JPH11304439A - Contactless extensometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contactless extensometer capable of accurately measuring the elongation accurately detecting the position of a reference line from the reference line image in the image picked up by cameras. SOLUTION: A device is provided with cameras 1, 2 for picking up image of reference lines R1, R2 on a test piece S, and the center of gravity of the reference line image in the image is obtained on the basis of the distribution of the image signal of the reference line picked up by the cameras in the extending direction of the test piece S, and position of the reference lines R1, R2 is obtained on the basis of the position of the center of gravity. Especially, projection of the image signal in the predetermined image area including the reference lines R1, R2 in a direction crossing the extending direction is obtained, and position of the center of gravity of the reference line image is obtained on the basis of the distribution of the projection component in the extending direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact extensometer capable of measuring the elongation of a test piece subjected to a tensile test in a non-contact manner and with high accuracy.

[0002]

2. Related Background Art A tensile test of various test pieces using a material testing machine is performed by applying a tensile load to the test pieces and measuring the tensile load and the elongation of the test pieces. In particular, recently, a non-contact extensometer that measures the elongation of the test piece without using a laser or a line sensor in a non-contact manner with the test piece has attracted attention. This type of non-contact extensometer basically detects two marked lines parallel to a test specimen at a predetermined distance in the direction of extension and optically detects the change in the distance between these marked lines. Is used to determine the elongation.

As one method of a non-contact extensometer, for example, as disclosed in Japanese Utility Model Publication No. Hei 6-31365, two cameras (optical heads) for imaging two marked lines attached to a test piece, respectively. Is provided so as to be able to translate in the direction of extension of the test piece, and while moving the cameras respectively in accordance with the change in the position of the mark associated with the extension of the test piece, the Some of them measure the elongation of the test piece according to the position. Incidentally, the non-contact extensometer disclosed in this publication controls the movement of the camera in real time so that the position of the marked line in the image captured by the camera always becomes the reference position of the image. The amount of elongation between the marked lines is measured from the camera position.

[0004]

When the camera is moved in accordance with the change in the position of the marking line accompanying the elongation of the test piece, the marking image in the image picked up by the camera,
The problem then is how to accurately detect the position. In particular, since the marked line itself attached to the test piece elongates along with the elongation of the test piece, not only does the width increase, but also the color of the mark decreases, and the level of the image signal decreases. For this reason, it is difficult to accurately detect the mark image in the image captured by the camera.

In the non-contact extensometer disclosed in the above publication, the image is binarized by a predetermined threshold value.
The width of the marked line image in the elongation direction of the test piece is determined from the digitized image signal. Then, the position of the mark is detected using the center of the binarized image signal (the position of 1/2 width). However, in this case, it cannot be denied that the binarized image signal changes depending on what level the threshold is set. In particular, the level of the image signal indicating the marked line image in the image decreases due to fading of the color due to the extension of the marked line, and so-called blurring occurs at the edge portion of the marked line. Therefore, the level is detected by binarization. The width of the marked line image itself is greatly affected by the threshold level.

The present invention has been made in view of such circumstances, and has as its object to accurately determine the position of a marked line from a marked line image in an image of a marked line attached to a test piece taken by a camera. The present invention provides a non-contact extensometer capable of detecting the elongation of the test piece and accurately measuring the elongation of the test piece.

[0007]

In order to achieve the above-mentioned object, a non-contact extensometer according to the present invention comprises a camera for picking up a mark on a test piece, and the mark is picked up by the camera. The center of gravity of the marked line image in the image is determined from the distribution of the image signal in the direction of extension of the test piece, and the position of the marked line is determined from the position of the center of gravity.

That is, the non-contact extensometer according to the present invention obtains the center of gravity of the marked line image in the image picked up by the camera from the distribution of the image signal in the direction of extension of the test piece, thereby obtaining the image signal. Without being affected by a level change or blurring at the edge of the marked line, the center of gravity of the marked line image is accurately obtained, and thereby, without being concerned with the extension of the marked line itself accompanying the extension of the test piece, It is characterized in that the position can be obtained with high accuracy.

In a preferred aspect of the present invention, an image signal in a predetermined image area including the reference line in an image picked up by the camera in a direction orthogonal to the extension direction is provided. The projection is obtained, and the distribution of the projection component in the extension direction, that is, the centroid of the mark image as the centroid of the area indicated as the image area and the three-dimensional space indicated as the distribution of the image signal level in the area. It is characterized in that the position is obtained.

According to a third aspect of the present invention, the camera is supported on a movable stage movable in the direction of extension of the test piece so as to be movable in accordance with the extension of the test piece. The position of the mark is obtained based on the position of the moving stage and the position of the center of gravity of the mark image in the image captured by the camera. Further, as described in claim 4, the camera is provided in correspondence with two marked lines parallel to the test piece at a predetermined distance in the direction of extension of the test piece, respectively. Is moved from the position of the marked line to the position to view each marked line in accordance with the position change of the marked line image in each of the images accompanying the elongation of the test piece, from the position of the marked line as described above, between the marked lines. It is characterized by measuring elongation.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-contact extensometer according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a non-contact extensometer according to this embodiment, where S is a test piece mounted on a material tester (not shown) and subjected to a tensile test, and R1 and R2 are the test pieces described above. S are two marked lines which are previously provided in parallel with each other in the extending direction at a predetermined distance. These marking lines R1,
R2 is a linear mark drawn using a paint or the like at a predetermined parallel portion of the test piece S at a distance of, for example, 50 mm.

A non-contact extensometer that is incorporated in a material testing machine and measures the elongation of the test piece S in a non-contact manner with the test piece S is a high-magnification second exfoliator that images each of the marked lines R1 and R2. First and second cameras 1, 2 and each of these cameras 1, 2,
The light sources 3 and 4 are attached to the sides of the camera 2 and illuminate the imaging area (each marked portion of the test piece S) by the cameras 1 and 2. These cameras 1 and 2 are supported by first and second moving stages 5 and 6, respectively, and are provided so as to be able to move in parallel in the extending direction of the test piece S. Incidentally, the moving stages 5 and 6 mesh with feed screws 7a and 8a driven by the pulse motors 7 and 8, and move in the extension direction of the test piece S under the rotation control of the pulse motors 7 and 8 ( (Up and down movement) to adjust the position.

Each of the cameras 1 and 2 incorporates, for example, a CCD image sensor (area sensor) as an image pickup element, and substantially captures a partial surface image of the test piece S including each of the reference lines R1 and R2. It is configured so that close-up imaging (macro imaging) is performed at an imaging magnification of 1 × to obtain an image signal with high resolution. The imaging of the surface image including the reference lines R1 and R2 by the cameras 1 and 2 is performed, for example, clearly in a focused state and while keeping the imaging magnification constant.

As described above, partial surface images (images) of the test piece S including the reference lines R1 and R2 captured by the cameras 1 and 2 are sent to the CPU via the image processing units 11 and 12. Is taken into the arithmetic processing unit 13 consisting of
After predetermined image processing is performed, the images are displayed in parallel on the display 14 as shown in FIG. 2, for example. Specifically, as shown in FIG. 2, the arithmetic processing unit 1 is provided in two image display areas A and B set in parallel on the display 14.
An image (processed image) including each of the marked line images subjected to the image processing in 3 is displayed. Incidentally, here, since the display 14 is a horizontally long display screen, the extending direction of the test piece S is set in the horizontal direction, and the image display areas A and B are displayed so that the images are displayed side by side in the horizontal direction. Is set. While the raw images captured by the cameras 1 and 2 are directly displayed on a TV monitor (not shown), the mark lines R1 and R1 obtained by the arithmetic processing unit 13 are displayed.
A processed image including the image of R2 may be displayed on the display 14.

As shown in FIG. 2, a soft switch for manually operating the movement of the cameras 1 and 2 and a soft switch for instructing initial settings for the cameras 1 and 2 are displayed on the display 14. In addition to the operation area C, a graph display area D for graphically displaying the relationship between the load and the elongation measured by the tensile test is provided. Using such a display screen of the display 14 as an interface, setting input of various conditions and the like for a tensile test and further, initial setting processing for an extensometer and the like are performed.

On the other hand, the arithmetic processing unit 13 detects a mark image in the images taken by the cameras 1 and 2 according to a software application for elongation measurement prepared in advance, and detects the mark image as described later. It has a function to find the position of the center of gravity of the line image. The reference line is positioned at the reference position from the difference (distance on the image) between the barycenter position of the reference line image obtained in each image and a preset reference position (eg, image center) in each image. The amount of deviation of the marked lines from the state in which they were moved, and thus the displacement positions of the marked lines R1 and R2 due to the elongation of the test piece S are detected. Incidentally, in this calculation, a distance (unit distance) per pixel in the image is obtained in advance in accordance with, for example, an imaging magnification of the cameras 1 and 2 and a pixel array pitch of the CCD image sensor, and the unit distance is calculated by the difference (Displacement amount on the image). The image signals obtained by the cameras 1 and 2 are enlarged while appropriately performing an interpolation operation, and the measurement is performed by detecting the displacement positions of the marking lines R1 and R2 from the enlarged image. It is also possible to increase the accuracy.

When the mark image deviates from the images picked up by the cameras 1 and 2, respectively, the arithmetic processing unit 13 puts the mark R1 displaced with the extension of the test piece S in other words. , R2 reaches the limit of the field of view of the cameras 1 and 2, the position control unit 1
5. Start 5,16. Then, according to the difference (distance on the image) between the barycentric position of the mark image obtained on the image at that time and the reference position, the position control units 15, 16 are determined.
Under the above control, the pulse motors 7 and 8 are respectively driven to move the cameras 1 and 2 in the moving directions of the mark lines R1 and R2, respectively. The movement of each of the cameras 1 and 2 by the position controllers 15 and 16 is performed such that the center of gravity of the mark image in the image captured by each of the cameras 1 and 2 becomes the reference position in each of the images. That is, the position of each of the cameras 1 and 2 is controlled so that the reference lines R1 and R2 are captured at the reference position in the captured image. Specifically, the pulse motors 7 and 8 are driven to move the cameras 1 and 2 by the amount corresponding to the difference between the barycentric position of the mark image obtained from each image and the reference position of the screen. Thus, the positions of the cameras 1 and 2 are changed following the movement of the reference lines R1 and R2 accompanying the elongation of the test piece S.

Here, the measurement of the elongation of the test piece S by detecting the position of the mark image in the images respectively captured by the cameras 1 and 2 will be described. Two mark lines R1 attached to the test piece S will be described. , R2 gradually move upward along with the elongation of the test piece S due to the upward pulling of the test piece S as shown in FIG. Therefore, each mark R1, R
The two cameras 1 and 2 that respectively capture the image 2 are moved in parallel in the upward direction along with the movement of each of the mark lines R1 and R2 so that the mark lines R1 and R2 are always captured at the reference position of the image. Then, the amount of elongation of the test piece S can be obtained from the moving distance of each of the cameras 1 and 2.

Specifically, the upper camera (first camera) 1
If the amount of movement of the test piece S is C _H and the amount of movement of the lower camera (second camera) 2 is C _L , the elongation E between the marked lines of the test piece S can be obtained as E = C _H −C _L. it can.

In a state where the positions of the cameras 1 and 2 are fixed, changes in the positions of the marked lines in the images taken by the cameras 1 and 2 indicate the marked lines R1 and R2 associated with the elongation of the test piece S. Can also be obtained for each position. Specifically, as shown in FIGS. 4A and 4B, displacement amounts L _H and L _L of the reference lines R1 and R2 from the reference positions of the images captured by the cameras 1 and 2, respectively, are obtained. Then, the displacement amounts L _H and L _{L of} each of the reference lines R 1 and R 2 on the image.
Thus, as described above, the elongation E between the marked lines of the test piece S can be equivalently obtained as E = L _H −L _L. The displacement L
_H, L _L is the displacement of the marked line image detected on the image is obtained by multiplying a coefficient which depends on the pixel pitch and the imaging magnification and the like.

However, there is a limit to the amount of elongation E between the reference lines R1 and R2 which can be obtained in this way. When the reference lines R1 and R2 deviate from the field of view of the cameras 1 and 2, naturally, Measurement becomes impossible. Therefore, in the arithmetic processing unit 13 according to this embodiment, the position of the marker image in the image area (in the image) captured by each of the cameras 1 and 2 is monitored. Is reached, the pulse motors 7 and 8 are driven to move the cameras 1 and 2 so that the cameras 1 and 2 catch the marking lines R1 and R2 at their reference positions. Then, the displacement amounts C _H and C _{L of the} cameras 1 and 2 at this time.
As described above, based on the displacements L _H and L _L of the marking lines R1 and R2 obtained from the positions of the marking lines in each image as described above, the elongation E between the marking lines is given by E = (L _H + C _H). ) − (L _L + C _L ).

Next, a description will be given of a process of detecting a marked line image in an image captured by each of the cameras 1 and 2. This mark line image detection process performs a characteristic function of the non-contact extensometer according to the present invention, and the accuracy of the elongation measurement is improved by this function. That is, the detection of the position of the marked line image in the images picked up by the cameras 1 and 2 is performed, for example, by distributing the image signal level in the extending direction of the test piece S as shown in FIGS. 5A and 5B. Based on the above, the position of the center of gravity of the image signal component is obtained.

More specifically, an image signal captured including the reference line R is focused on, for example, the level N of a noise component that depends on the surface condition of the test piece S, and is used in an image signal area exceeding this level N. Extract only image signal components. Then, the position of the center of gravity of the distribution of the image signal in the extension direction in the extracted image signal area is evaluated as the position of the mark image. That is, the distribution of the image signal component (for example, the luminance signal level) in the extension direction of the test piece S is obtained, and the barycenter position G of the mark image is obtained from the distribution of the image signal component.
More specifically, each position m in the elongation direction of the test piece S (m = 1,
2,3, when the level of the image signal is a A _m in ...),
The distribution of the image signal is shown as a sequence of A ₁ , A ₂ , A ₃ ,. Since the center of gravity G of the distribution of the image signal is represented as the center of gravity of the area represented by the signal sequence A ₁ , A ₂ , A ₃ ,..., G = Σ (m · A _m ) / ΣA _m (M = 1, 2, 3,...). The center of gravity G of the distribution of the image signal obtained in this way reflects the distribution shape itself, and is hardly affected by the elongation of the reference line R and the level change of the image signal accompanying this. , Can be accurately grasped as indicating the position of the marked line R itself.

When the image signal is binarized at a predetermined level, as shown in FIGS. 5 (a) and 5 (b),
It cannot be denied that the width of the reference line R shown as a binarized signal changes depending on the binarization level. In particular, since the level change of the image signal is greatly affected by the degree of elongation like the edge portion of the marking line R, the width of the marking line R greatly changes depending on the level of the set binarization threshold.
In addition, when the level of the image signal greatly changes due to noise, it cannot be denied that the level is affected by the noise.

In this regard, if the center of gravity G is obtained from the distribution of the image signal (image signal level A) as described above, the error factor accompanying the binarization does not enter, so that the reference line R (reference line image) Can be simply and highly accurately evaluated as the position of the center of gravity. In particular, as shown in FIG. 5 (b), the mark R
Is widened and the level A of the image signal is low, the position (center of gravity) of the reference line R can be accurately detected. As described above, the test piece S
Since the noise component is removed according to the level N of the noise component corresponding to the surface state of the test piece S and attention is paid only to the image signal component in the image signal region exceeding the level N, the noise caused by the surface state of the test piece S is reduced. Without being affected, the position of the center of gravity G of the marked line image can be detected, and the position of the marked line R (marked line image) can be accurately obtained.

For the detection of the position of the center of gravity based on the distribution of the image signals described above, for example, as shown in FIG. 6, the image signal at each position in a predetermined measurement area X in the image including the marked line R is detected. The projection in the direction orthogonal to the direction of extension of the test piece S may be obtained, and the center of gravity G may be obtained from the distribution of the projection component in the direction of extension. Thus, the area region including the marked line image, it means that the center of gravity is determined in a three-dimensional space of said image signal component in said area region, blurring at the edge portion R _E of the marked line R Even if the edge itself becomes unclear due to fluctuations or the like, the center of gravity G of the marked line R (marked line image) can be accurately obtained without being affected by this. There are advantages.

In the non-contact extensometer for measuring the elongation of the test piece S by obtaining the positions of the reference lines R1 and R2 based on the images taken by the cameras 1 and 2 as described above, for example, FIG. The measurement of elongation is performed according to the processing procedure shown in FIG. Specifically, first, the positions of the first and second cameras (upper camera and lower camera) 1, 2 are adjusted, and each of the cameras 1, 2 is positioned at a predetermined reference position on an image. Initial settings are made so as to capture R2 respectively (step S1). This initial setting is referred to as alignment of the measurement origin of the camera, and is executed prior to the start of the tensile test on the test piece S. After that, the cameras 1 and 2
Comprising movement amount C _H, the C _L is reset to zero (0), respectively [step S2], the execution of the tensile test for.

When the tensile test is started, first, it is determined whether or not the upper camera line 1 is imaged by the upper camera 1 [step S3]. This determination was made based on whether the test piece S was broken by the tensile test, and as a result, whether or not the broken upper test piece S was greatly displaced upward due to the tensile load and suddenly deviated from the visual field of the upper camera 1. Is to judge. The breakage may be detected based on whether or not the load applied to the test piece S has suddenly decreased. When the fracture of the test piece S is detected by this determination processing, the tensile test is immediately terminated.
In this case, the cameras 1 and 2 are respectively returned to the origin positions (measurement origins) as described later.

However, in a normal case, since the test piece S is not broken until the test piece S is stretched under a tensile load to a certain extent, the upper camera 1 is moved for a certain period from the start of the test. Thus, the upper mark R1 is captured in the image. Therefore, the following elongation measurement processing is executed.

[0031] That is, tensile when testing is started, the position of the marked line image in the image captured by the upper camera 1 (center of gravity position) and as detected and the P _H aforementioned Step S4], the target ray image Then, the displacement L _H of the upper marking line R1 is obtained from the position P _H and the reference position P _{HO of the} image [Step S5]. If the movement amount of the marked line image on an image, when the moving amount of the marked line R1 is one-to-one correspondence in the actual specimen on S, the test piece as L _H = P _H -P _HO displacement of L _H of the upper marked line R1 with the elongation of the S is determined. Similarly, the position (gravity position) P of the marked line image in the image captured by the lower camera 2
_L is detected [Step S6], and the position P _{L of the} marked line image is detected.
From the reference position P _LO of the image, obtaining the displacement amount L _L of the lower marked line R2 as _L L = P L -P _LO [Step S7].

Next, the displacement amounts L _H , L _{L of the} mark lines R 1, R 2 obtained from the images, and the movement amounts C _H , C of the respective cameras.
_L in accordance with the (initial 0 on), the elongation amount E between the marked lines as described above _{E = (L H + C H} ) - calculated as _(L L + C _L) [Step S8]. The elongation E is measured together with the tensile load applied to the test piece S. still,
The measurement of the tensile load and the elongation amount is, for example, 10
It is executed at a cycle of 0 mSec.

[0033] Thereafter, the position P _H of the marked line image in the image captured by the upper camera 1, whether reaches the limit of the image range, further imaged by the lower camera 2 Position P of mark image in image
_It is determined whether _L has reached the limit of the image range [Steps S9 and S10]. These determinations are made, for example, as to whether or not the displacement amounts L _H and L _{L of the} marking lines R 1 and R 2 obtained from the images have reached preset displacement limits L _H max and L _L max1 in the image, respectively. This is performed by determining whether And in the case where the position of each marked line image can afford respectively the image region (the displacement limit L _H max, if not reached L _L max1), while determining the end of the tensile test [Step S11] Then, the elongation measurement processing from step S3 described above is repeatedly executed.
The displacement limits L _H max and L _L max1 are set as a distance from the center of the image as a reference position in the image to the edge thereof.

When the displacement amount L _H of the upper mark R1 has reached the displacement limit L _H max (step S9), the elongation measurement process proceeds as it is, and the image of the upper mark R1 protrudes from the image. , The position of the marking line R1 cannot be obtained from the image. So in this case,
Each of the cameras 1 is moved by driving the pulse motor 7. Movement of the camera, first according to the displacement amount L _H of the upper marked line R1 determined as described above, the upper camera 1
The executed by moving upwards by the displacement amount L _H [Step S12]. Due to the movement of the upper camera 1, the upper camera 1 catches the upper mark R1 at its reference position again. Therefore amount that the image position of the upper marked line R1 is displaced to the reference position by the movement of the camera 1, and updates the movement amount C _H of the camera as the _{C H = C H + L H} [ Step S13].

When the upper camera 1 is moved as described above, since the visual field of the lower camera 2 has not been confirmed at this time, the position of the mark image in the image captured by the lower camera 2 is next determined. Determines whether the image has reached the limit of the image range [step S14].
This determination is performed by displacement of L _L of the lower marked line R2 as described above is, to determine whether reaches the limit L _L max2 a predetermined during the image. This limit L _L max2 is
Even if the position of the marked line image in the image does not reach the edge of the image, it is set as a position displaced to some extent.

Even when the mark R2 picked up by the lower camera 2 has reached the limit L _L max2 or when the upper camera 1 is not moved, the mark R2 picked up by the lower camera 2 remains When the above-mentioned limit L _L max1 has been reached, the lower camera 2 is similarly moved. This movement of the lower camera 2 in accordance with the displacement amount L _L of the lower marked line R2 obtained from the image captured by the camera 2, the lower portion camera 2 is performed by moving upwards by the displacement amount L _L [ Step S15]. Due to the movement of the lower camera 2, the lower camera 1 catches the lower mark R2 at its reference position again.
Therefore amount that the marked lines image is the reference position is displaced by the movement of the camera 2, and updates the movement amount C _L of the camera as the C _L = C _L + L _L [Step S16].

By moving each of the cameras 1 and 2 in this way and positioning each of the marking lines R1 and R2 at the reference position of the image, the marking can be performed in the same manner as when the marking was adjusted by the initial setting. It is possible to continuously measure the elongation between the lines. Therefore, the processing from step S3 described above is repeatedly executed. However, if you move the camera 1 and 2, the moving amount C _H of the camera 1 is as movement control described above as the initial position of the cameras 1 and 2, since the C _L is be given respectively, In this case, the elongation E between the marked lines is obtained as the difference E = C _H -C _L between these movement amounts C _H and C _L.

When the upper camera 1 is moved, generally, the position of the mark image in the image picked up by the lower camera 2 hardly changes.
Although there is still room in the imaging of the camera 2, when the elongation measurement is performed while displaying the images captured by the cameras 1 and 2, only the image of the upper marker R 1 captured by the upper camera 1 is used as a reference. When the position is shifted to the position, the display position of the mark image on the display image may be visually uncomfortable as if the displacement amount of the lower mark R2 is larger. Therefore, when the upper camera 1 is moved, the lower camera 2 is also moved at the same time, so that the upper marked line R1 is always displaced more.
What is necessary is just to display that image. On this occasion,
When the displacement of the lower marking line R2 is small, the lower camera 2 may be appropriately prevented from moving as described above.

While moving the cameras 1 and 2 in real time while following the displacement of the marking lines R1 and R2 accompanying the elongation of the test piece S, the amount of movement of each of the marking lines R1 and R2
When detecting the position of R2, the position of the center of gravity of the mark image may be detected in the same manner. In determining the distribution of the image signal, the removal level N of the noise component due to the surface state of the test piece S is determined based on, for example, the average level of the image signal in a region where the mark R is not attached. What should I do? Further, when calculating the center of gravity from the distribution of the image signal, for example, by calculating the gradient of the density difference (level difference) between adjacent pixels, the position of the center of gravity can be obtained with an accuracy of one pixel pitch or less by interpolation. It is possible. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0040]

As described above, according to the present invention, when determining the position of a mark based on a mark image in an image taken by a camera, the position of the mark is determined from the distribution of image signals in the direction of extension of the test piece. Since the center of gravity is obtained and the position of the center of gravity is evaluated as the position of the marking line, the center of gravity is not affected by the extension of the marking line and the change of the image signal level due to the extension of the test piece, and particularly the binarization of the image signal. The position of the marked line can be accurately obtained without including an error factor. Therefore, the elongation between the marked lines can be measured easily and with high accuracy. In particular, since the projection of the image signal in the direction perpendicular to the direction of elongation of the test piece is obtained and the position of the center of gravity is obtained from the distribution of this projection component, high accuracy without being affected by blurring at the edge of the marked line This provides a great effect in practical use, such as a simple measurement.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a non-contact extensometer according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a display screen on the non-contact extensometer according to the embodiment.

FIG. 3 is a diagram showing a positional relationship between movement of a marked line due to elongation of a test piece and a camera for imaging the marked line.

FIG. 4 is a view for explaining the principle of detecting the position of a marked line on an image in the non-contact extensometer according to the present invention.

FIG. 5 is a diagram showing the principle of detecting the position (center of gravity) of a mark image in an image, which is a characteristic processing function of the present invention.

FIG. 6 is a schematic diagram for explaining the effect of detecting the center of gravity of a mark using projection of an image signal in a specific image processing area.

FIG. 7 is a diagram showing a processing procedure for camera movement control and mark line position detection following a change in the mark line position caused by the elongation of the test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st camera 2 2nd camera 3,4 Light source 5 1st moving table 6 2nd moving table 7,8 Pulse motor 11,12 Image processing part 13 Arithmetic processing part 14 Display 15,16 Position control part S Test piece R1, R2 Marked line

Claims (4)

[Claims] 1. A non-contact extensometer for optically detecting the elongation of a test piece subjected to a tensile test in a non-contact manner with the test piece, and a camera for imaging a marked line attached to the test piece. Means for determining the center of gravity of the marked line image in the image from the distribution of the image signal of the marked line captured by the camera in the direction of extension of the test piece; Means for determining the position of the reference line from the position of the center of gravity. 2. The center of gravity of the mark image is obtained by calculating a projection of an image signal in a predetermined image area including the mark image in an image captured by the camera, in a direction orthogonal to the extension direction. The non-contact extensometer according to claim 1, wherein the non-contact extensometer is obtained from a distribution of a projected component in the elongation direction. 3. The camera is supported by a movable stage that is movable in a direction in which the test piece extends, and the position of the mark is determined by the position of the movable stage and an image captured by the camera. The non-contact extensometer according to claim 1, wherein the non-contact extensometer is obtained based on a barycentric position of the mark image in the image. 4. The camera is provided in correspondence with two marked lines parallel to the test piece at a predetermined distance from each other in a direction in which the test piece extends. The non-contact extensometer according to claim 3, wherein the non-contact extensometer is moved to a position in which each of the marked lines is viewed in accordance with a change in the position of each of the marked lines.