Phase analysis measurement apparatus and method

• US 8,792,707 B2
• Filed: 08/15/2008
• Issued: 07/29/2014
• 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, Featherstone, Timothy Charles
• Primary Examiner(s): Carter, Aaron W
• Application Number:
  US12/733,022
• Publication Number:
  US 20100158322A1
• Time in Patent Office: 2,174 Days
• Field of Search: 382/113, 382/141, 382/154, 382/195, 382/216
• 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 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 in any suitable order:

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

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

the projector and the at least one imaging device are in a fixed spatial relationship relative to each other and in which the position of the optical pattern on the object is moved between images in the set of the phase-shifted images by rotating the projector and the at least one imaging device relative to the object about the imaging device'"'"'s perspective centre.

2. A method as claimed in claim 1, in which the optical pattern as projected by the projector is the same for images in the set of phase-shifted images.

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

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

4. A method as claimed in claim 3, wherein processing the set of phase-shifted images comprises analysing the phase of the optical pattern on the surface.

5. A method as claimed in claim 3, wherein step iii) comprises processing at least one of the images in the set of phase-shifted images to compensate for any relative movement between the object and the imaging device.

6. A method as claimed in claim 3, wherein in step iii) corresponding points in the set of phase-shifted images represent different points on the object.

7. A method as claimed in claim 6, wherein step iii) comprises analysing the change in phase of the optical pattern across corresponding points in the set of phase-shifted images.

8. A method as claimed in claim 3, wherein determining the topographical surface data comprises calculating a phase map from the set of phase-shifted images.

9. A method as claimed in claim 3, wherein analysing the set of phase-shifted images comprises determining the gradient of the surface.

10. A method as claimed in claim 9, wherein determining the gradient of the surface comprises calculating a phase shift map from the set of phase-shifted images and obtaining a gradient map based on the phase shift map.

11. A method as claimed in claim 10, further comprising integrating the gradient map to obtain the topographical data.

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

13. A method as claimed in claim 3, wherein 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.

14. A method as claimed in claim 1, wherein the optical pattern is a periodic optical pattern.

15. 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 in a fixed spatial relationship with the projector and configured to obtain a plurality of phase-shifted images of the object on which the optical pattern is projected, wherein

the projector and the object are configured to be moved relative to each other by rotating the projector and the at least one imaging device relative to the object about the imaging device'"'"'s perspective centre between obtaining the phase-shifted images to cause a change in phase of the periodic optical pattern on the object.

16. A non-transitory computer-readable storage medium storing a computer program that, when executed by a controller, causes the controller to control at least one projector, imaging device and image analyser to execute a non-contract method for inspecting an object via phase analysis, the program comprising in any suitable order:

i) instructions for causing a projector to project an optical pattern onto the surface of an object to be inspected;

ii) instructions for causing at least one imaging device to obtain a set of phase-shifted images of the optical pattern on the surface, wherein

the projector and at least one imaging device are in a fixed spatial relationship relative to each other and in which the position of the optical pattern on the object is moved between images in the set of the phase-shifted images by rotating the projector and the at least one imaging device relative to the object about the imaging device'"'"'s perspective centre.