Applications of a White Light Interferometer for Wear Measurement of Cylinders

The authors have been working on the development of a white light interferometer to measure both inner and external cylindrical surfaces. High precision diamond turned conical mirrors were used to shape the light beam appropriately. Collimated light from a Michelson-like white light interferometer was directed to the conical mirror. The reflected light was radially directed to the cylindrical part to be measured. A telecentric lens system captured the image of the measured cylindrical part reflected on the conical mirror surface. Scanning of the measured volume was performed in cylindrical coordinates by linear displacement of a flat mirror in the reference arm of the interferometer. A cloud of points was directly built in cylindrical coordinates. The present paper focus on two main topics of recent development: wear measurement of cylinders and cylindrical part alignment. An appropriate mathematical model was developed to fit the cylindrical cloud of points to the experimental data. The use of the least absolute method instead of the least squares method for fitting the model is presented and discussed. This model is used to align two measured cloud of points to a same reference coordinate system, one acquired before and the other after a wearing test. Direct comparison between both clouds of points allowed computing the volume of the removed material by wearing. Results are presented and discussed for both cases.