Modeling and control of ferromagnetic shape memory alloy actuators

Ferromagnetic Shape Memory Alloy materials such as Ni-Mn-Ga have attracted significant attention over the last few years. As actuators, these materials offer high bandwidth, large stroke, and high displacement resolutions. In this dissertation, the main interests are to model the constitutive behavior of Ni-Mn-Ga under simultaneously changing fields and stress and design new actuator based on Ni-Mn-Ga.; In this research, a comprehensive approach is used to model the behavior of FSMA actuators. To this end, an enhanced phenomenological model for FSMA actuators is developed based on the approach of Likhachev and Ullakko. This enhanced model is integrated with dynamics of the actuator as well as the dynamics of an electromagnet to study the hysteresis behavior of the system. In order to improve the accuracy of the model, a field-induced strain model is combined with the strain decomposition and Kelvin-Voigt model to account for the inherent damping effect of the material. Simulations have been performed and the results are compared with the experimental measurement to verify the model.; The closed loop simulations results indicate that the inherent nonlinearities of the material are the main challenges for position control with FSMA actuators. A Variable Structure Controller (VSC) is proposed to overcome these issue. The algorithm improves both the transient response and tracking performance of the FSMA actuators. A SMA wire based experimental setup is constructed to verify the effectiveness of the control algorithm for the FSMA based actuators. Because of the inherent similarity between SMA and FSMA actuators in low working frequencies, the experimental results are applicable to both actuators. The experimental measurement demonstrate the effectiveness of VSC in both of positioning and tracking.