A finite element test bed for development of feedback control laws for electrostatic MEMS



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Texas Tech University


This project presents the ANSYS simulation techniques for an electrostatically-actuated MEMS device incorporating feedback control laws. The electrostatic MEMS device consists of a movable electrode, suspended on flexible, elastic structures, and one or more fixed drive electrodes. Nonlinear feedback control laws are simulated in ANSYS multi-physics solver and a transducer element. ANSYS multi-physics solver is limited for these types of simulations. ANSYS doesn’t support multiframe restart and the combined circuit and electrostatic analysis are incompatible. This work presents simulation techniques based on numerical methods to circumvent these limitations. The proposed technique eliminates the circuit elements from the model, and instead propagates the associated states in an APDL macro. ANSYS auto time stepping method is not applicable for closed-loop feedback control systems because loads are calculated at each step based on simulation output at the previous step. An adaptive step size Runge-Kutta integration routine is incorporated within APDL macro to develop an efficient simulation technique. The simulation efficiency of the static closed loop feedback control systems is increased by a factor more than 100. However, a dynamic closed loop feedback control systems exhibits only a brief initial transient, and then does not permit further step size increases. To increase the simulation efficiency of such systems, the adaptation logic is turned off once the step size stabilizes. Simulation results for representative MEMS devices including a one-DOF piston microactuator and a two-DOF rotating/translating microactuator demonstrate the efficiency of these simulation techniques.