Abstract:
A developing device includes a rotatable developer carrying member for carring a developer; a magnet roller provided in the developer carrying member; a first electrode portion connected electrically with the developer carrying member, the first electrode portion being rotatable with the developer carrying member; a second electrode portion provided with a contact portion in sliding contact with the first electrode portion, the contact portion being disposed outside a longitudinal end portion of the magnet roller substantially at a center of rotation of the developer carrying member.

Description:
FIELD OF THE INVENTION AND RELATED ART  
         [0001]    The present invention relates to such a developing apparatus that develops an electrostatic image formed on an image bearing member, with the use of developer. This type of a developing apparatus is preferably used as a developing apparatus for an image forming apparatus such as a copying machine, printer, and the like.  
           [0002]    As the cumulative usage time of an electrophotographic image forming apparatus reaches a certain point, it becomes necessary to replace the photosensitive drum, to replenish or replace developer, and/or to adjust, clean, and/or replace the charging device, cleaning means container, and the like. These maintenance operations have been generally difficult, except for service personnel with professional knowledge.  
           [0003]    In order to eliminate this inconvenience, a process cartridge, or a cartridge in which an image bearing member (photosensitive drum), and a single or plural image processing means, for example, a developing apparatus, a cleaning apparatus, and the like, are integrally placed, has been commercialized.  
           [0004]    As a result, it has become simple for users themselves to maintain an image forming apparatus, or replace the aforementioned processing means as it becomes necessary for an image forming apparatus to be maintained. Therefore, it has become easy and inexpensive to obtain high quality images.  
           [0005]    The aforementioned developing apparatus, or one of the components which a process cartridge comprises, has a development roller as a developer bearing member which is placed in a manner to oppose a photosensitive drum as an image bearing member. The development roller has a development sleeve, and a magnetic roll. The magnetic roll is non-rotational placed in the development sleeve, and the development sleeve is rotated about the magnetic roll. In order to transfer the toner uniformly borne on the peripheral surfaces of the development sleeve, onto an electrostatic latent image on the peripheral surfaces of the photosensitive drum, bias is applied to the development sleeve. As for a means for applying bias to the development sleeve, a method illustrated in FIG. 12 has been proposed. According to this method, a flange  102  formed of electrically conductive material is fixed to one of the longitudinal ends of a development sleeve  101 , and an electrode  105  in the form of a compression coil spring is fitted around the flange  102  in a manner to allow electricity to flow between the two components. One end of the electrode  105  is attached to the housing  104  of a developing apparatus so that, as the developing apparatus is mounted in the main assembly of an image forming apparatus, the electrode  105  is placed in contact with an electrical contact electrically connected to a power supply provided on the main assembly side.  
           [0006]    As for a means for supporting a magnetic roll  103 , the housing  104  of the developing apparatus is provided with a positioning hole  104   a , the axial line of which coincides with that of the development sleeve  101 , and in which the smaller diameter portion  103   a  of the magnetic roll  103  is fitted to dictate the distance between the peripheral surfaces of the magnetic roll  103  and development sleeve  101 . However, a much simpler magnetic roll supporting method than the above described one has been desired.  
           [0007]    In the case of the above described magnetic roll supporting method, the electrode  105  or flange  102  rotates with the development sleeve  101  which sliding on the contact on the main assembly side. Therefore, it is a common practice to coat the contact areas of the electrode  105  and contact on the main assembly side. This contact area is desired to be as small as possible so that the interface in which the two components slide against each other becomes as small as possible.  
           [0008]    In order to stabilize the contact pressure between the electrode  105  and contact on the main assembly side, it is desirable to reduce the spring constant of the elastic contact (compression coil spring which constitutes electrode  105 ), so that the amount of flexing of the electric contact increases. For this purpose, it is necessary to provide the aforementioned developing apparatus with an internal space long in terms of the longitudinal direction of the developing apparatus.  
         SUMMARY OF THE INVENTION  
         [0009]    The primary object of the present invention is to provide a developing apparatus, the sliding contact of which is smaller than a conventional one.  
           [0010]    Another object of the present invention is to provide a developing apparatus, the sliding contact of which is more reliable than a conventional one.  
           [0011]    Another object of the present invention is to provide a developing apparatus, the magnetic roll of which is positioned with a higher degree of accuracy than in the conventional one.  
           [0012]    Another object of the present invention is to provide a developing apparatus, the spacial efficiency of which in terms of the longitudinal direction of the developing apparatus is superior than that of the conventional one.  
           [0013]    These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic sectional view of the process cartridge in an embodiment of the present invention, at a plane perpendicular to the longitudinal direction of the process cartridge.  
         [0015]    [0015]FIG. 2 is a schematic sectional view of the main assembly of an image forming apparatus in which a process cartridge is exchangeably mountable, at a plane perpendicular to the longitudinal direction of the process cartridge.  
         [0016]    [0016]FIG. 3 is an exploded perspective view of the frame portions of the process cartridge illustrated in FIG. 1.  
         [0017]    [0017]FIG. 4 is a perspective view of the process cartridge illustrated in FIG. 1  
         [0018]    [0018]FIG. 5 is a perspective view of the developing means frame portion of the process cartridge illustrated in FIG. 1.  
         [0019]    [0019]FIG. 6 is a plan view of the longitudinal end of the process cartridge, prior to the placement of the side cover, on the side from which the process cartridge is not driven.  
         [0020]    [0020]FIG. 7 is a drawing for depicting the movements of the two frame portions of the process cartridge relative to each other.  
         [0021]    [0021]FIG. 8( a ) is a perspective view of the contact plate on the sleeve side, and FIG. 3( b ) is perspective view of the magnetic roll bearing.  
         [0022]    [0022]FIG. 9 is an exploded perspective view of the development roller in an embodiment of the present invention.  
         [0023]    [0023]FIG. 10 is an exploded perspective view of the development roller and side cover in an embodiment of the present invention.  
         [0024]    FIGS.  11 ( a, b  and  c ) are vertical sectional drawings for showing the order in which the development roller illustrated in FIG. 9 is assembled.  
         [0025]    [0025]FIG. 12 is a vertical sectional view of the contact on the sleeve side of a conventional process cartridge, and its adjacencies. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Hereinafter, the preferred embodiments of the present invention will be described with reference to FIGS.  1 - 11 .  
       [Description of Process Cartridge and Image Forming Apparatus Main Assembly] 
       [0027]    [0027]FIG. 1 is a sectional view of the process cartridge in an embodiment of the present invention, at a plane perpendicular to the longitudinal direction of the process cartridge, and FIG. 2 is a sectional view of the image forming apparatus in the embodiment of the present invention, in which the process cartridge illustrated in FIG. 1 is exchangeably mountable, at a plane perpendicular to the longitudinal direction of the process cartridge in the image forming apparatus.  
         [0028]    This process cartridge has an electrophotographic photosensitive drum (hereinafter, “photosensitive drum”) as an image bearing member, and a single or plural processing means. As for the processing means, there are, for example, a charging means for charging the peripheral surfaces of the photosensitive drum, a developing apparatus for developing an electrostatic latent image on the photosensitive drum into a toner image, and a cleaning means for removing the toner remaining on the peripheral surfaces of the photosensitive drum.  
         [0029]    Referring to FIG. 1, the process cartridge in this embodiment comprises: a photosensitive drum  11  as an image bearing member, a charge roller  12  as a charging means, a development roller  18  as a developer bearing member, a development blade, a toner holding portion  16  in which toner is held, a cleaning blade  14  as a cleaning means, and a housing in which the preceding components are integrally placed so that they can be removably mounted in the main assembly C of an image forming apparatus. The development roller  18  and development blade are components of a developing apparatus. These components, except for the photosensitive drum  11 , are placed around the peripheral surfaces of the photosensitive drum  11 .  
         [0030]    Referring to FIG. 2, the process cartridge  15  is mounted in the image forming apparatus main assembly C to be used for image formation. In an image forming operation, a sheet S is fed out of a sheet cassette  6  mounted in the bottom portion of the image forming apparatus, by a conveying roller  7 . In synchronism with this feeding of the sheet S, the peripheral surfaces of the photosensitive drum  11  is selectively exposed to a beam of light projected from an exposing apparatus  8 , to form a latent image on the peripheral surfaces of the photosensitive drum  11 . Thereafter, the toner stored in the toner contained  16  is coated in a thin layer on the peripheral surfaces of the development roller  18  by a development blade, and development bias is applied to the development roller  18 . As a result, the toner is supplied to the peripheral surfaces of the photosensitive drum  11  in accordance with the latent image, forming a toner image. This toner image is transferred onto the sheet S, which is being conveyed, by the application of bias voltage to transfer roller  9 . Then, the sheet S is further conveyed to a fixing apparatus  10 , in which the toner image is fixed to the sheet S. Then, the sheet S is discharged into a delivery portion  2  located on top of the apparatus main assembly, by a sheet discharging roller  1 .  
       [Structure of Process Cartridge Frame] 
       [0031]    [0031]FIGS. 3 and 4 are perspective views of the process cartridge. FIG. 3 is a drawing prior to the process cartridge assembly, whereas FIG. 4 is a drawing after the completion of the process cartridge assembly.  
         [0032]    The process cartridge  15  comprises three frame portions: a cleaning means frame portion which integrally supports the photosensitive drum  11 , charge roller  12 , and cleaning blade  14 ; a developing means frame portion which supports the development roller  18  and development blade; and a toner holding frame portion  16  which holds toner. Three frame portions are positioned so that the developing means frame portion  17  is interposed between the cleaning means frame portion  13  and developer holding frame portion  16 .  
         [0033]    Further, in order to keep these three frame portions held together, side covers  19  and  20  are attached to the longitudinal ends of the three frame portions, one for one.  
         [0034]    (1) Cleaning Means Frame Portion  13   
         [0035]    In the cleaning means frame portion  13 , the cleaning blade  14  is fixed to the cleaning means frame portion  13  with the use of small screws or the like, and the charge roller  12  is rotationally supported by a bearing (unillustrated) located at each of the longitudinal ends of the process cartridge to support the metallic core portion of the charge roller  12 .  
         [0036]    Also in the cleaning means frame portion  13 , the photosensitive drum  11  is rotationally supported by the cleaning means frame portion  13 , with the interposition of bearings  22  which supports the flange portions  11   a  and  11   b  located at the ends of the photosensitive drum  11 , one for one.  
         [0037]    (2) Toner Holding Frame Portion  16   
         [0038]    The toner holding portion  16  contains a toner conveying member (unillustrated) as well as toner. The details of the developing means frame portion  17  will be described later. The side cover  19  on the non-driven side, that is, the side opposite to the side from which driving force is transmitted to the process cartridge  15  from the image forming apparatus main assembly, has a size which matches the size of the cross section of the process cartridge  15  at a plane perpendicular to the longitudinal direction of the process cartridge  15 . The side cover  19  is placed on one of the longitudinal ends of the process cartridge  15 , and holds together the cleaning means frame portion  13  and toner holding frame portion  16 .  
         [0039]    The side cover  19  is positioned in such a manner that the axial line of the hole  19   a  of the side cover  19  coincides with that of the axial line of the photosensitive drum  11  within the cleaning means frame portion  13 . The position of the side cover  19  can be highly precisely fixed with the interposition of the bearing  22 . The positioning portion  19   b  of the side cover  19  is located on the inward surface of the side cover  19  so that the distance between the positioning portion  19   b  and the photosensitive drum  11  after the attachment of the side cover  19  to the cleaning means frame potion  13  and developer holding frame portion  16  becomes as large as possible. The attitude of the side cover  19  relative to the cleaning means frame portion  13  is dictated by the engagement of the positioning portion  19   b  with a positioning portion  13   b  provided on the outward surface of the side wall of the cleaning means frame portion  13 . The side cover  19  and cleaning means frame portion  13  are fixed to each other, with the use of several small screws.  
         [0040]    The toner holding frame portion  16  is provided with positioning portions  16   a  and  16   b , which are located on the side wall of the toner folding frame portion  16 . The attitude of the toner holding frame portion  16  relative to the side wall  19  is dictated by the engagement of the positioning portions  16   a  and  16   b  with the positioning portions  19   c  and  19   d , respectively, located on the inward side of the side cover  19 . The side cover  19  and toner holding frame portion  16  are fixed to each other with the use of several small screws.  
         [0041]    Also, the side cover  20 , or the side cover on the driven side of the process cartridge, positions the developing means frame portion  17  with the use of a method which will be described later.  
         [0042]    The bearing  22  doubles as a member for positioning the process cartridge  15  relative to the image forming apparatus. Since toner is supplied to the development sleeve  18  from the toner holding frame portion  16 , the toner holding frame portion  16  and developing means frame portion  17  are provided with holes  17   a  and  16   c , respectively.  
         [0043]    The developing means frame portion  17  and toner holding frame portion  16  are connected to each other, with the interposition of a sealing member  21 , in such a manner that the holes  17   a  and  17   c  align with each other.  
       [Toner Holding Frame Portion] 
       [0044]    The toner holding frame portion  16  is fixed to the side covers  19  and  20 , and the developing means frame portion  17  is fixed to the cleaning means frame portion  13 . Therefore, it is possible that either the developing means frame portion  17  or toner holding frame portion  16  will be deformed due to the errors in the dimensions of the two frame portions. Therefore, the sealing member is formed of flexible material.  
         [0045]    With the provision of the above described structural arrangement, even if the amount of toner is increased, the load from the toner falls on the side covers; it does not fall on the development sleeve. In other words, since the load from toner is not transmitted to the developing means frame portion  17  regardless of the amount of the toner within the toner holding frame portion  16 , the positional relationship between the development sleeve  18  and photosensitive drum  11  is precisely maintained. Therefore, the photosensitive drum  11  is not subjected to an excessive amount of load, making it possible for the image forming apparatus to continuously produce high quality images.  
         [0046]    In addition, this structural arrangement of connecting these frame portions by their longitudinal ends makes it possible to position these frame portions relative each other, with the use of only side covers, which in turn makes it possible to connect these frame portions with a high degree of precision.  
       [Structure of Developing Means Frame Portion] 
       [0047]    The developing means frame portion  17  holds the development roller, the development blade, and a magnetic seal (unillustrated). The development roller comprises the development sleeve  18  and magnetic roll  26 .  
         [0048]    The magnetic roll  26  is supported by the internal surface of the development roller in a manner to keep contact the gap between the magnetic roll  26  and the development sleeve  18 . The power to the development sleeve  18  is supplied through an electrical contact point placed within the development sleeve  18 . These arrangements will be described in detail later. The development roller is provided with spacer rings (unillustrated), which are fitted around the development roller to maintain a predetermined gap between the development roller and photosensitive drum  11 .  
         [0049]    Referring to FIG. 6, the developing means frame portion  17  is supported in such a manner to allow the developing means frame portion  17  to pivot about the axial line of the hole  17   d  of the developing means frame portion  17  located on the driven side (right side in FIG. 3) of the development sleeve  18 , in such a manner that the axial line of the development sleeve  18  moves toward the axial line of the photosensitive drum  11 .  
         [0050]    In other words, the developing means frame portion  17  comprising the development sleeve  18  is attached to the driving side of the cleaning means frame portion  13  in a manner to allow the developing means frame portion  17  to pivot about the axial line of the hole  17   d . Since the cleaning means frame  13  and toner holding frame portion  16  are solidly fixed to each other as described above, the developing means frame portion  17  is movable relative to the toner holding frame portion  16 .  
         [0051]    In addition, referring to FIGS. 5 and 6, the non-driven end of the developing means frame portion  17  in terms of the longitudinal direction of the development sleeve  18  is provided with a developer roller pressing sleeve  17   e  (one end of the magnetic roll  26  is fitted in this sleeve  17   e ), the axial line of which coincides with the axial line of the development roller. The developing means frame portion  17  is structured so that the axial line of this development roller pressing sleeve  17   e  is pressed toward the axial line of the photosensitive drum  11 .  
         [0052]    The development roller pressing sleeve  17   e  is inserted in an elongated groove  19   e  (in this embodiment, elongated straight hole parallel the radial direction of the photosensitive drum  11 ) in such a manner that the axial line of the development roller pressing sleeve  17   e  is allowed to move in the direction parallel to radial direction of the photosensitive drum  11 . Also referring to FIGS.  5  and  6 , within the elongated groove  19   c , a coil spring  43   b , the one end of which is provided with a contact plate  43   a , is placed in a manner to press the development roller pressing sleeve  17   e  toward the axial line of the photosensitive drum  11 .  
         [0053]    This groove  19   e  also plays a role in regulating the moving direction of the development sleeve  18 .  
         [0054]    The developing means frame portion  17  is structured in such a way that the developing means frame portion  17  is made to pivot about the axial line of the hole  17   d  by the resiliency of a spring  44  in the direction to cause the gears (these the gears of the photosensitive drum  11  and development roller are not illustrated, but are meshed with each other), with which the photosensitive drum  11  and development roller are provided to drive the photosensitive drum  11  and development roller, to mesh deeper with each other as driving force applies to the development roller and the photosensitive drum  11 . In other words, the developing means frame portion  17  is structured so that the driving force does not work in the direction to cause the photosensitive drum  11  and development sleeve  18  to separate from each other. Further, the development sleeve  18  is also kept pressed toward the photosensitive drum  11  by the above described development roller pressing sleeve  17   e.    
         [0055]    In other words, in this embodiment, the developing means frame portion  17  and toner holding frame portion  16  are movable relative to each other, and therefore, the two frame portions  17  and  16  are connected to each other, with the interposition of a sealing member  21  capable of tolerating the movement of the two frame portions  17  and  16  relative to each other within a predetermined range, to prevent toner leakage. The sealing member is desired to be shaped to be small in the resiliency which acts to interfere with the movement of the developing apparatus. More specifically, it is desired to be shaped to have a minimum of one folding line, or preferably, to be in the form of a section of bellows.  
         [0056]    The sealing member  21  in this embodiment is formed of elastomer, and has two folding lines (unillustrated) to reduce the resiliency. However, materials superior in flexibility such as foamed urethane, rubber with a low degree of hardness, silicone rubber, and the like, may be used as the material for the sealing member  21 . In such a case, if the material is low in resiliency, the sealing member  21  can provide the same effects as if it had folding lines or was shaped like a section of bellows, even if it is not shaped to have folding lines or to look like a section of bellows.  
       [Structure for Supplying Development Roller with Electrical Power, and Structure for Supporting Magnetic Roll] 
       [0057]    At this time, the structure for supplying the development roller with electrical power, and the structure for supporting the magnetic roll, in this embodiment, will be described in detail.  
         [0058]    [0058]FIG. 8( a ) and FIG. 8( b ) are perspective views of the sleeve contact plate  25  and magnetic roll bearing  27 , respectively. FIG. 9 is an exploded perspective view of the components of the development roller prior to their assembly, and FIG. 10 is a perspective view of the development roller and side cover before they are put together. FIG. 11 is a sectional view of the development roller at a plane which includes the axial line of the development roller.  
         [0059]    The development roller comprises the development sleeve  18 , sleeve flange  23 , and magnetic roll  26 . Referring to FIG. 9, the development sleeve  18 , or a component of the development roller, is a cylindrical member formed of metallic material such as aluminum, stainless steel, or the like, and is approximately 16-20 mm in external diameter, and approximately 0.5-1 mm in cylinder wall thickness. In order to improve the efficiency with which developer is charged, the surface of the development roller  18  is coated with carbon, is sandblasted, or is subjected to the like processes. In this embodiment, it is simply coated with carbon. Each of the longitudinal ends of the development sleeve  18  has a section into which a sleeve flange  23 , which will be described later, is fixed by press-fitting.  
         [0060]    Referring to FIG. 9, the sleeve flange  23  is formed of metallic material such as aluminum, stainless steel, or the like, and is fixed to each of the longitudinal ends of the development sleeve  18 , by being pressed into the longitudinal end of the development sleeve  18 . The sleeve flange  23  is a stepped cylindrical member. In FIG. 9, only the driven side is illustrated, but the non-driven side has the same structure.  
         [0061]    The sleeve flange  23  is made up of a cylindrical portion  23   c  with a larger external diameter, and a cylindrical portion with a smaller external diameter compared to that of the larger external diameter portion. The cylindrical portion with the larger external diameter is a portion which is pressed into the through hole of the development sleeve  18  to fix the sleeve flange  23  to the development sleeve  18 . The sleeve flange  23  is non-rotationally fixed to the development sleeve  18  by being pressed into the development sleeve  18  as described above. Thus, the sleeve flange  23  rotates with the development sleeve  18 .  
         [0062]    If the alignment between the development sleeve  18  and sleeve flange  23  is not proper, an image which is not uniform in density, or an image with the like defect, is likely to be produced. Therefore, the development sleeve  18  and sleeve flange  23  are precisely fixed to each other.  
         [0063]    The sleeve flange  23  is also provided with a portion  23   e , that is, a portion of the internal surface of the portion  23   c  to be pressed in, to which the magnetic roll bearing  27 , which will be described later, is anchored, and a groove  23   d  for regulating the rotation of the magnetic roll bearing  27 . The portion  23   e  and groove  23   d  are within the portion  23   c  to be pressed in.  
         [0064]    A portion  23   b  of the sleeve flange  23  on the immediately outward side of the portion  23   c  is smaller in diameter than the portion  23   c , and remains outside the development sleeve  18  after the pressing of the portion  23   c  of the sleeve flange  23  into the development sleeve  18 . The axial lines of the portions  23   b  and  23   c  coincide.  
         [0065]    Around the circumference of this portion  23   b  of the sleeve flange  23 , a gap regulating member  29  for regulating the distance between the peripheral surfaces of the development sleeve  18  and photosensitive drum  11 , a sleeve bearing  30  by which the development roller is rotationally supported by the developing means frame portion  17 , and a sleeve gear  31  through which driving force is transmitted to the development sleeve  18  from the photosensitive drum  11  to rotate the development sleeve  18 , are fitted.  
         [0066]    The sleeve bearing  30  is fixed to the developing means frame portion  17 ; the sleeve bearing  30  is fitted in a bearing hole  30   a  of the developing means frame portion  17 . Further, the sleeve gear  31  is non-rotationally fixed to the development roller. The sleeve gear  31  has a through hole  23 , the axial line of which coincides with that of the outside portion  23   b  of the sleeve flange  23 . Through this through hole  23   a , a metallic electrode  24  in the form of a shaft, which will be described later, is put to transmit electrical power inward of the development sleeve  18 . A surface  23   f  of the sleeve flange  23 , or the inward surface, perpendicular to the longitudinal direction of the development roller, of the sleeve flange  23 , is a surface for fixing the position of the magnetic roll bearing  27 , which will be described later, in terms of the longitudinal direction of the development roller.  
         [0067]    Referring to FIG. 9, the magnetic roll  26  has a portion  26   a  with a larger diameter, and two shaft portions  26   b  with a smaller diameter, located on each side of the portion  26   a . The large diameter portion  26   a  is placed within the development roller, and is provided with a plurality of magnetic poles which are distributed in the circumferential direction of the magnetic roll  26  and are exposed at the peripheral surfaces of the magnetic roll  26 . Normally, the magnetic roll  26  is positioned so that one of its magnetic poles squarely opposes the photosensitive drum  11  while the other poles are also properly distributed in terms of the circumferential direction of the magnetic roll  26 . In this embodiment, the number of the magnetic poles is four.  
         [0068]    In order to keep the magnetic force stable at the peripheral surface of the development sleeve  18 , the distance between the peripheral surfaces of the large diameter portion  26   a  and the peripheral surfaces of the development sleeve  18  must be kept constant. In order to keep this distance constant, one of the shaft portions  26   c  is supported by the side cover  19  illustrated in FIG. 3. This shaft portion  26   c  is non-rotationally fitted in the development roller pressing sleeve  17   e , and this development roller pressing sleeve  17   e  is fitted in the elongated groove  19   e  of side cover  19 , being therefore supported by the side cover  19 .  
         [0069]    More specifically, the D-cut portion  26   c   1  of the shaft portion  26   c  is fitted into the hole of the development roller pressing sleeve  17   e , with a D-shaped cross section, so that the positions of the magnetic poles in terms of the circumference direction of the development roller are fixed.  
         [0070]    The shaft portion  26   b , or the other shaft portion, of the magnetic roll  26  is supported by the magnetic roll bearing  27 , which is anchored to the portion  23   d , or a portion of the internal surface of the large diameter portion, of the sleeve flange  23 . The portion  23   d  of the sleeve flange  23  will be described later.  
         [0071]    Referring to FIGS.  8 ( b ) and  9 , the magnetic roll bearing  27  is a molded member with a D-shaped cross section.  
         [0072]    The magnetic roller bearing  27  has a main portion  27   d  with the D-shaped cross section, a rotation controlling portion  27   c  in the form of a dowel. The main portion  27   d  has a flat surface  27   f  comparable to the straight line of a letter D. The main portion  27   d  with the D-shaped cross section is anchored to the portion  23   e  of the sleeve flange  23  illustrated in FIG. 9, and the rotation controlling portion  27   c  is fitted in the groove  23   d . Therefore, the magnetic roll bearing  27  rotates with the sleeve flange  23 .  
         [0073]    The dowel-like rotation controlling portion  27   c  projecting from the flat surface  27   f  in the direction perpendicular to the axial line of the development sleeve  18 , and the flat surface  27   f , supports and accurately position, the sleeve contact plate  25 , which will be described later.  
         [0074]    The bearing hole of the magnetic roll bearing  22  also doubles as a positioning hole  27   a . This hole  27   a  is 5-10 mm in diameter, and 3-8 mm in depth. In order to precisely position the magnetic roll, the hole  27   a  is finished very precisely, more specifically, with its accuracy in internal diameter being in class 8-9, and its surface roughness R being at about 0.8 μm.  
         [0075]    The magnetic roll  26  is non-rotationally fixed, whereas the magnetic roller bearing  27  and sleeve flame  23  rotate with the development sleeve  18 . Therefore, the peripheral surfaces of the shaft portion  26   b  and the cylindrical surface of the hole  27   a  slide on each other. Therefore, material superior in slipperiness against the magnetic roll  26 , for example, PPS or the like, is used as the material for the magnetic roll bearing  27 . Further, the magnetic roller bearing  27  has a collar portion  27   g , which is placed in contact with the end surface  23   f  of the sleeve flame  23  to fix the position of the magnetic roller bearing  27  relative to the development sleeve  18  in terms of the longitudinal direction of the development roller, and a dowel-like projection  27   b  to which the sleeve contact plate  25  is fixed. The dowel-like projection  27   b  projects from the collar portion  27   g.    
         [0076]    Referring to FIGS.  8 ( a ) and  9 , the sleeve contact plate  25  is a U-shaped member having opening first and second portions virtually perpendicularly to the longitudinal direction of the development roller, and a rectangular center portion  25   g  which connects these first and second portions. It is formed of 0.1-0.3 mm thick plate of electrically conductive, springy material (for example, Cu alloy, or Fe alloy such as SUS). It is fixed to the magnetic roller bearing  27  in such a manner that the opposing two portions and rectangular portion  25   g  partially cover the end surfaces and flat surface  27   f  of the magnetic roller bearing  27 , respectively. More specifically, the dowel-like projection  27   b  of the magnetic roller bearing  27  is fitted in a hole  25   b  formed in one of the opposing two portions of the sleeve contact plate  25 , and the dowel-like rotational controlling portion  27   c  of the magnetic roll bearing  27  is fitted in the hole  25   e  formed in the rectangular portion  25   g  of the sleeve contact plate  25 , with the rectangular portion  25   g  placed flatly in contact with the flat surface  27   f , comparable to the straight line of a letter D, of the magnetic roller bearing  27 .  
         [0077]    The fixation of the dowel-like portions in the holes is accomplished by thermal welding supersonic welding, glueing, or the like methods. During this process, the dowel-like projections  27   c  and  27   e  of the magnetic roller bearing  27  are approximately semispherically reshaped. It should be noted here that although the dowel-like projection  27   c  is on the flat surface  27   f , the dowel-like projection  27   c  after its semispherical reshaping is not high enough for the highest portion of the reshaped projection  27   c  to extend beyond the imaginary cylindrical extension of the cylindrical surface of the main potion  27   d  of the magnetic roller bearing  27 . Therefore, the portion  23   e , or a part of the internal surface of the sleeve flange  23  has only to be made cylindrical, eliminating the cost otherwise necessary for complicated processing.  
         [0078]    The sleeve contact plate  25  is provided with arm portions  25   a  and  25   h  which contact the internal surface of the development sleeve  18 , and are electrically connected with the development sleeve  18 . These arm portions  25   a  and  25   h  are symmetrically positioned with respect to the rotational axis of the development sleeve  18 . This positional arrangement is made to equalize the insertion resistance generated during the insertion of the sleeve contact plate  25  into the development sleeve  18 . Referring to FIG. 11( c ), the arm portions  25   a  and  25   h  are bent at an acute angle relative to the magnetic roll bearing insertion direction so that, as the sleeve flane  23  is inserted into the development sleeve  18 , the arm portions  25   a  and  25   h  are bent backward in terms of the direction in which the sleeve flange  23  is inserted as indicated by an X mark, in other words, they are bent in the direction to counter the force which works in the direction to move the magnetic roller bearing  27  out of the sleeve flange  23 . Therefore, a problem such that the magnetic roll bearing  27  comes out of the sleeve flange  23  does not occur.  
         [0079]    Further, as described above, the collar portion  27   g  of the magnetic roller bearing  27  contacts the end surface  23   f  of the sleeve flange  23 , and therefore, the positions of the magnetic roller bearing  27  and sleeve contact plate  25  relative to the development sleeve  18  in terms of the longitudinal direction of the development roller are perfectly fixed. There is a through hole  25   c  between the arm portions  25   a  and  25   h , which is slightly greater in diameter than the shaft portion  26   b  of the magnetic roll  26 , and the axial line of which coincides with that of the magnetic roll  26 .  
         [0080]    Therefore, while the magnetic roll  26  is supported by the magnetic roller bearing  27 , the magnetic roll  26  does not contact the sleeve contact plate  25 . A portion  25   d , or one of the opposing two portions of the sleeve contact plate  25 , is provided with arm portion  25   f , which is formed by cutting a slit through the portion  25   d  and bending the portion surrounded by the slit, to make it elastically contact the shaft-like electrode  24 , which will be described later. This arm portion  25   f  is rendered springy. The portions of the sleeve contact plate  25  which elastically deform are the arm portion  25   f  sliced and bent out of the portion  25   d , and the portion  25   d.    
         [0081]    In order to keep constant the contact pressure at the contact point between the arm portion  25   f  and the shaft-like electrode  24  even if the positional relationship between the shaft-like electrode  24  and arm portion  25   f  changes due to the change in the position of the development sleeve  18  in its longitudinal direction, the spring constant of the arm portion  25   f  is desired to be as small as possible. For that purpose, making longer the spring portions (portion  25   d , or one of the opposing two portion of the sleeve contact plate  25 , arm portion  25   f , and the like) is effective.  
         [0082]    Further, the spring portions should be give a certain length in consideration of fatigue. However, the range in which the arm portion  25   f  is allowed to flex in terms of the direction perpendicular to the axial direction of the development roller is 10-15 mm in terms of the radial direction of the development roller, and in addition, the requirement that the overall size of the apparatus must be small, makes it impossible to elongate the arm portion  25   f  in the axial direction of the development roller. In this embodiment, therefore, a U-shaped hole  25   i  is punched out of the aforementioned spring portion  25  to provide the spring portion with a longer effective length, that is, the combined length of the portion  25   d  (peripheral edge) and the arm portion  25   f  (center portion).  
         [0083]    Further, the arm portion  25   f  and portion  25   d  are bent relative to each other in terms of the axial direction of the development roller so that they form a letter Z as seen from the direction perpendicular to the axial direction of the development roller, and so that they settle in the same plane perpendicular to the axial line of the development roller as the shaft-like electrode  24  makes contact with the arm portion  25   f.    
         [0084]    Referring to FIGS. 9 and 10, the shaft-like electrode  24  projects from the inward surface of the side cover  20  in such a direction that the axial line of the shaft-like electrode  24  coincides with that of the development sleeve  18 . The material for the shaft-like electrode  24  is plated steel, stainless steel, or the like. The shaft-like electrode  24  is 2 mm in external diameter. It is formed as an integer part of the side cover by insert molding, or non-rotationally and inseparably fixed to the side cover by being pressed into the side cover after the two are separately formed.  
         [0085]    When the side cover  20  is attached, this shaft-like electrode  24  is put through the through hole  23   a  of the sleeve flange  23 , and its tip portion  24   a  causes the arm portion  25   f  of the sleeve contact plate  25  to flex, so that a predetermined amount of contact pressure is maintained between the shaft-like electrode  24  and arm portion  25   f . The tip portion  24   a  of the shaft-like electrode  24  is formed semispherical to assure that the sleeve contact plate  25  and arm portion  25   f  contact each other at a single point. This arrangement is made because the shaft-like electrode  24 , which does not rotate, and the sleeve contact plate  25 , which rotates, must be placed in contact with each other, and yet it must be assured that electrical power is satisfactorily conducted through the interface in which the tip of the shaft-like electrode  24  and arm portion  25   f  slide on each other. With this arrangement, the shaft-like electrode  24  is positioned so that its axial line coincides with the rotational axis of the development sleeve  18 , and therefore, the size of the range in which the tip of the shaft-like electrode  24  and arm portion  25   f  slide on each other is smaller. Further in order to reduce the wear caused by the sliding, it is desirable that electrically conductive grease is placed in the interface between the tip portion  24   a  of the shaft-like electrode  24  and the arm portion  25   f . It is assumed that the shaft-like electrode  24  does not contact the internal surface of the through hole  23   a  of the sleeve flane  23 . This arrangement is made to prevent the shaft-like electrode  24  from affecting the position of the development sleeve  18 . The base portion of the shaft-like electrode  24  is in contact with a contact plate  28  which contacts the contact on the main assembly side.  
         [0086]    Referring to FIGS. 9 and 10, the contact plate  28  for contacting the main assembly is a 0.1-0.3 mm thick metallic (SUS, Cu alloy, or the like) springy plate, and is attached to the side cover  20  in such a manner that the actual contact portion  28   b  of the contact plate  28  is exposed from the process cartridge  15  through the hole  20   z  of the size cover  20  after the process cartridge assembly. It is structured so that when the process cartridge  15  is in the apparatus main assembly, it remains electrically in contact with the electrode (illustrated) in the apparatus main assembly.  
         [0087]    The contact plate  28  is structured so that its tip portion  28   a  electrically contacts the shaft-like electrode  24 . As for the method for keeping the shaft-like electrode  24  and contact plate  28  in contact with each other, a simple crimping method, a method in which the contact plate  28  is provided with a shaft-like electrode contacting elastic portion which is placed in contact with the shaft-like electrode  24 , and the like methods, may be listed.  
         [0088]    Further, a method, in which an electrically conductive member (for example, SUS plate) is attached to the shaft-like electrode  24  by crimping or the like, and this electrically conductive member is electrically connected to the contact plate  28 , may be employed. Also, the shaft-like electrode  24  and the contact plate  28  may be integrally formed so that this integral combination of the shaft-like electrode  24  and contact plate  28  is attached to the side cover  20 .  
         [0089]    To repeat the above described structure following the order of assembly with reference to FIGS. 9 and 11, first, the press-fitting portion  23   c  of the sleeve flange  23  is pressed into the press-fitting hole  18   a  of the development sleeve  18 , so that the sleeve flange  23  is perfectly immovably fixed to development sleeve  18 . Next, the magnetic roller bearing  27  to which the sleeve contact plate  25  has been fixed is inserted into the development sleeve  18  from the side (right side in FIG. 9), into which the sleeve flange  23  has not been pressed, until the collar portion  27   g  contacts the end surface  23   f  of the sleeve flange  23 . During this insertion of the magnetic roller bearing  27 , it does not occur that the magnetic roller bearing  27  fits askew due to the insertion resistance, because the arm portions  25   a  and  25   h  are positioned with even intervals in terms of the circumferential direction of the sleeve flange  23 . Also as described above, the magnetic roller bearing  27  remains accurately positioned relative to the development sleeve  18  by the force generated by the arm portions  25   a  and  25   h . Next, the magnetic roll  26  is inserted into the development sleeve  18 , and the other sleeve flange  23  (unillustrated) is fitted to complete the development roller.  
         [0090]    Next, the gap regulating member  29 , sleeve bearing  33 , and sleeve gear  31  are attached to the developing means frame portion (unillustrated) in the listed order. FIG. 11( a ) shows the development sleeve  18  at his stage of assembly. In this state, the arm portion  25   f  of the portion  25   d  of the sleeve contact plate  25  are yet to come into contact with the shaft-like electrode  24 , and therefore, is simply in contact with the anchoring portion  23   e  or the internal surface of the sleeve flange  23 .  
         [0091]    Thereafter, as the side cover  20  is attached, the tip portion  24   a  of the shaft-like electrode  24  comes into contact with the arm portion  25   f  of the sleeve contact plate  25 . In the state in which the attachment of the side covers  19  and  20  has been completed, the arm portion  25   f  of the portion  25   d , and the portion  25   d , are virtually in the same plane as seen from the direction perpendicular to the axial line of the development roller, contributing to the spacial efficiency in terms of the axial direction or the development roller.  
         [0092]    Also in this state, the passage for electricity from the high voltage electricity supplying contact point (unillustrated) of the image forming apparatus main assembly to the development sleeve  18  through the contact plate  28 , shaft-like electrode  24 , and sleeve contact plate  25 , has been completed.  
         [0093]    In terms of the longitudinal direction of the development roller, the contact portions are located in the adjacencies of the inward and outward sides of the magnetic roller bearing  27 , improving spacial efficiency in terms of the axial direction of the development roller. Further, the sliding contact point, or the only contact point, between the shaft-like electrode  24  and the sleeve contact plate  25 , is located within the sleeve flange  23 , and therefore, it is more difficult for contaminants such as dust to enter the contact point, stabilizing the performance of the contact point.  
         [0094]    Further, the position of the magnetic roll  26  is fixed by the magnetic roller bearing  27  anchored to the internal surface of the sleeve flange  23 , and therefore, the peripheral surfaces of the magnetic roll  26  and development sleeve  18  are positioned relative to each other with higher accuracy, and the distance between the two surfaces is kept more constant, compared to the prior structural arrangement.  
         [0095]    As described above, according to the present invention, the contact pressure between the sliding first and second electrodes for applying bias voltage to a developer bearing member such as a development sleeve can be stabilized, and the sliding contact portions are located within the development sleeve. Therefore, the spacial efficiency in terms of the longitudinal direction of the process cartridge is improved. Further, placing the sliding contact portions within the development sleeve prevents contaminants such as dust from entering between the contact portions.  
         [0096]    In particular, the magnetic roll bearing and the power supplying portion of the development roller are located close to each other, and therefore, spacial efficiency in terms of the longitudinal direction of the development roller is improved.  
         [0097]    Further, the position of the magnetic roll is fixed by the internal surface of developer bearing member such as a development sleeve, with the interposition of the magnetic roll bearing as the magnetic roll holder, and therefore, the position of the magnetic roll relative to the development sleeve is fixed with high accuracy.  
         [0098]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.