Abstract:
In a developing apparatus, a sealing member has a first part contacting an axial end part of a developing roller and a second part including a first side surface. A roller body of a supply roller includes a contact surface that contacts the peripheral surface, and a second side surface located at an end of the contact surface in the axial direction. The restricting member has a one side and another side. The one side is opposed to the second side surface in the axial direction. The another side is opposed to the first side surface in the axial direction with a gap. The gap is communicated with an interior space of a developer accommodating frame such that the developer is capable of moving away from a nip position between the supply roller and the developing roller toward the bottom wall of the developing frame in the gap.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/560,646, filed Jul. 27, 2012, which claims priority from Japanese Patent Application No. 2011-167377 filed Jul. 29, 2011 and Japanese Patent Application No. 2011-167378 filed Jul. 29, 2011. The entire contents of the priority applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a developing apparatus mounted to an electrographic image forming apparatus and a developing method using the developing apparatus. 
       BACKGROUND 
       [0003]    There is known, as an electrographic printer, a printer provided with a photosensitive member and a developing apparatus that supplies the photosensitive member with toner. 
         [0004]    One such a developing apparatus mounted to a printer include a developing roller that carries the toner, a supply roller that supplies the developing roller with the toner, and a layer-thickness regulating blade that regulates thickness of the toner on the developing roller to a predetermined value. 
         [0005]    In this developing apparatus, the layer-thickness regulating blade includes a support portion made of iron or stainless steel, a plate spring attached to a distal end of the support portion, and a semicylindrical pressing member formed of silicone rubber and provided on the plate spring. The layer-thickness regulating blade is brought into contact with the developing roller at a curved part of the pressing member. 
         [0006]    Further, in this developing apparatus, the side end of a side seal slides the side end surface of the supply roller. 
       SUMMARY 
       [0007]    In the above developing apparatus, additional toner may be deposited on toner that is directly carried on a surface of the developing roller. 
         [0008]    In this state, the additional toner is carried on the developing roller though the toner directly carried on the surface of the developing roller, resulting in an insufficient image force of the additional toner. 
         [0009]    Thus, when a peripheral velocity of the developing roller is increased so as to increase an image forming speed of the printer, the additional toner carried on the developing roller is disadvantageously separated from the surface of the developing roller by a centrifugal force of the developing roller. 
         [0010]    An object of the present invention is to provide a developing apparatus capable of preventing a developer from being separated from the developing roller and thus increasing an image forming speed and a developing method using the developing apparatus. 
         [0011]    Further, in the above developing apparatus, toner supplied to the contact part between the developing roller and the supply roller is not supported, is excluded from the contact part, and enters a space between the side seal and the developing roller. Especially, when the peripheral velocity of the developing roller is increased so as to increase the image forming speed of the printer, the toner is melted by the frictional heat between the developing roller and the side seal. By this frictional heat, the side seal is broken. The broken side seal no longer seals the end of the developing roller, and thus, the toner may be leaked. 
         [0012]    Another object of the present invention is to provide a developing apparatus to prevent the toner from being leaked from an axial end of a developing roller. 
         [0013]    In order to attain the above and other objects, the invention provides a developing apparatus. The developing apparatus includes a housing, a developing roller, a supply roller, a thickness regulating member, a sealing member, and a restricting member. The housing includes: a developer accommodating frame configured to accommodate developer; and a developing frame communicated with the developer accommodating frame. The developing frame includes a supply-roller accommodating part and a bottom wall. The developing roller rotatably is supported by the supply-roller accommodating part and has a peripheral surface configured to carry the developer. The peripheral surface extends in an axial direction and includes an axial end part. The supply roller is rotatably supported in the developing frame, contacts the developing roller at a nip position, and is configured to supply the toner to the developing roller. The supply roller is shorter than the developing roller. The thickness regulating member includes a contact member contacting the developing roller. The contact member is configured to regulate a thickness of the developer on the developing roller. The sealing member is located in the developing frame and has a first part contacting the axial end part and a second part including a first side surface. The restricting member is located in the developing frame. The supply roller includes a rotational shaft and a roller body. The rotational shaft extends in the axial direction, and has axial ends supported by the developing frame. The roller body includes: a contact surface that contacts the peripheral surface and covers the rotational shaft while exposing the both axial ends of the rotational shaft; and a second side surface located at an end of the contact surface in the axial direction. The restricting member has a one side and another side opposite to the one side. The one side of the restricting member is opposed to the second side surface of the supply roller in the axial direction. The another side of the restricting member is opposed to the first side surface in the axial direction with a gap. The gap is communicated with an interior space of the developer accommodating frame such that the developer is capable of moving away from the nip position toward the bottom wall in the gap. 
         [0014]    According to another aspect, the present invention provides a developing apparatus. A developing apparatus includes a housing, a developing roller, a supply roller, and a thickness regulating member. The housing is configured to accommodate developer that includes developer particles having a mean volume diameter. The developing roller rotatably is supported in the housing and has a peripheral surface configured to carry the developer. The supply roller is rotatably supported in the housing, contacts the developing roller, and is configured to supply the toner to the developing roller. The thickness regulating member includes a contact member contacting the peripheral surface. The contact member is configured to regulate a thickness of the developer on the peripheral surface such that an average of the thickness of the developer on the peripheral surface becomes smaller than or equal to the mean volume diameter. The developing roller rotates in a rotational direction. The peripheral surface of the developing roller has a region. The contact member has a thickness being larger than a thickness of the developer on the region. The thickness of the developer on the region is larger than the mean volume diameter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a cross section of a printer taken along a center thereof according to an embodiment of a present invention; 
           [0017]      FIG. 2  is a cross section of a developer cartridge shown in  FIG. 2 ; 
           [0018]      FIG. 3  is a perspective view of an agitator shown in  FIG. 2  seeing from upper left side; 
           [0019]      FIG. 4  is a cross section of the developer cartridge taken along a line A-A shown in  FIG. 2 ; 
           [0020]      FIG. 5  is a cross section of the developer cartridge taken along a line B-B shown in  FIG. 2 ; 
           [0021]      FIG. 6  is a cross section of the developer cartridge taken along a line C-C shown in  FIG. 2 ; 
           [0022]      FIG. 7  is an explanatory diagram illustrating an image force of overlapped tonner particles; 
           [0023]      FIG. 8  is a side cross section of a developing cartridge according to a modification; 
           [0024]      FIG. 9(   a ) is a side cross section of a developing cartridge according to a modification; 
           [0025]      FIG. 9(   b ) is a front view of a crankshaft shown in  FIG. 9(   a ); 
           [0026]      FIG. 10(   a ) is a side cross section of a developing cartridge according to a modification; and 
           [0027]      FIG. 10(   b ) is a front view of a slide member shown in  FIG. 10(   a ). 
       
    
    
     DETAILED DESCRIPTION 
     1. Overall Configuration of Printer 
       [0028]    As illustrated in  FIG. 1 , a printer  1  includes a casing  2 , a paper supply section  3  for supplying a paper P, and an image forming section  4  for forming an image onto the supplied paper P. 
       (1) Body Casing 
       [0029]    The casing  2  is substantially formed into a box-shape in side view and accommodates the paper supply section  3  and image forming section  4 . A front cover  5  is formed on one side wall of the casing  2  for mounting or removing a developing cartridge  14  (described later). The front cover  5  is provided so as to be swingable about a lower end portion thereof relative to the casing  2 . 
         [0030]    In the following description, a side (right side in  FIG. 1 ) on which the front cover  5  is provided is defined as front side, and the opposite side (left side of  FIG. 1 ) thereof is defined as rear side. Further, left-right direction is defined as viewed from the front side. That is, the near side of the paper surface of  FIG. 1  is defined as left side, and the far side of the paper surface of  FIG. 1  is defined as right side. 
       (2) Paper Supply Section 
       [0031]    The paper supply section  3  is provided at a lower portion of the casing  2 . The paper supply section  3  includes a paper supply tray  6  for storing the paper P and a pickup roller  7  provided on an upper portion of a front end portion of the paper supply tray  6 . The paper supply section  3  further includes a paper supply path  8  extending rearward from an upper side of the pickup roller  7  and a pair of upper and lower registration rollers  9  arranged at a rear portion of the paper supply path  8 . 
         [0032]    The paper sheets P are stacked in the paper supply tray  6  and fed one by one starting from the topmost paper P by a rotation of the pickup roller  7 . One paper P picked up by the pickup roller  7  is fed between the pair of registration rollers  9  through the paper supply path  8  and is then fed toward a portion between a photosensitive drum  13  (to be described later) and a transfer roller  16  (to be described later) at a predetermined timing. 
       (3) Image Forming Section 
       [0033]    The image forming section  4  includes a scanner unit  10 , a process unit  11 , and a fixing unit  12 . 
       (3-1) Scanner Unit 
       [0034]    The scanner unit  10  is disposed at an upper portion of the casing  2 . The scanner unit  10  emits laser beam toward a photosensitive drum  13  (to be described later) based on image data to expose the photosensitive drum  13 . 
       (3-2) Process Cartridge 
     (3-2-1) Configuration of Process Cartridge 
       [0035]    The process unit  11  provided in the casing  2  is disposed below the scanner unit  10  and above the paper supply section  3  and includes the photosensitive drum  13  and the developing cartridge  14  that is detachably mounted to the front side of the photosensitive drum  13 . 
         [0036]    The photosensitive drum  13  is provided to extend along the left-right direction. A scorotron charger  15  and the transfer roller  16  are disposed around the photosensitive drum  13 . 
         [0037]    The scorotron charger  15  is disposed on the upper rear side of the photosensitive drum  13 , and opposes the photosensitive drum  13  at a predetermined interval. 
         [0038]    The transfer roller  16  is disposed below and opposes the photosensitive drum  13 . The transfer roller  16  is brought into pressing contact with the photosensitive drum  13  from below. 
         [0039]    The developing cartridge  14  includes a developing roller  17 . The developing roller  17  extends in the left-right direction, and is rotatably supported at a rear end portion of the developing cartridge  14  such that the rear side of the developing cartridge  14  is exposed. The developing roller  17  is brought into pressing contact with the photosensitive drum  13  from the front side. The developing roller  17  includes a metal developing roller shaft  25  and a resin developing roller body  27 . The developing roller body  27  covers the surface of the developing roller shaft  25  while exposing both end portions of the developing roller shaft  25  in the left-right direction. A negative developing bias is applied to the developing roller  17  from a power supply (not shown) in the casing  2 . 
         [0040]    The developing cartridge  14  includes a supply roller  18  that supplies the developing roller  17  with toner and a layer-thickness regulating blade  19  that regulates thickness of the toner supplied to the developing roller  17 . The toner, specifically non-magnetic one-component spherical toner, is contained in a front space (toner accommodating frame  32  (to be described later)) relative to the supply roller  18  and the layer-thickness regulating blade  19 . 
         [0041]    To obtain the spherical toner, a resin solution containing a binder resin such as a polyester resin and a colorant such as carbon black is emulsified in water to prepare a dispersion liquid of resin fine particles, and thereafter the resin fine particles are subjected to condensation and fusion reaction. 
         [0042]    A mean volume particle diameter of the spherical toner is, in terms of median size, e.g., 3 μm to 12 μm, preferably, 6 μm to 10 μm. That is, the mean volume particle diameter is a median value of the diameters of the particles weighted by the volumes of the particles. The mean volume particle diameter can be measured using, e.g., a Nanotrac particle size distribution measuring apparatus (UPA150 manufactured by Nikkiso Co., Ltd). In this measurement, refractive index of a solvent may be set to 1.33, and refractive index of a dispersion to 1.9. 
       (3-2-3) Developing Operation in Process Cartridge 
       [0043]    The toner in the developing cartridge  14  is supplied to the supply roller  18  and then to the developing roller  17 . Then, the toner is friction-charged to a positive polarity at a nip N1 (see  FIG. 2 ) between the supply roller  18  and developing roller  17 . 
         [0044]    The toner supplied to the developing roller  17  is regulated in thickness by the layer-thickness regulating blade  19  with a rotation of the developing roller  17 , and is carried on the surface of the developing roller  17  as a toner layer TL (see  FIG. 2 ) having a certain thickness. 
         [0045]    The surface of the photosensitive drum  13  is uniformly positively charged by the scorotron charger  15  with a rotation of the photosensitive drum  13  and is thereafter exposed by high-speed scanning of laser beam emitted from the scanner unit  10 . As a result, an electrostatic latent image corresponding to an image to be formed onto the paper P is formed on the surface of the photosensitive drum  13 . 
         [0046]    Further, when the photosensitive drum  13  rotates, the positively charged toner carried on the surface of the developing roller  17  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  13 . As a result, the electrostatic latent image on the photosensitive drum  13  is visualized, and a toner image based on reversal development is carried on the surface of the photosensitive drum  13 . 
         [0047]    When the paper P is passed between the photosensitive drum  13  and the transfer roller  16 , the toner image carried on the photosensitive drum  13  is transferred onto the paper P. 
       (3-3) Fixing Unit 
       [0048]    The fixing unit  12  is disposed at the rear of the process unit  11  and includes a heating roller  20  and a pressure roller  21  opposing to the heating roller  20 . The toner image transferred onto the paper P in the process unit  11  is thermally fixed onto the paper P by heat and pressure while being passed between the heating roller  20  and the pressure roller  21 . 
       (4) Paper Discharge Section 
       [0049]    The paper P onto which the toner image has been fixed is passed through a paper discharge path  22  toward a paper discharge roller  23 . Thereafter, the paper P is discharged by the paper discharge roller  23  on a paper discharge tray  24  provided above the scanner unit  10 . 
       2. Details of Developing Cartridge 
     (1) Cartridge Frame 
       [0050]    As illustrated in  FIG. 2 , the developing cartridge  14  includes a cartridge frame  31  as an example of a casing. 
         [0051]    The cartridge frame  31  includes a toner accommodating frame  32  in which the toner is stored and a developing frame  33  that supports the developing roller  17 . 
         [0052]    The toner accommodating frame  32  constitutes a front part of the cartridge frame  31  and is formed into a double cylindrical shape formed by joining two cylinders arranged in the radial direction thereof. More specifically, the toner accommodating frame  32  includes a first toner accommodating frame  38  and a second toner accommodating frame  39 . 
         [0053]    The first toner accommodating frame  38  is a front side cylindrical portion of the toner accommodating frame  32  and is formed substantially into a cylindrical shape whose left and right ends are closed. 
         [0054]    The second toner accommodating frame  39  is a rear side cylindrical portion of the toner accommodating frame  32  and is formed substantially into a cylindrical shape whose left and right ends are closed. The second toner accommodating frame  39  is connected to a rear end portion of the first toner accommodating frame  38 . 
         [0055]    The toner accommodating frame  32  is formed with a first communication port  40  for passing the toner in the first toner accommodating frame  38  to the second toner accommodating frame  39  at a position between the first and second toner accommodating frames  38  and  39 . 
         [0056]    Further, the second toner accommodating frame  39  is formed with a second communication port  34  at a rear end thereof for passing the toner in the second toner accommodating frame  39  to the developing frame  33 . 
         [0057]    The second toner accommodating frame includes a partition wall  49  positioned below the second communication port  34 . The partition wall  49  extends in the vertical direction for partitioning the second toner accommodating frame  39  and the developing frame  33 . The upper end portion of the partition wall  49  is disposed below the nip N1. 
         [0058]    An upper end edge of the partition wall  49  is disposed below a center axial line of a supply roller shaft  26  (described later). Thus, the upper end edge of the partition wall  49  is disposed below the nip N1 between the developing roller  17  and the supply roller  18 . Further, both end portions of the partition wall  49  in the left-right direction are formed so as to be inclined downward toward outside with respect to the left-right direction (see a broken line of  FIG. 5 ). 
         [0059]    An agitator  41  is provided in each of the first and second toner accommodating frames  38  and  39  of the toner accommodating frame  32 . 
         [0060]    As shown in  FIGS. 2 and 3 , the agitator  41  includes an agitator shaft  42  extending in the left-right direction and an agitating blade  43  supported by the agitator shaft  42 . 
         [0061]    The agitator shaft  42  is formed substantially into a columnar shape extending in the left-right direction. 
         [0062]    The agitator blade  43  includes a support portion  44  and an agitating portion  45 . 
         [0063]    The support portion  44  is formed substantially into a wedge shape in side view protruding outside of the agitator shaft  42  in the radial direction (hereinafter, referred to as “outside in the radial direction”) from the agitator shaft  42  and extending in the left-right direction. 
         [0064]    The agitating portion  45  is formed of an elastic resin film and is substantially formed in a plate shape extending outside in the radial direction from an outside end portion of the support portion  44  in the radial direction so as to curve toward in an upstream side of the agitator  41  in the rotational direction (hereinafter, referred to as “upstream side in the rotational direction”). The agitating portion  45  has three openings  46  ( FIG. 3 ). 
         [0065]    The openings  46  are arranged, side by side, in the left-right direction with a predetermined interval provided therebetween and each is substantially formed in a rectangular shape that is formed by penetrating the resin film. 
         [0066]    The end portions of each agitator  41  in the left-right direction are rotatably supported by the left and right side walls of corresponding one of the first and second toner accommodating frames  38  and  39 . 
         [0067]    As shown in  FIGS. 2 ,  4 , and  5 , the developing frame  33  is formed continuously from a rear end portion of the toner accommodating frame  32  and includes a pair of left and right side walls  35 , an upper wall  36 , and a lower wall  37 . 
         [0068]    The left and right side walls  35  are formed into substantially plate shapes extending rearward continuously from the respective left and right side walls of the second toner accommodating frame  39 . A supply roller shaft support hole  53  is formed so as to penetrate each of the side walls  35 . The supply roller shaft  26  is inserted through the supply roller shaft support hole  53 . 
         [0069]    The upper wall  36  is formed into substantially a plate shape extending rearward continuously from an upper end portion of the second toner accommodating frame  39 . The upper wall  36  bridges upper end portions of the side walls  35 . A rear end portion of the upper wall  36  is disposed frontward of rear end portions of the side walls  35 . 
         [0070]    The lower wall  37  extends rearward continuously from a lower end portion of the second toner accommodating frame  39 . The lower wall  37  bridges lower end portions of the side walls  35 . The lower wall  37  includes a supply roller housing portion  47  for housing the supply roller  18  and a receiving portion  48  disposed below the developing roller  17 . 
         [0071]    The supply roller housing portion  47  is substantially U-shaped opened upward in cross section and is continuously formed from the partition wall  49  of the second toner accommodating frame  39 . When projected in the front-rear direction, an upper end of the supply roller housing portion  47  at its rear end is disposed above the upper end of the partition wall  49 . 
         [0072]    A pair of left and right restricting walls  51  are provided in the supply roller housing portion  47  (see  FIG. 4 ). 
         [0073]    The both restricting walls  51  are disposed inside of the both side walls  35  with respect to the left-right direction while opposing corresponding end of a supply roller body  28  (to be described later) in the left-right direction. A supply roller shaft insertion holes  52  are formed by penetrating the restricting walls  51 . The supply roller shaft  26  (to be described later) is inserted through the supply roller shaft insertion holes  52 . 
         [0074]    The receiving portion  48  is formed substantially in a plate extending rearward from the upper rear end portion of the supply roller housing portion  47 . When projected in the vertical direction, a rear end of the receiving portion  48  is disposed rearward of the rear end of the upper wall  36  and substantially flush with the rear ends of the side walls  35 . 
       (2) Supporting Supply Roller in Cartridge Frame 
       [0075]    As shown in  FIGS. 2 ,  4 , and  6 , the supply roller  18  includes the metal supply roller shaft  26  and a resin supply roller body  28 . The resin supply body  28  covers the surface of the supply roller shaft  26  while exposing both end portions of the supply roller shaft  26  in the left-right direction. The length of the supply roller body  28  in left-right direction is shorter than that of the developing roller body  27 . 
         [0076]    The supply roller  18  is accommodated in a front end portion of the supply roller housing portion  47  such that end portions of the supply roller shaft  26  in the left-right direction are inserted through the supply roller shaft insertion holes  52  of the restricting walls  51  and are rotatably supported in the supply roller shaft support holes  53 . 
         [0077]    Two shaft seals  61  ( FIG. 4 ) are fit on end portions of the supply roller shaft  26  in the left-right direction. Each shaft seal  61  is disposed between the corresponding restricting wall  51  and side wall  35 . Further, a supply roller drive gear  62  is provided at a right end portion of the supply roller shaft  26 . 
         [0078]    The shaft seal  61  is formed of resin foam and is substantially formed in a plate shape having a thickness in the left-right direction. A supply roller shaft insertion hole  64  is formed so as to penetrate the shaft seal  61 . The supply roller shaft insertion hole  64  has a diameter slightly smaller than the diameter of the supply roller shaft  26 . The supply roller shaft  26  is inserted through the supply roller shaft insertion hole  64 . 
         [0079]    The supply roller drive gear  62  is disposed on the right side of the right side wall  35  and supported at the right end portion of the supply roller shaft  26  so as not to be relatively rotated. The supply roller drive gear  62  is engaged with a developing coupling (not shown) rotatably mounted to a right wall of the cartridge frame  31 . The supply roller drive gear  62  transmits, to the supply roller shaft  26 , a drive force input from the casing  2  to the developing coupling (not shown). 
         [0080]    As shown in  FIGS. 2 and 5 , an auger screw  50   a  is provided in the supply roller housing portion  47  and disposed at a position between the partition wall  49  and the supply roller  18 . 
         [0081]    The auger screw  50  extends in the left-right direction and has a smaller diameter than the diameter of the supply roller  18 . The auger screw  50  is rotatably provided in the supply roller housing portion  47  such that an upper end of the auger screw  50  is disposed below the upper end of the partition wall  49 . An auger drive gear  63  (see  FIG. 5 ) is provided at a right end portion of the auger screw  50 . 
         [0082]    The auger drive gear  63  is disposed on the right side of the right side wall  35  and supported at the right end portion of the auger screw  50  so as not to be relatively rotated. The auger drive gear  63  is engaged with the developing coupling (not shown) and transmits, to the auger screw  50 , a drive force input from the casing  2  to the developing coupling (not shown). The toner is accumulated in the supply roller housing portion  47  at a portion above the upper end portion of the auger screw  50 . 
       (3) Supporting Developing Roller in Cartridge Frame 
       [0083]    As shown in  FIGS. 2 and 6 , the developing roller  17  is disposed above the receiving portion  48  such that end portions of the developing roller shaft  25  in the left-right direction are rotatably supported by the side walls  35  and that the developing roller body  27  is brought into contact with the supply roller body  28  from the upper rear side thereof. 
         [0084]    A developing roller drive gear  82  is provided at a right end portion of the developing roller shaft  25 . Further, two side seals  81  (see  FIG. 4 ) are brought into contact with end portions (end surfaces) of the developing roller body  27  in the left-right direction. 
         [0085]    The developing roller drive gear  82  is disposed on the right side of the right side wall  35  and supported at the right end portion of the developing roller shaft  25  so as not to be relatively rotated. The developing roller drive gear  82  is engaged with the developing coupling (not shown). The developing roller drive gear  82  transmits, to the developing roller shaft  25 , a drive force input from the casing  2  to the developing coupling (not illustrated). 
         [0086]    As shown in  FIG. 6 , each side seal  81  is substantially formed a plate shape having flexibility which is obtained by laminating a foam layer  83  formed of resin foam and a felt layer  84  formed of non-woven cloth. Each side seal  81  is supported inside the developing frame  33  and is brought into contact with the developing roller body  27  from the lower front side of the developing roller  17  so as to follow the peripheral surface of the developing roller body  27 . Further, each side seal  81  is disposed on outside of the outer end of the supply roller body  28  in the left-right direction and disposed on outside of the restricting wall  51  in the left-right direction. That is, each side seal  81  is separated from the corresponding side surface of the supply roller body  28  in the left-right direction. The inner surface of each side seal  81  is separated from the corresponding restricting wall  51  with a gap G in the left-right direction. That is, a space TG is formed between each side seal  81  and the corresponding restricting wall  51 . 
       (4) Supporting Layer-Thickness Regulating Blade in Cartridge Frame 
       [0087]    As shown in  FIGS. 2 and 4 , the layer-thickness regulating blade  19  is supported at a rear end portion of the upper wall  36  of the developing frame  33  by screws (not shown). The layer-thickness regulating blade  19  includes a blade member  71  to be brought into contact with the developing roller  17  and first and second support members  72  and  73  that support the blade member  71 . 
         [0088]    The blade member  71  is formed of an elastic thin metal plate and is substantially formed in a rectangular plate shape in front view extending in both the vertical direction and the left-right direction. An contacting member  74  is provided on the rear surface of the lower end portion of the blade member  71 . The contacting member  74  contacts the peripheral surface of the developing roller body  27   
         [0089]    The contacting member  74  is formed of a conductive resin and is substantially in a rectangular plate shape in cross section having a thickness in the front-rear direction. A lower surface  75  of the contacting member  74  extends in the front-rear direction. 
         [0090]    The first support member  72  is formed of a metal plate having a thickness larger than the thickness of the blade member  71 . The first support member  72  is substantially L-plate shaped in cross section. That is, the first support member  72  extends in the front-rear direction and is bent downward at its rear end portion. 
         [0091]    The second support member  73  is formed of a metal plate having a thickness larger than the thickness of the blade member  71 . The second support member  73  is substantially L-plate shaped in cross section. That is, the second support member  73  extends in the front-rear direction, and is bent downward at its rear end portion. The second support member  73  is stacked on the first support member  72  from above in such that the rear end portion (downward bending portion) of the second support member  73  is opposed to the rear end portion of the first support member  72  from the rear side thereof. 
         [0092]    An upper end portion of the blade member  71  is held between the rear end portion of the first support member  72  and the rear end portion of the second support member  73 . A lower end portion of the contacting member  74 , which is positioned above the supply roller  18 , contacts a front end of the developing roller body  27  from the front side thereof. 
         [0093]    An angle θ defined between a tangent line T and the lower surface  75  of the contacting member  74 . Here, the tangent line T passes through a lower end edge of a nip N2 between the developing roller body  27  and contacting member  74 . The angle θ is greater than or equal to 90°. The nip N1 is located below the nip N2. 
         [0094]    A blade seal  76  is interposed between the blade member  71  and a rear surface of the developing frame  33 . 
         [0095]    The blade seal  76  is formed of resin foam and is substantially formed in a rectangular plate shape in cross section having a thickness in the front-rear direction. 
       3. Developing Operation 
       [0096]    As shown in  FIGS. 1 and 2 , in a state where the developing cartridge  14  has been attached to the casing  2 , toner level L1 in the toner accommodating frame  32  is below the upper end of the partition wall  49  when projected in the front-rear direction. 
         [0097]    When the developing cartridge  14  is driven in an image forming operation, the agitators  41  in the toner accommodating frame  32  are each rotated clockwise as viewed from the left side as shown in  FIG. 2 . Further, both the developing roller  17  and the supply roller  18  are rotated counterclockwise as viewed from the left side. That is, the developing roller  17  is rotated such that the peripheral surface of the developing roller  17  passes upward through the point of the nip N2. 
         [0098]    The rotation of the agitators  41  causes the toner in the first toner accommodating frame  38  to be supplied through the first communication port  40  to the second toner accommodating frame  39  and further causes the toner in the second toner accommodating frame  39  to be supplied through the second communication port  34  to the developing frame  33 . An amount of the toner to be supplied to the developing frame  33  is controlled by the openings  46  ( FIG. 3 ) of the agitating member  45  in order to prevent the amount of toner in the developing frame  33  from being excessively increased. 
         [0099]    The toner supplied to the developing frame  33  is accumulated in the supply roller housing portion  47  to a level above the upper end portion of the partition wall  49 . 
         [0100]    The toner accumulated in the supply roller housing portion  47  is agitated by a rotation of the auger screw  50  and collected, by its own weight, into the second toner accommodating frame  39  through the space formed above the both end portions (see  FIG. 5 ) of the partition wall  49  in the left-right direction. 
         [0101]    Toner level L2 in the supply roller housing portion  47  is maintained near the level of a center axial line of the supply roller  18  by a balance between the toner supply amount from the second toner accommodating frame  39  to the developing frame  33  and the collection amount of the toner to be collected into the second toner accommodating frame  39  through the space formed above the both end portions (see  FIG. 5 ) of the partition wall  49  in the left-right direction. 
         [0102]    That is, the toner level L2 in the supply roller housing portion  47  is below the nip N2 between the contacting member  74  of the layer-thickness regulating blade  19  and the developing roller  17 . The toner level L2 is also below the nip N1. 
         [0103]    As described above, the toner in the supply roller housing portion  47  is supplied to the nip N1 between the supply roller  18  and the developing roller  17  by a rotation of the supply roller  18 . Thus, the toner is friction-charged and carried on the surface of the developing roller  17 . 
         [0104]    At this time, as shown in  FIG. 7 , direct coating particles  91  and overlapping toner particles  92  are carried on a peripheral surface S of the developing roller  17 . Specifically, the direct coating particles  91  directly contact the peripheral surface S, and the overlapping toner particles  92  is stacked (overlapped) on the direct coating toner particles  91 . 
         [0105]    A thickness of a toner later TL (see  FIG. 2 ) carried on the developing roller  17  is smaller than the thickness of the contacting member  74  but exceeds the mean volume particle diameter of the toner. Specifically, the contacting member  74  has a thickness larger than the thickness of the toner TL on the developing roller  17  in a region on the developing roller  17  upstream of the nip N2 in the rotational direction. 
         [0106]    Assuming that charges of the toner particles (the direct coating toner particles  91  and the overlapping toner particles  92 ) are almost equal, an image force F of each toner particle with respect to the surface S is inversely proportional to the square of a distance between each toner particle and surface S. 
         [0107]    That is, an image force F2 of the overlapping toner particle  92  with respect to the surface S is smaller than the image force F1 of the direct coating toner particle  91  with respect to the surface S. 
         [0108]    More specifically, assuming that one overlapping toner particle  92  is carried on two adjacent direct coating toner particles  91 , a distance between the overlapping toner particle  92  and the surface S is about 2.7 (just 1+√3) times larger than a distance between the direct coating toner particles  91  and the surface S. Accordingly, the image force F2 of the overlapping toner particles  92  with respect to the surface S is about 1/7.3 of the image force F1 of the direct coating toner particles  91  with respect to the surface S. 
         [0109]    As shown in  FIG. 2 , the toner carried on the surface of the developing roller  17  is fed upward by a rotation of the developing roller  17  from the nip N1 between the supply roller  18  and the developing roller  17 , and subsequently is brought into contact with the lower surface  75  of the contacting member  74  of the layer-thickness regulating blade  19  from the below. 
         [0110]    When the developing roller  17  is further rotated, the overlapping toner particles  92  are restricted from entering the nip N2 between the developing roller  17  and the contacting member  74  by the lower surface  75  of the contacting member  74  and eventually separated from the surface S of the developing roller  17  against the image force F2. 
         [0111]    The overlapping toner particles  92  separated from the surface S fall near the nip N1 between the supply roller  18  and the developing roller  17 , and thus, the toner is accumulated near the contact portion N1 between the supply roller  18  and the developing roller  17 . The toner level L1 in the toner accommodating frame  32  is lower than the toner level L2 in the supply roller housing portion  47 , so that when the toner level L2 exceeds the partition wall  49 , the toner accumulated near the nip N1 flows over the partition wall  49  and into the toner accommodating frame  32 . This prevents the toner near the nip N1 from being excessively accumulated in a portion above the partition wall  49 . 
         [0112]    Further, although the toner that has flowed into the gap G between the supply roller  18  and the side seal  81  is likely to flow into a contact portion between the developing roller  17  and the side seal  81  due to a rotation of the end surface of the supply roller body  28 , this inflow of the toner is prevented by the restricting wall  51  (see  FIG. 4 ). 
         [0113]    Further, although the overlapping toner particles  92  are separated from the surface S of the developing roller  17 , the direct coating toner particles  91  are strongly adhered to the surface S of the developing roller  17  by the image force F  1  thereof. Thus, the direct coating toner particles  91  are not separated from the surface S but enter the nip N2 between the developing roller  17  and the contacting member  74 . 
         [0114]    As a result, almost only the direct coating toner particles  91  are left on the surface S of the developing roller  17 , and the average value of the thickness of the toner layer TL on the downstream side relative to the nip N2 in the rotational direction becomes equal to or less than the mean volume particle diameter of the toner. That is, almost all particles contact directly on the surface S at the downstream side to the nip N2. In this case, when the average value of the thickness of the toner layer TL is precisely measured, the average value of the thickness of the toner layer TL becomes generally smaller than or equal to the mean volume particle diameter of the toner. 
         [0115]    More specifically, the average value of the toner layer TL on the downstream side relative to the nip N2 in the rotational direction is, e.g., 3.5 μm to 7.0 μm, preferably, 4.5 μm to 6.0 μm. 
         [0116]    The average value of the thickness of the toner layer TL can be measured by using a measuring apparatus capable of measuring a surface state in a non-contact manner, such as Ultra-deep color 3D profile measurement microscope VK-9500 manufactured by KEYENCE. 
         [0117]    Thereafter, as described above, the toner carried on the surface of the developing roller  17  is supplied to the electrostatic latent image formed on the photosensitive drum  13  to develop the electrostatic latent image. 
       4. Operations and Effects 
       [0118]    (1) According to a developing method using the developing cartridge  14 , as shown in  FIG. 6 , the average value of the thickness of the toner layer TL carried on the surface S of the developing roller  17  can be reduced to equal to or less than the mean volume particle diameter of the toner, that is, almost all the toner particles can be directly carried on the surface S of the developing roller  17 . 
         [0119]    This reduces the number of the overlapping toner particles  92  carried on the surface S of the developing roller  17  in an overlapping manner. 
         [0120]    As a result, after the toner passes through the nip N2, separation of the toner from the developing roller  17  can be prevented, which in turn leads to an increase in the image forming speed. 
         [0121]    (2) Further, according to a developing method using the developing cartridge  14 , as shown in  FIG. 2 , the lower surface  75  of the contacting member  74  is brought into contact with the developing roller  17  so as to form an angle θ of equal to or more than 90° with respect to the tangent line T of the developing roller  17  that passes through the lower end edge of the nip N2. 
         [0122]    That is, the contacting member  74  can contact the surface S of the developing roller  17  so as to scrape off the toner carried on the surface S of the developing roller  17 . 
         [0123]    As shown in  FIG. 7 , the overlapping toner particles  92  carried on the surface S in an overlapping manner is small in terms of image force F2 with respect to the surface S of the developing roller  17 , so that the overlapping toner particles  92  are scraped off from the surface S of the developing roller  17  by the contacting member  74 . 
         [0124]    On the other hand, the direct coating toner particles  91  directly carried on the surface S of the developing roller  17  are strongly adhered to the surface S of the developing roller  17  by the image force F1, so that the direct coating toner particles  91  are not scraped off by the contacting member  74  but passed through the nip N2 between the contacting member  74  and the developing roller  17  while being carried on the surface S of the developing roller  17 . 
         [0125]    As a result, the number of the overlapping toner particles  92  can be reduced. 
         [0126]    (3) Further, according to the developing cartridge  14 , as shown in  FIG. 2 , the thickness of the toner layer TL on the lower side of the lower end portion of the contacting member  74  (on the upstream side of the developing roller  17  in the rotational direction) is smaller than the thickness of the contacting member  74 . 
         [0127]    Thus, the overlapping toner particles  92  can reliably be brought into contact with the lower surface  75  of the contacting member  74  and can be separated from the developing roller  17 . 
         [0128]    Further, the scraping-off of the toner by the contacting member  74  is likely to be insufficient when an excessive amount of toner is accumulated around the nip N2; however, this can completely be prevented by reducing the thickness of the toner layer TL. 
         [0129]    (4) Further, according to a developing method using the developing cartridge  14 , the contacting member  74  is formed of a conductive resin. 
         [0130]    This can prevent the contacting member  74  from being charged with a reverse polarity (negative charge) to a toner polarity (positive charge) when being brought into (frictional) contact with the toner. 
         [0131]    (5) Further, according to the developing cartridge  14 , as shown in  FIGS. 2 and 6 , the both ends of the supply roller body  28  in the left-right direction are disposed spaced apart from the inner surfaces of the side seals  81  in the left-right direction. Further, the upper end portion of the partition wall  49  is disposed below the nip N1 between the developing roller  17  and the supply roller  18 . 
         [0132]    Thus, even if a part of the toner supplied to the nip N1 between the developing roller  17  and the supply roller  18  is not carried on the developing roller  17  but pushed outward in the left-right direction from the nip N1, the pushed toner can be collected in the supply roller housing portion  47  through gaps (the space TF in  FIG. 6 ) between the end of the supply roller body  28  in the left-right direction and the inner surface of the side seals  81  in the left-right direction. 
         [0133]    This can prevent the toner pushed outward in the left-right direction from the nip N1 from entering between the side seals  81  and the developing roller  17 . 
         [0134]    As a result, toner leakage from the end portions of the developing roller  17  in left-right direction can be prevented. 
         [0135]    (6) Further, according to the developing cartridge  14 , as shown in  FIG. 5 , the restricting walls  51  for restricting passage of the toner are provided between the end portions of the supply roller body  28  in the left-right direction and the side seals  81 . 
         [0136]    This configuration prevents a rotation of the end surfaces of the supply roller body  28  from influencing the toner that has entered the gaps G and restricts the toner from being passed to the contact portions between the developing roller  17  and the side seals  81  by a rotation of the end surfaces of the supply roller body  28 . Thus, this configuration prevents an increase in the toner amount in the gaps between the ends of the supply roller body  28  in the left-right direction and the inner surfaces of the side seal  81  with respect to the left-right direction. 
         [0137]    As a result, toner leakage from the both end portions of the developing roller  17  in the left-right direction can be further prevented. 
         [0138]    (7) Further, according to the developing cartridge  14 , as shown in  FIG. 2 , the toner in the supply roller housing portion  47  can be agitated by the auger screw  50  provided between the partition wall  49  and the supply roller  18 . 
         [0139]    Thus, even if the toner level L2 in the supply roller housing portion  47  is low, the toner can be supplied uniformly and stably to the supply roller  18 . 
         [0140]    (8) Further, according to the developing cartridge  14 , as shown in  FIG. 2 , the toner is accumulated in the supply roller housing portion  47  at a portion above the upper end portion of the auger screw  50 . 
         [0141]    Thus, a variation in the toner level L2 in the supply roller housing portion  47  is prevented by a rotation of the auger screw  50 , thereby stabilizing the toner level L2. 
         [0142]    (9) Further, according to the developing cartridge  14 , as shown in  FIG. 2 , the toner is accumulated in the supply roller housing portion  47  at a portion below the nip N1 between the developing roller  17  and the supply roller  18 . 
         [0143]    Thus, even if a part of the toner supplied to the nip N1 between the developing roller  17  and the supply roller  18  is not carried on the developing roller  17  but pushed outward in the left-right direction from the nip N1, the pushed toner can be made to fall for collection in the supply roller housing portion  47  through gaps between the end of the supply roller body  28  in the left-right direction and the inner surfaces of the side seals  81  in the left-right direction. 
         [0144]    This configuration can prevent the toner pushed outward in the left-right direction from the nip N1 from entering between the side seals  81  and the developing roller  17 . 
         [0145]    As a result, toner leakage from the end portions of the developing roller  17  in the left-right direction can be prevented. 
       5. Modifications 
       [0146]    While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention. 
         [0147]    In the following modifications, the same reference numerals are given to the same parts as in the above embodiment, and the descriptions thereof will be omitted. 
         [0148]    In the above embodiment, the toner in the supply roller housing portion  47  is agitated by the auger screw  50 . 
         [0149]    Alternatively, as shown in  FIG. 8 , a brush  96  is substantially formed in a columnar shape extending in the left-right direction may be used in place of the auger screw  50  to agitate the toner in the supply roller housing portion  47 . 
         [0150]    Further, as shown in  FIGS. 9(   a ) and  9 ( b ), a crankshaft  97  having a shape bent in a U-shape may be used in place of the auger screw  50  to agitate the toner in the supply roller housing portion  47 . A shaft drive gear  98  for inputting a drive force to the crankshaft  97  is supported at a right end portion of the crankshaft  97  so as not to be relatively rotated. 
         [0151]    Further, as illustrated in  FIGS. 10(   a ) and  10 ( b ), a slide member  100  that is substantially U-shaped may be supported at end portions of a circulation part of the crankshaft  97  so as to be relatively rotated. In this case, the crankshaft  97  is rotated, as well as the slide member  100  is slid in the front-rear direction so as to agitate the toner in the supply roller housing portion  47 . 
         [0152]    In the above embodiment, the contacting member  74  of the layer-thickness regulating blade  19  is formed of a conductive resin. Alternatively, the contacting member  74  may be formed of a metal plate spring (conductive elastic body).