Abstract:
A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, includes an electrophotographic photosensitive drum; developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum; drum frame supporting the electrophotographic photosensitive drum; a developing frame supporting the developing roller, the developing roller being movable relative to the drum frame between a contacting position in which the developing roller is in contact with the electrophotographic photosensitive drum and a spacing position in which the developing roller is spaced from the electrophotographic photosensitive drum; a force receiving member, provided movably relative to the developing frame, for receiving an external force, wherein the force receiving member is capable of taking an operating position for moving the developing frame from the contacting position to the spacing position by receiving the external force, and a stand-by position retracted from the operating position; an urging portion for urging the force receiving member from the stand-by position toward the operating position; and an engaging portion for engaging with the force receiving member to hold the force receiving member in the stand-by position against an urging force of the urging portion.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a process cartridge made up of an electrophotographic photosensitive drum and a development roller (which processes photosensitive drum), in particular, a process cartridge, the electrophotographic photosensitive drum and development roller of which can be placed in contact with, or separated from, each other. The present invention also relates to an electrophotographic image forming apparatus employing the above described process cartridge. 
         [0002]    In recent years, a process cartridge system has come to be widely used in the field of an image forming apparatus which uses an electrophotographic image forming process. A process cartridge system is one of the electrophotographic image forming systems. It uses a cartridge in which an electrophotographic photosensitive drum, and a development roller, that is, a roller for processing an electrophotographic photosensitive drum, are integrally disposed to make them removably mountable in the main assembly of an image forming apparatus. Thus, the employment of a process cartridge system makes it possible for a user to maintain an electrophotographic image forming apparatus without relying on a service person. This is why a process cartridge system has come to be widely used in the field of an electrophotographic image forming apparatus. 
         [0003]    A process cartridge is structured so that its development roller is kept pressured toward its electrophotographic photosensitive drum with the application of a preset amount of pressure, in order to keep the development roller in contact with the photosensitive drum when forming an image. In a case of a so-called contact development method, that is, a development method which places a development roller in contact with a photosensitive drum to develop a latent image on the photosensitive drum, the elastic layer of the development roller is kept pressed upon the peripheral surface of the photosensitive drum so that a preset amount of contact pressure is maintained between the peripheral surface of the development roller and that of the photosensitive drum. 
         [0004]    Therefore, if a process cartridge is left unused in the main assembly of an image forming apparatus for a substantial length of time, the elastic layer of the development roller sometimes deforms. Thus, if an image forming apparatus in which a process cartridge has been left unused for a substantial length of time is used for the first time thereafter, it is possible that a latent image will be nonuniformly developed. Further, in the case of a so-called contact development method, a development roller is in contact with a photosensitive drum during development. Therefore, developer sometimes transfers from a development roller onto the points of the peripheral surface of a photosensitive drum, to which developer is not to supposed to adhere. Further, not only do a photosensitive drum and a development roller rotate in contact with each other during development, but also, during processes other than development. Therefore, a so-called contact development method exacerbates the deterioration of a photosensitive drum, a development roller, and developer. 
         [0005]    One of the solutions to the above described problem is proposed in Japanese Laid-open Patent Application 2003-167499. According to this patent application, an image forming apparatus is provided with a mechanism which acts on a process cartridge to keep an electrophotographic photosensitive drum and a development roller separated from each other when an image is not actually being formed (Patent Document 1). 
         [0006]    In the case of the image forming apparatus proposed in Patent Document 1, its main assembly is structured so that four process cartridges are removably mountable in the main assembly. Each cartridge is made up of a photosensitive member unit and a development unit. The photosensitive member unit has a photosensitive member. The development unit supports a development roller, and is connected to the photosensitive member unit so that it can be rotationally moved relative to the photosensitive member unit. Further, the main assembly of the image forming apparatus is provided with a separation plate, whereas the process cartridge is provided with a force receiving portion. As the separation plate is moved, the force receiving portion receives the force from the separation plate, causing the development unit to move relative to the photosensitive member unit. As a result, the development roller, which was in contact with the photosensitive drum, separates from the photosensitive drum. 
         [0007]    According to the prior art, the force receiving portion, that is, the portion which catches the force for separating a development roller and a photosensitive member from each other, remains projecting beyond the external contour of the development unit. Therefore, it is liable to be damaged while a user handles a process cartridge, or a process cartridge is conveyed alone. Further, the presence of the above described force receiving portion has been one of the major problems which arose when studies were made to reduce in size a process cartridge structured so that its electrophotographic photosensitive member and development roller can be placed in contact with, or separated from, each other, and also, when studies were made to reduce in size the main assembly of an image forming apparatus in which such a process cartridge as the one described above is removably mountable. 
       SUMMARY OF THE INVENTION 
       [0008]    The primary object of the present invention is to provide a process cartridge, the electrophotographic photosensitive drum and development roller of which can be placed in contact with, or separated from, each other, and which is significantly smaller in size than a counterpart in accordance with the prior art, and also, to provide an electrophotographic image forming apparatus in which a process cartridge in accordance with the present invention, is removably mountable. 
         [0009]    Another object of the present invention is to provide a process cartridge, the force receiving portion of which is significantly less liable to be damaged while the process cartridge is transported alone, than a counterpart in accordance with the prior art. 
         [0010]    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, comprising an electrophotographic photosensitive drum; developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; drum frame supporting said electrophotographic photosensitive drum; a developing frame supporting said developing roller, said developing roller being movable relative to said drum frame between a contacting position in which said developing roller is in contact with said electrophotographic photosensitive drum and a spacing position in which said developing roller is spaced from said electrophotographic photosensitive drum; a force receiving member, provided movably relative to said developing frame, for receiving an external force, wherein said force receiving member is capable of taking an operating position for moving said developing frame from the contacting position to the spacing position by receiving the external force, and a stand-by position retracted from the operating position; an urging portion for urging said force receiving member from the stand-by position toward the operating position; and an engaging portion for engaging with said force receiving member to hold said force receiving member in the stand-by position against an urging force of said urging portion. 
         [0011]    According to another aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, said apparatus comprising: 
         [0012]    (i) a movable force applying member; 
         [0013]    (iii) mounting means; 
         [0014]    (iii) a process cartridge detachably mounted to said mounting means, said process cartridge including an electrophotographic photosensitive drum, developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum, drum frame supporting said electrophotographic photosensitive drum, a developing frame supporting said developing roller, said developing roller being movable relative to said drum frame between a contacting position in which said developing roller is in contact with said electrophotographic photosensitive drum and a spacing position in which said developing roller is spaced from said electrophotographic photosensitive drum, a force receiving member, provided movably relative to said developing frame, for receiving an external force when the force applying member moves, wherein said force receiving member is capable of taking an operating position for moving said developing frame from the contacting position to the spacing position by receiving the external force, and a stand-by position retracted from the operating position, an urging portion for urging said force receiving member from the stand-by position toward the operating position, and an engaging portion for engaging with said force receiving member to hold said force receiving member in the stand-by position against an urging force of said urging portion, and 
         [0015]    (vi) feeding means for feeding the recording material. 
         [0016]    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 DRAWINGS 
         [0017]      FIG. 1  is a schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0018]      FIG. 2  is a schematic sectional view of the process cartridge in the first embodiment of the present invention. 
           [0019]      FIG. 3  is also a schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0020]      FIG. 4  is another schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing how the process cartridges therein are replaced. 
           [0021]      FIG. 5  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the first embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0022]      FIG. 6  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the first embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0023]      FIG. 7  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the first embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0024]      FIG. 8  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the first embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0025]      FIG. 9  is a perspective view of the process cartridge in the first embodiment of the present invention, as seen from the side from which the cartridge is driven. 
           [0026]      FIG. 10  is a perspective view of the process cartridge in the first embodiment of the present invention, as seen from the side from which the cartridge is driven. 
           [0027]      FIG. 11  is a perspective view of the process cartridge in the first embodiment of the present invention, as seen from the opposite side from the side from which the cartridge is driven. 
           [0028]      FIG. 12  is a perspective view of the process cartridge in the first embodiment of the present invention, as seen from the opposite side from the side from which the cartridge is driven. 
           [0029]      FIG. 13  is a perspective view of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0030]      FIG. 14  is another perspective view of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0031]      FIGS. 15(   a ) and  15 ( b ) are detailed schematic drawings of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0032]      FIGS. 16(   a ) and  16 ( b ) also are detailed schematic drawings of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0033]      FIG. 17  is another detailed schematic drawing of the force receiving member and releasing member, in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0034]      FIG. 18  is another detailed schematic drawing of the force receiving member and releasing member, in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0035]      FIG. 19  also is a detailed schematic drawing of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0036]      FIG. 20  is another detailed schematic drawing of the force receiving member and releasing member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0037]      FIG. 21  is a schematic detailed drawing of the force receiving member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0038]      FIG. 22  is another detailed schematic drawing of the force receiving member in the first embodiment of the present invention, showing in detail the mechanical structure thereof. 
           [0039]      FIG. 23  is a schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0040]      FIG. 24  is a schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0041]      FIG. 25  is a schematic sectional view of the electrophotographic image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0042]      FIG. 26  is a schematic drawing of the guiding hole of the electrophotographic image forming apparatus in the first and second embodiments of the present invention. 
           [0043]      FIG. 27  is a schematic drawing of the force applying first member in the first embodiment of the present invention, showing the operation of the force applying member. 
           [0044]      FIG. 28  also is a schematic drawing of the force applying first member in the first embodiment of the present invention, showing the operation of the force applying first member. 
           [0045]      FIG. 29  is a perspective view of the electrophotographic image forming apparatus in the first embodiment of the present invention. 
           [0046]      FIG. 30  is a partially cutaway perspective view of the electrophotographic image forming apparatus in the first embodiment of the present invention. 
           [0047]      FIG. 31  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the second embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0048]      FIG. 32  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the second embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0049]      FIG. 33  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the second embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0050]      FIG. 34  is a schematic sectional view of one of the process cartridges, and its adjacencies, in the electrophotographic image forming apparatus in the second embodiment of the present invention, at a plane perpendicular to the axial line of the photosensitive drum. 
           [0051]      FIG. 35  is a schematic perspective view of the force applying second member, and force receiving member of the process cartridge in the second embodiment of the present invention, showing the operations thereof. 
           [0052]      FIG. 36  also is a schematic perspective view of the force applying second member, and force receiving member of the process cartridge in the second embodiment of the present invention, showing the operations thereof. 
           [0053]      FIG. 37  is a schematic sectional view of the electrophotographic image forming apparatus in the second embodiment of the present invention, showing the general structure of the apparatus. 
           [0054]      FIG. 38  also is a schematic sectional view of the electrophotographic image forming apparatus in the second embodiment of the present invention, showing the general structure of the apparatus. 
           [0055]      FIG. 39  is another a schematic sectional view of the electrophotographic image forming apparatus in the second embodiment of the present invention, showing the general structure of the apparatus. 
           [0056]      FIG. 40  is a schematic sectional view of the electrophotographic image forming apparatus in the second embodiment of the present invention, showing how the process cartridges therein are replaced. 
           [0057]      FIG. 41  is a schematic drawing of the force applying second member in the second embodiment of the present invention, showing the operation of the force applying second member. 
           [0058]      FIG. 42  is a partially cutaway perspective view of the electrophotographic image forming apparatus in the second embodiment of the present invention. 
           [0059]      FIG. 43  is a schematic drawing of the force applying first member in the second embodiment of the present invention, showing the operation of the force applying first member. 
           [0060]      FIG. 44  also is a schematic drawing of the force applying first member in the second embodiment of the present invention, showing the operation of the force applying first member. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0061]    Next, referring to  FIGS. 1-4 , the process cartridges and electrophotographic image forming apparatuses in this preferred embodiment of the present invention will be described. 
         [0062]      FIG. 1  is a schematic sectional view of the electrophotographic image forming apparatus  100  (which hereafter will be referred to simply as apparatus main assembly), in which multiple (four) process cartridges  50   y ,  50   m ,  50   c , and  50   k  (which hereafter may be referred to simply as cartridges  50 ) which have been removably mounted. The multiple (four) cartridges  50  store yellow, magenta, cyan, and black toners (developers), one for one.  FIG. 2  is a schematic sectional view of the cartridge itself.  FIGS. 3 and 4  are schematic sectional drawings of the electrophotographic image forming apparatus in this embodiment, which are for showing how any cartridge or cartridges  50  are removed from the main assembly of the image forming apparatus. 
       {General Structure of Electrophotographic Image Forming Apparatus} 
       [0063]    The electrophotographic image forming apparatus in this embodiment is structured to carry out the following image forming operation. Referring to  FIG. 1 , first, the uniformly charged area of the peripheral surface of each of the electrophotographic photosensitive drums (which hereafter will be referred to as photosensitive drums)  30   y ,  30   m ,  30   c , and  30   k  is scanned by a beam of laser light  11  projected by a laser scanner  10 , with which the apparatus main assembly  100  is provided, while being modulated with pictorial signals. As a result, an electrostatic latent image is effected on the peripheral surface of each photosensitive drum  30 . This electrostatic latent image is developed by a development roller  42 , into a visible image; an image is formed of toner (developer) on the peripheral surface of the photosensitive drum  30 . In other words, yellow, magenta, cyan, and black toner images are formed on the photosensitive drums  30   y ,  30   m ,  30   c , and  30   k , respectively. Then, these toner images are sequentially transferred by the voltages applied to transfer rollers  18   y ,  18   m ,  18   c , and  18   k , onto a transfer belt  19  supported and stretched by rollers  20 - 22 . Thereafter, the toner images on the transfer belt  19  are transferred by a transfer roller  3 , onto a sheet of recording medium P delivered by a recording medium conveyance roller  1  as a recording medium conveying means. Then, the recording medium P is conveyed to a fixation unit  6  made up of a driver roller, and a fixation roller having an internal heater. In the fixation unit  6 , heat and pressure is applied to the recording medium P and the toner images thereon. As a result, the toner images on the recording medium P are fixed to the recording medium P. Then, the recording medium P is discharged onto a delivery tray  9  by a pair of discharge rollers  7 . 
       {General Structure of Process Cartridge} 
       [0064]    Next, referring to  FIGS. 1 ,  2 ,  5 - 8 ,  29  and  30 , the cartridges  50  ( 50   y ,  50   m ,  50   c , and  50   k ) in this embodiment will be described. The multiple (four) cartridges  50  in this embodiment are the same in structure although they are different in the color of the toner T they store. Thus, the structure of the cartridges  50  will be described with reference to the cartridge  50   y.    
         [0065]    Referring to  FIG. 2 , the cartridge  50   y  is provided with a photosensitive drum  30 , and processing means which process the photosensitive drum  30 . The processing means in this embodiment are a charge roller  32  which is the charging means for charging the photosensitive drum  30 , a development roller  42  which is the developing means for developing a latent image formed on the photosensitive drum  30 , a blade  33  which is the cleaning means for removing the residual toner remaining on the peripheral surface of the photosensitive drum  30 , etc. The cartridge  50   y  is made up of a drum unit  31  and a development unit  41 . 
       {Structure of Drum Unit} 
       [0066]    Referring to  FIGS. 2 ,  4 ,  9 - 12 , and  30 , the drum unit  31  includes the above-mentioned photosensitive drum  30 , charge roller  32 , and blade  33 . It also includes a waste toner storing portion  35 , a drum unit main frame  34 , and lateral covers  36  and  37  (which hereafter will be referred to simply as cover). Referring to  FIGS. 9 ,  10 ( a ) and  10 ( b ), one of the lengthwise end portions of the photosensitive drum  30  is rotatably supported by the supporting portion  36   b  of the cover  36 , whereas the other lengthwise end of the photosensitive drum  30  is rotatably supported by the supporting portion  37   b  of the cover  37  as shown in  FIGS. 11 and 12 . The covers  36  and  37  are firmly attached to the lengthwise ends of the drum unit main frame  34 , one for one. Next, referring to  FIGS. 9 ,  10 ( a ), and  10 ( b ), the lengthwise end portion of the photosensitive drum  30  is provided with a coupling member  30   a  for transmitting driving force to the photosensitive drum  30 . The coupling member  30   a  engages with a first coupling member  105  of the apparatus main assembly  100 , shown in  FIGS. 4 and 30 , as the cartridge  50   y  is mounted into the apparatus main assembly  100 . Thus, as driving force is transmitted from a motor (unshown) with which the apparatus main assembly  100  is provided, to the coupling member  30   a , the photosensitive drum  30  rotates in the direction indicated by an arrow mark u in  FIG. 2 . The charge roller  32  is supported by the drum unit main frame  34  so that it is rotated in contact with the photosensitive drum  30  by the rotation of the photosensitive drum  30 . The blade  33  is supported also by the drum unit main frame  34  so that it remains in contact with the peripheral surface of the photosensitive drum  30  with the presence of a preset amount of pressure between the blade  33  and the peripheral surface of the photosensitive drum  30 . The covers  36  and  37  are provided with holes  36   a  and  37   a  for supporting the development unit  42  in such a manner that the development unit  42  is rotationally movable relative to the drum unit  31 . 
       {Structure of Development Unit} 
       [0067]    Referring to  FIGS. 2 ,  10 ( a ), and  10 ( b ), the development unit  41  has the abovementioned development roller  42 . It also has a development blade  43 , a development unit main frame  48 , a bearing unit  45 , and a pair of lateral covers  46 . The development unit main frame  48  has a toner storage portion  49  in which the toner to be supplied to the development roller  42  is stored. It supports the development blade  34  which regulates the thickness to which toner is coated on the peripheral surface of the development roller  42 . Referring to  FIGS. 10(   a ) and  10 ( b ), the bearing unit  45  is firmly attached to one of the lengthwise end portions of the development unit main frame  48 . It rotatably supports the development roller  42 , one of the lengthwise end portions of which has a development roller gear  69 . Further, the bearing unit  45  is provided with an idler gear  68 , which transmits driving force from a coupling member  67  to the development roller gear  69 . The cover  46  is securely attached to the outward side of the bearing unit  45 , in terms of the lengthwise direction of the bearing unit  45 , in a manner to cover the coupling member  67  and idler gear  68 . Further, the cover  46  is provided with a cylindrical portion  46   b , which protrudes outward from the outward surface of the cover  46 . The coupling member  67  is exposed through the hollow of the cylindrical portion  46   b . The apparatus main assembly  100  and process cartridge  50   y  are structured so that as the process cartridge  50   y  is mounted into the apparatus main assembly  100 , the coupling portion  67   a  of the coupling member  67  engages with the second coupling member  106  of the apparatus main assembly  100 , which is shown in  FIG. 30 , transmitting thereby driving force from the motor (unshown) with which the apparatus main assembly  100  is provided, to the process cartridge  50   y.    
       {Connection of Development Unit to Drum Unit} 
       [0068]    Referring to  FIGS. 10(   a ) and  10 ( b ), the development unit  41  and drum unit  31  are connected in the following manner: First, at one end of the process cartridge  50   y , the cylindrical portion  46   b  is fitted into the supporting hole  36   a . At the other end, a projection  48   b  which projects from the development unit main frame  48  is fitted into the supporting hole  37   a . As a result, the development unit  41  is connected to the drum unit  31  in such a manner that the development unit  41  is rotationally movable relative to the drum unit  31 . Next, referring to  FIGS. 9 and 11 , the development unit  41  is kept pressured by a compression spring  95 , which are elastic members, in the direction to be rotated about the cylindrical portion  46   b  and projection  48   b  so that the development roller  42  is kept in contact with the photosensitive drum  30 . That is, the development unit  41  is kept pressed by the resiliency of the compression spring  95  in the direction indicated by a narrow mark G, generating a moment H which acts in the direction to rotate the development unit  41  about the cylindrical portion  46   b  and projection  48   b . Thus, the development roller  42  is kept in contact with the photosensitive drum  30  with the presence of the preset amount of contact pressure between the development roller  42  and photosensitive drum  30 . The position in which the development unit  41  is when it is kept in contact with the photosensitive drum  30  is referred to as “contact position”. 
         [0069]    Referring to  FIGS. 9 and 11 , the compression spring  95  in this embodiment is located on the opposite side from one of the lengthwise end portions, where the coupling member  30   a  of the photosensitive drum  30 , and the coupling member  67  of the development roller  42 , are located. This is for the following reason: As the coupling member  67  of the development roller  42  receives driving force from the coupling member  106  of the apparatus main assembly  100 , the moment H is generated in the direction to rotate the development unit  41  about the cylindrical portion  46   b , as shown in  FIG. 2 . Thus, at the lengthwise end of the cartridge  50   y , the development roller  42  is pressed upon the photosensitive drum  30 , generating thereby the preset amount of contact pressure between the development roller  42  and photosensitive drum  30 , whereas, at the other lengthwise end, the development roller  42  is kept pressed upon the photosensitive drum  30  by the compression spring  95 . 
       {Force Receiving Member} 
       [0070]    Referring to  FIGS. 5-8 , the cartridge  50   y  is provided with a force receiving member  70  for placing the development roller  42  and photosensitive drum  30  in contact with each other, or separating them from each other, in the apparatus main assembly  100 . Next, referring to  FIGS. 10(   a ),  10 ( b ),  13 , and  14 , the force receiving member  70  has a hook portion  70   a . The hook portion  70   a  is connected to one end of a spring  21  for keeping the force receiving member  70  pressured, whereas the other end of the spring  21  is connected to the hook portion  48   a  of the development unit frame  48 , as shown in  FIGS. 13 and 14 . 
         [0071]    Referring to  FIG. 10(   b ), the force receiving member  70  is attached to a bearing unit  45  by engaging a rotational shaft  70   g , which is a part of the force receiving member  70 , with the guiding portion of the bearing unit  45 . After the attachment of the force receiving member  70 , the cover  46  is attached to the development unit frame  45  in a manner to cover the bearing unit  45  from the direction parallel to the axial line of the development roller  42 . The detail of the operation of the force receiving member  70  will be given later. 
       {Cartridge Tray of Electrophotographic Image Forming Apparatus Main Assembly} 
       [0072]    Next, the cartridge tray  13 , which is in the form of a drawer, will be described. 
         [0073]    Referring to  FIG. 4 , the cartridge tray  13  is attached to the apparatus main assembly  100  in such a manner that, in practical terms, it can be horizontally and linearly moved relative to the apparatus main assembly  100 . That is, the cartridge tray  13  can be moved (pushed into, or pulled out of, the apparatus main assembly  100 ) in the direction indicated by an arrow mark D 1  or D 2 , respectively, which is virtually horizontal direction. The apparatus main assembly  100  is structured so that the cartridge tray  13  can be locked in the innermost position (image forming position, shown in  FIG. 1 , in the apparatus main assembly  100 ), and the outermost position (cartridge replacement position: cartridge mounting or removing position, shown in  FIG. 4 , which is the farthest position to which the cartridge tray  13  can be pulled out). The cartridge  50  is mounted into the cartridge tray  13  by an operator in the direction indicated by an arrow mark C, which is virtually parallel to the direction of gravity, as shown in  FIG. 4 . The cartridge tray  13  is structured so that as the cartridges  50  are mounted into the cartridge tray  13 , the cartridges  50  become arranged in tandem, in the direction parallel to the direction in which the cartridge tray  13  is movable, with their lengthwise direction (which is parallel to axial lines of photosensitive drum  30  and development roller  42 ) being perpendicular to the moving direction of the cartridge tray  13 . As the cartridge tray  13  is pushed into the apparatus main assembly  100 , the cartridges  50  in the cartridge tray  13  enter the apparatus main assembly  100 , with the presence of a preset amount of gap f 2  ( FIG. 5 ) between the photosensitive drum  30  in each cartridge  50 , and an intermediary transfer belt  19  located below the cartridge path in the apparatus main assembly  100 . Then, as the cartridge tray  13  is moved into its innermost position in the apparatus main assembly  100 , each cartridge  50  is properly positioned in the apparatus main assembly  100  by the cartridge positioning portion  101   a  provided in the apparatus main assembly  100  ( FIGS. 5 and 30 ). The cartridge positioning operation will be described later in detail. A user is to close the door  12  after pushing the cartridge tray  13  all the way into the apparatus main assembly  100 . Closing the door  12  ensures that each cartridge  50  is properly mounted into the apparatus main assembly  100 . Therefore, in terms of operability, this structural arrangement for the apparatus main assembly  100  and cartridges  50  is superior to the structural arrangement of an electrophotographic image forming apparatus in accordance with the prior art, which requires the cartridges  50  to be individually mounted into the apparatus main assembly  100  by a user. 
         [0074]    Next, referring to  FIGS. 23-26 , the operation of the cartridge tray  13  will be described.  FIGS. 23-26  do not show the cartridges  50 , in order to make it easier to understand the operation of the cartridge tray  13 . 
         [0075]    The cartridge tray  13  is supported by a pair of tray supporting members  14  in such a manner that the cartridge tray  13  can be pulled out of the apparatus main assembly  100  while remaining supported by the tray supporting members  14 . The tray supporting members  14  are moved by the movement of the door  12  which can be opened or closed by an operator (user). The door  12  is attached to the apparatus main assembly  100  so that it can be rotationally moved about its rotational axis  12   a . The door  12  is rotationally movable between a position (shut position) in which it completely covers an opening  80 , as shown in  FIG. 23 , and a position (open position) in which it fully exposes the opening  80  as shown in  FIG. 24 . 
         [0076]    When it is necessary to take out any cartridge  50  or cartridges  50  in the apparatus main assembly  100 , the door  12  is to be rotationally moved from the shut position to the open position. As the door  12  is rotationally moved, a pair of projections  15  (connective pins) with which the door  12  is provided, move in the clockwise direction about the rotational axis  12   a , while moving in a pair of elongated holes  14   c , one for one, with which the tray supporting member  14  is provided, from the bottom end  14   c   2  of the elongated hole  14   c  to the top end  14   c   1  of the elongated hole  14   c , as shown in  FIG. 24 . As a result, the tray supporting members  14  are moved by the projections  15  in the direction indicated by the arrow mark z 1 . As the tray supporting members  14  are moved in the abovementioned direction z 1 , the projections  14   d   1  and  14   d   2 , which project from each of the tray supporting members  14  are guided by the guiding holes  107  with which the apparatus main assembly  100  is provided, as shown in  FIG. 25 . Referring to  FIG. 26 , each guiding hole  107  has three sections, that is, two horizontal sections  107   a   1  and  107   a   3 , and one diagonal section  107   a   2 . The diagonal section  107   a   2  extends diagonally upward from the horizontal section  107   a   1  to the horizontal section  17   a   3 . Therefore, as the door  12  is moved from the shut position to the open position, as shown in  FIG. 24 , the projections  14   d   1  and  14   d   2  are guided by the guiding hole  107 , sequentially through the horizontal section  107   a   1 , diagonal section  107   a   2 , and horizontal section  107   a   3 . Thus, the tray supporting members  14  are first moved in the direction indicated by the arrow mark z 1  ( FIG. 24 ), and then, are moved in the direction indicated by an arrow mark y 1  ( FIG. 24 ), that is, direction to move away from the transfer belt  19 . With the tray supporting members  14  moved all the way in the direction indicated by the arrow mark y 1 , the cartridge tray  13  can be pulled out of the apparatus main assembly  100  through the opening  80  in the direction indicated by the arrow mark D 2 , as shown in  FIG. 25 .  FIG. 30  is a partially cutaway perspective view of the image forming apparatus after the cartridge tray  13  has been pulled out of the apparatus main assembly  100  to its outermost position. 
         [0077]    Next, the case in which any cartridge or cartridges  50  are mounted into the apparatus main assembly  100  will be described. Referring to  FIG. 25 , the cartridge tray  13  is to be pushed into the apparatus main assembly  100  in the direction of the arrow mark D 1  through the opening  80 , with the door  12  kept in the open position. Thereafter, the door  12  is to be moved into the shut position as shown in FIG.  23 . As the door  12  is moved, each of the projection  15  of the door  12  moves in the counterclockwise direction about the rotational axis  12   a , while moving in the corresponding elongated hole  14   c  of the tray supporting member  14 , to the bottom end  14   c   2  of the elongated hole  14   c , as shown in  FIG. 23 . Thus, the tray supporting member  14  is moved in the direction of the arrow mark z 2  ( FIG. 23 ) by the pair of projections  15 . Therefore, as the door  12  is moved into the shut position as shown in  FIG. 23 , the projections  14   d   1  and  14   d   2  are guided by the horizontal section  107   a   1 , diagonal section  107   a   2 , and horizontal section  107   a   3 , in the listed order, as shown in  FIG. 23 . Therefore, the tray supporting members  14  move, first, in the direction of the arrow mark z 2  ( FIG. 23 ), and then, in the direction of the arrow mark y 2  ( FIG. 23 ), that is, the direction to move closer to the transfer belt  19 . 
       {Positioning of Process Cartridge Relative to Electrophotographic Image Forming Apparatus Main Assembly} 
       [0078]    Next, referring to  FIGS. 5-8 ,  23 - 25 , and  30 , the positioning of the cartridge  50  in the apparatus main assembly  100  will be described. Referring to  FIGS. 5 and 30 , the apparatus main assembly  100  is provided with multiple pairs (four pairs in this embodiment) of cartridge positioning portions  101   a  for positioning a cartridge  50  relative to the apparatus main assembly  100 . That is, each cartridge compartment of the cartridge tray  13  is provided with a pair of cartridge positioning portions  101   a , which are located at the lengthwise ends of the corresponding compartment, one for one, in terms of the direction parallel to the lengthwise direction of the cartridge  50 , in a manner to sandwich the transfer belt  19 . Next, referring to  FIGS. 6 and 23 , as the door  12  is moved from the opening position to the shut position, the cartridge tray  13  and cartridges  50  move in the direction indicated by an arrow mark y 2  ( FIG. 23 ), causing the drum unit positioning portion  31   b , with which the drum unit  31   y  is provided, to come into contact with the corresponding cartridge positioning portion  101   a  of the apparatus main assembly  100 . As a result, the cartridge  50   y  is positioned relative to the apparatus main assembly  100 . 
         [0079]    At this time, a releasing member  75 , which is moved by the movement of the door  12 , will be described. Referring to  FIGS. 23-25 , as the door  12  is moved from the open position to the shut position, the tray supporting member  14  is moved by the direction indicated by the arrow mark y 2  ( FIG. 23 ). This movement of the tray supporting members  14  causes the projection  31   b , with which the drum unit frame  34  is provided, to be properly positioned by the positioning portion  101   a  of the apparatus main assembly  101 , as shown in  FIG. 6 . 
         [0080]    Referring to  FIGS. 5 and 6 , as the tray supporting member  14  and cartridges are moved in the direction indicated by the arrow mark y 2 , a releasing member pushing member  102 , which is firmly attach to the apparatus main assembly  100 , pushes up the releasing member  75 , with which the cartridge  50  is provided. The releasing mechanism of the releasing member  75  will be described later in detail. 
       {Development Roller Separating Mechanism of Electrophotographic Image Forming Apparatus Main Assembly} 
       [0081]    Next, referring to  FIGS. 5-8 ,  10 ,  13 , and  14 , the mechanism for moving the force receiving member  70 , with which the cartridge  50   y  is provided, will be described.  FIGS. 5-8  are schematic sectional views of the cartridge  50   y  in the apparatus main assembly  100 , at a plane perpendicular to the axial line of the photosensitive drum  30 , and  FIG. 10(   a ) is a detailed perspective view of the cartridge  50   y , as seen from the side from which the cartridge  50   y  is driven.  FIGS. 13 and 14  are detailed perspective views of a part of the development unit  41 . 
         [0082]    As described above, as the door  12  is moved from the open position to the shut position, the drum frame projection  31   a  of the cartridge  50   y  is moved in the direction indicated by the arrow mark y 2  ( FIG. 6 ), being thereby positioned by the positioning portion  101   a  of the apparatus main frame  100 . During this movement of the drum frame projection  31   a , the bottom end portion  75   d  (portion of contact) of the releasing member  75  comes into contact with the releasing member pushing member  102 . Thus, the releasing member  75  is pushed in the opposite direction from the direction indicated by the arrow mark y 2 , being therefore pushed up. That is, as the door  12  is closed, the releasing member  75  receives external force (second external force) from the releasing member pushing member  102 . Next, referring to  FIGS. 5 and 13 , initially, the releasing member  75  is in contact with the force receiving member  70 . However, as the releasing member  75  is pushed up, it becomes separated from the force receiving member  70 . As a result, the force receiving member  70  rotates about the rotational axle  70   g  ( FIG. 13 ), with which the force receiving member  70  is provided, in a manner to rotate from its standby position, shown in  FIG. 5 , outward of the development unit  41 , that is, the direction to move away from the rotational axis  46   b  of the development unit  41 , as shown in  FIGS. 6 and 14 . 
         [0083]    Next, the operation of the force applying first member  60  will be described. 
         [0084]    Referring to  FIGS. 1 and 3 , in terms of the vertical direction of the apparatus main assembly  100 , the force applying first member  60  is positioned so that after the proper positioning of the each cartridge  50  in the apparatus main assembly  100 , the force applying first member  60  is above the cartridge  50 . In terms of the direction parallel to the axial line of the photosensitive drum  30 , the force applying first member  60  is positioned so that it is enabled to come into contact with the force receiving portion  70   a  of the force receiving member  70  which is at the corresponding lengthwise ends of the cartridge  50 . 
         [0085]    Referring to  FIGS. 27 and 28 , driving force is transmitted from a motor  110  (mechanical power source) with which the apparatus main assembly  100  is provided, to a gear  112  through a gear  111 . As the driving force is transmitted to the gear  112 , the gear  112  rotates in the direction indicated by an arrow mark L, rotating thereby the cam portion  112   a , which is an integral part of the gear  112 , in the direction indicated by the arrow mark L. The cam portion  112   a  is in contact with the moving force receiving portion  60   b , with which the force applying first member  60  is provided. Therefore, as the cam portion  112   a  rotates, the first applying first member  60  is moved in the direction indicated by an arrow mark E or B. 
         [0086]      FIG. 27  shows the force applying first member  60  after it has moved in the direction indicated by the arrow mark E. When the force applying first member  60  is in the state shown in  FIG. 27 , the development roller  42  and photosensitive drum  30  are still in contact with each other ( FIG. 7 ).  FIG. 28  shows the force applying first member  60  after it has moved in the direction indicated by the arrow mark B. When the force applying first member  60  is in the state shown in  FIG. 28 , the force receiving member  70  is in contact with the rib  60   y , and therefore, it receives force from the force applying first member  60 . As the force receiving member  70  receives force from the force applying first member  60 , it rotationally moves the development unit  41  about the rotational axis  46   b , causing the development roller  42  to separate from the photosensitive drum  30  ( FIG. 8 ). This position of the development unit  41 , shown in  FIG. 28 , will be referred to as the separation position of the development unit  41 . 
         [0087]    While each cartridge  50  is moved into the apparatus main assembly  100 , the force receiving member  70  of the cartridge  50  remains in the standby position ( FIG. 5 ). Therefore, the force applying first member  60  can be positioned significantly closer to the cartridge path in the apparatus main assembly, without allowing the force applying first member  60  and cartridge  50  to interfere with each other during the mounting of the cartridge  50 , compared to the force applying member of an image forming apparatus in accordance with the prior art, making it possible to minimize the wasted space, and therefore, making it possible to significantly reduce the apparatus main assembly  100  in vertical dimension. 
         [0000]    {Description of Mounting of Process Cartridge into Electrophotographic Image Forming Apparatus Main Assembly, and Force Receiving Member} 
         [0088]    Next, the operational sequence from the beginning of the mounting of the cartridge  50  into the apparatus main assembly  100 , to the separation of the development roller  42  from the photosensitive drum  30 , will be described. 
         [0089]    Referring to  FIG. 4 , it is after the cartridge tray  13  is pulled out of the apparatus main assembly  100  to its outermost position, that each cartridge  50  can be mounted into, or removed from, the cartridge tray  13  in the vertical direction, which is indicated by the arrow mark C. 
         [0090]    After the mounting of the cartridge(s)  50  into the cartridge tray  13 , the cartridge tray  13  is to be moved into the apparatus main assembly  100  in the direction indicated by the arrow D 1 , through the opening  80 . That is, in this embodiment, each cartridge  50  is horizontally moved into the apparatus main assembly  100 , from the direction which is intersectional (roughly perpendicular) to the axial line of the photosensitive drum  30 . 
         [0091]    Referring to  FIG. 3 , the cartridge  50   y  is mounted most downstream in the cartridge tray  13  in terms of the direction in which the cartridge tray  13  is moved (mounted) into the apparatus main assembly  100 . That is, the cartridge  50   y  moves below the ribs  60   k ,  60   c , and  60   m  of the force applying first member  60  from upstream to downstream. 
         [0092]    Also in terms of the direction in which the cartridge tray  13  is into the apparatus main assembly  100 , the cartridge  50   m  is mounted in the second cartridge compartment from the downstream end of the cartridge tray  13 . Thus, when the cartridge tray  13  is mounted into the apparatus main assembly  100 , the cartridge  50   m  is moved below the ribs  60   k  and  60   c  of the force applying first member  60 , which act on the cartridge  50   k  and  50   c , from upstream to downstream. Also in terms of the direction in which the cartridge tray  13  is into the apparatus main assembly  100 , the cartridge  50   c  is mounted in the third cartridge compartment from the downstream end of the cartridge tray  13 . Thus, when the cartridge tray  13  is mounted into the apparatus main assembly  100 , the cartridge  50   c  is moved below the ribs  60   k  of the force applying first member  60 , which acts on the cartridge  50   k , from upstream to downstream. 
         [0093]    Moreover, in terms of the direction in which the cartridge tray  13  is into the apparatus main assembly  100 , the cartridge  50   k  is mounted in the most upstream cartridge compartment from the downstream end of the cartridge tray  13 . Thus, as the cartridge tray  13  is mounted into the apparatus main assembly  100 , the cartridge  50   k  is moved deep enough into the apparatus main assembly  100  for the force receiving member  70  to move under the force applying portion  60   k  of the force applying first member  60 , which acts on the cartridge  50   k , from upstream to downstream. 
         [0094]    If the cartridge  50  were designed so that its force receiving member  70  remains projecting while the cartridge  50  is moved into the apparatus main assembly  100 , the force applying first member  60  would have to be positioned higher than where it is in this embodiment, in order to prevent the force receiving member  70  and force applying first member  60  from interfering with each other. In this embodiment, however, the cartridge  50  is designed so that the force receiving member  70  is kept in its standby position, that is, the position in which it does not project from the cartridge  50 . Therefore, the force applying first member  60  can be positioned closer to the cartridge path, because the distance by which the force receiving member  70  projects does not need to be taken into consideration. In other words, designing the cartridge  50  so that its force receiving member  70  remains in its standby position while the cartridge  50  is mounted into the apparatus main assembly  100  makes it possible to reduce the apparatus main assembly  100  in vertical dimension. 
         [0095]    Thus, in this embodiment, when the cartridge tray  13 , which is holding the cartridges  50 , is moved into the apparatus main assembly  100 , there are a gap f 1  between the force applying first member  60  and force receiving member  70 , and a gap f 2  between the photosensitive drum  30  and transfer belt  19 , as shown in  FIG. 5 , preventing thereby each cartridge  50  and apparatus main assembly  100  from interfering with each other while the cartridge  50  is mounted into the apparatus main assembly  100 . 
         [0096]    Referring to  FIGS. 23-25 , after the cartridge tray  13  is pushed all the way into the apparatus main assembly  100 , the door  12  is to be moved into the shut position. As the door  12  is moved into the shut position, the tray supporting members  14  are moved toward the transfer belt  19  (direction indicated by arrow mark y 2 ). Hereafter, the vertical component of this movement of the tray supporting members  14  in the direction indicated by the arrow mark y 2  will be referred to as a distance f 2 . As the tray supporting members  14  are moved in the direction indicated by the arrow mark y 2 , the cartridges  50  are moved toward the transfer belt  19  by the movement of the tray supporting members  14 , causing thereby the peripheral surface of the photosensitive drum  30  in each cartridge  50  to come into contact with the surface of the transfer belt  19 , as shown in  FIG. 6 . Thus, by the time the peripheral surface of the photosensitive drum  30  comes into contact with the surface of the transfer belt  19 , the gap f 1  between the force receiving apparatus  70  and force applying first member  60  widens to the sum of the gaps f 1  and f 2 . 
         [0097]    Further, referring to  FIG. 6 , as the door  12  is moved into the shut position, the cartridge positioning member  31   b  of each cartridge  50  comes into contact with the corresponding cartridge positioning portion  101   a , with which the apparatus main assembly  100  is provided, properly positioning thereby the cartridge  50  relative to the apparatus main assembly  100 . 
         [0098]    As described above, the restriction upon the movement of the force receiving member  70  by the releasing member  75  is removed by the function of the releasing member pushing member  102 , with which the apparatus main assembly  100  is provided. Thus, as the restriction placed on the force receiving member  70  by the releasing member  75  is removed, the force receiving member  70  rotates from its standby position in the direction to make its force receiving portion  70   a  move out of (project from) the development unit  41  of the cartridge  50   y , that is, in the direction to move away from the rotational axis  46   b  of the development unit  41 , as shown in  FIG. 6 . 
         [0099]    However, as the force receiving member  70  rotates as described above, the top surface of the force receiving member  70  comes into contact with the bottom surface of the rib  60   y  of the force applying first member  60 . As a result, the movement of the force receiving member  70  is regulated by the rib  60   y  (state shown in  FIG. 6 ). This position of the force receiving member  70  will be referred to as the intermediate position. 
         [0100]    In this embodiment, a position of the force applying first member  60 , which corresponds to the above described intermediate position of the force receiving member  70 , is made to be the home position of the force applying first member  60 . This is for the following reason. That is, while the image forming apparatus is not used for image formation after the mounting of the cartridges  50 , each cartridge  50  remains in the state shown in  FIG. 8 , that is, the state in which the force applying first member  60  has moved in the direction indicated by the arrow mark B, and the force receiving member  70  has come into contact with the rib  60   y , being thereby prevented from moving further. It is in this state that the photosensitive drum  30  and development roller  42  remain separated from each other. That is, it is in this state, shown in  FIG. 8 , in which the photosensitive drum  30  and development roller  42  remain separated from each other, that the cartridge  50  is removed from the apparatus main assembly  100 . Thus, when the cartridge  50  is mounted into the apparatus main assembly  100  next time, the force receiving member  70  comes into contact with the rib  60   y , because the force applying first member  60  is in the position shown in  FIG. 8 . Therefore, as the force receiving member  70  is rotated out of its standby position, it comes into contact with the bottom surface of the rib  60   y , as shown in  FIG. 6 . 
         [0101]    Incidentally, the surface of the force receiving member  70 , by which the force receiving member  70  receives external force (first external force) from the force applying first member  60 , faces the direction from which each cartridge  50  is moved into the apparatus main assembly  100 . Making the force receiving surface of the force receiving member  70  face in the above described direction ensure that as the force receiving member  70  receives force from the force applying first member  60 , the development unit  41  is efficiently moved relative to the photosensitive drum  30 , and also, that the photosensitive drum  30  and development roller  42  are kept separated from each other. 
         [0102]    As the force applying first member  60  is moved from the position shown in  FIG. 6  to the position shown in  FIG. 7  in the direction indicated by the arrow mark E, the force receiving portion of the force receiving member  70  is rotated farther outward of the cartridge  50   y , entering thereby the path of the rib  60   y . This position of the force receiving member  70 , that is, the position in which the force receiving portion of the force receiving member  70  has moved all the way into the path of the rib  60   y , will be referred to as the protrusive position (active position). That is, when the force receiving member  70  is in its protrusive position, it projects more from the cartridge  50   y  than it is in its standby position or intermediary position, which is obvious. In order for the force receiving member  70  to come into contact with the fore applying first member  60  when the cartridge  50  is moved into the apparatus main assembly  100 , the distance by which the force receiving member  70  projects when the force receiving member  70  is in the protrusive position needs to be greater than the sum of the gaps f 1  and f 2 . Further, the operation of the force applying first member  60  is started after the mounting of each cartridge  50  into the apparatus main assembly  100 , and immediately before the starting of the next image forming operation. 
         [0103]    Next, the force applying first member  60  is moved in the direction indicated by the arrow mark B as shown in  FIG. 8 . As the force applying first member  60  is moved, the lateral surface  70   e  of the force receiving member  70 , that is, the force applying first member contacting surface of the force receiving member  70  which is in the path of the force applying first member  60 , receives the external force (first external force) from the rib  60   y  of the force applying first member  60 . As a result, the development unit  41  is rotationally moved about the rotational axis  46   b  (shaft), causing the development roller  42  to separate from the photosensitive drum  30  by a distance of α. 
         [0104]    Thus, when an image forming operation is carried out next time, the force applying first member  60  is to be moved in the direction indicated by the arrow mark E to place the development roller  42  in contact with the photosensitive drum  30 . As the force applying first member  60  is moved in the direction indicated by the arrow mark E, the force receiving member  70  becomes separated from the force applying first member  60 , stopping thereby receiving force from the rib  60   y , as shown in  FIG. 7 . Consequently, the development roller  42  is placed in contact with the photosensitive drum  30  by the resiliency of the spring  95  placed between the development unit  41  and drum unit  31 , readying thereby the cartridge  50   y  for image formation. It should be noted here that the rotation of the photosensitive drum  30  is started before the development roller  42  is placed in contact with the photosensitive drum  30 . Further, the development roller  42 , which rotates by receiving driving force from the apparatus main assembly  100  through the coupling portion  67   a , also begins to be rotated before the development roller  42  is placed in contact with the photosensitive drum  30 , for the following reason. That is, with both the rotation of the photosensitive drum  30  and rotation of the development roller  42  started before the placement of the development roller  42  in contact with the photosensitive drum  30 , the difference in the peripheral velocity between the photosensitive drum  30  and development roller  42  is significantly smaller than otherwise. Therefore, the cartridge  50  in this embodiment is significantly smaller in the frictional wear which occurs to the photosensitive drum  30  and development roller  42  when they are placed in contact with each other than a process cartridge structured otherwise. It should be noted here that this arrangement regarding the timing of the starting of the rotation of the photosensitive drum  30  and development roller  42  is possible because the cartridge  50  is structured so that the axial line of the cylindrical portion  46   b  coincides with that of the coupling portion  67   a , in order to ensure that even when the development unit  41  is rotationally moved about the cylindrical portion  46   b , the coupling portion  67   a  does not change in position. After the completion of image formation, the development roller  42  is separated from the photosensitive drum  30  by moving the force applying first member  60  in the direction indicated by the arrow mark B as described above. It is after the separation of the development roller  42  from the photosensitive drum  30  that the rotation of the development roller  42  and photosensitive drum  30  is stopped. Therefore, the cartridge  50  in this embodiment is significantly smaller in the difference in peripheral velocity between the photosensitive drum  30  and development roller  42 , being therefore significantly smaller in the amount of the frictional wear which occurs, when the development roller  42  is separated from the photosensitive drum  30 , than a process cartridge structured otherwise. Consequently, the electrophotographic image forming apparatus in this embodiment is significantly superior in image quality to a comparable image forming apparatus in accordance with the prior art. 
       {Relationship Between Force Receiving Member and Releasing Member} 
       [0105]    Next, referring to  FIGS. 5-6 ,  13 - 15 ( b ), the relationship between the force receiving member  70  and releasing member  75  will be described.  FIGS. 15(   a ) and  15 ( b ) are detailed schematic drawings of the force receiving member and releasing member  75 , showing the mechanical structure for releasing the force receiving member  70 . 
         [0106]    Referring to  FIG. 2 , the cartridge  50   y  is provided with the force receiving member  70 , which is for placing the development roller  42  and photosensitive drum  30  in contact with each other, or separating them from each other, in the apparatus main assembly  100 . Next, referring to  FIGS. 13 and 15(   a ), the force receiving member  70  is provided with a hook portion  70   a , to which the tension spring  21  is attached as a tension generating member, by one of its lengthwise ends. The other end of the tension spring  21  is attached to the hook portion  48   a  of the development unit frame  48 . Thus, the force receiving member  70  remains under the tension of the tension spring  21 , which works in the direction to pull the force receiving member  70  from the standby position to the protrusive position. Referring also to  FIGS. 13 and 15(   a ), the force receiving member  70  is provided with the force receiving portion  70   e  ( FIGS. 7 and 8)  and the contact portion  70   b . The force receiving portion  70   e  is the portion of the force receiving member  70 , by which the force receiving member  70  receives external force from the force applying first member  60 . The contact portion  70   b  is the portion of the force receiving member  70 , with which the releasing member  75  comes into contact. While the contact portion  70   b  is in contact with the contact portion  75   b  with which the releasing member  75  is provided, the force receiving member  70  is prevented from rotationally moving from the standby position to the protrusive position. 
         [0107]    Referring also to  FIGS. 13 and 15(   a ), the releasing member  75  is provided with a hook portion  75   c , to which the second tension spring  22  is attached by one of its lengthwise ends. The other end of the second tension spring  22  is connected to the hook portion  48   c , with which the development unit frame  48  is provided. Thus, the releasing member  75  is kept pulled in the direction indicated by an arrow mark y 3  ( FIG. 3) . Further, the development unit frame  48  is provided with a releasing member regulating portion  48   b , which is for regulating the movement of the releasing member  75  which remains pulled in the abovementioned direction indicated by the arrow mark y 3 . 
         [0108]    Next, the movement of the force receiving member  70  from its standby position to its protrusive position will be described. 
         [0109]    Referring to  FIGS. 5 ,  6 , and  13 - 15 ( b ), when the cartridge  50  is properly positioned relative to the apparatus main assembly  100  by the cartridge positioning portion  101   a  of the apparatus main assembly  100 , the releasing member pushing member  102 , which is solidly attached to the image forming apparatus main frame, comes into contact with the contact portion  75   d  of the releasing member  75 , and presses on the contact portion  75   d . Thus, the releasing member  75  moves in the direction indicated by an arrow mark y 4  ( FIG. 14 ), causing its contact portion  75   b  to separate from the contact portion  70   b  of the force receiving member  70 . As a result, the force receiving member  70  is rotationally moved from its standby position to its protrusive position by the resiliency (tension) of the tension spring  21 . 
         [0110]    In the following mathematical expressions, f 3 , f 4 , f 4 , and g stand for the amount of the resiliency of the tension spring  21 , amount of the resiliency of the tension spring  22 , amount of the force by which the cartridge  50  is pushed (positioned) upon the cartridge positioning portion  101   a  of the main assembly frame, and self weight of the cartridge  50 , respectively. In this embodiment, in order to prevent the releasing member  75  from releasing the force receiving member  70 , the relationship among the abovementioned forces is set as follows: F 3  is made to be greater than f 4  (f 3 &gt;f 4 ). The amount of the upward force, which the cartridge  50  receives as the releasing member  75  is pressed by the releasing member pushing member  102  solidly fixed to the main assembly frame, is f 4 , whereas the downward force which the cartridge  50  receives as the releasing member  75  is pressed by the releasing member pushing member  102 , equals the sum of f 3 , f 5 , and g, that is, (f 3 +f 5 +g). Thus, the force receiving member  70 , releasing member  75 , springs  21 , and spring  22  are designed to satisfy the following inequality: f 4 &lt;f 3 +f 5 +g. Therefore, it does not occur that the releasing member  75  releases the force receiving member  70  when the cartridge  50  is not in the apparatus main assembly  100 , and also, that the cartridge  50  floats from the cartridge positioning portion  101   a  of the apparatus main assembly  100  after it is properly positioned in the apparatus main assembly  100 . 
         [0111]    In this embodiment, the releasing member  75  is provided with the contact portion  75   b  as a part of mechanism for releasing the contact portion  70   b  of the force receiving member  70 . However, instead of providing the releasing member  75  with the contact portion  75   b , the drum unit  31  or development unit  41  may be provided with a member, such as a contact portion  775   b  shown in  FIGS. 17 and 18 . In the case of the force receiving member releasing mechanism shown in  FIGS. 17 and 18 , the drum unit frame  34  which is one of the structural components of the drum unit  31 , or development unit frame  48  which is one of the structural components of the development unit  41 , is provided with the contacting portion  775   b . In this case, as the cartridge  50  is mounted into the apparatus main assembly  100 , the contact portion  775   b  is pushed by the releasing member pushing member  102  solidly fixed to the apparatus main assembly  100 , in the direction indicated by an arrow mark in  FIG. 18 . More specifically, the contact portion  775   d  receives external force (second external force) from the releasing member pushing member  102 . Therefore, the contact portion  775   b  moves in the direction indicated by an arrow mark H ( FIG. 18 ), disengaging thereby from the contact portion  70   b  of the force receiving member  70 . That is, the releasing member  775  is provided with an elastic connective portion  775   e , by which the releasing member  775  is attached to the drum unit frame  34  or development unit frame  48 . Therefore, as the force receiving portion  775   d  of the releasing member  75  is pushed by the releasing member pushing member  102 , the connective portion  75   e  is deformed by the force received by the force receiving portion  775   d . As a result, the contact portion  775   b  is moved away from the contact portion  70   b  of the force receiving member  70 , allowing thereby the contact portion  70   b  to rotationally move as described above. In this case, the drum unit frame  34  or development unit frame  48  is provided with the releasing portion  775 . However, the structural component other than the drum unit frame  34  or development unit frame  48  may be provided with the releasing portion  775 . Further, in this embodiment, the releasing member pushing member  102  of the apparatus main assembly  100  is positioned below the corresponding cartridge compartment. However, the releasing member pushing member  102  may be positioned anywhere, as long as the location enables the releasing member pushing member  102  to push the releasing member  75  when the cartridge  50  is in the apparatus main assembly  100 . Further, the releasing member pushing member  102  may be in any shape, as long as the shape enables the releasing member pushing member  60  to move the releasing member  70  by coming into contact with the releasing member  70 . For example, it may be U-shaped in cross section, instead of being in the form of a projection as it is in this embodiment. 
         [0112]    Further, the tension spring  21  may be eliminated by extending the hook portion  70   a  of the force receiving member  70  so that the hook portion  70   a  itself can elastically deform and can be directly engaged with the hook portion  48   a  of the development unit frame  48 , as shown in  FIGS. 16  ( 16 ( a ) and  16 ( b )). 
         [0113]    Further, referring to  FIGS. 19 and 20 , the releasing member  75  may be replaced with a releasing member, such as a releasing member  875  which can be moved by the utilizing the driving force, which the coupling member  67  of the development unit  41  receives from the apparatus main assembly  100 . More specifically, the cartridge  50  is provided with a gear  123  having a projection  123   a  (pin) for pushing the releasing member pushing member  875  in the direction indicated by an arrow mark y 4 . Further, the releasing member  875  is provided with a contact portion  875   e  with which the abovementioned projection  123   a  (pin) comes into contact. Thus, as the gear  123  is rotated in the direction indicated by an arrow mark G by the abovementioned driving force, the projection  123   a  pushes up the contact portion  875   a  of the releasing member  875 . As a result, the contact portion  875   b  of the releasing member  875  is disengaged from the contact portion  70   b  of the force receiving member  70 , allowing thereby the force receiving member  70  to rotationally move into its protrusive position. As the projection  123   a  of the gear  123  is disengaged from the contact portion  875   a  of the releasing member  875 , the releasing member  875  is pushed down (in the direction indicated by arrow mark y 5 ) by the resiliency of the tension spring  22 . Thereafter, as long as the driving force is transmitted to the cartridge  50 , the gear  123  continues to rotates, but the projection  123   a  of the bear  123 , and the contact portion  875   e  of the releasing member  875  do not come into contact with each other. 
         [0000]    {Removal of Process Cartridge from Main Assembly of Electrophotographic Image Forming Apparatus} 
         [0114]    Next, the operation for removing the cartridge  50  from the apparatus main assembly  100  will be described. 
         [0115]    Referring to  FIG. 24 , as the door  12  is rotationally moved from the shut position to the open position, the tray supporting members  14  are moved upward, that is, in the direction (indicated by arrow mark y 1 ) to be moved away from the transfer belt  19  as shown in  FIG. 24 . As a result, each cartridge  50  is moved upward with the cartridge tray  13 , causing the photosensitive drum therein to separate from the transfer belt  19 . 
         [0116]    Further, as the cartridge tray  13  is moved in the direction to be pulled out (direction indicated by arrow mark z 1  in  FIG. 24 ), the cartridge  50  changes in state from the one shown in  FIG. 8  to the one shown in  FIG. 7 . That is, the force receiving member  70  stops being kept pressed by the force applying first member  60 . When the cartridge  50  is in this state, that is, the state shown in  FIG. 7 , the force receiving member  70  is kept in the protrusive position by the resiliency of the tension spring  21 , as shown in  FIGS. 7 and 14 . Referring to  FIGS. 21 and 22 , the force receiving member  70  is provided with a contact portion  70   c  having a slant surface, which is on the opposite side from the lateral surface  70   e  ( FIG. 8 ) by which the force receiving member  70  receives force from the force applying first member  60 . 
         [0117]    As the tray supporting members  14  are pulled in the direction indicated by the arrow mark z 1  ( FIG. 24 ), the contact portion  70   c  comes into contact with the force receiving member returning portion  60   zm  of the force applying first member  60 , which also has a slanted surface. Thus, as the tray supporting members  14  are pulled further, the force receiving member  70 , which is in the protrusive position, is pushed down by the force receiving member returning portion  60   mz  in the direction indicated by an arrow mark K ( FIG. 22 ), allowing thereby the force receiving member  70  to move under the rib  60   m , allowing thereby the cartridge  50  to be moved outward of the apparatus main assembly  100 . Then, the cartridge  50  is moved under the ribs  60   c  and  60   k , and is moved out of the apparatus main assembly  100  through the opening  80 . 
         [0118]    When the cartridge  50  is mounted again into the image forming apparatus main assembly  100  after being removed therefrom, the force receiving member  70 , which is in the protrusive position, can be moved back into the standby position by pressing down the force receiving member  70 . This operation of pressing the force receiving member  70  back into its standby position can be easily carried out by a user, because both the releasing member  75 , and the second tension spring  22  connected to the releasing member  75 , are elastic. 
         [0119]    In the case of the releasing member  875  which must be moved by the abovementioned driving force, the gear  123  must be rotated back into a preset position before the releasing member  875  can be moved back into the standby position. The releasing member  875  can be rotated back to the preset position by manually turning a gear connected to the gear  123 , or with the use of a tool (driver or the like). 
         [0120]    As described above, the electrophotographic image forming apparatus in this embodiment is structured so that as the door  12  is moved into its shut position after the mounting of the cartridge(s)  50  into the apparatus main assembly, the force receiving member  70 , which is for moving the development unit  41 , is rotated in the direction to make its contact portion  70   c  to project outward from the development unit  41 . 
         [0121]    Therefore, the cartridge  50  in this embodiment is significantly smaller than a cartridge in accordance with the prior art (which hereafter may be referred to simply as conventional cartridge). Further, while the cartridge  50  is mounted into the apparatus main assembly  100 , the force receiving member  70  remains in its standby position. Therefore, the apparatus main assembly  100  in this embodiment can be made significantly smaller in the vertical dimension of the cartridge path than the apparatus main assembly of a conventional electrophotographic image forming apparatus. Therefore, the opening  80  can be made significantly smaller than the corresponding opening of a conventional electrophotographic image forming apparatus. Further, the force applying first member  60  can be positioned significantly closer to the cartridge path than the counterpart of a conventional electrophotographic image forming apparatus. Therefore, the apparatus main assembly  100  can be significantly reduced in its vertical dimension compared to the apparatus main assembly of a conventional electrophotographic image forming apparatus. 
         [0122]    Further, before the cartridge  50  is mounted into the apparatus main assembly  100 , the force receiving member  70  is in its standby position. Therefore, it is unlikely to be occur that the force receiving portion  70  is damaged while the cartridge  50  is handles by a user or transported alone. 
       Embodiment 2 
       [0123]    In the first embodiment, the releasing member  75  is disengaged by the projection  102  (releasing member pushing member) solidly attached to the main assembly frame. In this embodiment, however, the cartridge is structured so that the releasing member moves by receiving force from the movable force applying second member, with which the apparatus main assembly is provided. 
         [0124]    This embodiment also will be described with reference to a cartridge, more specifically, a cartridge  950   y , which stores the yellow developer. Incidentally, the description of this embodiment will be centered around the structural features of the electrophotographic image forming apparatus in this embodiment, which are different from those in the first embodiment. 
       {Cartridge Tray of Main Assembly of Electrophotographic Image Forming Apparatus} 
       [0125]    Next, referring to  FIGS. 37-39 , the operation of the cartridge tray  13  in this embodiment will be described. 
         [0126]    In order to make it easier to understand the operation of the cartridge tray  13 , the cartridges  50  are not shown in  FIGS. 37-39 . 
         [0127]    The cartridge tray  13  is supported by a pair of tray supporting members  14  in such a manner that the cartridge tray  13  can be pulled out of the apparatus main assembly  100  while remaining supported by the tray supporting members  14 . The tray supporting members  14  are moved by the movement of the door  12  which can be opened or closed by an operator (user). The door  12  is attached to the apparatus main assembly  900  so that it can be rotationally moved about its rotational axis  12   a  (shaft by which door  12  is held to apparatus main assembly  100 ). The door  12  is rotationally movable between a position (shut position) in which it completely covers an opening  80 , as shown in  FIG. 27 , and a position (open position) in which it fully exposes the opening  80 , as shown in  FIG. 28 . 
         [0128]    When it is necessary to take out any cartridge or cartridges in the apparatus main assembly  900 , the door  12  is to be rotationally moved from the shut position to the open position. As the door  12  is rotationally moved, a pair of projections  15  (connective pins) with which the door  12  is provided moves in the clockwise direction about the rotational axis  12   a , while moving in a pair of elongated holes  14   c , with which the tray supporting members  14  are provided, one for one, from the bottom end  14   c   2  of the elongated hole  14   c  to the top end  14   c   1  of the elongated hole  14   c , as shown in  FIG. 38 . As a result, the tray supporting members  14  are moved by the projections  15  in the direction indicated by an arrow mark z 1 . As the tray supporting members  14  are moved in the abovementioned direction, the projections  14   d   1  and  14   d   2 , which project from each of the tray supporting members  14  are guided by the guiding holes  107  with which the apparatus main assembly  900  is provided. Referring to  FIG. 26 , each guiding hole  107  has three sections, that is, two horizontal sections  107   a   1  and  107   a   3 , and one diagonal section  107   a   2 . The diagonal section  107   a   2  extends diagonally upward from the horizontal section  107   a   1  to the horizontal section  17   a   3 . Therefore, as the door  12  is moved to the open position, as shown in  FIG. 38 , the projections  14   d   1  and  14   d   2  are guided by the guiding hole  107 , sequentially through the horizontal section  107   a   1 , diagonal section  107   a   2 , and horizontal section  107   a   3 . Thus, the tray supporting members  14  are first moved in the direction indicated by the arrow mark z 1 , and then, are moved in the direction indicated by an arrow mark y 1 , that is, the direction to move away from the transfer belt  19 . With the tray supporting members  14  moved all the way in the direction indicated by the arrow mark y 1 , the cartridge tray  13  can be pulled out of the apparatus main assembly  900  through the opening  80  in the direction indicated by an arrow mark D 2 , as shown in  FIG. 39 .  FIG. 42  is a partially cutaway perspective view of the image forming apparatus after the cartridge tray  13  has been pulled out of the apparatus main assembly  900  to its outermost position. 
         [0129]    Next, the case in which any cartridge or cartridges are mounted into the apparatus main assembly  900  will be described. Referring to  FIG. 39 , the cartridge tray  13  is to be pushed into the apparatus main assembly  900  in the direction of the arrow mark D 2  through the opening  80 , with the door  12  kept in the open position. Thereafter, the door  12  is to be moved into the shut position as shown in  FIG. 37 . As the door  12  is moved, each of the projections  15  of the door  12  moves in the counterclockwise direction about the rotational axis  12   a , while moving in the corresponding elongated hole  14   c  of the tray supporting member  14 , to the bottom end  14   c   2  of the elongated hole  14   c , as shown in  FIG. 37 . Thus, the tray supporting member  14  is moved in the direction of an arrow mark z 2  by the pair of projections  15 . Thus, as the door  12  is moved into the shut position as shown in  FIG. 37 , the projections  14   d   1  and  14   d   2  are guided by the guiding hole  107 , that is, the horizontal section  107   a   3 , diagonal section  107   a   2 , and horizontal section  107   a   1 , in the listed order. Therefore, the tray supporting members  14  move, first, in the direction of the arrow mark z 2 , and then, in the direction of the arrow mark y 2 , that is, the direction to move closer to the transfer belt  19 . 
       {Positioning of Process Cartridge Relative to Main Assembly of Electrophotographic Image Forming Apparatus} 
       [0130]    Next, referring to  FIGS. 31 ,  35 ,  36 ,  41 , and  42 , the positioning of the cartridge  950  ( 950   y ,  950   m ,  950   c , and  950   k ) in the apparatus main assembly  900  will be described. Referring to  FIG. 42 , the apparatus main assembly  900  is provided with multiple pairs (four pairs in this embodiment) of cartridge positioning portions  901   a  for positioning a cartridge  950  relative to the apparatus main assembly  900 . That is, each cartridge compartment of the cartridge tray  13  is provided with a pair of cartridge positioning portions  901   a , which are located at the lengthwise ends of the corresponding compartment, one for one, in terms of the direction parallel to the lengthwise direction of the cartridge  950 , in a manner to sandwich the transfer belt  19 . Referring to  FIGS. 41(   a ) and  41 ( b ), the main assembly  900  is also provided with force applying second members  61 , which are located above the tray supporting members  14 . Each force applying second member  61  is provided with a hole  61   d , through which a force applying second member supporting shaft  55 , with which the apparatus main assembly  900  is provided, is put to rotatably support the force applying second member  61 . 
         [0131]    At this time, the mechanism for moving the force applying second member  61  by using the movement of the door  12  will be described. The force applying second member  61  is connected to a connective member  62 , which is for moving the force applying second member  61  by utilizing the movement of the door  12 . The connective member  62  is provided with a hole, in which the supporting shaft  55  is fitted, and a supporting pin  62   b , which fits in an elongated hole  14   b  ( FIG. 41(   b )) of the tray supporting member  14 . Referring to  FIG. 41 , as the door  12  is moved from the open position to the shut position, the tray supporting member  14  moves in the direction indicated by the arrow mark y 2  ( FIG. 41) , whereby the supporting pin  62   b  in the elongated hole  14   b  is forced to move also in the direction indicated by the arrow mark y 2 . As a result, the connective member  62  is rotationally moved about the supporting pin  62   b  in the elongated hole  14   b  in the direction indicated by an arrow mark Z ( FIG. 41 ). 
         [0132]    This movement of the connective member  62  which is in connection to the force applying second member  61  causes the pressing portion  62   e , with which the connective member  62  is provided, to press on the force receiving surface  31   a , which is a part of the top surface of the drum unit frame  34 . Therefore, the cartridge  950   y  moves in the direction (downward) indicated by the arrow mark y 2  in  FIG. 41(   b ), causing the cartridge positioning portion  931   b  ( FIG. 7) , with which the drum unit  931   y  is provided, to come into contact with the cartridge positioning portion  901   a  with which the apparatus main assembly  900  is provided. As a result, the cartridge  950   y  is properly positioned relative to the apparatus main assembly  900  ( FIG. 6 ). 
         [0133]    The other cartridges  950   m ,  950   c , and  950   k  also are properly positioned relative to the apparatus main assembly  900  in the same manner as the cartridge  950   y  is positioned as described above. 
         [0134]    Referring to  FIGS. 35 and 36 , the cartridge  950   y  is provided with a spring  66 , which is between the force applying second member  61  and connective member  62 . The spring  66  is supported by the supporting shaft  55 , and is in contact with the pressing portion  62   e  of the connective member  62 , and the projection  61   e  of the force applying second member  62 . Incidentally, the apparatus main assembly  900  may be structured so that this spring  66  directly presses on the force receiving surface of the drum unit frame. 
       {Operation of Force Applying Member} 
       [0135]    Next, referring to  FIGS. 43 and 44 , the operation of the force applying first member  60  will be described. 
         [0136]    Driving force is transmitted from a motor  110 , which is a mechanical driving force source with which the apparatus main assembly  900  is provided, to the gear  112  through a gear  111 , as it is in the first embodiment. As the driving force is transmitted to the gear  112 , the gear  112  rotates in the direction indicated by an arrow mark L, rotating thereby the cam portion  112   a , which is integral with the gear  112 , also in the direction indicated by the arrow mark L direction. The cam portion  112   a  is in contact with the moving force receiving portion  60   b , with which the force applying first member  60  is provided. Therefore, as the cam portion  112   a  rotates, the force applying first member  60  is moved in the direction indicated by an arrow mark E or B. 
         [0137]      FIG. 43  shows the case in which the force applying first member  60  has been moved furthest in the direction indicated by the arrow mark E. In this case, the development roller  42  and photosensitive drum  30  is still in contact with each other ( FIG. 33 ).  FIG. 44  shows the case in which the force applying first member  60  has been moved furthest in the direction indicated by the arrow mark B. In this case, the force receiving member  70  is under the pressure from the rib  60   y . As the force receiving member  70  is pressed by the rib  60   y , it causes the development unit  941  to rotationally move about the rotational axis  946   b  (axle), causing thereby the development roller  42  to separate from the photosensitive drum  30  ( FIG. 34 ). This position of the development unit  41  will be referred to as “separative position”. 
         [0138]    While the cartridge  950  is moved into the apparatus main assembly  900 , the force receiving member  970  remains in its standby position ( FIG. 31 ). Therefore, the force applying first member  60  and force applying second member  61  can be positioned significantly closer to the cartridge path, without allowing them to interfere with the cartridge  50  during the mounting of the cartridge  50 , compared to the counterparts of a conventional image forming apparatus, making it possible to minimize wasted space, making it thereby possible to significantly reduce the apparatus main assembly  900  in vertical dimension. 
         [0000]    {Description of Mounting of Process Cartridge into Main Assembly of Electrophotographic Image Forming Apparatus, and Operation of Force Receiving Apparatus} 
         [0139]    Next, the operational sequence from the beginning of the mounting of the cartridge(s)  950  into the apparatus main assembly  900 , to the separation of the development roller  42  from the photosensitive drum  30 , will be described. 
         [0140]    Referring to  FIG. 40 , it is after the cartridge tray  13  is pulled out of the apparatus main assembly  900  to its outermost position that each cartridge  950  can be mounted into, or removed from, the cartridge tray  13  in the vertical direction indicated by the arrow mark C. 
         [0141]    After the mounting of the cartridge(s)  950  into the cartridge tray  13 , the cartridge tray  13  is to be moved into the apparatus main assembly  900  in the direction indicated by the arrow D 1 , through the opening  80 . That is, in this embodiment, each cartridge  950  is horizontally moved into the apparatus main assembly  900 , from the direction which is intersectional (roughly perpendicular) to the axial line of the photosensitive drum  30 . 
         [0142]    Referring to  FIG. 40 , the cartridge  950   y  is mounted most downstream in the cartridge tray  13  in terms of the direction in which the cartridge tray  13  is moved into the apparatus main assembly  900 . That is, as the cartridge tray  13  is pushed into the apparatus main assembly  900 , the cartridge  950   y  moves below the force applying second members  61   k ,  61   c , and  61   m  ( FIG. 39 ) which are to act on the other cartridges, that is, cartridge  950   m ,  960   c , and  950   k , respectively, and also, below the ribs  60   k ,  60   c , and  60   m  of the force applying first member  60 , from upstream to downstream. 
         [0143]    Also in terms of the direction in which the cartridge tray  13  is moved into the apparatus main assembly  900 , the cartridge  950   m  is mounted second from the downstream end of the cartridge tray  13 . Thus, as the cartridge tray  13  is pushed into the apparatus main assembly  900 , the cartridge  950   m  moves below the force applying second members  61   k , and  61   c  ( FIG. 39 ) which are to act on the other cartridges, that is, cartridge  950   c  and  950   k , respectively, and also, below the ribs  60   k  and  60   c  of the force applying first member  60  from upstream to downstream. 
         [0144]    Also in terms of the direction in which the cartridge tray  13  is moved into the apparatus main assembly  900 , the cartridge  950   c  moves below the force applying second members  61   k  ( FIG. 39 ) which is to acts on the  950   k , and also, below the rib  60   k  of the force applying first member  60  from upstream to downstream. 
         [0145]    Moreover, in terms of the direction in which the cartridge tray  13  is into the apparatus main assembly  900 , the cartridge  950   k  is mounted most upstream. Thus, as the cartridge tray  13  is mounted into the apparatus main assembly  900 , the cartridge  950   k  is moved far enough into the apparatus main assembly  900  for the force receiving member  970  to move below the force applying first member  61   k , which is to acts on the cartridge  950   k , from upstream to downstream. 
         [0146]    Regarding this upstream to downstream movement of the force receiving member  970  below the force applying second member  61 , the other cartridges, that is, the cartridges  950   y ,  950   m , and  950   c , are the same as the cartridge  950   k.    
         [0147]    That is, if the cartridge  950  were designed so that its force receiving member  970  remains projecting while the cartridge  950  is moved into the apparatus main assembly  900 , the force applying second member  61  and force applying first member  60  would have to be positioned higher than where they are in this embodiment, in order to prevent the force receiving member  970  from interfering with the force applying second member  61  and force applying first member  60 . In this embodiment, however, the cartridge  950  is designed so that the force receiving member  970  is kept in its standby position, that is, the position in which it does not project, the force applying second member  61  and force applying first member  60  can be positioned closer to the cartridge path, because the distance by which the force receiving member  970  projects does not need to be taken into consideration. In other words, designing the cartridge  950  so that its force receiving member  970  remains in its standby position while the cartridge  950  is mounted into the apparatus main assembly  900  makes it possible to reduce the apparatus main assembly  900  in its vertical dimension. Further, referring to  FIGS. 31 and 32 , in this embodiment, the force receiving member  970 , force applying second member  61 , and force applying first member  60  overlap in terms of the direction parallel to the axial line of the photosensitive drum  30 , significantly reducing the cartridge  950  in dimension in terms of the direction perpendicular to its lengthwise direction. 
         [0148]    Further, referring to  FIGS. 31 ,  32 ,  35 , and  36 , the pressing portion  61   e  of the force applying second member  61  comes into contact with the contact portion  975   b  ( FIGS. 32 and 36 ), and presses the contact portion  975   b , when the contact portion  975   b  is in the first position ( FIGS. 31 and 35 ). That is, it is when the contact portion  975   b  is in the first position that the contact portion  975   b  receives external force (second external force). As the pressing portion  61   e  presses on the contact portion  975   b , the releasing member  975  is disengaged from the force receiving member  970 , and the releasing member  975  moves to the second position ( FIGS. 32 and 36 ). The force applying second member  61  in this embodiment is equivalent to the releasing member pushing member  102  in the first embodiment. 
         [0149]    As the releasing member  975  is disengaged from the force receiving member  970 , the force receiving member  970  rotates about the force receiving member supporting shaft, moving out of its standby position, that is, in such a manner that the contact portion  70   b  of the force receiving member  70  projects from the development unit  941 , that is, in the direction to cause the contact portion  70   b  to move away from the rotational axis  946   b  of the development unit  41  (active position). The image forming operation which occurs thereafter is the same as that in the first embodiment, and therefore, will not be described here. 
         [0150]    Next, the operation for removing the cartridges  950  from the apparatus main assembly  900  will be described. 
         [0151]    As the door  12  is moved from the shut position to the open position, the force applying second member  61  rotates from the position shown in  FIGS. 32 and 36  to the position shown in  FIGS. 31 and 35 . With this movement of the force applying second member  61 , the pressure having been kept on the releasing member  975  by the force applying second member  61  is removed. However, the force receiving member  970  is kept in the protrusive position by the resiliency of the spring  921 , as shown in  FIG. 33 . Referring to  FIG. 36 , the force receiving member  970  is provided with a contact portion  970   c  having a slant surface which is located opposite from the lateral surface by which the force receiving member  970  receives force from the force applying first member  60 . Thus, as the cartridge tray  13  is pulled out in the direction indicated by the arrow mark D 2  in  FIG. 39 , the force receiving member  970 , which is in the protrusive position as is the force receiving member  70  in the first embodiment, comes into contact with the force receiving member returning member  60   zm ,  60   zcy , and  60   zk , with which the force applying first member  60 , and is pushed down, being allowed to pass by the ribs  60   m ,  60   c , and  60   k , enabling thereby the cartridge  950   y  to be moved out of the apparatus main assembly  900  through the opening  80 . 
         [0152]    As described above, the cartridge  950  is structured so that it is when the door  12  is moved to the shut position after the cartridges  950  are mounted into the apparatus main assembly  900 , that the contact portion  970   b  of the force receiving member  970  for moving the development unit  941  projects outward from the development unit  941 . Therefore, the cartridge  950  is significantly smaller in vertical dimension than a conventional cartridge. Further, when the cartridge  950  is mounted into the apparatus main assembly  900 , the force receiving member  970  remains in the standby position. Therefore, the cartridge path in the apparatus main assembly  900  can be less in vertical dimension than the cartridge path of the main assembly of a conventional electrophotographic image forming apparatus, and so is the opening  80  than the opening of the apparatus main assembly of a conventional electrophotographic image forming apparatus. Further, the force applying first member  60  can be positioned closer to the cartridge path, making it possible to reduce the apparatus main assembly  900  in vertical dimension. 
         [0153]    Further, when the cartridge  950  is outside the apparatus main assembly  900 , the force receiving member  970  remains in the standby position. Therefore, the force receiving member  970  is unlikely to be damaged while the cartridge  950  is handled by a user, or is transported alone. 
         [0154]    According to the present invention, it is possible to reduce in size a process cartridge, the electrophotographic photosensitive drum and development roller of which can be placed in contact with each other, or separated from each other, and also, to reduce in size an electrophotographic image forming apparatus which employs the above described process cartridge. Further, it is possible to structure the above described process cartridge so that when the cartridge is transported alone, its force receiving member for separating the development roller from the electrophotographic photosensitive drum is unlikely to be damaged. 
         [0155]    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. 
         [0156]    This application claims priority from Japanese Patent Applications Nos. 172743/2007 and 162312/2008 filed Jun. 29, 2007 and Jun. 20, 2008, respectively, which are hereby incorporated by reference.