A new calibration method is proposed to separate the profile error caused by the sphericity of the scanning stylus in 3- dimensional contact profilometry. To reduce uncertainty in surface profile measurements, compensation of the stylus sphericity has become a critical issue. In optical flat testing, the three-flat method, which can separate the reference error from the measured deviations, is well known. Although there are also several methods of calibration of the stylus sphericity in contact profilometry, to extract the error precisely remains a challenge. Here we consider a new algorithm for this that uses four measurements including new combinations of the two styluses. The algorism yields four deviation data of the sum of the object profile and the stylus sphericity. With this method, we can extract the surface profile, while keeping the stylus error minimum.
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