INTERNATIONAL COMPARISON OF ROUNDNESS PROFILES WITH NANOMETRIC ACCURACY

Roundness profiles are compared which were obtained from measurements carried out at five national metrology laboratories. The object used f or this comparison was a zirconium-oxide sphere with a profile contain ing higher harmonics and a total roundness deviation of about 42 nm. T he measurement results were obtained using different and independent m easuring instruments and different evaluation methods for spindle erro r separation. The number of data points used ranged from 50 to 4096. B efore the analysis, the profiles were transformed to a common digital data format containing 1024 points and a correlation analysis was carr ied out to determine a common zero position for the profiles. In the a nalysis, standard deviations and maximum deviations were calculated fr om point-by-point differences of the profiles with reference to one an other or to the average profile. Fourier analysis was used to select a spectral area for an analysis at the edge of the significance limit. The comparison shows that each participating laboratory is able to mea sure a roundness profile with a standard deviation in each data point of less than 2 nm.