Prototype Fabrication of Reluctance-Type Combined Radial-Axial Magnetic Bearing with Multi-Disk

Magnetic bearings (MBs) can support a rotating shaft without any contacts using electromagnetic force. A typical five-degree-of-freedom magnetic levitation system uses two radial MBs and one axial MB. However, such a configuration tends to become large due to the combination of three MBs, and it poses an issue of reduced critical speed as the shaft length increases. Therefore, combined radial-axial MBs (CRAMBs) have been proposed to address these challenges. CRAMB can generate support forces in three degrees of freedom using a single unit. In our study, we have proposed an innovative reluctance-type CRAMB with multi-disk (CRAMB-MD) to enlarge the opposing surface area where magnetic attractive force acts, enabling three-degree-of-freedom support with a high support force density. Since the proposed CRAMB-MD does not require permanent magnets, it offers advantages such as ease of assembly and suitability for cryogenic or high-temperature environments. This paper presents the design and fabrication of a prototype. The axial and radial support force characteristics are calculated using three-dimensional finite element method, and experimental measurements are conducted using a load cell. A qualitative agreement was observed between the analytical and experimental results. The findings demonstrate the validity and effectiveness of the proposed structure, offering a promising approach for compact and high-performance magnetic levitation systems.