A Pilot Study of an Ankle Assistive Device With a Reaction Wheel and Mechanical Braking for Impulsive Push-off Torque Generation

Abstract

This study proposes a novel ankle assistive device using a reaction wheel mechanism with mechanical braking to support push-off in gait. Unlike conventional joint-aligned exoskeletons, the proposed design avoids axis misalignment and enables ankle assistance without generating torque along the joint axis. Kinetic energy is stored in a high-speed spinning wheel and rapidly released using a pawl-ratchet mechanism, producing an impulsive torque without requiring a high-power motor. Experiments using a pendulum-type testbed demonstrated that the device can generate over 8 Nm of torque in just 0.03 seconds, satisfying the push-off phase timing requirements. Human-subject trials showed an average anterior-posterior ground reaction force increase of approximately 11.5% of body weight during activation, confirming the device’s assistive potential. A nonlinear model was also established to estimate key parameters using least-squares optimization and stochastic analysis. These results demonstrate the feasibility of ankle assistance using impulsive momentum.