PURPOSE: To detect a gap between the works to be welded with high accuracy by extracting a peak level from an electrical signal outputted by an ultrasonic transmitting and receiving means, comparing a reference peak level with the above-mentioned peak level and outputting a correction signal to perform proper welding according to its result.
CONSTITUTION: A work 1 and a work 2 form a gap (g) and are assembled. The ultrasonic transmitting and receiving means 3 transmits ultrasonic waves toward the gap (g). A transmitted pulse is reflected on the works 1 and 2 and reflected waves are received by the ultrasonic transmitting and receiving means 3. Pt and Pr denote a transmitted pulse waveform and a received pulse waveform, respectively. The received pulse Pr is attenuated by multiple reflection on the gap (g) and a peak value of the received pulse Pr decreases. In addition, the peak value Ep increases proportionally in accordance with an increase of the gap (g). This is due to the fact that the edge Q of the work 2 approaches the ultrasonic transmitting and receiving means 3 in accordance with the increase of the gap (g). When there is no gap, a peak level EPs is obtained and stored and this value is compared with the peak level EP during welding. Consequently, the gap (g) can be detected with high accuracy.
HANEDA MITSUAKI
SAITO NOBORU
