Miniaturization of a one-axis-controlled magnetic bearing

The design of a novel micro-magnetic bearing (MMB) for a 2-mm-diameter rotor is discussed. The bearing is supported by magnetic couplings generated by permanent magnets and is stabilized by a one-axis controller. The structure of the MMB is greatly simplified, not only in terms of machining and assembly of micro- and precision parts, but the number of mechanical parts is also reduced in comparison with previous designs of MMB. To increase the magnetic stiffness used to support the rotor in the passively controlled directions and to realize stable levitation using one-axis control, the dimensions of the mechanical parts that affect the magnetic stiffness are investigated using a finite element method. An MMB for a 2-mm-diameter rotor was constructed, such that the rotor could be levitated without mechanical contact and which rotated at 39,000 rpm. The static and dynamic characteristics of the MMB are evaluated, including magnetic stiffness, rotational accuracy and power consumption.