A Lightweight, Fully Integrated Ankle Exoskeleton With High-Torque Density Series-Elastic Actuation

Powered ankle exoskeletons have the potential to improve mobility by assisting the ankle joint during ambulation. To achieve this goal, ankle exoskeletons must provide substantial assistive torque (up to 50 Nm) in a small and lightweight form. Unfortunately, most exoskeletons are too heavy and bulky for practical application. They often lack protective covers and require wearing a backpack with wires running down the user’s legs, which reduces their effectiveness in the real world. This article presents the design of a lightweight and compact powered ankle exoskeleton with fully integrated and enclosed actuation, batteries, and electronics. The proposed design features a linear series-elastic actuator (SEA), achieving high torque/power density while enabling high-fidelity closed-loop torque control. The proposed ankle exoskeleton was demonstrated using a variable stiffness impedance controller with three healthy subjects walking on a treadmill. The results of benchtop experiments show a -3 dB bandwidth exceeding 19 Hz. The results of human experiments show a torque density of 37 Nm/kg and a power density of 81.5 W/kg. This compact and lightweight design satisfies practical requirements for real-world use while providing sufficient torque density to improve mobility.