Method and Apparatus for Precision Azimuth Measurement

• US 20100088063A1
• Filed: 10/01/2009
• Published: 04/08/2010
• Est. Priority Date: 10/01/2008
• Status: Abandoned Application

• Current Assignee: Tech Corporation Company Limited
• Original Assignee: Tech Corporation Company Limited
• Inventors: Laughlin, Darren R.
• Application Number:
  US12/572,181
• Publication Number:
  US 20100088063A1
• Time in Patent Office: Days
• US Class Current: 702/151
• CPC Class Codes: G01C 19/14 Fluid rotors
• CPC Class Codes: G01C 19/38 with north-seeking action by other than magnetic means, e.g. gyrocompasses using earth's rotation

Abstract

Method and apparatus for precise measurement of azimuth. An angular rate sensor is rotated so its sensitive axis periodically aligns with the horizontal component of the earth'"'"'s spin rate (north). A preferably sinusoidal signal is analyzed with respect to the relative angle of the sensor and a desired direction in order to determine the azimuth of that direction.

Claims

1. An apparatus for measuring azimuth, the apparatus comprising:

an angular rate sensor disposed on a turntable; and

a data collector for collecting an output from said angular rate sensor while said turntable is rotating.

2. The apparatus of claim 1 wherein a sensitive axis of said angular rate sensor is substantially parallel to said plane of rotation.

3. The apparatus of claim 1 wherein said turntable rotates at a substantially constant rotation rate.

4. The apparatus of claim 3 wherein said rotation rate is between approximately 0.5 Hz and approximately 30 Hz.

5. The apparatus of claim 1 wherein said turntable comprises an encoder for providing an angle of rotation of said turntable relative to a turntable base.

6. The apparatus of claim 1 wherein a size of said apparatus is less than approximately 200 cc.

7. The apparatus of claim 6 wherein a size of said apparatus is less than approximately 150 cc.

8. The apparatus of claim 1 wherein a weight of said apparatus is less than approximately 1 kg.

9. The apparatus of claim 8 wherein a weight of said apparatus is less than approximately 500 g.

10. The apparatus of claim 9 wherein a weight of said apparatus is less than approximately 250 g.

11. The apparatus of claim 1 comprising two or more angular rate sensors.

12. The apparatus of claim 1 wherein said turntable is oriented so that its plane of rotation is approximately normal to a gravity vector or its axis of rotation is parallel to a gravity vector.

13. A method for detecting azimuth, the method comprising the steps of:

selecting a zero angle of a turntable to be coincident with a desired direction;

rotating an angular rate sensor on the turntable;

collecting an output signal from the sensor while the sensor is rotating;

measuring an angle of rotation of the turntable relative to the zero angle; and

calculating the azimuth of the desired direction.

14. The method of claim 13 wherein the rotating step comprising rotating the angular rate sensor at a substantially constant rotation rate.

15. The method of claim 14 wherein the rotation rate is between approximately 0.5 Hz and approximately 30 Hz.

16. The method of claim 13 wherein the calculating step comprises correlating the angle of rotation to a characteristic of the output signal.

17. The method of claim 16 wherein the characteristic is selected from the group consisting of phase, maximum, minimum and zero crossing point.

18. The method of claim 17 further comprising the step of applying a bandpass filter to the output signal prior to detecting the zero crossing points.

19. The method of claim 18 wherein the bandpass filter cutoff frequency is approximately a rotation rate of the turntable.

20. The method of claim 13 wherein the calculating step comprises applying a Fast Fourier Transform to the output signal.

21. The method of claim 13 wherein the rotating step comprises rotating the angular rate sensor clockwise at a constant rotation rate and counterclockwise at the same constant rotation rate.

22. The method of claim 21 further comprising adding a clockwise output signal phase to a counterclockwise output signal phase.

23. The method of claim 13 wherein the azimuth is detected with an accuracy of less than approximately 1 mrad in less than approximately one minute from beginning the rotating step.

24. The method of claim 23 wherein the azimuth is detected with an accuracy of less than approximately 0.1 mrad in less than approximately one minute from beginning the rotating step.