Abstract:
A developing apparatus including a developing roller for developing an electrostatic latent image formed on a photosensitive member, wherein the developing apparatus is detachably mountable to a main assembly of an electrophotographic image forming apparatus in an axial direction of the developing roller, the developing apparatus includes a drive transmission member, provided at one end of the developing roller, for receiving a driving force from the main assembly and transmitting the driving force to the developing roller; an urging member, provided at other end, for urging the developing roller in the axial direction; an abutting portion, provided adjacent the one end, for being abutted by the shaft of the developing roller by an urging force of the urging member to position the developing roller with respect to the axial direction; and a contact member contactable to a main assembly contact provided in the main assembly when the developing apparatus is mounted to the main assembly, wherein the contact member contacts to a peripheral surface of the shaft of the developing roller adjacent the one end to apply a voltage to the developing roller.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a developing apparatus, a process cartridge, and an electrophotographic image forming apparatus which uses a process cartridge. 
         [0002]    Here, an electrophotographic image forming apparatus means an apparatus which forms an image on recording medium with the use of an electrophotographic image forming method. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for example, laser beam printer, LED printer, etc.), a facsimile apparatus, a wordprocessor, etc. 
         [0003]    A process cartridge means a cartridge in which an electrophotographic photosensitive drum and one or more processing apparatuses, that is, a charging means, a developing means, and a cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. More specifically, a process cartridge means a cartridge in which an electrophotographic photosensitive drum, a charging means, and a developing means or cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. It also means a cartridge in which an electrophotographic photosensitive drum, and at least one among a charging means, a developing means, and a cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. Further, it also means a cartridge in which an electrophotographic photosensitive drum and a developing means are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. 
         [0004]    In the field of an electrophotographic image forming apparatus which uses an electrophotographic image formation process, it has been common practice to employ a process cartridge system, which integrally disposes an electrophotographic photosensitive drum and one or more means for processing the electrophotographic photosensitive drum in a cartridge so that they can be removably mountable in the main assembly of an image forming apparatus. A process cartridge system enables in effect a user to maintain an electrophotographic image forming apparatus by himself or herself, that is, without relying on a service person. Thus, it can drastically improve an electrophotographic image forming apparatus in operational efficiency. Therefore, a process cartridge system is widely in used in the field of an electrophotographic image forming apparatus. 
         [0005]    An electrophotographic image forming apparatus forms an electrostatic latent image on its photosensitive drum by projecting a beam of light emitted by a laser, an LED, an ordinary lamp, or the like, while modulating the beam of light with the information regarding an image to be formed. 
         [0006]    Then, it develops the electrostatic latent image on the photosensitive drum into a toner image. More specifically, it applies a development bias to the development roller with which its developing apparatus is provided. As a result, the electrostatic latent image on the photosensitive drum is developed into a toner image with the toner on the development roller. Then, it transfers the toner image on the photosensitive drum onto recording medium. 
         [0007]    Thus, the development unit  4  is provided with electrical contacts for applying bias voltage to the development roller, etc. The electrical contacts are formed of electrically conductive plate or the like. Thus, it is common practice to structure an electrophotographic image forming apparatus so that as a developing apparatus or a process cartridge is mounted into the main assembly of the image forming apparatus, its electrical contacts come into contact with the counterparts of the main assembly of the image forming apparatus. 
         [0008]    As one of the means for driving the development roller in a process cartridge, such as the one described above, the driving means disclosed in Japanese Laid-open Patent Application 2004-12523 has been well-known. In the case of this development roller driving means, one of the lengthwise ends of the shaft of the development roller, which is to be fitted with a driving force transmitting (receiving) member, for example, a helical gear, is given such a cross-sectional shape (for example, D-shaped or H-shaped) that prevents the driving force transmitting member from slipping relative to the shaft in terms of the rotational direction. 
         [0009]    More specifically, in terms of the direction of the teeth of the helical gear, the helical gear is structured so that as driving force is applied (transmitted) to the helical gear from the main assembly of the image forming apparatus, thrust is generated in the direction to push the development roller in the lengthwise direction of the development roller. Further, the electrical contacts for supplying the development roller with the development bias are disposed so that they contact the opposite lengthwise end of the shaft of the development roller from the helical gear in terms of the lengthwise direction of the axial line of the development roller. 
         [0010]    There is another well-known means for driving the development roller, which is disclosed in Japanese Laid-open Patent Application H11-338211. In the case of this development roller driving means, an Oldham&#39;s coupling is used as the member for transmitting driving force to the developing device. The usage of the Oldham&#39;s coupling makes it possible to ensure that even if the rotational axis of the driving force output shaft (driving shaft of main assembly) becomes misaligned with the rotational axis of the driving force input shaft (drive shaft of developing device), the development roller driving force is reliably transmitted to the development roller. 
         [0011]    In the case of a developing apparatus an electrophotographic image forming apparatus structured so that its developing apparatus is mounted into its main assembly in the direction parallel to the axial line of the development roller, it is also structured so that the developing apparatus receives the development roller driving force through its leading end (downstream end) in terms of the developing apparatus insertion direction, and further, so that the electrical contacts of the developing apparatus, which are for supplying the development roller with development bias, make contact with the counterparts of the main assembly of the image forming apparatus, also at the leading end. 
         [0012]    Thus, conventional image forming apparatuses require a large amount of space for routing wiring for the bias contacts. 
         [0013]    Further, in a case where an Oldham&#39;s coupling is used as the member for the developing apparatus to receive the mechanical force from the main assembly of an image forming apparatus, the thrust generated by the transmission of the driving force is not as large as the thrust generated in a case where a helical gear is used as the member for the developing apparatus to receive the mechanical force from the main assembly of the image forming apparatus. Thus, in the case where an Oldham&#39;s coupling is used, it becomes a serious concern how to make the bias contact precisely (reliably) contact, and remain in contact, with the development roller. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention was made in consideration of the above described concern. Thus, its primary object is to provide a developing apparatus, a process cartridge, and an electrophotographic image forming apparatus, which are characterized in that the electrical contact for the development roller precisely (reliably) contact, and remain in contact, with the development roller. 
         [0015]    According to an aspect of the present invention, there is provided a developing apparatus including a developing roller for developing an electrostatic latent image formed on a photosensitive member, wherein said developing apparatus is detachably mountable to a main assembly of an electrophotographic image forming apparatus in an axial direction of said developing roller, said developing apparatus comprising a drive transmission member, provided at one end of said developing roller, for receiving a driving force from the main assembly and transmitting the driving force to said developing roller; an urging member, provided at other end, for urging said developing roller in the axial direction; an abutting portion, provided adjacent said one end, for being abutted by said shaft of said developing roller by an urging force of said urging member to position said developing roller with respect to the axial direction; and a contact member contactable to a main assembly contact provided in the main assembly when said developing apparatus is mounted to the main assembly, wherein said contact member contacts to a peripheral surface of said shaft of said developing roller adjacent said one end to apply a voltage to said developing roller. 
         [0016]    According to another aspect of the present invention, there is provided a process cartridge including a photosensitive member, a developing roller for developing an electrostatic latent image formed on said photosensitive member, wherein said process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus in an axial direction of said developing roller, said process cartridge comprising a drive transmission member, provided at one end of said developing roller, for receiving a driving force from the main assembly and transmitting the driving force to said developing roller; an urging member, provided at other end, for urging said developing roller in the axial direction; an abutting portion, provided adjacent said one end, for being abutted by said shaft of said developing roller by an urging force of said urging member to position said developing roller with respect to the axial direction; and a contact member contactable to a main assembly contact provided in the main assembly when said process cartridge is mounted to the main assembly, wherein said contact member contacts to a peripheral surface of said shaft of said developing roller adjacent said one end to apply a voltage to said developing roller. 
         [0017]    According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, said apparatus comprising (i) a photosensitive member; (ii) a developing device including a developing roller for developing an electrostatic latent image formed on a photosensitive member, wherein said developing device is mounted to a main assembly of an electrophotographic image forming apparatus in an axial direction of said developing roller, said developing device further including a drive transmission member, provided at one end of said developing roller, for receiving a driving force from the main assembly and transmitting the driving force to said developing roller, an urging member, provided at other end, for urging said developing roller in the axial direction, an abutting portion, provided adjacent said one end, for being abutted by said shaft of said developing roller by an urging force of said urging member to position said developing roller with respect to the axial direction, and a contact member contactable to a main assembly contact provided in the main assembly when said developing apparatus is mounted to the main assembly, wherein said contact member contacts to a peripheral surface of said shaft of said developing roller adjacent said one end to apply a voltage to said developing roller; (iii) mounting means for detachably mounting said developing apparatus; and (iv) feeding means for feeding the recording material. 
         [0018]    According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, said apparatus comprising (i) a process cartridge including a photosensitive member, a developing roller for developing an electrostatic latent image formed on said photosensitive member, wherein said process cartridge is mounted to a main assembly of an electrophotographic image forming apparatus in an axial direction of said developing roller, said process cartridge further including a drive transmission member, provided at one end of said developing roller, for receiving a driving force from the main assembly and transmitting the driving force to said developing roller, an urging member, provided at other end, for urging said developing roller in the axial direction, an abutting portion, provided adjacent said one end, for being abutted by said shaft of said developing roller by an urging force of said urging member to position said developing roller with respect to the axial direction, and a contact member contactable to a main assembly contact provided in the main assembly when said process cartridge is mounted to the main assembly, wherein said contact member contacts to a peripheral surface of said shaft of said developing roller adjacent said one end to apply a voltage to said developing roller; (ii) mounting means for detachably mounting said process cartridge; and (iii) feeding means for feeding the recording material. 
         [0019]    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 
         [0020]      FIG. 1  is a schematic sectional view of the electrophotographic color image forming apparatus in the first preferred embodiment of the present invention, which depicts the general structure of the apparatus. 
           [0021]      FIG. 2  is a schematic sectional view of the cartridge for the image forming apparatus shown in  FIG. 1 . 
           [0022]      FIG. 3  is a perspective view of the image forming apparatus in  FIG. 1  prior to the mounting of the cartridge into the main assembly of the image forming apparatus. 
           [0023]      FIG. 4  is a top plan view of the cartridge, which shows the general structure of the cartridge. 
           [0024]      FIG. 5  is a side view of the cartridge, as seen from the leading side of the cartridge in terms of the direction in which the cartridge is mounted into the main assembly of the image forming apparatus, which also depicts the structure of the cartridge. 
           [0025]      FIGS. 6(   a ) and  6 ( b ) are schematic sectional views of the lengthwise end portion of the development roller, from which the development roller is driven. 
           [0026]      FIGS. 7(   a ) and  7 ( b ) are sectional views of the lengthwise end portion of the development roller, in another embodiment of the present invention, from which the development roller is driven. 
           [0027]      FIG. 8  is a perspective view of the lengthwise end portion of the development roller, in the first preferred embodiment, by which the development roller is driven. 
           [0028]      FIG. 9  is a perspective view of the lengthwise end portion of the development roller, in another preferred embodiment, from which the development roller is driven. 
           [0029]      FIG. 10  is a schematic, perspective, and exploded view of one of the lengthwise end portion of the development roller pressing member, and its adjacencies, from which the developing apparatus is not driven, which is for describing the structure of the pressing member. 
           [0030]      FIG. 11  is a side view of the development unit in the first preferred embodiment, as seen from the deepest end of the apparatus main assembly in terms of the cartridge insertion direction, with the Oldham&#39;s coupling  40  removed. 
           [0031]      FIG. 12  is a side view of the development unit  4  in another embodiment, as seen from the deepest end of the apparatus main assembly in terms of the cartridge insertion direction, with the Oldham&#39;s coupling  40  removed. 
           [0032]      FIG. 13  is an exploded perspective view of the Oldham&#39;s coupling, which is for describing the structure of the coupling. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    In the following descriptions of the preferred embodiments of the present invention, the electrical contacts and driving force transmitting member disclosed in the claim portion of this application will be referred to as development roller contacts and Oldham&#39;s coupling, respectively. Further, the surface of the main assembly of the image forming apparatus, upon which the development roller is kept pressed, will be referred as regulating surface. 
       Embodiment 1 
       [0034]    Next, the process cartridge (which hereafter will be referred to simply as cartridge) and electrophotographic image forming apparatus (which hereafter will be referred simply as image forming apparatus) in the first preferred embodiment of the present invention will be described with reference to the appended drawings. 
       (General Structure of Image Forming Apparatus) 
       [0035]    First, referring to  FIGS. 1 and 3 , the image forming apparatus in this embodiment will be described regarding its general structure. The image forming apparatus  100 , shown in  FIG. 1 , has four cartridge chambers  22  ( 22   a - 22   d ), where four cartridges are mounted one for one), which are placed in tandem at a preset angle relative to the horizontal direction ( FIG. 3 ). The four cartridges  7  ( 7   a - 7   d ) in the four cartridge chambers ( 22   a - 22   d ) are provided with four electrophotographic photosensitive drums  1  ( 1   a - 1   d ), respectively. 
         [0036]    The electrophotographic photosensitive drum  1  (which hereafter will be referred to simply as photosensitive drum  1 ) is rotated by a driving member (unshown) in the clockwise direction, shown in  FIG. 1 . In the adjacencies of the peripheral surface of the photosensitive drum  1 , multiple means for processing the photosensitive drum  1  are disposed. More specifically, a cleaning member  6  ( 6   a - 6   d ), a charge roller  2  ( 2   a - 2   d ), and a development unit  4  ( 4   a - 4   d ) are disposed in the listed order. The cleaning member  6  is for removing the developer (which hereafter may be referred to as toner) remaining on the peripheral surface of the photosensitive drum  1  after the abovementioned transfer of the toner image from the photosensitive drum  1 . The charge roller  2  is for uniformly charging the photosensitive drum  1  ( 1   a - 1   d ), respectively, across their peripheral surfaces. The development unit  4  is for developing the abovementioned electrostatic latent image on the photosensitive drum  1  with the use of the toner. As for the main assembly of the image forming apparatus, it is provided with a scanner unit  3  and an intermediary transfer belt  5 . The scanner unit  3  forms an electrostatic latent image on the photosensitive drum  1  by projecting a beam of light on the photosensitive drum  1  while modulating the beam with the information regarding the image to be formed. The intermediary transfer belt  5  is the belt onto which four monochromatic toner images, different in color, are sequentially transferred in layers from the four photosensitive drums  1 . The photosensitive drum  1 , cleaning member  6 , charge roller  2 , and development unit  4  are integrally disposed in a cartridge  7 , which can be removably mountable in the main assembly  100   a  of the image forming apparatus  100  by a user. 
         [0037]    The intermediary transfer belt  5  is suspended by a driver roller  10  and a tension roller  11 . Further, the main assembly  100   a  of the image forming apparatus  100  (which hereafter will be referred to simply as apparatus main assembly  100   a ) is provided with four primary transfer rollers  12  ( 12   a - 12   d ), which are disposed in the loop which the intermediary transfer belt  5  forms. To the intermediary transfer belt  5 , a transfer bias is applied by a bias applying means (unshown). 
         [0038]    After the formation of a toner image on the photosensitive drum  1 , the toner image is carried by the photosensitive drum  1  in the direction indicated by an arrow mark Q, while the intermediary transfer belt  5  is circularly rotated in the direction indicated by an arrow mark R, and a positive bias is applied to the primary transfer rollers  12 . As a result, the four monochromatic toner images, different in color, are sequentially transferred (primary transfer) in layers onto the intermediary transfer belt  5 . Then, the four monochromatic toner images layered on the intermediary transfer belt  5  are conveyed by the intermediary transfer belt  5  to a secondary transfer portion  15  while remaining layered. 
         [0039]    Meanwhile, a sheet S of recording medium (which hereafter will be referred to simply as sheet S) is conveyed to the secondary transfer portion  15  by a recording medium feeding apparatus  13 , a pair of registration rollers  17 , etc., in synchronism with the progression of the above described image forming operation. The recording medium feeding apparatus  13  has: a recording medium feeder cassette  24 , in which multiple sheets S of recording medium are stored; a feeder roller  8  for feeding recording mediums into the apparatus main assembly  100   a ; and a pair of conveyer rollers  16  for conveying further the fed sheet S. The feeder cassette  24  can be pulled out of the apparatus main assembly  3  in the frontward direction. The recording sheets S in the feeder cassette  24  are kept pressed against the feeder roller  8  so that the top sheet S is kept pressed on the feeder roller  8 . They are fed into the apparatus main assembly  100   a  by a separation pad  9  in such a manner that only the top sheet S is fed into the apparatus main assembly  100   a  while being separated from the other recording mediums S in the feeder cassette  24  (separating system based on friction). 
         [0040]    After being fed into the apparatus main assembly  100   a  from the recording medium feeding apparatus  13 , each sheet S is conveyed to the secondary transfer portion  15  by the pair of registration rollers  17 . In the secondary transfer portion  15 , a positive bias is applied to a secondary transfer roller  18 . Thus, the four monochromatic toner images, different in color, on the intermediary transfer belt  5  are transferred together (secondary transfer) onto the sheet S while the four toner images and the sheet S are conveyed through the secondary transfer portion  15 . 
         [0041]    A fixing portion  14 , which is a fixing means, is a portion for fixing an unfixed color toner image on the sheet S, to the sheet S by applying heat and pressure to the sheet S and the unfixed toner image thereon after the transfer of the color toner image onto the sheet S. The fixation belt  14   a  is cylindrical, and is guided by a belt guiding member (unshown) having heating means, such as a heater, bonded to the belt guiding member. The fixation belt  14   a  and a pressure roller  14   b  are kept pressed upon each other by a preset amount of pressure to form a fixation nip between the belt  14   a  and roller  14   b.    
         [0042]    After the formation of an unfixed toner image on the sheet S in the image forming portion, the sheet S is conveyed from the image forming portion to the fixing portion  14 , and then, is conveyed through the fixation nip, which is the interface between the fixation belt  14   a  and pressure roller  14   b . While the sheet S is conveyed through the fixation nip, the sheet S and the multicolor toner images thereon are subjected to heat and pressure. As a result, the unfixed multicolor toner image becomes fixed to the sheet S. Thereafter, the sheet S, that is, the sheet to which the multicolor toner images has just been fixed, is discharged into a delivery tray  20  by a pair of discharge rollers  19 . 
         [0043]    Meanwhile, the toner remaining on the peripheral surface of each of the photosensitive drums  1  after the primary transfer of the toner image, is removed by the cleaning member  6 . The removed toner is recovered into a toner chamber with which the latent image formation units  26  ( 26   a - 26   d ) are provided. 
         [0044]    The toner remaining on the intermediary transfer belt  5  after the transfer (secondary transfer) of the multicolor toner image onto the sheet S is removed by a transfer belt cleaning apparatus  23 . The removed toner is recovered into a waste toner recovery container disposed in the rear end portion of the apparatus main assembly  100   a.    
       (Cartridge) 
       [0045]    Next, referring to  FIG. 2 , the cartridge in this embodiment will be described.  FIG. 2  is a schematic section view of the cartridge  7 , which contains toner t, at a plane perpendicular to the lengthwise direction of the cartridge  7 . Incidentally, the cartridge for storing yellow toner t is referred to as cartridge  7   a , and the cartridge for storing magenta toner t is referred to as cartridge  7   b . Further, the cartridge for storing cyan toner t is referred to as cartridge  7   c , and the cartridge for storing black toner t is referred to as cartridge  7   d . The four cartridges  7   a - 7   d  are the same in structure. 
         [0046]    Each cartridge  7  is made up of a latent image formation unit  26  and a development unit  4 . The latent image formation unit  26  is provided with the photosensitive drum  1 , charge roller  2  (charging means), and cleaning member  6  (cleaning means). The development unit  4  has the development roller  25  (developing means). 
         [0047]    The photosensitive drum  1  is rotatably attached to the cleaning means frame portion  27  of the latent image formation unit  26 , with the bearings (which will be described later) disposed between the cleaning means frame portion  27  and the photosensitive drum  1 . During an image forming operation, the photosensitive drum  1  is rotated by transmitting driving force to the photosensitive drum  1  from a motor (unshown) for driving the latent image formation unit  26 . There are the charge roller  2  and cleaning member  6  in the adjacencies of the peripheral surface of each photosensitive drum  1  as described above. As the transfer residual toner, more specifically, the toner remaining on the peripheral surface of the photosensitive drum  1  is removed by the cleaning member  6 , it falls into the removed toner storage chamber  27   a . A pair of charge roller bearings  28  are attached to the cleaning means frame portion  27  in such a manner that they can be moved in the direction indicated by an arrow mark D which coincides with the axial line of the photosensitive drum  1  and the axial line of the charge roller  2 . The shaft  2   j  (rotational axle) of the charge roller  2  is rotatably supported by the pair of charge roller bearings  28 . Further, the charge roller bearings  28  are kept pressed toward the photosensitive drum  1  by a pair of charge roller pressing members  46 . 
         [0048]    The development unit  4  has a development roller  25  and a development unit frame  31 . The development roller  25  rotates in contact with the photosensitive drum  1  in the direction indicated by an arrow mark B. The development roller  25  is rotatably supported by the development unit frame  31  with a pair of bearings  32  ( 32 R and  32 L) disposed between the lengthwise end portions (in terms of direction parallel to axial line of development roller  25 ) and the right and left walls of the development unit frame  31 , respectively. Further, the development unit  4  is provided with a toner supply roller  34  and a development blade  35 , which are disposed in the adjacencies the peripheral surface of the development roller  25 . The toner supply roller  34  rotates in contact with the development roller  25  in the direction indicated by an arrow mark C. The development blade  35  is for regulating in thickness the layer of toner on the peripheral surface of the development roller  25 . Further, the development unit  4  is provided with a toner conveying member  36  for conveying the toner in the development unit  4  to the abovementioned toner supply roller  34  while stirring the toner. The toner conveying member  36  is disposed in the toner storage portion  31   a  of the development unit frame  31 . 
         [0049]    The development unit  4  is connected to the latent image formation unit  26  with the use of a pair of shafts  37  ( 37 R and  37 L) put through the holes  32 R and  32 L with which the bearings  32 R and  32 L are provided, respectively, in such a manner that the two units  4  and  26  are enabled to rotationally move relative to each other about the pair of shafts  37 . The development unit  4  is kept under the pressure by a pair of compression springs  38 . Thus, as the cartridge  7  is mounted into the apparatus main assembly  100   a , the development unit  4  rotates about the pair of shafts  37  in the direction indicted by an arrow mark A, causing the development roller  25  to come into contact with the photosensitive drum  1 , and ensures that the development roller  25  remains in contact with the photosensitive drum  1  during image formation. 
       (Structure of Oldham&#39;s Coupling) 
       [0050]    Next, referring to  FIG. 13 , the driving force transmitting member (which hereafter may be referred to as Oldham&#39;s coupling) in this embodiment will be described.  FIG. 13  is a perspective and exploded view of the Oldham&#39;s coupling. The Oldham&#39;s coupling  40  is attached to one of the lengthwise ends of the shaft  25   b  of the development roller  25  in terms of the direction parallel to the axial line of the development roller  25 . The Oldham&#39;s coupling  40  is made up of a driving force receiving portion  40   a , a center portion  40   b , and a driving force transmitting portion  40   c . The engaging portion  40   a   2  of the driving force receiving portion  40   a  receives the development roller driving force from the apparatus main assembly  100   a  by engaging with a coupling  100   b  ( FIG. 6 ) of the apparatus main assembly  100   a , which is connected to the drive shaft of the apparatus main assembly  100   a . Incidentally, the development roller shaft  25   b  is rotatably supported by the bearing  32 R ( FIG. 6(   b )), which is solidly fixed to the development unit frame (unshown). 
         [0051]    The driving force transmitting portion  40   c  is solidly fixed to the development roller shaft  25   b  in such a manner that their axes coincide. The driving force transmitting portion  40   c  has a rib  40   c   1 , which is an integrally formed part of the driving force transmitting portion  40   c . The driving force receiving portion  40   a  has three engaging portions  40   a   2  and a rib  40   a   1 , which are integrally formed parts of the driving force receiving portion  40   a . The center portion  40   b  has a groove  40   b   2  into which the rib  40   c   1  of the driving force transmitting portion  40   c  fits. It has also a groove  40   b   1  into which the rib  40   a   1  of the driving force receiving portion  40   a  fits. 
         [0000]    (Structural Arrangement for Keeping Development Roller Contact in Contact with Development Roller Shaft) 
         [0052]    Next, referring to  FIGS. 4 ,  5 ,  6 ,  8 ,  10 ,  11 , and  13 , the relationship between the electrical contact for the development roller  25 , and the development roller shaft, will be described. 
         [0053]      FIG. 4  is a top view of the cartridge  7 . A referential letter W in  FIG. 4  indicates the side from which the cartridge  7  is driven, in terms of the lengthwise direction of the cartridge  7 .  FIG. 5  is a side view of the cartridge  7  as seen from the cartridge driving side W.  FIG. 6  is a combination of enlarged sectional views of the lengthwise end portions of the development unit  4 , from which the development unit  4  is driven. More specifically,  FIGS. 6(   a ) and  6 ( b ) are enlarged sectional views of the lengthwise end portion of the development unit  4  prior to and after, respectively, the attachment of the development roller  25  to the development unit frame. Designated by a referential number  45  is the electrical contact (which hereafter will be referred to simply as development roller contact), which is on the reader&#39;s side of the plane of  FIG. 6 .  FIG. 8  is a perspective view of the lengthwise end portion of the development roller shaft  25   b , which is on the side from which the development roller  25  is driven.  FIG. 10  is a perspective exploded view of the a pressure applying member  41 , which is at the lengthwise end of the development roller shaft  25   b , from which development roller  25  is not driven.  FIG. 8  shows the structure of the pressure applying member  41 .  FIG. 11  is a side view of the development unit  4 , as seen from the driving side W ( FIG. 10) , with the Oldham&#39;s coupling  40  removed. 
         [0054]    Referring to  FIGS. 4 and 6 , the Oldham&#39;s coupling  40  (male coupling) is attached to the lengthwise end of the development roller shaft  25   b , on the side from which the development roller  25  is driven. As the cartridge  7  is mounted into the apparatus main assembly  100   a  of the image forming apparatus  100 , the driving force receiving portion  40   a  of the Oldham&#39;s coupling  40  engages with the coupling (female coupling)  100   b  ( FIG. 6(   b )), which is the driving force transmitting member of the apparatus main assembly  100   a , making it possible for the development roller driving force to be transmitted from the apparatus main assembly  100   a  to the development roller  25 . Next, referring to  FIG. 5 , also as the cartridge  7  is mounted into the apparatus main assembly  100   a , the contact point  45   c  of the development roller contact  45  comes into contact with the electrical contact  100   c  with which the apparatus main assembly  100   a  is provided, making it possible for the bias voltage to be applied to the development roller  25  from the apparatus main assembly  100   a  through the development roller contact  45 . 
         [0055]    Further, the development unit  4  is provided with the pressure applying member  41 , which is at the opposite lengthwise end of development unit  4  from the lengthwise end from which the development unit  4  is driven. Referring to  FIG. 10 , the pressure applying member  41  is made up of a nonelastic member  41   a  and an elastic member  41   b . The elastic member  41   b  applies pressure to the development roller shaft  25   b  through the nonelastic member  41   a , keeping thereby the development roller  25  pressured toward the driving side W. 
         [0056]    Next, referring to  FIG. 8 , the lengthwise end portion of the development roller shaft  25   b , which is on the driving side W, is reduced in diameter relative to the rest of the development roller shaft  25   b , providing thereby the development roller shaft  25   b  with a pressure taking surface  25   c . Next, referring to  FIG. 6(   a ), the bearing  32 R is provided with a roller shaft accommodating hole  32 Rd and a development roller shaft catching surface  32 Ra (which hereafter may be referred to as regulating surface  32 Ra). More specifically, the bearing  32 R is provided with a pair of development roller shaft catching portions, which extend from the main portion of the bearing  32 R toward the Oldham&#39;s coupling  40 . That is, the development roller shaft catching surface  32 Ra is the surface of the development roller shaft catching portion, which faces toward the development roller  25 . Further, the abovementioned development roller contact  45 , which is for applying the bias voltage to the development roller  25 , is attached to the electrical contact placement surface  32 Rc of the bearing  32 R. During the assembly of the development unit  4 , the shaft  25   b  of the development roller  25  is inserted into the bearing  32 R in the direction indicated by an arrow mark F in  FIG. 6(   a ). Next, referring to  FIG. 6(   b ), the development roller  25  is kept pressured toward the driving side W by the pressure applying member  41  ( FIG. 10) , which is located at the lengthwise end of the development roller  25 , from which the development roller  25  is not driven. Thus, the pressure taking surface  25   c  of the development roller shaft  25   b  is kept in contact with the regulating surface  32 Ra of the bearing  32 R; in other words, the development roller  25  is kept precisely positioned in terms of its lengthwise direction. Further, the development roller contact  45  is kept in contact with the development roller shaft  25   b , between the regulating surface  32 Ra and contact placement surface  32 Rc. More specifically, referring to  FIG. 11 , the development roller contact  45  contacts the peripheral surface of the development roller shaft  25   b  by its contact points  45   a  and  45   b.    
         [0057]    Even in a case where the combination of the Oldham&#39;s coupling  40  and pressure applying member  41  is used as it is in this embodiment, the space necessary for connecting the cartridge  7  to the apparatus main assembly  100   a  in mechanical and electrical terms can be significantly reduced (smallest possible without sacrificing function) by structuring an image forming apparatus so that the development roller contact  45  contacts the peripheral surface of the development roller shaft  25   b  on the side from which the development roller  25  is driven, instead of structuring an image forming apparatus so that the development roller contact  45  contacts the lengthwise end surface of the development roller shaft  25   b  on the side from which the development roller  25  is not driven. Further, because the development roller  25  is kept pressured toward the driven side W, the position of the contact between the development roller contact  45  and development roller shaft  25   b  is significantly closer to the referential point of contact between the cartridge  7  and apparatus main assembly  100   a , compared to the position of the contact between the development roller contact ( 45 ) and development roller shaft ( 25   b ) in a conventional image forming apparatus. Therefore, this structural design makes the image forming apparatus  100 , more specifically, the cartridge  7  and apparatus main assembly  100   a , less likely to be adversely affected by the tolerance of the components of the cartridge  7  and apparatus main assembly  100   a , making it possible to reduce in size the spaces to be provided in anticipation of the effects (rattling or the like) attributable to the tolerance. Thus, the structural design of the image forming apparatus in this embodiment can reduce in size the cartridge  7  by reducing in length the cartridge  7 . Further, the cartridge  7  and apparatus main assembly  100   a  in this embodiment are structured so that the development roller contact  45  and pressure taking surface  25   c  are positioned on the outward side of the hole  32 Rd of the bearing  32 R. Therefore, the portion of the development roller shaft  25   a , which is on the inward side of the bearing  32 R, and the portion of the development roller shaft  25   b , which fits in the hole  32 Rd of the bearing  32 R, can be formed continuous and the same in diameter. Therefore, it is unnecessary to take into consideration the geometrical tolerance regarding coaxially or the like, unlike the case where the portion of the development roller shaft  25   b , which is on the inward side of the bearing  32 R and the portion of the development roller shaft  25   b , which is on the outward side of the bearing  32 R, are different in diameter. Thus, the structural design for the image forming apparatus in this embodiment can reduces in amount the tolerance of the components of an image forming apparatus. Further, the portions by which the development roller  25  is supported, and the elastic portion  25   a  of the development roller  25 , which contacts the photosensitive drum  1 , are coaxial. Therefore, the development roller  25  is stable in rotation, ensuring that the image forming apparatus  100  remains stable in image quality. 
       Embodiment 2 
       [0058]    (Structural Arrangement for Keeping Development Roller Contact in Contact with Development Roller Shaft) 
         [0059]    Next, referring to  FIGS. 4 ,  5 ,  7 ,  9 ,  10 ,  12 , and  13 , the relationship between the development roller contact and development roller shaft in the second preferred embodiment of the present invention will be described. 
         [0060]      FIG. 4  is a top plan view of the cartridge  7 . A letter W in  FIG. 4  indicates the side from which the cartridge  7  is driven.  FIG. 5  is a side view of the cartridge  7  as seen from the driving side W.  FIG. 7  is a combination of enlarged sectional views of the lengthwise end of the development unit  4 , from which the development unit  4  is driven, and the bearing  32 R, in the second embodiment of the present invention. More specifically,  FIGS. 7(   a ) and  7 ( b ) are enlarged sectional views of the lengthwise end portion of the development unit  4 , from which the development unit  4  is driven, prior to and after, respectively, the attachment of the development roller  25  to the frame (bearing) of the development unit. Designated by a referential number  45  in  FIG. 7  is the development roller contact, which is on the reader&#39;s side of the plane of  FIG. 7 .  FIG. 9  is a perspective view of the lengthwise end portion of the development roller shaft  25   b , from which the development roller  25  is driven.  FIG. 10  is a perspective view of the a pressure applying member  41 , which is at the lengthwise end of the development roller shaft  25   b , from which development roller  25  is not driven, and shows the structure of the pressure applying member  41 .  FIG. 12  is a side view of the development unit  4 , as seen from the driving side W ( FIG. 10) , that is, the side from which the development roller  25  is driven, with the Oldham&#39;s coupling  40  removed. 
         [0061]    Referring to  FIGS. 4 and 7 , the Oldham&#39;s coupling  40  (male coupling) is attached to the lengthwise end of the development roller shaft  25   b , on the side from which the development roller  25  is driven. As the cartridge  7  is mounted into the apparatus main assembly  100   a  of the image forming apparatus  100 , the driving force receiving portion  40   a  of the Oldham&#39;s coupling  40  engages with the coupling  100   b  ( FIG. 7(   b )), which is the driving force transmitting member of the apparatus main assembly  100   a , making it possible for the development roller driving force to be transmitted from the apparatus main assembly  100   a  to the development roller shaft  25   b.    
         [0062]    Further, the development unit  4  is provided with the pressure applying member  41 , which is at the opposite lengthwise end of development unit  4  from the lengthwise end from which the development unit  4  is driven. Referring to  FIG. 10 , the pressure applying member  41  is made up of a nonelastic member  41   a  and an elastic member  41   b . The elastic member  41   b  applies pressure to the development roller shaft  25   b  through the nonelastic member  41   a , keeping thereby the development roller  25  pressured toward the driving side W. 
         [0063]    Next, referring to  FIG. 9 , the lengthwise end portion of the development roller shaft  25   b  on the driving side W is reduced in diameter relative to the rest of the development roller shaft  25   b , providing thereby the development roller shaft  25   b  with a pressure taking surface  56   c . Next, referring to  FIG. 7(   a ), the bearing  32 R is provided with a roller shaft accommodating hole  32 Rd and a regulating surface  53 Ra. More specifically, the bearing  32 R is provided with a pair of development roller shaft catching portions, which slightly protrude from the main portion of the bearing  32 R toward the direction from which the development roller shaft  25   d  is inserted into the bearing  32 R. The regulating surface  53 Ra is the surface of the development roller shaft catching portion, which faces toward the development roller  25 . Further, the abovementioned development roller contact  45  is attached to the electrical contact placement surface  32 Rc of the bearing  32 R. During the assembly of the development unit  4 , the shaft  25   b  of the development roller  25  is inserted into the bearing  32 R in the direction indicated by an arrow mark F in  FIG. 7(   a ). Next, referring to  FIG. 7(   b ), the development roller  25  is kept pressured toward the driving side W by the pressure applying member  41  ( FIG. 10) , which is located at the lengthwise end of the development roller  25 , from which the development roller  25  is not driven. Thus, the pressure taking surface  56   c  of the development roller shaft  25   b  is kept in contact with the regulating surface  53 Ra of the bearing  32 R; in other words, the development roller  25  is kept precisely positioned in terms of its lengthwise direction. Further, the development roller contact  45  is kept in contact with the development roller shaft  25   b , between the Oldham&#39;s coupling  40  and contact placement surface  32 Rc. That is, the development roller contact  45  contacts the peripheral surface of the development roller shaft  25   b  by its contact points  45   a  and  45   b  as shown in  FIG. 12 . 
         [0064]    Even in a case where the combination of the Oldham&#39;s coupling  40  and pressure applying member  41  is used as it is in this embodiment, the space necessary for connecting the cartridge  7  to the apparatus main assembly  100   a  in mechanical and electrical terms can be significantly reduced (smallest possible without sacrificing function) by structuring an image forming apparatus so that the development roller contact  45  contacts the peripheral surface of the development roller shaft  25   b , on the side from which the development roller  25  is driven, instead of structuring an image forming apparatus so that the development roller contact  45  contacts the lengthwise end surface of the development roller shaft  25   b , on the side from which the development roller  25  is not driven. Further, because the development roller  25  is kept pressured toward the driven side W, with the use of the pressure applying member  41 , the position of the contact between the development roller contact  45  and development roller shaft  25   b  is significantly closer to the referential point of contact between the cartridge  7  and apparatus main assembly  100   a , compared to the position of the contact between the development roller contact ( 45 ) and development roller shaft ( 25   b ) in a conventional image forming apparatus. Therefore, this structural design makes the image forming apparatus  100 , more specifically, the cartridge  7  and apparatus main assembly  100   a , less likely to be adversely affected by the tolerance of the components of the cartridge  7  and apparatus main assembly  100   a , making it possible to reduce in size the spaces to be provided in anticipation of the effects (rattling or the like) attributable to the tolerance. Thus, the structural design of the image forming apparatus in this embodiment can reduce in size the cartridge  7  by reducing in length the cartridge  7 . Further, the cartridge  7  and apparatus main assembly  100   a  are structured so that the development roller contact  45  and pressure taking surface  25   c  are positioned at the hole  32 Rd of the bearing  32 R (more specifically, on the upstream side as seen from side from which development roller shaft  25   b  is inserted into bearing  32 R). Therefore, it is possible to utilize a conventional bearing ( 32 ) without modifying it in shape and/or providing it with the space for mechanical and electrical connection. In other words, the present invention can reduce in size an image forming apparatus by simplifying in structure the bearings for supporting the development roller shaft. 
         [0065]    As described above, according to the present invention, both the member for transmitting mechanical driving force to the development roller, and the electrical contact for transmitting electrical power to the development roller, are positioned at one of the lengthwise ends of the development roller shaft (same lengthwise end), and therefore, it is unnecessary for the space for the electrical contact to be provided at the other lengthwise end. In other words, the present invention can reduce in size a developing apparatus and a process cartridge. Further, according to the present invention, a development roller is kept under pressure so that one of its lengthwise ends remains in contact with the surface of the corresponding development roller bearing. Therefore, it is ensured that the electrical contact for the development roller remains precisely positioned relative to the development roller shaft. 
         [0066]    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. 
         [0067]    This application claims priority from Japanese Patent Applications Nos. 138040/2008 and 107877/2009 filed May 27, 2008 and Apr. 27, 2009, respectively which are hereby incorporated by reference.