A Unidirectional Soft Dielectric Elastomer Actuator Enabled by Built-In Honeycomb Metastructures

Abstract

Dielectric elastomer actuators (DEAs) are able to undergo large deformation in response to external electric stimuli and have been widely used to drive soft robotic systems, due to their advantageous attributes comparable to biological muscles. However, due to their isotropic material properties, it has been challenging to generate programmable actuation, e.g., along a predefined direction. In this paper, we provide an innovative solution to this problem by harnessing honeycomb metastructures to program the mechanical behavior of dielectric elastomers. The honeycomb metastructures not only provide mechanical prestretches for DEAs but, more importantly, transfer the areal expansion of DEAs into directional deformation, by virtue of the inherent anisotropy. To achieve uniaxial actuation and maximize its magnitude, we develop a finite element analysis model and study how the prestretch ratios and the honeycomb structuring tailor the voltage-induced deformation. We also provide an easy-to-implement and scalable fabrication solution by directly printing honeycomb lattices made of thermoplastic polyurethane on dielectric membranes with natural bonding. The preliminary experiments demonstrate that our designed DEA is able to undergo unidirectional motion, with the nominal strain reaching up to 15.8%. Our work represents an initial step to program deformation of DEAs with metastructures.

Materials for Smart Soft Actuator Systems

“…The theoretical model predicts that the use of a negative Poisson’s ratio structures in linear actuator systems would lead to optimized work in a high-stroke, low-force configuration . Several studies have shown that materials with a negative Poisson’s ratio can exhibit shape memory behavior, which could be used for building thermally activated medical stents and soft actuators. ,, A honeycomb structure has been as well used for DEA preparation, where the use of this structure gives additional prestretching of the DE membrane and allows a high anisotropy that leads to uniaxial actuations . The concept of folding and unfolding of cells using a pneumatic actuation has been described as well by Overvelde et al A prepared actuator showed a high degree of freedom, being able to actuate in various dimensions and being able to be folded flat .…”

“…162,447,448 A honeycomb structure has been as well used for DEA preparation, where the use of this structure gives additional prestretching of the DE membrane and allows a high anisotropy that leads to uniaxial actuations. 449 The concept of folding and unfolding of cells using a pneumatic actuation has been described as well by Overvelde et al A prepared actuator showed a high degree of freedom, being able to actuate in various dimensions and being able to be folded flat. 450 Materials having a negative Poisson's ratio are interesting not only due to their mechanical properties but as well for their ability to exhibit an actuation to various dimensions.…”

Recent Trends and Innovation in Additive Manufacturing of Soft Functional Materials

“…The resulting curled-up structures followed predictions using minimization of energy approach and showcased how three-dimensional complex actuators could be built using intelligent design of printed patterns onto a DE substrate. Similarly, honeycombs of TPU were patterned using FDM into both sides of acrylic DE substrates to obtain anisotropic unidirectional actuators [ 65 ]. Higher degrees of anisotropy were obtained by varying the rib angle of the honeycombs and increasing the pre-stretch ratios of the DEs during print.…”

Light-Activated Elongation/Shortening and Twisting of a Nematic Elastomer Balloon

“…The nematic elastomer bears the most abundant mechanical properties and has been studied extensively [ 3 , 4 , 5 , 6 , 7 ]. Recently, nematic elastomer has been widely used in the fields of micro/nano devices, sensors and actuators [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”