Abstract:
An electrophotographic image forming apparatus is usable with a process cartridge having an electrophotographic photosensitive member. The apparatus includes a transfer member contactable to the photosensitive member to transfer a toner image from the photosensitive member thereonto, a tray carrying the cartridge and movable between a contact position where the photosensitive member contacts the transfer member and a spaced position spaced from the transfer member, a supporting member supporting the tray for movement parallel with a tangent line between the photosensitive member and the transfer member between a first position positioning the tray at the contact position and a second position retracted from the first position away from the transfer member in a perpendicular direction perpendicular to the photosensitive-member axial direction and to the tangent line to position the tray at the spaced position, and engageable and engaging portions engageable with each other. The engaging portion regulates tray movement.

Description:
This application is a divisional of U.S. application Ser. No. 11/622,183, filed Jan. 11, 2007, pending. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an electrophotographic image forming apparatus, in which a process cartridge is removably mountable, and which is for forming an image on recording medium. 
     Here, an electrophotographic image forming apparatus means an apparatus for forming an image on recording medium, with the use of an electrophotographic image forming method. As examples of an electrophotographic image forming apparatus, an electrophotographic copying machine, an electrophotographic printer (for example, laser beam printer, LED printer, etc.), a facsimile machine, word processor, etc., can be included. 
     A process cartridge means a cartridge in which an electrophotographic photosensitive member, and processing means, such as a charging means, a developing means, etc., which process the electrophotographic photographic member, are integrally disposed, and which is removably mountable in the main assembly of the image forming apparatus. 
     A process cartridge, described above, can be mounted into, or removed from, the image forming apparatus main assembly by a user himself or herself. Therefore, it can simplify the maintenance of the apparatus main assembly. 
     There are various means for replacing a cartridge in the main assembly of an image forming apparatus. U.S. Pat. No. 5,608,498 discloses one of these means. According to this means, the main assembly of an image forming apparatus is provided with a cartridge supporting plate  61 , which is raised or lowered as it is moved forward or rearward by the movement of the side cover  80  of the apparatus main assembly. A cartridge  30  is supported by the cartridge supporting plate  61 , with a pair of guiding members  70 , which are extendable in two stages, placed between the cartridge and cartridge supporting plate  61 . As the side cover  80  is opened, the cartridge supporting plate  61  is moved by the movement of the side cover  80  in the upwardly slanting direction from the image formation position (I) to the cartridge mounting-extracting position (II), to allow the cartridge  30  to be removed directly from the cartridge supporting plate  61 . With the employment of this structural arrangement, the cartridge supporting plate  61  can be moved into any location (specific position including intermediary stop position (III)) within the range in which the cartridge supporting plate  61  is movable, to mount or remove various devices, or deal with paper jam. 
     However, this structural arrangement in accordance with the prior art suffers from the following problem: when pushing the cartridge supporting plate  61  into the cartridge mounting-extracting position from the specific position including the intermediary stop position (III), the side cover  80  (door) can be closed even when the cartridge supporting plate  61  is not in the position (II). That is, it is not stated in U.S. Pat. No. 5,608,498 that the side cover  80  cannot be closed unless the operation for moving the guiding members  71  from the position (III) to the position (II) is completed. 
     In other words, if the side cover  80  is closed before the operation for moving the guiding members  71  from the position (III) to the position (II) is completed, it is possible that the downwardly facing area of the peripheral surface of the electrophotographic photosensitive member in the cartridge  30  will develop scars and/or permanent memories by being rubbed by the objects which are in the adjacencies of the downwardly facing area of the peripheral surface of the electrophotographic photosensitive member. 
     SUMMARY OF THE INVENTION 
     Thus, the primary object of the present invention is to provide an electrophotographic image forming apparatus in which a process cartridge is removably mountable, and which is characterized in that it does not suffer from the problem that the electrophotographic photosensitive member in a process cartridge develops scars and/or memories by being rubbed by the objects in its adjacencies. 
     According to an aspect of the present invention, there is provided an electrophotographic image forming apparatus with which a process cartridge having an electrophotographic photosensitive member is usable, said electrophotographic image forming apparatus comprising a transfer member contactable to said electrophotographic photosensitive member to transfer a toner image from said electrophotographic photosensitive member thereonto; a tray for carrying said process cartridge, said tray being movable between a contact position in which said electrophotographic photosensitive member is contacted to said transfer member in a state that tray carries said process cartridge and a spaced position in which said electrophotographic photosensitive member is spaced from said transfer member in the state that tray carries said process cartridge; a supporting member for supporting said tray for movement in a tangent line direction which is parallel with a tangent line between said electrophotographic photosensitive member and said transfer member as seen in an axial direction of said electrophotographic photosensitive member between a first position for positioning said tray at the contact position and a second position which is retracted from the first position away from said transfer member in a perpendicular direction perpendicular to the axial direction and to the tangent line and in the tangent line direction to position said tray at the spaced position; a portion to be engaged; and an engaging portion provided in said tray and engageable with said portion to be engaged to regulate movement of said tray in the tangent line direction when said tray is at the contact position, wherein said engaging portion is disengaged from said portion to be engaged after said electrophotographic photosensitive member is spaced from said transfer member by movement of said tray in the perpendicular direction in a state of engagement with said portion to be engaged, when said supporting member moves from the first position toward the second position. 
     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 DRAWINGS 
         FIG. 1  is an external perspective view of the image forming apparatus in the first embodiment of the present invention. 
         FIG. 2  is a vertical sectional view of the image forming apparatus shown in  FIG. 1 , as seen from the left side of the apparatus. 
         FIG. 3  is an external perspective view of the image forming apparatus, the front door of which is open. 
         FIG. 4  is a vertical sectional view of the image forming apparatus, shown in  FIG. 3 , the front door of which is open, as seen from the left side of the apparatus. 
         FIG. 5  is an external perspective view of the image forming apparatus, shown in  FIG. 1 , the cartridge tray of which is in its outermost position. 
         FIG. 6  is a vertical sectional view of the image forming apparatus, shown in  FIG. 5 , the cartridge tray of which is in its outermost position, as seen from the left side of the apparatus. 
         FIG. 7  is an external perspective view of the cartridge, as seen from the side from which the cartridge is driven. 
         FIG. 8  is an external perspective view of the cartridge, as seen from the side from which the cartridge is not driven. 
         FIG. 9  is a perspective view of the cartridge tray. 
         FIG. 10  is a perspective view of the mechanical linkage between the door and tray holding members. 
         FIGS. 11(   a )- 11 ( c ) are schematic drawings showing the movement of the tray holding member, which is caused by the rotational door movement which occurs when the door is opened. 
         FIG. 12  is an enlarged view of the guiding slot. 
         FIGS. 13(   a ) and  13 ( b ) are enlarged views of the protrusion (pin) as a tray movement regulating means, and a hole (groove). 
         FIG. 14  is a perspective view ( 1 ) of the interfacial components and the portions thereof, which are located in the adjacencies of the cartridge bay, and are engaged or disengaged by the movement of the tray holding members. 
         FIG. 15  is a perspective view ( 2 ) of the interfacial components and the portions thereof, which are located in the adjacencies of the cartridge bay, and are engaged or disengaged by the movement of the tray holding members. 
         FIGS. 16(   a ) and  16 ( b ) are perspective views ( 3 ) of the interfacial components and the portions thereof, which are located in the adjacencies of the cartridge bay, and are engaged or disengaged by the movement of the tray holding members. 
         FIG. 17  is a drawing ( 1 ) showing the tray position regulating means. 
         FIG. 18  is a drawing ( 2 ) showing the tray position regulating means. 
         FIGS. 19(   a ) through  19 ( c ) are drawings ( 3 ) showing the tray position regulating means. 
         FIGS. 20(   a ) through  20 ( c ) are drawings ( 4 ) showing the tray position regulating means. 
         FIG. 21  is a drawing ( 1 ) showing the means for supplying electric power to a cartridge. 
         FIG. 22  is a drawing ( 2 ) showing the means for supplying electric power to a cartridge. 
         FIG. 23  is a drawing ( 3 ) showing the means for supplying electric power to a cartridge. 
         FIG. 24  is a perspective view of the left and right stays. 
         FIG. 25  is a drawing ( 1 ) showing the structure of the stay. 
         FIG. 26  is a drawing ( 2 ) showing the structure of the stay. 
         FIG. 27  is a drawing ( 3 ) showing the structure of the stay. 
         FIG. 28  is a drawing ( 4 ) showing the structure of the stay. 
         FIG. 29  is a drawing showing a comparative structural arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     (General Structure of Image Forming Apparatus) 
       FIG. 1  is an external perspective view of the image forming apparatus  100  in this embodiment, and  FIG. 2  is a vertical sectional view of the image forming apparatus  100 , as seen from the left side of the apparatus. This image forming apparatus is a full-color laser printer based on four primary colors. It uses an electrophotographic process. It forms an image on recording medium (recording paper) in response to electric picture signals inputted from an external host apparatus (unshown) such as a personal computer, an image reader, a sending facsimile machine, etc. 
     In the following description of the preferred embodiment of the present invention, the front side (front surface side) of the image forming apparatus (which may be referred to as apparatus main assembly) means the side which has a door  31 . The rear side of the image forming apparatus is the side opposite to the front side. “Frontward” means “in a direction toward front as seen from the rear side of the apparatus main assembly”, and “rearward” means the direction opposite to “frontward”. “The left and right sides of the apparatus main assembly” means the left and right sides of the apparatus main assembly as seen from the front side of the apparatus main assembly. “Leftward” means “in a direction toward left as seen from the front side”, and “Rightward” means the direction opposite to “leftward”. 
     There are four process cartridges (first to fourth), that is, PY, PM, PC, and PK, in the apparatus main assembly (main frame  80 ). The four cartridges PY, PM, PC, and PK are horizontally arranged in the listed order in terms of the rear-to-front direction (which may be referred to as inline or tandem arrangement). The four cartridges are the same in structure, although they are different in the color of the toners they store. Each cartridge in this embodiment is made up of: an electrophotographic photosensitive drum  1  as a first image bearing member; processing means, that is, a charging means  2 , a developing means  3 , and a cleaning device  4 , which process the photosensitive drum  1 ; and a cartridge frame  5  ( FIGS. 7 and 8 ), in which the preceding components are integrally disposed. The charging device  2  in this embodiment is a contact charge roller. The developing device  3  in this embodiment has a development roller  3   a , and a developer container in which developer (toner) is stored. The cleaning device  4  is of the blade type. 
     The developing device  3  of the first cartridge PY stores yellow (Y) toner. On the peripheral surface of the drum  1  in the cartridge PY, a toner image of yellow (Y) color is formed. The developing device  3  of the second cartridge PM stores magenta (M) toner. On the peripheral surface of the drum  1  in the cartridge PM, a toner image of magenta (M) color is formed. The developing device  3  of the third cartridge PC stores cyan (C) toner. On the peripheral surface of the drum  1  in the cartridge PC, a toner image of cyan (C) color is formed. The developing device  3  of the fourth cartridge PK stores black (K) toner. On the peripheral surface of the drum  1  in the cartridge PK, a toner image of black (K) color is formed. 
     In the area above the cartridges PY, PM, PC, and PK, a laser scanner unit  11  is disposed. This scanner unit  11  exposes the peripheral surface of the drum in each cartridge. That is, the picture information regarding the image to be formed by each cartridge is inputted into the scanner unit  11  from an external host apparatus, and the scanner unit  11  outputs a beam of laser light L while modulating it with the picture information, so that the peripheral surface of the photosensitive drum in each cartridge is scanned (exposed) by the beam of laser light L through the exposure window  6  ( FIGS. 7 and 8 ) with which the top wall of the cartridge frame  5  is provided. 
     In the area below the cartridge PY, PM, PC, and PK, an intermediary transfer belt unit  12  as a transferring member is disposed, which has an endless belt  13 , a driver roller  14 , a turn roller  15 , and a tension roller  16 . The endless belt  13  is formed of a dielectric substance, and is flexible. It is stretched around the driver roller  14 , turn roller  15 , and tension roller  16 , being thereby suspended by them, so that it can be circularly driven. The driver roller  14  and tension roller  16  are disposed in the rear portion of the apparatus main assembly, whereas the turn roller  15  is disposed in the front portion of the apparatus main assembly. Each cartridge is disposed so that while the drum  1  in the cartridge and the endless belt  13  are driven, rotationally and circularly, respectively, the downwardly facing portion of the peripheral surface of the drum  1  remains in contact with the upwardly facing portion of the external surface of the endless belt  13 . On the inward side of the loop which the belt  13  forms, four primary transfer rollers  17  are disposed. Each transfer roller  17  is disposed so that it opposes the drum  1  in the corresponding cartridge, with the portion of the endless belt  3 , which corresponds to the top portion of the loop, pinched between the transfer roller  17  and photosensitive drum  1 . The driver roller  14  is kept pressed against a secondary transfer roller  22 , with the belt  13  pinched between the two rollers  14  and  22 . 
     In the area below the belt unit  12 , a paper feeder unit  18  is disposed, which has a paper feeder tray  19 , a paper feeder roller  20 , a paper separation pad  21 , etc. The paper feeder tray  19  is removably mountable in the apparatus main assembly from the front side (front loading). 
     In the top portion of the rear portion of the apparatus main assembly, a fixing apparatus  23  and a paper discharging roller pair  24  are disposed. Further, the top wall of the frame (housing) of the apparatus main assembly is shaped so that a part of the housing is utilized as a delivery tray  25 . The fixing apparatus  23  has a fixation film assembly  23   a  and a pressure application roller  23   b . The paper discharging roller pair  24  has a paper discharging rollers  24   a  and  24   b.    
     When each cartridge is in its latent image formation position in the apparatus main assembly, it is securely held in the latent image formation position by the pressure applied by a pressing member, which will be described later. Further, the driving force input portion of the cartridge is in engagement with the driving force output portion of the apparatus main assembly, and the electrical contacts of the cartridge are in connection with the corresponding electrical contacts of the apparatus main assembly, making it possible to provide the cartridge with the electric power from the power supply system on the apparatus main assembly side. 
     The operation carried out by this image forming apparatus to form a full-color image is as follow: Each of the first to fourth cartridges PY, PM, PC, and PK is rotationally driven at a preset (controlled) velocity in the counterclockwise direction indicated by an arrow mark. Further, the belt  13  is circularly driven in the clockwise direction indicated by an arrow mark (subordinate direction to rotational direction of photosensitive drum) at a velocity which corresponds to the peripheral velocity of the photosensitive drum  1 . The scanner unit  11  is also driven. In synchronization with the driving of the scanner  11 , the charge roller  2  in each cartridge uniformly charges the peripheral surface of the photosensitive drum  1  to preset polarity and potential, with a preset (controlled) timing. The scanner unit  11  scans (exposes) the peripheral surface of each photosensitive drum  1  with the beam of laser light L while modulating the beam of laser light L with the picture signals for forming an monochromatic image of the primary color assigned to each cartridge. As a result, an electrostatic latent image, which reflects the picture signals corresponding to the primary color assigned to the cartridge, is effected on the peripheral surface of the photosensitive drum  1 . This electrostatic latent image is developed by the developing device  3  into a visible image, that is, an image formed of toner (which hereafter will be referred to as toner image). 
     Through the above described electrophotographic image formation process, a yellow toner image, which corresponds to the yellow color component of an intended full-color image is formed on the drum  1  of the first cartridge PY. This yellow toner image is transferred (primary transfer) onto the belt  13 . 
     On the drum  1  of the second cartridge PM, a magenta toner image, which corresponds to the magenta color component of the full-color image is formed, and this toner image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow toner image which is already on the belt  13 . 
     On the drum  1  of the second cartridge PC, a cyan toner image, which corresponds to the cyan color component of the full-color image is formed, and this toner image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow and magenta toner images which are already on the belt  13 . 
     On the drum  1  of the second cartridge PK, a black toner image, which corresponds to the black color component of the full-color image, is formed, and this toner image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow, magenta, and cyan toner images which are already on the belt  13 . 
     Consequently, an unfixed full-color toner image is effected on the belt  13  by the four monochromatic color images, that is, the yellow, magenta, cyan, and black color images. 
     After the primary transfer of the toner image onto the belt  13 , the toner remaining on the peripheral surface of the drum  1  in each cartridge is removed by the cleaning device  4 . 
     Meanwhile, the paper feeder roller  20  is driven with the preset (controlled) timing. As the paper feeder roller  20  is driven, the topmost sheet of recording paper P, as recording medium, of the stack of sheets of recording paper P on the paper feeder tray  19  is separated from the rest of the sheets of recording medium by the coordination of the sheet feeder roller  20  and separation pad  21 , and is fed into the apparatus main assembly by the sheet feeder roller  20 . The recording paper P is introduced into the nip (secondary transfer nip), that is, the interface between the secondary transfer roller  22  and belt  13 , and then, is conveyed through the nip while remaining pinched by the secondary transfer roller  22  and belt  13 . While the recording paper P is conveyed through the nip, the four layers of toner images different in color are transferred together onto the recording paper P as if they were peeled away from the belt  13 , starting their leading edges. 
     The recording paper P is separated from the surface of the belt  13 , and is introduced into the fixing apparatus  23 , and is subjected to heat and pressure in the fixation nip of the fixing apparatus  23 . As a result, the four layers of toner images different in color are fixed to the recording paper P. Thereafter, the recording paper P is moved out of the fixing apparatus, and then, is discharged as a full-color copy onto the delivery tray  25  by the discharge roller pair  24 . 
     In this embodiment, after the separation of the recording paper P from the belt  13 , the toner remaining on the surface of the belt  13  is electrostatically adhered to the peripheral surface of the drum  1  of the first process cartridge PY, for example, in the primary transfer area between the first process cartridge and photosensitive drum  1 , and then is removed by the cleaning device  4  of the first process cartridge PY. 
     (Method for Replacing Cartridge) 
     As an image forming operation is carried out by each of the first to fourth cartridges PY, PM, PC, and PK, the developer (toner) stored in the developing device  3  of each cartridge is consumed. Eventually, therefore, the amount of the developer in the developing device  3  becomes too small to form an image which is satisfactory to the user who purchased the cartridge; in other words, the cartridge loses its commercial value. 
     Thus, the image forming apparatus is provided with a means (unshown) for detecting the amount of the toner remaining in each cartridge. The detected amount of the toner in each cartridge is compared, by the control portion of the image forming apparatus, with a threshold value preset for issuing a warning, such as the cartridge is near the end of its service life, or the cartridge has reached the end of its service life. If the detected amount of the residual toner in the cartridge is smaller than the preset threshold value, the message which warms the user that the cartridge is close to the end of its life or has reached the end of its life is displayed on the screen of the monitor; in other words, the image forming apparatus prompts the user to prepare a replacement cartridge, or to replace the cartridge, in order to maintain a preset level of image quality. 
     In order to improve the image forming apparatus in usability, the image forming apparatus in this embodiment is provided with a cartridge drawer (tray) which can be pulled out frontward to make it easier for a user access the cartridges from the front side of the apparatus, in order to replace the cartridge. 
     More specifically, the front wall of the image forming apparatus is provided with an opening  30  ( FIG. 2 ), through which the cartridge can be inserted into, or removed from, the apparatus main assembly. That is, the apparatus main assembly (apparatus main frame  101 ) has the opening  30 . 
     Further, the apparatus main assembly is provided with a door  31 , which is attached to the main assembly frame  101  so that it can be rotationally moved between the closed position and open position. 
     In this embodiment, this door  31  is rotationally moved relative to the apparatus main assembly about a horizontal shaft  32  (door hinge shaft) located at one of the horizontal edges of the door. That is, the door  31  is rotated about the hinge shaft  32  so that it can be moved into the closed position (roughly vertical position), in which it remains shut against the apparatus main frame, covering the opening  30 , as shown in  FIGS. 1 and 2 , and also, so that it can be rotated frontward about the hinge shaft  32  into the open position (roughly horizontal position), as shown in  FIGS. 3 and 4 , widely exposing the opening  30  of the front panel of the apparatus main frame  101 . Designated by a referential character  31   a  is a recess for finger placement, with which the door  31  is provided to make it easier for an operator to open or close the door  31 . 
     The left and right panels  81 L ( FIG. 17) and 81R  which constitute the primary components of the apparatus main assembly are provided with a pair of tray holding (supporting) members  34 L and  34 R, respectively, which are on the inward side of the left and right panel  81 L and  81 R, and the lengthwise direction of which coincides with the fore-and-aft direction of the apparatus main assembly. The holding members  34 L and  34 R oppose each other. Between the holding members  34 L and  34 R, a cartridge tray (moving member)  35 , which is in the form of a box frame, is disposed. The holding members  34 L and  34 R hold the tray  3  so that the tray  35  can be horizontally slid in the fore-and-aft direction of the apparatus main assembly. The tray  35  holds the cartridges PY, PM, PC, and PK. 
     As the door  31  is opened, the holding members  34 L and  34 R are moved both frontward and upward of the apparatus main assembly by preset distances, by the movement of the door  31  transmitted to the holding members  34 L and  34 R through a mechanical linkage. This movement of the holding members  34 L and  34 R will be described later in more detail. As a result, the holding members  34 L and  34 R come out of the apparatus main assembly through the opening  30  so that the front end portion of each holding member  34  extends outward of the apparatus main assembly by a preset distance, as shown in  FIGS. 3 and 4 . The mechanical linkage which causes the movement of the door  31  to move the holding members  34 L and  34 R will be described later in more detail. 
     As the holding members  34 L and  34 R are moved, the driving force output portions on the apparatus main assembly side are disengaged from the corresponding driving force input portions of the cartridges PY, PM, PC, and PK, respectively. Further, the pressure applied to each cartridge by the pressure application member to secure the cartridge is removed from the cartridge (pressure removal). Further, the electrical contacts of each cartridge are disengaged from the counterparts on the apparatus main assembly side, making it thereby impossible for electric power to be supplied to the cartridge from the power supplying system on the apparatus main assembly side (electrical disengagement). Moreover, the tray  35  is rendered freely movable. 
     The front portion of the frame portion of the tray  35  is provided with a handle  35   a . Thus, as the door  31  is opened, the handle  35   a  is exposed through the opening  30 . An operator is to place a finger on the handle  35   a  and pull the tray  35  horizontally frontward to cause the tray  35  to slide on the holding members  34 L and  34 R until the tray  35  fully comes out through the opening  30  to a preset position, as shown in  FIGS. 5 and 6 . 
     As the tray  35  is pulled out to the abovementioned preset position, the first-fourth cartridges PY, PM, PC, and PK held in the tray  35  are all moved out of the apparatus main assembly through the opening of the apparatus main assembly, being exposed from the apparatus main assembly; the top surface of each cartridge is exposed. The apparatus main assembly is structured so that as the tray  35  is pulled out by a preset distance which is sufficient to expose all the cartridges, it is prevented by a stopper portion (unshown) from being pulled out further, and also, so that once the tray  35  is fully pulled out, it is securely retained in this outermost position by the holding members  34 L and  34 R. 
     The tray  35  is structured so that each cartridge held in the tray  35  can be moved out straight upward from the tray  35 , and also, so that the replacement cartridge for each of the first to fourth cartridges can be mounted into the tray  35  from directly above. Thus, the cartridge or cartridges, which are to be replaced, that is, the cartridge or cartridges, the life of which has expired, can be extracted from the tray  35  by simply lifting it, and then, a bran-new cartridge or cartridges can be fitted, from directly above, into the vacated space or spaces, one for one, in the tray  35 . 
     Incidentally, if the removed cartridge is provided with a manual drum cover (unshown) for protecting the bottom side of the drum  1 , the cover is to be manually closed after the removal of the cartridge from the tray  35 . As for a brand-new cartridge to be mounted as a replacement cartridge into the tray  35 , its cover should be manually opened before it is placed in the tray  35 . On the other hand, if the removed cartridge is provided with an automatic drum cover (unshown) for protecting the bottom side of the drum  1 , the cover is automatically closed as it is lifted directly upward from the tray  35 . As for a brand-new cartridge to be mounted as a replacement cartridge into the tray  35 , its cover is automatically opened as it is fitted into the tray  35  from directly above. 
     The tray  35  described above is a member that is movable in the direction intersectional to the axial direction of the drum  1  in each cartridge. Further, the tray  35  is enabled to take the outermost position (cartridge mounting or removing position), the latent image formation position (contact position), and the transitional position. The outermost position is the position in which the cartridge  35  will be after it is drawn out from the apparatus main assembly through the opening  30  as far as possible, and also, is the position in which the tray  35  allows the cartridges to be mounted into, or removed from, the tray  35 . The latent image formation position is the position which is in the main assembly frame  101 , and in which the tray  35  enables the image forming apparatus to form an electrostatic latent image on the drum  1  in each cartridge in the tray  35 . The transitional position means a position between the outermost position and latent image formation position. Incidentally, when the tray  35  is in the transitional position or outermost position, the drum  1  in each cartridge is not in contact with the belt  13 . 
     The left and right holding members  34 L and  34 R constitute a means for controlling the movement of the tray  35 . That is, they move upward the tray  35  from the latent image formation position before they move the tray  35  to the abovementioned outermost position. They also move downward the tray  35  into the abovementioned latent image formation position. In other words, the holding members  34 L and  35 R are enabled to take the first position, in which they allow the tray  35  to be moved between the abovementioned outermost position and transitional position, and the second position, in which they retain the tray  35  in the abovementioned latent image formation position. As the door  31  is closed, the holding members  34 L and  34 R are moved from the first position to the second position by the movement of the door  31 . 
       FIGS. 7 and 8  are external perspective views of one of the cartridges, as seen from the side from which the cartridge is driven, and the side from which the cartridge is not driven, respectively. 
     In this embodiment, when a cartridge is in the apparatus main assembly, the leftward or rightward direction of the cartridge is the direction parallel to the axial line of the drum  1 . Each cartridge is an assembly of various components, and is roughly in the form of a rectangular parallelepiped, the lengthwise direction of which coincides with the above-mentioned leftward or rightward direction. The drum  1  in each cartridge is disposed between the right and left walls of the frame  5  (housing) of the cartridge, being supported by a pair of bearing portions  51  and  52  with which the right and left walls are provided, respectively; in other words, the drum  1  is rotatably supported by the housing  5 . The right bearing portion  51  is provided with a coupler  53  as a portion through which the drum driving force is inputted. Further, the right wall of the housing  5  is provided with a coupler  54  as a portion through which the development roller driving force is inputted. The left wall of the housing  5  is provided with electrical contacts  55  of the cartridge. The housing  5  is provided with a pair of overhangs  56 , which extend from the right and left ends of the top wall of the housing  5 , respectively. In the following description of the cartridge, the right-hand side of the cartridge, that is, the side having the couplers  53  and  54 , may be referred to as drivable side, and the left-hand side, that is, the opposite side from the right-hand side, may be referred to as nondrivable side. 
       FIG. 9  is an external perspective view of the tray  35 . The tray  35  has a rectangular main frame, which is made up of four sections  35   b  (front),  35   c  (rear),  35   d  (left), and  35   e  (right), which are formed of a metallic substance and are joined at their lengthwise ends. The space within the rectangular main frame is partitioned into four sub-spaces of roughly the same size by three partition walls  35   f  which extend in the fore-and-aft direction, connecting the left and right sections of the main frame. Hereafter, these four sub-spaces will be referred to as first-fourth spaces  35 ( 1 )- 35 ( 4 ), listing from the rear section  35   c  side toward the front section  35   b . These sub-spaces  35 ( 1 )- 35 ( 4 ) are the spaces in which the first to fourth cartridges PY, PM, PC, and PK are held. The portions of the rear section  35   e  of the main frame of the tray  35 , which correspond to the sub-spaces  35 ( 1 )- 35 ( 4 ), are provided with a hole  35   g , which is for allowing the development roller driving coupler  35   g  to move into, or out of, the corresponding sub-space. 
     Further, the tray  35  is provided with intermediary electrical contacts  72   a - 72   d  ( FIG. 21 ), each of which makes contact with the electrical contact  55  ( FIG. 8 ) of the corresponding cartridge. These intermediary electrical contacts  72   a - 72   d  are electrically connectible to the electrical contacts  75   a - 75   d  ( FIGS. 21 and 22 ) with which the apparatus main assembly is provided. These electrical contacts and their connection will be described later. 
     Each cartridge is to be inserted from directly above into one of the sub-spaces of the tray  35 , which has been predesignated for the cartridge. As the cartridge is inserted, the left and right overhangs  56  are caught, by their bottom surfaces, by the top surfaces of the left and right sections  35   d  and  35   e  of the main frame of the tray  35 ; in other words, the cartridge is supported by the tray  35 . That is, the tray  35  supports each cartridge so that the cartridge can be removed from the tray  35  in the vertically upward direction; in other words, as each cartridge is moved downward into the tray  35  from directly above the tray  35 , the cartridge is supported by the tray  35 . With the employment of the above described structural arrangement, the four cartridges PY, PM, PC, and PK are precisely positioned in the tray  35 , without being fastened to the tray  35 . Therefore, they can be easily replaced. 
     The inward surface of the left holding member  34 L and the inward surface of the right holding member  34 R are provided with a guiding groove  34   a  ( FIGS. 6 ,  10 , and  21 ) which extends in the fore-and-aft direction. The left and right sections of the main frame of the tray  35  fit in these grooves  34   a , one for one. Thus, not only is the tray  35  supported between the left and right holding members  34 L and  34 R, but also, it is allowed to slid in the fore-and-aft direction, with the front and rear sections  35   d  and  35   e  of its main frame sliding in the guiding grooves  34   a  of the holding members  34 L and  34 R. 
     Referring to  FIGS. 5 and 6 , after the tray  35  is drawn out into its outermost position, and the cartridge, or cartridges, in the tray  35 , which are to be replaced, are replaced, the tray  35  is to be pushed in the direction opposite to the direction in which it is pulled out of the apparatus main assembly; in other words, the tray  35  is to be pushed back into the apparatus main assembly (it is to be moved back into the transitional position). Then, the tray  35  is to be moved back into the latent image formation position). Then, the tray  35  is to be returned to the position, shown in  FIGS. 3 and 4 , in which the tray  35  was before it was pulled out. Thereafter, the door  31  is to be closed against the housing of the apparatus main assembly, as shown in  FIGS. 1 and 2 . 
     As the door  31  is closed, the holding members  34 L and  34 R are moved downwardly rearward, by the preset distance, by the movement of the door  31 . As a result, the tray  35  is moved from the transitional position into the latent image formation position. Further, the movement of the holding members  34 L and  34 R causes the cartridge pressing members to apply pressure to the corresponding cartridges to secure the cartridges in their preset positions. As a result, the downwardly facing area of the peripheral surface of the drum  1  in each cartridge comes into contact with the point (area) of the belt  13 , which coincides with the specific point preset for each cartridge, in terms of the fore-and-aft direction. Then, each of the driving force outputting portions of the apparatus main assembly engages with the driving force input portion of the corresponding cartridge, and the power supply system of the apparatus main assembly is electrically connected to the electrical contact of each cartridge. 
     (Mechanical Linkage Between Door  31  and Tray Holding Members  34 L and  34 R) 
       FIG. 10  is a perspective view of the mechanical linkage between the door  31  and tray holding members  34 L and  34 R. The hinge shaft  32  of the door  31  is horizontally disposed in parallel to the left and right direction of apparatus main assembly. The hinge shaft  32  is rotatably supported at its lengthwise ends by, and between, the left and right frames  80 L and  80 R ( FIG. 17 ) of the apparatus main assembly, with a pair of bearings placed between the hinge shaft  32  and left and right frames  80 L and  80 R, one for one. The door  31  is solidly attached to the hinge shaft  32 . Thus, as the door  31  is opened or closed, the hinge shaft  32  rotates with the door  31 . The hinge shaft  32  is provided with a pair of connective arms  37 L and  37 R, which are attached to the portions of the hinge shaft  32 , which are close to the left and right lengthwise ends of the hinge shaft  32 . The arms  37 L and  37 R are solidly attached to the hinge shaft  32  so that they are the same in rotational phase. The arms  37 L and  38 R are provided with their own horizontal shaft  37   a . The horizontal arm  37   a  of the left arm  37 L is fitted in a hole  34   b  with which the bottom front portion of the left holding member  37 L is provided, and the horizontal shaft  37   a  of the right arm  37 R is fitted in a hole  34   b  with which the bottom front portion of the right holding member  34 R is provided. Both holes  34   b  are elongated in cross-section. 
     In other words, the hinge shaft  32  is connected to the holding members  34 L and  34 R, with the interposition of the arms  37 L and  37 R, horizontal shafts  37   a , and holes  34   b . Thus, as the door  31  is opened or closed, the force applied to the door  31  to move the door  31  is transmitted to the left and right holding members  34 L and  34 R in a manner to move them in the fore-and-aft direction. 
     Each of the holding members  34 L and  34 R is provided with a pair of pins  34   c , which protrude from the front and rear portions (with presence of preset distance) of the holding member. Further, each of the left and right frames  80 L and  80 R are provided with a pair of guiding slots  36 . The pins  34   c  are fitted in these guiding slots  36 , one for one, whereby the holding members  34 L and  34 R are supported by the left and right frames  80 L and  80 R. 
       FIGS. 11(   a )- 11 ( c ) show the two pins  34   c  of the left holding member  34 L, and the guiding slots  36  of the left frame  80 L. It does not show the right holding member  34 R. But, the right holding member  34 R is the same as the left holding member  34 L, except that its pins  34   c  and the corresponding guiding slots  36  of the left frame  80 L are symmetrically positioned relative to those of the left holding members  34 L and the corresponding guiding slots  36 . 
     Therefore, the left and right holding members  34 L and  34 R are allowed to move relative to the left and right frames  80 L and  80 R, within the range set by the guiding slots  36 . That is, the holding members  34 L and  34 R are supported by the frame (housing)  101  of the apparatus main assembly so that they are allowed to move relative to the frame  101 . 
       FIG. 12  is an enlarged view of one of the guiding slot  36 . Each guiding slot  36  is made up of first, second, and third guiding section  36   a ,  36   b , and  36   c . The first guiding section  36   a  horizontally extends in the fore-and-aft direction. The second guiding section  36   b  extends frontward from the front end of the first section  36   a , slanting upward. The third guiding section  36   c  horizontally extends from the front end of the second guiding section  36   b , being therefore positioned higher than the first guiding section  36   a . The third guiding section  36   c  constitutes the section which catches and holds the pin  34   c.    
     As the door  31  is opened, the pins  34   c  (and the holding members  34 L and  34 R) are moved a distance a 1 , by the movement of the door  31 , while being horizontally (direction parallel to line which is tangential to peripheral surface of drum  1  and coincides with center of contact area between drum  1  and belt  13 ) guided by the first guiding section  36   a  of the guiding slot  36 , and then, is moved slantingly upward (horizontally moved by distance a 2 , and vertically (direction perpendicular to above-mentioned tangential line and axial line of photosensitive drum  1 ) moved by distance b) while being guided by the second guiding section  36   b . Then, finally, they are horizontally moved a distance a 3  while being guided by the third guiding section  36   c . Thus, as the door  31  is opened, the holding members  34 L and  34 R are moved in the same manner as the pins  34   c , because the pins  34   c  are attached to the holding members  34 L and  34 R. 
       FIG. 11(   a ) shows the state of the mechanical linkage between the door  31  and tray holding members  34 L (R), in which the door  31  is completely shut. When the mechanical linkage is in this state, the holding members  34 L and  34 R are in their rearmost positions in the apparatus main assembly. The holding members  34 L and  34 R are supported by the apparatus main assembly with the presence of the hinge shaft  32 , connective arms  37 L and  37 R, horizontal shafts  37   a , and holes  34   b  between the door  31  and holding members  34 L and  34 R. Further, the pin  34   c  is located at the rear end of the first guiding section  36   a  of the guiding slot  36 . Therefore, the holding members  34 L and  34 R are in their lowest positions (abovementioned second positions) relative to the left and right frames  80 L and  80 R. Therefore, the tray  35  is also in its lowest position (abovementioned latent image formation position), because the tray  35  is held by the holding members  34 L and  34 R. 
     Each of the cartridges PY, PM, PC, and PK in the tray  35  is under the pressure applied to its left and right shoulder portions by the above-mentioned pressing member. Thus, the bottom side (by which cartridge is accurately positioned) of the peripheral surface of the bearing  51 , that is, the bearing on the driven side, and the bottom side (by which cartridge is accurately positioned) of the peripheral surface of the bearing  52 , that is, the bearing on the nondriven side, are pressed upon the positioning portions, one for one, with which the stays (internal panels) of the apparatus main assembly is provided. The cartridge tends to rotate about the axial lines of the bearings  51  and  52 . However, the contact between the rotation stopper, as the cartridge positioning portion, with which the rear section  35   d  of the tray  35  is provided, and a part of the cartridge, prevents the cartridge from rotating about the axial lines of the bearings  51  and  52 . That is, the metallic rear section  35   d  of the tray  35  also serves as the cartridge positioning portion. Thus, each cartridge is accurately positioned relative to the apparatus main assembly. Also, when the mechanical linkage is in the state shown in  FIG. 11(   a ), the downwardly facing area of the drum  1  in each cartridge reliably remains in contact with the outward surface of the top side of the belt  13  of the belt unit  12 . 
     The coupler  53  and  54  of each cartridge are coupled with the drum driving coupler and development roller driving coupler, respectively, with which the apparatus main assembly is provided. 
     To the electrical contact  55  of each cartridge, electric power can be supplied from the apparatus main assembly through the corresponding intermediary electrical contact. 
     The tray  35  (metallic rear section  35   d ) is provided with a protrusion  67 , which protrudes downward from the bottom left portion of the tray  35  (metallic rear section  35   d ). An intermediary transfer belt holding member  68 , which is a stationary member of the apparatus main assembly, is provided with a hole  69  ( FIGS. 11(   a ),  11 ( b ),  11 ( c ), and  13 ( a )). The tip portion of the protrusion  67  of the tray  35  is fitted (engaged) in the hole  69 , whereby the tray  35  is precisely positioned relative to the apparatus main assembly. 
     Further, the tray  35  (metallic rear section  35   d ) is provided with a notch  110 , which is in the bottom right portion of the tray  35  (metallic rear section  35   d ) ( FIGS. 13(   b ) and  14 ). On the other hand, the right frame  80 R is provided with a pin  111 . The pin  111  is fitted in the notch  110 , contributing to the precise positioning of the tray  35  relative to the apparatus main assembly. Incidentally, as the means for precisely positioning the tray  35  relative to the apparatus main assembly, one of the above-mentioned left and right positioning means is sufficient. 
     As described above, the metallic rear section  35   d  is provided with the cartridge rotation stopping portion (positioning portion), and the regulating portions (protrusion  67  and notch  110 ) which prevent the tray  35  from moving in the direction parallel to the abovementioned tangential line, when the tray  35  is in the contact position. This structural arrangement is very effective to prevent the drum  1  from sustaining the frictional damages attributable to the unwanted shifting of the tray  35 . 
       FIG. 11(   b ) shows the state of the mechanical linkage between the door  31  and the tray holding members  34 L ( 34 R), in which the door  31  is partially open. As the door  31 , which is in the closed position as shown in  FIG. 11(   a ), is opened, the holding members  34 L and  34 R are moved frontward, in the apparatus main assembly, by the movement of the door  31 . More specifically, first, the tray holding members  34 L and  34 R are horizontally moved frontward in the apparatus main assembly, by the distance a 1 , since the pins  34   c  of the holding members  34 L and  34 R are horizontally guided by the distance a 1  by the first guiding section  36   a .  FIG. 11(   b ) shows the state of the mechanical linkage, in which the holding members  34 L and  34 R have just finished being horizontally moved frontward by the distance a 1 . While the left and right holding members  34 L and  34 R are moved by the distance a 1  as described above, the drum driving coupler and development roller driving coupler of each cartridge are disengaged from the counterparts on the apparatus main assembly side, and also, the pressure applied to each cartridge by the pressing member to keep the cartridge precisely positioned is removed. Further, the tip portion of the protrusion  67  remains in the hole  69 , with which the stationary member  68  on the apparatus main assembly side is provided, remaining thereby precisely positioned, and therefore, preventing the tray  35  from following the movement of the holding members  34 L and  34 R. 
     As the door  31  is opened further, the holding members  34 L and  34 R are moved further frontward by the movement of the door  31 . However, during this frontward movement of the holding members  34 L and  34 R, the pins  34   c  are guided by the second guiding section  36   b , and therefore, the holding members  34 L and  34 R are moved frontward in the slantingly upward direction. During this slantingly upward movement of the holding members  34 L and  34 R, the electrical contact of each cartridge is disengaged from the counterpart on the apparatus main assembly, breaking thereby the electrical connection between the cartridge and apparatus main assembly. 
     Referring to  FIG. 13(   a ), a referential character c stands for the distance by which the protrusion  67  enters the hole  69 , and a referential character b stands for the distance by which the holding members  34 L and  34 R holding the tray  35  are vertically displaced while they are moved frontward in the slantingly upward direction. During this slantingly upward movement of the holding members  34 L and  34 R, as long as the protrusion of the tray  35  remains in the hole  69  (c&gt;b), the protrusion  67  follows only the vertical component of the movement of the holding members  34 L and  34 R. Then, as the holding member  34 L ( 34 R) is displaced upward by a certain distance (c&lt;b), the protrusion  67  comes out of the hole  69 . With the provision of the above described structural arrangement, as long as the downwardly facing area of the peripheral surface of the photosensitive drum  1  of each of the cartridges PY, PM, PC, and PK in the tray  35  is in contact with the belt  13 , the tray  35  is not allowed to horizontally move. Therefore, the drum  1  is prevented from sustaining the scratches which are attributable to the rubbing of the peripheral surface of the photosensitive drum  1  by the belt  13 , and/or from developing the memories which also are attributable to the above described rubbing. Incidentally, the dimensional relationship between the notch  110  and pin  111 , more specifically, the distance by which the pin  111  enters the notch  110 , is the same as the above described dimensional relationship between the protrusion  67  and hole  69  ( FIG. 13(   b )). 
       FIG. 11(   c ) shows the state of the mechanical linkage, in which the door  31  is completely open. In this state, the holding members  34 L and  34 R have finished their slantingly upward movement effected by the second guiding section  36   b  of the guiding slot  36 , and therefore, the pins  34   c  are in the third guiding section  36   c  of the guiding slot  36 , which is horizontal. That is, the holding members  34 L and  34 R have been horizontally moved after they were moved slantingly upward. The reason for the provision of the above described structural arrangement is to keep the cartridges and holding members  34 L and  34 R steady in terms of the vertical direction, and also, to prevent the holding members  34 L and  34 R from shifting rearward when replacing the cartridge(s). 
     When the mechanical linkage is in the state shown in  FIG. 13(   c ), the protrusion  67  and pin  111  have already come out of the hole  69  and notch  110 , respectively, and therefore, the tray  35  is free from the positional restriction; in other words, the tray  35  can be horizontally moved (slid) relative to the holding members  34 L and  34 R in the fore-and-aft direction. 
     The above described protrusion  67  and hole  69  (notch  110  (recess) and pin  111  (protrusion)) make up the cartridge movement regulating means which prevents the drum  1  in each cartridge, and the belt  13 , from moving relative to each other in the direction intersectional to the direction in which the drum  1  comes into contact with the belt  13 , when the tray  35 , which is a movable member, is in the latent image formation position in the apparatus main assembly. The restriction placed upon the tray  35  by this movement regulating means  67  and  69  to prevent the above described deviatory movement of the tray  35  is removed after the tray  35  is moved upward by the vertical component, that is, the component of the movement of the left and right tray holding members  34 L and  34 R, as the tray moving means, in the direction to separate the drum  1  from the belt  13 . 
     The holding means  34 L and  34 R as the moving means move (first movement), while being guided by the first guiding section  36   a , in the direction intersectional to the direction in which the drum  1 , which each cartridge has, is separated from the belt  13 . Next, the holding members  34 L and  34 R move (second movement) in the upwardly slanting direction, that is, the direction having two directional components: the abovementioned separative direction, and the direction intersectional to the separative direction. Thereafter, the holding members  34 L and  34 R move (third movement) in the intersectional direction. While the holding members  34 L and  34 R are making the first movement, the driving of the cartridges are ceased. Then, as the tray  35  follows the abovementioned separative movement of the holding members  34 L and  34 R, it becomes disengaged from the tray movement regulating means  67  and  69  ( 110  and  111 ). 
     As described above, the cartridges are mounted in the movable member (tray), which is vertically moved by the vertical component of the movement of the tray moving means (tray holding means) to make it easier for the cartridge(s) to be replaced. In other words, the present invention can improve an image forming apparatus in usability. Further, it can achieve the aforementioned object of providing an image forming apparatus which has a process cartridge drawer (tray) for simplifying a cartridge replacement operation, and yet, does not suffer from the problem that a photosensitive drum is scarred and/or develops memory by being rubbed by, or rubbing against, an intermediary transfer belt. Further, it does not require to increase an image forming apparatus in size to achieve the aforementioned object. 
     (Interface Portion) 
       FIGS. 14 ,  15 ,  16 ( a ), and  16 ( b ) are illustrations drawn for describing the interfacial components which are engaged or disengaged by the movement of the tray holding members, and their adjacencies. 
       FIG. 14  is a perspective view of, primarily, the holding members  34 L and  34 R, tray  35 , and right frame  80 R, which are in the state in which the door  31  is closed as shown in  FIGS. 1 and 2 , and no cartridge is in the tray  35 .  FIG. 15  is a perspective view of, primarily, the holding members  34 L and  34 R, tray  35 , and right frame  80 R, which are in the state in which the door  31  is open, and the tray  35  has been completely pulled out. 
     On the right-hand side in the apparatus main assembly, drum driving force transmission couplers  39  and development roller driving force transmission couplers  40  (which hereafter will be referred to simply as drum coupler and development roller coupler, respectively) are disposed. The drum coupler  39  and development roller coupler  40  constitute the driving force output portions on the apparatus main assembly side, and couple with the driving force input portions  53  and  54  (couplers) ( FIG. 7 ) on the cartridge side. The drum coupler  39  and development roller coupler  40  transmit rotational driving force to the drum  1  and development roller  3   a , respectively, in each cartridge. 
     On both the left- and right-hand sides in the apparatus main assembly, cartridge positioning portions  41  are located, which are parts of the left and right stays  81 L and  81 R of the apparatus main assembly ( FIG. 24 ). Each cartridge positioning portion  41  supports the corresponding bearing portions  51  ( 52 ) by the downwardly facing portion of the peripheral surface of the cartridge bearing portion  51  ( 52 ). Also on both the left and right sides in the apparatus main assembly, cartridge pressing members  42  are located, which are for keeping the cartridges secured in their preset positions. More specifically, each cartridge pressing member  42  presses on the left and right end portion of the top surface of the corresponding cartridge to keep stable the bearing portion  51  ( 52 ) supported by the above-mentioned cartridge positioning portion  41 . The pressing member  42  is provided with a spring which generates the pressure to be applied by the pressing member  42 . 
       FIG. 16(   a ) is an enlarged view of the pressing member  42 , drum coupler  39 , development roller coupler  40 , and their adjacencies, which are shown in  FIG. 14 . 
     Each pressing member  42  is rotatably attached to the apparatus main assembly. The pressure generated by the abovementioned spring  43  is applied to the left (right) end portion of the top surface of the corresponding cartridge through the pressing lever portion  45  of the pressing member  42 . When the pressing member  42  is in the state shown in  FIG. 16(   b ), in which the pressing member  42  is not pressing the cartridge, the pressing level portion  45  of the pressing member  44  has been pushed up by the pressing member raising portion  46  of the holding member  34 R, being kept away from the cartridge. That is, the pressure applied to the cartridge has been removed by the movement of the tray holding member  34 R. 
     A release ring  48  (decoupling means for decoupling couplers to prevent driving force from being transmitted to cartridge) is provided with a release pin  47 . The release ring  48  is fitted around the drum coupler  39  to retract the drum coupler  39 . As the holding member  34 R is moved, the release pin  47  is moved by the movement of the holding member  34 R from the position shown in  FIG. 16(   a ) to the position shown in  FIG. 16(   b ), causing thereby the release ring  48  to move from the position shown in  FIG. 16(   a ) to the position shown in  FIG. 16(   b ). This movement of the release ring  48  causes the drum coupler  39  and development roller coupler  40  to retract to the positions shown in  FIG. 16(   b ). That is, the drum coupler and development roller coupler of each cartridge are disengaged from the counterparts on the apparatus main assembly side. 
       FIG. 15  shows the states of the drum couplers  39 , development roller couplers  40 , and pressing members  42 , and holding members  34 L and  34 R, in which the drum couplers  39  and development roller couplers  40  have been disengaged from the counterparts on the apparatus main assembly, by the movement of the holding members  34 L and  34 R, and the pressing members  42  have been disengaged from the cartridges by the movement of the holding members  34 L and  34 R. When the abovementioned components are in the states shown in  FIG. 15 , the tray  35  can be freely slid; the tray  35  can be moved in the direction to be pushed back into the apparatus main assembly, or in the direction to be pulled out of the apparatus main assembly. 
     As described above, the holding members  34  R and  34 L are moved by the opening or closing movement of the door  31 . Thus, in order to reduce the amount of force necessary to open or close the door  31 , it is desired that the image forming apparatus is structured so that the timing with which the above-mentioned pressure is removed from the cartridges is slightly different from the timing with which the couplers are disengaged. 
     That is, the drum driving force transmission coupler  39 , development roller driving force transmission coupler  40 , and cartridge pressing member  42  are rendered slightly different in disengagement timing. More specifically, the release ring pin  47  and pressing member raising portion  46  are made different in position to render the drum coupler  39  and pressing member  43  slightly different in disengagement timing, and the four cartridges are rendered slightly different in the drum coupler disengagement timing and pressing member disengagement timing. Therefore, the employment of this structural arrangement spreads across a preset span of time, the amount of the load which bears on the door  31 , reducing thereby the peak load. Therefore, it can reduce the amount of force which a user has to apply to open or close the door  31 . 
     As described above, in this embodiment, not only are the driving force transmitting means (coupler  39  and  40 ) retracted by the movement of the holding members  34 R and  34 L, but also, the tray  35  is vertically moved by the movement of the holding members  34 R and  34 L. That is, the role of disengaging the driving force transmitting means and the role of vertically moving the tray  35  are carried out by the same mechanism, contributing to the reduction of the apparatus main assembly size. 
     (Tray Position Regulating Means) 
       FIG. 17  shows the states of the holding members  34 R and  34 L, tray  35 , and their adjacencies, in which the holding members  34 R and  34 L and tray  35  have been pushed up all the way by the movement of the door  31  and the tray  35 , but have not been completely pushed back into the apparatus main assembly.  FIG. 18  shows the states of the holding members  34 R and  34 L, tray  35 , and their adjacencies, in which the tray  35  has been pushed back into the apparatus main assembly as far as possible.  FIGS. 19(   a ) through  19 ( c ) are schematic drawings showing the movement of the cartridge positioning regulating means disposed in the left rear portion in the apparatus main assembly. 
     If the door  31  is closed when the tray  35  is in the state shown in  FIG. 17 , in which the tray  35  has not been pushed back as far as possible, the rear end of the holding member  34 R ( 34 L) strikes a stopper  70  (first regulating member), as shown in  FIG. 19(   a ) in which the stopper is in the position in which it regulates the closing movement of the door  31 , while the holding member  34 R ( 34 L) is moved into the apparatus main assembly by the movement of the door  31 . Therefore, the door  31  cannot be closed further to move the holding member  34 R ( 34 L) in the downwardly slanting direction. However, the tray  35  can be pushed back into the apparatus main assembly. At this point, therefore, the tray  35  is to be push inward of the apparatus main assembly so that the tray  35  will be completely pushed back into the apparatus main assembly as shown in  FIG. 18 . As the tray  35  is pushed inward of the apparatus main assembly, the rear end of the tray  35  (which constitutes first releasing member which disengages first regulating member) comes into contact with the stopper  70 , and moves the stopper  70  from the regulating position to the releasing position (permissive position) against the resiliency of the spring  71 , as shown in  FIG. 19(   b ). When the tray  35  is in the position shown in  FIG. 18  ( FIG. 19(   b )), the stopper  70  does not interfere with the rear end of the holding member  34 R ( 34 L) when the holding member  34 R is moved rearward by the closing movement of the door  31 . In  FIG. 19(   b ), the stopper  70  is in the position in which it allows the door  31  to be closed, allowing therefore the holding member  34 R to be moved rearward, indicated by an arrow mark in  FIG. 19(   c ). Therefore, the door  31  can be closed all the way to rearwardly move the holding members  34 R and  34 L and tray  35  in the downwardly slanting direction. 
     That is, while the tray  35  is in a position which is away from the transitional position in the apparatus main assembly (while the position of the tray  35  is off from the transitional position toward the position in which the cartridges are mountable or removable), the stopper  70  prevents the door  31  from moving from the open position to the closed position. Further, as the tray  35  is moved into the transitional position in the apparatus main assembly, it removes the restriction which the stopper  70  places. That is, as the tray  35  removes the restriction which the stopper  70  places, allowing thereby the door  31  to move from the open position to the closed position. 
     In this embodiment, the cartridges can be easily replaced from the front side of the apparatus main assembly. More specifically, the image forming apparatus is provided with a cartridge tray (drawer), in which the cartridges are placed. When the cartridges are mounted into the apparatus main assembly, they are accurately positioned relative to the apparatus main assembly by the components on the apparatus main assembly side. The drawer (tray) loosely holds the cartridges, and is movable between the outermost position and the transitional position in the apparatus main assembly. Therefore, all that is necessary for a user to do in order to ensure that a cartridge, or cartridges, are precisely positioned in the preset positions when the user mount the cartridge(s) or replace the cartridge(s) in the apparatus main assembly is for the user to place the cartridge(s) in the cartridge tray (drawer) from directly above the tray, push the tray  35  into the transitional position, and then, close the door  31 . That is, the user does not need to pay attention to the positioning of the cartridges relative to the apparatus main assembly. In other words, this embodiment can provide an image forming apparatus which is simple in the operation which must be carried out by the user to mount a cartridge into the apparatus main assembly, or replace a cartridge in the apparatus main assembly, and yet, ensures that as a cartridge is mounted into the apparatus main assembly, it is precisely positioned relative to the apparatus main assembly. 
     Incidentally, if the tray  35  is operated before the tray  35  is fully raised, for example, when the door  31  is half open, it is possible that the drum  1  in a cartridge will rub against the belt  13 . If the drum  1  rubs against the belt  13 , it is possible that a defective image will be formed. In this embodiment, however, the image forming apparatus is provided with the member which regulates the movement of the door  31 , and the position of which is controlled by the positioned of the tray  35 , and/or the member which regulates the movement of the tray, and the position of which is controlled by the opening or closing movement of the door  31 , so that unless the door  31  is fully opened, the tray  35  cannot be moved, or so that unless the tray  35  is completely pushed back into the apparatus main assembly, the door  31  cannot be closed. Therefore, a user is prevented from making operational errors when mounting a cartridge into the apparatus main assembly, or replacing a cartridge in the apparatus main assembly. 
     Incidentally, instead of providing the above described stopper  70  for regulating the movement of the holding member  34 , the above described protrusion  67  and hole  69  ( FIGS. 11(   a ),  11 ( b ),  11 ( c ),  13 ( a ), and  13 ( b ) can be utilized. This setup will be described next, with reference to  FIGS. 17 ,  18 ,  19 ( a ),  19 ( b ), and  19 ( c ). 
     When the tray  35  is in the state shown in  FIG. 17 , in which the tray has not been completely pushed back into the apparatus main assembly, the protrusion  67  of the tray  35  is not in alignment with the hole  69  of the intermediary transfer belt supporting member  68  (second regulating member). If an attempt is made to close the door  31  when the tray  35  is in this state, the holding members  34 R and  34 L are lowered by the closing movement of the door  31 , through the connective arms  37 R and  37 L, and therefore, the tray  35  is lowered. However, the protrusion  67  strikes a regulating portion  66  (edges) provided around the hole  69 , preventing thereby the door  31  from being closed. 
     On the other hand, if the tray  35  is lowered when the tray  35  is in the state shown in  FIG. 18 , in which it has been completely pushed back into the apparatus main assembly, the protrusion  67  enters the hole  69  as shown in  FIGS. 20(   b ) and  20 ( c ); the protrusion  67  as an engaging portion engages with the hole  69  as an portion to be engaged. In other words, the hole  69  functions as the portion which allows the tray  35  to be lowered. Therefore, the door  31  can be closed to lower the tray holding members  34 R and  34 L to lower the tray  35 . 
     Therefore, the tray  35  can be lowered only when the tray  35  is in the transitional position in the apparatus main assembly, in terms of the horizontal direction of the apparatus main assembly. Therefore, each cartridge is precisely positioned by the cartridge positioning member  41 . 
     Referring to  FIGS. 17 and 18 , in this embodiment, each of the left and right sides of the apparatus main assembly is provided with two protrusions  67  which are the same in shape, and two hole  69  which are the same in shape. However, the number and shape of the protrusions  67  and holes  69  do not need to be as shown in  FIGS. 17 ,  18 ,  20 ( a ),  20 ( b ), and  20 ( c ). Further, when two or more protrusions and holes are provided, they do not need to be the same in shape. Further, the manner in which each protrusion  67  fits into the corresponding hole  69  does not need to be exactly as shown in  FIGS. 17 ,  18 ,  20 ( a ),  20 ( b ), and  20 ( c ). Moreover, the hole  69  does not need to be a part of the intermediary transfer belt supporting member. The role which the protrusion  67  and hole  69  play can be played by the combination of the pin  111  and notch  110 , just as effectively as by the combination of the protrusion  67  and hole  69 . Also in the case in which the pin  111  and notch  110  are used, their number, location, and shape do not need to be exactly as shown in  FIG. 14 . 
     (Structure Arrangement for Supplying Cartridge with Power) 
       FIGS. 21-23  are drawings for describing the method for supplying electric power to each cartridge from the apparatus main assembly. 
       FIGS. 21 and 22  show the state of the tray  35 , tray holding members  34 R and  34 L, and their adjacencies, in which the tray  35  has been completely pulled out by opening the door  31 . The tray  35  is provided with multiple intermediary electrical contact springs  72   a - 72   d , which are aligned in the direction parallel to the horizontal direction of the apparatus main assembly. One end of each spring  72  is electrically connected to the corresponding electrical contact ( FIG. 8 ) of the cartridge. That is, the tray  35  is provided with the intermediary electrical contacts  72   a - 72   d , which are electrically connected to the electrical contacts  55  of the cartridge. 
     The apparatus main assembly (main assembly frame  101 ) is provided with a power supply  74 , and electrical contact springs  75   a - 75   d  connected to the power supply  74 . The power supply  74  is located on the outward side of the left frame  80 L. The electrical contact springs  75   a - 75   d  are aligned in the direction parallel to the horizontal direction of the apparatus main assembly. The electrical contact springs  75   a - 75   d  are put through the hole of the left frame  80 L and the hole of the holding member  34 L, and are extended toward the tray  35 . 
       FIGS. 23(   a ) and  23 ( b ) show how the intermediary electrical contact spring  72 , with which the tray  35  is provided, is electrically connected to, or disconnected from, the electrical contact spring  75  on the apparatus main assembly side.  FIGS. 23(   a ) and  23 ( b ) show the same portions of a sectional view of the tray  35 , intermediary electrical contact spring  72 , left tray holding member  34 L, left frame  80 L, electrical contact springs  75  on the apparatus main assembly side, electrical contact spring holder  76  on the apparatus main assembly side, and power supply portion  74  on the apparatus main assembly side, as seen from the front side of the apparatus main assembly. 
       FIG. 23(   a ) shows the state of the abovementioned components, in which the door  31  is in the closed position, and the left tray holding member  34 L and tray  35  are in their latent image formation positions, into which they have been lowered. When they are in this state, the electrical contact spring  75  on the apparatus main assembly side is electrically in contact with the intermediary electrical contact spring  72 . 
       FIG. 23(   b ) shows the state of the abovementioned components, in which the door  31  is in the open position, and the left tray holding member  34 L and tray  35  are at their top levels to which they have been raised from the latent image formation positions. When they are in this state, there is no electrical contact between the electrical contact spring  75  on the apparatus main assembly side and the intermediary electrical contact spring  72 . In order to prevent the tray  35  from contacting the portion of the electrical contact spring  75  on the apparatus main assembly, which is protruding toward the tray  35  beyond the holding member  34 L, the tray  35  is provided with a groove  77  which extends in the fore-and-aft direction of the apparatus main assembly. Therefore, the tray  35  can be pulled out without coming in contact with the electrical contact spring  75  of the apparatus main assembly. 
     More specifically, the apparatus main assembly is provided with electrical contacts  75   a - 75   d , which are disposed so that their positions do not coincide with the path of the intermediary electrical contacts  72   a - 72   d . The apparatus main assembly is structured so that the electrical connection between the intermediary electrical contacts and corresponding electrical contacts of the apparatus main assembly can be broken by moving upward (raising) the tray  35  from the latent image formation position by the holding members  34 L and  34 R, and can be established by moving downward (lowering) the tray  35  toward its latent image formation position by the holding members  34 L and  34 R. 
       FIGS. 21-23  show the power supplying method for supplying one section of each cartridge, which needs to be supplied with electric power, with electric power through one electrical contact of the apparatus main assembly, which is dedicated to this section of the cartridge, and the intermediary elastic electric contact dedicated to this section of the cartridge. However, this setup can also be used when each cartridge has multiple sections which need to be supplied with electric power. Further, this setup can be used even for a cartridge having multiple sections which need to be supplied with electric power and are different in the position in terms of the vertical direction of the apparatus main assembly; all that is necessary is to provide the tray with the same number of grooves, as the number of the sections of the cartridge, which need to be supplied with electric power, which match in vertical position the electrical contacts of the cartridge, which are connected to the sections of the cartridge which need to be supplied with electric power. 
     Further, when the multiple cartridges are the same in the bias to be applied thereto, the tray  35  may be provided with an electrically conductive member, which functions as an intermediary electrical contact, and can be connected to, or disconnected from, the single electrical contact of the apparatus main assembly. To this electrically conductive member of the tray  35 , one end of each of the multiple electrical contact springs is electrically connected, and the other end is rendered electrically connectible to, or disconnectable from, the corresponding electrical contact of the cartridge, which is connected to one of the cartridge sections which need to be supplied with electric power. This structural arrangement makes it possible to reduce the number of the electrical junctions between the intermediary electrical contact spring and electrical contact springs of the apparatus main assembly. Incidentally, the shape of the electrical contact spring of the apparatus main assembly, shape of the intermediary electrical contact spring, and the direction of the contact pressure in each electrical junction, do not need to be as shown in  FIGS. 21-23 . 
     That is, an image forming apparatus may be structured so that the electrically conductive member is disposed in the tray  35 , and the number of the electrical junctions between the intermediary electrical contacts and the electrical contacts of each cartridge is greater than the number of the electrical junctions between the intermediary electrical contacts and the electrical contacts of the apparatus main assembly. The employment of such a structural arrangement can make it possible to reduce the component count of an image forming apparatus, making it therefore possible to reduce the cost of the image forming apparatus, provided that the image forming apparatus is designed so that the multiple cartridges, which are different in the color of the toner they use, are the same in voltage requirement. 
     As described above, the cartridges are placed in the movable member (tray  35 ) so that they can be easily accessed from the front side of the apparatus main assembly to replace them, and the movable member is provided with an intermediary electrical contacts which are connected to, or separated from, the electrical contacts of the apparatus main assembly, by the upward or downward displacement of the movable member. Therefore, it is possible to provide an image forming apparatus which employs a process cartridge drawer (tray) system which makes it easier to replace the process cartridges, and yet, is no higher in cost and size than an image forming apparatus in accordance with the prior art. Incidentally, in the preferred embodiment described above, the transferring member was the transfer belt. However, the present invention is also applicable to an image forming apparatus which does not employ the transfer belt, and instead, employs a conveyance belt for conveying recording medium onto which a toner image is directly transferred from an image bearing member. 
     Further, the movable member is displaced upward or downward by the movement of the member which exposes or covers the opening of the apparatus main assembly through which a cartridge is mounted or removed. Therefore, the method for replacing any of the cartridges in the apparatus main assembly is virtually self explanatory to a user. 
     Further, multiple electrical contacts are horizontally aligned; they are rendered the same in vertical position. Therefore, in terms of the vertical direction of the apparatus main assembly, they do not take up as much internal space of the apparatus main assembly as those of an image forming apparatus in accordance with the prior art. Therefore, this embodiment can reduce the size of the main assembly of an image forming apparatus. 
     (Stay) 
       FIG. 24  is a perspective view of the left and right stays  81 L and  81 R, respectively. These stays  81 L and  81 R are screwed to the inward surfaces of the left and right frames  80 L and  80 R, respectively. That is, the stays  81 L and  81 R oppose each other. It is in the space between the left and right stays  81 L and  81 R that the scanner unit  11 , tray holding members  34 R and  34 L, and belt unit  12  are disposed. 
     The stays  81 L and  81 R are components formed through the process of folding and process of punching. Each stay  81  is provided with a scanner unit positioning portion  82 , a cartridge positioning portion  41 , and a belt unit positioning portion  83 . Therefore, the level of accuracy at which the scanner unit  11 , cartridges PY, PM, PC, and PK, and belt unit  12  are positioned relative to each other can be determined by the preciseness of the stays  81 L and  8 R alone. 
     Further, the scanner unit positioning portion  82 , cartridge positioning portion  41 , and belt unit positioning portion  83  are in the same plane, that is, the plane of the stay. Therefore, when manufacturing the stays, all the positioning portions can be formed through a single punching (piecing) process after the folding process. Therefore, the stays can be manufactured at a higher level of precision. 
     Referring to  FIGS. 25-28 , the stay  81 R ( 81 L) is shaped so that a recess is provided between its cartridge positioning portion  41  and scanner unit positioning portion  82 . The provision of this recess makes it possible to move the tray  35  when replacing the cartridges. If the scanner unit positioning portion is attached to the frame  80 R ( 80 L) as shown in  FIG. 29 , a space S shown in  FIG. 28  cannot be utilized, and therefore, it is possible that the apparatus main assembly may be increased in size. Further, the distance from the scanner unit  11  to the frame is greater, which makes it more likely to allow the scanner unit  11  to vibrate. Therefore, it is possible that banding will deteriorates. 
     The stay  81 R ( 81 L) is perpendicularly bent at the line between the portion by which it is fixed to the frames  80 R ( 80 L) and the rest. Therefore, the scanner unit positioning portion  82  and cartridge positioning portion  41  are prevented from being bent by the weight of the scanner unit  11  and cartridges, and/or by the forces applied to the scanner unit  11  and cartridges to press them against the scanner unit positioning portions  82  and cartridge positioning portions  41 . 
     That is, the stay  81 R ( 81 L) has the first positioning portions  41  for accurately positioning the cartridges, and the second positioning portions  82  for accurately positioning the scanner unit  11  which forms an electrostatic latent image on the electrophotographic photosensitive member in each cartridge. Therefore, not only is it assured that the cartridges are positioned at a high level of accuracy relative to the scanner unit  11 , but also, the apparatus main assembly is increased in rigidity. Using metallic plate as the material for the stay makes it easier to ensure that the cartridges and scanner are positioned at a high level of accuracy relative to each other. Further, the stay  81 R ( 81 L) has the third positioning portion  83  for accurately positioning the belt unit  12 . Since the stay has the portion for accurately positioning belt unit, it is easier to ensure that the cartridges are positioned at a high level of accuracy relative to the belt unit. 
     Further, the stay  81 R ( 81 L) has the recess which accommodates a part of the tray  35  when the tray  35  is moved. In terms of the vertical direction of the apparatus main assembly, this recess is between the first positioning portion  41  and second positioning portion  32 . In terms of the direction parallel to the axial direction of the drum, this recess indents toward the lateral panels of the main frame, with reference to the first positioning portions  41  and second positioning portions  82 . 
     Further, each of the first positioning portions  41  belongs to a portion of the stay, which is formed by bending, in the vertical direction of the apparatus main assembly, the portion of the stay, by which the stay is attached to the main frame, and each of the second positioning portions  82  belongs to another portion of the stay, which is also formed by bending, in the vertical direction of the apparatus main assembly, another portion of the stay, by which the stay is attached to the main assembly. 
     Attaching the stays to the lateral frames of the apparatus main assembly, that is, the frames which are perpendicular to the drum axis, makes it easier to highly accurately position the various components. The cartridge positioning portions and scanner positioning portions are formed as parts of the portion of the stay, which are effected by perpendicularly bending the precursor of the stay along the line between the portion by which the stay is attached to the apparatus main assembly and the rest. Therefore, the stays in this embodiment are stronger than the stays of an image forming apparatus in accordance with the prior art. 
     The present invention is also applicable to an image forming apparatus which has only one stay, that is, either the left stay  81 L or right stay  81 R. 
     Not only can the above described preferred embodiment prevent the electrophotographic photosensitive member in a process cartridge from sustaining the scratches attributable to the rubbing of the photosensitive drum, but also, it can prevent the photosensitive member from developing memories attributable to the rubbing of the photosensitive drum. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Application No. 004023/2006 filed Jan. 11, 2006 which is hereby incorporated by reference.