A micro-magnetic bearing using capacitive axial displacement sensing

This paper describes a one-axis-controlled micro-magnetic bearing (MMB) system that utilizes capacitive axial displacement sensing (CADS). The axial rotor displacement is measured using the variation in capacitance between the rotor and the electromagnet cores, which take the form of a flange. An MMB structure is proposed and designed to realize the CADS and achieve high magnetic stiffness for supporting the rotor. Experimental results for an MMB with 6-mm-diameter rotor show that the CADS was able to measure the axial rotor displacement with a resolution of about 1 μm in 10 kHz bandwidth and ±20 μm range. By using the CADS output as a feedback signal, the rotor could be levitated stably and rotated at about 10,000 rpm without external displacement sensors.