Optical arrangement for an infrared intrusion detector

The invention relates to an optical arrangement for an infrared intrusion detector.

Such arrangements take on the threat posed by a person in the monitored area infrared radiation and transmit them to a sensor element. If the monitored area is divided into several separate reception areas with intervening dark fields, so every movement of a person causes a modulation of the received by the sensor element infrared radiation, which can be evaluated by a known Aufwerteschaltung to display an intruder and an alarm signal.

In order to create the required separate reception areas, it is for example from US 3,703,718, US 4,058,726 or US 4,081,680 known to provide a plurality of reflectors, which are oriented in different directions and focus the incident from various reception areas radiation to the same sensor element. Here each reflector is assigned to another lobby and bundles only radiation from this lobby to the sensor element. The disadvantage here is that the entire receiving surface is divided into many small segments. only a small amount of radiation from the individual receiving areas therefore each added so that the sensitivity of such infrared intruder detectors is often insufficient, especially if many reception areas are provided.

This disadvantage can indeed with the in US 3,760,399, US 3,829,693 or US avoid arrangements described 3,958,118, in which a single reflector is provided for all reception areas and the division is in the different areas by means of several juxtaposed sensor elements. Thus, although available for all reception areas a common, relatively large reflector surface available, but many sensor elements require a complicated and error-prone circuit, also the number of possible sensor elements and thus the reception areas is severely restricted.

From GB-A 2012045 and EP-A 0014825 arrangements have already become known, in which the bundling of the IR radiation is carried out on a common sensor member by multiple reflection. However, the first reflection takes place in turn to individual mirror segments, each of which another receiving area is assigned. Such arrangements therefore also have the disadvantage that from the individual receiving areas, only a small amount of radiation is absorbed and therefore the sensitivity is often insufficient. To achieve still good sensitivity, it was therefore necessary in such previously known infrared intrusion detectors to use relatively large mirror segments, so that the dimensions of such detectors had to be selected relatively large, so that an unobtrusive attachment as often desired burglary protection devices and required was virtually impossible.

The US-A-4052616 shows an arrangement with a hemispherical reflector or a Fresnel lens for all reception areas as well as optical fibers which enter the infrared radiation on a sensor. The number of light guides is limited by the size of the sensor surface, so that the amount of radiation incident on the sensor is insufficient. Furthermore, the fixing of the ends of the fibers on the internal surface and on the sensor surface is difficult.

The US Patent 3,702,937 describes a motion detector, which is used instead of reflectors, a lens arrangement which divides the image of the monitored area into two parts and are two photocells, which are integrated in a bridge circuit. At different illumination of the monitored area, the electrical bridge circuit is brought into imbalance, and generates an alarm. The reaching of a photocell amount of radiation is low.

The invention aims to eliminate the significant disadvantage of the prior art, which is, despite various lens and reflector assembly in the low uptake of the amount of radiation in order to increase the sensitivity of the intrusion detector. Further, the intrusion detector is to have small spatial dimensions, so that it can be discreetly attached to its place of use. Another purpose of the invention resides in the simple construction of the optical arrangement.

The object of the invention is achieved by the features of claim 1.

The invention will be described with reference to exemplary embodiments illustrated in the figures.<ul><li>Figure 1 shows a first optical arrangement with centrally attached sensor element.</li><li>Figure 2 shows a second optical arrangement with peripherally attached sensor element.</li><li>Figure 3 shows another optical arrangement with peripherally attached sensor element.</li><li>Figure 4 shows an infrared intruder detector with linear reflector assembly.</li></ul>

In the optical arrangement shown in Figure 1 is a convergent lens 1 is provided as the first bundling means is configured as a Fresnel lens.

Such steps lenses can be produced in a simple manner from a suitable transparent material by pressing or casting. It is particularly expedient is to choose a material such as a suitable plastic material, which in the long-wave infrared radiation is preferably transparent, such as polyethylene, or As₂S₃, Se, or As / Se glasses, these glasses can be deposited as a filter on the polyethylene lens.

In irradiation direction behind the Fresnel lens is arranged a plurality of individual reflectors 2, 3, ... 6th These reflectors can be designed as a concave or convex spherical, paraboloid or ellipsoid segments or as mutually inclined plane mirror. In the center of the Fresnel lens 1, a detecting element 7 is provided, the sensitivity is matched to the receiving infra-red radiation, for example, lithium tantalate (LiTaO_a). Polyvinyl fluoride (PVF₂), Lead zirconate titanate (PZT) or other suitable pyroelectric sensor.

The focal length of the Fresnel lens 1, the curvature, the orientation and spacing of the reflectors 2, 3, ... 6 can be chosen so that the best possible picture of the incoming of certain desired directions infrared radiation takes place. The individual receiving areas are in this case to reception directions with a relatively small opening angle, which depends on the accuracy of the optical components and their adjustment, as well as the dimensions of the sensor element. If another form is desired of receiving areas, for example, rectangular or strip form, the reflectors may be aspheric.

With the described optical arrangement is achieved that incident infrared radiation from the first bundling means, that is received by the Fresnel lens 1 with their full surface and is only then fed to the individual, the various reception areas associated mirror segments. Each mirror segment 2, 3, ... 6 receives this radiation from the full face of the Fresnel lens 1 and then bundles these rays on the sensor element 7. This is therefore the greatest amount of incident infrared radiation captured and detected. The sensitivity of a vehicle equipped with such an arrangement, infrared intruder detector is therefore considerably increased. The dimensions of the reflectors are not crucial, so that even when a plurality of receiving areas small device dimensions are possible.

Figure 2 shows a similar arrangement which is different from the first embodiment in that the sensor element 7 peripheral, ie disposed on the edge of the Fresnel lens first Thus, the entire aperture of fresnel lens for receiving infrared radiation and are available through the sensor element, no losses occur. In this example, it is expedient, the reflectors 2 and 4 only slightly curved or flat form to keep aberrations due to oblique radiation invasion as small as possible.

Figure 3 shows an infrared intrusion detector comprising a housing 10 having a front panel 11 and a rear side 12th The front panel 11 carries a Fresnel lens 1 and the rim a sensor element 7, which is connected to an integrated evaluation circuit 8, which may be designed, for example, according to US 4179 691 or US 4166 955th The output of this evaluation circuit 8 is taken at the output terminals. 9 The back 12 carries a facet mirror 13, whose individual facets correspond to the reflector 2, 3, ... 6 d. The configuration and orientation of the individual facets is such that a bundle of many reception directions or portions with a small aperture angle is produced in cooperation with the Fresnel lens. 1

In the expedient development, a plurality of juxtaposed sensor elements (7, 7 ', 7 ") may be provided instead of a single sensor element. Each element receives this radiation from a plurality of reception areas. The number of reception areas can thus be multiplied according to the number of sensor elements wherein no substantial intensity or loss of sensitivity occurs because each sensor element has received a large portion of the radiation from the common bundling means. Suitably it may be, to use as a sensor element, a "sensor array", in which the individual elements are arranged in a line next to each other. The individual receiving areas are thereby split each in a lying in a plane bundle several reception areas. This can be created in a simple manner, a number of an intruder passing radiation curtains.

Figure 4 shows a very flat embodiment of an infrared intrusion detector, in which the entire front face 11 is occupied by a segment of a Fresnel lens 1, is mounted in the center of which das.Sensorelement 7th At the rear 12 individual reflectors 2, 3, ... 6 are provided in a row next to each other. On the base plate 14, the evaluation circuit 8 is mounted. With this arrangement can be a fan of in-plane reception areas, or a curtain form. The detector may be arranged thanks to its flat design inconspicuously in a small gap, wherein the front surface 11 is utilized optimally for receiving infrared radiation from receiving areas.

In an advantageous development of the focusing lens 1, one or more prisms may be provided by the individual receiving beams can be split into a number of beams before or after parts. Thereby, the number of radiation receiving areas are multiplied, if a certain amount of intensity attenuation of the different areas can be accepted.

In the infrared intrusion detector shown in Figure 4, for example, in front of both sides of the Fresnel lens 1 prisms 15, his 15 'arranged. These cause the incident on the prisms radiation at a certain angle is deflected, while the lens directly impinging radiation remains unaffected. Every lobby is therefore split into three separate areas.

The prism element may be combined with the converging lens and integrated into this by being designed as a multi-zone lens having zones of different optical axis. For example, the sides of the Fresnel lens 1 on her front or back, the shape of wedges 16, 16 ', respectively, which the prisms 15, 15' replace and show the same optical effect in FIG. 4 Such an optical element is particularly simple to produce and does not require any special adjustment.

The illustrated infrared intruder detector, despite its flat form and understated its small size optimal sensitivity, and has a particularly simple and troublefree design to on. It is particularly suitable for uses where an infrared curtain is desired with closely juxtaposed in a plane receiving areas.