A design method of a mode control and an unbalance vibration control for five-axes active magnetic bearing systems

Mass unbalance of magnetically levitated rotors causes deteriorations of dynamic and static characteristics. To avoid this problem, it is necessary that mode matrices (i.e., a mode selection/distribution matrices) are adjusted appropriately. This is because these matrices are set based on the rotor's centre of gravity and magnetic force coefficients of electromagnets. It takes long time to adjust the parameters of the mode matrices by trial and error. To design these parameters efficiently, we propose an adjustment method based on experimental analysis. Experimental results of step response show effectiveness of the proposed method. On the other hand, the eccentricity of the rotor causes unbalanced vibration, which is a common problem in rotating machinery. To suppress the vibration, automatic balancing system (ABS) and peak-of-gain control (PGC) are utilised. By using the ABS (the PGC), the bearing stiffness at rotational frequency is decreased (increased). In previous works, implementation methods for these have not been presented fully. Thus, in this paper, we considered the implementation of the ABS and the PGC. Moreover, practical advantages of the PGC/ABS are demonstrated by rotational tests of a turbo molecular pump.