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Nonlinear modeling for control of Terfenol-D-based actuators

Nonlinear modeling and control methods can be used to increase the usable range of operation of Terfenol-D. Presently, in dynamic applications the usable range of Terfenol-D is often limited to approximately 850ppm. This limitation is imposed by harmonic distortion, spurious vibration, and/or tracking error considerations. These nonlinear effects are due to large variations in the magnetoelastic parameters and hysteresis. The preliminary results of this program indicate that a large performance advantage may be gained through proper control of the nonlinearities. As an example, a recently designed reaction mass actuator that weighs 1.125lbm can produce peak forces as high as 125lbf. However, to limit the open-loop total harmonic distortion to less than 2 percent requires that peak forces be limited to roughly 65lbf. To determine the magnetoelastic parameters, quasi-static experiments were performed with a specially designed apparatus. The research included modeling and simulation based on the static nonlinear magnetoelastic equations. Under assumptions of quasi-static magnetoelastic behavior, a fourth-order linear model was extended with the static nonlinearities. The model is compared with preliminary experiments. These types of models will allow nonlinear control strategies to be developed for Terfenol-D based actuators, thus extending the harmonic-free operating range.