DEVICE FOR INSPECTING SURFACE DEFECT OF SCREW

PURPOSE:To detect an abnormal state of each part of a screw,by irradiating light along a normal passing through the center of the screw, also scanning along the axial direction, and detecting a variation of this reflected light. CONSTITUTION:Light passes through a half-mirror 3, is scanned in the axial direction along a normal passing through the center of a screw to the screw 1, and becomes scanned incident light 2. Reflected light from the screw 1 is reflected by the mirror 3, and is made incident to a photoelectric element 4. In this case, light from a crest part 5, a root part 6 and an edge line part 7 of a screw is elongated on the same straight line, and is made incident to the element 4 efficiently. An electric signal obtained by the element 4 becomes a regular repeated waveform which conforms with the number of screw threads under the scanning area of the incident light 2. Accordingly, by detecting a variation of a maximum value 8b and a minimum value 8a of a signal waveform, and a part 8c extending from the maximum value to the minimum value, each abnormal state of the root part 6 of the screw, the crest part 5 of the screw and the edge line part 7 of the screw can be detected.