Robust shape control of two SMA actuators attached to a flexible beam based on DK iteration

There has been great demand for shape memory alloy (SMA) wires as actuators for shape control of flexible structures. The experimental setup of this study consists of a flexible beam actuated by two active SMA actuators. The input applied to the SMA actuator in this setup is electrical current while the output is the strain or position. To control strain of the actuator, the SMA wire is heated resistively in order to reach the desired temperature calculated by inverse of the phenomenological model. In heating the SMA wire resistively, the controllable quantity is the heat input to the wire via an applied current. In controller design, changes of physical properties of SMA wires and the surrounding air due to temperature change must be taken into consideration. This adds uncertainty to the presented model. Furthermore, both wires must approach the desired temperature while maintaining the same temperature history. Moreover, a suitable shape control requires overdamped response. A 2-DOF robust controller is designed in this study in order to achieve all the above requirements. The robust controller by the DK iteration method is designed after modeling of the system uncertainties. Required simulations are performed for evaluation of the controller. Obtained results show the ability of controller against time variant uncertainties.