Automated centration measurement and quality inspection of aspheric lenses

Thanks to their size and weight reduction and error correction potential, aspheric designs are seeing an industry-wide adoption. This not only increases demand for precise fabrication processes, but also fast and flexible metrology solutions for aspheric lenses. While many systems support measuring the surface topography, the process is limited to a specific design or based on a time-consuming scanning process. Centration measurement with such systems requires additional probes or the inclusion of external reference surfaces in the measurement process. In this paper, we describe how our automated lens testing system AspheroCheck UP is used for centration measurement and quality inspection of aspheres. It is based on the well-established AspheroCheck principle. The paraxial centering errors of both optical surfaces are measured in reflection using a focusing autocollimator. This centration measurement is combined with a fully motorized, non-contact distance sensor that measures the aspheric surface run-out at a single or at multiple locations along the surface. The sensor can also be used to measure various surface shape errors, outer diameter, flange and/or interlock surfaces and even double-aspheric lenses, enabling inspection of both inner and outer centration. A five-axis motorized table enables the automatic alignment of the optical axis of the sample to the rotation axis. This significantly reduces setup time and allows for fully automatic testing without user interaction, ensuring both high measurement accuracy and high repeatability independent of the operator. In addition to supporting standard polynomial surfaces, the system supports most other rotationally symmetric surface types, including Fresnel and diffractive surfaces.