Measurement method of Wolter-I type mandrel based on a contact-type profilometer

Abstract

Contraposing the surface quality testing of a Wolter-I type mandrel after ultraprecise turning, we propose a measuring method based on a contact-type profilometer and fabricate an adjusting device to assist in measurements. By coordinating probe translational motion in the Z and Y directions, this device provides 6 degrees of freedom. Extracting the feature point on the curve of a meridian section contour, the measurement data of the two aspherical surfaces that constitute a Wolter-I type mandrel can be segregated. This feature point is used as a reference point to make the measurement coordinate and machine coordinate systems coincide with each other in order to calculate the dimensional errors of the mandrel. By choosing samples of different lengths, some property indexes of the mandrel surface, such as roughness, waviness, and form error, can be extracted from the contour error signals via the wavelet transform method. This proposed method can solve the problem that the aspheric surface dimension error and contour form error of the Wolter-I mandrel surface cannot be measured by the profilometer when the aspheric reference vertex cannot be determined. Using this method, only one measuring instrument is required to evaluate the mandrel after diamond turning, which can improve the measurement efficiency, and cover the full spatial wavelength range from the figure error to the surface roughness. In addition, this method has the potential to achieve the in situ measurement of the surface of the Wolter-I type ultra-precision mandrel.