A tethered lift wing multicopter recovery method without position or speed sensors

Abstract

The application provides a tethered lift wing multi-rotor recovery method without relying on position or speed sensors, and comprises the following steps: step one, establishing a complete dynamics model of the tethered lift wing multi-rotor and a winding device; step two, designing a controller for the tethered lift wing multi-rotor; the controller output control quantity is a three-dimensional vector of rotor thrust, which is finally changed into a rotor total thrust control quantity and an expected control quantity of attitude through bottom layer control distribution; step three, designing a cable recovery controller. The tethered lift wing multi-rotor does not need any position or speed sensors in the process of automatic landing on a mobile platform, and only needs an internal gyroscope to maintain attitude balance. In a harsh recovery and landing environment, such as a global positioning navigation system rejection environment, a strong wind environment and a smoke environment, the control method designed by the application can be used to realize automatic landing of the tethered lift wing multi-rotor under the dragging of the tethered cable.

Description

Technical Field

[0001] This invention proposes a tethered lifting wing multirotor recovery control method that requires only the built-in gyroscope of the tethered lifting wing multirotor and does not require position or velocity sensors. This method can be used for the automatic landing of tethered lifting wing multirotor UAVs on mobile platforms in environments where GPS is denied, and belongs to the field of aircraft control. Background Technology

[0002] Drone technology has developed rapidly in recent years. However, for tasks requiring long-term flight, such as emergency lighting and emergency communication, conventional drones are inadequate, necessitating the use of tethered drones. Tethered drones are unmanned systems that connect the drone to the ground via a tether cable. The cable can power the tethered multi-rotor lifting wings from the ground and can also be used for data transmission, enabling communication with the ground and achieving long-term flight.

[0003] The lifting-wing multirotor is a new type of vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) that combines the characteristics and advantages of both multirotor and fixed-wing UAVs. The lifting-wing multirotor can utilize its multirotor structure for vertical takeoff and landing, maintaining attitude stability. Furthermore, it can effectively utilize high-altitude wind energy through its fixed-wing structure, while simultaneously improving the aircraft's static stability in the air. A tethered lifting-wing multirotor is a tethered unmanned system that connects the lifting-wing multirotor to the ground via cables, such as... Figure 1 As shown. Compared to common tethered drones, tethered lifting wing multi-rotor drones can effectively utilize high-altitude wind energy, thereby reducing energy consumption. At the same time, the wing structure can effectively improve its static stability in the air.

[0004] Under normal circumstances, tethered drones need to use GPS or other sensors such as cameras and infrared targets to determine their position relative to the landing area when landing on mobile platforms such as vehicles or ships. However, in some harsh environments, such as GPS denial conditions, strong winds preventing the drone from approaching the landing area, or heavy fog and dust preventing the drone from recognizing the landing area, conventional positioning methods cannot be used, and tethered drones cannot complete automatic landing.

[0005] To address the problem of achieving automatic landing of tethered lifting multirotors on mobile platforms without positioning information, this invention proposes a control method for achieving automatic landing of tethered lifting multirotors on mobile platforms without requiring positioning or velocity information, relying solely on a built-in gyroscope. Summary of the Invention

[0006] This invention proposes a control method for a tethered lifting multirotor that achieves automatic landing on a mobile platform without relying on position or velocity sensors, but solely on a built-in gyroscope. First, a dynamic model of the tethered lifting multirotor is established. Then, the feasibility of the control method is discussed from both the vertical and horizontal directions. The overall steps are as follows: Figure 6 As shown, the detailed steps are as follows:

[0007] Step 1: Establish a complete dynamic model of the tethered lifting multirotor and its reel. The forces acting on the tethered lifting multirotor in the air include gravity, aerodynamic forces, tether rope tension, and rotor thrust. Therefore, the dynamic model can be obtained as follows:

[0008]

[0009] in, e p represents the position of the tethered lifting multirotor. e v is the velocity of the tethered lifting multi-rotor, and m is the mass of the tethered lifting multi-rotor. e T r The rotor thrust experienced by a tethered lifting multi-rotor in the geodetic coordinate system. e F c The tension in the tethering rope acting on the tethered multirotor is given by g = [0 0 g]. T It is the acceleration due to gravity. e F a The wind force experienced by the tethered lifting multi-rotor.

[0010] The dynamic model of the reel can be represented as:

[0011]

[0012] Where L is the length of the mooring rope, v c J is the tether rope retrieval speed. w Let ω be the moment of inertia of the winding reel. w τ is the rotational angular velocity of the cable reel, r is the radius of the cable reel, and τ is the angular velocity of the cable reel. w F is the torsional torque of the cable reel. c This refers to the tension in the tethering rope.

[0013] Step Two: Design a controller for tethered lifting multi-rotor rotors. The controller involved in this invention outputs a three-dimensional vector of rotor thrust, which, through underlying control allocation, can ultimately be transformed into the desired control quantities for the total rotor thrust and attitude. The overall control scheme is as follows: Figure 2 As shown.

[0014] In the vertical direction, the control method proposed in this invention is inspired by kites. Kites in the air are only subject to gravity, aerodynamic forces, and rope tension, with the lift force being greater than gravity. This means that a kite is very similar to an inverted pendulum; it can autonomously return to a stable equilibrium point at a high altitude without external disturbance. The relevant process is as follows: Figure 3a , Figure 3b As shown.

[0015] In the vertical direction, the kite experiences more lift than gravity, causing it to continuously move towards its highest point, and the tethering line can be actively taut. In the horizontal direction, the kite is naturally damped by wind resistance, thus maintaining its balance.

[0016] Based on the above considerations regarding kites, a tethered lifting multi-rotor controller in the height direction can be designed as follows:

[0017] T rz =(1+∈)mg (3)

[0018] Among them, T rz ε is the rotor thrust in the height direction, and ε is the ratio of the amount by which the rotor thrust in the height direction exceeds gravity to gravity.

[0019] In the horizontal direction, the control variables for the tethered lifting multirotor are used to maintain attitude balance. This part is directly solved by the attitude controller to obtain T. rx and T ry Ultimately, the control variables for a tethered lifting multirotor can be expressed as:

[0020] e T r =[T rx T ry T rz ] T .

[0021] Step 3: Design the cable retrieval controller. In this invention, the tethered lifting multi-rotor, mimicking a kite, actively straightens the cable and positions it near a stable equilibrium point. At this point, the position of the tethered lifting multi-rotor relative to the mobile retrieval platform can be represented by the cable length. Therefore, when the cable length is retrieved to 0, the tethered lifting multi-rotor has completed its landing and retrieval on the mobile platform. This invention ultimately aims for uniform cable retrieval, and the PID controller is designed as follows:

[0022]

[0023] Where, k pω k iω k dω ω is the feedback coefficient. wref The desired reel recovery speed.

[0024] After completing the above steps, the tethered lifting multirotor controller can be downloaded to the Pixhawk4 open-source flight controller board via the RflySim toolchain using automatic code generation. The expected rotational angular velocity of the cable reel is set on the Ubuntu 18 platform, and a host computer controlling the cable reel motor is run on this platform to drive the cable reel for testing. The cable reel motor uses a GO-M8010-6 motor manufactured by Unitree Automation.

[0025] The beneficial effects of this invention are as follows:

[0026] The tethered lifting multirotor requires no position or velocity sensors during automatic landing on a mobile platform; it only needs a built-in gyroscope to maintain attitude balance. In harsh recovery and landing environments, such as GPS-denied environments, high-wind environments, and smoke environments, the control method designed in this invention can be used to achieve automatic landing of the tethered lifting multirotor under the drag of the tether cable. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a tethered lifting multi-rotor.

[0028] Figure 2 This invention relates to the overall controller structure of a tethered lifting multi-rotor system.

[0029] Figure 3a , Figure 3b This describes the characteristic of kites and inverted pendulums that they can autonomously return to a stable equilibrium point.

[0030] Figure 4 This is a simulation result of an automatic landing of a tethered lifting multi-rotor using this method.

[0031] Figure 5 This is a simulation of the automatic landing effect of a tethered lifting multi-rotor observed from the side.

[0032] Figure 6 This is the implementation process of the entire implementation steps of the present invention. Detailed Implementation

[0033] This invention presents a control method for a tethered lifting multirotor that can achieve automatic landing using only a built-in gyroscope, without requiring position or velocity sensors. Simulations were conducted on a computer running Windows 10 with a 3.20 GHz CPU and 32.00 GB of RAM, using MATLAB R2022b with the PX4PSP toolbox and RflySim toolchain. After successful simulation, code was automatically generated using the RflySim toolchain, allowing for real-world flight testing.

[0034] Step 1: Measure the parameters of the tethered lifting multi-rotor system and establish a mechanical model of the tethered lifting multi-rotor and the winding reel.

[0035] The tethered lifting multirotor has a mass of 1.2 kg, an installation angle of 34° relative to the multirotor, and a wing area of ​​0.09 m². 2 During the simulation, it is assumed that the direction of motion of the mobile platform is facing the wind field, the nose direction of the tethered lifting multi-rotor is in the same direction as the direction of motion of the mobile platform, the wind speed is 2.8 m / s, the moving speed of the mobile platform is 2 m / s, the horizontal positional error between the tethered lifting multi-rotor and the mobile platform is 7 m at the beginning of the simulation, the lifting multi-rotor is located directly behind the mobile platform, the initial retrieval height is 10 m, the cable retrieval speed is 1 m / s, and the radius of the reel is 0.05 m.

[0036] Step 2: Design a controller for the tethered lifting wing multi-rotor. Based on the tethered lifting wing multi-rotor parameters set in Step 1, set the value of ε to 0.2. The desired control quantity in the height direction can be obtained by referring to Equation (3). The force is distributed with the horizontal rotor thrust obtained by the attitude controller, and finally the control of the tethered lifting wing multi-rotor is realized.

[0037] Step 3: Refer to formula (4) to design the controller for the reel, and select k. pω =0.5, k iω =0,k dω =0.001. Based on the parameters set in step one, the desired angular velocity of the winding reel can be obtained as ω. wref = 20 rad / s.

[0038] The simulation was performed according to the above steps, and the resulting 3D position curve is shown below. Figure 4 As shown, the image viewed from the side is as follows Figure 5 As shown in the figure. Simulation results show that the tethered lifting multi-rotor can successfully complete automatic landing under the towing of the tether rope, and the entire process does not require position or speed sensors, but only requires the built-in gyroscope to maintain attitude balance.

Claims

1. A method for recovering a tethered lifting multi-rotor without relying on position or velocity sensors, but solely on a built-in gyroscope, characterized in that: The steps include the following: Step 1: Establish a complete dynamic model of the tethered lifting multi-rotor and its reel; the forces acting on the tethered lifting multi-rotor in the air include gravity, aerodynamic forces, tether rope tension, and rotor thrust; Step 2: Design a controller for tethered lifting multi-rotor; the controller outputs a three-dimensional vector of rotor thrust, which is ultimately distributed through the underlying control to become the desired control quantities of total rotor thrust and attitude. Step 3: Design the cable recycling controller; actively straighten the cable and bring it to a stable equilibrium point; at this point, the cable length is used to represent its position relative to the mobile recycling platform; In step two, the control parameters of the tethered lifting multi-rotor in the horizontal direction are used to maintain attitude balance. This part is directly solved by the attitude controller. and Ultimately, the control variables for the tethered lifting multi-rotor are expressed as follows: ； In step two, the tethered lifting multirotor controller in the height direction is designed as follows: (3) in, The rotor thrust in the height direction, The ratio of the amount by which the thrust provided by the rotor in the vertical direction exceeds gravity to gravity; In step three, when the cable length is reduced to 0, the tethered lifting multi-rotor completes its landing and retrieval on the mobile platform. To ensure uniform cable retrieval, a PID controller is designed as follows: (4) in, , , For feedback coefficients, The desired reel recovery speed.

2. The method for recovering a tethered lifting multi-rotor without relying on position or velocity sensors according to claim 1, characterized in that: In step one, the dynamic model is as follows: (1) in, To determine the location for tethering the lifting multi-rotor. To maintain the speed of the tethered lifting multi-rotor, For the mass of the tethered lifting multi-rotor, The rotor thrust experienced by a tethered lifting multi-rotor in the geodetic coordinate system. The tension in the tethering rope acting on the tethered multi-rotor lifting wing. It is the acceleration due to gravity. The wind force experienced by the tethered lifting multi-rotor.

3. The method for recovering a tethered lifting multi-rotor without relying on position or velocity sensors according to claim 1, characterized in that: In step one, the dynamic model of the reel is expressed as: (2) in, The length of the mooring rope. To determine the tether rope retrieval speed, The moment of inertia of the winding reel. The rotational angular velocity of the winding reel. The radius of the cable reel. For the torsional torque of the cable reel, This refers to the tension in the tethering rope.

4. A method for recovering a tethered lifting multi-rotor without relying on position or velocity sensors according to any one of claims 1-3, characterized in that: The tethered lifting wing multirotor controller was downloaded to the Pixhawk4 open-source flight controller board using the RflySim toolchain via automatic code generation. The expected rotational angular velocity of the reel was set on the Ubuntu 18 platform, and the reel motor control host computer was run on the platform to drive the reel and conduct experiments. The reel motor was a GO-M8010-6 motor manufactured by Unitree Technology.

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