Abstract:
An image forming apparatus, to which a plurality of cartridges are detachably mountable, with the cartridges each having a cartridge side identification portion, includes an image forming unit configured to form an image, a plurality of mounting portions to which the cartridges are demountably mountable, and an identification urging mechanism provided in each of the mounting portions. The identification urging mechanism permits a cartridge to be mounted to the mounting portion when the cartridge is to be properly mounted to the mounting portion on the basis of correspondence with the cartridge side identification portion, and urges the cartridge in a direction opposite a direction in which the cartridge is mounted when the cartridge is improper for the mounting portion. The identification urging mechanism permits, even when the cartridge is improper for the mounting portion, the cartridge to enter to a mount position where the proper cartridge is mounted.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus such as a copy machine, a printer, a facsimile machine, and the like. 
     Among electrophotographic image forming apparatuses which employ two or more process cartridges which are necessary for image formation, some of them are of the so-called inline type. An electrostatic image forming apparatus of the inline type is structured so that multiple process cartridges are sequentially aligned, and also, so that each cartridge is mounted into its designated slot. In other words, an electrophotographic image forming apparatus of this type is structured so that it is impossible for its process cartridges to be mounted into the process cartridge slots other than their designated slot, one for one. Further, even an electrophotographic monochromatic image forming apparatus, that is, an electrophotographic image forming apparatus which employs only one process cartridge, is structured so that it is only a process cartridge which matches the type and specifications of the main assembly of the image forming apparatus that can be mounted in the process cartridge slot of the apparatus. That is, the image forming apparatus is structured so that only a process cartridge which matches in specification and type to the image forming apparatus can be mounted in its process cartridge; a process cartridge which is different in function from the cartridge designated thereto cannot be mounted in the process cartridge slot of the apparatus. 
     Thus, there have been proposed many structural designs for preventing a process cartridge from being mounted into a wrong process cartridge slot. For example, the process cartridge slots of an electrophotographic image forming apparatus are provided with a cartridge screening portion, for example, a recess or projection, and not only are the cartridge slots made different in the position and/or shape of the cartridge screening portion, but also, the position and/or shape of the cartridge screening portion are made to correspond to the color of the toner in a process cartridge (Japanese Laid-open Patent Application 2003-084534). 
     The conventional technologies such as the one described above suffer from the following problem: Process cartridges and the main assembly of an electrophotographic image forming apparatus have to be made sturdy enough not to deform or break even if a process cartridge is mounted into a wrong cartridge slot. Thus, the process cartridges and the main assembly of an electrophotographic image forming apparatus may have to be larger in size. 
     SUMMARY OF THE INVENTION 
     Thus, the primary object of the present invention is to provide an electrophotographic image forming apparatus, which not only makes it easier for a user to recognize that a cartridge was inserted into a wrong cartridge slot of the image forming apparatus, or the cartridge in a cartridge slot of the image forming apparatus is a wrong one, but also, can prevent, without requiring the apparatus to be increased in size, the problem that when a cartridge is inserted into a wrong cartridge slot, or a cartridge which is being inserted into a cartridge slot is a wrong one for the cartridge slot, the main assembly of the image forming apparatus and/or the cartridge is deformed or damaged. 
     According to an aspect of the present invention, there is provided an image forming apparatus to which a plurality of cartridges are detachably mountable, the cartridges each having a cartridge side identification portion, said image forming apparatus comprising a plurality of mounting portions to which said cartridges are demountably mountable; and an identification urging means, provided in each of said mounting portions, for permitting a cartridge to be mounted to said mounting portion when said cartridge is properly to be mounted to said mounting portion on the basis of correspondence with said cartridge side identification portion, and for urging said cartridge in a direction opposite a direction in which said cartridge is mounted when said cartridge is improper for said mounting 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  is a schematic sectional view of the image forming apparatus in the first preferred embodiment of the present invention, and shows the general structure of the apparatus. 
         FIG. 2  is a schematic sectional view of the process cartridge in the first embodiment, and shows the general structure of the cartridge. 
         FIG. 3  is a perspective view of a combination of the image forming apparatus in the first embodiment and one of the process cartridges therefor, and shows how the process cartridge is mounted into, or removed from, the main assembly of the image forming apparatus. 
         FIG. 4  is a partial perspective view of a combination of one of the process cartridge slots of the image forming apparatus in the first embodiment, and the corresponding process cartridge, and shows how the cartridge is mounted into the cartridge slot. 
         FIG. 5  is a drawing for describing the changes which occur to the positional relationship between the cartridge positioning projection of a cartridge and the cartridge positioning torsional coil spring of the cartridge slot of the image forming apparatus, and the changes which occur to the shape of the torsional coil spring, in the first embodiment. 
         FIG. 6  is a perspective view of the process cartridge installation error preventing means, and its adjacencies, of the image forming apparatus in the first embodiment. It is for showing the structure and working of the means. 
         FIG. 7  also is a perspective view of the process cartridge installation error preventing means, and its adjacencies, of the image forming apparatus in the first embodiment. It is for showing the structure and working of the means. 
         FIG. 8  is a drawing for describing the changes which occur to the positional relationship between the cartridge positioning projection of a cartridge and the cartridge positioning torsional coil spring of the cartridge slot of the image forming apparatus, the changes which occur to the positional relationship between the cartridge identification projection and the cartridge positioning torsional coil spring, and the changes which occur to the shape of the cartridge positioning torsional spring, in the second preferred embodiment of the present invention. 
         FIG. 9  is a perspective view of the combination of one of the process cartridges, and the lengthwise ends of a couple of the process cartridge slots of the image forming apparatus in the second embodiment, and shows the structure of the combination. 
         FIG. 10  is a combination of a perspective view of one of the lengthwise ends of one of the process cartridges in the second embodiment, and the corresponding lengthwise end of the corresponding cartridge, and shows the process cartridge installation error preventing means. 
         FIG. 11(   a ) is a perspective view of the process cartridge in the third preferred embodiment of the present invention, and shows the general structure of the cartridge.  FIG. 11(   b ) is a perspective view of two of the left cartridge guides  110  in the third embodiment, and shows the structure of the left cartridge guide  110 . 
         FIG. 12  is a combination of a partial perspective view of one of the lengthwise ends of the process cartridge, and a partially phantom perspective view of the corresponding cartridge slot, and shows how the cartridge is mounted into the cartridge slot. 
         FIG. 13  is a drawing for describing the changes which occur to the positional relationship between the cartridge positioning projection of a cartridge and the cartridge locking member of the cartridge slot of the image forming apparatus, the changes which occur to the positional relationship between the cartridge identification projection and the cartridge locking member, and the changes which occur to the state of the tension spring for the cartridge locking member, when the cartridge is installed in a correct cartridge slot, in the third preferred embodiment of the present invention. 
         FIG. 14  is a drawing for describing the changes which occur to the positional relationship between the cartridge positioning projection of a cartridge and the cartridge locking member of the cartridge slot of the image forming apparatus, the changes which occur to the positional relationship between the cartridge identification projection and the cartridge locking member, and the changes which occur to the state of the tension spring for the cartridge locking member, when the cartridge is installed in a wrong cartridge slot, in the third preferred embodiment of the present invention. 
         FIGS. 15(   a ),  15 ( b ) and  15 ( c ) are sectional views of a combination of the left cartridge guide of one of the cartridge slots of the image forming apparatus, and the left end of the cartridge therein, in the first preferred embodiment of the present invention, at a plane which is parallel to the bottom or top wall of the image forming apparatus. They describe the changes which occur to the relationship between the cartridge positioning projection of a cartridge, and the cartridge position controlling portion  155  of the left guide of one of the cartridge slots of the image forming apparatus, when the cartridge is inserted into, or removed from, the cartridge slot, in the first preferred embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     First, referring to  FIG. 1 , the first preferred embodiment of the image forming apparatus in accordance with the present invention is described.  FIG. 1  is a schematic sectional view of the image forming apparatus in this embodiment, and shows the general structure of the apparatus. The image forming apparatus  100  has four photosensitive drums ( 1   a - 1   d ), as image bearing members, which are vertically aligned in tandem. The photosensitive drums  1  ( 1   a - 1   d ) are rotated by an unshown driving means. The image forming apparatus  100  has also an electrostatic transfer belt  11 , which is circularly moved in contact with all the photosensitive drums  1 . 
     Next, referring to  FIG. 2  along with  FIG. 1 , the apparatus  100  has four image forming stations. Each image forming station has a charge roller  2 , a scanner unit  3  ( 3   a ,  3   b ,  3   c  or  3   d ), a development unit  4 , an electrostatic transferring device  5 , and a cleaning device  6 , which are in the listed order in the adjacencies of the peripheral surface of the photosensitive drum  1 . The photosensitive drum  1 , charge roller  2 , development unit  4 , and cleaning device  6  are integrally placed in a cartridge, making up a process cartridge  7  ( 7   a ,  7   b ,  7   c  or  7   d ). Hereafter, each process cartridge  7  may be referred to simply as a cartridge  7 . 
     Referring also to  FIGS. 1 and 2 , the cartridges  7  are sequentially driven with their image formation timing. As each cartridge  7  is driven, the photosensitive drum  1  ( 1   a ,  1   b ,  1   c  or  1   d ) in the cartridge  7  is rotated in the counterclockwise direction, and the corresponding scanner unit  3  ( 3   a ,  3   b ,  3   c  or  3   d ) is driven. As the cartridge  7  and scanner unit  3  are driven, the peripheral surface of the photosensitive drum  1  is uniformly charged by the charge roller  2 , and the uniformly charged portion of the peripheral surface of the photosensitive drum  1  is scanned by a beam  30  ( 30   a ,  30   b ,  30   c  or  30   d ) of laser light projected by the scanner unit  30 . As a result, an electrostatic latent image is formed on the uniformly charged portion of the peripheral surface of the photosensitive drum  1 . Then, the latent image is developed by the development roller  40  in the development unit  4  into a toner image, that is, an image formed of toner. 
     Meanwhile, one of the sheets  9  of recording medium stored in layers in a sheet feeder cassette  8  is conveyed to the electrostatic transferring device  5 , and is conveyed through the device  5 , in synchronism with the progression of the sequential formation of the toner images, while a preset voltage is applied to the transfer roller  12  ( 12   a ,  12   b ,  12   c  or  12   d ). As a result, the toner image on the photosensitive drum  1  ( 1   a ,  1   b ,  1   c  or  1   d ) is transferred onto the sheet  9  of recording medium. Since the four image forming stations are sequentially operated, the four toner images, different in color, are sequentially transferred in layers onto the sheet P. After the transfer of the four toner images, different in color, onto the sheet  9 , the sheet  9  is conveyed to a fixing device  10 , and is conveyed through the fixing device  10 , while being subjected to the heat and pressure applied thereto by the fixing device  10 . As a result, the toner images on the sheet  9  are fixed to the sheet  9 . Then, the sheet  9  is discharged into a delivery tray  13 , which is an integral part of the top wall of the image forming apparatus  100 . 
     [Cartridge Installation into Apparatus Main Assembly, and Cartridge Removal from Apparatus Main Assembly] 
     Referring to  FIG. 3 , the image forming apparatus  100  has multiple (four) cartridge slots  101  ( 101   a - 101   d ) in which the multiple (four) cartridges  7  are removably installable. In consideration of the service life of each component (photosensitive drum  1 , charge roller  2 , development roller  40 , etc.) in the cartridge  7 , which is directly related to an image formation process; the service life of the toner in the cartridge  7 , also, the service life of the toner in the cartridge  7 , which also is directly related to an image formation process; and the amount of toner usage, each cartridge  7  is replaced with a brand-new one as the cumulative length of its usage reaches a preset value, or cumulative number of images formed with the use of the cartridge  7  reaches a preset value. As for the method for replacing the cartridge  7 , first, the front cover  14  of the image forming apparatus  100  is to be opened, and then, the cartridge which needs to be replaced is to be pulled out of its slot  101  ( 101   a ,  101   b ,  101   c  or  101   d ) of the image forming apparatus  100 . Then, a brand-new cartridge  7 , which matches the removed cartridge  7 , is to be inserted into the vacated cartridge slot  101 , in such an attitude that the photosensitive drum  1  in the cartridge  7  will be on the front side of the main assembly of the apparatus  100 , in the direction (indicated by arrow mark E) perpendicular to the front wall of the main assembly. 
     The image forming apparatus  100  has an opening  102  through which the cartridges  7  ( 7   a - 7   d ) are installed into, or removed from, the apparatus  100 . It has also left guides  110  ( 110   a - 110   d ) and right guides  120  ( 120   a - 120   d ), which are for guiding cartridges  7  ( 7   a ,  7   b ,  7   c  and  7   d ) into the cartridge slots  101  ( 101   a ,  101   b ,  101   c  and  101   d ), respectively, in the image forming apparatus  100 . The left and right guides  110  and  120  are on the left and right ends of the opening  102 , one for one. 
     Next, referring to  FIG. 4 , each cartridge  7  is provided with a cartridge positioning projection  71  and a boss  72 , which project outward from the lengthwise end surfaces of the cartridge  7 , one for one. The axial line of the projection  71  coincides with the axial line of the photosensitive drum  1 . The projection  71  is for precisely positioning the cartridge  7  relative to the image forming apparatus  100 . The boss  72  is at the leading end of the cartridge  7  in terms of the direction in which the cartridge  7  is inserted into the image forming apparatus  100 . It is for properly positioning the cartridge relative to the image forming apparatus  100  in terms of its attitude. When it is necessary to install any of the cartridges  7  into the corresponding cartridge slot  101 , the cartridge  7  is to be inserted so that the boss  72  fits into the groove  111  of the left guide  110 , and then, the projection  71  rides onto the cartridge positioning surface  112  of the left guide  110 . Next, referring to  FIGS. 4 and 15(   a ), each cartridge slot  101  is provided with a projection  115  for preventing the problem that in a case where a cartridge  7  is inserted into a wrong cartridge slot  101 , it falls out of the cartridge slot  101  as soon as an installer releases the cartridge  7 . The projection  115  is flexible, and is at the front end of the groove  111 . Thus, as a cartridge  7  is inserted into the corresponding cartridge slot  101  in the direction indicated by an arrow mark D, the boss  72  comes into contact with the slanted surface  155   a  of the cartridge position controlling portion  155 , which is on the entrance side of the projection cartridge screening member  16 . Then, as the cartridge  7  is inserted deeper, the projection cartridge screening member  16  is flexed by the boss  72  in the direction indicated by an arrow mark S, that is, the direction to give away to the boss  72  ( FIG. 15(   b )), allowing thereby the boss  72  to ride over the projection cartridge screening member  16  and enter the groove  111  ( FIG. 15(   c )). Then, as the cartridge  7  is inserted all the way into the cartridge slot  101 , the projection  71  is pressed upon the cartridge positioning surfaces  112  and  113  of the left guide  110 , by a torsional coil spring  15  with which the main assembly of the image forming apparatus  100  is provided. As a result, the cartridge  7  is properly positioned relative to the image forming apparatus  100 . 
     Next, referring to  FIG. 5(   e ), the torsional coil spring  15  is rotationally fitted around the boss  114  with which the left guide  110  is provided. The anchorage end  156  of the torsional coil spring  15  is fitted in a hole  117  of the left guide  110 , being thereby immovably attached to the left guide  110 . When the spring  15  is fitted around the boss  114 , it is torqued in such a direction that as it is pressed by the boss  72  as described above, it presses the cartridge positioning projection  71  toward the cartridge positioning surfaces  112  and  113  (moment generated by spring  15  works in direction indicated by arrow mark P). The other end  157  of the spring  15  is loosely fitted in a groove  103  with which the cartridge slot  101  is provided. Thus, it is prevented from rotationally moving in the direction indicated by the arrow mark P. The spring  15  is shaped so that its portion between its coiled portion  158  and its lengthwise end  157  (loosely fitted in groove  103 ) is bent by roughly 90 degrees, and the portion between the point of bend and the coiled portion  158  functions as the portion  151  for pressing the cartridge positioning projection  71 , and the portion between the lengthwise end  157  and the point of bend functions as the portion  152  by which the lengthwise end  157  is pushed upward. 
     Referring to  FIG. 5(   a ), as a cartridge  7  is inserted into its correct cartridge slot in the image forming apparatus  100 , first, the projection  71  comes into contact with the portion  152  of the spring  15 , by which the spring  15  is pushed upward. Next, referring to  FIG. 5(   b ), as the cartridge  7  is inserted further, the projection  71  pushes up the portion  152  of the spring  15  in the direction indicated by an arrow mark R, against the resiliency of the spring  15 . Then, as the cartridge  7  is inserted into the cartridge slot even further, the projection  71  moves past the point of bend of the spring  15 , and comes into contact with the cartridge positioning (pressing) portion  151  of the spring  15 , being thereby properly positioned relative to the image forming apparatus  100 , as shown in  FIG. 5(   c ). As the projection  71  comes into contact with the surfaces  112  and  113  and is pressed upon the surfaces  112  and  113  by the cartridge positioning portion  151  of the spring  15  in the direction (indicated by arrow mark P), the cartridge  7  is properly positioned for image formation, in the cartridge slot  101 . The shape of the lengthwise end  157  of the spring  15 , and the shape of the groove  103 , are such that when the projection  71  is in contact with the surfaces  112  and  113 , there is a certain amount of gap between the lengthwise end portion  157  of the spring  15  and the corresponding surface of the groove  103 , as shown in  FIG. 5(   d ). Therefore, the cartridge positioning portion  151  of the spring  15  can keep the projection  71  in contact with the surfaces  112  and  113 , whereby the cartridge  7  can be kept properly positioned for image formation, in the cartridge slot  101 . 
     [Means for Preventing Cartridge Installation Errors] 
     Referring to  FIG. 6 , each of the cartridges  7  ( 7   a - 7   d ) has an identification recess (cartridge identification portion of cartridge)  73  ( 73   a - 73   d ). The identification recess  73  is at the leading end of the cartridge  7 , in terms of the cartridge installation direction (indicated by arrow mark D). The shape and/or position of the identification recess  73  corresponds to the color of the toner in a cartridge  7 . That is, the identification recess  73  for a cartridge  7  which contains yellow toner, for example, is different in shape from those for cartridges  7  which contain other toners than yellow toner. More specifically, in this embodiment, the four process cartridges  7   a ,  7   b ,  7   c , and  7   d  are made different in the position of the identification recess  73 , in terms of the direction parallel to the front (rear) wall of the main assembly of the image forming apparatus  100 , so that each cartridge  7  can be identified, in terms of toner color, based on the positioned of its identification recess  73 . 
     As for the cartridge slots  101  ( 101   a - 101   d ) of the image forming apparatus  100 , they are provided with cartridge screening members  16  ( 16   a - 16   d ), one for one, which are different in position in terms of the direction parallel to the front (or rear) wall of the main assembly of the image forming apparatus  100 , and the position of which corresponds to the color of the toner in the cartridge  7 . The cartridge screening member  16  is attached to the rear wall  18  ( 18   a ,  18   b ,  18   c , or  18   d ) of the cartridge slot  101 . It is fitted with a compression spring  17  ( 17   a ,  17   b ,  17   c  or  17   d ), which keeps the cartridge screening member  16  pressed in the opposite direction (indicated by arrow mark E) from the cartridge installation direction. 
     Next, referring to  FIG. 6(   a ), as the cartridge  7   b , for example, is inserted all the way into the cartridge slot  101   b , that is, the correct cartridge slot for the cartridge  7   b , the cartridge screening member  16   b  fits into the identification recess  73   b , and therefore, the compression spring  17   b  is not compressed. At the same time, the torsional coil spring  15   b  presses the cartridge positioning projection  71   b  on the cartridge positioning surfaces  112   b  and  113   b , ending the installation of the cartridge  7   b.    
     However, if the cartridge  7   b  is inserted into the cartridge slot  101   a , that is, one of the wrong slots for the cartridge  7   b , as shown in  FIG. 6(   b ), the cartridge screening member  16   a  does not coincide in position to the identification recess  7   b . Thus, the cartridge screening projection  16   a  comes into contact with the front surface  74   b  of the cartridge  7   b  in terms of the cartridge insertion direction. Thus, as the cartridge  7   b  is pushed further inward, the cartridge  7   b  moves all the way into the cartridge slot  101   a  while pressing the cartridge screening projection  16   a  by the leading end (surface  74   b ) against the resiliency of the torsional coil spring  17   a , until the cartridge positioning projection  71   b  is pressed on the cartridge positioning surfaces  112   a  and  113   a  by the torsional coil spring  15   a . Regarding the relationship between the amount of force which the resiliency of the compression spring  17   a  generates in the upstream direction (indicated by arrow mark E), in terms of the cartridge insertion direction, and the amount of force which the spring  15   a  generates in the downstream direction (indicated by arrow mark D) in terms of the cartridge insertion direction, the image forming apparatus  100  is designed so that the former overwhelms the latter. Thus, if a user releases the cartridge  7   b  after the user pushed the cartridge  7   b  all the way into the cartridge slot  7   a , the cartridge  7   b  is pushed back in the direction of the arrow mark E by the resiliency of the compression spring  17   a  against the resiliency of the spring  15   a . As the cartridge  7   b  is pushed back, the boss  72   a  comes into contact with the cartridge blocking surface cartridge blocking surface  155   a  of the cartridge position controlling portion  155 , being thereby prevented from moving further in the direction indicated by the arrow mark E, as shown in  FIG. 15(   c ). In other words, the cartridge  7   b  is prevented from falling out of the main assembly of the image forming apparatus  100 . At this point, the cartridge  7   b  is still under the pressure applied to the cartridge  7   b  by the compression spring  17   a  in the direction of the arrow mark E, but, the amount of pressure applied to the cartridge  7   b  by the compression spring  17   a  at this point of the action of the cartridge  7   b  is not large enough to force the cartridge position controlling portion  155  to deform in the direction indicated by the arrow mark S. Thus, if a user wants to take the cartridge  7   b  out of the cartridge slot  101   a  at this point, the user has to move the cartridge  7   b  further in the direction of the arrow mark E. As the user moves the cartridge  7   b  further in the direction of the arrow mark E, the boss  72  presses on the surface  155   b , causing thereby the cartridge position controlling portion  155  to elastically bend (direction of arrow mark S in  FIG. 15(   b )). Thus, the boss  72  is allowed to ride over the portion  155  to come out of the groove  111  ( FIG. 15(   a )). Incidentally, if it is desired to ensure that the cartridge  7   b  is prevented from accidentally falling out of the main assembly of the image forming apparatus  100 , the surface  155   a  may be made greater in angle than the surface  155   b , provided that the increase in the angle of the surface  155   a  does not become problematic in terms of the extraction of the cartridge  7   b  from the cartridge slot  101   a . 
     In the case of this embodiment of the present invention, even if a cartridge  7  ( 7   a ,  7   b ,  7   c  or  7   d ) is inserted into a wrong cartridge slot  101  ( 101   a ,  101   b ,  101   c  or  101   d ), that is, the cartridge slot  101  which is not for the cartridge  7 , it is allowed to advance all the way into the wrong cartridge slot  101  as shown in  FIG. 6(   a ). Therefore, it is unlikely for a user to apply an excessive amount of force to the cartridge  7  when installing the cartridge  7 . Further, as the user releases the cartridge  7  ( 7   a ,  7   b ,  7   c  or  7   d ) after the user inserted the cartridge  7  all the way into the wrong cartridge slot  101 , the cartridge  7  is pushed back by the resiliency of the compression spring  17  ( 17   a ,  17   b ,  17   c  or  17   d ) in the direction of the arrow mark E. Thus, it is easy for the user to recognize the installation error. Moreover, as the cartridge  7  is pushed back by the spring  17 , it is prevented by the cartridge position controlling portion  155  from falling out of the main assembly of the image forming apparatus  100 . In other words, the present invention can prevent the cartridge damages attributable to the problem that when a cartridge  7  is inserted into a wrong cartridge slot of an image forming apparatus, it falls out of the main assembly. Further, the components for preventing the aforementioned installation error are elastic. Therefore, even if a user forces a cartridge  7  into a wrong cartridge slot of an image forming apparatus, the cartridge and/or the main assembly of the image forming apparatus are unlikely to be damaged. 
     In this embodiment, the cartridge identification recess  73  as a cartridge identification marker was at the leading end of each cartridge  7  in terms of the cartridge insertion direction indicated by the arrow mark D. However, a cartridge identification marker may be in the form of a projection  731  as shown in  FIG. 7 . In a case where a projection  731  ( 731   a ,  731   b ,  731   c  or  731   d ) as a cartridge identification marker is attached to a cartridge  7 , each cartridge slot of an image forming apparatus is provided with a cartridge screening plate  161  ( 161   a ,  161   b ,  161   c  or  161   d ). More specifically, the cartridge screening plate  161  is provided with a through hole  162  ( 162   a ,  162   b ,  162   c  or  162   d ), which corresponds in position to the cartridge identification projection  731  in terms of the direction parallel to the front wall of the image forming apparatus  100 . Further, the cartridge screening plate  161  is attached to a pair of compression springs  171  (screening plate supporting/pressing means), which are attached to the rear wall of the cartridge slot  101 . Thus, when a given cartridge  7  is inserted into the correct cartridge slot for the given cartridge, its identification projection  731  enters the through hole  162 , and therefore, the compression springs  171  are not compressed. Further, as soon as the cartridge  7  is inserted all the way into the cartridge slot, the torsional coil spring  15  presses the cartridge positioning projection  71  on the cartridge positioning surfaces  112  and  113 , ending thereby the cartridge installation. On the other hand, if a given cartridge  7  is inserted all the way into a cartridge slot which is incorrect for the given cartridge  7 , the identification projection  731  comes into contact with the screening plate  161 . Thus, the compression springs  171  are compressed. Then, as a user releases the cartridge  7 , the cartridge  7  is pushed back in the direction indicated by the arrow mark E by the resiliency of the compression springs  171  against the resiliency of the spring  15 . 
     Incidentally, not only is this means for preventing installation error employable by an electrophotographic image forming apparatus of the inline type, such as the one in this embodiment, but also, an electrophotographic monochromatic image forming apparatus, an electrophotographic color image forming apparatus of the rotary type, and the like, to find out whether or not a given cartridge is different in type or specification from a cartridge for a given electrophotographic image forming apparatus. In a case where this installation error preventing means is employed by an electrophotographic color image forming apparatus such as the one in this embodiment, the following effects which are specific to this type of image forming apparatus are obtained. That is, if one of the process cartridges for an electrophotographic image forming apparatus of the inline type, in which multiple process cartridges are positioned in tandem, is installed in a wrong cartridge slot of the apparatus, this cartridge protrudes a little compared to the cartridges in their correct slots as soon as the installer release the cartridge. Therefore, even if the amount by which a cartridge is made to protrude by its installation into a wrong cartridge slot is small, the installation error can be easily recognized. 
     Further, in this embodiment, the means for preventing the process cartridge installation error is used for preventing a process cartridge having a photosensitive drum from being installed in a wrong cartridge slot. However, this embodiment is not intended to limit the application of the present invention to a process cartridge having a photosensitive drum. That is, the present invention can also be applied to a developing device cartridge, a developer supply cartridge, and the like. In other words, the present invention is applicable to any cartridge or the like which is to be removably installed in the image assembly of an apparatus by a user. 
     Embodiment 2 
     Next, the image forming apparatus in the second preferred embodiment of the present invention is described with reference to the appended drawings. The components, portions, etc., of the image forming apparatus in this embodiment, which are the same in description as the counterparts in the first embodiment, are given the same referential codes as those given to the counterparts, and are not going to be described here.  FIG. 9(   a ) is a perspective view of the process cartridge in the second embodiment.  FIG. 9(   b ) is a perspective view of two of the left cartridge guides  110  in the second embodiment. 
     Referring to  FIG. 9(   a ), the left cartridge guide  110  in this embodiment is provided with a combination of an identification projection  75  (cartridge identifying means on cartridge side) and a torsional coil spring  19 , instead of the combination of the identification recess  73  and torsional spring  15  in the firsts embodiment. 
     The cartridges  7   a ,  7   b ,  7   c , and  7   d  are made different (specific) in the position of their identification projection  75  in terms of the direction indicated by an arrow mark F, which is roughly perpendicular to both the direction indicated by an arrow mark D and the axial line of the photosensitive drum  1 , so that they can be identified in terms of the color of the toner they contain. 
     Next, referring to  FIG. 9(   b ), like the torsional coil spring  15  in the first embodiment, the torsional coil spring  19  also has a cartridge positioning portion  191 , a cartridge catching portion  192  (by which spring  19  is pushed upward by cartridge positioning projection), an anchorage portion  196 , and a semi-free end portion  197  (loosely fitted in groove  103 ). Further, the four torsional coil springs  19  are provided with a cartridge screening portion  193  (cartridge screening/pressure applying means), and are different in the position of the cartridge screening slot portion  195  of the cartridge screening portion  193 . The cartridge screening portion  193  is the portion of the torsional coil spring  19 , which is between the cartridge catching portion  192  and semi-free portion  197 . It prevents a cartridge slot from accepting a wrong cartridge. The cartridge screening portion  193  has a cartridge contacting portion  194  and the U-shaped cartridge screening slot  195  (cartridge identification projection acceptance slot). The four torsional coil springs  19   a ,  19   b ,  19   c , and  19   d  are made different in the position of the U-shaped cartridge screening portion  195  so that the U-shaped portion  195  does not interfere with the cartridge identification projection  75  of a given cartridge only when the given cartridge is the right one. That is, if the cartridge  7  inserted into a given cartridge slot is a wrong one, the cartridge identification projection  75  of the cartridge  7  comes into contact with the cartridge blocking portion  194  of the torsional coil spring  19 . Thus, the cartridge  7  is prevented from entering further into the cartridge slot. 
     Next, referring to  FIG. 10(   a ), when the cartridge  7   a  is inserted into the cartridge slot  101   a , that is, the correct cartridge slot, the cartridge identification projection  75   a  is not hung up by the cartridge blocking portion  194   a ; the U-shaped portion  195   a  allows the cartridge identification projection  75   a  to pass. As the projection  75   a  passes through the U-shaped portion  195   a , the cartridge positioning projection  71   a  pushes up the torsional coil spring  19   a  by the cartridge contacting portion  192   a  of the coil spring, and the cartridge  7  moves into its image forming position, as in the first embodiment. 
     On the other hand, as a user tries to install the cartridge  7   a  into the cartridge slot  101   b , for example, that is, a wrong one, as shown in  FIGS. 10(   b ) and  8 ( a ), the identification projection  75   a  comes into contact with the cartridge blocking portion  194   b  before the cartridge positioning projection  71   a  comes into contact with the cartridge blocking portion  194   b . As the cartridge  7   a  is inserted further into the cartridge slot  101   b , the cartridge blocking portion  194   b  continues to block the identification projection  75   a . Consequently, the torsional coil spring  19   b  is elastically bent at its bend between the cartridge screening portion  193   b  and cartridge contacting portion  19   b  (by which coil spring  19   b  is pushed upward) in such a manner that the semi-free end portion  197   b  moves in the direction indicated by an arrow mark Q. Then, as the cartridge  7   a  is inserted further, the torsional coil spring  19   b  is further bent at its bend  192   b  in the direction of the arrow mark Q, and the cartridge screening portion  193   b  is tilted in the direction indicated by the arrow mark S. Consequently, the torsional coil spring  19   b  is torqued in such a direction (indicated by arrow mark P) that the portion  192   b  (by which spring  19   b  is pushed upward) comes into contact with the projection  71   a  and presses the projection  71   a  toward the cartridge positioning surface  112   b , as shown in  FIG. 8(   c ). At this point in the cartridge insertion, it becomes impossible for the torsional coil spring  19   b  to deform and/or to be further torqued, and therefore, the cartridge  7   a  is prevented from being inserted further. If the user releases the cartridge  7   a  at this point, the torsional coil spring  19   b , which is in the state in which it is elastically deformed in the direction indicated by the arrow mark Q, generates such a force that the portion  194   b  pushes back the identification projection  75   a  toward the entrance of the cartridge slot  101   b  (indicated by arrow mark E). Thus, the cartridge  7   a  moves in the direction of the arrow mark E. 
     Since the cartridges  7   a - 7   d  are made different in the shape and position of their identification portion  72  and projection  71  according to the color of the toner they contain, they can be installed only in the cartridge slots  101   a - 101   d , respectively. Therefore, regardless of which of the cartridges  7   a - 7   d  is inserted into a wrong cartridge slot  101 , or in which of the cartridge slots  101   a - 101   d  a wrong cartridge  7  is inserted, the same effects as those described above can be obtained. 
     In this embodiment, the torsional coil spring  19  plays two roles. That is, in a case where a given cartridge  7 , which is being inserted into a given cartridge slot  101 , is a correct one for the cartridge slot  101 , the torsional spring  19  plays the role of pressure applying means for properly positioning the cartridge  7  relative to the main assembly of the image forming apparatus  100 , for image formation, whereas in a case where the cartridge  7  is not the correct one for the cartridge slot  101 , the torsional spring  19  plays the role of pressure applying means for pressing the cartridge  7  toward the entrance of the cartridge slot  101 . 
     Further, in this embodiment, even when a cartridge  7 , which is being inserted in a given cartridge slot  101 , is a wrong one for the cartridge slot  101 , the cartridge  7  can be inserted into the cartridge slot  101  almost all the way. Therefore, it is unlikely for the cartridge  7  to be subjected to an excessive amount of force by a user (installer). In the first embodiment, if a cartridge  7 , which is being inserted into a given cartridge slot  101 , happens to be a wrong one for the cartridge slot  101 , the cartridge  7  has to be inserted against the cartridge screening-pressing means (compression spring  17 ) which is greater in the amount of resiliency than the positioning-pressing means (torsional coil spring  15 ). In comparison, in this embodiment, in a case where a cartridge  7  is inserted into a wrong cartridge slot  101  and is pushed back toward the entrance of the cartridge slot  101 , it is not necessary for the cartridge screening-pressure applying means to press the cartridge  7  against the positioning-and-pressure applying means. Therefore, the cartridge screening-pressure applying means in the second embodiment can be set to be lower in the amount of resiliency than the counterpart in the first embodiment. That is, this embodiment is smaller in the amount of the force necessary for a user to apply to a cartridge to install a cartridge  7  into the image forming apparatus  100 , and the amount of the load to which the identifying-pressure applying means and adjacent components are subjected when the cartridge  7  is installed. Moreover, in the second embodiment, a single component plays both the role of the positioning-pressure applying means and the role of the cartridge screening-pressure applying means. Therefore, the image forming apparatus in this embodiment is smaller in the component count. 
     Further, in this embodiment, the torsional coil spring  19  was at the entrance of each cartridge slot  101 , and was on the left inward surface of the cartridge slot  101 . However, the torsional coil spring  19  may be placed on both the left and right inward surfaces of each cartridge slot  101 . Placing the torsional coil spring  19  on both the left and right inward surfaces of each cartridge slot  101  makes it possible for a cartridge  7  to be pushed back from within the cartridge slot  101  in parallel to the main assembly of the image forming apparatus  100 . Further, in a case where both the left and right inward surfaces of each cartridge slot  101  is provided with the torsional coil spring  19 , the two torsional coil springs  19  may be made different in shape to increase the image forming apparatus  100  in the number of the process cartridges therefor, which can be screened by the apparatus  100 . 
     Referring to  FIG. 9 , also in this embodiment, each cartridge slot  101  is provided with the cartridge position controlling portion  155  for preventing the problem that a process cartridge  7  accidentally falls out of the main assembly of the image forming apparatus  100 , as in the first embodiment. Therefore, it does not occur that when a cartridge  7  inserted into a wrong cartridge slot  101  is pushed back, it falls out of the main assembly of the image forming apparatus. 
     Embodiment 3 
     Next, the third preferred embodiment of the present invention is described with reference to the appended drawings. The components, their portions, etc., of the image forming apparatus in this embodiment, which are the same in description as the counterparts in the first embodiment, are given the same referential codes as those given to the counterparts, and are not going to be described here.  FIG. 11(   a ) is a perspective view of the process cartridge in this embodiment.  FIG. 11(   b ) is a perspective view of the two of the left cartridge guides  110  in this embodiment. 
     Referring to  FIGS. 11(   a ) and  11 ( b ), in this embodiment, a cartridge identification projection  76  is provided in place of the cartridge identification recess  73 , which is provided in the first embodiment. Further, a combination of a cartridge locking member  20  and a tension spring  21  (cartridge screening means) is provided in place of the torsional coil spring  15  in the first embodiment. 
     In terms of the direction indicated by an arrow mark D, the identification projection  76  is on the same lateral wall of the cartridge  7  as the one on which the cartridge positioning projection  71  is. It is on the downstream side of the projection  71 . The four cartridges  7   a ,  7   b ,  7   c , and  7   d  are made different in the position of the identification projection  76 , in terms of the direction which is indicated by an arrow mark F and is roughly perpendicular to the rotational axis of the photosensitive drum  1  and the direction of the arrow mark D. That is, the position of the identification projection  76  corresponds to the color of the toner in a cartridge  7 . 
     As for the cartridges slot  101 , the left guide  110  of each cartridge slot  101  is provided with the cartridge locking member  20 , which is supported by a shaft  116  so that it is rotatable about the shaft  116 . Each cartridge slot  110  is also provided with the tension spring  21 , which is anchored to a spring hanger  104  and one end of the locking member  20 , remaining thereby tensioned (stretched). The locking member  20  has a pressure applying portion  201  for properly positioning, and keeping properly positioned, a cartridge  7 , and a portion  202  by which the locking member  20  is pushed upward by a cartridge  7 . Thus, the aforementioned one end of the locking member  20  is under the tensile force from the tension spring  21  (remaining pulled by spring  21 ). Therefore, as a cartridge  7  is inserted all the way into a cartridge slot  101 , the positioning-pressure applying portion  201  of the locking member  20  presses the projection  71  of the cartridge  7  toward the cartridge positioning surfaces  112  and  113  (as indicated by arrow mark P). As for the portion  202  by which the locking member  20  is pushed upward by a cartridge  7 , as a cartridge  7  is inserted into a cartridge slot  101 , the positioning projection  71  comes into contact with the portion  202 , and pushes the portion  202  against the resiliency of the tension spring  20  so that the locking member  20  rotates in the direction indicated by an arrow mark R. 
     Further, the locking member  20  is provided with a cartridge screening portion  203 , which is the portion between the end of the locking member  20 , to which the tension spring  21  is anchored, and the portion of the locking member  20 , at which the locking member  20  is supported by the shaft  116 . The cartridge screening portion  203  has a cartridge blocking portion  204  and a cartridge screening slot  205 . The slot  205  is for allowing the identification projection  76  of only a correct cartridge  7  to pass the cartridge screening portion  203 . That is, the cartridge slots  101   a ,  101   b ,  101   c , and  101   d  are made different in the position of the cartridge screening slot  205  so that the position of the slot  205  corresponds to the color of the toner in each cartridge  7 . In other words, when a cartridge  7 , which is being inserted into a given cartridge slot  101 , is a wrong one for the cartridge slot  101 , the identification projection  76  of the cartridge comes into contact with the cartridge blocking portion  204 , preventing thereby the cartridge  7  from being inserted further. 
     Next, referring to  FIGS. 12 and 13(   a ), when the cartridge  7   a  is inserted into the cartridge slot  101   a , that is, the correct one, the positioning projection  71   a  comes into contact with the portion  202   a  (by which locking member  20  is pushed upward by projection  71   a ) of the locking member  20   a . Then, as the cartridge  7   a  is inserted further, the projection  71   a  causes the locking member  20   a  in the direction indicated by the arrow mark R against the resiliency of the tension spring  21   a , until the projection  71   a  reaches the point  210   a  of the locking member  20   a , which is the downstream end of the portion  202   a  (by which locking member  20  is pushed upward by projection  71   a ) of the locking member  20   a , as shown in  FIG. 13(   b ). When the positioning projection  71   a  is at the point  210   a  of the locking member  20   a , the projection  76   a  and cartridge screening slot  205   a  coincide in position with each other. Therefore, the projection  76   a  is allowed to move through the slot  205   a , and the locking member  20   a  rotates in the direction indicated by an arrow mark P. Further, the projection  71   a  is pressed on the cartridge positioning surfaces  112   a  and  113   a , as shown in  FIGS. 13(   c ) and  13 ( d ). 
     On the other hand, if the cartridge  7   a  is inserted into the cartridge slot  101   b , that is, a wrong slot, the cartridge  7  is allowed to enter the slot  101   b  until the positioning projection  71   a  reaches as far as the point  210   b  of the locking member  20  as shown in  FIGS. 14(   a ) and  14 ( b ). In this case, however, the positioning projection  76   a  does not coincides in position with the cartridge screening slot  205   b  of the cartridge screening portion  203   b  of the locking member  20   b . Therefore, if the cartridge  7   a  is inserted further, the identification projection  76   a  causes the locking member  20   b  to rotate further in the direction of the arrow mark R, as shown in  FIG. 14(   c ). Eventually, the projection  71   a  comes into contact with the cartridge positioning surface  113   b , as shown in  FIG. 14(   d ). That is, the cartridge  7   a  is inserted all the way into the cartridge slot  101   b  and is placed in the image forming position of the cartridge  7   b . Then, as the user (installer) releases the cartridge  7   a , the locking member  20   b  is rotated in the direction indicated by the arrow mark P in  FIG. 14(   d ) by the resiliency of the tension spring  21 . Thus, the identification projection  76   a  is pushed by the locking member  20   b  in the direction indicated by the arrow mark E. Therefore, the cartridge  7   a  is pushed back in the direction of the arrow mark E. While the cartridge  7   a  is pushed back, the identification projection  76   a  remains in contact with the cartridge blocking portion  204   b  of the locking member  20  until the positioning projection  71   a  moves past the point  210   b  of the locking member  20   b . Therefore, the locking member  20  does not interfere with the movement of the positioning projection  71   a  in the direction of the arrow mark E. In other words, if a given cartridge  7  is inserted all the way into a wrong cartridge slot  101 , the cartridge  7  is pushed back at least to where the cartridge  7   a  is in  FIG. 14(   a ). 
     The cartridges  7   a - 7   d  are made different in the position of the identification projection  76  so that the position of the identification projection  76  corresponds to the color of the toner in a cartridge  7 . Further, the cartridges slots  101   a - 101   d  also are made different in the position of the cartridge screening slot  205  of the cartridge screening portion  203  of the locking member  20  so that the position of the cartridge screening slot  205  corresponds to the color of the toner in the correct cartridge  7  for the cartridge slot  101 . Therefore, the cartridges  7   a - 7   d  can be installed only in the cartridge slots  101   a - 101   d , respectively. Incidentally, what occurs if the cartridge  7   b ,  7   c , or  7   d  is inserted into a wrong cartridge slot  101  is similar to what occurs as the cartridge  7   a  is inserted into the cartridge slot  101   b , as described above. 
     In this embodiment, the tension spring  21  plays two roles, that is, the role of the means for pressing a cartridge  7  for properly positioning the cartridge  7  relative to a cartridge slot  101  when the cartridge  7  is a correct one for the cartridge slot  101 , and the role of the means for screening a process cartridge  7  and pressing the cartridge  7  toward the entrance of the cartridge slot  101  when the cartridge  7  is a wrong one for the cartridge slot  101 . 
     Also in this embodiment, a cartridge  7  can be inserted all the way into a cartridge slot  101  even if the cartridge  7  is a wrong one for the cartridge slot  101 , as in the first embodiment. Further, the amount of the pressure applied to the means for screening and pressing a cartridge  7  is as small as that in the second embodiment. Therefore, the image forming apparatus  100  in this embodiment is unlikely to suffer from the problem that when a cartridge which a user tries to install into a cartridge slot of the apparatus  100  is a wrong one for the cartridge slot, the user applies an excessive amount of force to the cartridge. Further, the cartridge installation error preventing means of the apparatus  100  is significantly smaller than any conventional cartridge installation error preventing means, in the amount of the load it adds to the amount of the force to be applied to a cartridge by a user when the cartridge needs to be installed into the apparatus  100 . 
     Also in the third embodiment, each cartridge slot is provided with the cartridge position controlling portion  155  for preventing a cartridge  7  from falling out of the main assembly of the image forming apparatus  100 . Therefore, it does not occur that when a cartridge  7  is inserted into a wrong cartridge slot  101 , it falls out of the main assembly of the apparatus  100  as it is pushed back toward the entrance of the cartridge slot  101 . 
     As is evident from the description of the first to third preferred embodiments of the present invention, not only can the present invention make it easier for a user of an image forming apparatus to recognize that a cartridge is inserted into a wrong cartridge slot of the image forming apparatus, or a cartridge which is being inserted into a cartridge slot of the image forming apparatus is a wrong one, but also, can prevent the problem that when a cartridge is inserted into a wrong cartridge slot, or a cartridge which is being inserted into a cartridge slot is a wrong one for the cartridge slot, the main assembly of the image forming apparatus and/or the cartridge is deformed or damaged. Further, the application of the present invention to an image forming apparatus does not require the apparatus to be increased in size. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Applications Nos. 232848/2010 and 131401/2011 filed Oct. 15, 2010 and Jun. 13, 2011, respectively, which are hereby incorporated by reference.