Apparatus for distinguishing between predetermined ranges of angles at which light rays leave a surface

摘要

The flanks of faults present in a surface produce abnormal reflection of a laser beam during linewise scanning of the surface by a laser beam. This apparatus deflects the angles of reflection from the surface, to indicate the presence of a flank, by a light conducting rod arranged parallel to the direction of linewise scanning for receiving reflected light on its surface and for conducting this light to its end face. The various light rays spread out transversely to the direction of scanning during their passage through the light conducting rod and are detected as they pass through a series of concentric annular apertures spaced from the end face of the light conducting rod. Each aperture is associated with a particular range of angles of incidence irrespective of the point on incidence along the surface of the rod and photoelectric detectors are used to sense the light passing through each aperture to provide the necessary indication of the presence or non-presence of a fault. Several types of transparent light guides are used to concentrate the light from the apertures onto the photoelectric detector and various signal processing circuits are described.