Surface self-compensated hydrostatic bearings

Abstract

It has long been known in the machine tool industry that hydrostatic bearing technology has several unique advantages over rolling element bearings. The thin fluid film between the bearing pads and the rail provides virtually infinite motion resolution due to lack of static friction, very low straightness ripple, high squeeze film damping, potentially infinite bearing life, immunity to fretting, tolerance to ceramic swarf, and superior shock load capacity. However, a major impediment to the use of hydrostatic bearings is that there are no standard, pre-engineered designs that are commercially available, and custom designing a bearing is often prohibitively expensive and time consuming. In light of the opportunity just mentioned, the goal of this thesis is to present and demonstrate the feasibility of a family of novel modular hydrostatic bearings which are well suited for mass production and are designed to be bolt-for-bolt compatible with modular rolling element bearings. A size 35 prototype of one of the novel designs is presented along with measured and predicted performance (load verses deflection, flow rate, pumping power). The novel design that is tested uses a set of auxiliary restricting surfaces on a profile rail and form fitting truck that make an acute angle relative to each load bearing pocket they supply, thus allowing the truck to be machined and ground as one piece, and eliminating the need for capillaries, diaphragms, or other unmachinable features. In addition to the first prototype work, a second engineered embodiment of the novel design is presented which, via a sophisticated mathematical model, is designed to have an acceptable stiffness and load capacity variation given realistic production manufacturing tolerances.