JP2001264419A - Distance detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy by improving the detection distance. SOLUTION: An antenna 21a receives the reflected wave by an object, and outputs it to a gain control unit 51. The gain control unit 51 amplifies the signal according to the distance of the received reflected wave, and outputs it to a detector 52. The detector 52 detects the signal inputted signal, and outputs it to a time extension unit 53 and a control unit 55. The control unit 55 detects the peak position based on the signal inputted from the detector 52. The control unit 55 detects the peak position, and controls the time extension unit 53 to achieve a plurality of samplings of the peak position densely in the vicinity of the detected peak position, and store the sampled result to a memory 55a. The control unit 55 controls an accumulation unit 54 to accumulate the result of the plurality of samplings, and outputs the total sampling results to an A/D 31 of a signal processing unit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

[0004]

By the way, as a radio wave used in the conventional pulse radar, a high output radio wave has been used. For this reason, interference waves caused by high-power radio waves
There was a great effect on the surroundings. In addition, there is a problem in that high-power radio waves used as pulse radars consume a large amount of energy required for their generation.

In order to solve this problem, it has been proposed to use a weak radio wave system in which the radio wave output is reduced. As a result, the effects on surroundings due to interference waves and the like generated by high-power radio waves and the problem of power saving have been solved.

However, in the weak radio wave system, since the output of the radio wave radiated 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 is inversely proportional to the square of the distance, for example, if the distance to the object is doubled, the round trip distance is quadrupled, so the reception level of the reflected wave is Is reduced to about 1/16 at the time of emission.

[0007] In practice, the reflected wave is detected at a low frequency by sampling the signal of the received reflected wave at a predetermined sweep cycle. However, the reception level of the reflected wave is reduced for the above-described reason, and the reception level is reduced to a level substantially equal to the background noise. Therefore, sufficient S / N (Signal to Noise Ratio)
However, there is a problem that it is difficult to increase the detection distance and improve the accuracy of the detection distance.

In order to solve this problem, a technique has been adopted in which sampling is performed a plurality of times, and noise is reduced by performing an averaging process. Sampling needs to be repeated over the entire measurement range, so that time is spent on the sampling, and the processing time is further consumed by handling a large amount of processing data sampled a plurality of times. There was a problem that.

The present invention has been made in view of such a situation, detects a peak position of a reflected wave, limits a 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 extended, and the detection accuracy is further improved.

[0010]

SUMMARY OF THE INVENTION A distance detecting apparatus according to the present invention includes a receiving means for receiving a signal of a reflected wave reflected by an object, and a peak position based on the signal of the reflected wave received by the receiving means. The peak position detecting means to be detected, 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, the peak position by the sampling means, and the sampling in the vicinity thereof a plurality of times Calculating means for calculating an average value of the signals.

The receiving means is, for example, the antenna 2 shown in FIG.
1a, which receives a reflected wave reflected by the object from among radio waves emitted from the antenna 21b toward 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 reduction section 22 shown in FIG.
The peak position is detected from the signal exceeding the threshold value from the signal input from.

The sampling means is, for example, the time extension processing section 53 of the frequency reduction section 22 shown in FIG. 2, and based on the peak position detected by the peak position detection means, A nearby signal is sampled a plurality of times and output to the control unit 55.

The arithmetic means is, for example, the accumulative addition processing section 54 of the frequency reduction section 22 shown in FIG. 2, and the peak position and the average value of the signals sampled a plurality of times near the peak position by the sampling means. Is calculated and output to the control unit 55.

In the distance detecting means of the present invention, a signal of a reflected wave reflected by the object is received, a peak position is detected based on the received reflected wave signal, and the detected peak position and The signal in the vicinity is sampled a plurality of times, and the peak position and the average value of the signals sampled in the vicinity a plurality of times are calculated.

According to the distance detecting means of the present invention, the detection distance and the detection accuracy can be improved even when a weak radio wave is used.

The sampling means may further include a 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 sampling means may further include a sampling interval setting means for setting a sampling interval of a signal in a range near the peak position based on the peak position detected by the peak position detecting means. .

[0019]

FIG. 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
Of the radio waves emitted from the antenna 21b, the object P
It receives the reflected wave reflected by the (liquid surface) and outputs the received reflected wave to the frequency reduction section 22 as a high-frequency signal.
The frequency reduction section 22 subjects the high-frequency signal input from the antenna 21a to time expansion processing, lowers the frequency, and outputs the signal to the A / D (Analog / Digital converter) 31 of the signal processing section 12. The details of the frequency reduction 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 the clock signal to the pulse generation unit 24. The pulse generator 24 generates a steep pulse based on the clock signal supplied from the clock generator 23,
b. The antenna 21b generates a radio wave based on the steep pulse input from the pulse generation unit 24 and irradiates the radio wave to the object P.

The A / D 31 of the signal processing section 12 converts the low-frequency analog signal supplied from the low-frequency section 22 of the radio wave processing section 11 into a digital signal and outputs the digital signal to the transmission removing section 41 of the arithmetic section 32. . The transmission removing unit 41 of the arithmetic unit 32 includes the antenna 21a out of the radio waves emitted from the antenna 21b.
, The signal transmitted directly, that is, the signal of the transmitted wave is first stored and subtracted, thereby removing the transmitted wave, and converting the signal into a signal of only the reflected wave from the object P and outputting the signal 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 to obtain the distance to the object P from the delay time between the transmitted wave and the reflected wave,
The detection distance data from the calculation result to the liquid surface is generated and output to the display unit 34.

The display unit 34 is provided with the arithmetic processing unit 4 of the arithmetic unit 32.
The detected distance data input from Step 2 is displayed. Power supply 35
Generates electric power, reduces 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 supply it to the display unit 34.

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

The gain control section 51 of the frequency reduction section 22 controls the gain of the signal of the received wave input from the antenna 21a. That is, the reflected wave radiated from the antenna 21b and reflected by the object P has a distance of 2 to the object P.
The signal is attenuated in inverse proportion to the power and received. 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 of the received wave with respect to the transmission, and outputs the gain to the detector 52. The details of the gain control unit 51 will be described later.

The detector 52 detects a signal input from the gain control unit 51 and converts the detected signal into a time extension processing unit 5.
3 and to the control unit 55. Time extension processing unit 53
Samples the input high-frequency signal at the sampling timing specified by the control unit 55, performs time expansion processing on the input high-frequency signal, converts the input high-frequency signal into a low-frequency signal, Output to
The time extension processing section 53 will be described later.

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

When a signal exceeding the threshold value is received based on the signal input from the detector 52,
This is detected as a peak position. The control unit 55
Determines the sampling range and sampling interval near the detected peak position, and controls the time expansion processing unit 53 to execute the time expansion process based on the determined sampling range and sampling interval. Further, the control unit 5
5 temporarily stores each sampling data input from the time expansion processing unit 53 in the memory 55a and outputs the data to the A / D 31 of the signal processing unit 12. Furthermore, the control unit 55
Outputs the sampling data sampled a plurality of times from the sampling results stored in the memory 55a to the accumulative addition processing unit 54, and causes the accumulative addition processing to be performed.

Next, the principle of operation of the liquid level meter 1 will be described. The pulse generator 24 of the liquid level meter 1 is configured as shown in FIG.
An extremely short rectangular wave (impulse) as shown in (A) is generated, and this is irradiated from the antenna 21b toward the object P (liquid level) from above the liquid level. At this time, when the impulse in FIG. 3A is irradiated from the antenna 21b, it is converted into a waveform substantially as shown in FIG. 4 and irradiated. 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 countless harmonics.

The impulse having the waveform shown in FIG. 3A (substantially, the impulse shown in FIG.
When the light is irradiated from 1b toward the object P (liquid surface), the reflected wave reflected by the object P is received by the antenna 21a as shown in FIG. 3B.

Here, as shown in FIG. 3A, the time when the antenna 21b transmits the impulse is set to time t ₀ ,
The time of reception of the reflected wave received by the antenna 21a and the time t _1. Since the propagation speed of the impulse is constant, the arithmetic unit 32 of the signal processing unit 12 of the liquid level meter 1
By measuring the time t ₁ -t ₀ and multiplying the time t ₁ -t ₀ by the propagation speed, the reciprocating 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 level.

Next, the details of the gain control section 51 will be described. As described above, the impulse used by the liquid level meter 1 for distance detection has a property of attenuating in inverse proportion to the square of the distance. 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 control unit 51. Here, the waveform P1 corresponds to the antenna 2
The radio wave radiated from 1b wraps around and the antenna 21
a is a waveform (transmitted wave) directly received by a. Waveform P2
Is a waveform of the reflected wave received by the antenna 21b.
The waveform P3 is a noise waveform. As described above, when the target object P is at a relatively short distance, the waveform P1 that is the transmitted wave
, A 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 control section 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
As shown in FIG. 6 (D), by multiplying the received signal by a gain coefficient (amplification coefficient) that changes according to the distance (changes according to the reception time of the reflected wave), as shown in FIG.
By changing the waveform P2 to the waveform P2 'and the waveform P12 to the waveform P12', control is performed such that the reflected wave is received with a constant gain.

Next, the details of the time extension processing section 53 will be described. As described with reference to FIG. 3, the liquid level meter 1 radiates one impulse on the object P and detects a reflected wave reflected from the object P in principle, thereby detecting the object. Although it is possible to detect the distance to the object P, actually, in order 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 is used. Waves need to be sampled at very high frequencies, which is not practical. Therefore, the impulse is continuously irradiated, and the reflected wave is continuously sampled.

FIG. 7 shows the sampling timing at this time. In FIG. 7, the reception waveform indicated by a thin line indicates a transmitted wave and a reflected wave continuously received by the antenna 21a. Thus, the transmitted wave and the reflected wave are periodically received. Therefore, the time extension processing unit 53
This signal is sampled at a timing (time t _{11 to} t ₁₇ ) shifted from the cycle of the transmitted wave and the reflected wave, so that each reflected wave is temporally expanded. The waveform of the bold line in FIG. 7 is a signal that has undergone time expansion processing.

In this case, the sampling timing t ₁₁
To each interval of t ₁₇ is slightly longer than the period of the transmitting and receiving waves, are equally set. Therefore, paying attention to the reflected wave, the signal is sampled at time t _12, rather than the signal that is sampled at time t _11, which samples the signal of position advanced reflection wave. Further, at time t
_13, the signal to be sampled, than the signal that is sampled at time t _12, which samples the advanced position of the reflected wave. By executing this for times t _{11 to} t ₁₇ and connecting the received signals, the received signal is expanded with respect to the time axis, that is, time expansion processing is performed. Note that the black dots in FIG. 7 indicate positions sampled at each sampling timing.

FIG. 8 shows a signal which has been time-expanded by the time-expansion processing section 53 when the sampling intervals are equalized. The signal received via the antenna 21a is sampled at predetermined intervals and time-expanded, as shown in FIG. The relationship between the sampling time and the sampling position at this time is shown in FIG.
This is shown in (B). As shown in FIG. 8 (B), the time and the sampling position are constantly (uniformly) changing.

As shown in FIG. 8, by making the sampling timing constant, one entire 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, after detecting the peak position based on the signal input from the detector 52, the control unit 55 increases the resolution near the detected peak value (dense the sampling interval), and furthermore, At the position detected as, the time expansion processing unit 53 is controlled so as to change the timing to perform sampling a plurality of times. Thereby, it is possible to accurately sample only the vicinity of the peak position without changing the sampling number.

FIG. 9 shows an example of a signal sampled by the time expansion processing section 53 when the sampling timing is changed. As shown in FIG.
In the vicinity of the peak, it is shown that sampling is performed a plurality of times at the same position, and in other ranges, sampling intervals are shown to be dense.

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

As described above, by changing the sampling interval depending on the sampling position, a necessary portion can be sampled densely, accurate data can be obtained, and a portion where detailed sampling is unnecessary can be roughly sampled. 55a for storing sampling results
Can be reduced, and the sampling speed can be increased.

Next, the cumulative addition processing section 54 will be described. Generally, the cumulative addition process is performed by using the waveform P3 in FIG.
, P32 ′, P32 ′, P32 ′, and P31 ″, P32 ″, etc., are sampled n times, and the sampled signal (for example, In the case where the frequency is 2 MHz,
10 (C) by time-expanding to a signal (for example, the frequency is 40 Hz in this case) as shown in waveforms P41, P42,.
, And P5n as shown in FIG. The signal level of this waveform P5n is shown in FIG.
Each of the waveforms 41, 42,... 4n of 0 (B) becomes n times,
The noise is multiplied by Δn. This is added to the number of 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 execute sampling n times over the entire detection range, execute time extension processing, and then perform cumulative addition processing, which causes a problem that measurement time is extra. is there. Therefore, for example, as shown in FIG.
Sample the same location above. At this time, FIG.
FIG. 11B shows the relationship between the sampling position and the distance corresponding to FIG. As shown in FIG. 11B, the sampling points (black points 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 over a plurality of times are cumulatively added,
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. Note that black points in FIG. 12 indicate sampling points sampled a plurality of times.

By dividing each sampled data on the waveform P73 subjected to the cumulative addition process by three, data in which the noise level is reduced to 1 / √3 times can be obtained.

Further, the control unit 55 includes the time extension processing unit 5
By controlling the cumulative addition processing unit 54 with 3, for example, when it is known that the liquid level always changes only within a predetermined range, as shown in FIG. By setting the starting point and the ending point of the sampling position, sampling of a necessary range is executed a plurality of times, accumulation and addition processing is performed, and the other range is not sampled, and a waveform P81 near a required peak position is set. Only the position near P83 (the position of the black point in FIG. 13) can be sampled a plurality of times, thereby enabling 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 generator 24 generates an impulse, and the antenna 21b irradiates the impulse as a radio wave toward the object P (liquid surface) to start scanning.

In step S2, the control section 55 determines whether or not a signal having a threshold value or more has been input, that is, whether or not the peak value of the reflected wave has been detected, based on the signal input from the detector 52. I do. If it is determined in step S2 that the peak of the reflected wave has not been detected, the process returns to step S1 and continues scanning until the peak value of the reflected wave is detected. If it is determined in step S2 that a peak value has been detected, the process proceeds to step S3.

In step S3, a start point and an 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 only needs to be in the vicinity of the waveform 92, and 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 the end point to 120 cm, and sets the sampling timing in the range L, N from the sampling start point as shown in FIG. 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 perform sampling a plurality of times.

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

In step S5, the control section 55 detects whether or not the peak value of the reflected wave has been detected within the set range. That is, it is determined whether 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 determined whether or not the sampling positions sampled a plurality of times have peak values. You. Step S
In 5, if no peak value is detected, the process returns to step S1, and the subsequent processes are repeated. If a peak value is detected, the process proceeds to step S6.

In step S6, the control unit 55 reads the data sampled a plurality of times from the sampling results stored in the memory 55a, executes the cumulative addition process, and, after the cumulative addition process is completed, the memory 55a.
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 to a digital signal, and outputs the signal to the arithmetic unit 32. In step S7, based on the signal input from the A / D 31, the arithmetic unit 32 calculates 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). The distance from the delay time to the liquid surface is calculated, and the calculation result is displayed on the display unit 34.

As described 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. Since it is possible to sample only the peak position a plurality of times, the S / N of the reflected wave can be improved. For this reason, the distance detection device
Even if a weak radio wave is used, the detection distance and the detection accuracy can be improved.

[0057]

According to the distance detecting means of the present invention, a signal of a reflected wave reflected by an object is received, a peak position is detected based on the received signal of the reflected wave, and the detected peak position, and Since the signal in the vicinity thereof is sampled a plurality of times, the peak position, and the average value of the signal sampled in the vicinity thereof a plurality of times is calculated,
Even if a weak radio wave is used, the detection distance and the detection accuracy can be improved.

[Brief description of the 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 of FIG. 1;

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

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

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

FIG. 6 is a diagram for explaining changing an amplification coefficient in proportion to a distance.

FIG. 7 is a diagram illustrating time expansion of a high-frequency waveform.

FIG. 8 is a diagram illustrating sampling positions when time is extended.

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

FIG. 10 is a diagram illustrating general cumulative addition.

FIG. 11 is a diagram illustrating cumulative addition used for the liquid level meter of FIG. 1;

FIG. 12 is a diagram illustrating cumulative addition used in the liquid level meter of FIG. 1;

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

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

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

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

[Explanation of symbols]

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

Continuing on the front page (72) Inventor Tetsuo Saidai O-Muron Co., Ltd. (10) Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto (72) Inventor Yoshitaka O-Muron Co., Ltd. 10-Hanazono Todo-cho, Ukyo-ku, Kyoto, Kyoto F term (reference) 5J070 AB08 AC02 AD02 AH31 AK22

Claims (3)

[Claims] 1. A distance detecting device that irradiates an object with radio waves, receives a signal of a reflected wave reflected from the object, and detects a distance to the object based on the received signal of the reflected wave. Receiving means for receiving a signal of the reflected wave reflected, a peak position detecting means for detecting a peak position based on a signal of the reflected wave received by the receiving means, and a 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 a calculation means for calculating a peak position by the sampling means, and an average value of the signals sampled in the vicinity a plurality of times. Distance detection device. 2. The apparatus according to claim 1, further comprising a sampling range setting unit configured to set a sampling range of a signal near the peak position based on the peak position detected by the peak position detecting unit. The distance detection device according to claim 1. 3. The apparatus according to claim 2, wherein the sampling unit further includes a sampling interval setting unit that sets a sampling interval of a signal in a range near the peak position based on the peak position detected by the peak position detecting unit. The distance detecting device according to claim 1, wherein