Restoring high accuracy to laser Doppler vibrometry measurements affected by vibration of beam steering optics

Laser Doppler vibrometers are now well-established as an effective non-contact alternative to traditional contacting transducers. Wide-ranging applications include those where beam steering optics are required to reach locations that are difficult to access but no attention has yet been given to mea...

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Bibliographic Details
Published in:Journal of sound and vibration 2017-09, Vol.405, p.144-157
Main Authors: Halkon, Ben J., Rothberg, Steve J.
Format: Article
Language:English
Subjects:
Accelerometers
Beam steering
Correction
Cylinders
Doppler effect
Error reduction
Laser beams
Laser doppler vibrometers
Laser Doppler vibrometry
Measurement uncertainty
Racing
Sensitivity
Sensitivity analysis
Transducers
Vibration
Vibration measurement
Vibration meters
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Summary:Laser Doppler vibrometers are now well-established as an effective non-contact alternative to traditional contacting transducers. Wide-ranging applications include those where beam steering optics are required to reach locations that are difficult to access but no attention has yet been given to measurement sensitivity to the vibration of those optics. In this paper, a thorough mathematical treatment of this sensitivity to steering optic vibration and its correction is set out. A very practical scheme requiring a single correction measurement, from the back-surface of the mirror at the incidence point and aligned with the mirror normal, delivers an error reduction typically in excess of 30dB. After validation in the laboratory, the scheme is then applied to a genuinely challenging measurement scenario on a single cylinder racing motorcycle. Correction is theoretically perfect for translational mirror vibrations but angular mirror vibrations require an adapted scheme using a triplet of accelerometers arranged around a circular path on the mirror back-surface and this is set out theoretically. •Sensitivity to steering optic vibration in beam direction derived theoretically.•Vector-based approach used to define required measurements for complete correction.•Theory confirmed experimentally with 30 dB magnitude error reduction and phase within 30 mrad RMS.•Single cylinder engine measurement described highlighting high level 1× vibration•Extension to accommodate also for angular vibration of steering optic described.
ISSN:0022-460X
1095-8568
DOI:10.1016/j.jsv.2017.05.014