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