JPH04160696A - Photoelectric smoke sensor - Google Patents

Abstract

PURPOSE:To reduce misinformation or missing of information and to improve detection sensitivity by respectively deflecting light made incident from a projecting element upon a smoke monitoring area and light made incident from the smoke monitoring area upon a photodetecting element by a projection mirror and a photodetecting mirror. CONSTITUTION:The projecting element 3 and the photodetecting element 4 are mounted on one face of a circuit substrate 5 so that their optical axes are almost orthogonal to the surface of the substrate 5. The projection mirror 8 for deflecting light projected from the element 3 so as to make the light incident upon the smoke monitoring area at a prescribed angle and the photodetecting mirror 7 for deflecting scattered light outputted from the smoke monitoring area so as to make the light incident upon the element 4 are fixed to an optical base 6 arranged on one side of the substrate 5. Even in a compact housing 1, stray light can be reduced, the variation of smoke particle detecting accuracy can be reduced and the quantity of scattered light due to smoke particles made incident upon the element 4 can be increased. Consequently, a smoke sensor reducing the generation of misinformation or missing of information and improving detection sensitivity can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention irradiates incident light from a light projecting element onto a smoke monitoring area, detects scattered light caused by smoke particles with respect to the incident light by a light receiving element, and detects smoke based on a change in the output of the light receiving element. This relates to a photoelectric smoke detector.

[Conventional technology]

As shown in Figure 4, this type of photoelectric smoke detector is
Incident light from a light emitting element 3 is introduced into a dark room 2 set inside a housing 1, and scattered light generated in response to the incident light when smoke particles are introduced into the dark room 2 is transmitted to a light receiving element 4.
There is a device that receives light from the light receiving element 4 and determines the presence or absence of smoke particles based on changes in the output of the light receiving element 4. A circuit board 5 is disposed inside the housing 1 along the inner bottom surface, and the circuit board 5 includes a light emitting element 3 and a light receiving element 4 as well as a drive circuit for controlling blinking of the light emitting element 3 and a light receiving element. element 4
A smoke detection circuit is implemented that determines the presence or absence of smoke based on the output. An optical base 6 is disposed on the lower surface side of the circuit board 5, and the space on the lower surface side of the optical base 6 in the internal space of the housing 1 is used as a dark room 2. A part of the darkroom 2 communicates with the external space via the labyrinth body 1.
1 is configured to allow smoke particles to pass through while blocking external light. By the way, the light emitting element 3 is held on an optical base 6 and arranged so as to emit incident light into the dark room 2 at a predetermined angle, and the light receiving element 4 is held in a direction substantially perpendicular to the surface of the circuit board 5. It has an optical axis. That is, the light receiving element 4
is incorporated on the integrated circuit 4a together with a smoke detection circuit, so that the output of the light receiving element 4 is not easily affected by external noise. As mentioned above, since the optical axis of the light receiving element 4 is set to be substantially perpendicular to the surface of the circuit board 5, the optical base is used to deflect the scattered light from the dark room 2 and make it enter the light receiving element 4. A light receiving mirror 7 is arranged on the stand 6. The light-receiving mirror 7 is formed as an incident surface 7a on which the scattered light enters, or a plane that is substantially perpendicular to the surface of the circuit board 5, and a convex curved lens surface 7b is formed on the exit surface facing the light-receiving element 4. It is formed in a shape having a reflecting surface 7C that deflects light rays incident on the surface 7a from a predetermined direction so as to exit from the lens surface 71. By arranging such a light-receiving mirror 7, the distance between the light-emitting element 3 and the light-receiving element 4 along the circuit board 5 can be reduced, and the housing 1 can be made smaller. Further, among the areas illuminated by the light projecting element 3 in the dark room 2, the area where light scattered by smoke particles enters the light receiving element 4 becomes a smoke monitoring area. On the other hand, when light rays other than scattered light enter the light receiving element 4, the output level of the light receiving element 4 changes less, and the detection accuracy of smoke particles decreases. Therefore, the light projecting element 3
The optical axis of the light emitting element 3 is tilted with respect to the surface of the circuit board 5 so that the direct light from the light does not enter the light receiving mirror 7. 6 is provided with a light shielding protrusion 6a.

[Invention or problem to be solved]

In the above configuration, the housing 1 can be made smaller by providing the light receiving mirror 7 that deflects the light incident on the light receiving element 4, and the light receiving element 4 can be integrated into the integrated circuit 4a together with the smoke detection circuit etc. This makes it less susceptible to noise. By the way, in order to further downsize the housing 1 in the above configuration, the light projecting element 3 must be moved closer to the light receiving mirror 7. When the light projecting element 3 is brought close to the light receiving mirror 7, a part of the light emitted from the light projecting element 3 directly enters the light receiving mirror 7, as shown by the broken line in FIG. Here, setting the reflective surface 7c of the light receiving mirror 7 at an appropriate angle prevents light beams incident on the incident surface 7a of the light receiving mirror 7 from entering the light receiving element 4 other than light scattered by smoke particles. is possible. However, a portion of the light rays scattered at the periphery of the incident surface 7a reaches the lens surface 7b without being deflected by the reflection surface 7c, so such light rays become stray light and enter the light receiving element 4. The scattered light at the periphery of the incident surface 7a of the light-receiving mirror 7 is easily affected by the adhesion of lumps, etc., so the amount of fluctuation in stray light increases, and the detection accuracy of smoke particles fluctuates, resulting in false alarms or missed alarms. The problem is that it is a problem. To avoid such problems, the angle of inclination of the light emitting element 3 with respect to the circuit board 5 is made small so that most of the scattered light at the periphery of the incident surface 7a of the light receiving mirror 7 is reflected by the reflecting surface 7c. It is possible to do so. However, in such a configuration, since the scattered light incident on the light receiving mirror 7 is also reduced, the change in the light receiving level of the light receiving element 4 due to the presence or absence of smoke particles is reduced, and there is a problem that the smoke particle detection sensitivity is reduced. arise. The present invention aims to solve the above-mentioned problems, and while reducing the size of the housing, it reduces the amount of stray light incident on the light receiving element without reducing the detection sensitivity of smoke particles, and improves the detection accuracy of smoke particles. The present invention aims to provide a photoelectric smoke detector that suppresses the occurrence of false alarms and missed alarms by preventing fluctuations in the number of smoke alarms.

[Means to solve the problem]

In order to achieve the above object, the present invention irradiates a smoke monitoring area set in a housing with incident light from a light emitting element, detects scattered light from smoke particles with respect to this incident light by a light receiving element, and receives the light. In a photoelectric smoke detector that detects smoke based on changes in the output of the element, the light emitting element and light receiving element are mounted on one side of a circuit board installed along the inner bottom of the housing sink. An optical base is disposed at a fixed position on one side of the circuit board, and the optical base emits light from the light emitting element. It has a light projecting mirror that deflects the light so that it enters the smoke monitoring area at a predetermined angle, and a light receiving mirror that deflects the scattered light from the smoke monitoring area in a direction that makes it enter the light receiving element.

[Effect]

According to the above configuration, the light emitting element and the light receiving element are mounted on one surface of the circuit board so that the optical axis faces in a direction substantially perpendicular to the surface of the circuit board, and the optical A light projecting mirror that deflects the light from the light projecting element so as to be incident on the smoke monitoring area at a predetermined angle, and a light receiving mirror that deflects the scattered light from the smoke monitoring area in a direction that makes it enter the light receiving element. Since the light emitting element is attached to the smoke monitoring area, the light entering the smoke monitoring area from the smoke monitoring area and the light entering the light receiving element from the smoke monitoring area are deflected by the emitting mirror and the light receiving mirror, respectively. The distance between the device and the circuit board can be set small, and while the positional relationship is set so that the light emitted from the emitter mirror does not directly enter the receiver mirror, the housing can be made smaller than before. It is possible to make it smaller. As a result, even though the housing is small, it is possible to reduce stray light, reduce fluctuations in smoke particle detection accuracy, and increase the amount of light scattered by smoke particles that enters the light receiving element. This makes it possible to provide a smoke detector with high detection sensitivity and fewer false alarms and missed alarms.

【Example】

As shown in FIG. 1, the housing consists of a bottomed cylindrical body 10 with an open bottom, a cylindrical labyrinth body 11 attached to the opening of the body 10 and forming a darkroom 2 inside, and a labyrinth body 11. It is formed by a cover 12 that covers the lower end surface of. The labyrinth body 11, as shown in FIG.
A substantially shaped smoke introduction path is formed between adjacent partition walls 13. One end of the smoke introduction path opens on the outer peripheral surface of the housing 1 to serve as a smoke introduction port, and the other end of the smoke introduction path opens into a dark room 2 with a circular cross section formed in the center of the labyrinth body 11.
It will be communicated to. The partition wall 1.3 is black to prevent reflection, and the smoke introduction path is curved, so that
This is to prevent outside light from entering the dark room 2. An insect screen 14 is attached to the circumferential surface of the labyrinth body 11 to prevent insects from entering the dark room 2. On the other hand, an optical base 6 and a circuit board 5 are housed in the body 10. The circuit board 5 is arranged along the inner bottom surface of the body 1o, and the optical base 6 is arranged on one surface of the body 10 opposite to the inner bottom surface with respect to the circuit board 5. An integrated circuit 4a is mounted on the circuit board 5, and this integrated circuit 4a
The light receiving element 4, which is made of a photodiode,
A smoke detection circuit that detects the presence or absence of smoke particles in the dark room 2 based on the output of the light receiving element 4, a drive circuit that drives the light projecting element 3, and a power supply circuit are incorporated. The smoke detection circuit includes an analog signal processing circuit that processes the output of the light receiving element 4, and a digital circuit that controls the switching circuit based on the output of the analog signal processing circuit. That is, this integrated circuit 4a incorporates all the circuits necessary for the smoke detector, except for parts that cannot be incorporated into the integrated circuit 4a or those that are not desirable to be incorporated into the integrated circuit 4a. The circuit board 5 includes a light emitting element 3 made of a light emitting diode,
Variable for adjusting the sensitivity of surge protection element ZNR2
Resistor VR and capacitor C are also mounted. The light projecting element 3 is a chip component and is surface mounted on a circuit board. The light projecting element 3 and the light receiving element 4 are mounted so that their optical axes are perpendicular to the surface of the circuit board 5. On the optical base 6, a light projecting mirror 8 is mounted at a position corresponding to the light projecting element 3, and a light receiving mirror 7 is mounted at a position corresponding to the light receiving element 4. Further, in the optical base 6, a light shielding protrusion 6 is provided between the light emitting mirror 8 and the light receiving mirror 7 in order to prevent the incident light from directly entering the light receiving mirror 7.
A is provided protrudingly. The light-receiving mirror 7 is a reflective surface 7 that reflects and deflects scattered light from smoke particles incident on the incident surface 7a, similar to the conventional configuration.
C and the light beam deflected by the reflecting surface 7C, the light receiving element 4
A lens surface 7b for converging light is integrally formed of a transparent material such as acrylic or polycarbonate. The entrance surface 7a is a plane, and the positional relationship is set such that the normal line of the entrance surface 7a and the optical axis of the lens surface 7b are substantially orthogonal. Further, the reflective surface 7c deflects the light beam using total reflection, and the smoke monitoring area (
The angle is set so that only the light rays in the same direction as the light scattered by smoke particles from the area where the light beam from the light projecting element 3 and the field of view of the light receiving element 4 overlap are incident on the light receiving element 4. As shown in FIG. 3, the light projection mirror 8 has an entrance surface 8a that forms part of a spherical surface equidistant from the light emission center of the light projection element 3, and an exit surface 8b that is a plane inclined with respect to the circuit board 5. The reflecting surface 8C, which deflects the light beam incident from the entrance surface 8a so as to exit from the exit surface 8b, is formed to be a paraboloid of rotation as shown by the broken line in FIG. 3(a). . Here, a reflective layer 8d made of a vapor-deposited aluminum film or the like is formed on the reflective surface 8c. Further, the light projecting mirror 8 is arranged so that the light emitting center of the light projecting element 3 is located at or near the focal point of the reflecting surface 8c. The reason why the entrance surface 8a is formed as a part of a spherical surface is because
This is to make it easier to manage the traveling direction of the light rays incident on the light projecting mirror 8 from the light projecting element 3. A light shielding wall 6b is formed on the optical base 6 in correspondence with the incident surface 8a of the light projecting mirror 8, and removes the light beams from the light projecting element 3 that do not reach the reflecting surface 8c, thereby preventing the generation of stray light. It's like preventing. Although configured as described above, when smoke particles are introduced into the dark room 2 from the outer peripheral surface of the labyrinth body 20, scattered light is generated in the smoke monitoring area in the dark room 2, and the light receiving element 4 detects this. Then, a smoke detection signal is output from the integrated circuit 4a. Moreover, since the light receiving element 4 is incorporated into the integrated circuit 4a together with the smoke detection circuit, it is less susceptible to the influence of external noise, and the signal-to-noise ratio can be improved. Furthermore, by using the light emitting mirror 8, the distance between the light emitting element 3 and the light receiving element 4 can be reduced, and the light emitting element 3 can be moved to the optical base 6 as in the conventional case.
Compared to the case where the housing 1 is attached to the housing 1, the structure of the light projecting portion can be made smaller as a whole (at least the lead wire is no longer required), so the housing 1 can be made smaller. Moreover, despite its small size, it is possible to prevent the light rays projected into the dark room 2 from directly entering the light receiving mirror 7 (see the light rays indicated by broken lines in FIG. 1). As a result, the difference in the output level of the light receiving element 4 (signal-to-noise ratio) between when the scattered light is not received and when the scattered light is received is increased, thereby increasing the detection sensitivity of smoke particles and suppressing fluctuations in detection accuracy. This reduces false alarms and missed alarms.

【Effect of the invention】

As described above, the present invention provides an optical system in which a light emitting element and a light receiving element are mounted on one surface of a circuit board so that the optical axis thereof faces in a direction substantially perpendicular to the surface of the circuit board, and an optical A light projecting mirror that deflects the light from the light projecting element so as to be incident on the smoke monitoring area at a predetermined angle, and a light receiving mirror that deflects the scattered light from the smoke monitoring area in a direction that makes it enter the light receiving element. Since the light emitting element is attached to the smoke monitoring area, the light entering the smoke monitoring area from the smoke monitoring area and the light entering the light receiving element from the smoke monitoring area are deflected by the emitting mirror and the light receiving mirror, respectively. The distance between the device and the circuit board can be set small, and while the positional relationship is set so that the light emitted from the emitter mirror does not directly enter the receiver mirror, the housing can be made smaller than before. This has the effect of being able to be made smaller. As a result, even though the housing is small, it is possible to reduce stray light, reduce fluctuations in smoke particle detection accuracy, and increase the amount of light scattered by smoke particles that enters the photodetector. Therefore, there is an advantage that a smoke detector with high detection sensitivity and less false alarms and missed alarms can be provided.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a bottom view showing the same with the cover removed, and Figs. 3 (a) and (b).
4 is a cross-sectional view and a front view showing a light projecting mirror used in the above, respectively, and FIG. 4 is a cross-sectional view showing a conventional example. 1...Housing, 2...Darkroom, 3...Light emitting element, 4
...Light emitting element, 5...Circuit board, 6...Optical base, 7...Light receiving mirror, 8...Light emitting mirror. Agent Patent Attorney Ishi 1) Chief 7 Figure 2 Figure 3 (a) b

Claims (1)

[Claims] (1) The smoke monitoring area set inside the housing is irradiated with incident light from the light emitting element, the light scattered by smoke particles with respect to this incident light is detected by the light receiving element, and the smoke monitoring area is detected based on the change in the output of the light receiving element. In a photoelectric smoke detector designed to detect It has an optical axis, and an optical base is disposed at a fixed position on the one side of the circuit board, and the optical base deflects the light from the light projecting element so as to enter the smoke monitoring area at a predetermined angle. A photoelectric smoke detector comprising a light projecting mirror and a light receiving mirror that deflects scattered light from a smoke monitoring area in a direction in which it enters a light receiving element.