| 摘要 |
PROBLEM TO BE SOLVED: To accurately examine the internal pressure of a can without rejecting conforming articles and overlooking the defectives even in a two-piece can having a plurality of strength peaks generated in a stroke test. SOLUTION: Stroke waveforms obtained by converting a sound generated by applying an electromagnetic impact to an elastic wall of a sealed can into electric signals by a microphone are frequency-converted to obtain stroke sound spectra, a first and a second peak of the obtained spectra are extracted and, when the strength ratio of the second peak to the first peak is within a prescribed range, the frequency of the first peak frequency is set to the stroke frequency and, when being out of the prescribed range, it is so judged that a corrected frequency obtained from the first and the second peaks is set to the stroke frequency.
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