A method and control system for controlling circling and steep landing of unmanned aerial vehicle

Abstract

The present invention relates to a control method and control system for a hovering and steep descent landing of an unmanned aerial vehicle (UAV). When the UAV receives a "landing" command, the aircraft maintains level flight and flies to the center of the hovering and steep descent circle. When it enters the circle, the hovering and steep descent control law is executed. When the approach window condition that the UAV's heading is consistent with the runway heading is met, the approach control mode is switched on. The longitudinal altitude and forward distance are jointly controlled by the elevator and throttle, and the lateral heading is a high-precision track control. At this time, the control law structure remains unchanged, the circular trajectory becomes the runway centerline, and the expected heading is the runway heading. By using a control method of hovering and descending at a specified position and approaching and landing at a specified height, the approach and landing distance of the UAV is effectively shortened. While controlling the UAV to land safely, it effectively avoids the restrictions on the use of landing sites and airspace by conventional UAV landing methods, and avoids collisions, excessive landing speeds, and even damage to the UAV during the landing phase due to limited landing conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicle (UAV) control, and relates to a method and a control system for controlling a UAV to hover and descend sharply and land. More specifically, the present invention relates to a control method for controlling a UAV to hover and descend sharply and achieve automatic landing in a narrow field condition. Background Art

[0002] There are various methods for automated landing control of taxiing drones. The most common method involves extending a certain distance from one end of the runway to allow for course adjustment during landing. To meet landing requirements for track deviation, altitude, and speed control, this distance is typically 6 to 8 kilometers. This requires open space and unrestricted airspace near the airport. However, this method is no longer suitable for situations where the runway extension is located near towers, hills, or sensitive areas where aircraft are not allowed to fly overhead. Therefore, there is an urgent need to develop a landing control system that can accommodate drones landing in confined spaces, reducing the 6 to 8 km required to less than 2 km, allowing aircraft to land smoothly even in confined spaces and airspace. Summary of the Invention

[0003] Technical problems to be solved

[0004] To overcome the shortcomings of existing technologies, the present invention proposes a method and control system for controlling a hovering and steep descent landing of a UAV. This method addresses the problem of a UAV being unable to land using conventional methods due to limited site and airspace. When conventional landing conditions are unavailable, the present invention automatically controls the UAV, controlling it to hover and descend to a lower altitude before entering an approach mode for landing. This effectively shortens the approach route and avoids site and airspace restrictions on UAV landing.

[0005] Technical Solution

[0006] A method for controlling a UAV to hover and steeply descend and land is characterized by the following steps:

[0007] Step 1: The drone flies to the hovering descent point: When the drone receives the "landing" command, it flies to the center of the descent in a level flight attitude;

[0008] Step 2: Confirm that the radius of the drone's circling and steep descent circular trajectory is r max With r min The middle value between min is the minimum value of the circular trajectory, and the maximum value of the circular trajectory radius r max is the safety distance d under site constraints safe 0.65 times;

[0009] The safety distance is the distance between the vertical line of the point where the drone cuts into the runway, i.e. the approach point, and the vertical line of the edge of the drone restricted area, which is called the safety distance for the landing process.

[0010] The minimum value of the circular trajectory is related to the maximum hovering angle allowed by the drone:

[0011]

[0012] Where: g is the acceleration due to gravity; v g is the expected speed of the drone when landing, is the maximum roll angle;

[0013] Step 3: Circling and descent: Once inside the circle, the circling and descent control law is executed, and the drone circulates and descends along the radius of the circular trajectory used for landing. Energy coordination control is used in the longitudinal direction to ensure that the speed and altitude of the drone are within the desired range during the circling and descent. Circular trajectory tracking control is used in the lateral direction, and Δy is the deviation between the actual position of the aircraft and the desired circular trajectory.

[0014] The spiral descent control law is:

[0015]

[0016] Among them, δ e is the elevator control quantity, δ a is the aileron control quantity, θ is the pitch angle, and p are the roll angle and roll velocity respectively, ψ is the heading angle, h is the height, v is the velocity, and y is the track;

[0017] Step 3: Runway Intercept: When the UAV reaches the approach altitude and meets the approach window conditions where the UAV's heading is consistent with the runway heading, the approach control mode is entered. The vertical altitude and forward distance are jointly controlled by the elevator and throttle, and the lateral heading is high-precision track control. At this time, the control law structure remains unchanged, but the expected track changes from a circular trajectory to the runway centerline, and the expected heading is the runway heading.

[0018] In the circling descent of step 3, when the satellite signal is valid, the satellite field height, i.e., the differential state, is first used; after the satellite signal fails, the corrected pressure field height is used as the altitude signal source; in the straight approach phase, the radio altitude signal is used as the altitude signal source to obtain higher accuracy.

[0019] The corrected air pressure field height is corrected using the radio altitude when the UAV is in a stable attitude state before entering into a circling and steep descent.

[0020] The expected speed v of the UAV when landing g , which is determined by the characteristics of the UAV itself and is a fixed value.

[0021] The maximum roll angle of the UAV Determined by the characteristics of the drone itself.

[0022] A control system for implementing the unmanned aerial vehicle (UAV) hovering and steep landing control method, characterized by: including an airspeed sensor, a heading attitude system, a Beidou positioning system, a radio altimeter, an elevator servo, an aileron servo, an engine throttle servo and a flight control computer; the airspeed sensor measures the flight speed of the UAV; the heading attitude system measures the pitch angle and roll angle of the UAV; the Beidou positioning system measures the altitude and position information of the UAV; the radio altimeter measures the field height of the UAV; the elevator servo is used to execute the elevator deflection instruction; the aileron servo is used to execute the aileron deflection instruction; the engine throttle servo is used to adjust the throttle size; the flight control computer collects the measurement information of each sensor and inputs it into the hovering and steep landing control module, calculates the control amount of the elevator surface, aileron surface and throttle, and then drives the UAV to hover and steeply descend at a specified position, switches to the approach mode after descending to the specified altitude, and then reaches the leveling altitude for leveling control until the aircraft lands.

[0023] Beneficial effects

[0024] The present invention proposes a method and control system for controlling a hovering and steep descent landing of a UAV. When the UAV receives a "landing" command, the aircraft maintains level flight and flies to the center of the hovering and steep descent circle. Once inside the circle, the hovering and steep descent control law is executed. When the approach window condition that the UAV's heading is consistent with the runway heading is met, the approach control mode is switched on. The vertical direction uses the elevator and throttle to implement joint control of altitude and forward distance, and the lateral heading is controlled with high precision. At this time, the control law structure remains unchanged, the circular trajectory becomes the runway centerline, and the expected heading is the runway heading. By using a control method of hovering and descending at a specified position and approaching and landing at a specified height, the approach and landing distance of the UAV is effectively shortened. While controlling the UAV to land safely, it effectively avoids the restrictions on the use of landing sites and airspace imposed by conventional UAV landing methods, and avoids collisions, excessive landing speeds, and even damage to the UAV during the landing phase due to restricted landing conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Control system for UAV hovering and steep landing

[0026] Figure 2 A side view diagram of the drone's circling and steep landing process

[0027] Figure 3 A bird's-eye view of a drone's circling and steeply descending circular trajectory DETAILED DESCRIPTION

[0028] The present invention will now be further described with reference to the embodiments and accompanying drawings:

[0029] The method for controlling a UAV's circling and steep landing is characterized by: using onboard sensors to collect the UAV's altitude, speed, attitude, and position information, and designing a circling and steep landing control algorithm. When the UAV receives the "land" command, it maintains level flight and flies to the center of the circling and steep landing circle. Once inside the circle, the circling and steep landing control law is executed:

[0030]

[0031] Among them, δ e is the elevator control quantity, δ a is the aileron control quantity, θ is the pitch angle, and p are the roll angle and roll angular velocity respectively, ψ is the heading angle, h is the altitude, v is the speed, and y is the track. Energy coordinated control is used in the longitudinal direction to ensure that the speed and altitude of the drone are within the expected range during the circling and steep descent process. Circular trajectory tracking control is used for the lateral heading, and Δy is the deviation between the actual position of the aircraft and the expected circular trajectory. In this method, determining the circular trajectory and its radius during landing is the key. First, the position of the trajectory is determined: the tangent of the circular trajectory of the drone circling and descending in the runway direction coincides with the centerline of the runway, so that the drone does not need to adjust the track after reaching the approach altitude and can directly cut into the runway centerline. Secondly, the radius of the trajectory is determined: the approach point of the drone refers to the point where the drone descends to the approach altitude, leaves the circling and descending state, and begins to descend straight down towards the runway. The distance between the perpendicular line of the approach point and the perpendicular line of the edge of the drone-restricted area (such as mountains, towers) is called the safety distance of the landing process. The maximum radius of the circular trajectory r max Determined by the safety distance, generally speaking, the safety distance d under site constraints safe It can be defined as 1.5 times the circular trajectory radius to ensure that even if there is an error in the trajectory control, there is still enough safe space between the drone and the prohibited area during landing. For example, if the safety distance requirement is 2km, the radius of the circular trajectory cannot exceed 1.3km. In addition, the maximum hovering angle allowed by the drone determines the minimum value of the circular trajectory. The radius of the circular trajectory can be calculated using the formula: To calculate, where v g is the expected speed of the UAV when landing, which is determined by its own characteristics and is a constant value. is the maximum available roll angle, determined by its own characteristics, g is the acceleration of gravity. The final circular trajectory radius is r max With r min It is recommended to take the middle value, which can ensure sufficient safety distance and make the drone's hovering angle not too large, without increasing the burden of fixed height control.

[0032] When the drone reaches the desired approach altitude (reference value: 30 meters), it will no longer descend, but will maintain a constant altitude and hover. When the approach window condition is met, the drone's heading is consistent with the runway heading, and the approach control mode is switched to. The vertical direction uses the elevator and throttle to implement joint altitude and forward distance control, and the lateral heading is controlled with high precision. At this time, the control law structure remains unchanged, but the expected track changes from a circular trajectory to the runway centerline, and the expected heading is the runway heading.

[0033] Because the control process of the circling steep descent method is shorter than that of the traditional method and the aircraft has a large roll angle, the acquisition of the altitude signal is very critical at this time. Because the radio altitude measurement error becomes larger at a large roll angle, it cannot always use radio altitude as the altitude signal source during the landing process as in the traditional method. The solution is: during the circling steep descent phase, when the satellite signal is valid, the satellite field height (differential state) is first used. After the satellite signal fails, the corrected pressure field height (radio altitude correction is used when the drone's attitude is stable before entering the circling steep descent) is used as the altitude signal source. During the straight-line approach phase, the radio altitude signal is used as the altitude signal source to obtain higher accuracy.

[0034] The flight control computer collects the measurement information of each sensor and inputs it into the spiral landing control module to calculate the control amount of the elevator, aileron and throttle.

[0035] like Figure 1 As shown in the figure, the hardware of the control system includes airspeed sensor, heading attitude system, Beidou positioning system, radio altimeter, elevator servo, aileron servo, engine throttle servo and flight control computer; the airspeed sensor measures the flight speed of the UAV; the heading attitude system measures the pitch angle and roll angle of the UAV; the Beidou positioning system measures the altitude and position information of the UAV; the radio altimeter measures the field height of the UAV; the elevator servo is used to execute the elevator deflection command; the aileron servo is used to execute the aileron deflection command; the engine throttle servo is used to adjust the throttle size; the flight control computer collects the measurement information of each sensor and inputs it into the hovering steep landing control module, calculates the control amount of the elevator surface, aileron servo and throttle, and then drives the UAV rudder deflection and throttle adjustment, drives the UAV to hover and descend sharply at the specified position, and switches to the approach mode after descending to the specified altitude, and then reaches the leveling altitude for leveling control until the aircraft lands.

[0036] exist Figure 1 In the figure, H_g is the altitude command; phi_g is the roll angle command; v_g is the speed command; δe is the elevator control amount; δa is the aileron control amount; δt is the throttle control amount; v is the flight speed; theta is the pitch angle; phi is the roll angle; LLA is the longitude, latitude and altitude; H_ref is the airport height.

[0037] like Figure 2 As shown in the figure, the control process of this control method is divided into five stages: flying to the circling descent point, circling steep descent, entering the runway, leveling off, and landing. After receiving the "landing" command, the aircraft maintains level flight and flies to the center of the circling steep descent circle. When entering the circle, the circling steep descent control is executed. The lateral heading adopts circular trajectory tracking control. The tangent of the circular trajectory in the runway direction coincides with the runway centerline. The radius of the circular trajectory is r max (determined by the safety distance constrained by the landing site) and r min (Calculated from the maximum allowable hover angle and the desired landing speed) between the two values. An intermediate value is recommended. Vertically, altitude control is employed, with the lower pitch angle limited to prevent excessive speed. The throttle is at minimum. Once the aircraft reaches a field altitude of 30 meters, maintain a constant altitude and hover until the approach window conditions are met. Approach control mode is then engaged. Vertically, altitude and forward distance are controlled jointly using the elevator and throttle. Laterally, high-precision track control is employed. At a field altitude of 5 meters, the flare control law is implemented until the aircraft touches down.

Claims

1. A method for controlling a UAV to hover and land steeply, characterized in that Here are the steps: Step 1: The drone flies to the hovering descent point: When the drone receives the "landing" command, it flies to the center of the descent in a level flight attitude; Step 2: Confirm that the radius of the drone's circling and steep descent circular trajectory is r max With r min The middle value between min is the minimum value of the circular trajectory, and the maximum value of the circular trajectory radius r max is the safety distance d under site constraints safe 0.65 times; The safety distance is the distance between the vertical line of the point where the drone cuts into the runway, i.e. the approach point, and the vertical line of the edge of the drone restricted area, which is called the safety distance for the landing process. The minimum value of the circular trajectory is related to the maximum hovering angle allowed by the drone: Where: g is the acceleration due to gravity; v g is the expected speed of the drone when landing, is the maximum roll angle; Step 3: Circling and descent: Once inside the circle, the circling and descent control law is executed, and the drone circulates and descends along the radius of the circular trajectory used for landing. Energy coordination control is used in the longitudinal direction to ensure that the speed and altitude of the drone are within the desired range during the circling and descent. Circular trajectory tracking control is used in the lateral direction, and Δy is the deviation between the actual position of the aircraft and the desired circular trajectory. The spiral descent control law is: Among them, δ e is the elevator control quantity, δ a is the aileron control quantity, θ is the pitch angle, and p are the roll angle and roll velocity respectively, ψ is the heading angle, h is the height, v is the velocity, and y is the track; Step 3: Runway Intercept: When the UAV reaches the approach altitude and meets the approach window conditions where the UAV's heading is consistent with the runway heading, the approach control mode is entered. The vertical altitude and forward distance are jointly controlled by the elevator and throttle, and the lateral heading is high-precision track control. At this time, the control law structure remains unchanged, but the expected track changes from a circular trajectory to the runway centerline, and the expected heading is the runway heading.

2. The method for controlling a UAV to hover and steeply descend and land according to claim 1, characterized in that: In the circling and steep descent of step 3, when the satellite signal is valid, the satellite field height, i.e., the differential state, is first used; after the satellite signal fails, the corrected pressure field height is used as the altitude signal source; During the straight-in approach phase, a radio altitude signal is used as the altitude signal source to obtain higher accuracy.

3. The method for controlling a UAV to hover and steeply descend and land according to claim 2, characterized in that: The corrected air pressure field height is corrected using the radio altitude when the UAV is in a stable attitude state before entering into a circling and steep descent.

4. The method for controlling a UAV to hover and steeply descend and land according to claim 1, characterized in that: The expected speed v of the UAV when landing g , which is determined by the characteristics of the UAV itself and is a fixed value.

5. The method for controlling a UAV to hover and steeply descend and land according to claim 1, characterized in that: The maximum roll angle of the UAV Determined by the characteristics of the drone itself.

6. A control system for implementing the method for controlling the hovering and steep descent landing of an unmanned aerial vehicle according to any one of claims 1 to 5, characterized in that: It includes airspeed sensor, heading attitude system, Beidou positioning system, radio altimeter, elevator servo, aileron servo, engine throttle servo and flight control computer; airspeed sensor measures the flight speed of the UAV; heading attitude system measures the pitch angle and roll angle of the UAV; Beidou positioning system measures the height and position information of the UAV; radio altimeter measures the field height of the UAV; The elevator servo is used to execute the elevator deflection command; the aileron servo is used to execute the aileron deflection command; the engine throttle servo is used to adjust the throttle size; the flight control computer collects the measurement information of each sensor and inputs it into the hovering and steep landing control module, calculates the control amount of the elevator surface, aileron surface and throttle, and then drives the UAV to hover and descend at the specified position. After descending to the specified height, it switches to the approach mode, and then reaches the leveling height for leveling control until the aircraft lands.

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