JPH065211B2 - Particle size distribution measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a particle size distribution measuring apparatus utilizing a diffraction phenomenon or a light scattering phenomenon generated by irradiating particles in a dispersed state with light.

<Prior Art> A particle size distribution measuring apparatus utilizing the diffraction or scattering phenomenon of light by particles measures the intensity distribution of the diffracted light or scattered light (diffraction angle or the relation between the scattering angle and the light intensity), and uses this for Fraunhofer diffraction. Alternatively, the particle size distribution is calculated by performing arithmetic processing based on the theory of Mie scattering.

The intensity distribution of diffracted light or scattered light is usually measured by forming a diffraction image or a scattered image at the focal position by using a condenser lens, and measuring the light intensity distribution of the image with a light from a ring detector or a photodiode array. It is carried out by detecting with a detector.

By the way, in the method of measuring the particle size distribution utilizing such a phenomenon, in general, when the particle size is 1 μm or more, the Fraunhofer diffraction theory is mainly used, and when the particle size is less than that, the Mie scattering theory is used to measure the light intensity distribution. Although it is converted into a distribution, it is necessary to measure light with a small diffraction angle with high accuracy in order to measure particles with a large diameter, and to measure particles with a small diffraction angle (scattering angle) in order to measure particles with a small diameter. It is necessary to measure light with a large angle.

Therefore, conventionally, the intensity distribution is measured by appropriately changing the focal length of the condenser lens according to the size of the particles to be measured. That is, when the particle size distribution of the sample particles is expected to be on the relatively small diameter side, a lens with a short focal length is used, and when it is expected to be on the relatively large diameter side, a lens with a long focal length is used. It is used to measure the intensity distribution.

As the detector, a ring detector with a large diameter is used so that it is possible to measure the distribution over a wide range of particle sizes at once, and a high-resolution detector is used to detect light with a minute diffraction angle. is doing.

Further, the light flux irradiating the sample is also extremely narrowed down in order to detect diffracted light at a minute angle.

<Problems to be Solved by the Invention> In the method in which the condensing lens is changed according to the particle size of the sample particles for measurement, if the range of particle size distribution is relatively narrow, high resolution measurement is performed according to the distribution. However, it is not possible to measure a sample having a wide range of particle size distribution.

It is possible to widen the measurement range to some extent even with the above method by increasing the detection range of the detector (angle, diameter for ring detector) or narrowing the light flux finely, but all of them have limitations in accuracy. Not only that, but the cost is high.

An object of the present invention is to provide a particle size distribution measuring apparatus capable of measuring a sample having a wide particle size distribution with high accuracy without using a detector having a large detection range.

<Means for Solving the Problems> In order to achieve the above object, the particle size distribution measuring apparatus of the present invention includes a plurality of condensing lenses having different focal lengths, and the condensing lenses are selectively used. A lens moving mechanism for selectively positioning the respective focusing lenses on the optical axis of the irradiation light to condense the diffracted light or the scattered light by using the photodetector for measuring the intensity distribution of the diffracted light or the scattered light. , A photodetector moving mechanism that positions the focus lens at a corresponding focal position according to the selection condition of the condenser lens, and a plurality of intensity distribution measurement results obtained by using the plurality of condenser lenses, respectively, are corrected by a predetermined correction. The conversion means for converting the light intensity distribution into a particle size distribution is characterized by converting the light intensity distribution into a particle size distribution while having a calculation means for combining by calculation.

<Operation> As shown in FIG. 3, a condenser lens 5 having a short focal length.
If the diffracted light (scattered light) is condensed using a, the distribution of the light at a large angle can be measured with high accuracy, but the resolution of the distribution of the light at a small angle is low. On the contrary, if light is condensed by using the condensing lenses 5b to 5c having a long focal length, the distribution of light of a small angle can be measured with high resolution, but the light of a large angle cannot be measured.

When diffracted light (scattered light) is focused on the detector 8 using each of the focusing lenses 5a to 5c and the intensity distribution thereof is measured, the measurement results are shown in FIGS. 4 (a) to (c). As shown.
The obtained light intensity distribution measurement results effectively utilize the detectability of the detector 8 in the angle range corresponding to the focal lengths of the respective condenser lenses 5a to 5c, and these can be used, for example, at angles ₂ and ₃ In the above, if either of the intensities I _a2 and I _b2 and I _b3 and I _c3 are corrected and combined, a high resolution light intensity distribution can be obtained over a wide angle range of 0 to ₁ .

<Embodiment> FIG. 1 is a block diagram of an embodiment of the present invention.

The laser light emitted from the laser light source 1 is collimated by the collimator lens 2 into a parallel light flux having a predetermined cross section, which is applied to the flow cell 3.

A sample suspension 4 in which sample particles are dispersed in a medium is flown in the flow cell 3, and the irradiated light is diffracted or scattered at an angle corresponding to the particle diameter.

Behind the flow cell 3, three condenser lenses 5a, 5b and 5c having different focal lengths are selectively arranged. That is, the condenser lenses 5a to 5c are
The lens driving mechanism 6 is configured so that any one of them can be selectively set on the optical axis of the irradiation light.

The lens drive mechanism 6 includes a movable rack 61 that supports the lenses 5a to 5c, a pinion gear 62 that meshes with the rack 61, a motor 63 that rotates the pinion gear 62, and the like. 63 is driven based on a command from the computer system 15 described later. Here, a protrusion 64 is formed on the rack 61, and the position detectors 7a, 7b and 7c are arranged along the moving direction of the rack 61 at a pitch according to the arrangement pitch of the lenses 5a, 5b and 5c. It is arranged. The computer system 15 includes position detectors 7a, 7
When the projection 64 arrives at the position where b or 7c is arranged, each focusing lens 5a, 5b or 5c is positioned on the optical axis by the detection signal output from each detector 7a, 7b or 7c. Configured to detect the presence of

Now, the intensity distribution of the light condensed by any of the condenser lenses 5a to 5c is detected by the photodetector 8 positioned at the condensing surface, that is, the focal position of the lens used.

The photodetector 8 is, for example, a so-called ring detector in which a plurality of photoelectric conversion elements having ring-shaped light-receiving surfaces having different radii with respect to the optical axis are concentrically arranged, and is a so-called ring (scattering) angle. The large light of is incident on the outer element and the small light of is incident on the inner element. Therefore, the light intensity signal for each diffraction (scattering) angle of each element is represented, and the intensity distribution of the diffracted (scattered) light is calculated based on this. Obtainable.

Further, the photodetector 8 is supported on a carriage 9 which is displaced by a detector driving mechanism 10 so as to move to the above-mentioned respective focal positions.

The detector drive mechanism 10 is composed of a guide 101, a wire 102, pulleys 103 to 106, and a motor 107. The guide 101 carries the carriage 9 and extends in the optical axis direction, and a wire 102 is connected to the carriage 9. This wire 102 is tensioned by pulleys 103-106,
It is driven by a motor 107 via a pulley 103. The motor 107 is used by the computer system 15
Drive control is performed based on a command from. The carriage 9 is provided with a protrusion 91, and along the guide 101,
Position detectors 11a, 11b and 11c are provided at positions corresponding to the focal positions of the condenser lenses 5a, 5b and 5c. The computer system 15 has a projection 91 at the position where the position detector 11a, 11b or 11c is provided.
Of the detectors 11a, 11b or 1
It is configured to detect that the photodetector 8 is located at the focal position of each condenser lens 5a, 5b or 5c by the detection signal output from 1c.

The outputs of the photoelectric conversion elements of the photodetector 8 are amplified by the preamplifiers 12 ... 12, respectively, and then sequentially guided to the AD converter 14 via the multiplexer 13, digitally converted and taken into the computer system 15. Be done.

The computer system 15 has a CPU 151 and a ROM 1.
52, a RAM 153, a CRT 154 for displaying a particle size distribution measurement result, a keyboard 155 for inputting measurement conditions and a system start command, and an input / output interface 156 for connection with various external devices. Based on the program written in the ROM, the data from the photodetector 8 is controlled in the ROM while controlling each part.
After importing into 153, calculate the particle size distribution and CRT1
54 can be displayed.

FIG. 2 is a flowchart showing the outline of the contents of the program written in the ROM 152, and the operation will be described below with reference to this figure.

When a start command is given after setting the measurement conditions and the like, first, the condenser lens 5a is selected and positioned on the optical axis.
At the same time, the photodetector 8 is positioned on the focal position of this lens 5a. Then, in this state, the light intensity distribution data from the photodetector 8 is collected and stored in the RAM 153.

Next, the condenser lens 5b is positioned on the optical axis by driving the motor 62, and the photodetector 8 is positioned at the focal position of the lens 5b by driving the motor 107. Then, in this state, light intensity distribution data is similarly sampled and stored in the RAM 153.

After that, the condenser lens 5c is further selected, and in the state where the photodetector 8 is positioned at the focal position of the lens 5c, the light intensity distribution data is similarly sampled and stored in the RAM 153.

The three types of light intensity distribution data obtained by the above operation are combined into one light intensity distribution by the correction calculation.
The synthetic method is shown below.

FIG. 3 is a diagram showing a change in the relationship between the diffraction (scattering) angle and the image height (light arrival radius on the detection surface) due to the difference in the focal lengths of the condenser lenses 5a to 5c. As shown in FIG. 6 (a), by using the short lens 5a of the focal length, the light of the _first angle position of r _a1 on the photodetector 8 and the light of the _two angles are also r _a2 Is projected at the position. On the other hand, when the lens 5b longer than the focal length is used as shown in FIG. 6B, the light of the angle of ₂ is projected to the position of r _b2 ,
Light with an angle of 0 to ₂ is magnified and projected on the photodetector 8. If a lens 5c with a longer focal length is used,
As shown in (c), the light of the minute angle ₃ is projected at the position of r _c3 , and the light of the angles of 0 to ₃ is expanded and enters the photodetector 8.

FIG. 4 shows an example in which the light intensity distribution measurement results obtained by using each of the condenser lenses 5a to 5c as described above are represented by a graph. In this figure, (a), (b) and (c) show the light intensity distributions when the same sample is measured using the condenser lenses 5a, 5b and 5c, respectively. The distribution between 0 and ₂ and 0 and ₃ in Fig. (a) is expanded (b)
It will be the figure and (c) figure. That is, the intensity I _b2 in the intensity I _a2 and (b) view in Figure (a) is supposed to be equal intensity because each is a light of the same angle _2, therefore, the I _b2 in example (b) Figure as the value is equal to I _a2, by correcting the entire data in consideration of the sensitivity of the photodetector 8 (b) Figure, (a) ₂ ~ _1-2 of the data (b) of Figures Figure ₃ data can be connected.
Furthermore, since ₃ of ₃ (c) view of (b) view is also a light of the same angle, I _b3 and I _c3 is should be the same value, the I _c3 in (c) view, the above-described correction Similarly, by correcting the entire data of FIG. (C) so that it becomes equal to I _{b3 of the} latter (b), (a)
The data of ₁ to ₂ , ₂ to ₃ and _{3 to} 0 in the figures, (b) and (c) can be connected, and three kinds of data can be combined into one light intensity distribution data.

The light intensity distribution data thus synthesized is then converted into a particle size distribution and displayed on the CRT 155.

A method for converting to a particle size distribution is known, but its outline is shown below.

Diffraction (scattering) per unit particle amount theoretically calculated from the Fraunhofer or Mie equation, the light intensity distribution with respect to the diffraction (scattering) angle is l (), the particle size distribution function is f (D).
If the light intensity is K (, D), the relationship between the diffracted (scattered) light and the particle size distribution is Indicated by.

Now, assume that the intensity distribution of diffracted (scattered) light is measured by a finite number of photoelectric conversion elements, and the particle size distribution is divided into n with a finite range, and each divided section is 1
Assuming that one particle size is represented by Can be approximated by Since this equation (2) is linear, it can be expressed as a vector or matrix. Becomes Solving this for f, is doing.

From the measurement result of the light intensity distribution 1 according to the equation (4), Then, the above-mentioned light intensity distribution data after combination is used as l.

Since the light intensity distribution obtained by synthesis contains light intensity information in a wide angle range from ₁ to 0 ° under high resolution, the obtained particle size distribution also has a correspondingly high resolution from fine particles. It has a wide particle size range up to coarse particles.

By the way, in order to achieve such a measurement result by using the light intensity distribution data obtained by one lens as in the conventional case, the resolution of the photodetector 8 must be made extremely high. That is, for example, be achieved using a lens 5a shown in FIG. 3 (a) is between 0 to R _a2 of the photodetector 8, extremely fine photoelectric conversion element, and, by increasing the positional accuracy It is necessary to arrange a large number. In other words, during the 0 to R _a2, we are necessary to Motas the same performance as the element group between 0 to R _a2 of FIG. 3 (b). Also, the lens 5b shown in FIG. 3 (b) or (c)
Alternatively, when 5c is used, the photodetector 8 needs to be extremely large, which is unrealistic.

In the above embodiments, an example in which three condensing lenses are provided is shown, but the number can be any number of two or more, and the order of the lenses used is arbitrary. Of course. Furthermore, the change of the lens and the movement of the photodetector do not have to be performed automatically, but can be manually positioned by the operator. Furthermore, as the photodetector, a photodiode array may be used instead of the ring detector, or a method of scanning the photomultiplier may be used.

<Effects of the Invention> As described above, according to the present invention, a plurality of light intensity distributions measured using each of a plurality of condenser lenses are combined into one light intensity distribution by calculation, and after the combination, Since the particle size distribution is obtained using the light intensity distribution of, it is possible to measure the light intensity distribution with high resolution over a wide angle range, and therefore, it is possible to obtain a highly accurate particle size distribution over a wide particle size range. Moreover, a detector having a large measuring range (a large light receiving area) or a detector having a high position resolution is unnecessary, and the above effect can be achieved without increasing the cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a flow chart showing the contents of a program written in the ROM 152, and FIG. 3 is diffraction (diffraction () due to a difference in focal length of the condenser lenses 5a to 5c. FIG. 4 is a graph showing an example of measuring the light intensity distribution using each of the condenser lenses 5a to 5c. 1 ・ ・ ・ ・ ・ ・ Laser light source 2 ・ ・ ・ ・ ・ ・ Collimator lens 3 ・ ・ ・ ・ ・ ・ Flow cell 4 ・ ・ ・ ・ ・ ・ ・ Sample suspension 5a , 5b, 5c ··· Condensing lens 6 ····· Lens driving mechanism 8 ····· Photodetector 10 ···· Detector driving mechanism 13 ... Multiplexer 14 ... A-D converter 15 ... Computer system

Claims (1)

[Claims] 1. A light receiving surface of a photodetector for collecting diffracted light or scattered light obtained by irradiating a sample particle dispersed in a medium with a parallel light beam by a condenser lens placed on the optical axis of the irradiation light. In the device for measuring the intensity distribution of the diffracted light or scattered light by condensing the light into the particle size distribution of the sample particles by the conversion means, a plurality of condensing lenses having different focal lengths are used. A lens moving mechanism that selectively positions each of the condenser lenses on the optical axis to condense the diffracted light or the scattered light by selectively using each of the condenser lenses. A photodetector moving mechanism that positions the lens at a corresponding focal position according to the selection condition of the condenser lens and a plurality of intensity distribution measurement results obtained by using the plurality of condenser lenses, respectively, are subjected to a predetermined correction calculation. Operation to synthesize by And has a stage, the conversion means is characterized by converting the intensity distribution after its synthesis in the particle size distribution, particle size distribution measuring apparatus.