An integrated magnetic actuator and sensor for use in linear or rotary magnetic bearings

An integrated magnetic bearing actuator and sensor was realized using a specially designed ferrite pole piece. Eight of these pole pieces have been used in a magnetic bearing system to suspend a 37 mm diameter shaft in a close tolerance bore (50 μm diametral clearance). The sensors measure radial position with a resolution better than 0.25 μm and negligible temperature drift; while each actuator provides a controllable force in the range of 0 - 10 N. A servo loop accurately controls the radial position of the shaft within the bore to prevent any mechanical contact, virtually eliminating friction and wear. This radial control system exhibits a bandwidth greater than 200 Hz and yields a static stiffness of 24 × 10⁶N/m (140,000 lbs/in).