Abstract: Load-bearing walking is an important requirement in fields such as industrial handling and fire rescue, but long-term load-bearing may cause irreversible damage to the human body. Assistive devices designed to improve load-bearing capacity have become a research hotspot, with lower limb exoskeletons attracting widespread attention as an effective solution. A semi-active electro-hydraulic driven lower limb exoskeleton robot is developed for load-bearing augmentation. In structural design, a novel semi-active electro-hydraulic joint is adopted to transfer the back load in the sagittal plane based on the angular velocity characteristic between the trunk and the thigh, as well as the torque characteristics of the knee joint. This research presents the kinematic and dynamic model of the joints. For the load disturbance in the motion process, the combination of double inverted pendulum model and state machine strategy is adopted to match the dynamic damping: During the stance phase, joint damping is adjusted according to acceleration characteristics to transfer dynamically varying loads. In the swing phase, the semi-active joints maintain backdrivability to ensure the free swing of the leg. Experimental tests verify that the semi-active joints exhibit a wide range of adjustable hydraulic damping coefficients and good backdrivability, ensuring effective damping adjustment during the stance phase and passive follow-up control during the swing phase. Furthermore, exoskeleton experiments indicate that, under different load conditions, the proposed semi-active hydraulic-electric driven exoskeleton achieves efficient load transfer and provides low back interaction force.

Key words: lower limb exoskeleton, semi-active joint, load-bearing augmentation, ground transferred force, back interaction force