Some advances in optical contouring of diffuse objects using moire and speckle techniques
2012-11-15T13:51:07Z (GMT) by
Optical contouring is a full field, non-contact technique capable of determining shape and deformation data from 3-D surfaces. The data, which are obtained from the optical contouring system, represent the surface geometry at evenly sampled points. The main objective of this thesis is to report some advances achieved by the author in the optical contouring field. Conditions for the design and construction of optical systems to measure object topography and deformation using the same hardware, as well as the optical working methodology and system parameters, are analysed. The conventional in-plane and out-of-plane optical setups for displacement sensitive ESP I systems are employed to contour. The contour maps are obtained by giving small displacements to optical fibres carrying the object and reference beam illumination. A rigorous mathematical treatment of shape contours generated by ESPI is given. It is experimentally verified that the fringe patterns produced are identical to projected fringe contours, and may be analysed in the same way. Then, practical systems which combine deformation and shape measurement in both in-plane and out-of-plane ESPI configuration are demonstrated. Comparison is made with shape measurement using two fringe projection moire techniques. The first moire technique uses electronic demodulation to obtain the contour maps. This technique encodes and analyses moire contours by using an electronic system similar to that used for Electronic Speckle Pattern Interferometry (ESPI). Hence automatic fringe detection and contour measurement is possible. The Talbot effect, where the self imaging of a periodic object is used as second moire technique. The Talbot image of a linear grating is imaged on the target surface. The grating lines are deformed according to the surface shape. Viewing this deformed grating image through a second reference grating, generates contour maps. A novel on-axis sensor which directly measures distance as a direct colour mapping is introduced. It is emphasized that all the techniques researched here can be extended to be applied as industrial tools for surface inspection or quality control. Phase-shift measurement and digital image processing are employed for data reduction.