Sensor for determining the angular position of a radiating point source in two dimensions and method of operation

• US 7,161,686 B2
• Filed: 11/13/2003
• Issued: 01/09/2007
• Est. Priority Date: 11/13/2003
• Status: Expired due to Fees

• Current Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Odell, Don, Duling, Alec
• Primary Examiner(s): Toatley, Jr.; Gregory J.
• Assistant Examiner(s): Nguyen; Sang H.
• Application Number:
  US10/705,853
• Publication Number:
  US 20050105101A1
• Time in Patent Office: 1,153 Days
• Field of Search: 356614-625, 356/638, 356/604, 356/610, 356/141.5, 356/141.2, 250/206.2, 250/206.1, 250/203.4, 250/203.R, 250/216, 250/237.R, 250/204.4
• US Class Current: 356/614
• CPC Class Codes: A61B 2090/3937 Visible markers
• CPC Class Codes: A61B 2090/3945 Active visible markers, e.g. light emitting diodes
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: G01D 2205/90 Two-dimensional encoders, i.e. having one or two codes extending in two directions
• CPC Class Codes: G01D 5/34 the beams of light being detected by photocells
• CPC Class Codes: G01D 5/347 using displacement encoding scales
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders
• CPC Class Codes: G01S 3/781 Details
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80

Abstract

A sensor for determining the angular position of a radiating point source in two dimensions includes a mask encoded in two skewed directions with waveforms consisting of several frequencies in prescribed patterns. The frequency spectra of the received detector patterns are computed. In order to facilitate such computations, the constituent frequencies are separated so as to be distinguished in the Fast Fourier Transform (FFT). Each of the frequency patterns that are coded on the variable transmissivity mask consists of a series of low frequencies followed by a series of variable frequencies, and a series of high frequencies. The variable frequencies exhibit frequency changes responsive to various image positions. The low and high frequencies are responsive in phase to variations in image position. The frequency variations in the variable frequencies are used to indicate coarse position while the phases of the fixed low and high frequencies are used to indicate medium and fine position. In a second embodiment, the mask pattern is formed by a first pattern including low variable and high frequency components, a second pattern with fixed low and high frequency components, and a third pattern with variable frequency components. The method of determining position is also disclosed.

Claims

1. A sensor for determining angular position of a radiating point source in two dimensions, comprising:

a) a point source of light located in a prescribed space;

b) a light detector adjacent said space;

c) a two-dimensional mask interposed between said detector and said space, said mask having a two-dimensional surface pattern thereon formed by a prescribed pattern of frequencies and said surface pattern being entirely exposed to said space;

d) whereby light from said source travels through said mask and onto said detector, said surface pattern causing at least one of phase or frequency changes to occur, said changes being used to calculate angular position of said point source of light with respect to said detector in two dimensions.

2. The sensor of claim 1, wherein said surface pattern includes at least one series of frequencies extending along a line consisting of at least one low frequency, at least one variable frequency, and at least one high frequency.

3. The sensor of claim 2, wherein said at least one series comprises a first series extending along a first line, and further including a second series extending along a second line and consisting of at least one low frequency, at least one variable frequency, and at least one high frequency.

4. The sensor of claim 3, wherein said first and second lines are orthogonal.

5. The sensor of claim 2, wherein said at least one series comprises a first series extending along a first line, and further including a second series extending along a second line.

6. The sensor of claim 5, wherein said second series consists of fixed low and high frequency components.

7. The sensor of claim 6, wherein a third series of frequencies is provided along a third line.

8. The sensor of claim 7, wherein said third series includes variable frequency components.

9. The sensor of claim 8, wherein said lines are non-parallel.

10. The sensor of claim 5, wherein said second series consists of variable frequency components.

11. The sensor of claim 10, wherein a third series of frequencies is provided along a third line.

12. The sensor of claim 11, wherein said lines are non-parallel.

13. The sensor of claim 2, wherein said at least one of phase or frequency changes comprises phase and frequency changes.

14. The sensor of claim 13, wherein said low and high frequencies exhibit phase variations.

15. The sensor of claim 13, wherein said variable frequency exhibits frequency variations on said detector.

16. The sensor of claim 15, wherein frequency variations are used to make coarse position measurements while phase variations are used to make medium and fine position measurements.

17. The sensor of claim 1, wherein said mask and detector lie in parallel planes.

18. The sensor of claim 1, wherein said at least one of phase or frequency changes comprises phase and frequency changes.

19. A sensor for determining angular position of a radiating point source in two dimensions, comprising:

a) a point source of light located in a prescribed space;

b) a light detector adjacent said space;

c) a two-dimensional mask interposed between said detector and said space, said mask having a two-dimensional surface pattern thereon formed by a prescribed pattern of frequencies, said frequency pattern comprising first and second orthogonal lines, each of said lines having a series of frequencies thereon consisting of at least one low frequency, at least one variable frequency, and at least one high frequency;

d) whereby light from said source travels through said mask and onto said detector, variations of frequency in said variable frequencies being used to calculate coarse position and variations in phase in said low and high frequency being used to calculate medium and fine position.

20. The sensor of claim 19, wherein said mask and detector lie in parallel planes.