Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-02-28
2001-08-07
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S627000, C356S338000, C356S438000
Reexamination Certificate
active
06271758
ABSTRACT:
TECHNICAL FIELD
The invention relates to a light projection device for a photoelectric smoke sensor in which a light beam is emitted into a monitored space and a fire is detected on the basis of attenuation of light due to smoke entering the monitored space, and particularly to a light projection device for a photoelectric smoke sensor in which the intensity distribution of a light beam is uniformalized.
BACKGROUND ART
Conventionally, in a smoke sensor of the reflection type which is used for performing fire monitoring in a wide area, a reflector plate is opposed to a smoke sensor main unit having a light projection device and a light reception device, being separated from the main unit by a predetermined monitored distance, for example, several tens of meters. A fire is detected on the basis of attenuation of light received from the light projection device which is caused by smoke entering the monitored space.
In this case, for example, a near infrared LED is used as a light emitting element for the light projection device. Light emitted from the near infrared LED is converged into beam light by a condenser lens. The beam light impinges on the reflector plate which is opposed to the light projection device being separated therefrom by the predetermined monitored distance, and is reflected thereby. The reflected light impinges on the light reception device, and a fire is detected on the basis of light attenuation due to smoke entering the monitored space.
In such a smoke sensor of the reflection type, the light projection device converts light from the near infrared LED into parallel beam light by using the condenser lens, and then emits the light into the monitored space. The beam light from the light projection device makes a round trip from the main unit and the reflector plate, and then impinges on the light reception device. In the case where the monitored distance between the light projection device and the reflector plate is as long as, for example, 40 meters, when the beam light reaches the reflector plate, the beam image is largely expanded by light diffusion. When the light reflected by the reflector plate returns to the light reception device, similarly, the beam image is largely diffused. Therefore, the light reception device can detect only a very small portion of the energy of the emitted light beam.
It has been reported that, even after a device is installed, a side wall of a building undergoes little temporal distortion. If the light intensity distribution in a section of the beam is not uniform, when a portion of a low light intensity is caused to impinge on the reflector plate by the distortion of the side wall, the light reception signal which is generated in the case where no smoke exists is very weak in level, with the result that a sufficient S/N ratio cannot be obtained. Furthermore, there arises a problem in that the maximum monitorable distance is shortened. Therefore, it is preferable that the light intensity distribution in a section perpendicular to the optical axis of beam light is made as uniform as possible.
In order to solve the problem of the nonuniform intensity distribution of beam light, for example, a light projector shown in
FIG. 9
has been proposed (Japanese patent publication (Kokai) No. HEI5-79979). Referring to
FIG. 9
, light from a light emitting diode
105
in the light projector is introduced into a waveguide
103
by an imaging lens
104
, so as to propagate in the waveguide
103
, whereby the energy distribution is uniformalized. Light emitted from the end face of the waveguide
103
is imaged at a distant position by a projection lens
102
.
In the structure of such a light projector which uniformalizes the energy distribution of a projection beam, the imaging lens, the waveguide, and the projection lens must be arranged in front of the light emitting diode. Therefore, the optical system for uniformalization is relatively complex, and the dimension in the optical axis direction is increased. As a result, the structure has a disadvantage that the light projector is bulky.
The invention has been conducted in view of the problems of the prior art. It is an object of the invention to provide a light projection device for a photoelectric smoke sensor in which beam light from a light emitting diode can be uniformalized in a beam section direction by a simple optical structure so as to compensate an optical axis deviation.
DISCLOSURE OF INVENTION
The invention relates to a light projection device for a photoelectric smoke sensor in which beam light is emitted into a monitored space and a fire is detected by receiving the beam light which is attenuated by smoke entering the monitored space, wherein the device comprises a light emitting diode and a condenser lens which are arranged in an optical axis direction, and the light emitting diode comprises: a main unit base; a cylindrical cover which is attached to a tip end of the main unit base and in which a lens is integrally disposed; a light emitting chip which is placed at a predetermined position inside the cover; a bonding wire through which a lead wire passing through the main unit base is electrically connected with the light emitting chip; and a reflector which is placed behind the light emitting chip.
In the thus configured light projection device, the light emitting chip may be used as a first light source, the position where light which is forward reflected by the reflector. impinges on the lens at the tip end of the cover may be set as a virtual second light source, and a focal point of the condenser lens may be located at a position of the second light source.
The light emitting chip may be used as a first light source, the position where light which is forward reflected by the reflector impinges on the lens at the tip end of the cover may be set as a virtual second light source, and a focal point of the condenser lens may be located at a position in the vicinity of the second light source.
The light emitting chip may be used as a first light source, the position where light which is forward reflected by the reflector impinges on the lens at the tip end of the cover may be set as virtual second light source, and a focal point of the condenser lens may be set located a position separated from the second light source.
The focal point of the condenser lens may be located between the second light source and a lens vertex of the tip end of the cover.
The focal point of the condenser lens may be located between the second light source and a position of a tip end of a bent portion of the bonding wire which is electrically connected with the light emitting chip.
In such a configuration, light which is generated in the front face of the chip and emitted mainly from the center portion of the tip end lens is blurred, and the blurred light is combined with light which is generated in the rear face of the chip, reflected by the reflector and emitted mainly from the peripheral portion of the tip end lens, whereby the light intensity distribution (energy intensity distribution) in a beam section perpendicular to the optical axis of the composite light can be substantially uniformalized.
Since the optical system of the light projection device is composed of only two parts, i.e., the light emitting diode and the condenser lens, the light intensity distribution in a beam section can be uniformalized by a very simple optical structure.
The invention may be used in a photoelectric smoke sensor having a reflection type smoke detecting structure in which a smoke sensor main unit having a light projection device and a light reception device; and a reflector member for reflecting light from the light projection device to the light reception device are disposed through a monitored space of a predetermined monitored distance. It is a matter of course that the invention may be used in a separation type extinction smoke sensor in which a reflector plate is not used and a light projection device and a light reception device are opposed to each other through a monitored space.
The light emitting diode ma
Matsukuma Hidenari
Nakamura Masatoshi
Shima Hiroshi
Hochiki Corporation
La Anh
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wu Daniel J.
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