A Multi-Point Measurement Technique for the Enhancement of Force Measurement with Active Magnetic Bearings (AMB)

Active magnetic bearings (AMBs) have the ability to act concurrently as support bearings and as load sensing measurement tools. Previous work in the area of AMB force measurement has relied upon basic magnetic equations requiring knowledge of coil currents and air gap lengths. Some researchers have utilized magnetic flux probes to eliminate the need for air gap measurements, but these are limited by physical size constraints and require complex hardware. This thesis presents a new method for measuring forces with AMBs that utilizes multiple current pairs with no gap measurement to provide accurate and precise force predictions.

Previous methods for force measurement with AMBs rely on the controlled environment of a laboratory setting for accurate measurements. The goal of this work is to develop a robust force measurement procedure for use in industrial and field applications, as well as the laboratory. The harsh environment of a factory floor makes air gap measurements difficult, which limits the use of current-based force equations. Additionally, the flexibility of AMB-equipped thrust measurement systems (TMSs) to measure many types of forces with little to no reconfiguration or calibration makes them appealing.

The multi-point method provides predictions of both shaft force and rotor position using only current pairs without air gap measurements. Static and dynamic load scenarios were investigated to determine the feasibility of this new approach to force measurement. For both, the effects of bearing load and rotor position within the bearing were analyzed. Under dynamic loading, different amounts of unbalance as well as various rotor speeds were used to provide multiple test cases. The multi-point predictions of rotor position were analyzed and compared with the measured rotor positions. It was shown that this new multiple-point method for measuring bearing loads with AMBs provides equivalent or better force predictions to analogous single-point methods for static loads while eliminating the need for measuring rotor position.