High-precision machining for highly accurate micro objectives from Leica Microsystems

Recently Leica Microsystems has been able to increase the precision of its micro objectives again considerably. This is due to the BMBF funded research project, FERMI, which - initiated by Leica - was dealt with in a consortium with LINOS Photonics, the machine manufacturer OptoTech Optikmaschinen, the Fraunhofer IOF Jena and Jenoptik. At the beginning of 2008 the final result, in the form of a combined measuring and processing machine weighing 6 tons, was heaved into the third floor at Leica Microsystems.

The new OptoTech machine, JDM 200 CNC, enables Leica Microsystems to produce mounted  lenses with extremely high diameter and spacing accuracies – reproducible in high order quantities.  "In this way we have been able to realize centering accuracies below 1µm for the first time, and also the diameter and vertex accuracy in the region of 1µm," enthused  Dr. Claus Gunkel, Manager of the Leica Optic Center in Wetzlar.

"FERMI" presents an enormous challenge for all the partners participating; nevertheless, it has also demonstrated the vigorous effect of projects where different competencies are successfully concentrated. The three PhotonicNet partners, Leica Microsystems, LINOS and OptoTech, who cooperated jointly with their Jena colleagues, were successful in an exemplary way. The future of the production site in Germany can profit immensely from cooperative ventures and networking of this kind.

The technology

The machine, which is produced entirely of granite and gray cast iron, with a hydrostatic bearing in all its axes, processes mounted optical subgroups with the utmost precision, corrects itself using the integrated measuring technology and is outstanding due to its process stability and precision, that have been unknown until now.

The lens mounts glued relatively inexactly in metal holders to begin with, are held in a special collet chuck and set in rotation using the high-precision, hydrostatic spindle. Two reflex imaging devices integrated in the machine, an amplifier electronic unit and a complex software algorithm now detect the inclined position of the optical axis in three dimensions. This data is used by the software for adjusting the optical axis completely automatically,

whereby two voice coils, using knocks of differing strength, displace the moveable magnetic chuck during the rotation in such a way, that the optical axis finally agrees with the rotation axis. Finally the metal mount is machined around it, whereby the machine measures the diameter of the housing between the turning processes, in order to compensate the wear of the turning tool.

The distance between the lens vertex and the upper join of the mount is also of particular importance, as this determines the distance apart of the lenses in the finished objective later on. This distance is measured automatically in the machine by a low coherence interferometer. Using this special technology, it is even possible to detect the lower lens vertex through the lens itself. The machine also uses this measurement for correcting the facing tool.

All the lens and mount data can be stored in a file system and called up for each batch. The adjusting process is to be carried out using a specially developed monitoring software and controlled parametrically.

Information about the project and the machine can be obtained from OptoTech Optikmaschinen.

Contact:
OptoTech Optikmaschinen GmbH
Dipl.-Ing. (FH) Matthias Pfaff
Business Unit Director Precision Optics
Sandusweg 2-4
D-35435 Wettenberg / Germany

P: +49 / 641 / 98203-819
F: +49 / 641 / 98203-900
E: m.pfaff@optotech.de
W: http://www.optotech.de

URL: http://www.photonicnet.de

Quelle: Kompetenznetz Optische Technologien