Displacement testing system and displacement testing method

Abstract

The present invention discloses a displacement test system, including a centrifuge, a micro-fiber probe, a characteristic point calibration label, a micro-fiber insertion part, an imaging and image acquisition device, a cold light source, an optical fiber image transmission bundle, an objective lens, an eyepiece, a network cable, and an industrial computer; the displacement test method includes calibration label image acquisition, calibration image processing, displacement / pixel parameter calculation, radial / circumferential displacement image acquisition, detection parameter setting, measurement image processing, and displacement display storage. In the present invention, the fiber endoscope is used in the centrifugal dynamic test task, giving full play to the advantages of the fiber endoscope. Compared with the traditional displacement measurement method, the product is less destructive, basically realizes in-situ testing, and is simple and easy to operate; the displacement is measured by optical imaging technology, and the precision and accuracy of displacement measurement can be improved by further exploring and developing image processing algorithms and technologies, and the precision can reach several μm level.

Description

Technical Field

[0001] The invention belongs to the field of testing technology, and in particular relates to a displacement testing system and a displacement testing method. Background Art

[0002] In the environmental adaptability test of complex structural products, it is often necessary to detect the radial and circumferential displacement of the structure and understand the dynamic response law of the corresponding displacement, so as to improve the scientific evaluation and prediction ability of equipment performance changes, and at the same time reduce the detection damage of the detection device to the product. Therefore, the demand for developing a long-distance, low-damage, high-precision displacement test system and carrying out related test technology research is becoming increasingly strong.

[0003] Traditional displacement measurement uses differential displacement sensors, eddy current sensors, laser displacement meters, etc. These devices can only measure displacement changes in a single direction and are large in size. During actual testing, the product requires a lot of reprocessing and is very destructive to the product. Although they can meet the requirements of radial displacement measurement of structures, they are basically ineffective in measuring circumferential displacement.

[0004] In order to solve the above problems, we have developed a displacement testing system and a displacement testing method. Summary of the invention

[0005] The purpose of the present invention is to provide a displacement testing system and a displacement testing method in order to solve the above problems.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] Displacement test system, including:

[0008] Centrifuge; the centrifuge includes a hanging basket, a centrifuge arm, and a main shaft, and the test product is placed in the hanging basket; an opening is provided on the outer wall of the test product;

[0009] Micro optical fiber probe; one end of the micro optical fiber probe is placed in the opening of the test product;

[0010] Characteristic point calibration labels: Characteristic point calibration labels are set on the upper structure and lower structure of the test product;

[0011] Micro optical fiber insertion part; the micro optical fiber insertion part is fixedly installed along the centrifuge arm;

[0012] Imaging and image acquisition equipment;

[0013] Cold light source; the cold light source, imaging and image acquisition equipment are all installed near the main axis; the illumination light emitted from the cold light source is used to illuminate the calibrated label after being transmitted through the optical fiber transmission beam;

[0014] Optical fiber image transmission bundle; the optical fiber light transmission beam and the optical fiber image transmission bundle are both arranged on the centrifuge arm;

[0015] Objective lens;

[0016] eyepiece;

[0017] Network cable;

[0018] Industrial computer; the feature point calibration label is imaged by the objective lens and then transmitted to the eyepiece through the optical fiber image bundle, where it is magnified. The imaging and image acquisition equipment is used to convert the optical signal into an electrical signal and transmit it to the industrial computer via the network cable.

[0019] Displacement test methods, including:

[0020] Calibration label image acquisition: Before measurement, use a standard extensometer calibrator and feature point calibration labels to calibrate the system and acquire feature point calibration label images;

[0021] Calibration image processing: image information is transmitted to the industrial computer, which performs digital image processing on the calibration image;

[0022] Displacement / pixel parameter calculation;

[0023] Radial / circumferential displacement image acquisition: During measurement, a label with the same characteristic points is attached to the object to be measured, and a fiber optic endoscope is installed to collect images of the measurement points;

[0024] Detection parameter setting; including setting the pixel value of the micro-fiber probe from the center of the characteristic point calibration label, the displacement value corresponding to each pixel and the displacement correction coefficient.

[0025] Measure image processing; perform corresponding image digitization processing, calculate the centroid coordinates of the feature points, and thus calculate the pixel value of the displacement. According to the pixel-displacement correspondence and displacement correction coefficient obtained by the calibration device, convert the image displacement into physical size and calculate the change value of the displacement.

[0026] Displacement display and storage: the above displacement change values ​​are displayed and stored on the industrial computer.

[0027] The beneficial effects of the present invention are:

[0028] The displacement testing system and displacement testing method of the present invention;

[0029] 1. This application uses a fiber optic endoscope in a centrifugal dynamic test task, giving full play to the advantages of a fiber optic endoscope. Compared with traditional displacement measurement methods, the product is less destructive, basically realizes in-situ testing, and is simple and easy to operate.

[0030] 2. Use optical imaging technology to measure displacement. Through further exploration and development of image processing algorithms and technologies, the precision and accuracy of displacement measurement can be improved, with the highest precision reaching several μm level.

[0031] 3. Since the diameter of the fiber endoscope is small, it is less destructive to the product. And the front end insertion part can be made into different lengths according to the needs to meet the testing requirements at different distances.

[0032] 4. Front-end imaging is a pure optical technology that does not involve photoelectric conversion and does not generate heat. It is safer, more stable and reliable when installed in some special products or next to them for measurement.

[0033] 5. Fiber optic endoscopes can also be connected to various special-purpose industrial cameras such as ultraviolet cameras, infrared cameras, high-speed cameras, etc. for external video imaging. The imaging is more direct, more realistic, and more three-dimensional and layered. Unlike electronic mirrors, the images are not flat. It is more real and reliable when collecting displacement images, and the accuracy can be higher when processing and calculating. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the displacement test system in this application.

[0035] Figure 2 It is a schematic diagram of radial displacement calculation of the present application;

[0036] Figure 3 It is a schematic diagram of circumferential displacement calculation of the present application;

[0037] Figure 4 It is a schematic diagram of the image grayscale processing in this application;

[0038] Figure 5 is the gray value histogram of the image in this application;

[0039] Figure 6 It is a schematic diagram of the image binarization processing in this application;

[0040] Figure 7 is a schematic diagram of image edge dilation processing in this application;

[0041] Figure 8 It is a schematic diagram of performing sobel edge detection on an image in this application;

[0042] Fig. 9 is a schematic diagram of feature point I identification in this application;

[0043] Fig.10 It is a schematic diagram of feature point II identification in this application;

[0044] Fig.11 It is a schematic diagram of the identification of feature point III in this application;

[0045] Fig.12 It is a schematic diagram of the identification of characteristic point IV in this application;

[0046] Fig.13is a flow chart of the displacement test method in this application;

[0047] Fig.14 It is a structural schematic diagram of the extensometer calibration instrument in this application.

[0048] In the figure: 1. hanging basket, 2. upper structure, 3. feature point calibration label, 4. lower structure, 5. micro fiber optic probe, 6. mounting bracket, 7. micro fiber optic insertion part, 8. image transmission bundle, 9. light transmission bundle, 10. centrifuge arm, 11. main shaft, 12. eyepiece, 13. imaging and image acquisition equipment, 14. cold light source, 15. network cable, 16. industrial computer, 17. extensometer calibrator, 18. upper concave calibration block, 19. lower convex calibration block. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings:

[0050] like Figure 1 As shown;

[0051] Displacement test system, including:

[0052] Centrifuge; the centrifuge includes a hanging basket 1, a centrifuge arm 10, and a main shaft 11, and the test product is placed in the hanging basket 1; an opening is provided on the outer wall of the test product;

[0053] A micro optical fiber probe 5; one end of the micro optical fiber probe 5 is placed in the opening of the test product;

[0054] A mounting bracket 6, on which the micro-fiber probe 5 is also fixed;

[0055] Characteristic point calibration label 3; Characteristic point calibration labels 3 are provided on both the upper structure and the lower structure of the test product;

[0056] The micro-fiber insertion part 7 is fixedly installed along the centrifuge arm; and protective measures are taken;

[0057] Imaging and image acquisition equipment 13;

[0058] Cold light source 14; the cold light source 14, the imaging and image acquisition device 13 are all installed near the main axis; the illumination light emitted from the cold light source 14 is used to illuminate the calibrated label after being transmitted through the optical fiber transmission light beam 9;

[0059] Optical fiber image transmission bundle 8; optical fiber transmission beam 9 and optical fiber image transmission bundle 8 are both arranged on the centrifuge arm;

[0060] Objective lens;

[0061] Eyepiece 12;

[0062] Network cable 15;

[0063] The industrial computer 16; the feature point calibration label 3 is imaged by the objective lens and then transmitted to the eyepiece 12 through the optical fiber image transmission bundle 8, and is magnified at the eyepiece 12. The imaging and image acquisition device 13 is used to convert the optical signal into an electrical signal and transmit it to the industrial computer 16 via the network cable 15.

[0064] like Figure 1 As shown, the micro-fiber probe 5 and the micro-fiber insertion part 7 are integrally arranged.

[0065] The resolution of the imaging and image acquisition device 13 should be higher than the resolution of the front-end micro-fiber probe 5 .

[0066] like Fig.13 As shown, the displacement test method includes:

[0067] Calibration label image acquisition: Before measurement, use a standard extensometer calibration instrument 17 (such as Fig.14 As shown) and feature point calibration label 3 are used for system calibration, and calibration label images are collected (feature point calibration labels are set at both the standard extensometer calibrator 17 and the test product, one for calibration and the other for formal measurement); specifically, a standard extensometer calibrator 17 with a measuring range of 25mm and a resolution of 0.0002mm is used, and an upper concave calibration block 18 and a lower convex calibration block 19 are provided as required. After the upper concave calibration block 18 is adjusted to a fixed position, the lower convex calibration block 19 is moved to control the distance between the calibration blocks; before calibration measurement, the lower convex calibration block 19 is raised to make the convex and concave surfaces of the surface model close to each other, and a feeler gauge is used to adjust the gap between the convex and concave surfaces to be small enough. At this time, the calibration is performed. The reading on the instrument is used as the initial gap, and feature point calibration labels are pasted on the upper concave calibration block 18 and the lower convex calibration block 19 respectively. The micro-fiber probe 5 is fixed on the mounting bracket 6, and is aligned with the feature point calibration labels on the upper concave calibration block 18 and the lower convex calibration block 19. The illumination light emitted by the cold light source 14 is transmitted to the probe end through the optical fiber transmission beam 9, and the feature point calibration labels on the illumination calibration block are imaged by the objective lens and then transmitted through the optical fiber transmission beam 8, amplified at the eyepiece 12, and then the optical signal image is converted into an electrical signal by the imaging and image acquisition device 13 placed behind the eyepiece 12, and transmitted through the network cable 15 for display on the external industrial computer 16, completing the feature point calibration label image acquisition.

[0068] Calibration image processing; the image information is transmitted to the industrial computer 16, and the industrial computer 16 performs image digital processing on the calibration image; the image digital processing method includes image grayscale processing, binarization and edge expansion processing, and feature point recognition.

[0069] Displacement / pixel parameter calculation; calculate the centroid coordinates of the feature point, thereby calculating the pixel value of the displacement, and then correspond the pixel value of the calibration image plane coordinates with the known displacement value, so as to obtain the actual distance between the centroids of the two feature points on the feature point calibration label; the calibration device produces a known and determined displacement, and the pixel-displacement correspondence is established by corresponding the change in the centroid of the feature point and the change in the displacement.

[0070] The method to obtain the actual distance between the centroids of the two feature points on the calibration label is:

[0071] Search and determine feature point I and feature point II in the binary image of the calibration image;

[0072] Determine the centroid coordinates of feature point I and feature point II;

[0073] The pixel value of the displacement is calculated according to the centroid coordinates of feature point I and feature point II. According to the pixel-displacement correspondence and displacement correction coefficient obtained by the calibration device, the image displacement is converted into physical size and the displacement change value is calculated.

[0074] The calculation method of the centroid coordinates of feature point I and feature point II is:

[0075]

[0076]

[0077] The actual distance calculation method of the double feature point centroid is:

[0078]

[0079] In the above formula, X i , Y i are the coordinates of the feature images respectively;

[0080] N is the total number of pixels that make up the feature point image;

[0081] X c , Y c are the centroid coordinates of the object.

[0082] In some embodiments, feature point labels are affixed to the upper and lower structures in advance. When the product produces radial or circumferential displacement, the centroid coordinates of the feature points will change. Compare n images at a certain time interval, determine the feature point in the binary image of the first image, and calculate the centroid coordinates of the feature point. Then, calculate the centroid coordinates of the same feature point in the 2nd, 3rd, 4th...nth images in turn, calculate the pixel value of the centroid coordinate deviation, and convert the image displacement (unit: pixel) into a physical size (unit: um) based on the pixel-displacement correspondence and displacement correction coefficient obtained from the calibration test, and calculate the displacement change value. Since the calibration device produces a known and determined displacement, the pixel-displacement correspondence can be established by corresponding the feature point centroid change and the displacement change. The calculation principle diagram is shown in the figure. Figure 2 , Figure 3 shown.

[0083] Radial / circumferential displacement image acquisition; during measurement, the same feature point calibration label is pasted on the measured object, and the fiber optic endoscope is installed to collect the measurement point image; specifically, the micro-fiber probe 5 is fixed on the mounting bracket 6, aligned with the feature point calibration label on the test product, and the illumination light emitted from the cold light source 14 is transmitted to the probe end through the fiber optic transmission beam 9, the feature point calibration label on the illumination calibration block is imaged through the objective lens and then transmitted through the fiber optic transmission beam 8, magnified at the eyepiece 12, and then the optical signal image is converted into an electrical signal through the imaging and image acquisition device 13 placed behind the eyepiece 12, and then transmitted through the network cable 15 for display on the external industrial computer 16.

[0084] Detection parameter setting; including setting the pixel value of the micro-fiber probe 5 from the center of the characteristic point calibration label, the displacement value corresponding to each pixel and the displacement correction coefficient (the deviation coefficient between the actual measured displacement and the calibrated measured displacement, the default value is 1).

[0085] Measure image processing; perform corresponding image digitization processing (grayscale transformation, binarization, feature point recognition and other image digitization processing through the image processing system), calculate the centroid coordinates of the feature points, and thus calculate the pixel value of the displacement. According to the pixel-displacement correspondence and displacement correction coefficient obtained by the calibration device, convert the image displacement (unit: pixel) into physical size (unit: um), and calculate the change value of the displacement.

[0086] Displacement display and storage; the above displacement change values ​​are displayed and stored on the industrial computer 16.

[0087] In some embodiments, during measurement, a calibration label with the same feature point is attached to the measured object, a fiber endoscope is installed to collect the measurement point image, the detection parameters are set, and then the corresponding image is digitized to obtain the plane coordinates of the centroid of the dual feature points of the calibration label, and then the actual distance between the centroids of the dual feature points is used to calculate the actual plane displacement change of the feature points on the feature point calibration label, which is displayed and stored on the industrial computer 16. The displacement calculation process of the present invention is specifically described below using the actual feature point image as an example.

[0088] Step 1: Grayscale image processing

[0089] Image grayscale processing is the basis of image segmentation and feature point extraction, so image grayscale processing is particularly important. Image grayscale processing is to convert a color image (not shown in the figure, represented as Figure 4 The color graphics) are processed into grayscale images through appropriate functions, and the color is removed to obtain its grayscale image. The grayscale image is obtained through matlab software processing. Figure 4 As shown. From the histogram (such as Figure 5 As shown in the figure, it can be seen that its grayscale value is mainly distributed between 140-180, indicating that the brightness is medium. According to the post-processing results, the brightness can meet the requirements.

[0090] Step 2: Binarization and edge dilation

[0091] The grayscale of an image is divided into different levels. By setting the grayscale threshold (threshold), the meaningful area or the boundary of the segmented object can be determined. The commonly used thresholding process is to binarize the image, that is, to select a threshold and convert the image into a black and white binary image for image segmentation and edge tracking. This application uses an adaptive thresholding method to select a threshold, and then performs edge expansion processing on the binary image, which can improve the recognition ability of image feature points. Figure 6 , after the image edge is expanded, Figure 7 .

[0092] Step 3: Edge detection analysis

[0093] Perform Sobel edge detection on the image after binarization and expansion, and the processed image is as follows Figure 8 As shown in the figure. Through image analysis, it can be seen that the image edge obtained by Sobel edge detection is clearly visible, and most of the noise caused by the background color in the image has been filtered out when threshold processing is used.

[0094] Step 4: Feature point acquisition and centroid calculation

[0095] The sobel edge detection method detects Figure 8After analysis, it can be seen that the image contains the feature points I, II, III, and IV that we want to identify. By recognizing and calculating the shape (perimeter and area) of the feature points and performing image matching, we can obtain Fig. 9 , Fig.10 , Fig.11 , Fig.12 The feature point image with noise completely removed is shown, and the centroid coordinate values ​​of feature points Ⅰ, Ⅱ, Ⅲ, and Ⅳ are obtained by calculation respectively.

[0096] The digitization process of other frames is completed in the same way to obtain the centroid data of the feature points of each frame. By comparing it with the centroid coordinates of the feature points of the first frame of video, the centroid (XY) change can be obtained. Since the calibration device produces a known and determined displacement, the pixel-displacement correspondence function relationship can be established through the correspondence between the feature point centroid change and the displacement change.

[0097] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A displacement test system, comprising a centrifuge; the centrifuge comprises a hanging basket, a centrifuge arm, and a main shaft, and the test product is placed in the hanging basket; an opening is provided on the outer wall of the test product; and the system is characterized in that: The displacement test system also includes: Micro optical fiber probe; one end of the micro optical fiber probe is placed in the opening of the test product; Characteristic point calibration labels: Characteristic point calibration labels are set on the upper structure and lower structure of the test product; Micro optical fiber insertion part; the micro optical fiber insertion part is fixedly installed along the centrifuge arm; Imaging and image acquisition equipment; Cold light source; the cold light source, imaging and image acquisition equipment are all installed near the main axis; the illumination light emitted from the cold light source is used to illuminate the calibrated label after being transmitted through the optical fiber transmission beam; Optical fiber image transmission bundle; the optical fiber light transmission beam and the optical fiber image transmission bundle are both arranged on the centrifuge arm; Objective lens; eyepiece; Network cable; Industrial computer; the feature point calibration label is imaged by the objective lens and then transmitted to the eyepiece through the optical fiber image bundle, where it is magnified. The imaging and image acquisition equipment is used to convert the optical signal into an electrical signal and transmit it to the industrial computer via the network cable.

2. The displacement testing system according to claim 1, characterized in that: The micro-fiber probe and the micro-fiber insertion part are integrally arranged.

3. The displacement testing system according to claim 1, characterized in that: The resolution of the imaging and image acquisition equipment should be higher than the resolution of the front-end micro-fiber probe.

4. A displacement test method, characterized in that: include: Calibration label image acquisition: Before measurement, use a standard extensometer calibrator and feature point calibration labels to calibrate the system and acquire feature point calibration label images; Calibration image processing: image information is transmitted to the industrial computer, which performs digital image processing on the calibration image; Displacement / pixel parameter calculation; Radial / circumferential displacement image acquisition: During measurement, a label with the same characteristic points is attached to the object to be measured, and a fiber optic endoscope is installed to collect images of the measurement points; Detection parameter setting; It includes setting the pixel value of the micro-fiber probe from the center of the characteristic point calibration label, the displacement value and displacement correction coefficient corresponding to each pixel; Measurement image processing: perform corresponding image digital processing, calculate the centroid coordinates of the feature points, and thus calculate the pixel value of the displacement. According to the pixel-displacement correspondence and displacement correction coefficient obtained by the calibration device, the image displacement is converted into physical size, and the displacement change value is calculated; Displacement display and storage: the above displacement change values ​​are displayed and stored on the industrial computer.

5. The displacement testing method according to claim 4, characterized in that: Use a standard extensometer calibrator and feature point calibration labels to calibrate the system. The feature point calibration label images collected include: According to the requirements, the upper concave calibration block and the lower convex calibration block are equipped. After the upper concave calibration block is adjusted to a fixed position, the lower convex calibration block is moved to control the distance between the calibration blocks. Before calibration measurement, the lower convex calibration block is raised to make the convex and concave surfaces of the surface model close to each other, and the gap between the convex and concave surfaces is adjusted to be small enough with a feeler gauge. At this time, the reading on the calibrator is used as the initial gap, and the feature point calibration labels are respectively pasted on the upper concave calibration block and the lower convex calibration block. The micro-fiber probe is fixed on the mounting bracket and aligned with the feature point calibration labels on the upper concave calibration block and the lower convex calibration block. The illumination light emitted from the cold light source is transmitted to the probe end through the optical fiber transmission beam to illuminate the feature point calibration label on the calibration block. After being imaged by the objective lens, it is transmitted through the optical fiber transmission beam and amplified at the eyepiece. Then, the optical signal image is converted into an electrical signal by the imaging and image acquisition equipment placed behind the eyepiece, and is displayed on the external industrial computer through network transmission to complete the feature point calibration label image acquisition.

6. The displacement testing method according to claim 4, characterized in that: Image digital processing methods include image grayscale processing, binarization and edge expansion processing, and feature point recognition.

7. The displacement testing method according to claim 4, characterized in that: The displacement / pixel parameter calculation includes: calculating the centroid coordinates of the feature point, thereby calculating the pixel value of the displacement, and then corresponding the pixel value of the calibration image plane coordinates with the known displacement value, so as to obtain the actual distance between the centroids of the two feature points on the calibration label; the calibration device produces a known and determined displacement, and the pixel-displacement correspondence is established by corresponding the change in the centroid of the feature point and the change in the displacement.

8. The displacement testing method according to claim 7, characterized in that: The method to obtain the actual distance between the centroids of the two feature points on the calibration label is: Search and determine feature point I and feature point II in the binary image of the calibration image; Determine the centroid coordinates of feature point I and feature point II; The pixel value of the displacement is calculated according to the centroid coordinates of feature point I and feature point II. According to the pixel-displacement correspondence and displacement correction coefficient obtained by the calibration device, the image displacement is converted into physical size and the displacement change value is calculated.

9. The displacement testing method according to claim 8, characterized in that: The calculation method of the centroid coordinates of feature point I and feature point II is: ， ， The actual distance calculation method of the double feature point centroid is: ， In the above formula, , are the coordinates of the feature images respectively; N is the total number of pixels that make up the feature point image; , are the centroid coordinates of the object.

10. The displacement testing method according to claim 4, characterized in that: Radial / circumferential displacement image acquisition includes: Fix the micro-fiber probe on the mounting bracket and align it with the characteristic point calibration label on the test product. The illumination light emitted from the cold light source is transmitted to the probe end through the optical fiber transmission beam, illuminating the calibration label on the calibration block. After being imaged by the objective lens, it is transmitted out through the optical fiber transmission beam and magnified at the eyepiece. The optical signal image is then converted into an electrical signal by the imaging and image acquisition equipment placed behind the eyepiece, and then transmitted through the network cable and displayed on the external industrial computer.

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