Torsional and Bending Vibration Measurement on Rotors Using Laser Technology

Laser Vibrometers and Contacting Transducers, Target Rotation and Six Degree-of-Freedom Vibration: What Do We Really Measure?

“…While it is not possible to measure any of the three rotational vibration sets in equation (5) with a single laser beam, the Laser Torsional Vibrometer, a dual beam instrument, has been used successfully to measure the rotation speed set [13] and two such instruments have been used for initial assessment of pitch and yaw vibration [8]. Using equation (5) as the building block, the velocity measured by a combination of any number of beams can be formulated and this will be the subject of a further publication.…”

“…A feature of much previous work has been prediction of acceptable performance in the presence of a single vibration component, neglecting the effects of other components present in the more complex motions likely to be encountered in practice. When previous studies have acknowledged cross-sensitivities, notably to radial vibration measurements [7] and torsional vibration measurements [8], these have merely been special cases of the totally general theory to be presented in this paper. Interestingly, investigators have already reported designs for a three 21:06 02/04/12 dimensional vibrometer [9] and a six-degree-of-freedom vibrometer [10].…”

On the application of laser vibrometry to translational and rotational vibration measurements on rotating shafts

“…The broad peak around 450Hz is a particularly significant feature in the data. Earlier modal tests on the stationary crankshaft [10] had indicated this to be the frequency of the first bending mode of the crankshaft which occurs in the range 456-475Hz depending on the angular position of the stationary crankshaft. Response around this frequency range can be seen in the pitch data even at the lowest RPM but the response grows considerably as the eighth and tenth engine orders close in on this frequency range at higher engine speeds.…”

“…Parallel beam arrangements have also been developed, first for torsional vibration measurement on rotors [8] and more recently for angular vibration measurement on non-rotating structures [9]. Such devices have also been used recently for assessment of crankshaft bending vibration [10].…”

“…A feature of much previous work has been prediction of acceptable performance but only in the presence of a single vibration component, neglecting the effects of other components present in the more complex motions likely to be encountered in practice. Previous studies have acknowledged cross-sensitivities (10,11) but these have merely been special cases of the totally general case. This paper summarises an analysis of the velocity sensed when laser beams are incident in an arbitrary direction on a target that is of substantial interest in engineering -a rotating shaft requiring three translational and three rotational co-ordinates to describe its vibratory motion fully.…”