SYSTEM AND METHOD FOR DETERMINING 3D SURFACE FEATURES AND IRREGULARITIES ON AN OBJECT

• US 20150213606A1
• Filed: 07/11/2014
• Published: 07/30/2015
• Est. Priority Date: 01/27/2014
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Akopyan, Mikhail, Jacobson, Lowell D., Wolff, Robert A.
• Granted Patent: US 11,176,655 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01B 11/0608 Height gauges
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G06T 2207/10028 Range image; Depth image; 3D point clouds
• CPC Class Codes: G06T 2207/30224 Ball; Puck
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/44 using image operators, e.g. filters, edge density metrics or local histograms

Abstract

This invention provides a system and method for determining the location and characteristics of certain surface features that comprises elevated or depressed regions with respect to a smooth surrounding surface on an object. A filter acts on a range image of the scene. A filter defines an annulus or other perimeter shape around each pixel in which a best-fit surface is established. A normal to the pixel allows derivation of local displacement height. The displacement height is used to establish a height deviation image of the object, with which bumps, dents or other height-displacement features can be determined. The bump filter can be used to locate regions on a surface with minimal irregularities by mapping such irregularities to a grid and then thresholding the grid to generate a cost function. Regions with a minimal cost are acceptable candidates for application of labels and other items in which a smooth surface is desirable.

Claims

1. A system for determining surface height variations on an object based upon a range image comprising.

a camera assembly that generates a range image;

a vision system that analyzes the range image;

a filter that (a) generates a best-fit surface about each of selected pixels in the range image, (b) establishes a normal to the best-fit surface, respectively for each of the pixels, and (c) determines a relative height displacement of a region about each of the pixels relative to the best-fit surface; and

a vision system tool that analyzes height displaced features localized by the filter.

2. The system as set forth in claim 1 wherein the filter includes a background region about each of the selected pixels from which the best-fit surface is established.

3. The system as set forth in claim 2 wherein the filter includes a foreground region, located proximate to the background region and including at least one of the selected pixels in which the relative height displacement is determined.

4. The system as set forth in claim 3 wherein at least one of a size and a shape of at least one of the background region and the foreground region is user-defined based upon at least one of a size and a shape of the object.

6. The system as set forth in claim 1 wherein the best-fit surface comprises a best-fit plane.

24. The system as set forth in claim 1 wherein the best-fit surface defines a surface of average height about each of the selected pixels in the range image.

5. The system as set forth in 1 wherein the camera assembly comprises a displacement sensor that projects a line of light on the object and receives light from the projected line at an imager in a manner that defines a plurality of displacement values in a height direction.

7. A method for determining surface height variations on an object based upon a range image comprising the steps of:

(a) generating a best-fit surface about each of selected pixels in the range image;

(b) establishing a normal to the best-fit surface, respectively for each of the pixels;

(c) determining a relative height displacement of a region about each of the pixels relative to the best-fit surface; and

(d) analyzing, with a vision system tool, localized height displaced features.

25. The method as set forth in claim 7 wherein the step of generating includes generating a best-fit surface of average height about each of the selected pixels in the range image.

8. A system for determining a region on a surface having low surface irregularity comprising:

a vision system tool that locates the surface and acquires a 3D image of at least a portion of the surface;

a filter that determines a relative height displacement for an area about each of a selected group of pixels on the 3D image; and

a location element that cost-values the height displacement for each region based upon results provided by the filter and that determines a minimal cost region that accommodates a predetermined area.

9. The system as set forth in claim 8 wherein the predetermined area is sized to accommodate a label, printing or other embellishment.

10. The system as set forth in claim 8 further comprising a mapping element that resolves the height displacement for each of a plurality of regions on the image into a grid element with a height value.

11. The system as set forth in claim 8 further comprising a thresholding element that resolves each height value respectively into a binary value based upon whether a height value is above or below at least one predetermined parameter.

12. The system as set forth in claim 11 wherein the predetermined parameter is at least one of (a) height displacement above or below a surrounding surface in the region and (b) area of a differing height displacement relative to the surrounding surface in the region.

13. The system as set forth in claim 8 wherein the filter (a) generates a best-fit surface of average height about each of selected pixels in the range image, (b) establishes a normal to the best-fit surface, respectively for each of the pixels, to (c) determine the height displacement of the about each of the pixels relative to the best-fit surface.

14. The system as set forth in claim 13 wherein the filter includes a background region about each of the selected pixels from which the best-fit surface is established.

15. The system as set forth in claim 14 wherein the filter includes a foreground region, located proximate to the background region and including at least one of the selected pixels in which the relative height displacement is determined.

16. The system as set forth in claim 15 wherein at least one of a size and a shape of at least one of the background region and the foreground region is user-defined based upon at least one of a size and a shape of the object.

18. The system as set forth in claim 8 wherein the location element determines if a suitable minimal cost region exists.

19. The system as set forth in claim 8 wherein each grid element comprises part of a regular grid of predetermined density on the image.

20. The system as set forth in claim 8 wherein the image includes at least one exclusionary zone thereon that is omitted from the minimal cost region.

21. The system as set forth in claim 20 wherein the exclusionary zone includes at least one of labels, printing and embellishments on the surface.

22. The system as set forth in claim 21 wherein the surface comprises at least part of a package and the minimal cost region is adapted to receive at least one of an applied label and printing.

23. The system as set forth in claim 8 wherein the surface comprises at least part of a package and the minimal cost region is adapted to receive at least one of an applied label and printing.

17. The system as set forth in 8 wherein the camera assembly comprises a displacement sensor that projects a line of light on the object and receives light from the projected line at an imager in a manner that defines a plurality of displacement values in a height direction.