JP2000321193A - Grain size distribution-measuring device of laser diffraction-scattering type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensitivity for a fine particle in a simple configuration. SOLUTION: In addition to a first illumination optical system 2 for applying a laser beam to a particle group to be measured in a dispersed state, a second illumination optical system 3 for generating a laser beam on a light axis nearly orthogonal to the light axis, and applies the laser beam to the particle group is provided, a photo detector 5 where a plurality of photo detectors are arranged via the particle group is provided on the light axis of the first illumination optical system 2, and the photo detector 5 is functioned as a forward scattering light sensor for the laser beam from the first illumination optical system 2, and at the same time is functioned as a side and rear scattering light sensor for the laser beam from the second illumination optical system 3, thus measuring the intensity of side and rear scattered light at a number of scattering angles without providing an exclusive sensor for measuring the spatial intensity distribution of the side and rear scattered light, and hence improving measurement sensitivity at a fine particle region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser diffraction / scattering type particle size distribution measuring device.

[0002]

2. Description of the Related Art In general, a laser diffraction / scattering type particle size distribution measuring apparatus measures the spatial intensity distribution of diffracted / scattered light obtained by irradiating a group of particles to be measured in a dispersed and flying state with laser light. Using the fact that the light intensity distribution follows Mie's scattering theory or Fraunhofer's diffraction theory,
From the measurement results of the spatial intensity distribution of the scattered light, the particle size distribution of the particles to be measured is measured by an operation based on Mie's scattering theory or Fraunhofer diffraction theory.

The measurement of diffraction / scattered light obtained by irradiating a laser beam to a particle group to be measured is performed, for example, as follows. That is, as schematically shown in FIG. 2, a basic configuration of a measurement system of this type of measurement apparatus, a laser beam from a laser light source 21 is parallelized to a particle group P to be measured via a collimator lens 22 and the like. When irradiated as a light beam, the laser light is diffracted or scattered by the particle group P, and a spatial light intensity distribution pattern is generated. Of the diffracted / scattered light, the forward diffracted / scattered light is condensed by the condenser lens 23 and forms a ring-shaped diffracted / scattered image on the detection surface at the focal position. This forward diffraction / scattered light intensity distribution pattern is detected by a forward scattered light sensor 24 including a plurality of light receiving elements arranged on the detection surface. Further, the scattered light to the side and the back is transmitted to the side scattered light sensor 2.
5 and the backscattered light sensor 26 respectively.

Here, the forward scattered light sensor 24 usually has a ring shape, a semi-ring shape, or a quarter of a radius different from each other in order to efficiently detect a ring-shaped diffraction / scattered image.
A sensor called a ring detector is used in which dozens of light receiving elements having a ring-shaped light receiving surface are arranged concentrically around the optical axis of the irradiation laser light. On the other hand, each of the side and back scattered light sensors 25 and 26 uses a single light sensor, and the total number is about several.

[0005]

In the measurement system of the conventional laser diffraction / scattering type particle size distribution measuring apparatus as described above, a large number of light-receiving elements are continuously used for forward diffracted / scattered light. A forward scattered light sensor consisting of an array of ring detectors continuously measures the light intensity at each of a number of diffraction and scattering angles spatially, but scattered light to the side and back is discretely arranged. Measurement is performed by only a few optical sensors. here,
Diffraction and scattered light obtained by irradiating laser light has a tendency to increase the pattern of scattered light in a large angle region as the diameter of the particle to be irradiated becomes smaller, that is, as the particle becomes finer. When this is used, it leads to a problem that the sensitivity to fine particles is inferior.

The present invention has been made in view of such circumstances, and does not increase the number of side scattered light sensors and back scattered light sensors, but rather does not provide them, and therefore has a relatively simple configuration. Another object of the present invention is to provide a laser diffraction / scattering type particle size distribution measuring device capable of improving the sensitivity to fine particles.

[0007]

In order to achieve the above object, a laser diffraction / scattering type particle size distribution measuring apparatus of the present invention comprises:
Laser diffraction to measure the spatial intensity distribution of the diffracted and scattered light obtained by irradiating the measured particles in the dispersed and flying state with laser light and calculate the particle size distribution of the measured particles from the measurement results.
In a scattering type particle size distribution measuring apparatus, a first irradiation optical system that irradiates a laser beam to a group of particles to be measured, and is arranged to face the first irradiation optical system via the group of particles to be measured, and An optical detector having a plurality of light receiving element groups arranged at different distances from the optical axis of the first irradiation optical system, and an optical axis substantially orthogonal to the optical axis of the first irradiation optical system. A second irradiation optical system that irradiates the laser beam to the particle group to be measured along, and the light detector that irradiates the laser beam from the first irradiation optical system to the particle group to be measured. The output from each light receiving element is used as the spatial intensity distribution measurement result of the forward diffracted / scattered light, and the output from each light receiving element of the light detector when the laser light from the second irradiation optical system is irradiated is Of the spatial intensity distribution of the forward and back scattered light In combination Te, characterized by that it comprises a calculating means for calculating a particle size distribution of the particles to be measured.

An object of the present invention is to achieve a desired object by using a forward scattered light sensor capable of disposing a large number of light receiving elements also as a side scattered light sensor and a back scattered light sensor.

In other words, when the first and second irradiation optical systems whose optical axes are substantially orthogonal to each other are provided as an optical system for irradiating a laser beam to the particle group to be measured, the first irradiation optical system applies the laser beam to the particle group. A light detector that functions as a forward scattered light sensor for the laser light irradiated by the second irradiation optical system, and a side or back scattered light sensor for the laser light irradiated to the particle group from the second irradiation optical system. Function. As a light detector in the present invention, for example, using a ring detector in which dozens of light receiving elements are frequently used as a forward scattered light sensor in this type of conventional measurement device,
By driving the first irradiation optical system, it is possible to spatially continuously measure the intensities at a large number of diffraction / scattering angles for the forward diffracted / scattered light by the particle group, similarly to the conventional apparatus. . On the other hand, if the driving of the first irradiation optical system is stopped and the second irradiation optical system is driven, each light receiving element of the photodetector functions as a side and back scattered light sensor. For the backward scattered light, the intensity at each of a large number of scattering angles can be measured spatially continuously in the same manner. Then, by combining the intensity distribution of the forward diffracted / scattered light measured as described above with the intensity distribution of the scattered light to the side and to the rear, the side and back scattered light sensors are actually completely Despite the absence of the sensor, a spatial intensity distribution of diffracted / scattered light substantially equal to the case where dozens of side and back scattered light sensors are provided in addition to the forward scattered light sensor equivalent to the conventional one is obtained. As a result, the sensitivity to fine particles can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram showing both a schematic perspective view of a measurement system and a block diagram showing an electrical configuration.

The particle group P to be measured is dispersed in a liquid medium to form a suspension, and flows through the sample cell 1. The sample cell 1 is selectively irradiated with laser light from the first irradiation optical system 2 and the second irradiation optical system 3. First irradiation optical system 2
And the second irradiation optical system 3 respectively
a and 3a, and collimator lenses 2b and 3b for shaping the output light into a parallel light flux.
The optical axis of the irradiation optical system 2 is set in the horizontal direction, and the optical axis of the second irradiation optical system 3 is set in the vertical direction perpendicular to it.

A condenser lens 4 and a ring detector 5 are arranged on the optical axis of the first irradiation optical system 2 on the opposite side of the sample cell 1 with the sample cell 1 interposed therebetween. The ring detector 5 is a known type in which a large number of light receiving elements having quarter-ring light receiving surfaces having different radii are arranged concentrically with no gap around the optical axis of the first irradiation optical system 2. The outputs from the respective light receiving elements are individually amplified by the amplifier 6, digitized by the A / D converter 7, and taken into the computer 8 at the timing described later.

The laser light sources 2a and 3a of the first and second irradiation optical systems 2 and 3 are driven / stopped by drive signals supplied from drivers 9 and 10, respectively. These drivers 9 and 10 operate according to control signals supplied from the computer 8.

In a state where the suspension in which the particle group P to be measured is dispersed flows in the sample cell 1,
Either one, for example, only the laser light source 2a of the first irradiation optical system 2 is driven, and in that state, a first data collection step of taking in output data from each light receiving element of the ring detector 5 is performed, The driving of the laser light source 2a of the first irradiation optical system 2 is stopped, the laser light source 3a of the second irradiation optical system 3 is driven, and the output data from each light receiving element of the ring detector 5 is taken in that state. Execute the data collection process. After that, these data are combined to form a set of diffraction / scattered light intensity distribution data, and using the intensity distribution data, the particle size of the particle group P is calculated by calculation based on the well-known Mie scattering theory or Fraunhofer diffraction theory. Calculate the distribution.

In the above embodiment of the present invention, the first
In the state where the laser light from the irradiation optical system 2 is applied to the particle group P in the sample cell 1, of the laser light diffracted and scattered by the particle group P, the forward diffracted / scattered light is collected by the condenser lens 4.
And enters the respective light receiving elements of the ring detector 5 via.
Accordingly, the spatial intensity distribution of the forward diffraction / scattered light by the particle group P is taken into the computer 8 by the first data collection step. On the other hand, the second irradiation optical system 3
Is irradiated on the particle group P in the sample cell 1, of the laser light diffracted and scattered by the particle group P, side and back scattered light is incident on each light receiving element of the ring detector 5.

Therefore, by the second data collection step,
The computer 8 receives the spatial intensity distribution of the side and back scattered light by the particle group P. By combining the data captured in the first and second data collection steps, the computer 8 The light intensity distribution for each angle corresponding to the number of light receiving elements of the ring detector 5 with respect to forward diffraction and scattered light by P, and the particle group P
, The light intensity distribution for each angle corresponding to the number of light receiving elements of the ring detector 5 with respect to the side scattered light and the back scattered light is stored. Intensity distribution data can be obtained. The spatial intensity distribution data of the diffracted and scattered light combined in this way is the data obtained by measuring the spatial intensity distribution with the number of light receiving elements of the ring detector 5 and also with several tens of sensors for the side and back scattered light. In particular, the sensitivity in the fine particle region is dramatically improved as compared with the conventional one, and it is possible to calculate a highly accurate particle size distribution in a wide particle size range.

Here, the light receiving surface of each light receiving element of the ring detector 5 has a ring-shaped spread centering on the optical axis of the first irradiation optical system 2, and the spread becomes particularly large as the light receiving element is located outside. When the spatial intensity distribution of the side scattered light and the back scattered light obtained when the laser light from the second irradiation optical system 3 is irradiated by such a ring detector 5 is measured, each light receiving element is caused by the above-mentioned spread. It is conceivable that an error occurs in the relationship between the angle and the scattering angle. In order to eliminate such an error, in the second data collection step of irradiating the particle group P with laser light from the second irradiation optical system 3,
Unnecessary regions on both sides of the light receiving element of the ring detector 5 may be appropriately masked.

In the above embodiment, side scattered light and back scattered light also enter the ring detector 5 through the condenser lens 4 and are directly transmitted to the conventional side scattered light sensor and back scattered light sensor. In comparison with the case of incidence, side and back scattered light will be detected at different angular positions by the amount of refraction by the condenser lens 4, but since the optical performance of the condenser lens 4 is known, The difference in angle due to the refraction can be easily corrected.

In the above embodiment, the first
The ring detector 5 is used as a light detector functioning as a forward diffraction / scattering light sensor for the laser light of the irradiation optical system 2 of the above. Although extremely effective for improving the measurement accuracy of light, the present invention is not limited to this. For example, a light-receiving element group having a dot-shaped light-receiving surface may be positioned at a distance from the optical axis of the first irradiation optical system 2 to the optical axis. It is needless to say that optical detectors arranged in a line with different from each other may be used.

In the above embodiment, the first
The optical axis of the irradiation optical system 2 is set to be horizontal and
In the present invention, an example is shown in which the optical axis of the irradiation optical system is vertical and the two optical axes are perpendicular to each other. However, in the present invention, when the laser beam from the first irradiation optical system 2 is irradiated on the particle group P, Ring detector 5 functioning as forward scattered light sensor
However, as long as the optical axis of each irradiation optical system is substantially orthogonal so that the laser beam from the second irradiation optical system 3 functions as a lateral or backscattered light sensor when the particle group P is irradiated. Need not be strictly orthogonal. In other words, if the angle between the two optical axes is known, each light receiving element on the ring detector 5 functioning as a side and back scattered light sensor when irradiating the laser light from the second irradiation optical system 3 is scattered. Since the relationship with the angle is known, no particular problem occurs.
The optical axis direction of each of the irradiation optical systems 2 and 3 is not limited to the horizontal direction and the vertical direction, and it goes without saying that any direction can be used as long as the above conditions are satisfied.

Further, according to the present invention, in addition to the so-called wet measurement in which the particle group P is dispersed in a medium and measured in a suspension state as in the above embodiment, the particle group P is converted into an aerosol state. Of course, the present invention is equally applicable to dry measurement.

[0022]

As described above, according to the present invention, it is possible to selectively irradiate the particle group to be measured with laser beams from two directions substantially orthogonal to each other, A light detector consisting of a plurality of light receiving elements for measuring the spatial intensity distribution of the forward diffracted and scattered light by the particle group to be measured when irradiating the laser light from the other irradiation optical system Since it is used as a light detector for measuring the spatial intensity distribution of the side and back scattered light by the measurement particle group, without separately providing a side scattered light sensor and a back scattered light sensor as in the related art, The number of measurement points for side scatter and back scattered light can be dramatically increased compared to the past, and especially the sensitivity to fine particles has been improved, and a highly accurate particle size distribution can be measured over a wide particle size range. Rukoto is possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, showing a schematic perspective view of a measurement system and a block diagram showing an electrical configuration.

FIG. 2 is a schematic perspective view showing a configuration example of a measuring system in a conventional laser diffraction / scattering type particle size distribution measuring device.

[Explanation of symbols]

 Reference Signs List 1 sample cell 2 first irradiation optical system 3 second irradiation optical system 2a, 3a laser light source 2b, 3b collimator lens 4 condenser lens 5 ring detector 6 amplifier 7 A / D converter 8 computer 9, 10 driver P Measurement particle group

Claims (1)

[Claims] 1. A laser diffraction method for measuring a spatial intensity distribution of diffraction / scattered light obtained by irradiating a laser beam onto a group of particles to be measured in a dispersed and flying state, and calculating a particle size distribution of the group of particles to be measured from the measurement result. A scattering particle size distribution measuring device, a first irradiation optical system for irradiating a laser beam to the particle group to be measured, and a first irradiation optical system opposed to the first irradiation optical system via the particle group to be measured; An optical detector having a plurality of light receiving element groups arranged at different distances from the optical axis of the first irradiation optical system; and an optical axis substantially orthogonal to the optical axis of the first irradiation optical system. A second irradiation optical system that irradiates the measured particle group with laser light along the line, and the light detector that irradiates the measured particle group with laser light from the first irradiation optical system. Output from each light receiving element And intensity distribution measurement result, and,
Combining the output from each light receiving element of the photodetector when irradiating the laser light from the second irradiation optical system as a result of measuring the spatial intensity distribution of lateral and backscattered light, the particle size distribution of the particle group to be measured A laser diffraction / scattering type particle size distribution measuring device, comprising a calculating means for calculating the particle size distribution.