Active magnetic bearing with auto position-detection

An active magnetic bearing with auto position-detection, comprising:

• first and second electromagnets disposed on opposite sides of a ferromagnetic body suspended without contact between said first and second electromagnets, the first and second electromagnets being oriented along an axis X--X' and each comprising both a respective magnetic circuit defining a respective air gap (e.sub.1, e.sub.2) with said body of mean value equal to a common predetermined value e.sub.0, and a respective excitation winding powered by a power amplifier whose input current is controlled by servo-control circuits as a function of the position of the body relative to the magnetic circuits of the first and second electromagnets, the active magnetic bearing being characterized
• in that the power amplifiers are constituted by chopper amplifiers;
• in that each chopper amplifier delivers unidirectional current independently of the current delivered by the other amplifier;
• in that excitation windings of the first and second electromagnets directly constitute inductive position detectors;
• in that means are provided for injecting a sinusoidal current I.sub.0 sin.omega.t of constant amplitude I.sub.0, of angular frequency .omega., and of identical phase simultaneously to the inputs of the power amplifiers powering the excitation windings of the first and second opposing electromagnets, in superposition with the main currents delivered by the servo-control circuits, a ratio of a detection voltage delivered by one of the amplifiers at the angular frequency .omega. to the voltage for providing the force exerted by the corresponding electromagnet being of the order of 5% to 20%, and preferably being close to 10%;
• and
• in that it includes circuits for extracting the position information determining the magnitude of the main current to be applied by the servo-control circuits to the power amplifiers directly from the voltages u.sub.1, u.sub.2 across the terminals of the excitation windings as measured at the frequency of the sinusoidal current constituting a carrier of angular frequency .omega..