A novel, adaptive system for 3-D optical profilometry using a liquid crystal light projector

A 3-D optical whole-field profilometer based on adaptive projection of structured light is presented. The system is based on the projection of gratings by means of an LCD unit. The gratings can be varied both in contrast and in period, to adapt to the shape of the object under measurement. A video camera acquires at a different angle the object-deformed pattern. Suitable pre-elaboration is performed, to decrease dependence on background illumination and nonuniform reflectivity of the surface. Adaptive demodulation of the pattern allows the object profile to be evaluated. The performance of the instrument has been evaluated by means of a system calibration against a traceable high-precision commercial Contact Measuring Machine (CMM). The overall accuracy of the system is equal to 0.15 mm with a precision of 0.2 mm. In this article, the theoretical aspects of the technique are discussed, and the description of the complete system is presented. Profile reconstruction, calibration, and certification of the system are also covered. The accuracy of the system is discussed, and experimental results are presented