Radial position deviation measurement for inductive micro-motor

An innovative capacitive gap-sensing readout circuit to replace traditional gap sensor is designed and verified by computer simulations and experiments 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 at motion mode. Each capacitor pair is constituted by the cross-sectional facet of iron core at electromagnetic pole and the circular brim of disc made of aluminum. As the radial position deviation of disc occurs, the capacitances of the corresponding capacitor pairs are altered due to air gap changes. The major functions of the proposed capacitive gap-sensing readout circuit are: (i) to amplify a micro-meter-scale signal to be of mini-meter-scale, (ii) to suppress the low-frequency noises caused by exerted 3-phase AC power, (iii) to rectify the induced AC gap-sensing signal into a DC output voltage, and (iv) to eliminate the undesired DC bias caused by parasitic capacitances. By commercial software, Multisim, and a few 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 327mV under the position deviation of the disc being 8μm.