Feedback Control of SMA-Wires for Position Determination: A Comparison of the Behavior Under Vacuum and Standard Conditions

Abstract

The possibilities of a technical application of the shape memory effect are comprehensive and widespread. Besides the usage of arbitrary geometries, e.g. in the medical sector, especially wires are of great interest for unlocking mechanisms or other kinds of actuators. One of the challenges of the application of shape memory alloys (SMA) is the small deformation factor that prevents actuations with large travels. A second property that is usually seen as a disadvantage is the thermal dependence of the position. It leads to the necessity of comparably high electrical power for holding a location, as the cooling has to be compensated constantly. Therefore, SMA are usually not in use for such applications. For special environments, this effect can still be an advantage. By using an SMA driven positioning actuator in vacuum, the low loss of heat leads to a very precise and low power consuming alignment. Such actuators can be used for example in satellites. This paper presents an analysis of the properties under atmospheric conditions in comparison to the behavior in vacuum. Along with a comprehensive interpretation of the experimental results, further characteristics, like the functional and structural fatigue, are presented in detail.