Design and Analysis of a Bio-Inspired Caudal Fin Using Shape Memory Alloys

Over the years, bio inspired robotics has become of particular relevance, especially with the construction of systems capable of reproducing a fluid and noiseless motion, capable also of exploring and monitoring the marine environment. This work aims to model and realize an active biomimetic caudal fin, which guaranties the generation of a controllable movement through the utilization of SMA (Shape Memory Alloy) wires. The main objectives of this research are to design and develop a soft robotic structure capable of emulating the kinematic behavior of real caudal fins of fish. The study focuses mainly on deformation and actuation performance and to demonstrate the efficiency of using SMA as actuators for underwater use. After an accurate study of the State of the Art, targeted to understand the kinematics and mechanism of the generation of water jets and vortices of fishes, a simplified model of the caudal fin motion was developed, focusing on the deformation profile and the dynamic response achievable through SMA actuation. To record the imbalance effects of the body and to verify the contribution of the fin in the pitching stabilization, an IMU sensor was integrated in the system. Tests highlighted that the fin was capable of reproducing regular and symmetric deformations, with a dynamic response similar to the natural movements of small fishes. The results showed that this biomimetic approach, associated to the use of smart and soft actuators, was extremely valid, showing the potential development of robotic fishes, capable of active control and to generate forces that allow 3D maneuvering in marine environment. Quantitative analyses confirmed the repeatability and symmetry of the motion, validating the efficiency of the actuation system and the reliability of the silicone-based structure under multiple test cycles. Moreover, the obtained data prove the feasibility of the fin driven by SMA wires, adding advantages, such as lightweight, silent and adaptable system for future bio-inspired robotic applications.