This paper presents the design and verification of a quasi-passive lower extremity exoskeleton (LEE) for jumping assistance and landing protection. Compared to the LEE actively actuated, it has no powerful electric, hydraulic or pneumatic actuators, only a clutched parallel elastic magnetorheological actuator (CPEMA) on the knee joint. To assist in joint force generation, the actuator integrated a fixed stiffness torsional spring, a planetary reducer, large-size magnetorheological fluid (MRF) bearings and single directional bearings is capable of storing and releasing the energy of human locomotion, overcoming the dependence on external energy supply. However, when augmented with a fixed stiffness spring, the accumulated energy is limited by the maximum deflection and the force generation ability of human limbs. Here, the augmentation method with CPEMAs is proposed to untie the biological constraints, where the generated force is amplified by the reducer and the storage of energy is repeatable due to single directional bearings and MRF bearings. So the exoskeleton with CPEMAs can store knee flexion energy repeatedly and release the accumulated energy instantaneously to achieve explosive torque output. Additionally, the CPEMA can function as a stiffness-damping vibration-absorbing system, dissipating the impact energy during the high drop, which enhances the impact resistance of the human-exoskeleton system. In this paper, we have theoretically analyzed and tested the performance of the CPEMA respectively, and the results show that it can provide high locking torque output of 226 Nm with a wide range of controllable damping. Using the exoskeleton prototype with CPEMAs, the processes of jumping assistance and dropping cushioning have been demonstrated to evaluate the performance of the exoskeleton experimentally. The experimental results indicate that the exoskeleton with CPEMAs can provide 124 Nm torque assistance to each knee joint, and the EMG signal shows that the muscular forces of the wearer are significantly reduced during the jump period. In the cushion period, the maximum pulse acceleration is reduced due to the improvement in impact resistance of the human-exoskeleton system.

lower extremity exoskeleton,magnetorheological actuator,quasi-passive,jump assistance,impact resistance