Non-contact dynamic displacement measurement system based on modal decomposition

Abstract

The present invention provides a non-contact dynamic displacement measurement system based on modal decomposition. Single-frequency laser and swept-frequency laser are combined and transmitted to an object to be measured through a probe. The object to be measured reflects an echo light signal back to the probe. The echo light signal carries a measurement distance and a measurement error introduced by a Doppler effect. The echo signal light is divided into two paths according to different frequencies. One path is converted into a swept-frequency detection electrical signal, and the other path is converted into a single-frequency detection electrical signal. The swept-frequency detection electrical signal is processed to obtain a measurement distance between the probe and the object to be measured. The single-frequency detection electrical signal is processed by a phase carrier generation algorithm based on orthogonal demodulation to extract a Doppler effect measurement error vector sum caused by each vibration, and then an empirical mode decomposition algorithm is used to separate the measurement error caused by vibration in the displacement measurement direction from the measurement error vector sum. According to the measurement distance and the measurement error, the actual distance between the probe and the object to be measured is determined, thereby determining the displacement of the object to be measured.

Description

Technical Field

[0001] The invention belongs to the field of displacement measurement, and in particular relates to a non-contact dynamic displacement measurement system based on modal decomposition. Background Art

[0002] The measurement uncertainty of non-contact distance measurement systems is usually in the micron range. It is of great significance in the field of metrology, especially in manufacturing and large scientific projects, and can directly improve the manufacturing efficiency and accuracy of large components. The non-contact distance measurement system is based on the swept frequency interferometry measurement technology. The swept frequency interferometry distance measurement technology has the advantages of non-contact, strong anti-interference ability, large measurement range, and high distance measurement accuracy. It has long been widely used in the field of large-size, high-precision distance measurement, such as the measurement of the tip interval and axial clearance of the engine, the calibration of the rivet hole position in the design of large wing shapes, and even in particle accelerators and colliders, which can help them achieve stricter alignment tolerances and thus achieve more complex and advanced designs.

[0003] The non-contact distance measurement system obtains the measured distance by demodulating the interference beat signal caused by the stable optical path difference in the interference measurement optical path. However, the optical path difference in the interference measurement optical path is fixed only under ideal conditions. In actual measurements (such as industrial measurements), vibration will introduce Doppler frequency shift into the interference beat signal, causing the optical path difference to change randomly, and ultimately causing a large measurement error in the measured distance obtained after demodulating the stable interference beat signal. In order to eliminate the measurement error introduced by the Doppler effect, such as Figure 1 As shown, the single-frequency laser generated by the single-frequency laser and the swept-frequency laser generated by the swept-frequency laser are combined and transmitted to the circulator through the wavelength division multiplexer W1. The circulator transmits the combined light to the probe, and the probe transmits the combined light to the object to be tested. After receiving the combined light, the object to be tested reflects the echo light signal back to the probe, and the probe transmits it to the wavelength division multiplexer W2 through the circulator. The wavelength division multiplexer W2 divides the echo light signal into two paths according to the frequency, one path is a single-frequency detection light signal, and the other path is a swept-frequency detection light signal. The photodetector D1 converts the single-frequency detection light signal into a single-frequency detection electrical signal, and the photodetector D2 converts the swept-frequency detection light signal into a swept-frequency detection electrical signal.

[0004] When determining the measurement error introduced by the Doppler effect, firstly, the time-frequency analysis method is used to analyze the swept frequency detection electrical signal, and the motion direction of the object to be measured is judged by the speed determination principle. At the same time, the frequency of the single-frequency detection electrical signal is estimated to obtain the absolute value of the motion speed of the object to be measured; then the motion direction and the absolute value of the motion speed are combined to obtain the actual value of the motion speed of the object to be measured; finally, the Doppler compensation principle is used to eliminate the measurement error introduced by the Doppler effect, thereby achieving accurate distance measurement. However, in a complex measurement environment, the vibration introduced by the Doppler effect is multi-directional, and the measurement error is a collection of multi-component measurement errors. The accuracy of the above method for determining the measurement error is still low. Summary of the invention

[0005] The present invention provides a non-contact dynamic displacement measurement system based on modal decomposition, so as to solve the problem that the measurement accuracy of Doppler effect measurement error is low in current displacement measurement, thus resulting in low displacement measurement accuracy.

[0006] According to a first aspect of an embodiment of the present invention, a non-contact dynamic displacement measurement system based on modal decomposition is provided, comprising a single-frequency laser, a swept-frequency laser, a first wavelength division multiplexer, a probe, a second wavelength division multiplexer, a first photodetector and a second photodetector, wherein the single-frequency laser is used to generate a single-frequency laser, and the swept-frequency laser is used to generate a swept-frequency laser. The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser and transmits them to the probe, and the probe transmits the combined light to the object to be measured. After receiving the combined light, the object to be measured reflects an echo light signal back to the probe, and the echo light signal carries the measurement distance information between the probe and the object to be measured and the measurement error information introduced by the Doppler effect. The probe transmits the echo light signal to the second wavelength division multiplexer; the second wavelength division multiplexer divides the echo signal light into two paths according to different frequencies, one path is a single-frequency detection light signal, and the other path is a swept-frequency detection light signal. The first photodetector converts the swept-frequency detection light signal into a swept-frequency detection electrical signal, and the second photodetector converts the single-frequency detection light signal into a single-frequency detection electrical signal;

[0007] Processing the frequency sweep detection electrical signal to obtain the measurement distance between the probe and the object to be measured;

[0008] The single-frequency detection electrical signal is processed by a phase carrier generation algorithm based on orthogonal demodulation to extract the Doppler effect measurement error vector sum caused by each vibration, and then the empirical mode decomposition algorithm is used to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum;

[0009] According to the measured distance and the measurement error, the actual distance between the probe and the object to be measured is determined, thereby determining the displacement of the object to be measured.

[0010] In an optional implementation, the processing of the swept frequency detection electrical signal to obtain the measured distance between the probe and the object to be measured includes: performing fast Fourier transform (FFT) on the swept frequency detection electrical signal and demodulating to obtain the measured distance between the probe and the object to be measured.

[0011] In another optional implementation, the empirical mode decomposition algorithm is an empirical mode decomposition-Hilbert Huang transform EMD-HHT algorithm.

[0012] In another optional implementation, the actual distance between the probe and the object to be measured is determined according to the measurement distance and the measurement error according to the following formula:

[0013]

[0014] Wherein, L represents the actual distance, R represents the measured distance, ΔL1(t) represents the measurement error caused by vibration in the displacement measurement direction, f0 represents the initial frequency of the swept laser, and B represents the modulation bandwidth of the swept laser.

[0015] In another optional implementation, a circulator is also included, the output end of the single-frequency laser is connected to the first input end of the first wavelength division multiplexer, the output end of the swept-frequency laser is connected to the second input end of the first wavelength division multiplexer, the output end of the first wavelength division multiplexer is connected to the first end of the circulator, the second end of the circulator is connected to the probe, and the third end is connected to the input end of the second wavelength division multiplexer; the first output end of the second wavelength division multiplexer is connected to the first photodetector, and the second output end is connected to the second photodetector.

[0016] In another optional implementation, it also includes a first coupler, a first frequency shift modulator and a second coupler, the output end of the single-frequency laser is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the first wavelength division multiplexer, the second output end is connected to the second input end of the second coupler through the first frequency shift modulator, the second output end of the second wavelength division multiplexer is connected to the first input end of the second coupler; the output end of the second coupler is connected to the second photodetector;

[0017] The first coupler divides the single-frequency laser generated by the single-frequency laser into two paths, one path is transmitted to the first wavelength division multiplexer, and the other path is used as a single-frequency reference laser, which is modulated by the first frequency shift modulator and transmitted to the second coupler;

[0018] The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser into a beam and transmits them to the circulator. The circulator transmits the combined light to the probe. The probe emits the combined light to the object to be tested. After receiving the combined light, the object to be tested reflects the echo light signal back to the probe. The probe transmits the echo light signal to the second wavelength division multiplexer through the circulator.

[0019] The second wavelength division multiplexer divides the echo signal light into two paths according to different frequencies, one of which is a single-frequency detection optical signal and is transmitted to the second coupler;

[0020] The second coupler couples the single-frequency reference laser and the single-frequency detection light signal and transmits them to the second photodetector. The second photodetector performs coherent heterodyne beat frequency on the single-frequency reference laser and the single-frequency detection light signal to generate the single-frequency detection electrical signal.

[0021] In another optional implementation, the device further includes a third coupler, a second frequency shift modulator and a fourth coupler, wherein the output end of the frequency sweep laser is connected to the input end of the third coupler, the first output end of the third coupler is connected to the second input end of the first wavelength division multiplexer, the second output end is connected to the first input end of the fourth coupler through the second frequency shift modulator, the first output end of the second wavelength division multiplexer is connected to the second input end of the fourth coupler; and the output end of the fourth coupler is connected to the first photodetector;

[0022] The second coupler divides the frequency sweeping laser generated by the frequency sweeping laser into two paths, one path is transmitted to the first wavelength division multiplexer, and the other path is used as a frequency sweeping reference laser, which is modulated by the second frequency shift modulator and transmitted to the fourth coupler;

[0023] The first wavelength division multiplexer combines the single-frequency laser and the one-way frequency sweeping laser into a beam and transmits them to the circulator. The circulator reflects the combined light and transmits it back to the probe. The probe transmits the combined light to the object to be tested. After receiving the combined light, the object to be tested transmits an echo light signal to the probe. The probe transmits the echo light signal to the second wavelength division multiplexer through the circulator.

[0024] The second wavelength division multiplexer divides the echo signal light into two paths according to different frequencies, one of which is a frequency sweep detection optical signal and is transmitted to the fourth coupler;

[0025] The fourth coupler couples the swept-frequency reference laser and the swept-frequency detection optical signal and transmits them to the first photodetector. The first photodetector performs coherent heterodyne beat frequency on the swept-frequency reference laser and the swept-frequency detection optical signal to generate the swept-frequency detection electrical signal.

[0026] In another optional implementation, an optical amplifier is provided between the second end of the circulator and the probe.

[0027] In another optional implementation, a first isolator is provided between the single-frequency laser and the input end of the first coupler.

[0028] In another optional implementation, a second isolator is provided between the frequency-sweeping laser and the input end of the third coupler.

[0029] The beneficial effects of the present invention are:

[0030] 1. When determining the measurement error caused by the Doppler effect, the present invention only needs to process the single-frequency detection electrical signal, first extract the Doppler effect measurement error vector sum caused by each vibration, and then use the empirical mode decomposition algorithm to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum, that is, when determining the actual distance between the probe and the object to be measured, the measurement error introduced by the Doppler effect in the displacement measurement direction is compensated in real time. Therefore, the present invention realizes the high-precision extraction and separation of the measurement error caused by the Doppler effect in a complex measurement environment, and the dynamic measurement accuracy of the measurement error in the displacement measurement direction is high, so that the dynamic measurement accuracy of the displacement is high; the present invention can realize real-time high-precision measurement of dynamic displacement;

[0031] 2. The present invention can generate a frequency difference between the single-frequency reference laser and the single-frequency detection light signal input to the second coupler by setting a first frequency shift modulator, so that when the second photoelectric detector performs coherent heterodyne beat frequency on the single-frequency reference laser and the single-frequency detection light signal, an intermediate frequency single-frequency detection electrical signal far away from the low-frequency region is generated, thereby improving the anti-noise ability of the single-frequency detection electrical signal; the present invention can improve the accuracy of the Doppler effect measurement error obtained based on the single-frequency detection electrical signal by optimizing the single-frequency detection structure and improving the anti-noise ability of the single-frequency detection electrical signal;

[0032] 3. The present invention can generate a frequency difference between the swept frequency reference laser and the swept frequency detection optical signal input to the fourth coupler by setting a second frequency shift modulator, so that when the first photodetector performs coherent heterodyne beat frequency on the swept frequency reference laser and the swept frequency detection optical signal, an intermediate frequency swept frequency detection electrical signal far away from the low frequency region is generated, thereby improving the anti-noise ability of the swept frequency detection electrical signal; the present invention can improve the accuracy of the measured distance obtained based on the swept frequency detection electrical signal by optimizing the swept frequency detection structure and improving the anti-noise ability of the swept frequency detection electrical signal;

[0033] 4. The present invention arranges the optical amplifier between the second end of the circulator and the probe, which can improve the signal-to-noise ratio of the echo optical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the circuit block diagram of the traditional displacement measurement system;

[0035] Figure 2 It is a schematic structural diagram of an embodiment of a non-contact dynamic displacement measurement system based on modal decomposition of the present invention;

[0036] Figure 3 It is a schematic structural diagram of another embodiment of the non-contact dynamic displacement measurement system based on modal decomposition of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0038] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0039] See also Figure 2 , is a schematic diagram of the structure of an embodiment of a non-contact dynamic displacement measurement system based on modal decomposition of the present invention. The non-contact dynamic displacement measurement system based on modal decomposition may include a single-frequency laser, a swept-frequency laser, a first wavelength division multiplexer, a probe, a second wavelength division multiplexer, a first photodetector, and a second photodetector. The single-frequency laser is used to generate a single-frequency laser, and the swept-frequency laser is used to generate a swept-frequency laser. The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser and transmits them to the probe. The probe emits the combined light to the object to be measured. After receiving the combined light, the object to be measured reflects an echo light signal back to the probe. The echo light signal carries the measurement distance information between the probe and the object to be measured and the measurement error information introduced by the Doppler effect. The probe transmits the echo light signal to the second wavelength division multiplexer; the second wavelength division multiplexer combines the echo signal light according to the frequency. The probe is divided into two paths according to different rates, one path is a single-frequency detection light signal, and the other path is a swept-frequency detection light signal, the first photodetector converts the swept-frequency detection light signal into a swept-frequency detection electrical signal, and the second photodetector converts the single-frequency detection light signal into a single-frequency detection electrical signal; the swept-frequency detection electrical signal is processed to obtain the measurement distance between the probe and the object to be measured; the single-frequency detection electrical signal is processed by a phase carrier generation algorithm based on orthogonal demodulation to extract the Doppler effect measurement error vector sum caused by each vibration, and then the empirical mode decomposition algorithm is used to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum; according to the measurement distance and the measurement error, the actual distance between the probe and the object to be measured is determined, thereby determining the displacement of the object to be measured.

[0040] In this embodiment, the system further includes a circulator, the output end of the single-frequency laser is connected to the first input end of the first wavelength division multiplexer, the output end of the swept frequency laser is connected to the second input end of the first wavelength division multiplexer, the output end of the first wavelength division multiplexer is connected to the first end of the circulator, the second end of the circulator is connected to the probe, and the third end is connected to the input end of the second wavelength division multiplexer; the first output end of the second wavelength division multiplexer is connected to the first photodetector, and the second output end is connected to the second photodetector. Among them, the acquisition card can collect the swept frequency detection electrical signal and the single-frequency detection electrical signal, and send the collected swept frequency detection electrical signal and the single-frequency detection electrical signal to the DSP (Digital Signal Processing, digital signal processing unit) for processing.

[0041] The processing of the swept frequency detection electrical signal to obtain the measured distance between the probe and the object to be measured includes: performing a fast Fourier transform FFT on the swept frequency detection electrical signal, and demodulating to obtain the measured distance between the probe and the object to be measured. The empirical mode decomposition algorithm may be an empirical mode decomposition-Hilbert Huang transform EMD-HHT algorithm. According to the measured distance and the measurement error, the actual distance between the probe and the object to be measured is determined according to the following formula:

[0042]

[0043] Wherein, L represents the actual distance, R represents the measured distance, ΔL1(t) represents the measurement error caused by vibration in the displacement measurement direction, f0 represents the initial frequency of the swept laser, and B represents the modulation bandwidth of the swept laser.

[0044] It can be seen from the above embodiments that when determining the measurement error caused by the Doppler effect, the present invention only needs to process the single-frequency detection electrical signal, first extract the Doppler effect measurement error vector sum caused by each vibration, and then use the empirical mode decomposition algorithm to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum, that is, when determining the actual distance between the probe and the object to be measured, what is compensated in real time is the measurement error introduced by the Doppler effect in the displacement measurement direction. Therefore, the present invention realizes the high-precision extraction and separation of the measurement error caused by the Doppler effect in a complex measurement environment, and the dynamic measurement accuracy of the measurement error in the displacement measurement direction is high, thereby making the dynamic measurement accuracy of the displacement high; in addition, unlike the prior art, the present invention only needs to process the single-frequency detection electrical signal to obtain the Doppler effect measurement error in the displacement measurement direction, without having to combine the swept frequency detection signal with the single-frequency detection signal for processing, so the present invention can realize real-time high-precision measurement of dynamic displacement.

[0045] See also Figure 3, is a schematic structural diagram of another embodiment of the non-contact dynamic displacement measurement system based on modal decomposition of the present invention. Figure 3 and Figure 2 The difference between the shown embodiments is that it also includes a first coupler, a first frequency shift modulator and a second coupler, the output end of the single-frequency laser is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the first wavelength division multiplexer, the second output end is connected to the second input end of the second coupler through the first frequency shift modulator, the second output end of the second wavelength division multiplexer is connected to the first input end of the second coupler; the output end of the second coupler is connected to the second photodetector PD2. The first coupler divides the single-frequency laser generated by the single-frequency laser into two paths, one of which is transmitted to the first wavelength division multiplexer, and the other is used as a single-frequency reference laser, which is modulated by the first frequency shift modulator and transmitted to the second coupler; the first wavelength division multiplexer combines the single-frequency laser with the swept-frequency laser and transmits them to the circulator, the circulator transmits the combined light to the probe, the probe emits the combined light to the object to be tested, and the object to be tested reflects the echo light signal back to the probe after receiving the combined light, and the probe transmits the echo light signal to the second wavelength division multiplexer through the circulator; the second wavelength division multiplexer divides the echo signal light into two paths according to different frequencies, one of which is a single-frequency detection light signal, which is transmitted to the second coupler; the second coupler couples the single-frequency reference laser and the single-frequency detection light signal and transmits them to the second photodetector PD2, the second photodetector PD2 performs coherent heterodyne beat frequency on the single-frequency reference laser and the single-frequency detection light signal to generate the single-frequency detection electrical signal.

[0046] In this embodiment, the single-frequency laser can be a single-frequency ultra-narrow linewidth laser to provide a single-frequency laser with low phase noise, and the first frequency shift modulator can be a first positive frequency shift modulator and a first negative frequency shift modulator connected in series, the first free ends of the two are connected to the second output end of the first coupler, and the second free ends are connected to the second input end of the second coupler. The present invention can generate a frequency difference between the single-frequency reference laser and the single-frequency detection light signal input to the second coupler by setting the first frequency shift modulator, so that when the second photodetector performs coherent heterodyne beat on the single-frequency reference laser and the single-frequency detection light signal, an intermediate frequency single-frequency detection electrical signal far away from the low-frequency region is generated, thereby improving the anti-noise ability of the single-frequency detection electrical signal; the present invention can improve the accuracy of the Doppler effect measurement error obtained based on the single-frequency detection electrical signal by optimizing the single-frequency detection structure and improving the anti-noise ability of the single-frequency detection electrical signal.

[0047] Figure 3 and Figure 2The difference between the illustrated embodiments is that it also includes a third coupler, a second frequency shift modulator and a fourth coupler, the output end of the frequency sweeping laser is connected to the input end of the third coupler, the first output end of the third coupler is connected to the second input end of the first wavelength division multiplexer, the second output end is connected to the first input end of the fourth coupler through the second frequency shift modulator, the first output end of the second wavelength division multiplexer is connected to the second input end of the fourth coupler; the output end of the fourth coupler is connected to the first photodetector PD1; the second coupler divides the frequency sweeping laser generated by the frequency sweeping laser into two paths, one path is transmitted to the first wavelength division multiplexer, and the other path is used as a frequency sweeping reference laser, which is modulated by the second frequency shift modulator and transmitted to the fourth coupler; the The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser and transmits them to the circulator. The circulator transmits the combined light to the probe. The probe emits the combined light to the object to be tested. After receiving the combined light, the object to be tested reflects the echo light signal back to the probe. The probe transmits the echo light signal to the second wavelength division multiplexer through the circulator; the second wavelength division multiplexer divides the echo signal light into two paths according to different frequencies, one of which is a swept-frequency detection light signal, which is transmitted to the fourth coupler; the fourth coupler couples the swept-frequency reference laser and the swept-frequency detection light signal and transmits them to the first photodetector PD1. The first photodetector performs coherent heterodyne beat frequency on the swept-frequency reference laser and the swept-frequency detection light signal to generate the swept-frequency detection electrical signal.

[0048] In this embodiment, the frequency sweeping laser can be a narrow linewidth frequency sweeping laser, and the second frequency shift modulator can be a second positive frequency shift modulator and a second negative frequency shift modulator connected in series, the first free ends of the two are connected to the second output end of the third coupler, and the second free ends are connected to the first input end of the fourth coupler. The present invention can generate a frequency difference between the frequency sweeping reference laser and the frequency sweeping detection optical signal input to the fourth coupler by setting the second frequency shift modulator, so that when the first photodetector performs coherent heterodyne beat on the frequency sweeping reference laser and the frequency sweeping detection optical signal, an intermediate frequency frequency sweeping detection electrical signal far away from the low-frequency region is generated, thereby improving the anti-noise ability of the frequency sweeping detection electrical signal; the present invention can improve the accuracy of the measured distance obtained based on the frequency sweeping detection electrical signal by optimizing the frequency sweeping detection structure and improving the anti-noise ability of the frequency sweeping detection electrical signal.

[0049] Since the echo light signal is relatively weak, it is usually necessary to amplify the echo light signal, such as Figure 1 As shown, however, when the optical amplifier is placed Figure 1When in the position shown, the optical amplifier will not only amplify the echo light signal, but also amplify the noise. In order to improve the signal-to-noise ratio of the echo light signal, the present invention arranges the optical amplifier between the second end of the circulator and the probe. In addition, a first isolator may be provided between the single-frequency laser and the input end of the first coupler, and a second isolator may be provided between the swept-frequency laser and the input end of the third coupler. It should be noted that the above-mentioned probe can be a fiber collimator GRIN lens, and an optical switch may also be provided between the second end of the circulator and the probe. By controlling the on and off of the optical switch, synchronous real-time data acquisition can be achieved.

[0050] In addition, in this embodiment, the intensity of the frequency sweep detection electrical signal can be expressed as:

[0051]

[0052] Among them, I1 and I2 represent the intensity of the swept reference laser and the swept detection light signal respectively, f0 represents the initial frequency of the swept laser, c represents the speed of light, L represents the actual distance, B represents the modulation bandwidth of the swept laser, and T represents the modulation period of the swept laser. In general, according to the beat frequency f beat By demodulating the swept frequency detection electrical signal, L can be obtained. However, due to the Doppler effect in the actual measurement process, the actual beat frequency is represents the Doppler frequency shift, thereby introducing the Doppler effect measurement error. Correspondingly, after processing the swept frequency detection electrical signal, the measured distance R obtained can be expressed as:

[0053]

[0054] Wherein ΔL(t) represents the vector sum of Doppler effect measurement errors caused by various vibrations, and in fact, the measurement error ΔL1(t) caused by vibration in the displacement measurement direction needs to be eliminated when measuring the distance R. Therefore, the present invention can determine the actual distance between the probe and the object to be measured according to the following formula based on the measurement distance and the measurement error:

[0055]

[0056] Wherein, L represents the actual distance, R represents the measured distance, ΔL1(t) represents the measurement error caused by vibration in the displacement measurement direction, f0 represents the initial frequency of the swept laser, and B represents the modulation bandwidth of the swept laser.

[0057] It can be seen from the above embodiments that when determining the measurement error caused by the Doppler effect, the present invention only needs to process the single-frequency detection electrical signal, first extract the Doppler effect measurement error vector sum caused by each vibration, and then use the empirical mode decomposition algorithm to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum, that is, when determining the actual distance between the probe and the object to be measured, what is compensated in real time is the measurement error introduced by the Doppler effect in the displacement measurement direction. Therefore, the present invention realizes the high-precision extraction and separation of the measurement error caused by the Doppler effect in a complex measurement environment, and the dynamic measurement accuracy of the measurement error in the displacement measurement direction is high, thereby making the dynamic measurement accuracy of the displacement high; the present invention can realize real-time high-precision measurement of dynamic displacement.

[0058] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0059] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A non-contact dynamic displacement measurement system based on modal decomposition, characterized in that: The invention comprises a single-frequency laser, a swept-frequency laser, a first wavelength division multiplexer, a probe, a second wavelength division multiplexer, a first photodetector and a second photodetector, wherein the single-frequency laser is used to generate a single-frequency laser, and the swept-frequency laser is used to generate a swept-frequency laser. The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser and transmits them to the probe, and the probe transmits the combined light to the object to be measured. After receiving the combined light, the object to be measured reflects an echo light signal back to the probe, and the echo light signal carries the measurement distance information between the probe and the object to be measured and the measurement error information introduced by the Doppler effect. The probe transmits the echo light signal to the second wavelength division multiplexer; the second wavelength division multiplexer divides the echo light signal into two paths according to different frequencies, one path is a single-frequency detection light signal, and the other path is a swept-frequency detection light signal. The first photodetector converts the swept-frequency detection light signal into a swept-frequency detection electrical signal, and the second photodetector converts the single-frequency detection light signal into a single-frequency detection electrical signal. Processing the frequency sweep detection electrical signal to obtain the measurement distance between the probe and the object to be measured; The single-frequency detection electrical signal is processed by a phase carrier generation algorithm based on orthogonal demodulation to extract the Doppler effect measurement error vector sum caused by each vibration, and then the empirical mode decomposition algorithm is used to separate the measurement error caused by the vibration in the displacement measurement direction from the measurement error vector sum; According to the measured distance and the measurement error, the actual distance between the probe and the object to be measured is determined, thereby determining the displacement of the object to be measured.

2. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 1 is characterized in that: The processing of the swept frequency detection electrical signal to obtain the measured distance between the probe and the object to be measured includes: performing fast Fourier transform (FFT) on the swept frequency detection electrical signal and demodulating the signal to obtain the measured distance between the probe and the object to be measured.

3. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 1 is characterized in that: The empirical mode decomposition algorithm is an empirical mode decomposition-Hilbert Huang transform EMD-HHT algorithm.

4. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 3 is characterized in that: According to the measurement distance and the measurement error, the actual distance between the probe and the object to be measured is determined according to the following formula: Wherein, L represents the actual distance, R represents the measured distance, ΔL1(t) represents the measurement error caused by vibration in the displacement measurement direction, f0 represents the initial frequency of the swept laser, and B represents the modulation bandwidth of the swept laser.

5. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 1, characterized in that: It also includes a circulator, wherein the output end of the single-frequency laser is connected to the first input end of the first wavelength division multiplexer, the output end of the swept-frequency laser is connected to the second input end of the first wavelength division multiplexer, the output end of the first wavelength division multiplexer is connected to the first end of the circulator, the second end of the circulator is connected to the probe, and the third end is connected to the input end of the second wavelength division multiplexer; the first output end of the second wavelength division multiplexer is connected to the first photodetector, and the second output end is connected to the second photodetector.

6. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 5, characterized in that: It also includes a first coupler, a first frequency shift modulator and a second coupler, wherein the output end of the single-frequency laser is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the first wavelength division multiplexer, the second output end is connected to the second input end of the second coupler through the first frequency shift modulator, the second output end of the second wavelength division multiplexer is connected to the first input end of the second coupler; and the output end of the second coupler is connected to the second photodetector; The first coupler divides the single-frequency laser generated by the single-frequency laser into two paths, one path is transmitted to the first wavelength division multiplexer, and the other path is used as a single-frequency reference laser, which is modulated by the first frequency shift modulator and transmitted to the second coupler; The first wavelength division multiplexer combines the single-frequency laser and the swept-frequency laser into a beam and transmits them to the circulator. The circulator transmits the combined light to the probe. The probe emits the combined light to the object to be tested. After receiving the combined light, the object to be tested reflects the echo light signal back to the probe. The probe transmits the echo light signal to the second wavelength division multiplexer through the circulator. The second wavelength division multiplexer divides the echo optical signal into two paths according to different frequencies, one of which is a single-frequency detection optical signal and is transmitted to the second coupler; The second coupler couples the single-frequency reference laser and the single-frequency detection light signal and transmits them to the second photodetector. The second photodetector performs coherent heterodyne beat frequency on the single-frequency reference laser and the single-frequency detection light signal to generate the single-frequency detection electrical signal.

7. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 6, characterized in that: It also includes a third coupler, a second frequency shift modulator and a fourth coupler, wherein the output end of the frequency sweep laser is connected to the input end of the third coupler, the first output end of the third coupler is connected to the second input end of the first wavelength division multiplexer, the second output end is connected to the first input end of the fourth coupler through the second frequency shift modulator, the first output end of the second wavelength division multiplexer is connected to the second input end of the fourth coupler; and the output end of the fourth coupler is connected to the first photodetector; The second coupler divides the frequency sweeping laser generated by the frequency sweeping laser into two paths, one path is transmitted to the first wavelength division multiplexer, and the other path is used as a frequency sweeping reference laser, which is modulated by the second frequency shift modulator and transmitted to the fourth coupler; The first wavelength division multiplexer combines the single-frequency laser and a frequency sweeping laser into a beam and transmits them to the circulator. The circulator reflects the combined light and transmits it back to the probe. The probe transmits the combined light to the object to be tested. After receiving the combined light, the object to be tested transmits an echo light signal to the probe. The probe transmits the echo light signal to the second wavelength division multiplexer through the circulator. The second wavelength division multiplexer divides the echo optical signal into two paths according to different frequencies, one of which is a frequency sweep detection optical signal and is transmitted to the fourth coupler; The fourth coupler couples the swept-frequency reference laser and the swept-frequency detection optical signal and transmits them to the first photodetector. The first photodetector performs coherent heterodyne beat frequency on the swept-frequency reference laser and the swept-frequency detection optical signal to generate the swept-frequency detection electrical signal.

8. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 7, characterized in that: An optical amplifier is arranged between the second end of the circulator and the probe.

9. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 6, characterized in that: A first isolator is arranged between the single-frequency laser and the input end of the first coupler.

10. The non-contact dynamic displacement measurement system based on modal decomposition according to claim 7, characterized in that: A second isolator is provided between the frequency sweeping laser and the input end of the third coupler.

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