Non linear motion and force control of shape memory alloys actuators

Among the numerous studies published in the field of shape memory alloys (SMA), an important part is devoted to the thermomechanical properties of these materials. Few studies have been done in order to develop control laws of SMA actuators for temperature, position and force control with guaranteed stability and performances. The reason is that these materials have an highly non linear dynamic behavior (including hysteresis) because of the physical principle of motions which is a solid-solid phase transition (between an austenitic and a martensitic phase). It is then difficult to guaranty stable control and to predict the dynamic behavior in closed-loop (trajectory and effort). For this purpose, this paper is focused on control of such actuators. To obtain a control law for the closed-loop motion or force control, we use a non linear dynamic model performed in a previous work. With this dynamic model, we use non linear control techniques based on the Lie algebra to obtain the control laws for the position or the force closed-loop. Experimentation show that the proposed method is very useful for the control of SMA actuators.