Human legs exhibit spring-like behavior during the walking stance phase, motivating the development of lightweight passive lower extremity exoskeletons with elastic energy storage. While such designs offer promise in improving gait economy and reducing muscular effort, they often compromise swing-phase kinematics. Here, we propose a quasi-passive knee exoskeleton equipped with Clutched Elastic Actuators (CEAs) to assist human walking. The CEA on the knee joint comprises a magnetorheological fluid (MRF) bearing unit that serves as a clutch mechanism and a torsional spring for energy recycling. When the spring is engaged, the CEA stores energy during knee flexion and releases it during knee extension. Then, the spring is disengaged to permit unrestricted limb motion and maintain natural gait kinematics during the swing phase. Benchtop tests confirm that the MRF bearing unit delivers sufficient locking torque and enables smooth, rapid engagement and disengagement of the spring. Furthermore, with the assistance of the knee exoskeleton, treadmill walking experiments demonstrate notable reductions in muscle activity. Our approach paves the way for developing lightweight, inexpensive, and quasi-passive exoskeletons that reduce muscular effort and make recreational walking more enjoyable.
Wang et al. (Sun,) studied this question.