Sensor fusion for model-based detection in pipe and cable locator systems

• US 20060055584A1
• Filed: 07/29/2005
• Published: 03/16/2006
• Est. Priority Date: 11/25/2003
• Status: Active Grant

• Current Assignee: MetroTech Corporation Inc.
• Original Assignee: MetroTech Corporation Inc.
• Inventors: Welaratna, Ruwan, Waite, James W.
• Granted Patent: US 7,834,801 B2
• Time in Patent Office: Days
• US Class Current: 342/22
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01V 11/00 Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00

Abstract

Line locator systems that fuse traditional sensors used in a combined pipe and cable locator (electromagnetic coils, magnetometers, and ground penetrating radar antennas) with low cost inertial sensors (accelerometers, gyroscopes) in a model-based approach are presented. Such systems can utilize inexpensive MEMS sensors for inertial navigation. A pseudo-inertial frame is defined that uses the centerline of the tracked utility, or an aboveground fixed object as the navigational reference. An inertial sensor correction mechanism that limits the tracking errors over time when the model is implemented in state-space form using, for example, the Extended Kalman Filter (EKF) is disclosed.

Claims

1. A line locator system, comprising:

one or more field sensors to detect a field from an underground line;

one or more inertial positioning sensors; and

a filter that fuses signals from the one or more field sensors and the one or more inertial positioning sensors to provide position and field values.

2. The system of claim 1, wherein the filter is a Kalman filter.

3. The system of claim 1, wherein the one or more field sensors includes electromagnetic field sensors.

4. The system of claim 1, wherein the one or more field sensors includes ground penetrating radar sensors.

5. The system of claim 1, wherein the filter treats the one or more field sensors and the one or more inertial positioning sensors as loosely coupled sensors.

6. The system of claim 1, wherein the filter treats the one or more field sensors and the one or more inertial positioning sensors as tightly coupled sensors.

7. The system of claim 1, wherein the filter treats the one or more field sensors and the one or more inertial positioning sensors as ultra-tightly coupled sensors.

8. The system of claim 1, wherein a depth of the underground line is continuously calculated.

9. The system of claim 1, wherein the one or more field sensors includes a radar emitting antenna, and a first radar detecting antenna.

10. The system of claim 9, wherein the one or more field sensors further includes a second radar detecting antenna.

11. The system of claim 1, wherein the one or more inertial position sensors includes sensors chosen from the group consisting of accelerometers, gyroscopes, magneto resistive sensors, and digital compasses.

12. The system of claim 1, further including a GPS receiver to provide an absolute position.

13. The system of claim 1, wherein the filter, in each time period, provides an updated state vector based on signals from the one or more field measurement sensors and the one or more inertial position sensors.

14. The system of claim 13, wherein the state vector X includes position, velocity, angular orientation, and bias parameters.

15. The system of claim 14, wherein the angular orientation parameters are quaternion parameters.

16. The system of claim 15, wherein the state vector also includes a depth parameter formed of the underground line.

17. The system of claim 15, wherein the state vector also includes a depth parameter formed by the product of a current in the underground line and the depth of the underground line.

18. The system of claim 15, wherein the state vector also includes a velocity parameter.

19. The system of claim 15, wherein the state vector further includes both a velocity parameter and a depth parameter.

20. The system of claim 15, wherein the state vector includes linearized parameters from an EM mode.

21. The system of claim 15, wherein the state vector includes linearized parameters from a GPR mode.

22. The system of claim 13, wherein the state vector is updated according to X=AX+BU, where A is the state transition matrix, B is the input mapping matrix, and U is the forcing function vector.

23. The system of claim 1, further including a mapping module that stores position and field values to create an electronic map of the position of the underground line.

24. The system of claim 1, further including one or more position locator devices, wherein the one or more position locator devices determine the position of the line locator system relative to a fixed point.

25. The system of claim 17, wherein the one or more position locator devices includes one or more of a group consisting of a GPS system, a laser rangefinder, and stereoscope range finder.

26. A method of locating an underground line, comprising:

measuring one or more field values;

measuring one or more inertial navigation values; and

fusing the one or more field values with the one or more inertial navigation values to obtain accurate values for the location of the underground line.

27. The method of claim 26, wherein measuring one or more field values includes measuring one or more values of magnetic field strength.

28. The method of claim 26, wherein measuring one or more field values includes measuring one or more values of time for signal return in a ground penetrating radar system.

29. The method of claim 26, wherein measuring one or more inertial navigation values includes measuring one or more parameters for a set consisting of linear acceleration, angular acceleration, and Earth magnetic field direction.

30. The method of claim 26, wherein fusing the one or more field values with the one or more inertial parameter values includes:

forming a state vector from the one or more inertial parameter values;

receiving one or more external position parameters; and

utilizing a Kalman filter to update the state vector.

31. The method of claim 30, further including performing a walkover determination utilizing the one or more field values.

32. The method of claim 26, wherein fusing the one or more field values with the one or more inertial parameter values includes:

forming a state vector from the one or more inertial parameter values; and

updating the state vector utilizing a Kalman filter and the one or more field values.

33. The method of claim 26, wherein fusing the one or more field values with the one or more inertial parameter values includes

forming a state vector from the one or more inertial parameter values and the one or more field values;

and

updating the state vector utilizing a Kalman filter.

34. A line locator, comprising:

means for receiving one or more field values from an underground line;

means for receiving one or more inertial position values; and

means for fusing the one or more field values with the one or more inertial position values.

35. The locator of claim 34, wherein the means for fusing includes a Kalman filter.

36. The locator of claim 34, wherein the means for receiving one or more field values includes means for receiving electromagnetic values from the underground line.

37. The locator of claim 34, wherein the means for receiving one or more field values includes means for receiving ground penetrating radar values from the underground line.