Noncontact measuring of the position of an object with magnetic flux

• US 8,564,281 B2
• Filed: 05/29/2009
• Issued: 10/22/2013
• Est. Priority Date: 05/29/2009
• Status: Active Grant

• Current Assignee: Calnetix Technologies, LLC (General Electric Company)
• Original Assignee: Calnetix Technologies, LLC (General Electric Company)
• Inventors: Filatov, Alexei V.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US12/475,052
• Publication Number:
  US 20100301840A1
• Time in Patent Office: 1,607 Days
• Field of Search: 324/207.2, 32420715-20725
• US Class Current: 324/207.2
• 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. A sensor head fixed relative to a stationary element includes a soft-magnetic core. A sensor target is fixed relative to a movable element, the soft-magnetic core and the sensor target separated by an air gap and defining a magnetic circuit. A coil around the soft-magnetic core is adapted to produce a magnetic flux in the magnetic circuit. A magnetic flux density sensor fixed relative to the sensor head resides in the gap between the soft-magnetic core and the sensor target and is configured to detect magnetic flux density in a portion of the gap. A controller in communication with the magnetic flux density sensor is configured to receive an output signal of the magnetic flux.

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 two parameters associated with a magnetic flux distribution in the air gap including a value of the total magnetic flux in the air gap and a value of the magnetic flux density in the portion of the air gap 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. The apparatus of claim 1, wherein the magnetic flux density sensor resides in the air gap proximate an interface between the different locations of the sensor target.

15. An electric machine system comprising

a rotor supported to rotate within a stator;

and

a position sensing device for determining the position of the rotor relative to the stator along a measurement axis, the position sensing device comprising;

a sensor head fixed in relation to the stator, the sensor head comprising a soft-magnetic core,

a sensor target fixed in relation to the rotor, the soft-magnetic core and the sensor target separated by an air gap and defining a magnetic circuit, the sensor target configured to rotate about the measurement axis,

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 two parameters associated with a magnetic flux distribution in the air gap including a value of the total magnetic flux in the air gap and a value of the magnetic flux density in the portion of the air gap detected by the magnetic flux density sensor.

16. The system of claim 15 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.

17. The system of claim 16, 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.

18. The system of claim 16, wherein the total magnetic flux sensor is a conductive coil.

19. The system of claim 15, 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.

20. The system of claim 19, 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.

21. The system of claim 15, wherein the magnetic flux density sensor is a conductive coil.

22. The system of claim 15, wherein the magnetic flux density sensor resides in the air gap proximate an interface between the different locations of the sensor target.

23. The system of claim 15, 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.

24. The system of claim 23, 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.

25. The system of claim 24, wherein the first portion of the sensor target comprises electrically isolated electrical steel laminations stacked in the measurement direction.

26. The system of claim 25, 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.

27. 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;

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;

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 a ratio determined from the total magnetic flux in the air gap sensed by the total magnetic flux sensor and magnetic flux density detected by the magnetic flux density sensor.

28. 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, the AC magnetic flux 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;

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 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.