Abstract:
A cartridge may include a frame; a photosensitive member that is rotatably supported about a rotation axis inside the frame; a discharge induction electrode that is supported inside the frame and detachably attachable to the frame from outside the frame in a direction perpendicular to the rotation axis of the photosensitive member; and a discharge electrode that is supported inside the frame opposite the discharge induction electrode and detachably attachable to the frame from outside the frame in the direction perpendicular to the rotation axis of the photosensitive member. The discharge electrode may be detachably attachable to the frame independent of the discharge induction electrode when the discharge induction electrode is supported inside the frame.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority from Japanese Patent Application No. 2005-92119, filed on Mar. 28, 2005, the entire subject matter of which is incorporated herein by reference.  
       BACKGROUND  
       [0002]     A known electrophotographic image forming apparatus includes a photosensitive drum, a charger, and a transfer roller. The charger charges a surface of the photosensitive drum, the charged surface of the photosensitive drum is irradiated with a laser beam, and an electrostatic latent image is formed on the surface of the photosensitive drum. Toner is applied to the electrostatic latent image, and the electrostatic latent image is developed into a toner image on the surface of the photosensitive drum. The toner image on the photosensitive drum is transferred to a recording medium such as a sheet of paper by a transfer roller, the transferred image is fixed by heat onto the recording medium by a fixing device, and thus the image is printed.  
         [0003]     In addition, such an image forming apparatus is generally structured to unitize a photosensitive drum, a charger, a transfer roller and other parts into a removable cartridge for easy exchange of consumables.  
         [0004]     The charger includes a discharge electrode that generates a corona discharge and a discharge induction electrode. The discharge electrode may be a wire. The discharge induction electrode is spaced from the discharge electrode. The charger is designed to charge the photosensitive drum by the corona discharge from the discharge electrode. The charger thus designed needs exchanging regularly because it deteriorates with use or mainly a discharging performance lowers due to adhesion of silica to the discharge electrode.  
         [0005]     Japanese Laid-Open Patent Application No. 9-68848 discloses a structure that enables only a charger to be removed from a process cartridge.  
         [0006]     The discharge electrode of the charger is subjected to application of higher voltage (or discharge bias) and deteriorates rapidly compared with the discharge induction electrode. Conversely, the discharge induction electrode of the charger is less prone to deteriorate and has a longer service life compared with the discharge electrode. However, the structure disclosed in Japanese Laid-Open Patent Application No. 9-68848 requires exchange of a whole charger. This means that the discharge induction electrode should be exchanged along with the discharge electrode even if it is still available, with the result that the discharge induction electrode is not used effectively.  
       SUMMARY  
       [0007]     Aspects of the invention provide a cartridge including a discharge electrode and a discharge induction electrode, which is designed to make effective use of parts.  
         [0008]     According to one illustrative aspect of the invention, a cartridge may include a frame;  
         [0009]     a photosensitive member that is rotatably supported inside the frame; a discharge induction electrode that is supported inside the frame and detachably attachable to a rotary shaft of the photosensitive member from outside the frame in a first direction perpendicular to the rotary shaft of the photosensitive member; and a discharge electrode that is supported inside the frame opposite to the discharge induction electrode and detachably attachable to the rotary shaft of the photosensitive drum from outside the frame in the first direction. The discharge electrode may be detachably attachable to the frame independently of the discharge induction electrode when the discharge induction electrode is supported inside the frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Illustrative aspects of the invention will be described in detail with reference to the following figures wherein:  
         [0011]      FIG. 1  is a side sectional view of a general structure of a laser printer as an image forming apparatus according to at least one aspect of the invention;  
         [0012]      FIGS. 2A and 2B  are explanatory views showing a structure of a scorotron charger according to at least one aspect of the invention;  
         [0013]      FIG. 3  is a perspective view of a process according to at least one aspect of the invention;  
         [0014]      FIGS. 4A, 4B , and  4 C are explanatory views showing a structure of a drum cartridge according to at least one aspect of the invention;  
         [0015]      FIGS. 5A and 5B  are explanatory views showing fixing places of a wire in a situation where a wire cleaner and an auxiliary frame are not shown according to at least one aspect of the invention;  
         [0016]      FIG. 6  is a perspective view of an upper frame of the drum cartridge according to at least one aspect of the invention;  
         [0017]      FIG. 7  is an explanatory view showing a detachable structure of a scorotron charger according to according to at least one aspect of the invention;  
         [0018]      FIGS. 8A and 8B  are explanatory views showing how the scorotron charger is detachably mounted according to at least one aspect of the invention;  
         [0019]      FIG. 9  is a perspective view of a wire supporting member according to at least one aspect of the invention;  
         [0020]      FIGS. 10A and 10B  are explanatory views of a discharge electrode whose one end functions as a terminal according to at least one aspect of the invention;  
         [0021]      FIG. 11  is an explanatory view showing a detachable structure of a scorotron charger according to another aspect of the invention;  
         [0022]      FIG. 12  is an explanatory view showing how wire supporting members are detachably mounted according to at least one aspect of the invention;  
         [0023]      FIG. 13  is an explanatory view showing how a shielding member is detachably mounted according to at least one aspect of the invention; and  
         [0024]      FIG. 14  is a perspective view of the shielding member according to at least one aspect of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0025]     It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect.  
         [0026]     General Structure  
         [0027]     Illustrative aspects of the invention will be described in detail with reference to drawings.  
         [0028]     As shown in  FIG. 1 , a laser printer I as an image forming apparatus according to at least one aspect of the invention includes in a main body casing  2 , a feeder portion  3  for feeding sheets P, which serve as a recording medium, and an image forming portion  4  for forming a specified image on a fed sheet P. In the following description, the right side of  FIG. 1  is referred to as a front of the laser printer  1 , and the left side of  FIG. 1  is referred to as a rear of the laser printer  1 .  
         [0029]     On the front side of the main body casing  2 , there is provided a front cover  5  that opens and shuts an opening through which a process cartridge  100  is inserted in or removed from the main body casing  2 . Specifically, the front cover  5  is supported by the main body casing  2  in such a manner as to be rotatable on a cover shaft (not shown) inserted into the front cover  5  at a lower end portion thereof. When the front cover  5  is closed on the cover shaft, the opening  6  is closed by the front cover  5 . When the front cover  5  is opened (tilted) on the cover shaft, the opening is opened by the front cover  5 , so that the process cartridge  100  can be inserted in or removed from the main body casing  2  via the opening  5 .  
         [0030]     The feeder portion  3  includes, at a bottom portion in the main body casing  2 , a sheet supply tray  8 , a sheet supply roller  9 , and resister rollers  13 . The sheet supply tray  8  is removably attachable. The sheet supply roller  9  is provided at an upper portion of the front end portion of the sheet supply tray  8 . The resister rollers  13  are provided at an upper rear side of the sheet supply roller  9 .  
         [0031]     The sheet supply tray  8  is configured to hold a stack of sheets P as recording media. The sheets P held in the sheet supply tray  8  are separated one by one by a rotation of the sheet supply roller  9  and fed between the register rollers  13 .  
         [0032]     The register rollers  13  are paired and designed to feed a sheet P to a transfer position of the image forming portion  4  (which is a nip position between a photosensitive drum  121  and a transfer roller  122  and a position where a toner image on the photosensitive drum  121  is transferred onto the sheet P) after skewing of the sheet P is accounted for.  
         [0033]     The image forming portion  4  includes a scanner portion  17 , the process cartridge  100 , and a fixing portion  19 .  
         [0034]     The scanner portion  17  is disposed at an upper portion in the main body casing  2 . The scanner portion  17  includes a laser light source (not shown), a polygon mirror  20  that is rotatably driven, an fθ lens  21 , a reflecting mirror  22 , a cylindrical lens  23 , and a reflecting mirror  24 . In the scanner portion  17 , as shown in a double-dotted chain line of  FIG. 1 , a laser beam emitted from the laser light source, based on print data, is deflected by the polygon mirror  20 , passes through the fθ lens  21 , is folded by the reflecting mirror  22 , passes through the cylindrical lens  23 , is bent downward by the reflecting mirror  24 , and is then directed to and scanned at a high speed over a surface of the photosensitive drum  121  of the process cartridge  100 , which will be described later.  
         [0035]     The process cartridge  100  is configured to perform an image formation process (charging, developing, transfer, cleaning of the photosensitive drum  121 ), and detachably mounted to the main body casing  2  below the scanner portion  17 . The process cartridge  100  includes a drum cartridge  110  and a developing cartridge  150  functioning as a developing device detachably mounted in the drum cartridge  110 . (Refer to  FIG. 3 .)  
         [0036]     The drum cartridge  110  is detachably attachable to the main body casing  2 . The drum cartridge  110  holds the developing cartridge  150  at the front and includes the photosensitive drum  121  functioning as a charged object (an image holding member), a scorotron charger  130 , a transfer roller  122 , and a cleaning brush  123  at the rear.  
         [0037]     The photosensitive drum  121  is formed by covering the drum body, which is a metal tube such as aluminum, with a photosensitive layer formed of an organic photoconductor that is predominantly composed of polycarbonate. The photosensitive drum  121  is rotatably driven in the same direction as the sheet P (namely, clockwise in  FIG. 1 ) at a nip portion with the transfer roller  122 .  
         [0038]     The scorotron charger  130  is spaced a specified distance from the surface of the photosensitive drum  121  upstream from a contact position with a developing roller  153  (upstream with respect to the rotation direction of the photosensitive drum  121 ). A detailed structure of the scorotron charger  130  will be described later.  
         [0039]     The transfer roller  122  is formed by covering a metal shaft member with a roller member made of a conductive elastic material (e.g. rubber). The transfer roller  122  is disposed to face and make contact with the photosensitive drum  121  vertically and form a nip with the photosensitive drum  121 . A transfer bias is applied to the transfer roller  122 .  
         [0040]     The cleaning brush  123  is disposed at a back of the photosensitive drum  121  so that the brush end makes contact with the surface of the photosensitive drum  121 .  
         [0041]     On the other hand, the developing cartridge  150  is detachably mounted to the drum cartridge  110 , and includes, in a housing  151 , a toner chamber  152 , the developing roller  153 , a supply roller  154 , and a layer-thickness regulating member  155 .  
         [0042]     The toner chamber  152  contains positively charged nonmagnetic single-component toner as a developing agent. The toner used according to this illustrative aspect is a polymerized toner obtained through copolymerization of styrene-based monomers, such as styrene, and acryl-based monomers, such as acrylic acid, alkyl (C1-C4) acrylate, and alkyl (C1-C4) methacrylate, using a known polymerization method, such as suspension polymerization. A coloring agent, such as carbon black, and wax are added to the polymerized toner. An external additive, such as silica, may also be added to the polymerized toner to improve flowability.  
         [0043]     The developing roller  153  is formed by covering a metal shaft member with a roller member made of a conductive elastic material (e.g. rubber). The developing roller  153  is disposed in contact with the photosensitive drum  121  from an opening formed in the housing  151 . The developing roller  153  is driven to rotate in the same direction as the photosensitive drum  153  at a nip portion with the photosensitive drum  121  (namely, in an opposite direction to that of the photosensitive drum  121 ). A developing bias is applied to the developing roller  153 .  
         [0044]     The supply roller  154  is made by covering a metal shaft member with a roller member made of a conductive foaming material (e.g. sponge). The supply roller  154  is disposed in contact with the developing roller  153 . The supply roller  154  is driven to rotate in an opposite direction to that of the developing roller  153  at a nip portion with the developing roller  153  (namely, in the same direction as the developing roller  153 ).  
         [0045]     The layer-thickness regulating member  155  includes a blade body made of a metal leaf spring member and a pressing portion having a generally semicircular shape in cross section, provided at a free end of the blade body, and made of insulative silicone rubber. The blade body is supported at one end by the housing  151 , and the pressing portion provided at the other end is pressed in contact with the surface of the developing roller  153  by an elastic force of the blade body.  
         [0046]     The fixing portion  19  is disposed at the rear of the process cartridge  100  and includes a heat roller  68  and a pressure roller  69 .  
         [0047]     The heat roller  68  includes a metal tube coated made of aluminum or the like, and a halogen lamp for heating placed in the metal tube. The heat roller  68  is rotatably driven in the same direction as the sheet P (namely, clockwise in  FIG. 1 ) at a nip portion with the pressure roller  69 .  
         [0048]     The pressure roller  69  is made by covering a metal shaft with a roller member made of a heat-resistant elastic member (e.g. rubber). The pressure roller  69  is disposed in a face-to-face relationship with the heat roller  49  so as to press against the heat roller  49  from underneath. The pressure roller  69  is rotated along with the rotation of the heat roller  68 .  
         [0049]     With this configuration, in the image forming portion  4 , toner in the toner chamber  152  is supplied to the developing roller  153  through the rotation of the supply roller  154 , while being positively and frictionally charged between the supply roller  154  and the developing roller  153 . Toner supplied onto the developing roller  153  goes in between the pressing portion of the layer-thickness regulating member  155  and the developing roller  153 . Along with the rotation of the developing roller  153 , the toner is uniformly regulated to a specified thickness as a thin layer and carried on the developing roller  153 .  
         [0050]     The surface of the photosensitive drum  121  is uniformly, positively charged by the scorotron charger  130 . Then, a laser beam from the scanner portion  17  is scanned at high speed on the surface of the photosensitive drum  121 , so that an electrostatic latent image corresponding to image data is formed on the surface of the photosensitive drum  121 .  
         [0051]     With the rotation of the developing roller  153 , the toner carried on the developing roller  153  and positively charged makes contact with the photosensitive drum  121  and is supplied to the electrostatic latent image formed on the photosensitive drum  121 . Namely, the toner is supplied to and selectively carried in an exposure portion of the uniformly, positively charged surface of the photosensitive drum  121 , where the potential has become low due to exposure to the laser beam. As a result, the latent image on the photosensitive drum  121  becomes visible. Thus, a toner image is formed on the photosensitive drum  121 .  
         [0052]     Then, the photosensitive drum  121  and the transfer roller  122  are rotated to pinch the sheet P therebetween, and the toner image carried on the surface of the photosensitive drum  121  is transferred onto the sheet P being fed between the photosensitive drum  121  and the transfer roller  122 .  
         [0053]     Paper dust of the sheet P adhered on the photosensitive drum  121  after the toner transfer is removed by the cleaning brush  123  sliding on the surface of the photosensitive drum  121  being rotated.  
         [0054]     In the fixing portion  19 , the toner transferred onto the sheet P is fixed by heat and pressure while the sheet P passes between the heat roller  68  and the pressure roller  69 . The sheet P, where toner is fixed by heat, is conveyed to a sheet ejection path  70  that extends upward toward the top surface of the main body casing  2 . The sheet P conveyed to the sheet ejection path  70  is ejected by ejection rollers  71 , disposed at an upper end of the sheet ejection path  70 , and is stacked on a sheet discharge tray  72  formed on the top surface of the main body casing  2 .  
         [0055]     Scorotron Charger Structure  
         [0056]     The structure of the scorotron charger  130 , which is a constituent part of the process cartridge  100  (specifically, the drum cartridge  110 ) will be described with reference to  FIGS. 2A and 2B .  
         [0057]      FIG. 2A  is a cross-sectional view of the scorotron charger  130 , which is perpendicular to an axial direction of the photosensitive drum  121 .  FIG. 2B  is a plan view of the scorotron charger  130  viewed from the photosensitive drum  121  (a plan view of a surface facing the photosensitive drum  121 ).  
         [0058]     As shown in  FIGS. 2A and 2B , the scorotron charger  130  includes a wire  131  and a shield member  132  that is spaced away from the wire  131 .  
         [0059]     The wire  131  is a tungsten wire, and is held taut in the axial direction of the photosensitive drum  121  at a fixed distance therefrom.  
         [0060]     The shield member  132  is a metal plate generally shaped in a square bracket in cross section, and includes an opening formation plate  133  and a pair of opposed plates  134 . The opening formation plate  133  is disposed between the wire  131  and the photosensitive drum  121 , is rectangular in shape whose length is parallel to a direction that the wire  131  is held taut (that is the axial direction of the photosensitive drum  121 ). The plates  134  extend vertically from long sides of the opening formation plate  133  and are disposed opposite to each other to interpose the wire  131  therebetween. The opening formation plate  133  is formed with a rectangular opening  133 A in which wires  135  are held taut in the axial direction of the photosensitive drum  121  and thus a grid electrode is formed.  
         [0061]     With this structure, in the scorotron charger  130 , when the wire  131  is subjected to voltage, it discharges corona ions by a corona discharge, the discharged corona ions pass the opening  133 A to charge the surface of the photosensitive drum  121 . At this time, an amount of corona ions passing through (or potential of a charged surface of the photosensitive drum  121 ) is controlled by applying voltage to the grid electrode.  
         [0062]     Detachable Structure of the Wire  
         [0063]     The following will describe how the wire  131  is attached to and removed from the drum cartridge  110 .  
         [0064]      FIG. 3  is a perspective view of the process cartridge  100 .  FIG. 4A  is a perspective view of the drum cartridge  110  in a situation that an upper frame  111  is removed from a lower frame  112 .  FIG. 4B  is a perspective view of the drum cartridge  110  in a situation that the upper frame  111  is mounted to the lower frame  112 .  FIG. 5A  is an enlarged view showing one end of the upper frame  111  where a wire cleaner  124  is not shown.  FIG. 5B  is an enlarged view showing the other end of the upper frame  111  where an auxiliary frame  113  is not shown.  FIG. 6  is a perspective view of the upper frame  111  viewed from a direction different from that of  FIG. 4B .  
         [0065]     As shown in  FIGS. 4A and 4B , the drum cartridge  110  includes the lower frame  112  and the upper frame  111 , which make up a casing of the drum cartridge  110 . The lower frame  112  is made of a resin and shaped in an open-top box. The upper frame  111  is made of a resin, shaped in an open-bottom box, and detachably mounted to an upper portion of a rear end of the lower frame  112  (or an upper portion of the photosensitive drum  121  installed in position). The scorotron charger  130  is accommodated in the upper frame  111 . The photosensitive drum  121 , the transfer roller  122  and the cleaning brush  123  are accommodated in the lower frame  112 .  
         [0066]     The scorotron charger  130  is supported by the upper frame  111  with its upper portion (an open side in the shield member  132 , and an opposite side to the photosensitive drum  121 ) covered. Specifically, the wire  131  of the scorotron charger  130  includes fixing members  131 A,  131 B, which are annular metal plates, at both ends as shown in  FIGS. 5A and 5B . Thus, the wire  131  is supported directly by the upper frame  111  by fixing the fixing members  131  A,  131 B at both ends with respect to a width of the upper frame  111  (with respect to the direction that the wire  131  is held taut and that is the axial direction of the photosensitive drum  121 ).  
         [0067]     That is, as shown in  FIG. 5A , one end of the wire  131  is fixed such that the fixing member  131 A is hooked in a wire fixing groove portion  111 B (having a width capable of inserting the wire  131  and incapable of inserting the fixing member  131 A) formed adjacent to a side wall  111 A that is provided at one side of the upper frame  111 . The side wall  111 A of the upper frame  111  is formed with a cut portion  111 C through which the fixing position (that is, the wire fixing groove portion  111 B) is exposed outside the upper frame  111  so that the wire  131  is detachably attachable from outside the upper frame  111 . However, to prevent the wire  131  from being touched by the user under normal use, the cut portion  111 C is hidden when the upper frame  111  is mounted to the lower frame  112  as shown in  FIG. 4B . Specifically, as shown in  FIG. 4A , the lower frame  112  is formed with a protrusion  112 A in such a position as to enable the cut portion  111 C to be hidden when the upper frame  111  is mounted. Thus, when the upper frame  111  is mounted to the lower frame  112  (under normal use), the fixing position of the wire  131  is covered with the protrusion  112 A ( FIGS. 3 and 4 B), and when the upper frame  111  is removed from the lower frame  112 , the fixing position of the wire  131  is exposed outside the upper frame  111  ( FIGS. 4A and 5A ).  
         [0068]     As shown in  FIG. 5B , the other end of the wire  131  is fixed such that the fixing member  131 B is hooked to a metal spring  125  fixed at an outer surface of a side wall  111 D via a cut portion  111 E formed at the side wall  111 D. The spring  125  has a function of applying tension to the wire  131  due to its elastic force and a function as a terminal to apply voltage to the wire  131  from a voltage application circuit (not shown) of the laser printer  1 . In this way, the position to fix the fixing member  131 B (that is, the spring  125 ) is exposed outside the upper frame  111  ( FIG. 5B ), so that the wire  131  is detachably attachable from outside the upper frame  111 . However, to prevent the wire  131  from being touched by the user under normal use, the fixing position of the wire  131  is covered with an auxiliary frame  113  that is designed to be detachably mounted to the side wall  111 D of the upper frame  111  as shown in  FIG. 6 . With this structure, when the auxiliary frame  113  is mounted to the upper frame  111  (under normal use), the fixing position of the wire  131  is covered with the auxiliary frame  113  ( FIG. 6 ), and when the auxiliary frame  113  is removed from the upper frame  111 , the fixing position of the wire  131  is exposed outside the upper frame  111  ( FIG. 5B ).  
         [0069]     A top wall  111 F of the upper frame  111  is formed with a groove portion  111 G that extends from the one side wall  111 A to the other side wall  111 D along the direction that the wire  131  is held taut so as to release the upper portion of the wire  131  (the open side of the shield member  132 ). With this structure, the wire  131  can be removed in a direction perpendicular to the direction that the wire  131  is held taut by removing the fixing members  131 A and  131 B, which are provided at both ends of the wire  131 . The groove portion  111 G is formed in such a constant width as not to allow a finger of the user to enter, except for both ends (near the fixing portions of the wire  131 ). The groove portion  111 G is configured to prevent the wire  131  from being touched via the groove portion  111 G from outside the upper frame  111 .  
         [0070]     The groove portion  111 G includes a wire cleaner  124  that is slidable along the groove portion  111 G. The wire cleaner  124  includes a cleaner member that is bent across the wire  131  and made of a foam material (e.g. sponge), and an operation member for moving the cleaner member by sliding it along the groove portion  111 G (or the wire  131 ). By sliding the wire cleaner  124 , the wire  131  is cleaned. The wire cleaner  124  is disposed at an end of the groove portion  111 G (where the cut portion  111 C is formed) to cover the fixing position of the wire  131  (that is, the wire fixing groove portion  111 B) from above ( FIGS. 4A, 4B , and  6 ).  
         [0071]     As described above, the laser printer I according to aspects of the invention is configured so that the wire  131  of the scorotron charger  130  is detachably attachable with the shield member  132  of the scorotron charger  130  accommodated in the drum cartridge  110  (more specifically, the upper frame  111 ). Thus, according to the laser printer  1 , the wire  131  only can be replaced without a need to replace the shield member  132 , with the result that the shield member  132  can be efficiently used. Moreover, as the wire  131  can be attached or removed without a need to remove the shield member  132  from the drum cartridge  110  (more specifically, the upper frame  111 ), the shield member  132  can be prevented from getting soiled or breaking.  
         [0072]     In the laser printer  1 , the spring  125  that applies tension to the wire  131  is used as a terminal for applying voltage to the wire  131 . Thus, there is no need to provide a terminal exclusively for applying voltage to the wire  131 , and the number of parts can be reduced.  
         [0073]     Moreover, in the laser printer  1 , the fixing positions on both ends of the wire  131  are covered with the protrusion  112 A of the lower frame  112  and the auxiliary frame  113 , respectively under normal use of the drum cartridge  110 . Thus, under normal use, the wire  131  can be prevented from being touched by the user. On the other hand, when the wire  131  is removed, the upper frame  111  is removed from the lower frame  112 , the auxiliary frame  113  is removed from the upper frame  111 , and the fixing members  131 A and  131 B on both ends of the wire. 131  are exposed, with the result that the wire  131  only can be easily attached to and removed from the upper frame  111 .  
         [0074]     Particularly, as the protrusion  112 A, which covers the fixing position of the wire  131  (that is, the wire fixing groove portion  111 B) from the side, is constituted as a part of the lower frame  112 , there is no need to provide an exclusive member additionally, and the number of parts can be reduced.  
         [0075]     The laser printer  1  in other aspects of the invention has substantially the same general structure and the scorotron charger structure as those in the aspects described above but differs in structure in that the wire  131  is attached and removed. The following description will be provided to the different structure. It is noted that elements similar to or identical with those shown in and described in the above aspects are designated by similar numerals, and thus the description thereof will be omitted for the sake of brevity.  
         [0076]     Detachable Structure of the Wire  
         [0077]      FIG. 7  is an explanatory view showing a detachable structure of the scorotron charger  130  according to aspects of the invention.  FIG. 8A  is a cross sectional view showing how the shield member  132  is attached to and removed from an upper frame  211 .  FIG. 8B  is a cross sectional view showing how the wire  131  and a wire supporting member  240  are attached to and removed from the upper frame  211 .  FIG. 9  is a perspective view of the wire supporting member  240 .  
         [0078]     As shown in  FIGS. 7, 8A  and  8 B, in the laser printer  1 , the scorotron charger  130  is accommodated in an accommodating portion  211  A formed on a top surface of the upper frame  211 , which is made of a resin and constituted as a casing of the drum cartridge  110 .  
         [0079]     The accommodating portion  211 A is formed with side walls  211 B and a regulating portion  211 C. The side walls  211 B make contact with outer surfaces of the opposed plates  134  of the shield member  132 , and the regulating portion  211 C makes contact with a periphery portion of the opening formation plate  133  of the shield member  132  to regulate the motion of the shield member  132  toward the photosensitive drum  121 . With this structure, the shield member  132  accommodated in the accommodating portion  211 A can be prevented from being deformed outward.  
         [0080]     In the accommodating portion  211 A where the shield member  132  is already accommodated, the wire supporting member  240  is accommodated. The wire supporting member  240  supports the wire  131  of the scorotron charger  130  and holds the shield member  132  in an enclosing manner with the upper frame  211 .  
         [0081]     As shown in  FIG. 9 , the wire supporting member  240  includes a lid plate  241  and two supporting plates  242 , which are integrally formed of resin. The lid plate  241  is shaped in a rectangle that is long in the direction that the wire  131  is held taut (in other words, in the axial direction of the photosensitive drum  121 ). The supporting plates  242  are vertically arranged on a surface of the lid plate  241  face to face with each other. The wire supporting member  240  is accommodated in the accommodating portion  211 A of the upper frame  211  and disposed in such a position as to enable the wire supporting member  240  to cover the open side of the shield member  132 . The lid plate  241  is formed with a number of slits  241 A, which function as intakes for efficiently flowing corona irons discharged from the wire  131  to the photosensitive drum  121 .  
         [0082]     Each of the supporting plates  242  is designed to position the wire  131  and is disposed adjacent to each end of the lid plate  241  with respect to the length thereof so as to make contact with the wire  131  in a non-image formation area on the photosensitive drum  121 , which is located outside a portion contributing to image formation in the wire  131  (or a portion opposite to an image formation area on the photosensitive drum  121 ). Each supporting plate  242  is formed with a V-shaped cut portion  242 A, and the wire  131  is positioned via the V-shaped cut portion  242 A. The wire  131  includes the fixing members  131 A,  131 B at both ends, and the fixing members  131 A,  131 B are fixed by the wire supporting member  240  outside the respective supporting plates  242 . Specifically, the wire  131  is fixed to the wire supporting member  240  so that the fixing member  131 A at one end is hooked to a wire fixing groove portion  242 B formed in the wire supporting member  240  and the fixing member  131 B at the other end is hooked to a spring (not shown) provided to the wire supporting member  240 .  
         [0083]     Each supporting plate  242  is shaped to make contact with facing surfaces (or inner surfaces) of the opposed plates  134  of the shield member  132  when the wire supporting member  240  is accommodated in the accommodating portion  211 A of the upper frame  211  (to have a width substantially equal to a distance between the opposed plates  134 ) as shown in  FIG. 7 . Thus, the shield member  132  is pinched and supported between the upper frame  211  and the wire supporting portion  240 , so that it can be prevented from being deformed.  
         [0084]     With such a structure, as shown in  FIG. 8B , the wire  131  is detachably attachable to the upper frame  211 , integrally with the wire supporting member  240 . As shown in  FIG. 8A , the shield member  132  is detachably attachable to the upper frame  211  when the wire supporting member  240  is removed from the upper frame  211 .  
         [0085]     As described above, the laser printer  1  can be configured so that the wire  131  of the scorotron charger  130  is detachably attachable to the drum cartridge  100  (more specifically, the upper frame  211 ) with the shield member  132  of the scorotron charger  130  accommodated in the drum cartridge  100 . Thus, according to the laser printer  1 , the wire  131  can be replaced without a need to replace the shield member  132 , with the result that the shield member  132  can be efficiently used. Moreover, as the wire  131  can be attached or removed without a need to remove the shield member  132  from the drum cartridge  110  (more specifically, the upper frame  111 ), the shield member  132  can be prevented from getting soiled or damaged. Since there is no need to disassemble the casing of the drum cartridge  100 , the wire  131  can be attached and removed relatively easily.  
         [0086]     In the laser printer  1 , the wire supporting member  240  is provided separately from the upper frame  211 , so that the wire supporting member  240  can be formed of a material different from that of the upper frame  211 . For example, while the wire supporting member  240  may be formed of a conductive resin to apply voltage to the wire  131  via the wire supporting member  240 , the upper frame  211  may be formed of a non-conductive resin, which is generally inexpensive compared with the conductive resin.  
         [0087]     Moreover, in the laser printer  1 , the wire supporting member  240  is configured to be detachably attachable to the upper frame  211 , integrally with the wire  131 . Thus, the wire  131  can be easily attached (in particular) and removed, compared with a structure where the wire  131  only is attached to or removed from the upper frame  211 .  
         [0088]     The wire supporting member  240  is configured to position the wire  131  via the V-shaped cut portions  242 A. Thus, the installation of the wire  131  is simplified, and the wire  131  can be prevented from wobbling. For example, if the wire  131  is positioned via a groove of constant width, the groove should have a constant width that is adequate to insert the wire  131  and prevent the wire  131  from wobbling. Thus, it can be difficult to install (or insert) the wire  131  in the groove and the wire  131  may wobble greatly in the installation position according to a dimension error. In contrast, a V-shaped cut portion facilitates the installation of the wire  131  and may prevent the wire  131  from wobbling.  
         [0089]     In addition, as the wire supporting member  240  is configured to support the wire  131  in the non-image formation area, it preserves the function the wire  131  has.  
         [0090]     In the laser printer  1 , the wire supporting member  240  is shaped to make contact with the facing surfaces (or the inner surfaces) of the opposed plates  134  of the shield member  132 . The shape prevents the opposed plates  134  from inclining inward. Since the wire supporting member  240  is used for preventing the opposed plates  134  from inclining inward, there is no need to provide an exclusive member additionally, and the number of parts can be reduced.  
         [0091]     In the laser printer  1 , when the wire supporting member  240  is removed from the upper frame  211 , the shield member  132  is detachably supported by the upper frame  211 . When the wire supporting member  240  is accommodated in the upper frame  211 , the shield member  132  is held in an enclosed manner between the wire supporting member  240  and the upper frame  211 . Thus, the shield member  132  can be prevented from being deformed. In addition, as the wire supporting member  240  is used to hold the shield member  132  in an enclosing manner, there is no need to provide an exclusive member additionally, and thus the number of parts can be reduced. Moreover, the structure is that the shield member  132  can be attached or removed after the wire supporting member  240  is removed from the upper frame  211 . Thus, this structure can be simplified when compared with a structure in which the shield member  132  only can be attached or removed regardless of whether the wire supporting member  240  is accommodated in the upper frame  211 .  
         [0092]     Other Illustrative Aspects  
         [0093]     While the invention has been described with reference to certain illustrative aspects, it is to be understood that the invention is not restricted to the particular forms shown and described therein. Various modifications and alterations can be made thereto without departing from the scope of the invention.  
         [0094]     Although the laser printer  1  can use the spring  125  to apply tension to the wire  131  as a terminal for applying voltage to the wire  131 , aspects of the invention are not limited to the details of the illustrated aspects. A discharge electrode may generally be used as a terminal. For example, a discharge electrode shown in  FIG. 10  may be used instead of the wire  131  used in the laser printer I of some aspects describe above.  
         [0095]     An aspect of a discharge electrode whose one end is exposed outside of the frame and functions as a terminal will be described with reference to  FIGS. 10A and 10B .  FIGS. 10A and 10B  are explanatory views of a saw-toothed electrode  331  as an example of such a discharge electrode.  
         [0096]     As can be seen, the saw-toothed electrode  331  is formed with a number of needles  331 A and a U-shaped bend portion  331 B at one end. The saw-toothed electrode  331  is a metal plate. The saw-toothed electrode  331  is configured so that it is supported at both ends by two supporting members  340  having groove portions  340 A in which the saw-toothed electrode  331  is inserted, and the bend portion  331 B of the saw-toothed electrode  331  is exposed outside the supporting member  340 . With this configuration, the bend potion  331 B of the saw-toothed electrode  331  can be used as a terminal.  
         [0097]     The laser printer  1  can be configured so that the wire supporting member  240  that supports the wire  131  of the scorotron charger  130  is provided separately from the upper frame  211  of the drum cartridge  110  and the wire supporting member  240  is detachably attachable together with the wire  131 . However, aspects of the invention are not limited to the details of the illustrated aspects. For example, the wire  131  may be detachable solely.  
         [0098]      FIG. 11  is a perspective view of the upper frame  211  with a modified scorotron charger  530  mounted.  FIG. 12  is a perspective view showing how wire supporting members  441 ,  442  are attached to or removed from the upper frame  211 .  FIG. 13  is a perspective view showing how a shield member  532  is attached to or removed from the upper frame  211 .  FIG. 14  is a perspective view of a modification of the shield member  532 .  
         [0099]     As shown in FIGS.  11  to  13 , the scorotron charger  530  is accommodated in the accommodating portion  211 A formed on the top surface of the upper frame  211  that is made of resin and functions as a casing of the drum cartridge  110 .  
         [0100]     As shown in  FIG. 13 , the accommodating portion  211 A is formed with the side walls  211 B and the regulating portion  211 C. The side walls  211 B make contact with outer surfaces of opposed plates  534  of the shield member  532 , and the regulating portion  211 C makes contact with a periphery portion of an opening formation plate  533  of the shield member  532  to regulate the motion of the shield member  532  toward the photosensitive drum  121 . One of the opposed plates  534  is formed with a cut portion  534 A that makes contact with a regulating plate  211 D vertically arranged on the bottom surface of the accommodating portion  211 A of the upper frame  211  and regulates the motion of the shield member  532  in a longitudinal direction of the shield member  532  (or in the direction that the wires  131  are held taut). As shown in FIG.  14 , the shield member  532  may include a groove portion  534 B capable of receiving the regulating plate  211 D instead of the cut portion  534 A.  
         [0101]     As shown in  FIGS. 11 and 12 , wire supporting members  441 ,  442  are accommodated in the accommodating portion  211 A where the shield member  532  has been already accommodated. The wire supporting members  441 ,  442  support the wire  131  of the scorotron charger  530  and sandwich the shield member  532  with the upper frame  211 .  
         [0102]     The wire supporting member  441  is a resin member shaped in a rectangular solid with flanges that extend outward on an upper end thereof. On a top surface of the wire supporting member  441 , there is a groove portion  441 A for securing the fixing member  131 A of the wire  131  in a hooked manner.  
         [0103]     The wire supporting member  442  is a resin member shaped as a rectangular solid with a V-shaped cut portion  442 A on a top surface thereof. The V-shaped cut portion  442 A is used for positioning the wire  131 . The fixing member  131 B of the wire  131  is fixedly hooked to the metal spring  125  fixed on an outer surface of the upper frame  211 . The wire supporting members  441 ,  442  are shaped to make contact with the facing surfaces (or the inner surfaces) of the opposed plates  534  of the shield member  532 . When the wire supporting members  441 ,  442  are accommodated in the accommodating portion  211 A of the upper frame  211 , they make contact with the facing surfaces (or the inner surfaces) of the shield member  532 . Thus, the shield member  532  is pinched and supported by the upper frame  211  and the wire supporting members  441 ,  442 , so that its deformation can be prevented.  
         [0104]     With such a structure, the wire  131  only is detachably attachable to the upper frame  211 , and the shield member  532  becomes detachably attachable to the upper frame  211  with the wire supporting member  441 ,  442  removed.  
         [0105]     Accordingly, the aspects of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention. Therefore, aspects of the invention are intended to embrace all known or later developed alternatives, modifications, variations, improvements and/or substantial equivalents.