Measurement of complex vibrational modes and surface form-a combined system

Abstract

A combined measurement system is presented that is based on TV holography for vibration or deformation measurement and structured light fringe projection for surface form measurement. A common CCD camera is used for both measurements thereby registrating the two data sets. In both cases novel fibre optic systems are used, incorporating fibre optic phase modulators to allow automation of the fringe analysis. The vibration measurements have been achieved using a novel eight-frame stroboscopic phase-stepping algorithm which can analyze complex vibrational modes for vibration amplitude and phase distributions. Both systems have been developed for operation in an industrial environment. The combined measurement system provides complementary operating ranges and therefore allows a more complete characterisation of components. It is also necessary to measure complex vibration modeshapes and the surface form of a structure to predict noise radiation. Noise radiation predictions are of increasing importance in the design and optimisation of motor vehicle structures. Noise radiation can be measured directly using microphones and analysis equipment but such techniques provide no direct information on the source of the noise, nor provide an insight on how to reduce the noise level.