JPH10318909A - Particle measuring device and laser doppler current meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the easy adjustment of the position of a light receiving system in a particle measuring device which measures the velocity and shape of particles. SOLUTION: A laser beam is divided by a laser light source and converged to one point by a lens 15. The converged light is converged and enlarged at another area by lenses 21 and 22. A mirror 23 with a slit is arranged between the lenses 21 and 22, and the optical axis is adjusted by rotating the mirror 23 with a slit to reflect light at the time of adjustment. By passing light after adjustment, the velocity and shape of particles are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser Doppler velocimeter and a particle measuring apparatus for measuring the velocity and shape of a particle by detecting a shadow of the particle passing through a measurement area using the laser Doppler velocimeter. Things.

[0002]

2. Description of the Related Art A laser Doppler velocimeter is used as an apparatus for measuring the flow velocity of fine particles floating in the air. The laser Doppler velocimeter crosses two laser beams to form an interference fringe in an intersection area, and detects the speed of particles passing through the intersection area based on the frequency of scattered light. Such a laser Doppler velocimeter can measure the velocity of the particles, but cannot obtain the shape information of the particles.

In Japanese Patent Application Laid-Open No. 7-55693, this laser Doppler velocimeter is used, and the intersection area is further enlarged by using an optical system to form a second intersection area.
2. Description of the Related Art A particle measuring apparatus has been proposed in which photoelectric conversion elements arranged in a dimension are used to measure the shape of particles based on the shadow of particles that block an intersection area. FIG. 9 is a block diagram showing an example of such a particle measuring device. As shown in the figure, the particle measuring apparatus has a beam splitter 101 disposed in front of a laser light source 100, splits a laser beam into two laser lights, shifts the frequency by frequency shifters 102 and 103, and collects a condensing lens. Cross at 104 at one point. Intersecting forms interference fringes in the intersection area. The mirror 105 and the condenser lens 106 collect the scattered light behind the particles passing through the intersection area, and the photodiode 107 and the frequency measuring device 108 determine the passing speed of the particles based on the frequency of the scattered light. It is to be measured. The laser beam having the crossed area formed thereon is condensed again by using the lenses 109 and 110 to form an enlarged crossed area. Then, the line sensor 111 is arranged at a position where the light is focused by the lens 110, and the photoelectric conversion signal obtained from the line sensor 111 at a constant speed is taken into the arithmetic unit 114 via the MPX 112 and the A / D converter 113. In this way, the shape of the particles can be measured by the calculating means 114 based on the speed of the particles passing through the intersection area and the information from the line sensor.

In such a conventional particle measuring apparatus, it is necessary to obtain the particle velocity by a photodiode 107 and a frequency measuring device 108 based on a Doppler signal from the particle. Here, as shown in FIG. 9, in order to easily adjust the optical system, a photoelectric conversion element is arranged behind the measurement area,
Backscattering type optical systems that receive scattered light scattered backward are mainly used.

[0005]

However, in such a conventional particle measuring apparatus, the intensity of the scattered light varies depending on the ratio between the laser wavelength λ and the particle diameter, but is substantially proportional to the sixth or second power of the particle diameter. I do. Therefore, as the size of the particles becomes smaller, the signal intensity becomes weaker, and the detection of the velocity of fine particles becomes impossible, so that the shape of the particles cannot be measured. In order to solve such a problem, it is conceivable to receive forward scattered light whose intensity of scattered light is about 100 times that of back scattered light. When receiving forward scattered light, it is necessary to arrange the mirror 105, the condenser lens 106, and the photodiode 107 between the lenses 109 and 110. However, there is a disadvantage that a laser Doppler velocimeter for backscattering which has already been used cannot be used.

It is also conceivable to use the optical system for receiving the backscattered light as it is and to receive the forward scattered light backward.
FIG. 10 shows the arrangement of the optical elements in this case.
15 are arranged. The corner cube 115 reflects the incident light in the incident direction as it is, and returns the forward scattered light to the lens 109 side. This allows the scattered light to be reflected by the mirror 105 via the lens 104 and received by the photodiode 107. At this time, the photodiode 107 also receives the backscattered light, but since the level of the forward scattered light is high, almost all of the forward scattered light is received. Also, if the focus of the lens 109 is adjusted to the measurement area, the forward scattered light passing through the lens 109 is also parallel light, so that the position of the corner cube 115 can be easily adjusted. However, whether the forward scattered light passing through the lens 109 is parallel light,
Whether or not the focus of No. 9 is in the measurement area cannot be confirmed only by the scattered light. To confirm this, use lens 1
Whether or not the focal points coincide with the measurement area can be confirmed by whether or not the direct beams from the two laser light sources passing through the lens 109 by removing 10 are parallel at a distance. However, this method has a disadvantage that the lens 110 needs to be attached and detached, and the adjustment is troublesome.

The diameter of the corner cube 115 is made larger than the distance between the two direct beams, and the two beams are returned directly to the lens 109 via the corner cube to make the lens 10.
It is also conceivable to adjust the optical system so that the original beam and the returned beam completely overlap between 4,109.
When this adjustment method is used, a simple mirror can be used instead of a corner cube. However, in this state, the laser beam is directly incident on the photodiode and the beam does not go to the lens 110, so that an enlarged crossing region cannot be created and cannot be used as a particle measuring device. Therefore, after adjusting the optical system, it was necessary to change to a corner cube having a small diameter.

The present invention has been made in view of such conventional problems, and has as its object to facilitate adjustment of an optical system in a particle measuring device and a laser Doppler velocimeter. .

[0009]

According to a first aspect of the present invention, there is provided a light source means for converging and intersecting two laser beams to form an interference fringe in a first intersection area; A first lens that converts a laser beam having an intersecting region into parallel light, a second lens that forms parallel light from the first lens in a second intersecting region to form interference fringes, A mirror disposed between the first and second lenses so as to be rotatable along a central axis perpendicular to the plane and having a passage area through which the two laser beams pass, and a mirror passing through the first intersection area A light receiving element for receiving scattered light forward and backward of the particles to be measured, a particle velocity measuring means for measuring the velocity of the particles based on the frequency of the scattered light received by the light receiving element, and A plurality of photoelectric conversions for receiving a shadow projected on the resulting second interference fringe Means, a particle velocity signal from the particle velocity measuring means, and a calculating means for configuring the shape of the particles by a time-series projection shape of the particles from the plurality of photoelectric conversion means, and Is what you do.

According to a second aspect of the present invention, in the particle measuring device of the first aspect, the mirror has a linear passing area including a central axis thereof.

According to a third aspect of the present invention, two laser beams are condensed and intersected to form an interference fringe in an intersecting region, and the laser beam having the intersecting region is converted into parallel light. A lens, a mirror disposed behind the lens so as to be rotatable along a central axis perpendicular to the plane thereof, and having a passage area through which the two laser beams pass, and scattering of particles passing through the intersection area. It has a light receiving element for receiving light, and a particle velocity measuring means for measuring the velocity of particles based on the frequency of scattered light received by the light receiving element.

[0012]

FIG. 1 is a block diagram for explaining a main part of a particle measuring apparatus according to an embodiment of the present invention, and FIG. 2 is a perspective view showing an optical system. As shown in the figure, a laser beam is generated by a laser light source 11 and radiated to a beam splitter 13 via a polarizing plate 12 as in the above-described conventional example. The beam splitter 13 converts the laser beam into two parallel laser beams B1, B2 at the same intensity.
A frequency shifter 14, for example, a Bragg cell, for shifting the frequency is provided for one of the laser beams. The focusing lens 15 focuses two parallel laser beams at one point. Laser light source 11, polarizing plate 12, beam splitter 13, frequency shifter 14
The condenser lens 15 constitutes a light source means for converging and intersecting two laser beams to form an interference fringe. In this way, interference fringes can be formed at the intersection area, as in the above-described conventional particle measuring apparatus. And a mirror 1 for reflecting scattered light from the first intersection area.
6 and a condenser lens 17 for condensing the scattered light,
Further, a photodiode 18 is arranged at the focal position. The photodiode 18 is a light receiving element that detects scattered light, and its output is provided to a frequency measuring device 20 via an A / D converter 19. The frequency measuring device 20 is a particle velocity measuring means for measuring the frequency of the intensity change of the scattered light of the particles passing through the interference fringes and obtaining the velocity information of the particles.

On the other hand, the lens 21 is a first lens that converts light passing through the first intersection area into parallel light, and the lens 22 is a second lens that condenses the parallel light again at one point. The focal lengths of the lenses 21 and 22 are f1 and f2, respectively, and the focal length f1 of the lens 21 is equal to the distance from the lens 21 to the intersection area. In this way, the laser beam is converted into parallel light again by the lens 21. Further lens 22
Is to cross the parallel laser beams again. In this case, the lens 22 can form a second intersection region at the condensing position of the two laser beams.

In this embodiment, a mirror 23 having a slit is provided between the lenses 21 and 22, as shown in FIG. The mirror 23 with a slit is a mirror having a circular shape, a slit portion 23a having a constant width penetrating the center portion thereof, and the portion other than this portion is configured to totally reflect incident light. Then, a magnifying lens 24 is arranged at the position of the second interference fringe as shown in the figure, and the interference fringe is magnified and received by an optical fiber. The optical fiber 25 is obtained by arranging a plurality of, for example, 64 optical fibers 25a to 25n in a straight line in a line along the Z-axis with their end faces coincident.

At the other end of the optical fiber 25, a photoelectric conversion element for detecting the light receiving level of each fiber, for example, a photodiode array (PD array) 26 is arranged. The photodiode array 26 photoelectrically converts light emitted from each optical fiber, and constitutes a photoelectric conversion unit together with the optical fiber 25. The photoelectric conversion output of the photodiode array 26 is amplified and provided to a multiplexer (MPX) 27. Multiplexer 27
Is to multiplex the photoelectric conversion output at a fixed cycle,
The output is given to the comparator 28. The comparator 28 converts the input signal from the multiplexer 27 into a shadow of the laser beams B1 and B2,
Discrimination is made between three values, that is, a penumbra state in which one of B1 and B2 is shielded, and a non-shadow state in which both laser beams enter, and the output is given to the memory 29. Memory 2
Numeral 9 is for storing a particle image based on a photoelectric conversion signal from each fiber when a detection signal of a Doppler frequency is obtained after the optical fiber 25 is set at a predetermined position. The calculating means 30 is also provided with the output of the frequency measuring device 20 described above, and forms the shape of the particles passing through the first intersection area based on the image data temporarily stored in the memory 29.

FIG. 3 is a sectional view showing a lens holder 41 in which the lenses 21 and 22 and the mirror 23 with a slit and the magnifying lens 24 sandwiched between them are integrated. The lens holder 41 has a cylindrical shape, holds the lenses 21 and 22 and the magnifying lens 24 along the center axis thereof, and rotatably holds the circular slit mirror 23 between the lenses 21 and 22. ing. And slit mirror 23
Can be set to an arbitrary angle by rotating its outer peripheral portion, and is configured to be fixed at a desired angle. For example, pin insertion holes may be provided at intervals of 15 ° on the outer peripheral surface of a ring-shaped holder that holds the outer peripheral portion of the mirror 23, and after setting to a desired angle, the pins may be fixed from outside the case with the pins. Good.

Next, the operation of this embodiment will be described. Laser light is emitted from the laser light source 11 and the polarizing plate 12
The light is split by the beam splitter 13 via the laser beam into two laser beams B1 and B2 having the same intensity. The frequency of the laser beam B1 is shifted by the frequency shifter 14. Shift frequency f _s varies by the speed of the particles to be measured is, for example, several MHz~ tens MHz. Then, the light is crossed in the measurement area by the condenser lens 15. FIG. 4 is a diagram showing the lens 15, the laser beams B1 and B2, and the first intersection area M1. The intersection area M1 is an elliptical rotator-shaped area where two laser beams intersect, and has interference fringes as shown in the figure. The interval d _f between the interference fringes is given by the following equation, where θ is the intersection angle of the laser beams B1 and B2, and λ is the wavelength of the laser beam. d _f = λ / {2 sin (θ / 2)}

[0018] While unless a frequency shifter 14 the interference fringes is fixed, when shifting the frequency of one laser beam using a frequency shifter 14, the interference fringes also corresponding to the shift frequency f _s movement I do. Distance d _f of the interference fringes at this time is formed in the intersecting region M1 is constant.
Therefore, when the fine particles pass in the X-axis direction in the figure, the intensity of the scattered light changes according to the interference fringes when the fine particles pass through the intersection area M1. Thus the condenser lens 17, and detects the scattered light by the photodiode 18, by measuring the frequency f _p by the frequency measuring device 20 can measure the velocity of the particle from the following calculation. Also, the direction of the particles can be measured according to the direction of the frequency change. That is, the Doppler frequency f _d is calculated by the following equation. by measuring the f _d = f _s -f _p and Doppler frequency f _d, the velocity V of the particle is expressed by the following equation. V = d _f × f _d

Now, as shown in FIGS. 5A and 5B, the first
Are focused again by the lenses 21 and 22 to form the second intersection area M1.
Form 2 The first intersection area M1 is the second intersection area M
2 is enlarged by the ratio of the focal points of the lenses 21 and 22, and the magnification X1 is expressed by the following equation. X1 = f2 / f1

At the time of adjustment, the slit mirror 23 is rotated 90 ° from the state shown in FIG.
2 is applied to portions other than the slit. In this case, the laser beams B1 and B2 are reflected by the slit mirror 23. At this time, the position and the optical axis of the lens holder 41 are adjusted so as to return to the original optical path via the lens 21 and the lens 15. After the adjustment of the position of the light receiving system is completed, the slit mirror 23 is rotated to return to the position shown in FIG. In this case, the beams B1 and B2 do not directly enter the photodiode 18, and the second intersection region M2 enlarged by the lens 22 can be formed.

Then, the second intersection area M2 is enlarged by the magnifying lens 24 into a third intersection area M3, and the enlarged projection light is received via the optical fiber 25. FIG. 5 (c)
Shows the shape of the third intersection region M3 and the optical fiber 25 at the end face of the optical fiber 25 in which the first intersection region M1 and the second intersection region M2 are enlarged. The magnification X2 from the second intersection area M2 to the end face of the optical fiber 25 corresponds to the distance L between the magnifying lens 24 and the end face of the optical fiber 25. However, it is not easy to measure the magnification X2. Absent. Therefore, in the present embodiment, the distance between the end face of the optical fiber 25 and the magnifying lens 24 is adjusted as follows. FIG.
Represents the amplitude of the photoelectric conversion signal from one fiber 25-i of the optical fiber 25 at different distances L.
Assuming that the diameter of the core on which the light of each optical fiber 25 enters is φ,
The photoelectric conversion signal obtained in each fiber corresponds to the brightness of the expanded interference fringe.

[0022] When the away end face of the optical fiber 25 from the magnification lens 24, the magnification of the third intersection region M3 increases, the interval D _f of the magnified fringes larger than phi (phi <
D _f ). Therefore, a sinusoidal signal is obtained from each fiber. If it brought closer to the end face of Matahikari fiber 25 to the magnifying lens 24 spacing D _f of relatively enlarged interference fringes as shown in FIG. 7 decreases (φ> D _f). Thus gradually to adjust to approach the end face of the optical fiber 25 to the lens 24 than the distance, it reaches a position coinciding with the interval D _f of the interference fringes core diameter φ of the optical fiber is expanded. At the position of φ = D _f , the interference fringes move along the time axis, but a constant level of photoelectric conversion signal is always obtained from each optical fiber regardless of the movement of the interference fringes. That is, the photoelectric conversion output of the optical fiber is a DC component. Such a change occurs simultaneously in all the optical fibers.

FIG. 6 is a graph showing a change in the amplitude of the AC component of the photoelectric conversion signal with respect to the distance L from the end face of the optical fiber to the magnifying lens 23 for one optical fiber 25-i. When the optical fiber 25 is moved toward the magnifying lens 24 from a distance, the AC component first reaches a distance L1 at which the AC component becomes almost zero level. This distance L1 indicates that the core diameter φ of the optical fiber coincides with _Df, and the amplitude of each optical fiber is almost the same at a zero level. Further, at the distance L2, the AC component of the photoelectric conversion value of the fiber becomes substantially zero again. This position is the second zero level point where _2Df and φ coincide. Similarly, at the point of 3D _f = φ, the photoelectric conversion value becomes substantially zero. In the present embodiment, the optical fiber 25
The moved toward the magnifying lens 23, and check the level of the AC component calculated by the calculating means 30 on the display unit 31, the first position where the AC component is substantially zero, that is, the D _f and φ coincide distance L1 It is set to be as follows.

After the adjustment is completed, the size of each pixel coincides with the interval between interference fringes. That resolution of the particle shape of the particles passing through the first intersecting region M1 is the measurement point coincides with the interval d _f of the interference fringes. That is, similarly to the laser Doppler velocimeter, the shape of the particles can be detected without calibration using actual particles. When the particles p passing through the center of the first intersection area M1 in the X-axis direction are measured with the positions adjusted in this manner, the velocity V of the particles is obtained by the frequency measuring device 20. Then, the time resolution of the photoelectric conversion value stored in the memory 29 is associated with the speed component. FIG. 7A shows an image obtained by reconstructing the output obtained from the photodiode array 26 along the time axis. In this way, an image on which the shadow of the particles is projected can be reconstructed from the output of the linear photodiode array 26 obtained in a time series, and the shape of the particles passing through the measurement region can be measured. In this image, the resolution of one pixel in the Z-axis direction perpendicular to the plane of FIG.
becomes _f . One pixel in the X-axis direction in FIG. 1 is a time interval T between one line read out from the photodiode array.
And the product of the particle velocity V and the particle velocity V. In this way, the size of the particles can be recognized, and the shape of the particles can be measured. In FIG. 7, the number of optical fibers is represented as 16.

Normally, the particles are displaced without passing through the center of the first intersection area M1, but in this case, a state occurs in which one of the laser beams is shielded, so that the memory 2
The image stored in 9 is as shown in FIG. Therefore, a shadow image can be reconstructed by removing one of the overlapping shadows. The movement direction of the particles can be simultaneously measured as a vector from the two shadow images.

In this embodiment, the lenses 21 and 22 and the mirror 23 with a slit are held in one holder so that the mirror 23 with a slit is rotatable. However, these are independent and only the mirror 23 is rotatable. You may make it. Further, in this embodiment, a slit 23a penetrating the center is formed in the mirror 23, but other various shapes can be used as long as the laser beams B1 and B2 can be switched between reflection and transmission by rotation. Conceivable. For example, as shown in FIG. 8A, another mirror 23A may be formed with a slot elongated in the radial direction except for the center portion. Further, as shown in a mirror 23B in FIG. 8B, a slit excluding only the center may be formed in the diameter direction.
A V-shaped notch may be provided as shown in FIG. Further, as shown in FIG.
Only an arc-shaped notch may be provided in 3D. In FIG. 8, only the hatched portion is a mirror portion that reflects light. If the distance between the two laser beams B1 and B2 does not change significantly, as shown in FIG.
It is also conceivable to provide a circular opening in E and allow the laser beam to pass through only that part.

Although the present embodiment describes a particle measuring apparatus for measuring the velocity and shape of particles, the present invention measures the velocity of particles using only the portion before the lens 21 and the mirror 23 with slits. It is also possible to apply to a laser Doppler velocimeter.

[0028]

As described above in detail, according to the present invention, the mounting and dismounting of each lens becomes unnecessary by providing a mirror having a light transmitting portion between the first and second lenses.
Optical position adjustment can be easily performed. Further, after the adjustment, by rotating the mirror, there is obtained an effect that scattered light due to forward scattering can be received.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a particle measuring device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of an optical system of the particle measuring device according to the present embodiment.

FIG. 3 is a sectional view showing a lens holder of the particle measuring device according to the embodiment.

FIG. 4A is a perspective view showing a converging lens and a first intersection region of the particle measuring device according to the embodiment, and FIG. 4B is an enlarged view thereof.

FIG. 5 is a diagram showing first and second intersection regions, an enlarged third intersection region, and an optical fiber of the particle measuring apparatus according to the embodiment.

FIG. 6 is a graph showing a change in amplitude of an AC signal received by one optical fiber with respect to a distance L from a second intersection region to an optical fiber.

FIG. 7 is a diagram showing image information reconstructed in a memory 29;

FIG. 8 is a front view showing another example of the mirror.

FIG. 9 is a block diagram showing a conventional particle measuring device.

FIG. 10 is a perspective view showing an optical system of another conventional particle measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Laser light source 12 Polarizer 13 Beam splitter 14 Frequency shifter 15, 17 Condensing lens 16, 23A-23E mirror 18 Photoelectric converter 19 A / D converter 20 Frequency measuring device 21, 22, Condensing lens 23 Mirror with slit 24 Enlarge Lens 25 Optical fiber 26 Photodiode array 27 Multiplexer 28 Comparator 29 Memory 30 Operation means 31 Display unit 41 Lens holder

Claims (3)

[Claims] 1. A light source means for converging and intersecting two laser beams to form an interference fringe in a first intersection area, and a light source means for converting the laser beam forming the first intersection area into parallel light. A first lens, a second lens that forms an interference fringe by converging parallel light from the first lens at a second intersection area, and is perpendicular to the surface between the first and second lenses. A mirror that is rotatably arranged along a central axis and has a passage area through which the two laser beams pass, and receives scattered light forward and backward of particles passing through the first intersection area. A light receiving element; a particle velocity measuring means for measuring the velocity of the particles based on the frequency of the scattered light received by the light receiving element; and receiving a shadow projected on a second interference fringe generated in the second intersection area. A plurality of photoelectric conversion means, and from the particle velocity measurement means Particle measuring apparatus comprising: the particle velocity signal, characterized by having a calculating means for constituting a shape of the particles by a series of projected shape when particles from the plurality of photoelectric conversion means. 2. The particle measuring apparatus according to claim 1, wherein the mirror has a linear passing area including a central axis of the mirror. 3. A light source means for converging and intersecting two laser beams to form an interference fringe in an intersecting region; a lens for converting the laser beam forming the intersecting region into parallel light; A mirror that is rotatably disposed along a central axis perpendicular to the plane and has a passage area through which the two laser beams pass; and a light receiving element that receives scattered light of particles passing through the intersection area. A laser Doppler velocimeter comprising: particle velocity measuring means for measuring the velocity of particles based on the frequency of scattered light received by the light receiving element.