| Highly magnetostrictive materials offer a higher force density output than is available from other materials with controllable strain characteristics. Consequently, these materials have found uses as the actuation elements in underwater acoustic projectors, active vibration control actuators and precision displacement actuators, among other applications. Effective operation in these situations requires precise control over the actuator output. The strain behavior of magnetostrictive materials, though, exhibits hysteresis and saturation, making it difficult to control. This research involves the development of an inverse model of the strain characteristics of the highly magnetostrictive material, Terfenol-D, to be used as part of a control system to linearize its behavior. The integration of a nonlinear inverse into the control of hysteretic material has proven to be much more effective than conventional means of control. A very accurate, real-time inverse model of Terfenol-D had yet to be developed.; Preisach modeling, historically used to characterize magnetization of magnetic recording media, is the basis of the models developed. Three novel models are introduced in the course of this research. The first is a Preisach magnetization model, modified for real-time control use. The second is a strain model applicable to low magnetostrictive material, such as nickel. Finally, the third model, called the bimodal magnetostriction model, is the strain model designed for Terfenol-D. The bimodal model predicts, with a high degree of precision, experimentally measured major loop, minor loop and reversal curve data of a Terfenol-D sample, including the pinched center portion of the major loop controlled by stress in the material.; The inverses of each of these original models are also developed and tested. Convergence of the iteratively solved magnetization model and inverse are proven under specified conditions. The numerical errors due to inversion of the magnetization model fall below 2% for the waveforms tested, and decrease with time. The bimodal strain inverse is shown to allow steady state tracking of strain waveforms that reach 95% of saturation to within 2% in an open loop configuration. The use of the bimodal magnetostriction inverse in a full control configuration is outlined. |
