Toward compliant, fast, high-precision, and low-cost manipulator with hydraulic hybrid servo booster

We propose a novel hydraulic hybrid servo drive for robotic applications. This method embeds a small servo-controlled pump into a hydraulic metering circuit. The circuit is compactly integrated into a servo-unit, then replicated for each joint, and connected to one common low-pressure line. Thanks to the boosting effect, one can simultaneously achieve high-load and high-precision servo control performance with low-cost components. The paper describes the principle of the new circuit and two realizations: one for a slider testbed with a single-rod cylinder, the other for a three-joint manipulator prototype. The slider experiments show that the proposed circuit can not only achieve the high piston velocity, but also exclusively generate large piston force with a small positional error up to the resolution of the servo-pump. Moreover, experiments on the manipulator demonstrate that the robot can compliantly respond to external perturbations, thanks to the high backdrivability of the servo-pump.