| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrasonic double feed detection device with enhanced detection accuracy of double feed by detecting an unsteady state in which amplitude and phase of a received signal fall into disorder to avoid erroneous double feed detection due to the unsteady state. SOLUTION: This ultrasonic double feeding detection device is provided with an ultrasonic wave transmitter arranged on one side of a sheet conveyance passage to generate ultrasonic wave for a sheet, an ultrasonic wave receiver 3 arranged on the other side of the conveyance passage to receive ultrasonic wave of the ultrasonic wave transmitter and output an ultrasonic wave receiving signal, a double feeding determining part 42 or 43 for determining whether sheets are fed in an overlapping manner or not based on waveform of the ultrasonic wave receiving signal, and a unsteady state determining part 44 for determining an ultrasonic wave receiving condition of the ultrasonic wave receiver based on waveform of the ultrasonic wave receiving signal. The unsteady state determining part compares a first set threshold value and a second set threshold value with amplitude of the ultrasonic wave receiving signal. It makes the result of determination of the double feeding determining part invalid when amplitude is between the first threshold value and the second threshold value. COPYRIGHT: (C)2005,JPO&NCIPI
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