Asymptotically Stable Disturbance Observer-Based Compliance Control of Electro-Hydrostatic Actuators

Abstract

This paper proposes a disturbance observer (DOB)-based compliance control strategy for electro-hydrostatic actu-ators (EHAs), particularly those with high gear reductions andlong hydraulic pipelines, which could lead to a high performanceinteractive robot system. EHAs suffer significantly from internal leakage and friction, which hampers the application of existing compliance control methods to EHAs. Therefore, a two-degree-of-freedom DOB is introduced to compensate for both undesirable effects separately; one degree of freedom handles friction observations and the other monitors internal leakage. Then, a compliance controller is designed without affecting the closed-loop stability. To this end, the state of the nominal plant, not the real plant, is used in the designs of the internal leakage observer and the compliance controller as it guarantees closed-loop stability. The asymptotic convergence of the closed-loop system is evaluated via simulations and experiments.