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Technical Briefs

Iterative and Feedback Control for Hysteresis Compensation in SMA

[+] Author and Article Information
Kam K. Leang1

Department of Mechanical Engineering, University of Nevada, Reno, Reno, NV 89557-0312kam@unr.edu

Seth Ashley, Guy Tchoupo

Department of Mechanical Engineering, Virginia Commonwealth University, Richmond, VA 23284

1

Corresponding author.

J. Dyn. Sys., Meas., Control 131(1), 014502 (Dec 05, 2008) (6 pages) doi:10.1115/1.3023131 History: Received November 07, 2006; Revised July 20, 2008; Published December 05, 2008

This paper investigates the design of an iteration-based controller combined with feedback control to address the positioning error caused by hysteresis in a shape memory alloy (SMA) actuator. Without compensation, the positioning error due to hysteresis can be excessively large (greater than 20%), therefore limiting the performance of SMAs in positioning applications. An iterative controller based on the Preisach hysteresis model is used to compensate for the hysteresis. However, one of the major challenges with SMA at or near the phase-transition zones, from martensite to austenite and vice versa, is the output response is shown to be sensitive to small changes in the input. In practice, an iterative controller provides limited performance due to lack of robustness. It is demonstrated that combining a simple feedback controller with an iterative controller provides the needed robustness to enable high-precision tracking. Experimental results are presented that show maximum tracking error of 0.15% of the total displacement range—this value is approximately the noise level of the sensor measurement.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The experimental SMA-based rotatory system

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Figure 2

Open-loop input-output response of experimental SMA actuator: (a) step response, output angle versus time; (b) input current versus time; (c) associated output response (angle) versus time; and (d) hysteresis curve (output versus input)

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Figure 3

Output response of SMA actuator subjected to the same input for 100 trials. In open-loop, the results show a significant variation in the output response even when the same input was applied 100 times. (a) Input current versus time, (b) output angle versus time, and (c) maximum output variation (error) versus trial number for the SMA system in the ambient environment (without hermetically sealed enclosure). The results from the same experiment but with the SMA system housed in the hermetically sealed enclosure are shown in plots (d)–(f). Under closed-loop control where the SMA was enclosed in a hermetically sealed box, the variation was reduced significantly, as shown in plots (g)–(i).

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Figure 4

Preisach hysteresis model for SMA: (a) experimentally determined Preisach weighting function μ; and (b) comparison of measured and model hysteresis curves

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Figure 5

Experimental tracking results. Iterative control only case: (a) block diagram showing the process at the kth iteration step, (c) output versus time, and (e) tracking error versus time for different iteration number k. Combined iterative and feedback controllers: (b) block diagram showing the process at the kth iteration step, (d) output versus time, and (f) tracking error versus time for different iteration number k.

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