FORCE VERSUS CURRENT AND AIR-GAP CALIBRATION OF A DOUBLE ACTING MAGNETIC THRUST BEARING

Force versus current and air gap measurements were obtained for the ac tuator component of a double acting magnetic thrust bearing constructe d from a powdered metal. Static force measurements were made for vario us air gap settings and bearing current combinations. The resulting da ta were reduced and an optimized expression representing the force ver sus current and air gap relationship of die actuator was found. In add ition, a theoretical force model was developed using simple magnetic c ircuit theory and constant material magnetic properties. The theoretic al model predicted force magnitudes approximately 20 percent greater t han the experimentally measured values. Hysteresis tests were conducte d with the thrust disk in the centered position for various current pe rturbation amplitudes about the design bias current. Hysteresis effect s were shown to cause a difference between the measured force as the c urrent was increasing as compared to when the current was decreasing. This difference varied from 10 to 7 percent of the peak force from eac h respective hysteresis loop. A second-order polynomial expression was developed to express the coercive force as a function of the perturba tion current amplitude. The bearing frequency response was examined by injecting sinusoidal currents of varying frequencies into the bearing . An actuator bandwidth of at least 700 Hz was determined. Above 700 H z the bearing frequency response could not be distinguished from the t est fixture frequency response.