Patent Publication Number: US-8967615-B2

Title: Reversing transporting device, image forming apparatus, and transporting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2011-072643 filed Mar. 29, 2011. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a reversing transporting device, an image forming apparatus, and a transporting device. 
     SUMMARY 
     According to an aspect of the invention, there is provided a reversing transporting device including a transport-in path for transporting a recording material into the reversing transporting device, the recording material having a first side, a second side, a front side, and a back side, the second side being positioned opposite to the first side, the front side intersecting the first side, the back side being positioned opposite to the front side; a first transporting section provided at the transport-in path, the first transporting section nipping the recording material that is transported into the reversing transporting device, and transporting the recording material in a first direction in which the front side of the recording material is a leading side; a second transporting section provided at the transport-in path, the second transporting section nipping the recording material that is transported by the first transporting section, and transporting the recording material in a second direction in which the first side of the recording material is a leading side; a reversing path connected to the transport-in path, the reversing path guiding the recording material that is transported by the second transporting section so that the first side and the second side of the recording material are reversed, to cause front and back surfaces of the recording material to be reversed; a third transporting section provided at the reversing path, the third transporting section transporting the recording material that is transported by the second transporting section in a third direction in which the first side is the leading side; a transport-out path connected to the reversing path, the transport-out path being for transporting out of the reversing transporting device the recording material that is transported in a state in which the front and back surfaces of the recording material are reversed by the reversing path and third transporting section; a fourth transporting section provided at the transport-out path, the fourth transporting section nipping the recording material that is transported by the third transporting section, and transporting the recording material in a fourth direction in which the first side is the leading side; and a fifth transporting section provided at the transport-out path, the fifth transporting section nipping the recording material that is transported by the fourth transporting section, and transporting the recording material in a fifth direction in which the front side of the recording material is the leading side. The first transporting section and the second transporting section each have a pair of rotating members contactably and separably disposed with the transport-in path being interposed therebetween. The fourth transporting section and the fifth transporting section each have a pair of rotating members contactably and separably disposed with the transport-out path being interposed therebetween. Each pair of rotating members includes a driving rotating member and a driven rotating member, the driving rotating member rotating by receiving outside driving force, the driven rotating member rotating by receiving the driving force from the driving rotating member when the driven rotating member is contacted by the driving rotating member. When the driving rotating members and the respective driven rotating members are separated from each other, in the first transporting section and the second transporting section, the driving rotating members retreat from the transport-in path, and, in the fourth transporting section and the fifth transporting section, the driving rotating members retreat from the transport-out path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  shows an image forming apparatus to which an exemplary embodiment is applied as seen from a near side; 
         FIG. 2  is a perspective view of an entire structure of a sheet reversing device; 
         FIG. 3  illustrates the relationship between each transport path provided in the sheet reversing device and a transport direction of a sheet in each transport path; 
         FIG. 4  is a perspective view of a case in which a second reversing guiding plate is set in an open state in the sheet reversing device shown in  FIG. 2 ; 
         FIG. 5  is a perspective view of a case in which a reversing section is set in an open state in the sheet reversing device shown in  FIG. 2 ; 
         FIG. 6  is a perspective view of a case in which the second reversing guiding plate is set in an open state in the sheet reversing device shown in  FIG. 5 ; 
         FIG. 7  is a perspective view of a case in which a second transporting-in guiding plate is set in an open state in the sheet reversing device shown in  FIG. 6 ; 
         FIG. 8  is a perspective view of a case in which a second transporting-out guiding plate is set in an open state in the sheet reversing device shown in  FIG. 6 ; 
         FIG. 9  illustrates the structure of each transporting section and each transport path in the sheet reversing device; 
         FIGS. 10A to 10E  each illustrate the structure of a pair of transport rollers provided at each transporting section of the sheet reversing device; 
         FIGS. 11A to 11E  each illustrate the relationship between the pair of transport rollers and the corresponding transport path in the sheet reversing device; 
         FIGS. 12A to 12D  each illustrate an exemplary structure of an advancing/retreating mechanism and a rotating mechanism of a pair of upstream-side first reversing rollers; 
         FIG. 13  illustrates the behavior of a sheet that passes through the sheet reversing device; 
         FIGS. 14A to 14E  each illustrate the relationship between a pair of transport rollers and a corresponding transport path in a sheet reversing device; and 
         FIGS. 15A and 15B  illustrate an exemplary structure of a rotating mechanism and an advancing/retreating mechanism of a pair of upstream-side first reversing rollers. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will hereunder be described in detail with reference to the attached drawings. 
     First Exemplary Embodiment 
       FIG. 1  shows an image forming apparatus  1  to which an exemplary embodiment is applied as seen from a near side. The image forming apparatus  1  shown in  FIG. 1  includes what is called a tandem structure. The image forming apparatus  1  includes image forming units  10  ( 10 Y,  10 M,  10 C, and  10 K) that form toner images of respective color components by electrophotography. The image forming apparatus  1  further includes, for example, a central processing unit (CPU), read only memory (ROM), and random access memory (RAM). The image forming apparatus  1  includes each device that forms the image forming apparatus  1  and a controller  80  serving as an exemplary stopping unit that controls the operation of each section. The image forming apparatus  1  further includes, for example, a touch panel and a user interface (UI)  90  that outputs an instruction received from a user to the controller  90  and that indicates to the user information from the controller  80 . Still further, the image forming apparatus  1  includes a receiving section  70  that receives, for example, image data from, for example, a personal computer (PC) or an image reading device (scanner). 
     Still further, the image forming apparatus  1  includes an intermediate transfer belt  20  and a second transfer device  30 . The toner images of the respective color components that are formed by the respective image forming units  10  are successively transferred to the intermediate transfer belt  20  by first transfer operations and held by the intermediate transfer belt  20 . The second transfer device  30  transfers the toner images on the intermediate transfer belt  20  by one second transfer operation to a sheet P serving as an exemplary rectangular recording material. 
     Each image forming unit  10  serving as an exemplary image forming section includes a rotatably mounted photoconductor drum  11 . In each image forming unit  10 , a charging device  12  that charges the photoconductor drum  11 , an exposure device  13  that exposes the photoconductor drum  11  to form an electrostatic latent image, and a developing device  14  that makes visible the electrostatic latent image on the photoconductor drum  11  by toner are provided around the photoconductor drum  11 . Each image forming unit  10  includes a first transfer device  15  and a drum cleaning device  16 . The first transfer devices  15  transfer to the intermediate transfer belt  20  the toner images of the respective color components formed on the respective photoconductor drums  11 . The drum cleaning devices  16  remove residual toner on the respective photoconductor drums  11 . 
     Next, the intermediate transfer belt  20  is placed around three rotatably provided rollers  21  to  23  so as to be rotatably provided. Of the three rollers  21  to  23 , the roller  22  drives the intermediate transfer belt  20 . The roller  23  is disposed so as to oppose a second transfer roller  31  with the intermediate transfer belt  20  being disposed therebetween. The second transfer roller  31  and the roller  23  constitute the second transfer device  30 . A belt cleaning device  24  that removes residual toner on the intermediate transfer belt  20  is provided at a position opposing the roller  21  with the intermediate transfer belt  20  being disposed therebetween. 
     A first transport path R 1 , a second transport path R 2 , a third transport path R 3 , and a fourth transport path R 4  are provided in the image forming apparatus  1 . A sheet P transported towards the second transfer device  30  passes along the first transport path R 1 . The sheet P that has passed the second transfer device  30  passes along the second transport path R 2 . The third transport path R 3  is branched from the second transport path R 2  at a location that is downstream from a fixing device  50  (described later), extends below the first transport path R 1 , and guides the sheet P to a sheet reversing device  100  (described later). The fourth transport path R 4  guides again the sheet P that has passed the sheet reversing device  100  (described later) to the first transport path R 1 . The sheet P is transported along the first transport path R 1  to the fourth transport path R 4  so that two opposing sides among the four sides of the sheet P (a first side and a second side that is positioned opposite to the first side) move along these transport paths R 1  to R 4 . 
     The image forming apparatus  1  according to the exemplary embodiment further includes the sheet reversing device  100  that reverses the front and back of the sheet P that has been transported therein from the third transport path R 3 , and that transports out the sheet P to the fourth transport path R 4 . The sheet reversing device  100  reverses the sheet P around an axis along a sheet transport direction in the third transport path R 3  and a sheet transport direction in the first transport path R 1 . That is, the sheet reversing device  100  according to the exemplary embodiment reverses the two side ends (sides) of the sheet P without reversing the front end and the back end of the sheet P in the sheet transport direction. The sheet reversing device  100  includes a transport-in path Ra, a transport-out path Rc, and a reversing path Rb. The transport-in path Ra is connected to the third transport path R 3 . The transport-out path Rc is connected to the fourth transport path R 4 . The reversing path Rb reverses the front and back of the sheet P supplied from the transport-in path Ra, and supplies the sheet P to the transport-out path Rc. 
     A sheet detecting sensor  60  detects the passage of the sheet P is mounted at the third transport path R 3  corresponding to a sheet-P transporting-in side in the sheet reversing device  100 . 
     Further, in the exemplary embodiment, an opening  3  is formed in a housing  2  of the image forming apparatus  1 . Here, among sheets P transported along the second transport path R 2 , the sheets P that are not guided to the third transport path R 3  are discharged outside the housing  2  from the opening  3 , and are stacked on a sheet stacking section (not shown). It is possible to provide a processing device (not shown) adjacent to the housing  2 , and, for example, punch out holes in the sheets P that are discharged from the opening  3 . 
     The image forming apparatus  1  further includes a first sheet supplying device  40 A and a second sheet supplying device  40 B. The first sheet supplying device  40 A supplies a sheet P to the first transport path R 1 . The second sheet supplying device  40 B is disposed downstream from the first sheet supplying device  40 A in the sheet-P transport direction, and supplies a sheet P to the first transport path R 1 . The first sheet supplying device  40 A and the second sheet supplying device  40 B have similar structures. The first sheet supplying device  40 A and the second sheet supplying device  40 B each include a sheet holding section  41  that holds sheets P, and a take-out roller  42  that takes out and transports the sheets P held in the sheet holding section  41 . 
     First transport rollers  44  that transport a sheet P in the first transport path R 1  towards the second transfer device  30  is provided at the first transport path R 1  and upstream from the second transfer device  30 . Further, second transport rollers  45  that transport the sheet P towards the first transport rollers  44 , third transport rollers  46  that transport the sheet P towards the second transport rollers  45 , and fourth transport rollers  47  that transport the sheet P towards the third transport rollers  46  are provided. 
     In addition to these transport rollers, transport rollers  48  that transport the sheet P that is positioned in the first transport path R 1 , the second transport path R 2 , the third transport path R 3 , and the fourth transport path R 4  are provided at the first transport path R 1 , the second transport path R 2 , the third transport path R 3 , and the fourth transport path R 4 . The first transport rollers  44 , the second transport rollers  45 , the third transport rollers  46 , the fourth transport rollers  47 , and the transport rollers  48  are rotatably provided, and are formed of a pair of rollers that are rotatably provided and that push each other. One of the roller members of each pair is rotationally driven to transport the sheet P. 
     In the exemplary embodiment, a contact member  43  with which an end of a sheet P contacts is provided between the second transport rollers  45  and the third transport rollers  46 . In the exemplary embodiment, when the end of the sheet P contacts the contact member  43 , skew of the sheet P (that is, tilting of the sheet P in the transport direction) is corrected. After correcting the skew of the sheet P using the contact member  43 , the contact member  43  retreats from the first transport path R 1 . 
     The image forming apparatus  1  further includes the fixing device  50  that fixes to this sheet P an image transferred to the sheet P by a second transfer operation by the second transfer device  30 . The fixing device  50  includes a heating roller  50 A and a pressing roller  50 B. The heating roller  50 A is heated by a built-in heater (not shown). The pressing roller  50 B presses the heating roller  50 A. In this fixing device  50 , when this sheet P passes a location between the heating roller  50 A and the pressing roller  50 B, the sheet P is heated and pressed, so that an image on the sheet P is fixed to the sheet P. 
     A belt transporting section  49  that transports to the fixing device  50  the sheet P that has passed the second transfer device  30  is provided between the second transfer device  30  and the fixing device  50 . The belt transporting section  49  includes a belt that rotates. The sheet P is placed on the belt to transfer the sheet P. In the exemplary embodiment, for example, the transport rollers that are provided at the first transport path R 1 , the second transport path R 2 , the third transport path R 3 , and the fourth transport path R 4  function as transporting units. 
     In the image forming apparatus  1  according to the exemplary embodiment, in addition to being possible to form an mage on a first surface of the sheet P supplied from the first sheet supplying device  40 A, etc., it is possible to form an image on a second surface of the sheet P. In the image forming apparatus  1 , the front and back of the sheet P that has passed the fixing device  50  are reversed, so that the sheet P with its front and back reversed is transported again to the second transfer device  30 . Thereafter, the second transfer device  30  transfers an image P to the second surface of the sheet P. Thereafter, the sheet P passes the fixing device  50  again, and the transferred image is fixed to the sheet P. By this, not only is the image formed on the first surface of the sheet P, but also the image is formed on the second surface of the sheet P. 
       FIG. 2  is a perspective view of an entire structure of the sheet reversing device  100  shown in  FIG. 1 . 
     The sheet reversing device  100  according to the exemplary embodiment, serving as an exemplary reversing transporting device or a reversing transporting section, includes a frame member  101  and a sheet guiding section  200 . The frame member  101  includes four support columns and stays connected to the respective support columns. The sheet guiding section  200  is mounted to the frame member  101  and is used for reversing and transporting a sheet P. 
     Of the frame member  101  and the sheet guiding section  200 , the sheet guiding section  200  includes a transporting-in section  210 , a reversing section  220 , and a transporting-out section  230 . The transporting-in section  210  causes a sheet to be transported into the sheet guiding section  200  from the third transport path R 3 . The reversing section  220  reverses the front and back of the sheet P transported from the transporting-in section  210 . The transporting-out section  230  transports the sheet P transported from the reversing section  220  out to the fourth transport path R 4 . Here, in the exemplary embodiment, the transporting-out section  230  is disposed above the transporting-in section  210 . In addition, as viewed from above the sheet guiding section  200 , the transporting-out section  230  and the transporting-in section  210  overlap each other. The reversing section  200  is disposed on the near side of the transporting-in section  210  and the transporting-out section  230  in  FIG. 2 , that is, the reversing section  200  is disposed on the near side of the image forming apparatus  1  shown in  FIG. 1 . Therefore, in the sheet reversing device  100 , a space is formed between the transporting-in section  210  and the transporting-out section  230  of the sheet guiding section  200 . In the exemplary embodiment, the transporting-in section  210  and the transporting-out section  230  function as exemplary transporting devices. 
     The transport-in path Ra for receiving a sheet P from the third transport path R 3  is provided in the transporting-in section  210 . The reversing path Rb for receiving the sheet P from the transport-in path Ra is provided in the reversing section  220 . The transport-out path Rc for receiving the sheet P from the reversing path Rb and transferring the received sheet P to the fourth transport path R 4  is provided in the transporting-out section  230 . Therefore, in the sheet guiding section  200 , the transport-in path Ra, the reversing path Rb, and the transport-out path Rc are connected to each other to form a continuous transport path. 
     Here, the transporting-in section  210  includes a first transporting-in guiding plate  211  and a second transporting-in guiding plate  212 , which form the transport-in path Ra by being disposed so as to oppose each other. In the exemplary embodiment, the first transporting-in guiding plate  211  is disposed at the outer side (lower side) of the sheet reversing device  100  as viewed from the second transporting-in guiding plate  212 . The aforementioned space is formed above the second transporting-in guiding plate  212 . 
     The reversing section  220  includes a first reversing guiding plate  221  (refer to  FIGS. 4 to 8  described later) and a second reversing guiding section  22 , which form the reversing path Rb by being disposed so as to oppose each other. In the exemplary embodiment, the second reversing guiding plate  222  is positioned at the outer side of the sheet reversing device  100  as viewed from the first reversing guiding plate  221 . Of sides of the second reversing guiding plate  222 , the side that is opposite to the first reversing guiding plate  221  is where the aforementioned space is formed. 
     Further, the transporting-out section  230  includes a first transporting-out guiding plate  231  and a second transporting-out guiding plate  232 , which form the transport-out path Rc by being disposed so as to oppose each other. In the exemplary embodiment, the first transporting-out guiding plate  231  is positioned at the outer side (upper side) of the sheet reversing device  100  as viewed from the second transporting-out guiding plate  232 . The aforementioned space is formed below the second transporting-out guiding plate  232 . 
     The transporting-in section  210 , the reversing section  220 , and the transporting-out section  230  are each provided with transporting rollers that transport sheets P. They will be described in detail below. 
       FIG. 3  illustrates the relationship between each transport path provided in the sheet reversing device  100  and a transport direction of a sheet P in each transport path. The transport paths shown in  FIG. 3  correspond to those when the sheet reversing device  100  are viewed obliquely from the inner side. 
     Here, in the exemplary embodiment, each portion of a sheet P that passes through the sheet reversing device  100  is defined as follows. First, the sheet P is a rectangular sheet. In the sheet P that is transported into the transport-in path Ra from the third transport path R 3 , a leading end thereof in the transport direction is called a sheet front end Pl, and a trailing end thereof is called a sheet back end Pt. In the sheet P that is transported into the transport-in path Ra from the third transport path R 3 , a left end thereof in the transport direction is called a sheet first side end Ps 1 , and a right end side thereof in the transport direction is called a sheet second side end Ps 2 . Further, in the sheet P that is transported into the transport-in path Ra from the third transport path R 3 , a surface thereof that faces upward is called a sheet front surface Pf, and a surface thereof that faces downward is called a sheet back surface Pb. In the exemplary embodiment, an image formation surface (aforementioned first surface), where an image is formed by each image forming unit  10 , is called the sheet back surface Pb, and the other surface (the aforementioned second surface) is called the sheet front surface Pf. 
     Here, in the exemplary embodiment, the sheet front end Pl corresponds to a front side, the sheet back end Pt corresponds to a back side, the sheet first side end Ps 1  corresponds to a first side, and a sheet second side end Ps 2  corresponds to a second side. 
     With the sheet front surface Pf facing upward, the sheet front end P 1  being the leading end, and the sheet back end Pt being the trailing end, the sheet P is transported from the third transport path R 3  to the transport-in path Ra in a transporting-in direction Da 1  along the sheet first side end Ps 1  and the sheet second side end Ps 2 . With the sheet front surface Pf facing upward, the sheet first side end Ps 1  being the leading end, and the sheet second side end Ps 2  being the trailing end, the sheet P is transported towards the reversing path Rb from the transport-in path Ra in a transfer direction Da 2  along the sheet front end Pl and the sheet back end Pt. 
     With the sheet front surface Pf facing upward, the sheet first side end Ps 1  being the leading end, and the sheet second side end Ps 2  being the trailing end, the sheet P is transported to the reversing path Rb from the transport-in path Ra in a reverse direction Db along the sheet front end P 1  and the sheet back end Pt. At a boundary between the transport-in path Ra and the reversing path Rb, the transfer direction Da 2  and the reversing direction Db are the same direction. Here, the reversing direction Db is a curved (U-shaped) direction. The sheet P is transported through the reversing path Rb so that, when viewed from above the sheet P, its sheet first side end Ps 1  and its sheet second side end Ps 2  are reversed, and its front and back (sheet front surface Pf and sheet back surface Pb) are reversed. Therefore, with the sheet back surface Pb facing upward, the sheet first side end Ps 1  being the leading end, and the sheet second side end Ps 2  being the trailing end, the sheet P is transported from the reversing path Rb in the reversing direction Db along the sheet front end Pl and the sheet back end Pt. 
     With the sheet back surface Pb facing upward, the sheet first side end Ps 1  being the leading end, and the sheet second side end Ps 2  being the trailing end, the sheet P is transported to the transport-out path Rc from the reversing path Rb in the transfer direction Dc 1  along the sheet front end Pl and the sheet back end Pt. At a boundary between the reversing path Rb and the transport-out path Rc, the reversing direction Db and the transfer direction Dc 1  are the same direction. With the sheet back surface Pb facing upward, the sheet front end Pl being the leading end, and the sheet back end Pt being the trailing end, the sheet P is transported towards the fourth transport path R 4  from the transport-out path Rc in the transport-out direction Dc 2  along the sheet first side end Ps 1  and the sheet second side end Ps 2 . 
     Here, in the exemplary embodiment, the transporting-in direction Da 1  corresponds to a first direction, the transfer direction Da 2  corresponds to a second direction, the reversing direction Db corresponds to a third direction, the transfer direction Dc 1  corresponds to a fourth direction, and the transport-out direction Dc 2  corresponds to a fifth direction. The transport-in path Ra and the transport-out path Rc correspond to transport paths. Further, in the transport-in path Ra, the transporting-in direction Da 1  corresponds to an input direction, and the transfer direction Da 2  corresponds to an output direction. Still further, in the transport-out path Rc, the transfer direction Dc 1  corresponds to an input direction, and the transporting-out direction Dc 2  corresponds to an output direction. 
     Accordingly, in the sheet reversing device  100  according to the exemplary embodiment, the sheet P supplied from the transport-in path Ra by supplying the sheet P to the reversing path Rb by reversing the direction of travel of the sheet P supplied from the third transport path R 3  by 90 degrees at the transport-in path Ra is rotated by 180 degrees at the reversing path Rb. By this, the front and back of the sheet P are reversed, and the sheet P is supplied to the transport-out path Rc. The direction of travel of the sheet P supplied from the reversing path Rb is reversed by 90 degrees at the transport-out path Rc, and the sheet P is supplied to the fourth transport path R 4 . At this time, the transporting-in direction Da 1  at the transport-in path Ra and the transporting-out direction Dc 2  at the transport-out path Rc are the same direction. Before and after the sheet P passes the sheet reversing device  100 , the relationship between the sheet front end Pl and the sheet back end Pt in the transport direction does not change, whereas the sheet front surface Pf and the sheet back surface Pb are reversed by reversing the sheet first side end Ps 1  and the sheet second side end Ps 2  with respect to the transport direction. 
     Next, the structure of the sheet reversing device  100  will be described in more detail. 
       FIG. 4  is a perspective view of a case in which the second reversing guiding plate  222  is set in an open state in the sheet reversing device  100  shown in  FIG. 2 . 
     In the exemplary embodiment, in the reversing section  220  of the sheet reversing device  100 , the second reversing guiding plate  222  is provided so as to be openable and closable with respect to the first reversing guiding plate  221 . Here, the reversing guiding plate  222  is rotatable with respect to a lower side (the transporting-in section  210  side) as an axis. Therefore, when, at the reversing section  220 , the second reversing guiding plate  222  is opened with respect to the first reversing guiding plate  221 , the reversing path Rb (see  FIG. 2 ), formed by the first reversing guiding plate  221  and the second reversing guiding plate  222 , is exposed so as to extend upward at the near side of the sheet reversing device  100  and the image forming apparatus  1  (see  FIG. 1 ). 
       FIG. 5  is a perspective view of a case in which the reversing section  220  is further set in an open state in the sheet reversing device  100  shown in  FIG. 2 . 
     In the exemplary embodiment, the reversing section  220  constituting the sheet reversing device  100  is provided so as to be openable and closable with respect to the frame member  101 . Here, the reversing section  220  rotates around columns provided at the illustrated near side and the illustrated inner side of the frame member  101  as axes. Therefore, the sheet reversing device  100 , by opening the reversing section  220  with respect to the frame member  101 , the space that is formed between the transporting-in section  210  and the transporting-out section  230  of the sheet reversing device  100  is exposed at the near side of the sheet reversing device  100  and the image forming apparatus  1  (see  FIG. 1 ). 
       FIG. 6  is a perspective view of a case in which the second reversing guiding plate  222  is set in an open state in the sheet reversing device  100  shown in  FIG. 5 . 
     Accordingly, in the sheet reversing device  100  according to the exemplary embodiment, after opening the reversing section  220  with respect to the frame member  101 , it is possible to further open the second reversing guiding plate  222  with respect to the first reversing guiding plate  221  in the reversing section  220 . 
       FIG. 7  is a perspective view of a case in which the second transporting-in guiding plate  212  is further set in an open state in the sheet reversing device  100  shown in  FIG. 6 . 
     In the exemplary embodiment, in the transporting-in section  210  of the sheet reversing device  100 , the second transporting-in guiding plate  212  is provided so as to be openable and closable with respect to the first transporting-in guiding plate  211  secured to the frame member  101 . Here, the second transporting-in guiding plate  212  rotates with respect to the inner side of the sheet reversing device  100  (serving as the inner side of the image forming apparatus  1  shown in  FIG. 1 ) as an axis. Therefore, in the sheet reversing device  100  whose reversing section  220  is set in an open state, when the second transporting-in guiding plate  212  is opened with respect to the first transporting-in guiding plate  211 , the transport-in path Ra (see  FIG. 2 ), formed by the first transporting-in guiding plate  211  and the second transporting-in guiding plate  212 , is exposed so as to extend towards the front at the near side of the image forming apparatus  1  and the sheet reversing device  100 . 
       FIG. 8  is a perspective view of a case in which the second transporting-out guiding plate  232  is set in an open state in the sheet reversing device  100  shown in  FIG. 6 . 
     In the exemplary embodiment, in the transporting-out section  230  of the sheet reversing device  100 , the second transporting-out guiding plate  232  is provided so as to be openable and closable with respect to the first transporting-out guiding plate  231  secured to the frame member  101 . Here, the second transporting-out guiding plate  232  rotates with respect to the inner side of the sheet reversing device  100  (serving as the inner side of the image forming apparatus  1  shown in  FIG. 1 ) as an axis. Therefore, in the sheet reversing device  100  whose reversing section  220  is set in an open state, when the second transporting-out guiding plate  232  is opened with respect to the first transporting-in guiding plate  231 , the transport-in path Rc (see  FIG. 2 ), formed by the first transporting-out guiding plate  231  and the second transporting-out guiding plate  232 , is exposed so as to extend towards the front at the near side of the image forming apparatus  1  and the sheet reversing device  100 . 
     Therefore, when a sheet P is jammed at the reversing section  220 , the jammed sheet P is capable of being removed by setting the sheet reversing device  100  in, for example, the state shown in  FIG. 4 . When a sheet P is jammed at the transporting-in section  210 , the jammed sheet P is capable of being removed by setting the sheet reversing device  100  in, for example, the state shown in  FIG. 7 . Further, when a sheet P is jammed at the transporting-out section  230 , the jammed sheet P is capable of being removed by setting the sheet reversing device  100  in, for example, the state shown in  FIG. 8 . A user is capable of removing such jammed sheets by operating respective portions of the sheet reversing device  100  from the near side of the image forming apparatus  1 . 
     A mechanism (not shown) for securing the second transporting-in guiding plate  212  to the first transporting-in guiding plate  211  is mounted to the transporting-in section  210 . A mechanism (not shown) for securing the second reversing guiding plate  222  to the first reversing guiding plate  221  is mounted to the reversing section  220 . A mechanism (not shown) for securing the second transporting-out guiding plate  232  with respect to the first transporting-out guiding plate  231  is mounted to the transporting-out section  230 . 
       FIG. 9  illustrates the structure of each transporting section and each transport path in the sheet reversing device  100  according to the exemplary embodiment.  FIG. 9  is a development plan view of the transport-in path Ra, the reversing path Rb, and the transport-out path Rc in the sheet reversing device  100 . 
     The sheet reversing device  100  includes an upstream-side reversing transporting section  400 A and a transporting-in transporting section  300 , provided at the transporting-in section  210 . The transporting-in transporting section  300  transports a sheet P along the transporting-in direction Da 1 . The upstream-side reversing transporting section  400 A transports a sheet P along the transfer direction Da 2 . The sheet reversing device  100  further includes a midstream-side reversing transporting section  400 B that is provided at the reversing section  220  and that transports a sheet P along the reversing direction Db. The sheet reversing device  100  still further includes a transporting-out transporting section  500  and a downstream-side reversing transporting section  400 C, provided at the transporting-out section  230 . The downstream-side reversing transporting section  400 C transports a sheet P along the transfer direction Dc 1 . The transporting-out transporting section  500  transports a sheet P along the transport-out direction Dc 2 . In the exemplary embodiment, the upstream-side reversing transporting section  400 A, provided at the transporting-in section  210 , the midstream-side reversing transporting section  400 B, provided at the reversing section  220 , and the downstream-side reversing transporting section  400 C, provided at the transporting-out section  230 , are collectively called the reversing transporting section  400 . 
     Here, in the exemplary embodiment, the transporting-in transporting section  300  corresponds to a first transporting section, the upstream-side reversing transporting section  400 A corresponds to a second transporting section, the midstream-side reversing transporting section  400 B corresponds to a third transporting section, the downstream-side reversing transporting section  400 C corresponds to a fourth transporting section, and the transporting-out transporting section  500  corresponds to a fifth transporting section. In the transporting-in section  210 , the transporting-in transporting section  300  corresponds to an input-side transporting section, and the upstream-side reversing transporting section  400 A corresponds to an output-side transporting section. Further, in the transporting-out section  230 , the downstream-side reversing transporting section  400 C corresponds to an input-side transporting section, and the transporting-out transporting section  500  corresponds to an output-side transporting section. 
     Of these sections, the transporting-in transporting section  300 , provided at the transporting-in section  210 , includes, from an upstream side in the transport-in direction Da 1 , a first transporting-in roller pair  301  (situated closest to the third transport path R 3 ), a second transporting-in roller pair  302 , a third transporting-in roller pair  303 , a fourth transporting-in roller pair  304 , a fifth transporting-in roller pair  305 , and a sixth transporting-in roller pair  306 . The upstream-side reversing transporting section  400 A, provided at the transporting-in section  210 , includes, from an upstream side in the transfer direction Da 2 , an upstream-side first reversing roller pair  401 , an upstream-side second reversing roller pair  402 , an upstream-side third reversing roller pair  403 , and an upstream-side fourth reversing roller pair  404  (situated closest to the reversing path Rb). 
     The midstream-side reversing transporting section  400 B, provided at the reversing section  220 , includes, from an upstream side in the reversing direction Db, a midstream-side first reversing roller pair  411  (situated closest to the transport-in path Ra), a midstream-side second reversing roller pair  412 , and a midstream-side third reversing roller pair  413  (situated closest to the transport-out path Rc). 
     The downstream-side reversing transporting section  400 C, provided at the transporting-out section  230 , includes, from an upstream side in the transfer direction Dc 1 , a downstream-side first reversing roller pair  421  (situated closest to the reversing path Rb), a downstream-side second reversing roller pair  422 , a downstream-side third reversing roller pair  423 , and a downstream-side fourth reversing roller pair  424 . The transporting-out transporting section  500 , provided at the transporting-out section  230 , includes, from an upstream side in the transport-out direction Dc 2 , a first transporting-out roller pair  501 , a second transporting-out roller pair  502 , a third transporting-out roller pair  503 , a fourth transporting-out roller pair  504 , a fifth transporting-out roller pair  505 , and a sixth transporting-out roller pair  506  (situated closest to the fourth transport path R 4 ). 
     In the transport-in path Ra, the upstream-side first reversing roller pair  401  to the upstream-side third reversing roller pair  403  of the upstream-side reversing transporting section  400 A are disposed between the third transporting-in roller pair  303  and the fourth transporting-in roller pair  304  of the transporting-in transporting section  300 . In the transport-out path Rc, the downstream-side second reversing roller pair  422  to the downstream-side fourth reversing roller pair  424  of the downstream-side reversing transporting section  400 C are disposed between the third transporting-out roller pair  503  and the fourth transporting-out roller pair  504  of the transporting-out transporting section  500 . 
     Here, in the exemplary embodiment, in transporting a sheet P from the third transport path R 3  to the transport-in path Rc, a central position between the sheet first side end Ps 1  and the sheet second side end Ps 2  (both of which are shown in  FIG. 3 ) of a sheet P that is being transported is aligned with a transporting-in-direction transport reference line La that is set linearly with respect to the third transport path R 3  and the transport-in path Ra. In the transport-in path Ra, the rollers of the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  of the transporting-in transporting section  300  are disposed on respective sides of the transporting-in direction transport reference line La. 
     In the exemplary embodiment, in transporting a sheet P from the transport-in path Ra to the transport-out path Rc through the reversing path Rb, a central position between the sheet back end Pt and the sheet front end Pl of the sheet P that is being transported is aligned with a reversing-direction transport reference line Lb that is set linearly with respect to the reversing path Rb and the transport-out path Rc. In the transport-in path Ra, the rollers of the upstream-side first reversing roller pair  401  to the upstream-side fourth reversing roller pair  404  of the upstream-side reversing transporting section  400 A are disposed on respective sides of the reversing-direction transport reference line Lb. Further, in the reversing path Rb, the rollers of the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  of the midstream-side reversing transporting section  400 B are also disposed on respective sides of the reversing-direction transport reference line Lb. Further, in the transport-out path Rc, the rollers of the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  of the downstream-side reversing transporting section  400 C are also disposed on respective sides of the reversing-direction transport reference line Lb. 
     Further, in the exemplary embodiment, in transporting a sheet P from the transport-out path Rc to the fourth transport path R 4 , a central position between the sheet first side end Ps 1 , and the sheet second side end Ps 2  (both of which are shown in  FIG. 2 ) of the sheet P that is being transported is aligned with a transporting-out-direction transport reference line Lc that is set linearly with respect to the fourth transport path R 4  and the transport-out path Rc. In the transport-out path Rc, the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506  of the transporting-out transporting section  500  are disposed on respective sides of the transporting-out-direction transport reference line Lc. 
       FIGS. 10A to 10E  each illustrate the structure of a pair of transport rollers provided at each transporting section of the sheet reversing device  100 . Here,  FIG. 10A  shows an exemplary structure of the first transporting-in roller pair  301  in the transporting-in transporting section  300  provided at the transporting-in section  210 .  FIG. 10B  shows an exemplary structure of the upstream-side first reversing roller pair  401  in the upstream-side reversing transporting section  400 A provided at the transport-in section  210 . Further,  FIG. 10C  is an exemplary structure of the midstream-side second reversing roller pair  412  in the midstream-side reversing transporting section  400 B provided at the reversing section  220 . Still further,  FIG. 10D  shows an exemplary structure of the downstream-side fourth reversing roller pair  424  in the downstream-side reversing transporting section  400 C provided at the transporting-out section  230 . Still further,  FIG. 10E  shows an exemplary structure of the first transporting-out roller pair  501  in the transporting-out transporting section  500  provided at the transporting-out section  230 . 
     As shown in  FIG. 10A , the first transporting-in roller pair  301  of the transporting-in transporting section  300  includes a transporting-in driving roller  300   a  and a transporting-in driven roller  300   b . The transporting-in driving roller  300   a  receives outside driving force. The transporting-in driven roller  300   b  is disposed so as to oppose the transporting-in driving roller  300   a , and rotates as the transporting-in driving roller  300   a  rotates. The second transporting-in roller pair  302  to the sixth transporting-in roller pair  306  of the transporting-in transporting section  300  also each include a transporting-in driving roller  300   a  and a transporting-in driven roller  300   b . In the exemplary embodiment, each transporting-in driving roller  300   a  of the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  is mounted to the first transporting-in guiding plate  211  (see  FIG. 3 ), serving as a fixed side in the transporting-in section  210 . Each transporting-in driven roller  300   b  of the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  is mounted to the second transporting-in guiding plate  212  (see  FIG. 3 ), serving as a movable side (openable-closable side) in the transporting-in section  210  (see  FIG. 3 ). 
     The first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  function as a pair of rotating members, with each transporting-in driving roller  300   a  functioning as a driving rotating member and each transporting-in driven roller  300   b  functioning as a driven rotating member. In the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306 , each transporting-in driving roller  300   a  functions as an input-side driving rotating member, and each transporting-in driven roller  300   b  functions as an input-side driven rotating member. 
     Here, each transporting-in driving roller  300   a  includes a shaft  3001   a , formed of metal and extending along the transfer direction Da 2  in the transport-in path Ra (see  FIG. 9 ), and two rubber rollers  3002   a , mounted to the shaft  3001   a . In each transporting-in driving roller  300   a , each rubber roller  3002   a  has a columnar shape. 
     Each transporting-in driven roller  300   b  includes a shaft  3001   b  and two resin rollers  3002   b . Each shaft  3001   b  is formed of metal and extends along the transfer direction Da 2  in the transport-in path Ra (see  FIG. 9 ). The resin rollers  3002   b  are mounted to positions of the shaft  3001   b  that are opposite to the respective rubber rollers  3002   a  provided at the transporting-in driving roller  300   a . In each transporting-in driven roller  300   b , one end side of each resin roller  3002   b , serving as a downstream side in the transfer direction Da 2 , has a columnar shape, whereas the other end side of each resin roller  3002   b , serving as an upstream side in the transfer direction Da 2 , is tapered (has a tapered portion). 
     As shown in  FIG. 10B , the upstream-side first reversing roller pair  401  of the upstream-side reversing transporting section  400 A includes a reversing driving roller  400   a  and a reversing driven roller  400   b . The reversing driving roller  400   a  rotates by receiving outside driving force. The reversing driven roller  400   b  is disposed so as to oppose the reversing driving roller  400   a , and rotates as the reversing driving roller  400   a  rotates. The upstream-side second reversing roller pair  402  to the upstream-side fourth reversing roller pair  404  of the upstream-side reversing transporting section  400 A also each include a reversing driving roller  400   a  and a reversing driven roller  400   b . In the exemplary embodiment, the reversing driving rollers  400   a  of the upstream-side first reversing roller pair  401  to the upstream-side fourth reversing roller pair  404  are mounted to the first transporting-in guiding plate  211  (see  FIG. 2 ), serving as the fixed side in the transporting-in section  210 . The reversing driven rollers  400   b  of the upstream-side first reversing roller pair  401  to the upstream-side fourth reversing roller pair  404  are mounted to the second transporting-in guiding plate  212  (see  FIG. 2 ), serving as the movable side (that is, the openable-and-closable side) in the transporting-in section  210  (see  FIG. 2 ). 
     The upstream-side first reversing roller pair  401  to the upstream-side fourth reversing roller pair  404  function as a pair of rotating members, with each reversing driving roller  400   a  functioning as a driving rotating member and each reversing driven roller  400   b  functioning as a driven rotating member. In each of the upstream-side first reversing roller pair  401  to the upstream-side fourth roller pair  404 , the reversing driving roller  400   a  functions as an output-side driving rotating member, and each reversing driven roller  400   b  functions as an output-side driven rotating member. 
     Here, each reversing driving roller  400   a  of the upstream-side reversing transporting section  400 A includes a shaft  4001   a , formed of metal and extending along the transporting-in direction Da 1  in the transport-in path Ra (see  FIG. 9 ), and two rubber rollers  4002   a , mounted to the shaft  4001   a . In each reversing driving roller  400   a  of the upstream-side reversing transporting section  400 A, each rubber roller  4002   a  has a columnar shape. 
     Each reversing driven roller  400   b  of the upstream-side reversing transporting section  400 A includes a shaft  4001   b  and two resin rollers  4002   b . Each shaft  4001   b  is formed of metal and extends along the transporting-in direction Da 1  in the transport-in path Ra (see  FIG. 9 ). The resin rollers  4002   b  are mounted to positions of the corresponding shaft  4001   b  that are opposite to the respective rubber rollers  4002   a  provided at the corresponding reversing driving roller  400   a . In each reversing driven roller  400   b  of the upstream-side reversing transporting section  400 A, one end side of each resin roller  4002   b , serving as a downstream side in the transporting-in direction Da 1 , has a columnar shape, whereas the other end side of each resin roller  4002   b , serving as an upstream side in the transporting-in direction Da 1 , is tapered (has a tapered portion). 
     In the reversing driving roller  400   a  of the upstream-side fourth reversing roller pair  404 , four rubber rollers  4002   a  are mounted to one shaft  4001   a . In the reversing driven roller  400   b  of the upstream-side fourth reversing roller pair  404 , four rubber rollers  4002   b  are mounted to one shaft  4001   b.    
     As shown in  FIG. 10C , the midstream-side second reversing roller pair  412  of the midstream-side reversing transporting section  400 B includes a reversing driving roller  400   a  and a reversing driven roller  400   b . The reversing driving roller  400   a  rotates by receiving outside driving force. The reversing driven roller  400   b  is disposed so as to oppose the reversing driving roller  400   a , and rotates as the reversing driving roller  400   a  rotates. The midstream-side first reversing roller pair  411  and the midstream-side third reversing roller pair  413  of the midstream-side reversing transporting section  400 B also each include a reversing driving roller  400   a  and a reversing driven roller  400   b . In the exemplary embodiment, the reversing driving rollers  400   a  of the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  are mounted to the first reversing guiding plate  211  (see  FIG. 2 ), serving as a fixed side in the reversing section  220  (see  FIG. 2 ). The reversing driven rollers  400   b  of the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  are mounted to the second reversing guiding plate  222  (see  FIG. 2 ), serving as a movable side (that is, an openable-and-closable side) in the reversing section  210  (see  FIG. 2 ). 
     Here, each reversing driving roller  400   a  of the midstream-side reversing transporting section  400 B includes a shaft  4001   a  and four rubber rollers  4002   a . Each shaft  4001   a  is formed of metal, crosses the reversing direction Db in the reversing path Rb (see  FIG. 9 ), and extends along the transporting-in direction Da 1  and the transporting-out direction Dc 2 . The four rubber rollers  4002   a  of each reversing driving roller  400   a  are mounted to the corresponding shaft  4001   a . In each reversing driving roller  400   a  of the midstream-side reversing transporting section  400 B, each rubber roller  4002   a  has a columnar shape. 
     Each reversing driven roller  400   b  of the midstream-side reversing transporting section  400 B includes a shaft  4001   b  and four resin rollers  4002   b . Each shaft  4001   b  is formed of metal, crosses the reversing direction Db in the reversing path Rb, and extends along the transporting-in direction Da 1  and the transporting-out direction Dc 2 . The resin rollers  4002   b  are mounted to positions of the corresponding shaft  4001   b  that are opposite to the respective rubber rollers  4002   a  provided at the corresponding reversing driving roller  400   a . In each reversing driven roller  400   b  of the midstream-side reversing transporting section  400 B, each resin roller  4002   b  has a columnar shape. 
     As shown in  FIG. 10D , the downstream-side fourth reversing roller pair  424  of the downstream-side reversing transporting section  400 C includes a reversing driving roller  400   a  and a reversing driven roller  400   b . The reversing driving roller  400   a  rotates by receiving outside driving force. The reversing driven roller  400   b  is disposed so as to oppose the reversing driving roller  400   a , and rotates as the reversing driving roller  400   a  rotates. The downstream-side first reversing roller pair  421  to the downstream-side third reversing roller pair  413  of the downstream-side reversing transporting section  400 C also each include a reversing driving roller  400   a  and a reversing driven roller  400   b . In the exemplary embodiment, each reversing driving rollers  400   a  of the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  are mounted to the first transporting-out guiding plate  231  (see  FIG. 3 ), serving as a fixed side in the transporting-out section  230  (see  FIG. 3 ). The reversing driven rollers  400   b  of the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  are mounted to the second transporting-out guiding plate  232  (see  FIG. 3 ), serving as a movable side (that is, an openable-and-closable side) in the transporting-out section  230  (see  FIG. 3 ). 
     The downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  function as a pair of rotating members, with each reversing driving roller  400   a  functioning as a driving rotating member and each reversing driven roller  400   b  functioning as a driven rotating member. In each of the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424 , the reversing driving roller  400   a  functions as an input-side driving rotating member, and the reversing driven roller  400   b  functions as an input-side driven rotating member. 
     Here, each reversing driving roller  400   a  of the downstream-side reversing transporting section  400 C includes a shaft  4001   a , formed of metal and extending along the transporting-out direction Dc 2  in the transporting-out path Rc (see  FIG. 9 ), and two rubber rollers  4002   a , mounted to the shaft  4001   a . In each reversing driving roller  400   a  of the downstream-side reversing transporting section  400 C, each rubber roller  4002   a  has a columnar shape. 
     Each reversing driven roller  400   b  of the downstream-side reversing transporting section  400 C includes a shaft  4001   b  and two resin rollers  4002   b . Each shaft  4001   b  is formed of metal, and extends along the transporting-out direction Dc 2  in the transport-out path Rc (see  FIG. 9 ). The resin rollers  4002   b  are mounted to positions of the corresponding shaft  4001   b  that are opposite to the respective rubber rollers  4002   a  provided at the corresponding reversing driving roller  400   a . In each reversing driven roller  400   b  of the downstream-side reversing transporting section  400 C, one end side of each resin roller  4002   b , serving as a downstream side in the transporting-out direction Da 2 , has a columnar shape, whereas the other end side of each resin roller  4002   b , serving as an upstream side in the transporting-out direction Da 2 , is tapered (has a tapered portion). 
     In the reversing driving roller  400   a  of the downstream-side first reversing roller pair  421 , four rubber rollers  4002   a  are mounted to one shaft  4001   a . In the reversing driven roller  400   b  of the downstream-side first reversing roller pair  421 , four rubber rollers  4002   b  are mounted to one shaft  4001   b.    
     As shown in  FIG. 10E , the first transporting-out roller pair  501  of the transporting-out transporting section  500  includes a transporting-out driving roller  500   a  and a transporting-out driven roller  500   b . The transporting-out driving roller  500   a  rotates by receiving outside driving force. The transporting-out driven roller  500   b  is disposed so as to oppose the transporting-out driving roller  500   a , and rotates as the transporting-out driving roller  500   a  rotates. The second transporting-out roller pair  502  to the sixth transporting-out roller pair  506  of the transporting-out transporting section  500  also each include a transporting-out driving roller  500   a  and a transporting-out driven roller  500   b . In the exemplary embodiment, the transporting-out driving rollers  500   a  of the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506  are mounted to the first transporting-out guiding plate  231  (see  FIG. 2 ), serving as a fixed side in the transporting-out section  230  (see  FIG. 2 ). The transporting-out driven rollers  500   b  of the first transporting-out roller pair  501  to the sixth reversing transporting-out roller pair  506  are mounted to the second transporting-out guiding plate  232  (see  FIG. 2 ), serving as the movable side (that is, the openable-and-closable side) in the transporting-out section  230  (see  FIG. 2 ). 
     The first transporting-out roller pair  501  to the sixth transporting roller pair  506  function as a pair of rotating members, with each transporting-out driving roller  500   a  functioning as a driving rotating member and each transporting-out driven roller  500   b  functioning as a driven rotating member. In each of the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506 , the transporting-out driving roller  500   a  functions as an output-side driving rotating member, and the transporting-out driven roller  500   b  functions as an output-side driven rotating member. 
     Here, each transporting-out driving roller  500   a  includes a shaft  5001   a , formed of metal and extending along the transfer direction Dc 1  in the transport-out path Rc (see  FIG. 9 ), and two rubber rollers  5002   a , mounted to the shaft  5001   a . In each transporting-out driving roller  500   a , each rubber roller  5002   a  has a columnar shape. 
     Each transporting-out driven roller  500   b  includes a shaft  5001   b  and two resin rollers  5002   b . Each shaft  5001   b  is formed of metal, and extends along the transfer direction Da 1  in the transport-out path Rc (see  FIG. 9 ). The resin rollers  5002   b  are mounted to positions of the corresponding shaft  5001   b  that are opposite to the respective rubber rollers  5002   a  provided at the corresponding transporting-out driving roller  500   a . In each resin roller  5002   b  of the transporting-out driven roller  500   b , one end side of each resin roller  5002   b , serving as a downstream side in the transfer direction Dc 1 , has a columnar shape, whereas the other end side of each resin roller  5002   b , serving as an upstream side in the transfer direction Da 1 , is tapered (has a tapered portion). 
       FIGS. 11A to 11E  each illustrate the relationship between the pair of transport rollers and the corresponding transport path in the sheet reversing device  100  according to the exemplary embodiment.  FIGS. 11A to 11E  correspond to  FIGS. 10A to 10E . That is,  FIG. 11A  shows the relationship between the transport-in path Ra and the first transporting-in roller pair  301  in the transporting-in section  210 . In addition,  FIG. 11B  shows the relationship between the transport-in path Ra and the upstream-side first reversing roller pair  401  in the transporting-in section  210 . Further,  FIG. 11C  shows the relationship between the reversing path Rb and the midstream-side second reversing roller pair  412  in the reversing section  220 . Still further,  FIG. 11D  shows the relationship between the transport-out path Rc and the downstream-side fourth reversing roller pair  424  in the transporting-out section  230 . Still further,  FIG. 11E  shows the relationship between the transport-out path Rc and the first transporting-out roller pair  501  in the transporting-out section  230 . 
     As shown in  FIG. 11A , the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  of the first transporting-in roller pair  301  are contactably and separably formed. When the rollers  300   a  and  300   b  of the first transporting-in roller pair  301  contact each other, the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  are in a state in which they are in the transport-in path Ra. In contrast, when the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  of the first transporting-in roller pair  301  are to be separated from each other, moving the transporting-in driving roller  300   a  away from the transporting-in driven roller  300   b  causes the transporting-in driven roller  300   b  to be kept in the transport-in path Ra, and the transporting-in driving roller  300   a  to retreat from the transport-in path Ra. The rollers of the second transporting-in roller pair  302  to the sixth transporting-in roller pair  306  that constitute the transporting-in transporting section  300  along with the first transporting-in roller pair  301  also contact and separate from each other as with the rollers of the first transporting-in roller pair  301 . 
     As shown in  FIG. 11B , the reversing driving roller  400   a  and the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  are contactably and separably formed. When the reversing driving roller  400   a  and the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  contact each other, the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are in the transport-in path Ra. In contrast, when the reversing driving roller  400   a  and the reversing driven roller  400   b  of the upstream-side reversing roller pair  401  are to be separated from each other, moving the reversing driving roller  400   a  away from the reversing driven roller  400   b  causes the reversing driven roller  400   b  to be kept in the transport-in path Ra, and the reversing driving roller  400   a  to retreat from the transport-in path Ra. The rollers of the upstream-side second reversing roller pair  402  to the upstream-side fourth reversing roller pair  404  that constitute the upstream-side reversing transporting section  400 A along with the upstream-side first reversing roller pair  401  also contact and separate from each other as with the rollers of the upstream-side first reversing roller pair  401 . 
     As shown in  FIG. 110 , the reversing driving roller  400   a  and the reversing driven roller  400   b  of the midstream-side second reversing roller pair  412  are formed so that they normally contact each other. At this time, both of the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are in the reversing path Rb. The midstream-side first reversing roller pair  411  and the midstream-side third reversing roller pair  413  that constitute the midstream-side reversing transporting section  400 B along with the midstream-side second reversing roller pair  412  are also formed so that their rollers normally contact each other as with the rollers of the midstream-side second reversing roller pair  412 . 
     As shown in  FIG. 11D , the reversing driving roller  400   a  and the reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  are contactably and separably formed. When the reversing driving roller  400   a  and the reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  contact each other, the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are in the transport-out path Rc. In contrast, when the reversing driving roller  400   a  and the reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  are to be separated from each other, moving the reversing driving roller  400   a  away from the reversing driven roller  400   b  causes the reversing driven roller  400   b  to be kept in the transport-out path Rc, and the reversing driving roller  400   a  to retreat from the transport-out path Rc. The rollers of the downstream-side first reversing roller pair  421  to the downstream-side third reversing roller pair  423  that constitute the downstream-side reversing transporting section  400 C along with the downstream-side fourth reversing roller pair  424  also contact and separate from each other as with the rollers of the downstream-side fourth reversing roller pair  424 . 
     As shown in  FIG. 11E , the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  of the first transporting-out roller pair  501  are contactably and separably formed. When the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  of the first transporting-out roller pair  501  contact each other, the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  are in a state in which they are in the transport-out path Rc. In contrast, when the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  of the first transporting-out roller pair  501  are to be separated from each other, moving the transporting-out driving roller  500   a  away from the transporting-out driven roller  500   b  causes the transporting-out driven roller  500   b  to be kept in the transport-out path Rc, and the transporting-out driving roller  500   a  to retreat from the transport-out path Rc. The rollers of the second transporting-out roller pair  502  to the sixth transporting-out roller pair  506  that constitute the transporting-out transporting section  500  along with the first transporting-out roller pair  501  also contact and separate from each other as with the rollers of the first transport-out roller pair  501 . 
       FIGS. 12A to 12D  each illustrate an exemplary structure of an advancing/retreating mechanism  600  and a rotating mechanism  700 . The advancing/retreating mechanism  600  causes one of the rollers of the upstream-side first reversing roller pair  401  to advance and retreat. The rotating mechanism  700  rotates the upstream-side first reversing roller pair  401 . Here,  FIG. 12A  shows the upstream-side first reversing roller pair  401 , whose rollers contact each other, and the advancing/retreating mechanism  600  as viewed from the downstream side in the transport-in direction Da 1 .  FIG. 12B  shows the upstream-side first reversing roller pair  401 , whose rollers are separated from each other, and the advancing/retreating mechanism  600  as viewed from the downstream side in the transporting-in direction Da 1 .  FIG. 12C  shows the upstream-side first reversing roller pair  401 , whose rollers are separated from each other, the advancing/retreating mechanism  600 , and the rotating mechanism  700  as viewed from a downstream side in the transfer direction Da 2 .  FIG. 12D  shows the rotating mechanism  700  as viewed from the downstream side in the transporting-in direction Da 1 . 
     The advancing/retreating mechanism  600  according to the exemplary embodiment includes an advancing/retreating motor  601 , a gear train  602 , a driving-side cam shaft  603 , and driving-side cams  604 . The advancing/retreating motor  601  causes the reversing driving roller  400   a  in the upstream-side first reversing roller pair  401  to advance towards and retreat from the reversing driven roller  400   b . The gear train  602  includes gears that are mounted to a rotary shaft of the advancing/retreating motor  601 . The driving-side cam shaft  603  is secured and mounted to one of the gears of the gear train  602 . The driving-side cams  604  are mounted to two locations of the driving-side cam shaft  603  in an axial direction. The advancing/retreating mechanism  600  also includes ball bearings  605 , driving-side bearings  606 , and driving-side bearing guides  607 . The ball bearings  605  are mounted to positions of the shaft  4001   a  of the reversing driving roller  400   a  opposing the two driving-side cams  604  provided at the driving-side cam shaft  603 . The driving-side bearings  600  are mounted to respective ends of the shaft  4001   a  of the reversing driving roller  400   a , and rotatably support the reversing driving roller  400   a . In correspondence with the two driving-side bearings  606 , the driving-side bearing guides  607  are secured and mounted to a surface of the first transporting-in guiding plate  211  at a side opposite to a surface of the first transporting-in guiding plate  211  where the transport-in path Ra is formed. The driving-side bearing guides  607  support the reversing driving roller  400   a  using the driving-side bearings  606  so that the reversing driving roller  400   a  is movable towards and away from the transport-in path Ra. The advancing/retreating mechanism  600  further includes driven-side bearings  611 , driven-side bearing guides  612 , and springs  613 . The driven-side bearings  611  are mounted to respective ends of the shaft  4001   b  of the reversing driven roller  400   b  in the upstream-side first reversing roller pair  401 , and rotatably support the reversing driven roller  400   b . In correspondence with the two driven-side bearings  611 , the driven-side bearing guides  612  are secured and mounted to a surface of the second transporting-in guiding plate  212  at a side opposite to a surface of the second transporting-in guiding plate  212  where the transport-in path Ra is formed. The driven-side bearing guides  612  support the reversing driven roller  400   b  so that the reversing driven roller  400   b  is movable towards and away from the transport-in path Ra. Both ends of the springs  613  are secured and mounted to the surface of the second transporting-in guiding plate  212  at the side opposite to the surface of the second transporting-in guiding plate  212  where the transport-in path Ra is formed. A central portion of each spring  613  is mounted to a portion of the corresponding driven-side bearing  611  that is disposed outwardly of a portion of the driven-side bearing  611  that is supported by the corresponding driven-side bearing guide  612 . 
     The rotating mechanism  700  according to the exemplary embodiment includes a rotating motor  701 , a motor-side pulley  702 , a roller-side pulley  703 , and a timing belt  704 . The rotating motor  701  is used for rotating the reversing driving roller  400   a  in the upstream-side first reversing roller pair  401 . The motor-side pulley  702  is mounted to a rotary shaft of the rotating motor  701 . The roller-side pulley  703  is secured and mounted to an end side of the shaft  4001   a  in the reversing driving roller  400   a . The timing belt  704  is an endless belt, and is placed on the motor-side pulley  702  and the roller-side pulley  703 . 
     The operation for causing the separated rollers of the upstream-side first reversing roller pair  401  to contact each other (hereunder referred to as “contacting operation”) will be described. In an initial state of the contacting operation, driving of the advancing/retreating motor  601  is stopped. The upstream-side first reversing roller pair  401  and the advancing/retreating mechanism  600  are positioned as shown in  FIGS. 12B and 12C . In  FIG. 12D , the rotating mechanism  700  is positioned as indicated by a solid line. In the initial state of the contacting operation, driving of the rotating motor  701  is stopped, and rotation of the reversing driving roller  400   a  and rotation of the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  are both stopped. At this time, each resin roller  4002   b  of the reversing driven roller  400   b  is in the transport-in path Ra, and is set at a position where it does not block the transport-in path Ra. In addition, each rubber roller  4002   a  of the reversing driving roller  400   a  is set at a position where it retreats from the transport-in path Ra. 
     As the contacting operation starts, the rotating motor  701  starts rotating. As the rotating motor  701  rotates, the motor-side pulley  702 , the timing belt  704 , and the roller-side pulley  703  cause rotation of the reversing driving roller  400   a  of the upstream-side first reversing roller pair  401  to start. Since, at this time, the reversing driving roller  400   a  and the reversing driven roller  400   b  are not in contact with each other, the rotation of the reversing driven roller  400   b  remains stopped. 
     Next, the advancing/retreating motor  601  starts rotating. As the advancing/retreating motor  601  rotates, rotation of each driving-side cam  604  starts through the gear train  602  and the driving-side cam shaft  603 . The advancing/retreating motor  601  stops rotating when each driving-side cam  604  is partially rotated from the state shown in  FIG. 12B  and returns to the state shown in  FIG. 12A . Such rotation of each driving-side cam  604  causes each ball bearing  605  to be pushed upward towards the transport-in path Ra by a cam surface of each driving-side cam  604 . As a result, the reversing driving roller  400   a  including the shaft  4001   a  to which each driving-side cam  604  is mounted approaches the reversing driven roller  400   b  opposing the reversing driving roller  400   a  with the transport-in path Ra being interposed therebetween. After the reversing driving roller  400   a  moves into the transport-in path Ra, the rubber rollers  4002   a  of the reversing driving roller  400   a  and the respective resin rollers  4002   b  of the reversing driven roller  400   b  contact each other in the transport-in path Ra. When a sheet P exists in the transport-in path Ra at this time, the reversing driving roller  400   a  and the reversing driven roller  400   b  contact each other through the sheet P. 
     When the reversing driving roller  400   a  comes into contact with the reversing driven roller  400   b , the reversing driven roller  400   b  receives a force acting in a direction away from transport-in path Ra from the reversing driving roller  400   a . As a result, the reversing driven roller  400   b  tries to move away from the transport path Ra. Here, in the exemplary embodiment, the driven-side bearings  611 , mounted to the respective ends of the shaft  4001   b  of the reversing driven roller  400   b , receive a force acting in a direction towards the transport-in path Ra through the springs  613 , mounted to the second transporting-in guiding plate  212 . Therefore, while a state in which the reversing driven roller  400   b  is supported at the second transporting-in guiding plate  212  by the driven-side bearings  611  and the driven-side bearing guides  612  is maintained, the reversing driven roller  400   b  is stationary at a position where a pushing force by the reversing driving roller  400   a  and a pushing force by the springs  613  balance. 
     When the reversing driving roller  400   a  comes into contact with the reversing driven roller  400   b , the reversing driven roller  400   b  receives driving force from the reversing driving roller  400   a  and starts rotating. At this time, the position where the reversing driving roller  400   a  and the reversing driven roller  400   b  contact each other is situated at an inner side of the transport-in path Ra. When a separation state changes to a contact state, the roller-side pulley  703  moves with respect to the rotating motor  701  and the motor-side pulley  702  from the position indicated by the solid line in  FIG. 12D  to a position indicated by a broken line in  FIG. 12D . At this time, the positional change between the motor-side pulley  702 , mounted to the rotating motor  701 , and the roller-side pulley  703 , mounted to the reversing driving roller  400   a , is absorbed by the timing belt  704 , so that the rotational driving of the reversing driving roller  400   a  is continued regardless of the positional change. 
     Next, the operation for separating the rollers  400   a  and  400   b  of the upstream-side first reversing roller pair  401  that are in contact with each other (hereunder referred to as “separating operation”) will be described. In an initial state of the separating operation, driving of the advancing/retreating motor  601  is stopped. The upstream-side first reversing roller pair  401  and the advancing/retreating mechanism  600  are positioned as shown in  FIG. 12A . In  FIG. 12D , the rotating mechanism  700  is positioned as indicated by the broken line. In the initial state of the separating operation, driving of the rotating motor  701  is continued, and the rotation of the reversing driving roller  400   a  and the rotation of the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  are both continued. At this time, each rubber roller  4002   a  of the reversing driving roller  400   a  and each resin roller  4002   b  of the reversing driven roller  400   b  are set at the positions where they are in the transport-in path Ra. 
     As the separating operation starts, the rotation of the rotating motor  701  is stopped. As the rotation of the rotating motor  701  is stopped, the rotations of the motor-side pulley  702 , the timing belt  704 , the roller-side pulley  703 , and the reversing driving roller  400   a  are stopped. In addition, as the rotation of the reversing driving roller  400   a  is stopped, the rotation of the reversing driven roller  400   b  that contacts the reversing driving roller  400   a  is also stopped. When a sheet P exists in the transport-in path Ra, transportation of the sheet P nipped by the reversing driving roller  400   a  and the reversing driven roller  400   b  is also stopped. 
     Next, the advancing/retreating motor  601  starts rotating. As the advancing/retreating motor  601  rotates, rotation of each driving-side cam  604  starts through the gear train  602  and the driving-side can shaft  603 . The advancing/retreating motor  601  stops rotating when each driving-side cam  604  is partially rotated from the state shown in  FIG. 12A  and returns to the state shown in  FIG. 12B . Such rotation of each driving-side cam  604  causes each ball bearing  605  to be pushed downward away from the transport-in path Ra by the cam surface of each driving-side cam  604 . As a result, the reversing driving roller  400   a  including the shaft  4001   a  to which each driving-side cam  604  is mounted moves away from the reversing driven roller  400   b  opposing the reversing driving roller  400   a  with the transport-in path Ra being interposed therebetween and contacting the reversing driving roller  400   a . In the transport-in path Ra, each rubber roller  4002   a  of the reversing driving roller  400   a  separates from its corresponding resin roller  4002   b  of the reversing driven roller  400   b , and retreats from the transport-in path Ra. 
     When the reversing driving roller  400   a  separates from the reversing driven roller  400   b , the reversing driven roller  400   b  no longer receives the force acting in the direction away from the transport-in path Ra from the reversing driving roller  400   a , whereas it continues receiving the force acting in the direction towards the transport-in path Ra through the springs  613  and the driven-side bearing guides  612 . As a result, the reversing driven roller  400   b  tries to move towards the transport-input path Ra. Here, in the exemplary embodiment, the movement of the driven-side bearings  611 , mounted to the respective ends of the shaft  4001   b  of the reversing driven roller  400   b , towards the transport-in path Ra is regulated by the driven-side bearing guides  612 , provided in correspondence with the driven-side bearings  611 . Therefore, while the state in which the reversing driven roller  400   b  is supported at the second transporting-in guiding plate  212  by the driven-side bearings  611  and the driven-side bearing guides  612  is maintained, the reversing driven roller  400   b  is stationary at a position where the reversing driven roller  400   b  abuts an end portion of each driven-side bearing guide  612  at a transport-in-path-Ra side by a pushing force by the springs  613 . At this time, while a state in which the resin rollers  4002   b  of the reversing driven roller  400   b  are in the transport-in path Ra is maintained, the resin rollers  4002   b  are positioned where they do not block the transport-in path Ra. 
     Although, here, the upstream-side reversing roller pair  401  is described as an example, the upstream-side second reversing roller pair  402  to the upstream-side fourth reversing roller pair  404  constituting the upstream-side reversing transporting section  400 A along with the upstream-side first reversing roller pair  401  are each also provided with an advancing/retreating mechanism  600  and a rotating mechanism  700 . In addition, the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  of the transporting-in transporting section  300 , the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  of the downstream-side reversing transporting section  400 C, and the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506  of the transporting-out transporting section  500  are each also provided an advancing/retreating mechanism  600  and a rotating mechanism  700 . Although the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  of the midstream-side reversing transporting section  400 B are each also provided with a rotating mechanism  700  for rotationally driving the corresponding midstream-side reversing roller pair, they are not provided with an advancing/retreating mechanism  600  for driving the corresponding reversing roller pair for causing its roller to advance or retreat. 
     In the exemplary embodiment, the driven-side bearings  611 , the driven-side bearing guides  612 , and the springs  613 , provided in correspondence with the transporting-in transporting section  300 , the upstream-side reversing transporting section  400 A, the downstream-side reversing transporting section  400 C, and the transporting-out transporting section  500  function as regulating sections. At the transporting-in section  210 , the driven-side bearings  611 , the driven-side bearing guides  612 , and the springs  613  of the transporting-in transporting section  300  function as input-side regulating sections, whereas the driven-side bearings  611 , the driven-side bearing guides  612 , and the springs  613  of the upstream-side reversing transporting section  400 A function as output-side regulating sections. At the transporting-out section  230 , the driven-side bearings  611 , the driven-side bearing guides  612 , and the springs  613  of the downstream-side reversing transporting section  400 C function as input-side regulating sections, whereas the driven-side bearings  611 , the driven-side bearing guides  612 , and the springs  613  of the transporting-out transporting section  500  function as output-side regulating sections. 
     The reversing and transporting of sheets P by the sheet reversing device  100  according to the exemplary embodiment will be described.  FIG. 13  illustrates the behavior of the sheets P that passes through the sheet reversing device  100 . In  FIG. 13 , a first sheet P 1  and a second sheet P 2  having different sizes are exemplified as the sheets P.  FIG. 13  shows a case in which the first sheet P 1  is a JISA3 size short end feed (SEF) sheet, and a case in which the second sheet P 2  is a JISA4 size long end feed (LEF) sheet. 
     In an initial state, the first transporting-in roller pair  301  to the sixth transporting-in roller pair  306  of the transporting-in transporting section  300  are each set in a separated state and a rotation stoppage state. In addition, the upstream-side first reversing roller pair  401  to the upstream-side fourth reversing roller pair  404  of the upstream-side reversing transporting section  400 A are each set in a separated state and a rotation stoppage state. Further, the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  of the midstream-side reversing transporting section  400 B are each set in a rotation stoppage state. Still further, the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller pair  424  of the downstream-side reversing transporting section  400 C are each set in a separated state and a rotation stoppage state. Still further, the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506  of the transporting-out transporting section  500  are each set in a separated state and a rotation stoppage state. 
     For example, when images are to be formed on both surfaces of a sheet P, the sheet P having an image formed on a first surface thereof by the image forming units  10  and the fixing device  50  is transported to the third transport path R 3  through the second transport path R 2 . At the third transport path R 3 , the sheet P is transported with its front end Pl being a leading end and a sheet surface Pf facing upward. At this time, on the basis of the length from a first side end Ps 1  to a second side end Ps 2  (hereunder referred to as “sheet width”) of the sheet P input using, for example, UI  90 , the controller  80  transports the sheet P so that a central position in the sheet width of the sheet P overlaps the transporting-in direction transport reference line La. 
     Next, at the third transport path R 3 , on the basis of a result of detection of a passage of the front end Pl of the sheet P by the sheet detecting sensor  60 , the controller  80  causes the transporting-in transporting section  300  to start rotating and to start a contacting operation. This causes the rollers of the transporting-in transporting section  300  to be set in a contact state and to start rotating at the transport-in path Ra. 
     Then, the sheet P is moved along the transporting-in direction Da 1  from the inside of the third transport path R 3  to the inside of the transporting-in path Ra. At this time, at the transport-in path Ra, the rollers of the transporting-in transporting section  300  are set in the contact state and rotate. In contrast, at this time, at the transport-in path Ra, the rollers of the upstream-side reversing transporting section  400 A are set in a separated state and their rotation is stopped. Therefore, the sheet P that enters the transport-in path Ra from the third transport path R 3  is moved along the transport-in direction Da 1  with the front end Pl being the leading end and the sheet surface Pf facing upward while the sheet P is nipped by the transporting-in transporting section  300 . Here, in the exemplary embodiment, the reversing driven rollers  400   b  of the upstream-side reversing transporting section  400 A that are set in the separated state are kept in the transport-in path Ra (see  FIG. 11B ). However, since the resin rollers  4002   b  of each reversing driven roller  400   b  are tapered (see  FIG. 10B ), each reversing driven roller  400   b  does not tend to interfere with the transportation of the sheet P in the transporting-in direction Da 1 . 
     Then, the sheet P stops in the transport-in path Ra. At this time, on the basis of the passage of time from when the passage of the front end Pl of the sheet P is detected by the sheet detecting sensor  60 , and on the basis of the length from the front end Pl to the back end Pt of the sheet P (hereunder referred to as “sheet length”) input by, for example, the UI  90 , the controller  80  causes the transporting-in transporting section  300  to stop rotating, and causes the separating operation of the transporting-in transporting section  300  to be started at a timing in which a central position in its sheet length of the sheet P reaches the reversing-direction transport reference line Lb. As a result, in addition to each reversing driving roller  400   a  of the upstream-side reversing transporting section  400 A, each transporting-in driving roller  300   a  of the transporting-in transporting section  300  no longer contacts the sheet P in the transport-in path Ra. As a result, the sheet P in the transport-in path Ra stops with its first side end Ps 1  opposing the reversing path Rb and its sheet front surface Pf facing upward. At this time, the sheet P that is stopped in the transport-in path Ra is such that, regardless of its size and orientation, the central position in its sheet width overlaps the transporting-in direction transport reference line La and the central position in its sheet length overlaps the reversing-direction transport reference line Lb. 
     Next, the sheet P moves along the transfer direction Da 2  in the transport-in path Ra. At this time, after the sheet P is stopped in the transport-in path Ra, the controller  80  causes the upstream-side reversing transporting section  400 A to rotate and to start the contacting operation. This causes the rollers of the upstream-side reversing transporting section  400 A to be set in the contact state and to start rotating at the transport-in path Ra. In contrast, at this time, at the transport-in path Ra, the rollers of the transporting-in transporting section  300  are set in a separated state and their rotation is stopped. Therefore, the sheet P that is stopped in the transport-in path Ra is moved along the transfer direction Da 2  with the front side end Ps 1  being the leading end and the sheet front surface Pf facing upward while the sheet P is nipped by the upstream-side reversing transporting section  400 A. Here, in the exemplary embodiment, the transporting-in driven rollers  300   b  of the transporting-in transporting section  300  that are set in the separated state are kept in the transport-in path Ra (see  FIG. 11A ). However, since the resin rollers  3002   b  of each transporting-in transporting roller  300   b  are tapered (see  FIG. 10A ), each transporting-in driven roller  300   b  does not tend to interfere with the transportation of the sheet P in the transfer direction Da 2 . 
     In the exemplary embodiment, in response to the starting of the rotation and the contacting operation of the upstream-side reversing transporting section  400 A, the rotation of the midstream-side reversing transporting section  400 B and the rotation and the contacting operation of the downstream-side reversing transporting section  400 C are started. This causes the rollers of the midstream-side reversing transporting section  400 B to start rotating at the reversing path Rb. In addition, this causes the rollers of the downstream-side reversing transporting section  400 C to be set in the contact state and to start rotating at the transport-out path Rc. 
     Then, the sheet P is moved from the inside of the transport-in path Ra to the inside of the reversing path Rb in the transfer direction Da 2 , and from the reversing path Rb to the transport-out path Rc in the reversing direction Db and the transfer direction Dc 1 . At this time, the rollers of the upstream-side reversing transporting section  400 A are set in the contact state and are rotating at the transport-in path Ra. In addition, at this time, the midstream-side reversing transporting section  400 B is rotating at the reversing path Rb. Further, at this time, the rollers of the downstream-side reversing transporting section  400 C are set in the contact state and are rotating at the transport-out path Rc. In contrast, at this time, the rollers of the transporting-out transporting section  500  are set in a separated state and their rotation is stopped at the transport-out path Rc. Therefore, the sheet P that has entered the reversing path Rb from the transport-in path Ra is moved such that its leading side is moved along the reversing direction Db and its back end is moved along the transfer direction da 2  with its first side end Ps 1  being the leading end and its sheet surface Pf facing upward while the sheet P is nipped at the upstream-side reversing transporting section  400 A and the midstream-side reversing transporting section  400 B. In addition, the sheet P that has entered the reversing path Rb is moved along the reversing direction Db with its first side end Ps 1  being the leading end and the state in which the sheet front surface Pf faces upward changing to the state in which the sheet back surface Pb faces upward while the sheet P is nipped at the midstream-side reversing transporting section  400 B. Thereafter, the sheet P that has entered the transport-out path Rc from the reversing path Rb is moved so that its leading side is moved along the transfer direction Dc 1  and its back end side is moved along the reversing direction with its first side end Ps 1  being the leading end and its sheet back surface Pb facing upward while the sheet P is nipped at the downstream-side reversing transporting section  400 C and the midstream-side reversing transporting section  400 B. During the time in which the sheet P reaches the transport-out path Rc from the transport-in path through the reversing path Rb, the sheet P is transported so that the central position in its sheet length overlaps the reversing-direction transport reference line Lb. Here, in the exemplary embodiment, the transporting-out driven rollers  500   b  of the transporting-out transporting section  500  that are set in the separated state are kept in the transport-out path Rc (see  FIG. 11E ). However, since the resin rollers  5002   b  of each transporting-out driven roller  500   b  are tapered (see  FIG. 10E ), each transporting-out driven roller  500   b  does not tend to interfere with the transportation of the sheet P in the transfer direction Dc 1 . 
     Then, the sheet P is stopped in the transport-out path Rc. At this time, for example, on the basis of the passage of time from when the transportation of the sheet P is started by the upstream-side transporting section  400 A, the controller  80  causes the downstream-side reversing transporting section  400 C to stop rotating, and causes the separating operation of the downstream-side reversing transporting section  400 C to be started at a timing in which the central position in its sheet width of the sheet P reaches the transport-out-direction transport reference line Lc. As a result, in addition to each transporting-out driving roller  500   a  of the transporting-out transporting section  500 , each reversing driving roller  400   a  of the downstream-side reversing transporting section  400 C no longer contacts the sheet P in the transport-out path Rc. As a result, the sheet P in the transport-out path Rc stops with its front end Pl opposing the fourth transport path R 4  and its back surface Pb facing upward. At this time, the sheet P in the transport-out path Rc is such that, regardless of its size and orientation, the central position is sheet length overlaps the reversing-direction transport reference line Lb and the central position in its sheet length overlaps the transporting-out-direction transport reference line Lc. 
     Here, in the exemplary embodiment, the distance from the transporting-in direction transport reference line La at the transport-in path Ra to the transporting-out-direction transport reference line Lc at the transport-out path Rc through the reversing path Rb is determined independently of the size of the sheet P that is transported. Therefore, the period in which the sheet P is transported from the transport-in path Ra to the transport-out path Rc through the reversing path Rb is constant regardless of the size of the sheet P when the transport speed of the sheet P is constant. 
     In the exemplary embodiment, the controller  80  starts the rotation stoppage operation and the separating operation of the upstream-side reversing transporting section  400 A and the rotation stoppage operation of the midstream-side reversing transporting section  400 B in response to the starting of the rotation stoppage operation and the separating operation of the downstream-side reversing transporting section  400 C. When these operations are started, the setting of the rollers of the upstream-side reversing transporting section  400 A to the separated state and the stoppage of the rotation of the rollers of the upstream-side reversing transporting section  400 A are started at the transport-in path Ra, and the midstream-side reversing transporting section  400 E stops rotating at the reversing path Rb. 
     Next, the sheet P moves along the transport-out direction Dc 2  in the transport-out path Rc. At this time, the controller  80  starts the rotation and the contacting operation of the transporting-out transporting section  500  after the controller  80  stops the sheet P in the transport-out path Rc. When these operations are started, the setting of the rollers of the transporting-out transporting section  500  to the contact state and the rotation of the rollers of the transporting-out transporting section  500  are started at the transport-out path Rc. In contrast, at this time, the rollers of the downstream-side reversing transporting section  400 C are set in the separated state and their rotation is stopped at the transport-out path. Therefore, the sheet P that has been stopped in the transport-out path Rc moves along the transport-out direction Dc 2  with its front end Pl being the leading end and its back surface Pb facing upward while the sheet P is nipped by the transporting-out transporting section  500 . Thereafter, the sheet P is transported out to the fourth transport path R 4  from the transport-out path Rc. Here, in the exemplary embodiment, each reversing driven roller  400   b  of the downstream-side reversing transporting section  400 C that is set in the separated state is kept in the transport-out path Rc (see  FIG. 11D ). However, since the resin rollers  4002   b  of each reversing driven roller  400   b  are tapered (see  FIG. 10B ), each reversing driven roller  400   b  does not tend to interfere with the transportation of the sheet P in the transport-out direction Dc 2 . 
     The controller  80  stops the rotation of the transporting-out transporting section  500  and starts the separating operation of the transporting-out transporting section  500  at a timing in which the sheet P is transported out of the transport-out path Rc. This causes the rollers of both of the downstream-side reversing transporting section  400 C and the transporting-out transporting section  500  to be in a separated state at the transport-out path Rc. 
     Then, the sheet P whose front and back have been reversed by the sheet reversing device  100  is transported again from the fourth transport path R 4  towards each image forming unit  10  and the fixing device  50  through the first transport path R 1 . 
     In the exemplary embodiment, the driving rollers (that is, the transporting-in driving rollers  300   a , the reversing driving rollers  400   a , and the transporting-out driving rollers  500   a ) retreat from both the transport-in path Ra or the transport-out path Rc of the sheet reversing device  100  due to the following reasons. 
     First, the driving rollers may receive outside rotational driving force. Therefore, when driving rollers that are not used for transporting a sheet P remain in a path, the driving rollers that are not used for transporting the sheet P may interfere with the transportation of the sheet P performed by the other driving rollers that are transporting the sheet P. In addition, in the exemplary embodiment, each driving roller includes rubber rollers whose coefficient of friction is higher than that of the resin rollers of each driven roller. Therefore, when driving rollers that are not used for transporting the sheet P remain in a transport path, the driving rollers that are not used for transporting the sheet P may interfere with the transportation of the sheet P performed by the other driving rollers that are transporting the sheet P. Consequently, in the exemplary embodiment, each driven roller including resin rollers are kept in its corresponding path, whereas each driving roller including rubber rollers retreat from its corresponding path. 
     Second Exemplary Embodiment 
     The basic structure according to the second exemplary embodiment is the same as that according to the first exemplary embodiment. In the first exemplary embodiment, the roller pairs of the transporting-in transporting section  300 , the upstream-side reversing transporting section  400 A, the downstream-side reversing transporting section  400 , and the transporting-out transporting section  500  of the sheet reversing device  100  are such that the driving rollers retreat. However, in the second exemplary embodiment, both driving rollers and driven rollers retreat. In the second exemplary embodiment, components that correspond to those in the first exemplary embodiment are given the same reference numerals and will not be described in detail. 
       FIGS. 14A to 14E  each illustrate the relationship between the pair of transport rollers and a corresponding transport path in the sheet reversing device  100  according to the exemplary embodiment. Here,  FIGS. 14A to 14E  correspond to  FIGS. 10A to 10E . That is,  FIG. 14A  shows the relationship between a transport-in path Ra and a first transporting-in roller pair  301  at the transporting-in section  210 .  FIG. 14B  shows the relationship between the transport-in path Ra and an upstream-side first reversing roller pair  401  at the transporting-in section  210 .  FIG. 14C  shows the relationship between a reversing path Rb and the midstream-side second reversing roller pair  412  at a reversing section  220 .  FIG. 14D  shows the relationship between a transport-out path Rc and a downstream-side fourth reversing roller pair  424  at a transporting-out section  230 .  FIG. 14E  shows the relationship between the transport-out path Rc and a first transporting-out roller pair  501  at the transporting-out section  230 . 
     As shown in  FIG. 14A , a transporting-in driving roller  300   a  and a transporting-in driven roller  300   b  of the first transporting-in roller pair  301  are contactably and separably formed. When the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  of the first transporting-in roller pair  301  contact each other, both of the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  are in a state in which they are moved in the transport-in path Ra. In contrast, when the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  of the first transporting-in roller pair  301  are separated from each other, the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  are moved away from each other, so that both of the transporting-in driving roller  300   a  and the transporting-in driven roller  300   b  retreat from the transport-in path Ra. The rollers of a second transporting-in roller pair  302  to a sixth transporting-in roller pair  306  constituting the transporting-in transporting section along with the first transporting-in roller pair  301  contact and separate from each other as with the rollers of the first transporting-in roller pair  301 . 
     As shown in  FIG. 14B , a reversing driving roller  400   a  and a reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  are contactably and separably formed. When the reversing driving roller  400   a  and the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401  contact each other, both of the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are moved in the transport-in path Ra. In contrast, when the reversing driving roller  400   a  and the reversing driven roller  400   b  of upstream-side first reversing roller pair  401  are separated from each other, the reversing driving roller  400   a  and the reversing driven roller  400   b  are moved away from each other, so that both of the reversing driving roller  400   a  and the reversing driven roller  400   b  are retreated from the transport-in path Ra. The rollers of an upstream-side second reversing roller pair  402  to an upstream-side fourth reversing roller pair  404  constituting the upstream-side reversing transporting section  400 A along with the upstream-side first reversing roller pair  401  contact and separate from each other as with the rollers of the upstream-side first reversing roller pair  401 . 
     As shown in  FIG. 14C , a reversing driving roller  400   a  and a reversing driven roller  400   b  of the midstream-side second reversing roller pair  412  are formed so as to be normally in contact with each other. Here, the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are moved in the reversing path Rb. The rollers of a midstream-side first reversing roller pair  411  and a midstream-side third reversing roller pair  413  constituting the midstream-side reversing transporting section  400 B along with the midstream-side second reversing roller pair  412  are formed so as to be normally in contact with each other as with the rollers of the midstream-side second reversing roller pair  412 . 
     As shown in  FIG. 14D , a reversing driving roller  400   a  and a reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  are contactably and separably formed. When the reversing driving roller  400   a  and the reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  contact each other, both of the reversing driving roller  400   a  and the reversing driven roller  400   b  are in a state in which they are moved in the transport-out path Rc. In contrast, when the reversing driving roller  400   a  and the reversing driven roller  400   b  of the downstream-side fourth reversing roller pair  424  are separated from each other, the reversing driving roller  400   a  and the reversing driven roller  400   b  are moved away from each other, so that both of the reversing driving roller  400   a  and the reversing driven roller  400   b  are retreated from the transport-out path Rc. The rollers of a downstream-side first reversing roller pair  421  to a downstream-side third reversing roller pair  423  constituting the downstream-side reversing transporting section  400 C along with the downstream-side fourth reversing roller pair  424  contact and separate from each other as with the rollers of the downstream-side fourth reversing roller pair  424 . 
     As shown in  FIG. 14E , a transporting-out driving roller  500   a  and a transporting-out driven roller  500   b  of the first transporting out roller pair  501  are contactably and separably formed. When the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  of the first transporting-out roller pair  501  contact each other, both of the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  are in a state in which they are moved in the transport-out path Rc. In contrast, when the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  of the first transporting-out roller pair  501  are separated from each other, the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  are moved away from each other, so that both of the transporting-out driving roller  500   a  and the transporting-out driven roller  500   b  are retreated from the transport-out path Rc. The rollers of a second transporting-out roller pair  502  to a sixth transporting roller pair  506  constituting the transporting-out transporting section  500  along with the first transporting-out roller pair  501  contact and separate from each other as with the rollers of the first transporting-out roller pair  501 . 
       FIGS. 15A and 15B  illustrate an exemplary structure of an advancing/retreating mechanism  600  that causes the upstream-side first reversing roller pair  401  to advance and retreat. Here,  FIGS. 15A and 15B  only show the reversing driven roller  400   b  of the upstream-side first reversing roller pair  401 . The advancing/retreating mechanism  600  that causes the reversing driving roller  400   a  to advance and retreat and a rotating mechanism  700  that rotates the reversing driving roller  400   a  are similar to those described in the first exemplary embodiment (see  FIGS. 12A to 12D ).  FIG. 15A  shows the reversing driven roller  400   b  that is in contact with the reversing driving roller  400   a , whereas  FIG. 15B  shows the reversing driven roller  400   b  that is separated from the reversing driving roller  400   a.    
     The advancing/retreating mechanism  600  according to the exemplary embodiment includes a driven-side cam shaft  621 , driven-side cams  622 , a lever shaft  623 , and a lever  624 . The driven-side cam shaft  621  is mounted to, for example, a gear train  602  (see  FIG. 12C ) through, for example, a clutch. The driven-side cams  622  are mounted to two locations of the driven-side cam shaft  621  in an axial direction. The lever shaft  623  is secured and mounted to, for example, the second transporting-in guiding plate  212 . The lever  624  is mounted so as to be rotatable around the lever shaft  623  as an axis, and is disposed so that one end side thereof contacts cam surfaces of the driven-side cams  622  and the other end side contacts a shaft  4001   b  of the reversing driven roller  400   b.    
     Although, here, the upstream-side first reversing roller pair  401  are described as an example, the upstream-side second reversing roller pair  402  to the upstream-side fourth reversing roller pair  404  constituting the upstream-side reversing transporting section  400 A along with the upstream-side first reversing roller pair  401  are each also provided with an advancing/retreating mechanism  600  and a rotating mechanism  700 . The first transporting-in roller pair  301  to the sixth transporting-in roller  306  of the transporting-in transporting section  300 , the downstream-side first reversing roller pair  421  to the downstream-side fourth reversing roller  424  of the downstream-side reversing transporting section  400 C, and the first transporting-out roller pair  501  to the sixth transporting-out roller pair  506  of the transporting-out transporting section  500  are each also provided with an advancing/retreating mechanism  600  and a rotating mechanism  700 . In contrast, the midstream-side first reversing roller pair  411  to the midstream-side third reversing roller pair  413  of the midstream-side reversing transporting section  400 B are each provided with a rotating mechanism  700  for rotationally driving the corresponding roller pair, but are not provided with an advancing/retreating mechanism  600  for driving the corresponding roller pair causing it to advance and retreat. 
     In the exemplary embodiment, by using such a structure, when the driving rollers and the driven rollers of the roller pairs of the transporting-in transporting section  300 , the upstream-side reversing transporting section  400 A, the downstream-side reversing transporting section  400 C, and the transporting-out transporting section  500  separate from each other, the driving rollers and the driven rollers of the roller pairs are capable of retreating from the respective transport paths. Therefore, when the transport and the sheet transport direction of a sheet P are changed in the transport-in path Ra and the transport-out path Rc, the tendency with which the transport roller pairs that are not used for transporting the sheet P interfere with the transport of the sheet P is further reduced. When the structure according to the exemplary embodiment is used, the driven rollers of the roller pairs of the transporting-in transporting section  300 , the upstream-side reversing transporting section  400 A, the downstream-side reversing transporting section  400 C, and the transporting-out transporting section  500  no longer need to be tapered as they are tapered in, for example,  FIGS. 10A and 10B  and  10 D and  10 E. 
     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 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.