Roundness Measurement with Software Datum Method —Comparison between Mixed Method and 3-point Method by Computer Simulations—

This paper presents a new software datum method for roundness measurement, which is called the mixed method. In this method, 2-point displacement and a tangent angle of either point are simultaneously measured using 2 probes. A differential operation of them cancels the vibrational eccentric motions due to the rotational error and a deconvoluting operation of the differential data gives the correct roundness. In this paper, the mixed method is compared with the 3-point method, the traditional method of roundness measurement, by analyzing their transfer functions, resolutions and sensitivities to some factors of errors, such as the drift, positioning error, etc. Differing from the 3-point method, the mixed method can measure high frequency components regardless of the probe distance. The mixed method can also improve its resolution in the whole frequency domain by widening the probe distance. The effectiveness and limitations of the mixed method for roundness measurement have been verified by simulations and some important information for the sensor-design of roundness measurement have been gotten by theoretical analyses.