Reflective grain defect scanning

Abstract

Grain structure defect scanning is accomplished by a pair of light detectors directed toward an inspection point illuminated by a collimated light beam incident upon the inspection surface at a given angle of incidence. One detector, the specular detector, is positioned generally along the specular angle of reflection as defined by the angle of incidence and the other detector, the diffuse detector, lies substantially along the angle of incidence. When specular reflection dominates, as when the inspection point corresponds to clearwood, the specular detector indicates a higher reflective light intensity than the diffuse detector. When diffuse reflection dominates, however, as when the inspection point corresponds to a grain defect, both detectors indicate similar reflective light intensity. Grain defect discrimination is accomplished by calculating a ratio of specular detector output to diffuse detector output. Further analysis of the relative magnitudes of the detector outputs provides a basis for identifying grading marks, such as ink and wax marks, at the inspection point.