Effects of the Varying Lateral Clearances on the Pressure Ripple of Internal Gear Pumps in Biped Robots  Internal gear pumps (IGPs) are commonly applied in biped robotsxe2x80x99 hydraulic actuation systems serving as the power unit. The pumpxe2x80x99s outlet pressure ripple does harm to accurate motion controls and is usually lowered by adopting an accumulator. This paper investigates the effects of the varying lateral clearances between the gear and the floating plate on the pressure ripple. It aims to provide advices on manufacturing the gears to lower the pumpxe2x80x99s outlet pressure ripple so that the accumulator could be smaller, which is of great importance to weight and space saving in biped robotsxe2x80x99 design. A mathematical model was established for evaluating the outlet pressure considering the lateral clearancesxe2x80x99 varying phenomenon. Moreover, the outlet pressure was measured by highfrequency pressure sensors for verifying the effects of the varying lateral clearances. The simulated and experimental results suggest that the outlet pressure concerning varying lateral clearances has small ripples characterized by high frequency and big ripples characterized by low frequency. Additionally, the pressure ripple, especially the big ripple, can be lowered by well manufacturing the gear pairxe2x80x99s lateral sides, ensuring the consistency of the tooth width of the gear.

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 highpower electrical motors in conventional mechanical transmission systems owing to spatial limitations. To address this problem, a hydraulic interlocking drive system that incorporates two hydraulic directdrive systems is proposed for biped humanoid robots. The hydraulic interlocking drive system connects the two hydraulic directdrive systems and concentrates the pump output on one side cylinder. The other side cylinder meterin flow rate is controlled by the meterout 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 directdrive 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.