is positioned opposite to the coupling portion  30   b  with respect to the drive portion  30   a.    
     The arm  41  is formed in an L-shape having a horizontal portion  41   a  and a vertical portion  41   b . The horizontal portion  41   a  horizontally extends radially outward from an outer circumferential surface of the tubular portion  40 . The vertical portion  41   b  extends upward from a radially outer end portion of the horizontal portion  41   a , and is fixed to the drive belt  32 . 
     A distance from an axis of the tubular portion  40  to the radially outer end portion of the horizontal portion  41   a  is substantially the same as a shortest distance from an axis of the shaft portion  30   c  to an outer circumferential surface of the drive belt  32 . Further, the vertical portion  41   b  has a length substantially the same as a vertical width of the drive belt  32 . 
     (2-2) Supporting Member 
     The supporting member  39  allows the sponge  38  to be supported by the fixing member  36 . The supporting member  39  integrally includes a frame  45 , an inserting portion  46 , and a pinching portion  47 . 
     The frame  45  is formed in a generally U-shape having a base portion and a pair of arm portion. The base portion is formed in a plate-shape and extends in frontward/rearward direction. The pair of arm portions extend diagonally downward from longitudinal ends of the base portion at a substantially right angle. 
     The base portion of the frame  45  has a surface from which the inserting portion  46  extends upwardly. The inserting portion  46  is formed in a cylindrical shape. An angle defined between the frame  45  and the inserting portion  46  is approximately 45 degrees. That is, the inserting portion  46  vertically extends while the frame  45  is inclined at 45 degrees relative to the inserting portion  46 . The inserting portion  46  is inserted into the lower open end of the tubular portion  40 , so that the inserting portion  46  is rotatable about its axis with respect to the tubular portion  40 . 
     The pinching portion  47  is formed in a generally U-shape having a base portion and a pair of arm portions. The base portion of the pinching portion  47  has a longitudinal length smaller than that of the base portion of the frame  45 . Each arm portion of the pinching portion  47  has a tip end formed with a tapered surface  48 . Each of the tapered surfaces  48  has configuration such that a distance defined between the tapered surfaces  48  is gradually increased toward the tip ends of the free end portions. 
     The sponge  38  is adapted to clean the charging wire  37 . The sponge  38  is folded into a substantially U-shape, and inserted into the pinching portion  47  maintaining the U-shaped folded state. The U-shaped sponge  38  has free ends that extend along the tapered surfaces  48 . The charging wire  37  is interposed between inner folded surfaces of the sponge  38  inserted into the pinching portion  47 . 
     (3) Coupling Belt 
     As shown in  FIG. 4C , an endless coupling belt  50  is provided over the four wire cleaner movement mechanisms  25 . More specifically, the coupling belt  50  is looped taut between the coupling portion  30   b  of the frontmost drive pulley  30  and the coupling portion  30   b  of the rearmost drive pulley  30  while being in rolling contact with the coupling portions  30   b  of the middle two drive pulleys  30 . 
     When a drive force is inputted into one of the four drive pulleys  30 , the corresponding drive portion  30   a  is driven to rotate. In association with rotation of the drive portion  30   a , the corresponding coupling portion  30   b  starts to rotate. In association with rotation of the coupling portion  30   b , the coupling belt  50  starts to circulate, thereby inputting the drive force into remaining three of the drive pulleys  30 . Accordingly, the coupling belt  50  enables the four wire cleaner movement mechanisms  25  to be driven in synchronism with one another. 
     (4) Drive Force Transmission Mechanism 
     As shown in  FIG. 4C , the rearmost wire cleaner movement mechanism  25  is connected to a drive force transmission mechanism  55 . The drive force transmission mechanism  55  includes a pinion gear unit  56  and a drive force transmission belt  57 . 
     (4-1) Pinion Gear Unit 
     The pinion gear unit  56  is disposed at a right rear end of the drum unit  3 . As shown in  FIGS. 7A and 7B , the pinion gear unit  56  is integrally provided with a flange portion  60 , a pulley portion  61 , and a gear portion (pinion gear)  62 . 
     The flange portion  60  is formed in a disk shape. The flange portion  60  has an upper surface and a lower surface in an axial direction thereof, and an outer circumferential surface. The pulley portion  61  has a disk shape having a diameter smaller than that of the flange portion  60 . The pulley portion  61  is fixed to the upper surface of the flange portion  60 . The gear portion  62  has a disk shape having a diameter smaller than that of the flange portion  60 . The gear portion  62  is fixed to the lower surface of the flange portion  60 . That is, the gear portion  62  is positioned opposite to the pulley portion  61  relative to the flange portion  60 . The gear portion  62  has a circumferential surface with gear teeth. The flange portion  60 , the pulley portion  61  and the gear portion  62  are respectively formed with through holes (not shown) extending in the axial direction. 
     The right side plate  21  has a rear end portion formed with a rectangular-shaped hole  63  extending through a thickness thereof. The hole  63  defines a surface from which a support shaft  64  protrudes upward. The support shaft  64  is inserted into the thorough holes formed in the flange portion  60 , the pulley portion  61 , and the gear portion  62  (the pinion gear unit  56 ). Hence, the pinion gear unit  56  is rotatably supported to the right side plate  21 . 
     While supported by the support shaft  64 , the pinion gear unit  56  is vertically movable relative to the support shaft  64 . That is, the pinion gear unit  56  is movable between a first position shown in  FIG. 7A  and a second position shown in  FIG. 7B . In the first position, the gear portion  62  is in contact with the right side plate  21  (the surface defined by the hole  63 ). In the second position, the gear portion  62  is positioned upward of and spaced apart from the right side plate  21  (the surface defined by the hole  63 ). In a state such that the pinion gear unit  56  is supported by the support shaft  64 , the outer circumferential surface of the flange portion  60  protrudes outward from an outer surface of the right side plate  21 . 
     (4-2) Drive Force Transmission Belt 
     As shown in  FIG. 4C , the drive force transmission belt  57  is an endless belt. The drive force transmission belt  57  is looped around and taut the pulley portion  61  of the pinion gear unit  56  and the shaft portion  30   c  of the rearmost drive pulley  30 . When a drive force is inputted into the pinion gear unit  56 , the pinion gear unit  56  starts to rotate. In association with rotation of the pinion gear unit  56 , the drive force transmission belt  57  starts to circulate, thereby rotating the rearmost drive pulley  30  via the shaft portion  30   c.    
     (5) Regulating Unit 
     As shown in  FIG. 8 , the drum unit  3  includes a regulating unit  70  for regulating reverse rotation of the pinion gear unit  56 . As shown in  FIG. 9 , the regulating unit  70  includes a supporting portion  71 , a support shaft  72 , and a main portion  73 . The supporting portion  71  is formed in a plate shape. The supporting portion  71  is disposed in front of the hole  63  and extends inward from an inner surface of the right side plate  21 . The support shaft  72  protrudes upward from an end portion of the supporting portion  71 . The main portion  73  is pivotally movable about the support shaft  72 . 
     The main portion  73  is formed in a bar shape and extends in the frontward/rearward direction. The main portion  73  has a rear end portion  73 A provided with an engaging portion  74  meshedly engagable with the gear portion  62  of the pinion gear unit  56  supported to the right side plate  21 . The main portion  73  has a front end portion  73 B whose tip end is in contact with the inner surface of the right side plate  21 . The front end portion  73 B can position the rear end portion  73 A of the main portion  73  to engage with the gear portion  62 , but is resiliently deformable so as to allow the rear end portion  73 A of the main portion  73  to disengage from the gear portion  62  while the free end of the front end portion  73 B maintains contact with the inner surface of the right side plate  21 . 
     When a force in a forward direction (a direction indicated by an arrow A shown in  FIG. 9 ) is applied to the pinion gear unit  56 , a force in a direction such that the rear end portion  73 A of the main portion  73  is separated from the right side plate  21  is applied to the engaging portion  74  by the gear teeth of the gear portion  62 . As a result, the main portion  73  is pivotally moved, so that the engaging portion  74  is disengaged from the gear portion  62 . Accordingly, the gear portion  62  (the pinion gear unit  56 ) can be rotated in the direction indicated by the arrow A. 
     On the other hand, when a force in a reverse direction (a direction opposite to the direction indicated by the arrow A) is applied to the pinion gear unit  56 , a force in a direction such that the rear end portion  73 A of the main portion  73  approaches the right side plate  21  is applied to the engaging portion  74  by the gear teeth of the gear portion  62 . As a result, the engaging portion  74  is tightly meshedly engaged with the gear portion  62 . Accordingly, rotation of the gear portion  62  (the pinion gear unit  56 ) can be regulated. 
     3. Internal Structure of Main Casing 
     As shown in  FIG. 8  and  FIGS. 10A to 10F , the main casing  2  has a right side plate  80 . The right side plate  80  has an inner surface from which a first switch portion  81 , a rail portion  82 , a second switch portion  83 , and a rack gear  84  protrude inward. 
     The first switch portion  81  is formed in a plate shape extending rearward from a front end portion of the right side plate  80 . For example, the first switch portion  81  has a length of two-fifths on a length of the right side plate  80  in the frontward/rearward direction. The first switch portion  81  has a rear end portion formed with a first slant surface  85 . The first slant surface  85  extends diagonally downward and frontward from a distal rear end of the first switch portion  81 . 
     The rail portion  82  is formed in a plate shape and extends in the frontward/rearward direction. The rail portion  82  is disposed rearward of the first switch portion  81 . The rail portion  82  has a front end portion positioned slightly spaced apart from the rear end of the first switch portion  81 . The rail portion  82  has a length of two-fifths on the length of the right side plate  80  in the frontward/rearward direction. The rail portion  82  has a vertical length (thickness) smaller than that of the first switch portion  81 . The rail portion  82  has a lower surface in flush with a lower surface of the first switch portion  81 . The front end face of rail portion  82  confronts the first slant surface  85 . 
     The second switch portion  83  is formed in a plate shape and extends in the frontward/rearward direction. The second switch portion  83  is disposed rearward of the rail portion  82 . The second switch portion  83  has a front end portion positioned slightly spaced apart from the rear end portion of the rail portion  82 . The rear end portion of the second switch portion  83  is slightly spaced apart from the rear end portion of the right side plate  80 . The second switch portion  83  has a vertical length (thickness) the same as that of the first switch portion  81 . Further, the front end portion of the second switch portion  83  is formed with a second slant surface  86 . The second slant surface  86  extends diagonally upward and rearward from a distal front end of the second switch portion  83 . The second switch portion  83  has an upper surface in substantially flush with the upper surface of the rail portion  82 . The rear end face of the rail portion  82  confronts the second slant surface  86 . 
     The rack gear  84  is formed in a plate shape extending in the frontward/rearward direction. The rack gear  84  is disposed below the rail portion  82  and spaced apart from the rail portion  82 . The rack gear  84  has a length slightly smaller than that of the rail portion  82  in the frontward/rearward direction. A vertical distance between the rack gear  84  and the rail portion  82  is substantially the same as a vertical distance between the upper surface of the flange portion  60  and an upper end face of the gear portion  62 . The rack gear  84  has an inner surface formed with gear teeth meshedly engageable with the gear teeth of the gear portion  62 . 
     The rack gear  84  has a length equivalent to one circular motion of the drive belt  32  when the pinion gear unit  56  is moved from a front end portion to a rear end portion of the rack gear  84 . The length of the first switch portion  81  is not limited to two-fifths on the length of the right side plate  80 . Further, the length of the rail portion  82  is not limited to two-fifths on the length of the right side plate  80 . The length of the first switch portion  81  and the length of the rail portion  82  can be appropriately changed depending on the length of the rack gear  84 . 
     4. Cleaning Operation 
     A cleaning operation will next be described while referring to  FIGS. 10A to 10F . 
     Before the drum unit  3  is moved to the pulled-out position from the accommodating position, each wire cleaner  35  (shown in  FIG. 4C ) is disposed rightward of the image forming region of the corresponding photosensitive drum  5  (shown in  FIG. 1 ). This position of the wire cleaner  35  will be referred to as an original position. 
     In a state such that the drum unit  3  is at the accommodating position at which the drum unit  3  is accommodated in the main casing  2  (shown in  FIG. 1 ), as shown in  FIG. 10A , the lower surface of the flange portion  60  is mounted on the upper surface of the second switch portion  83 . In this state, the pinion gear unit  56  is at the second position at which the gear portion  62  is positioned upward of and spaced apart from the lower surface of the hole  63  in the right side plate  21  as shown in  FIG. 7B . 
     Then, when the drum unit  3  is moved frontward, as shown in  FIG. 10B , the pinion gear unit  56  is moved frontward in association with movement of the drum unit  3 , and the flange portion  60  is moved to the upper surface of the rail portion  82  from the upper surface of the second switch portion  83 . Then, the flange portion  60  is slidingly moved frontward on the upper surface of the rail portion  82 . At this time, the gear portion  62  of the pinion gear unit  56  is moved frontward at a position upward of and spaced apart from the rack gear  84 . A path that the pinion gear unit  56  has been moved at this time will be referred to as a second path. 
     When the pinion gear unit  56  is moved frontward, the force in the reverse direction (the direction opposite to the direction indicated by the arrow A shown in  FIG. 9 ) is applied to the flange portion  60  by a frictional force generated by the rail portion  82  and the flange portion  60 . However, the regulating unit  70  provided in the right side plate  21  regulates the pinion gear unit  56  from rotating in the reverse direction. Therefore, reverse rotation of the pinion gear unit  56  does not occur. 
     Subsequently, the flange portion  60  is brought into contact with the first slant surface  85  from the rear. When the drum unit  3  is further moved frontward, the flange portion  60  is guided by the first slant surface  85  so as to be moved diagonally downward and frontward. As a result, as shown in  FIG. 10C , the upper surface of the flange portion  60  is brought into contact with the lower surface of the first switch portion  81  from the bottom. In this state, the pinion gear unit  56  is disposed at the first position at which the gear portion  62  is in contact with the lower surface of the hole  63  of the right side plate  21  as shown in  FIG. 7A . 
     Next, the drum unit  3  is further moved frontward. As shown in  FIG. 10D , when the pinion gear unit  56  is moved to a position confronting the front end portion of the right side plate  80 , further frontward movement of the drum unit  3  is prevented by a stop member (not shown). Then, the drum unit  3  is disposed at the pulled-out position (shown in  FIG. 8 ). 
     After the developing cartridge  7  is replaced with a new one, for example while the drum unit  3  is at the pulled-out position, the drum unit  3  is moved toward the accommodating position. 
     During the rearward movement of the pinion gear unit  56 , the pinion gear unit  56  is maintained at the first position (shown in  FIG. 7A ) because the upper surface of the flange portion  60  is in contact with the lower surface of the first switch portion  81 . 
     Then, when the drum unit  3  is further moved rearward, as shown in  FIG. 10E , the pinion gear unit  56  is moved rearward in association with movement of the drum unit  3 . The flange portion  60  is moved from the lower surface of the first switch portion  81  to the lower surface of the rail portion  82 . Then, the flange portion  60  is slidingly moved rearward on the lower surface of the rail portion  82 . At this time, the gear portion  62  of the pinion gear unit  56  is brought into meshing engagement with the rack gear  84 . 
     In association with rearward movement of the drum unit  3 , the pinion gear unit  56  rotates in the forward direction (the direction indicated by the arrow A shown in  FIG. 9 ). As a result, as shown in  FIG. 4C , the drive pulley  30  of the rearmost wire cleaner movement mechanism  25  is rotated via the drive force transmission belt  57 . In association with rotation of the drive pulley  30 , the drive belt  32  starts to circulate. 
     When the drive belt  32  circulates, the charging wire  37  (shown in  FIG. 5 ) is cleaned from the right to the left while the wire cleaner  35  fixed to the drive belt  32  is moved leftward. 
     When the drum unit  3  is moved rearward, and the pinion gear unit  56  reaches the middle of the rack gear  84  in the frontward/rearward direction, the wire cleaner  35  moves across the image forming region, and approaches the driven pulley  31 . The supporting member  39  of the wire cleaner  35  is rotationally movable relative to the fixing member  36  of the wire cleaner  35 . Hence, when the fixing member  36  moves around the driven pulley  31 , the supporting member  39  remains stationary. 
     Then, as shown in  FIG. 10F , the drum unit  3  is further moved rearward. The wire cleaner  35  again moves across the image forming region, and approaches the drive pulley  30 . When the gear portion  62  of the pinion gear unit  56  is spaced apart from the rear end portion of the rack gear  84  so as to be disengaged from the rack gear  84 , the wire cleaner  35  (shown in  FIG. 4 ) is returned to the original position. Thus, the cleaning operation of the wire cleaner  35  is completed. 
     As described above, the charging wire  37  is not positioned in alignment with the imaginary line connecting between the rotation axis of the shaft portion  30   c  and the rotation axis of the shaft portion  31 , but is positioned slightly ahead of the imaginary line ( FIG. 4B ). Therefore, the charging wire  37  does not cross an axis of the inserting portion  46 . The pinching portion  47  pinching the charging wire  37  is inclined at 45 degrees with respect to the frontward/rearward direction because of the inclination of the frame  45  relative to the inserting portion  46 . Therefore, when the tubular portion  40  is positioned coaxial with the drive pulley  30  or driven pulley  31 , i.e., when the vertical portion  41   b  is moved along the outer periphery of the drive portion  30   a  or the driven portion  31   a , a situation where the vertical portion  41   b  is positioned frontward of the drive portion  30   a  and the driven portion  31   a  provides a depth of the charging wire  37  into the sponge  38  of the pinching portion  47  greater than the depth in a situation where the vertical portion  41   b  is positioned rearward of the drive portion  30   a  and the driven portion  31   a . In other words, in the present embodiment, even if the charging wire  37  is not aligned with the imaginary line, the pinching portion  47  can always pinch the charging wire  37  without imparting load to the charging wire  37 , thereby enabling constant cleaning to the charging wire  37 , because the depth of the charging wire  37  relative to the sponge  38  is changeable. 
     A path of the pinion gear unit  56  from where the gear portion  62  of the pinion gear unit  56  has been meshedly engaged from the rack gear  84  to where the gear portion  62  of the pinion gear unit  56  has been disengaged from the rack gear  84  will be referred to as a first path. 
     In the color printer  1 , a diameter of the pinion gear unit  56  and the numbers of gear teeth is designed such that the drum unit  3  has a moving amount from the pulled-out position to the accommodating position greater than a moving amount of the wire cleaner  35 . However, the moving amount of the drum unit  3  from the pulled-out position to the accommodating position can be smaller than the moving amount of the wire cleaner  35  by changing the diameter of the pinion gear unit  56  and/or the numbers of gear teeth, as long as the wire cleaner  35  is configured to move across at least the entire width of the image forming region when the drum unit  3  moves from the pulled-out position to the accommodating position. 
     When the drum unit  3  is further moved rearward, the flange portion  60  is brought into contact with the second slant surface  86  of the second switch portion  83  from the front. When the drum unit  3  is still further moved rearward, the flange portion  60  is guided by the second slant surface  86  so as to be moved diagonally upward and rearward. As a result, as shown in  FIG. 10A , the lower surface of the flange portion  60  is brought into contact with the upper surface of the second switch portion  83  from the above. In this state, the pinion gear unit  56  is disposed at the second position, and further rearward movement of the drum unit  3  is restricted. Accordingly, the drum unit  3  is disposed at the accommodating position. 
     5. Operations and Effects 
     (1) Operation and Effect  1   
     As described above, the drum unit  3  is movable between the accommodating position at which the drum unit  3  is accommodated in the main casing  2  and the pulled-out position at which the drum unit  3  is pulled outward of the main casing  2 . The drum unit  3  includes the plurality of photosensitive drums  5  and the plurality of chargers  6 . Each of the chargers  6  includes the charging wire  37  for charging the surface of the corresponding photosensitive drum  5  and the wire cleaner  35  for cleaning the charging wire  37 . Each of the wire cleaners  35  is movable along the charging wire  37  while being in sliding contact with the charging wire  37 . 
     Further, the drum unit  3  includes the plurality of the wire cleaner movement mechanisms  25  and the pinion gear unit  56 . Within the main casing  2 , the rack gear  84 , the first switch portion  81 , and the second switch portion  83  are provided. When the drum unit  3  is moved from the pulled-out position to the accommodating position, the pinion gear unit  56  is moved on the first path. In association with this movement, the pinion gear unit  56  receives the drive force from the rack gear  84 . The drive force received by the pinion gear unit  56  is transmitted to the plurality of the wire cleaner movement mechanisms  25 . With this configuration, each of the wire cleaners  35  is moved along the charging wire  37  while being in sliding contact with the charging wire  37 . Hence, each of the charging wires  37  is cleaned by the wire cleaner  35 . Accordingly, whenever the drum unit  3  is moved from the pulled-out position to the accommodating position, each of the charging wires  37  is cleaned. Therefore, it is not necessary for the user to manually move the wire cleaners  35 , thereby saving time and effort of the user required to clean the charging wires  37 . 
     When the drum unit  3  is moved to a position where the pinion gear unit  56  is moved past the rear end portion of the rack gear  84 , the second switch portion  83  switches the position of the pinion gear unit  56  from the first path to the second path. Hence, when the drum unit  3  is moved from the accommodating position to the pulled-out position, the pinion gear unit  56  is moved on the second path. At this time, the pinion gear unit  56  does not receive the drive force from the rack gear  84 , and each of the wire cleaners  35  remains stationary. When the drum unit  3  is moved to a position where the pinion gear unit  56  is moved past the front end portion of the rack gear  84 , the first switch portion  81  switches the position of the pinion gear unit  56  from the second path to the first path. In case the drum unit  3  is moved toward the pulled-out position but not to the position where the pinion gear unit  56  is moved past the front end portion of the rack gear  84 , and returned to the accommodating position, each of the wire cleaners  35  is not moved. Thus, each of the charging wires  37  is not cleaned by the wire cleaner  35 . Consequently, non-uniform cleaning to the charging wires  37  can be prevented. Further, occurrence of non-uniform charge on the surfaces of the photosensitive drums  5  caused by the non-uniform cleaning can be prevented. 
     (2) Operation and Effect  2   
     The rail portion  82  is disposed above the rack gear  84 . The rail portion  82  is spaced apart from the rack gear  84  and extends parallel to the rack gear  84  in the frontward/rearward direction. The rail portion  82  guides the movement of the pinion gear unit  56  on the second path. Accordingly, reliable movement of the pinion gear unit  56  can be achieved. 
     (3) Operation and Effect  3   
     The rack gear  84  has a length such that the drive belt  32  makes one circular movement while the pinion gear unit  56  is moved from the front end portion of the rack gear  84  to the rear end portion thereof, that is, a length such that the pinion gear unit  56  is being meshedly engaged with the rack gear  84  while the wire cleaner  35  makes one back-and-forth movement in the portion of the charging wire  37  confronting the image forming region. Hence, the wire cleaner  35  reliably entirely cleans the portion of the charging wire  37  confronting the image forming region. 
     (4) Operation and Effect  4   
     When the drum unit  3  reaches a complete pulled-out position, the pinion gear unit  56  is moved to the first position (shown in  FIG. 7A ) by the first switch portion  81 . Accordingly, movement of the pinion gear unit  56  from the second position to the first position while the drum unit  3  is on its way to the complete pulled-out position can be reliably prevented. 
     Further, when the drum unit  3  reaches a complete accommodating position, the pinion gear unit  56  is moved to the second position (shown in  FIG. 7B ) by the second switch portion  83 . Accordingly, movement of the pinion gear unit  56  from the first position to the second position before the drum unit  3  reaches the complete accommodating position can be reliably prevented. 
     (5) Operation and Effect  5   
     The rack gear  84  extends in the frontward/rearward direction (that is, in a direction such that the drum unit  3  is moved) between the accommodating position and the pulled-out position. Further, the drive force transmission mechanism  55  includes the pinion gear unit  56  meshedly engageable with and disengageable from the rack gear  84 . With this configuration, when the drum unit  3  is moved to the accommodating position from the pulled-out position, the pinion gear unit  56  can be engaged with the rack gear  84 , and when the drum unit  3  is moved to the pulled-out position from the accommodating position, the pinion gear unit  56  can be disengaged from the rack gear  84 . Therefore, the drive force transmission mechanism  55  can be selectively switched between a transmitted state where the drive force is transmitted to the pinion gear unit  56  and a non-transmitted state where the drive force is not transmitted to the pinion gear unit  56 . 
     (6) Operation and Effect  6   
     The pinion gear unit  56  is provided at a position so as to be accommodated within the main casing  2  when the drum unit  3  is at the pulled-out position. Therefore, when the drum unit  3  is moved to the pulled-out position, engagement of the pinion gear unit  56  with the rack gear  84  can be maintained. 
     (7) Operation and Effect  7   
     The drum unit  3  includes the right side plate  21  extending in the frontward/rearward direction. The pinion gear unit  56  is disposed at the rear end portion of the right side plate  21 . Therefore, the right side plate  21  prevents the pinion gear unit  56  from being touched by the user when the user moves the drum unit  3  to the pulled-out position. 
     (8) Operation and Effect  8   
     The moving amount of the drum unit  3  from the pulled-out position to the accommodating position is greater than the moving amount of the wire cleaner  35  from when the wire cleaner  35  starts moving in association with movement of the drum unit  3  until the wire cleaner  35  has moved past the portion of the charging wire  37  confronting the image forming region. Therefore, while the drum unit  3  is moved from the pulled-out position to the accommodating position, the wire cleaner  35  reliably passes through the portion of the charging wire  37  confronting the image forming region. As a result, non-uniform cleaning to the charging wire  37  can be prevented. 
     (9) Operation and Effect  9   
     The rail portion  82  has a length greater than that of the rack gear  84 . When the drum unit  3  is moved from the accommodating position to the pulled-out position, the pinion gear unit  56  cannot be moved to the first position from the second position unless the moving distance of the drum unit  3  is greater than the entire length of the rack gear  84 . Accordingly, even if the drum unit  3  is moved from the accommodating position to the pulled-out position but placed at a position between the accommodating position and the pulled-out position, the charging wire  37  is not cleaned by the wire cleaner  35 . Thus, non-uniform cleaning to the charging wire  37  can be successfully prevented. 
     (10) Operation and Effect  10   
     The drum unit  3  is moved in the frontward/rearward direction that is perpendicular to the leftward/rightward direction parallel to the extending direction of the charging wire  37 . As a result, a distance between the accommodating position and the pulled-out position can become smaller than the entire length of the charging wire  37 . 
     (11) Operation and Effect  11   
     The four wire cleaners  35  are provided in one-on-one correspondence with respect to the four photosensitive drums  5 . The four wire cleaner movement mechanisms  25  are provided in one-on-one correspondence with respect to the four wire cleaners  35 . The four wire cleaner movement mechanisms  25  are operated in interlocking relation to one another by the coupling belt  50 . With this configuration, when the drive force is transmitted to one of the wire cleaner movement mechanisms  25  to move the corresponding wire cleaner  35 , the drive force can be transmitted to remaining three wire cleaner movement mechanisms  25  via the coupling belt  50 , thereby moving remaining three wire cleaners  35 . Accordingly, all the four wire cleaners  35  can be moved simultaneously. Thus, a structure for transmitting the drive force to the plurality of the wire cleaner movement mechanisms  25  can be simplified in comparison with a case where a drive force is transmitted to each of the four wire cleaner movement mechanisms  25  corresponding to the four wire cleaners  35 . Still however, each of the wire cleaners  35  may be provided with a pinion gear unit  56 . If this is the case, the coupling belt  50  can be dispensed with. 
     Further, in a configuration such that the four developing cartridges  7  are provided in one-on-one correspondence with respect to the four photosensitive drums  5 , for example, when the frontmost developing cartridge  7  is detached from the drum unit  3 , the drum unit  3  may be only slightly pulled outward of the main casing  2  to remove the frontmost developing cartridge  7  from the drum unit  3 . As described above, in this case, the cleaning operation of the charging wires  37  is not performed by the wire cleaners  35 . Accordingly, in the tandem type color printer, occurrence of non-uniform cleaning to the charging wires  37  can be reliably prevented. 
     6. Modifications 
     Various modifications are conceivable. 
     In the above described embodiment, the image forming device is the tandem type color printer. However, a monochromatic printer is also available. If this is the case, the monochromatic printer has a main casing in which a drum cartridge including a charging wire and a photosensitive drum is detachably mounted. The drum cartridge includes a single wire cleaner movement mechanism  25 . The coupling belt  50  is dispensed with. 
     The timing to switch the movement path of the pinion gear unit  56  to the second path from the first path (the timing to move the pinion gear unit  56  to a relatively higher position from a relatively lower position) can be a timing when the drum unit  3  starts to be moved from the accommodating position to the pulled-out position. Further, the timing to switch the movement path of the pinion gear unit  56  to the first path from the second path (the timing to move the pinion gear unit  56  to the relatively lower position from the relatively higher position) can be a timing when the drum unit  3  starts to be moved from the pulled-out position to the accommodating position. 
     Further, the direction such that the drum unit  3  is pulled out is not limited to the frontward/rearward direction, that is, the direction such that the photosensitive drums  5  are juxtaposed to each other. The drum unit  3  can be configured so as to be movable in a direction perpendicular to the juxtaposed direction of the photosensitive drums  5 . In association with the movement of the drum unit  3 , the cleaning operation of the charging wires  37  can be performed. 
     While the present invention has been described in detail with reference to the embodiment 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.