Energy-efficient tunable-stiffness soft robots using second moment of area actuation

TL;DR

This paper introduces a method for tunable soft robotic stiffness using inflatable rubber tubes that change the second moment of area, enabling energy-efficient control of stiffness for improved swimming performance.

Contribution

The authors demonstrate a novel approach to tunable stiffness in soft robots by manipulating the second moment of area with inflatable actuators, achieving significant stiffness variation and enhanced dynamic response.

Findings

Double the effective stiffness with 0.8 bar pressure and 2 J energy input.

Achieved 5-7 times amplitude gain at resonance.

Tripled the high-gain frequency range compared to fixed-stiffness foil.

Abstract

The optimal stiffness for soft swimming robots depends on swimming speed, which means no single stiffness can maximise efficiency in all swimming conditions. Tunable stiffness would produce an increased range of high-efficiency swimming speeds for robots with flexible propulsors and enable soft control surfaces for steering underwater vehicles. We propose and demonstrate a method for tunable soft robotic stiffness using inflatable rubber tubes to stiffen a silicone foil through pressure and second moment of area change. We achieved double the effective stiffness of the system for an input pressure change from 0 to 0.8 bar and 2 J energy input. We achieved a resonant amplitude gain of 5 to 7 times the input amplitude and tripled the high-gain frequency range comparedto a foil with fixed stiffness. These results show that changing second moment of area is an energy effective approach tot unable-stiffness robots.