Shear Mode Operated Radial Position Sensor for Bearingless Slice Motor

This paper presents a radial position sensor for the bearingless slice motors with magnet free rotor. The sensor operates on the principle of eddy currents by interacting with a conductive target attached to the rotor. The conductive target varies the flux linkage and hence induced EMF in the sensor coils which is used to obtain the position measurements. The sensor is capable of measuring the radial degrees of freedom by accessing the rotor bottom surface only. The bottom surface has higher sensitivity for axial and tilt measurement and a lower sensitivity for radial measurement. The radial sensitivity depends on the axial gap between the rotor and target. The variation in airgap varies the flux linkages in the measurement coils and couples the tilt and axial motion to the radial measurement. The coupling of radial measurement to the tilt is overcome by sensor and target design [6]. The axial coupling is solved by adding another coil in the sensor to measure axial gap between sensor and target and the axial measurement is used to actively decouple the radial measurement. The construction and operation of the sensor is explained and the axial decoupling is verified using the simulation and experimental results.