2010 Volume 3 Issue 2 Pages 16-23
This paper deals with the dynamic behaviors of friction observed in a hydraulic cylinder. Yanada and his coworkers have modified the LuGre model, which is the most widely utilized friction model, by incorporating lubricant film dynamics into the LuGre model and have shown that the dynamic friction behaviors of a hydraulic actuator can be simulated by the modified LuGre model with a relatively good accuracy. In addition, a method to identify the dynamic parameters included in the model has been proposed. However, the experiments were conducted using one type of oil at a fixed temperature. It has not been made clear how the dynamic behaviors of friction are affected by viscosity and type of oil. In this paper, the effects of the viscosity and type of oil on the dynamic behaviors of friction are examined using a hydraulic cylinder. It is shown that the type of oil affects the size of the hysteresis loop of the friction force-velocity curve to some degree and that the viscosity hardly has influence on the dynamic friction behaviors. It is also shown that the time constant of lubricant film dynamics is increased with increasing viscosity but its variation is relatively small and that the bristle stiffness and micro-viscous coefficient are not affected by the viscosity and the type of oil. A simple modification of the modified LuGre model taking the effects of the oil temperature into consideration is made. Comparisons between experimental and simulation results show that the improved model is appropriate.
