Patent Publication Number: US-6714750-B2

Title: Process cartridge, mounting mechanism for process cartridge and electrophotographic image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a process cartridge and a mounting mechanism (mounting-and-demounting mechanism) for a process cartridge, and an electrophotographic image forming apparatus. 
     Here, the electrophotographic image forming apparatus forms an image on a recording material through an electrophotographic image-formation-type process. Examples of the electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (a laser beam printer, an LED printer or a like), a facsimile machine, a word processor or a complex machine (multi-function printer or the like) or the like. 
     The process cartridge integrally contains an electrophotographic photosensitive drum, and charging means, developing means or a cartridge, in the form of a unit or a cartridge, which is detachably mountable to a main assembly of an image forming apparatus. The process cartridge may contain the electrophotographic photosensitive drum, and at least one of charging means, developing means and cleaning means, in the form of a cartridge which is detachably mountable to the main assembly of the image forming apparatus. Or, it may be a cartridge containing integrally at least developing means and an electrophotographic photosensitive member, the cartridge being detachably mountable to a main assembly of an image forming apparatus. 
     In an electrophotographic image forming apparatus using the electrophotographic image forming process, use has been made of process-cartridge type in which the process cartridge comprises as a unit the electrophotographic photosensitive member and process means actable on the electrophotographic photosensitive member, the unit being detachably mountable to the main assembly of the electrophotographic image forming apparatus. With the use of the process-cartridge-type apparatus, the maintenance operation can be carried out in effect by the users without the necessity of relying on a serviceman, and therefore, the operability is improved. Therefore, process-cartridge-type machines are widely used in the field of the image forming apparatus. 
     In order to provide satisfactory images by the electrophotographic image forming apparatus using such a process cartridge, it is necessary that the process cartridge is mounted at a predetermined position in the main assembly of the electrophotographic image forming apparatus to establish a correct connection of the interface portions such as various electrical contacts and a drive transmitting portion. 
     Referring first to FIG.  60  and FIG. 61, there are shown a process cartridge PC (FIG. 60) and a guide groove GL provided in the main assembly PR of the image forming apparatus (FIG.  61 ). FIG. 62 shows an image forming apparatus employing such a process cartridge PC. 
     As shown in FIGS. 60-62, in the mounting-and-demounting of the process cartridge PC relative to the main assembly PR of the image forming apparatus, a positioning boss CB is provided on the axis of an electrophotographic photosensitive member in the form of a photosensitive drum provided in the process cartridge PC, and on the other hand, the main assembly PR of the image forming apparatus is provided with a guide groove GL for guiding and positioning the positioning boss CB of the process cartridge. When the user inserts the process cartridge PC along the mounting guide (cartridge mounting guide) to a predetermined position, an abutting portion P provided on the main assembly PR of the image forming apparatus is abutted to the process cartridge PC to prevent rotation about the positioning boss CB. The apparatus of such a structure has been put into practice. 
     As shown in FIG. 62, the process cartridge PC is provided with a drum shutter DS which functions to cover the surface of the photosensitive drum when the process cartridge PC is out of the main assembly PR of the image forming apparatus and to expose the surface of the photosensitive drum when the process cartridge PC is mounted in the main assembly PR of the image forming apparatus. The opening and closing of the drum shutter DS is carried out in interrelation with an inserting operation of the process cartridge PC into the main assembly PR of the image forming apparatus or with the removal thereof. 
     An urging means for urging the process cartridge PC in the mounting direction has been proposed and put into practice, wherein the charging means is provided on the opening and closing cover C of the main assembly PR of the image forming apparatus. 
     As shown in FIG. 62, another proposal has been made in which a back cover UC having a shape corresponding to the outer configuration of the process cartridge PC is fixed to the inside of the cover C, and the process cartridge PC is urged to a regular position by closing the cover C. 
     The present invention provides a further development of the prior-art technique. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, in which the mounting operability for mounting the process cartridge to the main assembly of the apparatus, is improved. 
     It is another object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, in which the process cartridge can be automatically mounted to the mounting position of the main assembly of the apparatus. 
     It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, in which the process cartridge can be mounted to the mounting position of the main assembly of the apparatus in interrelation with a closing operation of an openable member. 
     It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable in which the process cartridge can be automatically mounted to or demounted from the mounting position of the main assembly of the apparatus. 
     It is a further object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, in which the mounting-and-demounting operability of the process cartridge relative to the main assembly of the apparatus is improved. 
     According to an aspect of the present invention, there is provided a process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus which includes an openable closing member, a first main assembly side guide movable in interrelation with the opening and closing action of the closing member, and a second main assembly side guide, the process cartridge comprising: an electrophotographic photosensitive drum; process means actable on the photosensitive drum; a first cartridge frame portion extending in a direction in which the cartridge is mounted to the main assembly of the apparatus, at one axial end portion of the photosensitive drum; a first cartridge guide projected from the first cartridge frame portion, the first cartridge guide moving the cartridge toward a cartridge mounting position by movement of the first main assembly side guide with the cartridge being supported on the first main assembly side guide, when the cartridge is mounted to the main assembly of the apparatus; a second cartridge frame portion extending in the mounting direction at the other axial end portion of the photosensitive drum; a second cartridge guide projected from the second cartridge frame portion, the second cartridge guide moving the cartridge toward a cartridge mounting position by movement of the second main assembly side guide with the cartridge being supported on the second main assembly side guide, when the cartridge is mounted to the main assembly of the apparatus; a first cartridge positioning portion for engaging with a first main assembly positioning portion provided in the main assembly of the apparatus to position the process cartridge relative to the main assembly of the apparatus when the process cartridge is mounted to the main assembly of the apparatus, the first cartridge positioning portion being projected outwardly from the first cartridge frame portion and coaxially with the photosensitive drum at the one axial end of the photosensitive drum; and a second cartridge positioning portion for engaging with a second main assembly positioning portion provided in the main assembly of the apparatus to position the process cartridge relative to the main assembly of the apparatus when the process cartridge is mounted to the main assembly of apparatus, the second cartridge positioning portion being projected outwardly from the second cartridge frame portion and coaxially with the photosensitive drum at the other axial end of the photosensitive drum. 
     These and other objects, features and advantages of the present invention will become more apparent upon a 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 schematic sectional view of an electrophotographic image forming apparatus according to an embodiment of the present invention. 
     FIG. 2 is a schematic sectional view of a process cartridge according to an embodiment of the present invention. 
     FIG. 3 is a perspective view of a process cartridge according to an embodiment of the present invention. 
     FIG. 4 is a perspective view of a process cartridge according to an embodiment of the present invention. 
     FIG. 5 shows perspective views of a movement guide and a guide stopper. 
     FIGS.  6 (A),  6 (B), and  6 (C) illustrate the relationship between the movement guide and the mounting guide. 
     FIG. 7 is a perspective view of a fixed guide and an inner bearing provided on a right-hand inner plate. 
     FIG. 8 is a perspective view of a cam plate. 
     FIG. 9 is a perspective view of a connection plate. 
     FIG. 10 is a perspective view of an opening and closing cover and a front guide. 
     FIG. 11 is an exploded perspective view of a bearing and a large gear including a coupling cam. 
     FIGS.  12 (A) and (B) are perspective views of a thruster rod. 
     FIG. 13 is perspective view of a fixed guide and a screw coil spring. 
     FIG. 14 is an exploded perspective view of a pushing arm and an inter-relating (interlocking) switch. 
     FIG. 15 is an exploded perspective view of a pushing arm and an inter-relating (interlocking) switch. 
     FIG. 16 is a perspective view of a process cartridge mounting-and-demounting mechanism. 
     FIG. 17 is an illustration of an inserting operation of the process cartridge into a process cartridge mounting-and-demounting mechanism. 
     FIG. 18 is an illustration of an inserting operation of the process cartridge into a process cartridge mounting-and-demounting mechanism. 
     FIG. 19 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism. 
     FIG. 20 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism. 
     FIG. 21 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism. 
     FIG. 22 is an illustration of a positional relation, in the longitudinal direction, of the back cap projection and a projection of the process cartridge at an opening W. 
     FIG. 23 is an illustration of an obstruction against insertion of the process cartridge into the process cartridge mounting-and-demounting mechanism in the process of opening and closing of the cover. 
     FIG. 24 is an illustration of an obstruction against insertion of the process cartridge into the process cartridge mounting-and-demounting mechanism in the process of opening and closing of the cover. 
     FIG. 25 is an illustration of an obstruction against insertion of the process cartridge into the process cartridge mounting-and-demounting mechanism in the process of opening and closing of the cover. 
     FIG. 26 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 27 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  26 . 
     FIG. 28 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as with FIG.  26 . 
     FIG. 29 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 30 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  29 . 
     FIG. 31 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  29 . 
     FIG. 32 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 33 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  32 . 
     FIG. 34 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  32 . 
     FIG. 35 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 36 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  35 . 
     FIG. 37 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  35 . 
     FIG. 38 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 39 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  38 . 
     FIG. 40 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  38 . 
     FIG. 41 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 42 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  41 . 
     FIG. 43 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  41 . 
     FIG. 44 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 45 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  44 . 
     FIG. 46 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  44 . 
     FIG. 47 is an illustration of a process cartridge inserting operation into the mounting-and-demounting mechanism of the process cartridge, more particularly an illustration of motion of the process cartridge, at the righthand side inner plate in the image forming apparatus. 
     FIG. 48 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the righthand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  47 . 
     FIG. 49 is an illustration of a process cartridge inserting operation into the process cartridge mounting-and-demounting mechanism, at the left-hand side inner plate in the image forming apparatus, as seen at the same timing as FIG.  47 . 
     FIGS.  50 ( a ), ( b ), and ( c ) show perspective views illustrating advancement and retraction of a large gear by rotation of a coupling cam. 
     FIG. 51 is an illustration of an obstruction against the thruster rod during transportation of the process cartridge. 
     FIG. 52 is an illustration of rotation of the coupling cam by the process cartridge mounting-and-demounting mechanism. 
     FIG. 53 is an illustration of rotation of the coupling cam by the process cartridge mounting-and-demounting mechanism. 
     FIG. 54 is an illustration of an operation of an inter-relating switch and a swing action of a pushing arm by the process cartridge mounting-and-demounting mechanism. 
     FIG. 55 is an illustration of an operation of an inter-relating switch and a swing action of a pushing arm by the process cartridge mounting-and-demounting mechanism. 
     FIG. 56 is an illustration of an operation of an inter-relating switch and a swing action of a pushing arm by the process cartridge mounting-and-demounting mechanism. 
     FIG. 57 is an illustration of an operation of an inter-relating switch and a swing action of a pushing arm by the process cartridge mounting-and-demounting mechanism. 
     FIG. 58 is an illustration of an operation of an inter-relating switch and a swing action of a pushing arm by the process cartridge mounting-and-demounting mechanism. 
     FIG. 59 is an illustration of supporting of the process cartridge in an operative state with the cover closed. 
     FIG. 60 is a perspective view of a process cartridge which is detachably mountable to a cartridge mounting guide provided in the main assembly of a conventional electrophotographic image forming apparatus. 
     FIG. 61 is a perspective view of a cartridge mounting guide provided in the main assembly of the conventional electrophotographic image forming apparatus. 
     FIG. 62 is an illustration of a back cover and a cartridge mounting guide provided in the main assembly of the conventional electrophotographic image forming apparatus. 
     FIG. 63 is a longitudinal sectional view illustrating a general arrangement of the electrophotographic image forming apparatus. 
     FIG. 64 is a longitudinal sectional view of a general arrangement of the process cartridge. 
     FIG. 65 is a perspective view of a process cartridge mounting-and-demounting mechanism. 
     FIG. 66 is a perspective view of a process cartridge. 
     FIG. 67 is an exploded perspective view of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 68 is an illustration of an operation of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 69 is a sectional side elevation illustrating an operation of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 70 is a sectional side elevation illustrating an operation of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 71 is a sectional side elevation illustrating an operation of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 72 is a sectional side elevation illustrating an operation of the process cartridge mounting-and-demounting mechanism shown in FIG.  65 . 
     FIG. 73 is a perspective view of a mounting-and-demounting guide used in an embodiment of the present invention. 
     FIG. 74 is a front view of a mounting-and-demounting guide used in an embodiment of the present invention. 
     FIG. 75 is a perspective view of a process cartridge used in an embodiment of the present invention. 
     FIG. 76 is a side view of a process cartridge used in an embodiment of the present invention. 
     FIG. 77 is a sectional side elevation illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 78 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 79 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 80 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 81 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 82 is a perspective view of a mounting-and-demounting guide used in an embodiment of the present invention. 
     FIG. 83 is a front view of a mounting-and-demounting guide used in an embodiment of the present invention. 
     FIG. 84 is a perspective view of a process cartridge used in an embodiment of the present invention. 
     FIG. 85 is a side view of a process cartridge used in an embodiment of the present invention. 
     FIG. 86 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 87 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 88 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 89 is a side view illustrating an operation of a process cartridge mounting-and-demounting mechanism used in an embodiment of the present invention. 
     FIG. 90 is a perspective view of a process cartridge which is detachably mountable to a cartridge mounting guide provided in the main assembly of a conventional electrophotographic image forming apparatus. 
     FIG. 91 is a perspective view illustrating a cartridge mounting guide provided in the main assembly of a conventional electrophotographic image forming apparatus. 
     FIG. 92 is a longitudinal sectional view illustrating a back cover and a cartridge mounting guide provided in the main assembly of the conventional electrophotographic image forming apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the process cartridge mounting mechanism (process cartridge mounting-and-demounting mechanism) and the process cartridge according to the present invention will be described in conjunction with the accompanying drawings. 
     In the following description, the longitudinal direction of a process cartridge is a direction in which a process cartridge is mounted to the main assembly of the apparatus (substantially perpendicular thereto), which is substantially parallel with the surface of the recording material and crossing with (substantially perpendicular to) a feeding direction of the recording material. The “left” and “right” directions are the left and right directions when the recording material is seen from the top in the feeding direction of the recording material. The top or upper surface or side of the process cartridge is the surface or side which takes an upper position when the process cartridge is mounted to the main assembly of the apparatus, and the bottom or lower surface or side of the process cartridge is the surface or side which takes a lower position when the process cartridge is mounted to the main assembly of the apparatus, respectively. 
     FIG. 1 illustrates an electrophotographic image forming apparatus according to an embodiment of the present invention. In this embodiment, a process cartridge shown in the FIG. 2 is detachably mountable to the electrophotographic image forming apparatus. FIG. 1 is a schematic illustration of the electrophotographic image forming apparatus when the process cartridge is mounted thereto, and FIG. 2 is a schematic illustration of the process cartridge. 
     A description will first be provided as to general arrangements of the process cartridge and the electrophotographic image forming apparatus using it, and then as to the process cartridge mounting-and-demounting mechanism. 
     (General arrangement) 
     In this embodiment, the electrophotographic image forming apparatus A (image forming apparatus) is in the form of a laser beam printer, and as shown in FIG. 1, it comprises an electrophotographic photosensitive member  7  in the form of a drum (photosensitive drum) as an image bearing member. The photosensitive drum  7  is electrically charged to a uniform potential by charging means in the form of a charging roller  8 , and then is exposed to information light on the basis of image information supplied from optical means (optical system), by which an electrostatic latent image is formed on the photosensitive drum  7 . The electrostatic latent image is visualized with a developer (toner) into a toner image. 
     In synchronism with the formation of the toner image, the recording material (recording paper, an OHP sheet, textile or the like) is fed one by one from a cassette  3   a  to an image transfer station by a pick-up roller  3   b  and a press-contact member  3   c  press-contacted thereto. The toner image formed on the photosensitive drum  7  is transferred onto the recording material  2  at the transfer station by application of a voltage to the transfer roller  4 . The recording material  2  now carrying the toner image transferred thereto is fed to fixing means  5  along a feeding guide  3   f.    
     In this embodiment, the fixing means  5  comprises a driving roller  5   a  and a fixing rotatable member  5   d.    
     The fixing rotatable member  5   d  comprises a cylindrical sheet containing therein a heater  5   b  and rotatably supported by a supporting member  5   c.  The fixing rotatable member  5   d  applies heat and pressure to the recording material  2  passing therethrough to fix the transferred toner image. The recording material  2  now having the fixed toner image fixed thereon is fed by discharging rollers  3   d,  and is discharged to a discharging portion  6  through a reverse feeding path. 
     In this embodiment, the feeding means or conveying means  3  is constituted by the pick-up roller  3   b,  the press-contact member  3   c,  discharging rollers  3   d  and so on. 
     The main assembly of the image forming apparatus contains the feeding means  3 , the fixing means  5  and driving means for driving the process cartridge B. The driving means receives a driving force from a motor (unshown) (driving source) and functions to rotate rotatable members through a gear train (unshown). 
     The driving force to be supplied to the process cartridge B is transmitted to a large gear  83  (FIG. 11) through the gear train (unshown), and is transmitted to the process cartridge B by the large gear  83 . The drive transmission between the large gear  83  and the process cartridge B is effected by coupling means disclosed in Japanese Patent No. 02875203 and Japanese Laid-open Patent Application Hei  10-240103,  for example. 
     As shown in FIG. 11, the coupling means comprises a large gear coupling  83   a  provided with a twisted recess having a substantially regular triangular cross-section and having an axis coaxial with a rotational center axis of the large gear  83 , and a twisted projection (driving force receiving portion or drum coupling  7   a   1 ) having a substantially regular triangular cross-section. The detailed description thereof will be provided hereinafter. The drum coupling  7   a   1  is formed coaxially with the rotational central axis of the photosensitive drum  7  on a gear flange (unshown) fixed to one end portion of the photosensitive drum  7 . The coupling means is brought into and out of the transmitting engagement by moving the large gear coupling  83   a  in the longitudinal direction of the photosensitive drum  7 . 
     By the engagement of the coupling, the axes of the large gear  83  and the photosensitive drum  7  are aligned, and the driving force transmission is enabled, and with the transmission of the driving force, the longitudinal position of the photosensitive drum  7  is determined. Therefore, in this embodiment, there is provided driving connection means for engagement and disengagement of the coupling means. 
     (Process cartridge) 
     The process cartridge B contains the electrophotographic photosensitive member and at least one process means. The process means includes charging means for electrically charging the electrophotographic photosensitive member, developing means for developing an electrostatic latent image formed on the electrophotographic photosensitive member, and cleaning means for removing the residual toner remaining on the photosensitive member. The process cartridge B according to this embodiment, as shown in FIG. 2, includes a rotatable photosensitive drum  7  which is an electrophotographic photosensitive member having a photosensitive layer. The surface of the photosensitive drum  7  is electrically charged to a uniform potential by application of a voltage to charging means in the form of a charging roller  8 . The photosensitive drum  7  thus electrically charged is exposed to image information (light image) supplied from an optical system  1  through an exposure opening. By doing so, an electrostatic latent image is formed on the surface of the photosensitive drum  7 . The electrostatic latent image is developed by developing means  10 . 
     In the developing means  10 , the toner is moved from a toner accommodating portion  10   a  to a developing roller  10   d  (rotatable developing member (developer carrying member)) by a rotatable feeding member  10   b  for feeding the toner. The developing roller  10   d  contains therein a stationary magnet  10   c.  By rotating the developing roller  10   d,  while keeping the magnet  10   c  stationary, and by regulating the thickness of a layer of the developer formed on the developing roller, a layer of the developer having a regulated thickness and having triboelectric charge is formed on the developing roller  10   d.  The toner on the surface of the developing roller  10   d  is transferred onto the photosensitive drum  7  in accordance with the electrostatic latent image, by which a toner (visualized) image is formed on the photosensitive drum  7 . 
     A transfer roller  4  is supplied with a voltage of a polarity opposite from the polarity of the toner image, by which the toner image is transferred onto the recording material  2 . Thereafter, the residual toner remaining on the surface of the photosensitive drum  7  is removed by a cleaning blade  11   a  of the cleaning means. The removed toner is received by a receptor sheet  11   b.  The received toner is collected in a removed toner accommodating portion  11   c.    
     The process cartridge B comprises a cleaning frame  11   d  rotatably supporting the photosensitive drum  7  and supporting the cleaning means  11  and the charging roller  8 , and a toner developing device frame  10   f  supporting the developing means  10 , and the toner accommodating portion  10   a.    
     The developing frame  10   f  is rotatably supported on the cleaning frame  11   d  so that the developing roller  10   d  of the developing means  10  may be opposed to the surface of the photosensitive drum  7  with a predetermined parallel gap. 
     At the opposite end portions of the developing roller  10   d,  there are provided spacers (unshown) for maintaining the predetermined gap between the developing roller  10   d  and the photosensitive drum  7 . 
     As shown in FIG. 3, at the sides of the toner developing device frame  10   f,  there are holder members  10   g.  Although not shown, it is provided with a hanging arm having a connecting portion for rotatably hanging the developing unit to the cleaning unit. In order to maintain the predetermined gap between the developing unit and the cleaning unit, a predetermined pressing force is applied. 
     The process cartridge B includes a toner developing device frame  10   f  constituted by a developing device frame  10   f   1  and a cap member  10   f   2  which are welded together, and a cleaning frame  11   d,  and these frames are coupled to constitute a cartridge frame CF. 
     At the opposite longitudinal ends of the cartridge frame CF, as shown in FIGS. 3,  4 , there are provided a first cartridge guide  18   b  and a second cartridge guide  18   b  (mounting guides  18   b ) for guiding mounting of the process cartridge in the direction indicated by an arrow X to the main assembly of the electrophotographic image forming apparatus (image forming apparatus)  14 , and a first cartridge positioning portion  18   a  and a second cartridge positioning portion  18   a  (positioning guides  18   a ) which are coaxial with the rotational center of the photosensitive drum  7  and which are to be supported by positioning means (a first main assembly positioning portion and a second main assembly positioning portion) provided in the main assembly of the image forming apparatus. 
     The positioning guides  18   a  are in the form of cylindrical bosses, in which the driving side cylindrical boss has a larger diameter. The positioning guide  18   a  at the non-driving side, as shown in FIG. 4, is provided with a mounting assisting guide  18   a   1  extended rearwardly with respect to the process-cartridge mounting direction. The trailing end of the mounting assisting guide  18   a   1  is formed into an outer surface  18   a   2 , also called a contact portion or pressure catching portion (see FIG. 43) to be urged, and is in the form of an arcuation coaxial with the positioning guide  18   a.    
     The mounting guide  18   b  to be guided has a portion to be supported  18   b   1  (lower or bottom surface or flat portion  18   b   1 ) which is to be supported by a first main assembly side guide  41  and a second main assembly side guide  41  (also called a movement or a moving guide  41 ) which will be described hereinafter, and a leading end portion  18   b   2  of the mounting guide  18   b  which takes the leading end of the process cartridge in the inserting direction. The leading end portion  18   b   2  has an arcuation continuing to the lower surface  18   b   1  and an arcuation continuing to the upper surface  18   b   6 , wherein the former has a diameter larger than that of the latter. The bottom corner portion or trailing end  18   b   3  of the lower surface  18   b   1  at the trailing end portion is formed into an inclined surface portion  18   b   4  (also called an inclined surface or an inclined portion) constituting an acute angle with the lower surface  18   b   1 . The trailing end portion of the upper surface includes an orthogonal or perpendicular surface  18   b   5  which is orthogonal with the upper surface  18   b   6 . 
     The center of gravity of the process cartridge is between the leading end and the trailing end of the mounting guide  18   b,  so that when the process cartridge B is supported at the trailing end of the mounting guide  18   b,  the process cartridge takes a front side down position at all times. 
     In this embodiment, the mounting guides  18   b  are provided on the end surfaces of the cleaning frame  11   d  above the positioning guides  18   a,  and the leading end portions  18   b   2  of the mounting guides are positioned downstream of a vertical plane passing through the rotational center of the photosensitive drum  7  which is coaxial with the positioning guides  18   a,  with respect to the mounting direction. However, the mounting guides  18   b  may be provided on the toner developing device frame  10   f  or on the holder members  10   g  provided at end portions of the toner developing device frame  10   f.    
     In this embodiment, the process cartridge B is provided with a drum shutter  12  which is rotatably supported on the cleaning frame  11   d,  and the drum shutter  12  is capable of simultaneously covering an exposure opening  9   b  and a transfer opening  9   a  to be opposed to the transfer roller  4 . 
     A description will be provided as to the structure of the drum shutter  12 . 
     As shown in FIGS. 1 and 2, the drum shutter  12  has a drum protecting portion  12   a  capable of covering the transfer opening  9   a  through which the photosensitive drum  7  and the transfer roller  4  are contacted to each other. The drum shutter  12  has a rotation shaft  12   b,  and is rotatably supported adjacent the exposure opening  9   b  of the cleaning frame  11   d.  The rotation shaft  12   b  has sliding portions  12   b   1  for sliding contact with the cleaning frame  11   d  at the opposite end portions of the rotation shaft  12   b,  respectively, a large diameter portion  12   b   2  having a diameter larger than that of the sliding portions  12   b   1  at the portion corresponding to the exposure opening  9   b  between the sliding portions  12   b   1 , and an exposure shutter portion  12   b   3  closing the exposure opening  9   b  when the drum shutter  12  is closed, the exposure shutter portion  12   b   3  being provided on the large diameter portion  12   b   2 . 
     To the outside of the large diameter portion  12   b   2  of the rotation shaft  12   b,  one end of a connecting portion  12   c  disposed at each of left and right positions is connected, and the other end is connected to the end portion of the protecting portion  12   a.    
     At the righthand side of the large diameter portion  12   b   2  of the rotation shaft  12   b,  there is disposed a cam portion  12   d  (FIG. 3) projected to the top side of the process cartridge. The righthand side connecting portion  12   c  of the drum shutter  12  is provided with a rib projected outwardly. The rib is received by a shutter guide  44   c  of a fixed guide  44  (FIG.  7 ), and functions to maintain the drum shutter  12  in the open state. In this embodiment, the above-described portions of the drum shutter  12  are integrally formed with resin material. As regards the positional relation of the righthand side mounting guide  18   b,  the rib and the cam portion  12   d  in the longitudinal direction, the mounting guide  18   b,  the rib and the cam portion  12   d  are arranged in the order named in the longitudinal direction from outside of the process cartridge. 
     The drum shutter  12  is urged in the direction of closing the photosensitive drum  7  by a coil spring (unshown). 
     By doing so, when the process cartridge B is out of the main assembly  14  of the apparatus, the drum shutter  12  keeps the transfer opening  9   a  closed as indicated by the chain lines in FIG.  2 . On the other hand, when the process cartridge is in the main assembly  14  and is in the operative position where it is capable of performing an image forming operation, the drum shutter takes the open position to expose the photosensitive drum  7  to permit the photosensitive drum  7  and the transfer roller  4  to contact each other through the transfer opening  9   a  as shown by solid lines in FIG.  2 . 
     (Process cartridge mounting-and-demounting mechanism) 
     Next, the mechanism for mounting or dismounting the process cartridge B into or from the image forming apparatus main assembly  14  will be described. 
     The process cartridge mounting/dismounting mechanism comprises: 
     (1) a pair of moving guides  41  which move between the optical system  1  and conveying means  3  while holding the process cartridge B; 
     (2) a pair of cam plates  50 , and a pair of inner plates  40  having guide rails  40   a  and  40   b,  for moving the moving guides  41 , during the front half of the process for opening an opening/closing cover  15  (which hereinafter will be referred to as opening/closing cover  15 ) and the latter half of the process for closing the opening/closing cover  15 ; 
     (3) a pair of connecting plates  51  for transmitting the rotational movement of the opening/closing cover  15  to the pair of cam plates  50 , one for one; 
     (4) a pair of pusher arms  52  for holding the process cartridge B to the process cartridge mounting place (which hereinafter will be referred to as the “image formation enabled position” or the “image formation location”) after the movement of the process cartridge B; and 
     (5) drum shutter opening/closing means for opening or closing the drum shutter  12  of the process cartridge B. 
     The process cartridge mounting/dismounting mechanism in this embodiment further comprises: 
     (6) a connecting means for coupling or uncoupling the coupling means which transmits the driving force, from the right side of the process cartridge B in terms of its lengthwise direction, during the front half of the process for opening the opening/closing cover  15  and the latter half of the process for closing the opening/closing cover  15 ; and 
     (7) an interlocking switch  54  which detects the completion of the closing of the opening/closing cover  15 , and allows electrical current to flow to enable the image forming apparatus to carry out an image forming operation. 
     In the process for closing the opening/closing cover  15 , first, the process cartridge B is conveyed by the movement of the moving guide  14  as a cartridge mounting member, and then, the coupling means is enabled to be coupled, by the connecting means, while moving the pusher arm  52 . Thereafter, the interlocking switch  54  is operated. In the process for opening the opening/closing cover  15 , first, the interlocking switch  54  is operated, and then, the connecting means and pushing arm  52  are disengaged, and lastly, the moving guide  41  is moved. In the following description of the process cartridge mounting/dismounting mechanism, first, the configuration of the various components of the mechanism are described, and then, the method for assembling the various components, and the method for mounting the process cartridge B into the image forming apparatus, will be described. Lastly, the movement of the process cartridge mounting/dismounting mechanism will be described following the rotational movement of the opening/closing cover  15 . 
     (Description of Structural Components) 
     (Moving guide and First and Second guides, on Main Assembly Side) 
     The pair of moving guides  41  are attached to the left and right inner plates  40 , one for one, being approximately symmetrically positioned with respect to the plane which divides the apparatus main assembly into the left and right halves in terms of the process-cartridge mounting direction. Referring to FIG. 5, each moving guide  41  is provided with a guiding groove  41   a  as a guiding portion, which is in the surface facing the process cartridge B, and in which the mounting guide  18   b  of the process cartridge B engages. Each moving guide  41  is also provided with first and second bosses  41   b  and  41   c,  which are for controlling the attitude of the process cartridge B within the apparatus main assembly, and are on the surface opposite to the surface in which the guiding groove  41   a  is located. The first and second bosses  41   b  and  41   c  are disposed on the downstream and upstream sides, respectively, of the guiding groove  41   a,  in terms of the direction X in which the process cartridge B is mounted into the apparatus main assembly. 
     The first boss  41   b  is provided with a through hole  41   b   2 , which is coaxial with the circumferential surface of the boss  41 . It is also provided with a snap-fit claw  41   b   1 , the end portion of which projects inward in terms of the radius direction of the through hole. The second boss  41   c  is provided with claws  41   c   1  and  41   c   2 , which are on the end portion of the boss  41   c  and project outward in terms of the radius direction of the boss  41   c.  These claws  41   c   1  and  41   c   2  are extended so that the direction, in which they extend, aligns with the line connecting the rotational center of the second boss  41   c  and the rotational center of the cam plate, which will be described later, after the process cartridge is moved by the process cartridge mounting/dismounting mechanism to the second position at which the process cartridge B is capable of carrying out an image forming operation. 
     The guiding groove  41   a  has two sections, that is, downstream and upstream sections in terms of the process-cartridge insertion direction, and the downstream section is slightly recessed from the upstream section, with the presence of a step between the two sections. The surface  41   a   1  of the downstream section of the guiding groove  41   a  is the retaining surface on which the mounting guide  18   b  of the process cartridge B rests while the moving guide  41  moves within the image forming apparatus, and the surface  41   a   2  of the upstream section, which is higher than the surface  41   a   1  of the downstream section, is a guiding surface, which is also called a catching surface, which guides the process cartridge B when the process cartridge B is inserted into, or pulled out of, the apparatus main assembly. The retaining surface  41   a   1  and guiding surface  41   a   2  are downwardly inclined in terms of the process-cartridge insertion direction, assuring that as a user inserts the process cartridge B into the image forming apparatus main assembly  14 , the process cartridge B is guided into the retaining surface  41   a   1 . 
     Referring to FIG. 6, the step portion between the retaining surface  41   a   1  and guiding surface  41   a   2  is given a function of pushing the trailing end  18   b   3  of the mounting guide  18   b  of the process cartridge B to assure that the process cartridge B is conveyed to a predetermined location, in spite of the conveyance load, to which the process cartridge B supported by the retaining surface  41   a   1  is subjected during the movement of the moving guide  41 . The stepped portion has an inclined portion or surface  41   a   4 , the theoretical extension of which forms an acute angle relative to the retaining surface  41   a   1 , and a perpendicular surface  41   a   3 , which is between the inclined portion  41   a   4  and retaining surface  41   a   1  and is approximately perpendicular to the retaining surface  41   a   1 . The inclined portion  41   a   4  prevents the mounting guide  18   b , supported by the retaining surface  41   a   1 , from being lifted from the retaining surface  41   a   1  by the resistance of the transfer roller  4 , which acts in the direction to lift the process cartridge B (FIG.  6 (B)). 
     Referring to FIG.  6 (A), in order to guide the mounting guide  18   b  of the process cartridge B from the guiding surface  41   a   2  onto the retaining surface  41   a   1 , the distance |g from the corner of the leading end of the retaining surface  41   a   1  in terms of the process-cartridge insertion direction, to the intersection between the inclined portion  41   a   4  and the guiding surface  41   a   2 , and the length |c of the bottom surface  18   b   1  of the mounting guide  18   b  in terms of the process cartridge inserting direction, must satisfy the following inequality: 
     |g&gt;|c. 
     In other words, the length of the retaining surface  41   a   1  is longer than the bottom surface  18   b   1  of the mounting guide  18   b.  Referring to FIG.  6 (C), if the guiding surface  41   a   2  and retaining surface  41   a   1  are connected by the inclined surface  41   a   4  alone, the retaining surface  41   a   1  will be longer by a length of δ, being unnecessarily longer than the bottom surface  18   b   1  of the mounting guide  18   b.  In such a case, the distance by which the moving guide  41  and process cartridge B slide relative to each other as the process cartridge B is subjected to the conveyance load, will be excessively long. Thus, in this embodiment, the length of the retaining surface  41   a   1  is adjusted, being reduced in length, by the addition of the perpendicular surface  41   a   3 , so that the trailing end of the mounting guide  18   b  can be more quickly pushed as the process cartridge B is subjected to the conveyance resistance. 
     The downwardly facing surface of the top wall of the guiding groove  41   a  is approximately parallel to the retaining surface  41   a   1 . It has top surfaces  41   a   5  and  41   a   6 , and a gently inclined top surface  41   a   7  which connects the top surfaces  41   a   5  and  41   a   6 . The top surfaces  41   a   5  and  41   a   6  are positioned so that their distance from the retaining surface  41   a   1  and guiding surface  41   a   2 , in terms of the direction perpendicular to the surfaces of the retaining surface  41   a   1  and guiding surface  41   a   2 , respectively, becomes slightly greater than the thickness of the mounting guide  18   b  of the process cartridge B, in terms of the direction perpendicular to the lengthwise direction of the mounting guide  18   b . 
     As for the configurations of the pair of moving guides  41 , which have been described up to this point, the left and right moving guides are symmetrically positioned relative to each other, with respect to the vertical plane which divides the process cartridge B into the left and right halves. However, the right moving guide is provided with a means for transmitting driving force to the process cartridge B, and therefore, the second boss  41   c  of the right moving guide is provided with a timing boss  41   d,  which extends beyond the claws  41   c   1  and  41   c   2  in the axial direction of the second boss  41   c.    
     Next, a cartridge conveying means, more specifically, the guide rails, the cam plate, and the connecting plate, which make up the moving guide moving means, will be described. The structure of the cartridge conveying means (moving guide moving means) does not need to be limited to the one which will be described next; it is optional. 
     (Guide Rails of Inner Plate) 
     FIG. 7 shows the right inner plate  40  of the image forming apparatus main assembly  14 . The right inner plate  40  is provided with a pair of guide rails, as the cartridge conveying means (means for holding the cartridge mounting member), with which the bosses  41   b  and  41   c  slidably engage, respectively. 
     The widths (dimension in terms of the direction perpendicular to the direction in which the guides rails extend) of the guide rails  40   a  and  40   b  are equal to, or slightly greater than, the diameters of the bosses  41   b  and  41   c,  respectively, allowing the moving guide  41  to easily slide. In this embodiment, the inner plate  40  is formed of an approximately 1 mm thick metallic plate, and the guide rails  40   a  and  40   b  are holes, which have been formed by burring, and the lips of which protrude outward of the image forming apparatus. The reason for using burring as the method for forming the guide rails  40   a  and  40   b  is as follows. That is, if the guide rails  40   a  and  40   b  are formed simply by punching, the surfaces of the guide rails  40   a  and  40   b,  across which the bosses  41   b  and  41   c  of the moving guide  41  slide, respectively, will be rough, and also will be only as wide as the thickness of the metallic plate, increasing the contact pressure which acts on the bosses  41   c  and  41   b.  Thus, as the moving guide  41  repeatedly slides on the guide rails, the bosses  41   b  and  41   c  will be shaved across the areas in contact with the edges of the guide rails  40   a  and  40   b,  respectively, which sometimes will result in the disengagement of the moving guide  41  from its predetermined position in the apparatus main assembly. This is the reason burring is used instead of simple punching. In other words, burring is used to create the guide rails  40   a  and  40   b,  which are smoother and wider, across the surfaces across which the bosses  41   b  and  41   c  slide, in order to prevent the bosses  41   b  and  41   c  from being prematurely shaved by the guide rails  40   a  and  40   b,  respectively. In other words, the usage of burring as the method for forming the guide rails  40   a  and  40   b  is a countermeasure for the premature shaving of the bosses  41   b  and  41   c  by the guide rails  40   a  and  40   b.    
     With the provision of the pair of guide rails  40   a  and  40   b,  and the pair of bosses  41   b  and  41   c  of the moving guide  41 , the moving guide  41  is allowed to move between the optical system  1 , and the conveyance path  3  for the recording medium  2 . 
     The first guide rail  40   a,  in which the first boss  41   b  engages, has a nearly horizontal portion  40   a   1 , which is on the opening/closing cover  15  side, and an inclined portion  40   a   2 , which is located at the deeper end of the guide rail  40   a,  and is inclined downward in terms of the process-cartridge insertion direction. The two portions  40   a   1  and  40   a   2  are connected by a smoothly curved portion. The second guide rail  40   b,  in which the second boss  41   c  engages, has an arcuate portion  40   b   1 , which bulges upward, and a vertical straight portion  40   b   2 , which is located on the first guide rail  40   a  side. The two portions  40   b   1  and  40   b   2  are connected by a smoothly curved portion. Further, the inner plate  40  is provided with a hole  40   c,  in which the rotational shaft  50   a  of the cam plate  50 , which will be described later, is borne. The axial line of the hole  40   c  coincides with the center of the curvature of the arcuate portion  40   b   1 . The inner plate  40  is also provided with an arcuate hole  40   d,  which is located near the hole  40   c,  and the center of the curvature of which coincides with the axial line of the hole  40   c.    
     In this embodiment, the hole  40   c  is also formed by burring. The arcuate hole  40   d  is provided with an assembly facilitation portion  40   d   1 , which is in the deeper end portion of the arcuate hole  40   d  in terms of the direction in which the opening/closing cover is closed, and is slightly wider in terms of the radius direction of its curvature. This assembly facilitation portion  40   d   1  is where the assembly facilitation claw  50   e  of the cam plate  50  (FIG. 8) is put through when the cam plate  50  is attached to the inner plate  40 . After the assembly facilitation claw  50   e  is put through the assembly facilitation portion  40   d   1  of the arcuate hole  40   d,  the cam  50  is rotated in the direction in which the opening/closing cover is opened. As the cam  50  is rotated, the back surface of the assembly facilitation claw  50   e  comes into contact with the upper edge of the arcuate hole  40   d,  preventing the cam plate  50  from disengaging from the inner plate  40  in terms of the axial direction of the rotational shaft  50   a.    
     (Cam Plate) 
     To the outward surface of the inner plate  40 , that is, the surface opposite to where the moving guide  41  is mounted, the cam plate  50  is attached, which is provided with a rotational shaft  50   a,  the rotational axis of which coincides with the center of the curvature of the arcuate portion  40   b   1  of the second guide rail  40   b.    
     Referring to FIG. 8, the cam plate  50  is provided with a cam hole  50   b, which has an arcuate portion  50   b   1  (which hereinafter may be referred to as an arcuate hole), and a straight portion  50   b   2  (which hereinafter may be referred to as a straight groove hole). The center of the curvature of the arcuate portion  50   b   1  of the cam hole  50   b  coincides with the axial line of the rotational shaft  50   a.  The straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  is continuous from the inward end of the arcuate portion  50   b   1  of the cam hole  50   b,  in terms of the direction in which the opening/closing cover  15  is closed, and extends outward in terms of the radius direction of the curvature of the cam hole  50   b.    
     Into this cam hole  50   b,  the second boss  41   c  of the moving guide  41  engages after being put through the second guide rail  40   b  of the inner plate  40 . The radius of the arcuate portion  50   b   1  of the cam hole  50   b  is smaller than that of the arcuate portion  40   b   1  of the second guide rail  40   b,  and is nearly equal to the distance between the bottom end of the straight portion  40   b   2  of the second guide rail  40   b  and the hole  40   c.  The distance between the tip of the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  and the rotational shaft  50   a  is slightly greater than the radius of the arcuate portion  40   b   1  of the second guide rail  40   b.  The widths of the arcuate portion  50   b   1  of the cam hole  50   b  and straight groove hole  50   b   2  are slightly greater than the diameter of the second boss  41   c  of the moving guide  41 . 
     At the leading end of the arcuate portion  50   b   1  of the cam hole  50   b,  in terms of the direction in which the opening/closing cover  15  is opened, an assembly facilitation portion  50   b   3  is provided, through which the claws  41   c   1  and  41   c   2  on the tip of the second boss  41   c  of the moving guide  41  are put during the apparatus assembly. The assembly facilitation portion  50   b   3  is shaped so that it extends from the end of the arcuate portion  50   b   1 , both outward and inward of the cam hole  50   b,  in terms of the radius direction of the arcuate portion  50   b   1  of the cam hole  50   b.  One or both of these two extending portions of the assembly facilitation portion  50   b   3  are rendered narrower than the diameter of the second boss  41   c  of the moving guide  41 , in order to prevent the second boss  41   c  of the moving guide  41  from entering the outward portion of the assembly facilitation portion  50   b   3 , with respect to the arcuate portion  50   b   1 , in terms of the radius direction of the cam hole  50   b,  during the apparatus assembly. Further, the cam plate  50  is provided with a temporary holding rib  50   c,  which is on the surface opposite to the surface facing the inner plate  40 , and in the adjacencies of the upstream end of the assembly facilitation portion  50   b   3  in terms of the direction in which the opening/closing cover  15  is closed. 
     The guide rails  40   a  and  40   b  of the inner plate  40  are such holes that have been formed by burring, and their lips slightly protrude toward the cam plate  50 . Therefore, in order to accommodate the guide rails  40   a  and  40   b,  the cam plate  50  is tiered around the cam hole  50   b  by a height equal to the distance by which the lips of the guide rails  40   a  and  40   b  protrude toward the cam plate  50 . The aforementioned temporary positioning rib  50   c  is located above this tiered portion of the cam plate  50 , so that as the claw  41   c   1  of the moving guide  41  goes over this temporary positioning rib  50   c  during the apparatus assembly, the cam plate  50  is flexed by this tiered portion. 
     The cam plate  50  is also provided with a connecting or timing boss  50   d,  which is in the adjacencies of the assembly facilitation portion  50   b   3 , that is, the trailing end of the cam hole  50   b,  on the surface opposite to the surface on which the rotational shaft  50   a  is present. The end portion of the connecting boss  50   d  constitutes a claw  50   d   1 . The assembly facilitation claw  50   e  is near the rotational shaft  50   a.  The assembly facilitation claw  50   e  is fitted into the arcuate hole  40   d  of the inner plate  40  to prevent the disengagement of the cam plate  50 . 
     The descriptions given above regarding the configuration of the cam plate  50  are common to both the left and right cam plates. 
     Next, the cam plate  50  on the driving means side (which hereinafter will be referred to as the right) will be described. The right cam plate  50  is provided with a raised portion, which is on the same side as the side on which the connecting boss  50   d  is provided, and is on the inward side of the cam hole  50   b  in terms of the radius direction of the cam hole  50   b.  The top surface  50   f  of this raised portion is slightly outward of the surface in which the cam hole  50   b  is present. The top surface  50   f  is provided with a second boss  50   g.  The distance by which the surface  50   f  is raised is greater than the height of the connecting boss  50   d.  The end portion of the second boss  50   g  is provided with a pair of claws  50   g   1  and  50   g   2 , which extend in the radius direction of the boss  50   g.    
     The cam plate  50  on the side from which the process cartridge is not driven (which hereinafter will be referred to as the left cam plate) is provided with the second cam portion  50   h,  which is located near the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  and on the outward side of the cam hole  50   b  in terms of the radius direction of the cam hole  50   b,  and a contact surface  50   i,  which is on the upstream side of the cam plate  50  in terms of the rotational direction in which the opening/closing cover  15  closes. The second cam  50   h  is a portion of the cam plate  50 , which is for driving the pushing arm  52  as the means for accurately positioning the left side of the process cartridge, and will be described later. It has a gently arcuated arm driving portion  50   h   1 , which extends from the edge of the arcuate periphery of the main structure of the cam plate  50 , approximately in the direction in which the opening/closing cover  15  closes, and a gently arcuated arm holding or retaining portion  50   h   2 , the center of the curvature of which coincides with that of the axial line of the rotational shaft  50   a  of the cam plate  50 . These portions  50   h   1  and  50   h   2  are in the form of a groove, the open side of which, in terms of the lengthwise direction of the process cartridge, faces the inner plate  40 . The second cam  50   h  protrudes further inward of the apparatus main assembly than the inwardly tiered portion of the cam plate  50  for accommodating the inwardly protruding lips of the guide rail  40   b.  The pushing arm  52  fits in the gap created by the difference between the distances by which the second cam  50   h  and the tiered portion of the cam plate  50  protrude inward of the apparatus main assembly. The contact surface  50   i  extends in the radius direction of the rotational shaft  50   a,  and its height in terms of the thickness direction of the cam plate  50  is the same as that of the bottom wall of the second cam  50   h.    
     (Connecting Plate) 
     The cam plate  50  and opening/closing cover  15  are connected by the connecting plate  51 , together forming a four-joint linkage. The connecting plate  51  has a hole  51   a,  which is located in one of the lengthwise end portions, and into which the connecting boss  50   d  of the cam plate  50  rotationally engages, and a shaft  51   b,  which is located at the other lengthwise end, and has a pair of snap-fitting claws  51   b   1 . The hole  51   a  is provided with a recess  51   a   1  for preventing the claw  50   d   1  of the connecting boss  50   d  of the cam plate  50  from hanging up on the connecting plate  51  when connecting the connecting plate  51  and the cam plate  50 . The recess  51   a   1  extends from one side of the connecting plate  51  to the other in terms of the axial direction of the shaft  51   b.  The pair of snap-fitting claws  51   b   1  are symmetrically positioned with respect to the line connecting the centers of the hole  51   a  and shaft  51   b.  Further, the shaft  51   b  is provided with a pair of intermediate portions, which are symmetrically positioned with respect to the line perpendicular to the line connecting the centers of the hole  51   a  and shaft  51   b,  being therefore at the middle of the intervals between the pair of snap-fitting claws  51   b   1  in terms of the circumferential direction of the shaft  51   b,  reinforcing the shaft  51   b  against the load which acts upon the shaft  51   b  in the direction of the line which connects the centers of the hole  51   a  and shaft  51   b  of the connecting plate  51 . 
     (Cover and Cover Backing) 
     Referring to FIG. 10, the opening/closing cover  15  is provided with a pair of hinges  15   b  having a center boss  15   a , and a pair of plates having a connecting hole  15   c  into which the shaft  51   b  of the connecting plate  51  fits. The pair of hinges  15   b  and the pair of plates having a connecting hole  15   c  are on the back side of the opening/closing cover  15 , near the lengthwise ends of the opening/closing cover  15 , one for one. The opening/closing cover  15  is also provided with a backing  16 , which is for increasing the rigidity of the opening/closing cover  15 , and is fixed to the inward surface of the opening/closing cover  15 . The backing  16  is provided with a pair of projections  16   a  and  16   b , which are located near the lengthwise end of the backing  16 , and function as guides for approximately guiding the process cartridge B when mounting the process cartridge B into the image forming apparatus. 
     (Front Guide) 
     Also referring to FIG. 10, there are front guides  43  between the left and right inner plate  40 , being fixed thereto. The front guide  43  is provided with a pair of supporting holes  43   a,  in which the pair of center bosses  15   a  of the opening/closing cover  15  are rotationally supported, one for one. The front guide  43  is also provided with a pair of side guide ribs or side guides  43   b  and a pair of contact ribs  43   c,  which are located near the lengthwise ends of the front guide  43 , one for one. 
     Each side guide  43   b  is disposed so that the position of its inward surface coincides with the inward surface of the corresponding moving guide  41 . Not only does it guide the positioning guide  18   a  of the process cartridge B and the process cartridge B itself, but also accurately positions the process cartridge B in terms of the lengthwise direction of the process cartridge B in coordination with the other side guide  43   b.  Each contact rib  43   c  is disposed on the inward side of the side guide  43   b  in terms of the lengthwise direction of the opening/closing cover  15 , and contacts the downwardly facing surface  10   f   4  of the toner/developing means holding frame  10   f  of the process cartridge B. 
     (Driving Means) 
     Referring to FIGS. 7 and 11, the right and left inner plates  40  are provided with an inward bearing  84 , which is located higher than the transfer roller  4 . With the provision of this inward bearing  84 , a large gear  83  having a large gear coupling  83   a  for transmitting a driving force to the photoconductive drum  7  is rotationally supported by the inner plate  40 . 
     The opposite side of the large gear coupling  83   a  of the large gear  83  is rotationally supported by an outward bearing  86  fixed to a gear cover (unshown) attached to the inner plate  40 . 
     The inward bearing  84  is provided with an arcuate cartridge catching/retaining portion  84   a  for holding the process cartridge B to a position in which the large coupling  83   a  of the process cartridge B is engageable (final process cartridge position in the apparatus main assembly: second location). The location of the arcuate cartridge catching/retaining portion  84   a  corresponds to the final process cartridge position in the apparatus main assembly, and the center of the curvature of the arcuate cartridge catching/retaining portion  84   a  coincides with the axial line of the large gear  83 . The arcuate cartridge catching/retaining portion  84   a  catches the positioning guide  18   a  of the process cartridge B. The inward bearing  84  is also provided with a cylindrical portion  84   b  and cam surfaces ( 84   c   1  and  84   c   2 ), both of which are on the large gear  83  side. The cam surfaces  84   c   1  and  84   c   2  face outward in terms of the radius direction of the cylindrical portion  84   b.    
     On the cam surfaces  84   c   1  and  84   c   1  side of the inward bearing  84 , a cylindrical coupling cam  85  is provided. The coupling cam  85  rotationally fits around the cylindrical portion  84   b,  and has a cam surfaces ( 85   a   1  and  85   a   2 ) which contact the cam surfaces  84   c   1  and  84   c   2 . Cam surfaces  85   a   2  and  84   c   2  are inclined surfaces and cam surfaces  84   c   1  and  85   a   1  are raised surfaces. As the coupling cam  85  rotates, it allows the large gear  83  to move in its axial direction due to the function of the cam surfaces. Further, the coupling cam  85  is provided with a boss  85   b,  which is located on the outward edge of the cylindrical peripheral surface of the coupling cam  85  in terms of the radius direction of the coupling cam  85 . More specifically, the coupling cam  85  is provided with a circumferential rib  85   c,  which is attached to the large gear  83  side of the cylindrical peripheral surface of the coupling cam  85 , and projects in the radius direction of the coupling cam  85 . The boss  85   b  is attached to this circumferential rib  85   c,  projecting in the axial direction of the coupling cam  85 . The tip of the boss  85   b  is provided with a claw  85   b   1 . Between the outward bearing  86  and large gear  83 , there is spring (not shown), which keeps the large gear  83  pressed toward the inward bearing  84 . 
     (Thruster Rod) 
     FIGS.  12 (A) and  12 (B) show a thruster rod  55 . The thruster rod  55  constitutes a connecting rod which connects the second boss  50   g  to the right cam plate  50  and the boss  85   b  of the coupling cam  85 . It is on the right inner plate  40 , and forms the second four-joint linkage. As shown in FIGS.  12 (A) and  12 (B), the thruster rod  55  is provided with two through holes: keyhole-shaped hole  55   a  and an elongated hole  55   b.  The keyhole-shaped hole  55   a  has a size and a configuration for allowing the claw  85   b   1  of the coupling cam  85  to be put through, and the boss  85   b  is slidably fitted therein. The elongated hole  55   b  is a hole through which the second boss  50   g  of the cam plate  50  is slidably put. The elongated hole  55   b  has three sections: a straight portion  55   b   1 , which extends downward approximately perpendicular to the line connecting the center of the end portion, on the keyhole-shaped hole  55   a  side, and the center of the keyhole-shaped hole  55   a;  an inclined portion  55   b   2 , which extends diagonally downward from the bottom end of the straight portion  55   b   1 ; and an arcuate portion  55   b   3 , which extends diagonally downward from the bottom end of the inclined portion  55   b   2 . Below the arcuate portion  55   b   3 , a boss is located, and the tip of the boss is provided with a claw. 
     Above the straight portion  55   b   1  of the elongated hole  55   b,  a lifting surface or portion  55   f  is provided, which is recessed in the lengthwise direction of the thruster rod  55 , appearing like a U-shaped groove which is laid on its side and opens toward the direction opposite to the keyhole-shaped hole  55   a.  Further, above the lifting surface  55   f,  a backup portion  55   g  is provided, which is an upwardly open recess. These portions are integral parts of the thruster rod  55 . 
     (Stationary Guide) 
     As is evident from FIG. 7, there is a stationary guide  44 , which surrounds the inward bearing  84 . The stationary guide  44  is approximately in the form of a letter E, being open toward the area, and extends beyond the cartridge catching/retaining portion  84   a  of the inward bearing  84 , and inward end of the first guide rail  40   a  of the inner plate  40 . 
     The stationary guide  44  is provided with: a butting portion or first positioning portion  44   a,  which surrounds the cartridge catching/retaining portion  84   a,  and is enabled to come into contact with the butting surface  18   c  located on one of the lengthwise ends of the process-cartridge B as the process cartridge B is mounted; a rotation controlling portion  44   b,  which is located higher than the butting portion  44   a,  and on the downstream side of the cartridge catching/retaining portion  84   a  in terms of the process cartridge mounting direction, and fixes the position of the process cartridge B in terms of the rotational direction of the process cartridge B, by being contacted by the butting surface  18   d  provided on the process cartridge frame to control the rotational movement of the process cartridge B, during an image forming operation; and a shutter guide portion  44   c,  which is located higher than the rotational controlling portion  44   b,  and constitutes one of the components of the mechanism for opening or closing the aforementioned drum shutter  12 . 
     Further, referring to FIG. 13, the stationary guide  44  is provided with a helical torsion coil spring  45 , which is located in the middle portion among the three horizontal portions of the approximately E-shaped stationary guide  44 , and is for keeping the positioning guide  18   a  of the process cartridge B pressed upon the cartridge catching/retaining portion  84   a,  on the upstream side of the cartridge catching/retaining portion  84   a  in terms of the cartridge-mounting direction. Thus, the surface of the stationary guide  44 , which is placed in contact with the inner plate  40  is provided with a recess  44   d,  in which the helical torsion coil spring  45  is placed and is allowed to play its role. In the recess  44   d  are, a boss  44   d   1 , around which the coiled portion of the helical torsion coil spring  45  is fitted, a claw  44   d   2  for preventing the stationary arm portion  45   b  of the helical torsion coil spring  45  from becoming dislodged, and a regulative claw  44   d   3  and a regulating rib  44   d   4  for regulating the position of the functional arm of  45   c  of the helical torsion coil spring  45 , in terms of the lengthwise direction of the process cartridge B. 
     Also, the stationary guide  44  is provided with a positioning rib  44   e   1 , which is for accurately positioning the stationary guide  44  relative to the right inner plate  40  and fixing it thereto, and is located on the surface opposite to the surface on which the rotation controlling portion  44   b  is provided, in correspondence to the rotation controlling portion  44   b.  The positioning rib  44   e   1  accurately positions the stationary guide  44  relative to the right inner plate, in terms of the vertical direction, by being engaged into the positioning hole (unshown) of the right inner plate  40 . The tip of the positioning rib  44   e   1  is provided with a claw  44   e   2 , which prevents the stationary guide  44  from becoming dislodged from the right inner plate  40 . Further, the stationary guide  44  is provided with three locking claws  44   f  for keeping the stationary guide  44  fixed to the right inner plate  40 , and a projection  44   g  for preventing the stationary guide  44  from horizontally sliding, ensuring that the stationary guide  44  remains firmly fixed to the right inner plate  40 , maintaining a proper attitude. 
     (Conveying Means Frame) 
     A bearing for rotationally supporting the transfer roller  4  is slidably attached to a conveying means frame  90  (FIG.  28 ), which provides a surface across which the recording medium is conveyed. The conveying means frame  90  is provided with a positioning portion  90   a,  which is located adjacent to, and above, the left end of the transfer roller  4 , in terms of the axial direction of the roller  4 , and the position of which corresponds to the position of the rotational axis of the large gear  83 . The positioning portion  90   a  holds the positioning boss  18   a  of the process cartridge B to the position in which the process cartridge B is capable of carrying out an image forming operation. This positioning portion  90   a,  and the pushing arm  52 , which will be described later, together constitute the means for accurately positioning the left side of the process cartridge B. 
     (Push Arm) 
     Referring to FIGS. 14 and 15, the left inner plate  40  is provided with a pushing arm  52 , which has a function of holding the positioning boss  18   a  of the process cartridge B to the positioning portion  90   a,  after the process cartridge B is moved by the process cartridge mounting/dismounting mechanism, the movement of which is linked to the closing movement of the opening/closing cover  15 . 
     The pushing arm  52  is rotationally supported by the left inner plate  40 ; the rotational shaft  52   a  of the pushing arm  52  is rotationally engaged in the hole  40   g  of the left inner plate  40 . Further, the pushing arm  52  is provided with a resilient pressing portion  52   b,  which is pushed through a fan-shaped hole  40   h  of the left inner plate  40 . 
     The pushing arm  52  is provided with a helical torsion coil spring  53 , which is fitted around the base portion of the rotational shaft  52   a,  and keeps the pushing arm  52  pressed upward to prevent the resilient pressing portion  52   b  from invading the path of the positioning guide  18   a  of the process cartridge B. 
     The tip of the resilient pressing portion  52   b  is provided with a boss  52   c,  which is for allowing the pushing arm  52  to oscillate, and engages in the second cam  50   h  of the cam plate  50 . Further, the pushing arm  52  is provided with claws  52   d   1  and  52   d   2 , which are for attaching the pushing arm  52  to the left inner plate  40 , and are located adjacent to the base portion of the resilient pressing portion  52   b,  and the rotational shaft  52   a,  respectively. The claws  52   d   1  and  52   d   2  are put through the fan-shaped hole  40   h  and key-shaped hole  40   i  of the left inner plate  40 , and latch on the back sides of the fan-shaped hole  40   h,  key-shaped hole  40   i  functioning as locking devices for preventing the pushing arm  52  from becoming disengaged from the left inner plate  40 . 
     In addition, the pushing arm  52  is provided with: a recess  52   e  in which the aforementioned helical torsion coil spring  53  is disposed; a rib  52   f  as a means for preventing the functional arm  53   b  of the helical torsion coil spring  53  from dislodging; a protective rib  52   g,  which is large enough to keep the helical torsion coil spring  53  almost completely covered, within the rotational range, after the stationary arm  53   c  of the helical torsion coil spring  53  supported by the spring anchor portion  40   j  of the left inner plate  40  is fixed; and a temporary holding rib  52   h,  which makes it possible to temporarily hold the stationary arm  53   c  of the helical torsion coil spring  53  to the pushing arm  52  before attaching it to the spring anchor portion  40   j.  They are near the base portion of the rotational shaft  52   a.    
     (Interlocking Switch) 
     Referring to FIGS. 14 and 15, the left inner plate  40  is provided with an interlocking switch  54 , which is rotationally supported by the plate  40 . It presses a microswitch  91  (FIG. 58) provided on a circuit board, at the very end of the closing of the opening/closing cover  15 . As the interlocking switch  54  presses the microswitch  91 , current flows through various parts of the image forming apparatus main assembly, readying it for an image forming operation. 
     The interlocking switch  54  comprises: a rotational shaft  54   a  which functions as a pivot; a lever  54   b  which presses the microswitch  91 ; an elastic portion  54   c  which elastically bends as it presses on the contact surface  50   i  of the cam plate  50 ; and a claw  54   d  for attaching the interlocking switch  54  to the inner plate  40 . The left inner plate  40  is provided with a hole  40   k,  the position of which corresponds to that of the rotational shaft  54   a,  and a hole  40     l   located outside the operational range of the lever  54   b.    
     (Assembly Method) 
     Next, the method for assembling the above described various components will be described. 
     As will be understood from FIGS. 5,  7 , and  15 , and the like drawings, the moving guide  41  is attached to the inner plate  40  in the following manner. First, the claws  41   c   1  and  41   c   2  located at the tip of the second boss  41   c  are aligned with the arcuate portion  40   b   1  of the second guide rail  40   b,  and put though the arcuate portion  40   b   1 . Then, the moving guide  41  is rotated. As the moving guide  41  is rotated, the claws  41   c   1  and  41   c   2  latch on the lips of the second guide rail  40   b,  preventing the second boss  41   c  from disengaging from the inner plate  40 . Then, the first boss  41   b  of the moving guide  41  is put through the first guide rail  40   a.  Next, the moving guide  41  is moved toward the inclined portion  40   a   2  of the first guide rail  40   a,  and a guide stopper  46  as a disengagement prevention device is fitted in the through hole  41   b   2  of the first boss  41   b.    
     Referring to FIG. 5, the guide stopper  46  comprises: a cylindrical portion  49   a   1  which is located in the center of the guide stopper  46 , and fits in the through hole  41   b   2 ; a shaft  46   a   2 , which is located also in the center of the guide stopper  46 , and is smaller in diameter than the cylindrical portion  46   a   1 ; and a bottom portion  46   b,  to which the cylindrical portion  49   a   1  is connected, with the interposition of the shaft portion  46   a   2 . The guide stopper  46  also comprises a pair of side walls  46   c,  which perpendicularly project from the lengthwise ends of the bottom portion  46   b,  one for one. 
     Thus, as the cylindrical portion  49   a   1  and shaft portion  49   a   2  of the guide stopper  46  are fitted into the through hole  41   b   2 , the snap-fitting claw  41   b   1  latches on the stepped portion between the cylindrical portion  49   a   1  and shaft portion  49   a   2 , and the pair of side walls  46   c  is enabled to contact the inner plate  40 , on the outward side of the lips of the guide rail  40   a  formed by burring. The first boss  41   b  is structured so that when the first boss  41   b  of the moving guide  41  is fitted through the inclined portion  40   a   2  of the guide rail  40   a,  the position of the snap-fitting claw  41   b   1  in terms of the circumferential direction of the first boss  41   b  coincides with the direction in which the inclined portion  40   a   2  diagonally extends. Therefore, the presence of the snap-fitting claws  41   b   1  does not adversely affect assembly efficiency. With the provision of the above described structural arrangement, even if the moving guide  41  is subjected to such force that might cause the moving guide  41  to fall into the inward side of the left or right inner plate, the snap-fitting claw  41   b   1  remains latched on the cylindrical portion  49   a   1  of the guide stopper  46 , and the pair of side walls  46   c  remain in contact with the inner plate  40 , preventing the moving guide  41  from disengaging from the inner plate  40 . 
     Each side wall  46   c  of the guide stopper  46  is rendered substantially taller than the lips of the first guide  40   a  formed by burring. Therefore, it does not occur that bottom portion  46   b  of the guide stopper  46  is shaved by coming into contact with the flush left on the lips of the first guide rail  40   a  when the first guide rail  40   a  is formed by burring. 
     After attaching the moving guide  41  to the inner plate  40 , the cam plate  50  shown in FIG.  8  and the like are attached. 
     When the moving guide  41  is in the position at which the second boss  41   c  contacts the bottom end of the straight portion  40   b   2  of the guide rail  40   b,  the direction in which the claws  41   c   1  and  41   c   2  of the second boss  41   c  extends aligns with the hole  40   c,  the axial line of which coincides with the rotational axis of the cam plate  50 . 
     Thus, the assembly facilitation hole  50   b   3  of the cam plate  50  is aligned with the second boss  41   c  of the moving guide  41 , and the rotational shaft  50   a  is inserted into the hole  40   c.  As the rotational shaft  50   a  is inserted into the hole  40   c,  the cam plate  50  comes into contact with the inner plate  40 , since the assembly facilitation claw  50   e  is positioned so that as the assembly facilitation hole  50   b   3  is aligned with the second boss  41   c,  the assembly claw  50   e  aligns with the assembly facilitation portion  40   d   1  of the arcuate hole  40   d.    
     In this state, the cam plate  50  is rotated in the direction in which the opening/closing cover  15  is opened. As the cam plate  50  is rotated, the temporary holding rib  50   c  passes the back side of the claw  41   c   1  of the second boss  41   c  of the moving guide  41 ; the claws  41   c   1  and  41   c   2  come into contact with the edge of the cam hole  50   b;  and the assembly facilitation claw  50   e  latches on the edges of the arcuate hole  40   d.  As a result, the cam plate is properly fixed to inner plate  40 . 
     In consideration of the variance in component size resulting from manufacturing errors, a gap is provided between the surface on which the temporary holding rib  50   c  is provided and the claws  41   c   1  and  41   c   2  located at the top of the second boss  41   c  of the moving guide  41 , and the height of the temporary holding rib  50   c  is rendered slightly greater than this gap. Therefore, the temporary holding  50   c  is caught by the claw  41   c   1  of the second boss  41   c  of the moving guide  41 , preventing the cam plate  50  from rotating far enough to allow the assembly facilitation hole  50   b   3  of the cam plate  50  to align with the second boss  41   c  of the moving guide  41 . Therefore, the boss  41   c  does not disengage from the assembly facilitation hole  50   b   3  of the cam plate  50 . 
     The right cam plate  50  is attached to the right inner plate  40  in the following manner. First, the thruster rod  55  is connected to the coupling cam  85 , and the elongated hole  55   b  of the thruster rod  55  is aligned with the claws  50   g   1  and  50   g   2  of the second boss  50   g.  Then, the right cam plate  50  is attached to the right inner plate  40 . Thereafter, the thruster rod  55  is rotated to make the elongated hole  55   b  intersect with the direction in which the claws  50   g   1  and  50   g   2  extend. Then, the coupling cam  85  is fitted around the cylindrical portion  84   b  of the inward bearing  84 , completing the four joint linkage comprising the cam plate  50 , coupling cam  85 , and thruster rod  55 . 
     Thereafter, the cam plate  50  is rotated, as described above, to complete the process for attaching the moving guide  41  and cam plate  50  to the inner plate  40 . 
     Referring to FIG. 13, after the helical torsion coil spring  45  is placed in the recess  44   d  of the stationary guide  44 , the positioning rib  44   e   1  and locking claws  44   f  of the stationary guide  44  are aligned with the positioning hole (unshown) and connecting holes (unshown) of the right inner plate  40 , and are fitted therein. Then, the stationary guide  44  is slid. As the stationary guide  44  is slid, the claw  44   e   2  of the positioning rib  44   e   1 , and the locking claws  44   f,  latch on the edges of the positioning hole and connecting holes, by their back surfaces. Further, the slide regulating projection  44   g  fits in the corresponding connecting hole (unshown), fixing the position of the stationary guide  44  relative to the inner plate  40  in terms of the direction in which the stationary guide  44  is slid. 
     Referring to FIGS. 14 and 15, before the pushing arm  52  is attached to the left inner plate  40 , the helical torsion coil spring  53  is attached to the pushing arm  52 . 
     More specifically, the coiled portion  53   a  of the helical torsion coil spring  53  is fitted around the rotational shaft  52   a,  and the functional arm  53   b  is set under the rib  52   f.  Then, the stationary arm  53   c  is rested on the temporary stationary arm rest  52   h,  which is on the back side of the protective rib  52   g.    
     The pushing arm  52  is structured so that as the resilient pressing portion  52   b  is aligned with the wider portion  40   h,  that is, the bottom end portion of the fan-shaped hole  40   h,  the claw  52   d   2  aligns with the wider portion  40   i   1  of the key-shaped hole  40   i.  When the pushing arm  52  is in the above described state, the spring anchor portion  40   j  of the left inner plate  40  can be seen above the protective rib  52   g.    
     The pushing arm  52  being in the above described state, the stationary arm  53   c  of the helical torsion coil spring  53  is transferred from the temporary stationary arm rest  52   h  to the spring anchor portion  40   j  by being held by its tip. As a result, the resiliency stored in the helical torsion coil spring  53  is released, and pivots the pushing arm  52  upward, causing the claw  52   d   1  located at the base portion of the resilient pressing portion  52   b,  and the claw  52   d   2  located near the rotational shaft  52   a,  to latch on the edges of the fan-shaped hole  40   h  and key-shaped hole  40   i,  respectively, completing the process for attaching the pushing arm  52 . 
     During this process, as the pushing arm  52  is rotated upward by the resiliency of the helical torsion coil spring  53 , the butting portion  52   b   3 , that is, the tip of the resilient pressing portion  52   b  comes into contact with the top end  40   h   2  of the fan-shaped hole  40   h,  allowing the pulling surface  52   b   2  located at the base portion of the resilient pressing portion  52   b,  to escape upward above the path of the positioning guide  18   a  of the process cartridge B, and then, remains on standby. As the pushing arm  52  enters into the standby state, the stationary arm  53   c  of the helical torsion coil spring  53  moves to a position at which it is hidden behind the protective rib  52   g  of the pushing arm  52 . 
     After the various components are attached to the left and right inner plates  40 , various units, for example, the conveying means frame  90  unit, to which the conveying means  3 , transfer roller  4 , fixing means  5 , and the like, have been attached, the optical system  1  unit, and the like units, are attached to the left and right inner plates  40 . Thereafter, the external trims and shells inclusive of the opening/closing cover  15  are attached to complete an image forming apparatus. 
     During the above described final stage of the assembly, the wide portion  40   h   1  of the fan-shaped hole  40   h  of the left inner plate  40  is plugged by the positioning portion  90   a  of the conveying means frame  90 , so that the pushing arm  52  is prevented from becoming disengaged after the image forming apparatus is completely assembled. 
     In order to attach the opening/closing cover  15 , the center boss  15   a  of each hinge  15   b  of the opening/closing cover  15  is fitted into the corresponding supporting hole  43   a  of the front guide  43 , by elastically deforming the hinge  15   b  in the lengthwise direction of the process cartridge B. The front guide  43  is fixed to the left and right inner plates  40 . 
     Next, the method for connecting plate  51  to the cam plate  50  and opening/closing cover  15  will be described. 
     As will be understood referring to, for example, FIG. 27, rotating the opening/closing cover  15  and cam plate  50  in the opening direction of the opening/closing cover  15  exposes the connecting boss  50   d  and connecting hole  15   c,  by which the cam plate  50  and opening/closing cover  15  are connected to each other. The claw  50   d   1  of the connecting boss  50   d  points outward in terms of the radius direction of the cam plate  50 . The recess  51   a   1  of the hole  51   a  of the connecting plate  51  extends toward the shaft  51   b.  Therefore, as the connecting plate  51  is pointed outward in terms of the radius direction of the cam plate  50 , the claw  50   d   1  and recess  51   a   1  engage with each other. As a result, the connecting plate  51  becomes attached to the cam plate  50 . 
     Thereafter, the shaft  51   b  is put through the connecting hole  15   c  by rotating the connecting plate  51 . As the shaft  51   b  is put through the connecting hole  15   c,  the snap-fitting claw  51   b   1  latches on the edge of the connecting hole  15   c,  preventing the shaft  51   b  from disengaging. 
     As a result, the opening/closing cover  15  and cam plate  50  rotationally supported by the image forming apparatus main assembly  14  form the four-joint linkage connected by the connecting plate  51 . With the provision of this structural arrangement, the linking mechanism becomes such a mechanism that the moving guide  41  is moved by the cam plate  50  during the first half of the process for closing the opening/closing cover  15 , and the latter half of the process for opening the opening/closing cover  15 . 
     (Mounting of Process Cartridge into Apparatus Main Assembly and Dismounting of Process Cartridge from Apparatus Main Assembly) 
     Next, referring to FIGS. 16-25, the processes carried out by an operator to mount the process cartridge B into, or dismount the process cartridge B from, the image forming apparatus A equipped with the process cartridge mounting/dismounting mechanism, will be described. 
     As the opening/closing cover  15  of the image forming apparatus main assembly A is fully opened (fully open state), an opening W, through which the process cartridge B is mounted or dismounted, is exposed. In this state, the moving guide  41  is tilted diagonally downward in terms of the process-cartridge insertion direction, as shown in FIG.  16 . On the upstream side, there are left and right auxiliary guides  42 , which are symmetrically fixed to the left and right inner plate  40 , one for one. 
     As will be more easily understood referring to FIG. 17, each auxiliary guide  42  has a mounting/dismounting assistance portion  42   a,  which is connected to the trailing end of the moving guide  41 , and a top regulating portion  42   b,  which has such a surface that is virtually in contact with, and flush with, the top surface  41   a   6  of the moving guide  41 . 
     The mounting/dismounting assistance portion  42   a  is provided with a front guiding surface  42   a   1  contiguous with the guiding surface  41   a   2 , an entry guiding surface  42   a   2 , which is contiguous with the front guiding surface  42   a   1 , and is gentler in inclination than the front guiding surface  42   a   1 , being virtually horizontal, and a bottom guide surface  42   a   3 , which is located below the front guiding surface  42   a   1  and entry guiding surface  42   a   2 , and extends toward the bottom surface of the moving guide  41 , being steeper in inclination than the front guiding surface  42   a   1 . 
     Further, the top regulating portion  42   b  is provided with a top regulating surface  42   b   1 , which is virtually continuous and flush with the top surface  41   a   6  of the moving guide  41 , and a top entry guiding surface  42   b    2 , which is contiguous with the top regulating surface  42   b   1 , being virtually parallel to the bottom guiding surface  42   a   3 , and extending diagonally upward from the top regulating surface  42   b   1 . 
     The side guide  43   b  of the above described front guide  43  is provided with an inclined surface  43   b   1 , which is virtually parallel to the guiding surface  41   a   2  of the moving guide  41 , being only slightly greater in inclination than the guiding surface  41   a   2  of the moving guide  41 , and a horizontal surface  43   b   2  which is on the opening/closing cover  15  side and is contiguous with the inclined surface  43   b   1 . 
     Thus, on the inward surface of each of the left and right inner plates  40  visible through an opening W which appears as the opening/closing cover  15  is opened, there are two guiding grooves: a top guide G 1  and a bottom guide G 2 . The top guide G 1  is wider on the entry side because of the configuration of the entry guiding surface  42   a   2  and top entry guiding surface  42   b   2 , is formed by the top regulating portion  42   b,  the mounting/dismounting assisting portion  42   a  of the auxiliary cover  42 , and the moving guide  41 , and extends diagonally downward in terms of the process-cartridge insertion direction. The bottom guide G 2  is wider on the entry side because of the configuration of the bottom guiding surface  42   a   3  and horizontal surface  43   b   2 , is formed by the mounting/dismounting assisting portion  42   a,  the moving guide  41 , and the side guide  43   b,  and extends diagonally downward in terms of the cartridge insertion direction. 
     Referring to FIG. 10, the center bosses  15   a  of the opening/closing cover  15  are on the bottom side of the opening/closing cover  15 . Therefore, the opening/closing cover  15  opens downward, causing the backing  16  to face upward toward the opening W. Each of the projections  16   a  of the backing  16  is provided with a loosely guiding surface  16   a   1 , which extends diagonally downward in terms of the process-cartridge insertion direction. 
     As described above, the process cartridge B comprises: the pair of positioning guides  18   a,  which are on both the lateral walls of the cartridge frame CF, one for one, and the axial line of which coincides with the rotational axis of the photoconductive drum  7 ; and the pair of mounting guides  18   b,  which are in the form of a rib, and extend in the direction in which the process cartridge B is mounted or dismounted. The process cartridge B also comprises a pair of projections  10   f   3 , which are located on the downwardly facing surface of the toner/developing means holding frame  10   f,  near the lengthwise ends thereof, one for one. 
     When inserting the process cartridge B through the opening W, the mounting guides  18   b  and positioning guides  18   a  of the process cartridge B are aligned with the top and bottom guides G 1  and G 2  on the side walls of the opening W, respectively, and the process cartridge B is inserted until the mounting guides  18   b  butt the deepest ends of the guiding grooves  41   a  of the moving guides  41 . During this process, the projections  16   a  and  16   b  of the backing  16  regulate the position of the process cartridge B at the opening W, to a certain degree; in other words, they function as rough guides which make it easier for the mounting guides  18   b  and positioning guides  18   a  of the process cartridge B to be guided to the top and bottom guides G 1  and G 2 , respectively. More specifically, a structural arrangement is made so that the distance h 1  from the loosely guiding surface  16   a   1  to the highest point of the entry guiding surface  42   a   2  on the opening/closing cover  15  side, and the distance h 2  from the downwardly facing surface of the toner/developing means holding frame  10   f  to the intersection between the bottom surface  18   b   1  and the leading end portion  18   b   2 , also called the leading end surface, the leading end, the inward end, and the end surface of the mounting guide  18   b,  are set to satisfy the following inequality: 
     
       
         h 1 &lt;h 2 . 
       
     
     Further, another structural arrangement is made so that the distance h 3  from the highest point of the entry guiding surface  42   a   2  on the opening/closing cover side to the higher point of the horizontal surface  43   b   2  of the side guide  43   b,  and the distance h 4  from the intersection between the bottom surface  18   b   1  and end surface  18   b   2  of the mounting guide  18   b  to the bottom surface of the positioning guide  18   a,  are set to satisfy the following inequality: 
     
       
         h 3 &gt;h 4 . 
       
     
     With the provision of these structural arrangements, as the process cartridge B is inserted while making the bottom wall of the toner/developing means holding frame  10   f  follow the loosely guiding surface  16   a   1 , that is, the top surface of the projection  16   a,  the mounting guide  18   b  and positioning guide  18   a  are spontaneously guided to the entrances of the top and bottom guides G 1  and G 2 , respectively, as shown in FIGS. 17 and 18. The position of the process cartridge B in this state is the position from which the process cartridge B is inserted into the apparatus main assembly  14  to mount the process cartridge B into the apparatus main assembly  14 , or the position from which the process cartridge B can be picked up by an operator. 
     Referring to FIG. 19, until the mounting guide  18   b  begins to slide onto the guiding surface  41   a   2  of the moving guide  41 , the projection  16   a  remains in contact with the trailing end of the toner/developing means holding frame  10   f,  and keeps the process cartridge B tilted downward in terms of the process-cartridge insertion direction, making it easier for the process cartridge B to be moved inward of the guiding groove  41   a  of the moving guide  41 , by the self-weight of the process cartridge B. 
     The reason why the projections  16   a  and  16   b  are located near the lengthwise ends of the backing  16 , and the center portion is kept low, is to secure a gap large enough for the hand of a user to be easily put through when mounting or dismounting, or when dealing with a paper jam. In other words, the configuration is made to make the opening W, which is exposed as the opening/closing cover  15  is opened, satisfy both the requirement for providing a region for the mounting of the process cartridge B and for providing a gap for a user to access the interior of the image forming apparatus. 
     At this time, referring to FIG. 22, the relationship between the projection  16   a  and process cartridge B, at the opening W, in terms of the lengthwise direction of the process cartridge B, will be described. 
     When the gap between the outward sides of the two projections  16   a  and  16   b  of the backing  16  is L 1 ; the gap between the outward surface of the left projection and the inward surface of the left auxiliary guide is L 2 ; the gap between the outward surface of the right projection and inward surface of the right auxiliary guide is L 3 ; the gap between the inward sides of the two projections  10   f   3  of the process cartridge B is l 1 ; the gap between the inward surface of the left projection and the left lateral wall of the cartridge frame CF is l 2 ; and the gap between the inward surface of the right projection and the lateral wall of the cartridge frame CF is l 3 , the following relations are satisfied: 
     
       
         (1) L 1 &lt;l 1   
       
     
     
       
         (2) L 2 l 2 +(l 1 −L 1 )/ 2 +((L 1 +L 2 +L 3 )−(l 1 +l 2 +l 3 ))/ 2   
       
     
     
       
         (3) L 3 l 3 +(l 1 −L 1 )/ 2 +((L 1 +L 2 +L 3 )−(l 1 +l 2 +l 3 ))/ 2   
       
     
     Thus, since inequity (1) is satisfied, the pair of projections  16   a  and  16   b  located near the lengthwise end of the backing  16  fit between the projections  10   f   3  on the bottom wall of the toner developing means holding frame  10   f,  and from Approximations (2) and (3), it is evident that by loosely aligning the projections  10   f   3  with the projections  16   a  and  16   b , the process cartridge B can be aligned with the opening W in terms of the lengthwise direction of the process cartridge B. 
     As described above, the front guiding surface, which is the bottom surface of the top guide G 1 , and the guiding surface  41   a   2 , are tilted downward in terms of the process-cartridge mounting direction, and the trailing end of the mounting guide  18   b  is extended beyond a point corresponding to the center of the gravity of the process cartridge B. Therefore, as the mounting guides  18   b  and positioning guides  18   a  of the process cartridge B are guided to the top and bottom guides G 1  and G 2  with the use of projections  16   a  and  16   b  of the backing  16  constructed as described above, the process cartridge B is tilted downward in terms of the process-cartridge mounting direction, being automatically guided inward of the moving guide  41  by its own weight. 
     As will be understood referring to FIG. 19, the inclined surface  43   b   1  of the side guide  43   b,  that is, the bottom surface of the bottom guide G 2 , is slightly greater in inclination than the guiding surface  41   a   2 . Therefore, as the process cartridge B is inserted deeper, the positioning guide  18   a  leaves the inclined surface  43   b   1  of the side guide  43   b.  For this reason, the process cartridge mounting/dismounting mechanism is structured so that as the process cartridge B is inserted through the opening W, the mounting guide  18   b  is caught by the moving guide  41 . 
     As the process cartridge B is inserted deeper after being caught by the guiding surface  41   a   2  of the moving guide  41 , the end surface  18   b   2  of the mounting guide  18   b  comes into contact with the inclined top surface  41   a   7  of the moving guide  41  (FIG.  20 ). The end surface  18   b   2  of the mounting guide  18   b  is smooth and arcuate, and the bottom side of the inclined top surface  41   a   7  forms a retaining surface  41   a   1 , which is lower than the guiding surface  41   a   2 . Therefore, as the process cartridge B is inserted inward of the guiding groove  41   a,  its attitude is changed by the function of the inclined top surface  41   a   7 , in the direction to increase its inclination. Consequently, the end surface  18   b   2  of the mounting guide  18   b  comes into contact with the deepest end of the retaining surface  41   a   1 , ending the mounting of the process cartridge B into the moving guide  41 , as shown in FIG.  21 . As is evident from the descriptions given up to this point, when the process cartridge B is mounted into the moving guide  41  by an operator, the process cartridge B is inserted diagonally downward into the apparatus main assembly. 
     Referring to FIGS. 20 and 21, when the attitude of the process cartridge B is changed in the direction to increase the inclination of the process cartridge B, the end of the contact rib  43   c  of the front guide  43  comes into contact with the bottom surface  10   f   4  of the toner/developing means holding frame  10   f,  and the process cartridge B tilts downward in terms of the process cartridge mounting direction, with the contact rib  43   c  and bottom surface  10   f   4  remaining in contact with each other. 
     The process cartridge mounting/dismounting mechanism is structured so that after the completion of the insertion of the process cartridge B into the moving guide  41 , the contact point between the bottom surface  10   f   4  of the toner/developing means holding frame  10   f  and the contact rib  43   c  will be on the trailing side with respect to the center of gravity of the process cartridge B in terms of the process cartridge mounting direction. Therefore, at the completion of the process cartridge B insertion into the moving guide  41 , the process cartridge B assumes such an attitude that the toner/developing means holding frame  10   f  side of the process cartridge B, that is, the side which becomes the trailing side in terms of the process-cartridge mounting direction, has been lifted. Thus, after being inserted through the opening W, the process cartridge is supported in such a manner that the bottom side of the end surface  18   b   2  of the mounting guide  18   b  is supported by the deeper end of the retaining surface  41   a   1  of the guiding groove  41   a,  and the bottom surface  10   f   4  of the toner/developing means holding frame  10   f  is supported by the contact rib  43   c  of the front guide  43 , as shown in FIG.  21 . For this reason, the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b  has been lifted. The contact rib  43   c  is structured so that the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b  will become level with the guiding surface  41   a   2  of the moving guide  41 . 
     At this time, the inclination of the guiding surface  41   a   2  will be described. 
     If the inclination of the guiding surface  41   a   2  is too gentle, it is impossible for the process cartridge B to be guided inward of the moving guide  41  by its own weight, and therefore, the process cartridge B must be pushed inward by a user. On the contrary, if the inclination of the guiding surface  41   a   2  is too steep, the process cartridge B slides down too fast into the apparatus main assembly as it is released by a user during the process cartridge B insertion. As a result, it is possible for the impact, to which the process cartridge B is subjected as it reaches the deepest end of the moving guide  41 , to become large enough to damage the process cartridge B and/or image forming apparatus main assembly  14 . Therefore, the inclination of the guiding surface  41   a   2  is desired to be in a range of 15 to 50 degrees relative to a horizontal direction. In this embodiment, the inclination of the guiding surface  41   a   2  is set to approximately 26 degrees relative to a horizontal direction. 
     As described previously, the process cartridge B is inserted into the moving guide  41 , from the point (first location) at which the guiding surface  41   a   2  of the guiding groove  41   a  connects to the front guide surface  42   a   1  of the auxiliary guide  42 . The moving guide  41  assumes such an attitude (first attitude) that it tilts downward in terms of the process-cartridge mounting direction, that is, such an attitude that when the process cartridge B is at the point beyond which the process cartridge B is mounted into the moving guide  41 , that is, the point at which the guiding surface  41   a   2  is contiguous with the front guiding surface  42   a   1 , the direction X in which the process cartridge B is mounted into the guiding groove  41   a  intersects with the direction in which the recording medium  2  is conveyed by the conveying means  3 . This is for the following reason. That is, as will be understood from FIG. 27, the process cartridge mounting/dismounting mechanism is structured so that when the opening/closing cover  15  is fully open, the second boss  41   c  of the moving guide  41  will be at the end of the straight portion (groove hole)  50   b   2  of the cam hole  50   b,  and the first boss  41   b  will be at the end of the first guide rail  40   a  on the opening/closing cover  15  side. 
     In this embodiment, the moving guide  41  of the process cartridge mounting/dismounting mechanism is structured so that its movement is linked to the opening or closing movement of the opening/closing cover  15 . Thus, if the moving guide  41  is structured so that the trailing end (end on the cover side) of the moving guide  41  can be pushed by the process cartridge B, the moving guide  41  escapes into the interior of the image forming apparatus, making it impossible to engage the mounting guide  18   b  of the process cartridge B into the guiding groove  41   a  of the moving guide  41 . Therefore, in this embodiment, the auxiliary guide  42  having the mounting/dismounting assisting portion  42   a  contiguous with the trailing end of the moving guide  41  is provided, being fixed to the inner guide  40 , on the upstream side of the moving guide  41  in terms of the direction X in which the process cartridge B is mounted. The above described problem is solved by this auxiliary guide  42 ; it is assured that the mounting guide  18   b  of the process cartridge B is guided to the guiding groove  41   a  of the moving guide  41 . 
     Further, the process cartridge mounting/dismounting mechanism is structured so that the process cartridge B is mounted into the moving guide  41 , the movement of which is linked to the opening or closing movement of the opening/closing cover  15 . Therefore, when the opening/closing cover  15  has been partially closed, the moving guide  41  has moved inward of the image forming apparatus, and therefore, a gap has been created between the moving guide  41  and the mounting/dismounting assisting portion  42   a  of the auxiliary guide  42 . When the opening/closing cover  15  has been only slightly closed, and therefore, the above described gap is small enough for the mounting guide  18   b  to easily slide over from the mounting/dismounting assisting portion  42   a  to the moving guide  41 , the process cartridge B can be mounted. However, as this gap widens to a certain extent, it becomes impossible for the mounting guide  18   b  of the process cartridge B to be engaged into the guiding groove  41   a  of the moving guide  41 . Further, as the gap becomes even wider, it is conceivable that the mounting guide  18   b  will slip into the wrong space in the image forming apparatus through this gap. 
     Thus, in this embodiment, the backing  16  is provided with the projections  16   a  and  16   b  to prevent the process cartridge B from being inserted when the opening/closing cover  15  has been partially closed. 
     In other words, when the opening/closing cover  15  has been closed by a substantial angle, the projection  16   a  of the backing  16  has come closer to the top regulating portion  42   b,  making the space between the projection  16   a  and the top regulating portion  42   b  too small for the insertion of the process cartridge B, as shown in FIG.  23 . 
     Referring to FIG. 24, when the opening/closing cover  15  has been partially closed, but the process cartridge B is still insertable, the projection  16   a  has been made to intrude into the normal path through which the process cartridge B is mounted or dismounted, and also the inclination of the loosely guiding surface  16   a   1  of the backing  16  relative to the horizontal direction has been increased, by the rotation of the opening/closing cover  15 . Therefore, it has become impossible for the process cartridge B to be inserted, unless the process cartridge B is inserted at an angle steeper than the normal angle. 
     When the opening/closing cover  15  has been partially closed, the guiding surface  41   a   2  of the moving guide  41  is uncontiguous with the front guiding surface  42   a   2  of the auxiliary cover  42 . Thus, if the process cartridge B is inserted into the apparatus main assembly, in this condition, at a steeper angle than the normal angle, in a manner to make the bottom surface of the process cartridge B follow the loosely guiding surface  16   a   1  of the projection  16   a,  the leading end surface  18   b   2  of the mounting guide  18   b  comes into contact with the trailing end  41   e  of the moving guide  41 . At this moment, the positioning guide  18   a  contacts the inclined surface  43   b   1  of the side guide  43   b,  and the bottom surface of the toner/developing means holding frame  10   f  contacts the projection  16   a  of the backing  16 . As a result, the process cartridge B is regulated in its attitude. 
     As the opening/closing cover  15  is further closed from the position at which there are three (six) contacts, that is, the leading end  18   b   2  of the mounting guide  18   b  is in contact with the trailing end  41   e  of the moving guide  41 ; the positioning guide  18   a  is in contact with the inclined surface  43   b   1  of the side guide  43   b ; and the bottom surface of the toner/developing means holding frame  10   f  is in contact with the projection  16   a,  the moving guide  41  moves inward of the image forming apparatus, and the projection  16   a  of the backing  16  rotates upward. As a result, the process cartridge B is caused to rotate counterclockwise. Consequently, the corner of the mounting guide  18   b,  at which trailing end of the top surface of the mounting guide  18   b  connects to the perpendicular surface  18   b   5  of the mounting guide  18   b,  comes into contact with the top guiding surface  42   b   2  of the auxiliary guide  42 , preventing the opening/closing cover  15  from being closed further (FIG.  25 ). In other words, when the process cartridge B is inserted into the apparatus main assembly, the opening/closing cover  15  of which has been partially closed, the opening/closing cover  15  cannot be closed, preventing the problem that the process cartridge B is improperly mounted into the apparatus main assembly. 
     Incidentally, even after the process cartridge B has been inserted into the apparatus main assembly, the opening/closing cover  15  of which has been partially closed, and the process cartridge B has become immovable, the process cartridge B can be pulled out of the apparatus main assembly, by rotating the opening/closing cover  15  in the opening direction. More specifically, as the opening/closing cover  15  is rotated in the opening direction, the moving guide  41  moves toward the opening W, and pushes the leading end  18   b   2  of the mounting guide  18   b,  forcing the process cartridge B outward. Then, as the opening/closing cover  15  is opened further, the aforementioned gap between the guiding surface  41   a   2  of the moving guide  41  and the front guiding surface  42   a   1  of the auxiliary guide  42  becomes smaller, and the mounting guide  18   b  moves across the gap, and settles in the guiding groove  41   a,  becoming ready for the mounting of the process cartridge B. 
     (Description of Movement of Process Cartridge Mounting/Dismounting Mechanism) 
     (Moving Guide Movement Linked to Opening/Closing Cover Movement) 
     Next, referring to FIGS. 26-49, the manner in which the moving guide  41 , on which the process cartridge B has rested, moves during the first half of the closing movement of the opening/closing cover  15 , will be described. FIGS. 26,  27 , and  28  are the same in terms of the timing of the movement of the moving guide  41 , and so are FIGS. 29,  30 , and  31 ; FIGS. 32,  33 , and  34 ; FIGS. 35,  36 , and  37 ; FIGS. 38,  39 , and  40 ; FIGS. 41,  42 , and  43 ; FIGS. 44,  45 , and  46 ; and FIGS. 47,  48 , and  49 . FIGS. 26,  29 ,  32 ,  35 ,  38 ,  41 ,  44 , and  47  show the movement of the process cartridge B in relation to the right inner plate as seen from the inward side of the image forming apparatus. FIGS. 27,  30 ,  33 ,  36 ,  39 ,  42 ,  45 , and  48  show the movement of the process cartridge B in relation to the right inner plate, as seen from the outward side of the image forming apparatus. FIGS. 28,  31 ,  34 ,  37 ,  40 ,  43 ,  46 , and  49  show the movement of the process cartridge B in relation to the left inner plate, as seen from the outward side of the image forming apparatus. 
     As the opening/closing cover  15  is closed by rotating it about the center boss  15   a,  the cam plate  50 , which is connected to the opening/closing cover  15  by the connecting plate  51 , and constitutes the follower of the four-joint linkage, also rotates, as shown in FIGS. 28-49. As a result, the second boss  41   c  of the moving guide  41  is moved by the top end of the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  of the cam plate  50 , along the first arcuate portion  40   b   1  of the second guide rail  40   b.    
     As described before, the center of the curvature of the first arcuate portion  40   b   1  coincides with the rotational axis  50   a  of the cam plate  50 , and the radius of the first arcuate portion  40   b   1  is slightly smaller than the distance from the rotational axis  50   a  of the cam plate  50  to the top end of the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  of the cam plate  50 . Therefore, the second boss  41   c  of the moving guide  41  is retained in the space surrounded by the first arcuate portion  40   b   1  of the second guide rail  40   b  and the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b,  and is moved by the rotation of the cam plate  50 . Consequently, the first boss  41   b  of the moving guide  41  also moves inward, in terms of the direction X in which the process cartridge B is mounted, along the horizontal portion  40   a   1  of the first guide rail  40   a.    
     The process cartridge B is in the apparatus main assembly, with its mounting guide  18   b  being in contact with the deeper end of the guiding groove  41   a  of the moving guide  41 , and the bottom surface of the toner/developing means holding frame  10   f  being in contact with the contact rib  43   c  of the front guide  43  (FIG.  21 ). 
     As the moving guide  41  is moved further inward of the image forming apparatus, the process cartridge B moves inward of the image forming apparatus, along with the moving guide  41 . As a result, the bottom surface  10   f   4  of the toner/developing means holding frame  10   f  becomes separated from the contact rib  43   c,  and the process cartridge B begins to be supported by the retaining surface  41   a   1  of the moving guide  41 , by the bottom surface  18   b   1  of the mounting guide  18   b  (FIG.  29 ). 
     The moving guide  41  supports the mounting guide  18   b  by the retaining surface  41   a   1 , and moves inward while changing its attitude in the clockwise direction as shown in FIGS. 29-47. During this movement of the moving guide  41 , the process cartridge B is conveyed in the image forming apparatus while changing its attitude in the clockwise direction, with the photoconductive drum  7  moving virtually horizontally. As the moving guide  41  moves while changing its attitude, the guide stopper  46  fitted around the first boss  41   b  follows the moving guide  41  while rotating, with the inward surface of the side wall  46   c  remaining in contact with the outward side of the lip of the first guide rail  40   a  formed by burring. 
     On the right side where the driving means is located, the helical torsion coil spring  45  for holding the process cartridge B in the position at which the driving force receiving portion of the process cartridge B can be connected to the driving force transmission mechanism of the apparatus main assembly, by the aforementioned coupling means, is disposed. This helical torsion coil spring  45  keeps the positioning guide  18   a  pressed upon the cartridge catching/retaining portion  84   a,  by its resiliency, to prevent the positioning guide  18   a  of the process cartridge B from being dislodged from the position, in which the driving force receiving portion of the process cartridge B can be engaged with the corresponding portion of the apparatus main assembly by the coupling portion, by the pressure generated by the spring  4 S to keep the transfer roller  4  pressed upon the photoconductive drum  7 . 
     Thus, as the opening/closing cover  15  is further closed, the process cartridge B moves closer to the image formation location located further inward of the image forming apparatus main assembly  14 , while gradually becoming horizontal, as shown in FIG.  38 . On the right side of the apparatus, the peripheral surface of the positioning guide  18   a  comes into contact with the contact portion of the functional arm  45   c  of the helical torsion coil spring  45  disposed in the recess  44   d  of the stationary guide  44 , in such a manner as to intrude into the upstream side of the path of the process cartridge B to the image formation location. 
     As described previously, the length of the retaining surface  41   a   1  of the moving guide  41  is greater than that of the bottom surface  18   b   1  of the mounting guide  18   b.  Thus, when the opening/closing cover  15  is further closed from the above described position, the process cartridge B is prevented by the resiliency of the helical torsion coil spring  45 , from moving further inward, as shown in FIG.  38 . As a result, the mounting guide  18   b  slides on the retaining surface  41   a   1 , within the guiding groove of the moving guide  41 , and the bottom corner  18   b   3  of the mounting guide  18   b,  on the trailing side, comes into contact with the perpendicular surface  41   a   3  of the guiding groove  41   a.    
     Thereafter, as the opening/closing cover  15  is further closed, the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b  is pressed by the perpendicular surface  41   a   3  of the guiding groove  41   a.  As a result, the functional arm  45   c  of the helical torsion coil spring  45  is bent upward, being forced out of the path of the positioning guide  18   a,  against the resiliency of the helical torsion coil spring  45 . Consequently, it becomes possible for the process cartridge B to be pushed further into the apparatus main assembly (FIG.  41 ). 
     Then, as soon as the positioning guide  18   a  passes the bend portion  45   c   2  of the helical torsion coil spring  45 , the latent resiliency of the helical torsion coil spring  45  acts upon the positioning guide  18   a  in the direction to push the positioning guide  18   a  into the cartridge catching/retaining portion  84   a  of the inward bearing  84  (FIG.  44 ). 
     Referring to FIG. 44, the helical torsion coil spring  45  in this embodiment contacts the peripheral surface of the positioning guide  18   a  by the bend portion  45   c   2  of the functional arm  45   c.  In order to prevent this bend portion  45   c   2  from deforming in a manner to become permanently bent when the peripheral surface of the positioning guide  18   a  passes the bend portion  45   c   2  during the mounting or dismounting of the process cartridge B, the radius of the curvature of the bend portion  45   c   2  is rendered relatively large (approximately 3 mm-4 mm). 
     Further, in order to prevent the functional arm  45   c  from dislodging from the intended position, in terms of the lengthwise direction of the process cartridge B, when the functional arm  45   c  of the helical torsion coil spring  45  is bent upward by the positioning guide  18   a,  the recess  44   d  of the stationary guide  44  is provided with a regulating claw  44   d   3  and a regulating rib  44   d   4 , which regulate the movement of the functional arm  45   c,  in terms of the lengthwise direction of the process cartridge B, by the portion of the functional arm  45   c  beyond the bend portion  45   c   2 . With the provision of this arrangement, the functional arm  45   c  deforms within the gap defined by the bottom surface of the recess  44   d,  regulating claw  44   d   3 , and regulating rib  44   d   4 , being regulated in its position in terms of the lengthwise direction of the process cartridge B. The functional arm  45   c  of the helical torsion coil spring  45  keeps the positioning boss  18   a  pressed upon the cartridge catching/retaining portion  84   a  with the application of a predetermined pressure (approximately 0.98 N to 4.9 N). 
     Near the point which the positioning guide  18   a  passes while deforming the helical torsion coil spring  45 , the first boss  41   b  of the moving guide  41  moves from the horizontal portion  40   a   1  of the first guide rail  40   a  to the inclined portion  40   a   2  of the first guide rail  40   a  (FIGS.  38 - 44 ). 
     While the first boss  41   b  moves along the horizontal portion  40   a   1  of the first guide rail  40   a,  the photoconductive drum  7  moves nearly horizontally. Then, as the first boss  41   b  transfers to the inclined portion  40   a   2  of the first guide rail  40   a,  the photoconductive drum  7  is moved to the Dr portion (FIG. 44) of its path, where the path points diagonally downward in terms of the process-cartridge mounting direction. Therefore, the photoconductive drum  7  moves toward the transfer roller  4 . 
     With the provision of the above described structural arrangement, such a component of the force applied in the direction to move the process cartridge B inward of the apparatus main assembly that acts in the direction to press the transfer roller  4  can be increased by increasing the angle between the direction Tr (FIG. 44) in which the transfer roller  4  is pressed by the spring  4 S, and the direction of the path of the photoconductive drum  7  after the photoconductive drum  7  comes into contact with the transfer roller  4  and begins to press the transfer roller  4  downward. 
     As is evident from the above description, constructing the first guide rail  40   a  so that its front end, in terms of the process cartridge mounting direction, tilts downward as described above makes it possible to efficiently press down the transfer roller  4  by the movement of the process cartridge linked to the rotation of the opening/closing cover  15 . 
     At this time, the relationship between the guiding groove  41   a  of the moving guide  41  and the mounting guide  18   b  when the photoconductive drum  7  of the process cartridge B presses down the transfer roller  4  will be described. 
     As described previously, while the process cartridge B is moved by the rotation of the opening/closing cover  15 , the mounting guide  18   b  is supported by the retaining surface  41   a   1  of the guiding groove  41   a  of the moving guide  41 . During this movement of the process cartridge B, as the process cartridge B is subjected to the forces (resistance) generated by the helical torsion coil spring  45 , as well as an electrical contact  92 , in the direction to push back the process cartridge B, the perpendicular surface  41   a   3  of the moving guide  41  moves the process cartridge B by coming into contact with the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b.    
     Toward the end of the conveyance of the process cartridge B, the photoconductive drum  7  comes into contact with the transfer roller  4  and presses down the transfer roller  4  against the spring  4 S. The pressure which the spring  4 S applies to the transfer roller  4  acts on the photoconductive drum  7  in the direction to lift the mounting guide  18   b  of the process cartridge B from the retaining surface  41   a   1  of the moving guide  41 . Being subjected to such a pressure, the mounting guide  18   b  tends to go over the stepped portion between the retaining surface  41   a   1  and guiding surface  41   a   2 . If the mounting guide  18   b  goes over the stepped portion between the retaining surface  41   a   1  and guiding surface  41   a   2 , it becomes impossible for the moving guide  41  to insert the process cartridge B against the resistive load in terms of the process-cartridge insertion direction; in other words, it becomes impossible to send the process cartridge B to the location at which image formation is possible. 
     As has been described with reference to FIG. 6, in this embodiment, the guiding groove  41   a  of the moving guide  41  is provided with the perpendicular surface  41   a   3 , which is located at the trailing end of the retaining surface  41   a   1  and is perpendicular to the retaining surface  41   a   1 , and the inclined portion  41   a   4 , which extends diagonally upward from the top end of the perpendicular surface  41   a   3  and connects to the guiding surface  41   a   2  in a manner to form an acute angle relative to the guiding surface  41   a   2 . Thus, as the process cartridge B is resisted by the force generated by the helical torsion coil spring  45  and electrical contact  92  in the direction opposite to the process-cartridge mounting direction, during the inward conveyance of the process cartridge B, the perpendicular surface  41   a   3  of the moving guide  41  moves the process cartridge B by coming into contact with the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b.  Then, the photoconductive drum  7  comes into contact with the transfer roller  4  due to the movement of the process cartridge B caused by the perpendicular surface  41   a   3  of the moving guide  41 , and is subjected to a force reactive to the force applied to the transfer roller  4  by the photoconductive drum  7 . As a result, the mounting guide  18   b  tends to go over the stepped portion of the guiding groove  41   a.  In this embodiment, however, the inclined surface portion  18   b   4  of the mounting guide  18   b,  which connects to the bottom corner  18   b   3  of the trailing end of the mounting guide  18   b  and forms an acute angle relative to the bottom surface  18   b   1 , comes into contact with the inclined portion  41   a   4 , which extends diagonally upward from the top end of the perpendicular surface  41   a   3 , as shown in FIG.  6 (B). Therefore, even if the mounting guide  18   b  is moved in the direction to go over the stepped portion of the guiding groove  41   a,  the inclined portion  41   a   4  catches the inclined surface portion  18   b   4 , making it possible for the moving guide  41  to push the process cartridge B inward against the force applied to the transfer roller  4  by the spring  4 S. 
     In the descriptions given above regarding the conveyance of the process cartridge B by the movement of the moving guide  41  linked to the rotation of the opening/closing cover  15 , it was stated that the right positioning guide  18   a  is kept pressed upon the cartridge catching/retaining portion  84   a  by the helical torsion coil spring  45 . 
     However, on the left side of the apparatus, a resilient pressing means which intrudes into the path of the positioning guide  18   a  is not provided. Further, a certain amount of play is provided between the mounting guide  18   b  and the retaining surface  41   a   1  of the moving guide  41 . Therefore, even after the left positioning guide  18   a  reaches near the positioning portion  90   a  of the conveying means frame  90 , it is not immediately caught by the positioning portion  90   a  due to the presence of the contact pressure between the transfer roller  4  and photoconductive drum  7 , and the contact pressure generated by various electrical contacts (FIG.  49 ). 
     The left positioning guide  18   a  is guided to the positioning portion  90   a  of the frame  90 , being thereby accurately positioned, by the movement of the pushing arm  52 , which will be described later. 
     Although the right positioning guide  18   a  is kept pressed upon the cartridge catching/retaining portion  84   a  by the helical torsion coil spring  45 , it eventually is separated from the cartridge catching/retaining portion  84   a  against the resiliency of the helical torsion coil spring  45 , and as the rotational axes of the large gear coupling  83   a  and drum coupling  7   a   1  are made to coincide with each other by the engagement between the two couplings caused by the coupling means, the position of the process cartridge B relative to the image forming apparatus, within the image forming apparatus, on the right side, becomes fixed. 
     After the right positioning guide  18   a  passes by the helical torsion coil spring  45 , the first boss  41   b  of the moving guide  41  transfers to the inclined portion  40   a   2  of the first guide rail  40   a,  and causes the photoconductive drum  7  to press down the transfer roller  4 . This virtually concludes the process-cartridge conveyance. 
     Next, the movements of the cam plate  50  and moving guide  41  linked to the rotation of the opening/closing cover  15 , which occur during above described process cartridge conveyance, will be described. 
     Near the area where the distance by which the positioning guide  18   a  pushes up the helical torsion coil spring  45  becomes a maximum, the second boss  41   c  of the moving guide  41  is at the portion of the second guide rail  40   b  where the first arcuate portion  40   b   1  and the straight portion  40   b   2  of the second guide rail  40   b  of the inner plate  40  connect to each other in a smooth curvature, and the first boss  41   b  of the moving guide  41  is at the point where it is about to move into the inclined portion of the first guide rail  40   a  of the inner plate  40  (FIGS. 41,  42 , and  43 ). 
     As the opening/closing cover  15  is further closed from the above described point, the range of the area surrounded by the cam hole  50   b  of the cam plate  50  and the second guide rail  40   b  of the inner plate  40  changes to the area between the inward side of the straight portion (straight groove hole)  50   b   2  of the cam hole  50   b  of the cam plate  50 , in terms of the radius direction of the cam hole  50   b,  and the straight portion  40   b   2  of the second guide rail  40   b,  and the second boss  41   c  of the moving guide  41  is moved within this area. Therefore, the first boss  41   b  of the moving guide  41  is moved downward along the inclined portion  40   a   2  while the second boss  41   c  of the moving guide  41  is moved to the bottom end of the straight portion  40   b   2 . Then, as the second boss  41  comes into contact with the bottom end of the straight portion  40   b   2 , the movement of the moving guide  41  concludes (FIGS. 47,  48 , and  49 ). 
     As a result, the moving guide  41  becomes virtually horizontal as the process cartridge B reaches the image-formation location. In other words, at the second location, the moving guide  41  assumes an attitude different from the attitude it assumes at the first location. The first guide rail  40   a  is slightly longer than the moving distance of the first boss  41   b  of the moving guide  41  as described before. Therefore, at the completion of the movement of the moving guide  41 , there is a gap between the first boss  41   b  and the end of the inclined portion  40   a   2  of the first guide rail  40   a.  Thus, it does not occur that the compression deformation occurs to the moving guide  41  due to the contact between the first boss  41   b  and the end of the inclined portion  40   a   2 . 
     (Mechanism for Opening or Closing Drum Shutter) 
     Up to this point, the manner in which the process cartridge moves in connection to the rotation of the opening/closing cover  15  has been described. Next, the opening and closing movements of a drum shutter  12  linked to the movement of the process cartridge B will be described. 
     According to the present invention, the drum shutter  12  is not opened or closed during the stage in which the process cartridge B is mounted into the moving guide  41  (FIG.  17 - 21 ). Instead, it is opened or closed in the stage in which the process cartridge B is moved within the apparatus main assembly by the rotation of the opening/closing cover  15  (FIGS.  26 - 47 ). 
     This arrangement is made to prevent a problem that as the drum shutter  12  is opened in the stage in which the process cartridge B is mounted into the apparatus main assembly (moving guide  41 ), the resistance generated by the opening of the drum shutter  12  adds to the load to which the process cartridge B is subjected when the process cartridge B is mounted into the moving guide  41 , and therefore, the inward movement of the process cartridge B is stopped before the mounting guide  18   b  is caught by the retaining portion  41   a   1  in the inward portion of the guiding groove  41   a.  For this reason, the structural design that caused a conventional apparatus to generate a negative load in terms of the process-cartridge inserting direction when the process cartridge B is mounted into the apparatus main assembly by a user has been eliminated; in other words, the drum shutter  12  is opened or closed in the stage in which the process cartridge B is moved within the apparatus, by the closing movement of the opening/closing cover  15 . 
     As the process cartridge B is moved by the closing movement of the opening/closing cover  15 , the drum shutter  12  rotationally supported by the process cartridge B is rotated and exposes the transfer opening  9   a  and exposure opening  9   b  for the photoconductive drum  7 , readying the process cartridge B for image formation. 
     Referring to FIG. 3, the rib  12   e  for keeping the drum shutter  12  open is on top of the cleaning means holding frame  11   d.  However, when it is seen from the direction parallel to the lengthwise direction of the process cartridge B, it is within the contour of the cleaning means holding frame  11   d,  and when it is seen from the direction perpendicular to the lengthwise direction of the process cartridge B, it is on the inward side of the contour of the surface of the cleaning means holding frame  11   d  facing the moving guide  41 . 
     The surface of the rib  12   e,  which contacts the shutter guide  44   c  (second contact portion) of the stationary guide  44 , faces the cleaning means holding frame  11   d,  and is exposed as the drum shutter  12  is opened. 
     As is evident from the above description, when the process cartridge B is outside the apparatus main assembly, that is, when the drum shutter  12  is closed, the rib  12   e  (second projection) for controlling the attitude of the drum shutter  12 , which is open when the process cartridge B is within the image forming apparatus main assembly, is within the contour of the cleaning means holding frame  11   d  as seen from either the lengthwise direction of the process cartridge B or the direction perpendicular thereto. Therefore, the rib  12   e  is not damaged by the impacts which occur while the process cartridge B is transported, or the manner in which the process cartridge B is handled while the process cartridge B is mounted or dismounted. 
     Referring to FIG. 26, as the process cartridge B is moved by the closing movement of the opening/closing cover  15 , the cam portion  12   d  (first projection) of the drum shutter  12  comes into contact with an optical system plate  1   f  (first contact portion), which is between the left and right inner plates within the image forming apparatus main assembly, and supports an optical system  1 . As a result, the drum shutter  12  is rotated in the clockwise direction, while resisting the resiliency of a shutter spring, by the movement of the process cartridge B, and begins to expose the transfer opening  9   a  and exposure opening  9   b.    
     As the drum shutter  12  is rotated in the clockwise direction, the rib  12   e,  which is attached to the connecting portion  12   c  (supporting portion), is moved away from the top surface of the cleaning means holding frame  11   d,  and therefore, the surface of the rib  12   e  which was in contact with the shutter guide  44   c  is exposed. As the process cartridge B is moved deeper into the apparatus main assembly, the cam portion  12   d  of the drum shutter  12 , which has come into contact with the corner of the optical system plate If, keeps moving, with the highest point  12   d   1  located at the end of the cam portion  12   d  remaining in contact with the bottom surface of the optical system plate If, as shown in FIG.  29 . Thus, as the process cartridge B is moved inward, the rib  12   e  comes into contact with the shutter guide  44   c  of the stationary guide  44 , causing the drum shutter  12  to be opened further. As a result, the highest point  12   d   1  (contact point) of the cam portion  12   d  is moved away from the bottom surface of the optical system plate If (FIG.  32 ). 
     The shutter guide  44   c  is disposed above the cleaning means holding frame  11   d,  overlapping therewith, and is wide enough to catch the rib  12   e.  Referring to FIG. 26, listing from the upstream side in terms of the direction in which the process cartridge B is inserted, the shutter guide  44   c  has a first inclined surface  44   c   1 , which is higher on the downstream side, a raised surface  44   c   2 , a second inclined surface  44   c   3 , which is lower on the downstream side, a horizontal surface  44   c   4 , and a vertical surface  44   c   5 , which is the most downstream surface in terms of the process-cartridge mounting direction. 
     As described above, the shutter guide  44   c  rotates the drum shutter  12  by keeping the cam portion  12   d  in contact with the optical system plate  1   f,  and catches the rib  12   e,  which has moved away from the cleaning means holding frame  11   d.  For this purpose, the shutter guide  44   c  is located on the downstream side of the stationary guide  44 , being outside the path through which the rib  12   e  comes up. Referring to FIG. 32, the shutter guide  44   c  catches the first inclined surface  44   c   1 , which is rendered lower on the upstream side so that it can easily scoop up the rib  12   e  as the rib  12   e  is moved toward the shutter guide  44   c  by the movement of the process cartridge B. After being caught by the first inclined surface  44   c   1 , the rib is slid up the first inclined surface  44   c   1  by the movement of the process cartridge B, increasing the angle at which the drum shutter  12  is open. 
     As the opening/closing cover  15  is closed further, and the process cartridge B is moved thereby further inward of the image forming apparatus main assembly  14 , the rib  12   e  of the drum shutter  12  comes into contact with the raised portion  44   c   2 , or the highest portion, of the shutter guide  44   c,  opening the drum shutter  12  wider. During this movement of the drum shutter  12 , the presence of a square notch  12   f  (FIG. 4) at the left front corner of the drum shutter  12  prevents the drum shutter  12  from colliding with the electrical contact  92  of the image forming apparatus (FIG.  35 ). 
     Thereafter, the rib  12   e  is moved onto the second inclined surface  44   c   3  of the shutter guide  44   c,  which is lower on the downstream side in terms of the process-cartridge mounting direction, and therefore, the drum shutter  12  temporarily moves a short distance in the closing direction. This second slanted surface  44   c   3  connects the raised surface  44   c   2 , which is rendered long to enable the drum shutter  12  to avoid the electrical contact  92 , and the horizontal surface  44   c   4 , which is lower than the raised surface  44   c   2 , and onto which the rib  12   e  finally moves. 
     Thereafter, as the first boss  41   b  of the moving guide  41  moves onto the inclined portion  40   a   2  of the first guide rail  40   a,  the rib  12   e  of the drum shutter  12  is supported by the horizontal portion  44   c   4 , remaining therefore at the same level, as shown in FIG.  41 . However, the process cartridge B moves downward toward the transfer roller  4 , increasing the angle at which the drum shutter  12  is open. 
     Eventually, the movement of the moving guide  41  linked to the rotation of the opening/closing cover  15  stops, ending the conveyance of the process cartridge B. In this stage, the rib  12   e  of the drum shutter  12  is supported by the horizontal surface  44   c   4  of the shutter guide  44   c,  keeping the drum shutter  12  open at a predetermined angle, and the transfer opening  9   a  and exposure opening  9   b  are exposed, with the process cartridge B being properly positioned in the image forming apparatus and ready for image formation, as shown in FIG.  44 . 
     Immediately after the movement of moving guide  41  linked to the closing movement of the opening/closing cover  15  ends in the first half of the entirety of the closing movement of the opening/closing cover  15 , the second boss  41   c  of the moving guide  41  is at the bottom end of the straight portion  40   b   2  of the second guide rail  40   b  of the inner plate  40 , and then, it moves to the arcuate portion  50   b   1  of the cam hole  50   b  of the cam plate  50  (FIG.  49 ). As described above, the arcuate portion  50   b   1  of the cam hole  50   b  is such a portion of the cam hole  50   b  that the center of its curvature coincides with the rotational axis of the rotational shaft  50   a;  the radius of its outward edge is equal to the distance from the rotational shaft  50   a  to the bottom end of the straight portion  40   b   2  of the second guide rail  40   b;  and its width (dimension in terms of its radius direction) is slightly greater than the external diameter of the second boss  41   c  of the moving guide  41 . Therefore, as the opening/closing cover  15  is further closed after the completion of the movement of the moving guide  41 , the cam plate  50  is allowed to rotate, with the edge of the arcuate portion  50   b   1  of the cam hole  50   b  of the cam plate  50  being guided by the second boss  41   c  of the moving guide  41 , and therefore, the opening/closing cover  15  can be completely closed. 
     Hereinafter, various mechanisms, the movements of which are linked to the latter half of the entirety of the closing movement of the opening/closing cover  15 , will be described. 
     (Movement of Means for Connecting Driving Force Transmitting Means, Linked to Opening/closing Cover Movement) 
     As described previously, the right inner plate  40  is provided with a driving means, which comprises a coupling means for transmitting a driving force to the process cartridge B, and a coupling means controlling means for engaging or disengaging the coupling means. Also as described above, the coupling means becomes engaged or disengaged as it is moved by the coupling means controlling means in the lengthwise direction of the process cartridge B, which is approximately perpendicular to the direction in which the process cartridge B is mounted into the apparatus main assembly. 
     The coupling means has the inward bearing  84 , outward bearing  86 , and large gear  83 . The inward bearing  84  rotationally supports the large gear  83  by the large gear coupling  83   a,  and is fixed to the inner plate  40 . The outward bearing  86  is attached to a gear cover (unshown) fixed to the inner plate  40 , and rotationally supports the other end of the large gear. The large gear  83  is rotationally supported by the inward and outward bearings  84  and  86  (FIG.  11 ). 
     The large gear coupling  83   a  is provided with a twisted hole, the cross section of which is in the form of a virtually equilateral triangle. The rotational axis of the large gear coupling  83   a  coincides with that of the large gear  83 . A gear flange (unshown) fixed to one of the lengthwise ends of the photoconductive drum  7  of the process cartridge B is provided with a drum coupling  7   a   1 , the rotational axis of which coincides with that of the photoconductive drum  7 , and is in the form of a twisted equilateral triangular pillar. The drum coupling  7   a   1  is within the hollow of the right positioning guide  18   a,  and the rotational axis of the drum coupling  7   a   1  also coincides with the axial line of the right positioning guide  18   a  (FIG.  3 ). 
     Referring to FIGS. 11,  50 (A),  50 (B), and  50 (C), the coupling means controlling means comprises: the cam surfaces ( 84   c   1  and  84   c   2 ) of the inward bearing  84 ; a coupling cam  85  positioned between the inward bearing  84  and large gear  83 ; and a spring (not shown), which is disposed between the large gear  83  and outward bearing  86 , and keeps the large gear  83  pressed toward the inward bearing  84 . 
     The coupling cam  85  is rotatably supported by the cylindrical portion  84   b  of the inward bearing  84 , and is provided with the cam surfaces ( 85   a   1 ,  85   a   2 , and  85   a   3 ). The cam surfaces of the inward bearing  84  have two portions symmetrically positioned with respect to the axial line of the cylindrical portion  84   b:  portion  84   c   1  and portion  84   c   2  which are contiguous with each other. The portion  84   c   1  is parallel to the inward surface of the inner plate  40 , and is raised a predetermined height toward coupling cam  85  in a direction parallel to the rotational axis of the large gear  83 , from the inward surface of the inner plate  40  (inward surface of inward bearing  84 ). The portion  84   c   2  is an inclined surface, which connects a predetermined point on the peripheral surface of the cylindrical portion  84   b  to the raised parallel portion  84   c   1 . The cam surfaces of the coupling cam  85  also comprise two portions: portion  85   a   1  and  85   a   2 . The portion  85   a   1  is parallel to the inward surface of the inner plate  40 , and is raised toward the inward surface of the inner plate  40 , from the base portion  85   a   3 , by a height equal to the height of the raised parallel portion  84   c   1  from the inward surface of the inner plate  40 . The portion  85   a   2  is an inclined surface and connects the raised parallel portion  85   a   1  and the base portion  85   a   3  of the cam surface of the coupling cam  85 . 
     Referring to FIG.  50 (C), as the coupling cam  85  is fitted around the cylindrical portion  84   b  of the inward bearing  84  in such a manner that the raised surface  84   c   1  contacts the bottom portion  85   a   3 , it approaches the inner plate  40 , with the presence of a small amount of play relative to the inward bearing  84  in terms of their rotational direction, and the coupling  83   a  of the large gear  83  is made to intrude into the image forming apparatus by the resiliency of the spring between the large gear  83  and the outward bearing  86 , becoming ready to be engaged with the drum coupling  7   a   1  of the process cartridge B. 
     Referring to FIG.  50 (B), as the coupling cam  85  is rotated, the inclined surfaces  84   c   2  and  85   a   2  come into contact with each other, and begin to slide against each other. As a result, the coupling cam  85  begins to be moved in the direction to move away from the inner plate  40 . Consequently, the back surface  85   d  of the coupling cam  85  begins to push out the large gear  83  in the direction to move away from the inner plate  40  against the resiliency of the spring (not shown) between the large gear  83  and the outward  86 , making the large gear coupling  83   a  begin to disengage from the drum coupling  7   a   1 . Further, as the raised surface  85   a   1  of the coupling cam  85  comes into contact with the raised surface  84   c   1  as the result of the rotation of the coupling cam  85 , the coupling cam  85  moves away from the inner plate  40  by a distance equal to the height of the raised portion  85   a   1  and base portion  85   a   3 , which in turn moves the large gear  83  into a retreat position where the coupling  83   a  of the large gear  83  is completely free from the drum coupling  7   a   1 . When the large gear  83  is at its retreat position, the end surface of the large gear coupling  83   a  is recessed from the inward surface of the inner plate  40 , and also has retreated from the moving path of the positioning guide  18   a  of the process cartridge B. 
     As has been described up to this point, the coupling means of the image forming apparatus in this embodiment is engaged or disengaged, that is, enabled or disabled to transmit a driving force, by being moved in the direction parallel to the rotational axis of the photoconductive drum  7 , that is, the direction perpendicular to the direction in which the process cartridge B is moved, by the coupling means controlling means. Thus, each step of the movements of the process cartridge B and coupling means controlling means must be always carried out in the proper sequence. When the large gear coupling  83   a  as the coupling means is ready to be engaged, it is partially in the path of the positioning guide  18   a,  within the hollow of which the drum coupling  7   a   1 , which engages with the large gear coupling  83   a,  is located. Therefore, if the large gear coupling  83   a  becomes ready for engagement prior to the mounting of the process cartridge B, the positioning guide  18   a  collides with the large gear coupling  83   a  during the mounting of the process cartridge B, preventing the process cartridge B from being inserted further. 
     Incidentally, when an attempt is made to take the process cartridge B out of the apparatus main assembly before the disengagement of the coupling means, the driven-side of the process cartridge B cannot be moved because of the engagement between the coupling on the process cartridge B side and the coupling on the apparatus main assembly side. 
     In the case that the two processes of conveying the process cartridge B and driving the coupling means controlling means are carried out by the rotational movement of the opening/closing cover  15 , it is necessary to provide a mechanism which guarantees that during the closing movement of the opening/closing cover  15 , the coupling means is readied for engagement by the coupling means controlling means, after the completion of the movement of the process cartridge B, whereas during the opening of the opening/closing cover  15 , the process cartridge B becomes ready for removal, after the disengagement of the coupling means by the coupling means controlling means. 
     Next, the mechanism for guaranteeing that the above described two processes will be carried out in the proper sequence, will be described. 
     When the opening/closing cover  15  is completely open (FIG.  27 ), the cam surfaces of the coupling cam  85  and inward bearing  84  are in contact with each other by the raised surface  84   c   1  and raised surface  85   a   1 , and the large gear  83  is in the retreat position, being away from the inner plate  40 . The contact surfaces of the raised surfaces of the coupling cam  85  and inward bearing  84  are inclined at a predetermined angle, and in order for the two raised surfaces to come into contact with each other, it is necessary for the coupling cam  85  to rotate through a certain angle. The thruster rod  55  is engaged with the boss  85   b  of the coupling cam  85 , the boss  85   b  being fitted in the keyhole-like hole  55   a  of the thruster rod  55 , and is in contact with the second boss  50   g  of the right cam plate  50  near the end of the arcuate portion  55   b   3  of the elongated hole  55   b.  A stopper rib  60  extending in the lengthwise direction of the process cartridge B from the surface of the inner plate  40  is within the recess of the backup portion  55   g.  The arcuate portion  55   b   3  of the elongated hole  55   b  is configured so that when the thruster rod  55  is in the above described state, the center of the curvature of the arcuate portion  55   b   3  virtually coincides with the axial line of the rotational shaft  50   a.  The claws  50   g   1  and  50   g   2  located at the end of the second boss  50   g  of the cam plate  50  remain outside the elongated hole  55   b,  always functioning to prevent the disengagement between the second boss  50   g  and thruster rod  55  during the movement of the thruster rod  55 . A tension spring  5  is stretched between the boss located below the arcuate portion  55   b   3  of the elongated hole  55   b,  and the inner plate  40 . The second boss  50   g  is kept in contact with the top wall of the arcuate portion  55   b   3  of the elongated hole  55   b.    
     Up to this point, the process, in which the moving guide  41  is moved by the rotational closing movement of the opening/closing cover  15 , and the process cartridge B is moved by the movement of the moving guide  41 , has been described. Next, the structure which prevents the coupling cam  85  as the coupling means controlling means from rotating will be described. 
     While the second boss  41   c  of the moving guide  41  is moving in the arcuate portion  40   b   1  of the second guide rail  40   b,  the second boss  50   g  of the cam plate  50  moves in the arcuate portion  55   b   3  of the elongated hole  55   b  of the thruster rod  55 . The center of the curvature of the arcuate portion  55   b   3  practically coincides with the axial line of the rotational shaft  50   a.  Therefore, during this movement of the second boss  50   g,  the thruster rod  55  maintains the attitude which it assumes when the opening/closing cover  15  is completely open. Thus, the coupling cam  85  is not rotated to move the large gear  83  (FIGS.  27 - 42 ). 
     Even if an unexpected external force acts upon the thruster rod  55  in the direction to make the thruster rod  55  advance, while the second boss  50   g  is moving in the arcuate portion  55   b   3  of the elongated hole  53   b,  the backup surface  55   g   1  of the backup portion  55   g  comes into contact with the stopper rib  60 , as shown in FIG. 51, ensuring that the thruster rod  55  is prevented from advancing, in order to prevent the coupling cam  85  from being rotated. In order for the backup surface  55   g   1  of the backup portion  55   g  to pass the stopper rib  60 , the thruster rod  55 , which is in the position shown in FIG. 27, must rotate about the axial line of the keyhole-like hole  55   a,  in which the boss  85   b  of the coupling cam  85  is fitted to connect the thruster rod  55  and coupling cam  85 , so that the top end of the backup surface  55   g   1  moves below the bottom end of the stopper rib  60 . However, such rotation of the thruster rod  55  is impossible while the second boss  50   g  of the cam plate  50  is in the arcuate portion  55   b   3  or inclined portion  55   b  of the elongated hole  55   b.  Therefore, the backup surface  55   g   1  and stopper rib  60  are made to remain in contact with each other, preventing the coupling cam  85  from beginning to rotate while the moving guide  41  is moving. 
     Referring to FIG. 36, as the second boss  41   c  of the moving guide  41  comes close to the border between the arcuate portion  40   b   1  and straight portion of the second guide rail  40   b,  a timing boss  41   d,  with which only the right moving guide  41  is provided, enters the U-shaped groove, which is located under the lifting portion  55   f  and is open toward the opening/closing cover  15 , and then, the second boss  50   g  of the cam plate  50  moves into the inclined portion  55   b  of the elongated hole  55   b  (FIG.  42 ). While the second boss  50   g  of the cam plate  50  is in the inclined portion  55   b  of the elongated hole  55   b,  the thruster rod  55  is prevented by the stopper rib  60  from advancing. Therefore, the rotation of the coupling cam  85  has yet to begin. 
     As the second boss  50   g  of the cam plate  50  reaches the border between the inclined portion  55   b  and straight portion  55   b   1  of the thruster rod  55 , the thruster rod  55  is rotated by the resiliency of a tension spring about the axial line of the keyhole-like hole  55   a  in the counterclockwise direction, guiding the second boss  50   g  of the cam plate  50  into the straight portion  55   b   1  of the elongated hole  55   b.  As a result, the thruster rod  55  begins to move in the direction to allow the backup portion  55   g  to pass the stopper rib  60 . However, when the second boss  41   c  of the moving guide  41  is above the straight portion  40   b   2  of the second guide rail  40   b  as shown in FIG. 45, the timing boss  41   d  located at the end of the second boss  41   c  of the moving guide  41  is in contact with the lifting surface  55   f  of thruster rod  55 . Therefore, it is impossible for the backup portion  55   g  of the thruster rod  55  to pass the stopper rib  60 . 
     Referring to FIG. 48, the cam plate  50  is rotated by the closing movement of the opening/closing cover  15  until the second boss  41   c  of the moving guide  41  moves downward in the straight portion  40   b   2  of the second guide rail  40   b,  and the timing boss  41   d  at the end of second boss  41   c  of the moving guide  41  also moves down and separates from the lifting portion  55   f.  As a result, the backup portion  55   g  of the thruster rod  55  is allowed to pass the stopper rib  60 , and is pulled down by the resiliency of the tension spring until the top end of the straight portion  55   b   1  of the thruster rod  55  butts against the second boss  50   g  of the cam plate  50 . 
     During the period between when the timing boss  50   d  comes into contact with the lifting surface  55   f  and when they separate from each other, the thruster rod  55  begins to rotate the coupling cam  85 . However, the angle by which the coupling cam  85  is rotated during this period is set in a range in which the coupling cam  85  and inward bearing  84  remain in contact with each other by their raised surfaces  85   a   1  and  84   c   1 , respectively. Therefore, the large gear coupling  83   a  does not begin to move. 
     As has been described above, while the moving guide  41  is moved by the rotation of the opening/closing cover  15 , the second boss  50   g  of the cam plate  50 , which drives the thruster rod  55 , moves in the arcuate portion  55   b   3  and inclined portion  55   b  of the elongated hole  55   b  of the thruster rod  55 . Therefore, the thruster rod  55  does not move. In addition, the movement of the thruster rod  55  is regulated by the condition that the stopper rib  60  is in the backup portion  55   g.  Thus, while the process cartridge B is conveyed by the movement of the moving guide  41  linked to the rotation of the opening/closing cover  15 , the large gear  83  as the coupling means does not become ready to be engaged for driving-force transmission, and therefore, does not interfere with the process-cartridge conveyance. 
     Referring to FIG. 52, as the opening/closing cover  15  is further closed after the completion of the movement of the moving guide  41 , the arcuate portion  50   b   1  of the elongated cam hole  50   b  (cam groove) of the cam plate  50  rotates along the second boss  41   c  of the moving guide  41 . Thus, the moving guide  41  remains in the second location in the image forming apparatus, and the end of the straight portion  55   b   1  of the elongated hole  55   b  of the thruster rod  55  is made to contact the second boss  50   g  of the cam plate  50 , by the resiliency of the tension spring, establishing the four-joint linkage comprising the thruster rod  55  and coupling cam  85 . 
     As a result, after the completion of the movement of the moving guide  41 , the coupling cam  85  is rotationally driven by the rotation of the cam plate  50 , causing the boss  85   b  of the coupling cam  85 , by which the coupling cam  85  is connected to the thruster rod  55 , to move downward. 
     Then, as the opening/closing cover  15  is further rotated, the state of the contact between the coupling cam  85  and inward bearing  84  shifts to the contact between their inclined surfaces  85   a   2  and  84   c   2 , and the large gear  83  comes under the pressure from the spring between the large gear  83  and outward bearing  86 . As a result, the large gear coupling  83   a  is forced to intrude into the hole of the inner plate  40 . When the twisted hole at the intruding end of the large gear coupling  83   a  is not coincidental in rotational phase with the twisted projection located at the end of the drum coupling  7   a   1  located in the hollow of the positioning guide  18   a  and coaxial with the positioning guide  18   a,  the intrusion of the large gear coupling  83   a  into the hole of the inner plate  40  stops as the intruding end of the large gear coupling  83   a  comes into contact with the end of the drum coupling  7   a   1 . 
     Then, before the opening/closing cover  15  completely closes, the coupling cam  85  rotates through a certain angle until it becomes possible for the base portion  85   a   3  of the cam surface of the coupling cam  85  to contact the raised surface  84   c   1  of the cam surface of the inward bearing  84 . By the time the opening/closing cover  15  completely closes, the inclined surfaces  84   c   2  and  85   a   2  of the inward bearing  84  and coupling cam  85  separate from each other, and remain separated, as shown in FIG.  53 . 
     In the preceding description of the present invention, it was stated that the end of large gear coupling  83   a  stops intruding into the hole of the inner plate  40  as it comes into contact with the end of the drum coupling  7   a   1 . However, when the opening/closing cover  15  is closed without mounting the process cartridge B, the large gear  83  moves until it comes into contact with the inward bearing  84 . Therefore, the large gear coupling  83   a  protrudes a substantial distance into the inward side of the inner plate  40 . 
     This concludes the description of the mechanism for ensuring that the process of conveying the process cartridge B by the movement of the moving guide  41  during the first half of the closing movement of the opening/closing cover  15 , and the process of readying the coupling means by the coupling means controlling means to be engaged for driving-force transmission during the latter half of the closing movement of the opening/closing cover  15 , are carried out in the correct order. 
     (Driving of Process Cartridge Positioning Means on Left Side) 
     As described before, during the process-cartridge conveyance by the movement of the moving guide  41  linked by the rotation of the opening/closing cover  15 , the left positioning guide  18   a  is not in the positioning portion  90   a  of the conveying means frame  90 . This is for the following reason. For the purpose of reducing the load which acts upon the process cartridge B during its conveyance, the left positioning guide  18   a  is not provided with a spring for keeping the left positioning guide  18   a  pressed upon the positioning portion  90   a.  Therefore, the process-cartridge conveyance by the moving guide  41  alone cannot engage the left positioning guide  18   a  into the positioning portion  90   a  against the contact pressure generated by the transfer roller  4  and various electrical contacts  92 . 
     On the outward side of the left inner plate  40 , the pushing arm  52  is provided, which functions as a process cartridge positioning means, and is driven by the cam plate  50 . The pushing arm  52  is provided with the resilient pressing portion  52   b,  which protrudes into the inward side of the inner plate  40  through the fan-shaped hole  40   h  of the left inner plate  40 , and is supported at a position away from the positioning portion  90   a,  that allows it to oscillate. 
     On the other hand, the left positioning guide  18   a  of the process cartridge B is provided with a mounting assistance auxiliary guide  18   a   1 , which extends backward in terms of the process-cartridge mounting direction. The rear end of this mounting assistance guide  18   a   1  constitutes a contact portion  18   a   2 , which comes into contact with the resilient pressing portion  52   b  of the pushing arm  52 . In this embodiment, the contact portion  18   a   2  is made arcuate so that the center of its curvature coincides with the axial line of the positioning guide  18   a.  With this structural arrangement, the variance in the positional relationship of the portion  18   a   2  relative to the resilient pressing portion  52   b  is minimized, when the positioning guide  18   a  settles into the positioning portion  90   a.    
     During the conveyance of the process cartridge B, the pushing arm  52  remains in the retreat position, in which the resilient pressing portion  52   b  of the pushing arm  52  is outside the paths of the positioning guide  18   a  and portion  18   a   1 . In this state, as the pushing arm  52  is driven by the cam plate  50 , the resilient pressing portion  52   b  pushes the positioning guide  18   a  into the positioning portion  90   a  after the completion of the cartridge conveyance, and comes to a retaining position because the positioning guide  18   a  must be prevented from being moved out of the positioning portion  90   a  by the external force which acts on the process cartridge B, for example, the force generated by the recording medium in the direction to lift the photoconductive drum  7  during image formation, in addition to the contact pressure from the transfer roller  4  and electrical contacts  92 . 
     In order to minimize the angle through which the pushing arm  52  must rotate to move the resilient pressing portion  52   b  from the retaining portion to retreat, the mounting assistance auxiliary guide  18   a   1 , which is behind the positioning guide  18   a  in terms of the process-cartridge mounting direction, is provided with the pressure catching portion  18   a   2 , which is located on the peripheral surface, keeping the resilient pressing portion  52   b  of the pushing arm  52  away from the rotational shaft  52   a.  If the angle, by which the pushing arm  52  must rotate to place the resilient pressing portion  52   b  of the pushing arm  52  in contact with the peripheral surface of the positioning guide  18   a,  is increased to keep the resilient pressing portion  52   b  away from the paths of the positioning guide  18   a  and mounting assistance auxiliary guide  18   a   1 , the distance between the retreat position of the boss  52   c,  which is driven by the cam plate  50  located ahead of the resilient pressing portion  52   b  in terms of the process-cartridge mounting direction, and the rotational shaft  50   a  of the cam plate  50 , increases. Consequently, the end of the arm driving portion  50   h   1  must be extended in the outward direction in terms of the radius direction of the cam plate  50 , requiring a larger space for the rotation of the cam plate  50 , which is a problem. 
     The top surface of the mounting assistance auxiliary guide  18   a   1  is an inclined surface  18   a   3 , tilting toward the peripheral surface of the positioning guide  18   a.  This inclined surface  18   a   3  assures that the pressure catching surface  18   a   2  contacts the resilient pressing portion  52   b  to minimize the protrusion of the mounting assistance auxiliary guide  18   a   1  from the path of the positioning guide  18   a,  within the area on the inward side of the rotational radius of the resilient pressing portion  52   b.  With this arrangement, the clearance between the resilient pressing portion  52   b  in its retreat position, and the path of the mounting assistance auxiliary guide  18   a   1 , is secured. 
     In other words, the pressure catching portion  18   a   2  is such a pressure catching portion that is located on the upstream side of the cartridge positioning portion  18   a,  in terms of the direction in which the process cartridge B is mounted into the apparatus main assembly  14 , and also is located away from the cartridge positioning portion  18   a.  It comes under the pressure from resilient pressing portion  52   b  of the apparatus main assembly  14 , as the process cartridge B is moved into the proper cartridge position S in the apparatus main assembly  14 . Further, the pressure catching portion  18   a   2  is in the form of an arc, the center of which coincides with the axial line of the photoconductive drum  7 . The cartridge frame CF, cartridge positioning portion  18   a,  and pressure catching portion  18   a   2 , are integrally formed of plastic. 
     The pressure catching portion  18   a   2  is located on the upstream side of the cartridge positioning portion  18   a,  in terms of the direction in which the process cartridge B is mounted into the apparatus main assembly  14 , and also is located away from the cartridge positioning portion  18   a.  It comes under the pressure from the resilient pressing portion  52   b  of the apparatus main assembly  14 , as the opening/closing cover  15  is closed. 
     The movement of the pushing arm  52  is similar to that of the coupling means controlling means in that it must be carried out in the proper order. In other words, it is necessary that during the closing movement of the opening/closing cover  15 , the pushing arm  52  begins to rotate after the completion of the conveyance of the process cartridge B, and during the opening movement of the opening/closing cover  15 , the process cartridge B begins to move after the completion of the rotation of the pushing arm  52 . More specifically, during the closing movement of the opening/closing cover  15 , the pushing arm  52  rotates, moving the process cartridge B to a predetermined location, after the completion of the movement of the moving guide  41 , and then, it retains the process cartridge B in the positioning portion. These functions of the pushing arm  52  will be described next. 
     When the pushing arm  52  is in the retreat position, in which it is holding up the resilient pressing portion  52   b,  by being pressured by the resiliency of the helical torsion coil spring  53 , the boss  52   c  is at a point at which it is about to cross the path of the open end of the arm driving portion  50   h   1  of the second cam  50   h,  after the cam plate  50  has moved the moving guide  41  to the second location. 
     Thus, as the opening/closing cover  15  is closed further after the completion of the movement of the moving guide  41 , the arm driving portion  50   h   1  of the second cam  50   h  of the cam plate  50  takes in the boss  52   c  of the pushing arm  52 . During the closing movement of the opening/closing cover  15 , the boss  52   c  contacts the outward wall of the second cam  50   h,  and rotates the pushing arm  52  in the clockwise direction about the arm driving portion  50   h   1  of the second cam  50   h  against the resiliency of the helical torsion coil spring  53 . Therefore, as the cam plate  50  rotates, the boss  52   c  moves deeper into the arm driving portion  52   h   1 . By this rotation of the pushing arm  52 , the resilient pressing portion  52   b  of the pushing arm  52  is moved closer to the mounting assistance guide  18   a   1  of the process cartridge B. 
     At this point, the positioning guide  18   a  of the process cartridge B has yet to fit into the positioning portion  90   a  of the conveying means frame  90 . Therefore, the mounting assistance auxiliary guide  18   a   1  on the peripheral surface of the positioning guide  18   a  is outside the rotational path of the pressure application surface  52   b   1  of the resilient portion  52   b  of the pushing arm  52 . 
     As the pushing arm  52  rotates about the rotational shaft  52   a  due to further rotation of the cam plate  50 , the pulling surface  52   b   2 , which is on the upstream side of the resilient pressing portion  52   b  in terms of the rotational direction of the pushing arm  52  and is tilted more in the outward direction, in terms of the radius direction of the rotation of the pushing arm  52 , comes into contact with the mounting assistance auxiliary guide  18   a   1  on the upstream side of the peripheral surface of the positioning guide  18   a,  in terms of the process cartridge mounting direction with respect to a predetermined position (FIG.  55 ). 
     As the resilient pressing portion  52   b  is further rotated after the pulling surface  52   b   2  comes into contact with the round corner  18   a   4  of the mounting assistance auxiliary guide  18   a   1 , which connects the inclined surface  18   a   3  and pressure catching portion  18   a   2  of the mounting assistance auxiliary guide  18   a   1 , the process cartridge B begins to be pressured by the slanted pulling surface  52   b   2  in the direction to fit the positioning guide  18   a  into the positioning portion  90   a,  and the round corner  18   a   4  of the mounting assistance auxiliary guide  18   a   1  comes into contact with the contact surface  52   b   1  of the resilient pressing portion  52   b,  on the rotational shaft  52   a  side. Then, as this contact surface  52   b   1  comes into contact with the pressure catching portion  18   a   2 , which is on the peripheral surface of the mounting assistance auxiliary guide  18   a   1 , the positioning guide  18   a  fits into the positioning portion  90   a,  as shown in FIG. 56, ending the positioning of the process cartridge B in the apparatus main assembly. 
     Even after pushing the positioning guide  18   a  into the positioning portion  90   a  by the resilient pressing portion  52   b,  the pushing arm  52  continues to rotate until the resilient pressing portion  52   b  entirely enters the path of the pressure catching portion  18   a   2  to begin to properly support and retain the process cartridge B (FIG.  57 ). 
     Thereafter, as the cam plate  50  rotates further, the boss  52   c  moves past the arm driving portion  50   h   1  and moves into the arm retaining portion  50   h   2 , the center of the curvature of which coincides with the rotational axis of the cam plate  50 . As the result, the rotation of the pushing arm  52  stops. 
     Thereafter, the cam plate  50  rotates further to a point at which it will ensure that the boss  52   c  of the pushing arm  52  has come into contact with the cam surface of the arm retaining portion  50   h   2 , and which corresponds to the completely closed position of the opening/closing cover  15  (FIG.  58 ). 
     At this point, the resilient pressing portion  52   b  of the pushing arm  52  is in contact with the pressure catching portion  18   a   2  of the process cartridge B, and also, is completely in the path of the positioning guide  18   a.  Therefore, the process cartridge B is regulated in movement; in other words, it is retained in the positioning portion  90   a.    
     In this state, the only direction in which the positioning guide  18   a  is allowed to move is the direction of the line connecting the resilient pressing portion  52   b  and rotational shaft  52   a.  Therefore, as an attempt is made to dislodge the process cartridge B from the positioning portion  90   a,  the reactive force which acts on the resilient pressing portion  52   b  is directed approximately toward the rotational shaft  52   a,  failing to rotate the pushing arm  52 . Without the rotation of the pushing arm  52 , the resilient pressing portion  52   b  does not unlatch from the pressure catching portion  18   a   2 . Therefore, the process cartridge B remains retained in the positioning portion  90   a,  being properly positioned. 
     Regarding the relationship between the boss  52   c  of the pushing arm  52  and the second cam  50   h  of the cam plate  50  while they are in contact with each other, when the image forming apparatus is ready for image formation, that is, after the complete closing of the opening/closing cover  15 , the boss  52   c  is in the arm retaining portion  50   h   2  of the second cam  50   h,  the center of the curvature of which coincides with the axial line of the rotational shaft  50   a  of the cam plate  50 , being supported thereby. Therefore, even if an attempt is made to rotate the pushing arm  52 , it is impossible for the pushing arm  52  to rotate the cam plate  50 . Thus, neither does the opening/closing cover  15  open, nor is the image forming apparatus adversely affected. 
     (Activation of Interlocking Switch) 
     Up to this point, the placement of the process cartridge B in the apparatus main assembly linked to the closing movement of the opening/closing cover  15 , the readying of the coupling means by the movement of the coupling means controlling means, for engagement, and the positioning and retaining of the left positioning guide of the process cartridge B by the pushing arm  52 , in the positioning portion, have been described. 
     These processes completely end before the opening/closing cover  15  is completely closed. Thus, as the opening/closing cover  15  is completely closed, the interlocking switch  54  is activated, allowing electrical current to flow to ready the image forming apparatus for image formation. More specifically, as the microswitch  91  (FIG. 58) on the power source circuit board is pressed by an oscillatory lever  91   a,  the image forming apparatus is turned on. Referring to FIGS. 54-58, the interlocking switch  54  is rotationally attached to the left inner plate  40 . It makes contact with the oscillatory lever  91   a  of the microswitch  91  (unshown in FIGS.  54 - 57 ), by the lever  54   b,  and is kept pressed upward by the resiliency of the microswitch  91 . 
     The left cam plate  50  is provided with a contact surface  50   i,  which is located on the inward side, in terms of the radius direction of the curvature of the second cam  50   h,  of the second cam  50   h  located at the leading end of the left cam plate  50  in terms of the rotational direction of the cam plate  50 . The contact surface  50   i  contacts the elastic portion  54   c  of the interlocking switch  54 . 
     As the opening/closing cover  15  is closed, and the left cam plate  50  guides the boss  52   c  of the pushing arm  52  to the arm retaining portion  50   h   2  of the second cam  50   h,  the contact surface  50   i  comes into contact with the elastic contact portion  54   c  of the interlocking switch  54 . Thereafter, while the cam plate  50  is moving the boss  52   c  of the pushing arm  52  to the outward wall of the arm retaining portion  50   h   2 , the interlocking switch  54  rotates about the shaft  54   a  against the resiliency of the microswitch  91 , causing the lever  54   b  to press the lever  91   a  downward to engage the microswitch  91 . As a result, the image forming apparatus is turned on. 
     In order to ensure that the interlocking switch  54  is activated during the last stage of the rotational movement of the cam plate  50 , the contact surface  50   i  of the cam plate  50  must be positioned as if it is partially in the contact portion of the interlocking switch  54  (FIG.  58 ), in consideration of the variance in the angle by which the cam plate  50  is rotated by the closing of the opening/closing cover  15 . Therefore, the contact portion  54   c  of the interlocking switch  54  is rendered elastic so that the elastic contact portion  45   c , elastically deforms to tolerate the hypothetical intrusion of cam plate  50 . 
     (Method for Positioning Process Cartridge) 
     The turning on of the image forming apparatus concludes the last movement of the various mechanisms linked to the closing of the opening/closing cover  15 ; in other words, the complete closing of the opening/closing cover  15  readies the image forming apparatus for image formation. Thereafter, as the motor of the driving means  80  rotates, the driving force is transmitted to the large gear  83 , rotating the large gear  83 . As the large gear  83  rotates, the twisted hole of the large gear coupling  83   a  becomes coincidental in rotational phase with the twisted projection of the drum coupling  7   a   1 . As the twisted hole and projection coincide in rotational phase, the large gear coupling  83   a  is advanced by the spring located between the large gear  83  and outward bearing  86 . Then, a force is generated by the twist of both the couplings in the direction to cause the two couplings to pull each other. As a result, the end of the twisted projection of the drum coupling  7   a   1  comes into contact with the bottom surface of the twisted hole of the large gear coupling  83   a,  and is kept in contact therewith, by the force which is acting upon both the couplings in the direction to cause the couplings to pull each other, fixing thereby the positions of both couplings in terms of the lengthwise direction of the process cartridge B. Since the cross section of the twisted hole of the large gear coupling  83   a  and the cross section of the twisted projection of the drum coupling  7   a   1  are both in the form of a virtually equilateral triangle, and the axial lines of the twisted hole and twisted projection coincide with the large gear coupling  83   a  and drum coupling  7   a   1 , respectively, the rotational axes of the large gear coupling  83   a  and drum coupling  7   a   1  become aligned with each other as the three lateral walls of the twisted hole come into contact with the corresponding three lateral edges of the twisted projection, allowing the driving force to be smoothly transmitted. 
     After the driving force begins to be transmitted by the engagement of the coupling means, and the rotational axes of the large gear coupling  83   a  and drum coupling  7   a   1  are aligned, the position of the right end of the process cartridge B, where the coupling means controlling means is located, is fixed by the coupling means. Referring to FIG. 59, the positioning guide  18   a,  which has been supported by the cartridge catching/retaining portion  84   a  until the coupling means is engaged, is separated from the cartridge catching/retaining portion  84   a  against the resiliency of the helical torsion coil spring  45 , and also, the mounting guide  18   b  is separated from the guiding groove  41   a  of the moving guide  41 . Further, as the process cartridge B begins to be driven as the result of the engagement of the coupling means, in other words, as the process cartridge B begins to be subjected to a rotational force, the butting surface  18   d,  which is on the right end of the cartridge frame, as seen from the trailing side in terms of the process-cartridge mounting direction, and on the leading end of the cartridge frame in terms of the process-cartridge mounting direction, and faces forward in terms of the rotational direction of the process cartridge B, comes into contact with the rotation controlling portion  44   b  of the stationary guide  44 . 
     As described above, in this embodiment, the image forming apparatus is structured so that the position of the process cartridge B within the image forming apparatus is fixed only after the driving force begins to be transmitted to the process cartridge B by the engagement of the coupling means. 
     After the driving force begins to be transmitted to the process cartridge B, the process cartridge B is retained in the proper position by the drum coupling  7   a   1 , which is coaxially attached to the right end of the photoconductive drum  7 , and the large gear coupling  83   a  rotationally supported by the right inner plate  40  of the image forming apparatus. The left end of the process cartridge B is properly positioned as the positioning guide  18   a  of the cartridge frame, the axial line of which coincides with the rotational axis of the photoconductive drum  7 , is fitted in the positioning portion  90   a  of the conveying means frame  90 , and is retained therein as the pressure catching portion  18   a   2  on the peripheral surface of the positioning guide  18   a  is kept pressed by the resilient pressing portion  52   b  of the pushing arm  52 . Further, the butting surface  18   d  of the cartridge frame, which is at the leading end, in terms of the process-cartridge mounting direction, and at the right end, as seen from the trailing side in terms of the process-cartridge mounting direction, remains in contact with the rotation controlling portion  44   b  of the stationary guide  44 . In other words, the process cartridge B is properly retained in the proper position in the image forming apparatus, by three points. 
     In order to place the process cartridge B in the above described proper position, the mounting guide  18   b  of the process cartridge B, which has been supported by the moving guide  41  while being conveyed by the movement of moving guide  41 , leaves the retaining surface  41   a   1  of the moving guide  41 , as the positioning portions (positioning guide  18   a,  and drum coupling  7   a   1 ), which are coaxial with the photoconductive drum  7  begin to be supported by the positioning means (positioning portion  90   a  of the conveyance frame, and large gear coupling  83   a ) on the image forming apparatus side. 
     As is evident from the above description, by supporting the positioning portions on the process cartridge B side, which are coaxial with the photoconductive drum  7 , by the positioning means of the image forming apparatus main assembly, the process cartridge B is placed and retained in the proper position in the image forming apparatus, and therefore, the process cartridge B is highly accurately positioned relative to such components as the optical system  1  and transfer roller  4 , the positional relationship of which relative to the photoconductive drum  7  must be guaranteed in accuracy. 
     (Movements of Process Cartridge Mounting/Dismounting Mechanism During Opening of Opening/Closing Cover  15 ) 
     Next, the sequence of turning off the image forming apparatus by deactivating interlocking switch  54  by opening the opening/closing cover  15 ; disengaging the pushing arm  52  and coupling means by further opening the opening/closing cover  15 ; moving the moving guide  41  by further opening the opening/closing cover  15 ; and taking out the process cartridge B from the moving guide  41 , will be described. In this sequence, the steps described above are carried out in the reverse order. 
     The opening/closing cover  15 , which is in the position shown in FIGS. 53,  58 , and  59 , is opened. On the left side of the image forming apparatus, as the opening/closing cover  15  is opened, the cam plate  50  rotates in the direction to move away from the interlocking switch  54 . As a result, the interlocking switch  54  is lifted by the resiliency of the microswitch  91 , and therefore, the current to various operational units of the image forming apparatus is cut off. Further, the elastic contact portion  54   c  is disengaged from the contact portion  50   i  of the cam plate  50  (FIGS.  55 - 58 ). 
     Next, the pushing arm  52  is disengaged from the coupling means. First, the disengagement of the left pushing arm  52  will be described. 
     As the cam plate  50  is rotated until the elastic portion  54   c  of the interlocking switch  54  becomes disengaged from the contact portion  50   i,  the boss  52   c  of the pushing arm  52  becomes disengaged from the arcuate surface of the arm retaining portion  50   h   2  of the second cam  50   h  (FIG.  56 ). Since the resiliency of the helical torsion coil spring  53  attached to the base of the pushing arm  52  is not strong enough to disengage the pushing arm  52  by lifting the pushing arm  52  by overcoming the friction between the resilient pressing portion  52   b  and pressure catching portion  18   a   2 , the cam plate  50  simply contacts the boss  52   c  by the inward wall of the arm driving portion  50   h   1  of the second cam  50   h,  in terms of the radius direction. Then, the pushing arm  52  is forced by the rotation of the cam plate  50  to move upward. 
     After this disengagement of the boss  52   c  and the inward wall of the arm driving portion  50   h   1  of the second cam  50   h,  the resilient pressing portion  52   b  of the pushing arm  52  is disengaged from the pressure catching portion  18   a   2  of the process cartridge B. The pushing arm  52  is placed in contact with the top end  40   h   2  of the fan-shaped hole  40   h  of the inner plate  40 , by the function of the helical torsion coil spring  53 , by the butting portion  52   b   3  at the top end of the resilient pressing portion  52   b,  and the resilient pressing portion  52   b  is moved to its retreat position where it will be out of the paths of the positioning guide  18   a  and pressure catching portion  18   a   2  of the process cartridge B (FIGS.  54 - 55 ). 
     As a result, the left positioning guide  18   a  of the process cartridge B is moved out of the positioning portion  90   a  by the contact pressure between the photoconductive drum  7  and transfer roller  4 , which acts in the direction to lift the photoconductive drum  7 . 
     At the same time as the disengagement of the pushing arm  52  on the left side, the coupling means is disengaged. 
     As the opening/closing cover  15  is opened, the coupling cam  85  connected to the right cam plate  50  by the thrust rod  55  rotates (FIG. 52) in the direction to cause the large gear coupling  83   a  to move away from the process cartridge B in terms of the direction of the rotational axis of the photoconductive drum  7 . 
     As described before, one end of the thruster rod  55  is connected to the second boss  50   g  of the right cam plate  50 , by the end of the elongated arcuate hole  55   b,  and the other end is connected to the boss  85   b  of the coupling cam  85 , by the keyhole-like hole  55   a.  The end of the elongated hole  55   b  is kept pressed upon the second boss  50   g  by the tension spring. It is as described above that the direction of the straight portion  55   b   1  of the elongated hole  55   b  of the thruster rod  55  is virtually perpendicular to the line connecting the top end of the straight portion  55   b   1  and keyhole-like hole  55   a.    
     The coupling means is constituted of a combination of the twisted projection and twisted hole, the cross sections of which are in the form of a virtual equilateral triangle. Therefore, in order to disengage the coupling means by moving the large gear coupling  83   a  in its axial direction, either the drum coupling  7   a   1  with the twisted projection or the large gear coupling  83   a  with the twisted hole must be rotated by such an angle that is necessary to dissolve the engagement between the twisted edges of the twisted projection and the twisted walls of the twisted hole. Therefore, a relatively large amount of force is necessary for the disengagement. 
     The thruster rod  55  transmits the driving force of the cam plate  50  to the coupling cam  85 , rotating the coupling cam  85 , and the rotation of the coupling cam  85  disengages the coupling means. Therefore, as the driving force is transmitted from the cam plate  50  to the coupling cam  85  to disengage the coupling means, the thruster rod  55  is subjected to a coupling means disengagement load Ff which acts in the direction of the line connecting the keyhole-like hole  55   a,  in which the boss  85   b  of the coupling cam  85  is fitted, and the top end of the straight portion  55   b   1  of the elongated hole  55   b,  which is in contact with the second boss  50   g  of the cam plate  50 , as shown in FIG.  52 . In order to prevent the second boss  50   g  from dislodging from the end of the elongated hole  55   b  when this coupling means disengagement load Ff is caught by the end of the elongated hole  55   b,  the wall surface of the end of the elongated hole  55   b  must be rendered either perpendicular to the direction of the coupling means disengagement load, or inclined in such a manner that the coupling means disengagement load, the major component of which is caught by the straight portion  55   b   1  of the elongated hole  55   b,  is directed toward the top end of the straight portion  55   b   1 . In this embodiment, the straight portion  55   b   1 , which constitutes the end portion of the elongated hole  55   b  is rendered virtually perpendicular to the line connecting the top end of the straight portion  55   b   1  and the keyhole-like hole  55   a,  and the tension spring is mounted so that the end of the straight portion  55   b   1  is kept pressed upon the second boss  50   g.    
     As the cam surfaces of the inward bearing  84  and the corresponding inclined surfaces  85   a   2  and  84   c   2  are placed in contact with each other by the rotation of the coupling cam  85 , the coupling cam  85  is moved by the function of the inclined surfaces, outward of the apparatus in terms of its axial direction, dissolving the engagement between the large gear coupling  83   a  and drum coupling  7   a   1 . Thereafter, the further rotation of the coupling cam  85  causes the raised surfaces  85   a   1  and  84   c   1  of the cam surfaces of the coupling cam  85  and inward bearing  84 , respectively, to contact each other. As the raised surfaces  85   a   1  and  84   c   1  contact each other, the inward end of the large gear coupling  83   a  is moved outward of the apparatus beyond the inward surface of the inner plate  40 , ending the disengagement of the coupling means. 
     In the description given above regarding the internal movements of the image forming apparatus linked to the opening of the opening/closing cover  15 , it was stated that the movement of the cam plate  50  was linked to the movement of the opening/closing cover  15 , and the various mechanisms were driven by the rotation of the cam plate  50 . However, the moving guide  41 , which had conveyed the process cartridge B, remains stationary during the opening of the opening/closing cover  15  to the above described point. This is due to that fact that during the rotation of the cam plate  50  up to the above described point, all that happens is for the top and bottom walls of the arcuate portion  50   b   1  of the elongated hole  50   b  to pass by the peripheral surface of the second boss  41   c  of the moving guide  41  located below the bottom end of the straight portion  40   b   2  of the second guide rail  40   b  of the inner plate  40 . In other words, until the pushing arm  52  and coupling means, which are the means for properly positioning and supporting the process cartridge B within the image forming apparatus, are completely disengaged, the process cartridge B is not conveyed by the moving guide  41 . 
     Thus, as the opening/closing cover  15  is further opened from the point corresponding to the end of the above described cover opening stage, the moving guide  41  begins to be moved by the cam plate  50 . 
     As the rotation of the cam plate continues, the moving guide  41  comes into contact with the second boss  41   c  at the intersection of the arcuate portion  50   b   1  and straight portion (straight groove hole)  50   b   2  of the elongated hole  50   b  of the cam plate  50 . As a result, the further rotation of the cam plate  50  begins to cause the straight portion (straight groove hole)  50   b   2  to make the second boss  41   c  of the moving guide  41  move upward into the straight portion  40   b   2  of the second guide rail  40   b  of the inner plate  40 . At this point, the moving guide  41  begins to be moved by the opening movement of the opening/closing cover  15 , for the first time. 
     At this time, the aforementioned disengagement of the thruster rod  55  will be described. 
     Referring to FIG. 52, while the coupling means is disengaged by the rotation of the cam plate  50 , the timing boss  41   d  of the moving guide  41  enters the space under the lifting surface  55   f  of the thruster rod  55 . The cam plate  50  begins to lift the moving guide  41  as the coupling cam  85  further rotates from the point at which the raised surfaces  85   a   1  and  84   c   1  of the cam surfaces of the coupling cam  85  and inward bearing  84 , respectively, come into contact with each other. At this point, the stopper rib  60 , which perpendicularly extends from the surface of the inner plate  40  has arrived above the recessed backup portion  55   g,  which is above the lifting surface  55   f,  and is open upward (FIG.  48 ). 
     As the timing boss  41   d  at the end of the second boss  41   c  of the moving guide  41  moves upward the lifting surface  55   f  of the thruster rod  55 , the thruster rod  55  rotates about the axial line of the keyhole-like hole  55   a.  This rotation causes the corner of the elongated hole  55   b  of the thruster rod  55 , where the straight portion  55   b   1  and inclined portion  55   b  of the elongated hole  55   b  meet, to move beyond the second boss  50   g  of the cam plate  50 , ending the driving of the thruster rod  55  by the cam plate  50 . Also, this rotation of the thruster rod  55  causes the stopper rib  60  to settle in the recessed backup portion  55   g,  beginning to regulate the movement of the thruster rod  55  (FIG.  45 ). 
     Then, the second boss  41   c  of the moving guide  41  is lifted by the cam plate  50 , and the first boss  41   b  of the moving guide  41  begins to move along the inclined portion  40   a   2  of the first guide rail  40   a.  As a result, the moving guide  41  is moved upward. Therefore, the bottom surface  18   b   1  of the mounting guide  18   b  of the process cartridge B, which was not in contact with the moving guide  41  up to this point, comes into contact with the retaining surface  41   a   1  of the moving guide  41 . Consequently, the process cartridge B will be supported by the moving guide  41  instead of the positioning means of the image forming apparatus main assembly. 
     The moving guide  41  makes contact with the end  18   b   2  of the mounting guide  18   b,  by the inward end of the catching surface  41   a   2 , and begins to pull the process cartridge B outward of the apparatus main assembly. During this movement of the moving guide  41 , on the right side of the apparatus main assembly, the process cartridge B is pulled outward of the apparatus main assembly in the diagonally upward direction, while the right positioning guide  18   a  pushes up the helical torsion coil spring  45  attached to the right stationary guide  44  (FIG.  44 ). 
     As the opening/closing cover  15  is further opened, the second boss  41   c  of the moving guide  41  is sandwiched by the first arcuate portion  40   b   1  of the second guide rail  40   b  of the inner plate  40 , and the leading end of the straight portion (straight groove hole)  50   b   2  of the elongated hole  50   b  (cam groove) of the cam plate  50 , and is moved toward the opening W, through which the process cartridge B is mounted or dismounted. At the same time, the first boss  41   b  is moved outward from the inclined portion  40   a   2  of the first guide rail  40   a  along the horizontal portion  40   a   1 . Consequently, the process cartridge B is conveyed to the location (cartridge removal location) at which the process cartridge B can be grasped by a user, with the photoconductive drum  7  being horizontally conveyed (FIGS.  26 - 44 ). 
     At the same time as this conveyance of the process cartridge B, the drum shutter  12 , rotationally supported by the cartridge frame of the process cartridge B, is moved following in reverse the steps it follows during the mounting of the process cartridge B. 
     As the first boss  41   b  of the moving guide  41  is made to climb the inclined portion  40   a   2  of the first guide rail  40   a  while moving the process cartridge B upward, the angle, at which the drum shutter  12  is open, temporarily narrows slightly. Then, as the process cartridge B begins to be conveyed toward the opening W, the rib  12   e  comes into contact with the second inclined surface  44   c   3  of the shutter guide  44   d  of the stationary guide  44 , increasing the angle at which the drum shutter is open. Then, the rib  12   e  is moved onto the raised surface  44   c   2 , drum shutter  12  avoiding the electrical contact  92 . Then, the rib  12   e  is moved onto the first inclined surface  44   c   1 , and is conveyed on the first inclined surface  44   c   1  toward the opening W, together with the process cartridge B, while allowing the angle, at which the drum shutter  12  is open, to be reduced by the force of the shutter spring (unshown). As the angle, at which the drum shutter  12  is open, dcreases, the highest point  12   d   1  of the cam portion  12   d  comes into contact with the bottom surface of the optical system plate  1   f,  and the rib  12   e  leaves the first inclined surface  44   c   1 . Then, as the highest point  12   d   1  of the cam portion  12   d  comes out of the bend portion of the optical system plate  1   f,  the cam portion  12   d  is rotated by a large angle by the force of the torsional coil spring. The drum shutter  12  continues to close until the cam portion  12   d  leaves the optical system plate  1   f,  when the transfer opening  9   a  and exposure opening  9   b  are completely covered by the drum shutter  12 . 
     When the highest portion  12   d   1  of the cam portion  12   d  of the drum shutter  12  is made to pass the bend portion of the optical system plate  1   f,  by the conveyance of the process cartridge B carried out by the movement of the moving guide  41  linked to the rotation of the opening/closing cover  15 , the bottom surface  10   f   4  of the toner/developing means holding frame  10   f  of the process cartridge B comes into contact with the contact rib  43   c  of the front guide  43  which constitutes the bottom wall of the opening W (FIG.  26 ). 
     When the process cartridge B assumes such an attitude that it contacts the contact rib  43   c,  the center of gravity of the process cartridge B is on the photoconductive drum  7  side with respect to the contact surface between the process cartridge B and contact rib  43   c.  Therefore, as the opening/closing cover  15  is further opened when the process cartridge B assumes the above described attitude, the moving guide  41  moves closer to the opening W, moving the process cartridge B toward the opening W, or toward an operator. While the process cartridge B is moved toward the opening W, it is rotated by the inclination of the contact rib  43   c  and bottom surface  10   f   4  of the toner/developing means holding frame  10   f,  in such a manner that the toner/developing means holding frame  10   f  side of the process cartridge B is lifted as if the inward end  18   b   2  of the mounting guide  18   b  is functioning as a fulcrum. The contact rib  43   c  is shaped so that as the opening/closing cover  15  continues to be opened until it becomes fully open as shown in FIG. 21, the process cartridge B is rotated until the outward bottom corner  18   b   3  of the mounting guide  18   b  moves beyond the inclined surface  41   a   4  located at the stepped portion of the guiding groove  41   a  of the moving guide  41 . 
     Therefore, as the guiding surface  41   a   2  of the guiding groove  41   a  of the moving guide  41  is made contiguous and level with the front guiding surface  42   a   1  of the auxiliary guide  42  (first location) by the final stage of the rotational movement of the opening/closing cover  15  before it becomes fully open, the process cartridge is enabled to be smoothly taken out of the apparatus main assembly, through the opening W, without such an occurrence that the outward bottom corner  18   b   3  of the mounting guide  18   b  hangs up on the inclined surface  41   a   4 , by being simply pulled toward the operator. 
     When the opening/closing cover  15  is in the fully open position, the second boss  41   c  of the moving guide  41  is placed in contact with the inward wall of the straight portion (straight groove hole)  50   b   2  (straight groove hole) of the elongated hole  50   b  of the cam plate  50 , and the end of the arcuate portion  40   b   1  of the second guide rail  40   b,  on the opening W side, is used as a stopper for preventing the opening/closing cover  15  from being further rotated. 
     As described above, during the first half of the entire rotational range of the opening/closing cover  15  for completely closing the fully open opening/closing cover  15 , the process cartridge mounting/dismounting mechanism in this embodiment moves the moving guide  41  from the first location, at which the process cartridge B can be mounted into, or dismounted from, the apparatus main assembly, to the second location, from which the process cartridge B is conveyed close to the location at which the process cartridge B functions for image formation. Then, the drum shutter  12  is opened by the conveyance of the process cartridge B by the movement of the moving guide  41 . Next, the process cartridge B is readied for an image forming operation, and is kept on standby near the location at which process cartridge B functions for image formation. During the latter half of the entire rotational range of the opening/closing cover  15  for closing the fully open opening/closing cover  15 , the process cartridge mounting/dismounting mechanism readies the coupling means for transmitting a driving force to the process cartridge B for engagement, and activates the positioning means for placing and supporting the process cartridge B in the location at which the process cartridge B can function for image formation. Then, it turns on the image forming apparatus. On the other hand, during the first half of the entire rotational range of the opening/closing cover  15  for fully opening the completely closed opening/closing cover  15 , first, the image forming apparatus is turned off by the initial opening movement of the opening/closing cover  15 . Then, the positioning means which has been retaining the process cartridge B in the position at which the process cartridge B can function for image formation, and the coupling means, are disengaged. Then, during the latter half of the entire rotational range of the opening/closing cover  15  for fully opening the completely closed opening/closing cover  15 , the process cartridge B is conveyed by moving the moving guide  41  from the aforementioned second location to the first location, while closing the drum shutter  12  by the conveyance of the process cartridge B. 
     With the provision of the above described mechanism, it becomes possible to move the process cartridge B by the opening or closing movement of the opening/closing cover  15 . Therefore, even if the design of an image forming apparatus is such that the process cartridge B is mounted into the deeper end of the image forming apparatus main assembly  14 , the operation for mounting or dismounting the process cartridge B can be easily carried out. 
     The description given above regarding one of the embodiments of the present invention can be summarized as follows. 
     The process cartridge B removably mountable in the electrophotographic image forming apparatus main assembly  14  having the process cartridge entrance opening/closing cover  15 , which can be opened or closed, and the first and second guides  41 , the movements of which are linked to the opening and closing movement of the opening/closing cover  15 , comprises: 
     the electrophotographic photoconductive drum  7 ; 
     processing means (charging means  8 , developing means  10 , and cleaning means  11 ), which act on the photoconductive drum  7 , 
     the first cartridge frame CF, which is located at one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the first cartridge guide  18   b , which projects from the first cartridge frame CF, and rests on the first guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process cartridge position S in the apparatus main assembly  14  by the movement of the first guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the second cartridge frame CF, which is located at the other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the second cartridge guide  18   b , which projects from the second cartridge frame CF, and rests on the second guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process cartridge position S in the apparatus main assembly  14  by the movement of the second guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the first cartridge positioning portion  18   a,  which is on one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the first cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the first positioning portion  44   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 ; and 
     the second cartridge positioning portion  18   a,  which is on the other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the second cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the second positioning portion  90   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 . 
     One end of the photoconductive drum  7  in terms of the axial direction of the photoconductive drum  7  is provided with the driving force receiving portion  7   a   1 , which receives the driving force for rotating the photoconductive drum  7 , from the apparatus main assembly  14  after the process cartridge B is mounted into the apparatus main assembly  14 . 
     Further, the aforementioned driving force receiving portion  7   a   1  is a projection approximately in the form of a twisted triangular pillar. In order to receive a driving force, it engages into the hole in the form of a twisted pillar, the cross section of which perpendicular to its axial line is approximately an equilateral triangle. 
     As seen in the lengthwise direction of the photoconductive drum  7  and also in terms of the process-cartridge mounting direction, the rear end of the first cartridge guide  18   b  and the rear end of the second cartridge guide  18   b  are on the upstream side with respect to the center of gravity of the process cartridge B. Further, the front end of the first cartridge guide  18   b  and the front end of the second cartridge guide  18   b  are on the downstream side of the center of gravity of the process cartridge B. 
     When the process cartridge B is in the position, at which it is to function for image formation, in the apparatus main assembly  14 , the front end of the first cartridge guide  18   b  and the front end of the second cartridge guide  18   b  are on the downstream side with respect to the vertical line intersecting the axial line of the photoconductive drum  7 . 
     The rear end of the first cartridge guide  18   b  has a flat portion  18   b   1  by which the rear end of the first cartridge guide  18   b  rests on the first guide  41  of the apparatus main assembly  14 , and an inclined surface  18   b   4 , which extends upstream in terms of the process cartridge mounting direction, tilting diagonally downward. It is pressed by the first guide  41  of the apparatus main assembly  14  in the process cartridge mounting direction, by the point of the first cartridge guide  18   b,  at which the portion  18   b   1  and inclined portion  18   b   4  meet. 
     Further, the rear end of the second cartridge guide  18   b  has a flat portion by which the second cartridge guide  18   b  rests on the second guide  41  of the apparatus main assembly  14 , and an inclined portion  18   b   4 , which extends upstream in terms of the process-cartridge mounting direction, tilting diagonally downward, and is pressed by the second guide  41  of the apparatus main assembly  14  in the process-cartridge mounting direction by the point of the second cartridge guide  18   b,  at which the portion  18   b   1  and inclined portion  18   b   4  meet. 
     The first cartridge guide  18   b  and second cartridge guide  18   b  are moved in the process-cartridge mounting direction, resting on the first and second guides  41  of the apparatus main assembly  14 . Then, they are subjected to the resistance generated by the spring  45  as the process cartridge B is further inserted. As they are subjected to the resistance, the rear end of the first cartridge guide  18   b  is pressed by the first guide  41  of the apparatus main assembly  14 , and the rear end of the second cartridge guide  18   b  is pressed by the second guide  41  of the apparatus main assembly  14 . When the process cartridge B is placed in the image-formation position in the apparatus main assembly  14 , the first cartridge guide  18   b  and second cartridge guide  18   b  are apart from the first guide  41  and second guide  41 , respectively, of the apparatus main assembly  14 . 
     Further, the process cartridge B is provided with the regulating portion  18   d  (butting surface), which comes into contact with the rotation controlling portion  44   b  of the stationary guide  44  of the apparatus main assembly  14 , and prevents the process cartridge B from being rotated about the first and second cartridge positioning portions  18   a  and  18   a  by the force, which is generated as the driving force receiving portion  7   a   1  receives the driving force from the apparatus main assembly  14 , and which acts in a direction to rotate the process cartridge B about the first cartridge positioning portion  18   a  and the second cartridge positioning portion  18   a.  The regulating portion  18   d  is on the external surface of the cartridge frame CF of the process cartridge B, which faces upward when the process cartridge B is in the image-formation position in the apparatus main assembly  14 . The first cartridge positioning portion  18   a  of the process cartridge B engages into the first positioning portion  44   a  of the apparatus main assembly  14 , and the second cartridge positioning portion  18   a  engages into the second positioning portion  90   a  of the apparatus main assembly  14 . When the regulating portion  18   d  is in contact with the rotation controlling portion  44   b  of the stationary guide  44  of the apparatus main assembly  14 , the process cartridge B is in the position in which it is to function for image formation. 
     The first cartridge positioning portion  18   a  and second cartridge positioning portion  18   a  are cylindrical, and the former is greater in diameter than the latter. 
     The process cartridge B is conveyed by the opening movement of the opening/closing cover  15  to the location from which it can be taken out of the apparatus main assembly  14 , with the first cartridge guide  18   b  and second cartridge guide  18   b  resting on the first and second guides  41 , respectively, of the apparatus main assembly  14 . While the process cartridge B is conveyed to the location from which it can be taken out of the apparatus main assembly  14 , the bottom surface of the process cartridge B comes into contact with the projection  16   a  of the apparatus main assembly  14 . As a result, the downstream side of the process cartridge B in terms of the direction in which the process cartridge B is taken out of the apparatus main assembly  14 , is lifted. 
     The aforementioned processing means comprises a minimum of one among the following means: the developing means  10  for developing an electrostatic latent image formed on the electrophotographic photoconductive drum  7 ; charging means  8  for charging the electrophotographic photoconductive drum  7 ; and cleaning means  11  for removing the developer remaining on the electrophotographic photoconductive drum  7 . 
     To supplement the above, the process cartridge mounting mechanism for mounting the process cartridge B into the electrophotographic image forming apparatus comprises: 
     (a) main assembly  14  comprising: 
     the first guide  41 ; 
     the second guide  41 ; 
     the first positioning guide  44   a;    
     the second positioning guide  90   a;    
     the process cartridge entrance opening/closing cover  15 , which can be opened or closed for mounting the process cartridge B into the apparatus main assembly  14 , or dismounting the process cartridge B from the apparatus main assembly  14 ; and 
     the moving means which is for moving the first and second guides  41  of the main assembly  14  so that the process cartridge B is moved toward the designated process-cartridge position in the apparatus main assembly  14 , and the movements of which are linked to the closing movement of the opening/closing cover  15 ; 
     (b) the process cartridge B comprising: 
     the electrophotographic photoconductive drum  7 ; 
     processing means which act on the photoconductive drum  7 ; 
     the first cartridge frame CF, which is located at one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the first cartridge guide  18   b  which projects from the first cartridge frame CF, and rests on the first guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process-cartridge position in the apparatus main assembly  14  by the movement of the first guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 , and which is pressed by the first guide  41  of the apparatus main assembly  14  in the process-cartridge mounting direction, by the rear end in terms of the process-cartridge mounting direction, when it is guided in the process-cartridge mounting direction; 
     the second cartridge frame CF, which is located at the other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the second cartridge guide  18   b  which projects from the second cartridge frame CF, and rests on the second guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process-cartridge position in the apparatus main assembly  14  by the movement of the second guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 ; 
     the first cartridge positioning portion  18   a,  which is on one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the first cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the first positioning portion  44   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 ; and 
     the second cartridge positioning portion  18   a,  which is on other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the second cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the second positioning portion  90   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 ; 
     wherein the first cartridge guide  18   b  and second cartridge guide  18   b  of the process cartridge B are rested on the first guide  41  and second guide  41  of the apparatus main assembly  14 , respectively, and the process cartridge B is conveyed to the designated process-cartridge position, by the movement of the opening/closing cover  15  from the fully open position to the completely closed position. 
     The apparatus main assembly  14  is provided with the large gear coupling  83   a , which is also called a driving force transmitting portion. The photoconductive drum  7  is provided with the driving force receiving portion  7   a   1 , which is attached to one end in terms of the axial direction, and receives the driving force for rotating the photoconductive drum  7  from the driving force transmitting portion  83   a  of the apparatus main assembly  14 , after the mounting of the process cartridge B into the apparatus main assembly  14 . 
     The driving force receiving portion  7   a   1  is a projection approximately in the form of a twisted triangular pillar. It receives the driving force by engaging into the twisted hole of the driving force transmitting portion  83   a,  which is coaxial with the driving force transmitting portion  83   a,  and the cross section of which, perpendicular to the axial line of the driving force transmitting portion  83   a  is virtually in the form of an equilateral triangle. 
     As seen in the lengthwise direction of the photoconductive drum  7 , and also in terms of the process-cartridge mounting direction, the rear end of the first cartridge guide  18   b  and the rear end of the second cartridge guide  18   b  are on the upstream side with respect to the center of gravity of the process cartridge B. Further, the front end of the first cartridge guide  18   b  and the front end of the second cartridge guide  18   b  are on the downstream side of the center of gravity of the process cartridge B. 
     When the process cartridge B is in the position, at which it is to function for image formation, in the apparatus main assembly  14 , the front end of the first cartridge guide  18   b  and the front end of the second cartridge guide  18   b  are on the downstream side with respect to the vertical line intersecting the axial line of the photoconductive drum  7 . 
     The rear end of the first cartridge guide  18   b  has a flat portion  18   b   1  by which the rear end of the first cartridge guide  18   b  rests on the first guide  41  of the apparatus main assembly  14 , and an inclined surface  18   b   4 , which extends upstream in terms of the process-cartridge mounting direction, tilting diagonally downward, and is pressed by the first guide  41  of the apparatus main assembly  14  in the process-cartridge mounting direction, by the point of the first cartridge guide  18   b  at which the portion  18   b   1  and inclined portion  18   b   4  meet. 
     Further, the rear end of the second cartridge guide  18   b  has a flat portion by which the second cartridge guide  18   b  rests on the second guide  41  of the apparatus main assembly  14 , and an inclined portion  18   b   4 , which extends upstream in terms of the process-cartridge mounting direction, tilting diagonally downward, and is pressed by the second guide  41  of the apparatus main assembly  14  in the process-cartridge mounting direction, by the point of the second cartridge guide  18   b  at which the portion  18   b   1  and inclined portion  18   b   4  meet. 
     Further, the apparatus main assembly  14  is provided with the spring  45 . The first cartridge guide  18   b  and second cartridge guide  18   b  are moved in the process-cartridge mounting direction, resting on the first and second guides  41  of the apparatus main assembly  14 . Then, they are subjected to the resistance generated by the spring  45  as the process cartridge B is further inserted. As they are subjected to the resistance, the rear end of the first cartridge guide  18   b  is pressed by the first guide  41  of the apparatus main assembly  14 , and the rear end of the second cartridge guide  18   b  is pressed by the second guide  41  of the apparatus main assembly  14 . When the process cartridge B is placed in the image formation position in the apparatus main assembly  14 , the first cartridge guide  18   b  and second cartridge guide  18   b  are apart from the first guide  41  and second guide  41 , respectively, of the apparatus main assembly  14 . 
     Further, the apparatus main assembly  14  is provided with the rotation controlling portion  44   b.  In comparison, the process cartridge B is provided with the regulating portion  18   d  (butting surface), which comes into contact with the rotation controlling portion  44   b  of the stationary guide  44  of the apparatus main assembly  14 , and prevents the process cartridge B from being rotated about the first and second cartridge positioning portions  18   b  by the force, which is generated as the driving force receiving portion  7   a   1  receives the driving force from the apparatus main assembly  14 , and which acts in the direction to rotate the process cartridge B about the first cartridge positioning portion  18   a  and second cartridge positioning portion  18   a.  The regulating portion  18   d  is on the external surface of the cartridge frame CF of the process cartridge B, which faces upward when the process cartridge B is in the image-formation position in the apparatus main assembly  14 . The first cartridge positioning portion  18   a  of the process cartridge B engages into the first positioning portion  44   a  of the apparatus main assembly  14 , and the second cartridge positioning portion  18   a  engages into the second positioning portion  90   a  of the apparatus main assembly  14 . When the regulating portion  18   d  is in contact with the rotation controlling portion  44   b  of the stationary guide  44  of the apparatus main assembly  14 , the process cartridge B is in the position in which it is to function for image formation. 
     The first cartridge positioning portion  18   a  and second cartridge positioning portion  18   a  are cylindrical, and the former is greater in diameter than the latter. 
     The process cartridge B is conveyed by the opening movement of the opening/closing cover  15  to the location from which it can be taken out of the apparatus main assembly  14 , with the first cartridge guide  18   b  and second cartridge guide  18   b  resting on the first and second guides  41 , respectively, of the apparatus main assembly  14 . While the process cartridge B is conveyed to the location from which it can be taken out of the apparatus main assembly  14 , the bottom surface of the process cartridge B comes into contact with the projection  16   a  of the apparatus main assembly  14 . As a result, the downstream side of the process cartridge B in terms of the direction in which the process cartridge B is taken out of the apparatus main assembly  14 , is lifted. 
     The aforementioned processing means comprises a minimum of one among the following means: the developing means  10  for developing an electrostatic latent image formed on the electrophotographic photoconductive drum  7 ; charging means  8  for charging the electrophotographic photoconductive drum  7 ; and cleaning means  11  for removing the developer remaining on the electrophotographic photoconductive drum  7 . 
     The apparatus main assembly  14  is provided with the spring  45 , which is for keeping the first cartridge positioning portion  18   a  pressed upon the first positioning portion  44  of the apparatus main assembly  14  by its resiliency, and is located at the entrance of the first positioning portion  44   a  of the apparatus main assembly  14 . As the advancement of the process cartridge B is resisted by the spring  45 , the first cartridge guide  18   b  is pressed by the first guide  41  of the apparatus main assembly  14  toward the designated cartridge position, by its rear end in terms of the process-cartridge mounting direction, so that the first cartridge positioning portion  18   a  enters the first positioning portion  44   a  of the apparatus main assembly  14 . 
     According to another characteristic aspect of the present invention, the electrophotographic image forming apparatus A, which is for forming an image on the recording medium  2 , and in which the process cartridge B is removably mountable, comprises: 
     the main assembly comprising: 
     (a) the first guide  41 ; 
     (b) the second guide  41 ; 
     (c) the first positioning guide  44   a;    
     (d) the second positioning guide  90   a;    
     (e) the process cartridge entrance opening/closing cover  15  which can be opened or closed for mounting the process cartridge B into the apparatus main assembly  14 , or dismounting the process cartridge B from the apparatus main assembly  14 ; 
     (f) the moving means which is for moving the first and second guides  41  of the main assembly  14  so that the process cartridge B is moved toward the designated process-cartridge position in the apparatus main assembly  14 , and the movements of which are linked to the closing movement of the opening/closing cover  15 ; 
     (g) the mounting means for removably mounting the process cartridge B comprising: the electrophotographic photoconductive drum  7 ; processing means which act on the photoconductive drum  7 ; the first cartridge frame CF, which is located at one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; the first cartridge guide  18   b  which projects from the first cartridge frame CF, and rests on the first guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process-cartridge position in the apparatus main assembly  14  by the movement of the first guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 , and which is pressed by the first guide  41  of the apparatus main assembly  14  in the process-cartridge mounting direction, by the rear end in terms of the process-cartridge mounting direction, when it is guided in the process-cartridge mounting direction; the second cartridge frame CF, which is located at the other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , and extends in the direction parallel to the direction in which the process cartridge B is mounted into the apparatus main assembly  14 ; the second cartridge guide  18   b  which projects from the second cartridge frame CF, and rests on the second guide  41  of the apparatus main assembly so that the process cartridge B is conveyed toward the designated process cartridge position in the apparatus main assembly  14  by the movement of the second guide  41 , when the process cartridge B is mounted into the apparatus main assembly  14 ; the first cartridge positioning portion  18   a,  which is on one end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the first cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the first positioning portion  44   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 ; and the second cartridge positioning portion  18   a,  which is at the other end of the process cartridge B in terms of the axial direction of the photoconductive drum  7 , projects outward from the second cartridge frame CF, and is coaxial with the photoconductive drum  7 , and which engages with the second positioning portion  90   a  of the apparatus main assembly  14 , in order to properly position the process cartridge B relative to the apparatus main assembly  14 , toward the end of the mounting of the process cartridge B into the apparatus main assembly  14 ; 
     wherein the first cartridge guide  18   b  and second cartridge guide  18   b  of the process cartridge B are rested on the first guide  41  and second guide  41  of the apparatus main assembly  14 , respectively, and the process cartridge B is conveyed to the designated process-cartridge position, by the movement of the opening/closing cover  15  from the fully open position to the completely closed position. 
     (Other Embodiments of the Present Invention) 
     Hereinafter, the other embodiments of the present invention will be described in detail with reference to the appended drawings. 
     In the following description of the present invention, the lengthwise direction of the process cartridge B is the direction perpendicular (virtually perpendicular) to the direction in which the process cartridge B is mounted into or dismounted from the apparatus main assembly. It is parallel to the surface of the recording medium, and perpendicular to (virtually perpendicular) to the direction in which the recording medium is conveyed. The left and right directions of the process cartridge B coincide with the left and right directions of the recording medium as seen from above, and behind in terms of the direction in which the recording medium is conveyed. The top and bottom surfaces of the process cartridge B are the surfaces of the process cartridge B which are at the top and bottom, facing upward, when the process cartridge B is in the apparatus main assembly. 
     Next, an embodiment of an electrophotographic image forming apparatus in accordance with the present invention will be concretely described with reference to the drawings. 
     First, referring to FIGS. 63 and 64, the process cartridge, and the main assembly of the electrophotographic image forming apparatus, in which the process cartridge is removably mountable, will be concretely described. FIG. 63 is a schematic sectional view of the electrophotographic image forming apparatus in which the process cartridge has been mounted, and depicts the general structure thereof. FIG. 64 is a schematic sectional view of the process cartridge, and depicts the general structure thereof. 
     As for the order of description, first, the process cartridge, and the electrophotographic image forming apparatus which employs the process cartridge, will be described regarding their general structures. Then, the process cartridge mounting/dismounting mechanism for removably mounting the process cartridge into the main assembly of the electrophotographic image forming apparatus will be described. 
     (General Structure) 
     Referring to FIG. 63, this electrophotographic image forming apparatus A (laser beam printer, which hereinafter will be referred to as “image forming apparatus”) forms an electrostatic latent image, on an electrophotographic photoconductive member  107  (which hereinafter will be referred to as “photoconductive drum”) in the form of a drum, by projecting a beam of light modulated with image data from an optical system  101 , on the photoconductive drum  107  from an optical system  101  as an optical means, and forms a toner image by developing the electrostatic latent image with developer (which sometimes will be referred to as “toner”). Meanwhile, recording media  102  (recording paper, OHP sheet, fabric, and the like) in a cassette  103   a  are fed into the apparatus main assembly, while being separated one by one, by a pickup roller  103   b,  and a pressing member  103   c  kept pressed upon the pickup roller  103   b,  and then, are conveyed one by one by a registration roller  103   e,  in synchronism with the toner image formation. While each of the recording media  102  is conveyed, the toner image on the photoconductive drum  107  of the process cartridge B is transferred onto the recording medium  102  by applying electrical voltage to a transfer roller  104  as a transferring means. Then, the recording medium  102  is conveyed to a fixing means  105 , being guided by a conveyance guide  103   f.  The fixing means  105  comprises a driving roller  105   a,  and a rotational fixing roller  105   d  which contains a heater  105   b  and is rotationally supported by a supporting member  105   c.  It fixes the unfixed toner image on the recording medium  102  by applying heat and pressure to the unfixed toner image on the recording medium  102 , and the recording medium  102 . Thereafter, the recording medium  102  is conveyed further, and discharged from the apparatus main assembly by a pair of recording medium discharge rollers  103   g  and a pair of recording medium discharge rollers  103   h,  through a recording medium reversing path, into a delivery tray  106 . Incidentally, in this embodiment, the pick-up roller  103   b,  pressing member  103   c,  registration roller  103   e,  and the like, constitutes a conveying means  103 . 
     (Process Cartridge) 
     The process cartridge B comprises the electrophotographic photoconductive member and a minimum of one processing means. The processing means are, for example, a charging means for charging the electrophotographic photoconductive member, a developing means for developing an electrostatic latent image on the electrophotographic photoconductive member, a cleaning means for removing the toner particles remaining on the electrophotographic photoconductive member, and the like. Referring to FIG. 64, the process cartridge B in this embodiment has such a structure that while the photoconductive drum  107 , that is, an electrophotographic photoconductive member, having a photoconductive layer, is rotated, the peripheral surface of the photoconductive drum  107  is uniformly charged by applying electrical voltage to the charging roller  108  as a charging means; an electrostatic latent image is formed on the charged peripheral surface of the photoconductive drum  107  by exposing the charged peripheral surface of the photoconductive drum  107  to a beam of light (optical image), which is modulated with image data and projected from the optical system  101 ; and the electrostatic latent image is developed by the developing means  110 . 
     The developing means  110  comprises: first and second rotatable toner conveying means  110   b   2  and  110   b   1 , which convey the toner in a toner storage portion  110   a,  outward of the toner storage portion  110   a;  a development roller  110   d  (developer bearing member), that is, a rotational member, which contains a stationary magnet  110   c;  and a development blade  110   e.  In operation, the toner within the toner storage portion  110   a  is conveyed to the adjacencies of the development roller  110   d,  which is being rotated, and a layer of toner with triboelectric charge is formed by the development blade  110   e,  on the peripheral surface of the development roller  110   d . Then, the toner particles in the layer of toner are transferred onto the peripheral surface of the photoconductive drum  107 , in accordance with the electrostatic latent image on the photoconductive drum  107 . As a result, the latent image is developed into a toner image, or a visible image. 
     Next, the toner image is transferred onto the recording medium  102  by applying to the transfer roller  104  such electrical voltage that is opposite in polarity to the toner image. Thereafter, the toner particles remaining on the peripheral surface of the photoconductive drum  107  are removed by the cleaning means  111 ; they are scraped down by the cleaning blade  111   a,  are caught by a toner catching sheet  111   b,  and are collected in a bin  111   c  for the removed toner particles. 
     The process cartridge B in this embodiment comprises: a cleaning means holding frame  113 , which rotatably supports the photoconductive drum  107  and holds the cleaning means  111  and charge roller  108 ; and a toner/developing means holding frame  112 , which holds the developing means  110  and contains the toner storage portion  110   a.  The toner/developing means holding frame  112  is attached to the cleaning means holding frame in such a manner that the toner/developing means holding frame  112  is rotatable relative to the cleaning means holding frame  113  and also that the development roller  110   d  of the developing means  110  in a parallel manner opposes the photoconductive drum  107  with the presence of a predetermined gap; a pair of spacers (unshown) are placed between the development roller  110   d  and photoconductive drum  107 , and a predetermined amount of pressure is applied to maintain the predetermined gap. 
     In other words, the photoconductive drum  107 , the charge roller  108 , the development roller  110   d,  the cleaning blade  111   a,  or the like, are integrally placed in a cartridge, or the process cartridge frame CF in this embodiment, which is formed by joining the cleaning means holding frame  113 , with the toner/developing means holding frame  112  formed by welding together a developing means holding frame  112   a,  a developing means bottom frame  112   b,  and a lid  112   c,  so that the photoconductive drum  107 , charge roller  108 , development roller  110   d,  cleaning blade  111   a,  and the like, can be removably mounted into the electrophotographic image forming apparatus main assembly  114  (which hereinafter will be referred to as “image forming apparatus main assembly”) in the direction indicated by an arrow mark X. 
     (Mechanism for Mounting/Dismounting Process Cartridge) 
     Next, referring to FIGS. 65-67, the structure of the process cartridge mounting/dismounting mechanism for mounting the process cartridge B into the image forming apparatus main assembly  114 , or dismounting the process cartridge B therefrom, will be described. 
     FIG. 65 is a perspective view of the right side of the process cartridge mounting/dismounting mechanism as seen from the upstream side in terms of the process-cartridge mounting direction, and FIG. 66 is an external perspective view of the process cartridge B. FIG. 67 is an exploded perspective view of the process cartridge mounting/dismounting mechanism shown in FIG.  65 . 
     Referring to FIG. 65, the process cartridge B is mounted or dismounted by opening a cover  115  which can be rotationally opened or closed. As the cover  115  is opened, an opening W for mounting or dismounting the process cartridge B is exposed. This opening W is given such a size that allows the process cartridge B to be mounted into the image forming apparatus main assembly  114 , in the direction indicated by the arrow mark X (FIG.  68 ), by being assisted by the mutually opposing left and right inner plates  140  as the side plates, which are located at the ends of the image forming apparatus main assembly  114 , one for one, in terms of the lengthwise direction of the process cartridge B (axial direction of the photoconductive drum  107 ), and a front blade  143 , which is located at the bottom edge of the opening W and extends in the lengthwise direction of the process cartridge B. On the inward surfaces of the inner plates  140 , a pair of mounting/dismounting guides  141 , as cartridge mounting members, and a pair of front guides  142 , as entrance guides, are provided, which are symmetrically disposed with respect to the vertical plane which is perpendicular to the opening W and divides the opening W into the left and right halves. 
     Each mounting/dismounting guide  141  has a guiding groove  141   a  as a guiding portion, which is in the inward surface of the mounting/dismounting guide  141 , and on the opening W side. This guiding groove  141   a  is tilted downward in terms of the process-cartridge mounting direction so that the process cartridge B can be inserted into the image forming apparatus main assembly  114  in the direction intersecting with the direction in which the recording medium  102  is conveyed. The mounting/dismounting guide  141  is structured and positioned so that as the process cartridge B is inserted into the image forming apparatus main assembly  114  through the opening W, the guide rib  118   b  (FIG. 66) as a part of the process cartridge B, by which the process cartridge B is guided, fits into the guiding groove  141   a,  causing the process cartridge B to be supported by the mounting/dismounting guide  141 . The mounting/dismounting guide  141  also has a recess  141   a   1  (FIG.  68 ), which is the bottom end portion of the guiding groove  141   a.  The process cartridge B is securely held in the image forming apparatus main assembly  114 , by fitting into the recess  141   a   1 , the projection  118   b   1  (FIG.  68 ), which is the leading end of the guide rib  118   b,  in terms of the process cartridge mounting direction. 
     The guide  142  is on the upstream side in terms of the process-cartridge mounting direction X with respect to the mounting/dismounting guide  141 , and has a guiding groove  142   a,  which is contiguous with the guiding groove  141   a  of the mounting/dismounting guide  141  in terms of the process-cartridge mounting direction X. The guide  142  is structured so that the process cartridge B can be guided into the mounting/dismounting guide  141  by engaging the guide rib  118   b  of the process cartridge B into the guiding groove  142   a.    
     The front plate  143  is at the bottom edge of the opening W. The surface  143   a  of the front plate  143 , which faces the opening W, is slanted at virtually the same angle as those of the guiding groove  141   a  of the mounting/dismounting guide  141  and the front guide  142 . The front plate  143  is a supporting member which facilitates the insertion of the process cartridge B into the image forming apparatus main assembly  114  through the opening W. 
     The image forming apparatus main assembly  114  is provided with the transfer roller  104 , and a positioning guide  144  as a positioning means. The transfer roller  104  is at the deeper end of the image forming apparatus main assembly  114  in terms of the process cartridge mounting direction X. The positioning guide  144  is above the ends of the transfer roller  104  in terms of its axial direction. It catches the process cartridge B, and retains it in the image-formation position (final process-cartridge position (second position)), that is a position in which the process cartridge B is to function for image formation. Also, the positioning guide  144  is solidly fixed to the inner plate  140  of the image forming apparatus main assembly  114 , and has a positioning portion  144   a  and a projection  144   b.  The positioning portion is a portion into which the positioning boss  118   a,  the position of which is to be fixed, is engaged. The projection  144   b  intrudes into the path of the positioning boss  118   a  to the positioning portion  144 . The projection  144   b  is on the upstream portion of the positioning guide  144 , in terms of the direction in which the process cartridge B is moved into the image-formation position; in other words, it is on the upstream portion of the positioning guide  144  in terms of the direction in which the mounting/dismounting guide  141  moves from a first position, which will be described later, to the second position. The projection  144   b  is rendered high enough to make the positioning boss  118   a  come into contact with the projection  144   b,  but not so high as to prevent the positioning boss  118   a  from going over the projection  144   b.    
     Referring to FIG. 67, the mounting/dismounting guide  141  has first and second bosses  141   b  and  141   c  as guides, which are the surface of the mounting/dismounting guide  141  reverse to the surface on which guiding groove  141   a  is, and project in the lengthwise direction of the process cartridge B. The first and second bosses  141   b  and  141   c  are on the downstream and upstream side, respectively, in terms of the process cartridge mounting direction X with respect to the guiding groove  141   a.  Further, the first boss  141   c  is positioned higher than the second boss  141   b.  The end of the first boss  141   b  is provided with a projection  141   e,  which projects in the radius direction of the first boss  141   b,  and the end of the second boss  141   c  is provided with a snap-fit claw, which is flexible in the radius direction of the second boss  141   c.    
     The inner plate  140  of the image forming apparatus main assembly  114  is provided with two guide rails  140   a  and  140   b,  as process cartridge mounting portion holding means, in which the bosses  141   b  and  141   c  of the mounting/dismounting guide  141  engage, one for one. The widths (dimensions in terms of the direction of the radius of the curvature of the rails) of the guide rails  140   a  and  140   b  are the same as, or slightly greater than, the diameters of the bosses  141   b  and  141   c.  With the engagement of the two bosses  141   b  and  141   c  in the two guide rails  140   a  and  140   b,  the mounting/dismounting guide  141  is allowed to move between the optical system  101  and the conveyance path of the recording medium  102 . In other words, the mounting/dismounting guide  141  moves the process cartridge B. The first guide rail  140   a  in which the first boss  141   b  fits is straight, and is positioned higher than the positioning guide  144 . It is tilted so that its inward end in terms of the process-cartridge mounting direction X is positioned higher than its outward end, and it intersects with the process-cartridge mounting direction X. The second guide rail  140   b  in which the second boss  141   c  fits has a first arcuate portion  140   b   1  and a second arcuate portion  140   b   2 . The first arcuate portion  140   b   1  extends upward in a curvature, the center of which coincides with the rotational axis of the rotational shaft  115   a,  or the rotational axis of the cover  115 . The second arcuate portion  140   b   2  is continuous with the first arcuate portion  140   b   1 , and the center (unshown) of the curvature of the second arcuate portion  140   b   2  is near the end of the first guide rail  140   a,  on the positioning guide  144  side, and the radius of the arcuate portion  140   b   2  is the same as the distance between the two bosses  141   b  and  141   c  of the mounting/dismounting guide  141 . 
     The cover  115  is provided with a pair of fan-shaped plates  115   b  (which hereinafter will be referred to as “fan-shaped plate”), which are flat members. They are on the end portions of the cover  115  in terms of its lengthwise direction (lengthwise direction of the process cartridge B), one for one, and have a rotational shaft  115   a  for the cover  115 . Each fan-shaped plate  115   b  is provided with a cam hole  115   c,  which comprises an arcuate portion  115   c   1  and a straight portion  115   c   2 . The center of the curvature of the arcuate portion  115   c   1  coincides with the rotational axis of the rotational shaft  115   a.  The straight portion  115   c   2  is continuous with the inward end of the arcuate portion  115   c   1  in terms of the closing direction of the cover  115 , and extends in the direction slightly off to the inward direction, in terms of the closing direction of the cover  115 , from the radius direction of the arcuate portion  115   c   1 . The arcuate portion  115   c   1  is smaller in radius than the first arcuate portion  140   b   1  of the first guide rail  140   b  of the inner plate  140 , and the distance between the end of the straight portion  115   c   2  and the rotational shaft  115   a  is virtually equal to the radius of the first arcuate portion  140   b   1  of the first guide rail  140   b  (FIG.  68 ). The fan-shaped plate  115   b  is a mobile linking member which links the cover  115  to the mounting/dismounting guide  141  of the cartridge mounting member. 
     The cover  115  and mounting/dismounting guide  141  are attached to the inner plate  140  of the image forming apparatus main assembly  114  in the following manner. 
     First, the rotational shaft  115   a  is fitted into the hole  140   c  of the inner plate  140  by elastically bending the fan-like plate  115   b  in the lengthwise direction of the process cartridge B. As a result, the cover  115  is rotatably supported by the image forming apparatus main assembly  114 , being allowed to cover or expose the opening W by being rotated about the rotational shaft  115   a  in the direction indicated by an arrow mark Q indicated in FIG.  63 . 
     Next, the projection  141   e  on the tip of the first boss  141   b  of the mounting/dismounting guide  141  is aligned with the arcuate portion (long portion) of the first guide rail  140   a,  and the projection  141   e  is put through the first guide rail  140   a.  Then, the mounting/dismounting guide  141  is rotated. As the mounting/dismounting guide  141  is rotated, the projection  141   e  latches on the back side of the inner plate  140 , preventing the mounting/dismounting guide  141  from becoming disengaged from the inner plate  140 . Next, the second boss  141   c  is put through the second guide rail  140   b,  and the cam hole  115   c  of the cover  115 . As a result, the snap-fit claw on the tip of the second boss  141   c  latches on the back side of the fan-like plate  115   b.    
     On the other hand, each of the end surfaces of the process cartridge B in terms of the lengthwise direction of the process cartridge B is provided with a guide rib  118   b  as a guide to be guided, and a positioning boss  118   a  as one of the portions by which the position of the process cartridge B is fixed in the image forming apparatus main assembly  114 , as shown in FIG.  66 . The guide rib  118   b  fits in the guiding groove  141   a  of the mounting/dismounting guide  141 , and the positioning boss  118   a  fits in the positioning guide  144 . The rotational axis of the positioning boss  118   a  coincides with the rotational axis of the photoconductive drum  107 . 
     Next, the steps through which the process cartridge B is mounted into, or dismounted from the process cartridge mounting/dismounting mechanism will be described with reference to FIGS. 68-72. 
     Referring to FIG. 68, as the cover  115  of the image forming apparatus main assembly  114  is fully opened, the front guide  142  and mounting/dismounting guide  141  linked to each other appear. In this state, the guiding groove  142   a  of the front guide  142  is continuous with the guiding groove  141   a  of the mounting/dismounting guide  141 . Also in this state, that is, in the state in which the guiding groove  142   a  of the front guide  142  is continuous with the guiding groove  141   a  of the mounting/dismounting guide  141 , the process cartridge B is inserted into the image forming apparatus main assembly  114 , with the guide rib  118   b  of the process cartridge B engaging in the guiding grooves  142   a  and  141   a  in the listed order, until the guide rib  118   b  of the process cartridge B comes into contact with the inward end of the guiding groove  141   a  of the mounting/dismounting guide  141  in terms of the process-cartridge mounting direction. As a result, the projection  118   b   1  (FIG. 68) of the guide rib  118   b  fits in the recess  141   a  of the guiding groove  141   a.  Therefore, the process cartridge B is supported by the mounting/dismounting guide  141  in such a manner that the process cartridge B is immovable relative to the mounting/dismounting guide  141 . In other words, the process cartridge B is mounted into the mounting/dismounting guide  141  when the mounting/dismounting guide  141  is in the position (first position) in which the guide groove  141   a  is continuous with the guiding groove  142   a  of the front guide  142 . When the mounting/dismounting guide  141  is in the position in which the process cartridge B is mountable into the mounting/dismounting guide  141 , that is, the guiding groove  141   a  is continuous with the guiding groove  142   a  of the front guide  142 , the mounting/dismounting guide  141  assumes such an attitude (first attitude) that the direction, in which the process cartridge B is inserted into the image forming apparatus main assembly  114  following the guiding groove  141   a  in the initial stage of the mounting, intersects with the direction in which the recording medium  102  is conveyed by the conveying means  103 , requiring (allowing) the process cartridge B to be tilted downward in terms of the process-cartridge mounting direction X. The reason for this is that the process cartridge mounting/dismounting mechanism is structured so that as the cover  115  is fully opened, the end of the straight portion  115   c   2  of the cam hole  115   c  of the fan-shaped plate  115  moves to the second boss  141   c  of the mounting/dismounting guide  141 , and the first boss  141   b  of the mounting/dismounting guide  141  remains in the end of the first guide rail  140   a  (on the opening W side). Referring to FIG. 68, the vertical distance h of the guide rib  118   b  from the bottom surface of the process cartridge B is virtually equal to the distance  1  between the inclined surface  143   a  of the front plate  143  and the guiding groove  141   a  of the mounting/dismounting guide  141 . Therefore, as the bottom surface of the process cartridge B is rested on the inclined surface  143   a  of the front plate  143 , the guide rib  118   b  is spontaneously guided into the guiding groove  141   a  of the mounting/dismounting guide  141 . 
     As described above, the guiding grooves  141   a  and  142   a  are inclined downward in terms of the process-cartridge mounting direction X. Therefore, once the guide rib  118   b  of the process cartridge B is guided into the guiding grooves  141   a  and  142   a,  the process cartridge B is guided inward of the mounting/dismounting guide  141  by its own weight. At this time, the inclination of the guiding grooves  141   a  and  142   a  will be described in detail. If the inclination of the guiding grooves  141   a  and  142   a  is too gentle, it is impossible for the process cartridge B to be guided inward of the mounting/dismounting guide  141  by its own weight. On the contrary, if the inclination of the guiding grooves  141   a  and  142   a  is too steep, it is possible that as the process cartridge is released from the hand of a user while the guiding rib  118   b  is still moving inward of the mounting/dismounting guide  141 , the process cartridge B will slide downward fast enough for the impact generated as the process cartridge B hits the inward end of the guiding groove  141   a  to damage the process cartridge and/or apparatus main assembly. Therefore, the inclination is desired to be in a range of 10-70 degrees relative to the horizontal direction. In this embodiment, the inclination of the guiding grooves  141   a  and  142   a  is set to 40 degrees relative to the horizontal direction. 
     The mounting/dismounting guide  141  in the process cartridge mounting/dismounting mechanism in this embodiment is structured so that the mounting/dismounting guide  141  is moved by the opening or closing movement of the cover  115 . Therefore, as the mounting/dismounting guide  141  is pushed by the process cartridge B, the mounting/dismounting guide  141  moves, disturbing the relationship between the distance from the inclined surface  143   a  of the front plate  143  to the guiding groove  141   a,  and the vertical distance from the bottom surface of the process cartridge B to the guide rib  118   b,  and therefore, reducing the operability of the image forming apparatus. In addition, if the mounting/dismounting guide  141  is excessively moved, it is possible that the guide rib  118   b  of the process cartridge B will slide into the space below the mounting/dismounting guide  141 , and fall into the image forming apparatus main assembly  114 . Therefore, in this embodiment, a front guide  142  is provided. It is fixed to the inner plate  140 , on the upstream side in terms of the process-cartridge mounting direction X, with respect to the mounting/dismounting guide  141 , and has the guide groove  142   a,  which connects to the guiding groove  141   a  of the mounting/dismounting guide  141 . The above described problem is solved by this front guide  142 ; the front guide  142  assures that the guide rib  118   b  is guided into the guiding groove  141   a  of the mounting/dismounting guide  141 . 
     Next, referring to FIGS. 68-72, the steps through which the process cartridge B supported by the mounting/dismounting guide  141 , by its guide rib  118   b,  is moved by the closing movement of the cover  115 , will be described. 
     Referring to FIGS. 68 and 69, as the cover  115  is closed by being rotated about the rotational shaft  115   a,  the second boss  141   c  of the mounting/dismounting guide  141  is moved by the end of the straight portion  115   c   2  of the cam hole  115   c  of the fan-shaped plate  115   b,  along the first arcuate portion  141   b   1  of the second guide rail  140   b.  As described previously, the center of the curvature of the first arcuate portion  140   b   1  coincides with the rotational axis of the rotational shaft  115   a  of the cover  115 , and its radius is equal to the distance between the end of the straight portion  115   c   2  of the cam hole  115   c  and the rotational shaft  115   a.  Thus, as the cover  115  is closed, the first boss  141   b  of the mounting/dismounting guide  141  also moves inward of the image forming apparatus main assembly  114  in terms of the process-cartridge mounting direction X, along the first guide rail  140   a.  As a result, the mounting/dismounting guide  141  moves inward while rotating in the clockwise direction, and consequently, changing the process cartridge B in attitude to cause the process cartridge B to assure the attitude for image formation. 
     As the cover  115  is further closed, the process cartridge B approaches the image-formation location in the deeper end of the image forming apparatus main assembly  114 , while gradually becoming horizontal, until the peripheral surface of the positioning boss  118   a  of the process cartridge B comes into contact with the projection  144   b  of the positioning guide  144 , which is on the upstream side, with respect to the positioning portion  144   a  of the positioning guide  144 , in terms of the locus of the process cartridge B moving toward the image-formation location (FIG.  70 ). 
     As the cover  115  is further closed, the mounting/dismounting guide  141  moves closer to the image-formation location, causing the recess  141   a   1  of the guiding groove  141   a  to push the projection  118   b   1  of the guide rib  118   b  of the process cartridge B. As a result, the positioning boss  118   a  is caused to go over the projection  144   b  of the positioning guide  144 . After going over the projection  144   b,  the positioning boss  118   a  falls a distance equal to the vertical distance between the highest point  144   b   1  of the projection  144   b  and the positioning portion  144   a  due to the weight of the process cartridge B (FIG.  71 ). As a result, the process cartridge B, which up to this point has been supported by the mounting/dismounting guide  141 , by the guide rib  118   b  in the guiding groove  141   a,  is supported by the positioning portion  144   a  of the positioning guide  144 , by the positioning boss  118   a,  which projects from the end wall of the process cartridge B in terms of the lengthwise direction of the process cartridge B, and the axial line of which coincides with the rotational axis of the photoconductive drum  107 . With the provision of this structural arrangement that the positioning boss  118   a  coaxial with the photoconductive drum  107  is supported by the positioning guide  144  fixed to the inner plate  140  of the image forming apparatus main assembly  114 , the process cartridge B is highly accurately positioned in the image forming apparatus main assembly  114 , in particular, regarding its relationship to such components as the optical system  101  and transfer roller  104 , the positional relationship of which relative to the photoconductive drum  107  must be assured to be accurate. As for the movements of the mounting/dismounting guide  141  and cover  115  during this period, the moment the positioning boss  118   a  of the process cartridge B goes over the projection  144   b  of the positioning guide  144 , the movement of the recess  141   a   1  of the mounting/dismounting guide  141  for pushing the process cartridge B inward of the image forming apparatus main assembly  114 , virtually ends, as shown in FIG.  70 . At this moment, the second boss  141   c  of the mounting/dismounting guide  141  is at the contact point (intersection) between the first and second arcuate portions  140   b   1  and  140   b   2  of the second guide rail  140   b  of the inner plate  140 , and the first boss  141   b  is at the top end of the first guide rail  140   a  of the inner plate  140  (inward end of the first guide rail in terms of the direction in which the process cartridge B is mounted). Therefore, the mounting/dismounting guide  141  assumes such an attitude that when the process cartridge B is at the image-formation location, the guiding groove  141   a  is virtually parallel to the direction in which the recording medium  102  is conveyed by the conveying means  103 . In other words, at the second location, the mounting/dismounting guide  141  assumes attitudes different from the attitude it assumes at the first location. 
     As the cover  115  is further closed, the second boss  141   c  of the mounting/dismounting guide  141  is moved to the second arcuate portion  140   b   2  of the second guide rail  140   b  by the inclination of the straight portion  115   c   2  of the cam hole  115   c,  as shown in FIG.  71 . As described previously, the center of the curvature of the second arcuate portion  140   b   2  is within the first guide rail  140   a,  and the radius of the second arcuate portion  140   b   2  is equal to the distance between the first and second bosses  141   b  and  141   c  of the mounting/dismounting guide  141 . Therefore, the movement of the mounting/dismounting guide  141  ends as the second boss  141   c  of the mounting/dismounting guide  141  comes into contact with the bottom end of the second arcuate portion  140   b   2 . 
     At this point, the cover  115  has rotated only approximately one half of its full rotational range. The reason for regulating the rotational angle of the cover  115  is as follows. For example, in the case of such a structure that, as the cover  115  is completely closed, the process cartridge B is pushed all the way to the image-formation location by the movement of the mounting/dismounting guide  141 , if a user inserts the process cartridge B into the image forming apparatus main assembly  114  as shown in FIG. 68, and pushes the process cartridge B in the direction in which the mounting/dismounting guide  141  moves, the cover  115  is rotated in the closing direction. In other words, in the case of such a structure that the entire rotational angle of the cover  115  is required to move the mounting/dismounting guide  141  and process cartridge B, as a user attempts to push the process cartridge B deeper into the image forming apparatus main assembly  114 , the arm of the user is pinched between the cover  115  and the area of the external surface of the image forming apparatus main assembly  114 , with which the cover  115  remains in contact when it is in the closed state. 
     In order to prevent the occurrence of the above described nuisance, in this embodiment, the process cartridge mounting/dismounting mechanism is structured so that only the first half of the entire range of the closing rotation of the cover  115  is used to move the process cartridge B. Therefore, even if a user pushes the process cartridge B deeper into the image forming apparatus main assembly  114 , there will remain a sufficient gap between the cover  115  and the area of the external surface of the image forming apparatus main assembly  114 , with which the cover  115  remains in contact when it is in the closed state, so that the arm of the user will not be pinched. 
     The resistance to which the positioning boss  118   a  of the process cartridge B is subjected as the positioning boss  118   a  goes over the projection  144   b  of the positioning guide  144 , provides a user with a feel of clicking that indicates to the user that the process cartridge B has been mounted into the normal position (image-formation location) by the closing movement of the cover  115 , whereby the user can recognize that the process cartridge B has been mounted into the normal position. 
     As the mounting/dismounting guide  141  is moved to the deepest end of its moving range, the second boss  141   c  of the mounting/dismounting guide  141  moves into the arcuate portion  115   c   1  of the cam hole  115   c  of the fan-shaped plate  115   b  (FIG.  72 ). As described before, the center of the curvature of the arcuate portion  115   c   1  coincides with the rotational axis of the cover  115 , and the width (dimension in terms of the its radius direction) of the arcuate portion  115   c   1  is slightly greater than the external diameter of the second boss  141   c  of the mounting/dismounting guide  141 . Therefore, as the cover  115  is further closed after the mounting/dismounting guide  141  is moved to the deepest end of its moving range, the second boss  141   c  of the mounting/dismounting guide  141  moves following the arcuate portion  115   c   1  of the cam hole  115   c,  being allowed to rotate with no contact with the mounting/dismounting guide  141  or the process cartridge B, until the opening W for mounting or dismounting the process cartridge B is completely covered by the cover  115  (completely closed state). This ends the closing of the cover  115 . 
     After the cover  115  is completely closed as described above, an image-formation command is sent to the control (unshown) of the image forming apparatus main assembly  114  to begin driving the main motor (unshown). As the main motor is driven, a driving force is transmitted to the photoconductive drum  107  by an unshown driving force transmitting means. As a result, the rotation controlling portion  120  of the process cartridge B, which is at the front end in terms of the process-cartridge mounting direction, comes into contact with the rotation controlling portion catching portion  119  of the image forming apparatus main assembly  114  (FIG.  63 ). The process cartridge B and image forming apparatus main assembly  114  are structured so that at this moment, that is, the moment the rotation controlling portion  120  comes into contact with the rotation controlling portion catching portion  119 , the process cartridge B becomes properly positioned in the image forming apparatus main assembly  114 , the left and right positioning bosses  118   a  supported by the left and right positioning guides  144 , respectively, and the rotation controlling portion  120 , and so that it is ensured that each guide rib  118   b  is lifted from the bottom wall, in terms of the vertical direction, of the guiding groove  141   a  of the mounting/dismounting guide  141  and remains floating in the guiding groove  141   a  in terms of the vertical direction. As for the reason for supporting the left and right positioning bosses  118   a  of the process cartridge B by the left and right positioning guides  144 , respectively, in order to provide highly precise images of high quality, the process cartridge B must be highly precisely positioned in the image forming apparatus main assembly  114 , and it is difficult to highly precisely position the process cartridge B in the image forming apparatus main assembly  114  with the use of the mounting/dismounting guide  141 , since the mounting/dismounting guide  141  is allowed to move within the image forming apparatus main assembly  114 , and it is not guaranteed where the mounting/dismounting guide  141  will stop. 
     Next, the steps which are taken to remove the mounting/dismounting guide  141  from the process cartridge B by opening the cover  115  will be described. In other words, the above described steps will be followed in reverse. 
     As the cover  115  in the state shown in FIG. 72 is opened, the second boss  141   c  of the mounting/dismounting guide  141  remains in the arcuate portion  115   c   1  of the cam hole  115   c  of the fan-shaped plate  115   b.  In other words, the only thing that happens throughout the first half of the entire range of the opening movement of the cover  115  is for the cover  115  to open. Referring to FIGS. 70-71, as the cover  115  is opened beyond the mid point of the entire range of its opening movement, the second boss  141   c  of the mounting/dismounting guide  141  is lifted into the first arcuate portion  140   b   1  of the guide rail  140   b,  by the straight portion  115   c   2  of the cam hole  115   c,  and the second arcuate portion  140   b   2  of the second guide rail  140   b  of the inner plate  140 . As the result, the mounting/dismounting guide  141  is rotated in the counterclockwise direction. In this step, the wall of the guiding groove  141   a  of the mounting/dismounting guide  141  comes into contact with the guide rib  118   b  of the process cartridge B, and the positioning boss  118   a  of the process cartridge B separates, and begins to move away, from the positioning portion  144   a  of the positioning guide  144 . As the cover  115  is further opened from this point, the second boss  141   c  of the mounting/dismounting guide  141  is moved toward the opening W for mounting or dismounting process cartridge B, by the first arcuate portion  140   b   1  of the second guide rail  140   b,  and the end of the straight portion  115   c   2  of the cam hole  115   c  of the fan-shaped plate  115   b.  As the second boss  141   c  is moved, the first boss  141   b  also moves in the first guide rail  140   a,  moving the process cartridge B to the location at which the process cartridge B can be grasped by a user. Then, as the cover  115  is opened all the way (fully open state), the mounting/dismounting guide  141  is moved to the location (first location) at which the guiding groove  141   a  of the mounting/dismounting guide  141  becomes continuous with the guiding groove  142   a  of the front guide  142 , as shown in FIG. 68, allowing the process cartridge B to be taken out of the image forming apparatus main assembly  114  through the opening W. 
     In the above described step, the second boss  141   c  of the mounting/dismounting guide  141  is moved to the end of the straight portion  115   c   2  of the cam hole  115   c  of the fan-shaped plate  115   b,  and is used as the stopper for preventing the cover  115  from being opened further. 
     As described above, in the process cartridge mounting/dismounting mechanism in this embodiment, by the closing movement of the cover  115  from the location at which it is fully open to the location at which it is completely closed, the two bosses  141   b  and  141   c  of the mounting/dismounting guide  141  are made to follow the two guide rails  140   a  and  140   b,  respectively, sliding on the walls of the guide rails  140   a  and  140   b.  During the first half of the closing movement of the cover  115 , the mounting/dismounting guide  141  is moved from the location at which the process cartridge B is removable from the mounting/dismounting guide  141 , to the second location at which the process cartridge B is to function for image formation, and during the latter half of the closing movement of the cover  115 , the boss  141   c  of the mounting/dismounting guide  141  is allowed to follow the cam hole  115   c  of the cover  115 , sliding on the walls of the cam hole  115   c,  so that the cover  115  can be completely closed. On the other hand, by the opening movement of the cover  115  from the location at which it is completely closed to the location at which it is fully open, the boss  141   c  of the mounting/dismounting guide  141  is made to follow the cam hole  115   c  of the cover  115 , allowing the cover  115  to be opened halfway, and during the latter half of the opening movement of the cover  115 , the two bosses  141   b  and  141   c  of the mounting/dismounting guide  141  are made to follow the guide rails  140   a  and  140   b,  respectively, sliding on the walls of the guide rails  140   a  and  140   b,  to move the mounting/dismounting guide  141  from the second location to the first location. 
     With the provision of the above described structural arrangement, the process cartridge B can be moved by the opening or closing movement of the cover  115 . Therefore, even in the case of an image forming apparatus structured so that the aforementioned image-formation location for the process cartridge B is in the deeper end of the image forming apparatus main assembly  114  in terms of the process-cartridge mounting direction, the process cartridge B can be easily mounted or dismounted. Further, the process cartridge B is moved in the image forming apparatus main assembly  114  by the first half of the opening movement of the cover  115 , and the latter half of the opening movement of the cover  115 . Therefore, even in the case of an image forming apparatus structured so that the image-formation location for the process cartridge B is in the deeper end of the image forming apparatus main assembly  114 , it is unnecessary to provide the image forming apparatus main assembly  114  with spaces in which fingers and/or a hand can be easily put when mounting or dismounting the process cartridge B, and further, even if a user pushes the process cartridge B deeper into the image forming apparatus main assembly  114 , the arm of the user will not be pinched by the cover  115  and the exterior of the image forming apparatus main assembly  114 . As is evident from the above descriptions, according to the present invention, the usability of an image forming apparatus can be maintained or improved without increasing the size of the image forming apparatus main assembly  114 , and also, the process cartridge B can be placed in the deeper end of the image forming apparatus main assembly  114  in terms of the process-cartridge mounting direction, affording more latitude in the placement of the various operational units in the electrophotographic image forming apparatus A. 
     Further, the mounting/dismounting guide  141  moves between the optical system  101  and conveying means  103 . More specifically, at the first location, it assumes such an attitude (first attitude) that it is tilted diagonally downward in the direction to make the direction X, in which the process cartridge B is inserted into the guiding groove  141   a,  intersect with the direction in which the recording medium  102  is conveyed by the conveying means  103 . At the second location, the mounting/dismounting guide  141  assumes an attitude different from the attitude it assumes at the first location. Therefore, it is possible to move the process cartridge B between the optical system  101  and conveying means  103 . Therefore, as the process cartridge B is mounted into the mounting/dismounting guide  141 , the process cartridge B slides into the guiding groove  141   a  due to its own weight and the downwardly inclining attitude of the mounting/dismounting guide  141 , until it butts against the deepest end of the guiding groove  141   a,  and then, the process cartridge B remains stationary relative to the mounting/dismounting guide  141  while the mounting/dismounting guide  141  is moved to the second location. 
     While the mounting/dismounting guide  141  is at the first location, and moves from the first location to the second location, the process cartridge B remains supported by the guiding groove  141   a,  by the guide rib  118   b,  and as the mounting/dismounting guide  141  reaches the second location, or the image-formation location, the position of the boss  118   a  of the process cartridge B is fixed by the positioning guide  144 , and begins to be supported thereby. Therefore, the process cartridge B is precisely retained in the predetermined position during an image forming operation. 
     Further, the fan-shaped plate  115   b  having the cam hole  115   c  for moving the mounting/dismounting guide  141  is provided as a part of the cover  115 , reducing the component count for the process cartridge mounting/dismounting mechanism, which in turn reduces the increase in the number of assembly steps. Therefore, a cost increase is suppressed. 
     Further, the process cartridge B is provided with the pair of guide ribs  118   b  supported by the pair of mounting/dismounting guides  141 , one for one, and the pair of positioning bosses  118   a  supported by the pair of positioning guides  144 , one for one. Therefore, the left and right mounting/dismounting guides  141 , and the left and right positioning guides  144 , respectively, can be symmetrically disposed with respect to the line which divides the process cartridge B into the left and right halves in terms of the process-cartridge mounting direction, and also can be disposed in the same position in terms of the direction perpendicular to the lengthwise direction of the process cartridge B. Therefore, the measurement of the process cartridge B in terms of its lengthwise direction does not increase. 
     The positioning guide  144  is provided with the positioning portion  144   a  in which the positioning boss  118   a  of the process cartridge B engages, and the projection  144   b  which is on the upstream side, with respect to the positioning portion  144   a  in terms of the direction in which the mounting/dismounting guide  141  moves from the first location to the second location, and is protruding in the theoretical straight path of the positioning boss  118   a  to the positioning portion  144   a.  Thus, as the process cartridge B is moved by the movement of the mounting/dismounting guide  141  from the first location to the second location, the positioning boss  118   a  of the process cartridge B comes into contact with the projection  144   b,  and then, is made to go over the projection  144   b  to be guided to the positioning guide  144 . Therefore, the process cartridge B is passed from the mounting/dismounting guide  141  to the positioning guide  144 . 
     Further, in terms of the process cartridge mounting direction X, the front guide  142  for guiding the process cartridge B during the mounting of the process cartridge B into the mounting/dismounting guide  141  is on the upstream side with respect to the mounting/dismounting guide  141 . Therefore, when the mounting/dismounting guide  141  is at the first location, it is prevented from being moved by the process cartridge B. 
     (Embodiments of Guiding Portions and Portion to be Guided) 
     Next, the configurations of the guiding portions and the portions to be guided will be described. 
     At the second location (operational location), in order for the transfer performance to be at a satisfactory level, the nip formed between the photoconductive drum  107  and transfer roller  104  needs to have a predetermined size. For this reason, the process cartridge mounting/dismounting mechanism is structured so that while the process cartridge B is moved from the first location to the second location, it is subjected to the reactive forces from the transfer roller  104  and various electrical contacts (unshown), near the second location. In order to ensure that the process cartridge B is moved to the second location, the process cartridge B must be pushed into the second location against these reactive forces. 
     Thus, in order to assure that the process cartridge B can be pushed into the second location against the reactive forces, the guiding grooves  141   a  and  141   h  of the mounting/dismounting guide  141  are connected by the step portion  141   f,  as shown in FIGS. 73 and 74. Further, the projecting corner of the step portion  141   f  is provided with a holding portion  141   g.  The mounting/dismounting guide  141  is configured so that the surface of this holding portion  141   g  of the mounting/dismounting guide  141 , which is parallel to the lengthwise direction of the mounting/dismounting guide  141 , forms an acute angle relative to the guiding groove  141   a.  This step portion  141   f,  and the holding portion  141   g,  that is, a portion of the step portion  141   f,  regulate the process cartridge B. In other words, this holding portion  141   g  is such a regulating portion that regulates the process cartridge B to regulate the attitude of the process cartridge B in the cartridge mounting space. The details of this regulation will be described later. 
     Referring to FIGS. 75 and 76, the guide rib  118   b  of the process cartridge B is provided with a holding portion  118   b   2 , which is on the bottom corner that faces the toner/developing means holding frame  112 , and is corresponds to the holding portion  141   g  of the mounting/dismounting guide  141 . This holding portion  118   b   2  on the guide rib  118   b  side is a portion which is engaged with, or disengaged from, the holding portion  141   g  on the mounting/dismounting guide  141  side; in other words, it is a portion regulated by the holding portion  141   g.  The angle of the cross section of the holding portion  118   b   2  at a plane perpendicular to the lengthwise direction of the process cartridge B is virtually equal to the angle between the surface of the holding portion  141   g  on the mounting/dismounting guide  141  side, which is parallel to the lengthwise direction of the mounting/dismounting guide  141 , and the guiding groove  141   h,  and is acute. 
     Referring to FIG. 77, the process cartridge B having been inserted into the image forming apparatus main assembly  114  is at the first location. The process cartridge B is moved to the second location by the closing movement of the cover  115 . As the process cartridge B is moved to the second location, it is subjected to a combination of the reactive forces from the transfer roller  104 , various electrical contacts (unshown), and the like. 
     Referring to FIGS. 78-80, this combination of the reactive forces act upon the process cartridge B in a manner to force the process cartridge B to be left behind, allowing only the mounting/dismounting guide  141  to move to the second location. However, as the mounting/dismounting guide  141  begins to move toward the second location, the holding portion  141   g  of the mounting/dismounting guide  141  engages with the holding portion  118   b   2  of the guide rib  118   b  of the process cartridge B. As a result, the process cartridge B remains held on the mounting/dismounting guide  141  which has begun to move toward the second location. 
     Referring to FIG. 80, the guide rib  118   b,  which is the side to be pushed, is subjected to a force which acts in the direction indicated by an arrow mark F. This force which acts in the direction F, is divided into two components: a force which acts in the direction indicated by an arrow mark F 1 , that is, the force which acts in the direction to push the process cartridge B toward the second location, and a force which acts in the direction indicated by an arrow mark F 2 , that is, the force which acts in the direction to press the guide rib  118   b  of the process cartridge B upon the mounting/dismounting guide  141 . 
     With the presence of the force acting in the direction F, the process cartridge B is held to the mounting/dismounting guide  141 . Therefore, it is assured that the process cartridge B is pushed into the second location, even though the process cartridge B remains subjected to the combination of the reactive forces from the transfer roller  104  and the like. 
     The structure for keeping the process cartridge B held to the mounting/dismounting guide  141  does not need to be limited to the above described one. For example, a structure shown in FIGS. 82-85 can provide the same effect as the one provided by the above described structure. In this case, the mounting/dismounting guide  141  is provided with a pocket  141   i,  which is located between the guiding grooves  141   a  and  141   h  of the mounting/dismounting guide  141 , whereas the guide rib  118   b  of the process cartridge B is provided with a vertical rib  118   c,  so that the vertical rib  118   c  engages into the pocket  141   i  as shown in FIG.  86 . 
     Referring to FIG. 87, in the case of a structure in which the mounting/dismounting guide  141  and the guide rib  118   b  of the process cartridge B are not provided with the holding portions  141   g  and  118   b   2 , respectively, and the surface of the step portion of the mounting/dismounting guide  141 , and the corresponding surface of the guide rib  118   b  of the process cartridge B, are perpendicular to the lengthwise directions of the mounting/dismounting guide  141  and guide rib  118   b,  respectively, the guide rib  118   b  is dislodged by the reactive force from the transfer roller  104 , from the mounting/dismounting guide  141 , as the process cartridge B is subjected to the reactive force from the transfer roller  104 , near the second location, as shown in FIGS. 88 and 89. However, since the movement of the mounting/dismounting guide  141  is linked to the closing movement of the cover  115 , only the mounting/dismounting guide  141  is moved to the second location, leaving the process cartridge B behind. In other words, in the case of the structure shown in FIG. 87, it is possible that the process cartridge B is incorrectly mounted into the image forming apparatus main assembly  114 . Incidentally, in the case of a structure in which no gap is provided between the guide rib  118   b  and mounting/dismounting guide  141  so that the former perfectly fits with the mounting/dismounting guide  141 , there is little possibility for the above described incorrect mounting of the process cartridge B. However, such a structural arrangement makes it troublesome to take the process cartridge B out of the image forming apparatus main assembly  114 , adversely affecting operational efficiency. Thus, a structure in which a certain amount of clearance is provided between the mounting/dismounting guide  141  and guide rib  118   b  is a desirable structure. 
     In this embodiment, each mounting/dismounting guide  141  is guided by the two guide rails  140   a  and  140   b,  in order to move the process cartridge B, and also, to control the attitude in which the process cartridge B is mounted or dismounted. However, the method for moving the process cartridge B does not need to be limited to the method in this embodiment. Neither does the method for controlling the attitude in which the process cartridge B is mounted or dismounted need to be limited to the method in this embodiment. For example, in order to guide the guide portions of a process cartridge, the left and right wall of the process-cartridge mounting portion of the image forming apparatus main assembly may be provided with a guide rail, which inclines downward in terms of the cartridge mounting direction, and the inclination of which is reduced toward the deeper end. Further, in order to move the process cartridge B into the cartridge mounting portion, or remove the process cartridge B therefrom, a slide or a linking mechanism may be provided. 
     Incidentally, it is not mandatory that the movement of the mounting/dismounting guide is linked to the movement of the cover. Rather, the aforementioned slide or linking mechanism may be manually operated. In such a case, the cover is opened or closed, independently from the movement of the mounting/dismounting guide. 
     As described hereinbefore, the present invention is applicable to an electrophotographic image forming apparatus and a process cartridge which is mountable to the main assembly of the image forming apparatus, the image forming apparatus comprising a movable mounting-and-demounting guide. 
     In the foregoing embodiments, the process cartridge is for forming monochromatic images, but the process cartridge according to this invention is applicable to a cartridge having a plurality of developing means for forming multicolor images, for example two-color images, three-color images and full-color images or the like. 
     The electrophotographic photosensitive member is not limited to the photosensitive drum. For example, the photosensitive member may be a photoconductor such as amorphous silicon, amorphous selenium, zinc oxide, oxide titanium, organic photoconductor (OPC) or the like. The photosensitive member may be in the form of a drum or belt. In the case of the drum type photosensitive member, the photoconductor is applied or evaporated on a cylinder made of aluminum alloy or the like. 
     Also, the present invention is preferably usable with various known developing methods such as the magnetic brush developing method using two component toner, the cascade developing method, the touch-down developing method, the cloud developing method. 
     The structure of the charging means described in the foregoing is of a so-called contact type charging method, but a known charging means comprising a tungsten wire which is enclosed with a metal shield of aluminum or the like at three sides, wherein positive or negative ions generated by application of a high voltage to said tungsten wire are directed to the surface of the photosensitive drum to uniformly charged the surface, is usable. 
     The charging means may be a roller type as described in the foregoing, a blade type (charging blade), a pad type, a block type, a rod type, a wire type or the like. 
     The charging means may be a roller type as described in the foregoing, a blade type (charging blade), a pad type, a block type, a rod type, a wire type or the like. 
     The process cartridge, for example, comprises an electrophotographic photosensitive member and at least one process means. The process cartridge is detachably mountable as a unit to the main assembly of apparatus, wherein the process cartridge contains an electrophotographic photosensitive member and charging means; contains an electrophotographic photosensitive member and developing means; contains an electrophotographic photosensitive member and cleaning means; or contains an electrophotographic photosensitive member and two or more process means. 
     In other words, the process cartridge contains an electrophotographic photosensitive member and charging means, developing means or cleaning means, the cartridge being detachably mountable as a unit to the main assembly of the apparatus. The process cartridge may contain an electrophotographic photosensitive member and at least one of a charging means, a developing means and a cleaning means in the form of a cartridge which is detachably mountable to a main assembly of an image forming apparatus. Or, it may be a cartridge containing integrally at least developing means and an electrophotographic photosensitive member, the cartridge being detachably mountable to a main assembly of an image forming apparatus. The process cartridge is mounted to or demounted from the main assembly of the apparatus by the user. This means that maintenance of the apparatus is carried out, in effect, by the user. 
     In the foregoing embodiments, a laser beam printer has been taken as an exemplary embodiment of an electrophotographic image forming apparatus, but the present invention is not limited to this, and is applicable to another electrophotographic image forming apparatus such as an electrophotographic copying machine, a facsimile machine, a word processor or the like. 
     The process cartridge mounting-and-demounting mechanism and the process cartridge according to the embodiments of the present invention, has the following characteristics. 
     (1) The operator inserts the process cartridge in an inclined downward direction into an electrophotographic image forming apparatus having a transfer roller, urged to a photosensitive drum, for transferring an image onto a recording material, and moves the process cartridge in such a direction that the photosensitive drum is advanced substantially in a horizontal direction in interrelation with a closing action of the closing member, and then when the photosensitive drum reaches a neighborhood of the transfer roller, the process cartridge is moved in such a direction that the photosensitive drum is advanced in an inclined downward direction. Therefore, the operator can easily insert the process cartridge, and the transfer roller is urged by the movement of the process cartridge caused by the closing of the cover. 
     (2) The first and second cartridges of the process cartridge are guided by the first and second main assembly guides toward the mounting position, and when the process cartridge is resisted by the spring provided in the main assembly of the apparatus, the first and second main assembly guides push trailing ends of the first and second cartridge guides, so that the process cartridge can be mounted at the correct position. 
     (3) After the process cartridge is mounted on the movement guide with the cover wide-open, the process cartridge is advanced in interrelation with the closing action of the cover, and the drum shutter opens in response to the movement of the process cartridge. Therefore, when the user mounts the process cartridge to the cartridge mounting member (movement guide), there is no liability that a process cartridge is stopped halfway due to the resistance against the opening of the drum shutter, and therefore, the process cartridge can be inserted deeply enough. 
     As described in the foregoing, according to the present invention, the mounting operability of the process cartridge to the main assembly of the electrophotographic image forming apparatus can be improved. 
     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 purpose of the improvements or the scope of the following claims.