Patent Publication Number: US-6661977-B1

Title: Electrophotographic image forming apparatus and process cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an electrophotographic image forming apparatus and a process cartridge. 
     Here, the process cartridge refers to charging means, developing means or cleaning means as process means and an electrophotographic photosensitive member integrally made into a cartridge which is made detachably mountable to the main body of an electrophotographic image forming apparatus. Or it refers to at least one of charging means, developing means and cleaning means as process means and an electrophotographic photosensitive member integrally made into a cartridge which is made detachably mountable to the main body of an electrophotographic image forming apparatus. Further, it refers to at least process means, developing means and an electrophotographic photosensitive member integrally made into a cartridge which is made detachably mountable to the main body of an electrophotographic image forming apparatus. 
     Also, the electrophotographic image forming apparatus uses the electrophotographic image forming process to form an image on a recording medium. For example, it covers an electrophotographic copying machine, an electrophotographic printer (such as an LED printer or a laser beam printer), an electrophotographic facsimile apparatus and an electrophotographic word processor. 
     2. Description of Related Art 
     In an electrophotographic image forming apparatus, there has heretofore been adopted a process cartridge system in which an electrophotographic photosensitive member and process means for acting on the electrophotographic photosensitive member are integrally made into a cartridge which is made detachably mountable to the main body of the image forming apparatus. According to this process cartridge system, a user himself can effect the maintenance of the apparatus without resort to a serviceman and therefore, operability could be markedly improved. So, this process cartridge system is widely used in electrophotographic image forming apparatuses. 
     An electrophotographic image forming apparatus of such a cartridge type is of such a structure in which only a cartridge matching in function with the main body of the image forming apparatus can be mounted. 
     That is, if an attempt is made to mount a cartridge not matching in function with the main body of an image forming apparatus, the design of the cartridge side or the main body side of the apparatus is such that the cartridge cannot be mounted. That is, the cartridge or the main body of the apparatus has a wrong insertion preventing function. The function of the cartridge differs depending on the specification, type, etc., of the apparatus. On the other hand, there are cartridges similar in appearance due to the commonness or the like of the their parts even if they are not fit for image formation in that apparatus. Therefore, if the erroneous mounting of a cartridge having no compatibility should be done, not only is good image formation not effected, but also trouble with the apparatus may be caused. 
     So, in the electrophotographic image forming apparatus, a construction for determining the compatibility of cartridges has heretofore been proposed and put into practice. There is known, for example, a method using a sensor for discriminating compatibility, or a driving mechanism or the like which can mesh with only the driven gear of a matching process cartridge. 
     According to the conventional art, however, if a sensor for the judgment of compatibility is to be used, an expensive sensor for discrimination will be required. Also, it will be necessary to mount a part for operating the sensor also on the cartridge side, and this will result in an increase in cost. 
     Also, in the case of a construction for giving an incompatible function by the meshing engagement between gears, compatibility is discriminated near the mounted position of the cartridge. Therefore, the timing for the discrimination of compatibility is delayed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-noted unsolved problem peculiar to the conventional art and an object thereof is to provide an electrophotographic image forming apparatus and a process cartridge which can reliably detect the incompatibility of the process cartridge by a simple construction. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus having a wrong mount preventing function of high reliability for the process cartridge. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus which can prevent a process cartridge not matching in function with the main body of the electrophotographic image forming apparatus from being mounted on a mounting portion provided in the main body of the apparatus. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus which enables only a cartridge matching in function with the main body of the electrophotographic image forming apparatus to be mounted on a mounting portion provided in the main body of the apparatus. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus which can prevent a process cartridge not matching in function with the main body of the electrophotographic image forming apparatus from being mounted on a mounting portion provided in the main body of the apparatus, by a simple construction. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus which permits a process cartridge matching in function with the main body of the electrophotographic image forming apparatus to be mounted on a mounting portion provided in the main body of the apparatus and in which a process cartridge not matching in function with the main body of the apparatus is hampered from being mounted on the mounting portion, by a portion of the process cartridge contacting a portion of the main body of the apparatus. 
     Another object of the present invention is to provide a process cartridge and an electrophotographic image forming apparatus which can prevent a process cartridge not matching in function with the main body of the electrophotographic image forming apparatus from being mounted on a mounting portion provided in the main body of the apparatus, by a shutter contacting a portion of the main body of the apparatus. 
     Another object of the present invention is to provide an electrophotographic image forming apparatus comprising a cartridge mounting portion for detachably mounting thereon a process cartridge provided with an electrophotographic photosensitive member, process means for acting on the electrophotographic photosensitive member, a shutter having a photosensitive member protecting portion for protecting the photosensitive member and movable between a protecting position for protecting the photosensitive member and a retracted position retracted from the protecting position to thereby expose the photosensitive member, and a shutter moving portion for moving the shutter from the protecting position to the retracted position, guide means for guiding the cartridge when the cartridge is to be mounted on the mounting portion, shutter opening means for coming into engagement with the shutter moving portion when the cartridge is guided by the guide means and is moved along a movement path toward the mounting portion, to thereby open the shutter from the protecting position to the retracted position, a wrong insertion preventing engagement portion adapted to be engaged with the shutter moving portion on the upstream side of an engagement position in which the shutter moving portion and the shutter opening means are engaged with each other, in the mounting direction in which the cartridge is mounted on the mounting portion when a cartridge not matching in function with the main body of the apparatus is inserted in the main body of the apparatus, to thereby open the shutter, and a main body shutter abutting portion adapted to abut against the shutter moved toward the retracted position by the shutter moving portion being engaged with the wrong insertion preventing engagement portion, to thereby restrict the insertion of the cartridge. 
     Another object of the present invention is to provide a process cartridge comprising an electrophotographic photosensitive member, process means for acting on the photosensitive member, a shutter having a photosensitive member protecting portion for protecting the photosensitive member and movable between a protecting position for protecting the photosensitive member and a retracted position retracted from the protecting position to thereby expose the photosensitive member, a shutter moving portion for coming into engagement with shutter opening means provided in the main body of an electrophotographic image forming apparatus when the cartridge is mounted on the main body of the apparatus, to thereby move the shutter from the protecting position to the retracted position, and adapted to be engaged with a wrong insertion preventing engagement portion provided in the main body of the apparatus, on the upstream side of an engagement position in which the shutter moving portion and the shutter opening means are engaged with each other, in the mounting direction in which the cartridge is mounted on the main body of the apparatus when the cartridge is inserted into the main body of the apparatus which does not match in function with the cartridge, to thereby move the shutter from the protecting position to the retracted position, and a cartridge shutter abutting portion provided on the shutter for abutting against a main body shutter abutting portion provided in the main body of the apparatus to restrict the insertion of the cartridge into the main body of the apparatus when the shutter is moved toward the retracted position by the shutter moving portion being engaged with the wrong insertion preventing engagement portion. 
    
    
     These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the general construction of an electrophotographic image forming apparatus. 
     FIG. 2 is a typical cross-sectional view showing the process cartridge of FIG.  1 . 
     FIG. 3 is a perspective view of the process cartridge of FIG. 1 as it is seen from the right side thereof (the rear as viewed in the figure). 
     FIG. 4 is a perspective view of the process cartridge of FIG. 1 as it is seen from the left side thereof (the side as viewed in the figure). 
     FIG. 5 is a perspective view showing only a drum shutter. 
     FIG. 6 illustrates the first step of inserting the process cartridge into the main body of the apparatus. 
     FIG. 7 illustrates the second step of inserting the process cartridge into the main body of the apparatus. 
     FIG. 8 illustrates the third step of inserting the process cartridge into the main body of the apparatus. 
     FIG. 9 illustrates the fourth step of inserting the process cartridge in operative association with the operation of closing the openable and closable member of the main body of the apparatus. 
     FIG. 10 illustrates the fifth step of inserting the process cartridge into the final position in operative association with the operation of closing the openable and closable member of the main body of the apparatus. 
     FIG. 11 illustrates a first embodiment. 
     FIG. 12 shows a case where in a second embodiment, a proper process cartridge is inserted. 
     FIG. 13 shows a case where in the second embodiment, an improper process cartridge is inserted. 
     FIG. 14 illustrates one side compatibility in the second embodiment. 
     FIG. 15 illustrates a third embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some embodiments of the present invention will hereinafter be described with reference to the drawings. 
     General Structure 
     FIGS. 1 to  10  illustrate the general constructions of electrophotographic image forming apparatuses according to first to fifth embodiments of the present invention and a mounting and dismounting guide mechanism which is a mounting guide means for a process cartridge. Herein, the lengthwise direction of the process cartridge is a direction intersecting with (substantially orthogonal to) the direction in which the cartridge is mounted to and dismounted from the main body of the apparatus, and is a direction parallel to the surface of a recording medium and intersecting with (substantially orthogonal to) the transport direction of the recording medium. Also, right or left is right or left when the recording medium P is seen from above it in accordance with the transport direction of the recording medium. Also, the upper surface of the process cartridge is an overlying surface in a state in which the process cartridge is mounted to the main body of the apparatus, and the lower surface of the process cartridge is an underlying surface in the same state. The term “recording medium P” includes, for example, recording paper, OHP sheets, etc. 
     As shown in FIG. 1, the electrophotographic image forming apparatus (laser beam printer) applies information light based on image information from an optical system  1  as optical means to a photosensitive drum  11  which is a drum-shaped electrophotographic photosensitive member in a process cartridge  2  to thereby form an electrostatic latent image on the photosensitive drum  11 . The electrostatic latent image is developed with a developer (toner) to thereby form a toner image. In synchronism with the formation of the toner image, recording media P are separated and fed one by one from the cassette  3   a  of a transporting system  3  by a pickup roller  3   b  and a pressure contact member  3   c  brought into pressure contact therewith. The toner image formed on the photosensitive drum  11  is transferred to the recording medium P by a voltage being applied to a transferring roller  4  as transferring means. The recording medium P is then transported to fixing means  5  by a transporting guide  3   f.    
     The fixing means  5  has a drive roller  5   a  and a fixing rotary member  5   d  containing a heater therein and comprised of a cylindrical sheet rotatably supported by a supporting member  5   c . It applies heat and pressure to the passing recording medium P to thereby fix the transferred toner image. The recording medium P is transported by delivery rollers  3   d  and is delivered to a delivery portion  6  through an inverter transport path. 
     An openable and closable member  101  and driving means for driving the transporting system  3 , the fixing means  5  and the process cartridge  2  are disposed in the main body  100  of the image forming apparatus. The driving means drives each rotary member by a driving force transmitted from a motor (not shown) as a drive source to each rotary member through a gear train (not shown). 
     The driving force to the cartridge  2  is transmitted to a large gear (not shown) also through the aforementioned gear train. The transmission of the driving force between the large gear and the cartridge  2  is effected by the meshing engagement between a main body coupling  110  and a drum coupling  15 . The main body coupling  110  (see FIG. 6) has a twisted-hole having a substantially equilateral triangular cross-section formed coaxially with the rotary shaft of the large gear. Also, the drum coupling  15  (see FIG. 3) has a twisted-protrusion having a substantially equilateral triangular cross-section provided on a gear flange fixed to one end portion of the photosensitive drum  11 , coaxially with the rotary shaft of the photosensitive drum  11 . The transmission of the driving force and the alignment and positioning of the large gear and the photosensitive drum  11  are effected by the connection of these couplings. 
     Internal Structure of the Process Cartridge 
     The process cartridge  2  has the photosensitive drum  11  which is an electrophotographic photosensitive member and developing member  20  as process means for acting thereon, namely, for developing the electrostatic latent image formed on the photosensitive drum  11 . 
     As shown in FIG. 2, the cartridge  2  rotates the photosensitive drum  11  having a photoconductive layer, and applies a voltage to a charging roller  12  as charging means to thereby uniformly charge the surface of the photosensitive drum  11 . The charged photosensitive drum  11  is exposed to information light (light image) L based on image information from the optical system  1  through an exposure opening portion  10   a . Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum  11 . The electrostatic latent image is then developed by the developing means  20 . 
     The developing means  20  is such that a developing roller  21  which is a developer bearing member containing a stationary magnet  21   a  therein is rotated and a toner layer given triboelectrification charges by a developing blade  22  is formed on the surface of the developing roller  21 . The toner is shifted to the photosensitive drum  11  in conformity with the latent image to thereby form a toner image. 
     A voltage opposite in polarity to the toner image is then applied to the transferring roller  4  to thereby transfer the toner image to the recording medium P. Thereafter, any toner residual on the photosensitive drum  11  is scraped off by a cleaning blade  13   a . The removed toner is dipped by a dip sheet  13   b  and is collected into a removed toner containing portion  13   c . The residual toner on the photosensitive drum  11  is removed by cleaning means  13  of such a construction. 
     As described above, the cartridge  2  has a cleaning frame  14  rotatably supporting the photosensitive drum  11  and provided with the cleaning means  13  and the charging roller  12 , and a developing frame provided with the developing roller  21 , a toner containing portion  23   a , a toner agitating member  23   b  and a developing chamber  23   c . The developing frame  24  is supported for pivoted movement relative to a cleaning frame (drum frame)  14  so that the developing roller  21  of the developing means can be opposed to the photosensitive drum  11  in parallel thereto with a predetermined spacing between them. Spacers (not shown) for maintaining the spacing between the developing roller  21  and the photosensitive drum  11  are disposed on the opposite end portions of the developing roller  21 . 
     As shown in FIG. 3, holder members  31  and  32  are disposed on the opposite sides of the developing frame  24 . These holder members  31  and  32  have suspending arms formed with coupling holes for rotatably suspending the developing frame  24  on the cleaning frame  14 . A predetermined pressure force is applied to between the developing frame  24  and the cleaning frame  14  by a spring (not shown) to maintain a spacing therebetween. 
     The cartridge  2  is constituted by the developing frame  24  comprising a developing frame member  24   a  and a lid member  24   b  welded together into a unit and the cleaning frame  14  coupled together by the holder members  31  and  32 . On the lengthwisely opposite sides of the cartridge, as shown in FIGS. 3 and 4, there are provided mounting guides  41  and  42  for detachably mounting the cartridge to the main body  100  of the image forming apparatus of FIG. 1 in the direction indicated by the arrow X. Also, there are provided positioning guides  43  and  44  lying coaxially with the rotary shaft of the photosensitive drum  11  and supported by positioning means provided in the main body  100  of the apparatus. The positioning guides  43  and  44  are cylindrical bosses differing in diameter from each other. The positioning guide  44  on the side opposite to the driving side is provided with a mounting auxiliary guide  44   a  extended rearwardly in the mounting direction of the cartridge. 
     The mounting guides  41  and  42  are provided with lower surfaces  41   a  and  42   a  received by a moving guide  111  (guide means; see FIG. 6) provided in the main body  100  of the apparatus, and distal end portions  41   b  and  42   b  are provided on the distal end sides of the mounting guides  41  and  42  in the direction of insertion of the cartridge (the direction indicated by the arrow X). These distal ends  41   b  and  42   b  have their arcs connected to the lower surfaces  41   a  and  42   a  made larger than their arcs connected to the upper surfaces. 
     Also, slope portions  41   d  and  42   d  having their contained angle with the lower surfaces  41   a  and  42   a  made acute are provided on rear end lower corners  41   c  and  42   c  provided on the rear end corners of the lower surfaces  41   a  and  42   a  in the direction of insertion thereof. The rear end portions of the upper surfaces in the direction of insertion have orthogonal surfaces  41   e  and  42   e  orthogonal to the upper surfaces. The rear ends of the mounting guides  41  and  42  are provided to the rear of the centroidal position of the cartridge  2 . When the cartridge  2  is supported by the guides  41  and  42 , the cartridge always maintains its forwardly downward posture. The guides  41  and  42  are provided on the side of the frame  14  above the guides  43  and  44 . 
     In the cartridge  2 , as shown in FIG. 2, a drum shutter  50  which is a shutter capable of integrally covering the transfer opening portion  10   b  and the exposure opening portion  10   a  of the photosensitive drum  11  which are opposed to the transferring roller  4  is rotatably provided on the cleaning frame (drum frame)  14 . The shutter  50  is not limited to that in the present embodiment, but may be, for example, one which openably and closably covers only the transfer opening portion  10   b  or only the exposure opening portion  10   a.    
     As shown in FIGS. 2 to  5 , the shutter  50  has a drum protecting portion  51  which is a photosensitive member protecting portion capable of covering the transfer opening portion  10   b  through which the photosensitive drum  11  contacts with the transferring roller  4 , a rotary shaft  52  to be rotatably supported in that portion of the cleaning frame  14  which is near the exposure opening portion  10   a , and sliding portions  53  and  54  sliding on the opposite ends of the rotary shaft  52  relative to the cleaning frame  14 . In a portion connecting the sliding portions  53  and  54  on the opposite ends together, there is provided a large-diametered portion  55  thicker than the sliding portions  53  and  54 , and an exposure shutter portion  56  for closing the exposure opening portion  10   a  when the shutter  50  is in its closed state. Further, the shutter  50  is provided with connecting portions  57  provided at two right and left locations for connecting the protecting portion  51  and the rotary shaft  52  together at the opposite end portions of the former and outside the latter, and a cam portion  58  which is a shutter moving portion disposed on the right end of the rotary shaft  52  and protruding to the upper side of the cartridge  2 . Furthermore, there is provided a rib  57   a  provided on the right connecting portion  57  and extending outwardly in the lengthwise direction of the shutter  50 . The rib  57   a  is received by the shutter guide of the main body of the apparatus and holds the shutter  50  in its opened posture. 
     A biasing force is applied to the shutter  50  by a torsion coil spring  53   a  (FIG. 5) in a direction in which the shutter  50  covers the photosensitive drum  11 . Thereby, in a state in which the cartridge  2  is being taken out of the main body  100  of the apparatus, the shutter  50  maintains its closed state for covering the transfer opening portion  10   b , as indicated by dots-and-dash line in FIG.  2 . In a state in which the cartridge  2  is in the main body  100  of the apparatus and is capable of performing the image forming operation, the shutter  50  is rotated by a drum shutter opening and closing mechanism which will be described later, and exposes the transfer opening portion  10   b  as indicated by the solid line in FIG.  2  and assumes its opened posture in which the photosensitive drum  11  and the transfer roller  4  can contact with each other. 
     That is, the shutter  50  has a photosensitive member protecting portion for protecting the photosensitive member, and is movable between a protecting position for protecting the photosensitive member and a retracted position retracted from the protected position to thereby expose the photosensitive member. 
     The operation of mounting the cartridge  2  will now be described with reference to FIGS. 6 to  10 . 
     When the openable and closable member  101  of the main body  100  of the apparatus is completely opened (fully opened), a main body opening portion  200  for mounting and dismounting the cartridge  2  therethrough appears. In this state, as shown in FIG. 6, it appears in a posture in which right and left movable guides  111  in the main body  100  of the apparatus are lowered to the inner side with respect to the direction of insertion of the cartridge  2 . On the upstream side of the movable guides  111  with respect to the direction of insertion, auxiliary guides  112  are fixed to main body side plates  102  substantially symmetrically at right and left. 
     As previously described, the positioning guides  43  and  44  and the rib-shaped mounting guides  41  and  42  have a shape along the direction in which the cartridge  2  is mounted and dismounted. Further, projected portions  31   a  and  32   a  protruding from the bottom surface of the developing frame  24  are provided on holder members  31  and  32 , respectively, at the lengthwisely opposite ends (see FIG.  4 ). 
     As the cartridge  2  is inserted through the opening portion of the main body  100  of the apparatus, the mounting guides  41  and  42  of the cartridge  2  are received by the right and left movable guides  111  and auxiliary guides  112  in the main body of the apparatus. 
     The cartridge  2  is mounted on the main body  100  of the apparatus in a direction intersecting with the photosensitive drum  11  with the developing frame  24  trailing the cleaning frame  14  (or with the cleaning frame  14  disposed forwardly and the developing frame  24  disposed rearwardly). At this time, the shutter  50  is retracted forwardly of the cleaning frame  14 . That is, the shutter  50  is retracted forwardly in the mounting direction. 
     As shown in FIG. 8, with the cartridge  2  inserted in the main body  100  of the apparatus, the lower surface of the developing frame  24  contacts with the abutting rib  113  in the main body  100  of the apparatus rearwardly of the centroidal position of the cartridge  2  in the direction of insertion. Therefore, the cartridge  2  assumes a posture in which it raises the developing frame  24 , which is on the rear side (upstream side) in the mounting direction. Therefore, the cartridge  2  inserted through the main body opening portion  200  has the lower sides of the distal ends  41   b  and  42   b  of the guides  41  and  42 , respectively, supported by the guide groove  111   a  of the guide  111  and has the lower surface of the developing frame  24  supported by the abutting rib  113 . Also, the lower corners  41   c  and  42   c  of the mounting guides  41  and  42 , respectively, are raised. 
     The guide  111  is moved to the inner part of the main body  100  of the apparatus in operative association with the opening and closing operation of the openable and closable member  101 . Therefore, when the cartridge  2  comes into engagement with the rear end (the end surface adjacent to the openable and closable member) of the guide  111 , the guide  111  escapes into the interior of the main body  100  of the apparatus. So, it becomes impossible to put the mounting guides  41  and  42  of the cartridge  2  into the guide groove  111   a  of the guide  111 . In order to prevent this, an auxiliary guide  112  constituting a mounting and dismounting auxiliary portion fixed to the side plate  102  of the main body and connected to the rear end of the guide  111  is provided upstream of the guide  111  in the mounting direction (the direction indicated by the arrow X) of the cartridge  2 . The above-noted problem is solved by the auxiliary guide  112 , and the mounting guides  41  and  42  of the cartridge  2  are reliably guided to the guide groove  111   a.    
     The state in which the cartridge  2  is moved in operative association with the rotation of the openable and closable member  101  has hitherto been described. A description will now be provided of the opening and closing operation of the shutter  50  resulting from the movement. 
     The opening and closing operation of the shutter  50 , as shown in FIGS. 6,  7  and  8 , is not performed at a stage whereat the cartridge  2  is mounted on the main body  100  of the apparatus, but is performed at a stage whereat the cartridge  2  is moved in the interior of the main body of the apparatus with the rotation of the openable and closable member  101  (see FIGS.  9  and  10 ). 
     That is, the shutter  50  is opened at a stage whereat the cartridge  2  is moved with the closing operation of the openable and closable member  101 . 
     When the cartridge  2  is moved to the inner part in operative association with the closing operation of the openable and closable member  101 , the shutter  50  rotatably supported by the cartridge  2  is rotated to thereby expose the transfer opening portion  10   b  and the exposure opening portion  10   a  and bring the cartridge  2  into a state in which it can effect image formation. 
     Describing in detail, when the cartridge  2  is moved in operative association with the closing operation of the openable and closable member  101 , as shown in FIG. 8, the cam portion  58  of the shutter  50  comes into contact with an optical unit  103  which is a shutter opening means loaded with the optical system  1  at a predetermined position in the main body  100  of the apparatus, or a supporting stand  103   a  which is the fixed stand therefor. The shutter  50  is then clockwisely rotated while resisting the resilient force of a shutter spring  53   a . Thereby, the transfer and exposure opening portions begin to be exposed. 
     As the cartridge  2  is moved toward the inner part, the cam portion  58  of the shutter  50  contacts with the corner of the optical unit  103  or the supporting stand  103   a , and thereafter is moved while having the vertex portion of its distal end made to abut against the lower surface of the optical unit  103  or the supporting stand  103   a  (FIG.  9 ). As the cartridge  2  lowers toward the frame  3   e  of the transporting system  3 , the shutter  50  makes its angle of opening greater. 
     The movement of the guide  111  operatively associated with the rotation of the openable and closable member  101  is stopped, and the transportation of the cartridge  2  resulting therefrom ends. Thereupon, as shown in FIG. 10, the shutter  50  assumes a predetermined angle of opening. The opening portion  10   b  and the opening portion  10   a  (FIG. 2) are exposed, and the cartridge  2  becomes capable of performing the image forming operation. 
     First Embodiment 
     FIG. 11 shows a first embodiment. This is provided with a wrong insertion preventing mechanism for preventing an improper cartridge  2   a  which does not match in function with the apparatus from being inserted into an electrophotographic image forming apparatus having the above-described general structure. This preventing mechanism is provided with a wrong insertion preventing engagement portion (interfering means)  104  such as a rib or a wall on the upper peripheral edge of the opening portion  200  of the main body  100  of the apparatus. When the improper cartridge  2   a  is inserted, the cam portion (shutter moving portion)  58   a  of the shutter  50   a  comes into engagement with the wrong insertion preventing engagement portion  104  and is rotatively driven. Thereby, the shutter  50   a  immediately after the insertion is opened. 
     The cam portion  58  (shutter moving portion) of the shutter  50  of a proper cartridge  2  which matches in function with the apparatus is provided at a lengthwise position different from that of the cam portion  58   a  of the shutter  50   a  of the improper cartridge  2   a . So, the cam portion  58  does not come into engagement with the engagement portion  104  but is inserted into the inner part of the main body  100  of the apparatus. Then, the cam portion  58 , as previously described, comes into engagement with the optical unit  103  which is shutter opening means, or the supporting stand  103 a thereof in operative association with the operation of closing the openable and closable member  101 , and opens the shutter  50  at a proper position. That is, it permits the cartridge  2  which matches in function with the apparatus to be mounted on the main body  100  of the apparatus. The optical unit  103  is a unit carrying thereon the optical system  1  comprised of a polygon mirror  103 - 1 , a lens  103 - 2  and a mirror  103 - 3 . This optical unit  103  is supported on the supporting stand  103   a . The optical unit  103  is formed with an opening  103   e . The opening  103   e  is for emitting therethrough a laser beam L to be applied to the photosensitive drum  11 . 
     A wrong insertion preventing wall may be provided and may be formed with an opening portion formed with an opening portion excluded only on the locus of the cam portion  58  of the proper cartridge  2 . 
     When the improper cartridge  2   a  is inserted (mounted) through the opening portion  200  of the main body  100  of the apparatus, the cam portion  58   a  of the shutter  50   a  abuts against the engagement portion  104  immediately thereafter. The shutter  50   a  is clockwisely rotated against the spring pressure of the spring  53   a  to thereby begin to open the transfer opening portion  10   b  and the exposure opening portion  10   a , and the shutter  50   a  becomes opened. 
     As described above, immediately after being inserted, the improper cartridge  2   a  has its shutter  50   a  opened, and the opened shutter  50   a  strikes against the side  103   c  or the supporting stand  103   a  of the optical unit  103 . Therefore, any further insertion of the improper cartridge  2   a  is blocked. 
     The improper cartridge  2   a  cannot be completely contained in the main body  100  of the apparatus and the openable and closable member  101  is not closed. Therefore, the image forming operation becomes impossible. 
     On the other hand, the design is made such that when the proper cartridge  2  is to be inserted, the engagement portion  104  does not interfere on the insertion locus of the cam portion  58  of the shutter. Therefore, the operation of opening the shutter  50  to a proper position and the image forming operation becomes possible. 
     Instead of adopting a construction in which a wall or the like for preventing wrong insertion is provided in the opening in the main body of the image forming apparatus to thereby enable only the cam portion of the shutter of the proper cartridge to pass, the number of the cam portions of the shutter may be increased to thereby cope with the problem. That is, a plurality of cam portions of the shutter may be provided in the lengthwise direction to thereby give a wrong insertion preventing mechanism similar to that described above. 
     According to the present embodiment, the positions of the cam portion of the shutter of the cartridge are made different in the lengthwise direction of the cartridge. Thus, the outer frame construction or the like of the cartridge is not changed greatly. Also, the number of parts is not increased as in a case where a sensor for detecting incompatibility is used. Further, the incompatibility of the cartridge can be given by a simple and inexpensive construction to thereby contribute to usability and a lower price. 
     Second Embodiment 
     FIGS. 12 to  14  show a second embodiment. 
     In this embodiment, as a wrong insertion preventing mechanism for preventing an improper cartridge from being inserted, a wrong insertion preventing engagement portion  105  such as a rib or a wall is provided on the upper edge of the opening portion  200  of the main body  100  of the apparatus. The cam portion  58   a  of the shutter  50  of a proper cartridge  2   a  shown in FIG. 12 is free to pass through the opening portion. A long cam portion  58   b  provided on the shutter  50   b  of an improper cartridge  2   b  shown in FIG. 13 comes into engagement with the engagement portion  105  and is rotatively driven. Thereby the shutter  50   b  is opened. 
     That is, the cam portion  58   a  of the shutter  50  of the proper cartridge  2   a  does not come into engagement with the engagement portion  105 , but is inserted into the inner part of the main body  100  of the apparatus. The shutter  50  is opened in operative association with the operation of closing the openable and closable member  101 , as previously described. 
     When the improper cartridge  2   b  is to be inserted into the main body  100  of the apparatus, the cam portion  58   b  of the shutter  50   b  of the cartridge  2   b  is long. Therefore, it abuts against the engagement portion  105 , and the shutter  50   b  performs its opening operation immediately after the cartridge  2   b  has been inserted. Then it strikes against the side (outer wall)  103   c  or the supporting stand  103   a  of the optical unit  103 , and any further insertion is blocked. 
     As shown in FIG. 14, the main body  100   b  of an apparatus on which the cartridge  2   b  is mounted as a proper cartridge is provided with an opening portion sufficient to pass the cam portion  58   b  of the shutter  50   b  of the cartridge  2   b  therethrough. In the process of the cartridge  2   b  being inserted into the inner part with a guide  111   b  by the operation of closing an openable and closable member  101   b , the cam portion  58   b  frictionally contacts with the optical unit  103  of an optical system  1   b  or the supporting stand  103   a . Thereby, the shutter  50   b  is opened at a proper position. Then, as previously described, the protecting portion  51   b  or the like is opened. 
     The one side compatibility of the cartridge can be realized simply by changing the shape of the cam portion of the shutter of the cartridge. 
     That is, the present embodiment not only has action and effect equal to those of the first embodiment, but is effective when incompatibility is required only on one side. 
     The aforedescribed Embodiments 1 and 2 are summed up as follows. 
     The electrophotographic image forming apparatus for forming an image on a recording medium is an electrophotographic image forming apparatus comprising a cartridge mounting portion  114  for detachably mounting thereon a process cartridge  2  provided with a photosensitive drum  11 , process means (at least one of charging means  12 , cleaning means  13  and developing means  20 ) for acting on the photosensitive drum  11 , a shutter  50  having a photosensitive member protecting portion (drum protecting portion  51 ) for protecting the photosensitive drum  11 , and movable between a protecting position for protecting the photosensitive drum  11  and a retracted position retracted from the protecting position to thereby expose the photosensitive drum  11 , and a shutter moving portion (cam portion  58 ) for moving the shutter  50  from the protecting position to the retracted position, guide means (guide  111 ) for guiding the cartridge  2  when the cartridge  2  is mounted on the mounting portion  114 , shutter opening means (optical unit  103 , supporting stand  103   a ) for coming into engagement with the shutter moving portion (cam portion  58 ) to thereby open the shutter  50  from the protecting position to the retracted position when the cartridge  2  is guided by the guide means (guide  111 ) and is moved along a movement path toward the mounting portion  114 , a wrong insertion preventing engagement portion  104 ,  105  adapted to be engaged with the shutter moving portion (cam portion  58 ) and open the shutter  50  on the upstream side of an engagement position at which the shutter moving portion (cam portion  58 ) and the shutter opening means (optical unit  103 , supporting stand  103   a ) are engaged with each other, in a mounting direction in which a cartridge  2 ,  2   a  not matching in function with the main body  100 ,  100   b  of the apparatus is mounted on the mounting portion  114 , when the cartridge  2 ,  2   a  is inserted into the main body  100 ,  100   b  of the apparatus, and a main body shutter abutting portion (optical unit  103 ., supporting bed  103   a ) for abutting against the shutter  50  moved toward the retracted position by the shutter moving portion (cam portion  58 ) being engaged with the wrong insertion preventing engagement portion  104 ,  105 , to thereby restrict the insertion of the cartridge  2 . 
     The wrong insertion preventing engagement portion  104 ,  105  is a peripheral edge portion  200   a  located above an opening portion  200  provided in the main body  100  of the apparatus for inserting the cartridge  2 ,  2   a  into the main body  100  of the apparatus therethrough. 
     Also, the shutter abutting portion (optical unit  103 , supporting stand  103   a ) is a portion of the outer wall  103   c  of the optical unit  103  containing therein an optical system for applying information light to the photosensitive drum  11 , or/and a portion of the optical unit supporting stand  103   a.    
     Also, the process cartridge  2  detachably mountable on the main body  100  of an electrophotographic image forming apparatus is a process cartridge having a photosensitive drum  11 , process means (at least one of charging means  12 , cleaning means  13  and developing means  20 ) for acting on the photosensitive drum  11 , shutter  50  having a photosensitive member protecting portion (drum protecting portion  51 ) for protecting the photosensitive drum  11 , and movable between a protecting position for protecting the photosensitive drum  11  and a retracted position retracted from the protecting position to thereby expose the photosensitive drum  11 , a shutter moving portion (cam portion  58 ) for coming into engagement with shutter opening means (optical unit  103 , supporting stand  103   a ) provided in the main body  100  of the apparatus to thereby move the shutter  50  from the protecting position to the retracted position when the cartridge  2  is mounted on the main body  100  of the apparatus, and coming into engagement with a wrong insertion preventing engagement portion  104 ,  105  provided in the main body  100  of the apparatus to thereby move the shutter  50  from the protecting position to the retracted position, on the upstream side of an engagement position at which the shutter moving portion (cam portion  58 ) and the shutter opening means (optical unit  103 , supporting stand  103   a ) are engaged with each other, in the mounting direction in which the cartridge  2  is mounted on the main body  100  of the apparatus when the cartridge is inserted into the main body  100  of the apparatus which does not match in function with the cartridge  2 ,  2   a , and a cartridge shutter abutting portion  50   f  provided on the shutter  50  for abutting against a main body shutter abutting portion (optical unit  103 , supporting stand  103   a ) provided in the main body  100  of the apparatus to restrict the insertion of the cartridge  2 ,  2   a  into the main body  100  of the apparatus when the shutter  50  is moved toward the retracted position by the shutter moving portion (cam portion  58 ) being engaged with the wrong insertion preventing engagement portion  104 ,  105 . The cartridge shutter abutting portion  50   f  is a portion of the outer surface of the shutter  50  (FIG.  2 ). 
     Third Embodiment 
     FIG. 15 shows a third embodiment. In this embodiment, an insertion guide  106  which is wrong insertion preventing guide means for blocking the wrong insertion of an improper cartridge  2   c  and inserting only a proper cartridge  2  is provided in the main body  100  of the apparatus. 
     For example, the projected portions  31   a  and  32   a  (FIG. 4) of the bottom of the proper cartridge  2  are provided with concave shapes which are wrong insertion preventing guide portions for realizing an insertion locus without interfering with the insertion guide  106 . Only when the improper cartridge  2   c  is inserted, the movement path is changed, and a drum shutter  50   c  is opened near the opening portion  200  of the main body and a drum protecting portion, etc., are opened to thereby prevent any further insertion. 
     A cut-away or the like can simply be provided in the bottom of the process cartridge. This leads to the advantage that it is not necessary to greatly change the size and shape of the frame of the cartridge. In the other points, the present embodiment is similar to the first embodiment. 
     Each of the aforedescribed embodiments to which the present invention is applied is constructed as described above and therefore achieves such effects as will be described below. 
     When a cartridge which does not match in function with the main body of the apparatus is mounted, the shutter opened near the opening portion of the main body of the apparatus strikes against the internal structure of the main body of the apparatus so that the cartridge cannot be inserted any further. Thereby, without resulting in any great change in design on the main body side of the apparatus and the cartridge side, reliable incompatibility can be given at a relatively low cost. Also, it can contribute to an improvement in usability. 
     Here, as the cases where the two do not match in function with each other, mention may be made of the discordance of the process speed of image formation, the presence or absence of the remaining amount detecting function of detecting the remaining amount of the developer, or the difference between a process cartridge for a facsimile apparatus and a cartridge for a laser beam printer, and a case where when a memory is carried on a cartridge, the main body of the apparatus is not provided with the function of effecting communication with the memory. 
     In the aforedescribed embodiments, the shutter opening means and the shutter abutting portion are used in common with each other. That is, any of them is the outer wall  103   c  of the optical unit  103  or the supporting stand  103   a  thereof. In the present invention, however, this is not restrictive, and the shutter opening means and the main body shutter abutting portion need not be used in common with each other. For example, any one of them may be a fixed wall provided in the main body  100  of the apparatus. Also, the two are not restricted to the optical unit  103  and the supporting stand  103   a , but may be, for example, a fixed wall provided in the main body  100  of the apparatus. Also, the shutter moving portion is not restricted to the cam portion  58 , but may be, for example, a portion of a link mechanism. 
     In other words, incompatibility is given by a simple and low-cost construction, whereby the sharing of the parts of the electrophotographic image forming apparatus can be expedited to thereby curtail the manufacturing cost. 
     As in the conventional art, a discriminating sensor or the like for giving incompatibility is not required, and the structure of not only the process cartridge but also the main body of the apparatus is not made complicated. The sharing of the assembling steps and an assembling apparatus among many parts and further, the diversion of the packaging form can also be realized. 
     According to the present invention, the highly reliable wrong mounting prevention of the process cartridge can be realized. 
     While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.