JP2000235000A - Light-scattering-type particle detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further miniaturize a detection sensor by preventing stray light entering a light trap once from exiting to the outside and preventing a capacity for attenuating the stray light from decreasing. SOLUTION: Two light traps A and B are provided with reflection surfaces 13 and 14 for reflecting incident light through apertures 11a and 12a of shades 111... and 121... and are formed in a shape for bending light being reflected by the reflection surfaces 13 and 14 so that it goes away from a detection region and approaches a light projection element 4 and a photo detector 5. Since the shades 111... and 121... with the smaller apertures 11a and 12a than the diameters of the light traps A and B are provided at the entrance of the light traps A and B, light with a shallow incidence angle is shaded by the shades 111... and 121..., thus preventing the reflection light from exiting to the outside of the light traps A and B and reducing the generation of stray light.

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 detector which is used for detecting dust or cigarette smoke in an air purifier or the like, or for detecting smoke particles in a photoelectric smoke detector or the like. It concerns a sensor.

[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. In this case, particles are detected by receiving, with the light receiving element, scattered light of 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 area. The case that forms the optical chamber has a double structure so that particles such as smoke and dust are likely to flow in and external light is difficult to enter, and a complicated maze (labyrinth) structure is used for the inflow portion of smoke particles and the like. ing.

[0003] In the above-described conventional example, light from the light projecting element is reflected by the inner wall of the optical chamber, and the light reaches the light receiving element as stray light, and the optical S
There was a problem that the / N ratio deteriorated.

Therefore, there is a light scattering type particle detection sensor which has solved the above-mentioned problem as disclosed in Japanese Patent Application Laid-Open No. 4-16097. In the light scattering type particle detection sensor described in this publication, a light shielding wall 31 is provided in an optical chamber 30 as shown in FIG. It has a structure that is reflected a plurality of times in a region surrounded by the inner wall or the like of the chamber 30. That is, in this light scattering type particle detection sensor, the power of stray light is reduced by increasing the number of reflections by utilizing the attenuation of light due to reflection. Note that the light emitting element 3 is provided between the light emitting element 32 and the light receiving element 33.
A light-shielding part 34 is provided to prevent the light from the second element from directly entering the light-receiving element 33.

However, in the light scattering type particle detection sensor described in the above publication, the area surrounded by the light shielding wall 31 and the inner wall of the optical chamber 30 needs to be enlarged in order to reflect and attenuate the stray light many times. There is a problem that the size of the case itself becomes large.

Therefore, the present inventors provided an optical trap for attenuating stray light at a position facing the light projecting element and the light receiving element, respectively. (A side opposite to the element), a light scattering type in which the tip is arranged toward the light receiving element and the light trap facing the light receiving element is arranged such that the end is directed toward the light emitting element as it advances from the opening. A particle detection sensor has been proposed (see Japanese Patent Application No. 10-46490). Thus, it is possible to improve the space utilization rate in the optical chamber by accommodating a part or all of the optical trap in the dead space in the optical chamber, and to achieve miniaturization without reducing the effect of attenuating stray light. it can.

[0007]

However, in the light scattering type particle detection sensor of the above application, stray light can be effectively trapped when the traveling direction of the light from the light projecting element is in the depth direction of the light trap. Although it is possible, when the traveling direction of the light is directed to the light emitting element side due to scattering due to dust or the like deposited on the inner wall of the optical trap, the light is easily emitted out of the optical trap.

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent stray light once entering a light trap from going outside and reduce the ability to attenuate stray light. It is an object of the present invention to provide a light-scattering type particle detection sensor that can be further downsized without causing the light-scattering.

[0009]

In order to achieve the above object, a first aspect of the present invention comprises a light projecting element and a light receiving element arranged in an optical chamber so as to cross optical axes, respectively. In the detection area where the light projecting area of the element and the light receiving area of the light receiving element overlap each other, particles are detected by receiving light scattered by the light emitting element due to particles such as smoke and dust from the light emitting element. In light scattering type particle detection sensor,
A light-shielding plate having an opening facing the detection region and arranged at a position facing at least one of the light-emitting element or the light-receiving element; and a light-shielding plate having a diameter larger than the opening of the light-shielding plate and opposite to the detection region. A light trap provided on the side of the light-shielding plate, the light trap having a reflection surface for reflecting light incident through the opening of the light-shielding plate, and moving the light reflected by the reflection surface away from the detection area and toward the light-emitting element or the light-receiving element. It is characterized by being formed in a shape that bends toward the direction, and because a light shielding plate is arranged at the entrance of the optical trap, particles such as dust accumulate in the optical trap and scattered light increases. Also, the stray light once entering the optical trap is prevented from going outside by the light shielding plate, and the size can be further reduced without reducing the ability to attenuate the stray light.

According to a second aspect of the present invention, in the first aspect of the invention, the stray light is formed such that the diameter of the optical trap becomes smaller as the distance from the light-shielding plate or the reflection surface becomes farther from the light-shielding plate. Can be more effectively attenuated.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the light emitting device is disposed on the optical axis of the light projecting element and is disposed on the optical axis of the light receiving element and the light receiving element. Comprising at least one of a light receiving lens for condensing light on the light receiving element,
The shape of the light-emitting lens or light-receiving lens and the shape of the opening of the light-shielding plate are made similar, so that the efficiency of the amount of light received by the light-receiving element with respect to the amount of light emitted from the light-emitting element can be increased. The opening area of the plate can be minimized, stray light can be suppressed, and the thickness can be reduced.

[0012] The invention of claim 4 is the invention of claim 1 or 2 or 3.
The light shielding element and the light trap provided at least at a position facing the light emitting element, and a light condensing means for condensing light from the light emitting element near an opening of the light shielding element. The opening area of the plate can be minimized, and generation of stray light can be suppressed.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, a light-shielding plate and an optical trap are provided at least at a position facing the light-receiving element, and light from the detection area is focused on the light-receiving element. In addition, a light receiving lens having an image forming position at a position farther from the light receiving element than the detection area is provided, and the thickness can be reduced.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, a light-shielding plate and an optical trap are provided at least at a position facing the light-receiving element, and light from the detection area is focused on the light-receiving element. An optical system is provided, and the dimensions of the optical trap are set so that a part other than the inner wall of the optical trap does not fall within the visual field range of the optical system, thereby further suppressing the generation of stray light.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, there is provided a case in which at least a light projecting element, a light receiving element, a light shielding plate, and an optical trap are housed,
An inlet for allowing external particles to flow into the detection area in the case, and an outlet for flowing particles in the case to the outside are provided in the case, and the diameter of the outlet is formed to be larger than the diameter of the inlet. Thus, the number of particles remaining in the optical chamber can be reduced to suppress the generation of stray light.

According to an eighth aspect of the present invention, in any one of the first to seventh aspects of the present invention, at least the front end of the detection area is opposite to the side where the light emitting element and the light receiving element are arranged. A plurality of light-shielding walls that separate a part of the optical chamber toward the light-emitting element and the light-receiving element, respectively, to prevent reflected light and scattered light generated by the optical trap from entering the light-receiving area. Thus, the amount of stray light reaching the light receiving element can be reduced.

According to a ninth aspect of the present invention, in any one of the first to eighth aspects of the present invention, the reflectance is substantially the same as the reflectance of the particles attached to a portion in the optical chamber where stray light is increased by the attachment of the particles. Characterized by having a reflecting means having
Even if dust particles and the like accumulate, the change in the stray light amount is small, and the correction process for the stray light amount becomes unnecessary.

[0018]

(Embodiment 1) FIG. 1 is a sectional view of the present embodiment, and FIG. 2 is an exploded perspective view.

In the light scattering type particle detection sensor of 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 of the present embodiment is used for condensing the 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) viewed 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 controls the size of the light projecting area of the light projecting element 4 and is used for removing light spreading in the light projecting direction which causes stray light. I have. The aperture 9 on the light receiving side is used to control the size of the light receiving area of the light receiving element 5 and to remove stray light reflected inside the cylinder in which the light receiving element 5 fits.
The light receiving element 5 is covered with a shield member 15 on the outer surface except for the light receiving surface in order to reduce the influence of electric noise.

The above-mentioned case 1 is formed of a base 1a formed in a rectangular box shape with one side open and having a labyrinth structure therein, and a cover 1b for closing the opening of the base 1a. An inlet 3 for allowing particles such as dust and smoke to flow into the optical chamber 2 is provided substantially at the center of the cover 1b.
Further, a substantially cylindrical tube portion 3a protrudes from the outer periphery of the inlet 3 on the outer surface of the cover 1b. Also, on the cover 1b side of the case 1, a printed circuit board 20 which constitutes a processing circuit for appropriately performing signal processing according to the output of the light receiving element
And a shield cover 10 for shielding the printed circuit board 20.

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 I from the inlet 3 provided in the cover 1b in accordance with the detection area A. The light emitted from the light emitting element 4 is the light emitting lens 1
7, light incident on the particles existing in the detection area A is scattered, and a part of the scattered light is
to go into. 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 and the concentration of dust can be measured.

In the light scattering type particle detection sensor according to the present embodiment, in order to remove stray light, the light projecting element 4 is viewed on the optical axis of the light (light projecting beam) emitted from the light projecting element 4 when viewed from the detection area A. 4 and three shading plates 11 ₁ to 11 ₃ which comprises an opening 11a facing the detection area b to the opposite side, the light blocking plate 11 ₁ to 11 ₃
The light blocking plate 11 ₁ to 11 ₃ than the opening 11a has a larger diameter
Trap A provided on the side opposite to the detection area A
When three of the light shielding plate 12 ₁ to 12 which on the optical axis when viewed from the detection area i comprises an opening 12a facing the detection area b on the side opposite to the light receiving element 5 of the light incident on the light-receiving element 5 (light beam)
It includes a _3, and a substantially tubular light trap B which is provided on the opposite side of the detection area b with respect to the light shielding plate 12 ₁ to 12 ₃ has a larger diameter than the opening 12a of the light shielding plate 12 ₁ to 12 ₃ ing.

The two optical traps A and B are provided with reflecting surfaces 13 and 14 for reflecting light incident through the openings 11a and 12a of the light shielding plates 11 ₁ ... 12 ₁ . Is formed so as to move the light reflected by the light source away from the detection area A and bend in the direction toward the light emitting element 4 and the light receiving element 5. In this embodiment, the reflecting surfaces 13 and 14 are concave, but may be convex or flat. Also, the number of the light shielding plates 11 _1, ..., 12 ₁ is not limited to three, but may be one, two, or four or more.

[0027] In Thus, the optical trap A, by forming a B on the shape, the light shielding plate 11 ₁ ..., 12 ₁ ... opening 11
a, 12a first enter the reflecting surfaces 13, 1
After being reflected at 4, the stray light can be attenuated as the light traps A and B are repeatedly reflected back. In addition, since the light traps A and B can be formed in a portion (dead space) other than the optical chamber 2 in the base 1b, the space utilization efficiency in the optical chamber 2 is improved and the attenuation effect of stray light is not reduced. The miniaturization of the light scattering type particle detection sensor (Case 1) can be achieved. Note that the shapes of the optical traps A and B in the present embodiment are merely examples,
For example, as shown in FIG. 3, the innermost portion may have a shape bent toward the light shielding plates 11 ₃ and 12 _3. In other words, the shape may be any shape that can reduce the size of the case 1 and attenuate stray light.

By the way, as described in the prior art, when the optical trap A, the particles such as dust and smoke on the inner wall surface of B attached, the light shielding plate 11 ₁ ..., 12 ₁ ... opening 11a, the light incident through 12a Is scattered by hitting the particles, and scattered light may be emitted outside the optical traps A and B. FIG. 4 shows reflection and scattering patterns of a general optical wall (resin molded product, metal surface). When light is incident on an optical wall, generally, both specular reflection light in the same direction as specular reflection and scattered light emitted in a line direction are generated. However, generally, there is a characteristic that the regular reflection light increases as the incident angle θ decreases. This has the same tendency regardless of whether particles adhere to the reflective surface. For this reason, of the light scattered in the optical traps A and B due to the accumulation of particles, light having a small incident angle θ jumps out of the optical traps A and B without being attenuated so much, and becomes a factor of generating large stray light.

[0029] However, in the present embodiment, the light shielding plate 11 ₁ having light trap A, the inlet to the light trap A of B, a small opening 11a than the diameter of B, and 12a ..., 12 ₁
Are provided, so that the reflected light of light having a small incident angle is shielded by the light shielding plates 11 ₁ , 12 ₁ , as shown in FIG.
The generation of stray light can be reduced by preventing the light traps A and B from going outside.

As a light trap for attenuating stray light, a trap called "Wood trap" has been conventionally known (see Masaru Tsuruta, "Pencil of Light" (pages 304 to 305)). However, when this Wood trap is applied to an optical trap of a light scattering type particle detection sensor, there is a disadvantage that the case 1 becomes large in order to enhance the effect of attenuating stray light. On the other hand, in the present embodiment, as described above, the openings 11a and 12a having diameters smaller than the diameters of the optical traps A and B are formed at the entrances of the optical traps A and B.
The light shielding plate 11 ₁ ... with 12 ₁ ... because the are provided, W
The optical traps A and B, which are extremely small and have a high effect of attenuating stray light, can be obtained as compared with the oud trap. Also in the present embodiment, since the light traps A and B are formed in such a shape that the diameter decreases as the distance from the light shielding plates 11 _1, ..., 12 ₁ ,. Is what you can do.

By the way, the openings 11a, 12a of the light shielding plates 11 _1, ..., 12 ₁ . However, the size and thickness (width) of the sensor are often limited due to the recent miniaturization of the sensor, and the shape of the lens is not only circular but also square or other shapes due to the improvement of processing technology. For this purpose, it is necessary that the opening shapes of the optical traps A and B are also made to match the opening shapes. Thus, also in the present embodiment, there is no particular limitation on the cross-sectional shape of the optical traps A and B on the back side of the reflection surfaces 13 and 14, and the same effect can be obtained with various shapes such as a circle and a rectangle. .

In the case where the radiation efficiency of the light projecting element 4 and the light receiving efficiency of the light receiving lens 7 are insufficient with a general circular light projecting lens 17, a rectangular lens may be used as far as possible in the thickness direction. Here, the light shielding plate 11 ₁ ..., 12 ₁ ... opening 11
The areas a and 12a need only be larger than the light projecting area and the light receiving area. However, when the size is limited in the thickness direction as described above or when the opening area is not desired to be large, the light projecting lens 17 and the light receiving lens are required. It is desirable that 7 has a similar shape. Therefore, in the present embodiment, in order to maximize the light projection efficiency and to make the optical system thin, the light projecting lens 17 and the light receiving lens 7 are formed into a square shape such as a substantially square as shown in FIGS. The light shielding plate 11 has such a lens shape.
By matching the shapes of the openings 11a, 12a of ₁ ..., 12 ₁ ..., The generation of stray light can be suppressed and the case 1 can be made thinner.

By the way, the smaller the openings 11a, 12a of the light shielding plates 11 _1, ..., 12 ₁ are, the higher the effect of reducing the amount of light that enters the optical traps A, B and is emitted to the outside. Therefore, as shown in FIG.
With the projection lens 17 as a light (projected beam) focused in the vicinity of the opening 11a of the light blocking plate 11 ₁ from an opening 1
There is an advantage that the area of 1a can be reduced.

As shown in FIG. 8, the image forming position of the light receiving lens 7 is generally set at the center of the detection area A, but the image is located farther than the light receiving lens 7 across the detection area A. The blurring makes the light receiving area larger than the detection area A. However, in order to reduce the size and thickness of the light scattering type particle detection sensor, it is generally only considered that the thickness of the inner wall of the optical chamber 2 (the thickness of the base 1a) is thicker than the thickness of the detection area A. In a portion farther than the detection region A, the bottom surface of the base 1a or the inner surface of the cover 1b of the case 1 often overlaps with the light receiving region. Therefore, the base 1a
When particles such as dust accumulate on the bottom surface or on the inner surface of the cover 1b, they become a source of stray light.
May be incident on Therefore, in the present embodiment, in order to solve the above-mentioned problem, the imaging position of the light receiving lens 7 (point A in FIG. 9) is set farther from the detection area A (point B in FIG. By suppressing the spread, sources of stray light such as the bottom surface of the base 1a and the inner surface of the cover 1b are prevented from entering. In this case, the amount of received light is sacrificed to some extent, but correct measurement can be performed by suppressing the generation of stray light. Alternatively, as shown in FIG. May be thicker than the thickness dimension L1 in other portions. Then, a part other than the inner wall of the optical trap B can be prevented from entering the visual field range of the light receiving lens 7, and the generation of stray light can be effectively suppressed without increasing the thickness of the entire case 1. .

An outlet 8 is provided at a position on the bottom surface of the base 1a opposite to the inlet 3 for discharging particles flowing into the optical chamber 2 from the inlet 3 to the outside of the case 1. As shown in FIG. 11, when air containing particles such as dust and smoke flows into the inflow port 3 from a vertical direction, the air is immediately passed through the inflow port 3 due to a pressure loss at the inflow port 3. The flow shows a tendency to spread in Case 1. This is because air is a viscous fluid, and when the shape of the flow path changes abruptly, a pressure loss occurs in that portion and the air flow changes. The range in which the inflow air spreads is maximum near the outlet 8. If the size of the outlet 8 is small, only a part of the inflow air cannot flow out through the outlet 8 and flow into the case 1. At this time, air vortices are generated in the vicinity of the outlet 8 and at the four corners of the case 1, and the air flowing into the case 1 and the vortexed air gradually stall, and eventually the velocity becomes zero. Dust particles adhere to the inner wall of the optical chamber 2 in the vicinity thereof. Thus, in the light scattering type particle detection sensor, when particles accumulate in the optical chamber 2, the reflectance of the inner wall of the optical chamber 2 increases, and the stray light component increases, so that the light receiving signal of the light receiving element 5 is saturated and accurate. Measurement may not be possible. Therefore, it is necessary to reduce the amount of dust accumulated in the optical chamber 2 itself.

In this embodiment, in order to prevent dust from accumulating in the optical chamber 2, the shapes of the inlet 3 and the outlet 8 are made similar (circular in this embodiment) as shown in FIG. And the opening diameter r1 of the inflow port 3
The opening diameter r2 of the outlet 8 is set to be larger than that.

When the inflow port 3 and the outflow port 8 are formed in a similar shape and their centers coincide with each other, the air spread immediately after passing through the inflow port 3 can be uniformly discharged from the outflow port 8. In addition, it is possible to prevent accumulation of dust without generating turbulence in the case 1. Further, since the inflow port 3 and the outflow port 8 are circular, there is no extra edge at the four corners as compared with the case where both are square, and the generation of turbulent flow can be suppressed. Here, FIG. 13 shows an experimental result of examining the accumulation amount of dust in the case 1 when the ratio (= r1 / r2) of the opening diameter r1 of the inlet 3 and the opening diameter r2 of the outlet 8 is variously changed. Shown in However, the thickness t of the case 1 (the dimension in the opposite direction between the inflow port 3 and the outflow port 8) is set to 13 mm, and the opening diameter r1 of the inflow port 3 and the opening diameter r2 of the outflow port 8 are set to 8 to 8 mm.
It is varied between 24 mm. As is clear from FIG. 13, when the thickness t is in the range of r1 <t <3 × r1, 1 <r
If the opening diameter r1 of the inflow port 3 and the opening diameter r2 of the outflow port 8 are set so that 1 / r2 <2.5, the effect of suppressing the accumulation amount of dust is high. Further, in the present embodiment, as shown in FIG. 14, the substantially cylindrical tubular portion 3a is protruded from the outer peripheral edge of the inflow port 3, so that the generation of air vortices in the case 1 is suppressed to accumulate dust. I try to suppress. In addition,
As shown in FIG. 15, the shape of the cylindrical portion 3a may be a substantially conical shape in which the opening diameter increases as it approaches the tip.

By the way, conventionally, in order to prevent the projected light beam from being reflected or scattered by the inner wall of the optical chamber and reaching the light receiving element 5, the light beam is optically provided on the side opposite to the light emitting element and the light receiving element when viewed from the detection area. There has been provided a light scattering type particle detection sensor provided with a light shielding wall for separating a part of a chamber into a light projecting element side and a light receiving element side (Japanese Patent Application Laid-Open Nos. 4-160697 and 8-16067).
No. 62136). However, since only one light-shielding wall is provided in the above-mentioned publication, when an attempt is made to reduce the size of the light-scattering type particle detection sensor, the light projection beam is reflected on the inner wall of the optical trap A. It was insufficient to prevent stray light generated by scattering from entering the light receiving region.

Therefore, in the present embodiment, at least the front end faces the light projecting area and the light receiving area on the side opposite to the side where the light projecting element 4 and the light receiving element 5 are arranged in the detection area A, and projects part of the optical chamber. multiple light shielding wall 16 _{1-16 3} (this embodiment three in form) which separates the optical element 4 and the light receiving element 5 side, are projected substantially parallel to one another than the inner wall of the base 1a. FIG.
As shown in 6, the light shielding wall 16 ₃ and 16 ₂ which is closer to the light trap A facing the light projecting element 4 is intended to prevent the scattered light generated by the light trap A reaches the light projection region The prevention effect can be enhanced as the light trap A is provided nearer. Further, as shown in FIG. 17, the light shielding wall 16 ₁ closer to the optical trap B facing the light receiving element 5.
And 16 ₂ is for scattered light projected beam reflected by the other light trap A light shielding wall 16 ₃ closer to prevent from entering the light trap B. The light shielding wall 16
By increasing the number of ₁ ..., The above-mentioned prevention effect can be further enhanced.

(Embodiment 2) By the way, when the light beam emitted from the light projecting element 4 is sufficiently attenuated by the optical trap A, the amount of stray light is small, and the particle concentration in the optical chamber 2 and the sensor output are reduced. Is as shown by a straight line b in FIG. However, when dust adheres to the inner wall of the optical chamber 2, stray light increases. Therefore, as shown by a straight line c in the figure, a state in which particles from the outside do not flow into the optical chamber 2 (hereinafter, referred to as an "initial state"). In such a case, the sensor output may increase, and accurate measurement may not be performed. In order to avoid such an unmeasurable state, a sensor output in an initial state is generally measured and a correction process is performed on an actual measurement value. Needs to store the sensor output in the initial state once.
However, in a general situation such as home or office, it is hardly considered that there is no dust, and the above-described correction processing is usually performed on the assumption that the minimum value of the sensor output in a predetermined period is the sensor output in the initial state. Therefore, it is hard to say that accurate measurement is being performed. Also, if the stray light increases too much, the sensor output may be saturated and the measurement itself may not be possible. For this reason, a structure is desirable in which the amount of stray light does not change even if dust accumulates inside the optical chamber 2.

On the other hand, the inner wall of the optical chamber 2 is usually made of black and low in reflectivity. However, if dust accumulates on the inner wall of the optical chamber 2 as described above, the reflectivity increases and stray light increases. It causes measurement error.

Therefore, in the present embodiment, the optical chamber 2
A process to obtain a reflectance similar to that of the dust is performed on a part where dust is easily accumulated or a part where stray light is likely to be generated, thereby intentionally increasing the stray light and suppressing a fluctuation of the stray light when the dust is deposited. Like that.

In general, it is known that house dust and the like have a characteristic of approximately 20% reflectance and a characteristic close to Lambertian distribution. This is close to a state where the inner wall of the optical chamber 2 is gray and the surface state is rough or satin. Therefore, in the present embodiment, the surface of the aperture 6, 9, as shown in FIG. 19, the light shielding plate 11 _1, 12 ₁ of the surface, the surface and the like (FIG. 19 of the reflecting surfaces 13 and 14 and the shielding wall 16 ₁ to 16 ₃ The above processing is performed on a portion where dust tends to accumulate or a portion where stray light is likely to increase (a portion indicated by a thick line). For the above-described processing, a processing method such as two-color molding or painting may be used.
Further, the above processing may be performed not on a part but on the whole.

According to the present embodiment, processing is performed such that a portion in the optical chamber 2 that increases stray light due to the attachment of particles has a reflectance substantially equal to the reflectance of the attached particles. Therefore, there is an advantage that the change of the stray light amount is small even if the dust particles and the like are accumulated, and the correction process for the stray light amount is unnecessary.

[0045]

According to a first aspect of the present invention, there is provided a light projecting element and a light receiving element which are arranged in an optical chamber so that optical axes cross each other. In the light scattering type particle detection sensor that detects 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 is superimposed, the light detection element faces the detection area A light-shielding plate having an opening and disposed at a position facing at least one of the light-emitting element and the light-receiving element; and a light-shielding plate having a diameter larger than the opening of the light-shielding plate and provided on a side opposite to the detection region with respect to the light-shielding plate. A light trap, the light trap having a reflection surface for reflecting light incident through the opening of the light shielding plate, and moving the light reflected on the reflection surface away from the detection area and toward the light emitting element or the light receiving element. Bending shape Since a light shielding plate is provided at the entrance of the optical trap, even if particles such as dust accumulate in the optical trap and the scattered light increases, the stray light once entering the optical trap is The light-shielding plate prevents the light from coming out, and the size can be further reduced without reducing the ability to attenuate the stray light.

According to the second aspect of the present invention, since the optical trap is formed in such a shape that its diameter becomes smaller as the distance from the light shielding plate further away from the light shielding plate or the reflection surface, stray light can be more effectively attenuated. This has the effect.

According to a third aspect of the present invention, there is provided a light projecting lens disposed on the optical axis of the light projecting element for condensing light and a light receiving element disposed on the optical axis of the light receiving element for condensing light on the light receiving element. Since at least one of the lenses is provided, and the shape of the light projecting lens or the light receiving lens and the shape of the opening of the light shielding plate are made similar, the efficiency of the amount of light received by the light receiving element with respect to the amount of light emitted from the light emitting element can be increased. In addition, the opening area of the light-shielding plate can be minimized, stray light can be suppressed, and the thickness can be reduced.

According to a fourth aspect of the present invention, a light-shielding plate and an optical trap are provided at least at a position facing the light-projecting element, and light-collecting means for condensing light from the light-emitting element near an opening of the light-shielding plate is provided. Therefore, the opening area of the light-shielding plate can be minimized, and there is an effect that generation of stray light can be suppressed.

According to a fifth aspect of the present invention, a light-shielding plate and an optical trap are provided at least at a position facing the light-receiving element, and the light from the detection area is condensed on the light-receiving element and is connected to a position further from the light-receiving element than the detection area. Since a light receiving lens having an image position is provided, there is an effect that the thickness can be reduced.

According to a sixth aspect of the present invention, a light shielding plate and an optical trap are provided at least at a position facing the light receiving element, and an optical system for condensing light from the detection area to the light receiving element is provided. Since the dimensions of the optical trap are set so that no part other than the inner wall of the optical trap enters the optical trap, there is an effect that the generation amount of stray light can be further suppressed.

According to a seventh aspect of the present invention, at least a light emitting element,
The case includes a case in which the light receiving element, the light shielding plate, and the optical trap are housed. The case has an inflow port through which external particles flow into a detection area in the case, and an outflow port through which particles in the case flow out. Since the diameter of the outlet is larger than the diameter of the inlet, there is an effect that the number of particles remaining in the optical chamber can be reduced and stray light can be suppressed.

According to an eighth aspect of the present invention, at least the front end faces the light projecting area and the light receiving area on the side of the detection area opposite to the side where the light projecting element and the light receiving element are arranged, and a part of the optical chamber is formed. And a plurality of light-shielding walls separated on the light-receiving element side, so that reflected light and scattered light generated by the optical trap are prevented from entering the light-receiving area, and the amount of stray light reaching the light-receiving element can be reduced. There is.

According to the ninth aspect of the present invention, the reflecting means having a reflectance substantially equal to the reflectance of the adhered particles is provided at a portion in the optical chamber where stray light is increased by the adhesion of the particles. The amount of stray light changes little even if
There is an effect that the correction processing for the stray light amount becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment.

FIG. 2 is an exploded perspective view of the same.

FIG. 3 is a sectional view showing another configuration of the above.

FIG. 4 is an operation explanatory view of the above.

FIG. 5 is an operation explanatory view of the above.

FIG. 6 is a diagram showing shapes of a light projecting lens and a light receiving lens in the above.

FIG. 7 is an operation explanatory diagram of the above.

FIG. 8 is an operation explanatory view of the above.

FIG. 9 is an operation explanatory view of the above.

FIG. 10 is a sectional view showing another configuration of the above.

FIG. 11 is an operation explanatory diagram of the above.

FIG. 12 is an operation explanatory view of the above.

FIG. 13 is an explanatory diagram of the operation of the above.

FIG. 14 is an operation explanatory view of the above.

FIG. 15 is an explanatory diagram of the operation of the above.

FIG. 16 is an operation explanatory view of the above.

FIG. 17 is an operation explanatory view of the above.

FIG. 18 is an operation explanatory diagram of the second embodiment.

FIG. 19 is a sectional view of the above.

FIG. 20 is a sectional view of a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 case 2 optical room 4 light emitting element 5 light receiving element 11 _{1 to} 11 ₃ light shielding plate 11 a opening 12 _{1 to} 12 ₃ light shielding plate 12 a opening 13, 14 reflecting surface A, B light trap

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Mori 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd. Terms (reference) 2G059 AA05 BB02 CC19 EE02 FF01 GG01 KK01 LL04 5C085 AA03 BA33 CA08 CA30 FA06 FA10 FA20

Claims (9)

[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. A light scattering type particle detection sensor that detects particles by receiving light scattered light from a light emitting element due to particles such as smoke and dust in an area by a light receiving element, the light emitting element having an opening facing the detection area, A light-shielding plate disposed at a position facing at least one of the light-receiving elements, and an optical trap having a diameter larger than the opening of the light-shielding plate and provided on a side opposite to the detection region with respect to the light-shielding plate; The trap is provided with a reflecting surface for reflecting the light incident through the opening of the light shielding plate, and is formed in a shape such that the light reflected on the reflecting surface is moved away from the detection area and bent in a direction toward the light emitting element or the light receiving element. That Characteristic light scattering type particle detection sensor. 2. The light-scattering type particle detection sensor according to claim 1, wherein the light trap is formed such that its diameter becomes smaller as the distance from the light shielding plate further away from the light shielding plate or the reflection surface. 3. A light-emitting lens disposed on the optical axis of the light-emitting element and condensing light, and a light-receiving lens disposed on the optical axis of the light-receiving element and condensing light on the light-receiving element. The light scattering type particle detection sensor according to claim 1, wherein the shape of the light projecting lens or the light receiving lens is similar to the shape of the opening of the light shielding plate. 4. A light-shielding plate and an optical trap are provided at least at a position facing the light-projecting element, and light-collecting means for condensing light from the light-emitting element near an opening of the light-shielding plate is provided. The light scattering type particle detection sensor according to claim 1. 5. A light-shielding plate and an optical trap provided at least at a position facing the light-receiving element to collect light from the detection area on the light-receiving element and to form an image-receiving position farther from the light-receiving element than the detection area. The light scattering type particle detection sensor according to claim 1, further comprising a lens. 6. A light shielding plate and an optical trap provided at least at a position facing the light receiving element, and an optical system for condensing light from the detection area to the light receiving element is provided, and an inner wall of the optical trap is provided within a field of view of the optical system. The light-scattering type particle detection sensor according to any one of claims 1 to 5, wherein the size of the light trap is set so that no part other than the light trap enters. 7. An inflow port through which at least a light projecting element, a light receiving element, a light shielding plate, and an optical trap are housed inside, and an inflow port through which external particles flow into a detection area in the case.
The light scattering type according to any one of claims 1 to 6, wherein an outlet for discharging particles in the case to the outside is provided in the case, and the diameter of the outlet is formed larger than the diameter of the inlet. Particle detection sensor. 8. At least a front end of the detection area opposite to the side on which the light emitting element and the light receiving element are arranged respectively faces the light emitting area and the light receiving area, and a part of the optical chamber is located on the light emitting element and the light receiving element side. The light scattering type particle detection sensor according to any one of claims 1 to 7, further comprising a plurality of light shielding walls for separation. 9. The optical system according to claim 1, wherein a reflection means having a reflectance substantially equal to the reflectance of the adhered particles is provided at a portion in the optical chamber where stray light is increased by the adhesion of the particles. The light scattering type particle detection sensor according to any one of the above.