Radial Measurement On The Axial Displacement Of AMB Rotor

Active Magnetic Bearing (AMB), also being called magnetic suspending bearing, is one kind of non-contact, unlubricated, frictionless bearing, which levitates rotor for high-speed spin with a constant gap between stator and rotor by magnetic force. AMB is suited with high-speed spin environment where lubricant can not be used, and it has a brilliant prospect in many fields such as high-speed machining, turbine, aerospace, vacuum technique, etc.Most magnetic bearings in engineering application are active magnetic bearings. When there is some exterior disturbance, the rotor center will deviate from its equilibrium position. The gap length between the rotor and the magnet that the rotor approaches decreases; and on the other side of the rotor, the gap increases. The magnetic force with negative stiffness leads to further deviation. This is a kind of unstable stress structure similar to inverted pendulum and can not levitate stably with constant exciting current. Thus, in order to work properly, AMB must adjust current on relevant magnet according to the signal of displacement from position sensors, and return the rotor to its geometrical center by the aid of controller. The measuring of both axial displacement and radial displacement of the rotor forms the base of controlling the whole AMB system.Traditionally, people get rotor axial displacement from measuring the distance between the thrust (or the axial rotor end) and the sensor which is put axially. Although this convenient method is of simple principle, not only the output is easily influenced by thermal expansion and radial swing of the rotor, but also it is hard to measuring axial displacement for some rotors with special structure.The main work of present dissertation is to measure the axial displacement of AMB rotor using eddy current sensors. There are some chief conclusions: (1) Firstly eddy current sensors are put radially to measuring the axial displacement of AMB rotor. Linear relationship between rotor axial displacement and sensor output is observed. The result gives a new prospect for measuring axial displacement. (2) Rotor axial displacement is measured radially under different material condition. The composite relationship among sensor output, rotor material, axial displacement and radial displacement is observed and analyzed. The rationality of measuring rotor axial displacement radially is proved and the traditional problems while measuring axial displacement are solved.