Multiple-scale digital image correlation pattern and measurement

Patent metadata

Field	Value
Publication number	US-11100657-B2
Application number	US-201615152151-A
Country	US
Kind code	B2
Filing date	May 11, 2016
Priority date	Dec 6, 2012
Publication date	Aug 24, 2021
Grant date	Aug 24, 2021

Abstract

A method and apparatus for digital image correlation. A camera system is used to obtain larger scale images of a larger scale dot pattern on a surface of a workpiece and smaller scale images of a smaller scale dot pattern on the surface of the same workpiece. The smaller scale dot pattern forms a larger dot in the larger scale dot pattern in the larger scale images. The larger scale images and the smaller scale images may be used to determine a measurement of the workpiece.

First claim

What is claimed is:

1. A method for measuring strain in a workpiece, comprising:
applying a first plurality of dots of a first size on a surface of the workpiece to form a first scale dot pattern, wherein the first plurality of dots together, at a first field of view greater than a second field of view at which individual ones of the first plurality of dots can be measured, form a first dot of a second size larger than any of the first plurality of dots of the first size;
applying a second plurality of dots of the first size on the surface of the workpiece to form second scale dot pattern of about a same scale as the first scale dot pattern, wherein the second plurality of dots together, at the first field of view, form a second dot of the second size;
wherein applying the second plurality of dots is performed such that the first dot and the second dot together form a third scale dot pattern that is larger than both the first scale dot pattern and the second scale dot pattern;
obtaining, by a camera system, a first set of images of the third scale dot pattern at the first field of view;
obtaining, by the camera system, second set of images of the first scale dot pattern at the second field of view; and
determining an amount of strain present in the workpiece by measuring strain using both the first set of images and the second set of images, whereby strain is measured in the workpiece at two different distance scales.

2. The method of claim 1 further comprising:
placing a template comprising a plurality of apertures on the surface;
applying the first plurality of dots and the second plurality of dots in an area on the surface defined by apertures in the plurality of apertures; and
applying additional dots of the second size on the surface in areas defined by the apertures, each of the plurality of additional dots comprising another plurality of dots of the first size.

3. The method of claim 2 , wherein applying dots of the first size comprises airbrush spraying in the number of selected apertures.

4. The method of claim 1 , wherein applying dots of the first size comprises printing the smaller scale dot pattern on the surface.

5. The method of claim 1 , wherein the first images and the second images are obtained at a same time by the camera system.

6. The method of claim 1 wherein:
the camera system comprises a first set of cameras configured to obtain the first scale images; and
the camera system comprises a second set of cameras configured to obtain the second scale images.

7. The method of claim 1 , wherein:
the camera system comprises a single set of cameras configured to obtain the first scale images; and
further comprising changing a configuration of the single set of cameras to obtain the second scale images.

8. A device for measuring strain in a workpiece having a multiple-scale dot pattern on the workpiece, comprising:
a first plurality of dots of a first size applied on a surface of the workpiece to form a first scale dot pattern, wherein the first plurality of dots together, at a first field of view greater than a second field of view at which individual ones of the first plurality of dots can be measured, form a first dot of a second size larger than any of the first plurality of dots of the first size;
a second plurality of dots of the first size applied on the surface of the workpiece to form second scale dot pattern of about a same scale as the first scale dot pattern, wherein the second plurality of dots together, at the first field of view, form a second dot of the second size;
wherein the first dot and the second dot together form a third scale dot pattern that is larger than both the first scale dot pattern and the second scale dot pattern;
a camera system configured to take a first set of images of the third scale dot pattern at the first field of view and to take a second set of images of the first scale dot pattern at the second field of view smaller than the first field of view; and
a processor configured to determine an amount of strain present in the workpiece by measuring strain using both the first set of images and the second set of images, whereby strain is measured in the workpiece at two different distance scales.

9. The device of claim 8 , wherein camera system is configured to take the first images and the second images are obtained at a same time.

10. The device of claim 8 , wherein the measurement is selected from a measurement of a displacement of the workpiece and a measurement of a strain on the workpiece.

11. The device of claim 8 wherein:
the camera system comprises a first set of cameras configured to obtain the first scale images; and
the camera system comprises a second set of cameras configured to obtain the second scale images.

12. The device of claim 8 , wherein:
the camera system comprises a single set of cameras configured to obtain the first scale images; and
further comprising changing a configuration of the single set of cameras to obtain the second scale images.

Assignees

• Boeing Co

Inventors

• Grossnickle James A
• Pillers James E
• Mccrary Kevin Earl

Classifications

• G01B11/16 Primary

  for measuring the deformation in a solid, e.g. optical strain gauge · CPC title

• G01N2203/0647

  Image analysis · CPC title

• G01B11/165

  by means of a grating deformed by the object · CPC title

• G06T7/32 Primary

  using correlation-based methods · CPC title

• H04N7/18

  Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast · CPC title