Nadir/zenith inertial pointing assistance for two-axis gimbals

Patent metadata

Field	Value
Publication number	US-9482530-B2
Application number	US-201314072559-A
Country	US
Kind code	B2
Filing date	Nov 5, 2013
Priority date	Nov 5, 2013
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

Abstract

Control systems and methods are provided for improved azimuthal pointing control near gimbal zenith/nadir in two-axis gimbal systems mounted to moveable platforms. The system includes a two-axis gimbal and a two-axis pointing device mounted to the two-axis gimbal. The two-axis pointing device directs a line of sight axis based upon a commanded steering direction and movement of the platform in the inertial frame of the line of sight. The two-axis gimbal follows the movement of the two-axis pointing device, keeping the two-axis pointing device from encountering its mechanical limits. In this manner, inertial pointing control is maintained in the near gimbal zenith/nadir regime.

First claim

What is claimed is:

1. A method of azimuthal pointing of a line of sight (LOS), comprising:
measuring, at a two-axis gimbal having an azimuth gimbal, an elevation gimbal, and a line of sight and kinematically coupled to a moveable platform:
an acceleration of the moveable platform in an inertial frame of the line of sight, due to a motion of the moveable platform; and
an acceleration of the azimuth gimbal relative to the platform, due to the motion of the moveable platform;

generating, by one or more processors, a first command signal commanding deflection of a two-axis pointing device kinematically coupled to the two-axis gimbal and positioned in the optical path of the line of sight, the first command signal based upon the measured acceleration of the moveable platform and an acceleration rate command representative of a relative target motion with respect to the azimuth gimbal;
measuring, in the line of sight inertial frame, the deflection of the two-axis pointing device responsive to the first command signal; and
generating, by the one or more processors, a second command signal commanding deflection of the azimuth gimbal based upon the deflection of the two-axis pointing device and the measured acceleration of the azimuth gimbal.

2. The method of claim 1 , wherein the first and second command signals are generated when the elevation gimbal is oriented at a selected angle.

3. The method of claim 1 , wherein generating the second command signal further comprises generating the second command signal based upon the relative target motion.

4. The method of claim 1 , further comprising generating, by the one or more processors, a third command signal commanding deflection of the azimuth gimbal, the third command signal based upon the measured acceleration of the azimuth gimbal and the second command signal, wherein upon receipt of the third command signal by the azimuth gimbal, the azimuth gimbal moves so as to counter at least a portion of the deflection of the two-axis pointing device.

5. The method of claim 4 , further comprising generating, by the one or more processors, an updated relative target motion based upon the deflection of the two-axis pointing device and the deflection of the azimuth gimbal responsive to the third command signal.

6. The method of claim 1 , wherein generating the first command signal further comprises converting the acceleration of the moveable platform and the target acceleration into a frame of reference of the two-axis pointing device.

7. The method of claim 1 , wherein generating the second command signal further comprises converting the acceleration of the azimuth gimbal into an azimuth gimbal angle in the frame of reference of the moveable platform and converting the deflection of the two-axis pointing device from a frame of reference of the two-axis pointing device into a deflection of the two-axis pointing device in the frame of reference of the moveable platform.

8. An azimuthal pointing system, comprising:
a two-axis gimbal kinematically coupled to a moveable platform, the two-axis gimbal further including an elevation gimbal, an azimuth gimbal, and a line of sight;
a two-axis pointing system kinematically coupled to the two-axis gimbal and inserted within the optical path of the line of sight;
a first sensor adapted to measure the angle and rate of the azimuth gimbal relative to the moveable platform;
a second sensor adapted to measure inertial motion of the line of sight;
one or more processors adapted to generate:
a first command signal commanding deflection of the two-axis pointing device, the first command signal based upon:
a measurement, by the second sensor, of an acceleration of the moveable platform in an inertial frame of the line of sight, due to a motion of the moveable platform; and
an acceleration rate command representative of a relative target motion with respect to the azimuth gimbal; and

a second command signal for commanding deflection of the azimuth gimbal, the second command signal based upon:
the deflection of the two-axis pointing device responsive to the first command signal; and
a measurement, by the first sensor, of an acceleration of the azimuth gimbal with respect to the moveable platform, due to the motion of the moveable platform.

9. The system of claim 8 , wherein the one or more processors is further adapted to generate the second command signal based upon the rate command.

10. The system of claim 9 , wherein the one or more processors is further adapted to generate a third command signal commanding deflection of the azimuthal gimbal, the third command signal based upon the acceleration of the azimuth gimbal and the second command signal.

11. The system of claim 8 , wherein the two-axis pointing device comprises an optical beam steering device adapted to steer the line of sight with respect to two rotation axes.

12. A non-transitory computer-readable medium having computer-readable program codes embedded thereon for comparing decision options, the computer-readable program codes including instructions that, when executed by a processor, cause the processor to:
measure, at a two-axis gimbal having an azimuth gimbal, an elevation gimbal, and a line of sight and kinematically coupled to a moveable platform:
an acceleration of the moveable platform, in an inertial frame of the line of sight, due to a motion of the moveable platform; and
an acceleration of the azimuth gimbal, relative to the platform, due to the motion of the moveable platform;

generate a first command signal commanding deflection of a two-axis pointing device kinematically coupled to the two-axis gimbal and positioned within the optical path of the line of sight, the first command signal based upon the measured acceleration of the moveable platform and a relative target motion with respect to the azimuth gimbal;
measure, in the line of sight inertial frame, the deflection of the two-axis pointing device responsive to the first command signal; and
generate a second command signal commanding deflection of the azimuth gimbal based upon the deflection of the two-axis pointing device and the measured acceleration of the azimuth gimbal.

13. The computer-readable medium of claim 12 , further including instructions that, when executed, cause the processor to generate the second command signal based upon the relative target motion.

14. The computer-readable medium of claim 12 , further including instructions that, when executed, cause the processor to generate a third command signal commanding deflection of the azimuth gimbal based upon the measured acceleration of the azimuth gimbal and the second command signal.

15. The computer-readable medium of claim 14 , further including instructions that, when executed, cause the processor to generate an updated acceleration command commanding deflection of the azimuth gimbal based upon the deflection of the two-axis pointing device and the deflection of the azimuth gimbal responsive to the third command signal.

16. The computer-readable medium of claim 12 , further including instructions that, when executed, cause the processor to convert the acceleration of the azimuth gimbal into an azimuth gimbal angle in the frame of reference of the moveable platform and converting the deflection of the two-axis pointing device from a frame of reference of the two-axis pointing device into a deflection of the two-axis pointing device in the frame of reference of the moveable platform.

Assignees

• Raytheon Co

Inventors

• Norman Walter W
• Villarreal Armando

Classifications

• H04N23/685

  performed by mechanical compensation · CPC title

• H04N23/68

  for stable pick-up of the scene, e.g. compensating for camera body vibrations · CPC title

• H04N23/6812

  based on additional sensors, e.g. acceleration sensors · CPC title

• G01C19/42

  for indicating rate of turn; for integrating rate of turn · CPC title

• G01P15/003

  Kinematic accelerometers, i.e. measuring acceleration in relation to an external reference frame, e.g. Ferratis accelerometers (G01P15/001, G01P15/16, G01P15/165 take precedence) · CPC title