System for determination of a location in three dimensional space

• US 6,141,104 A
• Filed: 09/09/1998
• Issued: 10/31/2000
• Est. Priority Date: 09/09/1997
• Status: Expired due to Term

• Current Assignee: Image Guided Technologies, Inc. (Stryker Corporation)
• Original Assignee: Image Guided Technologies, Inc. (Stryker Corporation)
• Inventors: Cormack, Robert, Schulz, Waldean A.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US09/150,345
• Time in Patent Office: 783 Days
• Field of Search: 356/375, 356/373, 356/376, 356/121, 356/152.1, 356/3.14, 356/141.4, 250/559.29, 250/222.1
• US Class Current: 356/616
• CPC Class Codes: G01D 5/34 the beams of light being detected by photocells
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G06F 3/0304 Detection arrangements using opto-electronic means constructional details of pointing devices not related to the detection arrangement using opto-electronic means G06F3/033; optical digitisers G06F3/042
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors

Abstract

An optical improvement for angular position sensors, which may be used to determine the spatial coordinates of a small source of light (or other energy) in a 3-dimensional volume. Such sensors normally include a linear photosensitive image detector such as a photodiode array or a charge-coupled device (CCD). An irregular pattern of parallel slits is described which increases the amount of light gathered while avoiding the undesirable characteristics of lens optics for this application. One optimal type of irregular pattern is the uniformly redundant array. A mathematical correlation function together with a polynomial interpolation function can determine the displacement of the image on the detector and thereby the location of the source relative to one angular dimension. Given the locations and orientations of several sensors in a 3-dimensional coordinate system and given the angles measured by each, the location of the point source can be computed.

Claims

1. In an apparatus for determining a location of at least one substantially point-like radiator of energy in a three dimensional volume comprising:

said at least one substantially point-like radiator of energy;

at least one detector adapted to be disposed in a known location within said three dimensional volume, and adapted to be positioned to intercept energy radiating from said substantially point-like radiator, wherein said detector comprises at least one array of elements adapted to detect said radiation and to convert said detected radiation into output signals; and

at least one pattern member, adapted to be disposed between said array and said radiator, comprising plural gradations of transparency, wherein said pattern is adapted to spatially modulate radiation that is incident thereon as a function of said gradations in transparency, and to project said modulated energy onto said array in the form of at least one real image; and

a signal processor adapted to convert output signals representative of said at least one modulated real image into a direction of said radiator relative to an assembly of said detector and said pattern member;

the improvement that comprises;

at least one substantially ideal reference image of said pattern member on said array;

said signal processor being adapted to compare said modulated image with said reference image;

said signal processor comprising a discrete mathematical correlation function that is adapted to characterize the degree of match between said modulated image and said reference image for a plurality of discrete displacements of said reference image with respect to said array,

said signal processor being adapted to identify at least one of said displacements that produces a correlation that is characterized by a well defined maximum value; and

said signal processor being adapted to convert said displacement(s) producing a maximum value into a direction of said radiator in said three dimensional volume with respect to the known location of said detector in said three dimensional volume.

2. The improved apparatus of claim 1 further comprising said signal processor being adapted to estimate the displacement of the maximum value of a continuous function, that equals the correlation function at said displacements interpolated between at least two discrete displacements of said correlation function;

and

said signal processor being adapted to convert said estimate into an interpolated, and therefore more precise, direction of said radiator in said three dimensional volume.

3. The improved apparatus of claim 1 wherein said plural gradations of transparency comprise a plurality of slits of varying width in an otherwise substantially opaque field.

4. The improved apparatus of claim 3 wherein said array is substantially one dimensional and comprises a linear strip of said radiation converters, wherein long dimensions of said slits are substantially normal to said linear strip.

5. The improved apparatus of claim 4 comprising a plurality of said arrays at least two of which are disposed substantially normal to each other;

and said signal processor is adapted to determine directions of said radiator with respect to said arrays in at least two dimensions corresponding to the dispositions of said normal arrays.

6. The improved apparatus of claim 4 comprising a plurality of said arrays at least three of which are disposed not all parallel to each other and said signal processor is adapted to determine directions of said radiator with respect to said arrays in at least three dimensions corresponding to the dispositions of said arrays whereby enabling said signal processor to determine the substantial point location of said radiator in said three dimensional volume.

7. The improved apparatus of claim 3 wherein the width of said slits are not digitally related to each other.

8. The improved apparatus of claim 3 wherein the widths of said slits correspond to a uniformly redundant array (URA) pattern.

9. The improved apparatus of claim 3 wherein said slits are of random width or random spacing.

10. The improved apparatus of claim 3 wherein said slits are disposed symmetrically about an arbitrary line that is contained in said real image and is transverse to said array.

11. The improved apparatus of claim 1 wherein said radiation is electromagnetic radiation.

12. The improved apparatus of claim 11 wherein said radiation is infra red.

13. The improved apparatus of claim 1 wherein said array comprises a plurality of photodetector elements.

14. The improved apparatus of claim 13 wherein at least some of said elements are linearly aligned.

15. The improved apparatus of claim 14 wherein said array comprises a charge coupled device (CCD).

16. The improved apparatus of claim 15 wherein said CCD comprises at least one linear row of photosensitive pixels.

17. In a method of determining the direction of at least one unknown point in a three dimensional volume, relative to a different, known location in said volume, which comprises:

disposing at least one substantially point source energy radiator in said three dimensional volume in known spatial relationship to at least one of said point(s);

disposing at least one detector, that is adapted to detect energy radiated by said radiator and impinged upon at least one linear array of elements that are adapted to detect said radiation and to convert detected radiation into output signals that are proportional to strength of said impinged energy on the elements of said array, wherein said detector is in known spatial relationship to said three dimensional volume;

operatively associating said detector(s) with a signal processor that is adapted to convert said output signals to a direction of incidence of said radiation on said detector(s);

the improvement that comprises;

interposing a pattern member, comprising plural areas having gradations of transparency to said radiation, between said radiator and said array;

radiating energy from said radiator to said array through said pattern member such that a modulated image of said pattern member is disposed on said array;

generating an output of said array that is representative of at least one displacement of a substantially ideal reference image of said pattern member;

in said signal processor, comparing said modulated image with at least one of said displaced reference images until a best match is found between a specific displaced reference image and said modulated image; and

in said signal processor, from said best match, determining a direction of said radiator with respect to said detector.

18. An improved method as claimed in claim 17 further comprising repeating said direction determination with said detectors at different spatial relationships to said volume, sufficient to establish the three dimensional coordinates of said unknown point.

19. An improved method as claimed in claim 18 wherein said array is a plurality of linear aligned plural elements that are adapted to convert impinged energy into output signals and further comprising repeating said improved method with at least three arrays disposed not all parallel to each other.

20. An improved method as claimed on claim 18 wherein said plural gradations of transparency comprise a plurality of slits of differing, non-digital widths that are longitudinally disposed normal to said array;

and further comprising causing said modulated image to comprise a set of lines transverse to said array.