JPH0616080B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a distance measuring device for measuring a distance to an object to be detected, such as in the ground, underwater, in snow, inside concrete, and the like, and particularly in the case of two adjacent frequencies. The present invention relates to a distance measuring device that measures a distance by measuring time expanded from real time by using an electromagnetic wave of a pseudo random signal.

[Prior Art] Conventionally, as a method of measuring the distance to an object to be detected in the ground or water using this type of electromagnetic wave, for example, Japanese Patent Publication No. 55-4
As shown in 4916, a method of using a monopulse of about several ns (10 ^-9 seconds), or instead of a pulse signal, for example, a document "Coded Underground Exploration Radar" (Suzuki et al., IEICE, Technical Research Report) , SANE 87-1, 1987), a method using a pseudo-random signal is considered.

FIG. 2 is a block diagram of a conventional radar device for underground or underwater exploration using pseudo random signals. In the figure, 7 is a power amplifier, 8 is a receiver amplifier, 9 is a transmitting antenna, 10 is a receiving antenna, 16 is an object in the ground or underwater, 17 is an M-sequence signal generator, and 18 is a sampling device. , 19 is a correlator, 20
-1, 20-2, 20-3 are attenuators.

FIG. 3 is a block diagram of the correlator, in which 21 is a delay line with taps, 22 is a code converter, and 23 is an adder.

The operation of FIGS. 2 and 3 will be described. First, a trigger signal is input to the M-sequence signal generator 17 at a constant repetition frequency. The M-sequence signal generator 17 is used as one of the pseudo-random signal generating means, and its code has a constant periodicity. The M-sequence signal generator 17 outputs an M-sequence signal for one cycle each time a trigger signal is input. The output signal from the M-sequence signal generator 17 is radiated into the ground or underwater as an electromagnetic wave from the transmitting antenna 9 via the attenuator 20-1, the power amplifier 7 and the attenuator 20-2. The radiated electromagnetic wave is reflected by the detection object 16 in the ground or underwater and detected by the receiving antenna 10. The output signal from the receiving antenna 10 is input to the sampling device 18 via the reception amplifier 8 and the attenuator 20-3. The sampling device 18 has a function of converting a high speed signal into a low speed signal. Assuming that N received signals having the same waveform are obtained by N times of trigger signals,
This received signal is divided into N in terms of time to be signals of x ₁ , x ₂ , ... X _N. Then, only the x ₁ signal is sampled from the first received signal, and only the x ₂ signal is sampled from the second received signal. Such a sampling operation is repeated to reproduce one reception signal x ₁ , x ₂ , ... X _n by N reception signals. In this way, the sampling device 18 converts the high speed reception signal into the low speed reception signal,
The output is supplied to the correlator 19. The correlator 19 has a function of correlating with the M-sequence signal stored in advance, and a detailed block diagram is shown in FIG. The input signal is introduced to the delay line with a tap 21, and a signal corresponding to the delay time is output from each tap. Output signals from the respective taps of the tapped delay line 21 are input to the code converter 22. "+" In the code converter 22 indicates that code conversion is not performed, and "-" indicates that code conversion is performed. The output signals of the code converter 22 are input in parallel to the adder 23, and the parallel input signals are added. As a result, the received signal is temporally compressed, its amplitude is increased, and it is output from the correlator 19.

[Problems to be Solved by the Invention] In the above-described conventional distance measuring device, since a sampling device is required in the device, there is a problem that the number of constituent elements increases, the device becomes large-scale, and the cost increases. . Further, since a delay line with a tap is required as a component, there is a problem that a measurement error occurs due to waveform distortion that occurs when a received signal is passed through the delay line.

Further, the method of A-D converting the received signal and configuring the correlator by digital signal processing is difficult to perform in real time due to the limit of the response speed of the circuit element, and thus has not yet been put to practical use as an apparatus. .

The present invention has been made to solve such a problem, and does not require the sampling device or a delay line with a tap in the device, and can measure the distance to the detection object in the ground or underwater with a simple device. The purpose is to obtain a measuring device.

[Means for Solving the Problem] A distance measuring apparatus according to claim 1 of the present invention is a means for generating a first pseudo-random signal having a clock frequency of f _1, and the generated first pseudo-random signal. Is transmitted to the object as an electromagnetic wave, a means for receiving the electromagnetic wave reflected from the object to obtain a reception signal, and the clock frequency f _{1 in the} same pattern as the first pseudo-random signal. Means for generating a second pseudo-random signal having a clock frequency f ₂ which is lower by a slight frequency equal to or less than 1/10000 of the f ₁ , and the first pseudo-random signal and the second pseudo-random signal First to multiply with
, A second multiplier for multiplying the acquired received signal by the second pseudo random signal, and a first low-pass filter for low-pass filtering the output signal of the first multiplier. A second low-pass filter for low-pass filtering the output signal of the second multiplier, and means for generating a first pulse when the maximum amplitude value of the output signal of the first low-pass filter is detected. Means for generating a second pulse when the maximum amplitude value of the output signal of the second low-pass filter is detected, and the second pulse from the time when the first pulse is generated.
Means for measuring the time to the pulse generation time, 1/2 of the measured time, and the propagation velocity of the electromagnetic wave are multiplied to obtain the product as the first calculated value, and the clock frequency f
The frequency difference obtained by subtracting the clock frequency f ₂ from _1, the clock divided by the frequency f ₁ to the quotient between the second calculated value, multiplying the first calculation value and said second calculation value Means for obtaining a third calculated value, which is the product of the measured values, as the distance to the object.

A distance measuring device according to a second aspect of the present invention is the distance measuring device according to the first aspect.
In the distance measuring device according to the above, the clock frequency f ₁
Is provided with a means for generating a first pseudo-random signal having a frequency of 100 MHz or more.

A distance measuring device according to claim 3 of the present invention is the distance measuring device according to claim 1.
Alternatively, the distance measuring device according to the second aspect is used to measure a distance to a detection object in the ground, water, snow, or concrete.

[Operation] In the distance measuring device according to claim 1 of the present invention,
The pseudo random signal generating means of ₁ generates a first pseudo random signal having a clock frequency of f _1, and the transmitting means transmits the generated first pseudo random signal to the object as an electromagnetic wave. The received signal receives the electromagnetic wave reflected from the object to obtain the received signal, and the second pseudo random signal generating means has the same pattern as the first pseudo random signal and uses the clock frequency f ₁ to Of the f ₁
A second pseudo-random signal having a clock frequency of f ₂ which is low by a slight frequency of 1/10000 or less is generated. First
The multiplier of 1 multiplies the first pseudo-random signal by the second pseudo-random signal, and the second multiplier multiplies the acquired received signal by the second pseudo-random signal. A first low pass filter low pass filters the output signal of the first multiplier, and a second low pass filter low pass filters the output signal of the second multiplier. The first maximum value detecting means generates a first pulse when detecting the maximum amplitude value of the output signal of the first low-pass filter, and the second maximum value detecting means outputs the output signal of the second low-pass filter. When the maximum amplitude value of is detected, a second pulse is generated, and the time measuring means measures the time from the generation time of the first pulse to the generation time of the second pulse. The distance calculation means multiplies 1/2 of the measured time by the propagation speed of the electromagnetic wave, sets the product as a first calculation value, and subtracts the clock frequency f ₂ from the clock frequency f ₁ to obtain the difference. The frequency is divided by the clock frequency f ₁ to obtain the quotient as the second operation value, the first operation value and the second operation value are multiplied, and the third operation value which is the product thereof is obtained. , The distance to the object.

Further, in the distance measuring device according to claim 2 of the present invention,
The first pseudo random signal generating means in the distance measuring device according to the first aspect generates a first pseudo random signal having a clock frequency f ₁ of 100 MHz or more.

A distance measuring device according to claim 3 of the present invention uses the distance measuring device according to claim 1 or 2 to detect a distance to an object to be detected in the ground, water, snow, or concrete. Can be measured.

The operation of the present invention is formulated as follows.

The repetition frequency of the first pseudo-random signal is f ₁ , the second
The repetition frequency of the pseudo random signal is set to f _2, and the pattern of each pseudo random signal is the same. Where f
₁ > f ₂ .

Letting T _B be the period when the reference signal obtained by correlating the first pseudo random signal and the second pseudo random signal to be transmitted has the maximum value, the first pseudo random signal included in this T _B is included. The difference in the wave number between the signal and the second pseudo random signal is the wave number N of exactly one cycle.

That is, T _B · f ₁ = T _B · f ₂ + N When the above is arranged, T _B is given by the following equation (1).

T _B = N / (f ₁ −f ₂ ) ... (1) That is, the smaller the difference between the two clock frequencies, the larger the period T _{B at} which the reference signal becomes the maximum value.

Then, the first pseudo-random signal is received and reflected by the object, and the signal received again after the elapse of the propagation time τ and the second
When the time difference between the time at which the detection signal obtained by correlation with the pseudo random signal of No. 1 has the maximum value and the time at which the reference signal has the maximum value is T _D , the second pseudo random generated between T _D Since the wave number of the signal is smaller than the wave number of the first pseudo random signal generated during T _{D by} the wave number of the first pseudo random signal generated in τ time, the following equation is established.

T _D · f ₂ = T _D · f ₁ −τ · f _{1 When the} above formula is arranged, T _D is given by the following formula (2).

T _D = τ · f ₁ / (f ₁ −f ₂ ) ... (2) Here, the propagation time τ is τ = 2x / v, where v is the propagation velocity and x is the distance to the object. From equation (2), the following equation (3) is obtained.

By measuring the time difference T _D by the formula (3), the distance x
Can be measured.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
1, 2 are clock generators, 3 and 4 are M-sequence signal generators,
5 and 6 are multipliers, 7 is a power amplifier, 8 is a reception amplifier, and 9
Is a transmitting antenna, 10 is a receiving antenna, 11 and 12 are low-pass filters, 13 and 14 are maximum value detectors, 15 is a time measuring device, 16 is an object, and 33 is a distance calculating means, such as a microprocessor. It is composed of

The first pseudo-random generating means is the clock generator 1
And M-sequence signal generator 3.

The second pseudo random generation means is composed of the clock generator 2 and the M-sequence signal generator 4.

The means for transmitting the output of the first pseudo random signal generating means to the object is composed of the power amplifier 7 and the transmitting antenna 9.

The receiving means for receiving the reflected signal from the object and obtaining the received signal is composed of the receiving antenna 10 and the receiving amplifier 8.

The first correlation calculation means is a multiplier 5 and a low-pass filter.
11 and the second correlation calculating means is composed of the multiplier 6 and the low-pass filter 12.

FIG. 4 is a block diagram of a 7-bit M-sequence signal generator,
24 is a shift register having a seven-stage configuration, and 25 is an exclusive OR circuit.

FIG. 5 is an output waveform diagram of the M-sequence signal generator.

FIG. 6 is a waveform diagram for explaining the operation of FIG.

The operation of FIG. 1 will be described with reference to FIGS. 4 to 6. The clock generator 1 generates a clock signal of frequency f _{1 and} the clock generator 2 generates a clock signal of frequency f ₂ . One of the characteristics of this occurrence is that this first
Frequency f ₂ of the second clock signal to the frequency f ₁ of the clock signal, from the clock frequency f _1, the f
It is only 1/10000 less than ₁ . Now, assuming f ₁ = 100.004MHz and f ₂ = 99.996MHz,
A case where the difference f ₁ −f ₂ = 8 kHz is about 1/12500 of f ₁ will be described. The clock signal of frequency f ₁ output from the clock generator 1 is generated in the M-sequence signal generator 3, and the clock signal of frequency f ₂ output from the clock generator 2 is generated in the M-sequence signal generator 4 respectively. It is supplied as a sync signal for. The M-sequence signal generators 3 and 4 are adopted as one of pseudo-random signal generating means, and instead of the M-sequence signal, for example, a Barker code (Baker Code) is used.
A generator may be used. In the case of this example, a 7-bit M-sequence code is used, and its configuration is shown in FIG. That is, a shift register 24 having a seven-stage configuration of flip-flops synchronized with a clock signal is provided, and the output signals of the sixth- and seventh-stage flip-flops are input to the first-stage flip-flops via the exclusive OR circuit 25. Then, a clock signal (not shown) is supplied to each stage of the flip-flop, and an output signal is obtained from the seventh flip-flop, so that an M-sequence code synchronized with the clock signal can be generated. The M-sequence code generated in this way is code "1"
And "0" or a combination of "+" and "-" is a cyclic cyclic code. In this example, the code "1" is a positive voltage (+ E) and "0" is a negative voltage, as shown in FIG. The signal of (-E) is generated. The cycle when this M-sequence signal is circulated and generated is 7 bits in this example, so 2 ⁷ −1 =
One cycle is completed when 127 signals are generated. Then, the same signal as the previous cycle is generated from the next 128th signal, and this cycle is repeated. Generally, this M-sequence signal is a random signal when viewed partially, but it is used as a signal that utilizes an autocorrelation function, and is applied to a pulse compression radar in the description of the conventional device.

The M-sequence signal generators 3 and 4 are composed of exactly the same circuits that generate the same 7-bit M-sequence signal, except that the frequencies f ₁ and f ₂ of the input clock signals are slightly different. . A shift register having a clock frequency of about 100 MHz can be easily realized by an ECL (emitter coupled logic) element, for example. The M-sequence signal generators 3 and 4 have 127 voltages + E and −, respectively, in one cycle.
The M series signals M ₁ and M ₂ of E are circulated and output. However, since the frequencies of the input clock signals are slightly different, one cycle of the _two M-series signals M ₁ and M ₂ is slightly different. Now, when the periods of the two M-sequence signals M ₁ and M ₂ are obtained, the period of M ₁ = 127 × 1 / 100.004M
Hz ≈ 1269.9492ns M ₂ cycle = 127 × 1 / 99.996MHz ≈ 12
It will be 70.0508ns. That is, two M-sequence signals M ₁ and M ₂
Has a period of about 1270 ns (10 ^-9 seconds), but there is a time difference of about 0.1 ns between the two. Therefore, if these two M-sequence signals M ₁ and M ₂ are generated in a circulating manner and the patterns of the two M-sequence signals match at a certain time ta, _a deviation of 0.1 ns occurs every time one cycle elapses. It occurs between both signals, and after 100 cycles, a deviation of 10 ns occurs between both signals. Here, since the M-sequence signal generates 127 signals in one cycle of 1270 ns, the generation time of one signal is 10 ns. Therefore, two M-sequence signals M
The deviation of 10 ns between ₁ and M ₂ corresponds to the deviation of one M-sequence signal. The timing relationship between them is shown in FIG. That is, in FIG.
(a) shows that the output of one cycle of the reference M-sequence signal generator 4 contains 127 signals, and the cycle is 1270 ns, and (b) shows the output from the M-sequence signal generator 4. M ₂ is -100
(C) shows that the output M ₁ from the M-sequence signal generator 3 is M ₂
0.1ns per cycle as compared to it at 100 cycles a short 10 ns, and the two M-sequence signals M ₁ and M ₂ are synchronized at time t _a, that the pattern of both signals match Shows. When the patterns of the two M-sequence signals M ₁ and M ₂ match at a certain time, the shift gradually increases and the patterns of the two signals match again after a lapse of a certain time. In this example, the M-sequence signals M ₁ and M ₂
Since both are 7-bit signals, the wave number N of one cycle is 2
⁷ −1 = 127, and the frequencies of M ₁ and M ₂ are f ₁ = 100.004MHZ and f ₂ = 99.996MHZ, respectively, so substituting these values into the equation (1) gives T _B = 15.875ms Becomes That is, the pattern matching of the _two M-series signals M ₁ and M ₂ is repeated every 15.875 ms.

The M-sequence signals M ₁ and M ₂ output from the M-sequence signal generators 3 and 4, respectively, are branched into two, and one of the signals is input to the multiplier 5.

The multipliers 5 and 6 are processors in the first half of the correlation calculation means, for example, a wide band double balanced mixer (DB).
M) is used to multiply two M-sequence signals.
Since the M-sequence signal is a positive or negative voltage signal as described above, the multiplication result with the same sign is a positive voltage, and the multiplication result with a different sign is a negative voltage, and the outputs of the multipliers 5 and 6 are positive or negative. A voltage signal is obtained. Therefore, now two M-sequence signals M ₁
And in the vicinity of the time t _a a pattern match of M _2, the output signal of the multiplier 5 is the first half of the processor of the first correlation calculation means is a pulse train of DC positive voltage or a positive voltage. However, the periods of the two M-sequence signals M ₁ and M ₂ are slightly different, and a deviation of 0.1 ns is generated between the two signals each time one period elapses. Then, 100 cycles after the time ta, _a deviation of 10 ns, that is, a deviation of one signal occurs between the _two M-sequence signals M ₁ and M ₂ . In this state, there is no correlation between the two signals, and positive and negative pulse train signals are randomly generated at the output of the multiplier 5. The output waveform of the multiplier 5 is shown in FIG.
It is shown in (e). The output signal of the multiplier 5 is a low-pass signal
It is supplied to the filter 11 and converted into a DC voltage. Low-pass filter 11 and 12 are the second half of the processor of the correlation calculation means, having a cut-off frequency f _c, respectively, to attenuate high frequency input components than the cutoff frequency f _c, performs integration processing of the input signal Have a function. The output signal of the low-pass filter 11 is a processor in the second half of the first correlation computing means, the maximum value at time t _a two M-sequence signals M ₁ and M ₂ of the pattern is matched, M from the time t _a time series signal M ₂ is shifted back and forth 100 cycles, i.e. t _a ± 12
It becomes the minimum value at the time of 7 μs. Then, the triangular wave voltage signal linearly decreases from this maximum value to the minimum value before and after. The output waveform of the low-pass filter 11 is shown in FIG. 6 (f). Also, this triangular wave voltage signal is
As described above, two M-sequence synchronization states occur 15.875ms
It is output from the low-pass filter 11 every time. Low pass
The output signal from the filter 11 is input to the maximum value detector 13. Maximum detectors 13 and 14 are low-pass filters 11 and
It has a function of detecting the maximum value of the triangular wave voltage signal input from 12, that is, the voltage at the apex of the triangular wave, and outputting one pulse signal at the time when the maximum voltage value is detected. As a method of detecting the generation time of the maximum voltage, for example, an A / D converter and a digital data comparator are provided,
Triangular wave analog signals input by a high-speed sampling signal are sequentially converted into digital data, and digital data obtained by the previous sampling signal and always,
The digital data obtained from the current sampling signal is compared with the digital data comparator for magnitude comparison,
It suffices to detect the time at which the input signal reverses from the increasing state to the decreasing state with respect to time. Similarly, the same function can be realized by sequentially comparing the sampled analog signals. If a small peak may appear due to noise or the like, a threshold value may be set and the peak value may be detected only for a signal exceeding this threshold value. The maximum value detector 13 uses the pulse output as the measurement start signal at the time when the maximum value of the input signal is detected.
Supply to 15. When the measurement start signal is input from the maximum value detector 13, the time measuring device 15 starts measuring time. This state is shown in FIGS. 6 (i) and (k). The other M-sequence signal M ₁ output from the M-sequence signal generator 3 and branched into two
Is input to the power amplifier 7 and the output power is increased to, for example, about 20 mW. The M-sequence output signal from the electrode amplifier 7 is fed to the transmitting antenna 9. The transmitting antenna 9 radiates the electromagnetic wave of the M-sequence signal to the propagation medium. This radiated electrode wave is reflected by the object 16 whose conductivity or permittivity is different from that of the propagation medium, and is detected by the receiving antenna 10. The reflected signal detected by the receiving antenna 10 is
The signal is input to the reception amplifier 8 and is subjected to signal amplification and waveform shaping. In the output signal M ₁ ′ of the reception amplifier 8, the M series signal M ₁ is radiated from the transmitting antenna 9 as an electromagnetic wave,
This signal is the same as the signal delayed by the propagation time of the electromagnetic wave reaching the receiving antenna 10 and reciprocating the distance to the object 13.
Strictly speaking, there are fixed signal delay times in the power amplifier 7 and the signal amplifier 8, but these fixed delay times are removed at the stage of measurement processing or output from the M-sequence signal generator 3. When the signal M ₁ is supplied to the multiplier 5, it is possible to eliminate it in terms of measurement by a method such as supplying a signal via a delay circuit having an equivalent delay time. In this way, the M-sequence signal M ₁ ′ having a delay time proportional to the distance from the transmitting and receiving antennas 9 and 10 to the object is output from the reception amplifier 8 and the first half processing of the second correlation calculating means. It is supplied to one input of the multiplier 6 which is a multiplier. Object 16 now
Exists in the atmosphere at a distance of 3 meters from the transmitting and receiving antennas 9 and 10. Since it takes 20 ns for the electromagnetic wave to propagate through the atmosphere and make a round trip of 3 meters, the M series signal M ₁ ′ output from the reception amplifier 8 is M.
Than the M-sequence signal M ₁ output from the sequence signal generator 3.
It is delayed by 20ns. This state is shown in FIG. 6 (d). Further, the other M-sequence signal M ₂ output from the M-sequence signal generator 4 and branched into _two is supplied to the other input of the multiplier 6. The multiplier 6 multiplies the two M-sequence signals M ₁ ′ and M _{2 in} the same manner as the multiplier 5. The multiplier 6 supplies the multiplication result of the _two M-sequence signals M ₁ ′ and M ₂ to the low-pass filter 12. The low-pass filter 12 which is the latter half processor of the second correlation calculation means has two M-sequence signals M ₁ ′.
And a voltage signal of a triangular wave whose apex is when the patterns of M ₂ are matched is generated, and this voltage signal is supplied to the maximum value detection circuit 14. The above operation is performed by the multiplier 5 and the low-pass filter.
The operation is exactly the same as described in 11. The only difference is the time when the patterns of the _two M-sequence signals M ₁ ′ and M ₂ match. M-sequence signal _{M 1} 'is to 20ns delay from _{M 1, M} 1 with respect to the M-sequence signal _{M 2} as a reference'
Because a 0.1 ns short period in one cycle, two patterns of the M-sequence signal _{M 1} 'and _{M 2} at time _{t b} delayed 200 cycles of the M-sequence signal _{M 2} from the time _{t a} is consistent. Since one cycle of M-sequence signal M ₂ is 1.27 μs, 200 cycles are 1.27 μs × 20
0 = 254 .mu.s, and the time _{t b} is present in 254 .mu.s delayed position than _{t a.} Since the maximum value detection circuit 14 generates a pulse output at the time when the maximum value of the input triangular wave voltage is detected, the pulse output is naturally generated at this time t _b . The operation of the maximum value detector 14 is similar to that of the maximum value detector 13 described above, and the generated pulse output is supplied to the time measuring device 15 as a measurement stop signal this time. Time measuring device 15 measures the time until t _b is the input of the measurement stop signal from the input time t _a of the measurement start signal. In this example, the above-mentioned 254 μs is obtained as the measurement result. The time measuring method may be, for example, a method in which a time gate from the measurement start time to the stop time is provided and the clock signal in this time gate is coefficientd. The time T _D measured by the time measuring device 15 is supplied to the distance calculating means 33. The distance calculating means 33 configured by a microprocessor or the like calculates the distance x to the target object by performing the calculation according to the equation (3).

That is, 1/2 of the measured time T _D is multiplied by the propagation speed v of the electromagnetic wave, and the product T _D · v / 2 is set as the first calculated value, and the clock frequency f ₁ to the clock frequency f ₂ are calculated. The frequency of the subtracted difference is divided by the clock frequency f ₁ and the quotient (f ₁ −f ₂ ) / f ₁ is taken as the second operation value, and the first operation value and the second operation value are The third calculation value, which is the product of the multiplications, is obtained as the distance x to the object.

For example, the measured time T _D is calculated by the distance calculating means 33.
Is 254 μs, the distance x is 3 meters and T _D is 25
In the case of 40 μs, the distance x can be calculated as 30 meters. Further, the point that the present invention is greatly different from a general radar device is that the time proportional to this distance is remarkably extended. That is, it takes 20ns (20 × 10 ^-9 seconds) to measure a distance of 3 meters with a general radar. According to the present invention, however, measuring a distance of 3 meters means measuring 254 μs (254 × 10 ⁻⁶ seconds). The expansion rate of this measurement time is calculated by the frequency f
₁ = 100.004MHZ, as calculated by substituting _{f 2 = 99.996MHZ, T D =} 12,500τ is obtained. That is, it is only necessary to measure a signal that has been magnified 12,500 times on the time axis and is extremely slowed down. Therefore, the radar device of the present invention has a great feature in that the measurement accuracy in a short distance is improved and the device can be easily configured by an inexpensive low-speed element as compared with the conventional device. The time measurement by the time measuring device 15 is performed every time the aforementioned measurement start signal is input every 16.1 ms.
Therefore, when the object moves, a change in the distance from the transmitting / receiving antenna to the object can be detected every 15.875 ms. Also, in the time measurement in this embodiment, 15.875 ms corresponds to a distance of about 188 meters. Although the maximum detection distance of 188 meters is sufficient for applications such as ordinary underground exploration, by selecting the frequencies of clock frequencies f ₁ and f ₂ ,
It is possible to change the enlargement ratio and the maximum detection distance on the time axis.

FIG. 7 is a block diagram showing an embodiment of the clock generator. In the figure, 26 is a crystal oscillator with a frequency of 3 MHz, 27-
1, 27-2, and 27-3 mix signals of two frequencies f _A and f _{B, and} a signal of sum frequency f _A + f _B and a frequency of difference f _A
-F _B signal output mixer, 28-1 is 4KHz oscillator, 28-2 is 97KHz oscillator, 29-1, 29-2, 29
-3 and 29-4 are bandpass filters, and the pass frequencies are selected as 3.004MHz, 2.996MHz, 100.004MHz and 99.996MHz respectively.

Explaining the operation of FIG. 7, the 3 MHz signal output from the crystal oscillator 26 and the 4 KHz signal output from the oscillator 28-1 are mixed in the mixer 27-1 composed of, for example, a balanced modulator. , Outputs 3.004MHz and 2.996MHz signals. Of the output signal of the mixer 27-1, the 3.004 MHz signal passes through the bandpass filter 29-1 to the mixer 27-2, 2.99 MHz.
The 6 MHz signal passes through the bandpass filter 29-2 and is supplied to the mixer 27-3. Mixer 27-2 is 3.004M
The Hz signal and the 97MHz signal supplied from the oscillator 28-2 are mixed and the sum and difference signals are output. Of these, the sum signal of 100.004MHz is the bandpass filter 29.
It passes through -3 and is output as the clock frequency f ₁ .
Similarly, the mixer 27-3 mixes and outputs the 2.996 MHz signal and the 97 MHz signal supplied from the oscillator 28-2, but the sum signal 99.996 MHz is output by the band pass filter 29.
It passes through -4 and is output as the clock frequency f ₂ .
With such a configuration, two clock frequencies f ₁ and f ₂
The frequency difference of is kept at exactly 8 KHz. In the present invention, the two clock frequencies f ₁ and f ₂ make
Since one pseudo-random signal is generated and the measurement is performed by utilizing the period difference between these two pseudo-random signals, it is important to accurately hold the difference between the clock frequencies in order to improve the measurement accuracy. Therefore, for example, a clock signal generator that keeps the frequency difference constant by using a technique such as PLL (Phase Lock Loop) may be configured.

FIG. 8 is a block diagram of an image display device for displaying the detection signal of the present invention as an image. In the figure, 5, 6,
11 and 12 are the same as the device shown in FIG. An image display device 30 includes an image conversion unit 31 and a display 32 inside. The image conversion unit 31 uses the output signal from the low pass filter 11 as a reference signal for measuring the distance.
The output signal from is used as the detection signal. The detection signal uses the time from the reference signal to the detection signal as position information of the corresponding distance, and displays it as a bright and dark video signal according to the received intensity.
Display on 32. Further, when the transmitting / receiving antenna is moved, the scanning start position is moved on the CRT in accordance with the moving distance. The characteristic point here is that the detection signal has a sufficiently low speed and can be directly supplied to the image conversion unit without using a sampling device as in the conventional case.

FIG. 9 is an image display diagram of the detection signal of the present invention. The figure shows an image display example of a detection signal of an underground buried object, for example, a plastic pipe having a depth of 3 meters. The horizontal axis of the figure shows the travel distance of the transmitting / receiving antenna traveling in the direction across the pipe, and the vertical axis shows the detection distance. The strength of the detection signal is displayed in light and dark. In the figure, the upper part of the semi-circular waveform display that opens downward indicates pipe detection. The shape of this semi-circular arc is an image generated due to insufficient directivity of the transmitting and receiving antennas, and is not a problem in practical pipe detection. In addition, when the reflected wave from the ground surface is strong and the reflected wave from the object is weak, a method of reducing the reflection from the ground surface by running the transmitting antenna and the receiving antenna independently is also effective.

Although the case of an underground or underwater exploration radar has been shown as an example of the present invention, the present invention can also be applied to distance measurement by TDR (Time Domain Refractry). TDR is a technique generally used for the purpose of detecting a fault position of an electric wire, and an electric pulse by a monopulse or a step pulse is input from one end of the electric wire. This electric pulse propagates through the line, travels, is reflected from a portion where the characteristic impedance changes due to a disconnection or short circuit of the line, and returns to the signal input end. The time from the input time of this electric pulse to the detection of the reflected wave and the propagation speed of the line are used to detect the changing point of the characteristic impedance. TDR can also be used for optical fibers to detect anomalies in the optical fiber by the same principle using optical pulses.

Instead of inputting an electric pulse signal into this TDR, a pseudo random signal of the present invention is input, and the time from the reference signal detection time until the maximum correlation output with the reflected wave is detected and the detection signal is obtained, and its propagation. Similarly, the change point of the propagation impedance can be detected from the velocity. The feature of this method is that even if noise is mixed in the reflected wave, the correlator does not malfunction due to noise, and stable measurement is possible.

[Effects of the Invention] As described above, according to the present invention, the first pseudo random signal having the clock frequency f ₁ used for transmission / reception to / from the detection target and the second pseudo random signal used as the reference signal. random signals in the same pattern, the clock frequency f ₁ of the first pseudo random signal, the clock frequency f ₂ of the second pseudo random signal, from f _1, the f ₁
It is set so that it is lowered by only a slight frequency of 1/10000 or less, and the time when the maximum correlation value between the reference second pseudo-random signal and the transmitted first pseudo-random signal is detected, and the second Detecting the time when the maximum correlation value between the pseudo random signal and the received first pseudo random signal is detected,
The time between these two maximum correlation value detection times was measured, and the distance to the target object was calculated based on the measured time. Further, the measurement time is significantly extended compared to the actual time required for propagation of electromagnetic waves in the conventional method, so that the time can be measured directly by the low speed signal. Therefore, the conventional sampling device required for high-speed signal processing in real time is not required, and the device can be configured with low-speed circuit elements, so that the device can be downsized and the cost can be reduced.

Further, in the time measurement proportional to the measurement distance, the measurement is performed by the time significantly extended from the real time, and the distance is calculated based on the measurement time, so that the distance measurement accuracy is improved. In particular, the correlation processing of the pseudo-random signal has the effect of improving the short-range resolution.

Furthermore, according to the present invention, the clock frequency f of the first pseudo-random signal transmitted toward the object as an electromagnetic wave.
_{Since 1 is set} to 100 MHz or more, the distance measuring device of the present invention can be used to measure the distance to the detection object in the ground, water, snow, or concrete with high accuracy. Have an effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional radar device for underground or underwater exploration using pseudo-random signals, and FIG. 3 is a blocker of a correlator.
4 is a block diagram of a 7-bit M-sequence signal generator, FIG. 5 is an output waveform diagram of the M-sequence signal generator, FIG. 6 is a waveform diagram for explaining the operation of FIG. 1, and FIG. Is a block diagram showing an embodiment of a clock generator, FIG. 8 is a block diagram of an image display device of the present invention, and FIG. 9 is an image display diagram of detection signals of the present invention. In the figure, 1 and 2 are clock generators, and 3, 4 and 17 are M
Sequence signal generator, 5, 6 are multipliers, 7 is a power amplifier, 8
Is a reception amplifier, 9 is a transmitting antenna, 10 is a receiving antenna, 11 and 12 are low-pass filters, 13 and 14 are maximum value detectors, 15 is a time measuring device, 16 is an object, 18 is a sampling device, 19 is a correlator, 20-1, 20-2, 20-3 are attenuators, 21 is a delay line with taps, 22 is a code converter, 23 is an adder, 24 is a shift register, 25 is an exclusive OR circuit. , 26 is a crystal oscillator, 27
-1, 27-2, 27-3 are mixers, 28-1, 28-2 are oscillators, 29-1,
29-2, 29-3, and 29-4 are bandpass filters, 30 is an image display device, 31 is an image conversion unit, 32 is a display device, and 33 is distance calculation means.

Claims (3)

[Claims] 1. A means for generating a first pseudo-random signal having a clock frequency of f ₁ , a means for transmitting the generated first pseudo-random signal as an electromagnetic wave toward an object, and the object means for obtaining a received signal by receiving a reflected wave, the first pseudo random signal in the same pattern, the clock frequency from f _1, the f ₁ 1/10000 following slight frequency lower by f means for generating a second pseudo random signal to ₂ clock frequency, a first multiplier for multiplying the first pseudo random signal and the second pseudo random signal, the received signal the acquired and A second multiplier that multiplies the second pseudo-random signal, a first low-pass filter that low-pass filters the output signal of the first multiplier, and an output signal of the second multiplier. Low A second low-pass filter for performing band-pass filtering; a means for generating a first pulse when the maximum amplitude value of the output signal of the first low-pass filter is detected; and a maximum amplitude of the output signal of the second low-pass filter. A means for generating a second pulse when a value is detected, a means for measuring the time from the generation time of the first pulse to the generation time of the second pulse, and 1/2 of the measured time , and the product from the first calculation value by multiplying the propagation speed of the electromagnetic wave, the quotient above the frequency of the subtracted difference the clock frequency f ₂ from the clock frequency f _1, is divided by the clock frequency f ₁ As a second calculated value, and a means for multiplying the first calculated value and the second calculated value to obtain a third calculated value which is a product thereof as a distance to the object. A distance measuring device characterized by . 2. The distance measuring device according to claim 1, further comprising means for generating a first pseudo-random signal which sets the clock frequency f ₁ to 100 MHz or more. 3. A distance measuring the distance to an object to be detected either in the ground, underwater, in snow, or in concrete using the distance measuring device according to claim 1 or 2. measuring device.