Gaging By Remote Image Tracking

A method is described for performing non-contact optical gaging of complex parts in a production environment. The operational concept of the system, known as Gaging by Remote Image Tracking, relies upon an optical triangulation technique. A spot of light is projected from a gage head onto the surface of the part being gaged., an image of this spot is focused on the center of a tracking photodetector, mounted within the gage head. If the part is translated in a direction perpendicular to the projection axis, the focus spot on the surface of the photodetector will move as the surface curvature of the part changes. As a result of this movement, voltage signals are generated which provide: 1) a measure of the spot displacement on the photo-detector, and 2) a signal for driving the optical head in a direction which recenters the image spot on the photodetector. The first signal, with appropriate scaling, provides virtually an instantaneous measure of the dimensional change of the part. The second signal is used to drive the system to a known distance from the part (system null). By monitoring the motion of the entire system with a linear encoder and adding this measurement to the instantaneous measure of surface curvature, the result is a fast, non-contact optical gaging system with large dynamic range.