| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and a device for detecting a double feed capable of detecting a double feed of sheet-form substances to be inspected with high sensitivity. SOLUTION: The double feed detecting device 10a is provided with a transmitted 32a and a receiver 32b of an ultrasonic sensor 32 with the transport passage surface of a transport passage 22 nipped therebetween, and rollers 34a and 34b and rollers 36a and 36b are provided in the front and rear in a transporting direction of the ultrasonic sensor 32. Only the roller 36a has a rotation speed lower than those of other rollers 34a, 34b, and 36b. When double feed documents 30 are fed, the document 30 (30b) making contact with the roller 36b has the upper stream side to which deflection A occurs, and a gap C is provided between the double feed documents 30. In the gap C, a sound remarkably damped due to a reflection effect at a boundary between an air layer and the document 30 is generated and the presence of the double feed of the documents 30 is detected by the sound.
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