Study on Hybrid Magnetic Bearing

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The dynamic characteristics of hybrid magnetic bearing that is combined by the hydrostatic air bearings and magnetic bearings is investigated. Basic specification of the spindle with the hybrid magnetic bearing proposed in this study is as follows : Diameter of the shaft ; 60mm Maximum speed ; 50000rpm (DN value=3,000,000) Radial load carrying capacity ; 1000n, Radial stiffness ; 100N/mum Axial load carrying capacity ; 5000N,Axial stiffness ; 500N/mumFirst of all, avobe described hybrid magnetic spindle is designed and manufactured and then the dynamic characteristics of the spindle is investigated. The reults obtained are follows. The load carrying capacity and static stiffness of the spindle are almost same values with the expected values and the multiple effect of the hydrostatic and magnetic bearings on the loard carrying capacity and stiffness of the spindle are observed in the experiment. It is declared from the tests of dynmic stiffnes of the system that tuning the PID parameters to obtain the maximum performance is very important. At high speed rotating tests, a significant deflection of the shaft is observed over 45,000rpm. From this result, the strength and manufacturing process of the shaft are rested to be more investigated. With respet to the dynamic stability at high speed rotation, relatively lower performance is obtained by the PID controll and also the spill-over phenomena of the higher bending vibration of the shaft is observed. These results sugest the limitation of the PID control system. Then H * digital control with DSP is applied to the system. The simulation of dynami characteristics with relatively lower order filtering model shows the good charcteristics, therefore, the digital control system is very usefull to obtain the higher dyanamic performance of the hybrid magnetic spindle and it has to be more investigated in future. 10. Key words