Dynamics Study Of A Magnetically Levitated Rotor Falling On An Electromagnetically Protected Bearing

As an important part of active magnetic bearing system(AMBs),auxiliary bearing(AB)can be used as a temporary support for the rotor,when AMBs fails or upload,to prevent the rotor from falling on the stator and causing damage.Because the traditional AB cannot eliminate the protective gap,the rotor produces dramatic vibration,and even whirls,resulting in damage to AB.In this paper,an electromagnetic auxiliary bearing(EAB)that can automatically eliminate the protective gap is proposed,and the relevant research is carried out.First of all,based on the equivalent magnetic circuit method,the electromagnetic mechanism of the magnetic circuit model is established to design its structure in parametric.Furthermore,the software of Maxwell is used to simulate and verify the designed structure,and the curve of electromagnetic force changing with the size of the air gap is obtained.Secondly,the rotor dynamic models before and after AMBs fails,collision model between the rotor and inner bushing,the dynamics of the rolling ball bearing and the kinematics models of EAB mechanism are established,respectively.The dynamic responses of the rotor dropping on EAB with different structural parameters are analyzed in detail.The research results show that:(1)The large unbalanced mass of the rotor will cause the collision force of the rolling ball bearing to increase significantly,even beyond its allowable contact stress value,and the performance of AB will reduce or even fail.(2)The increase of the angle of the cone will lead to the increase of the number of collisions between the rotor and inner bushing.When the angle of the cone is large,the high initial dropping speed of the rotor will cause AB fails.In contrast,reducing the cone angle can reduce the axial impact force on the inner ring of AB,also can improve the possibility of AB to eliminate the gap.However,when the radial protective gap is constant,the axial protective gap will increase.(3)The increase of electromagnetic force can improve the rotation accuracy of the rotor after stable support,and reduce the time required to eliminate the gap.However,the friction moment torque of the balls in the rolling ball bearing is significantly increased,resulting in serious heating of the bearing and reducing the service life of AB.(4)With the increase of the rotor's initial drop speed,the increasing trend of the collision force between the rotor and inner bushing increases with the increase of the friction coefficient.When the friction coefficient is small,it is easy to slip between the rotor and inner bushing,which causes serious heating between rotor and inner bushing and reduces the service life of AB.However,when the friction coefficient is large,due to the increase of collision force,AB may fail.(5)When the initial drop speed of the rotor is low,the installation position of the guide column has a great influence on the vibration displacement of the outer ring of AB.The amplitude under the situation of even pressure is obviously less than the under the situation of odd pressure.However,when the rotor initial drop speed is high,the installation position has no effect.EAB device proposed in this paper fundamentally can eliminates the possibility of whirls caused by the dropping of the rotor,significantly improving the working condition of the rolling ball bearing,prolongs its service life and improves the reliability.