Abstract:
The image forming apparatus is provided with: plural rotating members that are arranged rotatably; plural rotation side coupling members that are provided corresponding to the respective rotating members and transmit drive force to the respective rotating members; plural drive side coupling members that are connected to the respective rotation side coupling members and rotate and drive the respective rotating members via the rotation side coupling members; and an interconnecting unit that connects a predetermined number of the drive side coupling members among the plural drive side coupling members to the corresponding rotation side coupling members.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC §119 from Japanese Patent Application No. 2007-212851 filed Aug. 17, 2007. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image forming apparatus such as a printer and a copy machine, and a drive-switching method. 
     2. Related Art 
     In an image forming apparatus of so-called tandem system having photoconductor drums for respective colors, image formation in full colors is not always required, but image formation in a single color (for example, black) is required in some cases. In such cases, if photoconductor drums that are not used in the image formation are rotated, abrasion and the like of the photoconductor drums are facilitated by a cleaning blade and the like. 
     SUMMARY 
     According to an aspect of the invention, there is provided an image forming apparatus including: plural rotating members that are arranged rotatably; plural rotation side coupling members that are provided corresponding to the respective rotating members and transmit drive force to the respective rotating members; plural drive side coupling members that are connected to the respective rotation side coupling members and rotate and drive the respective rotating members via the rotation side coupling members; and an interconnecting unit that connects a predetermined number of the drive side coupling members among the plural drive side coupling members to the corresponding rotation side coupling members. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a view that shows an entire configuration of an image forming apparatus to which the first exemplary embodiment is applied; 
         FIG. 2  is a view that shows the image forming apparatus with the cover opened; 
         FIGS. 3A and 3E  are explanatory views each showing details around the paper transportation belt; 
         FIG. 4  is a perspective view that shows one side of the image forming unit; 
         FIG. 5  is a perspective view that shows the image forming units and the like viewed from the drive unit side; 
         FIG. 6  is a perspective view that shows the switching unit and the like viewed from the drive unit side; 
         FIG. 7  is a perspective view that shows the first movable plate, the second movable plate, and the advancing/retreating members; 
         FIG. 8  is a view that shows the inside of the switching unit in the first state; 
         FIG. 9  is an enlarged view that shows the peripheral of the drive side coupling member in  FIG. 8 ; 
         FIG. 10  is a perspective view that shows the advancing/retreating members, the first movable plate and the second movable plate after the first drive gear is rotated and driven; 
         FIG. 11  is a perspective view that shows the switching unit and the like after the first drive gear is rotated and driven, viewed from the drive unit side; 
         FIG. 12  is a view that shows the inside of the storing portion in the second state; 
         FIG. 13  is a side view that shows the side portion of the switching unit, including the cover and the like; 
         FIGS. 14A and 14B  are views for explaining the rotation mechanism; 
         FIGS. 15A to 15E  are views for explaining the operation of the rotation mechanism; 
         FIG. 16  is a view that shows the side portion of the switching unit when the rotation mechanism is in the state of  FIG. 15B ; 
         FIG. 17  is a view that shows the side portion of the switching unit; 
         FIG. 18  is a view that shows the inside of the switching unit; 
         FIG. 19  is a view that shows the side portion of the switching unit; 
         FIG. 20  is a view that shows the state after the downward sliding of the first movable plate and the second movable plate is completed; 
         FIG. 21  is a view that schematically shows the image forming apparatus in the second exemplary embodiment. 
         FIG. 22  shows the state after the sliding member is slid by the drive apparatus; and 
         FIG. 23  shows the state after the cover is opened from the state shown in  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the first exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a view that shows an entire configuration of an image forming apparatus  1  to which the first exemplary embodiment is applied. The image forming apparatus  1  shown in  FIG. 1  is what is termed as a tandem-type digital color printer with electrophotography, and includes an image forming process unit  24  that forms an image in response to image data of each color, inside of a cover  2  and an apparatus main body  3 . Further, the image forming apparatus  1  includes a controller  22  that controls operations of respective portions and apparatuses provided in the image forming apparatus  1 . Furthermore, the image forming apparatus  1  includes a image processing unit  21  that performs certain image processing on image data received from, for example, a personal computer (PC)  5 , an image reading apparatus  6  such as a scanner and the like, and a main memory  23  that is realized by, for example, a hard disk (hard disk drive) on which processing programs, image data and the like are recorded. 
     In the image forming process unit  24 , four image forming units  10 Y,  10 M,  10 C and  10 K (hereinafter, collectively referred to as the “image forming unit 10”) are arranged in parallel at a fixed interval in the up and down direction. The image forming unit  10  is provided with a photoconductor drum  11  serving as a rotating member and an image carrier, an electrically charging roll  12  that electrically charges a surface of the photoconductor drum  11 , a developing unit  13  that develops an electrostatic latent image formed on the photoconductor drum  11  by each color toner, and a drum cleaner  14  that cleans the surface of the photoconductor drum  11  after transfer. 
     The image forming unit  10  is arranged to be exchangeable (detachable) from the apparatus main body  3 . For example, in the case where the toner within the developing unit  13  is consumed, the photoconductor drum  11  comes to the end of the life or the like, each of the image forming units  10  is exchanged. It should be noted that, in order to make the exchange easier and the like, the image forming unit  10  is equipped with a grasp portion  17 that is grasped by a user. 
     The electrically charging roll  12  is formed by a roll member in which a conductive elastic-body layer and a conductive surface layer are laminated on a conductive core such as aluminum and stainless steel. The electrically charging roll  12  receives an electrically charging bias voltage from an electrically charging power source (not shown in the figure), and while rotating driven by the photoconductor drum  11 , electrically charges the surface of the photoconductor drum  11  uniformly at a fixed potential. 
     In each image forming unit  10 , the developing unit  13  holds a two-component developer including each color toner of yellow (Y), magenta (M), cyan (C) and black (K) and a magnetic carrier, and develops the electrostatic latent image formed on the photoconductor drum  11  by each color toner. 
     The drum cleaner  14  brings a plate member that is formed by a rubber material such as urethane rubber into contact with the surface of the photoconductor drum  11 , and removes the toner, paper dust and the like that are adhered on the photoconductor drum  11 . 
     Moreover, in the image forming apparatus  1  according to the first exemplary embodiment, a laser exposing unit  20  that exposes the photoconductor drum  11  arranged respectively in each image forming unit  10  is provided. The laser exposing unit  20  acquires image data for each color from an image processing unit  21 . By laser beam that is controlled for lighting on the basis of the acquired image data, the laser exposing unit  20  scans and exposes the surface of the photoconductor drum  11  of each image forming unit  10 , respectively. 
     Further, so as to move while being in contact with the photoconductor drum  11  of each image forming unit  10 , a paper transportation belt  30  that transports paper P serving as a recording medium (recording paper) is arranged in the image forming apparatus  1  of the first exemplary embodiment. The paper transportation belt  30  is formed by an endless belt in a film shape that electrostatically absorbs the paper P. The paper transportation belt  30  is hanged between an idle roll  32  and a drive roll  33  and cyclically moved. Between the paper transportation belt  30  and the photoconductor drum  11 , a paper transportation route M 1  is formed for transporting the paper P from the lower side to the upper side in the substantially vertical direction. 
     In positions inside the paper transportation belt  30  and opposed to each photoconductor drum  11 , transfer rolls  31   y ,  31   m ,  31   c  and  31   k  (hereinafter, collectively referred to as the “transfer roll 31”) are arranged. Each transfer roll  31  forms a transfer electric field between the transfer roll  31  and the photoconductor drum  11  so as to successively transfer a toner image of each color that is formed in each image forming unit  10  on the paper P that is held and transported by the paper transportation belt  30 . Moreover, on the outside of the paper transportation belt  30 , and on the downstream side of each transfer roll  31 , a discharge lamp (not shown in the figure) that removes electricity of the photoconductor drum  11  after the transfer is provided. 
     In the most upstream portion on the side where the photoconductor drum  11  of the paper transportation belt  30  is located, an absorption roll  34  that electrically charges the paper transportation belt  30  is arranged. The absorption roll  34  electrically charges a surface of the paper transportation belt  30  at a predetermined potential so that the paper P is stably electrostatically absorbed. 
     On the downstream side of the paper transportation belt  30  on the paper transportation route M 1 , a fixing unit  28  that performs a fixing treatment to a non-fixed toner image on the paper P with heat and pressure is provided. 
     Further, as a paper transportation system other than the paper transportation belt  30 , on the paper supplying side, a paper housing unit  50  that houses the paper P, a pickup roll  51  that takes out the paper P housed in the paper housing unit  50  at a predetermined timing and transports the paper P, a transportation roll  52  that transports the paper P brought by the pickup roll  51 , and a resist roll  53  that feeds the paper P to the paper transportation belt  30  corresponding to an image forming operation are provided. 
     Meanwhile, on the paper exit side, a paper exit roll  54  that transports the paper P fixed in the fixing unit  28  is provided. Additionally, on the paper exit side, a reverse roll  55  is provided The reverse roll  55 , in the case of single side printing, discharges the paper P to a paper exit unit  57  provided on an upper portion of the apparatus main body  3 , whereas the reverse roll  55 , in the case of both-side printing, rotates in the reverse direction so as to feed the paper P whose one side surface is fixed in the fixing unit  28  to a both-side transportation route M 2 . In addition, in the both-side transportation route M 2 , plural transporting rolls  56  are provided along the both-side transportation route M 2 . 
     In the image forming apparatus  1  according to the first exemplary embodiment, the image forming process unit  24  performs the image forming operation under control by a controller  22 . Specifically, the image processing unit  21  performs a predetermined image processing to the image data inputted from PC  5 , an image reading apparatus  6  or the like, and the image data is supplied to the laser exposing unit  20 . Then, for example, in the image forming unit  10 K of black (K), the surface of the photoconductor drum  11  that is uniformly electrically charged by the electrically charging roll  12  at a predetermined potential is scanned and exposed with the laser beam that is controlled for lighting by the laser exposing unit  20  on the basis of the image data from the image processing unit  21 , and the electrostatic latent image is formed on the photoconductor drum  11 . The formed electrostatic latent image is developed by the developing unit  13 , and on the photoconductor drum  11 , a toner image of black (K) is formed. In the image forming units  10 Y,  10 M and  10 C, in a similar manner, toner images of each color of yellow (Y), magenta (M) and cyan (C) are formed. 
     Meanwhile, when formation of the toner image of each color in each image forming unit  10  is started, the paper P that is taken out from the paper housing unit  50  is supplied to the paper transportation belt  30  by the resist roll  53  corresponding to a formation timing of the toner image. The surface of the paper transportation belt  30  is electrically charged by the absorption roll  34  at a predetermined potential. Thereby, the paper P is electrostatically absorbed on the paper transportation belt  30 . By the paper transportation belt  30  that is cyclically moved in the arrow direction of  FIG. 1 , the paper P is transported along the paper transportation route M 1 . In the middle course of the transportation, by the transfer electric field that is formed by the transfer roll  31 , the toner image of each color is successively transferred on the paper P. 
     The paper P where the toner image of each color is electrostatically transferred is detached from the paper transportation belt  30  on the downstream of the image forming unit  10 K, and transported to the fixing unit  28 . When the paper P is transported to the fixing unit  28 , the non-fixed toner image on the paper P is fixed to the paper P by receiving the fixing treatment with heat and pressure. The paper P where the toner image of each color is fixed is loaded in the paper exit unit  57  that is provided in an exit portion of the image forming apparatus  1 . Meanwhile, at the time of both-side printing, after a similar image forming operation is performed again via the both-side transportation route M 2 , the paper P is loaded in the paper exit unit  57 . 
     Further, the image forming apparatus  1  is explained. 
       FIG. 2  is a view that shows the image forming apparatus  1  with the cover  2  opened. 
     As mentioned above, the image forming apparatus  1  according to the first exemplary embodiment is provided with the cover  2  and the apparatus main body  3 . This cover  2  is arranged so as to be openable and closable to the apparatus main body  3  around a fulcrum  4  which is provided on the lower side. Further, to the cover  2 , the paper transportation belt  30 , the transfer roll  31 , the idle roll  32 , the drive roll  33 , and the absorption roll  34  and the like are attached. Therefore, when the cover  2  is opened, as shown in the figure, the paper transportation belt  30 , the transfer roll  31 , and the idle roll  32  and the like follow the cover  2 . As a result, when the cover  2  is opened, the image forming unit  10  is in an exposed state, and the user and the like may access the paper transportation route M 1 . Here, the image forming unit  10 , as mentioned above, is arranged to the apparatus main body  3  so as to be exchangeable, and when toner in the developing unit  13  is consumed, the image forming unit  10  is exchanged as a unit. In addition, the image forming apparatus  1  in the first exemplary embodiment is provided with a sensor (not shown in the figure) that performs a predetermined output when the cover  2  is closed. 
     Here,  FIGS. 3A and 3B  are explanatory views each showing details around the paper transportation belt  30 . In the image forming apparatus  1  according to the first exemplary embodiment, when an image formation is carried out by use of the image formation units  10 Y,  10 M,  10 C and  10 K of yellow (Y), magenta (M), cyan (C) and black (K), that is, when an image formation in full colors is carried out, the paper transportation belt  30  is arranged so as to be brought in contact with all the photoconductor drums  11 . Further, when an image formation is carried out by use of the image forming unit  10 K of black (K), that is, an image is formed in a single color, the paper transportation belt  30  is arranged so as to be separated from the photoconductor drums  11  in the image forming units  10 Y,  10 M and  10 C. 
     In more particular, as shown in  FIG. 3A , the image forming apparatus  1  according to the first exemplary embodiment (refer to  FIG. 1 ) is provided with a first supporting part  35   a  that rotatably supports the transfer roll  31   k , and a second supporting part  35   b  that rotatable supports the transfer rolls  31   y ,  31   m  and  31   c , at the inner circumferential side of the paper transportation belt  30 . Further, the image forming apparatus  1  is provided with a cam  38  that is arranged rotatably and functions as a separating unit, and a drive source (not shown in the figure) that rotates and drives the cam  38 . Furthermore, the image forming apparatus  1  is provided with a coil spring  37  that pushes the second supporting part  35   b  to the image forming unit  10  side. 
     The first supporting part  35   a , as mentioned above, is provided with a regulating roll  39   a  that rotatably supports the transfer roll  31   k , and regulates the moving direction of the paper transportation belt  30  that passes the transfer roll  31   k.    
     The second supporting part  35   b  is arranged on the opposite side of the image forming units  10 Y,  10 M and  10 C across the paper transportation belt  30 . Further, the second supporting part  35   b  is provided with an opening hole  35   d  into which the cam  38  is arranged, between the transfer roll  31   y  and the transfer roll  31   m . Furthermore, the second supporting part  35   b  is provided with a regulating roll  39   b  that regulates the moving direction of the paper transportation belt  30  that passes the drive roll  33 , on the upstream side of the transfer roll  31   y  in the moving direction of the paper transportation belt  30 . 
     Meanwhile, between the first supporting part  35   a  and the second supporting part  35   b , a fulcrum  35   c  for rotating (swinging) the second supporting part  35   b  to the first supporting part  35   a  is provided. 
     In the first exemplary embodiment, when an image formation in a single color is carried out by use of the image forming unit  10 K, the cam  38  is rotated clockwise in the figure by use of a drive source (not shown in the figure), and the second supporting part  35   b  is rotated clockwise in the figure against the pushing force by the coil spring  37 . As a result, as shown in  FIG. 3B , the paper transportation belt  30  is separated from the photoconductor drums  11  in the image forming units  10 Y,  10 M and  10 C. Then, when the paper transportation belt  30  is separated from the photoconductor drums  11  in the image forming units  10 Y,  10 M and  10 C, the rotation of the photoconductor drums  11  (photoconductor drums  11  in the image forming units  10 Y,  10 M and  10 C) is stopped by the movement of the paper transportation belt  30 . Meanwhile, when the paper transportation belt  30  is to be made to be brought in contact with the photoconductor drums  11  once again, the cam  38  is rotated counterclockwise in the figure, and the second supporting part  35   b  is rotated counterclockwise in the figure by the coil spring  37 . 
     Here, the photoconductor drums  11  in the image forming unit  10  are rotated by the drive unit and the like which are provided in the apparatus main body  3  (refer to  FIG. 1 ). 
       FIG. 4  is a perspective view that shows one side of the image forming unit  10 . As shown in the figure, in the first exemplary embodiment, to the one side of the image forming unit  10 , a drive unit  40  that rotates and drives the respective photoconductor drums  11  in the image forming unit  10  is arranged. Further, a switching unit  60  that transmits or does not transmit the drive force from the drive unit  40  to the photoconductor drums  11  is arranged. 
     Each of the image forming units  10  in the first exemplary embodiment is provided with, on the side thereof, photoconductor side coupling members  18   y ,  18   m ,  18   c  and  18   k  (hereinafter referred to also as “photoconductor side coupling members 18”) that are attached to the photoconductor drums  11 , rotate interlocking with the photoconductor drums  11 , and serve as an example of rotation side coupling members, a Y-color coupling member, a M-color coupling member, a C-color coupling member and a K-color coupling member. 
     On the other hand, the drive unit  40  is provided with a motor M 3  and drive side coupling members  43   y ,  43   m ,  43   c  and  43   k  that are arranged in correspondence with the respective photoconductor side coupling members  18  and are rotated and driven by the drive force generated by the motor M 3  (hereinafter, referred to also as “drive side coupling members 43”) Each of the drive side coupling members  43  that also functions as an example of a Y-color drive coupling member, a M-color drive coupling member, C-color drive coupling member and K-color drive coupling member is in an exposed state in four slots  62  formed in a housing  61  of the switching unit  60 . Further, the respective drive side coupling members  43  are interconnected with corresponding photoconductor side coupling members  18 . As a result, the respective photoconductor drums  11  are rotated and driven by the drive force from the motor M 3 . 
       FIG. 5  is a perspective view that shows the image forming units  10  and the like viewed from the drive unit  40  side. 
     As shown in the figure, the drive unit  40  in the first exemplary embodiment is provided with four shafts  42   y ,  42   m ,  42   c  and  42   k  that are arranged adjacently in the vertical direction, and rotatably arranged. Further, the drive unit  40  is provided with four gears  41   y ,  41   m ,  41   c  and  41   k  (hereinafter, referred to also as “gears 41”) that are attached to the shafts  42   y ,  42   m ,  42   c  and  42   k  respectively. These gears  41  are arranged in a state where the gears  41  are engaged with transmission gears (not shown in the figure) that transmit the drive force from the motor M 3 , and are rotated and driven by the drive force from the motor M 3 . Thereby, the shafts  42   y ,  42   m ,  42   c  and  42   k  are rotated and driven. 
     On the other hand, the switching unit  60  that functions as an example of an interconnecting unit is provided with a first drive gear  81  as an example of drive member that rotates and drives, and a second drive gear  82  that rotates and drives. Further, the switching unit  60  is provided with a first movable plate  83  that is arranged along the side surface of the housing  61 , receives the drive force from the first drive gear  81  and the like, and slides in the vertical direction. The first movable plate  83  in the first exemplary embodiment functions as an example of a first interconnecting mechanism. 
     Furthermore, the switching unit  60  is provided with a second movable plate  84  that is arranged along the side surface of the housing  61 , receives the drive force from the second drive gear  82  and the like, and slides in the vertical direction. The second movable plate  84  in the first exemplary embodiment functions as one of second interconnecting mechanisms. Further, the switching unit  60  is provided with a holding member  80  that is attached to the apparatus main body  3  side (refer to  FIG. 1 ), and holds the first drive gear  81  and the second drive gear  82  rotatably. 
     Here, the switching unit  60  is explained further in detail. 
       FIG. 6  is a perspective view that shows the switching unit  60  and the like viewed from the drive unit  40  side. Note that in this figure, the illustration of the drive unit  40  (refer to  FIG. 5 ) is omitted. 
     Although details are described later herein, the switching unit  60  is provided with four advancing/retreating members  70   y ,  70   m ,  70   c  and  70   k  (hereinafter, referred to also as “advancing/retreating members 70”) that advance to and retreat from the photoconductor side coupling members  18 , interlocking with the first movable plate  83  and the second movable plate  84 . Further the respective advancing/retreating members  70  are rotatably stored in four storing portions  63   y ,  63   m ,  63   c  and  63   k  (hereinafter, referred to also as “storing portions 63”) that are arranged in parallel in the vertical direction on the side portion of the housing  61 . Furthermore, the switching unit  60  is provided with, at the side portion thereof, a guide (not shown in the figure) that regulates the slide direction of the first movable plate  83  and the second movable plate  84 . In the first exemplary embodiment, the advancing/retreating members  70   y ,  70   m  and  70   c  function as an example of the first interconnecting mechanism, and the advancing/retreating member  70   k  functions as an example of a second interconnecting mechanism. 
     Further, the advancing/retreating members  70  and the like are explained in detail. 
     Herein,  FIG. 7  is a perspective view that shows the first movable plate  83 , the second movable plate  84 , and the advancing/retreating members  70 . 
     As shown in the figure, each of the advancing/retreating members  70  is provided with a ring portion  70   a  that has an opening hole at the center and is formed into a ring shape, an arm portion  70   b  that protrudes outward from the ring portion  70   a , and a opening hole  70   d  that is formed into a long hole shape at the end portion of the arm portion  70   b.    
     On the other hand, the second movable plate  84  is formed into a long and thin plate shape, and is provided with a protruding portion  84   a  that protrudes to the drive unit  40  side and is arranged through the opening hole  70   d  of the advancing/retreating member  70   k , at the drive unit  40  (refer to  FIG. 5 ) and at the upper end. Further, the second movable plate  84  is provided with a rack gear portion  84   e  that engages with the second drive gear  82  (refer to  FIG. 6 ), at one side surface and at the lower end portion. 
     Furthermore, the second movable plate  84  is provided with an upper long hole  84   b  that is made so as to penetrate the second movable plate  84  and formed along the slide direction of the first movable plate  83 , at the lower portion of the protruding portion  84   a . Moreover, the second movable plate  84  is provided with a middle long hole  84   c  that is made so as to penetrate the second movable plate  84  and formed along the slide direction of the first movable plate  83 , at the lower portion of the protruding portion  84   b . Further, the second movable plate  84  is provided with a lower long hole  84   d  that is made so as to penetrate the second movable plate  84  and formed along the slide direction of the first movable plate  83 , at the lower portion of the middle long hole  84   c , and at the upper portion of the rack gear portion  84   e . Furthermore, the second movable plate  84  is provided with a stopping portion  84   g  that the lower end portion of the first movable plate  83  reaches, at the lower end portion. 
     The first movable plate  83  is formed into a long and thin plate shape, in the same manner as the second movable plate  84 . Further, the first movable plate  83  is arranged closer to the housing  61  (refer to  FIG. 6 ) than the second movable plate  84 , and arranged to be lapped over the second movable plate  84 . Furthermore, the first movable plate  83  is arranged so as to slide in the slide direction of the second movable plate  84 . 
     Furthermore, the first movable plate  83  is provided with a first protruding portion  83   a  that is arranged through the upper long hole  84   b  and the opening hole  70   d  in the advancing/retreating member  70   c , on the surface opposed to the second movable plate  84  and at the upper end portion. Moreover, the first movable plate  83  is provided with a second protruding portion  83   b  that is arranged through the middle long hole  84   c  and the opening hole  70   d  in the advancing/retreating member  70   m , at the position lower than the first protruding portion  83   a . Further, the first movable plate  83  is provided with a third protruding portion  83   c  that is arranged through the upper long hole  84   d  and the opening hole  70   d  in the advancing/retreating member  70   y  at the lower position of the second protruding portion  83   b . Furthermore, the first movable plate  83  is provided with a rack gear portion  83   d  that engages with the first drive gear  81  (refer to  FIG. 6 ), at the side surface opposite to the side where the rack gear portion  84   e  is arranged, and at the lower end portion. 
     The figure shows a state where the first movable plate  83  is located at the lower position, and the lower end portion of the first movable plate  83  stops at the stopping portion  84   g  in the second movable plate  84  (hereinafter, this state is referred to as “first state”). In the first state, the first protruding portion  83   a  is located at the lower portion of the upper long hole  84   b , and the second protruding portion  83   b  is located at the lower portion of the middle long hole  84   c , and the third protruding portion  83   c  is located at the lower portion of the lower long hole  84   d . Since the first protruding portion  83   a , the second protruding portion  83   b  and the third protruding portion  83   c  are located as above, and as a result, the arm portions  70   b  in the advancing/retreating members  70   c ,  70   m  and  70   y  are directed diagonally downward (refer also to  FIG. 6 ). 
     Here,  FIG. 8  is a view that shows the inside of the switching unit  60  in the first state. 
     As mentioned above, the switching unit  60  in the first exemplary embodiment is provided with four storing portions  63   y ,  63   m ,  63   c  and  63   k  that store the advancing/retreating members  70   y ,  70   m ,  70   c  and  70   k  in the housing  61 , respectively. In the first exemplary embodiment, in the inside of the storing portions  63 , drive side coupling members  43   y ,  43   m ,  43   c  and  43   k  are arranged. 
     The respective drive side coupling members  43  are attached to the shafts  42   y ,  42   m ,  42   c ,  42   k , and pushed to the respective photoconductor side coupling members  18  by a coil spring (not shown in the figure). Thereby, the respective drive side coupling members  43  are interconnected with the corresponding photoconductor side coupling members  18 . In the first state, as shown in the figure, all the drive side coupling members  43  are interconnected with the corresponding photoconductor side coupling members  18 , and all the photoconductor drums  11  are rotated and driven. Therefore, in the first state, the image formation by use of all image forming units  10 , that is, the image formation in full colors is implemented. 
     Further, the inside structures of the switching unit  60  and the like are explained. 
       FIG. 9  is an enlarged view that shows the peripheral of the drive side coupling member  43   c  in  FIG. 8 . 
     The drive unit  40  in the first exemplary embodiment is provided with a pin  44  which is arranged through the shaft  42   c  and whose both end portions protrude from the outer circumferential surface of the shaft  42   c . The pin  44  is arranged in the inside of the drive side coupling member  43   c , and is arranged so as to reach a hitting surface  45  formed in the inside of the drive side coupling member  43   c  when the shaft  42   c  is rotated and driven by the motor M 3  (refer to  FIG. 4 ). As a result, interlocking with the rotation of the shaft  42   c , the drive side coupling member  43   c  also rotates. 
     The drive side coupling member  43   c  is arranged so as to be slidable along the axial direction of the shaft  42   c . In more particular, the drive side coupling member  43   c  in the first exemplary embodiment is provided with a opening hole  46  in which the shaft  42   c  is arranged, which is formed with a larger diameter than that of the shaft  42   c , and which is provided so as to penetrate from the drive unit  40  side to the image forming unit  10 C side. In addition, the drive side coupling member  43   c , as mentioned above, is provided with the hitting surface  45 . The hitting surface  45  is formed to be flat, and arranged along the axial direction of the shaft  42   c . Further, the drive side coupling member  43   c  is provided with an inward protruding portion  47  that protrudes in the opening hole  46 , on the photoconductor side coupling member  18   c  side. The inward protruding portion  47  reaches the end portion of the shaft  42   c , when the drive side coupling member  43   c  slides to the drive unit  40  side. 
     Further, the drive side coupling member  43   c  is provided with a concave slot  48  that is formed from the opening hole  46  to the outside of the drive side coupling member  43   c , and arranged so as to surround the outer circumferential surface of the shaft  42   c , on the side closer to the photoconductor side coupling member  18   c  than the hitting surface  45 . When the drive side coupling member  43   c  slides to the drive unit  40  side and the inward protruding portion  47  reaches the end portion of the shaft  42   c , the pin  44  is rotatably arranged in the concave slot  48 . Further, the drive side coupling member  43   c  is provided with an outward protruding portion  49  that protrudes outside, on the outer circumferential portion thereof. 
     On the other hand, the advancing/retreating member  70   c  in the first exemplary embodiment is provided with an inward protruding portion  70   e  that protrudes inward, on the inner circumferential surface of the ring portion  70   a.    
     The drive side coupling member  43   c  in the first exemplary embodiment is arranged in the inside of the ring portion  70   a . The drive side coupling member  43   c  is pushed by the coil spring (not shown in the figure), and as a result, the outward protruding portion  49  reaches the inward protruding portion  70   e , and the advancing/retreating member  70   c  reaches the housing  61 . As a result, the drive side coupling member  43   c  is positioned to a predetermined position in the storing portion  63   c . Further, the end portion of the drive side coupling member  43   c  is exposed from the advancing/retreating member  70   c , and this end portion is interconnected to the photoconductor side coupling member  18   c.    
     The drive side coupling member  43   c  in the first exemplary embodiment is configured by assembling two members of an interconnecting member  19   a  interconnected to the photoconductor side coupling member  18   c , and a supporting member  19   b  that supports the interconnecting member  19   a.    
     Here, in the first state (refer to  FIGS. 6 and 7 ), when the first drive gear  81  is rotated and driven, the first movable plate  83  receives the drive force from the first drive gear  81 , and slides upward. As a result, the first protruding portion  83   a  formed on the first movable plate  83  moves upward in the upper long hole  84   b , the second protruding portion  83   b  moves upward in the middle long hole  84   c , and the third protruding portion  83   c  moves upward in the lower long hole  84   d . Further, as the first protruding portion  83   a , the second protruding portion  83   b  and the third protruding portion  83   c  move upward, the respective advancing/retreating members  70   y ,  70   m  and  70   c  rotate in the arrow A direction in  FIG. 7 . The sliding of the second movable plate  84  is regulated by the second drive gear  82  arranged in a state where the second drive gear  82  interlocks with the cover  2 , when the first movable plate  83  slides. 
     When the upward sliding of the first movable plate  83  is complete, the state becomes one shown in  FIG. 10  and  FIG. 11 . Here,  FIG. 10  is a perspective view that shows the advancing/retreating members  70 , the first movable plate  83  and the second movable plate  84  after the first drive gear  81  is rotated and driven.  FIG. 11  is a perspective view that shows the switching unit  60  and the like after the first drive gear  81  is rotated and driven, viewed from the drive unit  40  side (refer to  FIG. 5 ). 
     When the first movable plate  83  slides upward, as mentioned above, the first protruding portion  83   a  moves upward in the upper long hole  84   b , the second protruding portion  83   b  moves upward in the middle long hole  84   c , and the third protruding portion  83   c  moves upward in the lower long hole  84   d . Further, the respective advancing/retreating members  70  except the advancing/retreating member  70   k  rotate in the arrow A direction as mentioned above. As a consequence, as shown in  FIG. 10  and  FIG. 11 , the first protruding portion  83   a  is positioned in the upper portion of the upper long hole  84   b , and the second protruding portion  83   b  is positioned in the upper portion of the middle long hole  84   c , and the third protruding portion  83   c  is positioned in the upper portion of the lower long hole  84   d . Furthermore, the arm portions  70   b  in the advancing/retreating members  70   y ,  70   m  and  70   c  are directed diagonally upward (hereinafter, this state is referred to as “a second state”). 
     Here,  FIG. 12  is a view that shows the inside of the storing portion  63   c  in the second state. 
     Although explanations are omitted in  FIG. 9 , the switching unit  60  in the first exemplary embodiment is provided with a guide protrusion  66  that is arranged to protrude inward and formed in a spiral shape, in the inside wall of the storing portion  63   c . Further, as mentioned above, when the first movable plate  83  (refer to  FIG. 10 ) slides upward and the advancing/retreating member  70   c  rotates, the advancing/retreating member  70   c  is guided by the guide protrusion  66 , and moves (retreats) in the direction leaving from the photoconductor side coupling member  18   c . Then, when the advancing/retreating member  70   c  moves in the direction leaving from the photoconductor side coupling member  18   c , the drive side coupling member  43   c  also moves (slides) in the direction leaving from the photoconductor side coupling member  18   c.    
     As a result, in the second state, as shown in  FIG. 12 , the interconnection of the photoconductor side coupling member  18   c  and the drive side coupling member  43   c  is in a released state. Therefore, the rotation of the photoconductor drum  11  (refer to  FIG. 11 ) by the drive side coupling member  43   c  is also stopped. Further, in the second state, since the pin  44  is positioned in the concave slot  48 , the rotation of the drive side coupling member  43   c  is stopped. In addition, in the second state, as shown in  FIG. 3B , the paper transportation belt  30  gets in a state where the paper transportation belt  30  is separated from the photoconductor drums  11  in the image forming units  10 Y,  10 M and  10 C. Therefore, the rotation of the photoconductor drum  11  by the paper transportation belt  30  is also stopped. 
     Meanwhile, in the shift from the first state to the second state, the rotation of the advancing/retreating member  70   k  is not carried out (refer to  FIG. 10  and  FIG. 11 ). Therefore, in the second state, the interconnection of the photoconductor side coupling member  18   k  and the drive side coupling member  43   k  is maintained, and the interconnection of the photoconductor side coupling members  18   y ,  18   m  and  18   c , and the drive side coupling members  43   y ,  43   m  and  43   c  is released. As a result, in the second state, only the photoconductor drum  11  in the image forming unit  10 K is rotated and driven, and the image formation by use of the image forming unit  10 K, that is, the image formation in a single color is implemented. 
     Here, the second drive gear  82  (refer to  FIG. 11 ) is configured so as to be rotated and driven interlocking with the cover  2 , when the cover  2  (refer to  FIG. 1 ) is opened. When the second drive gear  82  is rotated and driven interlocking with the opening of the cover  2 , the first movable plate  83  and the second movable plate  84  move upward, and all the interconnections of the drive side coupling members  43  and the photoconductor side coupling members  18  are released. Hereinafter, this configuration is explained. 
       FIG. 13  is a side view that shows the side portion of the switching unit  60 , including the cover  2  and the like. Note that in this figure, the cover  2  is simply illustrated. 
     As mentioned above, in the first exemplary embodiment, the first drive gear  81  that engages with the rack gear portion  83   d  provided on the first movable plate  83 , and the second drive gear  82  that engages with the rack gear portion  84 e provided on the second movable plate  84  are arranged. 
     Further, in the first exemplary embodiments a drive apparatus  85  that rotates and drives the first drive gear  81  is arranged. The drive apparatus  85  is provided with a motor M 4 , and a transmission gear  85   a  that is configured by plural gears and transmits the drive force generated by the motor M 4  to the first drive gear  81 . Meanwhile, the shift from the first state to the second state is carried out by the first drive gear  81  that is rotated and driven by the drive apparatus  85 . 
     Further, in the first exemplary embodiment, by rotating and driving the first drive gear  81  in the reverse direction by the drive apparatus  85 , the shift from the second state to the first state is also performed. As a result, the image forming apparatus  1  (refer to  FIG. 1 ) in the first exemplary embodiment switches the image formation in a single color and the image formation in full colors. 
     Furthermore, in the first exemplary embodiment, a first gear  87  that is arranged rotatably and engages with the second drive gear  82 , and a second gear  88  that is similarly arranged rotatably and engages with the first gear  87  are arranged. Moreover, a rotation mechanism  90  that rotates and drives the second gear  88  when the cover  2  is opened is arranged. 
     Here,  FIGS. 14A and 14E  are views for explaining the rotation mechanism  90 . In addition,  FIG. 14A  is a perspective view that shows the rotation mechanism  90  including the cover  2 , and  FIG. 14B  is a side view of the rotation mechanism  90 . 
     The rotation mechanism  90  in the first exemplary embodiment is provided with a interlocking arm  2   a  whose one end portion is attached to the rear portion of the cover  2 , and that moves interlocking with the opening and closing operations of the cover  2 , and a penetration shaft  2   b  that is arranged through the inside of the other end portion of the interlocking arm  2   a . Further, the rotation mechanism  90  is provided with a third movable plate  92  that is slidably arranged, a guide member  91  that guides the third movable plate  92 , and a rack gear member  93  that is attached to the lower side of the third movable plate  92  and that engages with the second gear  88 . Note that in  FIG. 14B , the illustration of the cover  2  and the interlocking arm  2   a  is omitted, and the third movable plate  92  is simply illustrated. 
     Two guide members  91  in the first exemplary embodiment are arranged on both sides of the interlocking arm  2   a . Further, the guide member  91  is fixed to t the apparatus main body  3  side (refer to  FIG. 1 ). Each of the guide members  91  is provided with a guide main body portion  91   a  that is formed into a long plate shape, and fixed to the apparatus main body  3 , a guide side long hole  91   b  that is arranged through the guide main body portion  91   a  and formed in the longitudinal direction of the guide main body portion  91   a , and a guide side protruding portion  91   c  that is formed so as to surround the guide side long hole  91   b  and regulates the sliding direction of the third movable plate  92 . 
     On the other hand, two third movable plates  92  are arranged on both sides of the interlocking arm  2   a , in the same manner as the guide member  91 . Further, the third movable plates  92  are arranged between the interlocking arm  2   a  and the guide member  91 . Each of the third movable plates  92  is provided with a plate side main body portion  92   a  that is formed into a long plate shape, and a plate side long hole  92   b  that is arranged through in the plate side main body portion  92   a  and formed in the longitudinal direction of the plate side main body portion  92   a . In addition, in the inside of the plate side long hole  92   b , the penetration shaft  2   b  is arranged. Moreover, the full length L 2  of the plate side long hole  92   b  is formed smaller than the full length L 1  of the guide side long hole  91   b.    
     Further, each of the third movable plates  92  is provided with a plate side protruding portion  92   c  that is formed so as to surround the plate side long hole  92   b  and arranged so as to protrude in the inside of the guide side long hole  91   b . The plate side protruding portion  92   c  is arranged so as to be brought in contact with the guide side protruding portion  91   c , and regulates the sliding direction of the third movable plate  92  together with the guide side protruding portion  91   c.    
     The rack gear member  93  is arranged to lie astride both plate side main body portions  92   a , and fixed to the lower edge portion of the plate side main body portions  92   a.    
     For example, when the image formation in full colors is finished, as shown in the figure, the third movable plate  92  is positioned at the right side of the guide member  91  in the figure, and the penetration shaft  2   b  is arranged at the center in the longitudinal direction of the plate side long hole  92   b . Then, when the cover  2  is opened from this state, the penetration shaft  2   b  moves in the direction shown by the arrow B in the figure interlocking with the interlocking arm  2   a . Hereinafter, the operation of the rotation mechanism  90  is explained in detail. 
       FIGS. 15A to 15E  are views for explaining the operation of the rotation mechanism  90 .  FIG. 15A  shows the same state as  FIG. 14B . 
     When the cover  2  (refer to  FIG. 14A ) is opened in the state of  FIG. 15  A, the interlocking arm  2   a  also moves interlocking with the cover  2 . As a result, as shown by the arrow B in the figure, the penetration shaft  2   b  moves in the direction to the left end portion of the plate side long hole  92   b.    
     Then, when the cover  2  is further opened, as shown in  FIG. 15B , the penetration shaft  2   b  reaches the plate side main body portion  92   a , at the left end portion of the plate side long hole  92   b . Moreover, when the cover  2  is further opened, the movement of the third movable plate  92  to the left side in the figure (refer to the arrow E) is started together with the movement of the penetration shaft  2   b.    
     When the movement of the third movable plate  92  to the left side is started, the second gear  88  that engages with the rack gear member  93  starts rotating in the direction shown by the arrow F in the figure. Then, when the rotation of the second gear  88  is started, the rotation of the second drive gear  82  (refer to  FIG. 13 ) is also started, and the second movable plate  84  starts sliding upward. Further, along with the upward sliding of the second movable plate  84 , the upward sliding of the first movable plate  83  is also started. 
     When the cover  2  is opened completely, as shown in  FIG. 15C , the third movable plate  92  positions to the left side of the guide member  91 , and the upward sliding of the first movable plate  83  and the second movable plate  84  (refer to  FIG. 13 ) is completed. 
     Further, when the closing operation of the cover  2  is started from the state in  FIG. 15C , the penetration shaft  2   b  moves in the direction shown by the arrow G in the figure, through the plate side long hole  92   b . Then, when the cover  2  is closed completely, the penetration shaft  2   b  is arranged to the right end of the plate side long hole  92   b , as shown in  FIG. 15D . 
     Meanwhile, the rotation mechanism  90  in the first exemplary embodiment is configured so that, when the cover  2  is closed, the penetration shaft  2   b  does not reach the plate side main body portion  92   a  (refer to  FIG. 14B ). As a result, by the closing operation of the cover  2 , the sliding of the third movable plate  92  is not carried out. Therefore, by the closing operation of the cover  2 , the rotation and drive of the second gear  88  are not carried out, and the rotation and drive of the second drive gear  82  (refer to  FIG. 13 ) and the sliding of the second movable plate  84  are not carried out. 
     Further, as shown in  FIG. 15D , when the second gear  88  is rotated and driven in the direction shown by the arrow H in the figure, the third movable plate  92  slides to the right side in the figure (refer to the arrow J). As a result, the rotation mechanism  90  gets in its initial state (the state shown in  FIG. 15A ). In addition, although details are described later herein, the rotation and drive of the second gear  88  is carried out by the downward sliding of the second movable plate  84  (refer to  FIG. 13 ). 
     Here, with reference to  FIGS. 15A to 15E , the operation of the advancing/retreating member  70  and the like when the opening and closing operation of the cover  2  is carried out is explained. 
       FIG. 16  is a view that shows the side portion of the switching unit  60  when the rotation mechanism  90  is in the state of  FIG. 15B . When the opening of the cover  2  is started, as already explained with reference to  FIG. 15A , the penetration shaft  2   b  moves in the direction to the left end portion of the plate side long hole  92   b . As a result, the rotation mechanism  90  gets in the state shown in  FIG. 15B , and the cover  2  and the like get in the state shown in  FIG. 16 . 
     When the cover  2  is further opened from the state shown in  FIG. 16 , as already explained with reference to  FIG. 15B , the third movable plate  92  slides in the direction shown by the arrow E, and the second gear  88  rotates in the direction shown by the arrow F. As a result, as shown in  FIG. 16 , the second drive gear  82  starts rotating in the direction shown by the arrow N in the figure. Therefore, the upward sliding (refer to the arrow P in the figure) of the second movable plate  84  is also started. Further, the first movable plate  83  is pushed by the stopping portion  84   g  as an example of the interlocking portion, and also starts sliding upward. Furthermore, along with the upward sliding of the first movable plate  83  and the second movable plate  84 , the respective advancing/retreating members  70  start rotating in the direction shown by the arrow Q in the figure. 
     Here,  FIGS. 17 and 18  show the state after the opening of the cover  2  is completed.  FIG. 17  is a view that shows the side portion of the switching unit  60 , and  FIG. 18  is a view that shows the inside of the switching unit  60 . 
     When the opening of the cover  2  is completed, the rotation mechanism  90  gets in the state shown in  FIG. 15C , and the upward sliding of the first movable plate  83  and the second movable plate  84  is completed. Then, when the upward sliding of the first movable plate  83  and the second movable plate  84  is completed, the rotation of the advancing/retreating members  70  is completed, and as shown in  FIG. 17 , the arm portions  70   b  are directed diagonally upward. 
     As a result, all the drive side coupling members  43  slide to the drive unit  40  side, and as shown in  FIG. 18 , all the interconnections of the drive side coupling member  43  and the photoconductor side coupling members  18  get in the released state. In addition, when the opening of the cover  2  is completed, as already shown in  FIG. 2 , the image forming unit  10  gets in an exposed state. Therefore, by the opening of the cover  2 , the user and the like may exchange the image forming unit  10 . 
     When the image forming unit  10  is exchanged and the cover  2  is closed, the rotation mechanism  90  gets in the state shown in  FIG. 15D  and the side portion of the switching unit  60  gets in the state shown in  FIG. 19  (a view that shows the side portion of the switching unit  60 ). As already explained with reference to  FIG. 15D , when the cover  2  is closed, the sliding of the third movable plate  92  is not carried out, and, the rotation and drive of the second drive gear  82  and the like are not carried out. As a result, since the rotation of the advancing/retreating members  70  is not carried out, even if the closing operation of the cover  2  is carried out, the interconnection of the drive side coupling member  43  and the photoconductor side coupling members  18  is not carried out, but left released. 
     When the cover  2  is closed completely and a predetermined output is made from a sensor (not shown in the figure), the first drive gear  81  is rotated and driven by the drive apparatus  85  in the direction shown by the arrow R in the figure. As a result, the downward sliding of the first movable plate  83  is started, and by the sliding of the first movable plate  83 , the downward sliding of the second movable plate  84  is also started. As a result, the respective advancing/retreating members  70  start rotating in the direction shown by the arrow S in the figure. Further, by the downward sliding of the second movable plate  84 , the second drive gear  82  starts rotating in the direction shown by the arrow T in the figure, and the second gear  88  starts rotating in the direction shown by the arrow H in the figure. As a result, as already shown in  FIG. 15D , the third movable plate  92  slides in the direction shown by the arrow J in the figure. 
       FIG. 20  is a view that shows the state after the downward sliding of the first movable plate  83  and the second movable plate  84  is completed. As shown in the figure, when the downward sliding of the first movable plate  83  and the second movable plate  84  is completed, the rotation of the respective advancing/retreating members  70  is completed, and the arm portions  70   h  are directed diagonally downward. As a result, as already shown in  FIG. 8 , all of the photoconductor side coupling members  18  and the drive side coupling members  43  are interconnected. 
     Next, a second exemplary embodiment is explained. 
       FIG. 21  is a view that schematically shows the image forming apparatus  1  in the second exemplary embodiment. Note that, in the figure, portions being different from those in the first exemplary embodiment are mainly illustrated. Further, it should be noted that the same numerals are given to the same functions as those in the first exemplary embodiment for omitting the repeated explanations thereof in all drawings for explaining the embodiments. Furthermore, in the figure, photoconductor drums  11  provided in the image forming units  10 Y,  10 M,  10 C and  10 K are shown as  11   y ,  11   m ,  11   c  and  11   k  respectively. 
     As shown in the figure, in the second exemplary embodiment, in the same manner as in the first exemplary embodiment, four advancing/retreating members  70   y ,  70   m ,  70   c  and  70   k  are provided. However, the advancing/retreating members  70   y ,  70   m  and  70   c  in the second exemplary embodiment do not have the arm portions  70   b  and the opening holes  70   d  (refer to  FIG. 7 ), and are in a state having only the ring portions  70   a . Further, each of the advancing/retreating members  70   y ,  70   m  and  70   c  (ring portion  70   a ) is provided with a gear (not shown in the figure) that engages with a first rack gear  101  to be described later herein, on the outer circumferential edge. On the other hand, in the same manner as in the first exemplary embodiment, the advancing/retreating member  70   k  has the ring portion  70   a , the arm portion  70   b  and the opening hole  70   d  (refer to  FIG. 7 ). 
     Furthermore, in the image forming apparatus  1  in the second exemplary embodiment, the fulcrum  4  is provided not at the photoconductor drum  11   y  side, but at the photoconductor drum  11   k  side. 
     Moreover, the image forming apparatus  1  in the second exemplary embodiment is provided with a drive apparatus  120 , a sliding member  100  that receives drive force from the drive apparatus  120  and the like and slides, and a link member  140  that makes the sliding member  100  slide interlocking with the opening operation and the closing operation of the cover  2 . 
     The sliding member  100  is arranged along the arrangement direction of the photoconductor drums  11   y ,  11   m ,  11   c  and  11   k  arranged in parallel in a straight line, and is provided so as to slide in the arrangement direction. Further, the sliding member  100  is provided with, at one edge portion (an upper edge portion in the figure), the first rack gear  101  that engages with the above described gears provided on the advancing/retreating members  70   y ,  70   m  and  70   c  (ring portion  70   a ). Furthermore, the sliding member  100  is provided with, on the other edge portion (a lower edge portion in the figure), a second rack gear  102  that receives the drive force from the drive apparatus  120 . Moreover, the sliding member  100  is provided with an opening hole  103 , at the end portion of the side where the photoconductor drum  11   k  is provided. In addition, the opening hole  103  is formed as a long hole along the sliding direction of the sliding member  100 . 
     The drive apparatus  120  is provided with a motor MS and a gear  121  that receives the drive force from the motor MS and rotates. In addition, the gear  121  is provided so as to engage with the above-mentioned second rack gear  102  in the sliding member  100 . 
     The link member  140  is provided with a plate shaped portion  141  that is formed into a long and thin plate shape, a first protruding portion  142  that laterally protrudes from the plate shaped portion  141 , and a second protruding portion  143  that laterally protrudes in the same manner. The plate shaped portion  141  is provided substantially along the sliding direction of the sliding member  100 , and one end portion thereof is attached to the cover  2 . The first protruding portion  142  is arranged through inside of the opening hole  70   d  (refer to  FIG. 7 ) provided in the advancing/retreating member  70   k . The second protruding portion  143  is arranged on the other end portion of the plate shaped portion  141 , and arranged to be positioned in the inside of the opening hole  103  provided in the sliding member  100 . 
     The figure shows the state where the cover  2  is closed and the sliding member  100  is positioned close to the left in the figure (close to the photoconductor drum  11   y ). In this state, all the drive side coupling members  43  and all the photoconductor side coupling members  18  are interconnected, and the image formation in full colors is performed. Here, in the state, the above-mentioned second protruding portion  143  is positioned on the photoconductor drum  11   k  side, in the opening hole  103 . Note that in the second exemplary embodiment, the drive apparatus  120 , the sliding member  100 , the advancing/retreating members  70   y ,  70   m  and  70   c  and the like function as an interconnecting unit, an interconnecting mechanism (first interconnecting mechanism). Further, in the second exemplary embodiment, the link member  140 , the advancing/retreating member  70   k  and the like function as a second interconnecting mechanism. Furthermore, in the second exemplary embodiment, the second protruding portion  143  functions as an example of interlocking portion. 
     In this state, when the sliding member  100  is slid by the drive apparatus  120  in the direction to the photoconductor drum  11   k  (the arrow A direction in the figure), the state becomes one shown in  FIG. 22 . 
       FIG. 22  shows the state after the sliding member  100  is slid by the drive apparatus  120 . 
     When the sliding member  100  is slid, by the first rack gear  101 , the respective advancing/retreating members  70   y ,  70   m  and  70   c  are rotated. As a result, the interconnection of the drive side coupling members  43   y ,  43   m  and  43   c , and the photoconductor side coupling members  18   y ,  18   m  and  18   c  is released. On the other hand, the sliding member  100  and the second protruding portion  143  in the second exemplary embodiment are configured and arranged so as not to bring in contact with each other, when the sliding member  100  is slid in the direction to the photoconductor drum  11   k  by the drive apparatus  120 . Therefore, even if the sliding of the sliding member  100  is carried out, the rotation of the advancing/retreating member  70   k  is not carried out, and the interconnection of the drive side coupling member  43   k  and the photoconductor side coupling member  18   k  is maintained. 
     As a result, only the photoconductor drum  11   k  in the image forming unit  10 K gets in a state to be rotated and driven, and the image formation by use of the image forming unit  10 K, that is, the image formation in a single color is performed. Meanwhile, when the sliding member  100  is shifted from this state to the original state (the state shown in  FIG. 21 ), the image formation in full colors is performed again. Further, in this state, as shown in  FIG. 3B , the paper transportation belt  30  is separated from the photoconductor drums  11   y ,  11   m  and  11   c  in the image forming units  10 Y,  10 M and  10 C. 
     Here,  FIG. 23  shows the state after the cover  2  is opened from the state shown in  FIG. 21 . When the cover  2  is opened, the link member  140  moves in the direction leaving from the sliding member  100  by the movement of the cover  2 . As a result, the rotation of the advancing/retreating member  70   k  is carried out. Further, when the cover  2  is opened, the sliding member  100  is pushed by the second protruding portion  143 , and slides in the direction where the photoconductor drum  11   k  is arranged. As a result, the rotation of the advancing/retreating members  70   y ,  70   m  and  70   c  is carried out. Therefore, also in the second exemplary embodiment, by the opening of the cover  2 , the interconnections of all the drive side coupling members  43  and all the photoconductor side coupling members  18  are released. 
     When the cover  2  is closed from this state, the advancing/retreating member  70   k  is rotated by the link member  140 , and the drive side coupling member  43   k  and the photoconductor side coupling member  18   k  are first interconnected. Then, by the drive apparatus  120 , the sliding member  100  is slid to the photoconductor drum  11   y  side, the advancing/retreating members  70   y ,  70   m  and  70   c  are rotated, and the drive side coupling members  43   y ,  43   m  and  43   c  and the photoconductor side coupling members  18   y ,  18   m  and  18   c  are interconnected. As a result, a state is realized in which all the drive side coupling members  43  and all the photoconductor side coupling members  18  are interconnected, and the image formation in full colors is performed. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.