Dynamic Characteristics Of Low Loss Motorized Spindle Suspended By Magnetic Bearings

Owing to the advantages such as high rotational speed, no contact wear and no lubrication,the motorized spindle with magnetic bearings is suitable for ultra-high-speed machining. However,the copper loss and the iron loss will cause lots of heat. In order to simplify the cooling parts andreduce the heat of the system, two homopolar radial magnetic bearings and one axial permanentmagnetic bearing were introduced into the motorized spindle.The experimental setup of the motorized spindle with magnetic bearings, including theelectrical and mechanical parts were designed and manufactured in this paper. The main structuralparameters of the system were presented. The calculation model of the force of the permanentmagnetic bearing was established using the equivalent magnetic charge method and the force withthe change of the clearance was calculated. The magnetic field distribution and the power loss ofthe homopolar active magnetic bearings were analyzed by the software ANSYS10.0. The dynamiccharacteristics of the low loss magnetic motorized spindle were investigated by the co-simulationof the softwares ADAMS and MATLAB, hammer exciting test and high-speed rotation test.The results show that the motorized spindle can get across the first two critical speeds andoperate at40,000rotations per minute safely, and the maximum amplitude of the rotor is7μm.This demonstrates that the motorized spindle with two homopolar radial magnetic bearings andone axial permanent magnetic bearing has higher performance, simpler structure and less powerconsumption.