Experimental validation of high-efficiency hydraulic direct-drive system for a biped humanoid robot-Comparison with valve-based control system

Biped robots require substantial amounts of power alternately on each leg while walking, hopping, and running. However, it is difficult to mount high-power large electrical motors in conventional mechanical transmission systems owing to spatial limitations. A hydraulic direct-drive system is proposed in which the size of the motor in each leg can be reduced by sharing the motor outputs between the legs. In this paper, the hydraulic direct-drive system is evaluated in an actual hydraulic system. Velocity followability, excellent energy saving, and virtually perfect position tracking are achieved with the proposed system. The results of performance comparison with a valve-based control system show that energy consumption is controlled and good position-following capability is achieved using the proposed system.