Laser doppler vibrometry for vibration measurements on rotating structures.
thesisposted on 09.08.2013, 13:42 by Ben J. Halkon
Laser Doppler Vibrometry is now a well-established and commercially viable technique enabling non-contact vibration measurements in the most challenging of environments. Rotating target vibration measurements are often highlighted as a major application of Laser Vibrometers due to their non-contact operation and illherent immunity to shaft run-out. This thesis describes advances in the application and interpretation of such measurements using Laser Vibrometers. It is readily accepted that a Laser Vibrometer measures target velocity in the direction of the incident laser beam but this measured velocity must be considered in terms of the various components of the target velocity. A previously derived theoretical description of the velocity sensed by an arbitrarily orientated laser beam on a rotating structure undergoing arbitrary six degree-of-freedom vibration provides the mathematical basis for the investigations contained herein. This comprehensive velocity sensitivity model presents the measured velocity as the sum of six terms, each the product of a combination of geometric parameters, relating to the laser beam orientation, and an inseparable combination of motion parameters, referred to as the vibration "sets". Resolution of the individual axial and torsional motion components is possible via particular arrangement of the laser beam(s) and by assuming that the effects of the cross-sensitivity terms within those particular vibration sets are negligible. It is not possible, however, to resolve the radial or pitch/yaw motion components in a similar manner; this can only be achieved by post-processing the outputs from simultaneous orthogonal measurements. In the study described in this thesis, a Lab VIEW software based solution has been developed enabling, for the first time, real-time frequency domain post-processing of the outputs from standard commercially available instrumentation. The resulting measurement system is rigorously examined in terms of performance and error sensitivity and implemented in several example measurement situations thereby demonstrating the potentially powerful vibration information that is available to the vibration engineer...cont'd
- Mechanical, Electrical and Manufacturing Engineering