Self calibrating contour measuring system using fringe counting

Abstract

A measuring arrangement is disclosed for measuring the contour of a two or three dimensional surface in which a redundant configuration of distance measuring systems is positioned above the surface being measured. Each distance measuring system monitors distance measurements to a point proximate the surface as the measuring point is moved across the surface. The distance measurements are taken from a sufficient number of points on the surface such that a sufficient quantity of data is obtained to define the system geometry and also to define the position of each measurement point. The data is transformed by recognized mathematical techniques into the coordinate positions of all of the measured points on the surface. In one embodiment for measuring the contour of a three dimensional surface, a tetrahedral arrangement of four distance measuring interferometers includes three interferometers positioned in a planar array above the measured surface and a fourth interferometer positioned at a central apex thereof. A retroreflector is placed adjacent to the measured surface to define the measuring point, and is selectively movable across the measured surface. A tetrahedral truss is positioned above the measured surface, and each interferometer has a beam steering head at one corner of the truss to aim the interferometer beam at the retroreflector during movements thereof. Each interferometer further includes a servo control system for controlling the beam steering head to maintain the interferometer beam aimed at the retroreflector.