JP2776234B2 - Indentation type hardness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indentation type hardness measuring apparatus, and more particularly, to a computer-based image processing method for measuring hardness according to an indentation type hardness test method such as a Vickers hardness test method or a Knoop hardness test method. The present invention relates to an indentation-type hardness measuring device.

[0002]

2. Description of the Related Art A polygonal indenter such as a Vickers hardness test and a Knoop hardness test is pressed against the surface of a test piece, and the hardness is measured from the diagonal length of the polygonal indentation generated on the test piece surface. Indentation hardness testing methods are well known and are often used to evaluate the mechanical properties of metallic materials.

[0003] As is well known, the Vickers hardness test method uses an indenter made of a diamond square pyramid, and the average value of two diagonal lengths of a square pyramid-shaped indentation formed on the surface of the test piece and the test piece of the indenter are used. The hardness is shown in relation to the pressing load, and the Knoop hardness test method uses an indenter with a diamond square pyramid, and the average value of the longer diagonal length of the long square pyramid-shaped indentation generated on the surface of the test piece and the indenter Shows the hardness in relation to the pressing load on the test piece.

An indentation type hardness measuring device for measuring the hardness by such a test method by image processing by a computer has already been proposed. As described in Japanese Patent Application Laid-Open No. HEI 1-312441, this indentation type hardness measuring apparatus takes an image of an indentation generated on the surface of a test piece by pressing an indenter by an imaging means such as a CCD camera connected to a microscope. Preliminary processing such as binarization is performed on the captured image data to extract boundaries (point sequence data) indicating each side of the indentation, and the extracted boundary is subjected to linear approximation conversion. The intersection of the straight line corresponding to the side is defined as the corner of the indent, the diagonal length of the indent is calculated by coordinate calculation, and the hardness is calculated based on the diagonal length, the pressing load value of the indenter, and the like.

[0005] As a conventional example of calculating the hardness by the same method, there is known a material testing technology Vol.38 No.1 January 1993
"Application of Image Processing to Vickers Hardness Measurement" on page 12
Can be mentioned. Here, a method of calculating a corner by approximating a straight line using the entire length of each side of an indentation is disclosed.

[0006]

Conventionally, in the above-mentioned indentation type hardness measuring apparatus, preprocessing such as binarization of captured image data is performed on all captured image data of the image captured by the imaging means. For this reason, pre-processing of the captured image data takes time, and this becomes more remarkable as the resolution of the imaging means increases for fine imaging.

[0007] The linear approximation conversion of the boundary indicating each side of the indentation is as follows.
According to a linear approximation formula such as the least squares method or half transformation, this is performed on the entire indentation side or the part excluding the vicinity of the corner of the indentation. Is assumed to be a straight line, and as shown in FIGS. 5A and 5B, if the indentation side s is a curve curved inward or outward, the straight line L obtained by the straight line approximation becomes The intersection point P of the straight line L is located at a position apart from the corner Ac of the indentation, and the intersection P does not correctly specify the corner Ac of the indentation. For this reason, if the indentation side is a curve, an accurate diagonal length cannot be obtained, and accurate hardness measurement cannot be performed.

An object of the present invention is to provide an indentation type hardness measuring apparatus which shortens the time required for pre-processing such as binarization of captured image data and performs high-precision hardness measurement even when the indentation side is a curve. It is an object.

[0009]

SUMMARY OF THE INVENTION The present invention relates to an indentation type hardness measuring device for pressing an indenter having a polygonal planar shape against the surface of a test piece and measuring the hardness from the polygonal indentation generated on the surface of the test piece. Imaging means for imaging the surface of the test piece with the mark, and two sides constituting the vicinity of the corner of the indentation based on image data of the image of the surface of the test piece imaged by the imaging means; Hardness calculating means for calculating coordinate values of the corners from two sides calculated by linear approximation based on the data in the vicinity of the corners and calculating the hardness of the test piece from these values and an indenter pressing load value; and With the provision of the above, the above-described object is achieved. An imaging unit configured to capture an image of the surface of the test piece provided with the indentation; an image memory configured to store captured image data of the surface of the test piece captured by the imaging unit; An image reduction processing unit that generates reduced image data by processing, a corner small area specifying unit that specifies a corner small area of an indentation from the reduced image data, and a captured image data stored in the image memory. A corner coordinate value calculating unit that performs image processing on captured image data of an area corresponding to the corner small area specified by the corner small area specifying unit, and calculates a coordinate value of a corner of the indentation; The object described above is achieved by providing a hardness calculating unit that calculates the hardness of the test piece from the coordinate values of the corners calculated by the coordinate value calculating unit and the indenter pressing load value.

[0010]

When the indenter having a polygonal planar shape is pressed against the surface of the test piece, the surface of the test piece including the polygonal indentation formed on the surface of the test piece is imaged by the imaging means. The captured image data is stored in the image memory. The coordinate values of the corners are calculated from the two sides calculated by the linear approximation based on the data near the corners in the captured image data, and the hardness of the test piece is calculated from the relationship with the load value. In addition, the image of the test piece surface based on the captured image data is subjected to reduction processing by the image reduction processing unit, and the corner small area of the indentation is specified from the reduced image data generated by the image reduction processing unit. The coordinate value of the corner of the indentation is calculated based on the captured image data of the area in the corresponding image memory. The hardness calculator calculates the hardness based on the coordinate values of the indentation corners.

[0011]

1 shows an embodiment of the indentation type hardness measuring apparatus according to the present invention. The indentation type hardness measuring device
A Vickers tester 3 that presses the indenter 1 of a square pyramid with a predetermined load against the surface of the test piece T on the stage 2, and the surface of the test piece when the indenter 1 of the Vickers tester 3 is pressed against the surface of the test piece T Camera (imaging means) that magnifies and images the indentation of the square contour generated in the microscope by the microscope 4
5 and an image processing device 6 by a computer which captures image data of the surface of the test piece taken by the CCD camera 5 and detects hardness (Vickers hardness) by image processing.

As shown in FIG. 2, the image processing device 6
Is an A / D converter 11 for converting an analog image signal output from the CCD camera 5 into a digital image signal;
An image memory 12 for storing a digital image signal from the conversion unit 11, that is, a captured image data, a captured image reduction processing unit 13, a reduced image memory 14, a smoothing processing unit 15,
The apparatus includes a binarization processing section 16, a corner small area specifying section 17, a corner coordinate value calculating section 18, a diagonal length calculating section 19, and a hardness calculating output section 20.

In this case, the contour of the indentation on the surface of the test piece is a regular square, and the test piece by the CCD camera 5 is adjusted so that the diagonal line of the indentation matches the coordinate axis of the image processing coordinate system (rectangular coordinates) in the image processing device 6. The imaging attitude of the front surface is determined, and thus the captured image data taken into the image memory 12 is one in which the diagonal line of the indent is aligned with the coordinate axes of the image processing coordinate system.

The captured image reduction processing section 13 performs reduced processing on the image of the test piece surface based on the captured image data to generate reduced image data. This reduction processing is performed by thinning out pixels constituting the image of the test piece surface, and the reduction ratio in this reduction processing may be about 1/8. When the reduction ratio is 1/8, the number of reduced images is 1/64 of the number of original size images based on the captured image data. FIG. 3A illustrates an original image, and FIG. 3B illustrates a reduced image. The reduced image data generated by the captured image reduction processing unit 13 is stored in the reduced image memory 14.

A smoothing processor 15 performs a smoothing process on the reduced image data to remove noise from the reduced image data stored in the reduced image memory 14, and a binarization processor 16.
Performs binarization on the reduced image data after the smoothing process with a predetermined threshold value.

The corner small area specifying unit 17 specifies a corner small area of the indentation A from the binarized reduced image data. The specification of the corner small area by the corner small area specifying unit 17 is shown in FIG.
As shown in FIG. 4A, which is an enlarged view of FIG. 4B, a point belonging to the indentation boundary from one point p in the indentation area and in each coordinate axis direction of the image processing coordinate system, here, the + X axis direction And the points Px1, Px2, Py1, and Py2 at the farthest positions in each of the -X axis direction, the + Y axis direction, and the -Y axis direction are extracted. The corner small areas Ex1, Ex2, Ey1, and Ey2 are specified on the image memory 12 centering on these points.

The corner coordinate value calculating section 18 stores the image memory 12
Above, image processing is performed on the captured image data (FIGS. 4B to 4E) of the corner small regions Ex1, Ex2, Ey1, and Ey2 specified by the corner small region specifying unit 17, and the corner of the indentation A is obtained. The coordinate values of the corners are calculated, and each of the corner small areas Ex1, Ex2,
A binarization processing unit 21 for binarizing the captured image data of Ey1 and Ey2, and a boundary extracting unit 22 for extracting a point sequence of two indentation boundaries for each corner small region from the binarized captured image data. A linear approximation conversion unit 23 that performs a linear approximation conversion of the point sequence of each indentation boundary extracted by the boundary extraction unit 22 using a least square method, a Hough transform, or the like; , An intersection point coordinate value corner calculation unit 24 that detects the coordinate value of the intersection point of the two straight lines obtained for the coordinates and uses the coordinate value as the coordinate value of the corner.

In this case, the threshold value for binarization in the binarization processing section 21 depends on the variation in image density in each small region due to unevenness in illumination of a test piece, uneven polishing of the surface of a test piece, and the like. The optimum value is individually set for each of the corner small regions Ex1, Ex2, Ey1, and Ey2. The threshold value may be set manually, or the density of each small area may be automatically determined and automatically set. Therefore, even if there is a variation in image density in each small corner area due to unevenness in illumination of a test piece, it is possible to cope with the adjustment of the threshold value, and it is not necessary to perform correction such as shooting on the entire image in advance.

The diagonal length calculator 19 calculates the diagonal length of the indentation A from the corner coordinate values calculated by the corner coordinate value calculator 18. The hardness calculation output unit 20 calculates the hardness based on the diagonal length of the indent and the pressing load value of the indenter calculated by the diagonal length calculation unit 19, and outputs the calculation result.

Next, the operation sequence of the indentation type hardness measuring apparatus having the above-described configuration will be described. (1) First, the indenter 1 is pressed against a test piece T placed on the stage 2 of the Vickers testing machine 3 with a predetermined load.
As a result, indentations are formed on the surface of the test piece T by the indenter 1 due to the square outline. (2) The indentation on the surface of the test piece T is magnified by the microscope 4 and imaged by the CCD camera 5. (3) The analog image signal output from the CCD camera 5 is A
The image data is converted by the / D converter 11 into captured image data based on a digital image signal, and is taken into the image memory 12.
FIG. 3A shows an example of an original size image based on the captured image data.

(4) Further, in parallel with the data acquisition in the section (3), an image (original-sized image) of the surface of the test piece based on the picked-up image data from the A / D converter 11 is reduced by the image reduction processor 13. The reduced image data obtained in this way is taken into the reduced image memory 14. (5) The reduced image data fetched into the reduced image memory 14 is subjected to a smoothing process by the smoothing processing unit 15 and then binarized by the binarization processing unit 16. As shown in FIG.
As shown in (b), an indentation A, which is an object to be imaged,
And the other part (background) B are separated, and the boundary C formed by each piece of the indentation A becomes clear.

(6) Next, the corner small area of the indentation A on the image memory 12 is specified by the corner small area specifying unit 17 based on the binarized reduced image data. As shown in FIG. 4 (a), the corner small area of the indentation A is a point belonging to an indentation boundary from an arbitrary point p in the area of the indentation A, and each point in the image processing coordinate system. The points Px1, Px2, Py1, and Py2 located at the farthest positions in the coordinate axis directions, that is, in the + X axis direction, the -X axis direction, the + Y axis direction, and the -Y axis direction are extracted, and a square having these points at the center is extracted. Corner small area Ex
This is performed by setting 1, Ex2, Ey1, and Ey2 as coordinate values on the image memory 12.

(7) Next, of the picked-up image data taken into the image memory 12, the corner small areas Ex1, Ex2, Ey
1. Image processing is performed on the captured image data of Ey2, and the coordinate values of the corners of the indentation are calculated. The calculation of the coordinate values of the corners of the indentation is performed by first calculating each corner small area Ex1, E on the image memory 12.
x2, Ey1, Ey2 captured image data is binarized by processing unit 2
In step 1, a point sequence of two indentation boundaries is extracted by the boundary extraction unit 22 for each corner small region Ex 1, Ex 2, Ey 1, Ey 2 from the binarized captured image data. Next, the extracted point sequence at each indentation boundary is subjected to straight-line approximation conversion by the least square method, Hough transform, or the like in the straight-line approximation conversion unit 23, and the straight-line approximation conversion is shown in FIGS. As described above, two straight lines L1-L2, L3-L4, L5-L6, L7-L8 are calculated for each of the corner small regions Ex1, Ex2, Ey1, and Ey2, and the intersections P1 to P4 of the two straight lines in each set are calculated. Are calculated by the intersection coordinate value calculation unit 24, and are used as the coordinate values of each corner of the indentation A.

(8) The diagonal length of the indentation A is calculated by the diagonal length calculating unit 19 from the coordinate values (x, y) of each corner, and the hardness is calculated by the hardness calculating output unit 20 based on the diagonal line. And outputs the operation result.

Although the above-described embodiment is based on the Vickers hardness test method, the indentation type hardness measuring apparatus according to the present invention is not limited to this. The same applies to a hardness test method of an indenter indentation method equivalent to the test method.

[0026]

As described above in detail, according to the indentation type hardness measuring apparatus according to the present invention, the coordinates of the corners from the two sides calculated by the linear approximation based on the image data near the corners of the indentation. Since the hardness of the test piece was calculated by calculating the value, the entire side forming the indentation was used as in the past, or the coordinate value of the corner from the part excluding the corner of those sides Measurement accuracy is improved as compared with the case where In addition, since the area where the corner of the indentation is present is narrowed down to a small area by the reduced image, and only the small area is subjected to the detailed image processing for calculating the corner coordinate value by the data of the original image, the entire image of the original image is reduced. The image processing time is reduced as compared with the case where detailed image processing is performed on data, and the load on a computer that executes this image processing is reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a press-in type hardness measuring device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of an image processing device of the indentation type hardness measuring device according to the present invention.

3A is a diagram showing original size image data of an image memory 12, and FIG. 3B is a diagram showing reduced image data.

4 (a) and 4 (b) are explanatory views showing an image processing procedure in the indentation type hardness measuring device according to the present invention.

FIGS. 5A and 5B are explanatory diagrams showing a mechanism for generating an indentation corner portion detection error in a conventional indentation type hardness measuring device.

[Explanation of symbols]

 Reference Signs List 3 Vickers testing machine 5 CCD camera 6 Image processing device 12 Image memory 13 Captured image reduction processing unit 14 Reduced image memory 16 Binarization processing unit 17 Corner small area specifying unit 18 Corner coordinate value calculation unit 19 Diagonal line length calculation unit Reference Signs List 20 Hardness calculation output unit 21 Binarization processing unit 22 Boundary extraction unit 23 Linear approximation conversion unit 24 Intersection coordinate value corner part calculation unit

Claims (2)

(57) [Claims] An indentation type hardness measuring device for pressing a polygonal indenter against the surface of a test piece and measuring the hardness from a polygonal indentation generated on the surface of the test piece. Imaging means for imaging, and two sides constituting the vicinity of the corner of the indentation, based on the image data of the surface of the test piece taken by the imaging means, based on the data near the corner of the indentation Hardness calculating means for calculating coordinate values of the corners from the two sides calculated by linear approximation, and calculating the hardness of the test piece based on these values and an indenter pressing load value. Indentation type hardness measuring device. 2. An indentation type hardness measuring device for pressing a polygonal indenter against the surface of a test piece and measuring hardness from a polygonal indentation generated on the surface of the test piece. An imager for imaging, an image memory for storing image data of the surface of the test piece imaged by the imager, and an image reduction for reducing the image of the surface of the test piece based on the image data to generate reduced image data A processing unit, a corner small region specifying unit that specifies a corner small region of the indentation from the reduced image data, and a corner small region specifying unit of the captured image data stored in the image memory, A corner coordinate value calculation unit that performs image processing on the captured image data of the area corresponding to the corner small area to calculate the coordinate value of the corner of the indentation; and the corner calculated by the corner coordinate value calculation unit And a hardness calculating section for calculating the hardness of the test piece based on the coordinate values of the test pieces, the values thereof, the indenter pressing load value, and the like.