Magnetic position measurement system with field containment means

• US 6,528,991 B2
• Filed: 07/03/2001
• Issued: 03/04/2003
• Est. Priority Date: 07/03/2001
• Status: Active Grant

• Current Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Ashe, Westley
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US09/897,083
• Publication Number:
  US 20030011359A1
• Time in Patent Office: 609 Days
• Field of Search: 324/207.17, 324/207.12, 324/207.14, 324/207.16, 324/207.23, 324/207.24, 324/207.25, 324/207.26, 336/84.R, 336/84.C, 336/84.M, 128/899, 600/424
• US Class Current: 324/207.17
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61B 5/062 using magnetic field

Abstract

A magnetic field position and orientation measurement system contains, confines and re-directs the magnetic field from one or more transmitters such that the fields are attenuated in areas outside of the operating volume in areas where metallic objects are commonly found. An attenuator made of a highly permeable material such as ferrite or mumetal may be placed on top of a conductive plate. The permeable attenuator may be as thin as 0.001 inches. on top of the permeable attenuator, a transmitter system is placed including at least three transmitters. In one embodiment, the transmitter consists of a PC board carrying the transmitter. The transmitter system, the permeable attenuator and the conductive plate, where used, may only be from ½ inch to ⅝ of an inch in thickness combined. The permeable attenuator may have a flat, planar configuration. Alternatively, it may be made to resemble, in cross-section, a cake pan having a flat central region with uplifted peripheral edges. Alternatively, the permeable attenuator may have a generally flat configuration with peripheral edges that taper outwardly from the top surface thereof to the bottom surface thereof with the taper making an angle with the bottom surface in the range of, preferably, 30° to 85°. The conductive plate is optional.

Claims

1. In a magnetic position measurement system, the improvement comprising means for containing a magnetic field used to conduct measurements of position of an object in at least three dimensions, said containing means comprising a magnetic field permeable attenuator located adjacent a region where position of said object in three dimensions is being measured by a magnetic field, said attenuator attenuating said magnetic field on a side of said attenuator remote from said region, said system including transmitter means for engaging said attenuator on a side thereof opposite said remote side, a number of transmit axes multiplied by a number of receive axes being at least equal to a desired number of measured degrees of freedom.

2. The system of claim 1, wherein said attenuator is flat.

3. The system of claim 2, wherein said attenuator has a uniform thickness of 0.01 to 0.25 inches.

4. The system of claim 3, wherein said attenuator is made of a material chosen from the group consisting of ferrite and mumetal.

5. The system of claim 4, wherein said attenuator has an upraised peripheral edge.

6. The system of claim 2, wherein said attenuator has an upraised peripheral edge.

7. The system of claim 2, wherein said attenuator has a peripheral edge tapered outwardly from a top surface of said attenuator to a bottom surface thereof.

8. The system of claim 4, wherein said attenuator has a peripheral edge tapered outwardly from a top surface of said attenuator to a bottom surface thereof.

9. The system of claim 1, wherein said attenuator has a V-shaped cross-section.

10. The system of claim 9, wherein said attenuator has a uniform thickness of 0.01 to 0.25 inches.

11. The system of claim 10, wherein said attenuator is made of ferrite.

12. The system of claim 10, wherein said attenuator is made of mumetal.

13. The system of claim 1, further including a conductive plate attached under said attenuator.

14. The system of claim 13, wherein said plate has a thickness of 0.1875 to 0.25 inches.

15. The system of claim 14, wherein said plate is made of non-ferrous metal.

16. The system of claim 14, wherein said plate is made of a conductive metal.

17. The system of claim 16, wherein said conductive metal is non-ferrous.

18. The system of claim 1, further wherein said transmitter means is mounted on top of said attenuator.

19. The system of claim 18, wherein said transmitter means comprises a PC board with said transmitters etched thereon.

20. The system of claim 19, wherein said PC board is 0.03125 to 0.125 inches thick.

21. The system of claim 3, wherein said magnetic field is created by a pulsed DC power source.

22. A magnetic position measurement system, comprising:

a) a magnetic field permeable attenuator;

b) a transmitter means above said attenuator for measuring in three dimensions;

c) said transmitter means and attenuator being laminated together.

23. The system of claim 22, wherein said transmitter means and attenuator have a combined thickness of 0.08 to 0.375 inches.

24. The system of claim 22, wherein said transmitter means comprises a PC board with a transmitting means etched thereon.

25. The system of claim 22, wherein said attenuator is made of a material chosen from the group consisting of ferrite and mumetal.

26. The system of claim 22, further including a conductive plate under said attenuator.

27. A method of measuring position of an object in a prescribed three dimensional space including the steps of:

a) defining a three dimensional space;

b) locating a magnetic field permeable attenuator adjacent said space;

c) placing transmitter means on a side of said attenuator facing said space, a number of transmit axes multiplied by a number of receive axes being at least equal to a desired number of measured degrees of freedom;

d) operating said transmitter means; and

e) measuring position of said object.

28. The method of claim 27, wherein said locating step includes the step of providing an attenuator with a uniform thickness of 0.01 to 0.25 inches.

29. The method of claim 28, wherein said providing step includes the step of making said attenuator of one of ferrite or numetal.

30. The method of claim 27, further including the step of installing a conductive plate under said attenuator.

31. The method of claim 30, wherein said installing step includes installing a conductive plate made of aluminum.

32. The method of claim 30, wherein said installing step includes installing a conductive plate having a thickness of 0.1875 to 0.25 inches.

33. The method of claim 30, further including the step of laminating together said transmitter means, attenuator and plate.