Position location system

• US 6,757,557 B1
• Filed: 06/21/1999
• Issued: 06/29/2004
• Est. Priority Date: 08/14/1992
• Status: Expired due to Term

• Current Assignee: British Telecommunications (BT Group Plc) (BT Group PLC)
• Original Assignee: British Telecommunications (BT Group Plc) (BT Group PLC)
• Inventors: Bladen, John Stuart, Anderson, Alan Patrick
• Primary Examiner(s): SHAW, SHAWNA JEANNINE
• Application Number:
  US09/336,723
• Time in Patent Office: 1,835 Days
• Field of Search: 600/407, 600/117, 600/424, 128/899, 324/207.17, 324/247, 324/207-1-2, 324/207.23, 702/152, 702/153
• US Class Current: 600/424
• CPC Class Codes: A61B 2034/107 Visualisation of planned trajectories or target regions
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/741 Glove like input devices, e.g. "data gloves"
• 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 34/74 Manipulators with manual electric input means
• CPC Class Codes: A61B 5/062 using magnetic field
• CPC Class Codes: A61B 5/6806 Gloves
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: H01F 2005/027 wound on formers for receiving several coils with perpendicular winding axes, e.g. for antennae or inductive power transfer

Abstract

Methods and apparatus are provided for locating the position, preferably in three dimensions, of a sensor by generating magnetic fields which are detected at the sensor. The magnetic fields are generated from a plurality of locations and, in one embodiment of the invention, enable both the orientation and location of a single coil sensor to be determined. The present invention thus finds application in many areas where the use of prior art sensors comprising two or more mutually perpendicular coils is inappropriate.

Claims

1. A method of determining a location and an orientation of a field sensor relative to a plurality of magnetic field sources of known location, the method comprising the steps of:

1) energizing each field source and measuring a respective field generated by each field source at the field sensor;

2) for each field source, calculating, from the measurements of the field generated by the field source and an estimate of the orientation of the sensor, an estimate of the distance from that particular field source to the sensor;

3) utilizing the estimates of distance from step

     2), and the known location of the field sources to calculate an estimate of the location of the sensor;

4) employing the estimated location of the sensor from step

     3) and the measurements of the field at the sensor to calculate a new estimate of the orientation of the sensor; and

5) repeating steps

     2) to

     4) iteratively with step

     2) employing the new estimate of sensor orientation from the preceding step

     4), to improve the estimates of location and orientation of the sensor.

2. A method as claimed in claim 1 wherein in step 1) each field source is energized in sequence so that only one field source is energized at any given time.

3. A method as claimed in claim 1, wherein in step 1) at least two field sources are simultaneously energized, each of these at least two field sources being energized at a different frequency from the other simultaneously energized field sources(s).

4. A method as claimed in claim 1, wherein at step 4), the estimated location of the sensor calculated in step 3) and the measurements of the field at the sensor are used to calculate, for each field source, the direction of the respective field at the sensor and from these field directions calculating a new estimate of the orientation of the sensor.

5. A method as claimed in claim 4 wherein, at step 1), the initial estimate of the orientation of the sensor is taken to be the orientation as calculated by the immediately preceding application of the method or, if this is the first application of the method, the axis of the sensor is initially assumed to be directed towards the respective field source.

6. A method of determining the location of a field sensor, relative to a field source, the method comprising the steps of:

1) energizing a single field source to establish a field,

2) measuring a value of the field strength at the field sensor which is dependent on the location of the sensor within the field,

3) repeating steps

     1) and

     2) for each field generating element,

4) calculating, by utilizing all the values measured in steps

     2) and

     3) and an estimate of the direction of the sensor from the field source, a direction dependent weighting factor for each field source so that the calculated field strength B is equal to the field strength B that would exist at the sensor if the axis of the field were directed towards the sensor,

5) iteratively altering the direction dependent weighting factors to maximize B and thus to determine to a desired level of accuracy the direction of the sensor from the field source, and

6) employing the measured values of the field strength to calculate the distance of the sensor from the field source and hence, from the direction of the sensor in step

     5), the location of the sensor relative to the field source.

7. A method of determining the location and the orientation of a field source relative to a plurality of field sensors of known location, the field source being energized and a measurement being made at the field sensors of the respective field generated by the field source, the method comprising the steps of:

1) for each field sensor calculating from measurements of the field detected at each sensor and an estimate of the orientation of the field source, an estimate of the distance from that particular sensor to the field source; and

2) utilizing the estimates of distance from step

     1), and the known location of the field sensors to calculate an estimate of the location of the field source;

3) employing the estimated location of the field source from step

     2) and the measurements of the field at the sensors to calculate a new estimate of the orientation of the field source;

4) repeating steps

     1) to

     3) iteratively, with step

     1) employing the new estimate of field source orientation from the preceding step

     3), to improve the estimates of location and orientation of the field source.

8. A method as claimed in claim 7 wherein, at step 1), the initial estimate of the orientation of the sensor is taken to be the orientation as calculated by the immediately preceding application of the method or, if this is the first application of the method, the axis of the sensor is initially assumed to be directed towards the respective field source.

9. An apparatus for determining the location and the orientation of a field sensor comprising:

a plurality of field sources,

energizing means operable for each field source to energize each of the plurality of field sources to produce a field within which the location and orientation of the sensor may be determined,

measurement means, connected to the field sensor, to measure and output a parameter of the field at the sensor, and

control means to control the energizing means, the control means comprising storing means to store parameters output by the measurement means, and calculating means to calculate, from the stored measurements of the fields, the location and orientation of the sensor, the calculating means comprising;

location estimating means being operable to calculate, from the stored measurements of the fields and an estimate of the orientation of the sensor, an estimate of the distance of the sensor from each of the field sources and, using the estimates of distance and the known location of the field sources, to calculate an estimate of the location of the sensor;

orientation estimating means being operable to calculate, from the estimate of sensor location by the location estimating means and the stored measurements of the field, a new estimate of the orientation of the sensor;

means to iteratively improve the estimate of the location and orientation of the sensor, which means in use repeatedly employ the location and orientation estimating means in sequence, wherein the output of the orientation estimating means is adopted by the location estimating means as the new estimate of sensor orientation at each iteration.

10. An apparatus as claimed in claim 9, wherein the energizing means are operable to sequentially energize each field source.

11. An apparatus as claimed in claim 9, wherein the energizing means are operable to simultaneously energize at least two field sources, and to energize each simultaneously energized field source at a distinct frequency.

12. An apparatus for determining the location of a field sensor as claimed in claim 9, wherein the field sensor comprises a coil of electrically conducting wire.

13. An apparatus for determining the location of a field sensor as claimed in claim 9, wherein the plurality of field sources include three mutually orthogonal field sources.

14. An endoscopy system for use in the endoscopy of a human or animal body, the endoscopy system comprising apparatus as claimed in claim 9.

15. Apparatus for determining the location and orientation of a sensor as claimed in claim 9, wherein one or more of said sensors are attached to parts of a glove, the output of said apparatus providing data defining the location and orientation of the respective parts of a glove wearer'"'"'s hand.

16. Apparatus as claimed in claim 15, wherein one or more sensors are attached to fingers of the glove.

17. An apparatus for determining the location of an object relative to a field source, the apparatus comprising:

a plurality of field sources,

energizing means to sequentially energize each of the field sources to produce a field within which the object may be located,

a sensor, to be attached to the object, able to sense a parameter of the field,

measurement means to measure and output parameters of the field sensed by the sensor when each field source is energized, and

control means to control the energizing means, store the parameters output by the measurement means and calculate the location of the sensor, relative to the field source wherein the control means comprises,

weighting means to weight each of the parameters, sensed by the sensor, by a direction dependent weighting factor, for each field source so that the calculated field strength B is equal to the field strength B that would exist at the sensor if the axis of the field were directed towards the sensor,

means to iteratively alter the direction dependent weighting factors until a maximum value of the field strength is found, and to determine the direction of the sensor from the field source to a desired level of accuracy, and

calculating means to calculate the distance of the sensor from the field source and hence the location of the sensor relative to the field source.

18. An apparatus for determining the location of an object as claimed in claim 17, wherein the field source comprises three mutually orthogonal field generating elements and the sensor comprises three mutually orthogonal field sensing elements.

19. An endoscopy system for use in the endoscopy of a human or animal body, the endoscopy system comprising apparatus as claimed in claim 17.