Method and apparatus for hardness tester
A hardness tester has an indentation former forming an indentation by pressing an indenter against a surface of a sample; an image capture controller controlling a CCD camera to capture an image of the surface of the sample and obtain image data; an indentation area extractor extracting an indentation area based on the obtained image data; and a hardness calculator calculating hardness of the sample based on the extracted indentation area. The indentation area extractor has a reduced image generator reducing the image obtained from the image data of the surface of the sample at a scale ratio selected from a plurality of predetermined scale ratios and generating a reduced image; and a pattern matcher performing pattern matching with respect to the generated reduced image and extracting the indentation area.
1. A hardness tester for measuring hardness of a sample by applying a predetermined test force to a surface of the sample with an indenter to form an indentation and measuring dimensions of the indentation, the hardness tester comprising:
a central processing unit, comprising
an indentation former configured to form the indentation in the surface of the sample by pressing the indenter against the surface of the sample;
an image capture controller configured to control an image capturer to capture an image of the surface of the sample and obtain image data of the surface of the sample;
an indentation area extractor configured to extract an indentation area formed in the surface of the sample based on the image data of the surface of the sample obtained by the image capture controller, the indentation area extractor comprising:
a reduced image generator configured to reduce the image obtained from the image data of the surface of the sample at a scale ratio selected from a plurality of predetermined scale ratios, the reduced image generator further configured to generate a reduced image; and
a pattern matcher configured to perform pattern matching with respect to the reduced image generated by the reduced image generator by comparing luminance values of the reduced image with luminance values of a scanning model and determining a degree of correlation between the reduced image and the scanning model, the pattern matcher further configured to extract the indentation area from the reduced image; and
a hardness calculator configured to calculate the hardness of the sample based on the indentation area extracted by the indentation area extractor,
wherein the degree of correlation between the reduced image and the scanning model based on the luminance values is calculated on a per column basis.
2. The hardness tester according to claim 1 , wherein the pattern matcher is further configured to extract the indentation area based on a degree of correlation calculated by scanning the reduced image with the scanning model including an indentation shape corresponding to the indenter.
3. The hardness tester according to claim 2 , wherein the pattern matcher is further configured to:
calculate the degrees of correlation by scanning the reduced image at the scale ratios in a predetermined sequence; and
extract an area showing the maximum degree of correlation as the indentation area when a maximum degree of correlation among the calculated degrees of correlation is determined to be equal to or greater than a predetermined threshold value.
4. The hardness tester according to claim 2 , wherein the pattern matcher is further configured to extract, as the indentation area, the area showing the maximum degree of correlation among all degrees of correlation calculated by scanning all reduced images at all scale ratios.
5. The hardness tester according to claim 3 , wherein the pattern matcher is further configured to extract, as the indentation area, the area showing the maximum degree of correlation among all degrees of correlation calculated by scanning all reduced images at all scale ratios.
6. The hardness tester according to claim 1 , further comprising a display controller configured to display, on a display, the hardness of the sample calculated by the hardness calculator.
7. The hardness tester according to claim 2 , further comprising a display controller configured to display, on a display, the hardness of the sample calculated by the hardness calculator.
8. The hardness tester according to claim 3 , further comprising a display controller configured to display, on a display, the hardness of the sample calculated by the hardness calculator.
9. The hardness tester according to claim 4 , further comprising a display controller configured to display, on a display, the hardness of the sample calculated by the hardness calculator.
10. The hardness tester according to claim 5 , further comprising a display controller configured to display, on a display, the hardness of the sample calculated by the hardness calculator.
11. A method of testing hardness with a hardness tester by applying a predetermined test force to a surface of a sample with an indenter to form an indentation and measuring dimensions of the indentation, the method comprising:
forming the indentation in the surface of the sample by pressing the indenter against the surface of the sample;
controlling an image capturer to capture an image of the surface of the sample and obtain image data of the surface of the sample;
extracting an indentation area formed in the surface of the sample based on the image data of the surface of the sample obtained in said controlling the image capturer, said extracting the indentation area comprising:
reducing the image obtained from the image data of the surface of the sample at a scale ratio selected from a plurality of predetermined scale ratios, and generating a reduced image;
performing pattern matching with respect to the reduced image generated in said reducing the image by comparing luminance values of the reduced image with luminance values of a scanning model and determining a degree of correlation between the reduced image and the scanning model; and
extracting the indentation area from the reduced image; and
calculating the hardness of the sample based on the indentation area extracted in said extracting an indentation area,
wherein the degree of correlation between the reduced image and the scanning model based on the luminance values is calculated on a per column basis.
12. The hardness tester according to claim 1 , wherein the scanning model is divided into a plurality of portions having different luminance values.
13. The hardness tester according to claim 12 , wherein one portion of the plurality of portions included in the scanning model corresponds to the indentation area.
14. The hardness tester according to claim 12 , wherein the portions in the scanning model have rectangular shapes.
15. The hardness tester according to claim 12 , wherein the degree of correlation between the reduce image and the scanning model is determined with respect to one portion of the scanning model at a time.
16. The hardness tester according to claim 1 , wherein the reduced image is rotated prior to performing the pattern matching.
17. The hardness tester according to claim 1 , further comprising:
determining measurements of the extracted indentation area for calculating the hardness of the sample.
18. The hardness tester according to claim 1 , wherein the pattern matching is performed by raster scanning in which the scanning model is shifted in a column direction to calculate the degree of correlation.