Abstract:
A process cartridge which is capable of being carried on a movable guide, which is movable relative to a main assembly of an electrophotographic image forming apparatus and which is provided in the main assembly, the movable guide being 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; a first positioning portion to be positioned relative to a main assembly, when the cartridge is mounted to the main assembly, the first positioning portion extending outwardly from the framee adjacent the one longitudinal end of the drum; a second positioning portion to be positioned relative to the main assembly, when the cartridge is mounted to the main assembly, the second positioning portion extending outwardly from the framee adjacent the other longitudinal end of the drum; a first portion to be carried, provided at one longitudinal end of the drum, for being supported by the movable guide, the first portion to be carried being disposed on a bottom surface of the framee; a second portion to be carried, provided at the other longitudinal end of the drum, for being supported by the movable guide, the second portion to be carried being disposed on a bottom surface of the framee; and a third positioning portion provided on at least one of the first portion to be carried and the second portion to be carried at a leading side with respect to a mounting direction in which the cartridge is mounted to the main assembly, wherein the third positioning portion has a first rotation stopper surface for stopping rotation of the cartridge about the first positioning portion and the second positioning portion by abutting to the movable guide.

Description:
FIELD OF THE INVENTION AND RELATED ART  
       [0001]     The present invention relates to an electrophotographic image forming apparatus, a process cartridge removably mountable in the main assembly of an electrophotographic image forming apparatus, and a process cartridge positioning mechanism.  
         [0002]     Here, an electrophotographic image forming apparatus means an apparatus which forms images on recording medium (for example, recording paper, OHP sheet, etc.) with the use of one of the electrophotographic image forming methods. As for 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, and an integral combination of two or more of the preceding apparatuses (multifunction printer, etc.).  
         [0003]     A process cartridge means a cartridge in which a charging means as a processing means, a developing means or a cleaning means as a processing means, and an electrophotographic photosensitive drum are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. It also means a cartridge in which a minimum of one processing means among a charging means, a developing means, and cleaning means, and an electrophotographic photosensitive drum are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. Further, it means a cartridge in which a minimum of a developing means as a processing means and an electrophotographic photosensitive drum are integrally disposed, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus.  
         [0004]     In the field of an electrophotographic image forming apparatus, the process cartridge system has been employed, according to which an electrophototraphic photosensitive drum (which hereinafter will be referred to as “photosensitive drum”) and a single or plurality of processing means, which act on the photosensitive drum, are integrally disposed in a cartridge removably mountable in the main assembly of an electrophotographic image forming apparatus. Also according to the process cartridge system, an electrophotoraphic image forming apparatus can be maintained by an operator alone, that is, without relying on service personnel. Thus, the process cartridge system drastically improves an electrophotographic image forming apparatus in operational efficiency. Therefore, the process cartridge system is widely in use in the field of an electrophotographic image forming apparatus.  
         [0005]     The process cartridge system is also employed in the field of an electrophotographic color image forming apparatus. In the case of an electrophotographic color image forming apparatus, a plurality of process cartridges different in the development color are removably mounted in the main assembly of the apparatus, assisting the operator in terms of operational efficiency.  
         [0006]     Also in the case of an electrophotographic color image forming apparatus, the plurality of process cartridges are vertically stacked in parallel, reducing thereby the footprint of the apparatus.  
         [0007]     In other words, in the case of an electrophotographic color image forming apparatus, the plurality of process cartridges must be mounted into predetermined positions in the main assembly of the apparatus, adding to the number of operations which an operator must carry out.  
         [0008]     Therefore, in the case of an electrophotographic color image forming apparatus, it has been desired to further improve the efficiency with which a process cartridge is mounted in the apparatus main assembly.  
         [0009]     It has been a common practice to provide the main assembly of an image forming apparatus with a cartridge mounting guide, which is movable relative to the main assembly, and into which a process cartridge is mounted. After the mounting of the process cartridge into the movable cartridge mounting guide, the guide is moved to carry the process cartridge into the predetermined position in the apparatus main assembly. It has been proposed to employ this cartridge mounting guide in order to improve the efficiency with which a process cartridge is mounted into the apparatus main assembly (for example, Japanese Laid-open Patent Application 4-90561).  
         [0010]     According to another proposal (for example, U.S. Pat. No. 6,351,620), a process cartridge is provided with a pair of guides, which are located at the lengthwise ends of the cartridge, one for one. As a process cartridge is mounted into the movable guide of the main assembly of an image forming apparatus, each guide of the process cartridge is seized between a cartridge catching portion and a springy member on the main assembly side, being thereby fixed in position to accurately position the cartridge relative to the apparatus main assembly.  
         [0011]     The present invention is the result of the further development of the above described prior arts.  
       SUMMARY OF THE INVENTION  
       [0012]     The primary object of the present invention is to provide a combination of a process cartridge, a process cartridge mounting mechanism, and an electrophotographic image forming apparatus, which is superior to the combinations in accordance with the prior arts in terms of the operational efficiency of the mounting of a process cartridge into the main assembly of an electrophotographic image forming apparatus.  
         [0013]     Another object of the present invention is to provide a combination of a process cartridge, a process cartridge mounting mechanism, and an electrophotographic image forming apparatus, which assures that a process cartridge is accurately mounted into the predetermined position in the main assembly of an electrophotographic image forming apparatus.  
         [0014]     Another object of the present invention is to provide a combination of a process cartridge, a process cartridge mounting mechanism, and an electrophotographic image forming apparatus, which regulates the rotation of a process cartridge about the first and second cartridge positioning portions, by the third cartridge positioning portion, in order to assure that a process cartridge is accurately mounted into the predetermined position in the main assembly of an electrophotographic image forming apparatus.  
         [0015]     Another object of the present invention is to provide a process cartridge which is mountable in the cartridge mounting guide movable relative to the main assembly of an electrophotographic image forming apparatus, is movable from the cartridge mounting position to the image formation position, by the movement of the cartridge mounting guide, and also, comprises: 
        a first cartridge supporting portion, by which the process cartridge is supported by the movable guide, and which is a part of the bottom surface of one of the lengthwise end portions of the cartridge frame;     a second cartridge supporting portion, by which the process cartridge is supported by the movable guide, and which is a part of the bottom surface of the other lengthwise end portion of the cartridge frame; and     a third cartridge positioning portion, which is located forward of either the first or second cartridge supporting portion, or both in terms of the direction in which the process cartridge is mounted into the apparatus main assembly, and which comprises a first rotation control surface, with which the process cartridge comes into contact, being thereby prevented from rotating further, as it is rotated about the axial lines of the first and second positioning portions by the force generated as driving force is transmitted to the process cartridge from the apparatus main assembly, a mechanism for positioning the process cartridge, and an electrophotographic image forming apparatus which employs the process cartridge.        
 
         [0019]     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  
       [0020]      FIG. 1  is a schematic sectional view of an image forming apparatus in accordance with the present invention, showing how the door of the apparatus is opened or closed.  
         [0021]      FIG. 2  is a schematic sectional view of a color laser printer, which is one of the embodiments of the present invention in the form of an electrophotographic image forming apparatus.  
         [0022]      FIG. 3  is a schematic perspective view of the movable guide and the process cartridges in the movable guide, in a preferred embodiment of the present invention, showing how the process cartridges are held by the movable guide.  
         [0023]      FIG. 4  is a schematic perspective view of the image forming apparatus in the preferred embodiment of the present invention, with one of its side covers removed, showing the mechanical linkage in the state in which the apparatus is in the image forming action.  
         [0024]      FIG. 5  is a schematic perspective view of the image forming apparatus in the preferred embodiment of the present invention, with its main door opened, showing the mechanical linkage.  
         [0025]      FIG. 6  is an enlarged schematic perspective view of the mechanical linkage, and its adjacencies, in the state in which the apparatus is in the image forming action.  
         [0026]      FIG. 7  is a schematic sectional view of the process cartridge in the preferred embodiment of the present invention.  
         [0027]      FIG. 8  is a schematic perspective view of the process cartridge in the preferred embodiment of the present invention.  
         [0028]      FIG. 9  is also a schematic perspective view of the process cartridge in the preferred embodiment of the present invention.  
         [0029]      FIG. 10  is a schematic view of the movable guide and a process cartridge, in the preferred embodiment of the present invention, showing how the process cartridge is mounted into the movable guide.  
         [0030]      FIG. 11  is a schematic vertical sectional view or the movable guide of the image forming apparatus, holding a pair of process cartridges, at a plane parallel to the front panel of the apparatus, in the preferred embodiment of the present invention.  
         [0031]      FIG. 12  is a schematic vertical sectional view of the process cartridge in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing the process cartridge positioning mechanism in the position in which the cartridge is mounted into the movable guide.  
         [0032]      FIG. 13  is a schematic vertical sectional view of the process cartridge in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing the process cartridge in the state in which it has been accurately positioned relative to the apparatus main assembly by the closing of the main door.  
         [0033]      FIG. 14  is a schematic vertical sectional view of the process cartridge, and its adjacencies, in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing the mechanism for separating the development roller from the photosensitive drum, in the process cartridge.  
         [0034]      FIG. 15  is a schematic vertical sectional view of the process cartridge in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing the state of the process cartridge in which the development roller has been separated from the photosensitive drum.  
         [0035]      FIG. 16  is a schematic sectional view of the process cartridge in the preferred embodiment of the present invention, at a plane parallel to the direction in which the cartridge is mounted into the movable glide, showing in particular the developer roller pressing member.  
         [0036]      FIG. 17  is a schematic vertical sectional view of the process cartridge in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing in particular the mechanism for opening or closing the shutter of the process cartridge, in the state in which the process cartridge has been completely mounted into the movable guide which is in the cartridge mounting positioned.  
         [0037]      FIG. 18  is a schematic vertical sectional view of the process cartridge in the movable guide of the image forming apparatus, in the preferred embodiment of the present invention, at a plane parallel to the side panel of the apparatus, showing in particular the mechanism for opening or closing the shutter of the process cartridge, in the state in which the process cartridge has been accurately position by the closing of the door of the apparatus main assembly.  
         [0038]      FIG. 19  is a perspective view of one of the lengthwise ends of the process cartridge in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]     Hereinafter, the preferred embodiment of the present invention will be described in detail with reference to the appended drawings. Incidentally, the measurements, materials, and configurations of the structural components, and the positional relationships among the structural components, in this embodiment, are not intended to limit the scope of the present invention. Further, once a given component is described, fits material, configuration, etc., will be the same throughout this patent application, unless specifically noted.  
         [0040]     Also hereinafter, the lengthwise direction of a process cartridge means the direction intersectional with (roughly perpendicular to) the direction in which a cartridge is mounted into, or removed from, the main assembly of an image forming apparatus. It also means the lengthwise direction of a photosensitive drum. The top and bottom surfaces of a cartridge means the surfaces of a cartridge which will be at the top and bottom of the process cartridge, respectively, after the accurate positioning of the cartridge in the main assembly of an image forming apparatus.  
         [heading-0041]     [Description of General Structure of Electrophotographic Color Image Forming Apparatus] 
         [0042]     First, the general structure of the electrophotographic color image forming apparatus will be described with reference to  FIG. 2 , which is a sectional view of a color laser printer, that is, one of the embodiments of the present invention in the form of an electrophotographic image forming apparatus employing an electrophotographic process, showing the general structure thereof.  
         [0043]     As shown in  FIG. 2 , the color laser printer (which hereinafter will be referred to as “printer”) is a four-drum type (inline type) printer, which comprises: four process cartridges  2  ( 2 Y,  2 M,  2 C, and  2 Bk); an intermediary transfer member (medium)  35 ; a fixing station  50  for fixing a color image transferred onto recording medium P (for example, recording paper, OHP sheet, etc.) to the recording medium P; and multiple pairs of discharge rollers  53 ,  54 , and  56  for discharging the recording medium P onto a delivery tray  56  on top of the apparatus main assembly.  
         [0044]     The four process cartridges  2  ( 2 Y,  2 M,  2 C, and  2 Bk) are mounted in the main assembly of the color printer A, being vertically stacked.  
         [0045]     The cartridge  2 Y stores developer of yellow color, and forms an image of the yellow developer.  
         [0046]     The cartridge  2 M stores developer of magenta color, and forms an image of the magenta developer. The cartridge  2 C stores developer of cyan color, and forms an image of the cyan developer. The cartridge  2 Bk stores developer of black color, and forms an image of the black developer.  
         [0047]     The intermediary transfer member  35  is a member onto which images formed of developers in process cartridges  2  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.  
         [0048]     The four cartridges  2  can be individually mounted into, or removed from, the main assembly A of the printer.  
         [0049]     Next, referring to  FIG. 2 , the various portions of the image forming apparatus will be described in structure in a logical order. Incidentally, where all the cartridges are the same regarding a given structural feature, only the cartridge  2 Y will be described regarding this structural feature, and the other process cartridges will not be given referential symbols, and will not be described regarding this structural feature.  
         [heading-0050]     [Photosensitive Drum] 
         [0051]     The photosensitive drum  21  comprises an aluminum cylinder, and a layer of organic photosensitive substance coated on the peripheral surface of the aluminum cylinder. It is rotatably supported by the drum frame  24 . At the back side ( FIG. 2 ) of the photosensitive drum  21 , 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. 7 ) indicated by an arrow mark in the drawing in synchronism with an image formation.  
         [heading-0052]     [Charging Means] 
         [0053]     A charging means employs a contact charging method. It has an electrically conductive roller (charge roller)  23  ( 23 Y), which is placed in contact with the peripheral surface of the photosensitive drum  21 . As voltage is applied to the charge roller  23 , the peripheral surface of the photosensitive drum  21  is uniformly charged.  
         [heading-0054]     [Exposing Means] 
         [0055]     The photosensitive drum  21  is exposed by a scanner portion  1  ( 1 Y). More specifically, as an image formation signal is given to a laser diode (unshown), the laser diode emits a beam of image formation light  10  ( 10 Y), in response to the image formation signal, toward a polygon mirror  11  ( 11 Y).  
         [0056]     The polygon mirror  11  is being rotated at a high speed by a scanner motor  12  ( 12 Y). The beam of image formation light  10  is reflected by the mirror  11 , and is guided through a focal lens  13  ( 13 Y) to the peripheral surface of the photosensitive drum  21 , which also is rotated at a constant peripheral velocity, selectively exposing numerous points on the peripheral surface of the photosensitive drum  21 . As a result, an electrophotographic latent image is formed on the peripheral surface of the photosensitive drum  21 .  
         [heading-0057]     [Developing Means] 
         [0058]     The developing means is for developing the electrostatic latent image into a visible image. Thus, it is provided with a development unit  2   b  ( FIG. 7 ) which makes it possible for the latent image to be developed with developer. The development unit  2   b  has a development roller  22  ( 22 Y), which is disposed in the position in which it is rotatable in contact with the photosensitive drum  21 . It uses developer to develop the latent image on the photosensitive drum  21 .  
         [heading-0059]     [Intermediary Transfer Member] 
         [0060]     The intermediary transfer member  35  is a member onto which multiple images formed of developers on the photosensitive drums  21 , by the developer units  2   b , one for one, are transferred in layers during color image formation. The intermediary transfer member  35  is rotationally driven in the clockwise direction ( FIG. 2 ) at the same peripheral velocity as that of the photosensitive drum  21 .  
         [0061]     After being formed on the photosensitive drums  21 , the images formed of developers on the photosensitive drums  21  are transferred in layers onto the intermediary transfer member  35  by the primary transfer rollers  34  ( 34 Y,  34 M,  34 C, and  34 Bk), one for one, in the primary transfer stations T 1  (T 1 Y, T 1 M, T 1 C, and T 1 Bk). Each transfer roller  34  is disposed so that it is kept pressed upon the corresponding photosensitive drum  21 , with the intermediary transfer member  35  sandwiched between the transfer roller  34  and photosensitive drum  21 .  
         [0062]     After the multiple images formed of developers are transferred in layers onto the intermediary transfer member  35 , the recording medium P is sandwiched between the intermediary transfer member  35  and secondary transfer roller  51 , and is conveyed by them. As a result the color images formed of developers, on the intermediary transfer member  35 , are transferred all at once onto the recording medium P.  
         [0063]     The intermediary transfer member (intermediary transfer belt)  35  in this embodiment is a seamless resin belt with a circumferential dimension of roughly 620 mm. It is stretched around a driving roller  31 , intermediary transfer member backing roller  32 , and tension roller  33 , being thereby supported by them. The tension roller  44  is kept pressured outward of the loop, which the intermediary transfer member  35  forms, by the pressure applied to the lengthwise ends of the roller  33 . With the provision of this structural arrangement, should the circumferential dimension of the intermediary transfer member (belt)  35  change due to the changes in the internal temperature and/or humidity of the apparatus main assembly A, the change is absorbed by the structural arrangement.  
         [0064]     Further, the intermediary transfer member  35  is pivotally held to the main assembly A of the apparatus (printer), being allowed to pivotally move about the rotational axis of the driving roller  31 . The driving force from a motor (unshown) is transmitted to the back end ( FIG. 2 ) of the driving roller  31 , rotating the intermediary transfer member  35  in the clockwise direction ( FIG. 2 ) in synchronism with image formation.  
         [heading-0065]     [Feeding Station] 
         [0066]     The feeding station is a station for conveying recording mediums P to the cartridges  2  in the main assembly A of the printer. It comprises a cassette  7  capable of containing multiple recording mediums P, a feed roller  41 , a separation pad  42 , a conveyance guide  43  and a pair of registration rollers  44 , etc.  
         [0067]     During image formation, the roller  41  is rotationally driven in synchronism with image formation, whereby the recording mediums P in the cassette  7  are fed one by one out of the cassette  7 , and guided by the guide  43  to the pair of registration rollers  44 , which carries out, in a predetermined sequence, the non-rotational process for keeping the recording medium P on standby and the rotational process for conveying the recording medium P toward the intermediary transfer member  35 , in order to make the recording medium P align with the images on the intermediary transfer member  35  during the subsequent process, that is, the image transfer process.  
         [heading-0068]     [Transfer Station] 
         [0069]     The transfer station has a secondary transfer roller  51 , which is rotationally driven, and is virtually vertically movable ( FIG. 2 ). In synchronism with the arrival of the color images at the transfer station, the transfer roller  51  is pressed against the intermediary transfer member  35  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  35  and transfer roller  51 . During this process, bias is applied to the transfer roller  51 . As a result, the images formed of developers, on the intermediary transfer member  35  are transferred onto the recording medium P. Incidentally, the intermediary transfer member  35  and transfer roller  51  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  35  and transfer roller  51  during the transfer process, is conveyed leftward ( FIG. 2 ), reaching a fixing device  60 .  
         [heading-0070]     [Fixation Station] 
         [0071]     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  50 , 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-0072]     [Image Forming Operation] 
         [0073]     Next, the operation for forming an image with the use of the apparatus structured as described above will be described.  
         [0074]     First, the feed roller  41  shown in  FIG. 2  is rotated, conveying thereby one of the recording mediums P in the cassette  1  to the pair of registration rollers  44 .  
         [0075]     Meanwhile, the photosensitive drum  21  and intermediary transfer member  35  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).  
         [0076]     After being charged by the charge roller  23  across it peripheral surface, the photosensitive drum  21  is exposed to the beam of laser light  10  (image formation light). As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  21 . Since the image forming operation is the same for all color component, the image formation operation for the yellow color components will be described here.  
         [heading-0077]     (Formation of Yellow Image)  
         [0078]     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  10 Y, corresponding to the yellow color component of the target image, projected from the scanner portion  1 Y. In synchronism with the formation of this latent image, the yellow development roller  22 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  22 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 or yellow developer, is transferred (primary transfer) onto the peripheral surface of the intermediary transfer member  35 , in the transfer station T 1 Y.  
         [0079]     Then, the processes for forming a latent image and developing the latent image, similar to those described above, are sequentially carried out for the magenta, cyan, and black color components. The formed developer images are transferred onto the intermediary transfer member  35 , in the primary transfer stations T 1 M, T 1 C, and T 1 Bk, respectively. As a result, a full-color image composed of four developers, that is, the yellow, magenta, cyan, and black developers, are formed on the peripheral surface of the intermediary transfer member  35 .  
         [0080]     Incidentally, prior to the completion of the transfer of the image formed of black developer onto the intermediary transfer member  35 , the recording medium P, which has been kept on standby by the above described pair of registration rollers  44 , is released by the pair of registration rollers  44  for further conveyance.  
         [0081]     Except for the period tn which the four color images are transferred onto the intermediary transfer member  35 , the transfer roller  51  is kept at the bottom position, being away from the intermediary transfer member  35 . However, immediately prior to the transfer of the four color images onto the intermediary transfer member  35 , the transfer roller  51 , is moved upward by a cam (unshown) in order to keep the recording medium P pressed against the intermediary transfer member  35  by the transfer roller  51 , in the second transfer station T 2 , 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  51 . As a result, the four color images, which make up a full-color image, on the intermediary transfer member  35 , are transferred all at once onto the recording medium P.  
         [0082]     Thereafter, the recording medium P is separated from the intermediary transfer member  35 , and is conveyed to the fixing device  50 , in which the images formed of the developers are fixed. Then, the recording medium P is discharged onto the delivery tray  56  on top of the main assembly of the printer, by the three pairs of discharge rollers, ending the operation for forming a full-color image on one of the recording mediums P.  
         [heading-0083]     [Method for Mounting Process Cartridge] 
         [0084]     Next the combination of the process cartridge  2 , process cartridge mounting mechanism, and electrophotographic image forming apparatus, in an preferred embodiment of the present invention will be described.  FIG. 1  is a schematic sectional view of the printer A, that is, one of the embodiments of the present invention in the form of an image forming apparatus, with its main door open.  
         [0085]     As shown in  FIG. 1 , the door  16  of the main assembly  100  of the image forming apparatus is pivotally movable relative to the main assembly  100  about the rotational axis located at the bottom front of the image forming apparatus (printer) A. The aforementioned intermediary transfer member  35  is attached to the door  16 . Thus, as the door  16  is opened, it becomes possible for an operator to access the process cartridges  2  ( 2 Y,  2 M,  2 C, and  2 Bk).  
         [0086]     The door  16  is to be opened or closed when. necessary to mount a single or multiple cartridges  2  into the apparatus main assembly A, or to remove a single or multiple cartridges  2  from the apparatus main assembly A.  
         [0087]     The movable guide  101  holds together multiple cartridges  2  ( 2 Y,  2 M,  2 C, and  2 Bk). The pivots  101   a - b  and  101   b - b  ( FIG. 3 ) are located at the top end portion of the apparatus main assembly A, and are connected to the door  16  with a set of mechanical linkages (which will be described later). With the provision of this structural arrangement, as the door  16  is opened, the movable guide  101  is pivoted frontward of the apparatus main assembly  100  about the pivots  101   a - b  and  101   b - b , and therefore, the cartridges  2  supported by the movable guide  101  are also moved frontward of the apparatus main assembly  100 .  
         [0088]     In this embodiment, the angle by which the movable guide  101  is pivotally moved by the opening of the door  16  is roughly 45°.  
         [0089]     With the movable guides  101  tilted as described above, an operator can easily mount cartridges  2  into, or take them out of, the movable guide  101 , since there is no obstruction in the direction indicated by an arrow mark in the drawing.  
         [0090]     Next, the mounting of the process cartridges  2  into the apparatus main assembly  100 , and the removing of the process cartridges  2  from the apparatus main assembly  100 , will be described.  
         [0091]      FIG. 3  is a perspective view of the movable guide  101 , and the cartridges  2  supported by the movable guide  101 . For the sake of descriptive convenience, the process cartridges  2 Bk and  2 C are not illustrated in the drawing.  
         [0092]     The movable guide  101  is provided with right and left plates  101   a  and  101   b . The right plate  101   a  supports the right end of each of the cartridges  2 Y,  2 M,  2 C, and  2 Bk, and the left plate  101   b  supports the left end of each of the cartridges  2 Y,  2 M,  2 C, and  2 Bk. In this embodiment, the right and left plates  101   a  and  101   b  of the movable guide  101  are separately manufactured for cost saving. However, the movable guide  101  may be manufactured as a single-piece component, or in multiple pieces which are assembled into the movable guide  101 .  
         [0093]     Also in this embodiment, the right and left plates  101   a  and  101   b  of the movable guide  101  are connected with a connective member (which will be described later), so that the right and left plates  101   a  and  101   b  remain synchronized in pivotal movement phase, and also, so that the movable guide  101  in this embodiment functions exactly the same as a single-piece movable guide.  
         [0094]     The right and left plates  101   a  and  101   b  are provided with guiding ribs  101   a - a  and  101   b - a , respectively, which support the cartridge  2  from underneath so that the cartridge  2  can be smoothly inserted between the right and left plates  101   a  and  101   b.    
         [0095]     The right and left plates  101   a  and  101   b  are also provided with the pivols  101   a - b  and  101   a - b . respectively, about which the movable guide  101 , in which multiple process cartridges  2  are stacked together, is pivotally movable.  
         [0096]     The right plate 101 a  is provided with openings 101 a - c , preventing thereby right plate  101   a  from interfering with the first and second driving force transmission portions  78  and  79  of each process cartridge  2 , through which the cartridge  2  receives driving force from the main assembly  100 . On the other hand, the left plate  101   b  is provided with openings 101 b - c , preventing thereby the left plate  101   b  from interfering with the cartridge positioning bearing  27  of each cartridge  2 .  
         [0097]     Further, the two plates  101   a  and  101   b  are provided with two bosses by which the plates are connected to the mechanical linkage, which will be described later.  
         [0098]     Next, the connection of the movable guide  101  to the mechanical linkage, and the operational movement the movable guide  101 , will be described.  
         [0099]      FIGS. 4, 5 , and  6  are schematic perspective internal views of the image forming apparatus, showing the set of mechanical linkages, which connects the right and left plates  101   a  and  101   b .  FIG. 4  is a schematic perspective view of the mechanical linkage in the state in which the image forming apparatus is in the image forming action, and  FIG. 5  is a schematic perspective internal view of the image forming apparatus in this embodiment, showing the mechanical linkage in the state in which the door  16  is open.  FIG. 6  is an enlarged schematic perspective view or the mechanical linkage shown in  FIG. 6 .  
         [0100]     First, referring to  FIGS. 4 and 6 , the mechanical linkage in the state in which the door  16  is closed will be described. In this state, the movable guide  101  is kept inside the apparatus main assembly  100  by the mechanical linkage, because a retaining spring  109  is keeping the mechanical linkage in the state in which the door  16  is closed. The mechanical linkage comprises: a door connection plate  105 ; an intermediary connective rod  104 ; a rotational rod  103 ; and a connective rod  102  connected to the movable guide  101 .  
         [0101]     In this state, each of the cartridges  2  in the movable guide  101  is kept pressed by a spring (unshown) so that each of the bearings  27  and  28  extending from the lengthwise ends of the cartridge  2 , one for one, remains in contact with the wall of the cartridge positioning slot  106   a  of the corresponding side wall  106  of the frame of the apparatus main assembly  100 .  
         [0102]     As will be evident from the above description, it is not the movable glide  101 , but the side walls  106  of the frame of the main assembly  100 , that accurately position the cartridges  2 . With the provision of the above described structural arrangement, the movable guide  101  functions simply as a vehicle for carrying the cartridge  2  into the immediate adjacencies of the final position for the cartridge  2  in the apparatus main assembly  100  when mounting the process cartridge  2  into the apparatus main assembly  100 . Therefore, it is unnecessary for an operator to become excessively concerned with the positioning of the cartridge  2  relative to the movable guide  101  when mounting the cartridge  2  into the movable guide  101 . In other words, when mounting the process cartridge into the movable guide  101 , it is unnecessary for an operator to confirm whether or not the cartridge  2  has been exactly positioned mounted in the movable guide  101 . Therefore, the efficiency with which the cartridge  2  is mounted into the apparatus main assembly  100  is improved.  
         [0103]     Next, referring to  FIG. 5 , the state of the mechanical linkage, in which the door  16  is fully open, will be described. As the door  16  is opened, the aforementioned connective plate  105 , intermediary rod  104 , rotational rod  103 , and connective rod  102 , which are moved by the movements the door  16 , are moved into their positions corresponding to the movable guide position  200  in which the cartridges are to be mounted into the movable guide  101 , and which is roughly 45° orbitally outward of the apparatus main assembly  100  from the movable guide position in which images are formed. In other words, as the door  16  is completely opened, it becomes easier for an operator to access the cartridge slots in the movable guide  101 , making it thereby easier for the operator to mount the cartridges  2  into the apparatus main assembly  100  or remove them therefrom.  
         [0104]     The above described cartridge mounting position  200  for the movable guide  101  is on the front side of the apparatus main assembly  100 , that is, the side where the door  16  is present, whereas the movable guide position in which images are formed (which hereinafter will be referred to as “image formation position  300 ”) is the position in the apparatus main assembly  100 , into which the movable guide  101  is moved by the closing movement of the door  16 , in order to accurately position the cartridges  2  relative to the apparatus main assembly  100 , for image formation.  
         [0105]     In other words, it is the position in which the bearings  27  and  28  are accurately positioned by the walls of the positioning slots  106   a  and  106   b  relative to the apparatus main assembly  100 .  
         [0106]     Incidentally, in this embodiment, the position of the cartridge  2  to which driving force is being transmitted from the apparatus main assembly  100  is slightly different from the predetermined final position in the apparatus main assembly  100 , into which the cartridge  2  is moved by the closing of the door  16 .  
         [heading-0107]     [Process Cartridge] 
         [0108]     Next, referring to  FIGS. 7, 8 , and  9 , the cartridge  2  in the preferred embodiment of the present invention will be described.  FIG. 7  is a schematic sectional view of the cartridge  2 , and  FIGS. 8 and 9  are perspective views of the cartridge  2 . Incidentally, the yellow, magenta, cyan, and black process cartridges are identical in structure.  
         [0109]     The cartridge  2  essentially comprises two units: a drum unit  2   a  and a development unit  2   b . The drum unit  2   a  supports the photosensitive drum  21 , charge roller  23 , and cleaning means  26 , whereas the development unit  2   b  supports the developing means for developing an electrostatic latent image formed on the photosensitive drum  21 .  
         [0110]     The units  2   a  and  2   b  are connected to each other so that they can be pivotally moved relative to each other.  
         [0111]     The drum unit  2   a  holds the photosensitive drum  21 , with the photosensitive drum  21  being rotatably supported by the bearings  27  and  28  attached to the drum frame  24 . The drum frame  24  holds the charge roller  23 , as a processing means, for uniformly charging the peripheral surface of the photosensitive drum  21 , and a cleaning blade  26   a , as a processing means, for removing the developer particles remaining on the peripheral surface of the photosensitive drum  21 .  
         [0112]     After the residual toner particles, that is, the toner particles remaining on the peripheral surface of the photosensitive drum  21 , are removed therefrom by the cleaning blade  26   a , they are sent by a toner conveying mechanism  29  into the toner chamber  30  for the removed toner, which is in the rear portion of the drum frame  24 . This toner chamber  30  is an integral part or the drum unit  2   a.    
         [0113]     The development unit  2   b  comprises: a development roller  22  as a processing means which is rotated in the direction indicated by an arrow mark Y by the contact between the development unit  2   b  and photosensitive drum  21 ; a developer container  70  in which developer is held: and a development frame  71  which supports the development roller  22 , and which comprises the developer container  70 . The development roller  22  is rotatably supported by the development frame  71 , with the interposition of bearings. Further, the development frame  71  internally holds a developer supply roller  72  and a development blade  73 . The developer supply roller  72  is rotated by its contact with the development roller  22 . The development frame  71  also internally holds a stirring member  74 , which is in the developer container  70  and conveys the developer in the developer container  70  to the developer supply roller  72  while stirring it.  
         [0114]     The development unit  2   b  is connected to the drum unit  2   a , being enabled to be pivotally moved relative to the drum unit  2   a . More specifically, the development unit  2   b  is provided with a pair of bearings  75  and  76 , which are located at the lengthwise ends of the development unit  2   b , one for one, and a pair of pins  77   a  are inserted into the holes  77  of the bearings  75  and  76 , one for one, making it possible for the entirety of the development unit  2   b  to be pivotally moved relative to the drum unit  2   a  about the axial lines of the holes  77  (pins  77   a ). In other words, the development unit  2   b  is suspended from the drum unit  2   a . With the provision of this structural arrangement, the development roller  22  is kept in contact with the photosensitive drum  21  by the rotational moment of tile development unit  2   b  about the axial lines of the holes  77  (pins  77   a ). Further, there is disposed a pair of compression springs  93  between the development units  2   b  and drum unit  2   a , assuring by its resiliency that the development roller  22  is kept pressed upon the photosensitive drum  21 .  
         [0115]     “Cartridge frame” is the term for the combination of the drum frame  24  and development frame  71 .  
         [0116]     In the development process, developer is conveyed by the stirring member  74  to the developer supply roller  72 , which is being rotated (in arrow Z direction). Then, as the developer is conveyed to the developer supply roller  72 , it is coated on the development roller  22 , which is being rotated (in arrow Y direction), because the peripheral surface of the developer supply roller  72  rubs against the peripheral surface of the development roller  22 ; in other words, the developer is borne on the peripheral surface of the development roller  22 . The developer borne on the peripheral surface of the development roller  22  reaches the development blade  73  due to the subsequent rotation of the development roller  22 , and is regulated by the development blade  73 , while being given a predetermined amount of electric charge. As a result, a development layer with a predetermined thickness is formed on the peripheral surface of the development roller  22 .  
         [0117]     The further rotation of the development roller  22  brings the uniform portion of the developer layer on the development roller  22  to the development station, that is, the contact area between the photosensitive drum  21  and development roller  22 , in which the latent image on the peripheral surface of the photosensitive drum  21  is developed by the DC voltage (development bias) applied to the development roller  22  from a power source (unshown). The developer particles remaining on the peripheral surface of the development roller  22  after the development are stripped from the peripheral surface of the development roller  22 , returning therefore into the developer container  70 , in which they are mixed with the developer in the container  70  by the stirring member  74 .  
         [heading-0118]     (Structure for Positioning Process Cartridge)  
         [0119]     Next, referring to  FIGS. 10-13 , the structure, in this embodiment, for mounting, removing, and positioning a process cartridge will be described.  FIG. 10  is a perspective view of the movable guide  101  and a process cartridge  2 , showing how the process cartridge is mounted into the movable guide  101 , and  FIG. 11  is a sectional view of the movable guide  101  in this embodiment, showing the configuration thereof.  FIG. 12  is a vertical sectional view, at a plane parallel to the cartridge mounting direction, of the process cartridge in the movable guide  101  in the cartridge mounting position, showing how the process cartridge has been positioned relative to the image forming apparatus main assembly (movable guide  101 ).  FIG. 13  is a vertical sectional view, at a plane parallel to the cartridge mounting direction, of the process cartridge, after it has been placed in the final position in the image forming apparatus main assembly, by the complete closing of the door  16 .  
         [0120]     Referring to  FIGS. 12 and 13 , the position of the movable guide  101 , in which cartridges are to be mounted into the movable guide  101 , will be described with reference to cartridge Bk, that is, the topmost cartridge in the image forming apparatus  100 . The cartridges other than the black process cartridge are not shown in the drawings. The portions of the movable guide  101 , into which the other cartridges are mounted, are identical in structure to the portion of the movable guide  101 , into which the black process cartridge is mounted.  
         [0121]     The cartridge  2  is provided with a pair of ribs  80 , which are at both ends of the cartridge  2 , one for one, in terms of the direction perpendicular to the direction in which the cartridge is mounted or removed. The ribs  80  are the portions of the cartridge  2 , by which the cartridge  2  is guided, while being supported, by the apparatus main assembly  100 .  
         [0122]     More specifically, the ribs  80  are integral portions of the ends of the cartridge  2  in terms of the lengthwise direction of photosensitive drum  21 .  
         [0123]     One of the lengthwise ends (right end) of the cartridge  2  is provided with a first driving force transmission portion  78 , in the form of a coupler, to which the driving force for rotating the photosensitive drum  21  is transmitted from the apparatus main assembly  100 , and a second driving force transmission portion  79  to which the driving force for rotating the development roller  22  and stirring member  74  is transmitted. The guiding surface  80   a  as a part of the guiding portion  80  is above the two driving force transmission portions  78  and  79 . It is a part of the top surface of the drum frame  24 .  
         [0124]     The guiding surface  80   b  as another part of the guiding portion  80  is below the two driving force transmission portions  78  and  79 . It is a part of the bottom surface of the development frame  71 .  
         [0125]     The other lengthwise end of the cartridge  2  is provided with electrical contacts  81   a  and  81   b  for applying voltage to the processing means. The guiding surface  80   c  as another part of the guiding portion  80  is above the electrical contacts  81   a  and  81   b . It is a part of the top surface of the drum frame  24 .  
         [0126]     The guiding surface  80   d  as another part of the guiding portion is below the electrical contact  81   a  and  81   b . It is a part of the bottom surface of the development frame  71 .  
         [0127]     The electrical contact  81   a  is the electrical contact through which the charge bias to be applied to the charge roller  23  is received from the apparatus main assembly  100 . The electrical contact  81   b  is the electrical contact through which the development bias to be charged to the development roller  22  is received from the apparatus main assembly  100 .  
         [0128]     The apparatus main assembly  100  is provided with guiding ribs  101   a - a  and  101   b - l  ( FIG. 3 ), which correspond in position to the guiding portions  80  or the cartridge  2 .  
         [0129]     Referring to  FIG. 12 , the development frame  71  is provided with a rotation controlling portion  82  as a third cartridge position portion, which is located forward or the guiding portion  80  in terms of the direction in which the cartridge  2  is mounted into the apparatus main assembly  100 . The rotation controlling portion  82  is shaped so that it also functions as the guide for placing the cartridge  2  on the guiding rib  101   a - a  of the movable guide  101 . The guiding rib  101   a - a  is provided with a cartridge positioning surface  101   a - f , which is a part of the inward end portion of the guiding rib  101   a - a , and opposes the rotation controlling portion  82  when the cartridge  2  is entirely rested on the guiding rib  101   a - a.    
         [0130]     Next, the mechanism for positioning the cartridge  2  relative to the apparatus main assembly  100  when mounting the cartridge  2  into the apparatus main assembly  100  will be described.  
         [0131]     The cartridge  2  is to be inserted into the movable guide  101  when the movable guide  101  is in the cartridge mounting position, into which the movable guide  101  is moved by being pivotally moved outward of the apparatus main assembly  100  by roughly 40° from the image formation position. When the movable guide  101  is in this position, the cartridge  2  can be casually mounted into the movable guide  101  (apparatus main assembly  100 ).  
         [0132]     Referring to  FIG. 12 , upon insertion of the cartridge  2  into the movable guide  101 , the cartridge  2  slides down on the guiding ribs  101   a - a  and  101   b - a , which are substantially slanted relative to the horizontal plane, because the movable guide  101  is in the cartridge mounting position. Then, slightly before the cartridge  2  reaches the deepest end of the guiding rib  101   a - a  ( 101   b - a ), the rotation controlling surface  82   a , which is the bottom surface of the rotation controlling portion  82 , comes into contact with the cartridge positioning surface  101   a - f.    
         [0133]     The cartridge positioning surface 101 a - f  is a part of the movable guide  101 . More specifically, the cartridge positioning surface  101   a - f  is a part of the downstream end portion of the movable guide  101 , in terms of the cartridge mounting direction X ( FIG. 13 ), and is slightly stepped up from the upstream side.  
         [0134]     Thus, as the cartridge  2  slides down on the guiding ribs  101   a - a  and  101   b - a , the cartridge positioning surface  82   a , that is, a part of the bottom surface of the cartridge frame, rides onto the cartridge positioning surface  101   a - f.    
         [0135]     Next, the door  16  is to be closed. As the door  16  is closed, the movable guide  101  is moved by the above described mechanical linkage connected to the apparatus main assembly  100 , into the image formation position  300 , that is, the position in which image formation is possible, shown in  FIG. 13 , in the apparatus main assembly  100 . As the movable guide  101  is moved into the image formation position  300 , the bearings  27  and  28 , which project from the lengthwise ends of the drum frame  24 , with their axial lines coinciding with the axial line of the photosensitive drum  21 , and which function as cartridge positioning portions as well as bearings, are fitted into the cartridge positioning slots  106   a  of the side walls  106 , one for one, of the main frame of the apparatus main assembly  100 . As the bearings  27  and  28  are fitted into the positioning slots  106   a , each of the bearings  27  and  28  is pressed against the rear and bottom surfaces of the corresponding positioning slot  106   a  ( 106   b ), being thereby fixed in terms of the position relative to the apparatus main assembly  100 , and therefore, accurately positioning the axis of the photosensitive drum  21  relative to the apparatus main assembly  100 .  
         [0136]     The bearings  27  and  28  bear the supporting shaft of the photosensitive drum  21 .  
         [0137]     Therefore, even when the movable guide  101  is moved into the image formation position (final position)  300 , the attitude of the cartridge  2  in terms of its rotational direction is controlled by the contact between the rotation controlling surface  82   a  of the cartridge  2  and the cartridge positioning surface  101   a - f  of the movable guide  101 .  
         [0138]     Next, referring to  FIGS. 13 and 19 , what occurs as the cartridge  2  begins to receive driving force from the image forming apparatus A will be described.  
         [0139]     The cartridge  2  is provided with a first driving force transmission portion (coupling)  78 , which is at one of the lengthwise ends. The coupling  78  is connected to the supporting shaft of the photosensitive drum  21 , and receives the driving force by coupling with the driving force transmitting means (unshown) of the apparatus main assembly  100 , rotating thereby the photosensitive drum  21  in the direction indicated by arrow marks (clockwise direction in  FIGS. 13 and 19 ). As the coupling  78  receives the driving force, the drum unit  2   a  is subjected to the rotational moments, that is, the reactive force generated by the driving force, which acts in the direction, indicated by the arrows, to rotate the drum unit  2   a  about the line connecting the axial lines of the bearings  27  and  28  as the first and second cartridge positioning portions, respectively.  
         [0140]     As a result, the rotation controlling surface  82   a  comes into contact with the cartridge positioning surface  101   a - f , catching the moment generated by the transmitted driving force. Therefore, the position of the cartridge  2  relative to the apparatus main assembly  100  becomes fixed, in terms of the direction in which the cartridge  2  is rotated by the driving force it receives from the apparatus main assembly  100 .  
         [heading-0141]     (Mechanism for Separating Development Roller from Photosensitive Drum)  
         [0142]     Next, referring to  FIGS. 14, 15 , and  16 , the mechanism for separating the development roller  22  from the photosensitive drum  21 , in the cartridge  2  in accordance with the present invention when mounting the cartridge  2  into the apparatus main assembly, or removing the cartridge  2  therefrom will be described.  FIG. 14  is a schematic sectional view of the process cartridge  2  in accordance with the present invention, and its adjacencies, at a plane perpendicular to the lengthwise direction of the cartridge  2 , showing the mechanism for separating the development roller  22  from the photosensitive drum  21 , and  FIG. 15  is a schematic sectional view of the process cartridge  2  in accordance with the present invention, and its adjacencies, at a plane perpendicular to the lengthwise direction of the cartridge  2 , in the state in which the cartridge  2  is in the image forming apparatus main assembly  100 , and in which the development roller has been separated from the photosensitive drum  21 .  FIG. 16  is a schematic sectional view of the process cartridge  2  in accordance with the present invention, at a plane perpendicular to the lengthwise direction of the cartridge  2 , showing the developer roller pressing members thereof.  
         [0143]     The apparatus main assembly  100  is provided with a separating means  110  for separating the development roller  22  from the photosensitive drum  21  against the resiliency of the pair of compression springs  93  of the cartridge  2 . The separating means  110  is located at the deepest (most downstream) end of the apparatus main assembly  100  in terms of the direction in which the cartridge  2  is mounted into the apparatus main assembly  100 . It has a developer separating portion (plate)  111  for pushing upward the force catching portion  92 , with which the lengthwise end of the development unit  2   b  is provided.  
         [0144]     The separating means  110  can be activated by a motor (unshown) to push up the separating plate  111  to the separation point at which there is no contact between the development roller  22  and photosensitive drum  21 , or to release the separating plate  111  to allow the separating plate  111  to return to the development point at which the development roller  22  is kept in contact with the photosensitive drum  21 ; the separating means  110  allows the development unit  2   b  to be in the developing position only during a period in which an image is actually formed.  
         [0145]     In this embodiment, the separating plate  111  is pushed up by a stepping motor (unshown) after the positioning of the cartridge  2  into its image formation position, which corresponds to the image formation position  300  of the movable guide lot, in the apparatus main assembly  100 . Incidentally, the cartridge  2  is structured so that the development unit  2   b  is suspended with the pair of pins  77   a  from the drum unit  2   a , being enabled to pivotally move about the pins  77   a .  
         [0146]     Thus, as the separating plate  111  is pushed upward, it comes into contact with the force catching portion  92  of the development unit  2   b , and pushes the force catching portion  92  upward. As a result, the rotation controlling surface  82   b , which is the top surface of the rotation controlling portion  82  of the drum unit  2   a , and which is for controlling the developer roller separating rotation of the cartridge  2 , comes into contact with the cartridge catching surface 101 a - g , which is a part of the guiding rib  101   a  of the movable guide  101 , and which corresponds in position to the rotation controlling surface  82   b , preventing the drum unit  2   a  (cartridge  2 ) from rotating further upward ( FIGS. 18 and 19 ).  
         [0147]     As the drum unit  2   a  is prevented from rotating further upward, the development unit  2   b  is rotated about the pins  77   a , causing therefore the development roller  22  to separate from the photosensitive drum  21 , creating a predetermined distance between the development roller  22  and photosensitive drum  21 .  
         [0148]     However, as soon as an image forming operation is started by a print signal, the force being applied to push tile separating plate  111  upward is stopped in synchronism with the timing of the developing operation, allowing the development roller  22  to be placed in contact with the photosensitive drum  21 , that is, readying the development roller  22  for development, so that an image can be formed. After the completion of a given image forming operation, the separating plate  111  is pushed up, and the development roller  22  is kept separated from the photosensitive drum  21 . With the provision of this structural arrangement, it is assured that even if the image forming apparatus A is kept unfused for a substantial length of time, the problem that the elastic layer of the development roller  22  is permanently deformed by being kept pressed on the photosensitive drum  21  for a substantial length of time will not occur.  
         [0149]     Further, the cartridge  2  is structured so that the development unit  2   b  is suspended from the drum unit  2   a , being allowed to pivotally move relative to the drum unit  2   a . Therefore, when the cartridge is not under any constraint, the development unit  2   b  is kept pressured by the resiliency of the springs  93 , in the direction to keep the development roller  22  in contact with the photosensitive drum  21 . Therefore, after the removal of the force which keeps the development roller  22  separated from the photosensitive drum  21 , that is, during an image forming operation, the development roller  22  is kept in contact with the photosensitive drum  21  solely by the resiliency of the springs  93 , without being affected by the structural arrangement on the apparatus main assembly side. Therefore, a predetermined amount of contact pressure is maintained between the development roller  22  and photosensitive drum  21 .  
         [0150]     The pair of compression springs  93  may be replaced with a pair of tension springs attached to the lengthwise ends of the cartridge  2 , one for one, with one end of each tension spring attached to the portion of the lengthwise end of the drum frame  2   a , which roughly corresponds in position to the axial line of the photosensitive drum  21 , and the other end attached to the portion of the lengthwise end of the development frame  2   b , which roughly corresponds to the axial line of the development roller  22 . In this embodiment, however, a pair of compression springs  93   a  is employed in combination with a pair of tension springs  93   b.    
         [0151]     Also in this embodiment, the bearings  27  (first positioning portion) and  28  (second positioning portion) are accurately positioned relative to the apparatus main assembly  100  by the positioning slots  106   a  and  101   b  of the side walls  106  of the main frame of the apparatus main assembly  100 . In other words, their positions are fixed by the apparatus main assembly  100 .  
         [0152]     Further, the rotational movement or the cartridge  2  about the axial lines of the bearings  27  and  28  caused by the transmission of driving force to the cartridge  2  from the apparatus main assembly  100  is controlled by the rotation controlling portion  82  positioning surface  82   a ). In other words, the position of the cartridge  2  is also fixed by the movable guide  101 .  
         [0153]     Therefore, even though the image forming apparatus A is structured so that the cartridges  2  are moved into their image formation positions corresponding to the image formation position  300  of the movable guide  101 , in the apparatus main assembly  100 , by the movement of the movable guide  101 , the cartridges  2  are reliably and accurately positioned relative to the apparatus main assembly  100 .  
         [0154]     Further, the upward movement of the inward end portion of the cartridge  2 , which occurs when separating the development roller  22  from the photosensitive drum  21 , is controlled by the rotation controlling portion  82  (positioning surface  82   b ). In other words, the cartridge  2  is fixed in position by the movable guide  101 .  
         [0155]     Therefore, even though the image forming apparatus A is structured so that the cartridges  2  are moved into their image formation positions corresponding to the image formation position  300  of the movable guide  101 , in the apparatus main assembly  100 , by the movement of the movable guide  101 , the cartridges  2  are kept reliably and accurately positioned relative to the apparatus main assembly  100 .  
         [0156]     Further, the bottom surface of the rotation controlling portion  82  constitutes the positioning surface  82   a , and the top surface of the rotation control portion  82  constitutes the positioning surface  82   b . In addition, the positioning surface 101 a - f  of the movable guide  101  is the top surface of the portion  101   a - h , which is the slightly thicker portion of the movable guide  101 .  
         [0157]     Therefore, as the cartridge  2  is inserted into the movable guide  101 , and slides deeper into the movable guide  101 , the bottom surface of the cartridge  2  rides onto the portion 101 a - h , reducing thereby the distance between the cartridge  2  and positioning surface  101 - f , and the distance between the cartridge  2  and the downwardly facing inward surface  101   a - i  of the movable guide  101 .  
         [0158]     Therefore, the cartridge  2  is prevented from unexpectedly shifting while movable guide  101  is moved.  
         [0159]     Further, in this embodiment, the rotation controlling portion  82  is on the side where the first and second driving force transmission portions  78  and  79  are present. Therefore, the rotation of the cartridge  2  can be better controlled. In this case, the three portions, that is, the bearings  27  and  28  and rotation controlling portion  82  of the cartridge  2 , remain in contact with the apparatus main assembly  100 , accurately positioning the cartridge  2  relative to the apparatus main assembly  100 . However, the rotation controlling portion may be on the other side of the cartridge  2 , that is, the side opposite to where it is in this embodiment, or may be located at both lengthwise ends of the cartridge  2 .  
         [heading-0160]     (Mechanism for Opening or Closing Process Cartridge Shutter)  
         [0161]     Next, referring to  FIGS. 17 and 18 , the mechanism for opening or closing the drum shutter which protects the photosensitive drum  21  of the cartridge  2  in accordance with the present invention will be described.  FIG. 17  is a schematic sectional view of the cartridge  2  in the movable guide  101  in its cartridge mounting position  200 , and its adjacencies, at a plane perpendicular to the lengthwise direction of the cartridge  2 , showing the mechanism for opening or closing the shutter, and  FIG. 18  is a schematic sectional view of the cartridge  2  in the movable guide  101  in its image formation position  300 , and its adjacencies, at a plane perpendicular to the lengthwise direction of the cartridge  2 , showing the slate of the mechanism for opening or closing the shutter, after the closing of the door  16 .  
         [0162]     The cartridge  2  is provided with a drum shutter for shielding the peripheral surface of the photosensitive drum  21 , which is rotatably attached to the cartridge frame. The shutter  87  comprises a shielding member  85  formed of black resinous substance, and a shutter rod  86 . The shutter rod  86  is rotatably attached to the drum unit  2   a  by one end, and is attached to the shielding member  85  by the other. Thus, as the shutter rod  86  is rotated, the shielding member  85  is moved, exposing thereby the peripheral surface of the photosensitive drum  21 .  
         [0163]     When the movable guide  101  is in the cartridge mounting position, the drum shutter  87  of the cartridge(s)  2  in the movable guide  101  is covering the photosensitive drum  21 . Then, as the door  16  of the apparatus main assembly  100  is closed, the cartridge(s)  2  is orbitally moved, together with the movable guide  101 , into its final position(s), that is, image formation position(s) which corresponds to the image formation position  300  of the movable guide  101 , in the apparatus main assembly  100 , by the mechanical linkage connected to the door  16  and movable guide  101 . During this movement, the shutter rod  86  of the shutter  87  comes into contact with a shutter controlling member  112  projecting inward from the apparatus main assembly  100 , being thereby rotated in the direction to move the shielding member  85  of the shutter  87  in the direction to expose the peripheral surface of the photosensitive drum  21 . The shutter controlling member  112  coincides in position with the shutter rod  86 , and is in the orbital path of the cartridge  2  from where it is in the movable guide  101  in the cartridge mounting position  200  to its image formation position, that is, its final position in the apparatus main assembly  100 , which corresponds to the image formation position  300  of the movable guide  101 .  
         [0164]     While the cartridge  2  is moving with the movable guide  101 , the above described positioning surface  82   a  and rotation controlling surface  82   b  control the attitude of the leading end of the cartridge  2  in the movable guide  101 , in terms of the cartridge mounting direction, assuring that the shutter rod  86  will come into contact with the shutter controlling member  112  as the cartridge  2  is orbitally moved into the apparatus main assembly  100 , and also that while the shutter  87  is opened by the movement of the cartridge  2  subsequent to the contact between the shutter rod  86  and shutter controlling member  112 , the cartridge  2  is prevented from being rattled in the movable guide  101  by the resistance from the shutter  87 , in order to prevent the shutter rod  86  from riding over the shutter controlling member  112 . In other words, the positioning surface  82   a  and rotation controlling surface  82   b  serve as rattle controlling means, assuring that the shutter  87  is properly opened.  
         [0165]     The above described embodiment of the present invention can be summarized as follows.  
         [0166]     The process cartridge  2  in accordance with the present invention is a process cartridge, which is placeable in the movable guide  101  attached to the main assembly  100  of an electrophotographic image forming apparatus A and movable relative to the apparatus main assembly  100  in order to move the cartridge  2  from the cartridge mounting position ( 200 ) to the image formation position ( 300 ), is characterized in that it comprises: 
        the electrophotographic photosensitive drum  21 ;     the processing means (for example, development roller  22 , charge roller  23 , and cleaning means  26 ) which act on the electrophotographic photosensitive drum  21 ;     the first cartridge positioning portion (bearing  27 ) which is for accurately positioning the process cartridge  2  relative to the apparatus main assembly  100  as the process cartridge  2  is mounted into the apparatus main assembly  100 , and which projects outward from one of the lengthwise ends or the cartridge frame (photosensitive drum  24  and development frame  71 ) in the lengthwise direction of the cartridge  2 ;     to the second cartridge positioning portion (bearing  28 ) which is for accurately positioning the process cartridge  2  relative to the apparatus main assembly  100  as the process cartridge  2  is mounted into the apparatus main assembly  100 , and which projects outward from the other lengthwise end of the cartridge frame (photosensitive drum  24  and development frame  71 ) in the lengthwise direction of the cartridge  2 ;     the first cartridge supporting portion (guiding surface  80   d ), by which the cartridge  2  is supported by the movable guide  101 , and which is a part of the bottom surface of one of the lengthwise end portions of the cartridge frame (drum frame  24  and development frame  71 );     the second cartridge supporting portion (guiding surface  80   b ), by which the cartridge  2  is supported by the movable guide  101 , and which is a part of the bottom surface of the other lengthwise end portion of the cartridge frame (drum frame  24  and development frame  71 ); and     the third cartridge positioning portion (rotation controlling portion  82 ), which is located forward of either the first or second cartridge supporting portion (guiding surface  80   d  or  80   b ), or both, in terms of the direction in which the process cartridge  2  is mounted into the apparatus main assembly  100 , and which comprises the first rotation controlling surface (attitude controlling surface  82   a ) with which the process cartridge  2  comes into contact, being thereby prevented from rotating further, as it is rotated about the axial lines of the first and second positioning portions (bearings  27  and  28 ) by the force generated as driving force is transmitted to the process cartridge  2  from the apparatus main assembly  100 .        
 
         [0174]     According to another characteristic aspect of the present invention, the above described process cartridge  2  comprises: 
        the force catching portion  92  for catching the external force which acts in the direction to separate the development roller  22 , as one of the aforementioned processing means, from the photosensitive drum  21 , in the process cartridge  2 ; and     the second rotation controlling surface (separation-rotation controlling surface  82   b ) for preventing the process cartridge  2  from being rotating about the first and second positioning portions (bearings  27  and  28 ) by the external force caught by the force catching portion  92 .        
 
         [0177]     According to another characteristic aspect of the present invention, the above described force catching portion  92  is located on the opposite side of the vertical plane which is parallel to the lengthwise direction of the process cartridge  2  and coincides with the axial lines of the connective portions (holes  77  and pins  77   a ) which connect the development frame  71  as a part of the cartridge frame, and the photosensitive drum supporting drum frame  24  as another part of the cartridge frame, in the manner to allow the two frames  71  and  24  to pivotally move relative to each other, with respect to where the development roller  22  is placed in contact with, or separated from, the photosensitive drum  21 .  
         [0178]     According to another characteristic aspect of the present invention, the third positioning portion (rotation controlling portion  82 ) is located at the same lengthwise end of the process cartridge  2  as the driving force receiving portions through which the process cartridge  2  receives driving force from the apparatus main assembly  100 .  
         [0179]     According to another characteristic aspect of the present invention, the third positioning portion (rotation controlling portion  82 ) is located on the downstream side, in terms of the process cartridge mounting direction, with respect to the driving force receiving portions through which the process cartridge  2  receives driving force from the apparatus main assembly  100 .  
         [0180]     According to another characteristic aspect of the present invention, the first positioning portion (bearing  27 ) is accurately positioned relative to the apparatus main assembly  100  by the first positioning portion (positioning slot  106   a ) of the apparatus main assembly  100 , whereas the second positioning portion (bearing  28 ) is positioned relative to the apparatus main assembly  100  by the second positioning portion (positioning slot  106   b ) of the apparatus main assembly  100 .  
         [0181]     According to another characteristic aspect of the present invention, the axial lines of the first and second positioning portions (bearing  27  and  28 ) coincide with the axial line of the electrophotographic photosensitive drum  21 .  
         [0182]     According to another aspect of the present invention, the apparatus main assembly  100  comprises the third cartridge positioning portion, which is an integral part of the leading end portion the movable guide  101  or the apparatus main assembly  100 , in terms of the direction in which the process cartridge  2  is mounted into the apparatus main assembly  100 , and which comprises: the first rotation controlling surface for preventing the process cartridge  2  from being rotated about the axial lines of the first and second positioning portions by the driving force transmitted from the driving means (unshown) of the apparatus main assembly  100 , and the second rotation controlling surface for preventing the process cartridge  2  from being rotated about the axial lines of the first and second positioning portions in the direction to separate the development roller  22  from the photosensitive drum  21  by the external force. The above described characteristics of the present invention provide the following effects.  
         [0183]     (1) It is possible to reduce the dimension of the process cartridge  2  in terms of its lengthwise direction, because the parts of the bottom surface of the cartridge frame (drum frame  24  and development frame  71 ) are utilized as the portions (guiding surfaces  80   b  and  80   d ) by which the process cartridge  2  is supported, and the cartridge positioning surface  82   a  is made integral with the cartridge supporting portions. Therefore, it is possible to reduce the footprint of the image forming apparatus main assembly  
         [0184]     (2) It is possible to assure that the process cartridge  2  will be accurately positioned relative to the apparatus main assembly  100  with the employment of a simple structural arrangement, because the cartridge attitude controlling surface  82   a  is provided as an integral part of the cartridge supporting portion (guiding surface  80   b ) by which the process cartridge  2  is supported by the apparatus main assembly  100 , and is located on the opposite side of the rotation controlling portion  82 , with respect to the cartridge attitude controlling surface  82   a . Therefore, it is possible to reduce the dimension of the process cartridge  2  in terms of its lengthwise direction as described in (1). Therefore, it is possible to reduce the footprint of the image forming apparatus A.  
         [0185]     (3) It is possible to prevent the shutter rod  86  from missing, or riding onto, the shutter controlling member  112 , in order to assure that the shutter rod  86  will come into contact with the shutter controlling member  112 , because the rotation controlling surface  82   a , and the rotation controlling surface  82   b  for preventing the development unit from rotating in the direction to separate the development roller  22  from the photosensitive drum  21 , are positioned so that they comes into contact with the cartridge positioning surface  101   a - f  and  101   a - g , respectively, of the movable guide  101 , controlling thereby the attitude of the process cartridge  2 , as the process cartridge  2  is mounted deeper into the movable guide  101 . Therefore, it is possible to assure that the shutter  87  will be properly opened.  
         [0186]     As described above, according to the present invention. It is assured that a process cartridge will be accurately positioned relative to the main assembly of an electrophotographic image forming apparatus.  
         [0187]     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.