Magnetic bearings have existed for many years, at least in theory. Earnshaw's theorem, formulated in 1842, concerns stability of magnetic suspensions, and states that not all axes of a bearing can be stable without some means of active control. In Beam's widely referenced experiments, a tiny (1/64 in diameter) rotor was rotated to the astonishing speed of 800,000 rps while it was suspended in a magnetic field. Despite a long history, magnetic bearings have only begun to see practical application since about 1980. The development that finally made magnetic bearings practical was solid state electronics, enabling power supplies and controls to be reduced in size to where they are now comparable in volume to the bearings themselves. An attempt is made to document the current (1991) state of the art of magnetic bearings. The referenced papers are large drawn from two conferences publications published in 1988 and 1990 respectively.

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Magnetic bearings - State of the art

In this work we will apply a linear quadratic regulator for the controller of the magnetic levitation of a rigid body. A successfull implementation with a diferentiator to estimate the velocity is showed, using a linear and not noisy displacement sensor. Another implementation with a pragmatic control policy that worked well with a noisy and strongly nonlinear sensor is presented.

P S Pierri

Papers

Design of a controller for magnetic levitation