Design, analysis, and simulation of a planar serial–parallel mechanism for a compliant robotic fish with variable stiffness

Zuo Cui,Hongzhou Jiang

doi:10.1177/1687814016660927

Zuo Cui, Hongzhou Jiang

Open Access

https://doi.org/10.1177/1687814016660927

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Abstract

Biological evidence suggests that fish use muscles to stiffen their bodies and improve their swimming performance. Inspired by this phenomenon, we propose a planar serial–parallel mechanism with variable stiffness to mimic a swimming fish. Based on Lighthill’s elongated-body theory, we present a general method to design the body stiffness, which is related to morphological parameters and the swimming frequency. The results show that the stiffness profile is directly proportional to the square of the driving frequency. Furthermore, a SimMechanics model of a robotic fish is innovatively built. Numerical results show that the fish with the designed stiffness has the maximum speed when the driving frequency is close to the resonance frequency of fish body, and that the maximum speed is linearly proportional to the resonance frequency. The range of the Strouhal number given by simulations is also consistent with the range 0.25 < St < 0.35 required by the optimal efficiency. All these results agree well with biological observations, indicating that the swimming performance of fish is significantly affected by the body stiffness and the driving frequency.

Highlights

Fish have attracted the interests of researchers because they have far more superior swimming performance to man-made underwater vehicles.[1]
This article aims to construct a robotic model with a planar serial–parallel mechanism that allows a detailed control over the variable body stiffness, which will contribute to the understanding of fish body stiffness
We propose a planar serial– parallel mechanism to mimic the biological structure of fish

Summary

Introduction

Fish have attracted the interests of researchers because they have far more superior swimming performance to man-made underwater vehicles.[1] Different types of fish have evolved to achieve different swimming performance, such as cruising long distances at a significant speed, maneuvering in tight spaces, and accelerating swiftly.[2] Various bio-inspired swimming robots have been built and applied to seabed exploration, underwater transportation, search and rescue, and so on.[3] These artificial fish-like robots provide innovative solutions to underwater propulsion and maneuvering. More detailed discussions on swimming fish can be found in Colgate and Kevin[2] and Lauder.[4].

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