Fuzzy-PID Control of Mechanisms with Contrary Shape Memory Alloy Actuators

Shape memory alloys (SMAs) are a special kind of smart materials with an intrinsic shape memory effect. This characteristic brings up SMAs as an actuator in dynamical mechanisms. These materials can recover their initial length under special thermal operations. This paper deals with fuzzy-PID control of contrary mechanisms actuating with a pair of SMA wires. The Brinson model combining with the Elahinia’s conditions are employed to describe the phase transformation models. By combining the Newton second law, transformation models, heat transfer and strain relations, the governing equations of the contrary mechanism is derived. Due to nonlinear behavior of SMA actuators, the non-model-based controllers are preferred compared with the model-based ones. Therefore, the fuzzy-PID control method is employed to control the position of the closed-loop system. The fuzzy rules are defined such that the coefficients of the PID controller are tuned according to the system response. Both numerical and experimental results are provided to illustrate the effectiveness of the proposed approach. It will be shown that under the proposed method, the tracking error will converge to zero asymptotically.