Uniaxial three-dimensional phase-shifting profilometry using a dual-telecentric structured light system in micro-scale devices

This paper presents a novel method for uniaxial microscopic three-dimensional (3D) profilometry using a structured light system with dual-telecentric lenses in micro-scale devices. Specifically, a telecentric lens can produce an orthographic view of an object and provide the exact size of objects in the x and y directions. An electronically focus-tunable lens attached to the projector rapidly and precisely changes the focal plane of the projected structured patterns, a camera captures the structured patterns from the same perspective and a computational framework analyzes the relationship between the captured structure images and the drive current of the electronically focus-tunable lens to obtain depth information for each pixel. By replacing the normal lens with telecentric lenses, the proposed method dodges perspective error and makes precision measurement easier. We developed a shadow-free coaxial 3D shape measurement system with dual-telecentric lenses that achieved a spatial resolution of approximately 5.86 µm and 4.08 µm root-mean-square error with a depth range of 1200 µm.