Abstract:
A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The cartridge includes an electrophotographic photosensitive drum, a drum unit supporting the drum, a developing unit supporting a developing roller and swingably coupled with the drum unit, drum and developing roller rotating force receiving portions, first and second positionable portions positioned at first and second main assembly side positioning portions by contacting by an urging force of first and second main assembly side urging members, a developing device spacing force receiving portion, first and second cartridge side rotation regulating portions for limiting rotation of the drum unit by abutting first and second main assembly side rotation regulating portions when the drum and developing roller rotating force receiving portions receive the rotating forces or when the developing device spacing force receiving portion receives the urging force from the main assembly.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a process cartridge, and an image forming apparatus which employs a process cartridge. 
         [0002]    Here, an “electrophotographic image forming apparatus” means an apparatus which forms an image on recording medium with the use of electrophotographic image forming method. As the examples of an electrophotographic image forming apparatus, an electrophotographic copying machine, an electrophotographic printer (for example, laser beam printer, LED printer, etc.), a facsimile machine, a wordprocessor, etc., may be included. 
         [0003]    A “process cartridge” means a cartridge in which an electrophotographic photosensitive drum, and processing means, more specifically, a charging means, a developing means or cleaning means, 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 an electrophotographic photosensitive drum, and at least one processing means, more specifically, 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 electrophotographic image forming apparatus. Further, it means a cartridge in which an electrophotographic photosensitive drum, and at least one processing means, more specifically, a developing apparatus, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
         [0004]    In the field of an electrophotographic image forming apparatus which uses an electrophotographic process, it has been a common practice to employ a process cartridge system, that is, a system that places an electrophotographic photosensitive drum, and one or more processing means for processing an electrophotographic photosensitive drum, in a cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. A process cartridge system makes it possible for a user to perform some of the ordinary maintenance operations by himself (herself), that is, without relying on a service person. Thus, the employment of a process cartridge system can significantly improve an electrophotographic image forming apparatus in operational efficiency. Therefore, a process cartridge system is widely in use in the field of an electrophotographic image forming apparatus. 
         [0005]    Roughly describing, the image forming operation of an electrophotographic image forming apparatus is as follows: A beam of light emitted from a laser, an LED, an ordinary light source, etc., is projected upon an electrophotographic photosensitive drum, while being modulated according to the information regarding an image to be formed. As the beam of light is projected upon the electrophotographic photosensitive drum, an electrostatic latent image is formed on the photosensitive drum. This electrostatic latent image is developed by a developing apparatus. Then, the developed electrostatic latent image on the photosensitive drum is transferred onto recording medium, yielding a print (copy), that is, recording medium having an intended image. 
         [0006]    As one of the structural designs for accurately positioning a process cartridge, such as the one described above, relative to the main assembly of an electrophotographic image forming apparatus, the following one has been known. That is, each of the left and right lateral plates located in the main assembly of the image forming apparatus is provided with a groove (recess) for positioning a photosensitive drum. Further, the main assembly of the image forming apparatus is provided with a pair of springs, which are located at the left and right ends of the main assembly, one for one, to keep a pair of bearings, with which the lengthwise ends of the photosensitive drum were provided, pressed upon the surfaces of the groove (recess) of the corresponding lateral plate. With the pair of bearings kept pressed upon the lateral plates, one for one, the cartridge is kept accurately positioned relative to the main assembly of the image forming apparatus. Further, as a cartridge is inserted into the main assembly of the image forming apparatus, the projection with which each of the abovementioned springs is provided comes into contact with the corresponding bearing, being thereby rotated by the pressure applied by the process cartridge. Then, as soon as the bearing rides over the projection, the projection presses the bearing upon the surfaces of the abovementioned groove (recess). Further, the regulating portion with which the drum unit of a cartridge is provided engages with the counterpart with which the main assembly of the image forming apparatus is provided, preventing thereby the photosensitive member unit from moving further. Further, the process cartridge is pressed upward (U.S. Pat. No. 6,681,088). 
         [0007]    It has been desired that even in the case of the combination of a process cartridge and an electrophotographic image forming apparatus, such as the one described above, the cartridge is positioned relative to the main assembly of the image forming apparatus just as accurately as a process cartridge in accordance with the prior art is positioned relative to the main assembly of an image forming apparatus in accordance with the prior art. 
       SUMMARY OF THE INVENTION 
       [0008]    The primary object of the present invention is to provide a process cartridge which is designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, and yet, can be reliably positioned relative to the main assembly, and an electrophotographic image forming apparatus compatible with the process cartridge. 
         [0009]    Another object of the present invention is to provide a process cartridge which is designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, and yet, is significantly higher in the level of accuracy at which a process cartridge is positioned relative to the main assembly of an image forming apparatus, than a process cartridge in accordance with the prior art, and also, to provide an electrophotographic image forming apparatus compatible with the process cartridge. 
         [0010]    Another object of the present invention is to provide a process cartridge which can be reliably positioned relative to the main assembly of an image forming apparatus even when it is receiving the rotational force for rotating its development roller and photosensitive drum from the main assembly, and also, to provide an electrophotographic image forming apparatus compatible with the process cartridge. 
         [0011]    Another object of the present invention is to provide a process cartridge which can be reliably positioned relative to the main assembly of an image forming apparatus even when it is receiving the force for separating its development roller from its photosensitive drum from the main assembly, and also, to provide an electrophotographic image forming apparatus compatible with the process cartridge. 
         [0012]    Another object of the present invention is related to a process cartridge which is designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, and is to provide a process cartridge which can be reliably positioned relative to the main assembly even when it is receiving the rotational force for rotating its development roller and photosensitive drum from the main assembly, and an electrophotographic image forming apparatus compatible with the cartridge. 
         [0013]    Another object of the present invention is also related to a process cartridge which is designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, and is to provide a process cartridge which can be reliably positioned relative to the main assembly even when it is receiving the force for separating its development roller from its photosensitive drum from the main assembly, and an electrophotographic image forming apparatus compatible with the cartridge. 
         [0014]    Another object of the present invention is also related to a process cartridge which is designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, and is to provide a process cartridge which can be accurately positioned relative to the main assembly even when it is receiving the rotational force for rotating its development roller and photosensitive drum from the main assembly, and an electrophotographic image forming apparatus compatible with the cartridge. 
         [0015]    According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein said apparatus includes a first main assembly side positioning portion, a second main assembly side positioning portion, a first main assembly side urging member for upward urging, a second main assembly side urging member for upward urging, a first main assembly side rotation regulating portion, a second main assembly side rotation regulating portion, a drum rotating force applying portion, a developing roller rotating force applying portion, and a developing device spacing force applying portion, said process cartridge comprising an electrophotographic photosensitive drum; a drum unit supporting said electrophotographic photosensitive drum; a developing unit supporting a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum while being in contact with said electrophotographic photosensitive drum, wherein said developing unit is swingably coupled with said drum unit; a drum rotating force receiving portion for receiving a rotating force for rotating said electrophotographic photosensitive drum from the drum rotating force applying portion in a state in which said process cartridge is mounted to the main assembly, wherein said drum rotating force receiving portion is provided at a leading end of said drum unit with respect to a mounting direction in which said process cartridge is mounted to the main assembly; a developing roller rotating force receiving portion for receiving a rotating force for rotating said developing roller from the developing roller rotating force applying portion in a state in which said process cartridge is mounted to the main assembly, wherein said developing roller rotating force receiving portion is provided at a leading end of said developing unit with respect to the mounting direction; first cartridge side portion-to-be-positioned for being positioned at the first main assembly side positioning portion by contacting to the first main assembly side positioning portion by an urging force of the first main assembly side urging member in said state, wherein said first cartridge side portion-to-be-positioned is provided on a downstream side of said drum unit with respect to the mounting direction; second cartridge side portion-to-be-positioned for being positioned at the second main assembly side positioning portion by contacting to the second main assembly side positioning portion by an urging force of the second main assembly side urging member in said state, wherein said second cartridge side portion-to-be-positioned is provided on an upstream side of said drum unit with respect to the mounting direction; a developing device spacing force receiving portion, provided on said developing unit, for receiving an urging force for spacing said developing roller from said electrophotographic photosensitive drum from the developing device spacing force applying portion in said state; a first cartridge side rotation regulating portion for limiting rotation of said drum unit by abutting to the first main assembly side rotation regulating portion in said state, when said drum rotating force receiving portion and said developing roller rotating force receiving portion receive the rotating forces from the main assembly or when said developing device spacing force receiving portion receives the urging force from the main assembly, wherein said first cartridge side rotation regulating portion is provided on a downstream side of said drum unit with respect to the mounting direction; and a second cartridge side rotation regulating portion for limiting rotation of said drum unit by abutting to the second main assembly side rotation regulating portion in said state, when said drum rotating force receiving portion and said developing roller rotating force receiving portion receive the rotating forces from the main assembly or when said developing device spacing force receiving portion receives the urging force from the main assembly, wherein said second cartridge side rotation regulating portion is provided on an upstream side of said drum unit with respect to the mounting direction. 
         [0016]    The present invention ensures that even a process cartridge designed to be positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly is accurately positioned relative to the main assembly. 
         [0017]    The present invention improves a process cartridge designed to be positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly, in terms of the level of accuracy at which a process cartridge is positioned relative to the main assembly of an image forming apparatus. 
         [0018]    According to the present invention, a process cartridge can be reliably positioned relative to the main assembly of an image forming apparatus even when the cartridge is receiving the force for rotating its development roller and photosensitive drum from the main assembly while the process cartridge is in the main assembly. 
         [0019]    According to the present invention, a process cartridge can be reliably positioned relative to the main assembly even when the cartridge is receiving the force for separating its development roller from its photosensitive drum from the main assembly while the process cartridge is in the main assembly. 
         [0020]    According to the present invention, even a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly can be reliably positioned relative to the main assembly even when the cartridge is receiving the force for rotating its development roller and photosensitive drum, from the main assembly while the process cartridge is in the main assembly. 
         [0021]    According to the present invention, even a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly can be reliably positioned relative to the main assembly even when the cartridge is receiving the force for separating its development roller from its photosensitive drum, from the main assembly while the process cartridge is in the main assembly. 
         [0022]    According to the present invention, even a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly can be accurately positioned relative to the main assembly even when the cartridge is receiving the force for rotating its development roller and photosensitive drum, from the main assembly while the process cartridge is in the main assembly. 
         [0023]    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 
         [0024]      FIG. 1  is a schematic drawing of the electrophotographic color image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0025]      FIG. 2  is a sectional view of the cartridge in the first embodiment of the present invention. 
           [0026]      FIG. 3  is a perspective view of the image forming apparatus in the first embodiment, into which one of the cartridges therefor is about to be inserted. 
           [0027]      FIG. 4  is an external perspective view of one of the cartridges in the first embodiment of the present invention. 
           [0028]      FIG. 5  is a schematic perspective view of the structural components, with which the main assembly of the image forming apparatus in the first embodiment is provided for positioning the process cartridge relative to the main assembly, and the pressing mechanism, with which the main assembly is provided for pressing the process cartridge. 
           [0029]      FIG. 6  is a detailed perspective view of the cartridge positioning assembly and cartridge pressing mechanical assembly, which are located at the rear end of the main assembly of the image forming apparatus in the first embodiment of the present invention. 
           [0030]      FIG. 7  is a detailed perspective view of the cartridge positioning assembly and bearing pressing mechanism, which are located at the front end of the main assembly of the image forming apparatus in the first embodiment of the present invention. 
           [0031]      FIG. 8  is a schematic drawing of the bearing pressing mechanism (assembly) located at the rear end of the main assembly of the image forming apparatus in the first embodiment, as seen from the right side of the main assembly, showing the cartridge pressing operation of the mechanism. 
           [0032]      FIG. 9  is a schematic drawing of the bearing pressing mechanism located at the downstream end of the main assembly of the image forming apparatus in the first embodiment, as seen from the downstream side in terms of the direction in which the cartridge is mounted, showing the cartridge pressing operation of the mechanism. 
           [0033]      FIG. 10  is a schematic drawing of the bearing pressing mechanism located at the front end, as seen from the left side of the main assembly, showing the cartridge pressing operation of the mechanism. 
           [0034]      FIG. 11  is a schematic drawing of the bearing pressing mechanism located at the upstream end of the main assembly of the image forming apparatus, in terms of the cartridge mounting direction, as seen from the upstream side, showing the cartridge pressing operation of the mechanism. 
           [0035]      FIG. 12  is a schematic drawing for showing the directions, indicated by arrow marks P 1  and P 2 , in which the bearing pressing member pressing portions  40   c  and  50   c  are pressed by the bearing pressing members  83  and  93 , in the first embodiment. 
           [0036]      FIG. 13  is an external perspective view of the cartridge in the first embodiment. 
           [0037]      FIG. 14  is a top plan view of the cartridge in the first embodiment of the process cartridge. 
           [0038]      FIG. 15  is a schematic sectional view of the cartridge in the first embodiment, which is in its image forming position in the main assembly of the image forming apparatus, and the development roller of which is in contact with photosensitive drum of the cartridge. 
           [0039]      FIG. 16  is a schematic sectional view of the cartridge in the first embodiment, which is in its image forming position in the main assembly of the image forming apparatus, and the development roller of which is holding a preset amount of distance from the photosensitive drum of the cartridge. 
           [0040]      FIG. 17  is a schematic drawing for describing the development roller supporting portion of the cartridge in the first embodiment, showing the structure of the portion. 
           [0041]      FIG. 18  is an exploded view of the development roller coupling and coupling bearing  45  of the cartridge in the first embodiment. 
           [0042]      FIG. 19  is a sectional view of the development roller coupling of the cartridge in the first embodiment. 
           [0043]      FIG. 20  is a perspective view of the couplings of the cartridge, and the couplings of the main assembly of the image forming apparatus, in the first embodiment. 
           [0044]      FIG. 21  is a perspective view of the cartridge driving first and second members of the main assembly of the image forming apparatus in the first embodiment. 
           [0045]      FIG. 22  is a schematic drawing for describing the movement of the couplings of the cartridge in the first embodiment, which occurs when the development roller is separated from the photosensitive drum. 
           [0046]      FIG. 23  is a schematic drawing for describing the movement of the couplings of the cartridge in the first embodiment, which occurs when the development roller is separated from the photosensitive drum. 
           [0047]      FIG. 24  is a schematic drawing for describing the movement of the couplings of the cartridge in the first embodiment, which occurs when the development roller is placed in contact with the photosensitive drum. 
           [0048]      FIG. 25  is a schematic drawing for describing the movement of the couplings of the cartridge in the first embodiment, which occurs when the development roller is placed in contact with the photosensitive drum. 
           [0049]      FIG. 26  is an external perspective view of the cartridge in the second embodiment. 
           [0050]      FIG. 27  is a schematic drawing for describing the movement of the couplings of the cartridge in the third embodiment, which occurs when the development roller is separated from the photosensitive drum. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0051]    Hereinafter, the process cartridge (which hereafter will be referred to simply as cartridge) and electrophotographic color image forming apparatus (which hereafter will be referred to simply as image forming apparatus), in the first embodiment of the present invention will be described with reference to the appended drawings. 
       (General Structure of Image Forming Apparatus) 
       [0052]    First, referring to  FIG. 1 , the general structure of the image forming apparatus will be described. The image forming apparatus  100  shown in  FIG. 1  has four cartridge compartments  22  ( 22   a - 22   d ) ( FIG. 3 ), into which four cartridges are mounted, one for one. The four cartridge compartments  22  are juxtaposed in tandem, in a straight line which is slanted relative to the horizontal direction. The cartridges  7  ( 7   a - 7   d ), which are to be mounted into the four cartridge compartments  22 , one for one, are provided with electrophotographic photosensitive members  1  ( 1   a,    1   b,    1   c,  and  1   d ), respectively; each cartridge  7  is provided with a single photosensitive drum  1 . 
         [0053]    The abovementioned electrophotographic photosensitive drum  1  (which hereafter will be referred to as photosensitive drum  1 ) is rotationally driven in the clockwise direction of the drawing by a driving member (unshown). Each process cartridge  7  is provided with multiple processing means, more specifically, a cleaning member  6  ( 6   a,    6   b,    6   c,  or  6   d ) and a charge roller  2  ( 2   a,    2   b,    2   c,  or  2   d ), which process the photosensitive drum  1 . The processing means are arranged in the adjacencies of the peripheral surface of the photosensitive drum  1  in the same order as the order in which they are listed above. The cleaning member  6  cleans the developer (which here after may be referred to as developer) remaining on the peripheral surface of the photosensitive drum  1  after the image transfer from the photosensitive drum  1 . The charge roller  2  uniformly charges the peripheral surface of the photosensitive drum  1 . The process cartridge  7  is also provided with a development unit  4  ( 4   a,    4   b,    4   c,  or  4   d ) which develops the abovementioned electrostatic latent image with the use of toner. Also arranged in the adjacencies of the peripheral surface of the photosensitive drum  1  are a scanner unit  3 , and an intermediary transfer belt  5 . The scanner unit  3  forms an electrostatic latent image on the peripheral surface of the photosensitive drum  1  by projecting a beam of laser light upon the peripheral surface of the photosensitive drum  1  while modulating the laser beam according to the information regarding the image to be formed. The intermediary transfer belt  5  is a belt onto which four toner images, different in color, formed on the photosensitive drums  1  are sequentially transferred in layers. The photosensitive drum  1 , cleaning member  6 , and charge roller  2  are integrated as a drum unit  26 . The drum unit  26  and development unit  4  are joined, making up a process cartridge  7  (which hereafter will be referred to simply as cartridge  7 ), which is removably mountable in the main assembly  100   a  of the image forming apparatus  100  by a user. 
         [0054]    The intermediary transfer belt  5  is stretched around a driver roller  10  and a tension roller  11 , being thereby suspended by the two rollers  10  and  11 . There are four primary transfer rollers  12  ( 12   a - 12   d ), which are inside the loop which the intermediary transfer belt  5  forms. The primary transfer rollers  12   a - 12   d  are positioned so that they oppose the photosensitive drums  1   a - 1   d,  with the intermediary transfer belt  5  sandwiched between the primary transfer rollers  12   a - 12   d  and photosensitive drums  1   a - 1   d,  respectively. To the transfer belt  5 , a transfer bias is applied by a bias applying means (unshown). 
         [0055]    As a toner image is formed on the peripheral surface of the photosensitive drum  1 , which is being moved in the direction indicated by an arrow mark Q, it is transferred (primary transfer), by applying a positive bias to the primary transfer roller  12 , onto the intermediary transfer belt  5 , which is being circularly moved in the direction indicated by an arrow mark R. The same image forming operations, except for the toner used by the developing unit, are sequentially carried out in the four process cartridges. As a result, four toner images, different in color, are deposited in layers on the intermediary transfer belt  5 , and are conveyed to the secondary transfer portion  15 . 
         [0056]    In synchronism with the abovementioned image forming operation carried out in each process cartridge, a sheet of recording medium S (which hereafter will be referred to simply as recording medium S) is fed into, and conveyed in, the apparatus main assembly  100   a  by a recording medium conveying means made up of a sheet feeding apparatus  13 , a pair of registration rollers  17 , etc. The sheet feeding apparatus  13  has a sheet feeder cassette  24 , a sheet feeding and conveying roller  8 , and a pair of sheet conveyance rollers  16 . The sheet feeder cassette  24  stores multiple sheets of recording medium S. The sheet feeding and conveying roller  8  feeds a sheet of recording medium S into the apparatus main assembly  100   a,  and conveys the recording medium S in the apparatus main assembly  100   a,  or feeds in succession multiple recording mediums S into the apparatus main assembly  100   a,  and conveys the recording mediums S in the apparatus main assembly  100   a.  The sheet feeder cassette  24  can be pulled out of the apparatus main assembly  100   a  in the frontward direction. As a recording medium S is fed into the apparatus main assembly  100   a  by the sheet feeding and conveying roller  8 , it is pressed upon the roller  8  by a separation pad  9 . Thus, if two or more recording mediums S are pulled out together from the sheet feeder cassette  24 , only the recording medium which is in contact with the roller  8  is conveyed into the apparatus main assembly  100   a  while being separated from the rest by the combination of the roller  8  and pad  9  (one-sided sheet separating method based on friction). 
         [0057]    As the sheet S is conveyed inward of the apparatus main assembly  100   a  by the sheet feeding apparatus  13 , it is conveyed to the secondary transfer portion  15  by the pair of registration rollers  17 . In the secondary transfer portion  15 , the positive bias is applied to the secondary transfer roller  18 . As a result, the four toner images, different in color, on the intermediary transfer belt  5  are transferred together (secondary transfer) onto the sheet S which is being conveyed through the secondary transfer portion  15 . 
         [0058]    A fixing portion  14 , which is a fixing means of the apparatus main assembly. It is a portion of the apparatus main assembly  100   a,  which fixes the toner images on the sheet S, onto the sheet S by applying heat and pressure to the sheet S and toner images thereon. A fixation belt  14   a  is cylindrical. It is guided by a belt guiding member (unshown) provided with a heat generating means, such as a heater, which is bonded to the belt guiding member. The fixation belt  14   a  is kept pressed upon the pressure roller  14   b,  forming a fixation nip, so that a preset amount of contact pressure is maintained between the fixation belt  14   a  and pressure roller  14   b.    
         [0059]    After the unfixed toner images are sequentially transferred onto the sheet S through the four image forming portions, the sheet S is conveyed to the fixing portion  14 , and is conveyed through the fixation nip, that is, the interface between the fixation belt  14   a  and pressure roller  14   b,  while being subjected heat and pressure. As a result, the unfixed toner images on the sheet S become fixed to the sheet S. After the fixation of the toner images to the sheet S, the sheet S is discharged into a delivery tray  20  by a pair of discharge rollers  19 . 
         [0060]    The toner remaining on the peripheral surface of the photosensitive drum  1  after the toner image transfer is removed by the cleaning member  6 . The removed toner is recovered into the removed toner chamber in the photosensitive member unit  26  ( 26   a - 26   d ). 
         [0061]    The toner remaining on the intermediary transfer belt  5  after the second transfer, that is, the transfer of the toner images onto the sheet S from the intermediary transfer belt  5 , is removed by a transfer belt cleaning apparatus  23 . The removed toner is conveyed through a waste toner conveyance passage (unshown), and is recovered into a waste toner recovery bin (unshown) located in the rear end portion of the apparatus main assembly  100   a.    
       (Cartridge) 
       [0062]    Next, referring to  FIG. 2 , the cartridge in this embodiment will be described.  FIG. 2  is a sectional view of the cartridge  7  in the first embodiment, at a plane parallel to the front panel of the image forming apparatus  100 . There is a toner t in the cartridge  7 . Incidentally, the cartridges  7   a,    7   b,    7   c,  and  7   d,  which correspond to yellow, magenta, cyan, and black toners t, respectively, are the same in structure. 
         [0063]    Each cartridge  7  is made up of a drum unit  26  and a development unit  4 . The drum unit  26  has the photosensitive drum  1 , charge roller  2  (charging means), and cleaning member  6  (cleaning means). The development unit  4  has a development roller  25  (developing means). The photosensitive drum  1  is rotatably supported by the frame  27  of the drum unit  26 , with a pair of bearings interposed between the drum unit frame  27  and photosensitive drum  1 . The bearings will be described later. The photosensitive drum  1  is rotationally driven in synchronism with the progression of an image forming operation, by the driving force transmitted from a motor (unshown) to the drum unit  26 . 
         [0064]    The charge roller  2  and cleaning member  6  are positioned in the adjacencies of the peripheral surface of the photosensitive drum  1  as described previously. As the residual toner, that is, the toner remaining on the peripheral surface of the photosensitive drums  1 , is removed by the cleaning member  6 , it falls into the toner chamber  27   a  for the removed residual toner. The drum unit frame  27  is fitted with a pair of charge roller bearings  28 , which are movable in the direction indicated by an arrow mark D, which coincides with the axial line of the photosensitive drum  1  and axial line of the charge roller  2 . The axle  2   j  of the charge roller  2  is rotatably supported by the pair of charge roller bearings  28 . Further, the bearings  28  are kept pressed toward the photosensitive drum  1  by a pair of charge roller pressing members  49 . 
         [0065]    The development unit  4  has the 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 end walls of the development unit frame  31 , in terms of the lengthwise direction of the cartridge  7 , are fitted with a pair of development roller bearing members  32  ( 32 R and  32 L), one for one. The development roller  25  is rotatably supported by the development unit frame  31  (bearings members  32 ). The development unit  4  is also provided with a toner supply roller  34  and a development blade  35 , which are positioned in the adjacencies of 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 toner layer on the development roller  25 . Further, the development unit  4  is provided with a toner conveying member  36 , which is in the toner storage portion  31   a  of the development unit frame  31 , and conveys the toner in the toner storage portion  31   a  to the toner supply roller  34  while stirring the toner. 
         [0066]    The development roller bearing members  32 R and  32 F (which hereafter will be referred to simply as bearing member  32 R and  32 F) of the development unit  4  are provided with holes  32 Rb and  32 Fb, respectively. The development unit  4  is connected to the photosensitive member unit  26 , with a pair of shafts (connective pins)  37  ( 37 R and  37 F) fitted in the abovementioned holes  32 Rb and  32 Fb of the bearing members  32 Rb and  32 Fb, in such manner that the development unit  4  is rotationally movable about the shafts (connective pins)  37  in the direction indicated by an arrow mark A. The development unit  4  is kept pressured by a pair of compression springs  38 . Thus, during an image forming operation, the development roller  25  is kept in contact with the photosensitive drum  1  by the compression springs  38 . 
         [0000]    (Structural Arrangement for Mounting Cartridge into Image Forming Apparatus Main Assembly) 
         [0067]    Next, referring to  FIG. 3 , the portions of the apparatus main assembly, which make it possible to removably mount the cartridge  7  into the apparatus main assembly  100   a,  will be described. 
         [0068]      FIG. 3  is a perspective view of the apparatus main assembly  100   a  when the cartridge  7   a  is about to be inserted into the apparatus main assembly  100   a.  Incidentally, the direction in which the cartridge  7  is mounted into the apparatus main assembly  100   a  in this embodiment is the direction indicated by an arrow mark F, which is parallel to the axial line of the photosensitive drum  1 . That is, the apparatus main assembly  100   a  is structured so that the cartridge  7  is to be inserted from the front side of the apparatus main assembly  100   a,  in the front-to-rear direction in  FIG. 1 , and also, so that the cartridge  7  is removably mountable in the apparatus main assembly  100   a.    
         [0069]    Referring to  FIG. 3 , the apparatus main assembly  100   a  is provided with a front cover  21 , which is attached to the front panel of the apparatus main assembly  100   a  and can rotatably opened frontward. As the front cover  21  is opened, the four cartridge compartments  22  ( 22   a - 22   d ), which accommodate the four cartridges  7  ( 7   a - 7   d ), respectively, are exposed. The four cartridge compartments  22  are juxtaposed in tandem, in a straight line which is slanted relative to the horizontal direction. Each cartridge compartment  22  is provided with a first cartridge guide  80  ( 80   a - 80   d ) and a second cartridge guide  81  ( 81   a - 81   d ). The first and second cartridge guides  80  and  81  are at the top and bottom ends, respectively, of the compartment  22 , and extend from the front end of the compartment  22  to the rear end of the compartment  22 . Correspondingly, the cartridge  7  is provided with a cartridge guiding projection  29  (first portion of cartridge  7  by which cartridge is guided into or out of cartridge compartment  22 ) and a cartridge guiding rib  30  (second portion of cartridge by which cartridge is guided into or out of cartridge compartment  22 ). If it is necessary to mount the cartridge  7  into the cartridge compartment  22 , the cartridge  7  is to be pushed in the direction indicated by the arrow mark F, with the cartridge guiding portions  29  and rib  30  of the cartridge  7  aligned with the first and second cartridge guides  80  and  81  of the cartridge compartment  22  (apparatus main assembly  100   a ). 
         [0070]    In terms of the direction in which the cartridge  7  is inserted into the cartridge compartment  22 , the abovementioned cartridge guiding first portion  29  (projection) of the cartridge  7  is at the leading end of the cartridge  7 . In terms of the vertical direction, it is at the top of the cartridge  7 . The cartridge guiding second portion  30  (rib) of the cartridge  7  is at the bottom of the cartridge  7 , and extends from the leading end of the cartridge  7  to the trailing end. 
         [0071]    As the cartridge  7  is inserted into the cartridge compartment  22  far enough for the leading end of the cartridge  7  to reach a preset point in the compartment  22 , the main assembly contacting portions  40   a  and  50   a  of the cartridge  7 , which are at the leading and trailing ends, respectively, of the cartridge  7 , are positioned relative to the apparatus main assembly  100   a,  positioning thereby the cartridge  7  relative to the apparatus main assembly  100   a.  This ends the mounting of the cartridge  7 . 
         [0072]    As the rotational force for rotating the photosensitive drum  1 , development roller  25 , etc., in the cartridge  7  is transmitted to the cartridge  7 , it tends to rotationally move the cartridge  7 . Thus, in order to prevent the cartridge  7  from being rotationally moved by this force, the cartridge  7  is provided with a projection  27   b  (cartridge rotation regulating portion) ( FIG. 4 ) and a groove  27   c  (second cartridge rotation regulating portion). The projection  27   b  is on the outward surface of the leading end wall of the cartridge  7 , in terms of the cartridge mounting direction F, and extends downstream in the direction parallel to the cartridge mounting direction F (cartridge advancement direction). The groove  27   c  is in the front end portion of the bottom surface of the cartridge  7 . It is U-shaped in cross section. Further, the apparatus main assembly  100   a  is provided with a projection  92   c  ( FIG. 5 ) and a hole  82   b  (cartridge rotation regulating first portion of apparatus main assembly  100   a ) ( FIG. 5 ). The projection  92   c  is on the inward surface of the front wall of the apparatus main assembly  100   a,  and perpendicularly projects inward of the apparatus main assembly  100   a.  The hole  82   b  is a part of the rear wall of the apparatus main assembly  100   a  and is elongated in cross section. As the cartridge  7  is moved into the image forming position in the apparatus main assembly  100   a,  the projection  27   b  of the cartridge  7  fits into the hole  82   b  of the apparatus main assembly  100   a,  and the projection  92   c  of the apparatus main assembly  100   a  fits into the groove  27   c  of the cartridge  7 . 
         [0073]    How the cartridge  7  is prevented from rotationally moving as the driving force is transmitted to the cartridge  7 , will be described later in detail. 
         [0074]    As described above, the cartridge guiding projection  29  of the cartridge  7  is on the top surface of the cartridge  7 , and is at the leading end, in terms of the direction in which the cartridge  7  is advanced in to the apparatus main assembly  100   a  when the cartridge  7  is mounted into the apparatus main assembly  100   a.  The cartridge guiding rib  30  of the cartridge  7  is on the bottom surface of the cartridge  7 , and extends from leading end to the trailing end of the cartridge  7 . Further, in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the projection  29  and rib  30  are on the same side of the photosensitive drum  1 . 
         [0075]    Thus, the cartridge  7  remains stable while it is advanced into the apparatus main assembly  100   a.    
         [0076]    The portions of the cartridge  7 , and the portions of the apparatus main assembly  100   a,  which are involved in the accurate positioning of the cartridge  7  relative to the apparatus main assembly  100   a,  will be described later in detail regarding their structure. 
         [0000]    (Structural Arrangement for Positioning Cartridge Relative to Image Forming Apparatus Main assembly, and Structural Arrangement for Keeping Cartridge Pressed) 
         [0077]    Next, referring to  FIG. 4-7 , and  14 , the structural arrangement for accurately positioning the cartridge  7  relative to the apparatus main assembly  100   a,  and the structural arrangement for pressing the cartridge  7  upon the cartridge positioning portions of the apparatus main assembly  100   a  and keeping the cartridge pressed thereupon, will be describe.  FIG. 4  is an external perspective view of the cartridge  7 , and  FIG. 14  is a top plan view of the cartridge  7 . 
         [0078]    Referring to  FIG. 4 , which is an external perspective view of the cartridge  7 , the photosensitive drum  1  which the cartridge  7  has is rotatably supported at the lengthwise ends of its rotational axle (unshown), by a pair of bearings  40  and  50 , one for one, which are solidly attached to the front and rear walls of the drum unit frame  27 , one for one. 
         [0079]    Referring to  FIGS. 4 and 14 , the bearing  40  of the cartridge  7 , which is at the rear end of the cartridge  7 , that is, the leading end of the cartridge  7  in terms of the direction in which the cartridge  7  advances in the apparatus main assembly  100   a  when it is mounted into the apparatus main assembly  100   a,  has the main assembly contacting first portion  40   a  (which has portions  40   a   1  and  40   a   2 ), which is a part of the top surface of the bearing  40 . More specifically the main assembly contacting first portion  40   a  (having portions  40   a   1  and  40   a   2 ), that is, the first portion of the bearing  40 , which is for accurately positioning the rear side of the cartridge  7  relative to the apparatus main assembly  100   a,  is a part of the upwardly facing portion of the peripheral surface of the bearing  40  which is arcuate in cross section. The bearing  40  is the drum shaft bearing first member, and supports the photosensitive drum  1  at one of the lengthwise ends of the drum  1  in terms of the axial direction of the photosensitive drum  1 . In terms of the cartridge advancement direction in the apparatus main assembly  100   a,  the bearing  40  is at the downstream end of the cartridge  7 . 
         [0080]    The bearing  40  is also provided with a bearing pressing member catching portion  40   b,  which is pressed by a bearing pressing member  83  (pressuring member, upwardly pushing member) ( FIG. 5 ), which will be described later. The portion  40   b  of the bearing  40  is below the main assembly contacting portion  40   a.    
         [0081]    Incidentally, the abovementioned cartridge advancement direction means the direction in which the cartridge  7  advances into the apparatus main assembly  100   a  when a user mounts the cartridge  7  into the apparatus main assembly  100   a.  That is, the cartridge advancement direction is the same as the abovementioned cartridge mounting direction F. 
         [0082]    The main assembly contacting portion  40   a  is made up of two portions, that is, the main assembly contacting portion  40   a   1  and main assembly contacting portion  40   a   2 , which are on the one side of the axial line I of the photosensitive drum  1  and the other ( FIG. 14 ), one for one. The axial line I is the axial line of the photosensitive drum  1 , which is parallel to the lengthwise direction of the photosensitive drum  1 . That is, the axial line I is parallel to the lengthwise direction of the cartridge  7 . In other words, the cartridge  7  is provided with the main assembly contacting first portion  40   a   1  and main assembly contacting second portion  40   a   2 , which are on one side of the axial line I and the other, respectively. Further, the main assembly contacting first and second portions  40   a   1  and  40   a   2  (which position leading end of cartridge relative to apparatus main assembly  100   a ) oppose each other across the axial line I ( FIG. 14 ). 
         [0083]    The bearing pressing member catching portion  40   b  of the bearing  40  is on the downstream side of the photosensitive drum  1  in terms of the abovementioned cartridge advancement direction. As seen from the direction, indicated by an arrow mark J ( FIG. 9(   c )), in which the bearing pressing member  83  (pressure applying first member, upwardly pressing member of apparatus main assembly  100   a ), presses on the bearing  40 , the bearing pressing member catching portion  40   b  is between the main assembly contacting first portion  40   a   1  and main assembly contacting second portion  40   a   2  (roughly at mid point between portions  40   a   1  and  40   a   2 ). This structural arrangement ensures that as the bearing pressing member catching portion  40   b  is pressed by the bearing pressing member  83 , the main assembly contacting portion  40   a  is placed in contact with a bearing catching portion  82   a  (cartridge positioning first portion of apparatus main assembly  100   a ), being thereby accurately positioned relative to the apparatus main assembly  100   a.    
         [0084]    In this embodiment, the cartridge  7  is provided with the main assembly contacting first portion  40   a   1  and main assembly contacting second portion  40   a   2 , in order to ensure that the leading end of the cartridge  7  is accurately positioned, and is kept accurately positioned, relative to the apparatus main assembly  100   a.  However, the number of the cartridge positioning portions at the leading end of the cartridge  7  in terms of the cartridge mounting direction, may be only one. 
         [0085]    Referring again to  FIG. 4 , the rear bearing  40  is provided with a bearing pressing member pressing portion  40   c  (bearing pressing member pressing first portion) for causing the bearing pressing member  83  to move back into its retreat position. In terms of the direction which is horizontal and perpendicular to the cartridge advancement direction, the bearing pressing member pressing portion  40   c  (which hereafter may be referred to simply as pressing portion  40   c ) is located farther from the center of the cartridge  7  than the abovementioned bearing pressing member catching portion  40   b  is. In terms of the cartridge advancement direction, the bearing pressing member pressing portion  40   c  is on the downstream end wall of the cartridge  7 , and perpendicularly projects downstream from the end wall. The tip portion of the pressing portion  40   c  is provided with a projection  40   d,  which projects downward. The projection  40   d  is triangular in cross section. That is, it has gently slanted surfaces  40   e  and  40   f,  which are on the downstream side and upstream side, respectively, of the apex of the projection  40   d,  in terms of the cartridge advancement direction. 
         [0086]    Also referring to  FIG. 4 , the top portion of the peripheral surface of the rear bearing  40  has a main assembly contacting first portion (surface)  40   h  (cartridge rotation regulating first portion of cartridge  7 ), which is positioned higher than the main assembly contacting portion  40   a.  The main assembly contacting first surface  40   h  is flat and is between the main assembly contacting first portion  40   a   1  and main assembly contacting second portion  40   a   2 . Further, the rear bearing  40  is provided with a surface  40   g,  which is positioned lower than the main assembly contacting first portion  40   h.  Further, the rear bearing  40  is provided with a main assembly contacting surface  40   i,  which is another surface of the bearing  40 , which positions the cartridge  7  relative to the apparatus main assembly  100   a  in terms of the lengthwise direction of the cartridge  7 . As the cartridge  7  is moved into the apparatus main assembly  100   a,  the main assembly contacting surface  40   i  comes into contact with the inward surface of the rear wall of the apparatus main assembly  100   a,  and remains in contact therewith, ensuring that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  in terms of the lengthwise direction of the cartridge  7 , and also, that the cartridge  7  remains accurately positioned relative to the apparatus main assembly  100   a  in terms of the lengthwise direction of the cartridge  7  after the mounting of the cartridge  7  into the apparatus main assembly  100   a.    
         [0087]    Next, the front bearing  50  (photosensitive drum axle bearing second bearing which is at the other end, in terms of direction parallel to axial line of photosensitive drum  1 , from the end supported by rear bearing  40 ), that is, the photosensitive drum axle bearing member located at the trailing end of the cartridge  7  in terms of the cartridge advancement direction, will be described. The front bearing  50  has a cartridge positioning second portion  50   a  of the cartridge  7  (which has portions  50   a   1  and  50   a   2 ) ( FIGS. 4 and 14 ), which is for positioning the front side of the cartridge  7  relative to the apparatus main assembly  100   a  in terms of the direction perpendicular to the abovementioned cartridge advancement direction. The cartridge positioning portion  50   a  is a top portion of the peripheral surface of the arcuate portion of the bearing  50 , being therefore accurate, as seen from the direction parallel to the axial line of the photosensitive drum  1 . The front bearing  50  is also provided with a bearing pressing member catching portion  50   b,  which comes into contact with the apparatus main assembly  100   a  as upward force is applied to the front bearing  50  by a cartridge lifting member  93  ( FIG. 5 ), which will be described later. The bearing pressing member catching portion  50   b  is positioned higher than the cartridge positioning portion  50   a.    
         [0088]    Like the main assembly contacting portion  40   a,  the above mentioned cartridge positioning front portion  50   a  has a cartridge positioning portion  50   a   1  (third cartridge positioning portion) and a cartridge positioning portion  50   a   2  (fourth cartridge positioning portion), which are on one side the axial line I of the photosensitive drum  1  and the other side, respectively. That is, the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  opposes each other across the axial line I ( FIG. 4 ). 
         [0089]    In terms of the cartridge advancement direction, the bearing pressing member catching portion  50   b  is on the downstream side of the photosensitive drum  1 . Further, as seen from the direction, indicated by a arrow mark K ( FIG. 11(   c )), in which the cartridge  7  is lifted by the cartridge lifting member  93  (cartridge pressing second member of main assembly  100   a ), the bearing pressing member catching portion  50   b  is between the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  (roughly at mid point between portions  50   a   1  and  50   a   2 ). This structural arrangement ensures that as upward force is applied to the bearing pressing member catching portion  50   b,  the cartridge positioning portion  50   a  is placed in contact with the cartridge contacting portion  92   a  of the apparatus main assembly  100   a,  accurately positioning the cartridge  7  relative to the apparatus main assembly  100   a.    
         [0090]    In this embodiment, the front bearing  50  has the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  as the portions for accurately positioning the rear side of the cartridge  7  relative to the apparatus main assembly  100   a.  Therefore, it is ensured that the cartridge  7  is more reliably pressed, and kept pressed, upon the cartridge contacting portion  92   a  of the apparatus main assembly  100   a.  However, the number of the cartridge positioning portion for positioning the rear side of the cartridge  7  may be only one. 
         [0091]    Also referring to  FIG. 4 , the front bearing  50  is provided with a bearing pressing member pressing portion  50   c  (pressing member pressing second portion) for causing the cartridge lifting member  93  to move back into its retreat position. In terms of the direction, which is horizontal, and perpendicular to the cartridge advancement direction, the bearing pressing member pressing portion  50   c  (which hereafter may be referred to simply as contacting portion  50   c ) is located farther from the center of the cartridge  7  than the abovementioned bearing pressing member catching portion  50   b  is. In terms of the cartridge advancement direction, the bearing pressing member pressing portion  50   c  is on the downstream end wall of the cartridge  7 , and perpendicularly projects downstream. The tip portion of the bearing pressing member pressing portion  50   c  is provided with a projection  50   d,  which projects downward. The projection  50   d  is triangular in cross section. That is, it has gently slanted surfaces  50   e  and  50   f,  which are on the downstream side and upstream side, respectively, of the apex of the projection  50   d,  in terms of the cartridge advancement direction. 
         [0092]    Referring again to  FIG. 4 , the front bearing  50  also has a main assembly contacting surface (portion)  50   h  (cartridge contacting second portion: cartridge positioning second portion of bearing  50 ), which is a part of the top surface of the front bearing  50 . The main assembly contacting portion  50   h  is positioned higher than the cartridge positioning portion  50   a  is. The main assembly contacting second portion  50   h  is flat and is between the cartridge positioning third portion cartridge  50   a   1  and cartridge positioning fourth portion cartridge  50   a   2 . Further, the front bearing  50  is provided with a surface  50   g,  which is positioned lower than the main assembly contacting second portion  50   h.    
         [0093]    Next, the portions of the structure of the apparatus main assembly  100   a,  which are for accurately positioning the cartridge  7  and keeping the cartridge  7  pressed upon the cartridge positioning portions of the apparatus main assembly  100   a  will be described.  FIG. 5  is a schematic drawing for describing the portions of the image forming apparatus main assembly, which are for accurately positioning the cartridge  7  and keeping the cartridge  7  pressed upon the cartridge positioning portions of the apparatus main assembly  100   a.    FIG. 6  is a detailed drawing for describing the rear portions of the image forming apparatus main assembly  100   a,  which are for accurately positioning the cartridge  7  and keeping the cartridge  7  pressed upon the cartridge positioning portions of the apparatus main assembly  100   a.    FIG. 7  is a detailed drawing for describing the front portions of the image forming apparatus main assembly, which are for accurately positioning the cartridge  7  and keeping the cartridge  7  pressed upon the cartridge positioning portions of the apparatus main assembly  100   a.    
         [0094]    Referring to  FIG. 5 , the apparatus main assembly  100   a  is provided with lateral plates  8  and  9 , which are at the rear and front ends of the apparatus main assembly  100   a,  in terms of the cartridge mounting direction. The lateral plate  92  is provided with an opening  92   b,  which makes it possible for the cartridge  7  to be removable mounted into the apparatus main assembly  100   a.  That is, it is through the opening  92   b  that the cartridge  7  is inserted into the apparatus main assembly  100   a.  More specifically, as the cartridge  7  is inserted into the apparatus main assembly  100   a  through the opening  92   b,  the cartridge  7  is guided into the apparatus main assembly  100   a  by the above described top cartridge guide  80  and bottom cartridge guide  81  ( FIG. 3 ) in the direction indicated by the arrow mark F. It is also through the opening  92   b  that the cartridge  7  is removed from the apparatus main assembly  100   a.  These operations are to be carried out by a user. 
         [0095]    Referring to  FIG. 6 , the lateral plate  82  is has the abovementioned bearing catching portion  82   a  (which has portions  82   a   1  and  82   a   2 ), that is, the bearing  40  positioning first portion of the apparatus main assembly  100   a,  which is for accurately positioning the bearing  40  (cartridge  7 ) relative to the apparatus main assembly  100   a  in terms of the direction perpendicular to the cartridge mounting direction (cartridge advancement direction). The lateral plate  82  is also provided with the bearing pressing member  83  (bearing pressing first member of apparatus main assembly  100   a ) for pressing the bearing  40  toward the bearing catching portion  82   a  by being under the pressure (elastic force) generated by a compression spring  85 . This bearing pressing member  83  functions as a member for keeping the bearing  40  (cartridge  7 ) pressed upward by being under the pressure from the compression spring  85 . The bearing pressing member  83  will be described later in detail. 
         [0096]    The bearing pressing member  83  is on the opposite side of the bearing  40  accommodating hole of the lateral plate  82  from the bearing catching portion  82   a.  It has a hole  83   a,  in which a shaft  84  fixed to the lateral plate  82  is fitted. More specifically, the bearing pressing member  83  is structured, and is attached to the lateral plate  82 , so that it is allowed to take a bearing pressing position, a retreat position, and a standby position. The bearing pressing position is the position for keeping the bearing  40  (cartridge  7 ) pressed upon the cartridge contacting portion  82   a.  The retreat position is the position into which it is moved to eliminate the pressure it applies to the bearing  40  (cartridge  7 ). The standby position is a position which corresponds to a preset point in the cartridge passage. 
         [0097]    Further, the bearing pressing member  83  is provided with a cartridge (bearing) pressing portion  83   b,  which presses on the bearing  40  (cartridge  7 ) when the bearing pressing member  83  is in the bearing (cartridge) pressing position; the bearing (cartridge) pressing portion  83   b  corresponds in position to the bearing pressing member catching portion  40   b  of the bearing  40  of the cartridge  7 . The bearing pressing member  83  is also provided with a bearing contacting first portion  83   c  for moving the bearing pressing member  83  into the retreat position. The bearing contacting first portion  83   c  corresponds in position to the bearing pressing member pressing portion  40   c.  The bearing contacting first portion  83   c  is provided with a projection  83   d,  which projects upward. The projection  83   d  is triangular in cross section. That is, it has gently sloped surfaces  83   e  and  83   f,  which are on the downstream side and upstream side, respectively, of the apex of the projection  83   d,  in terms of the cartridge advancement direction. In terms of the direction perpendicular to the cartridge mounting direction F, the bearing contacting first portion  83   c  is located farther from the axial line of the hole  83   a  than the bearing (cartridge) pressing portion  83   b  is. That is, in terms of the lengthwise direction of the bearing pressing member  83 , the axial line of the hole  83   a,  bearing pressing portion  83   b,  and bearing contacting first portion  83   c  are arranged in the listed order. 
         [0098]    Further, the lateral plate  82  is provided with a cartridge position regulating portion  86  (cartridge position regulating first portion of apparatus main assembly  100   a ) for regulating the upward movement of the cartridge  7  attributable to the reactive force generated when the bearing pressing member  83  is moved into its retreat position. The cartridge movement regulating portion  86  is formed of a resin, and is between the two portions  82   a   1  and  82   a   2  of the bearing catching portion  82   a  of the lateral plate  82 . 
         [0099]    Next, referring to  FIG. 7 , the lateral plate  92  has the abovementioned cartridge insertion opening  92   b.  Further, the lateral plate  92  is provided with a cartridge catching portion  92   a  (which has portions  92   a   1  and  92   a   2 ), that is, the cartridge positioning second portion of the apparatus main assembly  100   a,  which is for accurately positioning the cartridge  7  (bearing  50 ) relative to the apparatus main assembly  100   a  in terms of the direction perpendicular to the cartridge mounting direction. The two portions  92   a   1  and  92   a   2  of the bearing catching portion  92   a  are at the top of the cartridge insertion opening  92   b.  Further, the lateral plate  92  is provided with the cartridge lifting member  93  (bearing pressing second member of apparatus main assembly  100   a ) for pressing the cartridge  7  (bearing  50 ) toward the bearing catching portion  92   a  by being under the force (tension) generated by a tensile spring  95 . The cartridge lifting member  93  is positioned higher than the bearing catching portion  92   a.  Further, the lateral plate  92  is provided with a shaft  94 , which is solidly fixed to the lateral plate  92 , and the cartridge lifting member  93  is provided with a hole  93   a  (second hole of  93   a ). The shaft  94  is fitted in the hole  93   a.  The cartridge lifting member  93  is structured, and attached to the lateral plate  92 , so that it is allowed to take a bearing pressing position (bearing pressing position), a retreat position, and a standby position. The bearing pressing position is the position for keeping the bearing  50  pressed upon the bearing catching portion  92   a.  The retreat position is the position into which the cartridge lifting member  93  is moved to eliminate the pressure it applied to the bearing  50 . The standby position is a position which corresponds to a preset point in the cartridge passage. 
         [0100]    Further, the cartridge lifting member  93  is provided with a bearing pressing portion  93   b,  which presses the bearing  50  upward when the cartridge lifting member  93  is in the bearing pressing position; the bearing pressing portion  93   b  corresponds in position to the bearing pressing member catching portion  50   b  of the cartridge  7 . The cartridge lifting member  93  is also provided with a bearing contacting second portion  93   c  for moving the cartridge lifting member  93  into the retreat position. The bearing contacting second portion  93   c  corresponds in position to the bearing pressing member pressing portion  50   c.  The cartridge lifting member  93  is provided with a projection  93   d,  which projects upward. The projection  93   d  is triangular in cross section. That is, it has gently sloped surfaces  93   e  and  93   f,  which are on the downstream side and upstream side, respectively, of the apex of the projection  93   d,  in terms of the cartridge advancement direction ( FIG. 10 ). 
         [0101]    In terms of the direction perpendicular to the cartridge mounting direction, the bearing contacting second portion  93   c  is located farther from the axial line of the hole  93   a  than the bearing pressing portion  93   b.  That is, in terms of the lengthwise direction of the cartridge lifting member  93 , the axial line of the hole  93   a,  bearing pressing member  93   b,  and bearing contacting second portion  93   c  are arranged in the listed order. 
         [0102]    Further, the cartridge lifting member  93  is provided with a bearing position regulating portion  96  (cartridge position regulating second portion of apparatus main assembly  100   a ) for regulating the upward movement of the bearing  50  attributable to the reactive force generated when the cartridge lifting member  93  is moved into the retreat position. The bearing position regulating portion  96  is formed of a resin, and is between the two portions  92   a   1  and  92   a   2  of the bearing catching portion  92   a  of the lateral plate  92 . 
         [0103]    In this embodiment, the leading end portion of the cartridge  7  in terms of the cartridge mounting direction is pressed upward by the bearing pressing member  83  (bearing pressing member, cartridge lifting member) on the opposite side of the bearing accommodating hole of the lateral plate  82  from the bearing catching portion  82   a  so that the leading end portion of the cartridge  7  (bearing  40 ) is placed in contact with the bearing catching portion  82   a,  which is on the opposite side of the bearing accommodating hole of the lateral plate  82  from the bearing pressing member  83 . On the trailing side of the cartridge  7  in terms of the cartridge mounting direction, the trailing end portion of the cartridge  7  (bearing  50 ) is pulled upward by the cartridge lifting member  93  (cartridge pulling member), which is positioned so that it will be above the trailing portion (bearing  50 ) of the cartridge  7 , to place the bearing  50  in contact with the bearing catching portion  92   a  of the lateral plate  92 , which is the top portion of the edge of the cartridge insertion opening  92   b.  That is, while the cartridge  7  is in its image forming position in the apparatus main assembly  100   a,  the bearing  40  is pressed upon the bearing catching portion  82   a  (bearing contacting portion) by the bearing pressing member  83 . Therefore, the main assembly contacting first portion  40   a   1  and main assembly contacting second portion  40   a   2  (cartridge positioning portions at leading end of cartridge  7 ) are accurately positioned relative to the bearing catching portion  82   a  (cartridge positioning first portion of apparatus main assembly  100   a ). 
         [0104]    Further, the bearing  50  is pressed upward by the upward force applied thereto by the cartridge lifting member  93 . Therefore, the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  (portions for positioning trailing end portion of cartridge) are placed in contact with the bearing catching portion  92   a  (having portions  92   a   1  and  92   a   2 ) (cartridge positioning second portion of apparatus main assembly  100   a ), respectively. The above described structural arrangement makes it possible to provide the lateral plate  92  with the cartridge insertion opening  92   a  through which the cartridge  7  is removably mountable into the cartridge spaces (cartridge compartments  22 ) in the apparatus main assembly  100   a.  Therefore, the bearing  50 , which is the adjacencies of the cartridge positioning portion of the cartridge  7 , can be directly pressed by the bearing pressing member  92 , in the image forming apparatus  100  structured so that the cartridge  7  is to be mounted into the apparatus main assembly  100   a  in the direction parallel to the axial line of the photosensitive drum  1 . 
         [0105]    In other words, the above described structural arrangement makes it possible to directly press both the rear bearing  40  and front bearing  50 . That is, the above described structural arrangement stabilizes the force by which the cartridge  7  (rear and front bearings  40  and  50 ) is pressed, and is kept pressed, upon the cartridge positioning portions of the apparatus main assembly  100   a,  ensuring that the cartridge  7  is accurately positioned, and remains accurately positioned, relative to the apparatus main assembly  100   a.  Therefore, it is ensured that the photosensitive drum  1  is accurately positioned, and remains accurately positioned, in contact with the intermediary transfer belt  5 . 
         [0106]    As described above, the cartridge  7  is provided with the photosensitive drum axle bearing first member  40 , that is, the bearing which supports one end of the photosensitive drum  1  in terms of the direction parallel to the axial line of the photosensitive drum  1 . Further, the main assembly contacting first surface  40   h  and main assembly contacting portion  40   a  (having portions  40   a   1  and  40   a   2 ) are portions of the peripheral surface of the drum axle bearing first member  40 . In addition, the cartridge  7  is provided with the photosensitive drum axle bearing second member  50 , that is, the bearing which supports the other end of the drum  1 . The main assembly contacting second portion  50   h  and main assembly contacting portion  50   a  (cartridge positioning portion) (cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2 ) are portions of the peripheral surface of the drum axle bearing second member  50 . Therefore, it is ensured that the cartridge  7  is accurately positioned, and remains accurately positioned, relative to the apparatus main assembly  100   a.    
         [0107]    Further, in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the main assembly contacting surface  40   h,  that is, the main assembly contacting first portion (cartridge movement regulating first portion of cartridge  7 ), is rendered different in position from the main assembly contacting first portion  40   a  (having portions  40   a   1  and  40   a   2 ). Also in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the main assembly contacting surface  50   h,  that is, the main assembly contacting second portion (cartridge movement regulating second portion), is different in position from the bearing positioning second portion  50   a  (having portion  50   a   1  and  50   a   2 ) (cartridge positioning second portion). Further, in terms of the cartridge mounting direction, the main assembly contacting first surface  40   h  is at the leading end of the cartridge  7 , whereas the main assembly contacting second surface  50   h  is at the trailing end of the cartridge  7 . Therefore, it does not occur that the main assembly contacting portions  40   a  and  50   a  (cartridge positioning portions) rub against the apparatus main assembly  100   a  while the cartridge  7  is mounted into the apparatus main assembly  100   a.  Therefore, the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a.    
         [0108]    The summary of the description of the cartridge  7  and apparatus main assembly  100   a  in the first embodiment of the present invention is as follows: 
         [0109]    The apparatus main assembly  100   a  is provided with the bearing catching portion  82   a  (having portions  82   a   1  and  82   a   2 : cartridge positioning first portions) and bearing catching portion (having portions  92   a   1  and  92   a   2 ): cartridge positioning second portions). The apparatus main assembly  100   a  is also provided with the lateral plate  82  (bearing pressing first member, cartridge raising (bearing raising) first member) for pressing the cartridge  7  (bearing  40 ) upward, and the cartridge lifting member  93  (cartridge (bearing) pressing second member) for pressing the cartridge  7  (bearing  50 ) upward. More specifically, the bearing pressing member  83  presses the cartridge  7  (bearing  40 ) from under the cartridge  7  (bearing  40 ), whereas the cartridge lifting member  93  presses the cartridge  7  (bearing  50 ) upward by pulling the cartridge  7  (bearing  50 ) from above. 
         [0110]    It should be noted here that this embodiment is not intended to limit the present invention in the structure of the cartridge  7  and apparatus main assembly  100   a.  That is, in terms of the cartridge mounting direction, the bearing pressing member  93  and  83 , that is, the members for pressing the cartridge  7  (bearing  50 ) upward, and keeping it pressed upward, may be positioned at the rear and front ends of the apparatus main assembly  100   a,  respectively, instead of the front and rear of the apparatus main assembly  100   a,  respectively, as they are in this embodiment. However, it is by the structural arrangement employed in this embodiment that the above described effects of this embodiment are obtained. 
       (Operation of Cartridge (Bearing) Pressing Mechanism During Moving and Removing of Cartridge) 
       [0111]    Next, referring to  FIGS. 8-11 , the operation of the bearing pressing mechanism during the mounting of the cartridge into the image forming apparatus and the removing of the cartridge from the image forming apparatus  100  will be described. 
         [0112]    (a) Rear End: Operation of Bearing Pressing Mechanism During Mounting and Removing of Cartridge 
         [0113]      FIG. 8  is a schematic drawing of the bearing pressing mechanism (assembly) on the rear side, as seen from the right side of the main assembly of the image forming apparatus, and shows the operation of the bearing pressing member.  FIG. 9  is a schematic drawing of the bearing pressing mechanism on the rear side, as seen from the downstream side in terms of the direction in which the cartridge is mounted, and shows the bearing pressing operation of the mechanism. 
         [0114]    The cartridge  7  is mounted in the direction indicated by the arrow mark F, as described above. Referring to  FIGS. 8(   a ) and  9 ( a ), as the cartridge  7  is inserted into the apparatus main assembly  100   a,  the sloped surface  40   e  of the bearing pressing member pressing portion  40   c  comes into contact with the slanted surface  83   e  of the bearing contacting first portion  83   c  (standby position). Then, as the cartridge  7  is inserted further, the bearing pressing member  83  is gradually moved downward by the bearing pressing member pressing portion  40   c.  As a result, the projection  40   d  of the bearing pressing member pressing portion  40   c  comes into contact with the projection  83   d  of the bearing contacting first portion  83   c,  and then, causes the bearing pressing member  83  to retreat in the direction indicated by an arrow mark X (retreat position), as shown in  FIG. 8(   b ). 
         [0115]    More specifically, the bearing pressing member  83  is made to retreat into the position in which its does not contact the bearing pressing member catching portion  40   b  of the bearing  40  ( FIG. 9(   b )). Therefore, while the cartridge  7  is mounted, the bearing pressing member catching portion  40   b  is not pressed by the bearing pressing portion  83   b.  The pressure which the bearing  40  receives when the cartridge  7  is mounted is cancelled by the bearing pressing member pressing portion  40   c,  which is positioned farther from the axial line of the hole  83   a  than the bearing catching portion  82   a.  That is, the force necessary to moves the bearing  40  downward against the upward force (pressure) applied to the bearing  40  is reduced by the amount proportional to the ratio between the distance from the axial line of the hole  83   a  to the bearing pressing member catching portion  40   b  ( 83   b ), and the distance from the axial line of the hole  83   a  to the bearing pressing member pressing portion  40   c  ( 83   c ). Therefore, the amount of load to which the cartridge  7  is subjected when the cartridge  7  is mounted is sufficiently small relative to the amount of pressure applied to the cartridge  7  by the bearing pressing member  83 . That is, this embodiment can reduce the amount of force necessary to mount the cartridge  7 . 
         [0116]    At the same time, the bearing  40  is pressed upward by the reactive force generated by the bearing pressing member  83  as the bearing pressing member  83  is moved downward into its retreat position by the bearing pressing member pressing portion  40   c.  However, the main assembly contacting surface  40   h  comes into contact with the cartridge movement regulating portion  86  of the apparatus main assembly  100   a,  that is, the bearing contacting first portion of the apparatus main assembly  100   a,  regulating thereby the upward movement of bearing  40 . The positional relationship between the bearing position regulating portion  86  and main assembly contacting surface  40   h  is such that they remain in contact with each other until immediately before the main assembly contacting portions  40   a  comes into contact with the bearing catching portion  82   a,  that is, immediately before the main assembly contacting portions  40   a  is positioned by the bearing catching portion  82   a.  Therefore, during the mounting of the cartridge  7 , the cartridge movement regulating portion  86 , which is formed of a resin, and main assembly contacting surface  40   h  continuously rub against each other from the moment the cartridge  7  begins to be pressed upward by the bearing pressing member  83  until immediately before the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a,  whereas the main assembly contacting portions  40   a  does not contact the bearing catching portion of the lateral plate  82  of the apparatus main assembly  100   a,  which is formed of thin steel plate or the like. Therefore, the main assembly contacting portions  40   a  and bearing catching portion  82   a  do not shave each other. 
         [0117]    As the cartridge  7  is inserted even further, the bearing pressing member pressing portion  40   c  gradually disengages from the bearing contacting first portion  83   c,  allowing the bearing pressing member  83  to gradually move back from the retreat position to the bearing pressing position. The cartridge  7  is inserted until the rear lateral plate contacting portion  40   i  of the cartridge  7 , which is the portion for positioning the cartridge  7  in terms of the lengthwise direction of the cartridge  7 , comes into contact with the rear lateral plate  82  of the apparatus main assembly  100   a.  As the cartridge  7  is inserted as far as the rear lateral plate  82 , the bearing pressing member catching portion  40   b  comes into contact with the bearing (cartridge) pressing portion  83   b,  causing the bearing  40  to be pressed in the direction indicated by the arrow mark J (bearing pressing direction,  FIG. 9 ) (bearing pressing position), as shown in  FIGS. 8(   c ) and  9 ( c ). As a result, the main assembly contacting portions  40   a  is placed in contact with the bearing catching portion  82   a  of the rear lateral plate  82  of the apparatus main assembly  100   a,  accurately positioning the bearing  40  (rear end portion of cartridge  7 ) relative to the apparatus main assembly  100   a  in terms of the direction perpendicular to the cartridge mounting direction. Also during this movement of the cartridge  7 , the main assembly contacting surface  40   h  becomes disengaged from the cartridge movement regulating portion  86  of the apparatus main assembly  100   a,  creating a preset amount of gap between the cartridge movement regulating portion  86  and surface  40   g.  At the same time, bearing pressing member pressing portion  40   c  rides past the apex  83   d  of the bearing contacting first portion  83   c,  creating a preset amount of gap between the surface  40   j  and bearing pressing member  83 . 
         [0118]    As descried above, the bearing pressing member  83  is capable of taking the standby position, bearing pressing position (cartridge pressing position), and retreat position. To describe in more detail, listing from the top, the standby position, bearing pressing position, and retreat position of the bearing pressing member  83  are positioned in the stated order. Therefore, the bearing pressing member  83  can apply a sufficient amount of pressure upon the cartridge  7  while the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.    
         [0119]    Next, when it is necessary to take the cartridge  7  out of the apparatus main assembly  100   a,  the above described operation for mounting the cartridge  7  is to be carried in reverse. The pressure from the bearing pressing member  83 , under which the bearing  40  is, is cancelled, as it is when the cartridge  7  is mounted, by the bearing pressing member pressing portion  40   c,  which is located farther from the axial line of the hole  83   a  than the bearing pressing member catching portion  40   b  is. Therefore, the amount of force necessary to remove the cartridge  7  is just as smaller as the amount of force necessary to mount the cartridge  7 . 
         [0120]    Whether it is when the cartridge  7  is mounted into, or removed from, the apparatus main assembly  100   a,  the bearing pressing member  83  must be moved in the direction perpendicular to the cartridge mounting direction F. In this embodiment, however, the projection  83   d  with which the bearing contacting first portion  83   c  is provided, is provided with gently slanted surfaces, which are on the downstream and upstream sides in terms of the cartridge mounting direction, whereas the projection  40   d  of the bearing pressing member pressing portion  40   c  is provided with gently slanted surfaces, which are on the downstream and upstream sides in terms of the cartridge mounting direction. Thus, when the cartridge  7  is mounted, the slanted surface  40   e  of the bearing pressing member pressing portion  40   c  comes into contact with the slanted surface  83   e  of the bearing contacting first portion  83   c,  whereas when the cartridge  7  is removed, the slanted surface  40   f  of the bearing pressing member pressing portion  40   c  comes into contact with the slanted surface  83   f  of the bearing contacting first portion  83   c.  Thus, as the cartridge  7  is moved, the bearing pressing member  83  is moved in the direction indicated by the arrow mark X. Because the cartridge  7  and apparatus main assembly  100   a  are structured so that the bearing pressing member  83  is moved by the interaction between the abovementioned gently slanted surfaces, the cartridge  7  can be smoothly mounted or removed. 
         [0121]    (b) Front side: Operation of Bearing Pressing Mechanism During Mounting or Removing of Cartridge 
         [0122]      FIG. 10  is a schematic drawing of the bearing pressing mechanism on the front side, as seen from the left side of the main assembly, and shows the operation of the mechanism.  FIG. 11  is a schematic drawing of the bearing pressing mechanism on the upstream side in terms of the cartridge mounting direction, as seen from the downstream side in terms of the direction in which the cartridge is mounted, and shows the operation of the mechanism. 
         [0123]    Referring to  FIGS. 10(   a ) and  11 ( a ), as the cartridge  7  is inserted into the apparatus main assembly  100   a,  the slanted surface  50   e  of the bearing pressing member pressing portion  50   c  of the front bearing  50  comes into contact with the slanted surface  93   e  of the cartridge lifting member  93  (standby position). Then, as the cartridge  7  is inserted further, the cartridge lifting member  93  is gradually moved downward by the bearing pressing member pressing portion  50   c.  That is, as the cartridge  7  is inserted into the apparatus main assembly  100   a,  the projection  50   d  of the bearing pressing member pressing portion  50   c  comes into contact with the projection  93   d  of the cartridge lifting member  93 , and then, causes the cartridge lifting member  93  to retreat in the direction indicated by an arrow mark Y (retreat position), as shown in  FIG. 10(   b ). During this movement of the cartridge lifting member  93 , the cartridge lifting member  93  retreats into the position in which its bearing pressing portion  93   b  does not contact the bearing pressing member catching portion  50   b,  as shown in  FIG. 11(   b ). Therefore, while the cartridge  7  is mounted, the bearing pressing member catching portion  50   b  is not subjected to any pressure. 
         [0124]    The pressure which the bearing  50  receives from the cartridge lifting member  93  when the cartridge  7  is mounted is removed by the bearing pressing member pressing portion  50   c,  which is positioned farther from the axial line of the hole  93   a  than the bearing pressing member catching portion  50   b  is. Thus, the force necessary to move the cartridge lifting member  93  downward against the force (pressure) which presses the bearing  50  (cartridge  7 ) upward is reduced by the amount proportional to the ratio between the distance from the axial line of the hole  93   a  to the bearing pressing member catching portion  50   b  ( 93   b ), and the distance from the axial line of the hole  93   a  to the bearing pressing member pressing portion  50   c  ( 93 ). Therefore, the amount of load to which the bearing  50  (cartridge  7 ) is subjected when the cartridge  7  is mounted is sufficiently smaller than the amount of pressure which the bearing  50  (cartridge  7 ) receives from the cartridge lifting member  93 . Thus, this embodiment can reduce the amount of force necessary for the operation for mounting the cartridge  7 . 
         [0125]    Also during this movement of the cartridge  7 , the bearing  50  is pressed upward by the reactive force generated by the cartridge lifting member  93  as the cartridge lifting member  93  is moved downward into its retreat position. However, the main assembly contacting second portion  50   h  comes into contact with the cartridge movement regulating portion  96  of the apparatus main assembly  100   a,  that is, the cartridge contacting second portion of the apparatus main assembly  100   a,  regulating thereby the upward movement of the bearing  50  (cartridge  7 ). The positional relationship between the cartridge movement regulating portion  96  and main assembly contacting second portion  50   h  is such that they remain in contact with each other until immediately before the main assembly contacting portion  50   a  (cartridge positioning portion) comes into contact with the bearing catching portion  92   a,  that is, until immediately before the main assembly contacting portion  50   a  (cartridge positioning portion) is positioned by the bearing catching portion  92   a.  Therefore, during the mounting of the cartridge  7 , the cartridge movement regulating portion  96  of the apparatus main assembly  100   a,  which is formed of a resin, and main assembly contacting second portion  50   h  continuously rub against (slide upon) each other from the moment the cartridge  7  begins to be pressed upward by the cartridge lifting member  93  until immediately before the cartridge  7  is positioned relative to the apparatus main assembly  100   a,  whereas the main assembly contacting portion  50   a  (cartridge positioning portion) does not rub against the bearing catching portion  92   a  of the lateral plate  92  of the apparatus main assembly  100   a,  which is formed of thin steel plate or the like. Therefore, the main assembly contacting portion  50   a  (cartridge positioning portion) and  92   a  do not shave each other. 
         [0126]    As the cartridge  7  is inserted even further, the bearing pressing member pressing portion  50   c  gradually disengages from the cartridge lifting member  93 , allowing the cartridge lifting member  93  to gradually move back from its retreat position to the bearing pressing position. The cartridge  7  is to be inserted until the rear lateral plate contacting portion  40   i  of the cartridge  7 , which is the portion for positioning the cartridge  7  relative to the apparatus main assembly in terms of the lengthwise direction of the cartridge  7 , comes into contact with the rear lateral plate  82  of the apparatus main assembly  100   a.  As the cartridge  7  is inserted far enough for the rear lateral plate contacting portion  40   i  to come into contact with the rear lateral plate  82 , the bearing pressing member catching portion  50   b  comes into contact with the bearing pressing portion  93   b,  causing the bearing  50  (cartridge  7 ) to be pressed in the direction indicated by the arrow mark K (cartridge lifting direction,  FIG. 11 ) (cartridge pressing position), as shown in  FIGS. 10(   c ) and  11 ( c ). As a result, the main assembly contacting portion  50   a  (cartridge positioning portion) is placed in contact with the bearing catching portion  92   a  of the rear lateral plate  92  of the apparatus main assembly  100   a,  accurately positioning the bearing  50  (cartridge  7 ) relative to the apparatus main assembly  100   a  in terms of the direction perpendicular to the cartridge mounting direction. Also during this movement of the cartridge  7 , the main assembly contacting second portion  50   h  becomes disengaged from the cartridge movement regulating portion  96  of the apparatus main assembly  100   a,  creating a preset amount of gap between the cartridge movement regulating portion  96  and surface  50   g.  At the same time, the bearing pressing member pressing portion  50   c  moves past the bearing catching portion  93   c  of the cartridge lifting member  93 , creating a preset amount of gap between the surface  50   j  and bearing catching portion  93   c.    
         [0127]    As described above, the cartridge lifting member  93  is capable of taking the standby position, bearing pressing position (cartridge pressing position), and retreat position. To describe in more detail, listing from the top, the standby position, bearing pressing position, and retreat position of the cartridge lifting member  93  are positioned in the stated order. Therefore, the cartridge lifting member  93  can apply to the bearing  50  (cartridge  7 ) a sufficient amount of pressure necessary to keep the bearing  50  (cartridge  7 ) accurately positioned relative to the apparatus main assembly  100   a  after the amounting of the cartridge  7 . 
         [0128]    Next, when it is necessary to take the cartridge  7  out of the apparatus main assembly  100   a,  the above described operation for mounting the cartridge  7  is to be carried in reverse. The pressure from the cartridge lifting member  93 , under which the bearing  50  (cartridge  7 ) is, is cancelled, as it is when the cartridge  7  is mounted, by the bearing pressing member pressing portion  50   c,  which is located farther from the axial line of the cartridge lifting member  93  than the bearing pressing member catching portion  50   b  is. Therefore, the amount of force necessary to remove the cartridge  7  is just as small as the amount of force necessary to mount the cartridge  7 . 
         [0129]    Whether it is when the cartridge  7  is mounted into the apparatus main assembly  100   a,  or removed from the apparatus main assembly  100   a,  the cartridge lifting member  93  must be moved in the direction perpendicular to the cartridge mounting direction. In this embodiment, however, the projection  93   d  of the cartridge lifting member  93  is provided with gently slanted surfaces, which are on the downstream and upstream sides in terms of the cartridge mounting direction, whereas the projection  50   d  of the bearing pressing member pressing portion  50   c  is provided with gently slanted surfaces, which are on the downstream and upstream sides in terms of the cartridge mounting direction. When the cartridge  7  is mounted, the slanted surface  50   e  of the bearing pressing member pressing portion  50   c  comes into contact with the slanted surface  93   e  of the cartridge lifting member  93 , whereas when the cartridge  7  is removed, the slanted surface  50   f  of the bearing pressing member pressing portion  50   c  comes into contact with the slanted surface  93   f  of the cartridge lifting member  93 . Thus, as the cartridge  7  is moved, the cartridge lifting member  93  is moved in the direction indicated by the arrow mark Y. Because the cartridge  7  and apparatus main assembly  100   a  are structured so that the cartridge lifting member  93  is moved by the interaction between the abovementioned gently slanted surfaces, the cartridge  7  can be smoothly mounted or removed. 
         [0130]    It should be noted here that it is roughly at the same time that the bearing pressing (positioning) front and rear mechanisms press upon the bearings (cartridge  7 ), or release the bearings (cartridge  7 ), when the cartridge  7  is mounted or removed, respectively. Further, the rotational direction of the bearing pressing member  83  is opposite from the rotational direction of the cartridge lifting member  93 . 
         [0131]    To describe in more detail, referring to  FIGS. 12(   a ) and  12 ( b ), in terms of the direction perpendicular to the cartridge mounting direction, the hole  83   a,  that is, the hole of the cartridge pressing rear member  83  of the apparatus main assembly  100   a,  is on the left side of a line L which coincides with the axial line of the photosensitive drum  1  and extends in the direction in which the cartridge  7  is moved to be positioned relative to the apparatus main assembly  100   a,  whereas the bearing contacting first portion  83   c  is on the right side of the line L. On the other hand, the hole  93   a,  that is, the hole of the cartridge pressing front member  93  of the apparatus main assembly  100   a,  is on the right side of the line L, and the bearing catching portion  93   c  is on the left side of the line L. 
         [0132]    That is, the bearing pressing member  83 , which is on the rear side, moves into its retreat position by being rotated in the direction indicated by an arrow mark M, whereas the cartridge lifting member  93 , which is on the front side, moves into its retreat position by being rotated in the direction indicated by an arrow mark N. Thus, as the cartridge  7  is mounted or removed, the bearing member pressing member pressing portions  40   c  and  50   c  are pressed in the directions indicated by arrow marks P 1  and P 2 , by the bearing pressing members  83  and  93 , respectively, as shown in  FIGS. 12(   a ) and  12 ( b ). The direction indicated by the arrow mark P, that is, the direction in which the bearing pressing member pressing portion  40   c  pressed, and the direction indicated by the arrow mark P 2 , that is, the direction in which the bearing member pressing member pressing portion  50   c  are pressed holds a preset angle relative to the line L, which is parallel to the direction in which the bearings  40  and  50  (cartridge  7 ) are pushed up. Further, referring to  FIG. 12(   c ), the theoretical extension of the arrow mark P 1  and that of the P 2  are roughly symmetrical with respect to the line L. Therefore, the cartridge  7  remains stable in attitude when it is mounted or removed. Therefore, the image forming apparatus  100  in this embodiment is superior to an electrophotographic image forming apparatus in accordance with the prior art, in terms of the operation for mounting or removing a process cartridge. 
         [0133]    Further, during the mounting of the cartridge  7 , the cartridge movement regulating portions  86  and  96  of the apparatus main assembly  100   a,  which are formed of a resin, continuously rub against (slide upon) the main assembly contacting surface  40   h  and main assembly contacting portion  50   h,  respectively, from the moment the cartridge  7  begins to be pressed upward by the bearing pressing member  83  and  93  until immediately before the bearings  40  and  50  (cartridge  7 ) are accurately positioned relative to the apparatus main assembly  100   a,  whereas the main assembly contacting portions  40   a  and  50   a  do not rub against the bearing catching portion  82   a  and  92   a  of the lateral plate  82  and  92  of the apparatus main assembly  100   a,  which are formed of thin steel plate or the like. Therefore, the main assembly contacting portions  40   a  and bearing catching portion  82   a  do not shave each other, and the main assembly contacting portion  50   a  (cartridge positioning portion) and bearing catching portion  92   a  do not shave each other. 
         [0134]    As described above, the cartridge  7  and apparatus main assembly  100   a  in this embodiment are structured so that when the cartridge  7  is mounted or removed, the pressured applied to the cartridge  7  (bearings  40  and  50 ) by the bearing pressing portions of the bearing pressing members (cartridge positioning member), is cancelled by the combination of the bearing pressing member pressing portions of the cartridge  7  (bearing  40  and  50 ), and the bearing catching portions of the bearing pressing members, which are located farther from the rotational axes of the bearing pressing members than the bearing pressing portions of the bearing pressing member are. Therefore, the amount of force necessary to mount or remove the cartridge  7  is sufficiently smaller than the amount of load to which the cartridge  7  is subjected by the bearing pressing members of the apparatus main assembly  100   a  when the cartridge  7  is mounted or removed. In other words, this embodiment can significantly reduce the amount of force necessary for the operation to mount or removed the cartridge  7 , making it possible to provide an electrophotographic image forming apparatus which is significantly superior to a conventional electrophotographic image forming apparatus, in terms of the cartridge mounting or removing operation. 
         [0135]    Further, the main assembly contacting portions of the bearings (cartridge  7 ) and the cartridge contacting portion of the apparatus main assembly  100   a  are prevented from being shaved by their counterparts when the cartridge  7  is mounted into, or removed from, the apparatus main assembly  100   a.  Therefore, it is ensured that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  throughout its service life. 
         [0136]    Further, the image forming apparatus in this embodiment is structured so that the cartridge compartments are horizontally juxtaposed in tandem, and the intermediary transfer unit is placed above the space for the cartridge compartments, in order to make it possible to press the cartridges from below by the bearing pressing members to accurately position the cartridges relative to the main assembly of the image forming apparatus. However, this embodiment is not intended to limit the present invention in terms of the structure of an image forming apparatus. That is, the present invention is also applicable to an image forming apparatus in which its intermediary transfer unit is under its cartridge compartments so that the cartridges are to be pressed downward by the bearing pressing members. In the case of this structural arrangement, the photosensitive drums  1  are placed in contact with the intermediary transfer belt  5  by pressing the cartridges  7  downward. 
         [0137]    In the case of an electrophotographic image forming apparatus, such as the one in this embodiment, which is structured so that the cartridges are pressed from below, the amount of force necessary to accurately position the cartridges must be set in consideration of the weight of each cartridge. Thus, in terms of the amount of force necessary to accurately position the cartridges, an electrophotographic image forming apparatus structured as the one in this embodiment is greater than an image forming apparatus structured so that the cartridges are pressed downward for positioning. That is, the former is greater than the latter, in the amount of force necessary to press the bearing pressing members. Therefore, the effects of the present invention can be enhanced by structuring an electrophotographic image forming apparatus, like the one in this embodiment, so that when a cartridge is mounted or removed, the pressure (pressing force) applied to the cartridge by the bearing pressing portions (cartridge pressing portions) of the bearing pressing members is cancelled by the combination of the bearing pressing member pressing portions of the bearings of the cartridge, and the bearing catching portions of the bearing pressing members, which are located farther from the rotational axis of the bearing pressing member than the bearing pressing portions of the bearing pressing members. 
         [0138]    Further, in this embodiment, it is at both the front and rear ends of the apparatus main assembly  100   a  in terms of the cartridge mounting direction that when the cartridge is mounted or removed, the pressure applied to a cartridge by the bearing pressing portion of the bearing pressing member is cancelled by the combination of the bearing pressing member pressing portion of the bearing of the cartridge, and the bearing catching portion of the bearing pressing member, which is located farther from the rotational axis of the bearing pressing member than the bearing pressing portion of the bearing pressing member is. However, this embodiment is not intended to limit the present invention in terms of the structure of an image forming apparatus. That is, the present invention is also applicable to an electrophotographic image forming apparatus having only one bearing pressing member (cartridge pressing member), which is located at the front or rear end of the apparatus in terms of the cartridge mounting direction. However, providing both the front and rear ends of the main assembly of an image forming apparatus with a bearing pressing member (portion) can reduce the total amount of load to which the cartridge is subjected when it is mounted or removed. Further, providing both the front and rear ends of each cartridge compartment of an image forming apparatus with a bearing pressing member, and structuring the image forming apparatus so that the direction in which the cartridge is pressed upward by the bearing pressing member on the front end of the apparatus is symmetrical to the direction in which the cartridge is pressed upward by the bearing pressing member on the rear end of the apparatus, with respect to the axial line of the photosensitive drum, make it possible to keep the cartridge  7  stable in attitude when the cartridge  7  is mounted or removed. 
         [0000]    (Mechanism for Keeping Development Roller Separated from Photosensitive Drum When Cartridge is in Apparatus Main Assembly) 
         [0139]    Next, referring to  FIGS. 13 ,  15 , and  16 , the mechanism for keeping separated the photosensitive drum  1  and development roller  25  in the cartridge  7  in accordance with the present invention, will be described.  FIG. 13  is an external perspective view of the cartridge, and  FIG. 15  is a schematic sectional view of the cartridge in the first embodiment, which has been accurately positioned in the main assembly of the image forming apparatus, and the development roller of which is in contact with photosensitive drum of the cartridge  7 .  FIG. 16  is a schematic sectional view of the cartridge  7  in the first embodiment, which has been accurately positioned in the main assembly of the image forming apparatus, and the development roller of which has been separated from the photosensitive drum of the cartridge. 
         [0140]    In the first embodiment described above, the development roller  25  develops an electrostatic latent image, with the use of developer, while remaining in contact with the photosensitive drum  1 . Further, when the development roller  25  is not used for development, it is kept separated from the photosensitive drum  1  as necessary. 
         [0141]    Thus, the image forming apparatus  100  in this embodiment is structured so that the development roller  25  can be separated from the photosensitive drum  1 . 
         [0142]    More specifically, the apparatus main assembly  100   a  is provided with a development roller separating member  111  (development roller separating force applying portion), which is located in a preset position in the apparatus main assembly  100   a,  in terms of the direction in which the cartridge  7  is inserted into the apparatus main assembly  100   a  ( FIGS. 13 and 15 ). The development roller separating member  111  is movable between a cartridge pressing position and a retreat position. The cartridge pressing position is the position in which the development roller separating member  111  presses on the development roller separating member catching portion  31   b  (which will be described later) of the cartridge  7 . The retreat position is a preset distance away from the cartridge pressing position. The development roller separating member  111  separates the development roller  25  from the photosensitive drum  1  against the pressure applied to the development unit  4 . 
         [0143]    The development roller separating member  111  is a part of the apparatus main assembly  100   a,  and is moved between the abovementioned cartridge pressing position ( FIG. 15 ) and retreat position ( FIG. 16 ), by a cam (unshown) rotated by the rotational force from a motor (unshown) which rotates in response to a separation signal. 
         [0144]    The abovementioned pressure is the combination of the force generated by the compression springs  38  (elastic member) ( FIGS. 2 ,  15 , and  16 ) and the force generated by the tension springs (elastic members) (unshown). In terms of the cartridge mounting direction F, the compression spring  38  is at the downstream end of the cartridge  7 , remaining compressed between the development unit  4  and drum unit  26 , and the tension spring is at the upstream end of the cartridge  7 , remaining stretched by the development unit  4  and drum unit  26 . Both the resiliency of the compression spring  38  and the resiliency of the tension spring generate force in the direction to keep the two units  4  and  26  pressed toward each other. One development roller separating member  111  is provided for each of the four cartridges  7  ( 7   a - 7   d ), which use yellow, magenta, cyan, and black toners, respectively. 
         [0145]    The development unit  4  is provided with the development roller separating member catching portion  31   b  (development roller separation force receiving portion), which the development roller separating member  111  presses when it separates the development roller  25  from the photosensitive drum  1 . The development roller separating member catching portion  31   b  is on the bottom surface of the development unit frame  31 . On the other hand, the drum unit  26  is provided with a pair of shafts  27   b  and a pair of holes  27   c,  which are for regulating the rotational movement of the cartridge  7 , which occurs as the cartridge  7  receives the force for rotating the photosensitive drum  1 , development roller  25 , etc., from the apparatus main assembly  100   a,  and also, as the development roller separating member catching portion  31   b  is pressed by the development roller separating member  111 . That is, each of the end walls of the drum unit  26  in terms of the cartridge mounting direction F is provided with the shaft  27   b  and groove  27   c.  The shaft  27   b  is the cartridge rotation regulating first portion of the cartridge  7 , and the groove  27   c  is the cartridge rotation regulating second portion of the cartridge  7 . As the cartridge  7  is mounted into the apparatus main assembly  100   a,  the shaft  27   b  engages into the cross-sectionally elongated hole  82   b  (cartridge rotation regulating first portion) ( FIG. 5 ) of the apparatus main assembly  100   a,  and the shaft  92   c  (cartridge rotation regulating second portion) ( FIG. 5 ) of the apparatus main assembly  100   a  engages into the groove  27   c  of the cartridge  7 . 
         [0146]    The above described structural arrangement makes it possible to accurately position the front and rear sides of the cartridge  7  relative to the apparatus main assembly  100   a,  and also, to cause the cartridge rotation regulating portions of the cartridge  7  to engage with the cartridge rotation regulating portions of the apparatus main assembly  100   a,  simply by mounting the cartridge  7  into the apparatus main assembly  100   a,  even in the case of an image forming apparatus structured so that the cartridge  7  is to be mounted into the apparatus main assembly  100   a  in the direction parallel to the axial line of the photosensitive drum  1 . That is, the above described structural arrangement ensures that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a,  in spite of its simplicity. 
         [0147]    Also in this embodiment, the portions of the cartridge  7 , which are for regulating the rotation of the cartridge  7 , which occurs as the cartridge  7  receives the force for rotating the photosensitive drum  1  and development roller  25  from the apparatus main assembly  100   a,  are the same as the portions of the cartridge  7 , which are for regulating the rotation of the cartridge  7 , which occurs as the cartridge  7  receives the force for separating the development roller  25  from the photosensitive drum  1 . That is, the cartridge rotation regulating portions of the cartridge  7  are shaft  27   b  and groove  27   c,  whereas the cartridge rotation regulating portions of the apparatus main assembly  100   a  are the cross-sectionally elongated hole  82   b,  and the shaft  92   c.    
         [0148]    Referring to  FIG. 16 , when the apparatus main assembly  100   a  is not in action, the development roller separating member  111  is in the cartridge pressing portion. More specifically, as the apparatus main assembly  100   a  is stopped, the motor (unshown) is rotated in response to the development roller separation signal, moving the development roller separating member  111  in the direction indicated by an arrow mark G. Thus, the development roller separating member catching portion  31   b  of the development unit  4  is pressed in the direction indicated by the arrow mark G by the development roller separating member  111 . At this point of the operation, the shaft  27   b  of the drum unit  26  is in the cross-sectionally elongated hole  82   b  of the apparatus main assembly  100   a,  and the shaft  92   c  of the apparatus main assembly  100   a  is in the groove  27   c  of the drum unit  26 . Therefore, when the development unit  4  is pressed by the development roller separating member  111  in the direction indicated by the arrow mark G, the drum unit  26  does not move in the direction indicated by the arrow mark G. Therefore, the development unit  4  rotates (in direction indicated by arrow mark Y in  FIG. 16 ) about the shafts  37  ( 37 R and  37 F), that is, the shafts which connect the development unit  4  and drum unit  26 . As a result, the development roller  25  is separated from the photosensitive drum  1  by a distance V, shown in  FIG. 16 , and remains separated by the distance V ( FIG. 16 ). Therefore, even if the cartridge  7  is left unused for a long time in the apparatus main assembly  100   a,  the elastic layer of the development roller  25  does not deform. Therefore, the problem that the deformation of the elastic layer of the development roller  25  results in the formation of an image which is nonuniform in density does not occur. As described previously, the development roller  25  is made up of a core and a cylindrical rubber layer (elastic layer) fitted around the core ( FIG. 17 ). Therefore, if the development roller  25  is left in contact with the photosensitive drum  1  for a long time, the cylindrical rubber layer is liable to sustain a compressional scar. 
         [0149]    The shafts  37 R and  37 L are at one of the lengthwise end of the cartridge  7  and the other, respectively. 
         [0150]    Also referring to  FIG. 16 , the cartridge  7  is designed so that after it is properly mounted in the apparatus main assembly  100   a,  the photosensitive drum  1  and development roller  25  are above the horizontal plane which coincides with the axial line of the shaft  37 , and the development roller separating member catching portion  31   b  is below the same plane, and also, so that the shaft  27   b  is at the bottom end of one of the lengthwise end of the drum unit  26 , and the groove  27   c  is in the bottom end portion of the other (rear) lengthwise end of the drum unit  26 . Therefore, it is ensured that when the development roller separating member catching portion  31   b  is pressed by the development roller separating member  111 , the movement of the drum unit  26  is regulated by the cross-sectionally elongated hole  82 , and the shaft  92   c.    
         [0151]    Further, the cartridge  7  is designed so that after the proper mounting of the cartridge  7  into the apparatus main assembly  100   a,  the development roller separating member catching portion  31   b  projects downward of the development unit  4  ( FIG. 16 ). Therefore, there is a substantial distance between the point at which the development roller separating member catching portion  31   b  receives the pressure from the development roller separating member  111 , and the shaft  27   b,  enhancing the force (pressure) applied to the development roller separating member catching portion  31   b.    
         [0152]    Further, in terms of the cartridge mounting direction F, the shaft  27   b  is at the leading end of the cartridge  7 , and the groove  27   c  is at the trailing end, being in the portion of the development unit  4 , which protrudes downward ( FIGS. 15 and 16 ). Therefore, when the cartridge  7  is mounted into the apparatus main assembly  100   a  so that its lengthwise direction is parallel to its mounting direction, the cross-sectionally elongated hole  82   b  and shaft  92   c  of the apparatus main assembly  100   a  do not interfere with the mounting of the cartridge  7 . Incidentally, the groove  27   c  is not shown in  FIG. 2 , but, is shown in  FIGS. 5 and 13 . 
         [0153]    As seen from the rear end of the cartridge  7  in terms of its lengthwise direction, the rotational direction of the photosensitive drum  1  is clockwise (indicated by arrow mark Q), and the rotational direction of the development roller  25  is counterclockwise (indicted by arrow mark B). Further, the rotational direction of the toner supply roller  34  is counterclockwise (indicated by arrow mark C) ( FIG. 2 ). 
         [0154]    As an image forming operation is initiated by a print start signal, the abovementioned motor rotates in synchronism with the development operation starting timing, and the development roller separating member  111  moves into the retreat position ( FIG. 15 ), creating a distance U between the development roller separating member catching portion  31   b  and development roller separating member  111 . Thus, the development roller  25  is placed in contact with the photosensitive drum  1 , being readied for image formation, by a preset amount of pressure, that is, the combination of the force (pressure) applied by the compression spring  38  and the force (pressure) applied by the tension spring (unshown). 
         [0155]    In this embodiment, the development roller separating member catching portion  31   b  is on the bottom surface of the development unit frame  31 , and is on the opposite side from the development roller  25  with respect to the shafts  37  ( 37 R and  37 F), the axial line of which coincide with the rotational axis of the development unit  4 . Further, the distance between the development roller separating member catching portion  31   b  and shaft  37  is greater than the distance between the development roller  25  and shaft  37 . It should be noted here that the positioning of the development roller separating member catching portion  31   b  does not need to be limited to the one in this embodiment. However, positioning the development roller separating member catching portion  31   b  on the opposite side from the development roller  25  with respect to the shaft  37 , and farther from the shaft  37  than the development roller  25  is, makes it possible to reduce the amount of force necessary to separate the development roller  25  from the photosensitive drum  1 . Therefore, positioning the development roller separating member catching portion  31   b  on the opposite side from the development roller  25  with respect to the shaft  37 , and farther from the shaft  37  than the development roller  25  is, can reduce the amount of load to which the development roller separating member  111  is subjected when the development roller  25  is separated. 
         [0000]    (Structural Arrangement for Inputting Driving Force into Cartridge in Apparatus Main Assembly) 
         [0156]    Next, referring to  FIGS. 17-21 , the portion of the structure of the apparatus main assembly  100   a,  which is for inputting driving force into the cartridge  7  in the apparatus main assembly  100   a  will be described. 
         [0157]      FIG. 17  is a schematic drawing of one end (rear end) of the development roller  25  in terms of the lengthwise direction of the development roller  25 . 
         [0158]    Referring to  FIG. 17 , the shaft  25   j  of the development roller  25  is rotatably fitted in the center hole of the bearing  32 R, being in contact with the bearing  32 R. There is a spacer roller  47  between the rubber roller portion  25   g  of the development roller  25  and the bearing  32 R, being rotatably fitted around the shaft  25   j.  The spacer roller  47  is for regulating in size the area of contact between the development roller  25  and photosensitive drum  1 . Although described above is the development roller supporting structure of the rear end portion of the cartridge  7  in terms of the lengthwise direction of the development roller  25 , the development roller supporting structure on the front end portion is the same as that of the rear end portion. That is, the other end portion of the shaft  25   j  is rotatably fitted in the center hole of the development roller bearing portion, which is an integral part of the development roller bearing member  32 L. 
         [0159]    In this embodiment, an Oldham&#39;s coupling  41 , one of various couplings compatible with this embodiment, is used as the coupling (development roller coupling of cartridge, development roller rotating force receiving portion of cartridge) of the mechanism for inputting development roller driving force into the cartridge  7 . 
         [0160]    Next, referring to  FIGS. 18 and 19 , the structure of Oldham&#39;s coupling  41  will be described. In order to make it easier to describe the structure of the Oldham&#39;s coupling,  FIGS. 18 and 19  do not show the development roller bearing member  32 R. 
         [0161]    Referring to  FIG. 18 , the Oldham&#39;s coupling  41  has an engaging portion  42  on the development roller side, a middle engaging portion  43 , and an engaging portion  44  on the apparatus main assembly side. 
         [0162]    The engaging portion  42  is solidly attached to the end of the shaft  25   j.  As a means for solidly attaching the engaging portion  42 , a spring pin, a parallel pin, etc., are available. However, the Oldham&#39;s coupling  41  may be attached with the use of the method shown in  FIG. 18 . That is, the peripheral surface of the end portion of the shaft  25   j  is shaved flat (flattened portion  25   c ), and the engaging portion  42  is provided with a center hole, the cross section of which matches that of the flattened portion  25   c  so that the flatten portion  25   c  perfectly fits into the center hole of the engaging portion  42 . The shaft portion  44   b  of the engaging portion  44  is fitted in the hole  45   a  of the development roller coupling (Oldham&#39;s coupling) bearing member  45  (which hereafter will be referred to simply as bearing  45 ), being rotatably supported by the bearing  45 . Further, the engaging portion  44  is provided with multiple projections  44   c   1 - 44   c   4 , which engage with the development roller coupling  53  (development roller rotating force transmitting portion) of the main assembly  100   a,  which is the driving force transmitting second member of the apparatus main assembly  100   a.  The projections  44   c   1 - 44   c   4  are integral parts of the engaging portion  44 . The coupling  53  belongs to the apparatus main assembly  100   a.  The Oldham&#39;s coupling  41  can transmits the development roller driving force (second driving force) from the apparatus main assembly  100   a  to the development roller  25  while tolerating the misalignment between the axial lines of the coupling  53  and the axial line of the development roller  25 . Further, the Oldham&#39;s coupling  41  can transmit the rotational force (second driving force) from the apparatus main assembly  100   a  to the development roller  25  whether the development roller  25  is in contact with the photosensitive drum  1  or not. 
         [0163]    Next, referring to  FIG. 19 , the structure of the Oldham&#39;s coupling  41  will be described in detail.  FIG. 19(   a ) is a sectional view of the Oldham&#39;s coupling  41 , at a plane which is parallel to the direction indicated by an arrow mark H ( FIG. 18)  and coincides with the axial line of the Oldham&#39;s coupling  41 .  FIG. 19(   b ) is a sectional view of the Oldham&#39;s coupling  41 , at a plane which is parallel to the direction indicated by an arrow mark I ( FIG. 18)  and coincides with the axial line of the Oldham&#39;s coupling  41 . Referring to  FIG. 19(   a ), the engaging portion  42  is provided with a tongue  42   a,  which is an integrally formed part of the engaging portion  42 . The engaging portion  43  is provided with a groove  43   a.  The tongue  42   a  is fitted in the groove  43   a  so that the former can moved in the direction indicated by the arrow mark H ( FIG. 18) . Next, referring to  FIG. 19(   b ), the engaging portion  44  is provided with a tongue  44   a,  which is an integral part of the engaging portion  44 . The engaging portion  43  is provided with a groove  43   b.  The tongue  44   a  is fitted in the groove  43   b  so that the former can be moved in the direction indicated by the arrow mark I ( FIG. 18) . 
         [0164]      FIG. 20  is a drawing for showing the structure of the couplings with which the cartridge  7  is provided. 
         [0165]    The end surface of the engaging portion  44  of the Oldham&#39;s coupling  41  of the development unit  4  is provided with multiple projections  44   c   1 - 44   c   3 , which project in parallel to the axial line of the Oldham&#39;s coupling  41 . It is also provided with a centering boss  44   c   4  for aligning the axial line (rotational axis) of the Oldham&#39;s coupling  41  with the axial line of the coupling  53 . The centering boss  44   c   4  projects from the end surface of the engaging portion  44  in the direction parallel to the axial line of the Oldham&#39;s coupling  41 . On the other hand, one end of the photosensitive drum  1  in terms of the direction of its axial line has a drum coupling  1   b  (drum coupling of cartridge), which is in the form of a twisted triangular prism. Further, the guide portion  45   b  of the bearing  45  is fitted in the groove  48   a  of a side cover  48 , and is guided by the groove  48   a.  The direction in which the guide portion  45   b  is guided is perpendicular to the axial line of the development roller  25 . The side cover  48  is fixed to the development unit  4  with the use of small screws or the like (unshown). Thus, the engaging portion  44  is allowed to move in the direction perpendicular to the lengthwise direction of the development unit  4 . 
         [0166]      FIG. 21  is a perspective view of the driving force transmitting couplings with which the apparatus main assembly  100   a  is provided, and shows the structure of the couplings. 
         [0167]    Referring to  FIG. 21 , a coupling  66  (drum driving force transmitting coupling of apparatus main assembly, drum rotating force transmitting portion), which is for transmitting rotational force from the apparatus main assembly  100   a  to the photosensitive drum  1 , has a hole  66   a,  which is roughly triangular in cross section. More specifically, the hole  66   a  of the coupling  66  is roughly in the form of a triangular prism having multiple apexes (in cross section). Further, the coupling  53  (development roller driving force transmitting coupling of the main assembly, development roller driving force transmitting portion), which is for transmitting rotational force (second rotationally driving force) from the apparatus main assembly  100   a  to the development roller  25 , is provided with multiple holes  53   a - 53   c  (recesses). The coupling  66  is kept pressed toward the cartridge  7  by a pressing member  77 , such as a compression spring. The coupling  66  is allowed to move in the direction parallel to the axial line of the photosensitive drum  1 . If the coupling  1   b  is not in alignment with the hole  66   a  of the coupling  66  when the coupling  1   b  comes into contact with the coupling  66 , the coupling  66  retreats by being pushed by the coupling  1   b.  Then, as the coupling  66  is rotated, the coupling  1   b  becomes aligned with the hole  66   a  of the coupling  66 , and therefore, is allowed to engage with the coupling  66 . As a result, the rotational force is transmitted to the photosensitive drum  1  from the apparatus main assembly  100   a  through the couplings  66  and  1   b.    
         [0168]    The coupling  53  is kept pressed toward the cartridge  7  by a pressing member  73 , such as a compression spring, in the direction parallel to the axial line of the photosensitive drum  1 . However, the coupling  53  is attached to the apparatus main assembly  100   a  in such a manner that no play is provided for the coupling  53  in terms of the direction perpendicular to the axial line of the development roller  25 . That is, only direction in which the coupling  53  is allowed to move, besides the direction in which it is rotatable, is the direction parallel to its axial line. 
         [0169]    As the cartridge  7  is inserted into the apparatus main assembly  100   a,  the engaging portion  44  comes into contact with the coupling  53 . Sometimes, however, the projections  44   c   1 - 44   c   3  are not in alignment with the holes  53   a - 53   c  (recesses). In such a case, the ends of the projections  44   c   1 - 44   c   3  contact the portions of the coupling  53  other than the holes  53   a - 53   c  (recesses). Thus, the coupling  53  retreats against the pressure (elastic force) applied thereto by the pressing member  73 , in the direction parallel to the axial line of the coupling  53 . However, as the projections  44   c   1 - 44   c   3  become aligned with the holes  53   a - 53   c  (recesses) due to the rotation of the coupling  53 , the coupling  53  advances by being under the pressure applied thereto by the pressing member  73 , causing the projections  44   c   1 - 44   c   3  to engage into the holes  53   a - 53   c,  and also, causing the centering boss  44   c   4  (rotational force receiving member positioning portion) to fit into the centering hole  53   e  (rotational force transmitting member positioning portion). As a result, the axial line (rotational axis) of the engaging portion  44  and that of the coupling  53  align with each other, and rotational force is transmitted to the development roller  25  from the coupling  53 . 
         [0170]    While the rotational force (first and second rotational forces) is transmitted to the cartridge  7 , the shaft  27   b  ( FIG. 4 ) of the drum unit  26  is in the cross-sectionally elongated hole  83   b  ( FIG. 5 ) of the apparatus main assembly  100   a,  and the shaft  92   c  ( FIG. 5 ) of the apparatus main assembly  100   a  is in the groove  27   c  ( FIG. 3 ) of the drum unit  26 , which is U-shaped in cross section. Thus, the rotational movement of the cartridge  7 , which occurs as the rotational force is transmitted from the apparatus main assembly  100   a  to the cartridge  7  is regulated. 
         [0171]    The rotational force which is transmitted to the cartridge  7  through the couplings  66  and  53  is provided by a motor, or motors, located in the apparatus main assembly  100   a;  the apparatus main assembly  100   a  may be provided with four motors so that each cartridge  7  is driven by the motor dedicated thereto, or only a single motor so that the four cartridges  7  are driven by the same motor. 
       (Action of Oldham&#39;s Coupling During Development Roller Separation in Cartridge) 
       [0172]    Next, referring to  FIGS. 22-25 , the action of the Oldham&#39;s coupling  41 , which occurs when the development roller  25  of the cartridge  7  in the first embodiment of the present invention is separated from the photosensitive drum  1 , will be described. 
         [0173]      FIG. 22  is a side view of the cartridge  7  when there is a preset amount of gap between the development roller  25  and photosensitive drum  1 .  FIG. 23  is a sectional view of the lengthwise end portion of the cartridge  7  having the coupler  44 , when there is a preset amount of gap between the development roller  25  and photosensitive drum  1 , at a plane which coincides with the axial line of the development roller  25  and photosensitive drum  1 . 
         [0174]    Referring to  FIG. 22 , when the apparatus main assembly  100   a  is not in operation, the development roller  25  (outlined with broken line) remains separated from the photosensitive drum  1  (outlined with broken line). When the cartridge  7  is in the condition shown in  FIG. 22 , the arm portion  46   a  of the torsional coil spring  46  (pressure applying member) located in the side cover  48  is in contact with the engaging portion  45   c  of the coupling bearing  45 , and keeps the engaging portion  45   c  pressed. Therefore, the engaging portion  44  remains pressed in the direction (indicated by arrow mark W in  FIG. 23 ) perpendicular to the axial line of the development roller  25 , and the contacting portion  45   d  of the coupling bearing  45  remains in contact with the contacting portion  40   k  (holding portion) of the drum bearing  40 , that is, the photosensitive drum bearing rear member. Therefore, the coupling bearing  45  is kept accurately positioned. That is, the engaging portion  44  is kept in a preset position. The contacting portion  40   k  of the drum bearing  40  is V-shaped is cross section; it has two surfaces which are parallel to the axial line of the photosensitive drum  1 . The coupling bearing  45  is placed in contact with the contacting portion  43   k,  whereby the coupling bearing  45  is held so that its axial line remains parallel to the axial line of the photosensitive drum  1 . 
         [0175]    The drum bearing  40  is provided with the aforementioned main assembly contacting portion  40   a,  which is formed as an integral part of the drum bearing  40 . Therefore, the engaging portion  44 , which is rotatably supported by the coupling bearing  45 , is accurately positioned relative to the lateral plate  82 , relative to which the main assembly contacting portion  40   a  is positioned. The lateral plate  82  is a part of the apparatus main assembly  100   a.  Therefore, the engaging portion  44  is accurately positioned also relative to the axial line  53   d  of the coupling  53 . The engaging portion  44  of the Oldham&#39;s coupling  41  is rotatably borne by the coupling bearing  45 . In this state, therefore, the axial line  44   c   5  of the engaging portion  44  is not in alignment with the axial line  53   d  of the development roller  25 . Further, the axial line  44   c   5  is closer to the axial line  53   d  than the axial line  25   k  of the development roller  25  is. That is, where the engaging portion  44  is positioned is where the engaging portion  44  can smoothly engages with the coupling  53  as the cartridge  7  is inserted into the apparatus main assembly  100   a.  In this embodiment, the torsional coil spring  46  (pressure applying member) is used as the member for applying pressure to the coupling bearing  45 . However, the member for applying pressure does not need to be in the form of a torsional coil spring. For example, the coupling bearing  45  may be provided with an elastically deformable portion, which is integral with the coupling bearing  45  so that the coupling bearing  45  is kept pressed upon the contacting portion  40   k.    
         [0176]    Next, referring to  FIG. 23 , the action of the Oldham&#39;s coupling will be described in more detail. 
         [0177]    The image forming apparatus  100  in this embodiment is structured so that as the engaging portion  44  is rotated by the coupling  53  by becoming engaged with the coupling  53 , it is positioned by the coupling  53 , as will be described later. In other words, when the cartridge  7  is mounted into the apparatus main assembly  100   a,  the contacting portion  45   b  is not in contact with the contacting portion  40   k.  Therefore, when the advancement of the cartridge  7  into the apparatus main assembly  100   a  begins to cause the engaging portion  44  to engage with the coupling  53 , the axial line  44   c   5  of the engaging portion  44  is offset relative to the axial line of the coupling  53  by a distance d 3  toward the photosensitive drum  1 . Thus, as the cartridge  7  is advanced further into the apparatus main assembly  100   a,  the chamfered portion  44   c   6  ( FIG. 20 ) of the centering boss  44   c   4  comes into contact with the chamfered edge  53   f  ( FIG. 21 ) of the hole  53   e.  Therefore, the coupling  53  and  44  engage with each other while compensating for the misalignment between their axial lines. 
         [0178]    When the coupling  53  and engaging portion  44  are in the state shown in  FIG. 23 , there is a gap between the development roller  25  and photosensitive drum  1 . In this state, the axial line of the engaging portion  44  is not in alignment with the axial line  25   k  of the development roller  25 , as described above. That is, the distance d 1  between the axial line  1   c  (rotational axis) of photosensitive drum  1  and the axial line  44   c   5  of the engaging portion  44  is smaller than a distance d 2  between the axial line  1   c  of the photosensitive drum  1  and the axial line  25   k  of the development roller  25 . Therefore, the engaging portion  44  is closer to the photosensitive drum  1  than to the development roller  25 . 
         [0179]    Further, even when there is a gap between the development roller  25  and photosensitive drum  1 , the engaging portion  43  is in engagement with the engaging portion  44  and  42 . Therefore, even while the development roller  25  moves between the position in which it is in contact with the photosensitive drum  1  and the position in which it holds a preset amount of distance from the photosensitive drum  1 , the engaging portion  43  is allowed to move while remaining in engagement with the engaging portion  44  and  42 . 
         [0180]    Also when the coupling  53  and engaging portion  44  are in the state shown in  FIG. 23 , the engaging portion  44  is kept accurately positioned relative to the coupling  53  by the contacting portion  40   k.  Therefore, the chamfered portions  44   c   6  and  53   f  do not need to be very large, making it possible to reduce the engaging portion  44  and coupling  53  in size. 
         [0181]    Next, referring to  FIG. 25 , as the rotation of the coupling  53  causes the projections  44   c   1 - 44   c   3  to align with the holes  53   a - 53   c  (recesses) of the coupling  53 , the boss  44   c   4  fits into the hole  53   e,  causing thereby the axial line  44   c   5  of the engaging portion  44  to align with the axial line  53   d  of the coupling  53 . That is, the engaging portion  44  is positioned by the coupling  53 . As a result, the coupling bearing  45  becomes separated from the drum bearing  40 . At this point, the distance between the axial line  1   c  of the photosensitive drum  1  and the axial line  44   c   5  of the engaging portion  44  is a distance d 4 , which is larger by a distance d 3  than the distance d 1  shown in  FIG. 23 ; the axial line  44   c   5  of the engaging portion  44  is farther from the axial line  1   c  of the photosensitive drum  1  by d 3  than when the coupling  53  and engaging portion  44  are in the state shown in  FIG. 23 . However, the distance between the engaging portion  44  and the photosensitive drum  1  is smaller than that between the engaging portion  44  and development roller  25 . 
         [0182]      FIG. 24  is a side view of the cartridge  7  when its development roller  25  is in contact with its photosensitive drum  1 .  FIG. 25  is a sectional view of the driving force receiving end portion of the cartridge  7  when the development roller  25  is in contact with the photosensitive drum  1 . 
         [0183]    As an image forming operation is initiated, the development roller separating member  111  retreats to its preset position (retreat position), allowing the development unit  4  to rotationally move in the direction indicated by an arrow mark Z about the shaft  37 , which supports the development roller supporting rear bearing  32 R of the drum unit frame  27 . Thus, the development roller  25  comes into contact with the photosensitive drum  1 . At this point, the engaging portion  44  and coupling  53  have already engaged with each other. Therefore, even when the development unit  4  rotationally moves in the direction indicated by the arrow mark Z, the engaging portion  44  of the Oldham&#39;s coupling  41  remains in the same position while remaining engaged with the coupling  53 . That is, the engaging portion  44  does not rotationally move in the direction indicated by the arrow mark Z. Further, the engaging portion  44  and coupling  53  are in engagement with each other, with a gap remaining between the coupling bearing  45  and drum bearing  40 , as shown in  FIG. 25 . Further, the axial line  25   k  of the development roller  25 , the axial line  44   c   5  of the engaging portion  44 , and the axial line  53   d  of the coupling  53  are roughly in alignment. The distances from the axial lines  25   k,    44   c   5 , and  53   d  to the axial line  1   c  of the photosensitive drum  1  are the same, being the distance d 4 . 
         [0184]    As described above, in this embodiment, the couplings  53  and  66  rotate independently from each other. The coupling  66  inputs rotational force into the photosensitive drum  1 , and the coupling  53  directly inputs rotational force into the development roller  25  through the Oldham&#39;s coupling  41 . Therefore, not only is the rotation of the development roller  25  not affected by the rotation of the photosensitive drum  1 , but also, the development roller  25  can rotated more accurately. Therefore, it is possible to yield an image which is significantly superior in quality than an image formed by a conventional image forming apparatus. 
         [0185]    Further, the engaging portion  44  is positioned relative to the cartridge  7  so that a preset positional relationship is realized between the engaging portion  44  and cartridge  7 , and also, so that the engaging portion  44  is allowed to move in the direction perpendicular to the axial line  25   k  of the development roller  25 . Therefore, a large guide or the like, which a conventional image forming apparatus requires to make the coupling  53  and engaging portion  44  to engage with each other is unnecessary, making it possible to eliminate the space for the large guide or the like. Therefore, this embodiment can reduce an image forming apparatus in size, and also, can improves an image forming apparatus in terms of the operation for mounting a process cartridge into the main assembly of the image forming apparatus. 
         [0186]    Further, the engaging portion  44  can be kept in the preset position even though the development roller  25  remains separated from the photosensitive drum  1  when the cartridge  7  is mounted. Therefore, the image forming apparatus  100  in this embodiment is superior to a conventional image forming apparatus in terms of the operation for mounting a process cartridge into the main assembly of the image forming apparatus. 
         [0187]    Further, the Oldham&#39;s coupling  41  is used as the means for transmitting the rotational force from the apparatus main assembly  100   a  to the development roller  25 . Therefore, rotational force can be transmitted to the development roller  25  even when the development roller  25  is not in contact with the photosensitive drum  1 . Therefore, it is possible to start rotating the development roller  25  before the development roller  25  is placed in contact with the photosensitive drum  1 . Therefore, it is possible to give the toner on the development roller  25  a sufficient amount of triboelectric charge by the development blade  35  before the development roller  25  is placed in contact with the photosensitive drum  1 . Therefore, it is possible to prevent the problem that because it is impossible to give the toner on the development roller  25  a sufficient amount of triboelectric charge, the toner is transferred from the photosensitive drum  1  onto the secondary transfer roller  18  ( FIG. 1 ) by way of the intermediary transfer belt  5 , and then, soils the back surface of recording medium (for example, paper). 
         [0188]    Therefore, it is possible to prevent the problem that because the toner on the development roller  25  is not sufficiently charged before the development roller  25  is placed in contact with the photosensitive drum  1 , the waste toner storage bin of the belt cleaning apparatus  23  has be frequently replaced. 
         [0189]    Further, the employment of the Oldham&#39;s coupling  41  makes it possible to continue to rotate the development roller  25  even while the development roller  25  is moved from the separation position to the contact position. Therefore, it is possible to place the development roller  25  in contact with the photosensitive drum  1  while rotating both the development roller  25  and photosensitive drum  1 . Therefore, it is possible to minimize the impact to which the photosensitive drum  1  is subjected when the development roller  25  comes into contact with the photosensitive drum  1 . 
         [0190]    In this embodiment, the Oldham&#39;s coupling  41  is used as the means for transmitting rotational force from the apparatus main assembly  100   a  to the development roller  25 . However, the means for transmitting rotational force from the apparatus main assembly  100   a  to the development roller  25  does not need to be limited to the Oldham&#39;s coupling  41 . That is, any coupling (for example, lateral coupling) may be employed, as long as the coupling is capable of sufficiently absorbing (compensating for) the rotational anomalies which occur if the axial line of the coupling on the rotational transmitting side and that on the rotational force receiving side is not in alignment with each other. 
         [0191]    As described above, the structure of the cartridge  7  in this embodiment is as follows: 
         [0192]    The cartridge  7  has the drum unit  26 , which supports the photosensitive drum  1 . 
         [0193]    It has the development roller  25  for developing the electrostatic latent image formed on the photosensitive drum  1 . The development roller  25  develops the electrostatic latent image while remaining in contact with the photosensitive drum  1 . The development roller  25  is supported by the development unit  4 . The development unit  4  is connected to the drum unit  26  in such a manner that it is allowed to rotationally move relative to the drum unit  26 . 
         [0194]    Further, the cartridge  7  is provided with the drum coupling  1   b  (drum driving force receiving portion) for receiving the rotational force for rotating the photosensitive drum  1 , from the drum driving force transmitting coupling  66  (drum rotating force transmitting portion), when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  In terms of the direction indicated by the arrow mark F, in which the cartridge  7  is mounted into the apparatus main assembly  100   a,  the drum coupling  1   b  is at the leading end of the drum unit  26 . 
         [0195]    Also, the cartridge  7  has the Oldham&#39;s coupling  41  (development roller driving force receiving portion) for receiving the rotational force for rotating the development roller  25 , from the development roller driving force transmitting coupling  53  (development roller rotating force transmitting portion), when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  In terms of the cartridge mounting direction F, the coupling  41  is at the leading end of the development unit  4 . 
         [0196]    Further, the cartridge  7  has the main assembly contacting first portion (cartridge positioning first portion)  40   a  (having portions  40   a   1  and  40   a   2 ), which is positioned by the bearing catching portion  82   a  ( 82   a   1  and  82   a   2 ) when the cartridge  7  is mounted into the apparatus main assembly  100   a,  and also, remains positioned by the bearing catching portion  82   a  (having portions  82   a   1  and  82   a   2 ) while the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  The main assembly contacting portion  40   a  (cartridge positioning portion) is positioned by the bearing catching portion portion  82   a  by being placed in contact with the cartridge contacting portions  82   a  by the pressure (force) applied by the bearing pressing member  83 . In terms of the cartridge mounting direction F, the main assembly contacting portion  40   a  (cartridge positioning portion) is at the downstream end of the drum unit  26 . The bearing pressing member  83  is a member of the apparatus main assembly  100   a,  which is for keeping pressed, or pushing up, the main assembly contacting portion  40   a  (cartridge positioning portion). Further, the bearing catching portion  82   a  is the cartridge positioning first portion of the apparatus main assembly  100   a.    
         [0197]    The main assembly contacting portion  40   a  (having portions  40   a   1  and  40   a   2 ) is at one of the lengthwise ends of the photosensitive drum  1 . The portions  40   a   1  and  40   a   2  are two portions of the peripheral surface of the drum bearing  40 , which will face upward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  There are located close to each other. 
         [0198]    Further, the cartridge  7  has the drum bearing  40  (drum shaft bearing first member), which supports one of the lengthwise ends of the photosensitive drum  1 . The portions  40   a   1  and  40   a   2  of the main assembly contacting portion  40   a  (cartridge positioning portion) are the two portions of the peripheral surface of the drum bearing  40 . 
         [0199]    Further, the cartridge  7  has the main assembly contacting portion  50   a  (cartridge positioning portion) (having cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2 ), that is, the main assembly contacting second portion (cartridge positioning second portions) of the cartridge, which is positioned by the bearing catching portion  92   a  (having portions  92   a   1  and  92   a   2 ), when the cartridge  7  is mounted into the apparatus main assembly  100   a,  and while the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  The main assembly contacting portion  50   a  is accurately positioned relative to the bearing catching portions  92   a  by being placed in contact with the bearing pressing portions  92   a  by the pressure applied by the bearing (cartridge) lifting member  93 . In terms of the cartridge mounting direction, the main assembly contacting portion  50   a  (having cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2 ) is on the upstream side of the drum unit  26 . The bearing (cartridge) lifting member  93  is the bearing pressing second member of the apparatus main assembly  100   a.  The bearing catching portion  92   a  is the bearing (cartridge) positioning second portion of the apparatus main assembly  100   a.    
         [0200]    The main assembly contacting portion  50   a  (bearing positioning portion) (having cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2 ) is at the other lengthwise end of the cartridge  7 . The main assembly contacting portion  50   a  (cartridge positioning portion) is made up of the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  of the peripheral surface of the rear bearing  50  of the photosensitive drum, which face upward when the cartridge  7  is in its image forming portion in the apparatus main assembly  100   a.    
         [0201]    Therefore, in terms of the lengthwise direction of the cartridge  7 , one end of the cartridge  7  and the other are positioned relative to the apparatus main assembly  100   a  by coming into contact with the bearing catching portion  82   a  and  92   a,  respectively. Therefore, it is ensured that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  when it is mounted into the apparatus main assembly  100   a,  and also, so that the cartridge  7  remains accurately positioned relative to the apparatus main assembly  100   a  while it is in the apparatus main assembly  100   a.    
         [0202]    The portions  40   a   1  and  40   a   2  of the main assembly contacting portions  40   a  are the two portions of the peripheral surface of the drum bearing  40 , which face upward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  The portions  40   a   1  and  40   a   2  are located close to each other. Further, the cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  of the main assembly contacting portion  50   a  (cartridge positioning portion) are the two portions of the peripheral surface of the drum bearing  50 , which face upward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  The cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  are located close each other. 
         [0203]    This structural arrangement also ensures that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  when it is mounted into the apparatus main assembly  100   a,  and also, that the cartridge  7  remains accurately positioned relative to the apparatus main assembly  100   a  while it is in the apparatus main assembly  100   a.    
         [0204]    Further, the cartridge  7  has the drum bearing  50  (photosensitive drum shaft bearing second member), which supports the opposite end from the end supported by the drum bearing  40 . The cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2  of the main assembly contacting portion  50   a  are the two portion of the peripheral surface of the drum bearing  50 . 
         [0205]    Further, the main assembly contacting portions  40   a  (which has portions  40   a   1  and  40   a   2 ) is a part of the peripheral surface of the arcuate portion of the drum bearing  40 , being therefore arcuate in cross section. It is a preset distance apart from the axial line of the drum bearing  40 . The main assembly contacting portion  50   a  (cartridge positioning portion) (which has cartridge positioning third portion  50   a   1  and cartridge positioning fourth portion  50   a   2 ) is a part of the peripheral surface of the arcuate portion of the drum bearing  50 . It is a preset distance apart from the axial line of the drum bearing  50 . Therefore, it is ensured that the main assembly contacting portions  40   a  and  50   a  are accurately positioned relative to the bearing catching portions  82   a  and  92   a,  each of which has two slanted surfaces. 
         [0206]    As described above, the main assembly contacting portions  40   a  (which has portions  40   a   1  and  40   a   2 ) is a part of the drum bearing  40 , and the main assembly contacting portion  50   a  (cartridge positioning portion) (which has portions  50   a   1  and  50   a   2 ) is a part of the drum bearing  50 . Therefore, the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  so that the photosensitive drum  1  is accurately positioned relative to the apparatus main assembly  100   a.    
         [0207]    Further, the cartridge  7  has the development roller separating member catching portion  31   b  (development roller separating force receiving portion) for receiving from the development roller separating member  111  (development roller separating force applying portion), the pressure (force) for separating the development roller  25  from the photosensitive drum  1 . The development roller separating member catching portion  31   b  belongs to the development unit  4 . 
         [0208]    The roller separating member catching portion  31   b,  which is in the form of a rib, perpendicularly protrudes from the surface of the development unit  4 , which faces downward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  It extends in the lengthwise direction of the photosensitive drum  1 . 
         [0209]    Further, the cartridge  7  has the shaft  27   b.  The shaft  27   b  regulates the rotational movement of the drum unit  26 , which is liable to occur as the couplings  41  and  66  receive rotational force from the apparatus main assembly  100   a,  and also, when the development roller separating member catching portion  31   b  is pressed by the apparatus main assembly  100   a,  by engaging into the cross-sectionally elongated hole  82   b,  while the cartridge  7  is in the image forming position in the apparatus main assembly  100   a.  In terms of the cartridge mounting direction, the shaft  27   b  is at the downstream end of the drum unit  26 . The cross-sectionally elongated hole  82   b  is the cartridge rotation regulating first portion of the apparatus main assembly  100   a,  and the shaft  27   b  is the cartridge rotation regulating first portion of the cartridge  7 . 
         [0210]    In terms of the cartridge mounting direction F, the shaft  27   b  is at the downstream end of the cartridge  7 , and projects downstream. Further, when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a,  the shaft  27   b  is in the cross-sectionally elongated hole  82   b,  preventing thereby the drum unit  26  from rotating, by being in contact with the internal surface of the hole  82   b.    
         [0211]    Further, the cartridge  7  has the groove  27   c,  in which the shaft  92   c  fits to prevent the unit  26  from rotating, when the couplings  41  and  66  receive rotational force from the apparatus main assembly  100   a  while the cartridge  7  is in its image forming position in the apparatus main assembly  100   a,  and also, when the development roller separating member catching portion  31   b  receives pressure from the apparatus main assembly  100   a.  In terms of the cartridge mounting direction, the groove  27   c  is at the upstream (rear) end of the drum unit  26 . The groove  27   c  is the drum unit rotation preventing second portion of the cartridge  7 , whereas the shaft  92   c  is the drum unit rotation preventing second portion of the apparatus main assembly  100   a.  The coupling  66  is the drum rotating force receiving portion. 
         [0212]    The groove  27   c  belongs to the portion of the drum unit  26 , which projects downward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  The groove  27   c  is the groove in which the shaft  92   c  of the lateral plate  92  fits when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  That is, the drum unit  26  is prevented from rotating, by the contact between the shaft  92   c  of the lateral plate  92  and the internal wall of the groove  27   c.    
         [0213]    In terms of the lengthwise direction of the photosensitive drum  1 , the Oldham&#39;s coupling  41  (development roller rotating force receiving portion) is on the inward side of the coupling  66  (drum rotating force receiving portion). The Oldham&#39;s coupling  41  is attached to the development unit  4  in such a manner that it is allowed to move in the direction perpendicular to the abovementioned lengthwise direction. As the development roller  25  receives rotational force from the Oldham&#39;s coupling  41 , the development unit  4  tends to rotate in the counterclockwise direction (indicated by arrow mark B) as seen from the rear of the cartridge  7  in terms of the lengthwise direction of the cartridge  7  ( FIG. 2 ). On the other hand, the development unit  4  and drum unit  26  are pressured by the resiliency of the spring  38  in the direction to cause the development roller  25  to contact the photosensitive drum  1 . In addition, the drum unit  26  is prevented from rotating, by the abovementioned structural arrangement. Therefore, the counterclockwise movement of the development unit  4  is regulated by the resiliency of the spring  38 . Therefore, it is ensured that the development roller  25  flawlessly receives rotational force from the Oldham&#39;s coupling  41 . 
         [0214]    It is a part of the rotational force which the development roller  25  receives from the Oldham&#39;s coupling  41  that is transmitted to the toner supply roller  34 . 
         [0215]    As described above, according to this embodiment, when the cartridge  7  is mounted into, or removed from, the apparatus main assembly  100   a,  the pressure applied to the cartridge  7  by the bearing pressing portion of the pressing member  83  is cancelled by the portion of the bearing pressing member  83 , which is located farther from the rotational axis of the bearing pressing member  83  than the bearing pressing portion is. Further, the portions of the surface of the cartridge  7 , which directly contact the apparatus main assembly  100   a  when the cartridge  7  is mounted or removed, are rendered different from the cartridge positioning portions of the cartridge  7 . In addition, when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a,  the drum unit  26  is kept accurately positioned relative to the apparatus main assembly  100   a  by the cartridge positioning portion and cartridge rotation regulating portion. Thus, as the development roller separating member catching portion  31   b  is pressed by the development roller separating member  111 , the development roller  25  separates from the photosensitive drum  1 . 
         [0216]    Also in this embodiment, the rotational force for rotating the development roller  25  is transmitted directly from the power source to the development roller  25  by way of the Oldham&#39;s coupling  41 , that is, independently from the route through which rotational force is transmitted to the photosensitive drum  1 . Further, the engaging portion  44  of the Oldham&#39;s coupling  41 , which is the engaging portion of the Oldham&#39;s coupling located on the main assembly side, is positioned relative to the cartridge  7  so that a preset positional relationship is realized between the engaging portion  44  and cartridge  7 . 
         [0217]    As described above, in this embodiment, the cartridge  7  is positioned relative to the apparatus main assembly  100   a  by pressing the cartridge  7  upward with the use of the above described structural arrangement. Therefore, the amount of load to which the cartridge  7  is subjected by the bearing pressing members  83  and  93  when the cartridge  7  is mounted into the apparatus main assembly  100   a  is significantly smaller than the amount of load to which a conventional process cartridge is subjected when it is mounted into the main assembly of a conventional image forming apparatus. Therefore, the amount of force necessary to mount the cartridge  7  is significantly smaller than the amount of force necessary to mount a conventional process cartridge. 
         [0218]    Further, the main assembly contacting portions  40   a  does not rub against the apparatus main assembly  100   a.  Therefore, the main assembly contacting portions  40   a  is not shaved by the apparatus main assembly  100   a.  Therefore, it is ensured that the cartridge  7  is accurately positioned relative to the apparatus main assembly  100   a  throughout its service life. 
         [0219]    Further, the cartridge  7  is provided two cartridge rotation regulating portions, which are at one of the lengthwise end of the cartridge  7  and the other, respectively, more specifically, at the rear and front ends of the drum unit  26 , respectively. Therefore, it is ensured that the cartridge  7  remains accurately positioned relative to the apparatus main assembly  100   a  when the development roller  25  and photosensitive drum  1  receive rotational force from the apparatus main assembly  100   a,  and when the development roller separating member catching portion  31   b  is pressed by the apparatus main assembly  100   a.  Further, it is possible to position the engaging portion  44  relative to the cartridge  7  so that a preset positional relationship is realized between the engaging portion  44  and cartridge  7 . Therefore, when the cartridge  7  is in its image forming portion in the apparatus main assembly  100   a,  the engaging portion  44  is smoothly engaged with the rotational force transmitting means, with which the apparatus main assembly  100   a  is provided. Therefore, the cartridge  7  is significantly superior to a conventional process cartridge, in term of the cartridge mounting operation, and can be positioned relative to the apparatus main assembly  100   a  at a higher level of accuracy than the conventional process cartridge can be positioned relative to the main assembly of an image forming apparatus usable therewith, throughout its service life. 
       Embodiment 2 
       [0220]    Next, referring to  FIG. 26 , the structure of the image forming apparatus in the second embodiment of the present invention will be described. The basic structure of the image forming apparatus in this embodiment is the same as that of the image forming apparatus in the first embodiment. The portions of the image forming apparatus in this embodiment, which are similar in structure to the counterparts of the image forming apparatus in the first embodiment will not be described. That is, only the portions of the image forming apparatus in this embodiment, which are different from the counterparts of the image forming apparatus in the first embodiment, will be described. Further, the components of the image forming apparatus in this embodiment, which are the same in function as the counterparts of the image forming apparatus in the first embodiment are given the same referential symbols as those given to the counterparts. This practice will also be applied to the description of the third embodiment of the present invention. 
         [0221]    In the first embodiment, the cartridge  7  is provided with a single development roller separating member catching portion  31   b,  which the development roller separating member  111  contacts and presses to separate the development roller  25  from the photosensitive drum  1 . Further, the development roller separating member catching portion  31   b  is on the surface of the development unit frame  31  of the development unit  4 , which faces downward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  However, the cartridge  7  may be provided with multiple (two in this embodiment:  31   b  and  31   c ) development roller separating member catching portions, which are distributed in the lengthwise direction of the cartridge  7 , as shown in  FIG. 26 , and which the development roller separating members  111  contact and press, one for one, to separate the development roller  25  from the photosensitive drum  1 . 
         [0222]      FIG. 26  is an external perspective view of the cartridge  7  in this embodiment. The apparatus main assembly  100   a  is provided with a development roller separating first member  112  and a development roller separating second member  113 , which are the means for separating the development roller  25  from the photosensitive drum  1 . In terms of the direction in which the cartridge  7  is inserted, the development roller separating first member  112  is in a preset position at the front (leading) end of the cartridge  7 , and the development roller separating second member  113  is in the preset position at the rear (trailing end). The development roller separating first and second members  112  and  113  are movable between the position in which they contact cartridge  7 , that is, the position in which they keep the development roller  25  separated from the photosensitive drum  1 , and the positions into which they retreat to maintain a preset amount of distance from the cartridge  7 . Further, it is at the same time that the development roller separating member  112  and  113  move into their positions in which they keep the development roller  25  separated from the photosensitive drum  1 , or retreat into their positions in which they allow the development roller  25  to remain in contact with the photosensitive drum  1 . On the other hand, the cartridge  7  is provided with a development roller separating member caching first portion  31   c  and a development roller separating member catching portion second member  31   d,  which are on the surface of the development unit frame  31 , which faces downward when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a.  Further, the development roller separating member catching first and second portions  31   c  and  31   d  are positioned so that when the cartridge  7  is in its image forming position in the apparatus main assembly  100   a,  they oppose the development roller separating first and second members  112  and  113 , respectively. 
         [0223]    When the apparatus main assembly  100   a  is not in action, the development roller separating member catching first and second portions  31   c  and  31   d  of the development unit  4  remains under the pressure from the development roller separating first member  112  and the pressure from the development roller separating second member  113 , respectively. Also when the apparatus main assembly  100   a  is not in action, the shaft  27   b  projecting from one of end surfaces of the drum unit  26  is in the cross-sectionally elongated hole  82   b  of the apparatus main assembly  100   a,  and the shaft  92   c  of the lateral plate  92  of the apparatus main assembly  100   a  is in the groove  27   c  of the same end surface of the drum unit  26 . Therefore, the drum unit  26  is prevented from moving in the direction from which the development roller separating member catching first and second portions  31   c  and  31   d  are pressed by the development roller separating first and second members  112  and  113 . Therefore, the development unit  4  rotationally moves about the shafts  37  ( 37 R and  3 F) (connective pins), by which the development unit  4  is connected with the drum unit  26 , causing the development roller  25  to be separated, and remain separated, from the photosensitive drum  1 . Therefore, even if the cartridge  7  is left unused for a long time in its image forming position in the apparatus main assembly  100   a,  the elastic layer of the development roller  25  does not deform. Therefore, it does not occur that an image which is nonuniform in density, and the nonuniformity of which is attributable to the deformation of the elastic layer of the development roller  25 , which will occur if a conventional process cartridge is left unused in the apparatus main assembly  100   a  for a long time, is formed. In other words, the second embodiment can also provide the same effects as those provided by the first embodiment. 
         [0224]    As will be evident from the description of the second embodiment given above, providing the development unit  4  with multiple development roller separating member catching portions, which are distributed across the development unit  4  in terms of the lengthwise direction of the cartridge  7  is particularly useful for a process cartridge, such as a process cartridge for forming an image on a large sheet of recording medium, which is substantially longer than an ordinary process cartridge. It is also useful for a process cartridge which is substantially greater in capacity, that is, a process cartridge which is substantially greater in the amount of the pressure which the weight of the development roller  25  applies to the photosensitive drum  1 . That is, it can evenly distribute the force to which the development roller separating member catching portions, and the development roller separating force applying member, are subjected. Therefore, it can minimize the deformation of the development roller separating member and development roller separating member catching portion. 
       Embodiment 3 
       [0225]    Next, referring to  FIG. 27 , the structure of the image forming apparatus in the third embodiment will be described. In the first embodiment, the image forming apparatus was structured so that the development roller bearing member  45  is pressed upon the bearing  40  of the photosensitive drum  1 . However, it is feasible to provide a drum unit frame  27  with a development roller bearing member supporting portion (bearing member holding portion) as shown in  FIG. 27 . 
         [0226]      FIG. 27  is a plan view of the lengthwise end of the cartridge  7  in the third embodiment, as seen from the side having the couplers, when the development roller  25  is holding the preset amount of gap from the photosensitive drum  1 . The development unit  4  is in its preset position (outlined with broken line in  FIG. 27 ) in which its development roller  25  holds the preset amount of gap from the photosensitive drum  1 , and into which it has been moved by the development roller separating member  111  of the apparatus main assembly  100   a,  as it is in the first embodiment. When the development unit  4  is in the above described position, the arm portion  46   a  of the spring  46  (pressure applying member) located inside the side cover  48  is in contact with the engaging portion  45   c  of the coupling bearing  45 . Thus, the engaging portion  44  is kept pressed in the direction intersectional to the axial line of the development roller  25 . Therefore, the contacting portion  45   d  of the coupling bearing  45  comes into contact with the contacting portion  27   f  with which the drum unit frame  27 . The contacting portion  27   f  of the drum unit frame  27  is a groove which is V-shaped in cross section; it has two surfaces parallel to the axial line of the photosensitive drum  1 . Further, the drum unit frame  27  is provided with the drum bearing  40 , which has the main assembly contacting portions  40   a  which is an integrally formed part of the drum bearing  40 . Thus, also in this embodiment, the engaging portion  44  rotatably supported by the coupling bearing  45  is accurately positioned relative to the axial line  53   d  of the coupling  53 . 
         [0227]    According to each of the preceding embodiments described above, it is ensured that even a process cartridge designed to be positioned relative to the main assembly of an electrophotographic image forming apparatus by being pressed upward in the main assembly is reliably positioned relative to the main assembly. 
         [0228]    Also according to each of the preceding embodiments described above, it is possible to improve even a process cartridge designed to be accurately positioned relative to the main assembly of an electrophotographic image forming apparatus by being pressed upward in the main assembly, in terms of the level of accuracy at which it is positioned relative to the main assembly. 
         [0229]    Further, according to each of the preceding embodiments described above, a process cartridge can be reliably positioned relative to the main assembly even when it is receiving the rotational force for rotating the development roller and photosensitive drum from the apparatus main assembly. 
         [0230]    Further, according to each of the preceding embodiments described above, a process cartridge can reliably positioned relative to the main assembly even when it is receiving the force for separating the development roller from the photosensitive drum from the apparatus main assembly. 
         [0231]    Further, according to each of the preceding embodiments described above, it is ensured that a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly is reliably positioned relative to the main assembly even when it is receiving the rotational force for rotating the development roller and photosensitive drum from the apparatus main assembly. 
         [0232]    Further, according to each of the preceding embodiments described above, it is ensured that a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly is reliably positioned relative to the main assembly even when it is receiving the force for separating the development roller from the photosensitive drum from the apparatus main assembly. 
         [0233]    Further, according to each of the preceding embodiments described above, a process cartridge designed to be accurately positioned relative to the main assembly of an image forming apparatus by being pressed upward in the main assembly can be accurately positioned relative to the main assembly even when it is receiving the rotational force for rotating the development roller and photosensitive drum from the apparatus main assembly. 
         [0234]    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. 
         [0235]    This application claims priority from Japanese Patent Application No. 138045/2008 filed May 27, 2008 which is hereby incorporated by reference.