System and method for north finding

• US 9,417,064 B2
• Filed: 11/09/2011
• Issued: 08/16/2016
• Est. Priority Date: 11/11/2010
• Status: Active Grant

• Current Assignee: Israel Aerospace Industries Limited (Government of Israel)
• Original Assignee: Israel Aerospace Industries Limited (Government of Israel)
• Inventors: Kagan, Avraham, Benisty, Michael
• Primary Examiner(s): Tsai, Carol S. W.
• Application Number:
  US13/884,856
• Publication Number:
  US 20130238280A1
• Time in Patent Office: 1,742 Days
• Field of Search: 702/105, 702/150, 333/23, 333/24, 333/21, 333/18, 333/16, 735/040.2, 735/041.6, 735/041.2, 735/10, 342/60, 342/62
• US Class Current: 1/1
• CPC Class Codes: G01C 17/00 Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes using gyroscopic effect G01C19/00
• 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 21/18 Stabilised platforms, e.g. by gyroscope

Abstract

A payload including a gimbal assembly and gyro assembly that includes a gyro assembly control associated with the gyro assembly and operable to trigger the gyro assembly to obtain deviation measurements and process the measurements in a first dynamic range for stabilizing the payload utilizing the gimbal assembly. The gyro assembly control is operable to trigger the gyro assembly to obtain instantaneous measurements and process the measurements in a second dynamic range having different sensitivity than the first dynamic range, for finding deviation of the payload from the magnetic north of the earth.

Claims

1. A payload including a gimbal assembly and associated gyro assembly, comprising

a gyro assembly control associated with said gyro assembly and operable to trigger the gyro assembly to obtain deviation measurements in the azimuth plane and elevation plane and process the measurements in a first dynamic range corresponding to a first rotation rate range, for stabilizing the payload utilizing said gimbal assembly;

the gyro assembly control being operable to trigger the gyro assembly to obtain instantaneous measurements from an elevation rate gyro and process the measurements in a second dynamic range corresponding to a second rotation rate range having more sensitivity than said first dynamic range, for finding deviation of the payload from the north of the earth.

2. The payload according to claim 1, wherein said gyro assembly includes an azimuth rate gyro and an elevation rate gyro disposed perpendicularly thereto;

said gyro assembly control being operable to drive said elevation rate gyro to rotate about azimuth axis for obtaining and recording instantaneous measurements during at least 360°

rotation;

said gyro assembly control being further operable to derive a wander angle representative of said deviation from the north based on said recorded measurements.

3. The payload according to claim 2, wherein said gyro assembly control module is configured to calculate a sine wave that fits said measurements and derives said wander angle from said sine wave.

4. The payload according to claim 2 wherein the longer the duration t of said rotation about said azimuth axis, the lower the error of said measurements.

5. The payload according to claim 2, wherein said measurements yield:

Measurements=Ω

*cos(φ

)*cos(α

)

where Ω

stands for the earth rotation rate

φ

stands for the latitude

α

stands for the wander angle that changes according to instantaneous measurements of the elevation rate gyro during the at least 360°

rotation,

and wherein said deviation being a phase shift α

of the sine wave that fits said measurements.

6. The payload according to claim 1, further comprising a tilt sensor for sensing tilt measurements of the payload in either or both of roll and pitch axes, and wherein said gyro assembly control is configured to calculate compensation commands for transmission to said gimbal assembly for reducing or elimination said tilt measurements, whereby said payload is rendered leveled.

7. The payload according to claim 1, wherein said payload is fitted on a mobile platform that is subjected to spatial orientation deviations in either or both of azimuth plane or elevation plane, and wherein said spatial deviations are measured by said gyro assembly and wherein said measurements are processed by said gyro assembly control to obtain compensation commands for triggering the gimbal assembly to compensate for said spatial deviations and stabilize the payload.

8. The payload according to claim 2, wherein said payload is fitted on a mobile platform that is subjected to spatial orientation deviations in either or both of azimuth plane or elevation plane, and wherein said spatial deviations in the azimuth plane are measured by said azimuth rate gyro irrespective of said 360°

rotation and wherein said spatial deviations in said elevation plane are measured by said elevation rate gyro irrespective of said 360°

rotation and wherein said measurements are processed by said gyro assembly control to obtain data for triggering the gimbal assembly to compensate for said deviations and stabilize the payload.

9. The payload according to claim 1, wherein said sensitivity is dependent upon the rotation rate of the gyros in the stabilization mode of operation.

10. The payload according to claim 9, wherein the rotation rate is 100[°

/s].

11. The payload according to claim 1, wherein said sensitivity is dependent upon a tradeoff parameter.

12. The payload according to claim 11, wherein said tradeoff parameter is 5%.

13. A payload according to claim 1, wherein said sensitivity is dependent upon the rotation rate of the gyros in the stabilization mode of operation.

14. A method for dual mode utilization of a payload that includes a gimbal assembly and associated a gyro assembly, comprising:

(i) triggering the gyro assembly to obtain deviation measurements in the azimuth plane and elevation plane and process the measurements in a first dynamic range corresponding to a first rotation rate range, for stabilizing the payload utilizing said gimbal assembly;

(ii) triggering the gyro assembly to obtain instantaneous measurements from an elevation rate gyro and process the measurements in a second dynamic range corresponding to a second rotation rate range having more sensitivity than said first dynamic range, for finding deviation of the payload from the north of the earth.

15. The method according to claim 14 wherein said gyro assembly includes an azimuth rate gyro and an elevation rate gyro disposed perpendicularly thereto, further comprising driving said elevation rate gyro to rotate about azimuth axis for obtaining and recording instantaneous measurements during at least 360°

rotation; and

deriving a wander angle representative of said deviation from the north based on said recorded measurements.

16. The method according to claim 15, further comprising calculating a sine wave that fits said measurements and derives said wander angle from said sine wave.

17. The method according to claim 15, wherein the longer the duration t of said rotation about said azimuth axis, the lower the error of said measurements.

18. The method according to claim 15, wherein said measurements yield:

Measurements=Ω

*cos(φ

)*cos(α

),

where Ω

stands for the earth rotation rate

φ

stands for the latitude

α

stands for the wander angle that changes according to instantaneous measurements of the elevation rate gyro during the at least 360°

rotation, and wherein said deviation being a phase shift α

of the sine wave that fits said measurements.

19. The method according to claim 14, further comprising sensing tilt measurements of the payload in either or both of roll and pitch axes;

and calculating compensation commands for transmission to said gimbal assembly for reducing or elimination said tilt measurements, whereby said payload is rendered leveled.

20. The method according to claim 16, and further comprising measuring said spatial deviations and processing said measured deviations to obtain compensation commands for triggering the gimbal assembly to compensate for said spatial deviations and stabilize the payload.