Development of On-Machine Measurement Unit for Correction Processing of Aspheric Lens Mold with High Numerical Aperture

Abstract

Most ultra-precision machine tools for fabricating optical lenses and lens molds have on-machine measurement units that can be used for form measurement with the workpiece held on the main spindle. However, for lenses with high numerical apertures, such as pick-up lenses for Blu-ray discs and their molds, the form measurement needs to be made even at a large angle of inclination, which is not feasible with a conventional on-machinemeasurement unit. In this study, an on-machine measurement unit with a measurement angle range±75 degrees is developed. Its performance assessment shows that it has high measurement reproducibility. Ultra-precision cutting are then made to verify the effectiveness of the on-machine measurement unit in the correction processing. It is also reported that, in grinding process, high-form-accuracy workpieces can be made through the correction processing by repeatedly using the on-machine measurement unit to make time-series measurements of the grinding wheel wear and by predicting the wear.