FPGA enabled accurate angle-power matching method in MEMS mirrors-based structure light projection 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%.