A Lightweight Hip Exoskeleton with High Torque-To-Mass Ratio: Design, Gait-Synchronized Control, and Physiological Validation

Abstract

This paper presents the design, control, and experimental validation of a lightweight hip exoskeleton for walking assistance. By integrating quasi-direct drive actuators, single-piece stainless steel frames, and passive revolute joints, the device achieves a high torque-to-mass ratio while maintaining a compact and lightweight structure. A delayed output feedback control strategy synchronizes assistive torque with the gait cycle by actively leading the wearer's hip motion, with user studies identifying a consistent optimal phase difference across participants and walking speeds, eliminating repeated calibration. Surface electromyography validates the assistance, demonstrating substantial reductions in activation of the vastus medialis and vastus lateralis at the optimal time delay. Power analysis further confirms that this setting maximizes positive power transfer while minimizing resistive effects. The proposed exoskeleton delivers physiologically meaningful and energetically efficient hip assistance suitable for everyday mobility support.