Actuators based on shape memory alloys (SMA) can be small, simple, cheap, clean, silent, and have high force-to-weight ratios; but they also have disadvantages, including low efficiency, low speed and low accuracy. This project aims to improve the speed and accuracy of such actuators, so they can be used in robots, medical devices, consumer electronics, and so on. Our actuators employ antagonistic pairs of FlexinolTM wires, which are made of a nickel-titanium SMA called nitinol. These wires can be stretched easily when cool, but contract forcibly to their original length when heated. The big challenge is to develop control systems that deliver fast and accurate tracking of force and motion command signals. This is not easy, because SMAs exhibit highly nonlinear behaviour, including substantial hysteresis, which makes them very difficult to control.
movie 1 (9MB). This movie shows the pantograph robot tracking a square at speeds of up to 1Hz, using Grant's relay controller (see publication 1) augmented with our rapid heating algorithm. The speed is very good, but the tracking accuracy is poor.
movie 2 (4.5MB). This movie shows the step response and tracking response of a new motion control system (see publication 8) with and without the rapid heating algorithm.
We have demonstrated that SMA can respond at frequencies of 1kHz and higher, by building an SMA loudspeaker. Yes, SMA really can respond at audio frequencies, and here is the audio to prove it!
We have implemented an accurate stiffness control system, which makes the actuator behave like a programmable spring (unpublished).
Y. H. Teh 2003. A Control System for Achieving Rapid Controlled Motions From Shape Memory Alloy (SMA) Actuator Wires. B.Eng. Honours Thesis, Dept. Engineering, The Australian National University. Full Text.
R. Featherstone & Y. H. Teh 2004. Improving the Speed of Shape Memory Alloy Actuators by Faster Electrical Heating. Int. Symp. Experimental Robotics (ISER'04), Singapore, 18-21 June 2004. Full Text. Slides.
Y. H. Teh & R. Featherstone 2004. A New Control System for Fast Motion Control of SMA Actuator Wires. Shape Memory And Related Technologies (SMART 2004), Singapore, 24-26 November 2004. Full Text. Slides (powerpoint).
Y. H. Teh & R. Featherstone 2004. Experiments on the Performance of a 2-DOF Pantograph Robot Actuated by Shape Memory Alloy Wires. Australasian Conf. Robotics and Automation (ACRA 2004), Canberra, Australia, 6-8 December 2004. Full Text.
Y. H. Teh & R. Featherstone 2005. Experiments on the Audio Frequency Response of Shape Memory Alloy Actuators. Australasian Conf. Robotics and Automation (ACRA 2005), Sydney, Australia, 5-7 December 2005. Full Text.
Y. H. Teh & R. Featherstone 2007. Frequency Response Analysis of Shape Memory Alloy Actuators. Int. Conf. Smart Materials and Nanotechnology in Engineering (SMN 2007), Harbin, China, 1-4 July. Also in Proc. SPIE vol. 6423, p. J4232, 2007. Full Text.
Y. H. Teh & R. Featherstone 2008. An Architecture for Fast and Accurate Control of Shape Memory Alloy Actuators. Int. J. Robotics Research, vol. 27, no. 5, pp. 595-611. Full Text.
Y. H. Teh 2008. Fast, Accurate Force and Position Control of Shape Memory Alloy Actuators. Ph.D. Thesis, Dept. Information Engineering, The Australian National University. Full Text.
This is a Robotic Systems Group project.