Control-oriented friction modeling of hydraulic actuators based on hysteretic nonlinearity of lubricant film

Friction modeling of hydraulic actuators is essential to system control and the prediction accuracies of friction models (e.g., Stribeck, LuGre) need to be improved when they were applied to hydraulically actuated systems. The test platform for hydraulic cylinders was constructed and the friction forces of plunger type hydraulic actuators were measured under different operating conditions. The dynamic behaviors of film thickness of seal/ rod interface were investigated based on elastic hydrodynamic lubrication (EHL) method. The effects of acceleration of rod on friction force were examined using coherence function estimation technique. The Stribeck and LuGre model were modified by incorporating physically based hysteretic film dynamics and Bouc-Wen model into Stribeck function, respectively. It is shown that the Stribeck and LuGre model cannot preferably describe the friction force-velocity behavior, especially for the fluid lubrication regime. The modified Stribeck and LuGre model can simulate the hysteretic behavior of friction force-velocity loop more effectively than unmodified ones and the friction estimation accuracies of Stribeck and LuGre model were improved remarkably.