JP2002109653A - Photoelectric type smoke detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact photoelectric type smoke detector in which aberrations will not be generated. SOLUTION: In this photoelectric type smoke detector, a beam is emitted toward a smoke detecting area by a light-emitting element 3, the scattered light resulting from particles of smoke or the like present in the smoke detecting area is detected by a light-receiving element 5, whereby the smoke or the like is detected. This sensor comprises a first lens part for collecting the scattered light, a prism part for changing the advancing direction of the light collected by the first lens, and a second lens part for collecting the light changed in advancing direction by the prism part to the light-receiving element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a smoke detection area with a light beam using a light emitting element, and using a light receiving element to scatter light scattered by particles such as smoke, dust and aerosol existing in the smoke detection area. The present invention relates to a photoelectric smoke detector that detects smoke or the like by detecting the smoke.

[0002]

2. Description of the Related Art Conventionally, as a photoelectric smoke detector of this kind,
The one described in JP-A-3-111997 is known. 8 and 9 are a longitudinal sectional view and a transverse sectional view, respectively, of the smoke detector. As shown in the figures, a circuit board 2 is installed inside a bottom of a cylindrical housing 1 having a bottom. The light emitting element 2 includes a light emitting element 3 and a light receiving element 5 which are connected via an electric wire 4. A detection circuit and the like are mounted.

An optical base 6 installed so as to cover the circuit board 2 includes a prism lens 7 for condensing light scattered by smoke particles or the like on a light receiving element 5 and a light emitting element 3 inserted in a holding cylinder. It is installed. Here, the prism lens 7
Prism section 7b that reflects scattered light to change the traveling direction
And a lens portion 7c for condensing the light beam whose traveling direction has been changed by the prism portion 7b on the light receiving element 5 are integrally formed of a transparent material such as acrylic resin or polycarbonate. The traveling direction of the light beam is changed using total reflection.

[0004] The smoke introduction section 8 installed near the lower end of the optical base 6 is formed by connecting a plurality of partition walls 8a having a substantially U-shape in cross section in an annular shape. An insect net 12 is wound around the periphery, and a substantially disc-shaped lid 13 is fitted so as to cover the lower end of the smoke introduction section 8. The optical base 6 allows the inside of the housing 1 to move up and down 2
The circuit board 2 is disposed in a circuit storage area 14 which is an upper chamber, and a smoke detection area 10 which is a lower chamber is passed through a smoke inlet 8c formed between the partition walls 8a. , Smoke particles are introduced, light is emitted from the light emitting element 3, and scattered light caused by the smoke particles is received by the light receiving element 5, so that the presence or absence of the smoke particles can be detected. .

[0005]

The photoelectric smoke detector is generally mounted on a ceiling of a house or the like.
Those with a very large housing are not preferred,
There is a need for a more compact photoelectric smoke detector. To this end, it is conceivable to reduce the size of the optical system. More specifically, the focal length of the prism lens 7 may be reduced. However, in the conventional prism lens 7 used in the photoelectric smoke detector, Since there is only one lens unit, there is a problem that there is a limit in shortening the focal length.

As shown in FIG. 8, the surface of the conventional prism lens 7 that is exposed to the smoke detection area 10 (hereinafter, referred to as an incident surface) is substantially vertical. There is a problem that aberration is likely to occur because the light incident from the light does not cross the incident surface perpendicularly.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a compact photoelectric smoke detector which does not generate aberration.

[0008]

According to the present invention, a light emitting element irradiates a light beam to a smoke detection area and scatters light caused by particles such as smoke existing in the smoke detection area. In a photoelectric smoke sensor for detecting smoke or the like by detecting light with a light receiving element, a first lens unit that collects the scattered light, and light collected by the first lens is transmitted to the light receiving element. And a second lens unit for condensing light.

According to the second aspect of the present invention, the light emitting element irradiates a light beam to the smoke detection area, and the light receiving element detects scattered light caused by particles such as smoke existing in the smoke detection area. A first lens unit for collecting the scattered light, a prism unit for changing a traveling direction of the light collected by the first lens, and the prism The light whose traveling direction has been changed in the
A second lens unit for condensing the light on the light receiving element.

[0010] According to the third aspect of the present invention, the second aspect is provided.
The angle between the optical axis of the first lens unit and the plane perpendicular to the optical axis of the second lens unit is defined with respect to the optical smoke sensor of the second embodiment. The angle obtained by subtracting the right angle from the angle twice as large as the angle formed between the vertical surface and the reflecting surface of the prism portion.

According to the fourth aspect of the present invention, there is provided a second aspect.
Alternatively, in the photoelectric smoke detector according to claim 3, an angle formed between a surface perpendicular to an optical axis of the second lens unit and a reflection surface of the prism unit is set to be equal to or larger than a critical angle. Is what you do.

According to the fifth aspect of the present invention, there is provided a second aspect.
Alternatively, in the photoelectric smoke detector according to claim 3, an angle formed between a surface perpendicular to the optical axis of the second lens unit and the reflection surface of the prism unit is 45 ° to 70 °. It is a feature.

According to the sixth aspect of the present invention, there is provided a second aspect.
A photoelectric smoke detector according to any one of claims 1 to 5,
The light that enters the lens portion and does not impinge on the reflection surface of the prism portion is shielded.

According to the seventh aspect of the present invention, there is provided the first aspect.
7. The photoelectric smoke detector according to claim 6, wherein the first lens portion is formed to refract incident light into substantially parallel light.

According to the invention described in claim 8, claim 1 is provided.
8. The photoelectric smoke sensor according to claim 1, further comprising: a smoke introduction portion forming the smoke detection area; and the first lens portion provided in the smoke introduction portion. The focal length of the section is formed on the surface of the smoke introducing section opposite to the first lens section.

According to the ninth aspect of the present invention, the first aspect is provided.
8. The photoelectric smoke sensor according to claim 1, further comprising: a smoke introduction portion forming the smoke detection area; and the first lens portion provided in the smoke introduction portion. The focal length of the portion forms an image at an intermediate position between the center of the smoke detection area and the surface of the smoke introduction portion.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A photoelectric smoke detector according to the present embodiment will be described below in detail with reference to FIGS. 1 and 2 are a longitudinal sectional view and a transverse sectional view, respectively, showing the structure of the photoelectric smoke detector of the present embodiment, and as shown in the drawings, a bottomed cylindrical base 1a,
A housing 1 comprising a truncated cone-shaped mounting portion 1b provided at the lower end of the base portion 1a.
A circular concave portion 1ba for mounting the circuit board 2 and the like is formed at a lower end portion of the substrate.

The circuit board 2 is provided with a light emitting element 3 such as a light emitting diode and a light receiving element 5 such as a photodiode, which are connected via an electric wire 4, and a driving circuit of the light emitting element 3 and a light receiving element 5 connected thereto. A smoke detection circuit, a power supply circuit, and the like for determining the presence or absence of smoke or the like based on the output of the device are mounted. Here, the smoke detection circuit includes an analog signal processing circuit that processes the output of the light receiving element 5, a digital circuit that controls a switching circuit based on the circuit, and the like.

The optical base 6 provided so as to cover the circuit board 2 has a circular basin-shaped base portion 6a, and a light emitting element is provided near the periphery of the base portion 6a. The holding portion 6b and the lens holding portion 6c protrude from each other so as to be perpendicular to each other in a cross-sectional view. The light emitting element holding portion 6b is formed with a light emitting element mounting hole 6ba having a substantially circular shape in a vertical cross section in the direction of the central axis of the mounting portion 1b. The light emitting element mounting hole 6ba is inserted into the holding cylinder. The light emitting element 3 is mounted.

On the other hand, the lens holder 6c has a base 6
and a lens mounting hole 6ca in which a part of the lower end of the hole facing the central axis of the mounting portion 1b is formed in a substantially rectangular shape, and a rectangular mounting hole 6ca is formed. The prism lens 7 is mounted in the lens mounting hole 6ca.

The prism lens 7 is, as shown in FIG.
A first lens portion 7a for refracting light scattered by smoke or the like, a prism portion 7b for reflecting light incident on the lens portion 7a to change the traveling direction, and changing the traveling direction by the prism portion 7b The second lens portion 7c for condensing the light beam focused on the light receiving element 5 is formed integrally with a resin material such as acrylic or polycarbonate. The prism portion 7b, which is substantially triangular in cross section, performs total reflection. The direction of travel of the light beam is changed by utilizing this.

More specifically, the optical axis of the lens section 7a and
The angle formed by the surface perpendicular to the optical axis of the lens unit 7c is θ, the surface perpendicular to the optical axis of the lens unit 7c, and the prism unit 7b.
The angle formed by the long side (reflection surface R) of the triangle viewed from the cross section of is defined as プ リ ズ ム, and the lens unit 7 is formed by using the prism lens 7 formed so as to satisfy the condition represented by θ = 2ψ−90 ゜.
The light ray on the optical axis a is turned back by the prism part 7b and can be made to coincide with the optical axis of the lens part 7c.

As shown in FIGS. 1 and 2, the light-emitting element holder 6b and the lens holder 6c position the light-emitting element 3 and the prism lens 7, respectively. Is adjusted so that the direction of the light emitted by the light source and the optical axis of the prism lens 7 (the lens portion 7a) intersect each other, and the light from the light emitting element 3 which is a source of scattered light caused by smoke particles and the like. The emitted light is efficiently received by the light receiving element 5 via the prism lens 7.

The smoke introduction section 8 installed near the lower end of the optical base 6 has a substantially U-shaped partition wall section 8a in cross section.
Are connected to the peripheral portion on the disk-shaped base portion 8b in a ring shape, and a smoke inlet 8c is provided between each partition 8a.
Is formed, and an insect repellent net is wound around the periphery of the smoke introduction section 8 (not shown). A light-discharge hole 9aa whose opening area increases toward the light-emitting element holding portion 6b is formed in the substantially disk-shaped aperture 9a attached to the surface of the light-emitting element mounting hole 6ba. The light derived from is further provided with directivity.

On the other hand, in the vicinity of the surface of the lens holding portion 6c facing the central axis of the mounting portion 1b, the lens holding portion 6c is formed of a rod-shaped member having a substantially rectangular shape in cross section so as to be oriented at approximately 45 ° with respect to the surface. While the aperture 9b is provided, the mounting portion 1b
An aperture 9c having substantially the same shape as the aperture 9b is provided so that the center axis of the aperture 9b is symmetrical, so that irregularly reflected light from the partition wall 8a does not enter the prism lens 7.
The apertures 9b and 9c may be formed integrally with the base 6a or the base 8b, or may be formed as separate parts.

Then, the base part 6a, the light emitting element holding part 6
b, a space formed by the lens holding portion 6c, the partition 8a, and the base 8b, smoke particles are introduced through the smoke inlet 8c formed between the respective partitions 8a, and light is emitted from the light emitting element 3. The light receiving element 5 receives the scattered light caused by the smoke particles, thereby forming a smoke detection area 10 for detecting the presence or absence of the smoke particles.

As described above, by forming the two lens portions of the lens portion 7a and the lens portion 7c on the prism lens 7, the focal length of the prism lens 7 can be shortened by increasing the refractive power. Therefore, the optical system is reduced, and a compact photoelectric smoke detector can be provided. In addition, since the number of lens units is two,
It is possible to increase the degree of freedom of design such as improvement of aberration.

Also, by using the prism lens 7 under the condition of θ = 2 ° −90 °, the scattered light is
, The scattered light can be efficiently condensed on the light receiving element 5 without being substantially affected by the aberration due to the eccentricity or inclination of the lens portion 7a. Further, since the direction of the light emitted from the light emitting element 3 and the optical axis of the prism lens 7 intersect each other, the smoke detection area 1
The strong scattered light from the vicinity of the center of 0 can be condensed on the light receiving element 5 almost without being affected by the aberration of the prism lens 7, and a sufficient light receiving amount can be secured.

When the angle of intersection between the direction of light emitted from the light emitting element 3 and the optical axis of the prism lens 7 increases, the amount of light received by the light receiving element 5 increases, but the color ratio of white / black smoke increases. Because of the large size, white or black smoke causes a difference in sensitivity. On the other hand, when the crossing angle is reduced, the color ratio of white / black smoke is reduced, so that there is no difference in sensitivity due to white or black smoke. A light receiving element 5 must be used.

In view of this, the crossing angle is determined to be an angle having a good balance between the amount of received light and the color ratio of smoke. In the example of FIG. 2, the crossing angle is determined to be substantially a right angle. According to the results of trial and error by those, it is considered that around 110 ° is good. In addition, it is determined by various conditions, and is not limited to this. The angle may be set to 130 ° like a general photoelectric smoke detector.

Since it is sufficient that the scattered light can be sensed by the light receiving element 5, the direction of the light emitted from the light emitting element 3 and the optical axis of the prism lens 7 do not necessarily need to cross each other. Furthermore, although an example of a prism lens using a resin material such as acryl or polycarbonate has been described, the prism lens may be formed of a glass material such as BK7 without being limited to the resin material.

[Second Embodiment] The present inventors have two lens units, a lens unit 7a and a lens unit 7c, and have θ
By using the prism lens 7 that satisfies the condition of 2 = −90 °, it was possible to provide a compact photoelectric smoke detector capable of securing a sufficient amount of received light without being substantially affected by aberration. . However, there is a problem that the amount of light received by the light receiving element 5 may decrease due to the angle す formed between the surface perpendicular to the optical axis of the lens portion 7c and the reflection surface R of the prism portion 7b. In order to solve such a problem, the inventors of the present application have proposed a photoelectric smoke detector that does not reduce the amount of received light.

The prism portion 7b of the prism lens 7 shown in FIG. 3 cannot reflect the light incident from the lens portion 7a in any direction and guide it to the lens portion 7c. There is something called the reflection condition,
Light that does not satisfy the total reflection condition is transmitted through the prism portion 7b, which causes a decrease in light receiving efficiency. The total reflection condition is a condition for reflection without causing transmission, and as shown in FIG. 4, the reflection surface R of the prism portion 7b
A condition in which the incident angle is larger than a certain angle from the axis at a right angle is referred to as a critical angle φc.

The right-angled axis and the lens portion 7
The angle formed by the optical axis of a with the optical axis is φ, and the value obtained by subtracting the critical angle φc from φ is called the critical margin ω. The critical margin ω is perpendicular to the optical axis of the lens portion 7c. Occurs when the angle ψ formed by the reflection surface R of the prism portion 7b with the proper surface is larger than the critical angle φc. For example, when a light emitting element 3 having an output peak wavelength of about 950 nm is used and polycarbonate is used as a lens material, the refractive index n
Is about 1.57, and from the equation (1), the critical angle φc
Is approximately 39.6 °, so by setting ψ to be larger than 39.6 °, a critical margin ω can be obtained, and a constant total reflection area can be obtained.

[Formula 1] φc = sin ⁻¹ (1 / n) (1)

As described above, by making ψ larger than the critical angle φc and making the angle less than 90 ° which is the limit for generating the total reflection area, a constant total reflection area can be obtained, and the amount of received light can be reduced. Although the sensitivity can be increased without reducing the lens diameter, the lens diameter D of the lens portion 7a is given by Expression (2), and the reflection surface R (reflection side) of the prism portion 7b is
Since it is not possible to increase the size of the optical system due to the demand for making the optical system smaller, the larger the value of ψ, the smaller the lens diameter D, the smaller the amount of received light and the lower the sensitivity.

D = Rcosψ (2)

Therefore, ψ is set to an angle that can obtain a constant total reflection area and can sufficiently secure the amount of received light. According to the results of trial and error by the inventors of the present application, ψ is approximately 45.
The angle is preferably set to be from 70 to 70 °, and particularly preferably from 48 °.
Note that the refractive index n, the reflection surface R, and the like change depending on the size and material of the prism, and are not limited thereto. In addition, other configurations are the same as those of the first embodiment, and the description is omitted here.

[Third Embodiment] The inventors of the present application disclose a plane perpendicular to the optical axis of a lens section 7c and a prism section 7b.
By setting the angle ψ formed by the reflecting surface R to an angle at which a constant total reflection area can be obtained and a sufficient amount of received light can be obtained, the sensitivity can be increased without reducing the amount of received light. A photoelectric smoke detector could be provided.

However, as can be seen from the expressions (a) and (2) of FIG. 5, a surface perpendicular to the optical axis of the lens portion 7c has:
When the angle ψ formed by the reflection surface R of the prism portion 7b is 45 ° or more, the lens portion 7 has a larger diameter than the lens portion 7b.
Since the lens diameter of the lens c increases, of the scattered light from the smoke detection area 10 shown in FIG. Therefore, there is a problem that stray light which is not condensed on the light receiving unit 5 is generated and the S / N ratio of the light receiving element 5 is reduced.

In order to solve such a problem, the inventors of the present application shield light that is incident on the lens portion 7a but does not hit the reflection surface R of the prism portion 7b.
A photoelectric smoke detector that can prevent the generation of stray light and improve the S / N ratio of the light receiving element 5 has been proposed. More specifically, as shown in FIG. 5B, a substantially flat aperture 11 for blocking the light is provided on the front surface of the lens portion 7a.

By doing so, the amount of light received by the light receiving element 5 is not affected, and stray light can be significantly reduced.
The S / N ratio of the light receiving element 5 can be improved, and the light receiving characteristic does not largely change due to an increase in noise caused by the attachment of dust or the like to the partition wall 8a shown in FIG.
A highly reliable photoelectric smoke detector can be provided.

The shape of the aperture 11 is not limited to a flat plate, but may be a circular shape like the aperture 9a shown in FIG.
Any shape may be used as long as light that does not hit the reflecting surface R of b can be blocked. Further, a paint may be applied to the surface of the lens portion 7a so as to shield only a necessary portion from light instead of the aperture. Further, the other configuration is the same as that of the first embodiment, and the description is omitted here.

[Fourth Embodiment] The inventors of the present application provide a photoelectric smoke detector which can prevent the generation of stray light and improve the light receiving efficiency of the light receiving element 5 by providing an aperture. Although it could be provided, if the refractive power of the lens portion 7a is weak or too strong, the lens portion 7a
Is transmitted through the prism portion 7b without satisfying the total reflection condition described in the second embodiment and is condensed on the light receiving element 5 by the lens portion 7c. Therefore, there is a problem that the light receiving efficiency of the light receiving element 5 is reduced.

In order to solve such a problem, the present inventors adjusted the lens surface of the lens portion 7a as shown in FIG. 6 to substantially reduce the incident light incident on the lens portion 7a. By using the prism lens 7 that is refracted in parallel and makes the angle of incidence on the prism portion 7b constant,
The light passing near the periphery of the lens portion 7a also satisfies the condition of total reflection, is reflected by the prism portion 7b to the lens portion 7c, and is surely focused on the light receiving element 5.

More specifically, by making the lens surface of the lens portion 7a aspherical, the light from the smoke sensing area 10 shown in FIG. 2 can be refracted in parallel, and aberration can be generated. Therefore, it is possible to provide a photoelectric smoke detector in which the light receiving efficiency of the light receiving element 5 is improved. Incidentally, the lens surface of the lens portion 7a may have any surface shape as long as the light incident on the lens portion 7a is refracted within a range satisfying the total reflection condition. In this case, the cost of the prism lens 7 is increased. Therefore, from the viewpoint of workability, the shape of the lens surface is suitably a hyperboloid or a paraboloid. Note that the other configuration is the same as that of the first embodiment, and the description is omitted here.

[Fifth Embodiment] The inventors of the present application refracted the incident light incident on the lens portion 7a substantially in parallel, and made the prism lens 7 having a constant incident angle on the prism portion 7b.
By using, the photoelectric smoke detector in which the light receiving efficiency of the light receiving element 5 is improved can be provided. However, as the focal length of the lens part 7a is located outside the surface of the partition part 8a facing the lens part, the partition part 8a
Since the light-collecting area of the lens portion 7a on the surface of the light-receiving element 5 becomes large and irregular reflection of light generated on the surface of the partition wall portion 8a is captured, the S / N ratio of the light-receiving element 5 decreases. There is.

In order to solve such a problem, the inventors of the present invention set the focal length of the lens portion 7a so that the focal length of the lens portion 7a forms an image on the surface of the partition wall portion 8a opposed to the lens portion, as shown in FIG. A photoelectric smoke detector using a prism lens 7 is proposed. By doing so, the light-collecting area of the lens portion 7a on the surface of the partition 8a can be reduced as much as possible, and capture of irregular reflection of light generated on the surface of the partition 8a can be suppressed. S / N of light receiving element 5
The ratio can be improved.

However, instead of improving the S / N ratio, the amount of light received by the light receiving element 5 is reduced. On the other hand, when the surface shape of the lens portion 7a is set so that light emitted from near the center of the smoke detection area 10 is focused on the light receiving element 5, the amount of received light increases but the S / N ratio decreases. Becomes Therefore, the focal length of the lens unit 7a is preferably set to a distance that provides a good balance between the amount of received light and the S / N ratio.
As an example, it is appropriate to set the surface shape of the lens portion 7a so that an image is formed at an intermediate position between the center of the smoke detection area 10 and the surface of the partition wall portion 8a. Note that the other configuration is the same as that of the first embodiment, and the description is omitted here.

[0048]

As described above, according to the first aspect of the present invention, the first lens portion for collecting the scattered light and the first lens portion are provided.
By providing the second lens unit for condensing the light condensed by the lens on the light receiving element, the refracting power increases and the focal length can be shortened. It is possible to provide a compact photoelectric smoke detector, and it is possible to improve the aberration by using two lens units.

According to the second aspect of the present invention, the first lens section for collecting the scattered light, the prism section for changing the traveling direction of the light collected by the first lens, and the prism section The light whose traveling direction has been changed in step 2 is focused on the light receiving element.
With the provision of the lens unit, the refractive power is increased and the focal length can be shortened. Therefore, the optical system is reduced, and a compact photoelectric smoke detector can be provided. Has the effect that aberration can be improved.

According to the third aspect of the present invention, the angle formed by the optical axis of the first lens unit and the surface perpendicular to the optical axis of the second lens unit is determined by the angle of the second lens unit. By making the angle obtained by subtracting the right angle from twice the angle formed by the surface perpendicular to the optical axis and the reflection surface of the prism part, the scattered light is incident on the entrance surface of the first lens part. Since they intersect perpendicularly, there is an effect that the scattered light can be efficiently condensed on the light receiving element without being substantially affected by aberration due to the eccentricity or inclination of the first lens unit.

According to the fourth aspect of the present invention, the angle formed between the surface perpendicular to the optical axis of the second lens portion and the reflection surface of the prism portion is equal to or larger than the critical angle, thereby maintaining a constant angle. And the sensitivity can be increased.

According to the fifth aspect of the present invention, the angle formed between the surface perpendicular to the optical axis of the second lens unit and the reflecting surface of the prism unit is 45 ° to 70 °. In addition, a constant total reflection area can be obtained, and the amount of received light can be sufficiently ensured.

According to the sixth aspect of the present invention, the amount of light received by the light receiving element 5 is reduced by blocking light that enters the first lens portion but does not strike the reflecting surface of the prism portion. , And stray light can be significantly reduced, so that the S / N ratio of the light receiving element 5 can be improved. In addition, there is an effect that it is possible to provide a highly reliable photoelectric smoke sensor without largely changing the light receiving characteristics due to an increase in noise due to the attachment of dust and the like.

According to the seventh aspect of the present invention, since the first lens portion is formed so as to refract incident light into substantially parallel light, the vicinity of the peripheral portion of the first lens portion is reduced. The transmitted light also satisfies the condition of total reflection, and has the effect of providing a photoelectric smoke detector in which the light receiving efficiency of the light receiving element is improved.

In the invention according to claim 8, a smoke introduction portion forming a smoke detection area is provided, and a first lens portion is provided in the smoke introduction portion, and a focal length of the first lens portion is provided. However, by forming an image on the surface of the smoke introduction section opposite to the first lens section, the light collection area of the first lens section on the surface of the smoke introduction section can be reduced as much as possible. As a result, it is possible to suppress capture of irregular reflection of light generated on the surface of the smoke introduction section, so that the S / N ratio of the light receiving element can be improved. In addition, there is an effect that it is possible to provide a highly reliable photoelectric smoke sensor without largely changing the light receiving characteristics due to an increase in noise due to the attachment of dust and the like.

According to the ninth aspect of the present invention, a smoke introduction portion for forming a smoke detection area is provided, and a first lens portion is provided in the smoke introduction portion, and a focal length of the first lens portion is provided. However, since the image is formed at an intermediate position between the center of the smoke detection area and the surface of the smoke introduction section, the light condensing area of the first lens section on the surface of the smoke introduction section can be reduced. Since the capture of irregular reflection of light generated on the surface of the smoke introducing portion can be suppressed, the S / N ratio of the light receiving element can be improved and a sufficient amount of received light can be secured. Also,
Accordingly, there is an effect that a highly reliable photoelectric smoke detector can be provided without a large change in light receiving characteristics due to an increase in noise due to the attachment of dust or the like.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a photoelectric smoke detector according to a first embodiment.

FIG. 2 is a cross-sectional view showing the structure of the photoelectric smoke detector according to the first embodiment.

FIG. 3 is a view showing a prism lens incorporated in the photoelectric smoke detector according to the first embodiment.

FIG. 4 is a view showing a prism lens incorporated in a photoelectric smoke sensor according to a second embodiment.

FIG. 5A is a diagram showing a case where stray light occurs,
(B) is a diagram showing a third embodiment provided with an aperture.

FIG. 6 is a diagram showing a prism lens incorporated in a photoelectric smoke detector according to a fourth embodiment.

FIG. 7 is a longitudinal sectional view showing a structure of an optical system and the like of a photoelectric smoke detector according to a fifth embodiment.

FIG. 8 is a longitudinal sectional view showing the structure of a conventional photoelectric smoke detector.

FIG. 9 is a cross-sectional view showing the structure of a conventional photoelectric smoke detector.

[Explanation of symbols]

 Reference Signs List 3 light emitting element 5 light receiving element 7 prism lens 7a lens section (first lens section) 7b prism section 7c lens section (second lens section) 8 smoke introduction section 10 smoke detection area 11 aperture

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoyuki Nishikawa 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Inventor Takeshi Wada 1048 Odaka Kadoma Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. ( 72) Inventor Shoichi Oka 1048 Kadoma, Kazuma, Osaka Pref. Matsushita Electric Works Co., Ltd. F-term (reference) 5C085 AA03 AB01 AC03 BA33 CA08 CA30 DA07 DA08

Claims (9)

[Claims] 1. A photoelectric type of illuminating a smoke detection area with a light emitting element and detecting scattered light caused by particles such as smoke existing in the smoke detection area by a light receiving element. In the smoke detector, a first lens unit that condenses the scattered light and a second lens unit that condenses the light condensed by the first lens to the light receiving element are provided. And photoelectric smoke detector. 2. A photoelectric type in which a light emitting element emits light to a smoke detection area, and scattered light caused by particles such as smoke existing in the smoke detection area is detected by a light receiving element to detect smoke or the like. In the smoke detector, a first lens unit that collects the scattered light, a prism unit that changes a traveling direction of the light collected by the first lens,
And a second lens unit for condensing the light whose traveling direction has been changed by the prism unit on the light receiving element. 3. An angle between an optical axis of the first lens unit and a plane perpendicular to the optical axis of the second lens unit is defined by a plane perpendicular to the optical axis of the second lens unit. 3. The photoelectric smoke detector according to claim 2, wherein an angle obtained by subtracting a right angle from an angle twice as large as an angle formed between the prism surface and the reflection surface is obtained. 4. An angle between a surface perpendicular to an optical axis of the second lens portion and a reflection surface of the prism portion is equal to or larger than a critical angle. Photoelectric smoke detector. 5. An angle formed between a surface perpendicular to the optical axis of the second lens portion and a reflection surface of the prism portion is 45 ° to 70 °.
The photoelectric smoke sensor according to claim 2 or 3, wherein the angle is set to °. 6. The photoelectric smoke according to claim 2, wherein light incident on the first lens unit and not incident on the reflecting surface of the prism unit is blocked. sensor. 7. The photoelectric smoke sensor according to claim 1, wherein the first lens unit is formed so as to refract incident light into substantially parallel light. vessel. 8. A smoke introduction section forming the smoke detection area, wherein the smoke introduction section includes the first lens section, and a focal length of the first lens section is a first lens section. The photoelectric smoke sensor according to claim 1, wherein an image is formed on a surface of the smoke introduction portion facing the smoke detector. 9. A smoke introduction part forming the smoke detection area is provided, and the first lens part is provided in the smoke introduction part, and a focal length of the first lens part is equal to that of the smoke detection area. 8. The photoelectric smoke detector according to claim 1, wherein an image is formed at an intermediate position between the center and the surface of the smoke introduction section.