Analysis, Modelling and Simulation of the Large-Angle Magnetic Suspension Test Fixture

As part of a NASA program to demonstrate the magnetic suspension of objects over wide ranges of attitudes, a laboratory-scale research project has been undertaken, the Large-Angle Magnetic Suspension Test Fixture (LAMSTF). A cylindrical element containing a permanent magnet core is levitated, above a planar array of electromagnets, permitting demonstration of stability and control in five degrees-offreedom, and of controlled rotation in one degree-of-freedom over a range of 360 degrees. The LAMSTF features a large air-gap (around 0.1 meters), and hence differs fundamentally from typical bearing configurations. Following a brief review of the hardware and the objectives of the research effort, this paper concentrates on analysis, modelling and simulation efforts, considered to be directly relevant to magnetic bearing systems. Prediction of magnetic fields and forces is essential in magnetic suspension system design. This is particularly difficult in the presence of iron cores or yokes, unless the magnetic circuit approximation is used. A sophisticated finite element computer program, VF/GFUN, is being used to calculate magnetic fields for LAMSTF. Selected field calculations are presented with comparison to actual measurements. The design of LAMSTF deliberately includes eddy current paths. The effect of eddy currents on system dynamics is being studied with a view to incorporating modifications into the system dynamic model and digital controller. The latest results are presented. Linearized equations of motion have been developed for this class of configuration, in order to permit system modelling and the design and analysis of controllers. The development of these equations are reviewed briefly. A full, non-linear simulation is also being developed using MATRIXX . The status of this nonlinear model, and difficulties encountered in its development, are discussed.