METHOD AND SYSTEM FOR HEADING INDICATION WITH DRIFT COMPENSATION

• US 20090119937A1
• Filed: 11/13/2007
• Published: 05/14/2009
• Est. Priority Date: 11/13/2007
• Status: Active Grant

• Current Assignee: Watson Industries, Inc.
• Original Assignee: Watson Industries, Inc.
• Inventors: Watson, William S.
• Granted Patent: US 7,877,887 B2
• Time in Patent Office: Days
• US Class Current: 33/313
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism
• CPC Class Codes: G01C 19/38 with north-seeking action by other than magnetic means, e.g. gyrocompasses using earth's rotation
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719
• CPC Class Codes: G01C 19/5649 Signal processing

Abstract

An apparatus and method for compensation of the effects of various bias errors encountered by inertial rate gyroscopes, particularly vibrating element gyroscopes, configured to detect heading relative to true north. Certain embodiments are suitable for reducing rotational dynamic errors associated with rotating gyroscopes. Other embodiments may include compensation of biases not related to rotational dynamics, such as thermal drift. The various methods disclosed may also account for the bias by sampling the rotational vector of the earth at an arbitrary heading, and at a heading that is 180° offset from the arbitrary heading. The sequence may be repeated numerous times to compensate for bias drift. The bias drift may be constant with respect to time (linear) or changing over time (non-linear) during the data acquisition sequence. Some embodiments include methods that utilize data from accelerometers to infer the bank and elevation angles as well as earth latitude location relative to the equator.

Claims

1. A method for determining a heading direction, comprising:

selecting a gyroscope having a sensitive axis and defining a pointing vector, said gyroscope configured for detection of a rotation rate about said sensitive axis;

orienting said gyroscope in a first orientation such that when said gyroscope is in said first orientation said sensitive axis defines a heading axis and said pointing vector is oriented in a first direction;

using said gyroscope to measure a first set of indicated rotation rate data while said gyroscope is stationary and in said first orientation;

orienting said gyroscope in a second orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in a second direction substantially opposite said first direction;

using said gyroscope to measure a second set of indicated rotation rate data while said gyroscope is stationary and in said second orientation;

orienting said gyroscope in a third orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in substantially said first direction;

using said gyroscope to measure a third set of indicated rotation rate data while said gyroscope is stationary and in said third orientation;

calculating a corrected rotation rate of said gyroscope about said heading axis utilizing at least said first, second and third sets of indicated rotation rate data; and

determining said heading direction from said corrected rotation rate,

wherein each of said first, second and third sets of indicated rotation rate data include at least one data point, and

wherein said rotation rate about said sensitive axis of said gyroscope is caused by the earth'"'"'s rotation.

2. The method of claim 1 wherein said step of calculating the corrected rotation rate includes steps for calculating a corrected rotation rate.

3. The method of claim 1 wherein said step of orienting said gyroscope in said third orientation substantially returns said gyroscope to said first orientation.

4. The method of claim 1 further comprising:

orienting said gyroscope in a fourth orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in substantially said second direction; and

using said gyroscope to measure a fourth set of indicated rotation rate data while said gyroscope is stationary and in said fourth orientation, said fourth set of indicated rotation rate data including at least one data point,

wherein said step of calculating the corrected rotation rate further utilizes said fourth set of indicated rotation rate data.

5. The method of claim 4 wherein said step of calculating the corrected rotation rate includes steps for calculating a corrected rotation rate.

6. The method of claim 4 wherein said step of orienting said gyroscope in said fourth orientation substantially returns said gyroscope to said second orientation.

7. The method of claim 4 further comprising:

orienting said gyroscope in a fifth orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in substantially said first direction;

using said gyroscope to measure a fifth set of indicated rotation rate data while said gyroscope is stationary and in said fifth orientation, said fifth set of indicated rotation rate data including at least one data point;

wherein said step of calculating a corrected rotation rate further utilizes said fifth set of indicated rotation rate data.

8. The method of claim 7 wherein said step of calculating the corrected rotation rate includes steps for calculating a corrected rotation rate.

9. The method of claim 7 wherein said step of orienting said gyroscope in said fifth orientation substantially returns said gyroscope to said first orientation.

10. The method of claim 7 further comprising:

orienting said gyroscope in a sixth orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in substantially said second direction; and

using said gyroscope to measure a sixth set of indicated rotation rate data while said gyroscope is stationary and in said sixth orientation, said sixth set of indicated rotation rate data including at least one data point,

wherein said step of calculating the corrected rotation rate further utilizes said sixth set of indicated rotation rate data.

11. The method of claim 10 wherein said step of calculating the corrected rotation rate includes steps for calculating a corrected rotation rate.

12. The method of claim 10 wherein said step of orienting said gyroscope in said fourth orientation substantially returns said gyroscope to said second orientation.

13. The method of claim 1 wherein said step of orienting said gyroscope in said second orientation includes rotationally offsetting said gyroscope substantially 180°

about an axis that is substantially orthogonal to said sensitive axis.

14. The method of claim 1 wherein said step of orienting said gyroscope in said second orientation substantially aligns said sensitive axis with said heading axis.

15. The method of claim 1 wherein said step of selecting said gyroscope further includes selecting said gyroscope having said pointing vector in substantial alignment with said sensitive axis.

16. A method for determining a heading direction, comprising:

orienting a gyroscope in a first orientation, said gyroscope having a sensitive axis and defining a pointing vector, said sensitive axis defining a heading axis, said pointing vector oriented in a first direction;

measuring a set of rotational rate signals from said gyroscope with said gyroscope in said first orientation;

orienting said gyroscope in a second orientation, said sensitive axis being substantially parallel to said heading axis, said pointing vector being oriented in a second direction substantially opposite said first direction;

measuring another set of rotational rate signals from said gyroscope with said gyroscope in said second orientation;

alternating said gyroscope between said first orientation and said second orientation and measuring an additional set of rotational rate signals from said gyroscope after each alternating to obtain a plurality of sets of signals numbering at least three;

calculating a corrected rate of rotation of said gyroscope about said heading axis utilizing said plurality of sets of signals; and

determining said heading direction from said corrected rate of rotation.

17. The method of claim 16 wherein said step of calculating the corrected rate of rotation includes steps for calculating a corrected rate of rotation.

18. The method of claim 16 wherein said gyroscope is substantially stationary during each measuring step.

19. A method for determining a heading direction, a bank angle and an elevation angle, comprising:

(a) selecting a gyroscope comprising an angular rate sensor and an accelerometer, said angular rate sensor detecting a rotational rate about a first sensitive axis, said accelerometer detecting an acceleration along a second sensitive axis, said first and second sensitive axes having a known spatial relationship;

(b) defining a first orientation of said gyroscope with said first sensitive axis in alignment with a heading axis;

(c) defining a second orientation of said gyroscope with said first sensitive axis parallel with an elevation axis, said elevation axis being at a first projected right angle relative to said heading axis;

(d) defining a third orientation of said gyroscope with said first sensitive axis parallel with a lateral axis, said lateral axis being at a second projected right angle relative to said heading axis, said lateral axis being at a third projected right angle relative to said elevation axis;

(e) measuring a rotational rate data set with said angular rate sensor and a gravitational acceleration data set with said accelerometer, said gyroscope being stationary in said first orientation, each of said data sets including at least one data point;

(f) repeating step (e) with said first sensitive axis oriented parallel to and 180°

offset from said first orientation;

(g) alternating between steps (e) and (f) to obtain at least three of said rotational rate data sets and at least three of said gravitational acceleration data sets;

(h) utilizing said rotational rate data sets acquired in steps (e), (f) and (g) to calculate a corrected rate of rotation of said gyroscope about said heading axis;

(i) utilizing said gravitational acceleration data sets acquired in steps (e), (f) and (g) to calculate a corrected gravitational acceleration along said heading axis;

(j) repeating steps (e), (f) and (g) for said second orientation;

(k) utilizing said rotational rate data sets acquired in step (j) to calculate a corrected rate of rotation of said gyroscope about said elevation axis;

(l) utilizing said gravitational acceleration data sets acquired in step (j) to calculate a corrected gravitational acceleration along said elevation axis;

(m) repeating steps (e) through (g) for said third orientation;

(n) utilizing said rotational rate data sets acquired in step (m) to calculate a corrected rate of rotation of said gyroscope about said lateral axis;

(o) utilizing said gravitational acceleration data sets acquired in step (m) to calculate a corrected gravitational acceleration along said lateral axis;

(p) utilizing said corrected gravitational accelerations acquired in steps (l) and (o) to calculate said bank angle;

(p) utilizing said corrected gravitational accelerations acquired in steps (i), (l) and (o) to calculate said elevation angle; and

(q) utilizing said corrected gravitational accelerations acquired in steps (i), (l) and (o) and said corrected rates of rotation acquired in steps (h), (k) and (n) to calculate said heading direction.

20. The method of claim 19 further comprising utilizing said corrected gravitational accelerations acquired in steps (i), (l) and (o) and said corrected rates of rotation acquired in steps (h), (k) and (n) to calculate an earth latitude location of said gyroscope.

21. The method of claim 19 wherein said known spatial relationship of said gyroscope selected in step (a) includes said first sensitive axis being substantially parallel with said second sensitive axis.

22. The method of claim 21 wherein said substantially parallel first and second sensitive axes of said gyroscope selected in step (a) are substantially concentric.

23. The method of claim 19 wherein said step of calculating the corrected rate of rotation include steps for calculating a corrected rate of rotation.

24. A method for correcting a bias error, comprising:

(a) selecting a sensor having a sensitive axis, said sensor sensing a component vector of a total vector about said sensitive axis, said component vector having a magnitude proportional to a sine or a cosine of an angle between said component vector and said total vector;

(b) orienting said sensor in a first orientation that defines a first direction, said sensitive axis defining a spatial reference axis;

(c) measuring a set of signals from said sensor while said sensor is stationary in said first orientation, said set of signals including at least one signal;

(d) orienting said sensor in a second orientation that defines a second direction, said sensitive axis being substantially parallel with said spatial reference axis, said second direction being substantially opposite said first direction;

(e) repeating step (c) with said sensor in said second orientation;

(f) alternating between the orientations of steps (b) and (d) and performing step (c) after each alternating to obtain a plurality of sets of signals, said plurality of sets of signals numbering at least three; and

(g) calculating a corrected component vector of said sensor about said spatial reference axis utilizing said plurality of sets of signals.

25. The method of claim 24 wherein said step of calculating the corrected component vector includes steps for calculating a corrected component vector.

26. The method of claim 24, wherein said sensor is a gyroscope, said total vector is the earth'"'"'s rotational vector, said spatial reference axis is a heading axis, said component vector is a rate of rotation, and said corrected component vector is a corrected rate of rotation.

27. The method of claim 26 further comprising said step of determining a heading direction from said corrected rate of rotation.

28. A gyrocompass system assembly comprising:

a framework that supports at least one gyro resonator, each of said at least one gyro resonator defining a sensitive axis for detection of a rotation rate thereabout, said rotation rate being caused by the earth'"'"'s rotation, said gyroscope being rotatable about an axis of rotation, said axis of rotation and said sensitive axis of said at least one gyro defining a projected angle that is substantially 90 degrees;

at least one motive driver for rotation of said at least one gyro resonator about said axis of rotation; and

a control system operatively coupled with said at least one motive driver and said at least one gyro resonator for control of and measurement by said gyrocompass system assembly in response to a set of programmed instructions for;

orienting a first of said at least one gyro resonator in a first orientation, said sensitive axis of said first gyro resonator defining a heading axis and a first direction;

using said first of said at least one gyro resonator to measure a first set of indicated rotation rate data;

orienting said first of said at least one gyro resonator in a second orientation using said at least one motive driver, said sensitive axis being substantially parallel to said heading axis and being oriented in a second direction substantially opposite said first direction;

using said first of said at least one gyro resonator to measure a second set of indicated rotation rate data while said at least one gyro resonator is in said second orientation;

using said at least on motive driver to return said first of said at least one gyro resonator to said first orientation; and

using said first of said at least one gyro resonator to measure a third set of indicated rotation rate data while said at least one gyro resonator is in said first orientation.

29. The gyrocompass system assembly of claim 28 wherein said set of programmed instructions further include:

calculating a corrected rate of rotation of said gyrocompass system about said heading axis utilizing at least said first, second and third sets of indicated rotation rate data;

determining said heading direction from said corrected rate of rotation; and

outputting said heading direction.

30. The gyrocompass of claim 28 wherein said means for selectively manipulating and said control system are supported by said framework.

31. The gyrocompass of claim 28 wherein said at least one gyro resonator is selected from the group consisting of one gyro resonator, two gyro resonators and three gyro resonators.

32. A gyrocompass system comprising:

at least one gyro resonator, each of said at least one gyro resonator having a sensitive axis oriented in an initial direction; and

means for offsetting each of said at least one gyro resonators 180°

with respect to said initial direction of each of said at least one gyro resonator.

33. A method surveying a borehole, comprising:

selecting an inertial rate gyroscope configured for insertion into said borehole;

inserting said inertial rate gyroscope a distance into said borehole;

causing said gyroscope to become substantially stationary at said distance;

using said gyroscope while said gyroscope is substantially stationary to obtain a plurality of indicated angular rotation rates, said plurality of indicated angular rotation rates being caused by the earth'"'"'s rotation;

using said plurality of indicated angular rotation rates to cancel a bias associated with said indicated angular rotation rates to provide a plurality of corrected angular rotation rates; and

using said corrected angular rotation rates to infer a heading direction of said gyroscope.

34. The method of claim 33 wherein said step of using said plurality of indicated angular rotation rates to cancel a bias associated with said indicated angular rotation rates to provide a plurality of corrected angular rotation rates comprises steps for canceling a bias associated with said indicated angular rotation rates.

35. The method of claim 34 further comprising using said corrected angular rotation rates to infer a bank angle and an elevation angle of said gyroscope.

36. The method of claim 35 further comprising using said corrected angular rotation rates to infer an earth latitude location of said gyroscope.

37. The method of claim 33 wherein said step of using said plurality of indicated angular rotation rates to cancel said bias associated with said indicated angular rotation rates to provide a plurality of corrected angular rotation rates further comprises using said plurality of indicated angular rotation rates to cancel a change in said bias associated with said plurality of indicated angular rotation rates.

38. The method of claim 37 wherein said step of using said plurality of indicated angular rotation rates to cancel said bias and said change in said bias associated with said indicated angular rotation rates to provide a plurality of corrected angular rotation rates comprises steps for canceling a change in said bias associated with said plurality of indicated angular rotation rates.

39. The method of claim 33 wherein said selecting an inertial rate gyroscope includes selecting a vibrating element gyroscope.

40. A method for determining a heading direction, comprising:

providing an inertial rate gyroscope that includes

a framework that supports at least one gyro resonator, each of said at least one gyro resonator defining a sensitive axis for detection of a rotation rate thereabout, said rotation rate being caused by the earth'"'"'s rotation, said gyroscope being rotatable about an axis of rotation, said axis of rotation and said sensitive axis of said at least one gyro defining a projected angle that is substantially 90 degrees, and

at least one motive driver for rotation of said at least one gyro resonator about said axis of rotation;

providing a set of instructions for;

orienting a first of said at least one gyro resonator in a first orientation, said sensitive axis of said first gyro resonator defining a heading axis and a first direction;

using said first of said at least one gyro resonator to measure a first set of indicated rotation rate data;

orienting said first of said at least one gyro resonator in a second orientation using said at least one motive driver, said sensitive axis being substantially parallel to said heading axis and being oriented in a second direction substantially opposite said first direction;

using said first of said at least one gyro resonator to measure a second set of indicated rotation rate data while said at least one gyro resonator is in said second orientation;

using said at least on motive driver to return said first of said at least one gyro resonator to said first orientation; and

using said first of said at least one gyro resonator to measure a third set of indicated rotation rate data while said at least one gyro resonator is in said first orientation.

41. The method of claim 40 wherein said step of providing a set of instructions further includes:

calculating a corrected rate of rotation of said gyrocompass system about said heading axis utilizing at least said first, second and third sets of indicated rotation rate data;

determining said heading direction from said corrected rate of rotation; and

outputting said heading direction.

42. The method of claim 40 wherein the step of providing an inertial rate gyroscope includes providing a vibrating element gyroscope.

43. The method of claim 40 wherein the step of providing an inertial rate gyroscope includes providing said at least one gyro resonator selected from the group consisting of one gyro resonator, two gyro resonators and three gyro resonators.