Abstract:
An image reading device capable of reading images on the both surfaces of a document in order while moving the document at a prescribed speed includes a platen for reading the document moving at the prescribed speed, a reversible transferring device for moving the document at the prescribed speed along the platen, and a circulating passage for turning the document and sending back to the platen after reading the image on the obverse surface of the document. The circulating passage is composed of at least first and second turning paths for inverting a direction in which the document is transferred to turn the document upside down, so that the images on the obverse and reverse surfaces of the document can be continuously read with a compact mechanism and starting to scan from the same end of the document whenever the document is read.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an image reading device provided with a reading carriage which is placed at a prescribed fixing position so as to read a document transferred by a document transferring device. 
     2. Description of the Prior Art 
     An image reading device used for an image forming device such as a copying machine and facsimile apparatus has a document reading surface opposed to an image reading glass. A carriage of an image reading portion (hereinafter, simply referred to as an “image reading portion”) of the image reading device has a function of reading an image on a document while moving from a home position in a sub-scanning direction to subjecting the image of the document to main scanning. In a case that an automatic document feeder (hereinafter, simply referred to as an “ADF”) is attached thereto, the document is moved along the reading portion in the sub-scanning direction at a constant speed. Therefore, the aforesaid reading portion is retained at the prescribed standby position and serves to scan the documents fed from the ADF in succession in the main scanning direction so as to read images on the documents. Upon reading the images on the documents, the documents are discharged through a document discharge port. 
     However, in a case that the document has images on its both surfaces, the obverse and reverse surfaces (the image surface which is first read is called “obverse”, and the image surface surface which is secondly read is called “reverse” in the description including the appended claims) should be moved over the image reading position in succession. Accordingly, the image on the obverse surface is first read by moving the document from its one end in the forward direction in such a state that the obverse surface is opposed to the image reading position, and thereafter, the document is turned upside down to read the image on the reverse surface. That is, the turned document is moved over the aforementioned image reading position with its reverse surface opposed to the image reading position. Thus, upon reading the images on the both surfaces of the document, the document is sent out through the document discharge port. 
     Conventional document transferring mechanisms for use in the document reading device for reading the document having the images on its both surfaces have been disclosed in Japanese Patent Application Public Disclosures HEI 02-63262(A), 06-247642(A) and 08-133551(A). 
     FIGS.  16 ( a )- 16 ( d ) show a first example of the prior art devices as noted above. In this device, a document sent from a document entrance side on the right side of the drawing is moved from its one end in the forward direction through an image reading position at which a reading portion is placed under a reading feed roller (in the direction from the right side to the left side of the drawing) in such a state that one image surface to be first read faces downward. Consequently, the image on the obverse surface of the document is read by the reading portion FIG.  16 ( a ). Next, after the other end of the document passes through the reading position to complete the reading of the image on the obverse surface, the document stops for a while at the document discharge portion shown on the left side of the drawing FIG.  16 ( b ). Thereafter, the document moves from its other end and goes around the reading feed roller in the clockwise direction so as to pass through the reading position with the reverse surface facing the reading portion. Consequently, the image on the reverse surface of the document is read FIG.  16 ( c ). Then, the document is sent out in the document discharging direction toward the left side of the drawing FIG.  16 (D). 
     FIGS.  17 ( a )- 17 ( d ) show a second example of the prior art devices as noted above. In this conventional device, a document fed from the document entrance side on the right side of the drawing is moved from its one end in the forward direction through a reading position at which a reading portion is placed under a reading feed roller in such a state that one image surface to be first read faces downward in the same manner as the first example described above FIG.  17 ( a ). Consequently, the image on the obverse surface of the document is read by the reading portion. After reading the image on the obverse surface of the document, the document is moved from its one end toward the document discharge side on the left side of the drawing in the clockwise direction (may be moved even in the counterclockwise direction) so as to be turned upside down FIG.  17 ( b ). The turned document is next moved over the reading position in the reverse direction (from the left side to the right side of the drawing) with its reverse surface facing the reading portion, so that the image on the reverse surface is read FIG.  17 ( c ). Then, the document is moved around the reading feed roller in the counterclockwise direction while reading the image on the reverse surface of the document and sent out in the document discharging direction FIG.  17 ( d ). 
     However, in the first example of the conventional devices, the directions in which the images of the obverse and reverse surfaces of the document are read are opposite to each other. Namely, the obverse surface of the document to be first read is scanned from the leading end of the document, but the reverse surface to be read later is scanned from the tail end of the document. Thus, this conventional device entails problem such as difficulty in bringing the images, which are read from the obverse and reverse surfaces of the document and should be reproduced on a sheet of paper, into perfect coincidence on the both sides of the sheet. 
     On the other hand, the second example of the conventional devices is free from the disadvantage brought about by the first example, because the images on the obverse and reverse surfaces are read in the same direction in the second example. However, after reading the image on the obverse surface of the document, the document must be moved from its leading end to be turned upside down on the document discharge side on the left side of the drawing. Besides, even a document of any size is required to prevent its leading and tail ends from overlapping with each other at the reading position when turning on the document discharge side. Therefore, this conventional device calls for a large space for turning the document upside down on the document discharge side, resulting in a large overall size of the ADF device. 
     OBJECT OF THE INVENTION 
     An object of the present invention is to provide an image reading device capable of continuously reading images on the obverse and reverse surfaces of a document with a compact mechanism and starting to scan from the same end of the document whenever the document is read. 
     SUMMARY OF THE INVENTION 
     To attain the object described above according to this invention, there is provided an image reading device for reading the obverse and reverse surfaces of a document while moving the document at a prescribed speed, which comprises a platen for reading the document moving at the prescribed speed, reversible transferring means for moving the document at the prescribed speed along the platen, and a circulating passage for turning the document and sending back to the platen after reading the image on the obverse surface of the document. The circulating passage includes at least first and second turning paths for inverting a direction in which the document is transferred to turn the document upside down. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an image reading device according to this invention. 
     FIG. 2 is a seethrough view showing the image reading device of FIG.  1 . 
     FIG. 3 is a side view showing an image reading carriage situated at an image reading position for reading a document by using a document transferring mechanism. 
     FIG.  4 ( a ) and FIG.  4 ( b ) are explanatory side views of the image reading device, illustrating the states of changing the position of the image reading carriage. 
     FIG. 5 is a block diagram of a system for controlling the image reading operation and document transferring operation in the image reading device. 
     FIG. 6 is an enlarged view of the document transferring mechanism. 
     FIG. 7 is a flowchart of a process of a document prefeeding operation in the device of the invention. 
     FIG. 8 is a flowchart of a process for reading an image on one surface of the document in the device of the invention. 
     FIG. 9 is a flowchart of a process for reading images on both image surfaces of the document in the device of the invention. 
     FIG. 10 is a flowchart of a succeeding process following the process of FIG. 9 for reading images on both image surfaces of the document. 
     FIG.  11 ( a ) to FIG.  11 ( f ) are schematic side views showing movements of the document from the document prefeeding state to the state of reading the image on the obverse surface of the document. 
     FIG.  12 ( a ) to FIG.  12 ( f ) are schematic side views showing movements of the document from the document prefeeding state to the state of reading the images on the reverse surface of the document. 
     FIG.  13 ( a ) to FIG.  13 ( f ) are schematic side views showing succeeding movements of the document from the document prefeeding state to the state of reading the images on the reverse surface of the document, following the state of FIG.  12 ( f ). 
     FIG.  14 ( a ) and FIG.  14 ( b ) are side views showing the state in which a flapper in the document transferring mechanism is switched. 
     FIG.  15 ( a ) and FIG.  15 ( b ) are side views showing a document transferring manner in a modified embodiment of the document transferring mechanism of the invention. 
     FIG.  16 ( a ) to FIG.  16 ( d ) show a document transferring mechanism in a first conventional image reading device. 
     FIG.  17 ( a ) to FIG.  17 ( d ) show a document transferring mechanism in a second conventional image reading device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The image reading device having the document transferring mechanism according to the present invention will be described hereinafter in detail with reference to the accompanying drawings. 
     FIG. 1 is a perspective view showing the image reading device  1  according to this invention. The image reading device  1  functions as not only a document reader having the document transferring mechanism for reading a moving document, but also an image scanner for reading a stationary document. A frame  2  of the image reading device  1  may be divided into two parts. One of the divided parts is placed at one end portion of the frame  2  and comprises a document reading portion including the document transferring mechanism for sending the document into the inside of a frame  2   a  so as to enable various images on the document such as text and patterns to be read out, and a scanner portion for scanning and reading the images on the document placed on the top of a frame  2   b  by using a scanner. On one side of the frame  2   a,  there is installed a document feeding tray  18  for permitting a plurality of documents to be set thereon, so that the documents are sent one by one into the inside of the frame  2   a  to perform image reading. (Herein, the term “scanning and reading of images on the image surface of the document” is abbreviated simply as “image reading” in some cases.) 
     On the top of the frame  2   b,  there is disposed a cover  15  for depressing the document placed on upper surface of the frame  2   b.  The cover  15  is pivotally supported on the one side edge of the frame  2  in the state openably rotatable upward about a rotational shaft. FIG. 1 shows the closed state of the cover  15 . The cover  15  is provided on its upper surface with a pocket cover  16  independently operable upward so that a document jammed under the cover  15  can be removed. The frame  2   a  has an openable frame cover  2   e  so that a document jammed in the frame  2   a  can be removed. 
     FIG. 2 is a seethrough view of the image reading device  1  in the state of closing the cover  15 . On the side of the document feeding tray  18 , a document entrance port  2   c  is formed for introducing the document into the inside of the frame  2   a  therethrough. The document can be inserted and sent to the document transferring mechanism  17  in the frame  2   a  through the document entrance port  2   c.    
     On the opposite side to the document feeding tray  18 , a document discharge port  2   d  is formed for sending out the document from the document transferring mechanism  17 . 
     Within the cover  15 , a document accommodating portion  44  is formed for accommodating the document in the state of closing the pocket cover  16 . Thus, when the cover  15  is closed, the document sent out from the document transferring mechanism  17  can be temporarily stored in the document accommodating portion  44  so as not to take out by mistake the document temporarily sent out from the document transferring mechanism to the document accommodating portion  44 . Even when a document is present on the platen cover  15 , the document can be sent into the document accommodating portion  44  without being obstructed by the document on the platen cover. When the document temporarily entering the document accommodating portion  44  is jammed, it can be taken out therefrom by uncovering the pocket cover  16  from the cover  15 . 
     The upper surface of the frame  2   b  is covered with a document reading glass  13  on which the document is placed so as to read the image of the lower surface thereof. The cover  15  has a pad attached to its lower surface facing the document reading glass  13 . When the document placed on the document reading glass  13  is covered with the cover  15 , it is stably depressed against the document reading glass  13  by the pad. 
     Within the frame  2 , there is disposed a rail  3  extending from the cover  15  to the document transferring mechanism  17 . The rail  3  is provided with a mirror carriage  8  and an image reading carriage  7  for reading the image on the document, which are movable along the rail. The image reading carriage  7  and the mirror carriage  8  are moved by driving a motor and wire pulleys (not shown) and operating a driving system  4  including a wire for transmitting a driving force to the image reading carriage  7  and mirror carriage  8 . On the bottom of the frame  2 , there are installed a lens  6  for focussing light reflected from the document being scanned, and a CCD means  5  such as a CCD linear image sensor for converting the light focussed by the lens  6  into electric image signals. In place of the CCD linear image sensor, a two-dimensional CCD image sensor may be used though it calls on a control system for large ability of processing the image signals. 
     The image reading carriage  7  has functions of not only reading the document being transferred by the document transferring mechanism  17 , but also reading the document stationarily placed on the frame  2   b.    
     FIG. 3 shows the image reading carriage  7  located beneath the document transferring mechanism  17  for reading the document. The image reading carriage  7  can read documents transferred by an image reading transferring roller  36 , so that the document S transferred to a document reading position under the image reading transferring roller  36  can be read. 
     The image reading carriage  7  is composed of a lamp  10 , a mirror  9 , a reflecting plate  11 , and a timing sensor  12 . Beneath the image reading transferring roller  36 , an ADF platen glass  39  is fixedly mounted. Between the platen glass  39  and the roller  36 , a platen guide  38  is mounted. Along the platen guide  38 , a document transferring passage is formed for performing image reading of the document moving therethrough. The document S passes through between the platen guide  38  and the ADF platen glass  39 . The document S is moved along the document transferring passage by the image reading transferring roller  36  in rotation while being elastically urged downward by the platen guide  38  to come in contact with the upper surface of the ADF platen glass  39 . 
     The document S passing along the upper surface of the ADF platen glass  39  is illuminated from under the document by the lamp  10  of the image reading carriage  7 . The reflected light from the document is reflected by the mirror  9  as indicated by the broken line B in FIG.  2  and advances toward the mirror carriage  8  in parallel to the rail  3 . As shown in FIG. 2, mirrors  8   a  and  8   b  mounted on the mirror carriage  8  are opposed to each other, making a right angle with each other so as to allow the light reflected by the mirror  9  to be refracted toward a CCD  5 . The light reflected by the mirrors  8   a  and  8   b  is focussed by the lens  6  on the CCD  5 , so that image data on the document S are converted to electric image signals by the CCD  5 . 
     As the lamp  10 , there may be used, for instance, a slender xenon lamp which extends parallel to and over the image surface of the document. The reflecting plate  11  is symmetrically opposed to the lamp  10  relative to the reflected light from the document placed at the image reading position, so that the document S at the image reading position can be uniformly illuminated symmetrically from the right and left sides with the illuminating light emitted from the lamp  10  and the light irradiated by the reflecting plate  11 , which is obtained by reflecting the light from the lamp  10  with the reflecting plate  11 . 
     The timing sensor  12  serving to detect the document S passing by may be of a reflection type sensor composed of a light emitting element and a photodetecting element. The light emitting element emits a document detecting light toward the image reading position through which the document S is moved by the image reading transferring roller  36 . The photodetecting element has a function of receiving the light reflected by the document passing through the image reading position. The timing sensor  12  is turned on when the document S reaches an area illuminated by the light emitting element to cause the intensity of the light incident on the photodetecting element to be increased. As a reflecting member for reflecting the light emitted from the light emitting element, there may be used the surface of the platen guide  38  or the image reading transferring roller  36 , which is made low in reflectance. Instead, an additional reflecting member may of course be mounted on the side of the image reading transferring roller  36 . 
     By disposing the timing sensor  12  along with the mirror  9  on the image reading transferring carriage  7  so as to detect the document S on the ADF platen glass  39  at the upstream position of the image reading position extremely close to the ADF platen glass  39 , the scanning of the document S by use of the CCD  5  can be precisely started with ease without a time lag of starting the image reading because the leading end of the document S moving along the ADF platen glass  39  can be detected immediately before the commencement of reading. 
     FIGS.  4 ( a ) and  4 ( b ) are side views of the image reading carriage  7  at different positions. The image reading carriage  7  in FIG.  4 ( a ) is placed at the home position on the side of the frame  2   b  of the frame  2  shown in FIG. 1, and that in FIG.  4 ( b ) is moved toward the frame  2   a  and placed at a prescribed position for reading the document transferred by the document transferring mechanism  17  shown in FIG.  2 . 
     The image reading carriage  7  is movable along the rail  3  between the positions shown in FIGS.  4 ( a ) and  4 ( b ), so that the document on the document reading glass  13  is illuminated by the lamp  10  and optically scanned by the CCD  5  while moving the image reading carriage  7  under the document reading glass  13 , like an image scanner. At the same time, the mirror carriage  8  moves together with the image reading carriage  7 , but the moving extent in which the mirror carriage  8  is movable is just half that of the image reading carriage  7 . Thus, the optical path length from the image reading carriage  7  to the CCD  5  through the mirror  9  and the mirrors  8   a  and  8   b  of the mirror carriage  8  can be fixed. Therefore, the image reading device of the invention can be used both as a document reader by driving the document transferring mechanism  17  and an image scanner by moving the image reading carriage under the document reading glass  13 . Incidentally, the CCD  5  may be incorporated in the image reading carriage  7  so as to read the document by moving the CCD  5  along with the image reading carriage  7 . In this case, the optical path length from the image reading position to the CCD  5  must be fixed. 
     When moving the image reading carriage  7  from the image reading position of the scanner to the prescribed position capable of reading the image on the document with the document transferring mechanism  17  in order to read the image on the document by operating the document transferring mechanism  17 , the image reading carriage  7  is not always stopped precisely at the prescribed position. That is, strictly speaking, there are cases that the image reading carriage  7  stops at a position slightly deviating from the prescribed position due to tolerances of mechanical component parts constituting the document transferring mechanism and the inertia of the moving elements. 
     However, since the image reading device  1  of the invention is provided on the image reading carriage  7  with the lamp  10 , mirror  9  and timing sensor  12 , the positional relation between the light irradiating position, i.e. image reading position, at which the light is irradiated onto the document by the lamp  10  to detect the light reflected from the document through the mirror  9 , and the position at which the document is detected by the timing sensor  12  is always kept constant. In other words, the relation between the position at which the document on the ADF platen glass  39  is read by the CCD  5  and the position at which the leading end of the document is detected by the timing sensor  12  does not vary even when the image reading carriage  7  changes its position relative to the ADF platen glass  39 . Accordingly, by moving the document forward by the predetermined distance after detecting the document by the timing sensor  12 , the leading end of the document accurately arrives at the prescribed image reading position. Thus, the image reading carriage  7  can easily be controlled without need to go to the trouble of moving it exactly to the prescribed position for reading the document under the document transferring mechanism  17 . 
     As described above, the timing of moving the image reading carriage  7  synchronously with the other moving components of the device can easily be accomplished by mounting the timing sensor  12  on the image reading carriage  7  without precisely controlling the positioning of the image reading carriage  7  at the prescribed image reading position. Although the timing sensor  12  is mounted on the image reading carriage  7  as noted above, the timing sensor  12  may be mounted on the document transferring mechanism  17 . In that case, a reflecting member may be mounted on the image reading carriage  7 . As another modified embodiment, the timing sensor  12  may be of a transmission type optical sensor, instead of the reflection type optical sensor as in the foregoing embodiment. In the case of using the light transmission type optical sensor as the timing sensor, one of light emitting element and photodetecting element which constitute the optical sensor may be mounted on the image reading carriage  7 , and the other element may be mounted on the document transferring mechanism  17 , so as to allow the light issued from the light emitting element to be incident on the photodetecting element. In this case, when the document S does not arrive at between the light emitting element and the photodetecting element, the light emitted from the light emitting element reaches the photodetecting element. When the document S enters between the light emitting element and the photodetecting element, the light emitted from the light emitting element is blocked off by the document. Thus, the existence of the document can be recognized by checking the output signal from the timing sensor. By using the light transmission type optical sensor as the timing sensor, the problem suffered by the reflection type optical sensor such that the existence of the document is misjudged due to unevenness of the intensity of light reflected by the document can be solved. 
     Next, FIG. 5 is a block diagram of a controlling system for transferring the document to scan the document. A controller  60  consists of a CPU (central processing unit) for performing arithmetic operation for the image reading device  1 , and memory means including RAM and ROM for storing a program for controlling the device. The controller  60  controls separately the image scanning part and the document transferring mechanism  17  of the device  1 . 
     In the image scanning part, the CCD  5  and the lamp  10  for issuing the illumination light are controlled to perform the image reading operation as described above with reference to FIG. 3. A carriage home sensor  52  is disposed for detecting the image reading carriage  7  at the home position. By positioning the image reading carriage  7  at the home position before performing the document scanning operation as illustrated in FIGS.  4 ( a ) and  4 ( b ), the positional relation in which the image reading carriage  7  moves during the document scanning operation is determined. A scanner pulse motor  50  is used for moving the image reading carriage  7  along the rail  3 . The rotation produced by the pulse motor  50  is transmitted to a driving system  4  to move the image reading carriage  7 . With the movement of the image reading carriage  7 , the lower surface of the document is scanned. The size of the document placed on the document reading glass  13  is recognized by prescanning the document before reading the image on the document. Namely, in general, the document is roughly scanned in advance to determine the size of the document. In brief, since the image reading carriage  7  is used both as a document reader by driving the document transferring mechanism  17  and an image scanner by moving the image reading carriage under the document reading glass  13 , the timing sensor  12  is moved with the image reading carriage  7 . Therefore, the CCD  5  and the lamp  10  are shown on the scanner side in the block diagram for the convenience of description. 
     In the document transferring mechanism (ADF)  17 , the existence of the document on the document feeding tray  18  is detected by a document detection sensor  20 . A size sensor  61  serves to detect the width of the document. Under the control of a registration sensor  30  for checking whether or not the document is aligned, the document is on standby at a registration position. A document discharge sensor  62  serves to determine the position of the document when the document is discharged out of the frame  2   a  through the document discharge port  2   d.  A document feeding solenoid  55  is used as a driving source for aligning the edges of documents stacked on the document feeding tray  18  and depressing the documents when feeding the documents one by one into the inside of the document transferring mechanism  17 . A flapper solenoid  56 , document feeding clutch  57 , document discharging clutches  58  and  59 , and an ADF pulse motor  51  are controlled in accordance with the operation of performing obverse surface reading or reverse surface reading, as described in detail later. 
     FIG. 6 is an enlarged side view of the document transferring mechanism  17 . The document feeding tray  18  is disposed close to the document transferring mechanism  17 . Near the document entrance port  2   c  of the frame  2 , there is disposed a document detecting arm  19  rotatable about a rotational shaft  19   a.  When one or more documents are placed on the document feeding tray  18  and inserted into the document entrance port  2   c,  the document detecting arm  19  is depressed by the documents thus inserted and rotated around the rotational shaft  19   a  in the clockwise direction from the normal state shown in FIG.  6 . As a result, the document detection sensor  20  is switched on by an accompanying arm  19   b  moved in conjunction with the document detecting arm  19 , thus to recognize the existence of the documents set on the device. 
     The document detection sensor  20  is composed of a light emitting element and a photodetecting element, so that the photodetecting element is switched on or off to recognize the existence of the documents in accordance with the state in which the light emitted from the light emitting element is permitted to reach the photodetecting element or blocked off by the accompanying arm  19   b.  There is further disposed a sensor, though not shown, for detecting the size of the document, which is composed of sets of light emitting elements and photodetecting elements arranged opposite vertically relative to the surface of the document. On the rotational shaft  19   a,  a weight  22  which is operated by a not-shown document feeding solenoid is mounted for bringing the document into press contact with a pickup roller  24  when feeding the document. Further, a document shutter  21  is disposed for restricting the leading ends of the documents stacked on the document feeding tray  18 . Since the leading ends of the documents are trued up by the document shutter  21 , the documents are positioned appropriatedly on the document feeding tray. The document shutter  21  is actuated by the document feeding solenoid  55  as well as the weight  22 . The pickup roller  24  is formed in a semicircular column so as to transfer the document toward separation roller  26  and separation pad  27 , and driven by the ADF pulse motor  51  through the document feeding clutch  57  which is not illustrated. 
     In order to send out one of the documents stacked on the tray, the document feeding clutch  57  is engaged to rotate the ADF pulse motor  51  in the forward direction, and the document shutter  21  is shifted downward to release the documents on the tray. Then, the pickup roller  24  is rotated in the counterclockwise direction in FIG. 6, thus to send the document on the pickup roller  24  in the downsteam direction. 
     On the downstream thereof, there are disposed the separation roller  26 , separation pad  27 , pad holder  28  and pad-pressing spring  29 . The separation pad  27  is forced toward the separation roller  26  by means of the pad-pressing spring  29  through the pad holder  28  so as to come into contact with the peripheral surface of the separation roller  26 . As a result, only one of the documents stacked on the tray is allowed to pass through between the separation pad and separation roller, but the remaining documents are kept advancing. 
     Between the separation pad  27  and the document shutter  21 , there is placed a document dressing plate  25  with its free end slightly separated from the separation roller  26 . This document dressing plate  25  serves as a supplementary element for allowing only one document to pass through a gap between the separation pad  27  and the document dressing plate  25 , but preventing a plurality of documents from passing therethrough. Thus, with the document dressing plate  25 , only the lowermost document of the documents stacked on the tray and pressed downward by separation means as noted above is sent in the downstream direction, departing from the upper documents. The separation roller  26  is selectively connected to the ADF pulse motor  51  by operating the document feeding clutch  57  so as to rotate around rotational shaft  26   b  in the counterclockwise direction in the drawing. 
     Between the separation roller  26  and the image reading transferring roller  36 , there are placed a registration loop guide film  31 , the registration sensor  30  and the registration rollers  32  and  33 . By the registration loop guide film  31 , the document transferred by the separation roller  26  is supported, so as to block the leading end of the document to cause the document to be curved (loop state) in the standby state before effecting the image reading operation. The registration roller  33  is selectively driven by the ADF pulse motor  51  when disengaging the document feeding clutch  57 . The registration roller  32  is a follower roller rotatable with the movement of the document. 
     On the periphery of the image reading transferring roller  36 , there are disposed two flappers  34  and  37  rotatable about rotational shafts  34   a  and  37   a,  respectively. Adjacent to the registration roller  32 , a transferring roller  35  is mounted between the flappers  34  and  37  and comes into contact with the image reading transferring roller  36  so as to be rotated with the image reading transferring roller  36 . Further, a registration small roller  48  is mounted on the image reading transferring roller  36 , coming into contact with the roller  36  to be rotated with the roller  36 . The document transferring passage is formed around the image reading transferring roller  36  in conjunction with the flapper or sheet guide  37 . This mechanism makes it possible to allow the document fed through between the transferring roller  35  and the image reading transferring roller  36  to be sent exactly to between the image reading transferring roller  36  and flapper  37 , and the document to be transferred through the passage between the ADF platen glass  39  and the registration small roller  48  along the periphery of the image reading transferring roller  36 . Between the image reading transferring roller  36  and the ADF platen glass  39 , the platen guide  38  is disposed for pressing the document toward the ADF platen glass  39 . 
     On the side of the document discharge port  2   d  of the image reading transferring roller  36 , there is disposed a transferring roller  41  driven by the image reading transferring roller  36 . Flappers  42  and  43  rotatable about the rotational shafts  42   a  and  43   a  are provided for switching the direction of moving the document. Adjacent to the document discharge port  2   d,  there are disposed a discharge roller  45  and another discharge roller  46  driven by the discharge roller  45 . The flapper  42  serves to selectively direct the document sent by the transferring roller  41  toward a transferring guide  49  or a transferring guide  47 . The flapper  42  selectively forms a transferring passage from the transferring roller  41  to the discharge roller  45  or a transferring passage from the discharge roller  45  to the transferring guide  47 . 
     The flapper  37  of the four flappers  34 ,  37 ,  42  and  43  is driven by the flapper solenoid  56 . The function of each of flappers will be explained in detail later. 
     Next, the document transferring mechanism  17  shown in FIG. 6 will be described with reference to the flowcharts of FIG. 7 to FIG.  10  and the diagrams of FIG. 11 to FIG. 13 showing the document transferring process. 
     The document transferring mechanism  17  is operated primarily in three modes, i.e. document prefeeding mode, obverse reading mode, and reverse document reading mode. From these operation modes, one mode is selected in accordance with an operation command given by an operator. Upon reception of the operation command given by the operator, the image reading carriage  7  is moved to the prescribed position to stand ready for the desired image reading operation. 
     FIG. 7 is the flowchart of the operation in the document prefeeding mode. First, the width of the document is detected by the size sensor  61  (S 1 ), and then, the document feeding clutch  57  is engaged to connect the pickup roller  24  and the separation roller  26  (S 2 ). Then, by switching on the document feeding solenoid  55 , the document shutter  21  is shifted downward to release the leading ends of the documents, and the documents are depressed against the pickup roller  24  by the weight  22  (S 3 ). 
     Thereafter, the ADF pulse motor  51  is rotated in the forward direction to rotate the pickup roller  24  and the separation roller  26 , thereby to start feeding one document toward the registration roller  33  (S 4 ). FIG.  11 ( a ) shows the relation of the document S and the principal components of the document transferring mechanism  17  immediately after starting to send the document by the separation roller  26 . 
     Turning to the flowchart of FIG. 7, at this time, the registration sensor  30  observes the document S being fed (S 5 ), and when the sensor  30  detects the leading end of the document S, it outputs an ON signal to the controller  60 , so that the ADF pulse motor  51  is operated to move the document S by a prescribed feeding amount toward the registration roller  33  by the separation roller  26  (S 6 ). When the document moves by the prescribed feeding amount, the ADF pulse motor  51  is stopped to bring the document S into its standby state (registration state) (S 7 ). 
     Next, the document feeding clutch  57  is disengaged to cut off the transmission of rotation from the ADF pulse motor  51  to the separation roller  26  and drive the registration roller  33  (S 8 ). Consequently, the prefeeding operation of the document is completed. FIG.  11 ( b ) shows the document standby state in which the leading end part of the document S reaches between the registration rollers  32  and  33  upon completion of the prefeeding operation and comes into collision with the registration rollers  32  and  33  to be slightly curved, as described above. 
     FIG. 8 is the flowchart of performing the operation of reading an image on one surface of the document, following the prefeeding operation. When receiving an operation command of reading the image on one surface of the document, the flapper solenoid  56  is switched on to change the position of the flapper  37  (S 11 ). FIG.  14 ( b ) shows the state in which the flapper  37  assumes its changed posture. Although, under the normal condition, the flapper  34  is elastically urged in the counterclockwise direction by an elastic member such as a spring to assume the state shown in FIG.  14 ( a ), the flapper  34  is forced in the clockwise direction by the document S being forwarded by the registration roller  33  to be changed in position to the state shown in FIG.  14 ( b ), consequently introducing the document S into between the transferring roller  35  and the image reading transferring roller  36 . The flapper  37  has a document transferring surface having the substantially same curvature as the peripheral surface of the document transferring reading roller  36  to form a transferring passage to further forward the document nipped between the transferring roller  35  and the image reading transferring roller  36 . The front end  37   c  of the transferring surface  37   b  of the flapper relative to the direction toward the ADF platen glass  39  is shifted to the position higher than the upper surface of the ADF platen glass  39 . Therefore, the leading end of the document S transferred along the transferring surface  37   b  toward the ADF platen glass  39  is curved along the curved transferring surface  37   b  in the clockwise direction viewed in the drawing, thereby to send the document to the upper surface of the ADF platen glass  39  through the front end  37   c  of the transferring surface. 
     Turning to FIG. 8, at the time of switching on the flapper solenoid  56 , the document discharging clutches  58  and  59  are engaged. By variously operating the document discharging clutches  58  and  59 , the ADF pulse motor  51  and the discharge roller  45  can be driven in conjunction with or independently of each other. That is, the operation of the discharge roller  45  depends on the document discharging clutches  58  and  59 . When bringing the discharge clutch  58  into its engaged state, the discharge roller  45  is connected to the ADF pulse motor  51  rotating in the reverse direction to rotate the discharge roller  45  in the counterclockwise direction viewed in FIG. 6, consequently to send out the document S through the document discharge port  2   d  (S 11 ). By driving the ADF pulse motor  51  in the reverse direction at high speed, the document S nipped between the registration roller  32  and the registration roller  33  is forwarded toward the image reading transferring roller  36  at high speed. Further, the leading end of the document S is nipped between the image reading transferring roller  36  and the transferring roller  35 , and then, the document S is forwarded downward along a part of the side surface  34   b  of the flapper  34 . 
     At this time, the timing sensor  12  of the image reading carriage  7  observes whether or not the document S reaches. When the timing sensor  12  detects the document S to output an ON signal (S 13 ), the document S is further transferred by the prescribed quantity (S 14 ). Since the image reading transferring roller  36  is driven by the ADF pulse motor  51 , the quantity of movement of the document S depends on the rotation of the ADF pulse motor  51 . The rotating amount of the ADF pulse motor  51  depends on the number of the pulses given to the ADF pulse motor  51 . Thus, the quantity of movement of the document S transferred by the image reading transferring roller  36  is in proportion to the number of the pulses given to the ADF pulse motor  51 . 
     The timing sensor  12  for detecting the document S is positioned near the ADF platen glass  39  as described above. Accordingly, the document S can be precisely moved to the image reading position without causing a large positioning error even by operating the ADF pulse motor  51  from the time when the timing sensor  12  detects the document S. Besides, since the relative position of the image reading position at which the document S on the ADF platen glass  39  to the document detecting position by using the timing sensor  12  is constant, the timing of starting the image reading, i.e. the timing of positioning the document at the image reading position by driving the ADF pulse motor  51 , can be stabilized even if the image reading carriage  7  or the timing sensor  12  is out of position. Thus, the heading of the image read from the document by the image reading device is by no means dislocated. 
     When the transfer of the document S by the prescribed quantity is confirmed (S 14 ), the ADF pulse motor  51  is stopped for a while (S 15 ). At this time, the document S is rest just short of the image reading position defined on the ADF platen glass  39 . By the rotational force of the discharge roller  45 , the flapper  42  is switched according to the direction of the rotation of the discharge roller  45 . When the flapper  42  rotates in the direction of permitting the document S to be discharged by the discharge roller  45 , it assumes the position shown in FIG.  14 ( a ). FIG.  11 ( c ) shows the state just after the step S 15 , in which the document S is infallibly introduced onto the upper surface of the ADF platen glass  39  by means of the flapper  37 . Thereafter, by turning off the flapper solenoid  56 , the flapper  37  is retracted to the position shown in FIG.  14 ( a ) (S 16 ). At this time, the flapper  37  is rotated to position the front end  37   c  thereof below the upper surface of the ADF platen glass  39 , so that the document S is urged downward by the platen guide  38  to bring the leading end thereof into contact with the ADF platen glass  39 . However, the front end  37   c  of the flapper  37  is out of contact with the document S to make the space between the platen guide  38  and the transferring surface  37   b  of the flapper  37  relatively large. As a result, the space in which the document S comes in contact with the ADF platen glass  39  in the transferring direction is secured, so that the image reading operation can be stably performed without causing fluctuation in positioning the image reading carriage  7 , which results in decrease in image reading accuracy. Besides, since the front end  37   c  of the flapper  37  is out of contact with the document S, the movement of the document S is not suddenly fluctuated, so that the rear portion of the document S can also be stably read, when the tail end of the document S passing through the flapper  7  is sent onto the ADF platen glass  39 . 
     Turning to FIG. 8, the lamp  10  is turned on to illuminate the lower surface of the document S (S 17 ). However, the leading end of the document S does not yet reach completely the image reading position, since the document S is designed to have a prescribed distance from the image reading position at this time. So, the ADF pulse motor  51  is reversed to rotate the image reading transferring roller  36  in the clockwise direction viewed in FIG. 6, so that the document S is moved at the predetermined image reading speed (S 18 ). While the document S moves for the prescribed distance, a decision whether or not the leading end of the document S arrives at the image reading position is made on the basis of the amount of rotation of the ADF pulse motor  51  (S 19 ). When the document S is deemed to be moved for the prescribed distance, the image reading operation is started (S 20 ). Under the normal condition, the flapper  43  which is elastically urged in the counterclockwise direction by an elastic member such as a torsion coil spring (not shown) assumes its normal state shown in FIG.  14 ( a ). However, at that time, the flapper  43  is rotated in the clockwise direction due to the rigidity of the document S to be turned into the state shown in FIG.  11 ( d ), in which the document S being transferred through the passage formed by the flapper  42  and the flapper  43  partially passes through between the discharge roller  45  and the discharge roller  46 . 
     When the image reading operation is started, the timing sensor  12  is observed (S 21 ). Since the timing sensor  12  is turned off when the tail end of the document S passes through a sensing position at which the timing sensor  12  is mounted, the tail end of the document S can be recognized by observing the output of the timing sensor  12 . Furthermore, from the ON/OFF output of the timing sensor  12  and the amount of rotation of the ADF pulse motor  51 , the length of the document can be measured. Thus, the dimension of the document to be dealt with can be recognized in conjunction with the width of the document detected at Step S 1 . The quantity of movement of the document transferred from the time when the timing sensor is turned off to the time when the tail end of the document arrives at the image reading position is measured from the amount of rotation of the ADF pulse motor  51  (S 22 ). Upon transferring the document by the prescribed distance, the image reading operation is terminated (S 23 ), and then, the ADF pulse motor  51  is stopped for a while (S 24 ), and simultaneously, the lamp  10  is switched off (S 25 ). 
     Thereafter, by reversing the ADF pulse motor  51  at high speed, the document S is transferred at high speed (S 26 ). FIG.  11 ( e ) shows the process of transferring the document S at high speed. Then, a decision whether the discharge sensor  62  assumes its OFF state is made (S 27 ). After the discharge sensor  62  is turned off, the ADF pulse motor  51  is rotated by a prescribed amount to completely send out the document S through the document discharge port  2   d  (S 28 ). The discharge roller  45  is driven by the ADF pulse motor  51 , so that, when the ADF pulse motor  51  is reversed, the discharge roller  45  is rotated in the counterclockwise direction viewed in the drawing at the same circumferential speed as the image reading transferring roller  36 . FIG.  11 ( f ) shows the state in which the document S is discharged through the document discharge port  2   d  onto the cover  15  shown in FIG. 6 by being transferred by the prescribed amount after the discharge sensor  62  is turned off. 
     FIG.  9  and FIG. 10 are flowcharts of the process of reading images on the both surfaces of the document, following the document prefeeding process described above. After receiving a command for reading the images on the both surfaces of the document, a series of procedures from Step S 31  at which the flapper solenoid  56  is turned on to Step S 47  at which a decision whether the discharge sensor  62  is turned off is made, which is the same as Step S 11  to Step S 27  shown in FIG.  8 . Accordingly, the processes of transferring the document S as shown in FIGS.  12 ( a ) to  12 ( e ) are also the same as those of FIGS.  11 ( a ) to  11 ( e ). When the discharge sensor  62  is decided to assume its OFF state at Step S 47 , the transferring of the document by the prescribed amount is performed (S 48 ). The prescribed amount corresponds to the amount by which the document S is transferred just before the document is completely sent out by means of the discharge rollers  45  and  46 , that is, by which the tail end of the document S passes through the transferring passage formed by the flapper  43 . Next, by stopping the ADF pulse motor  51  (S 49 ), the tail end of the document S stops while being partially nipped between the discharge roller  45  and the discharge roller  46  (first turning path). When the tail end of the document S passes through the front end of the flapper  43 , the flapper  43  is automatically changed in its posture by the urging force of the elastic member such as a spring. As a result, the transferring passage extending toward the registration small roller  48  is formed between the flapper  43  and the transferring guide  47 . Next, by operating the ADF pulse motor in the forward direction at high speed, the discharge roller  45  is reversed in the clockwise direction to move backward the document S from the tail end thereof toward the registration small roller  48  (S 51 ). Then, a decision whether the tail end of the document S is detected by the discharge sensor  62  is made (S 52 ). Upon confirming the ON state of the discharge sensor  62  as the result of detecting the tail end of the document S, a decision whether the document S is transferred by the prescribed amount for standby to perform registration transferring is made on the basis of the rotating amount of the ADF pulse motor  51  (S 53 ). At this time, the tail end of the document S advances along the transferring passage formed the transferring guide  47  and the flapper  43  changed in posture toward the registration small roller  48 , but the tail end of the document S is kept from further advancing before the registration small roller  48  by the image reading transferring roller  36  which rotates in the counterclockwise direction viewed in FIG. 6, as shown in FIG.  12 ( f ). As a result, the tail end portion of the document S is partially curved upwardly (see FIG.  6 ). Since the discharge roller  45  rotates in the clockwise direction viewed in FIG.  12 ( f ), the flapper  42  is rotated upward in the counterclockwise direction as shown in FIG.  12 ( f ). 
     When the document is forwarded by the prescribed amount to be curved, the ADF pulse motor  51  is stopped to bring the document S into its standby state for reading image on the reverse surface of the document (registration state for the reverse surface) (S 54 ). Then, the discharge clutch  58  for connecting the ADF pulse motor  51  to the discharge roller  45  is disengaged to bring the discharge roller  45  into the free rotating state (S 55 ). At the time, the flapper solenoid  56  is turned on to bring the flapper  37  into the state shown in FIG.  14 ( b ). 
     Next, the ADF pulse motor is reversed at high speed to rotate the image reading transferring roller  36  at high speed in the clockwise direction viewed in FIG. 6 (S 57 ). The document S placed between the image reading transferring roller  36  and the flapper  34  is forwarded onto the ADF platen glass  39  along a part of the side surface  34   c  of the flapper  34  (see FIG. 14) and the transferring surface  37   b,  and then, the document further advances along a part of the curved surface  42   c  of the flapper  42  (second turning path). FIG.  13 ( a ) and FIG.  13 ( b ) show the processes of transferring the document S. 
     At this time, the timing sensor  12  of the image reading carriage  7  observes whether the leading end of the document S (front end of the document S in the direction opposite to the transferring direction) passes by the timing sensor. The timing sensor  12  outputs an OFF signal when the document passes thereby. When the output of the timing sensor  12  is the OFF signal (S 58 ), the document S is transferred by the prescribed amount (S 59 ). As already stated above, the sensing position at which the document S is detected by the timing sensor  12  is very close to the ADF platen glass  39 . Accordingly, in order for bringing the leading end of the document to the image reading position, it is sufficient to move the document a little by operating the ADF pulse motor  51  from the time the leading end of the document is detected. Thus, the document can be accurately transferred to the image reading position without causing a large positioning error. 
     When confirming that the document S is transferred by the prescribed amount from the rotating amount of the ADF pulse motor  51 , the ADF pulse motor  51  is stopped (S 60 ). Simultaneously, the flapper solenoid  56  for the flapper  37  is switched off to reverse the direction in which the document S is transferred (S 61 ). That is, the flapper  37  is rotated to permit the front end  37   c  thereof to retract below the upper surface of the platen glass  39  as shown in FIG.  14 ( a ). FIG.  13 ( c ) shows the relation between the document S and the flapper at that time, in which the leading end of the document S is rest just before the image reading position on the ADF platen glass  39 . 
     Next, the discharge clutch  58  is disengaged and the discharge clutch  59  is engaged to transmit the forward rotation of the ADF pulse motor  51  to the discharge roller  45 , so that the document S is transferred in the discharge direction by the discharge rollers  45  and  46  to be sent out through the document entrance port  2   c  (S 62 ). Thereafter, the lamp  10  is switched on to illuminate the lower surface of the document S (S 63 ). 
     Next, the ADF pulse motor  51  is driven in the forward direction to rotate the image reading transferring roller  36  in the counterclockwise direction viewed in FIG. 6, consequently to forward the document S from the leading end thereof in the reverse direction at the prescribed image reading speed (S 64 ). The forward rotation of the ADF pulse motor  51  causes the discharge roller  45  to rotate in the counterclockwise direction, thus forcing the flapper  42  to rotate in the clockwise direction. However, since the flapper  42  is connected to the discharge roller  45  through a not-illustrated torque limiter, when the document comes in partial contact with the document S, the flapper  42  withstands the rotational force of the discharge roller  45  due to the torque limiter to endure rotating. Accordingly, the document S is not excessively pressed downward by the flapper  42  due to the torque limiter interposed between the flapper  42  and the discharge roller  45 , so that the document can be transferred through between the flapper  42  and the discharge roller  45  without interference with the flapper  42 . 
     Next, a decision whether the leading end of the document S reaches the image reading position is made on the basis of the rotating amount of the ADF pulse motor  51  (S 65 ). When the rotating amount of the ADF pulse motor  51  reaches the prescribed value to move the document to the image reading position, the image reading operation is started from the leading end of the document (S 66 ). 
     The leading end of the document S is transferred along the passages formed around the image reading transferring roller  36  by the transferring surface  37   b  of the flapper  37  and a part of the side surface  34   c  of the flapper  34  (see FIG.  14 ( a )), and advances along the passage formed between the flapper  43  and the transferring guide  47  toward the discharge rollers  45  and  46  through the registration small roller  48 . FIG.  13 ( d ) shows the state in the process of reading the document S. The timing sensor  12  is operated to watch for the tail end of the document S passing thereby at all times. Thus, a decision whether the timing sensor  12  issues an OFF signal as the result that the tail end of the document S passes by the timing sensor is made (S 67 ). When the timing sensor  12  issues the OFF signal, the image reading operation on the reverse surface of the document is terminated (S 67 ) to stop the ADF pulse motor  51  for a while (S 69 ). Then, the lamp  10  is switched off (S 70 ), and the ADF pulse motor  51  is operated in the forward direction at high speed so as to transfer the document S at a speed higher than that of reading the image on the document (S 71 ). FIG.  13 ( e ) shows the document transferring state in which the document S is transferred toward the discharge rollers  45  and  46  through the flappers  37  and  34  and the transferring guide  47 . 
     At this time, the discharge sensor  62  checks whether the document S passes thereby. When the document S completely passes therethrough, the discharge sensor  62  assumes its OFF state. Therefore, when an OFF signal is issued from the discharge sensor  62  (S 72 ), the document is further transferred by a prescribed amount so as to be completely sent out through the document discharge port  2   d  by the discharge rollers  45  and  46  as shown in FIG.  13 ( f ) (S 73 ). 
     As described above, according to the document transferring mechanism  17  of the image reading device  1  of the invention, the image reading can always be carried out from the same end of the document S in reading the image on either of the obverse and reverse surfaces of the document. That is, the document is invariably read from its same end regardless of whether the obverse surface or reverse surface is scanned, and the image thus read can reliably be reproduced on a sheet of paper. Moreover, when turning the document upside down, the leading end and tail end of the document S do not overlap each other even if the document transferring mechanism is made small in dimensions. 
     Next, a modified embodiment of the document transferring mechanism  17  for performing the operation for reading images on the both surfaces of the document will be described with reference to FIGS.  15 ( a ) and  15 ( b ) showing schematically the process of transferring the document. However, the process of transferring the document is not limited to that shown in FIGS.  15 ( a ) and  15 ( b ). The image reading position in this embodiment corresponds to the position illuminated with light emitted from the image reading carriage  7 , from which the light illuminated is reflected and incident on the CCD  5 . The document transferring passage is depicted by the solid line, and the direction of transferring the document is depicted by the dotted line in these drawings. 
     First, the document is transferred from one side of the mechanism toward the image reading position to read the image on the obverse surface of the document (A 1 ). Subsequently, the document is moved backward with the rotation of the image reading transferring roller  36  used in FIG. 6, thus to be forwarded from the tail end of the document along the curved peripheral surface of the image reading transferring roller  36  in the clockwise direction (A 2 ). At this time, the document passes through the image reading position, but image reading is not effected. After the leading end of the document passes through the image reading position, the direction of transferring the document is reversed to forward the document from the leading end thereof in the direction opposite to that in which the document is transferred to read the image on the obverse surface of the document (A 3 ). Then, upon reading the image on the reverse surface of the document S, the document is discharged. 
     The document in the process of FIG.  15 ( b ) is transferred from the one side of the mechanism toward the image reading position in the same manner (A 1 ) as that shown in FIG.  15 ( a ). Then, the document is moved backward (B 2 ) to be turned upside down, and forwarded from the leading end thereof toward the image reading position. Subsequently, the document S is moved backward from the leading end thereof in the direction opposite to that in which the document is first transferred, and then, is discharged upon performing the image reading (B 3 ). 
     The processes of reading the image on the first surface of the document moving in the first direction (forward direction), and then, turning the document upside down to read the image on the second surface of the document in the embodiment shown in FIGS.  15 ( a ) and  15 ( b ) are fulfilled in the same manner as those in the foregoing embodiment shown in FIGS.  12 ( a ) to  12 ( f ) and FIGS.  13 ( a ) to  13 ( f ). According to this embodiment, the image reading can always be carried out from the same end of the document in reading the image on either of the obverse and reverse surfaces of the document. That is, the document is invariably read from its same end regardless of whether the obverse surface or reverse surface is scanned, and the image thus read can reliably be reproduced on a sheet of paper. Moreover, when turning the document upside down, the leading end and tail end of the document S do not overlap each other even if the document transferring mechanism is made small in dimensions. 
     Although the present invention has been described with reference to FIGS.  12 ( a ) to  12 ( f ), FIGS.  13 ( a ) to  13 ( f ) and FIGS.  15 ( a ) and  15 ( b ), it is to be understood that the invention is not limited to the specific embodiments thereof. For example, in the embodiment of FIG.  15 ( b ), the document S may be transferred in the reverse direction from the route B 3  to the route B 2  through the route A 1 .