Force and moment generation of fiber-reinforced pneumatic soft actuators

Soft actuators are found throughout nature from elephant trunks to round worms, demonstrating large specific forces without the need for sliding components. These actuators offer impact resilience, human-safe interaction, versatility of motion, and scalability in size. Biological structures often use a fiber-reinforcement around a fluid filled elastomeric enclosure, in which the elastomeric material will capture the distributed pressure and transfer it to the fibers, which will in turn direct the forces to the ends. We previously discovered an entire domain of fiber-reinforced elastomeric enclosures (FREEs), of which McKibben actuators are a small subset. The range of forces and moments possible with FREEs has not been previously investigated. 45 FREE actuators across the span of fiber angle configurations were fabricated and tested. The reaction force and moment of each actuator was determined across a gamut of pressures. Analytical models were generated using a variety of simplifying assumptions. These models were created to provide a closed form expression that models the force and moment data. The models were compared to the experimental values to determine their fit; this provides an understanding of which simplifying kinematic assumptions best represent the experimental results. Interpolated experimental results and the analytical models are all graphically represented for use as an intuitive design tool.