Abstract:
An electrophotographic photosensitive drum includes a cylinder having a photosensitive layer formed thereon, with the cylinder being rotatable about an axis thereof. A drum flange is provided at a longitudinal end of the cylinder, with the drum flange including (i) a gear encircling a peripheral portion of the drum flange, (ii) a hollow portion, provided inside of the drum flange having an opening disposed on a side of the drum flange opposite from the cylinder, and (iii) a rim provided between the gear and the cylinder in a longitudinal direction of the cylinder and projected more radially-outward of the drum flange than a peripheral portion of the cylinder.

Description:
[0001]    This application is a divisional of U.S. patent application Ser. No. 13/369,778, filed Feb. 9, 2012, which is a divisional of U.S. patent application Ser. No. 12/241,185, filed Sep. 30, 2008, now U.S. Pat. No. 8,135,304. 
     
    
     FIELD OF THE INVENTION AND RELATED ART 
       [0002]    The present invention relates to a process cartridge, and an electrophotographic image forming apparatus in which a process cartridge is removably mountable. 
         [0003]    In the case of the present invention, a process cartridge is a cartridge in which an electrophotographic photosensitive member, and means for processing an electrophotographic photosensitive member, are integrally disposed to enable the electrophotographic photosensitive member and processing means to be removably mounted in the main assembly of an electrophotographic image forming apparatus. For example, it is a cartridge in which an electrophotographic photosensitive member, and at least one processing means among a developing means, a charging means, and cleaning means, are integrally disposed, a cartridge in which an electrophotographic photosensitive member, and the charging means and cleaning means among the abovementioned processing means, are integrally disposed, or a cartridge in which an electrophotographic photosensitive member, and a developing means, that is, one of the abovementioned processing means, are integrally disposed. 
         [0004]    An electrophotographic image forming apparatus is an apparatus which forms an image on recording means with the use of an electrophotographic image forming method. As examples of an electrophotographic image forming apparatus, there may be included an electrophotographic printer (LED printer, laser beam printer, etc.), a facsimile apparatus, a word processor, etc. 
         [0005]    Further, the main assembly of an electrophotographic image forming apparatus is the portion of the image forming apparatus, which remains after the removal of all process cartridges in the image forming apparatus. 
         [0006]    A process cartridge system has long been in use in the field of an electrophotographic image forming apparatus, that is, an image forming apparatus which uses an electrophotographic image formation process. A process cartridge system makes it possible for a user to maintain an electrophotographic image forming apparatus without relying on a service person at all. Thus, it has significantly improved an electrophotographic image forming apparatus in maintainability. 
         [0007]    It has been known that it is from the main assembly of an image forming apparatus that a process cartridge in accordance with the art prior to the present invention receives the driving force for rotating its electrophotographic photosensitive drum (which hereafter may be referred to simply as photosensitive drum). It has also been known that the structural arrangement for the process cartridge to receive the driving force from the main assembly is as follows: 
         [0008]    The main assembly of an image forming apparatus is provided with a rotatable member for transmitting the driving of a motor to a process cartridge. The rotatable member has a hole, which is noncircular in cross section. More specifically, the hole is in the shape of a twisted polygonal column, having therefore multiple apexes, and its axial line coincides with that of the rotatable member. 
         [0009]    The process cartridge is provided with a projection, which is noncircular in cross section, having therefore multiple apexes. The projection is attached to one of the lengthwise ends of the photosensitive drum, and fits into the above-mentioned hole of the rotatable member of the apparatus main assembly. 
         [0010]    As the rotatable member of the apparatus main assembly is rotated after the mounting of the process cartridge into the apparatus main assembly, that is, the fitting of the abovementioned projection of the process cartridge into the hole of the rotational member of the apparatus main assembly, the projection is subjected to a force which acts in the direction to the pull the projection into the hole of the rotatable member of the apparatus main assembly, and the rotational force, which the rotational member possesses, is transmitted to the photosensitive drum, with the projection remaining under the above-mentioned force. That is, the rotational force for rotating the photosensitive drum is transmitted from the apparatus main assembly to the photosensitive drum (U.S. Pat. No. 2,875,203). 
         [0011]    This technology regarding the structure of an electrophotographic image forming apparatus is very effective to transmit rotational force to a photosensitive drum. 
         [0012]    The present invention is one of the results of the further development of the abovementioned prior technology. 
       SUMMARY OF THE INVENTION 
       [0013]    Thus, the primary object of the present invention is to provide a process cartridge capable of positioning its coupling, which is for receiving a rotational force from the main assembly of an image forming apparatus, relative to the rotational force transmitting portion of the apparatus main assembly, in terms of the axial line of the rotational force transmitting portion, at a significantly higher level of accuracy than a process cartridge in accordance with the art prior to the present invention. 
         [0014]    Another object of the present invention is to provide a process cartridge which can be mounted in the main assembly of an electrophotographic image forming apparatus having no mechanism for moving the rotational member of the apparatus main assembly, that is, the driving force transmitting portion of the apparatus main assembly, which is for transmitting a rotational force to the electrophotographic photosensitive drum. 
         [0015]    Another object of the present invention is to provide a process cartridge, the electrophotographic photosensitive drum of which rotates at a significantly higher level of accuracy than that of a process cartridge which employs nothing but gears to transmit a rotational force from the apparatus main assembly to the process cartridge. 
         [0016]    Another object of the present invention is to provide an electrophotographic image forming apparatus in which any of the above described process cartridges can removably mountable. 
         [0017]    Another object of the present invention is to provide a process cartridge capable of precisely aligning the axial line of its electrophotographic photosensitive member with the axial line of the counterpart of the main assembly of an electrophotographic image forming apparatus. 
         [0018]    Another object of the present invention is to provide a process cartridge capable of precisely aligning the axial line of its coupling with the axial line of the counterpart of the main assembly of an electrophotographic image forming apparatus. 
         [0019]    Another object of the present invention is to provide an electrophotographic image forming apparatus in which any of the process cartridges described above is removably mountable. 
         [0020]    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. The electrophotographic image forming apparatus includes a rotating force applying portion, comprising an electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum; a first frame unit supporting the electrophotographic photosensitive drum; a second frame unit supporting the developing roller and swingably connected with the first frame unit; a coupling, mounted to one end portion of the electrophotographic photosensitive drum, for receiving a rotating force for rotating the electrophotographic photosensitive drum from the rotating force applying portion in the state in which the process cartridge is mounted to the main assembly of the apparatus; a first cartridge side portion to be positioned engageable with a first main assembly side positioning portion provided in the main assembly of the apparatus to regulate movement of the first frame unit in a longitudinal direction of the electrophotographic photosensitive drum in the state in which the process cartridge is mounted to the main assembly of the apparatus; a second cartridge side portion to be positioned which is provided coaxially with an axis of the electrophotographic photosensitive drum at one longitudinal end of the first frame unit and which is engageable with a second main assembly side positioning portion provided in the main assembly of the apparatus to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a third cartridge side portion to be positioned which is provided coaxially with the axis of the electrophotographic photosensitive drum at the other longitudinal end of the first frame unit and which is engageable with a third main assembly side positioning portion provided in the main assembly of the apparatus to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a first unit side regulating portion provided in the first frame unit to regulate movement of the electrophotographic photosensitive drum in the longitudinal direction of the first frame unit; and a first drum side regulating portion provided on the electrophotographic photosensitive drum so as to contact the first unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the longitudinal direction of said first frame unit. 
         [0021]    According to another aspect of the present invention there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus. The electrophotographic image forming apparatus includes a rotating force applying portion, comprising an electrophotographic photosensitive drum; a drum flange provided at one end of the electrophotographic photosensitive drum, the drum flange including a gear and one end drum shaft; a coupling, mounted to the drum flange, for receiving a rotating force for rotating the electrophotographic photosensitive drum from the rotating force applying portion in the state in which the process cartridge is mounted to the main assembly of the apparatus; a developing roller rotatable by the rotating force received from the rotating force applying portion by the coupling to develop an electrostatic latent image formed on the electrophotographic photosensitive drum; a first frame unit for supporting the one end of the electrophotographic photosensitive drum through a bearing member supporting the one end side drum shaft and for supporting the other of the electrophotographic photosensitive drum through a bearing member supporting the other end side drum shaft; a second frame unit supporting the developing roller and swingably connected with the first frame unit; a first cartridge side portion to be positioned, provided on the bearing member, for engagement with a first main assembly side positioning portion provided in the main assembly of the apparatus to regulate movement of the first frame unit in a longitudinal direction of the electrophotographic photosensitive drum in the state in which said process cartridge is mounted to the main assembly of the apparatus; a second cartridge side portion to be positioned which is provided coaxially with an axis of said electrophotographic photosensitive drum at one longitudinal end of the first frame unit and which is engageable with a second main assembly side positioning portion provided in the main assembly of the apparatus to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a third cartridge side portion to be positioned which is provided coaxially with the axis of the electrophotographic photosensitive drum at the other longitudinal end of the first frame unit and which is engageable with a third main assembly side positioning portion provided in the main assembly of the apparatus to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; 
         [0022]    a first unit side regulating portion, provided at the one longitudinal end of the first frame unit, for regulating movement of the electrophotographic photosensitive drum in a direction from the one end toward the other end a second unit side regulating portion, provided on the bearing member, for regulating movement of the electrophotographic photosensitive drum in a direction from the other end toward the one end; and a first unit side regulating portion provided in the first frame unit so as to contact the first unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the direction from the one end to the other end of the electrophotographic photosensitive drum; a first drum side regulating portion provided on the electrophotographic photosensitive drum so as to contact the second unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the from the other end to the one end of the electrophotographic photosensitive drum. 
         [0023]    According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus including a main assembly of the apparatus to which a process cartridge is detachably mountable. The apparatus comprises 
         [0000]    i) a first main assembly side positioning portion;
 
ii) a second main assembly side positioning portion;
 
iii) a third main assembly side positioning portion;
 
iv) a rotating force applying portion;
 
v) the process cartridge including, a electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum; a first frame unit supporting the electrophotographic photosensitive drum; a second frame unit supporting the developing roller and swingably connected with the first frame unit; a coupling, mounted to one end portion of the electrophotographic photosensitive drum, for receiving a rotating force for rotating the electrophotographic photosensitive drum from the rotating force applying portion in the state in which the process cartridge is mounted to said main assembly of the apparatus; a first cartridge side portion to be positioned engageable with the first main assembly side positioning portion to regulate movement of the first frame unit in a longitudinal direction of the electrophotographic photosensitive drum in the state in which the process cartridge is mounted to the main assembly of the apparatus; a second cartridge side portion to be positioned which is provided coaxially with an axis of the electrophotographic photosensitive drum at one longitudinal end of the first frame unit and which is engageable with the second main assembly side positioning portion to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a third cartridge side portion to be positioned which is provided coaxially with the axis of the electrophotographic photosensitive drum at the other longitudinal end of the first frame unit and which is engageable with the third main assembly side positioning portion to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a first unit side regulating portion provided in the first frame unit to regulate movement of the electrophotographic photosensitive drum in the longitudinal direction of said first frame unit; and a first drum side regulating portion provided on the electrophotographic photosensitive drum so as to contact the first unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the longitudinal direction of the first frame unit.
 
         [0024]    According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus including a main assembly of the apparatus to which a process cartridge is detachably mountable, the apparatus comprising, 
         [0025]    i) a first main assembly side positioning portion; 
         [0026]    ii) a second main assembly side positioning portion; 
         [0027]    iii) a third main assembly side positioning portion; 
         [0028]    iv) a rotating force applying portion; 
         [0029]    v) the process cartridge including an electrophotographic photosensitive drum; a drum flange provided at one end of the electrophotographic photosensitive drum, the drum flange including a gear and one end drum shaft; a coupling, mounted to the drum flange, for receiving a rotating force for rotating the electrophotographic photosensitive drum from the rotating force applying portion in the state in which the process cartridge is mounted to the main assembly of the apparatus; a developing roller rotatable by the rotating force received from the rotating force applying portion by the coupling to develop an electrostatic latent image formed on the electrophotographic photosensitive drum; a first frame unit for supporting the one end of the electrophotographic photosensitive drum through a bearing member supporting the one end side drum shaft and for supporting the other of the electrophotographic photosensitive drum through a bearing member supporting the other end side drum shaft; a second frame unit supporting the developing roller and swingably connected with the first frame unit; a first cartridge side portion to be positioned, provided on the bearing member, for engagement with the first main assembly side positioning portion to regulate movement of the first frame unit in a longitudinal direction of the electrophotographic photosensitive drum in the state in which the process cartridge is mounted to the main assembly of the apparatus; a second cartridge side portion to be positioned which is provided coaxially with an axis of the electrophotographic photosensitive drum at one longitudinal end of the first frame unit and which is engageable with the second main assembly side positioning portion to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a third cartridge side portion to be positioned which is provided coaxially with the axis of the electrophotographic photosensitive drum at the other longitudinal end of the first frame unit and which is engageable with the third main assembly side positioning portion to position the electrophotographic photosensitive drum in a radial direction relative to the main assembly of the apparatus in the state in which the process cartridge is mounted to the main assembly of the apparatus; a first unit side regulating portion, provided at the one longitudinal end of the first frame unit, for regulating movement of the electrophotographic photosensitive drum in a direction from the one end toward the other end; a second unit side regulating portion, provided on the bearing member, for regulating movement of the electrophotographic photosensitive drum in a direction from the other end toward the one end; and a first unit side regulating portion provided in the first frame unit so as to contact the first unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the direction from the one end to the other end of the electrophotographic photosensitive drum; and a first drum side regulating portion provided on the electrophotographic photosensitive drum so as to contact the second unit side regulating portion thereby to regulate movement of the electrophotographic photosensitive drum in the from the other end to the one end of the electrophotographic photosensitive drum. 
         [0030]    According to the present invention, it is possible to precisely position the coupling of a process cartridge, which is for receiving a rotational force from the main assembly of an electrophotographic image forming apparatus, relative to the rotational force transmitting portion of the main assembly of the apparatus, in terms of the axial line of the rotational force transmitting portion. 
         [0031]    Also according to the present invention, it is possible to provide a process cartridge which can be mounted into the main assembly of an electrophotographic image forming apparatus having no mechanism for moving the a rotational member of the apparatus main assembly, that is, the driving force transmitting portion of the apparatus main assembly, which is for transmitting rotational force to the electrophotographic photosensitive drum. 
         [0032]    According to the present invention, it is possible to provide a process cartridge, the electrophotographic photosensitive drum of which rotates at a significantly higher level of accuracy than that of a process cartridge which employs nothing but gears to transmit rotational force from the apparatus main assembly to the process cartridge. 
         [0033]    According to the present invention, it is possible to provide a process cartridge capable of precisely aligning the axial line of its electrophotographic photosensitive member with the axial line of the counterpart of the main assembly of an electrophotographic image forming apparatus. 
         [0034]    Another object of the present invention is to provide a process cartridge capable of precisely aligning the axial line of its coupling with the axial line of the counterpart of the main assembly of an electrophotographic image forming apparatus. 
         [0035]    According to the present invention, it is possible to provide an electrophotographic image forming apparatus in which any of the process cartridges described above is removably mountable. 
         [0036]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a sectional view of the image forming apparatus in the preferred embodiment of the present invention. 
           [0038]      FIG. 2  is an enlarged sectional view of the cartridge in the preferred embodiment. 
           [0039]      FIG. 3  a perspective view of the process cartridge, showing the frame structure of the cartridge. 
           [0040]      FIG. 4  is a perspective view of the main assembly of the image forming apparatus. 
           [0041]      FIG. 5  is a perspective view of the cartridge driving shaft of the apparatus main assembly. 
           [0042]      FIG. 6  is a perspective view of the coupling of the process cartridge. 
           [0043]      FIG. 7  is a side view of the coupling and cartridge driving shaft when they are in engagement with each other. 
           [0044]      FIG. 8  is a sectional view of the coupling and cartridge driving shaft when they are in engagement with each other. 
           [0045]      FIG. 9  is a perspective view of the coupling. 
           [0046]      FIG. 10  is a perspective view of the spherical member. 
           [0047]      FIG. 11  is a sectional view of the coupling, the spherical member, and the connective pin after they were put together. 
           [0048]      FIG. 12  is a perspective view of the coupling, the spherical member, and the connective pin after they were put together. 
           [0049]      FIG. 13  is a plan view of the drum flange. 
           [0050]      FIG. 14  is a sectional view of the drum flange, at the plane S 2 -S 2  in  FIG. 13 . 
           [0051]      FIG. 15  is a sectional view of the coupling, the spherical member, the drum flange, and the connective pin, at the plane S 1 -S 1  in  FIG. 13 , before they are put together, showing the steps for attaching the coupling to the drum flange. 
           [0052]      FIG. 16  a sectional view of the combination of the coupling disengagement prevention plug, the coupling, the spherical member, drum flange, and the connective pin, at the plane S 1 -S 1  in  FIG. 13 , showing the steps for securely attaching the coupling to the drum flange. 
           [0053]      FIG. 17  is a perspective view of the photosensitive drum unit, as seen from the its driving force receiving side. 
           [0054]      FIG. 18  is a perspective view of the photosensitive drum unit, as seen from the opposite side from its driving force receiving side. 
           [0055]      FIG. 19  is a perspective view of the end portion of the photosensitive drum unit, and its adjacencies, on the driving force receiving side of the drum unit, showing the structural arrangement for supporting the end portion. 
           [0056]      FIG. 20  is also a perspective view of the driving force receiving end portion of the photosensitive drum unit, and its adjacencies, showing the structural arrangement for supporting the driving force receiving end of the photosensitive drum unit. 
           [0057]      FIG. 21  is another perspective view of the force receiving end portion of the photosensitive drum unit, and its adjacencies, showing the structural arrangement for supporting the driving force receiving end of the photosensitive drum unit. 
           [0058]      FIG. 22  is a perspective view of the opposite end portion of the photosensitive drum unit from the driving force receiving end, and its adjacencies, showing the structural arrangement for supporting the opposite end portion of the photosensitive drum unit. 
           [0059]      FIGS. 23(   a ) and  23 ( b ) are perspective views of the cartridge guiding rails of the apparatus main assembly, on the driving force transmitting side and the opposite side from the driving force transmitting side, respectively. 
           [0060]      FIGS. 24(   a ) and  24 ( b ) are schematic drawings for showing the structural arrangement for precisely positioning the coupling and apparatus main assembly relative to each other in terms of the direction parallel to the axial line of the coupling. 
           [0061]      FIG. 25  is a perspective view of the photosensitive drum and flange, showing the method for securely attaching the drum flange to the photosensitive drum. 
           [0062]      FIG. 26  is a sectional view of the photosensitive drum and drum flange, which is for showing the method for securely attaching them to each other. 
           [0063]      FIGS. 27(   a ) and  27 ( b ) are sectional views of the drum supporting portion of the cartridge frame, and the groove of the drum flange, showing their positional relationship. 
           [0064]      FIGS. 28(   a ) and  28 ( b ) are schematic phantom views of the image forming apparatus, showing the method for mounting the process cartridge into the main assembly of the apparatus. 
           [0065]      FIG. 29  is a schematic drawing for describing the movements of the coupling, which occur during the insertion of the cartridge into the main assembly of the image forming apparatus. 
           [0066]      FIG. 30  is also a schematic drawing for describing the movements of the coupling, which occur during the insertion of the cartridge into the main assembly of the image forming apparatus. 
           [0067]      FIG. 31  is yet another schematic drawing for describing the movements of the coupling, which occur during the insertion of the cartridge into the main assembly of the image forming apparatus. 
           [0068]      FIG. 32  is another schematic drawing for describing the movements of the coupling, which occur during the insertion of the cartridge into the main assembly of the image forming apparatus. 
           [0069]      FIGS. 33(   a )- 33 ( d ) are yet other schematic drawings for describing the movements of the coupling, which occur during the insertion of the cartridge into the main assembly of the image forming apparatus. 
           [0070]      FIGS. 34(   a )- 34 ( d ) are schematic drawings for describing the movements of the coupling, which occur during the extraction of the cartridge from the main assembly of the image forming apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0071]    Hereinafter, one of the preferred embodiments of the present invention will be described in detail with reference to the appended drawings. However, the functions, materials, shape of the structural components of the process cartridge and electrophotographic image forming apparatuses, and their positional relationship, are not intended to limit the present invention in scope, unless specifically noted. Further, if a given member of the image forming apparatus, which has been described regarding its material, shape, etc., is mentioned again, it is the same in material and shape, unless specifically noted. 
       Embodiment 
     (General Structure) 
       [0072]      FIG. 1  is a sectional view of a typical image forming apparatus, in accordance with the present invention, which is made up of the image forming apparatus main assembly  1  (which hereafter may be referred to simply as apparatus main assembly  1 ), and a process cartridge  2  (which hereafter may be referred to simply as cartridge  2 ).  FIG. 2  is an enlarged sectional view of the cartridge  2 . Next, referring to  FIGS. 1 and 2 , the general structure and image forming process of the image forming apparatus in this embodiment will be described. 
         [0073]    This image forming apparatus is a laser beam printer based on an electrophotographic technology. It employs the process cartridge  2 , which is removably mountable in the main assembly  1 . The apparatus main assembly  1  is provided with an exposing apparatus  3  (laser scanner unit) and a sheet tray  4 . The exposing apparatus  3  is located above the space for the cartridge  2 . The sheet tray  4  is located below the space for the cartridge  2 , and stores multiple sheets of recording medium P, which are the sheets of recording medium on which an image is formed. The apparatus main assembly  1  is also provided with a pickup roller  5   a , a pair of recording medium conveyance rollers  5   b , a pair of recording medium conveyance rollers  5   c , a transfer guide  6 , a transfer charge roller  7 , a recording medium conveyance guide  8 , a fixing apparatus  9 , a pair of recording medium discharge rollers  10 , a delivery tray  11 , etc., listing from the upstream side in terms of the direction in which the sheets P are conveyed. 
       (Image Formation Process) 
       [0074]    Next, the image formation process used by the image forming apparatus in the following preferred embodiment of the present invention will be described. The electrophotographic photosensitive drum  20  (which hereafter will be referred to as drum) is rotationally driven in the direction indicated by an arrow mark R 1 , at a preset peripheral velocity (process speed), in response to a print start signal. The peripheral surface of the drum  20  is in contact with a charge roller  12 , to which bias voltage is being applied. Thus, the peripheral surface of the drum  20  is uniformly changed by the charge roller  12 . 
         [0075]    The exposing apparatus  3  outputs a beam L of laser light while modulating the beam L of with sequential electrical digital picture element signals which reflect the information of the image to be formed. More specifically, the exposing apparatus  3  projects the beam L of laser light in such a manner that the beam L enters the cartridge  2  through the exposure window of the top wall of the cartridge  2 , and scans the peripheral surface of the drum  20 . As a result, an electrostatic latent image, which reflects the abovementioned information of the image, is formed on the peripheral surface of the drum  20 . This electrostatic latent image is developed by the developer T (which hereafter will be referred to as toner) in the second unit  40 , into a visible image, that is, an image formed of toner (which hereafter will be referred to as toner image). 
         [0076]    To describe in more detail, the charge roller  12  is positioned so that its peripheral surface is in contact with the peripheral surface of the drum  20  to charge the drum  20 . The charge roller  12  is rotated by the rotation of the drum  20 . The second unit  40  of the cartridge  2  supplies the portion of the peripheral surface of the drum  20 , which is in the development area, with toner to develop the latent image formed on the peripheral surface of the drum  20 . 
         [0077]    The abovementioned second unit  40  has a toner chamber  45 , a stirring member  43 , a toner supplying chamber  44 , a development roller  41 , a magnetic roller  41   a  (stationary magnet), and a development blade  42 . The magnetic roller  41   a  is in the hollow of the development roller  41 , which is a developer bearing member. The second unit  40  sends the toner T in the toner chamber  45  into the toner supplying chamber  44  by the rotation of the stirring member  43 , while rotating the development roller  41 . As the development roller  41  is rotated, a layer of toner, which is of a preset thickness, is formed on the peripheral surface of the development roller  41  while being frictionally charged, by the development blade  42 . Then, the second unit  40  transfers the toner particles in the toner layer on the development roller  41  onto the numerous exposed points of the latent image on the drum  20  to develop the latent image into a visible image, or a toner image. The development blade  42  is a blade for regulating the amount of toner that is allowed to remain coated per unit area of the peripheral surface of the drum  20 , and also, for frictionally charging the toner (for giving triboelectric charge to toner). 
         [0078]    Meanwhile, in synchronism with the timing with which the beam L of laser light is outputted, the sheet P is conveyed to the transfer area, which is the interface between the drum  20  and transfer charge roller  7 , by way of the transfer guide  6 , so that the toner image on the drum  20  arrives at the transfer area at the same time as the sheet P. In the transfer area, the toner image on the peripheral surface of the drum  20  is transferred onto the sheet P as if it were peeled away from the peripheral surface of the drum  20 . 
         [0079]    After the transfer of the toner image onto the sheet P, the sheet P is separated from the drum  20 , and is conveyed to the fixing apparatus  9  along the recording medium conveyance guide  8 . Then, the sheet P is conveyed through the nip between the fixation roller  9   a  and a pressure roller  9   b , which make up the fixing apparatus  9 . While the sheet P is conveyed through the nip, the sheet P and the toner image thereon are subjected to pressure and heat. As a result, the toner image becomes fixed to the sheet P. After the fixation of the toner image to the sheet P, the sheet P is conveyed to the pair of discharge rollers  10 , and is discharged into the delivery tray  11 . 
         [0080]    Meanwhile, the drum  20 , from which the toner image has just been transferred, is cleared of the transfer residual toner, that is, the toner remaining on the peripheral surface of the drum  20  after the toner image transfer, to be used for the next image forming process, which begins with the charging of the drum  20 . The toner removed from the drum  20 , that is, the waste toner, is stored in a waste toner chamber  52   a.    
         [0081]    The charge roller  12 , the development roller  41 , the cleaning blade  52 , etc., which were mentioned in the description of the image formation process given above, are the process means for processing the drum  20 . 
       (Structure of Process Cartridge Frame) 
       [0082]      FIG. 3  is a perspective view of the process cartridge  2 , and shows the structure of the cartridge frame. Next, the frame structure of the process cartridge  2  will be described with reference to  FIGS. 2 and 3 . 
         [0083]    Referring to  FIG. 2 , the drum  20 , the charge roller  12 , and the cleaning blade  52  are integrally attached to the drum supporting portion  51  of the frame of the cartridge  2 , making up a first unit  50  of the cartridge  2 . 
         [0084]    A second unit  40  of the cartridge  2  is made up of: the toner storage container  40   a  having the toner storage chamber  45  for storing toner and toner supply changer  44 ; and the lid  40   b . The toner storage container  40   a  and the lid  40   b  are joined to each other by welding or the like means. 
         [0085]    Next, referring to  FIG. 3 , the first unit  50  and second unit  40  are connected to each other with the use of a pair of connecting members  54 , such as a pair of round connective pins, so that they can be rotationally moved relative to each other about the pair of connecting members  54 . 
         [0086]    That is, referring to  FIG. 3 , the cartridge  2  is provided with a pair of side covers  55 , which are located at the lengthwise ends of the unit  40  (in terms of a direction parallel to axial line of development roller  41 ). Each side cover  55  is provided with an arm portion  55   a , the tip portion of which is provided with a hole  55   b , the axial line of which is parallel to the development roller  41 . The drum supporting portion  51  of the frame of the first unit  50  is provided with a hole  51   a , which aligns with the hole  55   b  of the second unit  40  as the arm portion  55   a  is inserted into a preset portion of the drum supporting portion  51  (hole  55   b  on left side is not shown in  FIG. 3 ). Inserting the connective members  54  into the holes  55   b  and  51   a  on the left side of the cartridge  2 , and the holes  55   b  and  51   a  on the right side of the cartridge  2  connects the first and second units  50  and  40  in such a manner that the two units  50  and  40  are rotationally movable relative to each other about the pair of connective members. Further, the cartridge  2  is provided with a pair of compression springs  46 , which are attached to the base portion of the abovementioned arm portions  55   a , one for one, so that they contact the drum supporting portions  51  to keep the second unit  40  pressed downward, ensuring that the development roller  41  ( FIG. 3 ) is kept pressured toward the drum  20 . Further, the lengthwise end portions of the development roller  41  are fitted with a pair of spacers (unshown), one for one, ensuring that a preset amount of gap is maintained between the peripheral surface of the development roller  41  and that of the drum  20 . 
         [0087]    One of the lengthwise ends of the first unit  50  is provided with a coupling  150 , through which a driving force is transmitted from the apparatus main assembly  1  to the cartridge  2  to rotate the drum  20 . Incidentally, hereafter, the lengthwise end of the cartridge  2 , in terms of the direction parallel to the lengthwise direction of the drum  20 , which has the coupler  150 , will be referred to as the driving force receiving end (side), whereas the opposite lengthwise end of the cartridge  2  from the driving force receiving end (side) may be referred to simply as the opposite end (side). 
       (Method for Transmitting Rotational Force to Process Cartridge) 
       [0088]      FIG. 4  is a perspective view of the apparatus main assembly  1 , the cartridge insertion (removal) door  109  (main assembly cover, main assembly door), which is open to show the interior of the apparatus main assembly  1 . The apparatus main assembly  1  shown in  FIG. 4  is not holding any process cartridge  2 . Next, referring to  FIG. 4 , the method for transmitting the rotational force to the cartridge  2  will be described. 
         [0089]    Referring to  FIG. 4 , the apparatus main assembly  1  is provided with a cartridge mounting means  130  for mounting or dismounting the cartridge  2 . Thus, the cartridge  2  is mounted into the apparatus main assembly  1  following the cartridge mounting means  130  (which hereafter may be referred to simply as mounting means). As the cartridge  2  is mounted into the apparatus main assembly  1 , the cartridge driving shaft  100  (which hereafter will be referred to simply as drive shaft  100 ) of the apparatus main assembly  1  engages with the coupling member  150  (which hereafter will be referred to as coupling,  FIG. 3 ), enabling the drum  20  to rotate by receiving a rotational force from the apparatus main assembly  1 . 
       1) Drive Shaft  100   
       [0090]      FIG. 5  is a perspective view of the drive shaft  100  of the apparatus main assembly  1 . The drive shaft  100  is in connection with an unshown driving force transmitting means, such as a gear train, with which the apparatus main assembly  1  is provided, and which is connected to a motor. The end portion  100   a  of the drive shaft  100  is semispherical, and is provided with a rotational force transmission pin  100   b.    
       2) Coupling  150   
       [0091]      FIG. 6  is a perspective view of the coupling  150 . The material of which the coupling  150  is formed is a resin, such as, polyacetal, polycarbonate, and PPS. However, in order to increase the coupling  150  in rigidity, glass fiber, carbon fiber, or the like, may be mixed into the above described material for the coupling  150 , by an amount proportional to the amount of the torque to which the coupling  150  will be subjected. Further, a piece or pieces of metal may be inserted into the coupling  150  to increase the coupling  150  in rigidity. Further, the entirety of the coupling  150  may be formed of a metallic substance to ensure that the coupling  150  is satisfactorily rigid. 
         [0092]    The end of the coupling  150  is provided with multiple (four in this embodiment) driving force catching projections  150   d  ( 150   d   1 - 150   d   4 ), by which the driving force from the drive shaft  100  is caught (received). Each of the driving force catching projections  150   d  ( 150   d   1 - 150   d   4 ) is provided with a rotational force catching portion  150   e  ( 150   e   1 - 150   e   4 ), the driving force catching surface of which is angled relative to the axial line L 150  of the coupling  150 . Further, the coupling  150  is provided with a conic recess  150   f , which is on the inward side of the driving force catching projections  150   d   1 - 150   d   4  in terms of the radius direction of the coupling  150 . 
         [0000]    3) Engagement between Drive Shaft  100  and Coupling  150   
         [0093]      FIG. 7  is a side view of the coupling  150  and driving shaft  100 , which are in engagement with each other.  FIG. 8  is a sectional view of the coupling  150  and driving shaft  100 , at the plane which coincides with both the axial line of the coupling  150  and the axial line of the drive shaft  100 . Next, referring to  FIGS. 7 and 8 , the engagement of the drive shaft  100  and coupling  150  will be described. 
         [0094]    The rotational force transmission pin  100   b  of the drive shaft  100  is in engagement with the rotational force catching portions  150   e  ( 150   e   1 - 150   e   4 ) of the coupling  150 . Although not shown in  FIG. 7 , the portion of the rotational force transmission pin  100   b , which is on the back side of the drawing, is in engagement with another rotational force catching portion  150   e , which is also on the back side of the drawing. Further, the end portion  100   a  of the drive shaft  100  is in contact with the surface of the conic recess  150   f  of the coupling  150 . Thus, as the drive shaft  100  rotates, a driving force is transmitted to the rotational force catching portions  150   e  from the rotational force transmitting pin  100   b . Further, each driving force catching portion  150   e  is angled relative to the axial line L 150  of the coupling  150 . Therefore, as the drive shaft  100  rotates, the coupling  150  and drive shaft  100  pull each other, ensuring that the end  100   a  of the drive shaft  100  comes into contact, and remains in contact, with the surface of the conic recess  150   f  so that the driving force is reliably transmitted from the drive shaft  100  to the coupling  150 . 
         [0095]    As described above, the coupling  150  is attached to one of the lengthwise ends of the drum  20 . It receives the rotational force for rotating the drum  20  from the apparatus main assembly  1  while the cartridge  20  is in its proper position and attitude for image formation, in the apparatus main assembly  1 . 
       4) Connective Components for Coupling  150   
       [0096]      FIG. 9  is a perspective view of the coupling  150 , and  FIG. 10  is a perspective view of the spherical member  160 .  FIG. 11  is a sectional view of the coupling  150  and the connective components for the coupling.  FIG. 12  is a perspective view of the coupling  150  and the connective components therefor. 
         [0097]    Referring to  FIG. 9 , the coupling  150  has a through hole  150   r , which is in the opposite end  150   s  of the coupling  150  from the end having the rotational force receiving portions  150   e . Next, referring to  FIG. 10 , the abovementioned opposite end portion  150   s  of the coupling  150  is fitted with a spherical member  160 , which is roughly spherical. The spherical member  160  is provided with a blind hole  160   a , and a through hole  160   b . The blind hole  160   a  is the hole into which the end portion  150   s  of the coupling  150  is inserted. The through hole  160   b  is the hole, through which a pin  155  (rotational force transmitting portion) is put in such a manner that it goes through the abovementioned hole  150   r  of the coupling  150 . The through hole  160   b  intersects the blind hole  160   a . The pin  155  will be described later in more detail. 
         [0098]    Referring to  FIGS. 12 and 13 , the end portion  150   s  of the coupling  150  is inserted into the blind hole  160   a  of the spherical member  160 , and the pin  155  is put through the through hole  160   b , with the through hole  160   b  being aligned with the through hole  150   r  of the coupling  150 . In this embodiment, the coupling  150 , the spherical member  160 , and the pin  155  are designed so that the coupling  150  loosely fits in the blind hole  160   a ; the pin  155  loosely fits in the through hole  150   r , while fitting tightly in the through hole  160   b . Thus, after the fitting of the pin  155  into the through hole  160   b , the pin  155  and the spherical member  160  are virtually integral with each other. This state of engagement hereafter will be referred to as the “universal coupling” after a universal joint. Receiving a driving force from the drive shaft  100 , the coupling  150  rotates about its axial line L 150 , causing the wall of the through hole  150   r  to come, and remain, in contact with the pin  155 . Thus, the rotational force from the apparatus main assembly  1  is turned into the rotational force, which rotates the pin  155  about the rotational axis L 150  of the coupling  150 . 
         [0000]    5) Transmission of Rotational Force to Drum  20  through “Universal Coupling” 
         [0099]      FIG. 13  is a schematic drawing of a drum flange  151  (which hereafter may be referred to simply as flange  151 ), which is for describing the flange  151 .  FIG. 14  is a sectional view of the flange  151 , at a plane S 2 -S 2  in  FIG. 13 .  FIG. 15  is a schematic sectional view of the spherical member  160 , the coupling  150 , and the flange  151 , at a plane S 1 -S 1  in  FIG. 13 , which is for describing the method of securely attaching the coupling  150  to flange  151 .  FIG. 16  is a schematic sectional view of the spherical member  160 , the coupling  150 , and the flange  151 , at a plane S 1 -S 1  in  FIG. 13 , which is for describing the method of fixing the coupling  150  to the flange  151 .  FIG. 17  is a perspective view of the photosensitive drum unit  21 , as seen from the driving force receiving side (side having coupling  150 ), which is for describing the photosensitive drum unit  21 .  FIG. 18  is a perspective view of the photosensitive drum unit  21 , as seen from the opposite side from the driving force receiving side (opposite side from coupling  150 ), which is also for describing the photosensitive drum unit  21 . 
         [0100]    Referring to  FIGS. 13 and 14 , an example of the flange  151  to which the coupling  150  is attached will be described.  FIG. 13  is a plan view of the flange  151 , as seen from the drive shaft side. Designated by reference codes  151   g  ( 151   g   1 - 151   g   4 ) in  FIG. 13  are four slots with which the flange  151  is provided. The depth direction of each slot  151   g  is parallel to the axial line of the flange  151 . When the coupling  150  is attached to the flange  151 , the pin  155  is put through the combination of the slots  151   g   1  and  151   g   3 , or the combination of the slots  151   g   2  and  151   g   4 . Further, the upstream wall of each of the slots  151   g , in terms of the clockwise direction, functions as a rotational force transmission or catching surface (rotational force catching surface)  151   h  ( 151   h   1 - 151   h   4 ). When the driving force is transmitted to the flange  151  from the pin  151 , the pin  155  comes into contact with the rotational force catching surface  151   h . Further, the center portion of the flange  151 , that is, the portion of the flange  151 , which is adjacent to the axial line of the flange  151 , is hollow (flange  151  is provided with recess  151   f ). 
         [0101]    The recess  151   f  is the space surrounded by the arcuate walls  151   j  ( 151   j   1 - 151   j   4 ), disengagement preventing portions  151   i  ( 151   i   1 - 151   i   4 ), and openings  151   k  ( 151   k   1 - 151   k   4 ). The arcuate walls (surfaces)  151   j  ( 151   j   1 - 151   j   4 ) coincide with a hypothetical cylindrical wall (surface)  151   a , which is the same in curvature as the arcuate walls  151   j , and the axial line of which coincides with the axial line L 151  of the flange  151 . The diameter φ of the hypothetical cylindrical wall (surface)  151   a  is D 151   a . Each of the disengagement preventing portions  151   i  ( 151   i   1 - 151   i   4 ) is also a roughly arcuate portion as the arcuate wall  151   j , and smoothly extends from the arcuate wall  151   j . That is, the disengagement preventing portions  151   i  coincide with a hypothetical cylindrical wall which is SR 151  in radius. Each of the openings  151   k  ( 151   k   1 - 151   k   2 ) is on the drive shaft side of the disengagement preventing portion  151   i , and its curvature is the same as the curvature of a circle which is D 151   b  in diameter φ. 
         [0102]    The relationship among the external dimension (diameter φ) D 160  of the spherical member  160 , and the measurements of the abovementioned portions of the flange  151  ( FIGS. 14 and 15 ), is as follows: 
         [0000]      φ D 151 b&lt;φD 160 &lt;φD 151 a&lt; 2 ×SR 151.
 
         [0103]    The spherical member  160  can be inserted into the recess  151   f , with the presence of a gap G. However, while the spherical member  160  is in the recess  151   f , it is not allowed to move toward the opening  151   k , in terms of the direction parallel to the axial line L 151 . Therefore, it does not occur that the spherical member  160  becomes disengaged from the flange  151  under the normal condition after the fitting of the spherical member  160  into the flange  151 . 
         [0104]    Next, referring to  FIGS. 15 and 16 , the process of inserting the coupling  150  into the flange  151 , and fixing the coupling  150  to the flange  151 , will be described. First, the end portion  150   s  is to be inserted into the flange  151  from the direction indicated by an arrow mark X 1 . Then, the end portion  150   s  is to be fitted with the spherical member  160  in a manner to cover the end portion  150   s  from the direction indicated by an arrow mark X 2 . Next, the spherical member  160  is to be positioned relative to the end portion  150   s  so that its through hole  160   b  aligns with the through hole  150   r  of the end portion of the  150   s . Then, the pin  151  is to be inserted from the direction indicated by an arrow mark X 3  so that the pin  151  extends from one end of the through hole  160   b  and the other, through the through hole  150   r . The through holes  160   b  and  150   r , and the pin  150 , are designed so that the hole  160   b  is smaller in diameter than the pin  155 . Therefore, there is a certain amount of friction between the pin  151  and the wall of the through hole  160   b  when the pin  151  is inserted. Incidentally, in this embodiment, the amount of difference between the diameter of the pin  151  and that of the through hole  160   b  is set to roughly 50 μm. 
         [0105]    Therefore, it does not occur that the pin  155  becomes disengaged from the spherical member  160  under the normal condition. That is, it is ensured that the coupling  150  remains engaged with the flange  151 . 
         [0106]    Then, the combination  156  (“universal coupling”) of the spherical member  160  and coupling  150  is to be moved in the direction indicated by an arrow mark X 4  to place the spherical member  160  in contact with, or close to, the disengagement prevention portion  151   i.    
         [0107]    Next, the disengagement preventing member  157  is to be inserted in the direction indicated by the arrow mark X 4  to solidly attach the disengagement preventing member  157  to the flange  151 . There remains a gap (play) between the disengagement preventing member  157  and spherical member  160  after the attachment of the disengagement preventing member  157 . Therefore, the coupling  150  is allowed to change in attitude. 
         [0108]    Next, referring to  FIGS. 17 and 18 , the structure of the photosensitive drum unit  21  will be described. After the combination  156  (“universal coupling”) is attached to the flange  151 , the flange  151  is to be solidly attached to one of the lengthwise ends of the drum  20  in such a manner that the driving force receiving projections  150   d  of the coupling  150  are exposed from the flange  151 . Further, the drum flange  152  is to be solidly attached to the opposite end of the drum  200  from the driving force receiving end. As for the method for solidly attaching the drum flanges  151  and  152  to the drum  20 , crimping, bonding, welding, or the like, may be used. 
         [0109]    Next, referring to  FIGS. 19-22 , the structural arrangement for supporting the photosensitive drum unit  21  will be described. The flange  151  attached to the driving force receiving end of the photosensitive drum unit  21  has a drum gear  151   c  and a shaft  151   v . The drum gear  151   c  is the gear for transmitting the rotational force, which the flange  151  received, to the development gear  41   b  of the development roller  41 . The shaft  151   v  functions as one of the drum shafts. The shaft  151   v  is rotatably supported by the supporting portion  158   d  of the bearing  158 . The gear  151   c  is an integral part of the flange  151 . Referring to  FIG. 22 , the opposite end of the photosensitive drum unit  21  from the shaft  151   v  is provided with a drum shaft  202 , by which the drum  20  is supported. The drum shaft  202  is solidly attached to the drum supporting portion  51  of the cartridge  2  by press-fitting or the like method. Thus, the photosensitive drum unit  21  is rotatably supported by the drum shaft  202  fitted in the hole  152   a  of the drum flange  152  on the opposite side of the photosensitive drum unit  21  from the driving force receiving side. 
         [0110]    The drum gear  151   c  is a helical gear, the teeth of which are tilted in such a direction that as the driving force is transmitted to the drum gear  151   c , the drum gear  151   c  is thrust toward the direction opposite from the gear  151   c . Incidentally, the lengthwise direction (axial line) of the drum  20  is parallel to the lengthwise direction of the cartridge  2 . 
         [0111]    The gear  151   c  transmits the rotational force, which the coupling  150  received from the drive shaft  100 , to the development roller  41  through the development gear  41   b , rotating thereby the development roller  41 . 
         [0112]    As described above, the drive shaft  100  is rotated by the rotational force transmitted thereto from the motor (unshown) of the apparatus main assembly  1  through the driving force transmitting means (unshown), such as the gears of the apparatus main assembly  1 . Then, the rotational force is transmitted to the cartridge  2  through the coupling  150 . Then, the driving force is transmitted from the coupling  150  to the flange  151  through the pin  155 . As a result, the driving force is transmitted to the drum  20 , to which the flange  151  is integrally attached. 
       (Structure Arrangement for Mounting or Dismounting Cartridge) 
       [0113]    Next, the structural arrangement for allowing the cartridge  2  to be removably mounted in the apparatus main assembly  1  will be described. Referring to  FIGS. 23(   a ) and  23 ( b ), the cartridge mounting means  130  of the apparatus main assembly  1  in this embodiment has a pair of guides  130 R and  130 L, which are located on the left and right ends, respectively, of the cartridge space in the apparatus main assembly  1 , facing each other across the cartridge space.  FIG. 23(   a ) corresponds to the driving force receiving side of the cartridge  2 , and  FIG. 23(   b ) corresponds to the opposite side of the cartridge  2  from the driving force receiving side. It is along these guides  130 R and  103 L that the cartridge  2  (unshown in  FIG. 23)  is mounted or dismounted. Incidentally, in order to mount the cartridge  2  into the apparatus main assembly  1 , the door  109  ( FIG. 4 ) of the apparatus main assembly  1  must be opened. The door  109  is to be closed after the mounting of the cartridge  2 . The closing of the door  109  concludes the process of mounting the cartridge  2  into the apparatus main assembly  1 . Also incidentally, the door  109  has to be opened also in order to remove the cartridge  2  from the apparatus main assembly  1 . These processes are to be carried out by a user (operator). 
         [0114]    Referring to  FIGS. 19 and 21 , the driving force receiving end of the first unit  50  of the cartridge  2  is provided with a pair of cartridge guides  51 R, which project outward of the cartridge  2  in the direction parallel to the lengthwise direction of the cartridge  2 , whereas the opposite end the first unit  50  of the cartridge  2  is provided with a pair of cartridge guides  51 L, as shown in  FIG. 22 . 
         [0115]    When the cartridge  2  is mounted into, or dismounted from, the apparatus main assembly  1 , the cartridge guides  51 R shown in  FIG. 21 , and the cylindrical portion  158   c  of the bearing  158 , are guided by the guide  130 R of the apparatus main assembly  1 , which is shown in  FIG. 23(   a ). Further, the pair of cartridge guides  51 L, and the cylindrical portion  51   e  of the drum supporting portion  51  of the cartridge  2 , are guided by the guide  130 L of the main assembly  1 , which is shown in  FIG. 23(   b ). With the provision of the above described structural arrangement, the cartridge  2  is mounted into, or removed from, the apparatus main assembly  1  in the direction which is practically perpendicular to the axial line of the drive shaft  100 . 
         [0116]    Next, referring to  FIGS. 28(   a ) and  28 ( b ), the operation for mounting the cartridge  2  into the apparatus main assembly  1  will be described.  FIGS. 28(   a ) and  28 ( b ) are schematic sectional views of the image forming apparatus shown in  FIG. 4 , at the plane S 1 -S 1  in  FIG. 4 , except that in  FIGS. 28(   a ) and  28 ( b ), there the cartridge  2  is in the apparatus. If a user wants to mount the cartridge  2  into the apparatus main assembly  1 , the user is to open the door  109  of the apparatus main assembly  1 , and to insert the cartridge  2  into the apparatus main assembly  1 , in such a manner that the cartridge guides  51 R, and cylindrical portion  158   c  are guided by the guides  130 R of the apparatus main assembly  1  (cartridge guide  51 L and cylindrical portion  51   e , which are on opposite side from driving force receiving side, are guided by guide  13 L of apparatus main assembly  1 ), as shown in  FIGS. 28(   a ) and  28 ( b ), in the direction indicated by an arrow mark X 5 . As the cartridge  2  is inserted, the coupling  150  of the cartridge  2  engages with the drive shaft  100 , and then, the cartridge  2  is placed in a preset position (image forming position). As the same time as the cartridge  2  is placed in the preset position, the coupling  150  becomes fixed in the position and attitude so that the rotational force can be transmitted to the cartridge  2  ( FIG. 28(   b )). 
         [0117]    As the cartridge  2  is moved into the abovementioned preset position, the drum shaft bearing portion  158   e  ( FIG. 21 ) of the bearing  158 , and the drum shaft bearing portion  51   g  of the drum supporting portion  51  ( FIG. 22 ) come under the pressure from the compression springs  188 R and  188 L shown in  FIGS. 23(   a ) and  23 ( b ). As a result, the cartridge  2  is precisely positioned relative to the apparatus main assembly  1 . 
         [0118]    At this time, why “practically perpendicular” is used instead of “perpendicular” will be described. That is, a small amount of gap is provided between the cartridge  2  and apparatus main assembly  1  to ensure that the cartridge  2  can be smoothly mounted into, or removed from, the apparatus main assembly  1 . Thus, it is possible that when the cartridge  2  is mounted into, or removed from, the apparatus main assembly  1 , the entirety of the cartridge  2  will become slightly tilted by an angle within the range afforded by the gap. Even in such a case, the present invention is effective. This is why “substantially perpendicular” was used to include the case in which the entirety of the cartridge  2  becomes slightly tilted due to the presence of the abovementioned small amount of gap. 
       (Movements of Coupling  150 ) 
       [0119]    Next, referring to  FIGS. 29 and 30 , the relationship among the guides  130 R and  130 L, that is, the cartridge guides of the apparatus main assembly  1 , the sliders  131 , and the coupling  150  will be described.  FIG. 29  is a side view of the driving force receiving end portion of the cartridge  2  which is being inserted into the apparatus main assembly  1 , as seen from the side where the drive shaft  100  is located.  FIG. 30  is a sectional view of the driving force receiving end portion of the cartridge  2 , at a plane Z-Z in  FIG. 29 . 
         [0120]    Referring to  FIG. 29 , when the cartridge  2  is mounted into the apparatus main assembly  1 , the driving force receiving end portion of the cartridge  2  moves inward of the apparatus main assembly  1 , with the cylindrical portion  158   c  of the bearing  158  remaining in contact with the guiding surface  130 R 1   b . During this stage of the mounting, there is a gap n 1  between the center portion  150   c  (in terms of lengthwise direction) of the coupling  150  and the guide rib  130 R 1   c , as shown in  FIG. 30 . Therefore, during this state, the coupling  150  is under no pressure. Next, referring to  FIG. 29 , the top left portion of the peripheral surface of the coupling  150  is in contact with the regulating portion  158   f . Therefore, the coupling  150  is allowed to tilt only in the direction indicated by the arrow mark X (cartridge mounting direction). The slider  131  is kept in its pressure applying position (uppermost position) by the resiliency of the compression spring  132 . 
         [0121]      FIG. 31  is a side view of the driving force receiving end portion of the cartridge  2  after the coupling  150  came into contact with the slider  131 , and the slider  131  was moved from its pressure applying position to its retreat position. Because of the advancement of the coupling  150 , which is capable of tilting only in the direction indicated by the arrow mark X 5 , into the apparatus main assembly  1 , the center portion  150   c  comes into contact with the slanted surface  131   a  ( FIG. 32 ) of the projecting portion of the slider  131 . Thus, as the cartridge  2  is inserted further, the slider  131  is pressed down into its retreat position. 
         [0122]      FIG. 32  shows the state of the driving force receiving end portion of the cartridge  2  after the coupling  150  went over the apex  131   b  of the slider  131 . As soon as the coupling  150  goes over the apex  131   b , the resiliency of the compression spring  132  begins to press the slider  131  out of the retreat position into the pressure applying position. During this stage of the mounting of the cartridge  2 , a part of the center portion  150   c  of the coupling  150  is pressed by the slanted surface  131   c  of the slider  131 . That is, the slanted surface  131   c  functions as a pressure applying portion, whereas a part of the center portion  150   c  functions as the force catching portion  150   p , which catches the force F applied by the slanted surface  131   c . The force F is separated into two components, that is, a force F 1  and a force F 2 . Also during this stage, the coupling  150  is regulated by the regulating portion  158   f , which is in contact with the top portion of the peripheral surface of the coupling  150 . Therefore, the coupling  150  is tilted in the cartridge mounting direction X 5  by the force F 2 . That is, the coupling  150  is moved into its drive shaft engagement starting position, in which the coupling  150  is ready in attitude to become engaged with the drive shaft  100 . 
         [0123]    Next, referring to  FIGS. 33(   a )- 33 ( d ), how the coupling  150  becomes engaged with the drive shaft  100  will be described.  FIGS. 33(   a )- 33 ( d ) are a vertical sectional views of the driving force receiving end portion of the drum  20 , coupling  150 , and drive shaft  100 , as seen from below the apparatus main assembly  1 . 
         [0124]    Referring to  FIG. 33(   a ), when the cartridge  2  is mounted into the apparatus main assembly  1 , the cartridge  2  is moved into the apparatus main assembly  1  (unshown) from the direction (indicated by arrow mark X 5 ), which is practically perpendicular to the axial line L 3  of the drive shaft  100 . When the coupling  150  is in the abovementioned drive shaft engagement starting position, the axial line L 2  of the coupling  150  is tilted relative to the axial line L 1  of the drum  20  so that the driving force receiving end of the coupling  150  is on the downstream side of the opposite end of the coupling  150 , in terms of the cartridge mounting direction X 5 . Because the coupling  150  is tilted as described above, the leading end portion  150 A 1  (part of coupling  150 ), in terms of the cartridge mounting direction X 5 , is closer to the drum  20  than to the tip portion  100   c   3  of the drive shaft  100 , in terms of the direction parallel to the axial line L 1 , whereas the leading end portion  150 A 2  (another part of coupling  150 ) is closer to the rotational force transmitting pin  100   b  than to the tip portion  100   c   3  of the drive shaft  100 . 
         [0125]    Referring to  FIG. 33(   b ), first, the leading end portion  150 A 1  passes by the tip portion  100   c   3  of the shaft  100 , and then, the surface of the driving force catching conic recess  150   f , the axial line of which coincides with the axial line of the coupling  150 , or driving force catching projection  150   d , comes into contact with the tip portion  100   c   3  of the drive shaft  100 , or the rotational force transmitting pin  100   b . At this stage, the surface of the driving force catching conic recess  150   f  and/or the driving force catching projection  150   d  is the drive shaft contacting portion on the cartridge side, and the tip portion  100   c   3  and/or rotational force transmitting pin  100   b  is the coupling contacting portion on the main assembly side. 
         [0126]    Referring to  FIG. 33(   c ), as the cartridge  2  is moved further into the apparatus main assembly  1 , the coupling  150  is gradually tilted back so that eventually, its axial line L 2  roughly aligns with the axial line L 3  of the drive shaft  100 . 
         [0127]    Next, referring to  FIG. 33(   d ), as the cartridge  2  becomes precisely positioned relative to the apparatus main assembly  1 , the coupling  150  becomes roughly aligned with the drive shaft  100 . That is, the axial line L 1  of the drum  20  becomes roughly aligned with the axial line L 2  of the coupling  150 . At the same time, the coupling  150  is changed in attitude from the drive shaft engaging attitude to the rotational force receiving attitude, which is also the driving force transmitting attitude. In other words, the coupling  150  becomes engaged with the drive shaft  100 . 
         [0128]    To summarize, the coupling  150  has the recess  150   f , the axial line of which coincides with the rotational axis of the coupling  150 . As the cartridge  2  is moved into the apparatus main assembly  1  in the direction which is practically perpendicular to the axial line L 1  of the drum  20 , the coupling  150  is changed in attitude from its drive shaft engaging attitude into its driving force receiving (transmitting) attitude. During this stage of the cartridge movement, the coupling  150  tilts in a manner to allow the downstream portion  150 A 1  of the coupling  150 , in terms of the direction in which the cartridge  2  is mounted into the apparatus main assembly  1 , to circumvent the drive shaft  100 . 
         [0129]    After the coupling  150  was moved into its rotational force transmitting position (attitude), the tip of the drive shaft  100  is in the recess  150   f . Further, as the drive shaft  100  is rotated, the rotational force catching portion  150   e  engages with the rotational force transmitting portion  100   b  of the drive shaft  100 , which is the end portion the drive shaft  100  projecting in the direction perpendicular to the axial line of the drive shaft  100 . Thus, as the drive shaft  100  is rotated, the coupling  150  receives the rotational force from the drive shaft  100 , and is rotated by the received rotational force. 
         [0130]    When the coupling  150  is in its drive shaft engagement starting position, the end portion  150 A 1 , which is a part of the coupling  150 , is on the drum  20  side of the drive shaft tip portion  100   c   3 , whereas when the coupling  150  is in its rotational force transmitting position (attitude), the end portion  150 A 1  is on the rotational force transmitting pin  100   b  side of the drive shaft tip portion  100   c   3 . This movement of the coupling  150  will be expressed as the “circumvention of the drive shaft by a part of the coupling”. 
         [0131]    Next, the movements the coupling  150 , which occurs when the cartridge  2  is removed from the apparatus main assembly  1  will be described.  FIGS. 34(   a )- 34 ( d ) are vertical sectional views of the driving force receiving end portion of the drum  20 , the coupling  150 , and the drive shaft  100 , as seen from below the apparatus main assembly  1 . 
         [0132]    Referring to  FIG. 34(   a ), immediately after the driving of the drum  20  is stopped, the coupling  150  is still in the driving force transmitting (receiving) position, in which it is proper in attitude for driving force transmission (reception). That is, the axial line L 2  practically coincides with the axial line L 1 . 
         [0133]    Next, referring to  FIG. 34(   b ), as the cartridge  2  is moved toward a user (in direction indicated by arrow mark X 6 ), the drum  20  moves toward the user. This movement of the drum  20  causes the recess  150   f  of the coupling  150  or projections  150   d , to come into contact with at least the tip portion  100   c   3  of the drive shaft  100 , beginning therefore to cause the coupling  150  (axial line of the coupling  150 ) to tilt in such a direction that the driving force receiving end of the coupling  150  is positioned on the downstream side of the opposite end of the coupling  150 , in terms of the cartridge removal direction X 6 . This direction in which the coupling  150  is tilted is the same as the direction in which the coupling  150  is tilted when the cartridge  2  is mounted into the apparatus main assembly  1 . 
         [0134]    Referring to  FIG. 34(   c ), as the cartridge  2  is moved further in the direction X 6 , the coupling  150  is continuously tilted until the end portion  150 A 3  of the coupling  150 , that is, the upstream end portion of the driving force receiving end of the coupling  150 , in terms of the direction X 6 , reaches the tip portion  100   c   3  of the shaft  100 . The position (attitude) of the coupling  150  when the end portion  15 A 3  reached the tip portion  100   c   3  of the shaft  100 , is the drive shaft disengaging position (attitude) of the coupling  150 . 
         [0135]    Next, referring to  FIG. 34(   d ), the coupling  150  passes by the tip portion  100   c   3  while remaining in contact therewith. The angle which the axial lines L 1  and L 2  form is different from that which they form when the cartridge  2  is mounted into the apparatus main assembly  1 . However, the manner in which the end portion  150 A 3 , that is, a part of the coupling  150 , circumvents the tip portion  100   c   3  during the removal of the cartridge  2  is the same as that during the mounting of the cartridge  2 , except for the direction. 
         [0136]    Thus, this movement of the coupling  150  will be also referred to as “circumvention of the drive shaft by a part of the coupling”. 
         [0137]    Incidentally, the position of the tip  150 A 3  is affected by the rotational phase of the coupling  150 ; the position of the tip  150 A 3  is determined by the rotational phase of the coupling  150  when the coupling  150  is stopped. That is, it may be the projection  150   d , the arcuate rib  150   g , or both that will be in contact with the tip portion  100   c   3  of the shaft  100  ( FIG. 9 ). Whether it is the projection  150   d  or the arcuate rib  150   d , the one which is farthest from the drum  20  constitutes the end portion  150 A. 
         [0138]    Thereafter, the cartridge  2  can be removed from the apparatus main assembly  1 . 
         [0139]    That is, when the cartridge  2  is moved out of the apparatus main assembly  1 , the movement of the cartridge, which is practically perpendicular to the axial line L 1  of the drum  20  causes the coupling  150  to change in attitude from the rotational force transmitting attitude to the drive shaft disengaging attitude. During this movement of the coupling  150 , the coupling  150  tilts in a manner to allow the portion  150 A 3 , which is a part of the coupling  150  and is on the rear side of the drive shaft  100  as seen from the direction opposite from the direction in which the cartridge  2  is removed, to circumvent the drive shaft  100 , thereby allowing itself to become disengaged from the drive shaft  100 . 
         [0140]    Further, the cartridge  2  is designed so that the coupling  150  is allowed to gyrate or incline in practically any direction relative to the axial line L 1  of the drum  20 . Therefore, the coupling  150  can smoothly tilt between the drive shaft engaging attitude and the rotational force transmitting attitude, and between the driving force transmitting attitude and the drive shaft disengaging attitude. Here, “gyration” of the coupling  150  does not mean that the coupling  150  itself rotates about the axial line L 1  of the drum  20 . It means that the coupling  150  gyrates or inclines as if the axial line L 2  of the tilted coupling  150  rotates about the axial line of the drum  20 . Further, it does not exclude the phenomenon that the coupling  150  itself rotationally moves about its axial line L 2  by an angle which is within the range corresponding to the amount of play or the intentionally provided gap. 
         [0141]    That is, the coupling  150  is allowed to gyrate or incline in such a manner that the end portion  150   a  of the coupling  150 , that is, the driving force receiving end portion of the coupling  150 , draws a circle, the center of which coincides with the axial line L 2 , with the end portion  150   b  of the coupling  150 , that is, the opposite end portion of the coupling  150 , remaining on the axial line of the drum  20 . 
         [0142]    Further, “practically any direction” (in which coupling  150  is capable of gyrating (tilting)) is a direction in a range in which the coupling  150  is allowed to tilt into the rotational force receiving (transmitting) position, regardless of the rotational phase of the drive shaft  100  having the rotational force transmitting portion  100   a , when a user mount the cartridge  2  into the apparatus main assembly  1 . 
         [0143]    Further, it is a direction in a range in which the coupling  150  is allowed to tilt into the aforementioned drive shaft disengaging attitude, regardless of the rotational phase of the drive shaft  100 , when a user moves the cartridge  2  out of the apparatus main assembly  1 . 
         [0144]    Further, in order to allow the coupling  150  to tilt in practically any direction relative to the axial line L 1 , a gap is provided between the pin  155  (rotational transmitting portion), and the rotational force transmitting surface  151   h  (rotational force catching surface) which engages with the pin  155 . That is, the coupling  150  is attached to the end of the drum  20  in such a manner that it is allowed to tilt as described above. Therefore, the coupling  150  is capable of tilting in practically any direction relative to the axial line L 1 . 
         [0145]    Further, according to the preferred embodiment described above, the process cartridge  2  can be mounted into, or removed from, the apparatus main assembly  1 , which is provided with the drive shaft  100 , in the direction which is practically perpendicular to the axial line L 3  of the drive shaft  100 . 
         [0146]    Also according to the preferred embodiment described above, the cartridge driving gear, with which the apparatus main assembly  1  is provided, does not need to be moved forward or backward in the direction of its axial line when the coupling  150  is mounted into, or moved out of, the apparatus main assembly  1 , by moving the process cartridge  2  in the direction which is practically perpendicular to the axial line L 3  of the drive shaft  100 . 
         [0147]    The driving force transmitting portion between the apparatus main assembly  1  and the process cartridge  2  in the above described embodiment can rotate the drum  20  more smoothly than a driving force transmitting portion in accordance with the prior art, which is made up of nothing but gears. 
       (Structure Arrangement for Positioning Coupling) 
       [0148]    Next, the structural arrangement for positioning the coupling  150  will be described.  FIGS. 19 and 20  are drawings for showing the internal structure of the photosensitive drum unit  21  (inclusive of the coupling  150 ), the drum supporting portion  51 , and the bearing  158 . The drum supporting portion  51  has a rib  200  as a drum displacement regulating first portion of the first unit  50 . The rib  200  has a tapered portion  200   a  and a tapered portion  200   b , which are on the upstream and downstream sides of the rib  200  in terms of the rotational direction of the drum  20 , respectively. The functions of the tapered portions will be described later. 
         [0000]    Incidentally, the cartridge  2  is to be mounted into, or moved out of, the apparatus main assembly  1  by a user in direction which is practically perpendicular to the lengthwise direction of the cartridge  2  (lengthwise direction of drum  20 ). 
         [0149]    The flange  151 , which is a part of the first unit  50 , has a drum displacement regulating surface  151   s  and a drum displacement regulating surface  151   t , which are on the coupling side of the flange  151  and the opposite side of the flange  151  from the coupling  151 , respectively. In this embodiment, the surface  151   s , which is a drum displacement regulating means, is one end of the flange  151 , in terms of the direction parallel to the axial line of the flange  151 , and the surface  151   t , which is also a drum displacement regulating means, is the other end of the flange  151 . 
         [0150]    Further, the bearing  158  has a surface  158   a  as the drum displacement regulating second portion of the first unit  50 . After the attachment of the photosensitive drum unit  21  to the drum supporting portion  51 , with the bearing  158  placed between the photosensitive drum unit  21  and drum supporting portion  51 , the rib  200  of the drum supporting portion  51  faces the surface  151   s  of the flange  151 , and the surface  151   t  of the flange  151  faces the surface  158   a  of the bearing  158 . 
         [0151]      FIGS. 21 ,  22 ,  23 ( a ) and  23 ( b ) are drawings for describing the cartridge positioning portions of the cartridge  2  and those of the apparatus main assembly  1 . Referring to  FIG. 21 , the bearing  158  has a groove  158   b  and a cylindrical portion  158   c . The groove  158   b  is the first cartridge positioning portion of the cartridge, and the cylindrical portion  158   c  is the second cartridge positioning portion of the cartridge. Referring to  FIGS. 23(   a ) and  23 ( b ), the guiding member  130 R of the apparatus main assembly  1  has a rib  130 Ra and a recess  130 Rb, which are the first and second cartridge positioning portions of the apparatus main assembly  1 . As the cartridge  2  is mounted into the apparatus main assembly  1 , the rib  130 Ra of the apparatus main assembly  1  fits into the groove  158   b  of the cartridge  2 , and the cylindrical portion  158   c  of the cartridge  2  fits into the recess  130 Rb of the apparatus main assembly  1 . 
         [0152]    That is, the cartridge  2  has the groove  158   b , in which the rib  130 Ra of the apparatus main assembly  1 , which is for regulating the movement of the first unit  50  in terms of the lengthwise direction of the drum  20 , when the cartridge  2  is mounted into the apparatus main assembly  1 . The groove  158   b  is a part of the first unit  50 . Further, the cartridge  2  has the cylindrical portion  158   c , which fits into the recess  130 Rb of the apparatus main assembly  1  to position the cartridge  2  relative to the apparatus main assembly  1  in terms of the radius direction of the drum  20 , when the cartridge  2  is mounted into the apparatus main assembly  1 . The cylindrical portion  158   c  is located at one of the lengthwise ends of the first unit  50 , and its axial line coincides with the axial line of the drum  20 . 
         [0153]    Referring to  FIG. 22 , the drum supporting portion  51  has a cylindrical portion  51   e , which is the cartridge positioning third portion of the cartridge  2 . Next, referring to  FIG. 23(   b ), the guiding member  130 L of the apparatus main assembly  1  has a recess  130 La, which is the cartridge positioning third portion of the apparatus main assembly  1 . The cylindrical portion  51   e  of the cartridge  2 , also fits into the recess  130 La of the apparatus main assembly  1  when the cartridge  2  is mounted into the apparatus main assembly  1 . 
         [0154]    That is, the cartridge  2  has the cylindrical portion  51   e  which fits into the recess  130 La to position the cartridge  2  relative to the apparatus main assembly  1  in terms of the radius direction of the drum  20  when the cartridge  2  is mounted into the apparatus main assembly  1 . The cylindrical portion  51   e  is a part of the opposite end of the first unit  50  from the driving force receiving end, and its axial line coincides with the axial line of the drum  20 . 
         [0155]    As described above, when the cartridge  2  is mounted into the apparatus main assembly  1 , the rib  130 Ra of the apparatus main assembly  1  fits into the groove  158   b  of the cartridge  2 , as the cartridge  2  is moved into a preset position, while leaving a small amount of a gap (play) between the two (rib  130 Ra and wall of groove  138   b ) in terms of the lengthwise direction of the drum  20 . Therefore, it is ensured that even if the two are slightly misaligned relative to each other when the cartridge  2  is moved into the preset position, the former eventually fits into the latter in the satisfactory manner. 
         [0156]    Further, the catching surface  51   f  of the cylindrical portion of the drum supporting portion  51 , shown in  FIG. 21 , engages with the catching portion of the guiding member  130 R shown in  FIGS. 23(   a ) and  23 ( b ). 
         [0157]    With the provision of the above described structural arrangement, it is ensured that the cartridge  2  is satisfactorily positioned relative to the apparatus main assembly  1 . 
         [0158]    Next, referring to  FIGS. 23(   a ) and  23 ( b ), the positional relationship between the drive shaft  100  of the apparatus main assembly  1  and the coupling  150  of the cartridge  2  will be described. 
         [0159]      FIGS. 24(   a ) and  24 ( b ) are schematic drawings of the cartridge positioning structure of the cartridge  2  and the cartridge positioning structure of the apparatus main assembly  1 .  FIG. 24(   a ) represents the case where the coupling  150  has moved toward the drive shaft  100 . As described above, the positional relationship between the bearing  158  and guide  130 R in terms of the lengthwise direction is set by the engagement of the rib  130 Ra of the guide  130 R of the apparatus main assembly  1  into the groove  158   b  of the bearing  158 . The rib  130 Ra, which fits into the groove  158   b , with the presence of a small amount of play, is on the drive shaft side of the groove  158   b . Further, the positional relationship between of the bearing  158  and flange  151  in terms of the lengthwise direction, is regulated by the contact between the surface  158   a  of the bearing  158  and the surface  151   t  of the flange  151 . When the two surfaces  158   a  and  151   t  are in contact with each other, the surface  151   s  of the flange  151  and the rib  200  of the drum supporting portion  51  are not in contact with each other; there is a small amount of gap between them. 
         [0160]      FIG. 24(   b ) shows the case in which the coupling  150  has moved away from the drive shaft  100 . That is, the position of the bearing  158  and the position of the guide  130  are determined by the fitting of the rib  130 Ra of the guide  130 R of the apparatus main assembly  1  into in the groove  150   b  of the bearing  158 . However, the rib  130 Ra, which is in the groove  158   b , is on the side opposite from the drive shaft  100 . Further, the surface  158   a  of the bearing  158  is not in contact with the surface  151   t  of the flange  151 ; there is a small amount of a gap between them. The positional relationship between the flange  151  and drum supporting portion  51  in terms of the lengthwise direction, is regulated by the contact between the surface  151   s  of the flange  151  and the rib  200  of the drum supporting portion  51 . 
         [0161]    Therefore, regardless of whether the rib  130 Ra is on the drive shaft side, or on the side opposite from the drive shaft, it is ensured that the rotational force transmitting pin  100   b  of the drive shaft  100 , and the rotational force catching portion  150   e  of the coupling  150 , maintain such a positional relationship that is necessary to transmit the driving force. 
         [0000]    (Description of Tapered Portions  200   a  and  200   b ) 
         [0162]    As described above with reference to  FIG. 24(   b ), when the photosensitive drum unit  21  is assembled as a part of the first unit  50 , the surface  151   s  of the flange  151  sometimes rubs against the rib  200  of the drum supporting portion  51 . It is possible that if the rib  200  fits into the recess  151   u  of the flange  151  as shown in  FIG. 25 , the drum  20  will fail to rotate at a constant speed, which results in the formation of an unsatisfactory image. The recess  151   u  of the flange  151  is necessary if the drum  20  and the flange  151  are joined by crimping during the manufacturing of the cartridge  2 . 
         [0163]    At this time, the meaning of “crimping” will be briefly described. In the case of this embodiment, “crimping” is a method for solidly attaching the drum  20  and flange  151  to each other by cutting and bending the end portion of the drum  20  (cut and bent portion  20   a ). It is one of the methods for solidly attaching the drum  20  and flange  151  to each other, and has long been used. Incidentally, there are cases where bonding, press-fitting, or the like is used, instead of “crimping” to attach the drum  20  and flange  151  to each other. 
         [0164]    Referring to  FIG. 26 , the drum  20  and flange  151  are held against each other, with the drum  20  pressed against the end surface  151   s  (unshown in  FIG. 26 , although shown in  FIGS. 24(   a ) and  24 ( b )). Then, the end portion of the drum  20 , which corresponds in position to the groove of the flange  151 , is cut and bent with the use of a tool  201  so that the drum  20  and flange  151  are held to each other by the bent portion of the drum  20 . This is why the end surface  151   s  ( FIG. 25)  of the flange  151  is provided with the recesses  151   u , which function as a clearance recess. 
         [0165]    In this embodiment, the photosensitive drum unit  21  is made by fastening the drum  20  and flange  151  to each other by crimping. 
         [0166]    Next, the relationship between the recess  151   u  and rib  200  will be described. Referring to  FIGS. 27(   a ) and  27 ( b ), the rib  200  extends in a manner to contact a part of the peripheral surface of the flange  151 . The flange  151  receives the rotational force (rotational driving force) from the apparatus main assembly  1 , and rotates in the direction indicated by an arrow mark. Thus, it is possible that as the flange  151  rotates, the rib  200  will hang up in the recess  151   u  at two locations, that is, the location where the rib  200  begins to fit into the recess  151   u  (state shown in  FIG. 27(   a )), and the location where the rib  200  begins to come out of the recess  151   u  (state shown in  FIG. 27(   b )). If the rib  200  hangs up in the recess  151   u  as described above, the drum  20  becomes unstable in rotational speed. In this embodiment, the flange  151  has two recesses  151   u . Therefore, there are four opportunities per rotation of the flange  151  that the rib  200  will hang up. 
         [0167]    Thus, the upstream and downstream edges of the rib  200  in terms of the rotational direction of the flange  151  are beveled to create tapered portions  200   a  and  200   b  to make it unlikely for the rib  200  to hang up in the recesses  151   u . That is, the upstream and downstream edges of the rib  200  in terms of the rotational direction of the flange  151  have the slanted surfaces  200   b  and  200   a , respectively, created by beveling the two edges, as shown in  FIG. 19 . The hatched areas in  FIGS. 27(   a ) and  27 ( b ) correspond to the beveled edges (tapered portions  200   a  and  200   b ) of the rib  200 . The provision of these tapered portions  200   a  and  200   b  made it possible to reduce the frequency with which an unsatisfactory image attributable to unstable rotation of the drum  20  is produced. 
         [0168]    Thus, the cartridge  2  is highly precisely positioned relative to the apparatus main assembly  1 , as described above. In other words, the above described structural arrangement made it unnecessary to structure the apparatus main assembly  1  so that the abovementioned rotational member of the apparatus main assembly could be moved in the direction parallel to the axial line of the rotational member, and also, made it possible to reduce in size an image forming apparatus, and a process cartridge therefor, compared to an image forming apparatus in accordance with the prior art, and a process cartridge therefor, respectively. 
         [0169]    Further, the above described embodiment of the present invention makes it possible to improve an image forming apparatus in terms of the accuracy with which an electrophotographic photosensitive drum is rotatable, compared to an image forming apparatus, in which the rotational force is transmitted from the apparatus main assembly to the process cartridge therein, through the meshing of the gear of the apparatus main assembly, and the gear of the process cartridge. 
         [0170]    Incidentally, according to the present invention, the clattering, vibrations, etc., which occur when the cartridge  2  is mounted into the apparatus main assembly  1  can be reduced, and also, it is possible to reduce in size the main assembly of an image forming apparatus, and a process cartridge therefor, compared to the counterparts in accordance with the prior art. 
         [0171]    The following is the summary of the above given description of the structure of the process cartridge  2 . 
         [0172]    (1) The process cartridge  2  is removably mountable in the main assembly of an electrophotographic image forming apparatus having the rotational force transmitting portion  100   a . The process cartridge  2  has: the electrophotographic photosensitive drum  20 ; the development roller  41  for developing an electrostatic latent image formed on the electrophotographic photosensitive drum  20 ; and the first unit  50  which supports the electrophotographic photosensitive drum  20 . The cartridge  2  also has the second unit  40  which supports the development roller  41  and is connected to the first unit  50  so that it is movable relative to the first unit  50  in an oscillatory manner. Further, the cartridge  2  has the coupling  150  by which the cartridge  2  receives the rotational force for rotating the electrophotographic photosensitive drum  20 , from the apparatus main assembly  1 , when the cartridge  2  is in the preset image forming position in the apparatus main assembly  1 . The coupling  150  is attached to one of the lengthwise ends of the electrophotographic photosensitive drum  20 . The cartridge  2  also has the cartridge positioning first portion  158   b , which engages with the cartridge positioning first portion  130 Ra of the apparatus main assembly  1 . The cartridge positioning first portion  158   b  of the cartridge  2  regulates the movement of the first unit  50  in terms of the lengthwise direction of the electrophotographic photosensitive drum, when the cartridge  2  is in the apparatus main assembly  1 . Further, the cartridge  2  has the cartridge positioning second portion  158   c , which engages with the cartridge positioning second portion  130 Rb of the apparatus main assembly  1 . This cartridge positioning second portion of the  158   c  of the cartridge  2  positions the electrophotographic photosensitive drum relative of the apparatus main assembly  1  in terms of the radial direction of the electrophotographic photosensitive drum  20 , when the cartridge  2  is in the apparatus main assembly  1 . The cartridge positioning second portion  158   c  of the cartridge  2  is attached to one of the lengthwise ends of the first unit  50 , and its axial line coincides with the axial line of the electrophotographic photosensitive drum  20 . Further, the cartridge  2  has the cartridge positioning third portion  51   e , which engages with the cartridge positioning third portion  130 La of the apparatus main assembly  1 . The cartridge positioning third portion  51   e  of the cartridge  2  positions the electrophotographic photosensitive drum  20  relative to the apparatus main assembly  1 , in terms of the radial direction of the photosensitive drum  20 , when the cartridge  2  is in the apparatus main assembly  1 . The cartridge positioning third portion  51   e  of the cartridge  2  is attached to the other lengthwise end of the first unit  50 , and its axial line coincides with that of the electrophotographic photosensitive drum  20 . Moreover, the cartridge  2  has the drum displacement first portion  200 , which is a part of the first unit  50  of the cartridge  2 , and regulates the displacement of the electrophotographic photosensitive drum  20  in terms of the lengthwise direction of the first unit  50 . The photosensitive drum unit  21  has the drum displacement regulating first portion  151   s  for regulating the displacement of the electrophotographic photosensitive drum  20  in terms of the lengthwise direction of the first unit  50 . The first regulating portion  151   s  regulates the abovementioned displacement of the electrophotographic photosensitive drum  20  by coming into contact with the first regulating portion  200  of the first unit  50 . 
         [0173]    With the provision of the above described structural arrangement, the coupling  150  of the process cartridge  2 , which receives the rotational force from the apparatus main assembly  1 , and the rotational force transmitting portion  100   b  of the apparatus main assembly  1 , can be precisely positioned relative to each other in terms of the direction parallel to the axial line of the rotational force transmitting portion  100   b . Further, the drum  20  can be precisely positioned relative to the apparatus main assembly  1  in terms of the direction parallel to its axial line. 
         [0174]    (2) The first regulating portion  151   s  of the flange  151  regulates the displacement of the electrophotographic photosensitive drum  20  toward the opposite end of the first unit  50  (cartridge  2 ) from the driving force receiving end. Further, the flange  151  has the second regulating portion  151   t , which regulates the displacement of the electrophotographic photosensitive drum  20  toward the driving force receiving end of the first unit  50 . The drum flange  151  is attached to the electrophotographic photosensitive drum  20  in such as manner that the second regulating portion  151   t  of the flange  151  regulates the abovementioned displacement of the electrophotographic photosensitive drum  20  by coming into contact with the second regulating portion  158   a  of the first unit  50 . 
         [0175]    With the provision of the above described structural arrangement, it is possible to regulate the displacement of the photosensitive drum  20  in the direction parallel to its axial line. Therefore, it is possible to ensure that the drum  20  is precisely position, and remains precisely positioned, relative to the apparatus main assembly  1  in terms of the direction parallel to the axial line of the drum  20 , and also, that the coupling  150  is precisely positioned, and remains precisely positioned, relative to the apparatus main assembly  1  in terms of the direction parallel to the axial line of the coupling  150 . 
         [0176]    (3) The electrophotographic photosensitive drum  20  is provided with the drum flange  151 , which is attached one of the lengthwise ends of the electrophotographic photosensitive drum  20 . The above described coupling  150  is attached to the drum flange  151  in such a manner that it is allowed to tilt relative to the drum flange  151 . Further, the bearing  158  for rotatably supporting the shaft portion of the drum flange  151  is attached to the drum supporting portion  51 . The abovementioned first positioning portion  158   b  of the cartridge  20  is a part of the bearing  158 , and so is the second regulating portion of the first unit  50 . Further, the drum displacement regulating first portion  151   s  is an integral part of the drum flange  151 , and so is the drum regulating second portion  151   t.    
         [0177]    With the provision of the above described structural arrangement, it is possible to precisely position the coupling  150  of the cartridge  2 , which receives a rotational force from the apparatus main assembly  1 , and the rotational force transmitting portion  100   a  of the apparatus main assembly  1 , relative to each other in terms of the direction parallel to the axial line of the rotational force transmitting portion  100   a.    
         [0178]    (4) The drum flange  151  has the gear  151   c , which transmits the rotational force which the coupling  150  received from the apparatus main assembly  1 , to the development roller  41 . 
         [0179]    With the employment of the above described structural arrangement, it is possible to integrate multiple components into a single components, and therefore, it is possible to reduce in cost an electrophotographic image forming apparatus. Further, the employment of the above described structural arrangement makes it possible to reduce in width the gears, and therefore, it is possible to provide an electrophotographic image forming apparatus which is significantly smaller in size than an electrophotographic image forming apparatus in accordance with the prior art. 
         [0180]    (5) The coupling  150  receives the rotational force for rotating the electrophotographic photosensitive drum  20 , by engaging with the rotational force transmitting portion  100   b  of the drive shaft  100  of the apparatus main assembly  1 . Further, the coupling  150  can change in attitude into the drive force transmitting (receiving) attitude in which it can transmit the driving force for rotating the electrophotographic photosensitive drum  20 , to the electrophotographic photosensitive drum  20 . The coupling  150  can also change in attitude to assume the drive shaft engaging attitude in which it tilts relative to the axial line of the electrophotographic photosensitive drum  20  in such a direction that the driving force receiving end of the coupling  150  is positioned on the downstream side of the opposite end of the coupling  150 , in terms of the cartridge mounting direction, and also, the drive shaft disengaging attitude in which the driving force receiving end of the coupling  150  is positioned on the downstream side of the opposite end of the coupling  150 , in terms of the cartridge removal direction. When a user inserts the process cartridge  2  into the apparatus main assembly  1 , in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 , in order to mount the cartridge  2  in the apparatus main assembly  1 , the coupling  150  is changed in attitude from the drive shaft engagement starting attitude into the rotational force transmitting attitude, in which the coupling  150  faces the drive shaft  100 . Further, when the cartridge  2  is moved out of the apparatus main assembly  1  in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 , the coupling  150  is changed in attitude from the rotational force transmitting attitude into the drive shaft disengagement starting position, thereby disengaging from the drive shaft  100 . 
         [0181]    The above described structural arrangement makes it possible to provide a process cartridge which can be mounted into the main assembly of an image forming apparatus, which does not have the mechanism for moving the rotational member, as the rotational force transmitting portion, of the apparatus main assembly, which is for transmitting a rotational force to the electrophotographic photosensitive drum  20 , in the direction parallel to the axial line of the rotational member, by utilizing the opening or closing movement of the cover (door) of the apparatus main assembly  1 . 
         [0182]    (6) The coupling  150  has the recess  150   f , the axial line of which coincides with the axial line of the coupling  150 . As the process cartridge  2  is mounted into the apparatus main assembly  1  in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 , the coupling  150  is changed in attitude from the drive shaft engagement starting attitude into the rotational force transmitting attitude. As the coupling  150  is changed in attitude, it tilts in a manner to allow its downstream portion, in terms of the direction in which the process cartridge  2  is mounted into the apparatus main assembly  1 , to circumvent the drive shaft  100 . Then, as the coupling  150  is moved into the drive shaft engagement starting attitude, it covers the tip of the drive shaft  100  in a manner to embracing the tip of the drive shaft  100  with its recess  151   e . Then, as the drive shaft  100  is rotated by the rotational force transmitted thereto, the rotational force catching portion  150   e  engages with the rotational force transmitting portion  100   b , which projects from the end portion of the drive shaft  100  in the direction perpendicular to the axial line of the drive shaft  100 . Thus, as the drive shaft  100  is rotated, the coupling  150  receives the rotational force from the drive shaft  100 , and is rotated by the rotational force it received from the drive shaft  100 . When it is necessary to move the process cartridge  2  from the apparatus main assembly  1 , a user (operator) is to pull the process cartridge  2  in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 . As the process cartridge  2  is pulled, the coupling  150  tilts in such a manner that its attitude changes from the rotational force transmitting attitude to the drive shaft disengaging attitude. That is, it tilts in such a manner to allow its portion, which is behind the drive shaft  100 , as seen from the direction opposite from the direction in which the process cartridge  2  is moved out of the apparatus main assembly  1 , to circumvent the drive shaft  100 , enabling thereby the coupling  150  to separate from the drive shaft  100 . 
         [0183]    The above described structural arrangement makes it possible to provide a process cartridge which can be mounted into the main assembly of an electrophotographic image forming apparatus which does not have the mechanism for moving the rotational member of the apparatus main assembly  1 , that is, the rotational force transmitting portion of the apparatus main assembly  1 , in the direction parallel to the axial line of the rotational member. 
         [0184]    (7) The first regulating portion  200  of the first unit  50  has the tapered portions  200   a  and  200   b , which correspond in position to the downstream and upstream sides of the first regulating portion  200  of the first unit  50  in terms of the rotational direction of the drum flange  151 . 
         [0185]    This structural arrangement made it possible to provide a process cartridge, the electrophotographic photosensitive drum of which is significantly less irregular in rotational speed, that is, significantly higher in the accuracy in rotational speed, than that of a process cartridge in accordance with the prior art. 
         [0186]    (8) The process cartridge  2  is removably mountable in the main assembly  1  of an electrophotographic image forming apparatus having the rotational force transmitting portion  100   a . It also has the electrophotographic photosensitive drum  20 , and the drum flange  151 , which is attached to one of the lengthwise ends of the electrophotographic photosensitive drum  20 , and has the gear  151   c  and drum shaft  151   v . It also has the coupling  150  which receives the rotational force for rotating the electrophotographic photosensitive drum  20 , from the rotational force transmitting portion  100   a , while it is in its proper position for image formation, in the apparatus main assembly  1 . This coupling  150  is attached to the drum flange  151 . Further, the cartridge  2  has the development roller  41 , which is for developing the electrostatic latent image formed on the electrophotographic photosensitive drum  20 , and which rotates by receiving the rotational force which the coupling  150  received from the apparatus main assembly  1 . Further, the process cartridge  2  has: the first frame unit  50 , which supports one of the lengthwise ends of the electrophotographic photosensitive drum  20 , with the presence of the bearing  153 , which supports the corresponding end of the drum shaft  151   v , between the first frame unit  153  and the lengthwise end of the drum shaft  151   v ; and the second frame unit  40 , which supports the development roller  41 , and which is connected to the first frame unit  50  in such a manner that it is allowed to move relative to the first frame unit  50  in an oscillatory manner. Further, the process cartridge  20  has the cartridge positioning first portion  158   b , which is an integral part of the bearing  158  and positions the process cartridge  2  relative to the apparatus main assembly  1  by engaging with the cartridge positioning first portion  130 Ra of the apparatus main assembly  1 . This structural arrangement regulates the movement of the first frame unit  50  in terms of the direction parallel to the lengthwise direction of the electrophotographic photosensitive drum  20  while the process cartridge  2  is in its image forming position in the apparatus main assembly  1 . The process cartridge  20  also has the cartridge positioning second portion  158   c  which positions the electrophotographic photosensitive drum  20  relative to the apparatus main assembly  1  in terms of the radial direction of the electrophotographic photosensitive drum  20 , by engaging with the cartridge positioning second portion  130 Rb of the apparatus main assembly  1 , when the process cartridge  2  is mounted into the apparatus main assembly  1 . The axial line of the cartridge positioning second portion  158   c  coincides with the axial line of the electrophotographic photosensitive drum  20 . The process cartridge  2  also has the cartridge positioning third portion  51   e , which is at the opposite end of the first unit  50  from the driving force receiving end, and which positions the electrophotographic photosensitive drum  20  relative to the apparatus main assembly  1  in terms of the radial direction of the electrophotographic photosensitive drum  20 , by engaging with the cartridge positioning third portion  130 La of the apparatus main assembly  1  at about the same time as the process cartridge  2  is moved into its image forming portion in the apparatus main assembly  1 . The axial line of the cartridge positioning third portion  51   e  of the process cartridge  2  coincides with the axial line of the electrophotographic photosensitive drum  20 . Further, the process cartridge  2  has the drum displacement regulating first portion  200 , which is a part of the first unit  50 , which is located close to the driving force receiving end of the first unit  50  to regulate the displacement of the electrophotographic photosensitive drum  20  toward the opposite side from the driving force receiving side, in terms of the lengthwise direction of the first unit  50 . Further, the process cartridge  2  has the drum displacement regulating second portion  158   a  for regulating the displacement of the electrophotographic photosensitive drum  20  toward the driving force receiving end of the first unit  50  in terms of the lengthwise direction of the first unit  50 . The drum displacement regulating second portion  158   a  is an integral part of the bearing  158 . Further, the process cartridge  2  has the drum displacement regulating portion  151   t  which is placed in contact with the drum displacement regulating second portion of the first unit  50  to regulate the drum displacement toward the opposite side from the driving force receiving end of the first unit  50  in terms of the lengthwise direction of the first unit  50 . The drum displacement regulating second portion  151   t  is an integral part of the drum flange  151 . 
         [0187]    The described structural arrangement makes it possible to more precisely position the coupling  150  of the process cartridge  2 , which receives a driving force from the apparatus main assembly  1 , and the rotational force transmitting portion  100   a  of the apparatus main assembly  1 , relative to each other in terms of the axial line of the rotational force transmitting portion  100   a , than the structural arrangement in accordance with the prior art. 
         [0188]    (9) The first drum displacement regulating portion  151   s  is a part of one end of the drum flange  151 , and the second drum displacement regulating portion  151   t  is a part of the other end of the drum flange  151  in terms of the direction parallel to the axial line of the drum flange  151 . 
         [0189]    This structural arrangement makes component integration possible for cost reduction. It also makes it possible to reduce the gear  151   c  in tooth width, making is possible to provide an electrophotographic image forming apparatus which is significantly smaller in size than a comparable apparatus in accordance with the prior art. 
         [0190]    (10) The downstream and upstream edges of the drum displacement regulating portion  200  of the first frame unit  50 , in terms of the rotational direction of the drum flange  151 , are beveled, thereby providing the tapered portions  200   a  and  200   b.    
         [0191]    This structural arrangement makes it possible to reduce the electrophotographic photosensitive drum  20  in the irregularity in the rotational speed, making it possible to provide an electrostatic image forming apparatus which was significantly more accurate in rotational speed of the photosensitive drum  20  than a comparable apparatus in accordance with the prior art. 
         [0192]    (11) The electrophotographic image forming apparatus structured so that the process cartridge  2  is removably mountable in its main assembly has: i) cartridge positioning first portion  130 Ra; ii) cartridge positioning second portion  130 Rb; iii) cartridge positioning third portion  130 La; and iv) rotational force transmitting portion  100   a ; v) the process cartridge structured as described below. The image forming apparatus employs the process cartridge  2  structured as follow: The process cartridge  2  has the electrophotographic photosensitive drum  20 , and the development roller  41  for developing the electrostatic latent image formed on the electrophotographic photosensitive drum  20 . The process cartridge  2  also has the first frame unit  50  which supports the electrophotographic photosensitive drum  20 , and the second frame unit  40  which supports the development roller  41  and is connected to the first frame unit  50  so that it is allowed to move relative to the first frame unit  50  in an oscillatory manner. The process cartridge  2  also has the coupling  150  for receiving the rotational force for rotating the electrophotographic photosensitive drum  20 , from the rotational force transmitting portion  100   a , when the process cartridge  2  is in its image forming position in the apparatus main assembly  1 . The coupling  150  is attached to one of the lengthwise ends of the electrophotographic photosensitive drum  20 . The process cartridge  2  has the cartridge positioning first portion  158   b , which engages with the cartridge positioning first portion of the apparatus main assembly  1  to regulate the displacement of the first unit  50  in terms of the lengthwise direction of the electrophotographic photosensitive drum  20 , virtually at the same time as the process cartridge  2  is moved into its image forming position in the apparatus main assembly  1 . Further, the process cartridge  2  has the cartridge positioning second portion  158   c , which engages with the cartridge positioning second portion of the apparatus main assembly  1  to precisely position the electrophotographic photosensitive drum  20  relative to the apparatus main assembly  1  in terms of the radial direction of the electrophotographic photosensitive drum  20 , virtually at the same time as the process cartridge  2  is moved into its image forming position in the apparatus main assembly  1 . The cartridge positioning second portion  158   c  is located at one of the lengthwise end of the first unit  50 , and its axial line coincides with that of the electrophotographic photosensitive drum  20 . The process cartridge  2  has the drum positioning third portion  51   e  which engages with the drum positioning third portion of the apparatus main assembly  1  to precisely position the electrophotographic photosensitive drum  20  relative to the apparatus main assembly  1 , in terms of the radial direction of the electrophotographic photosensitive drum  20 , virtually at the same time as the process cartridge  2  is moved into its image forming position in the apparatus main assembly  1 . The drum positioning third portion  51   e  is attached to the other lengthwise end of the first unit  50 , and its axial line coincides with that of the electrophotographic photosensitive drum  20 . Further, the process cartridge  2  has the drum displacement regulating first portion  200  for regulating the displacement of the electrophotographic photosensitive drum  20  in the direction parallel to the lengthwise direction of the first unit  50 . The drum displacement regulating first portion  200  is an integral part of the first unit  50 . The process cartridge  2  has the drum displacement regulating first portion  151   s , with which the drum flange  151  is provided to regulate the drum displacement in the direction parallel to the lengthwise direction of the first unit  50 , by coming into contact with the drum displacement regulating portion of the first unit  50 . 
         [0193]    The above described structural arrangement makes it possible to provide an electrophotographic image forming apparatus in which a process cartridge capable of precisely positioning its coupling  151  for receiving the rotational force from the apparatus main assembly  1 , relative to the rotational force transmitting portion of the apparatus main assembly  1 , in terms of the direction parallel to the axial line of the rotational force transmitting portion, can be removably mounted. 
         [0194]    (12) The drum displacement regulating first portion  151   s  of the drum flange  151  is the portion of the drum flange  151 , which is for regulating the displacement of the electrophotographic photosensitive drum  20  toward the lengthwise end of the first unit  50 , which is opposite from the rotational force input end of the first unit  50 . Further, the bearing  158  is provided with the drum displacement regulating second portion  158   a , and the drum flange  151  is provided with drum displacement regulating second portion  151   t , which regulates the displacement of the electrophotographic photosensitive drum  20  toward the opposite lengthwise end of the first unit  50  from the rotational force input end, by engaging with the drum displacement regulating second portion  158   a  of the first unit  50 . 
         [0195]    This structural arrangement makes it possible to prevent the displacement of the drum  20  in the direction parallel to the axial line of the drum  20 , making it possible to ensure that the drum  20  is precisely position relative the apparatus main assembly  1  in terms of the direction parallel to the axial line of the drum  20 . 
         [0196]    (13) The drum unit  21  is provided with the drum flange  151 , which is attached to one of the lengthwise end of the electrophotographic photosensitive drum  20 . To the drum flange  151 , the coupling  150  is attached in such a manner that not only is the coupling  150  allowed to tilt relative to the axial line of the latter, but also, it is allowed to move relative to the drum flange  151  in terms of the direction parallel to the axial line of the drum flange  151 . Further, the photosensitive drum unit  21  is provided with the bearing  158  for rotatably supporting the drum flange  151 . The bearing  158  is attached to the drum supporting portion  51  of the frame of the first unit  50 . The drum positioning first portion  158   b  of the cartridge  2 , and the drum positioning second portion  158   a  of the cartridge  2 , are integral parts of the bearing  158 . Further, the drum displacement regulating first portion  151   s  and the drum displacement regulating second portion  151   t  are integral parts of the drum flange  151 . 
         [0197]    This structural arrangement can precisely position the coupling  150  of the process cartridge  2 , which is for receiving the rotational force from the apparatus main assembly  1 , relative to the rotational force transmitting portion of the apparatus main assembly  1  in terms of the direction parallel to the rotational force transmitting portion, at an even higher level of precision. 
         [0198]    (14) The drum flange  151  has the gear  151   c , which transmits to the development roller  41  the rotational force which the coupling  150  received from the apparatus main assembly  1 . 
         [0199]    This structural arrangement makes component integration possible for cost reduction. It also makes it possible to reduce the gear in tooth width, making it thereby possible to provide an electrophotographic image forming apparatus which is significantly smaller in size than a comparable image forming apparatus in accordance with the prior art. 
         [0200]    (15) The coupling  150  is the component for receiving the rotational force for rotating the electrophotographic photosensitive drum  20 , by engaging with the rotational force transmitting portion  100   b  which the drive shaft  100  of the apparatus main assembly  1  is provided. The coupling  150  is enabled to change in attitude to assume the rotational force transmitting attitude, the drive shaft engaging attitude, in which the axial line of the coupling  150  is tilted relative to the axial line of the electrophotographic photosensitive drum  20  in such a manner that the rotational force receiving end of the coupling  150  is offset from the axial line of the electrophotographic photosensitive drum  20 , and the drive shaft disengaging attitude, in which the axial line of the  150  is also tilted relative to the axial line of the electrophotographic photosensitive drum  20  in such a manner that the rotational force receiving end of the coupling  150  is offset from the axial line of the electrophotographic photosensitive drum  20 . When the process cartridge  2  is mounted into the apparatus main assembly  1  by being moved in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 , the coupling  150  is changed in attitude from the drive shaft engaging attitude into the rotational force transmitting attitude, whereby it is made to squarely face the drive shaft  100 . When the process cartridge  2  is moved out of the apparatus main assembly  1  in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 , the coupling  150  is changed in attitude from the rotational force transmitting attitude into the drive shaft disengaging attitude, whereby the coupling  150  is allowed to disengage from the drive shaft  100 . 
         [0201]    This structural arrangement makes it possible to provide an electrophotographic image forming apparatus describable as follows: an electrophotographic image forming apparatus, the main assembly of which has no mechanism for moving its rotational force transmitting rotational member, in the direction parallel to the axial line of the rotational member, and in which a process cartridge is removably mountable by the utilization of the opening or closing movement of the cover (door) of the apparatus main assembly. 
         [0202]    (16) The coupling  150  has the recess  150   f , the axial line of which coincides with that of the coupling  150 . As the process cartridge  2  is moved in the direction X 5 , which is perpendicular to the axial line L 1  of the electrophotographic photosensitive drum  20  to be mounted into the apparatus main assembly  1 , the coupling  150  is changed in attitude from the drive shaft engaging attitude into the rotational force transmitting attitude. During this movement of the process cartridge  2 , the coupling  150  tilts in such a manner that the downstream portion  150 A 1  of the coupling  150 , in terms of the direction in which the process cartridge  2  is mounted into the apparatus main assembly  1 , is allowed to circumvent the drive shaft  100 . When the coupling  150  is in the rotational force transmitting position (attitude), the tip portion  100   c   3  is covered with the coupling  150 ; the tip portion  100   c   3  is in the recess  150   f  of the coupling  150 . Further, the coupling  150  has the rotational force catching portions  150   e , which project from the driving force receiving end of the coupling  150  in the direction perpendicular to the axial line of coupling  150 . As the drive shaft  100  rotates, the driving force catching portions  150   e  engage with the rotational force transmitting portions  100   b , one for one, which project from the driving force transmitting end of the drive shaft  100  in the direction perpendicular to the axial line of the drive shaft  100 , and therefore, the coupling  150  rotates by receiving the rotational force from the drive shaft  100 . When it is necessary to move the process cartridge  2  out of the apparatus main assembly  1 , the process cartridge  2  is to be moved in the direction perpendicular to the axial line of the electrophotographic photosensitive drum  20 . As the process cartridge  2  is moved, the coupling  150  is changed in attitude (tilted) from the rotational force transmitting attitude into the drive shaft disengaging attitude, and is disengaged from the drive shaft  100 . During this movement of the process cartridge  2 , the coupling  150  tilts in such a manner that a part of the rear portion of the coupling  150 , as seen from the direction opposite to the direction in which the process cartridge  2  is removed from the apparatus main assembly  1 , is allowed to circumvent the drive shaft  100 . 
         [0203]    This structural arrangement makes it possible to provide an electrophotographic image forming apparatus describable as follows: an electrophotographic image forming apparatus, the main assembly of which has no mechanism for moving its rotational force transmitting rotational member, in the direction parallel to the axial line of the rotational member, and in which a process cartridge is removably mountable by the utilization of the opening or closing movement of the cover (door) of the apparatus main assembly. 
         [0204]    (17) The downstream and upstream ends of the drum displacement regulating portion  200  of the first unit  50 , in terms of the rotational direction of the drum flange  151 , has the tapered portions  200   a  and  200   b.    
         [0205]    This structural feature can reduce the irregularity in the rotational speed of the electrophotographic photosensitive drum  20 , making it possible to provide a process cartridge  2  (electrophotographic image forming apparatus), the photosensitive drum  20  of which is significantly higher in the level of precision with which it rotates, than a comparable photosensitive drum in accordance with the prior art. 
         [0206]    (18) The electrophotographic image forming apparatus employing the process cartridge  2  removably mountable in its main assembly has: i) the cartridge positioning portion  130 Ra; ii) the cartridge positioning second portion  130 Rb; the cartridge positioning third portion  130 La; and the rotational force transmitting portion  100   a ; and v) the process cartridge  2  structured as described below. The process cartridge  2  has the drum flange  151  having the gear  151   c  and drum shaft portion  151   v . The drum flange  151  is attached to the drive force receiving end of the electrophotographic photosensitive drum  20 . The process cartridge  2  also has the coupling  150  attached to the drum flange  151  to receive the rotational force for rotating the electrophotographic photosensitive drum  20  from the rotational force transmitting portion  100   a , when the process cartridge  2  is in its image forming position in the apparatus main assembly  1 . The process cartridge  2  also has the development roller  41 , which is for developing the electrostatic latent image formed on the electrophotographic photosensitive drum  20 , and which rotates by receiving the rotational force which the coupling  150  received from the apparatus main assembly  1 . Further, the process cartridge  2  has: the first frame unit  50 , which supports the drum shaft portion  151   v  of the drum flange  151  attached to the driving force receiving end of the electrophotographic photosensitive drum  20 , with the presence of the bearing  158  between the drum shaft portion  151   v  and the first unit  50 , and also, supports the opposite end of the electrophotographic photosensitive drum  20  from the driving force receiving end, by the drum shaft  202 . 
         [0207]    The process cartridge  2  has the second frame unit  40 , which supports the development roller  41 . The second frame unit  40  is connected to the first frame unit  50  in such a manner that it is allowed to move relative to the first frame unit  50  in an oscillatory manner. Further, the process cartridge  2  has the cartridge positioning first portion  158   b , which is an integral part of the bearing  158 . The cartridge positioning first portion  158   b  precisely positions the process cartridge  2  relative to the apparatus main assembly  1  by engaging with the cartridge positioning first portion  130 Ra of the apparatus main assembly  1 . This structural arrangement regulates the displacement of the first frame unit  50  in terms of the direction parallel to the lengthwise direction of the electrophotographic photosensitive drum  20  while the process cartridge  2  is in its image forming position in the apparatus main assembly  1 . The process cartridge  2  has the cartridge positioning second portion  158   c , which engages with the cartridge positioning second portion  130 Rb of the apparatus main assembly  1 . The cartridge positioning second portion  158   c  is an integral part of the bearing  158  located at the driving force receiving end of the first unit  50 , and its axial line coincides with that of the electrophotographic photosensitive drum  20 . This structural arrangement keeps the process cartridge  2  precisely positioned relative to the apparatus main assembly  1  in terms of the direction parallel to the radius direction of the electrophotographic photosensitive drum  20 , while the process cartridge  2  is in its image forming position in the apparatus main assembly  1 . Further, the process cartridge  2  has the cartridge positioning third portion  51   e , which engages with the cartridge positioning third portion  130 La of the apparatus main assembly  1 . The cartridge positioning third portion  51   e  is an integral part of the drum supporting portion  51  of the opposite end of the first unit  50  from the driving force receiving end, and its axial line coincides with that of the electrophotographic photosensitive drum  20 . This structural arrangement keeps the process cartridge  2  precisely positioned relative to the apparatus main assembly  1  in terms of the direction parallel to the radius direction of the electrophotographic photosensitive drum  20 , after the mounting of the process cartridge  2  into the apparatus main assembly  1 . Further, the process cartridge  2  has the drum displacement regulating first portion  200  for regulating the drum displacement toward the opposite end of the first unit  50  (process cartridge  2 ) from the driving force receiving end. The drum displacement regulating first portion  200  is an integral part of the driving force receiving end of the first unit  50 . The process cartridge  2  also has the drum displacement regulating second portion  158   a  for regulating the drum displacement toward the driving force receiving end of the first unit  50  (process cartridge  2 ). The drum displacement regulating portion  158   a  is an integral part of the bearing  158 . Further, the process cartridge  2  has the drum displacement regulating portion  151   s  for regulating the drum displacement toward the opposite end of the first unit  50  (process cartridge  2 ). The drum displacement regulating first portion  151   s  is an integral part of the drum flange  151 . The process cartridge  2  has the drum displacement regulating second portion  151   t  for regulating the drum displacement toward the drive force receiving end of the first unit  50  by coming into contact with the drum displacement regulating second portion  158   a  of the bearing  158 . The drum displacement regulating second portion  151   t  is an integral part of the drum flange  151 . 
         [0208]    These structural arrangements make it possible to provide an electrophotographic image forming apparatus in which a process cartridge capable of precisely positioning its coupling  150  for receiving rotational force from the main assembly  1  of the image forming apparatus, relative to the rotational force transmitting portion of the apparatus main assembly  1 , in terms of the direction parallel to the axial line of the rotational member, is removably mountable. 
         [0209]    The drum displacement regulating first portion  151   s  is one of the end portions of the drum flange  151 , in terms of the direction parallel to the axial line of the drum flange  151 , and the drum displacement regulating second portion  151   t  on the drum side is the other end portion of the drum flange  151 . 
         [0210]    This structural arrangement makes it possible to reduce a process cartridge (electrophotographic image forming apparatus) in cost by component integration. It also makes it possible to reduce the gear  151   c  in tooth width, making it possible to reduce a process cartridge (image forming apparatus) in size. 
         [0211]    (20) The drum displacement regulating first portion  200  on the first unit  50  has the tapered portions  200   a  and  200   b , which are at the upstream and downstream ends of the regulating portion  200  in terms of the rotational direction of the drum flange  151 . 
         [0212]    The structural arrangement can reduce the electrophotographic photosensitive drum  20  in the irregularity in rotational speed, and therefore, can improve the electrophotographic photosensitive drum  20  in the level of precision at which it rotates. 
         [0213]    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. 
         [0214]    This application claims priority from Japanese Patent Application No. 161529/2008 filed Jun. 20, 2008 which is hereby incorporated by reference.