JP3433718B2 - Distance detection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detecting device, and more particularly to a distance detecting device capable of improving detection distance and accuracy with weak radio waves.

[0002]

2. Description of the Related Art Distance detecting devices are widely used in industrial equipment such as ships, aviation, weather, and plants.

As this distance detecting device, a device to which a pulse radar is applied is known. The pulse radar generates an electromagnetic wave pulse as a transmitted wave, irradiates the target object, receives the reflected wave reflected from the target object, and measures the delay time from the transmission time of the transmitted wave to the time of receiving the reflected wave. Thus, the distance is calculated by multiplying the delay time by the propagation speed of the electromagnetic wave.

[0004]

By the way, the radio waves used in the conventional pulse radar have been high-power radio waves. Therefore, the interfering waves generated by high-power radio waves
It had a great influence on the surroundings. Further, there is a problem that the high-power radio wave used as the pulse radar consumes a large amount of energy required for its generation.

Therefore, in order to solve this problem, it has been proposed to use a weak radio wave system with a small radio wave output. As a result, the influence of the interference wave generated by the high-power radio waves on the surroundings and the problem of power saving were solved.

However, in the weak radio wave system, since the output of the radio wave applied to the object is weak, it is difficult to detect the reflected wave reflected by the object. That is,
Since the output of the radio wave has the property of being inversely proportional to the square of the distance, for example, when the distance to the target object is doubled, the round-trip distance is quadrupled. Is reduced to about 1/16 at the time of radiating.

The reflected wave is actually detected by lowering the frequency by sampling the signal of the received reflected wave at a predetermined sweep period. However, since the reception level of the reflected wave is lowered for the above reason, the reception level is lowered to a level almost equal to the background noise. Therefore, sufficient S / N (Signal to Noise Ratio)
However, there is a problem that it is difficult to extend the detection distance and to improve the accuracy of the detection distance.

In order to solve this problem, therefore, a method has been taken in which sampling is performed a plurality of times and the noise is reduced by performing an averaging process. Since it is necessary to repeat sampling over the entire measurement range, it takes time to sample the data, and the processing time is further consumed by handling a large amount of processed data sampled multiple times. There was a problem.

The present invention has been made in view of such a situation, detects the peak position of a reflected wave, limits the sampling range based on the detected peak position, and densely samples only a necessary portion. By doing so, the detection distance in the weak radio wave method is lengthened, and the detection accuracy is further improved.

[0010]

SUMMARY OF THE INVENTION A distance detecting apparatus according to the present invention detects a peak position based on a receiving means for receiving a signal of a reflected wave reflected by an object and a signal of the reflected wave received by the receiving means. The peak position detecting means for detecting, the peak position detected by the peak position detecting means, and the sampling means for sampling the signal in the vicinity thereof a plurality of times, and the peak position detecting means for detecting the peak position.
Signal range in the vicinity of the peak position based on
Sampling interval setting procedure to set the pulling interval closely
Sumps at steps, peak positions, and their vicinity .
The sampling interval is set tightly by the ring interval setting means.
And a calculating means for calculating an arithmetic mean value of signals sampled a plurality of times by the sampling means in a fixed state .

The receiving means is, for example, the antenna 2 of FIG.
1a, which is a radio wave emitted from the antenna 21b toward an object, receives a reflected wave reflected by the object, and outputs the received signal to the frequency reduction unit 22.

The peak position detecting means is, for example, the control section 55 of the frequency lowering section 22 shown in FIG.
The peak position is detected from the signal input from the signal exceeding the threshold value.

The sampling means is, for example, the time extension processing section 53 of the frequency lowering section 22 of FIG. 2, and based on the peak position detected by the peak position detecting means, its peak position and its peak position. The signals in the vicinity are sampled a plurality of times and output to the control unit 55.

The calculating means is, for example, the cumulative addition processing section 54 of the frequency lowering section 22 shown in FIG. 2, and the arithmetic mean value of the signals sampled a plurality of times at the peak position and its vicinity by the sampling means. Is calculated and output to the control unit 55.

In the distance detecting apparatus of the present invention, the signal of the reflected wave reflected by the object is received, the peak position is detected based on the received signal of the reflected wave, and the detected peak position, and The signal in the vicinity is sampled multiple times and the peak is detected based on the detected peak position.
The sampling interval of signals in the range near the
At the peak position and its vicinity .
With the pulling interval set closely, the arithmetic mean value of the signals sampled a plurality of times is calculated.

According to the distance detecting means of the present invention, it is possible to improve the detection distance and the detection accuracy even if a weak radio wave is used.

The sampling means may be further provided with sampling range setting means for setting a sampling range of a signal near the peak position based on the peak position detected by the peak position detecting means.

[0018]

[0019]

1 is a block diagram showing the configuration of an embodiment of a liquid level meter 1 according to the present invention. The liquid level meter 1 includes a radio wave processing unit 11 and a signal processing unit 12. The antenna 21a of the radio wave processing unit 11 is
Of the radio waves emitted from the antenna 21b, the object P
The reflected wave reflected by the (liquid level) is received, and the received reflected wave is output to the frequency lowering unit 22 as a high frequency signal.
The frequency reduction unit 22 performs time extension processing on the high frequency signal input from the antenna 21 a, reduces the frequency, and outputs the signal to the A / D (Analog / Digital converter) 31 of the signal processing unit 12. The details of the frequency lowering unit 22 will be described later.

The clock generator 23 is driven by the electric power supplied from the power supply 35 of the signal processing unit 12, generates a clock signal, and supplies it to the pulse generating unit 24. The pulse generator 24 generates a steep pulse based on the clock signal supplied from the clock generator 23, and the antenna 21
output to b. The antenna 21b generates a radio wave based on the steep pulse input from the pulse generator 24 and irradiates the target P with the radio wave.

The A / D 31 of the signal processing unit 12 converts the low frequency analog signal supplied from the frequency lowering unit 22 of the radio wave processing unit 11 into a digital signal and outputs the digital signal to the transmission removing unit 41 of the arithmetic unit 32. . The transmission removal unit 41 of the calculation unit 32 uses the antenna 21a among the radio waves emitted from the antenna 21b.
The signal directly received by, that is, the signal of the transmitted wave is first stored and subtracted to remove the transmitted wave, and the signal of only the reflected wave from the object P is output to the arithmetic processing unit 42.

The arithmetic processing unit 42 arithmetically processes the signal of only the reflected wave input from the transmitted wave removing unit 41, obtains the distance to the object P from the delay time of the transmitted wave and the reflected wave, and
The detection distance data to the liquid surface is generated from the calculation result and is output to the display unit 34.

The display unit 34 is the arithmetic processing unit 4 of the arithmetic unit 32.
The detected distance data input from 2 is displayed. Power supply 35
Generates electric power to reduce the frequency of the radio wave processing unit 11,
The clock generator 23, the pulse generator 24, the clock generator 33 of the signal processor 12, and the calculator 3
2 and the display unit 34.

Next, the frequency lowering section 22 of the radio wave processing section 11 will be described with reference to FIG.

The gain control unit 51 of the frequency reduction unit 22 controls the gain of the signal of the received wave input from the antenna 21a. That is, the reflected wave emitted from the antenna 21b and reflected by the object P has a distance of 2 from the object P.
It will be received after being attenuated in inverse proportion to the power. The gain control unit 51 controls the gain to be constant (time gain control) based on the reception distance of the reflected wave, that is, the delay time with respect to the transmission of the received wave, and outputs the gain to the detector 52. The details of the gain controller 51 will be described later.

The detector 52 detects the signal input from the gain controller 51, and the detected signal is expanded by the time extension processor 5.
3 and the control unit 55. Time extension processing unit 53
At the sampling timing designated by the control unit 55, the input high-frequency signal is sampled, the input high-frequency signal is time-expanded, and converted into a low-frequency signal. Output to.
The time extension processing unit 53 will be described later.

The cumulative addition processing unit 54 is controlled by the control unit 55, and cumulatively adds the sampling results sampled a plurality of times from the same sampling position among the sampling results stored in the memory 55a of the control unit 55, and further, An average value is obtained by dividing this by the cumulative number and output to the control unit 55. Details of the cumulative addition processing unit 54 will be described later.

When the control unit 55 receives a signal exceeding the threshold value based on the signal input from the detector 52,
This is detected as the peak position. In addition, the control unit 55
Determines the sampling range and sampling interval near the detected peak position, and controls the time extension processing unit 53 to execute the time extension process based on the determined sampling range and sampling interval. Furthermore, the control unit 5
5 temporarily stores each sampling data input from the time extension processing unit 53 in the memory 55a and outputs it to the A / D 31 of the signal processing unit 12. Furthermore, the control unit 55
Of the sampling results stored in the memory 55a outputs the sampling data sampled a plurality of times to the cumulative addition processing unit 54 to perform cumulative addition processing.

Next, the operating principle of the liquid level meter 1 will be described. The pulse generator 24 of the liquid level meter 1 is shown in FIG.
An extremely short rectangular wave (impulse) as shown in (A) is generated, and this is irradiated from above the liquid surface toward the object P (liquid surface) from the antenna 21b. At this time, the impulse of FIG. 3 (A) is substantially converted into a waveform as shown in FIG. 4 and emitted when being emitted from the antenna 21b. The impulse shown in FIG. 4 shows a waveform distribution as shown in FIG. 5 when analyzed by a spectrum analyzer. That is, the impulse is composed of innumerable harmonics.

The impulse of the waveform shown in FIG. 3A (substantially the impulse shown in FIG. 4) is transmitted to the antenna 2
When the object P (liquid level) is irradiated from 1b, the reflected wave reflected by the object P is received by the antenna 21a as shown in FIG. 3 (B).

Here, as shown in FIG. 3A, the time at which the antenna 21b transmits the impulse is time t _0, and
The time when the reflected wave received by the antenna 21a is received is time t ₁ . Since the propagation speed of the impulse is constant, the calculation unit 32 of the signal processing unit 12 of the liquid level meter 1
By measuring this time t ₁ -t ₀ and multiplying it by the propagation velocity, the round trip distance to the object P can be obtained.
Based on such a principle, the liquid level meter 1 obtains the distance from the measurement position to the liquid surface.

Next, details of the gain controller 51 will be described. The impulse used by the liquid level meter 1 to detect the distance has the property of being attenuated in inverse proportion to the square of the distance as described above. This relationship is shown in FIG.

When the distance to the object P is relatively short,
A signal as shown in FIG. 6A is input to the gain controller 51. Here, the waveform P1 indicates the antenna 2
The radio wave emitted from 1b wraps around and the antenna 21
It is a waveform (transmission) directly received by a. Waveform P2
Is the waveform of the reflected wave received by the antenna 21b.
The waveform P3 is a waveform of noise. In this way, when the object P is at a relatively short distance, the waveform P1 that is the transmitted wave
After receiving, the waveform P2, which is a reflected wave, is received at a relatively early time t _P2 .

On the other hand, when the distance to the object P is relatively long, a signal as shown in FIG. 6B is input to the gain controller 51. Here, the waveform P11
Is the same as the waveform P1, the waveform P12 is the waveform of the reflected wave, and the waveform P13 is the waveform of the noise. Thus, when the object P is at a relatively long distance, the waveform P12 is received at a later time t _P12 than when the object is at a relatively short distance, and further compared to the waveform P2. , It can be seen that the reception level is attenuated.

For this reason, the gain control section 51 is configured as shown in FIG.
As shown in FIG. 6C, by multiplying the received signal by a gain coefficient (amplification coefficient) that changes according to the distance (changes depending on the reception time of the reflected wave), as shown in FIG.
By changing the waveform P2 to the waveform P2 'and changing the waveform P12 to the waveform P12', control is performed so that the reflected wave is received with a constant gain.

Next, details of the time extension processing section 53 will be described. As described with reference to FIG. 3, the liquid level meter 1 theoretically irradiates the target object P with one impulse and detects a reflected wave reflected from the target object P to detect the target wave. It is possible to detect the distance to the object P, but in reality, to measure the time difference between the transmitted wave and the reflected wave by one impulse, the reflection reflected on the order of several ns or several ps The waves need to be sampled at very high frequencies, which is not possible in practice. Therefore, the impulse is continuously emitted and the reflected wave is continuously sampled.

FIG. 7 shows the timing of sampling at this time. In FIG. 7, the reception waveform indicated by a thin line indicates a transmitted wave and a reflected wave that are continuously received by the antenna 21a. In this way, the transmitted wave and the reflected wave are periodically received. Therefore, the time extension processing unit 53
By sampling this signal at timings (time t _{11 to} t ₁₇ ) that deviate from the cycle of the transmitted wave and the reflected wave, each reflected wave is expanded in time. The waveform of the thick line in FIG. 7 is the time-expanded signal.

In the present case, the sampling timing t ₁₁
The intervals from t ₁₇ to t ₁₇ are slightly longer than the cycles of the transmitted wave and the received wave, and are evenly set. Therefore, focusing on the reflected wave, the signal sampled at the time t ₁₂ is a signal at a position where the reflected wave advances as compared with the signal sampled at the time t ₁₁ . Furthermore, time t
_The signal sampled at ₁₃ samples the position where the reflected wave advances as compared with the signal sampled at time t ₁₂ . By executing this from time t _{11 to} t ₁₇ and connecting them, the received signal is expanded with respect to the time axis, that is, time expansion processing is performed. The black dots in FIG. 7 indicate the positions sampled at each sampling timing.

FIG. 8 shows a signal subjected to time extension processing by the time extension processing unit 53 when the sampling intervals are made equal. The signal received via the antenna 21a is sampled at predetermined intervals and subjected to time extension processing, as shown in FIG. The relationship between the sampling time and the sampling position at this time is shown in FIG.
It is shown in (B). As shown in FIG. 8B, the time and the sampling position change uniformly (evenly).

As shown in FIG. 8, by keeping the sampling timing constant, the entire one reflected wave can be read with the same resolution. Therefore, the object
To measure the distance to P, its resolution is not so high. Therefore, the control unit 55 detects the peak position based on the signal input from the wave detector 52, and then increases the resolution in the vicinity of the detected peak value (sampling interval is tight), and further, the peak position is detected. At the position detected as, the time extension processing unit 53 is controlled so as to change the timing so as to sample a plurality of times. This makes it possible to accurately sample only the vicinity of the peak position without changing the number of samples.

FIG. 9 shows an example of a signal sampled by the time extension processing unit 53 when the sampling timing is changed. As shown in FIG. 9 (A),
It is shown that the sample is sampled multiple times at the same position near the peak, and that the sampling intervals are close in other ranges.

That is, as shown in FIG. 9B, in the ranges h and j, it is shown that the sampling position changes gently (dense sampling) with the change of sampling time. ing. In the range i, because of the peak position, the sampling position does not change with time. That is, it is shown that the peak position of the reflected wave is sampled multiple times.

As described above, by changing the sampling interval according to the sampling position, the required portion can be densely sampled to obtain accurate data, and the portion where detailed sampling is unnecessary can be roughly sampled. , A memory 55a for storing the sampling result
Can be reduced, and the sampling speed can be increased.

Next, the cumulative addition processing section 54 will be described. The cumulative addition process is generally performed by the waveform P3 in FIG.
1, P32 ..., Waveforms P31 ′, P32 ′ ..., And waveforms P31 ″, P32 ″ ..., Sampled over n times and sampled signals (for example, If the frequency is 2MHz)
0 (B) waveforms P41, P42, ... P4n (for example, in the present case, the frequency is 40 Hz) are time-expanded, and then synchronous addition is performed to obtain a signal as shown in FIG.
Is a process of forming waveforms P51, P52, ... P5n as shown in FIG. The signal level of this waveform P5n is as shown in FIG.
0 (B) waveforms 41, 42 ... 4n times n times,
The noise becomes √n times. This is the number of added waveforms,
That is, by dividing by n, the signal level can be returned to the level at the time of detection, and the noise level can be reduced to 1 / √n times.

However, in this method, it is necessary to perform n times of sampling over the entire detection range, perform time extension processing, and then perform cumulative addition processing, which results in an additional measurement time. is there. Therefore, for example, as shown in FIG. 11A, waveforms P61 to P63
Sample the same position above. FIG. 11 at this time
The relationship between the sampling position and the distance corresponding to (A) is shown in FIG. 11 (B). As shown in FIG. 11B, the sampling points (black dots in the figure) of the waveforms P61 to P63 detected in the portion where the sampling position does not change are added to the change in time.

As described above, when the values sampled at the same sampling position are cumulatively added a plurality of times,
As shown in FIG. 12, a waveform P72 is formed by accumulating the next waveform on the first waveform P71, and a waveform P73 is formed by accumulating the next waveform. The black dots in FIG. 12 indicate sampling points sampled a plurality of times.

By dividing each sampling data on the waveform P73 which has been subjected to the cumulative addition processing by 3, it is possible to obtain the data in which the noise level is reduced to 1 / √3 times.

Further, the control unit 55 has the time extension processing unit 5
By controlling 3 and the cumulative addition processing unit 54, for example, when it is known that the liquid level always changes only within a predetermined range, as shown in FIG. By setting the start point and the end point of the sampling position, sampling of the required range is performed a plurality of times, cumulative addition processing is performed, and the other range is not sampled, and the waveform P81 near the required peak position is set. Only the position near P83 (the position of the black dot in FIG. 13) can be sampled over a plurality of times, which enables accurate detection near the peak position.

Next, the operation of the liquid level meter 1 will be described with reference to the flowchart of FIG. In step S1, the pulse generation unit 24 generates an impulse, and the antenna 21b irradiates the target P (liquid level) with this impulse as a radio wave to start scanning.

In step S2, the control unit 55 determines, based on the signal input from the detector 52, whether or not a signal of a threshold value or more is input, that is, whether or not the peak value of the reflected wave is detected. To do. When it is determined in step S2 that the peak of the reflected wave is not detected, the process returns to step S1 and the scanning is continued until the peak value of the reflected wave is detected. When it is determined in step S2 that the peak value is detected, the process proceeds to step S3.

In step S3, the start point and end point of the sampling signal are set. For example, when the waveform P92 as shown in FIG. 15 is detected as the peak value of the reflected wave at the position of the sampling position Xcm, the sampling position is only near the waveform 92, and therefore the sampling position is about 100 to 120 cm. It will be good in the range of. Therefore, in this case, the control unit 55 sets the sampling start point to 100 cm and sets the end point to 120 cm, and the sampling timing is set in the ranges L and N from the sampling start point in the ranges L and N as shown in FIG. 15 is set to a different sampling interval and the waveform P9 in FIG.
In the range M in FIG. 16, which is the peak position X of 2,
The time extension processing unit 53 is controlled so as to sample a plurality of times.

In step S4, the control unit 55 causes the time extension processing unit 53 to start sampling and stores the sampling result in the memory 55a.

In step S5, the control unit 55 detects whether or not the peak value of the reflected wave is detected within the set range. That is, it is determined whether or not the signals detected in the ranges L and N in FIG. 16 are smaller than the signals detected in the range M, and it is confirmed whether or not the sampling positions sampled a plurality of times are the peak values. It Step S
In 5, when the peak value is not detected, the process returns to step S1 and the subsequent processes are repeated. When the peak value is detected, the process proceeds to step S6.

In step S6, the control unit 55 reads out the data sampled a plurality of times from the sampling result stored in the memory 55a, executes the cumulative addition processing, and after the cumulative addition processing ends, the memory 55a.
The sampling result stored in is output to the A / D 31.

In step S7, the A / D 31 converts the signal input from the radio wave processing unit 11 from an analog signal into a digital signal and outputs it to the arithmetic unit 32. In step S7, the calculation unit 32 determines the reception time of the transmitted wave (waveform P91 in FIG. 15) and the reception time of the reflected wave (waveform P92 in FIG. 15) based on the signal input from the A / D 31. The distance from the delay time to the liquid surface is calculated, and the calculation result is displayed on the display unit 34.

According to the above, even if the distance to the object P changes, the peak position of the reflected wave reflected by the object P can be detected and only the vicinity of the detected peak position can be densely sampled. Further, since only the peak position can be sampled a plurality of times, the S / N of the reflected wave can be improved. Therefore, the distance detection device
Even if a weak radio wave is used, it is possible to improve the detection distance and the detection accuracy.

[0057]

According to the distance detecting means of the present invention, the signal of the reflected wave reflected by the object is received, the peak position is detected based on the received signal of the reflected wave, and the detected peak position, and , The signal in the vicinity of the peak position is sampled multiple times, and based on the detected peak position,
Set the sampling interval of the range signal tightly , and at the peak position and its vicinity , the sampling interval
Since the addition average value of the signals sampled a plurality of times is calculated in the state where the signal is densely set, it is possible to improve the detection distance and the detection accuracy even if a weak radio wave is used.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid level meter to which the present invention is applied.

FIG. 2 is a block diagram of a frequency lowering unit in FIG.

FIG. 3 is a diagram illustrating the principle of distance detection.

FIG. 4 is a diagram showing a waveform of a generated radio wave.

5 is a diagram illustrating that the waveform of FIG. 4 is composed of infinite harmonics.

FIG. 6 is a diagram illustrating that the amplification coefficient is changed in proportion to the distance.

FIG. 7 is a diagram for explaining time extension of a high frequency waveform.

FIG. 8 is a diagram illustrating a sampling position when performing time extension.

FIG. 9 is a diagram illustrating sampling performed at unequal intervals.

FIG. 10 is a diagram illustrating general cumulative addition.

11 is a diagram illustrating cumulative addition used in the liquid level meter of FIG.

12 is a diagram illustrating cumulative addition used in the liquid level meter of FIG.

FIG. 13 is a diagram illustrating a sampling start point and a sampling end point.

FIG. 14 is a flowchart illustrating the operation of the liquid level meter.

FIG. 15 is a diagram showing an example of a sampled waveform.

16 is a diagram illustrating sampling at irregular intervals near the peak among the waveforms sampled in FIG.

[Explanation of symbols]

1 liquid level meter, 11 radio wave processing part, 12 signal processing part, 21a, 21b antenna, 22 low frequency part, 23
Clock generator, 24 pulse generator, 31 A / D,
32 arithmetic unit, 33 clock generator, 34 display unit,
35 power supply, 41 transmission elimination section, 42 arithmetic processing section, 5
1 gain control unit, 52 wave detector, 53 time extension processing unit, 54 cumulative addition processing unit, 55 control unit, 55a memory

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Inoue, No. 10 Hanazono Todocho, Ukyo-ku, Kyoto City, Kyoto Prefecture Omron Co., Ltd. (56) Reference JP-A-8-220214 (JP, A) JP-A-5- 209781 (JP, A) JP-A-2-135917 (JP, A) JP-A-3-220481 (JP, A) JP-A-3-85475 (JP, A) JP-A-51-138396 (JP, A) Actual Kaihei 5-66575 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S 7/00 -7/42 G01S 13/00-13/95

Claims (2)

(57) [Claims] 1. A distance detecting device for irradiating an object with a radio wave, receiving a signal of a reflected wave reflected from the object, and detecting a distance to the object based on the received signal of the reflected wave, wherein the object detects Receiving means for receiving the signal of the reflected reflected wave, based on the signal of the reflected wave received by the receiving means, the peak position detecting means for detecting the peak position, the peak detected by the peak position detecting means position,
And a sampling means for sampling a signal in the vicinity thereof a plurality of times, and the peak position detected by the peak position detecting means.
Based on the position of the signal in the range near the peak position.
Sampling interval setting procedure to set the pulling interval closely
And stage, the peak position, and in its vicinity, the San
Sampling intervals are tight due to pulling interval setting means
A distance detecting device comprising: a calculating means for calculating an arithmetic mean value of signals sampled a plurality of times by the sampling means in a set state . 2. The sampling means further comprises sampling range setting means for setting a sampling range of a signal near the peak position based on the peak position detected by the peak position detecting means. The distance detection device according to claim 1.