A holographic particle velocity measurement method and device using a continuous light source and a low frame rate single camera

Abstract

The present invention discloses a holographic particle velocity measurement method using a continuous light source and a low frame rate single camera: the light beam emitted by the continuous light source is filtered, expanded and collimated to form parallel light, and the parallel light is segmented; the measured particle passes through the segmented parallel light, and the low frame rate camera continuously records two or more frames of particle holograms; the hologram is reconstructed to obtain the three-dimensional position of the particle, thereby calculating the actual position of the particle, and using the particle matching algorithm to obtain the three-dimensional velocity of the particle. The present invention also discloses a holographic particle velocity measurement device: a continuous light source, a filtering, expanding and collimating system, a reflector and a low frame rate camera. The light beam emitted by the continuous light source is filtered, expanded and collimated to form parallel light, and the parallel light is segmented by the reflector and irradiated to the moving particles; the camera records continuous multiple frames of particle holograms. The measurement system used in the method and the device is simple in structure, low in cost and easy to implement; the segmented parallel light method greatly increases the upper limit of velocity measurement, and has strong adjustable performance.

Description

Technical Field

[0001] The present invention relates to the field of multiphase flow measurement, and in particular to a holographic particle velocity measurement method and device using a continuous light source and a low frame rate single camera. Background Art

[0002] In many fields of industrial production and scientific research, multiphase flow is a widespread physical process. Effective measurement of particle parameters is an important basis for in-depth understanding of the flow process mechanism, solving scientific problems and optimizing production.

[0003] The main methods for measuring particle velocity in multiphase flow include laser Doppler velocimetry, particle image velocimetry, spatial filtering, electrostatic method, and imaging methods such as multiple exposures, long exposures, and multi-frame shooting with high-speed cameras. The classic Doppler velocimetry technology has been widely used in the field of flow field diagnosis, but it is limited to single-point measurement, and is currently limited to laboratory environments due to the complexity of the system, expensive equipment, and difficulty in on-site layout. It is extremely difficult to apply it to industrial online measurement. Particle image velocimetry technology is also widely used in flow field diagnosis due to its full-field, non-contact, two-dimensional, transient, and high-precision characteristics. Like Doppler velocimetry technology, it is difficult to apply it to industrial sites due to its high price and complex equipment. The spatial filtering method is difficult to ensure measurement accuracy because the determination of the frequency peak is easily interfered by other factors. The electrostatic method generally measures the average particle velocity and cannot obtain the velocity of a single particle in the flow field. Imaging methods such as multiple exposures, long exposures, and multi-needle shooting have high requirements on the performance of the light source or camera, such as pulsed lasers or high-speed cameras, which are expensive, and in practical applications, they are easily affected by the problem that the measured particles adhere to the optical window and affect the measurement.

[0004] Digital holography is a three-dimensional measurement technology that uses digital recording and digital reconstruction to easily record and save holograms. Digital holography measures the particle field by measuring each particle in the particle field, and can obtain the motion information, geometric information and position information of each particle. For example, the Chinese patent with publication number CN109297874A discloses a holographic real-time measurement method for measuring the particle size of moving particles, including: a sheet laser beam expansion system generates a sheet laser and irradiates the moving particles; the scattered light of the sheet laser passing through the particles forms object light, and the sheet laser that has not passed through the particles is used as reference light. The object light and the reference light interfere to form one-dimensional holographic fringes, which are recorded; the hologram formed by the recorded one-dimensional holographic fringes is reconstructed to obtain a particle image, and the particle size is calculated based on the number and size of pixels in the particle image.

[0005] At present, the holographic technology is generally used for speed measurement using high-speed cameras and pulsed light sources, which has high measurement costs and complex systems. For example, the Chinese patent with publication number CN212410375U discloses a device for particle detection and particle size measurement in an atmospheric cloud field: a laser beam expansion parallel system, which generates a parallel beam to illuminate the particle detection area. When particles exist, the particles generate particle scattered light; a particle detection and holographic shooting system, including a digital camera, which is used to determine whether there are particles in the particle detection area. When particles exist, part of the particle scattered light enters the digital camera and records the particle hologram of the particle detection area under the control of the control and data processing system; the control and data processing system includes a photodetector, and another part of the particle scattered light triggers the photodetector to generate a pulse trigger signal; the control and data processing system uses the pulse trigger signal generated by the photodetector to control the digital camera to shoot the particle hologram, and reconstruct and process it to obtain the particle size. In addition, the holographic system using ordinary continuous light sources and low frame rate cameras is limited by the extremely limited frame rate speed measurement, and is mostly used for nearly static particle fields, such as particle measurement dispersed in a solution. Summary of the invention

[0006] The purpose of the present invention is to provide a holographic particle velocity measurement method and device using a continuous light source and a low frame rate single camera. The upper limit of velocity measurement is greatly improved by segmenting the parallel light beam, solving the problem that ordinary holographic systems using continuous light sources and low frame rate cameras can only measure particles with extremely low moving speeds.

[0007] The present invention provides the following technical solutions:

[0008] A holographic particle velocity measurement method using a continuous light source and a low frame rate single camera, the method comprising the following steps:

[0009] (1) The light beam emitted by the continuous light source is filtered, expanded and collimated to form parallel light, and the parallel light is segmented, and the number of segments is n, where n>1;

[0010] (2) The measured particle passes through segmented parallel light, and a low frame rate camera continuously records two or more frames of particle holograms;

[0011] (3) Reconstruct the hologram to obtain the three-dimensional position of the particle, thereby calculating the actual position of the particle and using the particle matching algorithm to obtain the three-dimensional velocity of the particle.

[0012] In step (3), the reconstruction method is a wavelet reconstruction algorithm, and the reconstructed three-dimensional position of the particle is (x h ,y h ,z h ), combined with the beam segment number n where the particle is located, the actual position of the particle in the system coordinates (xr ,y r ,z r ); the particle matching algorithm is the nearest neighbor method, and the origin of the camera target surface is the origin of the system coordinates.

[0013] The calculation formula of the beam segment number n is:

[0014]

[0015] Among them, "ceil" is the rounding function, and the length of the incident section on the camera target surface is l 0 , the length of other segments is l, and the distance between two adjacent segments is h;

[0016] The actual position of the particle in the system coordinates (x r ,y r ,z r ) is calculated as:

[0017] x r =x h

[0018] y r =(n-1)h+y h

[0019]

[0020] The particle velocity calculation method is:

[0021]

[0022] Among them, (u x ,u y ,u z ) particle three-dimensional velocity, δt is the time interval between frames, (x i ,y i ,z i ) is the actual position of the particle in a frame, (x j ,y j ,z j ) is the actual position of the matched particle in the next frame.

[0023] The present invention also provides a holographic particle velocity measuring device using a continuous light source and a low frame rate single camera, the holographic particle velocity measuring device comprising: a continuous light source, a filtering, beam expanding and collimating system, a reflector and a low frame rate camera; the light beam emitted by the continuous light source passes through the filtering, beam expanding and collimating system to form parallel light, the parallel light is segmented by the reflector and then irradiated to the moving particles; the low frame rate camera records continuous multi-frame particle holograms.

[0024] The filtering, beam expanding and collimating system comprises an objective lens, a pinhole and a lens.

[0025] The continuous light source may be a visible light source with a wavelength of 400nm to 700nm, such as a laser or a laser diode.

[0026] The low frame rate camera is a common industrial camera, the frame rate f is less than or equal to 100 frames per second, and the target surface size is W×H.

[0027] The reflector is a reflective prism.

[0028] The holographic particle velocity measuring device adopts a coaxial holographic system, that is, the object light and the reference light propagate in the same direction.

[0029] Generally, the particle flow speed is mainly in one direction, while the speeds in the other two directions are relatively small. The holographic particle velocity measurement method provided by the present invention using a continuous light source and a low frame rate single camera has an upper limit of speed measurement in each direction of:

[0030] u x,max =W·f

[0031] u y,max =[(n-1)h+H]·f

[0032] u z,max =L·f

[0033] Wherein L is the range of the particle field in the z-axis. From the above formula, it can be seen that the measurement method provided by the present invention can greatly improve the upper limit of the measurement of the velocity in the y-direction.

[0034] The main problem solved by the present invention is to solve the problem of complex system and high cost of the current particle velocity holographic measurement method, and at the same time solve the problem that the ordinary holographic system using continuous light source and low frame rate camera can only measure particles with extremely low moving speed. The upper limit of velocity measurement is greatly improved by segmenting the parallel light beam.

[0035] The advantages of the present invention are: 1. The present invention uses continuous laser and ordinary low frame rate camera, and the measurement system has a simple structure, low cost and easy implementation; 2. The present invention provides a parallel light segmentation method, which greatly improves the upper limit of speed measurement and has strong adjustable performance. The number of parallel light segments of the system can be changed according to actual measurement requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic structural diagram of a holographic particle velocity measurement device provided by the present invention;

[0037] Figure 2 A schematic structural diagram of another holographic particle velocity measurement device provided by the present invention;

[0038] Figure 3 The first frame of particle hologram recorded by the camera in the embodiment;

[0039] Figure 4 The second frame of particle hologram recorded by the camera in the embodiment;

[0040] Among them, 1. continuous light source, 2. filtering, beam expansion and collimation system, 3. parallel light, 4. measurement area, 5. particles in the previous frame, 6. reflector, 7. particles in the next frame, and 8. low frame rate camera. DETAILED DESCRIPTION

[0041] The specific implementation modes of the present invention will be further described below in conjunction with the accompanying drawings.

[0042] Example 1

[0043] like Figure 1 The holographic particle velocity measuring device shown uses a continuous light source and a low frame rate single camera. The light beam emitted by the continuous light source 1 passes through the filtering beam expansion collimation system 2 to form parallel light 3. The parallel light 3 irradiates the particles in the measurement area 4, and then irradiates the particles in the measurement area 4 again after being reflected by two reflectors 6. The low frame rate camera 8 records the holograms of the particles 5 in the previous frame and the particles 7 in the next frame respectively.

[0044] Specifically, in this embodiment, the continuous light source 1 adopts a semiconductor continuous laser with a wavelength of 532 nanometers. The frame rate of the low frame rate camera 8 is 100fps, and the time interval δt between two frames is 0.01s. The camera resolution is 2048×2045, the pixel size is 5 microns, and the camera target surface size is 10.24mm×10.24mm. The width of the measurement area is 40mm. In this embodiment, the number of parallel light segments n is 2, where a length l incident on the camera target surface 0 It is 60mm, and the distance h between two adjacent sections is 20mm.

[0045] It can be calculated that the upper limit of the three-dimensional velocity measurement of this device is u x,max =1.024m / s,u y,max =3.024m / s,u z,max =4m / s, the upper limit of speed measurement in the y direction is increased by nearly 3 times.

[0046] Figure 3 is the first frame of particle hologram recorded by the camera, and the three-dimensional position coordinates of the particle are reconstructed as (x h =4.107mm,y h =4.107mm,z h =120mm), according to the beam segment number n, the calculation formula is:

[0047]

[0048] It can be concluded that it is located in the second parallel light segment, that is, n = 2. According to the actual position of the particle in the system coordinates, the calculation formula is:

[0049] x r =x h

[0050] y r =(n-1)h+y h

[0051]

[0052] The actual three-dimensional position of the particle is (x r1 =4.107mm,y r1 =24.107mm,z r1 =20mm).

[0053] Same reason Figure 4 The second frame of particle hologram recorded by the camera is reconstructed to obtain the three-dimensional position coordinates of the particle (x h =7.110mm,y h =6.109mm,z h =40mm), located in the first parallel light segment, the actual three-dimensional position of the particle is (x r2 =7.110mm,y r2 =6.109mm,z r2 =40mm).

[0054] According to the particle three-dimensional velocity calculation formula:

[0055]

[0056] The three-dimensional velocity of the particle is (u x =0.3m / s,u y =1.8m / s,u z =2.0m / s).

[0057] Example 2

[0058] like Figure 2 The holographic particle velocity measuring device shown uses a continuous light source and a low frame rate single camera. The light beam emitted by the continuous light source 1 passes through the filtering beam expansion collimation system 2 to form parallel light 3. The parallel light 3 irradiates the particles in the measurement area 4, and then irradiates the particles in the measurement area 4 again after being reflected by two reflectors 6. After 4 reflections, the measurement area 4 is irradiated twice. The low frame rate camera 8 records the holograms of the particles 5 in the previous frame and the particles 7 in the next frame respectively. In this embodiment, the number of parallel light segments n is 4.

[0059] The method for measuring particle velocity using the holographic particle velocity measuring device of this embodiment is the same as that in Embodiment 1.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A holographic particle velocity measurement method using a continuous light source and a low frame rate single camera, characterized in that: The method comprises the following steps: (1) The light beam emitted by the continuous light source is filtered, expanded and collimated to form parallel light, and the parallel light is segmented, and the number of segments is n, where n>1; (2) The measured particle passes through segmented parallel light, and a low frame rate camera continuously records two or more frames of particle holograms; (3) Reconstruct the hologram to obtain the three-dimensional position of the particle, thereby calculating the actual position of the particle and using the particle matching algorithm to obtain the three-dimensional velocity of the particle; In step (3), the reconstruction method is a wavelet reconstruction algorithm, and the reconstructed three-dimensional position of the particle is (x h ,y h ,z h ), combined with the beam segment number n where the particle is located, the actual position of the particle in the system coordinates (x r ,y r ,z r ); the particle matching algorithm is the nearest neighbor method, and the origin of the camera target surface is the origin of the system coordinates; The calculation formula of the beam segment number n is: Among them, "ceil" is a rounding function, the length of the parallel light incident on the camera target surface is l0, the length of other parallel light segments is l, and the distance between two adjacent parallel light segments is h; The actual position of the particle in the system coordinates (x r ,y r ,z r ) is calculated as: x r =x h y r =(n-1)h+y h The particle velocity is calculated as: Among them, (u x ,u y ,u z ) particle three-dimensional velocity, δt is the time interval between frames, (x i ,y i ,z i ) is the actual position of the particle in a frame, (x j ,y j ,z j ) is the actual position of the matched particle in the next frame.

2. A holographic particle velocity measuring device using a continuous light source and a low frame rate single camera using the method of claim 1, characterized in that: The holographic particle velocity measuring device comprises: a continuous light source, a filtering, beam expanding and collimating system, a reflector and a low frame rate camera; the light beam emitted by the continuous light source passes through the filtering, beam expanding and collimating system to form parallel light, and the parallel light is segmented by the reflector and then irradiated to the moving particles; the low frame rate camera records continuous multi-frame particle holograms.

3. The holographic particle velocity measuring device using a continuous light source and a low frame rate single camera according to claim 2, characterized in that: The filtering, beam expanding and collimating system comprises an objective lens, a pinhole and a lens.

4. The holographic particle velocity measuring device using a continuous light source and a low frame rate single camera according to claim 2, characterized in that: The continuous light source may be a visible light source with a wavelength of 400nm to 700nm, such as a laser or a laser diode.

5. The holographic particle velocity measuring device using a continuous light source and a low frame rate single camera according to claim 2, characterized in that: The low frame rate camera is a common industrial camera, the frame rate f is less than or equal to 100 frames per second, and the target surface size is W×H.

6. The holographic particle velocity measuring device using a continuous light source and a low frame rate single camera according to claim 2, characterized in that: The reflector is a reflective prism.

7. The holographic particle velocity measuring device using a continuous light source and a low frame rate single camera according to claim 2, characterized in that: The holographic particle velocity measuring device adopts a coaxial holographic system.

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