Inspection system and process

• US 5,734,742 A
• Filed: 09/15/1995
• Issued: 03/31/1998
• Est. Priority Date: 09/19/1994
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Suzuki, Yutaka, Katabami, Sachiyo, Asaeda, Teruo, Imanisi, Masanori, Nousou, Kazunori
• Primary Examiner(s): Mancuso, Joseph
• Application Number:
  US08/528,868
• Time in Patent Office: 928 Days
• Field of Search: 382/103, 382/104, 382/107, 382/141, 382/149, 248/92, 248/94, 248/125, 248/126
• US Class Current: 382/141
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/30156 Vehicle coating
• CPC Class Codes: G06T 7/0004 Industrial image inspection

Abstract

In order to reliably detect a defect on an inspected surface, electronic pictures of the inspected surface are formed at different positions by moving an imaging area relative to the inspected surface. Defect candidate regions are extracted from a series of the pictures. The system examines whether a movement from one candidate region to another candidate region is proportional to the movement of the imaging area. If the movement between the candidate regions is in proportion to the movement of the imaging area, the system judges that the candidate regions are imagery of a defect on the inspected surface.

Claims

1. An inspection process for detecting a defect on an inspected surface of an object to be inspected, said inspection process comprising:

an image producing step of moving said inspected surface relative to an imaging area and forming a sequence of electronic pictures of the inspected surface within said imaging area; and

an image processing step of extracting defect candidate regions from said pictures, of determining a spatial separation from a position of one candidate region extracted from a previous picture which is one of the pictures, to a position of another candidate region extracted from a subsequent picture which is one of the pictures formed after the previous picture in said image producing step, of determining whether said spatial separation is in agreement with a movement of said inspected surface relative to said imaging area, and of judging that there exists a defect in the inspected surface when said spatial separation is in agreement with said movement.

2. An inspection process as claimed in claim 1:

wherein said image producing step comprises;

a moving step of moving at least one of said object to be inspected, and an imaging means viewing said inspected surface in said imaging area; and

an imaging step of forming said electronic pictures with said imaging means; and

wherein said image processing step comprises;

an extracting step of extracting a set of the candidate regions from said sequence of the pictures;

an examining step of examining positions of the candidate regions extracted from at least two of the pictures, determining a quantity of a positional change from the position of one candidate region extracted from said previous picture, to the position of another candidate region extracted from said subsequent picture, and examining whether said quantity of the positional change is proportional to a quantity of movement of said inspected surface relative to said imaging area from a time of image formation of said previous picture to a time of image formation of said subsequent picture; and

a deciding step of deciding that there exists a defect on the inspected surface and producing a defect detection signal when said quantity of the positional change is proportional to said quantity of the movement of said inspected surface.

3. An inspection process as claimed in claim 2 wherein said pictures are formed while a bright and dark pattern is projected in the imaging area on the inspected surface, so that each of said pictures is an image of the bright and dark pattern projected on the inspected surface.

4. An inspection process as claimed in claim 3 wherein each of said pictures formed by said imaging means comprises a bright zone and a dark zone;

said extracting step is performed by extracting the candidate regions only from the bright zones of said pictures; and

said examining step is performed by examining whether said quantity of the positional change between two of the candidate regions extracted from the bright zones is proportional to said quantity of the movement of said inspected surface.

5. An inspection process as claimed in claim 2 wherein

said examining step comprises a selecting step of selecting a subset from said set of the candidate regions;

said subset comprises a plurality of said candidate regions;

each of the candidate regions of said subset is one candidate region extracted from a unique one of a subsequence of said sequence of the electronic pictures, so that the candidate regions of said subset are all different in time of image formation;

all the candidate regions of said subset are arranged in an order of time of image formation substantially in a straight line in an image plane of said imaging means;

each of the candidate regions of the subset is spaced from another of the candidate region of the subset at a distance which is substantially proportional to a distance traveled by said inspected surface from the time of image formation of each of the candidate regions of said subset to the time of image formation of another of the candidate regions of said subset; and

said deciding step comprises an operation for allowing generation of said defect detection signal only when the number of the candidate regions of the subset selected in said selecting step is equal to or greater than a predetermined number.

6. An inspection process according to claim 1 wherein the image producing step comprises an operation for moving said inspected surface relative to said imaging area in a predetermined direction and an operation for forming the sequence of the electronic pictures of the inspected surface at different positions relative to the imaging area.

7. An inspection process according to claim 1 wherein the image producing step comprises a measuring operation for measuring a quantity of movement of said inspected surface relative to said imaging area, and the image processing step comprises a checking operation for comparing said spatial separation with the quantity of the movement to determine whether said spatial separation is in agreement with the movement of the said inspected surface.

8. An inspection system for detecting a defect in an inspected surface of an object to be inspected, said inspection system comprising:

an image producing means for moving said inspected surface relative to an imaging area and forming a sequence of electronic pictures of the inspected surface within said imaging area;

an image processing means for extracting defect candidate regions from said pictures, for determining a spatial separation from a position of one candidate region extracted from a previous picture which is one of the pictures, to a position of another candidate region extracted from a subsequent picture which is one of the pictures formed after the previous picture by said image producing means, for determining whether said spatial separation is in agreement with a movement of said inspected surface relative to said imaging area, and for judging that there exists a defect in the inspected surface when said spatial separation is in agreement with said movement.

9. An inspection system as claimed in claim 8:

wherein said image producing means comprises;

an imaging means for viewing said inspected surface in said imaging area, and forming said electronic pictures; and

a moving means for moving at least one of said object to be inspected, and said imaging means; and

wherein said image processing means comprises;

an extracting means for extracting a set of the candidate regions from the sequence of the pictures;

an examining means for examining positions of the candidate regions extracted from at least two of the pictures, for determining a quantity of a positional change from the position of one candidate region extracted from said previous picture, to the position of another candidate region extracted from said subsequent picture, and for examining whether said quantity of the positional change is proportional to a quantity of movement of said inspected surface relative to said imaging area from a time of image formation of said previous picture to a time of image formation of said subsequent picture; and

a deciding means for producing a defect detection signal indicating that there exists a defect on the inspected surface when said positional change is proportional to the movement of said inspected surface.

10. An inspection system as claimed in claim 9 wherein said image producing means further comprises an illuminating means for projecting a bright and dark pattern on said inspected surface, so that each of the pictures produced by said imaging means is an image of the bright and dark pattern projected on the inspected surface and comprises a bright zone and a dark zone.

11. An inspection system as claimed in claim 10 wherein said image processing means further comprises a boundary recognizing means for recognizing a boundary between a bright zone and a dark zone in said pictures of the bright and dark pattern;

and said extracting means includes a means for extracting said candidate regions in accordance with a change in luminance in a region other than said boundary.

12. An inspection system as claimed in claim 10 wherein said image processing means further comprises a picture storing means for storing said pictures sequentially produced by said imaging means, and said extracting means includes a means for extracting said candidate regions only from the bright zones of said pictures stored in said picture storing means.

13. An inspection system as claimed in claim 10 wherein said extracting means includes a means for extracting the candidate regions only from the bright zones of said pictures;

and said examining means includes a means for examining only the positions of the candidate region extracted from the bright zones in the pictures.

14. An inspection system as claimed in claim 9 wherein

said subsequent picture comprises one of the candidate regions and each of a plurality of said previous pictures comprises one of the candidate regions;

said examining means comprises;

a comparing means for comparing the candidate region extracted from said subsequent picture with the candidate regions extracted from each of the previous pictures formed sequentially before the subsequent image by said image producing means, to determine a quantity of displacement from the position of the candidate region extracted from each of the previous pictures to the position of the candidate region of said subsequent picture;

a measuring means for determining a quantity of movement of said inspected surface relative to said imaging area from an instant when each of said previous pictures is formed by said image producing means to an instant when said subsequent picture is formed by said image producing means; and

a checking means for determining whether said quantity of displacement to the position of the candidate region extracted from the subsequent picture from the position of the candidate region extracted from each of the previous picture is proportional to said quantity of movement of said imaging area from the instant of formation of a corresponding one of the previous picture to the instant of formation of the subsequent picture, to determine whether each of the previous pictures is a conformable picture or not, said conformable picture being a picture comprising a conformable candidate region from which said quantity of displacement to the position of the candidate region in the subsequent picture is proportional to said quantity of movement of said inspected surface from the instant of image formation of the conformable picture to the instant of image formation of the subsequent picture; and

said deciding means comprises a means for judging that the candidate region in the subsequent picture is a defect if the number of the conformable pictures is equal to or greater than a predetermined number.

15. An inspection system as claimed in claim 9 wherein

said examining means comprises a selecting means for selecting a subset from said set of the candidate regions;

said subset comprises a plurality of said candidate regions;

each of the candidate regions of said subset is one candidate region extracted from a unique one of a subsequence of said sequence of the electronic pictures, so that the candidate regions of said subset are all different in time of image formation;

all the candidate regions of said subset are arranged in an order of the time of image formation substantially in a straight line in an image plane of said imaging means;

each of the candidate regions of the subset is spaced from another of the candidate region of the subset at a distance which is substantially proportional to a distance traveled by said inspected surface from the time of image formation of each of the candidate regions of said subset to the time of image formation of another of the candidate regions of said subset; and

said deciding means comprises a means for allowing generation of said defect detection signal only when the number of the candidate regions of the subset selected in said selecting step is equal to or greater than a predetermined number.

16. An inspection system as claimed in claim 15 wherein said predetermined number is equal to or greater than three, said subsequence comprises a first selected picture which is one of said pictures of said sequence and a last selected picture which is one of said pictures of said sequence and which follows after said first selected picture in said sequence, and an intermediate picture which is intermediate between said first and last selected pictures in said sequence is excluded from said subsequence.

17. An inspection system according to claim 8 wherein the image producing means comprises a machine for moving said inspected surface relative to said imaging area in a predetermined direction along a straight line and a device for measuring the movement of the inspected surface relative to the imaging area.

18. An inspection system for detecting a defect on an inspected surface of an object to be inspected, said inspection system comprising:

an image producing subsystem for moving the inspected surface relative to an imaging area along a predetermined direction from a previous position to a subsequent position and forming a previous picture of the inspected surface within said imaging area at a previous time instant when the inspected surface is located at the previous position, and a subsequent picture of the inspected surface within the imaging area at a subsequent time instant when the inspected surface is located at said subsequent position; and

an image processing subsystem for extracting defect candidate regions as a candidate for a defect from said previous and subsequent pictures, for determining an image movement from an image location of the candidate region in said previous picture to an image location of the candidate region in said subsequent picture, for comparing said image movement with a movement of the inspected surface from said previous position to said subsequent position, and for producing a defect detection signal representing presence of a defect when said image movement is substantially in proportion to the movement of the inspected surface from the previous position to the subsequent position.

19. An inspection system as claimed in claim 18:

wherein said image producing means comprises;

an imager for producing a time series of pictures of said inspected surface within said imaging area, said previous and subsequent pictures being two of the pictures in said time series;

an illuminating means for illuminating said inspection surface in said image area; and

a moving means for producing relative motion between said inspected surface and said imager so that said inspected surface moves along a predetermined rectilinear direction in said imaging area, and producing a distance signal representing a distance traveled by said inspected surface in said imaging area; and

wherein said image processing means comprises;

a picture storage means for storing image data representing said time series of the picture;

an extracting means for extracting candidate regions from said time series of the pictures stored in said storage means;

an examining means for arranging said candidate regions extracted from said time series of the pictures in pairs each of which consisting of a first mate which is one candidate region extracted from said previous picture and a second mate which is one object region extracted from said subsequent picture, for determining the image movement between said first and second mates of each pair, for determining whether each pair is a matched pair or not by determining whether the image movement of each pair is substantially proportional to the movement of the inspected surface from the previous position to the subsequent position, and for grouping said matched pairs into a group of the matched pairs each of which comprises a single common one of the candidate regions; and

a deciding means for producing the defect detection signal when a number of the matched pairs in the group is equal to or greater than a predetermined number.

20. An inspection system as claimed in claim 18 wherein said illuminating means includes a means for projecting a bright and dark pattern on the inspected surface, said imaging area determined by said imager and said bright and dark pattern are held stationary, and said moving means comprises a conveyor for moving said object having said inspected surface so that an image point of a scene point fixed on the inspected surface moves along one of horizontal and vertical directions in an image plane of the imager.

21. An inspection system according to claim 18 wherein the image producing subsystem comprises a conveyor for moving the inspected surface relative to the imaging area, a detecting device for detecting the movement of the inspected surface relative to the imaging area and generating a distance signal representing a quantity of the movement, and a camera for forming pictures of the inspected surface within the imaging area and producing a video signal, and wherein the image processing subsystem is connected with the detecting device and the camera, and receives the distance signal and the video signal.