JPH0317112B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting the number of people from infrared rays emitted by human bodies, and more particularly to a temperature compensation circuit for reducing measurement errors due to the influence of ambient temperature.

The applicant had previously published Japanese Patent Application No. 57-172379 "Crowding Level Detection Device" with the aim of detecting the number of people from infrared rays emitted by the human body with high accuracy and with a simple and inexpensive configuration. - No. 192763 proposes ``crowding level detection device''. A detailed explanation of these will be omitted, but the basic configuration is as shown in Figure 1: a condenser lens 2, a scanning mirror 3 that rotates at a constant cycle, and an infrared ray that responds to changes in the incident infrared rays. A detection unit (sensor unit) 1 including a detection element (hereinafter simply referred to as detection element) 4, a preamplifier 10, a bandpass filter 11 for removing noise components, etc., and a sample value for providing a comparison reference potential. A clamper 12, a comparator 1 that outputs a pulse signal when the input signal is at a predetermined level or higher.
3. It consists of a digital multiplexer circuit 14 which emits an output 14a as a sequence of clock pulse numbers corresponding to the pulse width of the pulse signal, a synchronization circuit 15 which sets the detection field of view from the synchronization signal 3a of the scanning mirror 3, and outputs the output signal of the detection element 4. Using the relationship that the width of the waveform is approximately proportional to the number of people being measured, the output 14a
It counts the number of clock pulses and measures the number of people within the field of view. Note that FIG. 1 shows only one channel with one sensing element 4, and the other channels are omitted.

By the way, in this congestion degree detection device, a pyroelectric element having high quality, stable characteristics, and low cost is used as a detection element, but when the ambient temperature changes, its output signal changes accordingly.
Particularly important are the effects of element temperature (internal temperature of the detection unit) and background temperature on the signal. When the element surface is irradiated with infrared rays, it is absorbed, and the element temperature increases from T〓 to (T+△T)〓. At this time, the magnitude of the spontaneous polarization of the pyroelectric crystal becomes as shown in FIG.
Here, Tc is the Curie temperature, which is about 330°C in the case of PZT ceramics, but when used at around room temperature, it is in a range where there is no large decrease with temperature rise. Further, the pyroelectric coefficient λ is given by λ=ΔP _S /ΔT, and the generated voltage is proportional to λ.

This pyroelectric element is a differential type (however, the falling time constant is long and it is transformed into a somewhat integral wave shape).
An output proportional to the fourth power of the temperature difference between the background temperature and the object to be measured can be obtained. A characteristic of the pyroelectric type is that no output can be obtained if the element temperature rises to (T+△T) and becomes constant. If the target (human) does not exist within the visual field, the output waveform will be as shown by the solid line in FIG.

Here, point A indicates the generation timing of a start pulse that is emitted in synchronization with the rotation of the scanning mirror to set the field of view, points B and D indicate the edges of the field of view, and point C indicates the center of the field of view. Period B for viewing the floor background in the field of view compared to detection unit internal scanning period A to B
C, C to D are generally in the negative direction. The reason for this is the internal temperature of the detector (element temperature) due to the self-heating inside the detector (heat generated by the motor, LED, preamplifier) and the normal temperature distribution in the room (the ceiling is high and the floor is low - temperature difference between high and low levels). This is because the temperature is higher than the floor. Also, generally speaking, air temperature and floor temperature often differ, but the difference is at most ±2°C depending on the floor material and environmental conditions, so if you ignore that difference and consider that floor temperature and air temperature are equal, The curves B to C and C to D in FIG. 3 tend to rise as a result of the rise in . This will be explained with reference to FIG. That is, Figure 4 shows
This is a waveform of the amount of infrared radiation incident on the detection element 4. The vertical axis shows the radiation amount as an absolute amount. In the figure, T ₁ a to T ₃ a represent the sensor internal radiation at temperatures T ₁ to _{T 3} , respectively, and T ₁ b to _{T 3} b represent the sensor internal radiation at temperatures T 1 to T ₃ , respectively.
The radiation from the target at T ₃ and T ₁ c to T ₃ c also represent the radiation from the target at temperatures T ₁ to _{T 3} , respectively. In addition, the temperature here is T ₁
The relationship is >T ₂ >T ₃ , and an example is shown in which there is one target (human) at the center of the visual field and one near the edge of the visual field. The detection element 4 receives the sum of radiation from the target and radiation inside the sensor. In reality, radiation from the indoor floor also comes in, but we will ignore it here for simplicity (actual elevator hall floors are made of materials with low emissivity, such as well-polished marble or tiles). Figure 5 shows the total radiation dose distribution. T ₁ d to T ₃ d are the sum of radiation amounts at temperatures T ₁ to _{T 3} , respectively. Moreover, the absolute level of the radiation amount shown in FIG. 5 has no meaning (because a pyroelectric element is used), and only the variation becomes the weight. Here, the radiation from the target (human) largely depends on the difference △T between the surface temperature of the target and the air temperature, and the amount of radiation is determined by the Stefan-Boltzmann law of thermal radiation: W=A△T ^4where A: constant and Become. Now, if △T at temperatures T ₁ , T ₂ , and T ₃ are respectively △T ₁ , △T ₂ , and △T ₃ , then △T ₃ >△T ₂ >△T ₁ . (The surface temperature of the human body is also affected by the temperature to some extent, but the difference is, for example, in the case of the face, even if there is a difference in temperature of about 30 degrees Celsius - in summer and winter - at most 6 to 7 degrees Celsius.
It is about ℃. ) Therefore, the waveform at temperatures T ₁ , T ₂ , and T ₃ is as shown in Figure 5, but the pulsed waveform after passing through the comparator 13 when the threshold level is constant is (the above-mentioned patent application 57-172379, Figure 7) It will look like Figure 6.

T ₁ p to T ₃ p are the outputs of the comparator 13 at temperatures T ₁ to _{T 3} , respectively, and it can be seen that for the same target, the higher the temperature, the narrower the pulse width.
This output is sent to the digital multiplexer 14, which generates the number of clock pulses corresponding to the pulse width. However, if the oscillation frequency of the astable multivibrator in the multiplexer is constant, an error in measuring the number of people will occur depending on the temperature. Furthermore, when the temperature is extremely low (a few degrees Celsius or less), the radiation from the target becomes too strong, causing waveform saturation and linearity to collapse, making it difficult to perform measurements with a large number of people. Therefore, the following three types of temperature compensation can be considered.

(1) Change the amplification factor of the main amplifier.

(2) Change the threshold level.

(3) Change the oscillation frequency in the multiplexer.

As a result of experimentally examining these, we found that (1) is extremely effective for temperature compensation at low temperatures (e.g., below 5℃), (2) is at intermediate temperatures (e.g., 5 to 25℃), and (3) is extremely effective for temperature compensation at high temperatures. It is. That is, as can be easily considered from FIG. 4, the fundamental wave component caused by the scanning period is not affected much by the temperature, but the signal component caused by the radiation from the target is greatly affected. Particularly at low temperatures, the signal waveform rises significantly, which may cause the signal to become saturated or make it difficult to perform measurements by a large number of people. Therefore, it can be understood that the method (1) of varying the amplification factor is effective at low temperatures. Furthermore, the threshold level (2) is an effective and basic correction method for wide-area correction of temperature fluctuations. However, as the temperature rises, the linearity of the waveform breaks down and becomes as shown in Figure 7. However, in Figure 7, the target is 1.
The case of humans is shown. Here, T ₀ >T ₁ , and it becomes difficult to correct it even if the threshold voltage is changed. In such a case, it is easy to understand that the correction in (3) above becomes effective.

The present invention has been made in view of the above points, and an object of the present invention is to provide a highly accurate crowding degree detection device by performing the most appropriate temperature compensation in response to changes in ambient temperature.

The feature of the present invention is that the above-mentioned crowding level detection device is provided with a temperature sensor for detecting the ambient temperature, and it detects whether the ambient temperature is low or medium temperature depending on the detected ambient temperature. The main feature is that it is equipped with a temperature compensation circuit that performs compensation depending on the temperature, when the temperature is high, and when the temperature is high. Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 8 is a block diagram showing an example of the configuration of the congestion level detection device according to the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals.

Note that, like FIG. 1, only one channel is shown.

In FIG. 8, reference numeral 5 denotes a temperature sensor provided in the sensor unit 1 to measure the ambient temperature, and a thermistor or an IC as a temperature sensor controller may be used. For example, the latter type of IC, such as the μPC616C, has very excellent characteristics such as measurement accuracy, stability, and linearity, and its output can be directly taken out as an electrical signal, and its temperature change is also
There is one as large as 10mV/K. 10' is an AGC amplifier. 21 is a first-order delay circuit that stabilizes the output signal of the temperature sensor 5 5a. 22,
24 and 26 are level shift amplifiers, each with 2
The level of the temperature signal 1a is shifted to an appropriate value. Reference numerals 23, 25, and 27 are function generators, each of which is set as shown in FIGS. 9a to 9c, for example. 9th
In the figure, the horizontal axis indicates temperature, which are signal voltages 22a, 24a, and 26a, which are proportional to the temperature.
The figure shows the function of 27, and the figure c shows the function of 23. There is a relationship such as T ₃ ′<T ₂ ′<T ₁ ′, for example, T ₃ ′=
Set as 5℃ and T ₂ ′=25℃. Multiplexer 1
16 in 4' is VCO (Voltage Controlled
Oscillator) is a voltage-controlled oscillator that changes the oscillation frequency by controlling the voltage.
It is a type of Vf converter. 17 is a ring counter, 18 is a frequency divider, and 19 is an AND gate. (For details of these output waveforms, refer to the earlier application mentioned above.) With the above configuration, for example, if the temperature
When T _{1 ′ changes from T 2 ′} (see Figure 9), AGC becomes
The value determined by V ₁ and the threshold level remain the same as the value determined by V ₂ , but they increase by the amount that the voltage rises from the oscillation frequency V ₃ of the VCO to V ₃ '. In other words, the number of people will be corrected. (For example, even if the pulse width of the signal decreases from T ₁ e to T ₀ e in FIG. 7 (output of comparator 13), the oscillation frequency increases and the number of clock pulses increases (output of frequency divider 18). ), the target number of people is measured correctly).
Next, if the temperature is between T ₃ ′ and T ₂ ′ in Figure 9,
The oscillation frequency of VCO16 is determined by _V3 , AGC1
The gain of 0' is maintained at a value determined by _V1 , and only the threshold voltage Vr is determined by the characteristics shown in FIG. 9b. That is, as the temperature rises, Vr decreases, and even a small target signal is captured and corrected. (5th
It is well understood in the figure. ) Finally, when the temperature is below T ₃ ', the gain of AGC 10' is corrected according to the characteristics shown in Figure 9a. That is, the lower the temperature, the lower the AGC gain. This AGC can be easily realized using, for example, a photocoupler consisting of an LED and CdS (details omitted).

As mentioned above, AGC, threshold voltage,
By changing the oscillation frequency of the VCO depending on the temperature, it is possible to correct the negative error (small measured value) that occurs when the temperature rises, and the positive error (large measured value) that occurs when the temperature falls, making it extremely A highly reliable congestion level detection device can be realized. Furthermore, the 9th
In the figure, a linearized correction curve is used for simplicity, but it goes without saying that nonlinear characteristics are more desirable when considered from the theory of thermal radiation. Further, if the present detector is installed in a relatively stable environment, three corrections are not necessarily necessary, and for example, adjustment of the threshold voltage alone is sufficient.

As described above, according to the present invention, the most appropriate temperature compensation for the current temperature is performed in accordance with changes in the ambient temperature, so measurement errors due to the influence of the ambient temperature can be minimized and reliability is achieved. It can be very effective in improving sexual performance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventional congestion level detection device, Fig. 2 is a diagram showing the characteristics of a pyroelectric element,
FIG. 3 is a diagram showing an example of the output waveform of the sensing element, FIGS. 4 and 5 are diagrams showing the waveform of the amount of infrared radiation incident on the sensing element, and FIG. 6 is a diagram showing the pulsed waveform by the comparator. FIG. 7 is a diagram showing an example of the output waveform of the detection element, FIG. 8 is a diagram showing an example of the configuration of the congestion level detection device according to the present invention, and FIGS. 9 a to c
are diagrams showing the characteristics of the function generator, respectively. DESCRIPTION OF SYMBOLS 1...Detection part, 4...Detection element, 5...Temperature sensor, 10...Preamplifier, 10'...AGC amplifier, 11...Band filter, 12...Camper,
13... Comparator, 15... Synchronous circuit, 1
4, 14'...digital multiplexer circuit,
16...VCO, 17...Ring counter, 18
...Period division, 19...AND gate, 21...First-order delay circuit, 22, 24, 26...Level shift amplifier, 23, 25, 27...Function generator.

Claims (1)

[Scope of Claims] 1. A scanning mirror that rotates at a constant cycle, an infrared detection element that outputs a signal according to a change in infrared rays incident on the scanning mirror, and a signal synchronized with the rotation of the scanning mirror that detects the A synchronization circuit that sets the field of view of the infrared detection element, an amplifier that amplifies the output of the infrared detection element, a circuit that extracts only a signal that is equal to or higher than a predetermined value within the field of view set by the synchronization circuit from the output signal of the amplifier; For detecting ambient temperature in a crowding level detection device comprising a circuit that converts the width of the waveform of a signal equal to or greater than a predetermined value into the number of clock pulses, and determines the number of people in the field of view or the level of crowding based on the number of pulses. temperature sensor, and by changing the amplification factor of the amplifier when the detected ambient temperature is low, by changing the predetermined value when the detected ambient temperature is medium temperature, and changing the oscillation frequency of the clock pulse when the detected ambient temperature is high temperature. By letting
A congestion level detection device characterized by comprising a temperature compensation circuit that performs temperature compensation.