Automatic post-processing of laser vibrometry data for rotor vibration measurements

The Laser Vibrometer constitutes a potentially powerful vibration transducer for measurements directly from rotating components. Radial, axial, pitch/yaw and torsional vibrations can all be measured using either single beam or parallel beam Laser Vibrometers. Successful application, however, requires a clear appreciation of the effects of laser speckle and of how radial and pitch/yaw vibration measurements from rotors contain significant cross-sensitivities to motion perpendicular to the intended measurement. Making use of two orthogonal vibration measurements and an independent speed measurement it is possible to eliminate cross-sensitivity from measured data at all non-synchronous frequencies but a convenient, practical means to undertake the necessary data processing has not been available until now. A Lab VIEW based real-time version of this essential resolution technique will be presented for the first time in this paper. This paper describes a number of example measurements. Radial and pitch/yaw vibration measurements will demonstrate the use of the resolution technique to show effects such as the excitation of the first bending mode of the crankshaft. A torsional vibration measurement on a crankshaft pulley will show the influence of speckle noise and alignment issues will be discussed to limit the pitch/yaw vibration sensitivity. Differential torsional measurements on rotating components can be used to examine, for example, the twisting across a flexible coupling and the stretching of a drive belt; speckle effects are again important. © IMechE 2004