An on-line measuring technique for lapping large aspherical mirror

A low-cost on-line measuring technique used in fine grinding phase of large aspherical mirror is proposed. The high-precision length-measuring apparatus is integrated into a common digital- controlled machine tool which forms an on-line measuring system. The on-line measurement is carried out through measuring various spatial point on the profile of a workpiece, and transforming the measured data and error compensation. Compared with Leize three-dimension measuring machine for measuring the same surface shape, the error P-V between two results is 4.0μm and RMS is 0.8μm. The on-line surface shape measurement is carried out on a common digital-controlled lapping machine tool and the measuring accuracy is better than 5μm.