Effect of Coulomb Friction on Stability of Hydraulic Servomechanism

Stability and self-excited vibrations in a hydraulic servo system affected by Coulomb friction have been studied by digital simulation and a piecewise linear method. The neutral operating point of the servo is always stable for any supply pressure. The system has a multiple structure of stability, which consists of unstable and stable limit cycles around the stable operating point. Thus self-excited vibrations can occur only for disturbances beyond a certain critical value. The self-excited vibrations of small amplitude correspond to stick-slip vibrations different from the usual type.