Range adaptable system for determining the angular position and distance of a radiating point source and method of employing

• US 7,027,634 B2
• Filed: 02/13/2002
• Issued: 04/11/2006
• Est. Priority Date: 02/13/2002
• Status: Active Grant

• Current Assignee: Northern Digital Inc. (Roper Technologies, Inc.)
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Odell, Don
• Primary Examiner(s): Bali, Vikkram
• Assistant Examiner(s): TUCKER, WESLEY J
• Application Number:
  US10/073,335
• Publication Number:
  US 20030152290A1
• Time in Patent Office: 1,518 Days
• Field of Search: 382/144, 382/145, 3562372- 5
• US Class Current: 382/144
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves

Abstract

A patterned mask is located at a distance from a linear detector array. A point radiating source illuminates the aperture to cast an image onto the array. A computer is employed to identify frequencies in the frequency domain to determine the image scale and shift along the detector array axis. Determination of the magnification of the aperture image is made employing frequency domain techniques, the aperture pattern being re-scaled to match that of the actual image, so that determination of pattern shift can be made. A first embodiment of the present invention has two variations, one of which employs the use of multiple single frequency components and phase methodology, the second of which uses multiple single frequency components as well as a variable frequency component. In a second embodiment, a composite image is also used except that only one single frequency component is used in addition to a non-periodic function.

Claims

1. A system for determining the angular position and distance of a radiating source with respect to a detector, comprising:

a) a radiation detector;

b) a mask spaced in front of said detector, said mask having a plurality of apertures;

c) recording means for recording an image cast onto said detector by radiation passing through said mask;

d) computing means for computing data related to said image, said computing means computing a Fast Fourier Transform (FFT) of the image;

e) identifying means for identifying a highest single frequency of said FFT of the image, said highest single frequency comprising a spectral peak of said FFT;

f) said computing means including means for computing degree of magnification of said image on said detector as compared to size of said image as it passes through said mask by forming a ratio of maximum detected single frequency to known maximum mask single frequency; and

g) determining means for determining angular position of said radiation source with respect to said detector.

2. The system of claim 1, wherein said mask apertures comprise a transmissivity pattern varying in one dimension.

3. The system of claim 2, wherein said one dimension comprises a Y-axis.

4. The system of claim 1, wherein said detector and mask are planar and lie in parallel planes.

5. The system of claim 4, wherein said mask and detector are spaced apart by a known distance.

6. The system of claim 1, wherein said determining means includes means for measuring phase of a low frequency of said image to yield coarse position data.

7. The system of claim 1, wherein said determining means includes means for measuring a variable frequency peak of said image to yield coarse position data.

8. The system of claim 6, wherein said determining means includes means for determining phases of frequency components as well as pattern shifts.

9. The system of claim 7, wherein said determining means includes means for determining phases of frequency components as well as pattern shifts.

10. The system of claim 1, wherein said determining means includes means for magnifying a mask pattern by a desired degree.

11. The system of claim 10, wherein said determining means further includes means for comparing a detector image to a magnified mask pattern using cross-correlation.

12. The system of claim 11, wherein said determining means determines pattern shift of said magnified mask pattern.

13. The system of claim 1, wherein said determining means includes means for determining distance from said radiation source to said detector.

14. A method of determining the angular position and distance of a radiating source with respect to a detector, including the steps of:

a) providing a mask and a detector in parallel planes spaced apart a measured distance;

b) providing said mask with a plurality of apertures;

c) activating a point source of radiation which directs radiation through said apertures of said mask and onto said detector as an image;

d) recording said image;

e) computing a Fast Fourier Transform (FFT) of said image;

f) identifying a highest single frequency component of said FFT of said image, said highest single frequency component comprising a spectral peak of said FFT;

g) computing magnification of said image as compared to a size of said image at said mask by forming a ratio of maximum detected single frequency to known maximum mask single frequency;

h) determining phases of frequency components of said image from f₀ to f_n;

i) determining data resulting from pattern shifts of said frequency components of said image;

j) computing angle of incidence of said source with respect to said detector.

15. The method of claim 14, wherein before said determining phases step, further including the step of using a variable frequency mask to determine variable frequency peak and coarse position.

16. The method of claim 14, wherein, before said determining phases step, further including the step of determining the phase of a lowest frequency F₀ of said image to yield coarse position.

17. The method of claim 14, wherein said determining data step includes the steps of:

a) determining total pattern shift of said image as a sum of frequency component phase shifts;

b) determining shift of a magnified image Y_d; and

c) computing actual unmagnified mask pattern shift Y_m=Y_d/K_mwhere Y_m is the point source, Y_d a detected pattern position and K_m is a pattern magnification factor.

18. The method of claim 14, before said identifying step, further including the step of computing an FFT of said image.

19. A method of determining the angular position and distance of a radiating source with respect to a detector, including the steps of:

a) providing a mask and a detector in parallel planes spaced apart a measured distance;

b) providing said mask with a plurality of apertures;

c) activating a point source of radiation which directs radiation through said apertures of said mask and onto said detector as an image;

d) recording said image;

e) computing a Fast Fourier Transform (FFT) of said image;

f) identifying a highest frequency component of said FFT of said image, said highest frequency component comprising a spectral peak of said FFT;

g) computing magnification of said image as compared to a size of said image at said mask by forming a ratio of maximum detected single frequency to known maximum mask single frequency;

h) magnifying said image at said mask pattern by a magnification factor K_m;

i) comparing detector image to magnified mask pattern using cross-correlation; and

j) determining angle of incidence of said source with respect to said detector.

20. The method of claim 19, before said identifying step, further including the step of computing an FFT of said image.

21. The method of claim 19, wherein said determining angle of incidence step includes the steps of:

a) determining pattern shift of magnified image; and

b) computing actual unmagnified mask pattern shift.

22. The method of claim 19, wherein said identifying step includes the step of encoding a single frequency component sequentially.