JP4640447B2 - Infrared detector - Google Patents

Description

  The present invention relates to an infrared detector that detects infrared energy radiated from a human body and detects the presence and movement of a human body in a detection area.

  FIG. 6 shows a block diagram of a conventional infrared detector. The pyroelectric element 1 is widely used for infrared detection, and a current corresponding to a change in infrared radiation is output from the pyroelectric element 1, and the current is converted into a voltage by the current-voltage conversion circuit 2. The signal is amplified by the amplifying unit 25, and the comparison unit 26 compares the output with a preset threshold value. When the threshold value is exceeded, a detection signal is output as a human body is present or moved. .

Note that the frequency characteristics with respect to the gain of the entire circuit increase the detection sensitivity for the human body by configuring a bandpass filter centered around 1 Hz in accordance with frequency components close to the movement of the human body (for example, components centered on 1 Hz). At the same time, malfunctions with respect to other signals are suppressed.
JP-A-6-222159

  However, the pyroelectric element 1 may generate single-shot noise called popcon noise, and the human body may be erroneously detected by the popcon noise. Popcon noise is caused by differences in the thermal expansion coefficient of the pyroelectric element 1, the support base that supports the pyroelectric element 1, the adhesive that bonds the support base, and the circuit board on which the circuit components that constitute the circuit are mounted. It is thought that this occurs because compression / tensile stress concentrates on defects, microcracks, etc. existing in the electric element material, and unnecessary charges are generated.

  Therefore, conventionally, optimizing materials such as a support base, a circuit board, or a conductive adhesive against the popcon noise, and reducing the generation of popcon noise by changing the structure and shape of the pyroelectric element 1 I was trying. However, such a countermeasure cannot completely suppress the generation of popcon noise, and has a problem that a malfunction due to popcon noise occurs.

  In addition, malfunction may occur due to impact or electrical impulse noise.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an infrared detection device that prevents erroneous detection due to popcon noise, external instantaneous impact, or electrical impulse noise. is there.

In order to achieve the above object, a first aspect of the present invention is a pyroelectric element that receives infrared rays radiated from a human body existing in a detection area, and a current-voltage converter that converts an output current of the pyroelectric element into a voltage signal. And a detecting means for detecting the presence or absence or movement of a human body in the detection area by performing frequency analysis on the voltage signal output from the current-voltage converting means, and the detecting means is a first corresponding to the movement of the human body centered on 1 Hz. A first amplifier circuit that amplifies the voltage signal in one frequency band, a second amplifier circuit that amplifies the voltage signal in a second frequency band of about several tens to 100 Hz higher than the first frequency band, A first comparison circuit that compares the output signal amplified by one amplification circuit with a predetermined threshold value, and a second comparison that compares the output signal amplified by the second amplification circuit with a predetermined threshold value Comparison between the circuit and the first comparison circuit The first pulse width discrimination circuit for identifying a pulse width of the pulse signal corresponding to the result, a second pulse width discrimination circuit for identifying a pulse width of the pulse signal according to the comparison result of the second comparison circuit, the And a determination unit that determines the presence or absence or movement of a human body in the detection area based on the identification results of the first and second pulse width identification units, and the determination unit recognizes the pulse width identified by the first pulse width identification circuit. Is less than a predetermined value, it is determined to be due to popcon noise, and if the pulse width identified by the first pulse width identification circuit is greater than or equal to the predetermined value, it is determined that a human body is detected, and the first pulse width identification Even when the pulse width identified by the circuit is equal to or smaller than a predetermined value, it is determined that the human body is detected when the pulse width identified by the second pulse width identification circuit is zero.

  According to the first aspect of the present invention, the frequency of the voltage signal is analyzed, and the presence or movement of the human body is detected by the frequency component corresponding to the movement of the human body included in the voltage signal, so that popcon noise or instantaneous external shock is detected. Alternatively, it is possible to prevent erroneous detection due to the frequency component of the voltage signal corresponding to the electrical impulse noise, and it is possible to accurately detect the presence / absence and movement of the human body.

  Hereinafter, embodiments of the present invention will be described in detail. However, the basic concept of the present invention will be described before the embodiments of the present invention are described.

  FIG. 2 shows a frequency spectrum of the current output of the pyroelectric element 1 with respect to infrared rays from the human body existing in the detection area, and FIG. 3 shows a frequency spectrum of popcon noise included in the current output of the pyroelectric element 1. As is clear from FIG. 2, the frequency spectrum of the current output with respect to infrared rays from the human body is concentrated on the low frequency side in the vicinity of the frequency (approximately 1 Hz) corresponding to the movement of the human body, and the movement of the human body in the detection area (or Movement) for a relatively long time. On the other hand, as shown in FIG. 3, the frequency spectrum of popcon noise includes from about 1 Hz to a high frequency range of several hundred Hz or more, and is output only for a short time. Although not shown, external noise such as impact and electric impulse noise other than popcon noise includes frequency components from low to high and is output only for a short time.

  Therefore, if the current output of the pyroelectric element 1 is frequency-analyzed and appropriate signal processing is performed focusing only on the frequency component corresponding to the movement of the human body, the human body can be accurately detected without being affected by popcon noise or the like. be able to. Therefore, a configuration for detecting a human body based on such a basic concept will be described in the embodiment.

  In the present embodiment, the pyroelectric element is formed by a multi-divided light receiving lens formed of a so-called Fresnel lens array, which is formed in a dome shape and whose spherical surface is divided into, for example, a plurality of Fresnel lenses. 1 is condensed. Thereby, as shown in FIG. 4, the detection area is divided into a plurality of detection areas M... So that the current output change of the pyroelectric element 1 due to the movement of the human body H appears remarkably.

  FIG. 1 shows a block diagram of the present embodiment, in which an output current from the pyroelectric element 1 is converted into a voltage signal by the current-voltage conversion unit 2, and this voltage signal is amplified by the amplification unit 5 to be compared with the comparison unit 14. Is entered. The amplifying unit 5 includes a first amplifying circuit 5a that amplifies a voltage signal in a first frequency band centered on 1 Hz, and a voltage in a second frequency band that is higher than the first frequency band and approximately several tens to 100 Hz. And a second amplifier circuit 5b for amplifying the signal.

  The comparison unit 14 compares the voltage signal output from the first amplification circuit 5a of the amplification unit 5 with a predetermined threshold value Vr3, and the voltage output from the second amplification circuit 5b. And a second comparison circuit 14b for comparing the signal with a predetermined threshold value Vr4. Further, a pulse width identification unit 19 is provided after the comparison unit 14. The pulse width identification unit 19 includes a first pulse width identification circuit 19a that identifies the pulse width of the output signal of the first comparison circuit 14a and a second pulse width of the output signal of the second comparison circuit 14b. And a pulse width identification circuit 19b. Then, the determination unit 20 determines whether or not a human body is detected based on the two output signals of the pulse width identification unit 19.

  FIG. 5 shows output waveforms of the circuits of the amplifier 5 and the comparator 14. That is, since the frequency component of the voltage signal corresponding to the human body is in a low frequency range of several tens Hz or less, a large level voltage signal is output from the first amplifier circuit 5a as shown in FIG. As shown in FIG. 5B, only a very small level voltage signal is output from the second amplifier circuit 5b. Further, since the frequency component of the voltage signal corresponding to popcon noise is included up to a high frequency range such as several hundred Hz, the first and second amplifier circuits 5a and 5b have a frequency range as shown in FIGS. Both output a large level voltage signal.

  Here, the first and second comparison circuits 14a and 14b output a relatively narrow pulse signal for a voltage signal corresponding to popcon noise or the like, while corresponding to the human body. For a voltage signal, when the temperature difference between the background and the human body is large, the current output of the pyroelectric element 1 is large and the pulse width of the pulse signal is widened. The current output of the electric element 1 is reduced and the pulse width of the pulse signal is reduced. In this case, it is difficult to distinguish between a voltage signal corresponding to popcon noise and the like and a voltage signal corresponding to a human body only with a voltage signal in the first frequency band centered on 1 Hz.

  On the other hand, in the present embodiment, the output signal of the second comparison circuit 14b is reliably output for a voltage signal corresponding to popcon noise or the like, whereas for the voltage signal corresponding to a human body. Is not output from the second comparator circuit 14b because the output voltage of the second amplifier circuit 5b is very small.

  Therefore, the determination unit 20 determines that the pulse width identified by the first pulse width identification circuit 19a is equal to or less than a predetermined value because of popcon noise or the like. If the pulse width is equal to or greater than the predetermined value, the human body If the pulse width identified by the second pulse width identification circuit 19b is zero, that is, if there is no output from the second comparison circuit 14b, it is determined that the human body is detected. Like to do. As a result, the human body can be detected with higher accuracy than in the case where the determination is made only with the voltage signal in the first frequency band centered on 1 Hz.

It is a block diagram of an embodiment. It is a figure which shows the frequency spectrum of the electric current output corresponding to the human body of a pyroelectric element. It is a figure which shows the frequency spectrum of the current output corresponding to the popcon noise of a pyroelectric element. It is explanatory drawing of the detection area in the same as the above. It is a wave form diagram for operation explanation same as the above. It is a block diagram of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pyroelectric element 2 Current voltage conversion part 5 Amplification part 5a 1st amplification circuit 5b 2nd amplification circuit 14 Comparison part 14a 1st comparison circuit 14b 2nd comparison circuit 19 Pulse width identification circuit 19a 1st pulse width Identification circuit 19b Second pulse width identification circuit 20 Determination unit

Claims (1)

A pyroelectric element that receives infrared rays radiated from the human body in the detection area, a current-voltage conversion means that converts the output current of the pyroelectric element into a voltage signal, and a frequency analysis of the voltage signal output from the current-voltage conversion means Detection means for detecting the presence or absence or movement of the human body in the detection area, and the detection means amplifies the voltage signal in a first frequency band centered on 1 Hz and corresponding to the movement of the human body. A second amplifying circuit that amplifies the voltage signal in a second frequency band of about several tens to 100 Hz higher than the first frequency band, and an output signal amplified by the first amplifying circuit has a predetermined threshold. A first comparison circuit for comparing the value, a second comparison circuit for comparing the output signal amplified by the second amplification circuit with a predetermined threshold, and a pulse corresponding to the comparison result of the first comparison circuit To identify the pulse width of the signal Based of the pulse width discriminating circuit, a second pulse width discrimination circuit for identifying a pulse width of the second pulse signal according to the comparison result of the comparison circuit, the identification result of the first and second pulse width discrimination unit And a determination unit for determining the presence or absence of a human body in the detection area and movement, and the determination unit determines that the pulse width identified by the first pulse width identification circuit is due to popcon noise when the pulse width is less than a predetermined value. If the pulse width identified by the first pulse width identification circuit is greater than or equal to a predetermined value, it is determined that a human body has been detected, and even if the pulse width identified by the first pulse width identification circuit is less than or equal to the predetermined value, 2. An infrared detecting device, wherein when the pulse width identified by the pulse width identifying circuit 2 is zero, it is determined that a human body is detected.

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