Shape memory alloys - unconventional actuators

Abstract

The robot's designers attempt to use unconventional actuators more often now. Epitomes of these actuators are alloys with shape memory (SMA- shape memory alloy). This material is known since the first half of twentieth century. In 1958 SMA was for the first time used as a primitive type of actuator (Brussel's World's Fair). Thanks to sophistication of SMA materials and some problems that are connected with shape memory effect (hysteresis, degradation etc.) the actuators based on this principle are used minimally. The efficient control of actuators based on shape memory principle is immediately related to results given by modelling in combination with practical experiments. The properties of SMA classified these actuators to category of non-linear system. This article deals with potential approaches to modelling of SMA. There are introduced examples of designed models and control. The article also presents the results of practical measurement performed in Department of Control and Measurement at Brno University of Technology and a description of robot actuated by SMA. Design of SMA actuator and comparison with classical actuator is discussed in the last part of this article. At the end of the article there is a concise survey of fields, where the SMA elements are used both in static and dynamic applications.