Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention broadly relates to a new and
improved construction of an apparatus for detecting and
evaluating infrared radiation.
In its more specific aspects the present invention
relates to a new and improved construction of an infrared
intrusion detector, comprising at least one aspherical optical
arrangement for bundling the infrared radiation from at least
one strip-shaped region or zone of incident radiation directed
onto a sensor, and further including an evaluating circuit
connected to the sensor for generating an output signal as a
function of a predetermined amount of radiation change at the
sensor.
In other words, the infrared intrusion detector of
the present invention is of the type comprising an infrared
sensor for sensing infrared radiation~ at least one
strip-shaped reception zone for receiving the infrared
radiation, at least one aspherical optical arrangement for
focusing the infrared radiation on the infrared sensor, and an
evaluation circuit connected to the infrared sensor for
emitting a signal in response to a predetermined alteration in
the irradiation of the infrared sensor by the infrared
radiation.
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Such intrusion detectors are known, for instance,
from United States Patent No. 4,058,726, granted November 15,
1977, or German Patent No. 2,645,040, granted October 9, 1981.
Figure 4 of each of these patents depicts an intrusion
detection apparatus. Strip-shaped sectorial zones of the field
of reception are formed by cylindrical lenses, one lens per
sector, arranged in front of a detector. This method is quite
suitable for keeping a room under surveillance by providing a
number of vertically oriented, parallel, flat field sectors or
zones, which will reliably trigger an alarm upon their being
crossed by an intruder.
Such known arrangements however, are limited in
effectiveness when employed in applications requiring a single
sector or zone, or sectors or zones not in close proximity with
each other, yet having accurately defined border lines, such as
required for protective curtains in front of openings, such as
doors or windows, or as "flat gates" in front of protected
objects. First of all, the vertical incidence angle is limited
by the housing, and virtually never approaches the nearly 90
required for a fully effective protective curtain.
Furthermore, only the center portion of the cylindrical lens
can provide proper focusing, since only in this particular
location does the sensor lie within the focal area. For
eccentrically incident radiation, the sensor lies outside the
focal area, resulting in a defocused or blurred image. As a
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result, offset or eccentric incident radiation produces
diffused border lines and, under extreme conditions, adjacent
areas are likely to stray into the neighboring reception zone,
so that efficient protection becomes impossible.
A further disadvantage lies in the increasing
length of the optical path with increasing off-center or
eccentric orientation of the incident angle inherent in
cylindrical lenses. Since the far infrared absorption of the
material of the lens is no longer negligible for instance in
the 10~ range (peak body radiation of humans), radiation
attenuation becomes more pronounced with increasing off-center
or eccentric orientation of the incident radiation. Such an
intrusion detector therefore loses sensitivity with increasing
scope of the incident angle, and thus further limits the
usefulness of such an arrangement for a protective curtain type
application.
The intrusion detector described in U.S. Patent No.
4,375,034, granted February 22, 1983 for one or more receiving
regions or zones, shows an arrangement with improved borderline
definition and increased aperture or reception angle. It
includes a spherical reflector, comprising a special
arrangement of one or more cylindrical reflectors. This
requires a complicated optical arrangement, with precise
adjustment of reflectors with respect to each other, and this
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precise adjustment must be maintained throughout the lifetime
of the apparatus (i.e., many years). Furthermore, reflector
surfaces tena to age, and become soiled in time, causing a
progressive loss of reflectivity together with increased
scattering, so that the sensitivity, efficiency and operational
reliability of this type detector steadily decrease.
SUM~RY OF THE INVENTION
Therefore, with the foregoing in mind, it is a
primary object of the present invention to provide a new and
improved construction of an intrusion detecting apparatus which
does not exhibit the aforementioned drawbacks and shortcomings
of prior art constructions.
A further significant object of the present
invention is to provide a new and improved construction of an
infrared intrusion detecting apparatus for forming a protective
curtain, comprising at least one strip-shaped reception zone of
wide incident angle with closely defined zonal border lines,
and substantially uniform radiation sensitivity across the
entire aperture or field of protection defined by the Fresnel
lens.
Yet another noteworthy object of the invention is
to provide a new and improved construction of an apparatus for
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intrusion detection, as described hereinbefore, which apparatus
comprises a minimum of optical elements, in an efficient,
reliable arrangement, so as to assure long term operational
sensitivity, efficiency, and reliability.
Now in order to implement these and still further
objects of the invention, which will become more readily
apparent as the description proceeds, the intrusion detecting
apparatus of the present invention is manifested by the
features that the optical arrangement comprises at least one
substantially cylindrical Fresnel lens, which in its
longitudinal axis or direction defines an arc sector whose
radius is determined by its focal length, and wherein the
sensor is arranged at least in close proximity to the circle
center point, i.e., the focal point of the cylindrical Fresnel
lens.
In other words, the infrared intrusion detector
of the present invention is manifested by the features that
the at least one aspherical optical arrangement comprises at
least one substantially cylindrical Fresnel lens having a
longitudinal axis, a focal point and a focal length and
the lens being curved about or along an axis perpendicular
to the longitudinal axis to form a sector of a circle
having a center point. The sector of the circle has a radius
corresponding to the focal length and the infrared sensor is
Sa~ 2
arranged at least approximately in the center point and in the
focal point.
In accordance with the aforementioned
characteristics it is possible to improve the performance of
the apparatus with respect to the quality of the optical image,
thus providing improved borderline definitions of the reception
area or zone, as well as the radiation absorption, while
rendering the sensitivity of the detector independent of the
incident angle of radiation, thus making such a detector
particularly suitable for generating a flat field-type
protective curtain with a wide incident or aperture angle.
Furthermore, only a single, easily mountable optical element is
needed.
It is of particular advantage to construct the
infrared sensor element as a dual sensor element, which can be
incorporated in a differential circuit arrangement. A double
curtain arrangement with two receiving areas can thus be
constructed, by means of a circular Fresnel lens, providing
particularly interference-resistant and selective detection of
trespassing or intrusion attempts.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects
other than those set forth above will become apparent when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed
drawings wherein throughout the various figures of the drawings
there have been generally used the same reference characters to
denote the same or analogous components and wherein:
Figure 1 shows a first intrusion detection
apparatus in a perspective view; and
Figure 2 shows a second intrusion detection
apparatus in a horizontal cross-section, and a possible
positioning concept.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, it is to be
understood, that to simplify the showing thereof, only enough
of the structure of the infrared intrusion detection apparatus
has been illustrated herein, as is needed to enable one skilled
in the art to readily understand the underlying principles and
concepts of the present invention. Turning now specifically to
Figure 1 of the drawings, the infrared intrusion detector
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apparatus illustrated therein by way of example and not
limitation will be seen to comprise an infrared intrusion
detecting apparatus designated in its entirety with the
reference numeral 1', comprising a housing 1, in which is
arranged an infrared sensor 2, of which the peak sensitivity
preferably lies within the radiation spectrum of the human
body. e.g., within the range of 5...15 ~m and preferably in the
neighborhood of 10 ~m. The sensor 2 therefore may be
constructed as a pyroelectric detector. The sensor 2 may be
constructed as a single sensor possessing only one zone for
radiation reception, whenever only one single reception area or
zone is required for forming a single protecti~.~e curtain, or it
may be constructed in the form depicted in Figure 1, as a
double sensor construction, with two adjacent sensor elements 3
and 4, which are responsive to two adjacent detecting or
receiving zones or areas E3 and E4 functioning as protective
curtains. The sensor elements 3 and 4 may each have an
orientation extending in the longitudinal direction of the
detector or detecting apparatus 1'.
For this purpose the front side of the housing 1
comprises an optical arrangement comprising a substantially
cylindrical Fresnel lens 8. In a practical embodiment the
cylindrical Fresnel lens 8 has, in transverse orienta~ion, a
predetermined focal leng~h defining a transverse axis with
respect to its structure, and comprises numerous characteristic
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grooves 5. The optical thickness of the Fresnel lens 8 across
its entire width is limited to a predetermined maximum value,
and the transverse axis is preferably horizontally oriented.
Normally, no focusing takes place in the longitudinal
direction, which in practice is usually vertically oriented.
That is, focusing of the cylindrical Fresnel lens 8 has in
effect the characteristic of a cylindrical lens, focusable only
in the transverse direction, but without any further focusing
or refractive properties for rays. By constructing the
cylindrical Fresnel lens 8 as a cylindrical Fresnel lens with
uniform, limited thickness, lengthwise as well as transversely,
its flexibility and stability surpasses by far properties
commonly achieved with massive lens structures. This makes
feasible a practical construction in which the cylindrical
Fresnel lens, in the form of a sector of an arc, can be
arranged at the front section of the housing 1, with the center
portion or mid-region of the cylindrical Fresnel lens 8
protruding from the housing front side or wall. The open sides
of the Fresnel lens 8 can be obturated by shields 6, as
depicted in this practical example. The radius r of the
curvature of the Fresnel lens 8 is chosen to correspond as
closely as possible to the transverse focal length, so that the
sensor 2 is located closely to the center of the circle, thus
within th~e focal point, so that the distance of the sensox 2
from the lens 8 remains independent of the incident angle of
reception, remaining at a focal distance equal to the focal
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length in transverse direction. In order to obtain an optimal
effect, the arc of the cylindrical Fresnel lens 8 should have a
lengthwise radius r of curvature corresponding as closely as
possible to the value of the transverse focal length, and the
sensor should be located as closely as possible to the center
or focal point.
The outstanding features of this invention permit
the construction of an apparatus for producing a uniform, high
quality optical image, valid for the full range of the usable
incident angles, across the entire vertical input or reception
aperture. Thus, the reception zones or areas achieved
therewith are uniformly and precisely defined over the entire
reception or lens aperture, and permit establishing a
protective curtain with Pqual sensitivity over the entire
reception or lens aperture. In addition to the aforementioned
features, the optical path, as well as the radiation absorption
of the lens are not influenced by the incident angle, so that
no reduction of sensitivity is caused by increasing the width
of this incident angle. Furthermore, the curvature of the
Fresnel lens permits the construction of a housing with lower
depth, and also permits placing the sensor closer to the front
end of the housing, thus allowing a usable incident angle of up
to 90. These advantages can even be obtained with a single,
robust, and easily mountable optical element.
54~132
The detector arrangement described can be
implemented with one single sensor for forming only one, single
receiving zone or area, i.e., one single, protective or
evaluated curtain. The sensor output signal can be processed
in accordance with conventiona~ state-of-the-art methods, e.g.
as described in the United 5tates Patent No. 3,703,718, granted
November 21, 1972. When using a dual sensor arrangement
comprising two separate sensor elements for establishing a
double curtain configuration and forming two adjoining
reception areas or zones in close proximity to each other, it
can be advantageous to connect the sensors to a differential
circuit 7 which in turn is connected to a known, particularly
selectively functioning evaluation or processing circuit
indicated in Figure l by reference character 50, e.g.
constructed according to the United States Patent No.
4,339,748, granted July 13, 1982 to which reference may be
readily had.
If desired, it is also feasible to incorporate
several Fresnel lenses within the same housing, in order to be
able to simultaneously monitor a number of reception areas or
zones. Figure 2 shows an embodiment of such a detector 10,
which is arranged in a corner location of a room to be
monitored for attempted intrusion, and which embodiment permits
the simult:aneous use of two reception areas or zones E3 and E4,
to simultaneously monitor for intrusion two walls 11 and 12 of
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this room comprising doors and windows. For this purpose, the
two reception areas or zones must form a horizontal angle of
approximately 90 with respect to each other. This is achieved
by incorporating within the housing 1 an infrared sensor
arrangement 2, comprising a first sensor element 3 and a second
sensor element 4 (dual sensor~ connected to a differential
circuit 7, in accordance with the example first described with
reference to Figure 1. In place of a single Fresnel lens, this
embodiment comprises two substantially cylindrical Fresnel
lenses, a first Fresnel lens 8 and a second Fresnel lens 8 ,
which are arranged one each at adjacent sides of the housing 1.
Both cylindrical Fresnel lenses 31 and 82 again are bent to a
circular curvature with a corresponding radius, as required by
their focal length, whereas both focal lengths may be chosen
equal, or may differ, to best match special practical
requirements, e.g. highly rectangular, i.e. long and narrow,
rooms. The arrangement of these two lenses 31 and 82 is such
that a first sensor element 3 lies within the focal point of
the first cylindrical Fresnel lens 81 and a second sensor
element 4 lies within the focal point of the second cylindrical
Fresnel lens 82. The first sensor element 3 thus picks up
radiation from the reception area or zone E3, while the second
sensor element 4 picks up radiation from the reception area or
zone E4. To protect the sensor elements 3 and 4 from
undesirable radiation, originating from outside the receiving
zones or areas, such as from non-associated reception zones or
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from irrelevant substantially cylindrical Fresnel lenses, an
aperture or radiation entry window 9 is arranged in front of
the sensor elements 3 and 4. By this method it is possible to
monitor simultaneously, with one detector, two wall surfaces or
zones forming an angle of approximately 90 with respect to
each other. A certain amount of flexibility and adjustability
of ihe angle between both reception areas or zones can be
achieved by arranging the first and second cylindrical Fresnel
lenses 81 and 82 on arc-shaped sections 13 and 14 which are
pivotably arranged at the sides of the walls of the housing 1,
whereas the sensor elements 3 and 4 are located within the
center point of the arc formed therewith. The sensor 2 or the
sensor elements 3 and 4 may be arranged to pivot along arcuate
segments of the substantially cylindrical Fresnel lens 8 or
lenses 81 and 82.
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