| 摘要 |
PROBLEM TO BE SOLVED: To provide a detection device of a foreign matter at a paper sheet capable of detecting the foreign matter without receiving influence due to rocking of the thickness direction of the paper sheet by detecting the foreign matter without contacting to the carried paper sheet so as to improve the detecting limit of the foreign matter and so as to detect foreign matters distributed in the width direction of the paper sheet. SOLUTION: The transmitter 2 and the receiver 3 of ultrasonic wave are arranged so as to insert the paper sheet 1 and sound wave guides 4 and 5 are provided at the transmitter 2 and the receiver 3. These guides 4 and 5 have parts opposing the paper sheet 1 with a flat cross section and are installed with their long diameter parts parallel to the width direction of the paper sheets 1. Sound waves outputted from the transmitter 2 are converged along the guide 4 to irradiate the surface of the paper sheet 1 with it as a flat sound wave flux. A part of the sound wave flux with which the surface of the paper sheet 1 is irradiated is reflected by the surface of the paper sheet 1 and the other part passes through the paper sheet 1. These sound waves having passed through the paper sheet 1 are caught by the receiver 3. |
