JP3348766B2 - Electromagnetic induction sensor for detecting metal objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction sensor for detecting a metal object which is moved in only one direction, and which is buried in soil or concrete or the like and which cannot be seen from the ground. The present invention relates to an electromagnetic induction sensor for detecting a metal object, which is used for accurately detecting a buried position, a buried direction, and the like.

[0002]

2. Description of the Related Art Conventionally, as a sensor for detecting a metal object buried in the ground, an electromagnetic induction sensor for detecting a metal object using electromagnetic induction has been proposed by the present applicant (Japanese Patent Application No. Hei 8-8).
780). FIG. 3 is a block diagram of the electromagnetic induction sensor for detecting metal objects, and FIG. 4 is an external view of a transmitting coil and a receiving coil of the sensor. 1 is a transmitting coil for transmitting an AC magnetic field, 2a and 2b are receiving coils for receiving a change in the transmitting magnetic field, 3 is a core of the transmitting coil 1, 4a and 4b are cores of the receiving coils 2a and 2b, and 5 is A transmitting circuit for supplying an alternating current to the transmitting coil 1, a receiving coil 2 a,
A receiving circuit 2b receives a voltage induced in the receiving coil 2a, 2b receives a voltage induced in the receiving coil 2a, 2b. This is a receiving lead wire to be transmitted to the circuit 6.

[0003] The receiving coils 2 a and 2 b are arranged such that the midpoint thereof coincides with the center position of the core 3 of the transmitting coil 1. With such an arrangement, when there is no metal buried object nearby, in each of the receiving coils 2a and 2b, the voltages excited on the front side and the rear side of the intermediate point thereof are in opposite phases to each other and cancel each other out. So coil 2
The excitation voltages of a and 2b become zero. If there is a metal buried object nearby, in each of the coils 2a and 2b,
The magnetic flux density on the detection front side from the intermediate point increases due to the induced magnetic field induced from the metal object, and the balance between the front side and the rear side is lost, so that voltage is excited in the coils 2a and 2b.
In this way, a metal buried object such as a metal tube or a metal obstacle can be detected.

[0004]

However, the electromagnetic induction sensor for detecting a metal object as described above is mounted on a propulsion head.
When the direction control of the propulsion device head is performed to correct the traveling direction of the propulsion device, there is a problem that a metal object is erroneously detected even though there is no metal object in the propulsion direction. This is because when the direction control of the propulsion device head is performed, the positional relationship between the sensor and the propulsion device changes, so that a change occurs in the AC magnetic field passing through the receiving coil, and this change is erroneously recognized as a metal object. Because. The present invention has been made to solve the above problems, and has as its object to provide a metal object detecting electromagnetic induction sensor that does not erroneously detect a metal object even when the direction of the propulsion device head is controlled. .

[0005]

According to a first aspect of the present invention, there is provided an electromagnetic induction sensor for detecting a metal object, wherein an axial direction of a core is arranged at a tip of a propulsion device in a direction perpendicular to a detection direction. A transmitting coil for transmitting an alternating magnetic field in the orthogonal direction, and a receiving coil for receiving an induced magnetic field induced from a metal object by the transmitting magnetic field with the axial direction of the core arranged in the detecting direction, in a direction opposite to the detecting direction. A magnetic body is disposed immediately after the transmitting coil in the direction opposite to the detection direction so as to shield the transmitted transmission magnetic field. With such a configuration, the magnetic substance attracts the transmission magnetic field transmitted backward in the direction opposite to the detection direction, so that the transmission magnetic field transmitted backward from the magnetic substance is weakened, and the transmission magnetic field is controlled by controlling the direction of the tip of the propulsion device. Even if the positional relationship between the trust coil and the receiving coil and the propulsion device changes, the variation of the AC voltage peak value excited in the receiving coil becomes small. In addition, as described in the second aspect, the magnetic material is configured such that the amount of change in the AC voltage peak value during the direction control of the tip of the propulsion device is smaller than a predetermined value for determining whether a metal object is present. It is arranged in.

[0006]

FIG. 1 is a perspective view of the tip of a propulsion device equipped with an electromagnetic induction sensor for detecting a metal object according to a first embodiment of the present invention, and has the same configuration as that of FIGS. Are given the same reference numerals. Also in the present embodiment, the configuration of the sensor itself is the same as in FIGS. That is, the transmitting coil 1 is arranged so that the axial direction of the core 3 is orthogonal to the detection direction, the receiving coils 2a and 2b sandwich the transmitting coil 1 therebetween, and the axial directions of the cores 4a and 4b. Are arranged so as to face the detection direction.

The midpoint between the receiving coils 2a and 2b is located at the center of the core 3 of the transmitting coil 1 (dotted line in FIG. 4).
Are arranged to match. This receiving coil 2
The midpoint between a and 2b is defined as a point in each of the coils 2a and 2b where the number of turns in front of that point is T / 2 (T is the coil 2a,
2b), a position where the number of turns at the rear is also equal to T / 2.

In the case where there is no metal buried object, in each of the receiving coils 2a and 2b, the voltages excited on the front side and the rear side of the intermediate point thereof are in opposite phases to each other and cancel each other. The excitation voltage of the coils 2a, 2b becomes 0, no matter how strong the intensity of the AC magnetic field sent from 1 is.

When there is a metal buried object in the detection direction, the magnetic flux density of the coil 2a, 2b on the front side of the detection from the intermediate point increases by the induced magnetic field induced from the metal object, and the coil 2a, 2b Because the rear side balance is lost,
Voltage is excited in the receiving coils 2a and 2b. In this way, a metal buried object such as a metal tube or a metal obstacle can be detected.

As shown in FIG. 1, the electromagnetic induction sensor for detecting a metal object having such a configuration is mounted on the tip of a propulsion machine 10 such as an excavating machine or a boring machine for excavating and propelling an underground. The transmitting coil 1 and the receiving coils 2a and 2b are mounted on a propulsion head 11 at the tip of the propulsion device. The propulsion device head 11 is attached to the propulsion device head trailing portion 13 via the propulsion device neck 12.

A support mechanism (not shown) is provided at the root of the propulsion unit neck 12 (right side in FIG. 1). The propulsion unit head 11 and the propulsion unit neck 12 perform a swinging motion about this mechanism as a fulcrum. Supported as possible. When correcting the traveling direction of the propulsion device 10, the support mechanism directs the propulsion device head 11 in the direction to be corrected, and checks whether there is any metal buried object in that direction. Collision is prevented.

Therefore, when the direction control of the propulsion head 11 is performed, the positional relationship between the coils 1, 2a, and 2b and the metal propulsion head trailing portion 13 changes, so that the direction of the head 11 is changed. Even if there is no metal buried object, it is erroneously detected that a metal object exists. Therefore, in the present embodiment, the magnetic body 14 for shielding the magnetic field is disposed immediately after the propulsion device head 11, that is, immediately after the transmitting coil 1.

FIG. 2 is a diagram showing a state of a magnetic field transmitted from the transmitting coil 1. As shown in FIG. When the magnetic body 14 is disposed immediately after the transmission coil 1, the AC magnetic field 1 transmitted from the coil 1
5, the magnetic body 14 attracts the AC magnetic field sent backward in the direction opposite to the detection direction, so that the AC magnetic field sent backward from the magnetic body 14 is weakened. As a result, the alternating magnetic field that reaches the propulsion head trailing portion 13 is weakened,
By the above-mentioned direction control, the sensor and the propulsion head follower 13
Are changed, the two receiving coils 2a,
The fluctuation amount of the difference between the peak values of the AC voltages excited by 2b is smaller than in the conventional case.

That is, the receiving circuit 6 for determining the difference between the peak values of the AC voltages excited by the receiving coils 2a and 2b, respectively.
VTH is a predetermined value that recognizes the presence of a metal buried object, V1 is the amount of change in the difference between the AC voltage peak values excited in the coils 2a and 2b when the direction control of the propulsion head is performed in the conventional sensor, and V1 When the direction control is similarly performed in the sensor of the present embodiment provided with 14, the variation amount of the difference between the AC voltage peak values excited in the coils 2a and 2b is V2, and the relationship is V2 <VTH <V1.

Therefore, the variation amount V2 of the difference between the AC voltage peak values during the direction control of the propulsion head 11 can be made smaller than the predetermined value (threshold value) VTH. Does not erroneously be detected, and can be propelled without hindering metal object detection. In this embodiment, the metal object is detected by using the variation of the difference between the peak values of the AC voltage excited by the two receiving coils. However, the peak of the AC voltage excited by one receiving coil is detected. The variation of the value may be used.

[0016]

According to the present invention, by arranging the magnetic body immediately after the transmitting coil in the direction opposite to the detection direction, the direction of the tip of the propulsion device can be controlled to correct the traveling direction of the propulsion device. Since the fluctuation of the AC voltage peak value excited by the receiving coil is smaller than before, there is no hindrance to metal object detection, and it is possible to detect metal objects in the propulsion direction without erroneous detection. , And can be propelled without colliding with a metal object. As a result, it is possible to detect a metal object in the excavation direction without being affected by the metal of the propulsion unit behind the sensor.

[Brief description of the drawings]

FIG. 1 is a perspective view of a tip of a propulsion device equipped with an electromagnetic induction sensor for detecting a metal object according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a state of a magnetic field transmitted from a transmission coil.

FIG. 3 is a block diagram of a conventional electromagnetic induction sensor for detecting metal objects.

FIG. 4 is an external view of a transmitting coil and a receiving coil of the electromagnetic induction sensor for detecting a metal object in FIG. 3;

[Explanation of symbols]

1 ... Coil for transmission, 2a, 2b ... Coil for reception, 3, 4
a, 4b: core, 5: transmission circuit, 6: reception circuit, 7: transmission lead wire, 8a, 8b: reception lead wire, 10: propulsion device, 11: propulsion device head, 12: propulsion device neck portion, 13 …
Propeller head trailing part, 14 ... magnetic body.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-269688 (JP, A) JP-A-3-260706 (JP, A) JP-A-3-233392 (JP, A) JP-A-9-9 189772 (JP, A) Japanese Utility Model Application Hei 6-7082 (JP, U) Japanese Utility Model Application Hei 5-36386 (JP, U) Japanese Utility Model Application 53-113651 (JP, U) (58) Field surveyed (Int. ⁷ , DB name) G01V 3/10 G01R 33/02

Claims (2)

(57) [Claims] A transmitting coil for transmitting an AC magnetic field in the orthogonal direction with a core axis direction being orthogonal to a detection direction, and a core having a core axial direction being arranged in a detection direction at the tip of the propulsion device; A receiving coil for receiving an induction magnetic field induced from a metal object by a transmission magnetic field, and a metal object detecting electromagnetic induction sensor for detecting a metal object by detecting an AC voltage peak value excited by the receiving coil. An electromagnetic induction sensor for detecting metal objects, wherein a magnetic body is disposed immediately after a transmission coil in a direction opposite to the detection direction so as to shield a transmission magnetic field transmitted in a direction opposite to the detection direction. 2. The electromagnetic induction sensor for detecting a metal object according to claim 1, wherein the magnetic material determines whether or not the amount of change in the AC voltage peak value at the time of controlling the direction of the tip of the propulsion device is a metal object. An electromagnetic induction sensor for detecting metal objects, which is arranged so as to be smaller than a predetermined value for determination.