JP2000214071A - Fine-particle detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fine-particle detector which detects fine particles by making use of a light scattering operation, whose detecting region can be made substantially large even when the fine particles as an object to be detected are small, whose detecting sensitivity is increased, and which can detect the fine particles in a short time. SOLUTION: This fine-particle detector is constituted in such a way that the number and the size of dust particles are detected by measuring laser scattered light generated due to the dust particles by making use of a laser beam. In this case, the laser beam 13 is transmitted by an optical fiber 15 provided with a total-reflection generation part (a spiral part) 15b, the circumference of the total-reflection generation part 15b is used as a fine-particle detecting region, and detecting mechanisms (detecting units) 17 are installed in the circumference of the total-reflection generation part 15b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle detector and, more particularly, to a particle detector for detecting the number and size of particles such as dust generated in a vacuum apparatus by utilizing light scattering.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional fine particle detector utilizing the light scattering function of laser light. The laser light 52 emitted from the laser light source 51 enters the laser light absorber 55 after passing through the lens 53 and the slit 54. The laser light 52 is absorbed by the laser light absorber 55 so as not to leak outside. The lens 53 is used to narrow the laser beam 52 finely. The slit 54 is a lens 53
It is used to prevent the spread of the scattered light generated from. The laser light 52 is narrowed down between the slit 54 and the laser light absorber 55. In a region 56 between the slit 54 and the laser light absorber 55 near the place where the laser light 52 is narrowed, a photodiode 58 provided with an optical filter 57 on both sides of the laser light 52 and separated from the laser light 52. Are arranged in parallel.

When the dust particles 59 fly into the area 56 and pass through the area 56, the dust particles 59 hit the laser beam 52 to generate laser scattered light 60. Laser scattered light 60
Is the photodiode 5 after passing through the optical filter 57.
8 is incident. The photodiode 58 converts the incident laser scattered light into a photocurrent signal. Photodiode 58
The number of times the dust particles 59 have crossed the laser beam 52 is counted based on the number of times of output of the photocurrent signal from. In addition, the size of the dust particles 59 is identified by the magnitude of the photocurrent signal converted by the photodiode 58, because the larger the size of the dust particles, the greater the laser scattered light generated. The optical filter 57 is a filter that selectively allows light of the wavelength of the laser light 52 to pass therethrough, and is used to prevent light of another wavelength from outside the detector from being detected by the photodiode 58.

[0004]

In the conventional fine particle detector utilizing light scattering, a region 56 for detecting dust particles 59 and generating scattered light as described above has a slit 54 and a laser light absorber 55. Are formed as straight regions. The linear region 56 is a region formed corresponding to the sensor opening of the particle detector and is formed to face the length direction of the particle detector. It is decided. At present, the free space inside and outside the chamber of the vacuum apparatus tends to decrease, and therefore, it is necessary to reduce the size of the particle detector mounted on the vacuum apparatus. When the size of the particle detector is reduced, the length of the linear region 56 included in the particle detector is also reduced. At present, the length of the linear region 56 is, for example, 22 mm in design. As described above, when the length of the linear region 56 of the fine particle detector is reduced due to the mounting on the vacuum device, the scattered light generation region for detecting dust particles is limited to a small region, and the scattered light generation region is further reduced. If the number of dust particles in the vacuum device is small, the probability of the dust particles crossing the region becomes small, which causes a problem that dust particles cannot be detected in a short time.

In a conventional particle detector, a laser beam 5
2 is narrowed down into the space and emitted, so that the laser beam 5
2 to increase the intensity of scattered light from dust particles traversing the laser beam 52. However, when the laser light is emitted narrowly in parallel with the stop, the beam diameter of the laser light increases as the distance increases due to the diffraction effect of the light, and the power density of the laser light decreases. For this reason,
The laser light is emitted so that the beam diameter of the laser light is narrowed to the minimum within the region 56 surrounded by the photodiode 58. For this reason, the laser beam density at the most narrowed location is maximum, and the laser beam density decreases as the distance from the location increases.

It is assumed that the size of dust particles to be detected by the fine particle detector is, for example, 0.2 μm as a minimum. In this case, even if the laser beam density is small, if the size of the dust particles to be detected is relatively large, a sufficiently large scattered light intensity is generated with respect to noise, so that the detectable region is substantially wide. However, when the size of the dust particles to be detected is relatively small, the scattered light intensity for the same laser light density becomes small. It is limited to a small area near the place with the smallest diameter. That is, in the conventional particle detector, there is a problem that the smaller the size of the incident dust particles, the smaller the area on the laser light that generates detectable scattered light. Even if the fine particle detector has the sensitivity to detect small dust particles, the detection area where the dust particles on the laser beam can be detected is far Small, limited to the vicinity of the point,
A problem has arisen that it is almost difficult to detect.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem. In a particle detector for detecting fine particles by utilizing light scattering, even when the target fine particles are smaller, the detection area is substantially reduced. Can increase the detection sensitivity
An object of the present invention is to provide a fine particle detector capable of performing detection in a short time.

[0008]

In order to achieve the above object, the fine particle detector according to the first aspect of the present invention measures the laser scattered light generated by the fine particles using laser light. This is a particle detector that detects the size and number of particles, transmits laser light through an optical fiber equipped with a total reflection generation section, and sets the area around the total reflection generation section as a particle detection area and detects it around the total reflection generation section. It is configured to provide a mechanism.

In the present invention, a laser beam is incident from the end face of a single-core optical fiber made of a single glass material, and propagates while repeating total reflection at the boundary of the side surface of the optical fiber.
When total reflection occurs, a surface wave is generated outside the optical fiber, which travels in the axial direction of the optical fiber and whose amplitude decreases exponentially outward in the radial direction. Fine particles such as dust fly to a region where the surface wave is generated, and laser scattered light is generated. There is almost no power loss of the laser light propagating in the optical fiber, the power density of the surface wave is almost the same along the optical fiber, and the intensity of light scattered by the fine particles does not depend on the axial direction of the optical fiber. As described above, the scattered light detection area along the surface of the optical fiber can be made very large.

According to a second aspect of the present invention, in the particle detector according to the first aspect, the total reflection generating section is preferably a winding section formed by winding an optical fiber. When a curved portion exists, the laser beam transmitted through the optical fiber causes total reflection with a higher probability.

According to a third aspect of the present invention, in the particle detector according to the second aspect of the present invention, the detection mechanism comprises a plurality of rectangular plate-like detection units, and the detection unit has a long side at the center of the spiral portion. The plurality of detection units are arranged so as to be parallel to the axis and the short side thereof is oriented in the radial direction of the circle formed by the spiral portion, and the plurality of detection units are arranged at equal intervals along the circle.

According to a fourth aspect of the present invention, in the above-described third aspect of the present invention, the detection unit comprises a photoelectric conversion element, and a light receiving surface of the photoelectric conversion element transmits laser light. It is arranged to face the direction.

According to a fifth aspect of the present invention, there is provided a fine particle detector comprising:
In the invention, the optical filter is characterized in that an optical filter that transmits light having a wavelength of laser light is provided in front of the light receiving surface of the photoelectric conversion element.

According to a sixth aspect of the present invention, in the above-described invention, the total reflection generating section generates a surface wave outside the optical fiber when the laser light is totally reflected.
The laser scattered light is generated by the interaction between the arriving fine particles and the surface wave.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a front view showing a typical embodiment of a particle detector according to the present invention, and FIG. 2 is a side view as viewed from the direction A in FIG. 1 and 2 show a characteristic configuration for explaining the principle of detecting fine particles. In the fine particle detector according to the present embodiment for detecting fine particles such as dust, a scattered light method using laser light is used. Therefore, the particle detector according to the present embodiment also includes a laser light source (laser diode) 11 for emitting laser light and a laser light absorber 12 for receiving laser light. The laser light 13 emitted from the laser light source 11 is stopped down by the lens 14.

In the particle detector according to the present embodiment, FIG.
2, the laser light 13 emitted from the laser light source 11 is transmitted through the optical fiber 15 after being narrowed down by the lens 14. The optical fiber 15 is formed of a single-core single linear glass material, and is morphologically located at an end 15 a on the laser light source 11 side, an end 15 c on the laser light absorber 12 side, and substantially at the center. Spiral (spiral coil)
And a spiral portion (coil portion) 15b wound around the coil. The laser light 13 is applied to the end 1 of the optical fiber 15.
The light enters the end face of the optical fiber 5a, propagates through the spiral portion 15b, and is emitted from the end face of the optical fiber at the end 15c. Arrow 16 indicates the traveling direction of the laser beam. Spiral part 15b
Is arbitrary.

In the particle detector according to the present embodiment, a region around the spiral portion 15b of the optical fiber 15 is used as a particle detection region. The area of the particle detection area is
5b. In the fine particle detection region, for example, eight detection units 17 are arranged at, for example, equal intervals along a circle (the circular portion shown in FIG. 1) formed by the spiral portion 15b. The detection unit 17
It preferably has the form of a rectangular plate-like member, and is formed by overlapping an optical filter 18 and a photodiode (photoelectric conversion element) 19. That is, the photodiode 1
An optical filter 18 is arranged in front of the light receiving surface 9.
The plurality of detection units 17 having a rectangular plate shape include:
As shown in FIG. 2, the long side is arranged so as to be parallel to the central axis of the spiral portion 15b, and as shown in FIG. 1, the short side is radially directed toward the radial direction of the circle. In other words, the short side of the detection unit 17 is orthogonal to the tangent of the circle. Each of the plurality of detection units 17 includes a portion (outside portion) located outside the circle,
It is divided into a part (inner part) located inside the circle.

As an actual method of making the detection unit 17,
For example, in the detection unit 17 having a rectangular plate shape, a slit parallel to the long side is formed at the center position in the short side direction. In this case, the spiral portion 15b of the optical fiber 15 is
The optical fiber is arranged so as to be wound while being inserted into the slit. As another manufacturing method, the detection unit 17 is composed of two members, the member forming the outer portion and the member forming the inner portion, from the beginning. It is to be arranged at a predetermined position inside. Detection unit 17
An arbitrary configuration can be adopted as a method of producing.

In the above configuration, each of the plurality of detection units 17 is further arranged so that the incident light receiving surface of the photodiode 19 faces the direction in which laser light is transmitted. Although the structure for mounting the detection unit 17 is not shown in FIGS. 1 and 2, any structure can be adopted as the mounting structure.

FIG. 3 shows a part of the spiral portion 15b of the optical fiber 15, and shows a process of detecting fine particles. The detection operation of the particle detector according to the present embodiment will be described with reference to FIG. 3 and FIGS. 1 and 2 described above.

Laser light 1 emitted from laser light source 11
3 is stopped down by the lens 14 and is incident on the end face of the end 15 a of the optical fiber 15. Laser light is optical fiber 15
Of the optical fiber 15 after propagating through the helical portion 15b
The laser beam is emitted by the other end face of the laser beam 5c and absorbed by the laser beam absorber 12.

The laser light 13 propagates in the optical fiber 15 while repeating total reflection. When total reflection occurs, a surface wave is generated outside the optical fiber 15 that travels in the axial direction of the optical fiber and whose amplitude decreases exponentially outward in the radial direction of the optical fiber. The total reflection of the laser light 13 is particularly likely to occur in the spiral portion 15b of the optical fiber 15, and the region where the surface wave is generated is formed in the outer region and the inner region of the spiral portion 15b. As shown in FIG. 3, when the dust particles 22 fly to the area 21 where the surface wave is generated, laser scattered light 23 is generated. Laser scattered light 2
After passing through the optical filter 18 that transmits the laser wavelength, the light 3 enters the light receiving surface of the photodiode 19 and is converted into a photocurrent signal and detected.

Laser light 13 propagating in optical fiber 15
Are almost the same, and the power density of the surface wave generated by the total reflection of the laser light is almost the same along the optical fiber 15. Therefore, it is possible to detect the laser scattered light having the same intensity at any position in the axial direction where the laser light is totally reflected in the optical fiber 15. In particular, the total reflection of the laser light 13 in the optical fiber 15 is highly likely to occur in the spiral portion 15b formed by winding the optical fiber, and therefore, the region where the surface wave is likely to be generated is also outside and inside the spiral portion 15b. It is formed. A region along the wound optical fiber in the spiral portion 15b is used as a particle detection region. Therefore, as described above, eight detection units 17 are arranged around the inside and outside of the spiral portion 15b, and the generated laser scattered light 23 is detected by each of the eight detection units.

According to the above configuration, the area where the scattered light can be detected even if the size of the dust particles is small is not limited to the limited area in the axial direction unlike the conventional detector. Although the optical fiber has an incident angle limit at the end face, as long as the axial bending (bending R) in the helical portion 15b is kept at a certain value or more, the incident angle in the optical fiber at the circumferential portion is less than the critical angle. And no light leaks out. For this reason,
Although there is a limitation on the miniaturization of the detector size due to the bend R, by forming the spiral portion 15b while maintaining the bend R at a certain value or more, the scattered light fine particle detection area along the surface of the optical fiber can be made very large. Can be.

According to the above embodiment, the spiral portion 15b is formed by winding the optical fiber, and the area along the optical fiber where the total reflection of the laser light occurs is defined as the particle detection area. The length of the optical fiber can be increased by making the optical fiber helical even if the mounting size is reduced. A plurality of detection units 1 arranged inside and outside the spiral part 15b
In combination with 7, the laser scattered light 23 generated from the vicinity of the surface of the optical fiber due to the dust particles 22 is effectively detected.

In the above embodiment, the spiral portion is formed by winding the optical fiber, and the laser beam is totally reflected therefrom, thereby forming the fine particle detection area along the surface of the optical fiber. The structure for generating reflection (total reflection generating portion) is not limited to the spiral portion. Furthermore, in the above embodiment, the example of the optical fiber has been described, but another optical transmission line capable of performing the same optical transmission as the optical fiber can be used.

[0028]

As is apparent from the above description, according to the present invention, in a fine particle detector for detecting fine particles using light scattering, an optical fiber is used as a means for transmitting laser light, and A spiral is formed by winding an optical fiber to form a fine particle detection area using surface waves generated by total reflection, and a detection mechanism is provided along the optical fiber around this spiral, so the detector size The particle detection area can be extended by the length of the optical fiber in the spiral portion without increasing the particle size, so that the detection area does not extremely decrease even when the particles are small. Even when the particles to be detected are smaller, the detection area can be substantially enlarged, the detection sensitivity can be increased, and detection can be performed in a short time.

[Brief description of the drawings]

FIG. 1 is a front view showing a typical embodiment of a particle detector according to the present invention.

FIG. 2 is a side view seen from a direction A in FIG.

FIG. 3 is an enlarged view of a main part for describing a detection operation of fine particles.

FIG. 4 is a configuration diagram showing an example of a conventional particle detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Laser light source 12 Laser light absorber 13 Laser light 15 Optical fiber 17 Detection unit 18 Optical filter 19 Photodiode 21 Particle detector 22 Dust particle 23 Light scattered light

Claims (6)

[Claims] 1. A fine particle detector for detecting fine particles by measuring laser scattered light generated by the fine particles using a laser beam, wherein the fine laser beam is transmitted by an optical fiber having a total reflection generating section. A particle detection area around the total reflection generating section, and a detection mechanism provided around the total reflection generating section. 2. The particle detector according to claim 1, wherein the total reflection generating section is a winding section formed by winding the optical fiber. 3. The detecting mechanism comprises a plurality of rectangular plate-shaped detecting units, and the detecting unit has a long side parallel to a central axis of the spiral part and a short side formed by the spiral part. The particle detector according to claim 2, wherein the plurality of detection units are arranged so as to face in a radial direction of the circle, and the plurality of detection units are arranged at equal intervals along the circle. 4. The detection unit according to claim 3, wherein the detection unit comprises a photoelectric conversion element, and the photoelectric conversion element is arranged so that a light receiving surface thereof faces in a direction in which the laser light is transmitted. Particle detector. 5. The particle detector according to claim 4, wherein an optical filter that transmits light having a wavelength of the laser light is provided in front of the light receiving surface of the photoelectric conversion element. 6. The total reflection generating section generates a surface wave outside the optical fiber when the laser light is totally reflected,
The laser scattered light is generated by arriving fine particles and the surface wave acting on each other, wherein the laser scattering light is generated.
6. The fine particle detector according to any one of 5.