Biped robots require massive power on each leg while walking, hopping, and running. We have developed a flow-based control system-called hydraulic direct drive system- that can achieve high output while avoiding spatial limitations. To implement the proposed system with simple equipment configuration, a pump and single-rod cylinder are connected in a closed loop. However, because compensation for flow rate is impossible in a completely closed loop, owing to the difference in the pressure receiving area caused by the rod, a passive flow compensation valve is employed. This valve has a simple structure and is easy to implement. Further, an additional sensor is required to detect the open/close state because the valve state will cause an error in flow control. Therefore, we implemented a model in the controller to predict the state of the flow compensation valve and formulated a method of switching from flow control to pressure control according to the predicted state. Experimental results indicate that the error of the joint angle is reduced to less than 1.6 degrees for walking patterns, and stable walking is realized when the system is installed in biped humanoid robots.

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.

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.