Experimental oscillation and regulation control strategy for 1-DOF mechanical rotational systems with an antagonistic SMA actuator

Shape memory alloys (SMAs) have a wide field of applications due to their attractive properties. However, they also have specific characteristics, such as strongly non-linear dynamics and a slow actuation velocity, which make applying them to high precision and velocity tasks complex. Additionally, it is not recommended to arbitrarily increase the temperature in an SMA element to resolve these problems since there is a risk of altering or damaging their memorized shape. This article introduces a novel control strategy developed through rigorous experimentation to induce sustained oscillations in a rotational mechanism with one degree of freedom. The strategy, which involves placing two SMA springs in an antagonistic configuration, is designed to maximize oscillation frequency and amplitude while mitigating the risk of spring damage due to excessive temperatures. This innovative approach has also proven effective in regulating the system, as demonstrated by successfully integrating a saturated PID controller. We present the control strategy's experimental performance in generating oscillations with the highest average frequency of 0.132 Hz during tests while keeping the overall spring temperature under austenite finish (Af). Regarding the regulation problem, implementing the optimal voltage parameter and temperature limit obtained from the oscillating test, the regulation task was successfully performed while keeping the actuators within safety temperatures, and a small steady-state error was seen.