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Proceedings Paper

Reproducible and deterministic production of aspheres
Author(s): Ernst Michael Leitz; Carsten Stroh; Fabian Schwalb
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Paper Abstract

Aspheric lenses are ground in a single point cutting mode. Subsequently different iterative polishing methods are applied followed by aberration measurements on external metrology instruments. For an economical production, metrology and correction steps need to be reduced. More deterministic grinding and polishing is mandatory.

Single point grinding is a path-controlled process. The quality of a ground asphere is mainly influenced by the accuracy of the machine. Machine improvements must focus on path accuracy and thermal expansion. Optimized design, materials and thermal management reduce thermal expansion. The path accuracy can be improved using ISO 230-2 standardized measurements. Repeated interferometric measurements over the total travel of all CNC axes in both directions are recorded. Position deviations evaluated in correction tables improve the path accuracy and that of the ground surface.

Aspheric polishing using a sub-aperture flexible polishing tool is a dwell time controlled process. For plano and spherical polishing the amount of material removal during polishing is proportional to pressure, relative velocity and time (Preston). For the use of flexible tools on aspheres or freeform surfaces additional non-linear components are necessary. Satisloh ADAPT calculates a predicted removal function from lens geometry, tool geometry and process parameters with FEM. Additionally the tool´s local removal characteristics is determined in a simple test. By oscillating the tool on a plano or spherical sample of the same lens material, a trench is created. Its 3-D profile is measured to calibrate the removal simulation. Remaining aberrations of the desired lens shape can be predicted, reducing iteration and metrology steps.

Paper Details

Date Published: 11 October 2015
PDF: 4 pages
Proc. SPIE 9633, Optifab 2015, 96330I (11 October 2015); doi: 10.1117/12.2193950
Show Author Affiliations
Ernst Michael Leitz, Satisloh GmbH (Germany)
Carsten Stroh, Satisloh GmbH (Germany)
Fabian Schwalb, Satisloh GmbH (Germany)

Published in SPIE Proceedings Vol. 9633:
Optifab 2015
Julie L. Bentley; Sebastian Stoebenau, Editor(s)

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