Design of self-compensated, water-hydrostatic bearings

Abstract

A new type of hydrostatic bearing for precision machine linear motion axes has been developed and tested. The bearing has many of the traditional benefits of hydrostatic bearings systems including high stiffness (on the order of 2,000 N/μm at a supply pressure of 13.5 atm), excellent straightness characteristics (less than 0.5 μm vertical motion over 100 mm), which can exceed the straightness characteristics of the rails by using the averaging effect of the fluid, high damping, and low noise levels. Additionally, the bearings are modular in design, and use water-based cutting fluids (or pure water) as the hydrostatic fluid so it does not have the environmental problems associated with oil-based hydrostatic systems. The smallest passage is typically 3–5 mm in diameter, which virtually eliminates clogging of the hydrostatic passages. The design of the bearing system is simplified primarily by the deterministic design of the restrictor passages. The restrictors have a linear sensitivity with respect to stiffness. Fixed-compensation restrictors have a gap cubed sensitivity. This also helps manufacturing significantly because hand-tuning of restrictors is eliminated, and the restrictors are less sensitive to manufacturing errors than are traditional hydrostatic bearing systems.