Huichan Zhao

Optoelectronically innervated soft prosthetic hand via stretchable optical waveguides

Stretchable optical waveguides can sense curvature, elongation, and force in a prosthetic hand. Because of their continuous and natural motion, fluidically powered soft actuators have shown potential in a range of robotic applications, including prosthetics and orthotics. Despite these advantages, robots using these actuators require stretchable sensors that can be embedded in their bodies for sophisticated functions. Presently, stretchable sensors usually rely on the electrical properties of materials and composites for measuring a signal; many of these sensors suffer from hysteresis, fabrication complexity, chemical safety and environmental instability, and material incompatibility with soft actuators. Many of these issues are solved if the optical properties of materials are used for signal transduction. We report the use of stretchable optical waveguides for strain sensing in a prosthetic hand. These optoelectronic strain sensors are easy to fabricate, are chemically inert, and demonstrate low hysteresis and high precision in their output signals. As a demonstration of their potential, the photonic strain sensors were used as curvature, elongation, and force sensors integrated into a fiber-reinforced soft prosthetic hand. The optoelectronically innervated prosthetic hand was used to conduct various active sensation experiments inspired by the capabilities of a real hand. Our final demonstration used the prosthesis to feel the shape and softness of three tomatoes and select the ripe one.

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.

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.

Curvature control of soft orthotics via low cost solid-state optics

A soft orthotic with position control enabled via embedded optical fiber is presented. The design, manufacture, and integration of both the pneumatically powered actuators and optical sensors are described. This orthotic actuator-sensor pair is self-contained and worn on a human finger. When un-powered, the elastomeric actuator allows facile movement and, when pneumatically actuated, the orthotic causes bending of the wearers finger. Position control is achieved by measurement of signal intensity from a light-emitting diode (LED) input traveling through an embedded optical fiber-greater curvature results in increased light intensity. Both the static and dynamic states are monitored via the optical sensor and the prescribed curvatures are achieved accurately and with stability by a gain-scheduled proportional-integral-derivative (PID) controller implemented by applying pulse-width-modulation (PWM) signals to a solenoid valve to adjust the internal pressure of the actuator.

Soft Robotics: Poroelastic Foams for Simple Fabrication of Complex Soft Robots (Adv. Mater. 41/2015)

On page 6334, R. F. Shepherd and co-workers present pneumatically actuated soft machines based on elastomer foams. These foams are easily molded into complex, 3D shapes and retain an innate pore network for inflation. This is demonstrated through fabrication of both simple actuators and an entirely soft, functional fluid pump formed in the shape of the human heart.