Abstract:
A processing unit is provided. He processing unit comprises: a housing; a developing roller that carries developer on a surface thereof, the developing roller including, a hollow roller body, and a covering layer covering an outer circumferential surface of the roller body; a photosensitive drum that contacts the developing roller, wherein an end face of the photosensitive drum at a first side in an axial direction of the developing roller is located at an outer side in the axial direction compared to an end face of the developing roller at the first side in the axial direction, and wherein the developer on the developing roller is supplied to the photosensitive drum; and a supporting member that contacts an inner circumferential surface of the roller body at the first side in the axial direction, and supports the developing roller rotatably in the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from Japanese Patent Application No. 2010-016354 filed on Jan. 28, 2010, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    Aspects of the present invention relates to a processing unit including a developing roller that carries developer on a surface thereof. 
       BACKGROUND 
       [0003]    In an image forming apparatus such as a laser printer, a processing unit, which includes a casing, a developing roller that is rotatably supported by the casing, and a photosensitive drum which is opposed to the developing roller and on which an electrostatic latent image is formed, is provided. When toner that is carried on the developing roller opposes the electrostatic latent image of the photosensitive drum, a visible image is formed due to the toner being selectively transferred to the electrostatic latent image. 
         [0004]    Related-art discloses a developing roller used in such an image forming apparatus. The related-art developing roller is formed by providing an elastic rubber layer around a metal shaft. However, because a metal core cut from steel is used in the metal shaft, there is a problem that the weight of the developing roller increases. 
         [0005]    In view of this problem, related-art discloses a developing roller formed by providing a thin elastic rubber layer around a hollow pipe and press fitting a flange having a shaft into both ends of the pipe (JP-A-2000-275955). Thereby, the weight of the developing roller is reduced. 
         [0006]    When assembling the related-art developing roller including a hollow to a casing, the flange shaft is received by a shaft receiving unit, so as to be supported by the casing. Thus, as there are multiple elements between the pipe and the casing, an axial accuracy of the developing roller to the casing becomes low. 
         [0007]    The axial accuracy of the developing roller to the casing can be improved by not attaching the flange to the pipe but supporting an outer circumference of the pipe by a supporting member and attaching the pipe section directly to the casing. However, as there is little difference between an outer diameter of the developing roller including the elastic rubber layer and an outer diameter of the pipe section, when the outer circumference of the pipe section is supported by the supporting member, the supporting member interferes with the photosensitive drum. 
       SUMMARY 
       [0008]    Accordingly, it is an aspect of the present invention to provide a processing unit, wherein a supporting member that supports a hollow pipe type developing roller in a casing does not interfere with a photosensitive drum when the developing roller is attached to the casing, thereby enabling the developing roller to be assembled into the casing in high axial accuracy. 
         [0009]    According to an exemplary embodiment of the present invention, there is provided a processing unit, comprising: a housing; a developing roller that carries developer on a surface thereof, the developing roller including, a hollow roller body, and a covering layer covering an outer circumferential surface of the roller body; a photosensitive drum that contacts the developing roller, wherein an end face of the photosensitive drum at a first side in an axial direction of the developing roller is located at an outer side in the axial direction compared to an end face of the developing roller at the first side in the axial direction, and wherein the developer on the developing roller is supplied to the photosensitive drum; and a supporting member that contacts an inner circumferential surface of the roller body at the first side in the axial direction, and supports the developing roller rotatably in the housing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a central section view of a processing unit; 
           [0011]      FIG. 2  is a section view of a developer cartridge; 
           [0012]      FIG. 3  is an enlarged diagram showing a left end of the developer cartridge shown in  FIG. 2 ; 
           [0013]      FIG. 4  is an enlarged diagram showing a right end of the developer cartridge shown in  FIG. 2 ; 
           [0014]      FIG. 5  is an exploded perspective view of the developer cartridge; 
           [0015]      FIG. 6  is an enlarged diagram of a left end of the developing casing of  FIG. 5 ; 
           [0016]      FIG. 7  is a perspective view of a supporting member viewed from a right side; 
           [0017]      FIG. 8  is a perspective view of the supporting member viewed from a left side; 
           [0018]      FIG. 9  is a perspective view of the developer cartridge; 
           [0019]      FIG. 10  is a side view showing a positional relationship between the supporting member and a photosensitive drum in a front-rear direction. 
           [0020]      FIG. 11  is a side view showing the positional relationship between the supporting member and the photosensitive drum in an axial direction; and 
           [0021]      FIG. 12  is a diagram showing another example of the developing roller. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. 
         [0023]    In  FIG. 1 , the right side of the sheet plane is defined as the front side of the processing unit  4  and the left side of the sheet plane is defined as the rear side of the processing unit  4 . Further, the side of a left hand when the processing unit  4  is viewed from the front side (the front surface side of the sheet plane) is defined as the left side, and the opposite side (the back surface side of the sheet plane) is defined as the right side. Based on these definitions, the front and rear, right and left, and vertical directions, respectively, are indicated in  FIG. 1 . The respective directions shown in  FIGS. 2 to 12  are all indicated so as to correspond to the respective directions shown in  FIG. 1 . 
         [0024]    First, a configuration of a processing unit  4  installed on a laser printer body (not shown) will be described with reference to  FIG. 1 . 
         [0025]    The processing unit  4  includes a drum cartridge  2  including a photosensitive drum  8 , and a developer cartridge  1  that can be removably installed to the drum cartridge  2 . The developer cartridge  1  can be removed from the laser printer body in a state where it is installed to the drum cartridge  2 . 
         [0026]    The developer cartridge  1  mainly includes a developing roller  3 , a layer thickness regulating blade  10 , a supply roller  5  and an agitator  7  in a developing casing  13  that is a housing. Left and right ends of the photosensitive drum  8  extend further in an axial direction (left-right direction) compared to left and right ends of the developing roller  3  (see  FIG. 11 ). 
         [0027]    A toner storage chamber  6  that stores the agitator  7  is provided at the back side of the developing casing  13 . In the developer cartridge  1 , after toner that is an example of developer in the toner storage chamber  6  is stirred by the agitator  7 , the toner is supplied to the developing roller  3  by the supply roller  5 . Here, the toner gains positive charge produced by friction between the supply roller  5  and the developing roller  3 . With rotation of the developing roller  3 , the toner supplied to the developing roller  3  enters between the layer thickness regulating blade  10  and the developing roller  3 , is further charged by friction, and is carried by the developing roller  3  in a thin layer state having a constant thickness. 
         [0028]    The drum cartridge  2  mainly includes a photosensitive drum  8 , a scorotron charger  9  and a transfer roller  71 . Thus, in the drum cartridge  2 , after a surface of the photosensitive drum  8  is uniformly positively charged by the scorotron charger  9 , the surface is exposed by high-speed scanning of laser beam from a scanner unit (not shown) provided in the laser printer body. Potential of exposed areas decrease thereby, and an electrostatic latent image based on image data is formed. 
         [0029]    Next, by rotating the developing roller  3 , the toner carried by the developing roller  3  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  8 , and a toner image is formed on the surface of the photosensitive drum  8 . After that, the toner image carried on the surface of the photosensitive drum  8  is transferred to a sheet by conveying the sheet between the photosensitive drum  8  and the transfer roller  71 . 
         [0030]    Hereinafter, the developer cartridge  1  will be described with reference to  FIG. 2  to  FIG. 12 . 
         [0031]    First, the developing roller  3  will be described. 
         [0032]    As shown in  FIG. 2 , the developing roller  3  includes a hollow roller body  11  formed by metal such as aluminum, and an elastic rubber layer  12  that is a covering layer formed by conductive rubber to cover a surface of the roller body  11 . 
         [0033]    At a left end of the developing roller  3 , the roller body  11  extends further than the elastic rubber layer  12 , so as to form an extension part  65 . The extension part  65  extends to a left attaching groove  21 , which will be described later, when the developing roller  3  is attached to the developing casing  13 . In the exemplary embodiment, the thickness of the elastic rubber layer is 2 mm. By using such developing roller in the contact developing method of the exemplary embodiment, sufficient nip amount can be assured. 
         [0034]    Meanwhile, as shown in  FIG. 12 , a covering layer  80  may be formed by coating a coating solvent on the surface of the roller body  11  of the developing roller. In this case, the thickness of the covering layer  80  is about 0.1 mm. Such developing roller has high environmental stability and can be produced at low cost. 
         [0035]    A shaft end  28  is provided at the right end of the developing roller  3 . As shown in  FIG. 4 , the shaft end  28  includes a flange  29  pressed into the roller body  11 , a first shaft  30 , a diameter of which is smaller than that of the flange  29 , and a second shaft  31 , a diameter of which is further smaller than that of the first shaft  30 . 
         [0036]    A shaft receiving member  61  and a developing roller gear  62 , which will be described later, are fitted to an outer circumferential surface of the first shaft  30 . In addition, a first groove  32  is formed between the flange  29  and the first shaft  30 , and a second groove  33  is formed between the first shaft  30  and the second shaft  31 . 
         [0037]    When the developer cartridge  1  is installed on the laser printer body, a collar which will be described later is attached to the second shaft  31 . By securing the collar in the grooves (not shown) formed to the laser printer body, the position of the processing unit  4  in relation to the laser printer body is determined. 
         [0038]    Hereinafter, the developing casing  13  will be described. 
         [0039]    As shown in  FIG. 5 , the developing casing  13  includes a pair of left and right sidewalls  14  and  15  opposed to each other in the axial direction, a top wall  16  provided between upper edges of the left and right sidewalls  14  and  15 , a bottom wall  17  provided between lower edges of the two sidewalls, and a back wall  18  (see  FIG. 10 ) provided between back edges of the left and right sidewalls  14  and  15 . The pair of left and right sidewalls  14  and  15 , the top wall  16 , the bottom wall  17  and the back wall  18  are integrally formed with each other. In addition, an opening  19  that exposes the developing roller  3  is formed to the developing casing, by the front edges of the left and right sidewalls  14  and  15 , the top wall  16  and the bottom wall  17 . 
         [0040]    First, the left end of the developing casing will be described. 
         [0041]    A left partition  20  that partitions the opening  19  is provided at the left sidewall  14 . In the left partition  20 , a left attaching groove  21  that is cut toward the rear side in an arc-shape is formed. The left end of the developing roller  3  is supported by the developing casing  13  by attaching a supporting member  27  which will be described later to the left attaching groove  21 . 
         [0042]    A first engaged portion  68  that engages with a first engaging portion  38  of the supporting member  27  which will be described later is provided upper to the left attaching groove  21 . The first engaged portion  68  includes a rectangular engaging hole  25  that passes through a left surface  22  and a right surface  23 . 
         [0043]    A side seal attaching portion  47  that extends along a circumferential direction of the developing roller  3 , and to which a side seal (not shown) for preventing leakage of the developer, is provided to the left partition  20  in the axial direction. In addition, a second engaged portion  26  that engages with a second engaging portion  39  which will be described later is provided lower to the left partition  20 . As shown in  FIG. 3 , the second engaged portion  26  protrudes downwards from the side seal attaching portion  47  and engages with a second engaging claw  52  which will be described later at the right side of the protrusion. 
         [0044]    A rectangular groove  69  to which an outer frame  55  of the supporting member  27 , which will be described later, is fitted is provided at the back of the left partition  20 . A shaft  64  of the supply roller  5  protrudes from the center of the rectangular groove  69 . A third engaged portion (not shown) that engages with a third engaging portion  40  which will be described later is provided at the rear side of the rectangular groove  69 . 
         [0045]    The right sidewall  15  includes a right partition  34  that partitions the opening  19 . In the right partition  34 , a right attaching groove  35  that is cut to toward the rear side in an arc-shape is formed. The right attaching groove  35  has an opening  70  at the front end thereof, and the right end of the developing roller  3  is supported by the developing casing  13  by fitting the shaft receiving member  61  which will be described later into the opening  70 . 
         [0046]    The supporting member  27  that attaches the left end of the developing roller  3  to the developing casing  13  is attached to the left sidewall  14  of the developer cartridge  1 . 
         [0047]    The supporting member  27  is formed by conductive resin. As shown in  FIGS. 7 and 8 , the supporting member  27  includes a body  36 , a developing roller supporting portion  37 , first to third engaging portions  38  to  40  and a terminal portion  42 , which are integrally formed with each other. 
         [0048]    As the supporting member  27  is formed by conductive resin, the developing roller  3  can be charged via the supporting member  27  from the laser printer body, and other members for charging the developing roller  3  do not need to be provided. 
         [0049]    The developing roller supporting portion  37  is arranged at a front side of the body  36 , protrudes cylindrically to the right direction, and is pressed into an inner circumference of the extension part  65  of the developing roller  3 . An outer diameter D 1  of the developing roller supporting portion  37  is set, so that an outer surface of the developing roller supporting portion  37  contacts an inner surface of the roller body  11  (inner diameter D 2 ), and the rotation of the developing roller  3 , are possible. Conductive grease is coated on an outer circumference surface of the developing roller supporting portion  37  in advance. 
         [0050]    A cylindrical reinforcing portion  43  which is coaxial with the developing roller supporting portion  37  and has the same inner and outer diameters as those of the developing roller supporting portion  37  protrudes to the left direction from the left side of the body  36 . The reinforcing portion  43  reinforces the supporting member  27 , and prevents cavities formed by mold shrinking during metallic molding. 
         [0051]    The first engaging portion  38  is provided upper to the developing roller supporting portion  37 , and includes an extension part  44  extending from the upper edge of the body  36  and a first engaging claw  45  formed at the leading edge of the extension part  44 . When the extension part  44  is inserted into the engaging hole  25  of the developing casing  13 , the first engaging claw  45  engages with the right side  23  of the left partition  34  (see  FIG. 3 ). 
         [0052]    A leakage preventing member  46  protrudes to the right direction from a front edge and a lower edge of the body unit  36 . The leakage preventing member  46  includes a bottom cover  48  covering the bottom of the side seal attaching portion  47  and a front cover  49  covering the front of the side seal attaching portion  47 . Thus, the developer will not leak from the developing casing  13 . 
         [0053]    The second engaging portion  39  extends from the bottom cover  48 . The second engaging portion  39  is provided with a bended portion  24  that is bended to the left direction from the right end of the bottom cover  48 , and a second engaging claw  52  that is formed at the left end of the bended portion  24 . The second engaging claw  52  engages with the second engaging portion  26  when the supporting member  27  is attached to the developing casing  13 . 
         [0054]    The terminal portion  42  is provided at the upper rear side of the body unit  36 . The terminal portion  42  protrudes to the left direction from the upper edge of the body  36 , and a contact surface  51  that inclines downwards in the rear direction is provided. By elastically contacting the contact surface  51  with a body side electrode provided in the laser printer body when the drum cartridge  2  to which the developer cartridge  1  is installed is installed to the laser printer body, the developing roller  3  is charged via the supporting member  27 . 
         [0055]    A screw hole  57  is formed lower to the terminal portion  42 . By screwing a screw  58  into the screw hole  57  (see  FIG. 9 ), the supporting member  27  is firmly secured to a left side surface of the left sidewall  14  of the developing casing  13 . 
         [0056]    The supply roller supporting portion  41  is arranged obliquely below the developing roller supporting portion  37 , and supports the shaft  64  of the supply roller  5  (see  FIG. 5 ). The supply roller supporting portion  41  is provided with an outer frame  55  that is rectangular and recessed in the right direction and a supply roller shaft receiving unit  53  that is provided in the center of the outer frame  55  and covers the shaft  64  of the supply roller  5 . 
         [0057]    The third engaging portion  40  is provided obliquely below the supply roller supporting portion  41 . The third engaging portion  40  in which a third engaging claw  56  protruding to the right direction is provided engages with the third engaged portion that was previously explained and not shown. 
         [0058]    Next, the right end of the developer cartridge  1  will be described. As shown in  FIG. 4 , at the right end of the developer cartridge  1 , the shaft receiving member  61  receiving the shaft end  28  of the developing roller  3 , the developing roller gear  62  driving the developing roller  3 , and two ring members  59  and  60  are provided. 
         [0059]    The shaft receiving member  61  is fitted to the outer circumference of the first shaft  30  of the developing roller  3 . The shaft receiving member  61  includes a base  66  and a flange  67  provided at the left edge of the base  66 . It can be seen from the cross section view that, the base  66  has such a shape that two round areas are truncated linearly. The flange  67  protrudes in the radial direction from the linear portions (not shown) of the base  66 . A protrusion (not shown) that engages with an engaging groove (not shown) formed at the left side of the right sidewall  15  of the developing casing  13  is formed at the right side of the flange  67 . 
         [0060]    Similar to the shaft receiving member  61 , the developing roller gear  62  is fitted to the first shaft  30  at the right side of the shaft receiving member  61 , and transmits the driving force transmitted from the laser printer body to the developing roller  3 . 
         [0061]    The first ring  59  and the second ring  60  is fitted to the first groove  32  and the second groove  33  to nip the shaft receiving member  61  and the developing roller gear  62 , and the positions of the shaft receiving member  61  and the developing roller gear  62  in relation to the developing roller  3  are determined. 
         [0062]    In addition, a gear cover  63  (see  FIG. 9 ) is attached to the developing casing  13  to protect the developing roller gear  62  and other gears (not shown) for driving the supply roller  5 , and the like. 
         [0063]    Hereinafter, assembly of the developer cartridge  1  and the installation of the developer cartridge  1  to the drum cartridge  2  will be described. 
         [0064]    The shaft receiving member  61  and the developing roller gear  62  are installed to the first shaft  30  of the developing roller  3 . The first ring  59  and the second ring  60  are fitted to the first groove  32  and the second groove  33  to nip the shaft receiving member  61  and the developing roller gear  62 , and the shaft receiving member  61  and the developing roller gear  62  are secured in relation to the shaft end  28  of the developing roller  3 . 
         [0065]    Next, the right end of the developing roller  3  is attached to the developing casing  13 . Specifically, the base  66  of the shaft receiving member  61  is inserted into the right attaching groove  35  so that the flange  67  of the shaft receiving member  61  is arranged in the opening  70  when viewed from the axial direction. Then, the flange  67  is rotated counterclockwise when viewed from the left side, and a protrusion (not shown) provided on the flange  67  engages with an engaging groove (not shown) of the developing casing  13 . 
         [0066]    In this case, the right partition  34  is fitted between the left side of the developing roller gear  62  and the right side of the flange  67  formed at the shaft receiving member  61 , and the position of the developing roller  3  in the axial direction in relation to the developing casing  13  is determined. 
         [0067]    In addition, a collar (not shown) formed by resin is attached to the second shaft  31  provided at the right end of the developing roller  3 . 
         [0068]    Next, at the left end of the developing roller  3 , the extension part  65  of the roller body  11  is arranged in the left attaching groove  21 . Then, the developing roller supporting portion  37  of the supporting member  27  is inserted into the inner circumference of the extension part  65  of the developing roller  3  while the shaft  64  of the supply roller  5  is inserted into the supply roller shaft receiving unit  53 . The first engaging portion  38 , the second engaging portion  39  and the third engaging portion  40  are respectively engaged with the first engaged portion  68 , the second engaged portion  26  and the third engaged portion (not shown), and the supporting member  27  is thereby attached to the developing casing  13 . 
         [0069]    When the supporting member  27  is attached to the developing casing  13 , as shown in  FIG. 3 , the extension part  65  of the roller body  11 , into which the developing roller supporting portion  37  of the supporting member  27  is inserted, is spaced from an inner surface of the left attaching groove  21  of the developing casing  13  by a space S 1  in the radial direction. In addition, a left end side of the extension part  65  is spaced from a right side of the body  36  of the supporting member  27  by a space S 2  in the axial direction. 
         [0070]    Next, the developing casing  13  to which the developing roller  3  and the supporting member  27  are attached is installed to the drum cartridge  2 . In this case, as shown in  FIG. 11 , the body  36  of the supporting member  27  is arranged at the right side of the end face  72  of the flange  81  provided at the left side of the photosensitive drum  8 . In addition, as shown in  FIG. 10 , a distance L 1  from an axis center C of the developing roller  3  to the surface of the photosensitive drum  8  is set to be larger than a distance L 2  from the axis center C of the developing roller  3  to the end face (the front end face of the body  36 ) of the supporting member  27 , facing the photosensitive drum  8 . 
         [0071]    According to the developer cartridge  1  of the exemplary embodiment, the developing roller supporting portion  37  of the supporting member  27  is inserted to the inner circumference of the extension part  65  of the developing roller  3 , and the left end of the developing roller  3  is attached to the developing casing. Therefore, compared to related-art where a shaft end is attached to a hollow developing roller, and the shaft end is received by another section so as to attach the developing roller to the developing casing, as the roller body  11  can be directly supported by the supporting member  27 , axial accuracy of the developing roller  3  in relation to the developing casing  13  can be improved. 
         [0072]    In addition, as the supporting member  27  supports the inner surface of the roller body  11  when the developing roller  3  is attached to the developing casing  13 , the distance L 1  from the axis center C of the developing roller  3  to the surface of the photosensitive drum  8  can be set to be larger than the distance L 2  from the axis center C of the developing roller  3  to the end face of the supporting member  27 , facing the photosensitive drum  8 . Therefore, even if a part of the supporting member  27  is arranged at the right side of the left end face  72  of the photosensitive drum  8 , the developing roller  3  can be supported by the developing casing  13  without the supporting member  27  interfering with the photosensitive drum  8 , and the developer cartridge  1  can be reduced in size in the axial direction. 
         [0073]    In addition, by contacting the outer circumferential surface of the cylindrical developing roller supporting portion  37  with the inner circumferential surface of the roller body  11  to support the developing roller  3 , the left end of the roller body  11  can be stably secured to the developing casing  13 . 
         [0074]    In addition, by attaching the supporting member  27  to the developing casing  13  so that the first engaging portion  38 , the second engaging portion  39  and the third engaging portion  40  provided at the supporting member  27  respectively engages with the first engaged portion  68 , the second engaged portion  26  and the third engaged portion (not shown), the supporting member  27  can be firmly secured to the developing casing  13 . 
         [0075]    In addition, by determining the axial position of the developing roller  3  in relation to the developing casing  13  at the right end to which the developing roller gear  62  of the developing roller  3  is attached, at the left side, it is only required that the developing roller  3  is supported by inserting the developing roller supporting member  37  of the supporting member  27  into the extension part  65  of the roller body  11 . Therefore, the structure of the supporting member  27  can be simplified. 
         [0076]    In addition, when determining a position of an apparatus in a certain direction, if the distance between a place restricting movement of the apparatus in one direction and a place restricting the movement of the apparatus in another direction becomes long, the apparatus tends to become shaky and positioning accuracy becomes lower. Meanwhile, if the distance becomes short, it becomes less shaky and the positioning accuracy becomes higher. In the exemplary embodiment, by determining the position only at the right end of the developing roller  3  rather than at both the left and right ends which are far away, the positioning accuracy can be improved, and the erection tolerance of the developing roller  3  in relation to the developing casing  13  can be reduced. 
         [0077]    In addition, by coating conductive grease at the outer circumference of the developing roller supporting portion  37 , the conductivity between the roller body  11  and the supporting member  27  can be improved, and thus necessary bias can be stably applied to the developing roller  3 . 
         [0078]    In addition, by providing the radial space S 1  between the outer surface of the extension part  65  of the roller body  11  and the inner surface of the left attaching groove  21 , contact area between the developing roller  3  and the developing casing  13  can be reduced, and frictional force acting on the rotating developing roller  3  can be reduced. 
         [0079]    In addition, by providing the axial space S 2  between the left end of the extension part  65  and the right side of the body  36  of the supporting member  27 , the contact area between the developing roller  3  and the supporting member  27  can be reduced, and the frictional force acting on the rotating developing roller  3  can be reduced. 
         [0080]    While the present invention has been showed and described with reference to exemplary embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.