Estimation of Inertial Parameters of a Rigid Rotor Having Dynamic Unbalance on Active Magnetic Bearing

Abstract

Non-uniform distribution of mass in a rigid rotor causes dynamic unbalance, as none of its principal axes of inertia is oriented along or parallel to the axis of rotation and the centre of mass is offset from the spin axis. A set of linear differential equations having time-varying coefficients express the dynamic behaviour. This paper assumes the rotor suspended on at least two Active Magnetic Bearings (AMBs) with known properties. Offset of centre-of-mass from the bearing centreline and skewness of inertial principal axes with respect to it, are estimated by minimizing the least square value of difference in response (at two planes close to the AMBs), predicted by the model with dynamic unbalance and the one with no unbalance at each time step. The estimated inertial parameters are found to be very close to the values used to simulate the actual model. Since the rigid rotor model is generic in nature, the procedure may be used to identify the inertial properties in actual situation without stopping the rotor. Thus, AMBs may be utilized to identify inertial properties and for smart balancing.