Friction force identification method for trailing edge flap driving mechanism with bearing

Abstract

The invention provides a friction force identification method for a trailing edge flap driving mechanism with a bearing, and the method comprises the steps: applying a series of improved triangular waves with different speeds to a driver, carrying out the closed-loop control, carrying out the zero-phase digital filtering of a collected flap angle signal, and suppressing the interference of random noise to the signal, adjusting a buffeting phenomenon of a derivation step length inhibition speed to obtain a flap angular speed, then intercepting a constant-speed ascending section and a constant-speed descending section, then assigning a series of angular speeds, carrying out friction model identification on a relation between friction force and the speed, and then identifying a relation between parameters obtained by identification and a flap angle; finally, the friction force about the flap angle and the flap angular velocity in the flap driving mechanism is obtained.

Description

Technical Field

[0001] This application belongs to the technical field of active control of trailing-edge flaps for rotors, and particularly relates to a method for identifying the friction force of a trailing-edge flap drive mechanism with bearings. Background Technique

[0002] The vibration and noise caused by the rotor are the main sources of vibration and noise during helicopter flight, which seriously affect the service life of instruments and meters and the comfort of passengers. The active trailing-edge flap control (ACF), a helicopter vibration and noise active control technology developed in the past decade or so, has become one of the current research hotspots. The ACF rotor drives an additional flap at the trailing edge of the blade to deflect according to a given law through an actuator, thereby changing the aerodynamic force distribution of the rotor, reducing the alternating load at the hub or suppressing the blade disk noise, and achieving the purpose of vibration reduction or noise reduction.

[0003] The trailing-edge flap drive mechanism is generally located at the outer end of the blade and integrated in the cavity formed by the blade airfoil. The flap actuator is generally a piezoelectric actuator installed inside the blade. One end of it is fixed, and the other end is connected to the trailing-edge flap through a drive rod. The trailing-edge flap is fixed to the blade through a bearing or a flexible mechanism. During operation, the trailing-edge flap is driven to perform a flapping motion at a given frequency (single frequency or multi-frequency) under the action of voltage. Under the working state, the flap drive mechanism must bear the huge centrifugal force caused by the blade rotation, and the flap flapping motion must also overcome complex aerodynamic loads.

[0004] In order to achieve the flapping motion of the flap, joint bearings, thrust bearings, ball bearings, self-lubricating bushing bearings, etc. are often used in the design of the connections at both ends of the drive link and between the flap and the blade. When the flap works according to a sinusoidal excitation voltage, due to the existence of bearing friction, when the flap performs a low-frequency flapping motion, the sinusoidal flapping motion waveform of the flap often shows a flat top phenomenon at the wave crest, introducing unwanted frequency components such as the second harmonic and the third harmonic.

[0005] Regarding this phenomenon, it is very difficult to eliminate it through control laws such as PID. Therefore, it is very necessary to identify the friction force in the flap drive mechanism. On the one hand, it can guide the design of the flap drive mechanism to minimize the influence of friction force on the flap flapping motion. On the other hand, in the servo closed-loop control of the flap, a friction model based on identification can be introduced to compensate for the friction force, reduce or eliminate the flat top phenomenon at the sinusoidal wave crest, and improve the control accuracy.

[0006] Different from the conventional motor control based on speed control, the friction in motor speed control is generally only related to speed. Although there may be random changes in the load of the motor, generally only the torque changes, and the normal force between the stator and rotor of the rotating components changes little. In the deflection movement of the trailing edge flap, the planar movement of the actuator passes through the drive link and is converted into a deflection movement through the force arm of the flap, with an amplification effect at the same time. The load of the flap generally also changes with the angle, causing changes in the normal force of the friction surfaces such as the bearings at both ends of the drive link.

[0007] Therefore, the friction force of the trailing edge flap drive mechanism with bearings is not only a function of the flap flapping speed but also a function of the angle. In addition, due to the reverse of the friction force in the flap rising section (positive speed) and the falling section (negative speed), a sudden change in the flap driving force is caused, resulting in a large difference in the friction model parameters for positive and negative speeds.

[0008] In addition, different from the continuous rotation of loads such as motors, the flapping movement of the flap is a reciprocating movement, making it difficult to implement conventional friction identification based on constant speed tracking in the flapping movement of the flap. Summary of the Invention

[0009] Object of the Invention: To propose a method for identifying the friction force of a trailing edge flap drive mechanism with bearings, aiming to provide an identification method for the friction force varying with angle and angular velocity in the case of reciprocating motion.

[0010] The present application provides a method for identifying the friction force of a trailing edge flap drive mechanism with bearings, the method comprising:

[0011] Calculating the theoretical angular velocity range of flap deflection according to the angle range and deflection frequency of the flap deflecting according to a sine law;

[0012] Applying an excitation to the flap drive mechanism by using an improved triangular wave according to the theoretical angular velocity range of flap deflection, and adopting a PI closed-loop control to obtain a series of flap angle response signals and PI control output signals under positive and negative speeds of flap deflection;

[0013] Selecting a cut-off frequency based on the flap angle response signal;

[0014] Filtering the flap angle response signal according to the cut-off frequency by using a zero-phase digital low-pass filter to obtain a filtered flap angle response signal;

[0015] Selecting a differentiation step size, and differentiating the filtered flap angle response signal by using the differentiation step size to obtain the actual angular velocity of flap deflection;

[0016] Intercept the uniformly rising and falling segment signals in the filtered response signal and their corresponding PI control output signals according to the angular velocity of the actual flap deflection;

[0017] Fit the uniformly rising and falling segment signals with the PI control output signals to obtain the relationship between the uniformly rising and falling segment signals and the PI control output signals;

[0018] Based on the relationship between the uniformly rising and falling segment signals and the PI control output signals, obtain the stiffness and friction force of the flap elastic load.

[0019] Preferably, the method further includes:

[0020] Select a friction model based on the curve of the friction force varying with the angular velocity of the actual flap deflection;

[0021] Based on the friction model, identify the relationship between the friction force and the angular velocity of the actual flap deflection.

[0022] Preferably, the method further includes:

[0023] Based on the relationship between the friction force and the angular velocity of the actual flap deflection, identify the relationship between the friction force and the actual flap deflection angle and the angular velocity of the actual flap deflection.

[0024] Preferably, the calculating the theoretical angular velocity range of the flap deflection according to the angular range and deflection frequency of the flap deflecting in a sine law includes:

[0025] Obtain the deflection frequency of the flap deflecting in a sine law, the flap angle offset, and the amplitude of the flap sine motion;

[0026] Calculate the circular frequency of the flap according to the deflection frequency of the flap deflecting in a sine law;

[0027] Based on the circular frequency of the flap, the flap angle offset, and the amplitude of the flap sine motion, calculate the theoretical flap deflection angle;

[0028] Based on the theoretical flap deflection angle, obtain the theoretical angular velocity range of the flap deflection.

[0029] Preferably, the improved triangular wave is characterized in that the wave peaks and valleys are modified to be sinusoidal transitions, and the connections with the rising and falling segments of the triangular wave are smooth and the first derivative is smooth.

[0030] Preferably, the formula of the improved triangular wave is as follows:

[0031] u = A sin + A sin *cos(2πft - π), t ≤ Tsin

[0032] u = V*(t - T sin + T1), T sin < t ≤ T2 - T sin

[0033] u = A tri -A sin +A sin *cos(2πf(t - T2)), T2 - T sin < t ≤ T2 + T sin

[0034] u = A tri -V*(t - T2 - T sin + T1), T2 + T sin < t ≤ 2T2 - T sin

[0035] u = A sin +A sin *cos(2πf(t - 2T2)-π), T2 + T sin < t ≤ 2T2 - T sin

[0036] Among them, u represents the command signal, A tri represents the amplitude of the triangular wave, A sin represents the amplitude of the sine wave at the peak and valley of the improved triangular wave, V represents the speed of the ramp section of the triangular wave, T sin represents half of the duration of the sine wave at the peak or valley, T1 represents the time difference when u is equal at the uniform rising section of the original triangular wave and the improved triangular wave, and T2 represents half of the period of the improved triangular wave.

[0037] Preferably, selecting the cut-off frequency based on the response signal includes:

[0038] Select a zero-phase digital low-pass filter;

[0039] Filter the response signal using the zero-phase digital low-pass filter, and select the cut-off frequency by comparing whether there is attenuation in the amplitude of the signal before and after filtering.

[0040] Preferably, the expression for the relationship between the signals in the uniform rising and falling sections and the PI control output signal is:

[0041] f = k flap θ flap -u PI

[0042] Among them, f represents the frictional force, k flapDenote the stiffness of the elastic load related to the flap angle in the flap drive mechanism, u PI Denote the PI control output signal, θ flap Denote the flap angle response signals in the uniform ascending and descending segments.

[0043] Advantageous technical effects of this application:

[0044] 1. Under the condition of a limited flap flapping motion angle range, the angle range of the uniform change segment of the flap angle under closed-loop control can be increased by the improved triangular wave to improve the identification accuracy;

[0045] 2. When only the flap angle can be measured and the angular velocity cannot be directly measured, the influence of random noise and other factors of the signal can be suppressed by means such as zero-phase digital low-pass filtering and derivative step size setting to improve the speed identification accuracy;

[0046] 3. A friction identification method related to the angle and angular velocity is proposed. Conventional friction identification of rotating mechanisms is only related to the angular velocity. Description of the drawings

[0047] Figure 1 It is a flowchart for identifying the friction of a trailing-edge flap drive mechanism with bearings;

[0048] Figure 2 It is a comparison diagram between the improved triangular wave signal and the conventional triangular wave signal;

[0049] Figure 3 It is a schematic diagram of each time node in the improved triangular wave signal;

[0050] Figure 4 It is a schematic diagram of the trailing-edge flap drive mechanism;

[0051] Among them: 1, rhombic piezoelectric actuator; 2, drive link; 3, trailing-edge flap; 4, flap rotation axis. Specific implementation manners

[0052] This application provides a method for identifying the friction of a trailing-edge flap drive mechanism with bearings, aiming to provide an identification method for the friction varying with the angle and angular velocity in the reciprocating motion situation.

[0053] The present invention proposes a method for identifying the friction force of a trailing edge flap drive mechanism with bearings. By applying a series of improved triangular waves with different speeds to the actuator and performing closed-loop control, then suppressing the interference of random noise on the signal by zero-phase digital filtering of the collected flap angle signal, adjusting the derivative step size to suppress the speed jitter phenomenon to obtain the flap angular velocity, then intercepting the uniformly rising section and the uniformly falling section, and then specifying a series of angular velocities to identify the friction model of the relationship between the friction force and the speed, and then identifying the relationship between the identified parameters and the flap angle, finally obtaining the friction force in the flap drive mechanism regarding the flap angle and the flap angular velocity. The specific steps are as follows:

[0054] Step 1: Calculate the angular velocity range of the flap deflection according to the angular range and deflection frequency of the flap deflecting according to the sine law;

[0055] θ = θ0 + θ amp sin(ωt)

[0056]

[0057] In the above formula, θ represents the flap angle, represents the flap angular velocity, ω represents the flap circular frequency, θ0 represents the flap angle offset, and θ amp represents the amplitude of the flap sinusoidal motion.

[0058] Step 2: According to the angular velocity range obtained in Step 1, apply an excitation to the flap drive mechanism using an improved triangular wave, and use PI closed-loop control to obtain a series of responses under positive and negative flap deflection speeds;

[0059] The improved triangular wave is characterized in that the wave peaks and wave troughs are modified to be sinusoidal transitions, and the connections with the rising and falling sections of the triangular wave are smooth and the first derivative is smooth, which can avoid or reduce the oscillation phenomenon of the closed-loop controller at the wave peaks and wave troughs and increase the angular range of the uniform control section. The formula for the improved triangular wave is as follows:

[0060] u = u amp + u amp * cos(2πft - π), t ≤ T sin

[0061] u = V * (t - T sin + T1), T sin < t ≤ T2 - T sin

[0062] u = A - u amp + u amp * cos(2πf(t - T2)), T2 - T sin < t ≤ T2 + T sin

[0063] u = A - V * (t - T2 - T sin + T1), T2 + T sin < t ≤ 2T2 - T sin

[0064] u = u amp + u amp * cos(2πf(t - 2T2) - π), T2 + T sin < t ≤ 2T2 - T sin

[0065] In the above formula, A represents the amplitude of the triangular wave, u amp the amplitude of the sine wave at the peak and trough of the improved triangular wave, V represents the speed of the ramp section of the triangular wave, T sin represents half of the duration of the sine wave at the peak or trough, T1 represents the time from the minimum angle of the uniform rise section to the 0 angle in the improved triangular wave, and T2 represents half of the period of the improved triangular wave.

[0066] Step 3: Filter the signal using a 0-phase digital filter. By comparing the signals before and after filtering to check if there is any attenuation in the amplitude, select an appropriate cut-off frequency for the low-pass filter (which can suppress the noise interference in the signal and does not cause phase delay);

[0067] Step 4: Use an appropriate derivative step size to take the derivative of the measured angle signal to obtain the angular velocity (an appropriate derivative step size can suppress the chattering phenomenon that may occur in the first derivative of the angle signal, i.e., the angular velocity);

[0068] Step 5: According to the angular velocity obtained in Step 4, intercept the uniform rise section and fall section in the triangular wave signal;

[0069] Step 6: For the signal of the uniform control section intercepted in Step 5, fit the relationship between the angle and the control output voltage (or the output force of the actuator). According to the formula f = k flap θ - u, calculate the stiffness k of the flap elastic load flap ;

[0070] In the formula, f represents the frictional force, k flap represents the stiffness of the elastic load related to the flap angle in the flap drive mechanism, and u represents the actual control input;

[0071] Step 7: For the uniformly controlled segment signal intercepted in Step 5, fit the relationship between the angle and the control output voltage (or the driver output force) at different angular velocities. Keep the angle the same, calculate the positive velocity friction force and the negative velocity friction force corresponding to different angular velocities at this angle. According to the friction force vs. angular velocity change curve, select an appropriate friction model such as the Coulomb friction + viscous friction model, and identify the relationship between the friction force and the velocity at this angle;

[0072] The relationship between the excitation voltage applied to the flap drive mechanism and the flap angle can be expressed as follows:

[0073]

[0074] F load = f + k flap θ

[0075] In the above formula, J represents the flap moment of inertia, represents the flap angular acceleration, F load represents the load of the flap deflection movement.

[0076] To identify the friction force of the flap drive mechanism related to the recommended angular velocity and angle, by applying the triangular wave closed-loop control in Step 2, select the uniform speed segment under the closed-loop control. At this time, the flap angular acceleration There is:

[0077] u = f + k flap θ

[0078] When the angle is constant, for the friction model composed of Coulomb friction + viscous friction, the friction force f can be expressed as:

[0079]

[0080] In the above formula, represents the friction model coefficient when the velocity is positive, represents the friction model coefficient when the velocity is negative

[0081] Step 8: According to the flap deflection angle range, refer to Step 7 to identify the relationship between the friction force and the angular velocity at different angles. On this basis, further identify the relationship between the parameters in the friction model and the angle.

[0082] Within the flap angle range, specify different flap angles. Obviously, it is easy to identify a series of parameters of the friction model Then identify the relationship between this series of friction model parameters and the flap angle, and obtain:

[0083]

[0084] In summary, the friction force related to the flap drive mechanism, flap angle, and flap angular velocity can be identified through experiments.

[0085] In other embodiments of the present application, for an ACF rotor system with a set of 4 blades and a fundamental frequency of 6 Hz, the trailing edge flap drive mechanism (such as Figure 4 ) adopts a bearing connection structure for flap deflection, drive pull rods, etc. The maximum excitation frequency of the flap of the 4 blades is generally 5 / rev, that is, 30 Hz. If the flap deflection angle range is 0° to 6°. To identify the mechanism friction force within its working range, the steps are as follows:

[0086] Step 1: Calculate the flap circular frequency according to the maximum deflection frequency of the flap deflecting in a sine law. The formula is as follows:

[0087] ω = 2πf

[0088] In the above formula, f represents the deflection frequency, ω represents the flap circular frequency, and π represents the pi.

[0089] Step 2: Calculate the angular velocity range of the flap deflection according to the angle range and deflection circular frequency of the flap deflecting in a sine law. The formula is as follows:

[0090] θ = θ0 + θ amp sin(ωt)

[0091]

[0092] In the above formula, θ represents the flap angle, represents the flap angular velocity, ω represents the flap circular frequency, θ0 represents the flap angle offset, θ amp represents the amplitude of the flap sine motion, and t represents time.

[0093] Step 3: Apply an excitation to the flap drive mechanism with an improved triangular wave at a certain speed interval according to the angular velocity range calculated in Step 2, and adopt a PI closed-loop control to obtain a series of flap angle response signals at positive and negative flap deflection speeds;

[0094] The improved triangular wave is characterized in that the wave peaks and valleys of the triangular wave are modified to be sinusoidal transitions, and the connections with the rising and falling segments of the triangular wave are smooth and the first derivative is smooth, which can avoid or reduce the oscillation phenomenon of the closed-loop controller at the wave peaks and valleys, increase the angle range of the uniform speed control section, and avoid damage to the piezoelectric actuator due to the step response. The formula of the improved triangular wave is as follows:

[0095] u = A sin +A sin *cos(2πft - π), t ≤ T sin

[0096] u = V*(t - T sin + T1), T sin < t ≤ T2 - T sin

[0097] u = A tri - A sin + A sin *cos(2πf(t - T2)), T2 - T sin < t ≤ T2 + T sin

[0098] u = A tri - V*(t - T2 - T sin + T1), T2 + T sin < t ≤ 2T2 - T sin

[0099] u = A sin + A sin *cos(2πf(t - 2T2) - π), T2 + T sin < t ≤ 2T2 - T sin

[0100] In the above formula, u represents the command signal, A tri represents the amplitude of the triangular wave, A sin represents the amplitude of the sine wave at the peak and trough of the improved triangular wave, V represents the speed of the ramp section of the triangular wave, T sin represents half of the duration of the sine wave at the peak or trough, T1 represents the time difference when u is equal in the uniformly rising section of the original triangular wave and the improved triangular wave, T2 represents half of the period of the improved triangular wave. Each time quantity in the improved triangular wave and the triangular wave signal can be seen in Figure 2 and Figure 3 .

[0101] The PI closed-loop control is based on the basic PID control. The discrete expression of the PI control is

[0102]

[0103] e′(k) = SP(k) - PV(k)

[0104] In the above formula, u PI (k) represents the PI control output signal at the k-th control step in discrete control, Kp represents the proportional gain, Ki represents the integral gain, SP(k) represents the value of the improved triangular wave command signal u at the k-th control step, PV(k) represents the value of the feedback flap angle signal θ at the k-th control step, e′(k) represents the difference between the triangular wave command signal and the feedback flap angle signal at the k-th control step, that is, the control error, represents the cumulative sum of the errors from the 0-th control step to the k-th control step.

[0105] Step 4: Filter the series of flap angle response signals at positive and negative flap deflection velocities obtained in Step 3 using a 0-phase digital low-pass filter. The cut-off frequency of the low-pass filter is selected by comparing whether there is a significant attenuation in the amplitude of the signals before and after filtering;

[0106] Step 5: Take a derivative of the series of filtered flap angle signals obtained in Step 4 with a derivative step length of appropriate length to obtain a series of measured flap angular velocities. The derivative step length is selected based on whether there is a chattering phenomenon in the flap angular velocity signal obtained by taking the derivative.

[0107] Step 6: According to the series of measured flap angular velocities obtained in Step 5, intercept the PI control output signal u PI and the flap angle response signal θ flap .

[0108] Step 7: Fit the series of PI control output signals u PI and the flap angle response signals intercepted in Step 6 according to the following formula to obtain a series of relationships between the flap angle and the control output voltage (or the drive output force);

[0109] f = k flap θ flap - u PI

[0110] In the above formula, f represents the friction force, and k flap represents the stiffness of the elastic load related to the flap angle in the flap drive mechanism.

[0111] Step 8: Let the flap angle take the same value in the series of relationships between the flap angle and the control output voltage obtained in Step 7, then a series of friction force values at different flap angular velocities are obtained. For the series of friction force values and flap angular velocity values obtained at different flap angular velocities, select an appropriate friction model, such as a friction model composed of Coulomb friction + viscous friction, and identify the parameters of the friction model. The friction model is as follows:

[0112]

[0113] In the above formula, represents the friction model coefficient when the flap angular velocity is positive, represents the friction model coefficient when the flap angular velocity is negative, sgn is the sign function, represents the flap angular velocity calculated based on the measured flap angle.

[0114] Step 9: Repeat Step 8, with the flap angle in Step 8 taking values at certain step intervals within the flap angle range obtained in Step 2, and identify the friction model parameters between the frictional force and the flap angular velocity at different flap angles. Then, identify the relationship between this series of friction model parameters and the corresponding flap angles through polynomial fitting to obtain:

[0115]

[0116] In the above formula, a n , a0 represent and θ flap The polynomial coefficients obtained by fitting between them, b n , b0 represent and θ flap The polynomial coefficients obtained by fitting between them, c n , c0 represent and θ flap The polynomial coefficients obtained by fitting between them, d n , d0 represent and θ flap The polynomial coefficients obtained by fitting between them.

[0117] In summary, the relationship between the frictional force of the flap drive mechanism and the flap angle and the flap angular velocity is identified.

Claims

1. A method for identifying the friction force of a trailing edge flap drive mechanism with bearings, characterized in that, The method includes: Calculating the angular velocity range of the theoretical flap deflection according to the angular range and deflection frequency of the flap deflecting in a sine law; Applying an excitation to the flap drive mechanism by using an improved triangular wave according to the angular velocity range of the theoretical flap deflection, and adopting a PI closed-loop control to obtain a series of flap angle response signals and PI control output signals under positive and negative flap deflection speeds; Selecting a cut-off frequency based on the flap angle response signal; Filtering the flap angle response signal according to the cut-off frequency by using a 0-phase digital low-pass filter to obtain a filtered flap angle response signal; Selecting a derivative step size, and taking the derivative of the filtered flap angle response signal by using the derivative step size to obtain the angular velocity of the actual flap deflection; Intercepting the uniformly rising segment and falling segment signals in the filtered response signal and their corresponding PI control output signals according to the angular velocity of the actual flap deflection; Fitting the uniformly rising segment and falling segment signals with the PI control output signals to obtain the relationship between the uniformly rising segment and falling segment signals and the PI control output signals; Obtaining the stiffness and friction force of the flap elastic load based on the relationship between the uniformly rising segment and falling segment signals and the PI control output signals; 2. The method according to claim 1, characterized in that, The method further includes: Selecting a friction model based on the curve of the friction force varying with the angular velocity of the actual flap deflection; Identifying the relationship between the friction force and the angular velocity of the actual flap deflection based on the friction model; 3. The method according to claim 2, wherein The method further includes: Identifying the relationship between the friction force and the actual flap deflection angle and the angular velocity of the actual flap deflection based on the relationship between the friction force and the angular velocity of the actual flap deflection; 4. The method according to claim 3, characterized in that, The calculating the angular velocity range of the theoretical flap deflection according to the angular range and deflection frequency of the flap deflecting in a sine law includes: Obtaining the deflection frequency of the flap deflecting in a sine law, the flap angle offset, and the amplitude of the flap sine motion; Calculating the flap circular frequency according to the deflection frequency of the flap deflecting in a sine law; Calculating the theoretical flap deflection angle based on the flap circular frequency, the flap angle offset, and the amplitude of the flap sine motion; Obtaining the angular velocity range of the theoretical flap deflection based on the theoretical flap deflection angle; 5. The method according to claim 3, wherein The improved triangular wave is characterized in that the wave peaks and wave valleys are modified to be sinusoidal transitions, and the connections with the rising and falling segments of the triangular wave are smooth and the first derivative is smooth.

6. The method according to claim 5, wherein The formula of the improved triangular wave is as follows: u = A sin + A sin * cos(2πft - π), t ≤ T sin u = V * (t - T sin + T1), T sin < t ≤ T2 - T sin u = A tri -A sin +A sin *cos(2πf(t - T2)), T2 - T sin <t ≤ T2 + T sin u = A tri -V*(t - T2 - T sin + T1), T2 + T sin <t ≤ 2T2 - T sin u = A sin + A sin * cos(2πf(t - 2T2)-π), T2 + T sin <t ≤ 2T2 - T sin where u represents the command signal, A tri represents the amplitude of the triangular wave, and A sin represents the amplitude of the sine wave at the peak and valley transitions in the improved triangular wave, V represents the speed of the ramp segment of the triangular wave, and T sin represents half of the duration of the sine wave at the peak or valley transition, T1 represents the time difference when u is equal at the uniform rise segment of the original triangular wave and the improved triangular wave, and T2 represents half of the period of the improved triangular wave.

7. The method according to claim 3, wherein The selecting a cut-off frequency based on the response signal includes: Selecting a 0-phase digital low-pass filter; Filtering the response signal by using the 0-phase digital low-pass filter, and selecting the cut-off frequency by comparing whether the amplitude of the signal decays before and after filtering; 8. The method according to claim 3, wherein The expression of the relationship between the uniformly rising segment and falling segment signals and the PI control output signals is: f = k flap θ flap -u PI where f represents the frictional force, k flap represents the stiffness of the elastic load related to the flap angle in the flap drive mechanism, u PI represents the PI control output signal, θ flap represents the flap angle response signal in the uniform ascending and descending sections.

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