Large-depth-range 3D measurement based on optimized multi-focal projection system.

High-speed and large-depth-range 3D measurement technology is of great importance in a variety of fields. Conventional binary defocusing methods can achieve high measurement speed, but their depth range is limited because the defocusing effect is insufficient near the focal plane in the ordinary projection system. To address this problem, we propose an optimized multi-focal projection system by introducing a cylindrical lens with optimal parameter configuration. Compared to traditional methods, the proposed method could overcome the constraint of defocusing region to obtain high-quality sinusoidal fringe patterns over large depth range without sacrificing the measurement speed. In this paper, the principle of multi-focal projection system and the related scheme of parameter configuration are presented in order to illustrate the role of the cylindrical lens and system parameters on modulating the distribution of defocusing kernel and removing the limitations of defocusing region. Experimental results show that the proposed multi-focal projection system with optimal parameter configuration increased the depth range from 150 mm to 725 mm over the conventional single-focal system, achieving greater depth range and better measurement results.