Passive infrared detector

Details Passive infrared detector Passive infrared detector

1999-07-27

2001-05-29

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S342000, C250SDIG001, C340S567000

Reexamination Certificate

active

06239437

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved wide angle passive infrared system for detecting the presence of an infrared source and/or the presence of an infrared source entering, exiting or moving within a specific angular field of view and range.
2. Description of the Related Art
Motion detectors, intrusion alarms, occupancy sensors and other passive infrared radiation detection systems employ an infrared lens-detector system with an electrical output signal which varies by a measurable amount as a source of infrared radiation enters, exits or moves within its angular field of view and range. The detector output electrical signal is amplified and employed, for example, to activate an alarm, switch or other control system. The lens-detector system consists of a one or two-dimensional array of Fresnel lenses on a thin strip or sheet each of which focuses incident infrared radiation in a specific angular range onto a sensitive area of a detector. In the prior art a wide angular field of view is achieved by employing an array of Fresnel lenses on a strip or sheet which protrudes from the front surface of the unit. The protruding sectors collect infrared radiation from peripheral angles.
FIG. 1
is a schematic of the configuration of the lens-detector system for motion detectors, intrusion alarms, occupancy sensors and similar systems according to the prior art. A thin, segmented strip or sheet forming an array
10
covers the entrance aperture and extends to the exterior of the lens-detector system; i.e. exterior to the housing
12
. A section of a Fresnel lens
14
is molded or cut into each sector of the strip or sheet. In the schematic twelve sectors are indicated. Each individual Fresnel lens focuses incident infrared radiation at some angle onto one edge of a sensitive area of a detector. For example, the Fresnel lens
14
focuses the beam of infrared radiation indicated onto a sensitive area
16
of a detector
18
.
As the angle
20
increases the focal spot moves across the sensitive area
16
of the detector
18
and eventually moves off the opposite edge of the sensitive area
16
. The change in the electrical output signal of the detector
18
as a focal spot moves on or off the sensitive area
16
is interpreted as an infrared source moving across one of the critical angles for which the focal spot is on the edge of the sensitive area
16
of the detector
18
.
For a single infrared source within the overall field of view of the lens strip or sheet
10
there is a multiplicity of focal spots which move across the sensitive area
16
of the detector
18
as the source moves through the overall field of view of the system. An example of this is illustrated in the schematic of FIG.
2
. Incident infrared radiation from the enclosed angular ranges
22
, for example, is focused onto the corresponding sensitive area
16
of at least one detector
18
by one sector of the Fresnel lens array
10
. Infrared radiation incident from the open angular ranges
24
, for example, does not lead to a focal spot on a sensitive area of any detector. Thus the intensity of radiation on a sensitive area of one of the detectors will vary significantly as the infrared source moves into or out of one of the enclosed angular ranges. The resulting detector output signal is processed electronically to activate an alarm, switch or other control system.
The configuration of the Fresnel lens to be exterior to the housing allows radiation detection systems of the prior art to detect radiation over a wide range of angles of incidence
20
, including low angles such as angles less than about 30°. The angle of incidence
20
is measured relative to the exposed surface. Heretofore, such exterior positioning of the Fresnel lens may not be aesthetically appealing, and further may be suspectable to damage as well as accidents or injury. For example, a detector positioned for detecting people may be brushed against or otherwise contact such people, including children. As such, the exterior Fresnel lens may cause harm to such people.
In the prior art, the positioning of the Fresnel lens or other mechanisms internal to a housing may be more aesthetically pleasing and less susceptible to damage and injury, but such internal configurations heretofore reduce the range of detection, in which low angles of incidence
20
less than, for example, about 30° are not detectable.
SUMMARY OF THE INVENTION
Wide angle motion detectors, intrusion alarms, occupancy sensors and other passive infrared detection systems would be aesthetically more pleasing and less intrusive if the face of the unit was flat or nearly flat, while allowing for the detection of radiation having low angles of incidence, such as peripheral angles of less than about 30°. This would greatly enhance the value of these units in some installations. Also, sensitivity, range, angular field of view, angular resolution and other measures of performance can be improved over that of the prior art by employing larger or multiple infrared input windows which do not protrude and hence do not degrade the appearance of the unit or interfere with other functions.
A wide angle passive infrared motion detector with a flat or nearly flat front surface can be achieved by inverting the Fresnel lens array across the plane of the input aperture and/or employing input optical elements to direct and/or focus incident infrared radiation onto one or more internal Fresnel lens arrays or a sensitive area of a detector. The Fresnel lens arrays are totally within the unit but nevertheless collect, or by employing appropriate input optical elements can be made to collect, sufficient infrared radiation from peripheral angles to be useful. Each sector of the internal Fresnel lens array focuses a specific angular range of the incident infrared radiation onto one or more of the sensitive areas of one or more detectors. In order to increase the collecting power of the system and reduce the required width of the unit curved mirrors, lenses or prisms can be employed to direct and/or focus the incident infrared radiation onto an internal Fresnel lens array and/or a sensitive area of a detector.
In one embodiment of the invention one or more prisms which span the entire or almost the entire entrance aperture are employed to direct incident infrared radiation from peripheral angles towards the center of the unit. The orientation of the exit faces of the prism set can be chosen in such a way as to direct and/or focus the infrared radiation onto an appropriate sector of one or more conveniently placed internal Fresnel lens arrays and/or a sensitive area of a detector.


REFERENCES:
patent: 3036219 (1962-05-01), Thompson
patent: 3524180 (1970-08-01), Cruse
patent: 3631434 (1971-12-01), Schwarz
patent: 3703718 (1972-11-01), Berman
patent: 3886360 (1975-05-01), Reiss et al.
patent: 3958118 (1976-05-01), Schwarz
patent: 4321594 (1982-03-01), Galvin et al.
patent: 4342987 (1982-08-01), Rossin
patent: 4404468 (1983-09-01), Kleinschmidt
patent: 4420688 (1983-12-01), Le Bars
patent: 4429223 (1984-01-01), Wagli
patent: 4429224 (1984-01-01), Wägli et al.
patent: 4442359 (1984-04-01), Lederer
patent: 4717821 (1988-01-01), Messiou
patent: 4768020 (1988-08-01), Chen
patent: 4876445 (1989-10-01), McMaster
patent: 4912331 (1990-03-01), Owers
patent: 4978843 (1990-12-01), Yamakawa
patent: 5266807 (1993-11-01), Neiger
patent: 5491467 (1996-02-01), Tracy et al.
patent: 5929445 (1999-07-01), Barone
patent: 3615946 A1 (1987-11-01), None
patent: 87 12 893 (1988-01-01), None
patent: 3803277 A1 (1989-08-01), None
patent: 38 03 277 (A1) (1989-08-01), None
patent: 3906761 A1 (1989-09-01), None
patent: 0 050 750 (1982-05-01), None
patent: 0 050 751 (1982-05-01), None
patent: 0 256 651 (1988-02-01), None
patent: 0 358 929 (1990-03-01), None
patent: 54 998 (1979-01-01), None
patent: 54-998 (1979-01-01), None
patent: 3 95480 (1991-04-01), None
patent: WO 92/10819 (1992-06-01), None

Affiliated with

Also associated with

Rating

Passive infrared detector does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Passive infrared detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Passive infrared detector will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2524334