Fringe projection profilometry using a uniaxial MEMS micro-vibration mirror is becoming popular in three-dimensional (3D) reconstruction owing to the advantages of fast projection, small size, low cost, and no demand of focus optics. The calibration method is crucial and directly affects the accuracy of 3D reconstruction. In conventional phase-height calibration methods, there exists a problem of recalibration of system parameters if the maximum fringe frequency varies between the stages of calibration and reconstruction. In this paper, the fringe projection is realized by a MEMS mirror with a 1.15 kHz resonant frequency and a line laser. The voltage of line laser is modulated according to the scanning position, which is related to the vibration characteristics of MEMS mirror. Subsequently, the uniaxial MEMS-based 3D reconstruction system is constructed. We propose a novel calibration method for the uniaxial MEMS-based 3D reconstruction system. The proposed calibration method is derived from the scanning characteristics of a uniaxial vibration mirror and considers the camera distortion. The proposed method is free from the problem of recalibration and the limitations of installation. The experimental results show the proposed method can reconstruct the 3D shape of target in high resolution and verify the feasibility of the system.
Three-dimensional (3D) measurement based on structured light is widely applied in the diverse fields of industrial detection, face recognition, reverse engineering, and so on. Compared with typical dynamic structured light fringe projection system using DLP or DOE, the system based on MEMS mirror has the advantages of small size, low cost, no optical magnifying lens, no need for focusing, and a large field of view angle range, which can achieve sub-millimeter or even higher accuracy. In MEMS mirror-based system, structured light patterns are formed by matching the mirror angle and laser output power and accurate identification of the angle is key point for achievement of a high pattern quality. There is a big challenge in identifying the MEMS mirror’s angle since the pulse signal for driving the mirror is very narrow, around 20 ns. For meeting this requirement, a high speed and accurate FPGA is utilized to observe the narrow pulse signal of the MEMS mirror and simultaneously control the laser power output, generating precise sinusoidal fringes. A 250 MHz clock frequency for observing pulse signals position based on logic voltage comparison under an LVCMOS33 standard, successfully identifying the narrow pulse signal. This ensures a high accuracy of the light patterns. Total harmonic distortion (THD) is used to evaluate the sinusoidal property of the structured light patterns and results verify that the THD of the MEMS mirror structure light projection system controlled by FPGA is less than 5%.
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