Method and system for double feed detection

• US 6,761,352 B2
• Filed: 09/06/2002
• Issued: 07/13/2004
• Est. Priority Date: 11/14/2001
• Status: Expired due to Fees

• Current Assignee: Omron Canada, Inc. (Omron Corporation)
• Original Assignee: Omron Canada, Inc. (Omron Corporation)
• Inventors: Scicluna, Charles Paul, Neal, Jeffrey Charles, Browne, Douglas Craig
• Primary Examiner(s): Walsh, Donald P.
• Assistant Examiner(s): Bower, Kenneth W
• Application Number:
  US10/235,842
• Publication Number:
  US 20030091236A1
• Time in Patent Office: 676 Days
• Field of Search: 324/635, 324/644, 324/662, 324/671, 324/691, 324/716, 271/152, 271/153, 271/154, 271/663, 271/258.01, 271/258.02, 271/258.03, 271/258.04, 101/73
• US Class Current: 271/153
• CPC Class Codes: B65H 2220/03 indicating an entity which is measured, estimated, evaluated, calculated or determined but which does not constitute an entity which is adjusted or changed by the control process per se
• CPC Class Codes: B65H 2301/321 Standing on edge
• CPC Class Codes: B65H 2511/30 Numbers, e.g. of windings or rotations
• CPC Class Codes: B65H 2553/42 Cameras
• CPC Class Codes: B65H 2701/1315 side edges, i.e. regarded in context of transport
• CPC Class Codes: B65H 2701/1916 Envelopes and articles of mail
• CPC Class Codes: B65H 7/125 sensing the double feed or separation without contacting the articles

Abstract

A system for detecting overlapped flat objects in a sequence of flat objects have at least one of their edges exposed for viewing as they pass along a feed path. The system includes a sensor for generating a signal in response to detecting a flat object in the feed path and a camera responsive to the signal for capturing a digital image of the exposed edges of the detected flat object in the feed path. A vision system is coupled to the camera for receiving the digital image. The vision system analyzes at least a portion of the image to determine a pixel density variation along a direction perpendicular to the edges and uses the pixel density variation to output an indication of the number of edges in the image.

Claims

1. A method for detecting overlapped flat objects in a sequence of flat objects, the flat objects having at least one of their edges exposed for viewing as they pass along a feed path, said method comprising:

selecting a flat object in said feed path;

capturing a digital image of said exposed edges of said selected flat object;

processing at least a portion of said captured image encompassing said edges to determine a pixel density variation in a direction across said edges;

analyzing said pixel density variation to identify maxima and minima in said variation, wherein a start of an edge is identified by a maximum and an end of an edge is identified by a minimum; and

counting said maxima and minima to output an indication of a number of edges in said image.

2. The method of claim 1, further comprising determining an edge width of said flat object.

3. The method of claim 2, wherein determining said edge width further comprises:

computing an average pixel density in said processed portion;

assuming a first edge width if said average density is below a predetermined level; and

assuming a second edge width if said average density is above said predetermined level.

4. The method of claim 3, wherein counting further comprises:

counting maximum and minimum pairs that are spaced apart by less than said first edge width if said average density is below said predetermined level to output said indication of said number of edges; and

counting maximum and minimum pairs that are spaced apart by more than said second edge width if said average density is above said predetermined level to output said indication of said number of edges.

5. The method of claim 4, further comprising:

measuring a pitch between said counted maximum and minimum pairs; and

outputting an indication of an overlapped object if said number of edges is greater than or equal to a predetermined number and said average density is above said predetermined level, if said number of edges is greater than said predetermined number and said average density is below said predetermined level, or if said number of edges is equal to said predetermined number and said average density is below said predetermined level and said pitch is greater than a predetermined pitch.

6. The method of claim 1, wherein said flat object is a mail piece.

7. The method of claim 1, wherein said pixel density variation is a ratio of light to dark pixels.

8. The method of claim 3, wherein said average pixel density is a ratio of a total number of light pixels to a total number of dark pixels in said portion of said captured image.

9. The method of claim 5, wherein said predetermined number is two.

10. A system for detecting overlapped flat objects in a sequence of flat objects, said flat objects having at least one of their edges exposed for viewing as they pass along a feed path, said system comprising:

a sensor for generating a signal in response to detecting a flat object in said feed path;

a camera responsive to said signal for capturing a digital image of said exposed edges of said detected flat object in said feed path; and

,

a vision system coupled to said camera for receiving said digital image;

said vision system analyzing at least a portion of said image to determine a pixel density variation along a direction perpendicular to said edges and using said pixel density variation to output an indication of a number of edges in said image.

11. The system of claim 10, wherein an imaging region of said camera is spaced a predetermined distance before said sensor along said feed path.

12. The system of claim 11, wherein said predetermined distance is less than an expected length of said flat object.

13. The system of claim 10, wherein said vision system outputs an overlapped flat object signal if said number of edges is greater than or equal to a predetermined number and a measured average density for said image portion is above a predetermined level, if said number of edges is greater than said predetermined number and said average density is below said predetermined level, or if said number of edges is equal to said predetermined number and said average density is below said predetermined level and a measured pitch is greater than a predetermined pitch.

14. The system of claim 13, further comprising a controller for receiving said overlapped flat object signal from said vision system and said signal from said sensor, wherein said controller:

counts the number of overlapped flat object signals received and the number of signals received and stores an overlapped flat object count and a total flat object count;

outputs a fault signal if said overlapped flat object count increases by a first count without said total flat object count increasing by more than said first count or if said total flat object count increases by more than a second count without said overlapped flat object count increasing; and

outputs an overlapped flat object rejection signal if said overlapped flat object signal is received and said fault signal is not output.

15. The system of claim 14, wherein said first count is fifty.

16. The system of claim 15, wherein said second count is twenty.

17. The system of claim 15, wherein said second count is one.

18. The system of claim 14, further comprising:

a first sensor for generating a first signal in response to detecting said flat object in said feed path;

means for receiving said first signal from said first sensor and for outputting a first overlapped flat object signal if said signal from said sensor is received by said controller while said first signal from said first sensor is continuously received by said controller; and

means for combining said first overlapped flat object signal with said overlapped flat object signal.

19. The system of claim 18, wherein said first sensor is spaced a first predetermined distance before said sensor along said feed path.

20. The system of claim 19, wherein said first predetermined distance is greater than an expected length of said flat object.

21. The system of claim 14, further comprising:

a third sensor for generating a third signal in response to detecting said flat object in said feed path; and

means for delaying the output of said overlapped flat object rejection signal until said third signal is received by said controller.

22. The system of claim 21, wherein said third sensor is spaced a third predetermined distance after said sensor along said feed path.

23. The system of claim 10, wherein said camera is a digital camera.

24. The system of claim 10, wherein said flat object is a mail piece.

25. The system of claim 10, wherein said system is a mail sorting system.