Accurate target orientation measuring system

• US 20060192090A1
• Filed: 01/06/2006
• Published: 08/31/2006
• Est. Priority Date: 01/07/2005
• Status: Active Grant

• Current Assignee: Automated Precision Inc.
• Original Assignee: Automated Precision Inc.
• Inventors: Lau, Kam C.
• Granted Patent: US 7,400,416 B2
• Time in Patent Office: Days
• US Class Current: 250/221
• CPC Class Codes: G01S 3/784 using a mosaic of detectors

Abstract

A system for accurate determination of target orientation in a laser tracking system. A target aperture is configured to produce spatially distinct laser beam and background images. A processing unit is configured to determine a centroid of the laser beam image position using information collected from detected images, such as laser beam and background images. The laser beam image centroid position is used to determine an accurate target orientation. In one example, a process for determining target orientation includes the steps of collecting a background image passing through a first retro-reflector at a first laser light sensor; 2) collecting a measurement image passing through a second retro-reflector at a second laser light sensor; 3) establishing a common positional reference point for the measurement image and the background image; 4) subtracting the background image from the measurement image based on the common positional reference point.

Claims

1. A system for accurate target orientation measurement, comprising:

a target capable of pitch and yaw movements;

a measurement retro-reflector disposed within the target for transmitting a portion of a received laser beam;

an aperture disposed in the measurement retro-reflector that defines a transmitted laser beam;

a detector that registers a laser beam image of the transmitted laser beam; and

a processing unit that receives position information of the laser beam image and determines pitch and yaw movement of the target, wherein the aperture size is smaller than a critical size above which a background light image interferes with the laser beam image, the background light image formed from background light.

2. The system of claim 1, further comprising a reference retro-reflector configured to receive and transmit to the laser light sensor only background radiation, wherein the reference retro-reflector is substantially similar to the measurement retro-reflector, and wherein the reference retro-reflector is located adjacent to the measurement retro-reflector.

3. The system of claim 2, wherein the detector comprises:

a reference portion for detecting background radiation received through the reference retro-reflector; and

a measurement portion for detecting the transmitted laser beam and background radiation, wherein the portions are configured in a substantially similar fashion.

4. The system of claim 3, wherein the detector is a camera based on one of CMOS and CCD technology.

5. The system of claim 4, the camera having dimensions of about 0.5″

×

0.4″ and

having a pixel size of less than about 10 microns.

6. The system of claim 1, wherein the measurement retroreflector comprises a solid retro-reflector that includes a small flat polished surface that defines the aperture.

7. The system of claim 6, the aperture having a size less than about one mm.

8. The system of claim 1, further comprising a tracking unit that sends the laser beam to the target and screens out background light incident toward the target within a critical angular divergence from the laser beam.

9. The system of claim 1, further comprising a filter that preferentially filters background light and reduces image intensity of background light on the detector.

10. A method for accurate target orientation determination, comprising:

collecting a background image from background radiation transmitted through a first retro-reflector disposed within the target;

collecting a measurement image from a laser beam and background radiation transmitted through a second retro-reflector disposed within the target;

establishing a reference point within each image; and

subtracting the background image from the measurement image.

11. The method of claim 10, further comprising sending the background image and the measurement image to a processing unit, wherein the subtracting the background image from the measurement image produces a corrected measurement image.

12. The method of claim 11, further comprising determining an image centroid from the corrected beam image.

13. The method of claim 12, further comprising performing a pattern recognition routine to refine a position of the corrected measurement image.

14. A method for accurate target orientation determination, comprising:

collecting a background image at a position on a detector predetermined to be spatially separate from a laser beam image;

collecting a laser beam image of a laser beam passing through a target aperture and impinging on the detector;

determining a centroid of the laser beam image; and

determining the target orientation from a position of the centroid.

15. The method of claim 14, further comprising filtering background light transmitted through the target aperture.

16. The method of claim 14, further comprising performing a pattern recognition routine to refine a location of the laser beam image.

17. The method of claim 14, further comprising selecting an aperture size based on a critical angle, wherein background radiation passing through the aperture is separated from the laser beam image.

18. The method of claim 14, wherein the target aperture is defined by a polished surface of a solid retroreflector.

19. The method of claim 14, wherein the position of the centroid is defined relative to an origin position of the detector.

20. The method of claim 19, wherein a reference target orientation produces a laser beam image centered on the origin position.