An Autonomous UAV Inspection Method and System for Testing the Internal Forces of Cable-Bearing Bridges (Tensile / Suspension Cables)

Abstract

This invention relates to the field of non-destructive testing technology for bridges, and discloses an autonomous UAV inspection method and system for testing the internal forces of cable-stayed bridge tension / suspender cables. The method includes guiding the UAV to the spatial area where the target docking platform is located and completing autonomous docking; acquiring distance spectrum data at different scanning angles to construct an angle-distance matrix; performing calibration scanning to determine the optimal observation angle; performing static observation of the target tension / suspender cable to obtain vibration response signals; extracting the vibration frequency characteristics of the target tension / suspender cable; calculating the cable force of the target tension / suspender cable and outputting the cable force ratio to complete the detection task of a single observation point; and flying to the next docking platform according to the inspection path, repeating the inspection steps until all preset observation points are detected. This invention effectively overcomes problems such as wind disturbance, UAV vibration, insufficient endurance, and inaccurate positioning, significantly improving the detection accuracy and inspection efficiency of tension / suspender cable structures.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for bridges, and more specifically, to an unmanned aerial vehicle (UAV) autonomous inspection method and system for testing the internal forces of tension / suspender cables in cable-stayed bridges. Background Technology

[0002] With the widespread construction of bridges, especially large bridges such as cable-stayed bridges and suspension bridges, their tension / suspending cables, as key load-bearing components, have a significant impact on the safety and service performance of bridge structures. Tension / suspending cables typically span large distances, are located at high positions, are numerous, and have complex arrangements. Manual inspections suffer from high operational risks, low efficiency, insufficient coverage, and limited inspection accuracy. Especially under extreme conditions such as earthquakes, strong winds, and typhoons, the vibration characteristics of tension / suspending cables may change significantly, making it difficult to detect potential damage or loosening issues in a timely manner, thus increasing structural safety risks.

[0003] In recent years, drone technology has been increasingly applied in the field of structural inspection. Drones can carry various sensors (such as cameras, lidar, infrared sensors, and microwave radar) for detecting structural appearance, cracks, deformation, and vibration. Existing methods primarily involve drones hovering in the air to observe and collect data from key structural components. While these methods improve the flexibility of inspection to some extent, they still have significant limitations:

[0004] 1) Wind has a significant impact: Hovering drones are easily affected by wind, eddies and disturbances in the surrounding environment, which can cause jitter or errors in sensor observation data.

[0005] 2) Vibration interference from the drone itself: The drone generates its own vibration when flying or hovering. The inertial and dynamic interference will affect the measurement accuracy of sensors such as shooting, lidar and millimeter-wave radar, and increase the complexity of subsequent data processing and analysis.

[0006] 3) Positioning accuracy limitations: In high-altitude or complex environments, the positioning accuracy of UAVs is insufficient, which may lead to repeated observations or missed measurements, reduce detection efficiency, and affect the accuracy of transforming structural responses such as measured displacements into responses in the structural coordinate system.

[0007] 4) Battery life limitation: Due to battery capacity limitations, the hovering detection time of drones is limited, making it difficult to cover multiple detection points on large structures;

[0008] 5) Complex operation and low efficiency: In multi-point or multi-UAV joint inspection scenarios, hovering observation requires manual or semi-automatic control, which is complex and time-consuming, making it difficult to achieve long-term continuous inspection or multi-UAV collaborative inspection.

[0009] It is evident that existing UAV structural inspection methods are insufficient to meet the demands of multi-point, high-precision, high-efficiency, and long-term continuous monitoring of large structures. This is especially true for cable-stayed bridges and long-span structures, which require a large number of suspension cable components with complex spatial distribution, resulting in significant inspection needs. Therefore, a UAV inspection system is urgently needed to improve the stability of acquired inspection data, enhance the accuracy of data analysis, support collaborative work among multiple UAVs and sensors, and achieve efficient and continuous inspection. Summary of the Invention

[0010] To address the problems in related technologies, this invention proposes an autonomous UAV inspection method and system for testing the internal forces of cable-stayed bridge tension / suspension cables, thereby overcoming the aforementioned technical problems in existing related technologies.

[0011] Therefore, the specific technical solution adopted by the present invention is as follows:

[0012] According to one aspect of the present invention, an autonomous inspection method for unmanned aerial vehicles (UAVs) for testing the internal forces of cable-stayed bridge tension / suspension cables is provided, comprising the following steps:

[0013] S1. Guide the drone to the space area where the target docking platform is located according to the preset inspection path, and automatically identify the characteristic mark of the M-shaped support on the target docking platform based on the image information of the target docking platform;

[0014] S2. Based on the characteristic markings and image information of the M-shaped platform, the position and attitude of the UAV are corrected until the UAV lands on the target docking platform from the spatial area where the target docking platform is located, thus completing the autonomous docking of the UAV.

[0015] S3. Drive the millimeter-wave radar to perform angle scanning in the vertical plane, acquire range spectrum data at different scanning angles, and construct an angle-range matrix based on the range spectrum data at different scanning angles;

[0016] S4. Based on the peak energy at each scanning angle in the angle-range matrix, determine the reference observation angle, and drive the millimeter-wave radar to perform calibration scanning according to the reference observation angle. At the same time, determine the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle.

[0017] S5. Lock the observation attitude of the millimeter-wave radar according to the optimal observation angle, and use the millimeter-wave radar to perform static observation of the target cable-stayed / suspension cable to obtain the vibration response signal; extract the vibration frequency characteristics of the target cable-stayed / suspension cable based on the vibration response signal;

[0018] S6. Based on the vibration frequency characteristics of the target cable-stayed / suspended cable, and combined with the pre-imported structural parameters of the target cable-stayed / suspended cable, calculate the cable force of the target cable-stayed / suspended cable, and output the cable force ratio to complete the detection task of a single observation point.

[0019] S7. After the detection task of a single observation point is completed, the UAV exits the detection state, releases the dock and takes off again, flies to the next docking platform according to the inspection path, and repeats S2-S7 until the detection tasks of all preset observation points are completed.

[0020] Furthermore, the step of guiding the UAV to the spatial area where the target docking platform is located according to the preset inspection path, and automatically identifying the characteristic markings of the M-shaped support on the target docking platform based on the image information of the target docking platform, includes the following steps:

[0021] S11. Based on the bridge structure and inspection requirements of the target cable-stayed bridge, several drone docking platforms are deployed on the bridge, and the inspection path of the drones is automatically planned according to the location information of the drone docking platforms.

[0022] S12. According to the autonomously planned drone inspection path, control the drone to fly to the preset height of the space area where the target docking platform is located;

[0023] S13. Use drones to collect image information of the target docking platform and automatically identify the characteristic markings of the M-shaped platform on the target docking platform based on the image information.

[0024] The characteristic feature of the M-shaped support is the black and white circular coatings spaced apart on the surface of the M-shaped support, and the spaced black and white circular coatings are used for the visual positioning of the UAV.

[0025] Furthermore, after the drone completes its autonomous docking, it also includes: wirelessly charging the drone's battery using the wireless charging output on the target docking platform and the wireless charging input on the drone's landing gear.

[0026] Furthermore, the process of driving the millimeter-wave radar to perform angular scanning in the vertical plane, acquiring range spectrum data at different scanning angles, and constructing an angle-range matrix based on the range spectrum data at different scanning angles includes the following steps:

[0027] S31. After the UAV completes autonomous docking and enters a stable state, the millimeter-wave radar on the UAV is used to detect the target cable-stayed / suspension cable, obtain the target echo signal and perform range signal processing to form range spectrum data. The range spectrum data is data that characterizes the energy distribution of the target at different distance positions with the range unit as the horizontal axis and the echo energy as the vertical axis.

[0028] S32. Within a preset distance range, retrieve the peak point of the echo energy and select the distance cell corresponding to the nearest peak as the initial response position of the target cable-stayed / sling, so as to complete the initial identification of the target;

[0029] S33. After completing the initial target identification, drive the millimeter-wave radar to perform angle scanning in the vertical plane, collect range spectrum data at different scanning angles, and combine the range spectrum data at different scanning angles to construct an angle-range matrix with the scanning angle as the row index and the range cell number as the column index.

[0030] Furthermore, the expression for the distance spectral vector in a single measurement is:

[0031]

[0032] The expression for echo energy is:

[0033]

[0034] The expression for the distance cell where the target peak is located is:

[0035]

[0036] In the formula, Let E(M) be the range spectrum vector for a single measurement, R be the echo energy of the Mth range cell, M*1 be the dimension of the range spectrum vector, E(m) be the echo energy of the mth range cell, N be the number of sampling points used in a single range FFT process, s(n) be the received echo signal corresponding to the nth time-domain sampling point, and e be the natural constant. The imaginary unit, The total number of distance cells. Number the distance cell where the target peak is located. Number the starting distance unit for the preset effective distance range. Number the termination distance unit for the preset effective distance range.

[0037] Furthermore, the process of determining the reference observation angle based on the peak energy at each scanning angle in the angle-range matrix, driving the millimeter-wave radar to perform calibration scanning based on the reference observation angle, and determining the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle includes the following steps:

[0038] S41. After the angle-distance matrix is ​​constructed, retrieve the peak energy corresponding to the target distance cell at each scanning angle, compare the peak energy at different scanning angles, and select the angle with the largest peak response as the reference observation angle.

[0039] S42. Based on the reference observation angle, determine the angle range of the calibration scan, and drive the millimeter-wave radar to perform calibration scan according to the angle range of the calibration scan;

[0040] S43. Calculate the comprehensive energy of the set peak point under different calibration scanning angles, and take the angle corresponding to the maximum comprehensive energy as the optimal observation angle.

[0041] Furthermore, the formula for calculating the total energy is as follows:

[0042]

[0043]

[0044] In the formula, For comprehensive energy, The number of peak points involved in the calculation. These are the weighting coefficients. For angle The echo energy of the nth effective peak. The target distance.

[0045] According to another aspect of the present invention, an unmanned aerial vehicle (UAV) autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspender cables is provided, comprising a docking platform set on or near the bridge deck and close to the cable-stayed / suspender cable position, a solar power supply device being provided on one side of the top of the docking platform, a UAV being mounted on the top of the docking platform and connected to the docking platform via landing gear, and a detection device being mounted on the top of the UAV.

[0046] The docking platform includes a column, an M-shaped support at the top of the column, a drainage hole at the center of the top of the M-shaped support, and a wireless charging output terminal on the outer side of the top of the M-shaped support.

[0047] The drone is equipped with a main control board and a battery. The main control board is used to adjust the drone's flight attitude, process data from various sensors, and control the orientation of the detection device according to detection requirements.

[0048] The landing gear includes a disc, and the bottom end of the disc is configured as a conical structure that cooperates with the M-shaped support. A camera is provided at the bottom end of the conical structure. Several support feet are provided on the outer side of the bottom of the disc. A wireless charging input terminal that cooperates with the wireless charging output terminal is provided on the outer side of the bottom of the disc.

[0049] The detection device includes a rotating platform, with a rotating motor installed at the bottom of the rotating platform and the rotating motor being installed inside the UAV. A millimeter-wave radar is installed at the top of the rotating platform and is driven by a rotating motor located on one side of the top of the rotating platform.

[0050] Furthermore, the cross-section of the M-shaped support is M-shaped, and the M-shaped structure cooperates with the conical structure of the landing gear to perform mechanical guidance and position calibration of the UAV during the landing process.

[0051] The beneficial effects of this invention are as follows:

[0052] 1) This invention constructs a drone-based cable inspection solution with autonomous take-off and landing, fixed-point stable detection, and continuous operation capabilities. It can achieve high-efficiency, high-stability, and high-coverage detection of bridge cables without the need for close-range manual operation. It effectively overcomes problems such as wind disturbance, drone vibration, insufficient battery life, and inaccurate positioning, and significantly improves the detection accuracy and inspection efficiency of cable structures. It is suitable for long-term inspection and health monitoring of cables in cable-stayed bridges and other bridge structures.

[0053] 2) By having the drone land on the docking platform, the present invention can effectively avoid the effects of wind and its own vibration during hovering. The drone's attitude and altitude can be adjusted by the adjustment device on the platform, thereby improving the quality of the detection data. The sensor can directly measure the platform vibration and can be fused with the detection data to improve the accuracy of the analysis.

[0054] 3) The docking platform of the present invention is equipped with a charging device, which enables the drone to replenish its power during the inspection process and achieve long-term continuous inspection.

[0055] 4) This invention supports two or more UAVs to conduct simultaneous or synchronous inspections on different docking platforms, enabling multi-point collaborative inspections and shortening the inspection time for large structures.

[0056] 5) This invention can be flexibly deployed on large structures such as bridges, towers, and wind turbines, facilitating engineering implementation and obtaining multi-point vibration modes and structural dynamic information. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a flowchart of an unmanned aerial vehicle (UAV) autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to an embodiment of the present invention;

[0059] Figure 2 This is a schematic diagram of the structure of an unmanned aerial vehicle (UAV) autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables according to an embodiment of the present invention.

[0060] Figure 3 This is a schematic diagram of the docking platform in an autonomous inspection system for cable-stayed bridge tension / suspension cable internal force testing, according to an embodiment of the present invention.

[0061] Figure 4 This is a schematic diagram of the structure of a drone in an autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables, according to an embodiment of the present invention.

[0062] Figure 5 This is a schematic diagram of the landing gear structure in an autonomous inspection system for cable-stayed bridge tension / suspension cable internal force testing, according to an embodiment of the present invention.

[0063] Figure 6 This is a schematic diagram of the structure of a detection device in an autonomous inspection system for cable-stayed bridges, according to an embodiment of the present invention, for testing the internal forces of cable tension / suspension cables.

[0064] Figure 7 This is a flowchart of the autonomous docking of a UAV in an autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to an embodiment of the present invention;

[0065] Figure 8 This is a flowchart of the automatic detection process of the detection device in an unmanned aerial vehicle (UAV) autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to an embodiment of the present invention.

[0066] Figure 9 This is a schematic diagram of an unmanned aerial vehicle (UAV) autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables according to an embodiment of the present invention.

[0067] Figure 10 This is a schematic diagram of the layout and testing of an unmanned aerial vehicle (UAV) autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables, according to an embodiment of the present invention.

[0068] Figure 11 This is a schematic diagram of simultaneous upstream and downstream inspection by dual UAVs in an autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables, according to an embodiment of the present invention.

[0069] In the picture:

[0070] 1. Dock platform; 11. Column; 12. M-shaped support; 13. Drain hole; 14. Wireless charging output terminal; 2. Solar power supply device; 3. Drone; 31. Main control board; 32. Battery; 4. Landing gear; 41. Disc; 42. Camera; 43. Support legs; 44. Wireless charging input terminal; 5. Detection device; 51. Rotating platform; 52. Rotating motor; 53. Millimeter wave radar; 54. Rotating motor; I. ​​Cable-stayed / suspended cable; II. Autonomous route planning. Detailed Implementation

[0071] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0072] According to an embodiment of the present invention, an autonomous inspection method and system for unmanned aerial vehicles (UAVs) for testing the internal forces of cable-stayed bridge tension / suspension cables is provided.

[0073] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1 As shown, according to one aspect of the present invention, an autonomous inspection method for unmanned aerial vehicles (UAVs) for testing the internal forces of cable-stayed bridge tension / suspension cables is provided, comprising the following steps:

[0074] S1. Guide the drone to the space area where the target docking platform is located according to the preset inspection path, and automatically identify the characteristic mark of the M-shaped support on the target docking platform based on the image information of the target docking platform;

[0075] The step of guiding the UAV to the spatial area where the target docking platform is located according to the preset inspection path, and automatically identifying the characteristic markings of the M-shaped support on the target docking platform based on the image information of the target docking platform, includes the following steps:

[0076] S11. Based on the bridge structure and inspection requirements of the target cable-stayed bridge, several drone docking platforms are deployed on the bridge, and the inspection path of the drones is automatically planned according to the location information of the drone docking platforms.

[0077] S12. According to the autonomously planned drone inspection path, control the drone to fly to the preset height of the space area where the target docking platform is located;

[0078] S13. Use drones to collect image information of the target docking platform and automatically identify the characteristic markings of the M-shaped platform on the target docking platform based on the image information.

[0079] Specifically, the characteristic feature of the M-shaped support is the black and white circular coatings spaced apart on the surface of the M-shaped support, and the spaced black and white circular coatings are used for the visual positioning of the UAV.

[0080] S2. Based on the characteristic markings and image information of the M-shaped platform, the position and attitude of the UAV are corrected until the UAV lands on the target docking platform from the spatial area where the target docking platform is located, thus completing the autonomous docking of the UAV.

[0081] Specifically, after the drone completes its autonomous docking, the process also includes: wirelessly charging the drone's battery using the wireless charging output on the target docking platform and the wireless charging input on the drone's landing gear.

[0082] S3. Drive the millimeter-wave radar to perform angle scanning in the vertical plane, acquire range spectrum data at different scanning angles, and construct an angle-range matrix based on the range spectrum data at different scanning angles;

[0083] The process of driving the millimeter-wave radar to perform angular scanning in a vertical plane, acquiring range spectrum data at different scanning angles, and constructing an angle-range matrix based on the range spectrum data at different scanning angles includes the following steps:

[0084] S31. After the UAV completes autonomous docking and enters a stable state, the millimeter-wave radar on the UAV is used to detect the target cable-stayed / suspension cable, obtain the target echo signal and perform range signal processing to form range spectrum data. The range spectrum data is data that characterizes the energy distribution of the target at different distance positions with the range unit as the horizontal axis and the echo energy as the vertical axis.

[0085] S32. Within a preset distance range, retrieve the peak point of the echo energy and select the distance cell corresponding to the nearest peak as the initial response position of the target cable-stayed / sling, so as to complete the initial identification of the target;

[0086] S33. After completing the initial target identification, drive the millimeter-wave radar to perform angle scanning in the vertical plane, collect range spectrum data at different scanning angles, and combine the range spectrum data at different scanning angles to construct an angle-range matrix with the scanning angle as the row index and the range cell number as the column index.

[0087] Specifically, the expression for the distance spectral vector in a single measurement is:

[0088]

[0089] The expression for echo energy is:

[0090]

[0091] The expression for the distance cell where the target peak is located is:

[0092]

[0093] In the formula, This is the distance spectrum vector from a single measurement. For the echo energy corresponding to the Mth range cell, For the real number field, Let be the dimension of the distance spectral vector. Let N be the echo energy of the m-th range cell, and N be the number of sampling points used in a single range FFT process. Let e ​​be the received echo signal corresponding to the nth time-domain sampling point, and let e be the natural constant. The imaginary unit, The total number of distance cells. Number the distance cell where the target peak is located. Number the starting distance unit for the preset effective distance range. Number the termination distance unit for the preset effective distance range.

[0094] S4. Based on the peak energy at each scanning angle in the angle-range matrix, determine the reference observation angle, and drive the millimeter-wave radar to perform calibration scanning according to the reference observation angle. At the same time, determine the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle.

[0095] The process of determining a reference observation angle based on the peak energy at each scanning angle in the angle-range matrix, driving the millimeter-wave radar to perform calibration scanning based on the reference observation angle, and determining the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle includes the following steps:

[0096] S41. After the angle-distance matrix is ​​constructed, retrieve the peak energy corresponding to the target distance cell at each scanning angle, compare the peak energy at different scanning angles, and select the angle with the largest peak response as the reference observation angle.

[0097] S42. Based on the reference observation angle, determine the angle range of the calibration scan, and drive the millimeter-wave radar to perform calibration scan according to the angle range of the calibration scan;

[0098] S43. Calculate the comprehensive energy of the set peak point under different calibration scanning angles, and take the angle corresponding to the maximum comprehensive energy as the optimal observation angle.

[0099] Specifically, the formula for calculating the overall energy is:

[0100]

[0101]

[0102] In the formula, For comprehensive energy, The number of peak points involved in the calculation. These are the weighting coefficients. For angle The echo energy of the nth effective peak. The target distance.

[0103] S5. Lock the observation attitude of the millimeter-wave radar according to the optimal observation angle, and use the millimeter-wave radar to perform static observation of the target cable-stayed / suspension cable to obtain the vibration response signal; extract the vibration frequency characteristics of the target cable-stayed / suspension cable based on the vibration response signal;

[0104] S6. Based on the vibration frequency characteristics of the target cable-stayed / suspended cable, and combined with the pre-imported structural parameters of the target cable-stayed / suspended cable, calculate the cable force of the target cable-stayed / suspended cable, and output the cable force ratio to complete the detection task of a single observation point.

[0105] The formula for calculating the cable force is as follows:

[0106]

[0107] The formula for calculating the cable ratio is:

[0108]

[0109] In the formula, For cable force, Linear density, For the length of the rope, Let n be the nth frequency, where n is the frequency order. For sol-li, The first frequency of the current state. The first frequency of the reference state.

[0110] S7. After the detection task of a single observation point is completed, the UAV exits the detection state, releases the dock and takes off again, flies to the next docking platform according to the inspection path, and repeats S2-S7 until the detection tasks of all preset observation points are completed.

[0111] According to another aspect of the invention, such as Figures 2-6 As shown, an autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables is provided. The system includes a docking platform 1 set on or near the bridge deck and close to the cable tension / suspension cable. A solar power supply device 2 is installed on one side of the top of the docking platform 1. A drone 3 is installed on the top of the docking platform 1 and connected to the docking platform 1 via a landing gear 4. A detection device 5 is installed on the top of the drone 3.

[0112] The docking platform 1 includes a column 11, an M-shaped support 12 is provided at the top of the column 11, a water leakage hole 13 is provided at the middle of the top of the M-shaped support 12, and a wireless charging output terminal 14 is provided on the outer side of the top of the M-shaped support 12.

[0113] The UAV 3 is equipped with a main control board 31 and a battery 32. The main control board 31 is used to adjust the flight attitude of the UAV, process data information from multiple sensors, and control the orientation adjustment of the detection device according to the detection requirements.

[0114] The landing gear 4 includes a disc 41, and the bottom end of the disc 41 is configured as a conical structure that cooperates with the M-shaped support platform 12. A camera 42 is provided at the bottom end of the conical structure. Several support feet 43 are provided on the outer side of the bottom of the disc 41. A wireless charging input terminal 44 that cooperates with the wireless charging output terminal 14 is provided on the outer side of the bottom of the disc 41.

[0115] The detection device 5 includes a rotating platform 51, with a rotating motor 52 at the bottom of the rotating platform 51 and installed inside the UAV 3. A millimeter-wave radar 53 is installed on the top of the rotating platform 51 and is driven by a rotating motor 54 located on one side of the top of the rotating platform 51.

[0116] Specifically, the cross-section of the M-shaped support 12 is M-shaped, and the M-shaped structure cooperates with the conical structure of the landing gear 4 to perform mechanical guidance and position calibration of the UAV during the landing process.

[0117] To facilitate understanding of the above technical solutions of the present invention, the following further explains the above technical solutions of the present invention from the perspective of architecture and principle, as follows:

[0118] The purpose of this invention is to provide a drone-based inspection solution for cable-stayed structures, featuring autonomous takeoff and landing, stable fixed-point inspection, and continuous operation capabilities. By pre-setting a docking platform near the structure, the drone can land on the platform for inspection. The platform's fixing and adjustment devices ensure stable landing and sensor observation attitude, while the charging device provided by the platform extends the inspection endurance. The drone is equipped with an accelerometer and other sensors, enabling direct measurement of platform vibration for data fusion and improved accuracy. Simultaneously, it supports simultaneous inspection by two or more drones on different platforms, achieving multi-point collaborative observation and acquiring multi-point dynamic response information. This solution effectively overcomes problems such as wind disturbance, drone vibration, insufficient endurance, and inaccurate positioning, significantly improving the inspection accuracy and efficiency of cable-stayed structures.

[0119] like Figures 2-6 As shown, an autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables includes a drone, landing gear, docking platform, and testing devices.

[0120] The drone serves as the main executor of the inspection system, performing autonomous flight, positioning, and detection tasks within a pre-defined inspection area. Internally, it houses a main control board, which acts as the drone's core processor and includes a GNSS signal receiver. This board adjusts the drone's flight attitude, processes data from various sensors, and controls the orientation of the detection device according to inspection requirements, ensuring the device is aligned with the target detection location and achieving stable and reliable inspection.

[0121] The landing gear, mounted beneath the drone, comprises a disc structure, a conical structure, a camera, a wireless charging input, and support feet. The disc structure is located on the upper part of the landing gear and is fixedly connected to the drone. The disc structure houses the wireless charging input, which couples with the wireless charging output on the docking platform when the drone is docked, wirelessly charging the drone's battery. This allows for energy replenishment while docked, extending the drone's flight time and supporting long-term deployment. The conical structure is located below the disc structure and coaxially connected to it. It docks with the platform structure within the docking platform. During descent, the conical structure and platform structure work together to guide and calibrate the drone's landing position, enabling automatic docking. A downward-facing camera is located at the bottom of the conical structure, capturing images of the docking platform and surrounding environment during descent. This provides positioning assistance to the drone, improving landing and docking accuracy. The disc structure has four support feet evenly arranged around its circumference. After the drone docks on the docking platform, the support feet contact the platform to support and fix the drone, restricting the drone's horizontal movement and attitude changes while docked, and improving the stability of the drone after docking.

[0122] The docking platform comprises columns, a solar power supply unit, and an M-shaped support platform. The columns, serving as the platform's supporting structure, are fixed at their base to the ground, bridge deck, or other locations within the main structure, bearing the overall structural weight of the docking platform and providing stable support. The solar power supply unit, mounted on the columns, provides energy storage for the docking platform and is electrically connected to the wireless charging output of the M-shaped support platform for wireless charging of the drone while it is docked. The M-shaped support platform has an M-shaped structure; its cross-sectional boundary reveals a typical M-shaped profile. This structure is not a single inclined or flat platform, but rather a combination of different inclination angles on the inner and outer sides, creating multiple stress and guidance interfaces within a limited height, balancing stability, anti-slip capability, and assembly adaptability. The outer surface is at a 45° angle, consistent with and highly compatible with the inclination angle of the support legs in the landing gear, contributing to the stability of the support legs. The inner surface has an approximately 30° inclination angle, exhibiting a funnel-shaped geometry to mate with the conical structure inside the landing gear. Its top is equipped with a wireless charging output for power output, and the inner side features alternating black and white circular paint rings for drone visual positioning. During the drone's descent and docking, the M-shaped support platform guides the drone's landing gear through its structural shape, decomposing the drone's vertical displacement into a certain degree of lateral displacement, thereby guiding the drone to automatically move towards the predetermined docking position. This allows for position adjustment and calibration during the docking process, tolerating a certain range of landing position errors.

[0123] The detection device is mounted on the upper part of the UAV and includes a rotary motor, a rotating platform, a rotary motor, and onboard measuring equipment such as millimeter-wave radar and laser vibrometer. The rotary motor is fixed inside the UAV, and its output is connected to the rotating platform to drive the platform to rotate around its vertical axis for horizontal orientation adjustment. The rotary motor is fixed to the rotating platform and connected to sensors such as the rotating millimeter-wave radar for vertical adjustment. The measuring equipment, through the combined action of the rotary motor and the rotary motor, can adjust its attitude in multiple directions to achieve directional detection of the target cable / suspension.

[0124] Based on the aforementioned UAV, landing gear, docking platform, and detection device, this invention proposes an autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables. Through multi-level positioning and joint data calibration, it achieves stable fixed-point docking and automated high-precision detection of the UAV. The system introduction above describes the UAV positioning scheme, which uses multi-level positioning, including primary GNSS positioning, secondary visual positioning, assisted adjustment, and unique mechanical guidance positioning, to accurately dock the UAV to the designated platform. This is the multi-level positioning and autonomous docking technology solution; after stable docking, automated detection using millimeter-wave radar is performed. Combined with the structural detection technology solution based on joint data calibration, the two form a system and method: a UAV docking system and a cable force detection method, with the entire process being autonomous and iterative. Specifically, this technical solution includes the following:

[0125] I. Multi-level positioning and autonomous docking technology solution

[0126] like Figure 7 As shown, when the UAV performs an inspection mission, it first completes primary positioning based on GNSS (Global Navigation Satellite System) positioning information. That is, before performing the flight mission, it imports the GNSS position information of all docking platforms, including latitude, longitude, altitude, and target orientation, and guides the UAV to fly to a preset altitude (which can be set to 5m) in the space area where the preset target docking platform is located, as the initial condition for subsequent landing and docking.

[0127] After completing the primary positioning at the preset altitude, the UAV enters the secondary positioning stage based on vision and structure guidance. The UAV acquires images through the camera at the bottom of the landing gear, and the main control board processes the images, automatically identifies the black and white feature marks on the M-shaped platform, and uses them as position calibration to keep the features always in the center of the image. At the same time, the UAV is corrected for lateral position and attitude by combining the image analysis results, and the UAV is controlled to descend slowly to accurately align with the docking position and maintain horizontal stability.

[0128] As the drone descends slowly, the conical structure at the bottom of the landing gear gradually comes into contact with the M-shaped support. The M-shaped support, through its unique structural shape, provides mechanical guidance to the conical structure, converting the drone's vertical descent into appropriate lateral displacement. This automatically guides the drone to correct landing deviations and moves it towards the predetermined docking position, ensuring that it lands precisely at the designated location, thus completing the docking process.

[0129] After mechanical docking is completed, the wireless charging output on the docking platform and the charging input on the drone's landing gear achieve energy coupling, wirelessly charging the drone's battery, ensuring that the drone can dock stably for a long time and maintain sufficient power for subsequent inspection tasks.

[0130] After the drone completes docking and enters a stable state, the main control board controls the detection device to enter working mode. After data collection is completed, the drone leaves the docking platform. Further, the drone follows a pre-planned inspection path, flying sequentially to the next docking platform to repeat the docking and detection steps until all inspection points are completed, at which point it returns.

[0131] The entire process achieves fully automated operation of the UAV from primary GNSS positioning, secondary visual positioning, auxiliary adjustment, mechanical guidance calibration to stable docking, which greatly reduces environmental interference, flight deviation and operational complexity, and ensures that the UAV can safely, quickly and accurately complete the task preparation for each inspection and docking point.

[0132] II. Structural Inspection Technology Scheme Based on Joint Data Calibration

[0133] like Figure 8 As shown, after the UAV completes docking and enters a stable state, the main control board controls the detection device to enter the working state, and performs non-contact cable force measurement on tension components such as bridge cable-stayed / suspended cables. The positioning and control steps are as follows:

[0134] After the UAV completes docking and enters a stable state, the main control board controls the detection device to enter working mode, activating the millimeter-wave radar to detect the target cable-stayed bridge / suspension cable, acquiring the target echo signal and performing range signal processing to form range spectrum data. The range spectrum uses range cells as the abscissa and echo energy as the ordinate to characterize the energy distribution of the target at different distances. A range cell is a fundamental concept in radar, referring to the range resolution in the radar range direction, the smallest distinguishable range interval. Under single measurement conditions, the range spectrum vector can be expressed as:

[0135]

[0136] The echo energy corresponding to the m-th distance cell is:

[0137]

[0138] Within the preset effective distance range Within the range, the peak point of significant echo energy is retrieved, and the distance cell corresponding to the nearest peak is selected as the initial response position of the target cable / sling. The expression is as follows:

[0139]

[0140] In the formula, This is the distance spectrum vector from a single measurement. For the echo energy corresponding to the Mth range cell, For the real number field, Let be the dimension of the distance spectral vector. Let N be the echo energy of the m-th range cell, and N be the number of sampling points used in a single range FFT (Fast Fourier Transform) process. Let e ​​be the received echo signal corresponding to the nth time-domain sampling point, and let e be the natural constant. The imaginary unit, The total number of distance cells. Number the distance cell where the target peak is located. Number the starting distance unit for the preset effective distance range. Number the termination distance unit for the preset effective distance range.

[0141] It should be noted that the innovation of this invention is not the generation of a new distance spectrum, but rather the optimization of orientation based on an existing distance spectrum. It focuses on how to automatically achieve optimal angle measurement through the distance spectrum, thereby completing cable force detection. By combining two-degree-of-freedom motors and using the acquired distance spectrum data, orientation optimization is achieved. An angle-distance energy matrix is ​​formed, and a comprehensive evaluation is performed using the sum of the energy from a preset number of points to calculate the final positioning angle. The preset number of points is determined by the number of cable detection points on the docking platform.

[0142] After initial target identification, the main control board controls the rotating motor to drive the millimeter-wave radar to perform angular scanning in the vertical plane, gradually rotating from an initial horizontal angle of 0° to a vertical angle of 90°, with a scanning step size set to 1°. At each scanning angle... Below, the millimeter-wave radar acquires a corresponding set of range spectrum data:

[0143]

[0144] The distance spectra obtained at different scanning angles are combined to construct an angle-distance matrix:

[0145]

[0146] In this matrix, the row index corresponds to the scan angle. The column index corresponds to the distance cell number.

[0147] After the angle-distance matrix is ​​constructed, the main control board retrieves the peak energy corresponding to the target distance unit at each scanning angle, compares the peak energy at different angles, and selects the angle with the largest peak response as the reference observation angle. Based on this, the rotating mechanism performs a secondary fine scan (i.e., calibration scan) near the reference angle, with a rotation range of ±15° and a step angle of 1°. At each fine scan angle, energy weighting is performed on multiple set effective peak points, and the comprehensive evaluation function is:

[0148]

[0149]

[0150] In the formula, For comprehensive energy, The number of peak points involved in the calculation. The weighting coefficient is set to an exponential weight, which changes with the target distance, increasing as the distance increases. This is used to highlight the stability of distant targets and more accurately acquire target vibration signals. For angle The echo energy of the nth effective peak. The target distance is within the range of 0~30m. Within the range of 0 to 30, the weighting coefficient can be adjusted using the number 1 / 40. The overall level should be kept within 1 to 2.

[0151] With comprehensive energy The angle corresponding to the maximum value is taken as the optimal observation angle, and the observation attitude of the millimeter-wave radar is locked at this angle position.

[0152] At the optimal observation angle, millimeter-wave radar performs static observation of the target cable-stayed / suspended cable, continuously acquiring vibration response signals for a pre-set number of target distance units. Frequency domain analysis is then performed on these signals to extract the dominant vibration frequency characteristics of the cable-stayed / suspended cable. Combined with pre-imported structural parameters such as cable length and linear density, the corresponding cable force is calculated, and the cable force ratio is output. Cable force serves as the core mechanical indicator for cable-stayed / suspended cable detection, and the calculated cable force ratio is used for comparison with previous cable force data. Simultaneously, the consistency of the detection results is compared using the harmonic relationships of the cable-stayed / suspended cable vibration frequencies and historical cable force data.

[0153] The formula for calculating cable force is:

[0154]

[0155] The formula for calculating the cable ratio is:

[0156]

[0157] In the formula, For cable force, Linear density, For the length of the rope, Let n be the nth frequency, where n is the frequency order. The cable force ratio (dimensionless) represents the ratio of the current cable force to the cable force in the reference state. The first-order frequency (in Hz) of the current state is obtained by measuring the vibration frequency of the cable using radar. The first-order frequency (in Hz) of the reference state is the first-order natural frequency of the reference state (such as the design state or healthy initial state).

[0158] Specifically, the number of target distance units preset is determined by the observation range of the docking platform, which in turn is determined by the measurement range of the millimeter-wave radar. When installing the docking platform, the number of cables is determined based on the number of cables and the measurement range of the millimeter-wave radar. For example, if the observation range of the millimeter-wave radar is 15m, then the number of cables within that range is used as the observation quantity for this docking platform. Similarly, the number of cables measured for each docking platform will vary depending on the cable spacing, and is determined by the bridge structure.

[0159] The above method enables high-precision and automated detection of cable tension in cable-stayed / suspended cables by UAVs in an autonomous docking state, effectively reducing the impact of environmental disturbances and UAV vibrations on the measurement results and improving the stability and reliability of cable tension detection.

[0160] III. System Deployment and Methodological Implementation

[0161] like Figures 9-11 As shown, in bridge structure inspection applications, based on the structural form of the target bridge and inspection requirements, multiple UAV landing platforms are deployed on or near the bridge deck, close to the cable-stayed / suspended cables, according to pre-set observation quantities and spatial distribution requirements. Each landing platform corresponds to a fixed observation point for targeted inspection of the target cable-stayed / suspended cables or structural components.

[0162] During the system deployment phase, the positions of each docking platform are measured to obtain the corresponding Global Navigation Satellite System (GNSS) position information, including latitude, longitude, altitude, and platform orientation information. This position information is then uniformly imported into the UAV main control system as navigation and positioning reference data during mission execution.

[0163] During the actual inspection, the UAV, based on pre-imported GNSS point information, flies sequentially to the areas of each docking platform and completes fixed-point docking according to the aforementioned multi-level positioning, autonomous landing, and stable docking methods. After docking, the UAV's control and detection devices enter working mode, automatically detecting and collecting data on the cable-stayed / suspended cables or structural components at the corresponding observation points according to the aforementioned detection and control procedures. Once the detection task for a single observation point is completed, the UAV exits the detection state, releases the dock, and takes off again, flying to the next preset docking platform according to the mission plan, repeating the autonomous positioning, docking, and detection process until the detection tasks for all preset observation points are completed.

[0164] Similarly, for the upstream and downstream tension / suspension cables of a bridge, two drones establish point-to-point communication via a 2.4GHz wireless module to achieve real-time information exchange between nodes. After the drones dock, the drone that arrives at the docking platform first sends a "detection start request" command to the other drone and waits for confirmation. When the other drone receives the command, it sends an acknowledgment, and after the other drone completes two-way communication confirmation, the detection task is started simultaneously. Two drones can perform inspection tasks simultaneously, conducting synchronous detection on symmetrically arranged docking platforms upstream and downstream, thereby acquiring vibration frequency and dynamic response data of the tension / suspension cables under the same environmental conditions. By conducting detection in the same environment and within the same time period, the influence of temperature and external load is eliminated. This synchronous observation method can effectively avoid measurement errors caused by changes in time period or environment in single-drone inspections, improving the accuracy and reliability of tension / suspension cable frequency measurement.

[0165] Through the above system deployment and implementation methods, multi-point, automated, and continuous inspection of cable-stayed / suspended bridge structures has been achieved, effectively reducing the need for manual intervention and improving inspection efficiency and the consistency and reliability of inspection results.

[0166] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0167] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables, characterized in that, Includes the following steps: S1. Guide the drone to the space area where the target docking platform is located according to the preset inspection path, and automatically identify the characteristic mark of the M-shaped support on the target docking platform based on the image information of the target docking platform; S2. Based on the characteristic markings and image information of the M-shaped platform, the position and attitude of the UAV are corrected until the UAV lands on the target docking platform from the spatial area where the target docking platform is located, thus completing the autonomous docking of the UAV. S3. Drive the millimeter-wave radar to perform angle scanning in the vertical plane, acquire range spectrum data at different scanning angles, and construct an angle-range matrix based on the range spectrum data at different scanning angles; S4. Based on the peak energy at each scanning angle in the angle-range matrix, determine the reference observation angle, and drive the millimeter-wave radar to perform calibration scanning according to the reference observation angle. At the same time, determine the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle. S5. Lock the observation attitude of the millimeter-wave radar according to the optimal observation angle, and use the millimeter-wave radar to perform static observation of the target cable-stayed / suspension cable to obtain the vibration response signal; extract the vibration frequency characteristics of the target cable-stayed / suspension cable based on the vibration response signal; S6. Based on the vibration frequency characteristics of the target cable-stayed / suspended cable, and combined with the pre-imported structural parameters of the target cable-stayed / suspended cable, calculate the cable force of the target cable-stayed / suspended cable, and output the cable force ratio to complete the detection task of a single observation point. S7. After the detection task of a single observation point is completed, the UAV exits the detection state, releases the dock and takes off again, flies to the next docking platform according to the inspection path, and repeats S2-S7 until the detection tasks of all preset observation points are completed.

2. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 1, characterized in that, The process of guiding the UAV to the spatial area where the target docking platform is located according to the preset inspection path, and automatically identifying the characteristic markings of the M-shaped support on the target docking platform based on the image information of the target docking platform, includes the following steps: S11. Based on the bridge structure and inspection requirements of the target cable-stayed bridge, several drone docking platforms are deployed on the bridge, and the inspection path of the drones is automatically planned according to the location information of the drone docking platforms. S12. According to the autonomously planned drone inspection path, control the drone to fly to the preset height of the space area where the target docking platform is located; S13. Use drones to collect image information of the target docking platform and automatically identify the characteristic markings of the M-shaped platform on the target docking platform based on the image information. The characteristic feature of the M-shaped support is the black and white circular coatings spaced apart on the surface of the M-shaped support, and the spaced black and white circular coatings are used for the visual positioning of the UAV.

3. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 1, characterized in that, After the drone completes its autonomous docking, the process also includes: wirelessly charging the drone's battery using the wireless charging output on the target docking platform and the wireless charging input on the drone's landing gear.

4. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 1, characterized in that, The driving millimeter-wave radar performs angular scanning in a vertical plane to acquire range spectrum data at different scanning angles, and constructs an angle-range matrix based on the range spectrum data at different scanning angles, including the following steps: S31. After the UAV completes autonomous docking and enters a stable state, the millimeter-wave radar on the UAV is used to detect the target cable-stayed / suspension cable, obtain the target echo signal and perform range signal processing to form range spectrum data. The range spectrum data is data that characterizes the energy distribution of the target at different distance positions with the range unit as the horizontal axis and the echo energy as the vertical axis. S32. Within a preset distance range, retrieve the peak point of the echo energy and select the distance cell corresponding to the nearest peak as the initial response position of the target cable-stayed / sling, so as to complete the initial identification of the target; S33. After completing the initial target identification, drive the millimeter-wave radar to perform angle scanning in the vertical plane, collect range spectrum data at different scanning angles, and combine the range spectrum data at different scanning angles to construct an angle-range matrix with the scanning angle as the row index and the range cell number as the column index.

5. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 4, characterized in that, The expression for the distance spectrum vector in a single measurement is: The expression for echo energy is: The expression for the distance cell where the target peak is located is: In the formula, This is the distance spectrum vector from a single measurement. For the echo energy corresponding to the Mth range cell, For the real number field, Let be the dimension of the distance spectral vector. Let N be the echo energy of the m-th range cell, and N be the number of sampling points used in a single range FFT process. Let e ​​be the received echo signal corresponding to the nth time-domain sampling point, and let e be the natural constant. The imaginary unit, The total number of distance cells. Number the distance cell where the target peak is located. Number the starting distance unit for the preset effective distance range. Number the termination distance unit for the preset effective distance range.

6. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 1, characterized in that, The process of determining a reference observation angle based on the peak energy at each scanning angle in the angle-range matrix, driving the millimeter-wave radar to perform calibration scanning based on the reference observation angle, and determining the optimal observation angle based on the comprehensive energy of the peak points at the calibration scanning angle includes the following steps: S41. After the angle-distance matrix is ​​constructed, retrieve the peak energy corresponding to the target distance cell at each scanning angle, compare the peak energy at different scanning angles, and select the angle with the largest peak response as the reference observation angle. S42. Based on the reference observation angle, determine the angle range of the calibration scan, and drive the millimeter-wave radar to perform calibration scan according to the angle range of the calibration scan; S43. Calculate the comprehensive energy of the set peak point under different calibration scanning angles, and take the angle corresponding to the maximum comprehensive energy as the optimal observation angle.

7. The UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 6, characterized in that, The formula for calculating total energy is: In the formula, For comprehensive energy, The number of peak points involved in the calculation. These are the weighting coefficients. For angle The echo energy of the nth effective peak. The target distance.

8. A UAV autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables, used to implement the steps of the UAV autonomous inspection method for testing the internal forces of cable-stayed bridge tension / suspension cables as described in any one of claims 1-7, characterized in that, It includes a docking platform set on or near the bridge deck, close to the cable-stayed / suspender cable position. A solar power supply device is installed on one side of the top of the docking platform. A drone is installed on the top of the docking platform and connected to the docking platform via landing gear. A detection device is installed on the top of the drone. The docking platform includes a column, an M-shaped support at the top of the column, a drainage hole at the center of the top of the M-shaped support, and a wireless charging output terminal on the outer side of the top of the M-shaped support. The drone is equipped with a main control board and a battery. The main control board is used to adjust the drone's flight attitude, process data from various sensors, and control the orientation of the detection device according to detection requirements. The landing gear includes a disc, and the bottom end of the disc is configured as a conical structure that cooperates with the M-shaped support. The outer side of the bottom of the disc is provided with a wireless charging input terminal that cooperates with the wireless charging output terminal. The detection device includes a rotating platform, with a rotating motor installed at the bottom of the rotating platform and the rotating motor being installed inside the UAV. A millimeter-wave radar is installed at the top of the rotating platform and is driven by a rotating motor located on one side of the top of the rotating platform.

9. The UAV autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 8, characterized in that, A camera is installed at the bottom of the conical structure, and several supporting feet are provided on the outer side of the bottom of the disc.

10. The UAV autonomous inspection system for testing the internal forces of cable-stayed bridge tension / suspension cables according to claim 8, characterized in that, The M-shaped support has an M-shaped cross-section, and the M-shaped structure cooperates with the conical structure of the landing gear to perform mechanical guidance and position calibration of the UAV during the landing process.

Images