Compensation of rotor imbalance for precision rotation of a planar magnetic bearing rotor

Magnetic bearings provide an alternative for achieving precision rotation. But the rotational accuracy is sensitive to rotor imbalance. The system we study is a planar rotor supported by aerostatic suspension and positioned by a radial magnetic bearing of nanometer precision. We present compensation designs and experiment results for precision rotation about the geometric center and the mass center, respectively. In the former case, the base harmonic component at each sensor output is removed by explicit trigonometric compensation signals that are constructed in real time. In the latter case, a new double-loop compensation design is given. Each compensation loop is similar to that in the former case. The compensation, aided by a variable rotational speed that is changed up and down repeatedly, is shown to push the rotational center to approach the mass center. Once the mass center is reached, the rotor remains to rotate about the mass center at variable rotational speed without transient. Compared with the existing methods, which find the mass center or inertial axis at a fixed rotational speed and rely on exact values of plant parameters, our method may locate the mass center more accurately. Experiment data indicate that the mass center is located with an error of tens of nanometers.