JPH0433399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a pyroelectric infrared detection device using a dual structure pyroelectric infrared sensor.

<Prior Art> In recent years, pyroelectric infrared detection devices that detect low-level heat rays emitted from the human body have been increasingly used instead of light-emitting/receiving infrared devices (LEDs). The infrared sensor used in such a device is composed of two infrared elements, and prevents the occurrence of erroneous output due to the arrival of external thermal noise or changes in ambient temperature. In other words, the two infrared elements have a so-called dual structure in which they are connected in series or parallel with their polarization directions reversed, and when a hot ray is incident on the two infrared elements at the same time, the outputs of both elements cancel each other out, resulting in infrared radiation. This is a configuration in which no output is generated from the sensor.

<Problems to be solved by the invention> However, the currently widely used infrared detection devices have low input sensitivity of pyroelectric infrared sensors.
A concave condensing mirror with a large area is used, and an infrared sensor is placed near its focal point to increase the amount of heat rays incident on the infrared sensor, thereby improving the S/N ratio. Therefore, an infrared detection device with a good S/N ratio inevitably has the disadvantage of being large.

Further, some infrared detection devices have a multi-focal condenser mirror in which the condensing mirror is divided into multiple parts in order to sense when a detected object such as a human body approaches from various directions. However, even in this case, it is necessary to maintain a good S/N ratio of the output of the infrared sensor, so each divided mirror piece itself becomes large, resulting in the overall size of the infrared detection device and its installation. Space was severely restricted.

Further, the infrared detection device is mainly intended to detect the movement of a human body, and the frequency of the output of the infrared sensor due to the movement of the human body is about 0.1 Hz to 10 Hz. In a circuit that processes such low frequency signals, the capacitance of the capacitor of the filter circuit inevitably becomes large, and it has been difficult to downsize the infrared detection device in order to secure the space for accommodating the filter circuit.

<Means for Solving the Problems> An object of the present invention is to provide a pyroelectric infrared detection device that solves the above-mentioned drawbacks.

The principle of the apparatus of the present invention will be described with reference to FIG. 1. The infrared sensor 10 has a so-called dual structure in which two infrared elements 10a and 10b are disposed on one pyroelectric plate 10c. Infrared sensor 10
on the light-receiving surface side of the infrared elements 10a, 10b.
At least one condensing mirror piece 11 is arranged so as to stand upright on a plane located approximately in the middle of the plane. Both surfaces of the condensing mirror piece 11 are reflective surfaces, and are configured to reflect heat rays (far infrared rays) from the object to be detected and make them enter the infrared element 10a or 10b.

<Function> Assuming that the object to be detected moves parallel to the direction of the arrow at a constant speed on the light-receiving surface side of the infrared sensor 10, as shown in FIG. The hot rays 13 directly enter the infrared elements 10a and 10b. However, at point X where the detected object 12 is close to the infrared sensor, the heat rays from the detected object 12
0a, the direct incident portion 14a and the reflected portion 14b from the condensing mirror piece 11 are added together, and the heat rays enter the infrared element 10b, while the incidence of the heat rays is restricted or blocked. When the detected object 12 is at point B, the heat rays are directly incident on both the infrared elements 10a and 10b.

The outputs of the infrared elements 10a and 10b at this time are conceptually shown in FIG. 3. Output level a is the output when the heat ray is directly incident, and output level b is the output when the infrared element 10a is reflected by the condensing mirror piece 11. The output when the heated rays 14b are added and incident is shown. Therefore, the differential output from the infrared sensor, that is, the infrared elements 10a, 10 connected with opposite polarity.
The added output of b is as shown in Figure 4, and the output signal b when the reflection from the condensing mirror piece is superimposed.
The output level is nearly twice that of the output signal a in the case of direct incidence only, and the signal frequency is higher. The peak value of the output signal b is determined by the reflection coefficient of the condensing mirror piece 11. In addition, the pulse width of the output signal b is determined by the height h of the condensing mirror piece from the light receiving surface,
1 and the distance s between the infrared elements 10a and 10b. Since the interval s is usually constant, the height h and width w are determined as appropriate during design. The width w of the converging mirror piece is the infrared element 10a, 1
It is sufficient to have a width that temporarily restricts and preferably blocks the heat rays incident on 0b, and a small shape of the converging mirror piece is sufficient. Note that the dotted lines a ₁ and d ₁ in Figure 3
is the output when a phase difference occurs due to the interval s between the heat rays incident on the infrared elements 10a and 10b, and the differential output is shown by dotted lines a and b in FIG. Further, a two-dot broken line 15 indicates a plane that separates the two infrared elements 10a and 10b. When the detected object 12 moves beyond the broken line 15 to the point Y, the reflected portion 16b is superimposed on the directly incident portion 16a and is incident on the infrared element 10b.
As a result, as is clear from FIGS. 3 and 4, it can be seen that the outputs become symmetrical c and d with respect to point B.

<Examples> Examples of the present invention will be described in detail below with reference to the accompanying drawings.

In FIGS. 1 and 5, the dual structure infrared sensor 10 has two pyroelectric plates placed on one pyroelectric plate 10c.
The infrared elements 10a and 10b are arranged. Although not shown in the drawings, this infrared sensor 10 has the back surface of a pyroelectric plate 10c fixed onto a ceramic substrate via an electrode, and is housed inside a case 17 having a light entrance window. On the light-receiving surface side 18 of the infrared sensor 10, a U-shaped condensing mirror piece 19 is provided, which is a plane that bisects the two infrared elements 10a and 10b, and extends across the light-receiving surface. Both surfaces of the condensing mirror piece 19 are optically reflective surfaces, and its thickness is about 0.5 mm, and its length (width) in the direction perpendicular to the light receiving surface is about 6 to 7 mm. The case 17 is made of plastic, and contains FETs, filter circuits, etc. 20 is a terminal.

The operation will be described with reference to FIGS. 2 and 6. When the human body 12 approaches from the infrared element 10a side, the heat rays 13 emitted from the human body 12 are transmitted to both infrared elements 1.
0a and 10b, output voltages that gradually rise as shown by output voltages a ₁ and b ₁ in FIG. 6 appear in each infrared element. Human body 12 approaches further
When reaching the point, the heat rays emitted from the human body 12 begin to act as a shield against the infrared element 10b, increasing in intensity as the human body 12 moves in the direction of the arrow, and eventually are completely shielded, and the output voltage becomes zero b It becomes ₂ . On the other hand, for the infrared element 10a, in addition to the heat ray 14a directly incident from the human body 12, the heat ray 14b reflected from the condensing mirror piece 11 from the human body 12 reaching the vicinity of the X point is added, and the total incident amount is The heat ray dose is approximately 2 times that of direct incidence.
It will be doubled. Therefore, the output voltage appearing at the infrared element 10a increases rapidly as shown by _a2 in FIG. When the human body 12 further advances in the direction of the arrow, the reflection by the condensing mirror piece 11 on the infrared element 10a ends, leaving only the direct incident light. A broken line 21 in FIG. 6 shows a case where the human body 12 is located directly above the condensing mirror piece 11, and the heat rays are also directly incident on the infrared element 10b.

As the human body 12 moves further, the infrared element 10a
is blocked by the condensing mirror piece,
The output rapidly decreases as shown in a ₃ of FIG. 6, and after this, it leaves the area of influence of the condensing mirror piece 11 and is again directly exposed to the heat rays from the human body. on the other hand,
The infrared element 10b adds heat rays 16b reflected from the condensing mirror piece as the human body moves, and its output temporarily increases as shown in FIG. _3b3 .

Therefore, since the output obtained from the infrared sensor appears as a differential output of the infrared elements 10a and 10b, pulse-like outputs a and b with high peak values are obtained as shown in FIG. This output is the human body 12
Since the focusing mirror piece 11 has a short-term influence on the moving speed of the infrared element, the frequency is higher than that of the outputs Va and Vb when the heat rays are directly incident on the infrared element.

FIG. 8 shows an example of an amplifier circuit used in the device of the present invention and housed in the case 17. The infrared elements 10a and 10b are connected in series with opposite polarity, and their output is a field effect transistor (FET).
It is applied to the amplifier (AMP) through an impedance conversion circuit consisting of. A filter circuit consisting of a capacitor C and a resistor R is connected to the input side of the amplifier, and the negative feedback circuit of the amplifier is connected to a capacitor C ₁
and resistor _R1 . That is, the amplifier is
As shown in FIG. 9, a bandwidth is provided for the signal obtained from the infrared sensor. The lower limit frequency f ₁ of the bandwidth is determined by the capacitor C and the resistor R, and the upper limit frequency f ₂ is determined by C ₁ and R ₁ .

In the device of the present invention, the frequency of the output of the infrared sensor can be increased to about 10 Hz compared to the conventional 1 Hz. Therefore, for example, the value of the capacitor C that determines the lower limit frequency f ₁ can be set to about 1 in volume ratio. /13, making it possible to make the entire device extremely compact.

10 and 11 show the sensing area of the device according to the invention provided with a condensing mirror piece 19. FIG. When the X, Y, and Z coordinates are determined as shown in Figure 5,
The sensing area in the plane of the axis is the focusing mirror piece 19
It is wide in the plane direction of the converging mirror piece 19, that is, in the X-axis direction, and narrow in the direction perpendicular to the plane of the condensing mirror piece 19, that is, in the Y-axis direction. Further, the sensing region in the Y-axis and Z-axis plane extends in a direction perpendicular to the light-receiving surface 18, that is, in the Z-axis direction. As mentioned above,
By providing a condensing mirror piece, the sensing area has directionality. By utilizing this feature and installing the device of the present invention, for example, on the ceiling of a hallway, it is possible to provide a monitoring space that crosses the hallway.

<Other Embodiments> In the above embodiments, a case has been described in which a light receiving limiting plate 22 is not provided on the light receiving surface side of the infrared sensor, but a light receiving limiting plate 22 may be provided on the light receiving surface side as shown in FIG. good. With this configuration, when the heat rays enter the infrared elements 10a and 10b,
A phase difference occurs that is determined by the distance between the infrared elements 10a and 10b. For example, when the object to be detected moves in the direction of the arrow in FIG. 12, an output with a phase lag than that of the element 10a appears on the infrared element 10b, and the differential output from the infrared sensor 10 has a peak value as shown in FIG. The output is a mixture of signals c and d that are low and have a low frequency, and signals a and b that have a high peak value and a high frequency. The low frequency signal is removed by a bandpass filter as shown in FIG. 8, and the high frequency signal becomes the output of the infrared detection device.

<Effects> Since the device of the present invention has the above-described configuration, it has the following effects.

(1) Even though the condensing mirror piece is significantly smaller than conventional models, a high S/N ratio output can be obtained.
Further, the entire device can be configured to be extremely small, and there is an advantage that there are no restrictions on the installation location when installing the device.

(2) Even when the moving speed of the object to be detected is extremely slow, approximately 0.1 to 1 Hz, the condensing mirror piece itself allows heat rays to enter the infrared sensor differentially and has a heat ray reflection effect, so the output of infrared rays is reduced. It is possible to significantly increase the signal frequency and obtain an output with a high peak value. Therefore, the value of the capacitor used in the bandpass filter can be reduced to about 1/10, and the shape and dimensions of the capacitor can be extremely small, so the space occupied by the circuit incorporated into the device is small, and the entire device can be configured extremely compact. .

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram for explaining the principle of the device of the present invention, FIG. 2 is an explanatory diagram of the operation of the device of the present invention, FIG. 3 is a schematic diagram of the output of the infrared element according to the device of the present invention, and FIG. 5 is a perspective view showing an embodiment of the inventive device, FIG. 6 is an output characteristic diagram of each infrared element in the device of FIG. 5, and FIG. The figure shows the output characteristics of the infrared sensor in the device shown in Fig. 5, and Fig. 8 shows the output characteristics of the infrared sensor in the device shown in Fig. 5.
A wiring diagram showing an example of an amplifier circuit used in the device shown in the figure, FIG. 9 is an explanatory diagram of frequency band characteristics in the circuit of FIG. 8, and FIGS. 10 and 11 are explanatory diagrams of the sensing area of the device of FIG. 5. , FIG. 12 is a schematic configuration diagram showing another embodiment of the present invention, and FIG. 13 is a schematic explanatory diagram of the output of the infrared sensor in the apparatus of FIG. 12. In the figure, 10 is an infrared sensor, 10a and 10b are infrared elements, 11 and 23 are condensing mirror pieces, 12 is an object to be detected, 22 is a light reception limiting plate, C and C ₁ are capacitors, and R and R ₁ are resistors. be.

Claims (1)

[Claims] 1. In a pyroelectric infrared detection device using a dual-structure pyroelectric infrared sensor having two infrared elements, the sensor is located on the light receiving surface side of the infrared sensor and approximately midway between the two infrared elements. A pyroelectric infrared detection device characterized in that at least one condensing mirror piece, which is plate-shaped and has both surfaces serving as reflective surfaces, is provided on a plane.