Open-loop versus closed-loop control of MEMS devices: choices and issues

TLDR

MEMS devices can be actuated in open‑loop or closed‑loop, but feedback design is challenging because of limited sensor data, sensor dynamics, noise, and fast actuator dynamics, and a systematic performance comparison of these strategies has been lacking. The study presents experimental results comparing open‑ and closed‑loop control of MEMS to address driving and control issues. An optical MEMS switching device was used to conduct the experiments. Experiments and simulations reveal the advantages and disadvantages of each control strategy, highlight the unique challenges of MEMS compared to macro systems, and provide criteria for selecting an appropriate driving strategy.

Abstract

From a controls point of view, micro electromechanical systems (MEMS) can be driven in an open-loop and closed-loop fashion. Commonly, these devices are driven open-loop by applying simple input signals. If these input signals become more complex by being derived from the system dynamics, we call such control techniques pre-shaped open-loop driving. The ultimate step for improving precision and speed of response is the introduction of feedback, e.g. closed-loop control. Unlike macro mechanical systems, where the implementation of the feedback is relatively simple, in the MEMS case the feedback design is quite problematic, due to the limited availability of sensor data, the presence of sensor dynamics and noise, and the typically fast actuator dynamics. Furthermore, a performance comparison between open-loop and closed-loop control strategies has not been properly explored for MEMS devices. The purpose of this paper is to present experimental results obtained using both open- and closed-loop strategies and to address the comparative issues of driving and control for MEMS devices. An optical MEMS switching device is used for this study. Based on these experimental results, as well as computer simulations, we point out advantages and disadvantages of the different control strategies, address the problems that distinguish MEMS driving systems from their macro counterparts, and discuss criteria to choose a suitable control driving strategy.