System identification using vibration monitoring for fault diagnostics in manufacturing machinery

This paper outlines a different technique in vibration analysis, namely modal testing/analysis for preventive/predictive maintenance in productive machinery. Instead of just using a signal analysis approach as has been used widely, a system analysis approach is proposed in this paper. The system analysis has been widely used for passive structures (structures with no moving parts), however its application for machines with high speed rotating components has yet to be explored. An experimental set-up is used to demonstrate the feasibility and practicality of this technique with all the problems associated with this type of structure. Several excitation techniques are used, such as transient, random, sinusoidal, pseudo-random, to perturb the system. Several experiments are carried out with different combinations of excitation and response measurement locations (rotating and nonrotating) and the nature of the forcing function on the system. It is shown that the predicted gyroscopic effect may be detected by exciting the foundation and carrying out measurement on the rotor and vice-versa. The gyroscopic effect results in bifurcation of the critical speed of the rotor and this is reflected in the frequency response function measured on the system. The various results are compared and the damping effect is also measured.