Measurement method of dynamic characteristics of flexible cables

Abstract

The present invention provides a method for measuring the dynamic characteristics of a flexible cable, which is used in a dynamic measurement system. The dynamic measurement system includes two cameras and a moving platform. The method for measuring the dynamic characteristics of a flexible cable includes: setting a background wall and setting coding points on the background wall; obtaining a measurement range and determining the distance between two cameras; adjusting the parameters of the camera to obtain clear imaging; calibrating the camera according to the coding points; setting a marker on the flexible cable; fixing one end of the flexible cable and connecting the other end of the flexible cable to the moving platform; the moving platform moves up and down; the camera collects marker data; and the dynamic measurement system stops after recording a preset number of cycle data. By setting coding points on the background wall, determining the camera distance, adjusting the camera parameters of the camera, calibrating the camera, setting markers on the cable, fixing and connecting the cable to the moving platform, and collecting marker data, the problem of inaccurate measurement caused by the sensor affecting the cable characteristics in the traditional measurement method is effectively solved.

Description

Technical Field

[0001] The invention belongs to the field of testing and measurement, and in particular relates to a method for measuring the dynamic characteristics of a flexible cable. Background Art

[0002] Tethered UAVs are suitable for long-term missions such as communication relay, reconnaissance and surveillance due to their excellent endurance. Tethered cables can provide power supply for tethered UAVs to ensure their endurance and transmit information at the same time. However, as the load of the UAV, the tethered cable will also affect the efficiency of the entire system. Research on the dynamic characteristics between the tethered cable and the UAV can provide technical support for the stability of the tethered UAV system.

[0003] The tethered cable is mostly in a dynamic response state during the actual flight of the tethered UAV, and the simulation and calculation of the dynamic characteristics of the UAV-cable system are difficult. In addition, as a flexible object, the cable is relatively inaccurate in measurement by traditional displacement, velocity and other sensors.

[0004] Therefore, a method for measuring the dynamic characteristics of a flexible cable that can simulate and calculate the dynamic characteristics of the drone-cable system and improve the measurement accuracy has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] An embodiment of the present invention provides a method for measuring dynamic characteristics of a flexible cable.

[0006] In view of this, a first aspect of the present invention proposes a method for measuring the dynamic characteristics of a flexible cable, which is used in a dynamic measurement system. The dynamic measurement system includes two cameras and a moving platform. The method for measuring the dynamic characteristics of the flexible cable includes: setting a background wall and setting coding points on the background wall; obtaining a measurement range and determining the distance between two cameras; adjusting the parameters of the camera to obtain clear imaging; calibrating the camera according to the coding points; setting a marker on the flexible cable; fixing one end of the flexible cable and connecting the other end of the flexible cable to the moving platform; the moving platform moves up and down; the camera collects marker data; and the dynamic measurement system stops after recording data for a preset number of cycles.

[0007] Furthermore, there are no less than 5 coding points set on the background wall.

[0008] Furthermore, the distance between the two cameras is a measurement distance, and the measurement distance is 11 meters.

[0009] Furthermore, the camera parameters of the camera include measurement format, focal length and aperture.

[0010] Furthermore, the camera calibration includes intrinsic parameter calibration and extrinsic parameter calibration.

[0011] Furthermore, the thickness of the marker is less than 0.1 mm.

[0012] Furthermore, the flexible cable is fixed in such a way that the marker is facing the dynamic measurement system.

[0013] Furthermore, the up and down reciprocating motion of the moving platform is periodic.

[0014] Furthermore, the preset number of cycles is at least three cycles.

[0015] Furthermore, the method for measuring the dynamic characteristics of the flexible cable also includes using a software system to perform measurement acquisition, storage and data analysis.

[0016] The beneficial effects brought by the present invention are as follows: a three-dimensional dynamic measurement system can be used, marking points are set on the cable, and the motion characteristics of the discrete marking points are measured using optical measurement methods, and the motion characteristics of the moving marking points are fitted to the motion characteristics of the entire cable. The three-dimensional dynamic measurement system includes hardware parts such as cameras, lenses, light sources, control systems, support systems, long-distance transmission, workstations, calibration rulers, marking points, and software parts such as data processing. The system combines digital image correlation technology and binocular stereo vision technology to track target points on the surface of objects to achieve dynamic measurement of three-dimensional coordinates and displacements of key points on the surface of objects during movement. The marking points of this method can use paper labels with special patterns, which are light in weight, easy to install, and do not affect the characteristics of the measured object. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 One of the flow charts of the method for measuring the dynamic characteristics of a flexible cable provided in an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of a three-dimensional dynamic measurement system provided by an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of the comparison of results when the fixed point is located at the wave crest is provided for the embodiment of the present invention;

[0020] Figure 4 A schematic diagram of comparing results when a fixed point is located at a trough is provided for an embodiment of the present invention;

[0021] Figure 5 A schematic diagram of adjusting camera parameters of a camera is provided for an embodiment of the present invention;

[0022] Figure 6 The present invention provides an effect diagram of a marker being pasted.

[0023] 1 camera, 2 moving platform, 3 flexible cable, 4 marker, 5 coding point. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention proposes a method for measuring the dynamic characteristics of a flexible cable, such as Figure 1 As shown, it is used for a dynamic measurement system, the dynamic measurement system includes two cameras and a moving platform, and the method for measuring the dynamic characteristics of the flexible cable includes:

[0026] S101: Setting a background wall and setting coding points on the background wall;

[0027] S103: Acquire a measurement range and determine a distance between two cameras;

[0028] S105: adjusting the parameters of the camera to obtain clear imaging;

[0029] S107: Calibrate the camera according to the code points;

[0030] S109: Setting markers on the flexible cable;

[0031] S111: Fix one end of the flexible cable and connect the other end of the flexible cable to the moving platform;

[0032] S113: The moving platform moves up and down;

[0033] S115: The camera collects marker data;

[0034] S117: After recording the data of a preset number of cycles, the dynamic measurement system stops.

[0035] In this embodiment, by setting coding points on the background wall, determining the camera spacing, adjusting the camera parameters of the camera, calibrating the camera, setting markers on the cable, fixing and connecting the cable to the moving platform, and collecting marker data, a series of operations can be performed to measure the dynamic characteristics of the flexible cable using a dynamic measurement system, which effectively solves the problem of inaccurate measurement caused by the sensor affecting the cable characteristics in the traditional measurement method, and can accurately obtain the motion state of the cable at different times, providing reliable data support for the study of the dynamic characteristics of the cable and the drone in the tethered drone system, which helps to improve the stability of the tethered drone system. In actual application scenarios, for example, when the tethered drone performs a long-term air mission, accurate measurement of the dynamic characteristics of the cable can ensure the stability of power supply and information transmission, avoid system failures caused by unknown dynamic characteristics of the cable, and improve the success rate and safety of mission execution. At the same time, this measurement method provides basic data for the subsequent optimization design of the cable, the improvement of the drone flight control strategy, etc., and promotes the further development of tethered drone technology.

[0036] Furthermore, there are no less than 5 coding points set on the background wall.

[0037] In this embodiment, no less than 5 coding points are set on the background wall, which provides sufficient reference points for camera calibration, helps to improve the accuracy of camera calibration, and then improves the measurement accuracy of the entire measurement system, so that the measurement results are closer to the actual dynamic characteristics of the flexible cable. More coding points can better correct the distortion of the camera, especially when the measurement range is large, and the spatial coordinate system can be determined more accurately, so that when measuring the flexible cable, the three-dimensional coordinates of the marker can be obtained more accurately, reducing the measurement error caused by the inaccurate coordinate system, whether it is for the measurement of the cable shape or the analysis of the movement trend, it is more reliable, and the measurement advantage in complex environments is more obvious.

[0038] Furthermore, the distance between the two cameras is a measurement distance, and the measurement distance is 11 meters.

[0039] In this embodiment, the distance between the cameras is determined to be 11 meters based on the measurement distance, which ensures the stability and firmness of the measuring head, while taking into account the requirements of measurement range, acquisition frequency and measurement performance, which helps to obtain accurate flexible cable image information under stable measurement conditions and improve the reliability and effectiveness of the measurement. Appropriate camera spacing can optimize the binocular stereoscopic vision effect, so that the two cameras can better capture the stereoscopic information of the markers on the cable and accurately calculate the three-dimensional coordinates and displacement of the markers. At this specific distance, flexible cables of different lengths and motion states can be effectively measured, reducing the measurement blind area or measurement error caused by improper camera distance, and is suitable for tethered drone cable measurement in various models and application scenarios.

[0040] Furthermore, the camera parameters of the camera include measurement format, focal length and aperture.

[0041] In this embodiment, the camera's measurement format, focal length, aperture and other parameters are adjusted to obtain clear imaging, ensuring that the details of the markers on the flexible cable can be clearly captured, improving the accuracy of the measurement data, and laying the foundation for the subsequent accurate analysis of the dynamic characteristics of the cable. Clear imaging helps to more accurately identify the position changes of the markers, which is particularly important when analyzing the slight displacement and shape changes of the cable. The appropriate measurement format can cover the range of cables that need to be measured, and the adjustment of the focal length and aperture can adapt to different lighting conditions and the distance between the cable and the camera, ensuring that high-quality image data can be obtained in various environments, improving the adaptability and stability of the measurement system, and can work effectively in both indoor and outdoor environments.

[0042] Furthermore, the camera calibration includes intrinsic parameter calibration and extrinsic parameter calibration.

[0043] In this embodiment, the camera calibration includes internal parameter calibration and external parameter calibration. By accurately obtaining the internal and external parameters of the camera, an accurate spatial coordinate system can be established to achieve accurate three-dimensional coordinate measurement of the markers on the flexible cable, thereby accurately obtaining the dynamic characteristics of the cable and improving the accuracy and reliability of the measurement. The internal parameter calibration can correct the optical and geometric characteristics inside the camera, such as lens distortion, pixel size, etc., and the external parameter calibration determines the position and direction of the camera in space. The combination of the two enables the measurement system to accurately convert two-dimensional image information into three-dimensional spatial information. During the movement of the flexible cable, accurate spatial coordinate measurement can accurately calculate the dynamic characteristics of the cable, such as the degree of bending and tensile deformation, providing accurate data support for studying the interaction between the cable and the drone, and helping to optimize the design and control strategy of the tethered drone system.

[0044] Furthermore, the thickness of the marker is less than 0.1 mm.

[0045] In this embodiment, the thickness of the marker is less than 0.1 mm, it is light and easy to install, and it does not affect the characteristics of the flexible cable itself, ensuring that the natural dynamic behavior of the cable is not disturbed during the measurement process, thereby obtaining more realistic and accurate measurement results, while being easy to operate and apply. The thin marker has little effect on the quality and aerodynamic performance of the cable. In the actual flight scenario of the tethered drone, it will not change the stress state and motion characteristics of the cable, ensuring that the measurement data can truly reflect the dynamic situation of the cable under normal working conditions. Its easy installation feature allows markers to be set quickly and accurately on cables of different models and sizes, improving the versatility and operability of the measurement method and reducing measurement costs and time.

[0046] Furthermore, the flexible cable is fixed in such a way that the marker is facing the dynamic measurement system.

[0047] In this embodiment, the cable fixing method ensures that the marker is facing the dynamic measurement system, ensuring that the camera can accurately capture the motion information of the marker, reducing the measurement error caused by factors such as the angle deviation of the marker, and improving the accuracy and reliability of the measurement data. During the measurement process, the facing state of the marker enables the camera to obtain the clearest and most accurate image of the marker, and both the displacement and shape change of the marker can be accurately recorded. This is crucial for analyzing the dynamic characteristics of the cable, such as the motion trajectory and vibration frequency, and can provide high-precision data for the study of the dynamic characteristics of the tethered drone system, which helps to optimize the flight control algorithm of the drone and improve flight stability and safety.

[0048] Furthermore, the up and down reciprocating motion of the moving platform is periodic.

[0049] In this embodiment, the up and down reciprocating motion of the moving platform is periodic, simulating the dynamic conditions that the cable may encounter during the actual flight of the tethered UAV, making the measurement data more representative, and accurately reflecting the dynamic characteristics of the flexible cable under actual working conditions, providing effective data for system research. Periodic motion can reproduce the force changes of the cable under different flight attitudes and environmental conditions. Through multiple periodic measurements, the dynamic response of the cable under various typical conditions can be obtained, including the motion characteristics under different frequencies and amplitudes. This helps to further study the relationship between the dynamic characteristics of the cable and the flight performance of the tethered UAV, and provide a basis for optimizing the flight parameters of the UAV, improving energy efficiency, etc., and also provides a reference for the material selection and structural design of the cable.

[0050] Furthermore, the preset number of cycles is at least three cycles.

[0051] In this embodiment, the preset number of cycles is at least three cycles, which can obtain sufficient measurement data and reduce the impact of accidental errors. By analyzing the data of multiple cycles, the dynamic characteristics of the flexible cable can be more accurately grasped, and the reliability and stability of the measurement results can be improved. The data of multiple cycles can cover the situation of the cable in different starting phases and motion states. By statistically analyzing these data, more accurate information such as the average characteristics and fluctuation range of the cable movement can be obtained. When studying the long-term stability and fatigue characteristics of the cable, a sufficient number of cycles can provide more comprehensive data support, help predict the service life and reliability of the cable, and provide a scientific basis for the maintenance and management of the tethered drone system.

[0052] Furthermore, the method for measuring the dynamic characteristics of the flexible cable also includes using a software system to perform measurement acquisition, storage and data analysis.

[0053] In this embodiment, the software system is used for measurement acquisition, storage and data analysis, which realizes the automation of the measurement process and the efficiency of data processing, improves the measurement efficiency and the accuracy of data analysis, and facilitates in-depth research on the dynamic characteristics of flexible cables. The software system can collect image data taken by the camera in real time to ensure the timeliness and integrity of the data. In terms of storage, a large amount of measurement data can be managed in an orderly manner, which is convenient for subsequent inquiries and calls. The data analysis function can use a variety of algorithms to process the measurement data, such as digital image correlation technology, etc., to quickly and accurately extract the dynamic characteristic parameters of the cable, such as displacement, velocity, acceleration, etc., and can also perform data visualization to intuitively display the motion state of the cable, providing researchers with more convenient and efficient research tools, and accelerating the research and development process of tethered drone related technologies.

[0054] Furthermore, the measuring head is used to collect image information of the object under test as it responds to temperature and vibration, including camera 1, lens, and beam. The measuring head is mainly used to record sequential two-dimensional images during the experiment. The measurement format is 2000mm to 10000mm, taking into account the requirements of measurement range, acquisition frequency, and measurement performance. Marking point: its thickness is required to be less than 0.1mm, and the corresponding pasting method is different for different models. The basic requirement for fixing the marking point is that it cannot undergo relative displacement changes with the object under test during the test, otherwise it will affect the measurement results. Software system: used for measurement acquisition, storage, data analysis, etc.

[0055] Furthermore, the measurement method in this patent was used to conduct an experiment, and the measured test data was compared with the results of the model calculation. Two states were selected in which the moving end points of the flexible cable 3 were respectively at the highest point and the lowest point. The comparison results are as follows: Figure 2 and Figure 3 As shown, the dots are experimental measurement results, and the lines are theoretical calculation results. From the comparison of the results in the figure, it can be seen that the overall trend and change law of the shape of the flexible cable 3 measured during the movement are consistent with the theoretical calculation results. This measurement method can effectively measure the shape of flexible objects such as the flexible cable 3 in space at different times, and the movement state can be obtained through continuous measurement.

[0056] Furthermore, parameter calibration work needs to be carried out in the system measurement preparation stage, such as Figure 2 As shown, the calibration steps are as follows:

[0057] Step 1: Paste the marker 4 on the surface of the object to be measured and paste the coding point 5 on the wall.

[0058] Step 2: Calculate the distance between the two cameras 1 according to the measurement range and fix them to the beam. The measurement distance is about 11 meters, ensuring that the measuring head is stable and firm.

[0059] Step 3: If Figure 5As shown, adjust the format, adjust the measurement format, focal length, aperture and other parameters to make the camera 1 image clear.

[0060] Step 4: Calibrate camera 1, obtain internal and external parameters, and establish a spatial coordinate system.

[0061] like Figure 4 As shown, the intrinsic parameters of the left and right cameras 1 are first calibrated using a cross ruler, and then the extrinsic parameters of the two cameras 1 are calibrated using the coding point 5 of the wall.

[0062] Paste coding points 5 (at least 5) on the wall surface around the object to be measured;

[0063] The cross ruler is 12 meters away from the left camera (on the ground), and 8 postures are placed to complete the calibration of the parameters of the left camera 1;

[0064] The cross ruler is 12 meters away from the right camera (on the ground), and 8 postures are placed to complete the internal parameter calibration of the right camera 1;

[0065] The coordinates of all coded points 5 on the wall in step (1) are obtained using XTDP photogrammetry technology and used as global points.

[0066] Place the ruler at a distance of about 111 meters from the camera, with the left and right cameras 1 facing the ruler. The left and right cameras 1 synchronously capture an image of the ruler and the marker points around the object being measured. Import the global point in step (4) into the calibration software interface, and use the global point calibration to complete the external parameter calibration.

[0067] After completing the parameter calibration, you can start the measurement work. The measurement steps are as follows:

[0068] Step 1: Evenly paste several markers 4 on the flexible cable 3. The effect of the markers 4 is as follows: Figure 6 shown.

[0069] Step 2: Fix a section of the flexible cable 3 with the marker 4 attached to it at a fixed point.

[0070] Step 3: The other end of the flexible cable 3 is fixed on the ground moving platform 2.

[0071] Step 4: Adjust the direction of the flexible cable 3 and make the marker 4 face the dynamic measurement system.

[0072] Step 5: Set the moving platform 2 to reciprocate up and down, and start the ground moving platform 2;

[0073] Step 6: The dynamic measurement system starts to collect data, stops recording data after measuring data for no less than three cycles, and stops the ground dynamic platform 2.

[0074] Step 7: Complete the test and export and organize the test data.

[0075] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for measuring the dynamic characteristics of a flexible cable, characterized in that: For a dynamic measurement system, the dynamic measurement system includes two cameras and a moving platform, and the flexible cable dynamic characteristic measurement method includes: Setting a background wall and setting coding points on the background wall; Obtaining a measurement range and determining a distance between the two cameras; Adjusting the parameters of the camera to obtain clear imaging; Calibrate the camera according to the code points; Setting markers on the flexible cable; fixing one end of the flexible cable and connecting the other end of the flexible cable to the moving platform; The moving platform moves up and down; The camera collects the marker data; After recording data for a preset number of cycles, the dynamic measurement system stops.

2. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: There are no less than 5 coding points set on the background wall.

3. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The distance between the two cameras is the measuring distance, and the measuring distance is 11 meters.

4. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The camera parameters of the camera include measurement format, focal length and aperture.

5. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The camera calibration includes internal parameter calibration and external parameter calibration.

6. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The thickness of the marker is less than 0.1 mm.

7. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The flexible cable is fixed in such a way that the marker faces the dynamic measurement system.

8. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The up and down reciprocating motion of the moving platform is periodic.

9. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: The preset number of cycles is at least three cycles.

10. The method for measuring the dynamic characteristics of a flexible cable according to claim 1, characterized in that: It also includes the use of software systems for measurement acquisition, storage and data analysis.

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