Laser vibrometer method and system with resistance to baseline drift based on synchronous carrier recovery

Abstract

The present invention discloses a laser vibrometer method and system with resistance to baseline drift based on synchronous carrier recovery, which relates to the field of laser vibrometer technology. The method comprises: theoretically analyzing the causes of baseline drift in the demodulated signal of a laser Doppler vibrometer system and identifying the key optical path components that cause baseline drift; improving the optical path of the laser Doppler vibrometer system based on the causes of baseline drift and the key optical path components, adding a reference arm to change the optical path transmission mode and recover the synchronous carrier signal; using the improved laser Doppler vibrometer system, using a high-speed analog-to-digital converter to collect the Doppler signal and synchronous carrier signal, and using a lookup table method to perform temperature-gain and offset compensation on the collected signals; and processing the compensated Doppler signal and synchronous carrier signal using an adaptive filtering algorithm based on error trends and an I&Q orthogonal demodulation algorithm to demodulate and extract the vibration signal. The present invention can effectively eliminate baseline drift in the demodulated signal.

Description

Technical Field

[0001] The present invention relates to the technical field of laser vibration measurement, and in particular to a laser vibration measurement method and system with anti-baseline drift based on synchronous carrier recovery. Background Art

[0002] Considering that the vibration characteristics of key components of large-scale equipment and precision instruments can reflect their structural state, secure connectivity, and overall reliability and integrity, measuring these vibration characteristics can effectively determine the operating status of key components. For example, in the aerospace field, to accurately adjust the eigenfrequency of engine turbine blades, it is necessary to measure the dynamic characteristics of the blades, usually by measuring the vibration of the blade surface. The solar sail of a spacecraft, as a key power source, is also a vulnerable component. To extend its service life, its vibration mode analysis is necessary. Furthermore, in the field of industrial manufacturing, ultrasonic vibration testing of key parts can achieve non-destructive testing, detect potential defects and deviations, and thus improve manufacturing quality and production levels.

[0003] Laser Doppler vibrometer technology is a typical non-contact vibration measurement method, widely used due to its advantages such as high precision, wide bandwidth, and long-range measurement. However, during the vibration demodulation process, due to various environmental factors and optical component errors, the demodulation results often exhibit significant baseline drift. Moreover, the slope of this baseline drift is not constant, but rather exhibits nonlinear changes over time. This baseline drift introduces a nonlinear bias into the vibration measurement results, affecting measurement accuracy. For weak vibration signals, baseline drift can even drown out these signals. Therefore, effectively eliminating baseline drift is crucial for improving the measurement accuracy of laser Doppler vibrometer.

[0004] In recent years, differential laser Doppler vibrometers have garnered extensive attention and research to improve the accuracy of laser Doppler vibrometers. The principle of differential laser Doppler vibrometers is to simultaneously emit a measurement beam and a reference beam. The measurement beam is directed onto the object being measured, while the reference beam is directed onto a stationary object in the same environment as the measurement beam. Because these two beams experience nearly identical environmental interference, interference effectively cancels out background noise. While differential laser Doppler vibrometers effectively eliminate environmental noise, they cannot eliminate baseline drift, which can significantly impact the accuracy of these measurements.

[0005] To this end, current research has proposed other methods to avoid baseline drift:

[0006] (1) By bypassing the optical path, the least squares method is directly applied to the demodulated vibration signal for linear fitting to remove the baseline drift. Although the least squares method is widely used in engineering practice due to its intuitive and convenient characteristics and clear mathematical formulas and solution methods, it still has the following defects: First, the linear fitting assumes that the baseline drift in the demodulation result is a linear feature. However, in actual engineering applications, when the baseline drift exhibits nonlinear behavior, the linear fitting method cannot effectively capture this nonlinear change, resulting in its limited applicability; Second, the premise of the least squares linear fitting is to first accumulate and store the demodulated signal for a period of time, and then perform the least squares calculation. This process has high requirements for storage and computing resources, especially in the resource-constrained laser vibration measurement demodulation lower computer system. This high requirement will seriously affect the real-time performance and efficiency of the system.

[0007] (2) Baseline drift is processed by ellipse fitting. Although the ellipse fitting method performs well in removing certain nonlinear baseline drifts, it is extremely sensitive to noise and is therefore not suitable for weak vibration signals. In addition, the algorithm complexity of the ellipse fitting method is often higher than that of the least squares method, making it difficult to implement in a low-computing-power lower-level laser vibrometer demodulation system. Summary of the Invention

[0008] To address the deficiencies of the above-mentioned prior art, the present invention provides a laser vibrometry method and system with resistance to baseline drift based on synchronous carrier recovery. Based on the principle of Doppler laser vibrometry, the generation mechanism of baseline drift in the I&Q orthogonal demodulation process is deeply explored, and on this basis, the optical path is improved to realize the recovery of the synchronous carrier. By using the synchronous carrier and the trend-based variable step-size normalized LMS (TBVSSLMS) adaptive filtering I&Q orthogonal demodulation algorithm, the baseline drift in the demodulated signal is effectively eliminated. Compared with the existing methods, the signal processing method proposed in the present invention is fast, simple, has low computing power requirements and high demodulation accuracy.

[0009] In a first aspect, the present invention provides a laser vibrometer method with resistance to baseline drift based on synchronous carrier recovery.

[0010] A laser vibrometer method with resistance to baseline drift based on synchronous carrier recovery, comprising:

[0011] For the laser Doppler vibrometer system, theoretically analyze the causes of baseline drift in the demodulated signal and identify the key optical path components that cause baseline drift;

[0012] According to the causes of baseline drift and key optical path components, the optical path of the laser Doppler vibrometer system was improved, and a reference arm was added to change the optical path transmission mode and restore the synchronous carrier signal.

[0013] The improved laser Doppler vibrometer system uses a high-speed analog-to-digital converter to collect Doppler signals and synchronous carrier signals, and a lookup table method is used to perform temperature-gain and offset compensation on the collected signals.

[0014] Based on the compensated Doppler signal and synchronous carrier signal, an adaptive filtering algorithm based on error trend and an I&Q orthogonal demodulation algorithm are used to process and demodulate and extract the vibration signal.

[0015] In a second aspect, the present invention provides a laser vibrometer system with resistance to baseline drift based on synchronous carrier recovery.

[0016] A laser vibrometer system with an anti-baseline drift capability based on synchronous carrier recovery, comprising:

[0017] Theoretical analysis module is used to theoretically analyze the causes of baseline drift in the demodulated signal of the laser Doppler vibrometer system and identify the key optical path components that cause baseline drift;

[0018] The synchronous carrier recovery optical path improvement module is used to improve the optical path of the laser Doppler vibrometer system based on the cause of baseline drift and key optical path components, add a reference arm to change the optical path transmission mode, and recover the synchronous carrier signal;

[0019] The signal acquisition and compensation module is used to collect Doppler signals and synchronous carrier signals using a high-speed analog-to-digital converter through an improved laser Doppler vibrometer system, and perform temperature-gain and offset compensation on the collected signals using a lookup table method;

[0020] The demodulation module is used to process the compensated Doppler signal and the synchronous carrier signal using an adaptive filtering algorithm based on an error trend and an I&Q orthogonal demodulation algorithm to demodulate and extract the vibration signal.

[0021] In a third aspect, the present invention further provides an electronic device comprising a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps of the method described in the first aspect are completed.

[0022] In a fourth aspect, the present invention further provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the steps of the method described in the first aspect.

[0023] One or more of the above technical solutions have the following beneficial effects:

[0024] 1. The present invention provides a laser vibrometer method and system with resistance to baseline drift based on synchronous carrier recovery. Based on the principle of Doppler laser vibrometer, the generation mechanism of baseline drift in the I&Q orthogonal demodulation process is deeply explored, and on this basis, the optical path is improved to realize the recovery of the synchronous carrier. By using the synchronous carrier and the adaptive variable step size normalized LMS adaptive filtering I&Q orthogonal demodulation algorithm based on the error trend, the baseline drift in the demodulated signal is effectively eliminated. Compared with the existing methods, the signal processing method proposed in the present invention is fast, simple, has low computing power requirements and high demodulation accuracy.

[0025] 2. In the proposed laser vibrometer method with anti-baseline drift based on synchronous carrier recovery, the causes of baseline drift in laser Doppler vibrometer demodulation are deeply analyzed. Through theoretical derivation and practical testing, it is determined that the crystal oscillator error of the acousto-optic modulator (AOM) causes the carrier signal frequency of the I&Q quadrature demodulation to be inconsistent with the AOM drive frequency, thereby causing baseline drift. On this basis, to address the problem of carrier signal asynchrony, an interferometer reference arm is added to the optical path. By changing the laser transmission path, this improvement can restore the synchronous carrier and effectively eliminate baseline drift. At the same time, temperature accuracy compensation technology is introduced to effectively alleviate the temperature drift and temperature gain error of the reference voltage of the high-speed analog-to-digital converter (ADC), thereby improving the acquisition accuracy of the Doppler signal and the synchronous carrier signal. Finally, an adaptive filtering and demodulation technology is proposed. The synchronous carrier signal is used to generate two orthogonal signals. The improved TBVSSLMS adaptive filtering technology is applied to filter out noise in the orthogonal signals, thereby significantly improving the accuracy of I&Q quadrature demodulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 This is an overall flow chart of the laser vibrometer method for resistant baseline drift based on synchronous carrier recovery according to an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the optical path of a traditional laser vibrometer system;

[0029] Figure 3 Schematic diagram of the optical path of the improved laser vibrometer system based on synchronous carrier recovery in an embodiment of the present invention;

[0030] Figure 4 Flowchart of the laser Doppler signal vibration demodulation algorithm in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary only and are intended to describe specific embodiments and provide further explanation of the present invention, and are not intended to limit the exemplary embodiments according to the present invention. Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] Example 1

[0033] This embodiment provides a baseline drift-resistant laser vibrometer method based on synchronous carrier recovery, which mainly includes the following four parts: (1) Baseline drift formation mechanism exploration: In-depth research on the source of baseline drift in the demodulated signal to determine the key optical path components that affect the optimization design; (2) Synchronous carrier recovery optical path design: Optimize the optical path design and realize the recovery of the synchronous carrier by introducing a reference arm interferometer optical path; (3) Temperature compensation acquisition system: A high-speed analog-to-digital converter (ADC) with temperature compensation function is used to acquire the modulated laser Doppler signal and the synchronous carrier signal to ensure the accuracy and reliability of the data; (4) Adaptive filtering and demodulation analysis: The laser Doppler signal is processed using the TBVSSLMS adaptive filtering I&Q orthogonal demodulation algorithm to extract the vibration signal to be measured. Finally, the demodulated signal is compared and analyzed with the original signal to be measured to evaluate the demodulation accuracy.

[0034] like Figure 1 As shown, the method proposed in this embodiment is introduced in more detail through the following content.

[0035] Step S1: Exploring the formation mechanism of baseline drift. In this step, for the laser Doppler vibrometer system, the causes of baseline drift in the demodulated signal are theoretically analyzed to determine the key optical path components that cause baseline drift.

[0036] Specifically, the voltage signal output by the balanced photodetector is the original Doppler signal, which can be expressed as:

[0037]

[0038] Where U s Indicates the signal amplitude, which is related to the optical field intensity of the measurement light and the reference light; f AOM represents the driving frequency of the AOM; The phase generated by the target vibration.

[0039] Two orthogonal I&Q signals are generated according to the driving frequency of the acousto-optic modulator. In practical applications, due to factors such as crystal oscillator error and environmental noise, the frequency of the two orthogonal carrier signals is f′.AOM , which will be consistent with the actual driving frequency f of the AOM AOM There is a certain deviation. Assume that the two carrier signals are:

[0040]

[0041] The generated carrier signal u′ i (t) and u′ q (t) are mixed with the Doppler signal u(t) to obtain:

[0042]

[0043] After low-pass filtering, the high-frequency components are removed and the low-frequency components are retained, and we get:

[0044]

[0045] Finally, after arc tangent demodulation, the final demodulation result is obtained for:

[0046]

[0047] It can be seen from the above formula (4) that due to the crystal oscillator error of the AOM and the environmental noise, the frequency f′ of the generated carrier is AOM and the shift frequency f of the AOM AOM There is a frequency difference, which leads to the superposition of an approximately linear baseline drift 2π(f AOM -f′ AOM )t. Furthermore, since electronic components undergo thermal drift, aging and other natural attenuation processes during operation, these phenomena lead to f AOM and f′ AOM The baseline drift will change slightly and continuously over time, so the slope of the baseline drift is 2π(f AOM -f′ AOM ) is not constant but evolves dynamically. Therefore, using simple linear fitting methods to estimate or predict baseline drift will inevitably introduce deviations. To more accurately capture and compensate for this non-constant trend, this embodiment adopts a more flexible and advanced baseline drift reduction method, namely, an improved synchronous carrier recovery optical path.

[0048] Step S2: Synchronous carrier recovery optical path design. In this step, based on the causes of baseline drift and key optical path components, the optical path of the laser Doppler vibrometer system is improved, a reference arm is added to change the optical path transmission mode, and the synchronous carrier signal is recovered.

[0049] Based on step S1 above, it can be seen that the fundamental reason for the deviation introduced by the linear fit is the frequency difference between the generated carrier frequency and the drive frequency of the AOM. Therefore, based on the above analysis results, this embodiment improves the optical path of a traditional laser vibrometer (also called a vibrometer system) by adding a reference arm and modifying the optical transmission method to recover the synchronous carrier signal.

[0050] Specifically, the optical path of a traditional laser vibrometer is as follows Figure 2 As shown, the improved optical path based on synchronous carrier recovery proposed in this embodiment is as follows Figure 3 As shown. Since optical fibers are easy to integrate and more convenient to adjust, this embodiment adopts an all-fiber solution. First, a polarization-maintaining narrow-linewidth laser with a central wavelength of 1550 nm is selected as the light source. This light source is then split into measurement light, a first reference light (reference light 1), and a second reference light (reference light 2) by a first beam splitter (i.e., beam splitter 1).

[0051] The measurement light enters the measuring arm, passes through the first attenuator (i.e., attenuator 1), enters through the first port (i.e., port 1) of the optical circulator, exits through the second port (i.e., port 2) of the optical circulator, and is then emitted to the surface of the vibrating object through the zoom collimator. Due to the vibration of the vibrating object, the light beam undergoes a Doppler frequency shift. The echo light carrying the Doppler modulation information is collected by the zoom collimator and then emitted through the third port (i.e., port 3) of the optical circulator.

[0052] The first reference light (i.e., reference light 1) enters the first reference arm and is first modulated by the acousto-optic modulator to generate a frequency shift of 40 MHz. The light beam is then divided into two paths by the second optical beam splitter (i.e., optical beam splitter 2). One path is adjusted in power by the second attenuator (i.e., attenuator 2), and then combined with the echo light emitted from the third port of the optical circulator by the first beam combiner (i.e., beam combiner 1). The combined light is filtered by the first bandpass filter and interferes with the first balanced photodetector to output a Doppler signal. The other path is emitted to the second beam combiner (i.e., beam combiner 2) of the second reference arm and is combined with the second reference light (i.e., reference light 2) whose power is adjusted by the third attenuator (i.e., attenuator 3). The combined light is filtered by the second bandpass filter (i.e., bandpass filter 2), and then interferes with the second balanced photodetector (i.e., balanced photodetector 2) to output a synchronous carrier signal. Preferably, the Doppler signal and the synchronous carrier signal are both acquired by a dual-channel ADC acquisition card for subsequent demodulation.

[0053] Step S3: Temperature compensation acquisition system. In this step, the improved laser Doppler vibrometer system uses a high-speed analog-to-digital converter to acquire Doppler signals and synchronous carrier signals, and a lookup table method is used to perform temperature-gain and offset compensation on the acquired signals.

[0054] In this embodiment, a high-speed analog-to-digital converter (ADC) is used to acquire the modulated laser Doppler signal and the synchronous carrier signal. However, temperature compensation is crucial because temperature changes can affect the ADC's reference voltage, input resistance, and operational amplifier performance, leading to issues such as gain and offset errors.

[0055] To improve the ADC's acquisition accuracy, this embodiment employs a lookup table method for temperature compensation. First, a digital temperature sensor is added around the high-speed analog-to-digital converter (ADC). This digital temperature sensor detects the ambient temperature around the converter in real time and feeds back real-time temperature information to the converter via the ADC's control circuit. Next, multiple experimental measurements are conducted to investigate and measure the relationship between the gain error and temperature, as well as the offset error, of the ADC's acquired signal data at different temperatures. After these multiple measurements, corresponding temperature-error characteristic curves are generated, and a data lookup table is constructed based on the curve data.

[0056] Based on the above-mentioned pre-constructed temperature-error characteristic curve and data lookup table, in actual applications, a high-speed analog-to-digital converter is used to collect Doppler signals and synchronous carrier signals, and the ambient temperature of the high-speed analog-to-digital converter detected by the temperature sensor is detected and read in real time. Then, according to the pre-constructed temperature-error characteristic curve, the measurement data is gain compensated and offset compensated through the lookup table to improve the final measurement accuracy.

[0057] Step S4: Adaptive filtering and demodulation analysis: In this step, based on the compensated Doppler signal and the synchronous carrier signal, an adaptive filtering algorithm based on error trend and an I&Q orthogonal demodulation algorithm are used to process and demodulate and extract the vibration signal.

[0058] Laser vibrometers typically use an I&Q quadrature demodulation algorithm for signal extraction. This algorithm relies heavily on the orthogonality of the I and Q signals. If the two signals are not completely orthogonal, the demodulation result will be distorted. In engineering applications, due to the presence of environmental noise and the inevitable loss of accuracy, the I and Q signals are not perfectly orthogonal. Some random noise may exist in the signals, which directly affects the demodulation accuracy. Currently, a commonly used adaptive filtering method with low computational complexity is the LMS algorithm (Least Mean Square Algorithm). Its algorithm update formula is as follows:

[0059] ω(n+1)=ω(n)+lr·e(n)·x(n) (6)

[0060] Where ω(n+1) and ω(n) represent the weight vectors at time n+1 and time n, respectively. The purpose of the LMS algorithm is to adjust the weight vector to minimize the output error. lr is the step size parameter, which determines the convergence speed and stability. e(n) represents the error at time n. x(n) represents the input vector at time n.

[0061] Existing LMS algorithms have certain problems: changes in the energy of the input signal can affect the selection of the optimal step size. Therefore, if the input signal amplitude changes significantly, the step size needs to be adjusted at all times, otherwise it may lead to instability or slow convergence. To this end, this embodiment proposes an adaptive variable step size normalized TBVSSLMS filtering algorithm based on error trends. This method dynamically adjusts the step size based not only on the error size but also on the trend of error changes. This method can achieve more stable convergence when the signal and noise vary more dramatically.

[0062] The TBVSSLMS filtering algorithm proposed in this embodiment introduces the observation of the error change trend and uses the trend coefficient to dynamically adjust the step size. That is, the step size is adjusted not only according to the absolute value of the error, but also considering the error change trend at multiple consecutive moments. This can further identify whether the signal change is drastic, ensuring that the step size is kept low in a relatively stable environment, and increasing the step size when there is a drastic change to quickly respond to the change. In the above TBVSSLMS filtering algorithm, the filter coefficient update step includes:

[0063] Step S4.1, calculate the error trend coefficient. Specifically, use the errors of the previous M moments and calculate the weighted average of all errors to calculate the error trend coefficient T(n), which is:

[0064]

[0065] The above trend coefficient T(n) reflects the severity of the error.

[0066] Step S4.2: Dynamic step size adjustment. Specifically, based on the error trend coefficient T(n) and the current error size |e(n)|, the dynamic step size is adjusted to:

[0067] lr(n+1)=lr(n)+α·T(n)·|e(n)| (8)

[0068] Among them, α is the adjustment factor, which is set according to actual conditions.

[0069] Step S4.3: Update filter coefficients. Specifically, the filter coefficients are updated using the dynamic step size lr(n) and the standard normalized LMS formula, which is:

[0070]

[0071] Where ||x(n)|| 2 It represents the sum of the squares of the input signal x(n) and is used to normalize the step size; σ is a bias term that prevents the denominator from being zero.

[0072] The TBVSSLMS algorithm is suitable for signal scenarios with irregular frequency variations and unstable amplitudes, such as dynamic noise elimination, communication signal demodulation in complex environments, and signal processing with strong interference in laser vibrometers. Using the TBVSSLMS filtering algorithm to process I and Q signals can effectively filter out environmental noise.

[0073] Furthermore, commonly used orthogonal demodulation algorithms include differential cross multiplication algorithm and inverse tangent algorithm. Since the differential cross multiplication algorithm involves derivative and integral operations, it is more sensitive to noise; while the mathematical operation process of the inverse tangent algorithm is relatively simple and has strong anti-interference ability, which is suitable for efficient and accurate demodulation processing scenarios. Therefore, this embodiment selects the inverse tangent demodulation algorithm for signal processing. The specific demodulation process is as follows: Figure 4 shown.

[0074] First, the dual-channel acquisition card is used to simultaneously acquire the Doppler signal and the synchronous carrier signal. Generating a set of orthogonal I&Q signals is the prerequisite for demodulation. Therefore, based on the compensated synchronous carrier signal sin(2πf AOM t), and generates another orthogonal carrier signal cos(2πf AOM t), the two orthogonal signals are adaptively filtered using TBVSSLMS and then mixed with the Doppler signal. The mixed signals are then passed through a low-pass filter to obtain the low-frequency component. Arc tangent calculation and phase unwrapping are then used to obtain a preliminary demodulated vibration signal. Downsampling technology is then used to reduce the amount of data required for signal processing. Finally, bandpass filtering and differential processing are performed to obtain the final demodulated vibration signal. Preferably, the final displacement, velocity, and acceleration demodulation results can be obtained at this point, which can be compared with the actual vibration signal to analyze the vibration measurement accuracy.

[0075] Through the above method, the synchronous carrier signal is restored, and by directly using the original synchronous carrier signal for mixing operations, the generation of baseline drift is effectively avoided during the demodulation process. Compared with the traditional linear fitting method to remove baseline drift, the method proposed in this embodiment completely eliminates the interference of baseline drift at the source, thereby ensuring the purity and higher accuracy of the demodulation result. In addition, the synchronous carrier recovery method bypasses the least squares linear fitting step, significantly reduces the occupancy of storage resources, and greatly shortens the calculation time. This method is of great significance in engineering applications.

[0076] Example 2

[0077] This embodiment provides a laser vibrometer system with anti-baseline drift based on synchronous carrier recovery, including:

[0078] Theoretical analysis module is used to theoretically analyze the causes of baseline drift in the demodulated signal of the laser Doppler vibrometer system and identify the key optical path components that cause baseline drift;

[0079] The synchronous carrier recovery optical path improvement module is used to improve the optical path of the laser Doppler vibrometer system based on the cause of baseline drift and key optical path components, add a reference arm to change the optical path transmission mode, and recover the synchronous carrier signal;

[0080] The signal acquisition and compensation module is used to collect Doppler signals and synchronous carrier signals using a high-speed analog-to-digital converter through an improved laser Doppler vibrometer system, and perform temperature-gain and offset compensation on the collected signals using a lookup table method;

[0081] The demodulation module is used to process the compensated Doppler signal and the synchronous carrier signal using an adaptive filtering algorithm based on an error trend and an I&Q orthogonal demodulation algorithm to demodulate and extract the vibration signal.

[0082] Example 3

[0083] This embodiment provides an electronic device, including a memory and a processor, and computer instructions stored in the memory and executed by the processor. When the computer instructions are executed by the processor, the steps of the laser vibrometer method for resistant baseline drift based on synchronous carrier recovery are completed.

[0084] Example 4

[0085] This embodiment further provides a computer-readable storage medium for storing computer instructions. When the computer instructions are executed by a processor, the steps of the laser vibrometer method for resistant baseline drift based on synchronous carrier recovery are completed as described above.

[0086] The steps involved in the above embodiments 2 to 4 correspond to those in the method embodiment 1. For detailed implementation, please refer to the relevant description of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media that includes one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry an instruction set for execution by a processor and cause the processor to perform any method of the present invention.

[0087] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0088] The above description is only a preferred embodiment of the present invention. Although the specific implementation of the present invention is described in conjunction with the accompanying drawings, it does not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

Claims

1. A laser vibrometer method with anti-baseline drift based on synchronous carrier recovery, characterized in that: include: For the laser Doppler vibrometer system, theoretically analyze the causes of baseline drift in the demodulated signal and identify the key optical path components that cause baseline drift; According to the causes of baseline drift and key optical path components, the optical path of the laser Doppler vibrometer system was improved, and a reference arm was added to change the optical path transmission mode and restore the synchronous carrier signal. The improved laser Doppler vibrometer system uses a high-speed analog-to-digital converter to collect Doppler signals and synchronous carrier signals, and a lookup table method is used to perform temperature-gain and offset compensation on the collected signals. Based on the compensated Doppler signal and synchronous carrier signal, an adaptive filtering algorithm based on error trend and an I&Q orthogonal demodulation algorithm are used to process and demodulate and extract the vibration signal. Among them, by adding a reference arm to improve the optical transmission mode, and then improve the laser Doppler vibrometer system, the synchronous carrier signal is restored, including: The light source is divided into a measuring light, a first reference light, and a second reference light by a first beam splitter; The measuring light enters the measuring arm, passes through the first attenuator, enters through the first port of the optical circulator, exits through the second port of the optical circulator, and is then emitted to the surface of the vibrating object through the zoom collimator. The vibration of the light beam produces a Doppler frequency shift, and the echo light carrying the Doppler modulation information is collected by the zoom collimator and then emitted through the third port of the optical circulator. The first reference light enters the first reference arm and is modulated by the acousto-optic modulator to generate a frequency shift. The light beam is then split into two paths by the second optical beam splitter. One path is adjusted in power by the second attenuator and then combined with the echo light emitted from the third port of the optical circulator through the first beam combiner. The combined light is filtered by the first bandpass filter and interferes with the first balanced photodetector to output a Doppler signal. The other path is emitted to the second beam combiner in the second reference arm and combined with the second reference light whose power has been adjusted by the third attenuator. The combined light is filtered by the second bandpass filter and interferes with the second balanced photodetector to output a synchronous carrier signal. Both the Doppler signal and the synchronous carrier signal are acquired by a dual-channel acquisition card.

2. The laser vibrometer method with anti-baseline drift based on synchronous carrier recovery according to claim 1, characterized in that: The cause of the baseline drift is that in the laser Doppler vibrometer system, the crystal oscillator error of the acousto-optic modulator and the environmental noise cause the carrier signal frequency of the I&Q orthogonal demodulation to be inconsistent with the acousto-optic modulator driving frequency, thereby causing the baseline drift; the key optical path component causing the baseline drift is the acousto-optic modulator.

3. The laser vibrometer method with anti-baseline drift based on synchronous carrier recovery according to claim 1, characterized in that: The acquired signal is compensated for temperature, gain, and offset using a lookup table method, including: A high-speed analog-to-digital converter is used to collect Doppler signals and synchronous carrier signals, and the ambient temperature around the high-speed analog-to-digital converter is detected and read in real time; Perform gain compensation and offset compensation on the collected signal data according to the pre-built temperature-error characteristic curve and data lookup table; The construction of the temperature-error characteristic curve and the data lookup table includes: A digital temperature sensor is added around the high-speed analog-to-digital converter, which is used to detect the ambient temperature around the high-speed analog-to-digital converter in real time and feed back real-time temperature information to the high-speed analog-to-digital converter; The relationship between the gain error, offset error and temperature of the signal data collected by the high-speed analog-to-digital converter at different temperatures is measured multiple times to generate the corresponding temperature-error characteristic curve, and a data lookup table is constructed based on the curve data.

4. The laser vibrometer method with anti-baseline drift based on synchronous carrier recovery according to claim 1, characterized in that: Based on the compensated Doppler signal and synchronous carrier signal, an adaptive filtering algorithm based on error trend and an I&Q orthogonal demodulation algorithm are used to process and demodulate the vibration signal, including: Based on the compensated synchronous carrier signal, another orthogonal carrier signal is generated through the Hilbert transformer. The two orthogonal carrier signals are adaptively filtered respectively using an adaptive filtering algorithm based on error trend. After filtering, they are mixed with the Doppler signal respectively. The mixed signal is filtered through a low-pass filter to obtain the low-frequency component, and then the initial demodulated vibration signal is obtained through inverse tangent calculation and phase unwrapping. After that, the final demodulated vibration signal is obtained through downsampling, bandpass filtering, and differential processing.

5. The laser vibrometer method with anti-baseline drift based on synchronous carrier recovery according to claim 4, characterized in that: In the adaptive filtering algorithm based on error trend, the step of updating the filter coefficients includes: Based on the errors of the previous M moments, the error trend coefficient is calculated by calculating the weighted average of all errors: Adjust the dynamic step size based on the error trend coefficient and the current error size; The filter coefficients are updated using the standard normalized LMS formula with a dynamic step size.

6. A laser vibrometer system with anti-baseline drift based on synchronous carrier recovery, characterized in that: include: Theoretical analysis module is used to theoretically analyze the causes of baseline drift in the demodulated signal of the laser Doppler vibrometer system and identify the key optical path components that cause baseline drift; The synchronous carrier recovery optical path improvement module is used to improve the optical path of the laser Doppler vibrometer system based on the cause of baseline drift and key optical path components, add a reference arm to change the optical path transmission mode, and recover the synchronous carrier signal; The signal acquisition and compensation module is used to collect Doppler signals and synchronous carrier signals using a high-speed analog-to-digital converter through an improved laser Doppler vibrometer system, and perform temperature-gain and offset compensation on the collected signals using a lookup table method; The demodulation module is used to process the compensated Doppler signal and the synchronous carrier signal using an adaptive filtering algorithm based on error trends and an I&Q orthogonal demodulation algorithm to demodulate and extract the vibration signal. Among them, by adding a reference arm to improve the optical transmission mode, and then improve the laser Doppler vibrometer system, the synchronous carrier signal is restored, including: The light source is divided into a measuring light, a first reference light, and a second reference light by a first beam splitter; The measuring light enters the measuring arm, passes through the first attenuator, enters through the first port of the optical circulator, exits through the second port of the optical circulator, and is then emitted to the surface of the vibrating object through the zoom collimator. The vibration of the light beam produces a Doppler frequency shift, and the echo light carrying the Doppler modulation information is collected by the zoom collimator and then emitted through the third port of the optical circulator. The first reference light enters the first reference arm and is modulated by the acousto-optic modulator to generate a frequency shift. The light beam is then split into two paths by the second optical beam splitter. One path is adjusted in power by the second attenuator and then combined with the echo light emitted from the third port of the optical circulator through the first beam combiner. The combined light is filtered by the first bandpass filter and interferes with the first balanced photodetector to output a Doppler signal. The other path is emitted to the second beam combiner in the second reference arm and combined with the second reference light whose power has been adjusted by the third attenuator. The combined light is filtered by the second bandpass filter and interferes with the second balanced photodetector to output a synchronous carrier signal. Both the Doppler signal and the synchronous carrier signal are acquired by a dual-channel acquisition card.

7. An electronic device, characterized in that: The invention comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps of the laser vibrometer method for resisting baseline drift based on synchronous carrier recovery are completed as claimed in any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that The device is used to store computer instructions, which, when executed by a processor, complete the steps of the laser vibrometer method for resisting baseline drift based on synchronous carrier recovery according to any one of claims 1 to 5.

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