Research Papers

Sliding Mode Control of Mechanical Systems Actuated by Shape Memory Alloy

[+] Author and Article Information
Hashem Ashrafiuon, Vijay Reddy Jala

Depertment of Mechanical Engineering, Villanova Unidersity, Villanova, PA 19085

J. Dyn. Sys., Meas., Control 131(1), 011010 (Dec 08, 2008) (6 pages) doi:10.1115/1.3023121 History: Received November 27, 2007; Revised July 14, 2008; Published December 08, 2008

This paper presents a model-based sliding mode control law for mechanical systems, which use shape memory alloys (SMAs) as actuators. The systems under consideration are assumed to be fully actuated and represented by unconstrained equations of motion. A system model is developed by combining the equations of motion with SMA heat convection, constitutive law, and phase transformation equations, which account for hysteresis. The control law is introduced using asymptotically stable second-order sliding surfaces. Robustness is guaranteed through the inclusion of modeling uncertainties in the controller development. The control law is developed assuming only positions are available for measurement. The unmeasured states, which include velocities and SMA temperatures and stresses, are estimated using an extended Kalman filter based on the nonlinear system model. The control law is applied to a three-link planar robot for position control problem. Simulation and experimental results show good agreement and verify the robustness of the control law despite significant modeling uncertainty.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

A three-link planar robot arm with two SMA actuators and a servomotor

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Figure 2

The SMA actuators comprised of SMA wire and pulley

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Figure 3

Simulation results for position control of the SMA actuated joint angles

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Figure 4

Variations of the two sliding surface during joint position control

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Figure 5

The SMA wire and transformation temperature estimates during joint position control

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Figure 6

The estimated SMA wire stresses during joint position control

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Figure 7

The estimated SMA wire Martensite fractions during joint position control

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Figure 8

Experimental setup for position control of the three-link robot arm with two SMA actuators

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Figure 9

Comparison between joint position control experimental and simulation results

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Figure 10

Control voltages during heating and cooling



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