JP4787064B2 - Metal detector and metal detection method - Google Patents

Description

  The present invention relates to a metal detector and a metal detection method, and more particularly, to a metal detector that can detect a buried vehicle or the like at a collapse site and a metal detection method using the same.

  In order to detect a vehicle buried in earth and sand about several meters from the surface without mining, it is optimal to apply a geophysical exploration method. As is well known, geophysical exploration methods have many methods based on different principles. When considering the target depth and the object to be detected, the methods considered promising are electric exploration, magnetic exploration, electromagnetic exploration, and underground radar exploration (in the broad sense, they are in the category of electromagnetic exploration). It is done. Although electric exploration has a high exploration capability, it is difficult to reliably install the electrodes on the ground surface, assuming local conditions. Therefore, three methods of magnetic exploration, electromagnetic exploration, and underground radar exploration are promising.

  By the way, when assuming the local situation, the ground surface is considerably uneven, and from the viewpoint of ensuring safety, the measurement is performed by suspending a sensor from a flying object or a heavy machine. Among the three methods described above, the ground radar survey requires a sensor (antenna) to be measured along the ground, so the applicable field is considerably narrowed. Magnetic exploration and electromagnetic exploration are similar measurement methods when targeting shallow ground, but electromagnetic exploration is advantageous for determining the presence or absence of a detected object in real time from measurement data. However, there are few systems that incorporate a convenient real-time display device in electromagnetic exploration systems. Therefore, the present inventors decided to develop a metal detector specialized for detecting a deep metal buried in the metal while making use of the characteristics of the electromagnetic exploration device having a high exploration capability.

  Commercial metal detectors are: (1) detection of needles remaining in clothing products, (2) detection of knives etc. that are prohibited from being brought into public transportation, especially aircraft, (3) landmine detection (4) It is used for purposes such as treasure hunting (coin search), and the distance (depth) that can withstand practical use is almost 20 to 50 cm. That is, commercially available metal detectors are used to detect relatively small metals that are relatively close.

  On the other hand, the object to be detected according to the present invention is a vehicle having a size larger than that of a light vehicle and has a maximum buried depth of 3 m.

Under such conditions, a metal detector and a metal detection method that can preferably detect a detection target have not been known.
JP-A-8-105923 Japanese Patent Application Laid-Open No. 8-105979

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is a vehicle that is larger than a mini vehicle and has a maximum buried depth of about 3 m. An object of the present invention is to provide a metal detector and a metal detection method capable of detecting a detector.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by a predetermined metal detector and a predetermined metal detection method, and have completed the present invention. It was.

  That is, according to the present invention, the following metal detector and metal detection method are provided.

[ 1 ] A primary coil that generates magnetic field lines, and a secondary coil that has a magnetic axis substantially on the extension of the diameter of the primary coil and detects an induced magnetic field from the detected object, A method for detecting a detection object buried at a depth of 0 to 3 m in the ground using a metal detector having a diameter of a secondary coil larger than 20 cm and a diameter of the secondary coil of less than 16 cm. A metal detection method in which an alternating current having a frequency of 80 to 710 Hz is passed through the next coil to generate lines of magnetic force, and measurement is performed at a distance of 50 cm or more from the ground.

[2] and the primary magnetic field generated from the primary coil, according to [1] for performing detection by using the amplitude of the phase difference and the secondary field of secondary magnetic field induced by the locator from the primary field Metal detection method.

[ 3 ] A primary coil that generates magnetic field lines, and a secondary coil that has a magnetic axis substantially on the extension of the diameter of the primary coil and detects an induced magnetic field from the detected object, It was buried at a depth of 0 to 3 m in the ground using a metal detection system comprising a heavy machine or a flying body equipped with a metal detector having a diameter of a secondary coil larger than 20 cm and a diameter of the secondary coil of less than 16 cm . A method for detecting a detected object, which is a method for detecting a metal in a disaster in which an alternating current having a frequency of 80 to 710 Hz is passed through a primary coil to generate magnetic lines of force and measured at a distance of 50 cm or more from the ground.

  INDUSTRIAL APPLICABILITY The metal detector and metal detection method of the present invention can detect a detection object buried in 0 to 3 m in the ground, particularly a vehicle having a size larger than that of a light vehicle.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

  The metal detector and the metal detection method of the present invention are useful for a relatively large object to be detected. In particular, it is suitable for detecting a vehicle larger than a mini vehicle.

  In order to detect metals by the electromagnetic exploration method, (1) use one coil to switch between transmission and reception, (2) perform transmission and reception using two coils, and (3) use one coil. Any method of transmitting and receiving a plurality of components may be used. However, since the structure is simple, the method of performing transmission and reception using two coils of (2) is preferable.

  The arrangement method of the two coils may be any, but (1) there is no coupling of the primary magnetic field, (2) the ground response is large, but it is strong against the fluctuation of the sensor during measurement, and (3) the penetrating electromagnetic wave. Strong vertical arrangement is preferred. In addition, the vertically arranged apparatus has an effect that the number of parts is small and the device configuration can be simplified. From the above, a preferred metal detector of the present invention is schematically shown in FIG.

  In FIG. 1, the primary coil 1 and the secondary coil 2 are supported by a support shaft 3. The support shaft 3 is positioned along the longitudinal direction on the extension of the diameter 4 of the primary coil 1 passing through the center 5 of the primary coil 1. The support shaft 3 has one end fixed to the primary coil 1, and the secondary coil 2 is wound around the other end around the support shaft 3. Therefore, the magnetic axis of the secondary coil 2 is located on the extension of the diameter of the primary coil 1.

  The size of the primary coil 1 (diameter, area of the surface cut by the coil) depends on the size of the detected object. In order to detect a detection object having a size larger than that of a light vehicle, the sensitivity is poor when the diameter of the primary coil 1 is 20 cm or less. Therefore, the diameter of the primary coil 1 needs to be larger than 20 cm. Moreover, it is preferable in it being 48 cm or more. The shape of the surface cut by the coil may be any. Examples thereof include polygons such as a circle, an ellipse, a quadrangle, and a pentagon.

  The size of the secondary coil 2 needs to be determined so that the induced magnetic field from the detection target to be detected can be detected efficiently. When the distance is 16 cm or more, the sensitivity tends to be poor in detecting the induced magnetic field from the light vehicle. Therefore, the diameter of the secondary coil 2 is preferably less than 16 cm, and more preferably 2 cm or less.

  The metal detection system of the present invention can be configured by providing at least the above metal detector in a heavy machine or a flying body. As a preferable heavy machine, a backhoe having an arm with a high degree of freedom can be exemplified. Moreover, as a flying body, an unmanned small self-propelled aerial moving body can be exemplified, and a radio control helicopter, a radio control airplane, a radio control airship, and a kite plane are particularly preferable.

  The position at which the heavy equipment or the aircraft is provided with the metal detector may be any position, but it is necessary to provide the heavy equipment or the aircraft body so that the metal reaction of the heavy equipment or the aircraft body is not detected. It is preferable to keep the metal detector 3 m or more away from the heavy machinery or the flying object.

  In the metal detection method of the present invention, it is necessary to detect by flowing a current having a frequency of 80 to 710 Hz through the primary coil 1. It is also preferable to detect by flowing a current of 390 to 485 Hz.

  In the metal detection method of the present invention, the detector (sensor) is preferably detected 50 cm or more away from the ground, and more preferably 1 m or more away. The upper limit of the distance from the ground is not limited in terms of the magnetic field response of the ground, but the magnetic field generated from the primary coil 1 is inversely proportional to the cube of the distance from the primary coil 1, so it is far away. If it is too large, the magnetic field of the primary coil 1 will not reach the body to be detected, which is not preferable.

  In the metal detection method of the present invention, it is preferable to use the primary magnetic field generated from the primary coil 1, the phase difference between the secondary magnetic field induced by the detected object from the primary magnetic field, and the amplitude of the secondary magnetic field. More specifically, it is preferable to use the sum of the phase difference between the primary magnetic field generated from the primary coil 1 and the secondary magnetic field induced from the primary magnetic field by the detected object and the amplitude of the secondary magnetic field.

[Reference Example 1]
FIG. 2 shows the relationship between the frequency of the current flowing through the primary coil 1 and the phase angle deviation. The primary coil 1 was 450 mm in diameter, 54 turns, and 1.0 mm thick, and the object to be detected was an iron plate of 1 m × 1 m. From this figure, it can be seen that, at the same distance, the sensitivity is high at a frequency of 80 to 710 Hz, and among them, the sensitivity at a medium level (390 to 485 Hz) is the highest (the phase angle shift is large).

[Reference Example 2]
As a method of processing received electromagnetic waves, there are a method of processing in the time domain and a method of processing in the frequency domain, but in order to determine the presence or absence of metal in real time, a method using time domain data is preferable.

  The presence or absence of metal can be detected as a relative change between the transmission waveform and the reception waveform. As a method that can be suitably used, (1) a transmission current or a phase difference between a primary magnetic field and a secondary magnetic field, (2) an amplitude change of the secondary magnetic field, and (3) an amplitude of a signal received by a plurality of coils having different directions. Ratio and phase difference, (4) The electromagnetic wave of several frequencies can be transmitted / received and the response difference with respect to frequency can be mentioned. The (1) and (2) are suitable for processing in the time domain, and the (3) and (4) are suitable for processing in the frequency domain.

  There is a relationship of the following formula (A) between the magnetic field and the electric field at an arbitrary point other than the axis sufficiently away from the primary coil 1 as shown in FIG. 3 (Kaufmann).

  From the above formula, (1) the magnetic field generated from the primary coil 1 is proportional to the current flowing through the primary coil 1, and (2) the magnetic field generated from the primary coil 1 is proportional to the cross-sectional area of the primary coil 1. (3) The magnetic field generated from the primary coil 1 is inversely proportional to the cube of the distance from the primary coil 1. (4) The magnetic field is a vector and varies depending on the measurement point and the measurement direction. (5) 1 The relationship that the absolute value of the magnetic field in the axial direction in the secondary coil 1 is twice that in the horizontal direction is derived.

  FIG. 4 shows the relationship between the distance to the detected object (light car) and the relative sensitivity. As the primary coil 1, a coil having a diameter of 450 mm, 54 windings, and a thickness of 1.0 mm was used. Relative sensitivity is the phase angle or the sum of phase angle and amplitude. When a current of 300 mA is passed, the relative sensitivity of the phase angle and amplitude added at the same ratio shows the same tendency as the one that showed the relative sensitivity only by the phase angle, but the added one has the same sensitivity. It is rising.

  A normal electromagnetic exploration device makes a determination based on the amplitude of the secondary magnetic field, but from the above formula (A), the amplitude is inversely proportional to the cube of the distance, so that detection by the amplitude becomes difficult when the detected object is deep. On the other hand, it can be seen from FIGS. 2 and 4 that the phase is almost inversely proportional to the distance to the object. Therefore, it is advantageous to use the combined value of the phase difference and the amplitude in consideration of the stability of the response. More specifically, it is preferable to use the sum of the phase angle and the amplitude.

[Reference Example 3]
FIG. 5 is a diagram showing the magnetic characteristics of the ground. The soil and rocks that make up the ground also have electromagnetic reactions. Electromagnetic exploration uses this property to determine the resistivity and permeability of the ground. For metal detectors, these values are nothing but noise, but the physical properties of the ground are detected in the same way as electromagnetic exploration equipment. When detecting a detection object buried in a slightly deeper place, the secondary magnetic field generated from the ground cannot be ignored because the sensitivity of the metal detector is set high. Therefore, it is indispensable to adjust the equipment so that it is difficult to respond to the secondary electromagnetic field near the ground surface, and to relatively improve the response of the deep detection target. As the adjustment method, the method of Patent Document 1 can be adopted.

  Similar to the fact that the magnetic field changes when the distance between the detected object and the sensor changes, the secondary magnetic field from the ground also changes with the distance. That is, if the height of the sensor fluctuates, the metal detector is greatly affected. Therefore, the soil near the surface of the earth was considered to be uniformly distributed, and adjustments were made to cancel the influence as much as possible. The details of the metal detector used are shown in Table 1.

  FIG. 5A shows the sensitivity when the magnetic field response of the ground is reduced by adjusting, and FIG. 5B shows the response of the unadjusted device for reference. The details of the metal detector used are as shown in Table 1 above, but the diameter of the 50-16 type secondary coil is 16 cm. In (b), the 50-16 type has not been adjusted, and the others have been adjusted. In both figures, the horizontal axis represents the height from the ground surface to the sensor, and the vertical axis represents the relative electromagnetic response strength. In the unadjusted device, the detection value has an opening of about 4,000 at the sensor heights of 0.2 m and 1.0 m, but the adjusted one is only about 2. In the adjusted device, there is almost no fluctuation when the sensor height is 50 cm or more, and there is less fluctuation when the sensor height is 1 m or more. In other words, if the sensor height is measured at 50 cm or more, preferably 1 m or more, it will not be affected by the electromagnetic influence of the ground.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. Unless otherwise indicated, the specifications of the metal detector are as shown in Table 1 above.

  In the experimental yard, a flat ground was excavated with a backhoe up to a depth of 4 m at a depth of about 6 m × 20 m, and a light vehicle was buried. In order to simulate the collapse of natural disasters, backfilling was conducted with consideration given to avoiding compaction as much as possible. Further, the surface was not shaped, and the surface was uneven. Table 2 shows the burial conditions. In addition, FIG. 6 shows the vehicle layout and the like when the detection experiment yard is created.

  Measurement lines with an interval of 1 m were set in the long axis direction of the experimental yard, and measurement was performed while moving the metal detector along the measurement line. An outline of the procedure is shown below with reference to FIG.

  The sensor 8 of the metal detector 6 is set on the sled 9. Two sensor heights are 0.5m and 1.0m from the ground surface. Next, the sled 9 is measured from the start point (A point 14) to the end point (B point 15) on the first survey line 16. Further, the track is sequentially changed and the measurement up to the sixth measuring line 17 is performed. At that time, the direction of the sensor 8 is set to be the same as the arrangement direction on the first survey line 16.

  In FIG. 8, simple position information correction is performed based on digital data recorded for each survey line, and the strength of response to a planar two-dimensional coordinate is displayed in concentration using contour creation software. In Examples 1 and 2, the metal detector 6 of the present invention was used, and measurement was performed at a sensor height of 1 m and 50 cm. In Comparative Examples 1 and 2, the secondary coil diameter was 16 cm, and the others were measured under the same conditions as in Example 1 with a sensor height of 1 m and 50 cm, respectively. Comparative Example 3 was measured at a sensor height of 50 cm in the same manner as in Example 1 except that the primary coil diameter was 20 cm. These are summarized in Table 3.

  FIG. 8 clearly shows the planar position of the light passenger car at a depth of 1.5 m in all cases. On the other hand, the position of a light passenger car with a depth of 3.0 m cannot be detected with a conventional product having a primary coil of 20 cm, and cannot be detected even with a secondary coil of 16 cm.

  The towing speed of the sled was about 0.8 m / s (2.9 m / h). There is a trade-off between sensor movement speed and recording stability. The electromagnetic response itself is much faster than the moving speed of the sensor, but if the sensor is moved, noise is generated due to the shaking of the sensor and the stability is lost. Therefore, stabilization is achieved by obtaining an average measured value within a certain time and outputting the value (stabilization by extending the time constant). Under conditions where the metal response is large, that is, when the vehicle is buried in a shallow area and the sensor is not shaken, the buried vehicle can be detected even if measured at a speed of about 4 km / h or higher. When the depth of the object is 3 m, it is necessary to extend the time constant to some extent to determine the presence or absence of the metal response. In this embodiment, it is desirable to measure at a speed slower than about 3 km / h.

  A metal detection system was built with a metal detector in the backhoe bucket. The outline is shown in FIG. The backhoe and the backhoe bucket were separated from the metal detector by 3 m or more.

  A metal detection system was built with a metal detector at the bottom of the backhoe cabin. An outline is shown in FIG. When using a metal detector, the metal detector is lowered forward as shown in (a) so as to be 3 m or more away from the backhoe body, while the bucket is raised so as to be 3 m or more away from the metal detector. When excavating with a bucket, the metal detector is raised so as not to obstruct excavation as shown in (b).

  This system is excellent in that the backhoe operator can repeatedly turn and move, and judge on the spot to try excavation.

  If this system is equipped with a GPS (global positionig system) unit, the output from the metal detector and the information on the machine position and direction by GPS can be synthesized and the detection result can be mapped on the map. . An outline of this system is shown in FIG.

  FIG. 12 shows an outline of an example in which a metal detector is provided in an unmanned helicopter instead of a backhoe, and FIG. 13 shows an outline of an example in which an airship is provided.

  Although the present invention has been described using the embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiment, the detection object embedded in the earth and sand is detected, but the present invention is not limited to this. Needless to say, it is also effective for a detection object buried in snow, which has less magnetic properties than earth and sand.

  The present invention can be used when detecting a buried vehicle in a disaster or the like.

It is the schematic of the metal detector of this invention. It is a figure which shows the relationship between a frequency and a phase difference. It is a figure which shows the magnetic field in the point away from the coil. It is a figure which shows the relationship between the distance of a metal detector and a to-be-detected object, and relative sensitivity. It is a figure which shows the relationship between the height of a sensor, and relative sensitivity. (A) is after adjustment of the sensor, (b) is a comparison between before and after adjustment of the sensor. It is a figure which shows the embedment image of a detection target object. It is a schematic diagram of an Example. It is the photograph of the two-dimensional data of a detection result. It is the schematic of the metal detector system which provided the metal detector in the bucket of the backhoe. It is the schematic of the metal detection system which provided the metal detector in the cabin lower part of the backhoe. (A) is a figure during detection, (b) is a figure at the time of excavation. It is the schematic of the system which provided the metal detector in the cabin lower part of the backhoe, and was further provided with the GPS unit. It is the schematic of the metal detection system which made the unmanned helicopter equip the metal detector. It is the schematic of the metal detection system which made the airship equip the metal detector.

Explanation of symbols

1: primary coil, 2: secondary coil, 3: support shaft, 4: diameter of primary coil, 5: center of primary coil, 6: metal detector, 7: vehicle, 8: sensor, 9: sled 10: cable, 11: processing device, 12: battery, 13: recording device, 14: point A, 15: point B, 16: first line, 17: sixth line, 18: backhoe, 19: bucket, 20 : Cabin, 21: GPS unit, 22: GPS base station, 23: GPS satellite, 24: Camera, 25: Operator, 26: Computer, 27: Helicopter, 28: Airship, 29: Communication device

Claims (3)

A primary coil that generates magnetic field lines;
A secondary coil that has a magnetic axis on a substantially extension of the diameter of the primary coil and detects an induced magnetic field from the detected object;
A method of detecting a detection object buried at a depth of 0 to 3 m in the ground using a metal detector in which the diameter of the primary coil is larger than 20 cm and the diameter of the secondary coil is less than 16 cm. ,
An alternating current having a frequency of 80 to 710 Hz is passed through the primary coil to generate magnetic lines of force,
Metal detection method that measures 50cm or more away from the ground. The metal detection method according to claim 1 , wherein detection is performed using a primary magnetic field generated from a primary coil, a phase difference between a secondary magnetic field induced by a detection target from the primary magnetic field, and an amplitude of the secondary magnetic field. . A primary coil that generates magnetic field lines;
A secondary coil that has a magnetic axis on a substantially extension of the diameter of the primary coil and detects an induced magnetic field from the detected object;
Using a metal detection system comprising a heavy machine or a flying body equipped with a metal detector having a diameter of the primary coil larger than 20 cm and a diameter of the secondary coil of less than 16 cm, the depth of the underground coil is 0 to 3 m. A method for detecting a buried object,
An alternating current having a frequency of 80 to 710 Hz is passed through the primary coil to generate magnetic lines of force,
Metal detection method at the time of disaster that measures 50cm or more away from the ground.