Modeling and Control of a Large-Stroke Electrothermal MEMS Mirror for Fourier Transform Microspectrometers

A microelectromechanical systems (MEMS) mirror with large vertical displacement has been developed for Fourier transform microspectrometers, but there exists a large tilting during the large-stroke scanning of the MEMS mirror, which greatly compromises the usable range. In this paper, a closed-loop control method has been established to minimize the tilting of the MEMS mirror. According to experimental results, the tilting motion of the mirror plate can be modeled as a fourth-order system. A feedback controller consisting of a phase-lag compensator, a low-pass filter and a notch filter utilized to stabilize the closed-loop tilt system. A gain scheduling approach is also used to compensate the bias-dependent loop gain and thereby provide more consistent tilting rejection over a wide scan range. Compared with the open-loop drive approach, the closed-loop system offers a stable scan operation with much faster dynamic response and improved overall robustness. The experiments show that the residual tilting is reduced to below ±0.0015° during the full range scan of the MEMS mirror. With this control method, the MEMS mirror achieved a stable scan range up to 356.4 μm, so the measured spectral resolution reached 28 nm at 532 nm in a microspectrometer. The mirror tilting can be reduced dramatically by the proposed active control scheme, and thereby, the usable vertical scan range is increased significantly.