JP5416082B2 - Strain measuring apparatus and strain measuring method - Google Patents

Description

  The present invention relates to a strain measuring apparatus and a strain measuring method for measuring strain (deformation) of a material (test body, specimen) that is a measurement target.

  Materials are evaluated from various viewpoints, and one of them is, for example, strain measurement by a tensile test. Regarding this strain measurement, for example, there are technologies disclosed in Patent Document 1 and Patent Document 2.

  The video non-contact extensometer disclosed in Patent Document 1 obtains the amount of movement of each marked mark from image data obtained by imaging a test piece with two marked marks with a camera. A video non-contact extensometer that measures the elongation of the test piece between the marked marks, and always within the camera field of view, as long as the distance between the two marked marks taken by the camera does not exceed the camera field of view. One drive mechanism for controlling the position of the camera is provided so that two mark marks can be inserted in.

  The video non-contact extensometer disclosed in Patent Document 2 identifies each mark from a video signal obtained by imaging two marks attached to the sample surface with a video camera, and moves each mark. Is an extensometer equipped with a calculation means for calculating the momentary elongation between each mark from the difference in each movement amount, and has at least two video cameras having different field sizes, In accordance with a preset standard, it comprises a selection means for selecting one of each video signal from each video camera and subjecting it to calculation by the calculation means, and this selection means is accompanied by the progress of sample elongation, The video signal of the video camera with a narrow field of view is sequentially switched and supplied to the arithmetic means.

JP-A-11-237215 JP 10-221025 A

By the way, the video non-contact extensometer disclosed in Patent Document 1 controls the position of the camera along the extending direction so that two marked marks are always in the camera field of view. For this reason, the video non-contact extensometer disclosed in Patent Document 1 cannot measure the elongation of the test piece when at least one of the marked marks is out of the field of view of the camera. The camera's field of view cannot be exceeded. Therefore, in order to widen the measurement range by the technique disclosed in Patent Document 1 , it is necessary to use a camera with a wide field of view, and as a result, the resolution is relatively lowered.

  In this regard, the video non-contact extensometer disclosed in Patent Document 2 switches between a camera with a relatively narrow field of view and a camera with a relatively wide field of view as the elongation of the test piece proceeds, Realizes measurement over a wide measuring range. However, when the video non-contact extensometer disclosed in Patent Document 2 is switched from a camera with a narrow field of view to a camera with a wide field of view, the resolution decreases in a step-like manner, and the entire measurement range is relatively wide. It cannot be measured with high accuracy.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a strain measuring apparatus and a strain measuring method capable of expanding the measurement range while maintaining the resolution.

As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, the strain measuring apparatus according to one aspect of the present invention includes an imaging unit that includes a plurality of marks for imaging a specimen to be measured, and images of the specimen before and after applying an external force to the specimen. An image acquisition unit to be acquired by the photographing unit as an image before action and an image after external force action, and a reference distance between a position of one of the plurality of marks and a predetermined reference position, which is a tracking mark; Based on the position of the tracking mark in the image before the external force action and the position of the tracking mark in the image after the external force action, an arithmetic processing unit that obtains the expansion / contraction ratio of the specimen, the arithmetic processing unit, the located predetermined end area tracking mark in the external force after the image, and, when the two or more of the marks present on the external force action after image, said plurality And performing said with a different and tracking marks off a new said tracking marks a mark located outside the end region 換更 new process of the mark.

The strain measuring method according to another aspect of the present invention includes a plurality of marks, the images of the test body before and after applying an external force to the test object to be measured. As an image acquisition step acquired by the imaging unit, a tracking mark, a reference distance between a position of one of the plurality of marks and a predetermined reference position, and the tracking mark in the image before the external force action And a calculation processing step for obtaining an expansion / contraction ratio of the test body based on the position of the tracking mark in the image after the external force action, and the calculation processing step includes: located in a predetermined end area of, and, if the two or more of the marks present on the external force action after image, the tracking Ma of the plurality of marks Wherein the phrase with a different including switching 換更 new process step of newly said tracking marks a mark located outside the end region.

  In the strain measuring apparatus and strain measuring method configured as described above, a test body having a plurality of marks is photographed by the imaging unit, and an external force is applied to the position of the tracking mark and the reference distance between the predetermined reference positions and the test body. The expansion / contraction ratio of the test specimen is obtained based on the positions of the tracking marks in the images acquired before and after the test. Then, when obtaining the expansion / contraction ratio of the test body, if the tracking mark is located within the end region in the field of view of the imaging unit in accordance with the action of the external force, another mark located outside the end region is newly tracked. The mark is marked and a switching update process is performed. Therefore, the strain measuring apparatus and the strain measuring method having such a configuration can measure the expansion / contraction ratio of the test specimen as long as the tracking mark is captured by the imaging unit, so that the field of view of the imaging unit, that is, the resolution is reduced. The measurement range can be further expanded while maintaining.

  According to another aspect, in the above-described strain measuring apparatus, the photographing unit includes a first camera device that photographs the tracking mark, and the plurality of marks to be the predetermined reference position. A second camera device that captures a mark different from the tracking mark as a reference mark, and the image acquisition unit includes an image of the test body before and after applying an external force to the test body, The second camera is obtained as an image after the external force action by the first camera device, and images of the test body before and after applying an external force to the test body are used as a reference image before external force action and a reference image after external force action. Acquired by the apparatus, the arithmetic processing unit, the distance between the tracking mark and the reference mark as the reference distance, and the reference image before the external force action Based on the position of the reference mark and the position of the reference mark in the reference image after the external force action, the position of the tracking mark in the image before the external force action and the position of the tracking mark in the image after the external force action It is characterized in that the expansion / contraction rate of the test body is obtained.

  With such a configuration, a strain measuring apparatus is provided that can use one of a plurality of marks as a predetermined reference position.

According to another aspect, in the above-described strain measuring apparatus, the imaging unit captures one of the tracking mark and a mark different from the tracking mark as a reference mark in order to obtain the predetermined reference position. The image acquisition unit uses the image of the test body before and after applying an external force to the test body as the image before the external force action and the image after the external force action, and a reference image before the external force action and the external force. Acquired by the camera device as a post-action reference image , the arithmetic processing unit, the distance between the tracking mark and the reference mark as the reference distance, the position of the reference mark in the reference image before the external force action, and the The position of the reference mark in the reference image after the external force action, the position of the tracking mark in the image before the external force action, and the external force action Based on the position of the tracking mark in a subsequent image, and obtains the expansion ratio of the specimen.

  With such a configuration, there is provided a strain measuring device that can widen the measurement range while maintaining the resolution with a single camera device.

  According to another aspect, in the above-described strain measuring devices, the arithmetic processing unit is configured based on the position of the tracking mark in the image before the external force action and the position of the tracking mark in the image after the external force action. Based on a first movement amount calculation processing unit that calculates a movement amount of the tracking mark as a movement amount of the tracking mark, and a position of the reference mark in the reference image before the external force action and a position of the reference mark in the reference image after the external force action A second movement amount calculation processing unit that obtains a movement amount of the reference mark as a movement amount of the reference mark, and before and after applying the external force to the specimen based on the movement amount of the reference mark and the movement amount of the tracking mark An elongation amount calculation processing unit for obtaining an elongation amount of the test body, the reference mark before the external force is applied to the test body, and the Based on the amount of elongation distance and the specimen between the marks marks, characterized in that it comprises a stretch ratio calculation processing unit for obtaining the expansion ratio of the specimen.

  With such a configuration, there is provided a strain measuring device that can determine the expansion / contraction ratio of the test specimen based on the relative elongation of the test specimen without obtaining the absolute elongation of the specimen.

  According to another aspect, in the strain measurement apparatus, the first movement amount calculation processing unit searches the post-external force action image for a mark corresponding to the tracking mark in the pre-external force action image. The searched mark is set as the tracking mark in the image after the external force action, and the second movement amount calculation processing unit searches the reference image after the external force action in the reference image after the external force action in the reference image before the external force action. The searched mark is used as the reference mark in the reference image after the external force action.

  According to such a configuration, the reference mark in the reference image after the external force action is found by searching the reference image after the external force action in the image corresponding to the reference mark in the reference image before the external force action, and is tracked in the image after the external force action. The mark can be found by searching the post-external force image for a mark corresponding to the tracking mark in the pre-external force image.

According to another aspect, in the above-described strain measuring apparatus, the arithmetic processing unit further determines whether or not the tracking mark is positioned within a predetermined end region in the image after the external force action. When the tracking mark is located within a predetermined end region in the image after the action of the external force as a result of the determination by the processing unit and the determination processing unit, the reference mark and the tracking mark of the plurality of marks, Situated in newly said a switching processing unit for switching換更new process for the tracking marks, said end region outside, which is said new said tracking marks and the reference marks a mark located outside the end region with a different And a distance calculation processing unit for obtaining a distance between the marks .

  In such a configuration, even if the tracking mark is updated to a new mark, the distance between the reference mark and the new tracking mark can be obtained without obtaining the absolute extension of the test specimen. There is provided a strain measuring device capable of obtaining the expansion / contraction rate of the test body based on the relative elongation amount of the body.

  According to another aspect, in the above-described strain measuring apparatus, the photographing unit includes one camera device that photographs the tracking mark, and further includes a reference distance storage unit that stores the reference distance in advance. Features.

  With such a configuration, there is provided a strain measuring device that can widen the measurement range while maintaining the resolution with a single camera device.

  The strain measuring apparatus and strain measuring method according to the present invention can further expand the measurement range while maintaining the resolution.

It is a figure which shows the structure of the distortion | strain measuring apparatus in embodiment. It is a flowchart (the 1) which shows operation | movement of the distortion | strain measuring apparatus in embodiment. It is a flowchart (the 2) which shows operation | movement of the distortion | strain measuring apparatus in embodiment. It is a figure for demonstrating the calculating method which calculates | requires the expansion-contraction rate of a test body in the strain measuring apparatus of embodiment.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. Further, in this specification, when referring generically, it is indicated by a reference symbol without a suffix, and when referring to an individual configuration, it is indicated by a reference symbol with a suffix.

  FIG. 1 is a diagram illustrating a configuration of a strain measuring apparatus according to an embodiment. The strain measuring device S of the present embodiment is a device for measuring strain generated in the test body SM. For example, as shown in FIG. 1, a plurality of first and second camera devices 11 are used in the present embodiment. , 12, an image calculation processing unit 13, an input unit 14, and an output unit 15.

  The specimen (measuring object, subject, test piece) SM is a measuring object and may be any material. The test body SM may be, for example, a metal material, a resin material such as plastic, a biomaterial (specimen), a semiconductor material, or a ceramic material in a range where brittle fracture does not occur.

  The strain generated in the test body SM is given by applying a predetermined external force to the test body SM. For example, in the tensile test, the test body SM is clamped by a chuck (gripping tool) for fixing the test body SM in a known tensile tester (not shown), and an external force is applied to the test body SM by the tensile tester. Acting, strain is applied to the specimen SM.

  The test body SM is provided with a plurality of marks (marks or marks) M having an arbitrary shape in order to measure strain generated in the test body SM. In the case where the first and second camera devices 11 and 12 are configured, the plurality of marks M is used as one of the reference marks Ms and the remaining mark M as the tracking mark Mc. Three or more are preferable. The reference mark Ms and the tracking mark Mc will be described later. In the present embodiment, as shown in FIG. 1, five circular marks M1, M2, M3, M4, and M5 (Mn; n = 1, 2, 3, 4, 5) are present on the surface of the specimen SM. Provided. In the example shown in FIG. 1, these marks M are spaced apart by a predetermined distance substantially along the pulling direction in which the specimen SM is pulled by the tensile testing machine. The predetermined distances may be equidistant or unequal. In the example shown in FIG. 1, these marks M are arranged in order of the mark M1, the mark M2, the mark M3, the mark M4, and the mark M5 from one end to the other end along the pulling direction. The mark M is provided on the surface of the test body SM so as to be able to follow the strain such as elongation in the test body SM with a degree sufficient for strain measurement. The mark M is drawn, for example, by printing or by handwriting using ink or the like.

  In the present embodiment, the mark M has a circular shape, but is not limited thereto, and may be any shape such as a polygonal shape or an irregular shape. The mark M may be, for example, a metal base of a steel plate or a spray paint that is randomly sprayed. The plurality of marks M are preferably identical to each other.

  The input unit 14 is an apparatus that is connected to the image calculation processing unit 13 and inputs various commands such as a measurement start instruction to the strain measuring device S and various data such as attribute data of the specimen SM, for example. For example, a keyboard or a mouse. The output unit 15 is a device that is connected to the image calculation processing unit 13 and outputs commands and data input from the input unit 14 and measurement results (movement amount, elongation amount, expansion and contraction rate, etc.) of the strain measuring device S, and the like. For example, a display device such as a CRT display, LCD, organic EL display, or plasma display, or a printing device such as a printer.

  Each of the first and second camera devices 11 and 12 is a device that takes an image of the test body SM as a subject in order to monitor (observe and monitor) the test body SM. And an image generation unit. The photographing optical system is an optical system for forming an optical image (light image) of the specimen SM on the light receiving surface of the image sensor. The image sensor photoelectrically converts an optical image of the test body SM formed on the light receiving surface by the photographing optical system, and a signal corresponding to the amount of light in the optical image (a signal sequence of signals received in units of pixels). And outputs this signal to the image generation unit, such as a CCD type or CMOS type image sensor. The image generation unit generates a digital image signal by performing known image processing such as black level correction processing, pixel interpolation processing, shading correction processing, and the like on the signal obtained by the imaging device, and performs image calculation It is a circuit that outputs to the processing unit 13. Each of the first and second camera devices 11 and 12 may be a monochrome camera or a color camera, or may be a digital still camera that generates a still image, or a digital video that generates a moving image. It may be a camera.

  The first and second camera devices 11 and 12 are arranged so as to be able to photograph different portions of the test body SM provided with the plurality of marks M, respectively. By arranging the first and second camera devices 11 and 12 so as to be separated from each other by a predetermined distance in this way, the first camera device 11 can detect a certain mark (tracking mark) among the plurality of marks M. The second camera device 12 can photograph a region within a predetermined range including Mc, and the second camera device 12 can select another mark (reference mark) Ms different from the tracking mark (the certain mark) Mc of the plurality of marks M. A region within a predetermined range including (≠ Mc) can be photographed. In the example shown in FIG. 1, the first camera device 11 captures an area portion of a substantially circular range including the mark M1 located at one end of the plurality of marks M as the tracking mark Mc. The camera device 12 takes an image of a region of a substantially circular range including the mark M5 located at the other end of the plurality of marks M as the reference mark Ms. The reference mark Ms is a mark used for defining (defining) a predetermined reference position when obtaining the elongation amount of the test body SM. The tracking mark Mc is used when obtaining the elongation amount of the test body SM. This is a mark used for obtaining the distance lsc from the reference mark (reference position) Ms. In the present embodiment, the tracking mark Mc is switched to another mark when a predetermined condition is satisfied.

  The image arithmetic processing unit 13 is a circuit for obtaining the strain of the test body SM based on the image signals obtained by the first and second camera devices 11 and 12, and includes, for example, a microprocessor, a storage element, and its peripheral circuits. It is composed of a microcomputer or the like. In this embodiment, as shown in FIG. 1, the image calculation processing unit 13 is functionally functional with the first and second image acquisition control units 21 and 22 and the first and second movement amount calculation processing unit 23. , 24, an elongation amount calculation processing unit 25, an expansion / contraction rate calculation processing unit 26, a determination processing unit 27, a switching processing unit 28, and a distance calculation processing unit 29. The first and second image acquisition control units 21 and 22, the first and second movement amount calculation processing units 23 and 24, the elongation amount calculation processing unit 25, the expansion / contraction rate calculation processing unit 26, the determination processing unit 27, and the switching processing unit. 28 and the distance calculation processing unit 29 are functionally connected to the microcomputer by executing a strain measurement program that calculates the strain of the specimen SM based on the image signals obtained by the first and second camera devices 11 and 12, for example. Configured.

  In addition, when such a strain measurement program is not stored in the microcomputer, a recording medium such as a flexible disk or a CD-ROM that records the program is used, such as a flexible disk drive or a CD-ROM drive. The strain measuring device S may be configured to be installed in the microcomputer via an external storage device, and a communication network and a communication interface device (such as a network card) are connected from a server computer that manages the strain measuring program. The strain measurement device S may be configured so that the strain measurement program is downloaded via the network.

  Then, the first and second image acquisition control units 21 and 22 are first examples as an example of an imaging unit that captures images of the test body SM before and after applying an external force to the test body SM. And acquired by the second camera devices 11 and 12. More specifically, the first image acquisition control unit 21 acquires the images of the test body SM before and after applying an external force to the test body SM by the first camera device 11 as an image before the external force action and an image after the external force action, These images before external force action and images after external force action are output to the first movement amount calculation processing unit 23. The second image acquisition control unit 22 uses the second camera device 12 as the first image acquisition control unit 21 to set the images of the test body SM before and after applying an external force to the test body SM as the reference images before and after the external force action. Are acquired in synchronism with the image acquisition operation, and the reference image before the external force action and the reference image after the external force action are output to the second movement amount calculation processing unit 24. Therefore, the first and second camera devices 11 and 12 capture the specimen SM at the same timing so that the pre-external force action image and the pre-external force action reference image are synchronized with each other. While controlling to generate each of these images at the same timing, the specimen SM is photographed at the same timing so that the image after the external force action and the reference image after the external force action are synchronized with each other. Control is performed so as to generate these images at the same timing.

  More specifically, for example, when receiving the measurement start command from the input unit 14, the first and second image acquisition control units 21 and 22 cause the first camera device 11 to photograph the specimen SM, and the image before external force action. The image signal of the test body SM is acquired from the first camera device 11 and the second camera device 12 is photographed in synchronization with the second camera device 12 as a reference image before external force action. And then applying an external force to the test body SM by the tensile tester, the first camera device 11 is caused to photograph the test body SM, and an image after the external force is applied from the first camera device 11. The image signal of the test body SM is acquired, and the second camera device 12 is photographed in synchronization with the image signal of the test body SM. To get the issue. In the case where the first and second camera devices 11 and 12 are digital video cameras, an appropriate frame of the moving image photographed before the external force is applied to the specimen SM by the tensile tester is an external force. The pre-action image and the pre-external force action reference image, and an appropriate frame of the moving images taken after applying the external force to the specimen SM by the tensile tester are the post-external force action image and the post-external force action reference image. It only has to be done.

  Further, for example, when the first and second image acquisition control units 21 and 22 receive the measurement start command from the input unit 14, the first camera device 11 captures the specimen SM and the first camera device as an image before external force action. 11 obtains an image signal of the test specimen SM, synchronously causes the second camera device 12 to photograph the test specimen SM, and obtains an image signal of the test specimen SM from the second camera apparatus 12 as a reference image before external force action. Subsequently, while the external force is applied to the test body SM by the tensile tester, the first camera device 11 is photographed at a predetermined time interval, and the first camera device 11 outputs an image signal of the test body SM. Are acquired in synchronization with each other, and the second camera device 12 is photographed in synchronization with the second camera device 12 at the time interval, and image signals of the test sample SM are continuously acquired from the second camera device 12. . In this case, each image of the specimen SM taken at a certain time is compared with the image after the external force action and the reference after the external force action with respect to the image of the specimen SM taken at the timing immediately before the certain time. It becomes an image, and becomes an image before external force action and a reference image before external force action for each image of the specimen SM taken at the timing one time after the certain time. When the first and second camera devices 11 and 12 are digital video cameras, frames of the moving image of the specimen SM taken by the first and second camera devices 11 and 12 are framed at the time interval. And the image of the specimen SM taken at the certain time may be used.

  The first movement amount calculation processing unit 23 obtains the movement amount of the tracking mark Mc based on the position of the tracking mark Mc among the plurality of marks M in the image before external force action and the position of the tracking mark Mc in the image after external force action. The obtained movement amount of the tracking mark Mc is output to the elongation amount calculation processing unit 25. More specifically, the first movement amount calculation processing unit 23 corresponds to the tracking mark Mc (one of the marks M1 to M4 in the present embodiment, the mark M1 in the above example) in the pre-external force action image. (Corresponding tracking mark MAc (mark M1 in this example)) is searched from the image after the external force action as a tracking mark Mc in the image after the external force action by a search process, and the position (positional coordinates) of the tracking mark Mc in the image before the external force action and The movement amount of the tracking mark Mc is obtained from the position (positional coordinates) of the corresponding tracking mark MAc as the tracking mark Mc in the searched image after the action of the external force, and the obtained movement amount of the tracking mark Mc is calculated as an elongation amount calculation processing unit. To 25. This search process is performed using a known corresponding point search method for searching for points corresponding to each other between the pre-external force action image and the post-external force action image. More specifically, one of the pre-external force action image and the post-external force action image is a reference image and the other is a reference image, and the reference image pattern corresponding to the tracking mark Mc in the reference image is searched for correspondence. Searched by law. That is, the reference image pattern corresponding to the tracking mark Mc in the standard image is searched for as the corresponding tracking mark MAc by the correlation calculation between the standard image and the reference image.

  Similarly, the second movement amount calculation processing unit 24 determines the position of the reference mark Ms (the mark M5 in this embodiment) different from the tracking mark Mc among the plurality of marks M in the reference image before external force action and the reference image after external force action. The amount of movement of the reference mark Ms is obtained based on the position of the reference mark Ms at, and the obtained amount of movement of the reference mark Ms is output to the elongation amount calculation processing unit 25. More specifically, the second movement amount calculation processing unit 24 displays a mark (corresponding reference mark MAs (mark M5 in this example)) corresponding to the reference mark Ms (mark M5 in the above example) in the reference image before external force action. A search is performed as a reference mark Ms in the reference image after external force action from the reference image after external force action, and the position (positional coordinates) of the reference mark Ms in the reference image before external force action and the reference in the searched reference image after external force action are obtained. The movement amount of the reference mark Ms is obtained from the position (positional coordinate) of the corresponding reference mark MAs as the mark Ms, and the obtained movement amount of the reference mark Ms is output to the elongation amount calculation processing unit 25.

  Based on the movement amount of the tracking mark Mc and the movement amount of the reference mark Ms, the elongation amount calculation processing unit 25 obtains the elongation amount of the test body SM before and after applying an external force to the test body SM, and calculates the obtained elongation amount. This is output to the expansion / contraction rate calculation processing unit 26. The expansion / contraction rate calculation processing unit 26 calculates the expansion / contraction rate of the test body SM before and after applying an external force to the test body SM based on the amount of elongation of the test body SM, and outputs the calculated expansion / contraction rate to the output unit 15. It is.

Here, the expansion / contraction ratio ε is a distance between the tracking mark Mc provided on the test body SM and the reference mark Ms before the application of the external force as a reference length BLsc, and the tracking mark Mc and the reference mark Ms after the external force is applied. Is given by the following equation (1).
ε = (ELsc−BLsc) / BLsc (1)
Here, when the movement amount of the tracking mark Mc before and after the external force action is ΔDLc and the movement amount of the reference mark Ms before and after the external force action is ΔDLs, the following equation 2 is established.
ELsc = ΔDLc + BLsc + ΔDLs (2)
Therefore, Equation 1 becomes Equation 3 below by Equation 2.
ε = (ΔDLc + ΔDLs) / BLsc (3)
In the present embodiment, as described above, the movement amount ΔDLc is obtained by the first movement amount calculation processing unit 23, the movement amount ΔDLs is obtained by the second movement amount calculation processing unit 24, and the elongation amount calculation processing is performed. The amount of elongation (ΔDLc + ΔDLs) is obtained by the unit 25, and the expansion / contraction rate ε is obtained by the expansion / contraction rate calculation processing unit 26 using the above equation 3.

  Further, the determination processing unit 27 determines whether or not the tracking mark Mc is located in a predetermined end region in the image after the external force action, and the tracking mark Mc is located in the end region in the image after the external force action. In that case, a message to that effect is output to the switching processing unit 28. The predetermined end region is appropriately formed on the post-external force action image (the field of view of the first camera device 11 that captures the tracking mark Mc) on the moving direction side of the tracking mark Mc when an external force is applied to the specimen SM. For example, it is set to ½ region, １ ／ region, ５ region, or 1/10 region of the image after the external force action. Such an end region ER is, for example, a rectangular region at one end of the field of view of the first camera device 11 indicated by a dashed line in FIG.

  If the result of determination by the determination processing unit 27 is that the tracking mark Mc is located within the end region in the image after external force action, the switching processing unit 28 determines the current tracking mark Mc and the reference of the plurality of marks Mn. A switching and updating process is performed in which the mark Ms (for example, the mark M2) which is different from the mark Ms (in the above example, the mark M1 and the mark M5) and is located outside the end region is used as a new tracking mark Mc. (In this example, the mark M2) is output to the distance calculation processing unit 29.

  The distance calculation processing unit 29 obtains a distance between the reference mark Ms (mark M5 in the above example) and the new tracking mark Mc (mark M2 in the above example).

  Next, the operation of the strain measuring apparatus in the present embodiment will be described. 2 and 3 are flowcharts showing the operation of the strain measuring apparatus according to the embodiment. FIG. 4 is a diagram for explaining a calculation method for obtaining the expansion / contraction rate of the test body in the strain measurement apparatus of the embodiment.

  As a preparation for strain measurement, first, a plurality of marks M, in the present embodiment, five circular shapes M1 to M5 shown in FIG. 1 are provided on the surface of the test body SM as described above.

  As shown in FIG. 1, the marks M1 to M4 used as the tracking mark Mc have a circular shape similar to the mark M5 used as the reference mark Ms in the present embodiment. However, in FIG. Therefore, for the sake of convenience, the shapes are shown in different shapes, the mark M1 is indicated by ◯, the mark M2 is indicated by Δ, and the mark M3 is indicated by ◇. FIG. 4 also shows marks M1 to M3 at an initial time t0, a time t1 (> t0) when an external force is applied, and a time t2 (> t1) when an external force is further applied. ing. That is, the mark M1 is indicated by ● at time t0, indicated by a broken circle at time t1 and time t2, and the state of transition of the mark M1 due to the action of an external force is connected by “→” at each time. It is illustrated by Similarly, the mark M2 is indicated by ▲ at time t0, indicated by a broken line Δ at time t1 and time t2, and the state of transition of the mark M2 due to the action of an external force is indicated by “→” at each time. Illustrated by tying. Similarly, the mark M3 is indicated by ♦ at time t0, is indicated by broken lines ◇ at time t1 and time t2, and the state of transition of the mark M3 due to the action of external force is indicated by “→” at each time. It is illustrated by tying. In FIG. 4, the mark M4 is not shown.

  Then, in FIG. 2, in order to obtain the initial position of the desired mark M before the external force is applied to the test body SM, the image calculation processing unit 13 acquires the pre-external force action image A <b> 1 from the first camera device 11. The tracking mark Mc (mark M1 in the above example) is found from the acquired image A1 before external force action, the position of the tracking mark Mc is obtained (step S11-1), and the reference before the external force action is obtained from the second camera device 12. The image A2 is acquired, the reference mark Ms (mark M5 in the above example) is found from the acquired reference image A2 before the external force action, and the position of the reference mark Ms is obtained (step S11-2).

  More specifically, the pre-external force action image A1 and the pre-external force action reference image A2 of the test body SM are found, for example, the tracking mark Mc and the reference mark Ms by image processing such as pattern recognition of the shape of the mark M. Each position of the tracking mark Mc and the reference mark Ms is obtained. When a plurality of marks M are found in the image A1 before external force action, an appropriate mark M located outside the end region is selected as the tracking mark Mc. Each position of the tracking mark Mc and the reference mark Ms is, for example, a predetermined position (for example, one of the four corner points or a point intersecting the optical axis) on the image (light receiving surface of the image sensor) as a coordinate origin. An xy coordinate system is set in advance, and is represented by an x coordinate value and a y coordinate value of the xy coordinate system. When the optical image corresponding to the mark M is received by one pixel of the image sensor and the image corresponding to the mark M is formed by the image signal from the one pixel, the position of the mark M is the pixel. When the optical image corresponding to the mark M is received by a plurality of pixels of the image sensor and the image corresponding to the mark M is formed by an image signal from the plurality of pixels, the position of the mark M Is represented by a predetermined representative point of the mark M (for example, a center point, a center point of a circumscribed circle, a barycentric point, etc.), and is represented by a pixel position corresponding to the representative point. In addition, since the expansion / contraction rate ε is expressed by a predetermined ratio as described above, the distance may be expressed by an actual dimension, but may be a relative length based on a predetermined length. . For example, the distance can be expressed by the number of pixels of the image sensor.

  Subsequently, a tensile load is applied to the specimen SM as an external force by the tensile tester, and the external force is applied to the specimen SM.

  Then, in order to obtain the respective positions of the movement destinations of the tracking mark Mc and the reference mark Ms after the external force is applied to the test body SM, the first image acquisition control unit 21 images the post-external force action from the first camera device 11. B1 is acquired, and the first movement amount calculation processing unit 23 finds the tracking mark Mc from the acquired post-external force action image B1, and obtains the position of the tracking mark Mc (step S12-1). The image acquisition control unit 22 acquires the pre-external force action reference image B2 from the second camera device 12, and the second movement amount calculation processing unit 24 finds the reference mark Ms from the acquired pre-external force action reference image B2. The position of the reference mark Ms is obtained (step S12-2). In the process of finding the tracking mark Mc and the reference mark Ms from each of the image B1 after the external force action and the reference image B2 after the external force action, as described above, it is executed by the corresponding point search method. That is, in this embodiment, the corresponding tracking mark MAc corresponding to the tracking mark Mc in the image A1 before external force action is searched from the image B1 after external force action by the corresponding point search method as the tracking mark Mc in the image B1 after external force action. The corresponding reference mark MAs corresponding to the reference mark Ms in the reference image A2 before the external force action is searched by the corresponding point search method as the reference mark Ms in the reference image B2 after the external force action from the reference image B2 after the external force action.

  Here, after step S12-1, step S20 is executed, and thereafter step S13-1 is executed. On the other hand, after step S12-2, step S13-2 is executed.

  In step S13-1, the first movement amount calculation processing unit 23 determines the position of the tracking mark Mc in the pre-external force action image A1 and the tracking mark Mc (corresponding to the post-external force action image B1). The amount of movement of the tracking mark Mc is determined from the position of the tracking mark MAc). In step S13-2, the position of the reference mark Ms in the pre-external force reference image A2 and the reference searched in step S12-2 in the post-external force reference image B2 by the second movement amount calculation processing unit 24. The amount of movement of the reference mark Ms is determined from the position of the mark Ms (corresponding reference mark MAs).

  Subsequently, the elongation amount calculation processing unit 25 calculates the elongation amount (Δ of the test body SM before and after applying an external force to the test body SM from the movement amount ΔDLc of the tracking mark Mc and the movement amount ΔDLs of the reference mark Ms. DLc + ΔDLs) is obtained (step S14).

  Then, the expansion / contraction rate calculation processing unit 26 obtains the expansion / contraction rate ε of the test body SM before and after applying an external force to the test body SM based on the elongation amount (ΔDLc + ΔDLs) of the test body SM by the above formula 3. The obtained expansion / contraction rate ε is output to the output unit 15 (step S15).

  Here, the reference length BLsc which is the distance before the action of the external force between the tracking mark Mc and the reference mark Ms is a distance BL0 between the first and second camera devices 11 and 12 in the very first initial stage, for example, A distance BL0 between the optical axis of the first camera device 11 and the optical axis of the second camera device 12 is given to the strain measuring device S in advance, and the distance BL0 between the first and second camera devices 11 and 12 is This is given by the distance obtained based on the initial position of the tracking mark Mc obtained in step S11-1 and the initial position of the reference mark Ms obtained in step S11-2. After switching to the correct tracking mark Mc, it is given by the distance described later.

  Then, when the strain of the specimen SM is continuously measured, after executing the process of step S15, the image B1 after the external force action and the reference image B2 after the external force action in this process are the images A1 before the external force action in the next process. And it is treated as the reference image A2 before external force action, and the process is returned to step S12-1 and step S12-2. In this case, in the next processing, the pre-external force action image A1 and the pre-external force action reference image A2 are used as they are as the pre-external force action image and the pre-external force action reference image. May be taken in and updated as the post-external force action image C1 and the post-external force action reference image C2.

On the other hand, in step S20, the determination processing unit 27 determines whether or not the tracking mark Mc is located within a predetermined end region (end region ER in the above example) in the image after the external force action. If the result of this determination is that the tracking mark Mc is located within the end region ER in the post-external force image (YES), this is output to the switching processing unit 28, and step S21 is executed. On the other hand, the result of the determination, if the tracking marks Mc is not positioned at an end region of the external force after the image (NO), the above steps S13- 1 is executed.

In FIG. 3, in step S <b> 21, two or more marks M, that is, other tracking marks Mc other than the current tracking mark Mc are first placed in the field of view of the first camera device 11 (in the image after the external force action) by the switching processing unit 28. It is determined whether or not the mark M exists. This determination is performed, for example, by performing a process of searching for the mark M by image processing such as pattern recognition of the shape of the mark M with respect to an image outside the edge region. As a result of the determination, if two or more of the mark M in the field of view of the first camera device 11 is not present (NO), the above steps S13- 1 is executed. On the other hand, if two or more marks M exist in the field of view of the first camera device 11 as a result of the determination (YES), step S22 is executed.

  In the following description of steps S22 to S26, for convenience of explanation, the current tracking mark Mc (the currently used tracking mark Mc) is denoted as Mk, and a new tracking mark Mc (switching destination tracking mark). Mc) is written as Mm.

In step S22, the distance calculation processing unit 29 calculates the expansion / contraction rate ε _c (= ε _k ) of the tracking mark Mc from the amount of movement of the tracking mark Mc (= Mk). More specifically, the distance calculation processing unit 29 moves based on the position of the tracking mark Mk in the image A1 before the external force action and the position of the corresponding tracking mark MAk corresponding to the tracking mark Mk in the image B1 after the external force action. ΔDLk is obtained, and the expansion / contraction ratio ε _k (= ΔDLk / BLsk) is _obtained based on the obtained movement amount ΔDLk and the distance BLsk between the reference mark Ms and the tracking mark Mk before the action of the external force.

  Subsequently, another distance M that is not the current tracking mark Mk among the marks M searched in step S21 is set as a new tracking mark Mm (in this example, mark M2) by the distance calculation processing unit 29, and an external force action is performed. The distance 1 between the later tracking mark Mk (in this example, mark M1) and the new tracking mark Mm (in this example, mark M2) is the position of the tracking mark Mk in the post-external force image B1 and the post-external force image B1. Is obtained based on the position of the new tracking mark Mm at (step S23).

Subsequently, the distance 10 between the tracking mark Mk before the external force action and the new tracking mark Mm by the distance calculation processing unit 29 becomes the expansion / contraction rate ε _k obtained in step S22 and the external force action obtained in step S23. Based on the distance 1 between the tracking mark Mk and the new tracking mark Mm, the following equation 4 is obtained (step S24).
l0 = l / (1 + ε _k ) (4)
Subsequently, the distance Lsm between the reference mark Ms before the external force action and the new tracking mark Mm is obtained by the distance calculation processing unit 29 in step S24, and the tracking mark Mk before the external force action and the new tracking mark Mm are obtained. And the distance Lsk between the reference mark Ms before the external force action and the tracking mark Mk (the tracking mark Mc before the update (before the external force action), in this example, the mark M1). It is obtained by equation 5 (step S25).
Lsm = Lsk-l0 = Lsk-l / (1+ [epsilon] _k ) (5)
By executing the processes in steps S22 to S25, the distance calculation processing unit 29 obtains the distance Lsm between the reference mark Ms and the new tracking mark Mm.

Then, the switching processing unit 28 changes the tracking mark Mc (= Mk) to a new tracking mark Mc (= Mm) as shown in the following expressions 6 and 7, and the tracking mark Mc and the reference mark before the action of the external force replacing the reference length BLsc is the distance between the Ms to Lsm obtained in step S25 (step S26), then the processing returns to step S12- 1, step S12- 1 is executed.
Mc ← Mm (6)
BLsc ← Lsm (7)
The above operation will be described more specifically below with reference to FIG. In FIG. 4, at the first time t0 after the start of the tensile test, the first camera device 11 has photographed the mark M1 (; ● of t0) as the tracking mark Mc, and the right rectangular shape shown by a broken line in FIG. An image is obtained, and the second camera device 12 has taken the mark M5 (; ●) as the reference mark Ms, and a left-side rectangular image indicated by a broken line in FIG. 4 is obtained. At time t0, only the mark M1 is photographed in the image obtained by the first camera device 11, and the marks M2 to M4 are not photographed.

  Therefore, in this case, each process of step S11 (S11-1, S11-2) and step S12 (S12-1, S12-2) is executed, and subsequently, in step S20, mark M1 (tracking mark Mc). Is determined not to be within the edge region ER, each process of step S13 (S13-1, S13-2) is executed, and then each process of step S14 and step S15 is executed. In step S15, the expansion / contraction at time t0 is based on the movement amount ΔDL5 of the mark M5, the movement amount ΔDL1 of the mark M1, and the distance L51 (reference length BL51) between the mark M5 and the mark M1 before the external force is applied. The rate εt0 (= (ΔDL5 + ΔDL1) / BL51) is obtained. Here, the distance L51 between the mark M5 and the mark M1 before the external force action is the distance BL0 between the first camera device 11 and the second camera device 12, the position of the mark M1 obtained in step S11, and the mark M5. And based on the position.

  Then, at the next time t1 (> t0) when the tensile test is continued, the first camera device 11 is photographing the mark M1 (; broken line o of t1) as the tracking mark Mc and the mark M2 (t1 4 is also taken, and a rectangular image on the right side shown by the broken line in FIG. 4 is obtained, and the second camera device 12 is taking the mark M5 (; ●) as the reference mark Ms. A rectangular image on the left side indicated by a broken line in FIG. 4 is obtained. At this time t1, the mark M1 and the mark M2 are photographed in the image obtained by the first camera device 11, and the mark M3 and the mark M4 are not photographed.

  Therefore, in this case, the process of step S12 (S12-1, S12-2) is executed following step S15 in the above-described process, and subsequently, in step S20, the mark M1 (tracking mark Mc) is set to the end portion. Since it is determined that the area is within the region ER, the processes in steps S21 to S26 are executed.

That is, in step S21, it is determined that there are two marks M1 and M2 in the image after the external force action. In step S22, the movement amount ΔL1 (= ΔDL1) of the mark M1 and the mark M5 and mark M1 before the external force action are determined. The expansion / contraction ratio ε ₁ is obtained based on the distance L51 (= BL51) between them, and in step S23, the mark M2 that is not the mark M1 is set as a new tracking mark Mc, and the mark M1 after the external force is applied and the new tracking mark The distance l between the mark M2 as Mc is obtained based on the position of the mark M1 in the image after the external force action and the position of the mark M2 as the new tracking mark Ms in the image after the external force action. In step S24, on the basis of the expansion ratio epsilon ₁ and the said distance l, as a new tracking marks Mc mark M1 before external force Over the distance between the click M2 l0 (= l / (1 + ε 1)) is determined, in step S25, and the distance l0, tracking marks M5 and the mark M1 before external force (pre-update (before external force) Based on the distance L51 between the marks Mc), a distance L52 (= L51-l0) between the mark M5 before the external force action and the mark M2 as the new tracking mark Mc is obtained. In step S26, the tracking mark Mc is changed from the mark M1 to the mark M2, and the reference length BLcs, which is the distance between the reference mark Ms before the external force action and the tracking mark Mc, is the mark M5 before the external force action and the mark M2 as the new tracking mark Mc It is updated with the distance L52 between.

  During this time, the tensile test is continued, and at the next time t2 (> t1), the first camera device 11 has photographed the mark M2 (; a broken triangle of t2) as the tracking mark Mc. A right-side rectangular image indicated by a broken line in FIG. 4 is obtained, and the second camera device 12 has photographed the mark M5 (; ●) as the reference mark Ms, and the left-side rectangular shape indicated by the broken line in FIG. Images are obtained. At time t2, only the mark M2 is photographed in the image obtained by the first camera device 11, and the marks M1, M3, and M4 are not photographed.

Therefore, in this case, the process of step S12 (S12-1, S12-2) is executed, and subsequently, in step S20, it is determined that the mark M2 (tracking mark Mc) is not in the end region ER. Each process of step S13 (S13-1, S13-2) is performed, and then each process of step S14 and step S15 is performed. In step S15, the moving amount of the mark M5, based on the amount of movement of the mark M2, the distance between the mark M5 and mark M2 before external force (reference length), the expansion ratio at the time t2 epsilon is obtained.

  As described above, in the strain measuring device S of the present embodiment, the test body SM including the plurality of marks M on the test body SM is photographed by the first and second camera devices 11 and 12, and the test body is obtained. The expansion / contraction rate ε of the specimen SM is obtained from the position of the tracking mark Mc and the position of the reference mark Ms in each of the images A1, B1; A2, B2 acquired before and after applying an external force to the SM. Then, when obtaining the expansion / contraction ratio ε of the test body SM, the tracking mark Mc is in the field of view of the first camera device 11 (an image taken by the first camera device 11) in accordance with the action of the external force. If it is located inside, another mark M located outside the end region ER is set as a new tracking mark Mc, and a switching update process is performed. Accordingly, the strain measuring device S having such a configuration can measure the expansion / contraction ratio ε of the test body SM as long as the tracking mark Mc is photographed by the first camera device 11, and thus the first and second camera devices. The measurement range can be further expanded while maintaining the 11 and 12 fields of view, that is, the resolution.

  In addition, in the above-mentioned embodiment, each process which switches the mark of step S20 thru | or step S26 shown in FIG.2 and FIG.3 was performed only with respect to the image image | photographed with the 1st camera apparatus 11, However, 2nd camera apparatus 12 may be performed on the image captured by the image processing unit 12. In this case, a process similar to step S20 is inserted between step S12-2 and step S13-2 shown in FIG. 2, and thereafter, each process similar to each process of steps S21 to S26 shown in FIG. Processing is executed.

  In the above-described embodiment, the strain measuring device S includes a plurality of, in this example, the first and second camera devices 11 and 12, as an example of an imaging unit that images the test body SM including the plurality of marks M. Although configured, it may be configured to include one first camera device 11 that captures the tracking mark Mc. In this case, with respect to the reference length BLsc, which is the distance before the action of the external force, between the tracking mark Mc and the reference mark Ms, the first camera is the first and the first reference length BLsc as the first reference length BLsc. For example, the distance from the tracking mark Mc to be photographed by the user is measured in advance by a user or the like using a length measuring device such as a caliper, and the previously measured distance is input to the strain measuring device S before the measurement is started. The The image calculation processing unit 13 of the strain measuring apparatus S relates to the reference length BLsc that is the distance before the external force action between the tracking mark Mc and the reference mark Ms, and uses the distance as the first initial reference length BLsc. A reference distance storage unit (not shown) for storing is further provided functionally. In such a configuration, the strain measuring device S is configured relatively simply including the first camera device 11, and even with such a configuration, the strain measuring device S can measure while maintaining the resolution. The range can be expanded. The strain measuring device S having such a configuration is preferably used for, for example, a uniaxial tensile test in which the other end of the test body SM is fixed and an external force is applied to one end thereof. Arranged so that the tracking mark Mc except for the center (fixed point) can be observed.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

S Strain measuring device M (M1, M2, M3, M4, M5) Mark ER End region 11 First camera device 12 Second camera device 13 Image arithmetic processing unit 21 First image acquisition control unit 22 Second image acquisition control unit 23 first movement amount calculation processing unit 24 second movement amount calculation processing unit 25 elongation amount calculation processing unit 26 expansion / contraction rate calculation processing unit 27 determination processing unit 28 switching processing unit 29 distance calculation processing unit

Claims (8)

An imaging unit for imaging a test object to be measured, comprising a plurality of marks,
An image acquisition unit for acquiring images of the test body before and after applying an external force to the test body, as an image before external force action and an image after external force action, by the photographing unit;
The tracking mark is one of the plurality of marks and a reference distance between a predetermined reference position, a position of the tracking mark in the image before the external force action, and the position in the image after the external force action And an arithmetic processing unit for obtaining an expansion / contraction ratio of the specimen based on the position of the tracking mark,
When the tracking mark is located within a predetermined end region in the post-external force action image and there are two or more marks in the post-external force action image, the arithmetic processing unit The strain measurement apparatus is characterized by performing a switching update process in which a mark that is different from the tracking mark and located outside the end region is newly used as the tracking mark. The imaging unit includes a first camera device that captures the tracking mark, and a second camera that captures a mark that is different from the tracking mark among the plurality of marks to be the predetermined reference position. With the device,
The image acquisition unit acquires, by the first camera device, images of the test body before and after applying an external force to the test body as the image before the external force action and the image after the external force action, The images of the test body before and after applying an external force are acquired by the second camera device as a reference image before external force action and a reference image after external force action,
The arithmetic processing unit includes a distance between the tracking mark serving as the reference distance and the reference mark, a position of the reference mark in the reference image before the external force action, and a position of the reference mark in the reference image after the external force action. 2. The strain measurement according to claim 1, wherein an expansion / contraction ratio of the test body is obtained based on a position of the tracking mark in the image before the external force action and a position of the tracking mark in the image after the external force action. apparatus. The photographing unit includes one camera device that photographs the tracking mark and a mark different from the tracking mark as a reference mark in order to obtain the predetermined reference position.
The image acquisition unit sets the image of the test body before and after applying an external force to the test body as the image before the external force action and the image after the external force action, and as the reference image before the external force action and the reference image after the external force action. Acquired by the camera device,
The arithmetic processing unit includes a distance between the tracking mark serving as the reference distance and the reference mark, a position of the reference mark in the reference image before the external force action, and a position of the reference mark in the reference image after the external force action. 2. The strain measurement according to claim 1, wherein an expansion / contraction ratio of the test body is obtained based on a position of the tracking mark in the image before the external force action and a position of the tracking mark in the image after the external force action. apparatus. The arithmetic processing unit includes:
A first movement amount calculation processing unit for obtaining a movement amount of the tracking mark as a tracking mark movement amount based on the position of the tracking mark in the image before the external force action and the position of the tracking mark in the image after the external force action;
A second movement amount calculation processing unit that obtains a movement amount of the reference mark as a reference mark movement amount based on the position of the reference mark in the reference image before the external force action and the position of the reference mark in the reference image after the external force action When,
Based on the reference mark movement amount and the tracking mark movement amount, an elongation amount calculation processing unit for obtaining an elongation amount of the test body before and after the external force is applied to the test body;
A stretch rate calculation processing unit for obtaining a stretch rate of the test body based on a distance between the reference mark and the tracking mark and an extension amount of the test body before the external force is applied to the test body; The strain measuring device according to claim 2 or claim 3, wherein The first movement amount calculation processing unit searches the post-external force action image for a mark corresponding to the tracking mark in the pre-external force action image, and uses the searched mark as the tracking mark in the post-external force action image,
The second movement amount calculation processing unit searches the reference image after the external force action for a mark corresponding to the reference mark in the reference image before the external force action, and searches the reference mark in the reference image after the external force action. The strain measuring device according to claim 4, wherein the strain measuring device is a mark. The arithmetic processing unit further includes:
A determination processing unit that determines whether or not the tracking mark is positioned within a predetermined end region in the image after the external force action;
As a result of the determination by the determination processing unit, when the tracking mark is located within a predetermined end region in the post-external force image, the end mark is different from the reference mark and the tracking mark among the plurality of marks. A switching processing unit for performing a switching update process in which a mark located outside the area is newly set as the tracking mark;
The distance calculation processing part which calculates | requires the distance between the said reference mark and the said mark located outside the said edge part area | region newly set as the said tracking mark is provided. The strain measuring apparatus described. The photographing unit includes one camera device that photographs the tracking mark,
The strain measurement apparatus according to claim 1, further comprising a reference distance storage unit that stores the reference distance in advance. An image acquisition step of acquiring images of the test body before and after applying an external force to a test object to be measured, including a plurality of marks, by an imaging unit as an image before external force action and an image after external force action;
The tracking mark is one of the plurality of marks and a reference distance between a predetermined reference position, a position of the tracking mark in the image before the external force action, and the position in the image after the external force action And an arithmetic processing step for obtaining an expansion / contraction ratio of the test body based on the position of the tracking mark,
In the calculation processing step, when the tracking mark is located in a predetermined end region in the image after the external force action, and there are two or more marks in the image after the external force action , A strain measurement method comprising: a switching update processing step in which a mark that is different from the tracking mark and located outside the end region is newly used as the tracking mark.

Images