Examination of Magnet-Less 3-Axis Magnetic Bearing with Cylindrical Rotor

Abstract

　Conventional 5-axis active control system usually has a thrust magnetic bearing (TMB) with a disk rotor and two radial magnetic bearings (RMBs) as the rotor's suspension part. However, considering for the motor part, the number of the units in the 5-axis active control system increases, which resulting in not only the cost increases, but also length of the rotor increases and makes rotor's resonance frequency lower. In order to decrease the units of the entire system, one 3-axis active control T+RMB type magnetic bearing whose suspension force can active control thrust-axis and radial-axis as the suspension part is widely used. However, as a real problem, in applications such as turbo molecular pumps, even though T+RMB is applied as the suspension part of the system, the permanent magnets to generate a bias magnetic flux, leads to the deterioration of assembly during the insertion and removal of the rotor. In order to solve this real problem, a research of magnet-less 3-axis magnetic bearing with cylindrical rotor will be investigated in this paper. What is more, two types of magnet-less structure will be proposed and examined by suspension force and system loss. Finally, the structure with the better performance will be introduced, and the excellent characters of the magnet-less 3-axis magnetic bearing with cylindrical rotor will be shown in 3D-FEM.