METHOD FOR DETECTING LOOSENESS OF BOLT AND NUT

PURPOSE:To make it possible to detects looseness without being effected by the size and rigidity of a bolt and a nut or by personal differences by detecting the pulse waveform of the striking force of a striking hammer or acceleration and the ratio between the rising gradient and the falling gradient of the pulse waveform. CONSTITUTION:A sensor 15 using a piezoelectric element, a strain gage and the like is attached to a hammer 16. A nut 14 of a head part 12a of a bolt 12 is hit with the hammer 16 in the shearing direction. The obtained symbol is electrically processed, and a waveform is obtained. The waveform is further processed, and the tightening state between the bolt 12 and the nut 14 is judged. Namely, the generated time and the terminating time of the pulse and the force or acceleration between the generated time and the terminating time are detected as a strike pulse signal 25. The signal 25 is amplified in an amplifier 26 and undergoes A/D conversion in an A/D converter 18. Thereafter, the characteristic values of the rising angle or gradient and the falling angle or gradient are computed in an operating part 27. The results are displayed on a display part 19 or displayed as numerical values with an LED 30.