Cable force measurement system, method and storage medium

Abstract

The present invention discloses a cable tension measurement system, method, and storage medium, wherein the system includes an acceleration sensor, a camera, and a computer. The acceleration sensor is fixedly connected to the camera, and the Z axis of the acceleration sensor is parallel to the vertical direction of the camera imaging target surface. The acceleration sensor and the camera are both electrically connected to the computer. The cable tension measurement system according to the above technical solution eliminates interference frequencies by using the acceleration sensor fixedly connected to the camera. It can be directly installed on the bridge deck to measure the cable tension in a non-contact manner. It is suitable for cross-sea or cross-river bridges that cannot provide a relatively stable measurement environment for the camera. It is easy to implement and has low implementation cost.

Description

Technical Field

[0001] The present invention relates to the technical field of structural health monitoring, and in particular to a cable force measurement system, method and storage medium. Background Art

[0002] The measurement of cable tension is an important part of the acceptance of bridge projects. As the main force-transmitting component of the bridge, the stress state of the cable directly reflects the health status of the entire bridge and is a core indicator of bridge monitoring.

[0003] In recent years, non-contact cable tension measurement using camera images has gained widespread application due to its advantage of simultaneous full-field, multi-target measurement. Existing methods often require cameras to be mounted beneath bridges or on other stable surfaces. However, such mounting conditions are not always feasible for large river-sea bridges. Considering mounting the cameras on the bridge deck, while not disrupting traffic, bridge deck vibrations can interfere with the cable vibration signals captured by the cameras. Furthermore, long-span bridges generally experience significant wind loads on the deck, which can lead to the frequency peaks extracted from the image signals being mixed with noise from bridge deck and ambient vibrations. Without prior knowledge of this, cable frequency extraction and cable tension calculations are hampered. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a cable force measurement system that can eliminate interference frequencies, has low operating costs and is easy to set up.

[0005] Another object of the present invention is to provide a cable tension measurement method and a storage medium storing a computer program that instantiates the method.

[0006] Technical solution: The rope force measurement system described in the present invention includes: an acceleration sensor, a camera and a computer. The acceleration sensor is fixedly connected to the camera, the vertical axis of the target surface of the camera is parallel to the Z axis of the acceleration sensor, and the acceleration sensor and the camera are electrically connected to the computer.

[0007] The cable force measurement method of the present invention comprises the following steps:

[0008] S1: Fix the camera and the acceleration sensor together, adjust the camera focus to the measured cable, and let the camera and the acceleration sensor synchronously and continuously collect data from the measured cable for a period of time;

[0009] S2: Real-time tracking of the cable in the digital image captured by the camera, extracting the pixel displacement time history of the cable and converting it into a camera velocity signal through the first-order derivative;

[0010] S3: Performing Fourier transform on the camera speed signal and the sensor speed signal to obtain frequency spectrum curves of the camera speed signal and the sensor speed signal;

[0011] S4: Compare the frequency spectrum curve of the camera speed signal and the frequency spectrum curve of the sensor speed signal, and record the peak that appears only in the frequency spectrum curve of the camera speed signal as the vibration frequency of the cable;

[0012] S5: Calculate the cable tension based on the cable's vibration frequency and frequency method formula.

[0013] Furthermore, in step S2, a digital image correlation method is used to track the cable in real time.

[0014] The storage medium of the present invention stores a computer program, and the computer program is configured to implement the above-mentioned rope force measurement method when running.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following advantages: the interference frequency is eliminated by the acceleration sensor fixedly connected to the camera, and the cable force can be measured directly on the bridge deck in a non-contact manner, which is easy to implement and has low implementation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of a cable force measurement system according to an embodiment of the present invention;

[0017] Figure 2 is a flow chart of a cable force measurement method according to an embodiment of the present invention;

[0018] Figure 3 2 is an amplitude-frequency curve diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] Reference Figure 1 According to an embodiment of the present invention, the rope force measurement system includes an acceleration sensor 200, a camera 100 and a computer 300. The acceleration sensor 200 is fixedly connected to the camera 100. The Z axis of the acceleration sensor 200 is parallel to the vertical direction of the imaging target surface of the camera 100. The acceleration sensor 200 and the camera 100 are both electrically connected to the computer 300.

[0021] According to the cable tension measurement system described above, since the accelerometer 200 is fixedly connected to the camera 100, when the camera 100 is mounted on the bridge deck, it can detect the frequencies transmitted to the camera 100 by the vibrations of the bridge deck and the surrounding environment, i.e., the noise frequencies in the images captured by the camera 100 showing the vibrations of the cable 400. By analyzing the vibration frequencies of the cable 400 in the images captured by the camera 100 and combining them with the vibration frequencies detected by the accelerometer 200, the common frequencies between the two are the noise frequencies caused by the bridge and the surrounding vibrations, while the vibration frequencies detected only by the camera 100 are the vibration frequencies of the cable 400 itself. This measurement system can be directly mounted on the bridge deck to test the cable 400 tension without stopping traffic, or by mounting the camera 100 on more stable ground outside the bridge deck. It is suitable for measuring cable tension on river and sea crossing bridges. Measuring the cable tension of the cable 400 with the camera 100 eliminates the need to install sensors on the cable 400, reducing the measurement difficulty, shortening the testing cycle, and saving manpower, material, and financial resources required for the measurement.

[0022] In actual operation, in order to reduce the difficulty of data processing, when the acceleration sensor 200 is fixed on the camera 100, the X-axis or Y-axis of the acceleration sensor 200 needs to be in the same direction as the X-axis or Y-axis of the imaging target surface of the camera 100. During calculation, the amplitude-frequency curve of the vibration of the cable 400 obtained by the vibration image of the cable 400 detected by the camera 100 can be directly compared with the amplitude-frequency curve obtained by the acceleration sensor 200 to obtain the vibration frequency of the cable 400.

[0023] Reference Figure 2 According to the cable force measurement system of the embodiment of the present invention, the cable force of the cable 400 can be measured by the following method:

[0024] S1: The camera 100 and the acceleration sensor 200 are fixedly connected together, the camera 100 is adjusted to focus on the measured cable 400, and the camera 100 and the acceleration sensor 200 synchronously and continuously collect data from the measured cable 400 for a period of time;

[0025] S2: Tracking the cable 400 in the digital image captured by the camera 100 in real time, extracting the pixel displacement time history of the cable 400 and converting it into a velocity signal of the camera 100 through first-order derivation;

[0026] S3: Performing Fourier transform on the camera 100 velocity signal and the sensor velocity signal to obtain frequency spectrum curves of the camera 100 velocity signal and the sensor velocity signal;

[0027] S4: comparing the frequency spectrum curve of the speed signal of the camera 100 and the frequency spectrum curve of the speed signal of the sensor, and recording the peak value that appears only in the frequency spectrum curve of the speed signal of the camera 100 as the vibration frequency of the cable 400;

[0028] S5: Calculate the tension of the cable 400 according to the vibration frequency of the cable 400 and the frequency method formula.

[0029] In this embodiment, the camera 100 and the acceleration sensor 200 synchronously collect data continuously for 2 minutes. The computer 300 continuously tracks the calculation area of the cable 400 in the image captured by the camera 100 using digital image correlation (DIC) to extract the pixel displacement of the cable 400 in the horizontal direction of the image. The correlation function uses the zero-mean normalized sum of squared difference (ZNSSD) function, and the formula is as follows:

[0030]

[0031] Where f(x) and g(x) represent the reference image and the deformed image, respectively, where x = (x, y, 1). T Grayscale of the position; Represents an image subregion The average gray value of Represents an image subregion The average gray value of ξ=(Δx,Δy,1) T are the local coordinates of the pixel in each sub-area; w(ξ;Δp) and w(ξ;p) represent shape functions. Considering that the deformation of the cable 400 is very small, especially in long-distance image measurement, it is generally sufficient to use a zero-order shape function, that is, it is assumed that the target only undergoes rigid body translation. In this case, for C ZNSSD The shape function in the expression can be expressed as:

[0032]

[0033] Where p = (u, v) T is the pre-calculated displacement vector of the target subregion. u and v represent the horizontal and vertical displacements, respectively. However, in most cases, a zero-order shape function cannot accurately describe the shape change of the target image subregion after deformation. Therefore, a first-order shape function (which allows the deformed image subregion to undergo rigid body rotation, shear, or expansion deformation, or a combination thereof) is more commonly used:

[0034]

[0035]

[0036] In actual situations, other correlation functions may also be used, such as the normalized cross-correlation function (NCC).

[0037] Among them, the frequency method formula in step S5 is:

[0038]

[0039] where f n represents the nth order frequency, W represents the mass per meter of the cable, i.e., the linear density, L represents the length of the cable 400, E represents the elastic modulus of the cable 400 material, and I represents the moment of inertia. Figure 3 In this embodiment, by comparing the amplitude-frequency curve obtained by the camera 100 with the amplitude-frequency curve obtained by the acceleration sensor 200, the vibration frequencies of the cable 400 can be obtained as f1=0.6049, f2=1.207, f3=1.808, f5=3.038, f6=3.636, and f7=4.235. These frequencies are respectively substituted into the frequency method formula to obtain multiple T values. The average of these T values is the final cable force measurement value of the cable 400.

[0040] According to the storage medium of the embodiment of the present invention, a computer program instantiating the above-mentioned cable tension method is stored. The computer 300 can read and run the computer program in the storage medium, perform the above-mentioned processing on the data collected by the camera 100 and the acceleration sensor 200, and obtain the cable tension of the bridge cable 400.

Claims

1. A cable force measurement system, characterized in that: include: An acceleration sensor, a camera, and a computer; the camera is used to capture vibration images of the cable; the acceleration sensor is fixedly connected to the camera and is used to measure the camera's vibration; the Z axis of the acceleration sensor is parallel to the vertical direction of the camera's imaging target surface; the computer is electrically connected to the camera and the acceleration sensor and is used to process the captured images and acceleration signals to calculate the cable tension; The acceleration sensor is used to detect the frequency of bridge deck and environmental vibrations transmitted to the camera, and by combining it with image data, the interference frequency is eliminated, thereby accurately measuring the vibration frequency of the cable; The cable force measurement method includes the following steps: S1: Fix the camera and the acceleration sensor together, adjust the camera focus to the measured cable, and let the camera and the acceleration sensor synchronously and continuously collect data from the measured cable for a period of time; S2: Real-time tracking of the cable in the digital image captured by the camera is performed, and the pixel displacement time history of the cable is extracted and converted into a camera velocity signal through first-order derivation; the X-axis or Y-axis of the acceleration sensor is in the same direction as the X-axis or Y-axis of the imaging target surface of the camera, so that the amplitude-frequency curve of the cable vibration obtained from the cable vibration image detected by the camera is directly compared with the amplitude-frequency curve obtained by the acceleration sensor to obtain the vibration frequency of the cable; S3: Performing Fourier transform on the camera speed signal and the sensor speed signal to obtain frequency spectrum curves of the camera speed signal and the sensor speed signal; S4: Compare the frequency spectrum curve of the camera speed signal and the frequency spectrum curve of the sensor speed signal, and record the peak that appears only in the frequency spectrum curve of the camera speed signal as the vibration frequency of the cable; S5: Calculate the cable tension according to the vibration frequency of the cable and the frequency method formula; In step S2, the cable is tracked in real time using a digital image correlation method. The correlation function in the digital image correlation method uses a zero-mean normalized least square distance function, and a first-order shape function is used to describe the deformation pattern of the target area in the image.

2. A storage medium storing a computer program, characterized in that: The computer program is configured to implement the cable force measurement method according to claim 1 when executed.

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