Super-smooth polishing on aspherical surfaces (I): high-precision coordinate measuring and polishing systems

For the purpose of fabricating free-form optical elements with the accuracy of 80 nm PV, the Canon Super-Smooth Polisher has been developed. It has a high resolution on-machine coordinate measuring system that utilizes a contact probe. A unique probe structure is proposed, by which both inclination and motion errors of the probe are simultaneously compensated. The flaw problem is discussed from an experimental point of view, and it is found that the major cause of flaws is dirt on the probe or the workpiece. Fourteen axes interferometers are used to compensate for mechanical motion errors. The scanning speed of 4 mm/s is achieved by speeding up the force controller. The measurement results show good repeatabilities of 3 nm RMS for a 540 mm line measurement, and 9 nm RMS for a (phi) 500 mm aspherical surface measurement.