Accurate target orientation measuring system

• US 7,400,416 B2
• Filed: 01/06/2006
• Issued: 07/15/2008
• Est. Priority Date: 01/07/2005
• Status: Active Grant

• Current Assignee: Automated Precision Inc.
• Original Assignee: Automated Precision Inc.
• Inventors: Lau, Kam C.
• Primary Examiner(s): STAFIRA, MICHAEL PATRICK
• Application Number:
  US11/326,287
• Publication Number:
  US 20060192090A1
• Time in Patent Office: 921 Days
• Field of Search: 356 3- 22
• US Class Current: 356/614
• 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 received laser beam, the measurement retro-reflector having an aperture disposed therein for transmitting the laser beam;

a reference retro-reflector disposed within the target for transmitting only background radiation, wherein the reference retro-reflector is substantially similar to the measurement retro-reflector and is located adjacent to the measurement retro-reflector;

a laser light sensor that registers an image of the transmitted laser beam and the transmitted background radiation; and

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

2. The system of claim 1, wherein the laser light sensor comprises:

a reference portion for detecting the background radiation transmitted by the reference retro-reflector; and

a measurement portion for detecting the laser beam and the background radiation transmitted by the measurement retro-reflector, wherein the reference portion and the measurement portion are substantially similar.

3. The system of claim 2, wherein the laser light sensor includes a camera based on at least one of CMOS or CCD technology.

4. The system of claim 3, wherein the camera has dimensions of about 0.5 inches by 0.4 inches and a pixel size of about 10 microns or less.

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

6. The system of claim 5, wherein the aperture has a size of about one millimeter or less.

7. The system of claim 1, further comprising a tracking unit that emits the laser beam to the target, wherein the tracking unit is positioned to screen out the background radiation incident toward the target within a critical angle of divergence from the laser beam.

8. The system of claim 1, further comprising a filter positioned between the laser light sensor and one or more of the measurement retro-reflector or the reference retro-reflector, wherein the filter preferentially filters the background radiation transmitted by one or more of the measurement retro-reflector or the reference retro-reflector and reduces an intensity of the background radiation image registered by the laser light sensor.

9. 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 the background radiation transmitted through a second retro-reflector disposed within the target;

establishing a reference point within each of the background image and the measurement image; and

subtracting the background image from the measurement image using the reference points established for each of the background image and the measurement image.

10. The method of claim 9, 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.

11. The method of claim 10, further comprising determining an image centroid from the corrected measurement image.

12. The method of claim 11, further comprising performing a pattern recognition routine to refine a position of the corrected measurement image.

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

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

collecting the laser beam image from a laser beam passing through an aperture disposed within a target and impinging on the laser light sensor;

determining a centroid of the laser beam image; and

determining an orientation of the target from a position of the centroid.

14. The method of claim 13, further comprising filtering background radiation transmitted through the aperture.

15. The method of claim 13, further comprising performing a pattern recognition routine to refine a position of the laser beam image.

16. The method of claim 13, further comprising selecting a size for the aperture size based on a critical angle, wherein background radiation passing through the aperture within the critical angle is separated from the laser beam image.

17. The method of claim 13, wherein the aperture is defined by a polished surface of a solid retro-reflector.

18. The method of claim 13, wherein the position of the centroid is defined relative to an origin position of the laser light sensor.

19. The method of claim 18, wherein a reference target orientation produces a laser beam image centered on the origin position.