JP2015036666A - Microwave sensor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-frequency CM microwave sensor system capable of detecting horizontal movement of a target with high reliability with a simple structure and a simple signal processing method.SOLUTION: A microwave sensor system of a two-frequency CM system transmits first and second microwaves having different frequencies, receives reflection waves of the first and second microwaves from a target in the case where a target is present in the transmission direction of the first and second microwaves, and measures a distance to the target by use of phase difference between IF signals after mixing the reflection waves and the transmission waves. The microwave sensor system includes a pair of microwave sensors, an A/D converter, and a computer. The computer includes means for calculating an angle error signal with respect to a horizontal position x of the target, and calculating a relation between the angle error signal and the horizontal position x of the target on the basis of an n-th order approximate curve (where n is a natural number equal to two or greater) to thereby calculate a movement distance of the target.

Description

  The present invention relates to a two-frequency CW (continuous wave) type microwave sensor device capable of detecting a lateral movement of a target with high accuracy by a simple structure and a simple signal processing method.

  Inexpensive CW type microwave sensors are widely used for consumer security sensors. Since the CW sensor uses the Doppler effect, an intruder approaching the sensor can be detected. However, when the intruder crosses the monitoring area horizontally with respect to the sensor, the distance that the target approaches the sensor is so small that the sensor cannot detect the intruder, and it is known that the problem of passing through occurs. . To solve this problem, the lateral distance of the target is detected using a sequential roving method that compares the output levels of the two sensors arranged side by side, and the distance of the detected position is calculated as the distance traveled. A technique for deriving the above is known (Non-patent Document 1). However, in this method, in order to derive the moving distance, the target direction is estimated by replacing the characteristic of the angle error signal with a first-order approximation line, so the measurement result may have an error of almost twice as much as the maximum. It is shown.

  As a known microwave sensor, for example, the inventor proposed in Patent Document 1 transmits a plurality of microwaves having different frequencies toward a detection area, and reflects each microwave from an object existing in the detection area. In a microwave sensor that performs an object detection operation based on a wave, the amount of change per unit time of the relative distance to the object existing in the detection area is measured based on each reflected wave, and the amount of change is greater than or equal to a predetermined amount There is a microwave sensor provided with an object determination means that determines that an object is an object to be detected only when

JP2003-207462

Eiji Takemoto, Yasuhiro Sato, Takuya Fujimoto: "Two-frequency Doppler type intrusion detection sensor", Proceedings of the Conference on Systems Control Information Society, Vol.48, pp.13-14 (2004)

  Security sensor systems require more accurate detection methods. More specifically, the threshold for the distance traveled when detecting a target is narrowed to reduce false detections caused by car / vegetation shaking or noise. It is demanded.

  In the CW sensor, as described above, it is difficult to detect the movement of the monitoring area moving in the horizontal direction, and even if the method of Non-Patent Document 1 is used, an error of up to twice as much as the measurement result occurs. There is a problem. A method of moving the antenna mechanically such as a phased array and scanning the beam left and right and a monopulse method are also known, but there is a problem that it is too expensive for consumer use.

  Accordingly, an object of the present invention is to provide a two-frequency CW-type microwave sensor device that can detect the movement of the target in the lateral direction with a simple structure and a simple signal processing method.

  The inventor reduced the fitting error and reduced the measurement error by changing the approximate straight line conventionally used in fitting the angle error signal to an approximate curve using an n-order function close to the actual angle error signal. The detection accuracy can be increased.

That is, the present invention comprises the following technical means.
The first invention transmits the first and second microwaves having different frequencies, and when the target exists in the transmission direction of the first and second microwaves, the first and second microwaves from the target In a two-frequency CW-type microwave sensor device that receives reflected microwaves and measures the distance to the target based on the phase difference between the IF signals after mixing these reflected waves and their transmitted waves, A wave sensor, an A / D converter, and a computer. The computer calculates an angle error signal with respect to the lateral position x of the target, and the relationship between the angular error signal and the lateral position x of the target is n. A microwave sensor device comprising means for calculating a moving distance of a target by calculating based on a next approximate curve (where n is a natural number of 2 or more).
A second invention is characterized in that, in the first invention, the n-th order approximate curve is a fifth-order recent curve.
According to a third invention, in the first or second invention, the computer further comprises means for calculating the moving speed v of the target based on the difference between the positions x calculated every sampling time t. .
A fourth invention is the invention according to any one of the first to third aspects, wherein the microwave sensor is configured to include a microwave sensor unit, a pulse generator, and an amplifier circuit, and the microwave sensor unit includes: Voltage-controlled oscillator that outputs two different frequencies in a time-sharing manner, a double balanced mixer, a transmission antenna, a power divider connected to the double balanced mixer and the transmission antenna, and a reception connected to the double balanced mixer And an antenna.

  According to the present invention, it is possible to provide a two-frequency CW-type microwave sensor device that can detect a lateral movement of a target with high accuracy by a simple structure and a simple signal processing method.

Configuration diagram of a dual-frequency CW-type microwave sensor device according to an embodiment Configuration diagram of microwave sensor according to an embodiment Reflection signal of target moving laterally relative to microwave sensor front direction Angular error signal for target lateral position Measured signal level for lateral position Angular error signal for lateral position Distance to target for lateral position Coefficient of each order in the approximate curve of Equation 3 Calculated travel distance for lateral position Maximum value, average value, and minimum value of maximum error rate

The present invention discloses a technique for deriving a lateral movement distance of a target from a change in angular error using a two-frequency CW-type microwave sensor device that detects intrusion of a target using a sequential roving method. . Here, the sequential roving method is a method of calculating the angle of the target based on the ratio of the reception level of the reflected wave received from the angle of two adjacent antennas.
The microwave sensor of the present invention transmits two types of microwaves having different frequencies toward a detection area, and detects a phase difference between two intermediate frequency (IF) signals based on the respective reflected waves. Since this phase difference has a correlation with the distance to the target (detection target object such as a human body), the distance to the target can be measured by obtaining this phase difference.

In the present invention, the sensitivity of the two-frequency CW sensor arranged on the left and right is the same, and in the fitting of the angle error signal, the measurement error is reduced by performing processing that regards the angle error signal as an nth-order approximation curve. ing. Here, it is preferable that the n-th order approximate line is a fifth-order curve. That is, the target position is estimated by an approximate curve that represents the characteristics of the angle error signal using a quintic function, and the moving speed is obtained by taking the time difference between the target positions.
According to the present invention, it is possible to reduce, for example, an error by 72% while maintaining a simple configuration using a sequential roving method and a CW method sensor.

  Hereinafter, details of the present invention will be described with reference to examples, but the present invention is not limited to the examples.

≪Configuration≫
FIG. 1 is a configuration diagram of a two-frequency CW type microwave sensor device 1 according to the present embodiment.
The two-frequency CW type microwave sensor device 1 of the present embodiment includes two microwave sensors 10L and 10R, an A / D converter 20, and a computer 30.
The microwave sensors 10L and 10R are each directed outward by an angle θ.
The Doppler output signals from the microwave sensor 10L are v _d1L and v _d2L, and the Doppler output signals from the microwave sensor 10R are v _d1R and v _d2R . These Doppler output signal is converted into a digital signal by the A / D converter 20 is taken into the computer (PC) 30, where v and _d1L and v _d2L phase detection, v _d1L and v _d1R amplitude detection.

FIG. 2 is a configuration diagram of the microwave sensor 10.
The microwave sensor 10 includes a microwave sensor unit 11, a pulse generator 12, and an amplifier circuit 13.
The microwave sensor unit 11 includes a voltage-controlled oscillator (hereinafter referred to as “VCO”) 101, a power divider 102, a double balanced mixer 103, a transmission antenna 104T _x, and a reception antenna. 105R _x is configured. VCO101 output at from two different frequencies f ₁ and f ₂ are time division, some of which are input to the mixer 103 while being radiated from the transmission antenna 104T _x. Electric wave reflected from the target is received by the receiving antenna 105R _x, is input to the mixer 103. The output of the mixer 103 is taken to the amplifier circuit 13, the reflected wave f ₁ in the amplifier AMP1, a reflected wave f ₂ is amplified by the amplifier AMP2, is output as v _d1, v _d2, respectively. The characteristics of each amplifier are a band of 1 to 100 Hz and a gain of 90 dB.

Table 1 shows the specifications of the microwave sensors 10L and 10R used in the examples. This is set based on European wireless standards.
[table 1]

≪Detection method of laterally moving object≫
The computer 30 includes a calculation device and a storage device, and a program for performing a calculation for detecting a laterally moving object is stored in the storage device. This program calculates the angle error signal for the lateral position x of the target, and the relationship between the angular error signal and the lateral position x of the target is based on an nth order approximation curve (where n is a natural number of 2 or more). Means are provided for calculating the movement distance of the target by calculation.

FIG. 3 is a general output signal when the target moves laterally in the front direction of the dual-frequency microwave sensor. In FIG. 3, the dotted line represents the reflected signal level Lv _L of the sensor 10L, and the solid line represents the reflected signal level Lv _R of the sensor 10R. By using sensors with the same sensitivity, the two sensor outputs can be made symmetrical. Further, since the left and right sensors are provided to be opened at an angle θ with respect to the front direction, the peak interval between the sensor outputs becomes wider as the distance y in the front direction to the target increases.

FIG. 4 is a graph showing the angle error signal ε with respect to the horizontal position x of the target. The angle error signal ε indicates how much the target position is deviated from the front of the sensor, and can be obtained by substituting Lv _L and Lv _R into Equation 1 below.

[Formula 1]

When the two sensors respond to the target, the value of Equation 1 is normalized to vary from -1 to +1. Considering the directivity of the sensor, Lv _L and Lv _R take the maximum value in front of each sensor, so ε is-when the target is located on the left side of the center, ε is 0 when located on the center, and ε is on the right side. When positioned, ε becomes +. Further, as the distance y in the front direction between the target and the sensors 10L and 10R is increased, the peak interval is widened to the left and right. Therefore, if the angle error signal is regarded as a linear approximation line, the slope of ε decreases as y increases. When the angle error signal is regarded as a first-order approximation line, if the reciprocal of the inclination of the approximation line is g, the lateral position x of the target can be approximated by the following equation 2. The value of the reciprocal g of the inclination is unique to the sensor and is a known value.

[Formula 2]

Next, in order to accurately approximate the relationship between the angle error signal and the horizontal position x, an n-th order approximate curve is obtained. x is expressed by Equation 3 below using ε and coefficient g _i .
[Formula 3]

The value of the coefficient g _{i at} this time is a value unique to the sensor, and is obtained by fitting with the measured value by the least square method. Here, since the curve of ε changes as the distance y increases, the coefficient g _i takes a different value depending on the distance y.

When the approximate curve of x in Expression 3 is a function including the parameter of distance y, it is expressed by Expression 4 below. Here, a _i , b _i , and c _i are coefficients obtained by obtaining an approximate curve of the coefficient g _i with respect to the distance y by the least square method.

[Formula 4]

The distance R to the target when a two-frequency CW type microwave sensor is used can be obtained by the following formula 5. Where Δφ is the phase difference between v _d1 and v _d2 , Δf is the difference between the two frequencies f ₁ and f ₂ , and c is the speed of light.

[Formula 5]
Further, the relationship between the lateral position x of the distance R to the target and the distance y in the front direction is expressed by Equation 6 below.

[Formula 6]

When the target is located in the front direction of the sensor, the values of y and R are almost equal. Therefore, when y is replaced with R, Equation 4 is expressed by Equation 7 below.
[Formula 7]

  Equation 7 holds in the range where the angle error signal changes. This range is defined as a detectable range. The detectable range varies depending on the output power of the sensor, reception sensitivity, and target. The moving speed v of the target is obtained by taking the difference between the horizontal positions x calculated at every sampling time t, and is expressed by the following formula 8.

[Formula 8]
≪Measurement method and result≫

Using the two-frequency CW-type microwave sensor device 1 according to the system configuration of the example (FIG. 1), detection of lateral movement of a person was performed.
NI USB-6009 (National Instruments) was used for A / D conversion, and measurement software LabVIEW (National Instruments) was used for signal processing for phase detection and amplitude detection. The sampling rate for signal recording is 4 kHz, and the signal level is calculated by averaging 4000 samples.
The angle with respect to the radiation direction of the sensor is θ = 10 ° at which the angle error signal is nearly linear.
The measuring method is as follows.

A person with a height of 1.7m moves 40m horizontally to the sensor at a speed of 1.4m / s per second. The distance y in the front direction when moving is 10, 15, or 20m. The direction of movement is from left to right and is measured three times at each distance.
The order n in Equation 3 when representing the angle error signal as an approximate curve is n = 5 in order to fit well with the angle error signal at 5th order or more, and the result when the order n = 1 in Equation 2 (approximate straight line) Compare with

FIG. 5 shows the output signal levels of the two left and right sensors 10R and 10L with respect to the standard lateral position at each measured distance. FIG. 6 shows the angle error signal at each distance obtained by substituting the data of FIG. The marker is the measurement value. Table 2 shows coefficients obtained when the measured angle error signals at y = 10, 15, and 20 m are approximated by the equation 3.
[Table 2]

  FIG. 7 shows the measurement result of the distance to the target with respect to the standard lateral position at each distance, and the theoretical value of the distance to the actual target calculated using Equation 6. From FIG. 6 and FIG. 7, it can be confirmed that the measured values almost coincide with the theoretical values.

Next, coefficients a _i , b _i , and c _i (i = 0, 1, 2,..., 5) are obtained using Equation 4. FIG. 8 is a plot of the data in Table 2. Table 3 shows the coefficient values when approximated by a quadratic function to fit the plotted points.
[Table 3]

The solid line portion of the graph of FIG. 6 represents the approximate curve x (ε of the angular error signal obtained by substituting the values of a _i , b _i , and c _{i in} Table 3 and the distance y values of 10, 15, and 20 into Equation 4, respectively. , y). It can be seen that the approximate curve fits well to the measured values.

FIG. 9 summarizes the results of three measurements of the moving distance of the object with respect to the lateral position at y = 10, 15, and 20 m calculated using Equations 7 and 8. The maximum value and the minimum value (threshold value) of the calculated movement distance are indicated by broken lines. When the approximate straight line is used, the upper and lower limits of the calculated moving distance threshold are 2.59 m / s and 0.46 m / s, and the range is 2.13 m / s. When using an approximate curve, the upper and lower limits are 2.13 m / s and 0.89 m / s, and the threshold range is 1.24 m / s.
From this result, it can be seen that the threshold range can be narrowed by 72% by using a fifth-order approximation curve, and the accuracy of error is improved.

Also, the maximum error rate is defined as the difference between the calculated value of the travel distance in the detectable range in measurement and the theoretical value (the actual travel distance of 1.4m) divided by the theoretical value. . FIG. 10 shows the results obtained by obtaining the maximum value, average value, and minimum value of the maximum error rate at each distance for three measurements in the case of an approximate line and an approximate curve. The average value of the maximum error rate for three measurements is 61.6%, 58.5%, and 72.9% when y = 10, 15, and 20m for the approximate line, whereas 33.0% and 38.1% for the approximate curve. %, 32.2%.
Comparing the conventional example and the example, the errors decreased by 28.6%, 20.4%, and 40.7% at y = 10, 15, and 20 m, and it was confirmed that the error could be reduced by fitting using an approximate curve.
The two-frequency CW-type microwave sensor device 1 of the embodiment described above can detect the lateral movement of the target with high accuracy with a simple structure and a simple signal processing method. Use as a sensor can be greatly expected.

1 Dual frequency CW type microwave sensor device
10 Microwave sensor
20 A / D converter
30 Computer (PC)
11 Microwave sensor unit
12 Pulse generator
13 Amplifier circuit
101 Voltage controlled oscillator (VCO)
102 Power divider
103 double balanced mixer
104 Transmit antenna Tx
105 Receive antenna Rx

Claims (4)

When the first and second microwaves having different frequencies are transmitted and the target exists in the transmission direction of the first and second microwaves, the reflected waves of the first and second microwaves from the target are transmitted. In the two-frequency CW type microwave sensor device that receives and measures the distance to the target by the phase difference between the IF signals after mixing these reflected waves and their transmitted waves,
A pair of microwave sensors, an A / D converter, and a computer;
The computer calculates an angle error signal for the target position x in the horizontal direction, and calculates the relationship between the angle error signal and the target position x in the horizontal direction based on an nth-order approximation curve (where n is a natural number of 2 or more). And a means for calculating a moving distance of the target.   2. The microwave sensor device according to claim 1, wherein the n-th order approximate curve is a fifth-order recent curve.   3. The microwave sensor device according to claim 1, further comprising a computer that calculates a moving speed v of the target based on a difference between the positions x calculated every sampling time t. The microwave sensor includes a microwave sensor unit, a pulse generator, and an amplifier circuit.
The microwave sensor unit includes a voltage-controlled oscillator that outputs two different frequencies in a time division manner, a double balanced mixer, a transmission antenna, a power divider connected to the double balanced mixer and the transmission antenna, and a double balance. 4. The microwave sensor device according to claim 1, further comprising a receiving antenna connected to the mixer.