Movement detector

Details Movement detector Movement detector

1999-07-01

2001-06-12

Lee, Benjamin C. (Department: 2736)

Communications: electrical

Condition responsive indicating system

With particular system function

C340S565000, C340S567000, C340S584000, C340S587000, C348S164000, C396S061000, C382S103000, C250S338100, C250S342000

Reexamination Certificate

active

06246321

ABSTRACT:

PRIORITY APPLICATION
This application claims priority to European Application No. 98 112 460.5 filed on Jul. 6, 1998, and entitled “Bewegungsmelder,” by Martin Rechsteiner and Hansjürg Mahler, which is hereby incorporated by reference.
FIELD OF THE INVENTION
The invention relates in general to the field of electronic surveillance and intrusion detection. More particularly, the present invention relates to a movement detector having dual image sensors and an electronic evaluation system for using signals generated by the sensors to determine the location, movement and classification of moving objects.
BACKGROUND OF THE INVENTION
Conventional passive infrared (PIR) sensors are predominantly used in movement detectors, but although they are very inexpensive, they do not provide any spatial resolution and have difficulty detecting objects having low temperature contrasts as compared to their surroundings. Doppler detectors or movement detectors using the PIR principle and the Doppler principle also do not provide any spatial resolution. It is precisely this property, however, which is required not only for determining whether an object is located in a room under surveillance, but also for determining where the object is located in the room, in which direction it is moving, and the type or class of object concerned.
An obvious use of so-called “thermal-image sensors,” i.e., image-providing sensors operating in the wavelength region of about 5 to 15 &mgr;m, is undesirable in that conventional thermal-image sensors are so expensive that sufficiently high-resolution sensors cannot be used for movement detectors. As such, high resolution applications using thermal-image sensors are not practical.
Additionally, images of objects taken with conventional low-resolution thermal-image sensors, having in the range of about 4×4 pixels up to 32×32 pixels, often cannot be analyzed precisely enough for the required application. For example, such a resolution would be too low for distinguishing humans from non-human animals. Also, conventional thermal-image sensors have a low detection sensitivity for low temperature contrast at ambient temperatures around 30° C.
So-called “image sensors” are also known, which are image-providing sensors operating in the visible and near-infrared range, particularly in the wavelength range from about 0.4 to 1.8 &mgr;m. Conventional image sensors are inexpensive and widely used, but are generally used in environments having a minimal level of brightness. These sensors suffer the shortcoming that they are unable to function properly in the dark unless combined with a lighting system. In addition, to evaluate the signal of a conventional image sensor, the entire image always has to be processed, which requires a relatively high expenditure of memory capacity and computer processing time and, if the evaluation is not carried out locally, requires an expensive transmission of data across a communications media.
If low-resolution image sensors or those having the possibility of reading-out images with reduced resolution are used there is the risk that low contrast objects may be blurred and can therefore no longer be detected.
SUMMARY OF THE INVENTION
The above-described limitations and inadequacies of conventional movement detectors are substantially overcome by the present invention, in which a primary objective is to provide a movement detector that is fully usable even in the dark, which can operate with as little memory capacity and computer time as possible, with which low-contrast objects can also be reliably detected, and which has a spatial resolution which is sufficient for the detection and analysis of objects. The movement detector is intended not only to fulfill all the known criteria of burglary detection technology, but it is also intended to permit classification of the moving objects.
The movement detector of the present invention has an image-providing sensor, hereinafter designated as an “image sensor,” operating in the visible and near-infrared range, and an image-providing sensor, hereinafter designated as a “thermal-image sensor,” operating in the thermal radiation range and having a lower resolution than the image sensor, and wherein an electronic evaluation system receives corresponding image signals from the image and thermal-image sensors and performs a combined evaluation of the image signals to determine whether an alarm condition exists. The evaluation system determines whether one or both of the received image signals are to be evaluated to determine whether an alarm condition exists.
As a result of using image signals from a low resolution thermal-image sensor with signals from a higher resolution image sensor, the respective weaknesses of the two types of sensors can be compensated for, which increases the detectability of low-contrast objects and decreases the false-alarm rate. In addition, object classification is possible without using an expensive high-resolution thermal-image sensor.
The thermal-image sensor may measure either the absolute temperature or, with suitable differential interconnections of the individual sensor elements, temperature changes. Polyethylene Fresnel lenses can be used for low-resolution thermal-image sensors, and these are substantially cheaper than the high-quality zinc selenide lenses required for high resolution thermal-image sensors.
In a first preferred embodiment of the movement detector according to the present invention, prior to the evaluation of the signals of the sensors, a separate preliminary evaluation of the signals is carried out both for the image sensor and for the thermal-image sensor.
In a second preferred embodiment of the movement detector according to the present invention, the thermal-image sensor carries out an illumination-independent detection and approximate localization of moving objects, and the image sensor carries out a classification of the objects.
In a third preferred embodiment of the movement detector according to the present invention, the image sensor is formed by a pixel-wise addressable sensor, preferably an active pixel sensor. The pixel-wise addressable image sensor has the advantage that the reading-out can always be restricted to the image region of interest. Analysis of the image region, as opposed to the entire image, saves computer time and memory capacity and, in the case of non-local evaluation, transmission time.
In a fourth preferred embodiment of the movement detector according to the present invention, means for brightness measurement and for controlling the exposure time of the image sensor and/or temperature measurement means are provided and are connected to the electronic evaluation system.
In a fifth preferred embodiment of the movement detector according to the present invention, the detector can be operated in various operating modes adapted to the requirements of particular applications, and in addition, has various signal evaluation modes, wherein the selection of a evaluation mode takes place on the basis of the ambient or background conditions, preferably on the basis of the brightness and/or temperature measured by the aforementioned brightness measurement and/or temperature measurement.
The use of the means for brightness measurement and/or for temperature measurement has the advantage that the detector can determine the most important parameters in its surroundings and can set a suitable evaluation mode on the basis of the above-mentioned ambient conditions.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.


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patent: 6

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