Patent Publication Number: US-8526874-B2

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2008-325132, filed on Dec. 22, 2008, the disclosure of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus. 
     2. Description of the Related Art 
     A conventional image forming apparatus has been disclosed in Japanese Patent Application Laid-open No. 2002-302293. The image forming apparatus includes an image forming section which forms an image on a paper which is transported, a paper reverse section which turns over a paper which has passed through the image forming section, and a re-transporting section which re-transports the paper which has been turned over in the paper reverse section, to the image forming section along a re-transporting path. 
     The re-transporting section includes a motor as a driving mechanism which generates a driving force; a first transporting roller which transports the paper; a plurality of second transporting rollers which are positioned at an upstream side of the re-transporting path with respect to the first transporting roller, and which transport the paper together with the first transporting roller; and a transmission mechanism which transmits the driving force of the motor to the first transporting roller and the second transporting rollers. 
     The transmission mechanism includes a set of a belt and a pulley as a first transmitting section which transmits the driving force of the motor to the first transporting roller; and a plurality of sets of belts and pulleys as a second transmitting section which transmits the driving force of the first transmitting section to the second transporting rollers. As a belt and a pulley, for eliminating transmission loss due to slippage, generally, a timing belt and a pulley are used. The timing belt has a large number of projections formed on an outer peripheral surface thereof and lined up in a direction of circulation, and a pulley has grooves which engage with the projections of the timing belt. 
     In the conventional image forming apparatus having above described structure, the paper, which is turned over by the paper reverse section and the re-transporting section, is transported once again to the image forming section along the re-transporting path. In the re-transporting section, the driving force of the motor is transmitted to the first transporting roller and the second transporting rollers by the belts and the pulleys. 
     SUMMARY OF THE INVENTION 
     Incidentally, in the conventional image forming apparatus, when an appropriate tension is not imparted to the timing belt at the time of assembling, or, when the tension in the timing belt is reduced due to deterioration, there may occur tooth-skipping between the timing belt and the grooved pulley. Moreover, due to repetitive deformation of the timing belt, a crack may be developed around the projection, and the projection may be defective. When such defect is developed, the driving force of the motor is not transmitted appropriately to the first transporting roller and the second transporting rollers, and it becomes difficult to transport the paper favorably along the re-transporting path. 
     The present invention is made in view of the abovementioned circumstances, and an object of the present invention is to provide an image forming apparatus in which it is possible to transport the paper favorably along the re-transporting path. 
     According to an aspect of the present invention, there is provided an image forming apparatus which forms an image on a medium, including: 
     an image forming section which carries out formation of the image on the medium which is transported; 
     a reverse section which reverses the medium passed through the image forming section; and 
     a re-transporting section which transports the medium, reversed by the reverse section, again to the image forming section, the re-transporting section including: 
     a re-transporting path extending from the reverse section to the image forming section,
         a drive mechanism which generates a driving force for transporting the medium,   a first transporting roller which is connected to the drive mechanism to transport the medium,   a second transporting roller which transports the medium in cooperation with the first transporting roller,   a first transmitting section having a first gear which is rotatable integrally with the first transporting roller, and transmitting the driving force of the drive mechanism to the first transporting roller, and   a second transmitting section which transmits the driving force transmitted to the first transmitting section to the second transporting roller, having: a second gear which is engaged with the first gear; a shaft which is extended in a direction intersecting a rotational axis of the first transporting roller and a rotational axis of the second transporting roller, and which is rotatable integrally with the second gear; a third gear which is rotatable integrally with the shaft; and a fourth gear which is engaged with the third gear and which is rotatable integrally with the second transporting roller.       

     According to the image forming apparatus of the present invention, as compared to a structure in which a conventional timing belt is used, it is not necessary to control tension of the components of the transmission mechanism such as the first gear, the second gear, the third gear, the fourth gear, and the shaft, at the time of assembling. Moreover, as compared to a timing belt which is deformed repeatedly, the first gear to the fourth gear, and the shaft are hardly deteriorated. Therefore, in this image forming apparatus, it is possible to transmit appropriately the driving force from the driving mechanism to the first and second transporting rollers by the first gear to the fourth gear, and the shaft. 
     Consequently, according to the image forming apparatus of the present invention, it is possible to transport the paper favorably along the re-transporting path, and as a result, a defect such as paper jam hardly occurs. 
     Moreover, in the image forming apparatus of the invention, since the gears from the first gear to the fourth gear are engaged with each other, the first and second transporting rollers are biased toward one-end side or the other end side of a rotational axis of the first and second transporting of the rollers. Therefore, a play (backlash) of the first and second transporting rollers in the rotational axis direction hardly occurs. As a result, in this image forming apparatus, it is possible to suppress a defect of the re-transporting path fluctuating in the rotational axis direction of the first and second transporting rollers. 
     The first and second transporting rollers may be arranged in a zigzag form (staggered form) or may be arranged in a plurality of rows. 
     Moreover, ‘a structure which is rotatable integrally’ includes not only a structure which rotates integrally but also a structure which rotates by interposing a joint or a gear in between. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural view of an image forming apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing a re-transporting section in the image forming apparatus of the first embodiment, and shows a state in which a lid body (a lid member) has been removed; 
         FIG. 3  is an enlarged perspective view of main components showing the re-transporting section in the image forming apparatus of the first embodiment, and shows a state in which, the lid body and a bottom plate have been removed; 
         FIG. 4  is a perspective view showing the re-transporting section in the image forming apparatus of the first embodiment, and shows a state in which the lid body has been assembled; 
         FIG. 5  is a perspective view showing a first transporting roller, second transporting rollers, a transmission mechanism, and driven rollers in the image forming apparatus of the first embodiment; 
         FIG. 6  is a top view showing the first transporting roller, the second transporting rollers, the transmission mechanism, and the driven rollers in the image forming apparatus of the first embodiment; 
         FIG. 7  is a top view showing the first transporting roller, the second transporting rollers, the transmission mechanism, and the driven rollers in an image forming apparatus of a second embodiment; 
         FIG. 8  is a top view showing the first transporting roller, the second transporting rollers, the transmission mechanism, and the driven rollers in an image forming apparatus of another example of the image forming apparatus of the second embodiment; 
         FIG. 9  is a top view showing the first transporting roller, the second transporting rollers, the transmission mechanism, and the driven rollers in an image forming apparatus of a third embodiment; 
         FIG. 10  is a top view showing the first transporting roller, the second transporting rollers, the transmission mechanism, and the driven rollers in an image forming apparatus of a fourth embodiment; 
         FIG. 11  is a top view showing the first transporting roller, the second transporting roller, the transmission mechanism, and the driven rollers in an image forming apparatus of a fifth embodiment; and 
         FIG. 12  is a top view showing the first transporting roller, the second transporting roller, the transmission mechanism, and the driven rollers of an image forming apparatus having one second transporting roller. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments from a first embodiment to a fifth embodiment in which the present invention has been substantiated will be described below with reference to the accompanying diagrams. In  FIG. 1 , a frontward direction and a rearward direction, and an upward direction and a downward direction are defined as shown in the diagram. Further, a frontward side of a normal direction perpendicular to a paper surface is defined as a left side, and a rearward side (an inner side) of the normal direction is defined as a right side. Moreover, frontward/rearward directions, leftward/rightward directions, and upward/downward directions in  FIGS. 2 to 10  are indicated corresponding to directions defined in  FIG. 1 . 
     First Embodiment 
     A structure of a printer  1  as an image forming apparatus of a first embodiment will be described below. 
     &lt;Housing&gt; 
     A housing  70  is a casing having a box shape, and a frame member which is not shown in the diagram is provided at an inner side thereof. A paper feeding cassette  55 , a feeder section  80 , an image forming section  50 , a transporting mechanism  60 , a paper reverse section (a paper return section)  41 , and a re-transporting section  30  are assembled in the frame member. The image forming section  50  is positioned at a substantial center of the housing  70 . The paper feeding cassette  55  is positioned below the image forming section  50 , and the re-transporting section  30  is positioned above the paper feeding cassette  55 . 
     A paper discharge tray  72  is provided at an upper-surface side of the housing  70 . After the image formation is completed, papers and OHP sheets etc. (hereinafter, called as ‘paper’) discharged to an outside of the housing  70  are accumulated in the paper discharge tray  72 . 
     An openable panel  71 , which is pivotable frontward around a hinge  71   a  located at a lower-end of a front-side surface of the housing  70 , is installed on the front-side surface of the housing  70 . A part of the feeder section  80  excluding a paper feeding roller  81  etc. is fixed to an inner-wall surface of the openable panel  71  via a frame member which is not shown in the diagram. When the openable panel  71  is opened, the feeder section  80  is also pivoted frontward around the hinge  71   a , and a front-surface side of the housing  70  is opened. Moreover, when the paper feeding cassette  55  moves in a frontward/rearward direction in this state, it is possible to mount/dismount the paper feeding cassette  55  onto/from the housing  70 . 
     An openable panel  73 , which is pivotable rearward around a hinge  73   a  located at a lower-end side of the rear-surface side of the housing  70  and which opens the rear-surface side of the housing  70 , is installed at the rear-surface side of the housing  70 . When the re-transporting section  30  is moved in the frontward/rearward direction while the openable panel  73  opened, it is possible to mount/dismount the re-transporting section  30  onto/from the housing  70 . 
     &lt;Paper Feeding Cassette&gt; 
     The paper feeding cassette  55  is a box-shaped member having a paper accommodating chamber  55   a  which is openable upward. A pushing plate  56  is installed at a front of a bottom portion of the paper accommodating chamber  55   a . A front-end side of the pushing plate  56  is pivotable vertically (up and down). At the time of feeding a paper to the image forming section  50 , the pushing plate  56  is pivoted to push up a front-end side of a paper accommodated in the paper accommodating section  55   a , thereby pushing the paper against the paper feeding roller  81  located above the paper accommodating section  55   a . Moreover, a pair of width-direction guide plates  57   a  and  57   b  facing in left-right direction are provided in the paper accommodating chamber  55   a . The width-direction guide plates  57   a  and  57   b  make a contact with two ends of the paper, respectively, in a width direction of the paper, and position the transported paper with respect to a center line of the paper in the width direction. In the following description, transporting of a paper, in which the paper is not positioned at one-end of the paper in the width direction but is positioned with respect to the center line of the paper in the width direction is called as a ‘center register feeding’. 
     &lt;Feeder Section&gt; 
     The feeder section  80  includes the paper feeding roller  81 , transporting rollers  82  and  83 , and a register roller  84 . 
     The paper feeding roller  81  is provided above a front-end side of the paper feeding cassette  55 , and transports the paper mounted in the paper feeding cassette  55 , to the image forming section  50 . A separating pad which is not shown in the diagram is arranged below a front side of the paper feeding roller  81 . The separating pad imparts a predetermined transporting resistance to the paper to separate one-by-one the papers fed by the paper feeding roller  81 . 
     The transporting path P 1  includes a U-turn portion taking a U-turn at a frontward side in the housing  70 , and the paper fed from the paper feeding cassette  55  is transported to the image forming section  50  through a paper transporting path P 1 . The transporting roller  82  is arranged at the U-turn portion, of the paper transporting path P 1 . The transporting roller  82  applies a transporting force to the paper to transport to the image forming section  50  with the paper being bent in a substantial U-shape. 
     The register roller  84  is arranged at a downstream side, of the transporting path P 1 , than the transporting roller  82 , and makes a contact with a front end of the paper which is transported by the transporting roller  82 . Accordingly, the register roller  84  corrects a skewing of the paper, and transports the paper further toward the image forming section  50 . 
     The transporting roller  83  is arranged below the transporting roller  82  and at a front side of the re-transporting section  30 , and imparts a transporting force to the paper turned over by a reverse-transporting mechanism  40  to guide the reversed paper once again to the transporting path P 1 . 
     &lt;Transporting Mechanism&gt; 
     The transporting mechanism  60  includes a drive roller  61  which rotates in conjunction with the image forming section  50 , a driven roller  62  which is rotatably installed at a position away from the drive roller  61 , and a transporting belt  63  which is put around the drive roller  61  and the driven roller  62 . 
     Moreover, the transporting belt  63  rotates in a state of the paper P mounted thereon. Accordingly, the transporting belt  63  transports the paper which has been transported from the paper feeding cassette  55  along the transporting path P 1 , and sends to a lower side of a developer toner cartridge  52  of the image forming section  50 . 
     &lt;Image Forming Section&gt; 
     In the printer  1  of the first embodiment, the image forming section  50  of an electro-photographic type is used. In the image forming apparatus of the present invention, the image forming section is not restricted to the image forming section in the first embodiment, and it is possible to use an image forming apparatus of the electro-photographic type, a thermal type, an ink jet type, and other common image forming types. 
     The image forming section  50  is of a so-called direct tandem type capable of color printing, and includes a scanner section  51 , the developer toner cartridge (developing section)  52 , and a fixing unit (transfer section)  53 . 
     The developer toner cartridge  52  is a set of four cartridges corresponding to toners (developer) of four colors namely black, yellow, magenta, and cyan, and these four cartridges are arranged to be lined up serially along a direction of transporting of paper. The developer toner cartridge  52  includes photosensitive drums  52   a ,  52   b ,  52   c , and  52   d , a developing roller, a charger, and a toner accommodating portion (not shown in the diagram). 
     The scanner section  51  is provided at an upper portion in the housing  70 , and includes a laser source, a polygon mirror, an fθ lens, and a reflecting mirror. The scanner section  51  forms an electrostatic latent image on a surface of each of the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d  in the developer toner cartridge  52 . 
     The fixing unit  53  is arranged at a downstream side of the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d  in the transporting path P 1  of the paper. The fixing unit  52  includes a heating roller  53   a  and a pressurizing roller  53   b . The heating roller  53   a  is arranged toward an image forming surface of the paper. When the heating roller  53   a  is driven and rotated in synchronization with the transporting belt  63  etc., the heating roller  53   a  imparts a transporting force to the paper while heating the toner. Whereas, the pressurizing roller  53   b  is arranged at an opposite side of the heating roller  53   a , sandwiching the paper, and presses the paper toward the heating roller  53   a . The pressurizing roller  53   b  is driven and rotated upon receiving a rotational force from the heating roller  53   a  via the paper which is in contact with the heating roller  53   a.    
     A paper discharge sensor  54  which faces the transporting path P 1  is provided at a rear side of the heating roller  53   a  and the pressurizing roller  53   b . In the reverse-transporting of the paper which will be described later, a rear end of the paper is detected by the paper discharge sensor  54 , and at a predetermined timing after the detection, paper discharge rollers  45   a  and  45   b  rotating in the normal direction are made to rotate in the reverse direction. 
     The image forming section  50  having such structure forms an image on the paper as described below. In other words, when the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d  rotate, surfaces thereof are charged uniformly to positive polarity by a charger, and thereafter, are exposed by being scanned at a high speed by a laser beam irradiated from the scanner section  51 . Accordingly, electrostatic latent images corresponding to an image to be formed on the paper are formed on the surface of each of the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d.    
     Next, toner from a toner accommodating section is supplied to the surfaces of the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d  corresponding to the electrostatic latent images, and the toner carried on the surfaces of the photosensitive drums  52   a ,  52   b ,  52   c , and  52   d  is transferred to the paper. Further, the paper having the toner transferred thereto is transported to the fixing unit  53  and heated, and the toner is fixed to the paper and the image formation is completed. 
     &lt;Reverse-Transporting Mechanism&gt; 
     The reverse-transporting mechanism  40  is a mechanism for forming an image on both front and rear surfaces of the paper, and includes the paper reverse section  41  and the re-transporting section  30 . The paper reverse section  41  and the re-transporting section  30  are arranged such that, the paper which has passed through the fixing unit  53  is passes along a re-transporting path P 2  returning to the feeder section  80  via a lower portion of the paper feeding cassette  55  from a rear-surface side of the housing  70 . 
     The paper reverse section  41  includes the paper discharge rollers  45   a  and  45   b , a flapper  49 , re-transporting rollers  46  and  47 , and a guide  48 . 
     The paper discharge rollers  45   a  and  45   b  are a pair of rollers facing mutually, and can be switched to a rotation in a normal direction and a reverse direction. As it has been described above, the paper discharge rollers  45   a  and  45   b  rotate in a normal direction in a case of discharging the paper onto the paper discharge tray  72 , and rotate in a reverse direction in a case of transporting the paper to the re-transporting path P 2  upon reversing. 
     The flapper  49  is provided to face a branched portion of the transporting path P 1  and the re-transporting path P 2 . The flapper  49  is pivoted by excitation or non-excitation of a solenoid which is not shown in the diagram, and switches a transporting path for the paper, which is reversed by the paper discharge rollers  45   a  and  45   b , from the transporting path P 1  to the re-transporting path P 2 . 
     The re-transporting rollers  46  and  47 , and the guide  48  are arranged in a vertical direction along the re-transporting path P 2 , to be able to transport the paper from the paper discharger rollers  45   a  and  45   b  up to a rear-end side of the re-transporting section  30  installed at the lowermost side of the housing  70 . In the paper reverse section  41 , the paper is also transported by center register feeding. 
     As shown in diagrams from  FIGS. 1 to 6 , the re-transporting section  30  is arranged at a lower side of the paper feeding cassette  55 . A rear-end side of the re-transporting section  30  is arranged at a lower side of the paper reverse section  41 , and a front-end side of the re-transporting section  30  is arranged at a rear side of the transporting roller  83 . The re-transporting section  30  includes a drive mechanism  91 , a transporting tray  31 , a first transporting roller  32 A, second transporting rollers  32 B and  32 C, a transmission mechanism  20 , and driven rollers  36 A,  36 B, and  36 C. 
     As shown in  FIG. 1 , the drive mechanism  91  is provided between a bottom portion of the housing  70  and the transporting tray  31 . The drive mechanism  91  may have an electric motor, or may be a structure which distributes a part of a driving force transmitted to the transporting mechanism  60  and the image forming section  50 , to the re-transporting section  30 . It is possible to mount/dismount the re-transporting section  30  on/from the housing  70  when the re-transporting section  30  moves frontward/rearward in a state of the openable panel  73  opened. At this time, the drive mechanism  91  is engaged with or disengaged from the re-transporting section  30 . Here, as shown in  FIG. 4 , a spur gear  21 E near the transmission mechanism  20  is installed in an exposed form, at a left-side surface of the transporting tray  31 . Therefore, as shown in  FIG. 5 , a spur gear  91 E near the drive mechanism  91  is engaged with or disengaged from the spur gear  21 E near the transmission mechanism  20 . 
     As shown in  FIG. 2 , the transporting tray  31  is a resin molded body (resin molding) made of a resin such as ABS resin. A rear-end side of the transporting tray  31  has a bent shape which is bent toward an upper side. A plurality of guide ribs  31 A extended in a frontward and a rearward direction along the re-transporting path P 2  is formed integrally at a bottom portion of the transporting tray  31 . 
     A bottom plate  33  is mounted at a left side of each guide rib  31 A at a bottom portion of the tray  31 . An upper surface of the bottom plate  33  is also a flat surface extended in the frontward and rearward direction along the re-transporting path P 2 . 
     As shown in  FIG. 3 , an internal space  31 B is formed at a lower-surface side of the bottom plate  33  of the transporting tray  31 . The first transporting roller  32 A, the second transporting rollers  32 B and  32 C, and the transmission mechanism  20  are accommodated in a state of being supported by a plurality of sliding bearings  93 . In  FIGS. 5 and 6 , the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, and the transmission mechanism  20  are picked up to show. The details thereof will be described later. 
     As shown in  FIG. 2 , three openings  33 A,  33 B, and  33 C lined up in a frontward and rearward direction are formed in the bottom plate  33 . Upper portions of the first transporting roller  32  and the second transporting rollers  32 B and  32 C which are arranged in the internal space  31 B, are exposed through the openings  33 A,  33 B, and  33 C. A width-direction guide plate  34  is provided to be extended in a frontward and rearward direction at a further left side of the openings  33 A,  33 B, and  33 C in an upper surface of the bottom plate  33 . The width-direction guide plate  34  determines a position in a width direction (side register feeding) by making a contact with one-end side in a width direction of the paper when the paper is transported on the transporting tray  31  along the re-transporting path P 2 . 
     As shown in  FIG. 4 , lid bodies (lid members)  36  and  37  which are resin molded bodies (resin moldings) made of a resin such as ABS resin, are assembled at an upper side of the transporting tray  31 . A gap through which the paper can pass is formed between the lid bodies  36  and  37  and the guide ribs  31 A and between the lid bodies  36  and  37  and the bottom plate  33 . The lid body  36  is positioned at an upper side of the bottom plate  33 . The driven rollers  36 A,  36 B, and  36 C are provided in the lid body  36 , at sites positioned at an upper side of the openings  33 A,  33 B, and  33 C. The driven rollers  36 A,  36 B, and  36 C are facing in a vertical direction (upward and downward direction) with respect to the first transporting roller  32 A, and the second transporting rollers  32 B and  32 C. In  FIGS. 5 and 6 , the driven rollers  36 A,  36 B, and  36 C are picked up to show along with the first transporting roller  32 , the second transporting rollers  32 B and  32 C, and the transmission mechanism  20 . The details thereof will be described later. 
     A bias spring  36 E which applies a bias to the driven rollers  36 A,  36 B, and  36 C, toward the first transporting roller  32 A and the second transporting rollers  32 B and  32 C is arranged between the lid body  36  and the driven rollers  36 A,  36 B, and  36 C. The lid bodies  36  and  37  are made to be highly stiff by making thick or by forming a reinforcing rib in order to cope with a reactive force exerted by the bias spring  36 E. 
     Next, the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, the transmission mechanism  20 , and the driven rollers  36 A,  36 B, and  36 C will be described below in detail with reference to  FIGS. 3 ,  5 , and  6 . 
     The first transporting roller  32 A is positioned between the second transporting roller  32 B and the second transporting roller  32 C as viewed from the frontward and rearward direction. In other words, the second transporting roller  32 B is positioned at an upstream side of the re-transporting path P 2 , with respect to the first transporting roller  32 A, and the second transporting roller  32 C is positioned at a downstream side of the re-transporting path P 2 , with respect to the first transporting roller  32 A. 
     As shown in  FIGS. 5 and 6 , the first transporting roller  32 A is fixed at an intermediate portion of a rotating shaft  21 A of which rotational axis X 1 A is directed in a left-right direction, or in other words, a direction orthogonal to the re-transporting path P 2 . The spur gear  21 E is fixed at a left-side end portion of the rotating shaft  21 A. Whereas, a first gear  101  which is a bevel gear is fixed, in a state of gear teeth pointing toward a right side, to a right-side end portion of the rotating shaft  21 A. As shown in  FIG. 3 , two end sides of the rotating shaft  21 A are rotatably supported by two sliding bearings  93  respectively. The first gear  101  rotates integrally with the rotating shaft  21 A, the first transporting roller  32 A, and the spur gear  21 E. 
     As shown in  FIGS. 5 and 6 , the second transporting rollers  32 B and  32 C are also fixed at an intermediate portion of rotating shafts  22 B and  22 C of which rotational axes X 1 B and X 1 C are directed in a left-right direction, or in other words, the direction orthogonal to the re-transporting path P 2  as centers. As shown in  FIG. 3 , two ends of the rotating shafts  22 B and  22 C are rotatably supported by two sliding bearings  93  respectively. 
     As shown in  FIGS. 5 and 6 , at right-side end portion of the rotating shafts  22 B and  22 C, fourth gears  104 A and  104 B which are bevel gears are fixed to be in a state of gear teeth pointing toward a left-side. As shown in  FIG. 3 , the fourth gear  104 A rotates integrally with the rotating shaft  22 B and the second transporting roller  32 B while a flat surface at a right side thereof making a contact with an end surface of the sliding bearing  93 . The fourth gear  104 B also rotates integrally with the rotating shaft  22 C and the second transporting roller  32 C while a flat surface at a right side thereof making a contact with the end surface of the sliding bearing  93 . 
     As shown in  FIGS. 5 and 6 , a first shaft  100 A which is extended in a frontward and rearward direction, or in other words, in a direction orthogonal to the rotational axes X 1 A, X 1 B, and X 1 C is arranged between the first gear  101  and the fourth gear  104 A at the upstream side of the re-transporting path P 2 . As shown in  FIG. 3 , two end sides of the first shaft  100  are rotatably supported by two sliding bearings  93  respectively. 
     As shown in  FIGS. 5 and 6 , a second gear  102 A which is a bevel gear is fixed at a front-end portion of the first shaft  100 A in a state of being engaged with the first gear  101 , with gear teeth of the second gear  102 A pointing frontward. Whereas, a third gear  103  which is a bevel gear is fixed at a rear-end portion of the first shaft  100 A in a state of being engaged with the fourth gear  104 A, with gear teeth of the third gear  103  pointing rearward. The second gear  102 A and the third gear  103 A rotate integrally with the first shaft  100 A. 
     A second shaft  100 B which is extended in a frontward and rearward direction, or in other words, in a direction orthogonal to the rotational axes X 1 A, X 1 B, and X 1 C is arranged between the first gear  101  and the fourth gear  104 B at the downstream side of the re-transporting path P 2 . As shown in  FIG. 3 , two end sides of the second shaft  100 B are rotatably supported by two sliding bearings  93  respectively. The first shaft  100 A and the second shaft  100 B have same rotational axis. 
     As shown in  FIGS. 5 and 6 , a second gear  102 B which is a bevel gear is fixed at a rear-end portion of the second shaft  100 B in a state of being engaged with the first gear  101 , with gear teeth of the second gear  102 B pointing rearward. Whereas, a third gear  103 B which is a bevel gear is fixed at a front-end portion of the second shaft  100 B in a state of being engaged with the fourth gear  104 B, with gear teeth of the third gear  103 B pointing frontward. The second gear  102 B and the third gear  103 B rotate integrally with the second shaft  100 B. 
     A first transmitting section  21  which transmits the driving force of the drive mechanism  91  to the first transporting roller  32 A, includes the rotating shaft  21 A, the first gear  101 , and the spur gear  21 E. Moreover, a second transmitting section  22  which transmits the driving force of the first transmitting section  21  to the second transporting rollers  32 B and  32 C includes the second gears  102 A and  102 B, the first shaft  100 A, the second shaft  100 B, the third gears  103 A and  103 B, the fourth gears  104 A and  104 B, and the rotating shafts  22 B and  22 C. The transmission mechanism  20 , which transmits the driving force of the drive mechanism  91  to the first transporting roller  32 A and the second transporting rollers  32 B and  32 C, includes the first transmitting section  21  and the second transmitting section  22 . When the driving force is to be transmitted from the drive mechanism  91  to the rotating shaft  21 A via the spur gear  91 E and the spur gear  21 E by the transmission mechanism  20 , the first gear  101  and the second gears  102 A and  102 B are engaged. Accordingly, the driving force is transmitted to the first shaft  100 A and the second shaft  100 B. Furthermore, at this time, the third gears  103 A and  103 B, which are fixed to the end portions of the first shaft  100 A and the second shaft  100 B, are engaged with the fourth gears  104 A and  104 B which are fixed to the rotating shafts  22 B and  22 C, respectively. Accordingly, the driving force is transmitted to the rotating shafts  22 B and  22 C. In this manner, since the driving force is transmitted from the drive mechanism  91  to the first transporting roller  32 A and the second transporting rollers  32 B and  32 C via the rotating shafts  22 B and  22 C, the first transporting roller  32 A and the second transporting rollers  32 B and  32 C are rotated in a transporting direction of the paper along the re-transporting path P 2 . 
     As shown in  FIGS. 5 and 6 , rotational axes D 1 A, D 1 B, and D 1 C of the driven shafts  36 A,  36 B, and  36 C are inclined with respect to a left-right direction, or in other words, a direction orthogonal to the re-transporting path P 2 . The driven rollers  36 A,  36 B, and  36 C exert a force F (shown in  FIG. 6 ) which makes the paper skew (pass obliquely) toward a left side of the re-transporting path P 2  when the driven rollers  36 A,  36 B, and  36 C are driven to be rotated pinching the paper with the first transporting roller  32 A and the second transporting rollers  32 B and  32 C. Accordingly, the paper is transported along the re-transporting path P 2  while one-end in the width direction of the paper being pressed against the width-direction guide plate  34 . 
     In the printer  1  of the first embodiment having such structure, the paper having an image formed on the front surface is transported along the transporting path P 1 , and when a rear-end side thereof reaches up to the paper discharge rollers  45   a  and  45   b , the paper discharge rollers  45   a  and  45   b  are rotated in reverse direction. At this time, the flapper  49  switches the transporting path of the paper from the transporting path P 1  to the re-transporting path P 2 . When the transporting path is switched, the paper is transported to the re-transporting section  30  in a state of the front and rear side of the paper reversed. Moreover, the paper is transported by the side register feeding by the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, the driven rollers  36 A,  36 B, and  36 C, and the width-direction guide plate  34 , and is transported once again to the image forming section  50  in a state of being positioned in the width direction of paper. In this manner, the printer  1  is capable of forming a predetermined image on both front and rear surfaces of a paper. 
     In the printer  1  of the first embodiment, the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, the fourth gears  104 A and  104 B, the first shaft  100 A, and the second shaft  100 B are assembled easily, to be fitted between a plurality of ribs inside the internal space  31 B, in a state of the sliding bearings  93  mounted. Therefore, as compared to a timing belt which is commonly used, a tension control is unnecessary for the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, and the fourth gears  104 A and  104 B at the time of assembling. Moreover, the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, the fourth gears  104 A and  104 B, the first shaft  100 A, and the second shaft  100 B are hardly deteriorated as compared to the timing belt which is deformed repeatedly. In the printer  1  of the first embodiment, it is possible to transmit the driving force appropriately from the drive mechanism  91  to the first transporting roller  32 A and the second transporting rollers  32 B and  32 C by the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, the fourth gears  104 A and  104 B, the first shaft  100 A, and the second shaft  100 B. 
     Consequently, in the printer  1  of the first embodiment, it is possible to transport a paper favorably along the re-transporting path P 2 , and as a result, a defect such as jamming of paper hardly occurs. 
     Moreover, in the printer  1 , due to the engagement of the first gear  101  and the second gears  102 A and  102 B, the first transporting roller  32 A is biased toward a left end of the rotational axis X 1 A. Moreover, due to the engagement of the third gears  103 A and  103 B and the fourth gears  104 A and  104 B, the second transporting rollers  32 B and  32 C are biased toward a right end of the rotational axes X 1 B and X 1 C. Therefore, a play (backlash) in a direction of the rotational axes X 1 A, X 1 B, and X 1 C of the first transporting roller  32 A and the second transporting rollers  32 B and  32 C hardly occurs. As a result, in the printer  1 , it is possible to suppress a defect of the re-transporting path P 2  fluctuating in the left-right direction or in other words, in the direction of the rotational axes X 1 A, X 1 B, and X 1 C of the first transporting roller  32 A and the second transporting rollers  32 B and  32 C. 
     Furthermore, in the printer  1  of the first embodiment, the second transporting rollers  32 B and  32 C are positioned at the upstream side and the downstream side of the re-transporting path P 2 , with respect to the first transporting roller  32 A. In this case, it is possible to reduce the number of joints (joints of shafts) located in the route from the first transporting roller  32 A to which the driving force is transmitted directly from the drive mechanism  91 , up to the second transporting rollers  32 B and  32 C. In other words, as shown in  FIG. 5 , the number of joint portions from the first transporting path  32 A up to the second transporting path  32 B is two, and similarly, the number of joint portions from the first transporting path  32 A and the second transporting path  32 C is two. Whereas, in a case of arranging the two second transporting rollers  32 B and  32 C at one of the upstream side and the downstream side of the first transporting roller  32 A, the number of joint portions from the first transporting roller  32 A up to at least one of the second transporting rollers  32 B and  32 C is three or more. For instance, when the first transporting roller  32 A and the second transporting rollers  32 B and  32 C are arranged in an order of the second transporting rollers  32 B and  32 C, and the first transporting roller  32 A from the upstream side, the number of joint portions from the first transporting roller  32 A up to the second transporting roller  32 B is more than the number of joint portions from the first transporting roller  32 A up to the second transporting roller  32 C. In this case, since a transmission efficiency of the driving force transmitted from the drive mechanism  91  to the second transporting roller  32 B is lower than the transmission efficiency of the driving force transmitted from the drive mechanism  91  to the second transmitting roller  32 C, a variation in the driving force which is transmitted to the second transmitted rollers  32 B and  32 C becomes substantial. Whereas, in the printer  1  of the first embodiment, since it is possible to reduce the variation in the driving force which is transmitted to the second transporting rollers  32 B and  32 C, it is possible to improve the transmission efficiency of the driving force from the drive mechanism  91 . In a case of providing two second transporting rollers which are not directly coupled with the drive mechanism  91 , for one first transporting roller which is directly coupled with the drive mechanism  91 , it is desirable to provide one second transporting roller each to the upstream side and the downstream side of the first transporting roller as in the first embodiment, from a viewpoint of transmission efficiency of the driving force. 
     Moreover, in the printer  1  of the first embodiment, two shafts namely, the first shaft  100 A and the second shaft  100 B which are allocated separately for the upstream side and the downstream side, are used. Therefore, as compared to a case of using one long shaft, it is possible to suppress a twist of the first shaft  100 A and the second shaft  100 B. Therefore, in the printer  1 , it is possible to improve the transmission efficiency of the driving force from the drive mechanism  91 . 
     Furthermore, in the printer  1 , since the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, and the fourth gears  104 A and  104 B are bevel gears, it is possible to improve a strength and durability of gear teeth as compared to those a combination of crown gears and spur gears. 
     Second Embodiment 
     As shown in  FIG. 7 , in a printer according to a second embodiment, a layout of components such as the second transporting rollers  32 B and  32 C, the rotating shafts  22 B and  22 C, the first shaft  100 A, and the second shaft  100 B in the printer  1  of the first embodiment, is changed. The rest of the structure is same as the structure of the printer  1  of the first embodiment. Therefore, the above-mentioned changes will be described below in detail, and for the structure identical to the first embodiment, same reference numerals are assigned to components which are same as in the first embodiment, and the description of such components is omitted. 
     In the printer of the second embodiment, the first shaft  100 A is installed in a state of being inclined in a frontward and rearward direction by shifting a rear-end side of a rotational axis thereof toward a rightward direction. The second gear  102 A fixed to a front-end portion of the first shaft  100 A and the third gear  103 A fixed to a rear-end portion of the first shaft  100 A rotate integrally with the first shaft  100 A, around the rotational axis which is inclined with respect to the frontward and rearward direction. 
     Whereas, the second shaft  100 B is installed in a state of being inclined in a frontward and rearward direction by shifting a front-end side of a rotational axis thereof toward a rightward direction. The second gear  102 B fixed to a rear-end portion of the second shaft  100 B and the third gear  103 B fixed to a front-end portion of the second shaft  100 B rotate integrally with the second shaft  100 B, around the rotational axis which is inclined with respect to the frontward and rearward direction. 
     Regarding the second transporting roller  32 B and the rotating shaft  22 B, the rotational axis X 1 B is arranged in the left-right direction, or in other words, is arranged in a direction orthogonal to the re-transporting path P 2 . However, the second transporting roller  32 B and the rotating shaft  22 B are arranged to be shifted in the rightward direction, as compared to the arrangement in the first embodiment. Moreover, regarding the second transporting roller  32 C and the rotating shaft  22 C, the rotational axis X 1 C is arranged in the left-right direction, or in other words, is arranged in a direction orthogonal to the re-transporting path P 2 . However, the second transporting roller  32 C and the rotating shaft  22 C are arranged to be shifted in the rightward direction, as compared to the arrangement in the first embodiment. 
     The printer of the second embodiment having such structure, is also capable of showing a similar action and effect as the printer  1  of the first embodiment. 
     Moreover, in this printer, since the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, and the fourth gears  104 A and  104 B are bevel gears, it is possible to transmit the driving force even when the rotational axes X 1 A, X 1 B, and X 1 C of the first gear  101 , and the fourth gears  104 A and  104 B are not orthogonal to the rotational axes of the second gears  102 A and  102 B, and the third gears  103 A and  103 B. Therefore, it is possible to adjust appropriately a direction in which the first shaft  100 A and the second shaft  100 B are extended, not only in a direction parallel to the re-transporting path P 2 , but also in a direction inclined with respect to the re-transporting path P 2 . Therefore, in the printer of the second embodiment, a degree of freedom of layout of the first transporting roller  32 A and the second transporting rollers  32 B and  32 C is improved. For instance, as shown in  FIG. 8 , the first transporting roller  32 A may be arranged at a left side of the transporting tray  31 , and the second transporting rollers  32 B and  32 C may be transported at a right side of the transporting tray  31 . In this case, it is possible to impart a transporting force to both left and right ends of the paper which is transported, and to transport the paper stably. 
     For letting both the engagement of the first gear  101  and the second gear  102 A, and the engagement of the first gear  101  and the second gear  102 B to be in a suitable state, it is desirable to let an angle of intersection of the rotational axis X 1 A and the rotational axis of the first shaft  100 A same as an angle of intersection of the rotational axis X 1 A and the rotational axis of the second shaft  100 B as shown in  FIG. 7 . 
     Third Embodiment 
     In a printer of a third embodiment, with the relative positional relationship of the components such as the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, the rotating shafts  21 A,  22 B, and  22 C, the first shaft  100 A, and the second shaft  100 B in the printer of the second embodiment maintained as it is, the rotational axes X 1 A, X 1 B, and X 1 C of the first transporting roller  32 A and the second transporting rollers  32 B and  32 C shown in  FIG. 7  are changed to rotational axes X 3 A, X 3 B, and X 3 C shown in  FIG. 9 . In other words, a layout of the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, the rotating shafts  21 A,  22 B, and  22 C, the first shaft  100 A, and the second shaft  100 B in the printer of the second embodiment is changed to a layout as shown in  FIG. 9  by rotating in a clockwise direction, facing a paper surface in  FIG. 7 . At this time, a layout of the driven rollers  36 A,  36 B, and  36 C in the printer of the second embodiment is not changed. The rest of the structure is same as the structure of the printer  1  of the first embodiment. Therefore, the abovementioned changes will be described below in detail, and for the structure identical to the first embodiment, same reference numerals are assigned to components which are same as in the first embodiment, and the description of such components is omitted. 
     In the printer of the third embodiment, the rotational axes X 3 A, X 3 B, and X 3 C of the first transporting roller  32 A, and the second transporting rollers  32 B and  32 C are parallel to rotational axes D 1 A, D 1 B, and D 1 C of the driven rollers  36 A,  36 B, and  36 C. In other words, the rotational axes X 3 A, X 3 B, and X 3 C are inclined with respect to the direction orthogonal to the re-transporting path P 2 . In  FIG. 9 , an angle of inclination of the rotational axes X 3 A, X 3 B, and X 3 C is same. However the angle of inclination of the rotational axes X 3 A, X 3 B, and X 3 C can be set to be different. Moreover, in  FIG. 9 , the angle of inclination of the rotational axes X 3 A, X 3 B, and X 3 C is shown exaggeratedly. However, practically, the angle of inclination is set to a small angle of about 1° to few degrees. 
     Similarly as in the second embodiment, since the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, and the fourth gears  104 A and  104 B are bevel gears, it is possible to transmit the driving force even when the rotational axes X 3 A, X 3 B, and X 3 C of the first gear  101 , and the fourth gears  104 A and  104 B are not let to be orthogonal to the rotational axes of the second gears  102 A and  102 B, and the third gears  103 A and  103 B. 
     The printer of the third embodiment having such structure is also capable of showing a similar action and effect as the printer  1  of the first embodiment. 
     Moreover, in the printer of the third embodiment, the rotational axes X 3 A, X 3 B, and X 3 C are inclined with respect to the direction orthogonal to the re-transporting path P 2 . Therefore, the first transporting roller  32 A, the second transporting rollers  32 B and  32 C, and the driven rollers  36 A,  36 B, and  36 C strongly exerts a force F which skews the paper toward one side in the width direction of the re-transporting path P 2 . As a result, in the printer of the third embodiment, it is possible to exert assuredly the force F which skews the paper. Accordingly, it is possible to reduce a bias which presses the driven rollers  36 A,  36 B, and  36 C against the first transporting roller  32 A, and the second transporting rollers  32 B and  32 C. Therefore, in the printer of the third embodiment it is possible to simplify the bias spring  36 E, and to make the lid bodies  36  and  37  thin. As a result, a size reduction and a cost reduction are facilitated in the printer of the third embodiment. 
     In  FIG. 9 , an example in which the first transporting roller  32 A, and the second transporting rollers  32 B and  32 C are lined up in a straight line parallel to the re-transporting path P 2  has been cited. However, it is also possible to make an arrangement such that the first transporting roller  32 A, and the second transporting rollers  32 B and  32 C are lined up in a straight line parallel to the re-transporting path P 2  while inclining the rotational axes X 3 A, X 3 B, and X 3 C. 
     Fourth Embodiment 
     As shown in  FIG. 10 , in a printer of a fourth embodiment, a first gear  401  and fourth gears  404 A and  404 B which are crown gears, and second gears  402 A and  402 B as well as third gears  403 A and  403 B which are spur gears are used instead of the first gear  101 , the second gears  102 A and  102 B, the third gears  103 A and  103 B, and the fourth gears  104 A and  104 B in the printer of the first embodiment. The rest of the structure is same as the structure of the printer  1  of the first embodiment. Therefore, the abovementioned changes will be described below in detail, and for the structure identical to the first embodiment, same reference numerals are assigned to components which are same as in the first embodiment, and the description of such components is omitted. 
     In the rotating shaft  21 A, the first gear  401  which is a crown gear is fixed between the spur gear  21 E and the first transporting roller  32 A, with gear teeth of the first gear  401  pointing rightward. 
     The fourth gears  404 A and  404 B which are crown gears are fixed at a left-side end portion of the rotating shafts  22 B and  22 C, with gear teeth of the fourth gears  404 A and  404 B pointing leftward. 
     The second gears  402 A and  402 B, and the third gears  403 A and  403 B which are spur gears are fixed at a front-end side and a rear-end side of the first shaft  100 A and the second shaft  100 B. The second gears  402 A and  402 B, and the third gears  403 A and  403 B are engaged with one of the first gear  401 , and the fourth gears  404 A and  404 B. 
     The printer of the fourth embodiment having such structure is also capable of showing a similar action and effect as the printer  1  of the first embodiment. 
     Moreover, in the printer of the fourth embodiment, since crown gears and spur gears which have a simple structure, are used as the first gear  401 , the second gears  402 A and  402 B, the third gears  403 A and  403 B, and the fourth gears  404 A and  404 B, a reduction in a manufacturing cost is facilitated. 
     Fifth Embodiment 
     As shown in  FIG. 11 , in a printer of a fifth embodiment, as compared to the printer of the first embodiment, a position of the second transporting roller  32 C is changed to be between the first transporting roller  32 A and the second transporting roller  32 B. Moreover, one long shaft  500  is used instead of the first shaft  100 A and the second shaft  100 B. Furthermore, a first gear  501 , and fourth gears  504 A and  504 B which are crown gears, and a second gear  502  as well as third gears  503 A and  503 B which are spur gears, are used. The rest of the structure is same as the structure of the printer  1  of the first embodiment. Therefore, the above-mentioned changes will be described below in detail, and for the structure identical to the first embodiment, same reference numerals are assigned to components which are same as in the first embodiment, and the description of such components is omitted. 
     In the printer of the fifth embodiment, the second transporting rollers  32 B and  32 C are positioned at a downstream side of the re-transporting path P 2 , with respect to the first transporting roller  32 A. 
     In the rotating shaft  21 A, the first gear  501  which is a crown gear is fixed between the spur gear  21 E and the first transporting roller  32 A, with gear teeth of the first gear  501  pointing rightward. 
     The fourth gears  504 A and  504 B which are crown gears are fixed at a left-side end portion of the rotating shafts  22 B and  22 C, with gear teeth of the fourth gears  504 A and  504 B pointing leftward. 
     One long shaft  500  which is extended in a frontward and rearward direction, or in other words, a direction orthogonal to the rotational axes X 1 A, X 1 B, and X 1 C is provided between the first gear  501  and the fourth gear  504 B. Although it is omitted in the diagram, the shaft  500  is rotatably supported by the sliding bearings  93  at a plurality of locations. 
     The second gear  502  which is a spur gear, is fixed to a front-end side of the shaft  500 . The third gears  503 A and  503 B which are spur gears, are fixed to an intermediate portion and a rear-end side of the shaft  500 . Each of the second gear  502 , and the third gears  503 A and  503 B is engaged with one of the first gear  501 , and the fourth gears  504 A and  504 B. 
     The printer of the fifth embodiment having such structure is also capable of showing a similar action and effect as the printer  1  of the first embodiment. 
     Moreover, in the printer of the fifth embodiment, since it is possible to transmit the driving force to the second transporting rollers  32 B and  32 C by one shaft  500 , it is possible to realize a reduction of the number of components and a reduction of size of an apparatus. 
     The present invention has been described by referring to the embodiments from the first embodiment to the fifth embodiment. However the present invention is not restricted to the embodiments from the first embodiment to the fifth embodiment, and it is needless to mention that the present invention is also applicable to various modifications which fairly fall within the basic teachings herein set forth. For example, the number and arrangement of the first transporting roller and the second transporting rollers are not restricted to the number and the arrangement described in the embodiments from the first embodiment to the fifth embodiment, and may be set arbitrarily. For example, one second transporting roller may be provided at an upstream side of the first transporting roller  32 A as shown in  FIG. 12 . Although it is not shown in the diagram, one second transporting roller may be provided at a downstream side of the first transporting roller  32 A. In any of the cases, as compared to the printers described in the embodiments from the first embodiment to the fifth embodiment, it is possible to realize further reduction of the number of components and reduction of size of an apparatus. 
     It is possible to use the present invention in an image forming apparatus. The present invention is not restricted to an image forming apparatus having only a printer function as mentioned above. The present invention is also applicable to a multi-function device which also has functions such as a facsimile function and a copy function.