Abstract:
A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The process cartridge includes an electrophotographic photosensitive drum, a drum unit containing the electrophotographic photosensitive drum, a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum, and a developing unit swingably supported by the drum unit and containing the developing roller. The process cartridge also includes an urging member for urging the drum unit and the developing unit to each other so as to press the developing roller against the electrophotographic photosensitive drum. A space keeping member keeps space between the electrophotographic photosensitive drum and the developing roller by engaging with the developing unit and limiting swing of the developing unit against an urging force of the urging member.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus (for example, electrophotographic copying machine, electrophotographic printer and so on), a developing apparatus, and a process cartridge which is removably mountable in the main assembly of an image forming apparatus. 
     Here, an electrophotographic image forming apparatus means an apparatus which forms an image on recording medium with the use of an electrophotographic image forming method. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for example, laser beam printer, LED printer, etc.), a facsimile apparatus, a word processor, etc. 
     A process cartridge means a cartridge in which an electrophotographic photosensitive drum and one or more processing apparatuses, that is, a charging means, a developing means, and a cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. More specifically, a process cartridge means a cartridge in which an electrophotographic photosensitive drum, a charging means, and a developing means or cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. It also means a cartridge in which an electrophotographic photosensitive drum, and at least one among a charging means, a developing means, and a cleaning means, are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. Further, it also means a cartridge in which an electrophotographic photosensitive drum and a developing means are integrally disposed, and which is removably mountable in the main assembly of an image forming apparatus. 
     In the field of an electrophotographic image forming apparatus which uses an electrophotographic image formation process, it has been common practice to employ a process cartridge system, which integrally disposes an electrophotographic photosensitive drum and one or more means for processing the electrophotographic photosensitive drum in a cartridge so that they can be removably mountable in the main assembly of an image forming apparatus. A process cartridge system enables a user to maintain an electrophotographic image forming apparatus by himself or herself, that is, without relying on a service person. Thus, it can drastically improve an electrophotographic image forming apparatus in operational efficiency. Therefore, a process cartridge system is widely in used in the field of an electrophotographic image forming apparatus. 
     In an electrophotographic image forming apparatus, a beam of light is projected from a laser, an LED, an ordinary lamp, or the like, upon the electrophotographic photosensitive drum while being modulated with the signals reflecting the information of the image to be formed. As a result, an electrostatic latent image is formed on the photosensitive drum. This electrostatic latent image is developed by the developing apparatus of the image forming apparatus. Then, the developed electrostatic latent image on the photosensitive drum is transferred onto a recording medium; an image is formed on the recording medium. 
     There are electrophotographic color image forming apparatuses of the so-called inline type, which are structured so that multiple process cartridges can be disposed in tandem in their process cartridge placement chambers. One of the methods for developing a latent image on the electrophotographic photosensitive drum in a process cartridge employed by an electrophotographic color image forming apparatus of the inline type, is a developing method which places the developing means (more specifically, a development roller) in the process cartridge in contact with the electrophotographic photosensitive drum (this developing method hereafter may be referred to simply as a contact developing method). A contact developing method requires that during an image forming operation, a preset amount of contact pressure is maintained between the development roller and photosensitive drum. Thus, an electrophotographic color image forming apparatus of the inline type is structured so that during an image forming operation, the development roller(s) therein is (are) kept pressed upon the corresponding photosensitive drum(s). 
     In the case of this developing method, if a development roller remains in contact with a photosensitive drum for a long time, it is possible that the elastic layer of the development roller will become permanently deformed, which in turn will cause the development roller to develop a latent image on the photosensitive drum, into an abnormal image, more specifically, an image which reflects the pattern of the development roller deformation. 
     In order to prevent the occurrence of the above described problem, that is, in order to prevent the elastic layer of a development roller from permanently deforming, it is necessary that a substance which is unlikely to permanently deform is used as the material for the elastic layer, or that a developing means which can be set to so that it does not leave the pattern of its development roller deformation on recording medium as it develops a latent image is employed. 
     One of the solutions to this problem has been proposed in Japanese Laid-open Patent Application 2000-276190 (p. 01, FIG. 1). According to this application, an image forming apparatus and a process cartridge therefor are structured to keep separated the photosensitive drum and development unit of the process cartridge during process cartridge shipment. More specifically, the image forming apparatus and process cartridge are provided with means for preventing the development unit, which is holding the development roller, from moving in oscillatory manner relative to the drum unit which is holding the photosensitive drum. This means is used to keep the development roller separated from the photosensitive drum. 
     Further, it is desired to ensure that until a process cartridge is mounted into the main assembly of an image forming apparatus, the development roller is kept separated from the photosensitive drum. 
     SUMMARY OF THE INVENTION 
     The present invention is one of the further developments of the above-described conventional technologies. Thus, the primary object of the present invention is to provide a process cartridge designed to ensure that the photosensitive drum and development roller of the process cartridge remain separated from each other until the process cartridge is mounted into the main assembly of an image forming apparatus. 
     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, said process cartridge comprising an electrophotographic photosensitive drum; a drum unit containing said electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a developing unit swingably supported by said drum unit and containing said developing roller; an urging member for urging said drum unit and said developing unit to each other so as to press said developing roller against said electrophotographic photosensitive drum; a space keeping member for keeping space between said electrophotographic photosensitive drum and said developing roller by engaging with said developing unit and limiting swing of said developing unit against an urging force of said urging member, wherein said space keeping member is movable by being contacted by the main assembly of the apparatus in a direction crossing with a swing plane perpendicular to an axis of the swing, when said process cartridge is mounted to the main assembly of the apparatus in a direction of an axis of said electrophotographic photosensitive drum. 
     According to another aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, said main assembly comprising (i) a process cartridge demountably mounted to a main assembly of the apparatus, said process cartridge including, an electrophotographic photosensitive drum, a drum unit containing said electrophotographic photosensitive drum, a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum, a developing unit swingably supported by said drum unit and containing said developing roller, an urging member for urging said drum unit and said developing unit to each other so as to press said developing roller against said electrophotographic photosensitive drum, and a space keeping member for keeping space between said electrophotographic photosensitive drum and said developing roller by engaging with said developing unit and limiting swing of said developing unit against an urging force of said urging member, wherein said space keeping member is movable by being contacted by the main assembly of the apparatus in a direction crossing with a swing plane perpendicular to an axis of the swing, when said process cartridge is mounted to the main assembly of the apparatus in a direction of an axis of said electrophotographic photosensitive drum; and (ii) feeding means for feeding the recording material. 
     These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the lengthwise end portion of the process cartridge in the first preferred embodiment of the present invention, as seen from the front side of the image forming apparatus, before the separative member which has kept development roller separated from the photosensitive drum is moved during the mounting of the cartridge into the main assembly of the image forming apparatus. 
         FIG. 2  is a schematic sectional view of the electrophotographic color image forming apparatus in the first embodiment, which depicts the general structure of the apparatus. 
         FIG. 3  is a schematic sectional view of the process cartridge in the first embodiment, which depicts the general structure of the cartridge. 
         FIG. 4  is an external perspective view of the process cartridge in the first embodiment. 
         FIG. 5  is a perspective view of the development unit of the process cartridge in the first embodiment. 
         FIG. 6  is a perspective view of the image forming apparatus in the first embodiment. 
         FIGS. 7(   a )- 7 ( c ) are schematic drawings for depicting the steps in the operation for mounting the process cartridge into the main assembly of the image forming apparatus, in the first embodiment. 
         FIG. 8  is a perspective view of the process cartridge, which has just been precisely positioned in its image forming position in the main assembly of the image forming apparatus, in the first embodiment. 
         FIG. 9  is a sectional view of the process cartridge in the first embodiment, which is for depicting the operational step for separating the development roller from the photosensitive drum. 
         FIG. 10  is a sectional view of the process cartridge in the first embodiment cartridge, which is for depicting the operational step for allowing the development roller to be placed in contact with the photosensitive drum. 
         FIG. 11  is a schematic drawing of the user side portion of the process cartridge in the first embodiment before the member, with which the user side end portion of the process cartridge is provided to keep the development roller separated, is engaged. 
         FIG. 12  is a perspective view of the user side portion of the process cartridge in the first embodiment before the process cartridge is mounted into the main assembly of the image forming apparatus. 
         FIG. 13  is a schematic drawing of the user side portion of the process cartridge in the first embodiment after the member, with which the user side end portion of the process cartridge is provided to keep the development roller separated, is engaged. 
         FIG. 14  is a perspective view of the user side portion of the process cartridge, and the corresponding portions of the main assembly of the image forming apparatus, immediately before the completion of the mounting of the process cartridge into the main assembly. 
         FIG. 15  is a perspective view of the user side portion of the process cartridge, and the corresponding portions of the main assembly of the image forming apparatus, immediately after the completion of the mounting of the process cartridge into the main assembly. 
         FIG. 16  is a detailed perspective view of the user side portion of the process cartridge. 
         FIG. 17  is a perspective view of the opposite side portion of the process cartridge from the user side, and the corresponding portions of the main assembly of the image forming apparatus, immediately before the mounting of the process cartridge into the main assembly. 
         FIG. 18  is a perspective view of the opposite side portion of the process cartridge from the user side, and the corresponding portions of the main assembly of the image forming apparatus, immediately after the completion of the mounting of the process cartridge into the main assembly. 
         FIGS. 19(   a )- 19 ( c ) are schematic drawings for depicting the mechanism of the process cartridge, which is for moving the member for keeping the development roller separated from the photosensitive drum. 
         FIG. 20  is a perspective view of the user side end portion of the process cartridge in the second preferred embodiment, before the mounting of the process cartridge into the main assembly of the image forming apparatus in the second embodiment. 
         FIG. 21  is a perspective view of the user side end portion of the process cartridge in the second preferred embodiment, during the mounting of the process cartridge into the main assembly of the image forming apparatus in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the appended drawings. However, the structural components of the process cartridge and electrophotographic image forming apparatus in the following preferred embodiments are to be modified as necessary in measurement, material, shape, and positional relationship according to the structure of the apparatuses to which the present invention is applied, and the various conditions under which the apparatuses are operated. That is, unless specifically noted, the following preferred embodiments are not intended to limit the present invention in scope. 
     (General Structure of Image Forming Apparatus) 
     First, referring to  FIG. 2 , the electrophotographic image forming apparatus  100  (which hereafter will be referred simply as image forming apparatus) in this embodiment will be described regarding its general structure. The image forming apparatus uses four process cartridges  7  ( 7   a ,  7   b ,  7   c , and  7   d ), which are removably mountable in the main assembly of the apparatus by being assisted by a cartridge mounting member (unshown), as shown in  FIG. 2 . As the four cartridges  7  are mounted into the main assembly  100 A of the image forming apparatus  100 , they become aligned in tandem in a direction which is inclined relative to the horizontal direction. 
     The process cartridges  7  are provided with electrophotographic photosensitive drums  1  ( 1   a - 1   d ), and processing means, more specifically, charge rollers  2  ( 2   a ,  2   b ,  2   c , and  2   d ), development rollers  25  ( 25   a ,  25   b ,  25   c , and  25   c ), and cleaning members  6  ( 6   a ,  6   b ,  6   c , and  6   d , respectively). The electrophotographic photosensitive drum  1  and processing means are integrally disposed so that the processing means are in the adjacencies of the peripheral surface of the electrophotographic photosensitive drum  1  (which hereafter will be referred to simply as photosensitive drum  1 ). The charge roller  2  is for uniformly charging the photosensitive drum  1  ( 1   a - 1   d ) across the peripheral surface. The development roller  25  is for developing the abovementioned electrostatic latent image on the photosensitive drum  1  with the use of developer (which hereafter may be referred to as toner). The cleaning member  6  is for removing the developer remaining on the peripheral surface of the photosensitive drum  1  after the abovementioned transfer of the toner image from the photosensitive drum  1  onto an intermediary transferring means. 
     As for the main assembly of the image forming apparatus, it is provided with a scanner unit  3 , which forms a latent image on the photosensitive drum  1  by selectively exposing numerous points of the charged area of the peripheral surface of the photosensitive drum  1 , based on the information regarding the image to be formed. The scanner unit  3  is disposed so that it will be below the process cartridge  7  after the completion of the mounting of the process cartridge into the apparatus main assembly  100 A. 
     Mounted in the bottom portion of the apparatus main assembly  100 A is a cassette  17 , which contains multiple sheets of recording medium S. The apparatus main assembly  100 A is also provided with a recording medium conveying means, which is structured so that the recording medium S is conveyed upward of the apparatus main assembly  100 A by way of a secondary transfer roller  70  and a fixing portion  74 . That is, the apparatus main assembly  100 A is provided with: a recording medium conveying roller  54  which feeds the recording mediums S in the cassette  17  into the apparatus main assembly  100 A while separating the top recording medium S from the rest; a pair of recording medium conveying rollers  76  which convey further each of the fed recording mediums S; and a pair of registration rollers  55  which synchronize the delivery of each recording medium S to the interface between each photosensitive drum  1  and intermediary transfer means, with the arrival of the toner image on the photosensitive drum  1  at the interface. Further, located above the process cartridges  7  ( 7   a ,  7   b ,  7   c , and  7   d ) is an intermediary transferring means, more specifically, an intermediary transfer unit  5 , for transferring the toner images formed on the photosensitive drums  1  ( 1   a ,  1   b ,  1   c , and  1   d ). The intermediary transfer unit  5  has a transfer belt  9 , a driver roller  56 , a follower roller  57 , multiple (four in this embodiment) primary transfer rollers  58  ( 58   a ,  58   b ,  58   c , and  58   d ), and a belt backing roller  59 . The transfer belt  9  is suspended by the driver roller  57 , follower roller  57 , and belt backing roller  59 . The primary transfer rollers  58  are disposed so that they oppose the photosensitive drums  1 , one for one, with the presence of the transfer belt  9  between the transfer rollers  58  and photosensitive drums  1 . The belt backing roller  59  is disposed so that it opposes a transfer roller  70  with the presence of the transfer belt  9  between the two rollers  59  and  70 . The transfer belt  9  is circularly driven in contact with all the photosensitive drums  1 . As a preset voltage is applied to the primary transfer rollers  58  ( 58   a ,  58   b ,  58   c , and  58   d ) while the transfer belt  9  is circularly driven, the toner images on the photosensitive drums  1  ( 1   a ,  1   b ,  1   c , and  1   d ) are sequentially transferred (primary transfer) in layers onto the transfer belt  9 . Then, the toner images on the transfer belt  9  are transferred all at once (secondary transfer) onto the recording medium S by a preset voltage applied between the belt backing roller  59  (which is inside the loop which the transfer belt  9  forms) and secondary transfer roller  70 . 
     The image forming operation performed by this image forming apparatus is as follows: Each photosensitive drum  1  is rotated while being uniformly charged by the charge roller  2  across its peripheral surface. Then, numerous points of the uniformly charged area of the peripheral surface of the photosensitive drum  1  are selectively exposed by a scanner unit  3 . As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  1 . Then, the electrostatic latent image is developed by the development roller  25 . Thus, four monochromatic images, different in color, are formed of developer, on the four photosensitive drums  1 , one for one. Meanwhile, the pair of registration rollers  55  convey the recording medium S to the secondary transfer portion, that is, where the belt backing roller  59  and secondary transfer roller  70  are kept pressed against each other with the presence of the transfer belt  9  between the two rollers  59  and  70 , in synchronism with the progression of the above described image forming operation. Then, while the recording medium S is conveyed through the secondary transfer portion, a preset transfer bias is applied to the secondary transfer roller  70 . As a result, the developer images on the transfer belt  9  are transferred (secondary transfer) onto the recording medium S, effecting a single multicolor image formation on the recording medium S. After the formation of the multicolor image on the recording medium S, the multicolor image (formed of four monochromatic developer images) on the recording medium S is fixed to the recording medium S by the heat and pressure applied to the recording medium S and the multicolor image thereon by the fixing portion  74 . Then, the recording medium S is discharged into a delivery portion  75  by a pair of discharge rollers  72 . The fixing portion  74  is in the upper portion of the apparatus main assembly  100 A. Designated by a referential number  71  is a cleaning blade for removing the toner remaining on the transfer belt  9  after the transfer of the developer images from the transfer belt  9  onto the recording medium S. 
     (Process Cartridge) 
     Next, referring to  FIGS. 3-5 , the process cartridge in this embodiment will be described.  FIG. 3  is a sectional view of the process cartridge  7 , in which developer (which hereafter will be referred to as toner) is stored, at a plane perpendicular to the lengthwise direction of the cartridge  7 . Incidentally, the process cartridges  7   a ,  7   b ,  7   c , and  7   d , which store yellow magenta, cyan, and black toners, respectively, are the same in structure. 
     The process cartridges  7  ( 7   a ,  7   b ,  7   c , and  7   d ) have a latent image formation unit  26  ( 26   a ,  26   b ,  26   c , or  26   d ) and a development unit  4  ( 4   a ,  4   b ,  4   c , or  4   d ). The latent image formation unit  26  has the photosensitive drum  1  ( 1   a ,  1   b ,  1   c , or  1   d ), charge roller  2  ( 2   a ,  2   b ,  2   c , or  2   d ), and cleaning member  6  ( 6   a ,  6   b ,  6   c , or  6   d , respectively). The development unit  4  has the development roller  25  ( 25   a ,  25   b ,  25   c , or  25   d ). 
     It is by the cleaning means frame  27  of the latent image formation unit  26  that the photosensitive drum  1  is rotatably supported. More specifically, the cleaning means frame  27  is fitted with front and rear drum bearings  10  and  11  ( FIG. 4 ) by which the photosensitive drum  1  is rotatably supported. It should be noted here that the front and rear sides of the process cartridge  7  means the front and rear sides of the process cartridge  7  when the process cartridge is properly situated in the apparatus main assembly  100 A. The rear end of the photosensitive drum  1  is fitted with a drum coupling  16 , whereas the front end is fitted with flange  85 . 
     The charge roller  2  and cleaning member  6  are disposed in the adjacencies of the peripheral surface of the photosensitive drum  1  as described above. As the toner remaining on the peripheral surface of the photosensitive drum  1  is removed by the cleaning member  6 , it falls into a chamber  27   a  for the removed toner. The photosensitive drum  1  is rotated in synchronism with the progression of an image forming operation by the transmission of driving force to the latent image formation unit  26  from the motor (driving force source) with which the apparatus main assembly  100 A is provided. The charge roller  2  is rotatably supported by the cleaning means frame  27  with the placement of a pair of charge roller bearings  28  between the charge roller  2  and cleaning mean frame  27 . Further, the charge roller  2  is kept pressed toward the photosensitive drum  1  by a pair of charge roller pressing members  46 . It is rotated by the rotation of the photosensitive drum  1 . 
     The development unit  4  is made up of the development roller  25 , and a development unit frame  31  which supports the development roller  25 . The development roller  25  rotates in contact with the photosensitive drum  1  in the direction indicated by an arrow mark B. The development roller  25  is rotatably supported by the development unit frame  31  with front and rear development roller bearings  12  and  13  attached to the front and rear walls of the development unit frame  31 , respectively ( FIG. 5 ). Further, the development unit  4  is provided with a toner supply roller  34  and a development blade  35 , which are disposed in the adjacencies of the peripheral surface of the development roller  25 . The toner supply roller  34  rotates in contact with the development roller  25  in the direction indicated by an arrow mark C. The development blade  35  is for regulating in thickness the layer of toner on the peripheral surface of the development roller  25 . Further, the development unit  4  is provided with a toner conveying member  36  for conveying the toner in the toner storage portion  31   a  of the development unit  4  to the abovementioned toner supply roller  34  while stirring the toner. The toner conveying member  36  is disposed in the toner storage portion  31   a  of the development unit frame  31 . 
       FIG. 4  is an external perspective view of the process cartridge  7 . The development unit  4  is attached to the latent image formation unit  26  so that the former can be rotationally moved relative to the latter in an oscillatory manner. More specifically, the development unit  4  is provided with front and rear bearings  12  and  13 , which are provided with holes  12   a  and  13   a , respectively, into which the front and rear shafts  14  and  15  (axles) are fitted after being pressed through the corresponding shaft (axle) holes with which the front and rear walls of the cleaning unit frame  27  are provided, respectively, whereby the development unit  4  is supported by the cleaning means frame  27  in such a manner that the development unit  4  is allowed to rotationally move about the front and rear shafts  14  and  15 , respectively ( FIG. 3 ). Further, the cleaning means frame  27  is provided with the aforementioned front and rear drum bearings  10  and  11 , with which the photosensitive drum  1  is rotatably supported. More specifically, the rear drum bearing  11  supports the drum coupling  16  attached to the photosensitive drum  1 , whereas the front drum bearing  10  supports the flange  85 . The drum coupling  16  is the coupling for transmitting rotational driving force to the photosensitive drum  1  from the apparatus main assembly  100 A. 
     Referring to  FIG. 5 , the process cartridge  7  is structured so that while the process cartridge  7  is used for an actual image forming operation, the development roller  25  in the development unit  4  is kept pressed upon the photosensitive drum  1  in the latent image formation unit  26  by the compression spring  38  with which the development unit frame  31  is provided, and a tension spring  39  with which the front development roller bearing  12  is provided. The compression spring  38  and tension spring  39  generate the pressure that works in the direction to rotate the development unit  4  about the axes of the front and rear development roller bearings  12  and  13  so that the development roller  25  is placed, and kept, in contact with the photosensitive drum  1 . Thus, the theoretical line which coincides with the axial line of the hole  12   a  of the front bearing  12 , and the axial line of the hole  13   a  of the rear bearing  13  is the axial line  12   j  of the oscillatory movement of the development unit  4 . 
     In a case where the so-called contact developing method, which places the photosensitive drum  1  and development roller  25  in contact with each other when developing a latent image on the photosensitive drum  1 , it is desired that the photosensitive drum  1  is made as a rigid member, whereas the development roller  25  is provided with an elastic surface layer, for example, a layer of solid rubber. In consideration of the toner charging property of solid rubber, the solid rubber layer may be coated with resin. 
     Next, the sequential steps in the image forming operation of the process cartridge  7  will be described ( FIGS. 2 and 3 ). As the information regarding an image to be formed is sent to the image forming apparatus  100 , the motor (unshown) of the apparatus main assembly  100 A begins to be rotated, and the rotational driving force therefrom is transmitted to the photosensitive drum  1 , development roller  25 , toner supply roller  34 , and toner conveying member  36 . Then, a charge bias voltage is applied to the charge roller  2  from the apparatus main assembly  100 A, uniformly charging the peripheral surface of the photosensitive drum  1 . Then, the uniformly charged portion of the peripheral surface of the photosensitive drum  1  is exposed by the scanner unit  3 . As a result, a latent image is formed on the photosensitive drum  1 . 
     Meanwhile, the toner in the toner storage portion  31   a  is conveyed to the toner supply roller  34  by the rotation of the toner conveying member  36 . As the toner is conveyed to the toner supply roller  34 , it is supplied to the peripheral surface of the rotating development roller  25  by the toner supply roller  34 , which also is rotating. After being supplied to the peripheral surface of the development roller  25 , it is frictionally charged by the development blade  35 . To the development roller  25 , a development bias voltage is applied from an electric power source (unshown) with which the apparatus main assembly  100 A is provided. As a result, the electrostatic latent image on the photosensitive drum  1  is developed. Incidentally, the development roller  25  is disposed so that the peripheral surface of the development roller  25  faces the peripheral surface of the photosensitive drum  1 ; the image forming apparatus  100  is structured so that the development roller  25  contacts the photosensitive drum  1  to develop the electrostatic latent image formed on the photosensitive drum  1 . 
     (Structural Arrangement for Mounting Process Cartridge into Apparatus Main Assembly) 
     Next, referring to  FIGS. 6 and 7 , the structural arrangement of the apparatus main assembly  100 A, which is for allowing the process cartridge  7  to be removably mounted in the apparatus main assembly  100 A, will be described. 
       FIG. 6  is a perspective view of the image forming apparatus prior to the mounting of the process cartridge  7   a  into the main assembly  100 A of the image forming apparatus  100 . Incidentally, the image forming apparatus  100  in this embodiment is structured so that the process cartridge  7  is to be mounted into the apparatus main assembly  100 A in the direction indicated by an arrow mark E, which is parallel to the axial line of the photosensitive drum  1 , that is, from the front side (reader&#39;s side) of the page on which  FIG. 2  is on, to the rear side (opposite side from reader&#39;s side). Regarding the definition of the front and rear of the process cartridge  7  in this embodiment, the upstream side of the process cartridge  7  in terms of the direction in which the process cartridge  7  is mounted into the apparatus main assembly  100 A is referred to as the front, and the downstream side is referred to as the rear. 
     Referring to  FIG. 6 , the apparatus main assembly  100 A is provided with a front cover  73 , which can be opened frontward. As the front cover  73  is opened, four chambers  22  ( 22   a - 22   d ) for the four process cartridges  7  ( 7   a - 7   d ), respectively, are exposed. The four process cartridge chambers  22  are arranged in tandem at a preset angle relative to the horizontal direction. There are top (first) and bottom (second) guides  80  ( 80   a - 80   d ) and  81  ( 81   a - 81   d ), which are on the top and bottom sides, respectively, of the process cartridge chambers  22 . The top and bottom guides  80  and  81  extend in the direction perpendicular to the front and rear walls of the apparatus main assembly  100 A. As for the proper method for mounting the process cartridge  7  into the apparatus main assembly  100 A, first, the cartridge guiding top portion  11   c , with which the rear drum bearing  11  of the process cartridge  7  is provided, and the cartridge guiding bottom portion  27   b , with which the latent image formation unit  26  is provided, are to be engaged with the top and bottom guides  80  and  81 , respectively, of the apparatus main assembly  100 A, and then, the process cartridge  7  is to be pushed into the apparatus main assembly  100 A in the direction indicated by an arrow mark E in the drawing. 
     Incidentally, the abovementioned guiding portion  11   c  is a part of the top rear end of the process cartridge  7 , whereas the bottom guiding portion  27   b  is a part of the bottom wall of the process cartridge  7 . The bottom guiding portion  27   b  is on the outward side of the bottom wall of the process cartridge  7 , and extends in the direction parallel to the lengthwise direction of the process cartridge  7 . 
     Next, referring to  FIG. 7 , the mounting of the process cartridge  7  will be described regarding the direction parallel to the lengthwise direction of the cartridge  7 . 
       FIG. 7(   a ) is a schematic drawing of a combination of one of the process cartridge chamber of the apparatus main assembly  100 A and the corresponding process cartridge  7  positioned ready to be mounted into the process cartridge chamber. The process cartridge  7  is mounted into one of the process cartridge chambers  2  of the apparatus main assembly  100 A in the direction indicated by the arrow mark E in  FIG. 7(   a ), in such a manner that the top guiding portion  11   b , with which the rear drum bearing of the process cartridge  7  is provided, fits into the top guide  80 , with which the apparatus main assembly  100 A is provided, and also, that the bottom guiding portion  27   b , which is the integral part of the cleaning means frame  31 , fits in the bottom guide  81 , with which the apparatus main assembly  100 A is provided. The top and bottom guides  80  and  81  are the guides for precisely guiding the process cartridge  7  when the process cartridge  7  is removably mounted into the apparatus main assembly  100 A (process cartridge chamber  22 ). 
       FIG. 7(   b ) is a schematic drawing of the combination of one of the process cartridge chambers  22  of the apparatus main assembly  100 A, and the process cartridge  7  having been almost completely mounted into the apparatus main assembly  100 A. The top surface of the bottom guide  81  of the apparatus main assembly  100 A is provided with an upwardly inclined portion  81   e  (with reference to cartridge insertion direction), which is near the downstream end of the bottom guide  81 , whereas the cleaning means frame  27  is provided with a downwardly inclined portion  27   c  (with reference to upstream direction in terms of cartridge insertion direction). As the process cartridge  7  is mounted deep enough into the apparatus main assembly  100 A for the leading end of the process cartridge  7  to near the rearmost end of the apparatus main assembly  100 A, the bottom guiding portion  27   b  of the cleaning means frame  27  rides onto the inclined portion  81   e , and the inclined portion  27   c  of the cleaning means frame  27  rides onto the bottom guide  81 , whereby the process cartridge  7  is moved toward (upward) the intermediary transfer unit  5 . 
       FIG. 7(   c ) is a schematic drawing of the combination of one of the process cartridge chambers  22  of the apparatus main assembly  100 A, and the process cartridge  7  having just been completely mounted into the apparatus main assembly  100 A. As the mounting of the process cartridge  7  is continued while the process cartridge  7  is moved toward the intermediary transfer unit  5 , the bumper portion  27   d , which is an integral part of the cleaning means frame  27  comes into contact with the rear wall  83  of the apparatus main assembly  100 A, ending thereby the mounting of the process cartridge  7  into the apparatus main assembly  100 A. 
     As the process cartridge  7  is moved into the position shown in  FIG. 7(   c ), the pressure taking portion  11   a  of the rear drum bearing  11  comes into contact with a cartridge catching rear member  91 , with which the rear wall  83  of the apparatus main assembly  100 A is provided, whereby the rear drum bearing  11  is pushed up by a compression spring  92 . Also as the process cartridge  7  is moved into the position shown in  FIG. 7(   c ), the cartridge positioning portion  11   b , with which the top portion of the rear drum bearing  11  is provided, comes into contact with the cartridge catching portion  83   a  of the rear wall  83  of the apparatus main assembly  100 A, which also functions as a cartridge positioning portion. As a result, the leading end portion of the process cartridge  7  becomes precisely positioned relative to the apparatus main assembly  100 A. 
     Also as the process cartridge  7  is moved into the position shown in  FIG. 7(   c ), the catch portion  10   a  of the front drum bearing  10  engages with a pulling member  93 , with which the front wall  82  of the apparatus main assembly  100 A is provided. Since the drum pulling member  93  is attached to a tension spring  94 , with which the front wall  82  is provided, the catch portion  10   a  is moved upward, causing therefore the bumper portion  10   b  of the front drum bearing  10 , which doubles as the cartridge positioning member, to come into contact with the drum positioning portion  82   a  of the front wall  82  of the apparatus main assembly  100 A. As a result, the front side of the process cartridge  7  is precisely positioned relative to the apparatus main assembly  100 A. 
     Next, referring to  FIG. 8 , the cartridge positioning (catching) portion  83   a  of the rear wall  83  of the apparatus main assembly  100 A is roughly V-shaped in cross section. The apparatus main assembly  100 A and process cartridge  7  are structured so that the cartridge positioning surface  11   b  of the rear drum bearing  11  comes into contact with the cartridge positioning portion  83   a , and also, so that the drum pulling member  93  of the front wall  82  pulls the front drum bearing  10  in the direction indicated by an arrow mark P in the drawing, by becoming engaged with the catch portion  10   a  of the front drum bearing  10 . Regarding the positioning of the process cartridge  7 , the apparatus main assembly  100 A and process cartridge  7  are structured so that the front drum bearing  10  comes into contact with the drum positioning portion  82   a  of the front wall  82  of the apparatus main assembly  100 A, which is roughly V-shaped in cross section, in the same manner as the rear drum bearing  11  comes into contact with the rear wall  83 . Further, the pressures necessary to precisely position, and keeping precisely positioned, the photosensitive drum  1  (process cartridge  7 ) relative to the apparatus main assembly  100 A are applied to the front and rear drum bearings  10  and  11  in the directions indicated by arrow marks P and R, respectively. Therefore, the front and rear drum bearings  10  and  11 , which rotatably support the photosensitive drum  1 , and also, are for precisely position the process cartridge  7 , are accurately positioned relative to the apparatus main assembly  100 A. 
     Further, the process cartridge  7  is provided with a groove  27   f  and a boss  27   g , which also are the cartridge positioning portion, in addition to the front and rear drum bearings  10  and  11 . They are integral parts of the cleaning means frame  27 . Correspondingly, the apparatus main assembly  100 A is provided with a front boss  81   f  and a rear groove  51   a , which are the corresponding cartridge positioning portions of the apparatus main assembly  100 A. Thus, as the process cartridge  7  is mounted into the apparatus main assembly  100 A, the boss  27   g  of the process cartridge  7  fits into the groove  51   a  of the rear guide  51  of the apparatus main assembly  100 A, and the front boss  81   f  of the apparatus main assembly  100 A fits in the groove  27   f  of the process cartridge  7 . Therefore, the process cartridge  7  remains accurately positioned relative to the apparatus main assembly  100 A. 
     The cartridge positioning boss  27   g , and the cartridge positioning groove  51   a  of the rear guide  51 , are sized so that when the boss  27   g  is in the groove  51   a , there is a gap of several tens of micrometers between the boss  27   g  and the wall of the groove  51   a . Further, the groove  27   f  and front boss  81   f  are sized so that when the front boss  81   f  is in the groove  27   f , there is a 0.1-0.2 mm gap between the front boss  81   f  and the wall of the groove  27   f.    
     This structural arrangement is provided in anticipation of the possibility that as the separating member catching portion  31   b  of the developing means frame  31  is subjected to the force resulting from the operation of the development roller separating member  8  (which hereafter will be referred to simply as separating member  8 ) of the apparatus main assembly  100 A, the combination of the rear boss  27   g  and rear boss guide  51 , is insufficient for keeping the process cartridge  7  precisely positioned. In other words, the front groove  27   f  and front boss  81   f  are provided to eliminate, by the engagement between the front groove  27   f  and front boss  81   f , the problem that when the process cartridge  7  is subjected to the force attributable to the separating member  8 , the cleaning means frame  27  is rotated by the force about the axial lines of the front and rear bearings  10  and  11 . 
     Thus, the rear boss  27   g  and rear boss guide  51 , which are at the leading end of the cartridge  7 , are sized so that the gap between them is very small, whereas the front groove  27   f  and front boss  81   f , which are at the trailing end of the cartridge  7 , are sized so that the gap between them is relatively large. 
     (Mechanism for Keeping Photosensitive Drum and Development Roller Separated from Each Other) 
     Next, referring to  FIGS. 9 and 10 , the mechanism for separating, and keeping separated, the photosensitive drum  1  and development roller  25  in the process cartridge  7  in accordance with the present invention from each other will be described. 
     Referring to  FIG. 9 , the image forming apparatus  100  (unshown) is provided with the separating member  8 , which corresponds in position to a predetermined position of the process cartridge  7  in terms of the lengthwise direction of the process cartridge  7 . As the separating member catching portion  31   b  of the development unit frame  31  is pushed by the separating member  8  in the direction indicated by an arrow mark N, the development unit  4  of the process cartridge  7  is rotationally moved into the position in which it keeps the development roller  25  separated from the photosensitive drum  1 . Before the process cartridge  7  is moved into this position in the apparatus main assembly  100 A, the process cartridge  7  is kept precisely positioned relative to the apparatus main assembly  100 A by the front and rear drum bearings  10  and  11 , and the cartridge positioning boss  27   g  of the cleaning means frame  27  ( FIG. 8 ). As the process cartridge  7  is subjected to the force from the separating member  8 , it inclines to move in the direction indicated by the arrow mark N. If the process cartridge  7  were kept positioned by only three points (portions), that is, the front and rear drum bearings  10  and  11  and the rear positioning boss  27  ( FIG. 8 ), it is possible that the process cartridge  7  will be deformed. This is why the apparatus main assembly  100 A and process cartridge  7  are structured so that as the development unit  4  is rotationally moved to keep the development roller  25  separated from the photosensitive drum  1 , the front boss  81   f  comes into contact with the wall of the front groove  27   f  to prevent the process cartridge  7  from being deformed. 
     Next, referring to  FIG. 10 , as an image forming operation is started, the separating member  8  separates from the separating member catching portion  31   b  by being moved in the direction indicated by an arrow mark S. Thus, the development unit  4  is rotated in the direction indicated by an arrow mark T about the axial lines of the holes  12   a  and  13   a  of the front and rear development roller bearings  12  and  13  by the resiliency of the compression springs  38  and tension spring (unshown). As a result, the development unit  4  is moved into the position in which its development roller  25  remains in contact with the photosensitive drum  1 . It is by the front and rear drum bearings  10  and  11 , and the front positioning boss  27   g  ( FIG. 8 ) that the process cartridge  7  is supported (kept precisely positioned) during an image forming operation. 
     In other words, unless the process cartridge  7  is being used for an actual image forming operation, the development unit  4  is kept in the position, shown in  FIG. 9 , in which its development roller  25  is kept separated from the photosensitive drum  1 , by the above described mechanism for keeping the development roller  25  separated from the photosensitive drum  1 . That is, the mechanism prevents the image forming apparatus  100  from being affected in image quality by the deformation of the development roller  4 . 
     (Member for Separating, and Keeping Separated, Development Roller from Photosensitive Drum) 
       FIG. 12  depicts the lengthwise front end portion of the brand-new process cartridge  7  (before process cartridge  7  is mounted into apparatus main assembly  100 A). 
     The front end portion of the cleaning means frame  27  is provided with a development roller separating front member  67  for separating the development roller  25  (unshown) from the photosensitive drum  1  (unshown) and keeping them separated while the process cartridge  7  is not in the apparatus main assembly  100 A. The development roller separating front member  67  (which hereafter will be referred to simply as front separating member  67 ) is rotatably attached to a boss  27   j  (which functions as rotational axle), with which the cleaning unit frame  27  is provided. Further, it is kept covered with a cleaning means frame cover  23  (outlined by double-dot chain line), being thereby prevented from becoming disengaged from the boss  27   j.    
     The developing unit frame  31  ( FIG. 5 ) is provided with a retaining portion  31   e  for keeping the development roller  25  separated from the photosensitive drum  1 , and the cleaning means frame  27  is provided with a hole  27   h  for allowing the retaining portion  31   e  to be put through the cleaning means frame  27 . Further, the front separating member  67  is provided with a catch  67   a , which engages with the retaining portion  31   e.    
     Next, the method for engaging the catch  67   a  of the front separating member  67  with the retaining portion  31   e  will be described.  FIG. 1  is a perspective view of the front end portion of the process cartridge  7  before the engagement of the front separating member  67  with the retaining portion  31   e , and  FIG. 11  is a schematic drawing for depicting how the front separating member  67  is engaged with the retaining portion  31   e.    
     Referring to  FIGS. 1 and 11 , the front separating member  67  is attached to the cleaning means frame  27  so that it can be rotated about the aforementioned boss  27   j  in the direction indicated by an arrow mark M. Thus, as the development unit  4  is rotated about the front shaft  14  (and rear shaft  15 ) in the direction indicated by an arrow mark X as shown in  FIG. 1 , the retaining portion  31   e  of the developing means frame  31  also moves in the direction indicated by the arrow mark X as shown in  FIG. 11 . Then, the development unit  4  is rotated in the direction indicated by the arrow mark X, that is, the direction for separating the development roller  25  from the photosensitive drum  1 , and then, while the development unit  4  is kept in the position into which it has just been moved, the front separating member  67  shown in  FIG. 1  is rotated in the direction indicated by the arrow mark M, causing thereby the catch  67   a  of the front separating member  67  to come into contact with the retaining portion  31   e  having just been inserted through the hole  27   h . Further, the front separating member  67  is provided with a protrusion  67   b , which is a portion to be fit into the positioning groove  27   f , with which the cleaning means frame  27  is provided. As for the disengagement of the front separating member  67  and retaining portion  31   e  from each other, the catch  67   a  of the front separating member  67  can be disengaged from the retaining portion  31   e  by manipulating the aforementioned protrusion  67   b.    
       FIG. 13  is a schematic view of the front separating member  67  and retaining portion  31   e  when the two are in engagement with each other. As described previously, the rotational movement of the development unit  4  about the front shaft  14  ( FIG. 12 ) in the direction indicated by the arrow mark T ( FIG. 14 ) is prevented by the contact between the catch portion  67   a  of the front separating member  67  and the retaining portion  31   e . That is, the contact prevents the resiliency of the compression spring  38  ( FIG. 3 ) and tension spring  39  ( FIG. 5 ) from placing the development roller  25  in contact with the photosensitive drum  1 . 
     Next, referring to  FIGS. 14 and 15 , the method for disengaging the separating member  67  will be described.  FIG. 14  is a partially broken view of the front end portion of the process cartridge  7  and the front end portion of the apparatus main assembly  100 A when the process cartridge  7  is being mounted into the apparatus main assembly  100 A. When the process cartridge  7  is in the position depicted in  FIG. 14 , the engagement between the retaining portion  31   e  of the developing means frame  31  and the separating member  67  prevents the developing means frame  31  from rotating in the direction indicated by the arrow mark T about the front shaft  14  ( FIG. 12 ). 
     Referring to  FIG. 15 , as the process cartridge  7  is inserted further in the direction indicated by the arrow mark E, the front boss  81   f  with which the bottom guide  81  of the apparatus main assembly  100 A is provided, fits into the groove  27   f , that is, the cartridge positioning front portion of the cleaning means frame  27 . Then, the front boss  81   f  comes into contact with the separating member  67  and pushes the separating member  67 , causing the separating member  67  to rotate in the direction indicated by an arrow mark U about the boss  27   j . As a result, the catch portion  67   a  of the separating member  67 , which was in engagement with the retaining portion  31   e , is rotationally moved in the direction indicated by an arrow mark V, disengaging from the retaining portion  31   e.    
     As for the front end boss  81   f , it is inserted into the cartridge positioning portion  27   f , which is for precisely positioning the process cartridge  7  in the apparatus main assembly  100 A. 
     Thus, as the process cartridge  7  is mounted into the apparatus main assembly  100 A, the separating member  67  which has kept development roller  25  separated from the photosensitive drum  1  is disengaged, allowing the development roller  25  to be placed in contact with the photosensitive drum  1 . 
     Next, referring to  FIG. 16 , designated by a referential symbol h is an oscillatory plane, which is perpendicular to the axial line  12   j , about which the development unit  12  moves in an oscillatory manner. The main assembly of the image forming apparatus and the process cartridge are structured so that when the separating member  67  is disengaged, the catch portion  67   a  of the separating member  67 , which engages with the retaining portion  31   e , rotates in such a manner that the retaining portion catching surface of the catch portion  67   a  coincides with a plane k which is perpendicular to the oscillatory plane h (plane of retaining portion catching surface of catch portion  67   a  remains perpendicular to oscillatory plane h). 
     Thus, the force to which the catch portion  67   a  of the separating member  67  is subjected by being placed in contact with the retaining portion  31   e  of the development unit frame  31  to keep the development roller  25  separated from the photosensitive drum  1 , is perpendicular to the direction (indicated by arrow mark V in  FIG. 15 ) in which the separating member  67  is to be moved to be disengaged. 
     Further, the apparatus main assembly is structured so that when the separating member  67  rotates, the retaining portion ( 37 ) engaging surface  67   a  of the separating member  67  coincides with the plane k, which is intersectional to the direction in which the separating member  67  is pushed while remaining engaged with the retaining portion  31   e  of the development unit  31 . 
     Referring to  FIG. 16 , designated by a referential symbol  1  stands for the distance (length) between the retaining portion ( 37 ) engaging surface  67   a  of the separating member  67 , which engages with the retaining portion  31   e  of the development unit  31  ( FIG. 11 ), and the axis of the boss  27   j  (rotational axis of engaging surface  67   a ). Designated by a referential symbol m is the distance (length) between the projection  67   b  (portion to be inserted) of the separating member  67 , which comes into contact with the front boss  81   f  of the bottom guide  81  as the separating member  67  is disengaged, and the boss  27   j  (rotational axis of projection  67   b ). In this embodiment, 1&lt;m. Therefore, the amount of force necessary to disengage the separating member  67  is substantially smaller than that necessary to disengage a comparable separating member in accordance with any of the prior arts. 
     Further, the boss  27   j , with which the cleaning means frame  27  is provided to rotatably support the separating member  67  is perpendicular to the engaging portion  67   a  of the separating member  67 , which engages with the retaining portion  31   e  ( FIG. 11 ) of the development unit  31 . 
     Next, referring to  FIGS. 17-19 , the rear members  64  for keeping the development roller  25  separated from the photosensitive drum  1  will be described. First, referring to  FIG. 17  the development unit  4  is provided with a rear separating member  64  (which hereafter will be referred to simply as separating member  64 ) for keeping the development roller  25  separated from the photosensitive drum  1 . The rear separating member  64  keeps the rear end portion of the development roller  25 , that is, the inward end of the development roller  25  in terms of the cartridge mounting direction, separated from the photosensitive drum  1  by being engaged in the hole  27   e , with which the rear wall of the cleaning means frame  27  is provided. 
     Next, referring to  FIG. 18 , the apparatus main assembly  100 A is provided with a member  65  for disengaging the abovementioned rear separating member  64 . The rear separating member disengaging member  65  is located at the rear of the apparatus main assembly  100 A. As the process cartridge  7  is mounted into the apparatus main assembly  100 A, the rear separating member disengaging member  65  comes into contact with the rear separating member  64 , and disengages the rear separating member  64  from the hole  27   e , immediately before the process cartridge  7  is precisely positioned relative to the apparatus main assembly  100 A by the cartridge positioning portions  82   a  and  83   a  ( FIG. 8 ) of the apparatus main assembly  100 A. In other words, the apparatus main assembly  100 A and process cartridge  7  are structured so that as the process cartridge  7  is mounted into the apparatus main assembly  100 A, the rear separating member  64  is rotated out of the hole  27   e  in the direction indicated by an arrow mark G. 
     Hereafter, the position in which the rear separating member  64  remains after being moved out of the hole  27   e  will be referred to as the disengagement position. The disengagement of the rear separating member  64  allows the rear end portion of the development roller  25  to be placed in contact with the photosensitive drum  1  in the same manner as the disengagement of the front separating member  67  allows the front end portion of the development roller  25  to be placed in contact with the photosensitive drum  1 . 
     However, the apparatus main assembly  100 A is structured so that unless the image forming apparatus  100  is being used for an actual image forming operation, the separating member  8  of the apparatus main assembly  100 A remains in the position ( FIG. 9 ) in which it remains in contact with the separating member catching portion  31   b  of the developing means frame  31 . Therefore, even after the disengagement of the rear separating member  64  and front separating member  67 , which is caused by the mounting of the process cartridge  7  into the apparatus main assembly  100 A, the development roller  25  does not come into contact with the photosensitive drum  1  unless an image forming operation is started ( FIG. 9 ). 
     Next, referring to  FIG. 19 , the method for disengaging the rear separating member  64  will be described.  FIG. 19(   a ) depicts that the rear separating member  64  is provided with a boss  64   a . The boss  64   a  is rotatably fitted in a groove  31 c with which the development unit frame  31  is provided. The boss  64   a  is rotatably held in the groove  31   c  by a boss pressing portion  48   b  of the side cover  48 . As for the catch portion  64   b  of the rear separating member  64 , it remains in the hole  27   e  of the cleaning means frame  27 . Next, referring to  FIG. 18(   b ), as the process cartridge  7  is moved in the direction indicated by an arrow mark E while the process cartridge  7  is in the state depicted in  FIG. 19(   a ), the rear separating member disengaging member  65  enters the hole  27   e  of the cleaning means frame  27  as shown in  FIG. 19(   b ), and the rear separating member disengaging member  65  comes into contact with the rear separating member  64 , causing the rear separating member  64  to rotate about the axial line of the boss  64   a . As a result, the rear separating member  64  is disengaged from the cleaning means frame  27 . 
     Next, referring to  FIG. 19(   c ), as the rear separating member  64  is disengaged from the cleaning means from  27 , the development unit frame  31  is allowed to be moved in the direction indicated by an arrow mark L so that the development roller  25  comes into contact with the photosensitive drum  1 . 
     Next, referring to  FIG. 18 , the apparatus main assembly  100 A and process cartridge  7  are structured so that the direction in which the rear separating member  64  is rotationally moved to be disengaged coincides with a plane q intersectional to the aforementioned oscillatory plane h. 
     Therefore, the force (directed as indicated by arrow mark J in  FIG. 19(   a )), to which the rear separating member  64  is subjected as it comes into contact with the wall of the hole  27   e  of the cleaning means frame  27  is perpendicular to the direction (indicated by arrow mark K in  FIG. 19(   a )) in which the rear separating member  64  is moved to be disengaged. 
     After the completion of the mounting of the process cartridge  7 , an image forming operation is started by a print signal. As the image forming operation is started, the aforementioned separating member  8  ( FIG. 10 ) is moved in the direction indicated by the arrow mark S, being thereby separated from the catching portion  31   b , in synchronism with the progression of the developing operation. Thus, the development unit  4  is moved by the resiliency of the above described compression spring  38  and tension spring  39  ( FIG. 4 ), into the contact position, in which the development roller  25  remains in contact with the photosensitive drum  1 , being ready for development. 
     As soon as the development operation is completed, the separating member  8  is moved again in the direction indicated by the arrow mark N in  FIG. 9  to apply force to the separating member catching portion  31   b . As a result, the development unit  4  is moved into the separative position, in which it keeps the development roller  25  separated from the photosensitive drum  1 . Unless the image forming apparatus is actually forming an image, the development unit  4  is kept in this separative position. 
     As described above, the image forming apparatus  100  and process cartridge  7  are structured so that the development unit  4  can be selectively and easily moved between the position in which it keeps the development roller  25  separated from the photosensitive drum  1 , and the position in which it keeps the development roller  25  in contact with the photosensitive drum  1 . Thus, it is unnecessary to strictly select the material for the elastic layer of the development roller  25  just for preventing the elastic layer from deforming. 
     Further, simply placing a process cartridge in the main assembly of an image forming apparatus automatically places the development roller and photosensitive drum in the process cartridge in contact with each other, making it unnecessary for a user to perform the operation for placing the development roller in contact with the photosensitive drum. 
     Further, this embodiment makes it unlikely for the development roller separating members of the process cartridge  7  to disengage before the process  7  is mounted into the image forming apparatus  100 . Further, the image forming apparatus  100  and process cartridge  7  in this embodiment are substantially smaller in the amount of force necessary to mount the process cartridge  7  into the image forming apparatus  100  than those in accordance with the prior arts. 
     Embodiment 2 
     Next, referring to  FIGS. 20 and 21 , the second preferred embodiment of the present invention will be described. The basic structure of the image forming apparatus is the same as that in the first embodiment. Thus, the portions of the image forming apparatus in this embodiment, which are the same as the counterparts in the first embodiment, will not be described here. Further, the components, portions, etc., which are the same in function as the counterparts in the first embodiment will be given the same referential symbols. 
     In the first embodiment, the rear and front separating members are rotatably attached to the cleaning means frame  27 . However, they may be attached to the cleaning means frame  27  so that they can be slidingly moved as shown in  FIGS. 20 and 21 . 
       FIG. 20  shows the front end portion of the process cartridge  7  before the process cartridge  7  is mounted into the image forming apparatus main assembly  100 A. 
     The cleaning means frame  27  is provided with a guide  27   s . The separating member  67  is attached to the guide  27   s  so that it can be slidingly moved along the guide  27   s . Further, the cleaning means frame  27  is provided with the development roller retaining portion  31   e . Thus, the development roller  25  is kept separated from the photosensitive drum  1  by engaging the engaging portion  67   a  of the separating member  67  with the development roller retaining portion  31   e  of the cleaning means  27 . 
     Next, referring to  FIG. 21 , the bottom guide  81  ( FIG. 15 ) is provided with a front boss  81   f , which comes into contact with the separating member  67 . Thus, as the process cartridge  7  is mounted into the image forming apparatus main assembly  100 A, the front boss  81   f  comes into contact with the separating member  67 , and causes the separating member  67  to slide in the direction indicated by an arrow mark W. As a result, the engaging portion  67   a  of the separating member  67  is disengaged from the development roller retaining portion  31   e.    
     Thus, it becomes possible for the development roller  25  to contact the photosensitive drum  1 . 
     The other structural features of the image forming apparatus and cartridge in this embodiment are the same as those in the first embodiment, and offer the same effects as those in the first embodiment. 
     As described above, according to the present invention, the image forming apparatus and the process cartridge therefor are structured so that the plane parallel to the oscillatory movement of the development unit is intersectional to the plane parallel to the movement of the development roller separating member. 
     Therefore, when the process cartridge is not in the main assembly of an image forming apparatus, the impacts which occur during the transportation of a process cartridge, and the force for keeping the development roller in contact with the photosensitive drum, are unlikely to work in the direction to disengage the development roller separating member. In other words, the present invention is superior to the prior arts in terms of keeping the development roller separated from the photosensitive drum by the development roller separating member. 
     Further, the present invention can make it unnecessary to provide a process cartridge with additional mechanisms, or modifying the process cartridge in shape, in order to prevent the development roller separating member from being disengaged by the impacts occurring during the process cartridge shipment, and the abovementioned force applied to keep the development roller in contact with the photosensitive drum. Thus, the present invention makes it possible to provide a process cartridge which is inexpensive, and yet, the development roller separating member of which is unlikely to accidentally. 
     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. 
     This application claims priority from Japanese Patent Application No. 138043/2008 filed May 27, 2008, which is hereby incorporated by reference.