Patent Publication Number: US-6983115-B2

Title: Developing cartridge and process cartridge having first and second projected portions and image forming apparatus mounting such a developing cartridge

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a process cartridge, and a development cartridge, employed by an electrophotographic image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer, etc. It also relates to an electrophotographic image forming apparatus which employs such a process cartridge and a development cartridge. 
   Here, an electrophotographic image forming apparatus is an apparatus which forms an image on recording medium with the use of an electrophotographic image formation process. It includes, for example, various types of electrophotographic copying machines, electrophotographic printers (LED printers, laser beam printer, etc.), electrophotographic facsimile machines, electrophotographic word processors, etc. 
   A process cartridge is a cartridge which integrally contains an electrophotographic photoconductive member as an image bearing member, and a minimum of a charging means, a developing means, a cleaning means, or an intermediary transferring means, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
   A development cartridge means a cartridge which integrally contains a developing means for developing an electrostatic latent image formed on an electrophotographic photoconductive member, and a toner storage portion for holding toner, and which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
   A process cartridge system, in which an electrophotographic photoconductive member; and a single or plurality of means among a charging means, a developing means, a cleaning means, etc., are integrally disposed in a cartridge removably mountable in the image assembly of an electrophotographic image forming apparatus, has been employed quite a while. 
   A process cartridge system substantially improves an electrophotographic image forming apparatus in operational efficiency and convenience, and also makes it possible for a user him- or herself to maintain an electrophotographic photoconductive member, as well as processing means such as a charging member, a developing means, a cleaning means, etc. In other words, a process cartridge system makes it easy to maintain an electrophotographic image forming apparatus. Therefore, a process cartridge system has come to be widely used in the field of an image forming apparatus. 
   In recent years, demands have increased for an electrophotographic color image forming apparatus capable of forming a color image. With this trend, it has been desired that the price of a color image forming apparatus substantially comes down, more specifically, it comes down low enough for an average user to afford a color image forming apparatus of his or her own. 
   In order to make such a desire attainable, not only must a color image forming apparatus be substantially reduced in price, but also it must be further improved in operability, in consideration of the fact that it is used by an average user. 
   In order to accomplish at the same time two objectives, that is, cost reduction and operability improvement, it is necessary to further reduce a color image forming apparatus in size, and also to make sure that the apparatus can more easily be supplied with consumables, and that a paper jam or the like can be more easily taken care of. 
   Thus, color image forming apparatuses equipped with a rotary type developing apparatus (rotational developing apparatus) having a rotary member in which a plurality of development cartridges are mountable (Japanese Laid-open Patent Applications 7-121027, 10-221919, and 2000-231239) have been proposed, and also, attempts have been made to commercialize the proposed apparatuses. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a development cartridge and a process cartridge, which are higher in the accuracy with which they are positioned relative to the main assembly of an electrophotographic image forming apparatus when mounted in the main assembly, and an electrophotographic image forming apparatus in which such development cartridge and process cartridge are removably mountable. 
   Another object of the present invention is to provide a development cartridge and a process cartridge, which are easily and reliably mountable in the main assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus in which such a development cartridge and a process cartridge are removably mountable. 
   Another object of the present invention is to provide a development cartridge, which is accurately and reliably positioned relative to the rotary member rotatably attached to the main assembly of an electrophotographic image forming apparatus, and is capable of taking, regardless of rotary rotation, a development position in which an electrostatic latent image formed on the electrophotographic photo conductive member can be developed by the developing means of one of the developments cartridges in the rotary member, and the home position into which it retreats to move the development cartridge away from the development position, and an electrophotographic image forming apparatus in which such a development cartridge is removably mountable. 
   Another object of the present invention is to provide a development cartridge, the driving force input gear of which reliably engages with the driving gear of the main assembly of an electrophotographic image forming apparatus, and an electrophotographic image forming apparatus in which such a development cartridge is removably mountable. 
   Another object of the present invention is to provide a development cartridge, which is capable of improving the degree of accuracy with which an electrophotographic photoconductive drum and a developing means are positioned relative to each other, and an electrophotographic image forming apparatus in which such a development cartridge is removably mountable. 
   Another object of the present invention is to provide a development cartridge, which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and comprises: a frame; a developing means for developing an electrostatic latent image formed on an electrophotographic photoconductive member; a first projection, which projects from the frame, and engages with a first cartridge positioning portion of the main assembly to accurately position the development cartridge relative to the apparatus main assembly, when the development cartridge is mounted into the main assembly; a second projection, which projects from the frame, and engages with a second cartridge positioning portion of the main assembly to prevent the development cartridge from rotating about the first cartridge positioning portion, when the development cartridge is mounted into the main assembly; and a cartridge guiding member, which projects from the frame, guides the development cartridge by coming into contact with the cartridge guiding portion of the main assembly, when the development cartridge is mounted into the main assembly, and is pressed in the direction to be placed in contact with the second cartridge positioning portion, when the development cartridge is mounted into the main assembly, and an electrophotographic image forming apparatus in which such a development cartridge is removably mountable. 
   Another object of the present invention is to provide a process cartridge cartridge, which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and comprises: a frame; an electrophotographic photoconductive member; a developing means for developing an electrostatic latent image formed on an electrophotographic photoconductive member; a first projection, which projects from the frame, and engages with a first cartridge positioning portion of the main assembly to accurately position the process cartridge relative to the apparatus main assembly, when the process cartridge is mounted into the main assembly; a second projection, which projects from the frame, and engages with a second cartridge positioning portion of the main assembly to prevent the process cartridge from rotating about the first cartridge positioning portion, when the process cartridge is mounted into the main assembly; and a cartridge guiding member, which projects from the frame, guides the process cartridge by coming into contact with the cartridge guiding portion of the main assembly, when the process cartridge is mounted into the main assembly, and is pressed in the direction to be placed in contact with the second cartridge positioning portion, when the process cartridge is mounted into the main assembly, and an electrophotographic image forming apparatus in which such a process cartridge is removably mountable. 
   Another object of the present invention is to provide an electrophotographic image forming apparatus, which is for forming an image on recording medium, and comprises: (i) a guiding portion; (ii) a first cartridge positioning portion; (iii) a second cartridge positioning portion; (iv) a cartridge mounting means for removably mounting a development cartridge, which is removably mountable in the main assembly of an electrophotographic image forming apparatus, and comprises: a frame; a developing means for developing an electrostatic latent image formed on an electrophotographic photoconductive member; a first projection, which projects from the frame, and engages with a first cartridge positioning portion of the main assembly to accurately position the development cartridge relative to the apparatus main assembly, when the development cartridge is mounted into the main assembly; a second projection, which projects from the frame, and engages with a second cartridge positioning portion of the main assembly to prevent the development cartridge from rotating about the first cartridge positioning portion, when the development cartridge is mounted into the main assembly; and a cartridge guiding member, which projects from the frame, guides the development cartridge by coming into contact with the cartridge guiding portion of the main assembly, when the development cartridge is mounted into the main assembly, and is pressed in the direction to be placed in contact with the second cartridge positioning portion, when the development cartridge is mounted into the main assembly; and (v) conveying means for conveying the recording medium. 
   These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a vertical sectional view of the electrophotographic image forming apparatus in an embodiment of the present invention. 
       FIG. 2  is a sectional view of the development cartridge. 
       FIG. 3  is a perspective view of the development cartridge, as seen from the side from which the development cartridge is driven. 
       FIG. 4  is a perspective view of the development cartridge, for showing the movement of the slidable members of the development cartridge. 
       FIG. 5  is a perspective view of the development cartridge, as seen from the side from which the development cartridge is not driven. 
       FIG. 6  is a plan view of the development cartridge, as seen from the side from which it is driven. 
       FIG. 7  is a plan view of the development cartridge and rotary member, as seen from the side from which the development cartridge is driven, for showing the direction in which the development cartridge is inserted into the rotary member. 
       FIG. 8  is a plan view of the development cartridge and rotary member, as seen from the side from which the development cartridge is driven, for showing the development cartridge in the rotary. 
       FIG. 9  is a plan view of the development cartridge, as seen from the side from which it is not driven. 
       FIG. 10  is a plan view of the development cartridge and rotary member, as seen from the side from which the development cartridge is not driven, for showing the direction in which the development cartridge is inserted into the rotary. 
       FIG. 11  is a plan view of the development cartridge and rotary member, as seen from the side from which the development cartridge is not driven, for showing the development cartridge in the rotary member. 
       FIG. 12  is a perspective view of the rotary unit. 
       FIG. 13  is a perspective view of the rotary member, and a development cartridge which is being mounted into the rotary member, for showing the direction in which the development cartridge is mounted into the rotary member. 
       FIG. 14  is a perspective view of the rotary member, in which a development cartridge has been properly mounted. 
       FIG. 15  is a perspective view of the control portion for controlling the pivotal movement of the rotary member. 
       FIG. 16  is a phantom side view of the development cartridge and rotary unit, for showing how the development cartridge is placed in contact with the photoconductive drum and is driven. 
       FIG. 17  is a phantom side view of the development cartridge and rotary unit, for showing how the tips of the teeth of the driving force input gear of the development collide with their counterparts, and how the development cartridge is driven, when and after the development cartridge is orbitally moved to the development position by the rotary unit. 
       FIG. 18  is a phantom side view of the development cartridge and rotary unit, for showing how the driving force input gear of the development properly meshes with its counterpart, and how the development cartridge is normally driven, when and after the development cartridge is orbitally moved to the development position by the rotary unit. 
       FIG. 19  is a sectional view of the rotary member, and the development roller of one of the development cartridges in which it is in contact with the photoconductive drum. 
       FIG. 20  is a sectional view of the rotary unit in the half distance position. 
       FIG. 21  is a sectional view of the rotary unit in the full distance position. 
       FIG. 22  is a vertical sectional view of an electrophotographic image forming apparatus, in accordance with the present invention, for showing how the development cartridge is mounted into, or dismounted from, the main assembly of the apparatus. 
       FIG. 23  is a perspective view of a part of the rotary unit, for showing the locking mechanism for keeping the rotary locked in place. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the preferred embodiments of the present invention will be described in more detail with reference to the appended drawings. In the following descriptions, however, the measurements, materials, and shapes of the structural components in the embodiments, their positional relationships, etc., are not intended to limit the scope of the present invention, unless specifically noted. 
   Further, in the following descriptions of the preferred embodiments, the front side is the upstream side in terms of the direction in which a recording medium is conveyed from the transferring station to the fixing station (right side in  FIG. 1 ), and the left or right side of the main assembly of an electrophotographic image forming apparatus is the left or right side as seen from the front side of the apparatus. Further, the lengthwise direction is the direction parallel to the axial direction of the development roller as a developing means. 
   {General Description of Image Forming Operation of Color Image Forming Apparatus} 
   First, referring to  FIG. 1 , the general structure of a color image forming apparatus will be described. 
     FIG. 1  is a vertical sectional view of a color laser beam printer, as an example of an electrophotographic color image forming apparatus in accordance with the present invention, the main assembly of which is holding development cartridges, a drum cartridge, and an intermediary transfer member unit. It shows the general structure of the apparatus. 
   In this color image forming apparatus in  FIG. 1 , an electrostatic latent image is formed on the electrophotographic photoconductive member (which hereinafter will be referred to as photoconductive drum  1 ), by projecting an optical image in accordance with image formation information, from an exposing means, and the electrostatic latent image is developed, with use of a developing means, into a developer image (which hereinafter may be referred to as a toner image. In synchronism with the formation of the toner image, a recording medium (which hereinafter will be referred to as transfer medium) is conveyed to the transfer station, and also, the toner image formed on the photoconductive drum  1  is transferred onto the intermediary transfer belt  5   a.    
   Then, the toner image on the intermediary transfer belt  5   a  is transferred onto the transfer medium by the second transferring means  11 . Then, the transfer medium is conveyed to the fixing device  8  having a pressure roller  8   a  and a heat roller  8   b . In the fixing device  8 , the toner image on the transfer medium is fixed. Then, the transfer medium is discharged into a delivery tray  10 . 
   Next, the image forming steps will be described in more detail. 
   In synchronism with the rotation of the intermediary transfer belt  5   a , the photoconductive drum  1  is rotated in the direction (counterclockwise direction) indicated by an arrow mark in  FIG. 1 . While the photoconductive drum  1  is rotated, the peripheral surface of the photoconductive drum  1  is uniformly charged by a charging apparatus  2 . The uniformly charged portion of the peripheral surface of the photoconductive drum  1  is exposed by an exposing means  3 ; a beam of light modulated with the image formation information corresponding to the yellow component, for example, of an intended image, is projected onto the uniformly charged portion of the peripheral surface of the photoconductive drum  1 . As a result, an electrostatic latent image corresponding to the yellow component is formed on the peripheral surface of the photoconductive drum  1 . 
   More specifically, the uniformly charged portion of the peripheral surface of the photoconductive drum  1  is exposed by the exposing means in the following manner. The exposing means  3  projects a beam of light (optical image) modulated with the image formation information read in from an external apparatus or the like. The exposing means  3  comprises a laser diode, a polygon mirror, a scanner motor, a focusing lens, and a reflection mirror. 
   As image formation signals are given to the main assembly of an image forming apparatus from an external apparatus or the like, the laser diode emits light, as image formation light, in response to the image formation signals, and the light is projected onto the polygon mirror, which is being rotated at a high speed by a scanner motor. Thus, the light is reflected by the polygon mirror in a manner to be projected onto the peripheral surface of the photoconductive drum  1  by way of the focusing lens and a reflection mirror. As a result, the numerous points of the uniformly charged portion of the peripheral surface of the photoconductive drum  1  are selectively exposed. Consequently, an electrostatic latent image is formed on the uniformly charged portion of the peripheral surface of the photoconductive drum  1 . 
   While the electrostatic latent image is formed, the developing device  4 Y, that is, one of the development cartridges  4 , is orbitally moved into the development position, and a predetermined bias voltage is applied to the development cartridge  4 Y to develop the electrostatic latent image, that is, to adhere yellow toner to the electrostatic latent image. 
   Thereafter, a bias voltage, which is opposite in polarity to the toner, is applied to a primary transfer roller  5   j  disposed in a manner to oppose the photoconductive drum  1 , with the interposition of the intermediary transfer belt  5   a  between the photoconductive drum  1  and transfer roller  5   j . As a result, the yellow toner image on the photoconductive drum  1  is transferred (primary transfer) onto the intermediary transfer belt  5   a.    
   As the primary transfer of the yellow toner image is completed as described above, the next developing devices is orbitally moved into the development position in which it is positioned in a manner to oppose the photoconductive drum  1 . This process is also carried out for each of the cyan and black color components. As a result four toner images different in color are deposited in layers on the intermediary transfer belt  5   a.    
   While the above described steps are carried out, the secondary transfer roller  11  is kept away from the intermediary transfer belt  5   a , and so is the cleaning charge roller  51  functioning as a cleaning unit. 
   Then, after the deposition of the four toner images different in color on the intermediary transfer belt  5   a , the secondary transfer roller  11  is pressed upon the intermediary transfer belt  5   a  as shown in  FIG. 1 . In addition, in synchronism with the pressing of the secondary transfer roller  11  on the intermediary transfer belt  5   a , the transfer medium kept on standby at a predetermined location in the adjacencies of the pair of registration rollers  7  as a conveying means, is sent into the nip between the intermediary transfer belt  5   a  and secondary transfer roller  11 . 
   On the immediately upstream side of the pair of registration rollers  7 , a preregistration sensor  14  is disposed, which keeps a transfer medium on standby at a predetermined location, by cutting off the force for rotationally driving the pair of registration rollers  7  as it detects the leading end of the transfer medium. 
   The secondary transfer roller  11  is supplied with a bias voltage which is opposite in polarity to toner. Thus, the toner images on the intermediary transfer belt  5   a  are transferred (secondary transfer) all at once onto the surface of the transfer medium which has been sent to the aforementioned nip and is being conveyed through the nip. 
   The transfer medium, which is bearing the transferred toner images, is conveyed to the fixing device  8  by way of the conveyance belt unit  12 . In the fixing device  8 , the toner images are fixed to the transfer medium. Then, the transfer medium is further conveyed by the pair of discharge rollers  13  along the discharge guide  15 , and then, is discharged into the delivery tray located at the top of the color image forming apparatus, by the pair of discharge rollers  9 , concluding the image forming operation. 
   Meanwhile, after the completion of the secondary transfer, the cleaning charge roller  5   f  is pressed on the intermediary transfer belt  5   a , and the residual charge on the surface of the intermediary transfer belt  5   a , and the residual charge of the secondary residual toner, that is, the toner remaining on the intermediary transfer belt  5   a  after the secondary transfer, are removed by the application of a predetermined bias voltage. 
   The residual toner from which the residual charge has been removed is electrostatically transferred from the intermediary transfer belt  5   a  back onto the photoconductive drum  1  through the primary transfer nip; in other words, the surface of the intermediary transfer belt  5   a  is cleaned. 
   The secondary transfer residual toner having been transferred back onto the photoconductive drum  1  is removed by a cleaning blade  6  dedicated to the cleaning of the photoconductive drum  1 , and is recovered. 
   The recovered residual toner, that is, waste toner, is conveyed through the waste toner conveyance path, which will be described later, to the waste toner box  216 , and accumulated therein. 
   {Structure of Development Cartridge} 
   Referring to  FIG. 2 , the development cartridge  4  is roughly dividable into a toner storage portion  302  and a development portion  309 . 
   The toner storage portion  302  is filled with toner. As a stirring means  303  in the toner storage portion  302  is rotated, the toner is conveyed to the development portion  309  by a predetermined amount. 
   After being conveyed to the development portion  309 , the toner is coated onto the peripheral surface of the development roller  305  as a developing means, by the rotation of a spongy toner supplying roller  304 . Then, as the development roller  305  is further rotated, the body of toner on the peripheral surface of the development roller  305  is formed into a thin layer while being given electrical charge by the friction between the toner, and the combination of a development blade  332  in the form of a piece of thin plate and the development roller  305 . As the development roller  305  is further rotated, the thin layer of toner on the development roller  305  is conveyed to the development position, in which the electrostatic latent image on the photoconductive drum  1  is developed (visualized) into a toner image by the application of a predetermined development bias. 
   The residual toner on the peripheral surface of the development roller  305 , that is, the toner which did not contribute to the visualization of the latent image on the photoconductive drum  1  and remained on the peripheral surface of the development roller  305 , is stripped away by the toner supplying roller  304  while a fresh supply of toner is coated on the development roller  305  by the toner supply roller  304 . In other words, the development operation is continually carried out. 
   Referring to  FIG. 9 , the development cartridge  4  is provided with a first projection  352 L, (also called a positioning portion) and a guiding rib  354  as a cartridge guiding member, which are on the external surface of the end wall of the development cartridge  4 , on the side from which the development cartridge  4  is not driven. The guiding rib  354  is located next to the first projection  352 L. The two are integral parts of the end wall. The development cartridge  4  is also provided with electrical contact portions A and B, which are on the top surface of the guiding rib  354 , being therefore aligned in the direction parallel to the guiding rib  354 . 
   The electrical contact portion A is the input portion through the development bias is applied to the development roller  305  and toner supplying roller  304 , whereas the electrical contact portion B is the input portion through which bias is applied to the development blade  332 . 
   As described above, the electrical contact portions A and B are located near the positioning portion  352 L of the development cartridge  4 , minimizing thereby their positional deviation from the bias contact portions of the main assembly of the image forming apparatus, and therefore, assuring that they come into contact, and remain in contact, with their counterparts on the apparatus main assembly side. Further, since the electrical contact portions A and B in this embodiment are disposed on the top surface of the guiding rib  354  used when the development cartridge  4  is inserted, it is unnecessary for the electrical contact portions A and B to be protuberant from the cartridge wall, making it possible to minimize the cartridge size in terms of its lengthwise direction, which in turn makes it possible to reduce the size of the apparatus main assembly. 
   {Mounting and Dismounting of Cartridge} 
   Referring to  FIG. 22 , as the top cover  64  of the apparatus main assembly is opened in the counterclockwise direction, an opening  65 , through which cartridges are to be mounted into the apparatus main assembly, is exposed. All of the development cartridges  4  and the process cartridge  5  in this embodiment are made mountable or dismountable through this opening  65 . 
   Further, the apparatus main assembly is structured so that paper jam or the like problems can be dealt with by removing the process cartridge through this opening  65 . 
   In other words, such chores as supplying the image forming apparatus with consumables, dealing with paper jam or the like problems, etc., can be done by opening only a single door (top cover  64 ), improving thereby the image forming apparatus in operability. 
   {Mounting, Dismounting, and Positioning of Development Cartridge} 
   Next, the mounting, dismounting, and positioning of the development cartridge will be described. 
   The development cartridges  4  holding the yellow, magenta, cyan, and black toners, one for one, are solidly mounted into predetermined positions, one for one, in a rotary member  67  as a rotatable member. At this time, referring to  FIGS. 3–14 , and  22 , the method for accurately positioning each development cartridge  4  relative to the rotary member  67  will be described in detail. 
   Referring to  FIGS. 13 and 22 , the development cartridge  4  is mounted into the main assembly of the image forming apparatus by being inserted straight into the apparatus main assembly in the direction indicated by an arrow mark, through the opening  65 . 
   Referring to  FIG. 12 , within the apparatus main assembly, a rotary unit  66  is disposed, which is rotatable about the central axle  51  thereof. The rotary unit  66  is provided with a pair of flanges  50 L and  50 R in the form of a disc, which are solidly attached to the lengthwise ends of the central axle  51 , one for one. 
   The flange  50 L is provided with: a cartridge guiding groove  50   c , functioning as the cartridge guiding portion of the apparatus main assembly side, which guides a development cartridge when the cartridge is mounted or dismounted; a first cartridge positioning portion  50   a L as a primary reference portion, relative to which the development cartridge  4  is positioned; and a secondary cartridge positioning portion  50   b L as a portion for controlling the rotation of the development cartridge  4  ( FIG. 10 ). 
   Similarly, the flange  50 R is provided with: a cartridge guiding groove  50   c , which guides a development cartridge when the cartridge is mounted or dismounted; a fourth cartridge positioning portion  50   a R, also as a primary reference portion, relative to which the development cartridge  4  is positioned; and a third cartridge positioning portion  50   b R as a portion for controlling the rotation of the development cartridge  4  ( FIG. 7 ). 
   The bottom walls of the first and fourth cartridge positioning portions  50   a L and  50   a R are provided with a hole  50   d  for retaining the development cartridge. This hole  50   d  plays the role of a hole into which a projection of the development cartridge  4  engages to prevent the development cartridge  4  from falling out of the rotary member  67 . 
   In comparison, referring to  FIG. 9 , the lengthwise end wall of the development cartridge  4 , on the side from which the development cartridge  4  is not driven (which hereinafter will be referred to as non driven side) is provided with: a guiding rib  354  which guides the development cartridge  4  when the development cartridge  4  is mounted or dismounted; a first projection  352 L, as a primary reference portion, on the non-driven side, which is for accurately positioning the development cartridge  4  relative to the rotary member  67 , and is arcuate in cross section; and a second projection  353 L, which is for controlling the rotation of the development cartridge  4 , and is also arcuate in cross section. 
   Next, referring to  FIG. 6 , the lengthwise end wall of the development cartridge  4 , on the side from which the development cartridge  4  is driven (which hereinafter will be referred to as driven side), is provided with: a guiding rib  354  which guides the development cartridge  4  when the development cartridge  4  is mounted or dismounted; a fourth projection  352 R, as a primary reference portion, on the driven side, which is for accurately positioning the development cartridge  4  relative to the rotary member  67 , and is arcuate in cross section; and a third projection  353 R, which is for controlling (retaining) the lengthwise end of the development cartridge  4 , on the driven side, and is also arcuate in cross section. 
   The first and fourth projections  352 L and  352 R are aligned in the lengthwise direction of the development cartridge  4 , and so are the second and third projections  353 L and  353 R. In other words, they are aligned in the direction parallel to the generator (or axial line) of the development roller  305 . 
   Referring to  FIGS. 7 and 10 , the rotary member  67  is provided with a pair of springs  53 , functioning as pressure applying members, which are for keeping the development cartridge  4  pressured in the direction to rotate in the counterclockwise direction of the drawing, and are attached to the flanges  50 L and  50 R, one for one, so that the functional parts of the springs  53  protrude into the corresponding cartridge guiding grooves  50   c . In other words, each pressure applying member  53  keeps the cartridge pressured in the direction opposite to the direction in which the rotary member  67  is rotated. 
   Referring to  FIGS. 8 and 11 , the pressure N from the pressure applying springs  53  generates such a moment M, in the development cartridge  4 , that causes the development cartridge  4  to pivot about the first and fourth projections  352 L and  352 R, causing thereby the second and third projections  353 L and  353 R of the development cartridge  4  to be placed, and kept, in contact with the second and third cartridge positioning portions  50   b L and  50   b R of the flanges  50 L and  50 R, respectively. 
   As the rotary member  67  is rotated, the development cartridge  4  is subjected to centrifugal force which acts in the direction to eject the development cartridge  4  outward of the rotary member  67 . However, the retractable projections  380   a  and  380   b , which will be described later, settle in the corresponding holes  50   d . Therefore, the development cartridge  4  is pressured by the centrifugal force in the direction to pivot about the first and fourth projections  352 L and  352 R, in other words, in the direction to move the portions of the development cartridge  4  having the second and third projections  353 L and  353 R outward of the rotary member  67  in terms of the radius direction of the rotary member  67 . 
   In this embodiment, however, the pair of pressuring springs  53  are formed so that the amount of the pressure produced by the pair of pressuring springs  53  exceeds the amount of the above-described centrifugal force. Therefore, even though the development cartridge  4  is repeatedly orbitally rotated and stopped, the development cartridge  4  is prevented from floating or being dislodged from the second and third cartridge positioning portions  50   b L and  50   b R. 
   With the provision of the above-described structural arrangement, the position of the development cartridge  4  relative to the rotary member  67  remains accurately fixed. Therefore, the development roller  305  of the development cartridge  4  is kept in contact with the photoconductive drum  1  of the process cartridge  5 , while being kept parallel to the axial line of the photoconductive drum  1 . In addition, it is possible to reduce the difference between the amount of the pressure to which the left side of the development cartridge  4  is subjected and the amount of the pressure to which the right side of the development cartridge  4  is subjected. Therefore, it is possible to reduce the difference in density, between the left and right sides of an image, resulting from the unbalance between the left and right side of the development cartridge  4  in terms of the pressure to which they are subjected. 
   Next, referring to  FIG. 11 , the rotary member  67  and the development cartridge  4  are designed so that the second projection  353 L on the external surface of the lengthwise end wall of the development cartridge  4 , on the non-driven side, comes into contact with only one area of the cartridge contacting surface of the second cartridge positioning portion  50   b L of the flange  50 L. In terms of the radius direction of the rotary member  67 , this area of contact between the second projection  353 L and second cartridge positioning portion  50   b L is on the center side of the rotary member  67  with respect to the center of the cartridge contact surface of the second cartridge positioning portion  50   b L. 
   Referring to  FIG. 8 , the third projection  353 R of the driven side of the development cartridge  4  comes into contact with two areas of the cartridge contacting surface of the third cartridge positioning portion  50   b R of the flange  50 R. In terms of the radius direction of the rotary member  67 , one of the two contact areas between the third projection  353 R and the third cartridge positioning portion  50   b R is on the center side of the rotary member  67  with respect to the center of the cartridge contact surface of the third cartridge positioning portion  50   b R, and the other is on the outward side of the rotary member  67 . More specifically, the contact areas  353 R- 1  and  353 R- 2  of the cartridge positioning projection  353 R of the development cartridge  4  come into contact with the contact areas  50   b R- 1  and  50   b R- 2 , respectively, of the third cartridge positioning portion  50   b R of the flange  50 R. This structural arrangement is made because, as the development cartridge  4  receives a driving force, through its gear  307 , from the apparatus main assembly, it is subjected to a force F which acts in the direction indicated by an arrow mark, as shown in  FIG. 16 . In other words, the above-described structural arrangement is made to assure that the development cartridge  4  is accurately positioned relative to the rotary member  67  and remains therein. 
   The first and fourth projections  352 L and  352 R of the development cartridge  4  are the portions by which the development cartridge  4  is pivotally supported by the cartridge positioning portions of the rotary member  67 . The first projection  352 L of the development cartridge  4  is made to exactly engage with the first cartridge positioning portion  50   a L of the flange  50 L, whereas the fourth projection  352 R of the development cartridge  4  is made to engage with the fourth cartridge positioning portion  50   a R of the flange  50 R, with the presence of a certain amount of a gap. 
   Next, referring to  FIGS. 3 ,  4 , and  5 , the development cartridge  4  is provided with a pair of retractable projections  380   b  and  380   a , which are extendable from, or retractable into, the first and fourth projections  352 L and  352 R, respectively. 
   These retractable projection  380   b  and  380   a  are integral parts of the left and right lengthwise ends, respectively, of a pair of slidable members  380 , in the form of a rods, the length of which is roughly half the length of the development cartridge  4 . Thus, the retractable projections  380   b  and  380   a  can be made to project from, or retracted into, the ends of the first and fourth projections  352 L and  352 R, respectively, by slidably moving the slidable members  380 . 
   Further, the development cartridge  4  is provided with a hinge-like handle  381 , which is attached the roughly center portion, in terms of the lengthwise direction, of the top portion of the development cartridge  4 . The hinge-like handle  381  is kept pressured in the opening direction by an unshown torsion coil spring. 
   More specifically, the hinge-like handle  381  comprises the left and right members  381   a  and  381   b , which are connected to the pair of slidable members  380 , one for one. Thus, the slidable members  380  are slidably movable by rotationally moving the left and right members  381   a  and  381   b  of the hinge-like handle  381 . 
   Normally, the left and right members of the hinge-like handle  381  are kept apart by being pressured by the torsion coil spring, keeping thereby the retractable projection  380   a , that is, the end portion of the slidable member  380 , projecting from the end of the fourth projection  352 R. However, as the hinge-like handle  381  is grasped, the left and right members thereof are rotationally moved, causing the retractable projection  380   a , that is, the end portion of the slidable member  380  to retract into the fourth projection  352 R. 
   Further, the left and right rotational members  381   a  and  381   b  of the hinge-like handle  381  are provided with a toothed portion, which is on the side opposite to the side on which the fingers are placed to rotationally move the left and right members  381   a  and  381   b . The toothed portions of the left and right rotational members  381   a  and  381   b  are meshed with each other. Therefore, as one of the two rotational members  381   a  and  381   b  is rotationally moved, the other rotational member is rotationally moved by the rotational movement of the first rotational member. Thus, even if only one of the two rotational members  381   a  and  381   b  of the hinge-like handle  381  is rotationally moved, both of the slidable members  380  are reciprocally moved at the same time. 
   When inserting the development cartridge  4  into the rotary member  67 , first, the development cartridge  4  is to be grasped by the hinge-like handle  381 , and then, the development cartridge  4  is to be inserted, with the pair of guiding ribs  354  of the development cartridge  4 , which are on the external surfaces of the lengthwise end walls of the development cartridge  4 , fitted in the cartridge guiding groove  50   c  of the flange  50 L and the cartridge guiding groove  50   c  of the flange  50 R, one for one. 
   Then, the hinge-like handle  381  is to be released from the fingers as the first and fourth projections  352 L and  352 R of the development cartridge  4 , which are arcuate in cross section, come into contact with the first and fourth cartridge positioning portions  50   a L and  50   a R of the flange  50 L and  50 R, respectively. 
   Upon the release of the hinge-like handle  381 , the retractable projections  380   a  and  380   b  project from the first and fourth projections  352 L and  352 R, respectively, and enter the aforementioned hole  50   d  of the bottom wall of the first cartridge positioning portion  50   a L, and the hole  50   d  of the bottom wall of the fourth cartridge positioning portion  50   a R, respectively. 
   The first projection  352 L and retractable projection  380   b  are coaxial. Therefore, the development cartridge  4  is allowed to pivotally move about the axial line of the first projection  352 L. However, the cartridge pressuring springs  53  for keeping the development cartridge  4  pressured in the direction to rotate the development cartridge  4  in the counterclockwise direction of the drawing are partially projecting into the cartridge guiding grooves  50   c , one for one. Therefore, the second and third projections  353 L and  353 R of the development cartridge  4  are kept in contact with the second and third cartridge positioning portions  50   b L and  50   b R of the flanges  50 L and  50 R, respectively. As a result, the development cartridge  4  is accurately positioned, and kept accurately positioned, relative to the rotary member  67  ( FIG. 14 ). 
   On the other hand, in order to remove the development cartridge  4  from the rotary member  67 , first, the hinge-like handle  381  is to be grasped, as shown in  FIG. 4 , to retract the retractable projections  380   a  and  380   b  so that they allow the development cartridge  4  to be removed upward from the rotary member  67 , by disengaging from the holes  50   d.    
   As described above, the development cartridge  4  can be removed or mounted by the operation carried out by a user. Further, with the provision of the above described structural arrangement and method for solidly placing the development cartridge  4  in the rotary member  67 , the development cartridge  4  does not become disengaged from the rotary member  67  while the rotary member  67  is rotated. 
   {Structure of Mechanism for Driving Development Cartridge} 
   Next, the structure of the mechanism for driving the development cartridge  4  will be described in detail. 
   Referring to  FIG. 12 , the rotary flanges  50 L and  50 R are provided with a side plate  54 , which is on the outward side of each rotary flange. The center axle  51  of the rotary member  67  is disposed in a manner to penetrate the pair of flanges  50 L and  50 R, and the pair of side plates  54 . More specifically, the rotary flanges  50 L and  50 R and the center axle  51  are rotationally supported by the side plates  54  so that the development cartridges  4  can be orbitally moved. 
   To one of the side plate  54 , a gear train, that is, a set of gears meshed in a predetermined order, is attached. The driving force input gear  307  of the development cartridge  4 , shown in  FIG. 16 , meshes with the final gear, that is, the most downstream gear of the above described gear train on the side plate  54 , and rotationally drives the development roller  305 , coating roller, stirring members, etc. 
   In this embodiment, as the flanges  50 L and  50 R are rotated a predetermined angle, each development cartridge  4  is orbitally moved the same angle. Further, as the development cartridge  4  is orbitally moved, the input gear  307  of the development cartridge  4  is engaged with the final gear  55  on one of the side plates  54  of the rotary member  67 . 
   {Development Cartridge Engagement by Rotary Rotation, and Driving of Development Cartridge} 
   It is possible that when the development cartridge  4  is orbitally moved into the development position by the rotation of the rotary member  67 , the teeth of the driving force input gear  307  of the development cartridge  4  collide with the teeth of the final gear  55  of the side plate  54  of the rotary member  67 , and fail to properly mesh. In this embodiment, however, the development cartridge  4  is allowed to temporarily pivot backward about the fourth cartridge positioning portion  50   a R of the flange  50 R. Therefore, it is assured that the teeth of the driving force input gear  307  properly mesh with those of the final gear  55  on the side plate  54 . 
   To describe this process in more detail, referring to  FIG. 17 , when the input gear  307  of the development cartridge  4  is not in synchronism with the final gear  55  of the rotary member  67  in terms of tooth position, the teeth of the former collide with those of the latter. As a result, the input gear  307  is subjected to the reactive force F from the collision, which acts in the direction shown in  FIG. 17 . 
   The vectors resulting from the reactive force F generate such a moment M that acts in the direction to pivotally move the development cartridge  4  about the first and fourth projections  352 L and  352 R in the counterclockwise direction. This moment M 2  is greater than the moment M generated by the pressure N from the cartridge pressuring springs  53 . Therefore, the development cartridge  4  is pressured in the direction indicated by an arrow mark B. In addition, the development cartridge  4  is pressured rightward of the drawing, by a force Fx, which is the x component of the reactive force F. 
   In this embodiment, however, the cartridge contacting portion  50   b R- 2  of the third cartridge positioning portions  50   b R of the rotary member  67 , that is, the outward cartridge contacting portion of the rotary member  67  in terms of the radius direction of the rotary member  67 , is roughly perpendicular to the line connecting the center of the fourth projections  352 R, as the referential portion relative to which the development cartridge  4  is positioned, about which the development cartridge  4  is pivotally movable, and the center of the third projection  353 R. 
   Therefore, the development cartridge  4  is allowed to pivotally move in the direction indicated by the arrow mark B; in other words, it is allowed to escape outward. As a result, the condition in which the aforementioned collision between the teeth of the input gear  307  of the development cartridge  4  and the final gear  55  of the rotary member  67  occurred does not exist, allowing the two sets of teeth to mesh as shown in  FIG. 18 . 
   Then, the development cartridge  4  is accurately positioned relative to the flanges  50 L and  50 R, in the predetermined manner, by the above described cartridge pressuring springs  53  of the flanges  50 L and  50 R, respectively. 
   As for the non-driven side of the development cartridge  4 , the development cartridge  4  is allowed to pivotally move in the direction indicated by the arrow mark B about the first projection  352 L as the referential portion for development cartridge positioning, about which the development cartridge  4  is pivotally movable. In other words, the non-driven side of the development cartridge  4  moves in the same manner as the driven side of the development cartridge  4  moves, which is needless to say. 
   After the completion of the driving of a given development cartridge, the development cartridge is orbitally moved out of the development position by the rotation of the rotary member  67 . However, the final gear  55  of the flange  50 R sometimes fails to instantly disengage from the input gear  307  of the development cartridge, when the development cartridge is moved out of the development position. Such a problem is also solved by the above-described mechanism for allowing the development cartridge  4  to pivotally move; it is assured by the above described mechanism that the final gear  55  of the rotary member  67  smoothly disengages from the input gear  307  of the development cartridge  4 , allowing thereby the development cartridge  4  to be orbitally moved out of the development position. 
   The first and fourth projections  352 L and  352 R of the development cartridge  4  in this embodiment, about which the development cartridge  4  is pivotally movable, are located in the adjacencies of the downstream end of the development cartridge  4  in terms of the direction in which the development cartridge  4  is orbitally moved. However, as the input gear  307  of the development cartridge  4  collides with the final gear  55  of the rotary member  67 , the development cartridge  4  is pressured downward by the reactive force F resulting from the collision ( FIG. 18 ). 
   Thus, upon the collision, the first and fourth projections  352 L and  352 R of the development cartridge  4  are going to move downward. However, they are caught and supported by the first and fourth cartridge positioning portions  50   a L and  50   a R of the flange  50 L and  50 R, respectively. With the provision of the above described supporting structure, even if the development cartridge  4  is orbitally moved at a high speed, it does not occur that the development cartridge  4  dislodge from the flange  50 L and  50 R due to the collision which occurs in the driving force inputting portion. 
   {Pressure Applied to Development Cartridge during Development Cartridge Engagement, and Driving of Development Cartridge} 
   Referring to  FIG. 16 , as the input gear  307  of the development cartridge  4  is driven by the final gear  55  on the side plate  54  of the rotary member  67 , it is subjected to the force F resulting from the driving. In addition, the pressure N from the cartridge pressuring springs  53  acts on the guiding rib  354 , and therefore, a contact pressure W 2  acts on the development roller  305 . The combination of these three forces generate, in the development cartridge  4 , such a moment M that acts in a direction to pivotally move the development cartridge  4  about the first cartridge positioning portion  50   a L of the flange  50 L in the counterclockwise direction of the drawing. 
   The development roller  305  rotates at a peripheral velocity roughly 150% greater than that of the photoconductive drum  1 . In other words, the development roller  305  rotates roughly 1.5 times faster than the photoconductive drum  1 . 
   With the presence of this difference in peripheral velocity between the development roller  305  and photoconductive drum  1 , the development roller  305  is subjected to a force P which acts in the tangential direction. Therefore, the development cartridge  4  is subjected to such a moment M 2  that acts to pivotally move the development cartridge  4  about the first cartridge positioning portion  50   a L of the flange  50 L of the rotary member  67 , the counterclockwise direction of the drawing. 
   The clockwise moment M is substantially greater than the counterclockwise moment M 2 . Therefore, the second projection  353 L of the development cartridge  4 , that is, the projection on the non-driven side, is pressed on the second cartridge positioning portion  50   b L of the flange  50 L. Therefore, the development cartridge  4  is prevented from moving relative to the cartridge positioning point of the flange  50 L, during the driving of the development cartridge  4 . 
   Further, on the driven side of the development cartridge  4 , the force F resulting from the driving of the gear  307  of the development cartridge  4  by the final gear  55  on the apparatus main assembly side acts on the driving force input shaft  308 . Thus, the third projection  353 R ( 353 R- 1  and  353 R- 2 ) of the driven end of the development cartridge  4  is prevented by this force F from moving from the two contact portions, that is, the portions  50   b R- 1  and  50   b R- 2  of the third cartridge positioning portion  50   b R. 
   In this embodiment, the third projection  353 R of the development cartridge  4  is located on the downstream side of the force F which results from the driving of the driving force input gear  307  of the development cartridge  4  by the final gear  55  on the side plate  54  of the rotary member  67  and acts on the driving force input shaft. Therefore, it is assured that the third projection  353 R is firmly held by the third cartridge positioning portion  50   b R of the flange  50 R. 
   As described above, the development cartridge  4  is accurately positioned in the rotary member  67 , and firmly held therein. Therefore, the vibrations which are likely to occur due to the meshing of gears, in the driving force inputting portion, do not occur. 
   Incidentally, during a development operation, at the driven end of the development cartridge  4 , the third projection  353 R ( 353 R- 1  and  353 R- 2 ) functions as a positional reference, and the fourth projection  352 R functions as a rotation controlling portion. Further, after the accurate positioning of the development cartridge  4  in the rotary member  67 , there remains a small amount of play S ( FIG. 8 ) between the fourth projection  352 R of the development cartridge  4  and the fourth cartridge positioning portion  50   a R of the flange  50 R, allowing thereby the fourth projection  352 R, as the portion about which the development cartridge  4  is allow to pivotally move, to move slightly. 
   Therefore, the effects of the errors in component dimension can be absorbed by this play S, making it possible to prevent the development cartridge  4  from being mounted improperly in terms of its positional relationship relative to the rotary member  67 . 
   Also in this embodiment, the force for driving the development cartridge  4  begins to be transmitted to the development cartridge  4  before the development roller  305  comes into contact with the photoconductive drum  1 . Therefore, the pre-rotation time for the development roller  305  can be secured without the need for lengthening the cartridge switching time. 
   The force F generated by the driving of the driving force input gear  307  by the final gear  55  on the side plate  54  of the rotary member  67  is a part of the closed dynamic system confined within the rotary member  67 . Therefore, the force F has little effect upon the pressure applied to the photoconductive drum  1  by the development cartridge  4 , which will be described later. 
   Referring to  FIG. 18 , as the development cartridge  4  is moved from a position in which the driving force input gear  307  of the development cartridge  4  is not engaged with its counterpart on the rotary side, and therefore, the development cartridge  4  is not driven, to the position in which the driving force input gear  307  is engaged with its counterpart on the rotary member side, and therefore, the development cartridge  4  is driven, the development cartridge  4  and the input gear  307  therein are subjected to the reactive force, which results from the engagement and driving of the development cartridge  4 , and which acts in the normal rotational direction of the input gear  307 . Incidentally, the rotational direction of the driving force input gear  307  of the development cartridge  4  in this embodiment is the same as the direction (counterclockwise direction) in which the development cartridge  4  is orbitally moved. 
   Therefore, as the development cartridge  4  is orbitally moved from the aforementioned pre-engagement position to the engagement position, in other words, as the input gear  307  comes into contact with the final gear  55  of the rotary member  67 , the development cartridge  4  and the input gear  307  therein are subjected to the reactive force F which acts in the normal rotational direction of the input gear  307  shown in the drawing. 
   Since the reactive force F, to which the development cartridge  4  and its input gear  307  are subjected upon the engagement between the input gear  307  and final gear  55 , acts in the normal rotational direction of the input gear  307 , the development roller  305  is not rotated in reverse by the reactive force F. Therefore, it does not occur that the toner in the development cartridge  4  is conveyed backward by the reversal rotation of the development roller  305 . Therefore, it does not occur that the sealing member  356  or the like, shown in  FIG. 2 , is turned inside out by the reversal conveyance of the toner. Therefore, it does not occur upon the engagement between the input gear  307  and final gear  55  that the toner blows out of the development cartridge  4  due to the problem that the sealing member  356  or the like is turned inside out by the reversal conveyance of the toner, which is caused by the engagement. 
   {Structure of Mechanism for Applying Pressure on Development Cartridge} 
   In this embodiment, four development cartridges 4 different in the color of the toner contained therein are placed in the rotary member  67 , and each development cartridge  4  is kept pressed on the photoconductive drum  1  in the following manner. 
   Referring to  FIGS. 12 and 16 , the flanges  50 L and  50 R are rotatably supported by the side plates  54  of the rotary member  67 . More specifically, the side plates  54  are solidly attached to the shaft  60 , which is rotatably supported by the side walls of the apparatus main assembly. In other words, the side plates  54  of the rotary member  67  are accurately positioned relative to the apparatus main assembly by the shaft  60 . Therefore, the development cartridges  4 , flanges  50 L and  50 R, and side plates  54  of the rotary member pivotally move together. 
   Thus, the development cartridge  4  is pressed upon, or moved away from, the photoconductive drum  1 , by the pivotal movement of the combination of the development cartridges  4  and rotary  67 . 
   This structure of making the development cartridge  4  and rotary member  67  pivot in combination makes it possible to dispose the development cartridge pressing mechanism outside the rotary member, instead of inside. Therefore it is possible to reduce the rotary member  67  in size, and in addition, it is possible to simplify the mechanism for pressing the development cartridge. 
   The rotary member  67  is pivotally moved by rotating the rotary pivoting cam  94 , the axial line of which coincides with that of the rotational pressure application shaft  90 . The rotary member  67  can be set to two positions, that is, the position in which the development roller  305  is kept in contact with the photoconductive drum  1  ( FIG. 19 ) and the position in which it does not place the development roller  305  in contact with the photoconductive drum  1  ( FIG. 21 ), by switching the rotational direction of the motor (unshown) for driving the cam  94 . 
   Referring to  FIG. 15 , the rotary pivoting cam  94  is attached to the shaft  90 , and a flag  92  is attached to one end of the shaft  90 . The direction in which the rotary pivoting cam  94  is rotating is  92  blocks the sensor  93  ( FIG. 14 ). 
   The development roller  305  of the development cartridge  4  is placed in contact with the photoconductive drum  1 , by rotating forward the unshown cam driving motor for a predetermined length of time. With this forward rotation of the motor, the rotary pivoting cam  94  is rotated a predetermined angle, pressing thereby the tappet  99  downward ( FIG. 19 ). 
   As a result, the side plate  54  of the rotary member  67  is rotated about the shaft  60  by the downward movement of the tappet  99 , with the presence of a rotary pressing spring  98  between the tappet  99  and the side plate  54 . Therefore, the rotary member  67  is pushed (pivoted) toward the photoconductive drum  1 . 
   In order to move the rotary member  67  away from the photoconductive drum  1 , the operation carried out to move the rotary member  67  toward the photoconductive drum  1  is to be carried out in reverse; the unshown cam driving motor is to be rotated backward. 
   Incidentally, in this embodiment, the rotary member  67  can be set to two positions, that is, the half and full distance positions, in which the development roller  305  of the development cartridge  4  does not contact the photoconductive drum  1 . More specifically, when the rotary member  67  is in the half distance position, the distance between the development roller  305  and photoconductive drum  1  is roughly 2 mm (L/2=2 mm), whereas when the rotary member  67  is in the full distance position, the distance between the development roller  305  and photoconductive drum  1  is roughly 4 mm (L=4 mm). 
   In other words, the rotary member  67  is allowed to take three different positions: the contact position shown in  FIG. 19 ; the half distance position shown in  FIG. 20 , and the full distance position shown in  FIG. 21 . The rotary member  67  is placed in these three positions by rotating the unshown cam driving motor forward or backward so that the rotary pivoting cam  94  rotates 0°, 90°, or 180°. 
   Also in this embodiment, during an actual image forming operation, the rotary member  67  is pivotally moved only between the contact position, and the half distance position in which the rotary member  67  is rotated. The full distance position is used only to remove the development cartridge  4 , or to read, or write into, the memory tag of the development cartridge  4 . 
   When the rotary member  67  is pivotally moved toward the photoconductive drum  1  from the half distance position to place the development roller  305  of the development cartridge  4  in contact with the photoconductive drum  1 , the distance the rotary member  67  travels is substantially shorter (half) than that when the rotary member  67  is pivotally moved toward the photoconductive drum  1  from the full distance position to place the development roller  305  of the development cartridge  4  in contact with the photoconductive drum  1 . Therefore, the amount of the shock and operational noises to which the photoconductive drum is subjected when the rotary member  67  is moved from the half distance position is half the amount of shock and operational noises to which the photoconductive drum is subjected when the rotary member  67  is moved from the full distance position. 
   As described previously, the development cartridge  4  is positioned relative to the rotary member  67  at a total of four portions, that is, two portions at the left end and two portion at the right end. 
   Referring to  FIG. 3 , designated by a referential letter h is the line connecting the axial lines of the first and fourth projections  352 L and  352 R as the positioning portions, and designated by a referential letter p is the line connecting the axial lines of the second and third projections  353 L and  353 R. Further, designated by a referential letter v is the generator (which is parallel to axial line) of the development roller  305 . In this embodiment, the development cartridge  4  is structured so that the lines h and p become parallel to the generator v. 
   Further, the development roller  305  is disposed so that its axial line is placed between the lines h and p. Therefore, the contact pressure W which occurs between the development roller  305  and photoconductive drum  1  can be evenly borne by the four projections, preventing thereby the development cartridge  4  from being twisted. Therefore, it does not occur that one side of the development roller  305  is pressed harder on the photoconductive drum  1  than the other side. 
   {Control of Rotary Rotation} 
   Referring to  FIG. 12 , the peripheral portions of the flanges  501  and  50 R are in the form of a gear, and the rotary member  67  is provided with a pair of follower gears  59 , which are disposed at the lengthwise ends, one for one, and are engaged with the gear portions of the flanges  50 L and  50 R, one for one. The pair of follower gears  59  is connected by the rotational axle. Thus, when one of the rotary flanges, for example the flange  50 R, rotates, the other flange, that is, the flange  50 L, is rotated in the same phase through the pair of follower gears  59 . 
   With the provision of this driving structure, it is prevented that one of the flanges  50 L and  50 R is twisted while the flanges  50 L and  50 R are rotated to orbitally move the development cartridge  4 , or while the development cartridge  4  is driven. 
   The shaft  60  about which the side plates  54  are pivotally moved is provided with a rotary driving gear  59 , which rotates the flanges  50 R. This rotary driving gear  59  is connected to the rotary driving motor  61 . 
   To the end of the rotational axle of the rotary driving motor  61 , an encoder  62  of a known type is attached. The amount of the rotation of the rotary driving motor  61  is detected by this encoder  62  to control the revolution of the motor  61 . 
   The flange  50 L is provided with a flag  57 , which perpendicularly projects inward from the peripheral portion of the flange  50 L. This flag  57  passes a photo-interrupter  58  fixed to the side plate  54 , as shown in  FIG. 16 , as the rotary  67  is rotated. 
   In this embodiment, the rotation of the rotary member  67  for orbitally moving the development cartridges  4  is controlled so that the rotary member  67  is rotated through a predetermined angle with reference to the moment the flag  57  blocks the photo-interrupter  58 . The rotational angle of the rotary member  67  is detected from the revolution of the motor  61  detected by the aforementioned encoder  62 . It has been a common practice to control the rotation of the rotary member  67  with the use of a pulse motor or the like. In this embodiment, however, a DC motor is employed to rotate the rotary member  67 , more quietly driving the rotary member  67 . 
   It is possible that the development cartridge  4  is displaced from the development position by the unexpected rotation of the rotary member  67  caused by the driving of the development cartridge  4 . Therefore, the rotary member  67  must be locked in place in terms of rotation so that it does not rotate. 
   It is possible to electrically brake the DC motor as the rotary driving motor, in order to lock the rotary member  67  in terms of rotation. However, there is the possibility that braking the DC motor for a long time increases the temperature of the DC motor, which might result in the burnout of the coil in the motor. 
   In this embodiment, therefore, the rotational axle of the follower gear  59  is provided with a locking groove  95 , as shown in  FIG. 23 . Thus, each time the development cartridge  4  arrives at the predetermined position (development position), the claw of a stopper  96  is inserted into the locking groove  95 . 
   The stopper  96  is moved up or down by turning on or off a solenoid  97  with a predetermined timing. In other words, in this embodiment, a mechanical locking mechanism is employed to prevent the rotary member  67  from unexpectedly rotating. 
   The above described above-described embodiment of the present invention has the effects which will be described next. 
   (1) It is assured that the development cartridge  4  is accurately positioned relative to the rotary member  67 , and that the rotation of the rotary member  67  is stable. Therefore, it is possible to always print an excellent image. 
   (2) It is assured that the input gear  307  of the development cartridge  4  properly meshes with its counterpart, eliminating thereby the problem that the development roller  305  erratically rotates. Therefore, an excellent image can be formed. 
   (3) If the input gear  307  of the development cartridge  4  fails to properly mesh with the final gear  55  of the rotary member  67  immediately after the development cartridge  4  is orbitally moved to its designated position, the development cartridge  4  itself is allowed to temporarily and pivotally retract to assure that the input gear  307  properly meshes with the final gear  55 . Therefore, the formation of an abnormal image, or printing errors, can be prevented. 
   (4) The development cartridge  4  is moved in combination with the rotary member  67 , toward, or away from, the photoconductive drum  1 , eliminating the need for a complicated mechanism for individually moving the development cartridge  4 . Therefore, it is possible to reduce image formation apparatus cost. 
   (5) It is possible to begin driving the development cartridge  4  before the development roller  305  of the development cartridge  4  comes into contact with the photoconductive drum  1 . Therefore, it is possible to increase image formation speed. 
   As is evident from the above description of the embodiment of the present invention, not only does the present invention make it possible to reduce image forming apparatus cost, but also the embodiment makes it possible to improve image forming apparatus in operability. Further, the embodiment makes it possible to increase image formation speed. 
   As described above, the effects of the present invention are as follows. That is, it is possible to increase the degree of accuracy with which a development cartridge and a process cartridge are attached to the main assembly of an electrophotographic image forming apparatus, and it is possible to reduce in size a development cartridge, a process cartridge, and an electrophotographic image forming apparatus in which such development cartridge and process cartridge are removably mountable. Further, it is possible to more easily and more reliably mount a development cartridge and a process cartridge into the main assembly of an electrophotographic image forming apparatus. 
   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.