PHASE-LOCKED LOOP PROFILOMETRY

An innovative technique for obtaining automatic three-dimensional shap e information of a diffuse surface is presented. The technique is base d on a new approach of phase measuring from a fringe pattern. The targ et to be studied is first modulated by projecting a linear grating ont o its surface. The linear fringes are deformed according to the surfac e shape. Demodulation is carried out by determining the phase of these deformed fringes using a novel digital phase locked loop demodulation algorithm. The technique has the main advantage that the traditional phase unwrapping process is not required. The phase is determined cont inuously as the algorithm scans the two-dimensional fringe pattern. Ow ing to its sequential nature, this phase detection technique can be im plemented using a special purpose video processor for phase determinat ion at video rates, making it a very fast algorithm. The algorithm alo ng with experimental results of real surface profiles are presented.