Contactless sub-millimeter displacement measurements

Guus Sliepen; Aswin P. L. Jägers; Felix C. M. Bettonvil; Robert H. Hammerschlag

doi:10.1117/12.788320

23 July 2008 Contactless sub-millimeter displacement measurements

Guus Sliepen, Aswin P. L. Jägers, Felix C. M. Bettonvil, Robert H. Hammerschlag

Proceedings Volume 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation; 70181C (2008) https://doi.org/10.1117/12.788320
Event: SPIE Astronomical Telescopes + Instrumentation, 2008, Marseille, France

Abstract

Weather effects on foldable domes, as used at the DOT and GREGOR, are investigated, in particular the correlation between the wind field and the stresses caused to both metal framework and tent clothing. Camera systems measure contactless the displacement of several dome points. The stresses follow from the measured deformation pattern. The cameras placed near the dome floor do not disturb telescope operations. In the set-ups of DOT and GREGOR, these cameras are up to 8 meters away from the measured points and must be able to detect displacements of less than 0.1 mm. The cameras have a FireWire (IEEE1394) interface to eliminate the need for frame grabbers. Each camera captures 15 images of 640 × 480 pixels per second. All data is processed on-site in real-time. In order to get the best estimate for the displacement within the constraints of available processing power, all image processing is done in Fourier-space, with all convolution operations being pre-computed once. A sub-pixel estimate of the peak of the correlation function is made. This enables to process the images of four cameras using only one commodity PC with a dual-core processor, and achieve an effective sensitivity of up to 0.01 mm. The deformation measurements are well correlated to the simultaneous wind measurements. The results are of high interest to upscaling the dome design (ELTs and solar telescopes).

Citation Download Citation

Guus Sliepen, Aswin P. L. Jägers, Felix C. M. Bettonvil, and Robert H. Hammerschlag "Contactless sub-millimeter displacement measurements", Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 70181C (23 July 2008); https://doi.org/10.1117/12.788320

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