A Study on Active Closed-Loop Gap Control for Hydrostatic Bearing

Abstract

In this paper, a hydrostatic bearing controlled by servo-valve for precise closed-loop oil-film gap control is developed. Due to the increasing demands of larger dimension, heavier load and higher precision for current and future machine tools, the development of hydrostatic bearing has become a more and more important issue over the past decades. Nowadays, the most commonly used active pressure feedback restrictor for hydrostatic bearing is membrane type, in which a thin and flexible metal sheet serves as the key component to meter the hydraulic oil flow precisely. However, the membrane type pressure feedback restrictor is not quite suitable for extremely heavy load. Therefore, an alternative to design the active restrictor for hydrostatic bearing using servo-valve is presented in this paper. Different controllers are also designed and compared in this paper. There are two significant features regarding the proposed design. The first one is the introduced orifice restrictor inside the servo-valve which avoids the influence of possible oil temperature variation. The second feature is the introduced closed-loop oil-film gap control scheme that widens the application range effectively. Finally, a test rig of servo-valve controlled hydrostatic bearing is implemented and the experimental results prove the validity of the hydrostatic bearing with the proposed servo-valve and the closed-loop gap control scheme.