MEASURING THE POSITION OF AN OBJECT

• US 20100301840A1
• Filed: 05/29/2009
• Published: 12/02/2010
• Est. Priority Date: 05/29/2009
• Status: Active Grant

• Current Assignee: Calnetix Technologies, LLC (General Electric Company)
• Original Assignee: Calnetix Incorporated (General Electric Company)
• Inventors: Filatov, Alexei V.
• Granted Patent: US 8,564,281 B2
• Time in Patent Office: Days
• US Class Current: 324/207.11
• CPC Class Codes: F16C 2360/44 Centrifugal pumps in general F04D
• CPC Class Codes: F16C 2380/26 Dynamo-electric machines or combinations therewith, e.g. electro-motors and generators in general H02K
• CPC Class Codes: F16C 32/0446 Determination of the actual position of the moving member, e.g. details of sensors
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004

Abstract

Noncontact measuring of positions of objects is achieved through measurements of parameters characterized by the distribution of an AC magnetic flux in the air gap between stationary and moveable portions defining a sensor magnetic circuit.

Claims

1. An apparatus for determining the position of a movable element relative to a stationary element along a measurement axis, the apparatus comprising:

a sensor head fixed in relation to the stationary element, the sensor head comprising a soft-magnetic core;

a sensor target fixed in relation to the movable element, the soft-magnetic core and the sensor target separated by an air gap and defining a magnetic circuit;

a conductive excitation coil coiled around the soft-magnetic core and adapted to produce an AC magnetic flux in the magnetic circuit, the AC magnetic flux corresponding with a total magnetic flux in the air gap, the sensor target comprising different electromagnetic properties at different locations along the measurement axis that causes a distribution of the total magnetic flux in the air gap to change when the sensor target is displaced along the measurement axis;

a magnetic flux density sensor fixed in relation to the sensor head and residing in the air gap between the soft-magnetic core and the sensor target, the magnetic flux density sensor configured to detect magnetic flux density in a portion of the air gap; and

a controller in communication with the magnetic flux density sensor, configured to receive an output signal of the magnetic flux density sensor and determine the position of the sensor target along the measurement axis based on the total magnetic flux in the air gap and magnetic flux density detected by the magnetic flux density sensor.

2. The apparatus of claim 1 further comprising a total magnetic flux sensor fixed in relation to the sensor head and configured to sense the total magnetic flux in the air gap between the soft-magnetic core and the sensor target.

3. The apparatus of claim 2, wherein the controller is configured to determine the position of the sensor target along the measurement axis based on a ratio determined from the total magnetic flux in the air gap sensed by the total magnetic flux sensor and the magnetic flux density detected by the magnetic flux density sensor.

4. The apparatus of claim 2, wherein the total magnetic flux sensor is a conductive coil.

5. The apparatus of claim 1, wherein the AC magnetic flux is produced by an AC voltage of constant amplitude applied to the conductive excitation coil, the AC voltage of constant amplitude resulting in the total flux in the air gap being controlled to a known value.

6. The apparatus of claim 5, wherein the controller is configured to determine the position of the sensor target along the measurement axis based on a ratio determined from the total magnetic flux in the air gap of known value and the magnetic flux density detected by the magnetic flux density sensor.

7. The apparatus of claim 1, wherein the magnetic flux density sensor is a conductive coil.

8. The apparatus of claim 1, wherein the magnetic flux density sensor is a Hall Effect sensor.

9. The apparatus of claim 1, wherein the sensor target is divided along the measurement axis into a first portion and a second portion, the first portion and the second portion having different electromagnetic properties.

10. The apparatus of claim 9, wherein the first portion of the sensor target comprises a soft-magnetic, non-conductive material, and the second portion comprises a conductive, non-magnetic material.

11. The apparatus of claim 10, wherein the first portion of the sensor target comprises electrically isolated electrical steel laminations stacked in the measurement direction.

12. The apparatus of claim 1, wherein the soft-magnetic core comprises a nonmagnetic, conductive coating, the nonmagnetic, conductive coating comprising a non-conductive interrupt preventing formation of a closed conductive loop within the coating around the magnetic circuit.

13. The apparatus of claim 1, wherein the sensor target is configured to rotate about the measurement axis.

14. A method for sensing a position of a movable element relative to a stationary element along a measurement axis, the method comprising:

communicating a total magnetic flux in an air gap separating the stationary element from the movable element, the movable element comprising different electromagnetic properties along the measurement axis;

measuring a magnetic flux density in a portion of the air gap; and

determining the position of the movable element based on a ratio of the total magnetic flux in the air gap and the measured magnetic flux density.

15. The method of claim 14 further comprising measuring the total magnetic flux in the air gap, and wherein the ratio is determined from the total magnetic flux measured in the air gap and the measured magnetic flux density.

16. The method of claim 14, wherein communicating the total magnetic flux in the air gap comprises energizing an excitation coil with an AC current.

17. The method of claim 16, wherein communicating the total magnetic flux in the air gap comprises applying an AC voltage of constant amplitude to the excitation coil, the AC voltage of constant amplitude resulting in the total flux in the air gap to be controlled to a known value.

18. The method of claim 17, wherein determining the position of the movable element based on the ratio comprises:

determining a baseline ratio determined from the measured magnetic flux density and the total magnetic flux for a known position of the movable object; and

comparing the ratio to the baseline ratio.

19. An electric machine system, the system comprising:

a first element;

a second element configured to translate in a direction parallel to a measurement axis relative to the first element;

a third element fixed in relation to the first element, the third element comprising a soft-magnetic pole;

a fourth element fixed in relation to the second element, the third element and the fourth element separated by an air gap, the third element and the fourth element defining a magnetic circuit;

a source element fixed in relation to the third element, the source element configured to produce an AC magnetic flux in the magnetic circuit, the AC magnetic flux corresponding with a total magnetic flux in the air gap;

a sensor fixed in relation to the third element, adjacent the soft-magnetic pole, and residing between the third element and the fourth element, the sensor configured to measure magnetic flux density in a portion of the air gap; and

an electronics module in communication with the sensor, configured to measure an output of the sensor and determine a position of the fourth element along the axis based on the output of the sensor and the total magnetic flux in the air gap.

20. The electric machine system of claim 19 further comprising a total magnetic flux sensor fixed in relation to the third element and configured to sense a total magnetic flux confined between the third element and the fourth element.

21. The electric machine system of claim 20, wherein the sensor comprises a magnetic flux density sensor, and wherein the electronics module is configured to determine the position of the fourth element along the measurement axis based on a ratio determined from the output of the magnetic flux density sensor and total magnetic flux sensed in the air gap by the total magnetic flux sensor.

22. The electric machine system of claim 19 wherein the source element comprises a conductive coil wound around the third element, the conductive coil configured to produce the AC magnetic flux in the magnetic circuit based on an AC excitation current applied to the conductive coil.

23. The electric machine system of claim 22, wherein the AC excitation current in the conductive coil is controlled to maintain a total magnetic flux in the air gap of substantially constant amplitude of known value.

24. The electric machine system of claim 23, wherein the electronics module is configured to determine the position of the fourth element along the axis of motion based on a ratio determined from the output of the sensor and the known value of the total magnetic flux amplitude in the air gap.

25. The electric machine system of claim 19, wherein the first element comprises a rotor and the second element comprises a stator.