Prediction of motion accuracy in five degrees of freedom for hydrostatic rotary table with any recess number

Abstract

An approximate accuracy model in five degrees of freedom has been built to predict the motion accuracy of hydrostatic rotary tables with any recess number. It is found that the amplitudes of total averaging coefficients depend on the basic averaging coefficients, while the frequencies of total averaging coefficients depend on the layout averaging coefficients. The motion accuracies of journal bearing and those of the two thrust bearings are independent of each other. For the hydrostatic rotary table with any recess number $n_p$ , the harmonic waves of shaft or thrust plates with wave numbers $n$  =  $n_{p}i+1$ , $n_{p}i+n_p-1$ have a major impact on the radial or tilt motion accuracies, respectively. The harmonic waves of thrust plates with wave number $n$  =  $n_{p}i$ have a major impact on the axial motion accuracy. And $i$ is a non-negative integer. Increasing recess number can improve motion accuracy since the number of harmonic waves of shaft and thrust plates affecting error motions can be reduced. The recommended recess number 6 may be a compromise between structural complexity and motion accuracy. Both the theoretical and experimental studies show that, for the hydrostatic rotary table with recess number 4, the radial run-out is mainly resulted from the third components of shaft roundness errors which is the selective performance of the recess number, while the axial run-out is generally much smaller than the radial run-out. The theory discussed is very important for design of hydrostatic rotary table used widely in precision machine tools.