Characterization and Verification of Eddy-Current Position Sensing for Magnetic Levitation

Magnetically levitated drives are compelling in applications, where the long-lifetime operation or process chamber encapsulation is a requirement. To exploit these advantages, contactless position sensors are needed to estimate the position of the rotor. Off-the-market sensor technologies render high-performance magnetic levitation possible, yet their system integration may be challenging if a drive must be designed to fit existing sensor technology or bulky probes. In this work, a position-estimation system based on Eddy-current generation is proposed. Two integrated circuits (or only one for less time-critical applications) excite a two-axis differential array of four miniature coils that can resolve positions in the 100 mu m range. Coupled to a microcontroller, this system can sample the position of an electrically conductive target-in this study, the permanent magnet rotor of a magnetically levitated drive-with frequencies of over 3.5 kHz. This position estimation setup enables the successful levitation of two miniature bearingless disc drives and offers potential toward rotatory speeds in the 20 kr/min range.