A variable center of mass ducted unmanned aerial vehicle and a control method thereof

Abstract

The application discloses a variable center of mass ducted unmanned aerial vehicle structure and a control method thereof, a variable center of mass actuator and a slide rail are arranged, the extension direction of the slide rail is perpendicular to the central axis of the duct body, all the slide rails are uniformly distributed around the central axis of the duct body in the circumferential direction, the variable center of mass actuator automatically slides and cooperates with the slide rail, so that the center of mass of the unmanned aerial vehicle is changed, thereby adjusting the center of mass of the unmanned aerial vehicle. A pair of forward and reverse propellers on the central axis of the machine body provide thrust for the machine body, and the propeller torque generated by the speed difference is used to control the yaw direction attitude. The variable center of mass mechanism can be arranged in the machine body, the relative position relationship between the center of mass of the machine body and the thrust center is controlled through the position change of the variable center of mass mechanism, and attitude control torque in the tilting and rolling directions is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of unmanned aerial vehicles, and particularly relates to a variable center of mass ducted unmanned aerial vehicle structure and a control method thereof. BACKGROUND

[0002] A ducted unmanned aerial vehicle is a special type of rotary-wing unmanned aerial vehicle. It not only has the vertical take-off and landing capability of a conventional rotary-wing unmanned aerial vehicle, but also protects the rotor by using a duct to cover the rotor, greatly enhancing the through capability of the unmanned aerial vehicle in complex and compact environments such as jungles and indoor environments. In addition, the duct can reduce the generation of wingtip vortices, reduce induced drag, and provide additional lift to improve hovering performance. Therefore, the ducted unmanned aerial vehicle can provide the same lift as a conventional open rotor unmanned aerial vehicle with a smaller volume. Finally, the duct can also block part of the noise and provide installation conditions for the use of noise reduction and sound absorption materials.

[0003] At present, the ducted unmanned aerial vehicle mostly uses aero rudders to generate control moments for attitude control. The propeller of the ducted unmanned aerial vehicle generates thrust and provides airflow for the aero rudders. When the airflow blows through the aero rudders, it generates a moment relative to the center of mass of the unmanned aerial vehicle, realizing attitude control.

[0004] At present, the ducted unmanned aerial vehicle using aero rudders for attitude control has the problem of coupling of attitude control moments and thrust, and is easily disturbed by external airflow to affect the attitude control performance. SUMMARY

[0005] The purpose of the present application is to provide a variable center of mass ducted unmanned aerial vehicle structure and a control method thereof to solve the problems in the prior art.

[0006] The purpose of the present application is achieved by a variable center of mass ducted unmanned aerial vehicle structure, comprising:

[0007] A circular cylindrical duct body, the inside of which is provided with a duct, and a load device is detachably installed on the outer side wall of the duct body;

[0008] A skeleton fixedly connected to the inside of the duct body and having an up-and-down ventilation structure;

[0009] A propeller in the duct, which is provided with a flight driver for driving the propeller to rotate, and the rotation center axis of the propeller coincides with the center axis of the duct body;

[0010] A plurality of variable center of mass actuators and slide rails, the extension direction of the slide rails is perpendicular to the center axis of the duct body, all the slide rails are uniformly distributed around the center axis of the duct body, and the variable center of mass actuators automatically slide with the slide rails to change the center of mass of the unmanned aerial vehicle.

[0011] As another aspect of the present application, a control method is proposed based on the structure of the above unmanned aerial vehicle, which is as follows:

[0012] Input the current position, and determine whether the unmanned aerial vehicle meets the expected waypoint: if it meets the expected waypoint, end; if it does not meet the expected waypoint, perform position loop PID control to adjust the propeller thrust;

[0013] Input the current attitude, and determine whether the unmanned aerial vehicle meets the expected attitude: if it meets the expected attitude, proceed to the step of determining whether the unmanned aerial vehicle meets the expected waypoint; if it does not meet the expected attitude, perform attitude loop PID control to adjust the moment, enter the control distribution step, and the corresponding one or more variable center actuators slide along the slide rail by a distance to adjust the center of mass of the unmanned aerial vehicle, and then determine whether the unmanned aerial vehicle meets the expected attitude;

[0014] The relative position relationship between the body center of mass and the thrust center is controlled by the position change of the variable center actuator to obtain the attitude control moment in the tilt and roll directions.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] 1. Suitable for carrying acoustic equipment, the propeller of the ducted unmanned aerial vehicle adopted by the present application is covered by the duct structure, the tip vortex is suppressed, the aerodynamic performance is optimized, and the duct structure can be additionally provided with sound insulation, the noise performance is better than that of the conventional multi-rotor unmanned aerial vehicle, and the problem that the conventional multi-rotor unmanned aerial vehicle is difficult to carry acoustic measurement equipment can be solved.

[0017] 2. The attitude control anti-interference ability is enhanced, the variable center attitude control scheme is adopted in the present application, so that the moment required for attitude control is no longer dependent on the airflow generated by the propeller, the decoupling of the attitude control moment and the thrust is completed, and the problem of insufficient attitude control moment when the unmanned aerial vehicle generates small thrust is solved; since the attitude control mechanism in the present application is independent of the airflow, the problem of aggravating the wall adsorption effect when the conventional ducted unmanned aerial vehicle controlled by the traditional aerodynamic rudder is flown indoors is also avoided, and the present application is more suitable for stable flight in complex environments.

[0018] 3. The structure is simple and the weight is lighter, the variable center actuator is integrally designed with the variable center driving device and the sliding block in the present application, the additional weight caused by the split design is saved, the lift margin of the unmanned aerial vehicle is effectively improved, the flight performance of the unmanned aerial vehicle is improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic view of the cross section of the unmanned aerial vehicle of the present application.

[0020] Figure 2 is a diagram for analyzing the resultant moment of the body coordinate system.

[0021] Figure 3 is a flight control flow chart of the waypoint of the present application.

[0022] Reference numerals: 1 - duct body; 2 - propeller; 3 - flight driver; 4 - variable center of mass actuator; 5 - slide rail; 6 - skeleton; 7 - load device. DETAILED DESCRIPTION

[0023] According to Figure 1 As shown in the figure, a variable center of mass ducted unmanned aerial vehicle structure is proposed, comprising:

[0024] A circular cylindrical duct body 1, the inside of which is provided with a duct, and a load device 7 is detachably installed on the outer wall of the duct body 1;

[0025] A skeleton 6 fixedly connected to the inside of the duct body 1, and an up-and-down ventilation structure;

[0026] A propeller 2 in the duct, which is provided with a flight driver 3 to drive it to rotate, and the center axis of rotation of the propeller 2 coincides with the center axis of the duct body 1;

[0027] A plurality of identical variable center of mass actuators 4 and a plurality of identical slide rails 5, the variable center of mass actuators 4 have the functions of driving and mass sliding blocks, all the variable center of mass actuators 4 are distributed at the same height when the center axis of the duct is in a vertical state, and all the slide rails 5 are also distributed at the same height, the extension direction of the slide rails 5 is perpendicular to the center axis of the duct body 1, all the slide rails 5 are uniformly distributed around the center axis of the duct body 1 in the circumferential direction, and the variable center of mass actuators 4 are slidingly connected to the slide rails 5 and automatically slidingly matched with the slide rails 5 to change the center of mass of the unmanned aerial vehicle.

[0028] As a preferred scheme of the present embodiment, the skeleton 6 is provided as a cross-shaped rod structure, the number of the variable center of mass actuators 4 and the slide rails 5 is both four, all the slide rails 5 are distributed in a cross shape, and the center axis of rotation of the propeller 2 passes through the cross intersection point of the skeleton 6.

[0029] As a preferred scheme of the present embodiment, the power main shaft of the variable center of mass actuator 4 is sleeved with a gear, which is engaged with a rack fixed to the skeleton 6, and through the gear and rack engagement, the variable center of mass actuator 4 is guided to slide on the slide rail 5 accordingly, so as to adjust the center of mass of the unmanned aerial vehicle. In view of the problem of redundant structure of the existing variable center of mass actuator, the variable center of mass driving mechanism and the mass sliding block are designed in an integrated manner to form the variable center of mass actuator 4. A stepping motor integrated with a driver is used as the variable center of mass driving mechanism and the mass sliding block, and a linear slide rail 5 is used for limiting. A gear is installed on the output shaft of the stepping motor, which is engaged with a rack parallel to the linear guide rail, so as to realize the self-driving of the variable center of mass actuator 4 on the linear slide rail 5, thereby realizing the relative position control of the center of mass of the machine body and the center of lift.

[0030] The embodiment also provides a control platform, which controls the variable center of mass actuator 4 and the flight driver 3, and can be a remote controller, a smart mobile device or other devices.

[0031] The embodiment adopts a coaxial dual-rotor ducted unmanned aerial vehicle. Two propellers 2 are arranged in an upper and lower distribution, and the two propellers 2 are arranged as a pair of forward and reverse propellers to provide thrust for the entire unmanned aerial vehicle, and the propeller torque generated by the speed difference is used to control the yaw direction attitude. A variable center of mass mechanism (variable center of mass actuator 4) is arranged in the body, the relative position relationship between the center of mass and the thrust center of the body is controlled by the position change of the variable center of mass mechanism, and attitude control torque in the tilt and roll directions is obtained.

[0032] In view of the poor noise performance of the traditional multi-rotor unmanned aerial vehicle and the inability to carry acoustic measurement equipment, the propeller 2 is covered with a duct structure, and sound-absorbing materials are suitable for installation. The covering effect of the duct on the propeller 2 blocks the noise propagation, and the generation of the propeller tip vortex is suppressed by controlling the propeller tip distance, thereby improving the aerodynamic performance, enabling the unmanned aerial vehicle to obtain sufficient lift at a lower speed, and further reducing the noise level.

[0033] In view of the weak anti-interference performance of the traditional aerodynamic rudder, the variable center of mass attitude control method is used to completely decouple the attitude control actuator from the thrust and external airflow conditions, and the control problem is converted into a rigid body dynamics problem, thereby reducing the design difficulty of the control method.

[0034] The load device 7 is detachably installed on the outer wall of the duct body 1, does not affect the additional lift provided by the duct lip, and does not affect the flow of the duct airflow inlet and outlet.

[0035] Based on the above variable center of mass ducted unmanned aerial vehicle, the following control method is designed.

[0036] Ducted unmanned aerial vehicle modeling:

[0037] A ground coordinate system O-XYZ and a variable center of mass ducted vehicle body coordinate system o-xyz are established, the origin of the body coordinate system is the equivalent center of action of the lift generated by the propeller of the variable center of mass ducted vehicle, and the coordinate axis direction is the same as that of the ground coordinate system.

[0038] The variable center of mass mechanism has two in the x and y axis directions of the body coordinate system, respectively, and two are a group. The two groups of variable center of mass structures slide along the x and y axis directions, respectively, and the motion direction and speed of the two structures in the same group are the same, and the equivalent mass block. The equivalent mass block of the variable center of mass structure takes x and y coordinates as its rudder, respectively, and is l x and l y .

[0039] The velocity vectors of the two equivalent mass blocks relative to the ground coordinate system are respectively:

[0040]

[0041] where V0is the velocity of the variable center of mass air vehicle relative to the ground coordinate system, ω is the angular velocity of the air vehicle, is the velocity of the mass slider relative to the body coordinate system, r i is the position vector of the mass slider in the body coordinate system.

[0042] The center of mass motion velocity of the variable center of mass air vehicle is calculated by the center of mass motion theorem, and then we get:

[0043] mV c = m s V0+ m x V1+ m y V2

[0044] That is:

[0045]

[0046] where m is the overall mass of the variable center of mass air vehicle, m s = m - m1- m2.

[0047] PID position-pose cascade control:

[0048] Let the current position of the variable center of mass air vehicle in the ground system be P, and the desired position be P d , design a position loop PID controller, and the desired speed of the air vehicle is:

[0049]

[0050] The desired acceleration is:

[0051]

[0052] where e p and e v are the position error and speed error, respectively.

[0053] Considering the horizontal displacement, the desired acceleration is expressed as:

[0054]

[0055] Then the desired pitch and roll angles a d and b d are:

[0056]

[0057] where g is the current yaw angle.

[0058] The desired attitude of the air vehicle can be recorded as:

[0059] qd = [a d , b d , 0]

[0060] The attitude loop PID controller is designed, and the desired angular velocity of the aircraft is:

[0061]

[0062] The desired angular acceleration is:

[0063]

[0064] where e θ and e ω are the angle error and angular velocity error, respectively.

[0065] According to the desired angular acceleration, the desired total moment is calculated:

[0066]

[0067] Control allocation:

[0068] In the body coordinate system, the desired total moment is expressed as M d = [M dx , M dy , 0].

[0069] The equivalent sliders of the two groups of variable center of mass mechanisms (variable center of mass actuators 4) in the aircraft are m x and m y , and the center of mass of the aircraft excluding the variable center of mass mechanisms is m s , the position in the body coordinate system is defined as shown in Figure 2 .

[0070] The relationship between the total moment and the steering amount of the two groups of variable center of mass mechanisms is:

[0071]

[0072] where m sx = m s + m x = m s + m y .

[0073] And the center of mass position of the part of the aircraft excluding the variable center of mass mechanisms and the corresponding direction variable center of mass mechanism is:

[0074]

[0075] Thus, the control allocation relationship of the variable center of mass aircraft is:

[0076]

[0077] That is, the required resultant moment is obtained by controlling the rudder amount of the two sets of variable center of mass mechanisms.

[0078] Control logic:

[0079] As Figure 3 The control flow after the aircraft receives the waypoint flight instruction is shown:

[0080] Input the current position, and determine whether the UAV meets the expected waypoint: if it meets the expected waypoint, end; if it does not meet the expected waypoint, perform position loop PID control to adjust the propeller thrust;

[0081] Input the current attitude, and determine whether the UAV meets the expected attitude: if it meets the expected attitude, proceed to the step of determining whether the UAV meets the expected waypoint; if it does not meet the expected attitude, perform attitude loop PID control to adjust the moment, enter the control distribution step, and the corresponding one or more variable center of mass actuators 4 slide along the slide rail 5 by a distance to adjust the center of mass of the UAV, and then determine whether the UAV meets the expected attitude.

[0082] The relative position relationship between the center of mass of the machine body and the thrust center is controlled by the position change of the variable center of mass actuator 4 to obtain the attitude control moment in the tilt and roll directions.

[0083] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A variable-center-mass ducted UAV structure, characterized in that: include: A circular cylindrical duct body (1) is provided with a duct inside, and a load device (7) is detachably mounted on the outer wall of the duct body (1); a frame (6) is fixedly connected to the duct body (1) and is a structure with ventilation up and down; a propeller (2) in the duct is provided with a flight driver (3) for driving it to rotate, and the rotation center axis of the propeller (2) coincides with the center axis of the duct body (1); a plurality of variable center of mass actuators (4) and slide rails (5), the extension direction of the slide rails (5) is perpendicular to the center axis of the duct body (1), and all the slide rails (5) are uniformly distributed around the center axis of the duct body (1), and the variable center of mass actuators (4) automatically slide to match the slide rails (5) to change the center of mass of the drone; The variable center of mass actuator (4) is formed by an integrated variable center of mass drive mechanism and a mass slider. A stepper motor with an integrated driver is used as both the variable center of mass drive mechanism (4) and the mass slider. A linear guide rail (5) is used for positioning. A gear is installed on the output shaft of the stepper motor and meshes with a rack parallel to the linear guide rail (5). The variable center of mass actuator (4) is self-driven on the linear guide rail (5) to control the relative position of the center of mass of the machine body and the lift center.

2. The structure of a variable-center-of-mass ducted UAV according to claim 1, characterized in that: The skeleton (6) is configured as a cross-rod structure, the number of the variable center of mass actuator (4) and the number of the slide rails (5) are both four, all the slide rails (5) are distributed in a cross shape, and the rotation center axis of the propeller (2) passes through the cross intersection of the skeleton (6).

3. The structure of a variable-center-of-mass ducted UAV according to claim 1, characterized in that: The power main shaft of the variable center of mass actuator (4) is provided with a gear which meshes with a rack fixed on the frame (6).

4. The structure of a variable-center-of-mass ducted UAV according to claim 2, characterized in that: It also includes a control platform, which controls the variable center of mass actuator (4) and the flight drive (3).

5. The structure of a variable-center-mass ducted UAV according to claim 4, characterized in that: There are two propellers (2) distributed up and down, and the two propellers (2) are configured as a pair of forward and reverse propellers to provide thrust for the entire UAV, and the propeller torque generated by the speed difference is used to control the yaw direction attitude.

6. A control method using the variable center of mass ducted UAV structure according to claim 5, characterized in that: Input the current position and determine whether the drone meets the expected waypoint: if it meets the expected waypoint, then end; if it does not meet the expected waypoint, perform position loop PID control to adjust the propeller thrust; Input the current posture and judge whether the UAV meets the expected posture: if the expected posture is met, then the step of judging whether the UAV meets the expected waypoint is performed; if the expected posture is not met, the posture loop PID control is performed to adjust the torque, and the control allocation step is entered, and the corresponding one or more variable center of mass actuators (4) slide a distance along the slide rail (5) to adjust the center of mass of the UAV, and then judge whether the UAV meets the expected posture; The relative position relationship between the center of mass of the body and the thrust center is controlled by changing the position of the variable center of mass actuator (4), thereby obtaining attitude control torques in the tilt and roll directions.

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