OPTIMISATION AND DYNAMIC ANALYSIS OF THE VARIABLE RESTRIC TOR COMPENSATED HYDROSTATIC BEARING SYSTEM FOR MACHINE TOOLS

Abstract

Hydrostatic bearings have become indispensable in in the modern machine tool practice due to their capability of meting the high stiffness and load capacity requirements of the machine tools. A large variety of machine tools have to inevitably use hydrostatic bearings to meet more exacting machining requirements. This dissertation presents the results of a research on the performance characteristics of variable—restrictor compensated hydrostatic be aring systems from the view—point of the applications to the machine tools. The research was undertaken, and the results are presented, with a view to predict the bearing performance characteristics and to control them by matching the parameters of the bearing and the variable restrictor. Chapter I contains introductory and background material. The role of hydrostatic lubrication in the machine tools is highlighted. Also, the existing gaps in the available information have been identified and the objectives of the thesis are spelled out. Chapter II presents the analysis of the variable restrictor. Equations for the flow through the restrictor and restrictor film thickness have been obtained. The condi-tion ensuring that the lubricant always flows from the restric-tor to the bearing pocket has been established. The role played by tha, restrictor spring has been stressed in the analysis. ( iv) Chapter III is concerned with the analyses of the variable restrictor compensated circular Pad and rectangular Pad thrust bearings. Equations for the bearing film thick-ness, bearing flow, load capacity and the stiffness have been obtained. These equations for the rectangular pad are not exact relations and therefore their validity has been tested by comparing the values of the load capacity and flow calcula-ted from the approximate expressions with those obtained by the finite element method. Mathematical optimisation method has been used to determine the system parameters for the optimum stiffness of the bearing. Chapter IV presents the analysis of the variable restrictor compensated 4-pocket journal bearing for Type A loading with zero speed parameter. The analysis is based on the finite e lement me thod. The performance characteristics have been obtained and the optimisation of the bearing has been done by Parameteric studies. The stability of the bearing system has also been studied.