EP1184824B1 - Passive infrared detector - Google Patents

Abstract

A passive infrared sensor has sensors (S,S') with Fresnel lens focussing elements (An,An', Bm, Bm') for overlapping zones in front of the reflectors (R.R').

Description

The present invention relates to a passive infrared detector with heat-sensitive sensors and with a focusing elements having focusing device for bundling the from different monitoring areas on the detector falling heat rays on the Sensors.

Passive infrared detectors of this type have been known and widely used for years. They serve in particular to detect the presence or intrusion of unauthorized persons in one or a surveillance room by proof of the sent by these people typical infrared radiation, which is directed by the focusing on the sensor. As a focusing device either a Fresnel lens assembly is used, which in the the front of the detector housing integrated entrance window for the infrared radiation integrated is (see, for example, EP-A-0 559 110), or inside the detector housing arranged mirror consisting of individual reflectors (see, for example, EP-A-0 303 913).

Both the Fresnel lens arrangement and the mirror are designed so that the monitored Room with fan-shaped monitoring areas from the detector is. Once an object emitting heat radiation enters a surveillance area penetrates, the sensor detects the heat radiation emitted by this object, wherein the safest detection is when the object moves across the surveillance area.

EP-A-0 899 701 discloses a passive infrared detector of a first fixed detection system and a second, movable detection system and the detection the movement device of an object in the detection area allowed.

The passive infrared detectors of today's generation detect intruders within the Effective range of the detector very reliable, but provide no information about the position the burglar in the effective range. Although this is not for conventional, conventional applications required, but could be desirable for certain new applications.

Such a new application would be, for example, a passive infrared detector, in which individual Monitoring zones optionally, for example by an internal switch, active or inactive are adjustable. One could set up certain surveillance zones with such detectors during the day Visitor malfunction or alarm, ie active, and deactivate the remaining zones. Another Application possibility would be the monitoring of a room, such as the switch room a bank, with video cameras, the cameras store the images when the image processing this requires.

As is known, the cameras for monitoring a room have a large opening angle and therefore image quality is generally poor, it would be desirable to a camera with a narrow viewing angle and thus higher resolution or with zoom and to use these based on the signal of an infrared detector on the interested Align room area.

Previously proposed arrangements for detecting the position of an intruder use either a plurality of detector modules connected to a common computer (US-A-5 641 963), or a plurality of infrared sensors, each of the infrared sensors is provided for monitoring a specific room area. The different Spaces are discrete, separate areas. To reduce the number of required Sensors have been proposed in US-A-5,296,707, each of the infrared sensors not only to assign a discrete space area, but also a common overlap area provided. In this way, though with two infrared sensors three Spaces are monitored, but what a localization of a person in the room far from sufficient.

The invention will now be given a passive infrared detector, the low Extra effort the most accurate localization of an intruder in its effective range allows.

This object is achieved with a passive infrared detector of the type mentioned according to the invention achieved in that the focusing device for each monitoring area one of Number of sensors corresponding number of focusing elements, each of which each associated with a sensor so that each sensor has a pattern of surveillance areas has, that the mutually corresponding monitoring areas of the sensors each other overlap, and that each monitoring area of each sensor one unique identification the respective monitoring area enabling weighting is assigned.

If the number of infrared sensors and that provided for each monitoring area Focusing elements is equal to 2, and for example 3 different weighting levels used result in 7 clearly distinguishable directions and thus monitoring areas, their number increases to 37 with 3 infrared sensors and 3 weighting levels.

A first preferred embodiment of the inventive passive infrared detector is characterized characterized in that the mutually corresponding monitoring areas of the sensors overlap each other exactly.

A second preferred embodiment of the inventive passive infrared detector is characterized in that the weighting of the surveillance areas by a different optical aperture of the corresponding focusing takes place.

A third preferred embodiment of the inventive passive infrared detector is characterized in that the focusing device is formed by a mirror or Fresnel lens arrangement is formed, which from the individual focusing elements forming reflectors or Fresnel lenses exists.

A fourth preferred embodiment of the inventive passive infrared detector is characterized in that the weight of the reflectors by a change in reflectivity their reflective surfaces done.

In the Fresnel lenses, which are known to be integrated in a film, the weighting is done by a regional change in the thickness of this film.

Fig. 1

eine schematische Darstellung der Sensoren und der Fokussiereinrichtung eines erfindungsgemässen Passiv-Infrarotmelders,

Fig. 2

eine schematische Darstellung des mit der Fokussiereinrichtung von Fig. 1 erzeugten Überdeckungsmusters; und

Fig. 3

eine schematische Darstellung des Überdeckungsmusters eines mit 6 Sensoren ausgerüsteten, an einer Decke montierten Passiv-Infrarotmelders.

In the following the invention will be explained in more detail with reference to an embodiment shown in the drawings; it shows:

Fig. 1

a schematic representation of the sensors and the focusing device of a passive infrared detector according to the invention,

Fig. 2

a schematic representation of the overlay pattern generated with the focusing device of Figure 1; and

Fig. 3

a schematic representation of the overlap pattern of a equipped with 6 sensors, mounted on a ceiling passive infrared detector.

The detail shown in Fig. 1 Passive infrared detector contains two heat-sensitive Sensors S and S 'and a focusing device. The latter is by two conventional Mirror R, R 'are formed, each of which consists of a number of focusing elements or reflectors consists. The sensors S, S 'are, for example, pyrosensors or thermopile sensors (see EP-A-0 981 159). When in the following description of pyrosensors the Speech is, then that should not be understood as limiting. Of course, instead of The mirrors R, R 'also used a Fresnel lens arrangement, which is usually off Space and cost reasons will also be the case. The representation with the mirrors became out Chosen for clarity.

For example, as described in EP-A-0 303 913, the individual reflectors are each individual mirror designed so that the space to be monitored with outgoing from the detector Monitoring areas is fan-shaped covered, where corresponding to different Distances from the detector several such "fan areas" or surveillance zones are provided. For example, there are four monitoring zones, one remote zone, a middle zone, a near zone and a so-called look-down zone, separated by four in vertical Direction staggered rows of reflectors are covered.

These rows are at the mirror R the row containing the reflectors A _n for the far zone, the row containing the reflectors B _m for the middle zone, the row containing the reflectors C _k for the near zone and the row containing the reflector D for the look Down Zone.

The fan-shaped overlap is made by mutual displacement and rotation of the reflectors reached each row in the horizontal direction, wherein to achieve an approximately uniform Overlap pattern the number of reflectors per row with the distance of the respective monitoring zone of the detector increases.

Each reflector "looks" in the spatial direction of the corresponding zone, which receives from this Solid angle incident heat radiation and focuses these on the associated pyrosensor S or S '. Once an object emitting heat radiation enters a surveillance area penetrates, the sensor detects the heat radiation emitted by this object, whereupon the detector issues an alarm signal. This alarm signal indicates that a Object, such as an intruder, located in the interstitial space, but leaves none Conclusions about the exact position of the intruder in the interstitial space.

The previous information and considerations apply to a passive infrared detector with a single mirror R or R 'or with a Fresnel lens arrangement corresponding to such a mirror. If now several, as shown two, mirror R and R 'with several, are used according to two associated pyrosensors S and S ', is a Determination of the position of an intruder (so-called "tracking") possible, if one uses the Reflectors of each mirror and the pyrosensors combined so that a unique Identification of the azimuth of an intruder becomes possible.

FIG. 2 symbolically shows a detector with two pyrosensors S and S ', which contains a mirror arrangement of the type shown in FIG. The detector is mounted, for example, in a corner of a room to be monitored and covers the monitored areas designated Ü1 to Ü7 the remote zone (row with the reflectors A). The surveillance areas of the other zones are not shown; Reference is made in this connection to EP-A-0 303 913, in particular to FIG. 3 thereof. The reflectors A _n and A _n 'with n = 1 to 7 are arranged and formed such that a reflector with the index 1 receives heat radiation from the monitoring area Ü1, one with the index 2 heat radiation from the monitoring area Ü2, and so on. The reflectors thus define the surveillance areas. In the cited EP-A-0 303 913 it is also shown that the reflectors B1 and B5 receive heat radiation from the surveillance areas Ü1 and Ü7, respectively (though not from the remote zone but from the central zone) and the reflectors B3, C2 and D from the monitoring area Ü4.

The two mirrors R and R 'produce an identical overlay pattern and are also aligned so that their overlap patterns overlap one another exactly. This means, for example, that the surveillance area Ü7 casts its heat radiation both on the reflector A7 and on the reflector A7 ', the surveillance area Ü4 heats its thermal radiation onto the reflectors A4 and A4', and so on. This is indicated in FIG. 2 in that a line is drawn from each sensor S, S 'to each monitoring area U _n .

In addition, each monitoring area is assigned a weighting which is selected such that a unique identification of the respective monitoring area and thus of the azimuth of an intruder becomes possible. These weightings are plotted in FIG. 2 both next to the monitoring areas and next to the connecting lines between the sensors and the monitoring areas, the first and upper numbers respectively referring to the sensor S 'and the mirror R' and the second or lower number refers to the sensor S and the mirror R. Different weighting means that the heat radiation from the individual monitoring areas in a different strength caused by the weighting reaches the two sensors S and S ', so that the distribution of the intensity on the two sensors S and S' directly indicates from which monitoring area the Radiation comes. Table 1 below shows the weighting of the individual monitoring areas: monitoring area Weighting R ', S' Weighting R, S U1 1 0 U2 1 1.3 U3 1 2.3 U4 1 1 E5 2.3 1 E6 1.3 1 Ü7 0 1

The different weighting of the monitoring areas is done by a different optical aperture of the corresponding reflectors, which is shown schematically in Fig. 1. The hatched areas of the individual reflectors are not needed and are for example covered. The reflector A2, for example, is covered by two thirds and thus closed one third, which corresponds to the second number in the monitoring area Ü2 in FIG. The numbers in Fig. 2 thus indicate the relative optical aperture of the associated reflectors.

The optical aperture of existing passive infrared optics can be done in different ways be adjusted. For Fresnel lenses, the thickness of the film in which the Fresnel lenses integrated are, area-wise enlarged or reduced and at a mirror, for example the reflectivity of the reflective surface of the reflectors are changed. In the Practice, it will be cheaper to produce a new mirror without covered mirror parts, by modifying the uncovered reflectors or reflector parts so and arranges for the mirror to retain its original outlines.

In general, with 2 sensors and m weighting levels, 3 + 2 • (m-1) are clearly distinguishable Directions. These are distinguishable at m = 1 and the weighting level {1} 3 Surveillance areas, at m = 2 and the weighting levels {1/2 and 1} 5 distinguishable Monitoring ranges, at m = 3 and the weighting levels {1/3, 2/3 and 1} 7 distinguishable Monitored areas and at m = 4 and the weighting levels {1/4, ½, ¾ and 1} 9 distinguishable Monitoring areas.

For three sensors, the following number of distinguishable monitoring ranges are obtained: for m = 1 and the weighting stage {1} 7 distinguishable monitoring ranges, for m = 2 and the weighting levels {1/2 and 1} 19 distinguishable monitoring ranges and for m = 3 and Weighting levels {1/3, 2/3 and 1} total 37 distinguishable monitoring areas. Here, the number A _{U of} the distinguishable monitoring ranges is calculated according to the following formula: A _Ü = 7 + 6 • Σi (i = 2 to m). For example, for m = 4, this gives the value A _Ü = 7 + 6 (2 + 3 + 4) = 61.

To determine the relative weighting of a signal among several simultaneously occurring ones Signals calculate the normalized cross-correlation and require a value close to 1. The Quotients of the rms values of the individual signals then give the relative weighting of the signals, whereby the assignment to an azimuth is possible.

In the following formulas, S ₁ and S ₂ denote the signals of the sensors S 'and S, respectively. For example, to decide that the intruder is in the surveillance area Ü5 (azimuth + 15 °), the following conditions must be met: corr = ∫S 1 ( t ). S 2 ( t - τ). dt ( ∫S 1 2 ( t ). dt , ∫S 2 2 ( t ). dt ) 1.2 > corrØ ~ 90% τ → 0 b) ( ∫S 1 2 ( t ). dt ) 1.2 ( ∫S 2 2 ( t ). dt ) 1.2 ≅ 2.3 1

As an alternative to condition b) one could also use the maximum amplitudes and request that that their ratio is about 2/3/1.

The method of different weighting of different surveillance areas a passive infrared detector can not only for the determination of the azimuth but also for Determining the approximate distance of an intruder to the detector. So can a ceiling mounted detector with multiple sensors and optics with variable apertures, which can be uniquely assigned to the sensors, the location of an intruder in principle, two-dimensional dissolve.

When a person walks through multiple surveillance areas of a passive infrared detector very quickly moved, it may happen that the high-frequency components of the signal in the dominant low - frequency fractions disappear, thus providing a clear Signals to the corresponding monitoring area is difficult. This problem can with a digital filter bank of about three to five filters, one common in radar technology Procedure to be solved.

Fig. 3 shows a schematic representation of the overlay pattern of one with 6 sensors equipped ceiling detector, that is a difference to Fig. 2 not on a wall, but ceiling mounted passive infrared detector. The 6 sensors are represented by lines a to f symbolizes which each designate the normal vector to the same name sensor. For A more detailed description of a ceiling detector is made to DE-A-195 17 517, the disclosure of which is hereby expressly incorporated by reference.

The ceiling detector of Figure 3 has a resolution of 15 ° in the azimuth. for the individual surveillance areas each two weighting stages are provided, which in the figure with the values 1 or ½ are designated. The focusing device (not shown) for the sensors is so designed so that the sensors "look" directly vertically downwards, whereby the detector the Distant range may differ from the near range. This property can be used to to focus a camera on an intruder and take pictures.

In addition, the focusing device is designed so that each sensor in the with the relevant Letters denoted direction not in the distance but only in the vicinity "Looks". This means, for example, that sensor 8 has a total of 8 remote areas R1 to R8 are provided, which lie between the directions a and c, including these directions, but without the direction b. In the direction b, the sensor b only then speaks when an intruder is already close to the detector.

If, assuming that an intruder is transverse to those shown in Fig. 3 Directions moves, for example, the sensor a and the sensor c both simultaneously and with respond to the same amplitude, then located in the remote area of the sensor b an intruder. If now simultaneously or alone, the sensor b responds, then there is the Intruder not in the remote area but in the vicinity of the sensor b. In the vicinity corresponds to the Resolution of the number of sensors; in the illustrated embodiment, it is 60 °.

The ceiling detector is combined with advantage with a video camera and can in this constellation autonomously track intruders. But it can be used to assist a surgeon which serves a camera to provide a directional indication, with which the surgeon capture the intruder more safely and faster. The internal detector tracking of intruders takes place with the help of adapted tracking algorithms from radar technology. This allows a video camera with a narrow viewing angle on the moving intruder align, track and make a series of high resolution video recordings, which is not possible with the video surveillance devices available today. As a traceable Passive infrared detectors trace the path of an intruder in monitored areas, you can estimate the number of intruders, what security service and Police are of great interest.

Claims (10)

1. Passive infrared detector comprising heat-sensitive sensors (S, S') and comprising a focusing device (R, R'), having focusing elements (A_n, A_n'; B_m B_m'; C_k, C_k' D), for focusing onto the sensors (S, S') the heat rays falling onto the detector from various surveillance areas (Ü1 - Ü7), characterized in that for each surveillance area (Ü1 - Ü7) the focusing device (R, R') has a number, corresponding to the number of sensors (S, S'), of focusing elements (A_n, A_n'; B_m B_m'; C_k, C_k' D) of which each is respectively assigned a sensor (S and S' respectively) such that each sensor (S, S') has a pattern of surveillance areas, in that the mutually corresponding surveillance areas of the sensors (S, S') overlap one another, and in that each surveillance area of each sensor (S, S') is assigned a weighting enabling the unique identification of the respective surveillance area.
2. Passive infrared detector according to Claim 1, characterized in that the mutually corresponding surveillance areas of the sensors (S, S') overlap one another exactly.
3. Passive infrared detector according to Claim 1 or 2, characterized in that the weighting of the surveillance areas (Ü1 - Ü7) is performed by a different optical aperture of the corresponding focusing elements (A_n, A_n'; B_m B_m' ; C_k, C_k' D).
4. Passive infrared detector according to one of Claims 1 to 3, characterized in that the focusing device (R, R') is formed by a mirror arrangement or Fresnel lens arrangement which comprises reflectors (A_n, A_n'; B_m B_m'; C_k, C_k' D) or Fresnel lenses, respectively, which form the individual focusing elements.
5. Passive infrared detector according to Claim 4, characterized in that the weighting of the reflectors (A_n, A_n'; B_m B_m'; C_k, C_k' D) is performed by changing the reflectivity of their reflecting surfaces.
6. Passive infrared detector according to Claim 4, characterized in that in the case of a Fresnel lens arrangement with a foil in which the Fresnel lenses are integrated, the weighting is performed by a zone wise change in the thickness of this foil.
7. Passive infrared detector according to one of Claims 1 to 6, characterized in that the normalized cross-correlation is calculated in order to determine the relative weighting of one signal among a number of simultaneously occurring ones, a value close to 1 being required.
8. Passive infrared detector according to Claim 7, characterized in that the signals are assigned to a specific azimuth with the aid of the relative weighting of the signals which is obtained from the quotients of the root-mean-square values of the individual signals.
9. Passive infrared detector according to one of Claims 1 to 8, characterized in that intruders are tracked inside the detector with the aid of adapted tracking algorithms from radar technology.
10. Passive infrared detector according to Claims 1 to 9, characterized by connecting the detector to a video camera in order to train the latter onto a detected intruder or onto a region of space in which movement of an object has been detected.

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