Design and Experimental Evaluation of a Hydraulic Flexible Joint for Legged Robots

In this paper, a hydraulic flexible joint for legged robots is presented to meet the requirements of flexible control and variable stiffness in varies of conditions. A proportional flow valve for closed-loop position control and an inverse proportional pressure valve for output force regulation are combined in series in the hydraulic joint, and force-position hybrid control is adopted for this joint. The detailed design and control method are proposed and analyzed. The experiment results show that the hydraulic flexible joint not only can realize the high accurate position control, but also can proportionally adjust the stiffness in a wide range. When the force and displacement constraints are applied, the performance of hydraulic flexible joint is good under the force-position hybrid control.