Patent Publication Number: US-8126366-B2

Title: Image forming apparatus in which drive transmission member engages drive input member

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2007-340762, which was filed on Dec. 28, 2007, the disclosures of which are herein incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     Apparatuses and devices consistent with the present invention relate to an image forming apparatus such as an electro-photographic color printer. 
     BACKGROUND 
     Japanese unexamined patent application publication No. JP-A-2000-250310 (Hereinafter, Patent document 1) describes a related art image forming apparatus. In the related art image forming apparatus, process cartridges are made to be detachably mounted in an apparatus main body. 
     In an image forming apparatus of this type, no drive source is provided on the process cartridge, and a driving force for rotating photosensitive drums and developing rollers is supplied from a drive source provided in the apparatus main body. For example, a cartridge side coupling is provided on the process cartridge. A drive source and a main body side coupling to which a driving force is transmitted from the drive source are provided in the apparatus main body. When the process cartridge is mounted in the apparatus main body, the main body side coupling is coupled to the cartridge side coupling, whereby the driving force from the drive source is inputted into the cartridge side coupling via the main body side coupling. 
     In the related image forming apparatus, however, there have occurred cases where the main body side coupling is not coupled to the cartridge side coupling properly. 
     The invention has been made with a view to solving the problem and an object thereof is to provide an image forming apparatus which can attain an ensured engagement of a drive transmission member (a reciprocating member) with a drive input member. 
     SUMMARY 
     Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any of the problems described above. 
     According to a first exemplary embodiment of the invention, there is provided an image forming apparatus comprising: an apparatus main body; a process unit provided in the apparatus main body and having a drive input member; and a drive transmission member provided in the apparatus main body and configured to engage with the drive input member so as to transmit a driving force to the drive input member while permitting a positional gap of the drive input member within a predetermined range, wherein, the drive transmission member comprises: a guide core member comprising: a distal end core portion which is formed at an end portion lying a downstream side in an engagement direction of the drive transmission member with the drive input member and which has a first outside diameter; and a proximal end core portion which is formed upstream of the distal end core portion in the engagement direction and which has a second outside diameter that is larger than the first outside diameter; a reciprocating member in which the guide core member is inserted along the engagement direction, the reciprocating member comprising: a distal end cylindrical portion which has a first inside diameter; and a proximal end cylindrical portion which is formed upstream of the distal end cylindrical portion in the engagement direction and which has a second inside diameter that is larger than the first inside diameter; and a pressing member interposed between the guide core member and the reciprocating member for connecting the guide core member and the reciprocating member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be described in detail with reference to the following figures wherein: 
         FIG. 1  is a side sectional view showing an image forming apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective view of a process cartridge of the image forming apparatus of  FIG. 1 , as viewed from a right front direction of the process cartridge; 
         FIG. 3  is a left side view of the process cartridge of  FIG. 2 ; 
         FIG. 4  is a plan view of the process cartridge of  FIG. 2 ; 
         FIG. 5  is a perspective view of a drum cartridge of the process cartridge of  FIG. 2 , as viewed from a right front direction of the drum cartridge; 
         FIG. 6  is a perspective view of an interior of a body casing of the image forming apparatus of  FIG. 1 , as viewed from a right front direction of the body casing; 
         FIG. 7  is a left side view of a left-hand body frame of the body casing of  FIG. 6 ; 
         FIG. 8  is a perspective view of a driving force transmission mechanism and a first cover linkage mechanism of the image forming apparatus of  FIG. 1 , as viewed from a left front direction of the driving force transmission mechanism and the first cover linkage mechanism; 
         FIG. 9  is a left side view of the driving force transmission mechanism and the first cover linkage mechanism of  FIG. 8 , showing a state in which a top cover is closed; 
         FIG. 10  is a perspective view of the driving force transmission mechanism and the first cover linkage mechanism of  FIG. 8 , as viewed from a right front direction thereof, showing the state in which the top cover is closed; 
         FIG. 11  is a plan view of the driving force transmission mechanism of  FIG. 8 , showing the state in which the top cover is closed; 
         FIG. 12  is a left side view of the driving force transmission mechanism and the first cover linkage mechanism of  FIG. 8 , showing a state in which the top cover is opened; 
         FIG. 13  is a perspective view of the driving force transmission mechanism and the first cover linkage mechanism of  FIG. 8  as viewed from the right front direction, showing the state in which the top cover is opened; 
         FIG. 14  is a plan view of the driving force transmission mechanism of  FIG. 13 , showing a state in which the top cover is opened; 
         FIG. 15A  is a sectional view of a drum drive transmission member of the driving force transmission mechanism of  FIG. 8 , showing the drum drive transmission member in an advanced position, and  FIG. 15B  is a sectional view of the drum drive transmission member of the driving force transmission mechanism of  FIG. 8 , showing the drum drive transmission member in a retreating position; 
         FIG. 16  is a perspective view of a drum main body, a flange member, a connecting member and the drum drive transmission member of the driving force transmission mechanism of  FIG. 10 ; 
         FIG. 17A  is a right side view of the drum drive transmission member of  FIG. 16 ,  FIG. 17B  is a left side view of the connecting member of  FIG. 16 , and  FIG. 17C  is a left side view of the flange member of  FIG. 16 ; 
         FIG. 18A  is a sectional view of a developing drive transmission member of the driving force transmission mechanism of  FIG. 8 , when the developing drive transmission member is in an advanced position, and  FIG. 18B  is a sectional view of the developing drive transmission member of the driving force transmission mechanism of  FIG. 8 , when the developing drive transmission member is in a retreating position; 
         FIG. 19A  is a right side view of a reciprocating member of the developing drive transmission member of  FIG. 18A , and  FIG. 19B  is a left side view of a developing roller drive gear of the developing drive transmission member of  FIG. 18A ; 
         FIG. 20  is a left side view of a locking mechanism of the first cover linkage mechanism of  FIG. 8 , showing a state in which the top cover is closed; 
         FIG. 21  is a left side view of the locking mechanism of the first cover linkage mechanism of  FIG. 8 , showing a state in which the top cover is opened; 
         FIG. 22  is a right side view of part of a right-hand body frame of the body casing of  FIG. 6 , showing a state in which the top cover is closed; 
         FIG. 23  is a right side view of part of the right-hand body frame of the body casing of  FIG. 6 , showing a state in which the top cover is opened; 
         FIG. 24  is a left side view of a connecting and disconnecting translation cam of the body casing of  FIG. 6 ; 
         FIG. 25  is a right side view of a part of the left-hand body frame of the body casing of  FIG. 6 , showing a state in which the top cover is closed; 
         FIG. 26  is a right side view of the part of the left-hand body frame of the body casing of  FIG. 6 , showing a state in which the top cover is opened; 
         FIG. 27  is a left side view of the process cartridge, the locking mechanism, and a connecting and disconnecting mechanism of the image forming apparatus of  FIG. 1 , showing a state in which all developing rollers are in contact with photosensitive drums; 
         FIG. 28  is a left side view of the process cartridge, the locking mechanism of the image forming apparatus of  FIG. 1 , and a connecting and disconnecting mechanism, showing a state in which the yellow, magenta and cyan developing rollers are spaced apart from the photosensitive drums; 
         FIG. 29  is a left side view of the process cartridge, the locking mechanism, and the connecting and disconnecting mechanism of the image forming apparatus of  FIG. 1 , showing a state in which all the developing rollers are spaced apart from the photosensitive drums; and 
         FIG. 30  is a sectional view for explaining a difference between a reciprocating member and a guide core part. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION 
     1. Overall Configuration of Printer 
       FIG. 1  is a side sectional view showing an image forming apparatus according to an exemplary embodiment of the invention. The image forming apparatus is embodied in a printer. 
     A printer  1  is a tandem type color printer. Four process cartridges  3  are disposed in parallel within a body casing  2  as an example of an apparatus main body in such a manner as to be associated with respective colors of black, yellow, magenta and cyan. The respective process cartridges  3  can be mounted in and dismounted from the body casing  2  in such a state that a top cover  4  which is an example of a cover at an upper side of the body casing  2  is opened. 
     Each of the process cartridges  3  includes a drum cartridge  7  which holds therein a photosensitive drum  5  and a scorotron-type charger  6  and a developing cartridge  9  which holds therein a developing roller  8  and which is detachably attached to the drum cartridge  7 . A surface of the photosensitive drum  5  is charged uniformly by the scorotron-type charger  6  and is then exposed selectively by LEDs provided in a LED unit  10 . Accordingly, latent images based on image data are formed on the surfaces of the photosensitive drums  5  by static electric charges imparted thereto. The respective static latent images so formed are then visualized by toner carried on the developing rollers  8 , whereby toner images are formed on the surfaces of the photosensitive drums  5 . 
     Sheets P are accommodated in a feeding cassette  11  disposed in a bottom part of the body casing  2 . Sheets P accommodated in the feeding cassette  11  are conveyed sheet by sheet onto a conveyer belt  12  by various types of rollers. The conveyer belt  12  is disposed in such a manner as to confront the four photosensitive drums  5  from therebelow. A sheet P conveyed onto the conveyer belt  12  is conveyed to pass sequentially underneath the respective photosensitive drums  5  when the conveyer belt  12  is caused to run. Then, the toner images on the surfaces of the photosensitive drums  5  are transferred onto the sheet P by virtue of a transfer bias applied to transfer rollers  13 . The transfer rollers  13  are disposed in such a manner as to correspond to the respective photosensitive drums  5  across the conveyer belt  12 . 
     The sheet P on to which the toner images have been transferred is then conveyed to a fixing unit  14 . The toner images transferred on to the sheet P are thermally fixed in the fixing unit  14 . Thereafter, the sheet P is discharged into a sheet discharging tray  15  by various types of rollers. 
     Note that when discriminating a process cartridge  3  of a specific color from process cartridges  3  of the other colors, reference characters, such as K denoting black, Y denoting yellow, M denoting magenta and C denoting cyan, are used after the reference numeral  3  denoting the process cartridges to indicate a process cartridge of a certain color. For example process cartridge  3 K denotes the process cartridge loaded with black color toner. 
     In addition, an upstream side of a conveying direction of a sheet P by the conveyer belt  12  is referred to as a front side of the printer  1 , and when the printer is described with respect to its horizontal or left and right positions, those positions are generally based on the printer  1  as viewed from a front side thereof. With respect to the process cartridge  3 , in such a state that the process cartridge  3  is disposed horizontally, a side where the developing cartridge  9  is disposed to face the photosensitive drum  5  is referred to as a front side, and in some cases, when the process cartridge  3  is described with respect to its vertical or upper and lower positions, as well as right and left position, those positions are based on the process cartridge  3  as viewed from the front side. Arrows denoting front-back, up-down and right-left directions are depicted in the respective drawings. 
     2. Process Cartridge 
       FIG. 2  is a perspective view of the process cartridge  3  of the image forming apparatus of  FIG. 1 , as viewed from a right front direction thereof.  FIG. 3  is a left side view of the process cartridge.  FIG. 4  is a plan view of the process cartridge.  FIG. 5  is a perspective view of a drum cartridge  7  of the process cartridge of  FIG. 2 , as viewed from a right front direction thereof. 
     (1) Drum Cartridge 
     As is shown in  FIG. 5 , the drum cartridge  7  includes a drum frame  21 . The drum frame  21  has integrally a pair of drum side walls  22 ,  23 , a drum rear wall  24 , a drum upper wall  25  and a drum front wall  26 . 
     The pair of drum side walls  22 ,  23  are disposed in such a manner as to confront each other with a space provided in the right-left direction. 
     As is shown in  FIG. 3 , the drum side wall  22  on the left-hand side includes a left-hand side wall rear portion  27 , a left-hand side wall intermediate portion  28  and a left-hand side wall front portion  29 . 
     The left-hand side wall rear portion  27  has a substantially triangular shape as viewed from the side. A substantially cylindrical protecting portion  30  is formed on the left-hand side wall rear portion  27  in such a manner as to project outwardly sideways (leftwards). The protecting portion  30  projects, as is shown in  FIG. 4 , in such a manner that a projecting amount of a rear-side portion  31  becomes less than a projecting amount of a front-side portion  32 . In addition, an end face of the front-side portion  32  and an end face of the rear-side portion  31  are connected to each other via an inclined surface which is inclined closer to the left-hand side wall rear portion  27  as the inclined surface extends rearwards. In addition, a penetrating hole is formed in the left-hand side wall rear portion  27  at a portion which is surrounded by the protecting portion  30 , and a left drum bearing  33  is fitted in the penetrating hole so formed. 
     The left-hand side wall intermediate portion  28  has a substantially rectangular shape as viewed from the side which is lower in height than the left-hand side wall rear portion  27  and, as is shown in  FIG. 5 , the left-hand side wall intermediate portion  28  extends forwards from a front end lower portion of the left-hand side wall rear portion  27 , bends outwardly sideways at an intermediate portion along a length in a front-rear direction thereof, and bends again to the front to extend forwards further. In addition, an opening is formed in the left-hand side wall intermediate portion  28  at a bent portion  34  which lies intermediate along the length of the left-hand side wall intermediate portion  28  and which is bent outwards, and by cutting out a portion of the left-hand side wall intermediate portion  28  which extends from the opening to a position lying rewards than the bent portion  34  in such a manner that a resulting external shape has a substantially U-shape, an attachment guide groove  35  is formed. A plane which includes an upper surface of the attachment guide groove  35  passes through a rotational center of a developing roller drive gear  61 , which will be described later, as is shown in  FIG. 3  in such a state that the developing cartridge  9  is attached to the drum cartridge  27 . In addition, an elongated hole  36  in which a diameter in the front-rear direction is slightly larger than a diameter in the up-down direction is formed in the left-hand side wall intermediate portion  28  at a portion which lies further forwards than the bent portion. 
     The left-hand side wall front portion  29  is formed in such a manner as to extend obliquely upwards from an edge of a front end of the left-hand side wall intermediate portion  28  as the left-hand side wall front portion  29  extends forwards. 
     As is shown in  FIG. 5 , the drum side wall  23  on the right-hand side includes a right-hand side wall rear portion  37 , a right-hand side wall intermediate portion  38  and a right-hand side wall front portion  39 . 
     The right-hand side wall rear portion  37  has a substantially triangular shape as viewed from the side and is made to confront the left-hand side wall rear portion  27  in the right-left direction. A right drum bearing  40  is attached to the right-hand side wall rear portion  37 . 
     The right-hand side wall intermediate portion  38  has a substantially rectangular shape as viewed from the side which is lower in height than the right-hand side wall rear portion  37  and, as is shown in  FIG. 5 , the right-hand side wall intermediate portion  38  extends forwards from a front end lower portion of the right-hand side wall rear portion  37 , bends outwardly sideways at an intermediate portion along a length in a front-rear direction thereof, and bends again to the front to extend forwards further. In addition, an opening is formed in the right-hand side wall intermediate portion  38  at a bent portion  41  which lies intermediate along the length of the right-hand side wall intermediate portion  38  and which is bent outwards, and by cutting out a portion of the right-hand side wall intermediate portion  38  which extends from the opening to a position lying rewards than the bent portion  41  in such a manner that a resulting external shape has a substantially U-shape, an attachment guide groove  42  is formed. The attachment guide groove  42  is made to confront the attachment guide groove  35  in the left-hand side wall intermediate portion  28  in the right-left direction, and an upper surface of the attachment guide groove  42  is positioned on the same plane as that on which the upper surface of the attachment guide groove  35  is positioned. 
     The right-hand side wall front portion  39  is formed in such a manner as to extend obliquely upwards from an edge of a front end of the right-hand side wall intermediate portion  38  as the right-hand side wall front portion  39  extends forwards. 
     The photosensitive drum  5  is held by the left-hand side wall rear portion  27  of the drum side wall  22  and the right-hand side wall rear portion  37  of the drum side wall  23 . The photosensitive drum  5  includes a drum main body  44  and a drum shaft  45  which extends along a center axis of the drum main body  44 . Flange members  46  (a right-hand flange member  46  is not shown) are fixed to both end portions of the drum main body  44 , and the drum shaft  45  is inserted into centers of the respective flange members  46  in such a manner as to rotate relatively. A right end portion of the drum shaft  45  is inserted into the right drum bearing  40  in such a manner that a relative rotation thereof to the drum bearing  40  is prohibited. The right end portion projects rightwards from the right drum bearing  40 . On the other hand, the flange member  46  fixed to a left end portion of the drum main body  44  is held in the left drum bearing  33  in such a manner that a relative rotation thereof to the drum bearing  33  is allowed. Thus, the drum main body  44  of the photosensitive drum  5  is provided rotatably about the drum shaft  45  between the left-hand side wall rear portion  27  and the right-hand side wall rear portion  37 . 
     In addition, an end face of the left-hand flange member  46  is exposed in the portion surrounded by the protecting portion  30 . Then, a connecting member  47  is attached to the exposed end face of the flange member  46  (refer to  FIG. 3 ). 
     The drum rear wall  24  is provided in such a manner as to extend between a rear end portion of the drum side wall  22  and a rear end portion of the drum side wall  23 . 
     The drum upper wall  25  is provided in such a manner as to extend between an upper end portion of the left-hand side wall rear portion  27  of the drum side wall  2  and an upper end portion of the right-hand side wall rear portion  37  of the drum side wall  23 . 
     The drum front wall  26  is provided in such a manner as to extend between a lower end portion of the left-hand side front portion  29  of the drum side wall  22  and a lower end portion of the right-hand side front portion  39  of the drum side wall  23  and is formed in such a manner as to be inclined obliquely upwards as the drum front wall  26  extends forwards. Pressing levers  48  for pressing the developing cartridge  9  towards the photosensitive drum  5  are provided in two locations on the drum front wall  26  which confront each other in a right-left direction of the drum front wall  26  across a central portion thereof. 
     (2) Developing Cartridge 
     As is shown in  FIGS. 2 to 4 , the developing cartridge  9  is disposed between the left-hand side wall intermediate portion  28  and the left-side wall front portion  29  of the drum side wall  22  and the right-hand side wall intermediate portion  38  and the right-hand side wall front portion  39  of the drum side wall  23  in such a state that the developing cartridge  9  is attached to the drum cartridge  7 . 
     The developing cartridge  9  includes a housing  51 . The housing  51  has a box shape which is opened at a rear side thereof. As is shown in  FIG. 1 , a developing roller  8 , a supply roller  52 , a layer thickness control blade  53  and an agitator  54  are included in the housing  51 . In addition, toner is accommodated within the housing  51 . 
     As is shown in  FIG. 4 , the developing roller  8  is disposed in such a manner as to be exposed to the rear from the housing  51  and is supported rotatably on both side walls  55 ,  56  of the housing  51 . Specifically, as is shown in  FIGS. 2 and 3 , developing roller shaft bearing members  57 ,  58 , which are substantially cylindrical, are provided at rear end portions of both the side walls  55 ,  56  in such a manner as to project outwardly sideways. The developing roller shaft bearing members  57 ,  58  are disposed in positions which confront each other in the right-left direction. As is shown in  FIG. 4 , the developing roller  8  has a configuration in which a metallic developing roller shaft  59  is covered with a rubber roller  60  which is made from a conductive rubber. The developing roller  8  is supported rotatably on both the side walls  55 ,  56  by both end portions of the developing roller shaft  59  being inserted rotatably in the developing roller shaft bearing members  57 ,  58 , respectively. 
     In addition, as is shown in  FIG. 3 , the developing roller drive gear  61  to which a driving force for driving the developing roller  8  and the like is inputted is provided rearwards of the developing roller shaft bearing member  57  on the left-hand side wall  55  of the housing  51 . The developing roller drive gear  61  is made to confront the elongated hole  36  formed in the drum side wall  22  of the drum cartridge  7  in such a state that the developing cartridge  9  is attached to the drum cartridge  7 . A rotational force acting in a clockwise direction as viewed in  FIG. 3  is inputted to the developing roller drive gear  61 . 
     (3) Attachment of Developing Cartridge to Drum Cartridge 
     The developing cartridge  9  is attached to the drum cartridge  7  from the front of the photosensitive drum  5 . The developing roller shaft bearing members  57 ,  58  which project, respectively, leftwards and rightwards from the housing  51  of the developing cartridge  9  are fitted in the attachment guide grooves  35 ,  42 , respectively. Then, by the developing cartridge  9  being pressed to the rear, the developing cartridge  9  is moved to the rear while the developing roller shaft bearing members  57 ,  58  are guided by the attachment guide grooves  35 ,  42 , respectively. In the process of this rearward movement, the housing  51  of the developing cartridge  9  is brought into abutment with the pressing levers  48 , and the housing  51  is pressed downwards against the pressing force exerted by the pressing levers  48 , whereby the attachment of the developing cartridge  9  to the drum cartridge  7  is completed. In this state, in the developing cartridge  9 , the developing roller  8  is brought into press contact with the photosensitive drum  5  by virtue of the pressing force of the pressing levers  48 . Note that in a state in which the attachment has been completed, gaps are formed between the developing roller shaft bearing members  57 ,  58  and rear end portions of the guide grooves  35 ,  42 , respectively. 
     3. Body Frames 
       FIG. 6  is a perspective view of an interior of the body casing as viewed from a right front direction thereof. 
     Two body frames  62 ,  63  are disposed within the body casing  2  in such a manner as to face each other with a space provided therebetween. Each of the body frames  62 ,  63  has a substantially rectangular shape as viewed from the side. A black process cartridge  3 K, a yellow process cartridge  3 Y, a magenta process cartridge  3 M and a cyan process cartridge  3 C are mounted in this order as viewed from the front side between the body frames  62 ,  63 . 
     The body frames  62 ,  63  are connected together via four round-rod shaped connecting members  64 ,  65 ,  66 ,  67 . The connecting member  64  is provided at the front of the black process cartridge  3   k  in such a manner as to extend between respective upper end portions of the body frame  62 ,  63 . The connecting member  65  is provided below the black process cartridge  3 K in such a manner as to extend between respective lower end portions of the body frames  62 ,  63 . The connecting member  66  is provided at the front of the cyan process cartridge  3 C in such a manner as to extend between the respective upper end portions of the body frames  62 ,  63 . The connecting member  67  is provided at the front of the cyan process cartridge  3 C in such a manner as to extend between the respective lower end portions of the body frames  62 ,  63 . Thus, the body frames  62 ,  63  and the four connecting members  64  to  67  provide a robust and strong structure which reduces strain and deformation when the process cartridges  3  are mounted or dismounted. 
     (1) Left-Hand Body Frame 
       FIG. 7  is a left side view of a left-hand body frame. 
     Four process cartridge guide grooves  71  are formed on the left-hand body frame  62 . The process cartridge guide grooves  71  are formed by cutting out the body frame  62  from an upper edge thereof. Each of the process cartridge guide grooves  71  has a width corresponding to an outside diameter of the protecting portion  30  formed on the drum frame  21  and extends obliquely downwards and rearwards from the upper edge of the body frame  62  to a vertically central portion thereof. A first abutment portion  72  having a substantially rectangular shape as viewed from the side which projects upwards within the process cartridge guide groove  71  and a second abutment portion  73  having a substantially rectangular shape as viewed from the side which projects forwards within the process cartridge guide groove  71  are formed at a lower end portion of the process cartridge guide groove  71 . The four process cartridge guide grooves  71  are formed at equal intervals in the front-rear direction. 
     In addition, cylindrical projecting portions  74  which project leftwards are provided, respectively, in positions on the body frame  62  which are spaced apart obliquely downwards and forwards from respective lower end portions of the process cartridge guide grooves  71 . 
     Furthermore, guide holes  75  which penetrate through the body frame  62  are formed, respectively, in positions on the body frame  62  which are spaced apart forwards and slightly obliquely downwards from the respective projecting portions  74 . The guide hole  75  has a linear hole portion  76  which extends in the front-rear direction and an intersecting hole portion  77  which extends obliquely downwards and rearwards from a rear end of the linear hole portion  76 . In the frontmost guide hole  75  of the four guide holes  75 , the linear hole portion  76  is formed longer than the linear hole portions  76  of the other guide holes  75 . 
     In addition, arc-shaped holes  187  which are centered, respectively, at the projecting portions  74  are formed in positions on the body frame  62  which lie in front of the respective process cartridge guide grooves  71  and which are spaced apart obliquely upwards and forwards from the respective projecting portions  74 . 
     (2) Right-Hand Body Frame 
     As is shown in  FIG. 6 , four process cartridge guide grooves  78  are formed on the right-hand body frame  63  in positions which confront, respectively, the four process cartridge guide grooves  71  formed on the left-hand body frame  62  in the right-left direction. The guide grooves  78  are formed by cutting out the body frame  63  from an upper edge thereof and extend obliquely downwards and rearwards from the upper edge to a vertically central portion of the body frame  63 , while getting narrower as they extend downwards. 
     In addition, cylindrical projecting portions  79  which project rightwards are provided, respectively, in positions on the body frame  63  which are spaced apart obliquely downwards and forwards from respective lower end portions of the guide grooves  78 . 
     Guide holes  80  which penetrate through the body frame  63  are formed, respectively, in positions on the body frame  63  which are spaced apart forwards and slightly obliquely downwards from the respective projecting portions  79 . The guide hole  80  has a linear hole portion  81  which extends in the front-rear direction and an intersecting hole portion  81  which extends obliquely downwards and rearwards from a rear end of the linear hole portion  80 . In the frontmost guide hole  80  of the four guide holes  80 , the linear hole portion  81  is formed longer than the linear hole portions  81  of the other guide holes  80 . 
     4. Configuration for Transmission of Drive Force to Process Cartridges 
       FIG. 8  is a perspective view of a driving force transmission mechanism and a first cover linkage mechanism as viewed from a left front direction thereof.  FIG. 9  is a left side view of the driving force transmission mechanism and the first cover linkage mechanism, showing a state in which the top cover is closed.  FIG. 10  is a perspective view of the driving force transmission mechanism and the first cover linkage mechanism as viewed from a right front direction thereof, showing the state in which the top cover is closed.  FIG. 11  is a plan view of the driving force transmission mechanism, showing a state in which a top cover is closed.  FIG. 12  is a left side view of the driving force transmission mechanism and the first cover linkage mechanism, showing a state in which the top cover is opened.  FIG. 13  is a perspective view of the driving force transmission mechanism and the first cover linkage mechanism as viewed from the right front direction thereof, showing a state in which the top cover is opened.  FIG. 14  is a plan view of the driving force transmission mechanism, showing a state in which the top cover is opened. 
     Note that a connecting and disconnecting translation cam  153  as an example of a translation member and a connecting and disconnecting drive mechanism  211 , which will both be described in detail later, are shown in the respective figures from  FIG. 8  to  FIG. 14 . In addition, the process cartridges  3  and the top cover  4  are shown in  FIG. 8 . 
     (1) Drive Force Transmission Member 
     A driving force transmission mechanism  91  is provided on an outside of the left-hand body frame  62  (refer to  FIG. 10 ) for transmitting a driving force to the process cartridges  3 . Note that in  FIG. 8 , although the body frame  62  is disposed between the four process cartridges  3  and the driving force transmission mechanism  91 , the illustration of the body frame  62  is omitted for the sake of simplifying the drawing. 
     As is shown in  FIG. 10 , the driving force transmission mechanism  91  includes four drum drive transmission members  92 , four developing drive transmission members  93  and a driving translation cam  94 . 
     (1-1) Drum Drive Transmission Members 
     The four drum drive transmission members  92  are provided in such a manner as to be associated with the four process cartridges  3 . The drum drive transmission members  92  are disposed in positions that correspond to respective ones of the connecting members  47  (refer to  FIG. 3 ) which are provided on the photosensitive drums  5  of their associated process cartridges  3  when the process cartridges  3  are brought into abutment with preventive members  191 . The preventative members  191  will be described later. 
       FIGS. 15A and 15B  are sectional views of the drum drive transmission member  92 . 
     The drum drive transmission member  92  includes integrally a gear part  95  and a raised part  96  which projects rightwards from a central portion of the gear part  95 . 
     The gear part  95  has a substantially circular annular plate shape. A number of gear teeth into which driving force is inputted from a drum motor are formed on an outer circumferential surface of the gear part  95 . 
     The raised part  96  has a cylindrical proximal end side outer circumferential surface  97  which has a center axis in common with the gear part  95 . In addition, the raised part  96  has a cylindrical distal end side outer circumferential surface  98  which has a center axis in common with the gear part  95  to the right of the proximal end side outer circumferential surface  97 . The distal end side outer circumferential surface  98  is formed to have a smaller diameter than that of the proximal end side outer circumferential surface  97 . Furthermore, the raised part  96  has an annular rising surface  99  which is connected to a distal edge of the proximal end side outer circumferential surface  97  and a proximal edge of the distal end side circumferential surface  98  and an annular distal end face  100  which is connected to a distal edge of the distal end side outer circumferential surface  98 . A linear engagement groove  101  (refer to  FIG. 1 ) is formed on the distal end face  100  in such a manner as to be brought into engagement with the connecting member  47  (refer to  FIG. 16 ) attached to an end face of the flange member  46 . In addition, the raised part  96  includes integrally a cylindrical portion  102  which extends leftwards from a circumferential edge portion of an opening in the distal end face  100 . 
     In addition, a holder  103  is attached to an external surface of the body frame  62  in such a manner as to cover the driving force transmission mechanism  91 . Support shafts  104  are provided on the holder  103  in association with the respective drum drive transmission members  92  in such a manner as to project therefrom to extend rightwards. The support shaft  104  is inserted into the cylindrical portion  102  rotatably and slidably in the right-left direction. Thus, the drum drive transmission member  92  is supported rotatably about the support shaft  104  and is provided in such a manner as to move backwards and forwards in the right-left direction between an advanced position shown in  FIG. 15A  and a retreating position shown in  FIG. 15B . In addition, as is shown in  FIG. 8 , one end of a coil spring  105  which is provided in such a manner as to be wound round a circumference of the cylindrical portion  102  is fixed to the drum drive transmission member  92 . The other end of the coil spring  105  is fixed to the holder  103  (refer to  FIG. 15A ). The drum drive transmission member  92  is pressed rightwards by virtue of the pressing force (elastic force) of the coil spring  105 . 
       FIG. 16  is a perspective view of the drum main body, a flange member, a connecting member and the drum driving force transmission member.  FIG. 17A  is a right side view of the drum drive transmission member  92 .  FIG. 17B  is a left side view of the connecting member.  FIG. 17C  is a left side view of the flange member. 
     As is shown in  FIGS. 16 and 17A , an engagement groove  101  is formed on a straight line which passes through a center of the distal end face  100  of the drum drive transmission member  92 . 
     As is shown in  FIGS. 16 and 17B , the connecting member  47  includes integrally a flat cylindrical main body part  106 , two first-side projections  107  which are provided on one end face of the main body part  106  in such a manner as to project therefrom and two second-side projections  108  which are provided on the other end face of the main body part  106 . The first-side projections  107  are disposed in two positions which are point symmetrical (180 degrees rotationally symmetrical) with each other with respect to the center of the main body part  106 . The second-side projections  108  are point symmetrical (180 degrees rotationally symmetrical) with each other with respect to the center of the main body part  106  and are disposed in two positions which shift 90 degrees about the center of the main body part  106  with respect to the first-side projections  107 . 
     As is shown in  FIG. 17C , a substantially cylindrical drum side engagement part  109  is formed on an end face of the flange member  46  in such a manner as to project leftwards. Recessed portions  110  are formed in two positions which are point symmetrical (180 degrees rotationally symmetrical) with each other with respect to the center of the drum side engagement part  109  (the flange member  46 ). In addition, the connecting member is connected to the drum side engagement part  109  (the end face of the flange member  46 ) in such a manner as to shift in position in a direction in which the second-side projections  108  confront each other by the second-side projections  108  of the connecting member  47  being fitted in the recessed portions  110 , respectively. 
     In such a state that the drum drive transmission member  92  has advanced to the advanced position shown in  FIG. 15A , the first-side projections  107  of the connecting member  47  fit in the engagement groove  101  of the drum drive transmission member  92 , whereby a so-called Oldham coupling is made by the connecting member  47 , the drum drive transmission member  92  and the drum side engagement part  109 . Thus, even in the event that a slight shift in position is produced between a rotational center of the drum driving force transmission member and a rotational center of the flange member  46  (the photosensitive drum  5 ), the shift is permitted, and the rotation of the drum drive transmission member  92  is transmitted to the flange member  46 . 
     (1-2) Developing Drive Transmission Members 
     As is shown in  FIG. 8 , the four developing drive transmission members  93  are provided in such a manner as to be associated with the respective process cartridges  3 . The developing drive transmission members  93  are disposed in positions at which the developing drive transmission members  93  confront the developing roller drive gears  61  which are provided on their associated process cartridges  3  when a state results in which the process cartridges  3  are brought into abutment with the preventive members  191 . 
       FIGS. 18A and 18B  are sectional views of the developing drive transmission member  93 . 
     As is shown in  FIGS. 10 ,  18 A and  18 B, the developing drive transmission member  93  includes a developing drive gear  111 , a reciprocating member  12  and a coil spring  113 . 
     The developing drive gear  111  has integrally a substantially disc-shaped gear main body  114  and a substantially cylindrical guide core part  115  which projects rightwards from the gear main body  114 . 
     A number of gear teeth into which driving force is inputted from a developing motor, not shown, are formed on an outer circumferential surface of the gear main body  114 . 
     As is shown in  FIGS. 18A and 18B , a guide core part  115  is formed in such a manner that a center axis thereof coincides with a center axis of the gear main body  114 . The guide core part  115  has a distal end core portion  116  which has a relatively small first outside diameter at a distal end portion and a proximal end core portion  117  which has a relatively large second outside diameter at a proximal end portion thereof. An outer circumferential surface of the distal end core portion  116  and an outer circumferential surface of the proximal end core portion  117  are made to continue without difference in level by an inclined surface. 
     The reciprocating member  112  includes integrally a cylindrically shaped distal end cylindrical part  118  having a relatively small first inside diameter, a cylindrically shaped proximal end cylindrical part  119  which is provided adjacent to a left-hand side of the distal end cylindrical part  118  and which has a relatively large second inside diameter, an engagement part  120  which is provided adjacent to a right-hand side of the distal end cylindrical part  118 , and a collar portion  121  which is made to project circumferentially from an outer circumferential surface of the distal end cylindrical part  118 . The first inside diameter is substantially equal to or slightly larger than the first outside diameter of the distal end core portion  116 . The second inside diameter is substantially equal to or slightly larger than the second outside diameter of the proximal end core portion  117 . The guide core part  115  is inserted into the reciprocating member  112  from the left. The reciprocating member  112  can be made to move in the right-left direction with respect to the guide core part  115  to reciprocate or move backwards and forwards between an advanced position shown in  FIG. 18A  and a retreating position shown in  FIG. 18B . 
     A coil spring  113  is provided in such a manner as to be wound round a circumference of the guide core part  115  and is disposed between the reciprocating member  112  and the gear main body  114 . The reciprocating member  112  is pressed rightwards by virtue of the pressing force (elastic force) of the coil spring  113 . 
     In addition, support shafts  128  are provided on the holder  103  in association with the respective developing drive transmission members  93  in such a manner as to project therefrom to extend rightwards. By this support shaft  128  being inserted into the guide core part  115  in such a manner as to rotate but not to slide, the developing drive gear  111  is supported in such a manner as to rotate about the support shaft  128  but not to slide. 
       FIG. 19A  is a right side view of the reciprocating member. 
     An engagement part  120  of the reciprocating member  112  includes integrally a substantially cylindrical center portion  122  which extends in the right-left direction and two abutment projecting portions  123  which are connected to a circumferential surface of the center portion  122 . The two abutment projecting portions  123  are disposed on a straight line which passes through a center of the center portion  122  and are formed to have a 180-degree rotationally symmetrical shape. 
       FIG. 19B  is a left side view of the developing roller drive gear  61 . 
     A circular recessed part  124  is formed on an external end face of the developing roller drive gear  61 , and the circular recessed part  124  has a diameter which is substantially the same as an outside diameter of the center portion  122  of the engagement part  120 . In addition, two abutment parts  125  are provided along a circumference of the recessed part  124  on the external end face of the developing roller drive gear  61 . Each abutment part  125  has a substantially L-shape, as viewed from the side, which has a short piece portion  126  and a long piece portion  127  which intersects the short piece portion  126  at right angles. The short piece portion  126  of each abutment part  125  extends on a straight line which passes through a center of the recessed part  124 . The long piece portion  127  of each abutment portion  125  extends along a straight line which passes through the center of the recessed part  124  and intersects a straight line which passes through the two short piece portions  126  at right angles while being spaced apart from the straight line. In addition, the two abutment parts  125  are 180 degrees rotationally symmetrical with each other with respect to the center of the recessed part  124 . 
     In such a state that the reciprocating member  112  has advanced to the advanced position shown in  FIG. 18A , the center portion  122  of the engagement part  120  fits in the recessed part  124  of the developing roller drive gear  61  and the abutment projecting portions  123  of the engagement part  120  are brought into abutment with the long piece portions  127  of the respective abutment parts  125  in a circumferential direction of the developing roller drive gear  61 . Consequently, in this state, when a rotational force is inputted into the developing drive gear  111  and the reciprocating member  112  is caused to rotate together with the developing drive gear  111 , the rotational force is transmitted from the respective abutment projecting portions  123  to the respective abutment parts  125 , whereby the developing roller drive gear  61  rotates in the same direction as the reciprocating member  112 . 
     Then, the distal end core portion  116  and the proximal end core portion  117  of the guide core part  115 , as well as the distal end cylindrical part  118  and the proximal end cylindrical part  119  have dimensions in the right-left direction that satisfy the following two conditions (1) and (2). 
     Condition (1): In such a state that the reciprocating member  112  is positioned between the retreating position shown in  FIG. 18B  and a position where part of the respective abutment projecting portions  123  of the reciprocating member  112  are brought into abutment with the respective abutment parts  125  of the developing roller drive gear  61 , the distal end core portion  116  of the guide core part  115  is disposed within the distal end cylindrical part  118  of the reciprocating member  112 , and the proximal end core portion  117  of the guide core part  115  is disposed within the proximal end cylindrical part  119  of the reciprocating member  112 . 
     Condition (2): In such a state that the reciprocating member  112  has advanced to the advanced position shown in  FIG. 18A , the proximal end core portion  117  of the guide core part  115  is dislocated from the inside of the proximal end cylindrical part of the reciprocating member  112 , and the distal end core portion  116  of the guide core part  115  is disposed in the inside of the proximal end cylindrical part  119  of the reciprocating member  112 . 
     In such a state that the reciprocating member has advanced to the advanced position, a radial play of the reciprocating member relative to the guide core part  115  is increased by the operations described above. Thus, even though a shift in position is produced between a rotational center of the developing roller drive gear  61  and a rotational center of the developing drive transmission member  93  (the developing drive gear  111 ), in the event that the amount of shift between the rotational centers falls within a range of radial play of the reciprocating member  112  with respect to the guide core part  115 , the shift is permitted, and the rotational force is transmitted well from the developing drive transmission member  93  to the developing roller drive gear  61 . 
     (1-3) Driving Translation Cam 
     As is shown in  FIGS. 10 ,  11 ,  13  and  14 , the driving translation cam  94  is a member which is elongated in the front-rear direction and is attached to the body frame  62  (refer to  FIG. 6 ) in such a manner as to reciprocate in a straight line in the front-rear direction. As is shown in  FIGS. 11 and 14 , the driving translation cam  94  includes a rectangular plate-shaped main body part  131  which is elongated in the front-rear direction, four first cam portions  132  which are formed integrally on the main body part  131  and four second cam portions  133  which are formed integrally on the main body part  131 . 
     The main body part  131  is provided parallel to the body frame  62 . Four holes  134  are formed in the main body part  131 . The holes  134  are formed, respectively, in positions at which the holes  134  confront the four developing drive transmission members  93  in the right-left direction. Each hole  134  has an elongated hole shape which extends in the front-rear direction and has dimensions which permit vertical insertion and dislocation of the reciprocating member  112  of the developing drive transmission member  93 . As is shown in  FIG. 10 , in such a state that the driving translation cam  94  is disposed in a relatively forward position, the developing drive transmission members  93  confront, respectively, rear end portions of the holes  134 . On the other hand, as is shown in  FIG. 13 , in such a state that the driving translation cam  94  is disposed in a relatively rearward position, the developing drive transmission members  93  confront, respectively, front end portions of the holes  134 . 
     The first cam parts  132  are provided on a left-hand surface (i.e., on a surface opposite to a surface which confronts the body frame  62 ) of the main body part  131  in such a manner as to be associated with the respective holes  134 . The first cam part  132  has a substantially U-shape as viewed from the side which extends along substantially a front half of a circumferential edge of the hole  134 . In addition, as is shown in  FIG. 14 , the first cam part  132  has an inclined portion  135  which is inclined in such a manner as to be spaced apart from the main body part  131  as the inclined portion  135  extends forwards and a flat portion  136  which extends from a front end of the inclined portion  135  in such a manner as to be in parallel with the main body part  131  and is, consequently, formed to have a substantially trapezoidal shape as viewed from the top. 
     The secondary cam parts  133  are provided at lower end portions of the left-hand surface of the main body part  131  in such a manner as to be associated with the respective drum drive transmission members  92 . As is shown in  FIGS. 11 and 14 , each of the second cam parts  133  is formed at the rear of each of the first cam parts  132  in such a manner as not to overlap the first cam part  132  as viewed from the top. In addition, as is shown in  FIG. 14 , the second cam part  133  has an inclined portion  137  which is inclined in such a manner as to be spaced apart from the main body part  131  as the inclined portion  137  extends forwards and a flat portion  138  which extends from a front end of the inclined portion  137  in such a manner as to be in parallel with the main body part  131  and is, consequently, formed to have a substantially trapezoidal shape as viewed from the top. 
     In a state shown in  FIGS. 10 and 11 , the reciprocating members  112  of the respective developing drive transmission members  93  are inserted into the rear end portions of the holes  134 , the color portion  121  is in abutment with the left-hand surface of the main body part  131  of the driving translation cam  94 , and portions of the distal end cylindrical parts  18  and the engagement parts  120  project rightwards with respect to the main body part  131 . The respective first cam parts  132  are disposed forwards of the main body part  131 . In addition, the drum drive transmission members  92  are in abutment with the left-hand surface of the main body part  131  at the rising surfaces  99  thereof. The distal end portions (i.e., the portions where the distal end side outer circumferential surfaces  98  are formed) of the raised part  96  project rightwards relative to the main body part  131  below the main body part  131 . The respective second cam parts  133  are disposed forwards of the respective drum drive transmission members  92 . Namely, the respective drum drive transmission members  92  and the reciprocating members  112  of the developing drive transmission members  93  have both advanced to the advanced positions. 
     When the driving translation cam  94  is caused to move rearwards, the respective inclined portions  135  of the first cam parts  132  are brought into abutment with the respective collar portions  121  of the reciprocating members, and the inclined portions  137  of the second cam parts  133  are brought into abutment with the respective rising surfaces  99  of the drum drive transmission members  92 . When the driving translation cam  94  moves further rearwards, the reciprocating members  112  and the first cam parts  132  move relatively in such a manner that the collar portions  121  of the reciprocating members  112  ride, respectively, on the inclined portions  135  of the first cam parts  132 . Accordingly, the reciprocating members  112  receive a force in a leftward direction from the first cam parts  132  and are then caused to move leftwards against the pressing forces of the coil springs  113 . In addition, the drum drive transmission members  92  and the second cam parts  133  move relatively in such a manner that the rising surfaces  99  of the drum drive transmission members  92  ride on the inclined portions  137  of the second cam parts  133 . In conjunction with this, the second cam parts  133  receive a force in a leftward direction from the second cam parts  133  and are then caused to move leftwards against the pressing forces of the coil springs  105 . 
     In addition, in a state shown in  FIGS. 13 and 14 , the reciprocating members  112  are brought into abutment with the flat portions  136  of the first cam parts  132  at the collar portions  121  thereof, and only the engagement parts  120  are inserted into the front end portions of the holes  134 . In addition, the drum drive transmission members  92  are brought into abutment with the flat portions  138  of the second cam parts  133  at the rising surfaces  99  thereof, and the distal end portions of the raised parts  96  project slightly rightwards relative to the main body part  131 . Namely, the drum drive transmission members  92  and the reciprocating members  112  of the developing drive transmission members  93  have retreated to the retreating positions. 
     (2) First Cover Linkage Mechanism 
     In addition, in the printer  1 , the driving translation cam  94  is designed to move in association with the opening or closing of the top cover  4 . Namely, the printer  1  includes a first cover linkage mechanism  140  for causing the driving translation cam  94  to move in a linked fashion with the opening or closing of the top cover  4  (see  FIGS. 9 and 10 ). 
     As is shown in  FIG. 8 , the top cover  4  is provided in such a manner as to be opened and closed between a state in which a front end portion of the top cover  4  is lifted up from the body casing  2  (refer to  FIG. 1 ) to open the upper surface of the body casing  2  and a state in which the top cover  4  extends along the upper surface of the body housing  2  to close the upper surface of the body housing  2  by a shaft, not shown, being inserted rotatably in substantially C-shaped rotation support parts  141  which are provided at a rear end portion of the top cover  4 . 
     As is shown in  FIG. 9 , the first cover linkage mechanism  140  includes first cover link members  142  and second cover link members  143 . The first cover link members  142  and the second cover link members  143  are provided in relation to the left- and right-hand body frames  62 ,  63  (refer to  FIG. 6 ). Since the first cover link member  142  and the second cover link member  143  which are provided in relation to the left-hand body frame  62  and the first cover link member  142  and the second cover link member  143  which are provided in relation to the right-hand body frame  63  are configured laterally symmetrical, hereinafter, only the first cover link member  142  and the second cover link member  143  which are provided in relation to the left-hand body frame  62  will be described here. 
     As is shown in  FIG. 10 , the first cover link member  142  is formed into a long straight-line shape. One end portion of the first cover link member  142  is connected to an intermediate portion along the length of a left end portion of an inner surface of the top cover  4  in such a manner as to rotate about an axis extending along the right-left direction. The first cover link member  142  extends along the inner surface of the top cover  4  in the front-rear direction in such a state that the top cover  4  is closed. The other end portion  144  of the first cover link member  142  is connected to a rear end portion of the body frame  62  in such a manner as to rotate about an axis extending along the right-left direction. In addition, a connecting shaft  145  is formed at a rearmost end portion of the first cover link member  142  in such a manner as to project rightwards. 
     The second cover link member  143  is formed to have a V-shape as viewed from the side which opens at a relatively large angle (for example, an angle of about 135°). A support shaft  146  is formed at a bent portion of the second cover link member  143  in such a manner as to project rightwards. The second cover link member  143  is provided in such a manner as to rotate about the support shaft  146  by the support shaft  146  being supported rotatably at the rear end portion of the body frame  62 . The connecting shaft  145  of the first cover link member  142  is inserted rotatably into one end portion of the second cover link member  143 . A connecting shaft  147  is formed at the other end portion of the second cover link member  143  in such a manner as to project rightwards. An elongated hole  148  which is long in the vertical or up-down direction is formed at a rear end portion of the main body part  131  of the driving translation cam  94 , and the connecting shaft  147  is inserted in the elongated hole  148  in such a manner as to be loosely fitted therein so as not only to rotate but also to move in the up-down direction. 
     When the top cover  4  is opened from the state in which the top cover  4  is closed (the closed state is shown in  FIG. 10 ), the first cover link member  142  rotates about the other end portion  144  in such a manner as to be erected. In conjunction with the rotation of the first cover link  142 , the one end portion of the second cover link member  143  is pushed forwards and the second cover link member  143  rotates about the support shaft  146 , whereby the other end portion of the second cover link member  143  moves rearwards. In addition, by the other end portion of the second cover link member  143  moving rearwards, the driving translation cam  94  is pushed rearwards by the connecting shaft  147 , whereby the driving translation cam  94  moves rearwards. Then, when a state results in which the top cover  4  is fully opened, the driving translation cam  94  is disposed in a rearmost position as is shown in  FIG. 13 . 
     When the top cover  4  is closed, the first cover link member  142  rotates about the other end portion of the first cover link member  142  in such a manner as to fall in an inclined fashion. The one end portion of the second cover link member  143  is pushed rearwards in conjunction with the rotation of the first cover link member  142 , and the second cover link member  143  rotates about the support shaft  146 , whereby the other end portion of the second cover link member  143  moves forwards. In addition, the driving translation cam  94  is pushed forwards by the connecting shaft  147  by the other end portion of the second cover link member  143  moving forwards, whereby the driving translation cam  94  moves forwards. Then, when a state results in which the top cover  4  is fully closed, the driving translation cam  94  is disposed in a relatively forward position as is shown in  FIG. 10 . 
     5. Locking Mechanism 
       FIG. 20  is a left side view of a locking mechanism, showing a state in which the top cover is closed.  FIG. 21  is a left side view of the locking mechanism, showing a state in which the top cover is opened. 
     Note that the driving translation cam  94 , the first cover linkage mechanism  140  and the preventive members  191 , which will be described later, as well as a connecting-disconnecting drive mechanism  211  and a second cover linkage mechanism  231  are shown in  FIGS. 20 and 21 . 
     A locking mechanism  151  for locking the respective process cartridges  3  on to the body frames  62 ,  63  (refer to  FIG. 6 ) is provided in the printer  1 . 
     The locking mechanism  151  includes four left-hand fixing members  152 , four right-hand fixing members  172  (refer to  FIG. 22 ) and a left connecting and disconnecting translation cam  153  and a right connection and disconnecting translation cam  153 . 
     (1) Left-Hand Fixing Members 
     Four left-hand fixing members  152  are disposed on a left-hand side of the left-hand body frame  62 . In addition, the four left-hand fixing members  152  are provided in such a manner as to be associated with a respective process cartridge  3 . In such a state that the four process cartridges  3  are mounted in the body casing  2 , the left-hand fixing members  152  are disposed forwards of the protecting portions  30  (refer to  FIG. 3 ) of the respective process cartridges  3  (the drum cartridges  7 ). The left-hand fixing members  152  each include a lock lever  154 , a pressing lever  155  and a coil spring  156 . 
     The lock lever  154  is supported rotatably on the projecting portion  74  (refer to  FIG. 7 ) which is formed on the left-hand body frame  62  at one end portion (i.e., a proximal end portion) thereof. A substantially rectangular hole  157  is formed at a central portion of the lock lever  154  in such a manner as to penetrate therethrough. A front edge of the other end portion (i.e., a distal end portion) of the lock lever  154  is formed to have a curved shape which corresponds to an external shape of the protecting portion  30  of the process cartridge  3 . An operating portion  171  is formed on a right-hand surface of the lock lever  154  in a position which lies closer to the distal end portion than the hole  157  in such a manner as to project rightwards. 
     The pressing lever  155  is disposed forwards and to the right of the lock lever  154  and is supported rotatably on the projecting portion  74  (refer to  FIG. 7 ) at one end portion (a proximal end portion) thereof. A hook portion  158  is formed at a central portion of the pressing lever  155  in such a manner as to project forwards and to be bent leftwards at a distal end portion thereof. The distal end portion of the hook portion  158  is inserted into the hole  157  of the lock lever  154  from the right. In addition, a connecting shaft  159  is formed at the central portion of the pressing lever  155  in such a manner as to project leftwards from a left-hand surface thereof. Furthermore, a support portion  160  (refer to  FIG. 25 ) is formed at the central portion of the pressing lever  155  for supporting a spacing member  201 , which will be described later. The support portion  160  projects rightwards from a right-hand surface of the pressing lever  155  and is inserted into the hole  187  (refer to  FIG. 7 ), reaching a position lying on a right-hand side of the body frame  62  at a distal end thereof. 
     The coil spring  156  is interposed between the distal end portion of the lock lever  154  and the distal end portion of the pressing lever  155 . 
     (2) Right-Hand Fixing Members 
       FIG. 22  is a right side view of part of the right-hand body frame, showing a state in which the top cover is closed.  FIG. 23  is a right side view of part of the right-hand body frame, showing a state in which the top cover is opened. 
     The four right-hand fixing members  172  are provided in such a manner as to be associated with the respective process cartridges  3  and are disposed on a right-hand side of the right-hand body frame  63 . The right-hand fixing members  172  each include a lock lever  174 , a pressing lever  175  and a coil spring  176 . 
     The lock lever  174  is formed to have a substantially C-shape as viewed from the side. One end portion (a proximal end portion) of the lock lever  174  is supported rotatably on the projecting portion  79  formed on the right-hand body frame  63 . A substantially rectangular hole  177  is formed in the other end portion (a distal end portion) of the lock lever  174  in such a manner as to penetrate therethrough. In addition, a cutout portion  178  is formed in the lock lever  174  between the proximal end portion and the distal end portion thereof in such a manner as to be cut out into a recess which is recessed downwards. 
     The pressing lever  175  is disposed forwards and to the left of the lock lever  174  and is supported rotatably on the projecting portion  79  at one end portion (a proximal end portion) thereof. A locking portion  180  is formed at a distal end portion of the pressing lever  175  in such a manner as to project rightwards. A distal end portion of the locking portion  180  is inserted into the hole  177  of the lock lever  174  from the left. In addition, a connecting shaft  179  is formed at a central portion of the pressing lever  175  in such a manner as to project rightwards from a right-hand surface thereof. Furthermore, although not shown, a support portion is formed at the central portion of the pressing lever  175  in such a manner as to project rightwards from the right-hand surface of the pressing lever  175 , and the spacing member  201 , which will be described later, is supported rotatably by the support portion. 
     The coil spring  176  is interposed between the distal end portion of the lock lever  174  and the distal end portion of the pressing lever  175 . 
     (3) Connecting and Disconnecting Translation Cam 
       FIG. 24  is a left side view of the connecting and disconnecting translation cam. 
     Since the left and right connecting and disconnecting translation cams  153  have configurations which are laterally symmetrical with each other, hereinafter, only the left-hand connecting and disconnecting translation cam  153  will be described. 
     The connecting and disconnecting translation cam  153  is a member which extends in the front-rear direction and is attached on an inner surface of the body frame  62  (refer to  FIG. 6 ) in such a manner as to reciprocate in a straight line in the front-rear direction. 
     Four guide grooves  161  are formed on a left-hand surface of the connecting and disconnecting translation cam  153  in such a manner as to be associated with each connecting and disconnecting translation cam  153 . The guide groove  161  has a linear groove portion  162  which extends in the front-rear direction and an intersecting groove portion  163  which extends obliquely upwards and rearwards from a rear end of the linear groove portion  162 . 
     Four third cam portions  164  are formed on an upper surface of the connecting and disconnecting translation cam  153  at intervals in the front-rear direction. The four third cam portions  164  are each formed to have a substantially trapezoidal shape as viewed from the side which projects upwards from the upper surface  350  (i.e., a permissive surface) of the connecting and disconnecting translation cam  153  and each have a horizontal surface  165  (i.e., a spacing surface) which extends in the front-rear direction and an inclined surface  166  (i.e., a permissive surface) which continues to a rear end of the horizontal surface  165  and the upper surface of the connecting and disconnecting translation cam  153 . An interval defined between the frontmost third cam portion  164  and the third cam portion  164  which lies adjacent thereto is made longer than intervals defined between the other adjacent third cam portions  164 . 
     A rack gear  167  is formed on a lower surface of a front end portion of the connecting and disconnecting translation cam  153 . As is shown in  FIG. 10 , a pinion gear  168  is made to mesh with the rack gear  167  on the left-hand connecting and disconnecting translation cam  153 . As is shown in  FIG. 8 , a pinion gear  169  is made to mesh with a rack gear  167  on the right-hand connecting and disconnecting translation cam  153 . The pinion gears  168 ,  169  are attached, respectively, to a left end portion and a right end portion of a connecting shaft  170  in such a manner as not to rotate. When the left-hand connecting and disconnecting translation cam  153  moves in the front-rear direction, the right-hand connecting and disconnecting translation cam  153  moves leftwards in synchronism with the movement of the left-hand connecting and disconnecting translation cam  153  in the same direction and by the same shifting amount of the left-hand connecting and disconnecting translation cam  153 . 
     (4) Link Members 
     The respective left-hand fixing members  152  and the left-hand connecting and disconnecting translation cam  153  are connected to each other by link members  181  as is shown in  FIGS. 20 and 21 . 
     The connecting shaft  159  of the left-hand fixing member  152  is inserted into one end portion of the link member  181  in such a manner as to rotate within a predetermined angular range. Specifically, a substantially fan-shaped hole  182  is formed at the one end of the link member  181 . The connecting shaft  159  has a key hole shape as viewed from the side which has a projection on a circumferential surface thereof. In addition, when the connecting shaft  159  is inserted into the hole  182 , the link member  181  is made to rotate about the connecting shaft  159  within the angular range. On the other hand, a connecting shaft  183  is formed at the other end portion of the link member  181  in such a manner as to project rightwards. The connecting shaft  183  is inserted into the guide hole  75  of the body frame  62 , and a distal end portion thereof is fitted in the guide groove  161 . 
     The respective right-hand fixing members  172  and the right-hand connecting and disconnecting translation cam  153  are connected to each other by link members  184  as is shown in  FIGS. 22 and 23 . 
     The connecting shaft  179  of the right-hand fixing member  172  is inserted into one end portion of the link member  184  in such a manner as to rotate within an angular range. The angular range may be predetermined. Specifically, a substantially fan-shaped hole  185  is formed at the one end of the link member  184 . The connecting shaft  179  has a key hole shape as viewed from the side which has a projection on a circumferential surface thereof. In addition, when the connecting shaft  179  is inserted into the hole  185 , the link member  184  is made to rotate about the connecting shaft  179  within the angular range. On the other hand, a connecting shaft  186  is formed at the other end portion of the link member  184  in such a manner as to project leftwards. The connecting shaft  183  is inserted into the guide hole  80  of the body frame  63 , and a distal end portion thereof is fitted in the guide groove  161 . 
     6. Preventive Members 
     As is shown in  FIGS. 20 and 21 , four preventive members  191  are provided in the printer  1 . The four preventive members  191  are disposed, respectively, on left-hand sides of the left-hand fixing members  152 . 
     The preventive member  191  has an arm shape. An insertion hole  192  is formed at one end portion (i.e., a proximal end portion) of the preventive member  191 . A clamping shaft  351  (refer to  FIG. 7 ) which is provided on the body frame  62  (refer to  FIG. 7 ) in a position which is forward of the lower end portion of the process cartridge guide groove  71  with a slight interval provided therebetween is inserted into the insertion hole  192 . Thus, each preventive member  191  is supported rotatably about the insertion hole  192  (the clamping shaft  351 ) by the body frame  62 . A distal end portion of the preventive member is brought into abutment with the operating portion  171  of the left-hand fixing member  152  (the lock lever  154 ) from thereabove and extends in the front-rear direction. The distal end portion of the preventive member  191  extends upwards and is then folded back to have a hook shape. Note that in the right-hand fixing member  172 , the lock lever  174  corresponds to the preventive member  191  (refer to  FIG. 23 ). 
     7. Spacing Members 
       FIG. 25  is a right side view of part of the left-hand body frame, showing a state in which the top cover is closed.  FIG. 26  is a right side view of the part of the left-hand body frame, showing a state in which the top cover is opened. 
     A plurality of spacing members  201  (e.g., eight spacing members  201  in this exemplary embodiment) are provided in the printer  1  in such a manner as to be associated with the four left-hand fixing members  152  and the four right-hand fixing members  172  (refer to  FIG. 22 ). Since the spacing members  201 , which are provided in such a manner as to be associated with the left-hand fixing members  152  and the spacing members  201  which are provided in such a manner as to be associated with the right-hand fixing members  172 , are configured to be laterally symmetrical with each other, hereinafter, only the left-hand spacing members  201  will be described. 
     The four spacing members  201  are disposed on an inside (e.g., a right-hand side) of the left-hand body frame  62  in such a manner as to confront, respectively, their associated left-hand fixing members  152  in the right-left direction. 
     The spacing member  201  has a substantially triangular plate shape. The support portion  160  which is provided on the pressing lever  155  of the left-hand fixing member  152  is inserted in one angular portion  202  of the spacing member  201  in such a manner as to rotate relatively. Accordingly, the spacing member  201  is supported rotatably on the support portion  60 . 
     The spacing member  201  is provided in such a manner as to extend rearwards from the support portion and is caused to rest on an upper surface of the connecting and disconnecting translation cam  153 . A lower projecting portion  203  is formed at a rear end portion of the spacing member  201  in such a manner as to project downwards. The lower projecting portion  203  is brought into abutment with the upper surface of the connecting and disconnecting translation cam  153 . In addition, an upper projecting portion  204  is formed at the rear end portion of the spacing member  201  in such a manner as to project upwards. A front surface of the upper projecting portion  204  is made to function as a pressing surface  205 . 
     8. Connecting and Disconnecting Drive Mechanism 
     As is shown in  FIGS. 9 ,  10 ,  12  and  13 , a connecting and disconnecting drive mechanism  211  is provided in the printer  1  for reciprocating the connecting and disconnecting translation cam  153  in the front-rear direction. 
     The connecting and disconnecting drive mechanism  211  includes a motor gear  212  which rotates by virtue of driving force of a connecting and disconnecting motor  229  (refer to  FIG. 27 ) as an example of a motor, an intermediate gear  213  which is provided integrally with the pinion gear  168  and is adapted to rotate together with the pinion gear  168 , a planetary differential clutch  214  for engaging and disengaging the transmission of rotational force of the motor gear  212  to the intermediate gear  213 , and a clutch engaging lever  215  for switching between engaging and disengaging the transmission of the rotational force by the planetary differential clutch  214 . 
     As is shown in  FIGS. 10 and 13 , the planetary differential clutch  214  includes a shaft  216  which is held on the holder  103  (refer to  FIG. 15A ). An input gear  217 , an engagement gear  218  and an output gear  219  are supported rotatably on the shaft  216 . The motor gear  212  meshes with the input gear  217 . The engagement gear  218  is disposed at a right-hand side of the input gear  217  and has on an outer circumferential surface thereof a number of teeth with which the clutch engaging lever  215  is brought into engagement. The output gear  219  is disposed at a right-hand side of the engagement gear  218 . The output gear  219  has a smaller diameter than that of the input gear  217  and meshes with the intermediate gear  213 . 
     The clutch engaging lever  215  is disposed in such a manner as to extend in the front-rear direction above the engagement gear  218 . As is shown in  FIGS. 9 and 12 , the clutch engaging lever  215  is supported on a support member  220  which is attached to the holder  103  at a rear end portion thereof and is provided in such a manner as to swing about the support member  220 . As is shown in  FIG. 12 , a claw  221  is formed on a lower surface of a distal end portion of the clutch engaging lever  215 . 
     The other end of a coil spring  222  which is locked on the holder  103  at one end is locked on an intermediate portion of the clutch engaging lever  215 . The clutch engaging lever  215  is pressed in such a manner that the distal end portion thereof is lifted upwards by the coil spring  222 . In addition, in such a state that the driving translation cam  94  is disposed in a position shown in  FIGS. 12 and 13 , the distal end portion of the clutch engaging lever  215  is lifted upwards by virtue of the pressing force of the coil spring  222  and confronts a front end portion of the driving translation cam  94  with an interval provided forwards thereof. As is shown in  FIGS. 9 and 10 , when the driving translation cam  94  is caused to move to a frontmost position from the state described above, the driving translation cam  94  is brought into abutment with the clutch engaging lever  215  in the course of the movement, whereby the distal end portion of the clutch engaging lever  215  is pressed downwards against the pressing force of the coil spring  222  by the driving translation cam  94 . As a result, the claw  221  of the clutch engaging lever  215  enters between the teeth of the engagement gear  218 , whereby the clutch engaging lever  215  is brought into engagement with the engagement gear  218 . 
     In such a state that the clutch engaging lever  215  is in engagement with the engagement gear  218 , the engagement gear  218  is not allowed to rotate, and rotational force inputted into the input gear  217  from the motor gear  212  is transmitted to the output gear  219 . Namely, the planetary differential clutch  214  engages the transmission of the rotational force of the motor gear  212  to the intermediate gear  213 . Accordingly, the pinion gear  168  can be caused to rotate backwards and forwards together with the intermediate gear  213  by backward and forward rotations of the motor gear  212 , whereby the connecting and disconnecting translation cam  153  can be caused to reciprocate in the front-rear direction. 
     On the other hand, in such a state that the clutch engaging lever  215  is not in engagement with the engagement gear  218 , the rotational force that is inputted into the input gear  217  from the motor gear  212  is transmitted to the engagement gear  218  and is not transmitted to the output gear  219 . Namely, the planetary differential clutch  214  disengages the transmission of the rotational force of the motor gear  212  to the intermediate gear  213 . As this transition occurs, the output gear  219  is in such a state that the output gear  219  rotates freely, and hence, the connecting and disconnecting motor  229  (refer to  FIG. 27 ) does not constitute a load to the movement of the connecting and disconnecting translation cam  153 . 
     8. Second Cover Linkage Mechanism 
     In the printer  1 , the driving translation cam  94  is made to move in a linked fashion with the opening or closing of the top cover  4 , and the connecting and disconnecting translation cam  153  is made to move in a linked fashion with the movement of the driving translation cam  94 . Namely, the printer  1  includes the second cover linkage mechanism  231  for causing the connecting and disconnecting translation cam  153  to move in parallel with the linked movement of the driving translation cam  94  with the opening or closing of the top cover by the first cover linkage mechanism  140 . 
     The second cover linkage mechanism  231  includes a third cover link member  232  and a fourth cover link member  233 . 
     The third cover link member  232  is a member which extends in a straight line, and a shaft  234  is formed at an intermediate portion thereof in such a manner as to project leftwards. The shaft  234  is supported rotatably on the holder  103  (refer to  FIG. 15A ). The other end portion (i.e., an end portion opposite to one end portion which is connected to the driving translation cam  94 ) of the third cover link member  232  and a rear end portion of the fourth cover link member  233  are connected together in such a manner as to rotate about an axis which extends in the right-left direction. 
     The fourth cover link member  233  is a member which extends in a straight line and is fixed to a left-hand surface of the connecting and disconnecting translation cam  153  with a posture in which it extends substantially in the front-rear direction. The other end portion (i.e., an end portion opposite to the one end portion which is connected to the driving translation cam  94 ) of the third cover link member  232  and a rear end portion of the fourth cover link member  233  are connected to each other in such a manner as to rotate about an axis extending along the right-left direction. 
     In such a state that the top cover  4  is closed, as is shown in  FIG. 20 , the driving translation cam  94  is disposed in a relatively forward position, while the connecting and disconnecting translation cam  153  is disposed in a rearmost position. Accordingly, the one end portion of the third cover link member  232  is positioned further forwards than the rear end portion of the fourth cover link member  233 , and the third cover link member  232  and the fourth cover link member  233  form an acute angle therebetween. When the top cover  4  is opened and the driving translation cam  94  is caused to move rearwards, the one end portion of the third cover link member  232  moves rearwards, and the third cover link member  232  rotates about the shaft  234 . In conjunction with the rotation of the third cover link member  232 , the fourth cover link member  233  is pushed forwards by the other end portion of the third cover link member  232 , whereby the connecting and disconnecting translation cam  153  is caused to move forwards. In addition, when a state results in which the top cover is fully opened, as is shown in  FIG. 21 , the connecting and disconnecting translation cam  153  is disposed in a frontmost position. 
     In the course of the opening of the top cover  4 , by the rearward movement of the driving translation cam  94 , the driving translation cam  94  is disconnected from the clutch engaging lever  215 . Then, the distal end portion of the clutch engaging lever  215  is lifted upwards, whereby the engagement of the clutch engaging lever  215  with the engagement gear  218  is released. Accordingly, the connecting and disconnecting motor  229  (refer to  FIG. 27 ) does not constitute the load to the movement of the connecting and disconnecting translation cam  153 , whereby a smooth movement of the connecting and disconnecting translation cam  153  is attained. 
     In such a state that the top cover  4  is fully opened, as is shown in  FIG. 21 , the one end portion of the third cover link member  232  is positioned further rearwards than the rear end portion of the fourth cover link member  233 , and the third cover link member  232  and the fourth cover link member  233  form an obtuse angle therebetween. When the top cover  4  is closed and the driving translation cam  94  moves forwards, the one end portion of the third cover link member  232  moves forwards, and the third cover link member  232  rotates about the shaft  234 . In conjunction with the rotation of the third cover link member  232 , the fourth cover link member  233  is pulled rearwards by the other end portion of the third cover link  232 , whereby the connecting and disconnecting translation cam  153  moves rearwards. In addition, when a state results in which the top cover  4  is fully closed, as is shown in  FIG. 20 , the connecting and disconnecting translation cam  153  is disposed in a relatively rearward position. 
     9. Operations of Lock Mechanism (Left-Hand Fixing Members and Right-Hand Fixing Members) and Preventive Members in Conjunction with Opening or Closing of Top Cover 
     In such a state that the top cover  4  is opened, as is shown in  FIG. 21 , the respective connecting shafts  183  of the left-hand link members  181  are inserted into the linear hole portions  76  (refer to  FIG. 7 ) of the guide holes  75  of the body frame  62 , and the distal end portions of the connecting shafts  183  are fitted in the intersecting groove portions  163  (refer to  FIG. 24 ) of the guide grooves  161 . In addition, as is shown in  FIG. 23 , the connecting shaft  183  of each right-hand link member  184  is inserted into the linear hole portion  81  (refer to  FIG. 22 ) of the guide hole  80  of the body frame  63  and the distal end portion of the connecting shaft  183  is fitted in the intersecting groove portion  163  of the guide groove  161 . In addition, as is shown in  FIG. 21 , the left-hand fixing members  152  fall in an inclined fashion and retreat from mounting/dismounting paths of the process cartridges  3  to thereby be positioned at positions at which the left-hand fixing members  152  do not confront the process cartridge guide grooves  71  (refer to  FIG. 7 ) in the right-left direction. In addition, the respective preventive members  191  are brought into abutment with the operating portions  171  at most distal end portions of the preventative members  191  and are positioned at positions at which the preventative members  191  confront the lower end portions of the process cartridge guide grooves  71  in the right-left direction (i.e., preventive positions). Each respective right-hand fixing member  172  is, as is shown in  FIG. 23 , located in a position where the cutout portion  178  of the lock lever  174  confronts the lower end portion of the process cartridge guide groove  78  in the right-left direction and a bottom surface of the cutout portion  178  intersects a direction which extends along the process cartridge guide groove  78  at substantially right angles (i.e., a preventive position). 
     Thus, the process cartridges  3  can be mounted in or dismounted from the interior of the body casing  2 . When mounting the process cartridges  3 , the protecting portions  30  (refer to  FIG. 3 ) of the process cartridges  3  (i.e., the drum cartridges  7 ) are fitted in the process cartridge guide grooves  71 , while the right end portions of the drum shafts  45  are fitted in the process cartridge guide grooves  78 , and the process cartridges  3  are caused to move obliquely downwards and rearwards, whereby the process cartridges  3  are gradually mounted into the interior of the body casing  2  while the protecting portions  30  and the drum shafts  45  are being guided by the process cartridge guide grooves  71 ,  78 , respectively. In addition, when dismounting the process cartridges  3  from the body casing  2 , the process cartridges  3  are gradually pulled obliquely upwards and forwards while the protecting portions  30  and the drum shafts  45  are being guided by the process cartridge guide grooves  71 ,  78 , respectively. 
     In such a state that the top cover  4  is opened, since the preventive members  191  confront the lower end portions of the process cartridge guide grooves  71  in the right-left direction and the cutout portions  178  of the lock levers  174  confront the lower end portions of the process cartridge guide grooves  78  in the right-left direction, when the process cartridges  3  are mounted in the interior of the body casing  2 , the protecting portions  30  are brought into abutment with the preventive members  191  or the drum shafts  45  are brought into abutment with the lock levers  174 , whereupon the movement of the process cartridges  3  is prevented. Namely, the mounting of the process cartridges  3  into the body casing  2  is prevented at a point in time when the protecting portions  30  are brought into abutment with the preventive members  191  or the drum shafts  45  are brought into abutment with the lock levers  174 . 
     Then, when the top cover  4  is closed, the driving translation cam  94  moves forwards, while the connecting and disconnecting translation cam  153  moves rearwards. As is shown in  FIG. 21 , the distal end portions of the respective connecting shafts  183  of the left-hand link members  181  are fitted in the intersecting groove portions  163  (refer to  FIG. 24 ) of the guide grooves  161 . Accordingly, when the connecting and disconnecting translation cam  153  moves rearwards, the distal end portions of the connecting shafts  183  move to the rear along the linear hole portions  76  (refer to  FIG. 7 ) on the body frame  62  while kept fitted in the intersecting groove portions  163 . Thus, the respective link members  181  rotate in such a manner that the one end portions thereof are lifted up, and the respective left-hand fixing members  152  rotate rearwards about the projecting portions  74  (refer to  FIG. 7 ) which are formed on the body frame  62  in conjunction with the rotations of the link members  181 . As a result, the respective left-hand fixing members  152  are put in the locked state and are disposed on the mounting/dismounting paths of the process cartridges and the front ends of the distal end portions of the lock levers  154  are brought into abutment with the protecting portions  30  of the process cartridges  3 , whereby the protecting portions  30  are pressed obliquely downwards and rearwards. 
     In addition, as is shown in  FIG. 20 , the operating portions  171  move rearwards relative to the respective preventing members  191  in conjunction with the rotations of the respective left-hand fixing members  152 , and the respective preventive members  191  rotate in such a manner that their distal end portions are lowered to move to positions where the operating portions  171  is brought into abutment with the bent portions at the distal end portions. As a result, the process cartridges  3  move downwards and as is indicated by a broken line in  FIG. 7 , the protecting portions  30  are brought into the abutment portions  72 ,  73 , whereby the process cartridges  3  are fixed in place in the positions. 
     On the other hand, the distal end portions of the respective connecting shafts  186  of the right-hand link members  184  are fitted in the intersecting groove portions  163 . Accordingly, when the connecting and disconnecting translation cam  153  moves rearwards, the distal end portions of the connecting shafts  186  move to the rear along the linear hole portions  81  (refer to  FIG. 22 ) of the guide holes  80  on the body frame  63  while kept fitted in the intersecting holes  163 . Thus, the respective link members  184  rotate in such a manner that the one end portions thereof are lifted upwards, and the respective right-hand fixing members  172  rotate to the rear about the projecting portions  79  (refer to  FIG. 23 ) which are formed on the body frame  63  in conjunction with the rotation of the link members  184 . As a result, as is shown in  FIG. 22 , the respective right-hand fixing members  172  are put in the locked state, whereby the front end portions of the cutout portions  178  of the lock levers  174  are brought into abutment with the drum shafts  45 , respectively, and the drum shafts  145  are pressed obliquely downwards and rearwards. Accordingly, the photosensitive drums  5  are fixed in place at the left- and right-hand sides thereof. 
     In addition, in the course of the cop cover  4  being closed, the driving translation cam  94  is brought into contact with the clutch engaging lever  215 , and the distal end portion of the clutch engaging lever  215  is pushed downwards by the driving translation cam  94 , whereby the clutch engaging lever  215  is brought into engagement with the engagement gear  218 . Accordingly, after the top cover  4  has been closed, the connecting and disconnecting translation cam  153  can be caused to move by virtue of the driving force of the connecting and disconnecting motor  229  (refer to  FIG. 27 ). 
     In addition, in the course of the cop cover  4  being closed, when the driving translation cam  94  moves forwards, the respective drum drive transmission members  92  and the reciprocating members  112  of the respective developing drive transmission members  93  advance to the advanced positions. The drum drive transmission members  92  are connected, respectively, to the connecting members  47 , and the reciprocating members  112  are connected, respectively, to the developing roller drive gears  61 . As a result, the photosensitive drums  5  and the developing rollers  8  are allowed to be driven to rotate. 
     When the top cover  4  is opened from the closed state, the respective members and portions of the printer  1  perform opposite operations to the operations performed when the top cover is closed. In addition, the left-hand fixing members  152  and the right-hand fixing members  172  are put in the unlocked state where the process cartridges  3  are not fixed. 
     10. Connecting and Disconnecting Operations of Developing Rollers to and from Photosensitive Drums 
       FIGS. 27 to 29  are left side views of the process cartridges, the locking mechanism and the connecting/disconnecting drive mechanism.  FIG. 27  shows a state in which all the developing rollers are in contact with the photosensitive drums,  FIG. 28  shows a state in which the yellow, magenta and cyan developing rollers are spaced apart from the photosensitive drums, and  FIG. 29  shows a state in which all the developing rollers are spaced apart from the photosensitive rollers. 
     In such a state that the top cover  4  is closed, the connecting and disconnecting translation cam  153  can be caused to move by the driving force of the connecting and disconnecting motor  229  (refer to  FIG. 27 ). By the top cover  4  being closed, the connecting and disconnecting translation cam  153  moves, and after the connecting shafts  183  of the left-hand link members  181  have reached the intersecting holes  77  (refer to  FIG. 7 ) of the guide holes  75  of the body frame  62 , even though the connecting and disconnecting translation cam  153  is caused to move rearwards further, the distal end portions of the connecting shafts  183  move within the linear groove portions  162  (refer to  FIG. 24 ) of the guide grooves  161 , and the postures of the link members  181  do not change. In addition, after the connecting shafts  186  of the right-hand link members  184  have reached the intersecting hole portions  82  (refer to  FIG. 23 ) of the guide holes  80  on the body frame  63 , even though the connecting and disconnecting translation cam  153  is caused to move rearwards further, the distal end portions of the connecting shafts  186  move within the linear groove portions  162  of the guide grooves  161 , and the postures of the link members  184  do not change. Accordingly, in such a state that the top cover is closed, the state can be maintained in which the process cartridges  3  are fixed. 
     In a state after the top cover  4  has been closed, as is shown in  FIG. 25 , the spacing members  201  are in positions at which the lower projecting portions  203  are brought into abutment with the upper surface  350  (refer to  FIG. 24 ) of the connecting and disconnecting translation cam  153  (but are not brought into abutment with the third cam portions  164 ) and the upper projecting portions  204  are lowered relatively downwards (permissive positions). Accordingly, as is shown in  FIG. 27 , the respective upper projections  204  of the spacing members  201  are spaced apart from the developing roller shaft bearing members  57 ,  58  which project both leftwards and rightwards from the developing cartridges  9 , whereby a state results in which the developing rollers  8  (refer to  FIG. 1 ) are in contact with the photosensitive drums  5  (refer to  FIG. 1 ). 
     When the connecting and disconnecting translation cam  153  is caused to move rearwards from this state, the lower projecting portions  203  of the spacing members  201  which correspond to the yellow process cartridge  3 Y, the magenta process cartridge  3 M and the cyan process cartridge  3 C move on the inclined surfaces  166  of the third cam portions  164  to move from the horizontal planes  165  to the inclined surfaces  166 . Accordingly, the spacing members  201  are put in positions (spaced apart positions) where the lower projecting portions  203  are brought into abutment with the horizontal surfaces  165  while the upper projecting portions  204  are lifted upwards relatively, as is shown in  FIG. 26 . Accordingly, as is shown in  FIG. 28 , the pressing surfaces  205  of the upper projecting portions  204  press against the developing roller shaft bearing members  57 ,  58  of the yellow, magenta and cyan developing cartridges  9  from therebelow in such a state that the pressing surfaces extend along the up-down direction from the rear, whereby the yellow, magenta and cyan developing cartridges  9  are lifted upwards, and the developing rollers  8  which are equipped on the developing cartridges  9  are spaced apart from the photosensitive rollers  5 . As this occurs, the developing roller  8  equipped on the black developing cartridge  9  is kept in contact with the mating photosensitive drum  5 . 
     When the connecting and disconnecting translation cam  153  is caused to move rearwards further from this state, the lower projecting portion  203  of the spacing member  201  which corresponds to the black process cartridge  3 K moves on the inclined surface  166  of the third cam portion  164  to move from the horizontal surface  165  on to the inclined surface  166 , whereby the spacing member  201  is put in a position (a spaced apart position) in which the lower projecting portion  203  is brought into abutment with the horizontal surface  165  and the upper projecting portion  204  is lifted relatively upwards. As a result of this, as is shown in  FIG. 29 , the pressing surfaces  205  of the upper projecting portions  204  press against the developing roller shaft bearing members  57 ,  58  of the black developing cartridge  9  from therebelow in such a state that the pressing surfaces extend along the up-down direction from the rear, whereby the black developing cartridge  9  is lifted upwards, and eventually, the developing rollers  8  are spaced apart from the photosensitive rollers  5 . 
     Although the developing cartridges  9  are caused to move vertically in such a state that the reciprocating members  112  are connected, respectively, to the developing roller drive gears  61 , since the diameters in the front-rear direction of the elongated holes  36  into which the reciprocating members  112  are inserted are formed long, there occurs no situation in which the connection of the reciprocating members  112  with the developing roller drive gears  61  disturbs the vertical movement of the developing cartridges  9 . 
     11. Advantage 
     Thus, as has been described heretofore, the process cartridge  3  includes the developing roller drive gear  61 . The developing drive transmission member  93  is brought into engagement with the developing roller drive gear  61 , so that the driving force is transmitted from the developing drive transmission member  93  to the developing roller drive gear  61 . 
     The developing drive transmission member  93  includes the guide core member  115 , the reciprocating member  112  and the pressing member  113 . The guide core member  115  is inserted into the reciprocating member  112  from the upstream side in the engagement direction of the developing drive transmission member  93  with the developing roller drive gear  61 . The pressing member  113  is interposed between the guide core member  115  and the reciprocating member  112  so as to connect together the guide core member  115  and the reciprocating member  112 . 
     The guide core member  115  has the distal end core portion  116  and the proximal end core portion  117 . The distal end core portion  116  is formed at the end portion of the guide core member  115  which lies at the downstream side in the engagement direction. The outside diameter (the first core diameter) of the distal end core portion  116  is made smaller than the outside diameter (the second core diameter) of the proximal end core portion  117 . 
     The reciprocating member  112  has the distal end cylindrical portion  118  and the proximal end cylindrical portion  119 . The proximal end cylindrical portion  119  is formed upstream of the distal end cylindrical portion  118  in the engagement direction. The inside diameter (the first inside diameter) of the distal end cylindrical portion  118  is made smaller than the inside diameter (the second inside diameter) of the proximal end cylindrical portion  119 . 
     In such a state that the reciprocating member  112  is pushed to the guide core member  115  side against the pressing force of the pressing member  113  so as to disengage the engagement between the developing drive transmission member  93  (the reciprocating member  112 ) and the developing roller drive gear  61 , the distal end core portion  116  of the guide core member  115  is disposed within the distal end cylindrical portion  118  of the reciprocating member  112 , and the proximal end core portion  117  of the guide core member  115  is disposed within the proximal end cylindrical portion  119  of the reciprocating member  112 . Because of this, the reciprocating member  112  has no large radial play relative to the guide core member  115 . 
     When the force acting to push the reciprocating member  112  to the guide core member  115  side is released from this state, the reciprocating member  112  is caused to move towards the developing roller drive gear  61  by the pressing force of the pressing member  113 . In the event that the distal end core portion  116 , the proximal end core portion  117 , the distal end cylindrical portion  118  and the proximal end cylindrical portion  119  each have an appropriate dimension in the engagement direction, by the distal end core portion  116  being disposed within the distal end cylindrical portion  118  and the proximal end core portion  117  being disposed within the proximal end cylindrical portion  119 , the reciprocating member  112  starts to engage with the developing roller drive gear  61  while the reciprocating member  112  continues to have no large play relative to the guide core member  115 , whereby an ensured engagement of the reciprocating member  112  with the developing roller drive gear  61  can be attained. 
     Namely, in the event that the reciprocating member  112  has a large play relative to the guide core member  115  at a point in time when the reciprocating member  112  starts to engage with the developing roller drive gear  61 , the reciprocating member  112  is inclined largely relative to the guide core member  115 , whereby a distal end of the reciprocating member  112  is oriented to a position where the distal end of the reciprocating member  112  is offset from the developing roller drive gear  61 , and there may occur a case where the engagement of the reciprocating member  112  with the developing roller drive gear  61  fails to be attained. In contrast to this, in such a state that the distal end core portion  116  is disposed within the distal end cylindrical portion  118  and the proximal end core portion  117  is disposed within the proximal end cylindrical portion  119 , the reciprocating member  112  has a small play relative to the guide core member  115 , and since there occurs no case where the cylindrical portion is inclined largely relative to the guide core member  115 , by the state being maintained until the reciprocating member  112  starts to engage with the developing roller drive gear  61 , the distal end of the reciprocating member  112  can be prevented from being oriented to the position where the distal end of the reciprocating member  112  is offset from the developing roller drive gear  61 . As a result of this, an ensured engagement of the reciprocating member  112  with the developing roller drive gear  61  can be attained. 
     In addition, in the event that the distal end core portion  116 , the proximal end core portion  117 , the distal end cylindrical portion  118  and the proximal end cylindrical portion  119  each have the appropriate dimension in the engagement direction, the distal end core portion  116  of the guide core member  115  is disposed within the proximal end cylindrical portion  119  of the reciprocating member  112  in such a state that the engagement of the reciprocating member  112  with the developing roller drive gear  61  is completed, whereby the radial play of the reciprocating member  112  relative to the guide core member  115  is increased. As a result of this, since the engagement of the reciprocating member  112  with the developing roller drive gear  61  is maintained even in the event that there is caused a positional gap of the developing roller drive gear  61  within a range of radial play of the reciprocating member  112  relative to the guide core member  115 , the driving force can be transmitted from the developing drive transmission member  93  to the developing roller drive gear  61 . 
     In addition, the preventive member  191  is provided in such a manner as to move between the preventive position where the preventive member  191  is disposed on the mounting/dismounting path of the process cartridge  3  within the apparatus main body  2  and the retreating position where the preventive member  191  is caused to retreat from the mounting/dismounting path. When the process cartridge  3  is mounted in the apparatus main body  2 , in the event that the preventive member  191  exists at the preventive position, in the course of the process cartridge  3  being so mounted, the movement of the process cartridge  3  in the mounting direction is prevented by the preventive member  191 . This mounting preventive state is released by the preventive member  191  being caused to move from the preventive position to the permissive position. After the mounting preventive state has been so released, when the process cartridge  3  is caused to move in the mounting direction further, the process cartridge  3  is brought into abutment with the abutment portion provided on the body frame. 
     By this configuration, even though the process cartridge  3  is inserted into the apparatus main body  2  with force, since the process cartridge  3  can be prevented from being brought into strong abutment with the abutment portion, it is possible to prevent impact from being applied to the abutment portion. 
     In addition, even though there is caused a positional gap of the developing roller drive gear within the predetermined range (within the range of radial play of the reciprocating member  112  relative to the guide core member  115 ), since the engagement of the developing drive transmission member  93  with the developing roller drive gear  61  is maintained, even though the developing drive transmission member  93  is brought into engagement with the developing roller drive gear  61  and thereafter, the process cartridge  3  is caused to move to a position where the process cartridge  3  is brought into abutment with the abutment portion when the movement of the process cartridge  3  is prevented by the preventive member  191 , the state can be maintained in which the developing drive transmission member  93  is in engagement with the developing roller drive gear  61 . 
     Furthermore, in the configuration in which the plurality of process units  3  are provided, an all-at-once engagement or disengagement of the plurality of developing drive transmission members  93  with or from the plurality of developing roller drive gears  61  can be attained by a simple operation or a reciprocating straight-line movement of the driving translation member  94 . 
     In addition, as is shown in  FIG. 10 , since the moving direction (the front-rear direction) of the driving translation member  94  intersects the engagement direction (the width direction) of the developing drive transmission member  93  at substantially right angles, an external force directed in the moving direction of the driving translation member  94  may be exerted on the reciprocating member  112  of the developing drive transmission member  93  in conjunction with the movement of the driving translation member  94 . Even in the event that such actually occurs, however, according to the configuration of the invention, an ensured engagement of the reciprocating member  112  with the developing roller drive gear  61  (refer to  FIG. 3 ) can be attained. 
     12. Other Embodiments 
     While in the embodiment, the tandem type color printer  1  has been taken for description of the invention, the invention can also be applied to a multi-path intermediate belt transfer color printer in which toner images of respective colors are transferred on to an intermediate transfer belt from respective image carrier and thereafter the color images are transferred altogether on to a sheet from the intermediate transfer belt. 
     In addition, the invention can also be applied to a monochrome printer. 
     Further,  FIG. 30  shows a sectional view of the reciprocating member  112  and the guide core part  115 . As shown in  FIG. 30 , a length (L 1 ) of the distal end cylindrical part  118  is shorter than a length (L 3 ) of the distal end core portion  116  in the engagement direction of the developing drive transmission member  93  with the developing roller drive gear  61 . Further, as shown in  FIG. 30 , a length (L 2 ) of the cylindrically shaped proximal end cylindrical part  119  is shorter than a length (L 3 ) of the proximal end core portion  117  in the engagement direction of the developing drive transmission member  93  with the developing roller drive gear  61 . According to this configuration, in such a state that the distal end core portion  116  is disposed within the distal end cylindrical portion  118  and the proximal end core portion  117  is disposed within the proximal end cylindrical portion  119 , the reciprocating member  112  has a small play relative to the guide core member  115 , and since there occurs no case where the cylindrical portion is inclined largely relative to the guide core member  115 , by the state being maintained until the reciprocating member  112  starts to engage with the developing roller drive gear  61 , the distal end of the reciprocating member  112  can be prevented from being oriented to the position where the distal end of the reciprocating member  112  is offset from the developing roller drive gear  61 . As a result of this, an ensured engagement of the reciprocating member  112  with the developing roller drive gear  61  can be attained. Further, according to this configuration, the distal end core portion  116  of the guide core member  115  is disposed within the proximal end cylindrical portion  119  of the reciprocating member  112  in such a state that the engagement of the reciprocating member  112  with the developing roller drive gear  61  is completed, whereby the radial play of the reciprocating member  112  relative to the guide core member  115  is increased. As a result of this, since the engagement of the reciprocating member  112  with the developing roller drive gear  61  is maintained even in the event that there is caused a positional gap of the developing roller drive gear  61  within a range of radial play of the reciprocating member  112  relative to the guide core member  115 , the driving force can be transmitted from the developing drive transmission member  93  to the developing roller drive gear  61 . 
     As described above, according to a first aspect of the invention, there is provided an image forming apparatus including an apparatus main body, a process unit provided in the apparatus main body and having a drive input member, and a drive transmission member provided in the apparatus main body and adapted to be brought into engagement with the drive input member so as to transmit a driving force to the drive input member while permitting a positional gap of the drive input member within a predetermined range, wherein the drive transmission member includes a guide core member having a distal end core portion which is formed at an end portion lying a downstream side in an engagement direction of the drive transmission member with the drive input member and which has a first outside diameter and a proximal end core portion which is formed upstream of the distal end core portion in the engagement direction and which has a second outside diameter which is larger than the first outside diameter, a reciprocating member having a distal end cylindrical portion which has a first inside diameter and a proximal end cylindrical portion which is formed upstream of the distal end cylindrical portion in the engagement direction and which has an inside diameter which is larger than the first inside diameter and configured in such a manner that the guide core member is inserted thereinto in the engagement direction, and a pressing member interposed between the guide core member and the reciprocating member for connecting together the guide core member and the reciprocating member. 
     According to a second aspect of the invention, there is provided an image forming apparatus as set forth in the first aspect of the invention, wherein the process unit is a process cartridge made to be detachably mounted in the apparatus main body and includes a body frame provided in the apparatus main body and having an abutment portion which is brought into abutment with the process cartridge, and a preventive member disposed on a mounting/dismounting path of the process cartridge in the apparatus main body and provided in such a manner as to move between a preventive position where the preventive member prevents the abutment of the process cartridge with the abutment portion and a permissive position where the preventive member retreats from the mounting/dismounting path so as to permit the abutment of the process cartridge with the abutment portion. 
     According to a third aspect of the invention, there is provided an image forming apparatus as set forth in the first or second aspect of the invention, wherein there are provided a plurality of process units like the process unit in such a manner that the plurality of process units are aligned in parallel with one another in the apparatus main body, wherein there are provided a plurality of drive transmission members like the drive transmission member in such a manner as to be associated with the process units, and including a driving translation member provided in such a manner as to move in a straight line in a direction in which the process units are aligned for causing the respective drive transmission members to advance or retreat in the engagement direction altogether by its reciprocating straight-line movements. 
     According to a fourth aspect of the invention, there is provided an image forming apparatus as set forth in the third aspect of the invention, wherein a moving direction of the driving translation member intersects the engagement direction of the drive transmission member at substantially right angles. 
     According to the first aspect of the invention, the process unit includes the drive input member. The drive transmission member is brought into engagement with the drive input member, so that the driving force is transmitted from the drive transmission member to the drive input member. 
     The drive transmission member includes the guide core member, the reciprocating member and the pressing member. The guide core member is inserted into the reciprocating member from the upstream side of the engagement direction of the drive transmission member with the drive input member. The pressing member is interposed between the guide core member and the reciprocating member so as to connect together the guide core member and the reciprocating member. 
     The guide core member has the distal end core portion and the proximal end core portion. The distal end core portion is formed at the end portion of the guide core member which lies on the downstream side in the engagement direction. The outside diameter (the first core diameter) is made smaller than the outside diameter (the second core diameter) of the proximal end core portion. 
     The reciprocating member has the distal end cylindrical portion and the proximal end core portion. The proximal end cylindrical portion is formed upstream of the distal end cylindrical portion in the engagement direction. The inside diameter (a first inside diameter) of the distal end cylindrical portion is made smaller than the inside diameter (a second inside diameter) of the proximal end cylindrical portion. 
     In such a state that the reciprocating member is pushed to the guide core member side against the pressing force of the pressing member so as to disengage the engagement between the drive transmission member (the reciprocating member) and the drive input member, the distal end core portion of the guide core member is disposed within the distal end cylindrical portion of the reciprocating member, and the proximal end core portion of the guide core member is disposed within the proximal end cylindrical portion of the reciprocating member. Because of this, the reciprocating member has no large radial play relative to the guide core member. 
     When the force acting to push the reciprocating member to the guide core member side is released from this state, the reciprocating member is caused to move towards the drive input member by the pressing force of the pressing member. In the event that the distal end core portion, the proximal end core portion, the distal end cylindrical portion and the proximal end cylindrical portion each have an appropriate dimension in the engagement direction, by the distal end core portion being disposed within the distal end cylindrical portion and the proximal end core portion being disposed within the proximal end cylindrical portion, the reciprocating member starts to engage with the drive input member while the reciprocating member continues to have no large radial play relative to the guide core member, whereby an ensured engagement of the reciprocating member with the drive input member can be attained. 
     Namely, in the event that the reciprocating member has a large play relative to the guide core member at a point in time when the reciprocating member starts to engage with the drive input member, the reciprocating member is inclined largely relative to the guide core member, whereby a distal end of the reciprocating member is oriented to a position where the distal end of the reciprocating member is offset from the drive input member, and there may occur a case where the engagement of the reciprocating member with the drive input member fails to be attained. In contrast to this, in such a state that the distal end core portion is disposed within the distal end cylindrical portion and the proximal end core portion is disposed within the proximal end cylindrical portion, the reciprocating member has a small play relative to the guide core member, and since there occurs no case where the cylindrical portion is inclined largely relative to the guide core member, by the state being maintained until the reciprocating member starts to engage with the drive input member, the distal end of the reciprocating member can be prevented from being oriented to the position where the distal end of the reciprocating member is offset from the drive input member. As a result, an ensured engagement of the reciprocating member with the drive input member can be attained. 
     In addition, in the event that the distal end core portion, the proximal end core portion, the distal end cylindrical portion and the proximal end cylindrical portion each have the appropriate dimension in the engagement direction, the distal end core portion of the guide core member is disposed within the proximal end cylindrical portion of the reciprocating member in such a state that the engagement of the reciprocating member with the drive input member is completed, whereby the radial play of the reciprocating member relative to the guide core member is increased. As a result of this, since the engagement of the reciprocating member with the drive input member is maintained even in the event that there is caused a positional gap of the drive input member within a range of radial play of the reciprocating member relative to the guide core member, the driving force can be transmitted from the drive transmission member to the drive input member. 
     According to the second aspect of the invention, the preventive member is provided in such a manner as to move between the preventive position where the preventive member is disposed on the mounting/dismounting path of the process cartridge within the apparatus main body and the retreating position where the preventive member is caused to retreat from the mounting/dismounting path. When the process cartridge is mounted in the apparatus main body, in the event that the preventive member exists at the preventive position, in the course of the process cartridge being so mounted, the movement of the process cartridge in the mounting direction is prevented by the preventive member. This mounting preventive state is released by the preventive member being caused to move from the preventive position to the permissive position. After the mounting preventive state has been so released, when the process cartridge is caused to move in the mounting direction further, the process cartridge is brought into abutment with the abutment portion provided on the body frame. 
     By this configuration, even though the process cartridge is inserted into the apparatus main body with force, since the process cartridge can be prevented from being brought into strong abutment with the abutment portion, it is possible to prevent impact from being applied to the abutment portion. 
     In addition, even though there is caused a positional gap of the drive input member within the predetermined range (within the range of radial play of the reciprocating member relative to the guide core member), since the engagement of the drive transmission member with the drive input member is maintained, even though the drive transmission member is brought into engagement with the drive input member and thereafter, the process cartridge is caused to move to a position where the process cartridge is brought into abutment with the abutment portion when the movement of the process cartridge is prevented by the preventive member, the state can be maintained in which the drive transmission member is in engagement with the drive input member. 
     According to the third aspect of the invention, in the configuration in which the plurality of process units are provided, an all-at-once engagement or disengagement of the plurality of drive transmission members with or from the plurality of drive input members can be attained by a simple operation or a reciprocating straight-line movement of the driving translation member. 
     According to the fourth aspect of the invention, since the moving direction of the driving translation member intersects the engagement direction of the drive transmission member at substantially right angles, although an external force directed in the moving direction of the driving translation member may be exerted on the reciprocating member of the drive transmission member in conjunction with the movement of the driving translation member, even in the event that such actually occurs, according to the configuration of the fourth aspect of the invention, an ensured engagement of the reciprocating member with the drive input member can be attained. 
     While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.