Control method for ground electromagnetic ejection of unmanned aerial vehicle

Abstract

The invention discloses a control method for ground electromagnetic ejection of an unmanned aerial vehicle, belongs to the field of flight control of the unmanned aerial vehicle, and enables the unmanned aerial vehicle to enter a preset speed and flight attitude on the ground through electromagnetic ejection. The method comprises the following steps: binding an initial attitude, and confirming that the unmanned aerial vehicle is in a to-be-launched stage; in the electromagnetic acceleration stage, the pitch angle is controlled through acceleration; when the speed is greater than a certain value in the launching process, the pitch angle is controlled by using the airspeed until the aircraft reaches a safe take-off height; after the aircraft reaches the safe take-off height, pitching is controlled through the lifting rate, the maximum roll angle is limited, and the roll angle is prevented from being too large; after the aircraft reaches the cruising speed, pitching is controlled through the air speed, the attitude is stable, the unmanned aerial vehicle continues to fly at the cruising speed, and launching is completed.

Description

Technical Field

[0001] The invention belongs to the field of unmanned aerial vehicle flight control, and in particular relates to a control method for ground electromagnetic ejection of an unmanned aerial vehicle. Background Art

[0002] Drones are widely used in military and civilian fields, playing an important role in disaster prevention and rescue, material delivery, agricultural plant protection, aerial photography, ships with limited space and many other fields. In the application of drones in some fields, the launch phase is often considered to be one of the more difficult stages. Various countries have conducted a lot of research and attempts on the takeoff and launch of drones.

[0003] At present, the commonly used methods for launching drones include hand-throwing launch, in which the operator manually throws the drone and then starts the power system. However, it requires high skills and strength from the operator, is only suitable for small drones and is greatly affected by weather. Landing gear rolling launch relies on engine power to take off on the runway, but has high requirements for the site and a long preparation time. Catapult launch uses a variety of catapult devices to allow the drone to take off instantly at high speed. The disadvantage is that the maintenance and debugging of the device are complicated, and the control accuracy of launch parameters is required to be high. Vertical take-off and landing launch includes rotors and tilt-rotors, etc., with complex power systems, low endurance and load capacity, and great difficulty in attitude control. Air launch from a mother aircraft is to release the drone after the mother aircraft flies to a predetermined position. It is costly and has strict requirements on drone design and launch accuracy. Rocket-assisted launch relies on the thrust of the rocket engine to make the drone fly away from the launch device. It is dangerous, increases cost and complexity, and has high requirements for site safety.

[0004] The research on electromagnetic catapult technology in the field of UAV launch has made certain progress. Many scientific research teams and institutions have carried out relevant designs and analyses based on the characteristics of UAVs. For example, based on the characteristics and ejection requirements of folding-wing UAVs, the principle of three-phase asynchronous induction electromagnetic coil ejection is introduced, mathematical modeling is carried out, and system solutions and structural designs are designed. The finite element model is established through software for electromagnetic field and mechanical simulation analysis. The results show that the system can meet certain launch initial velocity and overload design requirements. The design and development of rail-type electromagnetic launchers and electrothermal launchers have also been completed in China. The structural performance of railguns and the problem of elastic buckling of coil shells have been analyzed and studied, and a finite element simulation model has been established. At present, electromagnetic catapult technology has received extensive attention and research due to its advantages of full electric operation, large thrust, stable thrust, high efficiency, controllable speed and acceleration, and stealthy launch, and has achieved relatively rich results in theory and simulation. However, this technology still has many shortcomings. It is difficult to dynamically adjust the electromagnetic thrust according to the changes of the ejected object, the real-time motion state of the object cannot be accurately positioned, and the initial velocity of the ejection cannot be accurately controlled. The energy supply demand is large, and there are losses in the actual conversion. The energy conversion efficiency of traditional energy storage methods is low, which can easily cause the power system to overload. Summary of the invention

[0005] The invention provides a control method for electromagnetic ejection of a UAV on the ground, which uses electromagnetic ejection to make the UAV enter a predetermined speed and flight posture on the ground.

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

[0007] A control method for electromagnetic ejection of a drone on the ground, comprising the following steps:

[0008] S1: Bind the initial posture and confirm that the drone is in the launch-ready stage;

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

[0010] S3: During the launch process, when the speed is greater than a certain value, the pitch angle is controlled using the airspeed until the aircraft reaches a safe takeoff altitude.

[0011] S4: After the aircraft reaches a safe takeoff altitude, the pitch is controlled by the vertical rate to limit the maximum roll angle to prevent the roll angle from being too large.

[0012] S5: After the aircraft reaches cruising speed, use airspeed to control pitch to achieve attitude stability.

[0013] Beneficial effects: The present invention provides a control method for electromagnetic ejection of a UAV on the ground, which has the following advantages over the prior art:

[0014] During the electromagnetic acceleration stage, the pitch angle is precisely controlled according to the change in acceleration to ensure that the UAV can climb smoothly. During launch, after the airspeed is greater than 30m / s, the pitch angle is controlled to a safe height using the airspeed, achieving coordinated control of airspeed and altitude to improve flight safety. After reaching a safe altitude and cruising speed, the pitch is controlled using the ascent and descent rate and airspeed respectively, and the roll angle is limited to achieve multi-stage attitude stabilization. Compared with traditional launch methods, it reduces takeoff energy consumption, improves endurance and flight performance, ensures the smooth completion of the mission, and broadens the scope of application of UAVs. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0016] Figure 2 : is a parameter diagram of the UAV in the state of waiting to launch in an embodiment of the present invention, wherein the upper left is the pitch angle and pitch angle command in the state of waiting to launch, the upper right is the throttle in the state of waiting to launch, the lower left is the elevator command in the state of waiting to launch, and the lower right is the acceleration in the state of waiting to launch;

[0017] Figure 3: is a state parameter diagram of the drone after launch in an embodiment of the present invention, wherein 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 A block diagram of a track angle tracking algorithm in an embodiment of the present invention;

[0019] Figure 5 : is a state parameter diagram of the pitch phase of the vertical speed control in an embodiment of the present invention, wherein the upper left is the vertical speed command, the upper right is the pitch angle command and the pitch angle, the lower left is the airspeed command and the airspeed, and the lower right is the pitch angle command and the pitch angle;

[0020] Figure 6 1 is a state parameter diagram of the cruise phase in an embodiment of the present invention, wherein the left side is the pitch angle command and the pitch angle, and the right side is the airspeed command and the airspeed. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0022] The take-off process of a drone is mainly divided into two stages:

[0023] 1. Achieve the drone reaches a safe height after launch

[0024] At the initial launch stage, when the acceleration of the drone reaches 1.2 times the acceleration of gravity, the pitch angle command is 1°, and when the acceleration decreases to 0.5 times the acceleration of gravity, the pitch angle command is 5°, and the roll angle is controlled to 0°. When the airspeed is greater than 30 meters per second, the pitch angle is controlled by the airspeed until the drone reaches a safe altitude.

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

[0026] After the UAV reaches a safe height and before reaching cruising speed, the pitch angle is controlled using the lift speed, with a lift speed instruction of 0.5 meters per second, allowing the UAV to safely reach cruising speed.

[0027] After the UAV reaches the cruising speed, continue to use the aircraft speed to control the pitch angle to achieve attitude stability.

[0028] like Figure 1 As shown, a control method for ground electromagnetic ejection of a UAV includes the following stages:

[0029] The first stage: Bind the initial posture to make the drone ready to launch, 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 drone is also basically 0;

[0030] The second stage: After ignition and takeoff, the throttle opening is 100%, and the UAV is accelerated by electromagnetic catapult, such as Figure 3 As shown in the figure, when the acceleration of the drone is greater than 1.2 times the acceleration of gravity, the pitch angle command is controlled to 1°. When the acceleration of the drone is less than 0.5 times the acceleration of gravity, the pitch angle is controlled to 5°, and the airspeed command is 29m / s to ensure that the drone can climb and accelerate normally. When the airspeed is greater than 30m / s, the pitch angle is controlled by the airspeed until the drone reaches a safe height. The pitch angle is controlled by the airspeed. The conversion relationship is: , in is the acceleration due to gravity, is the pitch angle gain, is the pitch angle command, is the airspeed command, is the actual airspeed;

[0031] Phase 3: Use the vertical speed to control the pitch angle, the vertical speed command is 0.5m / s, the airspeed command is the cruising speed of 35m / s, and the maximum roll angle is limited to 5° until the speed reaches the cruising speed of 35m / s; Convert to track inclination command , and then converted to get the pitch angle command ;

[0032] First of all, from the geometric meaning, we can know the lifting speed and track inclination The conversion relationship is shown as follows: , in is the ground speed of the UAV.

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

[0034] The relationship between pitch angle, angle of attack and track inclination is: , in, is the pitch angle, is the angle of attack, is the track inclination angle.

[0035] Consider that the relationship between the track inclination rate and the angle of attack is as follows: , in, is the track inclination change rate, is the air density, is the aircraft's airspeed, is the reference area of ​​the wing, is the derivative of the lift coefficient with respect to the angle of attack, is the quality of the drone, It is a parameter related to the derivative of the track inclination angle with respect to the angle of attack.

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

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

[0038] Design control law to deal with negative points , and the integrator is introduced at the same time, the control law is as follows: ,

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

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

[0041] By setting the corresponding damping ratio, the gain can be controlled by the pitch angle , and obtain the track angle tracking gain for: ,

[0042] In this stage, if Figure 5As shown in the figure, the vertical speed command hdot_c is set to 0.5m / s, the UAV vertical speed hdot gradually decreases from 6.5m / s, and the flight altitude rel_alt gradually stabilizes to enter the cruising speed stably. The airspeed command as_c is set to the cruising speed of 35m / s, and the UAV's indicated airspeed IAS is maintained at around 35m / s. At the same time, the reduction in vertical speed reduces the pitch angle command tht_c, and the UAV should lower its nose to fly.

[0043] Stage 4: After reaching the cruising speed, the drone continues to use airspeed to control the pitch angle, the method is the same as in the second stage, to ensure that the drone continues to fly at the cruising speed and maintains a stable attitude. Figure 6 As shown, the pitch angle is used to control the airspeed so that the UAV continues to fly at the cruising speed and the launch is completed.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A control method for electromagnetic ejection of a drone, characterized in that: The following steps are involved: S1: Bind the initial posture and confirm that the drone is in the launch-ready stage; S2: electromagnetic acceleration stage, the pitch angle is controlled by acceleration; S3: During the launch process, when the speed is greater than a certain value, the pitch angle is controlled using the airspeed until the aircraft reaches a safe takeoff altitude; S4: After the aircraft reaches the safe takeoff altitude, the pitch is controlled by the vertical rate to limit the maximum roll angle to prevent the roll angle from being too large. S5: After the aircraft reaches cruising speed, use airspeed to control pitch to achieve attitude stability.

2. The control method for ground electromagnetic catapult of a UAV according to claim 1, characterized in that: During the electromagnetic acceleration stage, when the acceleration of the drone is greater than 1.2 times the acceleration of gravity, the pitch angle command is controlled to 1°.

3. The control method of ground electromagnetic catapult of UAV according to claim 1, characterized in that: During the electromagnetic acceleration stage, when the acceleration of the drone is less than 0.5 times the acceleration of gravity, the pitch angle is controlled to 5°.

4. The control method of ground electromagnetic catapult of UAV according to claim 1, characterized in that: During the launch process, when the airspeed is greater than 30m / s, the pitch angle is controlled using the airspeed until the drone reaches a safe altitude.

5. The control method for ground electromagnetic catapult of a UAV according to claim 1 or 4, characterized in that: The conversion relationship of using airspeed to control pitch angle is: ， in, is the acceleration due to gravity, is the pitch angle gain, is the pitch angle command, is the airspeed command, is the actual airspeed.

6. The control method for ground electromagnetic catapult of a UAV according to claim 1, characterized in that: The pitch angle is controlled by using the vertical speed, which is converted into a track inclination instruction, and then converted into a pitch angle instruction.

7. The control method for ground electromagnetic catapult of a UAV according to claim 6, characterized in that: Lifting speed and track inclination The conversion relationship is shown as follows: ， in, is the ground speed of the drone, is the lifting speed, is the track inclination instruction.

8. The control method for ground electromagnetic catapult of a UAV according to claim 6, characterized in that: The process of converting the track inclination angle command into the pitch angle command is as follows: The transfer function from pitch angle command to track inclination is: ， Design control laws to deal with negative points , and the integrator is introduced at the same time, the control law is as follows: ， The closed-loop transfer function and the corresponding characteristic equation are: ， ， definition and are the bandwidth and damping ratio of the track angle control loop respectively, and the corresponding expressions are: ， By setting the corresponding damping ratio, the gain can be controlled by the pitch angle , and obtain the track angle tracking gain for: 。 9. The control method for ground electromagnetic catapult of a UAV according to claim 1, characterized in that: After the aircraft reaches the cruising speed, the pitch is controlled by airspeed in the same way as in S3.

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