Automated deflection measurement of 3-D objects by a modulated-fringe real time holographic interferometry technique

Abstract

Using a modulated-fringe technique with double exposure holographic interferometry results in a monotonically ordered fringe pattern. This monotonic feature removes the ambiguity in determining the fringe values. For relatively small flat objects, the carrier fringes are straight and parallel. Using a reference area around the object and in the same plane as the object allows for easy determination of the undeformed and deformed carrier fringes with a single hologram. For 3-D objects, the carrier fringes are curved and non-uniformly spaced. In this case, a single hologram can produce only one of the two necessary fringe patterns. This paper presents a method in which the undeformed and deformed carrier fringe patterns can be obtained and processed by computer. This technique utilizes real-time holography and computer imaging to produce the two fringe patterns without having to reproduce the exact motion of the point source which creates the carrier fringes. The removal of the ambiguity in determining the fringe orders in the two digitally stored fringe patterns allows for the automation of measuring surface deflections of 3-D objects.