Disturbance-Observer-Based PD Control of Electro-Hydrostatically Actuated Flexible Joint Robots

Abstract

A position-based proportional derivative (PD) controller is a well-known controller to be able to render compliant behaviors to a robot and it is usually used with a friction compensator for control performance improvement. Despite the previous methods are effective to the actuation systems with mechanical transmissions, they cannot be applied to the actuation systems that use fluid transmissions owing to their characteristics caused by fluid parameters. To solve this problem, this paper proposes a stability-guaranteed PD control methods incorporating two observers; one is for the observation of friction and the other is for the observation of flexible joint effects caused by fluid compliance and internal leakage. This allows the robots with fluid transmissions to asymptotically converge to the desired position. The proposed approach was verified through simulations and experiments.