Continuous Nonsingular Terminal Sliding-Mode Control of Shape Memory Alloy Actuators Using Time Delay Estimation

We have developed a continuous nonsingular terminal sliding-mode control with time-delay estimation (TDE) for shape memory alloys (SMA) actuators. The proposed method does not need to describe a mathematical model of a hysteresis effect and other nonlinearities; thus, it is simple and model free. The proposed control consists of three elements that have clear meaning: a TDE element that cancels nonlinearities in the SMA dynamics, an injection element that specifies desired terminal sliding-mode (TSM) dynamics, and a reaching element using a fast terminal sliding manifold that is activated accordingly when the system trajectory is not confined in the TSM. The proposed control has been successfully implemented in an SMA actuated system and experimental results show the proposed control is easily implementable and highly accurate. Once the TSM and the reaching condition are suitably specified, the tracking performance of the proposed control is improved compared with a conventional time delay control with a linear error dynamics.