A Novel Knee Exoskeleton Driven by Series Elastic Actuator for Gait Assistance in Level Walking and Stair Ascent

Abstract

Active knee exoskeletons should provide effective assistance while remaining lightweight and comfortable to wear. Common knee exoskeletons often place the actuator and structural components on one side of the joint, which can generate undesired interaction loads. Remote transmissions using Bowden cables may also reduce transmission efficiency during gait. To address these issues, this paper presents a lightweight knee exoskeleton that combines a two-side-support layout with a series elastic actuator and cable-roller transmission to reduce undesired interaction loads while improving transmission efficiency and enabling consistent torque control. A time-based gait phase estimation and torque control strategy is developed to provide continuous assistance during level walking and stair ascent. In experiments, the system achieved 98.5% torque tracking accuracy, resistive knee torque below $\mathbf{0.6 N} \cdot \mathbf{m}$ in zero-assistance walking, and stable gait-synchronized assistance in both tasks. Preliminary muscle activity results suggested reduced vastus lateralis and vastus medialis activity under assistance, with peak amplitudes decreasing by approximately 5%-12%.