System and method for measuring position and orientation using distortion-compensated magnetic fields
View Patent ↗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, 658 A-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.
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
sensor
(
s
)
=
k
∑
j
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
sensor
(
s
)
=
k
∑
j
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
sensor
(
s
)
=
k
∑
j
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
sensor
(
s
)
=
k
∑
j
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.