Grating Projection And Image Correlation For Three-dimensional Displacement Measurement

In this paper, two main research subjects are grating projection and imagecorrelation method for three-dimensional(3D) displacement measurement, relevantkey techniques are studied systematically.In profilometry, self-adaptive phase demodulation method based on wavelettransform and novel profilometry immune from aliasing are proposed. Phase can beretrieved correctly because of the self-adaptability of wavelet for the gratingfrequency variation.The fundamental component can be restored accurately byfrequency inversion method because the frequency aliasing is decreased greatlyafter the grating background is reconstructed by wavelet decomposition. Improvedautomatic reference and digital dual-frequency grating technique are proposed tosimplify operation and increase accuracy. The idealized phase distribution on thereference plane can be constructed numerically from the local specimen grating.The phase obtained from the compound grating of different sensitivity are appliedto synthesize continuous phase .The direct phase difference algorithm isintroduced into various profilometry to simplify phase unwrapping. Thesimulation system for projection grating is developed and realized to simulate thesingle and dual frequency grating system.Key techniques about how to increase speed and improve accuracy of digitalspeckle correlation method(DSCM), how to realize 3D displacement measurement arestudied. Hybrid algorithm for DSCM based on genetic algorithm and Quasi-Newtonmethod is established to resolve the contradiction between speed and accuracy.Normalized correlation coefficient is used as objective function, iterative initialvalue for Quasi-Newton method is determined by genetic algorithm and adjacentpoint initial estimate, speed and precision are improved simultaneously .The binocularstereo vision technique is introduced into DSCM, 3D DSCM and 3D marker methodare developed and realized. The system is established to measure 3D displacementof the thin crack rubber band stretched and thick rubber plate compressed. Imagecorrelation method is introduced into profilometry. 3D position of the object beforeand after deformation are obtained by projection grating method. Registration ofhomologous point is completed by image correlation identification method.3D displacement is determined by the position difference. The application domainof profilometry is extended.