High precision contouring. Recent advances

Shadow (projection moiré) is the oldest form of application of moiré method (1929); papers published in the literature on this subject in the order of hundreds. The multiplicity of papers is a consequence of diverse simplifications used to translate captured images information into the geometry of observed surfaces. Different authors have made different approximations while developing models for moiré contouring fringe data analysis, many times without a thorough evaluation of the adopted simplifications. This make it difficult to evaluate performance of different devices built to measure 3-D shape based on moiré technology. To clarify some of the basic requirements for a successful model, in the 2006 Spring meeting of SEM, a paper was presented proposing a model of moiré contouring based on projective geometry and differential geometry requirements. An application to the determination of the displacements of a large rectangular plate illustrated the proposed model. In this paper the basic ideas presented in the 2006 paper are applied to the contouring of a sample utilized to evaluate the accuracy of laser generated geometrical shapes through the process of laser stereo-lithography. The basic aspects of the process followed to obtain the surface contour are presented and discussed. Comparisons between the optically obtained result, the initial CAD design and a high precision tactile machine are made. These results provide a basis for the evaluation of the obtained result and the feasibility of high precision contouring using moiré contouring techniques. The obtained result show that high precision contouring can be achieved if one applies the correct model that satisfies the basic requirements of projective geometry, differential geometry and the physical optics.