Nonlinear stress-based control of a rotary SMA-actuated manipulator

In this paper a nonlinear stress-based controller is designed to position a single-degree-of-freedom shape memory alloy (SMA) actuated manipulator. A three-part model was constructed based on the dynamics/kinematics of the arm, the thermomechanical behavior of SMAs, and an assumed heat transfer model consisting of electrical heating and natural convection. Both sliding mode control and inverse dynamics control are used to calculate a desired stress, based on the position error. The desired stress is compared with the actual stress which is computed using an Extended Kalman Filter. The stress error is then used for control via a proportional-integral controller. Numerical simulations are performed to investigate tracking performance as well as other issues such as robustness. The results demonstrate that the variable structure controller designs are highly accurate in tracking both stationary and variable input signals.