JP6031821B2 - Displacement measuring method and material testing machine - Google Patents

Description

  The present invention relates to a displacement measuring method and a material testing machine for measuring deformation of a specimen in a material test.

  When a material test such as a tensile test is performed on a test specimen that is a specimen using a material testing machine, the deformation of the test specimen under load, that is, the amount of displacement of elongation and width, is measured during the test. The When measuring the elongation and width of such a test piece, an extensometer and a width meter are used. The extensometer and width meter have a contact method and a non-contact method. Among these, the non-contact method has recently been widely used to measure the amount of displacement of a test piece based on a still image or a moving image taken with a camera during a test. In such a non-contact type extensometer and width meter, the elongation is calculated by measuring the distance between a pair of gauge points formed on the test piece using a camera equipped with a CCD element, and the same. The displacement amount of the width is measured by measuring the distance between both edges of the test piece using the camera (see Patent Document 1).

  Further, as a technique for analyzing the deformation behavior of a composite material such as a metal material or a printed circuit board, there is a technique called a digital image correlation method (Digital Image Correlation = DIC). In the digital image correlation method, digital images before and after deformation of a specimen subjected to a load such as tension or compression are acquired, and the position to which any measurement point set on the specimen has moved after receiving the load is grasped. By doing so, the information regarding the deformation | transformation of a specimen is obtained (refer patent document 2).

  In the above-described measurement of elongation of the test piece and deformation analysis by the digital image correlation method, it is necessary to intentionally mark the specimen on the specimen. As a simple method of marking, there is a method of sticking a seal printed with a mark mark on a specimen. However, it is difficult to attach a seal to a material such as polypropylene that does not have a polar group associated with the seal adhesive, or a porous material that is difficult to adhere to the seal adhesive due to surface irregularities. In addition, even if the seal can be applied to the specimen at room temperature, the adhesive strength of the seal decreases in tests at low and high temperatures. In some cases, the specimen may fall out of the specimen, making measurement impossible. For this reason, a mark is directly written on such a specimen using a marking spray or a marking pen.

  On the other hand, a camera that collects an image of a specimen under test is often set to perform monochrome photography. The reason why color photography is not adopted is that the amount of information is three times that of monochrome photography, the focal length of the lens used in the camera is wavelength-dependent, and the processing of a huge amount of information And the software analysis algorithm that performs image processing to correct chromatic aberration is difficult.

  Further, in monochrome photography, there is a technique in which an acquired photographed image is expressed in 256 gradations from white to black based on the intensity (reflectance) of light reflected from an object. The seal printed with the mark is not affected by the background color of the specimen, so that the mark is made to stand out in monochrome photography, so that the mark is drawn in white on a black background or black on a white background A marked line is drawn.

  The test mark is written directly on the specimen that is difficult to attach the seal, but the mark is written with black or white ink on the colored specimen such as red, blue, green, yellow. In some cases, the contrast between the ground color of the specimen and the mark is not sufficient, and it may be difficult to identify the mark. For this reason, it has been proposed to enhance the contrast between the ground color and the target point by changing the irradiation angle of the light source for illuminating the specimen according to the ground color of the specimen (Patent Literature). 3).

Japanese Patent Laid-Open No. 2005-3577 JP 2007-78659 A JP-A-63-158436

  FIG. 7 is a schematic diagram for explaining the whitening of the test piece 10. FIG. 7A shows a state of the test piece 10 before executing the tensile test, and FIG. 7B schematically shows a state where the tensile test is executed and the test piece 10 is deformed. In FIG. 7, the ground color portion of the test piece 10 is hatched, and the mark M is shown in white.

  In the case where the ground color of the test piece 10 is a color that absorbs light, such as red, blue, and green, for example, in the image obtained by monochrome photography under illumination with a general white light source, Ten ground colors tend to be black. Therefore, the test mark M is written on such a test piece 10 with white ink that increases the contrast with the ground color. On the other hand, when the deformation of the test piece 10 proceeds by a tensile test or the like, whitening may occur on the surface of the test piece. Whitening is a phenomenon observed in specimens in material tests for resin materials, etc., and is a test based on minute cracks that enter the specimen surface when a load such as tension is applied, and environmental changes such as temperature changes and ultraviolet irradiation. This is a phenomenon in which a whitish region appears due to deterioration of one surface.

  When a fine crack is generated on the surface of the test piece near the mark M when a load such as tension is applied, the portion spreads in a white belt shape on the image as shown in FIG. It becomes the whitened portion W, and the boundary with the white mark M becomes unclear. If the whitened portion W becomes relatively large and the reference point M is lost, the reference point position after deformation of the test piece is not known and the displacement amount cannot be measured.

  In order to avoid losing sight of the mark position by whitening, when the mark M is written on the test piece 10 with black ink, in an image obtained by monochrome photography under illumination with a general white light source, The contrast between the ground color of the test piece 10 and the mark M is reduced. For this reason, the reference point M was unclear and the measurement accuracy of the displacement amount was lowered.

  The present invention has been made to solve the above-described problems, and provides a displacement measuring method and a material testing machine capable of improving the measurement accuracy of the displacement without losing sight of the gauge during the test. The purpose is to do.

The invention described in claim 1 is a material testing machine that includes a camera for photographing a specimen, and measures a displacement amount of the specimen deformed by a material test by a non-contact method. The specimen is made of a resin material. A colored specimen that causes whitening, and a light source that emits light in a plurality of wavelength ranges and the colored specimen in which a black mark is written at a predetermined position before the test is performed. When preliminarily shooting in monochrome with the camera, the light source is sequentially turned on for each wavelength range, and when shooting in monochrome with the camera during test execution, a light source control unit that turns on the light source in a specific wavelength range; a reflectance storage unit for storing the intensity of light at each wavelength region reflected from the specimen of the colored obtained in the preliminary imaging as reflectance, of the reflectance stored in the reflectance storage unit, The wavelength region having a large reflectance, and the wavelength-range selecting unit that selects the wavelength range of the light illuminating the specimen of the colored during the test run, in a test run, a specimen of the color, in the wavelength range selector unit A displacement amount calculation unit for obtaining a displacement amount of the colored specimen from the position information of the black mark in a photographed image obtained by photographing in monochrome with the camera while illuminating with light of a selected wavelength range; , Provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the light source includes a light emitting diode that emits light in different wavelength ranges.

According to a third aspect of the present invention, in the second aspect of the present invention, the light source includes a light emitting diode that emits red, blue, and green light.

Invention according to claim 4, in materials testing according to material testing machine equipped with a camera for photographing the specimen, a displacement amount measuring method of the amount of displacement of the specimen to be deformed measured by non-contact method, the test specimens are specimens of colored resulting in whitening made of a resin material, by lighting controls the light source that emits light of a plurality of wavelength bands for each wavelength region, wherein the gauge black is written in a predetermined position Obtained by the preliminary photographing step and the preliminary photographing step of photographing the colored specimen in monochrome with the camera while illuminating the colored specimen with light of each wavelength range before the test execution in which the colored specimen was arranged at the test position. A reflectance storage step for storing the intensity of light in each wavelength region reflected from the colored specimen as a reflectance , and a wavelength region having a maximum reflectance among the reflectances stored in the reflectance storage step. the, Selection and wavelength-range selecting step of selecting a wavelength band of light that illuminates the specimen of the colored during test run, in a test run, a specimen of the color, in the wavelength-range selecting step by lighting control said light source The amount of displacement of the colored specimen is calculated from the photographing step of photographing in monochrome with the camera while illuminating with the light in the wavelength range, and the position information of the black mark in the photographed image obtained by the photographing step. And a displacement amount calculating step to be obtained.

According to the first and fourth aspects of the present invention, pre-photographing is performed while illuminating the specimen with light of different wavelength ranges before the test is performed, and the ground of the colored specimen obtained by preliminary photography is obtained. Since the wavelength range of the light that illuminates the colored specimen during test execution is selected based on the reflectance of the light in each wavelength range with respect to the color, a monochrome image with clear marks written in black on the specimen is obtained. It becomes possible. Thereby, it is possible to improve the measurement accuracy of the displacement amount.

In addition, according to the invention described in claim 1 and claim 4 , of the reflectance of light in each wavelength region with respect to the ground color of the colored specimen obtained by the preliminary photographing, the wavelength region having the maximum reflectance. Since the light is used to illuminate the colored specimen when the test is performed, the contrast between the ground color of the specimen and the black mark can be increased, and a monochrome image with clearer marks can be obtained. Is possible.

According to the invention described in claim 2 , since the light source includes the light emitting diodes that emit light having different wavelength ranges, the black mark is more prominent on the monochrome image according to the ground color of the colored specimen. It is possible to illuminate the specimen with light in a wavelength range that can be applied.

According to the invention described in claim 3 , since the light source includes the light emitting diodes that emit red, blue, and green light, the black mark written on the test piece of various colors with a simple configuration. It is possible to cope with recognition with a monochrome image.

It is a schematic diagram of a material testing machine. It is a schematic diagram of the material testing machine by which the thermostat 40 was arrange | positioned. It is a front schematic diagram which shows the inside of the thermostat 40 and its periphery. It is a cross-sectional schematic diagram which shows the inside of the thermostat 40, and its periphery. 3 is a block diagram showing a main functional configuration in a control unit 33. FIG. 3 is a flowchart showing a procedure for measuring the displacement of a test piece 10. 2 is a schematic diagram for explaining whitening of a test piece 10. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 is a schematic diagram of a material testing machine.

  This material testing machine includes a table 18, a pair of support posts 19 erected on the floor, a pair of screw rods 17 (see FIG. 4 to be described later) erected so as to be rotatable inside each support column 19, and A cross head 23 movable along the screw rods 17, a load mechanism 30 for moving the cross head 23 to apply a test force to the test piece 10, and an operation signal of the load mechanism 30 are output. A control circuit 31 is provided.

  The cross head 23 is connected to the pair of screw rods 17 via nuts (not shown). The lower end portion of each screw rod 17 is connected to the load mechanism 30, and the power from the power source of the load mechanism 30 is transmitted to the pair of screw rods 17. As the pair of screw rods 17 rotate in synchronization, the cross head 23 moves up and down along the pair of support columns 19 that accommodate the pair of screw rods 17.

  The crosshead 23 is provided with an upper gripping tool 21 for gripping the upper end portion of the test piece 10 which is a colored specimen. On the other hand, the table 18 is provided with a lower gripping tool 22 for gripping the lower end portion of the test piece 10. When performing a tensile test, the test force (tensile load) is applied to the test piece 10 by raising the cross head 23 in a state where both ends of the test piece 10 are gripped by the upper gripping tool 21 and the lower gripping tool 22. ).

  At this time, the test force acting on the test piece 10 is detected by the load cell 24 and input to the control unit 33. The test piece 10 is photographed by the monochrome CCD camera 28, and the signal is input to the control unit 33. The monochrome CCD camera 28 and the control unit 33 function as a non-contact displacement meter. The control unit 33 is a computer having a storage device such as a CPU that executes logical operations, a ROM that stores an operation program necessary for controlling the device, and a RAM that temporarily stores data during control. It is configured to be connected to an input unit 34 such as a keyboard and a display unit 35 such as a liquid crystal display device, and is also connected to a control circuit 31 that controls the operation of the tester body.

  The monochrome CCD camera 28 is provided with a lens 27. The monochrome CCD camera 28 and the lens 27 are supported by an arm 29 disposed on the support column 19. Further, the monochrome CCD camera 28 and the lens 27 can shoot an area necessary for measuring deformation in the test piece 10 by adjusting the fixing position of the arm 29 to the support column 19 and the bending angle of the arm 29 itself. It is arranged at the position.

  Above the monochrome CCD camera 28, an LED light 37 having a plurality of light emitting diodes as a light source is disposed. The LED light 37 includes a red LED, a green LED, and a blue LED that emit light in different wavelength ranges, and is supported by an arm 39 disposed on the column 19. The LED light 37 supplies light in a wavelength range and light quantity necessary for photographing the test piece 10 by the monochrome CCD camera 28.

  FIG. 2 is a schematic diagram of the material testing machine in which the thermostatic chamber 40 is disposed. FIG. 3 is a schematic front view showing the inside of the thermostatic chamber 40 and its periphery. In addition, in this FIG. 3, the thermostat 40 and the bellows 45 are represented by the cross section. FIG. 4 is a schematic cross-sectional view showing the inside of the thermostatic chamber 40 and its periphery. In addition, the same code | symbol is attached | subjected about the member similar to the material testing machine shown in FIG. 1, and detailed description is abbreviate | omitted.

  The material testing machine shown in FIG. 1 is configured to perform a test at room temperature. However, when performing a test under a constant temperature condition, the table 18 is replaced with a table 18 as shown in FIG. A table 38 having a low height is installed, and a constant temperature bath 40 capable of storing the test piece 10 and the upper gripping tool 21 and the lower gripping tool 22 holding the test piece 10 is disposed on the table 38. A load mechanism 30 is arranged in the table 38.

  The temperature of the thermostatic chamber 40 can be adjusted in a temperature range of approximately -70 degrees Celsius to +230 degrees Celsius. The front of the thermostat 40 is a door that can be opened and closed, and a glass window 41 is provided on this door. The test piece 10 can be photographed by the monochrome CCD camera 28 through the glass window 41. Around the glass window 41 in the constant temperature bath 40, a plurality of LED lights 42 are disposed as light sources for illuminating the constant temperature bath 40. Similar to the LED light 37 described above, the LED light 42 includes a red LED, a green LED, and a blue LED that emit light in different wavelength ranges, and a wavelength range necessary for photographing the test piece 10 by the monochrome CCD camera 28. Supply light and light quantity.

  The LED lights 37 and 42 only need to be able to irradiate the test piece 10 with light in each wavelength region of red (R), green (G), and blue (B) by individual lighting control, for example, on the same chip. It may be a white LED called a multi-LED system in which RGB LEDs are arranged. Further, the light emitting diodes included in the LED lights 37 and 42 are not limited to the three colors RGB. Further, the test piece 10 may be irradiated with light in a set wavelength range by a visible light variable laser instead of the LED lights 37 and 42.

  In the upper part of the thermostatic chamber 40, an opening through which the inner rod 47 for suspending the upper gripper 21 in the thermostatic chamber 40 is formed. The upper gripper 21 includes the inner rod 47, the load cell, and the like. 24 is connected to the crosshead 23. On the other hand, the lower gripping tool 22 is disposed in the thermostatic chamber 40 by being connected to an in-chamber rod 48 that passes through the bottom of the thermostatic chamber 40 and is connected to the table 38.

  A bellows 45 is disposed at the upper part of the thermostatic bath 40 so as to cover the rod 47 in the bath. One end of the bellows 45 is sealed and fixed inside the opening of the thermostatic bath 40, and the other end is sealed to a bellows hanging plate 44 connected to the cross head 23 via a bellows hanging rod 43. It is fixed. Thereby, the airtightness in the thermostat 40 is ensured. The bellows 45 extends when the bellows suspension plate 44 rises as the crosshead 23 rises, and is pressed and folded when the bellows suspension plate 44 descends as the crosshead 23 descends. . This material testing machine is provided with a bellows 45 that expands and contracts in the moving direction of the crosshead 23, thereby heating and cooling the entire interior of the thermostatic chamber 40 without increasing the internal volume of the thermostatic chamber 40 more than necessary. It is the structure which can suppress useless energy. However, if the hole through which the in-bath rod 47 formed in the upper part of the constant temperature bath 40 passes is small, the inside of the bath can be kept at a constant temperature without the bellows 45.

  When the test is performed by the material testing machine shown in FIG. 1 or FIG. 2, the test piece 10 is placed at the test position by causing the upper gripping tool 21 and the lower gripping tool 22 to grip both ends of the test strip 10. During the execution of the test, the monochrome CCD camera 28 images the test piece 10 while tracking the mark M attached to the predetermined position of the test piece 10 with the marking pen. For this reason, as shown in FIG. 4, the monochrome CCD camera 28 is arranged so that the photographing angle is perpendicular to the surface on which the mark M of the test piece 10 is written. The same applies to the material testing machine in FIG. Further, when the test piece 10 is photographed through the glass window 41 as shown in FIG. 4, the surface of the lens 27 is parallel to the surface of the glass window 41 in order to avoid the influence of the reflection of the glass, that is, the photographing angle. The monochrome CCD camera 28 is arranged so that is vertical.

  FIG. 5 is a block diagram showing the main functional configuration of the control unit 33 for carrying out the present invention.

  The control unit 33 shown in FIGS. 1 and 2 selects the light source control unit 51 that controls the lighting of the LED lights 37 and 42 described above, and which wavelength range the test piece 10 is irradiated with during the execution of the test. A wavelength range selection unit 52 for performing the calculation, a displacement amount calculation unit 53 for calculating a displacement amount of the test piece 10 based on an image captured by the monochrome CCD camera 28, and a storage unit 54. The storage unit 54 includes a reflectance storage unit 55 that stores reflectance, which is information obtained from a captured signal from the monochrome CCD camera 28, and an image storage unit 56 that stores captured images.

  Next, the displacement measuring method in the material testing machine according to the present invention described above will be described. FIG. 6 is a flowchart showing a procedure for measuring the amount of displacement of the test piece 10.

  First, as a test preparation, the operator writes a black mark M with a marking pen at a predetermined position of the colored test piece 10. Then, the operator grips both ends of the test piece 10 with the upper gripping tool 21 and the lower gripping tool 22, arranges the test strip 10 at the test position, adjusts the arm 29, and moves the monochrome CCD camera 28 to the test strip 10. It arrange | positions in the imaging | photography position of the front of the surface where the mark M was written (refer FIG. 4).

  Preliminary photographing is performed in a state where the arrangement of the test piece 10 and the monochrome CCD camera 28 is completed (step S1). This preliminary photographing is performed when the light source control unit 51 causes the red LED, the green LED, and the blue LED of the LED lights 37 and 42 to individually emit light sequentially and illuminates the colored test piece 10 with light of each wavelength range. In this step, the reflectance, which is the intensity of the light reflected from the piece 10, is obtained from the photographing signal of the monochrome CCD camera 28. Depending on the ground color of the test piece 10, the reflectance of light when illuminated with light of each wavelength range is different, and the reflectance at this time is stored in the reflectance storage unit 55 in the storage unit 54 (step). S2).

  Among the reflectances stored in the reflectance storage unit 55, the light of the wavelength region having the highest reflectance (maximum reflectance), that is, the color of the LED is specified, and the test piece 10 is illuminated during the test execution. It selects as a wavelength range of the light to perform (step S3). The light in the wavelength region having the highest reflectance with respect to the ground color of the test piece 10 has the largest contrast (light quantity difference) with the mark M written on the test piece 10 in black, which is a color that absorbs light. Become. For this reason, during the execution of the test, the light in the wavelength region having the maximum reflectance is selected as the illumination color of the test piece 10 that can capture the mark M clearly. For example, when the ground color of the test piece 10 is red, the maximum reflectance is obtained when the test piece 10 is illuminated with red light. On the monochrome image, the test piece 10 appears white and the mark M Will appear black. This wavelength range selection step is performed in the wavelength range selection unit 52 of the control unit 33.

  The light source control unit 51 causes one of the red, green, and blue LEDs of the LED lights 37 and 42 to emit light in order to illuminate the test piece 10 only with light in the wavelength range selected by the wavelength range selection unit 52. Thereafter, the test is executed, a tensile load is applied to the test piece 10, and photographing with the monochrome CCD camera 28 is performed on the test piece 10 being executed (step S4). The imaging signal of the test piece 10 being tested is subjected to image processing and stored in the image storage unit 56 of the storage unit 54. Then, the elongation displacement amount of the test piece 10 with respect to the tensile load is calculated from the distance between the gauge points M in the images before the test execution, during the test execution, and after the test execution (step S5). This displacement amount calculation step is performed in the displacement amount calculation unit 53 of the control unit 33, and the result is displayed on the display unit 35 together with the captured image of the test piece 10 as necessary. When the test piece 10 is broken or when a preset test time elapses, the test is finished and the displacement amount measurement is also finished.

  In the embodiment described above, since the mark M is written in black on the test piece 10, the mark M is not lost even if whitening occurs on the test piece 10 during the execution of the test. And the light which illuminates the test piece 10 during test execution is selected based on the reflectance obtained by preliminary imaging. The light in the wavelength range having the maximum reflectivity becomes light in the wavelength range where the contrast of the black mark M with respect to the ground color of the test piece 10 is large. Therefore, the mark M is clearly displayed on the monochrome image. It becomes possible to do. Therefore, it is possible to improve the measurement accuracy of the displacement amount in the non-contact displacement meter that calculates the distance between the gauge points M from the captured image of the monochrome CCD camera 28.

  In the above-described embodiment, a tensile test that applies a tensile load to the test piece 10 has been described as an example. However, in the present invention, a specimen such as a semiconductor or an electronic component is disposed in the thermostat 40, and a rapid temperature change occurs. In a durability test (JIS C 0025) for evaluating the influence of repeated temperature changes on the specimen, it can also be used for DIC analysis used for measuring the deformation amount of the specimen. At this time, a plurality of marks are randomly attached with black paint on the surface of the specimen, and during the test execution based on the reflectance of light in each wavelength range with respect to the ground color of the specimen obtained by preliminary photography. The light source controller 51 controls the lighting of the LED light 42 so that only the light emitting diode that emits light in the selected wavelength region is emitted during execution of the test. What should I do?

DESCRIPTION OF SYMBOLS 10 Test piece 18 Table 19 Support | pillar 21 Upper grip 22 Lower grip 23 Crosshead 24 Load cell 27 Lens 28 Video camera 29 Arm 30 Load mechanism 31 Control circuit 33 Control part 34 Input part 35 Display part 37 LED light 38 Table 39 Arm 40 Constant temperature bath 41 Glass window 42 LED light 43 Bellows hanging rod 44 Bellows hanging plate 45 Bellows 47 Inside rod 51 Light source control unit 52 Wavelength range selection unit 53 Displacement amount calculation unit 55 Reflectance storage unit 56 Image storage unit M Mark

Claims (4)

A material testing machine equipped with a camera for photographing a specimen and measuring a displacement amount of the specimen deformed by a material test by a non-contact method,
The specimen is a colored specimen that causes whitening made of a resin material,
A light source that emits light in a plurality of wavelength ranges;
When pre-photographing the colored specimen in which a black mark is written at a predetermined position in monochrome with the camera before performing the test placed at the test position, the light source is sequentially turned on for each wavelength range, A light source control unit that turns on the light source in a specific wavelength range when shooting in monochrome with the camera during a test,
A reflectance storage unit for storing the intensity of light in each wavelength region reflected from the colored specimen obtained in the preliminary photographing as a reflectance;
Of the reflectance stored in the reflectance storage unit, the wavelength-range selecting unit wavelength range is selected as the wavelength range of the light illuminating the specimen of the colored during the test run with a maximum reflectance,
Position information of the black mark in a photographed image obtained by photographing the colored specimen in monochrome with the camera while illuminating the colored specimen with light in the wavelength range selected by the wavelength range selection unit From the displacement amount calculation unit for obtaining the displacement amount of the colored specimen,
A material testing machine characterized by comprising: The material testing machine according to claim 1,
The light source is a material testing machine including a light emitting diode that emits light in different wavelength ranges. The material testing machine according to claim 2,
The light source is a material testing machine including a light emitting diode that emits red, blue, and green light. In materials testing according to specimen material testing machine equipped with a camera for photographing a, a displacement amount measuring method of measuring a non-contact manner the displacement of the specimen to be deformed,
The specimen is a colored specimen that causes whitening made of a resin material,
By controlling lighting of light sources that emit light in a plurality of wavelength ranges for each wavelength range, the colored specimen with the black mark written at a predetermined position is placed at the test position before the test is performed. A pre-photographing step of photographing the specimen in black and white with the camera while illuminating the specimen with light of each wavelength range;
A reflectance storage step of storing, as a reflectance, the intensity of light in each wavelength region reflected from the colored specimen obtained by the preliminary photographing step;
Of the reflectance stored in the reflectance storage step, the wavelength-range selecting step of the wavelength range, is selected as the wavelength range of the light illuminating the specimen of the colored during the test run with a maximum reflectance,
During the test execution, the colored specimen is photographed in monochrome by the camera while illuminating with the light of the wavelength range selected in the wavelength range selection step by controlling the lighting of the light source, and
A displacement amount calculating step for obtaining a displacement amount of the colored specimen from the position information of the black mark in the photographed image obtained by the photographing step;
A displacement amount measuring method characterized by comprising:

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