Abstract:
An image forming apparatus for forming an image on a recording material includes a drum cartridge including an image bearing member, a developing cartridge including a developing unit for developing the image formed on the image bearing member, and a cartridge mounting member to which the drum cartridge and the developing cartridge are detachably mountable. In addition, a transferring unit transfers a visualized image on the image bearing member onto the recording material fed along a feeding path, and an opening and closing cover is provided across the feeding path from the image bearing member. A path of removing the detachable developing cartridge is accessed by opening the opening and closing cover and extends across the feeding path so as to permit the developing cartridge to pass through the feeding path without removing the drum cartridge.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus in which a cartridge is removably mountable. 
     Cartridges made up of various units different in service life have been in use for a long time. Generally speaking, a photosensitive drum, for example, is longer in service life than a development roller. Placement of components different in length of service life in different units, one for one, makes it possible to replace only the unit which contains the component necessary to be replaced. Thus, it can reduce an image forming apparatus in terms of cartridge cost. It can also contribute to efficient usage of natural resources. 
     On the other hand, demands have been increasing for image forming apparatuses which are better in terms of removal of a jammed sheet of recording medium. One of the structural arrangements for making it easier to remove a jammed sheet of recording medium from an image forming apparatus is to structure an image forming apparatus so that a user can easily access the jammed sheet of recording medium without removing a cartridge from the main assembly of an image forming apparatus. In recent years, image forming apparatuses have been substantially reduced in size. Thus, in order to make it easier to remove a jammed sheet of recording medium from the main assembly of an image forming apparatus, it has been studied to provide a door which can be rotationally opened to access the recording medium conveyance passage of the apparatus main assembly, from the opposite side of the recording medium conveyance passage from the cartridge in the apparatus main assembly. 
     For example, there has been disclosed in Japanese Laid-open Patent Application 2010-85797: Patent Document 1) an image forming apparatus structured so that its replaceable (consumable) components and supplies are placed in removable units, one for one. More specifically, the process cartridge employed by this image forming apparatus is structured so that it can be separated into a drum cartridge and a development cartridge after being moved out of the main assembly of the image forming apparatus. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, an image forming apparatus for forming an image on a recording material includes a drum cartridge including an image bearing member; a developing cartridge including developing means for developing the image formed on said image bearing member; a cartridge mounting member to which said image bearing member cartridge and said developing cartridge are detachably mountable; transferring means for transferring a visualized image provided by said developing means on said image bearing member, onto the recording material fed along a feeding path; and an opening and closing cover provided across said feeding path from said image bearing member, wherein said cartridge mounting member is capable of permitting said developing cartridge to be mounted thereto and dismounted therefrom across the feeding path through an opening provided by opening said opening and closing cover, without removing said drum cartridge. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for describing the mechanism for removably mounting a cartridge, in the first embodiment of the present invention. 
         FIG. 2  is a schematic sectional view of the image forming apparatus, in the first embodiment, having the mechanism for removably mounting a cartridge. 
         FIG. 3  is a schematic sectional view of the image forming apparatus, in the first embodiment, having the mechanism for removably mounting a cartridge, in which the cartridge is mounted into, or dismounted from, the main assembly of the image forming apparatus. 
         FIG. 4  is a detailed drawing of the mechanism, in the first embodiment, for removably mounting a cartridge. 
         FIGS. 5A, 5B and 5C  are illustrations of the process of removing a cartridge, in the first embodiment. 
         FIG. 6  is an exploded perspective view of the mechanism, in the second embodiment of the present invention, for removably mounting a cartridge. 
         FIG. 7  is a perspective view of the mechanism, in the second embodiment, for removably mounting a cartridge. 
         FIG. 8  is a drawing for describing the cover of the image forming apparatus, in the second embodiment, which can be rotationally opened or closed to remove a jammed sheet of recording medium. 
         FIG. 9  is a drawing for describing the cartridge guide movement caused by the opening or closing movement of the cover, in the second embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention are described. However, these embodiments are not intended to limit the present invention is scope. 
     Embodiment 1 
     Image Forming Apparatus 
       FIG. 2  is a schematic sectional view of an image forming apparatus having a mechanism, in accordance with the present invention. Hereafter, this mechanism will be referred to as “cartridge mounting-dismounting mechanism” or “cartridge mounting and dismounting mechanism”. It shows the general structure of the apparatus. The image forming apparatus in this embodiment is an electrophotographic image forming apparatus, more specifically, a laser beam printer. The main assembly A (which hereafter will be referred to as “image forming apparatus main assembly”) employs an electrophotographic photosensitive member  107  (which hereafter will be referred to simply as “photosensitive drum”), which is an image bearing member and is in the form of a drum. The photosensitive drum  107  is uniformly charged by a charge roller  108  as a charging means. Then, a beam of light is projected upon the photosensitive drum  107  from an optical system  101 , which is an optical means, while being modulated with the information of the image to be formed. Consequently, an electrostatic latent image is effected on the photosensitive drum  107 . This electrostatic latent image is developed with developer (which hereafter is referred to as “toner”) into a visible image, which is an image formed of developer (toner), and therefore, will be referred to as “toner image” hereafter. 
     While a toner image is formed, one of the sheets  102  of recording medium in a sheet feeding tray  103   d  is fed into the image forming apparatus main assembly by a combination of a pickup roller  103   a , and a separating member  103   b  which is kept pressed upon the pickup roller  103   a . Then, the sheet  102  is conveyed to a transfer position by a pair of sheet conveyance rollers  103   e . In the transfer position, the toner image formed on the photosensitive drum  107  is transferred onto the sheet  102  by the application of voltage to a transfer roller  104  as a transferring means. After the transfer of the toner image onto the sheet  10 , the sheet  102  is conveyed to a fixing means  105  by a sheet conveyance guide  103   f.    
     In this embodiment, the fixing means  105  has a driving roller  105   a  and a rotational fixing member  105   d . The rotational fixing member  105   d  has: an endless belt; a heater  105   b , which is on the inward side of the endless belt; and a supporting member, by which the endless belt is rotatably supported. This fixing means  105  fixes the transferred toner image on the sheet  102  of recording medium by applying heat and pressure to the sheet  102  and the toner image thereon while the sheet  102  is conveyed through the fixing means  105 . After the fixation of the toner image, the sheet  102  is conveyed further, and then, is discharged into a delivery tray  106  by a pair of discharge rollers  103   c.    
     There are various fixing methods which can be used by the fixing means  105 ; the fixing method to be used by the fixing means  105  does not need to be limited to the above described one. In this embodiment, the sheet conveying means  103  is made up of the pickup roller  103   a , separating member  103   b , sheet conveyance roller  103   e , discharge rollers  103   c , etc. 
     Referring to  FIG. 3 , the transfer roller  104  is held by a cover  115  which can be rotationally opened or closed by a user. Thus, the transfer roller  104  can be rotationally moved about the rotational axis  115   a  of the cover  115 , along with the cover  115 . That is, a user can open the cover  115  to replace the cartridge in the image forming apparatus main assembly, and also, to remove a jammed sheet in the main assembly. 
     The image forming apparatus main assembly A has the sheet conveying means  103 , fixing means  105 , and a driving means (unshown) for driving a process cartridge B ( FIG. 2 ). The driving means (unshown) drives each of various rotational members by transferring the driving force from a motor (unshown), which is a driving force source, to the rotational member through gear trains (unshown). 
     It is also through the above described gear trains that the driving force is transmitted to the process cartridge B. Further, the driving force from the image forming apparatus main assembly A is transmitted to the process cartridge B by a coupling means such as the one disclosed in Japanese Patent 02875208, and Japanese Laid-open Patent Application H10-240103, for example. 
     The coupling means disclosed in these patent applications are made up of a main assembly coupling and a cartridge coupling. The main assembly coupling has a helical hole, which is coaxial with the output gear shaft of the above-described gear train, and the cross section of which is roughly in the form of an equilateral triangle. The cartridge coupling has a helical protrusion the cross-section of which is roughly in the form of an equilateral triangle. Thus, the above described coupling means can be coupled or uncoupled by moving the main assembly coupling in the lengthwise direction of the photosensitive drum  107 , or the lengthwise direction of the development roller  112  which is described later. 
     Coupling of the main assembly coupling with the cartridge coupling causes the driving force transmitting portion of the image forming apparatus main assembly A to align with the driving force transmitting portion of the cartridge B, and also, to precisely position the image forming apparatus main assembly A and cartridge B relative to each other. In this embodiment, therefore, the image forming apparatus is provided with a means (unshown) for coupling or uncoupling this coupling means. 
     (Cartridge) 
     Next, referring to  FIG. 2 , the process cartridge B is described. The process cartridge B in this embodiment is made up of a drum cartridge  109 , and a development cartridge  111 , which can be independently mounted into, or dismounted from, the image forming apparatus main assembly A, from each other. 
     The drum cartridge  109  integrally holds: the photosensitive drum  107  which is an electrophotographic photosensitive member as an image bearing member; charge roller  108  which charges the peripheral surface of the photosensitive drum  107 ; a cleaning device  110  which removes the residual toner image on the photosensitive drum  107  and recovers the removed toner; etc. 
     As for the development cartridge  111 , it has a development roller  112  which is a developing means for developing an electrostatic latent image on the photosensitive drum  107  into a visible image. Further, the development cartridge  111  has a toner storage  113  in which the toner to be supplied to the development roller  112  is stored; multiple stirring members  114  for stirring the toner delivered from the toner container; and the like members. 
     (Mechanism for Mounting or Dismounting Cartridge) 
     Next, the structure of the above-mentioned mechanism for mounting or dismounting a cartridge is described.  FIG. 4( a )  is an exploded perspective view of the mechanism, in this embodiment, for mounting or dismounting a cartridge, in this embodiment. The structural components shown in  FIG. 4( a )  are assembled as shown in  FIG. 4( d )  ( FIG. 4( b )  is a top view). The cartridge mounting-dismounting mechanism in this embodiment has: a cartridge guide  116  which holds the drum cartridge  109  and development cartridge  111 ; and main assembly lateral plate  117 ; and the first spring  122  which continuously applies pressure to the cartridge guide  116 . 
     Further, the cartridge mounting-dismounting mechanism has: a rotation controlling member  119  which controls the cartridge holding member ( 116 ) in rotational movement; and the second spring  118  which continuously applies pressure to the rotation controlling member  119 . Further, it has a unlocking member  120  which is for freeing the rotation controlling member  119 ; a holding member  121  which holds the second spring  118 , rotation controlling member  119 , and unlocking member  120 , to the main assembly lateral plate  117 . 
     By the way,  FIG. 4( c )  is an external side view of the cartridge mounting-dismounting mechanism, which shows only a cartridge guide  116 , a part of the main assembly lateral plate  117 , a rotation controlling member  119 , and the first spring  122 . The first spring  122  is held by the main assembly lateral plate  117 . The position of the cartridge guide  116  in terms of the thrust direction is regulated (controlled) by the hook-shaped portion  116   c  of the cartridge guide  116 , and the surface  117   e  of the main assembly lateral plate  117  ( FIG. 4( b ) ). 
     Referring to  FIG. 4( a ) , the supporting shaft  116   a  of the cartridge guide  116  is rotatably supported by the main assembly lateral plate  117  by being put through the hole  117   a  (axial line of which will coincide with supporting shaft  116   a ), with which the main assembly lateral plate  117  is provided. The hook-shaped portion  116   c  of the cartridge guide  116  remains under the pressure generated by the first spring  122  in the direction indicated by a referential code β in  FIG. 4( c )  in a manner to rotate the supporting shaft  116   a.    
     Thus, the first controlling surface  116   b  of the cartridge guide  116  ( FIG. 4( a ) ) remains in contact with the controlling surface  119   c  ( FIG. 4( c ) ) of the rotation controlling member  119 . Thus, the cartridge guide  116  remains precisely positioned during an image forming operation. That is, the cartridge guide  116  which guides the drum cartridge  109  and development cartridge  111  when they are mounted or dismounted, remain in the first position (image formation position) in the image forming apparatus main assembly A during an image forming operation. 
     The first controlling surface  116   b  of the cartridge guide  116 , and the controlling surface  119   c  of the rotation controlling member  119  function as the positioning means for keeping the cartridge guide  116  in the first position. 
     On the other hand, during a cartridge replacement operation, the rotation controlling member  119  (controlling surface  119   c ) is freed from the control placed thereon by the cartridge guide  116  (first controlling surface  116   b ). Thus, the cartridge guide  116  is rotated by the first spring  122  as shown in  FIG. 1( b ) , as will be described later in detail. Thus, the second controlling surface  116   f  (FIG. ( 4 ( c )) of the cartridge guide  116  comes into contact with the controlling surface  117   d  ( FIG. 4( c ) ), being thereby precisely positioned by the controlling surface  117   d , through the curved guiding groove  117   c , as a guiding portion, with which the main assembly lateral plate  117  is provided. That is, the cartridge guide  116  which is a cartridge mounting member is enabled to take the second position in which it allows the drum cartridge  109  and development cartridge  111  to be mounted or dismounted. 
     The second controlling surface  116   f  of the cartridge guide  116 , and the controlling surface  117   d  of the main assembly lateral plate  117  function together as the positioning for positioning the cartridge guide  116  in the second position. 
     The rotation controlling member  119  comes into contact with the controlling surface  117   b  ( FIG. 4( b ) ) of the main assembly lateral plate  117 , being precisely position in terms of the vertical direction (top-bottom direction) in  FIG. 4( c ) . As for its position in terms of the horizontal direction, the position of the rotation controlling member  119  is regulated by a combination of the unlocking member  120  and holding member  121 , shown in  FIG. 4( b ) . 
     Referring to  FIG. 4( b ) , the rotation controlling member  119  remains under the pressure generated by the second spring  118  in the direction indicated by an arrow mark +X. Thus, the slanted surface  119   b  of the rotation controlling member  119  continuously presses the unlocking member  120  in the direction indicated by an arrow mark −Y. By the way, the disengagement prevention surface  120   b  ( FIG. 4( b ) ) of the unlocking member  120  remains in contact with the holding member  121 , preventing thereby the rotation controlling member  119  from disengaging in the direction indicated by the arrow mark −Y. 
     Referring to  FIG. 4( b )  which is a top view of the cartridge mounting-dismounting mechanism, the movement of the unlocking member  120  in the directions indicated by the arrow marks +X and −Y is controlled by the surface  117   e  of the main assembly lateral plate  117  and the surface  121   a  of the holding member  121 . Further, the contacting surface  120   a  of the unlocking member  120  is in contact with the slanted surface  119   b  of the rotation controlling member  119 . Thus, the pressing of the surface  120   c  of the unlocking member  120  by a user causes the rotation controlling member  119  to be moved in the direction indicated by the arrow mark −X against the resiliency of the second spring  118 . 
     That is, the pressing of the surface  120   c  by a user in the direction +Y in  FIG. 4( b )  causes the rotation controlling member  119  (controlling surface  119   c ) to separate from the cartridge guide  116  (first controlling surface  116   b ), by being guided by the slanted surface  119   b  of the rotation controlling member  119 . That is, the image forming apparatus main assembly A is structured so that as the cover  115  is opened, it becomes possible for a user to press the surface  120   c  of the unlocking member  120 . 
     The unlocking member  120  (surface  120   c ) and rotation controlling member  119  (controlling surface  119   b ) function as a means for switching the position of the cartridge guide  116  from the first position to the second position. 
     (Cartridge Replacement Operation) 
     Next, the operation, in this embodiment, for replacing the cartridge in the image forming apparatus main assembly A is described.  FIG. 1( a )  shows the position of the cartridge guide  116  during an image forming operation. If it is necessary for a user to replace the cartridge in the image forming apparatus main assembly A, the user is to open the cover  115  and press the surface  120   c  shown in  FIG. 4( b ) , by a preset amount. As the surface  120   c  is pressed, the rotation controlling member  119  moves in the direction indicated by the arrow mark −X in  FIG. 4( b )  until the rotation controlling member  119  separates from the cartridge guide  116 . 
     As the rotation controlling member  119  separates from the cartridge guide  116 , the cartridge guide  116  is rotationally moved by the first spring  122  in the direction β shown in  FIG. 4( c ) , being thereby rotated until its second controlling surface  116   f  of the charging device  112  comes into contact with the controlling surface  117   d  of the main assembly lateral plate  117  ( FIG. 4( c ) ). During this rotational movement of the cartridge guide  116 , the attitude of the cartridge guide  116  changes into the one (in second position) shown in  FIG. 1( b ) , in which the cartridge in the image forming apparatus main assembly A can be removed to be replaced. 
     By the way, until the cartridge guide  116  is returned into the position, in which it enables the image forming apparatus to form images, the rotation controlling member  119  remains under the pressure from the second spring  118 , remaining therefore in contact with the surface  116   d  ( FIG. 4( a ) ) of the cartridge guide  116 . That is, the cartridge guide  116  remains free from the rotation controlling member  119 . 
     In this embodiment, after the replacement of the development cartridge  111 , a user is to directly push the cartridge guide  116  in the direction −β to rotate the cartridge guide  116 . During this movement of the cartridge guide  116 , the unlocking member  120  (surface  120   c ) and rotation controlling member  119  (controlling surface  119   b ) function as the means for switching the position of the cartridge guide  116  from the second position to the first position. 
     As the cartridge guide  116  is rotated into the position ( FIG. 1( a ) ) in which it enables the image forming apparatus to form images, the rotation controlling member  119  becomes free from the surface  116   d  of the cartridge guide  116 , which prevents the rotation controlling member  119  from moving in the direction indicated by the arrow mark +X in  FIG. 4( b ) . Thus, the rotation controlling member  119  returns to the position shown in  FIG. 4( b ) . Thus, the first controlling surface  116   b  of the cartridge guide  116  comes into contact with the controlling surface  119   c  of the rotation controlling member  119 , whereby the cartridge guide  116  is kept in the position (first position) in which it allows the image forming apparatus to form images. 
     (Effects of Cartridge Mounting-Dismounting Mechanism in this Embodiment) 
     Lastly, the effects of the cartridge mounting-dismounting mechanism in this embodiment, structured as described above, is described after the above described issues are described in detail for the second time. To begin with, in order to make it easier for a user to remove a jammed sheet(s) of recording medium from an image forming apparatus, an image forming has to be structured so that a user can easily access the jammed sheet(s) of recording medium across the internal recording medium conveyance passage P of the image forming apparatus. That is, an image forming apparatus has to be structured so that the recording medium conveyance passage is positioned next to the cover  115  as shown in  FIG. 5A . 
     Next, the position of the development roller  112  is regulated by the fact that it enables an image forming apparatus to form images. It is also regulated by the positional relationship between the development roller  112  and recording medium conveyance passage P. It is common practice to structure an image forming apparatus so that in terms of cross-sectional view, the center of the development roller  112  is positioned on the opposite side of a line which coincides with the center of the photosensitive drum  107  and is parallel to the recording medium conveyance passage P, as shown in  FIG. 5A , for the purpose of reducing the main assembly of an image forming apparatus in height. 
     In  FIG. 5A , the angle between the line which coincides with the point of contact between the photosensitive drum  107  (as image bearing member) and development roller  112  (developing means) and is tangential to the peripheral surface of the development roller  112  (photosensitive drum  107 ), and the recording medium conveyance passage P, is roughly 30 degrees, which is relatively large. In the case of an image forming apparatus structured as shown in  FIG. 5A , in order to make it possible for a user to replace the developing device  4  independently from the drum cartridge  109 , the image forming apparatus main assembly A and process cartridge B have to be structured so that the photosensitive drum  107  can be moved away downward from the development cartridge mounting-dismounting passage, as shown in  FIG. 5A . This structural arrangement makes it necessary to increase the image forming apparatus main assembly A in size. 
     However, the cartridge mounting-dismounting mechanism in this embodiment is structured so that the cartridge guide  116  can be switched in position between the first position in which it enables the image forming apparatus to form images, and the second position in which it allows a user to replace the development cartridge  111 , as described above. That is, in the case of the cartridge mounting-dismounting mechanism in this embodiment, the cartridge guide  116  makes it possible for the development cartridge  111  to be moved between the first and second positions. By the way, the cartridge guide  116  enables the drum cartridge  109  also to move between the first and second positions. 
     In this embodiment, the second position is set as shown in  FIG. 5B , so that when the cartridge guide  116  is in the second position, it does not interfere with the other internal components. More specifically, the angle between the line which coincides with the point of contact between the photosensitive drum  107  and development roller  112  and is tangential to both the photosensitive drum  107  and development roller  112 , and the line which is perpendicular to the recording medium conveyance passage P, is roughly 10 degrees, which is smaller than when it is during an image forming operation (first position in  FIG. 5A ). That is, when the cartridge guide  116  is in the second position, the development roller  112  is closer to the recording medium conveyance passage P than when the cartridge guide  116  is in the first position. In other words, the second position is such a position that the position in which the development roller  112  is when the cartridge guide  116  is in the second position is on the upstream side, in terms of the rotational direction of the photosensitive drum  107 , of the position in which the development roller  112  is when the cartridge guide  116  is in the first position. 
     Also in this embodiment, the image forming apparatus is structured so that when the cartridge guide  116  is in the second position for cartridge mounting-dismounting (cartridge replacement), the center of the development roller  112 , in terms of cross sectional, is on the same side as the line which is parallel to the recording medium conveyance passage P, in the adjacencies of the photosensitive drum  107 , and coincides with the center of the photosensitive drum  107  in terms of cross sectional view. That is, the image forming apparatus is structured so that the rotational axis of the cartridge guide  116  coincides with the center of the circle which the theoretical extension of the above described curved guiding grooves  117   c  (guiding portion) forms. 
     Thus, it is possible to realize a cartridge mounting-dismounting mechanism which enables a user to easily replace the development cartridge  111 , independently from the photosensitive drum  107 , across the recording medium conveyance passage P, through the opening which is exposed as the cover is opened, without increasing the image forming apparatus main assembly A in size, as will be understood from  FIG. 5C . 
     Effects of this Embodiment 
     According to this embodiment, the drum cartridge  109  and development cartridge  111  which together make up the process cartridge B can be independently removed from the image forming apparatus main assembly A from each other, across the recording medium conveyance passage P. The direction in which the development cartridge  111  is removed, and the direction in which the drum cartridge  109  is removed, are the same (including roughly the same direction). That is, this embodiment makes it possible to replace the development cartridge  111  without removing the drum cartridge  109 . 
     That is, this embodiment makes it unnecessary for the drum cartridge  109  of the process cartridge B which is a combination of the drum cartridge  109  and development cartridge  111 , to be dismounted and remounted each time the development cartridge  111  needs to be replaced. Thus, it can improve an image forming apparatus and the process cartridge therefor in the efficiency with which a user can replace the development cartridge  111 . Generally speaking, a development cartridge  111  needs to replaced more frequently than a drum cartridge. According to this embodiment, it is only when the drum cartridge has to be replaced that the drum cartridge has to be moved out of the image forming apparatus main assembly A. Thus, this embodiment can reduce the possibility that a photosensitive drum will be damaged by a user. Thus, this embodiment makes it unnecessary for the image forming apparatus main assembly A to be provided with a drum shutter with which a conventional image forming apparatus (process cartridge) is provided to prevent drum damage, making unnecessary the space for a drum shutter. Thus, this embodiment can reduce in size the image forming apparatus main assembly A as well. 
     Embodiment 2 
     Next, the second embodiment of the present invention, which causes an operation for mounting or dismounting at least one of drum cartridge and development cartridge, to switch in position a cartridge guide between the first and second positions, is described. By the way, the components, portions thereof, etc, of the image forming apparatus and process cartridge therefore in this embodiment, which are the same in structure as the counterparts in the first embodiment are given the same referential codes as those given to the counterparts, one for one, and are not described. That is, this embodiment is described about its differences from the first embodiment. 
     There are only two major differences between the first and second embodiments. One is that in this embodiment, the position of the cartridge guide is switched from the first one to the second one by the opening movement of the cover  215  with which the image forming apparatus main assembly A having a cartridge mounting-dismounting mechanism is provided, unlike in the first embodiment, in which the rotation controlling member  119  has to be directly pushed by a user. More concretely, in this embodiment, the image forming apparatus is provided with a cover  215  which can be rotationally opened or closed by a user, and a rotation controlling member  220 . Further, the cover  215  is provided with a protrusion  215   b  ( FIG. 7 ), and the image forming apparatus is structured so that as the cover  215  is opened or closed, the protrusion  215   b  causes the rotation controlling member  220  to move. 
     The second difference is that in this embodiment, the cartridge guide  216  is switched in position from the second one to the first one by the opening of the cover  215  of the image forming apparatus main assembly A having the cartridge mounting-dismounting mechanism by a user, whereas in the first embodiment, a user has to directly push the cartridge guide  116  in order to move the cartridge guide  116  from the cartridge replacement position (second position) to the image formation position (first position). That is, in this embodiment, the controlling surface  215   c  ( FIG. 7 ) of the cover  215  is made to move the cartridge guide  216  by the closing movement of the cover  215 . Otherwise, the image forming apparatus main assembly and process cartridge therefor, in this embodiment, are the same in structure and operation as the counterparts in the first embodiment. 
       FIG. 6  is an exploded perspective view of the cartridge mounting-dismounting mechanism in this embodiment. The components shown in  FIG. 6  are assembled as shown in  FIG. 7 . The cartridge mounting-dismounting mechanism in this embodiment has: a cartridge guide  216 ; main assembly lateral plate  217 ; and the first spring  222  which presses on the cartridge guide  216 . It has also: a rotation controlling member  219  which controls the rotational movement of the cartridge guide  216  in the image formation position (first position); a unlocking member  220  which unlocks the rotation controlling member  219 ; and a rotationally movable cover  215 . Further, the unlocking member  220  is rotatably supported by the main assembly lateral plate  217 , and has a cam surface  220   c.    
     As a user rotationally moves the closed cover  215  by a preset angle in the opening direction, that is, the direction indicated by an arrow mark −α, the protrusion  215   b  of the cover  215  presses the cam surface  220   c  of the unlocking member  220 , causing thereby the unlocking member  220  to rotationally move by a preset angle in the direction indicated by an arrow mark γ in  FIG. 7 . Consequently, the rotation controlling member  219  is prevented from preventing the cartridge guide  216  from rotationally moving in the direction indicated by the arrow mark R, as in the first embodiment. 
     Further, the cover  215  which can be rotationally opened or closed has a controlling surface  215   c . Thus, as the cover  215  is rotationally moved in the closing direction by a user, the controlling surface  215   c  presses the surface  216   e  of the cartridge guide  216 , causing thereby the cartridge guide  216  to rotationally move in the direction indicated by the arrow mark −β. 
     Next, the operation of the cartridge mounting-dismounting mechanism in this embodiment is described. As the cover  115  is opened, the protrusion  215   b  of the cover  215  presses the cam surface  220   c  of the unlocking member  220 , as shown in  FIGS. 8 ( a ) and 8( b ) . 
     As a result, the rotation controlling member  219  is made to retreat in the direction indicated by the arrow mark −X against the resiliency of the second spring  218 . Thus, the rotation controlling member  219  separates from the first controlling surface  216   b , allowing thereby the cartridge guide  216  to move. Thus, the cartridge guide  216  is made to rotationally move in the direction β by the resiliency of the first spring  222 . 
     As the cartridge guide  216  rotationally moves in the direction β, the rotation controlling member  219  which is under the pressure from the second spring  218  comes into contact with the surface  216   d  of the cartridge guide  216 , being thereby prevented from moving in the direction +X. Then, as the cartridge guide  216  is rotationally moved by the preset angle, the second controlling surface  216   f  of the cartridge guide  216  comes into contact with the second controlling surface  217   d  of the main assembly lateral plate  217 , being thereby positioned in the cartridge replacement position (second position). 
     On the other hand, as the cover  215  is closed by a user, as shown in  FIG. 9( a ) , after the cartridge replacement, the controlling surface  215   c  of the cover  215  is made to press the surface  216   d  of the cartridge guide  216 , by the rotational movement of the cover  215  in the closing direction. Consequently, the cartridge guide  216  is moved in the direction −β against the resiliency of the first spring  222 . As the cover  215  is rotated in the closing direction by the preset angle, the cartridge guide  216  rotationally moves beyond the image formation position. 
     Being freed from the surface  216   d , the rotation controlling member  219  moves in the direction +X, shown in  FIG. 7 , preventing thereby the cartridge guide  216  from rotationally moving in the direction β, as in the first embodiment. Thereafter, as the cover  215  is rotationally moved further, the cover  215  stops controlling the movement of the cartridge guide  216 , as shown in  FIG. 9( b ) . Consequently, the surface  216   b  of the cartridge guide  216  is pressed on the controlling surface  219   c  of the rotation controlling member  219  by the resiliency of the first spring  222 . Thus, the cartridge guide  216  is kept in the image formation position (first position) by the resiliency of the first spring  222 . 
     In this embodiment, the cartridge mounting-dismounting mechanism is structured so that the cartridge guide  216  is rotationally moved by the opening movement of the door  215  into the position in which it allows a user to replace the development cartridge  211 . Therefore, this embodiment is superior to the first embodiment in terms of the efficiency with which the development cartridge  211  is replaceable. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2014-018378 filed on Feb. 3, 2014, which is hereby incorporated by reference herein in its entirety.