R3 measurement by white light interferometry

Radius, roundness and roughness, the three R are the necessary parameters to characterize ball bearings. Roundness is one of the most important geometric forms expected from circular features. Most traditional R3 measuring instruments are stylus type, including the coordinate measuring machines (CMMs). The accuracy requirements for roundness measurements range from a few 0.1 μm for work pieces down to below 10 nm for roundness standards such as precision spheres. White light interferometer is a suitable noncontact method for height profile measurement of objects able to furnish such values. White light interferometer (WLI) produced by Ambios Xi-100 was used to measure radius, roundness and roughness of steel ball bearings. Radius is calculated from the Newton rings easily observed in the interferometer, roundness is observed by limiting the height surface profile between two inner and exterior circles and roughness is RMS value for the best fit line to the ball profile. All the values can be easily obtained from the .txt files produced by the instrument software.