Design, Modelling and Validation of Hydraulic Servo Actuator With Passive Compliance for Legged Robots

The hydraulic driven legged robots walking on the ground always encounter impact forces due to the contacts between feet and ground. Aiming to reduce the impact forces, a novel passive compliance method is proposed by adding a miniature hydraulic accumulator to the piston chamber of the hydraulic actuator. And the overflow valve and the check valve are newly equipped to prevent overpressure operation and suction. The accumulator as an elastic component is used to reduce the increment of piston chamber pressure due to the impact forces. To demonstrate the effectiveness of the proposed actuator, a dynamic and hydraulic co-simulation platform for a single actuator is built. Both simulation and experiment results show that the new actuator has better passive compliant characteristics while ensuring rather high position servo precision. Under the control of the low bandwidth hydraulic servo valve, the impact forces are reduced by 30% within the scope of the study. The modeling methodology and experimental details give effective references for the legged robot design.