Method and apparatus for three-dimensional optical measurement of object surfaces

• US 5,307,151 A
• Filed: 07/30/1992
• Issued: 04/26/1994
• Est. Priority Date: 09/11/1991
• Status: Expired due to Fees

• Current Assignee: Carl-Zeiss-Stiftung
• Original Assignee: Carl-Zeiss-Stiftung
• Inventors: Hof, Albrecht, Hanssen, Adalbert
• Primary Examiner(s): Johnston, Jill A.
• Assistant Examiner(s): Freed, Rachel
• Application Number:
  US07/923,105
• Time in Patent Office: 635 Days
• Field of Search: 356/376, 250/237 G
• US Class Current: 356/604
• CPC Class Codes: G01B 11/2545 with one projection direction and several detection directions, e.g. stereo
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A single projector is used to project a grating pattern on the surface of the object being measured, and the grating pattern is recorded simultaneously by two cameras from two different directions relative to the direction of projection. Both cameras record images of the same object areas. The fringe phases of the image patterns recorded by each of the two cameras are computed separately; and the object coordinates, which are computed from the combination of the computed fringe phases of both cameras, are unambiguous within a large measured range.

Claims

1. A method for the three-dimensional optical measuring of an object surface area defining ambiguous object coordinates, said method comprising:

projecting a grating pattern on said object surface;

recording said projected grating pattern on two video cameras, each said camera having a plurality of pixels, and said projected grating pattern being recorded on each camera as an image pattern with a plurality of image points; and

using an analytical computer connected with said video cameras to compute the topography of said object surface by;

separately computing fringe phases for the image patterns recorded by each camera, and

using a combination of said separate fringe phases of both cameras to compute unambiguous object coordinates within a predetermined measuring area.

2. The method of claim 1 wherein said step for computing the unambiguous object coordinates further comprises:

determining a number of possible solution coordinates within a measured volume, basing said determination on one fringe phase at one said image point of a first one of said cameras; and

using said solution coordinates to determine corresponding image points on the recorded image of said second camera.

3. The method of claim 2 further comprising computing the fringe phases for said image points of the second camera by interpolating the fringe phases at adjacent camera pixels.

4. The method of claim 3 further comprising, prior to said interpolation step, eliminating order jumps between the fringe phases at adjacent camera pixels.

5. The method of claim 2 further comprising:

computing the differences between

the fringe phases at the image points of the second camera associated with the solution coordinates and

the fringe phase at the corresponding image point of the first camera;

selecting the image point of the second camera at which said computed difference is minimal; and

using the fringe phase of said selected image point to compute said unambiguous object coordinate for that point of the object surface.

25. The method of claim 3 further comprising:

arranging a projector to project said grating pattern onto said object surface by central projection; and

positioning said video cameras so that said grating patterns are imaged onto both said cameras in central projection.

6. The method of claim further comprising:

computing a second set of solution coordinates based on fringe phases at the image points of the second camera associated with said first set of solution coordinates; and

selecting the second solution coordinate exhibiting the smallest distance value relative to one of the first solution coordinates, whereby the selected solution coordinate represents said unambiguous object coordinate on said object surface.

7. In apparatus for three-dimensional measurement of object surfaces including a grating projector for the projection of grating patterns on the object surface, at least a first and a second video camera for recording video images of said grating pattern projected on the object surface, and an analytical computer connected with the video cameras for computation of the topography of the object surface, the improvement comprising:

positioning said cameras and said projector being positioned relative to each other so that

the lens of said first camera is located at a predetermined distance from the lens of the projector, said predetermined distance being substantially smaller than the distance between the lens of said second camera and the lens of said projector.

8. The apparatus of claim 7 wherein:

said predetermined distance between said first camera lens and said projector lens is selected so that the fringe phases computed from the grating patterns recorded with said first camera produce unambiguous approximate solutions for all object coordinates within a predetermined measured volume; and

said distance between said lenses of said second camera and said projector is selected so that the fringe orders associated with said video images of said second camera can be unambiguously computed from said video images of said first camera.

9. The apparatus of claim 7 wherein said projector further comprises a projection grating, said cameras each further comprise respective sensor areas, and said sensor areas are located on a common plane.

10. The apparatus of claim 9 wherein said lenses of said cameras and said projector further comprise main points, and all of said main points are located on a second plane.

11. The apparatus of claim 10 wherein said common plane and said second plane are parallel.

12. The apparatus of claim 8 wherein the optical axes of said lenses of said cameras and said projector all intersect at a common point within said preset measured volume of said object surface.

13. The apparatus of claim 12 wherein said projector further comprises a projection grating located perpendicular to the optical axis of said projection lens, and a respective sensor area is located perpendicular to the optical axis of each respective camera lens.

14. The apparatus of claim 7 wherein said projected grating pattern comprises light and dark lines having the same width.

15. The apparatus of claim 7 wherein said projected grating pattern exhibits a sinusoidal intensity characteristic transverse to the direction of the pattern lines.

16. In apparatus for three-dimensional measuring of object surfaces including a grating projector for the projection of a grating pattern on the object surface, at least a first and a second video camera for recording video images of the grating pattern projected on the object surface, and an analytical computer connected with said video cameras for the computation of the topography of the object surface, the improvement comprising:

the lenses of said two video cameras are each positioned at a different respective distance from the lens of the projector; and

the quantitative value of the difference between said respective distances is substantially smaller than the value of each said respective distance.

17. The apparatus of claim 16 wherein said camera lenses are positioned adjacent to each other.

18. The apparatus of claim 16 wherein said projector further comprises a projection grating, said cameras each further comprise respective sensor areas, and said sensor areas are located on a common plane.

19. The apparatus of claim 18 wherein said lenses of said cameras and said projector further comprise main points, and all of said main points are located on a second plane.

20. The apparatus of claim 19 wherein said common plane and said second plane are parallel.

21. The apparatus of claim 16 wherein the optical axes of said lenses of each said camera and of said projector all intersect at a common point within a preset measured volume of said object surface.

22. The apparatus of claim 21 wherein said projector further comprises a projection grating located perpendicular to the optical axis of said projector lens, and a respective sensor area is located perpendicular to the optical axis of each respective camera lens.

23. The apparatus of claim 16 wherein said projected grating pattern comprises light and dark lines having the same width.

24. The apparatus of claim 16 wherein said projected grating pattern exhibits a sinusoidal intensity characteristic transverse to the direction of the pattern lines.

26. In apparatus for three-dimensional measurement of object surfaces including a grating projector for the projection of grating patterns on the object surface, at least a first and a second video camera for recording video images of said grating pattern projected on the object surface, and an analytical computer connected with the video cameras for computation of the topography of the object surface, the improvement comprising:

said projector being arranged to project said grating patterns onto said object surface by central projection;

said video cameras being arranged so that said grating patterns are imaged onto both said cameras in central projection; and

said cameras and said projector being positioned relative to each other so that

the lens of said first camera is located at a predetermined distance from the lens of the projector, said predetermined distance being substantially smaller than the distance between the lens of said second camera and the lens of said projector.

27. In apparatus for three-dimensional measuring of object surfaces including a grating projector with a lens for the projection of a grating pattern on the object surface, at least a first and a second video camera with respective lenses for recording video images of the grating pattern projected on the object surface, and an analytical computer connected with said video cameras for the computation of the topography of the object surface, the improvement comprising:

the lens of said projector being arranged to project said grating patterns onto said object surface by central projection;

the lenses of said video cameras being arranged so that said grating patterns are imaged onto both said cameras in central projection; and

the lenses of said two video cameras also being each positioned at a different respective distance from the lens of the projector so that the quantitative value of the difference between said respective distances is substantially smaller than the value of each said respective distance.