Abstract:
An automatic document conveyance apparatus includes: a document feeding section on which a plurality of documents can be placed, for feeding documents one by one therefrom; a zigzag reversal path through which the document fed from the document feeding section is reversed with respect to front and back sides of each of the documents; a reading position forming device for forming an image reading position of the document fed zigzag from and conveyed to the zigzag reversal path; and a document ejection tray on which the document passed through the reading position forming device and ejected through an ejection path is placed. The document fed from the document feeding section is conveyed to the zigzag reversal path at which the document is reversed, the document is fed zigzag to the reading position at which one side of the document is read, the document is conveyed again to the zigzag reversal path at which the document is reversed again, the document is fed zigzag again from the zigzag reversal path to the reading position at which the other side of the document is read, and then the document is ejected from the reading position to the document ejection tray.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an automatic document conveyance apparatus used for conveying a document to a reading position for reading the document, and particularly to an automatic document conveyance apparatus by which the document can be conveyed such that obverse and reverse sides of the document are reversed, in order to read images on the obverse and reverse sides of the document. The automatic document conveyance apparatus according to the present invention is used for a copier, a facsimile device, and the like. 
     Preferred characteristics for the above-described automatic document conveyance apparatus are a small size, efficient reversing and conveying capabilities, and so on. As an automatic document conveyance apparatus to satisfy such requirements, for example, there is an apparatus disclosed in Japanese Tokkaihei No. 7-175279. 
     The automatic document conveyance apparatus disclosed in Japanese Tokkaihei No. 7-175279 has a reversal conveyance path to reverse both sides of the document, and after the document is conveyed such that its first side is read, the document is conveyed to the reversal conveyance path, and is reversed on the reversal conveyance path, and conveyed again to the reading position. The document whose second side has been read, is further reversed to align the page order at the delivery. 
     As described above, in the automatic document conveyance apparatus disclosed in the above patent publication, it is required that the document passes through the conveyance path 3 times in total in order to achieve reading of both sides thereof. Accordingly, in the conventional automatic document conveyance apparatus disclosed in the above patent publication, efficiency of the reading operation at the time of reading the both sides is not good, and high speed reading can not be performed, which is a problem. 
     SUMMARY OF THE INVENTION 
     Accordingly, in order to enable two-side reading, an object of the present invention is to solve the above-described problem of the conventional technology in the automatic document conveyance apparatus having the reversal conveyance function. 
     The above-described object of the present invention is attained by an automatic document conveyance apparatus which has: a sheet feeding source on which a large number of documents can be placed and which can feed the document one by one sheet; a reversal path through which the obverse and reverse sides of the document fed from the sheet feeding source is reversed; a reading position forming means for forming the reading position of the document which is fed from the reversal path and conveyed; and a delivery sheet tray on which documents, which pass through the reading position forming means and are delivered, are stacked, wherein the document fed from the sheet feeding source is conveyed onto the reversal path, and after the obverse and reverse sides of the document are reversed, the document is fed to the reading position forming means and the one side of the document is read, and the document whose one side is read is conveyed again onto the reversal path, and after the obverse and reverse sides of the document are reversed again, the document is fed again to the reading position and the other side of the document is read, and the document whose other side is read is delivered from the reading position forming means to the delivery tray. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view of an automatic document conveyance apparatus according to Embodiment 1 of the present invention. 
     FIG. 2 is a sectional view at the time of reversal before reading-out of the automatic document conveyance apparatus shown in FIG.  1 . 
     FIG. 3 is a sectional view at the time of reverse side reading of the automatic document conveyance apparatus shown in FIG.  1 . 
     FIG. 4 is a sectional view at the time of obverse side reading of the automatic document conveyance apparatus shown in FIG.  1 . 
     FIG. 5 is a sectional view at the time of one side reading of the automatic document conveyance apparatus shown in FIG.  1 . 
     FIG. 6 is a sectional view at the time of reversal before reading-out of the automatic document conveyance apparatus according to Embodiment 2 of the present invention. 
     FIG. 7 is a sectional view at the time of reverse side reading of the automatic document conveyance apparatus shown in FIG.  6 . 
     FIG. 8 is a sectional view at the time of obverse side reading of the automatic document conveyance apparatus shown in FIG.  6 . 
     FIG. 9 is a sectional view at the time of one side reading of the automatic document conveyance apparatus shown in FIG.  6 . 
     FIG. 10 is a sectional view at the time of reversal before reading-out of the automatic document conveyance apparatus according to Embodiment 3 of the present invention. 
     FIG. 11 is a sectional view at the time of reverse side reading of the automatic document conveyance apparatus shown in FIG.  10 . 
     FIG. 12 is a sectional view at the time of obverse side reading of the automatic document conveyance apparatus shown in FIG.  10 . 
     FIG. 13 is a sectional view at the time of one side reading of the automatic document conveyance apparatus shown in FIG.  10 . 
     FIG. 14 is a sectional view of the automatic document conveyance apparatus of a more preferable Embodiment applied to the Embodiment 2 of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment 1 
     (1) The structure of the automatic document conveyance apparatus. 
     FIG. 1 is a sectional view showing the structure in which an automatic document conveyance apparatus of Embodiment 1 is mounted in the frame of an image forming apparatus or the like. 
     As shown in the drawing, an automatic document conveyance apparatus  2  is provided in a frame  1  of the image forming apparatus. In a portion of the automatic document conveyance apparatus  2 , a sheet feeding tray  3  on which document sheets P are placed and fed is provided on a little slanting condition toward the sheet feeding direction. 
     On the sheet feeding tray  3 , a side plate  3 A to regulate the side end of the document sheet P and sensors MS 1  and MS 2  to detect the length of the document sheet P (the length in the document conveyance direction) are provided. Only one side plate  3 A is shown in the drawing, however, the side plates  3 A are provided on both sides of the sheet feeding tray  3 , and can move in the width direction of the document, and by this movement position, the width of the document sheet P is detected. 
     Further, a pick-up roller  4  to feed the documents on the sheet feeding tray  3  from the uppermost document sheet P, is provided. A pressure plate  5  to press the document sheet P to the pick-up roller  4  is provided, and this system is structured such that the leading edge of the document sheet P surely contacts with the pick-up roller  4 . 
     Next, a separation roller  6  and a retard roller  7  are oppositely provided so that the document sheet P fed by the pick-up roller  4  can be surely conveyed one by one sheet. 
     A pair of register rollers  8  and  9  are provided so that one document sheet P conveyed by the separation roller  6  is stopped a time to have sheet feeding timing, and a switching guide member  12  to switch the document path to either one of a guiding path  10  for the time of two-sided document reading-out or a guiding path  11  for the time of one side document reading-out, which are respectively formed on the downstream side of the register rollers  8  and  9 , is provided. A pair of conveyance rollers  13  and  14  to convey the document sheet P to the first reversal guiding path  111  formed on the downstream side of the guiding path  10  are provided, and reversal rollers  15  and  16 , which are rollers rotatable in the forward and backward direction, and which receive the document sheet P reversed on the first reversal guiding path  111 , convey it to the reversal section  18 , and re-feed the document sheet P, are provided. 
     A switching guide member  19  which conducts reversal guiding of the document sheet p, and by which the document sheet P can be re-fed onto the second reversal guiding path  20 , is provided on the shaft of the reversal roller  15 . Further, the reversal roller  15  contacts with the reversal roller  16  when the document sheet P is conveyed, and these rollers are structured such that they can be separated from each other with the interval with which  2  document sheets can pass by each other. Further, a document sheet guide member  16 A provided on the shaft of the reversal roller  16  is located at a position at which the guiding path  11  is always closed. Further, a conveyance roller  17  to convey the document sheet P conveyed from the guiding path  11  is provided in contact with the reversal roller  16 . 
     A pair of reversal rollers  21  and  22  to convey the document sheet P to an image reading exposure section R (refer to FIGS. 2 through 5) are provided on the second reversal guiding path  20  formed in the reversal conveyance direction of the document sheet P reversal-fed by the reversal rollers  15  and  16 , and further, this system is structured such that the document sheet P conveyed to the image reading exposure section R is conveyed while being nipped between a platen roller  23  and a sheet guide plate  24  formed of a transparent material. This system is structured such that irradiation light rays are irradiated by an irradiation lamp  25  onto the document sheet p passing the document reading position, the reflected light from the document is reflected by a mirror  26 , and guided to an image reading section R 1  through a lens L, and document reading is performed. 
     A switching guide member  28  to switch whether the document sheet P, reading of which has been completed, is guided to a guiding path  27  and a delivery sheet guiding path  30  as it is, or whether the document sheet P is guided again to a guiding path  112  to convey the document sheet P to the first reversal guiding path  111 , is provided. 
     The document sheet P guided by the delivery sheet guiding path  30  is delivered to a delivery sheet section  32  by a pair of conveyance rollers  14  and  29 , and a delivery sheet roller  31  provided opposite to the register roller  9 . 
     The automatic document conveyance apparatus according to the present embodiment is provided with sensors S 1 , S 2  and S 3  to detect the passage of the document (refer to FIGS.  2  through  5 ). 
     The sensor S 1  is provided on just upstream side of the first register rollers  8  and  9 , and by detecting the leading edge of the document, the rotation of the separation roller  6  is stopped. A time period of the stop of the separation roller  6  is set such that a loop of the document is formed on the upstream side of the first register rollers  8  and  9 . The sensor S 1  further detects the passage of the trailing edge of the document. The length of the document is detected from the time period passed from the re-start of register rollers  8  and  9  to the detection of the passage of the trailing edge. Further, from the detection of the trailing edge of the document, as will be described later, the time to stop the reversal rollers  15  and  16  is determined. 
     The sensor S 2  detects the leading edge and trailing edge of the document and determines the document reading start time and the reading completion time. 
     The sensor S 3  detects the delivery of the document sheet P, and also has the jam detection function. 
     (2) Two-side reading 
     Next, operations to read images on two sides of the two-sided document sheet P by the automatic document conveyance apparatus  2  will be described. 
     FIGS. 2-4 are sectional views of the automatic document conveyance apparatus, and show each step in two-side reading processes to read both of the obverse and reverse sides of the document sheet P. 
     As shown in FIG. 2, on the sheet feeding tray  3 , the document sheets P are placed such that the obverse sides show the odd numbered pages and the reverse sides show the even numbered pages, that is, obverse sides of the document sheets P face upward, and the document sheets P show page 1, 2, 3, . . . , n, in regular order from above, and the sheet feeding starts by the pick-up roller  4  in this state. 
     The first document sheet is fed by the rotation of the pick-up roller  4  and the separation roller  6 , however, a plurality of document sheets P of the second and the subsequent sheets are regulated by the retard roller  7  and the regulation member  5 A, and only the first document sheet P is conveyed by the separation roller  6 , and after being conveyed to the nip portion between register rollers  8  and  9 , the document sheet P is stopped once, and the conveyance of the document sheet P is started by the rotation of the register rollers  8  and  9 . 
     The loop of the leading edge portion of the document sheet P is formed at just the upstream side of the first registration rollers  8  and  9 . The time period necessary for formation of the loop, that is, the time period from the time when the leading edge of the document sheet P contacts with the first register rollers  8  and  9  to the time when the separation roller  6  stops, is determined from the leading edge detection time of the sensor  1 . 
     As shown in the drawing, the switching guide member  12  is placed at a position shown by a solid line when the conveyance starts in the case of the two-sided document reading, and guides the document sheet P to the guiding path  10  side. The document sheet P passes the guiding path  10 , and is conveyed to the first reversal guiding path  111  by the conveyance rollers  13  and  14 . Next, while being guided by the switching guide member  19  placed at the position shown by a solid line, the document sheet P is conveyed to a reversal section  18  by the reversal rollers  15  and  16  which are rotated in the direction shown by a solid line. 
     As described above, in the state that the obverse side of the first document sheet P, that is, the first page P 1  faces downward, and the reverse side, that is, the second page P 2  faces upward, its trailing edge is held by the reversal rollers  15  and  16 , and stops once. 
     Timing of stop of the reversal rollers  15  and  16  is obtained from the detection signal of the document trailing edge by the sensor S 1 . 
     Next, as shown in FIG. 3, conveyance of the document sheet P located in the reversal section  18  is started from the top which is the trailing edge of the document sheet. In this case, the switching guide member  19  is switched to a position shown by a one-dotted chain line and the second reversal guiding path  20  is opened, the document sheet P is conveyed on the second reversal guiding path  20 , and just after the leading edge of the document is detected by the sensor S 2 , conveyance rollers  21  and  22  are stopped once. 
     Next, the document sheet P is conveyed to the image reading exposure section R by the start of rotation of the conveyance rollers  21  and  22 . At the image reading exposure section R, the second page P 2  of the document sheet P is irradiated by the irradiation of the irradiation lamp  25 , while the document sheet P is being conveyed by the platen roller  23 , and an image on the second page P 2  is successively read out through the mirror  26  and the lens L at the image reading section R 1 . 
     After a predetermined time period from the start of rotation of the conveyance rollers  21  and  22 , the document reading start signal is sent to the image forming apparatus. 
     Next, the guiding path  112  is opened by the switching guide member  28  located at a position shown by one-dotted chain line, and the document sheet P whose second page P 2  has been read, is conveyed from the guiding path  112  to the reversal section  18  through the first guiding path  111  again by reversal rollers  15  and  16 . Herein, the second page P 2  of the document sheet P is turned to the reverse side and the first page P 1  is arranged on the obverse side, and further, the document sheet P is stopped in the state that the leading edge portion of the document sheet P is nipped between the reversal rollers  15  and  16 . 
     As shown in FIG. 4, the conveyance of the document sheet P, which is reversed by reversal rollers  15  and  16 , is started again from one end of the document sheet P from the reversal section  18 . On the other hand, when sheet re-feeding of the first document sheet P from the reversal section  18  is started, sheet feeding of the second document sheet P stacked on the sheet feeding tray  3  is started by the pick-up roller  4 , and the document sheet P is stopped once at the register rollers  8  and  9 . The first document sheet P is conveyed on the second reversal guiding path  20 , and stopped when the leading edge of the document is detected by the sensor S 2 . 
     Next, the conveyance rollers  21  and  22  are rotated and conveyance of the document sheet P is started, and when the conveyance of the conveyance rollers  21  and  22  is started, reversal rollers  15  and  16  stop their rotation, and both rollers are separated from each other. When conveyance rollers  21  and  22  start their rotation, conveyance of the document sheet P is started, and in parallel with this conveyance, register rollers  8  and  9  are rotated, and the second document sheet P is guided by the switching guide member  12 , and conveyed onto the first reversal guiding path  111  by conveyance rollers  13  and  14  through the guiding path  10 . 
     At this time, the trailing edge of the first document sheet P remains at the position of the reversal rollers  15  and  16 , and because the reversal roller  15  moves in the arrowed direction, and the reversal roller  15  and the reversal roller  16  are separated from each other, the leading edge of the second document sheet P is brought into contact with the trailing edge of the first document sheet P, however, these document sheets P are smoothly conveyed to the reversal section  18 . 
     Next, the first document sheet P conveyed by conveyance rollers  21  and  22 , is conveyed to the image reading exposure section R, and in the image reading exposure section R, the first page P 1  of the document sheet P is guided onto the surface of the sheet guiding plate  24  while being conveyed by the platen roller  23 , and the first page P 1  is irradiated by the irradiation lamp  23 , and the image of the first page P 1  is successively read through the mirror  26  and the lens L in the image reading section R 1 . 
     The document sheet P passed through the image reading exposure section R, is guided by the switching guide member  28  which is switched to a position shown by a solid line, and passes the guiding path  27 , and is conveyed onto the delivery sheet guiding path  30  by a pair of conveyance rollers  14  and  29 , and is delivered by the register roller  9  which functions as a delivery sheet roller, and the delivery sheet roller  31 . The document sheet P is stacked on the delivery sheet section  32  in the state that the first page P 1  faces the lower side and the second page P 2  faces the upper side. 
     The sensor S 3  detects the trailing edge of the document sheet P to be delivered and outputs a delivery sheet signal. When the delivery sheet signal is not outputted within the predetermined time corresponding to the size of the document sheet P, this situation is judged to be a jam. 
     Next second document sheet P is the same as described above, and is placed in the state that the third page P 3  faces the lower side, and the fourth page P 4  faces the upper side, and even after images of a large number of two-sided document sheets are read out, the document sheets are delivered in the state that the page order is successively aligned. 
     In a fixed size mode in which one kind of size of document sheets P are placed on the sheet feeding tray  3 , and the document sheet p is conveyed to the reading position and read, and a mixed-size mode in which various-sized document sheets P are placed on the sheet feeding tray  3 , and the document sheet p is conveyed to the reading position and read, the above-described processes of conveyance and reading of the document sheet P are performed. 
     However, detection of the document size in the fixed size mode is carried out by using the side plate  3 A, and sensors MS 1  and MS 2 . From the combination of the position information of the side plate  3 A and on/off information of sensors MS 1  and MS 2 , the longitudinal placement (the state that the document conveyance direction corresponds to the long side of the document) and the lateral placement (the state that the document conveyance direction corresponds to the short side of the document) are detected relating to each size of A 3 , A 4 , B 4  and B 5 . 
     In the mixed-size mode, the document length is detected by the sensor S 1  in the process in which the document sheet P is conveyed from register rollers  8  and  9  to the reversal section  18 , and the document size is calculated from the detected length. 
     (3) One side reading 
     FIG. 5 is a sectional view of the automatic document conveyance apparatus in the reading process of the image on the one side of the document. 
     In the one side reading, the document sheet P is placed on the sheet feeding tray  3  with its surface facing upward. Next, the document sheet P is fed by the pick-up roller  4  and successively conveyed one by one sheet by the separation roller  6 , and is guided by the switching guide member  12  which is switched to a position shown by a one-dotted chain line, and conveyed onto the guiding path  11  by register rollers  8  and  9 . 
     Next, the document sheet P is directly conveyed onto the second reversal guiding path  20  by the conveyance roller  17  which is in contact with the reversal roller  16 . In this case, the switching guide member  19  is switched to a position shown by a one-dotted chain line, and the document sheet P is guided from the second reversal guiding path  20  to conveyance rollers  21  and  22  and conveyed to the image reading exposure section R. In the image reading exposure section R, the image on one side, that is, the obverse side image is irradiated by the irradiation lamp  25 , and the image is successively read through the mirror  26  and the lens L in the image reading section R 1 . 
     The document sheet P passed the image reading exposure section R passes the guiding path  27  which is opened by the switching guide member  28  which is located at the position shown by a solid line, and is conveyed onto the delivery sheet guiding path  30  by a pair of conveyance rollers  14  and  29 , and is delivered onto the delivery sheet section  32  in the state that the image of the first document sheet P faces downside. 
     In the same manner, the second document sheet P is also conveyed from the guiding path  11  to the second reversal guiding path  20 , and after the image is read in the image reading exposure section R, the image on the document sheet P faces downward and is delivered onto the delivery sheet section  32  in the state that pages are aligned. 
     The above-described document conveyance process is a conveyance process in the fixed size mode in which a kind of document sheets are placed on the sheet feeding tray, and the document size detection in this mode is performed on the sheet feeding tray  3  by the side plate  3 A and sensors MS 1  and MS 2 . 
     In the mixed-size mode in which various-sized document sheets are placed on the sheet feeding tray, and the document conveyance and reading are conducted, the document is conveyed in the process which will be described below. 
     The document sheet P conveyed by the start of rotation of register roller  8  and  9 , is conveyed by conveyance rollers  21  and  22  through the second reversal guiding path  20 , and reaches the delivery sheet roller  31  through the platen roller  23 . In this conveyance process, document reading is not conducted, and document size detection by the sensor S 1  is conducted. The document size is detected from the time period passed from the start of rotation of register rollers  8  and  9  to the detection of the trailing edge of the document by the sensor S 1 . Conveyance of the document is stopped after a predetermined time period passed from detection of the trailing edge of the document by the sensor S 1 . When the document is stopped, the trailing edge of the document is located at a position shown by E. 
     Next, conveyance rollers  21  and  22  start the rotation in the direction as shown by a dotted line, and the document sheet P is conveyed to the reversal section  18 . The conveyance is stopped when the leading edge (the trailing edge in the process conveyed from conveyance rollers  21  and  22  to the reversal section  18 ) of the document sheet P is detected by the sensor S 2 . That is, the leading edge of the document is located at a position shown by F and the document conveyance is stopped. 
     Next, conveyance rollers  21  and  22  start the rotation in the directions shown by solid lines, and convey the document sheet P toward the delivery sheet roller  31  through the platen roller  23 . In this conveyance process, reading is conducted. 
     Embodiment 2 
     Next, although it is basically the same as the above-described embodiment 1, an automatic document conveyance apparatus of the embodiment in which the conveyance path of the document sheet P is varied, will be described. 
     (1) Two-side reading 
     FIGS. 6 through 8 are sectional views of the automatic document conveyance apparatus in two-side reading process. 
     As shown in FIG. 6, in the same manner as described above, two-sided document sheets P are placed, and sheet feeding is started by the pick-up roller  4  in this state. 
     Next, in the same manner as described above, only the first sheet P is conveyed by the separation roller  6  to a portion between register rollers  8  and  9 , after that, the document sheet P is stopped once, and conveyance of the document sheet P is started by the rotation of register rollers  8  and  9 . 
     As shown in the drawing, the switching guide member  12  is moved in the arrowed direction and set in a position shown by a one-dotted chain line and is switched to the guiding path  10  side for the time of two-sided document reading, and the document sheet P passes through the guiding path  10  and conveyed to the first reversal guiding path  111 , and conveyed to the reversal section  18  by reversal rollers  15  and  16 . 
     In such a manner as described above, in the reversal section  18 , the document sheet P is placed such that the first side P 1  of the first document sheet P faces downward and the second page P 2  faces upward, and reversal rollers  15  and  16  are stopped in the state that these rollers  15  and  16  nip the trailing edge of the document sheet P. 
     Next, as shown in FIG. 7, conveyance of the first document sheet P which is reversed by the reversal rollers  15  and  16 , is started from the trailing edge of the document sheet P, from the reversal section  18 . In this case, the switching guide member  12  is at the position shown by a one-dotted chain line, and the second reversal guiding path  20  is opened. The document sheet P is conveyed to the second reversal guiding path  20 , and is conveyed by a pair of conveyance rollers  40  and conveyance rollers  21  and  22 , and just after the leading edge of the document sheet P is detected by the sensor S 2 , the conveyance is stopped once. 
     When the rotation of conveyance rollers  21  and  22  is started, the document sheet P is conveyed to the image reading exposure section R. In the image reading exposure section R, the second side P 2  of the document sheet P is guided by the surface of the sheet guiding plate  24  while the document sheet P is conveyed by the platen roller  23 , and the second side P 2  is irradiated by the irradiation lamp  25 , and the image on the second side P 2  is successively read through the mirror  26  and lens L in the image reading section R 1 . 
     Next, the document sheet P is conveyed to the reversal section  18  by reversal rollers  15  and  16  which are rotated in the direction shown by a solid line, through the first reversal guiding path  111  again, from the guiding path  112  which is opened by the switching guide member  28  which is at a position shown by a solid line. Herein, the document sheet P is placed such that the second page P 2  of the document sheet P is on the lower side and the first page P 1  is on the upper side, and further, the document sheet P is stopped in the state that its trailing edge is nipped between reversal rollers  15  and  16 . 
     Next, as shown in FIG. 8, the reversal rollers  15  and  16  start the rotation in the direction shown by a dotted line, and conveyance of the document sheet P is started form its trailing edge as the top of the conveyance. In the conveyance process of the first document sheet P, the second document sheet P placed on the sheet feeding tray  3  is fed by the pick-up roller  4 , and stops once at register rollers  8  and  9 . The first document sheet P is reversal-conveyed on the first reversal guiding path  111  by reversal rollers  15  and  16 , and conveyed on the second reversal guiding path which is opened by the switching guide member  12 , by the conveyance rollers  40 , and just after the leading edge of the document is detected by the sensor S 2 , the document sheet P is stopped once. Conveyance of the document sheet P is started when conveyance rollers  21  and  22  start the rotation, and the stopped second document sheet P is guided to the switching guide member  12  by the rotation of register rollers  8  and  9 , and is conveyed from the guiding path  10  onto the first reversal guiding path  111 . When conveyance rollers  21  and  22  are rotated and the conveyance is started, reversal rollers  15  and  16  are separated from each other, and holding of the document sheet P is released. 
     Herein, the trailing edge of the first document sheet P remains at a position of reversal rollers  15  and  16 , and while the trailing edge of the first document sheet P and the leading edge of the second document sheet P are in contact with each other in the first reversal guiding path  111 , these documents P are conveyed. 
     Further, the leading edge of the second document sheet P is conveyed to the position of reversal rollers  15  and  16 , and even if the trailing edge of the first document sheet P remains between the reversal rollers  15  and  16 , because the reversal roller  15  is moved in the arrowed direction in FIG. 8, and the reversal rollers  15  and  16  are separated from each other, these document sheets P are smoothly conveyed to the reversal section  18  even if the leading edge of the second document sheet P is being in contact with the trailing edge of the first document sheet P. 
     Next, the first document sheet P conveyed by conveyance rollers  21  and  22 , is conveyed to the image reading exposure section R, and while being conveyed by the platen roller  23  in the image reading exposure section R, the document sheet P is guided onto the sheet guiding plate  24  surface, and the first page P 1  of the document sheet P is irradiated by the irradiation lamp  25 , and the image of the first page P 1  is successively read out in the image reading section R 1  through the mirror  26  and the lens L. 
     The document sheet P whose first page image is read out, is conveyed to the delivery sheet guiding path  30  by conveyance rollers  14  and  29 , and the first page P 1  of the first document sheet P is delivered with its surface facing downward onto the delivery sheet section  32  by a pair of delivery sheet rollers  31  and  31 A. 
     In such a manner as described above, the document sheet P on both sides of which images are formed, is delivered with the first page P 1  facing the lower side, and also the second document sheet P is delivered in the same manner with its third page P 3  facing the lower side, and a large number of document sheets P are successively conveyed and after images on obverse and reverse sides have been read out, the document sheets P are delivered in the state that the page order is aligned. 
     The document conveyance and reading in the fixed size mode, and the document conveyance and reading in the mixed-size mode are the same as those in the case of Embodiment 1, and there is no difference in the conveyance process of the document sheet P between both modes. 
     (2) One side reading 
     FIG. 9 is a sectional view of Embodiment 2 in the case of one side document reading. 
     Also in this case, the document sheet is placed on the sheet feeding tray  3  with the image of the document sheet P facing the upside. The document sheet P is fed from the first sheet of the document sheet P by the pick-up roller  4 , and is successively conveyed one by one sheet as described above, and conveyed onto the guiding path  11  by register rollers  8  and  9  after the guiding path  11  is opened by the switching guide member  12  set at the position shown by a solid line. 
     Next, the document sheet P is guided from the second reversal guiding path  20  by conveyance rollers  21  and  22  and conveyed to the image reading exposure section R. In the image reading exposure section R, the surface of the document sheet P is irradiated by the irradiation lamp  25 , and the image is read out in the image reading section R 1  through the mirror  26  and the lens L. The document sheet P passed the reading position is conveyed to the delivery sheet guiding path  30  by a pair of conveyance rollers  14  and  29  because the delivery sheet guiding path  30  is opened by the switching guide member  28  which is set at the position shown by a one-dotted chain line, and is delivered onto the delivery sheet section  32  in the state that the image of the first document sheet P faces the lower side by delivery rollers  31  and  31 A. 
     In the same manner, the second and subsequent document sheets P are conveyed from the guiding path  11  to the second reversal guiding path  20 , and after the image is read out in the image reading exposure section R, the image on the document sheet P faces down side and delivered onto the delivery sheet section  32  in the state that images and pages are aligned. 
     In the one side reading in the fixed size mode, the document size is detected by the side plate  3 A and micro-switches MS 1  and MS 2  in the same manner as in Embodiment 1. 
     Next, the one side reading in the mixed-size mode will be described. 
     The document sheet P conveyed by register rollers  8  and  9 , is conveyed by the conveyance roller  40 , and conveyance rollers  21  and  22 , guided by the switching guide member  28  located at the position shown by a dotted line, and conveyed onto the delivery sheet guiding path  30 . The document size is detected by the sensor S 1  in this conveyance process. That is, the document size is detected from the time period passed from the start of rotation of register rollers  8  and  9  to the detection of the trailing edge of the document by the sensor S 1 . In this conveyance process, reading is not carried out. 
     The conveyance of the document is stopped after a predetermined time period from the detection of the trailing edge by register rollers  8  and  9 , and the document sheet P is stopped in the state that its trailing edge is at a position shown by E. 
     Next, conveyance rollers  21  and  22  are reversely rotated as shown by a dotted line, and the document sheet P is reversely conveyed. The document sheet P is guided by the switching guide member  12  located at the position shown by a dotted line to the first reversal guiding path  111 , conveyed to the reversal section  18 , and by the detection of the trailing edge by the sensor S 2 , the leading edge (the trailing edge in the process conveyed from conveyance rollers  21  and  22  to the reversal section  18 ) is located at a position shown by a point F and stopped. 
     Next, conveyance rollers  21  and  22  are reversely rotated in the direction shown by a solid line and convey the document sheet P, and the document sheet P is conveyed through the platen roller  23 , and reading is carried out. The document sheet P is further conveyed through the delivery sheet guiding path  30 , and delivered onto the delivery sheet section  32  by the delivery sheet roller  31 . 
     Further, FIG. 14 is a sectional view of the automatic document conveyance apparatus showing a more preferable Embodiment applied to the Embodiment 2 of the present invention. The main difference from the Embodiment 2 is that there are disposed, for example, roll RL 1 , RL 2  in the conveyance path of a document in which curvature of the conveyance path is relatively large and friction resistance tends to be applied to the document, thereby conveyance performance can be improved. 
     Embodiment 3 
     (1) Two-side reading 
     Next, the automatic document conveyance apparatus of Embodiment 3 which is basically the same as Embodiments 1 and 2 and in which the conveyance path of the document sheet P is varied, will be described. 
     As shown in FIG. 10, two-sided document sheet P is placed in the same manner as described above, and sheet feeding is started by the pick-up roller  4  in this state. 
     Next, in the same manner as described above, only the first document sheet P is conveyed by the separation roller  6 , and after conveyed to a portion between register rollers  8  and  9 , the document sheet P is stopped once, and conveyance of document sheet P is started by rotation of register rollers  8  and  9 . 
     As shown in FIG. 10, the switching guide member  12  is moved in the arrowed direction and set at the position shown by a one-dotted chain line, and is switched to the guiding path  10  side for the time of two-sided document reading, and the document sheet P passes through the guiding path  10 , and is conveyed onto the first reversal guiding path  111  by a pair of conveyance rollers  40 , and conveyed to the reversal section  18  (the upper position of the delivery sheet section  32 ) by reversal rollers  15  and  16 . 
     In the manner as described above, in the reversal section  18 , the document sheet P is conveyed in the state that the first page P 1  of the first document sheet P faces the down side, and the second page P 2  faces the upside. Next, reversal rollers  15  and  16  are stopped in the state that the trailing edge of the document sheet P is nipped between reversal rollers  15  and  16 . 
     Next, as shown in FIG. 11, conveyance of the first document sheet P which is reversed by reversal rollers  15  and  16 , is started from the trailing edge of the document sheet P from the reversal section  18 . In this case, the switching guide member  12  is located at a position shown by a one-dotted chain line, and opens the second reversal guiding path  20 , the document sheet P is conveyed onto the second reversal guiding path  20 , and just after the leading edge of the document is detected by the sensor S 2 , the document sheet P is stopped once. When conveyance rollers  21  and  22  start their rotation, the document sheet P is conveyed to the image reading exposure section R. In the image reading exposure section R, the document sheet P is guided by the sheet guiding plate  24  while being conveyed by the platen roller  23 , and the second page P 2  is irradiated by the irradiation lamp  25 , and the image on the second page P 2  is successively read out in the image reading section R 1  through the mirror  26  and the lens L. 
     Next, the document sheet P is conveyed through the guiding path  112  by conveyance rollers  14  and  29 , and conveyed again to the reversal section  18  by reversal rollers  15  and  16 . Herein, the document sheet P is placed such that the second page P 2  of the document sheet P faces the downside and the fist page P 1  faces the upper side, and further, the document sheet P is stopped in the state that the trailing edge portion of the document sheet P is nipped between reversal rollers  15  and  16 . 
     Next, as shown in FIG. 12, reversal rollers  15  and  16  start their rotation in the direction shown by a dotted line, and start the conveyance. On the other hand, the second page of the two-sided document sheet placed on the sheet feeding tray  3  is fed by the pick-up roller  4 , and is stopped once at register rollers  8  and  9 . The first document sheet P is conveyed on the first reversal guiding path  111  by reversal rollers  15  and  16 , conveyed on the second reversal guiding path  20  which is opened by the switching guide member  12 , and stopped once just after the leading edge of the document is detected by the sensor S 2 . When conveyance rollers  21  and  22  start the rotation, conveyance of the document sheet P is started. On the other hand, the stopped second document sheet P is conveyed by the rotation of register rollers  8  and  9  from the guiding path  10  to the first reversal guiding path  111  while being guided by the switching guide member  12 . 
     Herein, the trailing edge of the first document sheet P remains at a position of reversal rollers  15  and  16 , and the trailing edge of the first document sheet P and the leading edge of the second document sheet P are conveyed being in contact with each other in the first reversal guiding path  111 , and when conveyance rollers  21  and  22  are rotated and start the conveyance, the reversal roller  15  and the reversal roller  16  are separated from each other, and holding of the document sheet P is released. 
     Further, the leading edge of the second document sheet P is conveyed at a position of reversal rollers  15  and  16 , and even if the trailing edge of the first document sheet P remains between reversal rollers  15  and  16 , the reversal roller  15  is moved in the arrowed direction, and because the reversal rollers  15  and  16  are separated from each other, even when the leading edge of the second document sheet P is in contact with the trailing edge of the first document sheet P, these document sheets P are smoothly conveyed to the reversal section  18 . 
     In the present embodiment, the following control is carried out: after a predetermined time has passed from the rotation start of reversal rollers  15  and  16  in the direction shown by a dotted line which is the start of the document conveyance at the time of the first page reading of the first document sheet P, for example, after the time period necessary when the document is conveyed by the distance of 50-60 mm, the leading edge of the second document sheet P reaches reversal rollers  15  and  16 . 
     Next, the first document sheet P conveyed by conveyance rollers  21  and  22 , is conveyed to the image reading exposure section R, and in the image reading exposure section R, the document sheet P is guided onto the sheet guiding palate  24  surface while being conveyed by the platen roller  23 , and the first page P 1  of the document sheet P is irradiated by the irradiation lamp  25 , and the image on the first page P 1  is successively read out in the image reading section R 1  through the mirror  26  and the lens L. 
     The document sheet P whose obverse side image is read out, passes through the guiding path  112  by conveyance rollers  14  and  29 , and is conveyed to the delivery sheet guiding path  30  against the rotation of reversal rollers  15  and  16  or following the rotation, and is delivered onto the delivery sheet section  32  in the state that the obverse side P 1  of the first document sheet P faces the down side. 
     In this manner, the document sheet P on both sides of which images are formed, is delivered with the first page facing downward, and next second document sheet P is delivered also in the same manner, with the third page P 3  facing downward, and even after images of a plurality of document sheets P with two-sided images are read, document sheets P are delivered in the state that the page order is aligned. 
     In either case of the fixed size mode or the mixed-size mode, the above-described document conveyance processes are carried out, and in the fixed size mode, the document size is detected by the side plate  3 A and micro switches MS 1  and MS 2 , and in the mixed-size mode, the document size is detected by sensor S 1  in the document conveyance processes. These document size detection is basically the same as in Embodiment 1. 
     (2) Single side reading 
     FIG. 13 is a sectional view of Embodiment 3 in the state of single side reading. 
     In this case also, the document sheet P is placed on the sheet feeding tray  3  with the image of the document sheet P facing upward. The document sheets P is fed by the pick-up roller  4  from the first sheet of the document sheets P, and is successively conveyed one by one sheet as described above, and conveyed onto the guiding path  11  by register rollers  8  and  9 , and the conveyance rollers  40  after the guiding path  11  is opened by the switching guide member  12  placed at the position shown by a solid line. 
     Next, the document sheet P is guided to conveyance rollers  21  and  22  from the guiding path  11 , and is conveyed to the image reading exposure section R. In the image reading exposure section R, the obverse side of the document sheet P is irradiated by the irradiation lamp  25 , and the image is read out through the mirror  26  and the lens L in the image reading section R 1 . The document sheet P passed the reading position, is conveyed onto the delivery sheet guiding path  112  by the conveyance rollers  14  and  29 , and reversal rollers  15  and  16  are rotated in the delivery sheet direction, and the document sheet P is delivered onto the delivery section  32  in the state that the image of the first document sheet P faces downward. 
     In the fixed size mode, the document size is detected by the side plate  3 A and micro switches MS 1  and MS 2 . 
     In the mixed document mode, the document sheet P is conveyed by register rollers  8  and  9 , further conveyed by conveyance rollers  21  and  22 , and through the platen roller  23 , conveyed to the reversal section  18 . In this conveyance processes, the size of the document sheet P is detected by the sensor S 1 . That is, the document size is detected by the time period from the rotation start of the register rollers  8  and  9  to the detection of the trailing edge by the sensor S 1 . The document conveyance is stopped after a predetermined time from the detection of the trailing edge of the document by the sensor S 1 . The document is stopped in the state that its trailing edge is located at a position shown by E. Reading is not conducted in this document conveyance processes. 
     Next, conveyance rollers  21  and  22  are reversely rotated in the direction shown by a dotted line, and the document sheet P is reversal-conveyed. The reversal-conveyed document sheet P is conveyed to the reversal section  18  through conveyance rollers  40  and the guiding path  113 , and the leading edge of the document (the trailing edge in the conveyance process from conveyance rollers  21  and  22  to the reversal section  18 ) is detected by the sensor S 2 , and the document sheet P is stopped by the detection signal. A one-way flapper  33  formed of an elastic plate is provided at the inlet of the guiding path  113 , and does not send the document sheet P conveyed from the guiding path  11  in the direction of the register rollers  8  and  9 , but surely guides it onto the guiding path  113 . 
     Next, conveyance rollers  21  and  22  start the rotation again in the direction shown by a solid line, and delivers the document sheet P onto the delivery sheet section  32  through the platen roller  23  and reversal rollers  15  and  16 . Reading is conducted in this conveyance process. 
     Three embodiments are described above, and in common to these embodiments, the document sheet P is first conveyed to the reversal section, the document is reversed, and after that, two-side reading is conducted. According to the structure of the present invention, when the document size is detected by the sensor provided on the document conveyance path and reading is conducted, a decrease of the reading speed due to providing the document size detection process, can be prevented. In the conventional document reading apparatus, however, when it is necessary to conduct document size detection by the sensor provided in the conveyance path, there is a problem in which the reading efficiency in the case where mixed-size documents are read is more decreased than the reading efficiency in the case of the fixed size document. However, in the above embodiments of the present invention, there is no such a problem, and the reading speed of the mixed-size documents is increased. 
     In the present invention, in the two-side reading which both sides of the document are read, is achieved. Initially the document is reversed, and after that, the document is conveyed to the reading position, so that the reading efficiency when both sides of a large number of document sheets are read is increased, and high speed two-side reading of a large number of document sheets can be attained. 
     Particularly, since a preceding document and a succeeding document can be positioned together simultaneously in the reversal path in which the document is reversed before reading, without any trouble in the document conveyance, a high speed reading can be attained.