Variable-pitch driving system of ducted fan and control method of variable-pitch driving system

Abstract

The invention discloses a variable-pitch driving system of a ducted fan and a control method of the variable-pitch driving system. The control method comprises the steps that firstly, the optimal pitch angle needed by the ducted fan is calculated according to the current flight state; a ducted fan blade variable pitch kinematic model is established, and the smoothness and stability of the ducted fan variable pitch process are ensured by dynamically adjusting variable pitch angular acceleration and angular velocity parameters; equivalently replacing the variable pitch kinematic model of the ducted fan blade with a kinematic model of a fixed ring; according to the optimal propeller pitch angle, given by an aircraft main control computer, of the ducted fan, fuzzy PID feedforward is adopted for controlling output of the two steering engines, the axial position of a fixed ring is collected in real time through a high-precision position sensor and fed back to a controller, and closed-loop feedback control is achieved; deviation exists between the actual propeller pitch angle and the theoretical value in the propeller pitch changing process, finally, error compensation is conducted on mechanical errors in the transmission process of an execution assembly of the propeller pitch changing mechanism, and the propeller pitch changing precision of the ducted fan is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ducted fan, and particularly relates to a variable-pitch driving system of a ducted fan and a control method thereof. BACKGROUND

[0002] Ducted fan is one of the key power devices on distributed electric propulsion eVTOL aircraft. The ducted fan with variable pitch can achieve the best performance of the aircraft in the vertical take-off and landing stage and the cruising stage. However, there are some problems in the traditional variable pitch drive system, such as insufficient driving force, slow dynamic response, poor control accuracy, lack of self-locking function, etc. In order to improve the comprehensive flight performance of the aircraft, it is an important problem to design a variable pitch drive system and method suitable for ducted fan with high driving force, fast dynamic response, high control accuracy and mechanical self-locking function. At present, some variable pitch drive systems and control methods have been published. The Chinese invention patent application with application number CN202010817222.8 proposes a wind turbine composite intelligent variable pitch control method based on laser wind measurement front feedback. This method realizes the adaptive adjustment of control parameters, and enhances the robustness and anti-interference of the variable pitch control algorithm. However, this method relies on multi-source real-time data input, which puts high requirements on the accuracy, sampling frequency and processing capacity of the data acquisition system, resulting in significant increase in system complexity and cost, making it difficult to be efficiently deployed in resource-limited scenarios. The Chinese invention patent application with application number CN202411814230.1 proposes a motor-driven variable pitch control system and control method. By setting the variable pitch motor and the variable pitch motor controller adjacent to each other, the driving line between the controller and the motor is shortened, reducing signal attenuation and interference problems. However, the layout in this method is difficult to apply to high speed. The Chinese invention patent application with application number CN202311319809.6 proposes an independent variable pitch control method. By using PID algorithm for wind turbine variable pitch control, the method realizes adaptive and fast response to disturbances caused by various factors, and ensures that the wind turbine pitch angle is adjusted properly. However, the PID parameters are fixed. The Chinese invention patent application with application number CN202411508788.7 proposes a propeller variable pitch control method and system for aircraft. By monitoring the flight state parameters in real time through sensors on the aircraft, the optimal pitch angle of the current flight stage is calculated based on the flight state parameters through a control algorithm. The actual pitch angle is monitored through a feedback system, and compared with the target pitch angle to adjust the control strategy in real time. However, the feedback is lagging, and a feedforward compensation mechanism is needed. The Chinese invention patent application with application number CN202211356566.9 proposes an adjustment method, device and equipment for unmanned aerial vehicle pitch angle, and a readable storage medium. The historical data is processed based on fuzzy neural network and particle swarm algorithm, and an optimal parameter is determined. The optimal parameter is processed through linear regression to determine the pitch angle adjustment angle, and to judge whether the error between the adjusted angle and the expected angle is less than a preset value until the error meets the preset value requirement.

[0003] This invention discloses a variable pitch drive system and control method for a ducted fan. It employs a structure design with two servos and a trapezoidal lead screw drive, achieving high torque output within a compact space. Based on the self-locking characteristic of the trapezoidal lead screw, the pitch angle is maintained even in the event of servo failure, reducing the risk of overheating due to continuous servo operation and extending servo lifespan. Fuzzy PID feedforward control of the servos is used, dynamically adjusting PID parameters to improve system response speed and stability. A high-precision position sensor is used to achieve closed-loop feedback control. During the two servo drive process, a cooperative control strategy is employed, monitoring the output angles of both servos in real time and performing synchronous compensation, improving system stability. A dynamic error compensation mechanism is used to address mechanical errors during pitch adjustment, ensuring pitch angle adjustment accuracy and improving the flight stability and safety of the ducted fan. This invention effectively improves the response speed and pitch angle accuracy of ducted fan variable pitch drive, enhancing aircraft stability at different flight stages. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a variable pitch drive system for ducted fans and its control method.

[0005] To achieve the above objectives, the technical solution provided by the present invention is: a variable pitch drive system for a ducted fan, comprising a controller, two servo motors, a transmission assembly, and an execution assembly. The controller is located inside the tail cone of the ducted fan, and the two servo motors are symmetrically arranged on both sides of the ducted fan motor shaft.

[0006] The transmission assembly includes gear one, driven gear, gear two, trapezoidal lead screw, stationary ring, rotating ring, high-precision position sensor, and lead screw sleeve. Two servo motors are synchronously driven, with their output shafts connected to gear one. Gear one meshes with the driven gear, which in turn meshes with gear two. Gear two is mounted on the trapezoidal lead screw, which is symmetrically arranged on both sides of the ducted fan motor shaft. A stationary ring is mounted on the trapezoidal lead screw; rotation of the lead screw drives the stationary ring to move axially along the output shaft of the ducted fan motor. The stationary ring is connected to the rotating ring. The lead screw sleeve is located inside the duct of the ducted fan, and the high-precision position sensor is mounted on the lead screw sleeve.

[0007] The actuator includes a hub, blades, pitch shaft, pitch rocker arm, and pitch tie rods. Six pitch tie rods are mounted on the moving ring, the pitch rocker arm is mounted on the pitch shaft, the pitch shaft is mounted inside the blade housing, and the hub is located on the motor shaft of the ducted fan. The pitch tie rods are connected to the pitch rocker arm, which converts the axial motion output from the ducted fan motor shaft into a circular motion around the axis of the pitch shaft. This causes the axial movement output from the stationary ring to drive the pitch shaft to rotate, thus achieving blade pitch variation.

[0008] Preferably, the two steering engines, the transmission assemblies and the execution assemblies constitute a variable pitch mechanism, the trapezoidal screw is threadedly connected with the stationary ring, so that the trapezoidal screw has mechanical self-locking property, the mechanical self-locking property of the trapezoidal screw is used to inhibit the overheating risk caused by the operation of the two steering engines, and when the two steering engines fail, the mechanical self-locking property of the trapezoidal screw is used to ensure that the variable pitch mechanism maintains the current pitch angle of the blades of the ducted fan.

[0009] The application further discloses a control method of the variable pitch driving system of the ducted fan.

[0010] Step S1: the optimal pitch angle required by the ducted fan is calculated according to the current flight state, a ducted fan blade variable pitch kinematic model is established, and the ducted fan blade variable pitch kinematic model is equivalently replaced by a kinematic model of the stationary ring; the kinematic model is defined as follows:

[0011]

[0012] Wherein, S current (t) is an initial position, a s (t) is acceleration, V s (t) is velocity.

[0013] The kinematic model indirectly realizes high-precision control of the pitch angle by dynamically adjusting the displacement acceleration and velocity parameters of the stationary ring through real-time calculation of the acceleration and velocity parameters and combination of kinematic formulas;

[0014] Step S2: according to the optimal pitch angle of the ducted fan given by the aircraft main control computer, a fuzzy PID feedforward control is adopted to drive the gear transmission groups of the two steering engines, the gear transmission groups include driven gears, gear one and gear two; the trapezoidal screw is driven to rotate through the gear transmission groups, the trapezoidal screw drives the stationary ring to move along the axial direction of the ducted fan motor shaft, so as to realize variable pitch of the ducted fan, and in the variable pitch process, a high-precision position sensor monitors the current position S current (t) of the stationary ring in real time, and feeds back the data to the controller, the controller adjusts the driving signals of the two steering engines based on the feedback information, forms a closed loop control, and the variable pitch control quantity follows the formula as follows:

[0015]

[0016] Wherein: K P is a proportional term, K i is an integral term, and K d is a differential term; out(t) is a controller output value; error(t) is an error term; the controller compares the actual position with the target position, that is: error(t) = S exec (t) - Scurrent (t);

[0017] And since the angle of attack of the airflow to the ducted fan propeller blades is real-time changes, resulting in two rudder driven nonlinear response, thus in the process of variable pitch prone to overshoot or oscillation phenomenon, therefore, using fuzzy PID controller dynamic adjustment of PID parameters, to achieve adaptive compensation of the nonlinear characteristics of two rudder;

[0018] The output parameter expression of fuzzy PID controller is:

[0019]

[0020] In the formula: K P0 , K i0 , K d0 PID controller initial parameters; ΔK P , ΔK i , ΔK d The parameter increment generated by the fuzzy controller in real time;

[0021] Step S3: in the actual operation process of two rudders, using the coordinated control strategy, two rudders through sharing control parameters and feedback information, real-time comparison of two rudder output angle, and the comparison of synchronous error control in ±0.3°, realize closed loop collaborative regulation, realize two rudder synchronization;

[0022] Step S4: through monitoring the real-time displacement of the stationary ring S current (t), combined with the kinematic model equivalent conversion to get the real-time pitch angle of the ducted fan; conversion formula as follows:

[0023] θ exec (t) = θ current (t) + k·S exec (t);

[0024] Wherein, k is the displacement and angle conversion coefficient, determined by the trapezoidal screw;

[0025] The actual pitch angle and the theoretical value exist deviation in the process of variable pitch; therefore, the dynamic error compensation mechanism is proposed, through the compensation function of dynamic error compensation mechanism to the mechanical error of the transmission process of the execution component error compensation, improve the variable pitch precision; compensation function expression as follows:

[0026] S new (t) = (1 + k a )·S current (t);

[0027] Wherein, k a is the compensation coefficient.

[0028] Preferably, the pitch speed in the pitch process adopts a pitch speed constraint strategy based on a kinematic model: Wherein, θ exec (t) is a target pitch angle, θ current (t) is an initial angle, a θ (t) is an angular acceleration, ω θ (t) is an angular velocity, and the pitch angular acceleration and angular velocity parameters are dynamically adjusted.

[0029] Preferably, the fuzzy PID controller is composed of three core modules, namely, fuzzification, fuzzy rule reasoning and defuzzification; the fuzzification module maps the input variables to a fuzzy set, the fuzzy rule reasoning module dynamically calculates the parameter increment based on a preset fuzzy rule table, and the defuzzification module converts the fuzzy output into an accurate value through the barycentric method; the specific defuzzification formula is as follows:

[0030]

[0031] Wherein, z0 is the accurate value after defuzzification; z i is a discrete value in the universe of discourse of the fuzzy control variable; μ(z i ) is the membership degree value of z i .

[0032] Preferably, the fuzzy PID feedforward control introduces a feedforward compensation mechanism on the basis of the traditional fuzzy PID control; the feedforward compensation mechanism estimates the dynamic characteristics of the system in advance to offset the hysteresis effect of the rudder and the trapezoidal screw, reduce the steady-state error and improve the rapid response ability of the system; the feedforward function is designed as: Wherein, G u (s) is the transfer function of the rudder, which realizes the optimization of the overall dynamic response by compensating the dynamic characteristics of the rudder in reverse.

[0033] The present application has the following advantages:

[0034] The two rudders of the present application adopt a synchronous driving mode and are combined with the trapezoidal screw (transmission connection) to realize high-torque output, improve the variable pitch driving force performance of the mechanism, and the structure of the two rudders and the trapezoidal screw transmission is a variable pitch mechanism; the trapezoidal screw transmission has a mechanical self-locking feature, which is used to suppress the risk of overheating caused by the operation of the two rudders, and when the two rudders fail, the mechanical self-locking function of the trapezoidal screw is used to ensure that the variable pitch mechanism maintains the current pitch angle, thereby ensuring the safe landing of the aircraft.

[0035] The two steering gears adopt a cooperative control strategy in the application, real-time monitoring of the output angles of the two steering gears is carried out during the driving process of the two steering gears, and real-time synchronous compensation is carried out, so that the synchronization error of the two steering gears is ensured to be less than or equal to 0.5 degrees, and the system stability is improved; the coordinated control strategy is adopted, the angle error in the output process of the steering gears is detected and compared in real time, and the error is compensated, so that the stability of the system is improved.

[0036] The control method proposed in the application adopts fuzzy PID control of the steering gear driving variable pitch angle, realizes dynamic adjustment of PID parameters, improves the response speed and stability, and realizes rapid and accurate pitch adjustment.

[0037] The control method proposed in the application adopts a feedback system to monitor the adjustment of the ducted fan variable pitch angle, and realizes closed-loop variable pitch driving control.

[0038] The control method proposed in the application increases a feedforward link based on fuzzy PID control, combines feedforward control and feedback control, reduces the steady-state error of the control system, and improves the rapid response capability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0039] The drawings described herein are used to provide further understanding of the application, and form a part of the application.

[0040] Figure 1 It is a schematic diagram of the overall structure of the preferred embodiment of the application.

[0041] Figure 2 It is a schematic diagram of the execution assembly structure of the ducted fan variable pitch mechanism of the application.

[0042] Figure 3 It is a schematic diagram of the steering gear installation of the application.

[0043] Figure 4 It is a schematic diagram of the connection structure of the transmission assembly and the execution assembly of the application.

[0044] Figure 5 It is a partial schematic diagram of the execution assembly structure of the application.

[0045] Figure 6 It is a variable pitch driving control flowchart of the application.

[0046] Figure 7 It is a variable pitch driving control principle diagram of the application.

[0047] FIGURE DESCRIPTION:

[0048] 10- steering engine, 20- transmission assembly, 30- execution assembly, 211- driven gear, 212- gear one, 213- gear two, 220- trapezoidal screw, 230- fixed ring, 240- movable ring, 250- position sensor, 260- screw sleeve, 310- oar shaft, 320- oar blade, 230- variable pitch shaft, 331- variable pitch rocker arm, 332- variable pitch pull rod. DETAILED DESCRIPTION

[0049] This part will describe the specific embodiments of the present application in detail, the preferred embodiments of the present application are shown in the drawings, the role of the drawings is to supplement the description of the text part with graphics, so that people can intuitively and visually understand each technical feature and the overall technical scheme of the present application, but it cannot be understood as a limitation on the protection scope of the present application.

[0050] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right and the like, is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation on the present application.

[0051] In the description of the present application, several meanings are one or more, and the meaning of multiple is more than two, greater than, less than, more than, etc. are not included in the number, and above, below, etc. are understood to include the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0052] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be understood broadly, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical scheme.

[0053] Reference Figures 1-7 , the preferred embodiment of the present application, a variable pitch drive system of ducted fan, the variable pitch drive system of ducted fan includes a controller, two steering engines 10, transmission assembly 20 and execution assembly 30, the controller is arranged in the tail barrel of the ducted fan, two steering engines 10 are arranged symmetrically on both sides of the motor shaft of the ducted fan;

[0054] The transmission assembly comprises a gear one 212, a driven gear 211, a gear two 213, a trapezoidal screw rod 220, a fixed ring 230, a movable ring 240, a high-precision position sensor 250 and a screw rod sleeve 260; the two steering wheels 10 are synchronously driven, the output shafts of the two steering wheels 10 are connected with the gear one 212, the gear one 212 is engaged with the driven gear 211, the driven gear 211 is engaged with the gear two 213, the gear two 213 is installed on the trapezoidal screw rod 220, and the trapezoidal screw rod 220 is symmetrically arranged on both sides of the ducted fan motor shaft; the fixed ring 230 is installed on the trapezoidal screw rod 220, the trapezoidal screw rod 220 drives the fixed ring 230 to move axially along the ducted fan motor output shaft, and the fixed ring 230 is connected with the movable ring 240; the screw rod sleeve 260 is arranged in the duct of the ducted fan, and the high-precision position sensor 250 is installed on the screw rod sleeve 260.

[0055] The execution assembly comprises a hub 310, a blade 320, a variable pitch shaft 330, a variable pitch rocker arm 331 and a variable pitch pull rod 332; the six variable pitch pull rods 332 are installed on the movable ring 240, the variable pitch rocker arm 331 is installed on the variable pitch shaft 330, the variable pitch shaft 330 is installed in the hub 310, the hub 310 is arranged on the motor shaft of the ducted fan, the variable pitch pull rod 332 is connected with the variable pitch rocker arm 331, so that the axial movement output by the ducted fan motor shaft is converted into the circumferential movement around the axis of the variable pitch shaft 330, thereby the axial movement output by the fixed ring 230 drives the variable pitch shaft 330 to rotate, and the variable pitch of the blade 320 is realized.

[0056] Further, the two steering wheels 10, the transmission assembly 20 and the execution assembly 30 form a variable pitch mechanism, the trapezoidal screw rod 220 is threadedly connected with the fixed ring 230, so that the trapezoidal screw rod 220 has mechanical self-locking property, the mechanical self-locking property of the trapezoidal screw rod 220 is used to inhibit the overheating risk caused by the operation of the two steering wheels 10, and when the two steering wheels 10 fail, the mechanical self-locking property of the trapezoidal screw rod 220 is used to ensure that the variable pitch mechanism keeps the current pitch angle of the blade of the ducted fan.

[0057] The application further discloses a control method of the variable pitch driving system of the ducted fan.

[0058] Step S1: the optimal pitch angle required by the ducted fan is calculated according to the current flight state, a ducted fan variable pitch kinematic model is established, and the variable pitch kinematic model is equivalently replaced by a kinematic model of the fixed ring 230; the kinematic model is defined as follows:

[0059]

[0060] Wherein, S current (t) is an initial position, a s (t) is acceleration, Vs (t) is the speed;

[0061] The kinematic model calculates acceleration and speed parameters in real time, and dynamically adjusts the displacement acceleration and speed parameters of the stationary ring 203 in combination with kinematic formulas, thereby indirectly achieving high-precision control of the pitch angle and ensuring the smoothness and stability of the variable-pitch process of the ducted fan;

[0062] Step S2: According to the optimal pitch angle of the ducted fan given by the aircraft main control computer, a fuzzy PID feedforward control is adopted to drive the gear transmission set of the two rudders 10, the gear transmission set includes driven gears 211, gear one 212 and gear two 213, and drives the trapezoidal lead screw 220 to rotate through the gear transmission set, the trapezoidal lead screw 220 drives the stationary ring 230 to move along the axial direction of the ducted fan motor shaft, thereby realizing variable-pitch of the ducted fan, and in the variable-pitch process, the high-precision position sensor 250 will monitor the current position S of the stationary ring 230 in real time current (t), and feedback the data to the controller, and the controller adjusts the drive signal of the two rudders 10 based on the feedback information to form a closed-loop control, and the variable-pitch control quantity follows the formula:

[0063]

[0064] Wherein: K P is the proportional term, K i is the integral term, and K d is the differential term; out(t) is the output value of the controller; error(t) is the error term; the controller compares the actual position with the target position, i.e. error(t) = S exec (t)-S current (t);

[0065] And since the angle of attack of the airflow on the ducted fan propeller blades changes in real time, it causes nonlinear response of the two rudders 10, thereby easily causing overshoot or oscillation phenomenon in the variable-pitch process, in order to improve the control precision and stability, a fuzzy PID controller is used to dynamically adjust the PID parameters, and realize adaptive compensation of the nonlinear characteristics of the two rudders 10;

[0066] The output parameter expression of the fuzzy PID controller is:

[0067]

[0068] Wherein: K P0 , K i0 , K d0 are the initial parameters of the PID controller; ΔK P , ΔK i , ΔK dThe parameter increment generated by the fuzzy controller in real time;

[0069] Step S3: During the actual operation of the two rudders 10, the output angles of the two rudders 10 may be out of synchronization due to mechanical manufacturing errors, load differences, or inconsistent control signals. During the actual operation of the two rudders 10, a coordination control strategy is adopted, and the two rudders 10 share control parameters and feedback information, compare the output angles of the two rudders 10 in real time, and control the synchronization error after comparison within ±0.3°, realizing closed-loop collaborative adjustment and synchronization of the two rudders 10.

[0070] Specifically, the two rudders 10 adopt a collaborative control strategy, monitor the output angles of the two rudders 10 in real time during the driving process of the two rudders 10, and perform real-time synchronization compensation on the error, ensuring that the synchronization error of the two rudders 10 is within ±0.3° and improving the stability of the system

[0071] Step S4: Due to the limited size of the ducted fan structure, it is not possible to directly install an angle sensor to monitor the pitch angle of the ducted fan blades in real time. By monitoring the real-time displacement S current (t) of the stationary ring 230, the real-time pitch angle of the ducted fan is obtained by equivalent conversion combined with the kinematic model. The conversion formula is as follows:

[0072] θ exec (t) = θ current (t) + k·S exec (t).

[0073] Wherein, k is the conversion coefficient of displacement and angle, which is determined by the trapezoidal screw 220.

[0074] Due to mechanical errors such as size errors, joint clearances, and rotating pair wear of the mechanism, there is a deviation between the actual pitch angle and the theoretical value during the variable pitch process. Therefore, a dynamic error compensation mechanism is proposed to compensate for the mechanical errors during the transmission process of the execution assembly 30 through a compensation function of the dynamic error compensation mechanism, thereby improving the variable pitch accuracy. The compensation function expression is as follows:

[0075] S new (t) = (1 + k a )·S current (t).

[0076] Wherein, k a is the compensation coefficient.

[0077] Further, the variable pitch speed during the variable pitch process adopts a variable pitch speed constraint strategy based on the kinematic model: Wherein, θ exec (t) is the target pitch angle, θ current (t) is the initial angle, aθ (t) is the angular acceleration, ω θ (t) is the angular velocity. By dynamically adjusting the pitch angular acceleration and angular velocity parameters, the smoothness and stability of the ducted fan pitch change process are ensured.

[0078] Furthermore, the fuzzy PID controller consists of three core modules: fuzzification, fuzzy rule inference, and defuzzification. The fuzzification module maps input variables to fuzzy sets, the fuzzy rule inference module dynamically calculates parameter increments based on a preset fuzzy rule table, and the defuzzification module converts the fuzzy output into precise values ​​using the centroid method. The specific defuzzification formula is as follows:

[0079]

[0080] Where z0 is the precise value after defuzzification; z i μ(z) represents the discrete value within the domain of the fuzzy control quantity; i ) for z i The membership degree value.

[0081] Furthermore, to overcome the shortcomings of the servo motor and trapezoidal lead screw structure in dynamic response, fuzzy PID feedforward control introduces a feedforward compensation mechanism based on traditional fuzzy PID control. This feedforward compensation mechanism, by predicting the dynamic characteristics of the system, preemptively offsets the hysteresis effect of the servo motor 10 and trapezoidal lead screw 220, reducing steady-state error and improving the system's fast response capability. Its feedforward function is designed as follows: Among them, G u (s) is the transfer function of servo motor 10. By inversely compensating for the dynamic characteristics of servo motor 10, the overall dynamic response of the system is optimized.

[0082] This invention employs fuzzy PID control of the servo motor 10 to drive the variable pitch angle, achieving dynamic adjustment of PID parameters, improving response speed and stability, and realizing fast and accurate pitch adjustment; and uses a feedback system to monitor the adjustment of the ducted fan pitch angle to achieve closed-loop variable pitch drive control.

[0083] This invention also adds a feedforward element to the fuzzy PID control, combining feedforward control with feedback control to reduce the steady-state error of the control system and improve the system's rapid response capability.

[0084] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0085] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means is within the protection scope of the present invention.

Claims

1. A variable pitch drive system for a ducted fan, characterized by: The ducted fan variable pitch drive system comprises a controller, two steering gears (10), a transmission assembly (20), and an execution assembly (30), the controller is arranged in the tail barrel of the ducted fan, the two steering gears (10) are symmetrically arranged on both sides of the shaft of the ducted fan motor; The transmission assembly comprises a gear one (212), a driven gear (211), a gear two (213), a trapezoidal screw rod (220), a fixed ring (230), a movable ring (240), a high-precision position sensor (250), and a screw rod sleeve (260); the two steering gears (10) are synchronously driven, the output shafts of the two steering gears (10) are connected with the gear one (212), the gear one (212) is engaged with the driven gear (211), the driven gear (211) is engaged with the gear two (213), the gear two (213) is installed on the trapezoidal screw rod (220), and the trapezoidal screw rod (220) is symmetrically arranged on both sides of the shaft of the ducted fan motor; the fixed ring (230) is installed on the trapezoidal screw rod (220), the trapezoidal screw rod (220) drives the fixed ring (230) to move axially along the shaft of the ducted fan motor in rotation, and the fixed ring (230) is connected with the movable ring (240); the screw rod sleeve (260) is arranged in the duct of the ducted fan, and the high-precision position sensor (250) is installed on the screw rod sleeve (260); The execution assembly comprises a hub (310), a blade (320), a variable pitch shaft (330), a variable pitch rocker arm (331), and a variable pitch pull rod (332); the six variable pitch pull rods (332) are installed on the movable ring (240), the variable pitch rocker arm (331) is installed on the variable pitch shaft (330), the variable pitch shaft (330) is installed in the hub (310), the hub (310) is arranged on the shaft of the ducted fan motor, the variable pitch pull rod (332) is connected with the variable pitch rocker arm (331), the axial movement of the shaft of the ducted fan motor is converted into the circumferential movement around the axis of the variable pitch shaft (330), so that the axial movement of the fixed ring (230) drives the variable pitch shaft (330) to rotate, and the variable pitch of the blade (320) is realized.

2. The variable pitch drive system for a ducted fan of claim 1, wherein: The two steering gears (10), the transmission assembly (20), and the execution assembly (30) constitute a variable pitch mechanism, the trapezoidal screw rod (220) is threadedly connected with the fixed ring (230), so that the trapezoidal screw rod (220) has mechanical self-locking property, the mechanical self-locking property of the trapezoidal screw rod (220) is used for inhibiting the overheating risk caused by the operation of the two steering gears (10), and when the two steering gears (10) fail, the mechanical self-locking property of the trapezoidal screw rod (220) is used for ensuring that the variable pitch mechanism keeps the current pitch angle of the blade of the ducted fan.

3. The control method of a variable pitch drive system of a ducted fan according to any one of claims 1-2, characterized in that: The control method specifically comprises the following steps: Step S1: calculating the optimal pitch angle required by the ducted fan according to the current flight state, establishing a ducted fan blade variable pitch kinematic model, and equivalently replacing the ducted fan blade variable pitch kinematic model with a kinematic model of the fixed ring (230); the kinematic model is defined as follows: where S current (t) is the initial position, a s (t) is the acceleration, V s (t) is the velocity; The kinematic model indirectly realizes high-precision control of the pitch angle by dynamically adjusting the displacement acceleration and speed parameters of the stationary ring (230) through real-time calculation of acceleration and speed parameters in combination with kinematic formulas; Step S2: According to the best pitch angle of the ducted fan given by the aircraft master computer, the two rudders (10) drive the gear transmission group by using fuzzy PID feedforward control, and drive the trapezoidal lead screw (220) to rotate through the gear transmission group. The trapezoidal lead screw (220) rotates to drive the fixed ring (230) to move along the axial direction of the ducted fan motor shaft, thereby realizing the variable pitch of the ducted fan. During the variable pitch process, the high-precision position sensor (250) will monitor the current position S of the fixed ring (230) in real time current (t), and feedback the data to the controller. The controller adjusts the drive signal of the two rudders (10) based on the feedback information, forms a closed-loop control, and the variable pitch control quantity follows the formula as follows: where: K P is a proportional term, K i is an integral term, K d is a derivative term; out(t) is the controller output value; error(t) is the error term; the controller compares the actual position to the target position, i.e. error(t) = S exec (t) - S current (t); And because the angle of attack of the airflow on the ducted fan propeller blades is real-time change, leading to nonlinear response of the two servo motors (10), thus easily causing overshoot or oscillation phenomenon in the process of variable pitch, therefore, a fuzzy PID controller is used to dynamically adjust the PID parameters, to realize adaptive compensation of the nonlinear characteristics of the two servo motors (10); The output parameter expression of the fuzzy PID controller is: wherein: K P0 , K i0 , K d0 are initial parameters of the PID controller; ΔK P , ΔK i , ΔK d are parameter increments generated in real time by the fuzzy controller; Step S3: In the actual operation process of the two servo motors (10), a coordinated control strategy is used, the two servo motors (10) share control parameters and feedback information, and the output angles of the two servo motors (10) are compared in real time, and the synchronization error after comparison is controlled within ±0.3°, to realize closed-loop coordinated regulation and synchronization of the two servo motors (10); Step S4: Real-time displacement S of the stationary ring (230) is monitored current (t), and the real-time pitch angle of the ducted fan is obtained by equivalent conversion combined with the kinematic model. The conversion formula is as follows: θ exec (t) = θ current (t) + k · S exec (t); Wherein, k is the conversion coefficient of displacement and angle, which is determined by the trapezoidal screw rod; There is a deviation between the actual pitch angle and the theoretical value in the process of variable pitch; therefore, a dynamic error compensation mechanism is proposed, which compensates the mechanical error in the transmission process of the execution assembly through a compensation function of the dynamic error compensation mechanism, to improve the variable pitch precision; the compensation function expression is as follows: S new (t) = (1 + k a ) · S current (t) ; where k a is a compensation factor.

4. The control method of a variable pitch drive system of a ducted fan according to claim 2, characterized in that: The pitch speed in the pitch process adopts a pitch speed constraint strategy based on a kinematic model: where θ exec (t) is the target pitch angle, θ current (t) is the initial angle, a θ (t) is the angular acceleration, ω θ (t) is the angular velocity, by dynamically adjusting the pitch angular acceleration and angular velocity parameters.

5. The control method of a variable pitch drive system of a ducted fan according to claim 2, characterized in that: The fuzzy PID controller is composed of three core modules of fuzzification, fuzzy rule reasoning and defuzzification; wherein, the fuzzification module maps the input variable to the fuzzy set, the fuzzy rule reasoning module dynamically calculates the parameter increment based on the preset fuzzy rule table, and the defuzzification module converts the fuzzy output to an accurate value through the barycentric method; the specific defuzzification formula is as follows: wherein z0is the accurate value after deblurring; z i is a discrete value in the domain of the fuzzy control variable; μ(z i ) is the membership value of z i .

6. The control method of a variable pitch drive system of a ducted fan according to claim 2, characterized in that: The fuzzy PID feedforward control introduces a feedforward compensation mechanism on the basis of the traditional fuzzy PID control; the feedforward compensation mechanism offsets the hysteresis effect of the rudder (10) and the trapezoidal screw (220) in advance by estimating the dynamic characteristics of the system, reduces the steady-state error and improves the rapid response ability of the system; the feedforward function is designed as: Wherein, G u (s) is the transfer function of the rudder (10), which realizes the optimization of the overall dynamic response by compensating the dynamic characteristics of the rudder (10) in reverse.

Images