Shape memory alloy microactuators

Abstract

Shape memory alloys (SMA) have been investigated as transducing materials for the development of actuators for robotic end-effectors. In this paper, basic concepts on the design and development of SMA actuating systems for robotic applications are discussed. The thermomechanical characterization of the SMA material is the basis on which the successive steps for the design of the actuating system have been developed. Isometric tests conducted on SMA wire specimens led to the definition of the limit curve concept, i.e. the locus of equilibrium points in the space of the status variables (stress, strain, temperature) which limit the SME behavior of the material. The second step in the design of SMA actuating systems involved the definition of appropriate geometries of SMA active elements in order to obtain the best performances in terms of the required forces and displacements. The definition of the whole actuating system started from the identification of the agonistic-antagonistic configuration as the most appropriate for SMA technology. As an example of the realization of practical SMA actuating systems, the performances obtained with two different SMA actuators incorporating an active element shaped by coiling thin SMA wires and ribbons, respectively, and arranged according to an agonistic-antagonistic configuration, are presented.