An autonomous docking control system for dynamic landing of a marine unmanned aerial vehicle on an unmanned surface vehicle and an autonomous recovery method thereof

Abstract

This invention provides an autonomous recovery method for an autonomous docking control system of a UAV dynamically landing on a dynamic unmanned surface vessel (USV). The UAV control system outputs the UAV's motion status and UWB tag signals to the USV control system, while the USV control system outputs the USV's heading and speed information, as well as its latitude and longitude information, to the UAV control system. This invention overcomes the aforementioned problems encountered when UAVs autonomously land on dynamic USVs. It allows the UAV to autonomously select the appropriate sensors to obtain precise relative position information and control parameters based on the relative distance between the UAV and the USV, thereby enabling precise and rapid autonomous docking of the UAV with the dynamic USV.

Description

Technical Field

[0001] This invention belongs to the field of collaborative control of marine robots, and in particular relates to an autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea and its autonomous recovery method. Background Technology

[0002] Unmanned surface vessels (USVs) are maritime vehicles with advantages such as long endurance, large payload capacity, low cost with unattended operation, good equipment expandability, and high data accuracy, making them widely used in fields such as ocean exploration, maritime security, and marine meteorological data collection. However, due to limitations in the sensor detection range, installation angle, and Earth's curvature, USVs are typically limited to observation and reconnaissance on a horizontal plane, unable to conduct multi-angle observation and photography, and have a relatively limited field of view, unable to observe higher aerial targets and surrounding terrain. Therefore, they may not meet the requirements in certain application scenarios. The search range and speed of USVs are limited by their own power and energy reserves, making it impossible to quickly search large areas of the sea surface, which may be insufficient in responding to emergencies or sudden events. To address these issues, unmanned aerial vehicles (UAVs) are often introduced to assist USVs in tasks such as target search, obstacle warning, and navigation in unfamiliar environments. Compared to USVs, UAVs have a wider field of view, enabling a more comprehensive and accurate understanding of the global information of the surrounding sea surface, and have a significant advantage in assisting USVs in completing tasks. Therefore, combining drones with unmanned surface vessels (USVs) can not only improve the efficiency and accuracy of maritime missions, but also better meet the needs of different tasks and expand the application areas of unmanned vessels at sea. The primary technical challenge in introducing drones into USVs is the autonomous takeoff and landing of drones on USVs. This includes landing accuracy, control algorithms and stability issues for both drones and USVs, and the availability of suitable sensors for maritime applications.

[0003] Existing technologies for autonomous landing of unmanned surface vessels (USVs) mostly employ GNSS positioning and onboard cameras for end-point guidance, but they face several challenges:

[0004] The positioning accuracy of civilian GNSS in open sea areas is around 2 meters. However, due to the small size of unmanned surface vessels (USVs) and their limited flight deck area, this positioning accuracy is insufficient for the autonomous landing accuracy of USVs. Furthermore, their data output frequency is low (<10Hz), which cannot meet the docking control requirements for high dynamic response.

[0005] Some solutions employ RTK (Real-Time Kinematic) technology, a high-precision positioning technology with sub-centimeter accuracy. However, its application is limited by the number of civilian positioning base stations. Currently, RTK base stations are mostly installed and deployed alongside 4G and 5G signal towers, rendering RTK ineffective in areas far from land.

[0006] Existing technologies utilize visual-guided tracking and recovery methods using drones. While the drone's onboard camera offers high accuracy, it requires the drone to fly over the unmanned surface vessel (USV) and collect real-time data on feature markers on the USV's flight deck. The images are then processed to determine the relative position. However, due to variable maritime weather conditions, including rain, fog, moisture, and lighting, the drone's onboard camera may malfunction. Furthermore, during nighttime operations, the USV's flight deck cannot provide guiding light for stealth purposes, limiting the drone's visual recovery capabilities. Additionally, image processors typically require significant computing power, consuming more of the drone's energy and reducing its mission endurance.

[0007] Existing technical solutions use UWB (Ultra-Wideband) positioning technology to measure the relative distance between UAVs and unmanned surface vessels (USVs), but this only measures the spatial distance between the two and does not calculate their accurate relative spatial coordinates. Furthermore, it does not analyze the error propagation of UWB positioning when the USV is installed on a vessel and experiences swaying due to wind and waves. Summary of the Invention

[0008] In view of this, the present invention aims to propose an autonomous docking control system and autonomous recovery method for the dynamic landing of unmanned aerial vehicles (UAVs) on maritime vessels, in order to overcome the aforementioned problems faced by UAVs in the autonomous landing of dynamic UAVs. The present invention can autonomously select the sensors used to obtain accurate relative position information and control parameters based on the relative distance between the UAV and the UAV, thereby achieving precise and rapid autonomous docking of the UAV with the dynamic UAV.

[0009] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0010] An autonomous docking control system for dynamic landing of a UAV and an unmanned surface vessel (USV) at sea is provided. The control system includes a UAV control system and an USV control system. The UAV control system outputs the UAV's motion status and UWB tag signals to the USV control system. The USV control system outputs the USV's heading and speed information and its latitude and longitude information to the UAV control system.

[0011] The UAV control system includes sensor group I, altitude control unit, thruster control unit and wireless data transmission unit I;

[0012] The sensor group I is used in conjunction with the sensors in the sensor group II of the unmanned surface vessel for bidirectional positioning.

[0013] The altitude control unit is used for drone position control;

[0014] The thrust control unit of the thruster is used for attitude control of the UAV;

[0015] The wireless data transmission unit I is used to transmit UAV attitude data;

[0016] The unmanned surface vessel control system includes sensor group II, motion controller, thrust distribution unit, and wireless data transmission unit II;

[0017] The sensor group II is used in conjunction with the sensors in sensor group II of the UAV for bidirectional positioning.

[0018] The motion controller is used for path planning of the unmanned surface vessel;

[0019] The thrust distribution unit of the propulsion system is used to control the speed and heading of the unmanned surface vessel.

[0020] The wireless data transmission unit II is used to transmit the pose data and image data of the unmanned surface vessel.

[0021] Furthermore, the sensor group I includes a UWB positioning tag, an inertial measurement unit (IMU) I, a GNSS positioning system, a barometer, and a laser sensor.

[0022] The sensor group II includes a UWB positioning base station, an inertial measurement unit (IMU II), a dual-antenna GNSS positioning and orientation system, and a meteorological sensor.

[0023] The UWB positioning tag is used in conjunction with a UWB positioning base station;

[0024] The inertial measurement unit IMUⅠ is used in conjunction with the inertial measurement unit IMUⅡ;

[0025] The GNSS positioning system is used in conjunction with a dual-antenna GNSS positioning and orientation system.

[0026] The barometer is used in conjunction with the meteorological sensor at the weather station.

[0027] Furthermore, the unmanned surface vessel is equipped with a flight deck at the stern for autonomous take-off and landing of the UAVs; four UWB positioning base stations are arranged around the deck, and by fixing the relative positions of the four UWB base stations, the relative spatial coordinates of the UAVs carrying UWB positioning tags in the air can be determined.

[0028] An autonomous recovery method for an autonomous docking control system for a dynamic landing of a marine unmanned aerial vehicle (UAV) on an unmanned surface vessel (USV), wherein the autonomous recovery method uses the aforementioned autonomous docking control system for a dynamic landing of a marine UAV on an USV, and the autonomous recovery method is divided into two parts: the UAV approaching the USV horizontally and the UAV landing on the USV vertically.

[0029] In the horizontal direction, the unmanned surface vessel (USV) transmits its latitude and longitude coordinates, heading, and speed information to the unmanned aerial vehicle (UAV) in real time via UWB data transmission. The UAV compares its own latitude and longitude with those of the UAV to determine the straight-line distance between them. When the distance is less than the available distance threshold for UWB data, UWB positioning coordinates are activated, and the UAV enters landing mode. The heading of the USV obtained by the UAV via UWB data transmission is used as its expected heading value. Based on the USV's speed, the expected speed increment is calculated by the docking controller and added to the USV's current speed to obtain the expected speed, thus completing the horizontal approach.

[0030] In the vertical direction, the UAV uses a combination of barometers and laser rangefinders. The UAV records the current air pressure value the moment it takes off from the flight deck of the unmanned surface vessel as the initial altitude value. The laser rangefinder is used within the flight deck area, and the barometer is used to obtain the altitude value on the sea surface outside the flight deck. During the autonomous landing process, the UAV obtains the estimated landing time by the difference between its current relative speed and the difference between its current horizontal distance. Based on the estimated landing time and the UAV's current altitude value, the descent speed value of the UAV is estimated to ensure a smooth and stable landing trajectory.

[0031] Furthermore, the specific method for determining the straight-line distance between the drone and the unmanned surface vessel is as follows:

[0032] S101. Enables the unmanned surface vessel to navigate in the direction of the wind and maintain a constant speed;

[0033] S102. Let the kinematic parameters P of the unmanned surface vessel be... usv With the kinematic parameters P of the UAV uav ;

[0034] S103. Based on the location of the UWB positioning base station on the unmanned surface vessel and the node tag of the UWB positioning tag on the unmanned surface vessel. uav GNSS system is used for navigation and approach, and Tag measurement is performed. uav The electromagnetic wave arrival time {τ} of the four ANCHORs to the deck of the unmanned surface vessel i If i = 1, 2, 3, 4}, multiply by the speed of light c to obtain the distance from TAG to each ANCHOR;

[0035] S104. By using multiple distances and parameters, a set of spherical equations are listed, and the relative coordinate position of TAG with respect to ANCHOR can be obtained iteratively using numerical methods.

[0036] Furthermore, let the kinematic parameters P of the UAV be... uav as follows:

[0037]

[0038] The coordinate vector of the UAV's geodetic coordinate system is [x a y a , z a ] T The velocity vector of the drone is V a =[v ax v ay v az ] T The Euler angles of the drone are The angular velocity of the drone in the body coordinate system is ω a =[p a g a r a ] T ;

[0039] Let the kinematic parameters P of the unmanned surface vessel be... usv as follows:

[0040]

[0041] The spatial coordinate vector of the unmanned surface vessel is [x s y s , z s ] T The velocity vector of the unmanned surface vessel is V. s =[u s v s w s ] T The Euler angles of the unmanned surface vessel are The angular velocity of the unmanned surface vessel in the body coordinate system is ω a =[p s q s r s ] T ;

[0042] The flight deck of the unmanned surface vessel (USV) is located at the rear, and four UWB positioning base stations {A1, A2, A3, A4} are arranged around the deck. The USV is equipped with tag nodes. uav It communicates and measures distances with four base station beacons by measuring the Tag. uav The electromagnetic wave arrival time {τ} of the four ANCHORs to the deck of the unmanned surface vessel i If i = 1, 2, 3, 4}, multiplying by the speed of light c, we can obtain the distance from TAG to each ANCHOR as shown in equation (1).

[0043] ρ i =cτ i , i = 1, 2, 3, 4 (1).

[0044] Furthermore, the specific steps of enabling UWB positioning coordinates and activating the UAV landing mode are as follows: Let the unmanned surface vessel be in the geodetic coordinate system {O... E X E Y E Z E The three-dimensional coordinates of the four base station nodes under} are {p si =[x si y si , z si ] T , i = 1, 2, 3, 4}, while the UAV in the geodetic coordinate system {O E X E Y E Z E The unknown three-dimensional coordinates under} are p Ea =[x a y a , z a ] T The system of equations for the sphere can be obtained as shown in (2).

[0045]

[0046] The spatial coordinates of the UAV can be determined.

[0047] Furthermore, the positioning coordinate system {O} of the UAV in UWB is specified. w X w Y w Z w The three-dimensional coordinates under} are p w =[x w y w , z w ] T ,

[0048] The velocity vector of the unmanned surface vessel relative to the unmanned aerial vehicle is defined as V. r =[v rx v ry v rz ] T ,like

[0049] V r =(V s -V a (4)

[0050] In the coordinate system {O usv X usv Y usv Z usvWithin}, the three-dimensional coordinate vector of the UAV is set as p. sa =[x sa y sa , z sa ] T , and p Ea The transformation relationship is as shown in (5).

[0051]

[0052]

[0053] Where Δt is a minimal time interval, because sinθ s ≈θ s cosθ s ≈1, Therefore, we can obtain (7).

[0054]

[0055] If the unmanned surface vessel is in a constant speed and orientation navigation state, its heading angle ψ s =0, the only difference between the drone and the unmanned surface vessel is the northward velocity, i.e., v ry =v rz =0; therefore, we can obtain equation (8).

[0056]

[0057] This leads to (9)

[0058]

[0059] As shown in (9), when the UAV lands on the unmanned surface vessel, it should be kept as close to the horizontal plane as possible to ensure the horizontal positioning accuracy of the UWB.

[0060] Furthermore, the desired velocity increment is specifically defined as the horizontal coordinate deviation e of the UAV in the UWB coordinate system. u =[e x e y ,0] T The desired horizontal velocity V in the UWB coordinate system ud Then the controller is

[0061]

[0062] Among them, [K p K i K d [ ] represents the proportional, integral, and derivative control parameters of the controller. The controller adjusts these parameters based on the different operating conditions caused by the horizontal distance and speed difference between the unmanned surface vessel and the unmanned aerial vehicle.

[0063] Furthermore, in the vertical direction, the docking time t is determined by the horizontal relative velocity of the UAV. arrive Estimate the vertical descent speed of the UAV as shown in equation (11) to determine the descent speed of the UAV. arrive The case where the value is 1 occurs when the UAV is near the flight deck of the unmanned surface vessel and is about to land. In this case, the UAV's movement in the X direction of the UWB coordinate system will inevitably slightly exceed the center point of the flight deck, and adjustments made by the horizontal motion controller will cause v to... ux A value greater than 0 causes the estimated docking time to become negative.

[0064]

[0065] The desired altitude value of the UAV's vertical motion controller varies depending on the straight-line distance between the UAV and the center point of the deck. The UAV uses a vertical speed controller as shown in equation (12).

[0066]

[0067] Compared to existing technologies, it has the following advantages:

[0068] (1) This invention can greatly avoid the interference of wind and waves on the docking process of unmanned surface vessels and drones.

[0069] (2) The present invention has an extremely high docking success rate (up to 80%-95%) and is applicable to docking tasks of rotorcraft and unmanned surface vessels under various working conditions.

[0070] (3) This invention can provide high-speed and accurate relative pose data to complete high-precision dynamic docking.

[0071] (4) This invention is applicable to all-weather environments on the sea surface and has extremely low additional energy consumption and load on drones. Attached Figure Description

[0072] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0073] Figure 1 This is a schematic diagram showing the relative position of the UAV on the UWB positioning base station of the unmanned surface vessel according to the present invention;

[0074] Figure 2 The present invention relates to an autonomous docking control system for unmanned aerial vehicles (UAVs) and unmanned surface vessels.

[0075] Figure 3 This is the autonomous docking control algorithm architecture of the present invention.

[0076] Figure 4 This is a flowchart of the autonomous docking method for ships and aircraft according to the present invention. Detailed Implementation

[0077] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0078] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0079] An autonomous docking control system for dynamic landing of a UAV and an unmanned surface vessel (USV) at sea is provided. The control system includes a UAV control system and an USV control system. The UAV control system outputs the UAV's motion status and UWB tag signals to the USV control system. The USV control system outputs the USV's heading and speed information and its latitude and longitude information to the UAV control system.

[0080] The UAV control system includes sensor group I, altitude control unit, thruster control unit and wireless data transmission unit I;

[0081] The sensor group I is used in conjunction with the sensors in the sensor group II of the unmanned surface vessel for bidirectional positioning.

[0082] The altitude control unit is used for drone position control;

[0083] The thrust control unit of the thruster is used for attitude control of the UAV;

[0084] The wireless data transmission unit I is used to transmit UAV attitude data;

[0085] The unmanned surface vessel control system includes sensor group II, motion controller, thrust distribution unit, and wireless data transmission unit II;

[0086] The sensor group II is used in conjunction with the sensors in sensor group II of the UAV for bidirectional positioning.

[0087] The motion controller is used for path planning of the unmanned surface vessel;

[0088] The thrust distribution unit of the propulsion system is used to control the speed and heading of the unmanned surface vessel.

[0089] The wireless data transmission unit II is used to transmit the pose data and image data of the unmanned surface vessel.

[0090] Furthermore, the sensor group I includes a UWB positioning tag, an inertial measurement unit (IMU) I, a GNSS positioning system, a barometer, and a laser sensor.

[0091] The sensor group II includes a UWB positioning base station, an inertial measurement unit (IMU II), a dual-antenna GNSS positioning and orientation system, and a meteorological sensor.

[0092] The UWB positioning tag is used in conjunction with a UWB positioning base station;

[0093] The inertial measurement unit IMUⅠ is used in conjunction with the inertial measurement unit IMUⅡ;

[0094] The GNSS positioning system is used in conjunction with a dual-antenna GNSS positioning and orientation system.

[0095] The barometer is used in conjunction with the meteorological sensor at the weather station.

[0096] Furthermore, the unmanned surface vessel is equipped with a flight deck at the stern for autonomous take-off and landing of the UAVs; four UWB positioning base stations are arranged around the deck, and by fixing the relative positions of the four UWB base stations, the relative spatial coordinates of the UAVs carrying UWB positioning tags in the air can be determined.

[0097] An autonomous recovery method for an autonomous docking control system for a dynamic landing of a marine unmanned aerial vehicle (UAV) on an unmanned surface vessel (USV), characterized in that the autonomous recovery method uses the aforementioned autonomous docking control system for a dynamic landing of a marine UAV on an USV, and the autonomous recovery method is divided into two parts: the UAV approaching the USV horizontally and the UAV landing on the USV vertically.

[0098] In the horizontal direction, the unmanned surface vessel (USV) transmits its latitude and longitude coordinates, heading, and speed information to the unmanned aerial vehicle (UAV) in real time via UWB data transmission. The UAV compares its own latitude and longitude with those of the UAV to determine the straight-line distance between them. When the distance is less than the available distance threshold for UWB data, UWB positioning coordinates are activated, and the UAV enters landing mode. The heading of the USV obtained by the UAV via UWB data transmission is used as its expected heading value. Based on the USV's speed, the expected speed increment is calculated by the docking controller and added to the USV's current speed to obtain the expected speed, thus completing the horizontal approach.

[0099] In the vertical direction, the UAV uses a combination of barometers and laser rangefinders. The UAV records the current air pressure value the moment it takes off from the flight deck of the unmanned surface vessel as the initial altitude value. The laser rangefinder is used within the flight deck area, and the barometer is used to obtain the altitude value on the sea surface outside the flight deck. During the autonomous landing process, the UAV obtains the estimated landing time by the difference between its current relative speed and the difference between its current horizontal distance. Based on the estimated landing time and the UAV's current altitude value, the descent speed value of the UAV is estimated to ensure a smooth and stable landing trajectory.

[0100] Furthermore, the specific method for determining the straight-line distance between the drone and the unmanned surface vessel is as follows:

[0101] S101. To enable the unmanned surface vessel to navigate with the wind direction and at a constant speed, the unmanned surface vessel obtains the current wind speed and direction values ​​on the sea surface through the weather station sensor installed on the mast, and navigates with the wind as its desired heading angle and at a certain speed, thereby improving the hydrodynamics of the hull and minimizing the impact of the hull being rocked by the sea waves.

[0102] S102. Let the kinematic parameters P of the unmanned surface vessel be... usv With the kinematic parameters P of the UAV uav ;

[0103] S103. Based on the location of the UWB positioning base station on the unmanned surface vessel and the node tag of the UWB positioning tag on the unmanned surface vessel. uav GNSS system is used for navigation and approach, and Tag measurement is performed. uav The electromagnetic wave arrival time {τ} of the four ANCHORs to the deck of the unmanned surface vessel i Multiplying the values ​​of i = 1, 2, 3, 4 by the speed of light c gives the distance from the TAG to each ANCHOR.

[0104] S104. By using multiple distances and parameters, a set of spherical equations are listed, and the relative coordinate position of TAG with respect to ANCHOR can be obtained iteratively using numerical methods.

[0105] Furthermore, the unmanned surface vessel (USV) obtains the wind direction information at the sea surface using its onboard weather station sensors, and uses this downwind direction as the USV's desired heading. The USV then navigates with the wind at a constant speed and direction, thus reducing its sway from the waves. The USV transmits its latitude, longitude, speed, and heading information to the unmanned aerial vehicle (UAV) via UWB communication. Upon receiving the latitude and longitude data, the UAV uses its own GNSS sensors to calculate the coordinates in the UTM coordinate system, thereby determining the distance between the two coordinates.

[0106] Let the kinematic parameters P of the UAV be... uav as follows:

[0107]

[0108] The coordinate vector of the UAV's geodetic coordinate system is [x a y a , z a ] T The velocity vector of the drone is V a =[v ax v ay v az ]T The Euler angles of the drone are The angular velocity of the drone in the body coordinate system is ω a =[p a q a r a ] T ;

[0109] Let the kinematic parameters P of the unmanned surface vessel be... usv as follows:

[0110]

[0111] The spatial coordinate vector of the unmanned surface vessel is [x s y s , z s ] T The velocity vector of the unmanned surface vessel is V. s =[u s v s w s ] T The Euler angles of the unmanned surface vessel are The angular velocity of the unmanned surface vessel in the body coordinate system is ω a =[p s q s r s ] T ;

[0112] The flight deck of the unmanned surface vessel (USV) is located at the rear, and four UWB positioning base stations {A1, A2, A3, A4} are deployed around the deck. Figure 1 As shown. With this base station configuration, a positioning accuracy of 10cm can only be achieved within 30m of the base station. Therefore, when the UAV is more than 30m away from the unmanned surface vessel (USV), it uses a GNSS system for navigation and approach; when within 30m, it uses a UWB positioning system for navigation and approach. The UAV is equipped with a tag node. uav It communicates and measures distances with four base station beacons by measuring the Tag. uav The electromagnetic wave arrival time {τ} of the four ANCHORs to the deck of the unmanned surface vessel i If i = 1, 2, 3, 4}, multiplying by the speed of light c, we can obtain the distance from TAG to each ANCHOR as shown in equation (1).

[0113] ρ i =cτ i , i = 1, 2, 3, 4 (1).

[0114] Furthermore, the specific steps of enabling UWB positioning coordinates and activating the UAV landing mode are as follows: Let the unmanned surface vessel be in the geodetic coordinate system {O... E X E YE Z E The three-dimensional coordinates of the four base station nodes under} are {p si =[x si y si , z si ] T , i = 1, 2, 3, 4}, while the UAV in the geodetic coordinate system {O E X E Y E Z E The unknown three-dimensional coordinates under} are p Ea =[x a y a , z a ] T The system of equations for the sphere can be obtained as shown in (2).

[0115]

[0116] The spatial coordinates of the UAV can be determined.

[0117] By simplifying and rearranging, we can obtain the following form:

[0118]

[0119] Furthermore, the UWB positioning system used during the autonomous landing of the UAV acquires relative position data with the unmanned surface vessel, defining the UAV's positioning coordinate system {D} in UWB. w X w Y w Z w The three-dimensional coordinates under} are p W =[x w y w , z w ] T Because the UWB positioning base station is fixed to the deck of the unmanned surface vessel (USV), and the USV is affected by wind and waves while sailing at sea, it will experience a six-degree-of-freedom periodic oscillating motion; the UWB positioning coordinates p acquired by the UAV... W It will cause some interference.

[0120] The velocity vector of the unmanned surface vessel relative to the unmanned aerial vehicle is defined as V. r =[v rx v ry v rz ] I ,like

[0121] V r =(V s -V a (4)

[0122] In the coordinate system {O usv Xusv Y usv Z usv Within}, the three-dimensional coordinate vector of the UAV is set as p. Sa =[x sa y sa , z sa ] T , and p Ea The transformation relationship is as shown in (5).

[0123]

[0124]

[0125] Where Δt is a minimal time interval, because sinθ s ≈θ s cosθ s ≈1, Therefore, we can obtain (7).

[0126]

[0127] If the unmanned surface vessel is in a constant speed and orientation navigation state, its heading angle ψ s =0, the only difference between the drone and the unmanned surface vessel is the northward velocity, i.e., v ry =v rz =0; therefore, we can obtain equation (8).

[0128]

[0129] This leads to (9)

[0130]

[0131] From (9), it is concluded that when the UAV lands on the unmanned surface of the unmanned surface of the vessel, it should try to stay close to the horizontal plane to ensure the horizontal positioning accuracy of the UWB. Therefore, when the UAV is more than 1.5m away from the center deck of the unmanned surface of the vessel, it should return at the expected air pressure altitude of 2m near the deck surface.

[0132] The laser sensors of drones will fail on the sea surface, so a barometer is used to set the altitude on the sea surface, while a laser sensor is used to set the altitude when over the flight deck of the unmanned surface vessel.

[0133] The control algorithm framework for the autonomous docking of UAVs with unmanned surface vessels is as follows: Figure 3 As shown, the docking control uses a fuzzy PID-based controller. After obtaining the distance and speed difference between the UAV and the unmanned surface vessel, the data is input into the controller to obtain motion control parameters adapted to the working condition. These parameters are multiplied by the deviation to obtain the desired speed increment, thereby completing the horizontal approach of the UAV.

[0134] Furthermore, the desired velocity increment is specifically defined as the horizontal coordinate deviation e of the UAV in the UWB coordinate system. u =[e x e y ,0] T The desired horizontal velocity V in the UWB coordinate system ud Then the controller is

[0135]

[0136] Among them, [K p K i K d [ ] represents the proportional, integral, and derivative control parameters of the controller. The controller adjusts these parameters based on the different operating conditions caused by the horizontal distance and speed difference between the unmanned surface vessel and the unmanned aerial vehicle.

[0137] Furthermore, in the vertical direction, the docking time t is determined by the horizontal relative velocity of the UAV. arrive Estimate the vertical descent speed of the UAV as shown in equation (11) to determine the descent speed of the UAV. arrive The case where the value is 1 occurs when the UAV is near the flight deck of the unmanned surface vessel and is about to land. In this case, the UAV's movement in the X direction of the UWB coordinate system will inevitably slightly exceed the center point of the flight deck, and adjustments made by the horizontal motion controller will cause v to... ux A value greater than 0 causes the estimated docking time to become negative.

[0138]

[0139] The desired altitude value of the UAV's vertical motion controller varies depending on the straight-line distance between the UAV and the center point of the deck. The UAV uses a vertical speed controller as shown in equation (12).

[0140]

[0141] In summary, the autonomous docking of UAVs and unmanned surface vessels has been introduced. The flowchart of their autonomous docking algorithm is as follows: Figure 4 As shown, the hardware and software control system architecture is as follows: Figure 2 As shown.

[0142] The above description is merely 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. An autonomous recovery method for an autonomous docking control system of a marine unmanned aerial vehicle (UAV) dynamically landing unmanned surface vessel (USV), characterized in that, The autonomous recovery method uses an autonomous docking control system for dynamic landing of a UAV and an unmanned surface vessel (USV). The control system includes a UAV control system and an USV control system. The UAV control system outputs the UAV's motion status and UWB tag signals to the USV control system, and the USV control system outputs the USV's heading and speed information and the USV's latitude and longitude information to the UAV control system. The UAV control system includes sensor group I, altitude control unit, thruster control unit and wireless data transmission unit I; The sensor group I is used in conjunction with the sensors in the sensor group II of the unmanned surface vessel for bidirectional positioning. The altitude control unit is used for drone position control; The thrust control unit of the thruster is used for attitude control of the UAV; The wireless data transmission unit I is used to transmit UAV attitude data; The unmanned surface vessel control system includes sensor group II, motion controller, thrust distribution unit, and wireless data transmission unit II; The sensor group II is used in conjunction with the sensors in the sensor group I of the UAV for bidirectional positioning; The motion controller is used for path planning of the unmanned surface vessel; The thrust distribution unit of the propulsion system is used to control the speed and heading of the unmanned surface vessel. The wireless data transmission unit II is used to transmit the pose data and image data of the unmanned surface vessel. The autonomous recovery method is divided into two types: the UAV approaches the unmanned surface vessel horizontally and the UAV lands on the unmanned surface vessel vertically. In the horizontal direction, the unmanned surface vessel (USV) transmits its latitude and longitude coordinates, heading, and speed information to the unmanned aerial vehicle (UAV) in real time via UWB data transmission. The UAV compares its own latitude and longitude with those of the UAV to determine the straight-line distance between them. When the distance is less than the available distance threshold for UWB data, UWB positioning coordinates are activated, and the UAV enters landing mode. The heading of the USV obtained by the UAV via UWB data transmission is used as its expected heading value. Based on the USV's speed, the expected speed increment is calculated by the docking controller and added to the USV's current speed to obtain the expected speed, thus completing the horizontal approach. In the vertical direction, the UAV uses a combination of barometers and laser rangefinders. The UAV records the current air pressure value the moment it takes off from the flight deck of the unmanned surface vessel as the initial altitude value. The laser rangefinder is used within the flight deck area, and the barometer is used to obtain the altitude value on the sea surface outside the flight deck. During the autonomous landing process, the UAV obtains the estimated landing time by the difference between its current relative speed and the difference between its current horizontal distance. Based on the estimated landing time and the UAV's current altitude value, the descent speed value of the UAV is estimated to ensure the smooth and stable landing trajectory of the UAV. The specific method for determining the straight-line distance between the drone and the unmanned surface vessel is as follows: S101. Enables the unmanned surface vessel to navigate in the direction of the wind and maintain a constant speed; S102. Define the kinematic parameters of the unmanned surface vessel. Kinematic parameters of drones ; S103. Based on the location of the UWB positioning base station on the unmanned surface vessel and the node of the UWB positioning tag on the unmanned surface vessel. GNSS system is used for navigation and approach, and measurement. Electromagnetic wave arrival time of the four ANCHORs to the deck of the unmanned surface vessel Multiplied by the speed of light After that, I obtained Distance to each ANCHOR; S104. Using multiple distances and parameters, several sets of spherical equations are listed, which can be iteratively solved using numerical methods. The relative coordinate position with respect to ANCHOR.

2. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 1, characterized in that, Let the kinematic parameters of the UAV be... as follows: The coordinate vector of the UAV's geodetic coordinate system is: The velocity vector of the drone is The Euler angles of the drone are The angular velocity of the drone in the body coordinate system is ; Let the kinematic parameters of the unmanned surface vessel be defined. as follows: Wherein, the spatial coordinate vector of the unmanned surface vessel is The velocity vector of the unmanned surface vessel is The Euler angles of the unmanned surface vessel are The angular velocity of the unmanned surface vessel in the body coordinate system is ; The flight deck of the unmanned surface vessel (USV) is located at the rear, and four UWB positioning base stations are deployed around the deck. The drone is equipped with tag nodes It communicates and measures distances with four base station beacons, through measurement Electromagnetic wave arrival time of the four ANCHORs to the deck of the unmanned surface vessel Multiplied by the speed of light Then, the distance from the TAG to each ANCHOR can be obtained as shown in equation (1). （1）。 3. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 2, characterized in that, The specific steps for enabling UWB positioning coordinates and activating the drone landing mode are as follows: The unmanned surface vessel is set in a geodetic coordinate system... The three-dimensional coordinates of the four base station nodes are And drones in the geodetic coordinate system The unknown three-dimensional coordinates are as follows The system of equations for the sphere can be obtained as shown in (2). The spatial coordinates of the UAV can be determined.

4. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 3, characterized in that, Define the UAV's positioning coordinate system in UWB The three-dimensional coordinates below are , The velocity vector of the unmanned surface vessel relative to the unmanned aerial vehicle is defined as follows: ,like （4） In the coordinate system of the unmanned surface vessel Inside, the three-dimensional coordinate vector of the UAV is set as , and its sum The transformation relationship is as shown in (5). in For an extremely small time interval, because , , , Therefore, we can obtain (7). (7)； If the unmanned surface vessel is in a constant speed and orientation navigation state, its heading angle The only difference between the drone and the unmanned surface vessel is their northward speed. Therefore, we can obtain equation (8). （8） This leads to (9) （9） As shown in (9), when the UAV lands on the unmanned surface vessel, it should be kept as close to the horizontal plane as possible to ensure the horizontal positioning accuracy of the UWB.

5. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 4, characterized in that, The desired velocity increment is specifically defined as the horizontal coordinate deviation of the UAV in the UWB coordinate system. Desired horizontal velocity in UWB coordinate system Then the controller is （10） in, These are the proportional, integral, and derivative control parameters for the controller. The controller adjusts these parameters based on the different operating conditions caused by the horizontal distance and speed difference between the unmanned surface vessel and the unmanned aerial vehicle.

6. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 1, characterized in that, The vertical direction refers to the docking time of the drone's horizontal relative velocity. Estimate the vertical descent speed of the UAV as shown in Equation (11) to determine the vertical descent speed of the UAV; The case of a value of 1 occurs when the UAV is near the flight deck of the unmanned surface vessel and is about to land. In this case, the UAV's movement in the X direction of the UWB coordinate system will inevitably slightly exceed the center point of the flight deck, and adjustments made by the horizontal motion controller will... This caused the estimated docking time to become negative. （11） The desired altitude value of the UAV's vertical motion controller varies depending on the straight-line distance between the UAV and the center point of the deck. The UAV uses a vertical speed controller as shown in equation (12). （12）。 7. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 1, characterized in that, The sensor group I includes a UWB positioning tag, an inertial measurement unit (IMU I), a GNSS positioning system, a barometer, and a laser sensor. The sensor group II includes a UWB positioning base station, an inertial measurement unit (IMU II), a dual-antenna GNSS positioning and orientation system, and a meteorological sensor. The UWB positioning tag is used in conjunction with a UWB positioning base station; The inertial measurement unit IMUⅠ is used in conjunction with the inertial measurement unit IMUⅡ; The GNSS positioning system is used in conjunction with a dual-antenna GNSS positioning and orientation system. The barometer is used in conjunction with the meteorological sensor used in weather stations.

8. The autonomous recovery method of the autonomous docking control system for dynamic landing of unmanned surface vessels (USVs) at sea according to claim 1, characterized in that, The unmanned surface vessel has a flight deck at the stern for autonomous take-off and landing of the drones; four UWB positioning base stations are arranged around the deck. By fixing the relative positions of the four UWB base stations, the relative spatial coordinates of the drones carrying UWB positioning tags in the air can be determined.

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