Realizing the potential of dielectric elastomer artificial muscles.

Soft robotics represents a new set of technologies aimed at operating in natural environments and near the human body. To interact with their environment, soft robots require artificial muscles to actuate movement. These artificial muscles need to be as strong, fast, and robust as their natural counterparts. Dielectric elastomer actuators (DEAs) are promising soft transducers, but typically exhibit low output forces and low energy densities when used without rigid supports. Here, we report a soft composite DEA made of strain-stiffening elastomers and carbon nanotube electrodes, which demonstrates a peak energy density of 19.8 J/kg. The result is close to the upper limit for natural muscle (0.4-40 J/kg), making these DEAs the highest-performance electrically driven soft artificial muscles demonstrated to date. To obtain high forces and displacements, we used low-density, ultrathin carbon nanotube electrodes which can sustain applied electric fields upward of 100 V/µm without suffering from dielectric breakdown. Potential applications include prosthetics, surgical robots, and wearable devices, as well as soft robots capable of locomotion and manipulation in natural or human-centric environments.

Bio-inspired Design and Additive Manufacturing of Soft Materials, Machines, Robots, and Haptic Interfaces.

Soft materials possess several distinctive characteristics, such as controllable deformation, infinite degrees of freedom, and self-assembly, which make them promising candidates for building soft machines, robots, and haptic interfaces. In this Review, we give an overview of recent advances in these areas, with an emphasis on two specific topics: bio-inspired design and additive manufacturing. Biology is an abundant source of inspiration for functional materials and systems that mimic the function or mechanism of biological tissues, agents, and behaviors. Additive manufacturing has enabled the fabrication of materials and structures prevalent in biology, thereby leading to more-capable soft robots and machines. We believe that bio-inspired design and additive manufacturing have been, and will continue to be, important tools for the design of soft robots.

A pipeline inspection robot for navigating tubular environments in the sub-centimeter scale.

In complex systems like aircraft engines and oil refinery machines, pipeline inspection is an essential task for ensuring safety. Here, we proposed a type of smart material-driven pipeline inspection robot (weight, 2.2 grams; length, 47 millimeters; diameter, <10 millimeters) that could fit into pipes with sub-centimeter diameters and different curvatures. We adopted high-power density, long-life dielectric elastomer actuators as artificial muscles and smart composite microstructure-based, high-efficiency anchoring units as transmissions. Fast assembling of components using magnets with an adjustable number of units was used to fit varying pipeline geometries. We analyzed the dynamic characteristics of the robots by considering soft material's unique properties like viscoelasticity and dynamic vibrations and tuned the activation voltage's frequency and phase accordingly. Powered by tethered cables from outside the pipe, our peristaltic pipeline robot achieved rapid motions horizontally and vertically (horizontal: 1.19 body lengths per second, vertical: 1.08 body lengths per second) in a subcentimeter-sized pipe (diameter, 9.8 millimeters). Besides, it was capable of moving in pipes with varying geometries (diameter-changing pipe, L-shaped pipe, S-shaped pipe, or spiral-shaped pipe), filled media (air or oil), and materials (glass, metal, or carbon fiber). To demonstrate its capability for pipeline inspection, we installed a miniature camera on its front and controlled the robot manually from outside. The robot successfully finished an inspection task at different speeds.

A Wearable Soft Haptic Communicator Based on Dielectric Elastomer Actuators.

Dielectric elastomer actuators exhibit an unusual combination of large displacements, moderate bandwidth, low power consumption, and mechanical impedance comparable with human skin, making them attractive for haptic devices. In this article, we propose a wearable haptic communication device based on a two-by-two array of dielectric elastomer linear actuators. We briefly describe the architecture of the actuators and their mechanical and electrical integration into a wearable armband. We then characterize the actuators' force, displacement, and thermal properties in a bench-top configuration. We also report on the power and drive circuit design. Finally, we perform a set of preliminary perception evaluations on participants using our haptic device, including detection threshold tests and identification tests for locations and directions on the forearm. Human testing with individual actuators demonstrates that the broadband actuation can be easily perceived on the forearm, providing the basis for both the development of a wearable actuator array and its use in more extensive perception evaluation as described herein.

3D printing antagonistic systems of artificial muscle using projection stereolithography.

The detailed mechanical design of a digital mask projection stereolithgraphy system is described for the 3D printing of soft actuators. A commercially available, photopolymerizable elastomeric material is identified and characterized in its liquid and solid form using rheological and tensile testing. Its capabilities for use in directly printing high degree of freedom (DOF), soft actuators is assessed. An outcome is the ∼40% strain to failure of the printed elastomer structures. Using the resulting material properties, numerical simulations of pleated actuator architectures are analyzed to reduce stress concentration and increase actuation amplitudes. Antagonistic pairs of pleated actuators are then fabricated and tested for four-DOF, tentacle-like motion. These antagonistic pairs are shown to sweep through their full range of motion (∼180°) with a period of less than 70 ms.

Poroelastic Foams for Simple Fabrication of Complex Soft Robots.

Open-celled, elastomeric foams allow the simple design of fully 3D pneumatic soft machines using common forming techniques. This is demonstrated through the fabrication of simple actuators and an entirely soft, functional fluid pump formed in the shape of the human heart. The device pumps at physiologically relevant frequencies and pressures and attains a flow rate higher than all previously reported soft pumps.