JPH11248628A - Light scattering type particle detecting sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light scattering type particle detecting sensor which can be enhanced further in sensitivity. SOLUTION: A light projecting element 4 and a light receiving element 5 are arranged in an optical room 2 in the form of crossing respective light axes so that scattered light from the light projecting element 4 due to particles of smoke and dust in a detection area (a) of overlapping a projection area of the light projecting element 4 with a receiving area of the light receiving element 5 can be received by the light receiving element 5 to detect particles. In this case, a first cylindrical light trap A which has an opening with the diameter gradually narrower from the opening and a second light trap B which is interconnected to the first light trap A so as to guide light having entered into the first light trap A and has an opening with the diameter wider from the connection to the first light trap A are provided in the optical room 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light scattering type particle detection sensor used for detecting dust or smoke from cigarettes, or for detecting smoke particles in a photoelectric smoke detector or the like. .

[0002]

2. Description of the Related Art A light scattering type particle detection sensor of this type includes a light projecting element and a light receiving element which are arranged in an optical chamber so that their optical axes cross each other. This is to detect particles by receiving light scattered light from the light emitting element due to particles such as smoke and dust in the detection area where the light receiving area overlaps with the light receiving element. The case that forms the optical chamber has a double structure or a labyrinth structure at the inflow portion of smoke particles and the like in order to make the structure such that particles such as smoke and dust easily flow in and external light does not easily enter.

In this type of conventional light scattering type particle detection sensor, light from a light projecting element is reflected by the inner wall of an optical chamber, and the light reaches a light receiving element as stray light, and the optical S
There is a problem that the / N ratio deteriorates.

FIG. 8 shows a light scattering type particle detection sensor which improves this point. In this light scattering type particle detection sensor, a light shielding wall 11 is provided in the optical chamber 2, and is surrounded by the light shielding wall 11, the inner wall of the optical chamber 2, and the like before the light from the light projecting element 4 enters the light receiving element 5. It has a structure that is reflected multiple times in the area. That is,
In this light scattering type particle detection sensor, the power of stray light is reduced by increasing the number of times of reflection by utilizing the attenuation of light due to reflection. In addition, between the light projecting element 4 and the light receiving element 5, there is provided a light shielding unit 10 for preventing light from the light projecting element 4 from directly entering the light receiving element 5.

In the light-scattering type particle detection sensor shown in FIG. 9, the light-emitting side light trap B formed by forming the inner wall of the optical chamber 2 at an acute angle on the surface facing the light-emitting element 4 and the light-receiving element 5 A light receiving side optical trap A having a similar configuration is provided on the facing surface. Accordingly, the light emitted from the light projecting element 4 and guided to the light projecting side light trap B travels to the back while being reflected on the inner wall, so that the power of the stray light can be reduced, and The guided light does not return to the light emitting element 4 side. Similarly, the light trap A on the light-receiving side has such a structure that the guided stray light hits the inner wall several times and is attenuated, and does not return to the light-receiving element 5 side.

As described above, in the light scattering type particle detection sensor shown in FIGS. 8 and 9, the light emitted from the light projecting element 4 is reflected on the inner wall of the optical chamber 2 and enters the light receiving element 5. In order to prevent measurement accuracy from deteriorating, stray light generation (stray light power /
The light emission power) is set to be weak, and the concentration of particles such as smoke and dust is to be accurately measured.

[0007]

However, the light scattering type particle detection sensor having the above-described structure has a problem that when dust or the like is generated in the optical chamber 2, the power of the stray light rapidly increases. . For example, in the light scattering type particle detection sensor shown in FIG. 8, since the angle between the inner wall where light emitted from the light projecting element 4 is reflected first and the light projecting axis is substantially a right angle,
If dust adheres to this position, scattered light due to dust is generated. When reflected on an ideal rough surface object, the scattered light has a Lambertian distribution, which spreads in almost all directions with respect to the irradiation point, but the intensity of the scattered light has the largest component in the regular reflection direction with respect to the incident direction. It will be. That is, in this light-scattering type particle detection sensor, the intensity of the scattered light due to dust is scattered in the incident direction because the angle with respect to the wall is almost perpendicular, and the scattered light jumps out of the area surrounded by the light shielding wall 11 and the like. It becomes stray light with large intensity. Regarding the light receiving axis, the effect of stray light due to dust on the optical axis poses a problem because the light receiving efficiency of light on the optical axis is highest.

[0008] In this type of light scattering type particle detection sensor, dust tends to accumulate at the sharp point at the end of the back of the optical trap. Therefore, in the light scattering type particle detection sensor shown in FIG. 9, as shown in FIG. 10, most of the light incident on the inner wall of the optical trap does not jump out of the optical trap unless it is reflected a plurality of times. When light is directly incident on the dust accumulated in the back, the light will jump out of the optical trap by only one reflection. In addition, the light reflected on the dust causes scattering which is reflected in all directions, and the strong light also causes the light to jump out of the trap. That is, if dust accumulates in the light receiving side light trap A or the light projecting side light trap B, the dust is scattered, and the generation of stray light is much larger than when there is no dust. Furthermore, light incident along the optical axis of the light projecting region generally has a high light intensity, and the effect of stray light due to dust on the optical axis is particularly problematic. Similarly, with respect to the optical axis of the light receiving region, the effect of stray light due to dust on the optical axis poses a problem because light on the optical axis has the highest light receiving efficiency. Further, in the light scattering type particle detection sensor shown in FIG. 9, it is difficult to completely sharpen the apex existing in the back of the light receiving side light trap A and the light projecting side light trap B due to manufacturing. For this reason, if this portion has a slightly rounded shape, the incident stray light may exit the optical traps A and B with only a small number of reflections, and the stray light power may be sufficiently attenuated. There may not be.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a light-scattering type particle detection sensor capable of further increasing the sensitivity. is there.

[0010]

According to the first aspect of the present invention,
A light-emitting element and a light-receiving element arranged in an optical chamber so that the optical axes cross each other, and smoke and dust in a detection area where a light-emitting area of the light-emitting element and a light-receiving area of the light-receiving element overlap. In a light scattering type particle detection sensor that detects particles by receiving light scattered from a light emitting element by a light receiving element by particles such as a first light trap having a cylindrical shape in which an opening diameter is gradually narrower than an opening. A second optical trap, which is connected to the first optical trap so that the light that has entered the first optical trap is guided, and has a larger opening diameter from a connection with the first optical trap, is provided in the optical chamber. It is characterized by having.

According to a second aspect of the present invention, in the light scattering type particle detection sensor according to the first aspect, the opening of the second optical trap is arranged so as to deviate from the optical axes of the light projecting element and the light receiving element. It is characterized by the following.

According to a third aspect of the present invention, in the light scattering type particle detection sensor according to the first or second aspect, a plurality of grooves are provided on an inner wall of the second optical trap. .

According to a fourth aspect of the present invention, in the light scattering type particle detection sensor according to the first to third aspects, the opening of the first optical trap is provided at a position facing the light emitting element and the light receiving element. It is characterized by the following.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 4, and a second embodiment with reference to FIGS. 5 to 7. FIG.

[First Embodiment] FIG. 1 is a longitudinal sectional view of a light scattering type particle detection sensor according to a first embodiment of the present invention. FIG. 2 is an exploded perspective view of the light scattering type particle detection sensor according to the first embodiment of the present invention. FIG. 3 is a longitudinal sectional view showing a state of light traveling in the light scattering type particle detection sensor. FIG. 4 is a schematic diagram showing how incident light is reflected.

In the light scattering type particle detection sensor according to the present embodiment, the optical chamber 2 is formed by the hollow rectangular case 1. For the case 1, a black ABS resin or the like is used in consideration of moldability while lowering the light reflectance. It is to be noted that, even when aluminum or the like subjected to black alumite treatment is used, the reflectance can be reduced, which is effective.

A light projecting element 4 and a light projecting lens 17 are provided at the upper left corner of the case 1, and are arranged such that the optical axis of the light beam emitted from the light projecting element 4 is emitted toward the diagonally lower right corner. I do. The range through which the light beam passes is referred to as a light projecting area.
Here, as the light emitting element 4, an LED, a semiconductor laser, a solid-state laser, or the like is used. Although the light projection lens 17 is not always necessary, the light scattering type particle detection sensor according to the present embodiment is used for condensing light emitted from the light projection element 4 and concentrating the light on the detection area A.

The light receiving element 5 and the light receiving lens 7 are provided at the upper right corner of the case 1 so that the optical axis of a region (light receiving area) that can be seen from the light receiving element 5 through the light receiving lens 7 is directed to the lower left corner at the diagonal position. To place. As the light receiving element 5, a photodiode, a phototransistor, or the like is used. Although the light receiving lens 7 is not always necessary, the light scattering type particle detection sensor according to the present embodiment is used to increase the light receiving efficiency.

The aperture 6 on the light projecting side is used to control the size of the light projecting area of the light projecting element 4 and to remove light spreading in the light projecting direction which causes stray light. . The aperture 9 on the light receiving side is also used for controlling the size of the light receiving area of the light receiving element 5 and for removing stray light reflected inside the cylinder in which the light receiving element 5 fits.

The above-described case 1 has a rectangular box shape with one side opened, and a printed circuit constituting a processing circuit for appropriately performing signal processing in accordance with the output of the light receiving element 5 on the outer surface of the optical chamber 2 serving as one side wall. It comprises a base 1a on which the substrate 20 is mounted, and a cover 1b attached to the opening of the base 1a.

The detection area A is an area where the light emitting area and the light receiving area overlap. Particles such as cigarette smoke and dust flow into the detection area A from the inflow port 3 provided corresponding to the detection area A. Since the inflow port 3 is provided for the purpose of allowing particles such as smoke and dust to flow into the optical chamber 2, it is not necessary that the inflow port 3 is located immediately below the detection area A, but may be provided at another position. Good.

The light emitted from the light projecting element 4 enters the detection area A through the light projecting lens 17, and the light hitting the particles existing in the detection area A is scattered, and a part of the scattered light enters the light receiving element 5. . As the number of particles entering the detection area A from the inlet 3 increases, the amount of scattered light increases, so that the amount of light received by the light receiving element 5 also increases. Therefore, by measuring the amount of received light,
The number of particles (smoke density) can be measured.

In the light scattering type particle detection sensor according to the present embodiment, a cylindrical shape is provided on the optical axis of the light beam emitted from the light projecting element 4 on the side opposite to the light projecting element 4 as viewed from the detection area A. A portion (hereinafter, referred to as a first light trap B1 on the light projecting side) having an opening for capturing a light projecting beam and having a gradually decreasing opening diameter is provided, and the first light trap B1 on the light projecting side is provided at the tip thereof. A space (hereinafter, referred to as a light projecting side second optical trap B2) is provided so as to be connected and to have a larger opening diameter from a connecting portion (hereinafter, referred to as a light projecting side connecting portion B3). The size of the opening of the first light trap B1 on the light projecting side is large enough to allow all the light emitted from the light projecting element 4 to enter the first light trap B1 on the light projecting side. The shape of the opening of the first light trap B1 on the light emitting side is not particularly limited, and may be various shapes such as a rectangle and a circle. In addition, the light emitting side second
The shape of the optical trap B2 is not limited to a circular vertical cross-sectional shape as in the present embodiment, but may be various shapes such as a polygonal shape.

When the light emitted from the light projecting element 4 is made incident on the opening of the first light trap B1 on the light projecting side, as shown in FIG. Attenuates while repeating reflections on the inner wall. In addition, since the first light trap B1 on the light projecting side has a cylindrical shape, the angle of incidence on the wall of the incident light is small, and the reflected light is in a direction close to the traveling direction of the first light, that is, the first light on the light projecting side. Since the reflection is repeated toward the back of the trap B1, light does not leak out of the first optical trap B1 even if the number of reflections increases. Then, once the light enters the light projecting side second optical trap B2, the light incident on the light projecting side second optical trap B2 becomes the second light due to the narrowing of the light projecting side connecting portion B3. It is difficult to get out of the trap. In addition, since the reflection is further repeated in the second light trap B2 on the light projecting side, even if the light may jump out of the second light trap B2 on the light projecting side, the intensity is extremely small. If the light projecting side connecting portion B3 is made smaller, it becomes more difficult for reflected light to exit from the light projecting side second optical trap B2. If the area of the inner wall of the light projecting side second optical trap B2 is made larger than the opening area of the light projecting side connecting part B3, the reflected light is relatively reflected in the light projecting side second optical trap B2.
Hard to get out of Therefore, the light-emitting side second optical trap B
The stray light may be reduced by increasing the area of the inner wall 2.

Also, when light is reflected by dust adhering to the wall,
As shown in FIG. 4, scattering occurs in all directions. In the present embodiment, even if dust adheres to the tip of the light projecting axis and light is scattered in all directions in the light projecting side second optical trap B2, the light projecting side connecting portion B3 is narrow and omnidirectional. Since the prospective angle of the light projecting side connecting portion B3 becomes small, the scattered light emitted from the light projecting side second optical trap B2 can be sufficiently weakened. It should be noted that the wider the second optical trap, the smaller the expected angle of the scattered light emitted from the light projecting side connecting portion B3, so that it is possible to further reduce stray light.

As described above, the light projected from the light projecting element 4 enters from the first light trap B1 on the light projecting side to the second light trap B2 on the light projecting side while being reflected. The generation of stray light due to the above can be sufficiently reduced.

On the other hand, on the light receiving side, on the optical axis of the light receiving area which enters the light receiving element 5, a light projecting element having an opening for covering the light receiving area is provided on the opposite side to the light receiving element 5 as viewed from the detection area A. 4 (the light-receiving side first)
(A shape composed of the light trap A1 and the second light trap A2 on the light receiving side). The light once entering the light trap facing the light receiving element 5 is, like the light emitting side,
Both the reflected light and the scattered light are attenuated, and the light leaking outside becomes sufficiently small. Thus, the intensity of the stray light incident on the light receiving element 5 can be suppressed to a very small value.

In the light scattering type particle detection sensor, the light scattered by the particles is extremely weak as compared with the incident light power. Therefore, how to prevent light that has not been scattered by the particles from entering the light receiving element 5 is a point in increasing the sensitivity of the light scattering type particle detection sensor. For example, consider the case where the light scattering particle detection sensor according to the present embodiment actually observes particles having a concentration of 0.1 mg / m ³ which is the regulation level of the suspended dust concentration in the building management standard. The detection area A in this embodiment is several cm ³
The intensity of light projected on the detection area b is several mW
In contrast to the order of magnitude, the scattered light intensity detected in the detection area A is on the order of several pW, and it is actually necessary to measure scattered light as weak as 10 ^{-9 with} respect to the projected light intensity.

In this embodiment, firstly, the incident light travels deeply while reflecting the first light trap B1 on the light projecting side many times, and the light that has entered the second light trap B2 on the light projecting side is almost outside. Do not leak to When black ABS resin or the like is used for the inner walls of the first light trap B1 on the light emitting side and the second light trap B2 on the light emitting side, the reflectance becomes 10% or less, so that the attenuation effect is higher and the stray light power is increased. Can be sufficiently attenuated. Further, in the conventional light scattering type particle detection sensor, the stray light incident on the light receiving element 5 has a shape composed of the first light trap A1 on the light receiving side and the second light trap A2 on the light receiving side, similarly to the light projecting side. Can be sufficiently attenuated.

According to this embodiment, the ratio of stray light to the power of projected light (stray light power / power of projected light) can be made extremely small, and high sensitivity measurement of particle concentration can be performed.

When an optical trap is provided in only one of the light projecting element 4 and the light receiving element 5, the intensity of stray light cannot be suppressed as compared with a case in which an optical trap is provided in both of them.
The effect is sufficiently large as compared with the conventional light scattering type particle detection sensor.

[Second Embodiment] FIG. 5 is a longitudinal sectional view of a light scattering type particle detection sensor according to a second embodiment of the present invention. FIG. 6 is an exploded perspective view of the light scattering type particle detection sensor according to the second embodiment of the present invention. FIG. 7 is a longitudinal sectional view showing a state of light traveling in the light scattering type particle detection sensor. In the light scattering type particle detection sensor according to the present embodiment, the same parts as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the light scattering type particle detection sensor according to the present embodiment, as shown in FIG. 5, the second light traps A2 and B2 are arranged so as to be deviated from the optical axes on the light projecting side and the light receiving side.
The inner walls of the first optical traps A1 and B1 are provided at an angle such that the light guided to the first optical traps A1 and B1 travels to the second optical traps A2 and B2 behind the first optical traps A1 and B1. I have. In particular, the light incident along the light projecting axis is reflected on the wall surface of the first light trap B1 on the light projecting side and is incident on the second light trap B2 on the light projecting side. For this reason,
The direct light from the light emitting element 4 having the highest light intensity is
As shown in FIG. 7, the second light trap A on the light emitting side is almost completely
2, the intensity of stray light can be further reduced. Similarly, along the light receiving axis, the light receiving element 5
The incident light is sufficiently attenuated by the first light trap B1 on the light projecting side and the second light trap B2 on the light projecting side, so that the influence of stray light can be further suppressed.

Even when dust adheres to the wall where light passing near the light projecting axis hits, the specular reflection component of the scattered light having the highest light intensity is reflected to the light projecting side second light trap B2. Therefore, the influence of dust is small.

According to the present embodiment, light of high intensity incident along the optical axis can be guided to the second optical traps A2 and B2 and attenuated. This makes it possible to reduce the light intensity of the stray light and perform a highly sensitive measurement of the particle concentration. In the light scattering type particle detection sensor shown in FIG. 5, light incident along the optical axis is the first light trap A1,
The wall corresponding to B1 is a curved surface, but may be a flat surface. In the case of the arrangement of the light emitting and receiving elements 5 as shown in this embodiment, a dead space between the light emitting side optical axis and the light receiving element 5 and a dead space between the light receiving side optical axis and the light emitting element 4 Since the second optical traps A2 and B2 can be provided in the dead space, it is possible to provide the wide second optical traps A2 and B2 without increasing the size of the case 1.

As shown in FIG. 5, a plurality of grooves 25 may be provided on the inner walls of the second optical traps A2 and B2. In the light scattering type particle detection sensor of the present embodiment,
As an example of the groove 25, a plurality of acute-angled triangular irregularities are provided on the inner walls of the second traps A2 and B2. Thereby, the area of the wall surface in the second optical traps A2 and B2 can be increased, and the number of times of reflection of the guided light can be further increased. The groove 25 provided in the second optical trap is not limited to the acute triangular unevenness.
It may be a projection-like unevenness having an acute-angled tip, such as a stylus of needles, or any shape that increases the number of reflections.
The deeper and sharper the irregularities, the more the number of reflections increases, and has the effect of attenuating the intensity of stray light. The groove 25 may be provided anywhere in the second optical trap, and particularly after light on the optical axis has been reflected several times.
When provided on a wall that strikes at an angle close to vertical, the number of reflections increases extremely, so that the effect of attenuating the intensity of stray light is high.

[0037]

As described above, according to the first aspect of the present invention, there are provided a light projecting element and a light receiving element which are arranged in the optical chamber so that the optical axes cross each other. A light-scattering type particle detection sensor that detects particles by receiving light scattered from the light-emitting element due to particles such as smoke and dust in the detection area where the light area and the light-receiving area of the light-receiving element overlap. , A cylindrical first optical trap whose opening diameter gradually becomes smaller than the opening, and a first optical trap connected to the first optical trap so that light entering the first optical trap is guided. Since the second optical trap whose opening diameter is widened from the connecting portion with the second optical trap is provided in the optical chamber, the S / N ratio is improved by guiding and attenuating the stray light to the optical trap, thereby further improving the sensitivity. Light scattering type particle detection sensor An effect that can be provided.

According to the second aspect of the present invention, there is provided the first aspect.
In the light scattering type particle detection sensor described above, since the opening of the second optical trap is arranged so as to be deviated from the optical axes of the light projecting element and the light receiving element, strong light incident along the optical axis is emitted. There is an effect that the light can be sufficiently attenuated by the second optical trap.

In the invention according to claim 3, claim 1 is
Or in the light scattering type particle detection sensor according to claim 2,
Since a plurality of grooves are provided on the inner wall of the second optical trap,
This makes it possible to increase the number of reflections within the optical trap, and to further reduce stray light leaking from the optical trap.

According to the fourth aspect of the present invention, there is provided the first aspect.
4. The light scattering type particle detection sensor according to claim 3,
Since the opening of the first optical trap is provided at a position facing the light projecting element and the light receiving element, the light trap arranged opposite to the light projecting element reliably attenuates the light emitted from the light projecting element, thereby reducing stray light. In addition to preventing the occurrence of light, the optical trap disposed opposite to the light receiving element has the effect of greatly reducing the light that has conventionally entered the light receiving element as stray light.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a light scattering type particle detection sensor according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of the light scattering type particle detection sensor according to the first embodiment of the present invention.

FIG. 3 is a longitudinal sectional view showing a state of light traveling in a light scattering type particle detection sensor.

FIG. 4 is a schematic diagram showing how incident light is reflected.

FIG. 5 is a longitudinal sectional view of a light scattering type particle detection sensor according to a second embodiment of the present invention.

FIG. 6 is an exploded perspective view of a light scattering type particle detection sensor according to a second embodiment of the present invention.

FIG. 7 is a longitudinal sectional view showing a state of light traveling inside the light scattering type particle detection sensor.

FIG. 8 is a longitudinal sectional view of a conventional light scattering type particle detection sensor.

FIG. 9 is a longitudinal sectional view of another conventional light scattering type particle detection sensor.

FIG. 10 is a schematic diagram showing how incident light is reflected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Optical room 4 Light emitting element 5 Light receiving element A1 First light trap on the light receiving side A2 Second light trap on the light receiving side B1 First light trap on the light emitting side B2 Second light trap on the light emitting side i Detection area

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yutaka Abe 1048 Odakadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd.

Claims (4)

[Claims] 1. A detection device comprising: a light projecting element and a light receiving element arranged in an optical chamber so as to intersect an optical axis, wherein a light projecting area of the light projecting element and a light receiving area of the light receiving element overlap. In a light scattering type particle detection sensor which detects particles by receiving light scattered from a light emitting element due to particles such as smoke and dust in an area by a light receiving element, a cylindrical second shape having an opening diameter gradually narrower than an opening. A first optical trap and a second optical trap that is connected to the first optical trap so that light that has entered the first optical trap is guided, and that has a larger opening diameter from a connection with the first optical trap. Provided in an optical chamber. 2. The light scattering type particle detection sensor according to claim 1, wherein the opening of the second optical trap is arranged so as to be deviated from the optical axes of the light projecting element and the light receiving element. 3. The light scattering type particle detection sensor according to claim 1, wherein a plurality of grooves are provided on an inner wall of the second optical trap. 4. The light scattering type particle detection sensor according to claim 1, wherein an opening of the first optical trap is provided at a position facing the light emitting element and the light receiving element.