Oscillations caused by solid friction in a hydraulic driving system. (In consideration of transitional friction characteristic curves for increasing and decreasing velocity motions)

The phenomena of 'stick-slip' oscillations in the hydraulic driving system are studied experimentally and analytically. The system consists of a table lying on a rectilinear sliding surface, an actuater cylinder, a 4-way servo valve, a relief valve and an oil pump. The transitional friction characteristics curves are considered for increasing and decreasing velocity motions of the table. The variations of friction are modelled as follows. (1) Kinetic friction varies with the impessed electric current passing through the servo valve and the sliding velocity. (2) Static friction changes with the electric current. The principal experimental variables considered are lubricant viscosity and the mass of the table. Their influences on the properties of 'stick-slip' oscillations are studied.