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High Strain Shape Memory Alloy Actuators and their Control

The actuators consist of fibers woven in a specific pattern which achieves a large amount of displacement amplification with very small losses. In one prototype, twelve fibers are run in parallel resulting in a 16 mm diameter package weighing 6 grams and capable of pulling 4 N. In this configuration, the strain is about 20% and the rise time shorter than 100 ms for an antagonist set-up in ambient air. A model of these actuators, which is relevant to control design, has been developed. The model is sufficiently accurate to allow controllers designed in simulation to be applied in practice without tuning. Variable structure controllers have been investigated with the purpose of achieving the control of position, force, and acceleration. Experimental performance results in the time domain demonstrate that this control can achieve very fast rise time, high rejection of disturbance, small tracking and steady state error, and quenching of limit cycles, despite their numerous nonlinear properties. Patent granted. (Figure 6.14).

D. Grant, V. Hayward


Figure 6.14: A single NiTi actuator package, 16 mm accross.



Annual Report

Mon Jun 26 21:22:20 GMT 2000