PositiveAssist: Energy-Gated Control for Positive Power Assistance of Exoskeleton in Walking, Running, and Stair...

Assistance timing is a critical factor in exoskeleton control. This article introduces the energy-gated controller, which uses only two thigh-mounted inertial measurement units to estimate hip kinematics and predicted mechanical power so that assistive torque is delivered primarily during positive work phases. Our proposed method combines a power-based gating mechanism with a biomechanics-informed torque synthesis strategy that reconstructs extension assistance from a delayed flexion profile, without gait-phase detection or task-specific mode switching. Experimental results from six participants $(n=6)$ show that using a single fixed parameter set selected a priori, over 97.8% ± 1.2% of delivered mechanical power remained positive during walking and above 94.8% ± 1.6% during running, across 0.75-3.5 m/s without parameter retuning. Under the same fixed parameters, the controller was further tested in five overground nonperiodic locomotion tasks and showed smooth assistance during the tested gait transitions, indicating potential for real-world deployment.