Shape Memory Alloy Based Caudal Fin for a Robotic Fish

Abstract

A bio-mimetic fin embedded with shape memory alloy (SMA) wires has been developed. The design of the bio-mimetic fin is based on the musculature of a cuttlefish fin. The musculature of cuttlefish is studied. SMA is chosen as an actuator among the other smart material for its low actuation voltage and high power to weight ratio. A stepwise fabrication process of a bio-mimetic fin has been described for consistency and better performance. A series of tensile tests have been conducted to optimize the annealing temperature and the required pre-straining of the SMA wire actuating the developed fin. The optimum annealing temperature and the required pre-straining has been found to be 410° C and 4--6% respectively. The details of the heat treatment process followed have also been described. The maximum bending angle of 60° has been obtained for the developed bio-mimetic fin. The developed bio-mimetic fin has been integrated into a fish-inspired robotic structure to validate the capability of the developed bio-mimetic fin. The developed robotic fish can perform subcarangiform locomotion. The robot is capable of swimming in the forward direction as well as turning swimming mode. A control scheme for forward and turning swimming mode has been described. The developed robot is untethered and controlled wirelessly. The swimming speed and turning radius obtained are 7.6 cm/s and 45 cm respectively.