WO2022126684A1 - 一种基于激光多普勒测振仪的图像振动测量系统 - Google Patents

一种基于激光多普勒测振仪的图像振动测量系统 Download PDF

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WO2022126684A1
WO2022126684A1 PCT/CN2020/138051 CN2020138051W WO2022126684A1 WO 2022126684 A1 WO2022126684 A1 WO 2022126684A1 CN 2020138051 W CN2020138051 W CN 2020138051W WO 2022126684 A1 WO2022126684 A1 WO 2022126684A1
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vibration
image
phase
cameras
point
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PCT/CN2020/138051
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English (en)
French (fr)
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傅愉
张青川
缪泓
盛志鹏
郜泽仁
于起峰
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深圳大学
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Publication of WO2022126684A1 publication Critical patent/WO2022126684A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means

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  • the application belongs to the technical field of vibration measurement, and in particular relates to an image vibration measurement system based on a laser Doppler vibrometer.
  • Structural vibration has always been an important issue in structural design and health monitoring of various major projects.
  • sensors are usually attached to the measured object to achieve contact measurement of the measured object.
  • the contact measurement has problems such as low spatial resolution, difficulty in full-field measurement, and additional weight of the sensor.
  • An embodiment of the present application provides an image vibration measurement system based on a laser Doppler vibrometer, including: a vibration test platform, a Laser-Doppler Vibrometer (LDV), a stroboscopic light source, and a controller , at least 2 cameras and electronic equipment, the frame rate of the camera is lower than the vibration frequency of the object to be measured;
  • LDV Laser-Doppler Vibrometer
  • the vibration test platform is used to carry the measured object, and apply an exciting force to the measured object;
  • the LDV includes a demodulation circuit based on a Field-Programmable Gate Array (FPGA), the LDV is connected to the controller, and is used to collect the vibration signal of point p of the object to be measured, and pass the
  • the demodulation circuit of the FPGA performs frequency identification and phase identification on the p-point vibration signal, determines a trigger signal according to the obtained identification result, the preset phase interval and the preset periodic interval, and sends the trigger signal to the Sent by the controller, the p point is any point of the measured object, and the preset periodic interval is determined according to the frame rate of one camera in the at least two cameras and the vibration frequency of the p point;
  • FPGA Field-Programmable Gate Array
  • the controller is respectively connected with the LDV, the stroboscopic light source and the at least two cameras, and is used to trigger the stroboscopic light source to be the surface of the measured object within a preset time period according to the trigger signal lighting, and triggering the at least two cameras to perform a shooting operation;
  • the at least two cameras are respectively connected to the electronic device, and are used to photograph the measured object respectively, and respectively send a plurality of obtained images in different phases to the electronic device;
  • the electronic device is configured to determine a three-dimensional vibration measurement result of the measured object within one vibration period according to the multiple images in different phases respectively sent by the at least two cameras.
  • the electronic device is also connected to the LDV for receiving the vibration signal at point p and the identification signal collected by the LDV, and displaying the time domain waveform and the corresponding time domain waveform of the vibration signal at point p and the identification signal.
  • spectrum wherein the identification signal is a signal obtained after the FPGA demodulation circuit performs frequency and phase identification on the p-point vibration signal.
  • the electronic device is also used for:
  • the parameters when the LDV collects the vibration signal of the point p of the measured object include at least the following two items: sampling frequency and speed measurement range;
  • the electronic device determines the three-dimensional vibration measurement result of the measured object within one vibration period according to the multiple images in different phases respectively sent by the at least two cameras, it is specifically used to: :
  • the image under the previous phase is used as the reference image, and the image under the next phase of the previous phase is used as the target image;
  • the reference image is divided into N reference sub-regions by the same division method, and the target image is divided into N target sub-regions, where N is an integer greater than 0;
  • For each reference sub-region calculate the correlation between each of the target sub-regions and the reference sub-region respectively, and obtain the deformed position of the reference sub-region in the target image;
  • the three-dimensional deformation information of the measured object within one vibration period is determined.
  • the electronic device before the determining of the three-dimensional deformation information of the measured object within one vibration period, the electronic device is further used for:
  • the calibration image is an image obtained by photographing the moved calibration board one by one with the fixed at least 2 cameras, or, after the calibration board is fixed, the at least 2 cameras are fixed at different positions. The image obtained after the calibration plate is photographed;
  • the electronic device determines the three-dimensional deformation information of the measured object within one vibration period according to the deformed position of each of the reference sub-regions in the target image and the positional relationship between different cameras. , specifically for:
  • the deformed position of each of the reference sub-regions in the target image, and the positional relationship between different cameras determine the three-dimensionality of the measured object within one vibration period deformation information.
  • the LDV performs frequency identification and phase identification on the p-point vibration signal through the FPGA demodulation circuit, and when the trigger signal is determined according to the obtained identification result, the preset phase interval and the preset periodic interval, Specifically for:
  • the LDV performs frequency identification and phase identification on the p-point vibration signal through the FPGA demodulation circuit to obtain an identification result, and the identification result includes frequency information and phase information;
  • a trigger signal is determined according to the frequency information, the phase information after phase compensation, a preset phase interval, and a preset period interval.
  • the preset periodic interval is determined in the following manner:
  • the frame rate of the camera is higher than or equal to the vibration frequency of the p point, set the preset periodic interval to be greater than or equal to 1;
  • the frame rate of the camera is lower than the vibration frequency of the p point, the number obtained by comparing the vibration frequency of the p point with the frame rate of the camera and then rounding up is taken as the minimum period interval.
  • the periodic interval of is greater than or equal to the minimum periodic interval.
  • the electronic device is also used for:
  • the vibration test platform includes a signal generator, a vibration exciter, and an amplifier, and/or includes the signal generator, a piezoelectric ceramic sheet, and the amplifier.
  • the included angle between each of the at least two cameras and the surface of the measured object ranges from 20° to 80°.
  • the measured object by applying an exciting force to the measured object, the measured object can be in a vibrating state, so that the LDV can collect the p-point vibration signal of the measured object.
  • the demodulation circuit of the FPGA included in the LDV performs frequency identification and phase identification on the vibration signal at point p, and after obtaining the corresponding identification result, the trigger signal is determined in combination with the preset phase interval and the preset periodic interval, because the preset periodic interval It is determined according to the frame rate of one of the at least 2 cameras included in the image vibration measurement system based on the laser Doppler vibrometer (hereinafter referred to as the image vibration measurement system) and the vibration frequency of point p. Therefore, the trigger signal and the vibration frequency of the p point are determined.
  • the frame rate of the camera is related to the preset phase interval, so that at least two cameras included in the image vibration measurement system can capture the object to be measured according to the trigger signal, that is, each camera can obtain images in different phases, and also That is, by adjusting the trigger signal, it can be ensured that the camera whose frame rate is lower than the vibration frequency of the measured object (eg, lower than the frame rate required by the sampling theorem) can capture the vibrating measured object. Since the controller triggers the strobe light source according to the trigger signal to illuminate the surface of the object to be measured and triggers at least two cameras to perform shooting actions within a preset time period, the images captured by each camera have a certain brightness and a certain brightness. The image will be helpful for subsequent electronic equipment to process the image.
  • At least two cameras included in the image vibration measurement system will perform one shot, that is, among the multiple images of different phases processed by the electronic device, the number of images corresponding to each phase is greater than or equal to 2, therefore, after processing by electronic equipment, the three-dimensional vibration measurement result of the measured object within one vibration period can be obtained.
  • LDV has high time resolution characteristics, it can generate trigger signals with high time resolution characteristics, and because the camera can capture the information of each point of the measured object, that is, it has high spatial resolution characteristics , so that the final three-dimensional vibration measurement result can have both high temporal resolution characteristics and high spatial resolution characteristics.
  • FIG. 1 is a schematic structural diagram of an image vibration measurement system based on a laser Doppler vibrometer provided by an embodiment of the present application;
  • Fig. 2 is the time domain waveform schematic diagram of p-point vibration provided by the embodiment of the present application.
  • FIG. 3 is a schematic structural diagram of another image vibration measurement system based on a laser Doppler vibrometer provided by an embodiment of the present application;
  • FIG. 4 is a schematic diagram of a working sequence of two cameras provided by an embodiment of the present application.
  • references in this specification to "one embodiment” or “some embodiments” and the like mean that a particular feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the present application.
  • appearances of the phrases “in one embodiment,” “in some embodiments,” “in other embodiments,” “in other embodiments,” etc. in various places in this specification are not necessarily All refer to the same embodiment, but mean “one or more but not all embodiments” unless specifically emphasized otherwise.
  • Existing non-contact measurement methods for example, use a scanning laser Doppler vibrometer to measure the displacement or velocity information of each point in space with high precision point by point. Although it can measure one surface of the object to be measured, it sacrifices Time resolution.
  • Using a multi-point laser Doppler vibrometer to simultaneously measure the displacement or velocity information of a preset number of points in space has a high temporal resolution, but at most 20 points can be measured.
  • the vibration test method of 3D digital image correlation combined with high-speed imaging technology has the following disadvantages: (1) The high-speed camera system is expensive and requires the use of high-speed data acquisition cards, which greatly limits the use of digital image correlation technology in high dynamic vibration.
  • an embodiment of the present application provides an image vibration measurement system based on a laser Doppler vibrometer, through which measurement data with high temporal resolution and high spatial resolution can be obtained simultaneously .
  • FIG. 1 shows a schematic structural diagram of an image vibration measurement system based on a laser Doppler vibrometer provided by an embodiment of the present application. For the convenience of description, only parts related to the embodiment of the present application are shown:
  • the image vibration measurement system 1 based on the laser Doppler vibrometer includes a vibration test platform 11, a laser-Doppler vibrometer (LDV) 12 including a demodulation circuit of an FPGA, a stroboscopic light source 13,
  • the controller 14 has at least two cameras 15 and an electronic device 16 .
  • the frame rate of each camera 15 is lower than the vibration frequency of the object to be measured.
  • the vibration test platform 11 of the embodiment of the present application is used to carry the object to be measured, and to apply an exciting force to the object to be measured;
  • the object under test when an exciting force is applied to the object under test (or the object to be tested), the object under test will vibrate at a certain frequency.
  • speckle is sprayed on the surface of the object to be measured, so as to enhance the reflectivity of the surface of the object to be measured and improve the correlation of the collected images, that is, by spraying speckle on the surface of the object to be measured, the The surface features of the object to be measured are further beneficial to improve the analysis speed of subsequent analysis of the object to be measured.
  • the LDV 12 of the embodiment of the present application includes a demodulation circuit of an FPGA, and the LDV is connected to the controller 14 for collecting the vibration signal of point p of the measured object, and performing the vibration signal of the point p through the demodulation circuit of the FPGA.
  • Frequency identification and phase identification determine the trigger signal according to the obtained identification result, the preset phase interval and the preset periodic interval, and send the trigger signal to the controller 14, the p point is any point of the measured object,
  • the preset periodic interval is determined according to the frame rate of one of the at least two cameras and the vibration frequency of the p point.
  • the highest frequency to be collected should be less than half of the collection frequency to ensure that the actual frequency to be collected can be restored, for example, for the vibration of a certain point of the object in the experiment, the frequency should be much lower than the collection frequency of the collection device, such as The frequency of the vibrating object is 5000Hz, and the collection frequency needs to be at least 10000Hz. Therefore, in this embodiment, in order to obtain sufficient vibration signals collected in the time domain, the collection frequency of the LDV12 can be set to be 3 to 7 times or higher than the vibration frequency of the measured object. .
  • an LDV with an acquisition frequency of 160 MS/sec and a velocity measurement range of 0.1 mm/s to 5000 mm/s can be selected as the LDV12.
  • the measured object only observes vibrations of several thousand Hz and below.
  • the high time of the LDV12 The resolution can accurately obtain the vibration information of the p point.
  • the steady-state vibration of any system it can be expressed as:
  • u is the displacement of the system at time t
  • x, y, and z are the corresponding three-dimensional coordinates.
  • a i is the i-th order displacement mode under the frequency response The contribution ratio of , ⁇ i represents the i-th order natural frequency, and ⁇ i is the initial phase of vibration.
  • the laser Doppler vibrometer can well restore the vibration of the point, which can be expressed as the following form:
  • the controller 14 in the embodiment of the present application is respectively connected with the LDV 12 , the stroboscopic light source 13 and the at least two cameras 15 mentioned above, and is used to trigger the stroboscopic light source 13 to illuminate the surface of the object to be measured for a preset period of time according to the trigger signal , and trigger the at least two cameras 15 to perform a shooting operation.
  • the at least two cameras 15 in the embodiment of the present application may be common industrial cameras with a frame rate lower than that required by the sampling theorem, that is, the frame rates of the at least two cameras 15 in the embodiment of the present application may be 30-90 fps, and the shortest exposure
  • the time is 40us, and the flashing time of the general strobe light source 13 is about 1-1000us, that is, the frame rate of the camera is low.
  • one camera 15 can be selected from at least two cameras 15 in the image vibration measurement system.
  • the frame rate of the image vibration measurement system and the vibration frequency of the above point p determine the preset periodic interval.
  • the frame rate of any camera is selected to participate in the calculation of the preset periodic interval. If the frame rates of the cameras of the image vibration measurement system are not equal, the frame rate of the camera with the smallest frame rate is selected to participate in the calculation of the preset periodic interval.
  • the FPGA phase-shift digital circuit is realized according to the principle of circuit phase-locked loop.
  • the phase-locked circuit can be simply understood as: the system inputs a sine wave signal, and the phase-locked circuit can output a signal of the same frequency or phase as the input at the same time.
  • the output is a signal that is multiplied by the input and has a different phase.
  • It can also be programmed to generate a signal with a rising edge at intervals of several output signal cycles.
  • a rising edge is generated at intervals of several cycles, and a rising edge of different phases is generated at intervals of several cycles.
  • the rising edges of the input signal ⁇ /12, ⁇ /6, 3 ⁇ /12.... phase positions are generated sequentially at intervals of several (such as 3) cycles. This rising edge is It is the trigger signal of this embodiment.
  • a phase is determined in the vibration signal at point p every 3 cycles, and then a trigger signal is determined according to the determined phase (the time corresponding to the trigger signal is as shown in Figure 2 ). discrete points), wherein the interval between the currently determined phase and the last determined phase is the above-mentioned preset phase interval.
  • the triggering moment of the stroboscopic light source 13 is shown as a discrete point in FIG. 2 , and the triggering timing is realized by the demodulation circuit based on FPGA in the LDV.
  • the above-mentioned preset duration is equal to the flashing time of the stroboscopic light source. For example, if the flashing time of the stroboscopic flash source 13 is about 1-1000us, the above-mentioned preset duration is also 1-1000us. When the flashing time of the flash source 13 reaches the nanosecond level, the above-mentioned preset duration is also in the nanosecond level.
  • the motion blur of the object can be eliminated through the stroboscopic exposure of the stroboscopic flash source 13 , and the stroboscopic exposure according to this method can enable a camera with a minimum exposure time of 40us to collect images with a stroboscopic time length.
  • the at least two cameras 15 in this embodiment of the present application are respectively connected to the above-mentioned electronic device 16 , and are used to photograph the above-mentioned object to be measured according to the above-mentioned trigger signal, and respectively send a plurality of obtained images in different phases to the above-mentioned electronic device 16 . send;
  • the same camera 15 shoots according to the trigger signal, multiple images with different phases will be obtained.
  • the images captured by the above-mentioned different cameras of the measured object are images in the same phase. For example, if camera 1 and camera 2 are triggered by the same trigger signal, , the camera 1 will get image 1, the camera 2 will get image 2, and the phase of image 1 and image 2 are the same.
  • the electronic device 16 in this embodiment of the present application is configured to determine the three-dimensional vibration measurement result of the object to be measured within one vibration period according to the plurality of images in different phases respectively sent by the at least two cameras 15 .
  • the three-dimensional information of the object under test can be obtained according to at least two images obtained at the same time, and since the obtained object is related to the object under test Therefore, the corresponding three-dimensional vibration measurement result can be obtained after the electronic device 16 analyzes and calculates at least two images at the same time.
  • the phase corresponding to each trigger signal satisfies the phase corresponding to one cycle, after processing the image corresponding to each trigger signal, the three-dimensional vibration measurement result of the measured object in one vibration cycle can be obtained.
  • the measured object by applying an exciting force to the measured object, the measured object can be in a vibrating state, so that the LDV can collect the p-point vibration signal of the measured object. Then the demodulation circuit of the FPGA included in the LDV performs frequency identification and phase identification on the vibration signal at point p, and after obtaining the corresponding identification result, the trigger signal is determined in combination with the preset phase interval and the preset period interval.
  • the interval is determined according to the frame rate of one of the at least two cameras included in the image vibration measurement system based on the laser Doppler vibrometer (hereinafter referred to as the image vibration measurement system for short) and the vibration frequency of the p point, so that the trigger signal is It is related to the frame rate of the camera and the preset phase interval, so that at least two cameras included in the image vibration measurement system can capture the object to be measured according to the trigger signal, that is, each camera can obtain images in different phases. That is, by adjusting the trigger signal, it can be ensured that the camera whose frame rate is lower than the vibration frequency of the measured object (eg, lower than the frame rate required by the sampling theorem) can capture the vibrating measured object.
  • the senor triggers the strobe light source to illuminate the surface of the object to be measured and triggers at least two cameras to perform shooting actions within a preset period of time according to the trigger signal
  • the images captured by each camera have a certain brightness, and the images with a certain brightness
  • the image will facilitate the processing of the image by subsequent electronic devices. Because under one trigger signal, at least two cameras included in the image vibration measurement system will perform one shot, that is, among the multiple images of different phases processed by the electronic device, the number of images corresponding to each phase is greater than or equal to 2, therefore, after processing by electronic equipment, the three-dimensional vibration measurement result of the measured object within one vibration period can be obtained.
  • LDV since LDV has high time resolution characteristics, it can generate trigger signals with high time resolution characteristics, and because the camera can capture the information of each point of the measured object, that is, it has high spatial resolution characteristics , so that the final three-dimensional vibration measurement result can have both high temporal resolution characteristics and high spatial resolution characteristics.
  • the electronic device 16 in order to facilitate the user to view the time domain waveform of the current vibration signal at point p, is also connected to the LDV 12 for receiving the vibration signal at point p and the identification signal collected by the LDV 12, and displaying the above point p The time domain waveform and spectrum corresponding to the vibration signal and the above identification signal, wherein the identification signal is a signal obtained after the FPGA demodulation circuit performs frequency and phase identification on the vibration signal at point p.
  • the electronic device displays the time-domain waveform and spectrum corresponding to the vibration signal at point p and the identification signal, that is, the electronic device displays the time-domain waveform and spectrum corresponding to the vibration signal before and after phase locking at point p, which is convenient for the user to judge the current Whether there is an error in the measurement method, for example, when the time domain waveform is abnormal or the frequency spectrum is abnormal, the user can correct the image vibration measurement system in time, so as to ensure accurate measurement results.
  • the above-mentioned electronic device 16 is also used for:
  • the parameters include at least two of the following: sampling frequency and speed measurement range;
  • the electronic device can adjust the phase interval by interacting with the user, thereby ensuring the reconstructed image.
  • the time resolution of the sequence meets user requirements.
  • the above-mentioned electronic device determines the three-dimensional vibration measurement result of the above-mentioned object to be measured within one vibration period according to the above-mentioned multiple images in different phases respectively sent by the above-mentioned at least two cameras, it is specifically used for:
  • the two adjacent images in the above-mentioned multiple images in different phases sent by the same camera take the image in the previous phase as the reference image, and take the image in the next phase of the previous phase as the target image; use the same
  • the above-mentioned reference image is divided into N reference sub-areas according to the division method, and the above-mentioned target image is divided into N target sub-areas, and the above-mentioned N is an integer greater than 0; for each reference sub-area, each above-mentioned target sub-area is calculated respectively.
  • the correlation between the area and the above-mentioned reference sub-area obtain the position of the above-mentioned reference sub-area in the target image after deformation;
  • the three-dimensional deformation information of the measured object in one vibration period is the correlation between the area and the above-mentioned reference sub-area, obtain the position of the above-mentioned reference sub-area in the target image after deformation; The three-dimensional deformation information of the measured object in one vibration
  • image 1 and image 2 are two adjacent images.
  • image 2 and image 3 are two adjacent images.
  • Image 1 and Image 2 are used as the reference image and Image 2 is used as the target image.
  • the reference image is divided into 3*3 reference sub-regions (assuming the first reference sub-region, the second reference sub-region, the third reference sub-region, the fourth reference sub-region, and the fifth reference sub-region , the 6th reference sub-region, the 7th reference sub-region, the 8th reference sub-region, the 9th reference sub-region), then the same division method is used to divide the target image into 3*3 target sub-regions. , and then calculate the difference between the first reference subregion and the first, second, third, fourth, fifth, sixth, seventh, eighth, and ninth target subregions respectively.
  • the target sub-region with the highest correlation as the deformed region of the first reference sub-region that is, the position of the target sub-region with the highest correlation in the target image is the first reference sub-region after deformation. position in the target image.
  • the obtained The deformation information of the measured object in camera 1 and camera 2 is combined with the position information between camera 1 and camera 2 to obtain the depth information of the measured object, and then the three-dimensional deformation information of the measured object is obtained.
  • each reference image is usually divided into 20*20 or more reference sub-regions, and each The number of pixels contained in the region (or the target sub-region) is usually not more than 100, and the accuracy of the obtained correlation can be improved by subdividing the reference image.
  • the correlation of the reference sub-region and the target sub-region is calculated according to a correlation function.
  • the correlation function can be a least square distance correlation function, a cross-correlation function, a zero-mean normalized least squares distance correlation function, a zero-mean normalized cross-correlation function, etc.
  • the zero-mean normalized cross-correlation function is expressed as:
  • f(x, y) represents the gray value at the point (x, y) in the reference sub-region
  • g(x', y') represents the gray value at the point (x', y') in the target sub-region value
  • Represents the gray mean value of the target sub-region. is the deformation parameter
  • M is the radius of a reference subregion (or a target subregion).
  • the three-dimensional deformation of images in two adjacent phases can be obtained. If the balance position As a reference image, the extreme value position As the target image, the three-dimensional maximum amplitude can be obtained through the above process.
  • the above-mentioned electronic device before the above-mentioned determination of the three-dimensional deformation information of the above-mentioned measured object within one vibration period, the above-mentioned electronic device is further used for:
  • the above-mentioned calibration image is an image obtained by shooting the moved calibration plate one by one with the above-mentioned at least 2 cameras that have been fixed, or, after the above-mentioned calibration plate is fixed, the above-mentioned at least 2 cameras at different positions on the fixed above-mentioned calibration
  • the surface of the object to be measured is sprayed with speckles and then fixed on the vibration test platform 11, then each camera is fixed, and the image captured by the fixed camera as the calibration image is obtained by moving the calibration plate, or, by fixing the calibration plate, The calibration board is photographed by moving each camera to different positions, and the obtained image is used as the calibration image.
  • Zhang Zhengyou's calibration method to calculate the calibration parameters, extract each corner point of each calibration image in turn, and then calculate the internal and external parameters between the cameras according to the extracted corner points. For example, if the image vibration measurement system includes two cameras , the internal and external parameters of the binocular camera included in the image vibration measurement system are calculated.
  • the specific use is: At:
  • the deformed position of each of the reference sub-regions in the target image, and the positional relationship between different cameras determine the three-dimensional deformation information of the measured object in one vibration period.
  • the internal and external parameters of the camera can be accurately obtained, thereby making the subsequent three-dimensional deformation information determined according to the internal and external parameters of the camera more accurate.
  • the above-mentioned LDV12 performs frequency identification and phase identification on the above-mentioned p-point vibration signal through the FPGA demodulation circuit, and when determining the trigger signal according to the obtained identification result, the preset phase interval and the preset periodic interval, specifically use At:
  • the above-mentioned LDV12 performs frequency identification and phase identification on the above-mentioned p-point vibration signal through the FPGA demodulation circuit, and obtains an identification result, and the above-mentioned identification result includes frequency information and phase information;
  • the trigger signal is determined according to the frequency information, the phase information after phase compensation, the preset phase interval and the preset period interval.
  • the trigger signal can be determined after phase compensation is performed on the phase information obtained by identification, that is, by reducing the phase error, the determined trigger signal can be improved.
  • the accuracy of the signal thereby improving the temporal accuracy of the images captured by the camera.
  • the phase compensation can use the gradient prediction method and the extreme value prediction method.
  • the preset periodic interval is determined in the following manner:
  • the frame rate of the camera is higher than or equal to the vibration frequency of the above point p, set the above preset periodic interval to be greater than or equal to 1;
  • the frame rate of the camera is lower than the vibration frequency of point p
  • the number obtained by comparing the vibration frequency of point p with the frame rate of the camera and then rounding up is the minimum period interval, and the preset period interval is greater than or equal to this minimum period interval.
  • the vibration frequency of point p is f p
  • the frame rate of the camera is f c
  • the minimum period interval L Indicates rounding up
  • the above-mentioned electronic device 16 is also used for:
  • one vibration period of the measured object is determined according to the coordinate information of the image of the measured object in one vibration period obtained by different cameras, the positional relationship between the different cameras, and the internal and external parameters between the different cameras. 3D coordinate information inside.
  • the three-dimensional digital image correlation method is used to first obtain the two-dimensional displacement field and strain field information of the image obtained by each camera, and then combine the internal and external parameters between the cameras to obtain the three-dimensional displacement field and strain field information within a vibration period. .
  • the vibration test platform 11 includes a signal generator, a vibration exciter, and an amplifier, and/or includes the signal generator, a piezoelectric ceramic sheet, and the amplifier.
  • the exciter is suitable for the excitation force of medium and low frequency, such as the excitation force of the frequency below 500Hz;
  • the piezoelectric ceramic sheet is suitable for the excitation force corresponding to each frequency with a small amplitude.
  • the vibration test platform 11 can select different excitation forces, the measurement of the object to be measured after being excited by different excitation forces can be realized.
  • the included angle between each of the at least two cameras and the surface of the object to be measured ranges from 20° to 80°.
  • the angle formed between each camera and the surface of the object to be measured is set to be within 20° ⁇ 80°. Further, in order to facilitate subsequent acquisition of accurate depth information between cameras, the included angle between different cameras cannot be set to 0, that is, cannot be parallel.
  • the number of strobe light sources 13 and the number of cameras 15 may be the same or different. In some embodiments, the number of strobe light sources 13 is the same as the number of cameras 15 , for example, if the number of cameras 15 is 2, the number of the strobe light sources 13 is also 2, as shown in FIG. 3 .
  • the electronic device 16 is a computer, but in an actual situation, it can also be a device of other forms, which is not limited here.

Abstract

一种基于激光多普勒测振仪的图像振动测量系统（1），属于振动测量技术领域，包括：振动测试平台（11）、激光多普勒测振仪LDV（12）、频闪光源（13）、控制器（14）、至少2个相机（15）以及电子设备（16）。通过该图像振动测量系统（1），能够同时得到具有高时间分辨率特性和高空间分辨率特性的三维振动测量结果。

Description

一种基于激光多普勒测振仪的图像振动测量系统
本申请要求于2020年12月14日在中国专利局提交的、申请号为202011466568.4、发明名称为“一种基于激光多普勒测振仪的图像振动测量系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请属于振动测量技术领域，尤其涉及一种基于激光多普勒测振仪的图像振动测量系统。
背景技术
结构振动一直是各类重大工程结构设计及健康监测中的重要问题，目前，通常在被测物体上附加传感器实现对该被测物体的接触式测量。但接触式测量存在着空间分辨率不高、全场测量困难、传感器附加重量等问题。
随着激光、相机和计算机技术的发展，出现了一系列新的用于测量结构振动的非接触式测量方法，包括：利用多点激光多普勒测振仪同步测量空间上预设数量点的位移或者速度信息；利用扫描型激光多普勒测振仪逐点高精度测量空间上各个点的位移或者速度信息，并拟合成全场信息。但根据现有的非接触式测量方法获得的测量数据难以满足高动态变形全场测量的迫切需求。
技术解决方案
为解决上述技术问题，本申请实施例采用的技术方案是：
本申请实施例提供了一种基于激光多普勒测振仪的图像振动测量系统，包括：振动测试平台、激光多普勒测振仪(Laser-Doppler Vibrometer，LDV)、频闪光源、控制器、至少2个相机以及电子设备，所述相机的帧率低于被测物体的振动频率；
所述振动测试平台用于承载被测物体，并对所述被测物体施加激振力；
所述LDV包含基于现场可编程门阵列(Field-Programmable Gate Array，FPGA)的解调电路，所述LDV与所述控制器连接，用于采集所述被测物体的p点振动信号，并通过所述FPGA的解调电路对所述p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号，将所述触发信号向所述控制器发送，所述p点为所述被测物体的任一点，所述预设的周期间隔根据所述至少2个相机中一个相机的帧率以及所述p点的振动频率确定；
所述控制器分别与所述LDV、所述频闪光源以及所述至少两个相机连接，用于根据所述触发信号触发所述频闪光源在预设时长内为所述被测物体的表面照明，以及触发所述至少两个相机执行拍摄操作；
所述至少2个相机分别与所述电子设备连接，用于分别对所述被测物体进行拍摄，并分别将得到的多张不同相位下的图像向所述电子设备发送；
所述电子设备用于根据所述至少2个相机分别发送的所述多张不同相位下的图像，确定所述被测物体在一个振动周期内的三维振动测量结果。
可选地，所述电子设备还与所述LDV连接，用于接收所述LDV采集的p点振动信号和识别信号，并显示所述p点振动信号和所述识别信号对应的时域波形及频谱，其中，所述识别信号为所述FPGA解调电路对所述p点振动信号进行频率和相位识别后得到的信号。
可选地，所述电子设备还用于：
设定所述LDV采集所述被测物体的p点振动信号时的参数，所述参数包括以下至少两项：采样频率、速度测量范围；
接收用户发出的相位间隔调整指令，根据所述相位间隔调整指令调整所述振动测量系统的相位间隔，并向所述控制器发送作为预设相位间隔的所述相位间隔，所述控制器用于将所述预设相位间隔发送至所述LDV。
可选地，所述电子设备在根据所述至少2个相机分别发送的所述多张不同相位下的图像，确定所述被测物体在一个振动周期内的三维振动测量结果时，具体用于：
对同一相机发送的所述多张不同相位下的图像中相邻的2张图像：
将前一相位下的图像作为参考图像，将所述前一相位的后一个相位下的图像作为目标图像；
采用相同的划分方式将所述参考图像划分为N个参考子区域，以及，将所述目标图像划分为N个目标子区域，所述N为大于0的整数；
针对每个参考子区域，分别计算各个所述目标子区域与所述参考子区域的相关性，得到所述参考子区域经变形后在目标图像中的位置；
根据所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息。
可选地，在所述确定所述被测物体在一个振动周期内的三维变形信息之前，所述电子设备还用于：
获取标定图像，所述标定图像为已固定的所述至少2个相机逐个拍摄移动后的标定板得到的图像，或者，为所述标定板固定后，所述至少2个相机在不同位置对固定后的所述标定板进行拍摄得到的图像；
依次提取所述标定图像的各个角点，根据提取的各个角点计算所述至少2个相机的内外参数；
对应地，所述电子设备在根据所述各个所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息时，具体用于：
根据所述至少2个相机的内外参数、所述各个所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息。
可选地，所述LDV通过所述FPGA解调电路对所述p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号时，具体用于：
所述LDV通过所述FPGA解调电路对所述p点振动信号进行频率识别和相位识别，得到识别结果，所述识别结果包括频率信息和相位信息；
对所述相位信息进行相位补偿后，根据所述频率信息和相位补偿后的相位信息、预设的相位间隔以及预设的周期间隔确定触发信号。
可选地，若所述至少2个相机的帧率相等，则所述预设的周期间隔通过以下方式确定：
若相机的帧率高于或等于所述p点的振动频率，则设置所述预设的周期间隔大于或等于1；
若相机的帧率低于所述p点的振动频率，则将所述p点的振动频率与所述相机的帧率作比后再向上取整得到的数作为最小周期间隔，所述预设的周期间隔大于或等于所述最小周期间隔。
可选地，所述电子设备还用于：
确定所述被测物体在一个振动周期内的三维坐标信息、位移场信息以及应变场信息。
可选地，所述振动测试平台包括信号发生器、激振器和放大器，和/或，包括所述信号发生器、压电陶瓷片和所述放大器。
可选地，所述至少2个相机中的各个相机与所述被测物体的表面夹角范围是20°～80°。
有益效果
本申请实施例中，通过对被测物体施加激振力，能够使得该被测物体处于振动状态，进而使得LDV采集到被测物体的p点振动信号。该LDV包含的FPGA的解调电路对p点振动信号进行频率识别和相位识别，得到对应的识别结果后，结合预设的相位间隔以及预设的周期间隔确定触发信号，由于预设的周期间隔根据基于激光多普勒测振仪的图像振动测量系统(后续简称为图像振动测量系统)包括的至少2个相机中的一个相机的帧率以及p点的振动频率确定，因此，使得触发信号与相机的帧率、预设的相位间隔有关，进而使 得图像振动测量系统包括的至少2个相机能够根据触发信号实现对被测物体的拍摄，即每一个相机均能得到不同相位下的图像，也即，通过触发信号的调整，能够保证帧率低于被测物体的振动频率(如低于采样定理所需帧率)的相机实现对振动的被测物体的拍摄。由于控制器根据触发信号触发频闪光源在预设时长内为被测物体的表面照明及触发至少2个相机执行拍摄动作，因此，使得各个相机拍摄得到的图像具有一定的亮度，而具有一定亮度的图像将有利于后续电子设备对该图像的处理。由于在一个触发信号下，图像振动测量系统包括的至少2个相机均会执行一次拍摄，也即，电子设备进行处理的多张不同相位下的图像中，每个相位对应的图像的数量均大于或等于2，因此，经过电子设备的处理后，能够得到被测物体在一个振动周期内的三维振动测量结果。综上，由于LDV具有高时间分辨率特性，因此，通过其能够生成具有高时间分辨率特性的触发信号，且由于相机能够拍摄到被测物体的各个点的信息，即具有高空间分辨率特性，因此，使得最后得到的三维振动测量结果能够同时具有高时间分辨率特性和高空间分辨率特性。
附图说明
为了更清楚地说明本申请实施例中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍。
图1是本申请实施例提供的一种基于激光多普勒测振仪的图像振动测量系统结构示意图；
图2是本申请实施例提供的p点振动的时域波形示意图；
图3是本申请实施例提供的另一种基于激光多普勒测振仪的图像振动测量系统结构示意图；
图4是本申请实施例提供的2个相机的工作序列的示意图。
本发明的实施方式
以下描述中，为了说明而不是为了限定，提出了诸如特定系统结构、技术之类的具体细节，以便透彻理解本申请实施例。然而，本领域的技术人员应当清楚，在没有这些具体细节的其它实施例中也可以实现本申请。在其它情况中，省略对众所周知的系统、装置、电路以及方法的详细说明，以免不必要的细节妨碍本申请的描述。
应当理解，当在本申请说明书和所附权利要求书中使用时，术语“包括”指示所描述特征、整体、步骤、操作、元素和/或组件的存在，但并不排除一个或多个其它特征、整体、步骤、操作、元素、组件和/或其集合的存在或添加。
还应当理解，在本申请说明书和所附权利要求书中使用的术语“和/或”是指相关联列出的项中的一个或多个的任何组合以及所有可能组合，并且包括这些组合。
另外，在本申请说明书和所附权利要求书的描述中，术语“第一”、“第二”、“第三”等仅用于区分描述，而不能理解为指示或暗示相对重要性。
在本申请说明书中描述的参考“一个实施例”或“一些实施例”等意味着在本申请的一个或多个实施例中包括结合该实施例描述的特定特征、结构或特点。由此，在本说明书中的不同之处出现的语句“在一个实施例中”、“在一些实施例中”、“在其他一些实施例中”、“在另外一些实施例中”等不是必然都参考相同的实施例，而是意味着“一个或多个但不是所有的实施例”，除非是以其他方式另外特别强调。
实施例一：
现有的非接触式测量方法，比如，利用扫描型激光多普勒测振仪逐点高精度测量空间上各个点的位移或者速度信息，其虽然能够测量被测物体的一个面，但牺牲了时间分辨率。而利用多点激光多普勒测振仪同步测量空间上预设数量点的位移或者速度信息，其时间分辨率较高，但至多能够实现对20个点的测量。再例如，三维数字图像相关结合高速成像技术的振动测试方法，其具有以下缺点：(1)高速摄像系统价格昂贵，需要使用高速的数据采集卡，极大限制了数字图像相关技术在高动态振动测试领域的推广应用；(2)高速摄像系统随着帧率的提高，其空间分辨率随之降低，位深度一般仅支持8位，导致测量精度不高；(3)受限于相机的采用频率，难以测得高频率的振动变形和模态信息。以价格50万以下的高帧率连续采集图像的高速摄像系统为例，当帧率达到2万帧时，其分辨率仅128x128，甚至更低，难以满足空间分辨率需求；(4)振动物体往往有较高的运动速度，容易产生运动模糊，降低数字图像相关计算的精度。也即，在现有的非接触式测量方法中，具有高时间分辨率的测量数据和具有高空间分辨率的测量数据是存在矛盾的，而对于高频振动或高频变形这类高动态力学过程，既需要获得高时间分辨率(高频率)的测量数据，也需要获得高空间分辨率(全场密集点)的测量数据。为了解决上述技术问题，本申请实施例提供了一种基于激光多普勒测振仪的图像振动测量系统，通过该图像振动测量系统，能够同时获得高时间分辨率和高空间分辨率的测量数据。
图1示出了本申请实施例提供的一种基于激光多普勒测振仪的图像振动测量系统结构示意图，为了便于说明，仅示出了与本申请实施例相关的部分：
该基于激光多普勒测振仪的图像振动测量系统1包括振动测试平台11、包含FPGA的解调电路的激光多普勒测振仪(Laser-Doppler Vibrometer，LDV)12、频闪光源13、控制器14至少2个相机15以及电子设备16。其中，各个相机15的帧率低于被测物体的振动频率。
本申请实施例的振动测试平台11用于承载被测物体，并对上述被测物体施加激振力；
在本实施例中，当对被测物体(或待测试件)施加激振力后，该被测物体将会以一定 的频率振动。
在一些实施例中，将被测物体的表面喷涂散斑，以便增强被测物体表面的反射率，提高采集到的图像的相关性，即通过在被测物体的表面喷涂散斑，能够增加该被测物体的表面特征，进而有利于提高后续对被测物体进行分析的分析速度。
本申请实施例的LDV12包含FPGA的解调电路，该LDV与该控制器14连接，用于采集该被测物体的p点振动信号，并通过该FPGA的解调电路对该p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号，将该触发信号向该控制器14发送，该p点为该被测物体的任一点，该预设的周期间隔根据该至少2个相机中一个相机的帧率以及该p点的振动频率确定。
考虑到待采集的最高频率应小于采集频率的二分之一才能保证还原出待采集的实际频率，例如，对于实验中物体某一点的振动，其频率应远低于采集设备的采集频率，例如振动物体频率5000Hz，采集频率至少需要10000Hz，因此，本实施例中，为了保证得到时域采集充分的振动信号，可设置LDV12的采集频率是被测物体的振动频率的3～7倍或更高。
在本实施例中，可选择采集频率达到160MS/sec，速度测量范围在0.1mm/s～5000mm/s的LDV作为LDV12，被测物体一般只观测几千Hz及以下的振动，LDV12的高时间分辨率能够准确获取p点的振动信息。对于任意系统的稳态振动，其可表示为：
Figure PCTCN2020138051-appb-000001
其中，u为系统在t时刻的位移，x、y、z为对应的三维坐标。a i为该频率响应下第i阶位移模态
Figure PCTCN2020138051-appb-000002
的贡献比例，ω i表示第i阶固有频率，θ i为振动的初相位。
对于振动物体表面任意一点p，激光多普勒测振仪能很好地还原该点的振动，可以表示为以下形式：
Figure PCTCN2020138051-appb-000003
由此可得到参数a i，ω i，
Figure PCTCN2020138051-appb-000004
θ i，LDV测得p点振动的时域波形为图2中的正弦波所示。
本申请实施例的控制器14分别与LDV12、频闪光源13以及上述至少2个相机15连接，用于根据该触发信号触发该频闪光源13在预设时长内为该被测物体的表面照明，以及触发该至少两个相机15执行拍摄操作。
其中，本申请实施例的至少2个相机15可以为常见的低于采样定理所需帧率的工业 相机，即本申请实施例的至少2个相机15的帧率可以为30～90fps，最短曝光时间为40us，而一般的频闪光源13的闪光时间约为1～1000us，也即相机的帧率较低，此时，可从图像振动测量系统的至少2个相机15中选出一个相机15的帧率以及上述p点的振动频率确定预设的周期间隔，例如，若图像振动测量系统的各个相机的帧率均相等，则选出任一个相机的帧率参与预设的周期间隔的计算，若图像振动测量系统的各个相机的帧率不相等，则选出具有最小帧率的相机的帧率参与预设的周期间隔的计算。
其中，FPGA移相数字电路是根据电路锁相环原理实现的，锁相电路可以简单理解为：系统输入一个正弦波信号，锁相电路能同时输出一路与输入一样频率或相位的信号，也可以输出一路与输入为倍频且不同相位的信号，还可以通过编程生成间隔几个输出信号的周期就产生一个上升沿的信号。在本实施例中，当系统输入LDV12采集的p点振动信号后，间隔几个周期产生一个上升沿，间隔几个周期再产生一个不同相位的上升沿。例如，假设一个周期是0～2π，间隔几个(如3个)周期依次产生在输入信号π/12，π/6，3π/12....相位位置上的上升沿，这个上升沿即为本实施例的触发信号。
本实施例中，当预设的周期间隔为3时，每隔3个周期在p点振动信号中确定一个相位，进而根据确定的相位确定一个触发信号(触发信号对应的时刻如图2中的离散点所示)，其中，当前确定的相位与上一次确定的相位之间的间隔为上述的预设的相位间隔。
本实施例中，频闪光源13触发的时刻如图2中的离散点所示，触发时序由LDV内基于FPGA的解调电路实现。
在一些实施例中，上述的预设时长与频闪光源的闪光时间相等，例如，假设频闪光源13的闪光时间约为1～1000us，则上述的预设时长也为1～1000us，若频闪光源13的闪光时间达到纳秒级别，那么上述的预设时长也为纳秒级别。本实施例中，通过频闪光源13的频闪曝光能够消除物体的运动模糊，按此方法的频闪曝光，能使最低曝光时间40us的相机采集频闪时间长度的影像。
本申请实施例的至少2个相机15分别与上述电子设备16连接，用于分别根据上述触发信号对上述被测物体进行拍摄，并分别将得到的多张不同相位下的图像向上述电子设备16发送；
本实施例中，由于同一个周期中，不同触发信号对应不同的相位，因此，同一个相机15根据触发信号进行拍摄后，将得到多张不同相位下的图像。需要指出的是，不同相机被同一个触发信号触发后，上述不同相机对被测物体进行拍摄得到的图像为同一相位下的图像，例如，若相机1和相机2在被同一个触发信号触发后，该相机1将得到图像1，相机2将得到图像2，且图像1和图像2的相位相同。
本申请实施例的电子设备16用于根据至少2个相机15分别发送的上述多张不同相位下的图像，确定上述被测物体在一个振动周期内的三维振动测量结果。
本实施例中，由于采用至少2个相机15对被测物体进行拍摄，因此，根据同一时刻得到的至少2张图像能够得到该被测物体的三维信息，且由于得到的是与该被测物体的振动有关的图像，故通过电子设备16对同一时刻的至少2张图像进行分析计算后，能够得到对应的三维振动测量结果。当各个触发信号对应的相位满足一个周期所对应的相位，则对根据该各个触发信号所对应的图像进行处理后，能够得到被测物体在一个振动周期的三维振动测量结果。
本申请实施例中，通过对被测物体施加激振力，能够使得该被测物体处于振动状态，进而使得LDV采集到被测物体的p点振动信号。再该LDV包含的FPGA的解调电路对p点振动信号进行频率识别和相位识别，得到对应的识别结果后，结合预设的相位间隔以及预设的周期间隔确定触发信号，由于预设的周期间隔根据基于激光多普勒测振仪的图像振动测量系统(后续简称为图像振动测量系统)包括的至少2个相机中的一个相机的帧率以及p点的振动频率确定，因此，使得触发信号与相机的帧率、预设的相位间隔有关，进而使得图像振动测量系统包括的至少2个相机能够根据触发信号实现对被测物体的拍摄，即每一个相机均能得到不同相位下的图像，也即，通过触发信号的调整，能够保证帧率低于被测物体的振动频率(如低于采样定理所需帧率)的相机实现对振动的被测物体的拍摄。由于器根据触发信号触发频闪光源在预设时长内为被测物体的表面照明及触发至少2个相机执行拍摄动作，因此，使得各个相机拍摄得到的图像具有一定的亮度，而具有一定亮度的图像将有利于后续电子设备对该图像的处理。由于在一个触发信号下，图像振动测量系统包括的至少2个相机均会执行一次拍摄，也即，电子设备进行处理的多张不同相位下的图像中，每个相位对应的图像的数量均大于或等于2，因此，经过电子设备的处理后，能够得到被测物体在一个振动周期内的三维振动测量结果。综上，由于LDV具有高时间分辨率特性，因此，通过其能够生成具有高时间分辨率特性的触发信号，且由于相机能够拍摄到被测物体的各个点的信息，即具有高空间分辨率特性，因此，使得最后得到的三维振动测量结果能够同时具有高时间分辨率特性和高空间分辨率特性。
在一些实施例中，为了便于用户查看当前p点振动信号的时域波形，上述电子设备16还与LDV12连接，用于接收LDV12采集的上述p点振动信号和识别信号，并显示上述上述p点振动信号和上述识别信号对应的时域波形及频谱，其中，该识别信号为该FPGA解调电路对该p点振动信号进行频率和相位识别后得到的信号。
本实施例中，通过电子设备显示p点振动信号和识别信号对应的时域波形及频谱，即 通过电子设备显示p点锁相前后的振动信号对应的时域波形及频谱，便于用户判断当前的测量方法是否存在错误，比如，当时域波形异常或频谱异常时，用户能够及时对图像振动测量系统进行修正，从而能够保证得到准确的测量结果。
在一些实施例中，上述电子设备16还用于：
设定LDV12采集该被测物体的p点振动信号时的参数，该参数包括以下至少两项：采样频率、速度测量范围；
接收用户发出的相位间隔调整指令，根据上述相位间隔调整指令调整上述图像振动测量系统的相位间隔，并向上述控制器14发送作为预设相位间隔的上述相位间隔，所述控制器14用于将所述预设相位间隔发送至所述LDV12。
本实施例中，当相位间隔越小，其得到的重建后的图像序列的时间分辨率也越高，因此，电子设备通过与用户交互，实现对相位间隔的调整，进而能够保证重建后的图像序列的时间分辨率符合用户需求。
在一些实施例中，上述电子设备在根据上述至少2个相机分别发送的上述多张不同相位下的图像确定上述被测物体在一个振动周期内的三维振动测量结果时，具体用于：
对同一相机发送的上述多张不同相位下的图像中相邻的2张图像：将前一相位下的图像作为参考图像，将上述前一相位的后一个相位下的图像作为目标图像；采用相同的划分方式将上述参考图像划分为N个参考子区域，以及，将上述目标图像划分为N个目标子区域，上述N为大于0的整数；针对每个参考子区域，分别计算各个上述目标子区域与上述参考子区域的相关性，得到上述参考子区域经变形后在目标图像中的位置；根据上述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定上述被测物体在一个振动周期内的三维变形信息。
例如，假设图像振动测量系统的相机有2个，相机1分别获得与相位1、相位2、相位3对应的图像1、图像2和图像3，则图像1和图像2为相邻的2张图像，图像2和图像3为相邻的2张图像。以图像1和图像2这2张相邻的图像为例，则图像1作为参考图像，图像2作为目标图像。假设将参考图像划分为3*3个参考子区域(假设为第1个参考子区域、第2个参考子区域、第3个参考子区域、第4个参考子区域、第5个参考子区域、第6个参考子区域、第7个参考子区域、第8个参考子区域、第9个参考子区域)，则采用相同的划分方式，将目标图像也划分为3*3个目标子区域，再分别计算第1个参考子区域与第1个、第2个、第3个、第4个、第5个、第6个、第7个、第8个、第9个目标子区域的相关性，并将相关性最高的目标子区域作为第1个参考子区域变形后的区域，即相关性最高的目标子区域在目标图像中的位置即为第1个参考子区域经变形后在目标图像中 的位置。同理，对相机1的参考图像中的其他参考子区域(非第1参考子区域)执行类似的处理，以及对相机2的参考图像中的所有参考子区域也执行类似的处理后，得到被测物体在相机1和相机2的变形信息，再结合相机1和相机2之间的位置信息得到被测物体的深度信息，进而得到该被测物体的三维变形信息。当然，若相机1和相机2得到一个振动周期内的相位下的图像，那么最后将能够得到该被测物体在一个振动周期的三维变形信息。需要指出的是，上述将参考图像划分为3*3个参考子区域仅为一个示例，在实际情况中，每个参考图像通常划分为20*20或更多个参考子区域，每个参考子区域(或目标子区域)所包含的像素个数通常不超过100个，通过对参考图像进行细分，能够提高得到的相关性的精度。在一些实施例中，为了进一步提高得到的相关性的精度，则设置相邻参考子区域(或模板子区域)之间存在重叠的像素，即两个相邻参考子区域之间存在重叠的区域。
在一些实施例中，根据相关函数计算参考子区域和目标子区域的相关性。其中，相关函数可以是最小平方距离相关函数、互相关函数、零均值归一化最小平方距离相关函数、零均值归一化互相关函数等，其中零均值归一化互相关函数表达式为：
Figure PCTCN2020138051-appb-000005
其中，f(x，y)表示参考子区域内点(x，y)处的灰度值；g(x′，y′)表示目标子区域内点(x′，y′)处的灰度值；
Figure PCTCN2020138051-appb-000006
表示参考子区域的灰度平均值，
Figure PCTCN2020138051-appb-000007
表示目标子区域的灰度平均值。
Figure PCTCN2020138051-appb-000008
是变形参量，M是一个参考子区域(或一个目标子区域)的半径。
用上述三维数字图像相关的方法可以获得相邻两个相位下的图像的三维变形。如果将平衡位置
Figure PCTCN2020138051-appb-000009
作为参考图像，极值位置
Figure PCTCN2020138051-appb-000010
作为目标图像，则可通过上述过程获得三维最大振幅。
在一些实施例中，在上述确定上述被测物体在一个振动周期内的三维变形信息之前，上述电子设备还用于：
获取标定图像，上述标定图像为已固定的上述至少2个相机逐个拍摄移动后的标定板得到的图像，或者，为上述标定板固定后，上述至少2个相机在不同位置对固定后的上述标定板进行拍摄得到的图像；依次提取上述标定图像的各个角点，根据提取的各个角点计算上述至少2个相机的内外参数；
具体地，将被测物体表面喷涂散斑后固定至振动测试平台11上，再把各个相机固定， 通过移动标定板得到固定的相机拍摄的作为标定图像的图像，或者，通过把标定板固定，在移动各个相机到不同位置对标定板进行拍摄，得到的图像作为标定图像。在获取标定图像后，利用张正友标定法进行标定参数计算，依次提取各个标定图像的各个角点，再根据提取的角点计算相机之间的内外参数，例如，若图像振动测量系统包括2个相机，则计算该图像振动测量系统包括的双目相机的内外参数。
对应地，上述电子设备在根据上述各个上述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定上述被测物体在一个振动周期内的三维变形信息时，具体用于：
根据上述至少2个相机的内外参数、上述各个上述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定上述被测物体在一个振动周期内的三维变形信息。
本实施例中，由于在确定三维变形信息之前，先对相机进行标定，因此，能够准确得到相机的内外参数，进而使得后续根据相机的内外参数确定的三维变形信息更准确。
在一些实施例中，上述LDV12通过FPGA解调电路对上述p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号时，具体用于：
上述LDV12通过FPGA解调电路对上述p点振动信号进行频率识别和相位识别，得到识别结果，上述识别结果包括频率信息和相位信息；
对上述相位信息进行相位补偿后，根据上述频率信息和相位补偿后的相位信息、预设的相位间隔以及预设的周期间隔确定触发信号。
本实施例中，由于在进行相位识别时可能存在一定的误差，因此可通过对识别得到的相位信息进行相位补偿后，再确定触发信号，也即，通过减少相位的误差，来提高确定的触发信号的准确性，进而提高相机拍摄的图像在时间上的精确性。其中，相位补偿可采用梯度预测法和极值预测法等。
在一些实施例中，若上述至少2个相机的帧率相等，则上述预设的周期间隔通过以下方式确定：
若相机的帧率高于或等于上述p点的振动频率，则设置上述预设的周期间隔大于或等于1；
若相机的帧率低于上述p点的振动频率，则将上述p点的振动频率与上述相机的帧率作比后再向上取整得到的数作为最小周期间隔，上述预设的周期间隔大于或等于该最小周期间隔。
本实施例中，假设p点的振动频率为f p，相机的帧率为f c，且f p>f c，则最小周期间隔L：
Figure PCTCN2020138051-appb-000011
Figure PCTCN2020138051-appb-000012
表示向上取整，预设的周期间隔大于或等于L。例如，若f p＝150Hz，f c＝60Hz，则L＝3。
在一些实施例中，上述电子设备16还用于：
确定上述被测物体在一个振动周期内的三维坐标信息、位移场信息以及应变场信息。
本实施例中，根据被测物体在不同相机得到的一个振动周期内的图像的坐标信息、该不同相机之间的位置关系以及该不同相机之间的内外参数，确定该被测物体一个振动周期内的三维坐标信息。
本实施例中，利用该三维数字图像相关方法先获得每个相机获得图像的二维位移场、应变场信息，再结合上述相机间的内外参数获得一个振动周期内的三维位移场和应变场信息。
在一些实施例中，上述振动测试平台11包括信号发生器、激振器和放大器，和/或，包括上述信号发生器、压电陶瓷片和上述放大器。
其中，激振器适用于中低频的激振力，如500Hz以下频率的激振力；压电陶瓷片适用于振幅较小的各个频率所对应的激振力。
本实施例中，由于振动测试平台11可以选取不同的激振力，因此，能够实现对被不同激振力激振后的被测物体的测量。
在一些实施例中，上述至少2个相机中的各个相机与上述被测物体的表面夹角范围是20°～80°。
本实施例中，为了使得相机拍摄到包含更多被测物体的信息的图像，则设置每一个相机与被测物体的表面所形成的夹角落入20°～80°。进一步地，为了便于后续从相机之间得到准确的深度信息，则设置不同相机之间的夹角不能为0，即不能平行。
频闪光源13的数量与相机15的数量可以相同也可以不同。在一些实施例中，频闪光源13的数量与相机15的数量相同，例如，若相机15的数量为2，则该频闪光源13的数量也为2，如图3所示的另一种基于激光多普勒测振仪的图像振动测量系统结构示意图，在图3中，相机16的数量和频闪光源13的数量均为2，且每个相机16附近均有一个频闪光源13，通过这样设置，使得每个相机15都能拍摄到具有足够亮度的图像，其中，图3中的2个相机(假设为相机A和相机B)的工作序列如图4所示。需要指出的是，在图3中，电子设备16为计算机，在实际情况中，其也可以为其他形态的设备，此处不作限定。
本领域技术人员可以意识到，结合本文中所公开的实施例描述的各示例的单元及算法步骤，能够以电子硬件、或者计算机软件和电子硬件的结合来实现。这些功能究竟以硬件还是软件方式来执行，取决于技术方案的特定应用和设计约束条件。专业技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能，但是这种实现不应认为超出本申请的范围。
以上所述实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围，均应包含在本申请的保护范围之内。

Claims (10)

  1. 一种基于激光多普勒测振仪的图像振动测量系统，其特征在于，包括：振动测试平台、激光多普勒测振仪LDV、频闪光源、控制器、至少2个相机以及电子设备，所述相机的帧率低于被测物体的振动频率；
    所述振动测试平台用于承载被测物体，并对所述被测物体施加激振力；
    所述LDV包含基于现场可编程门阵列FPGA的解调电路，所述LDV与所述控制器连接，用于采集所述被测物体的p点振动信号，并通过所述FPGA的解调电路对所述p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号，将所述触发信号向所述控制器发送，所述p点为所述被测物体的任一点，所述预设的周期间隔根据所述至少2个相机中一个相机的帧率以及所述p点的振动频率确定；
    所述控制器分别与所述LDV、所述频闪光源以及所述至少两个相机连接，用于根据所述触发信号触发所述频闪光源在预设时长内为所述被测物体的表面照明，以及触发所述至少两个相机执行拍摄操作；
    所述至少2个相机分别与所述电子设备连接，用于分别对所述被测物体进行拍摄，并分别将得到的多张不同相位下的图像向所述电子设备发送；
    所述电子设备用于根据所述至少2个相机分别发送的所述多张不同相位下的图像，确定所述被测物体在一个振动周期内的三维振动测量结果。
  2. 如权利要求1所述的图像振动测量系统，其特征在于，所述电子设备还与所述LDV连接，用于接收所述LDV采集的p点振动信号和识别信号，并显示所述p点振动信号和所述识别信号对应的时域波形及频谱，其中，所述识别信号为所述FPGA解调电路对所述p点振动信号进行频率和相位识别后得到的信号。
  3. 如权利要求2所述的图像振动测量系统，其特征在于，所述电子设备还用于：
    设定所述LDV采集所述被测物体的p点振动信号时的参数，所述参数包括以下至少两项：采样频率、速度测量范围；
    接收用户发出的相位间隔调整指令，根据所述相位间隔调整指令调整所述振动测量系统的相位间隔，并向所述控制器发送作为预设相位间隔的所述相位间隔，所述控制器用于将所述预设相位间隔发送至所述LDV。
  4. 如权利要求1所述的图像振动测量系统，其特征在于，所述电子设备在根据所述至少2个相机分别发送的所述多张不同相位下的图像，确定所述被测物体在一个振动周期内的三维振动测量结果时，具体用于：
    对同一相机发送的所述多张不同相位下的图像中相邻的2张图像：将前一相位下的图像作为参考图像，将所述前一相位的后一个相位下的图像作为目标图像；
    采用相同的划分方式将所述参考图像划分为N个参考子区域，以及，将所述目标图像划分为N个目标子区域，所述N为大于0的整数；
    针对每个参考子区域，分别计算各个所述目标子区域与所述参考子区域的相关性，得到所述参考子区域经变形后在目标图像中的位置；
    根据所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息。
  5. 如权利要求4所述的图像振动测量系统，其特征在于，在所述确定所述被测物体在一个振动周期内的三维变形信息之前，所述电子设备还用于：
    获取标定图像，所述标定图像为已固定的所述至少2个相机逐个拍摄移动后的标定板得到的图像，或者，为所述标定板固定后，所述至少2个相机在不同位置对固定后的所述标定板进行拍摄得到的图像；
    依次提取所述标定图像的各个角点，根据提取的各个角点计算所述至少2个相机的内外参数；
    对应地，所述电子设备在根据所述各个所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息时，具体用于：
    根据所述至少2个相机的内外参数、所述各个所述参考子区域经变形后在目标图像中的位置以及不同相机之间的位置关系，确定所述被测物体在一个振动周期内的三维变形信息。
  6. 如权利要求1所述的图像振动测量系统，其特征在于，所述LDV通过所述FPGA解调电路对所述p点振动信号进行频率识别和相位识别，根据得到的识别结果、预设的相位间隔以及预设的周期间隔确定触发信号时，具体用于：
    所述LDV通过所述FPGA解调电路对所述p点振动信号进行频率识别和相位识别，得到识别结果，所述识别结果包括频率信息和相位信息；
    对所述相位信息进行相位补偿后，根据所述频率信息和相位补偿后的相位信息、预设的相位间隔以及预设的周期间隔确定触发信号。
  7. 如权利要求1至6任一项所述的图像振动测量系统，其特征在于，若所述至少2个相机的帧率相等，则所述预设的周期间隔通过以下方式确定：
    若相机的帧率高于或等于所述p点的振动频率，则设置所述预设的周期间隔大于或等 于1；
    若相机的帧率低于所述p点的振动频率，则将所述p点的振动频率与所述相机的帧率作比后再向上取整得到的数作为最小周期间隔，所述预设的周期间隔大于或等于所述最小周期间隔。
  8. 如权利要求1至6任一项所述的图像振动测量系统，其特征在于，所述电子设备还用于：
    确定所述被测物体在一个振动周期内的三维坐标信息、位移场信息以及应变场信息。
  9. 如权利要求1至6任一项所述的图像振动测量系统，其特征在于，所述振动测试平台包括信号发生器、激振器和放大器，和/或，包括所述信号发生器、压电陶瓷片和所述放大器。
  10. 如权利要求1至6任一项所述的图像振动测量系统，其特征在于，所述至少2个相机中的各个相机与所述被测物体的表面夹角范围是20°～80°。
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