Design of Gear Pump of Electro-Hydrostatic Actuator for Robots

An electro-hydrostatic actuator (EHA) is suitable to force controlled robots that interact with surrounding objects because it has high robustness and backdrivabilityBackdrivability. The major issues of an EHA for robots are internal leakageInternal leakage and its size and weight. Especially, in the design of an EHA, it is important to pay attention to the internal clearances of a hydraulic pump, which is a major source of internal leakageInternal leakage. Since there is a trade-off between internal leakageInternal leakage and frictionFriction regarding internal clearances, it is necessary to adjust the clearance properly. In addition, since a pump of an EHA is bidirectional and variable pressure, it is required to consider the change of the state of the internal clearances. This paper summarizes the key points in the design of an external gear pump for an EHA focusing on the internal clearances from the previous researches.