Fuzzy Logic Position Control of a Shape Memory Alloy Wire

Due to the thermomechanical characteristics of Shape Memory Alloy wires, it is important to develop control systems in order to design new applications for these smart materials. This work presents three SMA wire position controls: a classic PD control with PWM modulation is compared to two different fuzzy logic controls. They are implemented on a SMA wire (Flexinol®)with a diameter of 250 mm and a length of about 200 mm. The so called Fuzzy logic is particularly suitable in case of uncertain conditions and in presence of data acquisition noise and it is widely used to model and control time dependent and/or non linear processes. The experimental tests comprise square wave response tests, sinusoidal wave tests and multiple step response tests. Interesting results are a maximum error during stability phase with the fuzzy logic control of about 2%, four times smaller than that obtained with the PD control, with reduced fluctuations amplitude. The PD control with fuzzy supervisor is a control more simple than the fuzzy control and lead to similar results for the sinusoidal tests and multiple step response tests, with fluctuation amplitude of about 0,01 mm, much more less than those observed with the PD or the fuzzy control.