Non-contact measurement apparatus and method

• US 8,923,603 B2
• Filed: 08/15/2008
• Issued: 12/30/2014
• Est. Priority Date: 08/17/2007
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: Weston, Nicholas John, Huddart, Yvonne Ruth, Moore, Andrew John
• Primary Examiner(s): Carter, Aaron W
• Application Number:
  US12/733,025
• Publication Number:
  US 20100142798A1
• Time in Patent Office: 2,328 Days
• Field of Search: 382/141, 382/154, 382/216, 382/285, 345419-427, 356 12- 14, 348 42- 60
• US Class Current: 382/154
• CPC Class Codes: G01B 11/007 feeler heads therefor
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01B 11/2527 with phase change by in-plane movement of the patern
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: G06T 7/593 from stereo images

Abstract

A non-contact method and apparatus for inspecting an object. At least one first image of the object on which an optical pattern is projected, taken from a first perspective is obtained. At least one second image of the object on which an optical pattern is projected, taken from a second perspective that is different to the first perspective is obtained. At least one common object feature in each of the at least one first and second images is then determined on the basis of an irregularity in the optical pattern as imaged in the at least one first and second images.

Claims

1. A non-contact method for inspecting an object comprising, in any suitable order:

i) obtaining at least one first image of the object on which an optical pattern is projected, taken from a first perspective;

ii) obtaining at least one second image of the object on which an optical pattern is projected, taken from a second perspective that is different to the first perspective; and

iii) identifying at least one common object feature in each of the at least one first and second images as a photogrammetric target feature, on the basis of an irregularity in the optical pattern caused by a feature of the object deforming the optical pattern as imaged in the at least one first and second images.

2. A method as claimed in claim 1, in which at least one of the relative position and relative orientation of the object and a projector of the optical pattern at step i) is different to that of the object and the projector of the optical pattern at step ii).

3. A method as claimed in claim 1, in which the projector of the optical pattern imaged at step i) and the projector of the optical pattern imaged at step ii) are provided by a common optical pattern projector unit comprising at least one projector, and in which the method further comprises relatively moving the object and the common optical pattern projector unit between steps i) and ii).

4. A method as claimed in claim 3, comprising moving the optical pattern projector unit relative to the object.

5. A method as claimed in claim 3, in which the projector of the optical pattern imaged at step ii) is the projector of the optical pattern imaged at step i).

6. A method as claimed in claim 1, in which the optical pattern projected on the object in step i) and step ii) is the same.

7. A method as claimed in claim 1, in which the at least one first image and the at least one second image are obtained by a common imaging device unit comprising at least one image sensor, and in which the method comprises moving the common imaging device unit from the first perspective to the second perspective.

8. A method as claimed in claim 3, in which the optical pattern projector unit and an imaging device unit are in a fixed spatial relationship relative to each other.

9. A method as claimed in claim 8 in which the optical pattern projector unit and the imaging device unit are mounted on a coordinate positioning apparatus.

10. A method as claimed in claim 8, in which the optical pattern projector unit and the imaging device unit are provided as a single probe.

11. A method as claimed in claim 1, further comprising using the at least one first and second images to measure a common feature.

12. A method as claimed in claim 11, in which measuring the common feature comprises determining a position of the common feature within a measurement volume.

13. A method as claimed in claim 1, in which:

step i) comprises obtaining from a first perspective a set of first images of the object; and

step ii) comprises obtaining from a second perspective a set of second images of the object;

and in which a position of the optical pattern on the object is different for each image in a set.

14. A method as claimed in claim 13, in which step iii) comprises:

a) calculating at least one first phase map from the set of first images;

b) calculating at least one second phase map from the set of second images; and

c) identifying at least one common irregularity in each of the at least one first and second phase maps as a common object feature.

15. A method as claimed in claim 14, in which:

step a) comprises calculating a set of first phase maps from the set of first images, each phase map in the set being calculated using a unique order of the set of first images;

step b) comprises calculating a set of second phase maps from the set of second images, each phase map in the set being calculated using a unique order of the set of second images; and

step c) comprises identifying at least one corresponding irregularity in the set of at least one first phase maps and set of at least second phase maps as a common object feature.

16. A method as claimed in claim 14, in which the phase maps are wrapped phase maps and in which step c) comprises discarding false irregularities caused by wrapped phase data.

17. A method as claimed in claim 16, in which discarding false irregularities comprises comparing each of the wrapped phase maps in a set and discarding non-commonly identified irregularity points between each of the wrapped phase maps.

18. A method as claimed in claim 1, in which identifying at least one common irregularity comprises identifying corresponding features of the object between the images of the different perspectives.

19. A method as claimed in claim 1, in which the method comprises identifying in each of the at least one first image and the at least one second image a plurality of irregularities in the optical pattern formed on the object as a plurality of common object features, and determining the three-dimensional coordinates of each of the common object features on the object within a measurement space from the at least one first image and the at least one second image.

20. A method as claimed in claim 1, further comprising determining topographical data regarding the surface of the object on which the optical pattern is projected by analysing the deformation of the optical pattern as imaged by at least one of the at least two images.

21. A method as claimed in claim 19, further comprising combining the three-dimensional coordinates of the plurality of common object features with the topographical data to obtain three-dimensional model data of the object.

22. An apparatus for inspecting an object, the apparatus comprising:

at least one projector configured to project an optical pattern onto an object to be measured;

at least one imaging device configured to obtain from a first image perspective at least one first image of the object on which an optical pattern is projected and configured to obtain from a second image perspective at least one second image of the object on which an optical pattern is projected; and

an image analyser configured to identify an irregularity in the optical pattern caused by the feature of the object deforming the optical pattern in each of the at least one first and second images as a common object feature that is a photogrammetric target feature.

23. An apparatus as claimed in claim 22, in which the apparatus comprises a projector unit comprising the at least one projector and in which the projector unit and object are configured to be relatively moved between first and second projector perspectives.

24. An apparatus as claimed in claim 22, in which the apparatus comprises an imaging device unit comprising the at least one imaging device and in which the imaging device unit and object are configured to be relatively moved between the first and second image perspectives.

25. An apparatus as claimed in claim 23, in which the projector unit and imaging device unit are in a fixed spatial relationship.

26. An apparatus as claimed in claim 22 in which the projector unit and imaging device unit are mounted to the moveable part of a coordinate positioning machine.

27. An apparatus as claimed in claim 25, in which the projector unit and imaging device unit are provided as a single probe.

31. The apparatus as claimed in claim 22, wherein the at least one projector is configured to project the optical pattern from at least first and second projector perspectives onto the object to be measured, and wherein the at least one first image is obtained of the object with the optical pattern projected from the first projector perspective, and the at least one second image is obtained of the object with the optical pattern projected from the second projector perspective.

28. A computer implemented method comprising:

receiving first image data representing at least one first image of an object on which an optical pattern is projected, taken from a first perspective;

receiving second image data representing at least one second image of the object on which an optical pattern is projected, taken from a second perspective that is different to the first perspective; and

analysing the first and second image data to identify at least one common object feature as a photogrammetric target feature, on the basis of an irregularity in the optical pattern caused by a feature of the object deforming the optical system as imaged in the at least one first and second images.

29. A non-transitory computer-readable storage medium storing a computer program that when executed by a processor device, causes the processor device to execute a non-contact method for inspecting an object comprising, in any suitable order:

i) obtaining at least one first image of the object on which an optical pattern is projected, taken from a first perspective;

ii) obtaining at least one second image of the object on which an optical pattern is projected, taken from a second perspective that is different to the first perspective; and

iii) identifying at least one common object feature in each of the at least one first and second images as a photogrammetric target feature, on the basis of an irregularity in the optical pattern caused by a feature of the object deforming the optical pattern as imaged in the at least one first and second images.

30. A machine controller, comprising:

a processor; and

the non-transitory computer-readable storage medium according to claim 29.