Abstract:
A process cartridge detachably mountable to an image forming apparatus includes a contact portion contactable to a first movable member of the apparatus in the process of mounting the cartridge to the image forming apparatus. The contact portion passes the first movable member in the inserting direction, and the first movable member moves from the retracted position to the projection position, and then a second movable member moves from the blocking position to the open position, and the contact portion passes the second movable member in the inserting direction, by which the process cartridge can be mounted to a proper image forming apparatus.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus, a cartridge, and an image forming apparatus system, which are for forming an image on recording medium. 
     Here, an image forming apparatus means an apparatus which forms an image on recording medium, with the use of one of various known image formation principles and methods, such as an electrophotographic process, an electrostatic recording process, and a magnetic recording process. For example, it includes a copying machine, a printer (laser printer, LED printer, etc.), a facsimile machine, a word processor, an image displaying apparatus, (electronic blackboard, electronic whiteboard), etc. Recording medium means an object on which an image can be formed by an image forming apparatus. It includes paper, OHP sheet, secondary transferring member. 
     A cartridge means a cartridge in which an image bearing member on which an image is formed, and a part or parts of the image forming sections of an image forming apparatus, which has means for processing the image bearing member, are disposed together. It is removably installed in the main assembly of an image forming apparatus, and contributes to the process for forming an image on recording medium. The main assembly of an image forming apparatus is the portion of an image forming apparatus, which remains after the removal of a process cartridge (cartridges) from the image forming apparatus. 
     An image bearing member is a component on which an image can be formed with the use of one of various image formation principles and methods. For example, an electrophotographic photosensitive component used for an electrophotographic process, a dielectric component used for an electrostatic recording process, a magnetic component used for a magnetic recording process, etc., can be listed as an image bearing member. An image formation process means is a means for processing an image bearing member to form an image on the image bearing member. 
     Hereinafter, for convenience sake, the present invention is described with reference to an electrophotographic image forming apparatus which employs a cartridge system. Examples of a cartridge are a process cartridge and a development cartridge. 
     A process cartridge is a cartridge in which an electrophotographic photosensitive member as an image bearing component, and at least one among a charging means, a developing means, and a cleaning means, which are electrophotographic processing means, are disposed together so that they can be removably installed in the main assembly of an image forming apparatus. Hereafter, the main assembly of an electrophotographic image forming apparatus will be referred to simply as apparatus main assembly. 
     Thus, a process cartridge includes a cartridge in which a developing means as a processing means, and an electrophotographic photosensitive member, are disposed together so that they can be removably installed in the apparatus main assembly, and a cartridge in which an electrophotographic photosensitive member, and a charging means, a developing means or cleaning means as a processing means, are disposed together so that they can be removably installed in the apparatus main assembly. 
     A process cartridge in which an electrophotographic member and a developing means are disposed together is referred to as a process cartridge of the so-called all-in-one type, whereas a process cartridge in which an electrophotographic photosensitive member and processing means other than a developing means, are disposed together is referred to as a process cartridge of the so-called separation type. Thus, a process cartridge which is used in combination with a development unit having a developing means, to form an image is referred to as a process cartridge of the separation type. 
     A process cartridge can be installed into, or removed from, the apparatus main assembly by a user him- or herself. Thus, it can make it easier for a user to maintain an electrophotographic image forming apparatus. 
     A development cartridge has a development roller (developer bearing member for applying developer to electrophotographic photosensitive member). It contains powdery developer (toner) to be used for developing an electrostatic latent image formed on an electrophotographic photosensitive member. It is removably installable in the apparatus main assembly. 
     In the case of an electrophotographic image forming apparatus which employs a development cartridge, its electrophotographic photosensitive member is attached to the apparatus main assembly, its cartridge supporting member, or the process cartridge of the aforementioned process cartridge of the so-called separation type (which does not have developing means). A development cartridge also is removably installable in the apparatus main assembly. Therefore, it also makes it easier to maintain an electrophotographic image forming apparatus. 
     That is, a cartridge includes the above-mentioned process cartridge of the so-called all-in-one type, and also, the abovementioned process cartridges of the so-called separation type. Further, it includes a cartridge which is used in combination with a development cartridge, that is, a process cartridge of the separation type. Further, it includes a cartridge which is used by an electrophotographic image forming apparatus, the electrophotographic photosensitive member of which is attached to the apparatus main assembly, or a cartridge supporting member, and in which a development cartridge is removably installable to process the electrophotographic photosensitive member. Further, it includes a unit which is in the form of a cartridge and is removably installable in the apparatus main assembly to contribute to the image formation process for forming an image on recording medium. 
     In the case of an image forming apparatus which employs a cartridge system, it is possible that a cartridge which is not compatible with the apparatus will be inserted into the cartridge chamber of the apparatus main assembly, instead of a cartridge which is compatible with the apparatus. In other words, it sometimes occurs that a cartridge is inserted into the main assembly of an image forming apparatus which is incompatible with the cartridge. Hereinafter, a cartridge which perfectly fits in the main assembly of a given electrophotographic image forming apparatus is referred to as a compatible cartridge of the apparatus, whereas a cartridge which does not perfectly fit in the apparatus main assembly of a given image forming apparatus is referred to as an incompatible cartridge for the apparatus. 
     An incompatible cartridge includes a cartridge which is incompatible in that it is not intended for a given image forming apparatus to which it is going to be inserted. It includes also a cartridge which is compatible in that it is intended for a given image forming apparatus to which it is going to be inserted, but incompatible in that it is going to be inserted into one of the cartridge slots (space) intended for other cartridges in terms of developer color. 
     One of the methods for preventing the insertion of an incompatible cartridge, such as the one described above, is proposed in Japanese Patent No 3658381. According to this patent, a cartridge is provided with a protective shutter for a photosensitive drum, which is moved by the inward movement of the cartridge into the main assembly of an image forming apparatus. Thus, if an incompatible cartridge is inserted into the main assembly of an image forming apparatus, its protective shutter is opened, and comes into contact with a part of the main assembly shutter, sooner than when a compatible cartridge is inserted. Thus, the incompatible cartridge is prevented from being inserted further into the apparatus main assembly. 
     There is proposed another method for preventing the insertion of an incompatible cartridge, in Japanese Patent No. 4667444. According to this patent, the main assembly of an image forming apparatus is provided with a regulating member which is movable relative to the apparatus main assembly by a cartridge as the cartridge is inserted into the apparatus main assembly. Further, a cartridge is provided with a movable member. Thus, as an incompatible cartridge is inserted into the image forming apparatus, the movable member of the apparatus main assembly is made to retreat by the movable member of the cartridge to prevent the cartridge from being inserted further into the apparatus main assembly. 
     In the case of the electrophotographic image forming apparatus disclosed in the first patent, even an incompatible cartridge can be inserted deeply into the cartridge chamber of the apparatus main assembly. Thus, it was sometimes difficult for a user to recognize that the cartridge being inserted is an incompatible one. 
     In the case of the electrophotographic image forming apparatus disclosed in the specification of the second patent, both the cartridge, and the apparatus main assembly, are provided with a member for preventing the insertion of an incompatible cartridge. Thus, in a case where the erroneous cartridge insertion has to be prevented among multiple image forming apparatuses, which are different in type, and multiple cartridges, which are different in type, the second invention makes an image forming apparatus and the process cartridge therefor excessively complicated in structure, which was likely to result in cost increase. 
     Further, according to the prior art described above, the movable member(s) has to be disposed at one, or both of, the lengthwise ends the main assembly of the image forming apparatus. Therefore, the prior art is likely to increase an image forming apparatus in length. 
     SUMMARY OF THE INVENTION 
     The present invention is one of the results of further development of the above described prior art. Thus, the primary object of the present invention is to provide a combination of an electrophotographic image forming apparatus and a cartridge therefor, which is simple in structure, and yet, ensures that it is only a compatible cartridge that can be installed in the apparatus main assembly. 
     According to an aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording material, wherein a cartridge is detachably mountable to said image forming apparatus, said image forming apparatus comprising a first movable member movable between a projection position in which said first movable member is in an insertion path of a contact portion provided on said cartridge when said cartridge is mounted to a main assembly of said image forming apparatus, and a retracted position in which said first movable member is retracted from the insertion path, wherein said first movable member moves from the projection position to the retracted position by being contacted by the contact portion; and a second movable member movable between an open position for permitting said cartridge toward downstream with respect to an inserting direction in which said cartridge is mounted to said main assembly and a blocking position for preventing said cartridge from moving toward the downstream by contacting said contact portion, said second movable member being interrelated with said first movable member so that when said first movable member is in the projection position, said second movable member takes the open position, and when said first movable member is in the retracted position, said second movable member takes the blocking position, wherein in the process of mounting said cartridge to said main assembly, said contact portion passes said first movable member in the inserting direction, and said first movable member moves from the retracted position to the projection position, and then said second movable member moves from the blocking position to the open position, and said contact portion passes said second movable member in the inserting direction. 
     According to another aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an image forming apparatus for forming an image on a recording material, wherein a cartridge is detachably mountable to the image forming apparatus, the main assembly of the image forming apparatus including, a first movable member movable between a projection position in which said first movable member is in an insertion path of a contact portion provided on said cartridge when said cartridge is mounted to the main assembly of said image forming apparatus, and a retracted position in which first movable member is retracted from the insertion path, wherein said first movable member moves from the projection position to the retracted position by being contacted by the contact portion; and a second movable member movable between an open position for permitting said cartridge toward downstream with respect to an inserting direction in which said cartridge is mounted to said main assembly and a blocking position for preventing said cartridge from moving toward the downstream by contacting said contact portion, said second movable member being interrelated with said first movable member so that when said first movable member is in the projection position, said second movable member takes the open position, and when said first movable member is in the retracted position, said second movable member takes the blocking position; said process cartridge comprising a contact portion contactable to the first movable member in the process of mounting said cartridge to said main assembly, wherein said contact portion passes said first movable member in the inserting direction, and said first movable member moves from the retracted position to the projection position, and then said second movable member moves from the blocking position to the open position, and said contact portion passes said second movable member in the inserting direction. 
     According to a further aspect of the present invention, there is provided an image forming apparatus system for forming an image on a recording material, said image forming apparatus system comprising (i) a first cartridge; (ii) a first image forming apparatus for forming an image on a recording material, wherein the first cartridge is detachably mountable to said first image forming apparatus, said first image forming apparatus including a first movable member movable between a projection position in which said first movable member is in an insertion path of a first contact portion provided on said first cartridge when said first cartridge is mounted to a first main assembly of said first image forming apparatus, and a retracted position in which said first movable member is retracted from the insertion path, wherein said first movable member moves from the projection position to the retracted position by being contacted by the first contact portion; a second movable member movable between an open position for permitting said first cartridge toward downstream with respect to an inserting direction in which said first cartridge is mounted to said first main assembly and a blocking position for preventing said first cartridge from moving toward the downstream by contacting said first contact portion, said second movable member being interrelated with said first movable member so that when said first movable member is in the projection position, said second movable member takes the open position, and when said first movable member is in the retracted position, said second movable member takes the blocking position; wherein in the process of mounting said first cartridge to said first main assembly, said first contact portion passes said first movable member in the inserting direction, and said first movable member moves from the retracted position to the projection position, and then said second movable member moves from the blocking position to the open position, said first contact portion passes said second movable member in the inserting direction; (iii) a second cartridge; and (iv) a second image forming apparatus for forming an image on a recording material, wherein the second cartridge is detachably mountable to said second image forming apparatus, said second image forming apparatus including a third movable member movable between a projection position in which said third movable member is in an insertion path of a second contact portion provided on said second cartridge when said second cartridge is mounted to a second main assembly of said second image forming apparatus, and a retracted position in which third movable member is retracted from the insertion path, wherein said third movable member moves from the projection position to the retracted position by being contacted by the second contact portion; a fourth movable member movable between an open position for permitting said second cartridge toward downstream with respect to an inserting direction in which said second cartridge is mounted to said second main assembly and a blocking position for preventing said second cartridge from moving toward the downstream by contacting said second contact portion, said fourth movable member being interrelated with said third movable member so that when said third movable member is in the projection position, said fourth movable member takes the open position, and when said third movable member is in the retracted position, said fourth movable member takes the blocking position; wherein in the process of mounting said second cartridge to said second main assembly, said second contact portion passes said third movable member in the inserting direction, and said third movable member moves from the retracted position to the projection position, and then said fourth movable member moves from the blocking position to the open position, said second contact portion passes said fourth movable member in the inserting direction, wherein when said second cartridge is mounted to said first image forming apparatus, said second movable member taking the blocking position contacts said contact portion before said second contact portion passes said first movable member in the inserting direction, and when said first cartridge is mounted to said second image forming apparatus, said fourth movable member taking the blocking position contacts said contact portion before said first contact portion passes said third movable member in the inserting direction. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for describing the structural components, and their operations, of the image forming apparatus, in the first embodiment of the present invention, for preventing an incompatible cartridge from being inserted into the apparatus main assembly. 
         FIG. 2  is a perspective view of the image forming apparatus in the first embodiment. 
         FIG. 3  is a perspective view of a combination of the apparatus main assembly and one of the cartridges removably installable in the apparatus main assembly, in the first embodiment, when the main door of the apparatus main assembly is open, and the cartridge is positioned to be inserted into the apparatus main assembly. 
         FIG. 4  is a schematic sectional view of the image forming apparatus, at a vertical plane parallel to the direction in which the cartridge is inserted into the apparatus main assembly, as seen from the left side of the apparatus. 
         FIG. 5  is an enlarged view of the cartridge portion of  FIG. 4 . 
         FIG. 6  is a partially exploded view of the cartridge; the cleaning unit and development unit are not in connection to each other. 
         FIG. 7(   a ) is a perspective view of the cartridge guiding left member of the apparatus main assembly, its adjacencies, of the cartridge chamber, and  FIG. 7(   b ) is a perspective view of the cartridge guiding right member, and its adjacencies, of the cartridge chamber. 
         FIG. 8  is a drawing for describing how the cartridge is to be inserted, or removed from, the apparatus main assembly. 
         FIG. 9  is a perspective view of the erroneous cartridge insertion preventing member of the apparatus main assembly, and describes the structure of the member. 
         FIG. 10  is a sectional view of the erroneous cartridge insertion preventing member of the apparatus main assembly, and describes the structure of the member. 
         FIG. 11  is a drawing for describing the structure of the erroneous cartridge insertion preventing member of the apparatus main assembly, and that of a cartridge which is incompatible with the apparatus. 
         FIG. 12  is an enlarged view of a combination of the erroneous cartridge insertion preventing member of the apparatus main assembly, and the erroneous cartridge insertion prevention bosses of the incompatible cartridge. 
         FIG. 13  is a drawing for describing the structure of the erroneous cartridge insertion preventing member of the apparatus main assembly, and that of the incompatible cartridge. 
         FIG. 14  is a drawing for describing the operation of the erroneous cartridge insertion preventing member of the apparatus main assembly, and that of the erroneous cartridge insertion preventing member of the incompatible cartridge, which occurs as the incompatible cartridge is inserted into the apparatus main assembly. 
         FIG. 15  is a drawing for describing the erroneous cartridge insertion preventing member for the apparatus main assembly, which is different from the one for the image forming apparatus in the first embodiment. 
         FIG. 16  is a drawing for describing the operation of the erroneous cartridge insertion preventing member of the apparatus main assembly which is different from that in the first embodiment, and the operation of the erroneous cartridge insertion preventing member of the cartridge in the first embodiment, which occurs as the cartridge is inserted into the apparatus main assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention is described in detail with reference to the embodiments of the present invention, and the appended drawings. 
     Embodiment 1 
     (1) General Description of Typical Image Forming Apparatus to which Present Invention is Applicable 
       FIG. 21  is a perspective view of the image forming apparatus  100  in this embodiment, and  FIG. 3  is a perspective view of a combination of the apparatus main assembly A, and a cartridge B removably installable in the apparatus main assembly A, when the door  13  of the apparatus main assembly A is open.  FIG. 4  is a sectional view of the image forming apparatus  100 , at a vertical plane parallel to the direction in which the cartridge B is removably inserted into the apparatus main assembly A, as seen from the left side of the apparatus main assembly. 
     The image forming apparatus  100  in this embodiment is an electrophotographic laser printer (electrophotographic image forming apparatus) which employs a cartridge system. It forms an image on a sheet P of recording medium (which hereafter may be referred to simply as sheet P) with the use of an electrophotographic image formation process. It can form an image which reflects electrical information of an image to be formed, which is inputted into the control circuit (controlling means)  200  of the image forming apparatus  100 , from an external host apparatus  300  ( FIG. 4 ) such as a personal computer. 
     A referential code  102  stands for the control panel of the image forming apparatus  100 , through which various information such as image formation conditions can be inputted into the control section  200 . The control panel  102  has a display across which various information is displayed. In this embodiment, the control section  102  is a part of the door  13  of the apparatus main assembly A. 
     Regarding the direction of the image forming apparatus  100 , the front side (user side) of the apparatus  100  means the side from which a sheet tray  4  in which multiple sheets P can be stored in layers can be roughly horizontally inserted into, or moved out of, the apparatus main assembly A. The back (rear) side of the image forming apparatus  100  means the opposite side of the image forming apparatus  100  from the front side. The left and right sides of the image forming apparatus  100  are the left and right sides as seen from the front side of the apparatus  100 . The top and bottom sides of the image forming apparatus  100  are the top and bottom sides with reference to the gravity direction. The main assembly A of the image forming apparatus  100  (which hereafter is referred to as apparatus main assembly A) is the assembly of the structural components of the image forming apparatus  100 , minus the cartridges B. 
     Regarding the direction of the cartridge B, and its structural components, in this embodiment, their lengthwise direction is such a direction that is parallel to the axial line of the electrophotographic photosensitive drum  62  as the image bearing member. It is the direction perpendicular to the directions indicated by arrow marks G 1  and G 2  ( FIG. 3 ) in which the cartridge B is inserted into, or moved out of, the apparatus main assembly A. Its widthwise direction means such a direction that is parallel to the directions indicated by the arrow marks G 1  and G 2 , in which the cartridge B is inserted into, or moved out of, the apparatus main assembly  100 A. The front side of the cartridge B means the upstream surface of the cartridge B in terms of the direction in which the cartridge B is inserted into the apparatus main assembly A. The back side of the cartridge B means the opposite side of the cartridge B from the front side (downstream side in terms of direction G 1  in which cartridge B is inserted into apparatus main assembly A). The left and right sides of the cartridge B are the left and right sides as seen from the front side of the cartridge B. 
     Referring to  FIG. 4 , a substantial space, which is roughly in the center of the apparatus main assembly A, is the cartridge chamber  101 , that is, the space into which the cartridge B is removably installed. The cartridge B in this embodiment is a process cartridge of the so-called all-in-one type, which will be described later in detail. That is, it has an electrophotographic photosensitive drum  62  (which hereafter is referred to simply as drum) as an image bearing member on which an image is formed, and processing means, more specifically, a charging means  66 , a developing means  32 , and a cleaning means  77 , which are for processing the drum  62 . 
     In this embodiment, the charging means  66  is in the form of a roller (charge roller: electrically conductive elastic roller). The developing means  32  also is in the form of a roller (development roller). It is of the so-called no-contact-development type. It uses single-component magnetic toner as developer. The cleaning means  77  is in the form of a blade (cleaning blade). 
     It is only when the cartridge B is in the preset image formation positions of the cartridge chamber  101  of the apparatus main assembly A that the image forming apparatus  100  can perform an image forming operation. That is, when the image forming apparatus  100  can form an image, the driving force receiving section  63  of the cartridge B is in engagement with the driving force outputting section (unshown) of the apparatus main assembly A. Thus, the driving force from the cartridge driving system (unshown) of the apparatus main assembly A is transmitted to the cartridge B, making it possible for the rotational components such as the drum  62 , development roller  32 , developer conveying member  43 , etc., to be rotationally driven. In the case of the image forming apparatus  100  in this embodiment, the right-hand side of the apparatus main assembly A, and the right-hand side of the cartridge B, are referred to as the drive side, whereas the left-hand sides are referred to as the non-drive side. 
     Further, the electrical contacts (unshown) of the cartridge B are electrically in contact with the electrical contacts (unshown) of the apparatus main assembly A. Thus, bias can be applied to the bias receiving members, such as the charge roller  66 , development roller  32 , etc., of the cartridge B from the electric power supply section (unshown) of the apparatus main assembly A. 
     The apparatus main assembly A is provided with a laser scanner unit  3  as an exposing apparatus (exposing means), which is above the cartridge chamber  101 . This unit  3  outputs a beam L of laser light while modulating the beam L with the electrical information of the image to be formed, which is inputted into the control circuit  200  from the external host apparatus  300 . The beam L of laser light enters the cartridge B through the exposure window  74 , with which the top wall of the cartridge B is provided, and scans (exposes) the peripheral surface of the drum  62 . The downwardly facing area of the peripheral surface of the drum  62  is in contact with the peripheral surface of a transfer roller (transferring means)  7 , forming a transfer nip. The transfer roller  7  is an electrically conductive elastic roller, to which a preset transfer bias is applied. 
     Further, the apparatus main assembly A is provided with a sheet tray  4 , which is below the transfer roller  7 , and in which multiple sheets P of recording medium are storable. This tray  4  can be roughly horizontally inserted into, or moved out of, the apparatus main assembly A, from the front side of the image forming apparatus  100  (front loading). That is, the tray  4  can be pulled out of the apparatus main assembly A, like a drawer, toward a user so that it can be replenished with sheets P of recording medium. Obviously, the tray  4  can be pushed back into its preset position in the apparatus main assembly A. Referring to  FIGS. 2 and 4 , the directions indicated by arrow marks V 1  and V 2  are the directions in which the tray  4  can be pulled out of the apparatus main assembly A, and pushed into the apparatus main assembly A, respectively. A component designated by a referential code  4   a  is a handhold with which the front wall of the tray  4  is provided. 
     Further, the apparatus main assembly A is provided with a pickup roller  5   a , a pair of retard rollers  5   b , a pair of recording medium conveyance rollers  5   c , a pair of registration rollers  5   d , and a transfer front guide  6 , which are disposed in the listed order, on the front side of the apparatus main assembly A. These components make up the sheet conveyance passage which extends from the tray  4  to the transfer roller  7 . 
     Further, the apparatus main assembly A is provided with a fixing device (fixing means)  9 , which is made up of a heat roller  9   a  and a pressure roller  9   b , and is in the deeper end portion of the apparatus main assembly A. There is disposed a sheet guide  8  between the transfer roller  7  and fixing device  9 . There are also disposed a pair of recording medium conveyance rollers  10   a  and a sheet conveyance passage  10   b , on the rear side of the fixing device  9 , in the apparatus main assembly A. The recording medium conveyance passage  10   b  extends upward from the pair of recording medium conveyance rollers  10   a . A part of the top surface of the apparatus main assembly A is utilized as a delivery tray  11 . 
     The image forming operation of the image forming apparatus  100  in this embodiment is as follows: The control circuit  200  starts up the driving force generating section in response to a printing operation start signal, whereby the drum  62  begins to be rotationally driven in the clockwise direction, indicated by an arrow mark R in  FIG. 4 , at a preset peripheral velocity (process speed), and the laser scanner unit  3 , development roller  32 , developer conveying member  43 , transfer roller  7 , fixing device  9 , etc., also begin to be driven in the preset directions and/or speeds. The charge roller  66  is rotated by the rotation of the drum  62 . To the charge roller  66 , a preset charge bias is applied from the power supply section, whereby the peripheral surface of the drum  62  is uniformly charged to preset polarity and potential level. 
     The uniformly charged area of the peripheral surface of the drum  62  is scanned by (exposed to) the beam L of laser light outputted from the laser scanner unit  3  while being modulated with the image formation signals. Consequently, an electrostatic image, which reflects the exposure pattern is formed on the peripheral surface of the drum  62 . This electrostatic image is developed by the development roller  32  into a toner image (developer image), and is moved into the transfer nip, which is between the drum  62  and transfer roller  7 . 
     Meanwhile, the pickup roller  5   a  begins to be driven with a preset control timing, in synchronism with the timing with which the beam L of laser light is outputted. Thus, the sheets P in the sheet tray  4  are pulled out of the tray  4 , one by one, by the pair of retard rollers  5   b , and are conveyed further into the apparatus main assembly A. Then, each sheet P is conveyed further by the pair of conveyance rollers  5   c , and pair of registration rollers  5   d , so that it will be introduced into the transfer nip with a preset control timing. Then, the sheet P is conveyed through the transfer nip while remaining pinched by the drum  62  and transfer roller  7 . While the sheet P is conveyed through the transfer nip, a preset transfer bias is applied to the transfer roller  7  from the power supply section, whereby the toner image on the drum  62  is transferred onto the surface of the sheet P as if it is peeled away from the drum  62 . 
     After being conveyed through the transfer nip, the sheet P is separated from the peripheral surface of the drum  62 , and is introduced into the fixing device  9  by the conveyance guide  8 . After the separation of the sheet P from the peripheral surface of the drum  62 , the transfer residual toner is removed by the cleaning blade  77  (peripheral surface of drum  62  is cleaned), so that it can be repeatedly used for image formation. 
     As the sheet P is introduced into the fixing device  9 , it is conveyed through the fixation nip while remaining pinched by the drum  62  and transfer roller  7  and being subjected to heat and pressure. Thus, the unfixed toner image becomes fixed as a permanent image, to the surface of the sheet P. After being conveyed out of the fixing device  9 , the sheet P is conveyed further by the pair of conveyance rollers  10   a , sheet conveyance passage  10 , and pair of discharge rollers  10 , in the listed order. Then, it is discharged, as a permanent print, onto the delivery tray  11 . An arrow mark D indicates the direction (recording medium conveyance direction) in which the sheet P is conveyed. 
     (2) Cartridge 
     Next, referring to  FIGS. 5 and 6 , the structure of the cartridge B is described.  FIG. 5  is an enlarged view of the cartridge portion of  FIG. 4 . The cartridge B in this embodiment is of the so-called all-in-one type, which is a united combination of a cleaning unit  60  and development unit  20 .  FIG. 6  is a perspective view of the combination of the cleaning unit  60  and development unit  20  when the cleaning unit  60  and development  20  are not in connection to each other. 
     The cleaning unit  60  has a cleaning unit frame  71 , the lengthwise direction of which is parallel to the left/right direction of the apparatus main assembly A. It is to this frame  71  that the drum  62 , as an image bearing member, on which an image is formed, the charge roller  66  and cleaning blade  77 , as means for processing the drum  62 , are attached. 
     The drum  62  is disposed between the left and right plates  71 L and  71 R of the frame  71 , being rotatably supported by the left and right plates  71 L and  71 R with the placement of a pair of bearings between the lengthwise left and right ends of the drum  62  and the left and right plates  71 L and  71 R, respectively. 
     The charge roller  66  is disposed on the top side of the drum  62 , being in parallel to the drum  66 . It also is disposed between the left and right plates  71 L and  71 R, being rotatably supported by the left and right plates  71 L and  71 R, with the placement of a pair of the bearings between the left and right ends of the charge roller  66  and plates  71 L and  71 R, respectively. Further, the charge roller  66  is kept pressed upon the peripheral surface of the drum  62  by a preset amount of pressure generated by a pair of pressing members (unshown). 
     The cleaning blade  77  is an elastic blade. It is fixed to a preset portion of the waste toner chamber  71   b  of the frame  71 , with the placement of a rigid blade supporting member  77   a , which is made of a metallic substance or the like, between the actual blade portion of the cleaning blade  77  and the frame  71 . The blade  77  is disposed in such an attitude that its cleaning edge is on the upstream side of the blade supporting member  77   a , in terms of the rotational direction of the drum  62  indicated by the arrow mark R. It is kept pressed on the peripheral surface of the drum  62  so that a preset amount of contact pressure is maintained between the cleaning edge of the cleaning blade  77  and the peripheral surface of the drum  62 . 
     The development unit  20  in this embodiment is a developing device of the non-contact type. It uses single-component magnetic toner as developer T. This unit  20  is an assembly made up of a toner container  21 , a top cover  22 , a development chamber  23 , a development blade  42 , a development roller  32 , a magnetic roller  34 , a developer conveying member  43 , a left (first) side cover  26 L, a right (second) side cover  26 R, a pair of pressure applying members  46 L and  46 R, etc. 
     The single-component magnetic toner T as developer is stored in the toner chamber  29  made up of the toner container  21 , top cover  22 , first side cover  26 L and second side cover  26 R. The development chamber  23  is in connection to the toner chamber  29  through an opening  29   a . The developer conveying member  43  is disposed in the toner chamber  29 . It is rotationally driven in the clockwise direction, indicated by an arrow mark C in  FIG. 5 . 
     The development roller  32  is disposed in the development chamber  23 . It is a hollow roller (sleeve). It is rotatably supported between the first (left) and second (right) side covers  26 L and  26 R, with the placement of a pair of bearings between the lengthwise ends of the development roller  32 , and the first and second side covers  26 L and  26 R, respectively. The left and right ends of the development roller  32  are fitted with a pair of spacer rings  38 L and  38 R, as space maintaining members, respectively, which are concentric with the development roller  32 . The spacer rings  38 L and  38 R are the same in external diameter. They are greater in external diameter than the development roller  32 . 
     There is concentrically disposed a stationary magnetic roller (fixed magnet)  34  in the hollow of the development roller  32 . The development blade  42  is fixed to the wall of the development chamber  23  by its base portion. It is an elastic member, and is placed in contact with the peripheral surface of the development roller  32  in such an attitude that the portion of the development blade  42 , which is adjacent to the opposite lengthwise edge from the base portion, presses on the peripheral surface of the development roller  32 . It is a member for regulating in thickness the layer of toner borne on the peripheral surface of the development roller  32 . It is positioned so that the portion of its peripheral surface, which is on the opposite side from the opening  29   a  of the toner chamber  29 , is exposed from the development chamber  23 . 
     The cleaning unit  60  and development unit  20  are connected to each other by the left and right connective members  75 L and  75 R in such a manner that the two units  60  and  20  are rotationally movable about the connective members  75 L and  75 R. To describe in detail this connection between the two units  60  and  20  with reference to  FIG. 6 , the left and right ends of the development roller container  23  are provided with left and right arms  23   a L and  23   a R, which are provided with cylindrical holes  23   b L and  23   b R, respectively, which are parallel to the rotational axis of the development roller  32 . As for the cleaning device frame  71 , its left and right plates  71 L and  71 R are provided with left and right holes  71   a L and  71   a R, through which the left and right connective members  75 L and  75 R are put, respectively. 
     Thus, all that is necessary to connect the cleaning unit  60  and development unit  20  to each other is to position the two units  60  and  20  in such a manner that the holes  23   b L and  23   b R of the left and right arms  23   a L and  23   a R of the cleaning unit  60  align with the left and right holes  71   a L and  71   a R of the cleaning unit frame  71 , and put the left and right connective members  75 L and  75 R through the holes  23   b L and  23   b R, and the holes  71   a L and  71   a R, respectively. The holes are positioned so that after the connection of the two units  60  and  20  to each other, the left and right connective members  75 L and  75 R are in alignment with each other in terms of the lengthwise direction. 
     Since the cleaning unit  60  and development unit  20  are connected to each other as described above, the cleaning unit  60  and development unit  20  are rotationally movable about the connective members  75 L and  75 R. 
     As the cleaning unit  60  and development unit  20  are connected to each other as described, the left and right pressure applying members (coil springs)  46 L and  46 R attached to the base portions of the left and right arms  23   a L and  23   a R are pressed upon the cleaning unit frame  71 . Thus, the resiliency of these pressure applying members  46 L and  46 R acts in the direction to rotationally move the development unit  20  about the left and right connective members  46 L and  46 R. Thus, the development unit  20  is kept pressed toward the cleaning unit  60 . 
     Therefore, it is ensured that the left and right spacer rings  38 L and  38 R of the development roller  32  are kept pressed upon the peripheral surface of the left end portion of the drum  62 , and that of the right end portion of the drum  62 , respectively, providing thereby a preset amount of gap a between the peripheral surface of the development roller  32  and the peripheral surface of the drum  62 . The aforementioned exposure window  74  is between the cleaning unit  60  and development unit  20 . 
     When the cartridge B is in its preset image formation position in the cartridge chamber  101 , the cleaning unit  60  of the cartridge B is kept pressed on the cartridge positioning section of the apparatus main assembly A by the cartridge positioning mechanism (unshown) of the apparatus main assembly A. Thus, the cartridge B is kept precisely positioned relative to the apparatus main assembly A, with the driving force receiving section  63  ( FIG. 3 ) of the cartridge B being in engagement with the driving force output section (unshown) of the apparatus main assembly A, and also, the electrical contacts (unshown) of the cartridge B being electrically in contact with the electrical contacts (unshown) of the apparatus main assembly A. It is when the image forming apparatus  100  is in the above described state that the image forming apparatus  100  is ready for image formation. 
     That is, the drum  62  is rotationally driven in the clockwise direction indicated by the arrow mark R in  FIG. 5  at the preset speed, and the charge roller  66  is rotated by the rotation of the drum  62 . The development roller  32  is rotationally driven around the magnetic roller  34  in the counterclockwise direction indicated by an arrow mark U at a preset speed. To the charge roller  66  and development roller  32 , preset charge bias and development bias, respectively, are applied with preset control timings. 
     The developer conveying member  43  is rotationally driven in the clockwise direction indicated by an arrow mark C at a preset speed. As the developer conveying member  43  is rotated, the toner T in the toner chamber  29  is conveyed by a sheet (paddle)  43   a , with which the developer conveying member  43  is provided, into the toner supplying chamber  28  in the development roller container  23 , through the opening  29   a . The sheet  43   a  is made of flexible substance such as PPS, PC, PET, etc., and conveys the toner T while stirring the toner T. 
     As the toner T is conveyed into the toner supplying chamber  28 , a part of the body of the toner T in the chamber  28  is borne on the peripheral surface of the development roller  32  by the magnetic force of the magnetic roller  34 , and is conveyed toward the drum  62  by the rotation of the development roller  32 . While the layer of the toner T on the peripheral surface of the development roller  32  is conveyed toward the drum  62 , it is regulated in thickness by the development blade  42 . Then, the layer of the toner T, which has been regulated in thickness, is conveyed further by the further rotation of the development roller  32 , to the development area, that is, the area in which the peripheral surface of the development roller  32  directly faces the peripheral surface of the drum  62 , in which it is used for the development of the electrostatic image on the drum  62 . The toner which remained in the layer of the toner T after the development of the electrostatic latent image is returned to the toner supplying chamber  28  by the subsequent rotation of the development roller  32 . Then, the development roller  32  is supplied again with the toner in the toner supplying chamber  28 . 
     After the transfer of the toner image on the drum  62  onto the sheet P of recording medium, the toner remaining on the peripheral surface of the drum  62  is removed by the cleaning blade  77 , and the drum  62  is used again for image formation process. The toner removed from the drum  62  is stored in the waste toner storage chamber  71   b  of the cleaning unit  60 . 
     (3) Cartridge Replacement Method 
     As the cartridge B is used for image formation, the developer (toner) T stored in the development unit  20  is consumed. 
     Thus, the cartridge B is provided with a means (unshown) for detecting the amount of the residual developer in the cartridge B. The detected amount of the residual developer is compared by the control circuit  200  with a threshold value preset for warning a user of the estimated length of the residual life of the cartridge B, or the arrival of the end of the service life of the cartridge B. If the control circuit  200  determines that the amount of the residual developer in the cartridge B is no more than the threshold value, it shows on the display of the control panel  102 , the estimated length of the residual service life of the cartridge B, or the message which informs a user of the arrival of the end of the service life of the cartridge B, prompting thereby the user to prepare a replacement cartridge B, or replace the cartridge B in the apparatus main assembly A, so that the image forming apparatus  100  remains at a preset level in terms of image quality. 
     The aforementioned door  13 , with which the front side of the apparatus main assembly A of the image forming apparatus  100  in this embodiment is provided, is given such a shape and a size that as it is opened, it can expose roughly top half of the front side of the apparatus main assembly A, and roughly front half of the top side of the apparatus main assembly A. The door  13  is hinged to the apparatus main assembly A so that it can be rotationally opened or closed about the hinge (center of rotation)  13   a . More specifically, the door  13  can be locked in a horizontal position W 1 , in which it remains (when it is completely closed) as shown in  FIGS. 2 and 4 , and in an upright position W 2 , in which it will remain as it is opened up and rearward, as seen from the front side, as shown in  FIG. 3 . 
     When the door  13  is in its closed position W 1 , it is kept locked by a locking means (unshown). Thus, when it is necessary for a user to unlock the door  13 , the user is to place his or her finger on the handhold  13   b  of the door  13 , and move a lock releasing member, with which the hand hold  13   b  is provided, so that the door  13  is unlocked. With the door  3  unlocked, the door  3  can be moved from its closed position W 1  to its open position W 2 . In this embodiment, in order for the cartridge B in the apparatus main assembly A to be replaced, the door  13  has to be wide open as shown in  FIG. 3 . 
     As the door  13  is moved from the closed position W 1  to the open position W 2 , it is held upright in the open position W 2  by a door holder  3   c . Consequently, an opening  103 , which extends across roughly the top half of the front side of the apparatus main assembly A (that is, roughly front half of top side of apparatus main assembly A), becomes exposed as shown in  FIG. 3 . This opening  103  is large enough to allow the cartridge B to pass when the cartridge B is inserted into, or extracted from, the apparatus main assembly A. 
     When the door  3  is open, and the cartridge B is in its image formation position in the cartridge chamber  101  of the apparatus main assembly A, the front side of the cartridge B (development unit side) remains exposed through the opening  103 . When the cartridge B is not in the cartridge chamber  101 , the cartridge chamber  101  is visible ( FIG. 3 ). 
     As the door  13  is moved from its closed position W 1  to its open position W 2  when the cartridge B is in the cartridge chamber  101 , the cartridge B is unlocked from the preset cartridge position by a mechanism (unshown) which is driven by the movement of the door  13 . Further, the driving force receiving section  63  of the cartridge B is disengaged from the driving force output section of the apparatus main assembly A by the mechanism. Thus, it becomes possible for the cartridge B to be extracted from the cartridge chamber  101 . 
     Referring to  FIGS. 6 and 8 , the cartridge B is provided with a pair of insertion-extraction guide bosses  72 La and  72 Lb (by which cartridge is guided), and a pair of insertion-extraction guide bosses  72 Ra and  72 Rb, which are on the outward surface of the left plate  71 L of the cleaning unit frame  71 , and the outward surface of the right plate  71 R of the cleaning unit frame  71 , respectively. The two pairs of guide bosses are symmetrically disposed in terms of the lengthwise direction of the cartridge B. 
     In this embodiment, in terms of the direction G 1  in which the cartridge B is inserted into the apparatus main assembly A, the insertion-extraction guide bosses  72 La ( 72 Ra) and  72 Lb ( 72 Rb) are the upstream and downstream bosses, respectively. They are aligned in the cartridge insertion direction G 1 , with the provision of a preset distance between the two guide bosses  72 La ( 72 Ra) and  72 Lb ( 72 Rb). 
     Referring to  FIGS. 7(   a ) and  7 ( b ), the apparatus main assembly A is provided with cartridge guiding left and right members  12 L and  12 R, which are on the inward side of the left and right plates  16 L and  16 R of the cartridge chamber  101 , respectively, being symmetrically positioned in terms of the direction perpendicular to the cartridge insertion direction G 1 . As seen from the front side of the apparatus main assembly A, the guiding members  12 L and  12 R extend diagonally downward. These cartridge guiding members  12 L and  12 R are provided with a pair of grooves  12 La and  12 Ra, respectively, which are symmetrically positioned in terms of the left/right direction of the apparatus main assembly A. As seen from the front side of the apparatus main assembly A, they also extend diagonally downward. 
     Next, referring to  FIG. 8 , the width H of each of the guiding groove  12 La and  12 Ra is slightly greater than the diameter I of each of the insertion-extraction guide bosses  72 La,  72 Lb,  72 Ra and  72 Rb of the cartridge B. 
     When the cartridge B is in its image formation position in the cartridge chamber  101 , the insertion-extraction left guide bosses  72 La and  72 Lb are in engagement with the guiding groove  12 La of the cartridge guiding left member  12 L, and the insertion-extraction right guide bosses  72 Ra and  72 Rb of the cartridge B are in engagement with the cartridge guiding groove  12 Ra of the cartridge guiding right member  12 R. That is, the guide bosses  72 La and  72 Lb are guided by the groove  12 La, whereas the guide bosses  72 Ra and  72 Rb are guided by the groove  12 Ra. 
     The operation to be performed to extract the cartridge B from the cartridge chamber  101  of the apparatus main assembly A is as follows. First, a user (operator) is to grasp the front side, that is, the development unit side, of the cartridge B, which is exposed through the opening  103 . Then, the user is to move the cartridge B in the cartridge extraction direction indicated by the arrow mark G 2  in  FIG. 8 , while allowing the left insertion-extraction guide bosses  72 La and  72 Lb, and right insertion-extraction guide bosses  72 Ra and  72 Rb, to follow the guiding groove  12 La of the left guiding member  12 L, and the guiding groove  12 Ra of the right guiding member  12 R, respectively, until the cartridge B comes out of the apparatus main assembly A. 
     The operation to be performed to install the cartridge B into the cartridge chamber  101  of the apparatus main assembly A is as follows. First, the user (operator) is to grasp the development unit side of the cartridge B, and insert the cartridge B into the cartridge chamber  101  through the opening  103 , while holding the cartridge B so that the cartridge B enters the cartridge chamber  101  from the cleaning unit side. Then, the user is to engage the left insertion-extraction guide bosses  72 La and  72 Lb, and right insertion-extraction guide bosses  72 Ra and  72 Rb, into the guiding grooves  12 La and  12 Ra of the cartridge guiding left and right guiding members  12 L and  12 R, respectively. 
     Then, the user is to move the cartridge B further into the apparatus main assembly A in the cartridge insertion direction indicated by the arrow mark G 2 , while allowing the left pair of insertion-extraction guide bosses  72 La and  72 Lb, and the right pair of insertion-extraction guide bosses  72 Ra and  72 Rb, to remain engaged in the guiding groove  12 La of the left guiding member  12 L, and the guiding groove  12 R of the right guiding member  12 R, respectively. In other words, the movement of the left pair of insertion-extraction guide bosses  72 La and  72 Lb, and the right pair of insertion-extraction guide bosses  72 Ra and  72 Rb, is regulated by the guiding grooves  12 La and  12 Ra. Therefore, the cartridge B is kept in the proper attitude. The cartridge B is to be inserted until its inward movement is regulated by a regulating section (unshown). 
     Then, the door  3  is to be rotationally moved about the hinge  13   a  from the open (upright) position W 2  to the closed (horizontal) position W 1 , against the resiliency of the door holding member  13   c . As the door  3  is moved into the closed position W 1 , it is locked in the closed position W 1  by the locking means. While the door  3  is moved from the open (upright) position W 2  to the closed (horizontal) position W 1 , the mechanism for positioning the cartridge B is made to operate by the aforementioned linkage moved by the movement of the door  3 . Consequently, the cartridge B is moved into its image formation position in the apparatus main assembly A, and is locked in the image formation position. Further, the driving force receiving section  63  of the cartridge B becomes engaged with the driving force output section of the apparatus main assembly A. 
     (4) Structure of Erroneous Cartridge Insertion Prevention Mechanism 
     Next, the structure of the erroneous cartridge insertion prevention mechanism is described. First, its operation is described with reference to a case (4-1) in which a cartridge B, which is compatible with the apparatus main assembly A, is inserted into the apparatus main assembly A. Then, a case (4-2) in which a cartridge B 2 , which is incompatible with the apparatus main assembly A is inserted into the apparatus main assembly A, and a case (4-3) in which the cartridge B which is incompatible with an apparatus main assembly A 2 , which is different from the apparatus main assembly A, is inserted into the apparatus main assembly A 2 , are described in the listed order. 
     A case where the cartridge B 2  is inserted into the apparatus main assembly A 2  is the same as the case where the cartridge B is inserted into the apparatus main assembly A, in terms of the operation of the erroneous cartridge insertion prevention mechanism. Therefore, it is not described here. In the following descriptions of these cases, the structural components of the apparatus main assembly A 2  and the structural components of the cartridge B 2 , which are the same in function as the counterparts of the apparatus main assembly A and the cartridges B, are given the same referential codes as those given to the counterparts. 
     (4-1) Case in which Cartridge B which is Compatible with Main Assembly a is Inserted into Apparatus Main Assembly A 
     First, referring to  FIGS. 1 ,  3 , and  6 - 16 , the case in which the cartridge B (first cartridge) which is compatible with the apparatus main assembly A of the image forming apparatus  100  is inserted into the apparatus main assembly A is described. 
     Referring to  FIGS. 6 and 8 , the cleaning unit frame  71  of the cartridge B is provided with a pair of contacting sections, more specifically, the first and second contacting sections  73   a  and  73   b  (which hereafter are referred to as erroneous insertion prevention bosses  73   a  and  73   b ), which are on the outward surface of the left plate  71 L, on the non-drive side. 
     It is not mandatory that both the drive side and non-drive sides of the cartridge B are provided with the erroneous insertion prevention bosses. That is, it may be only one of the two sides (driven side and non-driven side) of the cartridge B that is provided with the erroneous insertion prevention bosses  73 . However, the description of the operation of the erroneous cartridge insertion prevention mechanism in this embodiment is given with reference to the case where the non-drive side of the cartridge B is provided with the erroneous insertion prevention bosses  73  ( 73   a  and  73   b ). 
     The apparatus main assembly A also has to be provided with structural components for preventing the insertion of an incompatible cartridge into the apparatus main assembly A. Further, the structural components have to be on the same side as the erroneous insertion prevention bosses  73   a  and  73   a . Thus, the structural components of the erroneous cartridge insertion prevention mechanism of the apparatus main assembly A, which are on the non-drive side, are described. 
     Referring to  FIGS. 3 ,  7 ( a ), and  9 - 11 , the cartridge guiding left guide  12 L of the apparatus main assembly A is provided with an erroneous insertion prevention groove  12 Lb. Referring to  FIG. 11 , a letter J stands for the distance between the top surface  12 Lb 1  of the erroneous insertion prevention groove  12 Lb, and the bottom surface  12 La 1  of the erroneous insertion prevention groove  12 La. A letter K stands for the distance between a line K 1  which is tangential to the bottom side (which faces erroneous insertion prevention bosses  73   a  and  73   b ) of the insertion-extraction guide bosses  72 La and  72 Lb, and the erroneous insertion prevention bosses  73   a  and  73   b . The distance J is set to be less than the distance K. 
     Thus, when it is necessary to insert the cartridge B into the apparatus main assembly A, the cartridge B is to be inserted so that the insertion-extraction guide bosses  72 La and  72 Lb follow the cartridge guiding groove  12 La to allow the erroneous insertion prevention bosses  73   a  and  73   b  to pass through the erroneous insertion prevention groove  12 Lb. 
     In this embodiment, the apparatus main assembly A is structured so that the difference between the distance K between the aforementioned tangential line K 1  and the erroneous insertion prevention bosses  73   a  and  73   b , and the distance J between the top and bottom surfaces  12 Lb 1  and  12 La 1  is greater than the distance between the width H of the guiding groove  12 La and the diameter I of the insertion-extraction guide boss  72 La (K−J&gt;H−I). Therefore, when the cartridge B is inserted into the apparatus main assembly A, the erroneous insertion prevention bosses  73   a  and  73   b  can be made to pass the erroneous insertion prevention groove  12 Lb by simply making the insertion-extraction guide bosses  72 La and  72 Lb follow the guiding groove  12 La as described above. 
     In other words, while the cartridge B is inserted into the apparatus main assembly A, the cartridge B is controlled in attitude because the insertion-extraction guide bosses  72 La and  72 Lb of the cartridge B are regulated by the cartridge guiding groove  12 La as described above. 
     Referring to  FIGS. 3 and 7(   a ), the apparatus main assembly A is provided with an erroneous insertion prevention member (first movable member)  15 , which partially protrudes into the erroneous insertion prevention groove  12 Lb of the cartridge guiding left member  12 L. It is also provided with a rotational member (second movable member)  80 , which is rotated by the movement of the erroneous insertion preventing member  15 . 
     Next, referring to  FIG. 9(   a ) which is an exploded perspective view of the cartridge guiding member  12 L, the guiding member  12 L is provided with a recess  12 Lc, which is in the surface of the guiding member  12 L, which is in contact with the lateral plate  16 L of the apparatus main assembly A. The recess  12 Lc is shaped so that its depth M is greater than the width N of the erroneous insertion prevention member  15  (dimension in terms of lengthwise direction (left/right direction of apparatus)). Next, referring to  FIG. 10 , the erroneous insertion preventing member  15  is held in the recess  12 Lc of the guiding member  12 L, and is kept under the pressure from a pair of compression springs  17   a  and  17   b , which keep the erroneous insertion preventing member  15  pressed in the direction indicated by an arrow mark E. Thus, the erroneous insertion prevention member  15  is allowed to retreat in the direction indicated by an arrow mark F. 
     The distance by which the erroneous insertion preventing member  15  is allowed to protrude from the guiding member  12 L is controlled by the contact between the protrusions  15   a  and  15   b , with which the erroneous insertion preventing member  15  is provided, and the protrusions  12 Ld and  12 Le, with which the guiding member  12 L is provided. Thus, the erroneous insertion preventing member  15  is held in its protruding position Y, in which it partially protrudes into the erroneous insertion prevention groove  12 Lb of the guiding member  12 L. 
     On the other hand, referring to  FIGS. 9 and 11 , the rotational member  80  is provided with a hole  80   b , and a protrusion  80   c  for regulating the amount by which the rotational member  80  is rotationally moved. The protrusion  80   c  is on the surface of the rotational member  80 , which faces the guiding member  12 L. Further, the guiding member  12 L is provided with a rotational member supporting boss  12 Lf and a protrusion  12 Lg, which are in the recess  12 Lc of the guiding member  12 L. Further, there is disposed a torsional coil spring  17   c  between the rotational member  80  and guiding member  12 L. 
     The rotational member  80  is rotatably attached to the guiding member  12 L in such a manner that the rotational member supporting boss  12 Lf is fitted in the hole  80   b  of the rotational member  80 , with the torsional coil spring  17   c  attached to the rotation amount regulating protrusion  80   c  and the rotation amount regulating protrusion  12 Lg. 
     Therefore, the rotational member  80  is kept rotationally pressed by the torsional coil spring  17   c  so that it rotates in the clockwise direction in  FIG. 10  about the rotational member supporting boss  12 Lf. Thus, when the erroneous insertion preventing member  15  is in the above described protruding position Y, the surface  80   a  of the rotational member  80  is in contact with the surface  15   c   4  of the erroneous insertion preventing member  15 . Therefore, the rotational member  80  remains held in its non-blocking position X 1 , in which it does not protrude from the recess  12 Lc of the guiding member  12 L. 
     As described above, as the cartridge B is inserted into the apparatus main assembly A, the insertion-extraction guide bosses  72 La and  72 Lb of the cartridge B pass through the cartridge guiding groove  12 La, and the erroneous insertion prevention bosses  73   a  and  73  pass through the erroneous insertion prevention groove  12 Lb. That is, the cartridge B can be inserted all the way into the apparatus main assembly A by moving the cartridge B in the cartridge insertion direction G 1 , along the cartridge guiding member  12 L, as shown in  FIG. 11 . 
     Next, referring to  FIGS. 1(   a )- 1 ( f ), and  12 , the action of the erroneous cartridge insertion preventing means, which occurs as the cartridge B is inserted into the apparatus main assembly A, is described in detail.  FIG. 12  is auxiliary to FIG.  1 , and is an enlarged view of the erroneous insertion prevention bosses  73   a  and  73   b  of the cartridge B, and the erroneous insertion preventing member  15  of the apparatus main assembly A. Hereafter, the action of the erroneous cartridge insertion preventing means is described in the order of  FIGS. 1(   a )- 1 ( f ). 
     (a): The cartridge B is moved in the cartridge insertion direction G 1  shown in  FIG. 1(   a ), so that the insertion-extraction guide bosses  72 La and  72 Lb fit into the guiding groove  12 La, and follow the groove  12 La. During this process, the erroneous insertion preventing member  15  is free from the regulatory components, and is in its protruding position Y, partially protruding from the recess  12 Lc (guiding member  12 L). Therefore, the rotational member  80  is held in the non-blocking position X 1 , in which it does not protrudes from the recess  12 Lc of the guiding member  12 L.
 
(b): As the cartridge B is moved further into the apparatus main assembly A, the erroneous insertion prevention boss  73   a  comes into contact with the contacted portion  15   c  (which hereafter may be referred to simply as protrusive portion  15   c ) of the erroneous insertion preventing member  15 , which is in the protruding position Y. During this process, the surface  80   a  of the rotational member  80  is not being pressed by the surface  15   c   4  of the erroneous insertion preventing member  15 . Therefore, the rotational member  80  remains held in the non-blocking position X 1 . As the surface  73   a   1  of the erroneous insertion prevention boss  73   a  comes into contact with the slanted surface  15   c   1  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 , the erroneous insertion prevention boss  73   a  causes the erroneous insertion preventing member  15  to retract in the direction indicated by the arrow mark F.
 
(c): The erroneous insertion preventing member  15  retracts to the retraction position Z in which the surface  15   c   2  of its protrusive portion  15   c  comes into contact with the surface  73   a   2  of the erroneous insertion prevention boss  73   a . Thus, it becomes possible for the cartridge B to move further in the direction indicated by the arrow mark G 1 . Then, as the cartridge B is further moved, the surface  73   b   2  of the erroneous insertion prevention boss  73   b  comes into contact with the surface  15   c   2  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 . Thus, the erroneous insertion preventing member  15  is kept in the retraction position Z.
 
(d): As the protrusive portion  15   c  of the erroneous insertion preventing member  15  is made to retract from the paths of the erroneous insertion prevention bosses  73   a  and  73   b  of the cartridge B, in the direction indicated by the arrow mark F, the erroneous insertion prevention bosses  73   a  and  73   b  are allowed to move past the surface  15   c   2  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 .
 
     As for the surface  80   a  of the rotational member  80 , it is remaining in contact with the surface  15   c   4  of the erroneous insertion preventing member  15 . Therefore, it is pressed by the force S 1  in the direction indicated by the arrow mark F, as shown in  FIGS. 1(   c ) and  1 ( d ), because the erroneous insertion preventing member  15  was made to retract in the direction indicated by the arrow mark F as described above. 
     Therefore, the rotational member  80  rotates counterclockwise about the rotational member support boss  12 Lf, from the non-blocking position X 1  to the blocking position X 2 , in which the rotational member  80  partially protrudes in the direction indicated by the arrow mark E in  FIG. 1(   d ), from the recess  12 Lc of the guiding member  12 L, and therefore, it can come into contact with the erroneous insertion prevention boss  73   a.    
     (e): As the cartridge B is moved further into the apparatus main assembly A, the surface  73   a   2  of the erroneous insertion prevention boss  73   a  disengages from the surface  15   c   2  of the erroneous insertion preventing member  15 , and the surface  73   b   3  of the erroneous insertion prevention boss  73   b  comes into contact with the slanted surface  15   c   3  of the erroneous insertion preventing member  15 . Thus, the erroneous insertion preventing member  15  moves from its non-protruding position Z toward the protruding position Y in the direction indicated by the arrow mark E, with the surface  15   c   3  of the erroneous insertion preventing member  15  sliding on the surface  73   b   3  of the erroneous insertion prevention boss  73   b.    
     Meanwhile, as the erroneous insertion preventing member  15  begins to be moved in the direction indicated by the arrow mark E in  FIG. 1(   e ), the amount of the pressure S 2  which the surface  80   a  of the rotational member  80  receives from the surface  15   c   4  of the erroneous insertion preventing member  15  becomes smaller than the aforementioned amount of the pressure S 1 , because as the erroneous insertion preventing member  15  moves in the direction indicated by the arrow mark E from its non-protruding position Z to its protruding position Y, the compression springs  17   a  and  17   b  reduce in the amount of the pressure they apply to the erroneous insertion preventing member  15 , reducing thereby the amount of the pressure which the surface  80   a  of the rotational member  80  receives from the surface  15   c   4  of the erroneous insertion preventing member  15 . As a result, the rotational member  80  begins to rotates clockwise about the rotational member supporting boss  121   f  from its blocking position X 2 . 
     (f): Then, as the cartridge B is moved further into the apparatus main assembly A, the projection  15   a  and  15   b  of the erroneous insertion preventing member  15 , which are for regulating the amount by which the erroneous insertion preventing member  15  is allowed to protrude from the recess  12 Lc, come into contact with the protrusions  12 Ld and  12 Le of the guiding member  12 L, which are for regulating the amount by which the erroneous insertion preventing member  15  is allowed to protrude from the recess  12 Lc. Thus, the erroneous insertion preventing member  15  is kept in its protruding position Y. 
     As the cartridge B is further moved inward of the apparatus main assembly A, the surface  73   b   3  of the erroneous insertion prevention boss  73   b  disengages from the surface  15   c   3  of the erroneous insertion preventing member  15 , and therefore, the surface  80   a  of the rotational member  80  stops receiving pressure from the surface  15   c   4  of the erroneous insertion preventing member  15 . Thus, the rotational member  80  is held in the non-blocking position X 1  as described above, allowing thereby the erroneous insertion prevention bosses  73   a  and  73   b  to pass by the rotational member  18 , on the side indicated by the arrow mark E. 
     Because the erroneous insertion prevention bosses  73   a  and  73   b  of the cartridge B are allowed to pass by the protrusive portion  15   c  of the erroneous insertion preventing member  15 , and the rotational member  80 , on the side indicated by the arrow mark E, as described above, it becomes possible for the cartridge B to be inserted into its image formation position in the apparatus main assembly A. 
     The action of the structural components of the image forming apparatus (inclusive of cartridge B) which occurs when the cartridge B is extracted from the apparatus main assembly A is the reversal of the above described action of the structural components, which occurs when the cartridge B is inserted into the apparatus main assembly A. That is, as the cartridge B in the cartridge chamber  101  is pulled outward in the cartridge extraction direction G 2 , the means for preventing the insertion of an incompatible cartridge from being carried out in reversal sequence the steps shown in  FIGS. 1(   f )→ 1 ( e )→ 1 ( d )→ 1 ( c )→ 1 ( b )→ 1 ( a ), allowing thereby the cartridge B to be extracted from the apparatus main assembly A. 
     (4-2) Case in which Incompatible Cartridge B 2  is Inserted into Apparatus Main Assembly A 
     Next, referring to  FIGS. 13 and 14 , a case in which a cartridge B 2  (second cartridge), which is incompatible with the first image forming apparatus  100 , is inserted into the apparatus main assembly A of the image forming apparatus  100  is described.  FIG. 13  is a drawing for describing the erroneous insertion prevention boss of the cartridge B 2 .  FIG. 14  is a drawing for describing the movements, which occur to the structural components of the erroneous cartridge insertion preventing means if the cartridge B 2  is inserted into the apparatus main assembly A. 
     Referring to  FIG. 13 , the non-drive end (left end plate  71 L) of the cleaning unit frame  71  of the cartridge B 2  is provided with erroneous insertion prevention bosses  73   c  and  73   d , like the erroneous insertion prevention bosses  73   a  and  73   b  of the cartridge B ( FIG. 11 ). However, the distance O 2  between the erroneous insertion prevention bosses  73   c  and  73   d  in terms of the cartridge insertion direction indicated by the arrow mark G 1  in  FIG. 13  is set greater than the distance O 1  between the erroneous insertion prevention bosses  73   a  and  73   b  of the cartridge B shown in  FIG. 11 . 
     Referring to  FIGS. 14(   a )-( c ), the operation, which is carried out by the means for preventing the insertion of an incompatible cartridge, as the cartridge B 2  is inserted into the apparatus main assembly A, is described in detail. 
     (a): The cartridge B 2  is inserted into the apparatus main assembly A in the direction indicated by an arrow mark G 1 , in such a manner that the insertion-extraction guide bosses  72 La and  72 Lb of the cartridge B 2  follow the guiding groove  12 La of the guiding member  12 L. During this process, the erroneous insertion preventing member  15  is free from the regulatory components, and is in its protruding position Y. Therefore, the rotational member  80  is in its non-blocking position X 1 , remaining entirely in the recess  12 Lc. 
     Therefore, the erroneous insertion prevention boss  73   c  comes into contact with the protrusive portion  15   c  of the erroneous insertion preventing member  15 , like the protrusive portion  15   c  of the erroneous insertion preventing member  15  of the cartridge B. Thus, the surface  73   c   1  of the erroneous insertion prevention boss  73   c  comes into contact with the surface  15   c   1  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 , causing the erroneous insertion preventing member  15  to retreat in the direction indicated by an arrow mark F. 
     (b): Thus, the contact between the surface  73   c   2  of the erroneous insertion prevention boss  73   c  and the surface  15   c   2  of the protrusive portion  15   c  of the erroneous insertion preventing member  15  keeps the erroneous insertion preventing member  15  in the non-protruding position Z, allowing thereby the cartridge B to move further in the direction indicated by the arrow mark G 1 . 
     As for the rotational member  80 , its surface  80   a  is in contact with the surface  15   c   4  of the erroneous insertion preventing member  15 . Thus, as the erroneous insertion preventing member  15  is made to retreat in the direction indicated by the arrow mark F, the surface  80   a  is subjected to an amount S 1  of pressure by the surface  15   c   4 . Thus, the rotational member  80  rotationally moves counterclockwise about the rotational member supporting boss  12 Lf, from the non-blocking position X 1  into the blocking position X 2 , while gradually protruding from the recess  12 Lc of the guiding member  12 L, being enabled to contact the erroneous insertion prevention boss  73   a.    
     (c): As the cartridge B 2  is moved further, the surface  73   c   1  of the erroneous insertion prevention boss  73   c  comes into contact with the rotational member  80  for the following reason. That is, at this point, the erroneous insertion prevention boss  73   d  is in contact with the surface  15   c   2  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 , and therefore, the erroneous insertion preventing member  15  is in the non-protruding position Z. Therefore, the rotational member  80  is kept in the blocking position X 2 . 
     Therefore, it is impossible for the cartridge B 2  to be moved further in the direction indicated by the arrow mark G 1 . That is, it is impossible for the cartridge B 2  to be inserted into the image formation position in the apparatus main assembly A. 
     As for the extraction of the cartridge B 2  from the apparatus main assembly A when the cartridge B 2  is in the above described position, it is possible because as the cartridge B 2  is pulled outward, the surface  73   c   2  of the erroneous insertion prevention boss  73   c  comes into contact with the surface  15   c   1  of the protrusive portion  15   c  of the erroneous insertion preventing member  15 , and keeps the erroneous insertion preventing member  15  in the non-protruding position Z ( FIG. 14(   b )). As soon as the cartridge B 2  is extracted, the erroneous insertion preventing member  15  becomes free from the regulatory components, and therefore, returns to its protruding position Y, and the rotational member  80  returns to its non-blocking position X 1  ( FIG. 14(   a )). 
     (4-3) Case in which Cartridge B is Inserted into Apparatus Main Assembly A 2  which is Incompatible with Cartridge B 
     Described next referring to  FIGS. 15 and 16  is a case in which the cartridge B is inserted into the main assembly A 2  of the second image forming apparatus  200 , which is different from the first image forming apparatus  100 , in terms of the structural arrangement for preventing the insertion of an incompatible cartridge into the apparatus main assembly A.  FIG. 15  is a drawing for describing the structure of the apparatus main assembly A 2 , which is different from the apparatus main assembly A, in terms of their structural arrangement for preventing the problem that a cartridge which is incompatible with a given image forming apparatus is inserted into the apparatus.  FIG. 16  is a drawing for describing the operation of the structural arrangement of the apparatus main assembly A 2 , which is for preventing the cartridge B from being inserted into the image formation position in the apparatus main assembly A 2 . 
     Referring to  FIG. 15 , the non-drive side of the apparatus main assembly A 2  is provided with an erroneous insertion preventing member  18  (third movable member), as the non-drive side of the apparatus main assembly A is provided with the erroneous insertion preventing member  15 . However, in terms of the direction, indicated by an arrow mark G 1 , in which the cartridge B is to be inserted into the apparatus main assembly A 2 , the distance Q 2  between the erroneous insertion preventing member  18  and rotational member (fourth movable member)  80  is set to be less than the distance Q 1  between the erroneous insertion preventing member  15  and rotational member  80  of the apparatus main assembly A, for the following reason. 
     That is, this setup is for making it possible for the cartridge B 2 , which is compatible with the apparatus main assembly A 2 , to be inserted into its image formation position in the apparatus main assembly A 2 , like the cartridge B is installable in its image formation position in the apparatus main assembly A. That is, this setup is for positioning the erroneous insertion preventing member  18  and rotational member  80  so that the cartridge B 2  can be inserted into its image formation position in the apparatus main assembly A 2 . More specifically, it is for ensuring that after the erroneous insertion prevention boss  73   c  moves past the erroneous insertion preventing member  18 , on the side indicated by the arrow mark E, the erroneous insertion prevention boss  73   d  does not come into contact with the erroneous insertion preventing member  18 , and the erroneous insertion prevention boss  73   c  does not come into contact with the rotational member  80 . 
     Referring to  FIGS. 16(   a )- 16 ( c ), the action which takes place in the apparatus main assembly A 2  as the cartridge B is inserted into the apparatus main assembly A 2  is described in detail. 
     (a): A user is to move the cartridge B in the cartridge insertion direction indicated by an arrow mark G 1  while causing the insertion-extraction guide bosses  72 La and  72 Lb to follow the guiding groove  12 La of the guiding member  12 L. During this movement of the cartridge B, the erroneous insertion preventing member  18  is free from the regulatory components, and is in the protruding position Y. Therefore, the rotational member  80  is kept in the non-blocking position X 1  where the rotational member  80  does not protrude from the recess  12 Lc of the guiding member  12 .
 
(b): Thus, the erroneous insertion prevention boss  73   a  comes into contact with the protrusive portion  18   c  of the erroneous insertion preventing member  18 , like when the cartridge B is inserted into the apparatus main assembly A. Thus, the erroneous insertion preventing member  18  is made to retreat in the direction indicated by the arrow mark F by the erroneous insertion prevention boss  73   a , more specifically, the contact between the surface  73   a   1  of the erroneous insertion prevention boss  73   a  and the surface  18   c   1  of the protrusive portion  18   c  of the erroneous insertion preventing member  18 .
 
     Thus, the erroneous insertion preventing member  18  is moved into its non-protruding position Z by the contact between the surface  73   a   2  of the erroneous insertion prevention boss  73   a  and the surface  18   c   2  of the protrusive portion  18   c  of the erroneous insertion preventing member  18 , making it possible for the cartridge B to move further in the direction indicated by the arrow mark G 1 . 
     Meanwhile, the surface  80   a  of the rotational member  80  is in contact with the surface  18   c   4  of the erroneous insertion preventing member  18 . Thus, as the erroneous insertion preventing member  18  is made to retreat in the direction indicated by the arrow mark F, the surface  80   a  of the rotational member  80  is subjected to the pressure S 1  which acts in the direction indicated by the arrow mark F. Therefore, the rotational member  80  is rotationally moved counterclockwise about the rotational member supporting boss  12 Lf, from the non-blocking position X 1 , while being made to gradually protrude from the recess  12 Lc of the guiding member  12 L, to the blocking position X 2 , in which it partially protrudes from the recess  12 Lc of the guiding member  12 L, ensuring that the erroneous insertion prevention boss  73   a  comes into contact with the rotational member  80 . 
     (c): As the cartridge B is moved further inward of the apparatus main assembly A 2 , the surface  73   a   1  of the erroneous insertion prevention boss  73   a  comes into contact with the rotational member  80  for the following reason. That is, the erroneous insertion prevention boss  73   b  is in contact with the surface  18   c   2  of the protrusive portion  18   c  of the erroneous insertion preventing member  18 . Therefore, the erroneous insertion preventing member  18  remains in the non-protrusive position. Therefore, the rotational member  80  is kept in the blocking position. 
     Therefore, it is impossible for the cartridge B to be moved further in the direction indicated by the arrow mark G 1 . In other words, it is impossible for the cartridge B to be inserted into the image formation position in the apparatus main assembly A 2 . 
     The cartridge B which is in the position shown in  FIG. 16(   c ) can be easily extracted from the apparatus main assembly A 2 , because as the cartridge B is pulled in the cartridge extraction direction (indicated by arrow mark G 2 ), the surface  73   a   2  of the erroneous insertion prevention boss  73   c  comes into contact with the surface  18   c   2  of the protrusive portion  18   c  of the erroneous insertion preventing member  18 , and making it possible for the erroneous insertion preventing member  18  to move to the non-protruding position Z ( FIG. 16(   b )). Thus, the erroneous insertion preventing member  18  is freed from the regulatory components, and therefore, it returns to the protruding position Y, and so does the rotational member  80  return to the non-blocking position X 1  ( FIG. 16(   a )). 
     (5) Summary 
     The structure of the image forming apparatus  100  in the first embodiment of the present invention can be summarized as follows. 
     1) The image forming apparatus  100  is an apparatus for forming an image on a sheet P of recording medium. It employs the cartridge B which has the first and second portions  73   a  and  73   b  for contact, and is removably installable in the apparatus main assembly A. It has the portion  15   c  with which the cartridge B comes into contact, and the movable member  15  which is movable between its protrusive and non-protrusive positions Y and Z. It has also the rotational member  80 , which is rotationally movable in such a manner that when the abovementioned movable member  15  is in the protruding position Y, it is in its non-blocking position X 1 , whereas as the movable member  15  moves to the non-protruding position Z, the rotational member  18  is moved into the blocking position X 2  by the movable member  15 . 
     As the cartridge B is inserted into the apparatus main assembly A, the second portion  73   b  for contact disengages from the portion  15   c  of contact of the movable member  15  after the first portion  73   a  of contact passes by the movable member  15 , on the side indicated by the arrow mark E in which the movable member  15  protrudes. Therefore, it is possible for the first portion  73   a  of contact to pass by the rotational member  80 , on the side to which the rotational member  80  was protruding. 
     2) As the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes by the movable member  15 , on the side of the portion  15   c  of contact. Thereafter, the second portion  73   b  of contact makes the movable member  15  retreat into the non-protrusive position Z. At this point in time, there is no contact between the first portion  73   a  of contact and rotational member  80 . 
     3) The movable member  15  has a flat surface  15   c   3  which is tilted in such an attitude that its upstream side in terms of the direction G 1  in which the cartridge B is inserted into the apparatus main assembly A, is on the downstream side in terms of the direction, indicated by the arrow mark F, in which the movable member  15  is made to retreat. 
     4) The movable member  15  has the flat surface  15   c   1  which is tilted in such an attitude that its upstream side in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A, is on the upstream side in terms of the direction, indicated by the arrow mark E, in which the movable member  15  protrudes. 
     5) The movable member  15  is disposed on the upstream side of the rotational member  80  in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A. 
     6) The movable member  15  is under the pressure generated by the pressure applying means  17   a  and  17   b  so that when it is free from the regulatory components other than the pressure applying means  17   a  and  17   b , it is in the protruding position Y. 
     7) The movable member  15  is held by the guiding member  12 L which guides the cartridge B when the cartridge B is inserted into the apparatus main assembly A. Further, the cartridge B is provided with insertion-extraction guide bosses  72 La and  72 Lb, which are guided by the guiding member  12 L while the cartridge B is inserted into the apparatus main assembly A. 
     The structure of the cartridge B is as follows: 
     1) The cartridge B is such a cartridge which is removably installable in the main assembly A of the image forming apparatus  100  which forms an image on a sheet P of recording medium. The apparatus main assembly A has the movable member  15 , which has the portion  15   c  with which the cartridge B comes into contact while the cartridge B is inserted into the apparatus main assembly A. The movable member  15  is movable between the protruding position Y and non-protruding position Z. Further, the apparatus main assembly A has also the rotational member  80 , which is rotationally movable between the non-blocking position X 1  in which it is when the movable member  15  is in the protruding position Y, and the blocking position X 2  in which it is when the movable member  15  is in the non-protruding position Z. 
     The cartridge B is provided with the first and second portions ( 73   a  and  73   b ) of contact. While the cartridge B is inserted into the apparatus main assembly A, it is after the first portion  73   a  of contact moves past the movable member  15 , on the side toward which it protrudes as indicated by the arrow mark E, that the second portion  73   b  of contact becomes disengaged from the first portion  15   c  of contact. Therefore, it is possible for the first portion  73   a  to pass by the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     2) While the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes the movable member  15 , on the side of the portion  15   c  of contact, and disengages from the portion  15   c  of contact. Thereafter, when the second portion  73   b  of contact causes the movable member  15  to retreat into the non-protrusive position, the first portion  73   a  of contact is not in contact with the rotational member  80 . 
     The structure of the main assembly A is as follows: 
     1) The main assembly A of the image forming apparatus  100  which forms an image on a sheet P of recording medium is such an assembly in which the cartridge B having the first and second portions  73   a  and  73   b  of contact is removably installable. It has the movable member  15  and rotational member  80 . The movable member  15  has the portion  15   c  with which the cartridge B comes into contact. The movable member  15  is movable between the protruding position Y and non-protruding position Z. When the movable member  15  is in the protruding position Y, the rotational member  80  is in the non-blocking position X 1 , whereas as the movable member  15  is made to retreat into the non-protruding position Z, the rotational member  80  is rotationally moved into the blocking position X 2  by the movable member  15 . 
     Also while the cartridge B is inserted into the apparatus main assembly A, the second portion  73   b  of contact becomes disengaged from the protrusive portion  15   c  of the movable member  15  after the first portion  73   a  passes the movable member  15 , on the side toward which the movable member  15  protrudes. Therefore, the first portion  73   a  of contact is allowed to pass the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     2) While the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes the movable member  15 , on the side toward which the protrusive portion  15   c  protrudes, and disengages from the portion  15   c  of contact. Thereafter, when the second portion  73   b  of contact causes the movable member  15  to retreat into the non-protrusive position, the first portion  73   a  of contact is not in contact with the rotational member  80 . 
     3) The movable member  15  has the flat surface  15   c   3 , which is tilted in such an attitude that the downstream side of the flat surface  15   c   3  in terms of the cartridge insertion direction indicated by the arrow mark G 1  is on the upstream side in terms of the direction, indicated by the arrow mark F, in which the movable member  15  is made to retreat. 
     4) The movable member  15  has the flat surface  15   c   1 , which is tilted in such an attitude that its upstream side in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A, is on the downstream side in terms of the direction, indicated by the arrow mark E, in which the movable member  15  protrudes. 
     5) The movable member  15  is disposed on the upstream side of the rotational member  18  in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A. 
     6) The movable member  15  is kept pressed toward the protruding position Y by the elastic pressing means  17   a  and  17   b.    
     7) The movable member  15  is held by the guiding member  12 L which is for guiding the insertion-extraction guide bosses  72 La and  72 Lb, with which the cartridge B is provided, while the cartridge B is inserted into the apparatus main assembly A. 
     The structure of the system for preventing the problem that a process cartridge is installed into an electrophotographic image forming apparatus which is not compatible with the process cartridge is as follows: 
     This system is for preventing the problem that a cartridge B, which is removably installable in the main assembly A of an image forming apparatus  100  for forming an image on a sheet P of recording medium, is erroneously installed into the main assembly of an image forming apparatus which is not compatible with the cartridge B. The apparatus main assembly A has the movable member  15  and rotational member  80 . The movable member  15  has the portion  15   c  with which the process cartridge B comes into contact. It is movable between the protruding position Y and non-protruding position Z. The rotational member  80  is movable between its non-blocking position X 1 , in which it is when the movable member  15  is in the protruding position Y, and the blocking position X 2 , in which it is when the movable member  15  is in the non-protruding position Z. Further, the cartridge B is provided with the first and second portions  73   a  and  73   b  of contact. 
     While the cartridge B is inserted into the apparatus main assembly A, it is the first portion  73   a  of contact that passes first the movable member  15 , on the side, indicated by the arrow mark E 1 , toward which the movable member  15  protrudes. Further, it is after the first portion  73   a  of contact passes the portion  15   c  of the movable member  15  that the second section  73   b  of contact becomes disengaged from the portion  15   c  of the movable member  15 . Therefore, the first portion  73   a  of contact is allowed to pass the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     The system, in this embodiment, for preventing the problem that a process cartridge is installed in the main assembly of an electrophotographic image forming apparatus which is not compatible with the process cartridge, is structured as described above. Therefore, the system can be positioned close to the cartridge entrance of the apparatus main assembly A. Further, the system is structured so that the erroneous insertion preventing member  15  is disposed in the recess  12 Lc of the cartridge guiding member  12 L, and is enabled to move in the direction indicated by the arrow mark E or F to allow the erroneous insertion prevention bosses  73   a  and  73   b  to pass the erroneous insertion preventing member  15 , on the side indicated by the arrow mark E. Therefore, the employment of this system does not affect the apparatus main assembly A in dimension in terms of the lengthwise direction. Further, the system is simple in structure, and yet, can ensure that the above-described problem is prevented regardless of any combination between a process cartridge, and an image forming apparatus incompatible with the cartridge, vice versa. 
     Therefore, it is possible to provide a combination of an image forming apparatus and a process cartridge therefor, which is simple in structure, can make it possible to determine whether the cartridge which is being inserted into the apparatus main assembly A is compatible with the apparatus main assembly A, while the cartridge is in the adjacencies of the cartridge entrance of the apparatus main assembly A, and yet, can reliably prevent the installation of a cartridge into an image forming apparatus incompatible with the cartridge. Further, the employment of this system does not affect an image forming apparatus in length. 
     Embodiment 2 
     The image forming apparatus in the first embodiment can be modified in structure so that in order to prevent the problem that a cartridge is inserted all the way into the main assembly of an image forming apparatus, the apparatus main assembly A is provided with the first and second portions  73   a  ( 73   e ) and  73   b  ( 73   f ) of contact, and the cartridge B is provided with the movable member  15  ( 18 ) and rotational member  80 . 
     That is, the structure of the image forming apparatus  100  in this embodiment is as follows: 
     1) The image forming apparatus  100  in this embodiment is an apparatus for forming an image on a sheet P of recording medium, and employs a cartridge B which is removably installable in the apparatus main assembly A. The cartridge B is provided with a movable member  15  and a rotational member  80 . The movable member  15  has a portion  15   c  which comes into contact with the counterpart of the apparatus main assembly. It is movable between the protruding position Y and non-protruding position Z. The rotational member  80  is rotationally movable between the non-blocking position X 1 , in which it is when the movable member  15  is in the protruding position Y, and the blocking position X 2 , in which it is when the movable member  15  is in the non-protruding position Z. The apparatus main assembly A has the first and second portions  73   a  and  73   b  of contact. 
     As the cartridge B is inserted into the apparatus main assembly A, the cartridge contacting first portion  73   a  passes by the movable member  15 , on the side, indicated by the arrow mark E, toward which the movable member  15  protrudes. The cartridge catching section  73   b  becomes disengaged from the protrusive portion  15   c  of the movable member  15 . Therefore, the first portion  73   a  is allowed to pass the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     2) While the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes by the movable member  15 , on the side of the protrusive portion  15   c , and disengages from the protrusive portion  15   c . It is before the first portion  73   a  of contact disengages from the protrusive portion  15   c  that the second portion  73   b  comes into contact with the protrusive portion  15   c  and causes the movable member  15  into the non-protrusive position Z. Therefore, the first portion  73   a  of contact is not in contact with the rotational member  80 . 
     3) The movable member  15  has a flat surface  15   c   3  which is tilted in such an attitude that its downstream side in terms of the direction G 1  in which the cartridge B is inserted into the apparatus main assembly A, is on the upstream side in terms of the direction, indicated by the arrow mark F, in which the movable member  15  is made to retreat. 
     4) The movable member  15  has the flat surface  15   c   1  which is tilted in such an attitude that its upstream side in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A, is on the downstream side in terms of the direction, indicated by the arrow mark E, in which the movable member  15  protrudes. 
     5) The movable member  15  is disposed on the upstream side of the rotational member  80  in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A. 
     6) The movable member  15  is under the pressure generated by the pressure applying means  17   a  and  17   b  so that when it is free from the regulatory components other than the pressure applying means  17   a  and  17   b , it is in the protruding position Y. 
     7) Further, the cartridge B is provided with insertion-extraction guide bosses  72 La and  72 Lb, which are guided by the guiding member  12 L while the cartridge B is inserted into the apparatus main assembly A. 
     The structure of the cartridge B is as follows: 
     1) The cartridge B is such a cartridge which is removably installable in the main assembly A of the image forming apparatus  100  which forms an image on a sheet P of recording medium. It is provided with the first and second portions  73   a  and  73   b  of contact. It has a movable member  15  and a rotational member  80 . The movable member  15  has the portion  15   c  with which the cartridge B comes into contact with the counterpart of the apparatus main assembly while the cartridge B is inserted into the apparatus main assembly A. The movable member  15  is movable between the protruding position Y and non-protruding position Z. The rotational member  80  is rotationally movable between the non-blocking position X 1  in which it is when the movable member  15  is in the protruding position Y, and the blocking position X 2  in which it is when the movable member  15  is in the non-protruding position Z. 
     While the cartridge B is inserted into the apparatus main assembly A, it is after the first portion  73   a  of contact moves past the movable member  15 , on the side toward which it protrudes as indicated by the arrow mark E, that the second portion  73   b  of contact becomes disengaged from the first portion  15   c  of contact. Therefore, it is possible for the first portion  73   a  to pass by the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     2) While the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes the movable member  15 , on the side of the portion  15   c  of contact, and disengages from the portion  15   c  of contact. Thereafter, when the second portion  73   b  of contact causes the movable member  15  to retreat into the non-protrusive position Z, the first portion  73   a  of contact is not in contact with the rotational member  80 . 
     3) The movable member  15  has the flat surface  15   c   3 , which is tilted in such an attitude that the upstream side of the flat surface  15   c   3  in terms of the cartridge insertion direction indicated by the arrow mark G 1  is on the downstream side in terms of the direction, indicated by the arrow mark F, in which the movable member  15  is made to retreat. 
     4) The movable member  15  has the flat surface  15   c   1 , which is tilted in such an attitude that its upstream side in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A, is on the downstream side in terms of the direction, indicated by the arrow mark E, in which the movable member  15  protrudes. 
     5) The movable member  15  is disposed on the upstream side of the rotational member  18  in terms of the direction, indicated by the arrow mark G 1 , in which the cartridge B is inserted into the apparatus main assembly A. 
     6) The movable member  15  is kept pressed toward the protruding position Y by the elastic pressing means  17   a  and  17   b.    
     The structure of the image forming apparatus main assembly A is as follows: 
     1) The image forming apparatus  100  in this embodiment is an apparatus for forming an image on a sheet P of recording medium, and employs a cartridge B which is removably installable in the apparatus main assembly A. The cartridge B is provided with a movable member  15  and a rotational member  80 . The movable member  15  has a portion  15   c  which comes into contact with the counterpart of the apparatus main assembly A. It is movable between the protruding position Y and non-protruding position Z. The rotational member  80  is rotationally movable between the non-blocking position X 1 , in which it is when the movable member  15  is in the protruding position Y, and the blocking position X 2 , in which it is when the movable member  15  is in the non-protruding position Z. The apparatus main assembly A has the first and second portions  73   a  and  73   b  of contact. 
     As the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes by the movable member  15 , on the side, indicated by the arrow mark E, toward which the movable member  15  protrudes. Thereafter, the second portion  73   b  of contact separates from the protrusive portion  15   c , and the first portion  73   a  of contact can pass by the rotational member  18 , on the side toward which the rotational member  80  protrudes. 
     2) While the cartridge B is inserted into the apparatus main assembly A, the first portion  73   a  of contact passes by the movable member  15 , on the side of the protrusive portion  15   c , and disengages from the protrusive portion  15   c . It is before the first portion  73   a  of contact disengage from the protrusive portion  15   c  that the second portion  73   b  comes into contact with the protrusive portion  15   c  and causes the movable member  15  into the non-protrusive position Z. Therefore, the first portion  73   a  of contact is not in contact with the rotational member  80 . 
     3) The apparatus main assembly A has the guiding member  12 L which guides the insertion-extraction bosses  72 La and  72 Lb, with which the cartridge B is provided, while the cartridge B is inserted into the apparatus main assembly A. 
     The structure of the system for preventing the erroneous insertion of the cartridge B is as follows. 
     The system is for preventing the cartridge B, which is removably installable in the main assembly A of the image forming apparatus  100  for forming an image on a sheet P of recording medium, from being erroneously inserted. The apparatus main assembly A has the first and second portions  73   a  and  73   b  of contact. The cartridge B has the movable member  15  and rotational member  80 . The movable member  15  has the protrusive portion  15   c , and is movable between the protrusive position Y, and the non-protrusive position Z. The rotational member  80  is movable between non-blocking position X 1 , in which it is when the movable member  15  is in the protrusive position Y, and the blocking position X 2 , in which it is when the movable member  15  is in the non-blocking position. 
     While the cartridge B is inserted into the apparatus main assembly A, it is after the first portion  73   a  of contact passes by the movable member  15 , on the side, indicated by the arrow mark E, toward which the movable member  15  protrudes, that the second portion  73   b  of contact separated from the protrusive portion  15   c . Therefore, the first portion  73   a  is allowed to pass by the rotational member  80 , on the side toward which the rotational member  80  protrudes. 
     The effects of the second embodiment described above are the same as those obtainable by the first embodiment. 
     [Miscellanies] 
     1) The functions, materials, and shapes of the structural components of the image forming apparatuses in the preceding embodiments of the present invention, and the positional relationship among the structural components, are not intended to limit the present invention in scope, unless specifically noted. 
     2) The image forming apparatuses to which the present invention is applicable are not limited to the electrophotographic image forming apparatuses in the preceding embodiments. That is, they include image forming apparatuses which use various known image formation principles and methods, for example, an electrostatic recording process, a magnetic recording process, etc., other than the electrophotographic process. 
     3) The image forming apparatuses to which the present invention is applicable are not limited to image forming apparatuses which employs only a single cartridge. That is, they include image forming apparatuses which employ multiple cartridges (different in color of developer (toner) they contain, and removably installable in preset cartridge chambers), and form a color image, and the like. 
     4) The cartridges to which the present invention is applicable are not limited to those, in the preceding embodiments, of the so-called all-in-one type. They include also process cartridges of the so-called separation type, and development cartridges equipped with developing means for developing a latent image formed on an image bearing member. They include also units which are removably installable in the main assembly of an image forming apparatus and contributes to the process for forming an image on recording medium. 
     As will be evident from the detailed description of the embodiments of the present invention, the present invention makes it possible to place the system for preventing the problem that a cartridge is installed in an image forming apparatus which is incompatible with the cartridge, in the adjacencies of the cartridge entrance of an image forming apparatus. It can provide a reliable system for preventing the above described problem, regardless of combination between an image forming apparatus and a cartridge, which is simple in structure, does not affect an image forming apparatus in the length of its main assembly. That is, the present invention can provide a reliable system for preventing the problem that a cartridge is installed in an image forming apparatus incompatible with the cartridge, which is simply in structure, does not require the apparatus to be increased in length, and can inform a user whether or not a cartridge being installed in the apparatus is compatible with the apparatus, while the cartridge is still in the adjacencies of the cartridge entrance of the apparatus. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Application No. 210765/2012 filed Sep. 25, 2012, which is hereby incorporated by reference.