JPH0275916A - Infrared ray detector - Google Patents

Abstract

PURPOSE:To prevent a malfunction caused by disturbance light by setting the distance between the filtrating surface of an optical filter and infrared ray detecting elements so that the three-dimensional angle for viewing the detecting elements from one point of the optical filter can be <=1/8pi steradian. CONSTITUTION:When an optical filter 8 is brought nearer to an optical system while the filter 8 is irradiated with the disturbance light of a lighting lamp condensed by the optical system C, the irradiated area of the filter 8 becomes larger. This becomes equivalent to a smaller degree of the condensation of incident light and the quantity of heat per unit area of the filter becomes lower sine the produced heat is uniformly distributed over the whole wide irradiated area. Therefore, influences of secondary heat radiation to infrared ray detecting elements 2a and 2b becomes remarkably low, since the secondary heat radiation is reduced and the distance L between the filter 8 and elements 2a and 2b is sufficiently long. Moreover, when the distance L is set so that the three- dimensional angle for viewing the elements 2a and 2b can become <=1/8pi steradian, a malfunction caused by disturbance light can be prevented surely.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention, for example, can be used in combination with an optical system such as a split lens or a split mirror to detect images within a predetermined detection area set by the viewing angle of this optical system. The present invention relates to an infrared detection device that can constitute an infrared type moving human body detection device that non-contactly detects the presence or absence of a human body in a vehicle and controls the opening and closing of automatic doors and the operation of a security alarm system.

<Prior art> Moving human body detection used for activation switches to control the operation of security alarm systems, automatic doors, etc. by detecting when a moving human body enters or exits a predetermined detection area. Various devices have been put into practical use. The mainstream non-contact type currently in use is the passive infrared type, which utilizes fluctuations in the radiated infrared light flux based on the temperature difference between the background and the moving human body. This moving human body detection device focuses radiant energy from a predetermined detection area set by the viewing angle of the optical system onto an infrared detector using a mirror or lens optical system. After the element converts the change in the infrared flux incident through the optical filter into an electrical signal and amplifies this electrical signal, it determines whether or not this amplified signal is above the detection level. When a human body is detected, a human body detection signal is output.

As the infrared detector used in the above-mentioned moving human body detection device, a differential type sensor called a twin type sensor or dual type sensor, in which two types of pyroelectric elements with different polarities are differentially connected, is generally used. ing.

This differential infrared detector can eliminate noise caused by external factors such as disturbance light by canceling each other out using a pair of pyroelectric elements. In other words, for a moving human body, each detection signal from a pair of pyroelectric elements is output with a time difference, whereas a physical change due to an external factor, such as sunlight irradiation, is output to both pyroelectric elements at the same time. Since the signals are applied equally, each of these pyroelectric elements outputs a signal at the same time, and since they are connected differentially, voltages with opposite polarities and the same magnitude are generated and cancel each other out, and the detector There is no output as . Furthermore, the light entrance window on the light entrance side of this pyroelectric element is equipped with an optical filter that transmits only light with a wavelength of 6 to 14 μm.This optical filter removes disturbance light and only infrared rays are transmitted. It is designed to be transparent.

<Problems to be Solved by the Invention> The infrared detector has a canceling effect by a pair of pyroelectric elements, and an optical filter that transmits only infrared rays and removes visible light, so that the pyroelectric element itself has essentially no problem. It should be possible to eliminate the influence of noise caused by other external factors (for example, noise caused by illumination light such as discharge lamps or incandescent lamps, or disturbance light from automobile headlights). However,
In reality, it may malfunction due to external factors. for example,
In a crime prevention alarm system, an alarm is emitted by the lighting of a patrolling security guard or the headlights of a traveling vehicle. For example, in 1983, there were
An infrared detector No. 14130 has been proposed, in which the viewing angle difference between a pair of light receiving electrodes connected in anti-series is set in the range of 5 to 10''. This is to equalize the irradiation of disturbance light to the object and improve the canceling effect against the disturbance light.However, in a configuration in which such a difference in viewing angle is reduced, the required It cannot be applied to a type of infrared detector that has only a single pyroelectric element.However, even in an infrared detector with such a configuration, it is difficult to combine it with an optical system. In this case, erroneous output will occur when ambient light is directly irradiated.

The inventors investigated the cause of such malfunctions and found the cause. In other words, manufacturers of infrared detectors do not test the performance of infrared detectors in combination with optical systems, and in this way, when ambient light is directly irradiated to an infrared detector without going through an optical system, In this case, the optical filter of the infrared detector scatters visible light other than infrared rays and does not transmit it, thereby preventing malfunction. Therefore, as a result of focusing on the fact that the above-mentioned malfunction occurs due to the combination of an infrared detector and an optical system when constructing a moving human body detection device, etc., the following was found. In other words, because the optical system condenses the infrared light beam to the pyroelectric element, the energy of the light incident on the optical filter is relatively high, and the light enters the optical filter without passing through or reflecting it. The optical filter generates heat due to the high energy of the light absorbed by the filter, and secondary heat radiation is generated from the heat generating portion of the optical filter to the pair of pyroelectric elements.

Here, since materials such as silicon used for optical filters are expensive, it is necessary to make the area of the optical filter as small as possible and widen the viewing angle, and to make the entire detector compact. For this purpose, the optical filter is placed as close as possible to the pyroelectric element, and is generally 0.5 to 1, as shown in the above-mentioned Utility Model Application Publication No. 14130/1983 as 1.5. It is set at about .5 cranes. With this distance, each pyroelectric element 2a is
2b spread angle θ'5. θ'2 will be considerably different, and a difference will occur in the amount of light received by both pyroelectric elements 2a and 2b, so that the canceling effect will not work, and as a result, a human body detection signal will be erroneously output. Even in an infrared detector having only a single pyroelectric element, the pyroelectric element reacts to the secondary thermal radiation energy of the optical filter and malfunctions.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an infrared detection device that does not produce erroneous output due to noise caused by external factors such as ambient light even when combined with an optical system. This is a technical issue.

<Means for Solving the Problems> In the present invention, as a technical means for achieving the above-mentioned problems, an infrared detection device is configured as follows. That is,
In an infrared detection device comprising an optical filter that transmits only infrared rays and an infrared detection element that converts the infrared flux incident through the optical filter into an electrical signal according to the amount of variation thereof, the filter surface of the optical filter and the infrared detecting element such that the solid angle at which the infrared detecting element is viewed from any one point on the optical filter is 1/8π steradian or less.

Further, the distance between the filter surface of the optical filter and the infrared detection element can be set to two or more cranes.

In this infrared detection device, the distance between the filter surface of the optical filter and the infrared detection element is set such that the solid angle at which the infrared detection element is viewed from any one point on the optical filter is 1/8π steradian or less, The distance to the optical filter is varied depending on the size of the infrared detection element. An infrared detection element (pyroelectric element) with a size of 1 x 2 m that is commonly used at present has a distance of 'ltm, which is sufficiently long compared to the 1.5 m distance of existing detectors. Therefore, when an infrared moving human body detection device is configured in combination with an optical system, the optical filter is placed further away from the infrared detection element and closer to the optical system than in existing infrared detectors, and the filter surface of the optical filter is The irradiation area of the disturbance light from the optical system is wider than the irradiation area of the disturbance light in the optical filter of existing infrared detectors, and the degree of light condensation is correspondingly low, so the entire wide irradiation area is There is no local high heat generation caused by heating. However, since the distance to each infrared detection element is relatively long, the spread angle at which heat is radiated from the heating part of this optical filter to each pair of infrared detection elements is approximately the same for each infrared detection element, and each infrared detection element has a relatively long distance to each infrared detection element. Since there is almost no difference between the respective outputs of the detection elements, they cancel each other out and are not output as a detection signal from the detection device.

In addition, the experimental results show that regardless of the size of the infrared detection element, if the distance M (spacing) between the filter surface of the optical filter and the infrared detection element is small (both 2f1 or more), the optical system when combined with the optical system It was found that there was no difference in the outputs of the pair of infrared detection elements regardless of the focal length of the sensor.

<Example> Hereinafter, preferred examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a longitudinal section of an embodiment of the present invention when applied to an infrared type moving human body detection device, in which the infrared radiation from detection areas E1 to E5 and el-e5, which are set according to the respective viewing angles, is divided. The infrared detecting elements 2a and 2b, which are each made of a pair of pyroelectric elements that convert the infrared light flux incident from the optical system C into an electrical signal according to the amount of variation thereof, are each made of a conductive material. Each infrared detecting element 2a, 2b is attached to a separate conductive support 4 using an adhesive 3, and the light incident surface of each infrared detecting element 2a, 2b is covered with a surface electrode 5. Both infrared detecting elements 2a and 2b are differentially connected to each other as shown in FIG. 2, and are also connected to a field effect transistor 6. A light entrance surface of the outer case 7 that encloses each of these infrared detection elements 2a, 2b and the field effect transistor 6 is opened, and an optical filter 8 is disposed in this opening 7a to form a light entrance window. There is. Further, the optical filter 8 has a main body made of silicon, and has a non-reflection coating surface formed on one surface, and a wide band filter surface having a transmission wavelength of 6 to 14 μm formed on the other surface by multilayer thin film coating. This configuration itself is almost the same as existing infrared detectors, but the difference is that
The optical filter 8 is such that the distance between its filter surface and the pair of infrared detection elements 2a, 2b is such that the solid angle at which the infrared detection elements 2a, 2b are viewed from any one point on the optical filter 8 is 1/8π steradian or less, Or, it is in a configuration where two or more cranes are positioned.

FIG. 2 is an electrical circuit diagram of FIG. 1, in which charges generated by an incident infrared light beam in a pair of differentially connected infrared detection elements 2a and 2b are discharged through an input resistor R1 having a high resistance value, and The impedance is converted by the field effect transistor 5, and the field effect transistor 5 is connected to the DC power supply element B.
It has a source follower configuration in which the amplified signal is taken out through two amplification resistors R2 and R3 connected in series through the amplification resistor R2 and R3.

Next, the operation of the embodiment described above will be explained in detail with reference to FIGS. 3 to 6. When disturbance light from a lighting lamp or the like is collected by the optical system C and irradiated onto the optical filter 8, the optical filter 8 is closer to the optical system C than the optical filter 1 of the existing infrared detector. As shown by the dashed line in FIG. 3 for comparison, the irradiation area B of the optical filter 8 of the infrared detector according to this embodiment is larger than the irradiation area B of the optical filter 1 of the infrared detector of the existing device due to the disturbance light. A is infinitely larger. This is equivalent to a smaller degree of condensation of the incident light, and since heat is evenly distributed over the wide irradiation area A, the amount of heat per unit of the optical filter 8 is The optical filter 8 and the infrared detecting element 2a also reduce secondary heat radiation.

2b is sufficiently larger than the distance 1 between the optical filter 1 and the infrared vA detection element in existing infrared detectors, secondary heat radiation is caused by the infrared detection element 2a,
The influence on 2b will be significantly reduced.

However, as shown in FIG. 5, the distance between the optical filter 8 and the infrared detecting elements 2a and 2b is sufficient compared to the distance l between the optical filter 1 and the infrared detecting elements 2a and 2b of the existing infrared detector. Because of the large size, in the optical filter 1 of the existing infrared detector, each infrared detection element 2a during secondary heat radiation.

2b, the respective divergence angles θ′1. θ'2 are considerably different from each other, whereas each infrared detecting element 2a of the secondary heat radiation from the heat generating part 8a of the optical filter 8 of the above embodiment
, the spread angle θl to 2b.

There is almost no difference in θ2, and the pair of infrared detection elements 2a+
2b increases the signal canceling effect.

For example, if L is 2.5w and l is 0.8 cranes, (θ
1-θ2)21.

FIG. 4 shows the filter surface of the optical filter 8 and the above-mentioned 1fl.
Infrared detection elements 2a, 2b of general size of X2fl
This figure shows the actual measured value of the relationship between the distance between the two and the output voltage of the output terminal 0 in FIG. As is clear from this characteristic diagram, by setting the distance to 2 cranes or more, it is possible to reduce the heat generation due to the irradiation of the disturbance light in the optical filter 8 and to obtain the canceling effect by the pair of infrared detection elements 2a and 2b. This effect can be obtained by setting the distance to two days or more, regardless of the size of the infrared detection elements 2a, 2b.

On the other hand, the optical filter 8 and the infrared detection element 2a.

To explain the basis for setting the distance from 2b to the aforementioned 1/8π steradian or less, as explained in Fig. 4,
Infrared detection element 2a of general size of 1 dragon x 2 fins,
2b may be located at a distance of 2f1 or more from the optical filter 8, the above-mentioned solid angle at that time will be IX2 1 1 4π22 23π 8π. That is, making the distance 2fi or more is equivalent to making the solid angle less than 1/8π steradian. As a result, the infrared detection element 2a.

The distance ML of the infrared detection elements 2b to the optical filter 8 is set to be larger than 2N so that the solid angle becomes 1/8π steradian or less as the size of the infrared detection elements 2a and 2b becomes larger than 1m x 2M, and By decreasing the solid angle to 1/8π steradian or less as the solid angle decreases, the same effect as described above can be obtained.

By the way, the characteristics shown in FIG. 4 differ slightly depending on the focal length of the optical system C to be combined. That is, as shown in FIG. 6, when using the optical system C with a large focal length f2, the optical filter 8 and the infrared detecting elements 2a and 2b are Unless the focal length is increased, the above-mentioned reduction in heat generation and cancellation effect cannot be obtained sufficiently.
It has been found from actual measurements that even with optical system C as large as 0 cranes, sufficient effects can be obtained as long as the distance is set to 2u or more or the solid angle is set to 1/8π steradian or less.

Alternatively, a configuration as shown in FIG. 7 may be adopted. That is, in this figure, the same or substantially the same parts as in FIG. 1st
It is constructed in the same manner using the same structural members as shown in the figure, and the distance 1 between the optical filter 8 and the infrared detection element 23.2b is
It has an infrared detector 9 similar to existing infrared detectors in which the infrared rays are set to about 0.7, and an external optical filter 10 is disposed between the infrared detector 9 and the optical system C. ing. The external optical filter 10 is similar to the optical filter 8 of the infrared detector 9, and is similar to the optical filter 8 of the infrared detector 9.
is held between the optical filter 8 of the infrared detector 9 and the optical system C, and the filter surface of the external optical filter 10 and the pair of infrared detection elements The distance between 2a and 2b is 2
+w or more or the solid angle is set to be 1/8π steradian or less. Therefore, in addition to obtaining the same effect as described above, there is an advantage that the existing infrared detector 9 can be used as is. In addition, external optical filter 1
0, the optical filter 8 of the infrared detector 9 is not particularly required. Therefore, the opening 7a may be sealed with a sealing member instead of the optical filter 8. However, in this case, the sealing member does not require a filter function since the external optical filter 10 acts to transmit only infrared rays, but it is necessary to use a material that has the property of transmitting at least light including visible light. There is.

It should be noted that the present invention is not limited to the above-mentioned description and illustrated examples, but may include various modifications without departing from the scope of the claims. For example, we have explained the case where a pyroelectric element is used as an infrared detection element, but any device that converts the incident infrared light flux into an electrical signal according to the amount of variation in the infrared light flux may be used. A thermocouple type) can also be used. Furthermore, it goes without saying that the optical system to be combined is not limited to a split lens, and the same effect can be obtained even when a split mirror or a combination of a plurality of lenses and mirrors is used.

Furthermore, it goes without saying that similar effects can be obtained with a tamp having only a single infrared detection element.

<Effects of the Invention> Since the present invention is configured and operates as described above, it produces the following effects. That is, the distance between the filter surface of the optical filter and the infrared detecting element is such that the solid angle at which the infrared detecting element is viewed from any one point on the optical filter is 1.
/8π steradian or less, or 2fi or more, so when combined with an optical system, the optical filter that absorbs the disturbance light is relatively close to the optical system, so that it absorbs the disturbance light. Since the degree of convergence of the irradiation is low, there is little local heat generation, and the distance to the infrared detecting element is relatively large, so the influence of secondary heat radiation on the infrared detecting element is small. Therefore, even in a type having only a single infrared detection element, malfunctions due to ambient light can be reliably prevented.

In addition, in the case of twin type devices in which a pair of infrared detection elements are arranged side by side, the distance from the optical filter to the infrared detection element is long, so that the secondary heat radiation from the optical filter affects each infrared detection element. The respective spread angles are approximately the same, and the canceling effect of both infrared detection elements is increased, making it possible to more reliably prevent malfunctions caused by ambient light.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of one embodiment of the present invention when applied to an infrared moving human body detection device, FIG. 2 is an electric circuit diagram of FIG. 1, and FIG. 3 is an optical filter of FIG. An explanatory diagram showing a comparison of the irradiation area due to disturbance light with the optical filter of a conventional detector. Fig. 4 shows the detection sensitivity showing the relationship between the distance from the infrared detection element with the filter surface of the optical filter of Fig. 1 and the output voltage. Characteristics diagram. Figure 5 is an explanatory diagram showing a comparison of the spread angles of secondary thermal radiation to each infrared detection element between the device in Figure 1 and the conventional detector. Figure 6 is the focal point of the optical system to be combined. An explanatory diagram showing the relationship between the appropriate distance between the optical filter and the infrared detecting element with respect to the distance. FIG. 7 is a schematic vertical cross-sectional view of another embodiment of the present invention. 2a, 2b - Infrared detection element 8.10 - Optical filter Patent applicant Obtex Co., Ltd. Agent Patent attorney Nishi 1) New-111,i- LM (%J Figure 6 Figure 7

Claims (2)

[Claims] (1) In an infrared detection device comprising an optical filter that transmits only infrared rays and an infrared detection element that converts an infrared flux incident through the optical filter into an electrical signal according to the amount of variation thereof, the optical filter The distance between the filter surface and the infrared detecting element is determined by the solid angle at which the infrared detecting element is viewed from any one point on the optical filter is 1/
An infrared detection device characterized in that the infrared radiation is 8π steradians or less. (2) An infrared detection device characterized in that the distance between the filter surface of the optical filter and the infrared detection element is 2 mm or more.