Estimating unbalance and misalignment of a flexible rotating machine from a single run-down

Earlier studies have suggested that the reliable estimation of the state of unbalance (both amplitude and phase) at multiple planes of a flexibly supported rotating machine from measured vibration data is possible using a single machine run-down. This paper proposes a method that can reliably estimate both the rotor unbalance and misalignment from a single machine run-down. This identification assumes that the source of misalignment is at the couplings of the multi-rotor system, and that this will generate constant synchronous forces and moments at the couplings depending upon the extent of the off-set between the two rotors, irrespective of the machine rotating speed. A flexible foundation model is also estimated. The method is demonstrated using experimental data from a machine with two bearings and a flexible coupling to the motor. A sensitivity analysis has also been carried out for the proposed approach with perturbation errors in the rotor and bearing models, to confirm the robustness of the method.