Fire detector unit

• US 20020154018A1
• Filed: 01/09/2002
• Published: 10/24/2002
• Est. Priority Date: 04/24/2001
• Status: Active Grant

• Current Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Toyoda, Kenji, Nagasawa, Naoya, Sakamoto, Koji, Wada, Takeshi, Nishikawa, Takayuki, Kirihata, Shinji, Kawano, Yasuyuki, Oka, Shoichi
• Granted Patent: US 6,737,977 B2
• Time in Patent Office: Days
• US Class Current: 340/630
• CPC Class Codes: G08B 17/06 Electric actuation of the alarm, e.g. using a thermally-operated switch
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details
• CPC Class Codes: G08B 29/183 Single detectors using dual technologies G08B13/1672, G08B13/2448, G08B13/2494 take precedence

Abstract

An improved fire detector unit has a plastic base defining a smoke chamber for detection of a smoke density in terms of light scattering due to the smoke particles in the smoke chamber. The base carries a circuit board mounting a light emitting element, a light receiving element, and other components forming a fire detecting circuit responsible for generating a fire warning signal based upon the detected smoke density. A metal-made electromagnetic shield is molded into the base to protect the light receiving element from electromagnetic radiation noises. The electromagnetic shield includes a ground terminal for connection with a ground line of the circuit board. In addition, terminal pins are molded into the base for electrical and physical connection of the circuit board to the base.

Claims

1. A fire detector unit comprising:

a base made of a molded plastic to have a labyrinth wall which projects on the circumference of said base to define therein a smoke chamber, said labyrinth wall permitting an entry of smoke particles but prohibiting the entry of an ambient light into said smoke chamber;

a light projector carried on said base and directing an incident light from a light emitting element into said smoke chamber;

a light collector carried on said base and collecting a light scattered by the smoke particles in said smoke chamber to a light receiving element, said light receiving element generating an electric signal indicative of the amount of the light received;

a fire detecting circuit being connected to receive said electric signal so as to provide a fire warning signal based upon said electric signal; and

a circuit board mounting said light emitting element, said light receiving element, and electronic components forming said fire detecting circuit;

a metal-made electromagnetic shield which protects said light receiving element from electromagnetic radiation noises;

wherein

said electromagnetic shield is integrally molded into said base and has a ground terminal for connection with a ground line of said circuit board,

said circuit board being fixed to said base by means of metal-made terminal pins which are integrally molded into said base and are electrically connected to said fire detecting circuit, said terminal pins projecting through the circuit board for connection with an external line so as to transmit said fire warning signal.

2. The fire detector unit as set forth in claim 1, wherein

said labyrinth wall is molded together with said base to form a unitary structure in which said electromagnetic shield is embedded.

3. The fire detector unit as set forth in claim 1, wherein

said electromagnetic shield and said terminal pins are prepared from a single metal sheet by striking the metal sheet and bending struck portions thereof.

4. The fire detector unit as set forth in claim 1, further including

an insect deterring cover molded from a plastic material to have a side wall and a bottom wall, said side wall being in the form of a screen which surrounds said labyrinth wall so as to prevent flying insects or the like foreign matters from entering said smoke chamber, and has a number of air vents permitting the entry of the smoke particles into the smoke chamber through said labyrinth wall, said bottom wall covering an open bottom of said base to close said smoke chamber,

the bottom wall of said cover being formed on its interior surface with first and second masks respectively for making said light projector intact from a light not coming directly from said light emitting element and making the light collector intact from a scattered light not due to the presence of the smoke particles.

5. The fire detector unit as set forth in claim 4, wherein

the side wall of said insect deterring cover is formed with at least one blind section devoid of said air vents, said blind section extending over a limited circumferential portion of said labyrinth wall in an immediately opposed relation to one of said light projector and said light collector,

the air vents on opposite of said blind section being so oriented as to direct the ambient air towards said labyrinth wall along a direction generally parallel to a line connecting said blind section to a geometric center of said base.

6. The fire detector as set forth in claim 1, wherein

said labyrinth wall comprises a plurality of L-shaped studs each having an outside corner and an inside corner, said L-shaped studs being arranged circumferentially around said base in such a manner that the outside corner of the L-shaped stud projects into the inside corner of the adjacent L-shaped stud,

two said L-shaped studs disposed forwardly of the light collector along an optical axis of the light collector being joined at the outside corners to form a combined stud of a generally X-shaped configuration.

7. The fire detector as set forth in claim 6, wherein

said combined stud gives a light trap in the form of a V-shaped recess which opposes to said light collector with respect to the optical axis thereof, said light trap preventing the incident light from reflecting towards the light collector.

8. The fire detector as set forth in claim 7, wherein

the V-shaped recess of said light trap is defined by a pair of first and second legs each being a part of said combined stud with the first leg located closer towards said light projector than the second leg,

said light trap including a shield ledge projecting from said first leg and a concave at the bottom of the recess, said concave being hidden behind said shield ledge from said light projector.

9. The fire detector as set forth in claim 7, wherein

said light trap includes a reflecting section in the form of a serration which is opposed to said light collector and is configured to reflect the incident light deep into said V-shaped recess away from said light collector.

10. The fire detector as set forth in claim 7, wherein

said base includes a shielding post projecting at a location between said light trap and said light projector in a spaced relation respectively therefrom for interruption of the light from said light projector towards said light trap.

11. The fire detector as set forth in claim 10, wherein

said shielding post is located outside of an incident angle of said light collector.

12. The fire detector as set forth in claim 1, wherein

said circuit board is fixed to said base with the individual optical axes of said light emitting element and said light receiving element being generally perpendicular to a plane of the base,

said light projector having a light projecting axis (PX) which extends within the smoke chamber in parallel with a plane of said base,

said light collector having a light collecting axis (CX) which extends within the smoke chamber in parallel with the plane of said base and crosses with said light projecting axis,

said light projector forming a first light guide which changes the direction of the light beam from said light emitting element to direct it along the light projecting axis, and

said light collector forming a second light guide which changes the direction of the light collected along the light collecting axis (CX) to direct it along the optical axis of said light receiving element.

13. The fire detector as set forth in claim 12, wherein

said light projector and said light collector are each in the form of an optical prism.

14. The fire detector as set forth in claim 13, wherein

the optical prism defining said light collector includes an integrally formed converging lens which converges the collected light towards the light receiving element.