Abstract: In order to weaken or eliminate force coupling and moment coupling existed in a rotor system of active magnetic bearings, taken the relative bias between a rotor and a stator as the variable, the magnetic force distributions are analyzed and calculated for 8-polar magnetic bearings without regard of the factor of time. The force at any point around the circumference of a radial bearing is formulated. Two concepts of force coupling and moment coupling relative to the rotor system of a magnetic bearing are presented. The formulae are derived of the intercross coupling coefficient. The result shows that force coupling and moment coupling always exist, which can not be decreased or eliminated by structural design but by control compensation.

Key words: Active magnetic bearing, Coupling, Rotor