title: Tiny hydraulics for powered orthotics.
abstract: Untethered, powered orthotics require an actuation system with power supply and control, transmission line and actuator. Fluid power has unmatched force-to-weight and power-to-weight compared to electromechanical systems, but it is unclear if those same advantages hold for small systems in the 10 to 100 W range. A systems analysis approach suggests that a fluid power system will be lighter than an electromechanical system with the same output power and efficiency if the fluid power is run at pressures over about 200 psi. A theoretical analysis of small bore cylinders suggests that eliminating the piston seal will result in a higher efficiency actuator if the clearance gap is small. A demonstration, battery powered electrohydraulic actuator assembled from off-the-shelf components had the force and power suited to a powered ankle orthosis, but is too large and too heavy, suggesting the need to develop custom components.
authors.affiliation: University of Minnesota, Minneapolis, USA. wkdurfee@umn.edu
authors.forename: William
authors.initials: W
authors.lastname: Durfee
authors.forename: Jicheng
authors.initials: J
authors.lastname: Xia
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hsiao-Wecksler
mesh_terms: D001696:Biomechanical Phenomena; D004867:Equipment Design; D006801:Humans; D007700:Kinetics; D009989:Orthotic Devices