System for checking defects on a flat surface of an object

Abstract

A checking system for checking defects on an optically flat surface of an object to be checked is adapted to spirally scan the surface of the object with a laser beam which is projected from an optical head. The laser beam is reflected from the surface of the object and converted by a photodetector to an electric signal. The level of the electric signal is compared with a reference level to produce a defect signal. The rotation of the object is detected by a position sensor. A counter counts a position signal in response to the defect signal and the contents of the counter is stored, as data representing a defect start position, in a defect position memory. The length data of the defect signal is counted and stored in a defect length memory. Predetermined defect position data is read out of a defect position memory, while defect length data corresponding to the defect position data is read out of the defect length memory. Position data associated with an area to be displayed is compared with defect position data. When both data coincide with each other, the corresponding defect length data is counted down. During the down count period, defect picture element data is stored in a refresh memory. The picture element data stored in the refresh memory is delivered to a CRT where it is displayed as defect data.