Experimentally Control of a Shape Memory Alloy (Sma) Wire in Three Specific Regions of Phase Change and Under Varying Loads

Abstract

Shape memory alloy (SMA) wires are commonly utilized in actuator technologies due to their high energy density relative to their volume. When heated, they transition from the martenzitic phase to the austenitic phase, performing work by recovering the applied pre-strain through the force they generate. The temperature-strain path during heating and cooling does not follow the same trajectory, resulting in hysteresis. The hysteresis varies depending on loading conditions, as the phase transition temperatures change. Incomplete phase transitions during heating or cooling can lead to minor hysteresis curves within the major hysteresis curve. This thermomechanical behavior makes the strain control procedure challenging. Developing a model to determine controller gains is complex. Thus, many controllers with experimentally determined gains have been tested in the literature. As a part of novelty, this study assessed controller performance in three critical regions: fully martenzitic, phase transition, and fully austenitic hysteresis curves. It was observed that PI (Proportional-Integral) controller exhibited high performance. Generally, no destabilizing effects were observed; even with increasing frequency of the sinusoidal reference signal, tracking remained effective. Tracking error analysis indicated that, particularly with high-frequency strain references at the highest strain demands and phase transition regions, the error increased. The controller proved to be robust across all tested scenarios. This study is valuable as it offers insights suggesting that improving whole reference tracking in these three regions may be achieved through a stable gain scheduling action among controllers having different gains. Additionally, the controller demonstrated robust performance, as well, when subjected to time-varying load as a disturbance. © 2025, Gazi Universitesi. All rights reserved.