The application of shape memory alloys in actuator systems has been well studied and continues to be an important topic of research in various fields of engineering including aerospace, biomedical, and robotics. Of particular concern is precision control of the actuator position. Many approaches have been investigated for position control, but most of these depend upon feedback of the actuator position as measured by a sensor. Research into the material properties of shape memory alloys has revealed a significant relationship between the electrical resistance and strain. This correlation has been used to model the strain as a function of the electrical resistance in order to predict the actuator position and remove the need for sensor feedback. However, the presence of R-phase in the microstructure of the alloy as well as the influence of applied stress make modeling difficult. The work presented here focuses on the development of a new predictive model of the relationships between electrical resistance, applied stress, and strain in Ni-Ti shape memory alloy. Characterization of the material was performed and the results used in order to develop the model based on empirical relationships. The model was then simulated for verification and successfully used to replace sensor feedback in a simple position control experiment.

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Conference 24th International Conference on Adaptive Structures and Technologies, ICAST 2013
Lynch, B. (Brian), Jiang, X.-X. (Xin-Xiang), Nitzsche, F, & Ellery, A. (2013). Modeling the stress-strain-resistance behaviour of shape memory alloy for sensorless actuator position control. In ICAST 2013 - 24th International Conference on Adaptive Structures and Technologies (pp. 86–97).