The Effect of a Limited Underactuated Posterior Joint on the Speed and Energy Efficiency of a Fish Robot

Abstract

Autonomous underwater vehicles (AUVs) commonly use screw propellers to move in a water environment. However, compared to the propeller-driven AUV, bio-inspired AUVs feature a higher energy efficiency, longer lifespan (due to a lack of cavitation), and better eco-friendliness (due to lower noise, a lack of vibrations, and a weaker wake). To generate propulsion, the design of fish robots—viewed as a special case of a bio-inspired AUV—comprise multiple actuated joints. Underactuated joints have also been adopted in bio-inspired AUVs, primarily for the purpose of achieving a simpler design and more realistic and biologically plausible locomotion. In our work, we propose a limitedly underactuated posterior (tail) joint of a fish robot with the intention of achieving a higher swimming speed and better energy efficiency of the robot. The limited underactuation is achieved by allowing the joint to move freely but only within a limited angular range. The experimental results verified that, for relatively small angular ranges, the limitedly underactuated joint is superior to both fully actuated and fully underactuated joints in that it results in faster and more energy-efficient locomotion of the fish robot.