Method and Apparatus for Sensing of Levitated Rotor Position

Abstract

A pump with magnetically-levitated rotor includes a position sensor having an eddy-current sensor coil that operates as a resonating element in a low frequency oscillator located within the pump housing. The oscillator is operably interconnected with additional electronics that shift the frequency of the oscillator output signal to a lower frequency. The lower frequency signal is directed to a frequency measurement circuit that provides a value representing a position of the rotor.

What is claimed is: 
     
         1 . A pump system configured to provide fluid flow, comprising:
 a stator housing having an inlet and an outlet and a fluid pathway;   a rotor disposed within the fluid pathway between the inlet and the outlet, the rotor hub comprising a body having a leading portion positioned adjacent the inlet, a trailing portion positioned adjacent the outlet;   an eddy current sensor coil positioned external the fluid pathway and operable to determine a position of the rotor hub relative to the stator housing, the sensor coil operating as a resonating element in a low-frequency oscillator.   
     
     
         2 . The pump system of  claim 1 , further comprising a frequency shifting device that shifts a frequency of an output signal from the oscillator to a lower frequency signal. 
     
     
         3 . The pump system of  claim 2 , further comprising a frequency measurement circuit that measures the frequency of the lower frequency signal and outputs a value representative of a position of the rotor hub relative to the stator housing. 
     
     
         4 . The pump system of  claim 3 , wherein the value output from the frequency measurement circuit is in the form of a binary number, an electrical current, or an electrical voltage. 
     
     
         5 . The pump system of  claim 1 , further comprising a phase-locked loop that locks a phase of an output from the oscillator. 
     
     
         6 . The pump system of  claim 1 , further comprising a frequency-locked loop that locks a frequency of an output from the oscillator. 
     
     
         7 . The pump system of  claim 1 , further comprising a memory element containing at least one of calibration, characterization and correction parameters for the sensor coil. 
     
     
         8 . The pump system of  claim 2 , further comprising a high speed counter configured to measure an interval of time between cycles of the lower frequency signal. 
     
     
         9 . The pump system of  claim 2 , further comprising a high speed counter configured to measure a number of cycles of the lower frequency signal over a specified time interval. 
     
     
         10 . The pump system of  claim 1 , further comprising a pump housing, the stator housing, the rotor hub, and the sensor coil are positioned in the pump housing. 
     
     
         11 . The pump system of  claim 10 , further comprising a microprocessor positioned remote from the pump housing. 
     
     
         12 . The pump system of  claim 1 , further comprising at least one permanent magnet bearing and a magnet motor, the magnet motor comprising a motor magnet carried by the rotor hub and a motor coil carried by the stator housing, the at least one permanent magnet bearing levitating the rotor hub within the stator housing, and the magnet motor operable to rotate the rotor hub within the stator housing. 
     
     
         13 . A sensor assembly for a pump with magnetically-levitating rotor, the sensor assembly comprising:
 a sensor coil positioned on a stator of the pump;   a rotor of the pump arranged within the stator and having a conductive surface;   a low frequency oscillator positioned within a housing of the pump;   wherein the sensor coil operates as a resonating element in the low frequency oscillator in response to a change in relative position between the rotor and sensor coil, and an output signal from the low frequency oscillator is used to adjust a position of the rotor relative to the stator.   
     
     
         14 . The sensor assembly of  claim 13 , wherein an output of the low frequency oscillator is in the range of about 200 kHz to about 350 kHz. 
     
     
         15 . The sensor assembly of  claim 14 , wherein an output of the low frequency oscillator is a sine wave signal. 
     
     
         16 . An active magnetically levitating pump system configured to provide fluid flow, comprising:
 a stator housing having a fluid pathway;   a rotor disposed within the fluid pathway;   an eddy current sensor coil positioned external the fluid pathway and operable to determine a position of the rotor with respect to a defined axis of the stator housing, the sensor coil operating as a resonating element in a low-frequency oscillator.   
     
     
         17 . The active magnetically levitating pump system of  claim 16 , wherein the eddy current sensor coil is operable to determine a position of the rotor with respect to a longitudinal axis of the stator housing. 
     
     
         18 . The active magnetically levitating pump system of  claim 16 , wherein the eddy current sensor coil is operable to determine a position of the rotor with respect to a lateral axis of the stator housing. 
     
     
         19 . The active magnetically levitating pump system of  claim 16 , further comprising a pump housing, the stator housing, rotor and eddy current sensor coil being positioned in the pump housing. 
     
     
         20 . The active magnetically levitating pump system of  claim 16 , wherein the low-frequency oscillator is positioned in the pump housing. 
     
     
         21 . A method of determining a rotor position in a stator housing, the method comprising:
 providing a stator housing having a fluid pathway, a rotor hub positioned in the fluid pathway, a sensor coil positioned external the fluid pathway, and an oscillator;   inducing eddy currents in the rotor hub via the magnetic field of the sensor coil, which eddy currents in turn produce magnetic fields that interact with the magnetic fields of the sensor coil as the rotor hub is moved relative to the stator housing;   determining a position of the rotor hub relative to the stator housing using an output of the oscillator.   
     
     
         22 . The method of  claim 21 , further comprising shifting a frequency of a signal output from the oscillator to create a lower frequency signal, measuring the lower frequency signal, and providing a correction value for the measured lower frequency signal, the correction value representing a position of the rotor hub relative to the stator housing. 
     
     
         23 . The method of  claim 21 , further comprising locking a phase of a signal output from the oscillator to create a phase locked signal, measuring the phase locked signal, and providing a correction value for the measured phase locked signal, the correction value representing a position of the rotor hub relative to the stator housing. 
     
     
         24 . The method of  claim 21 , further comprising locking a frequency of a signal output from the oscillator to create a frequency locked signal, measuring the frequency locked signal, and providing a correction value for the measured frequency locked signal, the correction value representing a position of the rotor hub relative to the stator housing. 
     
     
         25 . The method of  claim 21 , further comprising magnetically-levitating the rotor hub in the fluid pathway, and controlling a longitudinal position of the rotor hub relative to the stator housing in response to the determined position of the rotor hub. 
     
     
         26 . A method of determining a position of a rotor within a housing in a pump with magnetically-levitating rotor system, the method comprising:
 providing a controller and a pump, the pump having a rotor, a stator, a position sensor, and an oscillator, the rotor being positioned inside the stator, the position sensor being positioned on the stator, and the position sensor comprising a coil;   creating a change in frequency in the oscillator with the position sensor in response to a change in position of the rotor relative to the stator;   processing an output signal of the oscillator with the controller to create a correction value representative of the change in relative axial position;   correcting a position of the rotor based on the value.   
     
     
         27 . The method of  claim 26 , further comprising correcting the position of the rotor with a voice coil. 
     
     
         28 . The method of  claim 26 , further comprising providing a controller that is positioned remote from the oscillator, the controller comprising a microprocessor configured to determine the correction value using the output signal of the oscillator.