A workpiece is passed through a beam of either continuous or pulsed light which is interrupted thereby. The light impinges on a phototransducer such as a phototransistor, which is connected to an evaluation circuit. The evaluation circuit evaluates instantaneous light values with respect to movement...http://www.google.es/patents/US4217053?utm_source=gb-gplus-sharePatente US4217053 - Apparatus and method to test workpieces for size, relative position, material integrity, and the like
Apparatus and method to test workpieces for size, relative position ...
