JP2012083309A - Strain measuring device and strain measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain measuring device and a strain measuring method capable of improving the measuring accuracy and reducing an information processing amount while taking account of deformation of a prescribed feature pattern.SOLUTION: In the strain measuring device Sa and method according to the present invention, a tentative expansion/contraction ratio is acquired by a pattern matching, from an image A of a test piece SM before applying external force to the test piece SM and an image B thereof after applying the external force to the test piece SM, the pattern in the image A before the external force application or the image B after the external force application is deformed using the acquired tentative expansion/contraction ratio, and an expansion/contraction ratio is acquired by the pattern matching, from the image B of the test piece SM after the external force application based on the deformed pattern.

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 non-contact displacement measuring device disclosed in Patent Document 1 has a gripping tool for fixing a test piece having a mark portion, and further includes at least two imaging devices and an image processing device for observing the mark portion. The displacement of the target point is extracted by the imaging device, the displacement is obtained from the amount of the shift by template matching, and the displacement between the test piece target point portions is measured in a non-contact manner. In the contact-type displacement measuring device, two triangular reference portions are provided in the convex target portion, stored, and thereafter, the image portion is always searched for, and the elongation is measured by the movement of the image. .

  In addition, the image processing method disclosed in Patent Document 2 includes an image data acquisition process in which the image data acquisition means accepts pre-change image data and post-change image data of an object, and an analysis point on the pre-change image data by the parameter acquisition means. Parameter acquisition process that accepts numerical data in the analysis area movement amount analysis range, rotation angle analysis range, and strain analysis range, and the rotation processing means affine transforms the micro area And a rotation processing process for generating a mask rotated by a predetermined angle in the rotation angle analysis range, and the first correlation value calculating means scans each mask in the movement amount analysis range on the pre-change image data, The first correlation value calculation process for calculating the correlation value of the position and the position angle at which the position angle detection means detects the position and angle at which the maximum correlation value is obtained. A detection process, an expansion / contraction process for generating a secondary mask in which a mask having a maximum correlation value is expanded / contracted by a predetermined expansion / contraction ratio in a distortion analysis range by affine transformation, and a second correlation value calculation unit is provided for each secondary A second correlation value calculation process for calculating a correlation value between the mask and the image data after change, an expansion / contraction ratio detection process in which the expansion / contraction ratio detection means detects the expansion / contraction ratio at which the maximum correlation value is obtained, and the state determination means determines the maximum correlation value. And a state determination process for determining the movement amount, rotation angle, and distortion of the analysis point from the given position, angle, and expansion / contraction rate.

Japanese Patent Laid-Open No. 08-278109 JP 2007-333647 A

  Usually, the strain measurement is performed by comparing the shape of the test body before applying strain to the test body by applying an external force to the test body and the shape of the test body after applying strain. In the technique disclosed in Patent Document 1, two triangular reference portions are provided at the convex mark portion of the test piece, and from the image after applying the distortion, the triangular reference portion before applying the distortion is displayed. The reference portion of the triangle is searched by template matching using an image as a template, the amount of deviation is obtained, and the displacement is obtained from this amount of deviation. However, since the distortion covers the entire test piece, the triangular reference portion is also deformed. Therefore, in the template matching, the accuracy of pattern matching in the images before and after the distortion is deteriorated, and the measurement accuracy and its reliability are reduced. Sexuality decreases. As a result, the amount of deviation cannot be obtained with high accuracy, and the displacement cannot be obtained with high accuracy.

  On the other hand, in the technique disclosed in Patent Document 2, the deformation of the analysis point caused by applying the strain is caused by various deformations of the minute region generated by variously deforming the minute region around the analysis point by affine transformation. This is taken into account by providing a mask. However, since it is necessary to perform image correlation calculation on such a large number of masks, 60 masks in the rotation process, and 440 masks in the expansion / contraction process, the amount of information processing is large. Therefore, it takes time for information processing.

  The present invention has been made in view of the above-described circumstances, and its object is to provide a strain measuring apparatus capable of improving measurement accuracy and reducing the amount of information processing while considering deformation of a predetermined feature pattern. And providing a strain measurement method.

  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 measurement apparatus according to one aspect of the present invention acquires an image of the test body before and after applying an external force to the test body that is a measurement target, as an image before the external force action and an image after the external force action, by the photographing unit. An acquisition control unit; a first search processing unit that searches for a pattern in the post-external force action image corresponding to a predetermined feature pattern in the pre-external force action image; and a position of the feature pattern in the pre-external force action image And a temporary expansion / contraction rate calculation processing unit for determining the expansion / contraction rate of the test body as a temporary expansion / contraction rate based on the position of the temporary corresponding pattern in the post-external force action image searched by the first search processing unit, and the expansion / contraction rate Based on the temporary expansion / contraction rate obtained by the arithmetic processing unit, the feature pattern or the external force in the image before the external force action A deformation processing unit that deforms the temporary corresponding pattern in the post-use image to generate a deformation pattern, and the external force corresponding to the feature pattern in the image before the external force action based on the deformation pattern generated by the deformation processing unit A second search processing unit for re-searching a pattern in the post-action image as a measurement-corresponding pattern; and the position of the feature pattern in the pre-external force action image and the post-external force action image re-searched by the second search processing unit. And a measurement expansion / contraction rate calculation processing unit that obtains the expansion / contraction rate of the specimen as a measurement expansion / contraction rate based on the position of the measurement feature pattern. Preferably, in the above-described measurement apparatus, the deformation processing unit generates a deformation pattern by converting the feature pattern in the image before the external force action using the temporary expansion / contraction rate obtained by the expansion / contraction rate calculation processing unit. Then, the second search processing unit re-searches the pattern in the image after the external force action corresponding to the deformation pattern as a measurement corresponding pattern. Preferably, in the above-described measuring apparatus, the deformation processing unit reversely transforms the temporary corresponding pattern in the image after the external force action using the reciprocal of the temporary expansion / contraction rate obtained by the expansion / contraction rate calculation processing unit. A pattern is generated, and the second search processing unit re-searches a pattern in the post-external force action image corresponding to the feature pattern in the pre-external force action image as a measurement corresponding pattern based on the deformation pattern. .

  The strain measurement method according to another aspect of the present invention includes an image acquisition step of acquiring images of the test body before and after applying an external force to the test body as a measurement target as an image before external force action and an image after external force action. A first search processing step of searching as a temporary corresponding pattern a pattern in the post-external force action image corresponding to a predetermined feature pattern in the pre-external force action image, and a position of the feature pattern in the pre-external force action image and the first Based on the position of the temporary corresponding pattern in the post-external force action image searched by one search processing step, a temporary expansion / contraction rate calculation processing step for determining the expansion / contraction rate of the test body as a temporary expansion / contraction rate, and the expansion / contraction rate calculation processing step The feature pattern in the pre-external force action image or the post-external force action image based on the temporary expansion / contraction rate obtained by A deformation processing step for generating a deformation pattern by deforming the temporary corresponding pattern in the image, and the image after the external force action corresponding to the feature pattern in the image before the external force action based on the deformation pattern generated by the deformation processing step. A second search processing step of searching for a pattern in the measurement as a measurement corresponding pattern, the position of the feature pattern in the image before the external force action, and the specific corresponding pattern in the image after the external force action re-searched by the second search processing step And a measurement expansion / contraction rate calculation processing step for obtaining the expansion / contraction rate of the test body as a measurement expansion / contraction rate based on the position. Preferably, in the strain measurement method described above, the deformation processing step converts the feature pattern in the image before the external force action using the temporary expansion ratio obtained by the expansion / contraction ratio calculation processing step, and converts the characteristic pattern into a deformation pattern. The second search processing step is to re-search the pattern in the image after the external force action corresponding to the deformation pattern as a measurement corresponding pattern. Preferably, in the strain measurement method described above, the deformation processing step reversely converts the temporary corresponding pattern in the image after the external force action using an inverse number of the temporary expansion / contraction rate obtained by the expansion / contraction rate calculation processing step. A deformation pattern is generated, and the second search processing step re-searches a pattern in the image after the external force action corresponding to the feature pattern in the image before the external force action as a measurement corresponding pattern based on the deformation pattern. is there.

  In the strain measuring apparatus and the strain measuring method having such a configuration, a temporary expansion / contraction rate is obtained, and a deformation pattern is generated. For this reason, deformation of the feature pattern is taken into consideration, and it is not necessary to perform search processing for a large number of deformation patterns obtained by variously deforming the feature pattern. Therefore, the strain measuring apparatus and strain measuring method having such a configuration can improve the measurement accuracy and reduce the amount of information processing while taking into account the deformation of the feature pattern.

  According to another aspect, the above-described strain measuring apparatus further includes a photographing unit that photographs the specimen, and the photographing unit is a single camera device.

  According to this configuration, the feature pattern is photographed by one camera device, and the strain measuring device can be configured more simply, and the cost can be suppressed.

  According to another aspect, the above-described strain measuring apparatus further includes a photographing unit that photographs the specimen, and the photographing unit is a plurality of camera devices.

  According to this configuration, it is possible to individually photograph patterns necessary for the calculation of the expansion / contraction ratio with each camera device, and to obtain images before and after the action of external force with higher resolution.

  According to another aspect, in the above-described strain measuring apparatus, the feature pattern is a dot pattern composed of a plurality of dots spaced from each other.

  According to this configuration, it is possible to provide a strain measuring apparatus that can calculate the expansion / contraction rate by calculating the distance between dots.

  According to another aspect, in the strain measurement apparatus described above, the plurality of dots are in a linearly independent relationship with the dots in the first dot group arranged along a predetermined first direction. And dots of a second dot group arranged along a second direction.

  According to this configuration, it is possible to calculate a linearly independent expansion / contraction rate in two directions. Note that the dots of the first dot group and the dots of the second dot group may be separate and independent, and there may be some overlap.

  In another aspect, in the above-described strain measuring apparatus, the plurality of dots are divided into a plurality of regions, and the dots in each region are randomly arranged.

  According to this configuration, since a plurality of randomly arranged dots can be regarded as one pattern, a pattern in an image after external force action corresponding to a predetermined feature pattern in an image before external force action can be searched more accurately. Can do.

  The strain measuring apparatus and strain measuring method according to the present invention can improve the measurement accuracy and reduce the amount of information processing while taking into account the deformation of the feature pattern.

It is a figure which shows the structure of the distortion | strain measuring apparatus in 1st Embodiment. It is a flowchart which shows operation | movement of the distortion | strain measuring apparatus in 1st Embodiment. It is a figure for demonstrating the calculation method which calculates | requires the measurement expansion-contraction rate of a test body in the distortion | strain measuring apparatus of 1st Embodiment. It is a figure which shows the structure of the distortion | strain measuring apparatus in 2nd Embodiment. It is a figure for demonstrating the calculation method which calculates | requires the measurement expansion-contraction rate of a test body in the strain measuring apparatus of 2nd Embodiment. It is a figure which shows the predetermined pattern in a 1st deformation | transformation aspect. It is a figure which shows the predetermined pattern in a 2nd deformation | transformation aspect.

  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.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a strain measuring apparatus according to the first embodiment. The strain measuring device Sa of the present embodiment is a device that measures strain generated in the specimen SM, and includes, for example, a camera device 10 and an image processing unit 20 as shown in FIG.

  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 predetermined pattern MP in order to measure the strain generated in the test body SM. The predetermined pattern MP is a mark (a mark or a mark) having a predetermined shape. In the present embodiment, as shown in FIG. 1, two pairs of circular shapes provided on the surface of the test body SM are used. This is a pattern MPa composed of the first and second dot patterns D1 and D2. The pair of first and second dot patterns D1 and D2 in the predetermined pattern MPa are arranged apart from each other by a predetermined distance along the pulling direction in which the test body SM is pulled by the tensile tester. The predetermined pattern MPa is provided on the surface of the test body SM so as to follow deformation such as elongation in the test body SM. The predetermined pattern MPa is drawn, for example, by printing or by handwriting using ink or the like.

  In the present embodiment, the dot pattern D has a circular shape, but is not limited thereto, and may be any shape such as a polygonal shape or an irregular shape.

  The camera device 10 is a device that photographs a specimen SM as a subject in order to monitor (observe and monitor) the specimen SM, and includes, for example, a photographing optical system, an image sensor, and an image generation unit. Is done. 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, and shading correction processing on the signal obtained by the imaging device, It is a circuit that outputs to the unit 20. The camera device 10 may be a monochrome camera, a color camera, a digital still camera that generates a still image, or a digital video camera that generates a moving image.

  And the camera apparatus 10 can image | photograph the part of the test body SM provided with the predetermined pattern MPa, and image | photographs a pair of 1st and 2nd dot pattern D1, D2 in this predetermined pattern MPa together. Is arranged so that

  The image processing unit 20 is a circuit for obtaining the strain of the specimen SM based on the image signal obtained by the camera device 10, and is configured by, for example, a microcomputer having a microprocessor, a storage element, and its peripheral circuits. . In the present embodiment, as shown in FIG. 1, the image processing unit 20 functionally includes an image acquisition control unit 21, a first search processing unit 22, a temporary expansion / contraction rate calculation processing unit 23, and a deformation process. A unit 24, a second search processing unit 25, and a measurement expansion / contraction rate calculation unit 26 are configured. The image acquisition control unit 21, the first search processing unit 22, the temporary expansion / contraction rate calculation processing unit 23, the deformation processing unit 24, the second search processing unit 25, and the measurement expansion / contraction rate calculation unit 26 are obtained by the camera device 10, for example. The microcomputer is functionally configured by executing a strain measurement program for calculating the strain of the specimen SM based on the image signal.

  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 Sa may be configured to be installed in the microcomputer via an external storage device, and a communication network and a communication interface device (network card, etc.) from a server computer that manages the strain measuring program. The strain measurement device Sa may be configured so that the strain measurement program is downloaded via the. In the present embodiment, the image signal of the test specimen SM is obtained from the camera device 10 in substantially real time. However, the present invention is not limited to this mode, and data for measuring the strain of the test specimen SM is as follows. The strain measuring device Sa may be configured to be input to the strain measuring device Sa via an external storage device by a recording medium storing this data, and from the server computer managing this data to the communication network and communication The strain measuring device Sa may be configured to be input to the strain measuring device Sa via the interface device.

  Then, the 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 as an image before the external force action and an image after the external force action, and these images before the external force action and the external force action. The subsequent image is output to the first search processing unit 22. More specifically, for example, when receiving the measurement start command from an input device (not shown), the image acquisition control unit 21 causes the camera device 10 to photograph the test body SM and from the camera device 10 as an image before external force action. After obtaining an image signal of SM and subsequently applying an external force to the specimen SM by the tensile tester, the camera apparatus 10 is caused to photograph the specimen SM, and an image after the external force is applied is obtained from the camera apparatus 10 as the specimen SM. The image signal of is acquired. In the case where the camera device 10 is a digital video camera, an appropriate frame of the moving images photographed before the external force is applied to the test body SM by the tensile tester is set as the pre-external force action image. An appropriate frame of the moving images taken after applying an external force to the specimen SM by the tensile tester may be used as the image after the external force action. For example, when the image acquisition control unit 21 receives a measurement start command from an input device (not shown) (keyboard, mouse, or the like), the camera device 10 causes the test body SM to be photographed, and the test is performed from the camera device 10 as an image before external force action. An image signal of the body SM is acquired, and then, the external force is applied to the test body SM by the tensile tester, and the test body SM is photographed by the camera device 10 at a predetermined time interval. The image signal is continuously acquired. In this case, the image of the specimen SM taken at a certain time becomes an image after the application of external force to the image of the specimen SM taken at the timing immediately before the certain time, and the or For the image of the specimen SM taken at the timing one time after the first time, an image before external force action is obtained. When the camera device 10 is a digital video camera, frames are selected at the predetermined time interval from the moving images of the specimen SM photographed by the camera device 10 and photographed at the certain time. An image of the test body SM may be used.

  The first search processing unit 22 searches for a pattern in the image after the external force action corresponding to the predetermined pattern MPa in the image before the external force action as a temporary corresponding pattern, and outputs the search result to the temporary expansion / contraction rate calculation processing unit 23. It is. 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 set as a reference image and the other is set as a reference image, and a reference image pattern corresponding to a predetermined pattern MPa in the reference image is searched for correspondence. Searched by law. That is, the pattern of the reference image corresponding to the predetermined pattern MPa in the standard image is searched by the correlation calculation between the standard image and the reference image.

  Based on the position of the predetermined pattern MPa in the pre-external force action image and the position of the temporary corresponding pattern in the post-external force action image searched by the first search processing unit 22, the temporary expansion / contraction rate calculation processing unit 23 Is calculated as a temporary expansion / contraction ratio, and the calculated temporary expansion / contraction ratio is output to the deformation processing unit 24.

  Based on the temporary expansion / contraction rate obtained by the expansion / contraction rate calculation processing unit 23, the deformation processing unit 24 deforms the predetermined pattern MPa in the image before the external force action or the temporary corresponding pattern in the image after the external force action to generate a deformation pattern. The deformation pattern is generated and output to the second search processing unit 25. More specifically, for example, in the present embodiment, the predetermined pattern MPa in the image before the external force action is multiplied by the temporary expansion / contraction rate, and a deformation pattern of the predetermined pattern MPa in the image before the external force action is generated.

  Based on the deformation pattern generated by the deformation processing unit 24, the second search processing unit 25 re-searches the pattern in the post-external force action image corresponding to the predetermined pattern MPa in the pre-external force action image as a measurement corresponding pattern, This search result is output to the measurement expansion / contraction rate calculation processing unit 26.

  Then, the measurement expansion / contraction rate calculation processing unit 26 is based on the position of the predetermined pattern MPa in the image before the external force action and the position of the measurement corresponding pattern in the image after the external force action re-searched by the second search processing unit 25. The expansion / contraction ratio of the test body SM is obtained as the measurement expansion / contraction ratio, and the obtained measurement expansion / contraction ratio of the test body SM is output.

  The measured expansion / contraction ratio of the test body SM is output to a downstream (downstream) device, for example, an output device (not shown). The output device is, 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.

Here, the expansion / contraction rate ε is defined as a distance between the pair of first and second dot patterns D1 and D2 before the action of the external force in the predetermined pattern MPa provided on the test body MP as a reference length L0. When the distance between the first and second dot patterns D1 and D2 is the expansion / contraction length L1, the following equation 1 is given.
ε = (L1−L0) / L0 (1)

Here, if the displacement amount of the first dot pattern D1 before and after the external force action is ΔL1, and the displacement amount of the second dot pattern D2 before and after the external force action is ΔL2, the following equation 2 is established.
L1 = ΔL1 + L0 + ΔL2 (2)

Therefore, Equation 1 becomes Equation 3 below by Equation 2.
ε = (ΔL1 + ΔL2) / L0 (3)

In the present embodiment, as described above, the first search processing unit 22 does not take into account the deformation of the predetermined pattern MPa due to the action of external force, that is, the deformation of the dot pattern D, and does not take into account the predetermined predetermined in the image before the external force action. Since the pattern in the image after the external force action corresponding to the pattern MPa is searched as a temporary corresponding pattern, the position of the searched temporary corresponding pattern may be deviated from the position of the true (actual, actual) pattern. And may contain errors. Therefore, the expansion / contraction ratio ε of the test body SM obtained by the temporary expansion / contraction ratio calculation processing unit 23 is set to the temporary expansion / contraction ratio ε0 ′, and is given by Expression 4 based on the same idea as Expression 3 above.
ε0 ′ = (ΔL1 ′ + ΔL2 ′) / L0 (4)

  Here, the temporary displacement amount ΔL1 ′ is a dot pattern (first temporary corresponding dot pattern) corresponding to the first dot pattern D1 obtained by the first search processing unit 22 without considering the deformation of the first dot pattern D1. ) The displacement amount of the first dot pattern D1 of the predetermined pattern MPa based on the position of DA1 ′, and the temporary displacement amount ΔL2 ′ is calculated by the first search processing unit 22 without considering the deformation of the second dot pattern D2. This is the amount of displacement of the second dot pattern D2 of the predetermined pattern MPa based on the position of the dot pattern (second provisional corresponding dot pattern) DA2 ′ corresponding to the obtained second dot pattern D2.

  On the other hand, as described above, the second search processing unit 25 considers the deformation of the predetermined pattern MPa due to the action of the external force, that is, the deformation of the dot pattern D, so that the predetermined search pattern MPa in the image before the external force action becomes Since the corresponding pattern in the image after the external force action is searched as the measurement corresponding pattern, the position of the searched measurement corresponding pattern is closer to the true pattern position than the temporary corresponding pattern position. And the error is reduced. The expansion / contraction rate ε of the test body SM obtained by the measurement expansion / contraction rate calculation processing unit 26 as described above is therefore set to the measurement expansion / contraction rate ε0, and is given by Equation 3 (ε0 = ε). In this case, the displacement amount ΔL1 is the measured displacement amount, and the dot pattern corresponding to the first dot pattern D1 obtained by the second search processing unit 25 by considering the deformation of the first dot pattern D1. (First Measurement Corresponding Dot Pattern) The displacement amount of the first dot pattern D1 of the predetermined pattern MPa based on the position of DA1, and the displacement amount ΔL2 is the measured displacement amount, taking into account the deformation of the second dot pattern D2. The displacement amount of the second dot pattern D2 of the predetermined pattern MPa based on the position of the dot pattern (second measurement corresponding dot pattern) DA2 corresponding to the second dot pattern D2 obtained by the second search processing unit 25 is there.

  Next, the operation of the strain measuring device Sa of the present embodiment will be described. FIG. 2 is a flowchart showing the operation of the strain measuring apparatus according to the first embodiment. FIG. 3 is a diagram for explaining a calculation method for obtaining the measured expansion / contraction ratio of the test body in the strain measurement apparatus of the first embodiment. FIG. 3A is a schematic diagram illustrating an image before external force action, and FIG. 3B is a schematic diagram for explaining image processing in which the first search processing unit 22 processes an image after external force action. FIG. 3C is a schematic diagram showing a deformation pattern with respect to the predetermined pattern MPa of the image before the external force action, and FIG. 3B is an image in which the image after the external force action is processed by the second search processing unit 25. It is a schematic diagram for demonstrating a process.

  As preparation for strain measurement, first, a predetermined predetermined pattern MPa is provided on the test body SM. Subsequently, a reference length L0 that is a distance between the pair of first and second dot patterns D1 and D2 in the predetermined pattern MPa is measured (step S11). The measurement of the reference length L0 is performed using, for example, an image of the specimen SM in which an image signal photographed by the camera device 10 is taken and a region including the predetermined pattern MPa is photographed. More specifically, the position of the pair of first and second dot patterns D1 and D2 in the predetermined pattern MPa is determined for the image of the test body SM by image processing such as edge determination, for example, and the pair of first and second pairs The distance between the dot patterns D1 and D2 is obtained. Each position of the first and second dot patterns D1 and D2 is, for example, a predetermined position (for example, one of the four corner points or a point intersecting with the optical axis) in the image (light receiving surface of the image sensor). An xy coordinate system is set in advance at the coordinate origin, 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 dot pattern D is received by one pixel of the image sensor and the image corresponding to the dot pattern D is formed by the image signal from the one pixel, the position of the dot pattern D is When the optical image corresponding to the dot pattern D is received by a plurality of pixels of the image sensor and the image corresponding to the dot pattern D is formed by image signals from the plurality of pixels. The position of the dot pattern D is represented by a predetermined representative point (for example, the center point, the center point of the circumscribed circle, the center of gravity point, etc.) of the dot pattern D, and is represented by the position of the pixel corresponding to the representative point. Further, for example, the measurement of the reference length L0 may be performed using a measure, a caliper, or the like. In this case, the reference length L0 actually measured by an unillustrated input device is input to the strain measuring device Sa. 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, the image acquisition control unit 21 captures the specimen A before the external force action when the camera device 10 captures the specimen SM, and the image A before the external force action is taken into the image processing unit 20 from the camera device 10. (Step S12). This image A before external force action is, for example, an image shown in FIG.

  Subsequently, as shown by a broken line in FIG. 3A, the first search processing unit 22 extracts the pair of first and second dot patterns D1 and D2 in the predetermined pattern MPa from the pre-external force action image A, respectively. A predetermined size range is set in each of the first and second dot patterns D1 and D2 as areas A1 and A2, and is selected as a template (step S13). In the present embodiment, for example, the region A is a rectangular region set so that the position of the dot pattern D coincides with the intersection of the diagonal lines.

  Subsequently, a tensile load is applied as an external force to the test body SM by the tensile tester, and an external force is applied to the test body SM (step S14).

  Subsequently, the image acquisition control unit 21 captures the image B after the external force action when the camera device 10 captures the specimen SM, and the image B after the external force action is acquired from the camera device 10 into the image processing unit 20. (Step S15). This post-external force image B is, for example, the image shown in FIG.

  Subsequently, the first search processing unit 22 searches for a pattern in the image B after the external force action corresponding to the predetermined pattern MPa in the image A before the external force action using the corresponding point search method as a temporary correspondence pattern, and performs a temporary expansion / contraction rate calculation process. The temporary displacement amount ΔL1 ′ of the first dot pattern D1 and the temporary displacement amount ΔL2 ′ of the second dot pattern D2 are obtained by the unit 23 (step S16).

  More specifically, the image A before external force action is used as the standard image A and the image B after external force action is used as the reference image B, and includes the first dot pattern D1 in the predetermined pattern MPa of the image A before external force action. Using the set area A1 as a template, an area matching the area A1 is searched from the image B after the external force action. In this matching process, correlation calculation is performed between the area A1 and a partial area in the image B after the external force action, which is the same size as the area A1, and after the external force action while shifting the partial area at a predetermined interval. By scanning over the entire surface of the image B, a region matching the region A1 (region having the largest correlation value) is searched from the image B after the action of the external force. Then, the searched dot pattern DA1 'in the area matching the area A1 is set as the first temporary corresponding dot pattern DA1' corresponding to the first dot pattern D1. Similarly, using the region A2 set to include the second dot pattern D2 in the predetermined pattern MPa of the image A before external force action as a template, a region matching this region A2 is searched from the image B after external force effect. In this matching processing, correlation calculation is performed between the area A2 and a partial area in the image B after the external force action, which is the same size as the area A2, and after the external force action while shifting the partial area at a predetermined interval. By scanning over the entire surface of the image B, a region matching the region A2 (region having the largest correlation value) is searched from the image B after the action of the external force. The searched dot pattern DA2 'in the area matching the area A2 is set as a second provisional corresponding dot pattern DA2' corresponding to the second dot pattern D2.

  Then, the temporary expansion / contraction ratio calculation processing unit 23 obtains the positions (coordinate values) of the first and second temporary corresponding dot patterns DA1 ′ and DA2 ′, and the positions (coordinate values) of the first temporary corresponding dot pattern DA1 ′. ) And the position (coordinate value) of the first dot pattern D1, the temporary displacement amount ΔL1 ′ of the first dot pattern D1 is obtained, and the position (coordinate value) of the second temporary corresponding dot pattern DA2 ′ and the second dot pattern The temporary displacement amount ΔL2 ′ of the second dot pattern D2 is obtained from the position (coordinate value) of D2.

  Subsequently, the temporary expansion / contraction rate calculation processing unit 23 calculates the expansion / contraction rate (distortion amount) ε as the temporary expansion / contraction rate ε0 '(step S17). More specifically, the temporary expansion / contraction rate calculation processing unit 23 obtains the temporary expansion / contraction rate ε0 ′ according to the equation (4).

  As described above, the temporary expansion / contraction rate calculation processing unit 23 determines the position of the first dot pattern D1 of the predetermined pattern MPa in the image A before external force action and the temporary corresponding pattern in the image B after external force action searched by the first search processing unit 22. The temporary displacement amount ΔL1 ′ of the first dot pattern D1 is obtained from the position of the first temporary corresponding dot pattern DA1 ′ corresponding to the first dot pattern D1, and the first predetermined pattern MPa in the image A before the external force action is obtained. The position of the 2-dot pattern D2 and the position of the second temporary corresponding dot pattern DA2 ′ corresponding to the second dot pattern D2, which is the temporary corresponding pattern in the image B after the external force action searched by the first search processing unit 22 From this, the temporary displacement amount ΔL2 ′ of the second dot pattern D2 is obtained, and the temporary expansion / contraction rate ε0 ′ is obtained by the above equation 4.

  Subsequently, the deformation processing unit 24 deforms the predetermined pattern MPa in the image A before external force action based on the temporary expansion / contraction rate ε0 ′ obtained by the expansion / contraction rate calculation processing unit 23 to generate a deformation pattern MPa ′ ( Step S18). More specifically, as shown in FIGS. 3 (A) and 3 (C), in the image of the region A1 set to include the first dot pattern D1 in the predetermined pattern MPa of the image A before external force action, The provisional expansion / contraction ratio ε0 ′ is multiplied to generate an image of the deformation area A1 ′. The image of the deformation area A1 'is used as a new template for the first dot pattern D1. The first dot pattern D1 is also deformed by the multiplication of the temporary expansion / contraction ratio ε0 'to become the first deformed dot pattern D1'. Similarly, the image of the region A2 set to include the second dot pattern D2 in the predetermined pattern MPa of the image A before external force action A is multiplied by the temporary expansion / contraction ratio ε0 ′ to generate an image of the deformation region A2 ′. . The image of the deformation area A2 'is used as a new template for the second dot pattern D2. By the multiplication of the temporary expansion / contraction rate ε0 ', the second dot pattern D2 is also deformed to become a second deformed dot pattern D2'.

  Subsequently, based on the deformation pattern MPa ′ generated by the deformation processing unit 24 by the second search processing unit 25, the pattern in the image B after the external force action corresponding to the predetermined pattern MPa in the image A before the external force action is a measurement corresponding pattern. And the measured expansion / contraction rate calculation processing unit 26 obtains the measured displacement amount ΔL1 of the first dot pattern D1 and the measured displacement amount ΔL2 of the second dot pattern D2 (step S19). ).

  More specifically, using the deformation area A1 'as a template, an area that matches the deformation area A1' is searched from the image B after the action of external force. In this matching process, a correlation operation is performed between the deformation area A1 ′ and a partial area in the image B after the external force action and the same size as the deformation area A1 ′, and the partial area is shifted at a predetermined interval. However, by scanning over the entire surface of the image B after the external force action, a region matching the deformation region A1 ′ (region having the largest correlation value) is searched from the image B after the external force effect. Then, the searched dot pattern DA1 in the area matching the deformation area A1 'is set as the first measurement corresponding dot pattern DA1 corresponding to the first dot pattern D1. Similarly, using the deformation area A2 'as a template, an area that matches the deformation area A2' is searched from the image B after the external force action. In this matching processing, a correlation operation is performed between the deformation area A2 ′ and a partial area in the image B after the external force action and the same size as the deformation area A2 ′, and the partial area is shifted at a predetermined interval. However, by scanning over the entire surface of the image B after the external force action, a region matching the deformation area A2 ′ (region having the largest correlation value) is searched from the image B after the external force effect. Then, the searched dot pattern DA2 in the area matching the deformation area A2 'is set as the second measurement corresponding dot pattern DA2 corresponding to the second dot pattern D2. In the matching process in step S19, since the deformation area A1 'and the deformation area A2' are used, the correlation value is larger than that in the above-described matching process in step S16, and a more reliable correlation result is obtained.

  Then, each position (coordinate value) of the first and second measurement corresponding dot patterns DA1 and DA2 is obtained by the measurement expansion / contraction rate calculation processing unit 26, and the position (coordinate value) of the first measurement corresponding dot pattern DA1 and the first position. The measurement displacement amount ΔL1 of the first dot pattern D1 is obtained from the position (coordinate value) of the one dot pattern D1, and the position (coordinate value) of the second measurement corresponding dot pattern DA2 and the position (coordinates) of the second dot pattern D2 Value), the measured displacement amount ΔL2 of the second dot pattern D2 is obtained.

  Subsequently, the expansion / contraction rate (distortion amount) is calculated as the measurement expansion / contraction rate ε0 by the measurement expansion / contraction rate calculation processing unit 26 (step S20). More specifically, the measurement expansion / contraction rate calculation processing unit 26 obtains the measurement expansion / contraction rate ε0 (= ε) by the equation 3.

  Then, the measured expansion / contraction rate ε 0 obtained by such an operation is output from the image processing unit 20.

  As described above, the strain measuring device Sa according to the present embodiment tentatively obtains the expansion / contraction rate of the predetermined pattern MPa using the pre-external force action image and the post-external force action image before and after applying the external force to the test body SM. The deformation pattern MPa ′ is generated by deforming the predetermined pattern MPa using the rate ε0 ′, and the expansion / contraction rate of the predetermined pattern MPa is obtained again using the deformation pattern, so that the deformation of the predetermined pattern MPa can be considered. There is no need to perform a search process on a large number of deformation patterns MPa ′ obtained by variously deforming the predetermined pattern MPa. Therefore, the strain measuring device Sa in the present embodiment can improve the measurement accuracy and reduce the information processing amount in consideration of the deformation of the predetermined pattern MPa.

  In addition, since the strain measuring device Sa in the present embodiment can photograph the pair of first and second dot patterns D1 and D2 having the predetermined pattern MPa with one camera device 10, the device is configured more simply. This can reduce costs.

  Next, another embodiment will be described.

(Second Embodiment)
FIG. 4 is a diagram illustrating a configuration of a strain measuring apparatus according to the second embodiment. FIG. 5 is a diagram for explaining a calculation method for obtaining a measurement expansion / contraction ratio of a test body in the strain measurement apparatus according to the second embodiment. FIG. 5A is a schematic diagram showing an image before external force action, and FIG. 5B is a schematic diagram showing an image after external force action. 5A and 5B show images before and after external force action taken by the first camera device 31, and are shown in FIGS. 5A and 5B. In the lower part, an image before the external force action and an image after the external force action taken by the second camera device 32 are shown.

  As shown in FIG. 1, the strain measuring device Sa in the first embodiment is configured such that the photographing unit that photographs the specimen SM includes one camera device 10, but the strain measuring device Sb in the second embodiment. Is configured such that an imaging unit for imaging the specimen SM includes a plurality of camera devices 30. Such a strain measuring device Sb in the second embodiment includes, for example, a camera device (camera device system) 30 including first and second camera devices 31 and 32, an image processing device 40, as shown in FIG. It is configured with.

  Each of the first and second camera devices 31 and 32 is a device that photographs each portion of the predetermined pattern MPa using the test body SM as a subject in order to monitor (observe and monitor) the test body SM. For example, the first camera device 31 is arranged so as to be able to photograph a predetermined range area portion including the first dot pattern D1 of the predetermined pattern MPa, and captures the predetermined range area portion according to the first embodiment. The same configuration as the camera apparatus 10 of FIG. Then, the second camera device 32 is arranged so as to be able to photograph a region of a predetermined range including the second dot pattern D2 of the predetermined pattern MPa, photograph the region of the predetermined range, and the first embodiment. The same configuration as the camera apparatus 10 of FIG.

  The image processing unit 40 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 31 and 32, and is configured by, for example, a microcomputer. The image processing apparatus 40 includes an image acquisition control unit 21, a first search processing unit 22, a temporary expansion / contraction rate calculation processing unit 23, a deformation processing unit 24, and a second search processing unit 25 in the image processing unit 20 of the first embodiment. In addition, each component similar to the measurement expansion / contraction rate calculation unit 26 is functionally provided, but the first and second dot patterns D1 and D2 are included in one image (in the image signal) as in the first embodiment. The first camera device 31 is configured not to include the first dot pattern D1, and the second camera device 32 is configured to capture the second dot pattern D2. Is different in that the image captured by the first camera device 31 and the image captured by the second camera device 32 are individually processed.

  That is, the distortion of the specimen SM is measured in the same order in the same processes as in steps S11 to S20 described with reference to FIG. 2 in the first embodiment, but the processes for the first dot pattern D1 are performed as follows: Each process for the second dot pattern D2 is performed on the pre-external force action image A and the external force action image B photographed by the first camera device 31, and the pre-external force action image A photographed by the second camera device 32. And the image B after the external force action.

  More specifically, in each process similar to step S11 to step S16 for the first dot pattern D1, in step S13, as shown in the upper part of FIG. A range of a predetermined size including the first dot pattern D1 is set as the region A1 as the first dot pattern D1 with respect to the image before the external force action, and is selected as a template. In step S16, this region A1 is used as a template. A region matching the region A1 is searched from the post-external-force image B taken by the first camera device 31, and the searched dot pattern DA1 ′ in the region matching the region A1 corresponds to the first dot pattern D1. The first temporary corresponding dot pattern DA1 ′ is used, and these first temporary corresponding dot patterns DA 'Position of (coordinates) and the position of the first dot pattern D1 (coordinate value) and the temporary displacement of the first dot pattern D1 △ L1' is obtained. Similarly, in each process similar to step S11 to step S16 for the second dot pattern D2, in step S13, as shown in the lower part of FIG. 5A, before the external force action photographed by the second camera device 32. A range of a predetermined size including the second dot pattern D2 is set to the second dot pattern D2 as a region A2 and selected as a template for the image, and in step S16, the region A2 is used as a template in this region A2. The matching area is searched from the post-external force action image B photographed by the second camera device 32, and the searched dot pattern DA2 ′ in the area matching the area A2 corresponds to the second dot pattern D2. Corresponding dot pattern DA2 ', the position of these second temporary corresponding dot pattern DA2' Temporary displacement from the (coordinate value) and the position of the second dot pattern D2 (coordinates) the second dot pattern D2 △ L2 'is obtained. When the reference length L0 that is the distance between the first and second dot patterns D1 and D2 is obtained based on the images obtained by the first and second camera devices 31 and 32, the first A distance between the camera device 31 and the second camera device 32, for example, a distance between the optical axis of the first camera device 31 and the optical axis of the second camera device 32 is given to the image processing unit 40 in advance.

  And in each process similar to step S17 thru | or step S20 with respect to the 1st dot pattern D1, in step S18, the 1st dot pattern D1 in the predetermined pattern MPa of the image A before the external force action image | photographed with the 1st camera apparatus 31 is shown. The image of the area A1 set to include is multiplied by the temporary expansion / contraction ratio ε0 ′, and the image of the deformation area A1 ′ is generated as a new template of the first dot pattern D1, and in step S19, the deformation area A1 ′. Is used as a template, a region matching the deformation region A1 ′ is searched from the post-external force image B photographed by the first camera device 31, and a dot pattern DA1 in the searched region matching the deformation region A1 ′ is found. First measurement corresponding dot pattern DA corresponding to the first dot pattern D1 As shown in the upper part of FIG. 5B, the first dot pattern D1 is measured from the position (coordinate value) of the first measurement corresponding dot pattern DA1 and the position (coordinate value) of the first dot pattern D1. A displacement amount ΔL1 is obtained. Similarly, in each process similar to step S17 to step S20 for the second dot pattern D2, in step S18, the second dot pattern D2 in the predetermined pattern MPa of the image A before external force action photographed by the second camera device 32. The image of the area A2 set to include the image is multiplied by the temporary expansion / contraction rate ε0 ′, and the image of the deformation area A2 ′ is generated as a new template of the second dot pattern D2. In step S19, the deformation area A2 A region that matches the deformation region A2 ′ is searched for from the image B after the action of the external force photographed by the second camera device 32 using 'as a template, and the searched dot pattern DA2 in the region that matches the deformation region A2 ′. Corresponds to the second dot pattern D2 and corresponds to the second measurement dot pattern DA. As shown in the lower part of FIG. 5B, the second dot pattern D2 is measured from the position (coordinate value) of the second measurement corresponding dot pattern DA2 and the position (coordinate value) of the second dot pattern D2. A displacement amount ΔL2 is obtained.

  As described above, except for the points described above, by operating in the same manner as in the first embodiment, the strain measuring device Sb in the present embodiment measures the measurement expansion / contraction rate ε0 (= ε) of the test body SM by the above-described equation 3. be able to.

  And although the strain measuring device Sa in 1st Embodiment must image | photograph the range containing area | region A1 and area | region A2 with the camera apparatus 10, 1st camera apparatus 31 is area | region in the strain measuring apparatus Sb in this embodiment. When the range including A1 is captured and the second camera device 32 only needs to capture the range including the region A2, the first and second camera devices 31 and 32 use devices having the same specifications as the camera device 10. Therefore, it is possible to photograph with higher resolution and to measure the expansion / contraction rate with higher accuracy.

  In the strain measuring devices Sa and Sb in the first and second embodiments described above, the predetermined pattern MPa including two pairs of the first and second dot patterns D1 and D2 that are separated from each other is used. It is not limited. Other patterns can also be used.

  FIG. 6 is a diagram illustrating a predetermined pattern in the first modification. FIG. 7 is a diagram showing a predetermined pattern in the second modification.

  For example, the predetermined pattern includes dots of a first dot group arranged along a predetermined first direction and second dot groups arranged along a second direction that is linearly independent of the first direction. It may be a predetermined pattern MPb having a plurality of dots including dots. More specifically, as shown in FIG. 6, the predetermined pattern MPb is used for the test body SM extending in two directions of the x direction and the y direction orthogonal to each other, and is provided along the x direction on one surface thereof. A pair of first dots D11 and second dots D12 (first dot group), and a pair of first dots D13 and second dots D14 (second dot group) provided along the y direction on the one surface. And is configured. As shown in FIG. 6, when the test body SM has a cross shape and a pair of opposite ends facing each other is pulled in the x direction and the y direction, the first and second dot groups The dots D11, D12; D13, D14 are arranged in a region where the x direction and the y direction intersect in the cross-shaped specimen SM. Here, in the deformation of the dot pattern by the temporary expansion / contraction rate, each direction is handled independently. That is, the temporary expansion ratio in the direction of the first dot group is obtained using the first dot group, and the temporary expansion ratio in the direction of the second dot group is obtained using the second dot group. The dot pattern is deformed in each direction using the expansion / contraction rate, and the entire dot pattern is deformed. By using such a predetermined pattern MPb, linearly independent two-direction expansion / contraction ratio ε, and in the example shown in FIG. 6, the x-direction expansion / contraction ratio εx and the y-direction expansion / contraction ratio εy can be calculated.

  Note that the dots of the first dot group and the dots of the second dot group may be separate and independent as described above, or some of them may overlap. For example, as indicated by a broken line in FIG. 6, the dot D15 provided at the intersection where the x direction and the y direction intersect on the surface of the test body SM is the second dot D12 (or the first dot of the first dot group described above). The dot D11) may be replaced with the second dot D14 (or the first dot D13) of the second dot group described above.

  Further, for example, the predetermined pattern may be a predetermined pattern MPc including a plurality of dots that are divided into a plurality of areas and in which the dots of each area are randomly arranged. More specifically, as shown in FIG. 7, the predetermined pattern MPc includes a first dot group D20 including a set of four first to fourth dots D21 to D24 arranged randomly within a predetermined range; A second dot group D30 having a set of four first to fourth dots D31 to D34 randomly arranged within a predetermined range, and the first dot group and the second dot group are along the tensile direction. Are separated from each other by a predetermined distance. By using such a predetermined pattern MPc, a plurality of randomly arranged dots can be regarded as one pattern. Therefore, the pattern in the image B after the external force action corresponding to the predetermined pattern MPc in the image A before the external force action is obtained. It is possible to search more accurately. The arrangement pattern of the first to fourth dots D21 to D24 of the first dot group D20 and the arrangement pattern of the first to fourth dots D31 to D34 of the second dot group D30 are the same or different. May be.

  In the first and second embodiments described above, by applying the temporary expansion / contraction rate ε0 ′ to the regions A1 and A2 of the image A before external force action, more specifically, by multiplying the temporary expansion / contraction rate ε0 ′. The strain measuring devices Sa and Sb are configured to generate the deformation areas A1 ′ and A2 ′ and perform matching processing with the image B after the external force action using the deformation areas A1 ′ and A2 ′ as new templates. By making the temporary expansion / contraction ratio ε0 ′ act on the first and second temporary corresponding patterns DA1 ′ and DA2 ′ of the image B after the external force action in reverse to the temporary expansion / contraction ratio ε0 ′, more specifically, the temporary expansion / contraction ratio ε0 ′ A distortion measurement device is generated by generating a deformation pattern by multiplying the reciprocal, and using the regions A1 and A2 of the image A before external force action as a template and matching processing with the image after the external force action including the deformation pattern. Devices Sa and Sb may be configured. In addition, before and after multiplying the reciprocal of the temporary expansion / contraction rate ε0 ′, the representative points of the patterns before and after the same are matched.

  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.

SM Specimen MPa, MPb, MPc Predetermined patterns D1, D2, D11 to D14, D21 to D24, D31 to D34 Dot pattern Sa, Sb Strain measuring device 10, 31, 32 Camera device 20, 40 Image processing unit 21 Image acquisition control Unit 22 First search processing unit 23 Temporary expansion / contraction rate calculation processing unit 24 Deformation processing unit 25 Second search processing unit 26 Measurement expansion / contraction rate calculation processing unit

Claims (7)

An image acquisition unit for acquiring images of the test body before and after applying an external force to the test body to be measured as an image before and after an external force action;
A first search processing unit that searches for a pattern in the image after the external force action corresponding to a predetermined feature pattern in the image before the external force action as a temporary corresponding pattern;
Based on the position of the feature pattern in the image before the external force action and the position of the temporary corresponding pattern in the image after the external force action searched by the first search processing unit, the expansion ratio of the test body is obtained as the temporary expansion ratio. A provisional expansion / contraction rate calculation processing unit;
A deformation processing unit that generates a deformation pattern by deforming the feature pattern in the pre-external force action image or the temporary corresponding pattern in the post- external force action image based on the temporary expansion / contraction ratio obtained by the expansion / contraction rate calculation processing unit; ,
A second search processing unit that re-searches a pattern in the post-external force action image corresponding to the feature pattern in the pre-external force action image as a measurement corresponding pattern based on the deformation pattern generated by the deformation processing unit;
Based on the position of the feature pattern in the image before the external force action and the position of the pattern corresponding to the measurement in the image after the external force action re-searched by the second search processing unit, the expansion / contraction ratio of the test body is used as the measurement expansion / contraction ratio. A strain measurement apparatus comprising: a measurement expansion / contraction rate calculation processing unit to be obtained. It further comprises a photographing unit for photographing the test body,
The strain measuring apparatus according to claim 1, wherein the photographing unit is a single camera device. It further comprises a photographing unit for photographing the test body,
The strain measuring device according to claim 1, wherein the photographing unit is a plurality of camera devices. The strain measuring device according to any one of claims 1 to 3, wherein the feature pattern is a dot pattern composed of a plurality of dots spaced apart from each other. The plurality of dots includes a dot of a first dot group arranged along a predetermined first direction and a second dot group arranged along a second direction that is linearly independent of the first direction. The strain measuring device according to claim 4, comprising dots. The strain measuring apparatus according to claim 4, wherein the plurality of dots are divided into a plurality of regions, and the dots in each region are randomly arranged. An image acquisition step of acquiring images of the test body before and after applying an external force to the test body to be measured as an image before and after an external force action;
A first search processing step of searching for a pattern in the image after the external force action corresponding to a predetermined feature pattern in the image before the external force action as a temporary corresponding pattern;
Based on the position of the feature pattern in the image before the external force action and the position of the temporary corresponding pattern in the image after the external force action searched by the first search processing step, the expansion ratio of the specimen is obtained as the temporary expansion ratio. Temporary expansion / contraction rate calculation processing step,
A deformation processing step of generating a deformation pattern by deforming the feature pattern in the image before the external force action or the temporary corresponding pattern in the image after the external force action based on the temporary expansion ratio obtained by the expansion rate calculation processing step; ,
Based on the deformation pattern generated by the deformation processing step, a second search processing step of searching a pattern in the post-external force action image corresponding to the feature pattern in the pre-external force action image as a measurement corresponding pattern;
Based on the position of the feature pattern in the image before the external force action and the position of the specific corresponding pattern in the image after the external force action re-searched by the second search processing step, the expansion / contraction ratio of the test body is used as the measurement expansion / contraction ratio A strain measurement method comprising: a required measurement expansion / contraction rate calculation processing step.

Images