A heterodyne laser Doppler vibration measurement device

Abstract

The present invention discloses a heterodyne laser Doppler vibration measurement device, comprising: an optical front-end module, comprising a lens and a laser, for generating laser through the laser, and emitting the laser to the outside through the lens; a subcarrier insertion module, connected between the optical front-end module and the object to be measured, comprising an ultrasonic transducer with a reflector, for receiving the laser emitted by the optical front-end module via the lens, reflecting the laser to the object to be measured, and reflecting the light diffusely reflected by the object to be measured back to the lens again; wherein the reflector vibrates at a predetermined frequency and a predetermined amplitude, and introduces a predetermined frequency and a predetermined amplitude optical path change in the vibration measurement optical path. The present invention can improve the signal-to-noise ratio of the modulated signal and increase the measurement distance under the condition that the lens aperture and the laser output power are limited.

Description

Technical Field

[0001] The invention relates to a vibration measuring device, in particular to a heterodyne laser Doppler vibration measuring device, and belongs to the technical field of optical precision measurement. Background Art

[0002] Laser vibration measurement technology is a non-contact vibration measurement technology. It is increasingly favored by various high-precision measurement fields due to its high accuracy, high sensitivity, and long measurement distance. It has been widely used in mechanical manufacturing, aerospace, micro-machining, construction and other fields. At present, the technologies based on laser vibration measurement mainly include: Doppler reference light vibration measurement technology, speckle method vibration measurement technology, Moire fringe method, holographic interferometry vibration measurement technology, etc.

[0003] Among them, the Doppler reference light vibration measurement technology is mainly realized by using optical heterodyne technology and optical Doppler effect, including heterodyne vibration measurement technology and homodyne vibration measurement technology. Homodyne vibration measurement technology does not require frequency shift processing of the reference light, eliminates the acousto-optic frequency shift device, and simplifies the optical system. However, due to the large system noise and interference in the optical system and the electrical system at the zero intermediate frequency, the anti-interference ability of homodyne vibration measurement technology is not as good as that of heterodyne vibration measurement technology. The working principle of heterodyne vibration measurement technology is to make the carrier frequencies of the two mutually interfering optical signals entering the photodetector different, and a difference frequency signal will be generated after interference. In order to improve the anti-interference ability of the measurement system, an acousto-optic modulator is usually used to pre-shift the signal light to a higher frequency, and the frequency shift frequency is usually 40MHz or 55MHz.

[0004] In the U.S. patent application “Tunable Optical Frequency Converter Based on a DopplerVibration Mirror” (US 2014 / 0327956 A1), the inventor proposed an adjustable frequency shift module based on a Doppler vibration mirror. The module uses a mirror and a small number of optical devices to achieve a large frequency conversion range, high frequency conversion efficiency and large output power. However, this technical solution only involves the optical frequency shift function and does not consider the vibration measurement function. In addition, in the Chinese patent application “A Pulsed Laser Heterodyne Doppler Vibration Measurement Structure” (CN 105043527 A), the inventor proposed using a pulse signal to control two acousto-optic modulators, and using two lenses to realize the reflection and reception of the laser respectively, so as to realize long-distance vibration measurement. However, this technical solution requires the use of two lenses, and it is difficult to focus when performing vibration measurement.

[0005] In summary, existing heterodyne laser vibration measurement devices will have carrier leakage signals to a certain extent due to the end face reflection of the optical device and the limited isolation of the circulator. The carrier leakage signal and the measurement signal completely overlap in the spectrum. When measuring at a long distance, the influence of the carrier leakage signal on the demodulation of the measurement signal mainly has three aspects: first, it reduces the signal-to-noise ratio of the measurement signal and shortens the measurement distance; second, it introduces nonlinearity when demodulating the signal; third, the vibration of the vibration measurement device locally will be modulated into the carrier leakage signal, further affecting the measurement accuracy. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a heterodyne laser Doppler vibration measuring device with an improved design.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A heterodyne laser Doppler vibration measuring device, comprising:

[0009] An optical front-end module, comprising a lens and a laser, for generating laser light through the laser and emitting the laser light to the outside through the lens;

[0010] A subcarrier insertion module is connected between the optical front-end module and the object to be measured, and includes an ultrasonic transducer with a reflector, which is used to receive the laser emitted by the optical front-end module via the lens, reflect the laser to the object to be measured, and reflect the light diffusely reflected by the object to be measured back to the lens again; wherein,

[0011] The reflector vibrates at a predetermined frequency and a predetermined amplitude, and introduces an optical path change of the predetermined frequency and the predetermined amplitude on the vibration measurement optical path.

[0012] Preferably, the ultrasonic transducer drives the reflector to vibrate at a predetermined frequency.

[0013] Preferably, the subcarrier insertion module further includes an ultrasonic signal source; the ultrasonic signal source is configured to generate an electrical signal of a predetermined frequency, and output the electrical signal to the ultrasonic transducer so that the ultrasonic transducer converts the electrical signal into ultrasonic vibration.

[0014] Preferably, the reflector is rigidly connected to the ultrasonic transducer and has an angle of 45 degrees with the axis of the lens.

[0015] Preferably, the heterodyne laser Doppler vibration measurement device further comprises: a signal processing module connected to the optical front-end module, comprising a power divider, an upper sideband filter, a lower sideband filter and a combiner; wherein,

[0016] The power divider is used to receive the intermediate frequency signal output by the optical front-end module, and distribute the power of the intermediate frequency signal to obtain two signals, one of which flows into the upper sideband filter, and the other flows into the lower sideband filter;

[0017] The combiner is used to combine the signal processed by the upper sideband filter and the signal processed by the lower sideband, and input them into a lower-level processing module.

[0018] Preferably, the signal processing module further includes an amplifier, an anti-aliasing filter, an analog-to-digital converter and an FPGA processor; wherein,

[0019] The amplifier is used to amplify the intermediate frequency signal output by the optical front-end module and transmit the amplified intermediate frequency signal to the power divider;

[0020] The anti-aliasing filter is used to receive the signal output by the combiner and perform anti-aliasing filtering on the output signal;

[0021] The analog-to-digital converter is used to receive the upper and lower sideband signals after the anti-aliasing process, and convert the upper and lower sideband signals after the anti-aliasing process from analog form to digital form;

[0022] The FPGA processor is used to demodulate the upper and lower sideband signals in the digital domain to obtain the vibration parameters of the object under test.

[0023] Preferably, the optical front-end module and the subcarrier insertion module are constructed of sound-absorbing or vibration-damping materials to prevent the ultrasonic signal from being picked up by the optical front-end module.

[0024] Compared with the prior art, the heterodyne laser Doppler vibration measurement device provided in the embodiment of the present invention adds a subcarrier insertion module to the optical path. The module introduces optical path changes of specific frequency and specific amplitude on the vibration measurement optical path. Such a design can improve the signal-to-noise ratio of the modulated signal and increase the measurement distance under the conditions of limited lens aperture and laser output power. Moreover, the design improves the linearity of the demodulation of the measurement signal, mainly because there is no nonlinear interference from the carrier leakage signal. In addition, the noise of the measurement signal is more stable than that of the traditional system, which is conducive to signal post-processing to further improve the accuracy. Furthermore, the influence of the local vibration of the vibration measurement device on the vibration signal of the target object is weakened, so there is no need to use dual optical path detection to suppress common-mode interference signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a working principle diagram of a heterodyne laser vibration measurement device in the prior art;

[0026] Figure 2It is a schematic diagram of a carrier leakage signal in the prior art;

[0027] Figure 3 A schematic diagram of the overall structure of a heterodyne laser Doppler vibration measurement device provided by an embodiment of the present invention;

[0028] Figure 4 Schematic diagram of the first kind of Bezier function curve.

[0029] Figure 5 FIG. 4 is a schematic diagram of a carrier leakage signal in an embodiment of the present invention.

[0030] Figure 6 Schematic diagram of the structure of a signal processing module in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1 As shown, in an example of the prior art, the heterodyne laser vibration measurement device includes a laser 101a, a beam splitter 102a, an acousto-optic modulator (AOM) 103a, a local oscillator 104a, a circulator 105a, a lens 106a, a beam combiner 107a, a photodetector 108a and a demodulator 109a. The laser output by the laser 101a is divided into two optical signals after passing through the beam splitter 102a, one for realizing the reference light and the other for realizing the measurement light. The measurement light is frequency shifted after passing through the acousto-optic modulator 103a. In order to realize the frequency shift function, the acousto-optic modulator requires the local oscillator 104a to provide an angular frequency of ω. c The frequency-shifted measurement light passes through the lens 106a and is irradiated on the surface of the vibrating object 110a to be measured, and then returns to the lens 106a after diffuse reflection. After the reflected light interferes with the reference light, it is converted by the photodetector 108a to obtain an intermediate frequency signal with modulated vibration parameters, and the angular frequency of the intermediate frequency signal is exactly ω c .

[0033] exist Figure 1 In the heterodyne laser vibration measurement device shown in the figure, in addition to the measurement light and the reference light, there is also leakage light with the same frequency as the measurement light. After the leakage light and the reference light interfere, they are converted by the photodetector to generate a carrier leakage signal. This carrier leakage signal is also called residual carrier, which is an unavoidable problem in heterodyne laser vibration measurement. Its main manifestation is the presence of a narrowband interference signal in the measurement signal, such as Figure 2There are two main reasons for the formation of carrier leakage signal: 1) the limited isolation of the circulator, that is, part of the measurement light directly leaks into the receiving optical path; 2) reflection from the end face of the optical device, such as the end face of the lens, the end face of the optical fiber, etc. Figure 1 shown.

[0034] The ideal intermediate frequency signal is a frequency modulated signal with constant amplitude. The basic principle of coherent demodulation is that the Doppler frequency shift signal can be obtained after orthogonal down-conversion, low-pass filter, phase solution, and differential. However, due to various non-ideal reasons, the actual intermediate frequency signal not only has a non-constant amplitude, but also has a carrier leakage interference signal. The formula for expressing the intermediate frequency signal under non-ideal conditions is as follows:

[0035] S total (t) = A sig (t)cos[ω c t+φ sig (t)]+A lk (t)cos[ω c t+φ lk (t)] (1)

[0036] Among them, A sig (t) is the amplitude of the measured signal changing with time, φ sig (t) is the Doppler phase, A lk (t) is the amplitude of carrier leakage, φ lk (t) is the phase of the carrier leakage. The I-channel signal and Q-channel signal obtained after orthogonal down-conversion and low-pass filtering of the intermediate frequency signal defined in formula 1 are shown in the following formulas (2) and (3):

[0037] I total (t) = A sig (t)cos[φ sig (t)]+A lk cos[φ lk ] (2)

[0038] Q total (t) = A sig (t)sin[φ sig (t)]+A lk sin[φ lk ] (3)

[0039] After phase demodulation, we get:

[0040]

[0041] When A sig (t)>>A lk When , the influence of the carrier leakage signal can be ignored, then:

[0042] Phase(t)≈φ sig (t) (5)

[0043] When A sig (t)< lk When , the influence of Doppler signal can be ignored, then:

[0044] Phase(t)≈φ lk (6)

[0045] From formula (4), we can see that the influence of the carrier leakage signal is mainly the introduction of nonlinear components in the phase demodulation process, which reduces the measurement accuracy. The maximum phase error Δφ sig (t) can be expressed by the following formula (7). According to formula (7), when the phase measurement accuracy is required to be less than 0.01π, the measured signal should be 30dB greater than the carrier leakage signal. However, in actual measurement, it is difficult to meet the above conditions. Therefore, it is generally necessary to estimate the leakage signal related parameters and compensate the measurement results accordingly.

[0046]

[0047] From the above analysis, it can be seen that heterodyne laser vibration measurement devices will have more or less carrier leakage signals due to the end face reflection of optical devices and the limited isolation of circulators. The carrier leakage signal and the measurement signal completely overlap in the spectrum. When measuring at a long distance, the influence of the carrier leakage signal on the demodulation of the measurement signal mainly has three aspects: first, it reduces the signal-to-noise ratio of the measurement signal and shortens the measurement distance; second, it introduces nonlinearity when demodulating the signal; third, the local vibration of the vibration measurement device will be modulated into the carrier leakage signal, further affecting the measurement accuracy.

[0048] In order to fundamentally solve the above problems, the present invention proposes an improved heterodyne laser Doppler vibration measurement device, which actively uses ultrasonic vibration to introduce periodic changes in the optical path, separates the measurement signal and the carrier leakage signal in the frequency domain, and then extracts the measurement signal through a filter for demodulation.

[0049] Figure 3 Schematic diagram of a heterodyne laser Doppler vibration measurement device provided in an embodiment of the present invention. The difference between the heterodyne laser Doppler vibration measurement device and the traditional vibration measurement optical path is that an ultrasonic transducer with a reflector is added to the optical path. The laser output by the lens is reflected by the reflector and then used to measure the object to be measured, and the signal diffusely reflected by the object to be measured will also pass through the reflector and return to the lens. When the ultrasonic transducer is at an angular frequency of ω sc When the optical path of the vibration measurement is vibrated, the reflector will vibrate together with it. This process will introduce an angular frequency of ω​sc The total intermediate frequency signal after subcarrier insertion is shown in formula (8):

[0050]

[0051] Among them, S sig_1 (t) is the measured signal after subcarrier insertion, S lk (t) Carrier leakage signal, β FM is the frequency modulation index of the subcarrier (determined by the amplitude), A sig is the amplitude of the measured signal, ω c is the main carrier angular frequency, ω sc is the vibration angular frequency of the ultrasonic transducer (i.e., the predetermined frequency), which is also the subcarrier angular frequency, φ sig (t) is the phase corresponding to the vibration displacement, A lk is the amplitude of the leakage signal, φ lk is the phase of the leakage signal.

[0052] The measured signal is analyzed below, and formula (9) can be obtained by trigonometric function expansion:

[0053]

[0054] Among them, cos(β FM sinω sc t) and sin(β FM sinω sc t) can be further expanded into trigonometric functions with Bessel functions as coefficients, namely,

[0055]

[0056] In the above two formulas, J n (β FM ) is the first kind nth order Bessel function, which is n (n is a positive integer) and the frequency modulation index β FM The value of is calculated by formula (11). Figure 4 The curves of the Bessel function when n=0, 1, 2, and 3 are given.

[0057]

[0058] Substituting formula (10) into formula (9), we can obtain formula (12):

[0059]

[0060] Formula (12) consists of four terms: The first term is the main carrier component A sig cos(ω c t+φ sig(t))J0(β FM ), which overlaps with the carrier leakage signal spectrum and is a useless term; the second term 2A sig J1(β FM )sin(ω c t+φ sig (t))sinω sc t is the subcarrier component, which contains the measurement information φ sig (t), and the amplitude can be large enough to be a useful term; the third term is the cosine component of each harmonic signal of the subcarrier This also includes φ sig (t), but it is unnecessary due to its small amplitude and is also a useless item; the fourth item is the sinusoidal component of each harmonic signal of the subcarrier This also includes φ sig (t), but due to its small amplitude, it is also a useless term. The relationship between each frequency component and Bessel coefficient is as follows Figure 5 shown.

[0061] Formula (12) can also be rearranged as

[0062]

[0063] From formula (13), we can see that the Bessel coefficients determine the components of each carrier. According to the properties of the Bessel function (formula 14), we can see that subcarrier insertion does not increase signal power, but only changes the power distribution of the signal on each carrier.

[0064]

[0065] Figure 4 In the 0th order Bessel function J0(β FM ) is the amplitude coefficient of the signal component on the main carrier, J1(β FM ) is the amplitude coefficient of the signal component on the subcarrier, and the others are the amplitude coefficients of the signal components on the subcarrier higher harmonics. Figure 4 It is easy to see that the frequency modulation index β FM It is not that the bigger the better, but the frequency modulation index β FM =1.85, J ±1 (β FM )≈0.58 is the maximum value, that is, the signal amplitude on the subcarrier is the largest. At this time, demodulating the signal on the subcarrier can obtain the minimum power loss. The subcarrier signal is divided into two signal components, the upper and lower sidebands. It is easy to deduce that when the frequency modulation index β FM =1.85, if only one sideband is demodulated, the useful signal power loss is 4.7dB; if the signals on the upper and lower sidebands are demodulated at the same time, the useful signal power loss is only 1.7dB.

[0066] Based on the above theoretical analysis, the heterodyne laser Doppler vibration measurement device provided by the embodiment of the present invention is as follows: Figure 3 As shown, it includes a subcarrier insertion module 1, an optical front-end module 2 and a signal processing module 3. Among them, the subcarrier insertion module 1 includes an ultrasonic signal source module 101, an ultrasonic transducer 102 and a reflector 103, which are used to introduce optical path changes of specific frequency and specific amplitude in the laser vibration measurement optical path. As mentioned above, unlike the traditional vibration measurement optical path, the heterodyne laser Doppler vibration measurement device provided in the embodiment of the present invention adds an ultrasonic transducer with a reflector to the optical path. The laser output by the lens is reflected by the reflector and then used to measure the object to be measured, and the signal diffusely reflected by the object to be measured will also pass through the reflector and return to the lens. When the ultrasonic transducer is at an angular frequency ω sc When it vibrates, it will vibrate with the reflector. This process will introduce an angular frequency of ω in the optical path. sc The optical path changes.

[0067] The ultrasonic signal source module 101 is used to generate a frequency of ω sc The cosine electrical signal is output to the ultrasonic transducer 102. The ultrasonic transducer 102 is used to convert the electrical signal into ultrasonic vibration. The reflector 103 is used to reflect the laser output by the lens 201 and reflect the optical signal reflected by the object 4 to the lens 201 again. It is rigidly connected to the ultrasonic transducer 102, with an angle of 45° with the lens axis, and driven by the ultrasonic transducer 102 to move at ω sc In some embodiments of the present invention, the rigid connection may be that the ultrasonic transducer fixes the reflector in the form of a metal clamp.

[0068] In some embodiments, in order to reduce the loss of light intensity, the reflector 103 has a higher reflectivity at a predetermined wavelength, for example, greater than a predetermined threshold, which can be determined according to actual application needs, so that the laser output from the reflector 103 is reflected as much as possible, and the light signal reflected from the object to be measured is reflected to the lens as much as possible. The reflector 103 is also configured to have a higher flatness, for example, the flatness is less than a predetermined threshold, which can be selected according to process requirements, so as to ensure that more light enters the detector. The reflector 103 is also preferably selected to be light in weight, for example, less than a predetermined weight, so as to ensure a larger amplitude under the action of the ultrasonic transducer.

[0069] In some embodiments, the ultrasonic transducer is a piezoelectric ceramic transducer. In other embodiments, other forms of transducers may also be selected. The vibration frequency of the super energy transducer needs to be appropriately selected, for example, preferably a frequency range that is inaudible to the human ear, and the frequency should not be too high or too low. If it is too high, the vibration amplitude is not enough, and if it is too low, it will form a large self-interference. In some specific embodiments, the vibration frequency of the super energy transducer is 50KHz to 100KHz.

[0070] The optical front-end module 2 can adopt a traditional heterodyne laser Doppler vibration measurement optical path, which outputs an intermediate frequency signal with a carrier frequency of 40MHz to the signal processing module 3, including a lens 201, a circulator 202, a beam combiner 203, an acousto-optic modulator 204, a local oscillator 205, a laser 206, a beam splitter 207 and a photodetector 208. Among them, the laser output by the laser 206 is divided into two optical signals after passing through the beam splitter 207, one for realizing the reference light and the other for realizing the measurement light. The measurement light is frequency shifted after passing through the acousto-optic modulator. In order to realize this function, the acousto-optic modulator 204 needs the local oscillator 205 to provide an angular frequency of ω c The frequency-shifted measurement light is irradiated on the surface of the vibrating object to be measured through the lens 201, and then returns to the lens after diffuse reflection. After the reflected light interferes with the reference light, it is converted by the photodetector 208 to obtain an intermediate frequency signal with modulated vibration parameters, and the angular frequency of the intermediate frequency signal is exactly ω c Each module in the optical front-end module 2 can be implemented by using various devices known in the art that are suitable for heterodyne laser Doppler vibration measurement.

[0071] In some embodiments of the present invention, the optical front-end module 2 and the subcarrier insertion module 1 are structured using sound absorbing or vibration reducing materials to prevent the ultrasonic signal from being picked up by the optical front-end module 2. For example, rubber pads may be provided on the optical front-end module and the subcarrier insertion module.

[0072] Traditional vibration measuring devices only need to demodulate the measurement signal on the main carrier to obtain vibration parameters, while the intermediate frequency signal output by the heterodyne laser Doppler vibration measuring device provided in the embodiment of the present invention needs to simultaneously demodulate the upper and lower sideband signals of the subcarrier and then combine them to avoid power waste of the measurement signal. Figure 6 The structure diagram of the signal processing module according to the embodiment of the present invention is shown. The signal processing module 3 is used to demodulate the subcarrier signal containing the measurement parameter, and includes an amplifier 301, a power divider 302, an upper sideband filter 303, a lower sideband filter 304, a power combiner 305, an anti-aliasing filter 306, an ADC (analog-to-digital converter) 307 and an FPGA (field programmable gate array) processor 308.

[0073] The intermediate frequency signal output from the optical front-end module 2 is input to the signal processing module 3, and after being amplified by the amplifier 301, it is divided into two paths by the power divider 302 (Power Divider, full name power divider), one path passes through the upper sideband filter 303 to extract the upper sideband signal, and the other path passes through the lower sideband filter 304 to extract the lower sideband signal. It should be pointed out that various sideband filters known in the art can be used for sideband filtering processing, which is not specifically limited in the present invention.

[0074] The upper sideband signal extracted by the upper sideband filter 303 and the lower sideband signal extracted by the lower sideband filter 304 are synthesized into one signal after passing through the combiner 305 (also called a combiner), and input to the anti-aliasing filter 306. The anti-aliasing filter 306 performs anti-aliasing filtering on the synthesized signal. It should be noted that the anti-aliasing filtering can adopt various anti-aliasing filtering processing algorithms known in the art, which are not specifically limited in the present invention.

[0075] The signal processed by the anti-aliasing filter is converted into a digital signal by the analog-to-digital converter 307 and output to the FPGA processor 308. The FPGA processor 308 demodulates the upper and lower sideband signals in the digital domain to obtain the vibration parameters of the object under test.

[0076] Compared with the prior art, the heterodyne laser Doppler vibration measurement device provided by the embodiment of the present invention has the following advantages: first, the signal-to-noise ratio of the modulated signal is improved, and the measurement distance is increased under the conditions of limited lens aperture and laser output power; second, the linearity of the measurement signal demodulation is high, mainly due to the nonlinear interference of the carrier leakage signal; third, the noise of the measurement signal is more stable than that of the traditional heterodyne laser vibration measurement device, which is conducive to further improving the accuracy of the signal after post-processing; fourth, the influence of the local vibration of the vibration measurement device on the vibration signal of the target object is weakened, so there is no need to use a dual optical path detection method to suppress common-mode interference signals.

[0077] It should be noted that the embodiments described above are only a part of the embodiments of the present invention, rather than all of them. The various embodiments described above can be combined in various ways as needed. The terms and expressions used in the specification of the present invention are only for illustration and are not intended to limit the claims of the present invention.

[0078] Those skilled in the art will appreciate that various changes may be made to the details of the above embodiments without departing from the basic principles of the disclosed embodiments. Therefore, the scope of the present invention is determined solely by the claims, in which, unless otherwise specified, all terms are to be interpreted in the broadest reasonable sense.

[0079] For those skilled in the art, any obvious changes made to the invention without departing from the essential content of the invention will constitute an infringement of the patent right of the invention and the person skilled in the art will bear the corresponding legal liability.

Claims

1. A heterodyne laser Doppler vibration measurement device, characterized in that include: An optical front-end module, comprising a lens and a laser, for generating laser light through the laser and emitting the laser light to the outside through the lens; a subcarrier insertion module, connected between the optical front-end module and the object to be measured, comprising an ultrasonic transducer with a reflector, for receiving the laser emitted by the optical front-end module via the lens, reflecting the laser to the object to be measured, and reflecting the light diffusely reflected by the object to be measured back to the lens again; wherein the reflector vibrates at a predetermined frequency and a predetermined amplitude, and introduces an optical path change of a predetermined frequency and a predetermined amplitude on the vibration measurement optical path; The ultrasonic transducer drives the reflector to vibrate together at a predetermined frequency; The subcarrier insertion module further includes an ultrasonic signal source; the ultrasonic signal source generates an electrical signal of a predetermined frequency and outputs the electrical signal to the ultrasonic transducer so that the ultrasonic transducer converts the electrical signal into ultrasonic vibration; The reflector is rigidly connected to the ultrasonic transducer, and the angle between the reflector and the lens axis is 45 degrees; The signal processing module is connected to the optical front-end module.

2. The heterodyne laser Doppler vibration measuring device according to claim 1, characterized in that: The signal processing module is connected to the optical front-end module, and includes a power divider, an upper sideband filter, a lower sideband filter and a combiner; wherein the power divider is used to receive the intermediate frequency signal output by the optical front-end module, and distribute the power of the intermediate frequency signal to obtain two signals, one of the two signals flows into the upper sideband filter, and the other signal flows into the lower sideband filter; the combiner is used to combine the signal processed by the upper sideband filter and the signal processed by the lower sideband, and input them into the lower processing module.

3. The heterodyne laser Doppler vibration measuring device according to claim 2, characterized in that: The signal processing module also includes an amplifier, an anti-aliasing filter, an analog-to-digital converter and an FPGA processor; wherein the amplifier is used to amplify the intermediate frequency signal output by the optical front-end module and transmit the amplified intermediate frequency signal to the power divider; the anti-aliasing filter is used to receive the signal output by the combiner and perform anti-aliasing filtering on the output signal; the analog-to-digital converter is used to receive the upper and lower sideband signals after the anti-aliasing processing and convert the upper and lower sideband signals after the anti-aliasing processing from analog form to digital form; the FPGA processor is used to demodulate the upper and lower sideband signals in the digital domain to obtain the vibration parameters of the object under test.

4. The heterodyne laser Doppler vibration measuring device according to claim 3, characterized in that: The optical front-end module and the subcarrier insertion module are structured using sound-absorbing or vibration-reducing materials to prevent the ultrasonic signal from being picked up by the optical front-end module.

5. The heterodyne laser Doppler vibration measuring device according to claim 4, characterized in that: The sound absorbing or vibration reducing material is a rubber pad.

6. The heterodyne laser Doppler vibration measuring device according to claim 1, characterized in that: The ultrasonic transducer is a piezoelectric ceramic transducer.

7. The heterodyne laser Doppler vibration measuring device according to claim 1, characterized in that: The predetermined frequency is 50KHz to 100KHz.

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