Surface defect inspection system

• US 4,403,294 A
• Filed: 11/28/1980
• Issued: 09/06/1983
• Est. Priority Date: 11/30/1979
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd., Japan Nuclear Fuel Limited
• Original Assignee: Hitachi, Ltd., Japan Nuclear Fuel Limited
• Inventors: Hamada, Toshimitsu, Makihira, Hiroshi, Nakagawa, Yasuo, Udaka, Makoto
• Primary Examiner(s): Chin, Gary
• Application Number:
  US06/211,113
• Time in Patent Office: 1,012 Days
• Field of Search: 364/507, 364/515, 364/525, 358/101, 358/106, 358/107, 356/430, 356/431, 356/237, 356/239, 250/202, 250/562, 250/563, 250/572, 340/146.3 AC, 340/146.3 AE
• US Class Current: 702/40
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

A surface defect inspection system comprises an image pick-up device for picking up an image by sequentially scanning the surface of an object two-dimensionally, a threshold circuit for quantizing the image signal produced from the image pick-up device as a binary code, a pattern feature extracting device for making calculations for extracting the features of image patterns from the quantized signal in synchronism with the scanning, and for temporarily storing the result of the calculations, a pattern region end decision device for deciding that individual pattern regions have ended in one direction, and a defect decision device for reading out from the pattern feature extracting device the result of the calculations on the pattern features corresponding to the positions each of the patterns in the direction perpendicular to the one direction each time of the decision that each pattern region has ended, so that the feature of each pattern scanned is compared with a predetermined reference, thus deciding and an indication of producing the presence or absence of a defect.

Claims

1. A surface defect inspection system comprising:

an image pick-up means for picking up an image by sequentially raster scanning the surface of an object two-dimensionally in abscissa and ordinate directions;

threshold means for quantizing an image signal produced from said image pick-up means as a binary signal in accordance with a predetermined threshold and sampling the quantized signal;

register means having a storage capacity corresponding to at least one raster scan line for sequentially and temporarily storing the sampled quantized signal delivered from said threshold means;

holding means for, when the sampled quantized signal corresponding to a defect pattern is delivered from said threshold means

for the first time at a certain abscissa in a certain ordinate corresponding to a certain raster scan line, holding the sampled quantized signal corresponding to the defect pattern at a portion corresponding to the abscissa of the corresponding defect pattern in said register means during succeeding scanning operations in the ordinate direction as long as the sampled quantized signal delivered from said threshold means includes at least one quantized signal corresponding to a defect pattern in an abscissa area having an abscissa of the defect pattern where said register means includes quantized signals corresponding to a defect pattern continuously in the abscissa direction, in each of succeeding raster scan lines;

pattern region end decision means for deciding that the defect pattern region has ended in the ordinate direction when the sampled quantized signal delivered from said threshold means includes no quantized signal corresponding to a defect pattern in the abscissa area having an abscissa of the defect pattern in a succeeding raster scan line;

pattern feature extracting means for extracting features of the defect pattern in accordance with the sampled quantized signal delivered from said threshold means in synchronism with the scanning in the abscissa direction;

memory means having a storage capacity corresponding to at least one raster scan line for temporarily and sequentially storing the result of the calculation delivered from said pattern feature extracting means to a storage area corresponding to the abscissa where the defect pattern exists;

reading means for, when said pattern region end decision means decides that the defect pattern region has ended in the ordinate direction, reading the features of the defect pattern from the storage area of said memory means corresponding to the abscissa where the defect pattern exists; and

defect decision means for comparing the features of each of the defect patterns separately read out of said reading means with a predetermined reference to thereby decide whether the defect pattern is acceptable or not.

2. A surface defect inspection system according to claim 1, wherein said holding means comprises a first shift register forming said register means so as to be able to shift said input sampled quantized signal, and a logical circuit for obtaining a logic combination between said sampled quantized signal delivered from said threshold means and a sampled quantized signal delivered from said shift register.

3. A surface defect inspection system according to claim 2, wherein said pattern region end decision means further comprises:

second shift register having a storage capacity corresponding to at least one raster scan line capable of storing no sampled quantized signal corresponding to the defect pattern when no sampled quantized signal corresponding to the defect pattern is delivered from said threshold means;

first rewriting means for rewriting the second shift register by the contents of said first shift register when the sampled quantized signal corresponding to the defect pattern is delivered from said first shift register, and from the time when the sampled quantized signals corresponding to the defect pattern are delivered from both of said threshold means and said first shift register, to the time when the output signal from said first shift register is changed from the sampled quantized signal to no sampled quantized signal corresponding to the defect pattern; and

second rewriting means for rewriting the contents of the second shift register when no sampled quantized signals corresponding to the defect pattern are delivered from both of said threshold means and said first shift register.

4. A surface defect inspection system according to claim 2, wherein said pattern region end decision means further comprises a third shift register having a storage capacity corresponding to at least one raster scan line for storing the sampled quantized signal delivered from the first shift register, and a logical circuit for obtaining a logic combination between the sampled quantized signal delivered from the first shift register and the sampled quantized signal delivered from the third shift register.

5. A surface defect inspection system according to claim 1, wherein when the feature of the defect pattern is an area thereof, said pattern feature extracting means calculates the sampled quantized signal delivered from said threshold means for each abscissa through calculating means, and said memory means stores the result of the calculation delivered from said calculating means for each abscissa.

6. A surface defect inspection system according to claim 1,

wherein said pattern feature extracting means extracts the area of a pattern, the region length and the maximum width of the pattern along X axis and the region length and the maximum width of the pattern along Y axis as a feature thereof, from the binary signal delivered from said threshold means, and

wherein said defect decision means classifies patterns having an area larger than a predetermined value ε

₁ into pits and cracks, and includes means deciding that a pit having an area smaller than a predetermined value ε

₃ is a tolerable defect, said means deciding that a crack having a maximum width smaller than a predetermined value ε

₅ is a tolerable defect.

7. A surface defect inspection system according to claim 6, wherein defects are classified into pits and cracks by use of a ratio between the product of the region lengths of the pattern along X and Y axes respectively and the area of the pattern, and the ratio of the region lengths of the pattern along X and Y axes.

8. A surface defect inspection system comprising image pick-up means for picking up an image of a surface of an object including defect patterns by sequentially scanning the surface of an object line by line, binary converter means for converting the image signal produced from said image pick-up means into a binary code signal which represents the patterns on the surface, means for extending each pattern in a direction perpendicular to the direction of scan line to an end scan line for the pattern beyond which the pattern no longer exists and combining extended patterns, when they overlap to each other during said extending, into one extended pattern, pattern feature extracting means for extracting features of each extended pattern including at least one pattern in synchronism with the scanning, and for temporarily storing the features being extracted, pattern region end detection means for detecting the end scan line of each extended pattern, and defect discrimination means for reading out from said pattern feature extracting means the features of the extended pattern upon detection of the end scan line of the extended pattern, comparing the features of each extended pattern with at least one predetermined reference, and discriminating the extended pattern according to a predetermined classification based on the result of said comparison.

9. A surface defect inspection system according to claim 8, wherein said pattern region end detection means generates an end signal at each position of the end scan line corresponding to the width of the extended pattern.

10. A surface defect inspection system according to claim 8, wherein said pattern feature extracting means extracts the area of a pattern, the lengths of the pattern and the extended pattern in the directions along the scan line and perpendicular to the scan line.

11. A surface defect inspection system according to claim 8, wherein said defect discriminating means classifies patterns having an area larger than a predetermined value ε

₁ into pits and cracks, said means deciding that a pit having an area smaller than a predetermined value ε

₃ is a tolerable defect, said means deciding that a crack having a maximum width smaller than a predetermined value ε

₅ is a tolerable effect.

12. A surface defect inspection system according to claim 9, wherein defects are classified into pits and cracks by use of the ratio of the product of the lengths of the extended pattern along the two directions to the area of the pattern, and the ratio of the lengths of the pattern along the two directions.