Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1982-09-14
1985-04-30
Smith, Alfred E.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
250353, G08B 1318, G01J 508
Patent
active
045146306
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical system of a device for detecting intruders which makes use of a straight beam of light or infrared rays.
BACKGROUND ART
Presently known intruder detectors making use of a straight beam of light or infrared rays generally utilize a parabolic mirror as an optical element to increase the density of a collected beam in a projecting or an accepting direction, the focal position of the mirror being occupied by a photo-electric transducer.
A passive type intruder detector compares infrared energy radiated from an intruder's body with infrared energy radiated from a background material object and generates an output signal when there is a difference above a predetermined level. An intruder detecting device of this type is disclosed in Japanese Laid-Open Utility Model Publication No. 97,534 of 1980 and Japanese Laid-Open Patent Publication No. 143,694 of 1980. Because the visual field of this infrared detector is a maximum angle of 90 degress, any extension of a detecting region beyond said visual field is dependent upon the optical elements in the system. In the device disclosed by said Laid-Open Patent Publication No. 143,694 of 1980, the sensing region may be extended to an angle of approximately 180 degrees by combining a parabolic mirror with an alignment structure of plane mirrors. However, where the device is mounted on the ceiling of a structure, the device has no sensitivity in the backward direction or generally in the downward direction. It should also be noted that the alignment structure of the plane mirrors is arranged into steps of mirrors, and therefore, it is different to incline each of the divided plane mirrors with respect to the optical axis of the parabolic mirror so as to obtain a larger number of directions sensitive to intruders, and to equalize all the effective projecting areas of the divided mirrors onto the parabolic mirror. Another difficult problem in the prior device is that each of the outer distributed plane mirrors cannot project their whole mirror surface onto the parabolic mirror, and therefore a substantial difference exists between the sensitivity of the inner and the outer mirrors.
It is an object of the invention to solve the above technical problems by providing a simply constructed optical system for an intruder detector in which the detecting region expands an angle of 360 degrees, and in which no substantial difference in sensitivity is present for the various detecting directions.
DISCLOSURE OF THE INVENTION
To achieve the above object of the invention, an infrared ray detecting element is disposed at the focal position of a parabolic mirror. Facing the parabolic mirror is a conical reflecting mirror which is disposed in such a manner that it surrounds the infrared detecting element so that its visual field covers the periphery of the parabolic mirror. The reflecting mirror is comprised of a plurality of divided mirror elements. Each of the mirror elements is directed to a particular detecting region so that all the mirror elements together cover a detecting field having an angle of 360 degrees around the infrared detecting element. If the angle of inclination of each mirror element with respect to the optical axis of the parabolic mirror is modified, the angular extent of the detecting field may be varied. Perforated through the central portion of the parabolic mirror, perpendicular to its optical axis, is an opening having an inner diameter substantially the same as the outer diameter of the infrared detecting element. A convex lens mounted in the opening is focused on the activation surface of the infrared detecting element. The parabolic mirror is mounted to a base member through a cylindrical window member which is transparent to infrared rays. An optical masking plate is provided with a plurality of slits each corresponding to one of the gaps between adjacent divided mirrors. The masking plate is disposed in a fixed position between the parabolic mirror and the reflecting mirror to allow the slit portions
REFERENCES:
patent: 1818120 (1931-08-01), Doane
patent: 3551676 (1970-12-01), Runnels
patent: 3984178 (1976-10-01), Bergqvist
patent: 4258255 (1981-03-01), Guscott
patent: 4271360 (1981-06-01), Ward
Hannaher Constantine
Smith Alfred E.
Takenaka Engineering Co. Ltd.
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