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

• US 7,834,801 B2
• Filed: 07/29/2005
• Issued: 11/16/2010
• 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.
• Primary Examiner(s): Lobo; Ian J
• Application Number:
  US11/193,100
• Publication Number:
  US 20060055584A1
• Time in Patent Office: 1,936 Days
• Field of Search: 342/22, 324/326, 324/329
• 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. An underground pipe and cable locator system, comprising:

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

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 real-time position and field values of the underground pipe or cable relative to the locator system, wherein the real-time position includes a centerline location and a depth of the underground pipe or cable.

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 the depth of the underground pipe or cable 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 pipe or cable.

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 pipe or cable and the depth of the underground pipe or cable.

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 pipe or cable.

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 range finder, and stereoscope range finder.

26. A method of locating an underground pipe or cable, 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 real-time location of the underground pipe or cable relative to a locator, wherein the real-time position includes a centerline location and a depth of the underground pipe or cable.

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. An underground pipe and cable locator, comprising:

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

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 to provide real-time position and field values of the underground pipe or cable relative to the locator, wherein the real-time position includes a centerline location and a depth of the underground pipe or cable.

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 pipe or cable.

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 pipe or cable.

38. An underground pipe and cable locator system, comprising:

one or more electromagnetic field sensors to detect an electromagnetic field from the underground pipe or cable and from which field parameters are determined;

one or more inertial positioning sensors from which position data is determined; and

a filter that utilizes a state vector that includes position data, field parameters, and inertial sensor bias data, and wherein a real-time position of the underground pipe or cable relative to the locator system is determined from the state vector, and wherein the real-time position includes a centerline location and a depth of the underground pipe or cable.

39. The locator system of claim 38, wherein the state vector is given by

X=[xyz{dot over (x)}{dot over (y)}ż

q₁q₂q₃q₄b_{{umlaut over (x)}}b_ÿ

b_{{umlaut over (z)}}b<sub>Δ

p</sub>b<sub>Δ

q</sub>b<sub>Δ

r</sub>Id],

where x, y, and z represent position relative to the locator system, {dot over (x)}, {dot over (y)}, and ż

are first derivatives with respect to time of the positions x, y, and z, q₁, q₂, q₃, and q₄ are quaternion states, b_{{umlaut over (x)}}, b_ÿ

, b_{{umlaut over (z)}}, b<sub>Δ

p</sub>, b<sub>Δ

q</sub>, and b<sub>Δ

r</sub>, are inertial sensor bias adjustments, and Id is derived from y_d=LId(h_d/h_b²) where y_d is an off-centerline state variable for a L/R coil configuration, I is current, d is a depth of the pipe or cable, h_d is a difference component of the magnetic field, h_b is a horizontal component of the magnetic field, and L is a parameter that sets a slope of y_d to 1.

40. The locator system of claim 38, wherein the state vector is given by

X=[xyz{dot over (x)}{dot over (y)}ż

q₁q₂q₃q₄b_{{umlaut over (x)}}b_ÿ

b_{{umlaut over (z)}}b<sub>Δ

P</sub>b<sub>Δ

q</sub>b<sub>Δ

r</sub>d],

where x, y, and z represent position relative to the locator system, {dot over (x)}, {dot over (y)}, and ż

are first derivatives with respect to time of the positions x, y, and z, q₁, q₂, q₃, and q₄ are quaternion states, b_{{umlaut over (x)}}, b_ÿ

, b_{{umlaut over (z)}}, b<sub>Δ

p</sub>, b<sub>Δ

q</sub>, and b<sub>Δ

r</sub>, are inertial sensor bias adjustments, and d is derived from y_v=Md(h_v/h_b) where y_v is an off-centerline state variable for a null-coil configuration, d is a depth of the pipe or cable, h_v is a vertical component of a magnetic field at the null coil, h_b is a horizontal component of the magnetic field, and M is a parameter that sets a slope of y_v to 1.

41. The locator system of claim 38, wherein the field parameter is current.

42. The locator system of claim 38, wherein the field parameter is depth calculated from y_v=Md(h_v/h_b).

43. The locator system of claim 38, wherein the filter corrects inertial sensor bias data utilizing the field parameters.

44. The locator system of claim 38, wherein the position includes a depth of the pipe or cable, which is continuously presented to a user in real time.

45. The locator system of claim 44, wherein the position includes a right/left indication directing the user towards a point over the center of the pipe or cable.

46. The locator system of claim 38, wherein the filter is a Kalman filter.

47. A method of locating an underground cable or pipe, comprising:

receiving electromagnetic signals from one or more electromagnetic field sensors that detect an electromagnetic field from the underground pipe or cable;

determining field parameters from the electromagnetic signals;

receiving inertial signals from one or more inertial positioning sensors;

determining position data from the inertial signals; and

filtering, utilizing a state vector that includes position data, field parameters, and inertial sensor bias data, to determine a real-time position of the underground pipe or cable relative to the locator system, and wherein the real-time position includes a centerline location and a depth of the underground pipe or cable.

48. The method of claim 47, wherein the state vector is given by

X=[xyz{dot over (x)}{dot over (y)}ż

q₁q₂q₃q₄b<sub>{umlaut over (x)}bÿ

b{umlaut over (z)}</sub>b<sub>Δ

p</sub>b<sub>Δ

q</sub>b<sub>Δ

r</sub>Id],

where x, y, and z represent position relative to the locator system, {dot over (x)}, {dot over (y)}, and ż

are first derivatives with respect to time of the positions x, y, and z, q₁, q₂, q₃, and q₄ are quaternion states, b_{{umlaut over (x)}}, b_ÿ

, b_{{umlaut over (z)}}, b<sub>Δ

p</sub>, b<sub>Δ

q</sub>, and b<sub>Δ

r</sub>, are inertial sensor bias adjustments, and Id is derived from y_d=LId(h_d/h_b²) where y_d is an off-centerline state variable for a L/R coil configuration, I is current, d is a depth of the pipe or cable, h_d is a difference component of the magnetic field, h_b is a horizontal component of the magnetic field, and L is a parameter that sets a slope of y_d to 1.

49. The method of claim 47, wherein the state vector is given by

X=[xyz{dot over (x)}{dot over (y)}ż

q₁q₂q₃q₄b_{{umlaut over (x)}}b_ÿ

b_{{umlaut over (z)}}b<sub>Δ

p</sub>b<sub>Δ

q</sub>b<sub>Δ

r</sub>d],

where x, y, and z represent position relative to the locator system, {dot over (x)}, {dot over (y)}, and ż

are first derivatives with respect to time of the positions x, y, and z, q₁, q₂, q₃, and q₄ are quaternion states, b_{{umlaut over (x)}}, b_ÿ

, b_{{umlaut over (z)}}, b<sub>Δ

p</sub>, b<sub>Δ

q</sub>, and b<sub>Δ

r</sub>, are inertial sensor bias adjustments, and d is derived from y_v=Md(h_v/h_b) where y_v is the off-centerline state variable for a null-coil configuration, d is the depth of the pipe or cable, h_v is a vertical component of a magnetic field at the null coil, h_b is a horizontal component of the magnetic field, and M is a parameter that sets a slope of y_v to 1.

50. The method of claim 47, wherein the field parameters include current.

51. The method of claim 47, wherein the field parameters include depth calculated from y_v=Md(h_v/h_b).

52. The method of claim 47, wherein filtering includes correcting inertial sensor bias data utilizing the field parameters.

53. The method of claim 47, wherein the position includes a depth of the pipe or cable and further including continuously presenting the depth to a user in real time.

54. The method of claim 53, wherein the position includes a right/left indication, and further including directing the user towards a point over the center of the pipe or cable with the right/left indication.

55. The method of claim 47, wherein filter including utilizing a Kalman filter.