Experimental validation of an energy balance approach for design of horizontal lifeline systems.

The energy balance approach is one of the design approaches approved in fall protection standards Z359.6, Z259.16 and SS 607 to ensure that horizontal lifeline systems (HLLSs) are adequately designed. However, this study found that theoretical calculations predicting the total fall distance (hTFD) and maximum arrest load (MAL) using an energy balance approach need to be corrected before they can be used safely. Based on the data from 48 drop tests, the authors determined that energy balance calculations differ significantly from the empirical hTFD and MAL values of HLLSs. As a result, further correction factors are introduced into the theoretical calculations to estimate hTFD and MAL conservatively. These correction factors are estimated from a regression equation derived based on experimental results and theoretical calculations.

Maximal Performance of an Antagonistically Coupled Dielectric Elastomer Actuator System.

Dielectric elastomer actuators (DEAs) have been shown to produce electrically induced strains beyond 500%. The ability to undergo large deformation allows the DEA to store large amounts of elastic energy by electrical actuation; it also allows the DEA to perform flexibly in a diverse range of motions. Existing studies used different methods to maximize actuation strain for soft robotic applications. In this article, we examine the actuation of our antagonistically coupled DEAs, reminiscent to that of human muscles. We perform an analysis to reveal optimal conditions that maximize its actuation stroke, actuation force, and output energy. We quantify actuation stroke by the displacement sweep due to electrical actuation, between two fixed points, expressed as a percentage, and refer to this as "actuation sweep." From the analysis, we predicted an optimal prestretch for the DEA that corresponds to a 59% actuation sweep. In our experiment, we realized a 55% actuation sweep. We further characterized the output force and the mechanical work done for complete performance appraisal of the antagonistic system both theoretically and experimentally. We realized an antagonistic soft actuator system with simple geometry that provides significant electrically induced displacement, force, and work done, similar to that of biological muscle systems, and demonstrated its efficacy.

High-k, Ultrastretchable Self-Enclosed Ionic Liquid-Elastomer Composites for Soft Robotics and Flexible Electronics.

Soft robotics focuses on mimicking natural systems to produce dexterous motion. Dielectric elastomer actuators (DEAs) are an attractive option due to their large strains, high efficiencies, lightweight design, and integrability, but require high electric fields. Conventional approaches to improve DEA performance by incorporating solid fillers in the polymer matrices can increase the dielectric constant but to the detriment of mechanical properties. In the present work, we draw inspiration from soft and deformable human skin, enabled by its unique structure, which consists of a fluid-filled membrane, to create self-enclosed liquid filler (SELF)-polymer composites by mixing an ionic liquid into the elastomeric matrix. Unlike hydrogels and ionogels, the SELF-polymer composites are made from immiscible liquid fillers, selected based on interfacial interaction with the elastomer matrix, and exist as dispersed globular phases. This combination of structure and filler selection unlocks synergetic improvements in electromechanical properties-doubling of dielectric constant, 100 times decrease in Young's modulus, and ∼5 times increase in stretchability. These composites show superior thermal stability to volatile losses, combined with excellent transparency. These ultrasoft high-k composites enable a significant improvement in the actuation performance of DEAs-longitudinal strain (5 times) and areal strain (8 times)-at low applied nominal electric fields (4 V/µm). They also enable high-sensitivity capacitive pressure sensors without the need of miniaturization and microstructuring. This class of self-enclosed ionic liquid polymer composites could impact the areas of soft robotics, shape morphing, flexible electronics, and optoelectronics.

A Lesson from Plants: High-Speed Soft Robotic Actuators.

Rapid energy-efficient movements are one of nature's greatest developments. Mechanisms like snap-buckling allow plants like the Venus flytrap to close the terminal lobes of their leaves at barely perceptible speed. Here, a soft balloon actuator is presented, which is inspired by such mechanical instabilities and creates safe, giant, and fast deformations. The basic design comprises two inflated elastomer membranes pneumatically coupled by a pressurized chamber of suitable volume. The high-speed actuation of a rubber balloon in a state close to the verge of mechanical instability is remotely triggered by a voltage-controlled dielectric elastomer membrane. This method spatially separates electrically active and passive parts, and thereby averts electrical breakdown resulting from the drastic thinning of an electroactive membrane during large expansion. Bistable operation with small and large volumes of the rubber balloon is demonstrated, achieving large volume changes of 1398% and a high-speed area change rate of 2600 cm2 s-1. The presented combination of fast response time with large deformation and safe handling are central aspects for a new generation of soft bio-inspired robots and can help pave the way for applications ranging from haptic displays to soft grippers and high-speed sorting machines.

Electrically-Induced Actuation of Acrylic-Based Dielectric Elastomers in Excess of 500% Strain.

Conventional robots are typically actuated by hard actuators, while biological entities consist mostly of soft muscles. Being soft imparts a functionality of compliance, thereby greatly enhancing the range of actuation and the degrees of freedom. Here, we demonstrate a soft electromechanically-active polymer capable of an electrically-induced linear strain beyond 500% that is continuously tunable by voltage. Previous experiments on the same material have demonstrated that by harnessing and bypassing electromechanical instability, soft electroactive polymers may bi-stably switch between an actuated state and an uncharged state of about 323% linear strain. In this paper, we use theory to inspire the possibility of suppressing electromechanical instability using pre-stretch by applying a non-isotropic pre-stretch onto the membrane, so as to achieve an ultra-large actuation strain that is continuously tunable by voltage. This geometry that enables such a large magnitude of actuation is simple and highly amenable to integration in robotic systems. With an electrically-induced strain of at least two orders of magnitude larger than conventional actuators, we expect our demonstration to expand the range of application for soft actuators.