A control method for unmanned aerial vehicle ground electromagnetic catapult

Abstract

The application discloses a control method of unmanned aerial vehicle ground electromagnetic ejection, belongs to the field of unmanned aerial vehicle flight control, and uses electromagnetic ejection to make the unmanned aerial vehicle enter a predetermined speed and flight attitude on the ground. The method comprises the following steps: binding an initial attitude, confirming that the unmanned aerial vehicle is in a stage of being ready to be launched; in an electromagnetic acceleration stage, the pitch angle is controlled through acceleration; in a launching process, when the speed is greater than a certain value, the pitch angle is controlled by using air speed until the aircraft reaches a take-off safety height; after the aircraft reaches the take-off safety height, the pitch is controlled by using the lift speed, the maximum roll angle is limited, and the roll angle is prevented from being too large; after the aircraft reaches a cruising speed, the pitch is controlled by using the air speed, attitude stability is achieved, the unmanned aerial vehicle continues to fly at the cruising speed, and launching is completed.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicle (UAV) flight control, and specifically relates to a control method for ground electromagnetic catapult launch of UAVs. Background Technology

[0002] Drones are widely used in military and civilian fields, playing an important role in disaster relief, material delivery, agricultural plant protection, aerial photography, and space-constrained ships. However, in some applications, the launch phase of drones is often considered one of the more difficult phases, and various countries have conducted extensive research and experimentation on drone take-off and launch.

[0003] Currently, common methods for launching drones include: manual launch, where the operator manually launches the drone and then activates its power system; however, this requires high skill and strength from the operator, is only suitable for small drones, and is greatly affected by weather conditions; landing gear launch, which relies on engine power to take off from the runway, but requires specific site conditions and has a long preparation time; catapult launch, which uses various catapult devices to allow the drone to take off at high speed instantly, but has the disadvantages of complex device maintenance and debugging, and high requirements for the precision control of launch parameters; vertical takeoff and landing (VTOL) launch, including rotor and tiltrotor launch, involves complex power systems, low endurance and payload capacity, and high difficulty in attitude control; mother-air launch, where the mother aircraft flies to a predetermined location and releases the drone, is costly and requires strict design and launch precision; and rocket-assisted launch, which uses rocket engine thrust to propel the drone away from the launch device, is dangerous, increases cost and complexity, and has high requirements for site safety.

[0004] Research on electromagnetic catapult technology in the field of UAV launch has made some progress. Many research teams and institutions have conducted relevant designs and analyses based on the characteristics of UAVs. For example, based on the characteristics and catapult requirements of folding-wing UAVs, they have introduced the principle, mathematically modeled, and designed the system scheme and structure of a three-phase asynchronous induction electromagnetic coil catapult. Finite element models have been established using software for electromagnetic field and mechanical simulation analysis, and the results show that the system can meet certain initial launch velocity and overload design requirements. Domestically, the design and development of rail-mounted electromagnetic launch devices and electrothermal launch devices have also been completed. Analysis and research have been conducted on the structural performance of railguns and the elastic buckling problem of coil projectiles, and finite element simulation models have been established. Currently, electromagnetic catapult technology has received widespread attention and research due to its advantages such as all-electric operation, large and stable thrust, high efficiency, controllable speed and acceleration, and stealthy launch, resulting in relatively rich achievements at both the theoretical and simulation levels. However, this technology still has many shortcomings. It is difficult to dynamically adjust the electromagnetic thrust according to the changes of the launched object, the positioning of the object's real-time motion state is inaccurate, and the initial velocity of the launch cannot be precisely controlled. The energy supply demand is large, there are losses in actual conversion, the energy conversion efficiency of traditional energy storage methods is low, and it is easy to cause power system overload. Summary of the Invention

[0005] This invention provides a control method for ground electromagnetic catapult launch of unmanned aerial vehicles (UAVs), which uses electromagnetic catapult launch to enable the UAV to reach a predetermined speed and flight attitude on the ground.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A control method for ground electromagnetic catapult launch of an unmanned aerial vehicle (UAV) includes the following steps:

[0008] S1: Set the initial attitude and confirm that the drone is in the ready-to-launch phase;

[0009] S2: Electromagnetic acceleration phase, pitch angle is controlled by acceleration;

[0010] S3: During launch, once the speed exceeds a certain value, use airspeed to control the pitch angle until the aircraft reaches a safe takeoff altitude.

[0011] S4: After the aircraft reaches the safe takeoff altitude, use the rate of climb to control the pitch and limit the maximum roll angle to prevent the roll angle from becoming too large.

[0012] S5: After the aircraft reaches cruise speed, it uses airspeed to control pitch and achieve attitude stability.

[0013] Beneficial effects: This invention provides a control method for ground electromagnetic catapult launch of unmanned aerial vehicles (UAVs), which has the following advantages compared with the prior art:

[0014] During the electromagnetic acceleration phase, the pitch angle is precisely controlled based on acceleration changes to ensure the UAV climbs smoothly. At launch, once the airspeed exceeds 30 m / s, the pitch angle is controlled using airspeed to reach a safe altitude, achieving coordinated control of airspeed and altitude to improve flight safety. After reaching the safe altitude and cruising speed, the pitch angle is controlled using both the rate of climb and the airspeed, while limiting the roll angle to achieve multi-stage attitude stabilization. Compared to traditional launch methods, this reduces takeoff energy consumption, improves endurance and flight performance, ensures successful mission completion, and broadens the application scope of UAVs. Attached Figure Description

[0015] Figure 1 This is a flowchart of the electromagnetic catapult process for the UAV in an embodiment of the present invention;

[0016] Figure 2 This is a parameter diagram of the UAV in the launch-ready state in an embodiment of the present invention. The upper left is the pitch angle and pitch angle command in the launch-ready state, the upper right is the throttle in the launch-ready state, the lower left is the elevator command in the launch-ready state, and the lower right is the acceleration in the launch-ready state.

[0017] Figure 3This is a diagram of the state parameters of the UAV after launch in an embodiment of the present invention. The upper left is the acceleration after launch, the upper right is the airspeed command and airspeed after launch, the lower left is the throttle command after launch, and the lower right is the pitch angle command after launch.

[0018] Figure 4 This is a block diagram of the track angle tracking algorithm in an embodiment of the present invention;

[0019] Figure 5 This is a diagram of state parameters for the pitch phase of the climb / deceleration control in an embodiment of the present invention. The upper left is the climb / deceleration command, the upper right is the pitch angle command and pitch angle, the lower left is the airspeed command and airspeed, and the lower right is the pitch angle command and pitch angle.

[0020] Figure 6 This is a state parameter diagram for the cruise phase in an embodiment of the present invention, where the left side represents the pitch angle command and pitch angle, and the right side represents the airspeed command and airspeed. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0022] The takeoff process of a drone is mainly divided into two stages:

[0023] 1. Achieve safe altitude after drone launch.

[0024] During the initial launch phase, when the UAV's acceleration reaches 1.2 times the gravitational acceleration, the pitch angle command is 1°. When the acceleration decreases to 0.5 times the gravitational acceleration, the pitch angle command is 5°, and the roll angle is controlled at 0°. Once the airspeed exceeds 30 meters per second, the pitch angle is controlled by airspeed until the UAV reaches a safe altitude.

[0025] 2. Implement UAV attitude stabilization strategy after reaching a safe altitude.

[0026] After the drone reaches a safe altitude, before reaching cruising speed, the pitch angle is controlled by the climb rate. The climb rate command is 0.5 meters per second, which allows the drone to safely reach cruising speed.

[0027] Once the drone reaches cruising speed, it continues to use the aircraft's speed to control the pitch angle, thereby achieving attitude stability.

[0028] like Figure 1 As shown, a control method for ground electromagnetic catapult launch of an unmanned aerial vehicle (UAV) includes the following stages:

[0029] Phase 1: Setting the initial attitude to put the drone in a ready-to-launch state, such as... Figure 2 As shown, at this time, the pitch angle command tht_c, the throttle command throttle_c, and the elevator command de_c are all 0, and the forward acceleration ax of the UAV is also basically 0.

[0030] Phase Two: After ignition and takeoff, with the throttle at 100%, the drone is accelerated via electromagnetic catapult. Figure 3 As shown, when the drone's acceleration exceeds 1.2 times the gravitational acceleration, the pitch angle command is 1°; when the drone's acceleration is less than 0.5 times the gravitational acceleration, the pitch angle is controlled at 5°, and the airspeed command is 29 m / s², ensuring the drone can climb and accelerate normally. When the airspeed exceeds 30 m / s², the pitch angle is controlled using airspeed until the drone reaches a safe altitude. The conversion relationship between airspeed and pitch angle is as follows: , in It is the acceleration due to gravity. For pitch gain, For pitch angle command, For airspeed command, This is the actual airspeed;

[0031] Phase 3: Control the pitch angle using climb rate. The climb rate command is 0.5 m / s, the airspeed command is cruise speed 35 m / s, and the maximum roll angle is limited to 5° until the airspeed reaches cruise speed 35 m / s; then adjust the climb rate... Convert to track tilt command Then, after conversion, the pitch angle command is obtained. ;

[0032] First, we can determine the acceleration and deceleration speed from a geometric perspective. and track inclination The transformation relationship is shown in the following formula: , in This represents the ground speed of the drone.

[0033] like Figure 4 As shown, the track angle command Convert to pitch command The process is as follows:

[0034] The relationship between pitch angle, angle of attack, and track inclination angle is as follows: , in, The pitch angle, For the angle of attack, The inclination angle of the flight path.

[0035] Considering the following relationship between the rate of change of the track inclination and the angle of attack: , in, The rate of change of the track inclination. air density, The airspeed of the aircraft. This is the reference area of ​​the wing. This is the derivative of the lift coefficient with respect to the angle of attack. It's about the quality of the drone. The parameters related to the derivative of the track inclination angle with respect to the angle of attack are:

[0036] Combining the above two equations, we can obtain the transfer function from pitch angle to track inclination angle as follows: ,

[0037] The pitch angle controller can quickly track commands and has good robustness. The pitch angle command to pitch angle transition can be considered a first-order dynamic process, i.e.: , in, The control bandwidth of the pitch angle loop, For the Laplace operator; combining the above two equations, the transfer function from pitch angle command to track inclination angle can be described as: ,

[0038] Design control laws to address negative points Meanwhile, an integrator is introduced, and the control law is as follows: ,

[0039] The closed-loop transfer function and its corresponding characteristic equation are as follows: , ,

[0040] definition and Here, represents the bandwidth and damping ratio of the track angle control loop, respectively, and the corresponding expressions are: ,

[0041] By setting the appropriate damping ratio, the gain can be controlled via the pitch angle. Calculate the tracking gain of the track angle. for: ,

[0042] During this stage, such as Figure 5As shown, the climb / descendancy command hdot_c is set to 0.5 m / s. The drone's climb / descendancy hdot gradually decreases from 6.5 m / s, and the flight altitude rel_alt gradually stabilizes, indicating a stable entry into cruise speed. The airspeed command as_c is set to the cruise speed of 35 m / s. The drone's indicated airspeed (IAS) remains around 35 m / s. Simultaneously, the decrease in climb / descendancy causes the pitch angle command tht_c to decrease, indicating that the drone should lower its nose.

[0043] Phase Four: After reaching cruising speed, the UAV continues to control its pitch angle using airspeed, in the same manner as in Phase Two, to ensure that the UAV continues to fly at cruising speed and maintains stable attitude. Figure 6 As shown, the pitch angle is used to control airspeed, allowing the UAV to continue flying at cruising speed until launch is complete.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for ground electromagnetic catapult launch of an unmanned aerial vehicle (UAV), characterized in that, Includes the following steps: S1: Set the initial attitude and confirm that the drone is in the ready-to-launch phase; S2: During the electromagnetic acceleration phase, the pitch angle is controlled by acceleration, and the roll angle is controlled to be 0°; when the drone's acceleration is greater than 1.2 times the gravitational acceleration, the pitch angle command is controlled to be 1°, and when the drone's acceleration is less than 0.5 times the gravitational acceleration, the pitch angle command is controlled to be 5°. S3: During launch, once the airspeed exceeds 30 m / s, use airspeed to control the pitch angle until the aircraft reaches a safe takeoff altitude; the conversion relationship for using airspeed to control the pitch angle is as follows: ,in, It is the acceleration due to gravity. For pitch gain, For pitch angle command, For airspeed command, This is the actual airspeed; S4: After the aircraft reaches the safe takeoff altitude, the pitch angle is controlled using the climb rate. The climb rate is converted into a track inclination command, which is then converted into a pitch angle command. Through integral and proportional control laws, the maximum roll angle is limited to 5° to prevent excessive roll. The conversion relationship between climb rate and track inclination is shown in the following formula: ， in, The ground speed of the drone. For the speed of ascent and descent, For track tilt angle command; Incline of the flight path Convert to pitch angle The process is as follows: The transfer function from pitch angle command to track tilt angle is: ， Design control laws to address negative points Meanwhile, an integrator is introduced, and the control law is as follows: ， The closed-loop transfer function and its corresponding characteristic equation are as follows: ， ， definition and Here, represents the bandwidth and damping ratio of the track angle control loop, respectively, and the corresponding expressions are: ， By setting the appropriate damping ratio, the gain can be controlled via the pitch angle. Calculate the tracking gain of the track angle. for: ； S5: After the aircraft reaches cruising speed, it uses airspeed to control the pitch angle to achieve attitude stability.

2. The control method for ground electromagnetic catapult launch of an unmanned aerial vehicle according to claim 1, characterized in that, After the aircraft reaches cruising speed, pitch is controlled by airspeed, using the same method as in S3.

Images