METHOD AND DEVICE FOR DETECTING FLAW OF SCREW

PURPOSE:To automate the inspection for flaws of screws and to eliminate errors in inspection for flaws in oil well pipes by comparing the parts where the time axes of the signals for the shapes of the longitudinal sections of screws differ. CONSTITUTION:A pipe 10 which is threaded in an end part is fixed near a scanner 40. A shape measuring device 41 is disposed on one side of the pipe 10, and the X/Y stages 42/43, and a vertical moving device 44 of the device 41 are provided with detecting means 42b, 43b, 44b for positions. In the optical system of the device 41, the beam from a laser 411 is made incident through a scanner 412, and lenses 413, 414 to a photodetector 415, and the screw part in a light projecting area is subjected to two-dimensional scanning. The incident light to the photodetector is regulated by the screw shape in a horizontal plane running the center of the pipe 10. The secular change of the photodetection output is made into the signal indicating the shape of the longitudinal section of the screw, which signal is applied to a photoresistor 53 afte A/D conversion 51. The respective outputs of the photoresistor are applied via a switch 54 to a differential amplifier 52. When the difference thereof from the output of the converter 51 exceeds a set value, an alarm is emitted 55.