Bending continuous structures with SMAs: a novel robotic fish design

TLDR

Shape memory alloys enable motor‑less, gear‑less robots, inspired by fish red muscles that bend flexible structures during steady swimming. The study aims to demonstrate that a fish‑like robot can reproduce standard swimming patterns using SMA‑based actuators, and to evaluate their actuation speed and position accuracy. The robot’s continuous backbone is bent by SMA actuators, and the design process—from physiological inspiration to mechatronics, control, simulations, and experimental trials—was reviewed to achieve this motion. A swimming underwater fish‑like robot was successfully developed, with movements generated by SMAs.

Abstract

In this paper, we describe our research on bio-inspired locomotion systems using deformable structures and smart materials, concretely shape memory alloys (SMAs). These types of materials allow us to explore the possibility of building motor-less and gear-less robots. A swimming underwater fish-like robot has been developed whose movements are generated using SMAs. These actuators are suitable for bending the continuous backbone of the fish, which in turn causes a change in the curvature of the body. This type of structural arrangement is inspired by fish red muscles, which are mainly recruited during steady swimming for the bending of a flexible but nearly incompressible structure such as the fishbone. This paper reviews the design process of these bio-inspired structures, from the motivations and physiological inspiration to the mechatronics design, control and simulations, leading to actual experimental trials and results. The focus of this work is to present the mechanisms by which standard swimming patterns can be reproduced with the proposed design. Moreover, the performance of the SMA-based actuators' control in terms of actuation speed and position accuracy is also addressed.