ESPI for contouring of surfaces with discontinuities

A. Purde; N. Werth; A. Meixner; A. W. Koch

doi:10.1117/12.612589

13 June 2005 ESPI for contouring of surfaces with discontinuities

A. Purde, N. Werth, A. Meixner, A. W. Koch

Proceedings Volume 5856, Optical Measurement Systems for Industrial Inspection IV; (2005) https://doi.org/10.1117/12.612589
Event: Optical Metrology, 2005, Munich, Germany

Abstract

Electronic speckle pattern interferometry (ESPI) can provide accurate contour measurement in the micron range and short measurement times far below one second. An advantage of this method is that illumination axis and observation axis can be identical in contrast to e.g. triangulation. Therefore ESPI represents an interesting alternative to other optical measurement principles used for surface profiling. Typical surfaces in industrial applications often show discontinuities, like steps or holes. An unambiguous measurement of such surfaces is only possible if the synthetic wavelength is chosen larger than the largest surface step. Since the noise level introduced to the measurement increases proportional to the synthetic wavelength, unambiguous measurements suffer from a loss of accuracy. The solution for this problem is the combination of two or more synthetic wavelengths. In contrast to other publications (hierarchical, pixel-wise approach or temporal phase unwrapping) our novel area-based approach uses only two synthetic wavelengths minimizing measurement time and device complexity. The use of areas instead of pixels allows a lower signal to noise ratio and a smaller number of synthetic wavelengths (in our case only two) respectively, compared to the hierarchical pixel based approach. In this paper we present the steps required during pre-processing (laser tilt and wave front compensation) and the opportunities and drawbacks of different algorithms used for the fusion of the two images gained from different synthetic wavelengths.

Citation Download Citation

A. Purde, N. Werth, A. Meixner, and A. W. Koch "ESPI for contouring of surfaces with discontinuities", Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005); https://doi.org/10.1117/12.612589

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