Precise landing method and system for unmanned aerial vehicle and unmanned aerial vehicle

Abstract

The invention discloses an unmanned aerial vehicle accurate landing method and system and an unmanned aerial vehicle. The method comprises the following steps: establishing a longitudinal relative motion model between an unmanned aerial vehicle and a ground target point to obtain a sight angle and a sight angle rate required by guidance in real time; based on a longitudinal relative motion model and an optimal control theory, constructing an optimal guidance law containing terminal falling angle constraints; in the gliding process of the unmanned aerial vehicle, whether the unmanned aerial vehicle is switched to the optimal guidance law for control or not is judged based on the real-time states of the flight height, the sinking rate and the wind speed; and when the optimal guidance law is adopted for control, a guidance instruction is generated based on the sight angle and the sight angle rate, and dynamic amplitude limiting is performed on the guidance instruction according to the sinking rate safety allowable range corresponding to the current flight height, so that the unmanned aerial vehicle realizes accurate landing under the double constraints of the sinking rate and the terminal falling angle. According to the invention, accurate landing of the unmanned aerial vehicle in a windless or wind disturbance scene can be realized, and meanwhile, the stability and safety of the landing process are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of unmanned aerial vehicle control, and more particularly relates to an unmanned aerial vehicle precise landing method and system and unmanned aerial vehicle. BACKGROUND

[0002] As a kind of unmanned aerial vehicle, the unmanned aerial vehicle has been widely used in logistics distribution, geographic mapping, emergency rescue, power inspection and other fields due to its low requirement for take-off and landing environment and strong survival ability. The complete flight process of the unmanned aerial vehicle mainly covers three core stages of take-off, autonomous flight and landing. Among them, the take-off stage and the autonomous flight stage have matured, and the stability and reliability of the related control system have been fully verified.

[0003] However, the landing stage, as a key closing link of the unmanned aerial vehicle flight task, still faces many technical problems and becomes the core bottleneck restricting the safe and efficient application of the unmanned aerial vehicle. In the actual landing scene, the unmanned aerial vehicle needs to land accurately on the preset target point, but its landing accuracy is easily affected by many factors: on the one hand, the existing unmanned aerial vehicle landing control method (such as the traditional sink rate control method) has inherent defects. This method needs to adjust the pitch angle of the unmanned aerial vehicle at the near point of the glide process to maintain the sink rate in a reasonable range. This operation will directly affect the landing point accuracy, and it is difficult to control the landing error within a small range. On the other hand, the flight speed of the unmanned aerial vehicle is low during the landing stage, and the resistance to external disturbances is significantly weakened. Especially the environmental factors such as wind disturbance will cause the flight attitude of the unmanned aerial vehicle to deviate, further expand the landing error, and even cause flight safety accidents in severe cases.

[0004] In addition, most of the existing guidance technologies cannot simultaneously consider the dual requirements of terminal landing angle constraint and sink rate constraint: some guidance laws only focus on landing angle control, ignoring the problem of too large landing impact caused by sink rate overrun; another part of the methods pays attention to sink rate adjustment, but lacks precise constraint on the terminal landing angle, and cannot meet the requirements of smooth landing in complex scenarios. These technical shortcomings greatly limit the application of the unmanned aerial vehicle in high-precision landing scenarios (such as precise equipment delivery, narrow area take-off and landing, precise delivery of emergency supplies, etc.). How to realize the precise, smooth and safe landing of the unmanned aerial vehicle in complex environments has become a technical problem to be solved in the field.

[0005] Therefore, in view of the defects of the existing unmanned aerial vehicle landing method, such as insufficient landing accuracy, weak anti-wind disturbance ability, and difficulty in simultaneously meeting multiple constraint conditions, it is urgent to develop an unmanned aerial vehicle precise landing technology that can consider landing point accuracy, terminal landing angle constraint, sink rate control and anti-interference performance, in order to ensure the safety and reliability of the unmanned aerial vehicle landing process and further expand the application boundary of the unmanned aerial vehicle. SUMMARY

[0006] The application aims to provide a UAV precision landing method, system and UAV, solve the technical problems of insufficient landing precision, weak wind disturbance resistance and difficulty in simultaneously meeting the double constraints of sink rate and terminal landing angle of the existing UAV landing method, realize the precise landing of the UAV in a windless or wind disturbance scene, ensure the stability and safety of the landing process, and expand the application boundary of the UAV in high-precision landing demand scenes.

[0007] To achieve the above-mentioned purpose, in a first aspect, the application provides a UAV precision landing method, comprising:

[0008] A longitudinal relative motion model between the UAV and the ground target point is established to obtain the line-of-sight angle and line-of-sight angle rate required for real-time guidance;

[0009] Based on the longitudinal relative motion model and optimal control theory, an optimal guidance law containing terminal landing angle constraints is constructed;

[0010] During the UAV descent process, based on the real-time state of flight height, sink rate and wind speed, it is judged whether to switch to the optimal guidance law for control;

[0011] When the optimal guidance law is used for control, a guidance instruction is generated based on the line-of-sight angle and line-of-sight angle rate, and the guidance instruction is dynamically limited in amplitude according to the sink rate safety allowable range corresponding to the current flight height, so that the UAV realizes precise landing under the double constraints of sink rate and terminal landing angle.

[0012] Optionally, the longitudinal relative motion model is:

[0013]

[0014] Wherein, r is the relative distance between the UAV and the ground target point, q is the line-of-sight angle between the UAV and the ground target point, V M is the UAV velocity vector, V T is the ground target point velocity vector; ε M , ε T are the front angles of the UAV and the ground target point respectively, θ M , θ T are the angles between the UAV velocity vector and the ground target point velocity vector and the reference line respectively, a M , a T are the normal accelerations of the UAV and the ground target point respectively.

[0015] Optionally, the calculation expression of the line-of-sight angle and line-of-sight angle rate is:

[0016]

[0017] Wherein, For the line-of-sight angular rate of the UAV and the ground target point, (R x ,R y )and These represent the relative position and relative velocity components of the UAV and the ground target point in the longitudinal plane, respectively. x =x T -x M R y =y T -y M , (x M ,y M (x) represents the position coordinates of the UAV in the longitudinal plane. T ,y T The coordinates of the ground target point in the longitudinal plane.

[0018] Optionally, the optimal guidance law is:

[0019]

[0020] Among them, u * (t) represents the guidance command, t go This represents the remaining flight time for the drone to reach the ground target. V R Let q be the relative approach speed between the drone and the ground target point. f For the desired terminal landing angle, R xy This represents the relative straight-line distance between the drone and the ground target point.

[0021] Optionally, determining whether to switch to the optimal guidance law for control based on the real-time status of flight altitude, sink rate, and wind disturbance includes:

[0022] The criterion is activated when the flight altitude is less than or equal to the first preset altitude.

[0023] If the current descent rate is less than the first threshold, or the current descent rate is greater than the second threshold, or the wind speed is greater than the preset wind speed threshold, or the flight altitude is less than the second set altitude, then switch to the optimal guidance law; otherwise, control the UAV to descend normally according to the original control mode.

[0024] Optionally, the safe allowable range of sinking rate is set in segments according to flight altitude, including:

[0025] When the flight altitude H is within the first altitude range, the safe allowable range for the sinking rate is:

[0026] When the flight altitude is in the second altitude range, the safe allowable range for the sinking rate is:

[0027] Wherein, the first altitude range is: second set altitude ≤ H ≤ first set altitude; the second altitude range is: H < second set altitude; first threshold < third threshold < second threshold; and H is the flight altitude of the drone. This represents the sinking rate of the drone.

[0028] Optionally, the step of dynamically limiting the guidance command based on the safe allowable range of the sink rate corresponding to the current flight altitude includes:

[0029] If the current flight altitude is within the first altitude range, the vertical velocity command calculated by the guidance command will be restricted to the range [first threshold, second threshold].

[0030] When the current flight altitude is within the second altitude range, the vertical velocity command calculated by the guidance command is restricted to the range (third threshold, second threshold).

[0031] Optionally, the first set height is 50m, the second set height is 10m, the preset wind speed threshold is 5m / s, the first threshold is -4m / s, the second threshold is -0.5m / s, and the third threshold is -1.5m / s.

[0032] Secondly, this invention proposes a precision landing system for unmanned aerial vehicles (UAVs), comprising:

[0033] The model is established and acquired to create a longitudinal relative motion model between the UAV and the ground target point, so as to acquire the line-of-sight angle and line-of-sight angular rate required for guidance in real time.

[0034] The construction module is used to construct an optimal guidance law that includes terminal landing angle constraints based on the longitudinal relative motion model and optimal control theory.

[0035] The judgment module is used to determine whether to switch to the optimal guidance law for control during the descent of the UAV, based on the real-time status of flight altitude, sink rate and wind speed.

[0036] The generation and limiting module is used to generate guidance commands based on the line-of-sight angle and line-of-sight angle rate when using the optimal guidance law for control, and to dynamically limit the guidance commands according to the safe allowable range of the sink rate corresponding to the current flight altitude, so that the UAV can achieve precise landing under the dual constraints of sink rate and terminal landing angle.

[0037] Thirdly, the present invention proposes an unmanned aerial vehicle (UAV) including the UAV precision landing system described in the second aspect.

[0038] The beneficial effects of this invention are as follows: By establishing a longitudinal relative motion model between the UAV and the ground target point to obtain accurate line-of-sight angle and line-of-sight angular rate in real time, reliable data support is provided for guidance and control. Combined with optimal control theory, an optimal guidance law with terminal landing angle constraints is constructed to ensure the accuracy of landing angle control. At the same time, during the descent, the timing of guidance law switching is adaptively judged based on the real-time status of flight altitude, sink rate, and wind speed, effectively improving the resistance to external disturbances such as wind disturbances. Furthermore, by dynamically setting the safe allowable range of sink rate according to the current flight altitude, the guidance command is targeted and limited, achieving the dual constraint satisfaction of sink rate and terminal landing angle. Ultimately, the UAV can achieve accurate landing in both windless and windy scenarios, significantly improving the stability and safety of the landing process, and greatly expanding the application adaptability of the UAV in high-precision landing scenarios.

[0039] The system of the present invention has other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0040] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0041] Figure 1 A flowchart illustrating the steps of a precise landing method for a drone according to Embodiment 1 of the present invention is shown.

[0042] Figure 2 A flowchart of the optimal guidance law control criterion according to Embodiment 2 of the present invention is shown.

[0043] Figure 3 A schematic diagram of the pitch angle-time curve of the glide landing segment according to Embodiment 2 of the present invention is shown.

[0044] Figure 4 A schematic diagram of the sinking rate-time curve of the glide landing segment according to Embodiment 2 of the present invention is shown.

[0045] Figure 5 A schematic diagram of the altitude-range curve of the glide landing segment according to Embodiment 2 of the present invention is shown.

[0046] Figure 6 A schematic diagram of the altitude-distance curve for a normal descent using the sink rate method under wind disturbance, according to Embodiment 2 of the present invention, is shown.

[0047] Figure 7 A schematic diagram of the altitude-range curve of a UAV descending under wind disturbance and employing a precision landing method based on the optimal guidance law according to Embodiment 2 of the present invention is shown. Detailed Implementation

[0048] The invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0049] Example 1

[0050] like Figure 1 As shown, this embodiment provides a method for precise landing of a drone, including:

[0051] S1. Establish a longitudinal relative motion model between the UAV and the ground target point to obtain the line-of-sight angle and line-of-sight angular rate required for guidance in real time;

[0052] Specifically, a longitudinal relative motion model between the UAV and the ground target point is constructed based on a fixed ground coordinate system, laying the foundation for the real-time acquisition of core parameters required for guidance. First, key positional information in the ground coordinate system is defined. The UAV's position changes in real time during flight, while the ground target point (the preset landing point) remains fixed. By collecting real-time spatial positional data of both, the relative motion distance parameters in the longitudinal plane are further calculated, including the positional difference in the horizontal direction, the positional difference in the vertical direction, and the straight-line distance between the UAV and the ground target point. Simultaneously, by continuously monitoring the dynamic changes in the positions of the UAV and the target point, the real-time rate of change of their relative positions in the horizontal and vertical directions is captured, i.e., the relative motion velocity in the corresponding directions. Based on these acquired relative motion distance and velocity data, combined with geometric relationships, the core parameters in the guidance process are derived: the line-of-sight angle (LAS) and the LAS angular rate. The LAS refers to the angle formed between the line connecting the UAV and the ground target point and the horizontal baseline of the ground coordinate system, used to accurately characterize their relative orientation; the LAS angular rate is the real-time rate of change of the LAS over time, reflecting the dynamic trend of the relative orientation change between the UAV and the target point. Through real-time calculation of this longitudinal relative motion model, accurate and continuous line-of-sight angle and line-of-sight angular rate data can be continuously output, providing key and reliable basic input parameter support for subsequent calculation of the optimal guidance law and generation of guidance and control commands.

[0053] In this step, the longitudinal relative motion model is as follows:

[0054]

[0055] Where r is the relative distance between the UAV and the ground target, q is the line-of-sight angle between the UAV and the ground target, and V M V is the velocity vector of the UAV. T ε is the velocity vector of the ground target point; M ε T θ represents the leading angle of the drone and the ground target point, respectively. M θ T These are the angles between the UAV velocity vector and the ground target point velocity vector and the baseline, respectively. M a T These represent the normal accelerations of the drone and the ground target point, respectively.

[0056] In this step, the expressions for calculating the line-of-sight angle and line-of-sight angular rate are:

[0057]

[0058] in, For the line-of-sight angular rate of the UAV and the ground target point, (R x ,R y )and These represent the relative position and relative velocity components of the UAV and the ground target point in the longitudinal plane, respectively. x =x T -x M R y =y T -y M , (x M ,y M (x) represents the position coordinates of the UAV in the longitudinal plane. T ,y T The coordinates of the ground target point in the longitudinal plane.

[0059] S2. Based on the longitudinal relative motion model and optimal control theory, construct an optimal guidance law that includes terminal landing angle constraints;

[0060] Specifically, based on the established longitudinal relative motion model, by introducing optimal control theory, a guidance law capable of precisely controlling the UAV's terminal landing attitude can be designed. This method first defines the UAV's guidance process as an optimal control problem with terminal state constraints. Its core lies in constructing a performance index that comprehensively evaluates energy consumption and control accuracy during flight, and incorporating the requirement that the UAV's line-of-sight angle at the terminal moment must equal the preset desired landing angle as a key boundary condition into the system design. By applying the variational method or minimum principle in optimal control theory to solve this problem, an analytical form of the guidance command expression can be derived. This command consists of two parts: one part is proportional to the line-of-sight rotation rate, its function being to actively suppress any deviation in the line-of-sight direction in real time, ensuring that the flight path always points towards the target; the other part is proportional to the deviation between the current line-of-sight angle and the desired terminal landing angle, and its corrective effect dynamically increases as the remaining flight time decreases, thus specifically used to eliminate terminal angle errors. Ultimately, this design enables the generated guidance law to not only guide the UAV to fly accurately to the target point, but also to intelligently adjust the glide trajectory to ensure that at the moment of arrival at the target point, the UAV's flight path angle forms a pre-set angle with the ground that is conducive to a smooth and safe landing, thus seamlessly integrating the terminal landing angle constraint into the entire optimal control framework.

[0061] In this step, the optimal guidance law is:

[0062]

[0063] Among them, u * (t) represents the guidance command, t go This represents the remaining flight time for the drone to reach the ground target. V R Let q be the relative approach speed between the drone and the ground target point. f For the desired terminal landing angle, R xy This represents the relative straight-line distance between the drone and the ground target point.

[0064] S3. During the descent of the drone, based on the real-time status of flight altitude, sink rate and wind speed, determine whether to switch to the optimal guidance law for control;

[0065] Specifically, after the drone enters the descent and landing phase, a guidance law switching criterion mechanism is specifically set up to ensure the accuracy and stability of the landing process. This mechanism uses real-time monitoring data of flight altitude, descent rate, and wind speed as the core judgment basis to dynamically decide whether to activate the optimal guidance law. First, flight altitude serves as the basic threshold for triggering the criterion. When the drone descends to a preset key altitude node, the criterion mechanism is officially activated and begins to continuously monitor various parameters. At this time, it is crucial to focus on whether the drone's current altitude is within the range requiring high-precision control, ensuring that the switching decision is triggered only during the critical landing phase. Second, the descent rate, as a core indicator reflecting the drone's vertical descent speed, needs to be judged in real time to ensure it is within a safe and reasonable range. If the descent rate is detected to be too fast or too slow, exceeding the preset allowable range for smooth landing, it indicates a risk of deviation in the current flight state, requiring timely correction through the optimal guidance law. Simultaneously, wind speed, as a major external disturbance factor, requires real-time monitoring of the wind field's interference intensity on the drone's longitudinal motion. If excessive wind speed is detected, causing instability in the drone's flight attitude or potentially leading to landing trajectory deviation, it is determined as a scenario requiring intervention with the optimal guidance law. During the execution of the judgment criteria, the three parameters mentioned above are monitored in real time. If any one or more of these parameters reach the preset switching trigger condition, the UAV is immediately switched from the current conventional glide control mode to the optimal guidance law control mode, and this mode is maintained until landing is completed. If all parameters are within the preset safety range, the original conventional control mode is maintained to ensure the continuity and stability of the glide process. This adaptive switching mechanism based on the real-time status of multiple parameters can accurately grasp the intervention timing of the optimal guidance law, avoiding control redundancy caused by premature switching and responding promptly to various deviations and disturbances during flight, thus ensuring a precise landing.

[0066] In this step, determining whether to switch to the optimal guidance law for control based on the real-time status of flight altitude, sink rate, and wind disturbance includes:

[0067] The criterion is activated when the flight altitude is less than or equal to the first preset altitude.

[0068] If the current descent rate is less than the first threshold, or the current descent rate is greater than the second threshold, or the wind speed is greater than the preset wind speed threshold, or the flight altitude is less than the second set altitude, then switch to the optimal guidance law; otherwise, control the drone to descend normally according to the original control mode.

[0069] Specifically, a clear decision-making process was designed to manage the switching of control modes during the drone's descent. This process relies on a preset altitude condition: when the drone's altitude drops to a first preset altitude or lower, the system enters and initiates a real-time criterion state. In this state, the system evaluates four key conditions in parallel; if any one condition is met, a switching action is triggered: First, it determines whether the current descent rate is below a first threshold, i.e., it detects whether the drone is descending too quickly beyond the safety limit; second, it determines whether the current descent rate is above a second threshold, i.e., it detects whether the drone is descending too slowly or even showing an upward trend, which could lead to drift or abnormal approach energy management; third, it determines whether the real-time wind speed or wind disturbance intensity exceeds a preset tolerance threshold, i.e., it assesses whether environmental interference has exceeded the robustness of the basic control mode; fourth, it determines whether the flight altitude has fallen below a smaller second preset altitude, indicating that the drone has entered the final landing phase requiring higher control precision, necessitating the use of a more advanced guidance law to ensure terminal accuracy. These conditions are comprehensively judged using a logical "OR" relationship. If any one of these conditions is met, the system will immediately issue a command to switch control from the original conventional descent mode to the optimal guidance law; conversely, if none of the conditions are met, it indicates that the current flight status is stable and the environment is good, and the system will maintain the UAV in the original set mode to continue to descend normally, thereby optimizing the overall operating efficiency of the system while ensuring safety and accuracy.

[0070] S4. When using the optimal guidance law for control, guidance commands are generated based on the line-of-sight angle and line-of-sight angle rate, and the guidance commands are dynamically limited according to the safe allowable range of the sink rate corresponding to the current flight altitude, so that the UAV can achieve precise landing under the dual constraints of sink rate and terminal landing angle.

[0071] Specifically, when the UAV switches to optimal guidance law for control, the system enters a high-precision closed-loop guidance phase. First, based on the real-time acquired line-of-sight azimuth angle and its rate of change, the system uses an embedded optimal control algorithm to calculate the required flight control commands in real time. The core objective of these commands is to simultaneously drive the UAV precisely to the target point and ensure it touches the ground at a preset ideal angle. However, solely pursuing terminal accuracy may neglect safety during descent, especially the vertical descent rate. Therefore, the system simultaneously introduces a descent rate safety protection mechanism linked to flight altitude. This mechanism predefines two altitude segments, each with corresponding maximum and minimum allowable descent rates, the range of which narrows as altitude decreases, with stricter requirements in the final stage near the ground. After the guidance command is generated but before being sent to the actuator, the system calls the corresponding descent rate safety range based on the UAV's current flight altitude and performs real-time verification and dynamic limiting of the components in the command that directly affect vertical motion. If the calculated command causes the vertical velocity to exceed the safety boundary, the system will automatically limit the command component within the boundary value, thereby ensuring that the actual sinking rate of the UAV is always constrained within the safe allowable range. Through this deep synergy between precise control of the terminal angle and active protection of the sinking rate, the system ultimately guides the UAV to land safely at a predetermined precise attitude and a strictly controlled, stable speed, achieving a high degree of unity between process safety and terminal accuracy.

[0072] In this step, the safe allowable range for sinking rate is set according to flight altitude segments, including:

[0073] When the flight altitude H is within the first altitude range, the safe allowable range for the sinking rate is:

[0074] When the flight altitude is in the second altitude range, the safe allowable range for the sinking rate is:

[0075] The first altitude range is defined as: second set altitude ≤ H ≤ first set altitude; the second altitude range is defined as: H < second set altitude; the first threshold < third threshold < second threshold, where H is the drone's flight altitude. This represents the sinking rate of the drone.

[0076] Specifically, in this step, the safe allowable range of the sinking rate is set in segments based on flight altitude to adapt to the stability and safety requirements of the drone's descent and landing at different stages, ensuring that the sinking rate remains within a reasonable range. First, the criteria for dividing two core altitude ranges are clarified: the first altitude range is the stage where the drone's flight altitude is between the second and first set altitudes; the second altitude range is the stage where the drone's flight altitude is below the second set altitude. The fact that the second set altitude is lower than the first set altitude means that as the drone descends, it will gradually move from the first altitude range into the second altitude range, which is closer to the ground. The threshold settings for the safe allowable range of the sinking rate differ for different altitude ranges: within the first altitude range, the sinking rate must be between the first and second thresholds to ensure a stable and controllable descent speed during this stage; after entering the second altitude range, the safe allowable range of the sinking rate is adjusted to be between the third and second thresholds, with the third threshold being greater than the first threshold and less than the second threshold. That is, the lower limit of the sinking rate in the second altitude range is higher than in the first altitude range, thus limiting the sinking rate within a more stringent range during the critical stage of approaching the ground. This segmented design is based on the practical need for greater stability of the descent rate as the drone gets closer to the ground. By dynamically adjusting the safety boundary, it ensures the descent efficiency during the mid-to-low altitude glide phase while precisely controlling the descent speed at the end of the landing phase. This avoids landing risks caused by descents that are too fast or too slow. Through dynamically adapted descent rate protection boundaries, the drone is guided to meet both accurate positioning requirements and achieve a stable and safe landing attitude upon final touchdown.

[0077] In this step, the guidance commands are dynamically limited based on the safe allowable range of the sink rate corresponding to the current flight altitude, including:

[0078] If the current flight altitude is within the first altitude range, the vertical velocity command calculated from the guidance command will be limited to the range [first threshold, second threshold].

[0079] When the current flight altitude is in the second altitude range, the vertical velocity command calculated from the guidance command will be limited to the range (third threshold, second threshold).

[0080] Specifically, once the system identifies the specific stage of the UAV based on its flight altitude, it activates a corresponding dynamic command limiting mechanism to strictly enforce preset descent rate safety constraints. If the UAV is in the higher first flight stage, the system monitors the vertical channel control commands generated by the optimal guidance law in real time and forcibly constrains them within a closed interval defined by a first threshold and a second threshold. This means that if the original command value exceeds the upper limit of the interval, it is replaced by the upper limit value; if it is below the lower limit, it is replaced by the lower limit value, thus ensuring that no command will cause a descent rate exceeding the allowable range for that stage. When the UAV descends further to the second flight stage, closer to the ground, the system adopts a more stringent set of command limiting rules. At this time, the vertical control commands are restricted to a new, narrower range, with the lower limit defined by a third threshold with a smaller absolute value, while the upper limit remains unchanged. Through this dynamic limiting process that is linked to flight altitude in real time, the system fundamentally eliminates the potential risk of excessive descent rates caused by guidance commands, transforming theoretical safety constraints into direct and reliable technical restrictions on control commands, thereby ensuring the smoothness and safety of the landing process at the source of control.

[0081] In this step, the first set height is 50m, the second set height is 10m, the preset wind speed threshold is 5m / s, the first threshold is -4m / s, the second threshold is -0.5m / s, and the third threshold is -1.5m / s.

[0082] Example 2

[0083] This embodiment provides a method for precise landing of a UAV based on an optimal guidance law, including:

[0084] Step 1: Establish the equations of relative motion between the UAV guidance system and the target:

[0085] During the guided landing phase of the UAV, the relative motion model between the UAV and the ground target can be considered as consisting of two planar motions: longitudinal and lateral. For the longitudinal motion of the UAV, the geometric equations relating the relative motion between the UAV and the ground target can be established, yielding:

[0086]

[0087] Where r is the relative distance between the UAV and the ground target, q is the line-of-sight angle between the UAV and the ground target, and V M V is the velocity vector of the UAV. T ε is the velocity vector of the ground target point; M ε T θ represents the leading angle of the drone and the ground target point, respectively. M θ TThese are the angles between the UAV velocity vector and the ground target point velocity vector and the baseline, respectively. M a T These represent the normal accelerations of the drone and the ground target point, respectively.

[0088] Assuming the current position coordinates of the UAV in the ground coordinate system are (x... M ,y M The target location coordinates are (x...). T ,y T The longitudinal relative motion between the two can be expressed as follows:

[0089]

[0090] The formulas for calculating the line-of-sight angle and the rate of change of the line-of-sight angle in the longitudinal plane are:

[0091]

[0092] in, For the line-of-sight angular rate of the UAV and the ground target point, (R x ,R y )and These represent the relative position and relative velocity components of the UAV and the ground target point in the longitudinal plane, respectively.

[0093] Step 2: Optimal guidance law with landing angle constraint in the longitudinal plane;

[0094] An optimal guidance law with landing angle constraints is designed based on optimal control theory. It can find the optimal guidance law according to the required performance based on various initial conditions, process and terminal constraints.

[0095] First, the state-space equations of the UAV guidance system are given:

[0096]

[0097] Considering the constraint of the drone's guidance landing angle, a quadratic performance function can be established:

[0098]

[0099] Where A is the system matrix, B is the input matrix, and S is the system matrix. f R is the weight matrix; t f x is the time from the start to the end of guidance. f Let u(τ) be the constraint of the terminal, τ be the control vector, and J be the quadratic performance index.

[0100] According to optimal control theory, the optimal solution based on the state feedback method can be obtained:

[0101] u * (t)=-R -1 B T η T (t f ,t)S f [x(t f )-x f ];

[0102] In the formula:

[0103] Let t be the state transition matrix. go Let T be the waiting time (i.e., remaining flight time) between the UAV and the target point, and let T be the transpose matrix.

[0104]

[0105] Therefore, we can write the optimal control u under constraints containing weighted functions. * The solution to (t) is:

[0106]

[0107] In the formula, s1 and s2 are the weighting coefficients for the precise landing point and landing angle, respectively; y(t) and Constraints on terminal timing.

[0108] Letting s1→∞ and s2→∞ ensures the accuracy of the UAV's guided descent in the terminal phase and satisfies the landing angle constraint. After transformation, the optimal guidance law is obtained:

[0109]

[0110] In the formula, V R R is the relative velocity between the drone and the target point. xy This refers to the relative distance.

[0111] The above equation represents the optimal guidance law for the glide phase of a UAV with a landing angle constraint. Since the target of the UAV during descent is a stationary landing point, at this time:

[0112]

[0113] Step 3: Criteria for switching the optimal guidance law during the descent of the UAV:

[0114] During the drone's glide landing phase, a real-time criterion is applied based on altitude conditions. The flowchart of this criterion is as follows: Figure 2 As shown. When H≤50m, the criteria are started, and conditional criteria are applied to its sinking rate, wind disturbance and flight altitude. Whether the optimal guidance law should be adopted is determined by whether the conditions are met.

[0115] Step 4: Optimal guidance law control command satisfying the sinking rate constraint:

[0116] Regarding the sinking rate at the final stage of the UAV landing, it is equivalent to the vertical velocity of the UAV in the optimal guidance law. Therefore, in order to meet the sinking rate constraint conditions, by setting the maximum value and the minimum value of the sinking rate constraint, a dynamic limit is imposed on the overload command generated by the optimal guidance law.

[0117] When the height from the ground is 10m < H < 50m, when the sinking rate makes thus generating the maximum value of the vertical velocity command of the optimal guidance law, -0.5m / s; when the sinking rate makes thus generating the minimum value of the vertical velocity command of the optimal guidance law, -4m / s. When the height from the ground is H < 10m, the sinking rate constraint range becomes and the optimal guidance control command is generated.

[0118] As Figures 3-5 shown, the simulation is carried out using the UAV precise landing method based on the optimal guidance law. As can be seen from Figure 3 , the pitch angle will continuously increase until it remains at about 3° at landing after switching to the optimal guidance law control; as can be seen from Figure 4 , the sinking rate remains near -1m / s after switching to the optimal guidance law control; as can be seen from Figure 5 (the blue curve corresponds to the actual flight height of the UAV, and the orange curve corresponds to the height command, that is, the expected height to reach), the height and range can accurately land on the target point after switching to the optimal guidance law control, both meeting the index requirements. Figure 6 And Figure 7 (the blue curve corresponds to the actual flight height of the UAV, and the orange curve corresponds to the height command, that is, the expected height to reach) are the simulation diagrams of the UAV landing section with wind disturbance using the sinking rate method and the UAV precise landing method based on the optimal guidance law. It can be seen that when using the sinking rate method to control the landing, there is a large deviation between the actual landing point and the ideal landing point; when using the UAV precise landing method based on the optimal guidance law to control, the actual landing point and the ideal landing point are basically the same, with a small deviation. From this comparison, it can be concluded that the UAV precise landing method based on the optimal guidance law can achieve precise landing while meeting the sinking rate constraint and the landing angle constraint, and has strong anti-interference ability when facing wind disturbance.

[0119] Example 3

[0120] This embodiment provides a precision landing system for unmanned aerial vehicles (UAVs), including:

[0121] The model is established and acquired to create a longitudinal relative motion model between the UAV and the ground target point, so as to acquire the line-of-sight angle and line-of-sight angular rate required for guidance in real time.

[0122] The module is used to construct the optimal guidance law, which includes terminal landing angle constraints, based on the longitudinal relative motion model and optimal control theory.

[0123] The judgment module is used to determine whether to switch to the optimal guidance law for control during the descent of the drone, based on the real-time status of flight altitude, sink rate and wind speed.

[0124] The generation and limiting module is used to generate guidance commands based on the line-of-sight angle and line-of-sight angle rate when using the optimal guidance law for control, and to dynamically limit the guidance commands according to the safe allowable range of the sink rate corresponding to the current flight altitude, so that the UAV can achieve precise landing under the dual constraints of sink rate and terminal landing angle.

[0125] Example 4

[0126] This embodiment provides a drone, including the drone precision landing system described in Embodiment 3.

[0127] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for precise landing of a drone, characterized in that, include: Establish a longitudinal relative motion model between the UAV and the ground target point to obtain the line-of-sight angle and line-of-sight angular rate required for guidance in real time; Based on the aforementioned longitudinal relative motion model and optimal control theory, an optimal guidance law including terminal landing angle constraints is constructed. During the descent of the drone, based on the real-time status of flight altitude, sink rate and wind speed, it is determined whether to switch to the optimal guidance law for control; When using the optimal guidance law for control, guidance commands are generated based on the line-of-sight angle and line-of-sight angle rate, and the guidance commands are dynamically limited according to the safe allowable range of the sink rate corresponding to the current flight altitude, so that the UAV can achieve precise landing under the dual constraints of sink rate and terminal landing angle.

2. The method for precise landing of a drone according to claim 1, characterized in that, The longitudinal relative motion model is as follows: Where r is the relative distance between the UAV and the ground target, q is the line-of-sight angle between the UAV and the ground target, and V M V is the velocity vector of the UAV. T ε is the velocity vector of the ground target point; M ε T θ represents the leading angle of the drone and the ground target point, respectively. M θ T These are the angles between the UAV velocity vector and the ground target point velocity vector and the baseline, respectively, a. M a T These represent the normal accelerations of the drone and the ground target point, respectively.

3. The method for precise landing of a drone according to claim 2, characterized in that, The calculation expressions for the line-of-sight angle and line-of-sight angular rate are as follows: in, For the line-of-sight angular rate of the UAV and the ground target point, (R x ,R y )and These represent the relative position and relative velocity components of the UAV and the ground target point in the longitudinal plane, respectively. x =x T -x M R y =y T -y M , (x M ,y M (x) represents the position coordinates of the UAV in the longitudinal plane. T ,y T The coordinates of the ground target point in the longitudinal plane.

4. The method for precise landing of a drone according to claim 3, characterized in that, The optimal guidance law is: Among them, u * (t) represents the guidance command, t go This represents the remaining flight time for the drone to reach the ground target. V R Let q be the relative approach speed between the drone and the ground target point. f For the desired terminal landing angle, R xy This represents the relative straight-line distance between the drone and the ground target point.

5. The method for precise landing of a drone according to claim 1, characterized in that, The step of determining whether to switch to the optimal guidance law for control based on the real-time status of flight altitude, sink rate, and wind disturbance includes: The criterion is activated when the flight altitude is less than or equal to the first preset altitude. If the current descent rate is less than the first threshold, or the current descent rate is greater than the second threshold, or the wind speed is greater than the preset wind speed threshold, or the flight altitude is less than the second set altitude, then switch to the optimal guidance law; otherwise, control the UAV to descend normally according to the original control mode.

6. The method for precise landing of a drone according to claim 5, characterized in that, The safe allowable range for sinking rate is set in segments according to flight altitude, including: When the flight altitude H is within the first altitude range, the safe allowable range for the sinking rate is: When the flight altitude is in the second altitude range, the safe allowable range for the sinking rate is: Wherein, the first altitude range is: second set altitude ≤ H ≤ first set altitude; the second altitude range is: H < second set altitude; first threshold < third threshold < second threshold; and H is the flight altitude of the drone. This represents the sinking rate of the drone.

7. The method for precise landing of a drone according to claim 6, characterized in that, The dynamic limiting of the guidance command based on the safe allowable range of the sink rate corresponding to the current flight altitude includes: If the current flight altitude is within the first altitude range, the vertical velocity command calculated by the guidance command will be restricted to the range [first threshold, second threshold]. When the current flight altitude is within the second altitude range, the vertical velocity command calculated by the guidance command is restricted to the range (third threshold, second threshold).

8. The method for precise landing of a drone according to claim 7, characterized in that, The first set height is 50m, the second set height is 10m, the preset wind speed threshold is 5m / s, the first threshold is -4m / s, the second threshold is -0.5m / s, and the third threshold is -1.5m / s.

9. A precision landing system for unmanned aerial vehicles (UAVs), characterized in that, include: The model is established and acquired to create a longitudinal relative motion model between the UAV and the ground target point, so as to acquire the line-of-sight angle and line-of-sight angular rate required for guidance in real time. The construction module is used to construct an optimal guidance law that includes terminal landing angle constraints based on the longitudinal relative motion model and optimal control theory. The judgment module is used to determine whether to switch to the optimal guidance law for control during the descent of the UAV, based on the real-time status of flight altitude, sink rate and wind speed. The generation and limiting module is used to generate guidance commands based on the line-of-sight angle and line-of-sight angle rate when using the optimal guidance law for control, and to dynamically limit the guidance commands according to the safe allowable range of the sink rate corresponding to the current flight altitude, so that the UAV can achieve precise landing under the dual constraints of sink rate and terminal landing angle.

10. A drone, characterized in that, Including the drone precision landing system as described in claim 9.

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