3 - Hydrostatic bearings

Abstract

Hydrostatic bearings operate with relatively thick oil films of large area and therefore have the potential for extremely low motion errors coupled with high damping, high stiffness and high load capacity. They are available from specialist bearing companies, generally in the form of sub-assemblies such as spindles, rotary tables and slides, but as dimensional and geometric tolerances are not unusually precise many machine builders also choose to design and manufacture their own bearing systems. The purpose of this chapter is to provide basic calculations that can be used to evaluate bearing performance, define bearing specifications or to aid bearing design. These cover calculations for the load capacity, static stiffness, damping capacity and power consumption of popular hydrostatic bearing geometries and the mechanisms by which hydrostatic bearings generate motion error and estimation of the levels of bearing surface roundness and flatness necessary to achieve low motion errors.