JPH09166663A - Vehicle detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To install an apparatus at a low cost as a whole and with a simple construction work by detecting sound waves which are generated by a vehicle and judging the existence of the vehicle on the basis of their detection value. SOLUTION: The output signal of a microphone 1 which is installed at a road side part or the like is passed through an amplifier 2, and it is full-wave- rectified by a rectifying circuit 3 so as to be average by an averaging and processing circuit 4. The processed signal is passed through a logarithmic conversion circuit 5 so as to be sent to a comparator 7. When a logarithmic conversion processing operation is executed to the signal, the low-level part of the signal is emphasized so as to become a waveform whose change portion is large even in the case of a quiet vehicle. On the other hand, a reference-value setting part 6 samples the output signal of the circuit 5 only for a definite time at a prescribed cycle, and it finds a little higher-level reference value Th1 than its means value so as to be input to the comparator 7. In addition, the reference value Th1 is updated whenever the signal is sampled. Then, the comparator 7 generates an output when an input signal exceeds the reference value Th1 , it judges the passage of a vehicle, and the number of passed vehicles is displayed on a display device 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detecting device for a vehicle passing on a road or the like.

[0002]

2. Description of the Related Art Conventionally, as a method for detecting a vehicle passing on a road or the like, there are an ultrasonic method and a loop coil method.

Among these methods, the ultrasonic method outputs ultrasonic waves toward a region where a vehicle is detected and detects reflected waves of ultrasonic waves generated when the vehicle passes, thereby detecting the presence or absence of the vehicle. This is the method of discrimination. On the other hand, the loop coil method is a method of detecting the presence / absence of a vehicle from the change in the inductance of the coil due to the presence of the vehicle on the loop coil or the like.

[0004]

By the way, according to the vehicle detection apparatus adopting the above-mentioned ultrasonic method, a transmitting section (ultrasonic oscillator or the like) having a large power is required, and therefore the apparatus becomes expensive. There is.

On the other hand, in the vehicle detection device adopting the loop coil method, the loop coil is buried in the road and used, so that road excavation is required, and the coil itself is considerably large, so that the installation work becomes very large. There's a problem.

The present invention has been made in view of such circumstances, and an object thereof is to provide a vehicle detection device which is inexpensive and easy to install.

[0007]

In order to achieve the above-mentioned object, a vehicle detection device according to a first aspect of the invention is a sound detector (for example, a microphone) for detecting the sound pressure of a sound wave from a vehicle, and the sound detector. An amplifier for amplifying the detection output, a rectifier circuit for rectifying the amplified signal, a logarithmic conversion circuit for logarithmically converting the rectified sound pressure signal, and comparing the output signal of this logarithmic conversion circuit with a predetermined reference value. It is characterized in that it is provided with a comparing means, and the output of the comparing means is used as information for determining the presence or absence of a vehicle.

In the above structure, when the sound detector captures the sound wave from the vehicle, the output signal of the sound detector rises in a pulse shape, and the comparing means produces an output when the level exceeds the reference value. Therefore, the number of passing vehicles can be known by counting the output (pulse signal) of the comparison means.

In the present invention, the input of the amplified / rectified sound pressure signal to the logarithmic conversion circuit is to improve the S / N ratio at a minute level in the sound pressure signal and to adjust the gain by expanding the dynamic range. This is to obtain the effect such as unnecessary.

Further, by performing logarithmic conversion processing on the sound pressure signal, the sound pressure signal at the measuring section can be made a signal proportional to the distance between the sound source and the measurement point. That is, in a semi-free sound field, the distance r (m) from a point source with acoustic power P (W)
The intensity I of the sound at points separated by is represented by the following equation.

I = P / (2πr ² ) (W / m ² ) Therefore, if the sound pressure signal is logarithmically converted, the sound pressure signal in the measuring section and the distance between the sound source and the measuring point have a linear relationship. .

Next, in addition to the device of the first aspect of the present invention, the vehicle detection device of the second aspect of the present invention is provided with a differential processing means at the next stage of the logarithmic conversion circuit, and outputs the signal after the differential processing. It is characterized in that it is configured to compare with a reference value.

In this way, when the sound pressure signal after logarithmic conversion is differentiated, the degree of the signal change is emphasized. Therefore, even if the background noise level fluctuates due to environmental changes such as rain and wind, its influence is affected. As a result, the reference value in the comparison means can be made a constant value.

On the other hand, in the vehicle detection device according to the third aspect of the present invention, the peak detection section is provided at the next stage of the logarithmic conversion circuit instead of comparing the sound pressure signal after the logarithmic conversion process with the reference value in the comparison means. It is characterized in that it is provided so that the peak value of the sound pressure signal after logarithmic conversion processing is obtained.
In addition to the device of the invention of claim 3, the vehicle detection device of the invention described in 1) is provided with a differential processing means in the next stage of the logarithmic conversion circuit,
The feature is that the peak value of the signal waveform after the differential processing is obtained.

Further, in the vehicle detection device of the fifth aspect of the present invention, like the device of the fourth aspect of the present invention, a differential processing means is provided at the next stage of the logarithmic conversion circuit, and the signal waveform after the differential processing is provided. The first positive peak value and the next negative peak value are detected, and the presence or absence of the vehicle is determined from the detection result of the positive and negative peak values.

[0016]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. First, in this example, a microphone 1 having a sharp directivity is used as a means for detecting a sound wave from a vehicle. This microphone 1 is installed on the roadside or the like of a road.

Output signal of the microphone 1 (sound pressure signal)
Is amplified by an amplifier 2 and further subjected to full-wave rectification (absolute value conversion) in a rectifier circuit 3 and then input to an averaging processing (including a low-pass filter etc.) circuit 4. The signal after the averaging process is led to the comparator 7 through the logarithmic conversion circuit 5.

On the other hand, the reference value setting unit 6 includes a logarithmic conversion circuit 5
The output signal of is sampled for a fixed time (for example, 10 seconds) at a predetermined cycle (for example, a cycle of several minutes), and the signal level for each sampling is averaged to obtain the average value (background noise level). For the average value A) of
Obtain the reference value Th1 (see FIG. 2) at a level higher by α,
The reference value Th1 is input to the comparator 7. The reference value Th1 is sequentially updated every time the signal is sampled.

Then, in the comparator 7, the output signal of the logarithmic conversion circuit 5 is compared with the reference value Th1, and the comparator 7 produces an output only when the output signal exceeds the reference value Th1. Therefore, the comparator 7 generates an output only when the vehicle passes or exists on the road, and the number of output signals (pulse signals) is counted by the display device 8 in the next stage and passes (stops). The number of vehicles is displayed.

FIG. 2 is a timing chart showing the operation of the embodiment shown in FIG. 1, and the operation will be described below with reference to this figure. First, assuming that three vehicles pass on the road, the output signal (sound pressure signal) of the microphone 1 will have a waveform as shown in the figure. If this is amplified and rectified and then averaged, the signal waveform Has a waveform such that the three protrusions smoothly continue as shown in the figure. Next, when the logarithmic conversion processing is applied to the sound pressure signal after the averaging processing, the low-level part of the signal is emphasized, and the waveform has a large variation even in a quiet vehicle. The waveform is input to the comparator 7.

The input signal of the comparator 7 is the reference value Th1.
The output pulse is guided to the display unit 8 when the output pulse is exceeded. In this example, since three vehicles have passed, the comparator 7 outputs three pulses as shown in the figure, whereby the number of vehicles “3” is digitally displayed on the display device 8.

In the embodiment shown in FIG. 1 above, the reference value Th1 of the comparator 7 is set based on the sound pressure signal from the microphone 1, so that the background noise level of the surrounding environment of the road is rainy. Even if it fluctuates due to wind or wind, the reference value Th1 of the comparator 7 changes following the fluctuation,
There is no risk of malfunction in the comparator 7, and an accurate vehicle detection signal can always be obtained.

Here, in the embodiment shown in FIG.
When the vehicle stops within the sound pickup range of the microphone 1 due to traffic congestion or the like, the reference value Th1 of the comparator 7 gradually increases due to the sound from the stopped vehicle, and in such a situation, When a stopped vehicle leaves the sound collection range and then a quiet vehicle enters the sound collection range, the vehicle may become undetectable. To avoid this, for example, the comparator 7 holds the reference value Th1 when the output signal indicates that the vehicle is present, and then the comparator 7 releases the reference value hold when the output signal indicates that the vehicle is not present. You should take measures such as doing.

In the above embodiment, the averaging process for smoothing the signal waveform is performed only once before the logarithmic conversion process of the sound pressure signal. May be performed after the logarithmic conversion process. Furthermore, the number of times of processing is not limited to once, and may be multiple times.

In addition to the configuration of the above embodiment,
A high pass filter or a band pass filter may be provided between the amplifier 2 and the rectifier circuit 3. In this case, the directivity of the microphone 1 can be improved.
In other words, the characteristics of the microphone have sharper directivity at high frequencies, so by using a high-pass filter to pass only high-frequency components, even microphones with the same characteristics should be used with sharpened directivity. You can

A plurality of such filters may be provided for one microphone. In this case,
If the signal processing circuit system is provided as many as the number of filters and the sound pressure signal from the microphone 1 is processed in parallel, it is possible to perform processing such as compensating the data missed by one filter with another filter. Therefore, the vehicle detection accuracy can be further improved. Further, even if a method of providing a plurality of filters between the amplifier 2 and the rectifier circuit 3 and using a waveform obtained by adding a sound pressure signal passing through the plurality of filters or a waveform obtained by subtracting the sound pressure signal is used, You can improve.

FIG. 3 is a block diagram showing the structure of another embodiment of the present invention. The difference between the embodiment shown in FIG. 3 and the structure shown in FIG. 1 is that a differential circuit 16 is provided at the next stage of the logarithmic conversion circuit 5 and the signal after the differential processing is input to a comparator 17. There is a point to do.

When the output signal of the logarithmic conversion circuit 5 is subjected to the differential processing in this way, the processed signal becomes a signal having a waveform in which the degree of change is emphasized, as shown in the timing chart of FIG. The fluctuation of the level will be a level that can be ignored. Therefore, by performing such differential processing,
Even if the reference value Th2 in the comparator 17 is set to a constant value, there is no risk of malfunction. However, since the signal waveform after the differential processing swings in both positive and negative, the reference value Th2 is set to either positive or negative. In the timing chart of FIG. 4, the signal waveform up to the logarithmic change process is the same as that shown in FIG.

Here, also in the embodiment shown in FIG. 3, if one or a plurality of high-pass filters or band-pass filters are provided between the amplifier 2 and the rectifier circuit 3, the same effect as above can be achieved. .

Further, in the embodiment shown in FIGS. 1 and 3, all of the sound pressure signal averaging process, the differentiating process, the comparing process, or a part of these processes is executed by calculation by a microcomputer. It may be configured as follows.

FIG. 5 is a block diagram showing the structure of another embodiment of the present invention. The embodiment shown in FIG. 5 is characterized in that a peak detector 27 is provided in place of the comparator 7 used in the embodiment shown in FIG.

As shown in FIG. 6, the peak detector 27 includes a sample hold circuit 27a, a clock 27b and a comparator 27c, and as shown in the timing chart of FIG. 7, outputs the output signal S of the logarithmic conversion circuit 5. , The data sampled for each clock pulse (sampling value of the signal S) are sequentially compared, and when the level of the output signal S becomes equal to or lower than the sampling data, that is, the output signal S of the logarithmic conversion circuit 5 peaks (upper). The comparator 27c is configured to generate an output when it reaches the (convex) position, and the output signal of the comparator 27c is guided to the display device 8 as a signal indicating the presence of a vehicle.

As the peak detecting section 27, it is possible to adopt a digital type instead of the above analog type. As the method, for example,
The output signal of the logarithmic conversion circuit 5 is taken into a microcomputer at a predetermined sampling cycle via an A / D converter, and the sampled value and the immediately preceding sampling value are sequentially compared in the microcomputer. However, there is an arithmetic processing method in which it is considered that there is a vehicle when the current value becomes smaller than the value one sampling before.

FIG. 8 is a block diagram showing the structure of still another embodiment of the present invention. The difference between the embodiment shown in FIG. 8 and the structure shown in FIG. 5 is that a differentiating circuit 36 is provided at the next stage of the logarithmic converting circuit 5 and the positive or negative peak of the signal waveform after the differentiating process is performed. The point is that the peak detector 37 detects the value.

In the embodiment of FIG. 8 also,
An analog type peak detector as described with reference to FIGS. 6 and 7 may be used, or a sound pressure signal is converted into a numerical value (A / D conversion) and the peak value is detected in a microcomputer or the like. It is also possible to adopt a digital method in which the processing for executing is performed.

Here, in the embodiment of FIG. 8, when the actual differential waveform is viewed, there may be a plurality of peaks. Even in such a case, in order to detect the number accurately,
It suffices to provide a flip-flop that sets at the positive peak of the differential waveform and resets at the negative peak or when it passes through the zero point, and count the output.

[0037]

As described above, according to the vehicle detection device of the present invention, the sound wave generated by the vehicle is detected, and the presence or absence of the vehicle is determined from the detected value.
As a result, an expensive output unit such as an ultrasonic wave oscillating source is not required and only the detecting unit is required, resulting in a low cost of the entire apparatus. Further, since the road need not be excavated at the time of installation and only a small device such as a microphone needs to be mounted on the road side or upper part of the road, the installation work is easy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the embodiment.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention.

FIG. 4 is a timing chart showing the operation of the embodiment.

FIG. 5 is a block diagram showing a configuration showing another embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a peak detection unit 27 of the embodiment.

FIG. 7 is a timing chart showing the operation of the peak detector 27.

FIG. 8 is a block diagram showing still another embodiment of the present invention.

[Explanation of symbols]

 1 Microphone 2 Amplifier 3 Rectifier circuit 4 Averaging processing circuit 5 Logarithmic conversion circuit 6 Reference value setting unit 7,17 Comparator 8 Display device 16,36 Differentiation circuit 27,37 Peak detection unit

Claims (5)

[Claims] 1. A sound detector for detecting the sound pressure of a sound wave from a vehicle, an amplifier for amplifying the detected output, a rectifier circuit for rectifying the amplified signal, and a logarithmic conversion of the rectified sound pressure signal. A logarithmic conversion circuit and a comparison means for comparing the output signal of the logarithmic conversion circuit with a predetermined reference value, and is configured to use the output of the comparison means as information for determining the presence or absence of a vehicle. Vehicle detection device. 2. A sound detector for detecting the sound pressure of a sound wave from a vehicle, an amplifier for amplifying the detected output, a rectifying circuit for rectifying the amplified signal, and a logarithmic conversion of the rectified sound pressure signal. A logarithmic conversion circuit, differential processing means for differentiating the output signal of the logarithmic conversion circuit with time as a parameter, and comparison means for comparing the signal after the differential processing with a predetermined reference value, and the output of the comparison means A vehicle detection device configured to use as the information for determining the presence or absence of a vehicle. 3. A sound detector for detecting the sound pressure of a sound wave from a vehicle, an amplifier for amplifying the detected output, a rectifying circuit for rectifying the amplified signal, and a logarithmic conversion of the rectified sound pressure signal. A logarithmic conversion circuit and a peak detection unit for detecting the peak value of the output signal of the logarithmic conversion circuit are provided, and the detection result of the peak value is configured to be used as information for determining the presence or absence of a vehicle. Vehicle detection device. 4. A sound detector for detecting the sound pressure of a sound wave from a vehicle, an amplifier for amplifying the detected output, a rectifier circuit for rectifying the amplified signal, and a logarithmic conversion of the rectified sound pressure signal. A logarithmic conversion circuit, a differential processing means for differentiating the output signal of the logarithmic conversion circuit with time as a parameter, and a peak detection section for detecting the peak value of the signal after the differential processing, and the detection result of the peak value A vehicle detection device configured to use as the information for determining the presence or absence of a vehicle. 5. A sound detector for detecting the sound pressure of a sound wave from a vehicle, an amplifier for amplifying the detected output, a rectifier circuit for rectifying the amplified signal, and a logarithmic conversion of the rectified sound pressure signal. A logarithmic conversion circuit, a differential processing means for differentiating the output signal of the logarithmic conversion circuit with time as a parameter, and a peak detection section for detecting the peak value of the signal after the differential processing, and the signal after the differential processing Vehicle detecting device configured to detect the first positive peak value and the next negative peak value, and use the detection result of the positive and negative peak values as information for determining the presence or absence of a vehicle. .