Michael Wehner

An integrated design and fabrication strategy for entirely soft, autonomous robots

Soft robots possess many attributes that are difficult, if not impossible, to achieve with conventional robots composed of rigid materials. Yet, despite recent advances, soft robots must still be tethered to hard robotic control systems and power sources. New strategies for creating completely soft robots, including soft analogues of these crucial components, are needed to realize their full potential. Here we report the untethered operation of a robot composed solely of soft materials. The robot is controlled with microfluidic logic that autonomously regulates fluid flow and, hence, catalytic decomposition of an on-board monopropellant fuel supply. Gas generated from the fuel decomposition inflates fluidic networks downstream of the reaction sites, resulting in actuation. The body and microfluidic logic of the robot are fabricated using moulding and soft lithography, respectively, and the pneumatic actuator networks, on-board fuel reservoirs and catalytic reaction chambers needed for movement are patterned within the body via a multi-material, embedded 3D printing technique. The fluidic and elastomeric architectures required for function span several orders of magnitude from the microscale to the macroscale. Our integrated design and rapid fabrication approach enables the programmable assembly of multiple materials within this architecture, laying the foundation for completely soft, autonomous robots.

A Resilient, Untethered Soft Robot

A pneumatically powered, fully untethered mobile soft robot is described. Composites consisting of silicone elastomer, polyaramid fabric, and hollow glass microspheres were used to fabricate a sufficiently large soft robot to carry the miniature air compressors, battery, valves, and controller needed for autonomous operation. Fabrication techniques were developed to mold a 0.65-meter-long soft body with modified Pneu-Net actuators capable of operating at the elevated pressures (up to 138kPa) required to actuate the legs of the robot and hold payloads of up to 8kg. The soft robot is safe to interact with during operation, and its silicone body is innately resilient to a variety of adverse environmental conditions including snow, puddles of water, direct (albeit limited) exposure to flames, and the crushing force of being run over by an automobile.

A lightweight soft exosuit for gait assistance

In this paper we present a soft lower-extremity robotic exosuit intended to augment normal muscle function in healthy individuals. Compared to previous exoskeletons, the device is ultra-lightweight, resulting in low mechanical impedance and inertia. The exosuit has custom McKibben style pneumatic actuators that can assist the hip, knee and ankle. The actuators attach to the exosuit through a network of soft, inextensible webbing triangulated to attachment points utilizing a novel approach we call the virtual anchor technique. This approach is designed to transfer forces to locations on the body that can best accept load. Pneumatic actuation was chosen for this initial prototype because the McKibben actuators are soft and can be easily driven by an off-board compressor. The exosuit itself (human interface and actuators) had a mass of 3500 g and with peripherals (excluding air supply) is 7144 g. In order to examine the exosuits performance, a pilot study with one subject was performed which investigated the effect of the ankle plantar-flexion timing on the wearers hip, knee and ankle joint kinematics and metabolic power when walking. Wearing the suit in a passive unpowered mode had little effect on hip, knee and ankle joint kinematics as compared to baseline walking when not wearing the suit. Engaging the actuators at the ankles at 30% of the gait cycle for 250 ms altered joint kinematics the least and also minimized metabolic power. The subjects average metabolic power was 386.7 W, almost identical to the average power when wearing no suit (381.8 W), and substantially less than walking with the unpowered suit (430.6 W). This preliminary work demonstrates that the exosuit can comfortably transmit joint torques to the user while not restricting mobility and that with further optimization, has the potential to reduce the wearers metabolic cost during walking.

An untethered jumping soft robot

Locomoting soft robots typically walk or crawl slowly relative to their rigid counterparts. In order to execute agile behaviors such as jumping, rapid actuation modes are required. Here we present an untethered soft-bodied robot that uses a combination of pneumatic and explosive actuators to execute directional jumping maneuvers. This robot can autonomously jump up to 0.6 meters laterally with an apex of up to 0.6 meters (7.5 times its body height) and can achieve targeted jumping onto an object. The robot is able to execute these directed jumps while carrying the required fuel, pneumatics, control electronics, and battery. We also present a thermodynamic model for the combustion of butane used to power jumping, and calculate the theoretical maximum work output for the design. From experimental results, we find the mechanical efficiency of this prototype to be 0.8%.

Lower Extremity Exoskeleton Reduces Back Forces in Lifting

We propose a lower extremity exoskeleton device which adds a passive extensor moment (restoring moment) about the hips during squat lifting, thus reducing forces on the lower back by reducing the required extensor muscle force. Video sequences were recorded of normal speed sagittal squat lifting 44.5 N (10 lb) and 133.5 N (30 lb) packages for marker tracking. Calculations suggested that the device reduces maximum spine compressive forces by approximately 1300 N. Surface electromyography (EMG) was performed on 6 subjects supporting 44.5 N (10 lb) and 133.5 N (30 lb) packages in the static squat posture. With the device, back muscles demonstrated a 54% reduction in muscle activity. This exoskeleton device includes features not available on other devices including highly adjustable moment profile and elimination of high contact stress in the lower extremities by connecting directly with the ground.Copyright

Bio-Inspired Design of Soft Robotic Assistive Devices: The Interface of Physics, Biology, and Behavior

Wearable assistive robotic devices are characterized by an interface, a meeting place of living tissue and mechanical forces, at which potential and kinetic energy are converted to one or the other form. Ecological scientists may make important contributions to the design of device interfaces because of a functional perspective on energy and information exchange. For ecological scientists, (a) behavioral forms are an assembly of whole functional systems from available parts, emerging in energy flows, and (b) nature explores for informationally based adaptive solutions to assemble behavioral forms by generating spontaneous patterns containing fluctuations. We present data from ongoing studies with infants that demonstrate how infants may explore for adaptive kicking solutions. Inspired by the ecological perspective and data from developing humans, ecological scientists may design interfaces to assist individuals with medical conditions that result in physical and/or mental impairment. We present one such device, what is called the “second skin,” to illustrate how a soft, prestressed material, worn on the skin surface, may be used synergistically with synthetic and biological muscles for assisting action. Our work on the second skin, thus far, suggests a set of ecologically inspired principles for design of wearable assistive robotic devices.

Man to Machine, Applications in Electromyography

The study of electrical signals due to muscle activation has been evolving since Francesco Redi found electrical generation in the muscles of the electric ray fish in 1666 (Fishman, Wilkins, 2011), Dubois discovered electrical activation in voluntary muscles in 1849 (Blanc, Dimanico, 2010), and Mari coined the term Electromyography in 1922 (Raz, et al., 2006). Evolving over the following decades, electromyography has found widespread use in clinical settings as well as extensive use in ergonomic assessment and biomechanics research laboratories. As with many technologies, the discovery of electromyography occurred long before inexpensive and robust hardware was developed to utilize the vast amount of information available from myoelectric signals. Until recently, existing technology could not support efficient generation of repeatable robust signals for even highly sophisticated research laboratories, let alone the widespread availability of affordable, robust hardware required to propagate electromyography through the research communities. New high-speed computation tools make real-time analysis feasible. With the emergence of low cost hardware, high speed wireless communication technology, and low cost, high speed computing/signal processing equipment, Electromyography is becoming available to a whole new set of experimenter. With these advances making electromyography a feasible option in many situations, we see the emergence of a key period in the evolution of the technology. Surface electromyography (sEMG) provides a convenient and relatively noninvasive avenue for determining muscle activation, particularly as highly portable devices become available. Of course with the benefits of wider availability, we must consider the risks inherent in this spread, as the practitioners involved move from electromyography specialists, to technologists in other fields, using electromyography either part time, or only occasionally. Electromyography is a detailed art, and can easily lead to erroneous conclusions if not practiced carefully. With new applications, particularly where electromyography is employed as a means for humans to control electromechanical systems, care must be taken to insure that these systems are developed with robust safety systems, and improper assumptions about electromyography do not cause harm, injury, or even death.

A Soft Combustion-driven Pump for Soft Robots

This paper describes the design and manufacture of a monolithic high-pressure diaphragm pump made entirely of soft elastomer material and driven by a combustion chamber incorporated within the soft pump structure. The pump can deliver pressures up to 60 kPa and can reach output flows up to 40 ml/min. Methane (CH4) combustion is used as the actuation source. The pump uses two soft flap-structured check valves for directing the flow. Pumping pressure and frequency dependence were measured and analyzed. Results show that controlled and repeatable combustion of methane is possible without damaging the soft structure. Experimentally, 6–10% methane is identified as the ideal air-fuel ratio for combustion. With continuous delivery of reactants, a 1 Hz pumping frequency was achieved. The volume of the combustion chamber and the material stiffness are identified to be major determinants of the stroke volume.Copyright

Population and climate change: who will the grand convergence leave behind?

Author(s): Campbell, Martha M; Casterline, John; Castillo, Federico; Graves, Alisha; Hall, Thomas L; May, John F; Perlman, Daniel; Potts, Malcolm; Speidel, J Joseph; Walsh, Julia; Wehner, Michael F; Zulu, Eliya Msiyaphazi