Method of and apparatus for electrooptical inspection of articles

摘要

An electrooptical system in which workpieces are illuminated from a generally uniform source of light and are line scanned for light intensity deviations characteristic of defects. Pulse trains from photoelectric detectors of a line array have pulse magnitudes which are a function of the light on discrete areas of the workpiece. Pulses having magnitude deviations from adaptively established signal levels are considered events characteristic of the defects. At the beginning of each scan the initial signals are rejected and the pulse train video signal is validated only after the video signal passed by a low pass filter exceeds a threshold. Thereafter data for the event signals of the scan are stored. In order to facilitate storage and processing of data, those event signals which occur for contiguous pulses are identified as event strings, and when an event string achieves greater than a threshold number of events, the stored data is compressed. In data compression, further storage of data and event counting are terminated until the end of the string. The data for the initial event of the string and for the end of the string is stored with a flag indicating that it represents compressed data.