JP2003035770A - Microwave sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the distance up to a target even in a case that many frequency components are contained in the reflected wave from the target, in a microwave sensor constituted so as to measure the distance up to the object by utilizing a plurality of microwaves different in frequency. SOLUTION: Two kinds of microwaves different in frequency are transmitted to a detection area and a plurality of IF signal waveforms obtained by the reflected waves thereof are formed as rectangular waves. The rectangular waves are sampled as data over a predetermined time and XNOR(exclusive negative OR) of them is integrated and a value obtained by dividing the integrated value by the number of the sampling data is calculated as a correlation value. The distance up to the target is measured on the basis of this correlation value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave sensor (hereinafter referred to as "MW sensor") which is an active sensor using an electromagnetic wave having a lower frequency than visible light.
In particular, the present invention relates to an improvement of an MW sensor that measures a distance to an object using a plurality of microwaves having different frequencies.

[0002]

2. Description of the Related Art Conventionally, as one of the crime prevention devices, a microwave is transmitted toward a detection area, and when a human body is present in the detection area, a reflected wave from the human body (modulated by the Doppler effect is modulated. An MW sensor that receives a microwave) to detect a human body (intruder) is known (for example, Japanese Patent Laid-Open No. 7-37176).

Further, as one type of MW sensor, there is known a type in which a plurality of microwaves having different frequencies are used to measure a distance to an object. This type of sensor transmits, for example, two types of microwaves having different frequencies toward a detection area, and two types of microwaves based on the respective reflected waves are transmitted.
The phase difference between the two IF signals is detected. This phase difference has a correlation with the distance to the target (object such as a human body), and the phase difference tends to increase as the distance to the target increases. That is, it is possible to measure the distance to the target by obtaining this phase difference. Hereinafter, the phase difference detection operation of the IF signal in this type of sensor will be described.

An IF signal based on reflected waves of two kinds of microwaves having different frequencies is a sine wave I as shown in FIG.
In the case of Fout1 and IFout2 (having a phase difference according to the distance to the target), rectangular waves A and B formed from these IF signals are as shown in FIG. 7B, respectively. Then, the distance to the target can be measured by detecting the phase difference between the rectangular waves A and B (the phase difference Δt at the rising portion of the rectangular wave in the figure).

[0005]

However, when microwaves are actually reflected by the human body, the reflected waves include those reflected from the parts of the human body such as the hands and feet that are performing complicated movements. Therefore, it contains many frequency components. Therefore, the IF signal actually obtained is
It is obtained as a complicated waveform as shown in FIG. 8A, and cannot be obtained in the above-mentioned sine wave state.

IF obtained as such a complicated waveform
When a rectangular wave is formed from the signals IFout1 and IFout2,
As shown in FIG. 8B, there is a high possibility that the phase difference between the rectangular waves A and B does not accurately reflect the distance to the target. That is, since the position of the target is originally constant or gradually changes, each rectangular wave A,
The phase difference between B is always constant or gradually changes (the phase difference gradually decreases when the target approaches, and the phase difference gradually increases when the target moves away). Is normal. However, FIG.
In the case shown in (b), the phase difference between the rectangular waves A and B does not reflect it.

That is, although the MW sensor using a plurality of microwaves can theoretically measure the distance to the target as described with reference to FIG. 7, it actually measures the distance to the target accurately. Further improvements were needed to make the measurements.

The present invention has been made in view of the above points, and an object of the present invention is to provide an MW sensor which measures a distance to an object using a plurality of microwaves having different frequencies. The object is to enable the distance to the target to be accurately measured even when the reflected wave from the target contains many frequency components.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention samples the data in a rectangular wave formed from an IF signal for a predetermined time, and XOR these data. (Exclusive OR) or XN
By integrating OR (exclusive NOR), the error contained in the waveform of each frequency component can be canceled.

-Solution means-Specifically, according to the present invention, a plurality of microwaves having different frequencies are transmitted toward a detection area, and when an object exists in the detection area, reflection of each microwave by the object. It is premised on a microwave sensor that detects an object by receiving waves. For this microwave sensor, a plurality of IF signal waveforms obtained by the reflected waves of the respective microwaves are shaped as rectangular waves, and the rectangular waves of these IF signals are data-sampled for a predetermined period of time to obtain these X signals.
Distance measurement that integrates OR (exclusive OR) or XNOR (exclusive NOT), divides this by the number of sampling data as a correlation value, and measures the distance to the object based on this correlation value It is equipped with means.

Due to this specific matter, even when a human body or the like is detected by the MW sensor, even when a reflected wave containing many frequency components due to complicated movements of the human body or legs is received, The error of each frequency component can be canceled by each other, and the distance to the target can be accurately measured.

The time for sampling the IF signal is set to be longer than one cycle of the waveform having the lowest frequency among the frequency components contained in the reflected wave reflected by the object. For example, when the frequency of the lowest frequency waveform is 15 Hz, setting the sampling time to 0.2 sec can be mentioned. By sampling the IF signal for a time longer than the wavelength of the waveform of each frequency component included in the reflected wave in this way, the error of each frequency component can be reliably canceled, and the distance to the target can be increased. Can be measured even more accurately.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Here, a case will be described in which the present invention is applied to an MW sensor that measures the distance to an object using two types of microwaves having different frequencies.

-Description of MW Sensor Configuration- FIG. 1 shows a circuit configuration of the MW sensor 1 according to the present embodiment. As shown in this figure, the MW sensor 1 includes an RF module 2 and a signal processing unit 3.

The RF module 2 includes an oscillator 21 for oscillating a microwave, a modulator 22 for switching the frequency of the microwave oscillated from the oscillator 21, and an oscillator 21.
A transmitting antenna 23 for transmitting the microwave oscillated from the antenna to the detection area, a receiving antenna 24 for receiving the reflected wave of the microwave reflected by an object such as a human body, the received microwave and the voltage waveform of the oscillator 21. Is provided with a mixer 25 for mixing and outputting. In other words, the microwave transmitted from the transmitting antenna 23 toward the detection area is received by the receiving antenna 24 when the frequency of the reflected wave from the human body is modulated by the Doppler effect when the human body exists in the detection area. To be done. The received reflected wave is mixed with the voltage waveform of the oscillator 21 by the mixer 25, and then output from the RF module 2 to the signal processing unit 3 as an IF output signal (IFout0).

On the other hand, the signal processing section 3 includes a transmitting antenna 23.
A first output line L1 and a second output line L2 are provided corresponding to each microwave of each frequency transmitted from. The power sources 31, 32, 33, and
The IF amplifiers 34 and 35 and the comparators 36 and 37 are provided, and a distance measuring calculation unit 38 as a distance measuring unit that is a feature of the present embodiment is provided on the output side of the comparators 36 and 37.

The IF amplifiers 34 and 35 are connected to the output side of the RF module 2 via the first switch SW1. The first switch SW1 connects to the first output line L1 when one of the two types of microwaves is transmitted from the transmitting antenna 23, and the other microwave is transmitted from the transmitting antenna 23. If so, it is switched to connect to the second output line L2.
That is, the IF output signal (IFout1) related to the reflected wave reflected by the human body or the like during the transmission of one microwave is output to the first output line L1 and reflected by the human body or the like during the transmission of the other microwave. The IF output signal (IFout2) related to the wave is output to the second output line L2.

Further, each of the power sources 31 and 32 is connected to the RF via the second switch SW2 which is interlocked with the first switch SW1.
It is connected to the input side of module 2. The second switch SW2 is also adapted to switch the connection state to the power sources 31 and 32 depending on which microwave of the two types of microwaves is transmitted from the transmitting antenna 23. That is, the second switch SW2 is connected to the one power source 3
The modulator 22 switches the frequency of the microwave depending on whether it is connected to the power source 1 or the power source 32 on the other side, whereby the frequency of the microwave transmitted from the transmitting antenna 23 is switched. Has become.

In this way, the switches SW1 and SW
In accordance with the switching operation of 2, the microwave of one frequency is transmitted from the transmitting antenna 23 toward the detection area, and the IF output signal (IFout1) based on the reflected wave is output to the first output line L1 of the signal processing unit 3. The first processing operation of outputting and performing signal processing on the first output line L1 and the microwave of the other frequency are transmitted from the transmitting antenna 23 toward the detection area, and I based on the reflected wave is transmitted.
The F output signal (IFout2) is output to the second output line L2 of the signal processing unit 3 and the second processing operation in which the signal processing is performed on the second output line L2 has a predetermined time interval (for example, several msec). It can be switched. Then, in each processing operation, the IF output signal output from the RF module 2 is amplified by the IF amplifiers 34 and 35, and the outputs from the IF amplifiers 34 and 35 are shaped into rectangular waves by the comparators 36 and 37. It is adapted to be output to the distance measurement calculation unit 38.

Further, each processing operation will be described in detail. When no human body is present in the detection area,
Since the frequencies of the microwaves transmitted from the transmitting antenna 23 and the microwaves received by the receiving antenna 24 are equal, the IF in the output signals from the IF amplifiers 34 and 35 is
The frequency becomes “0”, and no signal is output from the comparators 36 and 37. On the other hand, when a human body or the like exists in the detection area, the microwave received by the receiving antenna 24 is modulated with respect to the frequency of the microwave transmitted from the transmitting antenna 23, so that the comparator 3
The output signal waveforms of Nos. 6 and 37 change, and this rectangular wave is output to the distance measurement calculation unit 38.

-Processing Operation of Distance Measurement Calculation Unit 38- Next, the processing operation of the distance measurement calculation unit 38 which receives the output signal waveforms from the comparators 36 and 37 will be described.

In the distance measuring / calculating section 38, the rectangular waves A and B of the two types of IF signal waveforms received from the comparators 36 and 37 are data-sampled for a predetermined time, and XNOR (exclusive NOR) of these data is sampled. ) Is integrated, and a value obtained by dividing this by the number of sampling data is obtained as a correlation value. Then, the distance to an object such as a human body is measured based on this correlation value. The details will be described below.

Now, the rectangular waves of the two types of IF signal waveforms received from the comparators 36 and 37 are waveforms A and B shown in FIG.
And For these waveforms, the following equation (1) gives
These XNs are sampled by sampling data for a predetermined time.
OR (see the waveform at the bottom of FIG. 2) is integrated, and a value obtained by dividing this by the sampling data number n is obtained as a correlation value.

[0024]

[Equation 1]

This correlation value becomes "1" when the two types of rectangular waves A and B match (when the phase difference is 0),
When the phase difference between the two types of rectangular waves A and B is 180 °, the value is “0”. FIG. 3 is a graph showing the relationship between the phase difference between these two types of rectangular waves A and B and the correlation value.

Using the correlation value thus obtained, the distance R to the object can be obtained by the following equation (2).

[0027]

[Equation 2]

Where Δφ is the phase difference between the rectangular waves A and B, Δ
λ is the frequency difference between the two types of microwaves oscillated by the oscillator 21.

In this way, when the correlation value is obtained and the distance to the object is calculated by using the correlation value, the phase differences of many waveforms are averaged and the errors contained in the individual waveforms are canceled out. Will be. Therefore, the distance to the object can be accurately measured even when the reflected wave from the object includes many frequency components.

FIG. 4 is a graph showing the relationship between the correlation value and the distance to the object.

The time for sampling the IF signal is
It is preferable to set the time sufficiently longer than the time for one cycle of the waveform having the lowest frequency among the frequency components included in the Doppler signal detected by IFout. this is,
This is because the above error can be more surely canceled out as the sampling length is set longer. The degree of offsetting the error when the sampling length is set short and when it is set long will be described below.

Now, the IF obtained on the first output line L1
A case where the signal (IFout1) has the waveform shown in FIG. 5 and the IF signal (IFout2) obtained on the second output line L2 has the waveform shown in FIG. 6 will be described.

Each IF signal (IFout1, IFout2) is obtained as a composite wave of two different reflected waves.
Specifically, the IF signal (IFout1) obtained at the first output line L1 is obtained as a composite wave of the reflected waves α1 and β1, and the IF signal (IF at the second output line L2 is obtained.
out2) is obtained as a composite wave of the reflected waves α2 and β2. Further, here, each IF signal (IFout1, IFo
The phase difference of ut2) is 90 ° (IF signal (IFout
2) is delayed by 90 ° from the IF signal (IFout1)). That is, the original correlation value is set to be "0.5" according to FIG.

Then, each IF signal (IFout1, IFout
36 points are sampled for one wavelength in 2). The “Hi” part of the rectangular wave formed by the XNOR of the data at each point is marked with a circle, “L”.
The portion marked with “o” is indicated by x, and the portion where only the voltage value of one waveform is “0” is indicated by ●, which is indicated on each waveform. That is, at each sampling point, each I
At the points where the F signals (IFout1, IFout2) are both positive or both negative, the rectangular wave to be formed is "Hi", and therefore the above-mentioned mark O is attached. In addition, each IF signal (IFou
At the point where one of t1 and IFout2) is positive and the other is negative, the rectangular wave to be formed is “Lo”, so the above-mentioned x mark is added. Furthermore, each IF signal (IFout1, IFout
2) At the point where one is a positive or negative value and the other is "0", the mark ● is added.

At each sampling point, the "Hi" portion is "1", the "Lo" portion is "0",
The portion where only the voltage value of one waveform is “0” is “0.
The correlation value was calculated as "5".

In this case, the correlation value of the first half wavelength of each IF signal (time T1 in FIGS. 5 and 6) is "11.
5/18 = 0.64 ”. On the other hand, the correlation value of the latter half wavelength of each IF signal (time T2 in FIGS. 5 and 6) is “6.5 / 18 = 0.36”. In this way, when the sampling time of the IF signal is short, the original correlation value (here, each IF signal (IFout1, IFout1,
Since the phase difference of IFout2) is set to 90 °, the original correlation value may be “0.5”).

On the other hand, one wavelength of each IF signal (see FIG.
Also, the correlation value when sampling is performed over time T1 and T2 in FIG. 6 is “18/36 = 0.5”, and the original correlation value is obtained. As described above, the longer the sampling length is set, the more reliably the above error can be canceled.

-Other Embodiments-In the above-described embodiment, the distance measurement calculation unit 38 integrates the XNOR (exclusive NOR) of the rectangular waves of the two types of IF signal waveforms sampled over a predetermined time. Then
A value obtained by dividing this by the number of sampling data is obtained as a correlation value. The present invention is not limited to this, and the XOR (exclusive OR) of the rectangular waves of the two types of IF signal waveforms sampled over a predetermined time is integrated, and a value obtained by dividing this by the number of sampling data is a correlation value. You may ask as.

Further, in the above embodiment, the case where the present invention is applied to the MW sensor which measures the distance to the object by utilizing the two kinds of microwaves having different frequencies has been described. The present invention is not limited to this, and 3
You may make it measure the distance to an object using the microwave more than a kind.

[0040]

As described above, according to the present invention, a rectangular wave formed from an IF signal is applied to an MW sensor that measures the distance to an object by using a plurality of microwaves having different frequencies. XOR (exclusive OR) or XNO of these data is sampled for a predetermined time.
By integrating R (exclusive NOR), the error contained in the waveform of each frequency component is canceled and the distance to the object can be measured. Therefore, when detecting a human body, even if a reflected wave containing many frequency components due to complicated movements such as limbs of the human body is received, the errors of each frequency component cancel each other out. It is possible to accurately measure the distance to an object such as a human body.

Further, when the time for sampling the IF signal is set to a time longer than one cycle of the waveform having the lowest frequency among the frequency components included in the reflected wave reflected by the object, the comparison is performed. By sampling the IF signal for a relatively long time, it is possible to reliably cancel the error of each frequency component described above, and it becomes possible to measure the distance to the object more accurately, and the reliability of the MW sensor is improved. It is possible to improve the sex.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an MW sensor according to an embodiment.

FIG. 2 is a rectangular wave of two types of IF signal waveforms received from each comparator and their XNOR (exclusive NOR)
It is a figure which shows a waveform.

FIG. 3 is a diagram showing a relationship between a phase difference between two types of rectangular waves and a correlation value.

FIG. 4 is a diagram showing a relationship between a distance to an object and a correlation value.

FIG. 5 is a diagram for explaining a degree of offsetting an error when a sampling length is set short and when it is set long.

FIG. 6 is a diagram showing each IF signal and a rectangular wave obtained thereby when the IF signal is a sine wave.

FIG. 7 is a diagram showing each IF signal and a rectangular wave obtained thereby in a conventional example.

FIG. 8 is a diagram showing each IF signal and a rectangular wave obtained by the IF signal when the reflected wave includes many frequency components in the conventional example.

[Explanation of symbols]

1 Microwave sensor 38 Distance measurement calculation unit (distance measuring means)

Claims (2)

[Claims] 1. An object is detected by transmitting a plurality of microwaves having different frequencies toward a detection area and receiving a reflected wave of each microwave when the object is present in the detection area. In the microwave sensor, a plurality of IF signal waveforms obtained by the reflected waves of the above microwaves are shaped as rectangular waves, and the rectangular waves of these IF signals are data-sampled for a predetermined time to obtain these X signals.
Distance measurement that integrates OR (exclusive OR) or XNOR (exclusive NOT), divides this by the number of sampling data as a correlation value, and measures the distance to the object based on this correlation value A microwave sensor comprising means. 2. The microwave sensor according to claim 1, wherein the time for sampling the IF signal is longer than the time for one cycle of the waveform having the lowest frequency among the frequency components included in the reflected wave reflected by the object. A microwave sensor characterized by being set for a long time.