Abstract:
A color electrophotographic image forming apparatus includes a movable member supporting a plurality of process cartridges in juxtaposition and movable between positions inside and outside a main assembly in a direction crossing a longitudinal direction of a drum of the cartridge when cartridges are supported, a common electroconductive member extended on the movable member in the movement direction thereof and being provided adjacent to longitudinal ends of the supported cartridges, an electrical contact provided on the movable member, connected with the common electroconductive member, and electrically connectable with a cartridge electrical contact provided on each of the cartridges, and a main assembly electrical contact electrically connectable with the common electroconductive member to supply electric power to the common electroconductive member and each of the cartridges from the main assembly.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to an electrophotographic color image forming apparatus employing a process cartridge which has an electrophotographic photosensitive drum, and means for processing the electrophotographic photosensitive member, and which is removably mountable in the main assembly of the image forming apparatus. 
   Here, an electrophotographic color image forming apparatus is an apparatus, such as an electrophotographic color copying machine, an electrophotographic color printer (color laser printer, color LED printer, etc.), or the like, which forms a color image on recording medium, with the use of an electrophotographic image forming process. 
   Recording means is medium, such as recording paper, OHP sheet, label, or the like, on which an image is formed with the use of the electrophotographic image forming process. 
   A process cartridge means a cartridge in which an electrophotographic photosensitive drum, and one or more process means for processing the electrophotographic photosensitive drum, are integrally disposed so that they can be removably mountable in the main assembly of the image forming apparatus. More specifically, a process cartridge is a cartridge in which an electrophotographic photosensitive drum, and at least one among the abovementioned processing means, such as a developing means, a charging means, and a cleaning means, are integrally disposed. 
   The main assembly of an electrophotographic image forming apparatus means what is left after the removal of the process cartridges from the electrophotographic image forming apparatus. 
   A process cartridge is removably mountable in the main assembly of an image forming apparatus by a user himself or herself. Therefore, a process cartridge makes it possible for a user to maintain an image forming apparatus without relying on service personnel. Therefore, the employment of a process cartridge system drastically improves an electrophotographic image forming apparatus in operability. 
   There have been known various structural arrangements for establishing electrical connection between a process cartridge and the main assembly of an electrophotographic color image forming apparatus. 
   For example, an electrophotographic image forming apparatus is structured so that multiple process cartridges are vertically juxtaposed in the movable guide rotatable about its axis. The process cartridges are moved by the rotational movement of the movable guide between the preset cartridge positions (image forming positions) in the apparatus main assembly, and the preset outward positions where they are mountable into, or removable from, the movable guide (apparatus main assembly). Further, the movable guide is provided with an intermediary electrical contact(s). 
   In this structural arrangement, the electrical connection between the electrical contact on the cartridge side and the electrical contact on the apparatus main assembly side is established through the intermediary electrical contact (U.S. Pat. No. 7,092,657). 
   This structural arrangement ensures that electrical connection is established between the electrical contacts on the cartridge side and those on the apparatus main assembly side. That is, it is excellent in terms of the electrical connection between the main assembly of an image forming apparatus, and a process cartridge. 
   In recent years, in the field of an electrophotographic color image forming apparatus, it has been thought of structuring an image forming apparatus so that multiple process cartridges are supported in the apparatus main assembly by being placed side by side in a movable member which is linearly movably relative to the apparatus main assembly. This structural arrangement is smaller in the amount of space required for the movement of the movable member than the structural arrangement in which the movable member is rotationally moved. 
   The present invention is one of the further developments of the above described structural design for an electrophotographic color image forming apparatus. 
   SUMMARY OF THE INVENTION 
   Thus, the primary object of the present invention is to provide an electrophotographic color image forming apparatus structured to ensure that electrical connection is made between the electrical contacts on the process cartridge side and the corresponding electrical contacts smoothly on the apparatus main assembly side. 
   Another object of the present invention is to provide an electrophotographic color image forming apparatus structured so that electrical connection is made between the sets of electrical contacts which multiple process cartridges have, and the corresponding sets of electrical contacts on the apparatus main assembly side, with the use of an electrically conductive common member which is shared by the sets of electrical contacts on both sides. 
   Another object of the present invention is to provide an electrophotographic color image forming apparatus which uses an electrically conductive common member to make electrical connection between the sets of electrical contacts of on the process cartridge side, and the sets of electrical contacts on the main assembly side of the image forming apparatus, being therefore significantly smaller in the number of components for making electrical connection between the process cartridge side and main assembly side than an electrophotographic color image forming apparatus in accordance with the prior art, the number of the components of which for electrical connection between the cartridge side and main assembly side is roughly proportional to the number of the process cartridges it uses. 
   According to an aspect of the present invention, there is provided a color electrophotographic image forming apparatus including a main assembly to which process cartridges each including an electrophotographic photosensitive drum and process means actable on said electrophotographic photosensitive drum are detachably mountable, said color electrophotographic image forming apparatus comprising a movable member having a supporting portion for supporting a plurality of said process cartridges in juxtaposition, said movable member being movable between a set position inside said main assembly of the apparatus and a position outside said main assembly of the apparatus in a direction crossing a longitudinal direction of said electrophotographic photosensitive drum of said process cartridge in a state in which a plurality of said process cartridges are supported on said supporting portion; a common electroconductive member extended on said movable member in a direction of movement of said movable member, said common electroconductive member being provided adjacent to longitudinal ends of said process cartridges supported on said supporting member; an electrical contact portion which is provided, for each of said supporting portions, on said movable member and which is electrically connected with said common electroconductive member, said electrical contact portion being electrically connectable with a cartridge electrical contact provided on each of said process cartridges; a main assembly electrical contact electrically connectable with said common electroconductive member to supply electric power to said common electroconductive member from said main assembly of the apparatus at least when said movable member is placed at the set position, wherein the electric power can be supplied from the main assembly of the apparatus to each of the process cartridges supported on said supporting portion of said movable member placed at the set position through said main assembly electrical contact, said common electroconductive member and each of said electrical contact portions. 
   The present invention makes it possible to provide an electrophotographic color image forming apparatus which is no greater in the component count, and yet, is significantly more reliably in terms of the electrical connection between the electrical contacts on the cartridge side and the electrical contacts on the main assembly of the apparatus, than an electrophotographic color image forming apparatus in accordance with the prior art. 
   These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an external perspective view of the image forming apparatus in one of the preferred embodiments 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, shown in  FIG. 1 , the font door of which is open. 
       FIG. 4  is a vertical sectional view of the image forming apparatus, shown in  FIG. 3 , as seen from the left side of the apparatus main assembly. 
       FIG. 5  is an external perspective view of the image forming apparatus, shown in  FIG. 1 , the tray of which has been pulled out further from the tray position shown in  FIG. 3 . 
       FIG. 6  is a vertical sectional view of the image forming apparatus, shown in  FIG. 4 , the tray of which has been pulled out further from the tray position shown in  FIG. 4 , 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. 9A  is a perspective view of the tray. 
       FIG. 9B  is a perspective view of the ground contact of the apparatus main assembly, the intermediary electrical contact (which also doubles as tray reinforcing member) on the tray, and the left front corner portion of the tray in terms of the inward movement of the tray, when the ground contact is in contact with the intermediary electrical contact. 
       FIG. 9C  is a perspective view of the ground contact of the apparatus main assembly, the intermediary electrical contact (which also doubles as tray reinforcing member) on the tray, and the left front corner portion of the tray in terms of the inward movement of the tray, when the ground contact is not in contact with the intermediary electrical contact. 
       FIG. 9D  is a perspective view of the electrical contact on the main assembly side, the ground contact of the apparatus main assembly, the intermediary electrical contact (which also doubles as tray reinforcing member) on the tray, and the left front corner portion of the tray in terms of the inward movement of the tray, when the electrical contact on the main assembly side is in contact with the intermediary electrical contact. 
       FIG. 10  is a perspective view of the mechanical linkage between the door and tray holding members. 
       FIG. 11  is a schematic drawing 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. 
       FIG. 13  is an enlarged view 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. 
       FIG. 16  is a perspective view ( 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. 
       FIG. 19  is a drawing ( 3 ) showing the tray position regulating means. 
       FIG. 20  is a drawing ( 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. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment 
   General Structure of Electrophotographic Image Forming Apparatus 
     FIG. 1  is an external perspective view of the electrophotographic color image forming apparatus  100  in this embodiment.  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. This image forming apparatus  100  is a full-color printer, which employs an electrophotographic image forming process, and uses four inks different in color. It forms an image on recording medium in response to electrical picture signals inputted from an external host apparatus (unshown), such as a personal computer, an image reader, a facsimile machine (from which image is sent), and the like. 
   In the following description of the preferred embodiment of the present invention, the front side (front surface side) of the image forming apparatus  100  means the side which has a door  31 . The rear side of the image forming apparatus is the side opposite to the front side. The fore-and-after direction includes both the frontward and rearward directions. 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. The side to side direction includes both the leftward and rightward directions. 
   In the main assembly A of the image forming apparatus  1 , multiple process cartridges (first to fourth), that is, PY, PM, PC, and PK are contained. The four cartridges PY, PM, PC, and PK are horizontally arranged in the listed order in the rear-to-front direction of the apparatus main assembly A (which may be referred to as inline or tandem arrangement). 
   The four cartridges PY, PM, PC, and PK are the same in structure, although they are different in the color of the developers they store. 
   Each cartridge in this embodiment is an assembly which has: an electrophotographic photosensitive drum  1 ; processing means, more specifically, a charging means  2 , a developing means  3 , and a cleaning means  4 , which process the drum  1 ; and a cartridge in which the preceding components and means are integrally disposed. As the charging means  2 , a charge roller is used. As a developing means  3 , a development roller  3   a  is used. In the developer container  3   b  of the developing means  3 , developer is stored. As the cleaning means  4 , a cleaning blade is used. 
   The developer container of the first cartridge PY stores yellow (Y) developer. On the peripheral surface of the drum  1  in the first cartridge PY, a developer image of yellow (Y) color is formed. The developer container of the second cartridge PM stores magenta (M) developer. On the peripheral surface of the drum  1  in the second cartridge PM, a developer image of magenta (M) color is formed. The developer container of the third cartridge PC stores cyan (C) developer. On the peripheral surface of the drum  1  in the third cartridge PC, a developer image of cyan (C) color is formed. The developer container of the fourth cartridge PK stores black (K) developer. On the peripheral surface of the drum  1  of the fourth cartridge PK, a developer 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  1  in each cartridge. That is, the scanner unit  11  outputs a beam of laser light L while modulating it with the information regarding the monochromatic color images to be formed by the cartridges, which is inputted from an external host apparatus (unshown). As a result, the peripheral surface of the photosensitive drum  1  in each cartridge is scanned (exposed) by the beam of laser light L through the exposure window  6 , 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  is disposed, which has a flexible endless belt  13 , a driver roller  14 , a turn roller  15 , and tension roller  16 . The endless belt  13  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 A, whereas the turn roller  15  is disposed in the front portion of the apparatus main assembly A. Each cartridge is disposed so that 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  13 , which corresponds to the top portion of the loop, pinched between the transfer roller  17  and drum  1 . A secondary transfer roller  22  is disposed outside the belt loop so that it opposes the driver roller  14 , with the belt  13  pinched between the two rollers. 
   In the area below the belt unit  12 , a paper feeder unit  18  is disposed, which has a paper tray  19 , a paper feeder roller  20 , a paper separation pad  21 , etc. In the paper tray  19 , sheets of recording paper as recording medium are stored in layers. The paper tray  19  is removably mountable in the apparatus main assembly A from the front side (front loading). 
   In the top portion of the rear portion of the apparatus main assembly A, a fixing apparatus  23  and a pair of discharge rollers  24  are disposed. Further, the top wall of the apparatus main assembly A is shaped so that a part of the wall 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 pair of discharge rollers  24  are rollers  24   a  and  24   b.    
   When each of the cartridges PY, PM, PC, and PK is correctly situated in its preset position (which hereafter may be referred to as image forming position, or latent image forming position) in the apparatus main assembly A, it remains securely held to the cartridge positioning portion of the apparatus main assembly A by the pressure applied by a cartridge pressing member (which will be described later in detail), being thereby correctly positioned relative to the apparatus main assembly A. Further, the driving force input portion of the cartridge is engaged with the driving force output portion of the apparatus main assembly. Further, the input electrical contact portion of the cartridge is electrically in connection to the power supply system with which the apparatus main assembly A is provided. 
   The operation carried out by this image forming apparatus to form a full-color image is as follow: 
   The drum  1  in each of the first to fourth cartridges PY, PM, PC, and PK is rotationally driven at a preset 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 drum  1 . The scanner unit  11  is also driven. In synchronization with the driving of the scanner unit  11 , the charge roller  2  in each cartridge uniformly charges the peripheral surface of the drum  1  to preset polarity and potential, with a preset (controlled) timing. The scanner unit  11  scans (exposes) the peripheral surface of each 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 drum  1 . This electrostatic latent image is developed by the development roller  3   a  into a visible image (image formed of development). 
   Through the above described electrophotographic image formation process, a yellow developer 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 developer image is transferred (primary transfer) onto the belt  13 . 
   On the drum  1  of the second cartridge PM, a magenta developer image, which corresponds to the magenta color component of the full-color image, is formed, and this developer image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow developer image which is already on the belt  13 . 
   On the drum  1  of the third cartridge PC, a cyan developer image, which corresponds to the cyan color component of the full-color image, is formed, and this developer image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow and magenta developer images which are already on the belt  13 . 
   On the drum  1  of the fourth cartridge PK, a black developer image, which corresponds to the black color component of the full-color image is formed, and this developer image is transferred (primary transfer) onto the belt  13  so that it is layered on the yellow, magenta, and cyan developer images which are already on the belt  13 . 
   Consequently, an unfixed full-color developer image is effected on the belt  13  by the four monochromatic color developer images, that is, the yellow, magenta, cyan, and black color development images. 
   After the primary transfer of the developer image onto the belt  13 , the developer remaining on the peripheral surface of the drum  1  in each cartridge is removed by the cleaning means  4 . 
   Meanwhile, the paper feeder roller  20  is driven with the preset (controlled) timing. As the paper feeder roller  20  is driven, one of the sheets of recording medium P (recording paper, OHP sheet, etc.,) stacked in the paper tray  19  is separated from the rest of the sheets of recording medium P by the coordination of the sheet feeder roller  20  and separation pad  21 , and is fed into the apparatus main assembly A by the sheet feeder roller  20 . Then, the recording medium P is introduced into the nip (secondary transfer nip), that is, the interface between the secondary transfer roller  17  and belt  13 , and then, is conveyed through the nip (secondary transfer nip) which the secondary transfer roller  22  and belt  13  form, while remaining pinched by the secondary transfer roller  22  and belt  13 . While the recording medium P is conveyed through the nip, the four layers of developer images, different in color, on the belt  13  are transferred together onto the recording medium P as if they were peeled away from the belt  13 , starting at their leading edges. 
   The recording medium 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 developer images different in color are fixed to the recording medium P while being blended. Thereafter, the recording medium P is moved out of the fixing apparatus  23 , and then, is discharged as a full-color copy onto the delivery tray  25  by the pair of discharge rollers  24 . 
   After the separation of the recording medium P from the belt  13 , the secondary transfer residual developer, that is, the developer remaining on the surface of the belt  13  after the separation of the recording medium P from the belt  13 , is removed by a cleaning means  4 . That is, in this embodiment, the secondary transfer residual developer electrostatically adheres to the peripheral surface of the drum  1  in the primary transfer nip of the first cartridge PY, for example, and then, it is removed from the drum  1  by the cleaning means  4 . 
   (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 stored in the developing means  3  of each cartridge is consumed. 
   Thus, the image forming apparatus is provided with a means (unshown) for detecting the amount of the developer remaining in each cartridge. The detected amount of the developer in each cartridge is compared, by the control portion (unshown), with a threshold value preset for issuing a warning, such as a warning that 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 developer in the cartridge is smaller than the preset threshold value, the message which warns 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 monitor portion (unshown); 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 tray (cartridge drawer: movable member which is movable while holding cartridges), which can be pulled out frontward to make it easier for a user to access the cartridges from the front side of the apparatus, in order to replace the cartridge. 
   The cartridge tray  35  is provided with multiple cartridge supporting portions (cartridge bays), in which multiple cartridges are held one for one. The cartridge supporting portion (cartridge bays) are juxtaposed in parallel. 
   In this embodiment, the cartridge tray  35  is provided with four cartridge supporting portions  35 Y,  35 M,  35 C, and  35 K ( FIG. 9A ), in which first to fourth cartridge PY, PM, PC, and PK are placed, being supporting thereby, respectively. The cartridge tray  35  is movable in the direction perpendicular to the lengthwise direction of the drum  1  in the cartridge held in the cartridge tray  35 , between its innermost position, that is, its image formation position, in the apparatus main assembly A, and its outermost position from the apparatus main assembly A. 
   When the cartridge tray  35  is in the most outward position relative to the apparatus main assembly A, all the cartridges in the tray are outside the apparatus main assembly A, making it easier for the user to replace any cartridge in the tray. 
   More specifically, the front wall of the image forming apparatus is provided with an opening  30 , through which the cartridge (cartridge tray) can be inserted into, or removed from (pulled out of), the apparatus main assembly A. That is, the apparatus main assembly A has the opening  30  ( FIG. 2 ) through which the cartridge (cartridge tray) is allowed to pass. 
   Further, the apparatus main assembly A is provided with a door  31 , which can be rotationally moved between the closed position in which it covers the opening  30 , and the open position in which it exposes the opening  30 . 
   In this embodiment, this door  31  is rotationally movable relative to the apparatus main assembly A about a horizontal shaft  32  (door hinge shaft) located at the bottom edge of the door  31 . That is, the door  31  is rotatable about the hinge shaft  32  in a manner to be rotationally raised upward so that it can be moved into the closed position, in which it remains shut against the apparatus main assembly A, covering the opening  30  ( FIGS. 1 and 2 ), and also, so that it can be rotated frontward about the hinge shaft  32  into the open position, in a manner to be laid down ( FIGS. 4 and 5 ) to widely expose the opening  30 . Designated by a referential character  31   a  is a handle, with which the door  31  is provided. 
   The apparatus main assembly A is provided with a pair of tray supporting members  34 L and  34 R (tray moving means) ( FIG. 4 ), which are attached one for one to the inward side of the left and right panels  81 L and  81 R of the main frame ( FIG. 17 ) of the apparatus main assembly A, opposing each other. The cartridge tray  35  is supported between the pair of holding members  34 L and  34 R, and by the pair of holding members  34 L and  34 R, being enabled to horizontally slide in the fore-and-after direction of the apparatus main assembly A. The cartridges PY, PM, PC, and PK are supported by the supporting portions  35 Y,  35 M,  35 C, and  35 B of the tray  35 . 
   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 A, that is, slantingly upward, by preset distances, by the movement of the door  31 . As a result, the holding members  34 L and  34 R are pulled out of the apparatus main assembly A through the opening  30  so that the front end portion of each holding member  34  extends outward of the apparatus main assembly A by a preset distance ( FIGS. 4 and 5 ). The mechanism which causes the holding members  34 L and  34 R to be moved by the movement of the door  31  will be described later. 
   As the holding members  34 L and  34 R are moved outward, the driving force output portions of the apparatus main assembly are disengaged from the corresponding driving force input portions of the cartridges PY, PM, PC, and PK, respectively (disengagement of driving force transmitting means). Further, the pressure applied to each cartridge by the pressure applying member to secure and correctly position the cartridge is removed from the cartridge (pressure removal). Further, the electrical contacts of each cartridge are disengaged from the power supply system of the apparatus main assembly, 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). Further, the tray  35  is freed from its positional restriction. 
   At this point, the user is to grasp the handle  35   a  exposed through the opening  30 , and pull the tray  35  in the horizontal and frontward direction to slide the tray  35  relative to the pair of holding members  34 L and  34 R so that the tray  35  comes out of the apparatus main assembly A through the opening  30 , and moves into its preset most outward position ( 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 A through the opening  30 , being exposed from the apparatus main assembly A; the top surface of each cartridge is exposed. The apparatus main assembly A 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 pair of stoppers (unshown) from being pulled out further, and also, so that once the tray  35  is pulled out to the preset most outward position, it is securely retained in this most outward position by the holding members  34 L and  34 R. 
   The tray  35  is structured so that each cartridge 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 straight downward into the tray  35  from directly above. Thus, the user is to extract from the tray  35  the cartridge or cartridges, which are to be replaced, that is, the cartridge or cartridges, the life of which has expired, by simply lifting it, as indicated by a double-dot chain line in  FIG. 6  and then, fit a brand-new cartridge or cartridges, from directly above, into the vacated space or spaces, one for one, in the tray  35 . 
   In the embodiment described above, the tray  35  is a movable member which is movable in the direction intersectional (perpendicular) to the lengthwise direction (axial line) of the drum  1  of the cartridge, and is enabled to move between its preset most inward position (image formation position) in the apparatus main assembly A and its preset most outward position from the apparatus main assembly A. More specifically, the tray  35  can be moved outward of the apparatus main assembly A through the abovementioned opening  30  to its preset outermost position where the cartridges can be removed from, or mounted into, the tray  35 , and also, can be moved inward of the apparatus main assembly A, into its preset transitional position, from which it is moved diagonally downward. Further, the tray  35  can be moved into the latent image formation position where an electrostatic latent image can be formed on the drum  1 . 
   In this embodiment, the tray  35  holds the cartridges PK, PC, PM, and PY, in which the developers of K, C, M, and Y colors, respectively, are stored. The order in which the cartridges PK, PC, PM, and PY are arranged in the tray  35  is the same as they are listed above. Namely, in terms of the upstream to downstream direction, that is, the direction in which the tray  35  is moved inward of the apparatus main assembly A from outward of the apparatus main assembly A, the cartridges PK, PC, PM, and PY are arranged in the listed order. In other words, in this embodiment, the cartridges are arranged according to the amount of developer consumption, so that the cartridge highest in developer consumption, that is, the cartridge highest in replacement frequency, is placed closest to the front side, that is, the side from which the user operates the image forming apparatus. Therefore, the distance by which the tray  35  must be pulled out of the apparatus main assembly to expose the cartridge PK is very small. Thus, the image forming apparatus A in this embodiment is superior in operability to an image forming apparatus in accordance with the prior art, in terms of the efficiency with which the cartridge PK can be replaced. 
   The left and right holding means  34 L and  34 R are the means for diagonally upwardly moving the tray  35  from its preset innermost position before moving the tray  35  into the area in which the cartridge(s) can be removed from, or placed into, the tray  35 . They also constitute the means for downwardly moving the tray  35  into its preset innermost position. In other words, the holding means  34 L and  34 R are members for supporting the tray  35 . In terms of the vertical direction, they are enabled to move to, and remain at, a first level, or a second level. The first level allows the tray  35  to be moved between the area in which the cartridge(s) can be mounted into, or removed from, the tray  35 , and the abovementioned transitional position. The second level keeps the tray  35  in the abovementioned latent image formation position. Further, as the door  31  is closed, the holding members  34 L and  34 R moves from the first level to the second level. 
     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. 
   Each cartridge is an assembly which is roughly in the form of a rectangular parallelepiped, and its left-and-right direction, that is, the lengthwise direction, is parallel to the axial line of the drum  1 . The drum  1  is rotatably supported between the bearing portions  51  and  52 , with which the right and left panels of the cartridge frame  5  formed of synthetic resin are provided, respectively. The right bearing portion  51  is provided with a coupler  53  as a drum driving force input portion. Further, the right panel of the cartridge frame  5  is provided with a coupling  54  as a developing means driving force input portion for driving the development roller  3   a . The left wall of the cartridge frame  5  is provided with electrical contacts  55  of the cartridge. More specifically, each cartridge is provided with four electrical contacts  55  (different in locations), which are for the charge roller  2 , development roller  3   a , developer supply member (unshown), and developer regulating member (unshown), one for one. Of the four electrical contacts  55  of the cartridge, the electrical contact designated by a referential letter a is in connection to the development roller  3   a , and receives the development bias supplied to the development roller  3   a  from the apparatus main assembly A. The electrical contact designated by a referential letter b is in connection to the developer regulating member (unshown), and receives the developer regulating member bias supplied to the developer regulating member (unshown) from the apparatus main assembly A. The electrical contact designated by a referential letter c is in connection to the charge roller  2 , and receives the charge bias supplied to the charge roller  2  from the apparatus main assembly A. The electrical contact designated by a referential letter d is in connection to the developer supply member (unshown), and receives the developer supply member bias supplied to the developer supply member from the apparatus main assembly A. 
   The three electrical contacts a, b, and c are exposed at the outward surface of one of the end walls of the cartridge in terms of the lengthwise direction of the photosensitive drum  1 , whereas the electrical contact d is exposed at the outward surface of the leading wall of the tray  35 , in terms of the direction in which the tray  35  is moved from outside the apparatus main apparatus into the apparatus main assembly. 
   Of the cartridges described above, the right-hand side of each 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 drivable side, may be referred to as non-drivable side. 
     FIG. 9A  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 dielectric 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 plates  35   f  which extend in the direction parallel to the left-and-right direction of the apparatus main assembly, connecting the left and right sections of the main frame. Hereafter, these four sub-spaces will be referred to as first-fourth cartridge bays  35 ( 1 )- 35 ( 4 ), listing from the rear section  35   c  side toward the front section  35   b . These cartridge bays  35 ( 1 )- 35 ( 4 ) are the first to fourth cartridge supporting portions  35 Y,  35 M,  35 C, and  35 K (cartridge compartments) in which the first to fourth cartridges PY, PM, PC, and PK are held, respectively. The portions of the rear section  35   e  of the main frame of the tray  35 , which correspond to the cartridge bays  35 ( 1 )- 35 ( 4 ), are provided with a hole  35   g , which is for allowing the development roller driving coupler to move into, or out of, the corresponding cartridge bay. 
   Incidentally, designated by a referential number  200  ( FIGS. 2 ,  4 , and  6 ) is a cartridge placement second space (cartridge storage compartment, cartridge placement position, image formation position). Each cartridge held in the cartridge placement spaces  200  receives driving force from the apparatus main assembly A through the drum driving coupler  39  and development roller driving coupler  40 . Further, when the cartridges are in the cartridge placement second space  200 , they are electrically in connection to the apparatus main assembly A. 
   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. Incidentally, the electrical contacts  75   a - 75   d  on the main assembly side is indirectly connected to the electrical contacts  55   a - 55   d  on the cartridge side, respectively. The electrical contact a is for supplying development roller  3   a  with development bias, and the electrical contact b is for supplying the developer regulating member (unshown) with regulating member bias. Further, the electrical contact c is for supplying the charge roller  2  with charge bias, and the electrical contact d is for supplying the developer supply member (unshown) with supply member bias ( FIGS. 8 and 21 ). Incidentally, the electrical contacts  72   a - 72   d  correspond to the cartridge supporting portions  35 Y,  35 M,  35 C, and  35 K. 
   Each cartridge is to be inserted from directly above into one of the sub-spaces (cartridge supporting portions  35 Y,  35 M,  35 C, and  35 K) 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 . The tray  35  loosely supports each cartridge. This structural arrangement makes it easier for a user to replace the process cartridges. 
   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 ). 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 left and right 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 all the way into the apparatus main assembly. That is, 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 user is to close the door  31  against the frame 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 rotational closing movement of the door  31 . As a result, each cartridge is moved into its designated position in the apparatus main assembly. 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 addition, each of the driving force outputting portions of the apparatus main assembly engages with the driving force input portion of the corresponding cartridge, and also, electrical connection is established between the power supply system of the apparatus main assembly and the electrical contacts of each cartridge. That is, while each cartridge is moved downward by the downward movement of the tray  35 , the abovementioned intermediary electrical contacts  72   a - 72   d  become electrically connected to the electrical contacts  75   a - 75   d  (electrical contacts on the main assembly side), respectively, establishing thereby the electrical connection between the contacts  75   a - 75   d  on the main assembly side and the electrical contacts  55  on the cartridge side. 
   (Mechanical Linkage between Door  31  and Holding Members  34 L and  34 R) 
     FIG. 10  is a perspective view of the mechanical linkage between the door  31  and 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 A. 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. The door  31  is solidly attached to the hinge shaft  32 . Thus, as the door  31  is rotationally 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, 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 are protruding 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, respectively. 
     FIG. 11  shows 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 . 
     FIG. 12  is an enlarged view of one of the guiding slots  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 , in the diagonally upward direction. The third guiding section  36   c  horizontally extends frontward 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 securely 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 opening movement of the door  31 , while being horizontally 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  while being vertically 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.    
     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 against the apparatus main assembly. When the mechanical linkage is in this state, the left and right 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 remain supported by the apparatus main assembly with the presence of the hinge shaft  32 , connective arms  37 L and  37 R, shafts  37   a , and holes  34   b  between the door  31  and holding members  34 L and  34 R. Further, each 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 levels (abovementioned second levels) relative to the left and right frames  80 L and  80 R, respectively. Therefore, the tray  35 , which is remaining held by the holding members  34 L and  34 R, is also in its lowest level (abovementioned latent image formation position). 
   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 abovementioned 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 drivable 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 non-drivable side, are pressed upon the positioning portions  41  ( FIGS. 14-14 , and  24 ), one for one, with which the stays (internal panels) of the apparatus main assembly A is provided. Thus, each cartridge is accurately positioned and held relative to the apparatus main assembly A. Also, when the mechanical linkage is in the state described above, 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 of the belt unit  12 . 
   The coupler  53  and  54  of each cartridge are in engagement with the drum driving coupler and development roller driving coupler, respectively, with which the apparatus main assembly is provided. 
   To the electrical contacts  55   a - 55   d  of each cartridge, electric power can be supplied from the apparatus main assembly through the corresponding electrical contacts  72   a - 72   d.    
   The tray  35  is provided with a protrusion  67 . An intermediary transfer belt supporting member  68 , which is a stationary member of the apparatus main assembly, is provided with a hole  69 . The protrusion  67  of the tray  35  is fitted in the hole  69 , whereby the tray  35  is precisely positioned relative to the apparatus main assembly ( FIGS. 11(   a ) and  12 ). 
     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 pulled frontward, in the apparatus main assembly, by the movement of the door  31 . Therefore, 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. However, 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 pulled further frontward by the rotational movement of the door  31 , in the apparatus main assembly. Therefore, the holding members  34 L and  34 R move in the diagonally upward direction, with the pins  34   c  being guided by the second guiding section  36   b  of the guiding slot  36 . During this slantingly upward movement of the holding members  34 L and  34 R, the electrical contacts  55  of each cartridge are electrically disconnected from the counterparts on the apparatus main assembly. That is, the intermediary electrical contacts  72   a - 72   d  become separated from the electrical contacts  75   a - 75   d  on the apparatus main assembly side, respectively, breaking thereby the electrical connection between the cartridge and apparatus main assembly. 
   Referring to  FIG. 13 , a referential letter X stands for the distance by which the protrusion  67  enters the hole  69 , and a referential letter Y stands for the distance by which the holding members  34 L and  34 R, which are 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  (X&gt;Y), 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 (X&lt;Y), 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  does not 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. 
     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 , and therefore, the pins  34   c  are in the third guiding section  36   c , 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. 11(   c ), the protrusion  67  has already come out of the hole  69 , 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  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 abovementioned preset position (image formation position) in the apparatus main assembly A. The restriction placed upon the tray  35  by this tray 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, which are 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, comes into contact with the belt  13 . This first movement is a linear movement. Next, the holding members  34 L and  34 R move (second movement) in the slantingly upward direction, that is, the direction having two directional components: the abovementioned separative direction, and the direction intersectional to the separative direction. The second movement is a downward movement. Thereafter, the holding members  34 L and  34 R move (third movement) in the direction intersectional to the direction in which the drum  1  and belt  13  come into contact with each other. 
   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 movement of the holding members  34 L and  34 R in the direction to cause the drum  1  and belt  13  to separate from each other, the tray movement regulating means  67  and  69  are disengaged from each other. As the holding members  34 L and  34 R make the first to third movements, the tray  35  is made to linearly move in the horizontal direction, or diagonally upward (or downward) direction, by the movements of the holding members  34 L and  34 R. 
   For the improvement in usability, not only are the cartridges mounted in the movable member (tray) to make it easier for the cartridge(s) to be replaced, but also, the movable member (tray) is moved upward or downward by the vertical component of the movement of the moving means (tray holding members). Therefore, the employment of this embodiment makes it possible to make the intermediary electrical contacts  72   a - 72   d  come smoothly in contact with the electrical contacts  75   a - 75   d  on the apparatus main assembly side, respectively, without increasing the apparatus cost and main assembly size. Moreover, it can achieve the aforementioned object of providing an image forming apparatus which has a process cartridge drawer (tray), 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. 
   (Driving Force Transmitting Portion between Cartridge and Apparatus Main Assembly) 
     FIGS. 14-16  are schematic drawings for describing the driving force transmitting components of each cartridge, which are engaged or disengaged by the movement of the tray holding members  34 L and  34 R, 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 pulled out all the way. 
   On the right-hand side in the apparatus main assembly A, 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 A, 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 A ( FIG. 24 ). Each cartridge positioning portion  41  supports the corresponding bearing portions  51  ( 52 ), that is, the bearing portion on the drivable side (non-drivable side), 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 (image forming position). More specifically, each cartridge pressing member  42  presses on the left and right end portions of the top surface of the corresponding cartridge to keep stable the bearing portion  51  ( 52 ), that is, the bearing portion on the drivable side (non-drivable side), supported by the abovementioned cartridge positioning portion  41 . The pressing member  42  is provided with a spring  43  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 in the state shown in  FIG. 14 .  FIG. 16(   b ) is an enlarged view of the pressing member  42 , drum coupler  39 , development roller coupler  40 , and their adjacencies, which are in the state shown in  FIG. 15 . 
   Each pressing member  42  is attached to the apparatus main assembly A so that it is rotatable about a pivot  44 . 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 lever 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 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 ring 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 abovementioned 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. 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  are in their topmost positions, into which they were pushed up by the opening movement of the door  31 , and the tray  35  is not completely in 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.  FIG. 19  is a schematic drawing showing the movement of the cartridge position 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 ), 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) further rearward into the apparatus main assembly in the diagonally downward 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 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 diagonally downward direction. 
   That is, while the tray  35  is in a position which is away from the transitional position in the apparatus main assembly, the stopper  70  prevents the door  31  from moving from the open position to the closed position. Further, as the tray  35 , which is the first releasing member, is moved into the transitional position in the apparatus main assembly A, it removes the restriction which the stopper  70  places upon the movement of the holding member  34 R. That is, 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 image formation 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 image formation position in the apparatus main assembly, 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 image formation position (cartridge placement second space  200 ), and then, close the door  31 . In other words, this embodiment makes it possible to 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. 
   In this embodiment, however, the image forming apparatus is provided with the member which regulates the movement of the door  31  in coordination with the positioning of the tray  35 , and/or the member which regulates the movement of the tray in coordination with 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. That is, it does not occur that the tray  35  is operated when the tray  35  is not in its topmost position. Therefore, it does not occur that the drum  1  is rubbed by the belt. 
   Incidentally, the above described combination of the protrusion  67  and hole  69  ( FIGS. 11 and 13 ) can be utilized as the substitute for the stopper  70  for the tray  35 . This setup will be described next, with reference to  FIGS. 17 ,  18 , and  19 . 
   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  (stationary 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 the intermediary transfer belt supporting member  68 , 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 ). 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 A. Therefore, each cartridge is precisely positioned by the cartridge positioning portion  41 . 
   Referring to  FIGS. 17 and 18 , in this embodiment, each of the left and right sections of the primary frame of the tray  35  is provided with two protrusions  67  which are the same in shape, and each of the left and right end portions of the intermediary transfer belt holding member  68  is provided with 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 , and  20 . 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 , and  20 . Moreover, the hole  69  does not need to be a part of the intermediary transfer belt supporting member. 
   (Structural 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 pulled out all the way by the opening of the door  31 . The tray  35  is provided with multiple sets  72   a - 72   d  of electrical contacts, which are aligned in the direction parallel to the horizontal direction, and also, vertical direction, of the apparatus main assembly A. Each electrical contact  72  is formed of an electrically conductive substance, and is in the form of a spring. Referring to  FIG. 23 , each electrical contact  72  is provided with a first electrical contact point α, which is on the inward side of the tray  35 , and a second electrical contact point β, which is on the outward side of the tray  35 . The first electrical contact point a is electrically connectible to the electrical contact point  55  on the cartridge side. 
   When the cartridge is in the tray  35 , being thereby supported by the tray  35 , the first electrical contact point a is in contact with the electrical contact point  55  on the cartridge side, and therefore, there is electrical connection between the cartridge and tray  35 . The first electrical contact point α is elastic, and protrudes slight into the corresponding cartridge bay ( 35 ( 1 )- 35 ( 4 )) of the tray  35 . Therefore, while the cartridge settles into one of the abovementioned cartridge bays  35 ( 1 )- 35 ( 4 ) after it is released by a user, the first electrical contact point α elastically deforms as it comes into contact with the electrical contact  55  on the cartridge side. Therefore, the first electrical contact point α smoothly connects with the electrical contact  55  on the cartridge side. 
   The apparatus main assembly is provided with multiple sets  75   a - 75   d  of electrical contacts, which are on the inward side of the apparatus main assembly, being aligned along the path of the tray  35 . More specifically, each electrical contact  75  is formed of an electrically conductive elastic substance, and is in the form of a spring. It is electrically connected to the electrical power supply portion  74  on the apparatus main assembly side, which is located outside the left frame  80 L, that is, the left section of the main frame of the apparatus main assembly. The multiple sets  75   a - 75   d  of the electrical contacts are aligned in the horizontal direction, and also, vertical direction, of the apparatus main assembly. Each electrical contact  75  protrudes toward the tray  35  through the hole with which the left frame  80 L is provided, and the hole with which the left holding member  34 L is provided. The abovementioned second electrical contact point β of the electrical contact  72  is electrically connectible to this electrical contact  75  on the apparatus main assembly side. 
     FIGS. 23(   a ) and  23 ( b ) show how the electrical contact  72 , with which the tray  35  is provided, is electrically connected to, or disconnected from, the electrical contact  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 , electrical contact  72 , left tray holding member  34 L, left frame  80 L, electrical contact  75  on the apparatus main assembly side, electrical contact 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 image formation positions, into which they have been lowered, in the apparatus main assembly. When they are in this state, the electrical contact  75  on the apparatus main assembly side is electrically in contact with the electrical contact  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 image formation positions in the apparatus main assembly. When they are in this state, there is no electrical connection between the electrical contact  75  on the apparatus main assembly side and the second electrical contact point β of the electrical contact spring  72 . In order to prevent the tray  35  from contacting the portion γ of the electrical contact  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 space (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  75  of the apparatus main assembly. 
   The second electrical contact point β of the electrical contact  72  is above the space  77 . 
   The abovementioned space  77  is located between the tray  35  and the electrical contact  75  on the main assembly side, preventing thereby the tray  35  from coming into contact with the electrical contact  75  on the apparatus main assembly side while the tray  35  is moved from inside the apparatus main assembly to the outside of the apparatus main assembly. The second electrical contact point β of the electrical contact  72  becomes electrically connected with the end portion (extending portion) γ of the electrical contact  75  on the apparatus main assembly side, which is inwardly protruding toward the tray  35 , while the tray  35  is moved downward after it is horizontally moved into the apparatus main assembly from outside the apparatus main assembly. 
   The top end of the main assembly electrical contact  75  constitutes a fixation point δ. The abovementioned horizontal movement of the tray  35  into the apparatus main assembly from outside the apparatus main assembly causes the extending portion γ of the electrical contact  75  to enter the space  77  (groove) of the tray  35 . Then, while the tray  35  is moved downward, the extending portion γ comes into contact with the second electrical contact points β of the electrical contact  72 , being thereby elastically deformed. 
   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  of the tray  35 . The apparatus main assembly is structured so that the electrical connection between the electrical contacts of the cartridges and corresponding electrical contacts of the apparatus main assembly can be broken by moving upward (raising) the tray  35  from the preset position (image formation position) by the holding members  34 L and  34 R, or can be established by moving downward (lowering) the tray  35  toward its image formation position by the holding members  34 L and  34 R. 
   In this embodiment, the apparatus main assembly has: an electrical contact c for supplying the charge roller  2  with the charge bias for charging the drum  1 ; an electrical contact a for supplying the development roller  3   a  with the development bias for developing the electrostatic latent image formed on the drum  1 ; an electrical contact d for supplying the developer supply member (unshown) with the supply bias; and an electrical contact b for supplying the developer regulating member (unshown) with regulation bias. The cartridge has: the electrical contact c which contacts the charge bias contact c of the apparatus main assembly; an electrical contact a which contacts the development bias contact a of the apparatus main assembly; an electrical contact d which contacts the supply bias contact d of the apparatus main assembly; and an electrical contact b which contacts the electrical contact b of the apparatus main assembly. 
   Incidentally, the shape of the electrical contact  75 , shape of the electrical contact  72 , and the direction of the contact pressure in each electrical junction, do not need to be as shown in  FIGS. 21-23 . 
     FIGS. 21 and 23  show the method for supplying the set of electric power receiving contacts of each cartridge, with electric power, with the use of the single springy electrical contact of the apparatus main assembly, and the single springy intermediary electrical contact. However, the present invention is also useful even if each cartridge is provided with two or more portions through which it receives electric power. Further, the present invention is also useful even if the abovementioned two or more portions, through which each cartridge receives electric power, are different in position in terms of the vertical direction of the apparatus main assembly; the apparatus main assembly is provided with multiple springy electrical contacts, which are different in the position in terms of the vertical direction, and the tray  35  is provided with multiple grooves, which match the springy electrical contacts of the apparatus main assembly, in the position in terms of the vertical direction of the apparatus main assembly. 
   As described above, in this embodiment, the process cartridges are mounted in the movable member (tray) so that the process cartridge or process cartridges can be replaced from the front side of the apparatus main assembly. Further, the movable member is provided with the intermediary electrical contacts, and the electrical contact between each process cartridge and the apparatus main assembly is established or broken by the vertical movement of the movable member. Therefore, the image forming apparatus in this embodiment, which employs a cartridge drawer, which makes it easier to replace the cartridge or cartridges, is no higher in cost and no greater in main assembly size than an image forming apparatus in accordance with the prior art, which employs a cartridge drawer. 
   Also in this embodiment, the movable member is moved upward or downward by the movement of the member which exposes or covers the cartridge replacement opening of the apparatus main assembly. Therefore, the cartridge or cartridges can be replaced through a cartridge replacement sequence, which can be easily predictable by a user. 
   Also in this embodiment, multiple sets of electrical contacts are horizontally arranged in a straight line so that the corresponding electrical contacts in the multiple sets of electrical contacts are positioned at the same level. Therefore, the amount of space, which the apparatus main assembly in this embodiment requires for the electrical contacts in terms of the vertical direction is significantly smaller than that, which the apparatus main assembly in accordance with the prior art requires. Therefore, the image forming apparatus in this embodiment is substantially smaller in the size of the main assembly than an image forming apparatus in accordance with the prior art, which employs a cartridge drawer. 
   The tray  35  is movable in the direction intersectional (perpendicular) to the lengthwise direction of the electrophotographic photosensitive drum of each process cartridge, while holding multiple process cartridges. Further, it can moved into, or out of, the apparatus main assembly A, while holding multiple process cartridges. 
   Further, the electrical contacts  75  are positioned inside the apparatus main assembly A, and aligned along the path of the tray  35 . 
   Further, each electrical contact  75  is provided with the first and second electrical contact points α and β. The first and second electrical contact points α and β are attached to the tray  35 . The first electrical contact point α is positioned inside the tray  35 , whereas the second electrical contact point β is positioned outside the tray  35 . The first electrical contact point α makes electrical contact with the electrical contact  55  of the cartridge, and the second electrical contact point β makes electrical contact with the electrical contact  75 . 
   Further, the space  77  is provided between the tray  35  and electrical contacts  75  to prevent the tray  35  from coming into contact with the electrical contacts  75  with which the apparatus main assembly A is provided. In this embodiment, the space  77  is provided on the outward side of the frame section  35   d  (lateral plate) of the tray  35 , and faces the electrical contacts  75 . More concretely, the space  77  is provided by providing the outward side of the frame section  35   d  (lateral plate) of the tray  35  with a groove which extends in the direction parallel to the moving direction of the tray  35 . In this embodiment, the space  77 , or groove  77 , is in the bottom side of the path of the tray  35 . 
   The tray  35  is linearly moved into the apparatus main assembly A from outside, and then is moved diagonally downward. This downward movement of the tray  35  establishes electrical connection between the second electrical contact point β and electrical contact  75 . 
   Therefore, the structural arrangement, in this embodiment, for supplying the cartridges with power, ensures that the electrical contacts  55  of the cartridges make contact with the electrical contacts  75 , even through multiple cartridges are supported side by side in the tray  35  which is linearly movable relative to the apparatus main assembly A. 
   Incidentally, the second electrical contact point β is separated from the electrical contact  75  of the apparatus main assembly by the tray movement which occurs as the tray  35  is moved out of the apparatus main assembly A from the image formation position in the apparatus main assembly A, and which is opposite in direction from the above described inward tray movement. 
   Further, in the case of the structural arrangement, in this embodiment, for supplying the cartridges with power, as the tray  35  is moved into the apparatus main assembly A from outside, the tip γ (tip of one of straight end portions) of the electrical contact  75  ( a, b,  and  c ) enters the space  77  (groove). Then, while the tray  35  is moved diagonally downward after the abovementioned linear inward movement, the tip γ comes into contact, and remains in contact, with the second electrical contact point β (a, b, and c), which is in the top portion of the space  77  (groove) ( FIGS. 23(   a ) and  23 ( b )). 
   Further, the tip γ of the electrical contact  75 ( d ) is in the space  77 , which is in the bottom portion of the path of the tray  35 . Then, while the tray  35  is moved downward after its inward linear movement described above, the tip γ of comes into contact, and remains in contact, with the second electrical contact point β (d) (unshown), which is on the top surface (which is next to bottom surface of tray  35 ) of the space  77 . 
   Therefore, the structural arrangement, in this embodiment, for supplying the cartridges with power ensures that the electrical contacts  55  (a, b, c, and d) of the process cartridges smoothly come into contact with the electrical contacts  75  (a, b, c, and d) of the apparatus main assembly, respectively. 
   In the preferred embodiment of the present invention described above, the image forming apparatus was structured so that the tray  35  is linearly movable in the direction parallel to the surface on which the apparatus main assembly A is placed. However, the preferred embodiment is not intended to limit the present invention in scope. For example, the present invention is also applicable to an image forming apparatus structured so that the tray  35  is linearly moved out of the apparatus main assembly A in the diagonally upward direction, and is linearly moved into the apparatus main assembly A in the diagonally downward direction, or so that the tray  35  movable in the linearly moved out of the apparatus main assembly A in the diagonally downward direction, and is linearly moved into the apparatus main assembly A in the diagonally upward direction. Obviously, such an image forming apparatus has to be also structured so that the tray  35  is moved downward after being linearly moved into the apparatus main assembly. 
     FIGS. 9A-9D  show the structural features of an image forming apparatus, which characterize the present invention. 
   In this embodiment, the tray  35  is provided with an electrically conductive common member  78 , which is shared by the multiple cartridges in the tray  35 . The electrically conductive common member  78  is attached to the lengthwise end of the tray  35 , in terms of the lengthwise direction of the drum  1  in each of the cartridges held side by side in parallel in the tray  35 . The electrically conductive common member  78  is a long and narrow piece of electrically conductive metallic plate, and is attached to the end of the tray  35 , in terms of the direction perpendicular to the direction in which the tray  35  formed of an electrically nonconductive resin is movable. The electrically conductive common member  78  is attached to the abovementioned end of the tray  35  in such a manner that it straddles the top end (surface) of the abovementioned end of the tray  35 . In this embodiment, this electrically conductive common member  78 , or the log and narrow piece of metallic plate, is shaped like a channel iron having a U-shaped cross section, and is positioned so that its open side faces downward. It is attached to the top end of the left section  35   d  of the frame of the tray  35  in such a manner that it straddles the top end of the left section  35   d . The electrically conductive common member  78 , that is, the piece of metallic plate, in this embodiment is formed of galvanized sheet iron (SECC). 
   The tray  35  is an electrically nonconductive component, whereas the electrically conductive common member  78  is an electrically conductive component. Incidentally, the tray  35  may be made up of electrically conductive components. In the case in which the tray  35  is made up of electrically conductive components, the electrically conductive common member  78  and the other electrical contacts are to be attached to the tray  35  with the interposition of an electrically nonconductive member between the tray  35  and each of the electrically conductive members. 
   The tray  35  is provided with four cartridge supporting portions  35 Y,  35 M,  35 C, and  35 K, in which the first to fourth cartridge PY, PM, PC, and PK are supported. Further, the tray  35  is provided with four electrical contacts  72 , which are positioned so that they make electrical contact with the four electrical contacts  55 , one for one, which the first to fourth cartridges PY, PM, PC, and PK have one for one. Further, the electrical contacts  72  are electrically in connection to the electrically conductive common member  78 . 
   In order to supply each cartridge in the tray  35  with electric power at least when the tray  35  is in its image formation position, the apparatus main assembly A is provided with the electrical contact  75  (springy electrical contact), which remains in contact with the electrically conductive common member  78  when the tray  35  is in its image formation position. 
   Thus, when the cartridges PY, PM, PC, and PK are in their image formation positions in the apparatus main assembly A, electric power is supplied to the processing means of each cartridge from the apparatus main assembly A, through the electrical contact  75  of the apparatus main assembly A, the electrically conductive common member  78  of the tray  35 , and the electrical contacts of each cartridge. An example of the processing means of each cartridge, which receive electric power through the electrical contact  75  of the apparatus main assembly A, the electrically conductive common member  78  of the tray  35 , and the electrical contacts of each cartridge, is the charge roller  2  which charges the drum  1 . 
   The employment of the above described structural arrangement for supplying the cartridges with electric power makes it possible to reduce the number of electrical junctions between the cartridges and apparatus main assembly A, and therefore, it can ensure, without increasing component count, that the electrical contacts of each cartridge are connected to the electrical contacts of the apparatus main assembly A. 
   The electric power can also be supplied to the development roller  3   a , developer regulating member, developer supplying member, etc., with the use of electrical conductive common member similar to the above described electrically conductive common member  78 . 
   The electrical contacts  75  and electrically conductive common member  78  are connected or disconnected by the movement of the downward or upward movement of the electrically conductive common member  78 , which is caused by the downward or upward movement of the tray  35 . 
     FIG. 9D  shows the inward end portion of the left section  35   d  of the frame of the tray  35  when the tray  35  is in the image formation position, into which the tray  35  was lowered by the closing of the door  31 . When the tray  35  is in this position, the electrical contact  75  (springy electrical contact) is in contact with the electrically conductive common member  78 , which was moved down to the electrical contact  75 ; there is electrical connection between the two electrical contacts  75  and  78 . 
   That is, the contact between the electrically conductive common member  78  and electrical contact  75  occurs while the tray  35  is moved down into the image formation position after being linearly and horizontally moved into the apparatus main assembly A from outside the apparatus main assembly A. 
   As the door  31  is opened when the tray  35  is in the position shown in  FIG. 9D , the tray  35  is moved diagonally upward from the position shown in  FIG. 9D . This diagonally upward movement of the tray  35  moves the electrically conductive common member  78  upward, causing the electrically conductive common member  78  to separate from the electrical contact  75 , and therefore, breaking the electrical connection between the electrical contact  75  and electrically conductive common member  78 . 
   In the case of the above described structural arrangement in this embodiment, the electrical contacts  75 , that is, the electrical contacts of the apparatus main assembly, are solidly attached to the apparatus main assembly A, and the electrical connection between the electrical contacts  75  and the electrically conductive common member  78 , that is, the electrical contact on the tray  35 , is made by the diagonally downward movement of the tray  35 . However, the above described structural arrangement is not intended to limit the present invention in scope. That is, the present invention is also compatible with a structural arrangement which does not move the tray  35  downward. For example, the present invention is effectively applicable to an image forming apparatus structured so that the electrical contacts  75  are placed in contact with the electrically conductive common member  78  by being moved by the movement of members, such as the tray holding members  34 L and  34 R, which are moved by the movement of the door  31 . 
   As for the electrical disconnection between the electrical contacts  75  and electrically conductive common member  78 , it is achieved by moving the tray  35  diagonally upward from the image formation positions ( FIGS. 9C and 9D ). In this case, the electrically conductive common member  78 , that is, the electrical contact on the tray  35 , comes into contact with the ground contact  79  (grounding plate, discharging member, or the like), which is an electrically conductive member connected to the apparatus main assembly A before the tray  35  reaches its highest level ( FIG. 9B ). Therefore, the electric charge having accumulated in the electrically conductive common member  78  is released to the ground contact  79 . That is, while the tray  35  is moved, the ground contact  79  comes into contact with the electrically conductive common member  78 , that is, the electrical contact on the tray  35 , discharging the electric charge having accumulated in the electrical contacts of the cartridges. Designated by a referential number  82  is the portion of the apparatus main assembly A, to which the ground contact  79  is attached. 
   The ground contact  79  is electrically connected to the apparatus main assembly A to ground the electrically conductive common member  78 , and is positioned next to the path of tray  35 . 
   Regarding the contact between the electrically conductive common member  78  and electrical contact  75 , and the contact between the electrically conductive common member  78  and ground contact  79 , the electrical contact  75  comes into contact with the bottom side of the electrically conductive common member  78 , whereas the ground contact  79  comes into contact with the top side of the electrically conductive common member  78 . 
   The contact between the electrically conductive common member  78  and ground contact  79  occurs while the tray  35  is moved diagonally upward from its image formation position, whereas the separation of the electrically conductive common member  78  from the ground contact  79  occurs as the tray  35  is moved outward of the apparatus main assembly A. 
   Also regarding the contact between the electrically conductive common member  78  and electrical contact  75 , and the contact between the electrically conductive common member  78  and ground contact  79 , the leading end of the electrically conductive common member  78 , in terms of the moving direction of the tray  35 , comes into contact with the electrical contact  75  and ground contact  79  as the tray  35  is moved inward of the apparatus main assembly A from outside the apparatus main assembly A. 
   Also in the case of the above described structural arrangement in this embodiment, the ground contact  79  is solidly attached to the apparatus main assembly A, and the electrical connection between the ground contact  79  and the electrically conductive common member  78 , that is, the electrical contact on the tray  35 , is made by the diagonally upward movement of the tray  35 . However, the above described structural arrangement is not intended to limit the present invention in scope. That is, the present invention is also compatible with a structural arrangement which does not move the tray  35  upward. For example, the present invention is effectively applicable to an image forming apparatus structured so that the ground contact  79  is placed in contact with the electrically conductive common member  78  by being moved by the movement of members, such as the tray holding members  34 L and  34 R, which are moved by the movement of the door  31 . 
   As for the timing with which the ground contact  79  is disconnected from the electrically conductive common member  78 , the ground contact  79  is disconnected from the electrically conductive common member  78  after the high voltage applied to the electrical contacts  75  during image formation is cut off. As for the means for cutting off the high voltage, a structural arrangement may be made so that the electrical contact  75  can be physically separated from the electrically conductive common member  78 , or the apparatus main assembly A may be provided with an electrical switch interlocked with the door  31 , so that the high voltage is cut off by the opening movement of the door  31 . 
   The electrically conductive common member  78  is formed of a piece of metallic plate which is thick enough for the electrically conductive common member  78  to serve not only as an electrical contact, but also, as a member for reinforcing the tray  35 . Further, the electrically conductive common member  78  is given a U-shaped cross section so that it can serve as a member for reinforcing the tray  35 , in addition to functioning as an electrical contact. That is, the electrically conductive common member  78 , that is, the member formed of the abovementioned material and shaped as described above, is effective to reinforce the tray  35 , which is provided with a substantial number of holes for accommodating a substantial number of electrical contacts. 
   The employment of the electrically conductive common member  78  for supplying multiple cartridges with electric power can reduce the number of components necessary for applying biases to the multiple cartridges, provided that the multiple cartridges are the same in the bias applied thereto. Therefore, it can achieve cost reduction. It also can ensure, without increasing component count, that electrical connection is made between the electrical contacts of each cartridge and those of the apparatus main assembly A. 
   As described above, according to the present invention, multiple process cartridges are mounted in a movable member (tray) so that the cartridges can be replaced from the front side of an image forming apparatus. Further, the movable member is provided with the electrically conductive common member  78 , and the electrical contacts of the movable tray are organized so that those which are the same in the potential level of the electric power transmitted through them receive electric power (bias) from the apparatus main assembly A through a single point (of electrical contact of apparatus main assembly A). Therefore, an electrophotographic color image forming apparatus can be reduced in component count. Further, the movable member (tray) can be increased in the amount of strength necessary for the movable member to withstand the force to which it is subjected as it is moved outward or inward of the apparatus main assembly A. Thus, it is possible to provide an image forming apparatus having an easily movable cartridge holding member (tray) for making it easier to replace the cartridges. 
   Also according to the present invention, the movable member is moved upward or downward by the member of the apparatus main assembly, which exposes or covers the opening of the apparatus main assembly, which is for the movable member. Therefore, a cartridge or cartridges can be replaced by a user through an easily predictable operational sequence. 
   Further, multiple sets of electrical contacts are horizontally aligned so that an electrical contact in one set is positioned at the same level as the corresponding electrical contacts in the other sets. Therefore, the space which is required to accommodate the electrical contacts in terms of the vertical direction is substantially smaller than that which the prior art requires. In other words, the present invention can substantially reduce in size the main assembly of an image forming apparatus employing a movable cartridge holding member. 
   Also according the present invention, the tray  35  is provided with the electrically conductive common member  78  for distributing electric power to the cartridges in the tray  35 , and the number of electrical junctions between the electrically conductive common member  78  and the electrical contacts of the cartridges, is greater than the number of electrical junctions between the electrically conductive common member  78  and electrical contact  75 . Therefore, the number of the components necessary to apply biases to the multiple cartridges in the tray  35  is significantly smaller than that in accordance with the prior art, provided that the multiple cartridges are the same in the biases applied thereto. Therefore, the present invention can achieve cost reduction. In other words, the present invention can ensure, without increasing component count, that the electrical contacts of the cartridges are connected to the electrical contacts of the apparatus main assembly. 
   The contact between the electrically conductive common member  78  and electrical contact  75  occurs while the tray  35 , which is a movable member, is moved diagonally downward into the image formation position after being linearly moved into the apparatus main assembly A from outside the apparatus main assembly A. Therefore, when the tray  35  is horizontally moved, the electrically conductive common member  78  and electrical contact  75  do not rub against each other; the two are prevented from unnecessary rubbing against each other. Further, the mechanism for moving the electrical contact  75  between the position in which the electrical contact  75  is in contact with the electrically conductive common member  78 , and the position in which it is not in contact with the electrically conductive common member  78 , is unnecessary. 
   Incidentally, the ground contact  79  has to be away from the electrically conductive common member  78  while the image forming apparatus is forming an image. According to the present invention, however, the ground contact  79 , which is placed in contact with the apparatus main assembly A to ground the electrically conductive common member  78 , is positioned next to the path of the tray  35 . Therefore, the mechanism for placing the ground contact  79  in contact with the electrically conductive common member  78 , or separating the ground contact  79  from the electrically conductive common member  78  is unnecessary. In other words, the present invention can simplify in structure an image forming apparatus having a movable cartridge holding member. 
   If the ground contact  79  is in the path of the tray  35 , the ground contact  79  is repeatedly rubbed by the electrically conductive common member  78 . In order to prevent this problem, a mechanism is necessary for keeping the ground contact  79  outside the path of the tray  35  when the electrically conductive common member  78  does not need to be grounded. According to the present invention, however, an image forming apparatus having a movable cartridge holding member is structured so that the contact between the electrically conductive common member  78  and grounding contact  79  occurs while the tray  35  is moved diagonally upward from the image formation positions. Thus, not only can the present invention solve the problem described above, but also, it can simplify in structure an image forming apparatus having a cartridge holding movable member. 
   Further, in the preferred embodiment described above, the processing means which receives electric power from the apparatus main assembly A through the electrical contact  75 , electrically conductive common member  78 , and electrical contacts  72  is the charge roller for charging the electrophotographic photosensitive drum. To elaborate, the development biases applied to the development bias supplying rollers of the cartridge PY, PM, PC, and PK, one for one, must be set to be different in value because of the difference among the developers in the cartridges. However, the biases applied to the charge rollers of the cartridges PY, PM, PC, and PK are to be set by the relationship between the drum and charge roller, and therefore, may be the same in value. 
   Further, the electrically conductive common member  78  is formed of electrically conductive metallic plate, and the tray  35  is formed of an electrically nonconductive resin. The electrically conductive common member  78  is attached to one end of the tray  35  in terms of the direction perpendicular to the moving direction of the tray  35 . It is an ordinary practice to place interfacial electrical contacts on one side of the tray  35 , because such a practice requires only a single substrate. However, this practice tends to significantly weaken the tray on the side having the electrical contacts, because the tray has to accommodate multiple electrical contacts for each cartridge. Therefore, forming the electrically conductive common member  78  of metallic plate is effective to reinforce the portion of the tray  35 , which is to accommodate the multiple electrical contacts. In other words, in this embodiment, the electrically conductive common member  78 , that is, a piece of metallic plate, doubles as a member for reinforcing the tray  35 . That is, the piece of metallic plate prevents the tray  35  from unexpectedly deforming. 
   Further, the metallic plate  78  is given a U-shaped cross section, being thereby stiffened, and is attached to the tray  35  in a manner to straddle the top edge of the abovementioned section of the tray  35 . Therefore, the tray  35  is further increased in strength. 
   Further, regarding the contact between the electrically conductive common member  78  and electrical contact  75 , and the contact between the electrically conductive common member  78  and ground contact  79 , the leading end of the electrically conductive common member  78 , in terms of the inward movement of the tray  35  relative to the apparatus main assembly, comes into contact with the electrical contact  75  and ground contact  79  as the tray  35  is moved inward of the apparatus main assembly A from outside the apparatus main assembly A. Therefore, it does not occur that the electrically conductive common member  78  continuously rubs against the electrical contact  75  during the movement of the tray  35 . The longer or more frequent the rubbing of the electrically conductive common member  78  against the electrical contact  75 , the greater the amount by which they shave each other. In this embodiment, therefore, the amount by which they shave each other is reduced by making the two electrical contacts  78  and  75  make contact at the end of the inward movement of the tray  35 . Further, the electrically conductive common member  78  is grounded before the tray  35  is pulled out of the apparatus main assembly A (before the tray  35  is touched by a user). Further, the electrically conductive common member  78  comes into contact with the ground contact  79  by its top side. That is, the electric charge which the electrically conductive common member  78  has is removed by the diagonally upward movement of the tray  35 , which is caused by the opening movement of the door  31 . Therefore, more latitude is afforded regarding the positioning of the ground contact  79 . Further, the electrically conductive common member  78  is placed in contact with the electrical contact  75  by the diagonally downward movement of the tray  35 , that is, the tray movement for moving the cartridges into their image formation positions, which is caused by the closing movement of the door  31 . Therefore, more latitude is afforded regarding the positioning of the electrical contact  75 . 
   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. 122493/2007 filed May 7, 2007 which is hereby incorporated by reference.