A self-calibration method for rotary tables’ five degrees-of-freedom error motions

Abstract

The paper proposed a novel self-calibration method for five degrees-of-freedom error motions of rotary tables. Two encoders with multiple reading heads were installed on the spindle’s different positions to measure rotation angles. By analyzing indication differences between the reading heads, the two grid discs’ radial motions were obtained. After Fourier analysis, measurement errors caused by the installation errors of the grid discs were eliminated and two different positions’ error motions of the spindle were obtained. Therefore, the rotary table’s 5-DOF error motions, including angular positioning (ECC) error motions, radial (EXC, EYC) and tilt (EAC, EBC) error motions defined in ISO 230-7 and ANSI/AMSEB89.3.4, were self-calibrated. In order to verify the proposed self-calibration method, roundness errors of a cylinder were measured on a rotary table with a self-calibration system. During the measurement of the roundness errors, the error motions of the rotary table were measured simultaneously by the self-calibration system. After error compensations and eliminating influences of error motions of the rotary table, measurement data of the roundness errors were obtained. Compared with the calibration of three-point method for measuring roundness errors, the residual errors were less than ±0.5 μm. In order to verify dynamic measurement, external forces were loaded on the rotary table intentionally during the measurement process. The error motions of the rotary table changed with intermittent external forces, which were also detected accurately by the self-calibration system on line. After error compensations, the calibrations trend and magnitude with three-point method showed that error motions self-calibration of the rotary table are effectiveness and feasibility.