Retraction of Soft Growing Robots without Buckling

TL;DR

This paper introduces a model and device to prevent buckling in soft growing robots during retraction, enabling controlled inversion and new capabilities like exploring forks and retrieving samples.

Contribution

A novel predictive model and a retraction device that together prevent buckling, allowing soft robots to invert reliably during retraction.

Findings

Model accurately predicts buckling conditions.

Retraction device enables controlled inversion.

Robots perform new tasks like branch exploration and sample retrieval.

Abstract

Tip-extending soft robots that "grow" via pneumatic eversion of their body material have demonstrated applications in exploration of cluttered environments. During growth, the motion and force of the robot tip can be controlled in three degrees of freedom using actuators that direct the tip in combination with extension. However, when reversal of the growth process is attempted by retracting the internal body material from the base, the robot body often responds by buckling rather than inverting the body material, making control of tip motion and force impossible. We present and validate a model to predict when buckling occurs instead of inversion, and we present an electromechanical device that can be added to a tip-extending soft robot to prevent buckling during retraction, restoring the ability of steering actuators to control the robot's motion and force during inversion. Using our retraction device, we demonstrate three previously impossible tasks: exploring different branches of a forking path, reversing growth while applying minimal force on the environment, and bringing back environment samples to the base.