Abstract An innovative capacitive gap-sensing readout circuit to replace traditional gap sensor is designed to measure the motion of the levitated micro-disc embedded in an inductive micro-motor. Twelve equivalent capacitor pairs are constructed to detect the position deviation of the disc. As the position deviation of disc occurs, the capacitances of the corresponding capacitor pairs are altered. In addition, by applying the effects of inertial force and centrifugal force, an innovative non-contact measurement method to quantify the unbalance degree of the micro-disc, i.e., eccentricity, is also proposed. By commercial computer simulations and realistic experiments undertaken, the performance of the proposed capacitive gap-sensing readout circuit has been successfully verified. The mean of output voltage of gap-sensing readout circuit is about 327 mV under the position deviation of the disc being 8 μm. Moreover, the unbalance degree of the disc is approximately proportional to the square of the position deviation of the disc.
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