A dual probe non-contact ball roundness measurement method is presented in this paper. With two probes aligned in opposite directions, the direct measurement of diameter variation can be obtained. The relationships between diameter variation and out of roundness of a precision ball are discussed. Attempts of error separation using multiple measurements are carried out and the eccentricity of ball and spindle axis is measured. Measurement results indicated that other than the spindle radial run out, which is synchronous in nature, there also exists high frequency non-synchronous variations. Such non-synchronous errors can be effectively eliminated with the dual probe arrangement for diameter variation measurement. The measurement results showed that such set up is capable of measuring high precision balls for diameter variation and out of roundness with uncertainty of less than 10nm. Single measurement can be completed in 10 seconds with over 10,000 data points. Faster measurement is possible with improved air bearing spindle. The method is suitable for online application of precision ball diameter variation and out of roundness measurement.

While measurement accuracy can be increased through continuously improving instrument precision, certain measurement errors can be eliminated via data processing using properly devised processing algorithms. Multi-point roundness error separation methods that are the subjects of study in this paper are reviewed, in particularly, three-point method and other multi-point methods that are based on three-point roundness error separation method, such as two-point method, mixed method and four-point method are summarized. Finally a comparison between each separation methods mentioned in this paper is made. Our views of future development trend in multi-point roundness error separation methods are presented.