JPH0580968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared detection device for detecting a heat source such as a human body using a dual-structure infrared sensor element.

[Conventional technology]

Recently, detection devices using pyroelectric infrared sensors have been frequently used to detect human bodies, etc., because they are easier to install and handle than devices using LEDs. .
This pyroelectric sensor usually has electrodes formed on the front and back surfaces of a pyroelectric plate, and it is sensitive to even the slightest temperature difference, so while it has good sensitivity, it is vulnerable to thermal noise and is sensitive to noise such as car lights. It sometimes malfunctioned due to heat sources or sudden changes in ambient temperature.

In order to avoid malfunctions caused by such noise components, a so-called "dual sensor element" in which two elements with opposite polarization states are coupled in series or parallel (Figure 4 A and B) has been proposed and put into practical use. There is. This dual sensor element utilizes the differential output of the signals obtained from the two elements, and changes in temperature or ambient temperature applied to the two elements at the same time cause the signal outputs from the two elements to overlap each other. Since it acts in a canceling manner, there is no malfunction due to such external noise, and stable human body detection is performed. When this dual sensor element is used, for example, as shown in FIG. If we move from point to point γ at constant speed,
Upon movement from the α point to the γ point, the first element 4 generates an output signal a as shown in FIG. 6A, and the second element 5 generates an output signal b. The differential output of these two signals yields a signal level as shown in FIG. 6B.

[Problem that the invention seeks to solve]

Obtaining the signal level shown in Figure 6 (b) means that a large differential output is obtained when a heat source such as a human body enters the detection area and when it leaves the detection area. In this case, the differential output at the center C of the area becomes low, resulting in an undetectable state.

The present invention has been made to solve the above conventional problems, and its purpose is to create an area with a high output level at the center C of the differential output signal, that is, at the center of the detection area, and to increase the detectable area. The aim is to make it as wide as possible.

[Means for solving problems]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention provides a dual structure pyroelectric infrared sensor element having a pair of elements; a Fresnel lens disposed near the pyroelectric infrared sensor element to guide infrared rays to the pyroelectric infrared sensor element; In the pyroelectric infrared detection device, the Fresnel lens includes a lens that transmits infrared rays to one element within a common detection range of each of the pair of elements in a direction crossing the arrangement direction of the pair of elements. The structure is characterized in that a blocking body is embedded therein.

[Effect]

In the present invention configured as above,
When a heat source such as a human body enters the detection area of the pyroelectric infrared sensor element, the infrared rays emitted from the heat source are guided by a Fresnel lens and enter a pair of elements of the pyroelectric infrared sensor element. in this case,
In conventional devices, as mentioned above, when a heat source enters the part where the detection areas of each element overlap, that is, the central part of the detection area, the intensity of the infrared rays entering each element is almost equal, so there is no difference between the two elements. The dynamic output signal becomes almost zero, making it impossible to detect the heat source. However, in the present invention, since the Fresnel lens is provided with a shield, even if the heat source enters the central part of the detection area, infrared rays will enter one side of the pair of elements and will not penetrate the other side. This creates a region in the element that is blocked by the shield and infrared rays do not enter. Therefore, when a heat source is present in this area, there will be a difference in the output levels of both elements, that is, a differential output will be obtained, and this will easily create a detectable area for the heat source in the center of the detection area. It is possible,
The detection area is expanded.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 shows the configuration of an embodiment of a pyroelectric infrared detection device according to the present invention.

In the figure, a housing 1 is made of a metal material that shields infrared rays.
An opening 2 is formed at a desired position. A pyroelectric infrared sensor element 3 is disposed inside the housing 1. This pyroelectric infrared sensor element 3 has a first element 4 and a second element 5 which are arranged adjacent to each other, and the light receiving surfaces of both elements 4 and 5 face the opening 2. When the elements 4 and 5 receive infrared rays, their polarization state is disrupted and they output electrical signals corresponding to the intensity of the infrared rays. Both elements 4,
As in the conventional example, elements 5 are connected in series or parallel as shown in Figure 4 A and B with their polarization states reversed, and when a difference occurs between the output levels of both elements 4 and 5. A detection signal is outputted from the pyroelectric infrared sensor element 3.

On the other hand, a transmission plate 6 that transmits infrared rays is fitted into the opening 2, and a Fresnel lens 7 is disposed at a position sandwiching the transmission plate 6 and facing the pyroelectric infrared sensor element. This Fresnel lens 7 is made of, for example, plastic resin such as polyethylene, and guides infrared rays emitted from a heat source such as a human body to the pyroelectric infrared sensor element 3 (more specifically, the elements 4 and 5).

The present invention aims to expand the detectable range of the heat source by creating a detectable area within the non-detectable area that occurs at the center of the detection area. As a means for realizing the present invention, in this embodiment, a metal shielding rod (shielding body) 8 for shielding infrared rays is provided in the Fresnel lens 7 for the elements 4 and 5.
It is embedded in the common detection range of , in a direction intersecting the arrangement direction of the elements 4 and 5 (in this embodiment, a direction intersecting at right angles).

If this shielding rod 8 is not embedded in the Fresnel lens 7, the detection area of the element 4 will be within the area A (within the circle A), as shown in FIG. The detection area of element 5 of No. 2 is within the range of area B (within the range of circle B).
At this time, the output levels of both elements 4 and 5 are almost the same in the overlapping area of area A and area B, and there is almost no difference in level, so the non-detection area of the heat source C
becomes. On the other hand, if the Fresnel lens 7 is provided with a shielding rod 8 as in this embodiment, as shown in FIG. In the non-detection area C, there is a region D where the infrared rays do not reach because it is blocked by the rod 8, and a region E where the infrared rays do not reach the first element 4 but reach the second element 5. Created. Therefore, if the heat source moves and enters areas D and E, there will be a difference in the output levels of both elements 4 and 5.
It becomes possible to detect heat sources. In other words, by providing the shielding rod 8 on the Fresnel lens 7, the detectable area of the heat source is expanded. When embedding the shielding rod 8 in the Fresnel lens 7, by embedding the shielding rod 8 in the lens corresponding to the non-detection area C in FIG. will be created.
In other words, by providing the shielding rod 8 in a direction intersecting the arrangement direction of the elements 4 and 5 in the lens corresponding to the common detection range of the elements 4 and 5 of the pyroelectric infrared sensor element 3, the non-detection area C is Among the infrared rays entering the Fresnel lens 7, the infrared rays emitted from the lens to one element are blocked by the shielding rod 8, and the infrared rays are emitted unobstructed to the other element, so that they can be detected in the non-detection area C. You can create an area.

By the way, when increasing the diameter of the Fresnel lens 7 to enlarge the heat source detection area, if a polyethylene Fresnel lens without the shielding rod 8 is used, the lens will expand and contract over time, causing unevenness on the lens surface. occurs, infrared rays are scattered, etc.
A problem arises in that the focusing effect of infrared rays is impaired and the reliability of heat source detection is lost, but if the shielding rod 8 is buried inside the lens as in this embodiment, deformation of the lens due to changes over time can be suppressed. As a result, highly reliable heat source detection can be ensured over a long period of time, and furthermore, changes in the detection area due to thermal deformation of the lens can be prevented.

In addition, although the shielding rod 8 is used as a shielding body in the above embodiment, the present invention is not limited to this, and a reflecting plate or a plate-shaped shielding plate may be used as a shielding body.

Furthermore, in this embodiment, one shielding rod 8 is embedded in the Fresnel lens 7, but a plurality of shielding rods 8 are embedded in the Fresnel lens 7.
may be buried in a desired position of the lens 7 as appropriate.

〔Effect of the invention〕

As explained above, the present invention includes a Fresnel lens in which infrared rays are transmitted to one element in a common detection range of each element of a pair of pyroelectric infrared sensor elements in a direction intersecting the arrangement direction of the pair of elements. Since a shield is provided to prevent transmission, it is possible to create an area where heat sources can be detected in areas that were previously undetectable, thereby greatly expanding the area where heat sources can be detected. It becomes possible. In addition, when increasing the diameter of the Fresnel lens to enlarge the heat source detection area, if you use a polyethylene Fresnel lens without a shield, the lens will expand and contract over time, causing unevenness on the lens surface. However, if a shielding body is buried inside the lens as in the present invention, the problem is that the infrared condensing effect is impaired and the reliability of heat source detection is lost due to the scattering of infrared rays. As a result of suppressing lens deformation,
It is possible to ensure highly reliable heat source detection over a long period of time, and furthermore, it is possible to prevent changes in the detection area due to thermal deformation of the lens.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the heat source detection area when no shielding rod is provided in the Fresnel lens, Figure 3 is an explanatory diagram showing the heat source detection area when the shielding rod is embedded in the Fresnel lens, and Figure 4 A and B are A wiring diagram of elements in a dual structure pyroelectric infrared detection device, Fig. 5 is an explanatory diagram showing a conventional infrared detection device, Fig. 6
Figures A and B are output waveform diagrams of the dual-type infrared sensor element used to explain the conventional example. DESCRIPTION OF SYMBOLS 1...Housing, 2...Aperture, 3...Pyroelectric infrared sensor element, 4...First element, 5
... second element, 6 ... transmission plate, 7 ... Fresnel lens, 8 ... shielding rod (shielding body), 10 ...
…Condenser lens.

Claims (1)

[Claims] 1 A pyroelectric infrared sensor element with a dual structure having a pair of elements; a Fresnel lens disposed near the pyroelectric infrared sensor element to guide infrared rays to the pyroelectric infrared sensor element; In the electro-infrared detection device, the Fresnel lens includes a shielding member within a common detection range of each of the pair of elements for blocking infrared rays from passing through to one element in a direction intersecting the arrangement direction of the pair of elements. A pyroelectric infrared detection device characterized by being buried.