Closed-loop performance of a six degree-of-freedom precision magnetic actuator

The slotless permanent-magnet self-bearing motor (SBM) technology is used to fully provide radial bearing and motoring functionality simultaneously in a six degree-of-freedom magnetic actuator for potential precision pointing and tracking applications in space such as intersatellite laser communications. This novel precision magnetic actuator incorporates two SBMs to produce both radial bearing forces and motoring torque, and one active magnetic bearing to provide axial support, and thus allows for a complete electromagnetic suspension and precision noncontact pointing. An analytical representation of the overall dynamic system is presented for controller design. Six decoupled proportional-integral-derivative controllers are designed, and a feedback control system is implemented. The closed-loop performance confirms experimentally that the precision magnetic actuator is capable of smooth angular slewing while maintaining good stabilization. The most encouraging result is that the actuator achieves a high angular resolution of 754 nrad over a large azimuth range of ±45°.