Flight control structure of tilting transition mode of electric tilting six-rotor unmanned aerial vehicle

Abstract

The invention discloses a flight control structure of an electric tilting six-rotor unmanned aerial vehicle in a tilting transition mode, and aims to solve the problem that the electric tilting six-rotor unmanned aerial vehicle is difficult to control due to violent pneumatics, redundancy of an actuating mechanism and strong coupling of a channel in the tilting transition mode. The invention discloses a flight control system structure of an electric tilt-rotor unmanned aerial vehicle in a tilt transition mode. A hybrid control weight and control distribution mechanism is established based on the tilt angle to realize undisturbed switching and coupling suppression; a composite control path of'differential nacelle dip angle + rotor reaction torque / tail vane cooperation 'of a transition period yaw channel is provided; a hybrid execution mechanism distribution method based on a control distribution matrix is provided, and continuous weighted mapping of accelerator, rolling, pitching and yawing instructions between a motor and a control surface according to a tilt angle is achieved; and the stability of dynamic pressure and height is kept through speed feed-forward and inclination angle scheduling. According to the method, rolling / yawing can be controlled in the tilting process without obvious disturbance, pitching and height deviation is controllable, and compared with a traditional method, the method has faster dynamic response, better steady-state precision and good robustness and engineering realizability.

Description

Technical Field

[0001] This invention belongs to the field of aircraft flight control technology, specifically relating to the flight control system structure of an electric tilt-rotor hexacoach UAV in tilt transition mode, covering rotor / rudder hybrid control, tilt angle scheduling, control allocation, fuzzy PID and PID dual-loop controller design, etc. Background Technology

[0002] In helicopter mode, the flight control of an electric tiltrotor aircraft relies on rotor thrust to provide lift and control attitude, offering significant advantages such as vertical takeoff and landing (VTOL) without the need for a runway, and the ability to adapt to complex takeoff and landing environments. However, flight control in helicopter mode faces numerous technical challenges, such as the susceptibility of aerodynamic characteristics to ground effect, which can affect the accuracy of flight dynamics; and the difficulty of dynamically adapting to complex operating conditions due to fixed parameters in traditional PID controllers. Therefore, there is an urgent need to design a dedicated flight control system architecture to improve the control accuracy and flight stability of the electric tiltrotor aircraft's flight control system in helicopter mode. Summary of the Invention

[0003] Technical problems to be solved The technical problem this invention aims to solve is the strong coupling challenge caused by the drastic changes in aerodynamic characteristics and actuator redundancy during the transition phase of an electric tiltrotor aircraft. In the tilt transition mode, the rotor tilt angle of the tiltrotor aircraft changes from... (Vertical) gradually becomes (Horizontal), airspeed increases from zero to cruise speed. This process results in an extremely complex airflow environment. In tilt transition mode, the aircraft must accelerate while maintaining altitude. In the initial phase, lift is provided entirely by the vertical component of rotor thrust. As the aircraft tilts, the vertical component of the thrust decreases sharply, at which point the wing must generate sufficient lift. To compensate. At the same time, during the transition, the aircraft also needs to undergo a conversion of the main control surfaces from rotor to rudder surfaces.

[0004] Technical solution This invention discloses a flight control system structure for an electric tiltrotor six-rotor UAV in tilt transition mode. The top view and rotor steering of the targeted six-electric tiltrotor aircraft are shown below. Figure 1As shown, rotors 1, 4, and 5 rotate clockwise, while rotors 2, 3, and 6 rotate counter-clockwise, forming pairs of dual rotors 1 and 3, pairs of dual rotors 2 and 4, pairs of dual rotors 5 and 6, pairs of tri-rotors 1, 4, and 5, and pairs of tri-rotors 2, 3, and 6. In tilt transition mode, the electric tilt-rotor hexacopter UAV employs a hybrid control method for vertical motion, simultaneously changing the rotational speeds of all six rotors and manipulating the deflection of the V-tail control surfaces. Roll motion also employs a hybrid control method, simultaneously changing the rotor speeds and manipulating the aileron deflection. Pitch motion employs a hybrid control method, simultaneously changing the rotor speeds and manipulating the deflection of the V-tail control surfaces. Yaw motion employs a hybrid control method, simultaneously changing the rotor speeds and manipulating the deflection of the V-tail control surfaces.

[0005] like Figure 2 As shown, in tilt transition mode, both the propeller aircraft controller thread and the helicopter controller thread are maintained simultaneously. The outputs of these two controllers are then weighted and averaged to obtain the control output for tilt transition mode. During tilt transition, the final motor output command is a superposition of four sets of virtual control outputs: roll control, pitch control, yaw control, and throttle control. Each set of control outputs is derived from the superposition of the helicopter mode control output and the propeller aircraft mode control output.

[0006] Taking the tilting process from helicopter mode to propeller aircraft mode as an example, in the initial stage, the rotor shaft tilt angle is small and the flight speed is low, with rotor control as the primary method and control surface control as a secondary method. As the rotor shaft tilt and flight speed increase, the effectiveness of control surface control gradually increases, and the control ratio gradually rises; the effectiveness of rotor control gradually decreases, and the control ratio gradually falls, until the rotor shaft tilt is complete, rotor control completely exits, and only control surface control remains, entering propeller aircraft mode. By establishing the functional relationship between rotor control, control surface control, and rotor shaft tilt angle, the change in the control ratio during the rotor shaft tilt process is reflected. Furthermore, during the tilting process, for the roll motion of the UAV, the rotor shaft tilt angle is selected at a specific angle... At that time, rotors 3, 4, 5, and 6 are out of control; rotor shaft tilt angle Previously, rotors 1 and 2 were controlled differentially; rotor shaft tilt angle At this time, rotors 1 and 2 are out of control, and the roll control is then achieved entirely by the deflection of the aileron control surfaces.

[0007] Beneficial effects The beneficial effects of this invention are mainly reflected in the following aspects: 1. Smooth and undisturbed mode switching and attitude stabilization were achieved: The system was designed based on tilt angle. The hybrid control weighting mechanism is particularly innovative in the roll channel, employing a "graded degradation / exit logic": by setting first and second threshold angles, the roll control of different rotor subsets is smoothly exited in stages and gradually transferred to the ailerons.

[0008] 2. Solved the problem of strong coupling and allocation of multiple actuators: By establishing a hybrid control weighting and allocation mechanism based on rotor tilt angle, the problem of strong coupling caused by drastic changes in aerodynamic characteristics during the transition period and the redundancy of actuators was effectively solved, and a smooth and disturbance-free switch from rotor-dominated to control surface-dominated was achieved; in particular, the "graded degradation / exit logic" of the roll channel and the "differential nacelle tilt angle + rotor anti-torque / tail rudder" collaborative control strategy of the yaw channel significantly suppressed attitude disturbances.

[0009] 3. Ensures dynamic pressure build-up and altitude stability during the transition: By combining the thrust / velocity management module with feedforward control, the altitude drop during the dynamic pressure build-up process is effectively prevented, thus ensuring that the UAV has faster dynamic response, higher steady-state accuracy and excellent flight robustness throughout the tilt transition process. Attached Figure Description

[0010] Figure 1 Top view and rotor steering diagram of an electric tilting hexacopter UAV Figure 2 Tilting transition mode flight control system structure diagram Figure 3 Rotor shaft tilt curve over time Figure 4 Velocity curves of the drone in three directions over time Figure 5 The curves of the drone's position in three directions over time Figure 6 The attitude angles of the UAV in three directions change over time. Detailed Implementation Step 1: According to... Figure 2 The controller structure shown is used to build a corresponding flight control simulation structure in SIMULINK. This structure includes a flight mode management module, a propeller aircraft flight control module, a helicopter mode flight control module, and a tilt strategy fusion module. The corresponding flight control program is implemented in MATLAB according to the tilt strategy described in the invention.

[0011] Step 2: Write the above flight control program into the Function module in SIMULINK, and connect the flight control systems of helicopter mode and propeller plane mode to this module via bus. During simulation, once the UAV reaches the tilt condition, simply issue a tilt command and wait for the flight control system to automatically complete the tilt transition. No manual adjustment is required during the tilt process; the tilt transition can be determined by observing the rotor shaft tilt angle. Set the tilt command from helicopter mode to propeller plane mode to 1, and the reverse tilt command from propeller plane mode to helicopter mode to -1.

[0012] Step 3: Set the initial state of the flight control system to helicopter mode, altitude... 0m, initial climb rate The initial attitude angle is 0 m / s. All Initial attitude angular rate All values ​​are 0 rad / s. The simulation process requires climbing and hovering in helicopter mode, then tilting the rotor shaft, then tilting the rotor shaft backward again after entering propeller plane mode, and finally returning to helicopter mode.

[0013] Step 4: Full flight simulation, lasting a total of 70 seconds. At the start, a climb rate command is given and maintained until the 13th second. From the 13th to the 16th second, the drone is in helicopter mode, hovering at a fixed altitude. At the 16th second, a forward tilt command is given, lasting 9 seconds. From the 25th to the 50th second, the drone is in propeller aircraft mode. At the 50th second, a backward tilt command is given, also lasting 9 seconds. From the 59th to the 70th second, the drone is in helicopter mode. Observe the system response throughout the tilt process.

[0014] Step 4: Observe the simulation results. The simulation results are as follows: Figures 3-6 As shown, it can be seen that whether tilting forward from helicopter mode to propeller plane mode or tilting backward from propeller plane mode to helicopter mode, the drone's attitude remains stable during the nacelle tilting process, and there is no roll or yaw motion throughout the entire process. Figure 6 The response curves for Phi (roll angle) and Psi (yaw angle) are shown. Figure 3 The changes in rotor shaft tilt angle throughout the flight are shown. In tilt transition mode, the rotor shaft tilt process lasts for 9 seconds and is smooth. In helicopter mode and propeller plane mode, the rotor shaft tilt angle remains unchanged.

[0015] from Figure 4 Ve_z (velocity in the Z direction in the Earth's axis) curve Figure 5 The Xe_z curve and Figure 6The Theta (pitch angle) curve reveals that during the tilt transition from helicopter mode to propeller plane mode, a slight pitch attitude change occurs, ultimately leading to an altitude change. This is because, during this phase, the airspeed is slightly insufficient, requiring the UAV to adjust its pitch attitude to maintain stability. However, the overall attitude change is minor, and the altitude change remains within an acceptable range. The simulation results demonstrate the feasibility of flight control under this tilt strategy.

Claims

1. A flight control structure for a tilt transition mode of an electric tiltrotor hexarotor, applied to an electric tiltrotor unmanned aerial vehicle comprising six tilt rotors, wing ailerons, and a V-tail, characterized in that, The flight control system structure includes: a. Sensing and estimation module, used to acquire the rotor shaft tilt angle in real time. State variables such as three-axis angular velocity, attitude angle, airspeed / ground speed, rate of climb, and altitude; b. Tilting angle scheduling and hybrid manipulation weighting module, based on tilt angle Constructing rotor side weights Weight of control surfaces ,in For follow A continuous function that is monotonically decreasing. Used for continuous weighting of rotor and control surface commands across various control channels; c. Transitional channel-specific degradation / exit logic: Set a first threshold angle in the roll-over channel. With the second threshold angle ( < ), and continuously degrade the roll control gain of at least two different rotor subsets using cosine gate functions, when When the corresponding subset exits the roll control, This causes another subset to exit roll control, allowing roll control to be smoothly transferred from the rotor differential to the aileron. d. Hybrid control allocation module, employing a control allocation matrix. Transmit the throttle, pitch, roll, and yaw commands according to the four channels. , The weighted mapping is represented by the speeds of the six motors and the deflection angle of the control surface, and the matrix elements vary with... Continuous scheduling is achieved through gate functions and weights; e. Yaw composite control path, supporting coordinated control of "differential nacelle tilt angle" and "rotor anti-torque / tail rudder deflection" simultaneously during the transition period, wherein the differential tilt angle is based on... , It is produced in the form of For tilt angle yaw gain, The yaw rate is a command or measurement, and is subject to... Scheduling; f. Thrust / velocity management module, based on The forward thrust and total rotor lift are weighted and distributed according to the desired airspeed, where the longitudinal / vertical force components on the rotor side are calculated as follows: Attenuation, forward propulsion Increase to maintain dynamic pressure and high stability during the transition period.

2. The flight control system structure according to claim 1, characterized in that, The hybrid control weighted rotor side weight Choose cosine function rudder side weight and in Internally continuous differentiable and limited to .

3. The flight control system structure according to claim 1, characterized in that, The two-stage degeneracy gate function of the roll channel is a cosine smoothing function. , They act on different rotor subsets, among which For the first threshold angle, when hour , For the second threshold angle, when hour Preferred for , for This allows for segmented exits and seamless switching.

4. The flight control system structure according to claim 1, characterized in that, The thrust / velocity management module allocates longitudinal thrust in accordance with the following requirements: rotor-side virtual thrust command. Forward thrust side virtual thrust command In the formula, The desired thrust or equivalent command value for the throttle channel is given, and pitch / climb rate feedforward is introduced to suppress altitude deviation during dynamic pressure buildup.

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