The modeling of magnetization in magnetostrictive materials is studied in this article. Magnetostrictive materials elongate in the presence of a magnetic field, and can be useful as actuators. These materials are highly nonlinear, and hence, difficult to control. Accurate models are important to the development of stabilizing controllers with good performance. Here, Terfenol-D, a commonly used magnetostrictive material, is studied. A setup is designed to measure magnetic flux density and stress applied to a Terfenol-D sample. Displacement, electrical current sent to a magnet generating the requested magnetic field, and temperature at different locations are measured. Using experimental data, the Preisach, homogenized energy, and Jiles—Atherton models are evaluated. For each model, the parameters are identified for Terfenol-D. The ease of use and accuracy of these models in the prediction of Terfenol-D behavior are compared.
We have used ellipsometry to measure the initial stages of interface healing in bilayer polystyrene films. We also used ellipsometry to measure the glass transition temperature T(g) of the same or identically prepared samples. The results indicate that as the film thickness is decreased, the time constant for the interface healing process increases, while at the same time the measured glass transition temperature in the same samples decreases as the film thickness is decreased. This qualitative difference in the behavior indicates that it is not always possible to make inferences about one probe of polymer dynamics from measurements of another. We propose a reason for this discrepancy based on a previously discussed origin for reduction in the T(g) value of thin films.
SUMMARYPosition control of a wide class of hysteretic systems, which includes those described by a Preisach model, is considered. The main focus of this paper is stability, tracking and the trajectories of a hysteretic system controlled by a PI controller. The system output (not its derivative) is measured and controlled. It is shown that, for arbitrary reference signals, the closed-loop system is bounded-input-bounded-output-stable with a finite gain of one. Furthermore, the absolute value of the error decreases monotonically for a constant reference signal. In this case, provided that the desired output is within the limits of the system output, zero steady-state error is guaranteed. A bound on the time required to achieve a specified error is obtained. Only a simple condition on the controller parameters is required. The results imply that stability and position control are guaranteed, even if large errors in the model exist.
Magnetostrictive materials can be used to construct high bandwidth actuators with a higher force and a larger stroke than are provided by other materials. However, their use is hindered by their complex nonlinear and hysteretic response. This response displays a significant dependence on mechanical loading. In this paper, a modeling technique is introduced for reproducing hysteresis curves at different loads. The classic Preisach model is used, although the approach can be used to include load dependence in other models. Predicted values are compared with the homogenized energy model and also with experimental data.
Magnetostrictive materials display large force and displacement in response to an applied field, as well as short response time. However, their nonlinear and hysteretic behavior has hindered their use. We prove, using the physics of the material, that these materials are passive. The corresponding energy storage function is shown to be the Helmholtz energy. This result is independent of the model used. The effect of varying load is included. Passivity is important because it can be used to obtain control systems that maintain stability despite uncertainties and disturbances. The minima of the storage function are also obtained. The storage function is written explicitly in the case of a common model for these materials, the Preisach model.
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