Modeling and Motion Control of a Soft SMA Planar Actuator

Soft actuators are versatile and can readily perform various functions and interact safely with humans and the environment owing to their deformability. Shape memory alloys (SMAs) have advantages of high power-to-weight ratio, silent operation, and high response speed, which make them suitable for fabricating soft, compact, and muscle-like soft actuators with various transformation capabilities. However, it is challenging to precisely control SMA-based soft actuators and robots because of the lack of explicit dynamics-based control method. In this article, a linear phase transition model of SMA is derived to express the dynamic model of an SMA planar actuator (SPA) in an explicit form. Then, a model-based feedback controller considering constraints of strain of the SMA, temperature increment of the SPA, and load increment was built. Strain gauges are used to obtain the bending angle of the SPA as the feedback signal for the controller. Various capabilities of the SPA, such as step response, position tracking with constant angular speed, and motion control with load, were experimentally evaluated. The developed method is meaningful for modeling and control of various SMA-based actuators and robots.