NASA 1996 SBIR Phase I


PROPOSAL NUMBER : 96-1 04.03-1215

PROJECT TITLE : Saturable Self-Sensing Magnetic Bearings

TECHNICAL ABSTRACT (LIMIT 200 WORDS)

The proposed SBIR Phase I project focuses on ferromagnetic saturation effects in "self-sensing" active magnetic bearings (AMBs), which employ collars of electromagnets to levitate rotors. AMBs completely eliminate mechanical contact and the concomitant needs for lubrication systems and continual maintenance. Stable on-line operation requires that controllers be provided the instantaneous values of rotor displacement (in both transverse directions) and coil currents. Self-sensing AMBs exploit the fact the inductive coupling between rotor and stator is displacement-dependent; the driving current signals thus provide sufficient information to infer rotor position.

The demodulation process, however, becomes complicated in the saturation regime because the displacement as a function of coupling inductance is nonlinear and not even single-valued. Other nonlinear effects that may complicate inductance measurements and displacement inference are hysteresis, eddy currents, and flux leakage. In the proposed research, we shall develop a dynamical simulation model that accounts for saturation and interpolar coupling effects, explore a differential sensing scheme for overcoming the indeterminacy of displacement, and develop a closed-loop control methodology to simulate AMB operation under saturation.

POTENTIAL COMMERCIAL APPLICATIONS
Magnetic bearings offer decisive advantages over fluid-film and rolling-element bearings: absence of mechanical contact, elimination of need for lubrication systems, ability to operating in extreme thermal and chemical environments. Magnetic bearings capable of operating under saturation can support maximal load capacities; this will have profound implications in avionic and aerospace engine technology. Elimination of displacement sensors promises to solve major design impediment: high cost of specialized sensors, difficulty of deploying such instrumentation in extreme environments, placement of sensors within the bearing apparatus, wire routing, added parts and material count. Sensor elimination will enjoy the greatest commercial impact in high-volume, low-cost magnetic bearing applications: small pumps, air-conditioning and refrigeration compressors, energy-storing flywheels for automotive applications.
NAME AND ADDRESS OF PRINCIPAL INVESTIGATOR
Edward C. Larson
Barron Associates, Inc.
3046A Berkmar Drive
Charlottesville, VA 22901-1444

NAME AND ADDRESS OF OFFEROR
Barron Associates, Inc.
3046A Berkmar Drive
Charlottesville, VA 22901-1444