JP2001133386A - Particle-size distribution measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply adjust the optical axis of a particle-size distribution measuring device by a low-cost mechanism. SOLUTION: The mechanism 40 for optical axis adjustment is disposed on the light-source side of a scatter field 10. The mechanism 40 has a lens 42 for optical axis adjustment and a drive mechanism for moving the lens 42 in a plane crossing the optical axis. The focal distance F of the lens 42 is sufficiently longer than the distance L between this and a condensing lens 16. When the lens 42 is moved, the position of the optical axis on a detector 18 is moved by the product of the moved amount multiplied by L/F. A relatively large movement of the lens 42 can provide fine adjustment of the optical axis on the detector 18, thus allowing relatively low-cost components to be used for the drive mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle size distribution measuring apparatus for measuring the particle size of a granular sample by measuring the scattering state of light applied to the sample.

[0002]

2. Description of the Related Art When a particle dispersed at an appropriate concentration is irradiated with light, a scattering phenomenon occurs. It is known that the intensity distribution of the scattered light with respect to the scattering angle is different depending on the particle size (particle size) of the particles, and a particle size distribution measuring device that uses this to determine the particle size of a particulate sample is known.

A particle size distribution measuring device having the following basic configuration is known. That is, it has a laser light source for irradiating the sample with light and a detector having a plurality of light receiving elements for receiving light scattered by the sample. In addition, it has a condensing lens that condenses the light scattered by the sample at a predetermined position on the detector for each scattering angle. The plurality of light receiving elements of the detector are provided corresponding to a predetermined range of the scattering angle. This light receiving element outputs an electric signal according to the amount of light received. Therefore, if the output of each detector, that is, the output of each light receiving element is measured, the intensity distribution of the scattered light can be obtained, and the particle size of the sample can be obtained therefrom.

[0004] Most of the scattered light scattered by the particles is condensed in a range where the scattering angle is small as the diameter of the particles (hereinafter, referred to as the particle diameter) increases. Therefore, the distance between the image forming positions of the scattered light on the detector and the light directly arriving from the light source without being scattered (hereinafter, referred to as direct light) is also reduced. For this reason, it is necessary to separate the scattered light and the direct light with sufficient accuracy, and the light receiving elements of the detector are also arranged with the accuracy corresponding thereto. However, if the direct light condensing position, that is, the optical axis position is shifted from the original position on the detector before that, accurate measurement cannot be performed. In Japanese Patent No. 2522880, light-receiving elements for adjusting the optical axis are arranged at 90 ° intervals on a circumference centered on the optical axis of the detector, and among these light-receiving elements, the light-receiving elements are located symmetrically about the optical axis. A technique for adjusting the position of a detector or a light source so that the outputs of the elements are substantially equal is disclosed.

[0005]

However, as the particle size increases, the image formation positions of scattered light and direct light become closer,
Very precise optical axis position adjustment is required. When a detector or the like is directly moved as in the above-mentioned patent, the accuracy of the optical axis adjustment is directly required for the control of this drive. However, there is a problem that a driving mechanism having high accuracy is expensive and increases product cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to reduce the size, cost, and accuracy of a drive mechanism for adjusting the position of an optical axis on a detector. I do.

[0007]

In order to solve the above-mentioned problems, a particle size distribution measuring apparatus according to the present invention comprises: a condenser lens for condensing light scattered by a sample at each scattering angle; A detector disposed at a light condensing position of the lens for detecting a scattering state, an optical axis adjusting lens disposed on a light source side of the sample and having a focal length sufficiently longer than a distance to a condensing lens, and the optical axis Moving means for moving the adjusting lens in a plane intersecting the optical axis.

By moving the optical axis adjusting lens, the focusing position on the detector can be moved. At this time, the ratio of the movement amount of the optical axis adjustment lens to the movement amount of the focusing position is the ratio of the focal length of the optical axis adjustment lens to the distance between the optical axis adjustment lens and the condenser lens. Therefore, the movement of the light condensing position becomes smaller with respect to the relatively large movement of the lens for optical axis adjustment, and more precise position adjustment can be performed.

[0009]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. FIG.
It is a figure showing the schematic structure of the particle size distribution measuring device of this embodiment. The sample to be measured is placed in the scattering field 10 in an appropriately dispersed state. The sample placed in the scattering field 10 is irradiated with a substantially parallel light beam from the laser light source 12 via the collimator 14 and the optical axis adjustment mechanism 40. The optical axis adjusting mechanism 40 will be described later in detail. In the scattering field 10,
Light striking the sample particles is scattered. Distribution of scattered light, that is, the angle (scattering angle) θ of the scattered light with respect to the irradiated light
The distribution of the light intensity for each sample changes depending on the particle size of the sample. The light that has passed through the scattering field 10 passes through the condenser lens 16 and reaches the detector 18. The condenser lens 16 is a lens that collects light at a predetermined position on the detector 18 for each scattering angle θ. That is, even if the light scattered by the particles at different positions in the scattering field 10 has the same scattering angle θ, the detector 18
The upper condensing position is the same.

FIGS. 2 and 3 show the detailed configuration of the detector 18 as viewed from the light irradiation direction. Detector 18
Has a substantially fan shape as shown in FIG. 2, and the tip O of the fan shape is arranged so as to coincide with the center of the optical axis from the light source 12. In particular, FIG. 3 is an enlarged view showing the vicinity of the front end O in detail. The detector 18 is divided into a plurality of sections by a concentric circle centered on the tip O, and a light receiving element 20 for detecting scattered light is arranged for each section. Therefore, one light receiving element 20 has a shape that becomes a part of a ring. Due to this arrangement, a certain range of the scattering angle θ is condensed on one light receiving element 20. The light receiving element 20 is an element that outputs an electric signal according to the received light amount. As shown in the figure, the light receiving element 2
The area of 0 is narrow near the tip O and wide near the tip O. This considers that the output of each light receiving element 20 is made as uniform as possible in response to the intensity distribution of the scattered light having a small scattering angle θ, that is, a distribution in which more light is collected near the tip O. It was done.

As shown in FIG. 3, light receiving elements 21A-21E for adjusting the optical axis are arranged near the tip O of the detector. In the following description, the light receiving element 21A-
When it is not necessary to distinguish and describe 21E in particular, and when showing the entire light receiving element for optical axis adjustment, the description is simply made using the reference numeral 21. The light receiving element 21E is a circular light receiving element centered on the tip O of the detector 18. Light receiving element 2
1A to 21D are arranged at 90 ° intervals on a circumference centered on the front end O. Most of the light from the laser light source 12 reaches the detector 18 without being scattered by the sample. This light beam is the above-mentioned direct light, and the axis of this light beam will be hereinafter described as the optical axis. When the optical axis coincides with the front end O of the detector, the light receiving elements 2A and 21C and the light receiving elements 21B and 21D which are arranged to face the front end O respectively form a set of the light receiving elements 2A and 21C.
1 will be equal. Conversely, when the outputs of the light receiving elements 21 forming a pair are not equal, it can be seen that the optical axis is shifted from the detector tip O. By adjusting the relative position between the optical axis and the detector 18 so as to make this output equal, the optical axis adjustment is achieved.

FIG. 4 shows a part of a processing system for an output signal of the light receiving element 20. Outputs of the light receiving elements 20 and 21 are amplified by preamplifiers 22 arranged one for each of the light receiving elements 20 and 21 and sent to a multiplexer 24. In the multiplexer 24, the output of one light receiving element 20 is selectively sent to the amplifier 26, the output to be selected is switched, and the outputs of all the light receiving elements 20 are sequentially sent out. FIG.
, The output of the amplifier 26 is sent to the arithmetic and control unit 30 via the A / D (analog / digital) converter 28, where the scattered light is Of the sample is measured, and the particle size of the sample is measured. When adjusting the optical axis, the shift of the optical axis is measured based on the output of the light receiving element 21 for adjusting the optical axis, and the position is adjusted so as to eliminate the shift. The measurement result of the scattered light is output to an output device 3 such as a printer or a display.
Sent to 2.

FIG. 5 is a diagram for explaining the principle of optical axis adjustment according to the present embodiment. The optical axis adjusting lens 42 of the optical axis adjusting mechanism 40 is movably supported in a plane intersecting the optical axis. The optical axis adjusting lens 42 has a sufficiently long focal length F with respect to the distance L to the condenser lens 16. In this configuration, when the optical axis adjusting lens 42 is moved by a moving amount X in a plane intersecting the optical axis, the image on the detector 18 moves by a moving amount X ′. This movement amount X,
The relationship of X 'is

X ′ / X = L / F (1) On the other hand, the laser light passing through the scattering field 10 needs to be parallel light, but is strictly not parallel light by the optical axis adjusting lens 42. However, if a lens having a focal length sufficiently longer than the distance L between the two lenses 16 and 42 is used as an optical axis adjusting lens, it is possible to make the lens sufficiently parallel light. According to the equation (1), the moving amount X ′ of the optical axis on the detector 18 can be L / F times the moving amount X of the optical axis adjusting lens 42. In other words, even if the optical axis adjusting lens 42 is moved relatively large, the optical axis on the detector 18 moves only slightly, and fine position adjustment can be easily performed.

FIG. 6 shows details of the optical axis adjusting mechanism 40 as viewed from the optical axis direction. Optical axis adjustment lens 4
2 is fixed on the inner slider 44. The left and right sides of the inner slider 44 are outer sliders 46.
And is slidable along the guide 48, that is, in the vertical direction in the figure. The upper and lower sides of the outer slider 46 are the guides 5 of the frame 50.
2 and is slidable along the guide 52, that is, in the left-right direction in the figure. Inner slider 44
Are driven by a stepping motor 54. When the rotor rotates, the stepping motor 54 moves the rod 56 forward and backward by an amount corresponding to the rotation angle. The rod 56 is in contact with a plate 58 provided on the inner slider 44. When the rod 56 advances, the inner slider 44 moves downward. The inner slider 44
Is urged upward by an elastic member (not shown) with respect to the outer slider 46, and the rod 56 and the plate 58 are always in contact with each other. The same applies to the outer slider 46. That is, the stepping motor 60
The rod 62 is driven leftward in the figure by the rod 62 which moves forward and backward. Further, the elastic member (not shown) urges the frame 50 rightward in the drawing, so that the contact state between the rod 62 and the plate 64 is always maintained.

The optical axis adjusting lens 42 is driven by the stepping motors 54 and 60, and the position of the optical axis on the detector 18 moves by an amount corresponding to the moving amount. The arithmetic and control unit 30 monitors the output of the light receiving element 21 for optical axis adjustment, and controls the stepping motors 54 and 60 so that these outputs indicate the coincidence between the optical axis and the tip O of the detector. Done. As described above, the inner slider 44, the outer slider 46, the frame 50, the stepping motors 54 and 60, which support the optical axis adjusting lens 42, and the mechanisms attached thereto function as moving means for the lens 42. Further, the arithmetic and control unit 30 functions as an optical axis adjustment control unit.

[0016]

Next, specific numerical values will be described. The diameter of the beam converted into parallel light by the collimator is 6 mm. The lens for adjusting the optical axis is a plano-concave lens, and the focal length F is 1000 mm. Optical axis adjustment lens and condenser lens 1
The distance L of No. 6 is 100 mm. Stepping motor 5
In rods 4 and 60, the rods 56 and 62 advance and retreat in steps of 25 μm. One step of the stepping motor (= 25 μm)
Then, the optical axis adjusting lens 42 moves by 25 μm. At this time, on the detector 18, the optical axis becomes 2.5
Move μm. Therefore, an optical axis adjustment of 2.5 μm can be performed by a stepping motor of 25 μm per step. On the other hand, when the detector 18 or the light source 12 is directly moved, a stepping motor of 1 step-2.5 μm is required to maintain the same step, which is more expensive than the motor described above. Becomes At this time, the spread angle of the light beam in the scattering field 10 is 3 mrad.
In the particle size measurement, it can be regarded as substantially parallel light.

As described above, the drive mechanism for adjusting the optical axis can be constructed relatively inexpensively as compared with the case where the light source 12 and the detector 18 are directly driven. It is also possible to provide a ball screw mechanism with a micrometer in place of the stepping motors 54 and 60, and manually adjust the optical axis.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of the present embodiment.

FIG. 2 is a diagram showing a configuration of a detector.

FIG. 3 is a diagram showing the configuration of a detector, particularly details in the vicinity of a tip.

FIG. 4 is a diagram illustrating a configuration of a detector and a signal processing system.

FIG. 5 is a diagram for explaining the principle of optical axis adjustment.

FIG. 6 is a diagram showing details of an optical axis adjustment mechanism.

[Explanation of symbols]

10 scattering field, 12 light source, 16 condenser lens, 18
Detector, 20 light receiving elements for detecting scattered light (division of detector), 21, 21A-21E light receiving elements for adjusting optical axis,
22 preamplifier (signal processing system), 30 arithmetic and control unit, 40 optical axis adjusting mechanism, 42 optical axis adjusting lens.

Claims (1)

[Claims] 1. A particle size distribution measuring apparatus for measuring the particle size of a sample by measuring the scattering state of light applied to a dispersed granular sample, wherein light scattered by the sample is collected at each scattering angle. A condenser lens, a detector for detecting a scattering state disposed at a condenser position of the condenser lens, and an optical axis adjustment disposed on the light source side of the sample and having a focal length sufficiently longer than a distance to the condenser lens A particle size distribution measuring device, comprising: a lens for movement; and moving means for moving the optical axis adjustment lens in a plane intersecting the optical axis.