Patent Publication Number: US-8538291-B2

Title: Developing cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2009-294592 filed on Dec. 25, 2009, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Apparatuses and devices consistent with the invention relate to a developing cartridge that is detachably mounted to a main body of an image forming apparatus. 
     BACKGROUND 
     There is known an image forming apparatus such as laser printers, in which a developing cartridge is detachably mounted to a main body of the apparatus. 
     The developing cartridge includes a developing roller and a supply roller for supplying toner to the developing roller. A shaft of the developing roller is rotatably supported by a developing frame that configures a housing of the developing cartridge. In addition, a shaft of the supply roller is rotatably supported by the developing frame, and a circumferential surface of the supply roller contacts a circumferential surface of the developing roller. 
     As long as the supply roller contacts the circumferential surface of the developing roller, it is not necessary to position the supply roller in an axial direction with high precision. However, when the supply roller is highly moved in the axial direction, the supply roller may contact another member in the developing cartridge or toner may not be supplied to a part within a range corresponding to a printing area of the developing roller, so that an inferior developing may occur. 
     SUMMARY 
     In order to prevent the above problem, a restraint member may be provided to restrain the supply roller from moving in the axial direction. However, when the restraint member is provided, the number of parts is increased, so that the costs of the developing cartridge are increased. 
     Therefore, illustrative aspects of the invention provide a developing cartridge capable of restraining a supply roller from moving in an axial direction without increasing the costs. 
     According to one illustrative aspect of the present invention, there is provided a developing cartridge comprising: a housing; a developing roller that is rotatable about a developing roller axis line, which extends in a direction between a pair of opposite sidewalls of the housing; a supply roller, which is arranged between the pair of opposite sidewalls, which comprises a supply roller shaft extending in the direction between the opposite side walls, and which supplies developer to the developing roller; a bearing member, which rotatably holds the supply roller shaft, and which secures the supply roller shaft in a radial direction thereof and which allows the supply roller shaft to move in an axial direction thereof; a supply electrode, which is disposed opposite to an end face of the supply roller shaft at a first end side of the supply roller shaft, and which is electrically connected to the supply roller shaft; a supply gear, which is attached to the supply roller shaft so as to not be rotatable relative to the supply roller shaft, and which is arranged at an outer side of the sidewall of the housing at a second end side of the supply roller shaft that is opposite to the first side; and a gear cover, which is attached to the housing, and which covers the supply gear, wherein the supply roller shaft is axially restrained by the supply electrode and the gear cover. 
     According thereto, the developing cartridge includes the developing roller and the supply roller. The developing roller is rotatable about the developing roller axis line extending in an opposite direction of both sidewalls of the housing. The supply roller includes the supply roller shaft. The supply roller shaft extends in the opposite direction of both sidewalls and is rotatably held by the bearing member. In addition, the supply roller shaft is allowed to move in the axial direction and is secured in the radial direction by the bearing member. The supply electrode is opposed to an end face of one end side of the supply roller shaft. The supply electrode is electrically connected to the supply roller shaft. In addition, the supply gear is arranged at an outer side of the sidewall of the other end side of the housing. The supply gear is attached to the supply roller shaft so that the supply gear cannot be relatively rotated. The supply gear is covered by the gear cover that is attached to the housing. 
     The supply roller shaft is positioned in the axial direction by the supply electrode and the gear cover, so that the supply roller shaft is restrained from moving in the axial direction thereof. Accordingly, it is not necessary to separately provide a member for restraining the axial movement of the supply roller shaft. As a result, it is possible to restrain the axial movement of the supply roller without increasing the costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of a printer having a developing cartridge according to an exemplary embodiment of the invention; 
         FIG. 2  is a plan view of the developing cartridge; 
         FIG. 3  is a right side sectional view of the developing cartridge; and 
         FIG. 4A  is a sectional view of the developing cartridge taken along a line IV-IV of  FIG. 3 , and  FIG. 4B  is a partial enlarged view of  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an exemplary embodiment of the invention will be described in detail with reference to the drawings. 
     (1) Printer 
     As shown in  FIG. 1 , a printer  1  (one example of an image forming apparatus) includes a body casing  2  (one example of a main body). 
     A process cartridge  3  is provided at a center portion in the body casing  2 . The process cartridge  3  is detachably mounted to the body casing  2  via a front cover  4  that is provided at one sidewall of the body casing  2 . 
     In the following descriptions, a side at which the front cover  4  is provided to the body casing  2  is referred to as the front side and a side opposite to the front side is referred to as the back side. In addition, the left and the right are assigned based on viewing the printer from the front side of the printer  1 . Additionally, regarding a developing cartridge  32 , which will be described later, the front, back, left and right are set based on the state in which the developing cartridge is mounted to the body casing  2 . 
     The process cartridge  3  includes a drum cartridge  31  and a developing cartridge  32 . The developing cartridge  32  is detachably mounted to the drum cartridge  31 . 
     The drum cartridge is provided with a rotatable photosensitive drum  6 . The drum cartridge  31  includes a charger  7  and a transfer roller  9 . 
     The photosensitive drum  6  is rotatable about an axis line extending in a direction perpendicular to a sheet face of  FIG. 1 . 
     The charger  7  is a scorotron-type charger and is arranged to be opposite to a circumferential surface of the photosensitive drum  6  with a predetermined interval provided between the charger  7  and the photosensitive drum. 
     The developing cartridge  32  includes a developing housing  10  (one example of the housing) that accommodates toner. In the developing housing  10 , a developing chamber  33  and a toner accommodating chamber  34  (one example of a developer accommodating chamber), which accommodates toner supplied to the developing chamber  33 , are provided adjacent to each other. 
     A developing roller  11  and a supply roller  37  are held in the developing chamber  33  such that the developing roller  11  and the supply roller  37  are rotatable with respect to the developing chamber  33 . 
     The developing roller  11  has a circumferential surface, a part of which is exposed from a back end portion of the developing housing  10 . In addition, the supply roller  37  has a circumferential surface that contacts a front side of the developing roller  11 . The developing cartridge  32  is mounted to the drum cartridge  31  so that the part of the developing roller  11  exposed from the developing housing  10  contacts a circumferential surface of the photosensitive drum  6 . 
     An agitator  25  is kept in the toner accommodating chamber  34  such that the agitator  25  is rotatable with respect to the toner accommodating chamber  34 . Toner in the toner accommodating chamber  34  is supplied into the developing chamber  33  while being agitated by rotation of the agitator  25 . 
     The transfer roller  9  is provided at a lower side of the photosensitive drum  6 . The transfer roller  9  is rotatable about an axis line parallel to a rotation axis line of the photosensitive drum  6  and is arranged so that a circumferential surface of the transfer roller  9  contacts the circumferential surface of the photosensitive drum  6 . 
     In the body casing  2 , an exposure unit  5  that can emit laser and the like is arranged above the process cartridge  3 . 
     When forming an image, the photosensitive drum  6  rotates at a constant speed in a clockwise direction in  FIG. 1 . In accordance with rotation of the photosensitive drum  6 , the circumferential surface of the photosensitive drum  6  is uniformly charged by electric discharge from the charger  7 . In the meantime, based on image data received from a personal computer (not shown) connected to the printer  1 , a laser beam is emitted from the exposure unit  5 . The laser beam passes between the charger  7  and the developing cartridge  32  and is irradiated on the circumferential surface of the photosensitive drum  6  that is positively charged to be uniform. Thereby, the circumferential surface of the photosensitive drum  6  is selectively exposed, and the electric charges are selectively removed from the exposed part, so that an electrostatic latent image is formed on the circumferential surface of the photosensitive drum  6 . 
     When the electrostatic latent image is opposed to the developing roller  11  by rotation of the photosensitive drum  6 , toner is supplied to the electrostatic latent image from the developing roller  11 . Thereby, a toner image is formed on the circumferential surface of the photosensitive drum  6 . 
     A sheet feeding cassette  12  that stores sheets P is arranged at a bottom part of the body casing  2 . A pickup roller  13  for sending the sheet from the sheet feeding tray  12  is provided above the sheet feeding cassette  12 . 
     A conveyance path  14 , which has an S shape when seen from the side face, is formed in the body casing  2 . The conveyance path  14  reaches a sheet discharge tray  15  formed at an upper surface of the body casing  2  via a portion between the photosensitive drum  6  and the transfer roller  9  from the sheet feeding cassette  12 . A separation roller  16  and a separation pad  17 , which are arranged to be opposite to each other, a pair of feeder rollers  18 , a pair of register rollers  19  and a pair of sheet discharge rollers  20  are provided on the conveyance path  14 . 
     The sheets P are fed from the sheet feeding cassette  12  one at a time while passing between the separation roller  16  and the separation pad  17 . Then, the sheet P is fed toward the register rollers  19  by the feeder rollers  18 . Then, the sheet P is registered by the register rollers  19  and is conveyed toward a portion between the photosensitive drum  6  and the transfer roller  9  by the register rollers  19 . 
     The toner image formed on the circumferential surface of the photosensitive drum  6  is electrically attracted and transferred onto the sheet P by the transfer roller  9  when the toner image is opposed to the sheet P passing between the photosensitive drum  6  and the transfer roller  9  by the rotation of the photosensitive drum  6 . 
     On the conveyance path  14 , a fixing unit  21  is provided at a downstream side of a conveyance direction of the sheet P from the transfer roller  9 . The sheet P, on which the toner image is transferred, is conveyed through the conveyance path  14  and passes through the fixing unit  21 . The fixing unit  21  fixes the toner image on the sheet P by heating and pressing so as to form an image on the sheet P. 
     As operation modes, the printer  1  includes a one-sided mode for forming an image (toner image) on one side of the sheet P and a duplex mode for forming an image on one side of the sheet P and then forming an image on the other side of the sheet P. 
     In the one-sided mode, the sheet P having an image formed on one side thereof is discharged to the sheet discharge tray  15  by the sheet discharge rollers  20 . 
     As a structure for realizing the duplex mode, the body casing  2  is formed therein with a reverse conveyance path  22 . The reverse conveyance path  22  extends between the conveyance path  14  and the sheet feeding cassette  12  from the vicinity of the sheet discharge rollers  20  and is connected to a part between the feeder rollers  18  and the register rollers  19  on the conveyance path  14 . On the reverse conveyance path  22 , a pair of first reverse conveying rollers  23  and a pair of second reverse conveying rollers  24  are provided. 
     In the duplex mode, the sheet P having an image formed on one side thereof is conveyed to the reverse conveyance path  22  rather than being discharged to the sheet discharge tray  15 . Then, the sheet P is conveyed through the reverse conveyance path  22  by the first reverse conveying rollers  23  and the second reverse conveying rollers  24  and two sides thereof are reversed, so that the other side of the sheet P, on which no image is formed, is sent to the conveyance path  14  with being opposed to the circumferential surface of the photosensitive drum  6 . Then, an image is formed on the other side of the sheet P, so that the images are formed on both sides of the sheet P. 
     (2) Developing Cartridge 
     The developing housing  10  of the developing cartridge  32  has a box shape having an opened back side. 
     As shown in  FIG. 2 , the developing housing  10  includes a pair of sidewalls  36 , which are opposed to each other in the left-right direction. As shown in  FIGS. 2 and 3 , an upper wall  38  and a bottom wall  39  are bridged between the sidewalls  36 . The upper wall  38  and the bottom wall  39  are connected at a front end portion of the developing housing  10 . The connected part includes a holding part  40 . The holding part  40  is extended toward the front-upper direction from the front end portion of the developing housing  10  and has a sectional U shape having an opened front side. 
     The developing roller  11  and the supply roller  37  (refer to  FIG. 1 ) are rotatably held between the sidewalls  36 . 
     (2-1) Developing Roller 
     As shown in  FIGS. 2 and 3 , the developing roller  11  is arranged between back end portions of the sidewalls  36 . As shown in  FIG. 5 , the developing roller  11  includes a cylindrical developing roller main body  45  extending in the left-right direction and a developing roller shaft  46  extending along a central axis line of the developing roller main body  45 . 
     Both end portions of the developing roller shaft  46  penetrate the sidewalls  36  of the housing  10 . 
     (2-2) Supply Roller 
     As shown in  FIG. 1 , the supply roller  37  is arranged at a position of the front-lower direction of the developing roller  11 . As shown in  FIG. 5 , the supply roller  37  includes a cylindrical supply roller main body  55  extending in the left-right direction and a supply roller shaft  56  extending along a central axis line of the supply roller main body  55 . 
     A circumferential surface of the supply roller body  55  contacts a circumferential surface of the developing roller body  45  from a front-lower side. 
     Both end portions of the supply roller shaft  56  penetrate both sidewalls  36  of the developing housing  10 . 
     (2-3) Bearing Member 
     As shown in  FIGS. 3 and 4 , a right bearing member  47 , which is one example of a bearing member, is provided at an outer side of the right sidewall  36 . The right end portions of the developing roller shaft  46  and the supply roller shaft  56  are supported by the right sidewall  36  via the right bearing member  47  so that they can be rotated relative to each other. In other words, the right bearing member  47  collectively holds the right end portion of the developing roller shaft  46  and the right end portion of the supply roller shaft  56 , thereby securing the developing roller shaft  46  and the supply roller shaft  56  in their radial directions. 
     As shown in  FIG. 3 , the right bearing member  47  has a substantially triangle shape when seen from a side face. 
     As shown in  FIG. 4A , the right bearing member  47  is formed with a first shaft insertion penetration hole  63 , into which the developing roller shaft  46  is inserted. The first shaft insertion penetration hole  63  has an inner diameter that is substantially the same as an outer diameter of the developing roller shaft  46 . A leading end portion of the developing roller shaft  46  is further protruded in the outer side (right side) than the right bearing member  47 . 
     Further, as shown in  FIG. 4A , a second shaft insertion penetration hole  64  is formed in the right bearing member  47  at a position opposed to the supply roller shaft  56  in the left-right direction. The second shaft insertion penetration hole  64  includes a substantially angled hole having a size that is larger than an outer diameter of the supply roller shaft  56 . A right end portion of the supply roller shaft  56  is inserted into the second shaft insertion penetration hole  64 , and a leading end portion thereof is further protruded in the outer side (right side) than the right bearing member  47 . In addition, a gap is formed between an inner surface of the second shaft insertion penetration hole  64  and the supply roller shaft  56 . 
     Left bearing members  49 ,  58  are provided at an outer side of the left sidewall  36 . 
     The left end portion of the developing roller shaft  46  is supported to the left sidewall  36  via the left bearing member  49  so that the left end portion of the developing roller shaft  46  can be relatively rotated. 
     In addition, the left end portion of the supply roller shaft  56  is supported by the left sidewall  36  via the left bearing member  56  so that the left end portion of the supply roller shaft  56  can be relatively rotated. 
     (2-4) Gear Device 
     As shown in  FIGS. 2 and 4 , a gear cover  42  is attached to the left end portion of the developing cartridge  32 . 
     As shown in  FIG. 4A , the left end portion of the developing roller shaft  46  is protruded from the gear cover  42  in the left direction, and the protruded portion is attached with a cylindrical collar member  41 . 
     A developing gear  50  is attached to developing roller shaft  46  between the gear cover  42  and the left sidewall  36  so that the developing gear  50  cannot be relatively rotated. Driving force for driving the developing roller  11  is input to the developing gear  50  under a state in which the developing cartridge  32  (process cartridge  13 ) is mounted in the body casing  2 . 
     The left end portion of the supply roller shaft  56  is arranged between the gear cover  42  and the left sidewall  36 . In addition, a supply gear  59  is attached to the supply roller shaft  56  between the gear cover  42  and the left sidewall  36  so that the supply gear  59  cannot be relatively rotated. Specifically, an insertion hole  60  is formed in the supply gear  59 . The left end portion of the supply roller shaft  56  is cut to have a D-shape section formed by partially cutting a part of the circumferential surface of the left end portion of the supply roller shaft  56 . The D-shape part is inserted into the insertion hole  60  of the supply gear  59 . According thereto, the supply gear  59  is attached to the supply roller shaft  56  so that the supply gear  59  cannot be relatively rotated. 
     A left end face  56 A of the supply roller shaft  56  is not protruded from the supply gear  59  in the left direction, and a left end face of the supply gear  59  is contacted to an inner side face (right side face) of the gear cover  42 . Thereby, the supply roller shaft  56  is restrained from moving in the left direction. 
     (3) Structure for Supplying Power to Developing Roller and Supply Roller 
     As shown in  FIG. 3 , a developing electrode  48  and a supply electrode  57  are provided at an outer side of the right sidewall  36 . 
     (3-1) Developing Electrode 
     The developing electrode  48  is made of conductive resin. The developing electrode  48  integrally includes a developing connection part  70 , a developing protrusion  71  and a developing coupling part  72 . 
     The developing connection part  70  has a cylindrical shape. As shown in  FIG. 4A , the protruded portion of the developing roller shaft  46 , which protrudes rightward from the right bearing member  47 , is inserted in the developing connection part  70 . Thereby, the developing electrode  48  contacts the circumferential surface of the developing roller shaft  46 , so that the developing electrode  48  and the developing roller shaft  46  are electrically connected. 
     As shown in  FIG. 3 , the developing protrusion  71  has a plate shape that is further protruded in the left direction than the developing connection part  70  at the rear-upper position of the developing connection part  70 . 
     The developing coupling part  72  has a plate shape extending in the substantially front-rear direction. The developing coupling part  72  couples the developing connection part  70  and the developing protrusion  71 . A screw hole (not shown) is formed in the developing coupling part  72 . A screw  73  is engaged with the right sidewall  36  through the screw hole, so that the developing electrode  48  is fixed to the developing housing  10  of the developing cartridge  32 . 
     When the process cartridge  3 , in which the developing cartridge  32  is mounted to the drum cartridge  31 , is mounted in the body casing  2 , a main body-side developing electrode (not shown) provided in the body casing  2  is connected to the developing protrusion  71 . When a developing bias is input to the developing protrusion  71  from the main body-side developing electrode, the developing bias is applied to the developing roller shaft  46  through the developing coupling part  72  and the developing connection part  70 . 
     (3-2) Supply Electrode 
     The supply electrode  57  is made of conductive resin. The supply electrode  57  integrally includes a supply connection part  75 , a supply protrusion  76  and a supply coupling part  77 . 
     The supply connection part  75  has a cylindrical shape. A right end portion of the supply connection part  75  is sealed by a seal plate  78 . As shown in  FIGS. 4A and 4B , a protrusion  79 , which protrudes toward the left direction, is formed at a central portion of a left side face of the seal plate  78 . 
     The supply connection part  75  is fitted to a gap between the protruded part of the supply roller shaft  56 , which is rightward protruded from the right bearing member  47 , and the second shaft insertion penetration hole  64  formed at the right bearing member  47 . Thereby, the right end portion of the supply roller shaft  56  is inserted into the cylindrical supply connection part  75 , and the supply electrode  57  is fixed to the right bearing member  47 . In addition, the protrusion  79  of the seal plate  78  is contacted to a right end face  56 B of the supply roller shaft  56 . Thereby, the supply roller shaft  56  is restrained from moving in the right direction. 
     In addition, since the protrusion  79  of the seal plate  78  contacts the supply roller shaft  56 , the supply electrode  57  and the supply roller shaft  56  are electrically connected via the seal plate  78 . 
     As shown in  FIG. 3 , the supply protrusion  76  has a plate shape that is further protruded in the left direction than the supply connection part  75  at the rear-upper position regarding the supply connection part  75 . In addition, the supply protrusion  76  is arranged at the front of the developing protrusion  71  of the developing electrode  48 . In other words, the developing protrusion  71  and the supply protrusion  76  are arranged side by side in the front-rear direction. 
     The supply coupling part  77  has a plate shape extending from the rear-lower side to the front-upper side and couples the supply connection part  75  and the supply protrusion  76 . Further, a screw hole (not shown) is formed in the supply coupling part  77 . A screw  80  is engaged with the right sidewall  36  through the screw hole, so that the supply electrode  57  is fixed to the developing housing  10  of the developing cartridge  32 . 
     When the process cartridge  3  (refer to  FIG. 1 ), in which the developing cartridge  32  is mounted to the drum cartridge  31 , is mounted in the body casing  2 , a main body-side supply electrode (not shown) provided in the body casing  2  is connected to the supply protrusion  76 . When a supply bias is input to the supply protrusion  76  from the main body-side supply electrode, the supply bias is applied to the supply roller shaft  56  through the supply coupling part  77  and the protrusion  79  of the supply connection part  75 . 
     As described above, the developing cartridge  32  includes the developing roller  11  and the supply roller  37 . The developing roller  11  is rotatable about the developing roller shaft  46  extending in the left-right direction of the developing housing  10 . The supply roller  37  includes the supply roller shaft  56 . The supply roller shaft  56  extends in the left-right direction and is rotatably held to the right bearing member  47 . In addition, the supply roller shaft  56  is allowed to move in the left-right direction and is secured in the radial direction by the right bearing member  47 . The supply electrode  57  is provided which is opposed to the right end face  56 B of the supply roller shaft  56 . The supply electrode  57  is electrically connected to the supply roller shaft  56 . In addition, the supply gear  59  is arranged at an outer side of the left sidewall  36  of the developing housing  10 . The supply gear  59  is attached to the supply roller shaft  56  so that it cannot be relatively rotated. The supply gear  59  is covered by the gear cover  42  that is attached to the developing housing  10 . 
     The supply roller shaft  56  is positioned in the left-right direction by the supply electrode  57  and the gear cover  42 , so that the supply roller shaft  56  is restrained from moving in the left-right direction. Accordingly, it is not necessary to separately provide a member for restraining the axial (left-right) movement of the supply roller shaft  56 . As a result, it is possible to restrain the axial movement of the supply roller  37  without increasing the costs. 
     The insertion hole  60 , into which the supply roller shaft  56  is inserted, is formed in the supply gear  59 . The supply roller shaft  56  is inserted into the insertion hole  60  so that it does not protrude from the supply gear  59  in the left direction. Thereby, the left end face (the end face of the part inserted into the supply gear  59 ) of the supply roller shaft  56  is not contacted to the gear cover  42 . According thereto, it is possible to prevent the gear cover  42  from being worn due to the contact of the gear cover to the supply roller shaft  56  even when the end portion of the supply roller shaft  56  is D-cut. 
     Further, as the protrusion  79  formed at the supply electrode  57  contacts the right end face  56 B of the supply roller shaft  56 , the supply electrode  57  and the supply roller shaft  56  are electrically contacted. The protrusion  79  has a shape protruding toward the supply roller shaft  56 . Accordingly, the protrusion  79  is point-contacted to the supply roller shaft  56 . Therefore, it is possible to minimize the friction occurring between the supply roller shaft  56  and the supply electrode  57 , and thus it is possible to reduce the resistance that is generated by the supply roller shaft  56  due to the friction. 
     (4) Modified Exemplary Embodiment 
     An exemplary embodiment of the invention has been described above. However, the invention can be implemented according to another exemplary embodiment. 
     For example, in the above exemplary embodiment, a white-black printer has been described as an example of the image forming apparatus. However, a color printer may be adopted as an example of the image forming apparatus. In this case, the invention can be applied to a developing cartridge that is detachably mounted to the color printer.