SYSTEM AND A METHOD FOR MAPPING A MAGNETIC FIELD

• US 20110238399A1
• Filed: 11/05/2009
• Published: 09/29/2011
• Est. Priority Date: 11/19/2008
• Status: Active Grant

• Current Assignee: Elbit Systems Limited
• Original Assignee: Elbit Systems Limited
• Inventors: Efrat, Ilan, Gandelsman, Mark, Ophir, Yoav, Mencel, Guy, Izmirli, Alon, Eichler, Uzi
• Granted Patent: US 8,700,376 B2
• Time in Patent Office: Days
• US Class Current: 703/13
• CPC Class Codes: G01R 33/072 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors
• CPC Class Codes: G06F 30/33 Design verification, e.g. functional simulation or model checking

Abstract

A system for mapping a magnetic field in a volume of interest, the system includes a magnetic field transmitter, generating a magnetic field in the volume of interest, at least one freestanding magnetic field detector, operative to freely move within the volume of interest, the at least one freestanding magnetic field detector acquiring measurements of the flux of the magnetic field at a plurality of poses, and a processor, coupled with the magnetic field detector, the processor re estimating parameters characterizing the magnetic field model according to deviations between the measurements of the flux of the magnetic field and according to predictions of the flux, the predictions being determined according to a stored magnetic field model, thereby, the processor estimating a new magnetic field model.

Claims

1. A system for mapping a magnetic field in a volume of interest, the system comprising:

a magnetic field transmitter, including at least one magnetic field generator, generating a magnetic field in the volume of interest;

at least one freestanding magnetic field detector, including at least one magnetic field sensor, operative to freely move within said volume of interest, said at least one freestanding magnetic field detector acquiring measurements of the flux of said magnetic field at a plurality of poses; and

a processor, coupled with said magnetic field detector, said processor re-estimating parameters characterizing said magnetic field model according to deviations between said measurements of said flux of said magnetic field and according to predictions of said flux, said predictions being determined according to a stored magnetic field model, thereby, said processor estimating a new magnetic field model,

wherein the number of the generators times the number of the sensors is larger then the number of degrees of freedom required to track an object in said volume of interest, and

wherein, the combined number of said at least one magnetic field generator and said least one magnetic field sensor is at least three.

2. The system according to claim 1, further including a freestanding mapping handle operative to freely move within said volume of interest, said at least one freestanding magnetic field detector being firmly coupled with said freestanding mapping handle;

3. The system according to claim 2, further including a mechanical arm, said mapping handle being coupled with said mechanical arm.

4. The system according to claim 3, further including a mechanical arm interface coupled with said processor and with said mechanical arm, said processor directing said mechanical arm interface to freely move mechanical arm within said volume of interest.

5. The system according to claim 1, wherein said processor is further coupled with said magnetic field transmitter.

6. The system according to claim 1 further including a memory coupled with said processor, said memory storing said stored magnetic field model, said memory further stores said new magnetic field model with said new magnetic field model instead of said stored magnetic field model, thereby said new magnetic field model becomes said stored magnetic field model.

7. The system according to claim 1, wherein said at least one freestanding magnetic field detector is moved within said volume of interest at a random trajectory.

8. The system according to claim 1, wherein said at least one freestanding magnetic field detector is moved within said volume of interest through a plurality of mapping regions.

9. The system according to claim 1, further including a guide, said guide guiding an operator to freely move freestanding magnetic field detector within said volume of interest.

10. The system according to claim 9, wherein said guide guides said operator to freely move freestanding magnetic field detector within said volume of interest at a random trajectory.

11. The system according to claim 9, wherein said guide guides said operator to freely move freestanding magnetic field detector within said volume of interest through a plurality of mapping regions.

12. The system according to claim 11, wherein said guide is a display displaying representations of said mapping regions and freestanding mapping magnetic field detector, said representations being marked when said magnetic field detector passes there through.

13. The system according to claim 9, wherein said guide sounds audio signals corresponding to directions.

14. The system according to claim 1, further including an imager coupled with said at least one freestanding magnetic field detector, said imager acquiring at least one image of articles present within said volume of interest, said processor determines the poses of said imager and said at least one freestanding magnetic field detector in a reference coordinates system according to said at least one image and the known pose of said articles in said reference coordinate system.

15. The system according to claim 14, wherein said processor registers said magnetic coordinate system and said reference coordinate system according the determined poses said at least one freestanding magnetic field detector in said magnetic coordinate system and said reference coordinate system.

16. The system according to claim 1, wherein said system comprises at least two magnetic field detectors.

17. The system according to claim 16, wherein each of said magnetic field detectors includes three magnetic field transmitters.

18. The system according to claim 16, wherein the spatial relationship between said two magnetic field detectors is known.

19. The system according to claim 1, wherein said processor re-estimates said parameters characterizing said magnetic field model by estimating said plurality of positions, relative to a magnetic coordinate system, according to said measurements and according to said stored magnetic field model, said processor re-estimating parameters characterizing said stored magnetic field model according to deviations between said measurements of said flux of said magnetic field and according to predictions of said flux at said estimated positions, thereby said processor estimates a new magnetic field model.

20. The system according to claim 1, wherein said magnetic field transmitters includes three magnetic field generators

21. A method for mapping a magnetic field in a volume of interest, the method comprising the procedures of:

freely moving at least one magnetic field detector within a volume of interest, said magnetic field detector including at least one magnetic field sensor;

acquiring measurements of magnetic field flux at a plurality of poses of the freestanding magnetic field detectors in the volume of interest, the magnetic field being generated by and magnetic field transmitter, said magnetic field transmitter including at least one magnetic field generator; and

re-estimating parameters characterizing a magnetic field model, according deviations between said measurements of said magnetic field flux and predictions of said magnetic field flux at said poses of said at least one magnetic field detector,

wherein, the number of the generators times the number of the sensors is larger then the number of degrees of freedom required to track an object in said volume of interest, and

wherein, the combined number of said at least one magnetic field generator and said least one magnetic field sensor is at least three.

22. The method according to claim 21, further including the preliminary procedure of determining a magnetic field model associated with a magnetic coordinate system.

23. The method according to claim 21, further including the preliminary procedure of determining a volume of interest associated with a reference coordinate system.

24. The method according to claim 21, further including the procedure of registering said magnetic coordinate system and said reference coordinate system.

25. The method according to claim 24 wherein said registering is performed by optically determining the pose of said at least one magnetic field detector relative to said reference coordinate system and determining the pose of said at least one magnetic field detector relative to the magnetic coordinate system.

26. The method according to claim 21, wherein said procedure of re-estimating parameters of a magnetic field model includes the sub-procedures of:

estimating said poses of said at least one magnetic field detector for each said measurement of said magnetic field flux according to said magnetic field model;

re-estimating parameters characterizing said magnetic field model according to said estimated poses thereby re-estimating said magnetic field model;

determining a model compatibility indicator of said magnetic field model; and

repeating from said procedure of estimating said poses when said model compatibility indicator is above a determined value.

27. The method according to claim 26 wherein said procedure of estimating said poses is performed by minimizing the squared differences between said measurements of said magnetic field flux and predictions of said magnetic field flux predicted by said previously stored magnetic field model.

28. The method according to claim 26, wherein said parameters characterizing said magnetic field model are estimated according to the deviations between said measurements of the magnetic field flux and predictions of said magnetic field flux, at said estimated poses said prediction of said magnetic field flux being determined according to said previously stored magnetic field model.

29. The method according to claim 28, wherein said deviations are determined by minimizing the sum of squared differences between said measurements of said magnetic field flux and said predictions of said magnetic field flux, at said estimated poses, said predictions are determined according to the stored magnetic field model.

30. The method according to claim 26, wherein said model compatibility indicator is a FOM.

31. The method according to claim 26, wherein said model compatibility indicator is the reciprocal of the number of repetitions from said procedure of estimating said poses.

32. The method according to claims 21, further including the procedure of storing the re-estimated parameters characterizing said magnetic field model, thereby storing a re-estimated magnetic field model instead of said previously stored magnetic field model.

33. A system for mapping a magnetic field in a volume of interest, the system comprising:

a magnetic field transmitter, generating a magnetic field in the volume of interest;

two freestanding magnetic field detectors, firmly coupled with a freestanding mapping handle, said two freestanding magnetic field detectors operative to freely move within said volume of interest, said two freestanding magnetic field detectors acquiring measurements of the flux of said magnetic field at a plurality of poses; and

a processor, coupled with said magnetic field detector, said processor re-estimating parameters characterizing said magnetic field model according to deviations between said measurements of said flux of said magnetic field and according to predictions of said flux, said predictions being determined according to a stored magnetic field model, thereby, said processor estimating a new magnetic field model.

34. The system according to claim 33, further including an imager coupled firmly coupled with said free standing mapping handle and with said two freestanding magnetic field detectors, said imager acquiring at least one image of articles present within said volume of interest, said processor determines the poses of said imager and said two freestanding magnetic field detectors in a reference coordinates system according to said at least one image and the known pose of said articles in said reference coordinate system.

35. The system according to claim 34, wherein said processor registers said magnetic coordinate system and said reference coordinate system according the determined poses said two freestanding magnetic field detectors in said magnetic coordinate system and said reference coordinate system.

36. The system according to claim 34, wherein the spatial relationship between said two freestanding magnetic field detectors is known.

37. The system according to claim 33, wherein said processor is further coupled with said magnetic field transmitter.

38. The system according to claim 33 further including a memory coupled with said processor, said memory storing said stored magnetic field model, said memory further stores said new magnetic field model with said new magnetic field model instead of said stored magnetic field model, thereby said new magnetic field model becomes said stored magnetic field model.

39. The system according to claim 33, wherein said two freestanding magnetic field detectors are moved within said volume of interest at a random trajectory.

40. The system according to claim 33, wherein said two freestanding magnetic field detectors are moved within said volume of interest through a plurality of mapping regions.

41. The system according to claim 33, further including a guide, said guide guiding an operator to freely move said two freestanding magnetic field detectors within said volume of interest.

42. The system according to claim 41, wherein said guide guides said operator to freely move said two freestanding magnetic field detectors within said volume of interest at a random trajectory.

43. The system according to claim 41, wherein said guide guides said operator to freely move said two freestanding magnetic field detectors within said volume of interest through a plurality of mapping regions.

44. The system according to claim 43, wherein said guide is a display displaying representations of said mapping regions and said two freestanding magnetic field detectors, said representations being marked when said magnetic field detector passes there through.

45. The system according to claim 41, wherein said guide sounds audio signals corresponding to directions.

46. The system according to claim 33, wherein each said two freestanding magnetic field detectors includes three magnetic field sensors.

47. The system according to claim 33, wherein said magnetic field transmitter includes three magnetic field generators