Abstract:
A recording-medium-transporting-direction-switching-mechanism including a transport-unit transporting the recording-medium in one/another directions; a guiding-unit rotatably supported and one-end-portion being provided to be capable of existing in a transport-path, the guiding-unit being rotated by a leading-end-portion of the recording-medium transported toward the transport-unit contacting the guiding-unit, and rotating in a reverse-direction after a trailing-end-portion of the recording-medium transported by the transport-unit in the one-direction passes therethrough, and guiding the recording-medium transported by the transport-unit in the other-direction after the trailing-end-portion of the recording-medium passes therethrough, the one-end-portion of the guiding-unit having substantially rectanglular-shape, and a direction in which the leading-end-portion of the recording-medium transported toward the transport-unit is directed intersecting at an acute angle with a surface of the guiding-unit against which the leading-end-portion of the recording-medium contacts; and a detecting-unit that detects a state where the recording-medium is passing through the guiding-unit by rotating integrally with the guiding-unit, is provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-080563 filed Mar. 27, 2009. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to a recording medium transporting direction switching mechanism, a fixing device and an image forming apparatus. 
       SUMMARY 
       [0003]    A recording medium transporting direction switching mechanism according to an aspect of the present invention includes: a transport unit that is provided in a transport path of a recording medium and that transports the recording medium in one direction and in the other direction; a guiding unit that is rotatably supported and whose one end portion is provided so as to be capable of existing in the transport path, the guiding unit being rotated by a leading end portion of the recording medium transported toward the transport unit contacting the guiding unit, and rotating in a reverse direction after a trailing end portion of the recording medium transported by the transport unit in the one direction passes therethrough, and that guides the recording medium transported by the transport unit in the other direction after the trailing end portion of the recording medium passes therethrough, the one end portion of the guiding unit being formed substantially into a rectangular shape when seen from a side, and a direction in which the leading end portion of the recording medium transported toward the transport unit is directed intersecting at an acute angle with a surface of the guiding unit against which the leading end portion of the recording medium contacts; and a detecting unit that detects a state in which the recording medium is passing through the guiding unit by rotating integrally with the guiding unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiments of the invention will be described in detail with reference to the following figures, wherein: 
           [0005]      FIG. 1  is a schematic side view of an image forming apparatus according to an exemplary embodiment of the present invention; 
           [0006]      FIG. 2  is a side view that schematically shows a fixing device immediately before a leading end portion of a recording medium hits against a guiding unit; 
           [0007]      FIG. 3  is a side view that schematically shows a fixing device immediately before a trailing end portion of a recording medium passes through a guiding unit; 
           [0008]      FIG. 4  is a side view that schematically shows a fixing device immediately after a trailing end portion of a recording medium passes through a guiding unit and is guided to a reversal portion; 
           [0009]      FIG. 5  is a perspective view that schematically shows a fixing device before a leading end portion of a recording medium hits against a guiding unit; 
           [0010]      FIG. 6  is a perspective view that schematically shows a fixing device when a recording medium is in the process of passing through a guiding unit; 
           [0011]      FIG. 7  is a side view that schematically shows a fixing device before a leading end portion of a recording medium hits against a guiding unit; 
           [0012]      FIG. 8  is a side view that schematically shows a fixing device when a recording medium is in the process of passing through a guiding unit; 
           [0013]      FIG. 9  is a side view that schematically shows a fixing device after a leading end portion of a recording medium hits against a guiding unit of a comparative example; and 
           [0014]      FIG. 10  is a side view that schematically shows a fixing device immediately before a trailing end of a recording medium passes through a guiding unit of a comparative example. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Exemplary embodiments of the present invention are hereinafter described on the basis of examples illustrated in the figures. As shown in  FIG. 1 , an image forming apparatus  10  includes an image forming apparatus main body  12 , and a paper feed unit (an example of an accommodating unit)  14  in which a recording sheet (an example of recording medium) P is accommodated is disposed at a lower portion of the image forming apparatus main body  12 . Then, a paper discharge unit (an example of a discharge unit)  18  from which the recording sheet P with a toner image (an image) being fixed thereon is discharged, is formed at an upper portion of the image forming apparatus main body  12 . 
         [0016]    The paper feed unit  14  includes a sheet cassette  16  in which a large number of recording sheets P are laminated and accommodated, and a feed roller  22  is disposed in an upper portion of the sheet cassette  16  at its one end side (in  FIG. 1 , at the rightward side of the sheet cassette). A retard roller  24  is provided so as to face the feed roller  22 . 
         [0017]    Accordingly, the recording paper P located at the uppermost position of the sheet cassette  16  is taken out by the feed roller  22 , and handled by cooperation of the feed roller  22  and the retard roller  24 , and further delivered to a transport path  20 . The recording sheet P delivered to the transport path  20  stops temporarily by a registration roller  26  disposed further at the upstream side in the sheet transporting direction than a photoreceptor  30 , and is sequentially transported toward the photoreceptor  30 . 
         [0018]    The photoreceptor  30  configuring a transfer member is supported in a rotatable manner. Provided around the photoreceptor  30  are a charging roller  32  that charges the photoreceptor  30  uniformly, a development device  34  that develops a latent image formed on the photoreceptor  30  with a toner (developer), and a cleaning device  36  that removes the toner remaining on the surface of the photoreceptor  30  after transfer of a toner image. 
         [0019]    A light writing device  38  is disposed between the charging roller  32  and the development device  34 . Due to the surface of the photoreceptor  30  being irradiated with light, a latent image comes to be formed on the surface of the photoreceptor  30 . A backup roller  28  configuring a transfer member is disposed so as to face the photoreceptor  30  with the transport path  20  interposed therebetween. 
         [0020]    Further, a fixing device  40  is provided further at the downstream side in the sheet transporting direction than the photoreceptor  30  and the backup roller  28 . In the fixing device  40 , a heat roller (an example of a fixing member)  42  and a press roller (an example of the fixing member)  44  are disposed so as to face each other, and the recording sheet P on which an unfixed toner image is transferred is nipped and transported by the heat roller  42  and the press roller  44  from the lower side to the upper side. In this manner, the unfixed toner image is fixed on the recording sheet P. 
         [0021]    A discharge roller (an example of a transporting member)  46  and a pinch roller set (an example of a transporting member)  48  are disposed so as to face each other at the downstream side of the heat roller  42  and the press roller  44  of the fixing device  40  in the sheet transporting direction. Accordingly, the recording sheet P on which a toner image is fixed is discharged onto the paper discharge unit  18  by being nipped and transported by the discharge roller  46  and the pinch roller set  48  while curling of the recording sheet toward the side of the heat roller  42  (toward the surface to be printed) is being straightened (reduced). 
         [0022]    In the fixing device  40 , the heat roller  42  and the discharge roller  46  are disposed at the lower side, and the press roller  44  and the pinch roller set  48  are disposed at the upper side. Further, provided in the transport path  20  between “the heat roller  42  and the press roller  44 ” and “the discharge roller  46  and the pinch roller set  48 ” is a reversal gate  52  (an example of a guiding unit) that guides the recording paper P to the reversal unit  50  when both surfaces of the recording sheet P are printed. 
         [0023]    The reversal gate  52  is, as shown in  FIG. 2  and  FIG. 5 , disposed such that the longitudinal direction thereof is along the sheet widthwise direction with having a comb-like tooth shape. A one end portion  56  of the reversal gate  52  is made to extend so as to be able to exist in the transport path  20  when the recording sheet P does not pass through the reversal gate  52 . The other end portion  54  of the reversal gate  52  is fixed on a rotating shaft  68  that is supported in a rotatable manner at a position above the press roller  44 . 
         [0024]    Further, the one end portion  56  of the reversal gate  52  is formed so as to have a substantially rectangular configuration when seen from the side, that is, seen from the axial direction of the rotating shaft  68  (seen from a direction which is a widthwise direction of the recording sheet P and is orthogonal to a transporting direction of the recording sheet P). That is to say, the one end portion  56  is formed substantially into a rectangle by a lower side corner portion  66   a  that forms a corner portion at the side of the lower end portion  60 B (described later) of the reversal gate  52  and an upper side corner portion  66   b  that forms a corner portion at the side of the upper end surface  58  (described later) of the reversal gate  52 . 
         [0025]    The lower side corner portion  66   a  and the upper side corner portion  66   b  are each an corner portion, but the tip end portion thereof may be formed as a curved surface, and in this case, the lower side corner portion  66   a  and the upper side corner portion  66   b  are corner portions whose curvatures are larger than those of a lower end portion  60 B, an upper end portion  58  and a leading end surface  66  (described later). It can be said that the lower side corner portion  66   a  and the upper side corner portion  66   b  are an upstream corner portion which is at the upstream side in the transporting direction of the recording sheet P and a downstream corner portion which is at the downstream side in the transporting direction of the recording sheet P, respectively. 
         [0026]    Further, the lower side corner portion  66   a  is formed such that, in the state in which the recording sheet P does not make to rotate the reversal gate  52 , that is, in the state in which the recording sheet P does not pass through the reversal gate  52 , the lower side corner portion  66   a  is positioned further at the side to which the recording sheet P is transported and comes thereat than the upper side corner portion  66   b,  that is, at the side opposite to a side at which the discharge roller  46  and the pinch roller  48  are disposed. 
         [0027]    Moreover, the lower side corner portion  66   a  is formed such that, in the state in which the recording sheet P makes to rotate the reversal gate  52 , that is, in the state in which the recording sheet P is passing through the reversal gate  52 , the lower side corner portion  66   a  is positioned further at the side at which the recording sheet P is transported and goes therefrom than the upper side corner portion  66   b,  that is, at the side of the discharge roller  46  and the pinch roller  48 . Or, the lower side corner portion  66   a  is positioned at the same position of the upper side corner portion  66   b  in the horizontal direction (the direction parallel to the surface at which the image forming apparatus is installed). 
         [0028]    In the present exemplary embodiment, in the state in which the recording sheet P is passing through the reversal gate  52 , the lower side corner portion  66   a  is located substantially at the same position as that of the upper side corner portion  66   b.  That is to say, the leading end surface  66  of the reversal gate  52  is formed into a substantially vertical surface extending substantially in the vertical direction in the state in which the recording sheet P is passing through the reversal gate  52 . In the reversal gate  52 , the length of the leading end surface (described later)  66  is the shortest among the leading end surface  66 , the lower end portion  60 B and the upper end portion  58 . 
         [0029]    As shown in  FIG. 3  and  FIG. 6 , the reversal gate  52  is rotated upward by the one end portion  56  thereof being pushed up by the recording sheet P that is nipped and transported by the heat roller  42  and the press roller  44 . Then, after the recording sheet P passes through the reversal gate  52 , the one end portion  56  of the reversal gate  52  moves back to its original position by rotating downward due to its own weight. In the case of performing double sided printing, the reversal gate  52  is adapted to guide, to the reversal unit  50 , the recording sheet P that is nipped and transported by reverse rotation of the discharge roller  46  and the pinch roller  48 . 
         [0030]    That is, as shown in  FIG. 4 , the recording sheet P which is to be subjected to double sided printing is guided by the upper end surface  58  of the reversal gate  52  and sent out toward the other direction, that is, in the direction toward the reversal unit  50 . 
         [0031]    The reversal gate  52  may be configured such that by using an elastic member such as a thread spring, a coil spring or the like (not shown in the drawings), it is being pressed so as to move back to its original position by the elastic member. Particularly, this structure becomes effective in a case which is different from the exemplary embodiment shown in  FIG. 1 , that is, in a case in which direction to which the recording sheet P passes and/or direction in which the reversal gate  52  is provided is set at the direction of being rotated at an angle of 90 degrees or 180 degrees from that of the exemplary embodiment. 
         [0032]    Further, the lower end portion  60  of the reversal gate  52 , that is from the one end portion  56  to the other end portion  54 , is formed so as to project out (swell out) downward, and an intermediate portion  62  of the lower end portion  60  is formed as an obtuse-angled portion when seen from the side. That is to say, as shown in  FIG. 2 , in the state in which the recording sheet P does not come into contact with the reversal gate  52 , a lower end portion  60 A provided from the other end portion  54  to the intermediate portion  62  is formed so as to extend substantially right angles with respect to the transport path  20  (the recording sheet P), and the lower end portion  60 B provided from the intermediate portion  62  to the one end portion  56  is formed so as to extend substantially in the horizontal (in a direction parallel to the plane on which the image forming apparatus  10  is installed). 
         [0033]    Due to the aforementioned structure (due to the lower end portion  60  formed so as to swell out), the rigidity of the reversal gate  52  is secured. Further, when seen from the side as shown in  FIG. 2 , “a direction to which the leading end portion of the recording sheet P transported toward the discharge roller  46  and the pinch roller  48  is directed” and “the lower end surface  64  in the lower end portion  60 B of the reversal gate  52  at which the leading end portion of the recording sheet P hits” are adapted to cross each other at an acute angle. 
         [0034]    In other words, an angle α formed by “the lower end surface  64  in the lower end portion  60 B, which is from the intermediate portion  62  to the one end portion  56 , of the reversal gate  52 ” and “the transport path  20  of the recording sheet P (the recording sheet P)”, which angle is formed at the side of the other end portion  54  (which is at the upper surface side of the recording sheet P), becomes an acute angle. In the exemplary embodiment, the angle a is less than or equal to 75 degree, preferably, less than or equal to 60 degree. Incidentally, the angle α is similar (equal to) an angle γ formed by the lower end surface  64  of the reversal gate  52  and an upper end surface  78 A of a guide member  78  when seen from the side as shown in  FIG. 4  and  FIG. 7 . 
         [0035]    Further, as shown in  FIG. 2  and  FIG. 3 , the leading end surface  66  of the one end portion  56  of the reversal gate  52  when the recording sheet P passes through the reversal gate  52  is adapted to be directed toward further the discharge roller  46  side when seen from the side than the leading end surface  66  of the one end portion  56  of the reversal gate  52  when the recording sheet P does not pass through the reversal gate  52 . 
         [0036]    In other words, the leading end surface  66  at the one end portion  56  of the reversal gate  52  is formed so as to be oriented obliquely downward when the recording sheet P does not pass through (is not in the process of passing through) the reversal gate  52 . To the contrary, when the recording sheet P passes through (is in the process of passing through) the reversal gate  52 , the leading end surface  66  is formed so as to be oriented toward the paper discharge unit  18 . 
         [0037]    That is, in the state in which the recording sheet P pushes up the reversal gate  52 , i.e., when the recording sheet P is in the process of passing through the reversal gate  52  (as shown in  FIG. 3 , immediately before at least the trailing end portion of the recording sheet P finishes passing through the reversal gate  52 ), as described above, the leading end surface  66  of the reversal gate  52  is formed into a substantially vertical surface extending substantially in the vertical direction. 
         [0038]    Further, as shown in  FIG. 5  through  FIG. 8 , the fixing device  40  is provided with a detecting portion (an example of a detecting unit)  70  that detects that the recording sheet P is in the process of passing through the reversal gate  52 , by rotating integrally with the reversal gate  52 . The detecting member  70  is provided to project from one end portion of a connecting member  72  having an S-shaped configuration when seen from the side in such a manner so as to extend outside in the axial direction of the rotating shaft  68  on which the reversal gate  52  is fixed, and the other end portion of the connecting member  72  is fastened to the rotating shaft  68 . 
         [0039]    The detecting member  70  is, as shown in  FIG. 7 , provided in a region between the press roller  44  and the pinch roller  48  along the transport path  20  of the recording sheet P when seen from the side. Further, in the fixing device  40 , a light emitting portion  74  and a light receiving portion  76 , which detect whether or not the detecting member  70  exists therebetween, are disposed to face each other at a predetermined interval therebetween. 
         [0040]    Accordingly, when the recording sheet P does not push up the reversal gate  52 , the detecting member  70  is interposed between the light emitting portion  74  and the light receiving portion  76  (refer to  FIG. 5  and  FIG. 7 ), and the state in which the recording sheet P does not pass through (is not in the process of passing through) the reversal gate  52  is detected. 
         [0041]    Then, when the recording sheet P pushes up the reversal gate  52 , the detecting member  70  moves upward and is away from a region between the light emitting portion  74  and the light receiving portion  76  (refer to  FIG. 6  and  FIG. 8 ), and the state in which the recording sheet P passes through (is in the process of passing through) the reversal gate  52 . 
         [0042]    Further, as shown in  FIG. 2  through  FIG. 8 , the guide member  78  that guides, to a region between the discharge roller  46  and the pinch roller  48 , the recording sheet P nipped and transported by the heat roller  42  and the press roller  44 , is disposed at the upstream side of the discharge roller  46  in the sheet transporting direction in such a manner that the longitudinal direction of the guide member  78  is along the sheet widthwise direction with having a comb-like tooth shape so as to engage with the one end portion  56  of the reversal gate  52 . 
         [0043]    When the recording sheet P does not pass through the reversal gate  52 , the upper end surface (portion)  78 A of the guide member  78  is structured so as to form an obtuse angle with the upper end surface  58  of the reversal gate  52  (such that the angle β formed by the upper end surface  78 A of the guide member  78  and the upper end surface  58  of the reversal gate  52  becomes an obtuse angle). 
         [0044]    The leading end surface  66  of the one end portion  56  of the reversal gate  52  in the state in which the recording sheet P does not pass through the reversal gate  52  is adapted to be away from a position in the transport path  20  (is adapted to be into the guide member  78 ) when seen from the side. Due to this structure, the leading end portion of the recording sheet P transported in the direction toward the reversal unit  50  (in the opposite direction) is prevented from being bent at the reversal gate  52 . 
         [0045]    In the image forming apparatus  10  having the aforementioned structure, the operation thereof is described hereinafter. First, the recording sheet P located at the uppermost position of the sheet cassette  16  is taken out by the feed roller  22 , and sent out to the transport path  20  by being handled by cooperation of the feed roller  22  and the retard roller  24 . Then, the recording sheet P sent out to the transport path  20  is sequentially transported by the registration roller  26  to the photoreceptor  30  side. 
         [0046]    The surface (peripheral surface) of the photoreceptor  30  is in advance charged by the charging roller  32  uniformly. Then, the surface of the photoreceptor  30  is scanned with light irradiated from the light writing device  38 , and a latent image based on image data is formed on the surface of the photoreceptor  30 . Subsequently, the latent image is developed by the development device  34  with a toner, and a toner image (a visible image) is formed on the surface of the photoreceptor  30 . 
         [0047]    When the recording sheet P is nipped and transported by the photoreceptor  30  and the back-up roller  28 , the toner image is transferred onto the surface of the recording sheet P, and the recording sheet P onto which an unfixed toner image is transferred is transported to the fixing device  40 . Incidentally, after the toner image is transferred onto the recording sheet P, the surface of the photoreceptor  30  is subjected to cleaning processing by the cleaning device  36 , and is made ready for subsequent image forming processing. 
         [0048]    The transferred unfixed toner image is fixed on the recoding sheet P supplied to the fixing device  40  due to the recording sheet being nipped and transported by the heat roller  42  and the press roller  44 . Immediately after nipping and transporting the recording sheet P by the heat roller  42  and the press roller  44  starts, the leading end portion of the recording sheet P hits against the lower end surface  64  of the reversal gate  52  (refer to  FIG. 2 ). 
         [0049]    At this time, the lower end surface  64  of the reversal gate  52  is disposed substantially in the horizontal position when seen from the side, and therefore, the leading end portion of the recording sheet P hits against the lower end surface  64  so as to form an acute angle therebetween (the former and the latter intersects with each other at an acute angle). That is to say, the lower end portion  60  of the reversal gate  52  is formed so as to swell out (the lower end portion  60  is made to swell out such that the intermediate portion  62  has an obtuse angle) such that angle a formed by the lower end surface  64  of the reversal gate  52  and the upper surface (of the leading portion) of the recording sheet P becomes an acute angle. Accordingly, the leading end portion of the recording sheet P hits against the reversal gate  52  at the early stage. 
         [0050]    As in the case of a reversal gate  80  according to a comparative example shown in  FIG. 9 , when a lower end portion  82  of the reversal gate  80  is not formed so as to swell out, a distance (time) after the recording sheet P pass through the heat roller  42  and the press roller  44  until the recording sheet P hits against the reversal gate  80  becomes longer. In addition, there is a possibility that the leading end portion of the recording sheet P may be transported to the other end portion  86  side along a lower end surface  84  of the reversal gate  80 . Consequently, there is a possibility that the leading end portion of the recording sheet may be damaged or paper jam may be caused. 
         [0051]    To the contrary, in the reversal gate  52  according to the present exemplary embodiment, the lower end portion  60  is formed so as to swell out, and therefore, occurrence of the aforementioned problems is prevented. Thus, the leading end portion of the recording sheet P is made to hit against the reversal gate  52  at the early stage, and the reversal gate  52  is smoothly rotated upward (around the rotating shaft  68 ). 
         [0052]    At the same time, the detecting member  70  fixed integrally with the reversal gate  52  moves away from the region between the light emitting portion  74  and the light receiving portion  76  to the upward direction, and therefore, the state in which the recording sheet P is in the process of passing through the reversal gate  52  is detected at the early stage, so the timing at which the recording sheet P is reversed is detected at the early stage. 
         [0053]    In this manner, the recording sheet P which is nipped and transported by the heat roller  42  and the press roller  44  and on which a toner image is fixed is subsequently nipped and transported by the discharge roller  46  and the pinch roller  48 . Then, when the trailing end portion of the recording sheet P finishes passing through the reversal gate  52 , the reversal gate  52  is rotated downward due to its own weight. 
         [0054]    When the recording sheet P passes through the reversal gate  52 , the leading end surface  66  of the reversal gate  52  is oriented toward the paper discharge unit  18  side when seen from the side. That is to say, the leading end surface  66  of the reversal gate  52  in the state that the recording sheet P is in the process of passing through the gate is disposed to be a substantially vertical surface when seen from the side (refer to  FIG. 3 ). Accordingly, the trailing end portion of the recording sheet P passes through the reversal gate  52  at the early stage, whereby the reversal gate  52  is rotated downward due to its own weight at the early stage. 
         [0055]    In other words, in the state in which the recording sheet P does not rotate the reversal gate  52 , that is to say, in the state in which the recording sheet P does not pass through the reversal gate  52 , the lower side corner portion  66   a  is positioned further at the side to which the recording sheet P is transported to come thereat than the upper side corner portion  66   b,  that is, the lower side corner portion  66   a  is positioned at the side opposite to a side at which the discharge roller  46  and the pinch roller  48  are provided with respect to the upper side corner portion  66   b.  For this reason, the leading end portion of the transported recording sheet P early passes through the reversal gate  52 . That is to say, the leading end portion of the recording sheet P early passes through the lower side corner portion  66   a.    
         [0056]    Further, in the state in which the recording sheet P rotates the reversal gate  52 , that is, in the state in which the recording sheet P is passing through the reversal gate  52 , the lower side corner portion  66   a  is positioned further at the side to which the recording sheet P is transported and goes therefrom than the upper side corner portion  66   b,  that is, the lower side corner portion  66   a  is positioned at the side at which the discharge roller  46  and the pinch roller  48  are provided with respect to the upper side corner portion  66   b.  Or, the lower side corner portion  66   a  is positioned at the same position as that of the upper side corner portion  66   b  in the horizontal direction (the direction parallel to the surface at which the image forming apparatus is installed). Therefore, the trailing end portion of the transported recording sheet P early passes through the reversal gate  52 . That is to say, the trailing end of the recording sheet P early passes through the lower side corner portion  66   a.    
         [0057]    To the contrary, as shown in the case of a reversal gate  90  according to a comparative example shown in  FIG. 10 , a leading end surface  94  of one end portion  92  has a triangular configuration when seen from the side. In the state in which the recording sheet P passes through the reversal gate  90 , the distance (time) of which the trailing end portion of the recording sheet P have passed through the reversal gate  90  becomes longer, and therefore the time until the reversal gate  90  rotates downward due to its own weight also becomes longer. 
         [0058]    That is to say, in the reversal gate  90  according to the comparative example shown in  FIG. 10 , in the case in which both sides of the recording sheet P are printed, the distance of which the recording sheet P is nipped and transported by the discharge roller  46  and the pinch roller  48  toward the paper discharge unit  18  side becomes longer, and therefore the time until the recording sheet P is sent out to the reversal unit  50  also becomes longer, thereby resulting in deterioration of productivity. 
         [0059]    In the reversal gate  52  according to the present exemplary embodiment, as described above, the recording sheet P passes through the gate  52  at the early stage and the reversal gate  52  can be rotated downward due to its own weight at the early stage. Therefore, in a case in which both sides of the recording sheet P are printed, the distance of which the recording sheet P is nipped and transported by the discharge roller  46  and the pinch roller  48  toward the paper discharge unit  18  side becomes short, and therefore the time until the recording sheet P is sent out to the reversal unit  50  becomes shorter, thereby resulting in improvement of productivity. 
         [0060]    In this manner, due to the passing of the recording sheet P through the reversal gate  52  being finished, the reversal gate  52  rotates downward due to its own weight. However, in a case in which one side of the recording sheet P is printed, the recording sheet P is discharged onto the paper discharge unit  18  without being reversed. On the other hand, in a case in which both sides of the recording sheet P are printed, rotation of the discharge roller  46  and the pinch roller  48  temporarily stop, and subsequently, they rotate in a reverse direction, so as to send out the nipped recording sheet P to the reversal unit  50 . 
         [0061]    That is, the recording sheet P nipped by the discharge roller  46  and the pinch roller  48  is sent out to the reversal unit  50  along the upper end surface  58  of the reversal gate  52 . At this time, the leading end surface  66  of the one end portion  56  of the reversal gate  52  is away from the position in the transport path  20  (end surface  66  of the one end portion  56  of the reversal gate  52  is positioned within the guide member  78 ), and the angle β formed by the upper end surface  58  and the upper end surface  78 A of the guide member  78  is formed as an obtuse angle when seen from the side. Therefore, the recording sheet P is guided smoothly to the upper end surface  58  side (refer to  FIG. 4 ) without being sent out toward the leading end surface  66  side (without the leading end portion of the recording sheet P being bent toward the leading end surface  66  side by the reversal gate  52 ). 
         [0062]    Then, the recording sheet P sent out to the reversal unit  50  is transported again to the photoreceptor  30 . When a toner image is transferred onto the back surface of the recording sheet, the recording sheet is transported to the fixing device  40  in the same manner as described above, and an unfixed toner image is fixed on the recording sheet. Subsequently, the recording sheet is nipped and transported by the discharge roller  46  and the pinch roller  48  and is discharged onto the paper discharge unit  18 . 
         [0063]    The recording medium transporting direction switching mechanism according to the present exemplary embodiment is described as above, but it is not limited to the examples illustrated in the figures. For example, the shape of the connecting member  72  that mounts the detecting member  70  may not be limited to the substantially S-shaped configuration when seen from the side. 
         [0064]    Further, in the present exemplary embodiment, the leading end portion of the recording sheet P hits against the reversal gate  52  at the early stage and the trailing end portion of the recording sheet P passes through the reversal gate  52  at the early stage. This makes it possible to shorten the distance between “the heat roller  42  and the press roller  44 ” and “the discharge roller  46  and the pinch roller  48 ”. In addition, due to the detecting member  70  being provided in a region between the press roller  44  and the pinch roller  48  along the transport path  20 , it suffices that the height of the detecting member  70  when rotating upward is low. Accordingly, reduction in the size of the fixing device  40  can be achieved, and consequently, reduction in the size of the image forming apparatus  10  can be achieved. 
         [0065]    Furthermore, in the present exemplary embodiment, the configuration in which the reversal gate  52  is provided between “the fixing device” and “the discharge roller  46  and the pinch roller  48 ” is described above, but the invention is not limited to the same. The reversal gate  52  may also be provided at any place such as a rear surface, a bottom surface or the like of the image forming apparatus  10 , as long as the reversal gate  52  is provided at the upstream side in the sheet transporting direction, with the recording sheet transported in one direction serving as the reference, with respect to a transport member such as a transport roller or a transport belt, which is capable of transporting the recording sheet P in one direction or in the other direction, the structure can also be applied.