A small shipborne cluster unmanned aerial vehicle skyhook recovery control method

Abstract

The application discloses a kind of small shipborne cluster unmanned aerial vehicle skyhook recovery control methods, belong to unmanned aerial vehicle control field;Specifically: for small shipborne cluster unmanned aerial vehicle, the relative position between unmanned aerial vehicle and ship, speed, heading and the attitude information of ship are obtained by differential satellite navigation, to guide unmanned aerial vehicle landing;The flight route in the process of unmanned aerial vehicle skyhook recovery is divided into three sections: approach segment flight control module controls unmanned aerial vehicle to reduce height and speed, aligns recovery device and enters follow-fly mode;The hooking point is constantly corrected by real-time attitude of ship in recovery section, and the lateral offset distance control and height control of unmanned aerial vehicle are constantly carried out by L1 guidance law and PID controller, to improve hooking accuracy;The state of unmanned aerial vehicle is monitored and judged at decision point and hooking point in flyback section, as long as entering flyback, reenter recovery mode by shortest route, to reduce recovery flight time, minimize the influence on subsequent unmanned aerial vehicle recovery in cluster.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicle (UAV) control, specifically relating to a method for controlling the recovery of a small shipborne swarm UAV using a skyhook. Background Technology

[0002] Currently, in order to enhance naval combat capabilities, enrich maritime combat methods, and improve the composition of air and sea forces, unmanned aerial vehicles (UAVs) are being gradually applied to various surface ships as a simple, efficient, low-cost, and low-risk combat platform to undertake tasks such as reconnaissance, surveillance, search, information relay, material transportation, and attack, greatly increasing the range of ship perception and attack capabilities.

[0003] Shipborne unmanned aerial vehicles (UAVs), due to their small size and lightweight design, can be equipped on warships such as aircraft carriers, destroyers, frigates, and amphibious ships, accompanying the motherships to various parts of the ocean to perform various combat missions, thus optimizing and expanding fleet combat modes. UAV swarms, as an important development direction, can significantly improve overall effectiveness compared to single UAVs, playing a crucial role in maritime application scenarios such as joint attacks, reconnaissance, and submarine detection.

[0004] Shipborne unmanned aerial vehicles (UAVs) can be broadly categorized as follows: fixed-wing UAVs, unmanned helicopters, tilt-wing UAVs, and compound-wing UAVs. Among these, fixed-wing UAVs offer advantages over other types, including larger payload capacity, higher speed, lower drag, simpler structure, higher reliability, and longer range. However, their takeoff and landing methods are the most complex, particularly landing and recovery. In swarm operations, managing the continuous landing and recovery of multiple UAVs will be a crucial challenge.

[0005] The main recovery methods for small shipborne fixed-wing UAVs include parachute landing, net landing, and hook landing. Parachute landing is highly susceptible to wind and requires additional equipment such as floats or airbags, as well as waterproofing the entire aircraft, so it is rarely used.

[0006] In recent years, an internationally developed rope-hook recovery system known as the "skyhook" has emerged, building upon net-collision recovery technology. This system typically consists of a capture device, a guidance device, and a buffer device. By guiding the drone near the capture device, precise navigation technology causes the drone to collide with the recovery rope. The rope slides along the wing to the wingtip, where a small hook catches and locks it. The drone then uses a gyratory deceleration mechanism to cushion the impact before being manually removed, completing the recovery process. Compared to net-collision recovery, the skyhook recovery device is simpler and has a longer longitudinal recovery window. However, it still requires a flight control system capable of precisely guiding the drone to collide with the capture device.

[0007] In shipboard applications, ships typically conduct drone recovery operations while at sea. Due to the limitations of the drone's wingspan and the effects of the ship's swaying and rolling motions, the vertical recovery rope, which is over ten meters long, will sway irregularly over a wide range. These factors not only increase the difficulty of recovering shipboard drones using the overhead hook, but also make the lateral trajectory tracking error of the drone a key factor affecting the success rate of recovery. Summary of the Invention

[0008] To address the problem of controlling the recovery of the overhead hook of fixed-wing UAVs in a shipborne environment, this invention provides a method for controlling the recovery of the overhead hook of small shipborne swarm UAVs. This method can effectively cope with the problem of large-scale swaying of the shipborne overhead hook device caused by sea waves in a maritime environment. At the same time, it has designed and optimized flight paths for issues such as go-around and swarm recovery.

[0009] The specific steps of the method for controlling the recovery of the small shipborne cluster UAV's skyhook are as follows:

[0010] Step 1: For small shipborne swarm drones, each small drone is equipped with a GD30 differential satellite navigation module and a flight control and navigation module, and small wingtip hooks are installed on both wingtips for retrieval of the grappling hook rope.

[0011] Step 2: Install the hook recovery device on the ship, raise the recovery rope, and set up a ground station and corresponding dynamic differential ground equipment in a safe area;

[0012] The shipborne hook recovery device has a recovery frame in which the recovery rope is vertically erected in an open space for the recovery of UAVs by hitting the hook; a rotating platform is installed at the bottom of the recovery frame, and the recovery rope is extended to three, which are evenly distributed along the circumference of the main rod of the recovery frame at 120-degree intervals; when the UAV successfully hits the hook, the recovery frame rotates 120 degrees and then fixes itself, and the next UAV can use the next recovery rope at the same time for the recovery operation.

[0013] Step 3: Set the required parameters for the hook recovery device in advance;

[0014] The parameters include the hook position offset, landing direction, relative altitude and speed when hitting the hook, distance between points on the landing path, error threshold of the go-around decision point, and the angle of the flight path.

[0015] Step 4: After the drone swarm completes its predetermined task, it issues a return command; three drones are divided into a group, returning in a fixed formation at fixed intervals, and then enter the recovery hook process.

[0016] When each group of drones is being recovered, the distance between the drones in front and behind should be maintained so that the hook recovery device automatically rotates 120 degrees via a turntable to the next task state.

[0017] Specifically:

[0018] Step 401: For the first UAV in the current group, its flight control and navigation module calculates the waypoints of the UAV's landing route in real time based on the received real-time position and attitude information of the ship, and continuously updates the route as the ship moves.

[0019] The landing route is rectangular and includes the following waypoints: follow point 1, approach point 2, decision point 3, hook point 4, go-around point 5, and transition point 6, with the four vertices being point 1, point 2, point 5, and point 6, respectively.

[0020] Step 402: When the UAV returns to the set range near the ship, it issues a landing command; it locks the latitude and longitude of waypoint 1 on the landing route at the moment the flight control and navigation module receives the landing command, and sets it as the target waypoint;

[0021] Step 403: During the process of the UAV flying to the target waypoint 1, gradually reduce to the preset altitude of the waypoint by means of ramp control.

[0022] Step 404: After the UAV reaches waypoint 1, it officially enters the landing phase. The target waypoint is switched to waypoint 2. The latitude and longitude of waypoint 2 at the time of the switch are locked. The UAV turns and descends to align with the landing route.

[0023] At waypoint 2, the actual flight path is the arc drawn by the minimum turning radius of the UAV.

[0024] Step 405: When turning at waypoint 2, switch the target waypoint to waypoint 3 and enter follow mode. The target waypoint (landing route) being pursued will move with the movement of the ship. Continue to descend while heading to waypoint 3 and eliminate side offset based on the L1 guidance law to align with the landing direction of the route.

[0025] Step 406: During the continuous correction of the flight path caused by the swing of the hook point waypoint 4, the target path at each moment is adjusted in real time, and the side offset is continuously corrected, that is, the current position of the UAV is continuously corrected by adjusting the roll attitude.

[0026] Step 407: When the UAV reaches waypoint 3, a go-around decision is made. If the decision is not met, the hook recovery is abandoned and an early go-around operation is performed; otherwise, the recovery operation is performed normally, and the process proceeds to step 408.

[0027] The go-around decision for waypoint 3 includes: determining whether the lateral offset is less than the lateral error threshold, whether the difference between the altitude and the desired hook point is less than the altitude error threshold, and whether the difference between the speed and the desired hook speed is less than the speed error threshold. If at least one of the above three conditions is not met, a go-around is performed.

[0028] When a go-around is initiated ahead of schedule, the point corresponding to waypoint 3 on the line connecting waypoints 5 and 6 is designated as waypoint 6', and the route formed by waypoints 1, 2, 3, and 6' is used as the new landing route. The flight control and navigation module determines and executes the latitude and longitude positions of waypoints 1, 2, 5, and 6' in the landing route at the go-around time, performs a circling go-around, and then re-executes the landing procedure.

[0029] During normal recovery operations, during the flight from waypoint 3 to waypoint 4, the yaw hook point is continuously tracked through lateral offset control and altitude control until hooking.

[0030] Step 408: When the UAV reaches waypoint 4, perform hook recovery. Determine if the instantaneous acceleration of the UAV is greater than 1.5G. If it is, the hook recovery is successful, the engine is shut down, and the UAV is removed after circling on the vertical recovery rope for buffering. Otherwise, the hook recovery fails, and a go-around operation is performed.

[0031] When going around the gate, the landing route is formed by waypoint 1, waypoint 2, waypoint 5 and waypoint 6. The go-around operation is the same as step 407.

[0032] Step 5: After the first drone in the group successfully hooks up or goes back to flight, the second drone flies normally to the recovery rack that has been rotated 120 degrees and also performs the hooking and recovery operation, followed by the third drone; the remaining drones hover and wait, ensuring that the distance between the drones in the current recovery group and the drones in the next standby group is such that at least one drone going back to flight can be inserted into the queue.

[0033] The advantages of this invention are:

[0034] (1) A small shipborne cluster UAV skyhook recovery control method, compared with arresting hook recovery, water surface parachute descent, net collision recovery and other methods, the device is simple, easy to assemble, occupies a small area, and can be mounted on most surface ships.

[0035] (2) A method for controlling the recovery of a small shipborne cluster UAV using a skyhook has been developed, which solves the problem of skyhook recovery under irregular swing conditions at sea and can maintain a high recovery success rate under certain wind and wave conditions. This method has been verified in a ground-based test.

[0036] (3) A method for controlling the recovery of small shipborne cluster UAVs by the skyhook, which is highly scalable and can be used to complete the skyhook recovery operation of small UAVs in various situations, including static ground sites, mobile ground platforms such as vehicles, and shipborne sites.

[0037] (4) A small shipborne cluster UAV skyhook recovery control method solves the application problem of using skyhook recovery device for cluster UAV recovery in shipborne environment, which enables UAV cluster to carry out reliable and efficient shipborne recovery operation, and further expands the application mode and scope of UAV cluster in marine environment. Attached Figure Description

[0038] Figure 1 This is a flowchart of a small shipborne cluster UAV skyhook recovery control method according to the present invention;

[0039] Figure 2 This is a schematic diagram of the design of the mobile station and the mobile base station for a small shipborne cluster UAV hook recovery control method according to the present invention;

[0040] Figure 3 This is a schematic diagram of the differential GNSS antenna design for a small shipborne cluster UAV skyhook recovery control method according to the present invention;

[0041] Figure 4 This is a schematic diagram of the design of a shipborne hook recovery device for a small shipborne cluster UAV hook recovery control method according to the present invention.

[0042] Figure 5 This is a plan view of the landing path of a small shipborne cluster UAV skyhook recovery control method according to the present invention (taking the landing direction as the left as an example);

[0043] Figure 6 This is a schematic diagram illustrating the follow-and-recovery route update of a small shipborne cluster UAV skyhook recovery control method according to the present invention.

[0044] Figure 7 This is a control flowchart for the landing phase of a small shipborne cluster UAV skyhook recovery control method according to the present invention;

[0045] Figure 8 This is a three-dimensional view of the landing path of a small shipborne cluster UAV skyhook recovery control method according to the present invention;

[0046] Figure 9 This is a diagram showing the route and waypoint altitude relationship of a small shipborne swarm UAV skyhook recovery control method according to the present invention;

[0047] Figure 10 This is a schematic diagram illustrating the lateral outer ring L1 guidance law used in this invention;

[0048] Figure 11 This is a schematic diagram of the time interval during the cluster recovery phase of a small shipborne cluster UAV skyhook recovery control method according to the present invention. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0050] This invention provides a method for controlling the recovery of small shipborne swarm UAVs using a skyhook, enabling small fixed-wing UAVs to land and be recovered using a skyhook recovery device in a shipborne environment. Figure 1 As shown, the specific steps are as follows:

[0051] Step 1: For small shipborne swarm drones, each small drone is equipped with a GD30 differential satellite navigation module and a flight control and navigation module, and small wingtip hooks are installed on both wingtips for retrieval of the grappling hook rope.

[0052] The drone selected is a small drone with a wingspan of approximately two meters; the GD30 differential satellite navigation module includes a mobile platform end and an airborne end:

[0053] The mobile platform is installed on the ship along with the ground station. It uses high-precision GNSS positioning and Beidou mobile reference station as a mobile base station. It transmits information such as the ship's attitude, position, heading, and speed back through the inertial navigation system and sends it to the airborne terminal in the form of differential messages.

[0054] The airborne terminal is installed on the UAV together with the flight control and navigation module. Through two differential GNSS antennas and a rover station, it measures the UAV's position and speed in real time and transmits the information back to the ground station. At the same time, it sends the received mobile platform information to the flight control and navigation module, which makes the recovery control decision.

[0055] The flight control and navigation module should be installed at the front of the fuselage away from the engine, and appropriate vibration reduction measures should be taken to prevent engine vibration from affecting the inertial navigation measurement. At the same time, it should be properly sealed to prevent airflow turbulence inside the fuselage compartment from affecting the measurement of equipment such as barometers.

[0056] Furthermore, the mobile station is installed in a suitable location and connected to the flight control and navigation module via a serial bus. The mobile station is designed as follows: Figure 2 As shown;

[0057] Furthermore, two differential GNSS antennas are mounted one in front of the other on the upper part of the fuselage, extending out through an opening. The line connecting the two antennas is parallel to the axis of the UAV and connected to the mobile station via a feeder.

[0058] Step 2: Install the hook recovery device on the ship, raise the recovery rope, and set up a ground station and corresponding dynamic differential ground equipment in a safe area;

[0059] The GD30 mobile base station should be installed at a high point in an open area to prevent signal obstruction and poor satellite signal reception. The design of the mobile base station is the same as that of the mobile station. Figure 2As shown. The dual antennas should also be arranged one in front of the other and aligned with the ship's axis to effectively measure the ship's heading. The dual antenna design diagram is shown below. Figure 3 As shown.

[0060] The shipborne air hook recovery device consists of a recovery frame, recovery rope, buffer device, and support frame. The recovery frame vertically sets up a recovery rope, which is several meters long, in an open space for the recovery of UAV hooks.

[0061] The overhead hook recovery device is specially designed for cluster application environments: a rotating platform is installed at the bottom of the recovery frame, and three recovery ropes are extended and evenly distributed around the main pole of the recovery frame at 120-degree intervals. After a drone successfully hits the hook, the recovery frame can rotate 120 degrees and then be fixed, allowing personnel to disassemble and recover the drone in a safe area. The next drone can then be recovered simultaneously using the next recovery rope. The design diagram of the shipborne overhead hook recovery device is shown below. Figure 4 As shown.

[0062] Step 3: Set the required parameters for the hook recovery device in advance;

[0063] The parameters include the hook position offset, landing direction, relative altitude and speed when hitting the hook, distance between points on the landing path, error threshold of the go-around decision point, and the angle of the flight path.

[0064] The offset of the hook position is the deviation between the actual measured position (installation position) of the differential motion base station and the position of the hook rope (actual hooking point), including the deviation in the direction of the ship's axis and the deviation in the direction perpendicular to the axis.

[0065] The landing direction is to choose to enter from the left or right, that is, to choose the direction of the landing route and the turning bend according to the actual situation of the ship.

[0066] The relative height when the hook hits the sky is the height difference between the desired hook point and the plane where the dynamic differential is located, i.e., the height offset;

[0067] The speed of the drone when it hits the hook should be the lowest speed it can maintain while flying straight and level. This ensures that the speed is low enough to reduce the impact energy on the aircraft, while preventing stall and maintaining the ability to go around. This speed should be set according to the specific performance of the drone.

[0068] like Figure 5 As shown, taking a landing approach from the left as an example, the landing path is rectangular and consists of 6 waypoints: 1. Follow-up point, 2. Approach point, 3. Decision point, 4. Hook-off point, 5. Go-around point, and 6. Transition point (6' is an advance transition point). The distance between adjacent waypoints needs to be set in advance, and the path is updated in real time as the ship moves. Figure 6 As shown;

[0069] The error threshold for the go-around decision point includes the lateral error threshold, the altitude error threshold, and the speed error threshold. When the UAV flies to waypoint 3, if any of the three factors—lateral deviation from the flight path, the difference between the current altitude and the hook altitude, or the difference between the current speed and the hook speed—is greater than the value set by the error threshold, it is determined that the UAV does not currently meet the hook-up conditions, and a go-around operation is immediately performed.

[0070] The approach angle is the angle between the approach side (the line connecting points 2, 3, 4, and 5) and the ship's axis.

[0071] Step 4: After the drone swarm completes its predetermined task, it issues a return command; three drones are divided into a group, returning in a fixed formation at fixed intervals, and then enter the recovery hook process.

[0072] When each group of drones is being recovered, the distance between the drones in front and behind should be maintained so that the hook recovery device automatically rotates 120 degrees via a turntable to the next task state.

[0073] like Figure 7 As shown, specifically:

[0074] Step 401: For the first UAV in the current group, its flight control and navigation module calculates the waypoints of the UAV's landing route in real time based on the received real-time position and attitude information of the ship and the preset parameters, and continuously updates the route as the ship moves.

[0075] like Figure 8 As shown, the four vertices of the landing path are point 1, point 2, point 5, and point 6.

[0076] The location of the retrieval rope for the hook is waypoint 4, calculated based on the latitude and longitude of the received ship's dynamic differential measurement position and the offset of the hook. The calculation method is as follows:

[0077] Lon4 = Lon D +(D x sinψ+D y cosψ) / (a*cos(Lat D ))

[0078] Lat4 = Lat D +(D x cosψ-D y sinψ) / a

[0079] Where Lon4 and Lat4 are the longitude and latitude of waypoint 4; Lon D and Lat D For the longitude and latitude of the location measured by dynamic differential measurement; D x and D yThese represent the offset forward along the ship's axis and the offset to the right perpendicular to the axis, respectively, in meters; ψ is the ship's heading; coefficient a is the conversion factor between latitude and longitude (°) and distance (m), a = 111195m / °.

[0080] The latitude and longitude of the remaining waypoints are calculated based on the location of waypoint 4, the angle of the route, and the relative distance between adjacent waypoints.

[0081] The altitudes of waypoints 1, 5, and 6 are the lower limit of the safe flight altitude for the UAV plus 20 meters; the altitudes of waypoints 3 and 4 are the relative altitudes at the time of the collision with the skyhook.

[0082] The altitude of waypoint 2 is derived from the distance ratios of waypoints 1 and 3, i.e.

[0083]

[0084] Where H1, H2, and H3 are the altitudes of waypoints 1, 2, and 3, respectively, and L 12 L is the horizontal distance between waypoints 1 and 2. 23 The horizontal distance between waypoints 2 and 3; the altitude relationships between waypoints are as follows: Figure 9 As shown.

[0085] Furthermore, the three-axis angles of the ship's roll are measured in real time using a dynamic differential system, thereby correcting the actual position of waypoint 4, which is the desired hook point on the recovery rope.

[0086] The correction method is as follows:

[0087] Establish a geodetic coordinate system with the base position of the hook retrieval rope after offset correction as the origin, with the x-axis pointing due north, the y-axis pointing due east, and the z-axis pointing vertically downward; similarly, establish a ship coordinate system with this point as the origin, with the x-axis pointing along the ship's axis towards the bow, the y-axis perpendicular to the x-axis pointing towards the right side of the ship, and the z-axis perpendicular to the ship's plane pointing downward.

[0088] At this point, with the ship stationary, the coordinates of the hook point in both coordinate systems are P = (0, 0, -H). e ) T H e This represents the relative height at the moment of impact with the hull hook. The three axis angles of the hull, measured via dynamic differential, are: roll angle... Given the pitch angle θ and yaw angle ψ, the transformation matrix between the two coordinate systems is:

[0089]

[0090] Assuming the hull and hook system are a rigid body, and neglecting factors such as deformation and relative displacement, the coordinates of the hook point in the hull coordinate system are always P. B =(0,0,-H) e) T .

[0091] Therefore, the coordinates of the hook point in the geodetic coordinate system at this time are P. G =T GB *P B .

[0092] Finally, the latitude corrections for the hook point were obtained as follows:

[0093] Lat=P G (1) / a

[0094] Lon = P G (2) / (a*cos(Lat b ))

[0095] H = P G (3)-P B (3) = P G (3)+H e

[0096] The latitude correction is Lat, the longitude correction is Lon, and the altitude correction is H; Lat b The latitude of the ship's hull.

[0097] Step 402: When the UAV returns to the set range near the ship, it issues a landing command; it locks the latitude and longitude of waypoint 1 on the landing route at the moment the flight control and navigation module receives the landing command, and sets it as the target waypoint;

[0098] Step 403: During the process of the UAV flying to the target waypoint 1, gradually reduce to the preset altitude of the waypoint by means of ramp control.

[0099] Among them, slope control is a height control method in which the UAV descends and descends along the slope of the line connecting two waypoints.

[0100] Step 404: After the UAV reaches waypoint 1, it officially enters the landing phase. The target waypoint is switched to waypoint 2. The latitude and longitude of waypoint 2 at the time of the switch are locked. The UAV turns and descends to align with the landing route.

[0101] At waypoint 2, the actual flight path is the arc drawn by the minimum turning radius of the UAV.

[0102] Step 405: When turning at waypoint 2, switch the target waypoint to waypoint 3 and enter follow mode. The target waypoint (landing route) being pursued will move with the movement of the ship. Continue to descend while heading to waypoint 3 and eliminate side offset based on the L1 guidance law to align with the landing direction of the route.

[0103] The side offset is the vertical distance between the UAV's current position and its current flight path, which in this case is the vertical distance between the UAV and the line connecting waypoints 2 and 3.

[0104] The specific control algorithm is as follows:

[0105] Depend on Figure 10 As shown, a reference point with a horizontal distance L1 from the current UAV position is selected on the target path, where d is the track error, V is the cruising speed (which can be taken as the ground speed of the UAV at this time), and η, η1, and η2 are the corresponding angles. Assuming that angle η is very small, the centripetal acceleration required for the UAV to make circular motion around the reference point at this time is:

[0106]

[0107] Depend on It can be seen that the above formula is equivalent to:

[0108] in

[0109] As can be seen from the above equation, in the case of linear tracking, the linear approximation model of this guidance law is a simple second-order system with a damping ratio of 0.707, and the natural frequency is determined by the ratio of velocity V to distance L1.

[0110] By selecting appropriate L1 distance parameters, measuring the magnitude and direction of the UAV's ground velocity vector V, and obtaining the target flight path based on the corrected waypoint 4 position at the current moment, the target's centripetal acceleration a can be calculated using the formula. aim From the equilibrium relationship of forces, the formula for calculating the target roll angle is:

[0111]

[0112] Where G is the weight of the drone;

[0113] The target roll angle is obtained through the L1 guidance law, which is then fed into the lateral inner loop control loop. The corresponding aileron control input is obtained through the inner loop PID controller. The calculation formula is as follows:

[0114]

[0115] in For the target roll angle, δ is the current roll angle. a For aileron rudder, These are, respectively, roll angle feedback gain, roll angle rate feedback gain, and roll angle integral gain. This represents the roll rate.

[0116] Step 406: As the flight path is constantly corrected due to the swing of the hook waypoint 4, the target path is adjusted in real time at each moment. The side offset is continuously corrected by the above control method. That is, the current position of the UAV is continuously corrected by adjusting the roll attitude in order to achieve real-time tracking of the swinging hook recovery rope.

[0117] Step 407: When the UAV reaches waypoint 3, a go-around decision is made. If the decision is not met, the hook recovery is abandoned and an early go-around operation is performed; otherwise, the recovery operation is performed normally, and the process proceeds to step 408.

[0118] The go-around decision for waypoint 3 includes: determining whether the lateral offset is less than the lateral error threshold, whether the difference between the altitude and the desired hook point is less than the altitude error threshold, and whether the difference between the speed and the desired hook speed is less than the speed error threshold. If at least one of the above three conditions is not met, a go-around is performed.

[0119] When a go-around is initiated ahead of schedule, the point corresponding to waypoint 3 on the line connecting waypoints 5 and 6 is designated as waypoint 6', and the route formed by waypoints 1, 2, 3, and 6' is used as the new landing route. The flight control and navigation module determines and executes the latitude and longitude positions of waypoints 1, 2, 5, and 6' in the landing route at the go-around time, performs a circling go-around, and then re-executes the landing procedure.

[0120] During normal recovery operations, during the flight from waypoint 3 to waypoint 4, the yaw hook point is continuously tracked through lateral offset control and altitude control until hooking.

[0121] Step 408: When the UAV reaches waypoint 4, perform hook recovery. Determine if the instantaneous acceleration of the UAV is greater than 1.5G. If it is, the hook recovery is successful, the engine is shut down, and the UAV is removed after circling on the vertical recovery rope for buffering. Otherwise, the hook recovery fails, and a go-around operation is performed.

[0122] When going around the gate, the landing route is formed by waypoint 1, waypoint 2, waypoint 5 and waypoint 6. The go-around operation is the same as step 407.

[0123] Step 5: After the first drone in the group successfully hooks up or goes back to flight, the second drone flies normally to the recovery rack that has been rotated 120 degrees and also performs the hooking and recovery operation, followed by the third drone; the remaining drones hover and wait, ensuring that the distance between the drones in the current recovery group and the drones in the next standby group is such that at least one drone going back to flight can be inserted into the queue.

[0124] Example:

[0125] The overall control and recovery strategy for the cluster is illustrated using a small fixed-wing UAV as an example:

[0126] This type of drone uses a rocket launch method, with a total of 18 drones forming a swarm. During the return journey after completing the mission, three drones are divided into groups, and each group returns in a fixed formation. By adjusting the speed, the drones are staggered at a certain distance from each other, and the recovery is completed in sequence.

[0127] During the recovery of each drone group, the distance between the drones should be sufficient to allow the hook recovery device to automatically rotate one-third of a revolution through the mechanical structure to reach the next mission state. During recovery, the remaining drone groups should hover in open airspace, ensuring that the distance between the current recovery group and the next standby group allows for at least one drone to rejoin the queue. Sufficient rejoining opportunities can significantly improve the overall recovery success rate of the cluster.

[0128] Actual testing showed that if the hook fails and the drone goes back to landing, it takes about 3 minutes to travel from waypoint 4 to waypoint 1 to re-enter the landing process. The hook recovery device rotates automatically through a mechanical structure. Assuming it takes about 1 minute to rotate one-third of a turn to the next mission state, and the drone can be manually removed before the recovery rope returns to the recovery position after the drone is successfully hooked.

[0129] Based on preliminary test data, assuming an 85% success rate for each drone to be successfully retrieved by the hook in a single attempt, and with a total of 18 drones to be retrieved by a single ship, the expected number of drones successfully retrieved on the first attempt is approximately 15, with an average of 3 drones failing to re-enter the airspace on the first attempt.

[0130] Considering only the scenario where hooking fails at waypoint 4 (ignoring the scenario of go-around at waypoint 3), and taking into account other factors, the overall cluster recovery process is designed as follows:

[0131] like Figure 11 As shown, three drones are grouped together for recovery, for a total of six groups. Each group of drones is positioned one minute apart, and based on the drone's cruising speed of 42 m / s, the distance between drones is approximately 2520 meters. During recovery, the remaining groups of drones hover in open airspace, ensuring a two-minute interval between each group. This allows for a drone to be inserted into the queue for a second recovery. Thus, the first drone in each group can directly join the queue for a go-around, while the second and third drones, if needing a go-around, can hover at staggered altitudes at waypoint 1, waiting to be inserted into the next group interval.

[0132] This allows the entire cluster retrieval queue to provide 5 re-entry opportunities, exceeding the expected 3. With an 85% success rate for each drone on the first attempt, the second re-entry opportunity can increase the success rate to 97.75%, significantly improving the likelihood of successful retrieval of a single drone. If the second retrieval attempt still fails, it indicates a potential malfunction in the drone, requiring manual intervention to implement protective measures. Assuming the last group of drones successfully hooks on the first attempt and no further re-entries occur, the total time required for retrieval of all drones is approximately 22 minutes.

Claims

1. A method for controlling the recovery of a small shipborne swarm UAV's overhead hook, characterized in that, The specific steps are as follows: Step 1: For small shipborne swarm drones, each small drone is equipped with a GD30 differential satellite navigation module and a flight control and navigation module, and small wingtip hooks are installed on both wingtips for retrieval of the hook rope. Step 2: Install the hook recovery device on the ship, raise the recovery rope, and set up a ground station and corresponding dynamic differential ground equipment in a safe area; Step 3: Set the required parameters for the hook recovery device in advance; Step 4: After the drone swarm completes its predetermined task, it issues a return command; three drones are divided into a group, returning in a fixed formation at fixed intervals, and then enter the recovery hook process. When each group of drones is recovered, the distance between the drones in front and behind should be maintained so that the hook recovery device automatically rotates 120 degrees via the turntable to the next task state; Specifically: Step 401: For the first UAV in the current group, its flight control and navigation module calculates the waypoints of the UAV's landing route in real time based on the received real-time position and attitude information of the ship, and continuously updates the route as the ship moves. The landing route is rectangular and includes the following waypoints: follow point 1, approach point 2, decision point 3, hook point 4, go-around point 5, and transition point 6, with the four vertices being point 1, point 2, point 5, and point 6, respectively. Step 402: When the UAV returns to the set range near the ship, it issues a landing command; it locks the latitude and longitude of point 1 on the landing route at the moment the flight control and navigation module receives the landing command, and sets it as the target waypoint; Step 403: During the flight of the UAV to the target waypoint, gradually descend to the preset altitude of the waypoint by means of ramp control; Step 404: After the UAV reaches the target waypoint, it officially enters the landing phase. The target waypoint is switched to point 2. The latitude and longitude of point 2 at the time of switching are locked. The UAV turns and descends to align with the landing route. The actual flight trajectory at point 2 is the arc drawn by the minimum turning radius of the drone; Step 405: When turning at point 2, switch the target waypoint to point 3 and enter follow mode. The target waypoints being chased will move with the movement of the ship. Continue to descend while heading to point 3 and eliminate the side offset based on the L1 guidance law to align with the landing direction of the flight path. Step 406: In the process of continuous flight path correction caused by the 4-point oscillation, adjust the target path at each moment in real time and continuously correct the side offset, that is, continuously correct the current position of the UAV by adjusting the roll attitude. Step 407: When the drone reaches point 3, a go-around decision is made. If the decision is not met, the hook recovery is abandoned and an early go-around operation is performed. Otherwise, proceed with the normal recycling operation and proceed to step 408; The three-point go-around decision includes: determining whether the lateral deviation is less than the lateral error threshold, whether the difference between the altitude and the desired hook point is less than the altitude error threshold, and whether the difference between the speed and the desired hook speed is less than the speed error threshold. If at least one of the above three conditions is not met, a go-around is performed. When the go-around is performed ahead of schedule, the corresponding point on the line connecting point 3 and point 5 and point 6 is designated as point 6'. The route consisting of points 1, 2, 3 and 6' is used as the new landing route. The latitude and longitude positions of points 1, 2, 5 and 6' in the landing route at the time of the go-around are locked by the flight control and navigation module. After the go-around is performed, the landing procedure is executed again. During normal recovery operations, during the flight from 3 o'clock to 4 o'clock, the lateral offset control and altitude control are used to continuously track the swing hook point until the hook is hooked. Step 408: When the drone reaches point 4, perform hook recovery. Determine if the instantaneous acceleration of the drone is greater than 1.5G. If it is, the hook recovery is successful, the engine is shut down, and the drone is taken off after circling on the vertical recovery rope for buffering. Otherwise, the hook recovery fails, and a go-around operation is performed. When going around the gate, the landing route consists of points 1, 2, 5, and 6. Step 5: After the first drone in the group successfully hooks up or goes back to flight, the second drone flies normally to the recovery rack that has been rotated 120 degrees and also performs the hooking and recovery operation, followed by the third drone; the remaining drones hover and wait, ensuring that the distance between the drones in the current recovery group and the drones in the next standby group is such that at least one drone going back to flight can be inserted into the queue.

2. The method for controlling the recovery of the overhead hook of a small shipborne swarm UAV as described in claim 1, characterized in that, The GD30 differential satellite navigation module in each small UAV includes both mobile platform and airborne components: The mobile platform is installed on the ship along with the ground station. It uses high-precision GNSS positioning and Beidou mobile reference station as a mobile base station. It transmits the ship's attitude, position, heading and speed information back through the inertial navigation system and sends it to the airborne terminal in the form of differential messages. The airborne terminal is installed on the UAV together with the flight control and navigation module. Through two differential GNSS antennas and a rover station, it measures the UAV's position and speed information in real time and transmits it back to the ground station. At the same time, it sends the received mobile platform information to the flight control and navigation module, which makes the recovery control decision.

3. The method for controlling the recovery of the overhead hook of a small shipborne swarm UAV as described in claim 1, characterized in that, The recovery frame in the hook recovery device vertically sets up the recovery rope in an open space for drones to be retrieved by hitting the hook; a rotating platform is installed at the bottom of the recovery frame, and the recovery rope is extended to three, evenly distributed along the circumference of the main rod of the recovery frame at 120-degree intervals; when the drone successfully hits the hook, the recovery frame rotates 120 degrees and then fixes itself, and the next drone can use the next recovery rope at the same time for the recovery operation.

4. The method for controlling the recovery of the overhead hook of a small shipborne swarm UAV as described in claim 1, characterized in that, The parameters include the hook position offset, landing direction, relative altitude at the time of hook collision, speed, distance between points on the landing path, error threshold of the go-around decision point, and the angle of the flight path.

5. The method for controlling the recovery of the overhead hook of a small shipborne swarm UAV as described in claim 1, characterized in that, In step 401, the hook point 4 refers to the location of the top hook recovery rope, and the calculation method is as follows: in and These are the longitude and latitude of the four points, respectively. and These are the longitude and latitude of the location measured by the dynamic differential measurement, respectively. and These are the offsets forward along the ship's axis and the offsets to the right perpendicular to the axis, respectively. For the ship's heading angle; coefficient This is the conversion factor between latitude / longitude and distance; The latitude and longitude of the remaining waypoints are calculated based on the positions of the four points, the angle between the flight paths, and the relative distances between adjacent waypoints. The altitudes at points 1, 5, and 6 are the lower limit of the safe flight altitude for drones plus 20 meters; the altitudes at points 3 and 4 are the relative altitudes at the point of impact. The height of point 2 is derived from the heights of points 1 and 3, using the ratio of distances between each point, i.e.: in , , The heights at points 1, 2, and 3 are respectively. The horizontal distance between points 1 and 2. The horizontal distance between points 2 and 3.

6. The method for controlling the recovery of the overhead hook of a small shipborne swarm UAV as described in claim 1, characterized in that, In step 401, the three-axis angles of the ship's sway are measured in real time by a dynamic differential system, and the actual positions of the four points, namely the desired hook points on the recovery rope, are corrected accordingly.

7. The method for controlling the recovery of the skyhook of a small shipborne swarm UAV as described in claim 1, characterized in that, In step 405, the side offset is the vertical distance between the current position of the UAV and the current flight path, which is the vertical distance between the UAV and the line connecting points 2 and 3. The target roll angle is obtained through the L1 guidance law, which is then fed into the lateral inner loop control loop. The corresponding aileron control input is obtained through the inner loop PID controller. The calculation formula is as follows: in For the target roll angle, The current roll angle, For aileron rudder, , , These are, respectively, roll angle feedback gain, roll angle rate feedback gain, and roll angle integral gain. This represents the roll rate.

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