Position Sensorless AMB in Four Degrees of Freedom

This paper reports on the first ever experiments to suspend a magnetic bearing rotor without position sensors in all four radial degrees of freedom. The rotor is an industrial turbo molecular pump. The position sensorless method used here, sometimes also called «self-sensing» bearings, relies on voltage control and current measurement as the only plant output-variable. The complete system is linear, i. e. there is no implicit position sensing through some HF-modulation or demodulation. The interesting properties of such bearings have been described in several earlier publications [1, 2, 3, 4, 7, 8]. .LU.L The main focus of this paper is a report on the operation in all four radial degrees of freedom. Motions in the x- and yradial bearing stator plane are treated separately. Special emphasis is put on the identification procedures necessary to achieve this goal. The plant structuration is described in detail. A rotational speed of 14400 rpm has been reached.