Precision measurement method for object surface out-of-plane displacement under high-frequency micro-vibration

Abstract

The invention discloses a precise measurement method for object surface out-of-plane displacement under high-frequency micro-vibration. The method comprises the following steps: exciting an object to generate high-frequency steady-state vibration through a vibration exciter, freezing a surface state at any vibration position of the object by adopting stroboscopic pulse laser with strictly same frequency as the vibration, and forming a shear speckle field by utilizing a Michelson interferometer comprising a piezoelectric ceramic driving phase-shifting mirror. The movement of the phase shift mirror and the acquisition of the high-speed camera as well as the actions of the stroboscopic laser and the vibration exciter are synchronously controlled through the double-signal controller, so that the accurate acquisition of multiple phase shift speckle interference images is realized. The image is processed based on a four-step phase shift algorithm, and the phase difference of the vibration position is calculated, so that the out-of-plane displacement derivative and the out-of-plane displacement in the shearing direction are calculated. According to the invention, the signal-to-noise ratio and the sensitivity of vibration measurement are obviously improved, and the method has full-field, non-contact and micro-nano displacement resolution capabilities, and is suitable for the fields of material nondestructive testing and structure health monitoring.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement and vibration analysis technology, specifically relating to a precision measurement method for the out-of-surface displacement of an object surface under high-frequency micro-vibration. Background Technology

[0002] Micro-vibration loading, as a non-contact and repeatable excitation method, is widely used in the fields of non-destructive testing of materials and structural health monitoring. Its basic principle is to induce high-frequency vibrations at the submicron or even micro-nano scale in the object under test through external excitation. If defects or damage exist in the structure, its vibration characteristics (such as resonant frequency and mode shapes) will undergo local changes, thereby enabling the identification and location of defects. In this type of application, precise measurement of the dynamic out-of-plane displacement and its spatial derivative on the object's surface under high-frequency vibration is crucial for accurately extracting defect characteristics and achieving quantitative assessment.

[0003] Existing measurement technologies generally face the following broader limitations: Optical measurement is the mainstream of non-contact high-precision measurement. Existing technologies, such as laser Doppler vibrometers, can achieve single-point accuracy at the nanometer level, but have low spatial resolution and struggle to capture full-field deformation. While visual measurement methods (such as those based on binocular stereo vision) offer high spatial resolution, their measurement accuracy is limited, making it difficult to meet the high-precision requirements at the micrometer / nanometer level. For example, CN110108348B is non-contact, has high spatial resolution, and can visualize micro-vibrations, but it is essentially an image grayscale analysis, with displacement measurement accuracy at the sub-millimeter level, far lower than the nanometer-level sensitivity of optical interferometry. Furthermore, it lacks phase information, making it impossible to directly provide quantitative out-of-plane displacement phase fields, hindering accurate modal analysis and quantitative defect assessment.

[0004] For minute vibrations that are not directly observable to the naked eye, operators find it difficult to determine and select the optimal measurement location. To obtain crucial data, it is often necessary to perform numerous repeated measurements at different locations on the object's surface, which is inefficient and difficult to implement.

[0005] Piezoelectric-based accelerometers are the most commonly used vibration measurement devices, but they require contact with the object being measured. For example, the HK1205628A requires two integrations of the acceleration to acquire the displacement signal, resulting in inherent signal processing lag and distortion. Furthermore, they have high requirements for the operating environment and operator skills, making widespread deployment in industrial settings difficult. In addition, while methods like the CN118790683A capacitance sensing are non-contact, they typically involve single-point measurements, making full-field analysis challenging.

[0006] Currently, laser speckle interferometry has become one of the main methods for measuring dynamic out-of-plane displacement due to its advantages such as full-field, non-contact, and high sensitivity. Among them, time-averaged shear speckle interferometry is a commonly used technique for non-destructive evaluation of vibrating objects. This method acquires a large number of speckle images of the object during its steady-state vibration period and performs time-averaging to obtain an interference fringe pattern related to the vibration amplitude gradient. The density of the fringes is proportional to the amplitude of the local vibration. When the excitation frequency is close to the resonant frequency of the defect, the abnormal vibration in the defect area will manifest as local distortion or concentration of the fringes. However, the time-averaging method is essentially an integral average of all random speckle signals within the vibration period. This process significantly reduces the signal-to-noise ratio and measurement sensitivity of the system, making it difficult to effectively extract the characteristics of weak vibration signals or early small defects, which is particularly evident when there is ambient light interference or when the object is in rigid body motion.

[0007] For example, CN118425159A also uses phase-shift shear speckle interferometry, but it mainly uses continuous laser illumination + vibration period time integral averaging, which cannot solve the problem of accurate capture and measurement of high-frequency micro-vibrations. CN114720998A is based on the laser Doppler principle and is a single-point measurement. It is suitable for steady-state simple harmonic motion and outputs a periodic average result, which cannot provide information on the full-field displacement distribution. The output of CN109357621B is a qualitative fringe pattern. Based on visual image analysis, the displacement measurement accuracy is usually at the sub-millimeter level, and it is difficult to directly obtain quantitative phase and displacement values.

[0008] To overcome the limitations of the time-averaging method, stroboscopic illumination technology has been introduced into shear speckle interferometry. Stroboscopic shear imaging utilizes short-pulse lasers synchronized with the object's vibration to "freeze" the transient state of the object's surface at specific phase points of vibration (such as the maximum positive displacement point and the maximum negative displacement point), thus transforming the dynamic measurement problem into a comparison of two or more quasi-static speckle fields. This method avoids signal attenuation caused by time integration, thus achieving higher signal-to-noise ratio and sensitivity. Furthermore, combining stroboscopic illumination with synchronously triggered phase-shifting technology allows for the rapid acquisition of multiple speckle patterns with fixed phase differences in each frozen state. A quantitative phase field is directly obtained through a phase extraction algorithm, and the out-of-plane displacement derivative is calculated. Integration yields the out-of-plane displacement, achieving a leap from qualitative fringe interpretation to quantitative phase measurement.

[0009] However, achieving synchronous precision measurement under high-frequency vibration in existing technologies still faces challenges: On the one hand, it is necessary to ensure strict timing synchronization and phase locking between the exciter, pulsed laser, phase shift mirror drive and high-speed camera acquisition, as any timing jitter will introduce measurement errors; on the other hand, while achieving high frame rate phase shift sampling, it is necessary to suppress the influence of slowly varying interferences such as environmental vibration and air disturbance on the stability of the interferometric field.

[0010] Among the existing technical solutions to address the aforementioned challenges, several patents have proposed their own approaches, each with its own scope of application and limitations. For example, in terms of synchronization control, patent CN118828228A combines a high-precision FPGA delay synchronizer with a piezoelectric drive platform to achieve micrometer-level alignment and nanosecond-level triggering of multiple cameras; patent CN117896611A focuses on adaptive phase synchronization processing of multiple data channels within a high-speed camera. These solutions emphasize synchronization at the electronic or mechanical level, but do not specifically address the system-level synchronization problem of the specific opto-mechanical-electric coupling process of "high-frequency micro-vibration excitation - stroboscopic laser freezing - phase shift interference acquisition". In terms of anti-interference, patent CN115839672A proposes adding an independent spectral domain interferometry system to the interferometric system to monitor and compensate for random phase shift errors caused by environmental disturbances in real time; patent CN118248114A utilizes piezoelectric metamaterials for active and passive vibration control to isolate the underlying vibration. The former increases the complexity and cost of the system's optical path, while the latter mainly deals with low-frequency overall vibrations and has limited ability to suppress high-frequency micro-interferences such as local air disturbances within the interference field.

[0011] In summary, existing technologies either focus on general synchronization and anti-interference methods or compensate for errors by adding subsystems. They lack an optimized design scheme that can deeply couple core components such as high-frequency excitation, stroboscopic illumination, and phase-shift interferometry to achieve integrated precision synchronization and anti-interference from the source. Therefore, how to construct a high-frequency micro-vibration out-of-plane displacement precision measurement system that is highly time-coordinated, robust to environmental interference, and easy to implement remains a pressing technical problem to be solved in this field. Summary of the Invention

[0012] To address the aforementioned problems in the existing technology, this invention provides a precise measurement method for the out-of-surface displacement of an object surface under high-frequency micro-vibration. The objective of this invention can be achieved through the following technical solution: A precision measurement method for out-of-plane displacement of an object surface under high-frequency micro-vibration includes: S1: Apply high-frequency steady-state micro-vibration excitation to the object under test through a vibrator; S2: The second signal controller controls the strobe laser to emit pulsed laser light at the same frequency as the vibration excitation, freezing the surface state when the object vibrates; S3: The scattered light from the surface of the object under test is received by a Michelson interferometer containing a phase-shifting mirror, forming a shear speckle interference field; S4: The first signal controller drives the phase shift mirror to move periodically and controls the high-speed camera to simultaneously acquire multiple phase shift speckle interference images; S5: Based on the phase-shifted speckle interferometry image, the phase difference of the vibration position is calculated using a phase extraction algorithm, and then the out-of-plane displacement derivative along the shear direction of the object surface is calculated. Finally, the out-of-plane displacement is obtained by integration. Among them, the out-of-plane displacement value of the maximum vibration deformation of the object surface is calculated based on the phase difference between the maximum positive displacement point and the maximum negative displacement point, and the out-of-plane displacement value of the vibration deformation at any vibration position is calculated by the phase difference between that vibration position and the stationary state.

[0013] Specifically, the first signal controller is connected to the driver and the high-speed camera respectively, and is used to issue a synchronous image acquisition control signal and a first drive control signal; the image acquisition control signal is used to control the high-speed camera to acquire images, and the first drive control signal is used to drive the piezoelectric ceramic to move the phase shift mirror continuously and periodically.

[0014] Specifically, the stroboscopic laser includes a laser controller and a stroboscopic laser; the excitation system includes a power amplifier and an exciter; the signal generator outputs a signal that controls the exciter through the power amplifier to give the object under test vibration excitation to produce surface deformation.

[0015] Specifically, the second signal controller is connected to the stroboscopic laser and the exciter respectively, and is used to issue a synchronous stroboscopic control signal and a second drive control signal. The stroboscopic control signal is used to control the drive of the stroboscopic laser to respond according to the frequency.

[0016] Furthermore, the second drive control signal is amplified by a power amplifier to drive the exciter.

[0017] Furthermore, the image acquisition control signal controls the high-speed camera to perform equal-interval sampling within a specific time window of the rising segment of the triangular wave signal.

[0018] Furthermore, within the specific time window, the high-speed camera performs four equally timed speckle interferometric image acquisitions within that interval, and the displacement of the phase-shifting mirror within the specific time window is three-eighths of the interference wavelength.

[0019] Specifically, the phase extraction algorithm for the out-of-plane displacement value of the maximum vibration deformation of the object surface adopts a four-step phase-shifting method; at the two states of the object's maximum positive displacement point and maximum negative displacement point, a complete four-step phase-shifting image acquisition and phase calculation process is executed once each, and the specific steps include: At the point of maximum positive displacement of the object's vibration, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at the point of maximum positive displacement of vibration, and the high-speed camera acquires four speckle interference images to obtain the phase distribution of the object at the point of maximum positive displacement of vibration. The pulse phase shift of the stroboscopic laser is 180° to freeze the surface state of the object at the point of maximum negative displacement of vibration. The high-speed camera then acquires four speckle interference images to obtain the phase distribution at the point of maximum positive displacement of vibration of the object. The phase difference generated by the maximum vibration deformation of the object is obtained by calculating the phase distribution at the point of maximum positive displacement and the point of maximum negative displacement of the object. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference, and the out-of-plane displacement of the maximum vibration deformation of the object is obtained by integration.

[0020] Specifically, the phase extraction algorithm for the out-of-plane displacement value of an object at any vibration position employs a four-step phase-shifting method. A complete four-step phase-shifting image acquisition and phase calculation process is executed once in each of the two states: before the object vibrates and deforms, and during the object vibrates and deforms at any vibration position. The specific steps include: The high-speed camera acquires four speckle interferometric images to obtain the phase distribution of the object in its static state before deformation. When the object is vibrating, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at any position of vibration deformation. The high-speed camera then acquires four speckle interference images to obtain the phase distribution at any position of vibration. The phase difference caused by vibration deformation at any position of the object is obtained by calculating the phase distribution of the object at rest and the phase distribution of the object at any position of vibration. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference. After integration, the out-of-plane displacement of the object at any position of vibration deformation is obtained.

[0021] Specifically, the method for calculating the out-of-plane displacement includes: Based on the four-step phase shifting method, the phase distribution of the object in the states of being at rest, vibrating at any position, at the point of maximum positive displacement, and at the point of maximum negative displacement is calculated from the acquired light intensity image. The mean is then filtered to obtain the filtered phase. The phase difference caused by vibration is calculated using the denoised phase value. Based on the phase difference, the out-of-plane displacement derivative is calculated according to the physical relationship between light wavelength and phase. After integration, the out-of-plane displacement is obtained.

[0022] Specifically, the exciter includes, but is not limited to, electromagnetic exciter or piezoelectric exciter, and can also achieve micro-vibration loading through mechanical excitation or audio excitation to adapt to the test objects of different materials, sizes and excitation requirements.

[0023] Specifically, the sampling frequency of the high-speed camera is at least twice the vibration excitation frequency to satisfy the Nyquist sampling theorem and ensure that the out-of-surface displacement information of the object surface can be accurately acquired.

[0024] The beneficial effects of this invention are as follows: This invention combines shear speckle interferometry with pulsed laser stroboscopic illumination to achieve precise measurement of surface displacement of an object under high-frequency micro-vibration. First, a high-frequency steady-state excitation is applied by an exciter, and a second signal controller ensures strict synchronization between the stroboscopic laser and the vibration excitation. This ensures precise freezing of the surface state at any vibration position, the point of maximum positive displacement, and the point of maximum negative displacement, avoiding signal-to-noise ratio loss caused by time-averaged integration and significantly improving the detection sensitivity of weak vibration signals. Second, a Michelson interferometer with a phase-shifting mirror is used to form a shear speckle interferometer field. Combined with the periodic movement of the phase-shifting mirror driven by the first signal controller and synchronous acquisition by a high-speed camera, multiple phase-shifting speckle interferometer images are rapidly acquired. In particular, the driving of the phase-shifting mirror and the equal-interval sampling strategy within a specific time window ensure the linearity of the phase shift and the synchronization of image acquisition, laying the foundation for the accuracy of subsequent phase extraction. Furthermore, based on a four-step phase-shifting algorithm, the phase difference between the vibration state and the reference state is calculated, enabling the calculation of the out-of-plane displacement derivative along the shear direction. Simultaneously, the out-of-plane displacement can be obtained through integration, providing richer information for analyzing the spatial distribution characteristics of vibration modes. In addition, key components of the system (exciter, stroboscopic laser, phase-shifting mirror, and high-speed camera) achieve multi-dimensional temporal coordination and phase locking through a dual-signal controller, effectively suppressing errors introduced by timing jitter. Simultaneously, it is compatible with both electromagnetic and piezoelectric exciters, adapting to the excitation needs of objects of different materials and sizes, thus improving the method's versatility. This method combines full-field non-contact measurement, high spatial resolution (micrometer and nanometer level) displacement sensitivity, and strong resistance to environmental interference, providing a reliable technical means for the quantitative assessment of high-frequency micro-vibration characteristics in fields such as non-destructive testing of materials and structural health monitoring. Attached Figure Description

[0025] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0026] Figure 1 This is a flowchart illustrating the method for precise measurement of surface displacement of an object under high-frequency micro-vibration according to the present invention. Figure 2 This is a block diagram showing the structural composition and signal connection of the measurement system in this invention; Figure 3 This is a schematic diagram showing the synchronization timing relationship between the camera, PZT phase shift drive, and excitation / stroboscopic movement in this invention. Figure 4 Comparison of shear speckle interferometry images obtained by different measurement methods: (a) time averaging method; (b) continuous laser four-step phase shift method; (c) the stroboscopic laser four-step phase shift method of the present invention. Detailed Implementation

[0027] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of example embodiments to those skilled in the art. Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring aspects of this disclosure. The blocks shown in the drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices. The flowcharts shown in the drawings are merely illustrative and do not necessarily include all contents and operations / steps, nor do they necessarily have to be performed in the order described. For example, some operations / steps can be broken down, while others can be combined or partially combined. Therefore, the actual execution order may change depending on the actual situation.

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0029] Please see Figure 1-4 A precision measurement method for the out-of-plane displacement of an object surface under high-frequency micro-vibration includes: S1: Apply high-frequency steady-state micro-vibration excitation to the object under test through a vibrator; S2: The second signal controller controls the strobe laser to emit pulsed laser light at the same frequency as the vibration excitation, freezing the surface state when the object vibrates; S3: The scattered light from the surface of the object under test is received by a Michelson interferometer containing a phase-shifting mirror, forming a shear speckle interference field; S4: The first signal controller drives the phase shift mirror to move periodically and controls the high-speed camera to simultaneously acquire multiple phase shift speckle interference images; S5: Based on the phase-shifted speckle interferometry image, the phase difference of the vibration position is calculated using a phase extraction algorithm, and then the out-of-plane displacement derivative along the shear direction of the object surface is calculated. Finally, the out-of-plane displacement is obtained by integration. The out-of-plane displacement value of the maximum vibration deformation of the object's surface is calculated based on the phase difference between the maximum positive displacement point and the maximum negative displacement point. The out-of-plane displacement value of the object's vibration deformation at any vibration position is calculated based on the phase difference between that vibration position and the stationary state.

[0030] In this embodiment, as Figure 2 As shown, the laser light shines at a near-perpendicular angle onto the surface of the target object. The resulting diffuse reflection enters the Michelson interferometer, while the sheared interference light strikes the CCD imaging target surface, forming a shear speckle interference field. The shear speckle interferometry system measures the gradient of the surface displacement of the object along the shear direction. When the surface of the target object deforms, the CCD camera records the light intensity information of the object surface before and after deformation.

[0031] Specifically, the first signal controller is connected to the driver and the high-speed camera respectively, and is used to issue a synchronous image acquisition control signal and a first drive control signal. The image acquisition control signal is used to control the high-speed camera to acquire images.

[0032] Specifically, the stroboscopic laser includes a laser controller and a stroboscopic laser; the excitation system includes a power amplifier and an exciter; the signal generator outputs a signal that controls the exciter through the power amplifier to give the object under test vibration excitation to produce surface deformation.

[0033] Specifically, the second signal controller is connected to the stroboscopic laser and the exciter respectively, and is used to issue a synchronous stroboscopic control signal and a second drive control signal. The stroboscopic control signal is used to control the drive of the stroboscopic laser to respond according to the frequency.

[0034] Furthermore, the second drive control signal is amplified by a power amplifier to drive the exciter.

[0035] Furthermore, the first drive control signal is used to drive the piezoelectric ceramic to move the phase shift mirror continuously and periodically.

[0036] Furthermore, the image acquisition control signal controls the high-speed camera to perform equal-interval sampling within a specific time window of the rising segment of the triangular wave signal.

[0037] Furthermore, within the specific time window, the high-speed camera performs four equally timed speckle interferometric image acquisitions within that interval, and the displacement of the phase-shifting mirror within the specific time window is three-eighths of the interference wavelength.

[0038] In this embodiment, the high-speed camera acquires four speckle interference images at four time points A, B, C, and D at equal time intervals within the middle 4t time period of the rising segment of the sinusoidal voltage signal with a period t, thereby obtaining the corresponding light intensity distribution I. A I B IC I D During the 4t time period, the displacement of the phase-shifting mirror is 3 / 8, which is the wavelength of the interference light. The 4t time period is less than the period T of the air disturbance or environmental vibration.

[0039] In this process, when the particle state is frozen at the point of maximum positive displacement of vibration, the high-speed camera acquires four speckle interference images at four time points A, B, C and D at equal time intervals within a 4t time period. The laser pulse phase shifts by 180°, and the stroboscopic illumination freezes the particle state at the point of maximum negative displacement of vibration. At this time, the high-speed camera acquires four speckle interference images again.

[0040] Specifically, the phase extraction algorithm for the out-of-plane displacement value of the maximum vibration deformation of the object surface adopts a four-step phase-shifting method; at the two states of the object's maximum positive displacement point and maximum negative displacement point, a complete four-step phase-shifting image acquisition and phase calculation process is executed once each, and the specific steps include: At the point of maximum positive displacement of the object's vibration, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at the point of maximum positive displacement of vibration, and the high-speed camera acquires four speckle interference images to obtain the phase distribution of the object at the point of maximum positive displacement of vibration. The pulse phase shift of the stroboscopic laser is 180° to freeze the surface state of the object at the point of maximum negative displacement of vibration. The high-speed camera then acquires four speckle interference images to obtain the phase distribution at the point of maximum positive displacement of vibration of the object. The phase difference generated by the maximum vibration deformation of the object is obtained by calculating the phase distribution at the point of maximum positive displacement and the point of maximum negative displacement of the object. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference, and the out-of-plane displacement of the maximum vibration deformation of the object is obtained by integration.

[0041] Specifically, the phase extraction algorithm for the out-of-plane displacement value of an object at any vibration position employs a four-step phase-shifting method. A complete four-step phase-shifting image acquisition and phase calculation process is executed once in each of the two states: before the object vibrates and deforms, and during the object vibrates and deforms at any vibration position. The specific steps include: The high-speed camera acquires four speckle interferometric images to obtain the phase distribution of the object in its static state before deformation. When the object is vibrating, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at any position of vibration deformation. The high-speed camera then acquires four speckle interference images to obtain the phase distribution at any position of vibration. The phase difference caused by vibration deformation at any position of the object is obtained by calculating the phase distribution of the object at rest and the phase distribution of the object at any position of vibration. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference. After integration, the out-of-plane displacement of the object at any position of vibration deformation is obtained.

[0042] Specifically, the method for calculating the out-of-plane displacement includes: Based on the four-step phase shifting method, the phase distribution of the object in the states of being at rest, vibrating at any position, at the point of maximum positive displacement, and at the point of maximum negative displacement is calculated from the acquired light intensity image. The mean is then filtered to obtain the filtered phase. The phase difference caused by vibration is calculated using the denoised phase value. Based on the phase difference, the out-of-plane displacement derivative is calculated according to the physical relationship between light wavelength and phase. After integration, the out-of-plane displacement is obtained.

[0043] The exciter includes, but is not limited to, electromagnetic exciters or piezoelectric exciters. It can also achieve micro-vibration loading through mechanical excitation or audio excitation to adapt to the test objects of different materials, sizes and excitation requirements.

[0044] Specifically, the sampling frequency of the high-speed camera is at least twice the vibration excitation frequency to satisfy the Nyquist sampling theorem and ensure that the out-of-surface displacement information of the object surface can be accurately acquired.

[0045] In this embodiment, as Figure 3 As shown, since the frequency of the camera trigger signal is several times or more than ten times that of the PZT phase shift drive signal, and the PZT phase shift drive signal is a triangular wave signal (replacing the step control signal in the prior art), it can ensure the precise measurement of the real-time phase.

[0046] Meanwhile, the frequency of the exciter and the stroboscopic laser is hundreds of times higher than the frequency of the camera trigger signal. Therefore, the stroboscopic laser has flashed hundreds of times within 4 seconds, without missing any deformation information of the object being tested.

[0047] The light intensity distribution of the four speckle patterns before the object vibrates and deforms is as follows: , , , , Among them, I A0 I B0 I C0 I D0 These represent the four equally spaced phase shift positions of the object before deformation in its stationary state, obtained through the four-step phase shift method. I0 is the average light intensity, μ is the modulation depth of the speckle field, and φ is the phase value. Calculate the random phase distribution of the object before vibration deformation based on the light intensity distribution of the object before deformation: , When the object vibrates and deforms at any position during vibration, repeat the four-step phase shift operation to obtain the phase distribution of the deformed object: , The phase difference Δφ generated by the vibration deformation of the object is obtained by calculating the random phase distribution before deformation and the phase distribution during vibration deformation. i ; At the point of maximum positive displacement of the object's vibration deformation, repeat the four-step phase shift operation to obtain the phase distribution at the point of maximum positive displacement of the object's vibration deformation: , The phase difference Δφ generated by the maximum positive displacement of the object's vibration deformation is obtained by calculating the random phase distribution before deformation and the phase distribution at the highest point of deformation vibration. j ; At the point of maximum negative displacement of the object's vibration deformation, repeat the four-step phase shift operation to obtain the phase distribution at the point of maximum negative displacement of the object's vibration deformation: , Based on the phase distribution at the point of maximum positive displacement and the phase distribution at the point of maximum negative displacement of the object's vibration deformation, the phase difference Δφ generated by the maximum vibration deformation of the object is obtained. k ; For φ0, φ i φ j φ k Mean filtering was performed to eliminate noise, and the following results were obtained: , , , This allows us to obtain the phase difference caused by deformation of the measured object at various times. , , The derivative of the out-of-plane displacement of an object's surface along the x-shear direction under high-frequency micro-vibration: , If shearing is performed along the y-direction, the derivative of the displacement from the surface is: , Where Δx and Δy are the shear values.

[0048] The out-of-plane displacement field of the object surface under high-frequency micro-vibration is obtained by Fourier transform integration. .

[0049] The derivative of the maximum vibration deformation of the object surface under high-frequency micro-vibration along the x-shear direction: , If shearing occurs along the y-direction, the derivative of the maximum vibration deformation out-of-plane displacement is: , Where Δx and Δy are the shear values.

[0050] The out-of-plane displacement field of the object surface under high-frequency micro-vibration is obtained by Fourier transform integration. .

[0051] like Figure 4 As shown, time averaging reduces the sensitivity of shear imaging. The proposed four-step phase-shift stroboscopic shearing method overcomes this limitation of the time-averaged shearing method. The abnormal field in the defect region of the object caused by vibration will be more obvious, the image will be clearer and the feature information will be more explicit. It is easier to identify the frequency and the characteristics of insensitivity to full-field measurement and rigid body motion, which will make the proposed method more practical in various industries.

[0052] Example 1: This embodiment provides a precision measurement system and method for out-of-plane displacement of an object surface under high-frequency micro-vibration. The system block diagram is shown below. Figure 2 As shown, it mainly includes: an excitation system, a stroboscopic laser illumination system, a shear speckle interferometric imaging system, and a synchronization control system.

[0053] Vibration excitation system: In this embodiment, it consists of a function signal generator (as a second signal controller), a power amplifier, and a vibrator. The function signal generator generates a sine wave signal (second drive control signal) that is consistent with the preset vibration frequency. After being amplified by the power amplifier, it drives the vibrator, thereby applying a high-frequency (e.g., 1kHz-20kHz), steady-state micro-vibration excitation to the object under test (such as composite material plates, turbine blades, etc.).

[0054] Stroboscopic laser illumination system: Composed of a single function signal generator, laser controller, and pulsed laser (stroboscopic laser). The function signal generator generates a TTL pulse signal (stroboscopic control signal) that is strictly synchronized and at the same frequency as the vibration excitation signal, and sends it to the laser controller to control the pulsed laser to emit short pulse lasers, precisely "freezing" the surface state of the object at the peaks and troughs of the vibration displacement.

[0055] The shear speckle interferometric imaging system, the core measurement unit, employs an optical path based on a Michelson interferometer. Scattered light returning from the surface of the object under test enters the interferometer and is split into two paths by a beam splitter: one path returns via a fixed mirror, and the other via a precisely movable phase-shifting mirror. The two paths rejoin and interfere. Due to a small lateral shearing factor δ, a shear speckle interference field is ultimately formed on the target surface of the high-speed CCD / CMOS camera. This system measures the gradient ∂w / ∂x of the out-of-surface displacement along the shear direction (x-direction) of the object's surface.

[0056] Phase shift mirror: mounted on a piezoelectric ceramic actuator, it can achieve linear displacement with nanometer-level precision by being driven by piezoelectric ceramic.

[0057] High-speed camera: used to acquire sequential speckle interferometry images.

[0058] Synchronization control system: contains two core synchronization control units.

[0059] The first synchronization control unit (first signal controller) is usually another signal generator or synchronization control card. It generates two synchronization signals: one is a triangular wave signal (first drive control signal) used to drive the piezoelectric ceramic, controlling the phase shift mirror to move continuously and periodically; the other is a camera trigger signal (image acquisition control signal), controlling the high-speed camera to perform exposure acquisition at specific moments.

[0060] Second synchronization control unit (second signal controller): namely the function signal generator mentioned above, which simultaneously controls the excitation and strobe lighting.

[0061] As an embodiment of the present invention, the specific steps for measuring the out-of-plane displacement of the maximum vibration deformation of the object surface are as follows: T max 1: Initial preparation and random phase acquisition of the static state.

[0062] Without activating the exciter, the random phase field of the object in its stationary state is first acquired. The first signal controller is activated, outputting a triangular wave to drive the phase-shifting mirror and triggering the high-speed camera. Within a specific time window (duration 4t, where t is the camera trigger period) of the rising phase of the triangular wave signal, the camera acquires four speckle patterns at equal time intervals (corresponding to phase shifts of 0, π / 2, π, and 3π / 2, respectively). During this period, the total displacement of the phase-shifting mirror is precisely controlled to 3λ / 8 (λ is the laser wavelength). According to the four-step phase-shifting method, the light intensity values ​​(IL, IL, IL) of these four images are used to determine the phase shift. A0 , I B0 , I C0 , I D0 The random phase distribution φ0 under static conditions can be calculated.

[0063] T max2: Vibration excitation and stroboscopic freezing are synchronized.

[0064] Turn on the excitation system and the stroboscopic laser system. The second signal controller ensures that the exciter and the pulsed laser operate at exactly the same frequency. Set the phase of the laser pulse to 0° so that it emits light when the object's vibration reaches its maximum positive displacement point, and freeze this state.

[0065] T max 3: Data acquisition of the state of the point of maximum positive displacement of vibration.

[0066] Under the synchronous control of the first signal controller, the high-speed camera repeats the above four-step phase shift acquisition process at the instant the laser freezes the point of maximum positive displacement of the vibration, obtaining a new set of four speckle images. Based on these images, the phase distribution φ at the point of maximum positive displacement of the vibration is calculated. j .

[0067] T max 4: Data acquisition of the state of the point of maximum negative displacement of vibration.

[0068] The second signal controller shifts the TTL pulse signal controlling the laser by 180°, causing the laser pulse to emit light when the object's vibration reaches its maximum negative displacement point, freezing this state. Maintaining the synchronization timing of the first signal controller, the high-speed camera acquires another set of four speckle images, and the phase distribution φ at the maximum negative displacement point of the vibration is calculated. k .

[0069] T max 5: Phase calculation and displacement information extraction.

[0070] For the three phase diagrams φ0, φ j , φ k After performing noise reduction processes such as mean filtering, a smoothed phase image is obtained.

[0071] Based on the principle of laser interference, the out-of-plane displacement derivative of the object surface along the shear direction under high-frequency vibration is calculated. By integration, the out-of-plane displacement (peak value - stationary) at the point of maximum positive displacement of the object vibration, the out-of-plane displacement (valley value - stationary) at the point of maximum negative displacement of the object vibration, and the out-of-plane displacement (peak value - valley value) at the point of maximum vibration deformation of the object surface are obtained respectively.

[0072] As an embodiment of the present invention, the specific steps for measuring the out-of-plane displacement of an object at any vibration position are as follows: T1: Initial preparation and random phase acquisition of the static state.

[0073] Without activating the exciter, the random phase field of the object in its stationary state is first acquired. The first signal controller is activated, outputting a triangular wave to drive the phase-shifting mirror and triggering the high-speed camera. Within a specific time window (duration 4t, where t is the camera trigger period) of the rising phase of the triangular wave signal, the camera acquires four speckle patterns at equal time intervals (corresponding to phase shifts of 0, π / 2, π, and 3π / 2, respectively). During this period, the total displacement of the phase-shifting mirror is precisely controlled to 3λ / 8 (λ is the laser wavelength). According to the four-step phase-shifting method, the light intensity values ​​(IL, IL, IL) of these four images are used to determine the phase shift. A0 , I B0 , I C0 , I D0 The random phase distribution φ0 under static conditions can be calculated.

[0074] T2: Vibration excitation and strobe phase setting.

[0075] The excitation system and the stroboscopic laser system are activated. The second signal controller ensures that the exciter and the pulsed laser are strictly synchronized. Based on the actual measurement requirements, the vibration phase angle θ corresponding to any position of the vibration to be measured is determined. The phase delay of the stroboscopic laser trigger pulse is adjusted by the second signal controller so that the laser pulse is emitted at the moment corresponding to the vibration phase angle, thereby "freezing" the surface state of the object at any position of the vibration.

[0076] T3: Vibration state data acquisition at any position.

[0077] Under the synchronous control of the first signal controller, the timing sequence of the phase-shifting mirror drive and camera acquisition remains unchanged. When the stroboscopic laser freezes the surface state at the vibration phase angle θ, the high-speed camera again executes the four-step phase-shifting acquisition process to obtain four speckle interference images at any position of the vibration, and calculates the phase distribution φ in this state. i .

[0078] T4: Comparison of the stationary phase diagram φ0 and the phase diagram φ at any position during vibration i After performing noise reduction processes such as mean filtering, a smoothed phase image is obtained. , This allows us to obtain the phase difference caused by deformation of the measured object at various times. , Based on this phase difference, and according to the principle of shear speckle interference, the derivative of the out-of-plane displacement along the shear direction of the object surface is calculated. The derivative of the out-of-plane displacement along the x-shear direction of the object surface under high-frequency micro-vibration is as follows: , If shearing is performed along the y-direction, the derivative of the displacement from the surface is: , Where Δx and Δy are the shear values.

[0079] By spatially integrating the derivative field, the out-of-plane displacement distribution of the object at any position during the vibration can be obtained. .

[0080] T5: Multi-location measurement and vibration process reconstruction.

[0081] By repeating steps T2 to T4 and changing the phase delay θ of the stroboscopic laser, the surface state at multiple different locations within the vibration cycle can be frozen and measured sequentially, thus obtaining a series of out-of-surface displacement distributions. By arranging and interpolating these displacement data in a temporal sequence, the dynamic out-of-surface displacement change process of the object throughout the entire vibration cycle can be reconstructed, achieving complete visualization and quantitative analysis of the vibration morphology.

[0082] The advantages of this invention are: High-precision synchronization: such as Figure 3 As shown, the camera trigger frequency is several to tens of times higher than the piezoelectric ceramic driving frequency, ensuring that a sufficient number of data points can be collected within one phase shift cycle. At the same time, the vibration frequency is hundreds of times higher than the camera frame rate. Combined with high-frequency strobe, this ensures that the object has been "frozen" by the laser hundreds of times within a single camera exposure window (4t), completely capturing the vibration information and avoiding motion blur.

[0083] Anti-environmental interference: The selected 4t data acquisition window is much smaller than the period T of typical environmental vibration and air disturbance, so that these slowly varying noises are approximated as static background in a single measurement and can be effectively suppressed by differential processing of the two vibration state phase diagrams.

[0084] High sensitivity and clear imaging: such as Figure 4 As shown in the comparison, (a) the time-averaged image is blurry and has low contrast; (b) the continuous laser phase-shifting method results in disordered stripes under vibration; (c) the image obtained by the stroboscopic laser synchronous phase-shifting method used in this invention is clear, the defect features (abnormal stripes in the figure) are obvious, and the signal-to-noise ratio and detection sensitivity are significantly improved.

[0085] Example 2: This embodiment is basically the same as Embodiment 1, except that the exciter and laser parameters are adapted for different test objects with different characteristics.

[0086] When the object being tested is a large metal structure, an electromagnetic vibrator is selected to apply excitation by taking advantage of its large output force and wide displacement range.

[0087] When the object being tested is a small, brittle ceramic or silicon wafer, a piezoelectric exciter or audio excitation method is selected to utilize its high frequency response and high resolution for precise excitation.

[0088] The output energy and pulse width of the pulsed laser can be adjusted based on the surface reflectivity and vibration amplitude of the object to obtain speckle images with optimal contrast on the camera.

[0089] The sampling frequency of the high-speed camera strictly follows the Nyquist sampling theorem and is set to be no less than twice the excitation frequency to ensure accurate acquisition of the vibration envelope signal.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A precision measurement method for the out-of-surface displacement of an object surface under high-frequency micro-vibration, characterized in that, include: S1: Apply high-frequency steady-state micro-vibration excitation to the object under test through a vibrator; S2: The second signal controller controls the strobe laser to emit pulsed laser light at the same frequency as the vibration excitation, freezing the surface state when the object vibrates; S3: The scattered light from the surface of the object under test is received by a Michelson interferometer containing a phase-shifting mirror, forming a shear speckle interference field; S4: The first signal controller drives the phase shift mirror to move periodically and controls the high-speed camera to simultaneously acquire multiple phase shift speckle interference images; S5: Based on the phase-shifted speckle interferometry image, the phase difference of the vibration position is calculated using a phase extraction algorithm, and then the out-of-plane displacement derivative along the shear direction of the object surface is calculated. Finally, the out-of-plane displacement is obtained by integration. Among them, the out-of-plane displacement value of the maximum vibration deformation of the object surface is calculated based on the phase difference between the maximum positive displacement point and the maximum negative displacement point, and the out-of-plane displacement value of the vibration deformation at any vibration position is calculated by the phase difference between that vibration position and the stationary state.

2. The method according to claim 1, characterized in that, The first signal controller is connected to the driver and the high-speed camera respectively, and is used to issue a synchronous image acquisition control signal and a first drive control signal; the image acquisition control signal is used to control the high-speed camera to acquire images, and the first drive control signal is used to drive the piezoelectric ceramic to move the phase shift mirror continuously and periodically.

3. The method according to claim 1, characterized in that, The stroboscopic laser includes a laser controller and a stroboscopic laser; the excitation system includes a power amplifier and an exciter; the signal generator outputs a signal that controls the exciter through the power amplifier to give the object under test vibration excitation to produce surface deformation.

4. The method according to claim 1, characterized in that, The second signal controller is connected to the stroboscopic laser and the exciter respectively, and is used to issue a synchronous stroboscopic control signal and a second drive control signal. The stroboscopic control signal is used to control the stroboscopic laser to respond according to the frequency, and the second drive control signal is amplified by the power amplifier to drive the exciter.

5. The method according to claim 2, characterized in that, The image acquisition control signal controls the high-speed camera to perform equal-time sampling within a specific time window during the signal rise phase; within the specific time window, the high-speed camera performs four equal-time speckle interference image acquisitions within that interval, and the displacement of the phase shift mirror within the specific time window is three-eighths of the interference wavelength.

6. The method according to claim 1, characterized in that, The phase extraction algorithm for the out-of-plane displacement value of the maximum vibration deformation of the object surface adopts a four-step phase-shifting method. At both the maximum positive displacement point and the maximum negative displacement point of the object vibration, a complete four-step phase-shifting image acquisition and phase calculation process is executed once each. The specific steps include: At the point of maximum positive displacement of the object's vibration, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at the point of maximum positive displacement of vibration, and the high-speed camera acquires four speckle interference images to obtain the phase distribution of the object at the point of maximum positive displacement of vibration. The pulse phase shift of the stroboscopic laser is 180° to freeze the surface state of the object at the point of maximum negative displacement of vibration. The high-speed camera then acquires four speckle interference images to obtain the phase distribution of the object at the point of maximum negative displacement of vibration. The phase difference generated by the maximum vibration deformation of the object is obtained by calculating the phase distribution at the point of maximum positive displacement and the point of maximum negative displacement of the object. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference, and the out-of-plane displacement of the maximum vibration deformation of the object surface is obtained by integration.

7. The method according to claim 1, characterized in that, The phase extraction algorithm for the out-of-plane displacement value of the object at any vibration position adopts a four-step phase-shifting method. A complete four-step phase-shifting image acquisition and phase calculation process is executed once in each of the two states: before the object vibrates and deforms, and when the object vibrates and deforms at any vibration position. The specific steps include: The high-speed camera acquires four speckle interferometric images to obtain the phase distribution of the object in its static state before deformation. When the object is vibrating, the pulse phase shift of the stroboscopic laser freezes the surface state of the object at any position of vibration deformation. The high-speed camera then acquires four speckle interference images to obtain the phase distribution at any position of vibration. The phase difference caused by vibration deformation at any position of the object is obtained by calculating the phase distribution of the object at rest and the phase distribution of the object at any position of vibration. The out-of-plane displacement derivative along the shear direction is calculated based on the phase difference. After integration, the out-of-plane displacement of the object at any position of vibration deformation is obtained.

8. The method according to claim 1, characterized in that, The method for calculating the out-of-plane displacement specifically includes: Based on the four-step phase shifting method, the phase distribution of the object at rest, at the point of maximum positive displacement and the point of maximum negative displacement, and at any position of vibration is calculated from the acquired light intensity image. The mean is then filtered to obtain the filtered phase. The phase difference caused by vibration is calculated using the denoised phase value. Based on the phase difference, the out-of-plane displacement derivative is calculated according to the physical relationship between light wavelength and phase. After integration, the out-of-plane displacement is obtained.

9. The method according to claim 1, characterized in that, The exciter includes, but is not limited to, electromagnetic exciters or piezoelectric exciters. It can also achieve micro-vibration loading through mechanical excitation or audio excitation to adapt to the test objects of different materials, sizes and excitation requirements.

10. The method according to claim 1, characterized in that, The sampling frequency of the high-speed camera is at least twice the vibration excitation frequency to satisfy the Nyquist sampling theorem and ensure that the out-of-surface displacement information of the object surface can be accurately acquired.

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