Bryan N. Peele

Highly stretchable electroluminescent skin for optical signaling and tactile sensing.

Make it stretch, make it glow The skins of some cephalopods, such as the octopus, are highly flexible and contain color-changing cells. These cells are loaded with pigments that enable rapid and detailed camouflaging abilities. Larson et al. developed a stretchable electroluminescent actuator. The material could be highly stretched, could emit light, and could also sense internal and external pressure. A soft robot demonstrated these combined capabilities by stretching and emitting light as it moved. Science, this issue p. 1071 Light emission, actuation, and sensing are combined in a stretchable electronic material suitable for soft robotics. Cephalopods such as octopuses have a combination of a stretchable skin and color-tuning organs to control both posture and color for visual communication and disguise. We present an electroluminescent material that is capable of large uniaxial stretching and surface area changes while actively emitting light. Layers of transparent hydrogel electrodes sandwich a ZnS phosphor-doped dielectric elastomer layer, creating thin rubber sheets that change illuminance and capacitance under deformation. Arrays of individually controllable pixels in thin rubber sheets were fabricated using replica molding and were subjected to stretching, folding, and rolling to demonstrate their use as stretchable displays. These sheets were then integrated into the skin of a soft robot, providing it with dynamic coloration and sensory feedback from external and internal stimuli.

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.

A Stretchable Multicolor Display and Touch Interface Using Photopatterning and Transfer Printing.

An intrinsically soft and stretchable multicolor display and touch interface is reported. Red, green, and blue pixels are formed separately by photopatterning transition-metal-doped ZnS embedded in silicone gels and transfer printing onto an elastomeric dielectric sheet. The device shows stable illumination while being stretched up to 200% area strain or under different deformation modalities. It also introduces capabilities for dynamic colorations and multipoint capacitive touch sensing.

Click chemistry stereolithography for soft robots that self-heal

Although soft robotics promises a new generation of robust, versatile machines capable of complex functions and seamless integration with biology, the fabrication of such soft, three dimensional (3D) hierarchical structures remains a significant challenge. Stereolithography (SLA) is an additive manufacturing technique that can rapidly fabricate the complex device architectures required for the next generation of these systems. Current SLA materials and processes are prohibitively expensive, display little elastic deformation at room temperature, or exhibit Youngs moduli exceeding most natural tissues, all of which limit use in soft robotics. Herein, we report a low-cost build window substrate that enables the rapid fabrication of high resolution (∼50 μm) silicone (polydimethylsiloxane) based elastomeric devices using an open source SLA printer. Our thiol-ene click chemistry permits photopolymerization using low energy (He < 20 mJ cm-2) optical wavelengths (405 nm < λ < 1 mm) available on many low-cost SLA machines. This chemistry is easily tuned to achieve storage moduli, 6 < E < 283 kPa at engineering strains, γ = 0.02; similarly, a large range of ultimate strains, 0.5 < γult < 4 is achievable through appropriate selection of the two primary chemical constituents (mercaptosiloxane, M.S., and vinylsiloxane, V.S.). Using this chemo-mechanical system, we directly fabricated compliant machines, including an antagonistic pair of fluidic elastomer actuators (a primary component in most soft robots). During printing, we retained unreacted pockets of M.S. and V.S. that permit autonomic self-healing, via sunlight, upon puncture of the elastomeric membranes of the soft actuators.

Stretchable transducers for kinesthetic interactions in virtual reality

Commercial virtual reality devices such as the Oculus Rift and HTC Vive enable experience designers to emulate a number of human sensory inputs with computer simulations. Commercial experiences have demonstrated plausibly realistic audiovisual sensory input, but somatosensory feedback has been more limited in scope. Most successful attempts in providing feedback to the human Kinesthetic system were considered power-demanding, expensive and potentially harmful to users, therefore somatosensory input has largely been addressed by vibration-based devices, like Linear Resonant Actuators and Eccentric Rotating Mass actuators, aimed at stimulating receptors near the surface of the skin. This method is widely accepted as a proxy in lieu of resisting to muscle tension, but it is not considered a path to realistic input.

Gait Synthesis for Modular Soft Robots.

Soft robots present a new opportunity for designing robots that can be produced quickly (on the order of hours), are capable of a variety of motions and behaviors, and are able to address a wide range of environments and tasks. The large design space of soft actuators can be leveraged to rapidly generate libraries of robotic components that can be used to compose modular soft robotic systems. To take full advantage of the large design space, we must have techniques for automatically synthesizing soft robot motions and behaviors. In this work, we develop a method for synthesizing gaits for walking soft robots, and show experimental results demonstrating synthesized gaits.