Theoretical Analysis and Numerical Simulation of Dynamic Characteristics of Hydrostatic Guides for Heavy NC Machine Tool

Based on analysis of hydrostatic bearing with circular pocket, equations of static pressure, volvme pressure and squeezing pressure which influence dynamic characteristics of hydrostatic guides with rectangle pocket have been deduced. The function and their influencing factors of the three kinds pressure mentioned above are clarified. The amplitude-phase-frequency characteristics of the hydrostatic guides system have been analyzed qualitatively and quantitatively, it is indicated that the sensitive oil volume has greater effect on the stability of the guide, the volume should be reduced as small as possible while the hydrostatic guides meet the needs of the field working situation. To increasing the oil visosity properly is also helpful to improve the dynamic performance of hydrostatic guides.

I. Introduction

Hydrostatic guide has the advantanges of greater in loadability and dynamic stiffness, higher in accuracy and longer in lifespan, and has became the leading means for modern heavy NC(numerical control) machine tool bearings. Lots of domestic and overseas schoolars and researchers have done great investigation on hydrostatic bearings and guides. Reference [1] applies the finite element method to analyze the static and dynamic performance of hydrostatic bearing with bearing pad having different geometrical structure, the research shows that the combination of the pad with different structure and the parameter of the restrictor is vital important. Refernece [2] introduces the design of the hydrostatic slideway, studies the pressure distribution of the oil film, proposes a technique of computing and analyzing the film stiffness and guide loading capacity with FEM. Reference [3] calculates and analyzes quatitatively and quantatitively the carrying capacity and stiffness of the hydrostatic guide used in machine tool for precision-machining and super precision-machining, puts forward a means of optimazing the guide. References [4], [5], [6] discusse the influence of the oil compressibilty, oil viscosity, oil gap and bearing area on the dynamic characteristics of the guides. Reference [7] investigates experimentally the oil film dynamic stiffness of the hydrostatic bearing with different means of pressure adjusting and flow restricting, theoretical proof has been summarized for the design of the hydrostatic bearing.