Laser Doppler velocity measurement system and velocity measurement method based on phase orientation recognition

Abstract

The present invention discloses a laser Doppler velocity measurement system based on phase direction recognition and its velocity measurement method. The system includes: a first optical splitter for splitting a continuous laser beam into a reference light and a signal light; a reflective device for returning the reference light and mixing it with the scattered light to generate the original mixed light; a second optical splitter for splitting the original mixed light into a first mixed light and a second mixed light; a photoelectric detection component having a first photosensitive surface and a second photosensitive surface located in the same plane, for converting the interference signals on the first photosensitive surface and the second photosensitive surface into a first electrical signal and a second electrical signal; and a signal processing module for calculating the speed and direction of the moving object being measured. The present invention is applied to the field of optical measurement technology and can effectively solve the problems of poor stability, large size and complex structure of the original laser Doppler velocity measurement system, and is conducive to the miniaturization development of direction-recognizable laser Doppler velocity measurement systems.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, in particular to a laser Doppler velocity measurement system and a velocity measurement method thereof based on phase orientation discrimination. Background Art

[0002] Laser Doppler velocimetry technology, due to its advantages such as non-contact measurement and fast dynamic response, has been widely used in fields such as aviation, aerospace, water conservancy, environmental protection, and medicine. While many mature products are available both domestically and internationally, most lack directional discrimination. This is because the laser Doppler velocimetry system detects the same frequency for two velocities of equal magnitude but opposite directions.

[0003] A commonly used method for direction discrimination is optical frequency shifting. This involves using a frequency shifting device to shift the frequency of a reference beam or signal beam, introducing an offset frequency. The direction of a moving object can be determined by determining whether the measured signal frequency is shifted up or down relative to the offset frequency. In practical applications, acousto-optic and electro-optical devices are commonly used as frequency shifting devices. However, electro-optical devices require high drive voltages and power, resulting in complex power supply structures and the potential for high-frequency interference in electronic equipment. While acousto-optic devices do not require ultra-high drive voltages, improving the diffraction efficiency and frequency shift bandwidth of the acousto-optic frequency shifter requires complex techniques such as increasing the bandwidth of the piezoelectric transducer and ultrasonic tracking. This results in a larger acousto-optic device. Therefore, using frequency shifting devices for direction discrimination is not conducive to the miniaturization and integration of speed measurement systems, and the system's stability is limited by the frequency shifter. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a laser Doppler velocity measurement system and velocity measurement method based on phase direction identification, so as to solve the problems of poor stability, large size and complex structure of the original velocity measurement system using frequency shifters for direction identification.

[0005] To achieve the above object, the present invention provides a laser Doppler velocity measurement system based on phase direction identification, comprising:

[0006] A laser, used for outputting continuous laser light;

[0007] a first optical splitter, located in the optical path of the continuous laser, for splitting the continuous laser into reference light and signal light, and reflecting scattered light in a direction opposite to that of the signal light;

[0008] a reflective device, located on the optical path of the reference light, for returning the reference light along the original path, and mixing the reference light with the scattered light through the first spectrometer to generate original mixed light;

[0009] a second light splitting device, located on the optical path of the original frequency-mixed light, for splitting the original frequency-mixed light into a first frequency-mixed light and a second frequency-mixed light with parallel emission directions;

[0010] A photoelectric detection assembly having a first photosensitive surface and a second photosensitive surface located in the same plane, wherein the first photosensitive surface is located in the optical path of the first mixed-frequency light, and the second photosensitive surface is located in the optical path of the second mixed-frequency light, and is used to convert the interference signals on the first photosensitive surface and the second photosensitive surface into a first electrical signal and a second electrical signal;

[0011] The signal processing module is electrically connected to the photoelectric detection component and is used to resolve the first electrical signal and the second electrical signal to obtain the speed and direction of the moving object being measured.

[0012] In one embodiment, the center distance between the first photosensitive surface and the second photosensitive surface is:

[0013]

[0014] Wherein, d represents the center distance between the first photosensitive surface and the second photosensitive surface, λ is the laser wavelength, n is the refractive index of the second spectrometer, and N is the periodic constant.

[0015] In one embodiment, the second light splitting device is a cemented trapezoidal prism composed of a right-angle prism and a rhombus prism.

[0016] In one embodiment, the path difference between the first frequency-mixed light and the second frequency-mixed light in the second optical splitter is equal to the center distance between the first photosensitive surface and the second photosensitive surface.

[0017] In one embodiment, the laser Doppler velocity measurement system based on phase identification further includes a neutral filter;

[0018] The neutral density filter is located between the reflective element and the first spectroscopic element, and is used to absorb part of the reference light so that the intensity of the reference light incident on the photoelectric detection component is as equal as possible to the intensity of the scattered light.

[0019] To achieve the above object, the present invention further provides a laser Doppler velocity measurement method based on phase direction identification, comprising the following steps:

[0020] The continuous laser beam output by the laser is split into reference light and signal light, and the signal light is irradiated on the surface of the moving object to be measured;

[0021] Reflect the reference light so that it mixes with the scattered light returning in the direction of the signal light to generate the original mixed light;

[0022] Splitting the original mixed-frequency light into a first mixed-frequency light and a second mixed-frequency light with parallel emission directions, and irradiating the first mixed-frequency light and the second mixed-frequency light onto the first photosensitive surface and the second photosensitive surface respectively to generate corresponding first electrical signals and second electrical signals;

[0023] The first electrical signal and the second electrical signal are resolved to obtain the speed and direction of the moving object being measured.

[0024] In one embodiment, the process of calculating the first electrical signal and the second electrical signal to obtain the speed direction of the moving object is as follows:

[0025] Obtain a first phase of a signal on the first photosensitive surface based on the first electrical signal, and obtain a second phase of a signal on the second photosensitive surface based on the second electrical signal;

[0026] When the first phase of the signal on the first photosensitive surface is ahead of the second phase of the signal on the second photosensitive surface, the speed direction of the moving object being measured is one of the positive direction and the negative direction;

[0027] When the second phase of the signal on the second photosensitive surface is ahead of the first phase of the signal on the first photosensitive surface, the speed direction of the moving object being measured is the other one of the positive direction and the negative direction.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] The present invention arranges a second spectrometer to split the original mixed light generated by mixing the reference light and the scattered light into a first mixed light and a second mixed light with an optical path difference and parallel emission directions. The first mixed light and the second mixed light are received respectively by the first photosensitive surface and the second photosensitive surface. The speed direction of the moving object to be measured can be identified based on the phase sequence of the signals on the first photosensitive surface and the second photosensitive surface. While increasing the direction identification function, the volume of the test system can be kept basically unchanged, which is conducive to the miniaturization development of the direction-identifiable laser Doppler speed measurement system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0031] Figure 1 FIG1 is a structural diagram of a laser Doppler velocity measurement system based on phase identification in an embodiment of the present invention;

[0032] Figure 2 1 is an equivalent optical path diagram of the reference beam laser Doppler velocimetry system in an embodiment of the present invention.

[0033] Reference numerals: laser 1, first spectrometer 2, neutral filter 3, reflector 4, moving object to be measured 5, second spectrometer 6, photoelectric detection assembly 7, first photosensitive surface 8, second photosensitive surface 9.

[0034] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0037] like Figure 1 The following is a diagram showing a laser Doppler velocity measurement system based on phase directionality disclosed in this embodiment, which primarily includes a laser 1, a first spectrometer 2, a neutral filter 3, a reflector 4, a second spectrometer 6, a photoelectric detection assembly 7, and a signal processing module. The laser 1, the first spectrometer 2, and the moving object 5 to be measured are sequentially spaced apart along a first direction, while the reflector 4, the neutral filter 3, the first spectrometer 2, the second spectrometer 6, and the photoelectric detection assembly 7 are sequentially spaced apart along a second direction, and the first and second directions are not parallel. Specifically:

[0038] Laser 1 is used to output continuous laser;

[0039] The first optical splitter 2 is located in the optical path of the continuous laser, and is used to split the continuous laser into reference light and signal light, and reflect scattered light in the opposite direction to the signal light;

[0040] The reflective element 4 is located on the optical path of the reference light and is used to return the reference light along the original path and mix it with the scattered light through the first optical splitter 2 to generate the original mixed light;

[0041] The neutral density filter 3 is located between the reflective element 4 and the first spectrometer 2 and is used to absorb part of the reference light so that the intensity of the reference light incident on the photoelectric detection assembly 7 is as equal as possible to the intensity of the scattered light.

[0042] The second optical splitter 6 is located on the optical path of the original mixed light, and is used to split the original mixed light into a first mixed light and a second mixed light with parallel emission directions and a certain optical path difference;

[0043] The photoelectric detection assembly 7 has a first photosensitive surface 8 and a second photosensitive surface 9 located in the same plane. The first photosensitive surface 8 is located in the optical path of the first mixed-frequency light, and the second photosensitive surface 9 is located in the optical path of the second mixed-frequency light. The photoelectric detection assembly 7 is used to convert the interference signals on the first photosensitive surface 8 and the second photosensitive surface 9 into a first electrical signal and a second electrical signal.

[0044] The signal processing module is connected to the photoelectric detection component 7 and is used to resolve the first electrical signal and the second electrical signal to obtain the speed and direction of the moving object 5 being measured.

[0045] In a specific implementation, first beam splitter 2 is a beam splitter prism, second beam splitter 6 is a laminated trapezoidal prism consisting of a right-angle prism and an rhombus prism, and reflector 4 is a full reflector. Photoelectric detection assembly 7 can either integrate the functional units of two photoelectric detectors into a single housing or utilize two separate photoelectric detectors.

[0046] In this embodiment, the path difference between the first mixed frequency light and the second mixed frequency light in the second beam splitter 6 is equal to the center distance between the first photosensitive surface 8 and the second photosensitive surface 9 .

[0047] The specific working process of the laser Doppler velocity measurement system based on phase identification in this embodiment is as follows:

[0048] The continuous laser light output by laser 1 passes through first spectrometer 2 and is split into two beams of equal intensity, one serving as reference light and the other as signal light. The reference light returns along its original path after passing through neutral filter 3 and reflector 4, then passes through first spectrometer 2 and second spectrometer 6 to reach first photosensitive surface 8 and second photosensitive surface 9 of photoelectric detection assembly 7. The signal light is directly incident on the surface of the moving object 5 being measured and scattered. The scattered light returning in the original direction of the signal light passes through first spectrometer 2 and second spectrometer 6 to reach first photosensitive surface 8 and second photosensitive surface 9 of photoelectric detection assembly 7, where it mixes with the reference light. The first and second electrical signals output by photoelectric detection assembly 7 are collected by the data acquisition card in the signal processing module and transmitted to a PC for processing, where the Doppler frequency is extracted and the velocity v of the moving object 5 being measured is obtained.

[0049] The relationship between the Doppler frequency and the motion speed of the optical path structure of the laser Doppler velocity measurement system in this embodiment is:

[0050]

[0051] Wherein, v is the velocity of the moving object 5 to be measured, θ is the angle between the signal light and the moving direction of the surface of the moving object 5 to be measured, and λ is the wavelength of the laser.

[0052] In this embodiment, the photoelectric detection assembly 7 has a first photosensitive surface 8 and a second photosensitive surface 9 located on the same plane.

[0053] In addition, the path difference between the first mixed light and the second mixed light reaching the first photosensitive surface 8 and the second photosensitive surface 9 of the photodetection assembly 7 within the second beam splitter 6 is d, and the optical path difference is δ=nd, where n is the refractive index of the second beam splitter 6. Because the first mixed light and the second mixed light are parallel and perpendicular to the first photosensitive surface 8 and the second photosensitive surface 9 of the photodetection assembly 7, the distance between the centers of the first photosensitive surface 8 and the second photosensitive surface 9 is equal to the path difference, that is, the distance between the centers of the first photosensitive surface 8 and the second photosensitive surface 9 is d.

[0054] The optical path structure of the reference beam laser Doppler velocimetry system is essentially a Michelson interference optical path, which can be equivalent to: Figure 2 model. Figure 2 In the figure, point S1 is the image of the moving object 5 to be measured with respect to the first spectrometer 2, point S2 is the position of the reflective device 4, the distance between point S1 and point S2 is l, the optical path from the reflective device 4 to the first photosensitive surface 8 is l1, the distance from point P on the first photosensitive surface 8 to the center of the first mixed light beam is r1, and the distance from point P′ on the second photosensitive surface 9 to the center of the laser beam is r2.

[0055] The optical path difference δ1 between the reference light and the signal light reaching the first photosensitive surface 8 is:

[0056]

[0057] Similarly, the optical path difference δ2 between the reference light and the signal light reaching the second photosensitive surface 9 can be obtained as follows:

[0058]

[0059] Among them, S1P is the distance between point S1 and point P, S2P is the distance between point S2 and point P, S1P′ is the distance between point S1 and point P′, and S2P′ is the distance between point S2 and point P′.

[0060] From the above equations (2) and (3), it can be seen that the interference fringes of the first mixed light and the second mixed light are circular fringes with the positions of the beam centers on the first photosensitive surface 8 and the second photosensitive surface 9 as the centers.

[0061] To simplify the problem, it is assumed that the electric field expressions of the reference light and the signal light incident on the photoelectric detection component 7 are:

[0062]

[0063]

[0064] Among them, E1 and E2 are the amplitudes of reference light and signal light respectively, f0 is the emission frequency of laser 1, and f D is the Doppler frequency, and are the initial phases of the reference light and the signal light, respectively. Ignoring the high-frequency terms, the light intensity I1 of the interference field on the first photosensitive surface 8 is obtained as:

[0065]

[0066] Considering the optical path difference between the reference light and the signal light in space, the above formula (6) should be changed to:

[0067]

[0068] The total phase difference is:

[0069]

[0070] From the above formula (8), we can know that when the moving object 5 is stationary, f D = 0, the fringes do not move. When the moving object 5 moves, the interference fringes will move in a certain direction as time changes.

[0071] Define the measured moving object 5 when it moves in the forward direction f D The sign of is positive, then the total phase difference of the signal on the first photosensitive surface 8 is Define f when the moving object 5 moves in the opposite direction D The sign is negative, then the total phase difference of the signal on the first photosensitive surface 8 is It can be seen from this that when the moving direction of the detected moving object 5 is different, the moving direction of the stripes is also different, so the moving direction of the object can be determined based on the moving direction of the stripes.

[0072] In order to identify the moving direction of the fringes, this embodiment uses a glued trapezoidal prism as the second beam splitter 6, and adds a channel of receiving light to the traditional laser Doppler velocimetry system, namely, the interference light incident on the second photosensitive surface 9.

[0073] The light intensity I2 of the interference field on the second photosensitive surface 9 is:

[0074]

[0075] For the center point O of the first photosensitive surface 8 and the center point O′ of the second photosensitive surface 9, Therefore, the total phase difference between the surface signals of the first photosensitive surface 8 and the second photosensitive surface 9 is And the phase difference satisfies:

[0076]

[0077] That is to say, the center distance d between the first photosensitive surface 8 and the second photosensitive surface 9 should satisfy:

[0078]

[0079] When the velocity direction of the moving object is positive:

[0080]

[0081] in, is the phase of the signal received by the first photosensitive surface 8, is the phase of the signal received by the second photosensitive surface 9 . At this time, the phase of the signal received by the second photosensitive surface 9 is ahead of the phase of the signal received by the first photosensitive surface 8 by π / 2.

[0082] When the velocity of a moving object is negative, so can be rewritten as:

[0083]

[0084] at this time:

[0085]

[0086] At this time, the phase of the signal received by the first photosensitive surface 8 leads the phase of the signal received by the second photosensitive surface 9 by π / 2.

[0087] Therefore, the velocity direction of the moving object 5 can be identified based on the phase sequence of the signals on the first photosensitive surface 8 and the second photosensitive surface 9. Equations (12) and (14) again illustrate that the direction of movement of the interference fringes corresponds to the direction of movement of the moving object, and the direction can be identified based on the lead or lag relationship between the phases of the two signals.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A laser Doppler velocity measurement system based on phase orientation, characterized in that: include: A laser, used for outputting continuous laser light; a first optical splitter, located in the optical path of the continuous laser, for splitting the continuous laser into reference light and signal light, and reflecting scattered light in a direction opposite to that of the signal light; a reflective device, located on the optical path of the reference light, for returning the reference light along the original path, and mixing the reference light with the scattered light through the first spectrometer to generate original mixed light; a second light splitting device, located on the optical path of the original frequency-mixed light, for splitting the original frequency-mixed light into a first frequency-mixed light and a second frequency-mixed light with parallel emission directions; A photoelectric detection assembly having a first photosensitive surface and a second photosensitive surface located in the same plane, wherein the first photosensitive surface is located in the optical path of the first mixed-frequency light, and the second photosensitive surface is located in the optical path of the second mixed-frequency light, and is used to convert the interference signals on the first photosensitive surface and the second photosensitive surface into a first electrical signal and a second electrical signal; The signal processing module is electrically connected to the photoelectric detection component and is used to resolve the first electrical signal and the second electrical signal to obtain the speed and direction of the moving object being measured.

2. The laser Doppler velocity measurement system based on phase orientation identification according to claim 1, characterized in that: The center distance between the first photosensitive surface and the second photosensitive surface is: Wherein, d represents the center distance between the first photosensitive surface and the second photosensitive surface, λ is the laser wavelength, n is the refractive index of the second spectrometer, and N is the periodic constant.

3. The laser Doppler velocity measurement system based on phase orientation discrimination according to claim 1 or 2, characterized in that: The second light splitting device is a cemented trapezoidal prism composed of a right-angle prism and a rhombus prism.

4. The laser Doppler velocity measurement system based on phase orientation identification according to claim 2, characterized in that: The path difference between the first frequency-mixed light and the second frequency-mixed light in the second light-splitting device is equal to the center distance between the first photosensitive surface and the second photosensitive surface.

5. The laser Doppler velocity measurement system based on phase orientation identification according to claim 1 or 2, characterized in that: Also includes neutral density filters; The neutral density filter is located between the reflective component and the first spectroscopic component.

6. A laser Doppler velocity measurement method based on phase orientation, characterized in that: Using the system according to any one of claims 1 to 5, the laser Doppler velocity measurement method based on phase direction identification comprises the following steps: The continuous laser beam output by the laser is split into reference light and signal light, and the signal light is irradiated on the surface of the moving object to be measured; Reflect the reference light so that it mixes with the scattered light returning in the direction of the signal light to generate the original mixed light; Splitting the original mixed-frequency light into a first mixed-frequency light and a second mixed-frequency light with parallel emission directions, and irradiating the first mixed-frequency light and the second mixed-frequency light onto the first photosensitive surface and the second photosensitive surface respectively to generate corresponding first electrical signals and second electrical signals; The first electrical signal and the second electrical signal are resolved to obtain the speed and direction of the moving object being measured.

7. The laser Doppler velocity measurement method based on phase orientation identification according to claim 6, characterized in that: The process of solving the first electrical signal and the second electrical signal to obtain the speed direction of the moving object is as follows: Obtain a first phase of a signal on the first photosensitive surface based on the first electrical signal, and obtain a second phase of a signal on the second photosensitive surface based on the second electrical signal; When the first phase of the signal on the first photosensitive surface is ahead of the second phase of the signal on the second photosensitive surface, the speed direction of the moving object being measured is one of the positive direction and the negative direction; When the second phase of the signal on the second photosensitive surface is ahead of the first phase of the signal on the first photosensitive surface, the speed direction of the moving object being measured is the other one of the positive direction and the negative direction.

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