Abstract:
A color electrophotographic image forming apparatus for forming a color image on a recording material, the apparatus includes a main assembly; a drum cartridge including an electrophotographic photosensitive drum and detachably mountable to the main assembly of the apparatus of an electrophotographic image forming apparatus; a plurality of developing cartridges each comprising a developing roller for developing an electrostatic latent image formed on electrophotographic photosensitive drum of the drum cartridge mounted to the main assembly; a main assembly side drum cartridge guide for guiding the drum cartridge; a main assembly side drum cartridge positioning portion for positioning the drum cartridge to the main assembly of the apparatus; wherein the drum cartridge is provided with a positioning portion for positioning the developing cartridge relative to the drum cartridge with respect to an entering direction of the developing cartridge, and the developing cartridge is provided with insertion guide means for guiding insertion of a developing cartridge right thereabove.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an electrophotographic color image forming apparatus which forms an image on recording medium with the use of multiple cartridges removably mountable in the main assembly of the image forming apparatus. It relates to also a cartridge removably mountable in the main assembly of an electrophotographic color image forming apparatus. 
         [0002]    In the following description of the present invention, the term “electrophotographic color image forming apparatus” means an apparatus for forming a color image on recording medium, with the use of an electrophotographic image formation process. Examples of an electrophotographic color image forming apparatus include an electrophotographic color copying machine, an electrophotographic color printer (color laser beam printer, color LED printer, etc.), a color facsimile machine, a color word processor, etc. The term “recording medium” means medium on which an image is formed by an electrophotographic image forming apparatus. “Recording medium” includes paper, OHP sheet, and the like, for example. 
         [0003]    The term “cartridge” means a process cartridge or a development cartridge, for example, which is removably mountable in the main assembly of an electrophotographic image forming apparatus and contributes to an image formation process for forming an image on recording medium. The term “process cartridge” means a cartridge in which an electrophotographic photosensitive drum, and at least one processing means among a charging means, a developing means, and a cleaning means, are integrally placed, and which is removably mountable in the main assembly of an image forming apparatus. A processing means is a means for processing an electrophotographic photosensitive drum (which hereafter may be referred to simply as drum). Thus, the term “process cartridge” includes: a cartridge in which a drum and a developing apparatus (processing means) are integrally placed, and which is removably mountable in the main assembly of an image forming apparatus; and a cartridge in which a drum, a charging means, and a developing means or cleaning means, are integrally placed, and which is removably mountable in the main assembly of an image forming apparatus. A cartridge in which a drum and a developing apparatus (processing means) are integrally placed is referred to as a cartridge of the integration type, whereas a cartridge in which a drum and processing means other than a developing means are integrally placed is referred to as a cartridge of the separation type. A process cartridge can be removably mounted in the main assembly of an image forming apparatus by a user himself or herself. Therefore, it can make easier the maintenance of the main assembly of an image forming apparatus. 
         [0004]    A development cartridge has a development roller. It stores the developer (toner) which is used by the development roller to develop an electrostatic latent image formed on the peripheral surface of a drum. It is removably mountable in the main assembly of an image forming apparatus. In the case of an image forming apparatus which employs a development cartridge, the main assembly of the image forming apparatus has a drum, or it employs a process cartridge of the separation type, which has a drum (but, does not have developing means). A development cartridge also can be removably mounted in the main assembly of an image forming apparatus. Therefore, it can make it easier to maintain the main assembly of an image forming apparatus. 
         [0005]    Thus, the “process cartridge” includes a process cartridge of the so-called integration type as well as separation type. Some electrophotographic image forming apparatuses employ a process cartridge of the so-called integration type, in combination with a process cartridge of the so-called separation type. There are also electrophotographic image forming apparatuses, the drum of which is attached to the main assembly of the apparatus. In the cases of the latter apparatuses, the drum is attached to the main assembly of the apparatus, and a development cartridge which is removably mountable in the main assembly is employed. 
         [0006]    In the field of an electrophotographic color image forming apparatus, a photosensitive drum and a development roller are different in durability. Therefore, a process cartridge is likely to be of the separation type. That is, a drum is placed only in a drum cartridge; it is not placed in a development cartridge which comprises a development roller and a frame (in which developer is stored). In such a case, a drum cartridge is precisely positioned relative to the main assembly of an image forming apparatus, by a pair of guides attached to the left and right plates of the main assembly, whereas a development cartridge is precisely positioned relative to the main assembly by another pair of guides attached to the left and right plates of the main assembly as disclosed in U.S. Pat. No. 6,898,402. Further, the lengthwise end portions of a development roller is fitted with a pair of rings which are coaxial with the development roller. Thus, the positional relationship, more specifically, the gap, between the drum in a drum cartridge, and the development roller in a development cartridge, is maintained by the contact between the rings and the peripheral surface of the drum. 
         [0007]    In the case of the conventional image forming apparatus described above, however, the drum cartridge and development cartridge are independently positioned from each other relative to the main assembly of the image forming apparatus. Thus, if the drum cartridge has to be replaced, all the development cartridges in the main assembly had to be removed, and then, remounted after the mounting of a replacement drum cartridge. Further, not only did the lateral plates of the main assembly have to be shaped to guide the development cartridges, but also, the lengthwise ends of each development cartridge had to be shaped so that the development cartridge could be guided by the lateral plates of the main assembly. This created a problem. That is, providing the lateral plates of the main assembly of the image forming apparatus with cartridge guiding members, or shaping the lateral plates of the main assembly so that they can guide the cartridges, made the main assembly wider. 
       SUMMARY OF THE INVENTION 
       [0008]    Thus, the primary object of the present invention is to provide an electrophotographic color image forming apparatus, the drum cartridge for which is significantly easier to mount or dismount, and narrower, than any of the conventional drum cartridges; the development cartridges for which also are significantly narrower, than any of the conventional development cartridges; and therefore, the main assembly of which is significantly smaller than the main assembly of any of the conventional electrophotographic image forming apparatuses. 
         [0009]    According to an aspect of the present invention, there is provided a color electrophotographic image forming apparatus for forming a color image on a recording material, said apparatus comprising a main assembly; a drum cartridge including an electrophotographic photosensitive drum and detachably mountable to said main assembly of the apparatus of an electrophotographic image forming apparatus; a plurality of developing cartridges each comprising a developing roller for developing an electrostatic latent image formed on electrophotographic photosensitive drum of said drum cartridge mounted to said main assembly; a main assembly side drum cartridge guide for guiding said drum cartridge; a main assembly side drum cartridge positioning portion for positioning said drum cartridge to said main assembly of the apparatus; wherein said drum cartridge is provided with a positioning portion for positioning said developing cartridge relative to said drum cartridge with respect to an entering direction of said developing cartridge, and said developing cartridge is provided with insertion guide means for guiding insertion of a developing cartridge right thereabove. 
         [0010]    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 
         [0011]      FIGS. 1A and 1B  are external perspective views of the electrophotographic color image forming apparatus in the first preferred embodiment of the present invention when the front door of the apparatus is closed and open, respectively. 
           [0012]      FIG. 2A  is a schematic vertical sectional view of the image forming apparatus in the first preferred embodiment of the present invention, as seen from the right-hand side of the apparatus, and  FIG. 2B  is an external perspective view of the drum unit of the image forming apparatus in the first preferred embodiment of the present invention. 
           [0013]      FIGS. 3A and 3B  are drawings for describing how the drum unit and development cartridges are mounted into, or removed from, the main assembly of the image forming apparatus. 
           [0014]      FIG. 4A  is a schematic vertical sectional view of the image forming apparatus in the first preferred embodiment of the present invention when the drum unit and development cartridges are properly positioned in the main assembly of the image forming apparatus, and  FIGS. 4B and 4C  are external perspective views of the development cartridge in the first preferred embodiment as seen from the top and bottom sides, respectively, of the cartridge. 
           [0015]      FIGS. 5A and 5B  are a drawing for illustrating how development cartridges are engaged with the drum cartridge. 
           [0016]      FIG. 6A  is a schematic perspective view of the electrophotographic color image forming apparatus in the second preferred embodiment of the present invention, and  FIG. 6B  is an external perspective view of the development cartridge for the electrophotographic color image forming apparatus in the third preferred embodiment of the present invention. 
           [0017]      FIGS. 7A ,  7 B,  7 C and  7 D are perspective views of the development cartridge legs, in the third preferred embodiment, for temporarily supporting the development cartridge, and describe how the legs temporarily support the development cartridge. 
           [0018]      FIGS. 8A ,  8 B and  8 C illustrate how the magenta development cartridge is mounted into, or removed from, the main assembly of the image forming apparatus, in the third preferred embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     (General Structure of Electrophotographic Image Forming Apparatus) 
       [0019]      FIGS. 1A and 1B  are external perspective views of the electrophotographic color image forming apparatus  100  (which hereafter may be referred to simply as “apparatus  100 ”) in the first preferred embodiment of the present invention when the front door of the apparatus  100  is closed and open, respectively.  FIG. 2A  is a schematic vertical sectional view of the image forming apparatus  100  in the first preferred embodiment of the present invention, as seen from the right-hand side of the apparatus  100 . The apparatus  100  is a full-color laser printer based on the four primary colors. It forms color images on a sheet S of recording medium in response to electrical image formation signals inputted to the control circuit  101  of the apparatus  100  from a host apparatus, such as a personal computer. The main assembly  100 A of the apparatus  100  (which hereafter may be referred to simply as “main assembly  100 A”) is structured so that a drum cartridge  50 , which has an electrophotographic photosensitive drum  1  (which hereafter may be referred to simply as “drum  1 ”) is removably mountable in the main assembly  100 A, and also, so that multiple development cartridges  4  ( 4   y ,  4   m ,  4   c , and  4   k ), which have development rollers  41  ( 41   y ,  41   m ,  41   c , and  41   k , respectively) are removably mountable. 
         [0020]    In the following descriptions of the preferred embodiments of the present invention, the front side, or front surface side, of the apparatus  100  is where the front door  102  of the apparatus  100  is. The rear side is the opposite side from the front side. Further, the front-rear direction means the rear-to-front direction (frontward direction) of the apparatus  100  as well as the front-to-rear direction of the apparatus  100  (rearward direction), that is, the opposite direction from the rear-to-front direction. The left-right direction means left-to-right direction (rightward direction) as well as the right-to-left direction (leftward direction), that is the opposite direction from the left-to-right direction. The upward and downward directions are relative to the gravity direction. The main assembly  100 A is what will remain after the removal of the cartridges  50  and  4 . 
         [0021]    The main assembly  100 A is structured so that after the proper mounting of the cartridge  50 , the drum  1  of the cartridge  50  is roughly at the center of the main assembly  100 A. The drum  1  is rotated in the counterclockwise direction indicated by an arrow mark. It is also structured so that after the proper mounting of the cartridge  50  and  4  into the main assembly  100 A, the charging device  2 , developing device  4 , drum cleaning device  6 , which are the drum processing means, are in the adjacencies of the peripheral surface of the drum  1 , listing in the order in which they process the drum  1  in terms of the drum rotation direction. The main assembly  100 A is also provided with an image writing device  3  (drum exposing device  3 ), and an intermediary transferring device  5 . 
         [0022]    The drum  1  is an organic photoconductive member. It comprises an aluminum cylinder, and an organic photoconductive layer coated on the peripheral surface of the aluminum cylinder. The drum  1  is rotatably supported between the left and right plates  52 L and  52 R ( FIG. 2B ) of the drum cartridge frame  51 , by the left and right plates  52 L and  52 R. More concretely, the left and right plates  52 L and  52 R are provided with a pair of bearing  53 , and the left and right end portions of the drum  1  are rotatably supported by the bearings  53 , one for one. One (driving side) of the lengthwise ends of the drum shaft is fitted with a driving force transmitting component (unshown), through which the drum  1  receives the drum driving force from the motor (unshown) of the main assembly  100 A. As the driving force is transmitted to this driving force transmitting component from the motor of the main assembly  100 A, the drum  1  rotates in the counterclockwise direction at a preset velocity. 
         [0023]    The charging device  2  in this embodiment is of the so-called contact type. It is an electrically conductive roller. The roller  2  is rotatably supported between the left and right plates  52 L and  52 R of the drum cartridge frame  51 , being in contact with the peripheral surface of the drum  1  and roughly in parallel to the drum  1 . It is rotated by the rotation of the drum  1 . As a preset charge bias (voltage) is applied to the roller  2  from the electric power source (unshown) of the main assembly  100 A, the peripheral surface of the drum  1  is uniformly charged to a preset polarity and a potential level. 
         [0024]    The image writing device  3  (drum exposing device  3 ) in this embodiment is a laser scanner. It is solidly attached to the bottom surface of a plate  103  which is a part of the bottom portion of the main assembly  100 A. The unit  3  has a laser diode, a polygon mirror, an F-θ lens, a deflection mirror, etc. It outputs a beam L of laser light while modulating the beam L according to the information regarding each of the yellow, magenta, cyan, and black monochromatic images, into which the image to be formed has been separated, inputted into the control circuit  101  from a host apparatus  200 . As the beam L is outputted from the unit  3 , it is made to converge to the downwardly facing portion of the peripheral surface of the drum  1 , through the exposure hole  103   a  of the frames  103 , and exposure hole  54   a  of the bottom plate  54  of the frame  51 , respectively. Thus, the uniformly charged portion of the peripheral surface of the drum  1  is scanned (exposed) by the beam L. Consequently, an electrostatic latent image, which reflects the pattern in which the peripheral surface of the drum  1  was exposed, is effected on the peripheral surface of the drum  1 . 
         [0025]    The developing device  4  is a device which develops an electrostatic latent image on the drum  1 , into a visible image, with the use of developer (toner). The image forming apparatus  100  in this embodiment employs four development cartridges  4 , that is, the first to fourth development cartridges  4  ( 4   y ,  4   m ,  4   c , and  4   k ), which are different only in the color of the developer they store. When the four developing cartridges  4  are in the main assembly  100 A, they are vertically stacked between the drum  1  and the front door  102  of the main assembly  100 A. In this embodiment, the first cartridge  4   y  is at the top, and the second cartridge  4   m  is immediately below the first cartridge  4   y . The third cartridge  4   c  is immediately below the second cartridge  4   m , and the fourth cartridge  4   k  is right at the bottom. Each cartridge  4  is removably mountable in the main assembly  100 A. This setup will be described later in more detail. Each cartridge  4  has: a development roller  41  ( 41   y ,  41   m ,  41   c , or  41   k ) which supplies the drum  1  with developer; and a frame  42 , a part of which stores the developer to be used by the development roller  41  to develop the electrostatic latent image. The first cartridge  4   y  stores yellow (y) developer, and will be referred to as a yellow cartridge, hereafter. The second cartridge  4   m  stores magenta developer, and will be referred to as a magenta cartridge, hereafter. The third cartridge  4   c  stores cyan (c) developer, and will be referred to as a cyan cartridge. The fourth cartridge  4   k  stores black (k) developer, and will be referred to as a black cartridge. The four cartridges  4   y ,  4   m ,  4   c , and  4   k  can be selectively operated and controlled to develop an electrostatic latent image on the peripheral surface of the drum  1 . That is, as the development roller  41 , etc., of the selected cartridge  4  is driven, and a preset development bias is applied to the roller  41  from the electric power source (unshown) of the main assembly  100 A, the electrostatic latent image on the drum  1  is developed by the corresponding cartridge  4 . In other words, the electrostatic latent image on the drum  1  is developed with the use of developer by the roller  41 . In this embodiment, the black cartridge  4   k , or the bottommost cartridge, is made greater in developer (toner) capacity, compared to the other cartridges  4   y ,  4   m , and  4   c , because the black developer (toner) is greater in the frequency of usage than the other developers (toners). 
         [0026]    An intermediary transferring device  5  in this embodiment is a unit onto which a toner image (developed electrostatic latent image) is intermediately transferred. This unit  5  has an intermediary transfer belt  5   a  (which hereafter may be referred to simply as belt  5   a ), which is endless, flexible, and made of a dielectric substance. The unit  5  has also: first and second rollers  5   b  and  5   c , respectively, by which the belt  5   a  is suspended and kept stretched; and a first transfer roller  5   d , which is between the rollers  5   b  and  5   c  in terms of the belt movement direction, and is kept pressed against the drum  1 , with the presence of the belt  5   a  between the roller  5   d  and drum  1 . The area of contact between the drum  1  and belt  5   a  is the first transfer nip T 1 . The unit  5  has also a second transfer roller  11 , the position of which corresponds to the portion of the roller  5   b , around which the belt  5  is wrapped. The roller  11  is switchable in position by a roller moving mechanism (unshown) between a first position in which the roller  11  is kept pressed against the roller  5   b  with the presence of the belt  5   a  between the roller  11  and roller  5   b , being therefore capable of transferring a toner image, and a second position in which the roller  11  is kept separated from the belt  5   a , being therefore incapable of transferring a toner image. When the roller  11  is not needed for toner image transfer, it is kept in the second position, that is, the position in which it is kept separated from the belt  5   a . When the roller  11  is needed for toner image transfer, it is moved, with preset control timing, to the first position, that is, the position in which it is enabled to transfer a toner image. The area of contact between the roller  11  and belt  5   a  when the roller  11  is in the first position is the second transfer nip T 2 . 
         [0027]    The image forming apparatus  100  is provided with a belt cleaning device  5   e  for cleaning the surface of the belt  5   a . The belt cleaning device  5   e  is positioned so that its position corresponds with the portion of the peripheral surface of the roller  5   c , around which the belt  5   a  wraps. The cleaning device  5   e  is switchable in position between a first position in which the cleaning member of the cleaning device  5   e  is in contact with the surface of the belt  5   a , and a second position in which the cleaning member is kept separated from the surface of the belt  5   a . When the cleaning device  5   e  is not needed, it is kept in the second position. When the belt  5   a  needs to be cleaned, the cleaning device  5   e  is moved to the second position with preset control timing. 
         [0028]    The image forming apparatus  100  is also provided with a cleaning device  6 , which is the means for removing from the peripheral surface of the drum  1 , the transfer residual toner, that is, the toner remaining on the peripheral surface of the drum  1  after the transfer of a developer image (toner image) from the drum  1  onto the belt  5   a . The cleaning member of the cleaning device  6  in this embodiment is a blade  6   a  (cleaning blade). After being removed from the peripheral surface of the drum  1 , the transfer residual toner is stored in a waste developer storage chamber  6   b , which in this embodiment is a part of the frame  51  (drum cartridge frame). 
         [0029]    As an image formation start signal is inputted, the control circuit  101  starts the main motor (unshown), whereby not only does the drum  1  begin to be rotated at a preset peripheral velocity, but also the belt  5   a  begins to be circularly driven at the same peripheral velocity as the drum  1 , in such a direction that the direction of its movement in the interface between the belt  5   a  and drum  1  is the same as the direction of the movement of the peripheral surface of the drum  1  in the interface. As for the roller  11  and cleaning device  5   e , they are kept in their second positions, in which they are away from the belt  5   a . Further, a preset charge bias begins to be applied to the charge roller  2 . Thus, as a given portion of the peripheral surface of the drum  1  comes into contact with the charge roller  2 , it is uniformly charged to a preset polarity and a potential level. Then, the uniformly charged portion of the peripheral surface of the drum  1  is scanned (exposed) by the beam L of laser light outputted from the unit  3  while being modulated with image formation signals which correspond to the yellow monochromatic image, that is, one of the four monochromatic images into which the full-color image to be formed was separated. As a result, an electrostatic latent image which reflects the pattern and gradation of the yellow monochromatic image is effected on the peripheral surface of the drum  1 . Then, this electrostatic latent image is developed into a monochromatic yellow image, that is, a visible image formed of yellow developer, by the yellow cartridge  4   y  which is under the control of the control circuit  101 . Then, the developed image, that is, the image formed of the yellow developer, is transferred (first transfer) onto the surface of the belt  5   a , in the first transfer nip T 1 , by the preset first transfer bias applied to the roller  5   d  from an electric power source (unshown) with a preset control timing. The first transfer bias is preset in potential level, and is opposite in polarity to the developer. After the first transfer, the peripheral surface of the drum  1  is cleaned by the cleaning device  6 . 
         [0030]    As the transfer of the image formed of the yellow toner onto the belt  5   a  is completed, the charging, exposing, and developing processes for forming a monochromatic image on the peripheral surface of the drum  1  are carried out to form on the peripheral surface of the drum  1 , an image of the developer of the magenta color, which is one of the primary color components of the image to be formed. Then, the image formed of the developer of the magenta color is transferred (first transfer) onto the belt  5   a  in such a manner it vertically aligns with the yellow developer image on the belt  5   a.    
         [0031]    As the transfer (first transfer) of the image formed of the magenta developer is completed, the charging, exposing, and developing processes are carried out to form on the peripheral surface of the drum  1 , an image of the developer of the cyan color, which is one of the primary color components into which the full-color image to be formed was separated. Then, this image formed of the developer of the cyan color is transferred (first transfer) onto the belt  5   a  in such a manner that it is layered in alignment with the monochromatic yellow and magenta developer images which have just been transferred in layers onto the belt  5   a.    
         [0032]    As the transfer (first transfer) of the image formed of the cyan developer is completed, the charging, exposing, and developing processes are carried out to form on the peripheral surface of the drum  1 , an image of the developer of the black color, which is one of the primary color components into which the full-color image to be formed was separated. Then, this image formed of the developer of the black color is transferred (first transfer) onto the belt  5   a  in such a manner that it is layered on the monochromatic yellow, magenta, and cyan developer images which have just been transferred in layers onto the belt  5   a , in alignment with the monochromatic yellow, magenta, and cyan images. 
         [0033]    Consequently, an unfixed full-color image comprises yellow, magenta, cyan, and black monochromatic images. Incidentally, the order in which four monochromatic images, different in color, are formed does not need to be limited to the order in which they are formed in this embodiment (y→m→c→k). That is, the order is optional. Before the leading edge of the unfixed full-color image made up of the four monochromatic images, different in color, on the belt  5 , is made to reach the second position of the roller  10  by the movement of the belt  5   a , the roller  11  is moved to its second position in which the roller  11  is in contact with the belt  5   a  and is capable of transferring developer images. Further, cleaning device  5   e  also is moved to its second position, or the position in which the cleaning device  5   e  can clean the belt  5   a , with preset control timing. 
         [0034]    Meanwhile, the sheet feeder roller  8  of the sheet feeding portion  7  begins to be driven. As the roller  8  is driven, one of the sheets S of recording medium in the cassette  9  is fed into the main assembly  100 A while being separated from the rest. The cassette  9  is removably mountable in the main assembly  100 A from the front side of the main assembly  100 A (front loading). After being fed into the main assembly  100 A, the sheet S of recording medium is introduced by a pair of registration rollers  10 , into the aforementioned second transfer nip T 2 , which is the area of contact between the roller  11  and belt  5   a , with a preset control timing. To the roller  11 , a second transfer bias, which is opposite in polarity to the developer and is preset in potential level, is applied from an electric power source (unshown) of the main assembly  100 A. Thus, as the sheet S of recording medium is conveyed through the second transfer nip T 2  while remaining pinched by the belt  5   a  and transfer roller  11 , the unfixed full-color image, which is made up of the four monochromatic images which are different in color, is transferred (second transfer) onto the surface of the sheet S of recording medium, as if being peeled away from the belt  5   a , starting from the leading edge in terms of the recording medium conveyance direction. 
         [0035]    Then, the sheet S of recording medium is separated from the surface of the belt  5   a , and is introduced into a fixing device  12 , which is for fixing (solidly adhering while mixing) the four developer images, different in color, on the sheet S, to the surface of the sheet S. The fixing device  12  has: a rotatable heat roller  12   a ; and a rotatable pressure roller  12   b  which is kept pressed upon the heat roller  12   a  to apply heat and pressure to the sheet S. More specifically, as the sheet S of recording medium, onto which the developer images have just been transferred from the belt  5   a , is conveyed through the fixing device  12  while remaining pinched by the pair of fixation rollers, that is, the heat roller  12   a  and pressure roller  12   b , heat and pressure are applied to the sheet S and the developer images thereon, whereby the four monochromatic toner images, different in color, on the sheet S are fixed to the surface of the sheet S. Then, the sheet S is conveyed out of the fixing device  12 , and then, is discharged as a full-color print (copy) into a delivery tray  14  by a pair of discharge rollers  13 . Incidentally, when the image forming apparatus  100  is in the monochromatic image formation mode, the image forming operation is carried out using only the black cartridge  4   k.    
       (Method for Replacing Cartridge) 
       [0036]    As the development cartridges  4  ( 4   y ,  4   m ,  4   c , and  4   k ) are used for image formation, the developer (toner) in each cartridge is consumed. Thus, the image forming apparatus  100  is provided with a means (unshown) for detecting the amount of the developer remaining in each development cartridge  4 . The detected amount of the developer in each development cartridge  4  is compared by the control circuit  101  with a threshold value for warning an operator of the image forming apparatus  100 , of the nearing of the end of the preset length of the service life of the cartridge, or the actual end of the service life. Then, if the detected amount of the developer remainder in any of the development cartridges became less than the threshold value, the information regarding the predicted remaining length of the service life of this development cartridge, or the arrival of the end of the service life of this development cartridge, is displayed on the display portion  104  of the apparatus  100  or host apparatus  200 , prompting thereby the operator to prepare a replacement for this development cartridge so that the level of quality at which the apparatus  100  outputs images remains at a preset level. 
         [0037]    In this embodiment, for the usability in terms of the replacement of the development cartridges  4  and drum cartridge  50 , the apparatus  100  is structured so that the development cartridges  4  and drum cartridge  50  in the main assembly  100   a  can be accessed from the front side of the apparatus  100 . More concretely, the opening  106  through which the cartridges  4  are inserted into, or removed from, the cartridge chamber  105  in the main assembly  100  A is on the front side of the main assembly  100 A. Further, the front side of the main assembly  100 A is provided with a door (front)  102 , which is rotationally movable between the position in which the door  102  keeps the opening  6  completely covered, and the position in which the door  102  keeps the opening  6  fully exposed. In this embodiment, the door  102  is hinged to the front end of the right frame  107 R of the main assembly  100 A, and can be rotatably moved about the hinge  108  to expose or cover the opening  106 . That is, the door  102  can be rotationally moved about the hinge  108  to cover the opening  106  of the main assembly  100   a  as shown in  FIG. 1A , or can be rotationally moved rightward about the hinge  108  to fully expose the opening  106  as shown in  FIG. 1B . Designated by a referential code  102   a  is a handle of the door  102 . As the door  102  is opened, the cartridge chamber  105  is exposed, exposing thereby the downstream end of each development cartridge  4  in terms of the development cartridge insertion direction, as shown in  FIG. 1B . Further, the handle  55  of the drum cartridge  50 , which is attached to the downstream end of the bottom plate  54  of the frame  51  in terms of the drum cartridge insertion direction A, is exposed. 
         [0038]    When the door  102  is fully open, the first to fourth development cartridges  4   y ,  4   m ,  4   c , and  4   k  can be sequentially removed from the main assembly  100 A, starting from the top one. As for the drum cartridge  50 , it can be removed from the main assembly  100 A together with all the development cartridges  4   y ,  4   m ,  4   c , and  4   k , or can be removed alone after the removal of all the development cartridges  4 . Obviously, the drum cartridge  50  and development cartridges  4   y ,  4   m ,  4   c , and  4   k  can be mounted into the main assembly  100 A in the opposite order from the above described order in which they can be removed. 
       (Drum Cartridge) 
       [0039]    Next, the structure of the drum cartridge  50  is described along with the portion of the main assembly structure, which is for allowing the drum cartridge  50  to be removably mounted in the main assembly.  FIG. 2B  is a perspective view of the cartridge  50 . The cartridge  50  in this embodiment comprises: the frame  51 ; drum  1 ; charge roller  2  as a means for processing the drum  1 ; and cleaning device  6  as a means for processing the drum  1 . The drum  1  and processing means (charge roller  2  and cleaning device  6 ) are attached to the frame  51  so that a preset positional relationship can be maintained among them. More specifically, the drum  1  is rotatably supported between the left and right plate  52 L and  52 R, respectively, of the frame  51 , by the left and right bearings  53  (right bearing is unshown) attached to the left and right plate  52 L and  52 R, respectively. The left and right bearings  53  perpendicularly project outward from the outward surfaces of the  52 L and  52 R, one for one, and function as cartridge positioning portions. The bottom plate  54  of the frame  51  roughly horizontally extends from the main portion of the frame  51  in the opposite direction B (cartridge removal direction) to the cartridge insertion direction A. The aforementioned handle  55  is on the upstream end of the bottom plate  54 , in terms of the drum cartridge insertion direction A, and is rotationally movable about the left and right shafts  56 . The handle  55  can be switched in position between the upright position (drawn in solid line in  FIG. 2B ) into which it is folded, and the horizontal position (drawn in two-dot chain line in  FIG. 2B ) in which it protrudes frontward of the main assembly  100 A so that it can be grasped by an operator to pull the drum cartridge  50  out of the main assembly  100 A. 
         [0040]    The bottom plate  54  is provided with a pair of grooves  26 , which are on the top side of the bottom plate  54 . The grooves  26  are for guiding the black cartridge  4   k , or the bottommost cartridge, when the cartridge  4   k  is mounted into, or removed from, the main assembly  100 A. They are in the adjacencies of the left and right edges of the bottom plate  54 , and extend in the cartridge insertion-removal direction A&lt;&lt;B. The bottom plate  54  is also provided with a positioning hole  27 , which is at the upstream end of the bottom plate  54  in terms of the cartridge insertion direction, and at the center of the bottom plate  54  in terms of the left-right direction. Further, the left and right plate  52 L and  52 R are provided with four recesses for positioning the development cartridges  4  relative to the drum cartridge  50  (drum  1 ) as the cartridges  4  are mounted into the main assembly  100 A. More specifically, the left plate  52 L is provided with recesses  22 Ly,  22 Lm,  22 Lc, and  22 Lk, listing from the top, for positioning the development cartridges  4   y ,  4   m ,  4   c , and  4   k , respectively, whereas the right plate  52 R is provided with recesses  22 Ry,  22 Rm,  22 Rc, and  22 Rk, listing from the top, for positioning the development cartridges  4   y ,  4   m ,  4   c , and  4   k , respectively. Further, the left plate  52 L is provided with development cartridge positioning-and-retaining springs  23 Ly,  23 Lm,  26 Lc, and  26 Lk, which are at the top edges of the recesses  22 Ly,  22 Lm,  22 Lc, and  22 Lk, respectively, whereas the right plate  52 R is provided with development cartridge positioning-and-retaining springs  23 Ry,  23 Rm,  26 Rc, and  26 Rk, which are at the top edges of the recesses  22 Ry,  22 Rm,  22 Rc, and  22 Rk, respectively. 
         [0041]    As for the cartridge chamber  105 , each of the left and right frames  107 L and  107 R is provided with a drum cartridge guiding member  60  (drum cartridge guide of main assembly  100 A), which is on the inward surface of each frame  107  as shown in  FIGS. 3A ,  3 B, and  4 A. The two drum cartridge members  60  are symmetrically positioned with reference to the vertical plane which coincides with the center of the main assembly  100 A and is parallel to the cartridge insertion direction A. Further, each of the left and right drum cartridge guiding members  60  is provided with a drum positioning recess  61  (drum cartridge positioning portion of main assembly  100 A), into which the corresponding drum bearing  53  (as drum cartridge positioning portion of drum cartridge  50 ) fits. Further, each of the left and right guides  60  is provided with a spring  62  for keeping the drum bearing  53  retained in the drum positioning recess  61 . 
         [0042]    The operational sequence for mounting the cartridge  50  into the main assembly  100 A is as follows: First, an operator is to hold the cartridge  50  by the left and right end portions of the cartridge  50 , insert the cartridge  50  from the drum side, into the cartridge chamber  105  of the main assembly  100 A through the opening  106 , so that the bottom surface of the bottom plate  54  of the frame  51  comes into contact with the top surface of the bottom frame  103  of the main assembly  100 A. Then, the operator is to slide the cartridge  50  rearward of the main assembly  100 A, in such a manner that the cartridge  50  is guided by the top surface of the bottom frame  103 . As the cartridge  50  is inserted close to the deepest end of the cartridge chamber  105 , the left and right drum bearings  53  (as cartridge positioning portions of cartridge  50 ) enter the recesses  61  of the left and right cartridge guiding members  60 , one for one, while pushing up the springs  62  against the resiliency of the springs  62 . Then, each bearing  53  comes into contact with the vertical wall (bearing catching wall) of the corresponding recess  61 , preventing thereby the cartridge  50  from being inserted further. From this point on, the bearing  53  is retained in the recess  61  by the resiliency of the spring  62 . Thus, the cartridge  50  becomes precisely positioned relative to the cartridge chamber  150  in terms of the front-rear, left-right, and vertical directions. The operational sequence for removing the cartridge  50  out of the cartridge chamber  150  is as follows: The operator is to rotationally move the handle  55  so that it becomes roughly horizontal and extends upstream from the upstream end of the bottom plate  54 , in terms of the cartridge insertion direction A. Then, the operator is to pull the cartridge  50  by grasping the handle  55  frontward of the main assembly  100 A (cartridge removal direction B) against the resiliency of the springs  62 . As the cartridge  50  is pulled, the left and right bearings  53  slip out of the corresponding recesses  61  while pushing the springs  62  upward against the resiliency of the springs  62 . That is, the bearings  53  are freed from the recesses  61 . Then, as the cartridge  50  is pulled out further by the operator by the handle  55 , the cartridge  50  slides frontward of the main assembly  100 A, on the top surface of the frame  103 , while being guided by the frame  103 . This is how the cartridge  50  can be moved out of the main assembly  100 A through the opening  106 . 
       (Development Cartridge) 
       [0043]    Next, the structure of the development cartridge  4  is described along with the portion of the structure of the main assembly  100 A, which is for mounting the development cartridges  4  into the main assembly  100 A or removing the development cartridges  4  from the main assembly  100 A. In this embodiment, the development cartridges  4   y ,  4   m ,  4   c , and  4   k  have development rollers  41   y ,  41   m ,  41   c , and  41   k , respectively, which are for supplying the drum  1  with developer. Further, each development cartridge  41  has a frame  42  (developer chamber) in which the developer to be used for developing an electrostatic latent image is stored. The development cartridge frame  42  is flat and parallelepipedic. Further, each development cartridge frame  42  contains: a coating member for coating the peripheral surface of the roller  41  with developer; a development blade which not only regulates the coated developer on the peripheral surface of the roller  41  in terms of the thickness of the uniform layer into which the coated developer is formed, but also, charges the developer as it regulates the coated developer; a member which conveys the developer while stirring the developer; etc., which are not illustrated in the drawings. The roller  41  is rotatably supported between the left and right plates of the frame  42  by the left and right bearings  43  which are at the downstream end of the frame  42  in terms of the development cartridge insertion direction. The positional relationship between the roller  41  and frame  42  is such that roughly half the peripheral surface of the roller  41 , in terms of the circumferential direction of the roller  41 , is exposed from the frame  42 , and the other half is inside the frame  42 . Each of the left and right ends of the roller  41  is fitted with a spacer ring  44  for regulating the gap between the peripheral surface of the roller  41  and the peripheral surface of the drum  1 . The spacer ring  44  is coaxial with the roller  41 . The spacer ring  44  is greater in diameter by a preset amount than the roller  41 . Further, the frame  42  is provided with a pair of handgrips  45 , which are at the left and right upstream ends of the frame  42  in terms of the cartridge insertion direction. The frame  42  is also provided with a cartridge positioning recess  27  and a cartridge positioning projection  28 . The recess  27  is at the top center of the upstream end of the frame  42 . The projection  28  is at the bottom center of the upstream end of the frame  42 . More specifically about the positioning projection  28 , the frame  42  is provided with a small plate  29  which perpendicularly projects downward from the bottom center of the upstream end of the frame  42 . The cartridge positioning projection  28  perpendicularly projects in the cartridge insertion direction A from the inward surface of the small plate  29 . Further, the top wall of the frame  42  is provided with a pair of guiding grooves  26  for guiding the cartridge  4  which is directly above. The guiding grooves  26  extend along the left and right edges of the frame  42 , that is, in the cartridge insertion-removal direction A&lt;&lt;B. The frame  42  is also provided with a pair of guiding ridges  25  which fit, one for one, in the guiding grooves  26  of the cartridge  4  which is directly below. The guiding ridges  25  also extend in the cartridge insertion-removal direction A         B. The guiding grooves  26  and guiding ridges  25  are for guiding each cartridge  4  when each cartridge  4  is engaged with the drum cartridge  50 , and also, when each cartridge  4  is disengaged from the drum cartridge  50 . 
         [0000]    (Engagement of Development Cartridge with Drum Cartridge) 
         [0044]    The first, second, third, and fourth development cartridges  4  ( 4   y ,  4   m ,  4   c , and  4   k ) are to be engaged with the drum cartridge  50  in the order of the fourth, third, second, and first. Referring to  FIG. 5A , the black cartridge  4 , or the bottommost cartridge, is to be positioned directly on the bottom plate  54  of the frame  51 . It is to be inserted into the cartridge chamber  150  of the main assembly  100 A from the development roller side, with its left and right guiding ridges  25  on its bottom surface fitted in the left and right guiding grooves  26 , respectively, in the top surface of the bottom plate  54 . Regarding the attitude of the handle  55 , when the development cartridge  4   k  is inserted into the cartridge chamber  150 , the handle  55  is to be kept horizontal to prevent the handle  55  from interfering with the cartridge  4   k . With the guiding ridges  25  engaged in the guiding grooves  26 , the operator is to push the cartridge  4   k  in the cartridge insertion direction A to cause the cartridge  4   k  to slide, on the bottom plate  54 , inward of the frame  51 . As the cartridge  4   k  is pushed inward of the frame  51 , the left and right bearings  43  of the cartridge  4   k  engage into the recesses  22 Lk and  22 Rk of the left and right plate  52 L and  52 R of the cartridge  50 , respectively. Then, the left and right bearings  43  are immediately pressed by the springs  23 Lk and  23 Rk in the cartridge insertion direction A, whereby the development roller  41   k  is precisely positioned relative to the drum  1 . Therefore, the cartridge  4   k  is kept pressed in the cartridge insertion direction A, whereby the development roller  41   k  is kept precisely positioned relative to the drum  1 . In this embodiment, as the left and right bearings  43  are pressed by the left and right springs  23 Lk and  23 Rk, the left and right spacer rings  44  are placed in contact with the left and right end portions of the drum  1 , whereby a preset distance is maintained between the rotational axis of the drum  1  and that of the roller  41   k , and therefore, the peripheral surface of the roller  41   k  is kept a preset microscopic distance away from the peripheral surface of the drum  1 . In other words, in this embodiment, the so-called non-contact developing method is employed. However, the application of the present invention is not limited to an electrophotographic image forming apparatus which employs the non-contact developing method. That is, the present invention is also applicable to an electrophotographic image forming apparatus which employs the contact developing method, that is, the developing method which places the roller  41  and drum  1  in contact with each other for development. Going back to the description of this embodiment, as the cartridge  4   k  is inserted inward of the frame  51 , the projection  28  of the cartridge  4   k  fits into the recess  27  of the bottom plate  54 , whereby the cartridge  4   k  is correctly set in its attitude relative to the cartridge  50 ; in other words, the cartridge  4   k  is precisely positioned relative to the drum cartridge  50  in terms of the cartridge insertion direction, left-right direction, and vertical direction. 
         [0045]    As for the mounting of the cyan cartridge  4   c  which is to be mounted on the cartridge  4   k  which is already in engagement with the drum cartridge  50 , first, the cartridge  4   c  is to be inserted into the cartridge chamber  150  from the roller ( 4   c ) side, in such a manner that the left and right guiding ridges  25  of the cartridge  41   c , which are on the bottom surface of the cartridge  41   c , fit into the left and right guiding grooves  26  of the cartridge  4   k , which are in the top surface of the cartridge  4   k . Then, with the ridges  25  engaged in the grooves  26 , the operator is to push the cartridge  4   c  in the cartridge insertion direction A so that the cartridge  4   c  slides on the cartridge  4   k , inward of the frame  51 . As the cartridge  4   c  is pushed inward of the frame  51 , the left and right bearings  43  of the cartridge  4   c  fit into the recesses  22 Lc and  22 Rc of the left and right plates  52 L and  52 R of the cartridge  50 , respectively, and are pressed by the springs  23 Lc and  23 Rc in the cartridge insertion direction A, whereby the roller  41   c  is precisely positioned relative to the drum  1 . Further, the projection  28  of the cartridge  4   c  fits into the recess  27  of the cartridge  4   k , whereby the cartridge  4   c  is precisely set in terms of its attitude relative to the cartridge  50 . That is, the cartridge  4   c  is precisely position in terms of the cartridge insertion direction, left-right direction, and vertical direction. 
         [0046]    As for the mounting of the magenta cartridge  4   m  which is to be mounted on the cartridge  4   c  which is already in engagement with the drum cartridge  50 , first, the cartridge  4   m  is to be inserted into the cartridge chamber  150  from the roller ( 41   m ) side, in such a manner that the left and right guiding ridges  25  of the cartridge  41   m , which are on the bottom surface of the cartridge  41   m , fit into the left and right guiding grooves  26  of the cartridge  4   c , which are in the top surface of the cartridge  4   c . Then, with the ridges  25  engaged in the grooves  26 , the operator is to push the cartridge  4   m  in the cartridge insertion direction A so that the cartridge  4   m  slides on the cartridge  4   c , inward of the frame  51 . As the cartridge  4   m  is pushed inward of the frame  51 , the left and right bearings  43  of the cartridge  4   m  fit into the recesses  22 Lm and  22 Rm of the left and right plates  52 L and  52 R of the cartridge  50 , respectively, and are pressed by the springs  23 Lm and  23 Rm in the cartridge insertion direction A, whereby the roller  41   m  is precisely positioned relative to the drum  1 . Further, the projection  28  of the cartridge  4   m  fits into the recess  27  of the cartridge  4   c , whereby the cartridge  4   m  is precisely set in terms of its attitude relative to the cartridge  50 . That is, the cartridge  4   m  is precisely positioned in terms of the cartridge insertion direction, left-right direction, and vertical direction.  FIG. 5B  shows the state of the drum cartridge  50 , and black, cyan, magenta, and yellow development cartridges  4   k ,  4   c ,  4   m , and  4   y , in which the black, cyan, and magenta development cartridge  4   k ,  4   c , and  4   m  are already in engagement with the drum cartridge  50 , whereas the development cartridge  4   y  is yet to be engaged with the drum cartridge  50 . 
         [0047]    As for the mounting of the yellow cartridge  4   y , which is to be mounted on the cartridge  4   m  which is already in engagement with the drum cartridge  50 , first, the cartridge  4   y  is to be inserted into the cartridge chamber  150  from the roller ( 41   y ) side, in such a manner that the left and right guiding ridges  25  of the cartridge  4   y , which are on the bottom surface of the cartridge  4   y , fit into the left and right guiding grooves  26  of the cartridge  4   m , which is in the top surface of the cartridge  4   m . Then, with the ridges  25  engaged in the grooves  26 , the operator is to push the cartridge  4   y  in the cartridge insertion direction A so that the cartridge  4   y  slides on the cartridge  4   m , inward of the frame  51 . As the cartridge  4   y  is pushed inward of the frame  51 , the left and right bearings  43  of the cartridge  4   y  fit into the recesses  22 Ly and  22 Ry of the left and right plates  52 L and  52 R of the cartridge  50 , respectively, and are pressed by the springs  23 Ly and  23 Ry in the cartridge insertion direction A, whereby the roller  41   y  is precisely positioned relative to the drum  1 . Further, the projection  28  of the cartridge  4   y  fits into the recess  27  of the cartridge  4   m , whereby the cartridge  4   y  is precisely set in terms of its attitude relative to the cartridge  50 . That is, the cartridge  4   y  is precisely position in terms of the cartridge insertion direction, left-right direction, and vertical direction. 
         [0048]    Incidentally, there are various ways to mount the drum cartridge  50  and development cartridges  4  into the main assembly  100 A. For example, the drum cartridge  50  and four development cartridges  4  can be mounted together after the four development cartridges  4  are engaged with the drum cartridge  50 , or the four development cartridges  4  may be mounted following the above described procedure, after the mounting of the drum cartridge  50 . When it is necessary to replace only one or more development cartridges  4 , the second method is to be used. As for the method for taking the drum cartridge  50  and development cartridge  4  out of the main assembly  100 A, there are also various methods. That is, first, the door  102  is to be opened. Then, the drum cartridge  50  and four development cartridges  4  can be taken together out of the main assembly  100 A, by pulling the drum cartridge  50  by the handle  55 , or the development cartridges  4  can be pulled out of the main assembly  100 A one by one, starting from the top development cartridge  4 , by grasping the handle  45 , while leaving the drum cartridge  50  mounted. 
         [0049]    In this embodiment, each development cartridge  4  is precisely positioned relative to the drum cartridge  50  which is holding the drum  1 . Therefore, it is assured that the roller  41  is precisely aligned, and kept aligned, relative to the drum  1 . Further, it is possible to insert the drum cartridge  50  and development cartridges  40  together into the main assembly  100 A, or remove them together from the main assembly  100 A. That is, the main assembly  100 A, drum cartridge  50 , and development cartridges  4  are structured so that multiple development cartridges  4  can be removed from the drum cartridge  50  in the main assembly  100 A, or the drum cartridge  50  in the main assembly  100 A can be removed with the development cartridges  4 . Further, the top surface of the bottom plate  54  of the frame  51  of the drum cartridge  50 , and the top surface of each of the development cartridge  4   k ,  4   c , and  4   m  is provided with guiding grooves  26  for guiding the development cartridge  4  which is immediately above, when the cartridges  4  are inserted, whereas the bottom surface of each development cartridge  4  is provided with the pair of guiding ridges  25 , by which the development cartridge  4  is guided when it is inserted into the cartridge chamber  150 . When the development cartridges  4  are to be mounted into the main assembly  100 A, they are to be sequentially mounted into the main assembly  100 A, and are to be sequentially engaged with the drum cartridge  50 , starting from the development cartridge  4   k , or the bottommost development cartridge. Since the drum cartridge  50  and development cartridges  4  are structured so that the development cartridge  4   m  is provided with the cartridge guiding grooves  26 , by which the cartridge guiding ridges  25  of the cartridge  4   y  are guided to guide the cartridge  4   y ; the cartridge  4   c  is provide with the cartridge guiding grooves  26 , by which the cartridge guiding ridges  25  of the cartridge  4   m  are guided to guide the cartridge  4   m ; the cartridge  4   k  is provide with the cartridge guiding grooves  26 , by which the cartridge guiding ridges  25  of the cartridge  4   c  are guided to guide the cartridge  4   c ; and the bottom plate  54  of the drum cartridge  50  is provided with the cartridge guiding grooves  26 , by which the cartridge guiding ridges  25  of the cartridge  4   k  are guided to guide the cartridge  4   k . Therefore, the development cartridges  4  in this embodiment are significantly less in thickness than any of conventional development cartridges. In other words, the application of the present invention leads to the reduction in the size of the main assembly of an electrophotographic image forming apparatus. 
       Embodiment 2 
       [0050]      FIG. 6A  is a drawing for describing the apparatus  100  in the second preferred embodiment of the present invention. The apparatus  100  in this embodiment is basically the same as the apparatus  100  in this first preferred embodiment. That is, the drum cartridge  50  is precisely positioned relative to the main assembly  100 A, and each development cartridge  4  is precisely positioned relative to the drum cartridge  50 . Further, the drum cartridge  50  and development cartridges  40  can be mounted together into the main assembly  100 A, or removed together from the main assembly  100 A. This embodiment differs from the first embodiment as follows. The door  102  has four projections  28  ( 28   y ,  28   m ,  28   c , and  28   k ) which are for precisely positioning the development cartridges  4 , one for one, to correctly set the cartridges  4  in attitude. The four projections  34  perpendicularly project from the inward surface of the door  102 . Thus, as the door  102  is closed, the four projections  28  fit into the cartridge positioning holes  27  ( 27   y ,  27   m ,  27   c , and  27   k ) of the four development cartridges  4 , which are at the downstream ends of the cartridges  4  in terms of the cartridge insertion direction A. The position of the each cartridge  4  in terms of the rotational direction of the development roller  41  in the cartridge  4  is roughly set by the cartridge  4  or cartridge  50  which is immediately below. Thus, as the door  102  is closed, the four projections  34  fit into the holes  27  of the cartridges  4 , one for one, whereby the cartridges  4  are precisely positioned relative to the main assembly  100 A and drum cartridge  50 . 
         [0051]    Also in this embodiment, the drum cartridge  50  and development cartridges  4  can be inserted together into the main assembly  100 A, or removed together from the main assembly  100   a  in the same manner as the counterparts in the first embodiment can. Further, the members for guiding the development cartridges  4  when the cartridges  4  are inserted into the main assembly  100 A are integral parts of the cartridges  4 . Therefore, the main assembly  100 A does not need to be provided with the members or portions for guiding the development cartridges  4  when the cartridges  4  are inserted into, or removed from, the main assembly  100 A. Thus, the image forming apparatus  100  in this embodiment is significantly narrower compared to any of conventional electrophotographic image forming apparatuses. In other words, the present invention can provide an electrophotographic image forming apparatus which is significantly narrower than any of conventional electrophotographic image forming apparatuses. Further, in the case of the image forming apparatus  100  in this embodiment, it is by the door  102  that the development cartridges  4  are precisely positioned. Therefore, it is not mandatory that the development cartridges  4  are placed in contact the adjacent ones. Thus, each development cartridge  4  is less likely to be affected by the oscillations of the other cartridges  4 . 
       Embodiment 3 
       [0052]      FIG. 6B ,  7 , and  8  are drawings for describing the apparatus  100  in the third preferred embodiment of the present invention. Each of the four development cartridges  4  ( 4   y ,  4   m ,  4   c , and  4   k ) is provided with a pair of (left and right) cartridge holding means (legs)  30  ( 30 L and  30 R) for temporarily holding the cartridge  4 . Each cartridge  4  is also provided with a development cartridge positioning means  32  having a cam  31  which serves as the means for regulating the cartridge holding means (legs)  30  for temporarily holding the development cartridge  4 . The left and right legs  30  are attached to a rotational shaft  33 , which is in engagement with the cam  31  of the development cartridge positioning means  32  to regulate the rotational movement of the legs  30 . Thus, as the development cartridge positioning means  32  is rotationally moved from the position shown in  FIG. 7A  into the position shown in  FIG. 7(   c ), the legs  30  are freed from the control from the positioning means  32 . As a result, the legs  30  are rotationally moved by the left and right springs  34 L and  34 R as shown in  FIG. 7(   c ).  FIG. 7A  is an enlargement of the circled portion of  FIG. 7A , and  FIG. 7(   d ) is an enlargement of the circled portion of  FIG. 7(   c ). 
         [0053]    Next, referring to  FIGS. 7 and 8 , the method for mounting or dismounting the development cartridge  4  in this embodiment is described. If it is necessary to pull the magenta cartridge  4   m , for example, out of the main assembly  100 A, the operator is to rotationally move the cartridge positioning means  32  of the yellow cartridge  4   y  from the position shown in  FIG. 7A  into the position shown in  FIG. 7(   c ) so that the cartridge positioning means  32  disengages from the magenta cartridge  4   m . As the cartridge positioning means  32  of the yellow cartridge  4   y  is moved as described above, the legs  30  of the yellow cartridge  4   y  are rotationally moved by the unshown springs while being guided by the top portion of the magenta cartridge  4   m , that is, the cartridge to be pulled out, as shown in  FIG. 8B . Consequently, the legs  30 L and  30 R of the yellow cartridge  4   y  stand erect on the cyan cartridge  4   c , that is, the cartridge which is immediately below the cyan cartridge  4   m , temporarily holding the yellow cartridge  4   y , as shown in  FIG. 8(   c ). In other words, the position in which each of the legs  30  of the yellow cartridge  4   y  is as shown in  FIG. 8(   c ) is the first position of the leg  30 , in which the leg  30  temporarily supports the yellow cartridge  4   y  when the development cartridge  4   m , that is, the development cartridge which is immediately below the cartridge  4   y , needs to be removed from the main assembly  100 A. Since the yellow cartridge  4   y  is temporarily supported by its legs  30  and the cyan cartridge  4   c , the magenta cartridge  4   m , which is between the yellow and cyan cartridges  4   y  and  4   c , can be pulled out with no interference. On the other hand, when it is necessary to insert the magenta cartridge  4   m  into the main assembly  100 A, the operator is to carry out in the reverse order, the above described steps carried out to extract the cartridge  4   m . That is, the operator is to insert the magenta cartridge  4   m  as shown in  FIG. 8(   c ). As the cartridge  4   m  is inserted, the legs  30  of the yellow cartridge  4   y , which are perpendicular to the cartridge  4   y  at this point, are rotationally moved upward by the magenta cartridge  4   m  as shown in  FIG. 8B , until they are stored into the recesses (leg spaces) of the yellow cartridge  4   y , as shown in  FIG. 8A . The position in which the leg  30  is in  FIG. 8A  is the second position for the leg  30 , that is, the position in which the leg  30  does not support the development cartridge to which it belongs. Then, the operator is to precisely position the magenta cartridge  4   m  with the use of the cartridge positioning means  32  of the yellow cartridge  4   y . That is, when the legs  30  of the positioning means  32  of a given development cartridge  4  are in their second position, the positioning means  32  of the cartridge is in the position in which it can precisely position the immediately adjacent development cartridge, whereas when the legs  30  of the given development cartridge  4  are in their first position, the positioning means  32  of the development cartridge remains retracted. Therefore, the downstream end of the magenta cartridge  4   m  is precisely position relative to the main assembly  100 A (drum cartridge  50 ), and also, the legs  30  of the yellow cartridge  4   y  do not weigh on the magenta cartridge  4   m , that is, the cartridge which is immediately below the yellow cartridge  4   y . The operational sequence for mounting or dismounting each of the other cartridges  4  is the same as the one for the development cartridge  4   m.    
         [0054]    As described above, each development cartridge  4  is provided with the pair of rotationally movable legs, and the development cartridge positioning means having the leg regulating means. Thus, no matter which development cartridge  4  is mounted into, or dismounted from, the main assembly  100 A, the mechanism for temporarily holding a development cartridge automatically functions. Therefore, even if the drum cartridge  50  and/or main assembly  100 A is not provided with the cartridge insertion (removal) guides, the development cartridges can be easily inserted or removed. Also in the third embodiment, development cartridges  4  are precisely positioned relative to the drum cartridge  50  (main assembly  100 A) by being engaged with the drum cartridge  50 , and therefore, they can be inserted together into, or removed together from, the main assembly  100 A, with the drum cartridge  50 . 
         [0055]    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. 
         [0056]    This application claims priority from Japanese Patent Application No. 140473/2010 filed Jun. 21, 2010 which is hereby incorporated by reference.