JPH0711580B2 - Method and apparatus for detecting metal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a method for detecting a metal object buried in soil and an apparatus therefor.

[0002]

2. Description of the Related Art There are the following conventional methods for detecting a metal buried object in the ground.

The horizontal coil type reception sensor detects an object to be energized and detects the magnitude of the induced voltage generated in the upper and lower coils only when the lower coil is larger than the upper coil. The cross-coil type reception sensor is for detecting when the object to be detected is energized and the induced voltages generated in the upper and lower combination coils of horizontal and vertical match with each other at the maximum and minimum. In addition, in the electromagnetic induction type sensor, the induction magnetic field from the transmission coil changes depending on the detected object,
It is detected by the imbalance of the receiving coils. Further, the differential coil type proximity sensor detects the magnetic flux due to the eddy current generated in the object to be detected by the difference between the detection coil and the comparison coil. Further, the high-frequency oscillation type proximity sensor is for detecting by stopping oscillation by a change in impedance of an oscillation coil in a high-frequency oscillation circuit.

[0004]

The above horizontal coil type and cross coil type receiving sensors can easily detect a conducting cable in a non-metal pipe, but cannot detect a conducting cable in a metal pipe. Since electromagnetic shielding occurs due to the pipe, it cannot be detected at the same sensitivity level as in the case of a non-metal pipe. In addition, the horizontal coil type reception sensor does not change the detection performance from the position directly above the cable and the position 300 mm laterally away from the cable, depending on the detection sensitivity setting position. It may be detected as if it were right underneath.

Further, the electromagnetic induction type sensor is almost unaffected by energization of the cable and the like, and is effective in the detection performance limited to only the metal tube. However, this electromagnetic induction type sensor has a short detection distance.

Further, the differential coil type and high frequency oscillation type sensors have a short detection distance, and when the target surface has an arcuate shape or a curved surface such as a pipe, it is detected by the ratio of deviation from the center. Performance is not constant under unspecified conditions such as lower sensitivity. In addition, the influence of metal around is great, and it is necessary to provide a space three times or more the detection distance.

The present invention has been made in view of the above points, and provides a method and a device for detecting a wide metal without an electric current, which has a very simple structure, and has a long detection distance and can be detected reliably. This is the purpose.

[0008]

[Means for Solving the Problems] As shown in FIG.
When a pulsed current is applied to (a), the adjacent metal plates
An eddy current is generated in (b), but in this case the system works to reduce the magnetic flux. Then, when the current is cut off, the system works by reducing the magnetic flux according to Faraday-Neumann's law.
As shown in, the counter electromotive force V is generated at both ends of the coil (a). As a result, the voltage does not drop instantaneously as shown in FIG.
On the other hand, if the metal plate (b) is not close to the counter electromotive force, the back electromotive force is lowered because the eddy current is not generated, and the voltage is instantly lowered.

Therefore, the present invention detects the presence of metal by observing the change in the transient response characteristic waveform of the reflected wave when a pulsed current is applied to the coil. The specific measuring method is as follows. The time until the waveform reaches a certain voltage is measured, and the presence or absence of metal is identified by the length of this time.

The specific structure is that a sensor coil is provided in the tip of a main body made of a non-magnetic material having a low conductivity, and a transmitter circuit and a receiver circuit for applying a pulsed current to the sensor coil are provided. In addition, an observation section for the transient response characteristic waveform by the receiving circuit is provided.

[0011]

In the invention of claim 1, the reflection waveform measured in advance in the absence of metal is compared with the actually measured reflection waveform. If there is a change, the metal is present, and if there is no change. It turns out that there is no metal.

According to the second aspect of the present invention, the time until the reflected waveform becomes a constant voltage when no metal is present is measured in advance, and this time is used as a reference time, and the reflected wave reaches a constant voltage according to the actually measured output waveform. It can be seen that the metal is present if the time until is longer than this reference time, and that the metal is not present otherwise.

According to the third aspect of the present invention, the observation waveform is compared with the reflection waveform measured in advance when the metal is not present and the reflection wave actually measured, and if there is a change, a signal is output. It turns out that exists. If there is no change, no signal is output, indicating that no metal is present.

In the case of detecting a magnetic substance, the impedance change appears as a function of the distance between the object and the coil and the demagnetization factor of the area of the object, and in the case of detecting a non-magnetic substance, the current applied. It is considered that the angular velocity of is a very large factor.

Since the pulse system of the present invention includes all frequency components when subjected to Fourier expansion, it is proved that the pulse system is a very effective means for the present invention in which it is necessary to detect both magnetic and non-magnetic conductors. Was done.

Further, since the change in impedance due to the magnetic material is directly expressed as a change in the time constant of the waveform and the counter electromotive force due to the non-magnetic conductor is expressed as a change in the voltage component of the waveform, a pulse wave is used. It is theoretically proved that both magnetic substance and non-magnetic substance can be detected by measuring the time from switching time to constant voltage.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

First, the device used in the method of the present invention will be described with reference to FIG. 4. The drilling rod tip portion 1 of the drilling device to be inserted while rotating and excavating in the ground is provided at the tip opening portion of the pipe 2, A joint 3 is screwed on, and a cylindrical FRP resin tip 4 is connected to the pipe joint 3 via a knock pin 5, and a ceramic head 6 is attached to the tip of the tip 4. It is fixed through 7.

A tip 8 made of a super hard synthetic resin such as ultimum is fixed to the tip surface of the head portion 6. Further, a flowing water passage 9 which penetrates the head portion 6 and the tip portion 4 and communicates with the inside of the pipe 2 is provided in the axial direction so as to send appropriate water to the cutting ground. An annular metal detection sensor coil 10 is provided in the tip portion 4 at an outer peripheral position of the flowing water channel 9 with the axial direction of the tip portion 4 as the center.

Further, a cable detecting sensor coil 11 for P mode and R mode detection is provided in the tip portion 4 at the rear of the sensor coil 10. The lead wires of the metal detecting sensor coil 10 and the cable detecting sensor coil 11 are led out into the pipe 2 through the inside of the tip portion 4, and are inserted into the urethane tube 13 connected to the pipe joint 12 in the pipe 2. Has been done.

Next, a transmission / reception circuit 14 for supplying a pulse current to the sensor coil 10 and detecting a reflected wave from the object to be detected will be described with reference to FIGS.

The transmitting circuit is a clock pulse generating circuit 15
6 generates a clock pulse shown in (a) of FIG. 6, outputs it to the drive circuit 17 through the timing circuit 16, and the drive circuit 17 outputs the clock pulse to the metal detection sensor coil 10 and (b) of FIG. The drive pulse shown in () is applied. The waveform in FIG. 6C shows the waveforms at both ends of the metal detection sensor coil 10 when the current on the pulse is cut off.

Further, the receiving circuit clips a portion other than the changed portion due to metal approach from the metal detection sensor coil 10 through the first waveform clipping circuit 18 and inputs it to the first receiving amplifier 19 so that only the necessary portion is inputted. Amplify, and similarly, clip through the second clip waveform circuit 20 and input to the second reception amplifier 21 to amplify only the waveform change portion due to the target metal approach, and this waveform passes through the comparator 22, ON by comparing with a predetermined reference voltage
It is configured to be converted into a -OFF signal.

The operation of the comparator 22 falls when the pulse applied to the metal detection sensor coil 10 is turned off, and the waveforms at both ends of the metal detection sensor coil 10 increase from negative to increase the reference voltage. Get up where you cross. Therefore, the obtained output waveform is expressed as the pulse width of the OFF portion converted into time by the change in the waveform due to the metal approach, which appears at both ends of the metal detection sensor coil 10.

Therefore, the output signal of the comparator 22 is output to the gate circuit 23, and the gate circuit 23 outputs the clock pulse output from the clock pulse circuit 15 corresponding to the OFF portion of the output signal of the comparator 22. It is configured to do.

Although not shown, the number of output clock pulses is then counted by a counter, and the number of clock pulses up to the reference voltage when metal is not present is counted to set a preset reference count number. If the number of counts is larger than the reference count number, a signal indicating that metal is present is output.

FIG. 6 shows waveforms at various points in FIG. 5, and (d) and (e) are input and output waveforms of the first receiving amplifier 19,
(f) and (g) show the input waveform and output waveform of the second receiving amplifier 21, and (h) and (i) show the input waveform and output waveform of the comparator 22, respectively.

Although the present invention is provided in the boring machine in the above embodiment, the present invention is not limited to this, and a sensor coil may be provided in an appropriate one to detect metal. However, in any case, the periphery of the sensor coil must be made of a non-magnetic material having a low conductivity. This is because if the material around the sensor coil is a magnetic material or a material having high conductivity, metal can be detected, but the detection distance becomes short.

[0029]

According to the method and apparatus of claims 1 and 3, a pulsed current is applied to the sensor coil, and when the current is cut off, the transient response characteristic of the reflected wave is changed so that the metal Since the presence or absence is detected, the structure is extremely simple, and if the waveform of the reflected wave when no metal is present is made into a graphic in advance, these can be compared very easily and the metal can be easily detected. . Further, there is an advantage that all the metals can be detected without energizing the metal as the object to be detected, and further the detection distance is long and reliable.

Further, in addition to the above advantages, the method of claim 2
The previously measured time until the reflected wave reaches a constant voltage in the absence of metal is used as a reference time, and the time until the actual measured reflected wave reaches a constant voltage is measured and compared with the above reference voltage. As a result, the presence or absence of metal is detected, and metal detection becomes more reliable. There is also a method to detect the reflected wave when a pulsed current is passed through the sensor coil and cut it off, by detecting the change in the voltage value after a certain period of time. It is more advantageous in CPU calculation and the like to detect by the change of time.

[Brief description of drawings]

FIG. 1 is a perspective view showing the principle of the present invention and showing a state of a metal plate when a pulsed current is applied to a coil.

FIG. 2 is a perspective view showing the principle of the present invention and showing a state of a metal plate when a pulsed current is cut off from a coil.

FIG. 3 is a graph showing the principle of the present invention, showing a state of a reflected wave when a pulsed current is cut off from a coil with and without a metal plate.

FIG. 4 is a cross-sectional view showing a state in which the sensor coil of the present invention is attached to the tip of a hole making rod.

FIG. 5 is a schematic configuration diagram of a transmission / reception unit of the present invention.

FIG. 6 is a timing chart showing waveforms at various parts of the transmitter / receiver of the present invention.

[Explanation of reference symbols] 1 tip of drilling rod 2 pipe 4 tip 6 head 8 chip 10 sensor coil for metal detection 14 transceiver circuit

Claims (3)

[Claims] 1. A sensor coil is provided in a tip portion of a main body made of a non-magnetic material having a low conductivity, and a pulsed current is applied to the sensor coil, and a reflected waveform of a pulse waveform when the current is cut off is provided. A metal detection method, characterized in that the presence or absence of metal is detected by a change in transient response characteristics. 2. A sensor coil is provided in the tip of a main body made of a non-magnetic material having a low conductivity, and a pulsed current is applied to the sensor coil, and the reflected wave is kept constant after the current is cut off. Characterized by detecting the presence or absence of metal by measuring the time to reach the voltage,
Metal detection method. 3. A sensor coil is provided in the tip of a main body made of a non-magnetic material having a low electrical conductivity, and a transmitter circuit and a receiver circuit for supplying a pulsed current to the sensor coil are provided, and the receiver circuit is further provided. The metal detection device is characterized in that a transient response characteristic waveform observation section is provided.