Abstract:
An automatic document feeder includes: an inlet; an outlet; a transfer system configured to transfer a document from the inlet to the outlet; an input transfer path configured to guide a document during transfer from the inlet passed a scanning point to an end point positioned above the inlet; an output transfer path configured to guide the document during transfer from the end point passed the scanning point to the outlet; a secondary system configured to feed the document from the inlet; and a drive system configured to drive the transfer elements and the secondary system, wherein the drive system controls the transfer system such that, in at least some instances, operation of the secondary system is independent of operation of the transfer system.

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION(S) 
     This application is based upon and claims priority from prior Japanese Patent Application No. 2005-317474 filed on Oct. 31, 2005, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Illustrative aspects of the present invention relate to a document feeder suited for the double-sided reading of documents. 
     BACKGROUND 
     In the prior art, in an image reading apparatus which is used in a copier, a scanner, a multi-function apparatus having the functions of the former is known to have an automatic document feeder called the ADF (Auto Document Feeder) for transferring the documents from an input tray through a transfer path to an output tray. There is also known an automatic document feeder for reading a document having its two first and second sides printed. In this device, the document is reversed at its leading end and trailing end by reversible rollers while it is being transferred. (for example, see JP-A-8-85649). 
       FIG. 17  shows a transfer route of the automatic document feeder of the prior art. As shown in  FIG. 17 , a document P placed on an input tray  100  with the first side (first page) thereof facing upward is fed to a feed path  102  by a feed roller  101 . In the feed path  102 , the document P is fed to feed rollers  103  which are suitably disposed according to cases. When the document P passes through a scanning position X, the first side of the document P is scanned by an image reading element such as a CCD or a CIS. When a sensor detects the trailing end of the document P after the first side thereof is scanned, reversible rollers  104  are stopped while nipping the trailing end of the document. 
     As shown in  FIG. 18 , bidirectional feed path the reversible rollers  104  reverse the transfer direction of the nipped document P to a return path  105 . The document P is fed from the bidirectional feed path  105  again to a side upstream of the scanning position X. The leading and trailing ends of the document P are reversed. The document P is fed by the feed rollers  103 , and when the document P passes through the scanning position X, the second side of the document P is scanned by the image read unit. When a sensor detects the trailing end of the document P after the second side of the document P is scanned, the reversible rollers  104  are again stopped in a state where the trailing end of the document P is nipped. Afterwards, the document P is sent back along the return path  105 . When the document P is moved from the return path  105  again into the feed path  102 , the document P is held in a state where the leading and trailing ends of the document P are reversed once more, that is, the first side of the document P is opposed to the scanning position X. The document P is delivered along the feed path  102  and is discharged into an output tray  106  with the first side thereof facing downward. As a result, both the first and second sides of the document P are scanned and the document P is discharged to the output tray  106  in the order that the sheets of the document P were placed on the input tray  100 . 
     SUMMARY 
     Illustrative aspects of the invention relate to a document feeder which is capable of feeding a document for double-sided reading and capable of maintaining a placement state of a document existing on a sheet feed tray, even when a leading end of a document projected from a bidirectional feed path is contacted with the document placing on the input tray. 
     Aspects of the invention relate to an automatic document feeder including: (a) an inlet; (b) an outlet; (c) a transfer system configured to transfer a document from the inlet to the outlet; (d) an input transfer path configured to guide a document during transfer from the inlet passed a scanning point to an endpoint positioned above the inlet; (e) an output transfer path configured to guide the document during transfer from the end point passed the scanning point to the outlet; (f) a secondary system configured to feed the document from the inlet; (g) and a drive system configured to drive the transfer elements and the secondary system, (h) wherein the drive system controls the transfer system such that, in at least some instances, operation of the secondary system is independent of operation of the transfer system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the present invention will be made more fully apparent from the following detailed description taken in conjunction with the accompanying drawings, in which; 
         FIG. 1  is a perspective view of the external structure of an image read apparatus  1  according to an exemplary aspect of the invention; 
         FIG. 2  is a sectional view of the internal structure of the image read apparatus  1 ; 
         FIG. 3  is an enlarged view of the structure of a crossing position  40 ; 
         FIG. 4  is an enlarged view of the structure of a connecting position  38 ; 
         FIG. 5  is an enlarged view of the structure of a first front sensor  52 ; 
         FIG. 6  is a block diagram of the structure of a controller  60 ; 
         FIG. 7  is a flow chart of the operation of a double-sided image reading mode; 
         FIG. 8  is a flow chart of the sheet feeding operation of the double-sided image reading mode; 
         FIG. 9  is a typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 10  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 11  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 12  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 13  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 14  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 15  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 16  is another typical view of the image reading operation of the double-sided image reading mode; 
         FIG. 17  is a typical view of a document feeding operation for reading the images of both sides of a document according to a conventional document feeder; and 
         FIG. 18  is a typical view of a document feeding operation for reading the images of both sides of a document according to a conventional document feeder. 
     
    
    
     DETAILED DESCRIPTION 
     Now, description will be given below of an image read apparatus  1  according to an aspect of the invention, with reference to the accompanying drawings. The present aspect is an example of the invention and thus the present aspect can be modified without departing from the spirit or scope of the invention. 
       FIG. 1  shows the structural of the appearance of the image read apparatus  1  according to the aspect of the invention.  FIG. 2  shows the structure of the main interior portions of the image read apparatus  1 . The present image read apparatus  1  can be realized as an image read portion which has a scanner function integrated therewith and used to read the images of a document, for example, in a copier, a facsimile, a scanner, and a multi-function device (MFD) having an integrated scanner function. 
     As shown in  FIGS. 1 and 2 , the present image read apparatus  1  is structured such that a document cover  4  is openably and closably mounted on a document placing table p  2  The document cover includes an ADF  3  functioning as an automatic document feed mechanism. The document placing table  2  is a flatbed scanner (FBS). 
     An operation panel  5  is disposed on the front side of the document placing table  2 . The operation panel  5  includes various operation keys  11  and a liquid crystal display part  12 . A user can input a desired instruction using the operation panel  5 . For example, the input of “Start” showing the commencement of reading a document and “Stop” showing the termination of such reading, as well as the choice of a one-sided reading mode or a double-sided reading mode can be carried out using the operation keys  11 . The CPU receives these given inputs, the image read apparatus  1  carries out a given operation. The image read apparatus  1  can also be operated by instructions other than the instructions inputted to the operation panel  5 . The image read apparatus  1  can also be connected to a computer and thus can be operated by instructions which are transmitted thereto from the computer through a printer driver, a scanner driver, or the like. 
     As shown in  FIG. 2 , on the document placing table  2 , and more specifically, on the top surface thereof facing the document cover  4 , there are disposed platen glass members  20 ,  21 . When the document cover  4  is opened, the platen glass members  20 ,  21  are exposed as the top surface of the document placing table  2 . When the document cover  4  is closed, the whole of the top surface of the document placing table  2  including the platen glass members  20 ,  21  is covered by the document cover  4 . In the interior of the document placement placing table  2 , there is incorporated an image reader  22  in such a manner as to be opposed to the platen glass members  20 ,  21 . 
     The platen glass member  20  is a member on which a document can be placed when the image read apparatus  1  is used as an FBS. For example, the platen glass member  20  may be composed of a transparent glass plate. In the center of the top surface of the document placing table  2 , there is formed an opening from which the platen glass member  20  can be exposed, whereby the area of the platen glass member  20  that is exposed from the opening provides a document read area in the FBS. 
     The platen glass member  21  functions as a scanning position when the ADF  3  of the image read apparatus  1  is used, and as an example, may be composed of a transparent glass plate. In the scanning position of the document placing table  2 , there is formed an opening from which the platen glass member  21  can be exposed. The platen glass member  21  exposed from the opening is extended in the depth direction of the image read apparatus  1  correspondingly to the length in the main scanning direction of the image reader  22 . 
     A positioning member  23  is interposed between the platen glass members  20  and  21 . The positioning member  23  is a long flat-plate-shaped member which is extended in the depth direction of the image read apparatus  1  similarly to the platen glass member  21 . When a document is placed onto the platen glass member  20  serving as the document placement surface of the FBS, the positioning member  23  is used as the positioning reference of the document. For this purpose, on the top surface of the positioning member  23 , there are disposed indications for indicating the position of the center as well as the positions of the two ends of various document sizes such as A4 size and B5 size. On the top surface of the positioning member  23 , there is further formed a guide surface by which a document passing on the platen glass  21  by the ADF  3  can be caught up and deflected and also can be then returned to the ADF  3 . 
     The image reader  22  is an image sensor which radiates the light from a light source onto the document through the platen glass members  20 ,  21 , gathers the reflected light from the document onto a light receiving element, and converts the light to electric signals. The image reader unit  22  can be forted of, for example, a close-contact type image sensor (CIS) or a charge coupled device (CCD) of a reduction optical system. The image reader  22  is disposed below the platen glass members  20 ,  21 . The image reader  22  can be moved back and forth by a belt drive mechanism. On receiving the drive force of a carriage motor, the image reader  22  can be moved back and forth parallelly to the platen glass members  20 ,  21 . 
     The document cover  4  includes the ADF  3  which successively feeds a document from an input tray  30  through a feed path  32  to an output tray  31 . In the feed process that is carried out by the ADF  3 , the document passes through the scanning position on the platen glass member  21  and the images of the document can be read by the image reader  22  which is located below the platen glass member  21 . 
       FIGS. 1 and 2  show that the document cover  4  includes the input tray  30  and output tray  31 . The input tray  30  is disposed on the output tray  31  On the input tray  30 , there can be placed a document the images of which are to be scanned by the ADF  3 . Two or more sheets of documents are placed onto the input tray  30  in such a manner that they are piled on top of one another with the first sides thereof facing upward and the leading ends thereof in the feed direction are inserted into the feed path  32 . The apparatus back side of the input tray  30  is curved downward to thereby form a protection wall  26 . The lower end of the protection wall  26  is connected to the top surface of the document cover  4 . When the document cover  4  is opened with respect to the document placing table  2 , the protection wall  26  prevents the document on the output tray  31  from falling down. Downward from the apparatus front side of the input tray  30 , there is formed a groove  27  in a part of the body of the ADF  3 . This groove  27  enhances the visibility of the document from the apparatus front surface side when the document is discharged to the output tray  31 . Especially, a document of a small size is generally difficult to see due to the input tray  30 . The groove  27  creates a space between the input tray  30  and output tray  31  to thereby be able to enhance the visibility of a document, especially, that of a small-sized document. 
     The output tray  31  is disposed below the output tray  30  while being spaced apart from the input tray  30  in the vertical direction. The output tray  31  is formed integrally with the top surface of the document cover  4 . Documents with images which have been scanned and which have been discharged from the ADF  3  are separated from documents existing on the input tray  30 , and are piled on the output tray  31  on top of one another with their first sides facing downward. The two side portions  28  of the output tray  31 , which are respectively composed of the apparatus front side and apparatus back side of the output tray  31 , are formed as slanting surfaces which gradually rise upwardly toward respective side. When the documents discharged to the output tray  31  are to be out therefrom, while holding the documents from above, the documents can be slid along the slanting surfaces of the two side portions  28  and can be taken out. The two side portions  28  facilitate removal of the documents from the sheet discharge tray  31 . 
     As shown in  FIG. 2 , in the interior of the ADF  3 , in order to be able to connect together the sheet feed tray  30  and sheet discharge tray  31  through the scanning position on the platen glass member  21 , there is formed the feed path  32 , the longitudinal section view of which has a substantially U-like shape facing sideways. The feed path  32  is continuously formed by a member, a guide plate, a guide rib and the like respectively constituting the main body of the ADF  3 , in the form of a path having a given width which allows the document to pass therethrough. In this manner, since the input tray  30  and sheet discharge tray  31  are disposed in the upper and lower stages and also since the feed path  32  having a sideways facing, substantially U-shaped longitudinal section is formed so as to be able to connect the two trays together, the width of the ADF  3  can be narrowed and thus the size of the ADF  3  can be reduced. 
     The feed path  32  is extended from the input tray  30  toward one end side (in  FIG. 2 , toward the left side) of the document cover  4 , and is curved downward in a reversing manner to reach the scanning position on the platen glass member  21 , and also extended from the scanning position toward the output tray  31 , whereby the longitudinal section view of the feed path  32  has a substantially U-like shape facing sideways. The feed path  32  is mainly composed of three portions, an upper portion  32 A and a lower portion  32 C which respectively constitute the straight line portions of the upper and lower stages forming the substantially U-like shape, and a curved portion  32 B curved in such a manner so as to connect the upper and lower portions  32 A and  32 C. The feed path  32  is used as a common document feed path through which the document can be fed by the ADF  3  not only when the images of one side of the document are read, but also when the images of both sides of the document are read. 
     The feed path  32  includes a feed unit for feeding documents existing on the input tray  30  to the feed path  32  and a document feed unit for feeding the documents from the input tray  30  to the output tray  31 . In detail, as shown in  FIG. 2 , the feed unit is composed of a pick-up roller  33  and a separation roller  34  respectively provided in the feed path  32 . The document feed unit is composed of feed rollers  35 A,  35 B,  35 C,  35 D, a sheet discharge roller  36 , and respective pinch rollers  37  to be pressure contacted with the feed rollers  35 A,  35 B,  35 C and  35 D. A drive force is transmitted from a motor  67  (a drive source; see  FIG. 6 ) to the respective rollers that constitute the feed unit and the document feed unit. 
     As shown in  FIG. 2 , the pick-up roller  33  and separation roller  34  are disposed in the most upstream portion of the feed path  32 , that is, in the neighborhood of the input tray  30 . The pick-up roller  33  is rotatably provided on the leading end portion of an arm  29  having its base end side pivotally supported on a shaft which pivotally supports the separation roller  34 . The separation roller  34  is rotatably provided at a position spaced from the pick-up roller  33  in the sheet feed direction in such a manner that it is in contact with the opposed surfaces of the feed path  32 . When the drive force from the motor  67  is transmitted thereto, the pick-up and separation rollers  33  and  34  can be driven and rotated. The arm  29  can also be moved up and down when the drive force is transmitted thereto from the motor  67 . The pick-up and separation rollers  33  and  34  have the same diameter and can be rotated at the same peripheral speed. At the opposite position of the separation roller  34 , there is disposed a friction pad which can be pressure contacted with the roller surface of the separation roller  34  to separate the document by means of friction. 
     The feed rollers  35 A,  35 B,  35 C and  35 D are respectively disposed at different positions in the feed path  32 . According to the present aspect, the feed roller  35 A is disposed on the immediate downstream side of the separation roller  34 , the feed roller  35 B is disposed in the upper portion  32 A of the feed path  32 , the feed roller  35 C is disposed on the immediate upstream side of the scanning position in the lower portion  32 C of the feed path  32 , and the feed roller  35 D is disposed on the immediate downstream side of the scanning position in the lower portion  32 C of the feed path  32 . This arrangement is given an example, and the number and arrangement of the feed rollers  35 A,  35 B,  35 C and  35 D can be changed while still maintaining the spirit and scope of the invention. 
     At the respective opposite positions of the feed rollers  35 A,  35 B,  35 C and  35 D, there are disposed the pinch rollers  37 . The shafts of the pinch rollers  37  are respectively elastically energized by their associated springs, whereby the pinch rollers  37  are respectively pressure contacted with the roller surfaces of the feed rollers  35 A,  35 B,  35 C and  35 D. When the feed rollers  35 A,  35 B,  35 C and  35 D are rotated, the pinch rollers  37  pressure contacted with these rollers are also rotated to follow the feed rollers. The pinch rollers  37  respectively press the document against the feed rollers  35 A,  35 B,  35 C and  35 D to thereby transmit the rotation forces of the feed rollers  35 A,  35 B,  35 C and  35 D to the document. 
     The sheet discharge roller  36  is disposed in the neighborhood of the furthest downstream portion of the feed path  32 , and similar to the feed rollers  35 A,  35 B,  35 C and  35 D, when the drive force from the motor is transmitted to the sheet discharge roller  36 , the sheet discharge roller  36  is driven and rotated. At the opposite position of the sheet discharge roller  36 , there is also disposed a pinch roller  37 , which is elastically energized by a spring and is thereby pressure contacted with the sheet discharge roller  36 . 
     A bidirectional feed path  39  is connected to a connecting position  38  in the lower portion  32 C of the feed path  32 . The bidirectional feed path  39  is a path which, when reading both sides of the document, reverses the leading and trailing ends of the document with the first surface thereof read at the scanning position and then feeds again the document from the portion of the feed path  32  downstream from the scanning position to the portion of the feed path  32  upstream from the scanning position. The bidirectional feed path  39  is extended obliquely upward from the connecting position  38  toward the upper side of the input tray  30 , and crosses the upper portion  32 A of the feed path  32 . The document, which has been switchback-fed from a crossing position  40  between the upper portion  32 A and bidirectional feed path  39 , is then returned back to the feed path  32 . 
     The terminal end  41  of the bidirectional feed path  39  is opened on the top surface of the ADF  3 . On the side of the input tray  30  that extends from the terminal end  41  of the bidirectional feed path  39 , there is formed a document support portion  42  in such a manner that it extends from the lower guide surface of the terminal end  41 . The document support portion  42  is used to support the document projected from the terminal end  41  of the bidirectional feed path  39 , and forms the upper cover  6  (see  FIG. 1 ) of the ADF  3  on the upper side of the feed roller  33  and separation roller  34 . The upper cover  6  is formed so as to be able to cover the whole of the ADF  3  including the feed roller  33  and separation roller  34 , while being able to be opened and closed. The document support portion  42 , which is formed as a portion of the upper cover  6 , is extended from the terminal end  41  toward the input tray  30  up to the upstream side of the sheet feed position to which the documents are fed by the sheet feed roller  33  and separation roller  34 . Thanks to this structure, in the double-sided reading operation, a portion of the document which has entered the bidirectional feed path  39  and is projected from the terminal end  41  outwardly from the ADF  3 , can be supported by the document support portion  41 . Also, when the upper cover  6  is opened, the feed path  32  and bidirectional feed path  39  within the ADF  3  are exposed in part, thereby enabling execution of a maintenance operation such as a jam removing operation. 
     On the side of the bidirectional feed path  39  that extends to the terminal end  41  from the crossing position  40 , there is disposed a reversible roller  43 . When a drive force is transmitted thereto from the motor  67 , the reversible roller  43  can be driven and rotated in both forward and backward directions (a pulling direction and a returning direction). A pinch roller  44  is arranged at the opposing position of the reversible roller  43 . Because the shaft of the pinch roller  44  is elastically energized by a spring, the pinch roller  44  is pressure contacted with the roller surface of the reversible roller  43 , and as the reversible roller  43  is rotated, the pinch roller  44  is rotated to follow the reversible roller  43 . The pinch roller  44  presses the document against the reversible roller  43 , whereby the rotational force of the reversible roller  43  is transmitted to the document. The reversible roller  43  and pinch roller  44  cooperate together in realizing a switchback feed unit which switchback-feeds the document. 
     Now,  FIG. 3  is an enlarged view of the structure of the neighboring portion of the crossing position. As shown in  FIGS. 2 and 3 , in the crossing position  40 , there are disposed a guide flap  46  and a guide flap  47  which are used to guide the document to a desired feed path. Specifically, the guide flap  46  can be rotated in a given range about a shaft  48  provided at a corner portion (in  FIG. 3 , on the lower left side) between the scanning position side of the feed path  32  in the crossing position  40  and the connecting position  38  side of the bidirectional feed path  39 . The guide flap  46  is composed of a vane-shaped flat plate, and the leading end of the guide flap  46  is projected into the crossing position  40 . In  FIG. 3 , only one guide flap  46  is shown. However, two or more guide flaps  46  may be disposed having the same shape at given intervals in the width direction of the feed path  32  (in  FIG. 3 , in the figure sheet vertical direction, or in the apparatus depth direction), in such a manner that the two or more guide flaps  46  may be rotated as an integral body. 
     When the guide flap  46  is rotated about the shaft  48 , the guide flap  46  changes it position between a third guide position shown by a solid line in  FIG. 3  and a fourth guide position shown by a chain double-dashed line in  FIG. 3 . Since the guide flap  46  is contacted with, for example, guide members provided in the feed path  32  or bidirectional feed path  39 , the guide flap  46  is prevented from rotating downward in  FIG. 3  from the third guide position and also from rotating upward in  FIG. 3  from the fourth guide position. When the guide flap  46  is in the third guide attitude, not only is the feed path, which extends from the input tray  30  side (in  FIG. 3 , the right side) of the feed path  32  to the scanning position side (in  FIG. 3 , the left side), allowed to be continuous, but also the feed path extending from the feed path  32  to the connecting position  38  side (in  FIG. 3 , the lower side) of the bidirectional feed path  39  is closed. As a result, the document, which has arrived at the crossing position  40  from the input tray  30  side of the feed path  32 , is allowed to enter the scanning position side of the feed path  32  and is prevented from entering the connecting position  38  side of the bidirectional feed path  39 . Also, the document, which has reached the crossing position  40  from the terminal end  41  side (in  FIG. 3 , the upper side) of the bidirectional feed path  39 , is allowed to enter the scanning position side of the feed path  32  and is prevented from entering the connecting position  38  side of the bidirectional feed path  39 . 
     When the guide flap  46  takes the fourth position, the feed path extending from the connecting position  38  side of the bidirectional feed path  39  to the terminal end  41  side is allowed to be continuous, whereas the feed path extending from the connecting position  38  side of the bidirectional feed path  39  to the scanning position side of the feed path  32  is closed. As a result, the document, which has arrived at the crossing position  40  from the connecting position  38  side of the bidirectional feed path  39 , is allowed to advance to the terminal end  41  side of the bidirectional feed path  39 , whereas it is prevented from advancing to the scanning position side of the feed path  32 . 
     The switching of the feed path by the guide flap  46  is achieved by the contact of the document with the guide flap  46 . The guide flap  46  is normally held at the third position as shown by a solid line in  FIG. 3 , due to its own weight or due to the energizing force of an elastic member such as a spring. When the document being delivered from the connecting position  38  toward the crossing position  40  along the bidirectional feed path  39  is contacted with the guide flap  46 , the guide flap  46  is rotated in such a manner that it is pushed aside upwardly in  FIG. 3 , so that the guide flap  46  takes the fourth position as shown by a chain double-dashed line in  FIG. 3 . On the other hand, the document being delivered from the terminal end  41  side of the bidirectional feed path  39  to the crossing position  40  is contacted with the guide flap  46 , but since the guide flap  46  is prevented from rotating downward in  FIG. 3  from the third guide position, the document is guided by the guide flap  46  to advance to the scanning position side along the upper portion  32 A of the feed path  32 . As to the vane shape of the guide flap  46 , there is employed a shape which not only can easily change the position of the guide flap  46  when it is contacted by the document being delivered from the connecting position  38  side of the bidirectional feed path  39  to the crossing position  40 , but also allows the document being delivered from the terminal end  41  side of the bidirectional feed path  39  to the crossing position  40  to be easily guided to the scanning position side of the feed path  32 . In this manner, when the guide flap  46  is formed such that it is able to change its position due to the contact of the document with the guide flap  46 , it is not necessary to change the position of the guide flap  46  positively by applying a drive force from the motor  67 , which makes it possible to realize the guide flap  46  with a simple structure. 
     Now, the guide flap  47  is disposed in such a manner that it can be rotated in a given range about a shaft  49  provided in a corner portion (in  FIG. 3 , on the upper side) between the input tray  30  side of the feed path  32  and the terminal end  41  side of the bidirectional feed path  39 . The guide flap  47  is composed of a flat plate having a vane-like shape, while the leading end of the guide flap  47  is projected into the crossing position  40 . In  FIG. 3 , there is shown only one guide flap  47 . However, two or more guide flaps  47  may disposed having the same shape at given intervals in the width direction of the feed path  32 , the two or more guide flaps  47  capable of being rotated together integrally. 
     When the guide flap  47  is rotated about the shaft  49 , the position of the guide flap  47  can be changed to a fifth guide position as shown by a solid line in  FIG. 3  and a sixth guide position as shown by a chain double-dashed line in  FIG. 3 . When the guide flap  47  is contacted with, for example, the guide members of the feed path  32  or bidirectional feed path  39 , the guide flap  47  is prevented from rotating to the right side (in  FIG. 3 ) of the fifth guide position and is also prevented from rotating upward (in  FIG. 3 ) from the sixth guide position. When the guide flap  47  is in the fifth guide position, not only the feed path extending from the terminal end  41  side of the bidirectional feed path  39  to the scanning position side of the feed path  32  is allowed to be continuous, but also the feed path extending from the connecting position  38  side of the bidirectional feed path  39  to the input tray  30  side of the feed path  32  is closed. As a result, the document, which has arrived at the crossing position  40  from the terminal end  41  side of the bidirectional feed path  39 , is allowed to advance to the scanning position side of the feed path  32 , whereas the document is prevented from advancing to the input tray  30  side. Also, the document having arrived at the crossing position  40  from the connecting position  38  side of the bidirectional feed path  39  is allowed to advance to the terminal end  41  side of the bidirectional feed path  39 , whereas the document is prevented from advancing to the input tray  30  side of the feed path  32 . 
     On the other hand, when the guide flap  47  is in the sixth guide position, not only the feed path from the input tray  30  side of the feed path  32  to the scanning position side is allowed to be continuous, but also the feed path from the input tray  30  side of the feed path  32  to the terminal end  41  side of the bidirectional feed path  39  is closed. As a result, the document, which has arrived at the crossing position  40  from the input tray  30  side of the feed path  32 , is allowed to advance to the scanning position side of the feed path  32  but is prevented from advancing to the terminal end  41  side of the bidirectional feed path  39 . 
     The switching of the feed path by the guide flap  47  is attained by the contact of the document with the guide flap  47 . The guide flap  47  is normally held at the fifth guide position as shown by a solid line in  FIG. 3 , due to its own weight or due to the energizing force of an elastic member such as a spring. When the document being delivered from the input tray  30  side of the feed path  32  is contacted with the guide flap  47 , the guide flap  47  is rotated in such a manner that it pushed aside to the left side (in  FIG. 3 ), so that it takes the sixth guide position as shown by a chain double-dashed line in  FIG. 3 . On the other hand, even if the document, which has been delivered from the connecting position  38  of the bidirectional feed path  39  to the crossing position  40 , is contacted with the guide flap  47 , because the guide flap  47  is prevented from rotating to the right side (in  FIG. 3 ) from the fifth guide attitude, the document is guided by the guide flap  47  so as to advance to the terminal end  41  side of the bidirectional feed path  39 . As to the vane shape of the guide flap  47 , there is employed a shape which not only can easily change the position of the guide flap  47  when it is contacted by the document being delivered from the input tray  30  side of the feed path  32  to the crossing position  40 , but also allows the document being delivered from the connecting position  38  side of the bidirectional feed path  39  to the crossing position  40  to be easily guided to the crossing position  40  from the connecting position  38  of the bidirectional feed path  39 . In this manner, when the guide flap  47  is formed such that it is able to change its position due to the contact of the document with the guide flap  47 , it is not necessary to change the position of the guide flap  47  positively by applying a drive force from a motor or the like, which makes it possible to realize the guide flap  47  with a simple structure. 
       FIG. 4  is an enlarged view of the structure in the vicinity of the connecting position  38 . As shown in  FIGS. 2 and 4 , a guide flap  50  is disposed in the connecting position  38 . The guide flap  50  can be rotated about a shaft  51 , and when a drive force is transmitted thereto from the motor  67 , the guide flap  50  can be rotated to a first guide position as shown by a solid line in  FIG. 4  and a second guide position as shown by a chain double-dashed line in  FIG. 4 . When the guide flap  50  is contacted with, for example, the guide member of the feed path  32  or bidirectional feed path  39 , it is prevented from rotating upward (in  FIG. 4 ) from the first guide attitude and is also prevented from rotating downward (in  FIG. 4 ) from the second guide position. When the guide flap  50  is held at the first guide position, the feed path from the scanning position side (in  FIG. 4 , the left side) of the feed path  32  to the output tray  31  side (in  FIG. 4 , the right side) is allowed to be continuous. As a result, the document having passed through the scanning position is guided in the connecting position  38  toward the output tray  31  along the lower portion  32 C of the feed path  32 . When the guide flap  50  is held at the second position, the feed path from the side of the lower portion  32 C of the feed path  32  existing downstream of the scanning position to the bidirectional feed path  39  is allowed to be continuous. As a result, the document having passed through the scanning position is guided in the connecting position  38  in such a manner that it advances into the bidirectional feed path  39 . In this manner, the guide flap  50  is disposed in such a manner that it can guide the document in the connecting position  38  to either the feed path  32  or bidirectional feed path  39 . In  FIG. 4 , there is shown only one guide flap  50 . However, two or more guide flaps  50  may be disposed having the same shape at given intervals in the width direction of the feed path  32 , while being able to be rotated together integrally. 
     As shown in  FIG. 2 , in the feed path  32  and bidirectional feed path  39 , there are disposed two or more sensors which are used to detect the feeding operation of the document. In the feed path  32 , just upstream and just downstream of the separation roller  34 , there are disposed a first front sensor  52  and a second front sensor  53  (a first document sensor), respectively. Just upstream of the scanning position, a rear sensor  54  (a second document sensor) is disposed. A feed distance from the nip position of the separation roller  34  of the feed path  32  to the rear sensor  54  is longer than the feed-direction length of the maximum document, both sides of which can be read by the image read apparatus  1 . The present image read apparatus  1  is capable of reading both sides of a document of up to A4 size (length×width=297 mm×210 mm) of a longitudinal feed type and thus the feed path  32  is formed such that the feed distance from the second front sensor  53  to the rear sensor  54  is longer than 297 mm. Therefore, there is no possibility that the second front sensor  53  and rear sensor  54  can detect a single sheet of A4-size document at the same time. Between the connecting position  38  and crossing position  40  of the bidirectional feed path  39 , there is interposed a switchback sensor  55 . These sensors are respectively composed of so called optical sensors, and they are similar in structure except that their detectors are different in shape from one another due to their different detecting positions. Thus, by way of illustration, description will be given below of the structure of the first front sensor  52 . 
       FIG. 5  is an enlarged view of the structure of the first front sensor  52 . As shown in  FIG. 5 , the first front sensor  52  includes: a detector  56  which projects out from the lower surface of the feed path  32 , and when it is contacted with the document, can be rotated so as to retreat from the feed path  32 , and a photo-interrupter  57  used to detect the rotational movement of the detector  56 . The detector  56  includes a shielding portion  58  which is formed integrally with the detector  56  and can be detected by the photo-interrupter  57 , while the detector  56  can be rotated about a shaft  59 . The detector  56  is elastically energized by an energizing unit such as a spring (not shown) to the position from which the detector  56  projects into the feed path  32  (in a clockwise direction in  FIG. 5 ). In a state where no external force is applied to the detector  56 , as shown by a solid line in  FIG. 5 , the detector  56  projects into the feed path  32  and the shielding portion  58  is situated between the light emitting portion and light receiving portion of the photo-interrupter  57 . Thus, the light transmission of the photo-interrupter  57  is cut off, to thereby turn off the first front sensor  52 . 
     When a document is placed onto the input tray  30 , the document is contacted with the detector  56  to thereby rotate the detector  56  so as to retreat from the feed path  32 . As the detector  56  is rotated, the shielding portion  58  is also rotated, and as shown by a chain double-dashed line in  FIG. 5 , the shielding portion  58  is caused to emerge from between the light emitting and receiving portions of the photo-interrupter  57 . As a result of this, the cutoff of the light transmission of the photo-interrupter  57  is removed to thereby turn on the first front sensor  52 . Depending on the on/off state of the first front sensor  56 , it can be detected whether or not a document is placed on the input tray  30 . 
     The second front sensor  53 , which is disposed just downstream of the separation roller  34 , is used to detect the leading or trailing end of the document fed to the feed path  32  depending on its own on/off state. For example, through detection of the leading end of the document by the second front sensor  53 , it can be checked whether or not the document has been fed from the input tray  30  to the feed path  32 . Also, by monitoring the number of rotations of the feed rollers  35 A,  35 B,  35 C and  35 D after detection of the trailing end of the document by the second front sensor  53  using an encoder or from the number of steps of the motor  67 , the position of the leading or trailing end of the document in the feed path  32  can be judged. 
     The rear sensor  54  disposed just upstream of the scanning position is a sensor which, according to its own on/off state, detects the leading and trailing ends of a document being fed along the feed path  32 . By monitoring the number of rotations of the feed rollers  35 A,  35 B,  35 C and  35 D after detection of the leading or trailing end of the document by the rear sensor  54  through the number of steps or the like of the encoder or motor  67 , it is judged whether or not the leading or trailing end of the document has arrived at a given position upstream in the feed direction of the scanning position or connecting position  38 . The image reading of the image reader  22  is controlled according to the detect signal of the rear sensor  54 . When the leading end of the document has arrived at the scanning position, the image reading is started. When the trailing end of the document has arrived at the scanning position, the image reading is ended. 
     The switchback sensor  55  interposed between the connecting position  38  and crossing position  40  of the bidirectional feed path  39  is a sensor which, according to its own on/off state, detects the leading or trailing end of a document being fed along the bidirectional feed path  39 . For example, by monitoring the number of rotations of the feed rollers  35 A,  35 B,  35 C and  35 D after detection of the leading or trailing end of the document by the switchback sensor  55  through a number of steps of the encoder or motor  67 , it is judged whether or not the trailing end of the document has passed through the crossing position  40 . 
       FIG. 6  shows the structure of the controller  60  of the image read apparatus  1 . The controller  60  is a part which controls not only the ADF  3 , but also the whole operation of the image read apparatus  1 . The controller  60 , as shown in  FIG. 6 , is structured as a microcomputer which is mainly composed of a CPU  61 , a ROM  62 , a RAM  63 , and an electrically erasable and programmable ROM (EEPROM)  64 , while the controller  60  is connected through a bus  65  to an application specific integrated circuit (ASIC)  66 . 
     In the ROM  62 , programs and the like are stored which are used to control various operations of the image read apparatus  1  and ADF  3 . The ROM  63  is used as a storage area or an operation area which temporarily stores therein various kinds of data used when the CPU  61  executes the above programs. The EEPROM  64  is a storage area which stores therein various settings and flags to be continuously stored even after the power supply is turned off. CPU  61 , ROM  62 , RAM  63  and EEPROM  64  cooperate together in realizing a drive control unit according to the invention. 
     The ASIC  66 , according to an instruction from the CPU  61 , generates a phase exciting signal to be electrically applied to the motor  67 , applies this phase exciting signal to the drive circuit  68  of the motor  67 , and electrically applies a drive signal to the motor  67  through the drive circuit  68 , thereby controlling the rotation of the motor  67 . The motor  67  is a motor which, through its rotation in both of the forward and backward directions, can apply a drive force to the pick-up roller  33 , separation roller  34 , feed rollers  35 A,  35 B,  35 C,  35 D, sheet discharge roller  36 , reversible roller (SB roller)  43  and guide flap  50 . The motor  67  serves as the drive source of the ADF  3 . 
     The drive circuit  68  is used to drive the motor  67 , and specifically, upon receiving an output from the ASIC  66 , the drive circuit  68  generates an electric signal for rotating the motor  67 . Upon receiving this electric signal, the motor  67  is rotated in a given rotational direction and the rotational force of the motor  67  is transmitted through the respective drive force transmission mechanisms to the pick-up roller  33 , separation roller  34 , feed rollers  35 A,  35 B,  35 C,  35 D, sheet discharge roller  36 , SB roller  43 , and guide flap  50 , respectively. 
     An image reader  22  is connected to the ASIC  66  and reads the images of a document being fed from the ADF  3  to the scanning position. Based on a control program stored in the ROM  62 , the image reader  22  reads the images of a document. Although not shown, a drive mechanism for reciprocating the image reader  22  is also operated when an output signal from the ASIC  66  is applied thereto. 
     The first front sensor  52 , second front sensor  53 , rear sensor  54  and switchback sensor  55  are connected to the ASIC  66 . In response to the on/off states of the respective sensors, the CPU  61 , based on the control program stored in the ROM  62 , allows the ASIC  66  to output a given output signal to thereby operate the motor  67  and image reader  22 . 
     A sheet feed solenoid  69  is connected to the ASIC  66 . The sheet feed solenoid  69  is used to transmit and cut off the drive force from the motor  67  to the pick-up roller  33  and separation roller  34 . The CPU  61 , according to a control program stored in the ROM  62 , allows the ASIC  66  to output an output signal at a given timing to thereby operate the sheet feed solenoid  69 . The sheet feed solenoid  69  is used to maintain a cutoff state in the transmission of the drive force from the motor  67  to the pick-up roller  33  and separation roller  34 . Specifically, when the sheet feed solenoid  69  is turned on, according to the rotation direction of the motor  67 , the drive force transmission can be switched from the cutoff state over to the transmission state. 
     The respective transmission mechanisms of the drive force from the motor  67  to the pick-up roller  33 , separation roller  34 , feed rollers  35 A,  35 B,  35 C,  35 D, sheet discharge roller  36 , SB roller  43 , and guide flap  50  may have an arbitrary structure using a gear train, an electromagnetic clutch and the like. As shown in  FIG. 1 , in a case where the ADF  3  is disposed on the top surface of the document cover  4 , the feed path  32  and the respective rollers are stored within a box body of the ADF  3 . The motor  67  and drive force transmission mechanisms are also stored within the box body of the ADF  3 . The motor  67  and drive force transmission mechanisms are disposed on an end side of the width direction of the feed path  32  of the ADF  3 . On end sides of the shafts of the separation roller  34 , feed rollers  35 A,  35 B,  35 C,  35 D, sheet discharge roller  36 , reversible roller  43  and guide flap  50 , there are disposed driven gears respectively. When the drive force is transmitted from the motor  67  to the respective driven gears through the respective drive force transmission mechanisms, the respective rollers can be driven. 
     For example, in the case of a drive force transmission mechanism which transmits the drive force from the motor  67  to the separation roller  34 , depending on the forward and backward rotation of the motor  67 , the drive force can be transmitted or cut off. This drive force transmission mechanism, depending on the switching of the rotational direction of the motor  67 , switches the drive force transmission from the motor  67  to the separation roller  34  from the transmission state over to the cutoff state. This drive force transmission mechanism, after the drive force transmission is switched over to the cutoff state, maintains the cutoff state, regardless of the switching of the rotation direction of the motor  67 , until the sheet feed solenoid  69  is turned on. When the sheet feed solenoid  69  is turned on, the drive force transmission mechanism can switch the drive force transmission from the cutoff state over to the transmission state according to the rotation direction of the motor  67 . By the thus structured drive force transmission mechanism, the drive force is transmitted from the motor  67  to the separation roller  34 , and further, the drive force is transmitted from the separation roller  34  to the pick-up roller  33 . 
     By the way, the drive force is transmitted from the motor  67  to the feed rollers  35 A-D, sheet discharge roller  36 , reversible roller  43  and guide flap  50 , through their associated drive force transmission mechanisms. The respective drive force transmission mechanisms can be composed of a gear train, an electromagnetic clutch and the like. However, the structures of these drive force transmission mechanisms are not related directly to the subject matter of the invention, and thus the detailed description thereof is omitted. 
     Now, description will be given below of the image reading operation to be executed by the present image read apparatus  1 . 
     The image read apparatus  1  not only can be used as an FBS but also can use the ADF  3 . However, detailed description regarding the use of the image read apparatus  1  as an FBS is omitted. When using the ADF  3 , it is considered that the document cover  4  is closed with respect to the document placement base member  2 . The opening and closing of the document cover  4  can be detected by sensors or the like disposed on the document placement base member  2 , and when the document cover  4  is closed, the ADF  3  can be used. A document Gn to be read is placed on the input tray  30  in a face-up manner such that the reading surface (first surface) of the document Gn faces upward. Also, the number of documents Gn may be one sheet or two or more sheets. For example, when reading the images of two or more sheets of documents Gn having the same size, the documents Gn are placed on the input tray  30  in such a manner that the first surface of the first document G 1  faces upward, that is, the documents Gn are superimposed on top of one another in a face-up manner. 
     When a read start instruction is input to the image read apparatus  1 , the motor  67  is driven so that the pick-up roller  33 , separation roller  34 , feed rollers  35 A,  35 B,  35 C,  35 D, sheet discharge roller  36  and reversible roller  43  are driven and rotated at their respective given timings. Also, the arm  29  is lowered down to thereby bring the pick-up roller  33  into pressure contact with the document G 1  placed on the input tray  30 . The documents Gn are separated one by one from the remaining documents and are fed into the feed path  32 , starting from the document G 1  that is placed at the highest position, and receives directly the rotation forces of the pick-up roller  33  and separation roller  34 . The fed document Gn is guided by the feed path  32  and is fed to the scanning position, where the images of the document Gn are read by the image reader  22  located below the scanning position. The document Gn, the images of which have been read, is discharged to the output tray  31 . In such an image reading operation, the feed path of the document Gn when the images of one side of the document Gn are read is different from that when the images of both sides of the document Gn are read. Whether the images of one side of the document Gn are read or the images of both sides of the document Gn are read is judged according to a one side reading mode (a one side reading feed mode) or a double-sided reading mode (a double-sided reading feed mode) which have been previously set before the read start instruction is input. 
       FIG. 7  is a flow chart which shows the operation of the image read apparatus  1  in a double-sided reading mode. Also,  FIG. 8  is a flow chart showing a sheet feed operation in the both side reading mode.  FIGS. 9 to 16  are respective typical views showing the feed state of a document Gn in the double-sided reading mode. In the figures, the surface of the document Gn shown to have a numeral “1” in the rear of G is a first surface which is read first in the double-sided reading operation, whereas the surface of the document Gn shown to have a numeral “2” is a second surface to be read later. The first and second surfaces are completely opposite to each other. 
     Before the document Gn is fed, as shown in  FIG. 9 , the guide flap  50  is held at a first guide position, that is, at a position which allows the feed path in the connecting position  38  to be continuous from the scanning position side of the feed path  32  to the output tray  31  side. The guide flap  46  is held at a third guide position, that is, at a position which allows the feed path in the crossing position  40  to be continuous from the input tray  30  side of the feed path  32  to the scanning position side. The guide flap  47  is held at a fifth guide position, that is, at a position which the feed path in the crossing position  40  is continuous from the terminal end  41  side of the bidirectional feed path  39  to the scanning position side of the feed path  32 . 
     When a scan start instruction is input to the image read apparatus  1  (S 1 ), it is checked by the first front sensor  52  whether or not the document Gn is placed on the input tray  30  (S 2 ). When it is found that the document Gn is placed at a given position of the input tray  30 , it is judged that the first front sensor  52  is on. When the document Gn is not placed on the input tray  30 , the first front sensor  52  is off. Depending on the on/off state of the first front sensor  52 , the controller  60  checks whether or not the document Gn is placed on the input tray  30 . When the controller  60  judges that the document Gn is not placed on the input tray  30  (S 2  (N)), the controller  60  controls the liquid crystal display portion  12  of the image read apparatus  1  to display an error message “No document” (S 3 ). When the document Gn is placed on the input tray  30 , the controller  60  carries out a sheet feed operation. 
     In the sheet feed operation, the controller  60  not only drives and rotates the motor  67 , but also turns on the sheet feed solenoid  69 . According to the rotation of the motor  67 , the drive force transmission becomes switchable from the cutoff state to the transmission state. Thus, according to the rotation of the motor  67 , the drive force is transmitted from the motor  67  to the separation roller  34  and also to the pick-up roller  33  (S 11 ). When the drive force from the motor  67  is transmitted, the arm  29  is lowered down and the pick-up roller  33  is pressure contacted with a document G 1  (first document) that is situated at the highest position on the input tray  30 . Also, the pick-up roller  33  and separation roller  34  are respectively rotated in the feed direction, whereby the document G 1  is fed into the feed path  32 . When two or more documents Gn are placed on the input tray  30 , in some cases, with the feeding of the document G 1  existing at the highest position, a document G 2  (second document) existing just below the document G 1  can be fed together with the document G 1 . However, the feeding of the document G 2  is prevented by a separation pad which is disposed at the opposite position of the separation roller  34 . 
     In the feed path  32 , a drive force from the motor  67  is transmitted to the feed rollers  35 A,  35 B,  35 C,  35 D and sheet discharge roller  36 , whereby these respective rollers are rotated so as to feed the document Gn from the upstream side of the feed path  32  to the downstream side thereof, that is, in the feed direction. The document G 1  fed from the input tray  30  to the feed path  32  is nipped between the feed roller  35 A and pinch roller  37 , and thus the rotation force of these rollers is transmitted to the document G 1 , whereby the document G 1  is fed to the crossing position  40  along the feed path  32 . 
     As shown in  FIG. 10 , as the document G 1  is fed to the feed path  32 , the second front sensor  53  detects the feed-direction leading end of the document G 1  and is thereby turned on (S 13  (Y)). Even if the pick-up roller  33  and separation roller  34  are respectively rotated in the feed direction, when the document G 1  is not fed from the input tray  30  to the feed path  32 , the second front sensor  53  is off. Therefore, in a case where, even when a given time T 1  has passed after transmission of the drive force to the pick-up roller  33  and separation roller  34  (S 12  (Y)), the second front sensor  53  is not turned on (S 13  (N)), and the controller  60  controls the liquid crystal display portion  12  to display a sheet feed error (S 14 ). 
     The guide flap  47  closes the feed path from the input tray  30  side of the document feed path  30  to the crossing position  40 , and therefore, the feed-direction leading end of the document G 1  being fed to the crossing position  40  is contacted with the guide flap  47 . As shown in  FIG. 10 , the guide flap  47  is pivoted in such a manner that it is pushed aside by the document G 1  being fed along the feed path  32 , whereby the position of the guide flap  47  is changed from the fifth guide position to the sixth guide position. As a result, the feed from the input tray  30  side of the feed path  32  to the scanning position side is continuous, and at the same time, the feed path to the terminal end  41  side of the bidirectional feed path  39  is closed. Also, the feed path to the connecting position  38  of the bidirectional feed path  39  is kept closed by the guide flap  46 . Therefore, the document G 1 , which has arrived at the crossing position  40  from the input tray  30  side of the feed path  32 , is guided by the guide flaps  46  and  47  and is fed to the scanning position side of the feed path  32  without advancing in either direction of the bidirectional feed path  39 . 
     The peripheral velocities of the respective feed rollers  35 A,  35 B,  35 C,  35 D and sheet discharge roller  36  are set to be faster than the peripheral velocity of the separation roller  34 . Also, in the separation roller  34 , there is provided a round clutch. Thus, the separation roller  34  can be rotated idly around in a non-engaged state. The separation roller  34  is combination rotated at a faster velocity than the originally transmitted peripheral velocity due to the document G 1  which is being fed in pressure contact with the separation roller  34  and nipped by the feed roller  35 A and pinch roller  37 . When the document G 1  is separated from the separation roller  34 , the drive shaft of the separation roller  34  rotates idly at a rate corresponding to the velocity that has accelerated due to the combination rotation, thereby causing the separation roller  34  to stop temporarily. Therefore, a document G 2  to be fed next is not fed to the feed path  32  while the separation roller  34  is temporarily stopped. On the other hand, the document G 1  is fed along the feed path  32  by the respective feed rollers  35 A˜D. As a result of this, as shown in  FIG. 11 , there is formed a given clearance (sheet space) in the feed direction between the first and second documents G 1  and G 2 . 
     As shown in  FIG. 11 , when the document G 1  is fed completely to the feed path  32 , the second front sensor  53  detects the feed-direction trailing end of the document G 1  and is thereby turned off (S 17 ). As described above, the feed distance of the feed path  32  from the second front sensor  53  to the rear sensor  54  is longer than the longitudinally feeding A4 size, that is, the maximum size that allows double-sided reading. According to the present aspect, in addition to this, there is formed a given sheet space between the documents G 1  and G 2 , the feed distance from the second front sensor  53  to the rear sensor  54  being longer than a length obtained by adding the sheet space to 297 mm. Therefore, there is no possibility that, before the second front sensor  53  detects the feed-direction trailing end of the document G 1  and is thereby turned off, the rear sensor  54  can detect the feed-direction leading end of the document G 1  and can be thereby turned on. Supposing that the rear sensor  54  turns on before the second front sensor  53  turns off (S 15  (Y)), the controller  60  is able to judge that the size of the document G 1  is larger than the double-sided readable maximum size. In this case, the controller  60  controls the liquid crystal display portion  12  to error display an error massage to the effect that the size of the document is larger than the readable maximum size (S 16 ). 
     After the document G 1  is completely fed to the feed path  32 , when the drive shaft is rotated idly and the temporary stop of the separation roller  34  is thereby ended, the separation roller  34  is rotated again in the feed direction. With the rotation of the separation roller  34 , the pick-up roller  33  is also rotated in the feed direction. As a result of this, the next document G 2  is fed from the input tray  30  into the feed path  32 . The second front sensor  53  detects the feed-direction leading end of the document G 2  and is thereby turned on (S 19  (Y)). Supposing that the pick-up roller  33  and separation roller  34  are rotated in the feed direction, when the document G 2  is not fed from the input tray  30  to the feed path  32 , the second front sensor  53  is off. Therefore, in a case where, even if a given time T 2  has passed after the second front sensor  53  detects the feed-direction trailing end of the document G 1  and is thereby turned off (S 18  (Y)), the second front sensor  53  does not turn on (S 13  (N)), and the controller  60  controls the liquid crystal display portion  12  to display a sheet feed error display (S 20 ). 
     When the second front sensor  53  detects the feed-direction leading end of the document G 2  and is thereby turned on (S 19  (Y)), the controller  60  cuts off the drive force transmission from the motor  67  to the separation roller  34  (S 21 ). Thus, the pick-up roller  33  and separation roller  34  are caused to stop, and the feed-direction leading end of the document G 2  is pressure contacted with the separation roller  34  and is thereby held by and between the separation roller  34  and separation pad. The controller  60 , even after the drive force transmission from the motor  37  to the separation roller  34  is cut off, does not cut off the drive force transmission to the respective feed rollers  35 A˜D but allows them to rotate in the feed direction. Since the feed-direction leading end of the document G 2  has not arrived at the nip position between the feed roller  35 A and pinch roller  37 , the rotation of the feed roller  35 A is not yet applied to the leading end of the document G 2  to thereby prevent the document G 2  from being fed due to such rotation. Thus, the document G 2  stands still in a state where it is pressed against the separation roller  34 . Also, the document G 1  is fed further along the feed path  32  by the feed rollers  35 A˜D. 
     Cutoff of the drive force transmission from the motor  67  to the separation roller  34 , as described above, is carried out, for example, by switching the rotation of the motor  67 . To switch the rotation of the motor  67 , the controller  60 , for example, outputs a stop instruction or a reversal instruction to the motor  67  which is rotating in the forward direction. On receiving such instruction, the motor  67  stops its rotation, and then rotates in the reversed direction. Such rotation switching of the motor  67  is carried out before the leading end of the document G 1  arrives at the detect position of the rear sensor  54 . Therefore, the leading end of the document G 1  has not arrived at the scanning position and the image reader  22  has not started the image reading of the first surface of the document G 1 . While the image reading of the first surface of the document G 1  is under execution, the rotation switching of the motor  67  is carried out, and the rotation speeds of the feed rollers  35 A˜D are caused to vary due to the stopping operation of the motor  67  in the rotation switching operation or the like. Therefore, the feed speed of the document G 1  being fed at the scanning position is also varied, thereby raising a fear that the image to be read can be deteriorated in quality, for example, the image can be distorted. As in the present aspect, when the rotation switching of the motor  67  is executed before the arrival of the feed-direction leading end of the document G 1  at the scanning position to thereby cut off the drive force transmission to the separation roller  34 , the deterioration of the reading image of the document G 1  can be prevented. 
     In this manner, the controller  60 , when the rear sensor  54  is off, judges that the feed-direction leading end of the document G 1  has not arrived at the scanning position, whereas, when the second front sensor  53  is on, it judges that the document G 2  has been pressure contacted with the separation roller  34 . The drive force transmission to the pick-up roller  33  and separation roller  34  is cut off, not only before the feed-direction leading end of the document G 1  has arrived at the scanning position, but also before the document G 2  is pressure contacted with the separation roller  34  and is fed by the feed roller  35 A and its associated pinch roller  37 . 
     As shown in  FIG. 12 , the document G 1  is fed in such a manner that it reverses downward along the curved portion  32 B of the feed path  32 , while the rear sensor  54  detects the feed-direction leading end of the document G 1  and is thereby turned on. Since the feed-direction leading end of the document G 1  arrives at the scanning position after passage of a given time since it was detected by the rear sensor  54 , the controller  60 , when the rear sensor  54  is turned on and after passage of a given time, allows the image reader  22  to apply a timing signal for start of reading to the image reader  22  to operate the image reader  22 , thereby reading the images of the document G 1  (S 5 ). The document G 1  passes through the scanning position with its first surface facing the image reader  22 , so that the images of the first surface of the document G 1  are read by the image reader  22 . The rear sensor  54  turns off when it detects the feed-direction trailing end of the document G 1 . When the rear sensor  54  turns on, the controller  60 , after passage of a given time, applies a timing signal for end of reading to the image reader  22 , to thereby end the image reading of the first side of the document G 1 . Data on the images of the first side of the document G 1  read by the image reader  22  are stored in a given area of the RAM  63 . 
     As shown in  FIG. 13 , the feed-direction leading end of the document G 1 , the first surface of which has been read, is guided by the guide flap  50  to advance along the connecting position  38  from feed path  32  to the bidirectional feed path  39 , whereby it is switchback-fed (S 6 ). The guide flap  50 , for example, according to the rotation switching of the motor  67 , is varied in position from the first guide position to the second guide position. The switchback sensor  55  detects the feed-direction leading end of the document G 1  which has entered the bidirectional feed path  39 , and is thereby turned on. The reversible roller  43 , to which a drive force has been transmitted from the motor  67 , is rotating in the pull-in direction. 
     Since the guide flap  46  closes the feed path from the bidirectional feed path  39  to the crossing position  40 , the feed-direction leading end of the document G 1  having entered the bidirectional feed path  39  is contacted with the guide flap  46  when it arrives at the crossing position  40 . The guide flap  46 , as shown in  FIG. 13 , is rotated in such a manner that it pushes up the switchback flap  39  onto the feed-direction leading end of the document G 1  to be fed, so that the guide flap  46  changes its position from the third guide position to the fourth guide position. As a result, the feed path from the connecting position  38  side of the bidirectional feed path  39  to the terminal end  41  side of the bidirectional feed path  39  is allowed to be continuous, and at the same time, the feed path to the scanning position side of the feed path  32  is closed. Also, the feed path to the input tray  30  side of the feed path  32  is closed by the guide flap  47 . Therefore, the feed-direction leading end of the document G 1 , which has arrived at the crossing position  40  from the connecting position  38  side of the bidirectional feed path  39 , is guided by the guide flaps  46  and  47  and is fed to the bidirectional feed path  39  without advancing to the feed path  32 . The feed-direction leading end of the document G 1  is nipped between the reversible roller  43  and its associated pinch roller  44 , and is fed to the terminal end  41  side of the bidirectional feed path  39  due to the pull-in-direction rotation of the reversible roller  43 . 
     As shown in  FIG. 14 , after the feed-direction trailing end of the document G 1  has completely entered the terminal end  41  side beyond the crossing position  40  of the bidirectional feed path  39 , the controller  60  switches the rotation of the motor  67 . The switchback sensor  55  detects the feed-direction trailing end of the document G 1  being fed along the bidirectional feed path  39  and is thereby turned off. After passage of a given time, the feed-direction trailing end of the document G 1  passes through the crossing position  40 . Therefore, the controller  60  judges, from the detect signal of the switchback sensor  55  as well as from the counted feed distance or feed time by the feed roller  35 D and reversible roller  43 , that the feed-direction trailing end of the document G 1  has completely entered the terminal end  41  side beyond the crossing position  40  of the bidirectional feed path  39 . Since the document G 1  passes through the crossing position  40  and parts away from the guide flap  46 , the guide flap  46  is rotated downward to return to the third guide position. 
     The feed-direction leading end of the document G 1 , the feed-direction trailing end of which has completely entered the terminal end  41  side from the crossing position of the bidirectional feed path  39 , is projected from the terminal end  41  to the outside of the ADF  3  toward the input tray  30 . As shown in  FIG. 1 , since the top cover  6  of the ADF  3  includes the document support portion  42 , part of the document G 1  is supported by the document support portion  42 . However, as the size of the document  1  increases, the portion of the document  1  that projects from the terminal end  41  also increases. Therefore, for example, when the document G 1  has an A4 size of a longitudinal feeding type which is the maximum size that can be read for both sides, or when the feed distance from the crossing position  40  of the bidirectional feed path  39  to the terminal end  41  is relatively short, there is a fear that the feed-direction leading end of the document G 1  can be contacted with the document G 2  existing on the input tray  30 . Since the feed-direction leading end side of the document G 2  on the input tray  30  is pressure contacted with the separation roller  34  and is held between the separation roller  34  and its associated separation pad, even when the document G 1  projecting from the terminal end  41  is contacted therewith, the document G 2  cannot be moved in the feed direction. Also, in the case where a document abuts on the lower side of the document G 2 , since the document G 1  will not be contacted therewith, unless the document G 2  moves, the document maintains its stationary state. This makes it possible to maintain the placement state of two or more documents including the document G 2  placed on the input tray  30 . As the controller  60  switches the rotation direction of the motor  67 , the document G 1 , which is projected from the terminal end  41  while it is nipped by the reversible roller  43  and pinch roller  44 , is returned to the crossing position  40 . Even when the rotation direction of the motor  67  is switched, a drive force in the feed direction is transmitted to the respective feed rollers  35 A˜D and sheet discharge roller  36 , whereby these rollers are rotated in the feed direction. 
     As shown in  FIG. 15 , the document G 1 , which has been returned from the bidirectional feed path  39 , is contacted in the crossing position  40  with the guide flap  46  held at the third guide position. The guide flap  46  is prevented from pivoting downward from the third guide position. Therefore, the feed path from the terminal end  41  side of the bidirectional feed path  39  to the scanning position side of the feed path  32  is allowed to be continuous, and at the same time, the feed path to the connecting position  38  side of the bidirectional feed path  39  is closed. Also, the guide flap  47  closes the feed path to the input tray  30  side of the feed path  32 . Thus, the document G 1  is guided by the guide flaps  46  and  47  and is fed from the terminal end  41  side of the bidirectional feed path  39  to the scanning position side of the feed path  32  without entering the connecting position  38  side of the bidirectional feed path  39  or the input tray  30  side of the feed path  32 . The document G 1  is returned to the upstream side of the scanning position of the feed path  32  from the bidirectional feed path  39 , whereby the document G 1  is fed again along the feed path  32  with the leading and trailing ends thereof reversed when compared with the state where the document G 1  was initially fed along the feed path  32 . In this manner, the document G 1  is switchback-fed. The document G 1  is fed along the feed path  32  with its second side facing the scanning position. 
     When the feed-direction leading end of the document G 1  is detected by the rear sensor  54  and the present feed-direction leading end arrives at the scanning position, as shown in  FIG. 16 , the controller  60  allows the image reader  22  to scan the images of the second side of the document G 1  (S 7 ). After the second side thereof has been scanned, the feed-direction leading end of the document G 1  is guided by the guide flap  50  and advances in the connecting position  38  from the feed path  32  to the bidirectional feed path  39 . When the feed-direction trailing end of the document G 1  is detected by the rear sensor  54  and the present trailing end arrives at the scanning position, the controller  60  ends the image reading of the second side of the document G 1  by the image reader  22 . Data on the images of the second side of the document G 1  scanned by the image reader  22  are stored in a given area of the RAM  63 . 
     The feed-direction leading end of the document G 1  having arrived at the crossing position  40 , similarly to  FIG. 13 , pushes up the guide flap  46  to change the guide flap  46  from the third guide position to the fourth guide position and advances in the crossing position  40  to the terminal end  41  side of the bidirectional feed path  39 . Similarly to  FIG. 14 , after the feed-direction trailing end of the document G 1  has completely entered the terminal end  41  side beyond the crossing position  40  of the bidirectional feed path  39 , the controller  60  switches the rotation direction of the motor  67  and rotates the reversible roller  43  in the return direction to thereby return the document G 1  to the crossing position  40 . Similarly to  FIG. 15 , the document G 1  having returned from the bidirectional feed path  39  is guided by the guide flaps  46  and  47  and is fed from the terminal end  41  side of the bidirectional feed path  39  to the scanning position of the feed path  32 . Therefore, the document G 1  is fed again to the feed path  32  while the leading and trailing ends thereof are reversed again, that is, in the state where the document G 1  was initially fed to the feed path  32  (S 8 ). In this switchback feeding operation, in some cases, there is a possibility that the feed-direction leading end of the document G 1  can be contacted with the document G 2  existing on the input tray  30 . As described above, since the feed-direction leading end side of the document G 2  on the input tray  30  is in pressure contact with the separation roller  34  and its associated friction pad arranged at the opposite direction of the separation roller  34 , the placement state of the document Gn can be maintained on the input tray  30 . 
     The document G 1 , which is switchback fed again, passes through the scanning position with its first side facing the scanning position, is guided in the connecting position  38  to the output tray  31  side by the guide flap  50 , and is then discharged with its first side facing downward to the output tray  31  by the sheet discharge roller  36  (S 9 ). Since the next document G 2  is placed on the input tray  30  (S 20  (Y)), the first front sensor  52  is on. The controller  60  turns on the sheet feed solenoid  69  to thereby provide a state in which the drive force transmission from the motor  67  to the separation roller  34  can be switched from the cutoff state over to the transmission state according to the rotation of the motor  67 , and transmits the drive force (S 11 ), thereby rotating the pick-up roller  33  and separation roller  34  in the feed direction. As described above, since the document G 2  is pressure contacted with the separation roller  34  by the separation roller  34  and is thereby made to stand still at a given position on the input tray  30  regardless of its contact with the document G 1 , as the pick-up roller  33  and separation roller  34  are rotated, the document G 2  can be fed positively to the feed path  32 . Therefore, there is no possibility that a sheet feed error can happen due to the shifted position of the document G 2 . With the document G 2  fed to the feed path  32 , there is executed a double-sided image reading operation similar to the above-mentioned case. 
     In the present aspect, description has been given of the double-sided image reading operation by the image read apparatus  1 , assuming that each document is discharged to the output tray  31  in a state where the order of two or more documents Gn placed on the input tray  30  is maintained. However, when it is not necessary to match the order of the documents Gn placed on the input tray  30  to the order of the documents Gn discharged to the output tray  31 , after the documents Gn are fed with their respective second sides facing the scanning position, without moving the documents Gn back to the bidirectional feed path  39  again, the documents Gn may be fed along the connecting position  38  to the output tray  31  side to thereby discharge the documents Gn to the output tray  31 . In this case, although the order of the documents Gn in the output tray  31  is not maintained, the last switchback feeding operation can be saved, thereby being able to shorten the time necessary to scan the images of both sides of the documents Gn. 
     Thus, according to the present aspect, the controller  60  cuts off the drive force transmission to the pick-up roller  33  and separation roller  34  at a timing which is not only before the feed-direction leading end of the document G 1  being fed along the feed path  32  arrives at the scanning position but also before the feed-direction leading end side of the document G 2  is pressure contacted with the separation roller  34  and the feed-direction leading end of the document G 2  is fed by the feed roller  35  and its associated pinch roller  37  respectively disposed at the most-upstream position of the feed path  32 . Thus, in the switchback feeding operation, even when the leading end of the document G 1  projected from the bidirectional feed path  39  is contacted with the document G 2  existing on the input tray  30 , the placement state of the document G 2  is maintained.