Optoelectronic instrument for contour comparison

A new technique is described for the comparison of two contours which are nominally identical. It is applicable to two-dimensional shapes and is intended to be used in the inspection of nominally identical mechanical components by comparison with a master component. The method uses the medium of a trace generated on a cathode-ray tube, as an exact copy of the master, by an optoelectronic feedback technique. This trace is then compared with the inspected contour. High overall accuracy is obtainable at relatively low cost because most of the elements of the system have no absolute accuracy requirements. The output signal measures the difference in size between the two components normal to the contour as they are scanned. A laboratory model has proved the feasibility of the method and shown an accuracy of ¿¿15 ¿¿m in this difference measurement in a range of ¿¿150 ¿¿m. Although, locally, this is a large proportional error, it does allow precise comparison and forms the basis of a useful instrument.