Abstract:
An automatic document feed apparatus includes a document tray having a document positioning surface extending along a transporting direction. A main roller receives a document from the document tray by rotating in the transporting direction. A return roller is pressed against the first roller and rotates in a direction opposite to the transporting direction with a constant torque. Further, a skew-corrective roller which rotates in the transporting direction is provided to prevent skewing of the document in cooperation with the second roller and the document positioning surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an automatic paper feed apparatus, particularly relates to an automatic paper feed apparatus which securely prevents skewing of transporting documents. 
     2. Description of the Related Art 
     As a first conventional example which prevents skewing of transporting documents, Japanese Utility Model Application Laid-Open No. 62-13948 proposes a technique using a document guide and a width determination plate. 
     Furthermore, as a second conventional example, Japanese Patent Application Lald-Open No. 9-240874 discloses a technique, which includes an image sensor for reading an image of a document, a feed roller provided In a position which faces the image sensor, a delivery roller provided on an upstream side of the image sensor, and a rubber plate member provided in a position which faces the delivery roller. A large friction area with a large coefficient of friction is formed on one portion of the feed roller in its longitudinal direction, and the rubber plate member is provided in a position of the delivery roller in its longitudinal direction which matches for the large friction area. 
     Therefore, according to the second conventional example, since the position of the large friction area of the feed roller matches for the position of the rubber plate member, a document can be transported suitably against a back tension generated on the document. Moreover, since the document is transported by a specified friction force even in right and left areas of the feed roller, all the documents can be transported uniformly. As a result, this technique produces an effect for efficiently preventing generation of pucker and skewing of the documents. Since the large friction area of the feed roller is provided in an approximately central portion of the longitudinal direction, the skewing of the documents at the time of transporting the documents by means of the feed roller can be efficiently prevented. 
     However, in the first conventional technique, since only the document guide and the width determination plate are used as means for preventing skewing, various mistakes such as miss-setting are frequently made, and thus the reliability is poor. 
     In addition, an object of the second conventional technique is to transport documents accurately against the back tension generated in the documents, and as a result skewing of the documents can be prevented just as a spillover effect. Therefore, similarly to the first conventional technique, skewing due to some reason cannot be reliably avoided. 
     SUMMARY OF THE INVENTION 
     The present invention is devised In such points in view in order to solve the above problems of the conventional techniques. 
     It is an object of the present invention to provide an automatic paper feed apparatus which is capable of preventing skewing of transporting documents completely and securely. 
     According to the present invention, a document tray is provided with a document positioning surface extending along a transporting direction in which a document is transported from the document tray. A main roller receives a document from the document tray by rotating in the transporting direction. A return roller is pressed against the first roller and rotates in a direction opposite to the transporting direction with a constant torque. Further, a skew-corrective roller which rotates in the transporting direction is provided to prevent skewing of the document In cooperation with the second roller and the document positioning surface. 
     A rotation speed of the skew-corrective roller rotates is preferably higher than that of the first roller. Further preferably, the skew-corrective roller is provided coaxlally with the second roller and at a position closer to the document positioning surface than the second roller. 
     A pressing means for pressing the skew-corrective roller towards the document is preferably provided to enhance the skew-correction capability of the skew-corrective roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing an automatic feed apparatus according to one embodiment of the present invention: 
     FIG. 2 is a perspective view that a document transporting surface of the automatic paper feed apparatus of the present invention is viewed from a slantingly upper direction: 
     FIG. 3 is a perspective view schematically showing a driving force transmission mechanism among a return roller, an auxiliary roller, a transport roller and the like; 
     FIG. 4 is an enlarged perspective view of the driving force transmission mechanism by means of a gear shown in FIG. 3; 
     FIG. 5 is a diagram for explaining an operation of the return roller and a main roller of the present invention; and 
     FIG. 6 is a diagram for explaining an operation of the auxiliary roller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An automatic paper feed apparatus according to one embodiment of the present invention will be described hereafter with reference to FIGS. 1 through 4. 
     As shown in FIG.  1 . an automatic paper feed apparatus is composed of a document set stand or document tray  1  on which a plurality of documents are stacked, a document positioning surface  1   a  provided on a side surface of the document set stand  1 , a main roller  11  for successively catching the stacked documents from its top one, a return roller  12  for preventing the second and thereafter documents from being caught, a correction roller  13  (see FIGS. 2 and 3) provided coaxially with the return roller  12  on a side of the document positioning surface  1   a  from the return roller  12 , and an auxiliary roller  14  for feeding the documents stacked on the document set stand  1  to the main roller  11 . 
     The documents which were caught by the main roller  11  pass through a document running path  20  by a transport roller  15 , a transport roller  16  and a discharge roller  17  so as to be discharged out of the apparatus. 
     The return roller  12  is held by return roller frames  31 ,  31 , as shown in FIG. 3, which are rotatably mounted to a drive shaft  16   a  of the transport roller  16  and as shown in FIG. 1 the return roller  12  is pressed against the main roller  11  by a spring  32 . The two return roller frames  31 ,  31  are connected with each other by a connecting member (not shown). 
     A driving force of the return roller  12  in a direction of an arrow B (see FIGS. 1 and 3) is transmitted from a drive gear  41  composed integrally with the transport roller  16  to a gear  42  fixed to a return roller shaft  12   a  via a series of gears including transmission gears  44  (small diameter portion (see FIG.  4 )) and  46  on the return roller frame  31 , and further is transmitted via a constant torque clutch  43  provided between the return roller shaft  12   a  and the return roller  12 . Therefore, the constant driving force in the direction of the arrow B is transmitted to the return roller  12 . 
     The correction roller  13  is rotated in a direction of an arrow C of FIGS. 2 and 3 by a driving force which is transmitted from the drive gear  41  via the transmission gear  44  (large diameter portion) on the return roller frame  31  to a correction roller gear  45 . The gear  42  and the correction roller gear  45  are operated independently. 
     A gear ratio from the drive gear  41  to the correction roller gear  45  is set so that a peripheral speed of the correction roller  13  is approximately equal to or slightly higher than a document transport speed of the main roller  11 . 
     Here, the correction roller  13  is composed integrally with the correction roller gear  45  and is freely rotatable with respect to the return roller shaft  12   a . Therefore, the correction roller  13  is driven in the direction of the arrow C at the document transport speed of the main roller  11 . 
     There will be detailed an operation of the embodiment of the present invention hereinafter. 
     When a drive motor  51  (see FIG. 2) rotates, Its driving force Is transmitted via the transmission mechanism (not shown) to the main roller  11 , the transport roller  15 , the transport roller  16  and the discharge roller  17 . Then, the auxiliary roller  14  descends and the documents are caught by the main roller  11  as shown in FIG.  1 . 
     In this embodiment, the auxiliary roller  14  is moved up and down and is driven by a mechanism which is realized by a technique disclosed in Japanese Patent Application Laid-Open No. 7-41191. For this reason, the transport speed of the main roller  11  is set to be slower than the document transport speed. 
     Thereafter as shown in FIG. 5, a first document  61  is caught by the main roller  11  and is carried in the direction of an arrow D. A second document  62  is stopped in a state that it is slightly caught by the main roller  11  and the return roller  12 . 
     Furthermore, when a backward end of the first document  61  passes through the main roller  11 , the main roller  11  and the return roller  12  slightly rotate reversibly so as to push back the second document  62  slightly. This is because the driving speed of the main roller  11  is slower than the document transport speed, and thus the driving force is not applied to the main roller  11  until play of the driving has been absorbed. 
     Therefore, at the moment that the backward end of the first document  61  passes through the main roller  11 , a force in a direction of an arrow X in FIG. 6 is applied to the second document  62  by the return roller  12 . 
     Furthermore, since a force in the direction of an arrow Y is kept being applied to the second document  62  by the correction roller  13 , a force obtained by adding the above two forces, namely, a rotating force in a direction of an arrow R 1  is applied to the second document  62 , but since there exists the document positioning surface  1   a , needless to say, the document cannot rotate. 
     Here, if the correction roller  13  is not provided, only the force in the direction of the arrow x is applied to the second document  62 , and thus the rotating force in an direction of an arrow R 2  is applied to the document  62  by an inertia force. As a result, if a width determination portion  2  does not hold the end surface of the document, the document rotates in the direction R 2 , resulting in skewed document. 
     Here, when the peripheral speed of the correction roller  13  is slower than the document transport speed of the main roller  11 , the transport speed on the side of the correction roller  13  becomes slow during the transportation of the document. As a result, the document tries to rotate in the direction R 2 , and thus it causes skewing. 
     Therefore, it is preferable that the transport speed of the correction roller  13  is set to be slightly faster so that even it the diameter of rollers slightly changes, the transport speed of the correction roller  13  does not become slower than the transport speed of the main roller  11 . 
     In the case where the transport speed of the correction roller  13  is fast, the force is applied to the document in the direction of the arrow R 1 , and the document is pressed against the document positioning surface  1   a . As a result, needless to say, the skewing does not occur. 
     There will be described below another embodiment of the present invention. 
     According to the above-mentioned embodiment of the present invention, document pressing means is not provided to the correction roller  13 , but when generally known auxiliary pressing means such as a plate spring and a weight are added, the operation of the correction roller  13  is further stabilized. 
     The present invention is constituted and functions as mentioned above, and the present invention produces the following effects. 
     According to the present invention, since the rotating force in the direction of the arrow R 1  is applied to a document by the correction roller  13 , even if the width determination portion  2  is not set securely, skewing of the document can be prevented.