AUTHOR=Geer Ryan , Iannucci Steven , Li Suyi 

TITLE=Pneumatic Coiling Actuator Inspired by the Awns of Erodium cicutarium

JOURNAL=Frontiers in Robotics and AI

VOLUME=Volume 7 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/robotics-and-ai/articles/10.3389/frobt.2020.00017

DOI=10.3389/frobt.2020.00017

ISSN=2296-9144

ABSTRACT=This study examines the coiling and uncoiling motions of a soft pneumatic actuator inspired by the awn tissue of  {\it Erodium cicutarium}.  These tissues have embedded cellulose fibers distributed in a {\it tilted} helical pattern, which induces hygroscopic coiling and uncoiling in response to the daily changes in ambient humidity.   Such sophisticated motions can eventually ``drill'' the seed at the tip of awn tissue into the soil: a drill bit in the plant kingdom.  Through finite element simulation and experimental testing, this study examines a soft pneumatic actuator that has a similar reinforcing fiber layout to the Erodium plant tissue.   This actuator, in essence, is a thin-walled elastomeric cylinder covered by tilted helical Kevlar fibers.  Upon internal pressurization, it can exhibit a coiling motion by a combination of simultaneous twisting, bending, and extension.  Parametric analyses show that the coiling motion characteristics are directly related to the geometry of tilted helical fibers.  Notably, a moderate tilt in the reinforcing helical fiber leads to many coils of small radius, while a significant tilt gives fewer coils of larger radius.  The results of this study can offer guidelines for constructing plant-inspired robotic manipulators that can achieve complicated motions with simple designs.