| 摘要 |
A detector for detecting the cracking sound of plate glass under polishing while discriminating it from the cracking sound of other plate glass. More specifically, sounds are collected by a microphone (30) and high frequency sounds are extracted by a filter (40). With regard to the high frequency sounds extracted through the filter (40), a sound level becoming highest within a predetermined time T1 (T1=10 msec) is acquired every predetermined time T1. Lowest sound level among the sound levels thus acquired within a predetermined time T2 (T2=300 msec) in the past is then acquired as a steady sound level. One count is added when the ratio between the current sound level acquired every predetermined time T1 and the steady sound level exceeds a predetermined value (2.5). The third process and the fourth process are repeated every predetermined time T1 until the count reaches 10. When the count reaches 10 within a predetermined time T3 (5 sec), a decision is made that plate glass G has cracked and a signal indicating cracking is delivered to a control section (24).
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