Method and apparatus for improved vision detector image capture and analysis

• US 20050226490A1
• Filed: 03/30/2005
• Published: 10/13/2005
• Est. Priority Date: 01/29/2002
• Status: Abandoned Application

• Current Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Original Assignee: Cognex Technology & Investment Corporation (Cognex Corporation)
• Inventors: Phillips, Brian S., Silver, William M., Mirtich, Brian V.
• Application Number:
  US11/094,650
• Publication Number:
  US 20050226490A1
• Time in Patent Office: Days
• US Class Current: 382/141
• CPC Class Codes: G06T 1/0007 Image acquisition
• CPC Class Codes: G06T 7/0004 Industrial image inspection

Abstract

Disclosed are methods and apparatus for improvements to image capture and analysis for vision detectors. The improvements provide for asynchronous capture and analysis and allow high frame rates to be maintained when image analysis may under certain conditions comprise a significantly longer time interval than image capture. The improvements prevent memory buffer overflow and provide for short and predictable decision delays even though an arbitrary and potentially unlimited number of images are captured and analyzed for each object.

Claims

1. A method for detecting and inspecting an object, comprising:

capturing a sequence of frames, each frame in the sequence of frames comprising an image of a field of view, the sequence of frames comprising a first plurality of frames for which the object is not present in the field of view and a second plurality of frames for which the object is present in the field of view; and

analyzing each frame in the sequence of frames to detect and inspect the object, wherein the analysis is responsive to the first plurality of frames and the second plurality of frames, and wherein capture and analysis of frames are substantially asynchronous.

2. The method of claim 1 wherein analyzing a frame in the sequence of frames takes less time when the object does not appear to be present in the field of view than when the object does appear to be present.

3. The method of claim 2, wherein

analyzing a frame in the sequence of frames comprises at least one detection substep and at least one inspection substep;

and

at least one inspection substep is skipped when the at least one detection substep determines that the object does not appear to be present in the field of view, resulting in less time being taken to analyze the frame.

4. The method of claim 1, further comprising

using a first thread to control capturing the sequence of frames;

and

using a second thread to control analyzing the sequence of frames.

5. The method of claim 1, wherein the second plurality of frames has a count comprising the number of frames in the second plurality of frames, and further comprising limiting the count so as not to exceed a predefined value.

6. The method of claim 1, wherein

capturing a frame in the first plurality of frames begins at a first time;

analyzing a frame in the first plurality of frames begins at a second time, the second time being later than the first time by a lag time;

and further comprising

limiting the lag time responsive to a predefined value.

7. The method of claim 1 further comprising

capturing at least one additional frame;

and

flushing without analyzing the at least one additional frame when analyzing the sequence of frames reveals that analyzing the at least one additional frame is not necessary to detect and inspect the object.

8. The method of claim 1 wherein

analyzing a frame in the sequence of frames comprises at least one detection substep and at least one inspection substep;

and

the at least one detection substep and the at least one inspection substep are substantially asynchronous.

9. The method of claim 8, further comprising

using a first thread to control capturing the sequence of frames;

using a second thread to control the at least one detection substep; and

using a third thread to control the at least one inspection substep.

10. The method of claim 1 wherein capturing the second plurality of frames occurs at a higher rate than capturing the first plurality of frames.

11. A system for detecting and inspecting an object, comprising:

a capture process that captures a sequence of frames, each frame in the sequence of frames comprising an image of a field of view, the sequence of frames comprising a first plurality of frames for which the object is not present in the field of view and a second plurality of frames for which the object is present in the field of view; and

an analysis process that analyzes each frame in the sequence of frames to detect and inspect the object, wherein the analysis is responsive to the first plurality of frames and the second plurality of frames, and wherein the capture process and the analysis process are substantially asynchronous.

12. The system of claim 11 wherein the analysis of a frame in the sequence of frames takes less time when the object does not appear to be present in the field of view than when the object does appear to be present.

13. The system of claim 12, wherein

the analysis process comprises a detection process and an inspection process;

and

for any frame wherein the detection process determines that the object does not appear to be present in the field of view, the inspection process is skipped, resulting in less time being taken to analyze the frame.

14. The system of claim 11, further comprising

a first thread that controls the capture process;

and

a second thread that controls the analysis process.

15. The system of claim 11, wherein the second plurality of frames has a count comprising the number of frames in the second plurality of frames, and further comprising a frame count limiting process that limits the count so as not to exceed a predefined value.

16. The system of claim 11, wherein

capturing a frame in the first plurality of frames begins at a first time;

analyzing a frame in the first plurality of frames begins at a second time, the second time being later than the first time by a lag time;

and further comprising

a lag limiting process that limits the lag time responsive to a predefined value.

17. The system of claim 11 wherein the capture process captures at least one additional frame, and further comprising a flushing process that flushes without analyzing the at least one additional frame when the analysis process reveals that analyzing the at least one additional frame is not necessary to detect and inspect the object.

18. The system of claim 11 wherein

the analysis process comprises a detection process and an inspection process;

and

the detection process and the inspection process are substantially asynchronous.

19. The system of claim 18, further comprising

a first thread that controls the capture process;

a second thread that controls the detection process; and

a third thread that controls the inspection process.

20. The system of claim 11 wherein the capture process captures the second plurality of frames at a higher rate than the first plurality of frames.