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This paper deals with experimental investigation and modeling of dynamic friction behaviors in the sliding regime of pneumatic cylinders. Using three pneumatic cylinders, friction characteristics are investigated and modeled under various conditions of velocity variation and pressures. It is shown that a hysteretic behavior can be seen at low velocities in the friction force-velocity relation and the friction force varies nearly linearly with the velocity at high velocities. The hysteretic loop is expanded to higher velocities when the frequency of the velocity variation is increased, and its size is increased with increasing driving pressure and is decreased with increasing resistance pressure. It is shown that such behaviors can be relatively accurately simulated by the new modified LuGre model in which a few static parameters are varied with the frequency of velocity variation.

This article examines the effect of friction model on the simulation accuracy of hydraulic cylinders by using three friction models: a steady-state friction model, the LuGre model, and the new modified LuGre model. Hydraulic cylinder’s behaviors are measured under different sinusoidal inputs to the servo valve. Simulations are conducted under the same conditions as the experiments. The comparisons of simulated results with measured ones show that the new modified LuGre model can predict accurately the hydraulic cylinder’s behaviors while the LuGre model may cause high-frequency oscillations in velocity, friction force, and pressures, which are not observed in experiments.

This paper proposes a new type of electrostatic oil filter and presents results of filtration experiments. Aiming at increasing the amount of electric charges on contaminants in oils and thus increasing the filtration speed of an electrostatic oil filter, electric charges are forcibly injected into oils by applying a high DC voltage to an electrode pair consisting of an electrode with many sharp projections on its both sides, called the emitter electrode, and of two smooth electrodes. Fourteen types of lubricating oils, into which a test powder is mixed at a fixed concentration, are used for filtration experiments. The experiments show that the filtration speed is increased to a great or some degree for most of the oils and that for the majority of the oils, the electrification polarity of a few tens to one hundred percent of powders can be inverted by injecting electric charges with the opposite polarity to the original electrification polarity of the powders. It is also shown that no definite correlation can be seen between the physical properties (conductivity and viscosity) of oils and the degree of the increase in the filtration speed due to charge injection.