Shape memory soft actuation exploiting multimaterial functionalization: design and control

Shape memory alloys (SMA) are often employed in the fabrication of soft actuators, thanks to their inherent flexibility and high energy density [1]. However, their bandwidth is limited by the rather slow cooling rates, unless active cooling is employed. This work explores opportunities offered by the embedding of the SMA element in a functionalized matrix able to address not only external mechanical interfacing, but also thermal exchange and controllability, without the need for active cooling. We shall present modelling and experimental results showing that an elastomeric matrix functionalized with carbon nanoparticles (CNP), particularly when coupled with a tailored switched controller that manages system nonlinearities, is able to improve the operation characteristics of multimaterial soft actuators based on SMA-based technology. Ternary NiTiCu has been selected thanks to its low hysteresis, providing faster response. The optimization of the SMA is carried out with an innovative technique that ensures high cyclic stability and mechanical properties [2]. The matrix characteristics, and the effect of variable CNP additions are described from the mechanical and calorimetric points of view. Furthermore, important aspects relating to the design of multimaterial interaction will be discussed. The methods employed in this work are suitable for the fabrication of soft miniactuators for application in different industrial and biomedical fields.