Camera theodolite system

• US 6,310,644 B1
• Filed: 03/26/1997
• Issued: 10/30/2001
• Est. Priority Date: 03/26/1997
• Status: Expired due to Fees

• Current Assignee: 3DM Devices Inc.
• Original Assignee: 3DM Devices Inc.
• Inventors: Keightley, John
• Primary Examiner(s): RAO, ANAND SHASHIKANT
• Application Number:
  US08/832,336
• Time in Patent Office: 1,679 Days
• Field of Search: 348/159, 348/143, 348/139, 348/135, 348/140, 348/141
• US Class Current: 348/159
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 11/245 using a plurality of fixed, simultaneously operating transducers G01B11/2408 - G01B11/2425, G01B11/255 take precedence
• CPC Class Codes: G01C 11/06 by comparison of two or more pictures of the same area

Abstract

A three-dimensional coordinate measuring system which includes first and second towers, first and second viewing devices mounted on the first and second towers, respectively, and a pair of targets mounted on each of the first and second towers a known distance apart. A tilt sensor is mounted on each of the first and second towers to measure the angle of each of the first and second towers with vertical and a host computer is coupled to each of the viewing devices and is programmed to perform photogrammetric algorithms so as to compute the coordinates of unknown points.

Claims

1. A three-dimensional coordinate measuring system, comprising:

a) first and second towers;

b) first and second camera assemblies mounted on said first and second towers, respectively;

c) a first pair of reference targets mounted to said first tower such that said reference targets of said first pair are a known distance apart, and a second pair of reference targets mounted to said second tower such that said reference targets of said second pair are a known distance apart;

d) a tilt sensor mounted on each of said first and second towers operative to measure the angle of each of said first and second towers with vertical; and

e) a host computer coupled to each of said camera assemblies and to said tilt sensors operative to receive automatically measurements from selected targets, from each pair of said reference targets and a tower angle to vertical measurements from each of said tilt sensors, said host computer being programmed to perform photogrammetric algorithms so as to compute the coordinates of unknown points.

2. A system according to claim 1, wherein said first and second camera assemblies are each a pair of cameras mounted on respective first and second towers in a fixed relationship to each other.

3. A system according to claim 1, wherein said reference targets are illuminated circular discs.

4. A system according to claim 2, wherein said cameras are CCD cameras and including interface electronics on each tower coupled to respective tilt sensors and CCD cameras and coupled to said host computer.

5. A system according to claim 1, wherein said towers are mounted on casters.

6. A system according to claim 4, wherein one of said cameras on each of said first and second towers is positionable and operative to view the reference targets on the other of said first and second towers while the other camera on said one tower views an object whose coordinates are to be determined.

7. A system according to claim 1, wherein object points are measured using a hand held probe having a plurality of targets spaced along a straight line in a geometric progression from a tip of said hand held probe.

8. A system according to claim 4, wherein said reference targets are pulsed light emitting diodes emitting in the near infra red and said CCD cameras have near infra red optical bandpass filters thereon.

9. A system according to claim 1, wherein said towers are height adjustable.

10. A system according to claim 1, wherein said camera assemblies are each a single camera and a beamsplitter.

27. A system according to claim 1, wherein said host computer continuously computes the positional relationship between said first camera assembly and said second camera assembly.

11. A three-dimensional coordinate measuring system, comprising:

a) first and second towers;

b) a pair of CCD cameras mounted on said first and second towers, respectively, in a fixed relationship with each other;

c) a first pair of reference targets mounted to said first tower such that said reference targets of said first pair are a known distance apart, a second pair of reference targets mounted to said second tower such that said reference targets of said second pair are a known distance apart and a pair of said reference targets on one of said first and second towers is visible to one of the said pair of CCD cameras on the other of said first and second towers;

d) a tilt sensor mounted on each of said first and second towers operative to measure the angle of each of said first and second towers with respect to vertical; and

e) an interface circuit mounted on each of said first and second towers, each interface circuit coupled to the CCD cameras and the tilt sensor mounted on an associated one of said first and second towers;

f) a host computer coupled to said interface circuits, said host computer operative to receive automatically measurements from selected targets, from each pair of said reference targets and a tower angle to vertical measurements from each of said tilt sensors, said host computer being programmed to perform photogrammetric algorithms so as to compute the coordinates of unknown points.

12. A system according to claim 11, wherein said reference targets are illuminated from the rear periodically by light emitting diodes emitting light in the near infra red and said cameras have near infra red optical bandpass filters.

13. A system according to claim 11, wherein said towers are movable and height adjustable.

14. A system according to claim 11, including an elongated hand held probe having targets spaced along a line in a geometric progression from a tip thereof.

15. A system according to claim 11, wherein said cameras are calibrated using as variables camera position, camera orientation, lens focal length, lens radial distortion, CCD array pixel size, and optical axis location.

16. A three-dimensional coordinate measuring system, comprising:

a) first and second towers;

b) a CCD camera and a beam splitter mounted on each of said first and second towers, respectively, in a fixed relationship with each other;

c) a first pair of reference targets mounted to said first tower such that said reference targets of said first pair are a known distance apart, a second pair of reference targets mounted to said second tower such that said reference targets of said second pair are a known distance apart and a pair of reference targets on one of said first and second towers is visible to said CCD camera on the other of said first and second towers;

d) a tilt sensor mounted on each of said first and second towers operable to measure the angle of each of said first and second towers with vertical; and

e) an interface circuit mounted on each of said first and second towers, each interface circuit coupled to a CCD camera and a tilt sensor mounted on an associated one of said first and second towers;

f) a host computer coupled to said interface circuits, said host computer programmed to perform photogrammetric algorithms so as to compute the coordinates of unknown points.

17. A system according to claim 16, wherein said reference targets are illuminated from the rear periodically by light emitting diodes emitting light in the near infra red and said cameras have near infra red optical bandpass filters.

18. A system according to claim 16, wherein said towers are movable and height adjustable.

19. A system according to claim 16, including an elongated hand held probe having targets spaced along a line in a geometric progression from a tip thereof.

20. A system according to claim 16, wherein said cameras are calibrated using as variables camera position, camera orientation, lens focal length, lens radial distortion, CCD array pixel size, and optical axis location.

21. A method of measuring the three-dimensional coordinates of an object in space, comprising:

a) positioning a first and second towers, each of said towers having a camera assembly, wherein a first pair of reference targets are mounted to said first tower such that said targets of said first pair are a known distance apart and a second pair of reference targets are mounted to said second tower such that said targets of said second pair are a known distance apart such that said camera assembly on each of said towers views the reference targets on the other of said towers and the object;

b) digitizing the image received on each camera assembly;

c) transferring at least a portion of said image to a host computer; and

d) performing a triangulation calculation on the two camera assemblies to determine the three-dimensional coordinates of the object.

22. A method according to claim 21, wherein said camera assembly on each of said towers is a pair of CCD cameras.

23. A method according to claim 21, wherein only pixels from said CCD cameras having an amplitude in excess of a threshold above a ‘

black level’

are transmitted to the host computer.

24. A method according to claim 21, wherein each said camera assembly is calibrated by measuring distortions in an image forming process and then constructing an analytical model and using that model to correct images subsequently taken by each said camera assembly.

25. A method according to claim 21, including establishing a frame of reference by measuring two immobile points and arbitrarily selecting one of said two points as an origin of a right hand Cartesian coordinate system.

26. A method according to claim 21, including calibrating each said camera assembly using a redundant set of data to determine camera parameters prior to determining three-dimensional coordinates of said object.

28. A method according to claim 22, further including the step of automatically and continuously computes the positional relationship between said two towers.

29. A method according to claim 22, including the calculation of the centroid of said object in space to subpixel resolution.