A variable pitch drive system for a ducted fan and a method of controlling the same

Abstract

This invention discloses a variable pitch drive system and control method for a ducted fan. First, the optimal pitch angle required by the ducted fan is calculated based on the current flight state. A kinematic model of the ducted fan blades' variable pitch is established, and the smoothness and stability of the pitch-changing process are ensured by dynamically adjusting the pitch-changing angular acceleration and angular velocity parameters. The kinematic model of the ducted fan blades' variable pitch is then equivalently replaced with a kinematic model of a stationary loop. Based on the optimal pitch angle of the ducted fan given by the aircraft's main control computer, fuzzy PID feedforward control is used to control the outputs of two servos. Furthermore, the axial position of the stationary loop is collected in real time by a high-precision position sensor and fed back to the controller to achieve closed-loop feedback control. Since there is a deviation between the actual pitch angle and the theoretical value during the pitch-changing process, error compensation is performed on the mechanical errors in the transmission process of the actuator components of the pitch-changing mechanism to improve the pitch-changing accuracy of the ducted fan.

Description

Technical Field

[0001] This invention relates to the field of ducted fan technology, and in particular to a variable pitch drive system and control method for a ducted fan. Background Technology

[0002] Ducted fans are one of the key power units on distributed electric propulsion (eVTOL) aircraft. Using variable-pitch ducted fans enables optimal performance during both vertical takeoff and landing (VTOL) and cruise phases. However, traditional variable-pitch drive systems suffer from insufficient driving force, sluggish dynamic response, poor control precision, and lack of self-locking functionality. To improve the overall flight performance of aircraft, designing a variable-pitch drive system and method suitable for ducted fans with high driving force, fast dynamic response, high control precision, and mechanical self-locking functionality is crucial. Several variable-pitch drive systems and control methods have been published. Chinese invention patent application CN202010817222.8 proposes a composite intelligent pitch control method for wind turbines based on laser wind measurement feedback. This method achieves adaptive adjustment of control parameters, enhancing the robustness and anti-interference capabilities of the pitch control algorithm. However, this method relies on multi-source real-time data input, placing high demands on the accuracy, sampling frequency, and processing power of the data acquisition system, leading to a significant increase in system complexity and cost, making efficient deployment difficult in resource-constrained scenarios. Chinese invention patent application CN202411814230.1 proposes a motor-driven variable pitch control system and method. By placing the variable pitch motor and the variable pitch motor controller close together, the drive line between the controller and the motor is shortened, reducing signal attenuation and interference problems; however, the layout of this method is difficult to apply to high speeds. Chinese invention patent application CN202311319809.6 proposes an independent variable pitch control method. It uses a PID algorithm to control the variable pitch of a wind turbine generator set, achieving adaptive and rapid response to disturbances caused by various factors, ensuring proper adjustment of the wind turbine generator set's pitch angle; however, its PID parameters are fixed. Chinese invention patent application CN202411508788.7 proposes a propeller variable pitch control method and system for an aircraft. It monitors flight status parameters in real time through sensors on the aircraft, calculates the optimal pitch angle for the current flight stage using a control algorithm based on the flight status parameters, monitors the actual pitch angle through a feedback system, compares it with the target pitch angle, and adjusts the control strategy in real time; however, its feedback is lagging, necessitating the design of a feedforward supplementary mechanism. Chinese invention patent application CN202211356566.9 proposes a method, device, equipment, and readable storage medium for adjusting the propeller pitch angle of a UAV. It processes historical data based on a fuzzy neural network and a particle swarm optimization algorithm to determine an optimal parameter. The optimal parameter is used to determine the propeller pitch angle adjustment angle through linear regression processing, and it is judged whether the error between the adjusted angle and the desired 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 pitch-changing mechanism consists of two servos, a transmission assembly, and an actuation assembly. The trapezoidal lead screw is threaded to the stationary ring, giving it mechanical self-locking properties. These properties suppress the risk of overheating when the two servos are working, and in the event of a failure of the two servos, they ensure that the pitch-changing mechanism maintains the current blade pitch angle of the ducted fan.

[0009] This invention also discloses a control method for the variable pitch drive system of a ducted fan described above, the control method specifically including the following steps:

[0010] Step S1: Calculate the optimal pitch angle required by the ducted fan based on the current flight status, establish a kinematic model of the ducted fan blades with variable pitch, and then replace the kinematic model of the ducted fan blades with an equivalent kinematic model of a fixed ring; the kinematic model is defined as follows:

[0011]

[0012] Among them, S current (t) is the initial position, a s (t) is acceleration, V s (t) is velocity;

[0013] The kinematic model calculates acceleration and velocity parameters in real time and dynamically adjusts the displacement acceleration and velocity parameters of the stationary ring by combining kinematic formulas, thereby indirectly achieving high-precision control of the propeller pitch angle.

[0014] Step S2: Based on the optimal pitch angle of the ducted fan given by the aircraft's main control computer, fuzzy PID feedforward control is used to drive two servo motors to a gear transmission group, which includes a driven gear, gear one, and gear two. The gear transmission group drives a trapezoidal lead screw to rotate, which in turn causes the stationary ring to move axially along the ducted fan motor shaft, thus achieving variable pitch for the ducted fan. During the pitch change process, a high-precision position sensor monitors the current position S of the stationary ring in real time. current (t), and feeds the data back to the controller. The controller adjusts the drive signals of the two servos based on the feedback information to form a closed-loop control. The pitch control quantity follows the formula as follows:

[0015]

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

[0017] Furthermore, since the angle of attack of the airflow on the ducted fan propeller blades changes in real time, it leads to the nonlinear response of the two servo motors, which can easily cause overshoot or oscillation during pitch changes. Therefore, a fuzzy PID controller is used to dynamically adjust the PID parameters to achieve adaptive compensation for the nonlinear characteristics of the two servo motors.

[0018] The expression for the output parameters of the fuzzy PID controller is:

[0019]

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

[0021] Step S3: During the actual operation of the two servos, a coordinated control strategy is adopted. The two servos share control parameters and feedback information, compare the output angles of the two servos in real time, and control the synchronization error after comparison within ±0.3° to achieve closed-loop coordinated adjustment and realize the synchronization of the two servos.

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

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

[0024] Where k is the conversion coefficient between displacement and angle, which is determined by the trapezoidal lead screw;

[0025] During pitch adjustment, the actual pitch angle deviates from the theoretical value. Therefore, a dynamic error compensation mechanism is proposed. This mechanism uses a compensation function to compensate for mechanical errors in the actuator's transmission process, thereby improving pitch adjustment accuracy. The compensation function expression is as follows:

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

[0027] Where, k a This is the compensation coefficient.

[0028] Preferably, the pitch change speed during the pitch change process is constrained by a pitch change speed 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, which is obtained by dynamically adjusting the pitch angular acceleration and angular velocity parameters.

[0029] Preferably, 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:

[0030]

[0031] 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.

[0032] Preferably, the fuzzy PID feedforward control introduces a feedforward compensation mechanism on the basis of traditional fuzzy PID control. This feedforward compensation mechanism, by predicting the dynamic characteristics of the system, offsets the hysteresis effect of the servo motor and the trapezoidal lead screw in advance, 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 the servo motor. By inversely compensating for the dynamic characteristics of the servo motor, the overall dynamic response is optimized.

[0033] Beneficial effects of this invention:

[0034] The present invention employs a synchronous drive for the two servos and a composite design with a trapezoidal lead screw (transmission connection) to achieve high torque output, thereby improving the pitch driving force performance of the mechanism. Furthermore, the structure of the two servos and the trapezoidal lead screw transmission constitutes a pitch mechanism. The trapezoidal lead screw transmission has mechanical self-locking characteristics to suppress the risk of overheating caused by the operation of the two servos. In the event of failure of the two servos, the mechanical self-locking function of the trapezoidal lead screw ensures that the pitch mechanism maintains the current pitch angle, guaranteeing a safe landing of the aircraft.

[0035] In this invention, the two servos employ a cooperative control strategy. During the driving process of the two servos, the output angles of the two servos are monitored in real time and real-time synchronous compensation is performed to ensure that the synchronization error of the two servos is ≤0.5°, thereby improving the system stability. The coordinated control strategy is adopted to detect and compare the angle error during the servo output process in real time and compensate for the error, thereby improving the system stability.

[0036] The control method proposed in this invention uses fuzzy PID control to drive the variable pitch angle of the servo motor, which realizes dynamic adjustment of PID parameters, improves response speed and stability, and achieves fast and accurate pitch adjustment.

[0037] The control method proposed in this invention uses a feedback system to monitor the adjustment of the ducted fan pitch angle, thereby achieving closed-loop pitch drive control.

[0038] The control method proposed in this invention 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. Attached Figure Description

[0039] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0040] Figure 1 This is a schematic diagram of the overall structure of a preferred embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the actuator structure of the ducted fan pitch control mechanism of the present invention;

[0042] Figure 3 This is a schematic diagram of the servo motor installation of the present invention;

[0043] Figure 4 Schematic diagram of the connection structure between the transmission component and the execution component of the present invention;

[0044] Figure 5 This is a partial schematic diagram of the structure of the execution component of the present invention;

[0045] Figure 6 This is a flowchart of the variable pitch drive control of the present invention;

[0046] Figure 7 This is a schematic diagram of the variable pitch drive control principle of the present invention.

[0047] Attached image captions:

[0048] 10-Servo motor, 20-Transmission assembly, 30-Actuation assembly, 211-Driven gear, 212-Gear 1, 213-Gear 2, 220-Trapezoidal lead screw, 230-Stationary ring, 240-Moving ring, 250-Position sensor, 260-Lead screw sleeve, 310-Propeller, 320-Propeller blade, 230-Pitch shaft, 331-Pitch rocker arm, 332-Pitch tie rod. Detailed Implementation

[0049] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0050] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0051] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0052] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0053] Reference Figures 1-7 According to a preferred embodiment of the present invention, a variable pitch drive system for a ducted fan includes a controller, two servo motors 10, a transmission assembly 20, and an execution assembly 30. The controller is disposed inside the tail cone of the ducted fan, and the two servo motors 10 are symmetrically arranged on both sides of the ducted fan motor shaft.

[0054] The transmission assembly includes gear 1 212, driven gear 211, gear 2 213, trapezoidal lead screw 220, stationary ring 230, rotating ring 240, high-precision position sensor 250, and lead screw sleeve 260. Two servo motors 10 are synchronously driven, with their output shafts connected to gear 1 212. Gear 1 212 meshes with driven gear 211, which in turn meshes with gear 2 213. Gear 2 213 is mounted on the trapezoidal lead screw 220, which is symmetrically arranged on both sides of the ducted fan motor shaft. A stationary ring 230 is mounted on the trapezoidal lead screw 220. Rotation of the trapezoidal lead screw 220 drives the stationary ring 230 to move axially along the output shaft of the ducted fan motor. The stationary ring 230 is connected to the rotating ring 240. The lead screw sleeve 260 is located inside the duct of the ducted fan, and the high-precision position sensor 250 is mounted on the lead screw sleeve 260.

[0055] The actuator includes a hub 310, blades 320, a pitch shaft 330, a pitch rocker arm 331, and pitch tie rods 332. Six pitch tie rods 332 are mounted on the moving ring 240, the pitch rocker arm 331 is mounted on the pitch shaft 330, the pitch shaft 330 is mounted inside the hub 310, and the hub 310 is located on the motor shaft of the ducted fan. The pitch tie rods 332 are connected to the pitch rocker arm 331, which transforms the axial motion output by the ducted fan motor shaft into a circular motion around the axis of the pitch shaft 330. This causes the axial movement output by the stationary ring 230 to drive the pitch shaft 330 to rotate, thereby achieving pitch variation of the blades 320.

[0056] Furthermore, the two servo motors 10, the transmission assembly 20, and the actuation assembly 30 constitute a pitch-changing mechanism. The trapezoidal lead screw 220 is threadedly connected to the stationary ring 230, giving the trapezoidal lead screw 220 mechanical self-locking property. The mechanical self-locking property of the trapezoidal lead screw 220 is used to suppress the risk of overheating caused by the operation of the two servo motors 10. In the event of failure of the two servo motors 10, the mechanical self-locking property of the trapezoidal lead screw 220 is used to ensure that the pitch-changing mechanism maintains the current blade pitch angle of the ducted fan.

[0057] The present invention also discloses a control method for a variable pitch drive system of a ducted fan according to the above description, the control method specifically including the following steps:

[0058] Step S1: Calculate the optimal pitch angle required by the ducted fan based on the current flight status, establish a variable pitch kinematic model of the ducted fan, and then replace the variable pitch kinematic model with an equivalent kinematic model of the stationary ring 230; the kinematic model is defined as follows:

[0059]

[0060] Among them, S current (t) is the initial position, a s (t) is acceleration, Vs (t) is velocity;

[0061] The kinematic model calculates acceleration and velocity parameters in real time, and dynamically adjusts the displacement acceleration and velocity parameters of the stationary ring 203 by combining kinematic formulas, thereby indirectly achieving high-precision control of the pitch angle and ensuring the smoothness and stability of the ducted fan pitch change process.

[0062] Step S2: Based on the optimal pitch angle of the ducted fan given by the aircraft's main control computer, fuzzy PID feedforward control is used to drive two servo motors 10 to drive a gear transmission group. The gear transmission group includes a driven gear 211, gear one 212, and gear two 213, which drive the trapezoidal lead screw 220 to rotate. The rotation of the trapezoidal lead screw 220 causes the stationary ring 230 to move axially along 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 monitors the current position S of the stationary ring 230 in real time. current (t), and feeds the data back to the controller. The controller adjusts the drive signals of the two servo motors 10 based on the feedback information to form a closed-loop control. The pitch control quantity follows the formula as follows:

[0063]

[0064] In the formula: K P It is a proportional term, K i It is an integral term, K d is the differential term; out(t) is the controller output value; 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] Furthermore, since the angle of attack of the airflow on the ducted fan propeller blades changes in real time, it leads to the nonlinear response of the two servo motors 10, which can easily cause overshoot or oscillation during the pitch change process. In order to improve control accuracy and stability, a fuzzy PID controller is used to dynamically adjust the PID parameters to achieve adaptive compensation for the nonlinear characteristics of the two servo motors 10.

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

[0067]

[0068] In the formula: K P0 K i0 K d0 ΔK represents the initial parameters for the PID controller. P ΔK i ΔK dThe parameter increments are generated in real time by the fuzzy controller;

[0069] Step S3: During the actual operation of the two servo motors 10, problems such as mechanical manufacturing errors, load differences, or inconsistent control signals may cause the output angles of the two servo motors 10 to be out of sync. During the actual operation of the two servo motors 10, a coordinated control strategy is adopted. The two servo motors 10 share control parameters and feedback information, compare the output angles of the two servo motors 10 in real time, and control the synchronization error after comparison within ±0.3° to achieve closed-loop coordinated adjustment and realize the synchronization of the two servo motors 10.

[0070] Specifically, the two servo motors 10 employ a cooperative control strategy. During the driving process of the two servo motors 10, the output angles of the two servo motors 10 are monitored in real time, and the errors are compensated synchronously in real time to ensure that the synchronization error of the two servo motors 10 is within ±0.3°, thereby improving the stability of the system.

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

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

[0073] Where k is the conversion coefficient between displacement and angle, which is determined by the trapezoidal lead screw 220;

[0074] Due to mechanical errors such as dimensional inaccuracies, clearances in moving parts, and wear on rotating parts, the actual pitch angle deviates from the theoretical value during pitch adjustment. Therefore, a dynamic error compensation mechanism is proposed. This mechanism uses a compensation function to compensate for mechanical errors in the transmission process of the actuator 30, thereby improving pitch adjustment accuracy. The expression for the compensation function is as follows:

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

[0076] Where, k a This is the compensation coefficient.

[0077] Furthermore, the pitch change rate during the pitch change process is constrained using a kinematic model-based pitch change rate constraint strategy: Where, 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 control method for a variable pitch drive system of a ducted fan, characterized in that: The system includes a ducted fan pitch drive system, which includes a controller, two servo motors (10), a transmission assembly (20), and an actuation assembly (30). The controller is located inside the tail cone of the ducted fan, and the two servo motors (10) are symmetrically arranged on both sides of the ducted fan motor shaft. The transmission assembly includes gear one (212), driven gear (211), gear two (213), trapezoidal lead screw (220), stationary ring (230), moving ring (240), high-precision position sensor (250), and lead screw sleeve (260); the two servo motors (10) are driven synchronously, and the output shafts of the two servo motors (10) are connected to gear one (212). Gear one (212) meshes with driven gear (211), and driven gear (211) meshes with gear two (213). Wheel 2 (213) is mounted on trapezoidal lead screw (220), which is symmetrically arranged on both sides of the ducted fan motor shaft; a stationary ring (230) is mounted on the trapezoidal lead screw (220), and the rotation of the trapezoidal lead screw (220) drives the stationary ring (230) to move axially along the output shaft of the ducted fan motor, and the stationary ring (230) is connected to the rotating ring (240); the lead screw sleeve (260) is set inside the duct of the ducted fan, and a high-precision position sensor (250) is mounted on the lead screw sleeve (260); The actuator includes a hub (310), blades (320), a pitch shaft (330), a pitch rocker arm (331), and pitch tie rods (332). Six pitch tie rods (332) are mounted on the moving ring (240), the pitch rocker arm (331) is mounted on the pitch shaft (330), the pitch shaft (330) is mounted inside the hub (310), the hub (310) is set on the motor shaft of the ducted fan, and the pitch tie rods (332) are connected to the pitch rocker arm (331), so that the axial motion output by the ducted fan motor shaft is converted into a circular motion around the axis of the pitch shaft (330), thereby causing the axial movement output by the stationary ring (230) to drive the pitch shaft (330) to rotate, thus realizing the pitch change of the blades (320). The control method specifically includes the following steps: Step S1: Calculate the optimal pitch angle required by the ducted fan based on the current flight state, establish a variable pitch kinematic model of the ducted fan blades, and then replace the variable pitch kinematic model of the ducted fan blades with an equivalent kinematic model of the stationary ring (230); its kinematic model is defined as follows: ； in, It is the initial position. It is acceleration, It's speed; The kinematic model calculates acceleration and velocity parameters in real time and dynamically adjusts the displacement acceleration and velocity parameters of the stationary ring (230) in combination with kinematic formulas, thereby indirectly achieving high-precision control of the propeller pitch angle. Step S2: Based on the optimal pitch angle of the ducted fan given by the aircraft's main control computer, fuzzy PID feedforward control is used to drive two servo motors (10) to drive the gear transmission group, and the gear transmission group drives the trapezoidal lead screw (220) to rotate. The rotation of the trapezoidal lead screw (220) drives the stationary ring (230) to move axially along the ducted fan motor shaft, thereby realizing the variable pitch of the ducted fan. During the pitch change process, the high-precision position sensor (250) will monitor the current position of the stationary ring (230) in real time. The data is fed back to the controller, which adjusts the drive signals of the two servos (10) based on the feedback information to form a closed-loop control. The pitch control quantity follows the formula as follows: ； In the formula: It is a proportional term. It is an integral term. It is a differential term; It is the controller output value; This is the error term; the controller compares the actual position with the target position, that is: ; Furthermore, since the angle of attack of the airflow on the ducted fan propeller blades changes in real time, it leads to the nonlinear response of the two servo motors (10), which can easily cause overshoot or oscillation during the pitch change process. Therefore, a fuzzy PID controller is used to dynamically adjust the PID parameters to achieve adaptive compensation for the nonlinear characteristics of the two servo motors (10). The expression for the output parameters of the fuzzy PID controller is: ； In the formula: These are the initial parameters for the PID controller; The parameter increments are generated in real time by the fuzzy controller; Step S3: During the actual operation of the two servo motors (10), a coordinated control strategy is adopted. The two servo motors (10) share control parameters and feedback information, compare the output angles of the two servo motors (10) in real time, and control the synchronization error after comparison within ±0.3° to achieve closed-loop coordinated adjustment and realize the synchronization of the two servo motors (10). Step S4: Monitor the real-time displacement of the stationary ring (230) The real-time pitch angle of the ducted fan is obtained by equivalent conversion using a kinematic model; the conversion formula is as follows: ； in, The conversion coefficient between displacement and angle is determined by the trapezoidal lead screw; During pitch adjustment, the actual pitch angle deviates from the theoretical value. Therefore, a dynamic error compensation mechanism is proposed. This mechanism uses a compensation function to compensate for mechanical errors in the actuator's transmission process, thereby improving pitch adjustment accuracy. The compensation function expression is as follows: ； in, This is the compensation coefficient.

2. The control method for a variable pitch drive system of a ducted fan according to claim 1, characterized in that: The pitch mechanism is composed of two servo motors (10), a transmission assembly (20), and an actuation assembly (30). It adopts a structure design of two servo motors (10) and a trapezoidal screw drive, which realizes high torque output in a compact space. The trapezoidal screw (220) is threadedly connected to the stationary ring (230), which gives the trapezoidal screw (220) mechanical self-locking property. The mechanical self-locking property of the trapezoidal screw (220) is used to suppress the risk of overheating caused by the operation of the two servo motors (10). In the event of failure of the two servo motors (10), the mechanical self-locking property of the trapezoidal screw (220) is used to ensure that the pitch mechanism maintains the current blade pitch angle of the ducted fan.

3. The control method for a variable pitch drive system of a ducted fan according to claim 1, characterized in that: The pitch change speed during the pitch change process is constrained using a kinematic model-based pitch change speed constraint strategy: ,in, It is the target pitch angle, It is the initial angle. It is angular acceleration, It is angular velocity, which is achieved by dynamically adjusting the pitch angular acceleration and angular velocity parameters.

4. The control method for a variable pitch drive system of a ducted fan according to claim 1, characterized in that: 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: ； in, The precise value after defuzzification; The discrete values ​​within the fuzzy control quantity domain; for The membership degree value.

5. The control method for a variable pitch drive system of a ducted fan according to claim 1, characterized in that: Fuzzy PID feedforward control introduces a feedforward compensation mechanism on the basis of traditional fuzzy PID control. This feedforward compensation mechanism anticipates the dynamic characteristics of the system and offsets the hysteresis effects of the two servo motors (10) and the trapezoidal lead screw (220) in advance, thereby reducing steady-state error and improving the system's fast response capability. Its feedforward function is designed as follows: ,in, The transfer function of the servo (10) is used to optimize the overall dynamic response by inversely compensating for the dynamic characteristics of the servo (10).

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