A Unified Active Assistance Control Framework of Hip Exoskeleton for Walking and Balance Assistance∗

To actively assist human walking and balance recovery, a unified active assistance control framework of the hip exoskeleton is proposed in this paper. At the beginning of this paper, the condition of active assistance is analyzed. And then, a novel virtual stiffness model is proposed based on the analysis of human hip joint torque during walking and balance recovery. The virtual stiffness model is utilized to generate the desired active assistance torque profile for active walking and balance assistance. Next, the unified active assistance control framework is established based on the virtual stiffness model. Finally, the effectiveness of the proposed control framework is demonstrated by walking experiments. The results of the forward walking experiment show that the muscle effort of iliopsoas is reduced and the amplitude of hip joint motion is enlarged with the assistance of hip exoskeleton. The walking forward pull experiments and the walking backward pull experiments show that when the human suffers from a forward or backward disturbance force during forward walking, exoskeleton can help human regain balance faster and can enlarge the margin of stability (MoS) of the human.