Autofocusing method for a digital fringe projection system with dual projectors

This paper presents a novel technique to achieve autofocusing for a three-dimensional (3D) profilometry system with dual projectors. The proposed system uses a camera that is attached with an electronically focus-tunable lens (ETL) that allows dynamic change of camera's focal plane such that the camera can focus on the object; the camera captures fringe patterns projected by each projector to establish corresponding points between two projectors, and two pre-calibrated projectors form triangulation for 3D reconstruction. We pre-calibrate the relationship between the depth and the current being used for each focal plane, perform a 3D shape measurement with an unknown focus level, and calculate the desired current value based on the initial 3D result. We developed a prototype system that can automatically focus on an object positioned between 450 mm to 850 mm. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement