Liquid Crystal Elastomer Strips as Soft Crawlers

TL;DR

This paper explores the use of liquid crystal elastomer strips as soft crawlers, demonstrating how cyclic actuation and directional friction can produce directed locomotion in miniaturized soft robots.

Contribution

It formulates and solves the evolution equations for nematic elastomer strips with directional friction, providing explicit formulas for motion and force, advancing soft robotic locomotion design.

Findings

Directed motion achieved through cyclic actuation and frictional anisotropy

Explicit formulas for displacement and axial force derived

Comparison between distributed and concentrated friction models

Abstract

In this paper, we speculate on a possible application of Liquid Crystal Elastomers to the field of soft robotics. In particular, we study a concept for limbless locomotion that is amenable to miniaturisation. For this purpose, we formulate and solve the evolution equations for a strip of nematic elastomer, subject to directional frictional interactions with a flat solid substrate, and cyclically actuated by a spatially uniform, time-periodic stimulus (e.g., temperature change). The presence of frictional forces that are sensitive to the direction of sliding transforms reciprocal, 'breathing-like' deformations into directed forward motion. We derive formulas quantifying this motion in the case of distributed friction, by solving a differential inclusion for the displacement field. The simpler case of concentrated frictional interactions at the two ends of the strip is also solved, in order to provide a benchmark to compare the continuously distributed case with a finite-dimensional benchmark. We also provide explicit formulas for the axial force along the crawler body.