Measuring the Rail Profiles of a Long Hydrostatic Guideway in a Precision Roll Lathe

Abstract

A system for measuring the rail profiles of a long hydrostatic guideway is proposed and applied to a precision roll lathe. The rail profiles, consisting of rail form errors and a parallelism error, are measured with four capacitive probes placed on the two rail surfaces, and a laser interferometer with angular optics. The form error of each rail is measured using a mixed sequential two-probe method, while the parallelism error between the rails is measured with two opposing capacitive probes. To eliminate the necessity for additional guidance mechanisms, theprobe table is guided by air bearings and the rails being measured. To verify the measurement results, two self-verification techniques are suggested and tested. Firstly, the linear motion errors of the probe table on the two rails are compared, yielding a difference of 0.79 μm in 2σ. Secondly, the sum of the rail form errors is compared with the slope-removed sum of the two capacitive probes used for the parallelism measurement, yielding a difference of 0.81 μm in 2σ. According to the self-verification results, the accuracy of the proposed measurement method is about 1 μm for a rail length of 2,825 mm.