<title>Shape measurement using phase-shifting speckle interferometry</title>

Abstract

To determine the in-plane strain components from the 3-D displacement vector data of a loaded object, its shape has to be known. The phase shifting speckle interferometric system, described in this paper, has been used for both the displacement vector measurements and for the acquisition of the essential shape information. The numerical shape data resulting from the application of a phase shifting technique allows further calculations, e.g. the determination of the object surface normal vector. The shape measurement method (a modified two- illumination-source technique) is discussed and the experimental system is described. An overview of the basic image processing algorithms, involved in the evaluation of the speckle interference patterns, is given. Improved algorithms concerning phase unwrapping and intensity averaging in the case of low light levels are presented more extensively. Results of shape measurements on a metal cube and a glass bottle are shown. The shape measurement error is estimated at 0.1 mm r.m.s.