AZ/EL gimbal housing characterization

• US 9,243,931 B2
• Filed: 11/28/2012
• Issued: 01/26/2016
• Est. Priority Date: 11/28/2012
• Status: Active Grant

• Current Assignee: DRS Sustainment Systems, Inc (Leonardo S.p.A.)
• Original Assignee: DRS Sustainment Systems, Inc (Leonardo S.p.A.)
• Inventors: Linton, Thomas D., Folmer, Jeffrey S., Fitzgerald, Jeffrey S.
• Primary Examiner(s): Fitzgerald, John
• Assistant Examiner(s): Woodward, Nathaniel T
• Application Number:
  US13/687,929
• Publication Number:
  US 20150285660A1
• Time in Patent Office: 1,154 Days
• Field of Search: 73/17.5, 73/10.1
• US Class Current: 1/1
• CPC Class Codes: G01C 19/54 with correction for acceleration forces due to movement of instrument
• CPC Class Codes: G01C 21/18 Stabilised platforms, e.g. by gyroscope
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

Methods, devices, and systems are presented for calibrating or otherwise correcting the pointing accuracy of a gimbal. Measurements of the actual planes of rotation of each of a gimbal'"'"'s rotatable elements is made using an off-board measurement device, such as a coordinate measuring machine (CMM). The measurements from the off-board device can be combined with those from native, on-board gimbal sensors of the rotation angles at which the planes are tilted/pitched with respect to their nominal planes of rotation. Information representing the error vectors between the nominal and actual planes of rotation is stored and used for correcting the pointing accuracy of the gimbal. The corrected pointing vector of the gimbal can be combined with measurements from an inertial measurement unit (INU) and rangefinder in order to accurately determine a geographic target position to which the gimbal points.

Claims

1. A method for calibrating a gimbal assembly, the method comprising:

providing a gimbal assembly having a non-rotatable base and a steerable section, the steerable section having portions configured to rotate around a nominal azimuth axis and a nominal elevation axis;

steadying the gimbal assembly base;

measuring locations of a first single point affixed to the steerable section at different rotation angles of the steerable section around the nominal azimuth axis;

measuring locations of a second single point affixed to the steerable section at different elevation angles of the steerable section around the nominal elevation axis;

calculating an actual azimuth axis from the measurements at the different rotation angles of the steerable section around the nominal azimuth axis;

calculating an actual elevation axis from the measurements at the different rotation angles of the steerable section around the nominal elevation axis;

determining an azimuth axis error between the actual azimuth axis and the nominal azimuth axis;

determining an elevation axis error between the actual elevation axis and the nominal elevation axis;

storing information representing the azimuth axis error and elevation axis error;

steering the steerable section of the gimbal assembly to point to a direction in space;

acquiring a nominal pointing vector of the steerable section from a rotation angle around the nominal azimuth axis and a rotation angle around the nominal elevation axis; and

transforming the nominal pointing vector to a corrected pointing vector using the stored information representing the azimuth and elevation axis errors.

2. The method of claim 1 wherein the acquiring is performed using an encoder connected with the gimbal assembly.

3. The method of claim 1 further comprising:

determining a geographic target position at which the gimbal assembly points using an inertial navigation unit (INU), encoders connected with the gimbal assembly, the stored information representing the azimuth axis error and elevation axis error, and a laser rangefinder.

4. The method of claim 1 further comprising:

inserting an alignment pin into the gimbal assembly between measuring around the nominal azimuth axis and measuring around the nominal elevation axis.

5. The method of claim 1 wherein the steadying the gimbal assembly base is selected from the group consisting of setting the base on a flat surface without attachment and bolting the base to an object.

6. The method of claim 1 further comprising:

measuring locations of points on an axle of the gimbal assembly in order to determine the nominal azimuth or elevation axis.

7. The method of claim 1 further comprising:

changing a temperature of the gimbal assembly;

repeating the measurings, calculatings, and determinings of axis errors in order to update the stored information representing the azimuth axis error and elevation axis error.

8. The method of claim 1 wherein at least one of the measurings is conducted using both a coordinate-measuring machine and an encoder connected with the gimbal assembly.

9. The method of claim 8 wherein the information representing the azimuth axis error and elevation axis error includes storing:

an angle magnitude of the azimuth axis error;

a direction of the azimuth axis error;

an angle magnitude of the elevation axis error,

a direction of the elevation axis error; and

wherein the stored direction of the azimuth axis error or direction of the elevation axis error is with respect to a direction indicated by the encoder.

10. The method of claim 1 wherein the gimbal assembly is selected from the group consisting of a pan-tilt gimbal and a ball head gimbal.

11. The method of claim 10 wherein the gimbal is a pan-tilt gimbal and includes a half-yoke or full-yoke assembly.

12. The method of claim 1 wherein the first and second points affixed to the steerable section are the same point.

13. The method of claim 12 further comprising:

attaching a removable construction ball to the steerable section for the measurements, wherein the first and second points are at a geometric center of the construction ball.

14. The method of claim 13 wherein the measuring is conducted using a coordinate-measuring machine.

15. The method of claim 13 wherein the construction ball is mounted on the end of a rod.

16. A method for calibrating a gimbal assembly, the method comprising:

measuring a first location of a point affixed to a steerable section of a gimbal assembly with a coordinate measuring machine (CMM) in conjunction with an encoder embedded in the gimbal assembly; and

then

rotating the steerable section around a first nominal axis of the gimbal assembly; and

then

measuring a second location of the same point affixed to the steerable section with the CMM and the encoder after the rotating; and

then

calculating a first actual axis around which the steerable section was rotated using the measurements of the CMM and encoder;

determining a direction and magnitude of an axis error between the first actual axis and the first nominal axis; and

transforming a nominal pointing vector indicated by the encoder to a corrected pointing vector using the direction and magnitude of the axis error.

17. The method of claim 16 further comprising:

revolving the steerable section around a second nominal axis of the gimbal assembly; and

then

measuring a third location of the same point affixed to the steerable section with the CMM and a second encoder after the revolving; and

then

calculating a second actual axis around which the steerable section was revolved using the measurements of the CMM and second encoder;

determining a direction and magnitude of a second axis error between the second actual axis and the second nominal axis; and

transforming a nominal pointing vector indicated by the second encoder to the corrected pointing vector using the direction and magnitude of the second axis error.

18. The method of claim 16 further comprising:

determining a geographic target position at which the gimbal assembly points using an inertial navigation unit (INU), the corrected pointing vector, and a laser rangefinder.

19. A method for calibrating a gimbal assembly, the method comprising:

selecting a point affixed to a steerable section of a gimbal assembly, the steerable section configured to be steered by rotating portions of the steerable section around at least two nominal axes;

measuring locations of the point at different rotation angles of the nominal axes using an off-board measuring device and on-board encoders embedded within the gimbal assembly;

calculating actual axes from the measurements;

determining errors between the calculated actual axes and their respective nominal axes; and

computing a transform between a nominal pointing vector indicated by the embedded encoders and a corrected pointing vector using the determined errors.

20. The method of claim 19 further comprising:

determining a geographic target position at which the gimbal assembly points using an inertial navigation unit (INU), the corrected pointing vector, and a laser rangefinder.