METHOD AND APPARATUS FOR SURFACE DEFECT DETECTION USING DETECTION OF NON-SYMMETRICAL PATTERNS OF NON-SPECULARLY REFLECTED LIGHT

摘要

A cylindrical metal object to be inspected for surface defects is rotated about its axis and a collimated laser beam is axially scanned across the object surface in a plane normal to the surface. A plurality of photoelectric detectors are symmetrically arranged on each side of the scanning plant to detect light non-specularly reflected from the object. Defects causing an unsymmetrical reflection to the detectors are sensed by summing the outputs of symmetrically disposed pairs of detectors and comparing the summed outputs to determine significant differences in the summed outputs and producing a defect signal when such differences occur.