Overpressure Compensation for Hydraulic Hybrid Servo Booster Applied to Hydraulic Manipulator

Abstract

This letter describes our novel hydraulic circuit, referred to as the hydraulic hybrid servo booster, and its application to hydraulic manipulator. The circuit embeds a servomotor-controlled pump into a valve bridge so that the high-speed position can be achieved in a hybrid, cost-effective, and precise manner. This letter focuses on the precise manipulation of heavy-load and the compliant joint torque control using the boost mode. The main obstacles includes: first, pressure difference caused by area differences of the single rod cylinder; second, quick changes of the inertial load due to the manipulator and load dynamics; third, limited response and precision of the low-cost cartridge valves; and last, limited output flow of the small servo-pump. All these factors lead to overpressure. We propose a model-based compensation scheme to mitigate the overpressure. This method comprises: first, nonlinear flow map of the valves, and second, relief control based on the estimated flow and pressure of the servo-pump. The effectiveness is validated through the joint position and torque control experiments on our hydraulic manipulator prototype.