Patent Publication Number: US-2011058233-A1

Title: Image scanning device and document transportation method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119 to Japanese Patent Application No. 2009-204355, filed on Sep. 4, 2009, which application is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to image scanning devices and document transportation methods, and more specifically, to improving an image scanning device that re-scans a document that is not finished with scanning when double sided scanning of the document is interrupted. 
     2. Description of Related Art 
     An image scanning device capable of automatically transporting two or more documents, and sequentially scanning such documents, is being widely used. An image scanning device capable of carrying out double sided scanning of the document through automatic transportation is also widely used. The image scanning device capable of carrying out the double sided scanning is known to include a one-path-two-scanner method of carrying out the double sided scanning of the document using two image sensors, and a two-path-one-scanner method of inverting the front and the back of the document during the automatic transportation and carrying out the double sided scanning of the document using one image sensor. 
     The double sided scanning of the two-path-one-scanner method includes a switchback method of passing the document twice in the same direction with respect to the image sensor by performing a switchback of switching the transporting direction during the transportation of the document, and a U-turn method of crossing transportation paths using a U-turn path and passing the document twice in opposite directions with respect to the image sensor. If the U-turn method is adopted, the transportation control is easier and the scanning time can be reduced as there is no need to switch the transporting direction. 
     Such an image scanning device makes an emergency stoppage of the transportation of the document and interrupts the scanning process when a stop condition, defined in advance, is detected during the document scanning. For example, the scanning process is interrupted when a document jam or a cover off (open door) is detected. In this case, a user needs to take out the document in the transportation path and place the document on a document tray. Thus, some of the conventional image scanning devices generate a display for distinguishing a document for which scanning has been completed from a document for which scanning has not finished. For example, there is known an image scanning device that displays from which number of document the scanning is to be resumed. In such an image scanning device, waste and redundancy of the document to be scanned can be avoided in the scanning process that is resumed after the interruption. 
     In the conventional image scanning device, documents other than the document for which scanning of both surfaces is finished at the time of interruption are targets of re-scanning when double sided scanning is interrupted. That is, whether or not the scanning is finished is determined in units of documents. Thus, the document with a first surface scanned and a second surface not scanned when scanning is interrupted becomes the target of re-scanning, and both surfaces are scanned after resuming the scanning. That is, the scanning is carried out twice for the first surface for such a document, thus causing a wasteful scanning process to be carried out. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide an image scanning device that prevents redundant scanning of the same document surface when double sided scanning of the document is interrupted and thereafter resumed. Preferred embodiments of the present invention also provide an image scanning device that prevents redundant scanning of each of the documents when only the scanning of one document surface is finished with respect to two or more documents when double sided scanning is interrupted. In addition, preferred embodiments of the present invention further provide an image scanning device capable of reducing a transportation time after resuming the scanning by avoiding such redundant scanning. 
     An image scanning device according to a first preferred embodiment of the present invention includes a scanning specifying unit, a first transportation path, a second transportation path, a path switching unit, and a document detection unit. The scanning specifying unit specifies either a double sided scanning or a single sided scanning for a scanning method of a document. The first transportation path is a transportation path for double sided scanning arranged to scan a first surface and a second surface of the document in order. The second transportation path is a transportation path for single sided scanning, which is shorter than the first transportation path, arranged to scan the second surface of the document. The path switching unit selects either the first transportation path or the second transportation path based on the specified scanning method. The document detection unit detects a document having its first surface scanned and its second surface not scanned when the double sided scanning is interrupted. The path switching unit selects the second transportation path for the transportation path of the first document in the resumed double sided scanning based on a detection result of the document detection unit. 
     With such a configuration, the second transportation path is selected for the transportation path of the first document in the resumed double sided scanning if the document with the first surface scanned and the second surface not scanned is detected when the double sided scanning is interrupted. Thus, the scanning of both sides of the document can be completed without redundantly scanning the first surface. Furthermore, the transportation time after the scanning is resumed can be shortened by avoiding the redundant scanning of the first surface as the second transportation path for scanning only the second surface, which is shorter than the first transportation path. 
     For example, when continuous scanning of two or more double sided documents is interrupted, the redundant scanning of the first surface can be avoided and the transportation time of the document can be shortened by having the user place the document on the document tray and resume scanning so that the document having its first surface already scanned and the second surface not scanned at the time of the interruption is transported first. 
     In the image scanning device according to a preferred embodiment of the present invention, in addition to the above-described configuration, the document detection unit is arranged to detect the number of documents having the first surface scanned and the second surface not scanned when the double sided scanning is interrupted, and the path switching unit switches from the second transportation path to the first transportation path based on the number of documents. 
     With such a configuration, in the image scanning device in which two or more documents may be in a state in which the first surface has been scanned and the second surface has not been scanned during the continuous scanning of the double sided document, the redundant scanning of the first surface after the scanning is resumed can be avoided and the transportation time of the document can be shortened for all documents having the first surface scanned and the second surface not scanned when the scanning is interrupted. 
     In the image scanning device according to a preferred embodiment of the present invention, in addition to the above-described configuration, the path switching unit switches the transportation path at a branching point of the first transportation path and the second transportation path, the first transportation path includes a first introducing path arranged to transport the document from the branching point to a scanning position, and a U-turn path arranged to cause the document that entered from the first introducing path and passed the scanning position to make a U-turn and again enter the scanning position, and the second transportation path includes a second introducing path that joins with the U-turn path without passing the scanning position. 
     With such a configuration, the document having its first surface scanned and the second surface not scanned when the scanning is interrupted can be transported to the second transportation path in the resumed double sided scanning, and can skip passing the path of one portion of the U-turn path. Thus, the second surface, on which scanning has not yet been performed, can be scanned while shortening the transportation time of the document. 
     In addition to the above-described configuration, the image scanning device according to a preferred embodiment of the present invention preferably further includes a counter unit and a notifying unit. The counter unit counts the number of documents that are finished with the double sided scanning during continuous scanning. The notification unit notifies the user of the document to be scanned in the resumed double sided scanning based on the count result of the counter unit when the continuous scanning is interrupted. 
     With such a configuration, the document to be scanned after the interruption is displayed (notified), and the user can place the document on the document tray and resume the scanning by looking at the display. That is, the user can resume scanning without being conscious of the document that has its first surface scanned and its second surface not scanned at the time of the interruption. 
     A scanning method according to another preferred embodiment of the present invention includes a scanning specifying step, a path switching step, and a document detecting step. In the scanning specifying step, either a double sided scanning or a single sided scanning is specified for a scanning method of the document. In the path switching step, any of a first transportation path for double sided scanning and a second transportation path for single sided scanning is selected based on the specified scanning method. In the document detecting step, a document having its first surface scanned and its second surface not scanned is detected when the double sided scanning is interrupted. In the path switching step, the second transportation path is selected in the resumed double sided scanning based on the detection result of the document detecting step. 
     The image scanning devices according to various preferred embodiments of the present invention prevent the same document surface from being redundantly scanned when the double sided scanning of the document is interrupted and thereafter resumed. If only the scanning of one document surface is finished for two or more documents when the double sided scanning is interrupted, redundant scanning can be prevented for each of the documents. Furthermore, the transportation time after the scanning is resumed can be shortened by avoiding such redundant scanning. 
     The above and other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an outer appearance view illustrating one configuration example of an image scanning device according to a preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view illustrating one configuration example of a main section of a multifunction peripheral  100  of  FIG. 1 . 
         FIGS. 3A to 3D  are explanatory views on continuous scanning of a sequential method. 
         FIGS. 4A to 4D  are explanatory views of double sided scanning of a batch method. 
         FIGS. 5A to 5D  is an explanatory view of double sided scanning of an alternate method. 
         FIGS. 6E and 6F  are explanatory views of double sided scanning of the alternate method. 
         FIGS. 7A to 7C  are explanatory views illustrating one example of a scanning order at a scanning position C 2  in each method of continuous scanning. 
         FIG. 8  is a block diagram illustrating one configuration example of a main section of the multifunction peripheral  100  of  FIG. 1 . 
         FIG. 9  is a flowchart illustrating one example of a scanning interrupting process in the multifunction peripheral  100  of  FIG. 8 . 
         FIG. 10  is a flowchart illustrating one example of a scanning process in the multifunction peripheral  100  of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
       FIG. 1  is an outer appearance view illustrating one configuration example of an image scanning device according to a preferred embodiment of the present invention, where a multifunction peripheral  100  is illustrated as one example of the image scanning device. The multifunction peripheral (MFP)  100  preferably includes an MFP main body section  20  arranged to perform image scanning, printing, facsimile transmission and reception, and the like, and an ADF (Auto Document Feeder) device  10  arranged to perform automatic transportation of documents at the time of image scanning. 
     An operation panel  21  of the MFP main body section  20  includes an operation inputting unit  21   a  such as a start key and a ten key for a user to carry out operation input, and a liquid crystal display unit  21   b  arranged to display and output an operation state to the user. For example, the user can specify a single sided scanning or a double sided scanning of the document by providing an operation input to the operation inputting unit  21   a.  An error display is made on the liquid crystal display unit  21   b  when a document jam or cover off condition is detected. Such error display includes the number of documents that are finished being scanned, and shows to the user the document(s) that requires re-scanning. 
     A contact glass (not illustrated) is preferably provided on an upper surface of the MFP main body section  20 , and the ADF device  10  is arranged in an openable and closable manner on the contact glass. That is, the multifunction peripheral  100  can scan the document in any of a flat bed method of scanning the document placed on the contact glass and an ADF method of scanning the document being automatically transported by the ADF device  10 . 
     The ADF device  10  includes a paper feed tray  11  and an output tray  12 , and is arranged at an interior along with a transportation path. The document in the paper feed tray  11  is separated and taken up one by one, transported along the transportation path, and discharged to the output tray  12 . The transportation path is arranged to pass on the contact glass of the MFP main body section  20 , so that the document is scanned by the MFP main body section  20  when passing on the contact glass. 
       FIG. 2  is a cross-sectional view illustrating one configuration example of the main section of the multifunction peripheral  100  of  FIG. 1 , and mainly schematically illustrates the internal structure of the ADF device  10 . In the figure, B 1  to B 5  denote transportation paths of the document, C 1  denotes a branching point of the transportation paths B 2  and B 5 , C 2  denotes a scanning position of the document, and C 3  denotes a merging point of the transportation paths B 3  and B 5 . 
     The scanner unit  22  includes an image sensor arranged to optically scan an image of a document A passing the scanning position C 2 , and includes a light projector  22   a  and a line sensor  22   b . Irradiation light from the light projector  22   a  is reflected by the document A on the contact glass, and detected by the line sensor  22   b  in which a great number of light receiving elements are linearly arranged. A two-dimensional image can be scanned by relatively moving the document A and the line sensor  22   b  in a direction intersecting the array direction of the light receiving elements. When performing the image scanning in the ADF method, the scanner unit  22  is made stationary and the image scanning is carried out on the document A being transported. The scanner unit  22  can also be used as a document detection sensor to detect arrival or passing of the document A with respect to the scanning position C 2 . 
     A two-pass-one-scanner method is adopted in the multifunction peripheral  100 , where the double sided scanning of the document is carried out using one scanner unit  22 . The two-pass-one-scanner method is a double sided scanning method of inverting the front and the back of the document and scanning the document twice with the same scanner unit  22 . In a typical image scanning device of the two-pass-one-scanner method, the document is switched back so that the front and the back of the document A are inverted, joined right before the scanner unit  22  through a different transportation path, and passed through the scanner unit  22  (scanning position C 2 ) twice in the same direction. 
     In the multifunction peripheral  100 , on the other hand, the front and the back of the document A are inverted by having the document A make a U-turn, and then the document A is passed through the scanner unit  22  (scanning position C 2 ) twice. In this case, the direction the document A passes the scanner unit  22  is the opposite for the first time and the second time. 
     The transportation paths B 1  to B 5  are provided in the ADF device  10 , where the transportation path of the document A differs for the single sided scanning and the double sided scanning. When carrying out the double sided scanning, the document is transported in the order of the transportation paths B 1 , B 2 , B 3 , and B 4 . This transportation path is called the double sided path. When carrying out the single sided scanning, the document is transported in the order of the transportation paths B 1 , B 5 , B 3 , and B 4 . This transportation path is called the single sided path. 
     The transportation path B 1  is a paper feed path for transporting the document A taken in from the paper feed tray  11  up to the branching point C 1 , and can be used for both the single sided scanning and the double sided scanning. 
     The transportation path B 2  is an introducing path dedicated for double sided scanning for transporting the document A for double sided scanning from the branching point C 1  to the scanning position C 2 , and transports the document A to the scanning position C 2  substantially linearly without making a U-turn. The document that entered from the transportation path B 2  and passed the scanning position C 2  from right to left enters the transportation path B 3 . 
     The transportation path B 3  is a U-turn path arranged to cause the document for double sided scanning to make a U-turn and inverting the front and the back. The document that passed the scanning position C 2  from right to left is entered to the lower side of the transportation path B 3  and transported in the clockwise direction to have the front and back inverted, and then returns to the scanning position C 2  from the upper side of the transportation path B 3  and passes the scanning position C 2  from left to right. That is, the scanning position C 2  is passed twice with the front and the back of the document inverted by passing the transportation path B 3 . In this case, the direction of passing the scanning position C 2  is the opposite for the first time and the second time. The downstream side than the merging point C 3  of the transportation path B 3  is also used in the single sided scanning. 
     The transportation path B 4  is a discharge path arranged to transport the document that passed the scanning position C 2  from left to right to a discharge port  18 , and to discharge the document to the output tray  12 , and is used for both the single sided scanning and the double sided scanning. 
     The transportation path B 5  is an introducing path dedicated for single sided scanning for transporting the document A for single sided scanning from the branching point C 1  to the merging point C 3  on the transportation path B 3 , where the transportation path B 5  and the transportation path B 3  configure a horizontal U-shaped transportation path. The document dedicated for single sided scanning that entered the transportation path B 3  from the merging point C 3  is passed through the scanning position C 2  from left to right, entered to the transportation path B 4 , and discharged to the output tray  12 , exactly in the same manner as the document for double sided scanning which second scanning is to be performed. 
     The paper feed tray  11  includes a platen  13  arranged to stack and place the documents, and a document stopper  14  arranged to position the documents. The platen  13  is biased upward by a biasing member such as a spring, for example, so that the uppermost document contacts a pickup roller  15   a.  The document on the platen  13  also has the leading edge (left end in the figure) in the feeding direction positioned by the document stopper  14 . Thus, the uppermost document has the leading edge positioned and has the vicinity of the leading edge pushed against the pickup roller  15   a.    
     The document take-in unit  15  is arranged to take in the document A in the paper feed tray  11  to the transportation path one at a time, and preferably includes the pickup roller  15 , a separation roller  15   b,  and a retarding roller  15   c.  The pickup roller  15   a  and the separation roller  15   b  are rotationally driven in the feeding direction of the document, and the retarding roller  15   c  is rotationally driven in the returning direction. Thus, the document A in the paper feed tray  11  is taken-in into the transportation path B 1  by the pickup roller  15   a  in order from the top, where only the uppermost document A of the documents A taken-in in a multi-feeding state is separated by the separation roller  15   b  and the retarding roller  15   c  that are rotating in opposite directions to each other, and transported in the feeding direction. 
     The transportation roller  16  includes a rotationally driven drive roller, and a driven roller arranged facing the drive roller with the transportation path in between. A great number of transportation rollers  16  are arranged on the transportation paths B 1  to B 5  at an interval shorter than the shortest document length, and the document A is transported on the transportation path by such transportation rollers  16 . The transportation roller  16  is rotationally driven by a transportation motor  36  (not illustrated), but a dedicated clutch and the like are required to drive some of the transportation rollers  16  asynchronously with the other transportation rollers  16 , whereby the configuration becomes complex and high cost. In the present preferred embodiment, therefore, all transportation rollers  16  are assumed to be driven by the same stepping motor, and rotated synchronously with respect to each other, for example. 
     A path switching unit  17  is a switching device (path switching unit) of the transportation path arranged to select any of the single sided path and the double sided path, and is arranged at the branching point C 1  of the transportation path. The path switching unit  17  preferably includes a nail-shaped rotation member  17   a  and a solenoid (not illustrated), and switches the transportation paths B 2  and B 5  by having the solenoid rotate the rotation member  17   a.  That is, the document A arriving at the branching point C 1  is transported to the transportation path B 2  if the double sided path is selected, and the document A is transported to the transportation path B 5  if the single sided path is selected. 
     Assuming the lower surface of the document A accommodated in the paper feed tray  11  is the first surface and the upper surface is the second surface, the document A is scanned twice in the order of the first surface and the second surface in the double sided path, and only the second surface of the document A is scanned in the single sided path. In other words, if the double sided path is selected, the document A is guided to the scanning position C 2  of the scanner unit  22  through the transportation path B 1 , the branching point C 1 , and the transportation path B 2  in this order, and has the first surface scanned. Thereafter, the document A is again guided to the scanning position C 2  through the transportation path B 3 , has the second surface scanned, and discharged from the discharge port  18  through the transportation path B 4 . If the single sided path is selected, the document A is guided to the scanning position C 2  of the scanner unit  22  through the transportation path B 1 , the branching point C 1 , the transportation path B 5 , the merging point C 3 , and the last half of the transportation path B 3  in this order, has its second surface scanned, and then discharged from the discharge port  18  through the transportation path B 4 . 
     The ADF device  10  preferably includes five document detection sensors DS 1  to DS 5 , for example. The document detection sensors DS 1 , DS 2  are arranged at the paper feed tray  11  to detect the document A placed on the platen  13 . The document detection sensors DS 3  to DS 5  respectively detect the arrival or the passing of the document A being transported at different detection positions. An optical sensor may be used for the document detection sensors DS 1  to DS 5 . 
     The document detection sensor DS 1  is a document placement detector arranged to detect whether or not the document A is placed on the paper feed tray  11 . For example, the presence of the document A can be determined by embedding a reflective optical sensor in the platen  13  near the document stopper  14 , and detecting the vicinity of the leading edge of the document A. 
     The document detection sensor DS 2  preferably is a document length detector arranged to detect the length of the document A in the feeding direction. For example, whether or not the document length is greater than or equal to a predetermined length can be determined by embedding an optical sensor in the platen  13  behind the document detection sensor DS 1 . In this case, the maximum document length can be detected if two or more documents A of different sizes are stacked and placed. Furthermore, detection can be made that the document length is a length within a predetermined range by arranging two or more document detection sensors DS 2  while making the positions in the feeding direction different from each other. 
     The document detection sensors DS 3  to DS 5  are transportation state detectors arranged to monitor the predefined detection position on the transportation path, and detect the position of the document A being transported, and detect the arrival or the passing of the document A with respect to the detection position. That is, determination can be made that the document A arrived at the detection position when detecting the leading edge of the document A, and determination can be made that the document A passed the detection position when detecting the trailing edge of the document A. 
     The document detection sensor DS 3  is arranged on the transportation path B 1  sandwiched by the separation roller  15   b  and the branching point C 1 , and detects the document A taken in from the paper feed tray  11  to the transportation path B 1  by the document take-in unit  15 . 
     The document detection sensor DS 4  is arranged on the transportation path B 2  sandwiched by the branching point C 1  and the scanning position C 2 . The document detection sensor DS 4  is a sensor arranged to obtain the scanning timing of the first surface by the scanner unit  22  in the double sided scanning, and is arranged at a position where the leading edge of the document A passes right before arriving at the scanning position C 2 . For example, the scanning start timing of the first surface can be obtained from the transportation distance after the document detection sensor DS 4  detects the leading edge of the document A. The scanning end timing of the first surface can be obtained from the transportation distance after the document detection sensor DS 4  detects the trailing edge of the document A. The transportation distance can be calculated from the rotation amount of the transportation motor  36 . 
     The document detection sensor DS 5  is arranged on the transportation path B 3  sandwiched by the merging point C 3  and the scanning position C 2 . The document detection sensor DS 5  is a sensor arranged to obtain the scanning timing of the second surface by the scanner unit  22  in the double sided scanning, and is arranged at a position where the leading edge of the document A passes right before arriving at the scanning position C 2 . For example, the scanning start timing of the second surface can be obtained from the transportation distance after the document detection sensor DS 5  detects the leading edge of the document A. The scanning end timing of the second surface can be obtained from the transportation distance after the document detection sensor DS 5  detects the trailing edge of the document A. The document detection sensor DS 5  is also a sensor arranged to obtain the scanning timing of the single sided scanning. 
     The scanning of the document is sometimes interrupted by stop conditions such as a document jam or a cover off condition. The cover off condition is when the cover of the ADF device  10  is opened. If the document A is being transported on the transportation path B 3  when the double sided scanning is interrupted, the transportation path of the document A is switched to the single sided path when scanning is resumed thereafter. That is, if there exists the document A for which scanning of the first surface is finished and the scanning of the second surface is not finished at the time point when the double sided scanning is interrupted, the transportation path of the document A is switched to the single sided path when the scanning is resumed thereafter. Since only the second surface of the document A will be scanned if the single sided path is selected, the second surface, which scanning is not finished, can be scanned without the first surface, which scanning is already finished, being redundantly scanned as the transportation path of the document A is switched to the single sided path. The distance along the transportation path from the branching point C 1  to the merging point C 3  is shorter for the single sided path than for the double sided path. As described above, the transportation path of the document A is switched to the single sided path, which is shorter than the double sided path, and hence the transportation time of the document A at the time the scanning is resumed can be shortened. 
       FIGS. 3A to 6F  are explanatory views illustrating a state in a case where two or more double sided documents A 1  to A 4  are continuously scanned using the ADF device  10  of  FIG. 2 . Generally, the ADF device  10  can shorten the scanning time per document at the time of continuous scanning by simultaneously transporting two or more documents. When referring to simultaneously transporting two or more documents, this means having two or more documents coexist in the transportation path. In the case of the ADF device  10 , since the double sided path intersects, a plurality of scanning methods can be considered depending on the order the double sided documents A 1  to A 4 , which are taken-in in order, pass the scanning position C 2 . In the present preferred embodiment, any one of the sequential method, the batch method, and the alternate method, for example, can be selected by the user. These scanning methods maybe selected based on the document size detected by the document detection sensor DS 2  on the paper feed tray  11 . 
       FIGS. 3A to 3D  are explanatory views on the continuous scanning of the sequential method, and illustrate the transportation state of the documents A 1 , A 2  on the transportation paths B 1  to B 5  in time-series order. In the sequential method, two or more documents are not simultaneously transported on the transportation path B 3  for U-turn, and the scanning of the subsequent document A 2  is started after both sides of the preceding document A 1  are scanned. 
     As illustrated in  FIGS. 3A to 3C , the document A 1  taken in first is transported on the transportation paths B 1  to B 3  in order, and passes the scanning position C 2  twice. As illustrated in  FIGS. 3C and 3D , the subsequent document A 2  is taken in before the preceding document A 1  is discharged to the output tray  12  so that the document A 2  arrives at the scanning position C 2  immediately after the document A 1  passed the scanning position C 2  twice. 
     The sequential method is a scanning method that reduces the scanning time per document by starting the take-in of the subsequent document A 2  before the preceding document A 1  is discharged. The sequential method can be applied as long as the document length is smaller than or equal to the length of the transportation path B 3  (U-turn path), and hence is suited for high speed scanning of a relatively long document. However, the scanning time per document becomes long compared to the other two methods, to be described later, since the document interval is very large. 
       FIGS. 4A to 4D  are explanatory views on the double sided scanning of the batch method, and illustrate the transportation state of the documents A 1  to A 3  on the transportation paths B 1  to B 5  in time-series order. In the batch method, two or more documents A 1 , A 2  are simultaneously transported without being redundant on the transportation path B 3  for U-turn, and the double sided scanning is carried out with such a document group as a unit. That is, the preceding documents A 1 , A 2  have the respective first surfaces scanned and then the respective second surfaces scanned, and the scanning of the subsequent document A 3  is started after both sides of the preceding documents A 1 , A 2  are scanned. 
     As illustrated in  FIGS. 4A and 4B , the documents A 1 , A 2  taken in order are transported in order on the transportation paths B 1  to B 3 , and are simultaneously transported on the transportation path B 3  after the respective first surfaces are scanned. Thereafter, the documents A 1 , A 2  are transported to the transportation path B 4  through the scanning position C 2 , and the respective second surfaces are scanned ( FIG. 4C ). The subsequent documents A 3 , A 4  are taken in before the preceding document A 2  is discharged to the output tray  12  so that the document A 3  arrives at the scanning position C 2  immediately after both documents A 1 , A 2  have passed the scanning position C 2  twice. 
     The batch method is a scanning method that reduces the scanning time per document by continuously entering the documents from any of transportation path B 2  and B 3  with respect to the scanning position C 2  and simultaneously transporting two or more documents on the transportation path B 3  to collectively carry out the double sided scanning of two or more documents A 1 , A 2 . Here, the scanning time per document is further reduced by starting the take-in of the subsequent document A 3  before both documents A 1 , A 2  are discharged. The batch method can further reduce the scanning time per document compared to the sequential method, but cannot be applied unless the document length is smaller than or equal to ½ of the length of the transportation path B 3  (U-turn path). The sequential method and the batch method are common in being the scanning method in which the first surface of the next document is scanned after the second surface of each document transported on the transportation path B 3  is scanned. 
       FIGS. 5A to 5D  and  FIGS. 6E to 6F  are explanatory views of the double sided scanning of the alternate method, and illustrate the transportation state of the documents A 1  to A 4  on the transportation paths B 1  to B 5  in time-series order. In the alternate method, two or more documents A 1 , A 2  are simultaneously transported with an interval on the transportation path B 3  for U-turn, and the document is alternately sent one at a time from the transportation paths B 2  and B 3  with respect to the scanning position C 2 . 
     As illustrated in  FIGS. 5A to 5C , the documents A 1 , A 2  that are sequentially taken-in are transported in order on the transportation paths B 1  to B 3 , and are simultaneously transported on the transportation path B 3  after the respective first surfaces are scanned. This method differs from the batch method of  FIGS. 4A to 4D  in that an interval that is equal to at least one document is formed between the documents A 1 , A 2 . That is, in the alternate method, the documents A 1 , A 2  are sequentially taken-in with an interval that is equal to at least one document. 
     The document A 1  is then entered to the scanning position C 2  from the transportation path B 3 , and the second surface thereof is scanned ( FIG. 5D ). After the document A 1  is transported to the transportation path B 4 , the document A 3  is entered to the scanning position C 2  from the transportation path B 2 , and the first surface thereof is scanned ( FIG. 6E ). Thereafter, the document A 3  is transported to the transportation path B 3 , the document A 2  is entered to the scanning position C 2  from the transportation path B 3 , and the second surface thereof is scanned ( FIG. 6F ). That is, at the scanning position C 2 , the second surface of the document A 1 , the first surface of the document A 3 , and the second surface of the document A 2  are scanned in this order.  FIGS. 5C and 6F  illustrate the same state with the document advanced by one document, and continuous scanning can be carried out by repeating the states of  FIGS. 5C to 6E  in order after the state of  FIG. 6F . 
     The alternate method is a method that simultaneously transports two or more documents on the transportation path B 3 , and alternately scans the first surface and the second surface at the scanning position C 2 , and is a scanning method that reduces the scanning time per document. The alternate method can further reduce the scanning time per document compared to the batch method, but cannot be applied unless the document length is smaller than or equal to ⅓ of the length of the transportation path B 3  (U-turn path). 
       FIGS. 7A-7C  are explanatory views illustrating one example of the scanning order at the scanning position C 2  in each method of continuous scanning.  FIGS. 7A-7C  respectively illustrate the order of document surfaces scanned in the case of the sequential method, the batch method, and the alternate method for the documents A 1  to A 5  taken-in in order. 
     As illustrated in  FIG. 7A , in the case of the sequential method, the first surface and the second surface of the document A 2  are scanned in order after the first surface and the second surface of the document A 1  are scanned in order. Time t R  from the scanning of the first surface to the scanning of the second surface of the same document corresponds to the time it takes the document to pass the transportation path B 3 . 
     As illustrated in  FIG. 7B , in the case of the batch method, the second surfaces of the documents A 1  and A 2  are scanned in order after the first surfaces of the documents A 1  and S 2  are scanned in order. The time t R  from the scanning of the first surface to the scanning of the second surface of the same document A 1  is the same as in the case of the sequential method, but the first surface of the document A 2  is scanned during that time. Thus, the throughput of the document scanning can be enhanced compared to the sequential method. 
     As illustrated in  FIG. 7C , in the case of the alternate method, the scanning of other documents is carried out twice from the scanning of the first surface to the scanning of the second surface of the same document excluding the document A 1 , which does not have a preceding document. For example, the second surface of the document A and the first surface of the document A 3  are scanned between the scanning of the first surface to the scanning of the second surface of the document A 2 . In this manner, the throughput of the document scanning can be further enhanced from the batch method by alternately scanning the first surface and the second surface of different documents. 
       FIG. 8  is a block diagram illustrating one configuration example on the main section of the multifunction peripheral  100  of  FIG. 1 . The multifunction peripheral  100  includes a stop condition detection unit  30 , a U-turn document detection unit  31 , a page counter  32 , an error informing unit  33 , a path control unit  34 , a transportation control unit  35 , and a transportation motor  36 . 
     The stop condition detection unit  30  includes a detector arranged to detect a stop condition that causes the transportation roller  16  to make an emergency stop while transporting documents, and outputting a stop signal. The stop condition is a factor determined based on the detection results of various types of sensors, and is defined in advance. For example, the stop signal is outputted when the occurrence of the document jam is detected based on the detection results of the document detection sensors DS 3  to DS 5 . The stop signal is also outputted when the cover off (open door) of the multifunction peripheral  100  is detected based on the output of the open/close sensor (not illustrated). 
     The U-turn document detection unit  31  detects the document having the first surface scanned and the second surface not scanned when the double sided scanning is interrupted based on the detection results of the document detection sensors DS 4 , DS 5 . That is, the U-turn document detection unit  31  detects the document (U-turn document) making the U-turn that was on the transportation path B 3  at the time of the interruption, and outputs U-turn document detection information when the stop signal is outputted from the stop condition detection unit  30  and the double sided scanning is interrupted. 
     Thus, the U-turn document detection information is outputted when the double sided scanning is interrupted, but is not outputted when the single sided scanning is interrupted. Only one U-turn document is detected at the most during the double sided scanning by the sequential method, but two or more U-turn documents are sometimes detected during the double sided scanning by the batch method or the alternate method. Thus, the U-turn document detection unit  31  detects not only the presence of the U-turn document but also the number of documents thereof, and outputs the U-turn document detection information including the number of U-turn documents. 
     The page counter  32  obtains the number of documents that are finished with the double sided scanning based on the detection result of the document detection sensor DS 5 . Since the double sided document is scanned in the order of the first surface and the second surface, the end of scanning of the second surface can be determined based on the detection result of the document detection sensor DS 5 . Thus, when performing continuous scanning, the number of documents that are finished with the double sided scanning can be obtained by counting the detecting signals of the document detection sensor DS 5 . 
     The error informing unit  33  makes an error display on the liquid crystal display unit  21   b  and informs the occurrence of the stop condition to the user when the scanning is interrupted by the stop condition. In this case, the document to be scanned in the subsequently resumed scanning is shown based on the number of documents that are finished with the double sided scanning obtained by the page counter  32 . For example, if the double sided scanning is finished up to the third document, a message urging to place the fourth and the subsequent documents again on the paper feed tray  11  is displayed on the liquid crystal display unit  21   b.  The user who sees such error display places the fourth and the subsequent documents on the paper feed tray  11  so that the fourth document is taken in first, operates the start key, and resumes the double sided scanning. 
     The path control unit  34  controls the path switching unit  17  based on the user operation. The double sided scanning or the single sided scanning is specified by the user operation to the operation inputting unit  21   a,  and the path control unit  34  outputs a path selection signal to the path switching unit  17  based on the user specification. That is, the selection signal of the double sided path is outputted if the double sided scanning is specified, and the selection signal of the single sided path is outputted if the single sided scanning is specified. 
     In the double sided scanning that is resumed after the interruption, the path selection signal is generated prioritizing the U-turn document detection information over the user specification. That is, if the U-turn document is detected by the U-turn document detection unit  31  at the time of the interruption, the selection signal of the single sided path is first outputted with respect to the document that is equal to the number of U-turn documents, and the selection signal of the double sided path is outputted with respect to the subsequent documents in the resumed double sided scanning. Therefore, with respect to the document with the first surface scanned and the second surface not scanned when the double sided scanning is interrupted, the single sided path shorter than the double sided path is used so that only the second surface is scanned in the resumed double sided scanning, thereby shortening the transportation time of the document. 
     The transportation control unit  35  controls the document take-in unit  15  and the transportation roller  36  based on the operation input of the user or the detection results of the document detection sensors DS 1  to DS 5 , and performs the transportation control of the document. The rotation of the transportation motor  36  starts based on the start operation of the user by the operation inputting unit  21   a,  and stops based on the detection result of the document detection sensor DS 1 . The taking in of the document by the document take-in unit  15  is carried out at the timing that ensures a predetermined document interval corresponding to the document scanning method based on the detection results of the sensors DS 3  to DS 5 . Furthermore, when the stop condition is detected by the stop condition detection unit  30 , the rotation of the transportation motor  36  is stopped based on the stop signal, and the taking in of the document by the document take-in unit  15  is also stopped. 
       FIG. 9  is a flowchart, and steps S 101  to S 105  illustrate one example of the scanning interrupting process in the multifunction peripheral  100  of  FIG. 8 . The scanning interrupting process starts when the stop condition, such as document jam or cover off, is detected during the document scanning. The stop condition detection unit  30  outputs the stop signal when detecting such a stop factor. 
     The transportation control unit  35  interrupts the scanning process based on the stop signal. That is, the transportation motor  36  makes an emergency stop to stop the document being transported on the transportation path (step S 101 ). The document take-in unit  15  is also stopped so that a new document is not taken in (step S 102 ). 
     The U-turn document is then detected by the U-turn document detection unit  31 , and the U-turn document detection information is generated (step S 103 , S 104 ). The U-turn document is the document with the first surface scanned and the second surface not scanned when the scanning is interrupted, and is detected only when the double sided scanning is interrupted. The number of U-turn documents is also detected in the case of the batch method or the alternate method. 
     Finally, the error informing unit  33  makes an error display on the liquid crystal display unit  21   b  (step S 105 ). For example, the stop condition detected by the stop condition detection unit  30 , and the document page to be placed on the paper feed tray  11  when resuming after the interruption is displayed. 
     Thus, when the stop condition is detected, the U-turn document (document making the U-turn at the time of interruption) is detected and the detection result is displayed as an error on the liquid crystal display unit  21   b.  The user who sees the error display places the document to be scanned on the paper feed tray  11 , operates the start key of the operation inputting unit  21   a,  and resumes the scanning process. 
       FIG. 10  is a flowchart, and steps S 201  to S 208  illustrate one example of the scanning process in the multifunction peripheral  100  of  FIG. 8 . The scanning process starts when the user operates the start key of the operation inputting unit  21   a.    
     The single sided scanning is performed if the single sided scanning is specified when the start key is operated (steps S 201 , S 202 ). In other words, the path switching unit  17  selects the single sided path, the document taken in by the document take-in unit  15  is transported to the scanning position C 2  through the single sided path, and only the second surface thereof is scanned. The relevant scanning process is terminated after such single sided scanning is performed on all the documents placed on the paper feed tray  11  (step S 203 ). 
     If the double sided scanning is specified when the start key is operated, whether or not the scanning process is the process resumed after the interruption is determined (step S 204 ). For example, if the start key is operated within a constant time after the scanning is interrupted without the reset button being operated, determination is made as the resumed scanning process. 
     When determined as the resumed scanning process, whether or not the next document is the U-turn document is determined based on the U-turn document detection information from the U-turn document detection unit  31  (step S 205 ). If it is the U-turn document, the single sided scanning is performed (step S 206 ). In other words, the path switching unit  17  selects the single sided path, the document taken in by the document take-in unit  15  is transported to the scanning position C 2  through the single sided path, and only the second surface thereof is scanned. Such single sided scanning is performed on all the U-turn documents. 
     After the single sided scanning is finished on all the U-turn documents, the double sided scanning is performed on the remaining documents (step S 207 ). In other words, the path switching unit  17  selects the double sided path, the document taken in by the document take-in unit  15  passes the double sided path, and the first surface and the second surface are scanned in order. The scanning process is terminated after such double sided scanning is performed on all the U-turn documents (step S 208 ). 
     The image scanning device according to a preferred embodiment of the present preferred embodiment includes the double sided path arranged to scan the first surface and the second surface of the document in order and the single sided path arranged to scan the second surface of the document, detects the U-turn document with the first surface scanned and the second surface not scanned when the scanning is interrupted, and transports the document of a number detected as the U-turn document at the time of the interruption to the single sided path in the resumed double sided scanning. Thus, the first surface of the same document can be prevented from being redundantly scanned when the double sided scanning of the document is interrupted and thereafter resumed. In particular, the scanning time can be shortened if the single sided path is shorter than the double sided path. 
     The image scanning device according to the present preferred embodiment detects the number of U-turn documents, and transports the document of the above number to be scanned first to the single sided path in the resumed double sided scanning. Thus, when two or more U-turn documents are present, the redundant scanning of the first surface can be prevented with respect to each of the documents. 
     In the present preferred embodiment, an example of the image scanning device in which the transportation path B 3  for U-turn is arranged and in which the first surface and the second surface of the document are scanned at the same scanning position C 2  has been described, but the present invention is not limited to such a case. For example, the present invention can be applied to an image scanning device in which the first surface and the second surface of the document are respectively scanned at different scanning positions. The present invention can also be applied to an image scanning device that does not include the transportation path B 3  for U-turn such as a switchback type image scanning device. 
     In the above-described preferred embodiments, an example of a configuration in which preferably the first surface and the second surface of the document are scanned in order in the double sided scanning and only the second surface is scanned in the single sided scanning has been described, but the present invention is not limited to such a case. In other words, the present invention can be applied to an image scanning device having a configuration in which the second surface and the first surface of the document are scanned in order in the double sided scanning and only the first surface is scanned in the single sided scanning. 
     While the present invention has been described with respect to preferred embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many preferred embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the present invention that fall within the true spirit and scope of the present invention.