The PREHydrA: A Passive Return, High Force Density, Electro-Hydrostatic Actuator Concept for Wearable Robotics

This letter presents the Passive Return Electro-Hydrostatic Actuator (PREHydrA), an actuator for use in wearable robotics. It eliminates conventional hydraulic systems’ fluid supply and valves, potentially making it lighter, more efficient, and simpler. It also avoids the configuration-dependent friction of Bowden cable transmissions. A physical port-based network model was created of the PREHydrA that predicts force tracking with a maximum error of about 4 N. Closed loop output force control was used in experiments to obtain a mean absolute tracking error below 4 N for force references from 300 N amplitude at 0.5 Hz to 20 N amplitude at 10 Hz. These forces, frequencies, and corresponding velocities (up to 0.47 m/s) demonstrate that the PREHydrA's performance is sufficient for many wearable applications.