Method for detecting and inhibiting resonance of two-axis photoelectric pod

Abstract

The invention discloses a method for detecting and inhibiting resonance of a two-axis photoelectric pod. Belongs to the technical field of photoelectric pod control systems, and particularly relates to the technical field of two-axis photoelectric pod resonance detection and suppression. According to the invention, a stable precision index is taken as a discrimination standard of a resonance condition, a self sensor is utilized, a resonance frequency automatic detection and identification method is adopted, filter parameters are adaptively adjusted according to resonance frequency point distribution characteristics, and the resonance frequency is suppressed through a signal processing algorithm, so that interference of the resonance frequency on a test is effectively avoided. According to the method, the self-adaptive capability of the photoelectric pod is enhanced, so that the photoelectric pod can cope with different external interference factors, and especially in a special vibration environment, the pod can keep relatively high stability and precision. According to the method, the problem of vibration interference in a traditional method can be effectively solved, and the adaptability of the photoelectric pod in a vibration environment can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectric pod control systems, and in particular relates to the technical field of two-axis photoelectric pod resonance detection and suppression. Background Art

[0002] Optoelectronic pods are widely used in aerospace, military, and measurement applications. As precision optical measuring instruments, they often require stability testing under rigorous conditions. To ensure the reliability and accuracy of optoelectronic pods, vibration table testing is a key method for evaluating their performance. Vibration table testing can simulate the vibrations a pod might encounter during flight or in other environments. However, due to the wide frequency range of the vibration table, resonance can occur in the pod at different azimuth and pitch angles. This resonance can make stability accuracy difficult to guarantee or even impossible to measure during testing.

[0003] Current solutions often rely on structural modifications, adding vibration dampers, or redesigning the pod to address resonance. However, these methods often involve high costs and long lead times, and may not completely eliminate the effects of resonance. Therefore, identifying and suppressing resonant frequencies in real time, without changing the pod structure, to improve test accuracy and efficiency, remains a major challenge in current optoelectronic pod testing technology. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for detecting and suppressing resonance of a two-axis photoelectric pod, the method comprising the following steps:

[0005] S1. Electro-optical pod stability accuracy test: With the pod in gyro-stabilized control mode, a rocking platform is used to simulate external environmental disturbances to test the electro-optical pod's line-of-sight stability. By acquiring gyro signals in real time, the stability accuracy of the pod's azimuth and pitch axes in a non-resonant state is calculated, which serves as the threshold for determining whether resonance occurs.

[0006] S2. Resonance state judgment: Real-time monitoring of the stability accuracy changes of the two axes of the pod. When the change of one axis exceeds the threshold, it is determined that the axis is in a resonance state;

[0007] S3. Resonance spectrum analysis: In the resonance state, the gyro signal is subjected to multiple fast Fourier transforms to extract the resonance frequency characteristics, providing data support for subsequent notch filter design;

[0008] S4. Adaptive notch filter design: Based on the extracted resonant frequency characteristics, the notch filter is adaptively designed to accurately suppress the resonant frequency;

[0009] S5. Adaptive wave limiter connection: Connect the designed adaptive wave limiter to the servo control loop, cut off the original gyro signal loop, and filter out the resonant frequency in real time;

[0010] S6. Real-time monitoring: Real-time monitoring of the amplitude change of the resonance frequency point, dynamic adjustment of the filter Q value according to the downward trend, if the amplitude of the resonance frequency point is significantly suppressed, the stable accuracy value is still greater than 3 times σ rms , it is considered that there are other resonant frequency points, and the process returns to step S3 and continues until all resonant frequency points are suppressed, σ rms is the RMS value of the stable accuracy.

[0011] Furthermore, the stability accuracy of the azimuth and pitch axes of the two-axis pod in the non-resonance state is calculated respectively.

[0012] Carry out, σ rms is the RMS value of the stable accuracy, θ i is the integral angle increment value, and N is the number of sampling points.

[0013] further, ω i is the gyro angular velocity at the i-th moment, ω i-1 is the gyro angular velocity at the i-1th moment, f s is the gyro sampling frequency.

[0014] Furthermore, the threshold in step S2 is specifically 3 times σ rms .

[0015] Furthermore, the resonant frequency characteristics are extracted as follows:

[0016] S51, data preprocessing: collect a set of gyro signals ω i (i=1, 2...N), preprocessing the gyro signal, wherein the preprocessing includes removing the DC component and performing windowing processing;

[0017] S52, multiple fast Fourier transforms: performing M times of Fourier transform on the preprocessed gyro signal to obtain a complex spectrum value of the gyro signal;

[0018] S53, calculate the average value of the complex spectrum value of the M-th Fourier transform to obtain the spectrum amplitude average value

[0019] S54, spectrum resolution calculation: through Calculate the frequency resolution Δf and determine the frequency interval between each frequency point, f s is the sampling frequency, N is the number of sampling points;

[0020] S55, Resonance frequency extraction: by calculating the average value of the spectrum amplitude Find the peak position of the spectrum, where the frequency point corresponding to the maximum amplitude is the resonant frequency f 共振 , f共振 =k 最大 Δf,k 最大 is the index of the maximum value in the magnitude spectrum.

[0021] Furthermore, the adaptive wave limiter is specifically designed as follows:

[0022] S61, set the bandwidth BW, quality factor Q and center frequency f of the limiter 中心 :f 中心 =f 共振 =BW·Q;

[0023] S62, setting the differential formula of the wave limiter, the differential formula is: n =ω n -2cos(W0)ω (n-1) +ω (n-2) +2cos(W0)y (n-1) -r 2 y (n-2) , where ω n is the current input gyro data, ω (n-1) The gyro data input at the previous moment, ω (n-2) The gyro data input in the first two moments,

[0024] y n is the current output gyro data, y (n-1) The gyroscope data output at the previous moment, y (n-2) The gyro data output in the first two moments, W0 is the normalized angular frequency, r is the notch filter pole radius,

[0025] S63, the notch filter selects a second-order IIR infinite impulse response notch filter.

[0026] Furthermore, the significant suppression of the amplitude of the resonance frequency point specifically means that the amplitude of the resonance frequency point decreases by more than or equal to 10 dB compared with the initial detection result.

[0027] The beneficial effects of the method of the present invention are:

[0028] The method described in the present invention is suitable for eliminating resonance caused by optoelectronic pods operating on a vibration table or in a real-world environment. To meet the requirements of different application environments, key performance indicators such as stability and accuracy of optoelectronic pods require testing on both rocking and shaking tables. Large two-axis optoelectronic pods are designed to carry more payloads, resulting in heavy overall design weight and low natural frequency. When tested on a shaking table, the wide vibration spectrum and high vibration magnitudes can cause resonance at specific azimuth and pitch angles, leading to test failures, delivery delays, and even project failure. Modifying the pod structure or shock absorber design can lead to high costs and the risk of delivery delays. To address this issue, the present invention provides a method for real-time detection and suppression of resonant frequencies. Using stability and accuracy as the criterion for determining resonance conditions, the method utilizes its own sensors, employs an automatic resonant frequency detection and identification method, adaptively adjusts filter parameters based on the distribution characteristics of resonant frequency points, and suppresses resonant frequencies through signal processing algorithms, effectively preventing resonant frequency interference with testing. This method enhances the optoelectronic pod's adaptability, enabling it to cope with diverse external interference factors. Especially in unusual vibration environments, the pod can maintain high stability and accuracy. This method can effectively solve the vibration interference problem existing in traditional methods and can significantly improve the adaptability of optoelectronic pods in vibration environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of the method of the present invention;

[0030] Figure 2 Schematic diagram of the location where the adaptive limiter is connected to the servo loop. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] like Figure 1 The figure shows a flow chart of the steps of the method described in the present invention. The method described in the present invention can detect and suppress the resonant frequency in real time, use the stability accuracy index as the judgment standard of the resonance condition, utilize its own sensor, adopt the automatic detection and identification method of the resonant frequency, adaptively adjust the filter parameters according to the frequency point distribution characteristics, and suppress the resonant frequency through the signal processing algorithm, thereby ensuring the stability of the optoelectronic pod on the vibration table or in the actual working environment, avoiding the structural changes and high costs in the traditional solution.

[0033] The method of the present invention includes 6 steps.

[0034] Step 1: Stability Accuracy Benchmark Test: With the pod in gyro-stabilized control mode, use a rocker to simulate external environmental disturbances to test the pod's line-of-sight stability. Gyro signals are collected in real time to calculate the stability accuracy of the pod's azimuth and pitch axes in a non-resonant state, which serves as the threshold for determining resonance.

[0035] The stability accuracy benchmark test method in step 1 is as follows:

[0036] In the gyro stabilization mode, the swing table is used to simulate the airborne environment, and the two-axis gyro output data are tested separately in the non-resonance state, that is, a group of gyro data of a certain axis is collected in real time. i (i=1,2…N), calculate the stability accuracy, the formula is as follows:

[0037]

[0038] σ rms is the RMS value of the stability accuracy, unit is °, ω i is the gyro angular velocity at the i-th moment, in degrees / s, θ i is the integral angle increment value, in degrees, f s is the gyroscope sampling frequency in Hz, N is the number of sampling points, and the stability accuracy value is a relatively stable indicator.

[0039] In the implementation, the gyro sampling frequency is 1000Hz, the sampling points are set to 1024, and in the line of sight stabilization mode, in the 2°@2Hz rocking table sinusoidal perturbation test, the azimuth axis and pitch axis σ rms Converted to radians, they are 50 μrad and 60 μrad respectively.

[0040] Step 2: Resonance state judgment: When the pod is working on a vibration table or in an actual environment, the stability accuracy changes of the two axes of the pod are monitored in real time. When the change of one axis exceeds the threshold, the axis is determined to be in a resonance state.

[0041] The method for judging the resonance state in step 2 is as follows:

[0042] On a vibration table or in an actual environment, when the pod is subjected to external excitation, resonance will occur when the excitation frequency is close to the natural frequency of the structure, resulting in a significant amplification of the response amplitude at that frequency, and the stability accuracy value may surge by dozens of times. If the stability accuracy of a certain axis is detected to be more than 3 times σ rms When , the axis is judged to be in a resonant state. Since the stability accuracy is based on the error statistics of a set of gyro data, the statistics are highly robust to occasional noise interference and can effectively avoid misjudgment. rmsCorresponding to the commonly used standards for abnormal fluctuations or significant deviations, in order to adapt to different resonance sensitivity requirements, the multiple threshold can also be configured to 3 to 5 times, and the parameters can be modified according to the pod structure characteristics and resonance risk level.

[0043] Step 3: Resonance spectrum analysis: In the resonant state, perform multiple fast Fourier transforms (FFTs) on the gyro signal to extract the frequency distribution and amplitude characteristics of the resonance, providing data support for subsequent notch filter design.

[0044] The resonance spectrum analysis in step 3 is to extract the resonance frequency points, including the following process:

[0045] (1) Data preprocessing

[0046] In order to reduce the influence of noise and interference signals, a set of gyro data ω is collected. i (i=1,2…N), preprocess the gyro data:

[0047] Remove DC component: Calculate the mean of the gyro signal data and de-average the signal:

[0048]

[0049] Windowing: Use a window function to add a window to the signal to reduce spectral leakage:

[0050] ω″ i =ω′ i ω(i);

[0051]

[0052] (2) Multiple Fast Fourier Transforms (FFTs)

[0053] X i [k] = FFT(ω″ i )i=1, 2, 3, ...M;

[0054]

[0055] X[k] is the complex spectrum value at the kth frequency point;

[0056] N is the total number of sampling points of the signal;

[0057] k is the frequency index;

[0058] M is the number of FFTs;

[0059] The pre-processed gyro signal ω i ", after M times of FFT transformation, the complex spectrum value of the gyroscope signal is obtained.

[0060] (3) Average spectrum amplitude

[0061]

[0062] Calculating the average value of the amplitude spectrum for each FFT can improve the accuracy of signal spectrum extraction and remove the influence of noise.

[0063] (4) Frequency resolution calculation

[0064]

[0065] Δf is the frequency resolution, which determines the frequency interval between each frequency point, f s is the sampling frequency, and N is the number of sampling points.

[0066] (5) Resonance frequency extraction

[0067] f 共振 =k 最大 Δf;

[0068] By calculating the average spectrum Find the peak position of the spectrum, where the frequency point corresponding to the maximum amplitude is the resonant frequency, k 最大 is the index of the maximum value in the magnitude spectrum.

[0069] Data preprocessing, multiple FFTs, and spectrum amplitude averaging are all designed to remove noise and ensure more accurate frequency extraction. Extracting the resonant frequency requires the pod system to be in a resonant state. In practice, during vibration table testing, the two-axis pod will resonate at specific pitch or azimuth angles, and only a single peak frequency point is extracted from the resonant frequency.

[0070] Step 4: Adaptive notch filter design: Based on the extracted resonant frequency characteristics, including parameters such as center frequency and bandwidth, the notch filter is adaptively designed to accurately suppress the resonant frequency.

[0071] The design method of the adaptive notch filter in step 4 is as follows:

[0072] (1) Relationship between bandwidth BW and Q value of notch filter:

[0073] f 中心 =f 共振 =BW·Q;

[0074] f 中心 is the center frequency of the notch filter, in Hz;

[0075] BW is the bandwidth of the notch filter, the suppression range of the notch filter, in Hz;

[0076] Q is the quality factor;

[0077] (2) Differential formula of notch filter:

[0078] y n =ω n -2cos(W0)ω (n-1) +ω (n-2) +2cos(W0)y (n-1) -r 2 y (n-2) ;

[0079] ω n is the current input gyro data;

[0080] ω (n-1) The gyro data input at the previous moment;

[0081] ω (n-2) The gyro data input in the previous two moments;

[0082] y n is the current output gyro data;

[0083] y (n-1) The gyroscope data output at the previous moment;

[0084] y (n-2) The gyroscope data output in the first two moments;

[0085] W0 is the normalized angular frequency,

[0086] r is the notch filter pole radius,

[0087] The notch filter uses a second-order IIR infinite impulse response notch filter, which uses repeated recursive iterative calculations on the data. It has low computational complexity and resource usage in the CPU and has good real-time performance.

[0088] Step 5: Connect the notch filter: Connect the designed notch filter to the servo control loop, cut off the original gyro signal loop, and filter out the resonant frequency in real time.

[0089] In step 5, a notch filter is connected to the loop as follows:

[0090] The designed notch filter is connected to the servo control loop, such as Figure 2 As shown, the original gyro signal feedback loop is cut off, and the notch filter is switched into the loop to filter out the resonant frequency component in real time and suppress the system oscillation caused by the resonant frequency.

[0091] Step 6: Repeat the iteration: If the frequency amplitude of the resonance point is detected to decrease and the system stability and accuracy are restored, the calculation is completed. Otherwise, repeat steps 3, 4, and 5 to detect and eliminate other resonance frequency points.

[0092] Step 6 is repeated iteratively as follows:

[0093] Monitor the amplitude change of the resonance frequency point in real time and dynamically adjust the filter Q value according to the downward trend. If the amplitude of the resonance frequency point drops by no less than 10dB compared with the initial detection result, the stable accuracy value is still greater than 3 times σ rms , there may be other resonant frequencies, meaning the system resonates at multiple frequencies. Repeat steps 3, 4, and 5, performing spectrum analysis and notch filter design, until all resonant frequencies are suppressed. In practice, the resonant frequency was extracted as 37Hz, with a quality factor of 10 and a bandwidth of 3.7. The amplitude of the resonant frequency decreased by approximately 20dB. Note that the amplitude suppression should not be too severe, as this will affect the dynamic response of the servo system.

Claims

1. A method for detecting and suppressing resonance of a two-axis photoelectric pod, characterized in that: The method comprises the following steps: S1. Electro-optical pod stability accuracy test: With the pod in gyro-stabilized control mode, a rocking platform is used to simulate external environmental disturbances to test the electro-optical pod's line-of-sight stability. By acquiring gyro signals in real time, the stability accuracy of the pod's azimuth and pitch axes in a non-resonant state is calculated, which serves as the threshold for determining whether resonance occurs. S2. Resonance state judgment: Real-time monitoring of the stability accuracy changes of the two axes of the pod. When the change of one axis exceeds the threshold, it is determined that the axis is in a resonance state; S3. Resonance spectrum analysis: In the resonance state, the gyro signal is subjected to multiple fast Fourier transforms to extract the resonance frequency characteristics, providing data support for subsequent notch filter design; S4. Adaptive notch filter design: Based on the extracted resonant frequency characteristics, the notch filter is adaptively designed to accurately suppress the resonant frequency; S5. Adaptive wave limiter connection: Connect the designed adaptive wave limiter to the servo control loop, cut off the original gyro signal loop, and filter out the resonant frequency in real time; S6. Real-time monitoring: Real-time monitoring of the amplitude change of the resonance frequency point, dynamic adjustment of the filter Q value according to the downward trend, if the amplitude of the resonance frequency point is significantly suppressed, the stable accuracy value is still greater than 3 times σ rms , it is considered that there are other resonant frequency points, and the process returns to step S3 and continues until all resonant frequency points are suppressed, σ rms is the RMS value of the stable accuracy.

2. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 1, characterized in that: Calculate the stability accuracy of the azimuth and pitch axes of the two-axis pod in the non-resonance state respectively by Carry out, σ rms is the RMS value of the stable accuracy, θ i is the integral angle increment value, and N is the number of sampling points.

3. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 2, characterized in that: ω i is the gyro angular velocity at the i-th moment, ω i-1 is the gyro angular velocity at the i-1th moment, f s is the gyro sampling frequency.

4. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 3, characterized in that: The threshold in step S2 is specifically 3 times σ rms .

5. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 4, characterized in that: The specific extraction of resonance frequency characteristics is: S51, data preprocessing: collect a set of gyro signals ω i (i=1, 2...N), preprocessing the gyro signal, wherein the preprocessing includes removing the DC component and performing windowing processing; S52, multiple fast Fourier transforms: performing M times of Fourier transform on the preprocessed gyro signal to obtain a complex spectrum value of the gyro signal; S53, calculate the average value of the complex spectrum value of the M-th Fourier transform to obtain the spectrum amplitude average value S54, spectrum resolution calculation: through Calculate the frequency resolution Δf and determine the frequency interval between each frequency point, f s is the sampling frequency, N is the number of sampling points; S55, Resonance frequency extraction: by calculating the average value of the spectrum amplitude Find the peak position of the spectrum, where the frequency point corresponding to the maximum amplitude is the resonant frequency f 共振 , f 共振 =k 最大 Δf,k 最大 is the index of the maximum value in the magnitude spectrum.

6. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 5, characterized in that: The adaptive wave limiter is specifically designed as follows: S61, set the bandwidth BW, quality factor Q and center frequency f of the limiter 中心 :f 中心 =f 共振 =BW·Q; S62, setting the differential formula of the wave limiter, the differential formula is: n =ω n -2cos(W0)ω (n-1) +ω (n-2) +2cos(W0)y (n-1) -r 2 y (n-2) , where ω n is the current input gyro data, ω (n-1) The gyro data input at the previous moment, ω (n-2) The gyro data input in the first two moments, y n is the current output gyro data, y (n-1) The gyroscope data output at the previous moment, y (n-2) The gyro data output in the first two moments, W0 is the normalized angular frequency, r is the notch filter pole radius, S63, the notch filter selects a second-order IIR infinite impulse response notch filter.

7. The method for detecting and suppressing resonance of a two-axis photoelectric pod according to claim 6, characterized in that: Specifically, the significant suppression of the amplitude of the resonance frequency point means that the amplitude of the resonance frequency point decreases by more than or equal to 10 dB compared with the initial detection result.

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