EP1184824A1 - 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 device having focusing elements for bundling the heat rays falling on the detector from different monitoring areas Sensors.

Passive infrared detectors of this type have been known and widely used for years. They serve in particular to determine the presence or intrusion of unauthorized persons into a surveillance room or a surveillance room by proof of those sent out by these persons typical infrared radiation, which is directed onto the sensor by the focusing device. Either a Fresnel lens arrangement is used as the focusing device entry windows for infrared radiation arranged on the front of the detector housing are integrated (see, for example, EP-A-0 559 110), or an inside the detector housing arranged mirror, which consists of individual reflectors (see for example EP-A-0 303 913).

Both the Fresnel lens arrangement and the mirror are designed so that the one to be monitored Room covered with monitoring areas starting from the detector in a fan shape is. As soon as an object that emits heat radiation is in a monitoring area penetrates, the sensor detects the heat radiation emitted by this object, whereby detection is safest when the object moves across the surveillance area.

Today's passive infrared detectors detect intruders within the Effective range of the detector is very reliable, but does not provide any information about the position of the burglar in the effective range. This is not the case for common, conventional applications required, but may 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. With such detectors, one could open up certain surveillance zones during the day Visitor disruption or alarm, i.e. active, and switch the remaining zones to inactive. Another A possible application would be to monitor a room, for example the counter room a bank, with video cameras, the cameras storing the images when the image processing this requires.

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

Use previously proposed arrangements to detect the position of an intruder either a plurality of detector modules connected to a common computer are (US-A-5 641 963), or more infrared sensors, each of the infrared sensors is intended for monitoring a specific area of the room. 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 assign a discrete spatial area, but also a common overlap area provided. In this way, three with two infrared sensors Room areas are monitored, but what a localization of a person in the room far from enough.

The invention is now intended to provide a passive infrared detector which is low Additional effort to locate an intruder as precisely as possible in its effective area allows.

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

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

This is a first preferred embodiment of the passive infrared detector according to the invention characterized that the corresponding monitoring areas of the sensors exactly overlap each other.

A second preferred embodiment of the passive infrared detector according to the invention is characterized in that the weighting of the monitoring areas by a different optical aperture of the corresponding focusing elements takes place.

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

A fourth preferred embodiment of the passive infrared detector according to the invention is characterized in that the weighting of the reflectors by a change in reflectivity their reflective surfaces.

In the Fresnel lenses, which are known to be integrated in a film, the weighting is carried out 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.

The invention is explained in more detail below on the basis of an exemplary embodiment illustrated in the drawings; it shows:

Fig. 1

1 shows 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 overlap pattern generated with the focusing device of FIG. 1; and

Fig. 3

is a schematic representation of the coverage pattern of a passive infrared detector equipped with 6 sensors and mounted on a ceiling.

The passive infrared detector shown in detail in Fig. 1 contains two heat-sensitive Sensors S and S 'and a focusing device. The latter is by two conventional ones Mirrors R, R 'are formed, each of which is made up of a number of focusing elements or reflectors consists. The sensors S, S 'are, for example, pyro sensors or thermopile sensors (see also EP-A-0 981 159). If in the following description of pyro sensors the Then there should be no limitation. Of course, instead of the mirror R, R 'also uses a Fresnel lens arrangement, which is usually what Space and cost reasons will also be the case. The representation with the mirrors has been removed Chosen for clarity.

As described for example in EP-A-0 303 913, the individual reflectors are each individual mirror designed so that the area to be monitored also emanates from the detector Surveillance areas are covered in a fan shape, with different ones correspondingly Distances from the detector of several such "subject areas" or surveillance zones are provided. A distinction is made between four surveillance zones, one remote zone, a middle zone, a near zone and a so-called look-down zone, divided by four in vertical Rows of reflectors offset in the direction are covered.

In the case of the mirror R, these rows are 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 zone. Down zone.

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

Each reflector "looks" in the spatial direction of the corresponding zone, receives that from it Incident thermal radiation and bundles this on the assigned pyro sensor S or S '. As soon as an object that emits heat radiation is in a monitoring area penetrates, the sensor detects the heat radiation emitted by this object, whereupon the detector emits an alarm signal. This alarm signal indicates that a Object, for example an intruder, is in the surveillance room, but does not leave any Conclusions about the exact position of the intruder in the surveillance room.

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, mirrors R and R 'with several, as shown, two assigned pyro sensors S and S 'are used, one Determination of the position of an intruder (so-called "tracking") possible if you look at the Reflectors of the individual mirrors and the pyro sensors combined so that a unique Identification of an intruder's azimuth becomes possible.

In Fig. 2, a detector with two pyro sensors S and S 'is symbolically drawn, which contains a mirror arrangement of the type shown in Fig. 1. The detector is mounted, for example, in a corner of a room to be monitored and covers the monitoring areas of the far zone designated with Ü1 to Ü7 (row with reflectors A). The surveillance areas of the other zones are not shown; in this connection reference is made 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 designed 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 therefore define the monitoring areas. EP-A-0 303 913 also shows that the reflectors B1 and B5 receive heat radiation from the monitoring areas U1 and U7 (if not from the far zone, but from the middle zone) and the reflectors B3, C2 and D from surveillance area Ü4.

The two mirrors R and R 'generate an identical overlap pattern and they are also aligned such that their overlap patterns overlap each other exactly. This means that, for example, the monitoring area Ü7 throws its heat radiation onto both the reflector A7 and the reflector A7 ', the monitoring area Ü4 its heat radiation onto the reflectors A4 and A4', and so on. This is indicated in FIG. 2 by the fact that a line is drawn from each sensor S, S 'to each monitoring area Ü _n .

In addition, a weighting is assigned to each surveillance area, which is selected such that a clear identification of the respective surveillance area and thus the azimuth of an intruder is possible. These weights are entered in FIG. 2 in addition to the monitoring areas as well as next to the connecting lines between the sensors and the monitoring areas, the first and upper numbers referring to sensor S 'and mirror R' and the second and lower numbers relates to the sensor S and the mirror R. Different weighting means that the heat radiation from the individual monitoring areas reaches the two sensors S and S 'in a different intensity caused by the weighting, so that the distribution of the intensity over the two sensors S and S' immediately indicates from which monitoring area the Radiation originates. The weighting of the individual monitoring areas is entered in Table 1 below: 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 one optical aperture of the corresponding reflectors, which is shown schematically in FIG. 1. The hatched areas of the individual reflectors are not required and are, for example covered. The reflector A2, for example, is covered by two thirds and therefore closed one third active, which corresponds to the second number in the monitoring area Ü2 in FIG. 2. The numbers in FIG. 2 thus indicate the relative optical aperture of the assigned reflectors.

The optical aperture of already existing passive infrared optics can be done in different ways be adjusted. In the case of Fresnel lenses, the thickness of the film into which the Fresnel lenses are integrated can be changed are enlarged or reduced in areas and, for example, with a mirror the reflectivity of the reflecting surface of the reflectors can be changed. In the In practice, however, it will be cheaper to produce a new mirror without covered mirror parts, by modifying the uncovered reflectors or reflector parts and orders the mirror to keep its original outline.

In general, with 2 sensors and m weighting levels 3 + 2 _* (m-1) there are clearly distinguishable directions. At m = 1 and the weighting level {1} there are 3 distinguishable monitoring areas, at m = 2 and the weighting levels {1/2 and 1} 5 distinguishable monitoring areas, at m = 3 and the weighting levels {1/3, 2/3 and 1} 7 distinguishable monitoring areas and at m = 4 and the weighting levels {1/4, ½, ¾ and 1} 9 distinguishable monitoring areas.

With three sensors, the following number of distinguishable monitoring areas results: with m = 1 and the weighting level {1} 7 distinguishable monitoring areas, with m = 2 and the weighting levels {1/2 and 1} 19 distinguishable monitoring areas and with m = 3 and the Weighting levels {1/3, 2/3 and 1} total of 37 distinguishable monitoring areas. Here the number A _{Ü of} the distinguishable monitoring areas 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 occurring simultaneously Signals are calculated using 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, which enables the assignment to an azimuth.

In the following formulas, S ₁ and S ₂ denote the signals from the sensors S 'and S, for example. In order to decide, for example, that the intruder is in the surveillance area Ü5 (azimuth + 15 °), the following conditions must be met: a) corr = ∫ S 1 ( t ). S 2 ( t - τ). dt (∫ S 1 2 ( t ). dt .∫ S 2 2 ( t ). dt ½ > corr⊘ ∼ 90% τ → 0 b) (∫ S 1 2 ( t ). dt ) ½ (∫ S 2 2 ( t ). dt ) ½ ≅ 2.3 1

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

The method of different weighting of the different surveillance areas A passive infrared detector can not only be used to determine the azimuth but also for Determination of the approximate distance of an intruder to the detector. So can a detector mounted on the ceiling with several sensors and optics with variable apertures, which can be clearly assigned to the sensors, the location of an intruder dissolve in two dimensions.

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

Fig. 3 shows a schematic representation of the coverage pattern of a with 6 sensors equipped ceiling detector, in contrast to Fig. 2 this is not on a wall, but Passive infrared detector mounted on a ceiling. The 6 sensors are marked by lines a to f symbolizes, which each denote the normal vector on the sensor of the same name. 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.

3 has a resolution of 15 ° in azimuth; for the individual surveillance areas Two weighting levels are provided, which in the figure have the values 1 or ½ are designated. The focusing device (not shown) for the sensors is like this trained that the sensors "look" directly vertically downwards, whereby the detector Can distinguish long-range from close-up. This property can be used to to point a zoom camera at an intruder and take pictures.

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

If assuming that an intruder is transverse to that shown in Fig. 3 Moves directions, for example sensor a and sensor c both simultaneously and with of the same amplitude, there is an intruder in the far range of sensor b. If sensor b responds simultaneously or alone, then there is Intruder not in the far range but in the close range of the sensor b. In the close range it corresponds to Resolution of the number of sensors; in the illustrated embodiment, it is 60 °.

The ceiling detector is advantageously combined with a video camera and can be used in this constellation autonomously track intruders. But it can be used by an operator, which operates a camera to provide a direction with which the operator can detect the intruder more safely and quickly. Internal tracking intruders are carried out 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 take a series of good-resolution video, which is not possible with the video surveillance systems available today. Since capable of trakking Passive infrared detectors trace the path of an intruder in monitored rooms, can you estimate the number of intruders, what security service and Police are of great interest.

Claims (10)

Passive infrared detector with heat-sensitive sensors (S, S ') and with a focusing device (R, R') with focusing elements (A _n , A _n '; B _m , B _m '; C _k , C _k '; D) of the heat rays falling on the detector from the various monitoring areas (Ü1 - Ü7) onto the sensors (S, S '), characterized in that the focusing device (R, R') has one of the number of for each monitoring area (Ü1 - Ü7) Sensors (S, S ') has a corresponding number of focusing elements (A _n , A _n '; B _m , B _m '; C _k , C _k '; D), each of which has a sensor (S or S ') is assigned so that each sensor (S, S ') has a pattern of monitoring areas, that the corresponding monitoring areas of the sensors (S, S') overlap one another, and that each monitoring area of each sensor (S, S ') has a unique one Identification of the respective monitoring area is assigned to enable weighting. Passive infrared detector according to claim 1, characterized in that the mutually corresponding monitoring areas of the sensors (S, S ') overlap each other exactly. Passive infrared detector according to claim 1 or 2, characterized in that the weighting of the monitoring areas (Ü1 - Ü7) by a different optical aperture of the corresponding focusing elements (A _n , A _n '; B _m , B _m '; C _k , C _k '; D) takes place. Passive infrared detector according to one of Claims 1 to 3, characterized in that the focusing device (R, R ') is formed by a mirror or Fresnel lens arrangement which consists of reflectors (A _n , A _n '; B _m , B _m '; C _k , C _k '; D) or Fresnel lenses. 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 carried out by changing the reflectivity of their reflecting surfaces. Passive infrared detector according to claim 4, characterized in that in a Fresnel lens arrangement with a film, in which the Fresnel lenses are integrated, the weighting is carried out by changing the thickness of this film in certain areas. Passive infrared detector according to one of claims 1 to 6, characterized in that for the determination of the relative weighting of a signal among a number of simultaneously occurring, the normalized cross-correlation is calculated, a value close to 1 being required. Passive infrared detector according to Claim 7, characterized in that the signals are assigned to a specific azimuth on the basis of the relative weighting of the signals, which is obtained from the quotients of the effective values of the individual signals. Passive infrared detector according to one of claims 1 to 8, characterized in that intruder detection of intruders is carried out with the aid of adapted tracking algorithms from radar technology. Passive infrared detector according to one of claims 1 to 9, characterized by a connection for connecting the detector to a video camera in order to align it to a detected intruder or to a spatial area with movement of an object detected therein.

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