JPH0444196A - Photoelectric smoke sensor - Google Patents

Abstract

PURPOSE:To surely detect smoke by condensing the diffracted light, which corresponds to smoke particles and is led by a holographic element, on a photodetector to decide the smoke. CONSTITUTION:Light projecting means 1 and 2 which lead collimated light having a single wavelength to a smoke monitor area 20, a holographic element 4 which leads diffracted light of an object in the smoke monitor area, which is obtained by the light led by these means 1 and 2, to a prescribed direction in accordance with the angle of diffraction, a photodetector 6 which receives diffracted light corresponding to smoke particles which is led by the holographic element 4, and a discriminating means 3 which discriminates the existence of smoke particles based on the reception light output of the photodetector 6 are provided. Thus, the object other than smoke is not detected as smoke regardless of the existence of the object like dust other than smoke in the smoke monitor area 20 because the angle of diffracted light of the object is different from that of diffracted light of smoke particles.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects diffracted light of an object existing within the smoke monitoring area by a light beam irradiated onto the smoke monitoring area from a light projecting element, and This invention relates to a photoelectric smoke detector that determines whether an object is smoke or not based on the direction of diffraction.

[Prior Art] Generally, photoelectric smoke detectors are disclosed in Japanese Patent Application Laid-Open No. 1983-1983. No. 147294, Utility Model Application No. 1988-109189, Utility Model Application No. 62-2035
As shown in No. 8, etc., smoke detection is performed by receiving scattered light from smoke particles. In other words, this type of photoelectric smoke detector has a light emitting element 18 as shown in FIG.
The light receiving element 19 receives scattered light from smoke particles of light irradiated onto the smoke monitoring area 20 to perform smoke detection.
The light emitting element 18 and the light receiving element 19 are arranged so that their optical axes intersect with each other as shown in the figure, and the light emitting element 18
A light-shielding plate or the like is arranged to prevent light from directly entering the light-receiving element 19, and only when smoke particles are present in the smoke monitoring area 20, scattered light generated by smoke particles enters one light-receiving element. It is designed to detect the presence of smoke.

On the other hand, there is a conventional method for detecting smoke by measuring the particle size, and a laser diffraction particle size measurement method is common for this method (for example, see Shimadzu Review Vol.
, 45. No. 1.2 1988.6 pages 78-84)
. This method will be explained based on FIG. 9. In this illustrated example, the laser beam emitted from the laser 21 is transferred to the lens 22.
The beam is collimated and irradiated onto the particle X to be measured. Here, light is diffracted by the particle to be measured X, and the traveling direction of the -order diffracted light differs from the irradiation direction by an angle θ.

Here, when the wavelength of the laser beam is λ, the following relationship exists between the particle diameter D of the particle to be measured X, the wavelength λ, and the diffraction angle θ.

sin θ=1.22λ/D −■ When this first-order diffracted light is imaged using the Fourier transform lens 23,
The image height r is r=1.22 person f/D. Note that f indicates the distance from the Fourier transform lens 23 to the imaging plane. Here, since the actual image is circular with the optical axis as the center, the light receiving element 24 constituting the image forming surface is composed of a plurality of light receiving elements arranged in concentric circles. Here, if λ and f are known, the particle diameter can be determined by the signal processing device 25 from the radius r of the light receiving element into which the diffracted light enters.

[Problems to be Solved by the Invention] By the way, in the conventional configuration shown in FIG.
Even if there are objects other than smoke inside the room, such as dirt, dust, or steam when a smoke detector is installed in an indoor kitchen, the light emitted from the light emitting element 18 may be affected by these objects. Since the scattered light is received by one light receiving element, there is a problem of false detection in which the signal processing means after the first light receiving element determines that smoke is present and generates a detection output. . This problem was a serious problem that needed to be solved, especially for smoke detectors, which are concerned with human life.

In general, the diameter of smoke particles that must be detected by photoelectric smoke detection and the particle diameter of objects that cause malfunction are each 1μ.
m ~ 3 μm and 5 μm or more (
Japanese Society of Fire Research 1989 Research Presentation Summary Collection, pages 37-38).

On the other hand, the laser diffraction particle size measurement method shown in FIG.
Since a special lens called the Fourier transform lens 23 is required, there is a problem in that the cost is high. Therefore, if a commonly used lens is used, the image height r
When 4 + nm, r=12.4 mm, which causes the diameter of the light-receiving element to become large, requiring a special light-receiving element, leading to an increase in cost.

The present invention was made in view of the above-mentioned problems, and its purpose is to enable smoke detection by measuring the size of smoke particles without using expensive parts, and to provide an inexpensive and reliable method. It is on offer to provide high quality photoelectric smoke detectors.

In addition, it is an object of the invention described in claims 3 and 4 to provide a photoelectric smoke detector using a light projecting means that is highly safe and inexpensive.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the invention according to claim 1 includes a light projection means for guiding collimated light of only a single wavelength to a smoke monitoring area, and a light projection means by the light projection means. A holographic element that guides diffracted light of an object existing within a smoke monitoring area obtained by the guided light in a predetermined direction according to a diffraction angle, and receives diffracted light corresponding to smoke particles guided by the holographic element. The apparatus includes a light-receiving element for detecting a smoke particle, and a determining means for determining the presence of smoke particles based on the light-receiving output of the light-receiving element.

In the second aspect of the invention, the light projecting means is constituted by a light projecting element made of a laser such as a semiconductor laser, and a lens that collimates the laser beam.

In addition, the invention according to claim 3 uses a light emitting element made of a light emitting diode, a lens that collimates the light from the light emitting element, and a diffraction grating that selects light of a single wavelength from the collimated light. It constitutes a light projecting means.

Furthermore, the invention according to claim 4 includes a light projecting element made of a photodiode, a concave mirror such as an off-axis parabolic reflector having a collimating function, and a single wavelength of light is selected from the collimated light disposed on the mirror surface of the concave mirror. The light projecting means is constituted by the diffraction grating.

[Function] According to the present invention, only when the object is a smoke particle, the diffracted light of the light irradiated onto an object existing within the smoke monitoring area is guided by the holographic element and focused onto the light receiving element. When the received light output reaches a predetermined level, the determining means determines that smoke particles are present. In other words, even if there is an object other than smoke such as dust within the smoke detection area, the angle of the diffracted light is different from the diffracted light from smoke particles, so objects other than smoke will not be detected as smoke, resulting in high reliability. You can get sex. It also eliminates the need for expensive components such as Fourier transform lenses.

Note that the invention according to claim 3 or 4, in which a light emitting diode is used as a light projecting element without using a laser, has higher safety than the use of laser light.

[Example] The present invention will be explained below with reference to Examples.

FIG. 1 shows an embodiment of the present invention. In this embodiment, the light projecting means is composed of a light projecting element 1 and a light projecting lens 2. A laser such as a semiconductor laser that emits light of one wavelength is used, and a collimating lens is used for the projection lens 2, so that the light from the projection element 1 is collimated and guided to the projection lens 2 to the smoke monitoring area 20. It has become.

A holographic element 4 is arranged on the opposite side of the light projecting means with respect to the smoke monitoring area 20, and the optical axis of this holographic element 4 and the optical axis 9 of the light projecting means are aligned.

Further, a light receiving element 6 is arranged behind the holographic element 4 and on an extension of the optical axis 9.

Note that this light receiving element 6 does not necessarily have to be arranged on an extension of the optical axis 9, but when it is arranged on an extension of the optical axis 9, the light emitted from the light emitting means is affected by the flow of smoke particles X, etc. In order to prevent the light from directly entering the light receiving element 6 when the light travels straight without receiving any light, it is necessary to provide a stopper 5 in front of the light receiving element 6 to block the light, as shown in the figure. The stopper 5 is connected to the holographic element 4 as shown in FIG. 2(a).
Alternatively, as shown in FIG. 2(b), an appropriate area (
A light shielding body 11 covers the area (excluding the incident area 10 of diffracted light caused by smoke particles Another light-receiving element (not shown) may be arranged behind the light-receiving element so that the optical axis can be adjusted using this light-receiving element.

The holographic element 4 has a function of guiding diffracted light in a predetermined direction, and FIG. 3 is a diagram for explaining the function. The holographic element 4 functions as follows.

First, assuming that the particle size of the smoke to be detected is 1 μm to 3 μm, and the wavelength of the light projecting element 1 is λ, the -order diffraction angle θ is determined by the above equation. Also, when the beam diameter of the irradiation light is W and the length of the smoke monitoring area 3 in the optical axis direction is l,
A region 10 in which the first-order diffracted light 7 due to smoke particles exists is shown in FIG. 2(b).

Here, if the distance from the smoke monitoring area 20 to the holographic element 4 is d, then the area where the diffraction path corresponding to the diffracted light 7 of the smoke particles X is written on the holographic element 4 is as shown by the diagonal line A in FIG. It is determined by

Next, consider the shape of the diffraction grating when the light receiving element 6 is located on the optical axis 9 of the light projecting system.

First, if the period of the diffraction grating is 8, then the optical axis direction component a, 1,) sin θ+ +l T,, ut l sin
Diffracted light 7 of smoke particles enters the light receiving element 6 when θo=lKl−=■ is satisfied. In addition, in equation 0, θ
1 is the incident light angle, θ0 is the output light angle, a, o is the direction vector of the incident light, ? , , indicates the outgoing light angle, and 1
? 8th - a. , , l−2π/λ, K indicates the grating vector of the diffraction grating, and 11;jl=2π/Δ. The shape of the diffraction grating may be determined so as to satisfy this relationship.

Note that since the diffracted light 7 is generated in a conical shape, the grooves of the diffraction grating are concentric circles centered on the optical axis 9. Furthermore, the diffraction grating is designed so that the diffracted light 8 generated from an object outside the lamp is focused on a light receiving element (not shown) provided at a location other than the optical axis 9. FIGS. 5(a) and 5(b) show an example of the state of the diffraction grating, where D is the outermost diameter at both ends of the region 13 where the diffracted light 7 due to smoke particles is incident, and D2 is the outermost diameter of the area 13 where the diffracted light 7 due to smoke particles is incident. Indicates the outermost diameter of the region 14 on which the diffracted light 8 enters, and the region 1
The period Δ2 of the diffraction grating in region 4 is smaller than the period Δ1 of the diffraction grating in region 13.

Of course, if the diffracted light 8 is not used for signal processing of a smoke detector,
The incident side surface of the porographic element 4 may be made a mirror surface to reflect the light to a place where it will not be affected.

The porographic element 4 can be produced by, for example, applying an electron beam resist 31 on a glass substrate 30 or the like and drawing a diffraction grating using an electron beam 32, as shown in FIG. Crow base 3 as shown in figure (b)
There is a method of coating a photoresist 33 on the etching layer 30a etc. of 0 and etching it by irradiating it with an ion beam 34 to form a diffraction grating.

The diffracted light 7 from the smoke particles X guided to the porographic element 4 is focused on the light receiving element 6, and the received light output is input to the circuit of the determining means 3 shown in FIG. 1(C) to detect the smoke. The presence or absence is determined. In other words, the received light output is amplified by the amplifier circuit 26 and then inputted to the comparison circuit 27 and then input to the reference value generation port FIPt.
When the level of the received light output exceeds the reference value, it is determined that smoke particles X are present in the smoke monitoring area 20, and a smoke detection signal is output from the output circuit 28.

In the above embodiment, a semiconductor laser is used as the light emitting element 1, but lasers such as semiconductor lasers and gas lasers have the risk of harming the human body if handled incorrectly, and are considerably more sensitive than light emitting diodes. It's expensive.

Therefore, as shown in FIG. 6(a), a light emitting diode is used as the light emitting element 1, and a lens 2 and a reflective type are used to collimate the emitted light from the light emitting element 1 with the wavelength shown in FIG. 6(b). The smoke monitoring area 20 may be irradiated with only the light of a single wavelength component shown in FIG. 6(C) using the diffraction grating 15.

Here, in the above equation 0, the desired wavelength λ. When the incident light angle θ and the grating period are determined, if the wavelength changes, the output angle θ. The unnecessary wavelength component λ due to the change in is shown in Figure 6 (a
), the smoke monitoring area 20 is not reached. Thus, with the above configuration, a safe and inexpensive light projecting means that does not use a laser can be achieved.

As shown in FIG. 7, instead of the lens 2 in the embodiment of FIG. 6, a concave mirror such as an off-axis parabolic reflector 17 is used to provide a collimate function, and a diffraction grating 15 is provided on the mirror surface 16 of the off-axis parabolic reflector 17. You can also place it.

In this embodiment, the light emitted from the light emitting element 1 consisting of a light emitting diode provided at the focal point of the off-axis parabolic reflector 17 is reflected by the mirror surface 16 of the off-axis parabolic reflector 17 and the diffraction grating 15, as shown in FIG. As in the example, the predetermined wavelength λ. collimates only the light and guides it to the smoke monitoring area 20,
The direction of light of other wavelengths λ may be removed from the smoke monitoring area 20. In this embodiment, the method for manufacturing the diffraction grating 15 is to apply a resist to a glass base material in the shape of an optical axis parabolic reflector 16 in advance, and to manufacture the diffraction grating 15 by a method not shown in FIG. Another method is to make a diffraction grating out of a material that can be easily bent or otherwise deformed, and then bond it to a mirror surface. The above configuration also provides a safe and inexpensive light projecting means that does not use a laser.

Although the holographic element 4 shown in FIG. 4 is only of a transmission type, it may be of a reflection type if the arrangement is changed appropriately.

Furthermore, the diffraction grating 15 used in FIGS. 6 and 7 may also be of a transmission type if the arrangement is changed appropriately.

Regarding the diffracted light, only the first-order diffracted light is shown, but the second-order and higher-order diffracted lights are omitted because their power is considerably inferior to that of the first-order diffracted light.

Further, although both the holographic element 4 and the diffraction grating 15 are shown as lamellar gratings in the drawings, they may of course have other shapes such as echelette gratings.

[Effect of the Invention 1 The invention as claimed in claim 1 includes a light projecting means for guiding collimated light of only a single wavelength to a smoke monitoring area, and a light projecting means that exists within the smoke monitoring area obtained by the light guided by the light projecting means. a holographic element that guides diffracted light from an object to a predetermined direction according to a diffraction angle, a light receiving element that receives diffracted light corresponding to smoke particles guided by the holographic element, and a light receiving element based on the light receiving output of the light receiving element. According to the present invention, the diffracted light of the light irradiated onto an object existing within the smoke monitoring area is guided by the holographic element only when the object is a smoke particle. The light can be focused on the light-receiving element, and smoke can be detected reliably, and even if there is an object such as dust outside the lamp within the smoke detection area, the object can be detected as smoke. The invention according to claim 3 also has the effect that high reliability can be obtained without the need for high-cost parts such as a Fourier transform lens, and manufacturing costs are reduced because it does not require the use of expensive parts such as Fourier transform lenses. The invention described in item 4 uses a light emitting diode as a light projecting element without using a laser, so it has the effect of increasing safety at low cost.

[Brief explanation of drawings]

FIG. 1(a) is an overall view of an embodiment corresponding to the invention described in claims 1 and 2, FIG. 1(b) is a perspective view of the holographic element portion of the same as above, and FIG. A circuit configuration diagram, FIG. 2(a) is a side view showing another example of the holographic element used in the same as above, FIG. 2(b) is a front view of another example of the holographic element used in the same as above, and FIG. 4(a) and 4(b) are diagrams explaining the method for manufacturing the holographic element, and FIGS. 5(a) and
b) is a front view and an enlarged side view of essential parts of the holographic element used in the above, FIG. 6(a) is a configuration diagram of an embodiment corresponding to the invention as claimed in claim 3, and FIGS. 6(b) and (c) is an explanatory diagram of the same operation as above, FIG. 7 is a configuration diagram of an embodiment corresponding to the invention as claimed in claim 4, FIG. 8 is an explanatory diagram of a conventional example, and FIG. 9 is an explanatory diagram of a laser diffraction particle size measuring method. It is. 1 is a light projecting element, 2 is a lens, 3 is a determining means, 4 is a holographic element, 5 is a stopper, 6 is a light receiving element, 7.8
is a diffracted light, 15 is a diffraction grating, 16 is a mirror surface, 17 is an off-axis parabolic reflector, 20 is a smoke monitoring area, and X is a smoke particle. Agent Patent Attorney Ishi 1) Long Seven Banquets, -= (', +'I'l 'f Ln t# To(', + %r+-Response! 3B History K"<Haketsupo,"S - Reproduction α Art = CoV Kaga "・O=r+ ('<l-N figure

Claims (4)

[Claims] (1) A light projection means that guides collimated light of only a single wavelength to a smoke monitoring area, and a diffraction angle of the diffracted light of an object existing within the smoke monitoring area obtained by the light guided by the light projection means. a holographic element that guides the smoke particles in a predetermined direction according to the direction of the smoke particles; a light receiving element that receives the diffracted light corresponding to the smoke particles guided by the holographic element; and a determining means that determines the presence of the smoke particles based on the light receiving output of the light receiving element. Photoelectric smoke detector with (2) The photoelectric smoke detector according to claim 1, wherein the light projecting means is constituted by a light projecting element made of a laser such as a semiconductor laser, and a lens that collimates the laser light. (3) The light projecting means is constituted by a light projecting element made of a light emitting diode, a lens that collimates the light from the light projecting element, and a diffraction grating that selects light of a single wavelength from the collimated light. The photoelectric smoke detector according to claim 1, characterized in that: (4) A light emitting element consisting of a light emitting diode, a concave mirror such as an off-axis parabolic reflector with a collimating function, and a diffraction grating arranged on the mirror surface of the concave mirror to select light of a single wavelength from the collimated light. 2. The photoelectric smoke detector according to claim 1, further comprising a light projecting means.