Nonlinear controls of a microelectromechanical mirror device



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Texas Tech University


Several methods are in use to actuate MEMS (MicroElectroMechanical Systems) devices, viz, piezoelectric, magnetic and electrostatic. Many MEMS applications such as optical gratings, variable capacitors and accelerometers use parallel-plate electrostatic actuators. Typically, these parallel plate actuators are controlled by voltage sources. The problem with voltage control is that a voltage source provides destabilizing positive feedback limiting the stable range of motion to 33% of the gap. This phenomenon is called “pull-in” or “snap-through”. There are number of techniques to increase the stable region. For example, increasing the gap by three times the required operating range, using nonlinear stiffening springs or by controlling the charge on the actuator. The first two methods require higher actuation voltages, while the third method uses complicated switched-capacitor charge control circuits and are difficult to fabricate under the same foot print of the actuator in large actuator arrays. We have demonstrated a non-linear control scheme using an Applied MEMS DuraScan mirror with extended range of motion, improved transient performance, improved positioning accuracy and reduced electrode contact. Further, we have proposed an analog implementation of this controller, which can be fabricated under the foot-print of an actuator.