Advances in Light Microscope Stereo Vision

ABSTRACT: The increasing research focus on small-scale mechanical systems has generated a need for deformation and strain measurement systems for micro-scale applications. Optical measurement systems, such as digital image correlation, present an obvious choice due to their non-contacting nature. However, the transfer of measurement technology developed for macroscale applications to the micro-scale presents unique challenges due to the differences in the required high-magnification optics. This article illustrates the problems involved in calibrating a stereo microscope using traditional techniques and presents a novel methodology for acquiring accurate, three-dimensional surface shape and deformation data on small-scale specimens. Experimental results demonstrate that stereo microscope systems can be accurately and reliably calibrated using a priori distortion estimation techniques in combination with traditional oundle-adjustment. The unique feature of the presented methodology is that it does not require a precision calibration target but relies solely on point correspondences obtained by image correlation. A variety of experiments is presented to illustrate the measurement performance of a stereo-microscope system. It is shown that the surface strains obtained from the full-field, three-dimensional measurements on tensile specimens undergoing large rigid body motions are within: 1:50 microstrain of strain gage measurements for strains ranging from 0 to 2000 microstrain.

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