Research On Key Technologies Of 3D Measurement Of Specular Objects

3D measurement of specular objects is an important part of industrial measurement.With the continuous improvement of manufacturing technology,such as automobile painting,precision polishing and free-form surface machining,the measurement needs of specular objects are growing.As a kind of specular 3D measurements,phase measuring deflectometry,which has the advantages of non-contact,high precision and low cost,is considered as the best specular objects measurement with the highest research value and greatest application prospect.At present,research on phase measuring deflectometry is conducted mostly in the laboratory environment,while its application in industrial measurement is seldom studied.Based on the characteristics of industrial specular measurement which include complex shapes and low reflectivity and so on,this paper studies the key technologies in phase measuring deflectometry from the following aspects:1.Calibration: a new method to calibrate the geometric relationship of stereo phase measuring deflectometry system using photogrammetry is proposed.By constructing some reflection points on the screen,a photogrammetry system can be utilized to establish the transform relationship between the screen coordinate system and the the camera coordinate system.The experiment result shows that the measuring system can reach an accuracy of 700 nm after calibration.2.Phase extraction: the paper analyzes the influence of the screen's nonlinear effect on the phase extraction.Study shows that multi-step phase-shifting has a good restraining effect on nonlinear error.The practical effects of phase unwrapping based on Gray code and phase unwrapping based on multi-frequency heterodyning are compared.Study shows that three-frequency four-step phase-shifting can effectively meet the requirements of phase extraction for industrial specular measurement.3.Reconstruction: the paper studies an improved Southwell zonal wavefront reconstruction algorithm.To solve the problem of poor gradient data,a preprocessing method is studied.Simulation and experiment prove that the new reconstruction method can meet the requirement of industrial specular measurement.