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Measurement of optical free-form surfaces with fringe projection

: Breitbarth, M.; Bräuer-Burchardt, C.; Kühmstedt, P.; Heinze, M.; Notni, G.


Huang, P.S. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Two- and Three-Dimensional Methods for Inspection and Metrology VI : 10-11 August 2008, San Diego, California, USA
Bellingham, WA: SPIE, 2008 (SPIE Proceedings Series 7066)
ISBN: 978-0-8194-7286-1
ISBN: 0-8194-7286-7
ISSN: 0277-786X
Paper 706605
Conference "Two- and Three-Dimensional Methods for Inspection and Metrology" <6, 2008, San Diego/Calif.>
Fraunhofer IOF ()
distortion correction; optical free form surface; fringe projection; 3D measurement; wavelet filter

Complex optical free-form surfaces are very common optical components for the use in modern illumination and lighting systems. In this paper we describe the use of high accurate fringe projection for the measurement of optical free-form surfaces with a resolution in the sub-µm-range. To achieve the required high accuracy the method of uniform measurement scale in fringe projection, proposed by the authors some years ago, is used 1. The basic idea is the exclusive use of phase values for the 3D-data calculation. Because of that, the accuracy of such a measurement set-up is mainly restricted by the lens distortion of the projection system. In order to compensate this we introduce a new method for a 3D-correction of the distortion of the projection lens taking into account spatial dependent distortion parameters. The distortion of the projection lens is determined by a measurement of reference planes which will be used to calculate a 3D-correction matrix. This matrix covers the whole measurement volume (lateral and vertical) and contains the determined distortion of the projection system. As a result the accuracy of the correction improved the absolute accuracy by a factor of four. Furthermore, the data quality is enhanced by a further factor of two using a wavelet filtering for noise reduction. The realized measurement set-up has a measurement field of up to 180 mm in diameter. It will be shown that the measurement of optical free form surfaces with medium range accuracy will be possible where we have reached a limit of 0.5 µm RMS error in a measuring field of 70 mm diameter.