On stabilizing hydraulic motion experiencing Stribeck friction via PI controller: Circle criterion approach

Abstract

A Friction is inevitable in a hydraulic actuator due to the presence of seal. Unfortunately, the existence of friction makes the system prone to limit cycle oscillation as PI controller is applied. This research investigates the maximum integrator constant of PI controller that can be introduced to the system while maintaining global asymptotic stability in Lyapunov sense. This condition is achieved as the system complies with circle criterion. In this research, a simplified hydraulic system which behaves linearly is adopted. Thus, the only source of nonlinearity is the Stribeck friction. The main contribution of this research is a formulation of stable PI strategy that is free from the effect of inertia. The PI strategy is suitable for a hydraulic testing machine of which the mass of device under the test is varying.