JP2687539B2 - Particle size distribution analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention uses a diffraction phenomenon or a scattering phenomenon generated by irradiating particles in a dispersed flying state with light to measure a particle size distribution based on a light diffraction / scattering method. Regarding the device.

<Prior Art> A particle size distribution measuring device utilizing the diffraction or scattering phenomenon of light by particles measures the intensity distribution of diffracted light or scattered light and performs arithmetic processing based on the Fraunhofer diffraction theory or Mie scattering theory. The particle size distribution of the sample particles is calculated by

By the way, in this type of measuring apparatus, laser light is generally used as the irradiation light because the irradiation light is required to have coherence or monochromaticity.

As a method of measuring diffracted / scattered light, a condensing lens and a ring shape with different radii or 1/2 or 1
There is a method of using a so-called ring detector in which a plurality of sensors each having a / 4 ring-shaped light receiving surface are concentrically formed on one wafer.

According to the measurement method using this condensing lens and ring detector, the light of each angle component can be measured at the same time, so the measurement time is short, and the diffracted / scattered light from all particles within the light irradiation area can be measured at each angle. Since each component is condensed, there are advantages that a sufficient amount of light can be obtained with each angle component and that it is not affected by polarization.

<Problems to be Solved by the Invention> By the way, in a measuring method using a condenser lens and a ring detector, the laser light transmitted through the particle dispersion system is at the center of the ring detector (optical center, hereinafter simply referred to as center).
The light intensity is extremely high, and the reflected light from the detector affects the measurement optical system as stray light and affects it, and part of it is converted into thermal energy on the detector surface. The detector may be heated to cause a measurement error due to its temperature characteristic.

The present inventor, in collaboration with others, has already developed a device in which a through hole is formed in the center of a ring detector and transmitted light is received by another detector at a position where it passes through the through hole and is diffused to some extent. Proposed (JP-A-62-1006)
No. 37).

Although this proposal improves stray light and thermal effects, it is difficult to open a through hole in the center of the detector (wafer) itself, and there is no other method other than laser processing. There is a problem in that the diameter of the through hole and the innermost sensor closest to the through hole cannot be reduced due to the heat effect of the above.

The present invention has been made in view of the above point, and the influence on the measurement optical system due to the reflection of the collected transmitted laser light on the detector surface without performing special processing such as hole processing on the wafer. It is also an object of the present invention to provide a particle size distribution measuring apparatus which realizes removal of the thermal influence of the transmitted laser light and is therefore inexpensive and has good photometric accuracy.

<Means for Solving the Problems> In order to achieve the above object, in the present invention, as shown in FIGS. 1A and 1B corresponding to the embodiment, a ring-shaped photosensor array (ring detector) is provided. At the optical center of 5,
A reflecting surface 6 having a diameter at least equal to the spot diameter of the transmitted laser light T collected by the lens 4 is integrally provided, and the ring-shaped photosensor array 5 is orthogonal to the optical axis of the irradiation laser light. The surface V is inclined by a predetermined minute angle θ.

<Operation> The transmitted laser light T collected by the lens 4 is incident on the reflecting surface 6 integrally provided at the optical center of the ring-shaped photosensor array 5 and is reflected. The rate of conversion to heat energy is greatly reduced.

The emitted light is emitted from the ring-shaped photo sensor array 5
By providing the entire reflecting surface 6 with the inclination angle θ, it is possible to guide the reflecting surface 6 to the outside of the measurement optical system and prevent it from becoming stray light.

<Embodiment> FIG. 1 is an explanatory view of an embodiment of the present invention, (a) is an overall configuration diagram of an optical system, and (b) is an enlarged front view in the vicinity of an optical center of a light receiving surface of the ring detector 5.

The laser light emitted from the laser light source 1 is collimated by the collimator 2
After the light beam is converted into a parallel light beam having a predetermined beam diameter by the, the flow cell 3 is irradiated with the light beam.

In the flow cell 3, a suspension S in which a group of particles to be measured is uniformly dispersed in a liquid medium is flowed, and a part of the irradiated laser light is diffracted or scattered by the dispersed particles, and other Is transparent.

A condensing lens 4 is disposed on the opposite side of the flow cell 3 from the collimator 2 coaxially with the optical axis of the irradiation laser light, and a ring detector 5 is disposed on the focal point of the condensing lens 4. ing.

The ring detector 5 is a known one in which a plurality of semiconductor photosensors each having a 1/2 ring-shaped light receiving surface with a different radius from each other are concentrically formed around one point on one wafer. A circular reflecting surface 6 having a predetermined diameter centered on the optical center (the above-mentioned one point) is formed on the light receiving surface.
Are formed.

The ring detector 5 is installed such that its optical center is located on the optical axis of the irradiation laser light and the condenser lens 4, and its light receiving surface is a predetermined distance from the surface V orthogonal to the optical axis. It is arranged in such a posture that it is inclined by a small angle θ, for example, several degrees.

Now, the diffracted (scattered) light D by the particles in the suspension S
Are condensed at respective radial positions on the ring detector 5 by the condensing lens 4 for each angular component, and the transmitted laser light T is similarly condensed at the optical center of the ring detector 5. The diameter of the reflecting surface 6 is slightly larger than the spot diameter of the transmitted laser light T on the detector 5, and is formed by evaporating a metal such as aluminum.

Therefore, all of the transmitted laser light T enters the reflecting surface 6 and is reflected with a large reflectance. The direction of the reflection is deviated by 2θ with respect to the optical axis of the measurement optical system based on the tilt angle θ of the ring detector 5. A beam stopper 7 is arranged on the optical path of this reflected light. The beam stopper 7 is, for example, a hollow horn-shaped inner surface that is subjected to a black body treatment, and all the reflected light is absorbed therein.

With the above configuration, the transmitted laser light T condensed by the condenser lens 4 does not affect the ring detector 5 thermally, and the reflected light by the detector 5 becomes stray light in the measurement optical system. There is no returning.

Next, consideration will be given to the influence of giving the tilt angle θ to the ring detector 5 on the measurement result.

Now, assuming that the focal length of the condenser lens 4 is l, the diameter of the condenser lens is d, and the reflected light from the reflecting surface 6 does not enter the condenser lens 4, ignoring the beam diameter, ltan2θ> 1 / 2d ... (1)

From the Fraunhofer diffraction theory, the ring detector 5
Must be perpendicular to the optical axis, and an inclination of about several degrees is not a problem, but a large inclination causes a large photometric error. Therefore, when the focal length 1 is small and the lens diameter d is large, θ given by the formula (1) becomes large and this system cannot be adopted. However, for example, in the case of l = 150 mm and d = 50 mm, θ <4.73 ° and only a slight inclination is required, and there is almost no photometric error. In addition, as in the example of FIG.
If the beam stopper 7 is arranged in the preceding stage to absorb the reflected light, θ can be made smaller than the condition of the expression (1).

The displacement of the light receiving surface from the vertical surface V due to the inclination of the ring detector 5 becomes larger outside the detector 5, but the outside of the detector 5 has a large scattering angle when viewed from the scattered light by the particles. This means that the scattered light from particles with a small particle size becomes dominant. When the particle diameter is small, the relationship between the scattering angle and the scattered light intensity changes gently, so that the influence caused by the position error of the light receiving surface due to the inclination is small and is not a problem.

FIG. 2 is an explanatory view of another embodiment of the present invention, in which (a) is a main part configuration diagram of the optical system thereof, and (b) is an enlarged front view of a light receiving surface of the reflected light measuring detector 11.

This embodiment is intended to positively utilize the reflected light of the transmitted laser light T from the reflecting surface 6, and instead of the beam stopper 7 in the embodiment of FIG. 1, a slit 10 and a reflected light measuring detector 11 are used. The feature is that the shielding plate 12 is provided.

That is, the reflected light from the reflecting surface 6 is guided to the reflected light measuring detector 11 via the slit 10. The reflected light measuring detector 11 is provided with four photosensors 11a, 11b, 11c and 11d centered on one point with their light-receiving surfaces at 90 ° intervals.

As a result, when the reflected light spot P on the reflected light measuring detector 11 deviates from the center of the detector, the amounts of light incident on the photosensors 11a to 11d differ, and therefore the photosensors 11a to 11d have different amounts. By individually monitoring the outputs, the deviation of the optical elements such as the condenser lens 4 from the optical axis can be monitored. In addition, all photo sensors 11
The concentration information of the suspension S can be obtained from the total value of the outputs a to 11d.

In this example, there is a possibility that the reflected light guided to the reflected light measuring detector 11 may be reflected again here and enter the measuring optical system, and the shield plate 12 is provided to prevent this.

The main object of the present invention is to remove the thermal influence of the condensed transmitted laser light T on the ring detector 5, and also to make the reflected light of the transmitted laser light T from the ring detector 5 of the measurement optical system. The purpose is to prevent stray light. Therefore, the processing of the reflected light by the reflecting surface 6 is not limited to the above-described embodiments, and is guided to the outside of the measurement optical system and returned to the optical system again. As long as there is no such processing, any processing can be adopted.

<Effects of the Invention> As described above, according to the present invention, a reflecting surface is integrally provided at the optical center of the ring detector to reflect the transmitted laser light with high reflectance, and the ring detector is also provided. Since the reflected light is guided to the outside of the measurement optical system by giving an inclination to the ring, the thermal effect of the transmitted laser light on the ring detector is greatly reduced, and the reflected light of the transmitted laser light from the detector is measured by the measurement optical system. Stray light will not be added to the measurement result.

Moreover, unlike conventional methods, it is not necessary to perform hole processing on a wafer that is expensive and has a low yield, and only metal vapor deposition for forming a reflective surface is necessary. Further, vapor deposition of aluminum or the like is not necessary for ordinary ring detectors. Since it is generally performed in the space between the ring-shaped light receiving surfaces to shield the light, the reflecting surface can be formed in the same process.

From the above, the present invention provides an inexpensive and highly accurate particle size distribution measuring device.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of the present invention, (a) is an overall configuration diagram of an optical system, and (b) is an enlarged front view of the ring detector 5 near the optical center. 2A and 2B are explanatory views of another embodiment of the present invention. FIG. 2A is a configuration diagram of a main part of an optical system, and FIG. 2B is a reflected light measuring detector 11 thereof.
FIG. 1 ... Laser light source 2 ... Collimator 3 ... Flow cell 4 ... Focusing lens 5 ... Ring detector 6 ... Reflecting surface 7 ... Beam stopper 10 ... Slit 11 ... Reflected light measurement detector 12 ... Shielding Plate S ... Suspension

Claims (1)

(57) [Claims] 1. A sample is obtained by focusing diffracted light or scattered light obtained by irradiating a sample particle in a dispersed flying state with laser light on a ring-shaped photosensor array with a lens and measuring the intensity distribution thereof. In a device for determining the particle size distribution of particles, at the optical center of the ring-shaped photo sensor array,
A reflecting surface having a diameter at least equivalent to the spot diameter of the transmitted laser light condensed by the lens is integrally provided, and the ring-shaped photosensor array is provided with respect to a surface orthogonal to the optical axis of the irradiation laser light. A particle size distribution measuring device characterized in that it is arranged so as to be inclined at a predetermined minute angle.