Abstract:
A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus including a positioning portion, a rotatable urging member taking an urging position for urging the cartridge to the positioning portion, and retracted and stand-by positions. The cartridge includes an electrophotographic photosensitive drum, a process device actable on the drum, a positionable portion, a displacing portion moving the urging member from the stand-by to the retracted position by contacting a portion-to-be-displaced disposed at a position remoter from the rotation axis of the urging portion than the urging portion when the cartridge advances along an axial direction of the drum in the main assembly, the displacing portion moving the urging member to the retracted position by contacting the urging member when the cartridge advances in the main assembly, and an urgable portion urgable by the urging portion when the cartridge is set in the main assembly.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a process cartridge, and an image forming apparatus which employs a process cartridge. 
         [0002]    Here, an “electrophotographic image forming apparatus” means an apparatus, such as an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, etc.), or the like, which forms an image on recording medium, with the use of an electrophotographic image forming method. 
         [0003]    A “process cartridge” means a cartridge in which an electrophotographic photosensitive drum, and one or more process means, that is, a charging means, and a developing means or a cleaning means, for processing the electrophotographic photosensitive drum, are integrally disposed so that they can be removably mountable in the main assembly of the image forming apparatus. More specifically, a process cartridge is a cartridge in which an electrophotographic photosensitive drum, and at least one among the abovementioned processing means, such as a developing means, a charging means, and a cleaning means, are integrally disposed. It also means a cartridge in which at least a developing means as a processing means, and an electrophotographic photosensitive drum, are integrally disposed so that they can be removably mountable in the main assembly of an electrophotographic image forming apparatus. 
         [0004]    In the field of an electrophotographic image forming apparatus which employs one of the electrophotographic image formation processes, a process cartridge system has long been employed, according to which an electrophotographic photosensitive drum, and a single or plurality of processing means which act on the electrophotographic photosensitive drum, are integrally disposed in a cartridge to make it possible for them to be removably mountable in the main assembly of the image forming apparatus. Also according to this process cartridge system, an image forming apparatus can be maintained by a user himself, without relying on a service person, drastically improving the image forming apparatus in operability. Thus, a process cartridge system is widely in use in the field of image forming apparatus. 
         [0005]    The image forming operation of an electrophotographic image forming apparatus is as follows: First, the electrophotographic photosensitive drum is exposed to a beam of light projected from a laser, an LED, an ordinary electric light, or the like, while being modulated with pictorial information, forming thereby an electrostatic latent image on the photosensitive drum. The electrostatic latent image is developed by the developing apparatus. Then, the developed image on the photosensitive drum is transferred onto recording medium; an image is formed on the recording medium. 
         [0006]    Referring to  FIG. 21 , as one of the image forming apparatuses which employ the above described process cartridge, an electrophotographic color image forming apparatus  200  of the inline type has been known, which is an image forming apparatus, which is an image forming apparatus in which multiple process cartridges  170  ( 170   a - 170   d ) are juxtaposed in a single straight row. 
         [0007]    As one of the structural arrangements for precisely positioning the above described process cartridge relative to the main assembly of an image forming apparatus, a structural arrangement which provides the left and right lateral plates in the image forming apparatus with a recess (recesses) or hole (holes) for positioning a photosensitive drum is disclosed in U.S. Pat. No. 6,483,527. According to this structural arrangement, a bearing with which each of the lengthwise end portions of the photosensitive drum is fitted is pressed against the preset portion (portions) of the edge of the abovementioned recess (recesses) or hole (holes), by a tortional coil spring (pressing member) to precisely position the photosensitive drum. More specifically, as the process cartridge is inserted into the main assembly of the image forming apparatus, a V-shaped projection, with which one end of the torsion spring is provided, comes into contact with the bearing, being thereby rotated against the resiliency of the torsion spring. Then, as soon as the bearing rides over the V-shaped projection, the V-shaped projection presses the bearing upon the abovementioned portion (portions) of the recess (recesses) or hole (holes). 
         [0008]    The operation for mounting a process cartridge into the main assembly of an image forming apparatus, or removing a process cartridge from the main assembly, is desired to be as simple as possible in the operation which an operator is required to carry out, and as small as possible in the amount of force required of an operator. 
         [0009]    The present invention is one of the further developments of the above described prior art. 
       SUMMARY OF THE INVENTION 
       [0010]    Thus, the primary object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly smaller in the amount of force required of an operator when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0011]    Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly better in operability when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0012]    Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly more stable when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0013]    Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly better in terms of the accuracy with which the process cartridge is positioned relative to the main assembly of the image forming apparatus when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0014]    Another object of the present invention is to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly more stable in the pressure applied for correctly positioning the process cartridge relative to the main assembly of the image forming apparatus, and is higher in the accuracy with which the process cartridge is positioned relative to the main assembly, when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0015]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly smaller in the amount of force necessary to mount the process cartridge into the main assembly of the image forming apparatus than that in accordance with the prior art. 
         [0016]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly better in operability when mounting the process cartridge into the main assembly of the image forming apparatus, and smaller in the amount of force necessary to mount the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0017]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly more reliable in terms of the positioning of the cartridge when mounting the process cartridge into the main assembly of the image forming apparatus. 
         [0018]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly higher in the accuracy with which the process cartridge is positioned relative to the main assembly of the image forming apparatus when mounting the process cartridge into the main assembly of the image forming apparatus than that in accordance with the prior art. 
         [0019]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly more reliable in terms of the positioning of the cartridge relative to the main assembly of the image forming apparatus, when mounting the process cartridge into the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0020]    The present invention makes it possible to provide a combination of a process cartridge and an electrophotographic image forming apparatus, which is significantly more stable in the pressure applied to the process cartridge, and is significantly more precise in the positioning of the cartridge relative to the main assembly of the image forming apparatus, than that in accordance with the prior art. 
         [0021]    According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein said main assembly of the apparatus includes a main assembly side positioning portion, an urging member rotatable about a rotation axis to take an urging position for urging said process cartridge to the main assembly side positioning portion, a retracted position retracted from the urging position and a stand-by position which is in a movement path of said process cartridge, and wherein said rotation axis, said urging portion and a portion-to-be-displaced are arranged in the order named, said process cartridge comprising an electrophotographic photosensitive drum; process means actable on said electrophotographic photosensitive drum; a portion to be positioned; a displacing portion provided to move the urging member from the stand-by position to the retracted position by contacting the portion-to-be-displaced disposed at a position remoter from the rotation axis than the urging portion when said process cartridge advances along an axial direction of said electrophotographic photosensitive drum in the main assembly, said displacing portion being effective to move the urging member to the retracted position by contacting the urging member when said process cartridge advances in the main assembly; a portion-to-be-urged to be urged by the urging portion in a state in which process cartridge is set in the main assembly, wherein when said process cartridge advances in the main assembly, said portion-to-be-urged is urged toward the main assembly side positioning portion so that portion to be positioned is abutted to the main assembly side positioning portion by the urging member moving to the urging position after being retracted to the retracted position by said displacing portion, wherein said portion to be positioned is positioned to the main assembly side positioning portion by said portion-to-be-urged being urged by the urging portion in a state in which process cartridge is set in the main assembly. 
         [0022]    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 
         [0023]      FIG. 1  is a schematic sectional view of the electrophotographic color image forming apparatus in the first of the preferred embodiments of the present invention, showing the general structure of the apparatus. 
           [0024]      FIG. 2  is a cross-sectional view of the cartridge, showing the general structure of the cartridge. 
           [0025]      FIG. 3  is a perspective view of the cartridge and image forming apparatus when the former is in the position from which it is mounted into the latter. 
           [0026]      FIG. 4  is an external perspective view of the process cartridge. 
           [0027]      FIG. 5  is a schematic drawing of the cartridge positioning portion of the main assembly of the image forming apparatus, and the cartridge pressing portion of the main assembly of the image forming, showing their structures. 
           [0028]      FIG. 6  is a detailed view of the cartridge positioning mechanism and cartridge pressing mechanism, on the rear side, of the main assembly of the image forming apparatus, showing their structures. 
           [0029]      FIG. 7  is a detailed view of the cartridge positioning mechanism and cartridge pressing mechanism, on the front side, of the main assembly of the image forming apparatus, showing their structures. 
           [0030]      FIG. 8  is a plan view of the cartridge pressing rear mechanism of the main assembly of the image forming apparatus, as seen from the right-hand side (as seen from front side of main assembly), showing the operation of the cartridge pressing mechanism. 
           [0031]      FIG. 9  is a plan view of the cartridge pressing rear mechanism of the main assembly of the image forming apparatus, as seen from the leading end side of the cartridge in terms of the direction in which the cartridge is mounted, showing the operation of the cartridge pressing mechanism. 
           [0032]      FIG. 10  is a plan view of the cartridge pressing front mechanism of the main assembly of the image forming apparatus, as seen from the left-hand side (as seen from front side of main assembly), showing the operation of the cartridge pressing mechanism. 
           [0033]      FIG. 11  is a plan view of the cartridge pressing front mechanism of the main assembly of the image forming apparatus, as seen from the trailing end side of the cartridge in terms of the direction in which the cartridge is mounted, showing the operation of the cartridge pressing mechanism. 
           [0034]      FIG. 12  is a schematic drawing which shows the directions in which force is applied during the mounting or removal of the cartridge. 
           [0035]      FIG. 13  is an external perspective view of the cartridge in the second embodiment of the present invention. 
           [0036]      FIG. 14  is a schematic drawing which depicts the cartridge positioning mechanism and cartridge pressing mechanism of the main assembly of the image forming apparatus in the second embodiment of the present invention. 
           [0037]      FIG. 15  is a sectional view of the cartridge, at a horizontal plane which coincides with the axial line of the photosensitive drum, as seen from above. 
           [0038]      FIG. 16  is a plan view of the cartridge pressing rear mechanism of the main assembly of the image forming apparatus in the second embodiment, as seen from the right-hand side (as seen from front side of main assembly), showing the operation of the cartridge pressing mechanism. 
           [0039]      FIG. 17  is a plan view of the cartridge pressing rear mechanism of the main assembly of the image forming apparatus in the second embodiment, as seen from the leading end side of the cartridge in terms of the direction in which the cartridge is mounted, showing the operation of the cartridge pressing mechanism. 
           [0040]      FIG. 18  is a perspective view of the drum grounding member and its adjacencies, showing their structures. 
           [0041]      FIG. 19  is a perspective view of the drum grounding portion of the cartridge, showing the structure thereof. 
           [0042]      FIG. 20  is a perspective view of the drum grounding portion of the cartridge, and the drum grounding portion of the main assembly, showing their structures. 
           [0043]      FIG. 21  is a schematic sectional view of an electrophotographic color image forming apparatus in accordance with the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0044]    Hereafter, the process cartridge (which hereafter will be referred to as “cartridge” and electrophotographic color image forming apparatus (which hereafter will be referred to as “image forming apparatus”) in the first of the preferred embodiments of the present invention will be described with reference to the appended drawings. 
       (General Structure of Image Forming Apparatus) 
       [0045]    First, referring to  FIG. 1 , the image forming apparatus in this embodiment will be described regarding its general structure. An image forming apparatus  100  shown in  FIG. 1  has four cartridge bays  22  ( 22   a - 22   d ), that is, the spaces into which four cartridges are mountable one for one ( FIG. 3 ). The four cartridge bays  22  are juxtaposed side by side (in parallel), in a single straight row angled relative to the horizontal direction. The cartridge  7  in each cartridge bay  22  ( 22   a - 22   d ) has one electrophotographic photosensitive drum  1  ( 1   a - 1   d ). 
         [0046]    The electrophotographic photosensitive drum  1  (which hereafter may be referred to as “photosensitive drum”) is rotationally driven in the clockwise direction of the drawing, by a driving member (unshown). Each cartridge  7  also has the following processing means, which are disposed in the adjacencies of the peripheral surface of the photosensitive drum  1  in a manner to surround the photosensitive drum  1 , in the order in which they will be listed next. They are a cleaning means  6  ( 6   a - 6   d ), which removes the developer (which hereafter may be referred to as “toner”) remaining on the peripheral surface of the photosensitive drum  1  after the transfer, a charge roller  2  ( 2   a - 2   d ) which uniformly charges the peripheral surface of the photosensitive drum  1 , a scanner unit  3  which forms an electrostatic latent image on the peripheral surface of the photosensitive drum  1 , by emitting a beam of laser light while modulating the beam of laser light with pictorial information, a development unit  4  ( 4   a - 4   d ) which develops the electrostatic latent image on the peripheral surface of the photosensitive drum  1  with the use of toner, and an intermediary transfer belt  5  onto which the four toner images on the photosensitive drums, one for one, which are different in color, are sequentially transferred. The photosensitive drum  1 , cleaning member  6 , charge roller  2 , and development unit  4  are integrated in the form of a cartridge (process cartridge), that is, the cartridge  7 , which is removably mountable in the main assembly  100   a  of the image forming apparatus  100  by a user. 
         [0047]    The intermediary transfer belt  5  is stretched around a driver roller  10  and a tension roller  11 , being thereby supported by them. The main assembly  100   a  of the image forming apparatus  100  is provided with first transfer rollers  12  ( 12   a - 12   d ), which are on the inward side of the loop which the intermediary transfer belt  5  forms. The first transfer rollers  12  are positioned so that they oppose the photosensitive drums  1  ( 1   a - 1   d ), one for one. To the transfer belt  5 , transfer bias is applied from a bias applying means (unshown). 
         [0048]    After the formation of a toner image on the photosensitive drum  1 , the toner image is transferred onto the intermediary transfer belt  5 . More specifically, four toner images are formed on the four photosensitive drums  1 , one for one. Then, as the four photosensitive drums  1  are further rotated in the direction indicated by an arrow mark Q, and the intermediary transfer belt  5  is rotated in the direction indicated by an arrow mark R, the four toner images are sequentially transferred (first transfer) in layers onto the intermediary transfer belt  5 , by the positive bias applied to the first transfer rollers  12 . Then, the four layers of toner images on the intermediary transfer belt  5 , which are different in color, are conveyed to a second transferring portion  15 . 
         [0049]    Meanwhile, in synchronism with the progression of the abovementioned image forming operation, a sheet S of recording medium is conveyed by a sheet conveying means made up of a sheet feeding-and-conveying apparatus  13 , a pair of registration rollers  17 , etc. The sheet feeding-and-conveying apparatus  13  has a sheet feeder cassette  24  in which multiple sheets S are storable, a sheet feeder roller  8  which conveys the sheet S, and a pair of sheet conveying rollers  16  which conveys further the sheet S after the feeding of the sheet S into the main assembly  100   a  of the image forming apparatus  100 . The main assembly  100   a  is structured so that the sheet feeder cassette  24  can be pulled out of the main assembly  100   a  in the frontward direction of the main assembly  100   a,  in  FIG. 1 . The sheets S in the sheet feeder cassette  24  are kept pressed by the sheet feeder roller  8 , and fed into the main assembly  100   a  by the sheet feeder roller  8 , while being separated one by one by a sheet separator pad  9  (friction-based sheet separating method). 
         [0050]    After being fed into the main assembly  100   a  from the sheet feeding apparatus  13 , the sheet S is conveyed to the second transfer portion  15  by the pair of registration rollers  17 . In the second transfer portion  15 , positive bias is applied to the second transfer roller  18 , whereby the four toner image on the intermediary transfer belt  5 , which are different in color, are transferred (second transfer) onto the sheet S as the sheet S is conveyed through the second transfer portion  15 . 
         [0051]    A fixing portion  14  as a fixing means is a portion of the image forming apparatus, which fixes the toner images on the sheet S by applying heat and pressure. A fixation belt  14   a  is cylindrical, and is guided by a belt guiding member (unshown) having a heat generating means, such as a heater, bonded to the belt guiding member. The fixation belt  14   a  and a pressure application roller  14   b  are kept pressed against with each other by the application of a preset amount of pressure thereto, forming thereby the fixation nip. 
         [0052]    After the transfer of the toner images (unfixed toner images) onto the sheet S from the image forming portion, the sheet S is conveyed to the fixing portion  14 , and then, is conveyed through the fixation nip between the fixation belt  14   a  and pressure application roller  14   b  in the fixing portion  14 . As the sheet S is conveyed through the fixation nip, the sheet S and the toner images thereon are subjected to heat and pressure. As a result, the unfixed toner images on the sheet S become fixed to the sheet S. Thereafter, the sheet S having the fixed toner images is discharged into a delivery tray  20  by a pair of sheet discharging rollers  19 . 
         [0053]    Meanwhile, the toner remaining on the peripheral surface of the photosensitive drum  1  after the toner image transfer is removed by the cleaning member  6 . Then, the removed toner is recovered into a chamber for the recovered toner, which is in the photosensitive member unit  26  ( 26   a - 26   d ). 
         [0054]    As for the toner remaining on the intermediary transfer belt  5  after the transfer (second transfer) of the toner images onto the sheet S, it is removed by a transfer belt cleaning apparatus  23 . The removed toner is recovered into a waste toner container (unshown) located in the rear portion of the image forming apparatus, through the waste toner passage (unshown). 
       (Cartridge) 
       [0055]    Next, referring to  FIG. 2 , the cartridge in this embodiment will be described.  FIG. 2  is a cross-sectional view of the cartridge  7 , in which a substantial amount of toner t is present. Incidentally, a cartridge  7   a,  that is, a cartridge in which the toner t of yellow color is present, a cartridge  7   b,  that is, a cartridge in which the toner t of magenta color is present, a cartridge  7   c,  that is, a cartridge in which the toner t of cyan color is present, and a cartridge  7   d,  that is, a cartridge in which the toner t of black color is present, are the same in structure. 
         [0056]    Each cartridge  7  is made up of a photosensitive member unit  26  and a development unit  4 . The photosensitive member unit  26  is provided with the photosensitive drum  1 , charge roller  2  (charging means), and cleaning member  6  (cleaning means). The development unit  4  has a development roller  25 . 
         [0057]    The photosensitive drum  1  is rotatably supported by the cleaning means frame  27  of the photosensitive member unit  26 , with the interposition of a pair of bearings which will be described later. In an image forming operation, the photosensitive drum  1  is rotationally driven, by transmitting to the photosensitive member unit  26  the driving force from a motor (unshown). There are the charge roller  2  and cleaning member  6  in the adjacencies of the peripheral surface of the photosensitive drum  1  as described above. As the above described transfer residual toner is removed from the peripheral surface of the photosensitive drum  1  by the cleaning member  6 , the removed toner falls into a chamber  27   a  for the removed toner. The cleaning means frame  27  is also provided with a pair of charge roller bearings  28 , which are attached to the cleaning means frame  27  in such a manner that the charge roller bearings  28  are movable in the direction indicated by a double-headed arrow mark D, which connects the centers of the charge roller  2  and photosensitive drum  1 . The shaft  2   j  of the charge roller  2  is rotatably supported by the charge roller bearings  28 , and the bearings  28  are kept pressured toward the photosensitive drum  1  by a pair of charge roller pressing members  46 . 
         [0058]    The development unit  4  has the development roller  25  and a developing means frame  31 . The development roller  25  rotates in contact with the photosensitive drum  1  in the direction indicated by the arrow mark B. The development roller  25  is rotatably supported by a developing means frame  31 . More specifically, the development roller  25  is supported by a pair of bearing members  32  ( 32 R and  32 L) attached to the lengthwise ends of the developing means frame  31 . The development unit  4  is provided with a toner supply roller  34  and a development blade  35 . The toner supply roller  34  rotates in contact with the development roller  25  in the direction indicated by an arrow mark C. The development blade  35  is for regulating in thickness the toner layer on the peripheral surface of the development roller  25 . Further, the development unit  4  has a toner conveying member  36  for conveying the toner in the toner storage portion  31   a  of the development unit  4  to the toner supply roller  34  while stirring the toner. The toner conveying member  36  is in the toner storage portion  31 a. 
         [0059]    The development unit  4  is connected to the photosensitive member unit  26 . More specifically, a pair of pins  37  ( 37 R and  37 L) are put through, one for one, the holes  32 Rb and  32 Lb of the bearing members  32 R and  32 L, respectively, so that the development unit  4  is pivotally movable relative to the photosensitive member unit  26  about the pins  37  ( 37 R and  37 L). The development unit  4  is under the pressure from pressure application springs  38 . Therefore, when the cartridge  7  is used for image formation in the main assembly of the image forming apparatus, the development unit  4  rotates about the pins  37  in the direction indicated by an arrow mark A, placing thereby the development roller  25  in contact with the photosensitive drum  1 . 
       (Structure of Means for Mounting Cartridge into Main Assembly of Image Forming Apparatus) 
       [0060]    Next, referring to  FIG. 3 , the portion of the cartridge, which allows the cartridge to be removably mounted into the main assembly of the image forming apparatus, and the portion of the main assembly of the image forming apparatus, which allows the cartridge to be removably mounted into the main assembly of the image forming apparatus, will be described regarding their structures. 
         [0061]      FIG. 3  is a perspective view of the cartridge and image forming apparatus when the former is in the position from which it is mounted into the latter. Incidentally, in this embodiment, the cartridge and the main assembly  100   a  of the image forming apparatus  100  are structured so that the former is inserted into the latter, in the front-to-rear direction, that is, the direction indicated by an arrow mark F, which is parallel to the axial line of the photosensitive drum  1 , so that the cartridge  7  can be removably mounted into the main assembly  100   a.    
         [0062]    Referring to  FIG. 3 , the main assembly  100   a  is provided with a cover  21  (front cover), which is on the front side of the main assembly  100   a.  The front cover  21  can be opened or closed. Opening the front cover  21  exposes the four cartridge bays  22  ( 22   a - 22   d ), which are for the cartridges  7  ( 7   a - 7   d ), one for one. The four cartridge bays  22  are juxtaposed side by side (in parallel), in a singe straight row angled relative to the horizontal direction. The main assembly  100   a  is provided with top cartridge guides  80  ( 80   a - 80   d ) as first cartridge guides of the main assembly  100   a,  and bottom cartridge guides  81  ( 81   a - 80   d ) as second cartridge guides of the main assembly  100   a.  The top and bottom cartridge guides  80  and  81  are located at the top and bottom of the four cartridge bays  22 , one for one, and extend from the front to rear of the main assembly  100   a.  The photosensitive member unit  26  of each cartridge  7  is provided with a projection  29  (first portion by which cartridge is guided), and a tongue-like portion  30  (second portion by which cartridge guided) by which the cartridge  7  is guided when the cartridge  7  is mounted into, or removed from, the corresponding cartridge bay  22 . More specifically, in order to mount the cartridge  7  into the corresponding cartridge bay  22 , the projection  29  and tongue-like portion  30  of the photosensitive member unit  26  are to be fitted in the cartridge guides  80  and  81  of the main assembly  100   a,  respectively, and then, the cartridge  7  is to be pushed into the cartridge bay in the direction indicated by an arrow mark F in the drawing. 
         [0063]    Incidentally, the abovementioned projection  29  (first portion of cartridge  7 , by which cartridge  7  is guided) is located at the top of the leading end of the cartridge  7 , in terms of the direction in which the cartridge  7  is inserted into the main assembly  100   a,  whereas the tongue-like portion  30  (second portion of cartridge  7 , by which cartridge  7  is guided) is on the bottom surface of the cartridge  7 , and extends from the leading end to the trailing end. 
         [0064]    Each cartridge  7  is also provided with a pair of cartridge positioning portions  40   a  and  50   a  (by which cartridge  7  is positioned relative to main assembly  100   a ), which are located at the leading and trailing ends of the cartridge  7 , in terms of the abovementioned cartridge insertion direction. The operation to mount the cartridge  7  into the main assembly  100   a  concludes as the cartridge  7  becomes correctly positioned in the main assembly  100   a.  Incidentally, for the purpose of controlling the rotation of the cartridge  7 , which occurs as driving force is transmitted to the cartridge  7 , the leading end of the cartridge  7  is provided with a shaft  27   b  ( FIG. 4 ), which protrudes in the direction parallel to the cartridge mounting direction (cartridge insertion direction), whereas the trailing end of the cartridge  7  is provided with a groove  27   c,  which is U-shaped in cross section. As the cartridge  7  becomes correctly positioned in the main assembly  100   a,  the shaft  27   b  fits into a hole  82   b  ( FIG. 5 ) of the main assembly  100   a,  which is elongated in cross section, and the shaft  92   c  ( FIG. 5 ) of the main assembly  100   a  fits into the groove  27   c  of the cartridge  7 . 
         [0065]    In terms of the direction in which the cartridge  7  advances as it is inserted into the main assembly  100   a,  the projection  29  (by which cartridge  7  is guided) of the cartridge  7  is located at the top of the leading end of the cartridge  7 , as described above. The tongue-like portion  30  of the cartridge  7  is on the bottom surface of the cartridge  7 , extending from the leading end of the cartridge  7  to the trailing end of the cartridge  7 . Further, in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the tongue-like portions  29  and  30  are on the same side of the photosensitive drum  1 . 
         [0066]    Therefore, it is ensured that the cartridge  7  reliably advances into the main assembly  100   a.    
         [0067]    As for the structural arrangement for correctly positioning the cartridge  7  in the main assembly  100   a,  it will be described later in detail. 
       (Structure for Correctly Positioning Cartridge, and Structure for Pressing Cartridge) 
       [0068]    Next, referring to  FIGS. 4-7 , the structural arrangement, in this embodiment, for correctly positioning the cartridge relative to the main assembly  100   a,  and the structural arrangement for pressing the cartridge to correctly positioning the cartridge, will be described. 
         [0069]      FIG. 4  is an external perspective view of the cartridge in this embodiment. The photosensitive drum  1 , which the cartridge  7  has, is rotatably supported, by the lengthwise end portions of its shaft (unshown), by a pair of bearings  40  and  50 , one for one, which are solidly attached to the cleaning means frame  27 . 
         [0070]    The bearing  40  (first bearing which supports one of lengthwise ends of shaft of photosensitive drum  1 ) is the bearing on the rear side, that is, the leading end side in terms the direction in which the cartridge  7  is made to advance in the main assembly  100   a  when it is mounted into the main assembly  100   a.  It is provided with a cartridge positioning first portions  40   a  ( 40   a   1 ,  40   a   2 ), which are two portions of the top side of the peripheral surface of the bearing  40   a.  More specifically, the cartridge positioning first portion  40   a  (which is made up of portions  40   a   1  and  40   a   2 ) is for correctly positioning the leading end of the cartridge  7  relative to the main assembly  100   a,  in terms of the direction vertical to the abovementioned cartridge advancement direction. It is arcuate in cross section. Incidentally, in terms of the cartridge advancement direction, the bearing  40 , that is, the bearing which will be at the deepest end of the cartridge bay, is located at the downstream end of the cartridge  7  ( FIG. 4 ). The cartridge  7  is also provided with a pressure catching portion  40   b,  which catches the pressure applied to the cartridge  7  by the cartridge pressing member  83  (which may be referred to as pressure applying member, or upwardly pushing member), which is a portion of the bottom side of the peripheral surface of the cartridge positioning first portion  40   a.  Incidentally, the abovementioned cartridge advancement direction is the direction in which the cartridge  7  is advanced into the main assembly  100   a  when a user mounts the cartridge  7  into the main assembly  100   a.    
         [0071]    Further, the abovementioned cartridge positioning portions  40   a  ( 40   a   1  and  40   a   2 ) is positioned so that it straddles the axial line I of the photosensitive drum  1  ( FIG. 15 ). That is, the cartridge  7  has the cartridge positioning first portion  40   a   1 , which is on one side of the axial line I of the photosensitive drum  1 , and the cartridge positioning second portion  40   a   2 , which is on the other side of the axial line I of the photosensitive drum  1 . The cartridge positioning first portion  40   a   1  (positioning portion on leading end side) is on the opposite side of the abovementioned axial line I from the cartridge positioning second portion  40   a   2  (positioning portion on trailing end side) ( FIG. 15 ). As for the abovementioned pressure catching portion  40   b,  it is on the downstream side of the photosensitive drum  1  in terms of the cartridge advancement direction. As seen from the direction J ( FIG. 9(   c )) in which upward pressure is applied by the abovementioned pressing member  83  (pressure applying member, upwardly pushing member), the pressure catching portion  40   b  is (roughly at the mid point) between the cartridge positioning first and second portions  40   a   1  and  40   a   2 . Therefore, as the pressure catching portion  40   b  is pressed, the cartridge positioning portion  40   a  is reliably pressed upon the cartridge catching portion  82   a  (cartridge positioning first portion on main assembly side), being thereby correctly positioned relative to the main assembly  100   a.  Incidentally, in this embodiment, the cartridge  7  is provided with the cartridge positioning first and second portions  40   a   1  and  40   a   2  as the cartridge positioning portions on the leading end side. Therefore, it is ensured that the cartridge  7  is more reliably pressed upon the cartridge catching (pressure catching) portion  82   a  of the main assembly  100   a.  However, the number of the cartridge positioning portions with which the leading end of the cartridge  7  is provided may be only one, as long as it is properly positioned. 
         [0072]    Further, the cartridge  7  is provided with a pushing member  40   c,  which is the first pushing member for moving the pressing member  83  into its retreat. With reference to the center of the cartridge  7 , in terms of the horizontal direction perpendicular to the abovementioned cartridge advancement direction, the pushing portion  40   c  is located closer to the lengthwise end wall of the cartridge  7  than the pressure catching portion  40   b.  The pushing portion  40   c  is protruding downstream from the downstream end wall of the cartridge  7  in terms of the cartridge advancement direction, and its end portion is provided with a projection  40   d  which is projecting downward. More specifically, the projection  40   d  of the pushing portion  40   c  is tapered, providing thereby gently slanted surfaces  40   e  and  40   f,  that is, the slanted surfaces on the downstream and upstream sides, respectively, which are slanted so that their intersection is the peak of the projection  40   d  (projection  40   d ). 
         [0073]    Further, the bearing  40 , that is, the bearing on the rear side, is provided with a first contact portion  40   h  (cartridge movement regulating first portion of cartridge), which protrudes further upward than the cartridge positioning portion  40   a.  The first contact portion  40   h  is flat across the top surface (end surface), and is between one end of the cartridge positioning first portion  40   a   1  and the other end of the cartridge positioning second portion  40   a   2 . That is, the first contact surface  40   h  is between the cartridge positioning first and second portions  40   a   1  and  40   a   2 ; the cartridge positioning first portion  40   a   1  is located next to one end of the first contact surface  40   h,  and the cartridge positioning second portion  40   a   2  is located next to the other end of the first contact surface  40   h.  Located on the upstream of the first contact surface  40   h  in terms of the cartridge mounting direction is a surface  40   g,  which is closer to the axial line of the photosensitive drum  1  than the top surface of the first contact surface  40   h.  Further, the bearing  40 , that is, the bearing on the rear end, is provided with a contact surface  40   i,  which is the surface for correctly positioning the cartridge  7  in terms of the lengthwise direction of the cartridge  7 . Incidentally, as the cartridge  7  is mounted into the main assembly  100   a,  the contact surface  40   i  comes into contact with the inward surface of the rear lateral panel of the main assembly  100   a,  ensuring that the cartridge  7  is correctly position in terms of the lengthwise direction of the cartridge  7 . 
         [0074]    Next, the bearing  50  (second bearing, that is, bearing which supports other end of photosensitive drum  1  in terms of direction parallel to axial line of photosensitive drum  1 ) will be described. The bearing  50  is the bearing on the front side, that is, the trailing side in terms of the abovementioned cartridge advancement direction. The bearing  50 , that is, the bearing on the front side, is provided with cartridge positioning second portions  50   a  ( 50   a   1  and  50   a   2 ), which are two portions of the top side of the peripheral surface of the bearing  50 . More specifically, the cartridge positioning second portions  50   a  (portions  50   a   1  and  50   a   2 ) are for correctly positioning the front end of the cartridge  7  relative to the main assembly  100   a,  in terms of the direction perpendicular to the abovementioned cartridge advancement direction. They are arcuate in cross section. The cartridge  7  is also provided with an upward pressure catching portion  50   b,  which catches the pressure applied to the cartridge  7  by an upwardly pulling member  93  ( FIG. 5 ). The pressure catching portion  50   b  is located farther from the axial line of the bearing  50   a  than the cartridge positioning first portion  50   a.    
         [0075]    As described above, the cartridge  7  has the first bearing  40 , which supports one of the lengthwise end portions of the photosensitive drum  1  in terms of the direction parallel to the axial line of the photosensitive drum  1 . The contact surface  40   h  and cartridge positioning first portions  40   a  ( 40   a   1  and  40   a   2 ) are portions of the peripheral surface of the first bearing  40 . Further, the cartridge  7  has the second bearing  50  which supports the other lengthwise end of the photosensitive drum  1  in terms of the direction parallel to the axial line of the photosensitive drum  1 . The contact portion  50   h  (contact surface) and cartridge positioning second portions  50   a  are portions of the peripheral surface of the second bearing  50 . 
         [0076]    Therefore, it is ensured that the cartridge  7  is precisely positioned relative to the main assembly  100   a.    
         [0077]    Incidentally, like the cartridge positioning portion  40   a,  that is, the cartridge positioning portion on the rear side, the cartridge positioning portion  50   a  has a cartridge positioning portion (cartridge positioning third portion  50   a   1 ), which is on one side of the axial line of the photosensitive drum  1 , and a cartridge positioning portion (cartridge positioning fourth portion  50   a   2 ), which is on the other side of the axial line of the photosensitive drum  1 . The cartridge positioning third portion  50   a   1  (positioning portion on leading end side) is on the opposite side of the abovementioned axial line I from the cartridge positioning fourth portion  50   a   2  (positioning portion on trailing end side) ( FIG. 15 ). As for the abovementioned pressure catching portion  50   b,  it is on the downstream side of the photosensitive drum  1  in terms of the cartridge advancement direction. As seen from the direction K ( FIG. 11(   c )) in which upward pressure is applied by the abovementioned upwardly pulling member  93  (pressure applying member, upwardly pushing member), the pressure catching member  50   b  is (roughly at the mid point) between the cartridge positioning third and fourth portions  50   a   1  and  50   a   2 . Therefore, as the pressure catching portion  50   b  is pressed, the cartridge positioning portions  50   a  are reliably pressed upon the pressure catching portion  92   a,  being thereby correctly positioned relative to the main assembly  100   a.    
         [0078]    Incidentally, in this embodiment, the cartridge  7  is provided with the cartridge positioning third and fourth portions  50   a   1  a  50   a   2  as the cartridge positioning portions on the trailing end side. Therefore, it is ensured that the cartridge  7  is more reliably pressed upon the pressure catching portions  92   a  of the main assembly  100   a.  However, the number of the cartridge positioning portions which the trailing end of the cartridge  7  is provided may be only one, as long as it is properly positioned. 
         [0079]    Further, the cartridge  7  is provided with a pushing member  50   c,  which is the second pushing member for moving the upwardly pulling member  93  into its retreat. With reference to the center of the cartridge  7 , in terms of the direction which is horizontal and perpendicular to the abovementioned cartridge advancement direction, the pushing portion  50   c  is located closer to the lengthwise end wall of the cartridge  7  than the pressure catching portion  50   b.  The pushing portion  50   c  is protruding downstream from the main portion of the bearing  50  in terms of the cartridge advancement direction, and its end portion is provided with a projection  50   d  which is projecting downward. More specifically, the projection  50   d  is tapered, providing thereby gently slanted surfaces  50   e  and  50   f,  that is, the slanted surfaces on the downstream and upstream sides, respectively, which are slanted in such a manner that their intersection is the peak of the projection  50   d  (projection  50   d ). Further, the bearing  50 , that is, the bearing on the front side, is provided with a second contact portion  50   h  (contact surface, which serves as cartridge movement regulating portion), which protrudes further upward than the cartridge positioning portion  50   a.  The second contact portion  50   h  is flat across the top surface (second contact surface), and is between one end of the cartridge positioning third portion  50   a   1  and the other end of the cartridge positioning fourth portion  50   a   2 . That is, the second contact surface  50   h  is between the cartridge positioning third and fourth portions  50   a   1  and  50   a   2 ; the cartridge positioning third portion  50   a   1  is located next to one end of the second contact surface  50   h,  and the cartridge positioning fourth portion  50   a   2  is located next to the other end of the second contact surface  50   h.  Located on the upstream of the contact surface  50   h  in terms of the cartridge mounting direction is a surface  50   g,  which is closer to the axial line of the photosensitive drum  1  than the top surface of the first contact portion  50   h.    
         [0080]    Further, in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the top surface (area of first contact) of the contact portion  40   h  is different in position from the cartridge positioning first portions  40   a  ( 40   a   1  and  40   a   2 ). Also in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the top surface (area of second contact) is different in position from the cartridge positioning second portions  50   a  ( 50   a   1  and  50   a   2 ). 
         [0081]    Further, in terms of the abovementioned cartridge advancement direction, the top surface (area of first contact) of the first contact portion  40   h  is on the leading end side, and the top surface (area of second contact) of the second contact portion  50   h  is on the trailing end side. 
         [0082]    Therefore, it is ensured that the cartridge  7  is precisely positioned relative to the main assembly  100   a.    
         [0083]    Further in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the top surface of the contact surface  40   h  is between one end of the cartridge positioning portions  40   a  ( 40   a   1  and  40   a   2 ) and the other end of the cartridge positioning portions  40   a  ( 40   a   1  and  40   a   2 ). Also in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , the top surface (area of contact) of the second contact portion  50   h  is between one end of the cartridge positioning second portions  50   a  ( 50   a   1  and  50   a   2 ) and the other. 
         [0084]    Therefore, it is ensured that the cartridge  7  is precisely positioned relative to the apparatus main assembly  100   a.    
         [0085]    Next, the structure of the cartridge positioning portion of the main assembly  100   a,  and the cartridge pressing mechanism of the main assembly  100   a,  will be described.  FIG. 5  is a schematic drawing for describing the structure of the cartridge positioning portion of the main assembly  100   a  of the image forming apparatus  100 , and the cartridge pressing mechanism of the main assembly  100   a,  and show the structures thereof.  FIG. 6  is a detailed drawing of the cartridge positioning portion and cartridge pressing mechanism, on the rear side, and shows the structures thereof.  FIG. 7  is a detailed drawing of the cartridge positioning portion and cartridge pressing mechanism, on the front side, and shows the structures thereof. 
         [0086]    Referring to  FIG. 5 , the main assembly  100   a  is provided with a rear lateral panel  82 , which is on the leading end side, in terms of the cartridge mounting direction, and a front lateral panel  92 , which is on the trailing end side. The lateral panel  92  is provided with a hole through which the cartridge  7  is removably mountable in the cartridge bay  22 . The cartridge  7  is inserted into the main assembly  100   a  through this hole. Further, the cartridge  7  is inserted into the cartridge bay  22  in the direction of the arrow mark F, along the above described cartridge guiding top guide  80  and cartridge guiding bottom guide  81  ( FIG. 3 ). 
         [0087]    The lateral plate  82  is provided with two cartridge catching portions  82   a  ( 82   a   1  and  82   a   2 ), that is, the first portions of the main assembly, which are for correctly positioning the cartridge  7  relative to the main assembly in terms of the direction perpendicular to the direction (advancement direction) in which the cartridge  7  is mounted. The lateral plate  82  is also provided with the pressing member  83 , which is for pressing the cartridge  7  toward the cartridge catching portion  82   a  by being under the pressure applied thereto by the resiliency (elastic force) of a compression spring  85 . This pressing member  83  functions as an upwardly pushing member which keeps the cartridge  7  pressed upward by being pressed upward by the pressure applied by the compression spring  85 . 
         [0088]    The pressing member  83  is located under the cartridge catching portion  82   a.  It is attached to the lateral plate  82 . More specifically, a shaft  84  solidly fixed to the lateral plate  82 , that is, the lateral plate on the rear side, of the main assembly, is put through the through hole  83   a,  the axial line of which coincides with the pivotal axis of the pressing member  83 , so that the pressing member  83  is enabled to take the cartridge pressing position in which it keeps the cartridge  7  pressed on the cartridge catching portions  82   a,  position in its retreat in which it does not press on the cartridge  7 , and the standby position in which it remains in the path of the cartridge  7 . 
         [0089]    Further, the pressing member  83  is provided with a cartridge pushing portion  83   b,  by which the pressing member  83  pushes the cartridge when the pressing member  83  is in the cartridge pressing position. The cartridge pushing portion  83   b  corresponds in position to the pressure catching portion  40   b  of the cartridge  7 . The pressing member  83  is also provided with a pressure catching first portion  83   c  for moving the pressing member  83  into the retreat. The pressure catching first portion  83   c  corresponds in position to the pushing portion  40   c  of the cartridge  7 . The pressure catching first portion  83   c  is provided with an upward projection  83   d.  The upward projection  83   d  is provided with gently slanted surfaces  83   e  and  83   f,  which are the upstream and downstream surfaces of the projection  83   d,  respectively, in terms of the cartridge mounting direction. The surfaces  83   e  and  83   f  are slanted so that the joint between the two surfaces is the peak of the projection  83   d.  Further, in terms of the direction perpendicular to the cartridge mounting direction, the pressure catching portion  83   c  is located further outward (in terms of the radium direction of hole  83   a ) from the axial line of the hole  83   a  than the cartridge pushing portion  83   b.  That is, in terms of the lengthwise direction of the pressing member  83 , the abovementioned axial line of the hole  83   a,  cartridge pressing portion  83   b,  and pressure catching portion  83   c,  are positioned in the listed order. 
         [0090]    The lateral plate  82  is provided with a cartridge movement regulating first portion  86  (cartridge movement regulating first portion of main assembly) which prevents the cartridge  7  from moving upward by the reactive force generated as the cartridge pushes the pressing member  83  into its retreat. The cartridge movement regulating first portion  86  is formed of resin, and is located between the two cartridge catching portions  82   a  ( 82   a   1  and  82   a   2 ) of the lateral plate  82 . 
         [0091]    Referring to  FIG. 7 , the lateral plate  92  is provided with the cartridge insertion hole  92   b,  and two cartridge catching portions  92   a  ( 92   a   1  and  92   a   2 ), which function as the cartridge positioning second portions of the main assembly. The cartridge catching portions  92   a  are two portions of the top portion of the inward surface of the hole  92   b,  and are for correctly positioning the cartridge  7  in terms of the direction perpendicular to the cartridge mounting direction. Further, the lateral plate  92 , that is, the frontal lateral plate of the main assembly, is provided with a cartridge pulling member  93  for upwardly pulling the cartridge  7  toward the cartridge catching portions  92   a,  by being under the tensional force generated by a pressure application spring  95 , which is a tension spring. The cartridge pulling member  93  is located upward of the cartridge catching portions  92   a.  It is pivotally supported by the lateral plate  92 ; a shaft  94  solidly attached to the lateral plate  92  is put though a hole  93   a  (whose axial line is rotational axis) of the cartridge pulling member  93 . The cartridge pulling member  93  is attached to (supported by) the lateral plate  92  so that it is enabled to take the position in which it keeps the cartridge  7  pressed upon the cartridge catching portions  92   a,  position in its retreat in which it is free from the force from the spring  95 , and standby position in which it is in the path of the cartridge  7 . 
         [0092]    Further, the cartridge pulling member  93  is provided with a cartridge pulling portion  93   b  for pulling the cartridge upward when the cartridge pulling member  93  is in the cartridge pulling position. The cartridge pulling portion  93   b  corresponds in position to the cartridge pulling force catching portion  50   b  of the cartridge  7 . The cartridge pulling member  93  is also provided with a cartridge catching second portion  93   c  for moving the cartridge pulling member  93  into its retreat. The cartridge catching second portion  93   c  corresponds in position to the pushing portion  50   c  of the cartridge  7 . It is provided with an upward projection  93   d,  which has gently slanted surfaces  93   e  and  93   f  ( FIG. 10 ) slanted so that their intersection is the peak of the upward projection  93   d.    
         [0093]    Further, in terms of the direction perpendicular to the cartridge mounting direction, the cartridge catching portion  93   c  is located further outward from the axial line of the hole  93   a  than the cartridge pulling portion  93   b.  That is, in terms of the lengthwise direction of the cartridge pulling member  93 , the hole  93   a,  cartridge pulling portion  93   b,  and cartridge catching portion  93   c  are positioned in the listed order. Further, the lateral plate  92 , that is, the frontal lateral plate of the main assembly, is provided a cartridge movement regulating second portion  96 , which is for preventing the cartridge  7  from being moved upward by the reactive force which occurs as the cartridge pulling member  93  is pushed into its retreat. The cartridge movement regulating portion  96  is between the abovementioned two cartridge catching portions  92   a  ( 92   a   1  and  92   a   2 ). 
         [0094]    Incidentally, in this embodiment, on the leading end side of the cartridge  7  in terms of the cartridge mounting direction, the pressure applying member  83  (pressing member, upwardly pushing member) is located below the cartridge catching portion  83   a  to press the cartridge upward from below to cause the cartridge  7  to bump into the cartridge catching portions  82   a,  whereas on the trailing side of the cartridge  7  in terms of the cartridge mounting direction, the cartridge pulling member  93  (cartridge pressing member) is positioned above the cartridge catching portions  92   a  to pull the cartridge  7  upward from above to cause the cartridge to bump into the cartridge catching portions  92   a  which are positioned above the cartridge. That is, as the cartridge  7  is moved into its image forming position in the main assembly  100   a,  the cartridge catching portion  82   a  (portion to be pressed) is pressed by the upward force from the cartridge pushing member  83 . Thus, the cartridge positioning first and second portions  40   a   1  and  40   a   2  (cartridge positioning portions of cartridge, on leading end side) are correctly positioned by the cartridge catching portions  82   a  (cartridge positioning first portion of main assembly). Further, the upwardly pulling force catching portion  50   b  is pushed by the upwardly pulling force from the upwardly pulling member  93 . Therefore, the cartridge positioning third and fourth portions  50   a   1  and  50   a   2  (cartridge positioning portions of cartridge, on trailing end side) are correctly positioned by the cartridge catching portions  92   a  ( 92   a   1  and  92   a   2 ) (cartridge positioning second portions of main assembly). Thus, the employment of this structural arrangement makes it possible to provide the lateral plate  92 , that is, the frontal lateral plate of the main assembly, with the hole through which the cartridge  7  can be mounted into the cartridge bay  22 . Therefore, the bearing  50 , that is, one of the bearings in the adjacencies of the cartridge positioning portion, can be directly pressed. Therefore, the pressure applied to the bearing  50  remains stable. Therefore, the cartridge  7  is precisely positioned and remains precisely positioned. Therefore, the photosensitive drum  1  is precisely placed in contact with the intermediary transfer belt  5 , and remains precisely in contact with the belt  5 . 
         [0095]    Incidentally, this embodiment is not intended to limit the present invention in structural arrangement. That is, the cartridge pressing member  83  and cartridge pulling member  93  may be positioned on the leading and trailing end sides, respectively, as elastically pressing members, in terms of the cartridge mounting direction, or vice versa. In either case, the above described effects can be obtained. 
       (Operation of Cartridge Pressing Mechanism During Mounting and Removal of Cartridge) 
       [0096]    Next, referring to  FIGS. 8-11 , the operations of the cartridge pressing mechanism during the mounting of the cartridge  7  into the image forming apparatus, and the removal of the cartridge  7  from the image forming apparatus, will be described. 
         [0000]    (a) Leading End Side: Operations of Cartridge Pressing Mechanism During Mounting and Removal of Cartridge 
         [0097]      FIG. 8  is a plan view of the right-hand side (as seen from front side) of the cartridge pressing rear mechanism of the main assembly.  FIG. 9  is a plan view of the rear side of the cartridge pressing rear mechanism (leading end side in terms of cartridge mounting direction) of the main assembly. 
         [0098]    The cartridge  7  is to be mounted in the direction indicated by the arrow mark F as described before. Referring to  FIGS. 8(   a ) and  9 ( a ), as the cartridge  7  is inserted, the slanted surface  40   e  of the pushing portion  40   c  of the bearing  40 , that is, the rear bearing of the cartridge  7 , comes into contact with the slanted surface  83   e  of the cartridge catching portion  83   c  (standby position). Then, as the cartridge  7  is inserted further, the pressing member  83  is gradually pushed down, causing the projection  40   d  of the pushing portion  40   c  to come into contact with the projection  83   d  of the cartridge catching portion  83   c,  as shown in  FIG. 8(   b ). Consequently, the pressing member  83  retreats in the direction indicated by an arrow mark X (position in retreat). 
         [0099]    More specifically, the pressing member  83  moves into the position in its retreat, in which its pressing portion  83   b  does not contact the pressure catching portion  40   b  of the cartridge  7 , as shown in  FIG. 9(   b ). Therefore, while the cartridge  7  is mounted, the pressure catching portion  40   b  is not subjected to any pressure. The pressure which the cartridge  7  receives from the pressing member  83  when it is mounted is removed by the pushing portion  40   c,  which is located further from the hole  83   a.  That is, the amount of force necessary to push down the pressing member  83  against the force which acts to upwardly push the cartridge  7  is reduced by the ratio between the distance from the axial line of the hole  83   a  to the pressure catching portion  40   b  (pushing portion  83   b ) and the distance from the axial line of the hole  83   a  to the pushing portion  40   c  (pressure catching portion  83   c ). Therefore, the amount of load to which the cartridge  7  is subjected when it is mounted is substantially smaller than the amount of pressure which the cartridge  7  receives from the pressing member  83 ; the amount of force required to mount the cartridge  7  is substantially smaller than the amount of the pressure which the cartridge  7  receives from the pressing member  83 . 
         [0100]    Further, when the cartridge  7  is mounted, the cartridge  7  is subjected to upward force, that is, the reactive force generated as the pressing member  83  is pushed down into its retreat. However, the contacting surface  40   h  comes into contact with the cartridge movement regulating portion  86 , that is, the cartridge contacting first portion of the main assembly. Therefore, the cartridge  7  is prevented from moving upward. Here, the cartridge movement regulating portion  86  of the main assembly and the main assembly contacting surface  40   h  are positioned so that they remain in contact with each other until immediately before the cartridge positioning portion  40   a  is correctly positioned by coming into contact with the cartridge catching portion  83 . Therefore, while the cartridge  7  is mounted, more specifically, from the moment the cartridge  7  begins to receive the upward pressure from the pressing member  83  until immediately before the cartridge  7  is correctly positioned, the cartridge movement regulating portion  86 , that is, the cartridge regulating portion of the main assembly, which is formed of resin, and the contacting surface  40   h,  slide on each other, and therefore, the cartridge positioning portion  40   a  does not rub against the cartridge catching portion  82   a  of the main assembly, which is formed of a thin sheet of steel or the like. Therefore, the problem that the cartridge positioning portion  40   a  is shaved by the cartridge catching portion  82   a  is prevented. 
         [0101]    As the cartridge  7  is inserted even further, the cartridge catching portion  83   c  is disengaged from the pushing portion  40   c,  and therefore, the pressing member  83  gradually returns to its pressing position from the retreat. Then, the cartridge  7  is inserted far enough for the contacting surface  40   i,  which is for correctly positioning the cartridge  7  in terms of the lengthwise direction of the cartridge  7 , to come into contact with the lateral plate  82 , that is, the rear lateral plate of the main assembly, the pressing portion  83   b  comes into contact with the pressure catching portion  40   b,  as shown in  FIGS. 8(   c ) and  9 ( c ), causing the cartridge  7  to be pressed (pressing position) in the direction indicated by an arrow mark J (pressing direction in  FIG. 9) . During this process, the cartridge positioning portion  40   a  of the cartridge  7  bumps into the cartridge catching portion  82   a  of the rear lateral plate  82  of the main assembly, correctly positioning thereby the cartridge  7  in terms of the direction perpendicular to the cartridge mounting direction. Also during this process, the cartridge movement regulating portion  86  of the main assembly becomes disengaged from the contacting surface  40   h;  a preset amount of gap is created between the cartridge movement regulating portion  86  and the surface  40   g  (recessed surface). At the same time, the cartridge catching portion  83   c  moves past the pushing portion  40   c;  a preset amount of gap is created between the cartridge catching portion  83   c  and the recessed surface  40   j.    
         [0102]    As described above, the cartridge pressing mechanism is structured so that the pressing member  83  can be in the standby position, pressing position, and retreat. More specifically, in terms of the top to bottom direction, the standby position, pressing position, and retreat are located in the listed order. Therefore, the pressing member  83  applies a sufficient amount of pressure to the cartridge  7 . 
         [0103]    When removing the cartridge  7  from the main assembly  100   a,  the cartridge mounting operation described above is to be carried out in reverse. The pressure which the cartridge  7  receives from the pressing member  83  is removed by the pushing portion  40   c,  which is more distant from the axial line of the hole  83   a  (rotational axis) than the pressure catching portion  40   b,  as it is during the mounting of the cartridge  7 . Therefore, the amount of force necessary for the operation to remove the cartridge  7  in this embodiment is smaller than the amount of force necessary for the operation to remove a cartridge  7  in accordance with the prior art, as it is during the mounting of the cartridge  7 . 
         [0104]    Incidentally, whether mounting the cartridge  7  into the main assembly  100   a,  or removing the cartridge  7  from the main assembly  100   a,  it is necessary to move the pressing member  83  in the direction perpendicular to the cartridge mounting direction. In this embodiment, however, the projection  83   d  of the pressure catching portion  83   c  is provided with the gently slanted surfaces on the upstream and downstream sides, one for one, in terms of the cartridge mounting direction. Further, the projection  40   d  of the pushing portion  40   c  is provided with gently slanted surfaces on the upstream and downstream, one for one, in terms of the cartridge mounting direction. Further, when the cartridge  7  is mounted, the slanted surface  40   e  of the pushing portion  40   c  comes into contact with the slanted surface  83   e  of the pressure catching portion  83   c,  whereas when the cartridge  7  is removed, the slanted surface  40   f  of the pushing portion  40   c  comes into contact with the slanted surface  83   f  of the pressure catching portion  83   c.  The movement of the pressing member  83  in the direction of the arrow mark X begins under the above described condition. In other words, the cartridge pressing mechanism in this embodiment is structured so that the slanted surfaces of the cartridge  7  remain in contact with the slanted surfaces of the main assembly  100   a  while the pressing member  83  moves. Therefore, the cartridge  7  smoothly moves into the main assembly when the cartridge is mounted, and also, smoothly comes out of the main assembly when the cartridge  7  is removed. 
         [0000]    (b) Trailing End Side: Operations of Cartridge Pressing Mechanism During Mounting and Removal of Cartridge 
         [0105]      FIG. 10  is a plan view of the left-hand side (as seen from front side) of the cartridge pressing front mechanism of the main assembly.  FIG. 11  is a plan view of the front side of the cartridge pressing front (trailing end side in terms of cartridge mounting direction) mechanism of the main assembly. 
         [0106]    As the cartridge  7  is inserted, the slanted surface  50   e  of the pushing portion  50   c  of the bearing  50 , that is, the front bearing of the cartridge  7 , comes into contact with the slanted surface  93   e  of the cartridge catching portion  93   c  (standby position), as shown in  FIGS. 10(   a ) and  11 ( a ). Then, as the cartridge  7  is inserted further, the upwardly pulling member  93  is gradually pushed down, causing the projection  50   d  of the pushing portion  50   c  to come into contact with the projection  93   d  of the cartridge catching portion  93   c,  as shown in  FIG. 10(   b ). Consequently, the upwardly pulling member  93  retreats in the direction indicated by an arrow mark Y (position in retreat). More specifically, the upwardly pulling member  93  retreats into a position in which its upward force applying portion  93   b  does not contact the upward force catching portion  50   b  of the cartridge  7 , as shown in  FIG. 11(   b ). Therefore, while the cartridge  7  is mounted, the upward force catching portion  50   b  is not subjected to the upward pressure. 
         [0107]    The pressure which the cartridge  7  receives from the upwardly pulling member  93  when it is mounted is removed by the pushing portion  50   c,  which is located further from the axial line of the hole  93   a  than the upward force catching portion  50   b.  That is, the amount of force necessary to push down the upwardly pulling member  93  against the force which acts to upwardly push the cartridge  7  is reduced by an amount equivalent to the ratio between the distance from the axial line of the hole  93   a  to the upward force catching portion  50   b  (upwardly pulling force applying portion  93   b ) and the distance from the axial line of the hole  93   a  to the pushing portion  50   c  (upwardly pulling member  93 ). Therefore, the amount of load to which the cartridge  7  is subjected when it is mounted is substantially smaller than the amount of pressure which the cartridge  7  receives from the upwardly pulling member  93 ; the amount of force required to mount the cartridge  7  is substantially smaller than the amount of force which the cartridge  7  receives from the upwardly pulling member  93 . 
         [0108]    Further, when the cartridge  7  is mounted, the cartridge  7  is subjected to upward force, that is, the reactive force generated as the upwardly pulling member  93  is pushed down into its retreat. However, the contacting surface  50   h  comes into contact with the cartridge movement regulating portion  96 , that is, the cartridge contacting second portion of the main assembly. Therefore, the cartridge  7  is prevented from moving upward. Here, the cartridge movement regulating portion  96  of the main assembly and the main assembly contacting surface  50   h  are positioned so that they remain in contact with each other until immediately before the cartridge positioning portion  50   a  is correctly positioned by coming into contact with the cartridge catching portion  92   a.  Therefore, while the cartridge  7  is mounted, more specifically, from the moment the cartridge  7  begins to receive the upward force from the upwardly pulling member  93  until immediately before the cartridge  7  is correctly positioned, the cartridge movement regulating portion  96 , that is, the cartridge regulating portion of the main assembly, which is formed of resin, and the cartridge contacting surface  50   h,  slide on each other, and therefore, the cartridge positioning portion  50   a  does not rub against the cartridge catching portion  92   a  of the main assembly, which is formed of a thin sheet of steel or the like. Therefore, the problem that the cartridge positioning portion  50   a  is shaved by the cartridge catching portion  92   a  is prevented. 
         [0109]    As the cartridge  7  is inserted even further, the cartridge catching portion  93   c  is disengaged from the pushing portion  50   c,  and therefore, the upwardly pulling portion  93  gradually returns to the upwardly pulling position from the retreat. Then, the cartridge  7  is inserted far enough for the contacting surface  50   i,  which is for correctly positioning the cartridge  7  in terms of the lengthwise direction of the cartridge  7 , to come into contact with the lateral plate  82 , that is, the rear lateral plate of the main assembly, the upwardly pulling portion  93   b  comes into contact with the cartridge catching portion  50   b,  as shown in  FIGS. 10(   c ) and  11 ( c ), causing the cartridge  7  to be pressed (pressing position) in the direction indicated by an arrow mark K (upwardly pulling direction in  FIG. 11) . During this process, the cartridge positioning portion  50   a  of the cartridge  7  bumps into the cartridge catching portion  92   a  of the frontal lateral plate  92  of the main assembly, correctly positioning thereby the cartridge  7  in terms of the direction perpendicular to the cartridge mounting direction. Also during this process, the cartridge movement regulating portion  96  of the main assembly becomes disengaged from the contacting surface  50   h;  a preset amount of gap is created between the cartridge movement regulating portion  96  and the recessed surface  50   g.  At the same time, the cartridge catching portion  93   c  moves past the pushing portion  50   c;  a preset amount of gap is created between the cartridge catching portion  93   c  and the recessed surface  50   j.    
         [0110]    As described above, the cartridge pressing mechanism is structured so that the upwardly pulling member  93  is enabled to move into the standby position, upwardly pulling (pressing) position, and retreat. More specifically, in terms of the top to bottom direction, the standby position, upwardly pulling (pressing) position, and retreat are located in the listed order. Therefore, the upwardly pulling member  93  applies to the cartridge  7  a sufficient amount of pressure for pulling up the cartridge  7 . 
         [0111]    When removing the cartridge  7  from the main assembly  100   a,  the cartridge mounting operation described above is to be carried out in reverse. The upward force which the cartridge  7  receives from the upwardly pulling member  93  is removed by the pushing portion  50   c,  which is more distant from the axial line of the hole  93   a  (rotational axis of pulling member  93 ) than the upward force catching portion  50   b,  as it is during the mounting of the cartridge  7 . Therefore, the amount of force necessary for the operation to remove the cartridge  7  in this embodiment is significantly smaller than the amount of force necessary for the operation to remove a cartridge  7  in accordance with the prior art, as the amount of the force necessary for the operation to mount the cartridge  7  in this embodiment is significantly smaller than the amount of force necessary for the operation to mount a cartridge in accordance with the prior art. 
         [0112]    Incidentally, whether mounting the cartridge  7  into the main assembly  100   a,  or removing the cartridge  7  from the main assembly  100   a,  it is necessary to move the upwardly pulling member  93  in the direction perpendicular to the cartridge mounting direction. In this embodiment, however, the projection  93   d  of the pressure catching portion  93   c  is provided with the gently slanted surfaces, which are on the upstream and downstream sides, one for one, in terms of the cartridge mounting direction. Further, the projection  50   d  of the pushing portion  50   c  is provided with gently slanted surfaces, which are on the upstream and downstream, one for one, in terms of the cartridge mounting direction. Thus, when the cartridge  7  is mounted, the slanted surface  50   e  of the pushing portion  50   c  comes into contact with the slanted surface  93   e  of the pressure catching portion  93   c,  whereas when the cartridge  7  is removed, the slanted surface  50   f  of the pushing portion  50   c  comes into contact with the slanted surface  93   f  of the pressure catching portion  93   c.  It is under this condition that the movement of the upwardly pulling member  93  in the direction of the arrow mark Y begins. In other words, the cartridge pressing mechanism in this embodiment is structured so that the slanted surfaces of the cartridge  7  remain in contact with the slanted surfaces of the main assembly  100   a  while the upwardly pulling member  93  moves. Therefore, the cartridge  7  smoothly moves into the main assembly when the cartridge is mounted, and also, smoothly comes out of the main assembly when the cartridge  7  is removed. 
         [0113]    Incidentally, when the cartridge  7  is mounted or removed, the operation of the cartridge pressing mechanism in this embodiment occurs on the leading and trailing end sides, in terms of the cartridge mounting direction, roughly at the same time. Further, the direction in which the pressing member  83 , that is, the rear pressing member, is rotated is opposite from the direction in which the pressing member  93  (upwardly pulling member), that is, the front pressing member, is rotated. 
         [0114]    To describe in more detail, referring to  FIGS. 12(   a ) and  12 ( b ), on the leading end side in terms of the direction perpendicular to the cartridge mounting direction, the axial line of the hole  83   a  is on the left side of Line L, which coincides with the axial line of the photosensitive drum  1  and extends in the direction parallel to the direction in which the cartridge  7  is moved to be correctly positioned, and the pressure catching portion  83   c  is on the right side of Line L. On the other hand, on the trailing end side, the axial line of the hole  93   a  is on the right-hand side of the abovementioned Line L, and the pressure catching portion  93   c  is on the left-hand side of Line L; the positional relationship between the hole and pressure catching portion of the pressing portion on the leading end side is opposite to that on the trailing end side. 
         [0115]    That is, the pressing member  83 , which is on the rear side of the main assembly, is rotated in the direction indicated by an arrow mark M when it is moved into the retreat, whereas the upwardly pulling member  93 , which is on the front side of the main assembly, is rotated in the direction indicated by an arrow mark N when it is moved into the retreat. Therefore, the loads from the pressing members  83  and  93 , that is, the pressing members on the rear and front sides of the main assembly, to which the pushing portions  40   c  and  50   c  are subjected when the cartridge  7  is mounted or removed, act in the directions indicated by arrow marks P 1  and P 2 , respectively, in  FIGS. 12(   a ) and  12 ( c ). The angles of the directions P 1  and P 2  of these loads are preset relative to Line L, which extends in the direction in which the cartridge is pushed up. Further, the abovementioned angles are roughly symmetrical with reference to Line L, which extends in the direction parallel to the directions P 1  and P 2  of the load, that is, the direction in which the cartridge  7  is upwardly pushed, as shown in  FIG. 12(   c O. Therefore, when the cartridge  7  is mounted or removed, its remains stable in attitude, being therefore significantly better in operability than a cartridge in accordance with the prior art. 
       (Structural Arrangement for Preventing Shaving of Cartridge Positioning Portion of Cartridge) 
       [0116]    The cartridge  7  in this embodiment is prevented from being shaved across its cartridge positioning portion when it is mounted into, or removed from, the main assembly  100   a.  This embodiment can reduce the problem that when the cartridge  7  is mounted into the main assembly  100   a,  the cartridge positioning first and second portions (portions  40   a  and  50   a ) of the cartridge  7  rub against the corresponding portions (members) of the main assembly  100   a.  Further, this embodiment can reduce the problem that when the cartridge  7  is mounted into the main assembly  100   a,  the abovementioned cartridge positioning first and second portions are placed in contact with the corresponding portions (members) of the main assembly  100   a.    
         [0117]    That is, as described above, the bearings  40  and  50 , that is, the bearings on the leading and trailing end sides, in terms of the cartridge mounting direction, are provided with the contacting portions  40   h  and  50   h,  which protrude upward beyond the cartridge positioning portions  40   a  and  50   a,  which also are the portions of their peripheral surfaces. These contacting portions  40   h  and  50   h  are flat across the top surface, and positioned on one side of the cartridge positioning portion of the cartridge  7 , and the other, respectively. 
         [0118]    As the cartridge  7  is inserted into the main assembly  100   a  structured as described above, the cartridge  7  is subjected to the upward force, that is, the reactive force generated as the pressing member  83 , that is, the cartridge pressing rear member, and the upwardly pulling member  93 , that is, the cartridge pressing front member, are pushed downward into their retreats. During this process, the contacting portion  40   h  (surface) comes into contact with the cartridge movement regulating portion  86 , that is, the cartridge contacting first portion of the main assembly, and the contacting portion  50   h  (surface) comes into contact with the cartridge movement regulating portion  96 , that is, the cartridge contacting second portion of the main assembly. Therefore, the cartridge  7  is prevented from moving upward. 
         [0119]    Here, the cartridge pressing mechanism is structured so that the cartridge movement regulating portion  86 , that is, the cartridge movement regulating portion of the main assembly, which is on the rear side of the main assembly, and the contacting portion  40   h  (surface) remain in contact with each other until immediately before the cartridge positioning portion  40   a  is correctly positioned by coming into contact with the cartridge catching portion  82   a.  Similarly, the cartridge movement regulating portion  96 , that is, the cartridge movement regulating portion of the main assembly, which is on the front side of the main assembly, and the contacting portion  50   h  (surface) remain in contact with each other until immediately before the cartridge positioning portion  50   a  is correctly positioned by coming into contact with the cartridge catching portion  92   a.    
         [0120]    Therefore, while the cartridge  7  is mounted, more specifically, from the moment the cartridge  7  begins to receive the upward force from the pressing member  83  and upwardly pulling member  93  until immediately before the cartridge  7  is correctly positioned, the cartridge movement regulating portions  86  and  96 , that is, the cartridge regulating portions of the main assembly, which is formed of resin, and the cartridge contacting surfaces  40   h  and  50   h,  slide on the cartridge movement regulating portions  86  and  96 , respectively, and therefore, the cartridge positioning portions  40   a  and  50   a,  which are on the rear and front sides, do not rub against the cartridge catching portions  82   a  and  92   a  of the main assembly, which are formed of a thin sheet of steel or the like. Therefore, the problem that the cartridge positioning portions  40   a  and  50   a  are shaved by the cartridge catching portions  82   a  and  92   a  is prevented. 
         [0121]    As described above, the cartridge pressing mechanism is structured so that the cartridge  7  is mounted or removed while cancelling the cartridge pressing force by the pressure applied to the point of the pressing member, which is farther from the portion of the pressing member, by which the pressing member presses on the cartridge  7 . Therefore, the amount of force necessary to mount or remove the cartridge  7  is sufficiently small relative to the amount of force (pressure) which the cartridge  7  receives from the pressing member. Thus, the amount of force required to mount the cartridge  7 , that is, the cartridge in this embodiment, into the main assembly of the image forming apparatus in this embodiment, or remove the cartridge  7  from the image forming apparatus in this embodiment, is significantly smaller than that required to mount a cartridge in accordance with the prior art into the main assembly of an image forming apparatus in accordance with the prior art, or removing the cartridge in accordance with the prior art from the main assembly of the image forming apparatus in accordance with the prior art. In other words, the present invention can provide a cartridge and an image forming apparatus, which are significantly better in operability in terms of the mounting of the cartridge. 
         [0122]    Further, when mounting the cartridge  7  into the main assembly  100   a,  or removing the cartridge  7  from the main assembly  100   a,  the cartridge positioning members are prevented from being shaved. Therefore, it is ensured that the cartridge  7  is correctly positioned. 
         [0123]    Incidentally, the structure of the image forming apparatus in this embodiment is such that the cartridges are juxtaposed side by side (in parallel) in a horizontal straight row, and also, that the intermediary transfer unit is disposed on the top side of the cartridges so that the cartridges can be pressed upward from below by the pressing members. However, this embodiment is not intended to limit the present invention in terms of image forming apparatus structure. For example, the present invention is also applicable to an image forming apparatus structured so that its intermediary transfer unit is on the under side of the cartridges, and the cartridges are pressed downward from above by the pressing member (pressuring member). In the case of such a structural arrangement, the photosensitive drum  1  is placed in contact with the intermediary transfer belt  5  by applying downward pressure to the cartridge  7 . 
         [0124]    In the case of an image forming apparatus, such as the one in this embodiment, which is structured so that the cartridges are pressed from below, the amount of force necessary to press a cartridge to correctly position the cartridge needs to be set in consideration of the weight of the cartridge itself. Therefore, it must be greater than the amount of force necessary to press a cartridge in an image forming apparatus structured so that the cartridge is pressed from above, and so is the amount of force necessary to push down the pressing member. Thus, the effects of the present invention can be further enhanced by structuring the image forming apparatus so that the cartridge can be mounted or removed while cancelling the pressure applied to the cartridge by the cartridge pressing portion of the cartridge pressing member, by the portion of the cartridge pressing member, which is farther from the rotational axis of the cartridge pressing member than the cartridge pressing portion of the cartridge pressing member. 
         [0125]    Also in this embodiment, it is on both the leading and trailing end sides of the cartridge, in terms of the cartridge mounting direction, that the force from the cartridge pressing member (inclusive of upwardly pulling member) is cancelled by the portion of the cartridge pressing member, which is farther from the axial line the pressing member than the cartridge pressing portion of the pressing member while the cartridge is mounted or removed. However, this embodiment is not intended to limit the present invention in scope in terms of the structure of an image forming apparatus. For example, an image forming apparatus may be structured so that only one end of the image forming apparatus, that is, either the leading or trailing end in terms of the cartridge mounting direction, is provided with the cartridge pressing member. However, an image forming apparatus having the pressing member on both the leading and trailing end in terms of the cartridge mounting direction is smaller in the total amount of force necessary to mount or remove the cartridge than an image forming apparatus having the cartridge pressing member on only the leading or trailing end in terms of the cartridge mounting direction. Also as described above, by structuring an image forming apparatus so that the cartridge pressing member on the rear side, and the cartridge pressing member (cartridge pulling member) on the front side, are symmetrical with respect to the direction in which the load from the pressing member is pushed up, it is possible to keep the cartridge  7  stable in attitude when mounting or removing the cartridge  7 , enhancing further the effects of this embodiment of the present invention. 
       Embodiment 2 
       [0126]    Next, referring to  FIGS. 13 and 14 , the second embodiment of the present invention will be described. By the way, this embodiment is the same in the basic structure of an image forming apparatus as the first embodiment described above. Therefore, this embodiment will be described regarding only the structural features different from those in the first embodiment to avoid the repetition of the same description. Further, the members, portions, etc., of the image forming apparatus in this embodiment, which are the same in function as those in the first embodiment described above, are given the same referential symbols. 
         [0127]      FIG. 13  is an external perspective view of the cartridge in this embodiment.  FIG. 14  is a schematic perspective view of the cartridge positioning member and cartridge pressing member on the rear side of the main assembly of the image forming apparatus, showing their structures. 
         [0128]    The image forming apparatus in the first embodiment was structured so that the bearing of the cartridge  7 , which is on the leading end, in terms of the direction in which the cartridge  7  is mounted into the main assembly of the image forming apparatus, is provided with the pressing member  83  having the pushing portion  83   c  for pushing down the cartridge  7 . In this embodiment, the image forming apparatus structured so that the pushing portion for pushing down the pressing member is a part of the development unit, will be described. 
         [0129]    Referring to  FIG. 12 , it is the development unit  4  that is provided with a pressing member pushing portion  140   c,  which is for moving the pressing member into its retreat. The pushing portion  140   c  protrudes downstream from the downstream end of the cartridge  7  in terms of the cartridge mounting direction. The end portion of the pushing portion  140   c  is provided with a projection  140   d,  which projects downward. The projection  140   d  is provided with two surfaces  140   e  and  140   f,  which are gently slanted so that the intersection of the two surfaces is the peak of the projection  140   d.  In terms of the direction perpendicular to the cartridge mounting direction, the pushing portion  140   c  is on the opposite side of the pressure catching portion  40   b  from the axial line of the hole  183   a  ( FIG. 14 ) of the cartridge pressing member  183  (pressure applying member), which will be described later. Further, the pushing portion  140   c  is located farther from the axial line of the hole  183   a  than the pressure catching portion  40   b.    
         [0130]    Referring to  FIG. 14 , as for the main assembly  100   a,  it is provided with the cartridge pressing member  183 , which is for pressing the cartridge  7  toward the cartridge catching portion  82   a  (pressure catching portion). The pressing member  183  is located below the cartridge catching portion  82   a.  The pressing member  183  is attached to the lateral plate  82 , that is, the lateral plate of the main assembly on the rear side; the shaft  84  solid attached to the lateral plate  82  is put through the hole  183   a  of the pressing member  183  so that the pivotal axis of the pressing member  183  coincides with the axial line of the hole  183   a.  Further, the pressing member  183  is rotatably attached to the lateral plate  82  so that it is rotatably movable to the cartridge pressing position, in which it presses the cartridge  7  upon the cartridge catching portion  82   a,  and the retreat into which it is moved to remove the pressure which it applies to the cartridge  7 . 
         [0131]    Further, the pressing member  183  is provided with a pressing portion  183   b,  which presses on the cartridge  7  when the pressing member  183  is in the pressing position. The pressing portion  183   b  corresponds in position to the pressure catching portion  40   b  of the cartridge  7 . The pressing member  183  is also provided with a pressure catching portion  183 c, which is for moving the pressing member  183  into the retreat. The pressure catching portion  183   c  corresponds in position to the pushing portion  140   c  of the cartridge  7 . 
         [0132]    The pressure catching portion  183   c  is provided with an upward projection  183   d,  which has two surfaces  183   e  and  183   f.  The surfaces  183   e  and  183   f  are on the downstream and upstream sides, respectively, in terms of the cartridge mounting direction, and are gently slanted so that their intersection is the peak of the projection  183   d.    
         [0133]    In terms of the direction perpendicular to the cartridge mounting direction, the pressure catching portion  183   c  is on the opposite side of the pressing portion  183   b  from the axial line of the hole  183   a.  Further, the pressure catching portion  183   c  is located farther from the axial line of the hole  183   a  than the pressing portion  183   b.    
         [0134]    Next, the movement of the components of the cartridge pressing mechanism in this embodiment, which occur when the cartridge  7  is mounted into the image forming apparatus  100 , will be described.  FIG. 16  is a plan view of the cartridge pressing rear mechanism, as seen from the left side (as seen from front side of image forming apparatus) of the main assembly of the image forming apparatus, and shows the operation of the cartridge pressing member, which occurs when the cartridge  7  is mounted into the main assembly  100 .  FIG. 17  is a plan view of the cartridge pressing rear mechanism, as seen from the leading end side of the cartridge  7  in terms of the cartridge mounting direction, and shows the operation of the pressing member. 
         [0135]    The cartridge  7  is mounted in the direction indicated by an arrow mark F shown in  FIG. 16(   a ). Referring to  FIGS. 16(   a ) and  17 ( a ), as the cartridge  7  is inserted, the slanted surface  140   e  of the pushing portion  140   c  of the development unit  4  comes into contact with the slanted surface  183   e  of the cartridge catching portion  183   c  (standby position). Then, as the cartridge  7  is inserted further, the pressing member  183  is gradually pushed down, causing the projection  140   d  of the pushing portion  140   c  to come into contact with the projection  183   d  of the cartridge catching portion  183   c,  as shown in  FIG. 16(   b ). Consequently, the pressing member  183  retreats in the direction indicated by an arrow mark T (position in retreat). More specifically, the pressing member  183  retreats into the position (position in retreat) in which its pressing portion  183   b  does not contact the pressure catching portion  140   b  of the cartridge  7 , as shown in  FIG. 17(   b ). Therefore, while the cartridge  7  is mounted, the pressure catching portion  140   b  is not subjected to any pressure. The pressure which the cartridge  7  receives from the pressing member  183  when it is mounted is cancelled by the pushing portion  140   c,  which is located further from the rotational axis of the pressing member  183 , which coincides with the axial line of the hole  183   a.  That is, the amount of force necessary to push down the pressing member  183  against the force which acts to upwardly pushing the cartridge  7  is reduced by the ratio between the distance from the axial line of the hole  183   a  to the pressure catching portion  140   b  (pushing portion  183   b ) and the distance from the axial line of the hole  183   a  to the pushing portion  140   c  (pressure catching portion  183   c ). Therefore, the amount of load to which the cartridge  7  is subjected when it is mounted is substantially smaller than the amount of pressure which the cartridge  7  receives from the pressing member  183 ; the amount of force required to mount the cartridge  7  is substantially smaller than the amount of the pressure required to mount a cartridge ( 7 ) in accordance with the prior art. 
         [0136]    Further, when the cartridge  7  is mounted, the cartridge  7  is subjected to upward force, that is, the reactive force generated as the pressing member  183  is pushed down into its retreat. However, the contacting surface  40   h  comes into contact with the cartridge movement regulating portion  86 , that is, the cartridge contacting first portion of the main assembly. Therefore, the cartridge  7  is prevented from being moved upward. Here, the cartridge movement regulating portion  86  of the main assembly and the main assembly contacting second surface  40   h  of the cartridge  7  are positioned so that they remain in contact with each other until immediately before the cartridge positioning portion  40  (a pressure catching portion) is correctly positioned by coming into contact with the cartridge catching portion  82   a.  Therefore, while the cartridge  7  is mounted, more specifically, from the moment the cartridge  7  begins to receive the upward pressure from the pressing member  183  until immediately before the cartridge  7  is correctly positioned, the cartridge movement regulating portion  86 , that is, the cartridge movement regulating portion of the main assembly, which is formed of resin, and the contacting surface  40   h,  slide on each other, and the pressure catching portion  40   a  (cartridge positioning portion of cartridge) does not rub against the cartridge catching portion  82   a  of the main assembly, which is formed of a thin sheet of steel or the like. Therefore, the problem that the cartridge positioning portion  40   a  is shaved by the cartridge catching portion  82   a  is prevented. 
         [0137]    As the cartridge is inserted even further, the cartridge catching portion  183   c  is disengaged from the pushing portion  140   c,  and therefore, the pressing member  183  gradually returns to the pressing position from the retreat. Then, the cartridge  7  is inserted far enough for the contacting surface  40   i,  which is for correctly positioning the cartridge  7  in terms of the lengthwise direction of the cartridge  7 , to come into contact with the lateral plate  82 , that is, the rear lateral plate of the main assembly, the pressing portion  183   b  comes into contact with the pressure catching portion  40   b,  as shown in  FIGS. 16(   c ) and  17 ( c ), causing the cartridge  7  to be pressed (pressing position) in the direction indicated by an arrow mark S (pressing direction). During this process, the cartridge positioning portion  40   a  of the cartridge  7  bumps into the cartridge catching portion  82   a  of the rear lateral plate  82  of the main assembly, correctly positioning thereby the cartridge  7  in terms of the direction perpendicular to the cartridge mounting direction. Also during this process, the cartridge movement regulating portion  86  of the main assembly becomes disengaged from the second contacting surface  40   h;  a preset amount of gap is provided between the cartridge movement regulating portion  86  and the surface  40   g  (recessed surface). At the same time, the cartridge catching portion  183   c  moves past the pushing portion  140   c;  a preset amount of gap is provided between the cartridge catching portion  183   c  and the recessed surface  140   j.    
         [0138]    Also in this embodiment, the pressing member  183  is enabled to apply a sufficient amount of pressure to the cartridge  7 . 
         [0139]    When removing the cartridge  7  from the main assembly  100   a,  the cartridge mounting operation described above is to be carried out in reverse. The upward force which the cartridge  7  receives from the pressing member  183  is cancelled by the pushing portion  140   c,  which is located farther from the axial line of the hole  183   a,  as it is during the mounting of the cartridge  7 . Therefore, the amount of force necessary for the operation to remove the cartridge  7  in this embodiment is significantly smaller than the amount of force necessary for the operation to remove a cartridge  7  in accordance with the prior art, as the amount of the force necessary for the operation to mount the cartridge  7  in this embodiment is significantly smaller than the amount of force necessary for the operation to mount a cartridge in accordance with the prior art. 
         [0140]    Further, as the cartridge catching portion  82   a  of the main assembly becomes disengaged from the pressure catching portion  40   a  (cartridge positioning portion of cartridge), the cartridge movement regulating portion  86  of the main assembly comes into contact with the second contacting surface  40   h.  Further, even during the removal of the cartridge  7 , the cartridge movement regulating portion  86  of the main assembly, which is formed of resin, and the second contacting surface  40   h,  slide against each other, preventing thereby the pressure catching portion  40   a  from rubbing against the cartridge catching portion  82   a  of the lateral plate of the main assembly, as long as the cartridge  7  is under the upward force applied by the pressing member  183 . Therefore, the problem that the pressure catching portion  40   a  (cartridge positioning portion of cartridge) is shaved by the cartridge catching portion  82   a  as it rubs against the cartridge catching portion  82   a  is prevented. 
         [0141]    In this embodiment, only the portion of the development unit  4 , which corresponds in position to the rear end side of the main assembly of the image forming apparatus, is provided with the pushing portion. However, it may be only the front end of the development unit that is provided with the pushing portion. The effects of providing only the front end of the development unit with the pushing portion are the same as that achievable by providing only the rear end of the development unit with the pushing portion. 
       Embodiment 3 
       [0142]    Next, referring to  FIGS. 18-20 , the third embodiment of the present invention will be described. By the way, this embodiment is the same in the basic structure of an image forming apparatus as the first embodiment described above. Therefore, this embodiment will be described regarding only the structural features different from those in the first embodiment to avoid repetition of the same description. Further, the members, portions, etc., of the image forming apparatus in this embodiment, which are the same in function as those in the first embodiment described above, are given the same referential symbols. 
         [0143]    In this embodiment, the photosensitive drum  1  is grounded through the upwardly pulling portion  93  (pressure applying portion). Next, referring to  FIGS. 18-20 , the portions of the image forming apparatus in this embodiment, which are for grounding the photosensitive drum  1 , will be described. 
         [0144]    Referring to  FIGS. 18(   a )- 18 ( c ), a drum grounding member  98  is attached to the upwardly pulling portion  93 . As will be evident from the drawing, the drum grounding member  93  is in the form of a tortional coil spring. Referring to  FIG. 18(   b ), this drum grounding member  98  has a contact portion  98   b,  which is rotatable in the direction indicated by an arrow mark about a rotational axle  98   a.  The contact portion  98   b  is a portion of the drum grounding member  93 , which makes contact with a grounding plate  50   i  of the cartridge  7 , which will be described later. 
         [0145]    When the cartridge  7  is out of the image forming apparatus, the drum grounding member  98  is in its standby position, in which is in contact with the stopper portion  93   g  of the upwardly pulling portion  93 ; as the cartridge  7  is removed from the image forming apparatus, the drum grounding member  98  rotates backward until it comes into contact with the stopper portion  93   g.  Further, the contact portion  98   c  of the drum grounding member  98  remains always in contact with the tension spring  95 . When the cartridge  7  is in its preset image forming position, the contact portion  98   c  is under the roughly 25 N of contact pressure for keeping the cartridge  7  in contact with the cartridge catching portion  92   a.    
         [0146]    The tension spring  95  is anchored to the tension spring anchoring hook  97  with which the lateral plate  92  of the main assembly is provided. As described above, as the cartridge  7  is mounted into the main assembly, the cartridge  7  comes into contact with the cartridge catching portions  92   a   1  and  92   a   2 , being thereby correctly positioned. As for the tension spring  95 , as the cartridge  7  is mounted into the main assembly, it comes into contact with the drum grounding member  98 , establishing electrical connection between the lateral plate  92  of the main assembly and the drum grounding member  98 . Therefore, it is ensured that the drum grounding member  98  is grounded. 
         [0147]    The contact portion  98   b  of the drum grounding member  98  is on the downstream side of the rotational axis of the drum grounding member  98 , that is, the axial line of the hole  98   a  of the drum grounding member  98 , in terms of the abovementioned advancement direction. It rotates while being regulated by the surfaces  93   d   1  and  93   d   2 . Therefore, the problem that when the cartridge  7  is inserted, the cartridge  7  hangs up and/or is deformed, or the like problems, are prevented. Therefore, it is ensured that the photosensitive drum  1  is grounded to the lateral plate  92  of the main assembly. Further, the drum grounding member  98  is positioned so that it is on the top side of the grounding plate  50   i.  This arrangement ensures that the contact pressure between the drum grounding member  98  and the grounding plate  50   i  remains stable regardless of the positional accuracy of the cartridge  7  in terms of its lengthwise direction. 
         [0148]      FIG. 19  shows the structure of the cartridge grounding portion of the cartridge  7 . The grounding plate  50   i  is attached to the bearing  50  so that it is placed below the upwardly pulling force catching  50   b.  The grounding plate  50   i  is electrically connected to the photosensitive drum  1  through a metallic shaft  50   j,  and a grounding plate  50   k  which is in contact with the internal surface of the photosensitive drum  1 . 
         [0149]    Next, the movement of the drum grounding member  98 , which occurs during the mounting of the cartridge  7 , will be described. 
         [0150]    Referring to  FIG. 20(   a ), until the cartridge  7  is mounted, the drum grounding member  98  remains on standby; it remains in contact with the stopper portion  93   g  of the upwardly pulling member. Next, referring to  FIG. 20(   b ), as the upwardly pulling member  93  begins to be rotated into its retreat by the mounting of the cartridge  7  into the main assembly, the drum grounding member  98  begins to be rotated by the rotation of the upwardly pulling member  93  about the axial line of the hole  93   a.  Therefore, the contact portion  98   b  of the drum grounding member  98  comes into contact with the bearing  50  of the cartridge  7 , causing thereby the drum grounding member  98  (contact portion  98   b ) to rotate in the direction indicated by an arrow mark in the drawing. Then, as the cartridge  7  is further inserted so that it moves into its designated position in the main assembly, the drum grounding member  98  comes into contact with the grounding plate  50   i  of the cartridge  7 , by the contact portion  98   b,  as shown in  FIG. 20(   c ). 
         [0151]    The drum grounding member  98  is electrically in contact with the lateral plate  92  of the main assembly, and the grounding plate  50   i  of the cartridge  7  is electrically in contact with the photosensitive drum  1 , as described above. 
         [0152]    As described above, as the cartridge  7  is mounted, the drum grounding member  98 , and the grounding plate  50   i  with which cartridge  7  is provided, come into contact with each other. As a result, electrical connection is established between the photosensitive drum  1  and the lateral plate  92  of the main assembly, grounding thereby the photosensitive drum  1 . 
         [0153]    When the cartridge  7  is removed, the operation carried out when the cartridge  7  is mounted is carried out in reverse. That is, the drum grounding member  98  rotates until its contact portion  98   b  comes into contact with stopper  93   g.  Then, the drum grounding member  98  remains in the abovementioned standby position; it remains in contact with the stopper  93   g,  by its contact portion  98   b.    
         [0154]    The amount of the contact pressure between the contact portion  98   b  of the drum grounding member  98  and the grounding plate  50   i  of the cartridge  7  is roughly 2.5 N. In other words, while the drum grounding member  98  is in contact with the grounding plate  50   i,  roughly 2.5 N of downward pressure, which is opposite in direction to the direction in which the cartridge  7  is pushed. The reactive force generated by the force applied to the cartridge  7  to push down the cartridge  7  is caught by the reactive force catching portion  93   h  with which the upwardly pulling member  93  is provided ( FIG. 18(   a )). 
         [0155]    Since the drum grounding member  98  and the components related thereto are structured as described above, the reactive force which the drum grounding member  98  receives from the grounding plate  50   j  can be utilized to upwardly push the upwardly pulling member  93 . Thus, the reactive force upwardly pushes the cartridge  7  toward the cartridge catching portions  92   a,  through the upwardly pulling member  93 , cancelling thereby the downward force applied to the cartridge  7  by the drum grounding member  98 . Therefore, it is unnecessary to make the tension spring  95  strong enough to match the reactive force from the grounding plate  50   i.  In other words, the amount of pressure which the tension spring  95  generates has only to be large enough to ensure that the cartridge  7  is placed, and remains, in contact with the cartridge catching portions  92   a   1  and  92   a   2 . Thus, the cartridge  7  is significantly smaller in the amount of force necessary to mount or remove it, being therefore better in operability, than a cartridge in accordance with the prior art. 
         [0156]    Since the drum grounding member  98  is attached to the upwardly pulling member  93  as described above, the cartridge  7  is not directly subjected to the reactive force attributable to the mounting of the cartridge  7 , although it is subjected to frictional force. Therefore, the cartridge  7  is significantly smaller in the amount of force necessary to mount or remove it, being therefore better in operability, than a cartridge in accordance with the prior art. 
         [0157]    Further, the electrical connection is complete within the upwardly pulling member  93 . Therefore, even if the cartridge  7  slightly changes in position, the contact pressure between the drum grounding member  98  and grounding plate  50   i  remains stable, ensuring thereby that as the cartridge  7  is mounted into the image forming apparatus  100 , the cartridge  7  becomes, and remains, electrically connected to the image forming apparatus  100 . 
         [0158]    Further, the drum grounding member  98  is placed on the top side of the grounding plate  50   i.  Therefore, the contact pressure between the two remains stable regardless of the positional accuracy of the cartridge  7  in terms of its lengthwise direction. 
         [0159]    Incidentally, this embodiment was described above with reference to the grounding of the photosensitive drum  1 . However, this embodiment is not intended to limit the present invention in scope. That is, the application of the present invention is not limited to the above described case in which the upwardly pulling member (which is for upwardly pulling cartridge) is used to establish electrical connection between the photosensitive drum and main assembly to ground the photosensitive drum. For example, the present invention is also applicable to the case in which the upwardly pulling member is utilized to establish electrical connection to provide the cartridge  7  with charge bias, development bias, etc. 
         [0160]    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. 
         [0161]    This application claims priority from Japanese Patent Applications Nos. 331309/2006 filed Dec. 8, 2006, and 266398/2007 filed Oct. 12, 2007, which are hereby incorporated by reference.