Large depth-of-field phase-3D mapping method based on electrically tunable lens

Abstract

Fringe projection profilometry (FPP) is one of the most representative three-dimensional (3D) measurement technology. However, it is difficult to complete accurate 3D measurement with large depth variations at one time, due to the limited depth of field (DOF) of convention lenses. Addressed on this issue, we develop an autofocusing FPP system consisting of a camera with an electrically tunable lens (ETL) and a Micro-Electro-Mechanical System (MEMS) galvanometer laser scanning projector to avoid the limitation of DOF. With this system, we propose a variable focus phase-3D imaging method involving autofocusing phase retrieval and multi-focal length coefficient calibration, to achieve large DOF 3D reconstruction. Autofocus phase retrieval is based on Wiener filter deconvolution algorithm to obtain deblurring fringes under single-frame zoom exposure. To calibrate the phase mapping coefficient, We discretize the continuously variable focal into several in-focus intervals according to the phase modulation function in the measurement depth, and then perform phase-3D mapping coefficient calibration in each focusing interval to finally obtain the multi-focal length mapping coefficient. Experimental results demonstrated that the proposed method can achieve high-efficiency 3D measurement for the depth range of approximately 1,000 mm (300 mm –1300 mm) with the measurement error of 0.05%.