Suspension bridge pin jointed sling rotation angle measurement method

Abstract

The present application relates to a kind of suspension bridge pin joint type sling rotation angle measurement method, comprising the following steps: S1, selecting the two places of sling of suspension bridge around lower pin shaft rotation site are carried out transverse marking and longitudinal marking;S2, the marked part of rotation site is videoed and frame is extracted, and the image sequence after frame extraction is obtained;S3, the image gray scale of image sequence after frame extraction is carried out using self-defined single channel method;S4, after the pre-processing of gray-scale image, all straight lines of image are identified using Hough transform, and the long straight line located at the edge of transverse marking and longitudinal marking is extracted;S5, the angle between long straight line respectively located at the edge of transverse marking and longitudinal marking is calculated, and the angle value of sling around pin shaft rotation with time variation in acquisition time period is obtained.The method proposed in the present application can realize the measurement of sling around pin shaft rotation angle, and provide reliable data basis for sling rotation law and related damage mechanism research.

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering technology and relates to a method for measuring the rotation angle of pin-connected suspension cables in suspension bridges. Background Technology

[0002] With the development and application of technologies such as computer vision, artificial intelligence, and big data, more and more technologies, algorithms, and equipment are being introduced into the field of bridge maintenance to solve practical engineering problems. Through the application of these technologies, accurate perception of bridge conditions can be achieved, and a comprehensive bridge information interconnection system can be established, thereby promoting the intelligent upgrading of bridge maintenance. This not only helps improve the efficiency and reliability of bridge maintenance but also provides strong guarantees for the safe operation of bridges, driving bridge maintenance towards refinement, scientification, and intelligence. Currently, digital image measurement methods can be summarized as angle measurement methods based on Hough transform, speckle methods based on digital image correlation, and angle recognition methods based on convolutional neural networks + You Only LookOnce (YOLO). While some progress has been made in measuring angles using digital image processing methods, due to the special nature of the operating bridge environment, there is a lack of a method for non-contact and convenient automated measurement of the rotation angle of suspension cables around the pivot pin.

[0003] Furthermore, for pin-connected cable clamps in suspension bridges, the longitudinal drift of the stiffening girder and the vibration of the cables can cause the cables to rotate around the pin, leading to a series of defects unique to suspension bridges, such as pin wear and cable clamp bolt loosening. To reveal the mechanisms of these defects, it is necessary to clarify the characteristics of cable rotation around the pin. However, currently, there is no method for on-site measurement of the cable rotation angle around the pin on actual bridges, making it impossible to provide a data foundation for studying the characteristics of cable rotation around the pin.

[0004] Therefore, proposing a method for measuring the rotation angle of pin-connected suspension cables in suspension bridges has significant engineering implications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring the rotation angle of pin-connected suspension cables in suspension bridges, which can solve the problem of measuring the rotation angle data of suspension bridge cables around the pin shaft.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for measuring the rotation angle of pin-connected suspension cables in a suspension bridge includes the following steps:

[0008] S1, mark the pin and ear plate of the suspension bridge cable rotating around the lower pin and mark the horizontal and vertical directions respectively;

[0009] S2, capture video of the marked part of the rotating part and extract frames to obtain a series of extracted image sequences;

[0010] S3, use a custom single-channel method to convert the image sequence after frame extraction to grayscale;

[0011] S4. After preprocessing the grayscale image, Hough transform is used to identify all straight lines in the image and extract long straight lines located at the edges of horizontal and vertical markers.

[0012] S5, calculate the angle between the long straight lines located at the edges of the horizontal and vertical marks respectively, that is, the angle of rotation of the sling around the pin, and obtain the angle value of the sling rotation around the pin as a function of time during the data collection period.

[0013] Furthermore, in S1, the transverse and longitudinal markings are located on the ear plate and the pin, with flat edges, and the marking color is the opposite of the pin's paint finish.

[0014] Furthermore, in S2, the frame extraction interval is 5-6 seconds.

[0015] Furthermore, in S2, the video capture time is 2-4 minutes.

[0016] Furthermore, in S3, the strategy for image grayscale conversion is to make the grayscale values ​​of the marker portion and the background in the grayscale image closer to 0 and 255, respectively. This allows the marker portion and the background to have a greater color difference in the grayscale image, facilitating recognition.

[0017] Furthermore, in S4, the image preprocessing process is as follows: the grayscale image is filtered and denoised using the median filtering method, and the image is binarized using a custom threshold. Finally, the Canny operator is used to edge-map the image.

[0018] Furthermore, in S4, the process by which the Hough transform identifies all straight lines in the image is as follows:

[0019] Calculate the angle θ between all lines and the horizontal axis, where 0 ≤ θ ≤ 180°. Define a vertical line as the line located at the edge of the vertical mark and whose angle with the horizontal axis is 70° < θ < 110°. Define a horizontal line as the line located at the edge of the horizontal mark and whose angle with the horizontal axis is 0 ≤ θ ≤ 20° or 160° ≤ θ ≤ 180°.

[0020] Furthermore, in S5, the process of calculating the angle between the long straight lines located at the edges of the horizontal and vertical marks is as follows:

[0021] First, calculate the length of all horizontal and vertical lines, select the longest horizontal and vertical lines, and mark them with the first color. Then, select the second longest horizontal and vertical lines and mark them with the second color. Next, obtain the coordinates of the endpoints of all horizontal and vertical lines marked with the first and second colors, calculate the angle between them and the horizontal axis, and take the average of the angles between the first and second colored horizontal lines as the angle α between the horizontal marker line and the horizontal axis. Take the average of the angles between the first and second colored vertical lines as the angle β between the vertical marker line and the vertical axis. Then, the angle between the long lines located at the edges of the horizontal and vertical markers is...

[0022] Furthermore, in S5, the first color is yellow.

[0023] Furthermore, in S5, the second color is red.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The characteristics of video measurement, such as non-contact and convenience, are fully utilized. Straight line identification is performed based on Hough transform, and the rotation angle of the sling around the pin is further calculated.

[0026] (2) In order to eliminate the interference of short lines accidentally identified during the line recognition process on the angle calculation, a long line screening method is proposed to screen and mark the lines located on the long side of the marking line so that they can represent the angle of the marking line and increase the accuracy of angle measurement.

[0027] (3) Accurately measuring the angle of rotation of the suspension bridge cable around the pin is the prerequisite for studying the rotation law of the cable around the pin and also the guarantee for studying related defects. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for measuring the rotation angle of a suspension bridge's pin-connected cable around a pin shaft;

[0029] Figure 2 It is 45 # Position markings for the sling pin and ear plate;

[0030] Figure 3 It is the image after the grayscale conversion step;

[0031] Figure 4 The image is after Hough transform and long line filtering are completed;

[0032] Figure 5 It is a schematic diagram of angle measurement using CAD line drawing;

[0033] Figure 6 It is the 45th bridge #Graph showing the change of sling rotation angle over time. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] Unless otherwise specified, the following embodiments or examples are conventional processing techniques or functional components, and are conventional components or structures used to achieve the corresponding functions.

[0036] To address the issue of non-contact measurement of the rotation angle of suspension bridge cables around a pivot pin, this invention provides a method for measuring the rotation angle of pin-connected suspension bridge cables, comprising the following steps:

[0037] S1. Considering that the upper pin of the suspension cable is difficult to reach due to its height, it is impossible to collect video data of the cable rotating around the upper pin. Due to the symmetry of the upper and lower suspension cables of the suspension bridge, the pin and ear plate of the suspension cable rotating around the lower pin of the suspension bridge are selected for horizontal and vertical marking.

[0038] S2, capture video of the marked part of the rotating part and extract frames to obtain a series of extracted image sequences;

[0039] S3, the image sequence after frame extraction is converted to grayscale using a custom single-channel method (the specific grayscale channel is determined by the paint color and the marker line color);

[0040] S4. After preprocessing the grayscale image, Hough transform is used to identify all straight lines in the image and extract long straight lines located at the edges of horizontal and vertical markers.

[0041] S5, calculate the angle between the long straight lines located at the edges of the horizontal and vertical marks respectively, that is, the angle of rotation of the sling around the pin, and obtain the angle value of the sling rotation around the pin as a function of time during the data collection period.

[0042] In some specific embodiments, in S1, the transverse and longitudinal markings are located on the ear plate and the pin, with flat edges, and the marking color is the opposite of the pin's paint finish.

[0043] In some specific implementations, in S2, the frame dropping is uniform, with an interval of 5-6 seconds, preferably 6 seconds.

[0044] In some specific implementations, the video acquisition time in S2 is 2-4 minutes, preferably 3 minutes, but it can also be adjusted according to the measurement time range.

[0045] In some specific implementations, in S3, the strategy for image grayscale conversion is to make the grayscale values ​​of the marker portion and the background in the grayscale image closer to 0 and 255, respectively. This allows the marker portion and the background to have a greater color difference in the grayscale image, facilitating recognition.

[0046] In some specific implementations, in S4, the image preprocessing process is as follows: the grayscale image is filtered and denoised using median filtering, the image is binarized using a custom threshold, and finally, the Canny operator is used to edge-map the image. This part of the image preprocessing is common knowledge in the art and is not an innovative point of this invention; therefore, it will not be described in detail here.

[0047] In some specific implementations, in S4, the process of Hough transform identifying all straight lines in the image is as follows:

[0048] Calculate the angle θ between all lines and the horizontal axis, where 0 ≤ θ ≤ 180°. Define a vertical line as the line located at the edge of the vertical mark and whose angle with the horizontal axis is 70° < θ < 110°. Define a horizontal line as the line located at the edge of the horizontal mark and whose angle with the horizontal axis is 0 ≤ θ ≤ 20° or 160° ≤ θ ≤ 180°.

[0049] In some specific implementations, in S5, the process of calculating the included angle between the long straight lines located at the edges of the horizontal and vertical marks is as follows:

[0050] First, calculate the length of all horizontal and vertical lines, filter out the longest horizontal and vertical lines, and mark them with the first color. Then, filter out the longest (i.e., the second longest overall) horizontal and vertical lines after clearing, and mark them with the second color. Next, obtain the coordinates of the endpoints of all horizontal and vertical lines marked with the first and second colors, calculate the angle between them and the horizontal axis, and take the average of the angles between the first and second colored horizontal lines as the angle α between the horizontal marker line and the horizontal axis. Take the average of the angles between the first and second colored vertical lines as the angle β between the vertical marker line and the vertical axis. Then, the angle between the long lines located at the edges of the horizontal and vertical markers is...

[0051] In a more specific implementation, in S5, the first color is yellow.

[0052] In a more specific implementation, in S5, the second color is red.

[0053] Each of the above implementation methods can be implemented individually, or in any combination of two or more.

[0054] Example 1:

[0055] Taking a certain suspension bridge as an example, we select 45° of the suspension bridge. # The slings near the mid-span of the sling assembly are selected as the research object. First, marking lines are affixed to the pin shaft and lug plate of this sling, as shown below. Figure 2 As shown. The yellow markings are the opposite color of the blue paint, while the black markings are used to cover up uneven areas of the yellow markings and, because they are similar to blue, will not be easily identified. A 3-minute video recording was then taken at this location using a mobile phone. The video was then uniformly segmented at 6-second intervals to obtain a sequence of 30 images. Next, the images in the sequence were converted to grayscale using a custom single-channel method. Since the paint is blue and the markings and rust are yellow, the R (red) channel was selected for grayscale processing. A certain image after grayscale processing is shown below. Figure 3 As shown. Median filtering is then used to denoise the image, and a custom threshold is used for binarization. Finally, the Canny operator is used for edge detection, completing the image preprocessing steps. Finally, Hough transform is performed for line recognition and long line filtering, calculating the angle between the lines. The resulting image, after line recognition and long line filtering, is shown below. Figure 4 As shown.

[0056] After completing the above steps, the changes in the rotation angle of 30 samples over 3 minutes were plotted and compared. Figure 5 and Figure 6 As shown, this method is believed to be able to measure the rotation angle of the sling around the pin and its changing trend.

[0057] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for measuring the rotation angle of pin-connected suspension cables in a suspension bridge, characterized in that, Includes the following steps: S1, mark the pin and ear plate of the suspension bridge cable rotating around the lower pin and mark the horizontal and vertical directions respectively; S2, capture video of the marked part of the rotating part and extract frames to obtain a series of extracted image sequences; S3, use a custom single-channel method to convert the image sequence after frame extraction to grayscale; S4. After preprocessing the grayscale image, Hough transform is used to identify all straight lines in the image and extract long straight lines located at the edges of horizontal and vertical markers. S5, calculate the angle between the long straight lines located at the edges of the horizontal and vertical marks respectively, that is, the angle of rotation of the sling around the pin, and obtain the angle value of the rotation of the sling around the pin over time during the collection period; In S3, the strategy for image grayscale conversion is to make the grayscale values ​​of the marker portion and the background in the grayscale image closer to 0 and 255, respectively. In S4, the Hough transform identifies all straight lines in the image as follows: Calculate the angles of all lines relative to the horizontal axis. ,in, Define the angle between the vertical mark edge and the horizontal axis that satisfies The straight line is a vertical line, defined as located at the edge of the horizontal mark and whose angle with the horizontal axis satisfies... or The straight line is a horizontal straight line; In S5, the process of calculating the angle between the long lines located at the edges of the horizontal and vertical marks is as follows: First, calculate the length of all horizontal and vertical lines, then select the longest horizontal and vertical lines and mark them with the first color. Next, select the second longest horizontal and vertical lines and mark them with the second color. Then, obtain the coordinates of the endpoints of all horizontal and vertical lines marked with the first and second colors, calculate the angle between them and the horizontal axis, and take the average of the angles between the first and second colored horizontal lines as the angle between the horizontal marker line and the horizontal axis. The average angle between the vertical lines of the first and second colors is recorded as the angle between the vertical marker line and the vertical axis. The angle between the long straight lines located at the edges of the horizontal and vertical marks is . .

2. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S1, the horizontal and vertical markings have flat edges, and the marking color is the opposite of the pin's paint finish.

3. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S2, the frame skipping interval is 5-6 seconds.

4. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S2, the video capture time is 2-4 minutes.

5. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S4, the image preprocessing process is as follows: the grayscale image is filtered and denoised using the median filtering method, and the image is binarized using a custom threshold. Finally, the Canny operator is used to edge-map the image.

6. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S5, the first color is yellow.

7. The method for measuring the rotation angle of a pin-connected suspension cable in a suspension bridge according to claim 1, characterized in that, In S5, the second color is red.

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