Effects on the Dynamic Behaviour of Rotors on AMB of the Electromechanical Coupling in Induction Motors

The role of the unbalanced magnetic pull exerted by the magnetic field of induction motors on rotors sup- ported by active magnetic bearings is investigated at least in the range of spin speeds corresponding to the rigid body behaviour. Under the assumptions that the forces of the bearings can be linearized and the rotor is axially symmetrical, the equations of mo- tion of the system are written including the negative stiffness of the motor due to non uniform air gap. Some numerical results are then compared to the ex- perimental data performed on a spindle on magnetic suspension, with five active axes. The effects at dif- ferent values of the spin speed and in presence of slip in the induction motor are then analysed with par- ticular care to the vibration condition monitoring of the whole machine.