Phase-sensitive vision technique for high accuracy position measurement of moving targets

Abstract

This paper presents a vision technique for position and displacement measurement of moving targets. An adapted phase reference pattern is fixed to the object to be controlled and allows the location of the object in the scene observed by a static camera with an accuracy better than 10/sup -2/ pixel. The phase reference pattern is scaled as a function of the desired field of observation and position accuracy. Then the system measurement performances can be chosen from the nanometer to the millimeter ranges (or even larger). Furthermore, the method is self calibrating in length, since the phase reference pattern includes its own length reference. Drifts in vision system magnification therefore do not affect the measurement accuracy. Applications can be used in different fields, for instance, the position control of masks and wafers in photolithography processes or the servo-control of micro-robots.