Apparatus and methods for contour measurement using movable sources

• US 6,031,612 A
• Filed: 02/02/1999
• Issued: 02/29/2000
• Est. Priority Date: 02/12/1996
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Shirley, Lyle
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): SMITH, ZANDRA V
• Application Number:
  US09/241,354
• Time in Patent Office: 392 Days
• Field of Search: 356/345, 356/357, 356/359, 356/360, 356/353, 356/349, 356/358
• US Class Current: 356/511
• CPC Class Codes: G01B 11/2531 using several gratings, projected with variable angle of incidence on the object, and one detection device

Abstract

Apparatus and methods of measuring position information of a point on the surface of an object. In one embodiment, the apparatus includes two sources of radiation positioned to illuminate the point on the surface of the object with radiation from each of the sources. The radiation from each of the sources is coherent with respect to the radiation from the other source. A control system moves each of the sources relative to the other and changes the phase of the radiation from at least one of the sources relative to the phase of the radiation from the other source as measured at the point on the surface of the object. A detector is positioned to receive radiation scattered by the point and a processor in communication with the detector calculates position information in response to the change in phase of the radiation from the source and the received radiation scattered by the point on the surface of the object.

Claims

1. A method for determining, on an object having a surface, three-dimensional position information of a point on said surface of said object, said method comprising the steps of:

providing two sources of radiation separated by a distance, said sources being coherent with respect to one another;

illuminating said point on said surface of said object with said radiation from each of said sources;

moving each of said sources relative to each other;

detecting radiation scattered by said point on said surface of said object; and

calculating position information in response to said movement of said sources and said detected radiation scattered by said point on said surface of said object.

2. The method of claim 1 further comprising the step of changing the phase of said radiation from one of said sources relative to the phase of said radiation from the other of said sources as measured at said point on said surface of said object.

3. The method of claim 1 wherein said sources of radiation are virtual sources of radiation.

4. The method of claim 1 wherein the step of moving each of said sources comprises changing said distance between said sources.

5. The method of claim 1 wherein said distance comprises a midpoint equidistant from each of said sources and wherein the step of moving each of said sources comprises changing said distance and keeping said midpoint fixed.

6. An apparatus for determining, on an object having a surface, position information of a point on said surface of said object, said apparatus comprising:

two sources of radiation separated by a distance, said sources being coherent with respect to one another;

a control system moving each of said sources relative to each other;

a detector positioned to receive radiation scattered from said point on said surface of said object; and

a processor receiving signals from said detector, said processor calculating position information in response to said movement of said sources and said received radiation scattered from said point on said surface of said object.

7. The apparatus of claim 6 wherein said control system changes the phase of at least one of said sources of radiation relative to the phase of said radiation from the other of said sources as measured at said point on said surface of said object.

8. The method of claim 6 wherein said sources of radiation are virtual sources of radiation.

9. The apparatus of claim 6 wherein said control system moves each of said sources relative to each other to change said distance.

10. The apparatus of claim 6 wherein said distance comprises a midpoint equidistant from each of said sources and said control system moves each of said sources relative to each other to change said distance and keep said midpoint fixed.

11. The apparatus of claim 6 further comprising an imaging system positioned between said detector and said point on said surface of said object, said imaging system imaging said point on said detector.

12. The apparatus of claim 11 further wherein said imaging system comprises a lens.

13. The apparatus of claim 12 wherein said lens comprises a telecentric lens.

14. The apparatus of claim 6 wherein said detector comprises a plurality of photodetectors.

15. The apparatus of claim 14 wherein said processor comprises a multiprocessor system having a plurality of processing units and each of said plurality of photodetectors is in electrical communication with a respective one of said plurality of processing units.

16. The apparatus of claim 6 wherein said two sources of coherent radiation comprises a source providing a beam of coherent radiation and a beam splitter positioned to divide said beam of coherent radiation into two beams of coherent radiation.

17. The apparatus of claim 16 further comprising a first mirror and a second mirror, said first mirror positioned to reflect a first beam of radiation from said beam splitter and said second mirror positioned to reflect a second beam of radiation from said beam splitter.

18. The apparatus of claim 17 further comprising a first focusing element and a second focusing element positioned in said first beam of radiation and said second beam of radiation, respectively, after reflection from said first mirror and said second mirror, respectively.

19. The apparatus of claim 17 wherein said first mirror and said second mirror are focusing elements.

20. The apparatus of claim 17 further comprising a first reflecting surface and a second reflecting surface wherein said first beam of radiation reflected from said first mirror is reflected from said first reflecting surface and said second beam of radiation reflected from said second mirror is reflected from said second reflecting surface,

wherein the relative movement of said first reflecting surface and said second reflecting surface with respect to said sources generates an apparent change in source position for each of said sources.

21. The apparatus of claim 20 wherein said first reflecting surface is coupled to said second reflecting surface.

22. A method for determining, on an object having a surface, position information of a point on said surface of said object, said method comprising the steps of:

providing two sources of radiation separated by a distance, said sources being coherent with respect to one another;

providing a detector at said point on said surface;

illuminating said point on said surface of said object with said radiation from each of said sources;

moving each of said sources relative to each other;

detecting said radiation at said point on said surface of said object; and

calculating position information in response to said movement of said sources and said radiation detected at said point on said surface of said object.

23. The method of claim 22 further comprising the step of changing the phase of said radiation from one of said sources relative to the phase of said radiation from the other of said sources as measured at said point on said surface of said object.

24. The method of claim 22 wherein said sources of radiation are virtual sources of radiation.

25. The method of claim 22 wherein the step of moving each of said sources comprises changing said distance between said sources.

26. The method of claim 22 wherein said distance comprises a midpoint equidistant from each of said sources and wherein the step of moving each of said sources comprises changing said distance and keeping said midpoint fixed.

27. An apparatus for determining, on an object having a surface, a depth coordinate of a point on said surface of said object, said apparatus comprising:

two sources of radiation separated by a distance, said sources being coherent with respect to one another;

a control system moving each of said sources relative to each other;

a detector positioned at said point on said surface of said object to receive radiation illuminating said point on said surface of said object; and

a processor receiving signals from said detector, said processor calculating position information of said point on said surface of said object in response to said movement of said sources and said radiation received at said point on said surface of said object.

28. The apparatus of claim 27 wherein said control system changes the phase of said radiation from one of said sources relative to the phase of said radiation from the other of said sources as measured at said point on said object.

29. The apparatus of claim 27 wherein said sources of radiation are virtual sources of radiation.

30. The apparatus of claim 27 wherein said control system moves each of said sources relative to each other to change said distance.

31. The apparatus of claim 27 wherein said distance comprises a midpoint equidistant from each of said sources and said control system moves each of said sources relative to each other to change said distance and keep said midpoint fixed.