Abstract:
An automatic document feeder comprising a reversing device and a discharge device is disclosed. The reversing device and the discharge device are disposed such that the distance in the horizontal direction from an original document reading position in the automatic document feeder to the discharge device is longer than the distance in the horizontal direction from the original document reading position to the reversing device. This configuration allows the use of original documents whose length in the transport direction is short, and also shortens the transport path in the automatic document feeder as well as the amount of time needed to read an original document. Furthermore, this configuration increases the visibility of original documents discharged to the discharge tray by the discharge device because the discharge device is disposed relatively far away from the original document reading position.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an automatic document feeder employed in copying machines, printers, facsimile machines, and the like that automatically transports original documents, and also relates to an image forming device comprising the same.  
           [0003]    2. Background Information  
           [0004]    Automatic document feeders employed in image forming devices such as copying machines, printers, and the like which automatically read image data and the like recorded on both sides of an original document are well known in the prior art.  
           [0005]    This type of automatic document feeder is disclosed in Japanese Published Patent Applications H07-175279 and H09-106116. These devices are schematically illustrated in FIGS. 6 and 7.  
           [0006]    The device shown in FIG. 6 is disposed along the path in which original documents D are transported (the path illustrated by the arrows a), and includes a loading tray  101 , a pick-up roller  102 , a paper supply roller  103 , a pair of transport rollers  104 , a transport drum  105 , transport rollers  106 ,  107 , and  108 , a pair of discharge/reverse rollers  110 , and a discharge tray  111 . In addition, an original document reading position R is disposed between the transport rollers  107  and  108 . Here, the upper surface of each original document D mounted in the loading tray  101  is the A side, and the lower surface thereof is the B side.  
           [0007]    When only the A side of an original document D is to be read out, the original document D is supplied from the loading tray  101 , the A side thereof is read, and is then discharged directly to the discharge tray  111  by the pair of discharge/reverse rollers  110 . More specifically, a plurality of original documents D placed in the loading tray  101  are first supplied and transported one sheet at a time by the pick-up roller  102 , the paper supply roller  103 , and the pair of transport rollers  104 . Next, while each original document D is transported by the transport drum  105  and the transport rollers  106 ,  107 , and  108 , the A side thereof is read at the original document reading position R. Then, after the A side of each original document D is read, they are transported in the direction illustrated by the arrow a by rotating the discharge/reverse rollers  110  in the directions shown, and are then discharged to the discharge tray  111  with the A side thereof facing downward.  
           [0008]    In contrast, when both the A side and the B side of an original document D are to be read, after the A side thereof is read, the original document D is transported in the direction of the arrows a by rotating the discharge/reverse rollers  110  in the same direction as described above. However, when the trailing edge of the original document D reaches the discharge/reverse rollers  110 , the discharge/reverse rollers  110  will reverse their rotations. Thus, each original document D is transported in the direction illustrated by the arrow b, transported to the original document reading position R by means of the transport drum  105  and the transport rollers  106 ,  107 , and  108  such that the B side of each is facing away from the transport drum  105 , and the B side of each is then read. After the B side of each original document D is read, each is transported around the transport drum  105 , and is discharged to the discharge tray  111 . More specifically, after the B side of the original document D is read, it is transported in the direction illustrated by the arrows a by rotating the discharge/reverse rollers  110  in the directions shown, and when the trailing edge of each reaches the discharge/reverse rollers  110 , each is transported in the direction illustrated by the arrow b by reversing the rotation of the discharge/reverse rollers  110 . Then, each original document D will transported by the transport drum  105  and the transport rollers  106 ,  107 , and  108  and discharged to the discharge tray  111  without being read. When this occurs, each original document D will be discharged with the A side of each facing downward.  
           [0009]    [0009]FIG. 7 will now be described.  
           [0010]    The device shown in FIG. 7 eliminates the structure used to reverse the orientation of the A and B sides of an original document D. Because the device shown in FIG. 7 has the same basic structure as the automatic document feeder shown in FIG. 6, only the differences between it and the device of FIG. 6 will be described below.  
           [0011]    This automatic document feeder is comprised of a drive roller  112 , driven rollers  113 ,  114 , a switching claw  115 , a pair of reverse rollers  116 , and an intermediate tray  117 . Note that in this device, the drive roller  112  and the driven roller  113  below it form a pair of discharge rollers.  
           [0012]    In this device, the switching claw  115  is placed in the position indicated by the dotted lines when only the A side of an original document D is to be read, and after the A side thereof is read, the original document D is discharged to the discharge tray  111  by rotating the drive roller  112  in the direction indicated by the arrow.  
           [0013]    In contrast, when both the A side and the B side of an original document D are to be read, after the A side thereof is read, the switching claw  115  is placed in the position indicated by the solid lines, and the original document D is guided to the intermediate tray  117  by rotating the drive roller  112  and the pair of reverse rollers  116  in the directions indicated by the respective arrows.  
           [0014]    When the trailing edge of the original document D reaches the reverse rollers  116 , the reverse rollers  16  reverse rotation, transport the original document D in the direction illustrated by the arrow b, and the B side thereof is then read at the original document reading position R. After the B side of the original document D is read, the orientation of the A and B sides is reversed and the original document D is discharged to the discharge tray  111 . More specifically, after the B side of an original document D is read, the switching claw  115  will be placed in the position indicated by the solid lines, and will be guided to the intermediate tray  117  by rotating the drive roller  112  and the reverse rollers  116  in the direction indicated by the respective arrows. Then, when the trailing edge of the original document D reaches the reverse rollers  116 , the reverse rollers  116  will reverse rotation, and will then transport the original document D in the direction indicated by the arrow b. The original document D is not read at this point. The switching claw  115  is placed in the position shown by the dotted line, and by rotating the drive roller  112  in the direction indicated by the arrow, the original document D is discharged to the discharge tray  111  with the A side thereof facing upward.  
           [0015]    As noted above, in an automatic document feeder that can automatically read both sides (the A side and B side) of an original document D, it is preferable that the pair of reverse rollers be disposed a relatively short distance away from the original document reading position R, and that the pair of discharge rollers be disposed a relatively long distance way from the original document reading position R.  
           [0016]    The reason for the former is that when the pair of reverse rollers is relatively far away from the original document reading position R, the pair of reverse rollers will also be relatively far away from the adjacent transport members (the transport rollers  106  or  108  in the example of FIG. 6), and thus an original document that is not large enough to extend between the pair of reverse rollers and an adjacent transport member cannot be transported thereby. In addition, in this situation, the original document transport path will be long, and thus the time needed to read the original document (especially the time needed to read the B side and then switch the orientation of the A and B sides) will increase. Note that in situations in which the distance between the reverse rollers and the adjacent transport members is relatively long, a small original document (one whose length in the transport direction is short) can be handled if a separate transport member is added in between the reverse rollers and the adjacent transport members. However, this will complicate the automatic document feeder.  
           [0017]    The reason for the latter is that when the pair of reverse rollers is relatively close to the original document reading position R, an original document D is discharged to a position further inside the device (the left side in FIGS. 6 and 7), and thus an original document D discharged to the discharge tray  111  cannot be easily seen due to the presence of the loading tray  101  or the intermediate tray  117 . Note that, in general, a person using the device can confirm that an original document D has been discharged to the discharge tray  111  by looking diagonally into the space between the loading tray  101  and the discharge tray  111 .  
           [0018]    Thus, regardless of whether it is preferable to have the reverse rollers relatively close to the original document reading position R, or whether it is preferable to have the discharge rollers relatively far away from the original document reading position R, neither of these structures can be achieved with the device shown in FIG. 6 because the device shown therein includes discharge/reverse rollers  110  which function as both reverse rollers and discharge rollers. More specifically, when the discharge/reverse rollers  110  are positioned relatively close to the original document reading position R, the original document discharge position will shift further toward the interior of the device than the loading tray  101  (the left side in FIG. 6), and an original document D that has been discharged to the discharge tray  111  will be less visible to a person operating the device. On the other hand, when the discharge/reverse rollers  110  are positioned relatively far away from the original document reading position R, an original document D discharged to the discharge tray  111  is easier to see, but the original document reading position R will be relatively far away from the discharge/reverse rollers  110 , and thus the time needed to read an original document will increase.  
           [0019]    In the automatic document feeder shown in FIG. 7, the reverse rollers  116  are disposed relatively far away from the original document reading position R, and the discharge rollers (the drive roller  112  and the driven roller  113 ) are disposed relatively close to the original document reading position R. Thus, when both sides of an original document D are to be read, the time needed to read them will be longer, and it will be difficult to confirm that the original document D has been discharged to the discharge tray  111 .  
         SUMMARY OF INVENTION  
         [0020]    It is therefore an object of the present invention to separate the reverse rollers from the discharge rollers, and by optimally setting the positional relationship between the reverse rollers and the discharge rollers, make it possible to read original documents whose length in the transport direction is short, reduce the time needed to read both sides of an original document, and increase the visibility of original documents when they are discharged.  
           [0021]    An automatic document feeder according to one aspect of the present invention is comprised of a loading unit, a supply device, a discharge device, a discharge unit, and a reversing device. Original documents are loaded into the loading unit. The supply device supplies the original documents loaded in the loading unit to an original document reading position. The discharge device discharges the original documents which were read at the original document reading position. The discharge unit supports the original documents discharged by the discharge device. The reversing device is disposed below the loading unit and above the discharge device, and reverses the orientation each original document with respect to the original document reading position and then re-supplies them to the original document reading position. The reversing device and the discharge device are disposed such that the distance in the horizontal direction from the original document reading position to the reversing device is longer than the distance in the horizontal direction from the original document reading position to the discharge device.  
           [0022]    According to another aspect of the present invention, the reversing device has an upper reverse roller and a lower reverse roller that form a reverse nip that grasps and transports an original document by mutually contacting the original document in a substantially vertical direction.  
           [0023]    According to another aspect of the present invention, the discharge device has an upper discharge roller and a lower discharge roller that forms a discharge nip that grasps and transports an original document by mutually contacting the original document in a substantially vertical direction.  
           [0024]    According to another aspect of the present invention, the reverse nip is disposed above the discharge nip.  
           [0025]    According to another aspect of the present invention, the automatic document feeder further comprises a switching member. The switching member can be selectively placed in either the reverse position in order to guide an original document read at the original document reading position to the reverse nip unit, or the discharge position in order to guide an original document read at the original document reading position to the discharge nip.  
           [0026]    According to another aspect of the present invention, an automatic document feeder further comprises an intermediate support member that supports a first end of an original document while a second end of the original document is in the grasp of the reverse nip.  
           [0027]    In another aspect of the present invention, an image forming device comprises an original document reading device, an automatic document feeder, an image forming unit, and a recording media transport device. The original document reading device reads an original document in an original document reading position. The automatic document feeder is the device disclosed above that supplies the original document to the original document reading position, and transports the original document read at the original document reading position away therefrom. The image forming unit forms an image on the recording media based upon image data read by the original document reading device. The recording media transport device supplies recording media to the image forming unit, and transports the recording media on which an image has been formed away therefrom.  
           [0028]    These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0029]    Referring now to the attached drawings which form a part of this original disclosure:  
         [0030]    [0030]FIG. 1 is a longitudinal section of an automatic document feeder according to one embodiment of the present invention;  
         [0031]    [0031]FIG. 2 is a flow chart showing the operational flow when one side of an original document is read;  
         [0032]    [0032]FIG. 3 is a flow chart showing the operational flow when both sides of an original document are read;  
         [0033]    [0033]FIG. 4 is a flow chart showing the operational flow when both sides of an original document are read;  
         [0034]    [0034]FIG. 5 is a longitudinal section which schematically illustrates an image forming device in which the automatic document feeder shown in FIG. 1 is disposed;  
         [0035]    [0035]FIG. 6 is a schematic illustration of a prior art automatic document feeder; and  
         [0036]    [0036]FIG. 7 is a schematic illustration of another prior art automatic document feeder. 
     
    
     DETAILED DESCRIPTION  
       [0037]    Embodiments of the present invention will be described below with reference to the figures.  
         [0038]    A. Automatic Document Feeder  
         [0039]    [0039]FIG. 1 shows a longitudinal section of the principal parts of an automatic document feeder  1  according to one embodiment of the present invention. Note that in the following description, the left side of the figure is the front of the device and the right side of the figure is the rear of the device.  
         [0040]    The automatic document feeder  1  is comprised of a loading tray  2  that serves as a loading unit in which a plurality of original documents D can be loaded, a supply device  3  that supplies the original documents D loaded in the loading tray  2  to an original document reading position R, a discharge device  4  that discharges the original documents D after they have been read, a discharge tray  5  that serves as a discharge unit which supports the original documents D discharged from the discharge device  4 , and a reversing device  6  that reverses the orientation of the original documents D with respect to the original document reading position after they are read and re-supplies them back to the original document reading position R.  
         [0041]    The loading tray  2  is disposed in the upper portion of the automatic document feeder  1 . The loading tray  2  is formed into an approximately planar shape, and is disposed such that it slopes gently downward toward the front of the device. A dividing wall  7  having an upwardly sloping surface is formed on the front end of the loading tray  2 . The leading edges of the original documents D that are loaded onto the loading tray  2  come into contact with the dividing wall  7 , and as noted below, the leading edge of each is dragged along and over the dividing wall  7  during document feeding. The original documents D loaded onto the loading tray  2  are loaded such that a first side (A or front side) is facing upward and a second side (B or rear side) is facing downward.  
         [0042]    A set switch  8  that acts as a sensor to detect the presence or absence of an original document D is disposed near the front of the loading tray  2 . The set switch  8  is an arm shaped member having a rotatable support shaft  8   a  and a leading edge  8   b . The set switch  8  is supported above the loading tray  2  such that it can pivoted about the rotatable support shaft  8   a  by applying a comparatively small amount of force thereto. When one or more original documents D are loaded onto the loading tray  2 , the leading edge  8   b  of the set switch  8  will be in a withdrawn position in which it lightly contacts the top of the original documents D. On the other hand, when there are no original documents D in the loading tray  2 , the leading edge  8   b  will enter an aperture provided in the loading tray (not shown in the figures), and will take the position shown by the solid lines in FIG. 1. At this time, the leading edge  8   b  of the set switch  8  will detect that there are no original documents D present by, for example, interrupting the light path of a transparent optical sensor (not shown in the figures).  
         [0043]    The supply device  3  includes a pick-up roller (forwarding roller)  10  that is disposed near the set switch  8 , a supply roller  11  that is disposed in front of the pick-up roller  10  (the left side in FIG. 1), a large diameter transport drum  12  that is disposed in front of and below the supply roller  11 , a pre-reading roller  13  that contacts with the transport drum  12  at approximately the front side thereof, and a post-reading roller  14  that contacts with the transport drum  12  at a lower rear portion thereof (the right side in FIG. 1).  
         [0044]    The pick-up roller  10  is connected to a supply motor  16  via a supply clutch  15 . When the pick-up roller  10  is rotatively driven in the clockwise direction by the supply motor  16  and the supply clutch  15 , it pivots about a CL point and moves from the home position illustrated by the solid lines in FIG. 1 to a supply position illustrated by the dotted lines therein. More specifically, the pick-up roller  10  moves to a position that lightly contacts with the A side of the uppermost original document D loaded into the loading tray  2 . In addition, when supply motor  16  rotates in the counterclockwise direction, the pick-up roller  10  will return to the home position. The supply motor  16  is a stepping motor capable of reciprocal rotation and which only rotates in a rotational angle (number of rotations) that is proportional to the number of pulses.  
         [0045]    The supply roller  11 , like the pick-up roller  10 , is connected to the supply motor  16  via the supply clutch  115 . The supply roller  11  contacts with the top of a divider pad  17 . The supply roller  11  is rotatively driven in the clockwise direction by the supply motor  16  and the supply clutch  15 , and feeds the original documents D that are transported from the pick-up roller  10  further downstream one sheet at a time. Note that even if a plurality of original documents D are transported from the pick-up roller  10 , the divider pad  17  will prevent more than one original document D at a time from being fed downstream.  
         [0046]    When the supply motor  16  rotates in the counterclockwise direction, the pick-up roller  10  and the supply roller  11  will rotate in the clockwise direction, and when the supply motor  16  rotates in the clockwise direction, the rotation thereof stops due to the operation of the supply clutch  15  (a one-way clutch).  
         [0047]    The transport drum  12  is disposed immediately above the original document reading position R, and is connected to a transport motor  20  via a transport clutch  18 . The transport motor  20  is connected to the discharge device  4  and reversing device  6  (both described below) via the transport clutch  18 . The transport motor  20  is, like the supply motor  16 , a stepping motor that is capable of reciprocal rotation. A one way clutch (not shown in the figures) is interposed between the transport drum  12  and the rotational shaft thereof, and the transport drum  12  will not rotate in the clockwise direction even if the transport motor  20  does rotate in the clockwise direction. More specifically, the transport drum  12  will rotate in the counterclockwise direction when the transport motor  20  rotates in the counterclockwise direction, but will be prevented from rotating in the clockwise direction when the transport motor  20  rotates in the clockwise direction.  
         [0048]    The pre-reading roller  13  is in contact with the surface of the transport drum  12 , and forms a first transport nip N 1  between it and the transport drum  12 . The pre-reading roller  13  is driven and rotated in the clockwise direction by the counterclockwise rotation of the transport drum  12 , and thus an original document D is interposed between it and the transport drum  12  and is transported thereby.  
         [0049]    A timing switch  21  is disposed immediately upstream (herein defined as the upstream side in the original document transport direction) from the pre-reading roller  13 . When the timing switch  21  comes into contact with the leading edge of an original document D, it moves to a withdrawn position illustrated by the dotted lines in FIG. 1 and is maintained in this state until the original document D has completely passed over it. When the trailing edge of the original document D has passed over it, it returns to an operational position illustrated by the solid lines in FIG. 1. When the timing switch  21  is disposed in the withdrawn position, it, for example, interrupts the light path of a transparent optical sensor (not shown in the figures), and thus can detect when the leading edge of an original document D arrives. In addition, the timing switch  21  can detect when the trailing edge of an original document D has passed over it by returning to the operational position and thereby allowing the light path to reconnect. The detection of the leading edge or trailing edge of an original document D with the timing switch  21  can be used as a reference for the operational timing of other rollers and timing members (described below).  
         [0050]    The post-reading roller  14  has the same structure as the pre-reading roller, and comes into contact with the front surface of the transport drum  12  to form a second nip N 2  in between it and the transport drum  12 . The post-reading roller  14  is driven and rotated in the clockwise direction by the counterclockwise rotation of the transport drum  12 , and thus an original document D is interposed between it and the transport drum  12  and is transported thereby.  
         [0051]    A slit glass  22  forms the original document reading position R, and is disposed below the transport drum  12 . In addition, an original document guide  23  is disposed above the slit glass  22 . The original document guide  23  serves to narrow the space in the radial direction of the original document D transport path formed around the periphery of the transport drum  12  near the original document reading position R, and is disposed opposite the slit glass  22  across an extremely small gap.  
         [0052]    A switching member  24  is disposed downstream from the post-reading roller  14 . The switching member  24  is supported by a support shaft  24   a  on the trailing end thereof which allows it to pivot thereabout. The switching member  24  is connected to a reverse/branching solenoid  25  which, when activated, will move the switching member  24  to a reverse position illustrated by the dotted lines in FIG. 1 and, when deactivated, will move the switching member  24  to a discharge position illustrated by the solid lines in FIG. 1. Original documents D that have already been read are guided to the discharge device  4  by moving the switching member  24  to the discharge position, or are guided to the reversing device  6  by moving the switching member  24  to the reverse position.  
         [0053]    The reversing device  6  is disposed behind the switching member  24  (the right side of FIG. 1), and the discharge device  4  is disposed further to the right (in FIG. 1) of the reversing device  6 . The reversing device  6  has an upper reverse roller  26  and a lower reverse roller  27  that contact each other in the approximately vertical direction, grasp an original document D therebetween, and form a reverse nip N 3 . The upper reverse roller  26  is connected to the transport motor  20  via the transport clutch  18 . The upper reverse roller  26  rotates in the clockwise and counterclockwise direction in accordance with the clockwise and counterclockwise rotation of the transport motor  20 . On the other hand, the lower reverse roller  27  is a driven roller, and is capable of moving in the vertical direction such that it comes into contact with or moves away from the upper reverse roller  26 . When a reverse/pressure solenoid  28  is activated and pulls inward, the lower reverse roller  27  moves to a separated position in which the reverse nip N 3  is open, illustrated by the dotted lines in FIG. 1, and when the reverse/pressure solenoid  28  is deactivated and returns to its former position, the lower reverse roller  27  moves to a contact position which forms the reverse nip N 3 , illustrated by the solid lines in FIG. 1.  
         [0054]    The reversing device  4  has an upper discharge roller  30  and a lower discharge roller  31  that contact each other in the approximately vertical direction, grasp an original document D therebetween, and form a discharge nip N 4 . Like the upper reverse roller  26 , the lower discharge roller is connected to the transport motor  20  via a transport clutch  18 . The lower discharge roller  31  rotates in the counterclockwise and clockwise directions in accordance with the respective clockwise and counterclockwise rotation of the transport motor  20 . On the other hand, the upper discharge roller  30  is a driven roller, and is driven and rotated in accordance with the drive rotation of the lower discharge roller  31 .  
         [0055]    The discharge tray  5  is disposed behind and below the discharge device  4  (the downstream side of the original document transport direction. The original documents D are sequentially discharged from the discharge device  4 , and are stacked in the discharge tray  5 . Note that regardless of whether the original documents D discharged to the discharge tray  5  have been read on one side only (the A side) or on both sides (the A side and B side), they are discharged with the A side facing downward.  
         [0056]    An intermediate tray  32  that serves as an intermediate support member is provided behind the reversing device  6  (the downstream side in the original document transport direction). The intermediate tray  32  is disposed such that it extends above the discharge tray  5 . An upper surface  32   a  of the front end thereof is at approximately the same height as the upper end of the upper discharge roller  30 , and a lower surface  32   b  of the front end thereof is positioned slightly higher than the discharge nip N 4  of the discharge device  4 . This structure allows an original document D transported from the reversing device  6  when the orientation thereof is to be reversed (described below) to have the end thereof that is farthest away from the original document reading position R to be supported from below. Moreover, this structure will not obstruct an original document D from being discharged to the discharge device  4  (described below).  
         [0057]    Here, the positional relationship between the discharge device  4  and the reversing device  6  of the present embodiment will be described in detail.  
         [0058]    In the device  1 , the reversing device  6  and the discharge device  4  are disposed such that the distance in the horizontal direction from the original document reading position R to the discharge device  4  is longer than the distance in the horizontal direction from the original document reading position R to the reversing device  6 . Thus, it is possible to shorten the distance from the reverse nip N 3  to the first transport nip N 1 , and the distance from the reverse nip N 3  to the second transport nip N 2  (the distance in which the original documents are transported). In other words, when the orientation of an original document D is to be reversed, it must be grasped by at least one of the reverse nip N 3  and the first transport nip N 1 , or at least one of the reverse nip N 3  and the second transport nip N 2 . However, an original document D whose length in the transport direction is short can be used because these distances are shortened in the present invention. In addition, by shortening these distances, the distance in which an original document D is transported can also be shortened, and in particular, the distance in which an original document D is transported when it is reversed and its orientation is changed can also be shortened. Note there will be a large cumulative reduction in time when a large number of original documents are processed. On the other hand, the discharge device  4  and the discharge tray  5  can be disposed to the rear of the reversing device  6  (the right side in FIG. 1) because the distance from the discharge nip N 4  formed between the upper discharge roller  30  and the lower discharge roller  31  to the second transport nip N 2  can be lengthened. Thus, the visibility of original documents D discharged from the discharge device  4  can be improved.  
         [0059]    In addition, an original document D is smoothly reversed, and its orientation is smoothly switched, because the height of the reverse nip N 3  is higher than that of the transport nip N 4 , and moreover, because the height of the upper surface of the rear end portion of the switching member  24 , the height of the reverse nip N 3 , the height of the upper end of the upper discharge roller  30 , and the height of the upper surface  32   a  of the front end of the intermediate tray  32 , are formed to be approximately the same.  
         [0060]    Furthermore, an original document D can be smoothly discharged because the height of the lower surface of the rear end portion of the switching member  24  when the switching member  24  is in the discharge position, the height of the lower end of the lower discharge roller  27  when in contact with the upper discharge roller  26 , and the height of the discharge nip N 4 , are formed to be approximately the same.  
         [0061]    Note that in the present embodiment, the distance from the second transport nip N 2  to the discharge nip N 4  is the same as the distance from the reverse nip N 3  and the first transport nip N 1 , and the discharge nip N 4  is positioned further to the rear, because the length of an original document D in the transport direction that can be employed is at least longer than the distance from the reverse nip N 3  to the first transport nip N 1 . However, in this situation, the discharge device  4  is disposed adjacent to the immediate rear of the reversing device  6 , which eliminates the need to enlarge the diameter of the gear that transmits driving force from the reverse roller  26  to the lower discharge roller  31 , and also eliminates the need to enlarge the number of gears provided.  
         [0062]    Note that an automatic document feeder  1  having this type of structure can be controlled by a controller (not shown in the figures).  
         [0063]    Next, the operation of the automatic document feeder  1  of the present embodiment will be described with reference to the flow charts shown in FIGS.  2  to  4 .  
         [0064]    First, the reading of one side of an original document D (the A side) will be described with reference to FIG. 2. Note that in the automatic document feeder  1 , when one side only (the A side) of a plurality of original documents D are read, a fixed gap is continuously maintained between a lead original document D and each subsequent original documents in order to improve efficiency.  
         [0065]    In addition, the path from the supply roller  11  to the first transport nip N 1  will be referred to as supply path P 1 , the path from the first transport nip N 1  to the second transport nip N 2  will be referred to as the read path P 2 , the path from the second transport nip N 2  to the discharge nip N 4  will be referred to as the discharge path P 3 , the path from the second transport nip N 2  to the reverse nip N 3  will be referred to as the pre-reverse path P 4 , and the path from the reverse nip N 3  to the first transport nip N 1  will be referred to as the post-reverse path P 5 .  
         [0066]    Furthermore, descriptions of the operation of the supply motor  16 , the supply clutch  15 , the transport motor  20 , and the supply clutch  18  have been omitted as needed for the sake of convenience, and instead the operation of each roller rotatively driven by these motors is described. Moreover, the control of the automatic document feeder  1  is carried out by counting the number of pulses when the timing switch  21  is turned on and when it is turned off, and when the supply motor  16  and the transport motor  20  begin rotating and stop rotating. However, as described below, the details of this are omitted.  
         [0067]    A summary of the flow of an original document D when one side thereof (the A side) is read is as follows. A original document D placed on the loading tray  2  is supplied to the supply path P 1  by the supply roller  11 , is read at the original document reading position R while being transported in the read path P 2  by the transport drum  12 , and is then transported in the discharge path P 3  and discharged to the discharge tray  5  by the discharge device  4 . The reading of a one-sided original document will be described in detail below.  
         [0068]    When an original document D is mounted on the loading tray  2  with its A side facing upward, it moves the set switch  8 , the leading edge  8   b  is withdrawn upward, and the document feeding device  1  is thereby turned on.  
         [0069]    On the other hand, the reverse/branching solenoid  25  is turned off, and the switching member  24  is disposed in the discharge position illustrated by the solid line in FIG. 1.  
         [0070]    In addition, the reverse/pressure solenoid  28  is turned on (the position in which it applies pressure), the lower reverse roller  27  is disposed in a contact position illustrated by the solid line in FIG. 1 to form the reverse nip N 3  between it and the upper reverse roller  26 .  
         [0071]    When the automatic document feeder  1  receives a start signal (Step S 1 , each step hereinafter referred to as S 1 , S 2 , S 3 , etc), the supply motor  16  rotates counterclockwise (hereinafter referred to as rotates left), and the pick-up roller  10  and the supply roller  11  begin rotating in the clockwise direction (hereinafter referred to as rotate right)(S 2 ). At this time, the pick-up roller  10  drops down from the home position to the paper supply position, comes into contact with the uppermost original document D on the loading tray  2 , and the pick-up roller  10  and the supply roller  11  rotate right. Paper supply (primary paper supply) begins toward the paper supply path P 1 .  
         [0072]    After the rotation of the supply motor  16  begins, if the timing switch  21  is not turned on (withdrawn to the position illustrated by the dotted lines) within a predetermined period of time (S 3  is no), then the flow enters into a retry control loop (S 4 ). This retry control temporarily stops the supply motor  16 , the pick-up roller  10 , and the supply roller  11  (S 5 ), then restarts the supply motor  16  and again rotates the pick-up roller  10  and the supply roller  11  (S 6 ), and then determines whether or not the timing switch  21  has been turned on within a predetermined time period (S 3 ). In the automatic document feeder  1 , the ability of the pick-up roller  10  and the supply roller  11  to transport original documents D can be improved, and insignificant problems with the transport of original documents D can be eliminated, because this type of retry control is carried out. This retry control is carried out five times, and if the timing switch  21  is not turned on after 5 cycles have been completed (S 3  is no, S 4  is yes), then it is determined that a paper jam has occurred (S 7 ).  
         [0073]    On the other hand, if the timing switch  21  is turned on within the predetermined time period before the five cycles of the retry control are completed (S 3  is yes), then when the transport motor  20  is not off, i.e., when the transport drum  12  rotates left due to the left rotation of the transport motor  20  and an original document D is read (S 8  is no), the supply motor  16 , the pick-up roller  10 , and the supply roller  11  are stopped (S 9 ), and the transport motor  20  and the transport drum  12  are stopped. Note that the transport motor  20  is stopped at the point when the trailing edge of an original document D passes over the original document reading position R.  
         [0074]    If the transport drum  12  has stopped (S 8  is yes), then the supply motor  16  rotates left, and the pick-up roller  10  and the supply roller  11  rotate right (S 10 ). Thus, because the trailing edge of an original document D is transported while the leading edge thereof is held stationary by the first transport nip N 1 , the original document D is flexed and a leading edge resist can be performed. After the leading edge resist is completed, the supply motor  16 , the pick-up roller  10 , and the supply roller  11  are stopped (S 11 ). Thus, the primary paper supply that transports an original document D up to the first transport nip N 1  is completed.  
         [0075]    Next, secondary paper supply will be initiated. Here, the transport motor  20  is rotated in the counterclockwise direction, and the transport drum  12  is rotated left (S 12 ). Thus, an original document D is supplied to the read path P 2  while in the grasp of the first transport nip N 1 , transported to the original document reading position R, and the A side thereof is read.  
         [0076]    When reading is executed, the trailing edge of the original document D passes over the timing switch  21  and thus the timing switch  21  is returned to the off position (S 13 ).  
         [0077]    At this time, if the set switch  8  is in the on position (S 14  is yes), then another original document D is in the loading tray  2 , and the transport thereof is initiated. At the point in which the reading of the previous original document D is completed, the supply motor  16  rotates left, and the pick-up roller  10  and the supply roller  11  rotate right (S 15 ). In addition, at the point in which the trailing edge of the previous original document D passes over the original document reading position R, the transport motor  20  and the transport drum  12  stop (S 16 ). After this, the process returns to Step S 2 , and initiates primary paper supply for the next original document D.  
         [0078]    On the other hand, in Step S 14 , if the set switch  8  is in the off position (S 14  is no), then the supply motor  16 , the pick-up roller  10  and the supply roller  11  stop rotating (S 17 ) because the original document D presently being transported is the last document. At this time, the pick-up roller  10  returns to the home position shown in FIG. 1 by means of the biasing force of a coil spring in a spring clutch (not shown in the figures). Then, at the point that the trailing edge of the original document D being transported passes over the discharge nip N 3 , the transport motor  20  and the lower discharge roller  31  are stopped (S 18 ). Thus, the reading of one side (the A side) of an original document D is completed.  
         [0079]    In this type of original document reading operation, the transport drum  12  rotates left, and an original document D is grasped and transported by the first and second transport nips N 1 , N 2 . At this time, when the rotational speed of the supply roller  11  is slower than the rotational speed of the transport drum  12 , the portion of an original document D positioned in the supply path P 1  while being read is pulled between the pre-reading roller  13  and the supply roller  11 . Therefore, a shock is generated when the trailing edge of an original document D leaves the supply roller  11 , and a load fluctuation is generated in the transport drum  12 . Thus, there is a concern that the transport speed of an original document D will subtly change and cause problems in the reading of the original document D.  
         [0080]    In order to stop this type of problem from occurring in the reading of the original document D, in the present invention, the rotational speed of the supply roller  11  is increased immediately before the trailing edge of an original document D that is being read passes over the supply roller  11 . The rotational speed of the supply roller  11  at this time is set such that, for example, the speed at which the trailing portion of an original document D is transported by the supply roller  11  is 1.5 times faster than the speed at which the original document D is transported by the transport drum  12 . Thus, the trailing portion of an original document D will come loose, and the generation of the aforementioned shock can be suppressed.  
         [0081]    Next, a situation will be described in which both sides (the A side and the B side) of an original document D are read, with reference to the flowcharts in FIGS. 3 and 4.  
         [0082]    A summary of the flow of an original document D when both sides thereof (the A side and the B side) are read is as follows. An original document D placed in the loading tray  2  is supplied to the supply path P 1  by the supply roller  11 , and the A side thereof is read at the original document reading position R while being transported in the read path P 2  by the transport drum  12 . After this, the orientation the original document D is reversed by means of the pre-reverse path P 4  and the post-reverse path P 5 . Then, the original document D is transported from the post-reverse path P 5  to the read path P 2 , the B side thereof is read at the original document reading position R, and the orientation of the original document D is again reversed by the pre-reverse path P 4  and the post-reverse path P 5 . Then, after the original document D is transported from the post-reverse path P 5  to the read path P 2 , and is transported to the original document reading position R in the read path P 2  without being read, it is transported to the discharge path P 3  and discharged to the discharge tray by the discharge device  4 .  
         [0083]    A detailed description of dual side reading of an original document D will now be provided below. Note that Steps S 1  to S 11  shown in FIG. 3 are identical to the one-sided reading described in FIG. 2, and thus a description thereof will be omitted.  
         [0084]    As shown in FIG. 3, if both sides of an original document D are read, the reversal of the original document D will be initiated after the primary paper supply is completed at Step S 11 .  
         [0085]    When the primary paper supply is completed, the transport motor  20  rotates left, and the transport drum  12  and the upper reverse roller  26  rotate left (S 21 ). Before the leading edge of an original document D reaches the switching member  24 , the reverse/branching solenoid  25  is turned on, and the switching member  24  is placed in the reverse position (S 22 ). Thus, the discharge path P 3  is closed, and the reverse path P 4  is opened. Then, the original document D is guided to the switching member  24  and is transported inside the reverse path  4  toward the reversing device  6 . Furthermore, the original document D is grasped and transported by the reverse nip N 3  by means of the left rotation of the upper reverse roller  26 , and the leading edge of the original document D continues rearward along the upper surface of the intermediate tray  32 . Then, when the trailing edge of the original document D passes over the timing switch  21  and the timing switch  21  is turned off (S 23 ), the reverse/branching solenoid  25  is turned off and the switching member  24  is placed in the discharge position (S 24 ) at the point at which the trailing edge of the original document D reaches the rear end of the switching member  24 . Thus, the pre-reverse path P 4  is closed, and the post-reverse path P 5  is opened. In addition, at approximately the same time, the transport motor  20  rotates right, thereby rotating the upper reverse roller  26  to the right. Thus, the trailing edge of the original document D now becomes the leading edge thereof, the original document D is moved in the approximately forward direction inside the reverse path P 5 , and is transported toward the pre-reading roller  13 . Note that at this time the transport drum  12  is stopped by operation of the aforementioned one-way clutch. Then, after the timing switch  21  is turned on by the leading edge of the original document D (S 26 ), the leading edge of the original document D comes into contact with the first transport nip N 1 , and the leading edge resist of the original document D occurs. After this, the upper reverse roller  26  stops (S 27 ) by stopping the transport motor  20 , and thus the reverse operation of the original document D is completed.  
         [0086]    After the reverse operation is completed, the secondary paper supply is initiated, and by rotating the transport motor  20  to the left, the transport drum  12  and the upper reverse roller  26  rotate to the left (S 28 ). Then, at approximately the same time that the secondary paper supply is initiated, the reverse/pressure solenoid  28  is retracted to the on state, the upper reverse roller  27  is placed in the spaced apart position, and the reverse nip N 3  is released (S 29 ). Thus, the original document D is transported inside the read path P 2 , and the B side thereof is read at the original document reading position R. Next, before the leading edge of the original document D reaches the switching member  24 , the reverse/branching solenoid  25  is turned on, and the switching member  24  is placed in the reverse position (S 30 ).  
         [0087]    After the timing switch  21  is turned off by the trailing edge of the original document D, the reverse/pressure solenoid  28  is turned on and returns to its original position, the lower reverse roller  27  is placed in the contact position, and the reverse nip N 3  is formed thereby (S 31 ). Thus, the original document D is grasped with its A side facing upward and transported to the intermediate tray  32  by the reverse nip N 3 , and the trailing edge of the original document D will continue to be in the grasp of the reverse nip N 3 .  
         [0088]    After that, Repeat  1  in FIG. 3 is repeated. Thus, in the re-reversed state, the original document D is stopped with its leading edge in contact with the first transport nip N 1  (e.g., the state when the original document D is first supplied to the supply path P 1  by the supply roller  11 ).  
         [0089]    After this, when the transport motor  20  and the transport drum  12  turn left (S 33 ), the original document D is grasped and transported by the first transport nip N 1 . When this occurs, the reverse/pressure solenoid  28  is turned on to the retracted position, the lower reverse roller  27  is placed in the spaced apart position (S 34 ), and the reverse nip N 3  is released so that the resistance of the reverse nip N 3  does not act upon the original document D. After this, when the timing switch  21  is turned off by the trailing edge of the original document D (S 35 ), the reverse/pressure solenoid  28  is turned on and returns to its original position, the lower reverse roller  27  is placed in the contact position (S 36 ), and the reverse nip N 3  is formed thereby. In this way, the discharge path P 3  is opened. Note that the original document D is sent into the read path P 2  by the first transport nip N 1  but is not read, and the original document D is sent into the discharge path P 3  by the second transport nip N 2  and is then discharged to the discharge tray  5  by the discharge device  4 .  
         [0090]    Here, when the reverse/pressure solenoid  28  is turned on and returns to its original position (S 36 ), and it is determined that the set switch in turned on (S 37  is yes), the supply of any remaining original documents D in the loading tray  2  is initiated. At the point in which the reading of the previous original document D is completed, the supply motor  16  rotates left, and the pick-up roller  10  and the supply roller  11  rotate right (S 38 ). Furthermore, at the point in which the trailing edge of the previous original document D passes over the original document reading position R, the transport motor  20  and the transport drum  12  stop (S 39 ). After this, the process returns to Step S 2 , and initiates primary paper supply for the next original document D.  
         [0091]    On the other hand, in Step S 37 , when the set switch  8  is in the off position (S 37  is no) because the original document D presently being transported is the last original document on the loading tray  2 , the original document D is discharged by the right rotation of the lower discharge roller  31 , and the transport motor  20  and the lower discharge roller  31  are stopped at the point in which the trailing edge of the original document D passes over the discharge nip N 3  (S 40 ).  
         [0092]    After this, the supply motor  16 , the pick-up roller  10 , and the supply roller  11  are stopped (S 41 ). Thus, the reading of both sides of the original document D is completed.  
         [0093]    The automatic document feeder  1  constructed as described above can handle an original document D whose length in the direction in which it is transported is short because the reversing device  6  is disposed close to the original document reading position R, and can also shorten the amount of time needed to read an original document D because the transport path is shortened. In addition, the automatic document feeder  1  can improve the visibility of an original document D discharged to the discharge tray  5  by the discharge device  4  because the discharge device  4  is disposed some distance away from the original document reading position R.  
         [0094]    B. Image Forming Device  
         [0095]    [0095]FIG. 5 shows a schematic view of an image forming device  50  according to one embodiment of the present invention, and which comprises an automatic document feeder.  
         [0096]    The image forming device  50  comprises an original document reading device  51 , an automatic document feeder  1 , an image forming unit  52 , a recording medium supply and transport device  53 , and a recording medium reversing device  54 .  
         [0097]    The automatic document feeder  1  according to the aforementioned embodiment can be used as the automatic document feeder  1  in this image forming device. An optical original document reading device known in the prior art can be used as the original document reading device  51 . The original document reading device  51  is a device for sequentially reading original documents supplied to the original document reading position R by the automatic document feeder  1 . The image forming unit  52  forms a toner image on a recording medium P such as paper or the like, based on image data read by the original document reading device  51 . The recording medium supply/transport device  53  is a device for supplying recording media P to the image forming unit  52 , and transporting the recording media P out of the image forming unit  52  after image formation is completed. The recording medium reversing device  54  is a device for reversing the front and back of a recording medium P on one side of which an image has been formed, and re-supplying that recording medium P to the image forming unit  52 . By equipping the image forming device  50  with the recording medium reversing device  54 , the images on both sides of an original document can be automatically formed as is onto both sides of a recording medium P.  
         [0098]    An ink jet system may, for example, be employed as the image forming unit  52 .  
         [0099]    In an image forming device  50  constructed in this manner, image formation can take place based on an original document D whose length in the transport direction is short, and the overall amount of time needed for image formation, including the time needed for reading the images, can be shortened. In addition, in the image forming device  50 , both an original document D and a copy thereof can be easily checked by the operator thereof due to the fact that both are readily visible inside the device.  
         [0100]    Terms of degree used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.  
         [0101]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.