JPH0755693A - Particle measuring instrument - Google Patents

Abstract

PURPOSE:To measure even aspherical particles with ease and high accuracy by passing particles through a crossing portion from one direction only, which is formed by the crossing of a plurality of laser beams at a predetermined angle. CONSTITUTION:A laser beam polarized by a polarizing plate 12 is split into two laser beams by a beam splitter 13. The laser beams pass through frequency shifters 14a, 14b, beam-direction regulating prisms 15a, 15b and a condenser lens 16 and form a crossing portion 17 where the two laser beams cross each other. Particles are passed through the crossing portion 17 from one direction only. The Doppler frequency of scattered light reflected by the particles is measured as the light beat signal of the scattered light, so as to detect the velocity of the particles. A photoelectric conversion means 20 detects the shape of projection of the particles from a projection that the light diffracted by the particles passing through the crossing portion 17 form on a line sensor 21. An arithmetic means 30 computes the size of the whole particles from the velocity of the particles delivered from a particle velocity detection means 10 and from the shape of the projection delivered from the conversion means 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle measuring apparatus for non-contact measuring the appearance form (hereinafter referred to as the size of the whole particle) such as the equivalent diameter and shape of particles made of suspended fine particles, and in particular. , LDV (Laser Doppler Velocity Meter).

[0002]

2. Description of the Related Art For example, powder materials used industrially such as metal powder, ceramic powder, chemical powder, pulverized coal for fuel, etc., or fine particles floating in the air, such as dust or droplets. As a means for measuring the size of the, the holography method, the forward small angle scattering method, etc. have been conventionally used.

[0003]

However, the holography method has a drawback that the measuring device is relatively large and the measurement takes a long time. This is not very practical due to the drawback that the error becomes very large when the shape is significantly different from the spherical shape.

Further, the scattered light intensity method,
Although there are methods such as the phase method, these methods only assume that the particles are spherical, and only make a pseudo measurement under statistical assumptions, and such a method also has a problem in accuracy, The particle size range that can be measured is narrow, and in the latter method, the refractive index of the particles must be known, so if industrial implementation is attempted, a large amount of statistical data will be prepared in advance depending on the specific system. Since there is a high possibility that the error will reach several hundred percent, there is a possibility that it will be a great obstacle to the device design and numerical prediction.

In particular, various particles such as the above-mentioned powder materials are mostly non-spherical, and the droplets in the shear flow are
Since the shape is distorted, it is the actual situation that such non-spherical particles cannot be experimentally measured in any industrially continuous manner.

The present invention has been made in order to solve the problems associated with the above-mentioned prior art, and provides a particle measuring apparatus capable of easily and highly accurately measuring non-spherical particles. With the goal.

[0007]

In order to achieve the above object, the inventors of the present invention have been able to apply a laser Doppler velocimeter having features such as non-contact measurement and high spatial resolution. Unlike the scattered light intensity method described above, it is possible to make an independent measurement from the scattered light intensity proportional to almost the square of the particle size without considering the dynamic range of the light receiving element when receiving the shadow of a particle. As a result of diligent research, focusing on the fact that it is convenient, we reconstructed the data of the particle velocity measured from this laser Doppler velocimeter and the time-series projection shape of particles obtained from the sensors arranged in a line. Then, it was found that the size of the whole particle can be easily measured, and the present invention has been completed based on this finding.

That is, according to the particle measuring apparatus of the present invention, the particles are scattered unidirectionally at the intersection formed by intersecting the optical axes of a plurality of laser beams at a predetermined angle. A particle velocity detecting means for measuring the velocity of a particle from the Doppler frequency of light, and a photoelectric conversion means comprising a plurality of sensors arranged in a line on which a shadow produced by blocking the particle itself passing through the intersection is projected. And a particle velocity from the particle velocity detection means, and a calculation means for calculating and reconstructing the size of the entire particle from the time-series projection shape of the particle from the photoelectric conversion means. is there.

Further, it is preferable that the photoelectric conversion means is constructed so that the shadow of the particles is enlarged and projected by a lens.

[0010]

In other words, in the present invention, particles are passed through an intersection where a plurality of laser beams cross each other for measurement, so that non-contact measurement independent of particle shape can be performed, and measurement of particle diameter, in particular, It can be used for any device that uses a multiphase flow as a working medium by analyzing the effect of its shape on particle behavior, measuring the equivalent diameter, elucidating the particle size distribution, behavior and its spatial distribution. Can be grasped online. In addition, if the shadow of the particle is enlarged and projected by a lens, the velocity of the particle, the volume mixing ratio of the particle, etc. can be measured instantaneously with high accuracy. You can understand the internal flow in detail. Further, since the shadow is measured instead of the transmitted light, even a particle whose optical characteristics such as a refractive index and an attenuation rate are unknown can be accurately measured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a schematic explanatory view of a particle measuring apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory view showing an example of photoelectric conversion means,
FIG. 3 is a block diagram of a control system of the particle measuring device, FIG. 4 is a flowchart showing the operation of the particle measuring device, and FIG. FIG. 6 is an explanatory view showing the signal level output from the photodiode array corresponding to the position where the particles pass through the intersection, and FIG. 7 is the relationship between the result measured by the particle measuring device and the actual particle system. It is a graph which shows.

As shown in FIG. 1, the particle measuring apparatus according to this embodiment unidirectionally passes through an intersection 17 formed by intersecting the optical axes of two laser beams at a predetermined angle. Particle velocity detecting means 10 composed of a laser Doppler velocimeter for measuring the velocity of particles, photoelectric conversion means 20 for projecting a shadow generated by the particles P themselves passing through the intersection 16, and the particle velocity detection. Particle velocity from means 10 and particle P from said photoelectric conversion means 20
The calculation means 30 calculates and reconstructs the size of the entire particle from the time-series projected shape of.

The particle velocity detecting means 10 is provided with a polarizing plate 12 in front of the laser oscillator 11, and this polarizing plate 1
The laser light polarized by 2 is the beam splitter 13
Is split into two laser beams.

Each of the laser beams has a frequency shifter 14a, 1
4b, the beam direction adjusting prisms 15a and 15b, and the condenser lens 16 to form a rugby ball-shaped intersection 17 where two laser beams cross each other.
The particles P are allowed to pass in one direction.

Due to the arrangement of the optical system, the scattered light from a laser beam of a general one light flux is extremely affected by multiple scattering and the depth of focus, which makes it difficult to put it into practical use. By using the LDV optical system based on the light flux, these influences can be eliminated and it becomes easy to apply to an actual flow field.

The scattered light reflected by the particles undergoes a frequency change proportional to the velocity due to the Doppler effect. The Doppler frequency is, for example, an avalanche photodiode and a sensor 18 for detecting the Doppler signal.
It is detected by using it as this, and this signal is input to the arithmetic means 30. That is, if the Doppler frequency of the reflected scattered light is measured as an optical beat signal of the scattered light, the velocity of the particle P can be detected.

On the other hand, the photoelectric conversion means 20 is shown in FIGS.
As shown in FIG. 5, the projection shape of the particle P is detected from the projection generated by the diffracted light of the particle P passing through the intersection 17 in one direction on the line sensor 21, which will be described later. That is, the size of the shadow generated by the particle P passing the intersection 17 in one direction blocking the laser light is measured, and the particle P is measured.
It senses the size of. Therefore, except for the portion shielded by the particles P, the so-called line composed of a CCD area sensor or a photodiode array or the like is used for the diffracted light emitted from the peripheral portion of the particles P from the lens group L (collective term of the lenses L1, L2, L3) The line sensor 21 guides the particle P onto the sensor 21, and the size of the particle P is detected by the line sensor 21.

The line sensor 21 has a plurality of independent elements arranged linearly. Each element photoelectrically converts the detected light, and the converted electric quantity is converted into an analog multiplexer 22 (CCD). It is unnecessary in the case of a sensor) and is input to the arithmetic means 30 via the A / D converter 23 and the like.

The calculating means 30 calculates and reconstructs the size of the entire particle from the particle velocity from the particle velocity detecting means 10 and the shape of the time-series projection S of the particle P from the photoelectric converting means 20. To do. For example, the measurement interval is determined based on the particle velocity from the particle velocity detection means 10, the size of the particle is specified in time series at each measurement interval, and the size of the entire particle is calculated. .

The calculation means 30 has a control system as shown in FIG. The light sensed by the line sensor 21 is photoelectrically converted by each element, and the quantity of electricity is input to the buffer amplifier 31, the extraction order is arranged by the analog multiplexer 22 and input to the A / D converter 23, and the address controller It is stored in a predetermined place in the static memory 33 designated by 32. The data in the stack memory 33 is adapted to be input to the host computer 37 through the data bus 35 and the buffer 36 in response to a command from the trigger circuit 34.

In FIG. 3, reference numeral "38" is I.
/ O controller.

Next, the operation of the above embodiment will be described.

The laser beam emitted from the laser oscillator 11 is polarized by the polarizing plate 12 and then split into two laser beams by the beam splitter 13, and the two laser beams are respectively frequency shifters 14a and 14b. The beam-direction adjusting prisms 15a and 15b and the condenser lens 16 are crossed to form an intersecting portion 17.

When the particles P pass through the intersection 17 unidirectionally from above to below or from below to above, the frequency of the scattered light reflected by the particles P is proportional to the velocity due to the Doppler effect. As the frequency changes, the Doppler frequency is detected by the sensor 18 as an optical beat signal of scattered light (S1).
As shown in FIG.
(S2). Since frequency data is input to the host computer 31 in advance, the velocity of the particle P is calculated by comparing this frequency data with the Doppler signal detected by the sensor 18 (S3). The velocity data of the particles P is stored in the host computer 37.

On the other hand, the diffracted light of the particle P passing through the intersection 17 in one direction is magnified by the lens group L,
A projection is generated on the line sensor 21. Therefore,
Since the behaviors of the particles P are all displayed in an enlarged manner, it is possible to measure the velocity of particles, the volume mixing ratio of particles, and the like with high accuracy. Even if it is a flow, it will be possible to grasp this in detail.

In particular, since the line sensor 21 has photoelectric elements and the like arranged in a straight line, the line sensor 21 itself detects only a part of the shadow of the particle P, but the particle P is Since the light passes through the intersection 17 in one direction, the shadow on the line sensor 21 changes every moment, and the shadow of the particle P is detected in detail in time series.

Each element of the line sensor 21 independently performs photoelectric conversion according to the sensed light, and the converted quantity of electricity is time-sequentially input to the buffer amplifier 31 every predetermined time (S4).

When the amount of electricity photoelectrically converted in this way is input to the buffer amplifier 31, as shown in FIG.
The analog multiplexer 22 takes out the data in order, and the electric quantities of the respective elements are stored in a predetermined location in the static memory 33 designated by the address controller 32 via the A / D converter 23. The data in the stack memory 33 is output to the host computer 37 through the data bus 35 and the buffer 38 in response to a command from the trigger circuit 34.

In the host computer 37, the shape of the particle P is reconstructed on the basis of the speed of the particle P calculated in the step S3 and the quantity of electricity after photoelectric conversion every predetermined time input in the step S4. Perform processing to Specifically, among all the elements forming the line sensor 21, the number of elements (elements for which a mapping has been generated) having a small amount of electricity after photoelectric conversion is input in time series. The cutting diameter in the horizontal direction (direction perpendicular to the passing direction) of the particles, which is calculated with respect to the amount of electricity and is input in time series, is calculated.

Next, a process of connecting the cutting diameters calculated for each time series with reference to the calculated speed is performed. The approximate shape of the projected particles is reconstructed by the above processing (S5).

In this process, the problem in calculating the accurate size of the particles P is that the particles P intersect at the intersection 17
Which position to pass. That is, the particle P
When passes through the center position of the intersection 17, it is not necessary to correct the shape calculated in step S5, as will be apparent from FIG. 5 described later. This is because it becomes necessary to make corrections due to different shadow forms.

The relationship between the shadow state caused by the particle P blocking the laser light and the quantity of electricity output according to the light sensed by the line sensor 21 is schematically shown in FIG.
And is as shown in FIG.

For example, as shown in FIG. 5 (a), when the spherical particle P passes through the central portion of the intersection 17, the state of the shadow S becomes a perfect circle and its size can be clearly seen. In this case, as for the quantity of electricity output according to the light sensed by the line sensor 21, only the sensor in the central portion outputs a low level quantity of electricity as shown in FIG. 6A.

As shown in FIG. 5B, when the spherical particle P passes through a position slightly deviated from the center of the intersection 17, the shadow S has two thin round shadows and their overlaps. There is a dark shadow. Therefore, FIG.
As shown in (b), only the sensor in the small portion in the center outputs a low level electricity quantity, and the sensors on both sides thereof output an intermediate level electricity quantity.

As shown in FIG. 5 (c), when the spherical particle P passes through a position that is considerably displaced from the intersection 17, the shadow S state has two independent light shadows. Therefore, as shown in FIG. 6C, the sensor located at a position slightly separated from the center outputs an intermediate level electricity quantity.

The host computer 37 determines the difference in the state of the shadow S due to the difference in the passing position of the particle P as described above by S5.
Recognize from the shape reconstructed in the step. Since the host computer 37 is preliminarily input with the data relating to the depth of focus of the optical system shown in FIG. 2, the passage position of the particle P is calculated based on the reconstructed shape and this depth of focus (S6). ).

Next, based on the size and shape of the projection of the particle P calculated in the step S5, the passing position of the particle P calculated in the step S6, and the depth of focus previously input. Finally, the equivalent diameter of the particle P and the particle shape are calculated. Through the above processing, the particles P
The overall shape and size will be known (S7).

The size of the whole particle P measured in this way is compared with the result of actual measurement of the particle P using a microscope or the like, as shown in FIG. In FIG. 7, the horizontal axis represents the size of the particle P measured using a microscope,
The vertical axis indicates the particle P measured by the particle measuring device according to the present invention.
Is the size of. As is clear from FIG. 7, the results of both measured values have a relationship of approximately 1: 1, and it can be seen that extremely favorable measuring results are obtained in terms of accuracy.

As described above, the fact that the size of the particle P can be measured becomes easy, for example, when the equivalent diameter of the particle P is known, or when the spatial distribution in which the particle exists is known. To know the equivalent diameter, the diameter of a circle equal to the calculated projected area of the particle can be calculated.To know the spatial distribution, the shadow position of the projected particle and the depth of focus The passing position of the particles may be obtained three-dimensionally from the information, and the particle concentration and volume mixing ratio can be calculated from the information of the passing position.

Further, in the present embodiment, the intensity of the incident light when it is directly incident from the laser light is set to the maximum intensity of the incident light to the photoelectric conversion device, so that the light receiving element for receiving the shadow of the particle is received. In addition to the advantage that the range of particle size to be measured can be set arbitrarily by increasing the number of elements without considering the dynamic range of, it is independent of the scattered light intensity that is almost proportional to the square of the particle size. There is also an advantage that it is possible to perform the measurement.

If the light condensed on the line sensor 21 deviates from the range of the line sensor 21, the magnification of the lens group L is adjusted appropriately,
It suffices to adjust the range of abutting light.

Although the above is a preferred embodiment of the present invention, the present invention is not limited to this embodiment, and various modifications can be made within the scope of the claims. For example, in the present invention, not only the intersecting portion is formed by two laser intersecting lines, but also the intersecting portion may be formed by a larger number of laser intersecting lines. Further, in the above embodiment,
Although the lens group L is used, depending on the size of the particle P, the lens group L is not always necessary.

[0043]

As described above, according to the present invention, the following excellent effects are obtained.

A) Non-contact measurement independent of particle shape is possible.

B) Several times to several times that of other optical measurement methods
Measurement can be performed with 0 times higher accuracy.

C) Particles whose optical characteristics such as refractive index and attenuation rate are unknown can be measured accurately.

D) A very precise particle concentration measurement with an air resolution of several μm or less can be performed in time series.

E) It is possible to instantaneously measure the velocity, volume mixing ratio, etc. of suspended fine particles, which have been conventionally used for photography, etc., and to grasp the flow in the equipment containing aspherical particles of complicated shape in detail. It will be possible.

F) Even when quality control is carried out in the powder manufacturing process or the like, it can be made online with high reliability, which is extremely convenient industrially.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a particle measuring apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of photoelectric conversion means.

FIG. 3 is a block diagram of a control system of the particle measuring device according to the embodiment.

FIG. 4 is a flow chart showing an operation of the particle measuring device of the embodiment.

FIG. 5 is an explanatory diagram showing a position where particles pass through an intersection and a projected shape corresponding to this position.

FIG. 6 is an explanatory diagram showing a signal level output from a photodiode array corresponding to a position where particles pass through an intersection.

FIG. 7 is a graph showing a relationship between a result measured by the particle measuring apparatus of the same example and an actual particle system.

[Explanation of symbols]

10 ... Particle velocity detecting means, 17 ... Intersection,
20 ... Photoelectric conversion means, 21 ... Line sensor, 30 ... Calculation means, L ...
Lens, P ... Particle, S ...
Shadow.

Claims (2)

[Claims] 1. The velocity of particles is measured from the Doppler frequency of scattered light generated by passing particles unidirectionally at the intersection formed by intersecting the optical axes of a plurality of laser beams at a predetermined angle. Particle velocity detecting means, photoelectric conversion means composed of a plurality of sensors arranged in a line on which a shadow generated by blocking the particles themselves passing through the intersection is projected, and particles from the particle velocity detecting means A particle measuring device having a speed and a calculation means for calculating and reconstructing the size of the entire particle from the time-series projection shape of the particle from the photoelectric conversion means. 2. The particle measuring device according to claim 1, wherein the photoelectric conversion means enlarges and projects a shadow of the particle by a lens.