Experimental Validation of Hydraulic Interlocking Drive System for Biped Humanoid Robot

Biped robots require substantial amounts of power on each leg alternately while walking, hopping, and running. However, it is difficult to adopt large high-power electrical motors in conventional mechanical transmission systems owing to spatial limitations. To address this problem, a hydraulic interlocking drive system that incorporates two hydraulic direct-drive systems is proposed for biped humanoid robots. The hydraulic interlocking drive system connects the two hydraulic direct-drive systems and concentrates the pump output on one side cylinder. The other side cylinder meter-in flow rate is controlled by the meter-out flow rate from the cylinder on which the pump is concentrated. Good position tracking and excellent energy saving are achieved with the proposed system. A performance comparison with a single hydraulic direct-drive system shows that the motor power of the hip pitch joint is reduced by 27.3% for walking patterns. This result shows that the rated output of the motor can be reduced, and smaller and lighter motors can be installed in biped robots.