JPH0638063B2 - Indentation type hardness tester - Google Patents

Description

The present invention relates to an indentation type hardness tester such as Vickers hardness and Brinell hardness.

[Conventional technology]

Vickers hardness and Brinell hardness are used to judge the mechanical properties of metallic materials. Especially, the Vickers hardness has a facing angle of 13
It is said that an indenter made of a 6 ° square pyramid made of diamond is pressed against the surface of the test piece, and the pressing load is divided by the surface area of the indentation formed by pressing.

A conventional indentation type hardness tester is disclosed in, for example, Japanese Patent Publication No. 63-10379. This is as shown in FIG.
The indenter 2 is pressed against the surface of the test piece 1 with a predetermined load, and the indentation 3
And a microscope 5 provided in the testing machine 4
And an A / D converter 8 for analog / digital converting the optical image information 7 of the indentation 3 projected on the image pickup device 6 into a grayscale level of 256 tones, for example.
A digital image processing unit 20 for extracting a point where the grayscale level digital image signal 9 from the A / D conversion unit 8 changes abruptly as an end of the indentation 3, and an indentation obtained by the digital image processing unit 20. The indentation size measuring unit 21 that measures the size of the indentation from the position of the end portion, and the hardness is calculated by the size of the indentation 3 measured by the indentation size measuring unit 21 and the pressing load of the indenter 2, and the printer 22 or the like. It is mainly configured by a hardness calculation unit 18 that outputs to.

The features of the above indentation type hardness tester will be described below.
If there is a portion of the matrix structure, a scratch, or a corroded portion that is as bright as the indentation, the end of the indentation 3 becomes unclear. Not only is this measured as an error, but in some cases, such as the upper apex of the indentation 3 in FIG. 7, this is not closed and measurement cannot be performed. Therefore, in the present invention, in order to prevent this, analog / digital conversion is performed at the gray level, and the brightness of each pixel is converted into a numerical value to be processed as a digital image.

The digital image processing unit 20 processes / analyzes the digital image signal 9 which is analog / digital converted at the gray level, and the obtained gray level curve 26 ′ has the points P1 and P2 at which the sharp change occurs. As shown in the figure, a search is made along the measurement axis A, and the end of the indentation 3 is extracted. FIG. 7B is a schematic trace of FIG. 7A, in which the vertical axis of the diagram is the gray level and the horizontal axis is the position.

[Problems to be Solved by the Invention]

There are the following problems (1) and (2) as problems of the indentation type hardness tester in the prior art.

(1) If a line B connecting the opposite corners of the indentation as shown in FIG. 8 is shifted to the measuring axis A, indentation size measuring part true value l ₁
, An incorrect value is output as the measured value l ₁ ′.

(2) As shown in FIG. 9, when the indenter does not have a clear shape when pressing the test piece, and especially when the corners of the indentation are not clear, the indentation size measuring unit measures the true value l ₂ against the measured value l ₂ . _An incorrect value is output as in ₂ '.

As described above, the measurement error is a serious problem because the quality characteristics of the steel material are erroneous. The above (1) occurs when there is minute mechanical backlash when moving the sample after indentation, and (2)
With respect to the above, it occurs when the hardness is not uniform on the metal structure, particularly in the welded portion, or due to uneven corrosion.

[Means for Solving the Problems]

The present invention advantageously solves the drawbacks of the prior art, and provides a tester capable of forming an indentation by pressing a pyramid indenter on the surface of a test piece with a predetermined load, and a microscope equipped with the tester. A connected image pickup device, an A / D conversion unit that performs analog / digital conversion of optical image information of the indentation projected on the image pickup device, and an indentation size is measured based on a digital image signal from the A / D conversion unit. In a push-in type hardness tester having a hardness calculation unit that calculates hardness using the measured value,
A processing unit that digitizes the digital image signal from the D conversion unit, and after storing all pixels corresponding to the side of the indentation from the digitized signal from the processing unit, excludes pixels near the end of the side. A digital image processing unit, an indentation size measuring unit that obtains an intersection of straight lines based on the linear approximation formula of each side calculated in the calculation process, and measures an indentation size from the intersection, and an indentation size measured by the indentation size measuring unit Therefore, a hardness calculation unit for calculating hardness is provided.
The present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an embedded hardness tester according to the present invention.

A tester 4 capable of pressing a square pyramid indenter 2 against the surface of a test piece 1 with a predetermined load to form an indentation 3, an imager 6 connected to a microscope 5 provided in the tester 4, and the imager The optical image information 7 of the indentation 3 shown in FIG. 6 is converted into an analog / digital conversion at the gray level and an A / D conversion unit 8 and a digital image signal 9 from the A / D conversion unit are used for the boundary line of the indentation. Corresponds to an image focusing control unit 11 that controls the autofocus unit 10 so that the gray level of the corresponding portion increases or decreases to the maximum extent, and a boundary line of the indentations processed by the image focusing control unit 11. Digital image signal 12
And a binarization processing unit 13 for binarizing the
The digital image processing unit 15 for selecting and storing the pixels corresponding to the four sides of the indentation and excluding the corners of the four sides in the digital image signal 14 from, and the pixels corresponding to the four sides of the indentation in the digital image processing unit 15. Classify each side and give coordinate points,
A calculation processing unit 16 that calculates a linear approximation formula, an indentation size measurement unit 17 that measures an indentation size by obtaining an intersection point of four regression expressions from the calculation processing unit 16, and the indentation size measurement unit 1
The hardness calculator 18 mainly calculates and outputs the hardness based on the area of the indentation measured by 7 and the pressing load of the indenter. Reference numeral 19 denotes a table on which the test piece is placed, which can be moved vertically by the autofocus unit 10 and can be moved laterally.

The function of the image focusing control unit 11 will be described with reference to FIGS. 2 and 3. 2 (a) and 3 (a) show a flow of moving the sample stage 19 to a portion corresponding to the boundary line of the indentation 3 substantially in the center of the visual field of the imaging device 6. The threshold levels corresponding to the indentations are set in advance in the x-axis direction Sx and the y-axis direction Sy, and the areas below Sx and Sy are designated as Lx ₁ and Lx ₂ , Ly ₁ and Ly ₂ , respectively. If Lx ₁ > Lx ₂ , the sample stage 19 moves in the Lx ₁ direction, and Lx ₁ <Lx ₂
If so, move in the Lx ₂ direction. The same applies to Ly ₁ and Ly ₂ .
When Lx ₁ = Lx ₂ , Ly ₁ , Ly ₂ , the alignment of the indentation is completed. The alignment may be performed in the x-axis direction → y-axis direction or the y-axis direction → x-axis direction.

2 (b), (c), and FIG. 3 (b) show a flow for focusing corresponding to the boundary line of the indentation 3. Scan SHi the threshold level as the higher side, set in advance the SLo as low side, the absolute value of the difference between when the indicates the position of the pixel at that time and x _1, x ₂ respectively x ₁ and x ₂ (|
The sample stage is moved up or down from the autofocus unit so that x ₁ −x ₂ |) becomes smaller than a preset value δ or becomes a minimum value. Note that FIG. 2 (b) shows before focusing, and FIG. 2 (c) shows after focusing.

4 and 5 explain the functions of the digital image processing unit 15 and the calculation processing unit 16. The boundary line of the indentation 3 is shown by the thick line in FIG. 4, and in particular, the four parts of the boundary line are not clear,
The case where the diagonal lines are also slightly displaced is shown. a-a ', b-b',
The method of determining the areas c-c 'and d-d' is Lx shown in Fig. 2 (a),
Ly (threshold level Sx, Sy or higher) is divided into two, which corresponds to a range of about 80 to 95% of the area. In this case, in the x-axis and y-axis directions, a-a ', b-b', c-
If c ′ and d−d ′ are tilted by approximately 45 °, and if they are not so, the division method should be predicted in advance and then the corners of the indentation should be removed in the same way as described above. −b ′,
Areas c-c 'and d-d' should be decided. Then a-
Pixels corresponding to a ', b-b', c-c ', d-d' are extracted for each. Each of the pixels included in aa ′ is coordinate point (X
i, Yi) to obtain a linear approximation formula A (y = α ₁ x + α ₂ ). The method of obtaining this linear approximation formula is most preferably the method of least squares. Or each coordinate point (Xi, Yi)
The deviation from and may be the smallest. b-b ', c-
Linear approximation formula B (y = β ₁ x + corresponding to c ′, d−d ′
β ₂ ), C (y = γ ₁ x + γ ₂ ), D (y = δ ₁ x + δ ₂ )
Is also the same. After obtaining the linear approximation formula in this way,
In the least-squares method, a-a ', b-b', c-c ', until the correlation coefficient exceeds a certain value or the deviation from each coordinate point is less than a certain value. The interval d−d ′ is narrowed and the above linear approximation formula is recalculated. Note that a-a ',
If the b-b ', c-c', d-d 'intervals are too small, the error increases conversely. Therefore, as described above, the interval width does not have to be above a certain value or below a certain value. Is reached,
The above feedback calculation should be terminated. Finally, the linear approximation formulas A, B, C,
Intersection H _a at its four straight line D, H _b, H _c, determining the size of the hardness by H _d.

The indentation size measuring unit 17 uses the H _a obtained as described above.
-H _b and -H _c -H _d recognize indentation Toshie example, the measurement performed by or linear or to measure the size of the diagonal, and the area calculated. The hardness calculator 18 may be, for example, Vickers hardness H.
In the case of obtaining v, when the pressing load is P, the surface area of the indentation is S, and the length of the diagonal line of the indentation is 1, it is expressed by the following equation.

Hv = P / S (1) = 2Psin 68 ° / I ² = 1.854P / I ² (kg / mm ² ) (2) [Advantages of the Invention] As described above, according to the present invention, (1) As shown in FIG. 8, the true value l ₁ can be measured even if the line B connecting the corners facing the indentation deviates from the measurement axis A.

(2) As shown in FIG. 9, the true value l ₁ can be measured even if the shape when the indenter is pressed against the test piece is not clear.

In this way, it becomes possible to apply the image processing technique to the hardness value, which is an important index indicating the quality characteristics of the steel material, as an accurate value without human intervention.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the indentation type hardness meter of the present invention, FIG. 2 (a) is an image processing diagram for placing the indentation at the center of the screen, and FIG. 2 (b) is the indentation of FIG. 2 (a). Fig. 2 (c) shows the boundary line before focusing, Fig. 2 (c) shows the boundary line after focusing on the indentation in Fig. 2 (b), and Fig. 3 (a) places the indentation at the center of the screen. Fig. 3 (b) is an image processing flow diagram in which the boundary line of the indentation is focused, Fig. 4 is a diagram showing the boundary line of the indentation and the image processed boundary line, and Fig. 5 is the image of the indentation line. FIG. 6 is a flow chart for obtaining a boundary line subjected to image processing from the boundary line, FIG. 6 is a schematic diagram of a conventional indentation type hardness tester, FIG. 7 (a) is an image processing diagram according to the conventional technology, and FIG. Image processing flow chart by the technology, FIGS. 8 (a) and 8 (b) are image processing diagrams in which the measurement axis A and the diagonal axis B are displaced from each other in FIG. 7, and FIGS. 9 (a) and (b) are in FIG. FIG. 7 is an image processing diagram in which a corner portion of an indentation is not clear. 1: test piece, 2: indenter, 3: indentation, 4: tester, 5: microscope, 6: imager, 7: optical image information, 8: A / D converter, 9: digital image signal, 10: auto Focus part,
11: Image focusing control unit, 12: Digital image signal, 13:
Binarization processing unit, 14: Digital image signal, 15: Digital image processing unit, 16: Calculation processing unit, 17: Indentation size measuring unit, 1
8: hardness calculation unit, 19: sample stage, 20: digital image processing unit, 21: impression size measuring unit, 22: printer, 23: control unit, 24: auto stage, 26: gray level curve

Claims (1)

[Claims] 1. A tester capable of forming an indentation by pressing a pyramidal indenter on the surface of a test piece with a predetermined load, an imager connected to a microscope provided in the tester, and an imager projected on the imager. A / D conversion unit for analog / digital converting optical image information of the indentation, and hardness calculation for measuring hardness based on the digital image signal from the A / D conversion unit and using the measured value In a push-in type hardness tester having a section, a processing section for digitizing the digital image signal from the A / D conversion section and all pixels corresponding to the side of the indentation based on the digitized signal from the processing section are stored. Then, a digital image processing unit excluding the pixels near the corners of the side, and an indentation size measuring unit that obtains an intersection of straight lines by the linear approximation formula of each side calculated in the calculation process and measures the indentation size from the intersection. , The indentation size measuring unit From the measured indentation size, indentation hardness tester, characterized in that it comprises a hardness calculating unit for calculating the hardness, the.