Load-Carrying Assistance of Articulated Legged Robots Based on Hydrostatic Support

This letter proposes a novel mechanical structure for traditional articulated-legged robots that uses a linkage-based approach and hydrostatic transmission to reduce the joint load caused by gravity. The wide application of legged robots is limited by their weight-bearing capacity and low energy efficiency. To address these issues, we built HyELeg2, a motor-actuated bipedal robot with the assistance of a hydraulic auxiliary mechanism. HyELeg2 employs one passive hydraulic cylinder per leg to counterbalance the joint torque induced by the body mass at both knee and hip joints. During the stance phase of walking, the cylinder can provide upward support force passively to reduce the energy cost of motors. To control the flow efficiently, a rotary-cage valve (RCV) was developed with low energy consumption and low flow resistance. Contrast experiments were conducted to investigate the energy-saving effects of HyELeg2 under different speed, gait frequency and load conditions. The results indicate that hydraulic assistance saves energy by more than 65% to perform the same walking tasks, and greatly reduces the cost of transport (CoT). This study has high practical value in the legged robot field.