Abstract:
A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, includes an electrophotographic photosensitive drum; a processor actable on the drum; an electroconductive shaft member supporting and electrically connected with the drum; a cartridge frame for rotatably supporting the drum; a grounding contact member mounted on the frame and including a sliding contact for sliding contact with the shaft member and a fixed contact contacted to an urging member provided in the assembly; a cartridge positioning member for positioning an axis of the drum, wherein the positioning member is urged to a positioning portion of the assembly by the fixed contact being urged by the urging member when the cartridge is mounted to the assembly, wherein by the fixed contact being contacted and urged by the urging member the drum is electrically grounded, and the cartridge positioning member is positioned relative to the positioning portion.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a process cartridge employed by a copying machine, a printer, etc., employing an electrophotographic method. It also relates to an electrophotographic image forming apparatus employing such a process cartridge. 
   Herein, an electrophotographic image forming apparatus means an apparatus which forms images on recording medium with the use of an electrophotographic method. It includes, for example, an electrophotographic copying machine, an electrophotographic printer, (for example, laser beam printer, LED printer, etc.) a facsimileing apparatus, a wordprocessor, etc. 
   A process cartridge means a cartridge in which a charging means, a developing means or a cleaning means, as processing means, and an electrophotographic photoconductive drum are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. It also means a cartridge in which at least one processing means among a charging means, a developing means, and cleaning means, as processing means, and an electrophotographic photoconductive member, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and a cartridge in which a least a developing means, as a processing means, and an electrophotographic photoconductive drum are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
   In an electrophotographic image forming apparatus (which hereinafter will be referred to simply as image forming apparatus), the peripheral surface of the photoconductive drum uniformly charged by the charging means is selectively exposed at numerous points. As a result, a latent image is formed on the peripheral surface of the photoconductive drum. The latent image is visualized with the developer (toner) supplied by the developing means. Then, the visualized image, that is, the image formed of developer, is transferred onto recording medium. Then, the developer image on the recording medium is fixed to the recording medium with the application of heat and pressure to make the developer image permanent. 
   Meanwhile, the developer remaining on the image bearing member after the transfer of the developer image is removed by a cleaning means, for example, a cleaning blade, and is stored, as residual developer (removed toner), in the cleaning means container. Thus, the development process for the following stage of an electrophotographic image forming operation can be carried out without the presence of the residual developer on the peripheral surface of the image bearing member. 
   Conventionally, an electrophotographic image forming apparatus using an electrophotographic image forming process employs a process cartridge system, according to which an electrophotographic photoconductive member, and a single or plurality of processing means which act on the electrophotographic photographic member, are integrally disposed in a cartridge removably mountable in the main assembly of an electrophotographic image forming apparatus. A process cartridge system enables a user to maintain an electrophotographic image forming apparatus by him/her self, that is, without relying on service personnel, drastically improving operational efficiency. Thus, a process cartridge system has been widely used in the field of an electrophotographic image forming apparatus. 
   Here, referring to  FIG. 9 , the method for grounding the above described electrophotographic photoconductive drum (which hereinafter will be referred to as photoconductive drum) when the photoconductive drum is employed by an image forming apparatus will be described. 
   The photoconductive drum  501  comprises a cylindrical aluminum member  501   a , the peripheral surface of which is covered with a layer of photoconductive substance, and a pair of flanges  502   a  and  502   b  formed of a resin and integrally inserted into the lengthwise ends of the aluminum cylindrical member  501   a , one for one. 
   The photoconductive drum  501  also comprises an electrically conductive shaft  503 , which is put through the center holes of the resin flanges  502   a  and  502   b . The electrically conductive shaft  503  rotates with at least the cylindrical member  501   a  and resin flange  502   a.    
   The photoconductive drum  501  also comprises a contact  506 , which is solidly fixed to the resin flange  502   a , being placed in contact with both the internal surface  501   a   1  of the cylindrical aluminum member  501   a  and the peripheral surface of the electrically conductive shaft  503 . 
   The electrically conductive shaft  503  extends from both of the lengthwise ends of the photoconductive drum  501  in the thrust direction (axial direction) of the photoconductive drum  501 . 
   The lengthwise end portions of the electrically conductive shaft  503 , which extend from the lengthwise ends of the photoconductive drum  501  one for one, are supported by a pair of bearings  504   a  and  504   b , one for one, by their peripheral surfaces. 
   The bearings  504   a  and  504   b  are fitted in the bearing supporting portions of the shell portion  505  of the cartridge. Therefore, the photoconductive drum  501  is accurately positioned relative to the shell portion  505  of the cartridge. 
   To one of the lengthwise ends of the electrically conductive shaft  503 , a cartridge driving force transmitting member  507  is solidly fixed. The outward surface of the cartridge driving force transmitting member  507 , in terms of the axial direction of the photoconductive drum  501 , is in the form of a coupler, so that the cartridge driving force transmitting member  507  is enabled to engage with the driving force transmitting member  508  on the main assembly side of the image forming apparatus to transmit driving force. 
   The image forming apparatus main assembly is provided with a drum grounding contact  509 , which is placed in contact with the lengthwise end  503   a  of the electrically conductive shaft  503 , grounding the photoconductive drum  501  by way of the following path: cylindrical member  501   a →contact  506 →electrical conductive shaft  503 →drum grounding contact  509 . 
   The present invention is the result of the further development of the above described prior art. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which ensures that the photoconductive drum of the process cartridge is grounded and remains grounded. 
   Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which grounds the process cartridge by making the pressure generating member for keeping the process cartridge accurately positioned relative to the main assembly of the image forming apparatus double as the process cartridge positioning member and process cartridge grounding member. 
   Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is capable of grounding the electrophotographic photoconductive drum of the process cartridge with the provision of a simple structural arrangement, that is, without providing the image forming apparatus with components dedicated to the grounding of the electrophotographic photoconductive drum. 
   Another object of the present invention is to provide a process cartridge comprising: an electrophotographic photoconductive drum comprising an electrically conductive shaft; a grounding contact which is attached to the frame of the process cartridge, and has a sliding contact point by which the grounding contact is placed in contact with the electrically conductive shaft, and a non-sliding contact point by which the grounding contact is directly pressed by a pressure applying member which is attached to the main assembly of the electrophotographic image forming apparatus and doubles as the grounding member on the main assembly side; and a cartridge positioning member which is kept pressed by the pressure applying member, on the cartridge positioning member on the electrophotographic image forming apparatus main assembly side, keeping thereby accurately positioned the axial line of the electrophotographic photoconductive drum relative to the apparatus main assembly, wherein as the grounding contact is kept pressed by the pressure applying member placed in contact with the non-sliding contact point of the grounding contact, not only is the electrophotographic photoconductive drum kept accurately positioned relative to the main assembly, but also, it is kept reliably grounded, and also, to provide an electrophotographic image forming apparatus in which such a process cartridge is removably mountable. 
   These and other objects, features, and advantages of the present invention will become more apparent upon 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 
       FIG. 1  is a vertical sectional view of the multicolor image forming apparatus in the first embodiment of the present invention. 
       FIG. 2  is a vertical sectional view of the process cartridge in the first embodiment of the present invention. 
       FIG. 3  is a perspective view of the process cartridge in the first embodiment of the present invention, for showing how the cleaner unit frame and developing apparatus of the process cartridge are connected to each other. 
       FIG. 4  is a sectional view of the photoconductive drum and photoconductive drum supporting portion of the process cartridge, in the first embodiment of the present invention. 
       FIG. 5  is a perspective view of the process cartridge and the process cartridge supporting portion of a multicolor image forming apparatus. 
       FIG. 6  is a side view of the process cartridge and the process cartridge supporting portion of the multicolor image forming apparatus in the first embodiment of the present invention, for showing the method for accurately positioning the process cartridge relative to the main assembly of the image forming apparatus. 
       FIG. 7  is a perspective view of the grounding contact located at one of the lengthwise ends of the photoconductive drum in the process cartridge in the first embodiment of the present invention, for showing the the structure of the grounding contact. 
       FIG. 8  is a side view of the grounding contact located at one of the lengthwise ends of the photoconductive drum in the process cartridge in the second embodiment of the present invention, for showing the structure of the grounding contact. 
       FIG. 9  is a side view of the grounding contact located at one of the lengthwise ends of the photoconductive drum in a typical conventional process cartridge, for showing the structure of the grounding contact. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (Embodiment 1) 
   Hereinafter, the first embodiment of a multicolor image forming apparatus in accordance with the present invention will be described in more detail with reference to FIG.  1 . 
   In the following descriptions, the lengthwise direction means the direction which is perpendicular to the direction in which recording medium is conveyed, and parallel to the surface of the recording medium. Regarding the alphanumeric references for the yellow, magenta, cyan, and black image forming portions, yellow, magenta, cyan, and black colors are represented by referential characters a, b, c, and k, respectively. Further, when any of the yellow, magenta, cyan, and black image forming portions, is referred to as an example of the image forming portions, or when all of them are referred to, the referential characters a, b, c, and d are not added to the numerical reference for the image forming portion; the image forming portion is referred to only by numerical references. 
   (General Structure of Multicolor Image Forming Apparatus) 
   First, the general structure of the multicolor image forming apparatus will be roughly described with reference to  FIG. 1 , which is a sectional view of a full-color laser beam printer as an example of an embodiment of a multicolor image forming apparatus in accordance with the present invention. 
   The main assembly  100  (which hereinafter may be referred to as apparatus main assembly) of the multicolor image forming apparatus in  FIG. 1  comprises four electrophotographic photoconductive drums  1   a ,  1   b ,  1   c , and  1   d  (which hereinafter will be referred to as photoconductive drums). The photoconductive drum  1  is rotationally driven by a driving means (unshown) in the counterclockwise direction of the drawing. In the adjacencies of the peripheral surface of the photoconductive drum  1 , a charging apparatus  2  ( 2   a ,  2   b ,  2   c , and  2   d ) as the primary charging means for uniformly charging the peripheral surface of the photoconductive drum  1 , a scanner unit  3  ( 3   a ,  3   b ,  3   c , and  3   d ) for forming an electrostatic latent image on the peripheral surface of the photoconductive drum  1  by scanning the peripheral surface of the photoconductive drum  1  with a beam of laser light modulated with image formation information, a developing apparatus  4  ( 4   a ,  4   b ,  4   c , and  4   d ) for developing the electrostatic latent image into a toner image, by adhering toner to the electrostatic latent image, an electrostatic transferring apparatus  5  for transferring the toner image on the photoconductive drum  1  onto a transfer medium S, as a recording medium, and a cleaning medium apparatus  6  ( 6   a ,  6   b ,  6   d , and  6   d ) for removing the toner particles remaining on the peripheral surface of the photoconductive drum  1  after the toner image transfer, etc., are disposed in the mentioned order, in terms of the rotational direction of the photoconductive drum  1 . 
   The photoconductive drum  1 , charging apparatus  2 , developing apparatus  4 , and cleaning apparatus  6  are integrally disposed in a cartridge, constituting the so-called process cartridge  7  (FIG.  2 ). 
   Next, the above mentioned components will be described in detail, starting from the photoconductive drum  1 . 
   For example, the photoconductive drum  1  as an image bearing member comprises an aluminum cylinder with a diameter of 30 mm, and a layer of photoconductor coated on the peripheral surface of the aluminum cylinder. The photoconductive drum  1  is rotationally supported by supporting members, by its lengthwise ends. It is rotationally driven in the counterclockwise direction by the driving force transmitted to one of its lengthwise ends from a motor (unshown) provided on the apparatus main assembly  100  side. 
   As for the charging method used by the charging apparatus  2 , one of the contact charging methods may be used. The charging member of the charging apparatus  2  is an electrically conductive member in the form of a roller. As charge bias is applied to the charge roller while the charge roller is kept in contact with the peripheral surface of the photoconductive drum  1 , the peripheral surface of the photoconductive drum  1  is uniformly charged. In this embodiment, or the first embodiment, one of the reversal developing methods is used. Therefore, the peripheral surface of the photoconductive drum  1  is charged to the negative polarity. 
   Referring to  FIG. 1 , the scanner unit  3  is disposed virtually level with the photoconductive drum  1 , and is structured so that a beam of image formation light, that is, the light emitted by the laser diode (unshown) of the scanner unit  3  while being modulated with image formation signals, is projected onto the polygon mirror  9  ( 9   a ,  9   b ,  9   d , and  9   d ), spun at a high velocity by the scanner motor (unshown), and so that the image formation light deflected by the polygon mirror  9  is focused by the focusing lens  10  ( 10   a ,  10   b ,  10   c , and  10   d ) on the charged peripheral surface of the photoconductive drum  1 , selectively exposing numerous points on the peripheral surface of the photoconductive drum  1 . Consequently, an electrostatic latent image is formed on the peripheral surface of the photoconductive drum  1 . 
   Next, referring to  FIG. 2 , the developing apparatuses  4   a ,  4   b,    4   c,  and  4   d  each have a toner container  41  containing yellow, magenta, cyan, and black toners, respectively. The toner in the toner container  41  is delivered by the toner delivery mechanism  42 , to the toner supply roller  43  which is rotating in the clockwise direction indicated by an arrow mark (Z) in FIG.  2 . The toner delivered to the toner supply roller  43  is coated onto the peripheral surface of the development roller  40 , which is rotating in the clockwise direction indicated by an arrow mark (Y) in  FIG. 2 , by the toner supply roller  43  and the development blade  44  kept pressed upon the peripheral surface of the development roller  40 . Thus, the toner is charged as it is coated onto the peripheral surface of the development roller  40 . 
   As development bias is applied to the development roller  40  opposing the photoconductive drum  1  bearing a latent image, the toner on the peripheral surface of the development roller  40  is adhered to the peripheral surface of the photoconductive drum  1  in accordance with the pattern of the latent image; in other words, the latent image on the photoconductive drum  1  is developed into a toner image. 
   Referring again to  FIG. 1 , the electrostatic transferring apparatus  5  comprises an electrostatic conveying belt  11 , which is circularly driven. The electrostatic conveying belt  11  is disposed in a manner to oppose all of the photoconductive drums  1   a ,  1   b ,  1   c , and  1   d,  so that it remain in contact with all of the photoconductive drums  1   a ,  1   b ,  1   c , and  1   d  as it is circularly driven in the direction indicated by an arrow X. As the material for the electrostatic conveying belt  11 , a film formed of a resin, or a multilayer film comprising a substrate layer formed of a rubber and a layer of a resin coated on the substrate layer, may be employed. The electrostatic conveying belt  11  is stretched around the driving roller  13 , follower roller  14   a , and tension roller  15 . As it is circularly moved, it keeps the transfer medium S electrostatically adhered to its outward surface, on the left-hand side, in terms of the loop it forms, in FIG.  1 . As a result, the transfer medium S is conveyed by the electrostatic conveying belt  11  to the transfer point, where the toner image on the photoconductive drum  1  is transferred onto the transfer medium S. 
   The electrostatic transferring apparatus  5  also comprises four transfer rollers  12   a ,  12   b ,  12   c , and  12   d , which oppose the four photoconductive drums  1   a ,  1   b ,  1   c , and  1   d , respectively, being placed in parallel and in contact with the inward surface of the electrostatic conveying belt  11 , in terms of the loop formed by the belt  11 . To the transfer roller  12 , bias voltage positive in polarity is applied to give the transfer medium S positive charge through the electrostatic transfer belt  11 . As the bias voltage positive in polarity is applied to the transfer roller  12 , the toner image on the photoconductive drum  1 , which is negative in polarity, is transferred onto the transfer medium S by the electric field generated by the bias application. 
   A transfer medium feeding/conveying portion  16  is for feeding the transfer medium S into the apparatus main assembly and conveying it to the image forming portion. A cassette  17  stores a plurality of transfer mediums S. During image formation, the feeding roller  18  (semicylindrical roller) and a registration roller pair  19  are rotationally driven in synchronism with the image formation, in order to separate the transfer mediums S in the cassette  7  one by one, and to sequentially feed the transfer mediums S into the apparatus main assembly and convey them to the transfer points. More specifically, as the leading edge of each transfer medium S comes into contact with the registration roller pair  9 , the transfer medium S is temporarily prevented from advancing. As a result, the transfer medium S slightly curves. Then, the transfer medium S is released by the registration roller pair  9  in synchronism with the image formation, onto the electrostatic transfer belt  11  so that the arrival of the transfer starting line on the transfer medium S at the transfer point (line) coincides with the arrival of the leading end (line) of the toner image on the photoconductive drum  1  at the transfer point (line). 
   The fixing portion  20  is for fixing to the transfer medium S a plurality of the unfixed toner images, different in color, which have been transferred onto the transfer medium S. It has a fixation roller pair  21  for applying heat and pressure to the transfer medium S. The fixing roller  21  comprises a rotational heat roller  21   a , and a pressure roller  21   b  kept pressed upon the rotational roller  21   a  to apply heat and pressure to the transfer medium S. 
   To describe the operation of the fixing portion  20 , as the transfer medium S, bearing the unfixed toner images which have been transferred from the photoconductive drum  1 , is passed through the fixing portion  20  by the fixation roller pair  21 , heat and pressure is applied to the transfer medium S by the fixation roller pair  21 . As a result, the plurality of unfixed toner images different in color are fixed to the surface of the transfer medium S. 
   As for the image forming operation, the process cartridges  7   a ,  7   b ,  7   c , and  7   d  are sequentially driven in synchronism with the printing timing, and the photoconductive drums  1   a ,  1   b ,  1   c , and  1   d  are rotationally driven in the counterclockwise direction in synchronism with the timing with which the process cartridges  7   a ,  7   b ,  7   c , and  7   d  are driven. Also, the scanner units  3   a ,  3   b ,  3   c , and  3   d , which oppose the process cartridges  7   a ,  7   b ,  7   c , and  7   d , respectively, in the process cartridges  7   a ,  7   b ,  7   c , and  7   d , are sequentially driven in synchronism with the rotations of the photoconductive drums  1   a ,  1   b ,  1   c , and  1   d , respectively. As the photoconductive drum  1  is rotationally driven, the peripheral surface of the photoconductive drum  1  is uniformly charged by the charge roller  2 , and is exposed to the beam of light projected by the scanner unit  3  while being modulated with the image formation signals. As a result, an electrostatic latent image is formed on the peripheral surface of the photoconductive drum. The development roller  40  in the developing apparatus  4  transfers the toner therein onto the points of the electrostatic latent image, which are lower in potential level. As a result, a visible image is formed of toner, on the peripheral surface of the photoconductive drum  1 ; the electrostatic latent image is developed into a toner image. 
   The rotation of the registration roller pair  19  is started to release each transfer medium S onto the electrostatic transfer belt  11  so that, as the electrostatic transfer belt  11  is circularly driven, the leading edge of the toner image on the peripheral surface of the photoconductive drum  1   a , that is, the most upstream photoconductive drum  1  in terms of the transfer medium conveyance direction, and the predetermined transfer starting line of the transfer medium S, arrive, at the same time, at a predetermined point (line) in the contact area between the photoconductive drum  1   a  and electrostatic transfer belt  11 . 
   Arriving at the contact area between the electrostatic adhesion roller  22  and electrostatic transfer belt  11 , the transfer medium S is nipped between the electrostatic adhesion roller  22  and electrostatic transfer belt  11 , being thereby pressed upon the electrostatic transfer belt  11 . Further, voltage is applied between the electrostatic transfer belt  11  and electrostatic adhesion roller  22 , inducing thereby electrical charge in the transfer medium S, which is dielectric, and the dielectric layer of the electrostatic transfer belt  11 . As a result, the transfer medium S is electrostatically adhered to the outward surface of the electrostatic transfer belt  11 , and is conveyed by the electrostatic transfer belt  11  up to the most downstream transfer portion, remaining reliably adhered to the electrostatic transfer belt  11 . The electrostatic adhesion roller  22  opposes the follower roller  14   a  with the interposition of the electrostatic transfer belt  11 . 
   While the transfer medium S is conveyed in the manner described above, the toner image on the photoconductive drum  1   a , toner image on the photoconductive drum  1   b , toner image on the photoconductive drum  1   c , and toner image on the photoconductive drum  1   d , are sequentially transferred onto the transfer medium S by the electric fields generated between the photoconductive drums  1   a ,  1   b ,  1   c , and  1   d , and the transfer rollers  12   a ,  12   b ,  12   c , and  12   d , respectively. 
   After the transfer of the four toner images different in color onto the transfer medium S, the transfer medium S is separated from the electrostatic transfer belt  11  due to the curvature of the belt driving roller  13 , and is conveyed into the fixing portion  20 , in which the four toner images are thermally fixed to the transfer medium S. Then, the transfer medium S is discharged from the apparatus main assembly by the discharge roller pair  23 , with its image bearing surface facing downward, through the print discharging portion  24 . 
   Next, referring to  FIGS. 2 and 3 , the process cartridge  7  in accordance with the present invention will be described in detail.  FIG. 2  is a sectional view of the process cartridge  7  at a plane perpendicular to the lengthwise direction of the photoconductive drum  1 , and  FIG. 3  is a perspective view of the process cartridge  7 . The process cartridges  7   a ,  7   b ,  7   c , and  7   d  for yellow, magenta, cyan, and black color components, respectively, are the same in structure. 
   The process cartridge  7  comprises a cleaner unit  50  and a developing apparatus  4 . The cleaner unit  50  comprises the photoconductive drum  1  as an image bearing member, primary charging means, and cleaning means, and the developing apparatus  4  has the developing means for developing the electrostatic latent image on the photoconductive drum  1 . The components of the developing apparatus  4  are unitized. Hence, the developing apparatus  4  is sometimes referred to as development unit  4 . 
   The cleaner unit  50  also comprises a cleaner unit frame  51  as a part of the cartridge frame, to which the photoconductive drum  1  is rotationally attached with the-interposition of the bearings  73   a  and  73   b . Disposed in contact with the peripheral surface of the photoconductive drum  1  are the charging apparatus  2  as the primary charging means for uniformly charging the photoconductive layer, which is the outermost layer of the photoconductive drum  1 , and the cleaning blade  60  for removing the developer (residual toner) remaining on the photoconductive drum  1  after the toner image transfer. After being removed from the peripheral surface of the photoconductive drum  1  by the cleaning blade  60 , the residual toner (removed toner) is gradually sent by the toner sending mechanism  52  into the removed toner chamber  53  located in the rear portion of the cleaner unit frame  51 . 
   The development unit  4  comprises the development roller  40 , toner container  41 , and development unit frame  45 . The development roller  40  rotates in the direction indicated by the arrow mark Y, in contact with the photoconductive drum  1 , and the toner container  41  stores the toner. The development roller  40  is rotationally supported by the development unit frame  45  with the interposition of bearings (unshown). The development unit  4  further comprises the toner supply roller  43  and development blade  44 , which are disposed in contact with the peripheral surface of the development roller  40 . The toner supply roller  43  rotates in the direction indicated by the arrow mark Z, in contact with the peripheral surface of the development roller  40 . The toner container also contains a toner conveying mechanism  42  for conveying the toner in the toner container to the toner supply roller  43  while stirring the toner. 
   The development unit  4  is provided with a pair of arms attached to the lengthwise ends of the development unit  4 , one for one, and the pair of arms are provided with bearings  47  and  48 , one for one. The development unit  4  is connected to the cleaner unit  50 , with a pair of development unit supporting pins  49   a  inserted in the holes  49  of the cleaner unit  50  and the bearing  47  and  48  of the development unit  4 , being suspended from the cleaner unit  50  in such a manner that the entirety of the development unit  4  is enabled to pivot about the pair of pins  49   a . The process cartridge  7  is provided with a pair of compression springs  54  disposed between the development unit  4  and cleaner unit  50  in such a manner that the development roller  40  is kept in contact with the photoconductive drum  1  by the resiliency of the compression springs  54 . 
   During development, the toner in the toner container  41  is conveyed to the toner supply roller  43  by the toner stirring mechanism  42 . As the toner is supplied to the toner supply roller  43 , which is rotating in the arrow Z direction, the toner is supplied to the development roller  40 ; as the toner supply roller  43  rotating in the arrow Z direction rubs against the development roller  40  rotating in the arrow Y direction, the toner is borne onto the development roller  40  by being rubbed onto the development roller  40 . 
   The toner borne on the development roller  40  is brought to the development blade by the rotation of the development roller  40 . At the toner blade  44 , the body of the toner on the development roller  40  is regulated in thickness, becoming a thin layer of toner, while being given a desired amount of electric charge. Then, as the development roller  40  rotates further, the thin layer of toner on the development roller  40  is conveyed to the development point, that is, the contact area between the photoconductive drum  1  and development roller  40 , in which the toner particles in the thin layer of toner on the development roller  40  are adhered to the electrostatic latent image on the peripheral surface of the photoconductive drum  1  (electrostatic latent image is developed), by the development bias voltage, that is, DC voltage applied to the development roller  40  from an unshown electric power source. As the development roller  40  is further rotated, the residual toner particles, that is, the toner particles which remained on the peripheral surface of the development roller  40  without contributing to the development of the electrostatic latent image, are moved back into the developing device, in which the residual toner particles are stripped from the peripheral surface of the development roller  40  by the toner supply roller  43  as the toner supply roller  43  rubs against the peripheral surface of the development roller  40 ; in other words, the residual toner particles are recovered. The recovered residual toner particles are mixed into the toner in the developing device by the toner stirring mechanism  42  as the recovered residual toner particles and the toner in the developing device are stirred together by the toner stirring mechanism  42 . 
   In the case of a contact developing method, which is a development method in which the photoconductive drum  1  is placed in contact with the  1   d  development roller  40  as in this embodiment, the photoconductive drum  1  is desired to be rigid, whereas the surface layer (portion which makes contact with photoconductive drum  1 ) of the development roller  40  is desired to be elastic. As the material for this elastic surface layer of the development roller  40 , solid rubber or the like is used. In consideration of the fact that the surface layer of the development roller  40  is required to give the toner a satisfactory amount of electric charge, the surface of the layer formed of solid rubber or the like may be coated with resin. 
   Described next will be the method for accurately positioning the photoconductive drum  1  relative to the apparatus main assembly  100 , and method for establishing electrical connection between the photoconductive drum  1  and apparatus main assembly  100 , as the process cartridge  7  in the first embodiment of the present invention is mounted into the apparatus main assembly  100 . 
   Referring to  FIG. 4 , the structure of the process cartridge  7  will be described. 
   The photoconductive drum  1  comprises: a cylindrical member  70 , the peripheral surface of which is coated with a layer of photoconductor; a pair of flanges  71   b  and  71   c , which are formed of a resin, and are fitted in the lengthwise ends (axial direction) of the cylindrical member  70 , one for one; and a contact  81  solidly fixed to the flange  71   b  or both the flanges  71   b  and  71   c , and placed in contact with the internal surface  70   a  of the cylindrical member  70 . These components of the photoconductive drum  1  are unitized as the photoconductive drum  1 . The resin flanges  71   b  and  71   c  are provided with through holes  71   b   1  and  71   c   1 , the axial lines of which coincide with the axial line of the cylindrical member  70 , and in which the electrically conductive shaft  72  is fitted. 
   The electrically conductive shaft  72  is in contact with the contact  81  at a contact point  81   a , establishing electrical connection between the cylindrical member  70  and electrically conductive shaft  72 . The electrically conductive shaft  72  extends outward from both of the lengthwise ends of the photoconductive drum  1 , constituting the extensions  72   a  and  72   b , by which the photoconductive drum  1  is rotationally supported by the bearings  73   a  and  73   b  which rotationally support the electrically conductive shaft  72 . The bearings  73   a  and  73   b  are solidly fixed to the bearing supporting portions  51   a  and  51   b  of the cleaner unit frame  51 . Thus, the photoconductive drum  1  is accurately positioned relative to the cleaner unit frame  51  with the interposition of the-bearings  73   a  and  73   b.    
   Next, referring to  FIGS. 5 and 6 , the positioning of the process cartridge  7  and photoconductive drum  1  relative to the apparatus main assembly  100  will be described. The bearings  73   a  and  73   b  are attached to the left and right metallic side plates  74  and  75 , respectively, (which correspond one for one to ends of axial line of photoconductive drum) of the apparatus main assembly  100 , being positioned so that their peripheral surfaces are in contact with the left and right side plates  74  and  75 . The left and right side plates  74  are provided with bearing positioning surfaces  74   a  and  74   b , and right side plate  75  is provided with bearing positioning surfaces  75   a  and  75   b . The peripheral surfaces of the bearings  73   a  and  73   b  are kept pressed against the bearing positioning surfaces  74   a  and  74   b , and the bearing positioning surfaces  75   a  and  75   b , respectively, whereby the photoconductive drum  1  is accurately positioned relative to the left and right side plates  74  and  75  with the interposition of the bearing  73   a  and  73   b , respectively. Further, for the positioning of the photoconductive drum  1 , the photoconductive drum  1  is kept pressed on the left and right side plates  74  and  75 . 
   Next, referring to  FIGS. 5 and 6 , the method for keeping the photoconductive drum  1  pressed upon the left and right side plate  74  and  75  will be described. Herein, the method will be described in detail regarding only one (right side plate  75 ) of the lengthwise ends of the photoconductive drum  1 . The method regarding the other end is the same as the method which will be described next. Referring to  FIG. 6 , except for the portions of the peripheral surface of the bearing  73   b , by which the bearing  73   b  is in contact with the bearing positioning surfaces  75   a  and  75   b  of the right side plate  75 , the peripheral surface of the bearing  73   b  is covered with the bearing supporting portion  51   b , that is, a part of the cleaner unit frame  51 , for supporting the bearing  73   b.    
   In comparison, the right side plate  75  is provided with a metallic shaft  76 , which is attached to the right side plate  75  by crimping. The shaft  76  supports a helical torsion spring  77 , which is kept wound in a manner to make the arm portions  77   a  and  77   b  of the helical torsion spring  77  come closer to each other so that force is generated by the resiliency of the spring  77  in the direction to move the two arm portions  77   a  and  77   b  away from each other. One of the arm portions  77   a , that is, one end of the piece of springy wire constituting the helical torsion spring  77 , is solidly attached to the right side plate  75  by being fitted in the hole  78  of the right side plate  75 , whereas the arm portion  77   b , or the other end of the piece of springy wire constituting the helical torsion spring  77 , is rested on the edge of the hole  79  of the right side plate  75 , with the bent portion of the arm portion  77   b  hitched to the edge of the hole  79 , being prevented from moving in the direction to unwind the helical torsion spring  77  when the process cartridge  7  is out of the apparatus main assembly  100 . When the process cartridge  7  is in the apparatus main assembly  100 , the arm portion  77   b , or the other end of the helical torsion spring  77 , is kept pressed upon the spring pressure bearing portion  51   c  of the cleaner unit frame  51 , accurately positioning the process cartridge  7  and photoconductive drum  1  relative to the right side plate  75 . 
   Next, referring to  FIGS. 5-7 , the method for grounding the photoconductive drum  1  will be described. The bearings  73   a  and  73   b  are rolling bearings, for example, and double as the positioning members on the cartridge side for accurately positioning the axis of the photoconductive drum  1  relative to the apparatus main assembly  100 . In comparison, on the apparatus main assembly side, the bearing positioning surfaces  74   a  and  74   b  of the left side plate  74 , and the bearing positioning surfaces  75   a  and  75   b  of the right side plate  75 , of the apparatus main assembly function as the members for accurately positioning the process cartridge  7  relative to the apparatus main assembly  100 . 
   The bearing supporting portion  51   b  of the id cleaner unit frame  51 , and its adjacencies, are structured as follows. Referring to  FIG. 6 , the housing portion  51   d  of the cleaner unit frame  51  for supporting the bearing  73   b  is provided with a positioning rib  51   e  for regulating the position of the bearing  73   b  in terms of the thrust direction of the photoconductive drum  1 . The process cartridge  7  is also provided with a grounding member  80 , which is attached to the housing portion  51   d , being on the inward side of the process cartridge  7  with respect to the bearing  73   b  in terms of the thrust direction of the photoconductive drum  1 . The grounding member  80  is configured so that its arm portion  80   a  makes contact with the electrically conductive shaft  72  which extends outward through the housing portion  51   d , and also, so that the grounding member  80  and the electrically conductive shaft  72  are enabled to move relative to each other, with the arm portion  80   a  of the grounding member  80  sliding on the peripheral surface of the electrically conductive shaft  72 . 
   A part of the grounding member  80  is placed on the pressure bearing surface  51   c  of the cleaner unit frame  51  in a manner to cover the pressure bearing surface  51   c , constituting the surface  80   b  which directly bears the pressure from the helical torsion spring  77 . The helical torsion spring  77  is disposed so that it directly presses on the pressure bearing surface  80   b , that is, non-sliding contact point of the grounding member  80 , so that the bearing  73   b , which doubles as positioning member, is kept pressed on the bearing positioning portions  75   a  and  75   b , which are the process cartridge positioning portions on the apparatus main assembly  100  side, with the interposition of the housing portion  51   d  of the process cartridge  7 . With the provision of this structural arrangement, not only can the process cartridge  7  be accurately positioned relative to the apparatus main assembly  100 , but also, the photoconductive drum  1  can be grounded through the following path: cylindrical member  70 →contact  81 →electrically conductive shaft  72 →grounding member  80 →helical torsion spring  77 →right side plate  75 . 
   In other words, the photoconductive drum  1  can be grounded without providing the image forming apparatus main assembly  100  with additional contacts; the photoconductive drum  1  is grounded through the pressure generating member and right side plate  75 . Herein, the side plates  74  and  75  are formed of metallic substance. As for the number and location of the photoconductive drum grounding means, a single photoconductive drum grounding means may be attached to, for example, the bearing supporting portion  51   a , or two photoconductive drum grounding means may be attached to the bearing supporting portions  51   a  and id  51   b , one for one. 
   According to the first embodiment, the grounding member  80  is kept pressed by the electrically conductive helical torsion spring  77  electrically connected to the right side plate  75  formed of metallic substance, and also, the peripheral surface of the bearing  73   b , which doubles as the photoconductive drum positioning member, is kept pressed on the bearing positioning portions  75   a  and  75   b , which are the process cartridge positioning portions on the apparatus main assembly  100  side. Therefore, it is assured that not only does the process cartridge  7  remain grounded, but also, it remains accurately positioned relative to the apparatus main assembly  100 . 
   Further, the metallic plate  75  comprises the bearing positioning portion  75   a  and  75   b , and the electrically conductive shaft  72  is grounded to the metallic plate  75  through the bearing  73   b  kept pressed on the metallic plate  75 . Thus, it is further assured that the photoconductive drum  1  remains grounded, provided that the bearing  73   b  is formed of a metallic or electrically conductive substance. 
   (Embodiment 2) 
   Next, referring to  FIGS. 4 and 8 , the second embodiment of the present invention will be described. 
   Herein, the members, portions, etc., in this embodiment, the descriptions of which are the duplicates of the descriptions of those in the first embodiment, will be given the same referential symbols as those given in the first embodiment, and will not be described. 
   The structure of the process cartridge  7  is as follows. Referring to  FIG. 4 , a photoconductive drum  1  comprises an electrically conductive shaft  72 , which is put through the through holes  71   b   1  and  71   c   1  of the photoconductive drum  1 , extending outward from both lengthwise ends of the photoconductive drum  1  in the axial direction of the photoconductive drum  1 . The electrically conductive member  72  is solidly attached to the photoconductive drum  1 , and rotates with the photoconductive drum  1 . The force for rotationally driving the photoconductive drum  1  is transmitted to the photoconductive drum  1  by an unshown driving force transmitting means, by way of one end of the electrically conductive shaft  72 . Referring to  FIG. 8 , in order to keep the electrically conductive shaft  72  and a helical torsion spring  77  electrically connected, a metallic compression spring unit  83  is employed, which comprises a pair of electrically conductive members constituting the lengthwise ends of the unit  83 , one for one. 
   More specifically, the metallic compression spring unit  83  comprises: a shaft contacting member  84  which constitutes one end of the unit  83 , a spring contacting member  85  which constitutes the other end of the unit  83 , and an electrically conductive compression spring  86  disposed between the members  84  and  85 . The shaft contacting member  84  and spring contacting member  85  are formed of an electrically conductive resin, and are placed in contact with the electrically conductive shaft  72  and helical torsion spring  77 , respectively. The cleaner unit frame  51  is provided with a housing portion  51   d  for holding a bearing  73   b . The housing portion  51   d  is provided with a rib  51   g  which fits in the groove  84   a  of the shaft contacting member  84 , and a rib  51   f  which fits in the groove  85   a  of the spring contacting member  85 . The metallic compression spring unit  83  is disposed within the housing portion  51   d , with the ribs  51   g  and  51   f  fitted in the grooves  84   a  and  85   a , respectively, so that the electrically conductive compression spring  86  remains compressed. 
   With the provision of the above described structural arrangement, the sliding contact is on the process cartridge side, which is shorter in service life compared to the image forming apparatus main assembly, and the contacts which keep the image forming apparatus main assembly  100  and process cartridge electrically connected are made non-sliding contacts. Therefore, the path through which the photoconductive drum  1  is grounded to the image forming apparatus main assembly  100  is more reliable. 
   According to the above described embodiments, the contact for keeping the photoconductive drum electrically connected to the main assembly of an image forming apparatus is attached to the portion of the cleaner unit frame, which bears the pressure from the pressure generating member attached to the metallic side plate of the apparatus main assembly to keep the photoconductive drum supporting bearing in contact with the bearing positioning portions of the metallic plate in order to keep the process cartridge accurately positioned relative to the main assembly. With the provision of this structural arrangement, the photoconductive drum can be grounded through the following path: cylindrical member of the photoconductive drum→pressure applying member→side plate; in other words, the photoconductive drum can be grounded without providing the image forming apparatus with electrical contacts dedicated to the grounding of the photoconductive drum. 
   Further, according to the above described embodiments, the contact for maintaining electrical connection between the photoconductive drum supporting member and the pressure applying member is attached to the cleaner unit frame, provided that the photoconductive drum supporting shaft is electrically conductive, is put through the photoconductive drum, and rotates with the photoconductive drum. With the provision of this structural arrangement, the electrically conductive drum supporting shaft and grounding member are electrically connected with the use of a sliding contact; in other words, the sliding contact is disposed within the process cartridge which is shorter in service life compared to the image forming apparatus main assembly, and the image forming apparatus main assembly and process cartridge are electrically connected with the use of non-sliding contacts. Therefore, the drum grounding path is more reliable. 
   As described above, according to the present invention, it is assured that a photoconductive drum remains grounded. 
   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.