Advanced control of MEMS probing devices

Abstract

This work is aimed at developing a control-system theoretic approach for addressing certain performance issues that arise in micro-electro-mechanical systems (MEMS). In particular, it focuses on applications such as nano-positioning, where control design becomes necessary to meet high resolution, bandwidth, and reliability (robustness) demands especially when there is significant model uncertainty and instrumentation noise. In this article, a systematic control design from robust control approach is demonstrated on a micro probing device with electrically separated sensing combs and driving combs. The system is identified through experimental input-output data and the hardware is setup in such a way that the resulting model is a linear time-invariant model with appropriate choice of variables even when the the underlying constitutive laws are nonlinear. Controllers are developed based on PID and H∞ control design methodologies. Control algorithms from PID control and robust control have been implemented on dSpace digital processing platform. The implemented control (H∞) design demonstrates a significant (≈ 400%) improvement in the bandwidth, where the bandwidths from the closed-loop sensitivity and complementary-sensitivity functions respectively are 68 Hz and 74 Hz. A significant improvement in reliability and repeatability (robustness to uncertainties) as well as noise attenuation is also demonstrated through this design.