JPH06130156A - Method and apparatus for searching embedded metal - Google Patents

Abstract

PURPOSE:To provide a method and apparatus for searching a metal embedded in the ground which has relatively long search limit distance and can be constituted easily. CONSTITUTION:The apparatus alpha for searching a metal X embedded underground comprises electrodes 10a, 10b embedded in the vicinity of search starting and ending points, an AC power supply 9 having output terminals connected with the electrodes 10a, 10b and generating an AC current of predetermined frequency, a search sensor alpha' comprising an LCR resonance circuit alphaa' resonant with the output frequency of the AC power supply 9, and an operational amplifier section 11 for amplifying, shaping and operating voltage or current induced in the search sensor alpha'. A display section 12 for displaying presence or the shape of embedded metal X operated at the operational amplifier section 11 is also provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for detecting a metal buried object buried in the vicinity of a ground such as a front or side of an underground excavating machine for excavating underground.

[0002]

2. Description of the Related Art Conventionally, underground excavation machines have to perform excavation work while avoiding obstacles such as buried objects in the ground, and have been equipped with a detection device for detecting these buried objects. A pulse radar method, an electromagnetic induction method, and the like have been used as the detection method used in this detection apparatus.

FIG. 5 shows the structure of a buried object detecting apparatus using the conventional pulse radar method, and FIG. 6 shows the buried object detecting apparatus using the electromagnetic induction method. In the figure, X is a buried object, A is an underground excavation machine, A'is a tip of an underground excavation machine, B is a radar antenna section, C is a search coil section, 1 is a transmission antenna, 2 is a reception antenna, and 3 is a pulse. The radar main body, 4 is a display unit, 5 is a transmission coil, 6 is a reception coil, 7 is an operational amplification unit, and 8 is a display unit.

In the buried object detecting method using the pulse radar method shown in FIG. 5, the radar antenna section B is arranged at the tip A'of the underground excavation machine, and the radar antenna section B concerned.
Is a transmitting antenna 1 that radiates an electromagnetic wave pulse P into the ground,
The receiving antenna 2 for receiving the electromagnetic wave pulse P'reflected by the buried object in the ground is arranged in parallel. Transmitting antenna 1
Is connected to the output terminal of the pulse radar main body 3, the receiving antenna 2 is connected to the input terminal of the pulse radar main body 3, and the output of the pulse radar main body 3 is connected to the display unit 4.

One or a plurality of electromagnetic wave pulses P having a predetermined pulse width are continuously output from the pulse radar main body 3 and radiated from the transmitting antenna 1 into the ground. The radiated electromagnetic wave pulse P is reflected by an underground buried object X having a relative dielectric constant different from that of the surrounding soil as shown by a broken line in the figure, and the reflected wave is received by the receiving antenna 2. The electromagnetic wave pulse P ′ received by the receiving antenna 2 is input to the pulse radar main body 3, undergoes amplification, demodulation, and waveform shaping, and is then processed.
Presence / absence, position, shape, etc. of the buried object are output to the display unit 4.

In the buried object detecting method using the electromagnetic induction method shown in FIG. 6, the search coil portion C is arranged at the tip portion A'of the underground excavating machine, and the search coil portion C generates a magnetic field M. A transmitting coil 5 for radiating and a receiving coil 6 for receiving an induced magnetic field M ′ generated from the embedded object X by the radiated magnetic field M and converting it into electric energy are arranged in parallel. The transmission coil 5 is connected to the output terminal of the operational amplifier 7,
The receiving coils 6 are respectively connected to the input terminals of the operational amplification section 7, and the output of the operational amplification section 7 is connected to the display section 8.

The operational amplifier 7 generates an alternating current and sends it to the transmitter coil 5. The transmission coil 5 generates an alternating magnetic field M and radiates it into the ground. If the buried object X having a relative magnetic permeability different from that of the surrounding soil exists, the magnetic flux density in the ground is not constant, and the magnetic field M ′ detected by the receiving coil 6 fluctuates. The magnetic field is converted into electric energy by the receiving coil 6 and input to the operational amplifier 7, where amplification, waveform shaping and arithmetic processing are performed,
It is output to the display unit 8 to display the presence / absence, position, shape, etc. of the embedded object X. Since the conventional buried object detection method is configured in this manner, it is possible to detect buried objects in the ground.

[0008]

However, the conventional buried object detecting method using the pulse radar method or the electromagnetic induction method has the following drawbacks. First, in both methods, since the transmitter and the receiver are arranged in parallel with the sensor, the radar pulse or the magnetic field line must pass through the route from the transmitter to the buried object, and from the buried object to the receiver. Since the attenuation of radar pulse or magnetic field lines in the soil that forms the path is extremely large, it has the drawbacks of low sensitivity and short detection limit distance.

In the pulse radar method, when it is mounted on a mechanical device such as a small underground excavating machine which is restricted in the mounting location of the detecting device, the transmitting antenna and the receiving antenna must be constructed in a small size. This shortens the wavelength of the electromagnetic pulse used. In the ground, the shorter the wavelength is, the larger the attenuation is. Therefore, it is difficult to extend the detection limit distance in consideration of the both. For example, if the antenna length is 20
In cm, the detection limit distance is about 50 cm,
Since the pulse radar main body requires an electromagnetic wave pulse generation circuit and a demodulation circuit, the circuit configuration is complicated, expensive, and the device is relatively large.

In the electromagnetic induction method, the size of the transmitting coil and the receiving coil is limited due to the mounting space of the tip of the underground excavating machine. For this reason, the capacity of the transmission coil is small, and the current that can flow is limited, so that the magnetic field lines radiated are small. Similarly, the receiving coil has a low sensitivity because it is impossible to increase the number of turns. Therefore, the detection limit distance is 10 cm ~
It had a short defect of about 15 cm. Here, the present invention provides a method and apparatus for detecting a metal buried object which has a relatively long detection limit distance of a metal buried object buried in the ground and can be easily constructed.

[0011]

The solution to the above-mentioned problems can be achieved by adopting the novel characteristic construction method and means listed in the following by the present invention. That is, the feature of the method of the present invention is to apply an AC voltage of a certain oscillation frequency to the ground from two points spaced apart from each other by a current, and to apply a current to a metal buried object in the ground between the two points to generate a magnetic field. Is generated, and the magnetic field is resonantly detected at the oscillation frequency by the detection sensor attached to the underground excavation machine, and the selectivity Q is increased to increase the Q of the induced voltage.
This is a method for detecting a metal buried object obtained by doubling the detection voltage.

The first feature of the device of the present invention is, in a metal buried object detecting device for detecting a metal buried object in the ground, an electrode buried near a detection start position and a detection end position, and an output terminal of the electrode. Is connected to generate an alternating current of a predetermined frequency, a detection sensor including a resonance circuit that resonates at the output frequency of the AC power supply, and a voltage or current generated in the detection sensor is amplified, waveform shaped, and calculated. A metal buried object detecting apparatus comprising: an operational amplifier section; and a display section that displays the presence, position, or shape of the metal buried object calculated by the operational amplifier section.

A second feature of the device of the present invention is a metal-buried object detecting device in which the detection sensor according to the first feature of the above-mentioned device is provided with a Hall element instead of the resonance circuit.

[0014]

Since the present invention has taken the above method and means, it is possible to increase the detection voltage or the detection current by utilizing the resonance action of the detection sensor by applying the AC voltage or the AC current from the ground. It will be possible.

[0015]

【Example】

(Example of Method) An example of the method of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a structural conceptual diagram showing a case where a metal buried object is buried orthogonally to the front of an underground excavation machine in this embodiment, and FIG.
FIG. 4 is a structural conceptual diagram showing a case where a metal buried object is buried along an underground excavating machine in this embodiment. In the figure, α
Is a metal buried object detection device, α ′ is a detection sensor, 9 is an AC power supply, 10a and 10b are electrodes, 11 is an operational amplifier, and 12 is a display. The same members as those in the conventional example are designated by the same reference numerals.

In the present method example shown in FIG. 1, the metal buried object detecting apparatus α is composed of an AC power source 9, electrodes 10a and 10b, an operational amplifier section 11 and a display section 12. The detection sensor α ′ is arranged at the tip A ′ of the underground excavation machine and has an LCR having a resonance frequency equal to the output frequency of the AC power supply 9.
It is a resonant circuit. The AC power supply 9 generates an AC current having the same frequency as the resonance frequency of the detection sensor α ′. Electrodes 10a and 10b are buried from the ground near the propulsion start point and the propulsion end point of the underground excavating machine A, respectively, and an AC power source 9
The output of is connected to the electrodes 10a and 10b, and an alternating current is made to flow in the ground.

At this time, the metal buried object X such as a metal pipe or a fume pipe has an inherent resistivity of 1/10 of the resistivity of the ground.
Since it is 1 / several millions, the flowed alternating current passes through the metal buried object X, if present. An alternating magnetic field M is generated around the metal buried object X by the alternating current flowing in the metal buried object X.

The magnetic field lines of the alternating magnetic field M are detected by the detection sensor α '.
The detection signal α ′ is resonated by the LCR resonance circuit of the detection sensor α ′, and then extracted as the detection signal S. The detection signal S detected by the detection sensor α ′ is input to the operational amplification unit 11, where amplification, waveform shaping and signal processing are performed, and the presence or absence of the metal buried object X on the display unit 12, distance, position and shape, etc. Is displayed.

Generally, the resistivity of the ground is 100 Ω / m.
Before and after, about 20 times the DC resistance of the transmission coil 5 used in the electromagnetic induction method shown in FIG. Since an AC voltage is applied in this example of the method, considering the impedance, the ground feedback circuit compared with the sensor circuit using the transmission coil 5 is about several times to ten times, so the applied voltage may be increased to this extent. . Since an AC voltage of about 5 V is applied to the transmission coil 5 in the electromagnetic induction method of FIG. 6, it is sufficient to apply an AC voltage of about 50 V per 1 m of soil thickness even if this method example is used.

(Apparatus Example) An embodiment of the apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a structural conceptual view showing a case where a metal buried object is buried orthogonally to the front of the underground excavating machine in this embodiment, and FIG. 2 is a metal buried object buried along the underground excavating machine in this embodiment. 3 is a conceptual diagram of the configuration of the detection sensor using the LCR series resonance circuit of the present invention device, and FIG. 4 is a principle circuit of the detection sensor using the LCR parallel resonance circuit of the present invention device. It is a figure. In the figure, α
a ′ is an LCR series resonance circuit, αb ′ is an LCR parallel resonance circuit, 13 is a coil, 14 is a capacitor, 15 is a resistor, 1
6 is a coil, 17 is a capacitor, and 18 is a resistor. The same members as those in the conventional example are designated by the same reference numerals.

In the example of the present apparatus shown in FIG. 1, the metal buried object detecting apparatus α includes a detecting sensor α ′, an AC power source 9, and an electrode 10.
a, 10b, an operational amplifier 11, and a display 12. A detection sensor α'is provided at the tip A'of the underground excavation device.
Is provided. The coil 13 provided in the detection sensor α ′ constitutes a series resonance circuit or a parallel resonance circuit together with the capacitor 14 and the resistor 15 so that the resonance frequency becomes equal to the output frequency of the AC power supply 9 and the selection rate thereof. The characteristic value of each element is selected so that the (Q value) has a value as high as possible. The coil 13 is a detection sensor α '
Is arranged at the foremost part of the No. 1 and has the highest detection sensitivity.

The AC power supply 9 generates an AC current having the same frequency as the resonance frequency of the detection sensor α '. Underground excavation machine A
Electrodes 10a and 10b are buried from the ground near the propulsion start point and the propulsion end point, respectively, and the output of the AC power supply 9 is connected to the electrodes 10a and 10b to pass an AC current in the ground. At this time, the inherent resistivity of the metal buried object X such as the metal pipe or the fume pipe is 1/10 to 1 / the resistivity of the ground.
Since it is several million, the flowed alternating current passes through the metal buried object X, if present.

An alternating magnetic field M is generated around the metal buried object X due to the alternating current flowing in the metal buried object X. The magnetic field lines of the alternating magnetic field M are detected by the coil 1 at the tip of the detection sensor α ′.
It is detected in 3 and resonated in the LCR resonance circuit, and then extracted as a detection signal. The detection signal S detected by the detection sensor α ′ is input to the operational amplification unit 11 where amplification, waveform shaping and signal processing are performed, and the display unit 12 displays the presence or absence of the metal buried object X, the distance and the shape, etc. To do.

Next, the principle of the reception sensor circuit used in this example of the apparatus will be described with reference to FIGS. FIG. 3 shows a receiving sensor circuit using the LCR series resonance circuit αa ′, and FIG.
The reception sensor circuits using the CR parallel resonance circuit αb are shown respectively. LCR series resonance circuit αa ′ of FIG.
In the reception sensor circuit using, the coil 13, the capacitor 14, and the resistor 15 are connected in series. Coil 1
The inductance of 3 is L, the capacity of the capacitor 14 is C,
If the resistance value of the resistor 15 is R, the impedance of the LCR series resonance circuit αa ′ is Z, the angular frequency is ω, and the frequency is f, then Z = (R ² + (ωL-1 / ωC) ² ) ^1/2 .

Assuming that the angular frequency at which the impedance of the series resonance circuit is minimum is ω _r and the resonance frequency is f _r , the condition that satisfies these conditions is ω _r L-1 / ω _r C = 0, and LC ω _r ² = than _{1 ω r = 1 / (LC} ) 1/2 ω r = 2πf r, it is _{f r = 1 / (2π (} LC) 1/2).

At this time, the selectivity Q is expressed by the following equation. Q = ω _r L / R = (2πf _r L) / R = 1 / (2πf _r CR)

At this time, assuming that the potential differences between the ends of the coil 13 and the capacitor 14 are E _L and E _C , respectively, E _L = (2πf _r L) / R · E E _C = 1 / (2πf _r CR) · E , Coil 1 of LCR DC resonance circuit αa 'at resonance
3 and the voltage applied to the capacitor 14 are both Q times,
A high detection voltage can be taken out by the resonance phenomenon.

FIG. 4 shows a receiving sensor circuit using an LCR parallel resonance circuit αb ', in which a coil 16 and a resistor 17 are connected in series, and a capacitor 18 is connected in parallel. When the impedances of the coil 16, the resistor 17, and the capacitor 18 are expressed as Z _L , Z _R, and Z _C , respectively, LC
The αb ′ impedance Z of the R parallel resonance circuit is Z = ((Z _R + Z _L ) · Z _C ) / (Z _R + Z _L + Z _C ).

At this time, if the DC resistance component Z _R is very small, the denominator can be ignored, and since Z _L and Z _C are equal at resonance, Z = (Z _L ) ² / R = (2πf _r L) ² / R = (1 / R) · (2πf _r L / 2πf _r C) = L / (C · R) = (2πf _r L) ² / R ² · R = Q ² · R

Therefore, the selectivity Q is Q = (Z / R) ^1/2 = (L / (C · R ² )) ^1/2 Therefore, the electromotive force E of the LCR parallel resonance circuit αb ′ is E = I ・ Z = I ・ (L / (C ・ R))

Therefore, the current I _L flowing through the coil 15 can be expressed by the following equation. I _L = E / ωL Since the selectivity Q at this time can be expressed in the same manner as in the case of the LCR series resonance circuit αa ′, it is substituted into the above equation, I _L = Q · I, and the current I flowing through the coil 16 at resonance is obtained. _L is Q times the current generated in the coil 16. Therefore, the detection current can be increased by using the LCR parallel resonance circuit αb ′ for the reception sensor.

Another example in which the Hall element is used in the sensor section will be described in detail. Since the Hall element increases the amount of current passing therethrough in proportion to the amount of passage of magnetic force lines and has a high detection sensitivity, the LCR resonance circuit αa ′ used in the detection sensor α ′,
It can be used as an alternative to αb ′.

The magnetic field lines of the alternating magnetic field M are detected by the Hall element of the detection sensor α'and extracted as a detection signal S. The detection signal S detected by the detection sensor α ′ is the operational amplifier 1
1 is input, amplification, waveform shaping and signal processing are performed,
The presence / absence of the metal buried object X, the distance, the shape, etc. are displayed on the display unit 12.

[0034]

As described above, according to the present invention, it is possible to significantly extend the detection limit distance by burying two electrodes connected to an AC power source installed on the ground and flowing an AC current into the ground. Becomes In addition, there is a source for detection on the ground, and it is possible to generate a magnetic field in a metal buried object without taking any means from the detection sensor, so there is no restriction on the size of the source. It has flexibility in the installation of the detection device.

Further, since it is not necessary to provide a transmission source at the tip of the underground excavation machine, there is an advantage that the tip can be made small and lightweight. In particular, when a hall element is used as a detection sensor, it can be made very small and lightweight.
Moreover, since the device configuration is easy and inexpensive,
Exhibits excellent economic efficiency and usefulness.

[Brief description of drawings]

FIG. 1 is a structural conceptual diagram showing a case where a metal buried object is buried orthogonally to the front of an underground excavation machine in the present invention.

FIG. 2 is a structural conceptual diagram showing a case where the same metal-embedded object is buried along an underground excavation machine.

FIG. 3 is a principle circuit diagram of a detection sensor using an LCR series resonance circuit of the device of the present invention.

FIG. 4 is a principle circuit diagram of a detection sensor using the same LCR parallel resonance circuit.

FIG. 5 is a conceptual diagram of a configuration of a buried object detection device using a pulse radar method of a conventional example.

FIG. 6 is a conceptual diagram of the configuration of a buried object detection device using an electromagnetic induction method of a conventional example.

[Explanation of symbols]

 α ... Metal buried object detection device α '... Detection sensor A ... Underground excavation machine A' ... Underground excavation machine tip B ... Radar antenna part C ... Search coil part αa '... LCR series resonance circuit αb' ... LCR parallel resonance Circuit X ... Metal buried object 1 ... Transmission antenna 2 ... Reception antenna 3 ... Pulse radar main body 4 ... Display unit 5 ... Transmission coil 6 ... Reception coil 7 ... Operation amplification unit 8 ... Display unit 9 ... AC power supply 10a, 10b ... Electrode 11 Computational amplification section 12 ... Display section 13 ... Coil 14 ... Capacitor 15 ... Resistor 16 ... Coil 17 ... Resistor 18 ... Capacitor

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Riki Nishimura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Junichi Masuda 1-16-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. From two points with a required distance to the ground,
Applying an AC voltage of a certain oscillation frequency, passing a current through the underground metal buried object between the two points to generate a magnetic field, and resonating at the oscillation frequency by the detection sensor attached to the underground excavation machine. A method for detecting a metal buried object, which comprises detecting and increasing the selection rate Q to obtain a detection voltage Q times the induced voltage. 2. A metal buried object detecting apparatus for detecting a metal buried object in the ground, an electrode buried near a detection start position and a detection end position, and an output terminal connected to the electrode, and an alternating current of a predetermined frequency. An AC power supply that generates an electric current, a detection sensor including a resonance circuit that resonates at the output frequency of the AC power supply, an operational amplification unit that amplifies the voltage or current generated in the detection sensor, shapes the waveform, and operates the operation amplification unit. A metal buried object detection apparatus, comprising: a display unit that displays the presence, position, or shape of the metal buried object calculated by the unit. 3. The metal embedded object detecting apparatus according to claim 2, wherein the detecting sensor includes a Hall element instead of the resonance circuit.