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Proceedings Paper

Quantification of displacement and velocity noise in vibrometer measurements on transversely moving or rotating surfaces
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Paper Abstract

The heterodyne interferometer (vibrometer) is a well established technique for measuring all kinds of mechanical vibrations in a broad range of applications. The non-contact measurement principle relies upon the Doppler (or phase-) shift that laser light experiences when it is reflected by the vibrating surface. The speckle nature of the reflected light imposes problems and creates additional measurement noise if the object is moving transversely through the laser spot or is rotating around an axis perpendicular to the laser direction. Another implication that can arise is cross coupling from in-plane vibrations into the out-of-plane measurement direction when small in-plane vibrations are present. A model is presented in this paper that describes the origin of these disturbances. Using this model it is possible to quantify the amplitude spectrum of the noise in displacement and velocity measurements. This enables the user to calculate the limits of resolvable vibration amplitudes when transverse motion is present. The results of the model have been confirmed well by measurements. In addition, the influence of the surface roughness and beam inclination on the out-of-plane vibration measurements at a tilted surface is investigated. The conditions for the measurability of the profile of a transversely moving surface are derived in this work. It is discussed that the Rq-roughness parameter has to be less than &lgr;/4 to obtain the slope information in the speckle-perturbed interferometer signal.

Paper Details

Date Published: 18 June 2007
PDF: 10 pages
Proc. SPIE 6616, Optical Measurement Systems for Industrial Inspection V, 661632 (18 June 2007); doi: 10.1117/12.726115
Show Author Affiliations
Alexander Dräbenstedt, Polytec GmbH (Germany)

Published in SPIE Proceedings Vol. 6616:
Optical Measurement Systems for Industrial Inspection V
Wolfgang Osten; Christophe Gorecki; Erik L. Novak, Editor(s)

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