Browsing by Author "Sanchez, Lilia Armida"
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Item Instantaneous screw axis identification using holographic interferometry(1988) Sanchez, Lilia Armida; Kleis, Stanley J.; Shoup, Terry E.; Anderson, Wallace L.; Mistree, Farrokh; Wood, Lowell T.; Ktonas, Preiklis Y.Exact description of human joint movement is difficult because it is likely to involve all six degrees of freedom allowable in three-dimensional space. A three-dimensional motion can be described by the movement of the instantaneous screw axis (ISA) so that the whole motion of a body at each instant can be given as a combination of a simple rotation about and translation along that axis. Double-exposure holographic interferometry is proposed as a noncontacting, noninvasive photo-optical technique for measuring small displacements of a body in space and approximating the ISA. Displacement measurements from double-exposure holograms generally involve a single hologram analysis which makes use of the static fringe-order method or a dynamic fringe-counting method. The static method requires identification of a zero-order fringe, which is often difficult or impossible. The dynamic method is severely restricted by the limited change in viewing direction bounded by the angle which the object subtends at the hologram. This restriction results in an ill-conditioned matrix of sensitivity vectors characteristic of the geometry of the experimental set-up. An improved measurement technique using a single double-exposure hologram is proposed which combines the dynamic and static methods to measure finite displacements resulting from rigid body motion. The dynamic fringe-counting method with a least-squares error analysis is used to extract the in-plane translations and rotations of the motion. A static fringe-order difference between two points on the surface of the object and the translations are used in the fringe-locus function to determine the out-of-plane rotations of the body. The existing dynamic method is also used for comparison of results. Both sets of experimental results for rigid body translations and rotations are compared to the actual micrometer readings. The results computed from the proposed dynamic fringe-counting/static fringe-order difference technique show considerable improvement over the dynamic method. The experimental ISA parameters compare very favorably with the the actual ISA parameters computed.