Closed Loop Electrostatic Actuation of Membrane Mirrors

摘要

Our recent work related to closed-loop electrostatic control of membrane mirrors is summarized in this presentation. We begin with a short description of electrostatic actuation as applied to membrane mirrors, and follow this up with a brief overview of the possible actuation control approaches. The main focus of this presentation is on the two techniques being studied in our laboratory: (1) area control, which involves switching control of conductor segments forming suitably located electrode clusters, and (ii) gap control, which consists of mechanical control of the electrode-membrane gap via a movable electrode substrate. Closed loop control strategies are investigated that provide deflections and bandwidths in the range of 60 micrometers and 500 Hz respectively. A Lyapunov potential method is used for stable tracking of trajectories consistent with these deflection-bandwidth criteria. While our initial emphasis is on small single-mode focus/defocus and tip/tilt mirrors, the method generalizes without much difficulty to multiple-mode actuation of larger mirrors. Results discussed here include time domain simulations and experiments on the closed-loop dynamics of singlemode mirrors under area and gap control, and static tests illustrating gap control of multiple-mode mirrors.