Force versus coil currents and air gap measurements were obtained for an 8-pole planar radial magnetic actuator constructed from laminated silicon iron. Static force measurements were made for journal eccentricities up to 2/3 of the nominal actuator radial clearance and various coil currents spanning the expected operating range. Three theoretical force models of varying degrees of complexity were developed using magnetic circuit theory and constant magnetic material properties. All three models were used to reduce the experimental data and an optimized expression representing the actuator force as a function of journal position and stator coil currents was found. The resulting optimized calibration model produced a proportionality constant and equivalent iron length significantly different from theoretically determined values, 29% and 130% greater respectively.
A detailed error analysis was conducted to quantify the uncertainty in the bearing calibration relationship such that uncertainty bounds can be applied to the in situ actuator force measurements.
Hysteresis testing was conducted for various journal positions. Hysteresis effects were shown to be approximately 2% of the peak force when comparing the differences between the actuator force as the currents were increasing and the forces generated when the currents were decreasing. The actuator frequency response was also examined. An actuator bandwidth of at least 700 Hz was determined. Above 700 Hz the actuator frequency response could not be distinguished from the test fixture frequency response.
