Control of SMA systems: Review of the state of the art

Shape memory alloy (SMA) actuators can be made very compact and simple. An effective control algorithm is an integral part of every SMA actuator. This article presents a review of the state of the art research on control of SMA systems. It is worth noting that almost exclusively all control systems applied to SMA actuators are not model-based control algorithms. In other words, the control system is designed based on the intuitive knowledge of the system, through a combination of simulations and experiments. Therefore, the controller is not appropriately designed based on the system's parameters. As a result, stability analysis, a major step in designing control systems, has rarely been done for SMA-actuated systems. It is also important to recognize the co-dependent relationship between stress, Martensite fraction, and transformation temperatures of the SMA materials. This complex nonlinear relationship causes many difficulties with regards to control system design for SMA actuators. It should be also noted that SMAs are one way actuators and they are sensitive to changes in the ambient temperature.