Control of shape memory alloy actuator using pulse width modulation

Shape memory alloys (SMA), in particular nickel–titanium alloy (or nitinol), have been used as actuators in some astronautic, aeronautic and industrial applications. The future will see more SMA application if less energy is required for actuation. This paper presents the design and experimental results of control of an SMA actuator using pulse width modulation (PWM) to reduce the energy consumption by the SMA actuator. A SMA wire test stand is used in this research. Open-loop testing of the SMA wire actuator is conducted to study the effect of the PWM parameters. Based on test results and parameter analysis of the pulse width (PW) modulator, a PW modulator is designed to modulate a proportional plus derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWM effectively saves actuation energy while maintaining the same control accuracy as compared to continuous PD control. PWM also demonstrates robustness to external disturbances. A comparison with a pulse width pulse frequency modulator is also presented.