Fast, Accurate Force and Position Control of Shape Memory Alloy Actuators

205 Pages·2008·5.17 MB·English

Fast, Accurate Force and Position Control
of Shape Memory Alloy Actuators
A thesis submitted for the degree
of Doctor of Philosophy of
The Australian National University
Yee Harn Teh
Department of Information Engineering
ANU College of Engineering and Computer Science
June 2008
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This thesis contains no material which has been accepted for the award of any
other degree or diploma in any university. To the best of the author’s knowledge
and belief, it contains no material previously published or written by another
person, except where due reference is made in the text.
Yee Harn Teh
June 2008
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Acknowledgements
Therearemanypeoplewhohavemadecontributions,bothdirectlyandindirectly,
towards the completion of this thesis. I would like to name a few.
First and foremost, I would like to express my sincerest gratitude to my
supervisor, Dr. Roy Featherstone. Roy’s help has been extremely enormous, and
his enthusiasm has sparked my own in this wonderful work. This work would
never have been completed without his advice and guidance.
Apart from Roy, I would also like to thank Dr. Zbigniew Stachurski and Dr.
Robert Mahony for being on my Ph.D. supervisory panel. Roy and Zbigniew
especially, thank you for the wonderful coffees and brilliant discussions together.
Iwouldalsoliketoexpressmygratitudetomyparents,andmythreebrothers,
who provided me with unconditional advice, support and love. They have never
been far from my heart.
And finally to Aya, my partner, thank you.
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Abstract
Shape memory alloy (SMA) actuators have great potential in niche applications
where space, weight, cost and noise are crucial factors. Despite many of the
advantages, they remain mostly as experimental actuators due to their perceived
slow response speed, low accuracy and controllability. Especially in situations
where there is a moving link or an external payload, the problem of limit cycles
has been pursued by various researchers but never fully solved. In this thesis,
practical, effective control systems are applied to achieve fast and accurate force
and position control of SMA wire actuators.
Investigations into very high-frequency responses from SMAs are initially ex-
plored, which produce surprising results of audio frequency responses. This dis-
covery has led us towards using high-bandwidth control systems as a possible
method of eliminating limit cycles. Frequency response analysis of SMA actua-
torshavealsobeencarriedout. Basedontheresults, linearforcemodelsforsingle
SMA wires as well as for an actuator comprising of an antagonistic pair of SMA
wires have been developed. A position model for an antagonistic SMA-actuated
robotic joint has also been developed based on the force models. These models
are integral in the design, tuning and simulation of various control systems for
SMA actuators.
High-bandwidth PID control has been employed in the force control of single
SMA wire actuators. More importantly, it forms the main control component in
the differential force control architecture for antagonistic SMA actuators. Other
components are the anti-slack mechanism, the rapid-heating mechanism and the
anti-overload mechanism. The closed loop response is fast and accurate, even in
the presence of external motion disturbances. There is generally no limit cycles in
theactuator’sdifferentialforceoutput; andtheperformanceisunaffectedbylarge
loadinertias. Thisthesisalsopresentsatwo-looparchitectureforpositioncontrol,
in which a position feedback loop is added to the force control architecture.
Experimental results demonstrate highly accurate position control with no limit
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cycles in the presence of external loads.
The accomplishments reported in this thesis represent a significant develop-
ment in making SMA actuators faster, more accurate and effective. It is aspired
that the results and control methods in this work can be utilised in enabling
practical SMA technologies for robotic and commercial applications.
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List of Source Publications
Most of the discussions and results presented in this thesis are based on the
following publications. Several passages in this thesis contain materials that
have been copied verbatim, or with some adaptation, from these publications.
All such copied materials were originally written by myself.
i. R. Featherstone and Y. H. Teh. Improving the Speed of Shape Memory
Alloy Actuators by Faster Electrical Heating. In Proceedings of the 9th
International Symposium on Experimental Robotics, Singapore, 18-21 June
2004.
ii. Y. H. Teh and R. Featherstone. A New Control System for Fast Motion
Control of SMA Actuator Wires. In The 1st International Symposium on
Shape Memory and Related Technologies, Singapore, 24-26 November 2004.
iii. Y. H. Teh and R. Featherstone. Experiments on the Performance of a 2-
DOF Pantograph Robot Actuated by Shape Memory Alloy Wires. In Pro-
ceedings of the 6th Australasian Conference on Robotics and Automation,
Canberra, Australia, 6-8 December 2004.
iv. Y. H. Teh and R. Featherstone. Experiments on the Audio Frequency
Response of Shape Memory Alloy Actuators. In Proceedings of the 7th
Australasian Conference on Robotics and Automation, Sydney, Australia,
5-7 December 2005.
v. Y.H.TehandR.Featherstone. AccurateForceControlandMotionDistur-
bance Rejection of Shape Memory Alloy Actuators. In Proceedings of the
IEEE International Conference on Robotics and Automation, Rome, Italy,
10-14 April 2007.
vi. Y.H.TehandR.Featherstone. AnArchitectureforFastandAccurateCon-
trol of Shape Memory Alloy Actuators. International Journal of Robotics
Research. Submitted for review, May 2007.
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vii. Y. H. Teh and R. Featherstone. Frequency Response Analysis of Shape
Memory Alloy Actuators. In Proceedings of the International Conference
on Smart Materials and Nanotechnology in Engineering, Harbin, China, 1-4
July 2007.
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