PHASE ANALYSIS MEASUREMENT APPARATUS AND METHOD

• US 20100158322A1
• Filed: 08/15/2008
• Published: 06/24/2010
• Est. Priority Date: 08/17/2007
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: Featherstone, Timothy Charles, Moore, Andrew John, Weston, Nicholas John, Huddart, Yvonne Ruth
• Granted Patent: US 8,792,707 B2
• Time in Patent Office: Days
• US Class Current: 382/113
• 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 via phase analysis. A projector projects an optical pattern onto the surface of an object to be inspected. At least first and second images of the surface on which the optical pattern is projected are then obtained. The phase of the optical pattern at the surface is changed between the first and second image by moving the projector relative to the object.

Claims

1. A non-contact method for inspecting an object via phase analysis, comprising:

i) a projector projecting an optical pattern onto the surface of an object to be inspected; and

ii) obtaining at least first and second images of the surface on which the optical pattern is projected,

in which the phase of the optical pattern at the surface is changed between the first and second image by moving the projector relative to the object.

2. A method as claimed in claim 1, in which the optical pattern as projected by the projector is the same for the at least first and second images.

3. A method as claimed in claim 1, in which the at least first and second images are obtained by an imaging device, and in which the imaging device and the projector are in a fixed spatial relationship relative to each other.

4. A method as claimed in claim 3 in which the projector and imaging device are moved between images by rotating the projector and imaging device about the imaging device'"'"'s perspective centre.

5. A method as claimed in claim 1, further comprising:

iii) processing the at least first and second images to obtain topographical surface data.

6. A method as claimed in claim 5 in which processing the at least first and second images comprises analysing the phase of the optical pattern on the surface.

7. A method as claimed in claim 5 in which step iii) comprises processing at least one of the at least first and second images to compensate for any relative movement between the object and the imaging device.

8. A method as claimed in claim 5, in which in step iii) corresponding points in the at least first and second images represent different points on the object.

9. A method as claimed in claim 8 in which step iii) comprises analysing the change in phase of the optical pattern across corresponding points in the at least first and second images.

10. A method as claimed in claim 5, in which determining the topographical surface data comprises calculating a phase map from the plurality of images.

11. A method as claimed in claim 5, in which analysing the plurality of images comprises determining the gradient of the surface.

12. A method as claimed in claim 11, in which determining the gradient of the surface relative comprises calculating a phase shift map from the plurality of images and obtaining a gradient map based on the phase shift map.

13. A method as claimed in claim 12, further comprising integrating the gradient map to obtain the topographical data.

14. A method as claimed in claim 1, in which the projector is mounted on a coordinate positioning apparatus.

15. A method as claimed in claim 5, in which the object is located in a measurement space and step iii) comprises determining the three-dimensional coordinates of the topographical data within the measurement space.

16. A method as claimed in claim 1 in which the optical pattern is a periodic optical pattern.

20. Computer program code comprising instructions which, when executed by a controller, causes the machine controller to control at least one projector, imaging device and image analyser in accordance with the method of claim 1.

21. A computer readable medium, bearing computer program code as claimed in claim 20.

17. An apparatus for inspecting an object via phase analysis, the apparatus comprising:

a projector configured to project an optical pattern onto the surface of an object to be measured, the projector being moveable relative to the object;

at least one imaging device configured to obtain a plurality of images of the object on which the optical pattern is projected; and

in which the projector is configured to be moved relative to the object between obtaining the phase-shifted images to cause a change in phase of the periodic optical pattern on the object.

18. A non-contact method for inspecting an object via phase analysis, comprising in any suitable order:

i) a projector projecting a periodic optical pattern onto the surface of an object to be inspected;

ii) at least one imaging device obtaining a plurality of phase-shifted images of the periodic optical pattern on the surface,

in which the projector and imaging device are in a fixed spatial relationship relative to each other and in which the position of the periodic optical pattern on the object is moved between images by relative rotation between the projector and object about the imaging device'"'"'s perspective centre.

19. A method as claimed in claim 18 further comprising:

iii) processing the phase-shifted images to obtain topographical surface data.