Abstract:
An image forming apparatus includes a cartridge supporting member movable between an inside position in a state of carrying a first cartridge and a second cartridge, and a drawn position in which said first cartridge and said second cartridge are mountable and demountable relative to said cartridge supporting member. The supporting member includes a first mounting portion for a first cartridge, and a second mounting portion for a second cartridge which is disposed upstream of said first mounting portion with respect to a supporting member drawing direction. A first guide portion for the first cartridge, and a second guide portion for said second cartridge, wherein a downward movement distance of said second cartridge when the cartridge is demounted from said second mounting portion is larger than that of said first cartridge.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an image forming apparatus which forms an image on recording medium, and in which multiple cartridges are removably installable in its main assembly. 
         [0002]    An image forming apparatus to which the present invention relates includes an apparatus which forms a color image on recording medium with the use of an electrophotographic image formation process, for example. Examples of an electrophotographic color image forming apparatus include an electrophotographic color copy machine, an electrophotographic color printer (color laser beam printer, color LED printer, etc., for example), a color facsimile machine, a color word processor, etc. 
         [0003]    “Recording medium” means medium on which an image is formed by an image forming apparatus. It includes paper, OHP sheet, and the like. 
         [0004]    A “cartridge” to which the present invention is related means a process cartridge or a development cartridge. It contributes to the process for forming an image on recording medium while remaining removably mounted in the main assembly of the image forming apparatus. Here, a “process cartridge” means a cartridge which integrally holds no less than one processing means among a charging means, a developing means, and a cleaning means, and an electrophotographic photosensitive drum, and is removably installable in the main assembly of an image forming apparatus. In other words, a “process cartridge” includes: a cartridge in which a developing means (processing means) and an electrophotographic photosensitive drum are integrally held, and which is removably installable in the main assembly of an image forming apparatus; a cartridge in which a charging means (processing means), a developing means (processing means) or cleaning means (processing means), and an electrophotographic photosensitive drum are integrally held, and which is removably installable in the main assembly of an image forming apparatus. Incidentally, a process cartridge in which an electrophotographic photosensitive drum and a developing means are held is referred to as a process cartridge of the integration type, whereas a process cartridge in which an electrophotographic drum and a process cartridge or process cartridges other than a developing means are integrally held is referred to as a process cartridge of the separation type. That is, a process cartridge which does not include a developing means, and therefore, has to be used in combination with a development unit (developing means cartridge) in order to form an image, is referred to as a process cartridge of the separation type. 
         [0005]    A process cartridge is removably installable in the main assembly of an image forming apparatus by a user himself or herself. Therefore, it can make it easier to maintain the main assembly of an image forming apparatus. “Processing means” is such means that processes an electrophotographic photosensitive drum. 
         [0006]    A development cartridge has a development roller. It contains developer (toner) which is used by the development roller to develop an electrostatic latent image formed on an electrophotographic photosensitive drum. It is removably installable in the main assembly of an image forming apparatus. In the case of an image forming apparatus which uses a development cartridge, its electrophotographic photosensitive drum is attached to the main assembly of the apparatus, or a process cartridge of the separation type (which does not have developing means). A development cartridge also can be removably installable in the main assembly of an image forming apparatus by a user himself or herself. Therefore, it can make it easier to maintain the main assembly of an image forming apparatus. 
         [0007]    That is, a “cartridge” includes both a cartridge of the integration type and a cartridge of the separation type. A process cartridge of the separation type is used in combination with a development cartridge. In the case of an image forming apparatus, the electrophotographic photosensitive drum of which is attached to its main assembly or cartridge supporting member (which will be described later), a development cartridge has to be removably installed in the main assembly of the image forming apparatus before it can be used for processing the electrophotographic photosensitive drum. Further, a “cartridge” related to the present invention includes such a developer cartridge that stores developer (toner) which is to be supplied to the aforementioned process cartridge or development cartridge. 
         [0008]    As described above, there has been known an electrophotographic image forming apparatus which forms an image on recording medium with the use of an electrophotographic image formation process. It has also been known that an electrophotographic image forming apparatus uses a process cartridge system, or a development cartridge system (which does not include photosensitive drum and has development unit). Further, it has been known that an electrophotographic image forming apparatus uses a developer cartridge system which stores developer. The process cartridge system, development cartridge system, and developer cartridge system together are referred to simply as “cartridge system”. The above-described process cartridge and development cartridge have a developer storage in which the developer (toner) for developing the above described electrostatic latent image is stored. 
         [0009]    On the other hand, in order to make it easier for a user to replace a cartridge in the main assembly of an image forming apparatus, some image forming apparatuses are provided with a cartridge drawer (cartridge supporting member) in which multiple cartridges are supportable. These image forming apparatuses are structured so that the drawer is movable between its preset position in their main assembly (inside position), and its preset position outside their main assembly (outside position). Thus, when it is necessary to replace any of the cartridges in the drawer, the drawer can be pulled out of their main assembly to the preset outside position where the cartridges can be replaced (Japanese Laid-open Patent Application 2007-213012). 
         [0010]    The above-described structural arrangement, however, suffers from the following technological problem. That is, even when the cartridge drawer is in the outside position (as far out of the main assembly of the image forming apparatus as possible), the cartridges in the upstream side of the drawer are close to the main assembly. Therefore, there is a substantial distance between these cartridges and a user, since the user has to replace the cartridges from the downstream end of the drawer. 
       SUMMARY OF THE INVENTION 
       [0011]    Thus, the primary object of the present invention is to provide an image forming apparatus which employs a cartridge drawer capable of holding multiple cartridges, and is significantly superior in operability in terms of the operation for installing a cartridge into the upstream side of the cartridge drawer, in terms of the direction in which the drawer is pulled out of the main assembly of the apparatus, or removing a cartridge from the upstream side of the cartridge drawer, than any image forming apparatus in accordance with the prior art. 
         [0012]    According to an aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording material, said image forming apparatus comprising a cartridge supporting member movable between an inside position in which said cartridge supporting member is inside a main assembly of said image forming apparatus in a state of carrying a first cartridge and a second cartridge, and a drawn position in which said cartridge supporting member is outside said main assembly of said apparatus and in which said first cartridge and said second cartridge are mountable and demountable relative to said cartridge supporting member, wherein said cartridge supporting member includes a first mounting portion to which said first cartridge is mountable, and a second mounting portion to which said second cartridge is mountable, said second mounting portion being disposed upstream of said first mounting portion with respect to a drawing direction in which said cartridge supporting member is moved from the inside position to the drawn position; a first guide portion, provided on said cartridge supporting member, for guiding mounting and demounting of said first cartridge relative to said first mounting portion; and a second guide portion, provided on said cartridge supporting member, for guiding mounting and demounting of said second cartridge relative to said second mounting portion, wherein a downward movement distance of said second cartridge when said second cartridge is demounted from said second mounting portion is larger than a downward movement distance of said first cartridge when said first cartridge is demounted from said first mounting portion. 
         [0013]    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 
         [0014]      FIG. 1  is an external perspective view of the image forming apparatus  100  in the first embodiment of the present invention. 
           [0015]      FIG. 2(   a ) is a vertical schematic sectional view of the image forming apparatus  100  at a vertical plane perpendicular to the front panel of the apparatus  100 , as seen from the right-hand side of the apparatus  100 . It shows the general structure of the apparatus  100 .  FIG. 2(   b ) is an enlargement of a part of  FIG. 2(   a ). 
           [0016]      FIG. 3  is a perspective view of the image forming apparatus  100 , the cartridge drawer of which is in its preset outside position. 
           [0017]      FIG. 4  is a schematic vertical sectional view of the image forming apparatus  100  at a vertical plane perpendicular to the front panel of the apparatus  100 , as seen from the right-hand side of the apparatus  100 , when the cartridge drawer of the apparatus  100  is in its preset outside position. 
           [0018]      FIGS. 5(   a ) and  5 ( b ) are perspective views of the cartridge drawer of the image forming apparatus  100 , as seen from the top-left and top-right sides, respectively, of the drawer. 
           [0019]      FIGS. 6(   a ) and  6 ( b ) are schematic vertical sectional views of the cartridge drawer in the first embodiment, at a vertical plane parallel to the moving direction of the drawer, as seen from the left and right sides, respectively of the apparatus  100 . 
           [0020]      FIG. 7  is an enlarged schematic sectional view of the frontmost cartridge slot, and its adjacencies, of the cartridge drawer in the first embodiment. 
           [0021]      FIGS. 8(   a ) and  8 ( b ) are perspective views of the cartridge Pk as seen from the top-left and top-right sides, respectively, of the cartridge Pk. 
           [0022]      FIGS. 9(   a ) and  9 ( b ) are perspective views of the cartridge Py as seen from the top-left and top-right sides, respectively, of the cartridge Py. 
           [0023]      FIG. 10  is a schematic vertical sectional view of the image forming apparatus  100 , at a plane parallel to the moving direction of its cartridge drawer, as seen from the right-hand side of the image forming apparatus  100 , when the drawer is in the preset outside position and the cartridges Pc and Py are being taken out of the drawer. 
           [0024]      FIG. 11  is an external perspective view of the image forming apparatus  200  in the second embodiment of the present invention. 
           [0025]      FIG. 12(   a ) is a vertical schematic sectional view of the image forming apparatus  200  at a vertical plane perpendicular to the front panel of the apparatus  200 , as seen from the right-hand side of the apparatus  200 . It shows the general structure of the apparatus  200 .  FIG. 2(   b ) is an enlargement of a part of  FIG. 12(   a ). 
           [0026]      FIG. 13  is a perspective view of the image forming apparatus  200 , the cartridge drawer of which is in its preset outside position. 
           [0027]      FIG. 14  is a schematic vertical sectional view of the image forming apparatus  200  at a vertical plane perpendicular to the front panel of the apparatus  100 , as seen from the right-hand side of the apparatus  200 , when the cartridge drawer of the apparatus  200  is in its preset outside position. 
           [0028]      FIGS. 15(   a ) and  15 ( b ) are perspective views of the cartridge drawer of the image forming apparatus  200 , as seen from the top-left and top-right sides, respectively, of the drawer. 
           [0029]      FIGS. 16(   a ) and  16 ( b ) are schematic vertical sectional views of the cartridge drawer in the second embodiment, at a vertical plane parallel to the moving direction of the drawer, as seen from the left and right sides, respectively of the apparatus  100 . 
           [0030]      FIG. 17  is an enlarged schematic sectional view of the frontmost cartridge slot, and its adjacencies, of the cartridge drawer in the second embodiment. 
           [0031]      FIG. 18  is perspective views of the cartridge Qy as seen from the top-left (a) and top-right (b) sides, respectively, of the cartridge Qy. 
           [0032]      FIGS. 19(   a ),  19 ( b ) and  19 ( c ) are schematic vertical sectional views of the image forming apparatus  200 , at a vertical plane parallel to the moving direction of the cartridge drawer of the image forming apparatus  200 , and shows the sequential steps for removing the cartridge Qk from the main assembly of the image forming apparatus  200 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Hereinafter, the embodiments of the present invention are described in detail with reference to the appended drawings. However, the measurement, material, and shape of the structural components in the following embodiments of the present invention, and the positional relationship among the structural components, are not intended to limit the present invention in scope in terms of these aspects of an image forming apparatus. 
       Embodiment 1 
       [0034]    (Overall Structure of Electrophotographic Color Image Forming Apparatus) 
         [0035]      FIG. 1  is an external perspective view of the image forming apparatus  100  (which hereafter may be referred to simply as image forming apparatus) in the first embodiment of the present invention. FIG.  2 ( a ) is a vertical schematic sectional view of the image forming apparatus  100  at a vertical plane perpendicular to the front panel of the apparatus  100 , as seen from the right-hand side of the apparatus  100 .  FIG. 2(   b ) is an enlargement of a part of  FIG. 2(   a ). The image forming apparatus  100  is a full-color laser printer based on four primary colors. It uses an electrophotographic process. It forms a full-color image on a sheet S of recording medium, based on the electrical image formation signals inputted from a host apparatus (unshown), such as a personal computer, an image reader, a facsimile machine (on transmitting side), etc. 
         [0036]    In the following description of the embodiments of the present invention, the front or front side of the image forming apparatus  100  is the side of the image forming apparatus  100 , which has a door  10  which covers the cartridge drawer. The rear side of the image forming apparatus  100  is the opposite side from the front side of the apparatus  100 . The front-to-rear direction means both the frontward and rearward directions. The left and right sides of the image forming apparatus  100  mean the left and right sides as seen from the front side of the apparatus  100 . The left-right direction means both the leftward and rightward directions. The main assembly  100 A of the image forming apparatus  100  means what remains after the removal of the cartridges from the image forming apparatus  100 . 
         [0037]    The image forming apparatus  100  in this embodiment is of the so-called horizontal tandem type. It employs four process cartridge P (Py, Pm, Pc and Pk) which form yellow (y), magenta (m), cyan (c) and black (k) developer (toner) images, respectively. The four process cartridges P are horizontally aligned in tandem. The image forming apparatus  100  is structured so that the multiple cartridges P are removably installable in its main assembly  100 A. It forms a color image on a sheet S of recording medium. 
         [0038]    More concretely, there are four process cartridges P (Py, Pm, Pc and Pk) in the apparatus main assembly  100 A. Listing from the rear side of the apparatus main assembly  100 A, the first to fourth process cartridges Py, Pm, Pc and Pk are roughly horizontally aligned. Each process cartridge P (which hereafter may be referred to simply as cartridge P) has an electrophotographic photosensitive drum  1  (which hereafter is referred to simply as drum  1 ), on which an electrostatic latent image is formed. Referring to  FIG. 2 , the drum  1  is rotated in the counterclockwise direction (indicated by arrow mark) in  FIG. 2(   b ). Each process cartridge P has also a charging mean  2 , a developing means  4  ( 4   y ,  4   m ,  4   c  or  4   k ), and a drum cleaning means  6 , which are means for processing the drum  1 . The drum processing means are in the adjacencies of the peripheral surface of the drum  1 , being arranged in the listed order in terms of the rotational direction of the drum  1 . 
         [0039]    This embodiment is described with reference to the aforementioned process cartridge of the so-called integration type. However, it is not intended to limit the present invention in terms of the process cartridge type. 
         [0040]    The drum  1  is made up of an aluminum cylinder, and an organic photoconductive layer formed on the peripheral surface of the aluminum cylinder by coating the peripheral surface of the aluminum cylinder with an organic photosensitive substance. 
         [0041]    The charging means  2  (processing means) uses a charge roller (electrically conductive roller). It uses one of the contact charging methods. The charge roller  2  is roughly parallel to the drum  1 , and is in contact with the peripheral surface of the drum  1 . It is rotated by the rotation of the drum  1 . As a preset charge bias (charge voltage) is applied to the charge roller  2  from an electric power source (unshown), the peripheral surface of the drum  1  is uniformly charged by the charge roller  2  to a preset polarity and a preset potential level. 
         [0042]    The developing means  4  (processing means) is in the form of a development unit  4 . It develops an electrostatic latent image on the peripheral surface of the drum  1  with the use of developer (toner). The development units  4  ( 4   y ,  4   m ,  4   c  and  4   k ), which the cartridges P (Py, Pm, Pc and Pk, respectively) have, have developer storages  41  ( 41   y ,  41   m ,  41   c  and  41   k , respectively), which store developers T (Ty, Tm, Tc and Tk, respectively). They have also a development roller  40  for developing an electrostatic latent image on the drum  1 . Further, they have: a developer conveyance member  42  which conveys the developer T in the developer storage  41 ; a developer supply roller  43  which coats the development roller  40  with the developer; and a development blade  44  which is a developer regulating member and is kept pressed upon the peripheral surface of the development roller  40 . 
         [0043]    The drum cleaning means  6  (processing means) is the means for removing the developer remaining on the peripheral surface of the drum  1  after the transfer (primary transfer) of a developer image on the peripheral surface of the drum  1  onto a transfer belt  50 . The cleaning means  6  in this embodiment employs a cleaning blade as a cleaning member. The developer removed from the peripheral surface of the drum  1  is stored in the storage  8  for the removed developer. 
         [0044]    Each cartridge P is made up of a photosensitive member unit  8  and a development unit  4  ( 4   y ,  4   m ,  4   c  and  4   k ) which are in connection to each other. The photosensitive member unit  8  has the aforementioned drum  1 , charge roller  2 , and drum cleaning unit  6 . Each cartridge P is removably installable in the apparatus main assembly  100 A; it is removably installable in a cartridge drawer which can be moved into, or out of, the apparatus main assembly  100 A. The details of the structure of the cartridge P, and the details of the structure of the cartridge drawer, are described later. 
         [0045]    The cartridge Py stores yellow (y) developer Ty in the developer storage  41   y  of its developer unit  4   y . It forms a yellow developer image on the peripheral surface of the drum  1 . The cartridge Pm stores magenta (m) developer Tm in the developer storage  41   m  of its developer unit  4   m . It forms a magenta developer image on the peripheral surface of the drum  1 . The cartridge Pc stores cyan (c) developer Tc in the developer storage  41   c  of its developer unit  4   c . It forms a cyan developer image on the peripheral surface of the drum  1 . The cartridge Pk stores black (k) developer Tk in the developer storage  41   k  of its developer unit  4   y . It forms a black developer image on the peripheral surface of the drum  1 . 
         [0046]    The apparatus main assembly  100 A has a laser scanner unit  3 , which is under the space into which the cartridges P (Py, Pm, Pc and Pk) are installed. It has also a transfer unit  5 , which is on the top side of the space for the cartridges. 
         [0047]    The scanner unit  3  is made up of a laser diode, a polygon mirror, an F-θ lens, a deflection mirror, etc. It scans (exposes) the uniformly charged area of the peripheral surface of the drum  1 , by emitting a beam L of laser light while modulating the beam L with the information of the monochromatic image of each of the primary colors (of which image is to be formed) inputted into a control circuit  199  from a host apparatus. As a result, an electrostatic latent image, which reflects the pattern of exposure, is formed on the peripheral surface of the drum  1 . 
         [0048]    The transfer unit  5  has an intermediary transfer belt  50  (endless belt), which is dielectric and flexible. It has also the first and second belt suspension rollers  51   a  and  51   b , by which the intermediary transfer belt  50  is suspended and kept stretched. Further, the transfer unit  5  has four primary transfer rollers  52  ( 52   y ,  52   m ,  52   c  and  52   k ), which are inside the loop which the intermediary transfer belt  50  forms. In terms of the moving direction of the intermediary transfer belt  50 , the primary transfer rollers  52  are between the first and second belt suspension rollers  51   a  and  51   b . They are kept pressed against the drum  1  of the corresponding cartridge P with the presence of the intermediary transfer belt  50  between themselves and drums  1 , one for one. The area of contact between the drum  1  of each cartridge P and intermediary transfer belt  50  is the primary transfer nip T 1 . Further, the transfer unit  5  has a secondary transfer roller  53 , which is kept pressed against the belt suspension roller  51   b  with the presence of the intermediary transfer belt  50  between itself and the belt suspension roller  51   b . The area of contact between the secondary transfer roller  53  and intermediary transfer belt  50  is the secondary transfer nip T 2 . 
         [0049]    The operation for forming a full-color image is as follows: The four cartridges P are sequentially driven with preset control timing. That is, each drum  1  is rotationally driven in the counterclockwise direction (indicated by arrow mark in  FIG. 2 ). The transfer belt  50  of the belt unit  5  is also driven, along with the scanner unit  3 . In synchronism with the driving of these components, the charge roller  2  in each cartridge P uniformly charges the peripheral surface of the drum  1  to a preset polarity and a preset potential level. The scanner unit  3  scans (exposes) the uniformly charged area of the peripheral surface of the drum  1  with a beam of laser light which it emits while modulating the beam with image formation signals. As a result, an electrostatic latent image, which reflects the image formation signals, is formed on the peripheral surface of the drum  1 . Then, the electrostatic latent image is developed by the development unit  4  ( 4   y ,  4   m ,  4   c  or  4   k ) (development roller  40 ) into a developer image, that is, an image formed of developer. 
         [0050]    Through an electrophotographic process such as the one described above, a monochromatic yellow developer image, which corresponds to the yellow component of the full-color image, is formed on the drum  1  of the cartridge Py. On the drum  1  of the cartridge Pm, a monochromatic magenta developer image, which corresponds to the magenta component of the full-color image is formed. On the drum  1  of the cartridge Pc, a monochromatic cyan developer image, which corresponds to the magenta component of the full-color image is formed. Further, on the drum  1  of the cartridge Pk, a monochromatic black developer image, which corresponds to the black component of the full-color image is formed. These monochromatic developer images are electrostatically and sequentially transferred in layers (primary transfer) onto the circularly moving intermediary transfer belt  50  in the primary transfer nips T 1 , one for one. As a result, an unfixed full-color developer image is effected by the layered four monochromatic developer images, that is, yellow, magenta, cyan and black monochromatic developer images on the intermediary transfer belt  50 . 
         [0051]    Meanwhile, a recording medium conveyance roller  18  of a recording medium feeder section  16  begins to be rotated with a preset control timing, whereby one of the sheets S of recording medium in a recording medium cassette  17  is fed into the apparatus main assembly  100 A while being separated from the rest. The cassette  17  is removably installable in the apparatus main assembly  100 A from the front side of the apparatus main assembly  100 A (front loading). Designated by a referential code  17   a  is a hand-hold, with which the front panel of the recording medium cassette  17  is provided. After being fed into the apparatus main assembly  100 A, the sheet S of recording medium is introduced into the secondary transfer nip T 2  by a pair of registration rollers  19  with a preset timing. To the transfer roller  53 , a preset transfer bias, which is opposite in polarity from the intrinsic polarity of the developer (intrinsic polarity of toner) and has a preset level of potential, is applied from an electric power source (unshown). Thus, yellow, magenta, cyan and black developer images are transferred in layers (secondary transfer) onto the sheet S of recording medium. That is, an unfixed full-color developer image is effected on the sheet S of recording medium. 
         [0052]    Next, the sheet S of recording medium is moved out of the secondary transfer nip T 2 , and is introduced into a fixation section  20 , which is a section for fixing the multiple monochromatic developer images, different in color, in the sheet S to the sheet S. The fixation section  20  has: a rotatable heat roller  20   a ; and a rotatable pressure roller  20   b  which is kept pressed upon the heat roller  20   a  to apply heat and pressure to the sheet S and the developer images thereon. After the formation of an unfixed full-color developer image on the sheet S, the sheet S is conveyed through the fixation section  20  while remaining pinched between the pair of fixation rollers  20   a  and  20   b , and being given heat and pressure by the pair of fixation rollers  20   a  and  20   b Consequently, the multiple developer images, different in color, are fixed to the surface of the sheet S of recording medium. Then, the sheet S is conveyed out of the fixation section  20  is conveyed further through a recording medium conveyance passage which includes a pair of discharge rollers  23 , and is discharged as a full-color print into an external delivery tray  25  of the apparatus main assembly  100 A through a print outlet  24 . In this embodiment, the toner remaining on the surface of the intermediary transfer belt  50  after the separation of the sheet S from the belt  50  is electrostatically adhered to the peripheral surface of the drum  1  in the primary transfer nip T 1  of the first cartridge  50   y , for example, and then, is removed by the drum cleaning unit  6 . 
         [0053]    Incidentally, when the image forming apparatus  100  is in the black-and-white mode, only the cartridge Pk is used for image formation. 
         [0054]    (Cartridge Replacement Method) 
         [0055]    The image forming apparatus  100  and cartridge P in this embodiment are structured so that as any of the cartridges P in the apparatus main assembly  100 A reaches the end of its service life due to the consumption of the developer therein, it can be replaced by a user. The image forming apparatus  100  is provided with a cartridge drawer  70  (as cartridge supporting member), which can be pulled out frontward from the apparatus main assembly  100 A to access the cartridges P in the drawer  70 . That is, when it is necessary to install a cartridge P into the apparatus main assembly  100 A or removing a cartridge P from the apparatus main assembly  100 A, the cartridge drawer  70  is to be pulled out of the apparatus main assembly  100 A so that the cartridge P can be installed into the drawer  70  or removed from the drawer  70 . Then, after the installation of a partridge P into the drawer  70  or the removal of a cartridge P from the drawer  70 , the drawer  70  is to be put back into the apparatus main assembly  100 A. This is how the cartridge P can be placed in its specific position in the apparatus main assembly  100 A. 
         [0056]    The front panel of the apparatus main assembly  100 A is provided with an opening  100   a , through which the cartridge drawer (cartridge supporting member) is pushed into, or pulled out of, the apparatus main assembly  100 A, in order to install the cartridge P into the apparatus main assembly  100 A, or remove the cartridge P from the apparatus main assembly  100 A. Further, the front panel of the apparatus main assembly  100 A is provided with a door, which is rotatably movable about a hinge  10   b  (which is at the bottom of the door  10 ) between a position in which it keeps the opening  100   a  covered, and a position in which it keeps the opening  100   a  exposed. That is, the door  10  is rotatable upward about the hinge  10   b  so that it becomes vertical to cover the opening  100   a  as shown in  FIGS. 1  and  FIG. 2(   a ), or downward about the hinge  10   b  so that is becomes horizontal to keep the opening  100   a  exposed as shown in  FIGS. 3 and 4 . Designated by a referential code  10   a  is the aforementioned hand-hold with which the front side of the door  10   a  is provided. 
         [0057]    When the door  10  is open, the cartridge drawer  70  can be pulled out of the apparatus main assembly  100 A through the opening  10   a , while being guided by a guiding means  14 , as shown in  FIGS. 3 and 4 . That is, the apparatus main assembly  100 A and drawer  70  are structured so that the drawer  70  is practically horizontally movable relative to the apparatus main assembly  100 A in the direction indicated by an arrow mark D 1  (rearward; direction in which drawer is to be put back into apparatus main assembly  100 A), or direction indicated by D 2  (outward direction (frontward) in which drawer  70  is pulled to be moved out of apparatus main assembly  100 A), which is opposite to the direction D 1 . The cartridge drawer  70  is provided with four cartridge slots so that it can support four cartridges P. It is structured so that each cartridge P is supported in its designated slot. The four cartridge slots are aligned in tandem (parallel to axial line of drum  1  and axial line of development roller  40 ) in the direction parallel to the moving direction of the drawer  70  (same direction as directions indicated by arrow marks D 1  or D 2 ). That is, the cartridge drawer  70  supports multiple (four) cartridges P (Py, Pm, Pc and Pk) so that the cartridges P are aligned in tandem in the moving direction of the drawer  70  so that the lengthwise direction of each cartridge P is parallel to the axial line of the drum  1  and the axial line of the development roller  40 . Further, when the door  10  is open, the cartridge drawer  70  is movable between an inside position A where the entirety of drawer  70  is in the apparatus main assembly  100 A, and an outside position B where the cartridges P can be installed into the drawer  70  or removed from the drawer  70 .  FIG. 2  shows the state of the image forming apparatus  100  when the drawer  70  is in the inside position A.  FIGS. 3 and 4  show the state of the image forming apparatus  100  when the drawer  70  is in the outside position B. 
         [0058]    When the door  10  is closed ( FIGS. 1 and 2 ), the cartridge drawer  70  is in the inside position A, which is the latent image formation position (image formation position) where the cartridges P in the drawer  70  can form an electrostatic latent image on the drum  1 . Further, when the cartridge drawer  70  is in the inside position A, the drum  1  of each cartridge P in the drawer  70  is in contact with the transfer belt  50 , and therefore, a developer image on the drum  1  can be transferred (primary transfer) onto the transfer belt  50 . Further, when the cartridge drawer  70  is in the inside position A, each cartridge P in the drawer  70  is under the pressure from a cartridge pressing member, being thereby firmly held in a preset position. Also when the cartridge drawer  70  is in the inside position A, the driving force input sections (couplers  47  and  48  in  FIG. 8 ) of each cartridge P are in connection to the driving force output sections (unshown) of the apparatus main assembly  100 A, and the electrical contacts (unshown) of each cartridge P are in connection to the electrical power supply system (unshown) of the apparatus main assembly  100 A. Also when the cartridge drawer  70  is in its inside position A, it is held to the apparatus main assembly  100 A by a drawer positioning means (unshown) so that it cannot move relative to the apparatus main assembly  100 A. It is when the image forming apparatus  100  is in the above-described state that the image forming apparatus  100  can form an image. 
         [0059]    As the door  10  is opened as shown in  FIGS. 3 and 4 , the opening  100   a  of the apparatus main assembly  100 A is exposed. Thus, the hand-hold of the front panel of the cartridge drawer  70  is exposed through the opening  100   a . Further, the belt unit  5  is moved upward to a preset position by a linkage (unshown), which is driven by the rotational movement of the door  10 . As a result, the transfer belt  11  is separated from the drum  1  of each cartridge P. That is, the drum  1  is separated from the belt  11 . Further, each of the driving force outputting portions of the apparatus main assembly  100 A becomes disconnected from the corresponding driving force input portion of the cartridge P (driving force removal). Further, the pressure applied by the cartridge pressing member to keep each cartridge P immovably held in the preset position is removed (pressure removal). Further, the power supply system of the apparatus main assembly  100 A is disconnected from the electrical contacts of each of the cartridges P (power supply disconnection). Further, the cartridge drawer  70  is released from the drawer positioning means which keeps drawer  70  immovably positioned relative to the apparatus main assembly  100 A. 
         [0060]    Then, a user is to grasp the hand-hold  71  of the cartridge drawer  70  and horizontally slide the drawer  70  frontward (outward), that is, in the direction D 2 , as far as the aforementioned outside position B through the opening  100   a . As the drawer  70  is pulled out to the outside position B, it is prevented by a stopper (unshown) from being pulled out further. While the drawer  70  is moved, the drum  1  in each cartridge P in the drawer  70  remains separated from the transfer belt  50 . Therefore, there is no friction between the drum  1  and belt  50 . 
         [0061]    The cartridge drawer  70  is structured so that each cartridge P (Py, Pm, Pc or Pk) can be pulled out upward from the drawer  70 , independently from the others, or can be inserted downward into the drawer  70  to be supported by the drawer  70 , independently from the other. In other words, a user is allowed to lift (upward in direction indicated by arrow mark C 1  in  FIG. 4 ) only a cartridge P to be replaced, that is, a cartridge whose service life has expired, out of the drawer  70 , and lower a brand-new cartridge into the cartridge slot vacated by the used-up cartridge P, from above, virtually in the gravity direction (indicated by arrow mark C 2  in  FIG. 4 ), so that the brand-new cartridge P is supported by the drawer  70 . 
         [0062]    After the replacement of the cartridge or cartridges in the cartridge drawer  70 , a user is to horizontally slide the drawer  70  back into the apparatus main assembly  100 A in the direction D 1  (opposite direction from direction D 2 ) as far as it can be slid, that is, until the drawer  70  is stopped by the stopper (unshown). While the drawer  70  is pushed back into the apparatus main assembly  100 A, the drum  1  of each cartridge in the drawer  70  remains separated from the transfer belt  50 . Therefore, there is no friction between the drum  1  and belt  50 . 
         [0063]    After pushing the cartridge drawer  70  into the apparatus main assembly  100 A as far as it can be, a user is to close the door  10  so that the opening  100   a  of the apparatus main assembly  100 A is covered by the door  10 . As the door  10  is closed, the drawer  70  is immovably positioned relative to the apparatus main assembly  100 A by the drawer positioning means, which is moved by the closing movement of the door  10  through the aforementioned linkage. Each cartridge P in the drawer  70  is firmly positioned by the cartridge pressing member (unshown). Further, the driving force output portion of the apparatus main assembly  100 A becomes connected to the driving force input portion of each cartridge P, and the electric power supply system of the apparatus main assembly  100 A becomes electrically connected to the electrical contacts of each cartridge P. Then, the transfer unit  5  lowers to the preset position, whereby the transfer belt  50  is placed in contact with the top portion of the peripheral surface of the drum  1  of each cartridge P. In this embodiment, it is when the image forming apparatus  100  is in the above described state that the image forming apparatus  100  is ready for an image forming operation. 
         [0064]    As described above, the multiple (four) cartridges P enter the apparatus main assembly  100 A with the cartridge drawer  70  while remaining supported by the drawer  70 . Thus, a user is to close the door  10  after pushing the drawer  70  all the way into the apparatus main assembly  100 A. Therefore, it is ensured that each of the multiple (four) process cartridges P is precisely positioned relative to the apparatus main assembly  100 A. Thus, the structural arrangement, in this embodiment, for an electrostatic image forming apparatus is superior in operational efficiency in terms of cartridge installation and removal than any of conventional structural arrangements for an electrophotographic image forming apparatus, which requires a user to place each cartridge P in the apparatus main assembly  100 A independently from the others. 
       (Cartridge Drawer) 
       [0065]    Next, referring to  FIGS. 5 to 7 , the cartridge drawer  70  (cartridge supporting member) is described.  FIGS. 5(   a ) and  5 ( b ) are perspective views of the cartridge drawer  70 , as seen from the top-left and top-right sides, respectively, of the drawer  70 .  FIGS. 6(   a ) and  6 ( b ) are schematic vertical sectional views of the cartridge drawer  70 , at a vertical plane parallel to the moving direction of the drawer, as seen from the left and right sides, respectively of the apparatus  100 .  FIG. 7  is an enlarged schematic sectional view of the frontmost cartridge slot  70   a , and its adjacencies, in  FIG. 6(   a ). The drawer  70  is provided with four drawer guiding portions  72   a - 72   d , by which the drawer  70  is guided by the left and right drawer guiding means  14  of the apparatus main assembly  100 A, and which are at the four corners of the bottom wall of the drawer  70 , one for one. The drawer guiding portions  72   a  and  72   c  are in engagement with the drawer guiding means on the right-hand side of the apparatus main assembly  100 A, and are guided by the drawer guiding means on the right-hand side of the apparatus main assembly  100 A. The drawer guiding portions  72   b  and  72   d  are in engagement with the drawer guiding means on the left-hand side of the apparatus main assembly  100 A, and are guided by the drawer guiding means on the left-hand side of the apparatus main assembly  100 A. 
         [0066]    The drawer guiding portions  72   a  and  72   b , which are on the upstream side of the drawer guiding portions  72   c  and  72   d  in terms of the direction D 2  (in which drawer  70  is pulled out of apparatus main assembly  100 A), prevent the drawer  70  from tilting relative to the apparatus main assembly  100 A when the drawer  70  is in the outside position B. That is, referring to  FIG. 5 , the drawing guiding portions  72   a  and  72   b extend upstream beyond the cartridge slot  70   a  (cartridge supporting slot) which is the most upstream cartridge slot in terms of the direction D 2  (outward direction). Each of the drawer guiding portions  72   c  and  72   d  is a cylindrical projection, and projects outward from the corresponding lateral wall of the drawer  70 , perpendicular to the direction D 2  (outward direction), at the downstream end of the drawer  70 . 
         [0067]    The front side of the front panel of the cartridge drawer  70  is provided with the hand-hold  71 , which is to be used by a user to move the drawer  70 . 
         [0068]    The cartridge drawer  70  is provided with four cartridge slots  70   a - 70   d  (which will be described later), which are aligned in tandem in the front-rear direction. In terms of the direction D (direction of outward movement of drawer  70 ), the first cartridge slot  70   a , which is for the cartridge Py, is the most upstream slot of the drawer  70 . The other three cartridge slots  70   b ,  70   c  and  70   d  for the cartridges Pm, Pc and Pk, respectively, are on the downstream side of the cartridge slot  70   a , in the listed order. There is a partition wall  70   e  between the adjacent two cartridge slots, functioning as a marker for assisting a user when the user inserts a cartridge P into a specific slot in the drawer  70 . The bottom wall of each cartridge slot is provided with an opening  70   f , through which the beam L of laser light from the laser scanner unit  3  scans (exposes) the peripheral surface of the drum  1 . 
         [0069]    The left and right walls of each of the cartridge slots  70   a - 70   d  are provided with a cartridge guiding means  75  for guiding a cartridge P when the cartridge P is inserted into the cartridge slot. The right-hand wall of the cartridge slot  70   a  (side from which cartridge is not driven) is provided with guides  75   a   1  and  75   a   3  for guiding the cartridge Pk when the cartridge Pk is inserted into the cartridge drawer  70  (cartridge slot  70   a ). The left-hand wall of the cartridge slot  70   a  (side from which cartridge is driven) is provided with guides  75   a   2  and  75   a   4  for guiding the cartridge Pk when the cartridge Pk is inserted into the cartridge drawer  70  (cartridge slot  70   a ). Similarly, the right-hand wall of the cartridge slot  70   b  is provided with guides  75   b   1  and  75   b   3  for guiding the cartridge Pc when the cartridge Pc is inserted into the cartridge drawer  70  (cartridge slot  70   c ). The left-hand wall of the cartridge slot  70   b  is provided with guides  75   b   2  and  75   b   4  for guiding the cartridge Pc when the cartridge Pc is inserted into the cartridge drawer  70  (cartridge slot  70   b ). The right-hand wall of the cartridge slot  70   c  is provided with guides  75   c   1  and  75   c   3  for guiding the cartridge Pm when the cartridge Pm is inserted into the cartridge drawer  70  (cartridge slot  70   c ). The left-hand wall of the cartridge slot  70   c  is provided with guides  75   c   2  and  75   c   4  for guiding the cartridge Pm when the cartridge Pm is inserted into the cartridge drawer  70  (cartridge slot  70   c ). Further, the right-hand wall of the cartridge slot  70   d  is provided with guides  75   d   1  and  75   d   3  for guiding the cartridge Py when the cartridge Py is inserted into the cartridge drawer  70  (cartridge slot  70 ). The left-hand wall of the cartridge slot  70   d  is provided with guides  75   d   2  and  75   d   4  for guiding the cartridge Py when the cartridge Py is inserted into the cartridge drawer  70  (cartridge slot  70   d ). 
         [0070]    In this embodiment, the guides  75   b ,  75   c  and  75   d , which are going to referred to as the first guides, are the same in shape. Thus, the first guide is described with reference to the guide  75   b . Referring to  FIG. 6(   a ), the right-hand wall of the cartridge slot  70   b  is provided with the guides  75   b   1  and  75   b   3 , as described above. In terms of the direction D 2  (outward direction), the guides  75   b   1  and  75   b   3  are on the upstream and downs stream sides, respectively. The two guides  75   b   1  and  75   b   3  are the same in width, and are roughly vertical. They are linear. Next, referring to  FIG. 6(   b ), the left-hand wall of the cartridge slot  70   b  is provided with the guides  75   b   2  and  75   b   4 , which are on the upstream and downstream sides, respectively, in terms of the direction D (outward direction). The two guides  75   b   2  and  75   b   4  are roughly vertical, and oppose the guides  75   b   1  and  75   b   3 , respectively, of the right-hand wall of the cartridge slot  70   b . The cartridge guide  63   g  of the cartridge Pm, which engages with the guide  75   b   2  of the cartridge drawer  70 , which is a cylindrical rib which surrounds a coupling  47 , as will be described later. Therefore, the guide  75   b   2  is different in width from the other guides. Thus, it is primarily the guides  75   b   3  and  75   b   4 , which extend further downward than the guides  75   b   1  and  75   b   2 , that guide the cartridge Pm. 
         [0071]    As for the guide  75   a  of the most upstream cartridge slot  70   a  in terms of the direction D 2  (outward direction), it is differently structured from the three downstream guides  75   b ,  75   c  and  75   d . The guides  75   a   1  and  75   a   2  are the same in shape as the above described guides  75   b   1  and  75   b   2 . The guides  75   a   3  and  75   a   4 , which are going to be referred to as the second guides, are made up of the two sections, that is, the top and bottom sections. The bottom sections  75   a   3   a  and  75   a   4   a  are roughly vertical as the guides  75   b   3  and  75   b   4 , but the top sections  75   a   3   b  and  75   a   4   b  are tilted frontward (outward direction D 2 ). Referring to  FIG. 7 , designated by a referential code θ 1  is the angle between the direction D 2  in which the cartridge drawer  70  is pulled out of the apparatus main assembly  100 A, and the direction C 1 , in which the cartridges Pm, Pc and Pk are to be pulled out of the drawer  70 , and which is roughly parallel to the bottom section of the guide  75   a   3 . The cartridge slot  70   a  is structured so that an angle θ 2  between the outward direction D 2 , and the direction D 3  in which the cartridge Py is moved when it is guided by the top section of the guide  575   a   3  is substantially smaller than 90°. That is, the guides  75   a   3  and  75   a   4  have slant sections  75   a   3   b  and  75   a   4   b , respectively, which are more tilted downstream in terms of the outward direction D 2  than the guides  75   b ,  75   c  and  75   d.    
         [0072]    The left wall of the cartridge drawer  70  (from which cartridge P is driven) has an opening  77  through which the drum coupling (unshown) put, and an opening  78  through which the developing means coupling (unshown) is put. Each coupling is put through the opening  77  or  78  by the closing movement of the door  10 . Then, it engages with the corresponding coupling (which will be described later) of the cartridge P, and transmits to the cartridge P the force for driving the cartridge P. 
       (Cartridge) 
       [0073]    Next, referring to  FIGS. 2(   b ),  8 ( a ),  8 ( b ),  9 ( a ) and  9 ( b ), the cartridge P, which is installed in (supported by) the cartridge drawer  70 , is described.  FIG. 2(   b ) is an enlarged schematic sectional view of the combination of the cartridge drawer  70 , cartridges P in the drawer  70 , and their adjacencies, in  FIG. 2(   a ), which is a schematic sectional view of the image forming apparatus  100  at a plane perpendicular to the front panel of the apparatus main assembly  100 A, as seen from the front side of the apparatus  100 . Here, the cartridge Pk is described as an example of the cartridge P. The cartridges Py, Pm and Pc are the same in structure as the cartridge Pk, although they are different from the cartridge Pk in the color of the toner they store. However, the cartridge Py is different from the other cartridges Pm, Pc and Pk in the shape of the hand-hold; it has a hand-hold  66 , which will be described later. 
         [0074]    The cartridge Pk is made up of a photosensitive member unit  8  and a development unit  4   k , which are in connection to each other. The unit  8  has the drum  1 , charge roller  2 , cleaning means  6 , and a developer storage  81  (in which developer removed by cleaning means  6  is stored). The development unit  4   k  has the development roller  40 , developer supply roller  43 , development blade  44 , and developer storage  41   k  (in which developer Tk for image formation is stored). 
         [0075]    The drum  1 , development roller  40  and developer supply roller  43  are rotationally driven in the direction indicated by arrow marks. The charge roller  2  is rotated by the rotation of the drum  1 . To the charge roller  2 , a preset charge bias is applied. To the development roller  40 , a preset development bias is applied. 
         [0076]    The developer Tk in the developer storage  41   k  is conveyed upward to the developer supply roller  43  by a developer conveyance member  42 , which is made up of a center shaft, and a sheet attached to the center shaft. Then, the developer Tk is coated on the peripheral surface of the development roller  40  by the developer supply roller  43 , and the development blade  44  which is kept pressed on the peripheral surface of the development roller  40 . As the developer Tk is coated on the peripheral surface of the development roller  40 , electrical charge with a preset polarity is given to the developer Tk by the blade  44 . To the development roller  40 , the preset development bias is applied from the apparatus main assembly  100 A, whereby an electrostatic latent image formed on the drum  1  is developed into a visible image formed of the developer. The developer remaining on the peripheral surface of the drum  1  after the transfer of the developer image onto a sheet S of recording medium is removed by the cleaning means  6 , and is stored in the developer storage  81  for the removed developer. 
         [0077]      FIGS. 8(   a ) and  8 ( b ) are perspective views of the cartridge Pk as seen from the top-right and top-left of the cartridge Pk, respectively. The lengthwise end of the cartridge Pk, from which the cartridge Pk is driven, has: a rotatable coupling  47 , through which the cartridge Pk receives the drum driving force from the drum coupling (unshown) of the apparatus main assembly  100 A; and a rotatable coupling  48 , through which the cartridge Pk receives the development roller driving force from the developer roller coupling (unshown) of the apparatus main assembly  100 A. 
         [0078]    The coupling  47  is attached to the left end of the drum  1  (from which drum  1  is driven). The driving force which the coupling  47  receives from the apparatus main assembly  100 A rotates the drum  1 . The driving force which the coupling  48  receives from the apparatus main assembly  100 A rotates the development roller  40 . It is also transmitted to the developer conveyance member  48  and developer supply roller  43  through intermediary gears (unshown). 
         [0079]    The left and right walls of the cartridge P are provided with guides  63 , one for one, which guide the cartridge P by engaging with the guide  75  when the cartridge P is inserted into the cartridge drawer  70 . More concretely, referring to  FIG. 8(   a ), the right wall of the cartridge Pk is provided with guides  63   p  and  63   r , which are cylindrical and project outward from the outward surface of the right wall. The guide  63   r  is below the guide  63   p . Next, referring to  FIG. 8(   b ), the left wall of the cartridge Pk is provided with guides  63   q  and  63   s , which are on the outward surface of the left wall. The guide  63   q  is cylindrical and surrounds the coupling  47 . The guide  63   s  is below the guide  63   q  and is cylindrical. 
         [0080]    The photosensitive member unit  8  is provided with holes  82 R and  82 L, whereas the development unit  4   k  is provided with projections  49 R and  49 L. The photosensitive member unit  8  and development unit  4  are in connection to each other, with the projections  49 R and  49 L fitted in the holes  82 R and  82 L, respectively. 
         [0081]      FIGS. 9(   a ) and  9 ( b ) are perspective views of the cartridge Py as seen from the top-left and top-right sides, respectively, of the cartridge Py. The cartridge Py is different from the cartridges Pm, Pc and Pk only in the shape of the hand-hold; the hand-hold  66  of the cartridge Py is different in shape from the hand-hold  66  of the cartridges Pm, Pc and Pk. Otherwise, the structure of the cartridge Py is the same as the above described structure of the cartridge Pk. Referring to  FIGS. 8(   a ) and  8 ( b ), the hand-holds  65  of the cartridges Pm, Pc, and Pk are roughly vertical. In comparison, the hand-hold  66  of the cartridge Py is tilted frontward. 
         [0000]    (Installation of Cartridge into Cartridge Drawer; Supporting of Cartridge by Cartridge Drawer) 
         [0082]    Next, referring to  FIGS. 6-10 , the installation of each cartridge P (Py, Pm, Pc and Pk) into the cartridge drawer  70  (supporting of each cartridge P by drawer  70 ) is described.  FIG. 10  is a schematic vertical sectional view of the image forming apparatus  100 , at a plane parallel to the moving direction of its cartridge drawer, as seen from the right-hand side of the image forming apparatus  100 , when the drawer is in the preset outside position and the cartridges Pc and Py are being taken out of the drawer. 
         [0083]    The cartridges Py, Pm, Pc and Pk are to be installed into the cartridge slots  70   a ,  70   b ,  70   c  and  70   d , respectively, of the cartridge drawer  70 . A user is to insert each cartridge P downward into the corresponding cartridge slot in the direction indicated by the arrow mark C 2 , which is virtually the same as the gravity direction. Here, the installation of the cartridge P into the cartridge drawer  70  is described using the cartridge Pc as an example. The cartridges Pm, Pc and Pk are the same in installation, except for their slot in the drawer  70 . The installation of the cartridge Py is described later. 
         [0084]    When it is necessary for a user to install the cartridge Pc into the cartridge slot  70   c  of the cartridge drawer  70 , the user is to grasp the hand-hold  65 , and insert the cartridge Pc into the cartridge slot  70   c  so that the guides  63   r  and  63   s  of the left and right walls of the cartridge Pc engage with the guides  75   c   3  and  75   c   4  of the cartridge slot  70   c , respectively. Thus, as the user insert the cartridge Pc into the cartridge slot  70   c , the cartridge Pc slides downward into the slot  70   c  in the direction C 2  while being guided by the guides  75   c   3  and  75   c   4 , which are in engagement with the guides  63   r  and  63   s . Then, the user is to engage the guides  63   p  and  63   q  with the guides  75   c   1  and  75   c   2 , respectively, and slide the cartridge Pc further downward in the direction C 2 . Eventually, the guide  63  comes into contact with the bottom of the guide  75 , completing the installation of the cartridge Pc into the cartridge drawer  70 . 
         [0085]    Next, the installation of the cartridge Py into the cartridge drawer  70  is described. The user is to grasp the hand-hold  66 , and insert the cartridge Py into the cartridge slot  70   a  so that the guides  63   r  and  63   s  of the left and right walls of the cartridge Py engage with the guides  75   a   3  and  75   a   4  of the cartridge slot  70   a , respectively. Then, the user is to allow the gravity to slide the cartridge Py downward in the direction C 2 . However, the guides  75   a   3  and  75   a   4  are tilted in the direction C 3  (frontward) as described above. Therefore, the cartridge Py lowers aslant; it slides downward while moving rearward. Lastly, the user is to engage the guides  63   p  and  63   q  with the guides  75   a   1  and  75   a   2 , respectively, and slide the cartridge Py further downward. Eventually, the guide  63  comes into contact with the bottom of the guide  75 , completing the installation of the cartridge Py into the cartridge drawer  70 . 
         [0086]    When it is necessary to take out a cartridge P in the cartridge drawer  70 , a user is to carry out in reverse the above-described operation for installing the cartridge P. More concretely, if a user wants to take the cartridge Pc out of the drawer  70 , the user is to grasp the hand-hold  65  the cartridge Pc, and pull the cartridge Pc in the direction D 2 , that is, the vertical direction. As the cartridge Pc is pulled upward, the guides  63   p  and  63   q  disengage from the guides  75   c   1  and  75   c   2 , and then, the guides  63   r  and  63   s  disengage from the guides  75   c   3  and  75   c   4 , allowing thereby the user to take the cartridge Pc out of the cartridge drawer  70 . The operation for taking the cartridge Pm out of the drawer  70 , and the operation for taking the cartridge Pk from the drawer  70 , are the same as the operation for taking the cartridge Pc from the drawer  70 . 
         [0087]    The operation for taking the cartridge Py out of the cartridge drawer  70  is as follows: First, a user is to grasp the hand-hold  66  of the cartridge Py, and pull up the cartridge Py in the direction C 2 , that is, the vertical direction, as the user has to do when taking the cartridge Pc out of the drawer  70 . As the cartridge Py is pulled upward, the guides  63   p  and  63   q  disengage from the guides  75   a   1  and  75   a   2 , respectively. Then, the user is to pull the cartridge Py further upward. As the cartridge Py is pulled, the guides  63   r  and  63   s  (which are in engagement with guides  75   a   3  and  75   a   4 , respectively), the cartridge Py (to which guides  63   r  and  63   s  belong) move askew in the direction C 4 , because the guides  75   a   3  and  75   a   4  are tilted in the direction D 3 . That is, the cartridge Py is moved upward while shifting frontward of the apparatus main assembly  100 A. Lastly, the guides  63   r  and  63   s  disengage from the guides  75   a   3  and  75   a   4 , allowing thereby the user to take the cartridge Py out of the cartridge drawer  70 . That is, the cartridge Py and cartridge slot  70   a  are structured so that the distance by which the guides  75   a   3  and  75   a   4  are moved in the direction D 2  (outward direction) when the cartridge Py is taken out of the cartridge drawer  70  is greater than the distance by which the cartridges Pk, Pc and Pm are moved whey they are taken out of the drawer  70 . 
         [0088]    It is from the front side of the image forming apparatus  100 , facing the front panel of the image forming apparatus  100 , that a user is to carry out the above described operation for installing or removing a cartridge P (front access). Therefore, when the user installs the cartridge Py into the cartridge drawer  70 , or takes the cartridge Py out of the drawer  70  after moving frontward the drawer  70  to the preset outside position by pulling the drawer  70  frontward, the cartridge slot  70   a  for the cartridge Py is the farthest of the four cartridge slots of the drawer  70  from the user. However, the guide  75   a  is differently structured from the guides  75   b - 75   d . Therefore, a user is enabled to engage the guide  63  of the cartridge Py with the guide  75   a  of the drawer  70 , or disengage the guide  63  of the cartridge Py from the guide  75   a  of the drawer  70 , at a point closer to the user than if the cartridge Py and cartridge slot  70   a  were structured the same as the other cartridges Pm, Pc, and Pk and cartridge slots  70   b ,  70   c  and  70   d . That is, when the cartridge Py is installed, it is guided into its cartridge slot, that is, the cartridge slot  70   a , from a point closer to the user than if the cartridge Py and the cartridge slot  70   a  were structured the same as the other cartridges and their slots in the drawer  70 . Further, when the cartridge Py is taken out of the cartridge drawer  70 , it is guided to a point closer to the user than if the cartridge Py and cartridge slot  70   a  were structured the same as the other cartridges and their slots in the drawer  70 . In other words, the structural arrangement for the cartridge Py (which is supported most upstream in cartridge drawer  70  in terms of direction D 2  (outward direction)), and the structural arrangement for the cartridge slot  70   a  for the cartridge Py, substantially improves the image forming apparatus  100  in operability in terms of the installation and removal of the cartridge Py. 
         [0089]    The guide  75   a  in this embodiment shifts frontward, the point at which the cartridge Py engages with the guide  75   a , or disengages from the guide  75   a  compared to a conventionally structured guide ( 75   a ). That is, the point at which the cartridge Py is engaged with the guide  75   a  when it is installed into the cartridge drawer  70 , or disengaged from the guide  70   a  when it is taken out of the drawer  70 , is farther from the apparatus main assembly  100 A than that in the case of a conventionally structured guide ( 75   a ). Therefore, the cartridge Py and apparatus main assembly  100 A are less likely to be made to contact with each other during the installation or removal of the cartridge Py. Therefore, the drum  1  of the cartridge Py surface of the cartridge Py, and surface of the apparatus main assembly  100 A, are less likely to be damaged. 
         [0090]    In this embodiment, the cartridge P is installed in the cartridge drawer  70  in such an attitude that the photosensitive member unit  8  which includes the drum  1  of the cartridge P will be on the front side of the development unit  4  of the cartridge P after the installation. In other words, the cartridge P is installed in the drawer  70  in such an attitude that the photosensitive drum unit  8  having the drum  1  will be farther away from the apparatus main assembly  100 A. Therefore, the drum  1  is less likely to be damaged. 
         [0091]    Further, it is possible that when a user grasps the cartridge P, the user will touch the drum  1 . In this embodiment, therefore, the hand-hold  65 , which is the hand-hold the second type, is positioned so that when the cartridge P is in the cartridge drawer  70 , the hand-hold  65  is on the front side of the drum  1 . Therefore, the user is unlikely to touch the drum  1  when the user is installing or uninstalling the cartridge P. Therefore, the drum  1  is unlikely to be damaged by the user when the cartridge P is installed or uninstalled. 
         [0092]    As described above, the hand-hold  66  of the cartridge Py is different in shape from the hand-hold  65 , that is, the hand-hold of the first type, of the cartridges Pm, Pc and Pk; it is shaped so that when the cartridge Py is in the cartridge drawer  70 , its front surface is tilted frontward. Therefore, as a user grasps the hand-hold  66  of the cartridge Py, the user can immediately know that the cartridge P grasped by the user is different from the other cartridges P in the manner in which it is to be installed or uninstalled. Further, tilting the hand-hold  66  of the cartridge Py frontward (toward user) can improve the cartridge Py in operability in terms of its installation or uninstallation. 
         [0093]    Also in this embodiment, the guides  75   a   3  and  75   a   4  of the guide  75   a  are shaped so that they are the same in the bottom section as the guides  75   b - 75   d , but, different in the top section from the guides  75   b - 75   d  (top section of the guides  75   a   3  and  75   a   4  are tilted frontward). It is possible to tilt frontward the guides  75   a   3  and  75   a   4  in entirety, or tilt their bottom section frontward and keep their top section vertical. Such modifications, however, makes it necessary to increase the cartridge drawer  70  in cartridge interval, and/or to provide the cartridges P with a recess. Therefore, the modifications are likely to result in an increase in image forming apparatus size and/or result in reduction in cartridge capacity, being therefore, undesirable. 
         [0094]    Also in this embodiment, each of the guides  75   a   3  and  75   a   4  is a combination of two straight sections which are different in angle. However, they may be straight, or a combination of three straight sections different in angle. Further, a part of them may be curved like an arc. 
         [0095]    Further, the cartridges Pm, Pc and Pk are structured so that their guides  75   b - 75   d  are linear, and also, so that when they are in the cartridge drawer  70 , their guides  75   b - 75   d  are vertical. However, this embodiment is not intended to limit the present invention in the shape and angle of the guides  75   b - 75   d . That is, the cartridge Pm, Pc and Pk may be structured so that when they are in the cartridge drawer  70 , the guides  75   b - 75   d  are tilted. Even if the front guides  75   b - 75   d  are tilted, the same effects as those obtainable by this embodiment can be obtained by forming the guide  75   a  so that the angle θ 2  becomes less than the angle θ 1 . 
       Embodiment 2 
       [0096]    Next, the second embodiment of the present invention is described. However, the components, portions, etc., of the image forming apparatus in this embodiment, which are the same in structure and function as the counterparts in the first embodiment, are given the same referential codes as those given to the counterparts, and are not going to be described here. That is, only those different in structure and function from the counterparts in the first embodiment are described. 
       (General Structure of Electrophotographic Color Image Forming Apparatus) 
       [0097]      FIG. 11  is an external perspective view of the electrophotographic color image forming apparatus  200  (which hereafter will be referred to simply as image forming apparatus  200 ) in this embodiment.  FIG. 12(   a ) is a vertical schematic sectional view of the image forming apparatus  200  at a vertical plane perpendicular to the front panel of the apparatus  200 , as seen from the right-hand side of the apparatus  200 .  FIG. 2(   b ) is an enlargement of a part of  FIG. 12(   a ). The image forming apparatus  200  is a full-color laser printer based on the four primary colors. It uses an electrophotographic process. 
         [0098]    In the following description of the second embodiment, the front side of the image forming apparatus  200  is the side having a door  10 . The rear (back) side of the image forming apparatus  200  is the opposite side of the apparatus  200  from the front side. The front-rear direction of the apparatus  300  includes both the front-to-rear direction (rearward direction) and the rear-to-front direction (frontward direction), that is, the opposite direction from the front-to-rear direction. The left-right direction means both the right-to-left direction (leftward direction) and the left-to-right direction (rightward direction). Further, the main assembly  200 A is what remains after the removal of the cartridges P from the image forming apparatus  200 . 
         [0099]    The image forming apparatus  200  in this embodiment is an image forming apparatus of the so-called horizontal type and also, of the so-called tandem type. That is, it employs four process cartridges Q (Qy, Qm, Qc and Qk) which form yellow (y), magenta (m), cyan (c) and black (k) developer images (toner images), respectively. The four process cartridges Q are horizontally aligned in tandem in the apparatus main assembly  200 A. They are removably installable in the apparatus main assembly  200 A to form a color image on a sheet S of recording medium. 
         [0100]    More concretely, in the apparatus main assembly  200 A, the four process cartridges Q, that is, the first to fourth process cartridges Qy, Qm, Qc and Qk, respectively, are roughly horizontally aligned in tandem in the front-to-rear direction in the apparatus main assembly  200 A. Each process cartridge Q (which hereafter is referred to simply as cartridge Q) has an electrophotographic photosensitive drum  1  (which hereafter is referred to simply as drum  1 ), on which an electrostatic latent image is formed. Referring to  FIG. 12 , the drum  1  is rotated in the clockwise direction of  FIG. 2 . Each process cartridge Q has also a charging mean  2 , a developing means  4  ( 4   y ,  4   m ,  4   c  or  4   k ), and a drum cleaning means  6 , which are means for processing the drum  1 . 
         [0101]    The apparatus main assembly  200 A has a laser scanner unit  3 , which is above the cartridge space, that is, the space into which the cartridges Q (Qy, Qm, Qc and Qk) are installed. It has also a transfer unit  5  (as transferring means), which is on the bottom side of the cartridge space. 
         [0102]    The transfer unit  5  has an electrostatic transfer belt  150  (which hereafter is referred to simply as transfer belt  150 ), which is dielectric and flexible. It has also the first (front) and second (rear) rollers  151   a  and  151   b , by which the transfer belt  150  is suspended and kept stretched. Further, the transfer unit  5  has four primary transfer rollers  152  ( 152   y ,  152   m ,  152   c  and  152   k ), which are inside the loop which the transfer belt  150  forms. In terms of the moving direction of the transfer belt  150 , the primary transfer rollers  52  are between the first and second rollers  151   a  and  151   b . They are kept pressed against the drums  1  of the corresponding cartridges Q with the presence of the transfer belt  150  between themselves and drums  1 , one for one. The area of contact between the drum  1  of each cartridge Q and the transfer belt  150  is the primary transfer nip. As the second roller  151   b  is driven, the transfer belt  150  is circularly moves in the clockwise direction (indicated by arrow mark in drawing) at a speed which corresponds to the rotational speed of the drum  1 . There is a belt cleaning means  153  under the transfer belt  150 . The belt cleaning means  153  removes the contaminants on the belt  150 . 
         [0103]    The operation for forming a full-color image is as follows: The four cartridges Q are sequentially driven with preset control timing. That is, each drum  1  is rotationally driven in the counterclockwise direction (indicated by arrow mark in  FIG. 2 ). Then, a developer image is formed the drum  1  of each cartridge Q through an electrophotographic process similar to the one in the first embodiment. 
         [0104]    Meanwhile, a sheet S of recording medium is fed into the apparatus main assembly  200 A by a sheet conveyance roller  18  of a recording medium feeder section  16  with a preset timing, and is moved onto the transfer belt  150  by a pair of registration rollers  19 , from the front side, with a preset timing. As the sheet S is moved onto the transfer belt  150 , it is electrostatically adhered to the transfer belt  150 . Then, it is sequentially conveyed through the transfer nips of the cartridges Qy, Qm, Qc and Qk by the circular movement of the transfer belt  150 . To each of the transfer rollers  152 , a preset transfer bias is applied from an electric power source (unshown), whereby four developer images, different in color (yellow, magenta, cyan, and black), are transferred in layers onto the sheet S of recording medium, effecting thereby an unfixed full-color developer image on the sheet S. 
         [0105]    Then, the sheet S of recording medium is separated from the surface of the belt  11 , and is introduced into a fixation section  20 , and is conveyed through the fixation section  20 . While the sheet S is conveyed through the fixation section  20 , the sheet S and the unfixed full-color developer image thereon are given heat and pressure by the pair of fixation rollers  20   a  and  20   b  of the section  20 . Thus, the unfixed full-color developer image made up of multiple (four) monochromatic images, different in color, is fixed to the surface of the sheet S. Then, the sheet S is conveyed through a recording medium conveyance passage which includes a pair of discharge rollers  23 , and is discharged into an external delivery tray  25  of the apparatus main assembly  200 A through a sheet delivery opening  24  of the apparatus main assembly  200 A. 
       (Cartridge Replacement Method) 
       [0106]    The method for replacing a cartridge P in the apparatus main assembly  200 A of the image forming apparatus  200  in this embodiment is similar to the method for replacing a cartridge P in the apparatus main assembly  100 A of the image forming apparatus  100  in the first embodiment. That is, the cartridges Q are placed in a cartridge drawer  170 , which is a cartridge supporting member having a cartridge supporting frame. The cartridge drawer  170  can be pulled out of the apparatus main assembly  200 A in the frontward direction, and therefore, the cartridges Q can be installed in the apparatus main assembly  200 A, or uninstalled from the apparatus main assembly  200 A, from the front side of the apparatus main assembly  200 A. 
       (Cartridge Drawer) 
       [0107]    Next, referring to  FIGS. 15 to 17 , the cartridge drawer  170  is described.  FIG. 15(   a ) is a perspective view of the cartridge drawer  170  as seen from the top-right of the drawer  170 .  FIG. 15(   b ) is a perspective view of the cartridge drawer  170  as seen from the top-left of the drawer  170 .  FIG. 6(   a ) is a schematic vertical sectional views of the cartridge drawer  170 , at a vertical plane parallel to the moving direction of the drawer  170  as seen from the right side of the apparatus  200 .  FIG. 16(   a ) is a schematic vertical sectional view of the cartridge drawer  170 , at a vertical plane parallel to the moving direction of the drawer  170 , as seen from the left side of the apparatus  200 .  FIG. 16(   b ) is a schematic vertical sectional view of the cartridge drawer  170 , at a vertical plane parallel to the moving direction of the drawer  170  as seen from the right side of the apparatus  200 . 
         [0108]    The right and left walls of the cartridge drawer  170  are provided with guides  172 R and  172 L, respectively, which are on the outward surface of the right wall and the outward surface of the left wall, respectively. The apparatus main assembly  200 A is provided with right and left guiding grooves  14 , in which the guides  172 R and  172 L engage to be guided by the guiding grooves  14 , respectively. With the guides  172 R and  172 L engaged in the guiding grooves  14 , the cartridge drawer  170  is roughly horizontally supported by the apparatus main assembly  200 A and is movable in the front-rear direction. 
         [0109]    The cartridge drawer  170  is provided with four cartridge slots  170   a - 170   d , in which four cartridges Q, different in color of the developer, are installable one for one. The cartridge slots  170   a - 170   d  are aligned in tandem in the front-to-rear direction. Listing from the upstream side of the drawer  170  in terms of the direction D 1  (in which drawer  70  is pushed into apparatus main assembly  200 A), they are a cartridge slots  170   a  (second type),  170   b  (first type),  170   c  (first type) and  170   d  (first type). The cartridge slots  170   a ,  170   b ,  170   c  and  170   k  are the slots into which the cartridges Qy, Qm, Qc and Qk are to be installed, respectively. There is a partition plate  170   c  between the adjacent two cartridge slots. The bottom wall of each of the cartridge slots  170   a - 170   d  is provided with an opening  170   f , through which the drum  1  of each cartridge Q contacts the transfer belt  150  or the sheet S of recording medium on the transfer belt  150 . 
         [0110]    The left and right walls of each of the cartridge slots  170   a - 170   d  are provided with a pair of guiding means  175 , one for one, which are for installing a cartridge Q into the cartridge drawer  170 . The right wall of the cartridge slot  170   a  is provided with guides  175   a   1  and  175   a   3 , whereas the left wall of the cartridge slot  170   a  is provided with guides  175   a   2  and  175   a   4 . The guides  175   a   1  and  175   a   2  oppose the guides  175   a   3  and  175   a   4 , respectively. Similarly, the right wall of the cartridge slot  170   b  is provided with guides  175   b   1  and  175   b   3 , whereas the left wall of the cartridge slot  170   b  is provided with guides  175   b   2  and  175   b   4 ; the right wall of the cartridge slot  170   c  is provided with guides  175   a   1  and  175   a   3 , whereas the left wall of the cartridge slot  170   c  is provided with guides  175   c   2  and  175   c   4 ; and the right wall of the cartridge slot  170   d  is provided with guides  175   d   1  and  175   d   3 , whereas the left wall of the cartridge slot  170   d  is provided with guides  175   d   2  and  175   d   4 . 
         [0111]    In this embodiment, the guides  175   a - 175   c  of the front three cartridge slots  170   a - 170   c , respectively, are the same in shape. However, the guide  175   d  of the rearmost cartridge slot  170   d  (which is most upstream cartridge slot in terms of direction D 2  (outward direction)) is different in shape from the guides  175   a - 175   c . Each of the guides  175   d   1  and  175   d   2  is a combination of two (top and bottom) sections which are linear. Each of the bottom sections  175   d   1   a  and  175   d   2   a  of the guides  175   d   1  and  175   d   2 , respectively, is tilted frontward (parallel to direction E 3 ), whereas each of the top sections  175   d   1   b  and  175   d   2   b  of the guides  175   d   1  and  175   d   2 , respectively, is tilted frontward (parallel to direction E 4 ). Further, each of the guides  175   d   3  and  175   d   4  is also a combination of two (top and bottom) linear sections. The bottom sections  175   d   3   a  and  175   d   4   a  of the guides  175   d   3  and  175   d   4 , respectively, are parallel to the bottom sections  175   d   1   a  and  175   d   2   a  of the guides  175   d   1  and  175   d   2 , respectively. 
         [0112]    Referring to  FIG. 17 , a referential code L 1  stands for the distance between the top and bottom ends of the guide  175   c   1  in terms of the horizontal direction, and a referential code L 2  stands for the distance between the top and bottom ends of the guide  175   d   1  in terms of the horizontal direction. The cartridge drawer  170  is structured so that L 2  is larger than L 1 . 
         [0113]    The rear wall of the cartridge slot  170   d  of the cartridge drawer  170  is provided with a recess  170   g , which is in the form of a triangular pole (triangular in cross section at plane parallel to moving direction of cartridge drawer  70 ). 
         [0114]    Further, the cartridge drawer  170  is provided with a pair of regulating sections  170   h , which are at the top rear end of the drawer  170 . Each regulating section  170   h  extends into the space above the cartridge slot  17   e  and recess  170   g , but is not tall enough to prevent the cartridge drawer  170  from moving through the opening  200   a  of the image forming apparatus  200 . 
       (Cartridge) 
       [0115]    Next, referring to  FIGS. 12(   b ) and  18 , the cartridge Q, which is to be installed into (supported by) the cartridge drawer  70  is described. Here, the cartridge Qy shown in  FIG. 18 , which is an external perspective view of the cartridge Qy, is described as a representative of the cartridges Qy, Qm, Qc and Qd, which are the same in structure although they are different in the color of the developer they store. The various structural components of the cartridge Q are the same as those of the cartridge P in the first embodiment. 
         [0000]    (Installation of Cartridge into Cartridge Drawer) 
         [0116]    Next, referring to  FIGS. 14 , and  19 ( a ) - 19 ( c ), the method for installing the cartridges Q (Qy, Qm, Qc and Qk) into the cartridge drawer  170  is described.  FIG. 14  is a schematic vertical sectional view of the image forming apparatus  200  at a vertical plane perpendicular to the front panel of the apparatus  200 , as seen from the right-hand side of the apparatus  200 , when the cartridge drawer  170  of the apparatus  200  is in its preset outside position and the cartridge Qm is being taken out of the drawer  170 .  FIGS. 19(   a ),  19 ( b ), and  19 ( c ) are schematic vertical sectional views of the image forming apparatus  200 , at a vertical plane parallel to the moving direction of the cartridge drawer of the image forming apparatus  200 , and show the sequential steps for removing the rearmost cartridge Qk from the cartridge drawer  170  (main assembly of image forming apparatus  200 ). 
         [0117]    All of  FIGS. 14 and 19  show the state of the image forming apparatus  200 , in which the cartridge drawer  170  is in a preset outside position. When the drawer  170  is in the preset outside position, the cartridge Qk, which is in the most upstream cartridge slot in the drawer  170  in terms of the direction D 2  (outward direction) is partially within the apparatus main assembly  200 A; a part of the photosensitive member unit  8  is within the apparatus main assembly  200 A. If the cartridge Qk is moved in the direction E 2  like the cartridges Qy, Qm and Qc, the apparatus main assembly  200 A interferes with the movement of the cartridge Qk, preventing thereby the cartridge Qk from being taken out. 
         [0118]    In this embodiment, however, the guide  175   d  is shaped as described above. Therefore, the cartridge Qk can be taken out of the cartridge drawer  170  through the following operation. That is, first, a user is to pull the cartridge drawer  170  out of the apparatus main assembly  200 A, to the preset outside position as shown in  FIG. 19(   a ). Then, the user is to grasp the hand-hold  65  of the cartridge Qk and pull the cartridge Qk upward. As the user pulls upward the cartridge Qk, the cartridge Qk is guided by the guides  175   d   1 - 175   d   4  with which the guides  63   p - 63   s  are in engagement. Therefore, the cartridge Qk moves upward while shifting rearward (direction E 3 ). As the cartridge Qk moves upward while shifting rearward, a part of the cartridge Qk (part of photosensitive drum unit  8 ) enters the recess  170   g  of the cartridge drawer  170 . 
         [0119]    As the cartridge Qk is lifted further, the guides  175   d   3  and  175   d   4 , with which the guides  63   r  and  63   s  are engaged, change in direction. Thus, the cartridge Qk begins to move upward while rotating in the counterclockwise direction as shown in  FIG. 19(   b ). At this point in time, a part of the cartridge Qk is already in the recess  170   g , which is provided as the space for the cartridge Qk to be allowed to rotate.  FIG. 19(   b ) shows the state of the image forming apparatus  200  in which the cartridge Qk has just ended its rotation guided by the guides  175   d   1 - 175   d   4 . At this point in time, the guides  63   r  and  63   s  disengage from the guides  175   d   3  and  175   d   4 , respectively. The image forming apparatus  200  is structured so that when it is in its state shown in  FIG. 19(   b ), the regulation section  170   h  is parallel and close to the cartridge Qk (rear surface of photosensitive unit  8 ). That is, the guides  175   d   3  and  175   d   4  are structured so that the distance by which the cartridge Qk is moved in the direction D 2  (outward direction) when it is taken out of the cartridge slot  170   d  is greater than the distance by which the other cartridges Qy, Qm and Qc are moved in the direction D 2  (outward direction) when they are taken out of their slots  170   a ,  170   b  and  170   c , respectively. 
         [0120]    Then, the guides  63   p  and  63   q  of the cartridge Qk engage with the guides  175   d   1  and  175   d   2 , and therefore, the cartridge Qk is guided by the guides  175   d   1  and  175   d   2 . Further, the rear surface of the photosensitive member unit  8  comes into contact with the regulation section  170   h . Therefore, the cartridge Qk is moved diagonally upward while being prevented from rotating. That is, the regulation section  170   h  prevents the cartridge Qk from coming into contact with the edges of the opening  100  of the apparatus main assembly  200 A, and their adjacencies. Therefore, the cartridge Qk can be smoothly taken out of the cartridge drawer  170 . 
         [0121]    As described above, the point at which the guides  63   p  and  63   q  disengage from the guides  175   d   1  and  175   d   2 , respectively, is on the front side of the point at which the guides  63   p  and  63   q  would disengage from the guides  175   d   1  and  175   d   2 , respectively, if the guide  175   d  were the same in shape as the guides  175   a - 175   c.    
         [0122]    The greater the distance by which the cartridge drawer of an image forming apparatus is pulled out, the more unbalanced in weight distribution is the apparatus, making it possible for the apparatus to tilt. Thus, in this embodiment, the image forming apparatus  200  is structured so that the distance by which its cartridge drawer can be pulled out is made substantially less than the distance by which the cartridge drawer of the image forming apparatus  100  in the first embodiment can be pulled out. However, the image forming apparatus  200  is structured as described above. Therefore, it allows the cartridge for the most upstream cartridge slot of its cartridge drawer to be installed in the drawer at a more frontword point. 
         [0123]    In order to lift a cartridge diagonally frontward by changing its moving direction by rotating the cartridge as the cartridge Qk is, a space is necessary in the rear portion of the cartridge slot. If the guides of all of the four cartridge slots  170   a - 170   d  are structured like the guide  175   d , the cartridge drawer may have to be increased in size, which may result in an increase in the size of an image forming apparatus. However, the space behind the rear end portion of the cartridge drawer  170 , that is, the rear side of the most upstream cartridge slot  170   d  in terms of the direction D 2  (outward direction) is a part of the space in which the drawer  170  moves. Therefore, it is a dead space when the drawer  170  is in the preset outside position. Therefore, utilizing this space to allow the most upstream cartridge Qk to rotate does not result in an increase in the size of the drawer  170  and/or image forming apparatus  200 . In a case where the cartridge drawer  170  is reduced in size by using a sheet of metallic plate as the material for the drawer  170 , it is possible to provide the rear wall of the cartridge drawer  170  with an opening in a preset position so that the opening function like the recess  170   g . This is why it is desired that only the most upstream cartridge slot  170   d , in terms of the outward direction of the drawer  170 , and its guide  175   d , are structured as described above. 
         [0124]    In the above, the cartridge Q removably installable in the cartridge drawer  170  was described as a process cartridge. However, the cartridge Q may be a development cartridge. That is, the cartridge drawer  170  may be provided with guides for removably installing a development cartridge for developing an electrostatic latent image on a photosensitive drum, in the drawer  170 . 
         [0125]    In this embodiment, the guides of only the most upstream cartridge slot, in terms of the outward direction of the cartridge drawer were given a section which is more tilted downstream in terms of the outward direction of the drawer than the guides of the other cartridge slots of the drawer. However, the guides of the other cartridge slots also may be provided with a section which is substantially more tilted downstream than the guides of the downstream cartridge slots in terms of the outward direction of the cartridge drawer. 
       (Summary) 
       [0126]    By structuring the guides of the most upstream cartridge slot in terms of the outward direction of the cartridge drawer as in the first and second embodiments, it is possible to start guiding a cartridge from a point substantially closer to the front side of an image forming apparatus than the point at which it is possible to start guiding a cartridge in the case of any image forming apparatus in accordance with the prior art, during cartridge installation, and also, to guide a cartridge to a point substantially closer to the front side of an image forming apparatus than in the case of any image forming apparatus in accordance with the prior art, during cartridge uninstallation. Therefore, it is possible to improve an image forming apparatus in operability in terms of the installation and uninstallation of a cartridge for the most upstream cartridge slot in terms of the outward direction of the cartridge drawer, and also, to make it unlikely for a cartridge, and the processing members of the cartridge, to be damaged during the installation and uninstallation of the cartridge. 
         [0127]    According to the present invention, it is possible to provide an image forming apparatus which is superior in operability than any image forming apparatus in accordance with the prior art, in terms of the installation of a cartridge into the cartridge drawer of the apparatus, and the uninstallation of a cartridge from the cartridge drawer of the apparatus. 
         [0128]    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. 
         [0129]    This application claims priority from Japanese Patent Application No. 110619/2011 filed May 17, 2011 which is hereby incorporated by reference.