Abstract:
A process cartridge which is capable of being carried on a movable guide provided in the main assembly of an electrophotographic image forming apparatus and which is movable from a receiving position toward a mount position in interrelation with movement of the movable guide, includes an electrophotographic photosensitive drum; process means actable on the drum; a cartridge frame supporting the drum and the process means; a first portion to be carried, provided at one longitudinal end of the drum, for being supported by the movable guide; a second portion to be carried, provided at the other longitudinal end of the drum, for being supported by the movable guide; a first positioning portion to be positioned relative to a main assembly, the first positioning portion extending outwardly from the cartridge frame adjacent the one longitudinal end of the drum; a second positioning portion to be positioned relative to the main assembly, the second positioning portion extending outwardly from the cartridge frame adjacent the other longitudinal end of the drum; and an engaging portion for engagement with a locking portion which is movable in interrelation with the movement of the movable guide to receive a pulling force for movement from the receiving position toward the mount position.

Description:
FIELD OF THE INVENTION AND RELATED ART  
       [0001]     The present invention relates to a process cartridge, a mechanism for mounting a process cartridge, and an electrophotographic image forming apparatus.  
         [0002]     Here, an electrophotographic image forming apparatus means an apparatus which forms an image on recording medium (for example, recording paper, OHP sheet, fabric, etc.) with the use of one of the electrophotographic image forming methods. As examples of an electrophotographic image forming apparatus, there are an electrophotographic copying machine, an electrophotographic printer (for example, laser printer, LED printer, etc.) a facsimileing machine, a wordprocessor, as well as a complex machine (multi-function printer, etc.) comprising a combination of two or more of the preceding apparatuses.  
         [0003]     A process cartridge means a cartridge which is removably mountable in the main assembly of an image forming apparatus, and in which a charging means as a processing means, a developing means or a cleaning means as a processing means, and an electrophotographic photosensitive member, are integrally disposed. It also means a cartridge which is removably mountable in the main assembly of an image forming apparatus, and in which an electrophotographic photosensitive member and a minimum of one processing means among a charging means, a developing means, and cleaning means are integrally disposed. It also means a cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and in which an electrophotographic photosensitive member and a minimum of one processing means, specifically, a developing apparatus, are integrally disposed.  
         [0004]     In the field of an electrophotographic image forming apparatus, a process cartridge system has long been employed, according to which an electrophotographic photosensitive drum (which hereinafter will be referred to as “photosensitive drum”), and a single or multiple processing means which act on the photosensitive drum are integrally disposed in a cartridge which is removably mountable in the main assembly of an image forming apparatus. Also according to a process cartridge system, an electrophotographic image forming apparatus can be maintained by an operator himself without any help from a service person, tremendously improving operational efficiency. Thus, a process cartridge system is widely in use in the field of an electrophotographic image forming apparatus.  
         [0005]     It has also been known that in the case of an image forming apparatus employing a cartridge system, as a certain cover of the main assembly of the image forming apparatus is opened or closed, the process cartridge in the main assembly is moved from the image formation position (mounted position) in the main assembly to the front area (mounting position) of the main assembly, or from the front area to the image formation position, respectively (Japanese Laid-open Patent Application 2-159790).  
         [0006]     According to the above patent document, a cartridge is to be mounted into the movable cartridge guide of the main assembly of an image forming apparatus from the front side of the main assembly. As the cover of the main assembly is closed, the movable cartridge guide is moved by the closing movement of the cover, conveying thereby the cartridge to the image formation position (mounted position).  
         [0007]     Therefore, it is unnecessary for an operator to push the cartridge to the inward end of the main assembly when mounting the process cartridge into the main assembly.  
         [0008]     Thus, this mechanical arrangement drastically improves the operational efficiency regarding the mounting of the process cartridge into the main assembly.  
         [0009]     The present invention is a result of further development of the above described prior art.  
       SUMMARY OF THE INVENTION  
       [0010]     The primary object of the present invention is to provide a combination of a process cartridge, a mechanism for mounting a process cartridge into the image assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus, which is superior, in operability regarding the mounting of a process cartridge into the main assembly, to that in accordance with the prior art.  
         [0011]     Another object of the present invention is to provide a combination of a process cartridge, a mechanism for mounting a process cartridge into the image assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus, which assures that a process cartridge is moved from the cartridge mounting position to the image formation position.  
         [0012]     Another object of the present invention is to provide a combination of a process cartridge, a mechanism for mounting a process cartridge into the image assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus, which keeps on pulling the cartridge in the cartridge insertion direction while the process cartridge is moved from the mounting position to the image formation position.  
         [0013]     Another object of the present invention is to provide a combination of a process cartridge, a mechanism for mounting a process cartridge into the image assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus, which keeps on pulling the cartridge in the cartridge insertion direction from the mounting position to the image formation position.  
         [0014]     Another object of the present invention is to provide a combination of a process cartridge, a mechanism for mounting a process cartridge into the image assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus, in which the process cartridge is mountable in the movable cartridge guides of the main assembly of an electrophotographic image forming apparatus; is movable by the movement of the movable cartridge guides from the cartridge mounting position to the image formation position; and comprises a first cartridge positioning portion, which is extended from one of the lengthwise ends of the cartridge in the direction parallel to the axial line of the photosensitive drum, to be placed in contact with the main assembly of the image forming apparatus in order to properly position the cartridge relative to the apparatus main assembly, and the axial line of which coincides with that of the photosensitive drum; a second cartridge positioning portion, which is extended from the other lengthwise end of the cartridge in the direction parallel to the axial line of the photosensitive drum, to be placed in contact with the main assembly of the image forming apparatus in order to properly position the cartridge relative to the apparatus main assembly, and the axial line of which coincides with that of the photosensitive drum; and catch portions with which the latches of the apparatus main assembly are made to engage, by the movement of the movable cartridge guides of the apparatus main assembly, in order to generate force in the direction to pull the cartridge in the cartridge mounting direction.  
         [0015]     These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a schematic perspective view of the process cartridge, being held by the movable cartridge guide of the main assembly of an image forming apparatus, in first embodiment of the present invention.  
         [0017]      FIG. 2  is a schematic sectional view of the image forming apparatus (color laser printer) employing an electrophotographic image formation process, in the first embodiment of the present invention.  
         [0018]      FIG. 3  is a schematic sectional view of the process cartridge in the first embodiment of the present invention.  
         [0019]      FIG. 4  is a schematic sectional view of the image forming apparatus, the cover of which is open, in the first embodiment of the present invention.  
         [0020]      FIG. 5  is a schematic sectional view of the image forming apparatus, the cover of which is open, in the first embodiment of the present invention.  
         [0021]      FIG. 6  is a top view of the process cartridge in the first embodiment of the present invention.  
         [0022]      FIG. 7  is a right side view of an essential portion of the movable cartridge guide, in which the cartridges have been mounted.  
         [0023]      FIG. 8  is a left side view of an essential section of the movable cartridge guide, in which the cartridges have been mounted.  
         [0024]      FIG. 9  is a schematic sectional view the image forming apparatus in the first embodiment of the present invention, showing how a process cartridge in this embodiment is mounted into the main assembly of the image forming apparatus.  
         [0025]      FIG. 10  is a schematic sectional view of the image forming apparatus in the first embodiment of the present invention, showing how the movable cartridge guide is pivoted.  
         [0026]      FIG. 11  is a schematic sectional view of the image forming apparatus in the first embodiment of the present invention, after the automatic mounting of the process cartridge into the main assembly of the image forming apparatus.  
         [0027]      FIG. 12  is a schematic side view of the cartridge retaining member, showing its movement.  
         [0028]      FIG. 13  is a schematic external perspective view of the process cartridge in the second embodiment of the present invention.  
         [0029]      FIG. 14  is a schematic sectional view of an essential portion of the image forming apparatus in the second embodiment of the present invention, showing the positioning of the cartridge retaining members.  
         [0030]      FIG. 15  is a schematic sectional view of one of the process cartridges, the cartridge retaining member therefor, and their adjacencies, in the image forming apparatus in the second embodiment of the present invention, showing the positioning of the cartridge retaining member.  
         [0031]      FIG. 16  is a schematic sectional view of the cartridge positioning portion of the process cartridge in the second embodiment of the present invention, showing how the cartridge positioning portion is accurately positioned.  
         [0032]      FIG. 17  is a schematic sectional view of an urging member according to a second embodiment.  
         [0033]      FIG. 18  is a schematic sectional view of an urging member according to a second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     Hereinafter, preferred embodiments of the present invention will be described with reference to the appended drawings. The measurements, materials, configurations of the structural components, and their positional relationships, in this embodiment, are not intended to limit the scope of the present invention, unless specifically noted. Also hereinafter, once a given element in this embodiment is described regarding its material, configuration, etc., it will be the same throughout this specification, unless specifically noted.  
         [0035]     In the following descriptions of the preferred embodiments of the present invention, the lengthwise direction of a process cartridge means the direction intersectional with (virtually perpendicular to) the direction in which a process cartridge is mounted into, or removed from, the main assembly of an image forming apparatus. The top and bottom surfaces of a process cartridge means the surfaces of the process cartridge, which will be on the top and bottom of the process cartridge, respectively, when the process cartridge is properly situated in the main assembly.  
         [heading-0036]     (Embodiment 1)  
         [0037]     Hereafter, referring to  FIGS. 1-12 , the process cartridge and electrophotographic color image forming apparatus in the first embodiment will be described.  
         [heading-0038]     [Description of General Structure of Electrophotographic Color Image Forming Apparatus] 
         [0039]     First, the general structure of the color image forming apparatus will be described with reference to  FIG. 2 , which is a sectional view of the image forming apparatus employing an electrophotographic process in this embodiment.  
         [0040]     As shown in  FIG. 2 , the color laser printer A (which hereinafter will be simply referred to as “printer”) is a four-drum type (inline type) printer, which comprises four process cartridges  20  ( 20 Y,  20 M,  20 C, and  20 Bk) and an intermediary transfer member (medium)  40 .  
         [0041]     The four process cartridges  20  ( 20 Y,  20 M,  20 C, and  20 Bk) are mounted in the main assembly of the color printer A, being vertically stacked. The cartridge  20 Y stores developer of yellow color, and forms an image of the yellow developer. The cartridge  20 M stores developer of magenta color, and forms an image of the magenta developer. The cartridge  20 C stores developer of cyan color, and forms an image of the cyan developer. The cartridge  20 Bk stores developer of black color, and forms an image of the black developer. The intermediary transfer member  40  is a member onto which images formed of developers in process cartridges  20  are temporarily transferred in layers, forming an image (color image) formed of the developers different in color, and from which the image (color image) is transferred onto a recording medium P.  
         [0042]     After the transfer of the color image onto the recording medium P, the recording medium P is conveyed to a fixing device  60 . Then, in the fixing device  60 , the color image is fixed to the recording medium P. Thereafter, three pairs  71 ,  72 , and  73  of discharge rollers discharge the recording medium P, to which the color image has just been fixed, to a delivery tray  70 , which is a part of the top surface of the main assembly.  
         [0043]     The four cartridges  20  can be individually mounted into, or removed from, the main assembly A of the printer.  
         [0044]     Next, referring to  FIGS. 2 and 3 , the various portions of the image forming apparatus will be described in structure in a logical order.  FIG. 3  is a schematic sectional view of the cartridge in this embodiment. Incidentally, where all the cartridges are the same regarding a given structural feature, only the cartridge  20 Y will be described regarding this structural feature, and the other process cartridges will not be described regarding this structural feature.  
         [heading-0045]     [Photosensitive Drum] 
         [0046]     The photosensitive drum  21  in this embodiment comprises an aluminum cylinder, and a layer of organic photosensitive substance coated on the peripheral surface of the photosensitive drum  21 . It is rotatably supported by the frame  26  of the cartridge  21 . At the back side ( FIG. 2 ) of the cartridge  20 , the driving force from a cartridge driving motor (unshown) is transmitted to the lengthwise end of the photosensitive drum  21 , whereby the photosensitive drum  21  is rotated in the counterclockwise direction ( FIG. 3 ) indicated by an arrow mark in the drawing in synchronism with an image formation.  
         [heading-0047]     [Charging Means] 
         [0048]     A charging means  22  ( 22 Y) is provided with a charge roller  22   a  capable of applying voltage. The peripheral surface of the photosensitive drum  21  is uniformly charged by the charge roller  22   a.    
         [heading-0049]     [Exposing Means] 
         [0050]     The photosensitive drum  21  is exposed by a scanner portion  50 . The scanner portion  50  in this embodiment is provided with two polygon mirrors  52  ( 52 YM and  53 CBk), each of which is capable of guiding an image forming beam of light to two cartridges  20 . Thus, an image forming beam of light can be guided to the total of four cartridges  20 . As image formation signals are sequentially given to a laser diode (unshown), the laser diode projects a beam of image formation light  51  ( 51 Y) reflecting the image formation signals to the polygon mirror  52 , which is being rotated at a high speed. The image formation light  51  is reflected (deflected) by the polygon mirror  52  ( 52 YM), and then, is reflected (deflected) by the reflective lens  54  ( 54 Y). Then, the image formation light  51  is guided through the focal lens  53  ( 53 Y) onto the peripheral surface of the photosensitive drum  21 , which is being rotated a predetermined peripheral velocity. As the image formation light  51  reaches the peripheral surface of the photosensitive drum  21 , the numerous points of the peripheral surface of the photosensitive drum  21  are selectively exposed, forming thereby an electrostatic latent image on the peripheral surface of the photosensitive drum  21 .  
         [heading-0051]     [Developing Means] 
         [0052]     The developing means has a development roller  23  ( 23 Y), by which the aforementioned electrostatic latent image is developed. For the development of the latent image, the development roller  23  is disposed in parallel to the photosensitive drum  21 , with its peripheral surface being in contact with the peripheral surface of the photosensitive drum  21 , and is rotated in such direction that, in the contact area between the development roller  23  and photosensitive drum  21 , the peripheral surface of the development roller  23  moves in the same direction as that of the photosensitive drum  21 . The development roller  23  forms a visible image, that is, an image formed of developer, on the peripheral surface  21 .  
         [heading-0053]     [Intermediary Transfer Member] 
         [0054]     The intermediary transfer member  40  is a member onto which multiple images formed of developers on the photosensitive drums  21 , by the developer rollers  23 , one for one, are transferred in layers during color image formation. The intermediary transfer member  40  is circularly driven in the clockwise direction ( FIG. 2 ) at the same peripheral velocity as that of the photosensitive drum  21 .  
         [0055]     After being formed on the photosensitive drums  21 , the images formed of developers are transferred onto the intermediary transfer member  40  by the primary transfer rollers  42  ( 42 Y,  42 M,  42 C, and  42 Bk), one for one. Each transfer roller  42  is disposed so that it is kept pressed upon the corresponding photosensitive drum  21 , with the intermediary transfer member  40  sandwiched between the transfer roller  42  and photosensitive drum  21 .  
         [0056]     After the multiple images formed of developers are transferred in layers onto the intermediary transfer member  40 , the intermediary transfer member  40  and secondary transfer roller  5  nip the recording medium P between them, and together convey the recording medium P. As a result, the color images formed of developers, on the intermediary transfer member  40 , are transferred all at once onto the recording medium P.  
         [0057]     The intermediary transfer member (intermediary transfer belt)  40  in this embodiment is a seamless resin belt with a circumferential dimension of roughly 620 mm. It is stretched around a driving roller  41 . Intermediary transfer member backing roller  43 , and tension roller  44 , being thereby supported by them. The tension roller  44  is kept pressured outward of the loop, which the intermediary transfer member  40  forms, by the pressure applied to the lengthwise ends of the roller  44 . With the provision of this structural arrangement, should the circumferential dimension of the intermediary transfer member  40  change due to the changes in the internal temperature and/or humidity, and the elapse of time, the change is absorbed by this structural arrangement, whereby the amount of the tension to which the intermediary transfer member  40  is subjected remains virtually constant.  
         [0058]     Further, the intermediary transfer member  40  is pivotally held to the main assembly A of the apparatus (printer), being allowed to pivot about the rotational axis of the driving roller  41 . The driving force from a motor (unshown) is transmitted to the back end ( FIG. 2 ) of the driving roller  41 , circularly rotating the intermediary transfer member  40  in the clockwise direction ( FIG. 2 ) in synchronism with image formation.  
         [heading-0059]     [Feeding Station] 
         [0060]     The feeding station is a station for conveying recording mediums P to the cartridges  20  in the main assembly A of the printer. It comprises a cassette  1  capable of containing multiple recording mediums P, a roller  2 , and a pair of registration rollers  3 , etc.  
         [0061]     During image formation, the roller  2  is rotationally driven in synchronism with image formation, whereby the recording mediums P in the cassette  1  are fed one by one out of the cassette  1 , toward the pair of registration rollers  3 , which carries out in a predetermined sequence, the process for keeping the recording medium P on standby and the process for conveying the recording medium P toward the intermediary transfer member  40 , in order to make the recording medium P align with the images on the intermediary transfer member  40  during the image transfer process.  
         [heading-0062]     [Transfer Station] 
         [0063]     The transfer station has a secondary transfer roller  5 , which is rotationally driven, and is roughly vertically movable ( FIG. 2 ). In synchronism with the arrival of the color images at the transfer station, the transfer roller  5  is pressed against the intermediary transfer member  40  by a cam (unshown) onto the recording medium P with the application of a predetermined amount of pressure, with the recording medium P nipped between the intermediary transfer member  40  and transfer roller  5 . During this process, bias is applied to the transfer roller  5 . As a result, the image formed of developers, on the intermediary transfer member  40  are transferred onto the recording medium P. Incidentally, the intermediary transfer member  40  and transfer roller  5  are driven independently from each other. Therefore, after the transfer process, the recording medium P, which has been kept sandwiched by the intermediary transfer member  40  and transfer roller  5  during the transfer process, is conveyed leftward ( FIG. 2 ), reaching a fixing device  60 .  
         [heading-0064]     [Fixation Station] 
         [0065]     In the fixation station, the color images formed of developers on the recording medium P are fixed to the recording medium P by the fixing device  60 , which comprises a film guide unit  61  and a pressure roller  62 . The film guide unit  61  contains a ceramic heater  63  for heating the recording medium P. The pressure roller  62  is for pressing the recording medium P against the film guide unit  61 . With the provision of this structural arrangement, the recording medium P is subjected to heat and pressure, whereby the color images formed of developers are fixed to the recording medium P.  
         [heading-0066]     [Image Forming Operation] 
         [0067]     Next, the operation for forming an image with the use of the apparatus structured as described above will be described.  
         [0068]     First, the feed roller  2  shown in  FIG. 2  is rotated, conveying thereby one of the recording mediums P in the cassette  1  to the pair of registration rollers  8 .  
         [0069]     Meanwhile, the photosensitive drum  21  and intermediary transfer member  40  are rotated independently from each other, in the direction indicated by the arrow ( FIG. 2 ) at a predetermined peripheral velocity (which hereinafter will be referred to as process speed).  
         [0070]     After being charged by the charge roller  22   a  across it peripheral surface, the photosensitive drum  21  is exposed to the beam of laser light (image formation light). As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  21 .  
         [0071]     1: Formation of Yellow Image  
         [0072]     A latent image corresponding to the yellow color component of a target image is formed by exposing the peripheral surface of the photosensitive drum  21 Y to the beam of laser light  51 Y, corresponding to the yellow color component of the target image, projected from the scanner portion  50 . In synchronism with the formation of this latent image, the yellow development roller  23 Y is rotated while voltage, the polarity of which is the same as that of the photosensitive drum  21 Y, is applied to the yellow development roller  23 Y in order to adhere yellow developer to the latent image on the photosensitive drum  21 Y, that is, in order to develop the latent image with the yellow developer. The developed latent image, that is, an image formed of yellow developer, is transferred (primary transfer) onto the peripheral surface or the intermediary transfer member  40 , at the location at which the transfer roller  42 Y is kept pressed against the photosensitive drum  21 Y, with the intermediary transfer member  40  being sandwiched between the transfer roller  42 Y and photosensitive drum  21 Y.  
         [0073]     2: Formation of Magenta Image  
         [0074]     Next, the peripheral surface of the photosensitive drum  21 M is exposed to the beam of laser light, corresponding to the magenta color component of the target image, projected from the scanner portion  50 , forming thereby a latent image corresponding to the magenta color component of the target image on the peripheral surface of the photosensitive drum  21 M. In this case, the latent image corresponding to the magenta color component is formed so that its leading edge, in terms of the rotational direction of the photosensitive drum  21 M, aligns with the leading edge, in terms of the moving direction of the intermediary transfer member  40 , of the image formed of yellow toner on the intermediary transfer member  40 . In synchronism with the formation of this latent image, the magenta development roller  23 M is rotated to develop the latent image corresponding to the magenta color component, as was the latent image corresponding to the yellow color component. The developed latent image, that is, an image formed of magenta developer, is overlaid (primary transfer) onto the image formed of yellow developer on the peripheral surface of the intermediary transfer member  40 .  
         [0075]     3: Formation of Cyan Image  
         [0076]     Next, a process similar to that carried out to form the magenta image is carried out to overlay an image formed of cyan developer (cyan image) onto the images formed of yellow and magenta developers, so that its leading edge aligns with the those of the yellow and magenta images on the peripheral surface of the intermediary transfer member  40 .  
         [0077]     4: Formation of Black Image  
         [0078]     Next, a process similar to that carried out to form the magenta image is carried out to overlay an image formed of black developer (black image) onto the images formed of yellow, magenta, and cyan developer, so that its leading edge aligns with the those of the yellow, magenta, and cyan images on the peripheral surface of the intermediary transfer member  40 .  
         [0079]     Referential symbols  21 C and  21 Bk, and referential symbols  42 C and  42 Bk, in the drawing designate the photosensitive drums and primary transfer rollers, respectively, corresponding to the cyan and black color components, one for one.  
         [0080]     As described above, the process comprising: the step for forming a latent image, the step for developing the latent image into a visible image, and the step for transferring the visible image onto the intermediary transfer member  40 , is sequentially carried out for the yellow, magenta, cyan, and black color components of the target image, in this order. As a result, a full-color image formed of four developers, that is, yellow, magenta, cyan, and black developers, is formed on the surface of the intermediary transfer member  40 .  
         [0081]     Incidentally, prior to the completion of the transfer of the image formed of black developer onto the intermediary transfer member  40 , the recording medium P, which has been kept on standby, is released by the pair of registration rollers  3  for further conveyance.  
         [0082]     Except for the period in which the four color images are transferred onto the intermediary transfer member  40 , the transfer roller  5  is kept at the bottom position, being away from the intermediary transfer member  40 . However, immediately prior to the transfer of the four color images onto the intermediary transfer member  40 , the transfer roller  5  is moved upward by a cam (unshown) in order to keep the recording medium P pressed against the intermediary transfer member  40  by the transfer roller  5 , in the second transfer station, while the four images are transferred. Further, during the secondary transfer of the four color images, bias opposite in polarity to the developers is continuously applied to the transfer roller  5 . As a result, the four color images, which make up a full-color image, on the intermediary transfer member  40 , are transferred all at once onto the recording medium P.  
         [0083]     Thereafter, the recording medium P is separated from the intermediary transfer member  40 , and is conveyed to the fixation station, in which the images formed of the developers are fixed. Then, the recording medium P is discharged onto the delivery tray  70  on top of the main assembly A of the printer, by the four pairs  71 ,  72 ,  73 , and  74  of discharge rollers, ending the operation for forming a full-color image on one of the recording mediums P.  
         [0084]     Next, the process cartridge, mechanism for mounting the process cartridge, and electrophotographic image forming apparatus, in this embodiment, will be described in detail.  
         [heading-0085]     [Process Cartridge] 
         [0086]      FIG. 3  is a sectional view of the cartridge  20 . The cartridge  20  comprises: the photosensitive drum  21 , charge roller  22   a  as a processing means, development roller  23  as a processing means, and cartridge frame  26  in which the preceding components, etc., are integrally disposed. As the amount of the developer in the cartridge  20  in the apparatus main assembly reduces to a critical level, it is to be replaced by an operator to maintain a high level of image quality. The inline full-color image forming apparatus in this embodiment employs four process cartridges  20 , that is, yellow, magenta, cyan, and black process cartridges ( 20 Y,  20 M,  20 C, and  20 Bk), which are independent from each other. The four process cartridges  20  different in development color become different in the length of service life, depending on the types of the images outputted by the image forming apparatus. Therefore, designing that image forming apparatus so that it can employs four process cartridges different in development color and independent from each other makes it possible to more efficiently use each of the four types of process cartridges.  
         [0087]     In this embodiment, the photosensitive drum  21 , cleaning blade  24 , and charge roller  22   a  are supported by the drum frame  26   a  as a part of the cartridge frame  26 , whereas the stirring member  29  for stirring developer, development roller  23 , sponge roller  28  for supplying the developer roller  23  with developer, and development blade  25  for regulating the amount by which developer is kept on the development roller  23 , are supported by the development frame  27 , which is another part of the cartridge frame  26 . The developer storage portion for storing developer is a part of the development frame  27 .  
         [0088]     In other words, the cartridge frame  26  in this embodiment comprises the drum frame  26   a  and development frame  27 .  
         [heading-0089]     [Method for Mounting Process Cartridge] 
         [0090]      FIG. 4  is a sectional view of the image forming apparatus in this embodiment, the cover of which is open.  
         [0091]     As shown in  FIG. 4 , the rotational axis  11  about which the cover  10  of the main assembly A of the image forming apparatus can be rotated is in the bottom front end portion of the main assembly A. The intermediary transfer member  40  is attached to the cover  10 . Therefore, as the cover  10  is opened, the intermediary transfer member  40  rotates about the rotational axis  11 , along with the cover  10 , allowing thereby an operator to access the cartridges  20  ( 20 Y,  20 M,  20 C, and  20 Bk).  
         [0092]     The cover  10  is to be opened or closed when necessary to mount a single or multiple cartridges  20  into the apparatus main assembly A, or to remove a single or multiple cartridges  20  from the apparatus main assembly A.  
         [0093]     The apparatus main assembly A is provided with a pair of movable cartridge guides  30  and  32 , which together hold cartridges  20  ( 20 Y,  20 M,  20 C, and  20 Bk). The rotational axes  36  of the movable cartridge guides  30  and  32  are in the top portion of the apparatus main assembly A. The movable cartridge guides  30  and  32  are mechanically connected to the cover  10  with a linking mechanism. Thus, the movable cartridge guides  30  and  32  are moved by the movement of the cover  10 ; as the cover  10  is opened, the movable cartridge guides  30  and  32  are pivoted a predetermined angle (roughly 35° in this embodiment) about the rotational axes  36  from the image formation position  200  ( FIG. 4 ) to the cartridge mounting position  300  ( FIG. 2 ) at which they are held while holding the cartridges  20  ( 20 Y,  20 M,  20 C, and  20 Bk) are mounted into, or removed from, the movable cartridge guides  30  and  32 .  
         [0094]     As for the locations of the movable cartridge guides  30  and  32  relative to the apparatus main assembly A, the movable cartridge guide  30  is at one end of the apparatus main assembly A in terms of the direction perpendicular to the direction in which the cartridges  20  are mounted into the apparatus main assembly A, and the movable cartridge guide  32  is at the other end. The movable cartridge guide  30  holds each cartridge  20  by one end of the cartridge  20  in terms of the lengthwise direction of the cartridge  20 , and the movable cartridge guide  32  holds each cartridge  20  by the other end. Further, the movable guides  30  and  32  are moved by the movement of the cover  10  as described above.  
         [0095]     The guides  30  and  32  are provided with cartridge mounts  34  and  35 , respectively, on which the cartridge  20  is mounted. When the movable cartridge guides  30  and  32  are in the image formation position  300  ( FIG. 2 ). The mounts  34  and  35  are tilted roughly 10° relative to the horizontal plane, whereas when the movable cartridge guides  30  and  32  are in the cartridge mounting position  200  ( FIG. 4 ) in which the cartridge  20  is mounted into the guides  30  and  32 , the mounts  34  and  35  are tilted roughly 45° relative to the horizontal plane.  
         [0096]     When removing the cartridge  20  from the apparatus main assembly A, the cartridge mounting position  200  ( FIG. 4 ) serves as the position in which the cartridge  20  is removed from the guides  30  and  32 .  
         [0097]     When mounting the cartridge  20  into the apparatus main assembly A, or removing the cartridge  20  from the apparatus main assembly A, the cartridge  20  is to be inserted onto, or removed from, the mounts  34  and  35  in the direction parallel to the mounts  34  and  35 , while keeping the apparatus main assembly A in the state shown in  FIG. 4 . In other words, when mounting the cartridge  20  into the guides  30  and  32 , or removing the cartridge  20  from the guides  30  and  32 , an operator can hold the process cartridge  20  at an angle of roughly 45° relative to the horizontal direction.  
         [0098]     Therefore, there is no obstruction in the direction in which the cartridge  20  is inserted or extracted, making it easier for an operator to insert or extract the cartridge  20 . Further, the guides  30  and  32  are tilted roughly 40°. Therefore, as the cartridge  20  is rested on the entrance portions of the guides  30  and  32 , the cartridge  20  automatically slides inward of the mounts  34  and  35  (guides  30  and  35 ).  
         [0099]     Then, the cartridge  20  stops as it hits the ends (surface  30   a ) of the mounts  34  and  35 . In other words, the above described structural arrangement makes the process for mounting the cartridge  20  into the movable cartridge guides  30  and  32  intuitive to an operator, while assuring that the process cartridge  20  is properly mounted into the movable cartridge guides  30  and  32 .  
         [0100]     The mount  34  is a part of the movable cartridge guide  30 , whereas the mount  35  is a part of the movable cartridge guide  32  ( FIG. 4 ). Thus, one end of the cartridge  20  rests on the mount  34 , and the other end of the cartridge  20  rests on the mount  35 .  
         [0101]     Next, referring to  FIGS. 7 and 8 , the first portions of the cartridge  20 , by which the cartridge  20  contacts the movable cartridge guides  30  and  32  to be supported by the movable cartridge guides  30  and  32  will be described.  
         [0102]     The first contact portions  26   a  and  30   b  ( FIG. 7 ) of the cartridge  20 , by which the cartridge  20  is supported by the movable cartridge guide  30  are at the lengthwise end of the process cartridge  20 , from which the cartridge  20  is driven (lengthwise end having coupling  87 ).  
         [0103]     Further, the first contact portions  26   a  and  30   b  are integral parts of the drum frame  26   b  which is a part of the cartridge frame  26 , and are supported by the mount  34  of the first movable cartridge guide  30  ( FIG. 1 ).  
         [0104]     The second contact portions  26   b ,  26   c ,  27   a , and  27   b  ( FIG. 8 ), by which the cartridge  20  is supported by the movable cartridge guide  32  are at the other lengthwise end of the process cartridge  20 , more specifically, the lengthwise end from which the cartridge  20  is not driven (lengthwise end without coupling  87 ). They are also parts of the cartridge frame  26 .  
         [0105]     They are supported by the mount  35  of the second movable cartridge guide  32  ( FIG. 1 ).  
         [0106]     Next, the steps to be followed to rest the first and second contact portions of the cartridge  20 , by which the cartridge  20  is rested on the mounts, will be described.  
         [0107]     First, the step for resting the first contact portion  26   a  and  30   b  on the mount  34  will be described with reference to  FIG. 7 .  
         [0108]     Referring to  FIG. 7 , one of the lengthwise ends of the cartridge  20  is to be rested in the first movable cartridge guide  30 , and then, to be pushed inward of the movable cartridge guide  30  (direction of arrow mark X), to make the cartridge  20  slide inward, so that the first contact portions  26   a  and  30   b  will be supported by the mount  34 . The first contact portion  26   a  is an integral part or the bottom wall of the drum frame  26   b.    
         [0109]     The first contact portion  30   b  is a rotation controller, and prevents the cartridge  20  from rotating while the cartridge  20  is receiving driving force from the apparatus main assembly A.  
         [0110]     Next, the step for resting the second contact portions  26   b ,  26   c ,  27   a , and  27   b  on the mount  35  will be described with reference to  FIG. 8 .  
         [0111]     Referring to  FIG. 8 , the other lengthwise end of the cartridge  20  is to be rested in the second movable cartridge guide  32 , and then, to be pushed inward of the movable cartridge guide  32  (direction of arrow mark X) to make the cartridge slide inward. As the cartridge  20  is pushed inward, the cartridge  20  moves inward, with the rest of the second contact portions of the cartridge  20 , that is, the portions  27   a  and  27   b  of the bottom wall of the development frame  27 , by which the cartridge  20  is supported by the movable cartridge guide  32 , sliding on the mount  35 .  
         [0112]     Then, the second portions  26   b ,  26   c ,  27   a , and  27   b , by which the cartridge  20  is supported by the movable cartridge guide  32 , climb onto the guiding rib  39  (mount  35 ); the second portions  26   b ,  26   c ,  27   a , and  27   b  of the cartridge  20  come to rest on the guiding rib  39  (mount  35 ).  
         [0113]     These second contact portion  27   a  and  27   b , by which the cartridge  20  is supported by the movable cartridge guide  32 , are integral parts of the bottom wall of the development frame  27  of the cartridge frame  26 . The second contact portions  26   b  and  26   c , by which the cartridge  20  is supported by the movable cartridge guide  32 , are bottom surfaces of the two projections, one for one, of the top portion of the drum frame  26   b.    
         [0114]     It is not mandatory that the first and second contact portions of the cartridge  20 , by which the cartridge  20  is supported by the movable cartridge guides  30  and  32 , are formed as described above; any form may be employed as long as the form allows the cartridge  20  to be properly supported by the movable cartridge guides  30  and  32 .  
         [heading-0115]     [Method for Solidly Positioning Process Cartridge in Printer Main Assembly] 
         [0116]      FIG. 1  is a schematic perspective view of the process cartridge properly positioned in the movable cartridge guides of the apparatus main assembly, with the cover  10  being in the open position ( FIG. 4 ).  FIG. 5  is a schematic sectional view of the image forming apparatus in this embodiment, the cover  10  of which is open.  FIG. 6  is a top view of the process cartridge in this embodiment.  
         [0117]     Incidentally, the cover  10  is to be opened or closed in order to mount the process cartridge into the apparatus main assembly A, or remove the process cartridge therefrom.  
         [0118]     In this embodiment, the movable cartridge guides  30  and  32  are made independent from each other for cost reduction. However, they may be formed as the two portions of a movable single-piece cartridge guide, or may be formed as the two portions of a movable multi-piece cartridge guide.  
         [0119]     Also in this embodiment, the movable cartridge guides  30  and  32  are connected by a linking member, which will be described later, so that they will remain synchronized in movement as if they are two parts of a movable single-piece cartridge guide.  
         [0120]     Both the movable right cartridge guide  30  and movable left cartridge guide  32  are provided with cartridge mounts  34  and  35 , respectively, for supporting the cartridge from below to make it possible for the cartridge to be smoothly inserted into the movable cartridge guides  30  and  32 .  
         [0121]     Referring to  FIG. 6 , the cartridge frame  26  is provided with cartridge positioning portions  85  and  86  for accurately positioning the cartridge  20  relative to the apparatus main assembly A. These positioning portions  85  and  86  project outward from the ends of the cartridge frame  26 , in terms of the lengthwise direction of the photosensitive drum  21 .  
         [0122]     Further, the cartridge positioning portions  85  and  86  accurately position the lengthwise ends  21   a  and  21   b  of the drum shaft  21   d  put through the photosensitive drum  21 , relative to the cartridge frame  26 , while allowing the drum shaft  21   d  to be rotated. More specifically, the positioning portions  85  and  86  are provided with bearings  85   a  and  86   a , respectively, with which the lengthwise ends  21   a  and  21   b  of the drum shaft  21   d  are rotatably supported by the cartridge frame  26  (positioning portions  85  and  86 ); the positioning portions  85  and  86  are accurately positioned relative to the apparatus main assembly A by the bearings  85   a  and  86   a.    
         [0123]     The lengthwise end  21   a  of the drum shaft  21   d , which is extending outward from the right positioning portion  85 , is provided with a coupling  87  through which driving force is transmitted to the photosensitive drum  21  from the driving means on the apparatus main assembly side.  
         [0124]     In this embodiment, the cartridge positioning portions  85  and  86  are positioned so that their axial lines coincide with the axial line of the photosensitive drum  21 . The positioning portion  85  is at one of the lengthwise ends of the photosensitive drum  21 , and the positioning portion  86  is at the other lengthwise end of the photosensitive drum  21 . The positioning portions  85  and  86  are the peripheral surfaces of the bearings  85   a  and  86   a , respectively, which support the drum shaft  21   d.    
         [0125]     Referring to  FIGS. 4 and 5 , the right side wall  100  of the apparatus main assembly A is provided with process cartridge positioning members  101  ( 101 Y,  101 M,  101 C, and  101 Bk), and the left side wall  110  of the apparatus main assembly A is also provided with process cartridge positioning members  101  (unshown). When the cartridge positioning members  101  of the left and right side walls  100  and  110  of the apparatus main assembly A are fixed to the left and right side walls, they are adjusted in position so that, as the cartridges  20 Y,  20 M,  20 C, and  20 Bk are mounted into the movable cartridge guides  30  and  32 , the drum shafts  21   d  in the cartridges are positioned in parallel with a high level of accuracy.  
         [0126]     Each cartridge positioning portion  101 , which engages with the positioning portions  85  or  86  extending from one or the other of the lengthwise ends of the cartridge  20 , is attached to the inward surface of the side wall of the apparatus main assembly A, projecting inward of the apparatus main assembly A.  
         [0127]     The cartridge positioning member  101  is provided with two cartridge catching surfaces: horizontal cartridge catching surface  101   a  and vertical cartridge catching surface  101   b  ( FIG. 12 ), by which the bearings  85   a  and  86   a  of the right and left positioning portions  85  and  86 , respectively, extending from the lengthwise ends, one for one, of the cartridge frame  26 , are directly caught. Because the frame  26  of each cartridge is directly supported by the side walls  100  and  110  of the apparatus main assembly A as described above, the photosensitive drum  21  in each cartridge is accurately positioned relative to the apparatus main assembly A.  
         [0128]     In other words, it is possible to position the four photosensitive drums  21  at a higher degree of parallelness.  
         [0129]     Referring to  FIGS. 1 and 6 , the cartridge frame  26  is provided with a pair of projections (which function as catches for sliding latches)  81  and  82 , which are located a small distance away from the main portion (contour  91 ) of the cartridge frame  26 . While the cartridge is moved from the cartridge mounting position to the image formation position, the pair of projections  81  and  82  are continuously subjected to the external force which acts in the cartridge mounting direction. The contour  91  simply means the external surface of the cartridge frame  26 , and does not need to be straight as shown in  FIG. 6 .  
         [0130]     In this embodiment, the right projection  81  extends from the right edge of the larger projection  83  of the cartridge frame  26 , roughly in parallel to the photosensitive drum  21 . For the sake of external appearance and reinforcement, the distance the larger projection  83  is extended toward the center of the cartridge frame  26  in terms of the lengthwise direction. However, the dimension of the right projection  83  in terms of the lengthwise direction may be only up to the broken line in the drawing. Similarly, the left projection  82  extends from the left edge of the larger projection  84  of the cartridge frame  26 , roughly in parallel to the photosensitive drum  21 .  
         [0131]     The apparatus main assembly A is provided with a pair of sliding latches  31  and  33 , which are attached to the movable cartridge guides  30  and  32 , being enabled to slide along the movable cartridge guides  30  and  32 , respectively. The pair of sliding latches  31  and  33  are provided with latches proper  37  and  38 , respectively, which engage with the above described projections (catches)  81  and  32 , respectively, of the cartridge frame  26 .  
         [0132]     The latches proper  37  and  38  engage with the projections (catches)  81  and  82 , respectively.  
         [0133]     The sliding latches  31  and  33  are moved by the closing movement of the cover  10  in the direction indicated by the arrow mark ( FIG. 1 ), that is, downward from the position in which the latches proper  37  and  38  are located higher than the top surfaces of the projections (latches)  81  and  82  of the cartridge  20 .  
         [0134]     As the sliding latches  31  and  33  are moved downward, the latches proper  37  and  38  engage with the projections (catches)  81  and  82 . Conversely, as the cover  10  is opened, the sliding latches  31  and  33  are moved upward by the opening movement of the cover  10 , causing the latches proper  37  and  38  to disengage from the projections (catches)  81  and  82 ; the cartridge  20  is unlocked from the apparatus main assembly A. Since the projections (catches)  81  and  82  are a small distance away from the main portion (contour  91 ) of the cartridge frame  26 , the cartridge frame  26  does not interfere with the engagement between the projections (catches)  81  and  82 , and the sliding latches  31  and  33 , respectively.  
         [0135]     Incidentally, the positional relationship in which the cartridge is mounted relative to the mounts  34  and  35  is not always exactly the same. Thus, in order to assure that the latches proper  37  and  38  will properly engage with the projections (catches)  81  and  82 , respectively, despite the variance in the positional relationship between the cartridge  20  and the mount  34 , and/or between the cartridge  20  and mount  35 , the latches proper  37  and  38  are provided with first portion  37   a  and  38   b , respectively, which are positioned closer to the cartridge  20  than the other portions of the latches proper  37  and  38 . The latches proper  37  and  38  are also provided with second portions  37   b  and  38   b , and guiding portions  37   c  and  38   c , respectively. The second portions  37   b  and  38   b  lock with the projections (catches)  81  and  82  to keep the cartridge locked in position while the cartridge is moved from the cartridge mounting position to the image formation position. The guiding portions  37   c  and  38   c  are the portions between the first portions  37   a  and  38   a , and second portions  37   b  and  38   b , respectively. They are slanted in such a direction that as the latches  31  and  32  are moved downward, they pull the cartridge  20 , along with the movable cartridge guides  30  and  32 , toward the sliding latches  31  and  33 , making it possible for the second portions  37   b  and  38   b  to lock the cartridge  20  in position while the cartridge  20  is moved from the cartridge mounting position  200  to the image formation position  300 .  
         [0136]     As the sliding latches  31  and  33  begin to be moved downward by the closing movement of the cover  10 , the first portions  37   a  and  38   a  of the latches proper  37  and  38  enter the gaps between the leading surface  20   a  of the cartridge  20 , and the projections (catches)  81  and  82 , respectively, preventing thereby the cartridge  20  from being separated from the movable cartridge guides  30  and  32  by the reactive force generated by the driving portion, projections, etc., of the apparatus main assembly A, during the rest of the cartridge mounting operation.  
         [0137]     The first portions  37   a  and  38   a  of the latches proper  37  and  38  are located closer to the movable cartridge guides  30  and  32  than the second portions  37   b  and  38   b  of the latches proper  37  and  38 , so that even if the cartridge  30  is mounted in the movable cartridge guides  30  and  32 , slightly offset from the normal position, the first portions  37   a  and  38   a , that is, the end portions, of the latches proper  37  and  38  are allowed to smoothly enter the gap between the leading surface  20   a  of the cartridge  20  and the projection (catch)  81 , and the gap between the rear leading  20   a  of the cartridge  20  and the projection (catch)  82 , without colliding with the projections (catches)  81  and  82 , respectively, as the first portions  37   a  and  38   a  are moved downward.  
         [0138]     As the sliding latches  30  and  33  are lowered further after the entrance of the first portions  37   a  and  38   a  into the gap between the leading surface  20   a  of the cartridge  20  and the projection (catch)  81 , and the gap between the leading surface  20   a  of the cartridge  20  and the projection (catch)  82 , respectively, the guiding portions  37   c  and  38   c  come into contact with the projections (catches)  81  and  82 , respectively. Thus, as the sliding latches  30  and  33  are moved further downward, force which acts in the direction to press the cartridge  20  against the mounts  34  and  35 , and force which acts in the direction to pull the cartridge  20  toward the inward end portion  30   a  and  32   a  of the right and movable left cartridge guides  30  and  32 , that is, forces which act in the direction to pull the cartridge inward of the apparatus main assembly A, are generated.  
         [0139]     Incidentally, the guiding portions  37   c  and  38   c  are desired to be shaped so that they allow the projections (catches)  81  and  82  to smoothly slide thereon from the portions  37   a  and  38   a  to the portions  37   b  and  38   b , respectively. In this embodiment, the guiding portions  37   a  and  38   c  are slanted so that the closer a given point of the guiding portion  37   c  or  38   c  to the second portion  37   b  or  38   b , respectively, the smaller the distance between the given point and the projection (catch)  81  or  82 .  
         [0140]     Next, how the cartridge  20  is positioned while it is mounted will be described in detail.  FIG. 7  is a side view of a part of the movable right cartridge guide, in this embodiment, which is holding the cartridge(s) in accordance with this embodiment.  FIG. 8  is a side view of a part of the movable left cartridge guide, in this embodiment, which is holding the cartridge(s) in accordance with this embodiment.  
         [0141]      FIGS. 7 and 8  are side views of the parts of the movable cartridge guides which are holding the cartridges  20  ( 20 Y and  20 M). The hatched portions in  FIGS. 7 and 8  schematically show the mounts  34  and  35 , and latches proper  37  and  38 , which engage with the cartridge  20 .  
         [0142]     Incidentally, the mount  35  and latch proper  38  are on the side opposite to the side shown in the drawings. Therefore, they are not shown in  FIG. 7 .  
         [0143]     Referring to  FIG. 7 , virtually the entirety of the lengthwise end of the cartridge is covered with the cartridge frame  26 .  
         [0144]     Referring to  FIGS. 7 and 8 , the mount  34  is roughly straight, and roughly parallel to the bottom wall of the cartridge frame  26 , with the presence of a certain amount of gap between the mount  34  and the bottom wall of the cartridge frame  26 . Therefore, when an operator mounts the cartridge  20  into the movable cartridge guide  30 , the cartridge slides on the mount  34  toward the inward end of the movable cartridge guide  30 , and stops as it hits the rear (inward) wall  30   a  of the movable cartridge guide  30 .  
         [0145]     The downstream portion of the mount  34  ( 34 Y and  34 M), in terms of the cartridge mounting direction, has a step with a height difference of roughly 1 mm. With the presence of this step on the mount  34 , the cartridge  20  is allowed to make contact with the guide  30  only by the limited area (contact area) of its surface, while it is in the movable cartridge guide  30 . This limited area (contact area) of the surface of the cartridge  20  functions as a rotation control area for preventing the cartridge  20  from rotating after the proper positioning of the cartridge  20  relative to the apparatus main assembly A.  
         [0146]     More specifically, as the cartridge  20  receives driving force from the apparatus main assembly A, the driving force acts in the direction to rotate the cartridge  20  about the axial lines of the positioning portions  85  and  86 , causing thereby the cartridge frame  26  to come into contact with the rotation control area (contact portion)  32   b . As a result, the cartridge  20  is prevented from rotating further, being thereby fixed in the position relative to the movable cartridge guide  30 .  
         [0147]     On tile right side of the image forming apparatus, the apparatus main assembly A and cartridge  20  are connected to each other so that driving force can be transmitted from the apparatus main assembly A to the cartridge  20 . More specifically, the driving force is transmitted from the apparatus main assembly A to the photosensitive drum  21  of the cartridge  20  through the coupling  87 , which is attached to the drum shaft  21   d , and the axial line of which coincides with that of the drum shaft  21   d . To the development roller  23 , the driving force is transmitted through the input gear  92  (contoured by single-dot broken line in drawing), the axial line of which coincides with the pivotal center of the development frame  27 . The gear  92  is driven in the clockwise direction indicated by an arrow mark ( FIG. 7 ). Therefore, as the driving force is transmitted, the cartridge  20  is rotated in the direction to cause the cartridge  20  to be supported by the right cartridge positioning portion  85 , and the aforementioned cartridge rotation control surface (contact portion)  30   b  as a cartridge movement regulating portion. As a result, the cartridge  20  is kept stable in position while the driving force is transmitted thereto from the apparatus main assembly A; in other words, the cartridge  20  is kept accurately positioned relative to the apparatus main assembly A during an image forming operation.  
         [0148]     The movable right cartridge guide  30  is provided with the sliding latch  31 , which is slidably attached to the movable cartridge guide  30 .  
         [0149]      FIG. 8  is a schematic side view of the combination of the movable left cartridge guide  32  and the cartridge  20 Y in the movable left cartridge guide  32 . The movable left cartridge guide  32  and left end portion of the process cartridge  20  will be described only regarding the portions different from those of the movable right cartridge guide  30  and the right end portion of the process cartridge  20 .  
         [0150]     The left end portion of the cartridge  20  is different from the right end portion thereof in that it comprises the top half  26   a , which is the drum frame  26   a , and the bottom half, which is the development frame  27  pivotally connected to the drum frame  26   a . Therefore, as the cartridge  20  is inserted into the movable cartridge guide  32 , the bottom wall of the development frame  27  slides on the mount  35  of the movable left cartridge guide  32 .  
         [0151]     As the cartridge  20  is slid on the movable cartridge guide  32  deeper into the movable cartridge guide  32 , the rib, with which the top portion of the leading end, in terms of the cartridge mounting direction, of the cartridge frame  26  is provided, smoothly slides onto the guide rib  39  ( 39 Y,  39 M) of the movable cartridge guide  32 . Then, as the cartridge  20  is slid deeper into the movable cartridge guide  32 , the cartridge  20  is fixed in position by the positioning portions  85  and  86 , the axial lines or which coincide with that of the axial line of the drum shaft  21   d , and the rotation control area  20   b  which is in contact with the cartridge rotation control area ( 30   b ) of the mount  34  ( 34 Y and  34 M) shown in the drawing of the movable right cartridge guide. Thus, after the proper positioning of the cartridge  20  in the apparatus main assembly A, there will be no contact between the mount  35  of the movable cartridge guide  32 , shown in the drawing of the movable left cartridge guide, and the cartridge  20 .  
         [0152]     The cartridge rotation control area  20   b  of the cartridge  20  is such a portion of the external surface of the cartridge  20  that belongs to the downstream side of the cartridge  20 , in terms of the cartridge mounting direction, and is at the right lengthwise end (which is provided with coupling  85 , and from which cartridge receives driving force from apparatus main assembly A) of the cartridge  20 . Further, the cartridge rotation control area  20   b  is a part of the exterior of the bottom wall of the cartridge frame  26 .  
         [0153]     In  FIGS. 1, 4 ,  5 ,  7 ,  8 , and  12 , the direction indicated by the arrow mark X is the direction in which cartridge is mounted, and the direction opposite thereto is the direction in which cartridge  20  is extracted from the apparatus main assembly A.  
         [0154]     The movable cartridge guide  32  is provided with the sliding latch  33 , which is slidably attached to the movable cartridge guide  32  as is the sliding latch  31  attached to the movable cartridge guide  30 .  
         [heading-0155]     [Sliding Latch] 
         [0156]     Next, the movable cartridge guides  30  and  32 , the connection of the movable cartridge guides  30  and  32  to the linking mechanism, and the movement of the movable cartridge guides  30  and  32 , will be described.  
         [0157]      FIG. 4 , which is a schematic sectional view of the image forming apparatus in this embodiment, shows the mechanical linkage which connects the movable right cartridge guide  30  to the cover  10 .  
         [0158]     Designated by a referential number  15  is a connective rod, as a linking member, connected to the movable right cartridge guides  30 . The connective rod  15  is roughly in the shape of a letter L. It is attached to the movable right cartridge guide  30  by its long portion, whereas the short portion, that is, the portion roughly perpendicular to the long portion, extends in the inward direction of the movable right cartridge guide  30 . The end of the short portion of the connective rod  15  is connected to a rotational rod  14  for delaying the movement or the connective rod  15  (movable right cartridge guide  30 ) a predetermined length of time relative to the beginning of the opening movement of the cover  10 . To the rotational rod  14 , on end of an intermediary connective rod  13  is connected, and the other end of the intermediary connective rod  13  is connected to the door lever  12  integral with the cover  10 .  
         [0159]     The time lag between the beginning of the opening of the cover  10  and the beginning of the movement of the connective rod  15  (movable right cartridge guide  30 ) is used for disengaging the couplings which transmit the force for circularly driving the intermediary transfer belt  40  to the driving roller  41 , and also, for disengaging the couplings which transmit driving force to the four photosensitive drums  21 .  
         [0160]     Next, referring to  FIGS. 9, 10 , and  11 , the mechanism for moving the movable cartridge guide  30 , and the force which acts on the cartridges as the movable cartridge guide  30  is moved, will be described.  FIG. 9  is a schematic sectional view of the image forming apparatus in this embodiment, showing how the cartridge  20  is mounted into the main assembly A of the image forming apparatus.  FIG. 10  is a schematic sectional view of the essential portion of the image forming apparatus in this embodiment, showing how the movable cartridge guide is pivoted.  FIG. 11  is a schematic sectional view of the essential portion of the image forming apparatus in this embodiment, after the automatic mounting of the cartridge into the main assembly A of the image forming apparatus.  
         [0161]      FIGS. 9, 10 , and  11  show the vertical section of the apparatus main assembly A, and left end of the cartridge  20 . They show the movable cartridge guide on the left side of the apparatus main assembly A, that is, the movable cartridge guide  32 , and also, the portions of the movable cartridge guide  32 , which act on the cartridge  20 . Further, they show only the portions of the side wall  110  of the apparatus main assembly A, which act on the cartridge  20 , and the components, which are attached to the side wall  110 , and act on the cartridge  20 . When the image forming apparatus is in the state shown in  FIG. 9 , the movable cartridge guide  32  of the apparatus main assembly A is tilted at roughly 35°, and the mount  35  is tilted at roughly 10° relative to the movable cartridge guide  32  as described above. Thus, when the image forming apparatus is ready for cartridge insertion, the angle of the mount  35  relative to the horizontal plane is roughly 45°.  
         [0162]     As a process cartridge, for example, the magenta cartridge  20 M shown in the drawing, is inserted in the direction indicated by an arrow mark, the cartridge  20  rests on the mounts  35  and  34  of the movable cartridge guides  30  and  32  by the parts of the bottom surface of the cartridge frame  26 . Then, the cartridge  20  virtually automatically slides on the mounts  35  and  34 , deeper into the movable cartridge guides  32  and  30 . As for the sliding latch  33  slidably attached to the movable cartridge guide  32 , it is kept pressured upward of the apparatus main assembly A by the resiliency of a spring (unshown). Therefore, the sliding latch  33  remains in contact with the top wall  105  of the apparatus main assembly A.  
         [0163]     With the sliding latch  33  being in contact with the top wall  105 , the latch proper  38  of the sliding latch  33  is kept in a position high enough not to interfere with the cartridge  20  while the cartridge  20  slides deeper into the movable cartridge guide  32  of the apparatus main assembly A.  
         [0164]     Next, referring to  FIG. 10 , as the cover  10  is closed, the movable cartridge guide  32 , which has been kept at roughly 35° relative to the vertical plane up to this point in the process, is rotated by the closing movement of the cover  10 , until its angle relative to the vertical plane becomes roughly 5°, while forcing the sliding latch  33  to move downward along the movable cartridge guide  32 . During this pivoting of the movable cartridge guide  32 , and resultant downward movement of the sliding latch  33 , the latch proper  38  of the sliding latch  33  engages with the left projection (catch)  82  of the cartridge  20 .  
         [0165]     The latch proper  38  is long enough to properly engage with the left projection (catch)  82  of the cartridge  20  while the sliding latch  33  is moved from the top end of its moving range to the bottom end. As the movable cartridge guide  32  of the apparatus main assembly A is pivoted, the cartridge  20  therein is moved with the movable cartridge guide  32 . Then, as the cartridge  20  approaches the cartridge positioning member  101  on the side wall of the apparatus main assembly A, three forces are generated, which act in the direction to resist the inward movement of the cartridge  20 .  
         [0166]     The first of these three forces, which act in the direction to resist the inward movement of the cartridge  20 , is the reactive force generated as the cartridge  20  is pressed directly against the cartridge positioning member  101 . This force acts on the cartridge retaining member  103 . The second force is the reactive force generated as the drum shutter rod  90  is rotated by the inward movement of the cartridge  20  after being made to contact the shutter moving member  102  disposed on the side wall of the apparatus main assembly A to open the drum shutter  89 . The third force is the reactive force generated as the process cartridge  20  is made to slide on the upwardly slanted surface of the cartridge catching member on the side wall of the apparatus main assembly A.  
         [0167]     Next, these three reactive forces will be described in detail.  FIG. 12  is a schematic view of the cartridge retaining member  103  for keeping the cartridge  20  pressed on the cartridge positioning member  101  of the apparatus main assembly A, showing sequentially the movements of the cartridge retaining member  103 .  
         [0168]     Referring to  FIG. 12 ( a ), the cartridge retaining member  103  ( 103 Y,  103 M,  103 C, and  103 Bk) is rotatably attached to the side wall  110  ( FIG. 9 ) of the apparatus main assembly A. It is kept under the tensional force generated by a tension spring  108  shown in the drawing. With the pivotal axis  107  of the cartridge retaining member  103  positioned as shown in the drawing, the tension spring  108  begins to be stretched as soon as the cartridge retaining member  103  begins to be pivoted. With the subsequent pivoting of the cartridge retaining member  103 . The tension spring  108  is continuously stretched until the cartridge retaining member  103  is pivoted to a reversal point. Then, as the cartridge retaining member  103  is pivoted past this reversal point, the tension spring  108  is allowed to shrink, causing therefore the cartridge retaining member  103  to press the cartridge  20  so that the left positioning member  86  of the cartridge  20  will hit the cartridge positioning member  101  of the apparatus main assembly A, and be kept in contact therewith. The amount of the force generated by the spring  108  is in the range of roughly 500 gf (4.9 N)-1 kgf (9.8 N).  
         [0169]     The cartridge retaining member  103  is pivoted by the cartridge  20  alone. More specifically, as the movable left cartridge guide  32  is pivoted, the left cartridge positioning member  86  approaches the cartridge retaining member  103 , eventually contacting the cartridge retaining member  103 . As soon as the left positioning member  86  contacts the cartridge retaining member  103  ( FIG. 12 ( b )), the tension spring  108  begins to be stretched, generating the reactive force which acts in the direction to push back the cartridge  20 . As a result, an operator begins to feel resistance.  
         [0170]     As the cartridge  20  is inserted deeper against the above described reactive force generated by the tension spring  108  while stretching the tension spring  103 , the cartridge retaining member  103  is pivoted beyond the aforementioned reversal point ( FIG. 12 ( c )). As soon as the cartridge retaining member  103  is pivoted beyond the reversal point, the resilience of the spring  108  begins to act in the direction to press the left cartridge positioning member  86  directly on the cartridge positioning member  101  of the apparatus main assembly A, as shown in  FIG. 12 ( d ).  
         [0171]     Thereafter, the cartridge positioning portion  86  of the cartridge  20  comes into contact with both the horizontal and vertical surfaces  101   a  and  101   b  of the cartridge positioning member  101  of the apparatus main assembly A, accurately positioning the cartridge  20  relative to the apparatus main assembly A.  
         [0172]     More specifically, the bearing  86   a , which is a part of the cartridge positioning portion  86 , is made to hit the horizontal and vertical surfaces  101   a  and  101   b . Incidentally, the bearing  86   a  is supporting the drum shaft  21   d  of the photosensitive drum  21 .  
         [0173]     Next, the drum shutter  89  will be described.  
         [0174]     The photosensitive drum  21  in the cartridge  20  has a photosensitive layer, which reacts to light, contributing thereby to image formation. In other words, the photosensitive drum  21  is sensitive to light. Therefore, the cartridge  20  is provided with the drum shutter  89  ( FIG. 7 ) in order to prevent the peripheral surface of the photosensitive drum  21  from being exposed to light while the cartridge  20  is out of the apparatus main assembly A, for example, during the shipment of the cartridge  20 .  
         [0175]     In this embodiment, a thin flexible sheet capable of blocking light is used as the material for the drum shutter  89 . The drum shutter  89  is bonded to the cartridge frame  26  by one edge, and the opposite edge is attached to the drum shutter rod, around which the drum shutter  89  can be wound. The shutter rod is provided with a spring  93 , which is attached to the right arm of the shutter rod and remains wound to generate force in the direction to rotate the shutter rod in the direction to close the drum shutter  89 .  
         [0176]     Referring to  FIG. 9 , while an operator inserts the cartridge  20  into the movable cartridge guide  32 , the drum shutter  89  remains closed. Then, as the cartridge  20  is positioned close to the cartridge positioning member  101  of the apparatus main assembly A, as shown in  FIG. 10 , by the pivoting of the movable cartridge guide  32 , the drum shutter rod  90  comes into contact with the shutter moving member  102  on the left side wall  110  of the apparatus main assembly A, beginning thereby to be rotated by the subsequent inward movement of the cartridge  20  resulting from the subsequent pivoting of the movable cartridge guide  32 , while folding the flexible drum shutter  89  as shown in  FIG. 10 .  
         [0177]     Next, referring to  FIG. 11 , as the cartridge  20  is locked into the predetermined position, the drum shutter  89  is completely folded, that is, completely retracted, upward by the drum shutter rod  90 . During this process, the flexible cartridge handle  88  is bent upward by the drum shutter rod  90 , generating thereby reactive force, which acts in the direction to push back the drum shutter rod  90 . Thus, this reactive force from the flexible cartridge handle  88  pushes the shutter moving member  102  through the drum shutter rod  90 , generating thereby reactive force which acts in the direction to push the drum shutter rod  90  in the direction opposite to the cartridge insertion direction. Consequently, the cartridge  20  receives such force that acts in the direction to move the cartridge  20  out of the movable cartridge guide  32 . The amount of this force which acts in the direction to push the cartridge  20  out of the movable cartridge guide  32  is the sum of the resiliency of the shutter spring  93 , resiliency of the flexible cartridge handle  88 , and resiliency of the drum shutter  89 , and is in the range of roughly 1 N (100 gf)-3 N (300 gf).  
         [0178]     Next, the reactive force generated as the cartridge  20  is forced to slide on the upwardly slanted surface of the cartridge catching member (cartridge positioning member) on the side wall of the apparatus main assembly will be described.  
         [0179]     This reactive force is generated immediately before the cartridge  20 , which is temporarily rested on the mount  35  of the movable cartridge guide  32 , is moved into the normal position, that is, the predetermined image formation position, in the apparatus main assembly A. The amount of this reactive force is determined by the weight of the cartridge  20  itself, and the distance by which the cartridge  20  is vertically moved as it is made to climb onto the horizontal surface  101   a  of the cartridge catching portion (cartridge positioning portion. As the cartridge  20 , which weighs roughly 1 kg, is pushed up along the surface, tilted upward at 45°, of the cartridge catching member (cartridge positioning member), its own weight generates force which acts on the cartridge  20  in the direction to push the cartridge  20  out of the movable cartridge guide  32 .  
         [0180]     As described above, while the process cartridge is mounted into the main assembly A of the image forming apparatus with the use of the automatic mounting system, the above described various reactive forces act on the cartridge  20  as the movable cartridge guides  30  and  32  are pivotally moved.  
         [0181]     In this embodiment, the movable cartridge guides  30  and  32  are provided with the sliding latches  31  and  33 , respectively, which are slidable along the movable cartridge guides  30  and  32 , respectively. The sliding latches  31  and  33  are slid by the opening or closing movement of the cover  10 . More specifically, as the movable cartridge guides  30  and  32  begin to be moved by the opening movement of the cover  10 , first, the latches proper  37  and  38  of the sliding latches  31  and  33  engage with the projections (catches)  81  and  82  of the cartridge  20 . Then, the reactive force generated by the cartridge retaining member  103  begins to act on the process cartridge  20 , and then, the reactive force generated as the drum shutter  89  is opened, acts on the process cartridge  20 . Lastly, the reactive force generated as the cartridge  20  is pushed along the upwardly tilted surface of the cartridge positioning member acts on the cartridge  20 .  
         [0182]     However, the cartridge  20  is guided to the cartridge catching surface  101   a  and  101   b  of the cartridge positioning member  101 , by the movable cartridge guides  30  and  32 , while the above described reactive forces are absorbed by the latches proper  37  and  38 . Thus, as the cartridge  20  comes into contact with the cartridge catching surfaces  101   a  and  101   b , the latches proper  37  and  38  disengage from the projections (catches)  81  and  82 .  
         [0183]     The aforementioned cartridge retaining member  103  continuously generates the reactive force until it is rotated to the position shown in  FIG. 12 ( c ). However, as soon as tile cartridge retaining member  103  is rotated past the position shown in  FIG. 12 ( c ), it begins to press on the positioning portion  86  of the cartridge  20  inward of the movable cartridge guide. As a result, the positioning portion  86  is slid on the horizontal surface  101   a  of the positioning member  101 , by the cartridge retaining member  103 , until it hits the vertical surface  101   b  of the cartridge retaining member  103 . As the cartridge  20  is slid on the horizontal surface  101   a , the latches proper  37  and  38  are disengaged from the projections (catches)  81  and  82 , respectively.  
         [0184]     Thereafter, the cover  10  is to be closed, and as the cover  10  is closed, the cartridge  20  is automatically and accurately moved into the image formation position  300  for the cartridge  20 , in the apparatus main assembly A.  
         [0185]     As described above, while the cartridge  20  is moved into the image formation position  300  in the apparatus main assembly A, it is retained by the latches proper  37  and  38 . Therefore, it is assured that the cartridge  20  is moved into the image formation position  300  in spite of the presence of the above described reactive forces which act on the cartridge  20 .  
         [0186]     Here, the image formation position  300  means the final position into which the cartridge  20  is moved for image formation, in the apparatus main assembly A. The position of the cartridge  20  while driving force is transmitted to the cartridge  20  from the apparatus main assembly A is slightly different from that while driving force is not transmitted to the cartridge  20 . In this specification, however, both of these cartridge positions are treated as the image formation position.  
         [heading-0187]     (Embodiment 2)  
         [0188]     Next, referring to  FIGS. 4 , and  13 - 18 , the process cartridge and image forming apparatus in the second embodiment of the present invention will be described. The structures of the process cartridge and image forming apparatus similar to those in the first embodiment will not be described, and only those which characterize this embodiment will be described in detail.  
         [0189]      FIG. 15  is a sectional view of the cartridge retaining member and its adjacencies in this embodiment, showing the positioning thereof.  FIGS. 16, 17 , and  18  are schematic sectional views of the cartridge retaining member in this embodiment.  
         [0190]     Referring to  FIG. 15 , the reactive forces which act on the cartridge  20  are generated by the first cartridge retaining member  94  ( 94   a ,  94   b ,  94   c , and  94   d ) on the side walls  100  and  110  of the apparatus main assembly A, and second cartridge retaining member  95  ( 95   a ,  95   b ,  95   c , and  95   d ) on the intermediary transfer member  40  integral with the cover  10 . Referring to  FIG. 16 , the cartridge  20  is pressed by the first cartridge retaining member  94  in the first direction (diagonally downward at roughly 45° relative to horizontal plane), and also, is pressed by the second cartridge retaining member  95  in the second direction (diagonally downward at roughly 15° relative to horizontal plane). In addition, the cartridge  20  is pressed by the resiliency of springs (unshown) in the direction to cause the positioning members  85  and  86  of the cartridge  20 , which also are bearings, to be pressed against the two surfaces, that is, the rear and bottom surfaces  101   c  and  101   d , of each the cartridge positioning members  101  on the side walls  100  and  110  of the apparatus main assembly A. As a result, the cartridge  20  is accurately positioned relative to the apparatus main assembly A.  
         [0191]     In this embodiment, the role of positioning the cartridge  20  relative to the apparatus main assembly A is carried out by the apparatus main assembly A independently from the movable cartridge guides  30  and  32 .  
         [0192]      FIG. 13  is an external perspective view of the cartridge  20  in this embodiment. As shown in  FIG. 13 , the portions of the cartridge  20 , by which the cartridge  20  is pressed, are first contact portion  96  ( 96   a  and  96   b ) and second contact portion  97  ( 97   a  and  97   b ) located at the lengthwise ends of the cartridge frame  26 , one for one. These contact portions are pressed by the above described first and second cartridge retaining members  94  and  95 , respectively. Further, the contact portions do not need to be parts of the cleaning frame of the cartridge frame  26 . For example, they may be components attachable to the cleaning frame, or the positioning portions  85  and  86 , which also are bearings, with which the development frame  27  is provided.  
         [0193]     Immediately before the cover  10  is completely closed, the cartridge  20  receives the pressure generated by the second cartridge retaining member  95  attached to the intermediary transfer member  40  integral with the cover  10 , in the direction to press the cartridge  20  toward the cartridge positioning member. More specifically, when the positioning portions  85  and  86  ride onto the first cartridge retaining member  94 , the cartridge  20  receives the reactive force which acts in the direction opposite to the cartridge insertion direction. In this embodiment, however, the two cartridge retaining members are used to press the cartridge  20  in steps. Therefore, when mounting the cartridge  20 , the reactive forces generated by the cartridge retaining members in the direction to push the cartridge  20  out of the apparatus main assembly A are relatively small, allowing the cartridge  20  to be smoothly mounted into the apparatus main assembly A.  
         [heading-0194]     [Forces Which Act on Process Cartridge After Mounting of Process Cartridge into Image Forming Apparatus] 
         [0195]     As the cover  10  is closed, as shown in  FIG. 8 , after the complete insertion of the cartridge  20  into the movable cartridge guides, the cartridge frame  26  is subjected to a force Fa generated by the first cartridge retaining member  94  in the diagonally downward direction, more specifically, at roughly 45° relative to the horizontal plane, and a force Fb generated by the second cartridge retaining member  95  in the diagonally downward direction, more specifically, at roughly 15° relative to the horizontal plane. Further, the photosensitive drum  21  is subjected, through intermediary transfer member  40 , to a force Fc (unshown) generated by the primary transfer roller  42  in the direction to keep the cartridge  20  properly positioned relative to the apparatus main assembly A, that is, in the direction virtually parallel to the bottom wall of the apparatus main assembly A. In other words, the cartridge  20  is kept accurately positioned relative to the cartridge positioning member  101  of the apparatus main assembly A, by being subjected to the forces Fa, Fb, and Fc.  
         [0196]     On the other hand, as driving force is transmitted to the cartridge  20  during image formation, the cartridge  20  is subjected to a force Fd (reactive force) generated by the transmission the driving force in the direction opposite to the cartridge mounting direction. The direction in which the force Fd is generated is determined by the position of the output gear (unshown) of the mechanical power source of the apparatus main assembly A, the position of the input gear (unshown) of the cartridge  20 , and the operating pressure angles of the two gears.  
         [0197]     Here, the forces which horizontally act are designated by referential symbols Pa 1 , Fb 1 , Fc 1 , and Fd 1 , and the forces which vertical act are designated by referential symbols Fa 2 , Fb 2 , Fc 2 , and Fd 2 . All that is necessary to assure that the cartridge is kept properly positioned is to satisfy the following inequality: Fa 1 +Fh 1 +Fc 1 &gt;Fd 1  (in terms of direction parallel to bottom wall of apparatus main assembly A). In term of vertical direction (direction virtually perpendicular to bottom wall of apparatus main assembly A), there is nothing to be concerned, because the forces Fa 2 , Fb 2 , Fc 2 , and Fd 2  act in the same direction, that is, vertically downward, and therefore, the inequality: Fd 2 +Fb 2 +Fc 2 +Fd 2 &gt;0 is always satisfied.  
         [0198]     The description of this embodiment given above can be summarized as follows:  
         [0199]     The process cartridge  20  which is mounted in the movable cartridge guides  30  and  32  of the main assembly A of the electrophotographic image forming apparatus (printer), and then, is moved by the movement of the movable cartridge guides  30  and  32  from the cartridge mounting position  200  to the image formation position  300 , comprises: 
        the electrophotographic photosensitive drum  21 ;     the processing means (for example, charge roller  22   a , development roller  23 , and cleaning blade  24 ) which act on the electrophotographic photosensitive drum  21 :     the cartridge frame  26  which supports the electrophotographic photosensitive drum  21  and processing means;     the first contact areas  26   a  and  30   b , by which the cartridge  20  is supported by the movable cartridge guide  30 , and which are located at one of the lengthwise ends of the photosensitive drum  21 ;     the second contact areas  26   b ,  26   c ,  27   a , and  27   b , by which the cartridge is supported by the movable cartridge guide  32 , and which are located at the other lengthwise end of the photosensitive drum  21 ;     the first cartridge positioning portion  85 , which is extended from one of the lengthwise ends of the cartridge  20  in the direction parallel to the axial line of the photosensitive drum  21 , to be placed in contact with the main assembly A of the image forming apparatus in order to properly position the cartridge  20  relative to the apparatus main assembly A, and the axial line of which coincides with that of the photosensitive drum  21 ;     the second cartridge positioning portion  86 , which is extended from the other lengthwise end of the cartridge  20  in the direction parallel to the axial line of the photosensitive drum  21 , to be placed in contact with the main assembly A or the image forming apparatus in order to properly position the cartridge  20  relative to the apparatus main assembly A, and the axial line of which coincides with that of the photosensitive drum  21 ; and     the projections (as catches)  81  and  82  which engage with the latches (sliding latches  31  and  33 ) movable by the movement of the movable cartridge guides  30  and  32 , and absorb the reactive force generated as the cartridge  20  is moved from the cartridge mounting position  200  to the image formation position  300 .        
 
         [0208]     With the provision of the above described structural arrangement, while the cartridge is moved from the cartridge mounting position  200  to the image formation position  300 , it is kept under the reactive force generated by the structural arrangement, being thereby prevented from substantially dislodging from the movable cartridge guides  30  and  32 . Therefore, it is assured that the cartridge  20  is easily moved to the image formation position  300 .  
         [0209]     The cartridge mounting position  200 , by the way, is the position at which the cartridge  20  is mounted into the movable cartridge guides  30  and  32 . The cartridge mounting position  200  is located on the cover  10  side of the movable cartridge guides  30  and  32 , making it therefore easier for an operator to insert the cartridge  20  into the movable cartridge guides  30  and  32 , or to move the cartridge  20  therefrom.  
         [0210]     The projections (catches)  81  and  82  of the cartridge  20  are located at the leading end of the cartridge frame  26  in terms of the cartridge mounting direction (X direction).  
         [0211]     According to this structural arrangement, the projections (catches)  81  and  82  are located a predetermined distance away from the leading end of the cartridge frame  26 , in the cartridge mounting direction, assuring that the cartridge  20  will be temporarily held to the movable cartridge guides  30  and  32  by the latches (sliding latches  31  and  33 ) provided on the main assembly side A of the image forming apparatus. Therefore, it is assured that the cartridge  20  will be moved to the position  300  in which the cartridge  20  is used for image formation.  
         [0212]     Also according to this structural arrangement, not only are the projections (catches)  81  and  82  located a predetermined distance away from the leading end of the cartridge frame  26 , in the cartridge mounting direction, but also are located a predetermined distance away, leftward and rightward, one for one, from the center of the photosensitive drum  21 , in the lengthwise direction of the photosensitive drum  21 .  
         [0213]     In other words, in terms of the lengthwise direction of the photosensitive drum  21 , the projection (catch)  81  is located the predetermined distance leftward of the center of the photosensitive drum  21  (center of leading edge of cartridge frame  26 ), and the projection (catch)  82  is located the predetermined distance rightward of the center of the photosensitive drum  21  (center of leading edge of cartridge frame  26 ).  
         [0214]     With the provision of this structural arrangement, in which not only are the projections (catches)  81  and  82  located a predetermined distance away from the leading end of the cartridge frame  26 , in the cartridge mounting direction (X direction), but also are located a predetermined distance away, leftward and rightward, one for one, of the center of the photosensitive drum  21 , in the lengthwise direction of the photosensitive drum  21 , the cartridge  20  can be temporarily held, by two locations thereof, to the movable cartridge guides  30  and  32  by the latches (sliding latches  31  and  33 ) provided on the main assembly side A. Therefore, the cartridge  20 , which is to be mounted into the apparatus main assembly A in the widthwise direction of the cartridge  20 , can be more easily and securely mounted into the apparatus main assembly A.  
         [0215]     Here, “widthwise direction” means the direction intersectional to the lengthwise direction of the photosensitive drum.  
         [0216]     Further, the catch portions  81  and  82  comprises the first projecting portions  83  and  84 , and second projecting portions  81  and  82 , respectively. The first projecting portions  83  and  84  project from the cartridge frame  26  in the cartridge mounting direction (X direction), in the direction roughly perpendicular to the lengthwise direction of the photosensitive drum  21 . The second projecting portions  81  and  82  project from the first projecting portions  83  and  84 , respectively, in the direction roughly parallel to the lengthwise direction of the photosensitive drum  21 .  
         [0217]     According to this structural arrangement, the recesses (voids) of the catch portions  81  and  82 , into which the sliding latches  31  and  33  fit, are in the shape of a key extending in the lengthwise direction, making thereby the catch portions  81  and  82  stronger. It is assured that the cartridge  20  will automatically and properly mounted into the main assembly A of the image forming apparatus.  
         [0218]     Further, the first cartridge positioning portion  85  and/or second cartridge positioning portion  86  are pressed toward, and kept pressed upon, the cartridge positioning members  101  of the main assembly A of the image forming apparatus, by the first cartridge retaining member  94  of the apparatus main assembly A for pressing the positioning portion  85  and/or second cartridge positioning portion  86  in the first direction, and the second cartridge retaining member  95  of the main assembly A for pressing the first cartridge positioning portion  85  and/or second cartridge positioning portion  86  in the second direction, respectively.  
         [0219]     With the provision of this structural arrangement, the cartridge positioning portions are pressed from two different directions. Therefore, not only is the cartridge more reliably and accurately positioned, but also the amount of the pressure which the cartridge receives from each member is smaller. Therefore, the reactive forces, for example, the reactive force generated by the friction, which the cartridge receives while the cartridge is moved from the mounting position to the image formation position, are smaller in magnitude. Therefore, it is further assured that the cartridge will be automatically and properly mounted into the main assembly A of the image forming apparatus.  
         [0220]     Further, the first cartridge positioning portion  85  and/or second cartridge positioning portion  86  are pressed toward, and kept pressed upon, the cartridge positioning members  101  of the image forming apparatus, by the first cartridge retaining member  94  attached to the frame (side walls  100  and  110 ) of the main assembly A of the image forming apparatus in order to press the first cartridge positioning portion  85  and/or second cartridge positioning portion  86  in the first direction, and the second cartridge retaining member  95  attached to the transfer unit (intermediary transfer member  40 ) on the main assembly A side of the image forming apparatus in order to press the first cartridge positioning portion  85  and/or second cartridge positioning portion  86  in the second direction, which is different from the first direction.  
         [0221]     Further, the latches (sliding latches  31  and  33 ) are attached to the movable cartridge guides  30  and  32  so that they are engaged with the catches, one for one, by the movement of the movable cartridge guides  30  and  32 .  
         [0222]     With the provision of this structural arrangement, as the cover  10  is opened, the latches (sliding latches  31  and  33 ) are slid upward by the opening movement of the cover  10 . Therefore, when the cartridge  20  is mounted into the movable cartridge guides  30  and  32 , the latches (sliding latches  31  and  33 ) do not interfere with the catch portions  81  and  82  of the cartridge  20 , allowing the cartridge  20  to be inserted deeper into the movable cartridge guides  30  and  32  in the cartridge mounting direction (X direction), further assuring the successful automatic mounting of the cartridge  20 .  
         [0223]     Further, the movable cartridge guides  30  and  32  is attached to the main assembly A of the image forming apparatus so that they are pivotally moved relative to the main assembly A by the opening or closing movement of the cover  10  of the apparatus main assembly A.  
         [0224]     With the provision of this structural arrangement, when automatically mounting the process cartridge  20  into the apparatus main assembly A, as the cover  10  is closed, the cartridge  10  is moved into the apparatus main assembly A while being continuously pulled toward the cartridge positioning portions  101 ,  101   a , and  101   b , further assuring that when the cartridge  20  is automatically mounted into the apparatus main assembly A of the image forming apparatus, it is properly positioned relative to the apparatus main assembly A.  
         [0225]     Further, each of the latches (sliding latches  31  and  33 ) has three portions, that is, leading end portion, mid portion (guiding portions  37   c  and  38   a ), and trailing portion, in terms of latching direction, making the distance between the leading portion and the catch portion  81  ( 82 ) different from the distance between the trailing portion and the catch portion  81  ( 82 ). Thus, at the beginning of the engagement of the latch with the catch portion  81  ( 82 ) of the cartridge  20 , the catch portion  81  ( 82 ) is not pulled toward the latch  31  ( 33 ). Then, as the movable cartridge guides  30  and  32  are further pivoted inward of the apparatus main assembly A, the catch portion  81  ( 82 ) begins to be gradually pulled toward the latch  81  ( 82 ).  
         [0226]     With the provision of this structural arrangement, in which each of the latches (sliding latches  31  and  330  has three portions, that is, leading end portion, mid portion (guiding portions  37   c  and  38   a ), and trailing portion, in terms of latching direction, making the distance between the leading portion and the catch portion  81  ( 82 ) different from the distance between the trailing portion and the catch portion  81  ( 82 ), the cartridge  20  is not pulled by the latch  31  ( 33 ) at the beginning of the engagement of the latch  31  ( 33 ) with the catch portion  81  ( 82 ). Then, as the movable cartridge guides  30  and  32  are further pivoted inward of the apparatus main assembly A, the cartridge  20  is gradually pulled toward the latch  81  ( 82 ). In other words, when mounting the cartridge  20  into the movable cartridge guides  30  and  32 , the cartridge  20  does not reach the inward ends of the movable cartridge guides  30  and  32 , remaining therefore slightly outward of the final position, that is, the image formation position. However, as the cover  10  begins to be closed, the movable cartridge guides  30  and  32  begins to be pivoted inward of the apparatus main assembly A by the closing movement of the cover  10 , causing thereby the latches (sliding latches  31  and  33 ) to begin to slide and engage with the catches  81  and  82 . Thereafter, as the cover  10  is further closed, the force is generated by the combination of the latches  31  and  33  and the catch portions  81  and  82 , in the direction to pull the cartridge  20  inward of the movable cartridge guides  30  and  32 . Therefore, it is further assured that the cartridge  20  is automatically and accurately mounted.  
         [0227]     As described above, according to the present invention, a process cartridge can be improved in its operability in terms of the mounting of the process cartridge into the main assembly of an electrophotographic image forming apparatus.  
         [0228]     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.