JPH0236111Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a small photoelectric smoke detector.

[Conventional technology]

The darkroom of conventional photoelectric smoke detectors has a complicated labyrinth structure or a double cover structure to prevent ambient light from entering the darkroom and to allow smoke to easily enter.

[Problems with conventional technology]

However, the structure described above is large and unsuitable for use as a sensor built into devices such as computers or installed in aircraft lavatories, and simply reducing the size of these sensors will result in poor signal-to-noise ratios. There were flaws.

[Means for solving problems]

A photoelectric smoke sensor in which a light emitter and a receiver are placed facing each other at a predetermined distance in a dark room, and their optical axes are shifted upward or downward to prevent the light emitted from the emitter from directly irradiating the receiver. The darkroom has left and right side walls erected substantially parallel to each other along a line connecting the emitter and receiver, and a bent side wall that is provided in front of the emitter to directly receive the light emitted from the emitter and reflect it on the left and right side walls. a front wall with a curved surface, and a rear wall with a curved surface that is provided at the rear of the projector and reflects the light reflected by the left and right side walls so as not to further irradiate the receiver; The photoelectric smoke detector has a mirror-like surface with good light absorption.

[Effect]

The photoelectric smoke detector of this invention has a light trapping function in the darkroom itself by having the above structure,
In other words, the light rays emitted from the projector are reflected many times through the front and rear walls onto the left and right side walls, which have mirror-like surfaces with good light absorption, to prevent direct reflected light from entering the light-receiving element of the receiver. By making it very weak even if it enters the smoke sensor, a small photoelectric smoke detector with a narrow measurement space without the need for an additional optical trap mechanism is created.

〔Example〕

An embodiment of the photoelectric smoke detector of this invention will be described below with reference to FIGS. 1 to 3. In the figure a
1 is a cross-sectional view of the darkroom of this invention, b is a cross-sectional view thereof, 1 is a light projector that emits a convergent beam of light that is equipped with a light source such as a light emitting diode and a lens, etc., and 2 is a light receiving element such as a solar cell and a lens, etc. receiver,
3 is a light shielding plate provided between the emitter and receiver 1 and 2;
Reference numerals 4 and 5 denote left and right side walls that are erected almost parallel to each other along the line connecting the emitter and receiver 1 and 2, and 6 is a wall that is installed in front of the emitter 1 so that the light from the emitter 1 is reflected at a predetermined angle with respect to the optical axis. The front wall 7 has a curved surface that reflects the light reflected from the left and right side walls 4 and 5 provided at the rear of the projector 1 at a predetermined angle so that the light does not directly illuminate the light receiving element of the receiver 2. The rear walls 8, 9 are provided with a bottom wall and a ceiling wall, and smoke inlet holes (not shown) are provided near the center of the bottom wall 8 and both ends of the ceiling wall 9. Note that the wall surface has a good light absorbing color, for example black, and is finished in a mirror shape. Furthermore, in the figure, s indicates the starting point of the ray, the arrow indicates the point where the ray reaches, and the black circle indicates the point of reflection with the side wall 4.
White circles indicate reflection points with the side wall 5, and triangles indicate reflection points with the ceiling wall 9. In addition, Fig. 1 shows that the optical axis is slightly to the left with respect to the receiver 2 and θ = 150°, and Fig. 2 shows that the optical axis is 5° to the left with respect to the receiver 2 and θ = 150°. In this case, FIG. 3 shows the case where the angle of the projector 1 in FIG. 1 is set upward.

Next, the function of the darkroom will be explained. For example, the first
In the figure, the convergent light beam emitted from the floodlight 1 is
It collides with the left wall surface of the front wall 6 and is absorbed by the black surface,
In addition, the light that cannot be absorbed is not diffusely reflected by the mirror-like surface, but is reflected as a nearly convergent light beam, and is reflected on the left side wall 4, then on the right and left side walls 5, 4, and then on the ceiling wall 9, the right side wall 5, It is reflected to the left side of the left side wall 4 and the rear wall 7, and collides with the outer wall of the light receiver 2. While the light emitted from the projector 1 is reflected several times, it is absorbed by the black surface and attenuated, acting as a light trap and becoming an extremely weak light. To further explain with reference to FIG. 2, the light emitted from the floodlight 1 is reflected to the left side of the front wall 6, reflected to the left side wall 4, and then to the right side.
The light is reflected to the right side of the left and right walls, the ceiling wall 9, the left wall 4, the right wall 5, and the rear wall 7, and collides with the outer wall of the light receiver 2.
In addition, in FIG. 3, the light emitted from the floodlight 1 is reflected to the left side of the front wall 6, the left side wall 4, the ceiling wall 9,
The light collides with the right, left, right, left side walls, the left side of the rear wall 7, and the outer wall of the projector 1, and is attenuated into weak light.

On the other hand, when smoke enters this dark room due to a fire outbreak, the scattered light illuminates the light receiving element of the light receiver 2,
An output is generated to notify that a fire has occurred. If the output of the light-receiving element is S when the smoke of a predetermined concentration that is determined to be a fire outbreak enters the dark room, the output during normal operation is N, and the angle of the front and rear walls 6 and 7 is θ, the characteristics shown in Fig. 4 are shown. showed that. According to this figure, the SN is sufficient for practical use when θ is below 140° and above 210°.
The ratio was obtained.

〔effect〕

In the photoelectric smoke detector of this invention, the darkroom has the above configuration and the darkroom itself has a light trapping function.In other words, the light rays emitted from the floodlight are transmitted through the front and rear walls into a mirror-like structure with good light absorption. Since the reflected light is reflected many times by the left and right side walls with surfaces, the direct reflected light will not be incident on the light receiving element of the light receiver, or even if it is incident, it will be extremely weak.
This has the effect of providing a small photoelectric smoke detector with a narrow measurement space without the need for additional optical trapping mechanisms.

[Brief explanation of drawings]

1 to 3 are schematic diagrams of the photoelectric smoke detector of this invention, in which a is a sectional view, b is a cross-sectional view thereof, and FIG. 4 is a characteristic curve diagram. 1... Emitter, 2... Light receiver, 3... Light shielding plate,
4...Left wall, 5...Right wall, 6...Front wall, 7...
...Back wall, 8...Bottom wall, 9...Ceiling wall.

Claims (1)

[Scope of utility model registration request] A photoelectric smoke detector in which a light emitter and a receiver are placed facing each other at a predetermined distance in a dark room, and their optical axes are shifted upward or downward so that the light emitted from the emitter does not directly illuminate the light receiver. The darkroom is provided with left and right side walls erected substantially parallel to each other along a line connecting the emitter and receiver, and a bent surface provided in front of the emitter to directly receive light emitted from the emitter and reflect it to the left and right side walls. a rear wall provided at the rear of the projector and provided with a bent surface that reflects the light reflected by the left and right side walls so as not to further irradiate the receiver, and a ceiling wall. A photoelectric smoke detector characterized by having a mirror-like surface with good light absorption.