Contour mapping of precision ball defects with laser Doppler vibrometry

Laser Doppler vibrometry is presented as an effective inspection technique for contour mapping of defects on precision roller bearing balls. Localized defects are characterized by measuring the Doppler shift of a laser beam incident on a rotating ball. Contour maps are obtained by scanning the ball at equally spaced azimuths with the laser beam as the ball rotates about a vertical axis. A technique for characterizing the repeatable runout of a ferrofluid spindle is discussed. Tests were performed on two different grades of ceramic ball bearings. With the experimental setup, a height resolution of 5.5 nm could be attained. Defects of 22 μm in width could be detected. Use of the contour mapping technique greatly enhances visualization of defects on ball bearing surfaces.