COAXIAL TILT-ROTOR UNMANNED AERIAL VEHICLE AND CONTROL METHOD THEREOF

Abstract

A coaxial tilt-rotor unmanned aerial vehicle (CTRUAV) and a control method thereof. CTRUAV comprises three rotor modules, five rotors with motors respectively and a control system. Three rotor modules are in an inverted triangle layout. The left and right coaxial tiltable rotor modules in the front of the CTRUAV can rotate around the plane of a fuselage. A rear rotor is installed on the rear fixed-axis rotor module. Two pairs of coaxial rotors are respectively installed on the left and right coaxial tiltable rotor modules. Namely, the left and right coaxial tiltable rotor modules consists of an upper rotor and a lower rotor respectively; the upper rotor and the lower rotor have opposite rotation directions and the same rotation speed during the flight. Moreover, in the two pairs of coaxial rotors, the rotors on same layers have opposite rotation directions, and therotors on different layers have the same rotation directions.

Claims

1. A coaxial tilt-rotor unmanned aerial vehicle (CTRUAV), comprising three rotor modules, five rotors with motors respectively and a control system, wherein the three rotor modules are respectively left coaxial tiltable rotor module and right coaxial tiltable rotor module located at the front, and fixed-axis rear rotor module located at the rear; the three rotor modules are in an inverted triangle layout; the left and right coaxial tiltable rotor modules in the front of the CTRUAV can rotate around the plane of a fuselage; a rear rotor is installed on the rear fixed-axis rotor module and driven by a motor installed on the rear fixed-axis rotor module; two pairs of coaxial rotors are respectively installed on the left and right coaxial tiltable rotor modules and each pair of coaxial rotors are driven by a pair of coaxial motors; the two motors of the same pair of coaxial motors have the same rotation speed and opposite rotation directions; then an upper rotor and a lower rotor installed on the same rotor shaft have the same rotation speed and opposite rotation directions; moreover, in the two pairs of coaxial rotors, the rotors on same layers have opposite rotation directions, and therotors on different layers have the same rotation directions; the control system is installed on the CTRUAV and used to receive position and attitude information of the CTRUAV, perform control operation, and then drive the three rotor modules to control the motion of the CTRUAV; the CTRUAC can roll around an X-axis, pitch around a Y-axis and yaw around a Z-axis, wherein a forward direction is taken as an positive direction of X-axis, a takeoff direction is taken as a positive direction of Z-axis, and a direction perpendicular to the positive direction of X-axis is taken as a positive direction of Y-axis; The CTRUAV has three modes: vertical takeoff and landing (VTOL) mode, fixed-wing mode and transition mode; VTOL mode and the fixed-wing mode are switched through the transition mode; when the CTRUAV is in the VTOL mode, the three rotor modules are perpendicular to the plane of the fuselage, and the five rotors provide lift forces to help the CTRUAV to take off or land quickly; when the CTRUAV is in the fixed-wing mode, the left and right coaxial tiltable rotor modules are parallel to the plane of the fuselage to provide horizontal forward thrust forces, and the rear fixed-axis rotor module is perpendicular to the plane of the fuselage to provide the lift force to ensure the smooth forward flight of the CTRUAV.

2. A control method of the coaxial tilt-rotor unmanned aerial vehicle (CTRUAV) of claim 1, comprising steps of: step 1: according to target and current positing and attitude, obtaining error between the target and current value, and then getting a set of forces and torques vectors [F.sub.x F.sub.z τ.sub.Φ τ.sub.θ τ.sub.ψ].sup.T after operation by the control system; wherein F.sub.x is a resultant force of three rotor modules in the x direction; F.sub.z is a resultant force of three rotor modules in the z direction; τ.sub.Φ is a resultant torque of three rotor modules around the x direction; τ.sub.θ is a resultant torque of three rotor modules around the y direction; and τ.sub.ψ is a resultant torque of three rotor modules around the z direction; step 2: calculating a set of forces [F.sub.5z F.sub.2z F.sub.2x F.sub.1z F.sub.1x].sup.T which are produced by the left, right and rear rotor modules respectively through the equations (1); $\begin{array}{cc}\left[\begin{array}{c}{F}_x\\ F_z\\ {\tau }_{\varphi }\\ {\tau }_{\theta }\\ {\tau }_{\psi }\end{array}\right]=\left[\begin{array}{ccccc}0& 0& 1& 0& 1\\ 1& 1& 0& 1& 0\\ 0& -L_1& 0& -L_1& 0\\ L_3& L_2& 0& -L_2& 0\\ 0& 0& L_1& 0& -L_1\end{array}\right]\left[\begin{array}{c}{F}_{5z}\\ F_{2z}\\ F_{2x}\\ F_{1z}\\ F_{1x}\end{array}\right]& \left(1\right)\end{array}$ wherein F.sub.5z is lift force of the fixed-axis rotor module; F.sub.2z and F.sub.2x are component forces of the right coaxial tiltable rotor module in the z direction and the x direction respectively; F.sub.1z and F.sub.1x are component forces of the left coaxial tiltable rotor module in the z direction and the x direction respectively; CoG is center of gravity (CoG) of the CTRUAV; L.sub.1 is half of a distance between left and right coaxial tiltable rotor module of the CTRUAV; L.sub.2 is a distance from a midpoint of a connecting line between left and right coaxial tiltable rotor module to CoG; and L.sub.3 is a distance from the rear rotor module to the CoG; step 3: calculating the rotation speed of the five motors of each rotor, tilt angles of the left and right coaxial tiltable rotor module in the front through equations (2); wherein in the equations (2), the force provided by each rotor is proportional to its rotation speed; k.sub.5, k.sub.2 and k.sub.1 are respectively scale factors corresponding to the rear rotor module, the right rotor module and the left rotor module; $\begin{array}{cc}\{\begin{array}{c}{F}_{5z}=k_5{\omega }_5^2\\ \sqrt{F_{2z}^2+F_{2x}^2}=F_2=k_2{\omega }_2^2\\ {\theta }_2=\arctan \left(F_{2z}/F_{2x}\right)\\ \sqrt{F_{1z}^2+F_{1x}^2}=F_1=k_1{\omega }_1^2\\ {\theta }_1=\arctan \left(F_{1z}/F_{1x}\right)\end{array}& \left(2\right)\end{array}$ wherein F.sub.1 is the force of the left coaxial tiltable rotor module; ω.sub.1 is the rotation speed of the coaxial motors on the left coaxial tiltable rotor module, and θ.sub.1 is the tilt angle of the left coaxial tiltable rotor module; F.sub.2 is the force of the right coaxial tiltable rotor module; ω.sub.2 is the rotation speed of the coaxial motors on the right coaxial tiltable rotor module, and θ.sub.2 is the tilt angle of the right coaxial tiltable rotor module; ω.sub.5 is the rotation speed of the motor on the rear rotor module; step 4: the set of data ω.sub.1, θ.sub.1, ω.sub.2, θ.sub.2 and ω.sub.5 which has already obtained in step 3 can drive the CTRUAV directly so that the rotation speed of the rear rotor module, and the rotation speeds and tilt angles of the left and right coaxial tiltable rotor modules, i.e., totally five degrees of control are changed so as to change the motion state of the CTRUAV to approach the target position and attitude gradually.

Description

DESCRIPTION OF DRAWINGS

[0023] FIG. 1 is a structural diagram of a CTRUAV designed in the present disclosure.

[0024] FIG. 2 shows schematic diagrams of three modes of a CTRUAV of the present disclosure, wherein (a) is a schematic diagram of a VTOL mode, (b) is a schematic diagram of a fixed-wing mode and (c) is a schematic diagram of a transition mode.

[0025] FIG. 3 shows working schematic diagrams of a CTRUAV which rotates around three axes in the VTOL mode, wherein (a) is a working schematic diagram of roll around an X-axis, (b) is a working schematic diagram of pitch around a Y-axis, and (c) is working schematic diagram of yaw around a Z-axis.

[0026] FIG. 4 shows working schematic diagrams of a CTRUAV which rotates around three axes in the fixed-wing mode, wherein (a) is a working schematic diagram of roll around an X-axis, (b) is a working schematic diagram of pitch around a Y-axis, and (c) is working schematic diagram of yaw around a Z-axis.

[0027] FIG. 5 is a working schematic diagram of a CTRUAV of the present disclosure when one of the left coaxial tiltable rotors or one of the right coaxial tiltable rotors is out of gear.

[0028] FIG. 6 is a schematic diagram of a control method of a CTRUAV of the present disclosure.

[0029] FIG. 7 is a schematic diagram of coaxial motors installed on left and right coaxial tiltable rotor modules of the present disclosure.

[0030] In the figures: n means rotor-n (n=1, 2, 3, 4, 5).

DETAILED DESCRIPTION

[0031] Specific embodiments of the present disclosure are described below in detail in conjunction with the drawings of the description.

[0032] FIG. 1 shows a structural diagram of a CTRUAV with three rotor modules and five rotors designed in the present disclosure. Specifically, a CTRUAV comprises three rotor modules, five rotors with motors respectively and a control system. The three rotor modules are in an inverted triangle layout. The left and right coaxial tiltable rotor modules in the front of the CTRUAV can rotate around the plane of a fuselage. Two pairs of coaxial rotors are respectively installed on the left and right coaxial tiltable rotor modules and each pair of coaxial rotors are driven by a pair of coaxial motors. The two motors of the same pair of coaxial motors have the same rotation speed and opposite rotation directions. As shown in FIG. 1: the rotor-1 and rotor-4 are the coaxial rotors on the left coaxial tiltable rotor module respectively; the rotor-1 is on the lower layer while the rotor-4 is on the upper layer; and the rotor-1 and the rotor-4 have opposite rotation directions; the rotor-2 and rotor-3 are the coaxial rotors on the right coaxial tiltable rotor module respectively; the rotor-2 is on the lower layer while the rotor-3 is on the upper layer; and the rotor-2 and the rotor-3 have opposite rotation directions; besides, the rotors on the same layer have opposite rotation directions but the rotors on different layers have the same rotation direction, which means the rotor-1 and the rotor-3 have the same rotation direction, while the rotor-2 and the rotor-4 have the same rotation direction which is opposite to the rotor-1 and rotor-3; moreover, a rear rotor is installed on the rear fixed-axis rotor module and driven by a motor installed on the rear fixed-axis rotor module, as shown by the rotor-5 in FIG. 1.

[0033] As shown in FIG. 2, the CTRUAV of the present disclosure has three modes, which are respectively the VTOL mode, the fixed-wing mode and the transition mode. As shown in FIG. 2(a), when the CTRUAV is in the VTOL mode, the three rotor modules are perpendicular to the plane of the fuselage, and the five rotors provide lift force to help the CTRUAV to take off or land quickly. As shown in FIG. 2(b), when the CTRUAV is in the fixed-wing mode, the rear rotor module provides lift force or stops working, and the left and right coaxial tiltable rotor module are parallel to the plane of the fuselage to provide horizontal forward and lift force to ensure the CTRUAV to fly forward smoothly. As shown in FIG. 2(c), the VTOL mode and the fixed-wing mode are switched through the transition mode.

[0034] FIG. 3 shows working schematic diagrams of the CTRUAV which rotates around three axes in the VTOL mode. If the rotation speed of a pair of coaxial tiltable rotors on the same front rotor module is increased, the balance of torque in the X-axis direction will be broken so that the CTRUAV will roll around the X-axis (Shown in FIG. 3(a)). If the rear rotor provides a torque in the Y-axis direction, the CTRUAV will pitch around the Y-axis (Shown in FIG. 3(b)). If the rotation speed of one of each pair of coaxial tiltable rotors (these two rotors have opposite rotation directions) is increased, the balance of torque in the Z-axis direction will be broken so that the CTRUAV will yaw around the Z-axis (Shown in FIG. 3(c)).

[0035] FIG. 4 shows the working schematic diagram of the CTRUAV which rotates around three axes in the fixed-wing mode. If the left and right rotor module are at proper angles and have proper speed, the torque of the X-axis will be generated (the torques in the other axes are balanced), so that the CTRUAV will roll around the X-axis (Shown in FIG. 3(a)). If the rear rotor provides a torque in the Y-axis direction, the UAV will pitch around the Y-axis (Shown in FIG. 3(b)). If the left and right rotor module are at proper angles and have proper speed, the torque of the Z-axis will be generated (the torques in the other axes are balanced), so that the CTRUAV will roll around the Z-axis (Shown in FIG. 3(c)).

[0036] FIG. 5 is a working schematic diagram of the CTRUAV of the present disclosure when one of the left coaxial tiltable rotors or one of the right coaxial tiltable rotors fails. At this time, the rotor which has the same rotation direction as the failing rotor in the other side is made to stop operating, and then the CTRUAV is operated in the three-rotor mode and still controllable. Only when a pair of coaxial tiltable rotors on the same side fails, the CTRUAV enters an uncontrollable state.

[0037] FIG. 6 is a schematic diagram of a control method of the present disclosure. In each sampling period, the CTRUAV is driven through the following steps:

[0038] step 1: according to the target and current positing and attitude, obtaining the error between the target and current value, and then getting a set of forces and torques vectors [F.sub.x F.sub.z τ.sub.Φ τ.sub.θ τ.sub.ψ].sup.T after operation by the control system (such as a PID controller); wherein F.sub.x is a resultant force of three rotor modules in the x direction; F.sub.z is a resultant force of three rotor modules in the z direction; τ.sub.Φ is a resultant torque of three rotor modules around the x direction; τ.sub.θ is a resultant torque of three rotor modules around the y direction; and τ.sub.ψ is a resultant torque of three rotor modules around the z direction;

[0039] step 2: calculating a set of forces [F.sub.5z F.sub.2z F.sub.2x F.sub.1z F.sub.1x].sup.T which are produced by the left, right and rear rotor modules respectively through the equations (1);

[00003]$\begin{array}{cc}\left[\begin{array}{c}{F}_x\\ F_z\\ {\tau }_{\varphi }\\ {\tau }_{\theta }\\ {\tau }_{\psi }\end{array}\right]=\left[\begin{array}{ccccc}0& 0& 1& 0& 1\\ 1& 1& 0& 1& 0\\ 0& -L_1& 0& -L_1& 0\\ L_3& L_2& 0& -L_2& 0\\ 0& 0& L_1& 0& -L_1\end{array}\right]\left[\begin{array}{c}{F}_{5z}\\ F_{2z}\\ F_{2x}\\ F_{1z}\\ F_{1x}\end{array}\right]& \left(1\right)\end{array}$

wherein F.sub.5z is the lift force of the fixed-axis rotor module; F.sub.2z and F.sub.2x are component forces of the right coaxial tiltable rotor module in the z direction and the x direction respectively; F.sub.1z and F.sub.1x are component forces of the left coaxial tiltable rotor module in the z direction and the x direction respectively; CoG is the center of gravity (CoG) of the CTRUAV; L.sub.1 is half of a distance between left and right coaxial tiltable rotor module of the CTRUAV; L.sub.2 is a distance from a midpoint of a connecting line between left and right coaxial tiltable rotor module to CoG; and L.sub.3 is a distance from the rear rotor module to the CoG;

[0040] step 3: calculating the rotation speed of the five motors of each rotor, the tilt angles of the left and right coaxial tiltable rotor module in the front through equations (2); wherein in the equations (2), the force provided by each rotor is proportional to its rotation speed; k.sub.5, k.sub.2 and k.sub.1 are respectively scale factors corresponding to the rear rotor module, the right rotor module and the left rotor module;

[00004]$\begin{array}{cc}\{\begin{array}{c}{F}_{5z}=k_5{\omega }_5^2\\ \sqrt{F_{2z}^2+F_{2x}^2}=F_2=k_2{\omega }_2^2\\ {\theta }_2=\arctan \left(F_{2z}/F_{2x}\right)\\ \sqrt{F_{1z}^2+F_{1x}^2}=F_1=k_1{\omega }_1^2\\ {\theta }_1=\arctan \left(F_{1z}/F_{1x}\right)\end{array}& \left(2\right)\end{array}$

wherein F.sub.1 is the force of the left coaxial tiltable rotor module; ω.sub.1 is the rotation speed of the coaxial motors on the left coaxial tiltable rotor module, and θ.sub.1 is the tilt angle of the left coaxial tiltable rotor module; F.sub.2 is the force of the right coaxial tiltable rotor module; ω.sub.2 is the rotation speed of the coaxial motors on the right coaxial tiltable rotor module, and θ.sub.2 is the tilt angle of the right coaxial tiltable rotor module; ω.sub.5 is the rotation speed of the motor on the rear rotor module;

[0041] step 4: the set of data ω.sub.1, θ.sub.1, ω.sub.2, θ.sub.2 and ω.sub.5 which has already obtained in step 3 can drive the CTRUAV directly so that the rotation speed of the rear rotor module, and the rotation speeds and tilt angles of the left and right coaxial tiltable rotor modules, i.e., totally five degrees of control are changed so as to change the motion state of the CTRUAV to approach the target position and attitude gradually.

[0042] FIG. 7 is a schematic diagram of coaxial motors installed on the left and right coaxial tiltable rotor modules of the present disclosure. Two pairs of coaxial motors are respectively installed on the left and right coaxial tiltable rotor modules of the CTRUAV. Two motors on the same rotor module are always keep the opposite rotation directions.