Double feed detection method and device

Abstract

A double feed detection method for detecting a double feed of a sheet-like detection object transported through a processing unit has an ultrasonic transmitter and an ultrasonic receiver positioned so as to sandwich a transport path along which the sheet-like detection object is transported so as to detect a double feed of the detection object. The double feed detection method has a step of forming a gap between the sheet-like detection objects where the sheet-like detection objects overlap when a double feed of the sheet-like detection objects occurs. Forming the gap between the sheets enhances an attenuation of an intensity of a response signal whenever a double feed occurs. As a result, a distinction between the intensity of the response signal when a double feed has occurred and when no double feed has occurred is sharpened and thus more easily detected, improving the double feed detection accuracy.

What is claimed is:  
     
         1 . A double feed detection method for detecting a double feed of a sheet-like detection object being transported through a processing unit, an ultrasonic transmitter and an ultrasonic receiver being positioned so as to sandwich a transport path along which the sheet-like detection object is transported so as to detect a double feed of the detection object, the double feed detection method comprising a step of forming a gap between the sheet-like detection objects where the sheet-like detection objects overlap when a double feed of the sheet-like detection objects occurs.  
     
     
         2 . A double feed detection device for detecting a double feed of a sheet-like detection object being transported through a processing unit using an ultrasonic sensor to detect a double feed of the detection object, the double feed detection device comprising: 
 an ultrasonic transmitter and an ultrasonic receiver positioned so as to sandwich a transport path along which the sheet-like detection object is transported; and    a gap-forming mechanism that forms a gap between the sheet-like detection objects where the sheet-like detection objects overlap when a double feed of the sheet-like detection objects occurs.    
     
     
         3 . The double feed detection device as claimed in    claim 2   , wherein the gap-forming mechanism comprises: 
 a transport part that sandwiches the sheet-like detection object at a trailing end of the transport path in a direction of transport of the sheet-like detection object by a transporting mechanism along the transport path; and    a brake part,    the brake part being a resistive element that reduces a speed with which the sheet-like detection object is transported by the transporting mechanism, the brake part generating a bulge, in the direction of transport of the sheet-like detection object along the transport path, in the sheet-like detection object that contacts the brake part.    
     
     
         4 . The double feed detection device as claimed in    claim 2   , wherein the gap-forming mechanism is provided at a trailing end of the transport path in the direction of transport of the sheet-like detection object by the transporting mechanism along the transport path and the gap-forming mechanism includes a transport part that sandwiches the sheet-like detection object at both lateral edges, the double feed detection device further comprising a part that presses the lateral edges of the sheet-like detection object inward toward a center of the sheet-like detection object, such that a width of a gap formed between double fed sheet-like detection objects is at a right angle to the direction of transport of the sheet-like detection object.  
     
     
         5 . The double feed detection device as claimed in    claim 3   , wherein the brake part and the transport part comprise at least one pair of rollers that sandwich the sheet-like detection object between them, the roller that constitutes the brake part having a rotation speed that is slower than a rotation speed of the roller that constitutes the transport part.  
     
     
         6 . The double feed detection device as claimed in    claim 3   , wherein the brake part is a pad-like member that scrapes one surface of the sheet-like detection object.  
     
     
         7 . An optical form reader comprising: 
 a scanner including a part that optically reads information stored on a form; and    a double feed detection device for detecting a double feed of a plurality of forms being transported through a processing unit using an ultrasonic sensor to detect a double feed of the detection object,    the double feed detection device comprising:    an ultrasonic transmitter and an ultrasonic receiver positioned so as to sandwich a transport path along which the forms are transported; and    a gap-forming mechanism that forms a gap between the forms where the forms overlap when a double feed of the forms occurs.