Method and apparatus for performing fixturing in a machine vision system

• US 6,751,361 B1
• Filed: 12/22/2000
• Issued: 06/15/2004
• Est. Priority Date: 12/22/2000
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Wagman, Adam
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): Alavi, Amir
• Application Number:
  US09/747,814
• Time in Patent Office: 1,271 Days
• Field of Search: 382/103, 382/145, 382/141, 382/147, 382/151, 382/154, 382/190, 382/195, 382/203, 382/287, 382/288, 382/289, 382/294, 382/306, 348/87, 348/94, 348/95
• US Class Current: 382/287
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 10/245 by locating a pattern; Special marks for positioning
• CPC Class Codes: H05K 1/0269 for visual or optical inspection
• CPC Class Codes: H05K 2201/09918 Optically detected marks used for aligning tool relative to the PCB, e.g. for mounting of components
• CPC Class Codes: H05K 3/0008 for aligning or positioning of tools relative to the circuit board H05K3/4638, H05K3/4679 take precedence; for manufacturing assemblages of components H05K13/0015

Abstract

A single non-rotationally symmetric fiducial mark, such as a Universal Alignment Target, is placed on an object and the alignment of the object is determined with a vision tool that can align objects with translation and at least one additional degree of freedom, such as angular orientation. Alternatively, if a unique non-rotationally symmetric feature occurs naturally on the object, that feature may be used instead of a fiducial mark. In one embodiment, a geometrical feature matching vision tool is used to locate the single fiducial mark. In another embodiment, a normalized correlation search tool is used to locate the mark. The tool internally generates a set of rotated and scaled patterns that are then stored. The stored patterns are subsequently used to perform the search. In still another embodiment, a normalized correlation search tool internally generates a set of rotated and scaled patterns at runtime when the search for the mark is being performed.

Claims

1. A method for determining the location and angular alignment of an object with respect to a fixed coordinate system in a machine vision system with a camera and processing system for obtaining an image of the object and a vision tool capable of aligning location and at least one other non-translational degree of freedom, the method comprising:

(a) placing a single non-rotationally symmetric fiducial mark on the object at a predetermined location on the object and at a predetermined angular orientation with respect to the object;

(b) using the vision tool to process the image and locate the fiducial mark in the image and to determine its location and angular orientation with respect to the fixed coordinate system; and

(c) using the location and angular orientation of the fiducial mark to calculate the location and angular orientation of the object with respect to the fixed coordinate system.

2. The method of claim 1 wherein the vision tool is a multiple pattern normalized correlation tool.

3. The method of claim 1 wherein the vision tool is a geometrical pattern matching tool.

4. The method of claim 1 wherein step (b) comprises locating a selected area of the object by means other than the vision tool and using the vision tool to process an image of the selected area.

5. The method of claim 1 wherein step (b) comprises determining the location and angular orientation of the fiducial mark directly from the outputs of the vision tool.

6. The method of claim 1 wherein step (b) comprises calculating the location and angular orientation of the fiducial mark from the outputs of the vision tool.

7. The method of claim 1 wherein the fiducial mark is a Universal Alignment Target.

8. Apparatus for determining the location and angular alignment of an object with respect to a fixed coordinate system in a machine vision system with a camera and processing system for obtaining an image of the object and a vision tool capable of aligning location and at least one other non-translational degree of freedom, the apparatus comprising:

means for placing a single non-rotationally symmetric fiducial mark on the object at a predetermined location on the object and at a predetermined angular orientation with respect to the object;

an image processing system that uses the vision tool to process the image and locate the fiducial mark in the image and to determine its location and angular orientation with respect to the fixed coordinate system; and

an object processing system that uses the location and angular orientation of the fiducial mark to calculate the location and angular orientation of the object with respect to the fixed coordinate system.

9. The apparatus of claim 8 wherein the vision tool is a multiple pattern normalized correlation tool.

10. The apparatus of claim 8 wherein the vision tool is a geometrical pattern matching tool.

11. The apparatus of claim 8 wherein the image processing system comprises a mechanism other than the vision tool that locates a selected area of the object and wherein the vision tool processes an image of the selected area.

12. The apparatus of claim 8 wherein the image processing system comprises a mechanism that determines the location and angular orientation of the fiducial mark directly from the outputs of the vision tool.

13. The apparatus of claim 8 wherein the image processing system comprises a mechanism that calculates the location and angular orientation of the fiducial mark from the outputs of the vision tool.

14. The apparatus of claim 8 wherein the fiducial mark is a Universal Alignment Target.

15. A method for determining the location and angular alignment of an object with respect to a fixed coordinate system in a machine vision system with a camera and processing system for obtaining an image of the object and a vision tool capable of aligning location and at least one other non-translational degree of freedom, the method comprising:

(a) selecting a single pre-existing non-rotationally symmetric feature that is at a predetermined location on the object and at a predetermined angular orientation with respect to the object;

(b) using the vision tool to process the image and locate the feature in the image and to determine its location and angular orientation with respect to the fixed coordinate system; and

(c) using the location and angular orientation of the feature to calculate the location and angular orientation of the object with respect to the fixed coordinate system.

16. The method of claim 15 wherein the vision tool is a multiple pattern normalized correlation tool.

17. The method of claim 15 wherein the vision tool is a geometrical pattern matching tool.

18. The method of claim 15 wherein step (b) comprises locating a selected area of the object by means other than the vision tool and using the vision tool to process an image of the selected area.

19. The method of claim 15 wherein step (b) comprises determining the location and angular orientation of the feature directly from the outputs of the vision tool.

20. The method of claim 15 wherein step (b) comprises calculating the location and angular orientation of the feature from the outputs of the vision tool.

21. Apparatus for determining the location and angular alignment of an object with respect to a fixed coordinate system in a machine vision system with a camera and processing system for obtaining an image of the object and a vision tool capable of aligning location and at least one other non-translational degree of freedom, the apparatus comprising:

means for selecting a single preexisting non-rotationally symmetric feature that is at a predetermined location on the object and at a predetermined angular orientation with respect to the object;

an image processing system that uses the vision tool to process the image and locate the feature in the image and to determine its location and angular orientation with respect to the fixed coordinate system; and

an object processing system that uses the location and angular orientation of the feature to calculate the location and angular orientation of the object with respect to the fixed coordinate system.

22. The apparatus of claim 21 wherein the vision tool is a multiple pattern normalized correlation tool.

23. The apparatus of claim 21 wherein the vision tool is a geometrical pattern matching tool.

24. The apparatus of claim 21 wherein the image processing system comprises a mechanism other than the vision tool that locates a selected area of the object and wherein the vision tool processes an image of the selected area.

25. The apparatus of claim 21 wherein the image processing system comprises a mechanism that determines the location and angular orientation of the feature directly from the outputs of the vision tool.

26. The apparatus of claim 21 wherein the image processing system comprises a mechanism that calculates the location and angular orientation of the feature from the outputs of the vision tool.

27. A machine vision system for determining the location and angular alignment of an object with respect to a fixed coordinate system, comprising:

a camera and processing system for obtaining an image of the object;

a vision tool capable of aligning location and at least one other non-translational degree of freedom;

means for selecting a single non-rotationally symmetric feature that is at a predetermined location on the object and at a predetermined angular orientation with respect to the object;

an image processing system that uses the vision tool to process the image and locate the feature in the image and to determine its location and angular orientation with respect to the fixed coordinate system; and

an object processing system that uses the location and angular orientation of the feature to calculate the location and angular orientation of the object with respect to the fixed coordinate system.

28. The machine vision system of claim 27 wherein the feature is a fiducial mark placed on the object for the purpose of calculating the location and angular orientation of the object.

29. The machine vision system of claim 27 wherein the feature is a pre-existing feature on the object.