Patent Publication Number: US-8523175-B2

Title: Sheet transport apparatus and image forming apparatus including the same

Description:
BACKGROUND OF THE INVENTION 
     This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-256199 filed in Japan on Nov. 16, 2010, the entire contents of which are herein incorporated by reference. 
     1. FIELD OF THE INVENTION 
     The present invention relates to a sheet transport apparatus applicable to an image forming apparatus such as a printer, copier, multifunctional peripheral, and the like, and an image forming apparatus. 
     2. DESCRIPTION OF THE RELATED ART 
     In conventional sheet transport apparatuses for transporting a sheet such as recording paper, there is known to be a sheet transport apparatus including a sheet transport portion for transporting a sheet both in a first transport direction and a second transport direction that is opposite to the first transport direction (e.g., see JP 2002-220160A (hereinafter referred to as “Patent Document 1”)). 
     Such a sheet transport apparatus is generally provided on the downstream side in the second transport direction of the sheet transport portion, and is often applied to an image forming apparatus including a curved transport path in which the transport path is curved along the transport direction. 
     An image forming apparatus including a sheet transport apparatus having a sheet transport portion that transports a sheet both in the first transport direction and the second transport direction, and a curved transport path provided on the downstream side in the second transport direction of the sheet transport portion is typically used as an image forming apparatus that is capable of image formation on both sides of the sheet and that includes a discharge configuration in which a sheet is transported in the first transport direction in the sheet transport portion and is discharged to the outside, and a switchback configuration in which a sheet transported in the first transport direction in the sheet transport portion is transported in the second transport direction by a switchback operation so as to be transported to the curved transport path, the front and back sides of the sheet are inverted through that transport, and the sheet is guided to the upstream side of an image forming portion (specifically, registration rollers). 
     In some conventional sheet transport apparatuses as described above, from the viewpoint of improving stacking quality of sheets on a discharge tray, a bending member is provided that corrugates the sheet in an orthogonal direction that is orthogonal to the transport direction of the sheet transported in the sheet transport portion and conforms to the sheet surface, and thereby bends without breaking the sheet (e.g., see JP 2006-151617A (hereinafter referred to as “Patent Document 2”)). 
     However, with a sheet transport apparatus provided with the bending member for bending a sheet by corrugating the sheet transported in the sheet transport portion in the orthogonal direction that is orthogonal to the transport direction of the sheet and conforms to the sheet surface, in a case where the sheet is guided to a curved transport path that is curved in the transport direction, since the sheet has corrugations, there is a problem that an abnormal sound occurs when the sheet is transported in the curved transport path. 
       FIG. 6  is a diagram illustrating an example of a sheet transport apparatus A 1  in which bending rollers B 3  serving as a bending member, and a bending guide portion B 4  are provided, and is a schematic side view of the transportation state of a sheet P as seen from a transport direction Y thereof. 
     The sheet transport apparatus A 1  shown in  FIG. 6  includes a plurality of first transport rollers B 1  arranged on the same axis, and a plurality of second transport rollers B 2  that are arranged on the same axis so as to oppose the first transport rollers B 1 , and a sheet transport portion A 2  in which the sheet P is transported held between the first transport rollers B 1  (drive rollers fixed on a drive roller shaft E 1 ) that are driven to rotate and the second transport rollers B 2  (idler rollers fixed on an idler roller shaft E 2 ) that are driven due to the rotation of the first transport rollers B 1 . 
     In the sheet transport portion A 2 , bending rollers B 3  are arranged on the same axis as the first transport rollers B 1 . The bending rollers B 3  each have a diameter larger than that of the first transport rollers B 1 , and are configured to rotate integrally with the first transport rollers B 1  (in the example shown in  FIG. 6 , fixed on the drive roller shaft E 1 ). 
     Also, the sheet transport apparatus A 1  includes the bending guide portion B 4  that is fixed to the sheet transport portion A 2  and corrugates the transported sheet P in an orthogonal direction X that is orthogonal to the transport direction Y and conforms to the sheet surface, thereby bending the sheet P. The bending guide portion B 4  is arranged at the central position in the orthogonal direction X of the transported sheet P, and bends without breaking mainly sheets P such as a small size sheet, an envelope, and the like, which do not reach the bending rollers B 3  when they are transported in a central portion in the orthogonal direction X by the transport rollers B 1  and B 2 . 
     However, in the sheet transport apparatus Al, there is a problem relating to corrugations formed in the sheet P by the bending rollers B 3  and the bending guide B 4 , in particular, a problem that in the case where the sheet P is guided to a curved transport path D (see  FIG. 7  described below) that is curved along the transport direction Y of the sheet P, an abnormal sound occurs due to the sheet P corrugated in the orthogonal direction X being transported in the curved transport path D that is curved in the transport direction Y. 
       FIG. 7  is a schematic cross-sectional view illustrating, in an example of the sheet transport apparatus A 1 , a state in which the sheet P corrugated in the orthogonal direction X that is orthogonal to the transport direction Y and conforms to the sheet surface is transported in the curved transport path D that is curved along the transport direction Y, as seen from the orthogonal direction X. 
     As shown in  FIG. 7 , when the sheet P transported (transported by the switchback operation) in a second transport direction Y 2  by the transport rollers B 1  and B 2  rotated in reverse by a switch-back function is guided to the curved transport path D (in this example, a reverse transport path for inverting the front and back sides of the sheet P that is used when images are formed on both sides), the sheet P corrugated in the orthogonal direction X is forcibly bent while it is transported on the curved transport path D that is curved along the transport direction Y, and corrugations in the sheet P are restored to the original condition as a result of the sheet P having been bent. When the corrugations in the sheet P are restored to the original condition, an abnormal sound (specifically, a crunching sound, for example) may occur. 
     This is particularly noticeable in a configuration in which the sheet P is moved to the curved transport path D while having relatively large corrugations therein (specifically, a small-sized image forming apparatus in which the distance from the bending rollers B 3  and the bending guide portion B 4  to the curved transport path D is relatively short). Furthermore, when the height of the bending guide portion B 4  is increased to form larger corrugations, although stacking quality on a discharge tray B 5  can be improved mainly for sheets P such as a small size sheet, an envelope, and the like, the problem occurs that an abnormal sound readily occurs when the sheet P corrugated by the bending guide portion B 4  is transported in the curved transport path D, due to the increased height. 
     In this respect, Patent Document 1 discloses a configuration in which curl in the sheet is corrected in the curved transport path. However, Patent Document 1 does not disclose a configuration which solves an abnormal sound that occurs when the corrugated sheet is transported in the curved transport path. 
     Also, Patent Document 2 discloses a configuration in which a bending roller and a transport roller are integrally rotated when a sheet is discharged, and at the time of reverse rotation, the bending roller is not rotated integrally with the transport roller, but is driven by the sheet. However, with the configuration disclosed in Patent Document 2, although the bending roller is driven by the sheet at the time of reverse rotation, it does not suppress the corrugations in the sheet. Thus, with this configuration as well, an abnormal sound that occurs when the sheet is transported in the curved transport path is not solved. 
     In view of this, the present invention aims to provide a sheet transport apparatus that is capable of suppressing occurrence of problems relating to corrugations formed in the sheet by the bending member (in particular, an abnormal sound that occurs when the sheet is transported in the curved transport path), while securing high stacking quality of sheets, and an image forming apparatus including such a sheet transport apparatus. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-described problems, the present invention provides a sheet transport apparatus including a sheet transport portion that transports a sheet in a first transport direction and a second transport direction that is opposite to the first transport direction; a bending member that bends without breaking the sheet by corrugating the sheet in an orthogonal direction that is orthogonal to the transport direction of the sheet and conforms to a surface of the sheet; and a restriction member that restricts, in a perpendicular direction that is orthogonal to both the first transport direction and the second transport direction, and the orthogonal direction, a corrugation in the sheet bent by the bending member, wherein the restriction member is provided on an upstream side in the first transport direction of the bending member. In the above-described configuration, the restriction member may be provided on the upstream side in the first transport direction of a tip in the perpendicular direction of the bending member. 
     Also, the present invention provides an image forming apparatus including the sheet transport apparatus according to the present invention; a curved transport path provided on a downstream side in the second transport direction of the sheet transport portion of the sheet transport apparatus; and a discharge configuration in which the sheet transport portion transports a sheet in the first transport direction and discharges a sheet to the outside, and a transport configuration in which the sheet transport portion transports a sheet in the second transport direction toward the curved transport path. 
     With the present invention, the restriction member that restricts corrugations in a sheet (specifically, recording paper or an original) bent by the bending member in the perpendicular direction is provided on the upstream side in the first transport direction (specifically, the direction in which the sheet is discharged onto a discharge tray) of the bending member (a specific example is the tip of the bending member in the perpendicular direction). Thus, it is possible to maintain corrugations formed by the bending member in the sheet transported (specifically, discharged) in the first transport direction from the restriction member, and also to reduce corrugations formed by the bending member in the sheet transported in the second transport direction (specifically, the direction toward a curved transport path curved in the transport direction, for example, the curved transport path in the image forming apparatus of the present invention). In this manner, it is possible to suppress occurrence of problems relating to corrugations in the sheet formed by the bending member (particularly, an abnormal sound that occurs when the sheet is transported in the curved transport path), while securing high stacking quality of sheets. 
     In the present invention, an aspect is possible in which the restriction member is provided opposing the bending member in at least one of the orthogonal direction and the perpendicular direction. Specific examples of this aspect include an aspect in which the restriction member overlaps the bending member in the orthogonal direction, an aspect in which the restriction member overlaps the bending member in the perpendicular direction, and an aspect in which the restriction member overlaps the bending member both in the orthogonal direction and the perpendicular direction. 
     With this specific matter, since the restriction member is provided opposing the bending member in at least one of the orthogonal direction and the perpendicular direction, it is possible to reliably reduce corrugations in the sheet that is transported in the second transport direction from the restriction member, the corrugations being in a position corresponding to the position of the bending member. 
     In the present invention, it is preferable that the sheet transport portion includes a pair of transport rollers for transporting the sheet, and the restriction member is provided on the upstream side in the first transport direction of a nip portion of the pair of transport rollers. 
     With this specific matter, since the restriction member is provided on the upstream side in the first transport direction of the nip portion of the pair of transport rollers, it is possible to, for example, prevent the restriction member from inhibiting the force with which the sheet is transported (specifically, discharged onto the discharge tray) in the first transport direction from the sheet transport portion to the outside. Therefore, it is possible to reliably transport a sheet in the first transport direction, and prevent deterioration of stacking quality of the sheet. 
     In the present invention, an aspect is possible in which the restriction member is a flexible member having elasticity that is smaller than a force with which the sheet transport portion transports the sheet. 
     With this specific matter, with the restriction member formed as a flexible member, it is possible for the restriction member to be bent allowing for an appropriate elasticity and thereby restrict the corrugation in the sheet, while keeping transportability of the sheet bent by the bending member. 
     In the present invention, an aspect is possible in which the restriction member is a sheet-shaped flexible member. 
     With this specific matter, by forming the restriction member as a sheet-shaped flexible member, it is possible to readily achieve both transportability of a sheet and an effect of restricting the corrugation in the sheet with an inexpensive and simple structure. 
     In the present invention, an aspect is possible in which at least a portion of the restriction member that comes into contact with the sheet is formed with a fluororesin. Note that a typical example of fluororesin is polytetrafluoroethylene. 
     With this specific matter, since at least a portion of the restriction member formed as the flexible member, the portion coming into contact with the sheet, is formed with a fluororesin, and the fluororesin generally has a friction coefficient that is much lower than that of the sheet, it is possible to reduce or eliminate a sound generated by the restriction member and the sheet rubbing against each other. 
     Here, the friction coefficient is a concept including both static friction coefficient and dynamic friction coefficient. That is, in the case where the friction coefficient of the fluororesin is a static friction coefficient, the friction coefficient of the sheet is also a static friction coefficient, and in the case where the friction coefficient of the fluororesin is a dynamic friction coefficient, the friction coefficient of the sheet is also a dynamic friction coefficient. 
     Also, in a case where the restriction member is a sheet-shaped flexible member, it is preferable that the restriction member formed as a sheet-shaped flexible member is made of a fluororesin. 
     With this specific matter, since the restriction member is formed as a sheet-shaped flexible member made of a fluororesin, it is possible to reduce or eliminate a sound generated by the restriction member and the sheet rubbing against each other, while readily achieving both transportability of a sheet and an effect of restricting the corrugation in the sheet with an inexpensive and simple structure. 
     In the present invention, it is preferable that the restriction member overlaps the bending member in the orthogonal direction, and secures a path for the sheet by allowing for elastic deformation due to transport of the sheet in the first transport direction. 
     With this specific matter, by adopting a configuration in which the restriction member that overlaps the bending member in the orthogonal direction allows for elastic deformation thereof due to transport of the sheet in the first transport direction, thereby securing a path for the sheet, it is possible to prevent the restriction member from obstructing transport of the sheet, and it is thereby possible to prevent occurrence of a jam (sheet jam). 
     As a specific aspect of the above-described configuration, an aspect is possible in which the restriction member includes a first opposing portion that opposes an end portion of the bending member that is on one side in the orthogonal direction in a contactless manner when the restriction member undergoes elastic deformation due to transport of the sheet in the first transport direction, and a second opposing portion that opposes an end portion of the bending member that is on the other side in the orthogonal direction in a contactless manner when the restriction member undergoes elastic deformation due to transport of the sheet in the first transport direction. 
     With this specific matter, in the restriction member, when it undergoes elastic deformation due to transport of the sheet in the first transport direction, the first opposing portion opposes an end portion of the bending member on one side in the orthogonal direction in a contactless manner, and the second opposing portion opposes an end portion of the bending member on the other end in the orthogonal direction in a contactless manner, and thus it is possible to reliably secure a path for the sheet transported in the first transport direction. 
     In the present invention, an aspect is possible in which the sheet transport portion includes a pair of transport rollers for transporting the sheet, and is configured to transport the sheet in a horizontal direction, diagonally upward or diagonally downward, the tip of the bending member is provided on a downstream side in the first transport direction of a nip portion of the pair of transport rollers, and the bending member is configured to bend a transported sheet by corrugating the transported sheet in the orthogonal direction from above, and the restriction member is configured to restrict the corrugation from below the sheet. 
     With this specific matter, a configuration is adopted in which the sheet transport portion transports a sheet in the horizontal direction, diagonally upward or diagonally downward, and even if the tip of the bending member is provided on the downstream side in the first transport direction of the nip portion of the pair of transport rollers, the bending member corrugates a sheet transported in the sheet transport portion from above and thereby bends without breaking the sheet. Therefore, for example, it is possible to prevent the bending member from inhibiting the force with which the sheet is transported (specifically, discharged onto the discharge tray) in the first transport direction from the sheet transport portion to the outside, and consequently it is possible to reliably transport the sheet in the first transport direction, and prevent deterioration of stacking quality of sheets. 
     In the present invention, an aspect is possible in which the sheet transport apparatus includes a plurality of first transport rollers provided on a same axis, a plurality of second transport rollers that are provided opposing the plurality of first transport rollers and on a same axis, a pair of transport rollers configured to transport the sheet while holding the sheet between the first transport rollers and the second transport rollers that are rotated, a bending roller that is provided on the same axis as that of at least one of the first transport rollers and the second transport rollers, and has a diameter larger than that of the transport rollers provided on the same axis as that of the bending roller, and a bending guide portion provided in a central position of a transported sheet in the orthogonal direction, and the restriction member restricts the corrugation in the sheet bent by the bending guide portion out of the bending roller and the bending guide portion. 
     With this specific matter, the corrugation in the sheet can be reduced with the restriction member that restricts the corrugation in the sheet that has been bent by the bending guide portion arranged in the central position, and in this manner, mainly, it is possible to suppress occurrence of problems relating to the corrugation in the sheet formed by the bending member (particularly, an abnormal sound that occurs when the sheet is transported in the curved transport path), while securing high stacking quality of sheets such as small size paper, an envelope and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of an image forming apparatus including a sheet transport apparatus according to an embodiment of the present invention as seen from the front. 
         FIG. 2  is a schematic cross-sectional view illustrating a transport path in the image forming apparatus shown in  FIG. 1 . 
         FIG. 3  is a schematic side view of the sheet transport apparatus of the image forming apparatus shown in  FIG. 1  as seen from the first transport direction of paper. 
         FIG. 4  is a schematic cross-sectional view of the sheet transport apparatus of the image forming apparatus shown in  FIG. 1  as seen from an orthogonal direction (axis line direction) that is orthogonal to the first transport direction and second transport direction and conforms to the paper surface. 
         FIG. 5  includes  FIGS. 5A ,  5 B,  5 C and  5 D, each schematically illustrating a configuration in which although a restriction member overlaps a bending guide portion in the orthogonal direction, the restriction member allows for elastic deformation thereof due to transport of paper in the first transport direction, thereby securing a path for the paper.  FIGS. 5A and 5B  are a schematic side view and a schematic plan view, respectively, showing a state of the restriction member when the paper is not passing the restriction member.  FIGS. 5C and 5D  are a schematic side view and a schematic plan view, respectively, showing a state of the restriction member immediately after the paper has begun passing the restriction member. 
         FIG. 6  is a diagram illustrating an example of a conventional sheet transport apparatus, in which bending rollers and a bending guide portion, each serving as a bending member, are provided, and is a schematic side view of a transportation state of a sheet as seen from the transport direction thereof. 
         FIG. 7  is a schematic cross-sectional view of a state in which, in an example of the sheet transport apparatus, a sheet corrugated in the orthogonal direction that is orthogonal to the transport direction and conforms to the sheet surface is transported in a curved transport path that is curved in the transport direction, as seen from the orthogonal direction. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           30  Sheet transport portion 
           31  First discharge rollers 
           31   a  Drive roller shaft 
           32  Second discharge rollers 
           32   a  Idler roller shaft 
           34  Bending roller (example of the bending member) 
           40  Rotation drive portion 
           77  Reverse transport path (example of the curved transport path) 
           100  Image forming apparatus 
           210  Bending guide portion (example of the bending member) 
           211  Upstream side end 
           212  Downstream side end 
           213  Tip 
           214  End face 
           215  End face 
           220  Restriction member 
           221  First opposing portion 
           222  Second opposing portion 
           223  Recessed portion 
           300  Sheet transport apparatus 
         N Nip portion 
         P Paper (example of the sheet) 
         X Orthogonal direction 
         Y Transport direction 
         Y 1  First transport direction 
         Y 2  Second transport direction 
         Z Perpendicular direction 
         β Central position 
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. The embodiments described below are only examples in which the present invention is embodied, and are not intended to limit the technical scope of the present invention. 
     Description of Overall Configuration of Image Forming Apparatus 
       FIG. 1  is a schematic cross-sectional view of an image forming apparatus  100  including a sheet transport apparatus  300  according to an embodiment of the present invention as seen from the front. 
     The image forming apparatus  100  shown in  FIG. 1  is a color image forming apparatus that forms images in multiple colors or in a single color on a sheet (hereinafter referred to as “paper”) P such as recording paper in accordance with image data transmitted from the outside. The image forming apparatus  100  includes an original reading apparatus  108  and an apparatus main body  110 , and the apparatus main body  110  is provided with an image forming portion  102  and a sheet transport system  103 . 
     The image forming portion  102  includes an exposure unit  1 , a plurality of development units  2 , a plurality of photosensitive drums  3 , a plurality of cleaning portions  4 , a plurality of charging devices  5 , an intermediate transfer belt unit  6 , a plurality of toner cartridge units  21 , and a fixing unit  7 . 
     Moreover, the sheet transport system  103  includes a paper feed portion  80  that includes a paper feed tray  81  and a manual paper feed tray  82 , below-described transport paths (a main transport path  76  and a reverse transport path  77 ), and a paper discharge tray  91 . 
     An original platen  92  composed of a transparent glass on which an original (a sheet) can be placed is provided in an upper portion of the apparatus main body  110 , and an optical unit  90  for reading the original is provided below the original platen  92 . Moreover, the original reading apparatus  108  is provided above the original platen  92 . The original reading apparatus  108  automatically transports the original onto the original platen  92 . Moreover, the original reading apparatus  108  is pivotably attached to the apparatus main body  110  so that a front side thereof can be opened, and it is possible to manually place the original there by uncovering an upper surface of the original platen  92 . 
     The original reading apparatus  108  can read originals that are automatically transported or originals that have been placed on the original platen  92 . An entire image of an original that has been read by the original reading apparatus  108  is sent to the apparatus main body  110  of the image forming apparatus  100  as image data. Then, in the apparatus main body  110 , an image is formed based on the image data and recorded on paper P. 
     The image data handled in the image forming apparatus  100  corresponds to a color image using a plurality of colors (here, the colors of black (K), cyan (C), magenta (M), and yellow (Y)). Therefore, more than one (here, four, respectively corresponding to black, cyan, magenta, and yellow) of the development units  2 , the photosensitive drums  3 , the cleaning portions  4 , the charging devices  5 , and the toner cartridge units  21  are provided, so that a plurality of types (here, four types) of images corresponding to individual colors are formed, and these units constitute a plurality of (here, four) image stations. 
     The charging devices  5  serve as charging means for uniformly charging the surface of photosensitive drums  3  at a predetermined electric potential. In addition to a charger-type charging device as shown in  FIG. 1 , a roller-type charging device or a brush-type charging device, which are of a contact-type, can be used. 
     The exposure unit  1  is configured as a laser scanning unit (LSU) including a laser emitting portion and a reflection mirror. The exposure unit  1  is provided with a polygon mirror that scans a laser beam and optical elements, such as a lens and a mirror, for guiding laser light that has been reflected by this polygon mirror to the photosensitive drums  3 . Moreover, concerning the exposure unit  1 , other techniques can also be adopted in which, for example, EL (electroluminescence) or a write head having an array of light emitting elements such as LEDs (light emitting diodes) is used. 
     The exposure unit  1  exposes each of the charged photosensitive drums  3  in accordance with the image data that has been input, thereby forming electrostatic latent images corresponding to the image data on the surfaces of the respective photosensitive drums  3 . 
     The toner cartridge units  21  are units that accommodate toners, and are adapted to supply the toners to development tanks of the development units  2 . In the apparatus main body  110  of the image forming apparatus  100 , the toners supplied from the toner cartridge units  21  to the development tanks of the development units  2  are controlled so as to keep the toner concentrations in developers in the development tanks constant. 
     The development units  2  make the electrostatic latent images formed on the respective photosensitive drums  3  visible using the four colors (Y, M, C, and K) of toners. Moreover, the cleaning portions  4  remove and collect residual toner on the surfaces of the photosensitive drums  3  after developing and transferring the images 
     The intermediate transfer belt unit  6  disposed above the photosensitive drums  3  includes an intermediate transfer belt  61  that acts as an intermediate transfer member, an intermediate transfer belt drive roller  62 , an intermediate transfer belt idler roller  63 , a plurality of intermediate transfer rollers  64 , and an intermediate transfer belt cleaning unit  65 . 
     Four rollers are provided as the intermediate transfer rollers  64  for the colors Y, M, C, and K, respectively. The intermediate transfer belt drive roller  62 , together with the intermediate transfer belt idler roller  63  and the intermediate transfer rollers  64 , stretches the intermediate transfer belt  61  in a tensioned manner, and when the drive roller is driven to rotate, the intermediate transfer belt  61  is moved around in a moving direction (the direction of arrow M in  FIG. 1 ), and with this movement, the idler roller  63  and the intermediate transfer rollers  64  are rotated. 
     A transfer bias for transferring the toner images formed on the photosensitive drums  3  onto the intermediate transfer belt  61  is applied to each of the intermediate transfer rollers  64 . 
     The intermediate transfer belt  61  is provided in contact with the photosensitive drums  3 . The toner images that have been formed on the photosensitive drums  3  in respective colors are sequentially transferred onto the intermediate transfer belt  61  in such a manner that the toner images are superimposed on top of one another, and thus, a color toner image (a multi-color toner image) is formed on the surface of the belt. The intermediate transfer belt  61  is, for example, an endless belt composed of a film having a thickness of approximately 100 μm to 150 μm. 
     Transfer of the toner images from the photosensitive drums  3  to the intermediate transfer belt  61  is performed by the intermediate transfer rollers  64  that are in contact with a back side of the intermediate transfer belt  61 . For transfer of the toner images, a high-voltage transfer bias (a high voltage with the opposite polarity (+) to the charge polarity (−) of the toners) is applied to the intermediate transfer rollers  64 . The intermediate transfer rollers  64  are rollers in which a metal (stainless steel, for example) shaft having a diameter of 8 mm to 10 mm is used as a base and the surface of the shaft is covered with a conductive elastic material (for example, a resin material such as EPDM (ethylene-propylene-diene rubber) or urethane foam). With this conductive elastic material, the intermediate transfer rollers  64  serve as transfer electrodes that uniformly apply a high voltage to the intermediate transfer belt  61 . In the present embodiment, roller-shaped transfer electrodes are used as the transfer electrodes. However, it is also possible to use other types of transfer electrodes such as brush-shaped transfer electrodes. 
     As described above, the toner images that have been made visible in respective hues on the photosensitive drums  3  are layered on top of one another on the intermediate transfer belt  61 . Due to the revolving movement of the intermediate transfer belt  61 , the layered toner images on the intermediate transfer belt  61  are transferred onto the paper P by a transfer roller  10  constituting a secondary transfer mechanism portion that is disposed at a position where the paper P and the intermediate transfer belt  61  come into contact with each other. However, the configuration of the secondary transfer mechanism portion is not limited to the transfer roller, and a transfer configuration such as a corona charger or a transfer belt can be used as well. 
     At this time, a voltage (a high voltage with the opposite polarity (+) to the charge polarity (−) of the toners) for transferring the toners onto the paper P is applied to the transfer roller  10  in a state in which a transfer nip is formed between the roller and the intermediate transfer belt  61 . The transfer nip is formed between the transfer roller  10  and the intermediate transfer belt  61  by the transfer roller  10  and the intermediate transfer belt drive roller  62  pressing against each other. In order to constantly obtain the transfer nip, either one of the transfer roller  10  and the intermediate transfer belt drive roller  62  is configured as a hard roller composed of a hard material (such as a metal), and the other roller is configured as an elastic roller composed of a soft material (a resin material such as elastic rubber or foam resin). 
     During transfer of the toner images on the intermediate transfer belt  61  onto the paper P by the transfer roller  10 , there are cases where the toners are not completely transferred onto the paper P, leaving residual toner on the intermediate transfer belt  61 . The residual toner on the intermediate transfer belt  61  may cause mixing of the color toners in the following processing. For this reason, the residual toner on the intermediate transfer belt  61  is removed and collected by the intermediate transfer belt cleaning unit  65 . Specifically, the intermediate transfer belt cleaning unit  65  is provided with a cleaning member (a cleaning blade, for example) that is in contact with the intermediate transfer belt  61 . The idler roller  63  supports the intermediate transfer belt  61  from an inner side (the back side), and the cleaning member is in contact with the intermediate transfer belt  61  in such a manner that the cleaning member presses the belt against the idler roller  63  from an outer side. 
     The paper feed tray  81  is a tray for storing beforehand paper P onto which an image is to be formed (printed), and is provided below the exposure unit  1  in the apparatus main body  110 . Moreover, paper P onto which an image is to be formed (printed) is placed in the manual paper feed tray  82 . The paper discharge tray  91  is provided above the image forming portion  102  in the apparatus main body  110 , and paper P on which an image has been formed (printed) is accumulated facedown in this tray. 
     Moreover, the apparatus main body  110  is provided with the main transport path  76  for conveying paper P fed from the paper feed tray  81  and the manual paper feed tray  82  to the paper discharge tray  91  via the transfer roller  10  and the fixing unit  7 . Pickup rollers  11   a  and  11   b , a plurality of (here, a first and a second) transport rollers  12   a  and  12   b , registration rollers  13 , the transfer roller  10 , and a heat roller  71  and a pressure roller  72  of the fixing unit  7  are disposed in the vicinity of the main transport path  76 . A plurality of (here, a third and a fourth) transport rollers  12   c  and  12   d  are disposed in the vicinity of the reverse transport path  77 . 
     The first to fourth transport rollers  12   a  to  12   d  are small rollers for promoting and assisting transport of paper P. Moreover, the pickup roller  11   a  is provided in the vicinity of a paper supply side of the paper feed tray  81  and picks up and supplies paper P sheet-by-sheet from the paper feed tray  81  to the main transport path  76 . Similarly, the pickup roller  11   b  is provided in the vicinity of a paper supply side of the manual paper feed tray  82  and picks up and supplies paper P sheet-by-sheet from the manual paper feed tray  82  to the main transport path  76 . 
     Moreover, the registration rollers  13  temporarily hold paper P during transport through the main transport path  76 . Then, the registration rollers  13  transport the paper P to the transfer roller  10  at the timing when a leading end of a toner image on the intermediate transfer belt  61  and a downstream side end (hereinafter referred to as a “leading end P 1 ”) in the first transport direction Y 1  (one of the transport direction Y) of the paper P are aligned. 
     The fixing unit  7  is for fixing an unfixed toner image onto the paper P and includes the heat roller  71  and the pressure roller  72 , which act as fixing rollers. The heat roller  71 , when driven to rotate, transports the paper P in conjunction with the rotated pressure roller  72  while sandwiching the paper P therebetween. Moreover, the heat roller  71  is heated by a heater  71   a  provided inside and is maintained at a predetermined fixing temperature based on a signal from a temperature detector  71   b . The heat roller  71  heated by the heater  71   a , in conjunction with the pressure roller  72 , bonds a multi-color toner image that has been transferred onto the paper P to the paper P by heat and pressure, whereby the multi-color toner image is fused, mixed, pressed against the paper P, and thus fixed to the paper P by heat. 
     Transport Path 
       FIG. 2  is a schematic cross-sectional view illustrating the transport paths  76  and  77  in the image forming apparatus  100  shown in  FIG. 1 . 
     As shown in  FIGS. 1 and 2 , the image forming apparatus  100  includes, as described above, the main transport path  76  and the reverse transport path  77  as transport paths through which the paper P is transported, and is configured such that the sheet is transported based on the central position thereof. The reverse transport path  77  is curved along the transport direction Y, and constitutes a curved transport path. 
     The main transport path  76  is a transport path for transporting the paper P between the paper feed portion  80  and a sheet transport portion  30  in the sheet transport apparatus  300 . 
     The reverse transport path  77  is a transport path through which the paper P is transported in a second transport direction Y 2  that is opposite to the first transport direction Y 1 , and is configured to be a transport path that is connected to a connection portion Sb (see  FIG. 1 ) to the main transport path  76 , the connection portion Sb being between the image forming portion  102  and the paper feed portion  80 , passing through a part of the main transport path  76  from the sheet transport apparatus  300  to a branching portion Sa between the fixing unit  7  and the sheet transport apparatus  300 . Accordingly, the transport path between the sheet transport apparatus  300  and the branching portion Sa is common to the main transport path  76  and the reverse transport path  77 . 
     A branching claw  84  is arranged in the branching portion Sa. The branching claw  84  is configured to take a first posture (posture indicated by the solid line in  FIG. 2 ) for guiding the paper P from the fixing unit  7  to the sheet transport apparatus  300 , and a second posture (posture indicated by the dashed double-dotted line in  FIG. 2 ) for guiding the paper P that is transported in the second transport direction Y 2 , which is the opposite direction to the first transport direction Y 1 , due to reverse rotation (rotation in the direction of arrow C 2  in  FIG. 2 ) of first discharge rollers  31  and second discharge rollers  32  described below in the sheet transport apparatus  300 , to the reverse transport path  77  side. 
     In the image forming apparatus  100  configured as described above, the paper P supplied from the paper feed trays  81  and  82  is transported to the registration rollers  13  by the first transport rollers  12   a  disposed along the main transport path  76 , and transported by the transfer roller  10  at a timing when the leading end P 1  of the paper P and the leading end of the toner image on the intermediate transfer belt  61  are aligned, and thereby the toner image is transferred onto the paper P. Thereafter, the paper P passes through the fixing unit  7  where unfixed toner on the paper P is fused and fixed by heat. 
     When an image is printed on one side of the paper P, the branching claw  84  is set to the first posture, and the paper P conveyed from the fixing unit  7  is transported by the first discharge rollers  31  and the second discharge rollers  32  that are rotated forward (rotated in the direction of arrow C 1  in  FIG. 2 ) via the second transport rollers  12   b , and is discharged onto the discharge tray  91  by the first discharge rollers  31  and the second discharge rollers  32 . 
     Also, when printing is performed on both sides of the paper P, first, the branching claw  84  is set to the first posture, and the leading end P 1  side of the paper P that has passed through the fixing unit  7  is temporarily transferred to the outside by the first discharge rollers  31  and the second discharge rollers  32 . Then, after the upstream side end (hereinafter referred to as a “trailing end”) P 2  in the first transport direction Y 1  of the paper P has passed through the branching portion Sa as a result of the paper P having been transferred by the first discharge rollers  31  and the second discharge rollers  32 , the branching claw  84  is set to the second posture. After the branching claw  84  is set to the second posture, the first discharge rollers  31  and the second discharge rollers  32  are rotated in reverse. As a result of the first discharge rollers  31  and the second discharge rollers  32  being rotated in reverse, the paper P is transported in the second transport direction Y 2  (transported through the switchback operation), and transported along the reverse transport path  77  by the third and fourth transport rollers  12   c  and  12   d  to the connection portion Sb on the upstream side of the registration rollers  13 . By transporting the paper P on the reverse transport path  77 , the front and back sides of the paper P transported to the connection portion Sb are reversed. Then, the paper P transported to the transfer nip via the registration rollers  13  is, after the printing is performed on its back side, transported by the first discharge rollers  31  and the second discharge rollers  32  that are rotated forward, and is discharged onto the discharge tray  91 . Note that the posture of the branching claw  84  is changed from the second posture to the first posture after the paper P has been transported in the second transport direction Y 2  and the leading end P 1  side of the paper P has passed the branching claw  84 . 
     Sheet Transport Apparatus 
       FIG. 3  is a schematic side view of the sheet transport apparatus  300  of the image forming apparatus  100  shown in  FIG. 1  as seen from the first transport direction Y 1  of the paper P. Also,  FIG. 4  is a schematic cross-sectional view of the sheet transport apparatus  300  of the image forming apparatus  100  shown in  FIG. 1  as seen from an orthogonal direction X (axis line direction) that is orthogonal to the first transport direction Y 1  and the second transport direction Y 2 , and conforms to the paper surface. 
     As shown in  FIGS. 2 to 4 , the sheet transport apparatus  300  according to the present embodiment includes the sheet transport portion  30  that transports the paper P and a rotation drive portion  40  (see  FIG. 3 ). The sheet transport portion  30  in the present embodiment is configured to transport the paper P in a substantially horizontal direction or slightly diagonally upward. Note that the sheet transport portion  30  may be configured to transport the paper P diagonally downward. 
     The sheet transport portion  30  includes, as a pair of transport rollers that are driven to rotate and thereby transport the paper P while holding the paper P therebetween, a plurality of (here, four) first discharge rollers (an example of the first transport roller)  31  and a plurality of (here, four) second discharge rollers (an example of second transport roller)  32 . The number of the first discharge rollers  31  and the second discharge rollers  32  are the same. The first discharge rollers  31  have the same diameter, and all of them are arranged on the same axis. The second discharge rollers  32  have the same diameter, and are arranged on the same axis in opposition to the first discharge rollers  31 . The sheet transport portion  30  transports the paper P while holding the paper P between the first discharge rollers (drive rollers)  31  that are driven to rotate, and the second discharge rollers (idler rollers)  32  that are rotated due to the rotation of the first discharge rollers  31 . Specifically, the sheet transport portion  30  transports the paper P in the first transport direction Y 1  toward the discharge tray  91  when the first discharge rollers  31  and the second discharge rollers  32  are rotated forward, and it transports the paper P in the second transport direction Y 2  toward the reverse transport path  77  when the first discharge rollers  31  and the second discharge rollers  32  are rotated in reverse. 
     The sheet transport portion  30  further includes a drive roller shaft  31   a  and idler roller shafts  32   a . The first discharge rollers  31  are fixed to the drive roller shaft  31   a . The second discharge rollers  32  are fixed to the idler roller shafts  32   a  in opposition to the first discharge rollers  31 . Also the sheet transport portion  30  further includes biasing members  33  (here, helical springs) that bias the second discharge rollers  32  toward the first discharge rollers  31  (see  FIG. 3 ). 
     The first discharge rollers  31 , the second discharge rollers  32  and the biasing members  33  are provided on a body frame  30   a  (see  FIGS. 2 and 3 ) of the sheet transport portion  30 , and one end of the drive roller shaft  31   a  on which the first discharge rollers  31  are provided protrudes in the orthogonal direction X from the main body frame  30   a  of the sheet transport portion  30  to the outside. 
     Here, a single drive roller shaft  31   a  is used, and is provided in the main body frame  30   a  of the sheet transport portion  30  so as to be capable of rotating about its axis line with respect to a first covering member  36  (see  FIG. 4 ) that covers the drive roller shaft  31   a.    
     In this case, a plurality of (here, two) idler roller shafts  32   a  are disposed in line in the orthogonal direction X, and a plurality of (here, two) second discharge rollers  32  are fixed to each of them. Each idler roller shaft  32   a  is provided in the main body frame  30   a  of the sheet transport portion  30  such that the second discharge rollers  32  are in opposition to the corresponding first discharge rollers  31 , and so as to be capable of rotating about the axis line with respect to a second covering member  37  (see  FIGS. 3 and 4 ) that covers the idler roller shafts  32   a , and capable of moving back and forth in a perpendicular direction Z (here, the vertical direction) that is orthogonal to the first transport direction Y 1 , the second transport direction Y 2  and the orthogonal direction X. The sheet transport portion  30  is configured such that the paper P is transported in a state in which it is pressed by the second discharge rollers  32  in a nip portion N between the first discharge rollers  31  and the second discharge rollers  32 , while being held therebetween. 
     Specifically, the biasing members  33  are configured to bias the second discharge rollers  32  toward the first discharge rollers  31 , and in this case, are disposed between the second discharge rollers  32  and the main body frame  30   a  of the sheet transport portion  30 . Specifically, the biasing members  33  are disposed between the idler roller shafts  32   a  to which the second discharge rollers  32  are fixed, and a portion of the main body frame  30   a  of the sheet transport portion  30  that is in the position opposite to the first discharge rollers  31  with respect to the idler roller shafts  32   a . Note that a pressing force that is applied to the first discharge rollers  31  by the second discharge rollers  32  due to the biasing members  33  is approximately a pressure under which proper transport of the paper P is not hindered. 
     The sheet transport portion  30  further includes a plurality of (here, four) bending rollers  34  that each act as a bending member for bending the paper P by corrugating the paper P in the orthogonal direction X. The bending rollers  34  are arranged on the same axis as that of the discharge rollers (here, the second discharge rollers  32 ) of at least one of the first discharge rollers  31  and the second discharge rollers  32 , and have a diameter larger than that of the second discharge rollers  32 . Note that the bending rollers  34  may be arranged on the same axis as that of one of the first discharge rollers  31  and the second discharge rollers  32 , or may be arranged on the same axes as that of both the first discharge rollers  31  and the second discharge rollers  32 . In the case where the bending rollers  34  are provided on both the first discharge rollers  31  and the second discharge rollers  32 , the bending rollers  34  on the first discharge rollers  31  side and those on the second discharge rollers  32  side are arranged so as not to overlap each other in the orthogonal direction X. 
     In this manner, when the sheet transport portion  30  transports the paper P, it provides the paper P with a shape corrugated in the orthogonal direction X using the bending rollers  34 , thereby bending the paper P. 
     Specifically, the bending rollers  34  are provided on the second discharge rollers  32  in an end portion thereof on one side X 1  or the other side X 2  in the orthogonal direction X. Note that the bending rollers  34  may be provided on the idler roller shafts  32   a.    
     Here, one bending roller  34  may be disposed for each second discharge roller  32  or at an interval of two or more second discharge rollers  32 . Alternatively, a plurality of bending rollers  34  may be arranged for each second discharge roller  32  or at an interval of two or more second discharge rollers  32 . Also, any combination of these arrangement configurations may be used. In the present embodiment, two bending rollers  34  are provided between each second discharge roller  32  on the outer end and the second discharge roller  32  inward thereof. 
     The rotation drive portion  40  drives the drive roller shaft  31   a  on which the first discharge rollers  31  are provided to rotate, and includes a transport drive motor  41  (here, stepping motor) and a drive transmission mechanism  42  for transmitting rotational drive from the transport drive motor  41  to the drive roller shaft  31   a.    
     The transport drive motor  41  is provided in the apparatus main body  110  such that a rotation shaft  41   a  thereof extends in the orthogonal direction X. 
     Here, the drive transmission mechanism  42  is constituted by a gear train in which a plurality of gears are combined, and includes a drive gear  42   a , a roller gear  42   b  and an intermediate gear  42   c.    
     The drive gear  42   a  is linked to the rotation shaft  41   a  of the transport drive motor  41 . The roller gear  42   b  is linked to an end portion of the drive roller shaft  31   a , the end portion protruding in the orthogonal direction X from the main body frame  30   a  of the sheet transport portion  30  to the outside. The intermediate gear  42   c  is supported by a rotation shaft  110   a  fixed to the apparatus main body  110  so as to be capable of rotation, and is engaged with the drive gear  42   a  and the roller gear  42   b.    
     The transport drive motor  41  is electrically connected to an output system of a control portion (not shown in the drawings) such that a drive signal (ON signal) or a drive stop signal (OFF signal) from the control portion is obtained. The control portion can drive the first discharge rollers  31  to rotate in one direction C 1  (the first transport direction Y 1 , see  FIGS. 2 and 4 ) or the other direction C 2  (the second transport direction Y 2 , see  FIGS. 2 and 4 ), by sending a rotation instruction signal instructing the rotational direction to the transport drive motor  41  so as to drive the transport drive motor  41 . 
     Here, a discharge configuration is constituted by a configuration that includes the first discharge rollers  31  and second discharge rollers  32 , the rotation drive portion  40 , and a control configuration of the control portion (not shown in the drawings) that controls the rotation drive portion  40  so as to transport the paper P in the first transport direction Y 1  and discharge the paper P onto the discharge tray  91 . Also, a transport configuration is constituted by a configuration that includes the first discharge rollers  31  and second discharge rollers  32 , the rotation drive portion  40 , and a control configuration of the control portion (not shown in the drawings) that controls the rotation drive portion  40  so as to transport the paper P in the second transport direction Y 2  toward the reverse transport path  77 . 
     The sheet transport apparatus  300  includes a first sheet transport guide  38  and a second sheet transport guide  39  (see  FIG. 4 ), which are provided opposing each other in the perpendicular direction Z with a gap provided therebetween, on the upstream side in the first transport direction Y 1  of the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 . The transported paper P is guided to a portion between the first sheet transport guide  38  and the second sheet transport guide  39 , and then to the nip portion N. 
     Also, the sheet transport apparatus  300  includes a bending guide portion  210  (see  FIGS. 3 and 4 ) that serves as a bending member that corrugates the paper P in the orthogonal direction X, thereby bending the paper P. Note that the bending guide portion  210  is not shown in  FIGS. 1 and 2 . 
     Specifically, the bending guide portion  210  is provided on the first covering member  36 , and has a curved shape including a curved surface in which an upstream side end  211  in the first transport direction Y 1  and a downstream side end  212  in the first transport direction Y 1  (upstream side end in the second transport direction Y 2 ) are positioned on one side (here, the upper side) in the perpendicular direction Z of the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 , and also a tip  213  (vertex portion) on the side coming into contact with the paper P in the perpendicular direction Z is positioned on the other side (here, the lower side) in the perpendicular direction Z of the nip portion N. Also, the upstream side end  211  of the bending guide portion  210  is disposed on the upstream side in the first transport direction Y 1  relative to the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 , and the tip  213  of the bending guide portion  210  is disposed on the downstream side in the first transport direction Y 1  relative to the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 . In the present embodiment, the bending guide portion  210  and the first covering member  36  are formed with resin, and the bending guide portion  210  and the first covering member  36  are formed as a single body. 
     In the sheet transport apparatus  300  described above, as shown in  FIGS. 3 and 4 , a restriction member  220  is provided for restricting, in the perpendicular direction Z, corrugations in the paper P bent by, out of the bending rollers  34  and the bending guide portion  210 , the bending guide portion  210 . Here, the restriction member  220  is provided in the sheet transport portion  30 . Note that the restriction member  220  is not shown in  FIGS. 1 and 2 . With this restriction member  220 , when the paper P transported through the switchback operation is guided to the reverse transport path  77  (see  FIG. 2 ), it is possible to suppress an abnormal sound that occurs when the paper P corrugated in the orthogonal direction X by the bending rollers  34  and the bending guide portion  210  is forcibly bent along the reverse transport path  77  curved in the transport direction Y, and is thereby restored from the corrugated state. 
     Specifically, the restriction member  220  is provided on the upstream side in the first transport direction Y 1  of the tip  213  (position thereof) in the perpendicular direction Z of the bending guide portion  210 . Also, in a state in which pressure from the paper is not applied to the restriction member  220  and thus it is not deformed as shown in  FIG. 4 , the restriction member  220  is provided on the upstream side in the first transport direction Y 1  of the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 . 
     In the present embodiment, since the restriction member  220  that restricts corrugations in the paper P bent by the bending guide portion  210  in the perpendicular direction Z is provided on the upstream side in the first transport direction Y 1  (here, the direction in which the paper P is discharged onto the discharge tray  91 ) of the position of the tip  213  in the perpendicular direction Z of the bending guide portion  210 , corrugations formed in the paper P by the bending guide portion  210  can be maintained in the paper P that is transported (here, discharged) from the restriction member  220  in the first transport direction Yl, whereas corrugations formed in the paper P by the bending guide portion  210  can be reduced in the paper P that is transported from the restriction member  220  in the second transport direction Y 2  (here, the direction toward the reverse transport path  77  curved in the transport direction Y). In this manner, it is possible to suppress occurrence of the problem relating to corrugations formed in the paper P by the bending rollers  34  and the bending guide portion  210  (particularly, an abnormal sound that occurs when the paper P is transported to the reverse transport path  77 ), while securing high stacking quality of the paper P. 
     In the present embodiment, the restriction member  220  is provided opposing the bending guide portion  210  in at least one of the orthogonal direction X and the perpendicular direction Z (here, at a central portion in the orthogonal direction X). In this manner, with respect to the paper P transported in the second transport direction Y 2  from the restriction member  220 , corrugations in a position corresponding to the position of the bending guide portion  210  can be reliably reduced. 
     Incidentally, if the restriction member  220  is provided on the downstream side in the first transport direction Y 1  of the nip portion N, the transport of the paper P transported in the first transport direction Y 1  from the sheet transport portion  30  to the outside (here, discharged onto the discharge tray  91 ) as in the present embodiment is obstructed by the restriction member  220  that is provided on the downstream side in the first transport direction Y 1  of the nip portion N, and the trailing end portion P 2  of the paper P is caught by the restriction member  220  (for example, the trailing end P 2  runs onto the restriction member  220 ), and the paper P is not discharged onto the discharge tray  91 , or stacking quality of the paper P readily deteriorates. 
     Accordingly, in the present embodiment, the restriction member  220  is provided on the upstream side in the first transport direction Y 1  of the nip portion N. In this manner, it is possible to prevent the restriction member  220  from inhibiting the force with which the paper P is transported (here, discharged onto the discharge tray  91 ) from the sheet transport portion  30  to the outside in the first transport direction Y 1 , and it is thereby possible to reliably discharge the paper P onto the discharge tray  91  and prevent deterioration of stacking quality of the paper P. 
     Also, in the present embodiment, the restriction member  220  is a flexible member that has elasticity that is smaller than the force with which the sheet transport portion  30  transports the paper P. 
     In this manner, with the restriction member  220  formed as a flexible member, it is possible for the restriction member  220  to be bent allowing for an appropriate elasticity and thereby restrict corrugations in the paper P, while keeping transportability of the paper P bent by the bending guide portion  210 . 
     Also, in the present embodiment, the restriction member  220  is formed as a sheet-shaped flexible member. Specifically, the restriction member  220  is disposed crossing the transport path of the paper P (for example, substantially at a right angle with respect to the transported paper P). Specifically, the restriction member  220  formed as a sheet-shaped flexible member is attached to a side face  37   a  on the upstream side in the first transport direction Y 1  of the second covering member  37  (see  FIG. 4 ) provided in the main body frame  30   a  of the sheet transport portion  30  with a tip portion  220   a  projecting toward the transport path side, such that a plane  220   b  on the upstream side in the first transport direction Y 1  (see  FIG. 4 ) comes into contact with the leading end P 1  of the transported paper P. Also, the tip portion  220   a  of the restriction member  220  is formed in a shape having a pair of members (see a first opposing portion  221  and a second opposing portion  222  described below), and as shown in  FIG. 3 , the bending guide portion  210  is provided between the pair of members of the tip portion  220   a.    
     In this manner, since the restriction member  220  is formed as a sheet-shaped flexible member, it is possible to readily achieve both transportability of the paper P and an effect of restricting corrugations in the paper P with an inexpensive and simple structure. 
     Incidentally, when the restriction member  220  formed as a flexible member comes into contact with the paper P for restricting corrugations in the paper P bent by the bending guide portion  210 , a sound may be generated by the restriction member  220  and the paper P rubbing against each other. This is particularly noticeable when an image (toner image) is formed on the side of the paper P that comes into contact with the restriction member  220 . 
     Accordingly, in the present embodiment, at least a portion of the restriction member  220  coming into contact with the sheet is formed with a fluororesin (specifically, polytetrafluoroethylene). Since the fluororesin generally has a friction coefficient that is much lower than that of the paper P, the sound caused by the restriction member  220  and the paper P rubbing against each other can be reduced or eliminated. 
     Specifically, the restriction member  220  formed as a sheet-shaped flexible member is a Teflon® film made of a fluororesin. In such a configuration, it is possible to reduce or eliminate a sound caused by the restriction member  220  and the paper P rubbing against each other, while readily achieving both transportability of the paper P and an effect of restricting corrugations in the paper P, with an inexpensive and simple structure. 
     Note that in the present embodiment, the restriction member  220  formed as a sheet-shaped flexible member is made of a fluororesin, the restriction member  220  may be formed by coating an elastic body with a fluororesin. 
     Incidentally, from the viewpoint of facilitating restriction of corrugations in the paper P bent by the bending guide portion  210 , it is preferable that the restriction member  220  overlaps the bending guide portion  210  in the orthogonal direction X. However, in this case, even if the restriction member  220  is elastically deformed due to transport of the paper P in the first transport direction Y 1 , unless the path for the paper P is secured, transport of the paper P is obstructed by the restriction member  220 , thereby causing a jam (paper jam). 
     Accordingly, in the present embodiment, the restriction member  220  is configured to overlap the bending guide portion  210  in the orthogonal direction X (see  FIG. 4 ), and also to allow for elastic deformation thereof due to transport of the paper P in the first transport direction Y 1  (see below-described  FIG. 5 ), thereby securing the path for the paper P. In this manner, it is possible to prevent the restriction member  220  from obstructing transport of the paper P, and thereby occurrence of a jam (paper jam) can be prevented. 
       FIG. 5  includes  FIGS. 5A ,  5 B,  5 C and  5 D, each schematically illustrating a configuration in which although the restriction member  220  overlaps the bending guide portion  210  in the orthogonal direction X, the path for the paper P is secured by allowing for elastic deformation of the restriction member  220  due to transport of the paper P in the first transport direction Y 1 .  FIGS. 5A and 5B  are a schematic side view and a schematic plan view, respectively, each showing a state of the restriction member  220  when the paper P is not passing the restriction member  220 , and  FIGS. 5C and 5D  are a schematic side view and a schematic plan view, respectively, each showing a state of the restriction member  220  immediately after the paper P has begun passing the restriction member  220 . Note that in  FIGS. 5B and 5D , the second discharge rollers  32  are not shown. 
     As shown in  FIG. 5 , the restriction member  220  includes the first opposing portion  221  (see  FIG. 5D ) that opposes an end face  214  on one side X 1  in the orthogonal direction X of the bending guide portion  210  in a contactless manner when it is elastically deformed due to transport of the paper P in the first transport direction Y 1  (see  FIGS. 5C and 5D ), and the second opposing portion  222  (see  FIG. 5D ) that opposes an end face  215  on the other side X 2  in the orthogonal direction X of the bending guide portion  210  in a contactless manner, when the restriction member  220  is elastically deformed due to transport of the paper P in the first transport direction Y 1  (see  FIGS. 5C and 5D ). 
     Specifically, when the paper P is not passing the restriction member  220  (see  FIGS. 5A and 5B ), the first opposing portion  221  does not oppose the end face  214  on the one side X 1  of the bending guide portion  210 , and the second opposing portion  222  does not oppose the end face  215  on the other side X 2  of the bending guide portion  210  (see  FIGS. 5A and 5B ). In contrast, immediately after the paper P has begun passing the restriction member  220 , the first opposing portion  221  opposes the end face  214  on the one side X 1  of the bending guide portion  210  in a contactless manner, and the second opposing portion  222  opposes the end face  215  on the other side X 2  of the bending guide portion  210  in a contactless manner (see  FIGS. 5C and 5D ). In this manner, the path for transporting the paper P in the first transport direction Y 1  can be reliably secured. 
     Specifically, a width d 1  (see  FIG. 3 ) in the orthogonal direction X of the tip portion  220   a  on the side coming into contact with the paper P of the restriction member  220  is larger than a width d 2  (see  FIG. 3 ) in the orthogonal direction X of a tip portion  210   a  on the side coming into contact with the paper P of the bending guide portion  210 . The restriction member  220  has a recessed shape that includes a recessed portion  223  such that the tip portion  220   a  does not come into contact with the tip portion  210   a  of the bending guide portion  210  when the restriction member  220  is elastically deformed due to transport of the paper P in the first transport direction Y 1 . 
     Incidentally, from the viewpoint of reduction in the size of apparatuses and various constituent elements such as detection means (specifically, a discharge switch (not shown in the drawings)) provided on the upstream side in the first transport direction Y 1  of the nip portion N between the first discharge rollers  31  and the second discharge rollers  32 , the tip portion of the bending guide portion may be provided protruding from below on the downstream side in the first transport direction Y 1  of the nip portion N. In this case, the transported paper P is corrugated in the orthogonal direction X from below by the bending guide portion, thereby bending the paper P. In this manner, when the bending guide portion corrugates the transported paper P in the orthogonal direction X from below and bends without breaking the paper P, in the case where the sheet transport portion  30  is configured to transport the paper P in a substantially horizontal direction or slightly upward (see the present embodiment), the transport of the paper P in first transport direction Y 1  from the sheet transport portion  30  to the outside (here, discharged onto the discharge tray  91 ) is obstructed by the tip portion of the bending guide portion that is provided on the downstream side in the first transport direction Y 1  of the nip portion N and that bends without breaking the paper P by corrugating the paper P from below. Specifically, the trailing end portion P 2  of the paper P is caught by the tip portion of the bending guide portion (for example, the trailing end portion P 2  runs on the tip portion), and consequently the paper P is not discharged onto the discharge tray  91 , or stacking quality of the paper P readily deteriorates. 
     Accordingly, in the present embodiment, the bending guide portion  210  is configured such that the tip  213  is provided on the downstream side in the first transport direction Y 1  of the nip portion N, and corrugates the transported paper P in the orthogonal direction X from above so as to bend the paper P, and the restriction member  220  is configured to restrict corrugations in the paper P from below. Specifically, the bending guide portion  210  has a curved shape having a curved surface raised downward such that the upstream side end  211  in the first transport direction Y 1  and the downstream side end  212  in the first transport direction Y 1  are positioned higher than the nip portion N, and the tip  213  in the perpendicular direction Z is positioned lower than the nip portion N. The restriction member  220  extends upward (specifically, substantially vertically) to a higher position than the tip  213  of the bending guide portion  210 , such that the tip portion  220   a  is a free end. 
     As in the present embodiment, even if the sheet transport portion  30  is configured to transport the paper P in a substantially horizontal direction or slightly upward, and the tip  213  of the bending guide portion  210  is provided on the downstream side in the first transport direction Y 1  of the nip portion N, by adopting a configuration in which the bending guide portion  210  bends without breaking the paper P transported in the sheet transport portion  30  by corrugating the paper P from above, it is possible to prevent the bending guide portion  210  from inhibiting the force with which the paper P is transported in the first transport direction Y 1  (here, discharged onto the discharge tray  91 ) from the sheet transport portion  30  to the outside. In this manner, the paper P can be reliably discharged onto the discharge tray  91 , and deterioration of stacking quality of the paper P can be prevented. 
     Also, in the present embodiment, the bending guide portion  210  is arranged in the central position of the transported paper P in the orthogonal direction X (see  6  in  FIG. 3 ). In this manner, corrugations in the paper P can be reduced with a restriction member  220  that restricts corrugations in the paper P that has been bent by the bending guide portion  210  arranged in the central position, and in this manner, mainly, it is possible to suppress occurrence of problems relating to corrugations in the paper P formed by the bending rollers  34  and the bending guide portion  210 , while securing high stacking quality of the paper P such as small size paper, an envelope and the like. 
     Note that although the bending guide portion  210  is provided in the central position in the orthogonal direction X in the present embodiment, the bending guide portion  210  may be provided in at least one position between the bending rollers  34 . 
     Also, in the present embodiment, the restriction member  220  restricts corrugations in the paper P bent by, out of the bending rollers  34  and the bending guide portion  210 , the bending guide portion  210 . However, corrugations in the paper P bent by the bending rollers  34  may be restricted. 
     Also, although the sheet transport portion  30  is provided in a position where the paper P on which an image is formed is transported, problems relating to corrugations in an original can be similarly prevented by providing the sheet transport portion  30  in a position where an original on which image reading performed is transported. 
     The present invention may be embodied in various other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all modifications or changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.