Working method of a video extensometer measuring device without marking points

Abstract

The present invention relates to a working method of a video extensometer measuring device without marking points. The device comprises a calibration plate, an industrial computer, a monocular camera, an audible and visual alarm, a programmable blue light source, a DA conversion module and a power supply, and includes the following three steps: system calibration, elongation measurement and result output. The present invention adopts a machine vision method for non-contact measurement, and uses the texture of the material itself to replace the traditional manual marking points, which can effectively improve the measurement accuracy and efficiency.

Description

Technical Field

[0001] The invention relates to the field of electronic measurement, in particular to a working method of a video extensometer measuring device without marking points. Background Art

[0002] The elongation of rubber or metal materials is an important quality parameter. The elongation needs to be measured indirectly by an extensometer. The traditional extensometer measurement method is: measure the elongation length of the material through an encoder; detect the material break time through a tensile gauge; after the material breaks, calculate the elongation by the ratio of the elongation length to the original length. However, this method belongs to contact measurement. Due to the limited accuracy of the encoder and tensile gauge, the final measured elongation accuracy is low. At present, there are also extensometers that measure by video, but they need to add marking points manually, which also leads to problems such as low measurement accuracy and low efficiency.

[0003] In order to solve the problems of low measurement accuracy and low measurement efficiency of existing extensometers, the present invention adopts machine vision to perform non-contact measurement, and uses the texture of the material itself to replace traditional manual marking points, which can effectively improve the measurement accuracy and efficiency. Summary of the invention

[0004] In order to solve the problems of low measurement accuracy and low measurement efficiency of existing extensometers, the present invention proposes a working method of a video extensometer measuring device without marking points.

[0005] To this end, the technical solution adopted by the present invention is: a video extensometer measurement device without marking points, including a calibration plate, an industrial computer, a monocular camera, an audible and visual alarm, a programmable blue light source, a DA conversion module and a power supply;

[0006] The calibration plate consists of 2×11 black squares, which are used to calibrate the horizontal and vertical dimensions of pixels in the image, where the black squares are 1 cm×1 cm in size and 1 cm apart;

[0007] The industrial computer is used for image processing and outputting measurement results. The industrial computer has 1 USB3.0 interface, 1 RS485 interface and 2 RS232 interfaces, wherein 1 RS232 interface is used for outputting measurement results, and the other RS232 interface is connected to an audible and visual alarm device;

[0008] The monocular camera is a grayscale camera, which is installed vertically and is used to collect images of test materials. The monocular camera is connected to the industrial computer via a USB3.0 interface;

[0009] The sound and light alarm is connected to the industrial computer via an RS232 interface, can receive instructions from the industrial computer, and sound and light alarm when the material breaks to remind the operator;

[0010] The program-controlled blue light source has an RS485 interface, which is connected to the RS485 interface of the industrial computer and is used to receive control instructions from the industrial computer so as to automatically adjust the light intensity;

[0011] The DA conversion module has an RS485 interface, which is connected to the RS485 interface of the industrial computer and is used to receive control instructions from the industrial computer and output the measurement results in the form of analog quantities;

[0012] The power supply is directly connected to the industrial computer and is used to supply power to the industrial computer.

[0013] A working method of a video extensometer measurement device without a marking point, comprising the following three steps: system calibration, extensometer measurement and result output;

[0014] The system calibration:

[0015] (1) Fix the calibration plate with a fixture, send control instructions to the programmable light source through the industrial computer, adjust the light intensity so that the image of the calibration plate received by the industrial computer can be clearly observed, and control the monocular camera through the industrial computer to take an image of the calibration plate;

[0016] (2) Establish a plane rectangular coordinate system with pixels as units on the image, with the origin at the lower left corner of the lower left square, the horizontal right direction is the positive direction of the x-axis, and the vertical upward direction is the positive direction of the y-axis; establish an actual position plane rectangular coordinate system on the calibration board; the origin is at the lower left corner of the lower left square, the horizontal right direction is the positive direction of the x-axis, and the vertical upward direction is the positive direction of the y-axis;

[0017] (3) Through image processing, the centroid coordinates of all squares are detected and {G mn} indicates that the unit is pixel, where m indicates the row number, ranging from 1 to 11, and n indicates the column number, ranging from 1 to 2;

[0018] (4) For the centroid ordinate {G m1.y} and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using an N-order polynomial to obtain the fitted coefficient sequence {C 1N};

[0019] (5) For the centroid ordinate {G m2.y} and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using an N-order polynomial to obtain the fitted coefficient sequence {C 2N};

[0020] (6) {C 1N} and {C2N}, and obtain the coefficient sequence {C N}, according to the coefficient sequence {C N}, the relationship between the actual position Y and the vertical pixel coordinate y is Y=f1(y);

[0021] (7) Through image processing methods, the mean of the horizontal coordinates of the centroids of the squares in the first column is x1, and the mean of the horizontal coordinates of the centroids of the squares in the second column is x2. The relationship between the actual position X and the horizontal pixel coordinate x is obtained as X=f2(x)= x*20 / (x2-x1);

[0022] Elongation measurement:

[0023] (8) Fix the test material with a fixture, send control instructions to the programmable light source through the industrial computer, adjust the light intensity so that the texture of the test material image received by the industrial computer can be clearly observed, and control the monocular camera through the industrial computer to take an initial image of the test material;

[0024] (9) Select two rectangular areas of equal width at both ends of the test material, the top is the upper selection area, and the bottom is the lower selection area;

[0025] (10) Perform feature point detection on the image in the upper selected area, and form a sequence {P K1.y}, the horizontal coordinates of the detected K1 feature points are combined into a sequence {P K1.x}, perform feature point detection on the image in the lower selected area, and form a sequence of the vertical coordinates of the K2 detected feature points {P K2.y}, the horizontal coordinates of the detected K2 feature points are combined into a sequence {P K2.x};

[0026] (11) The sequence {P K1.y} into Y=f1(y) to obtain the Y position of each feature point in the upper selection area. K1.x} into X=f2(x) to obtain the X-direction position of each feature point in the upper selection area. K2.y} into Y=f1(y) to obtain the Y position of each feature point in the lower selection area. K2.x Substitute each value of} into X=f2(x) to obtain the X-direction position of each feature point in the lower selection area;

[0027] (12) Take the arithmetic mean of the X and Y positions of the K1 feature points in the upper selected area to obtain the center position P of the upper selected area. U =(X1, Y1), calculate the arithmetic mean of the X and Y positions of the K2 feature points in the lower selection area to obtain the center position P of the lower selection areaD is (X2, Y2);

[0028] (13) The original length L1 of the test material is P U and P D The distance between two points;

[0029] (14) After the DT time has passed, the test material is stretched and deformed, and the monocular camera is controlled by the industrial computer to collect the image of the test material at the current moment;

[0030] (15) Detect feature points of the image and match them with the initial image. The ordinates of the K3 feature points that successfully match the selected area on the initial image form a sequence {P K3.y}, the horizontal axis forms the sequence {P K3.x}, and the ordinates of the K4 feature points that successfully match the selected area in the initial image form a sequence {P K4.y}, the horizontal axis forms the sequence {P K4.x};

[0031] (16) {P K3.y} and {P K3.x Substitute Y=f1(y) and X=f2(x) respectively, and perform arithmetic averaging on the results to obtain the center position Q of the selected area at the current moment. U = (X3, Y3), {P K4.y} and {P K4.x Substitute Y=f1(y) and X=f2(x) respectively, and perform arithmetic averaging on the results to obtain the center position Q of the selected area at the current moment. D is (X4, Y4);

[0032] (17) The length of the test material at the current moment, L2, is Q U and Q D The distance between two points;

[0033] (18) By repeating (13) to (16) continuously, the length change of the test material during the extension process can be obtained, and the length can be organized into a sequence {L T}. T represents a discrete time point;

[0034] (19) For the sequence {L T} Perform M-order polynomial fitting to obtain the relationship model between the length L of the test material and the time t: L=f3(t);

[0035] (20) If the test material breaks at time t0, then the length of the test material at the time of fracture is ;

[0036] (21) The elongation of the test material is expressed as ;

[0037] Result output:

[0038] (22) The industrial control computer sends a control command to the audible and visual alarm to remind the operator of the fracture of the test material in the form of sound and light;

[0039] (23) The industrial control computer outputs the elongation rate in digital quantity through the RS232 interface;

[0040] (24) The industrial control computer sends a control command to the DA conversion module to output the elongation rate in the form of analog voltage.

[0041] Further, in the step (4), N takes values from 3 to 8.

[0042] Further, in the step (10), K1 > 5 and K2 > 5.

[0043] Further, in the step (14), DT is the sampling time interval, and it is recommended that 20 < DT < 50, with the unit of millisecond.

[0044] Further, in the step (15), K3 > 5 and K4 > 5.

[0045] Further, in the step (19), M is recommended to take values from 3 to 5.

[0046] Further, in the step (20), F represents the photographing frequency of the camera, and it is recommended that 20 < F < 50, with the unit of Hz.

[0047] The advantages of the present invention are: The present invention adopts the method of machine vision for non-contact measurement, uses the texture of the material itself to replace the traditional artificial marking points, and can effectively improve the measurement accuracy and measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a system structure block diagram of the present invention.

[0049] Figure 2 It is a schematic structural diagram of the calibration plate of the present invention.

[0050] Figure 3 It is a schematic diagram of the test material being stretched of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0051] (I) System construction

[0052] The system consists of a calibration plate, an industrial control computer, a monocular camera, an audible and visual alarm, a programmable blue light source, a DA conversion module and a power supply.

[0053] The calibration plate consists of 2×11 black squares, which are used to calibrate the horizontal and vertical dimensions of the pixels in the image. The black squares are 1cm×1cm in size and 1cm apart. The calibration plate is best made of float glass.

[0054] The industrial computer is used for image processing and output of measurement results. The industrial computer has 1 USB3.0 interface, 1 RS485 interface and 2 RS232 interfaces. One RS232 interface is used to output the measurement results in the form of digital quantity.

[0055] The monocular camera is a grayscale camera, which is installed vertically to collect images of test materials. Since the extension direction is vertical, all cameras are installed vertically to expand the range. The monocular camera is connected to the industrial computer via a USB3.0 interface.

[0056] The sound and light alarm is connected to the industrial computer via an RS232 interface, can receive instructions from the industrial computer, and give sound and light alarms when the material breaks to remind the operator.

[0057] The program-controlled blue light source has an RS485 interface, which is connected to the RS485 interface of the industrial computer to receive the control instructions of the industrial computer so as to automatically adjust the light intensity. The wavelength range of the blue light source is relatively narrow, which can filter out environmental interference to the maximum extent.

[0058] The DA conversion module has an RS485 interface, which is connected to the RS485 interface of the industrial computer, and is used to receive control instructions from the industrial computer and output the measurement results in the form of analog quantities.

[0059] The power supply is directly connected to the industrial computer to supply power to the industrial computer.

[0060] 2. Working methods

[0061] The working method includes 3 steps: system calibration, elongation measurement and result output.

[0062] System calibration:

[0063] (1) Fix the calibration plate with a fixture, send control instructions to the programmable light source through the industrial computer, and adjust the light intensity so that the image of the calibration plate received by the industrial computer can be clearly observed. Use the industrial computer to control the monocular camera to take a picture of the calibration plate;

[0064] (2) Establish a plane rectangular coordinate system in pixels on the image. The origin is at the lower left corner of the lower left square, the horizontal right is the positive direction of the x-axis, and the vertical upward is the positive direction of the y-axis; establish the actual position plane rectangular coordinate system on the calibration plate. The origin is at the lower left corner of the lower left square, the horizontal right is the positive direction of the x-axis, and the vertical upward is the positive direction of the y-axis. Due to the distortion that the camera itself cannot eliminate, there can be no linear transformation relationship between the image coordinate system and the actual position coordinate system. In order to improve the measurement accuracy, it is necessary to establish a relationship model between the two.

[0065] (3) Through image processing, the centroid coordinates of the 22 squares on the calibration plate are detected and expressed as {G mn}, the unit is pixel, where m represents the row number, ranging from 1 to 11, and n represents the column number, ranging from 1 to 2.

[0066] (4) For the centroid ordinate {G m1.y} and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using a cubic polynomial, such as: the coefficient sequence after fitting is {C 1N}={0.0010,0.0015,20.202,5.102} from front to back are the cubic term, the quadratic term, the linear term and the constant term.

[0067] (5) For the centroid ordinate {G m2.y} and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using an N-order polynomial, such as: 2N}={0.0008,0.0017,20.200,5.122}.

[0068] (6) {C 1N} and {C 2N}, and obtain the coefficient sequence {C N}={0.0009,0.0016,20.201,5.111}. According to the coefficient sequence {C N}, the relationship between the actual position Y and the vertical pixel coordinate y is Y=f1(y)=0.0009y 3 +0.0016y 2 +20.201y+5.111.

[0069] (7) Through image processing methods, the mean value of the horizontal coordinates of the centroids of the squares in the first column is obtained, such as: x 1 =200, and the mean value of the horizontal coordinates of the centroids of the squares in the second column is obtained, such as x 2 =800. The relationship between the actual position X and the horizontal pixel coordinate x is obtained as X=f2(x)= x*20 / (x2-x1)=0.0333x. Since the test material is stretched longitudinally and the deformation in the horizontal direction is very small, in order to improve the calculation efficiency, a simplified algorithm is used for the horizontal model.

[0070] Elongation measurement:

[0071] (8) Fix the test material with a fixture. Use the industrial computer to send control instructions to the programmable light source to adjust the light intensity so that the texture of the test material image received by the industrial computer can be clearly observed. Use the industrial computer to control the monocular camera to take an initial image of the test material.

[0072] (9) Select two rectangular areas of equal width at both ends of the test material. The top is the upper selection area and the bottom is the lower selection area. The width of the rectangular area is recommended to be less than 5% of the total length of the test material.

[0073] (10) Perform feature point detection on the image in the upper selected area, and form a sequence {P K1.y}, the horizontal coordinates of the detected K1 feature points are combined into a sequence {P K1.x}. Perform feature point detection on the image in the lower selected area, and form a sequence of the vertical coordinates of the K2 detected feature points {P K2.y}, the horizontal coordinates of the detected K2 feature points are combined into a sequence {P K2.x}. K1 and K2 are the numbers of points that are actually matched successfully. It is recommended that K1 > 5 and K2 > 5.

[0074] (11) The sequence {P K1.y Substitute each value of} into Y=f1(y) to obtain the Y position of each feature point in the upper selection area. K1.x Substitute each value of} into X=f2(x) to obtain the X-direction position of each feature point in the upper selection area. K2.y Substitute each value of} into Y=f1(y) to obtain the Y position of each feature point in the lower selection area. K2.x Substitute each value of} into X=f2(x) to obtain the X-direction position of each feature point in the lower selection area.

[0075] (12) Take the arithmetic mean of the X and Y positions of the K2 feature points in the upper selected area to obtain the center position P of the upper selected area. U is (X1, Y1). Take the arithmetic mean of the X and Y positions of the K2 feature points in the lower selection area to obtain the center position P of the lower selection area. DIt is (X2, Y2).

[0076] (13)The original length L1 of the test material is P U and P D The distance between two points. Calculate the distance between two points through (X1, Y1) and (X2, Y2).

[0077] (14)After DT time, the test material is stretched and deformed. The industrial control computer is used to control the monocular camera to collect the image of the test material at the current moment. DT is the sampling time interval, and it is recommended that 20 < DT < 50, with the unit of millisecond.

[0078] (15)Detect the feature points of the image and match them with the initial image. The ordinates of K3 feature points that match successfully with the selected area on the initial image form a sequence {P K3.y}, and the abscissas form a sequence {P K3.x}. The ordinates of K4 feature points that match successfully with the selected area below the initial image form a sequence {P K4.y}, and the abscissas form a sequence {P K4.x}. K3 and K4 are the numbers of actually successfully matched points. It is recommended that K3 > 5 and K4 > 5.

[0079] (16)Substitute {P K3.y} and {P K3.x} into Y = f1(y) and X = f2(x) respectively, and perform arithmetic average processing on the results to obtain the center position Q U of the upper selected area at the current moment as (X3, Y3). Substitute {P K4.y} and {P K4.x} into Y = f1(y) and X = f2(x) respectively, and perform arithmetic average processing on the results to obtain the center position Q D of the lower selected area at the current moment as (X4, Y4).

[0080] (17)The length L2 of the test material at the current moment is the distance between Q U and Q D The distance between two points can be calculated through (X3, Y3) and (X4, Y4).

[0081] (18)Continuously repeat (13) - (16), and the length change of the test material during the stretching process can be obtained, and the lengths are formed into a sequence {L T}. T represents discrete time points.

[0082] (19)Perform a third - order polynomial fitting on the sequence {L T} to obtain the relationship model between the length L of the test material and time t as L = f3(t). This model can make up for the deficiency of measurement accuracy through mathematical methods.

[0083] (20) If the test material breaks at time t0, then the length of the test material at the break time . F represents the camera's photographing frequency. It is recommended that 20 < F < 50, with the unit Hz. This method corrects the above model through the extension rate to obtain more accurate results.

[0084] (21) The extension rate of the test material is expressed as ;

[0085] Result output:

[0086] (22) The industrial control computer sends a control command to the audible and visual alarm to remind the operator that the test material has broken in the form of sound and light.

[0087] (23) The industrial control computer outputs the extension rate in digital quantity through the RS232 interface.

[0088] (24) The industrial control computer sends a control command to the DA conversion module to output the extension rate in the form of analog voltage.

Claims

1. A working method of a video extensometer measuring device without a marking point, characterized in that: The measuring device includes a calibration board, an industrial computer, a monocular camera, an audible and visual alarm, a programmable blue light source, a DA conversion module and a power supply; The calibration plate consists of 2×11 black squares, which are used to calibrate the horizontal and vertical dimensions of pixels in the image, where the black squares are 1 cm×1 cm in size and 1 cm apart; The industrial computer is used for image processing and outputting measurement results. The industrial computer has 1 USB3.0 interface, 1 RS485 interface and 2 RS232 interfaces, wherein 1 RS232 interface is used for outputting measurement results, and the other RS232 interface is connected to an audible and visual alarm device; The monocular camera is a grayscale camera, which is installed vertically and is used to collect images of test materials. The monocular camera is connected to the industrial computer via a USB3.0 interface; The sound and light alarm is connected to the industrial computer via an RS232 interface, can receive instructions from the industrial computer, and sound and light alarm when the material breaks to remind the operator; The program-controlled blue light source has an RS485 interface, which is connected to the RS485 interface of the industrial computer and is used to receive control instructions from the industrial computer so as to automatically adjust the light intensity; The DA conversion module has an RS485 interface, which is connected to the RS485 interface of the industrial computer, and is used to receive control instructions from the industrial computer and output the measurement results in the form of analog quantities; The power supply is directly connected to the industrial computer and is used to supply power to the industrial computer; It includes the following three steps: system calibration, elongation measurement and result output; The system calibration: (1) Fix the calibration plate with a fixture, send control instructions to the programmable light source through the industrial computer, adjust the light intensity so that the image of the calibration plate received by the industrial computer can be clearly observed, and control the monocular camera through the industrial computer to take an image of the calibration plate; (2) Establish a plane rectangular coordinate system with pixels as units on the image, with the origin at the lower left corner of the lower left square, the horizontal right direction is the positive direction of the x-axis, and the vertical upward direction is the positive direction of the y-axis; establish an actual position plane rectangular coordinate system on the calibration board; the origin is at the lower left corner of the lower left square, the horizontal right direction is the positive direction of the x-axis, and the vertical upward direction is the positive direction of the y-axis; (3) Through image processing, the centroid coordinates of all squares are detected and {G mn } indicates that the unit is pixel, where m indicates the row number, ranging from 1 to 11, and n indicates the column number, ranging from 1 to 2; (4) For the centroid ordinate {G m1.y } and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using an N-order polynomial to obtain the fitted coefficient sequence {C 1N }; (5) For the centroid ordinate {G m2.y } and the actual position sequence {5, 25, 45, 65, 85, 105, 125, 145, 165, 185, 205}, in millimeters, are fitted using an N-order polynomial to obtain the fitted coefficient sequence {C 2N }; (6) {C 1N } and {C 2N }, and obtain the coefficient sequence {C N }, according to the coefficient sequence {C N }, the relationship between the actual position Y and the vertical pixel coordinate y is Y=f1(y); (7) Through image processing methods, the mean of the horizontal coordinates of the centroids of the squares in the first column is x1, and the mean of the horizontal coordinates of the centroids of the squares in the second column is x2. The relationship between the actual position X and the horizontal pixel coordinate x is obtained as X=f2(x)= x*20 / (x2-x1); Elongation measurement: (8) Fix the test material with a fixture, send control instructions to the programmable light source through the industrial computer, adjust the light intensity so that the texture of the test material image received by the industrial computer can be clearly observed, and control the monocular camera through the industrial computer to take an initial image of the test material; (9) Select two rectangular areas of equal width at both ends of the test material, the top is the upper selection area, and the bottom is the lower selection area; (10) Perform feature point detection on the image in the upper selected area, and form a sequence {P k1.y }, the horizontal coordinates of the detected K1 feature points are combined into a sequence {P k1.x }, perform feature point detection on the image in the lower selected area, and form a sequence of the vertical coordinates of the K2 detected feature points {P k2. }, the horizontal coordinates of the detected K2 feature points are combined into a sequence {P k2.x }; (11) The sequence {P k1.y } into Y=f1(y) to obtain the Y position of each feature point in the upper selection area. k1.x } into X=f2 (x) to obtain the X-direction position of each feature point in the upper selection area. k2.y } into Y=f1(y) to obtain the Y position of each feature point in the lower selection area. k2.x Substitute each value of} into X=f2(x) to obtain the X-direction position of each feature point in the lower selection area; (12) Take the arithmetic mean of the X and Y positions of the K1 feature points in the upper selected area to obtain the center position P of the upper selected area. U = (X1, Y1), calculate the arithmetic mean of the X and Y positions of the K2 feature points in the lower selected area to obtain the center position P of the lower selected area D is (X2, Y2); (13) The original length L1 of the test material is P U and P D The distance between two points; (14) After the DT time has passed, the test material is stretched and deformed, and the monocular camera is controlled by the industrial computer to collect the image of the test material at the current moment; (15) Detect feature points of the image and match them with the initial image. The ordinates of the K3 feature points that successfully match the selected area on the initial image form a sequence {P K3.y }, the horizontal axis forms the sequence {P K3.x }, and the ordinates of the K4 feature points that successfully match the selected area in the initial image form a sequence {P K4.y }, the horizontal axis forms the sequence {P K4.x }; (16) {P K3.y } and {P K3.x Substitute Y=f1(y) and X=f2(x) respectively, and perform arithmetic averaging on the results to obtain the center position Q of the selected area at the current moment. U = (X3, Y3), {P k4.y } and {Pk4.x} are substituted into Y=f1(y) and X=f2(x) respectively, and the results are processed by arithmetic mean to obtain the center position Q of the selected area at the current moment D is (X4, Y4); (17) The length of the test material at the current moment, L2, is Q U and Q D The distance between two points; (18) By repeating (13) to (16), the length change of the test material during the extension process can be obtained, and the length can be organized into a sequence {L T }; T represents a discrete time point; (19) For the sequence {L T } Perform M-order polynomial fitting to obtain the relationship model between the length L of the test material and the time t: L=f3(t); (20) If the test material breaks at time t0, then the length of the test material at the time of fracture is ； (21) The elongation of the test material is expressed as ; Result output: The industrial control computer sends a control instruction to the audible and visual alarm to remind the operator of the fracture of the test material in the form of sound and light; The industrial control computer outputs the elongation rate in digital quantity through the RS232 interface; The industrial control computer sends a control instruction to the DA conversion module to output the elongation rate in the form of analog voltage.

2. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (4), N takes values from 3 to 8.

3. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (10), K1 > 5 and K2 > 5.

4. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (14), DT is the sampling time interval, and 20 < DT < 50, with the unit of millisecond.

5. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (15), K3 > 5 and K4 > 5.

6. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (19), M takes values from 3 to 5.

7. The working method of the video extensometer measurement device without marking points according to claim 1, characterized in that: In the step (20), F represents the photographing frequency of the camera, and 20 < F < 50, with the unit of Hz.

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