Universal accuracy model for three different types of precision bearings with three basic structures under quasi-static conditions

Abstract

A universal accuracy model is established under quasi-static conditions to predict motion accuracies and directly compare error averaging abilities among three different types of precision bearings (including fluid hydrostatic, porous air, and cylindrical roller bearings) with three basic structures (including linear (i.e., guideway), journal, and thrust bearing structures) used widely in precision and ultra-precision machine tools. To introduce the universal accuracy model, three types of precision guideways are taken as examples. Uniform generalized coordinate systems are used to evaluate error motions and uniform averaging coefficients are defined to assess error averaging abilities. It is found that the total error averaging abilities consist of basic and layout error averaging abilities characterized by corresponding averaging coefficients. The total averaging coefficients are the products of basic and layout averaging coefficients which are independent of each other. The porous air bearings have strongest basic error averaging abilities, followed by the fluid hydrostatic bearings, and finally followed by the cylindrical roller bearings. The layout averaging coefficients are related to the number and layout of pads or rollers which are working like some structural filters for a certain kind of error motion. A summary of accuracy experiments based on previous studies provides evidence of the existence of layout error averaging abilities. The content discussed in this paper is of significant importance for the selection and design of precision bearings.