A Virtual Velocity Sensor for Improved Transient Performance of Electrostatically-Actuated MEMS

Electrostatically-actuated MEMS devices suffer from a non-linear bifurcation phenomenon called “snap-through” or “pull-in.” This bifurcation severely limits the operating region of such devices. Control schemes have been proposed to eliminate snapthrough. These stabilizing controllers can be implemented using relatively straight forward current and voltage measurements. However, in order to alter the transient behavior of the system, for example to reduce settling time, or to minimize the likelihood of contacting the bottom electrode, the controller should also include terms dependent on the velocity of the movable electrode. Direct sensing of this velocity during normal device operation is typically not feasible. In this paper we show how the electrode velocity may be indirectly sensed using only capacitance and voltage measurements. Our approach is based on well known techniques of nonlinear observer design, and provides arbitrary fast linear error dynamics. Simulation results show excellent performance.Copyright © 2003 by ASME