A Drosophila larvae-inspired vacuum-actuated soft robot

Abstract

Peristalsis is one of the most common locomotion patterns in limbless animals. This motion is generated by propagating muscular contraction and relaxation along the body axis. While the kinematics of peristalsis has been examined intensively, the kinetics and mechanical control of peristalsis remain unclear, partially due to the lack of suitable physical models to analyse the force and temporal control in soft-bodied animals locomotion. Here, based on a soft-bodied animal, Drosophila larvae, we proposed a vacuum-actuated soft robot replicating their crawling behaviour. The soft structure, made with hyperelastic silicon rubber, was designed to mimic the larval hydrostatic structure. To estimate the adequate range of pressures and time scales for control of the soft robots, a numerical simulation by the finite element method was conducted. Pulse-Width-Modulation (PWM) was used to generate time-series signals to control the vacuum pressure in each segment. Based on this control system, the soft robots could exhibit the peristaltic pattern resembling fly larval crawling. The soft robots reproduced two previous experimental results on fly larvae: slower crawling speed in backward crawling than in forward crawling, and the involvement of segmental contraction duration and intersegmental delay in crawling speed. Furthermore, the soft robot provided a novel prediction that the larger the contraction force, the faster the crawling speed. These observations indicate that the use of soft robots could serve to examine the kinetics and mechanical regulation of crawling behaviour in soft-bodied animals.