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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. [ABSTRACT FROM AUTHOR]

• Multilevel symmetric pattern is proposed for high-speed and high-accuracy 3D shape measurements. • The proposed method can achieve both speed and accuracy. • This method results in much better phase quality compared with conventional methods. • High-speed 3D shape measurement is performed at 667 Hz speed. The binary defocusing technique has enabled speed breakthroughs for 3D shape measurement, yet simultaneously achieving high accuracy and high speed remains difficult. To overcome this limitation, we propose to utilize multilevel symmetric pattern for high-speed and high-accuracy 3D shape measurement. Compared to conventional binary patterns, multilevel pattern could bring more flexibility for eliminating undesired high-frequency harmonics, thus has the potential to greatly enhance the phase quality and measurement accuracy. In this paper, the symmetric pattern design principle and related optimization procedure are presented in order to find the "best" multilevel fringe patterns. Both simulation and experiments verify that with respect to conventional methods, the proposed method could consistently generate better fringe patterns for a wide range of fringe periods. Furthermore, we developed an absolute 3D shape measurement system with the speed of 667 Hz, verifying that the proposed method is applicable for high-speed, high-accuracy applications. [ABSTRACT FROM AUTHOR]

Reducing the number of structured patterns for three-dimensional (3-D) reconstruction is of great importance for high-speed 3-D shape measurement. We present a method that reconstructs absolute 3-D shape using three projected binary patterns: one direct current (DC), one low-frequency, and one high-frequency fringe pattern. The procedures are (1) take the difference between the sinusoidal fringe patterns and the DC pattern; (2) apply Hilbert transform to the difference images to generate two phase maps; (3) employ the geometric-constraint-based phase unwrapping method to unwrap the low-frequency phase map; (4) unwrap the high-frequency phase map using the unwrapped low-frequency phase map; and (5) reconstruct 3-D shape. We developed a prototype system that can capture two-dimensional images at 6000 Hz, achieving 2000 Hz 3-D shape measurement speed. [ABSTRACT FROM AUTHOR]