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Proceedings Paper

Laser torquemeter: effects of axial shaft vibration
Author(s): Iain D. C. Tullis; Neil A. Halliwell; Steve J. Rothberg
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Paper Abstract

Laser speckle produced from a diffuse object may be used in determining the angular position of a rotating object. When the object rotates the backscattered speckle patterns are sampled by a suitably positioned photodetector. The photodetector output signal is periodic and one period is stored in memory as a reference. Shaft position is then determined by cross-correlating this stored reference signal with the current photodetector output signal. When the shift is axially displaced the back scattered speckle patterns change and the cross-correlation between the reference signal and the current signal is reduced. The Laser Torquemeter is an instrument designed to measure the time- resolved torque transmitted in a rotating shaft and uses two probe laser beams, axially separated on a shaft of known mechanical properties. In order to design a robust Laser Torquemeter it is necessary to determine the cross- correlation of the current photodetector output signal and the stored reference signal as a function of axial shift position because the reduced cross-correlation due to axial motion results in a loss of tracking which is determined to the performance of the Torquemeter. Experiments conducted to measure the photodetector output cross-correlation show that the ratio of decorrelation displacement to beam diameter can achieve a maximum value of 0.7. For a typical axial shaft vibration of 0.6 mm peak to peak, a minimum beam diameter of 1 mm is recommended and further details of the optical configuration necessary to achieve this optimum resistance to decorrelation are suggested.

Paper Details

Date Published: 23 August 1996
PDF: 9 pages
Proc. SPIE 2868, Second International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (23 August 1996);
Show Author Affiliations
Iain D. C. Tullis, Loughborough Univ. (United Kingdom)
Neil A. Halliwell, Loughborough Univ. (United Kingdom)
Steve J. Rothberg, Loughborough Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 2868:
Second International Conference on Vibration Measurements by Laser Techniques: Advances and Applications
Enrico Primo Tomasini, Editor(s)

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