Active Magnetic Bearings as Actuators and Sensor in Journal Bearing Measurements

The present paper shows the successful usage of active magnetic bearings (AMBs) to identify the dynamic characteristics of journal bearings in the frequency domain. A test rig is operated using two AMBs supporting a rigid rotor with a centric journal bearing. An identification procedure for the stiffness and damping coefficients of journal bearings is presented. This procedure incorporates the successful application of AMBs for positioning, supporting, sensing and actuating the rotor simultaneously. For identification the real excitation force is needed. Two methods to derive a force-current-position relationship are outlined and compared: an idealized mathematical relation and a measured force-current-position map. Finally, results for applying the pre-measured map and an example of the identified stiffness and damping coefficients are given.