Abstract
This study examines the coiling and uncoiling motions of a soft pneumatic actuator inspired by the awn tissue of Erodium cicutarium. These tissues have embedded cellulose fibers distributed in a 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.
Highlights
In our popular belief, plants are static and immobile, but this couldn’t be further from the truth
We focus on a intriguing plant motion: coiling in the seed awn of Erodium Cicutarium plant and its relatives (Stamp, 1984)
Further parametric analyses based on finite element simulations show that 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
Summary
Plants are static and immobile, but this couldn’t be further from the truth. Hydrogel-based bimorph materials with uniformly distributed fibers or stripes could bend or twist in response to different ambient stimuli (Wan et al, 2018) Their relatively simple reinforcing fibers are not sufficient to create coiling—a combination of twisting and bending—unless we add strainlimiting layers (Polygerinos et al, 2015) or a third fiber (BishopMoser and Kota, 2013; Uppalapati and Krishnan, 2018) to the standard helical fibers, or use multiple fluidic chambers (Martinez et al, 2013). This paper focuses on establishing the correlation between the pneumatically-driven coiling motion characteristics and the design of tilted helical fibers To this end, we fabricate prototypes of the plant-inspired actuator by casting thin-walled elastomeric tubes using 3D printed molds and wrap Kevlar fibers around them according to the prescribed tilted helical geometry.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have