1. Field of the Invention
The present invention relates to a heat source detector which detects a position of an infrared heat source such as a human body and a moving direction of a heat source position.
2. Description of the Related Art
Conventionally, radiation (infrared rays) emitted from an infrared heat source such as a human body is detected by an infrared sensor. An infrared sensor detects a heat source by using a passive method in which no light is irradiated onto an object such as a human body to be detected and radiation spontaneously emitted from a heat source is detected. Therefore, the heat source detection can be conducted without adversely affecting the measuring object such as a human body, and without illumination even during the night. Consequently, such a detection using an infrared sensor has a wide variety of applications.
FIG. 1 shows an example of a conventional heat source detector using an infrared sensor. In the figure, the heat source detector comprises a pyroelectric infrared sensor 1. A shield plate 18 having an aperture 12 is slidably disposed under the infrared sensor 1, and a plurality of Fresnel lenses 16 are arranged under the shield plate 18. In the thus configured detector, an image of radiation from a heat source in each of zones A to C shown in the figure is formed by the Fresnel lenses 16 on an infrared ray sensing device of the infrared sensor 1 so that the heat source is detected. When the aperture 12 of the shield plate 18 is positioned above the zone A as shown in the figure, the zone A constitutes the detection object zone. If a person is in the zone A, for example, an image of radiation from the body of the person is formed on the infrared ray sensing device of the infrared sensor 1, and it is detected that the human body functioning as a heat source is in the zone A. If no person is in the zone A, no radiation is detected. As a result, it is possible to know the presence or absence of a heat source in the zone A.
When the shield plate 18 is slidingly moved so as to be positioned above the zone B and the same operation as that described above is conducted, it is possible in the same manner to know the presence or absence of a heat source in the zone B. Similarly, it is possible also to know the presence or absence of a heat source in the zone C.
When the shield plate 18 is moved at regular time intervals and the presence or absence of a heat source is detected in each of the zones A to C, information can be obtained about the moving direction of a heat source, i.e., whether the heat source is moved from the zone A to the zone C or from the zone C to the zone A.
Another example of a conventional heat source detector using an infrared sensor is shown in FIG. 2(a). The detector has a structure wherein a pyroelectric infrared sensor 1 in which eight infrared ray sensing elements 7 are vertically arranged in a row is mounted so as to be reciprocally rotatable as indicated by an arrow A in the figure, a chopper 11 having an aperture 12 is rotatably mounted in the outer peripheral side of the infrared sensor 1, and an infrared lens 10 is disposed in front of the chopper 11. In the detector, radiation from a heat source passes through the aperture 12 of the chopper 11 and its image is formed on the infrared ray sensing elements 7 by the infrared lens 10. The infrared sensor 1 and the chopper 11 are rotated as indicated by the arrow A and an arrow B, respectively, so that radiation is detected while the chopper 11 conducts an opening operation 64 times, whereby the detection of radiation is conducted while changing the detection angle. Resulting signals are processed by a signal processor 24, and a CPU (microcomputer) 25 operates so as to display infrared images of 64.times.8 as shown in FIG. 2(b), thereby detecting the heat source and the moving direction of the heat source.
Today, visible light CCD cameras are also used in homes, etc. Such a camera is so configured that sensors for detecting visible light are arranged in a high density on a silicon wafer, and high-density wirings corresponding to the sensing devices are formed on the silicon wafer, thereby realizing a high-resolution camera. It is contemplated that the application of this technique to a heat source detector (infrared camera) may enhance the resolution of the heat source detector.
However, a pyroelectric infrared sensor used in a heat source detector is made of ceramics, etc., and hence it is difficult to integrate such sensors on silicon, thereby producing a problem in that, unlike the above-mentioned visible light CCD camera, it is impossible to arrange sensors in a high density on a silicon wafer and fix them to the wafer. It may be contemplated that infrared sensors are arranged by means of bonding so as to arrange them in a high density. However, this involves drawbacks that the bonding operation requires difficult steps, and that steps such as connecting adjacent infrared sensors to each other and drawing out wirings such as lead wires from infrared ray sensing devices of the infrared sensors must be conducted, thereby making the production process very difficult.
Consequently, a heat source detector such as those shown in FIGS. 1, 2(a) and 2(b) employs a structure wherein infrared sensors are arranged in a low density, and hence its resolution is not very high with the result that such a detector can detect only an approximate position of a heat source. Furthermore, the detector cannot finely determine the moving direction of a heat source. In other words, the detector can conduct only a very rough judgment on the moving direction, i.e., select one of the upper, lower, left, and right directions in the figure, as the moving direction of the heat source.
In order to solve the above-mentioned problems, for example, an infrared camera employing quantum infrared sensors which are made of a semiconductor such as HgCdTe or InSb has been proposed, and practically used in some fields. When such a quantum infrared sensor is to be operated, however, the elements of the sensor must be cooled to a very low temperature by using liquid nitrogen or the like, thereby producing problems in that the detector is bulky, and that the production cost of the detector is high.