System and method for measuring position and orientation using distortion-compensated magnetic fields

• US 7,373,271 B1
• Filed: 09/20/2004
• Issued: 05/13/2008
• Est. Priority Date: 09/20/2004
• Status: Active Grant

• Current Assignee: Northern Digital Inc. (Roper Technologies, Inc.)
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Schneider, Mark R.
• Primary Examiner(s): Lau; Tung S.
• Application Number:
  US10/945,277
• Time in Patent Office: 1,331 Days
• Field of Search: 702/150
• US Class Current: 702/150
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for

Abstract

An electromagnetic tracking system (600) and a distortion compensation method (500) that utilize a lead-lag network model to compensate for position and orientation distortion caused by eddy currents formed in one or more conductive distorters (330, 658A-C) located within a tracking environment during electromagnetic tracking of one or more objects (612). the method is adaptive relative to the amount of distortion cause by the conductive distorters.

Claims

1. A method of locating an object, comprising the steps of:

a) generating at least one magnetic field;

b) sensing said at least one magnetic field so as to generate at least one frequency response;

c) representing said at least one frequency response in terms of at least one lead-lag network; and

d) determining at least one of position and orientation of the object as a function of said at least one lead-lag network;

wherein step c) comprises representing said at least one frequency response as a transfer function, H_sensor(s), that is a function of parameters k, p_j and z_j, said transfer function being;

$H_{\mathrm{sensor}}<br><br>\left(s\right)=k<br><br>\underset{j}{\sum <br><br>}<br><br>\frac{s+z_j}{s+p_j}.$

2. A method according to claim 1, wherein step d) comprises collecting sufficient frequency response data so as to determine said parameters k, p_j and z_j in said transfer function.

3. A method according to claim 1, wherein step d) comprises solving for said parameters k, p_j and z_j in said transfer function.

4. A method according to claim 1, wherein step c) comprises representing said at least one frequency response in terms of at least two lead-lag networks.

5. A method of locating an object, comprising the steps of:

a) receiving at least one frequency response of at least one magnetic field sensor;

b) representing said at least one frequency response in terms of at least one lead-lag network; and

c) determining at least one of position and orientation of the object as a function of said at least one lead-lag network;

wherein step b) comprises representing said at least one frequency response as a transfer function, H_sensor(s), that is a function of parameters k, p_j and z_j, said transfer function being;

$H_{\mathrm{sensor}}<br><br>\left(s\right)=k<br><br>\underset{j}{\sum <br><br>}<br><br>\frac{s+z_j}{s+p_j}.$

6. A method according to claim 5, wherein step c) comprises collecting sufficient frequency response data so as to determine said parameters k, p_j and z_j in said transfer function.

7. A method according to claim 5, wherein step c) comprises solving for said parameters k, p_j and z_j in said transfer function.

8. A method according to claim 5, wherein step b) comprises representing said at least one frequency response in terms of at least two lead-lag networks.

9. A computer readable medium containing computer instructions for determining the location of an object, said computer instructions comprising:

a) a first set of instructions for receiving at least one frequency response of at least one magnetic field sensor;

b) a second set of instructions for representing said at least one frequency response in terms of at least one lead-lag network; and

c) a third set of instructions for determining at least one of position and orientation of the object as a function of said at least one lead-lag network;

wherein said second set of instructions comprises instructions for representing said at least one frequency response as a transfer function, H_sensor(s), that is a function of parameters k, p_j and z_j, said transfer function being;

$H_{\mathrm{sensor}}<br><br>\left(s\right)=k<br><br>\underset{j}{\sum <br><br>}<br><br>\frac{s+z_j}{s+p_j}.$

10. A computer readable medium according to claim 9, wherein said third set of instructions comprises instructions for collecting sufficient frequency response data so as to determine said parameters k, p_j and z_j in said transfer function.

11. A computer readable medium according to claim 9, wherein said third set of instructions comprises instructions for solving for said parameters k, p_j and z_j in said transfer function.

12. A computer readable medium according to claim 9, wherein said second set of instructions comprises instructions for representing said at least one frequency response in terms of at least two lead-lag networks.

13. A system for determining the location of an object, comprising:

a) at least one magnetic field sensor; and

b) a processor having an input operatively configured to receive at least one frequency response of said at least one magnetic field sensor, said processor operatively configured to;

i) represent said at least one frequency response in terms of at least one lead-lag network; and

ii) determine at least one of position and orientation of the object as a function of said at least one lead-lag network

wherein said processor is operatively configured to represent said at least one frequency response as a transfer function, H_sensor(s), that is a function of parameters k, p_j and z_j, said transfer function being;

$H_{\mathrm{sensor}}<br><br>\left(s\right)=k<br><br>\underset{j}{\sum <br><br>}<br><br>\frac{s+z_j}{s+p_j}.$

14. A system according to claim 13, wherein said processor is operatively configured to collect sufficient frequency response so as to determine said parameters k, p_j and z_j in said transfer function.

15. A system according to claim 13, wherein said processor is operatively configured to solve for said parameters k, p_j and z_j in said transfer function.

16. A system according to claim 13, wherein said processor is operatively configured to represent said at least one frequency response in terms of at least two lead-lag networks.

17. A system according to claim 13, further comprising a plurality of B-field generators and at least one sensor.

18. A system according to claim 13, further comprising at least one B-field generator, said processor being further operatively configured to excite said at least one B-field generator in a time division multiplexed manner.

19. A system according to claim 13, further comprising at least one B-field generator, said processor being further operatively configured to excite said at least one B-field generator in a frequency division multiplexed manner.