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Bearing failures are, according to long-term analyses at ebm-papst St. Georgen GmbH & Co. KG, responsible for 90% of all compact fan breakdowns. The working life of a fan can be increased considerably by using a magnetically levitated fan, where the impeller has no contact with the stator. This paper presents the design of a low-cost magnetically levitated fan with passive magnetic bearings (PMBs) to stabilise radial and tilt deflections of the rotor. The application of an optimised viscoelastic support to the stator introduces sufficient damping to the passively stabilised degrees of freedom. The optimisation of the stiffness and damping and the design of the key components, namely the PMB, the active magnetic bearing and the passive damping device is discussed. Finally, the built prototype is presented and the measurement results are analysed.

When designing passively magnetically stabilized rotor systems, introducing sufficient damping is key. We investigated two different dynamic systems-with one mass and two masses-to determine their theoretical optimal behavior and how they can be realized considering real-world specifications and limitations. Based on dimensionless formulations of reduced dynamic systems, we present fundamental correlations between, and the optimal choice of, physical parameters. Furthermore, we compare the two systems in terms of feasibility and efficiency of different damping methods. Our investigations used an eddy current damper and viscoelastic damping elements as exemplary damping methods for the one-mass and two-mass systems, respectively. Passive stabilization was realized by means of permanent magnetic bearings. We found that the two-mass system is preferable due to the broader range of damping possibilities.

The focus of this paper is on optimizing the stiffness of a permanent magnetic single-ring bearing solely by changing the magnetization pattern. More precisely, using rotating magnetization with two magnetic poles rather than homogeneous magnetization results in a 3.7-fold improvement in stiffness. Usually, rotating magnetization is realized by Halbach stacking, that is, stacking several homogeneously magnetized rings with different directions of magnetization. The approach followed in this work realizes a continuously rotating magnetization pattern using only one ring. Optimization of the magnetization process, as presented in this paper, is crucial to achieving the maximum possible stiffness for the specified bearing dimensions. Furthermore, an analytical stiffness calculation method for bearings with arbitrary magnetization pattern is introduced, and the results are compared with finite-element calculations and measurements.