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Data handling and representation of freeform surfaces

: Steinkopf, R.; Dick, L.; Kopf, T.; Gebhardt, A.; Risse, S.; Eberhardt, R.


Duparre, A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Fabrication, Testing, and Metrology IV : SPIE Optical System Design 2011, 5.-8.9.2011, Marseille, France
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 8169)
ISBN: 978-0-8194-8795-7
Paper 81690X
Conference "Optical Fabrication, Testing, and Metrology" <4, 2011, Marseille>
Fraunhofer IOF ()
freeform surface; diamond machining; classification; process chain

Freeform surfaces enable innovative optics. They are not limited by axis symmetry and hence they are almost free in
design. They are used to reduce the installation space and enhance the performance of optical elements. State of the art optical design tools are computing with powerful algorithms to simulate freeform surfaces. Even new mathematical approaches are under development /1/. In consequence, new optical designs /2/ are pushing the development of manufacturing processes consequently and novel types of datasets have to proceed through the process chain /3/. The complexity of these data is the huge challenge for the data handling. Because of the asymmetrical and 3-dimensional surfaces of freeforms, large data volumes have to be created, trimmed, extended and fitted. All these processes must be performed without losing the accuracy of the original design data. Additionally, manifold types of geometries results in different kinds of mathematical representations of freeform surfaces and furthermore the used CAD/CAM tools are dealing with a set of spatial transport formats. These are all reasons why manufacture-oriented approaches for the freeform data handling are not yet sufficiently developed.
This paper suggests a classification of freeform surfaces based on the manufacturing methods which are offered by
diamond machining. The different manufacturing technologies, ranging from servo-turning to shaping, require a
differentiated approach for the data handling process. The usage of analytical descriptions in form of splines and
polynomials as well as the application of discrete descriptions like point clouds is shown in relation to the previously
made classification. Advantages and disadvantages of freeform representations are discussed. Aspects of the data
handling in between different process steps are pointed out and suitable exchange formats for freeform data are
The described approach offers the possibility for efficient data handling from optical design to systems in novel optics.