Friction Characterization of a Cable-Driven Differential Actuation System for Lower-Limb Exoskeletons

2026-06-14

AI Summary

This study addresses the challenges of conventional independently actuated joints in lower-limb exoskeletons—namely, their mechanical complexity, excessive weight, and reliance on torque sensors—by proposing a cable-driven differential architecture tailored for hip–knee flexion–extension movements. The design employs two motors coupled with a linear differential mapping to enable coordinated torque distribution across joints. Combined with a model-based friction compensation strategy, this approach achieves, for the first time in a differential actuation module, high-precision joint torque estimation without the need for physical torque sensors. Experimental validation demonstrates that the proposed method substantially reduces system complexity and mass, offering an effective sensorless torque control solution for lightweight exoskeletons.

Abstract

Lower-limb exoskeletons require actuation systems that can provide accurate joint torque control while preserving low mass and encumbrance. Conventional architectures often rely on independently actuated joints and joint-level torque sensors, increasing system complexity and weight. This paper presents a novel differential actuation architecture for hip-knee flexion/extension, enabling cooperative torque sharing between two motors via a linear differential mapping between motor and joint. To compensate for transmission losses, a model-based friction estimation strategy is developed and experimentally implemented, allowing accurate joint torque estimation without the need for torque sensors. The proposed solution is validated on a physical prototype, demonstrating the feasibility of sensorless torque estimation in a differentially actuated hip-knee module of a lower-limb exoskeleton.

Problem

• lower-limb exoskeletons
• actuation systems
• joint torque control
• friction characterization
• torque sensing

Innovation

• differential actuation
• friction estimation
• sensorless torque estimation
• cable-driven transmission
• lower-limb exoskeleton