Abstract:
An electrophotographic image forming apparatus includes an opening provided in a main assembly of the apparatus; an openable member movable between a close position for closing the opening and an open position for opening it; a drawer member for supporting an electrophotographic photosensitive drum, the drawer member being movable in a direction crossing with an axis of the drum through the opening between an inside position inside the main assembly and an outside position outside the main assembly where the cartridge can be mounted and dismounted; a transfer unit movable about a rotation axis disposed downstream of the drum with respect to a mounting direction of the drawer member from the outside position to the inside position, between a contacting position contacting the drum and a spaced position spacing from the drum in a state that the drawer member is in the inside position; and an interrelating member interrelating the openable member and the transfer unit with each other, wherein the interrelating member moves the transfer unit from the contacting position to the spaced position with movement of the openable member from the close position to the open position, and moves the transfer unit from the spaced position to the contacting position with movement of the openable member from the open position to the close position.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an electrophotographic image forming apparatus which forms an image on recording medium with the use of one or more process cartridges mounted removably in the main assembly of the apparatus. 
         [0002]    In this specification, an “electrophotographic image forming apparatus” means an apparatus which forms an image on recording medium with the use of an electrophotographic image formation process. Its examples include an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, etc.), a facsimile apparatus, a word processor etc. “Recording medium” means medium on which an image can be formed with the use of an electrophotographic image forming apparatus. It includes ordinary paper, OHP sheet, etc. 
         [0003]    Further, a “cartridge” means a process cartridge or a development cartridge. That is, it means a cartridge which contributes to a process for forming an image on recording medium by being removably mounted in the main assembly of an electrophotographic image forming apparatus. More specifically, it means a process cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. It comprises: an electrophotographic photosensitive member; at least one processing means among a charging means, a developing means, a cleaning means; and a cartridge in which the electrophotographic photosensitive member and processing means are integrally placed. In other words, a process cartridge includes a cartridge in which an electrophotographic photosensitive member is integrally placed along with at least one among a charging means, a developing means, or a cleaning means so that they can be removably mountable in the main assembly of an image forming apparatus. Incidentally, a process cartridge which has an electrophotographic photosensitive member and a developing means is referred to as a process cartridge of the integration type. Further, a process cartridge which has an electrophotographic photosensitive member and one or more processing means other than a developing means is referred to as a process cartridge of the separation type. 
         [0004]    A process cartridge is removably mountable in the main assembly of an image forming apparatus by a user himself or herself. Thus, a process cartridge makes it easier to maintain an image forming apparatus. Incidentally, processing means are means for processing an electrophotographic photosensitive member. 
         [0005]    Further, a development cartridge, which is a developing means, has a development roller. The development cartridge contains developer (toner) to be used by the development roller to develop an electrostatic latent image on an electrophotographic photosensitive member. It also is removably mountable in the main assembly of an electrophotographic image forming apparatus. In the case of an electrophotographic image forming apparatus which uses a development cartridge, its electrophotographic photosensitive member is a part of the main assembly of the image forming apparatus, or a part of a process cartridge of the so-called separation type (which does not have developing means). A development cartridge also can be removably mountable in the main assembly of an electrophotographic image forming apparatus by a user himself or herself. Thus, it also makes it easier to maintain an electrophotographic image forming apparatus. 
         [0006]    That is, a “cartridge” includes both a process cartridge of the so-called integration type and a process cartridge of the so-called separation type. It also includes a process cartridge which is employed in combination with a process cartridge of the so-called separation type by an electrophotographic image forming apparatus. Further, it includes a development cartridge which is removably mountable in the main assembly of an image forming apparatus whose electrophotographic photosensitive member is an integral part of the main assembly, to process the electrophotographic photosensitive member. The present invention relates to an electrophotographic image forming apparatus which forms images on recording medium, and in the main assembly of which cartridges are removably mountable. 
         [0007]    As one of the methods (systems) for replacing a cartridge in the main assembly of an electrophotographic image forming apparatus, the one disclosed in Japanese Laid-open Patent Application 2006-184553 has been known. According to this patent document, a development cartridge is supported by a development cartridge drawer (tray), and the cartridge is replaced after the drawer is pulled out by a preset distance from the main assembly of the image forming apparatus in the frontward direction. The cartridge drawer is supported by a pair of drawer guiding members which are attached to the front door of the apparatus main assembly so that when the door is in its closed position, the drawer guiding members hold the cartridge drawer in the preset position in the apparatus main assembly, whereas as the door is opened, the movement of the door moves the drawer guiding members into their turn-out position. That is, the problem that when the cartridge drawer is moved into its cartridge mounting-and-dismounting position, a development cartridge comes into contact and/or interferes with a charging apparatus, etc., is prevented by structuring an image forming apparatus in such a manner that the cartridge drawer has to be roughly horizontally moved into its cartridge mounting-and-dismounting position after the pair of drawer guiding members are moved into their turn-out position. 
         [0008]    According to the prior art described above, in order to prevent the problem that as the cartridge drawer is pulled out of the apparatus main assembly, the cartridge in the cartridge drawer comes into contact with, interferes with, and/or rubs against the mechanical components, mechanical apparatuses, etc., of the apparatus main assembly, the apparatus main assembly is structured so that the cartridge drawer has to be moved into its turn-out position before it can be pulled out of the apparatus main assembly. That is, the apparatus main assembly is structured so that the cartridge drawer, which is relatively heavy because of the weight of the cartridge(s) it is holding, is vertically moved. Thus, the prior art described above is desired to be improved in terms of the operational efficiency of an image forming apparatus. Accordingly, the present invention is one of the further developments of the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    Thus, the primary object of the present invention is to provide an electrophotographic image forming apparatus characterized in that when its cartridge drawer is moved, the cartridge drawer and/or the cartridges in the cartridge drawer do not come into contact with, interfere with, and/or rub the components, mechanism, etc. of the apparatus main assembly, and that it is substantially better in terms of the operability of the cartridge drawer than any of the electrophotographic image forming apparatuses in accordance with the prior arts, which is similar in structure to the electrophotographic image forming apparatus in accordance with the present invention. Another object of the present invention is to provide an electrophotographic image forming apparatus which is simpler in structure and less in weight than any of the electrophotographic image forming apparatuses in accordance with the prior arts which are similar in structure to the electrophotographic image forming apparatus in accordance with the present invention. 
         [0010]    According to an aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, comprising an opening provided in a main assembly of the apparatus of the electrophotographic image forming apparatus; an openable member movable between a close position for closing said opening and an open position for opening said opening; a drawer member for supporting an electrophotographic photosensitive member, said drawer member being movable in a direction crossing with a longitudinal direction of the electrophotographic photosensitive member through said opening between an inside position inside the main assembly of the apparatus and an outside position outside said main assembly of the apparatus where said cartridge can be mounted and dismounted; a transfer unit movable about a rotation axis disposed downstream of said electrophotographic photosensitive member with respect to a mounting direction of said drawer member from the outside position to the inside position, between a contacting position contacting said electrophotographic photosensitive member and a spaced position spacing from said electrophotographic photosensitive member in a state that said drawer member is in the inside position; and an interrelating member interrelating said openable member and said transfer unit with each other, wherein said interrelating member moves said transfer unit from the contacting position to the spaced position with movement of said openable member from the close position to the open position, and moves said transfer unit from the spaced position to the contacting position with movement of said openable member from the open position to the close position. 
         [0011]    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 
         [0012]      FIGS. 1(   a ) and  1 ( b ) are vertical sectional views of the electrophotographic image forming apparatus in the first preferred embodiment of the present invention, as seen from the right side of the apparatus when the door of the main assembly of the image forming apparatus is in its closed position. 
           [0013]      FIG. 2(   a ) is an enlarged sectional view of one of the cartridges in  FIG. 1A , and  FIG. 2(   b ) is an enlarged side view of one of the cartridges in  FIG. 1A . 
           [0014]      FIGS. 3A and 3B  are vertical sectional views of the electrophotographic image forming apparatus in the first preferred embodiment of the present invention, as seen from the right side of the apparatus when the door of the main assembly of the image forming apparatus is in its open position. 
           [0015]      FIGS. 4A and 4B  are vertical sectional views of the electrophotographic image forming apparatus in the first preferred embodiment of the present invention, as seen from the right side of the apparatus when the door of the main assembly of the image forming apparatus is in its outermost position. 
           [0016]      FIGS. 5(   a ) and  5 ( b ) are enlarged vertical sectional views of a part of  FIG. 1A  and a part of  FIG. 1B , respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     General Structure of Electrophotographic Image Forming Apparatus 
       [0017]      FIG. 1A  is a vertical sectional view of the electrophotographic image forming apparatus  100  in this embodiment, as seen from the right-hand side of the apparatus, and  FIG. 1B  is a vertical sectional view of the same apparatus as the one in  FIG. 1A , at a sectional plane different from the one for  FIG. 1A , as seen from the right-hand side of the apparatus. This apparatus  100  is a laser beam printer based on four primary colors. It employs multiple (four) process cartridges  50  ( 50   y ,  50   m ,  50   c  and  50   k ) which are removably mountable in the main assembly  100 A of the apparatus  100 . It can form full-color images on a sheet P of recording medium with the use of an electrophotographic process. That is, it is an electrophotographic color image forming apparatus which can form full-color or monochromatic images on the sheet P of recording medium, based on the information (which is in the form of electrical signals) of an image to be formed, which is inputted into the control circuit portion  200  of the apparatus main assembly  100 A from an external host apparatus  300 , such as a personal computer, an image reader, a facsimile, and the like. The surface G of a printer table, a desk, a floor, etc., on which the apparatus  100  is placed is roughly horizontal. 
         [0018]    In the following descriptions of the preferred embodiments of the present invention, the “front” side of the apparatus  100  means the side where the door  15  (cartridge replacement door) is present. The “rear” side of the apparatus  100  means the opposite side of the apparatus  100  from the “front” side. The “frontward” direction means the rear-to-front direction, and the “rearward” direction means the opposite direction from the “frontward” direction. The “left and right” sides of the apparatus  100  mean the left and right sides of the apparatus  100  as seen from the “front” side of the apparatus  100 . The “left and right” mean the left and right, respectively, as seen from the “front” side of the apparatus  100 . The “upward and downward” directions of the apparatus  100  are the upward and downward directions, respectively, with reference to the direction of gravity. Further, the apparatus main assembly  100 A (which may be referred to simply as “main assembly A”) means the entirety of the image forming apparatus minus the cartridges  50 . 
         [0019]    After the proper installation of four cartridges  50 , that is, the first to fourth cartridges  50 ( 50   y ,  50   m ,  50   c , and  50   k ) in the main assembly  100 A of the image forming apparatus  100 , the first to fourth cartridges  50  are roughly horizontal, and are in alignment in parallel in the left-to-right direction. That is, the apparatus  100  is of the so-called inline or tandem type; it has multiple (four) image formation stations, which are for forming multicolor or full-color images with the use of electrophotographic technologies and are roughly in an sequential alignment. In this embodiment, the cartridges  50  are of the so-called integration type. They are the same in structure, and are different only in the color of the developer (toner) therein.  FIG. 2(   a ) is an enlarged view of one of the cartridges  50  in  FIG. 1A .  FIG. 2(   b ) is a right side view of the cartridge  50 . Each cartridge  50  has: an electrophotographic photosensitive drum  1  (which hereafter may be referred to simply as drum  1 ) which is rotatable image bearing member; and three means for processing the drum  1 , that is, a charging means  2 , a developing means  4 , and a cleaning apparatus  6 . These components of the cartridge  50  are attached to the cartridge frame  51 . They are integral with each other, and are preset in positional relationship among them, and also, relative to the cartridge frame  51 . 
         [0020]    The charging apparatus  2  is a means for uniformly charging the peripheral surface of the drum  1  to preset polarity and potential level. The charging apparatus  2  in this embodiment is in the form of a roller (charge roller). The developing apparatus  4  is a developing means for developing the latent image on the drum  1  with the use of developer t (toner). The developing apparatus  4  in this embodiment has: a development roller  4   a ; a development roller coating roller  4   b  which coats (supplies) the development roller  4   a  with the developer t; a developer container  4   c  in which the developer t is stored; a rotational developer stirring member  4   d ; etc. The development roller  4   a  is the developer bearing member for supplying the drum  1  with the developer t. The developer container  4   c  is the developer storing portion in which the developer t, which is to be used for developing the latent image, is stored. The cleaning apparatus  6  is a cleaning means for removing the developer remaining on the peripheral surface of the drum  1  after the transfer (first transfer) of the toner image from the drum  1 . The cleaning apparatus  6  in this embodiment is in the form of a blade. Stored in the first cartridge, that is, cartridge  50   y , is the developer t of yellow (y) color. Stored in the second cartridge, that is, cartridge  50   m , is the developer t of magenta (m) color. Stored in the third cartridge, that is, cartridge  50   c , is the developer t of cyan (c) color. Stored in the fourth cartridge, that is, the cartridge  50   k , is the developer t of black (k) color. 
         [0021]    The apparatus main assembly  100 A is provided with a laser scanner unit  3  as a drum exposing apparatus, which is under the space for the group of the cartridges  50  in the apparatus main assembly  100 A. The unit  3  scans (exposes) the downwardly facing portion of the peripheral surface of the drum  1  in each cartridge  50 , with a beam L of laser light (exposure beam). More specifically, the cartridges  50  are held by a cartridge drawer  60  of the apparatus main assembly  100 A. The bottom plate of the cartridge drawer  60  has four holes  60   a  (windows), which correspond one for one to the four cartridges  50  in the cartridge drawer  60 . The beam L of laser light outputted upward from the unit  3  enters the corresponding cartridge  50  through the corresponding hole  60   a  (window) mentioned above, and the opening  50   a  of the bottom wall of the cartridge  50 , and reaches the downwardly facing portion of the peripheral surface of the drum  1  through the gap between the charging apparatus  2  and developing apparatus  4 , forming thereby an electrostatic latent image line by line on the portion of the peripheral surface of the drum  1 , which has just been charged by the charge roller  2 . Then, the electrostatic latent image on the peripheral surface of the drum  1  is developed by the developing apparatus  4 , into a visible image, that is, an image formed of developer (toner); a visible image is formed of the developer on the peripheral surface of the drum  1 . 
         [0022]    The apparatus main assembly  100 A is provided with a transfer unit  5 , which is in the top portion of the main assembly  100 A and is above the space for the cartridges  50  ( 50   y ,  50   m ,  50   c  and  50   k ). The unit  5  has a frame  5   f , belt suspending first and second rollers  70  and  71 , a tension roller  72 , and four (first to fourth) first transfer rollers  73  ( 73   y ,  73   m ,  73   c  and  73   k ). The frame  5   f  is rectangular, and its lengthwise direction is parallel to the front-to-rear direction of the main assembly  100 A. The first and second belt suspending rollers  70  and  71  are rotatable, and are in the rear and front portions of the frame  5   f , being parallel to each other. Their axial lines are parallel to the left-to-right direction of the apparatus main assembly  100 A. The tension roller  72  and the first to fourth first transfer rollers  73  are between the two rollers  70  and  71 . The unit  5  has also an intermediary transfer belt  5   a  (endless belt), which is dielectric and flexible. The belt  5   a  is stretched around the abovementioned rollers  70 ,  71 ,  72  and  73 , being thereby kept stretched. The intermediary transfer belt  5   a  is in contact with the upwardly facing portion of the peripheral surface of the drum  1  in each cartridge  50 , by its downwardly facing portion of outward surface in terms of the loop which the belt  5   a  forms. Each roller  73  remains pressed against the top portion of the peripheral surface of the corresponding drum  1  with the presence of the belt  5   a  between the roller  73  and drum  1 . The area of contact between the drum  1  of each cartridge and the belt  5   a  is the first transfer nip T 1 . The roller  71  is kept pressed upon a second transfer roller  16  with the presence of the belt  5   a  between the two rollers  71  and  16 . The area of contact between the roller  16  and belt  5   a  is the second transfer nip T 2 . 
         [0023]    The frame  5   f  of the unit  5  is supported by the apparatus main assembly  100 A at its rear end in such a manner that it is rotatable about a shaft  5   p  by which the frame  5   f  is rotationally supported. That is, the frame  5   f  (unit  5 ) is rotationally movable about the frame supporting shaft  5   p  so that the front end of the frame  5   f  moves upward or downward. The transfer unit supporting shaft  5   p , about which the transfer unit  5  is rotationally movable, is positioned so that when the cartridge drawer  60  is holding the four cartridges  50  and is in its image formation position, the shaft  5   p  will be on the downstream side of the drum  1  of the most downstream cartridge  50 , that is, the cartridge  50   y , in the cartridge drawer  60 , in terms of the direction (indicated by arrow mark IN in  FIGS. 4A and 4B ) in which the cartridge drawer  60  is moved into the apparatus main assembly  100 A. Thus, the unit  5  is rotationally movable about the transfer unit supporting shaft  5   p  in such a manner that its front end moves upward or downward. When the door  15  is in its closed position C, the unit  5  is in its contact position E, in which it is in contact with the cartridges  50 , as will be described later. The contact position E of the unit  5  is the position in which the unit  5  keeps the belt  5   a  is in contact with the drums  1 . When the door  15  is in its open position D ( FIG. 3A ), the unit  5  is in its separation position F in which it remains separated from the cartridge  50 . The separative position F of the unit  5  is the position in which the unit  5  keeps the belt  5   a  separated from the drums  1 . Thus, by rotationally moving the unit  5  about its transfer unit supporting shaft  5   p , it is possible to prevent any of the cartridge  50  in the cartridge drawer  60  from coming into contact with the intermediary transfer belt  5   a  when the drawer  60  is moved back into the apparatus main assembly  100 A. In other words, this structural arrangement can minimize the space necessary to move the transfer unit  5  to move the cartridge drawer  60  relative to the apparatus main assembly  100 A, making it therefore possible to provide an image forming apparatus which is smaller in size than any of the image forming apparatuses in accordance with the prior arts. 
         [0024]    Further, the apparatus main assembly  100 A has a fixing apparatus  12 , which is in the front side of the top portion of the apparatus main assembly  100 A. It has also a delivery tray  14 , which is a part of the top wall of the apparatus main assembly  100 A. The fixing apparatus  12  in this embodiment has a fixation film unit  12   a  and a pressure roller  12   b . Further, the apparatus main assembly  100 A has a sheet feeder cassette  10 , which is below the unit  3 . The sheet feeder cassette  10  stores multiple sheets P of recording medium (which hereafter may be referred to simply as recording sheets P) in layers. 
         [0025]    The operation carried out by this image forming apparatus to form a full-color image is as follows. The drum  1  in each of the cartridge  50  begins to be rotated at a preset speed in the counterclockwise direction indicated by an arrow mark, in response to an image formation start signal. At the same time, the development roller  4   a , development roller coating roller  4   b , etc., of each developing apparatus  4  begin to be rotated at preset speeds, respectively, in the direction indicated by arrow marks. Further, the belt  5   a  begins to be circularly moved by the roller  71  (as belt driving roller) at a preset speed which corresponds to that of the drum  1 , in the clockwise direction (which is the same as that of drum  1 ) indicated by an arrow mark. Further, the unit  3  also begins to be driven. Then, the roller  2  uniformly charges the peripheral surface of the drum  1  to preset polarity and potential level in each cartridge  50 . The unit  3  scans (exposes) the uniformly charged portion of the peripheral surface of the drum  1 , with preset timing, with the beam L of laser light which it outputs while modulating the beam L in response to image formation signals for the formation of each of the four monochromatic images which are different in color. Thus, an electrostatic latent image which reflects the image signals for the formation of a monochromatic image of one of the primary colors, is formed on the peripheral surface of the drum  1  in each cartridge  50 . Then, the electrostatic latent image in each cartridge  50  is developed by the developing apparatus  4  into an image formed of developer (which hereafter may be referred to as developer image or toner image). In other words, developer images of y, m, c and k colors, which correspond to the four primary colors into which the full-color image to be formed was separated, are formed on the drums  1  in the cartridges  50   y ,  50   m ,  50   c  and  50   k , respectively, with preset control timing. Then, the developer image in each cartridge  50  is electrostatically transferred (first transfer) onto the belt  5   a , which is being circularly moved, in the corresponding transfer nip T 1 . In other words, the four monochromatic developer images, different in color, are sequentially transferred in layers onto the belt  5   a . Thus, an unfixed full-color developer image is effected of the four monochromatic developer images of y, m, c and k colors, one for one, on the belt  5   a . The transfer residual toner, that is, the toner remaining on the peripheral surface of the drum  1  in each cartridge  50  after the transfer (first transfer) of the developer image onto the belt  5   a  is removed by the apparatus  6 . Then, the portion of the peripheral surface of the drum  1 , from which the transfer residual toner has been removed, is used again for image formation. 
         [0026]    Meanwhile, a feed roller  11  begins to be driven with preset control timing, whereby one of the recording sheets P in the cassette  10  is fed into the apparatus main assembly  100 A while being separated from the rest. Then, the recording sheet P is conveyed upward through a vertical recording sheet conveyance passage Z, which is in the front portion of the apparatus main assembly  100 A. Then, the recording sheet P is introduced into, and conveyed through, the transfer nip T 2  (for second transfer). While the recording sheet P is conveyed through the second transfer nip T 2 , the layered four monochromatic developer images, different in color, on the belt  5   a  are electrostatically transferred together (second transfer) onto the recording sheet P, starting from the leading edge of the full-color image. Then, the recording sheet P is separated from the belt  5   a , introduced into the apparatus  12 , and subjected to heat and pressure in the fixation nip of the apparatus  12 . Thus, the layered four monochromatic images, different in color, on the recording sheet P are mixed, and fixed to the recording sheet P. Then, the recording sheet P is discharged as a full-color copy of the original, into the tray  14  through the recording sheet outlet  13  of the apparatus  12 . The toner remaining on the surface of the belt  5   a  after the separation of the recording sheet P from the belt  5   a  is electrostatically adhered to the peripheral surface of the drum  1  of the first cartridge  50   y , for example, in the corresponding first transfer nip T 1 , and is removed by the apparatus  6  of the first cartridge  50   y.    
       (Method for Replacing Cartridges) 
       [0027]    As each cartridge  50  is used for image formation, the developer t in the developer container  4   c  of the cartridge  50  is consumed. Eventually, the developer t in the container  4   c  is consumed to such an extent that it becomes impossible for the cartridge  50  to form images satisfactory to the user who purchased the cartridge  50 . At this point, the cartridge  50  loses its commercial value as a cartridge. Thus, a cartridge  50  is provided with a means for detecting the remaining amount of developer in the cartridge  50 . The remaining amount of developer in the cartridge is compared by the control circuit  200  of the apparatus main assembly  100 A, with the threshold value set for informing a user of the predicted remaining amount of service life of the cartridge and/or warning the user of the imminent ending of the service life of the cartridge. If it is determined by the control circuit portion  200  that any of the cartridges  50  is no more in the residual amount of developer therein than the preset threshold value, a warning regarding the residual service life of the cartridge is outputted on a display (unshown), suggesting thereby the user to prepare a replacement cartridge for the cartridge, or to replace the cartridge, in order to prevent the image forming apparatus from falling below a preset level in terms of image quality. The procedure to be carried out by the user of the apparatus  100  in this embodiment to replace a cartridge or cartridges in the apparatus main assembly  100 A is as follows. In order to make it easier for a user to replace the cartridge(s) in the image forming apparatus  100  in this embodiment, the apparatus  100  is structured so that the cartridges are mounted in the cartridge drawer  60  (cartridge supporting member or cartridge tray, which hereafter will be referred to simply as tray  60 ) of the apparatus main assembly  100 A), which can be pulled out of the apparatus main assembly  100 A virtually in entirety in the frontward direction. Therefore, the used is allowed to replace the cartridge(s)  50  from the front side of the apparatus main assembly  100 A (so-called front access). 
         [0028]    The front wall of the apparatus main assembly  100 A is provided with an opening  101 , through which the cartridges  50  are put through to be inserted into, or removed from, the apparatus main assembly  100 A. The front wall of the apparatus main assembly  100 A is also provided with a door  15 , which can be rotationally moved between its closed position and open position. When the door  15  is in the closed position, it keeps the opening  101  covered, whereas when it is in the open position, it keeps the opening  101  exposed. Referring to  FIGS. 1(   b ),  3 ( a ) and  3 ( b ), the door  15  is rotationally movable relative to the apparatus main assembly  100 A about the horizontal shaft  15   p  (hinge shaft: second rotation axle), which is at the bottom edge of the door  15 . Thus, when the door  15  is in its open position, it can be rotationally moved upward about the shaft  15   p  so that it is moved into its closed position C in which it keeps the opening  101  of the apparatus main assembly  100 A covered as shown in  FIGS. 1(   a ) and  1 ( b ). That is, as the door  15  is closed, the opening  101  is covered by the door  15 . Further, when the door  15  is in its closed position, it can be rotationally moved frontward of the apparatus main assembly  100 A about the shaft  15   p , into its open position D, as shown in  FIGS. 3(   a ) and  3 ( b ). That is, as the door  15  is opened, the opening  101  becomes exposed. The door  15  is provided with a pair of recording medium guiding ribs  15   a , which are on the inward surface of the door  15  and are the parts of the abovementioned vertical recording sheet passage Z. Further, the abovementioned second transfer roller  16  also is attached to the inward side of the door  15 . Thus, as the door  15  is opened or closed, the second transfer roller  16  moves out of, or into, the apparatus main assembly  100 A, respectively. 
         [0029]    The tray  60  is roughly in the form of a rectangular box, and its lengthwise direction is parallel to the front-to-rear direction of the apparatus  100 . It is provided with a pair of long and narrow portions  60   b  (by which tray  60  is guided), which are parts the left and right walls (long walls) of the tray  60 , one for one and extend in the front-to-rear direction. The pair of tray guiding portions  60   b  are symmetrically positioned with reference to the centerline of the tray  60  in terms of the widthwise direction of the tray  60 . Correspondingly, the left and right walls of the main frame of the main assembly  100 A are provided with the pair of tray guiding portions  103  ( 103 L and  103 R), which are on the inward side of the walls, one for one. The pair of the tray guiding portions  103  extend in the front-to-rear direction, and are symmetrically positioned with reference to the centerline between the two guiding portions  103 L and  103 R in terms of the widthwise direction of the apparatus main assembly  100 A. The above described pair of tray guiding portions  60   b  and the pair of tray guiding portions  103  engage with each other. The tray guiding portions  60   b  are in the form of a groove, whereas the tray guiding portions  101  are in the form of a rib, which fits in the tray guiding portion  60   b . Thus, the tray  60  is held between the left and right walls L and R, respectively, of the main frame of the apparatus main assembly  100 A by the engagement between the pair of tray guiding portions  60   b  and the pair of tray guiding portions  102 , being thereby enabled to roughly horizontally slide in the front-to-rear (rear-to-front) direction. Thus, when the door  15  is open as shown in  FIGS. 3A and 3B , the tray  60  is movable through the opening  101 , between its innermost position A, which is inside the apparatus main assembly  100 A, and its outermost position, which is outside the apparatus main assembly  100 A as shown in  FIGS. 4A and 4B . 
         [0030]    The tray  60  is capable of holding multiple (four in this embodiment) cartridges  50  ( 50   y ,  50   m ,  50   c  and  50   k ) in such a manner that the cartridges align in parallel, in the direction parallel to the moving direction of the tray  60 . More specifically, the tray  60  has four cartridge chambers (cartridge holding portions) created by partitioning the internal space of the tray  60  with partitioning walls, in the front-to-rear direction, to hold the four cartridges  50  ( 50   y ,  50   m ,  50   c  and  50   k ) one for one. Each cartridge  50  is supported by the tray  60  in such a manner that the lengthwise direction (axial line of drum  1 ) of the cartridge  50  in one of the abovementioned cartridge holding portions becomes parallel to the left-and-right direction. The tray  60  is linearly movable in the direction perpendicular to the lengthwise direction of the cartridge  50  in the tray  60 . The innermost position A of the tray  60  is where the tray  60  keeps the cartridge  50  positioned for image formation, whereas the outermost position B of the tray  60  is where the tray  60  allows the cartridge  50  to be moved into, or out of, the tray  60  by a user. 
         [0031]    When the door  15  is in its closed position C as shown in  FIG. 1 , the tray  60  is kept stationary in its preset innermost position A in the apparatus main assembly  100 A by a tray positioning-and-holding means (unshown). Further, each of the cartridges  50  in the tray  60  is kept immovable in its image forming position by a cartridge positioning-and-holding means (unshown), and the driving force input portion of each cartridge  50  (unshown coupling) is in engagement with the driving force output portion (unshown cartridge drive coupling) of the apparatus main assembly  100 A, making it possible for the driving force from the cartridge driving motor (unshown) of the apparatus main assembly  100 A to be transmitted to the cartridge  50 . Further, the electric power input portion of each cartridge  50  is electrically in contact with the electric power output portion of the apparatus main assembly  100 A, making it possible for the preset biases (charge bias, development bias, etc.) to be applied to each cartridge  50  from the electric power source (unshown) of the apparatus main assembly  100 A. Further, the transfer unit  5  is kept in its contact position E (transfer-possible position) in which it keeps the belt  5   a  in contact with the top portion of the peripheral surface of the drum  1  in each cartridge  50 . It is when the apparatus  100  is in the above described state that the apparatus  100  is ready for image formation. 
         [0032]    As the door  15  is opened, that is, as the door  15  is moved from its closed position C shown in  FIGS. 3A and 3B  to its open position D shown in  FIGS. 3A and 3B , the unit  5  is swung about the shaft  5   p  by the movement of a pair of linkage arms  80  ( 80 L and  80 R) which are moved by the movement of the door  15 , as will be described later. Thus, the unit  5  is moved from the abovementioned contact position E to the separation position F in which the unit  5  keeps the belt  5   a  separated from the top portion of the peripheral surface of the drum  1  in each cartridge  50 . Further, the driving force input portion and electric power input portion of each cartridge  50  are disengaged from the driving force output portion and electric power output portion of the apparatus main assembly  100 A, respectively. Then, a user is to grasp the handle  60   a  on the front wall of the tray  60  through the exposed opening  101 , and pull the handle  60   a  to move the tray  60  out of the apparatus main assembly  100 A through the opening  101  until the tray  60  is stopped by a stopper (unshown), that is, until the tray  60  which was in the innermost position A in the apparatus main assembly  100 A, shown in  FIGS. 3A and 3B , is moved to the outermost position B which is outside the apparatus main assembly  100 A, shown in  FIGS. 4A and 4B . With the tray  60  being virtually entirely out of the apparatus main assembly  100 A, all the cartridge  50  in the tray  60  are out of the apparatus main assembly  100 A, being thereby fully exposed upward. 
         [0033]    While the tray  60  is pulled out of the apparatus main assembly  100 A, the unit  5  is its separation position F, and therefore, there is a gap between the belt  5   a  and the top portion of the peripheral surface of each drum  1 . Therefore, the drums  1  and belt  5   a  do not rub against each other. Further, even after the tray  60  is horizontally pulled out of the apparatus main assembly  100 A, to the outermost position B, it is kept stable in attitude by the engagement between the pair of tray guiding portions  60   a  of the tray  60 , and the pair of tray guiding portions  101  of the apparatus main assembly  100 A. When the tray  60  is in the outermost position B, each cartridge  50  in the tray  60  is being supported by the tray  60  in such a manner than it can be upwardly removed from the tray  60 . Incidentally, each cartridge  50  can be supported by the tray  60  by being vertically lowered into the tray  60 . The tray  60  supports each cartridge  50 , in one of its cartridge chambers, with the presence of a small amount of play between the cartridge  50  and the walls of the corresponding cartridge chamber. Because of this structural arrangement, the cartridges  50  in the tray  60  can be easily replaced. 
         [0034]    In the case of the apparatus  100  in this embodiment, the cartridge order in the tray  60  in terms of the direction in which the tray  60  is moved from the innermost position A to the outermost position B is such that the cartridge  50   y  is positioned most upstream; the second is the cartridge  50   m ; the third is the cartridge  50   c ; and the cartridge  50   k  is positioned most downstream. That is, the four cartridges  50   y ,  50   m ,  50   c  and  50   k  which contain the developers of y, m, c and k colors, respectively, are supported in the listed order. In other words, among the multiple (four) cartridges  50 , the cartridge  50   k , that is, the cartridge which contains the black developer is supported most downstream in terms of the direction in which the tray  60  is moved from the innermost position A to the outermost position B. The cartridge  50   k  is substantially greater in developer consumption than the other cartridges  50   y ,  50   m  and  50   k . Thus, it is highest in replacement frequency. In other words, the cartridge  50   k  is supported by the tray  60  so that the cartridge  50   k  is the frontmost cartridge in the apparatus main assembly  100 A (tray  60 ). Therefore, when it is only the cartridge  50   k  that is necessary to be replaced among all the cartridges  50  in the apparatus main assembly  100 A, the tray  60  has to be pulled out of the apparatus main assembly  100 A only by a short distance, that is, a distance large enough for only the cartridge  50   k  to be exposed from the apparatus main assembly  100 A. In other words, when only the cartridge  50   k  has to be replaced, the tray  60  does not need to be pulled out of the apparatus main assembly  100 A far enough to be stopped by the stopper. That is, this arrangement improved the apparatus  100  in the efficiency with which the cartridge  50   k  can be replaced. That is, when the cartridge  50   k , which is the most downstream cartridge in terms of the direction in which the tray  60  is pulled out of the apparatus main assembly  100 A, is only one that needs to be mounted into, or moved out of, the tray  60 , the tray  60  does not need to be in the outermost position B. Even in the case such as this, the tray  60  has to be on the outward side of the position in which the tray  60  has to be for image formation, and therefore, the cartridge  50   k  is on the front side of its image formation position, more specifically, on the front side of the front wall of the apparatus main assembly  100 A, making it easier for a user to replace the cartridge  50   k . To sum up, the tray  60  supports the multiple (four) cartridges  50  in such a manner that as the tray  60  is moved from the innermost position A to the outermost position B, the cartridges  50  can be sequentially removed from the tray  60 , starting from the most downstream one in terms of the moving direction of the tray  60 , and also, that as the tray  60  reaches the outermost position B, all of the multiple cartridges  50  can be removed from the tray  60 . Further, the tray  60  is horizontally movable, and supports the cartridges  50  in such a manner that when the tray  60  is in the outermost position B, the cartridges  50  can be vertically removed upward from the tray  60 , or mounted into the tray  60  by being vertically lowered into the tray  60 . 
         [0035]    After the tray  60  is pulled out to the outermost position B, and all the cartridges to be replaced are replaced, the tray  60  is to be pushed back into the apparatus main assembly  100 A until it reaches the innermost position A (FIG.  4 A→ FIG. 4B ). As the tray  60  is pushed almost all the way into the apparatus main assembly  100 A, the trailing end portion of the tray  60  is caught by the cartridge catching portion  104  (stopper) of the apparatus main assembly  100 A, being thereby prevented from being pushed further into the apparatus main assembly  100 A. While the tray  60  is pushed into the apparatus main assembly  100 A, the unit  5  remains held in its separation position F, and therefore, the belt  5   a  remains separated from the top portion of the peripheral surface of the drum  1  in each cartridge  50 , being thereby prevented from rubbing against the drums  1 . Then, the door  15  is to be closed (FIG.  2 → FIG. 1A ). As the door  15  is closed, the tray  60  is moved into its preset innermost position A by the tray positioning-and-holding means (unshown) and the movement of the door  15 , and is kept in the innermost position by the tray positioning-and-holding means. Further, each cartridge  50  in the tray  60  also is moved into its image formation position by the cartridge positioning-and-holding means (unshown), and remains held in the image formation position by the cartridge positioning-and-holding means. As each cartridge  50  is moved into the image formation position, the driving force input portion (unshown) of the cartridge  50  engages with the driving force output portion (unshown) of the apparatus main assembly  100 A. Further, the electric power input portion (unshown) of each cartridge is electrically engaged with the electric power output portion (unshown) of the apparatus main assembly  100 A. Further, the transfer unit  5  is rotationally moved downward about the shaft  5   p  by the movement of the pair of linkage arms  80  ( 80 L and  80 R), from its separation position F. Thus, the unit  5  is moved into its contact position E, causing the belt  5   a  to come into contact with the top portion of the peripheral surface of each cartridge P in a preset manner. Then, the unit  5  is kept in the contact position E, readying again the apparatus  100  for image formation. 
       (Linkage Between Door  15  and Transfer Unit  5 ) 
       [0036]      FIG. 5(   a ) is an enlarged view of a part of the  FIG. 1B , and  FIG. 5(   b ) is an enlarged view of a part of  FIG. 1B . The transfer unit  5  is above the space for the tray  60  and the cartridges  50  therein. It is attached to the apparatus main assembly  100 A by its rear end portion. More specifically, the rear end portion of the unit  5  is supported by the transfer unit supporting shaft  5   p , which is attached to the left wall  102  L and right wall  102 R (unshown) of the main frame of the apparatus main assembly  100 A so that the unit  5  is rotationally movable upward or downward about the shaft  5   p . The unit  5  is provided with a pair of first projections  5   q  (first connectors), which are on the front portion of the left wall of the transfer frame  5   f  and the front portion of the right wall of the transfer frame  5   f , one for one. The pair of first projections  5   q  are symmetrically positioned to each other with reference to the centerline of the unit  5  in terms of the left-and-right direction. Correspondingly, the door  15  is provided with a pair of second projections  15   q  (second connectors), which are on the left and right end of the bottom edge portion of the door  15 , one for one, being next to the horizontal shaft  15   p  (hinge shaft), about which the door  15  is rotationally movable to be opened or closed. The pair of second projections  15   q  are symmetrically positioned to each other with reference to the center line of the door  15  in terms of the left-and-right direction. Further, the left and right ends of the unit  5  are connected to the left and right ends, respectively, of the door  15  with the pair of linkage arms  80  ( 80 L and  80 R). More concretely, the pair of first projections  5   q  are in the pair of first holes  80   a  of the top end portion of the linkage arms  80 , one for one, whereas the pair of second projections  5   q  are in a pair of second holes  80   b  of the bottom end portions of the linkage arm  80 , one for one. Thus, the linkages arms  80  are allowed to rotate about the pair of projections  5   q  and  15   q  while remaining in engagement with the unit  5  and door  15 . 
         [0037]    That is, the left and right linkage arms  80  ( 80 L and  80 R) are the members which are in connection to the unit  5  and door  15  and cause the unit  5  to be moved by the movement of the door  15 . Referring to  FIG. 5(   a ), when the door  15  is in its closed position C, and the transfer unit  5  is in its contact position E, each second projection  15   q  is at roughly the same level as the shaft  15   q , and is on the inward side of the shaft  15   p  in the apparatus main assembly  100 A. Thus, as the door  15  is moved from the closed position C to the open position D, the second projection  15   q  moves upward while lifting linkage arm  80 . Thus, the unit  5  is rotationally moved upward about the shaft  5   p . That is, the unit  5  is moved upward from its contact position E. Then, as the door  15  is opened further, the second projection  15   q  is positioned above the shaft  15   p  by the movement of the door  15 . Eventually, the second projection  15   q  is moved past a hypothetical line H which connects the center (axial line) of the first projection  5   q  and the center (axial line) of the shaft  15   p , and then, toward the opening  101 . Then, as the point  15   b  of contact of the door  15  is caught by the stationary point  105  of contact  105  (door stopper) of the apparatus main assembly  100 A, the door  15  is prevented by the door stopper  105  from opening further, and remains in its open position D. During the opening of the door  15 , the unit  5  is lifted by the linkage arms  80  from its contact position E to its separation position F. Thus, by the time when the door  15  will be in its open position D, the second projection  15   q  will be on the door side (upstream side in terms of cartridge mounting direction) of the above-described hypothetical line H. Therefore, when the door  15  is in its open position D, the weight of the door  15  works in the direction to cause the door  15  to rotationally move about the shaft  15   p  in the direction in which the door  15  is opened, that is, the direction to keep the point  15   b  of contact of the door  15  pressed upon the point  105  of contact of the apparatus main assembly  100 A. Thus, the door  15  remains stable in its open position D, which in turn keeps the unit  5  stable in its separation position F ( FIG. 5(   b )). 
         [0038]    As the door  15  is closed, that is, as the door  15  is moved from its open position D to its closed position C, the point of contact  15   b  of the door  15  separates from the point of contact  105  of the apparatus main assembly  100 A, and the second projection  15   q  moves inward of the apparatus main assembly  100 A, beyond the hypothetical line H, that is, in the opposite direction (downstream in terms of cartridge mounting direction) from the opening  101 . Then, as the door  15  is closed further, the movement of the door  15  lowers the second projection  15   q  from its position above the shaft  15   p  to the position which is slightly lower than the position of the shaft  15   p , moving thereby the linkage arm  80  downward. Thus, the unit  5  is rotationally moved downward about the transfer unit supporting shaft  5   p  by the downward movement of the linkage shaft  80 . That is, the unit  5  is moved downward from its separation position F. Toward the end of the closing movement of the door  15  into its closed position C, the transfer unit  5  descends into the contact position E, and therefore, the second projection  15   q  descends so that it will be at roughly same level as the shaft  15   p  and will be inward of the shaft  15   p  in the apparatus main assembly  100 A. When the door  15  is in its closed position C, the second projection  15   q  is on the opposite side of the theoretical line H from the opening  101 . Therefore, the weight of the unit  5  works in the direction to rotationally move the door  15  in the closing direction about the shaft  15   p . Thus, the door  15  is kept stable in its closed position C, which in turn keeps the unit stable in its contact position E ( FIG. 5(   a )). 
         [0039]    In this embodiment, the linkage arm  80  is the member which connects the door  15  with the unit  5  and causes the unit  5  to be moved by the movement of the door  15 . That is, as the door  15  is moved from its closed position C to its open position D, the linkage arm  80  causes the unit  5  from its contact position E to its separation position F ( FIG. 5(   a )→ FIG. 5(   b )). Further, as the door  15  is moved from the open position D to the closed position C, the linkage arm  80  causes the unit  5  from the separation position F to the contact position E ( FIG. 5(   b )→ FIG. 5(   a )). 
         [0040]    In other words, the image forming apparatus  100  is structured so that the transfer unit  5 , which has to be in contact with the cartridges  50  in order for the apparatus  100  to form images is moved from the contact position E in which the unit  5  is in contact with the cartridges  50 , to the separation position F in which it remains separated from the cartridges  50 , or from the separation position F to the contact position E, by the opening and closing movement of the door  15 , as described above. Therefore, the components, mechanisms, and the like, which are dedicated to the operation for vertically moving the tray  60  to prevent the problem that when the tray  60  is moved from its innermost position A to its outermost position B, and vice versa, the tray  60  and/or the cartridges  50  in the tray  60  contact, interfere with, and/or rub against the components, mechanisms, etc., of the apparatus main assembly  100 A, are unnecessary. That is, the image forming apparatus  100  does not require its user to vertically move the tray  60 , which is relatively heavy because of the weight of the cartridges  50  it is holding. Therefore, it is superior to any of the image forming apparatuses in accordance with the prior arts, in terms of the operational efficiency of the tray  60 . Moreover, the tray guiding members  108  ( 103 L and  103 R) of the tray  60  do not need to be movable. Therefore, the guiding members  103  may be formed as integral parts of the side walls  102  ( 102 L and  102 R) of the main frame of the apparatus main assembly  100 A to provide an image forming apparatus which is simpler in structure and lighter than any of the image forming apparatuses in accordance with the prior arts. 
         [0041]    Further, the tray supporting shaft  5   p , about which the transfer unit  5  is rotationally movable, is on the downstream side of the drum  1  of the cartridge  50   y , which is the most downstream cartridge in the cartridge drawer  60  (tray  60 ) in terms of the direction (indicated by arrow mark IN in  FIGS. 4A and 4B ) in which the cartridge drawer  60  (tray  60 ) is moved back into the apparatus main assembly  100 A. Therefore, as the transfer unit  5  is rotationally moved about the shaft  5   p  by the opening movement of the door  15 , the drums  1  in all the cartridges  50  in the cartridge drawer  60  are prevented from coming into contact with the intermediary transfer belt  5   a  when the cartridge drawer  60  is put back into the apparatus main assembly  100 A. Thus, it is possible to minimize the space necessary for moving the transfer unit  5  in order to put the cartridge drawer  60  back into the apparatus main assembly  100 A, making it thereby possible to reduce the image forming apparatus  100  in size. 
       Miscellaneous Embodiments 
       [0042]    (1) In the first embodiment, the tray  60  was linearly movable in the direction parallel to the surface G on which the apparatus main assembly  100 A is placed. However, the direction in which the tray  60  is moved does not need to limited to the direction in the first embodiment. That is, the present invention is also compatible with an image forming apparatus structured so that the tray  60  is linearly movable at an angle relative to the surface G on which the apparatus main assembly  100 A is placed. 
         [0043]    (2) The present invention is compatible with an image forming apparatus structured so that the tray  60  is removable from the apparatus main assembly  100 A by disengaging the stopper from the tray  60 . 
         [0044]    (3) In the first embodiment, the “cartridge mounting-and-dismounting position” is where the tray  60  is when the cartridge(s)  50  are mounted into, or removed from, the tray  60 . In terms of the direction in which the tray  60  is pulled out of the apparatus main assembly  100 A, the “cartridge mounting-and-dismounting position” is on the downstream side of the image formation position A of each cartridge  50 . Further, the “cartridge mounting-and-dismounting position” is such a position that enables a user to remove the cartridge(s)  50  in the tray  60 , or mounting the cartridge(s)  50  into the tray  60 , without intruding into the apparatus main assembly  100 A. In other words, when the tray  60  is in the “cartridge mounting-and-dismounting position”, the tray  60  does not need to be entirely outside the apparatus main assembly  100 A. 
         [0045]    (4) In the first embodiment, the number of the cartridges  50  supportable by the tray  60  was four. However, it does not need to be four. That is, the present invention is also compatible with a tray  60  which can hold only a single cartridge  50 , only two cartridges  50 , only three cartridges  50 , or five or more cartridges  50 , as well as the tray  60  which holds only four cartridges  50 . Also in the first embodiment, the image forming apparatus was an electrophotographic color image forming apparatus. However, the present invention is also compatible with an electrophotographic monochromatic image forming apparatus which employs only a single cartridge. 
         [0046]    (5) The transfer unit  5  of the image forming apparatus in the first embodiment may be replaced with an apparatus which conveys the recording sheet P in such a manner that developer images are directly transferred onto the recording sheet P from the drums  1 . That is, the transfer unit  5  may be a transfer apparatus which comprises a recording medium conveyance belt (as recording medium conveying means) which conveys the recording sheet P to transfer the developer images formed on the drums  1 , directly onto the recording sheet P. 
         [0047]    (6) In the first embodiment, the cartridges  50  supported by the tray  60  were of the so-called integration type. However, the present invention is also compatible with an image forming apparatus which employs a pair or pairs of a process cartridge of the so-called separation type and a development cartridge, and which is structured so that at least the development cartridge(s) are removably supported by the tray  60 . Incidentally, the process cartridge of the separation type is such a cartridge that has the drum  1  and the processing means  2  and  6 , that is, the processing means other than the developing means  4 . The development cartridge is such a developing means that has a developer storage portion which stores the developer to be used for developing a latent image formed on the drum  1 , and the development roller which is a developer bearing member for supplying the drum with the developer. 
         [0048]    According to the present invention, in terms of the direction in which the cartridge drawer is put back into the apparatus main assembly, the rotational axis of the transfer unit is on the downstream side of the electrophotographic photosensitive drum. Therefore, it can minimize the space which an image forming apparatus requires to move its transfer unit, making it thereby possible to provide an image forming apparatus which is substantially smaller in size than any of the image forming apparatuses in accordance with the prior arts. 
         [0049]    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. 
         [0050]    This application claims priority from Japanese Patent Applications Nos. 281426/2009 and 253575/2010 filed Dec. 11, 2009 and Nov. 12, 2010, respectively, which are hereby incorporated by reference.