New digital sensor design for rotor displacement measurement based on the coupled oscillators

Measurement of rotor position in bearingless motors is of essence for proper operation. Non accuracy and low sampling rate in measurement process leads to the collision of rotor and stator which could end with motor destruction. This paper presents new concept for rotor position measurement based on Eddy current principle and usage of Time to Digital Converters (TDC) with Digital Signal Processors (DSP) in order to get accurate digital information on rotor position. New concept presented in paper is based on injection locking phenomena between coupled oscillators. Two opposite pair of sensing oscillators is electrically coupled via resistor. In injection locking conditions phase shift between coupled oscillators is proportional to rotor movement. Phase shift is measured with TDC and information is passed to DSP over SPI communication link. DSP calculates the rotor position which is passed to power electronic circuit for rotor position control.